Why Electricity is Needed in Automobiles
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Transcript of Why Electricity is Needed in Automobiles
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Application of Electricity in
Automobile
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Outline
Why Electricity is needed in automobiles?Safety and other reasons.
Target power levels.
Architectures.
Points about engineering research needs.
Major applications: power steering,starter-alternators, etc.
Mild hybrid designs based on 42 V. Research opportunities.
Conclusion.
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Why Electricity is needed in automobiles?
The electrification of the automobile is amajor step in its evolution.
Electrical applications are beneficial for thesame reasons as for systems in aircraft:
Better efficiency More flexible control
Ease of energy conversion
Low-cost control and conversion of energy is
a key point. Electric power is rising because of electric
auxiliaries as well as more features.
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Why Electricity is needed in automobiles?
When electricity is used to power variouscomponents (steering, brakes, suspension,
air conditioning), the results are better
efficiency and more flexible performance.
Performance is decoupled from the engine.
Many estimates have been made, such as
10% fuel economy improvements by simple
electrification of existing functions.
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Why Electricity is needed in automobiles?
Possible new features: Combined starter-alternator to reduce costs and
enhance performance.
Regenerative braking.
Start on demand arrangements to avoid idleengines.
Improved, more efficient power steering and other
subsystems.
Active suspensions.
Electrical valves and engine elements --
ultimately the self-starting engine.
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Why Electricity needed in automobiles?
The conventional car is rapidly becoming more
electric.
The total electric load is about 1500 W today,
and is increasing toward 5000 W.
Conventional alternators cannot deliver morethan about 2000 W, and are not efficient.
A higher voltage system supports lower
current and loss.
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Why Electricity is needed in automobiles?
Three alternatives: Stick with 12 V. This limits effective power levels.
Get the voltage as high as possible (>100 V). This
requires a major overhaul of safety systems and
basic designs. Push the voltage as high as possible before
significant safety issues come into play.
42 V tries to do the last: get the voltage as
high as possible while avoiding severe safetyissues.
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Safety Issues
A cars electrical system is typically open. Complicated wiring harnesses with close
contact and hundreds of connections.
Regulatory agencies have set a level of about
60 V dc as the maximum reasonable level in
an open system.
Headroom is required to stay below this level
under all allowed conditions.
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Safety Issues
Industry premise: stay with an open electricalsystem for the foreseeable future.
This philosophy supports the option for
evolutionary change of automotive electric
power.
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Safety Issues
There are also fully regulated and batteryregulated systems.
Battery-regulated system ultimately defer to
the battery to set the voltage level.
A battery-regulated system must allow for
Polarity reversal
Disconnection: momentary or continuous
Wide voltage swings Inductive spikes from corrosion or deliberate
disconnect are significant.
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Safety Issues
12 V battery systems require undamagedoperation at12 V or from short-term spikes
up to 75 V.
At higher battery voltages, surge suppressors
and other add-ons will be needed to limit
these extremes to present levels.
In a battery regulated system, 36 V is about
the highest possible level (but these arecharged at 42 V) without excessive possibility
of damage and spikes much beyond 60 V.
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Safety Issues
In a fully regulated system, there is somebuffering between the battery and the rest of
the system.
With full regulation, the wide swings of a
battery system are not necessarilyencountered by the user.
48 V batteries are possible within the 60 V
limit, with such regulation. The higher voltages also support extra
efforts, such as anti-reversing diodes.
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Safety Issues
We can also consider a closed system, inwhich electrical contact is more protected.
Closed systems are used in todays hybrid
and electric cars.
The voltage levels there can exceed 300 V
dc.
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Power Levels
At 42 V, a cars electrical system rivals that ofa house.
But, 10 kW is not enough for traction power.
Voltage Typicalpower level
Maximumpower level
12 V 1200 W 2000 W
42 V 5000 W 10 kW
300 V 30 kW 100 kW
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Architectures
Each automotive voltage level hasadvantages for some loads.
12 V or less for lamps, sensors,
electronics, controls.
42 V for motors, pumps, and fans.
High voltage for electric traction
power.
Incandescent lamps, for example, are morerugged and more reliable at low voltages (but
they are disappearing).
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Architectures
Many possible architectures are possible. Most retain some 12 V capacity.
They are typically divided into single-battery
and dual-battery systems.
There is no consensus on which to select,
and we are likely to see several.
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ENGINE42V
ALTERNATOR
42V
BATTERY
42V
LOADS
12V LOADS
DCDC
Architectures
Single battery at 42 V:
Problem: jump starts?
Problem: charge balance.
www.hoppecke.com
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ENGINE42V
ALTERNATOR
BIDIRECTIONAL
DCDC
42V
BATTERY
42V
LOADS
12V LOADS
12V
BATTERY
Architectures
Dual battery:
The dc-dc converter mustbe bidirectional to support
starting and reliability.
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ENGINE
42V
STARTER/
ALTERNATOR
REGULATOR
42V
LOADS
12V LOADS
12V
BATTERY
BIDIRECTIONAL
DCDC
Architectures
12 V battery
Here a starter-alternatoris shown as well.
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ENGINE
42V
STARTER/
ALTERNATOR
42V
LOADS
LOADS
LOCAL
DC/DC
42V
BATTERY
Architectures
Distributed converters with 42 V battery.
Here there are many dc-dc
converters at the various
loads.
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Architectures
The ultimate is a true multiplexed system: Deliver a single 42 V power bus throughout the
vehicle, with a network protocol overlaid on it.
Local dc-dc converters provide complete local
operation and protection. A ring bus or redundant bus structure could be
used to enhance reliability.
What about fuses? No central point is available.
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Architectures
Costs would seem to dictate a single-batteryarrangement.
However, this involves either a high-power
42V to 12V converter (bidirectional) or a
troublesome 42 V battery.
Some researchers talk about a small dc-dc
converter just for jump starts.
Most systems are partially multiplexed (powerand network distribution rather than individual
loads).
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Issues
Key off loads: sensors, alarms, clocks,remote systems. All draw down power.
Flat loads draw roughly fixed power,
although the alternator output can vary.
Connectors.
Fusing.
Arcs: much above 12 V, it becomes possible
to sustain an arc in close quarters.
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Connectors
150 A connector for 42 V (AMP, Inc.prototype).
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Points About Research Needs
Many of the new challenges of 42 V havebeen addressed in other contexts:
48 V systems throughout the telephone network
(with battery regulation)
Higher dc voltages in several aerospaceapplications (with bigger arcing problems in low-
pressure ambients)
Methods need to be adapted to the low-cost
high-vibration automotive case.
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Points About Research Needs
Motors are of keen interest. Dc motors are cheap to build because of the
convenient wound-rotor structure.
The small machine design methods for cars do not
translate well to 42 V. At 42 V, ac motors make sense.
Butsmall ac motors have been expensive
in most contexts.
How to build cheap, small ac motors (with
electronic controls)?
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Points About Research Needs
Fusing is critical. Power semiconductor circuits capable of
acting as self fuses active devices used as
circuit breakers based on local sensing.
Actual fuses and circuit breakers with cost-
effective arc management suitable for
automotive environments.
Fusing issues (among others) have sloweddown the development of 42 V systems.
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Major Applications
Electric power steering. Two forms: assist pump and direct electric.
The assist pump uses an electric motor to
drive a conventional hydraulic unit.
The direct system
uses electric motors with
the steering rack.
In both cases, action canbe controlled independent
of the engine.Source: Delphi Corp., Saginaw Steering Systems Div.
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Major Applications
Electric air conditioning. Remove the air conditioning
system from engine belt drive.
Provides much better control
and flexibility.
Easier cycling,possible
heat pump application.
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Major Applications
Integrated starter-alternator (ISA). Build an electric machine into
or around the flywheel.
Both permanent magnet and
induction types are being
studied.
Source: Mechanical Engineering
Magazine online, April 2002.
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Major Applications
Provides on-demand starts. Supports regenerative braking.
The very fast dynamics of an ac machine
allows even active torque ripple cancellation.
If ripple can be cancelled, there is promise for
much quieter engines and much lower
vibration levels.
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Major Applications
Electromechanical engine controls. Valves.
Fuel.Source: FEV Engine Technology, Inc.
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Major Applications
Active suspensions. Use electromechanical actuators in
conjunction with mechanical suspension
members.
With enough actuator power, road bumps
(large and small) can be cancelled with an
active suspension.
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Major Applications
Catalyst management systems and exhausttreatment.
Today, most automotive emissions occur in
the first few minutes of operation, when the
catalyst is too cold to be effective.
Catalyst heaters or short-term exhaust
management systems can drastically reduce
tailpipe emissions in modern cars and trucks. Electrostatic precipitator methods can be of
value with diesel particulate exhaust.
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Additional Applications
http://auto.mit.edu/consortia_dis.nsf/DocId/DA54330A7588430F852569CF00763577/$file/autot1.gif -
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Mild Hybrids
The key limitation of 42 V is that it really doesnot support electric traction power levels.
As the promise of electric and hybrid vehicles
becomes clearer, engineers push for higher
power levelsbeyond the reach of 42 V.
A compromise is possible: the mild hybrid
vehicle.
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Mild Hybrids
A light hybrid or mild hybrid uses a smallmotor to manage
performance.
The engine can be
shut down at stops.
Braking energy
can be recovered.
The car does not operate in anall-electric regime.
The Honda Insight is a good example.
Source: www.familycar.com
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Mild Hybrids
For a mild hybrid approach, about 5 kW or socan provide a useful level of traction power.
The technique is accessible in a 42 V system,
although higher voltage (144 V in the Insight)
is beneficial.
A 42 V ISA has substantial promise for fuel
economy improvements, and straddles the
boundary between a conventional car with anISA and a mild hybrid.
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Other Hybrids
Higher-power hybrids require high voltage(240 V and up) for traction power.
Electrical accessories are essential.
Such cars can benefit from 42 V systems.
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Other Hybrids
All key
accessories areelectric.
The Toyota hybridsystem operates at
288 V, and reaches
30 kW.
Source: www.familycar.com
http://www.familycar.com/RoadTests/ToyotaPrius/Images/HybridSystem.jpg -
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Electric and Hybrid Gallery
General Motors EV1. 1300 lb battery pack at
312 V, 102 kW motor.
0-60 mph in less than 9 s.
Volvo turbine-based
hybrid prototype.
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Electric and Hybrid Car Gallery
This Ford Escort was the first true practicalprototype hybrida complete station wagon.
Second-gen
diesel hybrid.
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Electric and Hybrid Car Gallery
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Research Opportunities
Low-cost small ac motor systems: 42 V dc bus
Cheap inverters
Small ac motors that can be manufactured easily
Engine electromechanical devices andcontrols.
Protection and semiconductor fusing.
System-level analysis.
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Conclusion
The continuing increase in electric powerlevels in automobiles will require highervoltages.
42 V systems (batteries at 36 V or 48 V) are
the highest possible in an open electricalsystem.
There are fuel economy improvements just atthis level, but the extension to mild hybrids
offers much more. While the industry is now is a go slow mode
for 42 V, no one doubts its eventual use.
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The End!