DEVELOPMENT OF A HYBRID ELECTRIC VEHICLE by STEPHEN …
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DEVELOPMENT OF A HYBRID ELECTRIC VEHICLE by STEPHEN SCOTT AYLOR, B.S.E.E.. A THESIS IN ELECTRICAL ENGINEERING Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN ELECTRICAL ENGINEERING Approved May, 1996
Transcript of DEVELOPMENT OF A HYBRID ELECTRIC VEHICLE by STEPHEN …
DEVELOPMENT OF A HYBRID ELECTRIC VEHICLE
by
STEPHEN SCOTT AYLOR, B.S.E.E..
A THESIS
IN
ELECTRICAL ENGINEERING
Submitted to the Graduate Faculty of Texas Tech University in
Partial Fulfillment of the Requirements for
the Degree of
MASTER OF SCIENCE
IN
ELECTRICAL ENGINEERING
Approved
May, 1996
S05 1 I < ^ ^ ^ ACKNOWLEDGMENTS
I would like to thank all of the members of my thesis committee, Dr. Donald
Gustafson, Dr. Michael Giesselman, and my committee chairman Dr. Micheal Parten, for
their advice and consultation. I would like to thank aU of the members of the 1995 Texas
Tech Neon HEV Team for their enormous contributions to the project. FinaUy, I would
like to thank all of the sponsors of Texas Tech's entry in the 1995 Chrysler Hybrid
Electric Vehicle ChaUenge.
u
TABLE OF CONTENTS
ACKNOWLEDGMENTS ii
ABSTRACT vii
LIST OF TABLES viii
LIST OF FIGURES ix
CHAPTER
1. INTRODUCTION 1
2. MECHANICAL SYSTEMS 11
2.1 Introduction 11
2.2 Compressed Natural Gas Conversion 12
2.2.1 Powertrain Control Module 13
2.2.2 Gas Engine Management System 15
2.2.3 CNG Storage and Plumbing 16
2.3 ICE/Electric Motor Coupling 18
2.3.1 Power Transfer Case 19
2.3.2 Sprockets and Chain 20
2.3.3 Input Shaft Modification 21
2.4 Battery Boxes 22
3. ELECTRICAL SYSTEM 24
3.1 Introduction 24
3.2 Electric Motor 26
3.2.1 Theory of Operation 26
iii
3.2.2 Motor Specifications 28
3.3 Motor Controller 28
3.3.1 Theory of Operation 30
3.3.2 Motor Controller Operation 31
3.3.3 Motor Controller Specifications 32
3.4 Batteries 34
3.5 Auxiliary Systems 35
3.5.1 Cooling Systems 36
3.5.2 Battery Charger 37
3.5.3 Energy Meter 38
3.5.4 Fire Suppression System 38
3.5.5 Main Disconnect, Fusing and Soft Start Circuit 39
4. SYSTEM CONTROLLER HARDWARE 41
4.1 Introduction 41
4.2 System Controller Inputs 42
4.2.1 IC Engine and PCM Input Signals 42
4.2.2 Operator Input Signals 44
4.2.3 Battery Pack Voltage Signal 46
4.3 System Controller Outputs 46
4.4 M68HC11 Microcontroller Evaluation Board 47
4.4.1 68HC11 Architecture 48
4.4.2 M68HC1 lEVB Evaluation Board 50
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4.5 Interface Board 52
4.5.1 Isolation Subsystem 53
4.5.2 Digital-to-Analog Conversion Subsystem 54
4.5.3 Power Supply Subsystem 55
4.5.4 Printed Circuit Board Layout 56
5. SYSTEM CONTROLLER SOFTWARE 59
5.1 Introduction 59
5.2 System Controller Main Program 59
5.3 Data Acquisition 61
5.4 ZEV Mode 62
5.5 Internal Combustion Only Mode 65
5.6 HEV Mode 65
5.6.1 HEV Assist Routine 68
5.6.2 HEV Regeneration Routine 69
6. RESULTS 72
6.1 Introduction 72
6.2 ZEV Performance 72
6.3 HEV Performance 75
6.3.1 HEV Acceleration 75
6.3.2 Fuel Economy 75
6.3.3 Vehicle Emissions 77
6.3.4 Vehicle Range 78
6.4 Summary of Results 79
7. HEV MODEL 81
7.1 Introduction 81
7.2 System Controller Model 82
7.3 Electric Motor/Controller Model 83
7.4 Battery Pack Model 86
7.5 IC Engine Model 87
7.6 Transmission Model 89
7.7 Vehicle Dynamics Model 91
7.8 Model Results 94
8. CONCLUSIONS 98
8.1 Recommendations for Future Work 99
REFERENCES 102
VI
ABSTRACT
This thesis describes the development of a hybrid electric vehicle from concept to
completion. The vehicle described is Texas Tech's entry in the 1995 Chrysler Hybrid
Electric Vehicle Challenge. The mechanical systems' design and modifications to a 1995
Dodge Neon Sedan is presented. The electrical system used to convert the vehicle to a
hybrid electric vehicle (HEV) is documented. A design for the HEV system controUer is
discussed from a hardware and software perspective. A vehicle model developed from
known vehicle parameters and dynamic testing is introduced to aid in further optimization
of the vehicle. Results of dynamic testing with regards to fuel economy, vehicle range,
and emissions productions are presented to iUustrate the benefits of operating the vehicle
as an HEV. Conclusions and recommendations for future work are discussed.
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LIST OF TABLES
1.1 Emission Standards 2
3.1 Unique Mobility DR156s Parameters 29
3.2 Unique Mobility CR20-150 Parameters 34
6.1 Fuel Economy Test Results 77
Vlll
LIST OF FIGURES
1.1 Series and Parallel HEV Configurations 5
1.2 Effect of Mission on Component Sizing 7
2.1 PCM and GEM System Interface 14
2.2 Vehicle Layout 18
2.3 Powertrain Coupling 19
2.4 Power Transfer Case 20
2.5 Input Shaft Extension 22
3.1 HEV Electrical System 25
3.2 Simple Permanent-Magnet Motor 27
3.3 DR156S/CR20-150 System Efficiency Map 29
3.4 Three-Phase Motor Drive Circuitry 31
3.5 CR20-150 Three-Phase Signals 33
3.6 Charge Characteristic Curves 37
4.1 System Controller and Related Systems 41
4.2 System Controller Hardware Block Diagram 49
4.3 MC68HC11A8 Block Diagram 50
4.4 M68HC1 lEVB Block Diagram 52
4.5 Isolation Hardware 54
4.6 D/A Conversion Hardware 56
4.7 Component Side PCB Layout of Interface Board 57
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4.8 Solder Side PCB Layout of Interface Board 58
5.1 System Controller Main Flowchart 60
5.2 Data Acquisition Flowchart 62
5.3 ZEV Mode Flowchart 63
5.4 IC Only Mode Flowchart 66
5.5 HEV Mode Flowchart 67
5.6 HEV Assist Routine Flowchart 70
5.7 HEV Regeneration Routine Flowchart 71
6.1 Battery Discharge Characteristics for 30 mph Test 74
6.2 Battery Discharge Characteristics for 55 mph Test 74
6.3 Emissions Bracket Values 79
7.1 Neon HEV System Model 84
7.2 System Controller Model 85
7.3 Electric Motor/ControUer Model 86
7.4 Battery Pack Model 87
7.5 Battery Discharge Characteristics 88
7.6 IC Engine Model 90
7.7 IC Engine Torque Characteristics 90
7.8 IC Engine Fuel Flow Characteristics 91
7.9 Transmission Model Diagram 92
7.10 Vehicle Dynamics Model 93
7.11 Vehicle Speed for ZEV Acceleration Simulation (0-30 mph) 95
X
7.12 Vehicle Speed for ZEV Acceleration Simulation (0-55 mph) 95
7.13 Vehicle Distance for HEV Acceleration Simulation (l/8th mile) 96
7.14 Vehicle Speed for HEV Acceleration Simulation (l/8th mile) 97
XI
CHAPTER 1
INTRODUCTION
As air quahty decreases in urban areas across the United States, state and national
regulatory agencies are passing more stringent automobile emissions standards. In
addition, the need for alternative methods of transportation is growing as the United
States' dependency on foreign oil increases from year to year [1]. Electric vehicles, or
EVs, would seem to be the obvious solution. EVs do remedy some of the problems faced
by large metropolitan areas, but they also have their own problems.
California is the first state to take serious action with regard to automobile
emissions and fuel consumption. The California Air Resources Board has set a
requirement that two percent of aU passenger and light-duty vehicles sold by 1998 must
have zero tail-pipe emissions [2]. Very few independent companies actually produce
vehicles that meet this requirement. Some of the major auto manufacturers are silently
hoping that this legislation wUl not be enforced due to the fact that the percentages will
certainly increase.
California has already set a definite standard that low-emissions vehicles must be
introduced by 1997 [3]. The emission levels for the low-emission vehicle, LEV, are
included in Table 1.1. Automobile manufacturers already have plans to comply with the
LEV standard and one major automaker already has a vehicle complying with the standard
available on the market.
Due to the fact that there is reluctance on the part of automakers and consumers to
accept the zero-emissions vehicle (ZEV) standard, the Califomia board has devised a
tentative plan for a new class of vehicle. The equivalent zero-emission vehicle, or EZEV,
is a compromise between the ULEV and ZEV standards. This standard is based upon the
typical amount of poUution produced by power plants in charging battery-powered EVs.
This standard is stUl in the proposal stage and there are still some unresolved issues as far
as vehicle classification.
Certain states have taken action or are taking action against automobUes that have
poor fuel economy, due to the fact that they have large engines, by implementing a 'gas-
guzzler' tax. As petroleum resources are becoming more and more depleted, fuel
economy is a major issue with consumers as weU as regulatory agencies. The amount of
energy required to produce reformulated gasoline from crude oil further compounds the
inefficiencies associated with traditional automobUes.
Table 1.1. Emission Standards [3]
Category
Ultralow-emissions vehicle (ULEV) Equivalent zero-emission vehicle (EZEV) Zero-emissions vehicle (ZEV)
Emissions level, grams/mile (grams/kilometer)
Nitrogen Oxides (NOx)
0.20 (0.125)
0.02 (0.0125)
0.0 (0.0)
Nonmethane Organic Gases
(NMOG) 0.040
(0.025) 0.004
(0.0025) 0.0
(0.0)
Carbon Monoxide
1.7 (1.056)
0.17 (0.1056)
0.0 (0.0)
Particulate Matter
0.040 (0.025) 0.004
(0.0025) 0.0
(0.0)
Electric vehicles would seem to be the solution to most of these poUution and fuel
consumption problems. EVs are not new by any means, the first electricaUy powered
vehicles were proposed around the turn of the century. Electric vehicles have come a long
way from those humble beginnings, although they have not achieved the popularity and
success of the traditional automobile.
EVs were not always seen as a feasible solution to the ever-growing fuel
consumption and emission problems. The first EVs were large, heavy, and slow, not to
mention their Umited range. This was mainly due to the fact that the batteries needed to
store the energy to power the vehicle added a tremendous amount of weight to the
vehicle. The electric motors used to drive the vehicle were heavy and inefficient, further
compounding the problem. These vehicles would only be capable of moderate speeds by
traditional automobile standards, 30 to 45 miles per hour, and a very limited range of 20 to
30 mUes depending on driving conditions [4].
EVs have made dramatic improvements with respect to consumer acceptabiUty
over the last few decades. Advancements in materials and control systems have made EVs
better suited to customers expectations. Batteries have been developed that have higher
output and storage capacity while reducing overaU weight. Motor technology has also
improved, resulting in higher efficiencies, and power-to-weight ratios. Lightweight and
strong materials such as carbon fiber composites are being used in vehicle bodies to reduce
weight.
General Motors has initiated a program called the PrEView Drive Program where
50 of GM's electric vehicles, the Impact, are loaned for evaluation to typical U.S. drivers
in 12 cities around the country. Over 800 people wiU be allowed to test drive this vehicle
for as long as two weeks. This program is designed to inform the public about
improvements in EVs, and dispel some of the myths associated with them [5].
Although great improvements have been made in EV technology, they stiU faU
short in several areas as far as consumer acceptance. The major factor that has slowed the
acceptance of EVs is their limited range before the batteries must be recharged. EV range
is currentiy around 100 to 130 miles maximum between rechargings at highway speeds
and 75 to 90 mUes maximum during city driving patterns [5]. At the levels of discharge
required to attain these distances, recharging is not a trivial matter. Charge times from a
high level depth of discharge, or DOD, are around two to three hours. Faster charge rates
can be obtained, but these severely degrade the overall battery lifetime. Another area that
EVs tend to be lacking in is performance. EVs tend to be rather quick from a stop, but
often suffer at top speeds.
Until technology advances to the point where storage capacity, recharge times, and
vehicle performance are no longer problems for EVs, there needs to be an investigation of
alternatives. Hybrid electric vehicles are the main focus of this drive for alternatives to
traditional internal combustion engine (ICE) powered automobiles and electric vehicles. A
hybrid electric vehicle is defined as, "A hybrid electric vehicle (HEV) is a hybrid vehicle in
which at least one of the energy stores, sources, or converters can deliver electric energy."
This definition is one proposed by Technical Committee 69 (Electric Road Vehicles) of
the International Electrotechnical Commission [2].
There are two main classifications of HEVs, series and parallel. A series hybrid
uses only power supplied by an electric motor or motors for propulsion. Some sort of
thermal power, usually an engine-generator set, or E-G set, charges the battery or directiy
provides power for the electric motor or motors. A paraUel hybrid uses either or both the
IC engine and the electric motor to drive the wheels of the vehicle. In a parallel
configuration, the electric motor may also be used as a generator to charge the batteries.
These two configurations are shown in Figure 1.1.
Engine
Battery
— »
4-¥
Generator
Engine
Motor
— »
— •
4-*
Battery
Clutch
Clutch
4-¥
— »
4->
Motor
Drive Shaft
#—»
*-¥
Transmission
Transmission
i Ji ' 1
^ \
Figure 1.1. Series and Parallel HEV Configurations [2]
No optimum configuration for a HEV has been determined and there has been
fairly limited research into HEV technology. There is really no way to determine an
'optimal' design for a hybrid electric vehicle, because the criteria for evaluation are
subjective and not yet fuUy determined. Some consumers may value fuel economy and
low emissions over increased performance for example. Due to the diversity of criteria
and evaluation methods, there are infinitely many vehicle configurations.
The main objective of this investigation is to develop a hybrid electric vehicle that
is comparable in performance to simUar vehicles on the market, while substantiaUy
reducing tail-pipe emissions and increasing fuel-economy. What is meant by overall
vehicle performance is acceleration, handling, braking, vehicle range, and driveabiUty. The
ultimate goal is that the driver have no realization that he/she is driving a hybrid.
Since there is no one best design for a hybrid, vehicle configuration is determined
by what traits are deemed desirable by the user. This is clearly Ulustrated by Figure 1.2.
This figure shows the effect that component selection, in particular the IC engine and
electrical drive components, have on the tme operation of the vehicle [2]. The sizing of
Uiese components basicaUy determines how the vehicle wUl operate.
On this graph, the lower right hand corner represents vehicles that rely heavily on
their electrical power for normal operation and have increased range as ZEVs. These
vehicles have especiaUy low emission levels and extremely high fuel economy; however,
these vehicles' performance is dramaticaUy affected when their battery state-of-charge
(SOC) is at a low level. In this regard, they share many of the problems associated with
pure EVs. Due to the fact that they are so dependent upon electrical power, these
vehicles often tend to be heavy and cumbersome due to the large battery pack required for
reasonable storage levels. At low battery levels, these vehicles are not totally inoperable,
but their performance is so limited that this situation is often called the 'limp-home' mode.
True hybrids fall into the center of the graph. They rely equaUy on the ICE power
and electrical means for propulsion. True hybrids can perform equally weU on either
system independently. Only when both systems are used together can tme hybrids
perform up to traditional automobile standards. When a true hybrid has to perform solely
on electrical or thermal power, its performance can be severely limited. These vehicles
typically have low emission levels and high fuel economy, but as with any system that
relies heavUy on its electrical system for performance, practical range and electrical energy
storage are problems for true hybrids.
1 0 0 -
Internal combustion engine power, kW
5 0 -
1 0 "
0
ICE only
ICE plus
electrical assist
1
True hybrid
operation
1 1
Battery plus range-extending
ICE
Battery only
1 0 10 50 200
Range as zero-emissions vehicle, km
Figure 1.2. Effect of Mission on Component Sizing [2]
The upper left comer of Figure 1.2 refers to vehicles that rely more heavily on
their ICE power than their electrical system. These vehicles are characterized by higher
performance and practical range. They do, however, lose some of the fuel economy and
emissions savings of the two previously mentioned groups. Their range on purely electric
power is Umited, but this is usually not a problem as these systems are rarely asked to
perform purely by electrical means.
A paraUel structure with an electrical assist strategy is the platform used for the
particular HEV addressed in this thesis. The paraUel structure allows more flexibiUty in
vehicle operation. In a paraUel HEV, electrical power and/or ICE power can be used to
drive the car. This aUows the vehicle the flexibiUty to perform as a ZEV, HEV, or rely
solely on its IC engine capabiUty. The parallel stmcture also incorporates less conversion
losses. In a series hybrid, all energy must be converted into electrical, then kinetic energy.
In a paraUel, thermal as well as electrical energy may be converted into the kinetic energy
required to move the car. The component sizing previously mentioned is especiaUy
important in this parallel structure.
The electrical assist strategy is used for several reasons, most importantiy to
maintain vehicle performance, particularly with regards to vehicle range and acceleration.
While maintaining performance levels of traditional automobUes, the electrical assist
increases fuel economy and reduces emissions. How this electrical assist is controUed is of
vital importance in increasing the fuel economy and reducing emissions. The particular
electrical assist strategy used for this hybrid is discussed below.
Modern IC engine control has lead to fuel economy and emission levels that were
once thought unattainable. Most, if not all, of today's automobiles use microprocessor-
based control systems that very accurately control aU aspects of the engines' performance.
These systems also have adaptive capabUities that compensate for changes in environment,
fuel irregularities, and even varying driving patterns. These adaptive methods, often
referred to as closed-loop engine control, have a finite response time and often cannot
compensate for quickly changing engine conditions. Even the most powerful processors
and the most robust adaptive algorithms cannot solve some of the problems that plague
traditional IC engines.
The efficiency of an internal combustion engine as weU as the level of emissions it
produces are directiy affected by the conditions under which it is operated. Due to the
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closed-loop control methods used, the level of fuel consumption and emission production
can be precisely controlled under steady state conditions. Even moderate changes to the
operating state of the engine can be adapted to by microprocessor-based systems given the
proper time for the microcontroUer to react. Unfortunately, the typical urban daily driving
cycle has a rapidly changing nature that prevents the most efficient operation of the
engine. It is during these driving transients that engine emission and fuel consumption are
at their highest.
The electrical system can be used to remedy some of the problems that are caused
by the driving patterns that are common in large metropoUtan areas. The electric motor
can be used to smooth the transients on the traditional powertrain. During times of high
engine load, the electric motor is appUed, reducing the load 'seen' by the IC engine.
These high engine load conditions may occur during acceleration, cUmbing steep grades,
or when accessories such as air conditioning are used. These conditions severely affect
the fuel economy and emissions produced by the vehicle.
The electric motor is used in the opposite manner during times of low engine load.
The electric motor actually loads down the engine when there is Uttle load on the engine,
as during deceleration or when coasting down a steep grade. During this time, the motor
acts as a generator, and recovers some of the vehicle's kinetic energy. This process is
caUed regeneration. Regeneration is also used during braking, where the energy is
recovered into the batteries instead of wasting the energy as heat developed by friction.
The electric motor acts as a buffer for the IC engine in this system. The
relationship between the IC engine and electric motor uses the best aspects of each
system. The electric motor absorbs some of the transients encountered by the system.
The electric motor is more efficient than the IC engine during these transient periods,
although the motor is more efficient at steady state. The IC engine provides the extended
range that the electric motor cannot.
The particular vehicle used in this thesis is a 1995 Dodge Neon. This project was
done as part of the 1995 Chrysler Hybrid Electric Vehicle Challenge. The HEV challenge
involves over 800 students from 35 of the top engineering and research universities in
North America. Many of the important design decisions were made to comply with the
mles of the challenge. This vehicle was converted to operate as an HEV by a team of 18
undergraduate mechanical and electrical engineering students. My responsibUities were as
the team leader and designer of the control system.
This thesis detaUs aU aspects of the development of the 1995 Texas Tech Neon
HEV. Chapter 2 covers the mechanical aspects of the system. Chapter 3 detaUs the
electrical system, emphasizing the high-power hardware. Chapter 4 focuses on the
development of a system controller for the hybrid electric vehicle. Chapter 5 describes the
software implemented using the previously mentioned system controller. Chapter 6
discusses the results obtained during dynamic testing of the HEV. Chapter 7 introduces a
simulation of the HEV using MATLAB SimuUnk. Chapter 8 contains conclusions drawn
from the results and recommendations for future work
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CHAPTER 2
MECHANICAL SYSTEMS
2.1 Introduction
As previously mentioned, the basis for this hybrid electric vehicle is a 1995 Dodge
Neon sedan. The Neon is in the compact vehicle class. It provides an ideal test bed for
this project because the compact nature of the car aUows for smaller component size. A
larger vehicle would require more power, resulting in reduced fuel economy and increased
emissions.
The Neon HEV retains aU of the structural and functional aspects of a traditional
vehicle. Several aspects of the original mechanical system are modified to aUow the
vehicle to perform as a HEV, whUe maintaining the functionality of the original Neon. The
original IC engine for the Neon is a two-Uter, in-Une, four-cylinder engine, producing
approximately 130 horsepower. This engine, combined with the low relative weight of the
chassis, aUows for exceptional handling and performance. It is of vital importance that
these characteristics are preserved in the HEV conversion.
The electrical assist strategy requires a larger IC engine and a smaUer electric
motor to provide supplemental power or load as engine conditions dictate. The stock IC
engine for the Neon meets the requirements necessary for the electrical assist strategy.
The original powertrain is powerful enough so that the vehicle does not have to rely
heavUy on its electrical power for propulsion. The original engine and transmission
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configuration is specifically designed to fit this vehicle, so vehicle functionality is
preserved.
The major modifications to the mechanical systems of the vehicle are made to
increase fuel economy and reduce emissions by aUowing the vehicle to function as an
HEV. The original powertrain is converted to mn on compressed natural gas (CNG).
Compressed natural gas is a much cleaner burning fuel than traditional reformulated
gasoUne. The second significant mechanical modification is the powertrain coupUng of the
electric motor and the IC engine. The original transmission is retained and the electric
motor power is directly coupled via a power transfer case. The last major stmctural
modification is the addition of a safe storage area for the batteries required by the
electrical system. These modifications are necessary for the vehicle to function as a HEV,
but in no way do they compromise the original functionality of the vehicle.
2.2 Compressed Natural Gas Conversion
The original engine provides exceUent power for such a small vehicle;
unfortunately, one of the unwanted by products of this is increased vehicle emissions. A
smaller engine would produce less harmful emissions, but would compromise the power
provided by the original system. By using a cleaner burning fuel, in this case compressed
natural gas (CNG), the power level can be preserved whUe reducing emissions. There is a
sUght loss of power due to the properties of CNG, but this is much less significant than the
power deficit caused by using a smaller engine.
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The conversion of the traditional gasoUne system to CNG poses several significant
problems. Compressed natural gas, while being a much cleaner burning fuel due to the
fact that it is made up of mostiy methane, is less explosive and bums more slowly than
reformulated gasoline. Also CNG is a gas that is stored at high pressure, whereas gasoUne
is a liquid that is stored at atmospheric pressure. These dramatic differences in the
properties of the two fuels prevents the use of the original engine control system as the
primary means of engine control.
The differences in the properties of the two fuels dictates that a separate system be
used as the primary control for the engine. Mesa Environmental produces just such a
system for natural gas vehicles. The Gas Engine Management (GEM) system is developed
to convert fleet vehicles to mn on compressed natural gas. The GEM systems, however,
are produced mostly for large 6 and 8-cyUnder systems. Some of these incompatibilities
are the reason why the GEM is used in paraUel with the original engine control system.
Each controUer functions independently. Each controUer manages certain aspects of the
engine, whUe the two in conjunction achieve the overall goal of reducing emissions.
2.2.1 Powertrain Control Module
Figure 2.1 Ulustrates the relationship between the original engine control system or
powertrain control module (PCM) and the GEM system. Most of the sensors are 'shared'
by both systems, that is both systems read the output of a single sensor. Since the PCM is
designed to operate a gasoUne powered engine, it manages aspects of the engine that are
not fuel related. The two primary functions that the PCM controls are the ignition timing
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or spark control, and the idle speed control. It also manages many of the auxiUary systems
that are not as du-ectiy related to the engine.
The ignition timing or spark control of the engine is cmcial to the engine's proper
operation. The Dodge Neon uses a 'wasted spark' ignition system as opposed to the
traditional distributor-type spark control. In this system there are two coils that each fu-e
two spark plugs every power stroke. One spark occurs in a cylinder under compression,
while the other fu-es in a cyUnder in the exhaust stroke. The PCM determines when to
charge each of the two coils and when to actuaUy fu-e the spark plugs associated with
those cods. The PCM regulates this according to the state of the engine, which it
determines from the sensor inputs [6].
(loPOC) 12 V
to PtMHeuInt Pot. cw. fnxn P/S cwilch '
Figure 2.1 - PCM and GEM System Interface
14
The spark tuning is cmcial because it greatiy affects both the fuel economy and the
emission levels of the engine. If the spark timing is advanced, that is the spark plug is
fu-ed earUer, the result is a more complete bum of the fuel in the cylinder and more power
is produced. This does, however, increase the exhaust gases produced. When the spark
timing is retarded, that is the spark plug is fired later, less of the fuel is burned and less
power is produced. Since less fuel is being burned, the exhaust gases are reduced and the
level of emissions is lowered.
The idle air control is the other main aspect that the PCM controls. The throttie
body has a bypass passage for air to enter the engine during idle or closed-throttle
operation. The opening to this passage is controlled by the Idle Air Control (lAC) motor.
This motor is controlled by the PCM based upon the state of the engine, particularly to
compensate for engine load, coolant temperature, or barometric pressure variations [6].
The idle air control is not as cmcial as the spark timing, but it is obvious that a high idle
speed can result in unnecessary fuel consumption and increased emissions.
2.2.2 Gas Engine Management System
The Gas Engine Management System is added to the PCM as shown in Figure 2.1
The GEM system's main function is to compensate for the fuel differences between
compressed natural gas and gasoUne. In doing this it controls emissions and maximizes
the fuel economy for the CNG system. The GEM system also controls solenoids in the
high-pressure CNG line. It leaves control of non-fuel related aspects of the engine to the
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PCM. The main aspects of the engine it controls are the fuel-injector timing and pulse-
width, along with Uie exhaust gas recirculation (EGR) control.
The fuel-injector timing and pulse-width have a large effect on the emissions level
and fuel consumption of the ICE. When and how long the injector is pulsed determines
the amount of fuel that gets into the cyUnder. The more fuel that is injected into the
cylinder, the larger the explosion in the cylinder. This results in more power but also more
emissions. A separate controUer is needed to control the injectors because the fuel
difference is so dramatic. The GEM system is specifically designed to operate a natural
gas powered engine.
The exhaust gas recirculation (EGR) technique is one of the most effective ways to
reduce certain pollutants, particularly nitrogen oxides (NOx). When the air-fuel
combustion in the engine occurs at higher temperatures, a higher level of NOx is created.
To reduce the combustion temperature, exhaust gas is recirculated into the air-fuel
mixture to reduce the size of the explosion. More air or fuel in the cyUnder would disturb
the critical air-fuel ratio. This exhaust gas does not have an effect on the air-fuel mixture
because it is essentially inert. In effect, the exhaust gas just takes up space in the cylinder,
therefore lowering the NOx production. The GEM system controls the transducer that
regulates the amount of exhaust gas that is recirculated into the engine.
2.2.3 CNG Storage and Plumbing
The compressed natural gas conversion requires significant modifications to the
existing fuel storage and deUvery system. The main reason for this is the fact that the two
16
fuels are significantiy different. CNG is a high pressure gas made up of mostiy methane,
whUe reformulated gasoUne is a liquid.
Fuel storage for the CNG system is provided by two 32-liter aluminum tanks
instead of the original fuel tank. These tanks are rated to store a maximum of 3000
pounds per square inch (psi) of CNG. This amount of CNG converts to approximately 5
gallons of gasoline equivalent, resulting in a vehicle range of approximately 200 - 250
miles on a single tank using initial estimates of fuel economy. This amount of fuel gives a
considerable range between refueUng.
The CNG cylinders are approximately 10 inches in diameter and 35 inches in
length. These tanks are located behind the rear seat in the trunk area as shown in Figure
2.2. This is the only feasible place to store the tanks unless major modifications are made
to the vehicle structure, which might compromise its integrity. The mounting structure for
the tanks is designed to withstand a force 20 times the weight of the cylinders in the
fore/aft directions and 8 times their weight in aU other directions, with a maximum
deflection of 1/2 of an inch. The mounting structure is made up of 10-gauge ASTM A-
715 high carbon steel formed into C channels and is secured with 1/4-inch grade 8 bolts.
Fuel is routed from the high-pressure tanks to a fiU valve with 1/4 inch stainless
steel tubing rated at 5000 psi. The fiU valve is foUowed by a 1/4-tum valve that aUows for
a manual override of fuel flow. Also included is a lock-off valve that stops fuel flow when
the key is in the off position. The fuel line is routed in the channel where the original fuel
Unes were located. FinaUy, a high-pressure regulator regulates the pressure going into the
fuel raU to approximately 100 psi. This is necessary because the fuel-injectors require a
17
constant pressure for accurate engine control and wUl not withstand the high pressure
coming from the tanks. Pressure and temperature transducers are located near the tanks
and the high-pressure regulator to monitor fuel levels.
T —7 \ B
attery Box
Battery B
ox
. L
Drive Motor
CNG Regulator
^ ^ ' ^ 1/4-tum valve Fill valve and gauge
FRONT
Figure 2.2 - Vehicle Layout
2.3 ICE/Electric Motor Coupling
The paraUel stmcture of the Neon HEV requires that both electric power and the
IC engine must be able to provide power to the wheels. The electric motor is coupled to
the wheels via the original transmission. Figure 2.3 iUustrates how this is accompUshed.
A transfer case supports the electric motor and encloses a high-velocity chain drive that
connects to an extension from the transmission shaft. This is one of the most critical
aspects of the mechanical design.
18
2.3.1 Power Transfer Case
The power transfer case is constmcted of 7075 T6 aluminum with an average yield
strength of 85 kpsi (586 megapascals, Mpa). A solid block of this aluminum is mUled to
shape using a computerized CNC mUl. The cover for the power transfer case is mUled
from ASTM A-715 10-gauge steel with an average yield strength of 80 kpsi (552 Mpa).
Figure 2.4 shows a side view of the transfer case. The material selection is based upon the
event of chain failure during high speed operation. Holes are drilled to match those on the
end of the transmission. The shaft and mounting holes for the electric motor are slotted to
allow the chain tension to be adjusted. The electric motor is protected from leakage from
the oil bath by an oil seal and gasket.
Clutch Housing Transaxle
DC Brushless motor
Drive chain
Power transfer case
Figure 2.3 - Powertrain CoupUng
19
Figure 2.4 - Power Transfer Case
2.3.2 Sprockets and Chain
The chain is selected based upon the maximum speed and torque levels it must
withstand. The maximum torque supplied by the electric motor is 320 in-lbs (36.2 N-m).
The maximum speed of the electric motor is 6750 revolutions per minute (RPM),
although the rev limiter on the IC engine is set at 6000. A 3/8 in. (9.53 mm) pitch by 3/4
in. (19 mm) wide #HV-303 chain exceeds these specifications. The average ultimate
tensile strength of the chain is 5625 psi (38.78 Mpa) and the maximum rated velocity is
2500 feet per minute (FPM) using bath lubrication.
The sprockets for the transmission shaft and the electric motor shaft are of the
minimum recommended size to conserve space. Two #HV-303B25 sprockets containing
25 teeth each, are used to achieve the desired drive ratio of 1:1 between the original
transmission and the electric motor. The sprockets are hobbed with a generated involute
tooth form and have hardened teeth to prevent wear on tooth flanks. The entire chain-
20
sprocket assembly is lubricated using an oil bath. Under normal driving conditions,
pressure lubrication is not required.
2.3.3 Input Shaft Modification
Modification of the transmission input shaft is required to couple the electric motor
to the original transmission. The input shaft extension is shown in Figure 2.5. The input
shaft is originally constmcted with a 0.625 in. (15.9 mm) diameter x 4.5 in. (114 mm)
length bore into the end opposite the engine. This normally allows for oil to reach the
synchronizers and pin bearings in the transmission. This amount of oil is so smaU that
blocking the flow through the input shaft does not affect the normal operation of the
transmission. The input shaft bore is modified to have an overaU taper concentricity
tolerance of no more than ± 0.001 in.
The extension shaft that is pressed and pinned into the input shaft, has an
interference fit within the bore of .0001 in. The extension shaft is made of 1095 Q&T
steel with an average yield strength of 112 kpsi (772 Mpa). The extension shaft as weU as
the input shaft has a 0.2-mm hole to accommodate the 1095 Q&T steel pin that secures
the two shafts in place. Lock-Tite™ Red adhesive secures the pin in place. The original
transmission uses this modified input shaft to couple the power of the electric motor with
that of the IC engine.
21
Extension to Shaf-f /
S e c t i o n A—A
Original Input Shaft
R. JI3_J=U
II n-U rfu ]>
t=r i = p — i z z r
• v ^
.y^ 3 Modified Shaft
Figure 2.5 - Input Shaft Extension
2.4 Battery Boxes
Batteries are required to provide energy storage for the electric motor. These
batteries must be stored in a safe manner, so as not to endanger the passengers, while
maintaining the functionaUty of the vehicle. Figure 2.2 shows the location of the battery
boxes in the vehicle. They are located beneath the rear seat. This configuration preserves
rear passenger room while stUl providing safe ground clearance for the vehicle.
22
The battery boxes are constmcted of 18-gauge ASTM A-606 high-carbon steel.
This material provides high yield strength (50 kpsi, or 345 Mpa) as weU as exceUent
weldabUity and corrosion resistance. Each box has dimensions of 15.8 in. x 14.5 in. x 21.2
in. (40.1 cm x 36.8 cm x 21.2 cm). The boxes are welded into a supporting structure in
the floor of the car and the Uds are bolted to seal each box. This supporting stmcture is
constmcted of ASTM A-715 high-carbon steel that is formed into C channels. Two cross
members are welded to the side channels on the underside of the car and supports run
between the two cross members. This stmcture has a safety factor of 20 in the fore and
aft directions while having a safety factor of 8 in aU other directions.
23
CHAPTER 3
ELECTRICAL SYSTEM
3.1 Introduction
The electrical system of the Neon hybrid is of vital importance for its success as a
hybrid. Figiu-e 3.1 shows the major components of the electrical system. Not included are
some of the auxiUary subsystems that wUl be discussed later. This system is designed
around the overaU project goal, to make a vehicle that provides significant fuel economy
savings and reduction in emissions while maintaining vehicle performance via an electrical
assist strategy. The three main areas of the electrical system are the motor/controUer pair,
the battery pack, and the auxiUary subsystems.
The electric motor and controller are fundamental to the operation of the vehicle.
The motor is properly sized to aUow for significant electrical assist and some minimal
performance as a ZEV. The motor is able to operate at speeds similar to the IC engine
while being efficient enough to require a reasonable size battery pack. The battery pack is
necessary to provide the storage capacity for the electrical system but is not so large as to
compromise the performance of the vehicle. The auxUiary systems supplement the electric
motor/controller and batteries by providing convenience and safety features.
24
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25
3.2 Electric Motor
The sizing of the electric motor and controUer is of vital importance to the HEV
performance. The electric drive system is matched to operate with the existing
powertrain. Since the electric motor and IC engine are connected in a paraUel structure,
the maximum speed of the motor is at least that of the IC engine (6000 revolutions per
minute, rpm). The power output of the motor is also sized to aUow for some Umited
operation as a ZEV. The motor/controUer pair is physicaUy smaU enough to maintain the
functionality of the vehicle.
The electric motor selection is based upon two essential requirements. The fu-st
criteria requires a reasonable acceleration time from zero to 48 kilometers per hour (kph)
and the second criteria requires that the vehicle maintain a speed of 48 kph (30 mUes per
hour, mph) at a reasonable grade. The power requirements were determined using an
electric vehicle simulation program, DIANE v2.1 [7]. The results of this simulation
determined that 7.1 kUowatts (kW) are required to maintain speed at a 2% grade and 11
kW peak power is required to achieve the acceleration requirements [7]. These power
requirements wUl be detailed in the discussion of the system model in Chapter 6.
3.2.1 Theory of Operation
The electric motor used in this vehicle is the Unique MobUity, Inc. DR156s
bmshless-DC motor. The brushless-DC motor is made up of two main components, a
rotor and a stator. The stator is fixed and the rotor is free to rotate. An illustration of a
26
simple bmshless-DC motor is shown in Figure 3.2 [8]. There are permanent magnets
fixed to the rotor and coils are mounted on the stator poles.
The number of phases, or pairs of stator poles, and the number of rotor magnet
poles determines how the motor wiU operate. The DR156s has three phases, which is the
most common configuration. In general, the higher the number of magnet poles, the
greater the torque produced for the same amount of current. This relationship does have a
Umit because as the number of magnet poles increases, the area for each pole decreases.
When the spacing between the magnets becomes a significant portion of the total area of
the magnets, this limit is reached. The high pole count, 24, along with the high energy
neodymium iron boron magnets in the motor provide a very high power density.
Figure 3.2 - Simple Permanent-Magnet Motor
The coils on the poles are energized by applying a switched current to them. The
change in current results in a magnetic field produced by the coil. The poles then act as
electromagnets and exert a force on the permanent magnets on the rotor and cause the
rotor to aUgn with the magnetic field. This force produces an alignment torque. The
27
speed and torque of the motor are controUed by the current being applied to the coils. In
this respect, the bmshless-DC motor is similar to an induction motor.
3.2.2 Motor Specifications
The Unique Mobility DR156s is specifically designed for EV or HEV use. Table
3.1 lists the parameters for the DR156s [9]. This motor is ideaUy suited for this
application. The rated power exceeds that determined using the DIANE v2.1 for ZEV
acceleration and ZEV constant velocity. The maximum speed of 7500 rpm exceeds that
of the IC engine (6000 rpm). The torque speed characteristics of the DR156s are shown
in Figure 3.3 [9]. The torque produced is relatively constant regardless of motor speed.
This aUows for a wide variety of vehicle gearing options. The motor also has an extremely
high power-to-weight ratio and is very compact.
3.3 Motor Controller
The Unique Mobility CR20-150 motor controller is specifically designed for use
with the DR156s brushless-DC motor. The CR20-150 is designed for EV use but can be
adapted for use in HEVs as weU. The CR20-150 has many significant built-in features. It
features fuU forward and reverse direction closed loop control with speed setpoint and
feedback. An adjustable current limit that is factory preset is incorporated to prevent
motor damage. Regeneration control to zero speed allows for various braking and battery
charging options.
28
Table 3.1 - Unique MobUity DR156s Parameters
Parameter Value
Rated Power (kW)
Continuous Torque @ 6750 rpm (in-lb)
Peak Torque - Continuous Stall (in-lb)
Peak Torque - Intermittent StaU (in-lb)
Max No-Load Speed @ 180 Volts (rpm)
Motor EMF Constant (KE, V/Krpm)
Motor Torque Constant (Kj, in-lb/Amp)
Cooling Type - Forced Air
CooUng Req'd @ Rated Power (scfm)
Max Winding Temperature (°F)
Winding DC Resistance l-l 25°C (ohms)
Winding Inductance @ 25° ( iH)
Number of Poles
Rotor Inertia (in-lb-sec^)
Motor Weight (lbs)
15.8
198
220
320
7500
20, ± 10 %
1.63, ±10%
36.4
300
.024
45
24
0.184
18.5
Figure 3.3 - DR156s/CR20-150 System Efficiency Map
29
3.3.1 Theory of Operation
The CR20-150 aUows the DR156s bmshless-DC motor to be used on a mobUe
platform. The DR156s requires a three-phase voltage input to operate properly. This
three-phase power is avaUable from stationary sources but the only electrical power on the
HEV is from the DC batteries. The CR20-150 converts this DC battery power to the
three-phase AC voltage that the DR156s requires.
The previous discussion on the theory of operation of the brushless-DC motor
provides some insight as to how the controller works. An alignment torque is produced
by the rotor when a coU or phase is energized. This coU is energized by applying a voltage
across it and causing a current to flow. When the coils of the different phases are
energized sequentially, it causes the rotor to rotate to align with each phase as each phase
is energized. By applying a voltage across each phase at the appropriate time, the rotor
produces torque and spins continuously.
Figure 3.4 shows a simplified six-step drive scheme that is used to drive the
motor[8]. The DC voltage is converted to three-phase AC by switching. By controUing
the frequency of the switching, the motor speed is controlled. The motor torque is
controUed by the duty-cycle of the switches. These switches represent power
semiconductors, power MOS, that are in parallel to accommodate the high currents
required. The closed loop speed control, regeneration control, and current limiting
features are accompUshed by accurate control of these switches. The diodes are included
to protect these power switches from the back EMF (electromotive force) that is
produced as the coUs discharge.
30
K cc ©
SgX D , i s, rr i S, \ D,i
\ D A ? S 2 \
'C
D2? S 4 \
>
Q,?
9-
.r ^
A
Figure 3.4 - Three-phase Motor Drive Circuitry
3.3.2 Motor Controller Operation
The CR20-150 is controlled primarily through the user interface cable. This is a
15-pin, female "D-sub" connector that allows the user to control the various functions of
the motor/controUer pair. The primary input signals for the controller are the desired
speed signal and the regen limit signal. Other input signals include a logic ON signal and a
controller enable signal. Output signals such as voltage references, analog and digital
actual speed signals, and a ground reference are included in the user interface cable.
The desired speed input signal and the regen limit signal are the two main control
inputs for the system. The desired speed input is an analog signal that is similar to a
vehicle accelerator pedal, where lOV corresponds to maximum forward speed and -lOV
corresponds to maximum reverse speed. The forward direction is never used in the Neon
HEV because the transmission handles aU of the system gearing.
31
The regen Umit input signal determines the regeneration level of the CR20-150.
This regen Umit signal is an analog +1V to -lOV for regeneration control, where +1V
corresponds to zero regeneration current and -lOV corresponds to maximum regeneration
current. This allows the motor to coast if the actual speed of the motor is greater than
the desired speed and the regen Umit is set to zero. This prevents the motor from loading
down the system unnecessarUy.
The power for the controUer is provided via two DC bus connections to the
batteries. The three-phase currents are suppUed from the CR20-150 to the motor by three
high power connections. Some examples of these three-phase currents are shown in
Figure 3.5. A motor interface cable contains the motor position and temperature signals
that are monitored by the controller.
3.3.3 Motor Controller Specifications
Table 3.2 Usts the CR20-150 motor controUer parameters [9]. The CR20-150
used in conjunction with the DR156s can operate at up to 90 percent efficiency. The
CR20-150 operates on a wide input voltage range (30V - 200V) and has low no-load
current draw. The controller is also fairly Ughtweight and compact.
32
50ft-r "f^Wtp'Sw"
¥i M
W«^*v
H
50ft + OS D 1(11)
Smx^tpJ
M AUK' h — 1 —
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^ ^ c ^ " ^ a»^—!•
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1i«9.5l47, i42.22l» 1
""-^— 1 • <
Oft OHz i a I K I l )
Frequency
i 500Hz
Figure 3.5 - CR20-150 Three-Phase Signals
33
Table 3.2 - Unique Mobility CR20-150 Parameters
Parameter
Max Vm (Vdc)
Min Vin
Min - No Load Current (amps)
Input Capacitance (|LIF)
Controller Weight (lbs)
Value
200
30
0.12
14100
27
3.4 Batteries
Battery selection is critical to the performance of any HEV. The batteries for the
Neon HEV are based upon a range requirement as a zero-emissions vehicle. A range of 5
miles (11 km) on purely electric power is required for the vehicle to have any practical use
as a ZEV. This is the maximum requirement for the batteries since the HEV mode has a
charge maintaining strategy. The batteries need to be as Ught as possible to prevent a
compromise in vehicle performance and functionality. As with any engineering decision,
cost also plays a significant role in battery selection.
To predict the battery requirements for vehicle range as a ZEV, it is necessary to
know the amount of power required and time it takes to accompUsh this ZEV range. The
DIANE v2.1 sunulation results specify 7 kW for 30 mph on a reasonable grade. At this
speed, 10 minutes is required to travel 5 miles. This means that assuming an ideal case
only 1.17 kWh is necessary to accomplish this goal. Assuming 75% - 80% system
efficiency, the energy requked to accompUsh the ZEV range goal is 1.52 kWh. With a
180 volt battery pack, as recommended for the CR20-150 motor controller, this requires
8.5 Ah (Amp-hours). Finally, by derating the batteries by a factor of two due to the high
34
discharge rate necessary to accompUsh this goal, a 3.15 kWh battery pack with a 17.5 Ah
rating is used to power the vehicle.
The Neon HEV uses a battery pack consisting of fifteen 12 Volt batteries
connected in series. These batteries are PowerSonic PS-12180 sealed lead-acid batteries.
The PS-12180 has a 17.5 Ah rating for the 20 hour discharge rate and a 11.5 Ah rating for
the one hour rate. The PS-12180 is a sealed, maintenance-fi-ee, leak proof battery that is
usable in any position. The charge lifetime varies from 1000 to 300 cycles assuming a
30% - 50% depth of discharge per use. This battery is used due to its easy maintenance,
reliabUity, and low cost. More advanced batteries such as Nickel-Cadmium have higher
performance, but prohibitive costs and limited availabUity prevent this from being an
option at this time.
3.5 AuxiUary Systems
The auxiUary systems on the Neon HEV are in place to make the vehicle as safe
and reUable as possible. The cooling system is used to prevent overheating in vital system
components. An on-board battery charger aUows for long-term charging and battery
maintenance. The energy meter documents the battery state of charge (SOC) and system
fuel levels. A passive fire suppression system is in place in the event there is a vehicle
malfunction. Various other smaU system elements provide safety and instrumentation
features.
35
3.5.1 Cooling Systems
As with any high power devices, the dissipation of heat is a very major concern on
the Neon HEV. The electric motor requires forced air cooUng at a rate of 36.4 square
feet per minute. A high-speed blower is used to satisfy this requirement. Heat as weU as
hydrogen and oxygen are produced at certain times during battery charging. VentUation
fans are included in the battery boxes to evacuate these gases.
The Unique MobUity DR156s has a maximum heat sink temperature of 70°C and a
maximum stator temperature of 120°C. If either of these temperatures are reached, the
motor controUer limits the current to the motor, reducing power [9]. To prevent the
motor fi"om operating at these high temperatures, an Ametek brushless-DC blower and
controUer are used. The blower speed is based upon a voltage provided by a bridge circuit
using a thermistor in the motor itself By cooling the motor, higher currents, therefore
higher power levels can be sustained.
The PS-12180 batteries are sealed but they are designed with one-way vents to
aUow gases to escape during charging. The accumulation of oxygen and flammable
hydrogen in the battery boxes is a dangerous consequence. To prevent this accumulation
of gasses, a 24-Volt DC fan is incorporated into each battery box. These fans run
continuously during vehicle operation and during charging. The power for the battery box
fans as weU as the blower and controller are provided via a Cosel DAS 1 OOF-24 DC-to-DC
converter that runs from the main battery pack.
36
3.5.2 Battery Charger
As with any EV or HEV, battery charging and maintenance are a primary concern.
Proper battery charging and maintenance can greatly enhance the Ufetime of a battery. A
Zivan K2 battery charger is used for one method of battery recharging on the vehicle. The
Kivan K2 charger is a 1500 watt charger that uses microprocessor control to fit the
charging cycle that best fits the type of battery.
The Kivan K2 charger is factory preset for the sealed lead-acid battery used on the
Neon. It has an overaU efficiency of 85% and a tolerance of 1%. The programmed
charging profile is shown in Figure 3.6. The charger puts a constant 180V, lOA charge on
the batteries until the batteries reach an 80% SOC. A high voltage, 0.5A charge is then
applied for 40 minutes. The unit has an automatic shutdown at 14 hours. A temperature
sensor for the charger is located in the battery box to aUow for temperature compensation.
The charger is located in the rear of the tmnk.
.nX 2.A V/cdl re
14 hours
)40nun.'
14 hours
Figure 3.6 - Charge Characteristic Curves
37
3.5.3 Energy Meter
The Cmising Equipment Co. Kilowatt-hour-i-2 (KWH-H2) Meter is a
microprocessor-controlled energy monitoring device specifically for use with EVs or
HEVs. The KWH-i-2 keeps track of and displays not only the battery SOC, but also the
CNG temperate and pressure levels. The KWH-i-2 measures the current battery pack
voltage and current, and tracks these over time to show the kilowatt-hours and amp-hours
used. The KWH-i-2 monitors the electrical system for any chassis fault and has an auto-
shutdown relay that activates when a chassis fault is detected.
The KWH-I-2 uses a 50 mUUohm shunt in series with the positive battery pack Une.
From this the battery voltage and current are monitored within 0.1 A accuracy and IV
accuracy. The KWH-i-2 uses a pressure transducer in the fuel line near the tanks to
monitor tank pressure. A temperature transducer is fixed to one of the tanks to allow for
tank temperature measurements. The KWH-i-2 display unit also has an RS-232 output that
allows data from the energy meter to be written to a terminal program or data file. The
KWH-I-2 is powered by a separate 6 Ah medical instmmentation battery and is located
beneath the passenger seat. The display unit is mounted in the center console of the car
for easy access.
3.5.4 Fire Suppression System
Due to the experimental nature of the vehicle, a passive fire-suppression system is
included. The Pheonix Mark-IIA Fire Suppression System is a halon based
microprocessor controUed system that has multiple firing methods. This halon system
38
minimizes the residue produced when fu-ed. The system is powered by the 12V battery for
the IC engine and the halon bottle is stored in the tmnk area adjacent to the CNG tanks.
The Pheonix system has three possible methods for activation. The system can be
activated passively using temperature sensors. There are four thermal adjustable heat
detector switches, two located in the engine compartment and one located in the battery
boxes. In the event of a fire, these thermal switches open at a set temperature and cause a
solenoid to open the halon bottle. The halon is routed through aluminum tubing to four
port nozzles, two in the engine compartment and one in each battery box.
The fire suppression system is also activated manually in two ways. The bottle
may be fired by moving the three-position switch on the control panel to the upper
position. This electronically opens the solenoid for the bottie and releases the gas. The
system can be activated mechanicaUy by depressing the knob on the remote cable. This
feature is included in the event of a battery failure, although the system has an audible
alarm to warn when battery voltage reaches an unsafe level.
3.5.5 Main Disconnect. Fusing and Soft Start Circuit
The main disconnect for the batteries is the Square D KAL26150. This is
necessary to provide total isolation of the battery pack from the rest of the vehicle. The
disconnect switch is capable of carrying lOOOA and has a breaking capacity of 10,000A.
The disconnect is manuaUy closed but can be manuaUy or remotely disconnected. The
remote trip is controUed by a dash-mounted switch that can be used to disconnect the
batteries in the event of an emergency.
39
The high input capacitance of the Unique MobiUty CR20-150 motor controUer
requires that a soft start circuit be included on the DC bus connections for the controller.
A large current spike could occur when the main battery switch is closed if the soft start
circuit is omitted. To prevent this from occurring a 50 Ohm, 20 Watt, current-Umiting
resistor is connected in paraUel with a Kilovac PD150 contactor. A time delay relay
controls the PD150 contactor. When tiie vehicle key switch is turned on, the current to
the CR20-150 controUer is Umited by the 50 Ohm resistor. After the capacitor has had
time to fuUy charge through the resistor, approximately 8 seconds, the time delay relay
closes the PD150 contactor to bypass the current Umitmg resistor.
40
CHAPTER 4
SYSTEM CONTROLLER HARDWARE
4.1 Introduction
The system controUer for the Neon hybrid electric vehicle is a microprocessor
based system that manages the electric drive system for the vehicle. The objective of the
system controUer is to incorporate the electric motive power of the vehicle to increase fuel
economy and reduce emissions, whUe being transparent to the operator. A block diagram
of the system controller and related systems is shown in Figure 4.1. The system controUer
monitors several IC engine signals, the status of the battery pack, and the driver control
signals to determine the usage of electric motor power.
Neon PCM Battery Pack
• / -
Regen Control
] Controls, Sensors
IC! Engine
HCl
Volts
RPM ,
MAP TPS
I Controls, Sensors
GEM System
i Unique
Mobility CR20-150
Motor Controller
DRl56s DC Brushles Motor
Figure 4.1 - System ConfoUer and Related Systems
41
The system controUer for the Neon HEV is based upon the Motorola MC68HC11
microcontroller. This device is one of the pioneers for control applications in automotive
systems and is stiU in use today in many systems such as anti-lock braking systems and
vehicle traction control. This 8-bit microcontroller is incorporated into the system using a
product evaluation board to aUow for system development and to provide some of the
necessary extemal circuitry, i.e. memory addressing and communication hardware. The
input and output signals of the microcontroUer are conditioned to interface with different
systems on the vehicle through a custom designed interface board. This chapter deals
specificaUy with the system controUer input and output signals and the system controller
hardware.
4.2 System ControUer Inputs
The system controller monitors signals from three major systems: the IC engine
and powertrain control module (PCM), the driver input signals, and the main battery pack.
By observing these signals, the system controller can determine how much electric power
to deliver or absorb depending upon driving conditions. These signals come in a variety of
formats such as analog voltages, paraUel digital data, and TTL pulse signals. The
processing of these signals will be further discussed in Chapter 5.
4.2.1 IC Engine and PCM Uiput Signals
There are four main signals that are produced by sensors on the IC engine that are
of critical importance for HEV operation. The absolute intake manifold pressure or MAP
42
signal is observed using a pressure transducer mounted on the intake manifold. The
manifold pressure for this vehicle varies between 1 psia (pounds per square inch absolute)
and atmospheric pressure which is typicaUy around 14.7 psia depending on the altimde.
The transducer has an output voltage of 0.8 V to 4.14 V for these pressure values
respectively. The MAP sensor voltage is approximately 1.5 V at idle and 4.14 V at wide
open throttie. The manifold pressure reading is significant due to the fact that it directiy
relates to the load on the engine [13].
The engine speed signal in rpm, is significant as weU as the manifold pressure
because it has a dramatic effect on fuel economy. In general, for a given manifold
pressure, fuel consumption increases with engine speed [14]. This is due to the fact that
as the engine mns faster, more fuel is deUvered to the constant volume of the engine
cyUnders. The engine speed signal is measured from the tachometer output from the
PCM. This signal is a TTL signal whose frequency corresponds to engine rpm. The
frequency of the tachometer signal corresponds to lOOHz per 3000 rpm. The PCM
determines the engine speed based upon the crank and camshaft signals it receives.
The manifold pressure and engine speed can be used to determine an engine load
function that corresponds to the amount of torque being produced by the engine [13].
The equation for this relationship may be written as:
T,,,{J^,p) = k,{N) + k,{N)p.
where the engine torque produced, Teng, is a function of engine speed in rpm, N, and
manifold pressure p. The constants ki = -21.55 - 0.009 IN and k2 = l.l\5^ 0.0014N are
43
experimentally determined constants that are found using test data and Unear regression
analysis.
The engine coolant temperature signal is significant for similar reasons. Emissions
levels and fuel consumption are at their highest when the engine is relatively cold. The
engine coolant temperature (ECT) signal is a voltage from one of the PCM inputs. The
ECT sensor is a thermistor mounted in the engine block, where the coolant flows around
the thermistor housing. The PCM appUes a voltage to the thermistor through a resistive
network, forming a voltage divider. The voltage across the thermistor corresponds to the
coolant temperature. The standard operating temperature for the engine, 175°F,
corresponds to a voltage of around 2.3 V.
The oil pressure switch input is a digital signal that varies from 0 V to 12 V. The
oil pressure switch is on (-1-12 V) when the engine oU pressure reaches a minimum level.
This occurs only when the engine is miming. In ZEV mode, the engine must be off and, in
HEV mode, the engine must be running to determine the validity of the other engine
sensor signals.
4.2.2 Operator Input Signals
The operator input signals are perhaps the most important input signals because
they reflect the intentions of the driver. The throttie position signal is an analog voltage
that comes from a 10 KQ. potentiometer on the throttie body. The references for the
potentiometer are a 5 V signal and system controller ground. The voltage for 0% tiirottle
44
is approximately 0.7 V and the corresponding voltage for fuU throttie is 4.7 V. The TPS
is mainly used in the ZEV mode to aUow the operator to increase speed.
The brake position signal is similar to the TPS signal except that the output
voltage range is significantiy smaUer. This is due to the fact that there is much less travel
in the brake pedal, therefore the potentiometer rotates less. The output voltage for no
brake pedal depression is 1.0 V and fully applying the brakes results in an output voltage
of 3.5 V. The brake position signal is used to control the regenerative braking capabUities
of the vehicle in the HEV and ZEV modes of operation.
The clutch signal is a digital signal that represents the position of the clutch pedal.
This signal comes from a clutch switch mounted at the top of the clutch pedal. The
voltage references for this switch are the vehicle battery voltage and chassis ground.
When the clutch is at rest a low signal is output and when the clutch is slightiy depressed a
high signal is output. This signal is used differently for the various modes of operation. In
ZEV mode, it is necessary for the clutch to be fully engaged to prevent the electric motor
from turning the input shaft of the IC engine. In hybrid and IC mode, when the clutch is
depressed, no torque is being appUed to the transmission input shaft. This prevents the
motor from loading down the transmission and aUows for proper shifting.
The two other user selectable inputs are the vehicle mode and regeneration control
mputs. These inputs are digital signals that are provided by the two switches located in
the center console. The mode switch sets a two-bit pattem depending upon whether ZEV,
HEV, or IC mode is selected. The regeneration switch outputs a single bit that allows the
user to turn the regeneration control on or off during the IC and HEV modes. The
45
regeneration control in ZEV mode is not user selectable and is only regulated by the
system controUer.
4.2.3 Battery Pack Voltape Sign il
The battery pack voltage is of significant importance to the system controUer. The
battery pack voltage typicaUy varies from 120 V to 210 V depending in the battery state of
charge (SOC). This voltage is divided down to an analog voltage of 0 V to 5 V using a
high-impedance resistive network. The battery pack voltage is significant due to the
charge maintaining strategy of the hybrid vehicle. That is, the engine load function,
previously mentioned, can be modified to keep the batteries at as high a SOC as possible
for the given driving and operating conditions.
4.3 System Controller Outputs
The system controUer's primary function is to control the operation of the electric
motor . This is accompUshed via two main control signals that are input to the Unique
MobUity CR20-150 motor controller. The desired speed signal is analogous to a vehicle
accelerator pedal. This signal is carefully controUed to ensure the safety, reliabUity, and
functionality of the vehicle. The desired speed signal is an analog output voltage from the
system controUer that varies from 0 V to -12 V. This causes the motor to rotate from 0
rpm to 7500 rpm in the reverse direction. This counter-clockwise rotation is used to
match the rotation of the input shaft of the IC engine. The desired speed signal controls
46
tile amount of electrical assist in HEV mode. In ZEV mode, tiie desired speed signal
actually controls the speed of the vehicle.
The regen control signal determines tiie amount of braking torque that wiU be
appUed to the vehicle. This 0 V to -12 V analog output is sent from the system controUer
to the regen limit input of tiie CR20-150. This signal is used for several charging modes in
the vehicle. In the ZEV mode, the regen control output controls the regenerative braking
aspect of the vehicle. In tiie IC mode, the regen control signal allows for idle charging of
the batteries. In HEV mode, regenerative braking and idle charging during times of low
engine load are controUed by the regen control output signal.
The other output signals from the system controller are the voltage reference
signals that are necessary for the operator inputs to the vehicle. A 5 V regulated, isolated
reference is supplied to the throttle position and brake position potentiometers as well as
the mode and regeneration switches. The system controller ground is also supplied to the
switches and potentiometers.
4.4 M68HC11 MicrocontroUer Evaluation Board
The M68HC1 lEVB microcontroUer evaluation board is the platform used to
implement the 68HC11 in the system controller design. Figure 4.2 shows a basic block
diagram of the system controUer hardware. The M68HC1 lEVB provides aU of the
necessary hardware for system development and evaluation. Also included are some
software tools that wiU be furtiier discussed in Chapter 6.
47
4.4.1 68HC11 Architecture
The MC68HC11A8 is a highly sophisticated 8-bit microcontroller unit (MCU) that
has Umitiess applications in a variety of control systems. This MCU has advanced, on-chip
peripheral capabiUties, a relatively fast bus speed of 2 MHz, and low power consumption
via HCMOS technology. The A8 also incorporates on-chip read-only memory (ROM),
which is disabled for this appUcation, electricaUy erasable programmable ROM
(EEPROM), and random-access memory (RAM). Figure 4.3 shows a block diagram of
the MC68HC11A8 architecture [15].
The core of the MCU is the M68HC11 central processing unit (CPU). The
M68HC11 CPU is an 8-bit CPU tiiat has a 64K-byte memory map. The CPU performs all
of the software instmctions in tiieir programmed sequence. The M68HC11 CPU supports
more than 256 instruction opcodes that include 8-bit and 16-bit integer mathematic
operations, bit testing and manipulation, and memory manipulation. The M68HC11 CPU
supports several addressing modes and has its own machine-specific instruction set [15].
The strength of the MC68HC11A8 is in the on-chip peripheral subsystems. Port B
is an 8-bit parallel output port. In the system controller. Port B is used to generate a
digital value that corresponds to the desired speed and regen control signals. Port C is a
software-configurable, 8-bit parallel I/O (input/output) port. Port C is used to generate
some of the data latching signals for the desired speed and regen control signals, but its
main function is as an input port for the digital signals previously mentioned in the System
Controller Inputs section.
48
M68HCllEyB Evaluation
Board
+12/
+5>
GN )
•IT'
P(7
Ports
Interface Board
System Controller Power Supply
PE7 - PE3 y^
PC6 - PC2
ST IB
Digital-to-Analog Conversion Hardware
Isolation Hardware
System Controller
7^
' • ^
/
Regen Control
Desired Speed
Driver Inputs
Engine Sensors
Batteiy Pack
Figure 4.2 - System Controller Hardware Block Diagram
The MC68HC11A8 has an on-chip analog-to-digital (A/D) converter system. This
system is an 8-channel A/D converter system with 8-bit resolution. These 8 analog
channels are accessed through Port E on the A8. The successive-approximation A/D
converter uses a capacitive charge-redistribution technique for conversions and has a
typical accuracy of ± 1/2 of the least significant bit (LSB). The A/D converter has two
specific modes of operation. The A/D converter can read 4 of the 8 channels
simultaneously or take 4 successive samples of a single channel [15]. The on-chip A/D
converter is used to read the 5 analog inputs previously discussed is section 4.2.
The last of the peripheral systems used in the system controller is the main 16-bit
free mnning timer with real-time intermpt. There are several other peripheral systems
available that are not used in this appUcation. The main timer is a software-scaleable free
49
mnning timer that allows for accurate measurement or production of digital timing signals.
Three input-capture functions are incorporated to record the time of a selected transition
on a given input pin. This is used in tiie system controller to determine tiie frequency of
timing signals such as the tachometer input and the electric motor speed signal.
Kou - m g n t s
luin - ?!« Bncs
CEmOU-ii ; BYTES
Hint • Hi-m •
m • K\ •
P f 0 •
I <X3 « oa
L HnOOCWIEIIRUPI
oorwAiococ
ss SCK
M09
USO
90 •
tJU. •
AOonESS4Mi«au5
uooe -
UOOE aucT
HMOSHMStO
• ^ M tn , C H P
8 >'
JLXJL ! ! J L! JL
•<—•• p * ;
• - p «
> - P«5
• PA4
>• p «
•« Pm
•< PAl
• < P M
• « > - P05
<—*- nt *—>• roj
<—*- POJ
< — * - P01
< *- POO
(wnoKcnoNC
' ' " ' • ' ' ' ' ' ' ' ' " " ' •
1=
i S s i s " 9SSS999§ 'I' I«P««D
Figure 4.3 - MC68HC11A8 Block Diagram [15]
4.4.2 M68HC1 lEVB Evaluation Board
The M68HC1 lEVB is a development aid tiiat is commonly used in the
development of embedded microcontroUer applications. Since tiiis vehicle is a unique
system, the evaluation board (EVB) is an ideal basis for tiie system controUer. Figure 4.4
50
shows a system-level block diagram of the M68HC1 lEVB. From tiie diagram, it is
obvious that the MCU is only a small portion of what is included on the evaluation board.
The core of the evaluation board is tiie MC68HC11 itself. Figure 4.4 shows that
only Port A, the main timer port, Port D the serial communications port, and Port E, the
analog-to-digital conversion port, are accessible directiy from tiie MCU. Ports B and C
are used as address and data Unes for the evaluation board. These ports are replaced by
the MC68HC24FN Port Replacement Unit (PRU). The PRU allows tiie evaluation board
to operate in 'single-chip' mode, that is the evaluation board simulates the operation of a
single 68HC11 chip [16].
One main advantage of the EVB is the fact that it includes extemal memory and
addressing hardware. The EVB includes 8 kilobytes (Kb) of EPROM that contains the
BUFFALO (Bit User Fast Friendly to Logical Operations) monitor program. This
program has many useful utUities that are used in the software development process. The
EVB also contains the addressing hardware and support for 8 Kb of user RAM via an
MCM6164 8K X 8 RAM chip. This memory may be used to store data used in programs
or the actual programs themselves during the software development process. The EVB
also supports an additional 8 Kb of user RAM or EPROM. For the EVB's appUcation in
the system controller, this memory is an 8K x 8 EPROM (2764) that stores the system
controller program. Upon system reset, the instmctions in this EPROM are executed.
The M68HC1 lEVB communicates to an external terminal via an RS-232C
interface by using an MC68B50 ACIA (Asynchronous Communications Interface
Adapter). Another extemal host interface is an RS-232C port that is software
51
programmable. These communications interfaces aUow extemal programs to be loaded
onto the EVB and debugged using the BUFFALO monitor program. These two options
of EVB interface allow for flexibiUty in tiie software development process.
0007 \> ; S | 00-07 fS^
ACIA
-\ RiO
RS232C
onvtiis ANO
REaiVERS
^ TiO HOST
3 l r coMPUTtR CONTROL
;:>
• ^
IiO
RiO > TERMINAL
CONTROL
Figure 4.4 - M68HC1 lEVB Block Diagram [16]
4.5 Interface Board
The system controller interface board is a custom designed board that allows the
M68HC1 lEVB to function as a system controller for the HEV. The interface board
consists of three major parts: the isolation hardware, the digital-to-analog (D/A)
conversion hardware, and the power supply hardware. The entire system is implemented
using a custom designed printed circuit board (PCB).
52
4.5.1 Isolation Subsystem
The main battery pack is isolated from the chassis on the Neon HEV. To avoid
creating a potentially dangerous chassis fault problem through the system controller, all
signals that are referenced to the chassis are isolated as weU as all signals referenced to the
battery pack. These signals are both analog and digital with varying voltage levels, so
multiple isolation elements are needed. The isolation hardware is shown in Figure 4.5.
The digital inputs to the system controUer are isolated using an HI ILl Schmitt
trigger output optocoupler. This optocoupler is specifically designed for high-speed
appUcations and has a maximum data transfer rate of 1 MHz. The input current to the
photodiode on the input of the optocoupler is limited by a resistor. The value for this
resistor varies depending upon the signal being measured. The engine speed signal is a
TTL voltage level whUe the clutch switch and oil pressure signals vary from 0 V to 12 V.
The output signal from the Schmitt trigger requires a puU-up resistor for proper operation.
The output from these optoisolators is inverted so aU digital input signals are sent through
an MC74HC04 inverter before connecting to the 68HC11 [17].
The analog input signals to the system are isolated using the Texas Instmments
4N35 optocoupler [18]. Figure 4.5 shows the extemal circuitry required to aUow the
optocoupler to be biased properly. The transistor used on the input photodiode biases the
diode to allow it to operate in a Unear manner. The output of the phototransistor requkes
a pull-up resistor for proper operation. AU analog input signals to tiie system are 0 V to 5
volts, so aU analog isolation circuits are identical.
53
' 1
0^ »C1« WtK
J..-A <'-
HI IL : I
cu/ir» • — W \ — ^ Ift- ^ '
- ^ ^
Hl lLl
* 0 (A/I c u i m m
ML fUf«K£ • — - ^ 1
J^
K4 (*/• e—CllUi • 0 -
Figure 4.5 Isolation Hardware
4.5.2 Digital-to-Analog Conversion Subsystem
The D/A conversion subsystem is necessary to generate the analog desired speed
and regen control signals from a paraUel digital output. The parallel data for this
conversion is output through Port B of the 68HC11. This data is then converted into two
-i-12 V to -12 V signals for the corresponding desired speed and regen control signals via
two buffered D/A converters.
The parallel digital data that corresponds to the desired speed signal is sent to a
National Semiconductor DAC0830 digital-to-analog converter. This D/A converter is
ideal for this appUcation because it requires no extemal buffering or latching of standard
logic levels. The D/A converter produces two current outputs that are used in conjunction
with an op amp circuit to produce an output voltage. Figure 4.6 shows the D/A
54
conversion hardware. The circuit that produces the desired speed output signal requires
an extra op amp circuit on the output to allow for a bipolar output voltage swing, that is
-H2Vto-12V.
The regen control analog output signal only requires a unipolar output swing, 0 V
to -12 V, which eliminates the need for tiie additional output op amp stage. The parallel
data for the regen control signal is on the Port B Unes with the desired speed data. The
latching between the two sets of data is controlled by the latching control logic shown in
Figure 4.6. The latching logic is controUed by PC7 (bit 7 of Port C) and the STRB (strobe
B) signals. PC7 is a software controlled output that differentiates between the two sets of
data. The STRB signal is a digital signal that is asserted low every time there is a write
operation to Port B. By NANDing the PC7 and STRB inputs and the inverse of PC7
(PC7*) and STRB, the proper data is latched on the corresponding D/A converter.
4.5.3 Power Supply Subsystem
The power supply for the system controller provides isolated voltage levels
compatible with the microcontroller evaluation board and the interface board. The
evaluation board requires the majority of the power. The EVB requUes a 5 V signal rated
at 1 A, ±12 V supply rated at 250 mA [16]. These specifications are greatiy overrated.
The interface board requires the same voltage levels but only draws around 125 mA total.
The power supply is provided via tiie Power Convertibles WP15R12T12 triple
output DC-to-DC converter. The WP15R12T12 is a 15 Watt DC-to-DC converter that
can accept an input voltage range of 9 V to 18 V and draws 750 mA to 1650 mA. The
55
WP15R12T12 has a wide temperature operating range, high efficiency, and features short-
circuit protection. The WP15R12T12 requires no significant cooUng and has a very
compact package (2.8" x 2.4" x 0.44"), making it ideal for this appUcation.
4>i
12V
m IFH
ea
A
n; - V
•
1 B r
Figure 4.6 - D/A Conversion Hardware
4.5.4 Printed Circuit Board Layout
The custom nature of the interface board requires the fabrication of a printed
circuit board (PCB) layout for maximum reUabiUty. Figures 4.7 and 4.8 show the
component and solder side layouts of the interfacing hardware. This PCB is designed for
maximum functionaUty and reUabUity using P-CAD version 7.0 PCB layout editor.
56
CN(^
Figure 4.7 - Component Side PCB Layout of Interface Board
5-7
Figure 4.8 - Solder Side PCB Layout of Interface Board
58
CHAPTER 5
SYSTEM CONTROLLER SOFTWARE
5.1 Introduction
The software for the system controller is the most dynamic element of the overaU
system. Small changes in the control system software can have dramatic effects on the
fuel consumption, emissions, and performance characteristics of the vehicle. The control
software is written in 68HC11 assembly language. This allows for precise control of the
low-level operations required for this application and maximizes the speed of execution.
The M68HC1 lEVB evaluation board package provides assembly and debugging tools
that are essential in software development. These tools allow for extemal programming,
program tracing, memory access, and other related debugging techniques.
The system controller software is written to maximize the fuel economy and
performance of the vehicle while reducing tailpipe emissions. The software is designed to
make the vehicle easy to operate, regardless of driver experience with the HEV. Safety
features are also incorporated in software in the event of vehicle malfunction. The
software that accompUshes these goals is discussed in the following sections.
5.2 System Controller Main Program
Figure 5.1 shows the basic structure of the system controUer software. The
program is written in assembly language, so there are many low-level details tiiat wUl not
59
be discussed in tiieU entkety. The flowcharts in this chapter represent tiie higher level
actions of the system controller.
i ZEV Mode
i
Sensor Initialization
^ '
Data Acquisition
"
IC Mode
' '
X HEV Mode
i
Figure 5.1 - System ControUer Main Flowchart
When power is applied to the system, an initialization routine is executed. This is
the only time that this routine is executed. After the program is initialized, the program
mns in a continuous loop as shown above until the power to the system is disconnected,
which is when the vehicle key switch is tumed off. The first action in the initialization
routine is to send the electric motor controller data corresponding to zero speed and no
regeneration, to avoid any spurious output. The next action in initialization is to enable
the charge pump for the A/D converter and delay, about 100 ms, until the A/D
conversions can be assumed to be valid.
Four repetitive samples are taken of the manifold pressure (MAP), the throttie
position (TPS), and the brake position. The samples for each of these signals are averaged
to minimize any noise interference with tiiese analog signals and the values are stored in
RAM. This aUows the controller access to the atmospheric pressure, which varies with
60
altitude and weather conditions, and the initial positions of the throttie and brake. These
signals are used in the various routines to determine the engine conditions based upon an
offset from tiie initial sensor levels.
5.3 Data Acquisition
The data acquisition routine is responsible for updating the status of the vehicle by
reading the various sensors and inputs. Figure 5.2 shows a basic diagram of the data
acquisition routine. At various other times in the program individual sensors and inputs
may be sampled, but only this routine is responsible for data acquisition for the entire
system.
First the data acquisition routine makes four repetitive reads of the analog signals
from the MAP sensor, the TPS sensor, the engine coolant temperatiu-e (ECT) sensor, the
battery pack voltage, and the brake position. The four values for each analog signal are
averaged to minimize noise effects from the high power switching in the vehicle. These
values are then stored in RAM locations dedicated for each specific signal. These memory
locations hold the current data values until the data acquisition routine is mn again and
then they are overwritten.
The digital inputs are read through seven bits of the Port C on tiie HCl I. These
inputs are stored as a binary value in a memory location STATUS. The STATUS
information word is stored in RAM and is updated every time the data acquisition routine
is executed. At tiie end of tiie data acquisition section, the mode is determined via the
digital mode bits, and the corresponding mode routine is executed.
61
1 Take Repetitive
Sample of Analog Signals
Average Analog Signals
Store Analog Signals in Memory
Read Digital Signals
Store Mode, Regen, Clutch, and OU Pressure in
STATUS Memory Location
To Mode Routines
Figure 5.2 - Data Acquisition Flowchart
5.4 ZEV Mode
The ZEV mode routine allows the Neon HEV to operate purely on its electric
capabiUties. Driving the vehicle in ZEV mode is very simUar to driving a normal car with
a few minor adjustments. The accelerator pedal is stiU the primary input for the driver to
control the vehicle speed and the brake pedal performs basicaUy the same function as in a
normal vehicle. The main difference is in shifting gears in the HEV. The clutch must
62
always be engaged in ZEV mode to keep tiie electric motor from tuming the IC engine,
gear shifts are accomplished by simply moving the shifter to tiie desired gear position.
Figure 5.3 shows tiie flow control of tiie ZEV mode routine.
so
To Data Acquisition Routine
From Data Acquisition Routine
No
No
Yes
i Convert BP
to Regen Control
i Output Regen
Control
i
No
i Convert TPS
to Desired Speed
I Output Desired
Speed
Figure 5.3 - ZEV Mode Flowchart
The first step in the ZEV routine is to check the status of the clutch. If the clutch
is engaged the ZEV routine wiU continue, if the clutch is not engaged the ZEV routine is
exited. Next the program checks to make sure the engine is not mnning by checking the
oU pressure light. The current throttie position is retrieved from memory and this value is
checked for vaUdity. If there is a failure in the throttle potentiometer assembly, the value
of the TPS will be out of a range of expected values. If the TPS is out of range, the ZEV
63
routine is terminated. The same procedure is followed for the brake pedal input. This is
included as a safety feature to prevent tiie vehicle from operating using an erroneous input
signal.
The ZEV routine then branches to the brake input signal routine. If the brake
signal is above its initial condition plus a buffer value, tiie brake is assumed to be on. The
buffer value is larger to ensure the driver really wants to brake. The brake pedal may not
always return to its exact initial position due to brake fluid levels, engine conditions, etc.,
so this buffer is necessary for proper operation. Once the brake is determined to be on,
the brake position is converted to a digital word corresponding to the regen control signal.
This digital word is sent to the D/A converter for the regen control signal and a digital
word corresponding to zero desired speed is sent the D/A converter for the desired speed
output signal. The further the brake pedal is depressed, the more regenerative braking is
applied. The ZEV routine is then terminated and the data acquisition routine is executed,
while still generating the corresponding regen control signal.
If the brake pedal is not depressed, the current throttie position is accessed from
memory. By branching on the brake input signal instead of the throttie position signal, the
brake has a higher priority than the accelerator pedal. It is obvious why this safety feature
is important. The throttle position is converted to a digital word corresponding to the
desired speed signal and is sent to tiie D/A converter for the desired speed. A digital word
corresponding to zero regeneration is generated and sent to the D/A converter for the
regen control signal. The ZEV routine is then exited and the data acquisition routine is
executed, with the corresponding desired speed level still on the output.
64
5.5 Internal Combustion Onlv Mode
The internal combustion only (IC Only) routine is a simple routine that aUows the
user to recharge the batteries if so desUed. This is determined using the regen switch in
the center console. This feature is useful for idle charging the batteries if no extemal
charging source exists. This feature is also useful during long, steady drives when engine
transients are minimal. Since tiie IC only mode is of Umited use, this feature is mainly used
for idle charging. Figure 5.4 shows tiie IC only mode flowchart.
The IC routine checks tiie status of the clutch in the STATUS memory location. If
the clutch is engaged, there will be no regeneration and the program returns to the data
acquisition routine. This is to prevent the regenerative action of the motor from loading
down the transmission during shifts. The routine then verifies that the engine is mnning
and checks the regen switch position from the STATUS memory location. If regeneration
is selected and the engine is mnning, a digital word corresponding to the maximum
regeneration level is sent to the D/A converter for the regen control. The routine then
returns to the data acquisition routine.
5.6 HEV Mode
The HEV mode is the primary mode of operation for the vehicle. The paraUel
stmcture of the HEV makes precise electric motor control necessary for maximum
driveabiUty and functionality. The electrical assist strategy used in the HEV mode has
been previously discussed. This strategy is accomplished by observing the MAP, which
65
corresponds to the engine load. When the MAP is low, there is Uttie load on the engine
and when tiie MAP is high, the vehicle is under heavy load conditions. The flowchart for
the HEV mode routine is shown in Figure 5.5.
To Data Acquisition Routine
No
No
No
From Data Acquisition Routine
Set Regen Control to Max
I Output Regen
Control
I Figure 5.4 - IC Only Mode Flowchart
The routine first reads the clutch and engine mnning bits from the STATUS
memory location. Provided the clutch is not engaged and the engine is mnning, the
battery pack voltage and the engine coolant temperature are read from the corresponding
memory locations. These signals are used in calculating the thresholds for high and low
engine loads. If the battery pack is at a low voltage, the MAP threshold for low engine
66
load is raised to allow for more regeneration. When the engine is cold, the MAP threshold
for high engine load is lowered to use more electric power.
To Data Acquisition Routine ,
1 No i
i No
i
Medium
From Data 'Acquisition Routine
^ ^ U u t c l i ^ v ^ ^v^ngaged? , , ,^
WYes
^ ^ ^ ^ g i n ^ V ^ \ ^ 0 n ? ^ ^
yVes Read Battery
and Temperature
• Compensate
MAP Thresholds
t Read and
Average MAP
X ^ ^ ^ A ^ \ ^ ^ H i e h ' \ V a l u e ^ > H ^
WLOW
HEV Regen Routine
T
HEV Assist Routine
^ '
Figure 5.5 - HEV Mode Flowchart
The MAP value is read from its memory location and if it falls between the high
and low threshold values, the HEV routine is terminated and control returns to the data
acquisition routine. If the current MAP value is above the threshold for high engine load
67
tiie HEV assist routine is executed. If the current MAP value falls below the low
threshold, the HEV regeneration routine is executed. Program control returns to the data
acquisition routine at the end of the HEV assist and regeneration routines.
5.6.1 HEV Assist Routine
A flowchart for the HEV assist routine is shown in Figure 5.6. The effect of this
routine is to slowly ramp the desired speed of the electric motor untU it is maximum. This
increases the driveabUity of the vehicle because there is not a sudden 'jerk' when the
electric motor engages. The delay associated with ramping in the electric motor power is
variable, allowing for modifications to allow the vehicle to operate more responsively if
necessary.
The HEV assist routine keeps the desired speed signal at its maximum untU the
routine is exited in one of two ways. When the MAP drops below the threshold, the
routine slowly decreases the desired speed untU it reaches zero and then retums to the
data acquisition routine. This prevents a sudden 'jerk' when the electric motor is
disengaged. It is worth noting that the MAP threshold for disengaging the electric assist is
lower than the MAP threshold for engaging the electrical assist. This hysteresis is
included to prevent unwanted transitions when the MAP is very near the threshold level.
The HEV assist routine is also terminated when the clutch is depressed. This prevents the
electric motor from adding power during gear shifts, which could cause shifting problems
or even cause transmission damage.
68
5.6.2 HEV Regeneration Routine
The HEV regeneration routine is very similar to tiie HEV assist routine. Figure 5.7
shows tiie flowchart for tiie HEV regeneration routine. The routine slowly ramps up the
regeneration control signal until it reaches maximum regeneration current. This level is
maintained untU the MAP increases above tiie threshold. The regen control signal is
slowly decreased untU a signal corresponding to no regeneration current is reached. The
hysteresis mentioned above is also included in the regeneration routine to prevent
unwanted transitions. The clutch dependency is also included to prevent the electric
motor from 'locking down' the transmission during shifts.
69
To Data Acquisition Routine
From HEV Mode Routine
Yes
Output Desired Speed = 0
Output Desired Speed
I Sample and
Average MAP
Delay - Increase Desired Speed
Yes
Yes Delay - Decrease Desired Speed
Figure 5.6 - HEV Assist Routine Flowchart
70
To Data Acquisition Routine
Output Regen Control = 0
Yes
From HEV Mode Routine
Output Regen Control
I Sample and
Average MAP
Delay - Increase Regen Control
Delay - Decrease Regen Control
Figure 5.7 - HEV Regeneration Routine Rowchart
71
CHAPTER 6
RESULTS
6.1 Introduction
The previous chapters detaU the various aspects tiiat went into the development of
the Texas Tech Neon HEV project. This chapter focuses on the results of the finished
vehicle at this stage in development. Many of these results were obtained through testing
at the 1995 Chrysler Hybrid Electric Vehicle ChaUenge. This event was held the first
week of June 1995 at tiie Chrysler Technology Center (CTC) in Aubum HiUs, Michigan.
The main goal of the project was to increase fuel economy and reduce emissions as a
hybrid electric vehicle whUe maintaining the performance and functionaUty of the original
car. This chapter details how the design discussed in this thesis accompUshed this goal.
6.2 ZEV Performance
One major advantage of this design was the vehicle's abiUty to perform as a zero
emissions vehicle. The ZEV performance goal was to provide some limited capabiUty as a
ZEV for urban or emergency driving conditions. More specificaUy, the goal was to aUow
an effective range of five miles on purely electric power, while maintaining reasonable
dynamic performance.
The Neon HEV was subjected to two separate tests in ZEV mode. The first test
was used to measure its acceleration and to verify its range at a speed of 30 mph. The
second test was sunilar but required a 55 mph top speed. These tests were performed
72
multiple times to reduce any inconsistencies in the data coUected. For both tests the
batteries were fully charged at tiie beginning of the tests. The 30 mph test was performed
entirely in first gear, while the 55 mph test used fnst gear up to 30 mph and then second
gear up to 55 mph. The tests were terminated when the vehicle could no longer maintain
the designated speed.
Figures 6.1 and 6.2 show the results of the two ZEV mode tests. These curves
show the battery voltage and current levels that were obtained during these tests. These
graphs were obtained from the serial output of the KWH+2 energy meter on the vehicle.
Figure 6.1 shows that the effective range of the Neon, at a speed of 30 mph, is
approximately 10.5 mUes. This range more than doubles the original goal of five miles.
This increased range is due to the multiple safety factors used in the battery selection
process. Over the duration of the 30 mph test, the vehicle consumed 1.62 kWh. Not
shown on the graph is the acceleration time from 0 mph to 30 mph. From a total stop, the
vehicle reached 30 mph in approximately 27 seconds.
Figure 6.2 shows the results from the 55 mph ZEV test. The Neon was able to
reach a cmising speed of 55 mph in approximately 93 seconds. The vehicle was able to
maintain this speed for 5.9 miles, consuming 1.16 kWh of energy in the process. This is
considerably less than the 3.15 kWh rating of tiie battery pack, due to the high discharge
rate necessary for the test. Occasional discontinuities in the 55 mph graph are due to the
gear shifts that were necessary to maintain the vehicle speed.
73
ZEV 30MPH 250 -r
wffiiiiiimiiiHiiifiHwiiititif ffifflnid
o o o T - c v i c \ i c o c o T i - T t i r i i r ) < £ > < b r ^ o d c d o ) 0 )
CO OJ CD 00 o in 1- <£) o Tt
d o
DISTANCE (MILES)
•Amps Volts
Figure 6.1 - Battery Discharge Characteristics for 30 mph Test
ZEV 55MPH
UJ cc cc z> o Q
< LU O < I -_ l o >
300
250
200
ifvi'fi'fHHtMtH'ifii'HtffrtnninrtiiWfiiiiiMifiiiiiiiiiin to <o Tt CO <D O -"t "^ -^
•»- CO c a T-; Tf CD 00 ih in iri iri
00
in
DISTANCE (MILES)
•Volts Amps
Figure 6.2 Battery Discharge Characteristics for 55 mph Test
74
6.3 HEV Perform incp
The primary mode of operation for the Neon is the HEV mode. For this reason it
was the most thoroughly tested of aU modes. The HEV performance of tiie vehicle was
measured in four main areas: acceleration, fuel economy, emissions, and vehicle range.
The overall effectiveness of tiie vehicle was determined by measuring the vehicle's
performance in these four areas. This allows for identification of tiie stt-engths and
weaknesses of this particular sttategy.
6.3.1 HEV Acceleration
The parallel, electric-assist strategy lends itself to good vehicle acceleration. The
acceleration of the HEV was measured in two consecutive road tests. The Neon was
tested on the sttaight-away of the Evaluation Road at the Chrysler Technology Center in
Aubum Hills, Michigan. The objective of the test was to determine the amount of time it
would take for the vehicle to cover one-eighth of a mile. An automatic timing system with
optical sensing capabiUty was used to determine the exact time of each one-eighth mile
mn. A radar gun simUar to those used in police speed traps recorded the top speed of the
vehicle in each run. The times for the two runs were 11.28 seconds and 11.10 seconds
with top speeds of 57 mph and 59 mph, respectively.
6.3.2 Fuel Economv
The fuel economy of the vehicle is of critical importance to its success as a HEV.
The fuel economy of the Neon was measured in IC mode as well HEV mode to provide
75
some basis for comparison. The fu-st fuel economy test was intended to sunulate in-town
driving patterns. The test was performed on a 16.8 mile course with posted speed Umits
between 30 mph and 55 mph. The tests in IC mode and HEV mode were performed with
identical shifting patterns and at the same tune of day to reduce any inconsistencies. The
next higher gear was selected when tiie engine speed reached 3000 rpm or when the speed
limit was reached. The test was started at 12 noon on 5 consecutive days.
Similar tests were performed to simulate highway driving patterns. The vehicle
was driven at a constant speed of 55 mph for a distance of 50.4 miles. The pressure and
temperature of the fuel tank was measured at the beginning and end of each test to
determine the amount of fuel used. The KWH+2 energy meter recorded the electric usage
during the HEV tests. Figure 6.4 shows the results of these tests in tabular form. The
amount of fuel consumed during the tests is calculated using a spreadsheet for the state
equation for compressed natural gas provided by the National Renewable Energy
Laboratory (NREL). The parameters listed below the table, which characterize the fuel
used for these tests, were provided by ENERGAS.
The information in Table 6.1 shows that the Neon performed more efficientiy when
operating as a hybrid. The results of the in-town testing were the most dramatic. For in-
town driving in IC mode, the vehicle averaged 22.3 mUes per gaUon of gasoline (mpg).
When operating in HEV mode, tiie Neon averaged 30.4 mpg on strictiy CNG and 29.7
mpg when the energy provided by the electrical system is included. This was an average
improvement of 7.4 mpg which is approximately a 32 percent improvement in fuel
economy.
76
Table 6.1 - Fuel Economy Test Results
Dcy
Q/9IC 8y^hEV
8/10ICH 8/lOHB/H ei/121-EV 8/14 IC
e/14hEV e/161-EV
Tcrk \Ad
0n 3> vnJD
35G6
3«}5 3GQ5 3935 3505 3GQ5
Tcrk
Vd
r3) 225 225 225 225 225 225 225 225
Sot Res
( P ^ 2425 1893 2518 1743
1997 1601 2S?
3C 11MI
lOK 35E 677
Sot Terrp m
Bri Res
(pad
End Terrp
m 89 211) 9] 91 }W ^ 100 im 95 95 1023 55 93 21CP 93 75 1631 77 77 1296 :;^ 91 2216 91
i n i ^
EcMv.
Gdlons
-Q74 -Q© -1.25 -1.25 -Qffi -077 -QaB -Q52
Mies TrcMSl
1680 1680 515} 515) 1680 168C 168C 168C
Bcrcnnetricp'essLre htecT VdLB of GGBdine (Hq/gd) htet \/tlu9Cf NcT QcB (Plu/ffA3) OitTarpin cfeg Rrkine OitResI
IVPG Ecfiiv.
2268 31.47 4010 4023 2901 21.9C 2a^ 3246
KV\H
Used
000 -015 00] -014 -045 OOD
-Q52 -074
IVP9 w/Gedr ic
226E 31.Z 40 IC 4005 2a34 21.9C 2303 31.11
6.3.3 Vehicle Emissions
The vehicle was emissions tested at the Chrysler Technology Center in Auburn
Hills, Michigan. The emissions test performed consisted of two main parts, which are
called a 505 and a hot-start Urban Driving Dynamometer Cycle (UDDS). The 505 is the
first 505 seconds of the UDDS which covers approximately 3.8 miles. This allows the
vehicle to come to its normal operating temperature. The UDDS is a 1,371-seconds-long
dynamometer test, where typical city stop-and-go driving is simulated. This test covers
approximately 7.5 miles. The main gases that are measured during tiie UDDS are the non-
metiiane hydrocarbons (NMHC), carbon monoxide (CO), and oxides of nitrogen NOx •
Normally a HEV then goes through a battery depletion process to a lower state of
77
charge (SOC) and repeats the UDDS. This was not required due to the charge
maintaining strategy of the Texas Tech Neon.
Figure 6.3 shows the emissions brackets used in classifying vehicles. The brackets
vary from pre-emissions control standards (bracket I) to the highest future standards
(bracket 34). The Neon tested in tiie 19th bracket for nitrous oxides with an emission
level of 0.831 grams per mile, which was roughly twice tiie allowable amount for the 1994
Tier 1 designation. The vehicle surpassed the highest bracket standards which correspond
to tiie 1997 Califomia Ultra-Low Emissions Vehicle (ULEV) for CO and NMHC. The
CO level obtained was .01 grams per mile and the NMHC level obtained was .008 grams
per mile.
6.3.4 Vehicle Range
A vehicle range test was performed at the Evaluation Road of the CTC. The HEV
was given a full battery charge and approximately 1700 psi of CNG in the tanks, which
equates to about 2.9 gallons of gasoline. The vehicle was driven at an average speed of 42
mph until it ran out of fuel and battery power. The Texas Tech Neon completed 121.8
miles before running out of fuel. The tank pressure ended up at 14.7 psia and the battery
voltage at the end of the test was approximately 140 Volts. During the test, the HEV
averaged 42 mpg. At this rate of consumption, the vehicle would have an effective range
of 217 miles.
78
Log Scale Plot of Bracket Values
100.000
10.000
0>
(0
1.000 •'- t<> tr> t^ o> -~
0.100
0.010
1 t I [ \ I \ t ) ( 1 I i 1 [ 1 M M M [ 1 M !••
Bracket Number
Figure 6.3 - Emissions Bracket Values
6.4 Summary of Results
The results of tiie dynamic testing of tiie Neon HEV were mixed. The vehicle
performed very well in many areas while producing disappointing results in otiier areas.
The vehicle had very good dynamic performance characteristics witii regards to
acceleration and vehicle handling. The ZEV range of 10 miles at 30 mph was nearly twice
tiie required distance required by the competition guidehnes. However, at a more
practical speed such as illustrated by the 55 mph ZEV test the vehicle did not achieve a
similar range.
79
The fuel economy measurements obtained during testing of the IC and HEV
modes show a significant increase in fuel savings by operating tiie vehicle as an HEV.
The 32 percent improvement in fuel efficiency is quite substantial, but this factor may need
to be increased to make this HEV concept feasible. Another area where the Neon HEV
could use improvement is in the area of emissions productions. The CO and NMHC levels
produced during the emissions test are outstanding. The NOx levels are very
disappointing, being nearly twice that acceptable by the 1994 Tier 1 designation and four
times the allowable levels for the 1997 California ULEV standard.
The primary reason for the mixed results with respect to fuel economy and
emissions production is that the electric motor/controller pair and the CNG control system
are not fully optimized. If these two systems could be optimized to work in this HEV
configuration, substantial improvements in fuel economy and emissions production could
be achieved. Optimizing these two systems, however, is not a trivial task. It is for this
reason that a systems-level model of tiie Neon HEV is introduced in the next chapter.
This model allows for optimization of these individual subsystems using computer
simulation methods.
80
CHAPTER 7
HEV MODEL
7.1 Introduction
This chapter describes a system-level model tiiat was developed from known
characteristics and parameters of the vehicle, along witii actual test results. This model
was developed in order to simulate the vehicle performance without performing actual
dynamic testing. This allows changes in tiie dynamic elements of the system, such as the
system controller software, to be simulated before they are actually implemented in the
HEV. Small to moderate changes can be made to the vehicle to optimize its performance
to respect to the project goals. The complexity of the vehicle itself makes significant
changes hard to implement.
By developing a model of the existing vehicle, future experimental changes to the
vehicle can be simulated using a computer simulation package. This simulation shows the
effects of changes made on the vehicle before the vehicle is actually modified. It is
obvious that changing the vehicle model in simulation is much easier than making
significant physical changes to the car. Modifications can first be simulated to determine
their benefit before costiy changes are made to the vehicle. In doing this, the vehicle can
be optimized with respect to its main goal using the simulation. This chapter focuses on
the constmction of the model and does not include any attempts to optimize the vehicle.
The model for the HEV is based upon a combination of previous works and
known mathematical relationships regarding vehicle performance [13,14]. The model uses
81
published data as weU as experimentally acquired data to simulate the vehicle's
performance. These relationships and known data are modeled using tiie Matiab Simuhnk
simulation package. Simulink provides a graphical interface that makes model
constmction and debugging very simple. Simulink also incorporates a wide number of
simulation algoritiims that allow the user to control tiie accuracy and speed of the
simulation. Simulink is a very powerful tool that can simulate extremely complex systems,
making it ideal for this application.
Figure 7.1 shows tiie graphical representation of tiie Neon HEV in Simulink. This
stmcture is loosely based upon a previous model [14] with tiie individual submodels being
tailored to represent the Neon HEV. The system model for tiie Neon HEV is made up of
several main components. The system controller model smiulates the actions of the
microprocessor-based system controller for the vehicle. The electric motor and controller
pair are simulated in a single subsystem. The battery pack model is based upon published
specifications of the batteries used in the vehicle. The IC engine model is derived from
experimentally determined data and its structure is based upon previous work [13]. The
transmission model is an exact rephcation of a model used in a similar simulation that has
been assumed to be valid for this system [14]. The vehicle dynamics are simulated in a
model that uses known relationships and coefficients that are specific to the vehicle.
7.2 System ControUer Model
The model for the system controller on the vehicle is designed to simulate the
actions of a microprocessor-based system. Figure 7.2 shows the stmcture of the system
82
controller model. The inputs to the model are identical to those inputs to the actual
system and tiie desired speed and regen control output signals directiy correspond to tiieir
actual counterparts. The inputs to the model come directiy from the user so very exact
vehicle conditions can be simulated. The desired speed and regen control signals are input
to tiie electric motor/controller model that will be discussed in detail later.
The model of the system controller is comprised of three major sections, one for
each mode of vehicle operation. The IC only mode section of tiie model simply
determines the vehicle mode and if regeneration is selected, and sets the corresponding
level of the regen control output signal. The ZEV mode section detects the vehicle mode
and then translates the throttle and brake pedal inputs to valid desired speed and regen
control outputs. The HEV mode section uses a wide variety of linear and nonlinear blocks
to simulate the unique functions of the microcontroller in the actual system. By changing
the parameters in the system controller model, the effect on the overall model can be
observed. This can be used to optimize the software for the system controller to provide
maximum benefit to the entire system.
7.3 Electric Motor/Controller Model
The model of the electric motor and the motor controller are combined into a
single, system-level model. Figure 7.3 shows tiie block diagram of the electric
motor/controller model. The desired speed (0 - 6000 rpm) and regen control (0 - 100%)
signals from the system controller model are input to the electric motor/controller model.
The battery pack voltage (0 - 200V) and motor speed (0 - 6000 rpm) are also inputs to the
83
• o
in
>^ CO >
• c o
<u
DO
84
J j — • J N O T J - , in_1 L04
NOT ANC
'n_2 LOS Logical Operatorl
t AND
in_3 Logical Operator
Relay
Vi
z Relayl Rate Limiter
S >[Z Sum3 Relay2 Rate Limii er
^ ^ ^
Sum4
1
out 1
&?,
Switch 5
Sum out 2
in 16 E \
Switche
Figure 7.2 - System Controller Model
motor/controller from different systems in the overall vehicle model. It would seem that
the motor speed would be an output from the system but the motor speed is determined by
the actual speed of the vehicle, which dominates because of its large mass with respect to
the rest of the system. The two outputs from the system are the current demand (0 -
130A) which is sent to the battery model, and the output torque produced (-22.6 - 22.6 N-
m) that is input to the transmission model.
The structiu^e of the electric motor/controller is based upon the system efficiency
map shown in Figure 3.3. The CR20-150 controller has setpoint speed control; that is, it
delivers the maximum possible torque until tiie desired speed is reached. By knowing the
85
torque produced, the battery pack voltage, and tiie motor speed, a system efficiency is
determined using a two-dimensional look-up table. This system efficiency in conjunction
with the other variables mentioned allows a current demand from the batteries to be
calculated. The same system efficiency map is used in calculating the current being put
back into the batteries during regeneration. The motor/controller pair is also assumed to
be able to absorb as much power during regeneration as it normally produces. Another
aspect of the motor/controller that is not simulated is the current limiting feamre of the
CR20-150. A more detailed model may be required to better simulate the regeneration
characteristics of the motor/controller pair.
rn—Hi/u[iif in 1 Fen
scope
Figiu-e 7.3 - Electric Motor/Controller Model
7.4 Battery Pack Model
The battery pack model is shown in Figure 7.4. This model is based upon the
published specifications for the Powersonic batteries used in the Neon HEV. The inputs
to the battery model are the current demand (0-130 A) from tiie electric motor/controller
86
model, and tiie time (0 - 10000 sec) the simulation has been mnning. The outputs from
the model are the battery pack voltage (0 - 200 V) and the amount of power supplied by
the batteries (0-3.2 kWh). The battery discharge curves used in the model are shown in
Figure 7.5. These curves are entered in a battery look-up table that uses an interpolation
routine to determine the corresponding battery pack voltage. This model assumes that
each simulation begins with a full battery pack charge. This model does not consider the
effects of the number of charge/discharge cycles experienced by the batteries, due to the
charge maintaining strategy used in the vehicle.
2 " in 2
H u[1l 15—1 Fcn2
# BatterieLj—;;—
Saturationi
© • S ^
Product 1 :tll>
Saturatidn
^, , Battery Look Clock Up Table
f(u) Product Fen
X •
Q-i
1 /s -^ f u — • 2
Product2 Integrator kws to
kwh
out 2
Sampling Interval
T out 1
Figure 7.4 - Battery Pack Model
7.5 TC Engine Model
The model for the IC engine is based upon experimentally acquired data. This
model is based upon previous works [13] but is adapted for tiiis particular vehicle. The
87
(VJ 14.G
S 13.0
J 11.0 <
i ro.o e.o 8.0
I ' '» • ! f , f ^
AMftieNTTgM>eF|ATUfJR ao*C (68'^)
- ^ 1 . 7 5 A 0 . " 8 7 ^ A
mifl «4<M hn
DiSCHAf^QBTIMI
Figure 7.5 - Battery Discharge Characteristics
inputs to the IC engine model are the percent throttie (0 - 100%) and tiie engine speed (0 -
6000 rpm). As in the case of the electric motor/controller model, it would seem that the
engine speed would be an output. The actual speed of the vehicle is what determines the
engine speed because of the large vehicle inertia. The outputs of the model are the torque
produced and the rate of fuel flow. The IC engine torque output is fed directly to the
transmission model. The clutch that is present in the actual vehicle is not modeled in this
simulation. The rate of fuel flow is integrated with respect to time to give a total amount
of fuel consumed.
Figure 7.6 shows the stmcture of the IC engine model. This model is based upon
acmal data acquired diuing testing of the vehicle. The model is based upon two primary
relationships.
X.„, = / . ( ^ ) + /2(^)Tl
mf=f,(N) + fA^)'^
-3 / (N) = -21.5493-9.1 xlO'^N
88
/ (yV) = 7.7147-H 1.4 X10"'yv.
/3(yV) = 79.542-2.58 X10"'yv.
/4(yV) =-15.6704-h 8.9 X10"'yv .
The first equation produces an engine torque, Xeng, based upon a given engine speed, N,
and a given throttle percentage, r|. The second equation relates the fuel flow rate, w^, to
the same engine speed and throttie percentage. The coefficients in these equations are
determined by performing linear regression on the data shown in Figures 7.7 and 7.8.
Using this method requires several assumptions. First, the relationships are assumed to be
linear and second, the throttie position and output torque are assumed to change much
more quickly than the engine speed due to the large vehicle inertia.
7.6 Transmission Model
The model for the transmission used in the Neon HEV is shown in Figiu e 7.9.
This model is based upon previous work [14] but has been adapted for the specific
transmission on the Neon HEV. The inputs to the transmission model are the torques
produced by the IC engine and electric motor, and the gear selected. The only output
from the transmission model is the wheel output torque.
89
2 »T
in S
0.0014
Constants
3 J
in 3
-21.5493
Constant -0.0091
Constanti
7.7147 n« Inner — ^ +
Product2 I 1 Sum
Constant2
nner Products
inner Product4
79.542
Constants
-0.00258
Constants -15.6704
Constant7
0.0089
Constant8
Inner Producti
1 •
in 4
Switch out 1
Constant4
; : ; f ^ Inner
Products
J Inner Inner HroductS
Sum1
Inner Product7
Inner Products
out 2
Switch 1 Saturation out 3
Figure 7.6 - IC Engine Model
IC Engine Output Torque vs. MAP
o I -
CO 1 ^ Oi -^ -^
Manifold Absolute Pressure (psia)
~e— 1000 RPM — — 2000 RPM —K— 3000 RPM —aK— 4000 RPM - H — 5000 RPM
Figure 7.7 - IC Engine Torque Characteristics
90
Fuel Flow vs. MAP
400
E o o
o
CD 3
•MH" t • i - t- i" t" i ' " f"r-r f ' l f"<- f ' M i"t I'l I ' t 1 I f r M < \'i\ i i < i i u j i o o o o i n c q c o c q in
CM <D
t^ in r^ O)
Manifold Pressure (psia)
2000 RPM ^ ' •• 3000 RPM —3K—4000 RPM —X—5000 RPM
Figiu-e 7.8 - IC Engine Fuel Flow Characteristics
The transmission model converts the input torques from the electric motor and IC
engine to an output wheel torque based upon the gear selected. The gear ratio selector in
the transmission model simply outputs the corresponding gear ratio for a selected gear.
The output of the gearbox is sent through the final drive gear ratio. The model assumes a
tooth efficiency of 96% and incorporates a loss term due to the varying input torque level
and various mechanical losses [14]. These values were originally calculated for a four-
speed Volkswagen transmission and have been assumed to be valid for this simulation.
7.7 Vehicle Dynamics Model
The vehicle dynamics model is shown in Figure 7.10. Most of the parameters used
in the model are specifications for the Neon HEV. The model has the wheel torque
produced and the grade of the road as its inputs. The vehicle dynamics model outputs the
91
vehicle speed and the total distance traveled during the simulation. The vehicle speed is
fed back to the electric motor/controUer model and the IC engine model.
in 1
in 2
in 3
8 ••
in 8
Sum Sum1
f(u)
Gear Ratio Selector
t Producti
t Product
differential out 3
f(u) 1
Tooth Efficiency out 1
f(u) f(u) Fen Fcnl
-Hl/u[1] Fcn2
Lost Torque
Saturation out_2
Figure 7.9 - Transmission Model Diagram
The dynamics model sums the forces acting upon the vehicle and divides by the
vehicle mass to give a vehicle acceleration. This acceleration is integrated to give a
vehicle velocity and integrated again to give the total distance traveled. The forces acting
upon the vehicle are the forces produced by the powertrain, the aerodynamic drag forces,
the force produced by the rolling resistance of the tires, and the gravitational forces due to
the incline of the road. The following equation shows this relationship.
J vow J drag J n UV J now J drag J res
— = a.„. = -^ a dt "tot
m grav
vehicle
The individual forces are calculated using known vehicle parameters. These parameters
are used in the following equations show the various vehicle forces.
92
J pow I tire \^ out I 'tire )
fdrag =0 .5-p , ,v -C . 'A -v^ air '-' drag front ' *
fres = Cnre ' 8 ' COS(e , , , , ) .
a grav = g ' ^^(^ road) •
WhereTj,. ^ is the tire efficiency, x„„, is the output torque from the transmission, and r^^^ is
the radius of the tires. These quantities are used to calculate the forward force on the
vehicle. The p -^ is the density of air, C ^ ^ is the drag coefficient of the vehicle, A/ront is the
frontal area of the vehicle, and v is the vehicle velocity. These quantities are used to
calculate the drag force on the vehicle. The force due to tire rolling resistance, fes, is
calculated using the quantities Ctire, which is the coefficient of tire rolling resistance, g,
which is acceleration due to gravity, andG ^ , the grade of the road in radians.
> f(u)
in 1 tire radius and efficiency
1490 Mass, kg
.5 Const
1.206 Density of air,
kg/m3
.34
Drag Coeff.
2.109
Frontal Area, m2
0.0077
Tire Rolling Resistance Coefficient
.00001
Const2
in 2
• 1/u[1]
Fen
f(u)
t Product
Producti
gravity
f(u)
f(u) •
cos
Products
Product2
Product4 Products
• f(u) f(u)
deg. to rad sin gravity, m/s2
i / - • j l /S -f Inteora
Sum
Integrator
• 1 /s—• f(u) - ^ 1 Integratorl meters out_1
to miles_
f(u)
f(u) Saturatio i m/s to mph out_2
velocity''2
Acceleration
Figure 7.10 - Vehicle Dynamics Model
93
7.8 Model Results
The model of the Texas Tech Neon HEV is used to accurately predict the
performance of the vehicle for a given set of conditions. The purpose of the model is to
provide a basis for simulation of the vehicle. Changes to the model can be made and
simulated to determine their effect on the vehicle. To test the accuracy of the model,
simulations of actual tests were performed and the results were compared. The
simulations performed were the 30 mph ZEV acceleration test, the 55 mph ZEV
acceleration test, and the l/8th mile HEV acceleration test. These simulations were
performed on MATLAB Simulink for Windows.
The 30 mph ZEV acceleration simulation was performed in a similar manner to the
acmal test. The simulation was done entirely in first gear and on a level grade. Figure
7.11 shows a plot of the vehicle speed predicted by the model during the simulation. The
simulation showed that the vehicle would reach a speed of 30 mph in 27.5 seconds. In the
actual test, the HEV reached a speed of 30 mph in 27 seconds. This 0.5 second difference
is an error of approximately 2 percent.
The 55 mph ZEV acceleration simulation was not as accurate as the previously
mentioned 30 mph simulation. The 55 mph simulation was performed as closely to the
actual test as possible. The vehicle speed predicted during the simulation is shown in
Figure 7.12. The simulation predicted that the HEV would reach a speed of 55 mph in
103 seconds. In actuahty, the Neon took 93 seconds to reach its cmising speed of 55
mph. This 10 second difference results in a 10.8 percent error.
94
35
30
25
20
15
10
G
I • I 1 JF-C _ J
^ — — — — — — • • > . - — — -. — . ! _ _ _ - ^ ^ ^ . l _ _ _ _ _ _ ^ _ _ — —
f- - - , yK-, , ,
, -^\ 1 1 !
0 10 15 20 Time (second)
25
Figure 7.11 - Vehicle Speed for ZEV Acceleration Simulation (0 - 30 mph)
60
50
40
30
20
10
0
•I I I-
H - - - J , * * * - - . - * - - - - - - - - - ^
^ A , . . - . . . . . . L .
0 20 40 60 80 Time (second)
100
Figure 7.12 - Vehicle Speed for ZEV Acceleration Simulation (0 - 55 mph)
The HEV acceleration simulation was meant to simulate the l/8th mile
acceleration test in the Chrysler HEV Challenge. The vehicle was accelerated over a
0.125 mile distance on a level grade. Figure 7.14 shows the HEV speed during the
95
simulation and Figure 7.13 shows the distance traveled by the vehicle. The sunulation
predicted that the vehicle would take 12 seconds to cover l/8th of a mile at a top speed of
61.5 mph. In the actual tests, the vehicle covered the l/8th mile distance in an average of
11.2 seconds and at an average top speed of 57 mph. The simulation has an error of 7.2
percent with respect to the elapsed time and an error of 7.9 percent with respect to the
vehicle top speed.
0.2
0.15
0.1
0.05
0
T 1 1 1 I
-I r- -I 1 T
_i t - M 1 * Z^^-
- • • .1 .^<r _ • a
0 4 6 8 Time (second)
10 12
Figure 7.13 - Vehicle Distance for HEV Acceleration Simulation (l/8th mile)
96
100 -
80
60
40
20
0
^ ^ 1 ^ ^
- — — * — — ^ — — — ~ — — ^ . . — . — _ ^ _ _ _ _ . _ i . _ _ _ _ _ ^ * — — — — —
1 I J • J. _ --^.^ml^
. , , __,^<^ , .,
• - - - - — ^ - - jri. _ _ ^ . . — — — _ 4 — — — — _ . • — — — — — - « — — - - - -
0 4 6 8 Time (second)
10 12
Figure 7.14 - Vehicle Speed for HEV Acceleration Simulation (l/8th mile)
97
CHAPTER 8
CONCLUSIONS
The objective of this thesis was to develop a hybrid electric vehicle that provides a
significant increase in fuel economy and emissions control, while maintaining the
performance and functionality of traditional vehicles. The results in the previous chapter
show that the Texas Tech Neon HEV was successful in accomplishing many of the goals
set at the beginning of the project. Its second place finish in the 1995 Chrysler Hybrid
Electric Vehicle Challenge fiuther affirms its success in meeting the project objectives.
The ZEV mode performance of the Texas Tech Neon is an unexpected strength.
A major driving force behind many of the design decisions was to comply with the contest
requirement of a minimum range of 5 miles at 30 mph. In testing after the HEV
competition, a ZEV range of 10 miles was accomplished. This was due to the many safety
factors that were considered when selecting the batteries and the electric motor/controller
pair. The Tech Neon HEV also claimed the award for most efficient as a ZEV at the 1995
HEV ChaUenge.
The HEV mode fuel economy earned the best fuel economy award at the 1995
HEV Challenge. The 30 percent increase in measured fuel economy as an HEV is a
significant increase, but also comes at significant added cost. This added cost is in the
increased weight and money required to perform the conversion to an HEV. It is worth
considering the amount of time that it would take the fuel savings to equal the initial
outlay for the vehicle conversion. The fuel savings would probably need to be increased
98
to 40 to 45 percent to justify the significant cost required to convert the vehicle to an
HEV.
The reduction in emissions comes in two of the three major emissions categories.
The non-methane hydrocarbons (NMHC) and carbon monoxide (CO) levels were well
below the Califomia ULEV standard. The levels in these two categories were the lowest
recorded in the Neon class at the HEV ChaUenge. The nitrogen oxides (NOx) level
produced during the UDDS was twice that aUowable by the 1994 Tier I standard. This
resulted in an overall classification in the 20th bracket, and a second place finish in the
emissions event. This relatively poor classification definitely needs to be improved upon.
The overaU dynamic performance of the vehicle is definitely one of its strengths.
The ZEV acceleration is a bit slow, but the vehicle was not designed for its performance
as a ZEV. The HEV dynamic performance is excellent. The vehicle has exceUent
acceleration and braking capabUities. The only two areas that probably need improvement
are the vehicle weight and the rear suspension. The vehicle weight is a bit high at 3075
pounds, more than 600 pounds heavier than the stock Neon. Due to the increase in
weight, mostly at the rear of the vehicle, the rear suspension is a bit weak.
8.1 Recommendations for Futiu'e Work
The results obtained show that there is definite room for improvement in the Texas
Tech Neon HEV. The glaring limitation of the Neon is its poor emissions rating. This is
due to problems with GEM control system used in the CNG conversion. The system by
MESA Environmental is not calibrated to work with this particular engine. In particular,
99
the use of exhaust gas recirculation (EGR) has not been caUbrated for this engine. The
calibration of the EGR system wiU surely remedy the NOx production problem. This wUl
allow the vehicle to meet and exceed the ULEV standards.
To further improve the fuel economy of the HEV, a timing advance system could
be implemented. This timing advance is necessary to compensate for the slower-burning
compressed natural gas. The GEM system is unable to provide this timing advance
because it is designed for use with distributor-based ignition systems, whereas the Neon
has a wasted-spark ignition system. This timing advance could improve the fuel economy
by another two to four mpg. This timing advance would also help reduce the NOx
emission problem.
After the GEM control system is optimized, it would be useful to perform fuel
economy and emissions tests using the UDDS testing protocol. The tests should be
performed identically for HEV mode and IC mode. This would provide an exact test to
determine the merit of operating the vehicle as an HEV.
The system model can be a valuable tool for improvement of HEV performance.
By optimizing the model for a given set of objectives such as maximum fuel economy or
maximum performance, the vehicle can then be modified to match the characteristics of
the optimized model. The model is stUl in the preliminary stages of development. More
accurate models of the IC engine and electric motor/controller pair would definitely
improve the overaU performance of the model. A more detaUed study of the IC engine
might also include the emissions characteristics of the system. This would allow for
system model optimization with respect to emissions. FinaUy, more computing power is
100
necessary to perform long-term simulations of the HEV system. The model's complexity
makes extended testing prohibitive on a PC based platform. Matiab and Simulink can be
mn on workstations, which may provide the computing power necessary for acciu^ate,
long-term testing.
101
REFERENCES
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[2] Wouk, Victor. Hybrids: Then and Now, IEEE Spectrum. July 1995, pp. 15-21.
[3] Riezenman, Michael J.; Wouk, Victor. EV Watch, IEEE Spectrum. September 1995, pp. 72-73.
[4] Shacket, Sheldon R. The Complete Book of Electric Vehicles. Domus Books, New York, New York, 1979, pp. 22-30.
[5] Riezenman, Michael J. Road Test: the Impact electric car, IEEE Spectmm. September 1995, pp. 73-75.
[6] Chrysler Corporation. Service Manual: 1995 Neon Front Wheel Drive Passenger Vehicle. 1995, pp. 8A.1-8W.95.A9.
[7] Crittenden, Brent. EE 4334 Project Laboratory Notebook. Texas Tech University, August 1994, pp. 2-25.
[8] Hanselman, Duane C. Bmshless Permanent Magnet Motor Design. McGraw-HiU, New York, New York, 1994, pp. 7-12.
[9] Unique MobiUty Inc. Installation and Operating Instructions. Golden, Colorado, 1994, pp. 2-11.
[ 10] Power Sonic Corporation. Rechargeable Sealed Lead-Acid Battery PS-12180. Data Sheet, September 1993, pp. 1-2.
[II] Zivan Corporation. Battery Charger K2. Owners Manual, Italy, February 1995, pp. 1-5.
[ 12] Phoenix Fire Suppression Systems. The Phoenix Mark IIA Halon Fire Suppression System. Operation and InstaUation Instructions, Auburn, Washington, pp. 1-8.
[ 13] Masding, P.W.; Bumby, J.R. Identification and performance simulation of a hybrid i.c.-engine/batterv electric automotive power train. Transactions of the Institute of Measurement and Control, Vol: 12, 1990, pp. 27-39.
102
[ 14] Farrall, Simon. The development and validation of powertrain models for use in the design of high level hybrid vehicle powertrain controllers. Symposium Proceedings: the 11th Intemational Electric Vehicle Symposium, September 1992, pp. 1-12.
[15] Motorola Inc. M68HCI1 Reference Manual. Phoenix, Arizona, 1990, pp. 1.2-1.5.
[ 16] Motorola Inc. M68HC1 lEVB Evaluation Board User's Manual, Phoenix, Arizona, 1986, pp. 1.2-1.4.
[17] Motorola Inc. Optoelectronics Device Data. Phoenix, Arizona, 1983, pp. 3.31-3.33.
[ 18] Texas Instmments Inc. Optoelectronics and Image Sensors. DaUas, Texas 1990, pp. 3.19-3.20.
[19] Cosel U.S.A. Inc. DAS lOOF-24 DC to DC Converter. San Jose, Califomia, Data Sheet, 1993, pp. 2-9.
103
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