HYDRAULIC HYBRID VEHICLE - University of Idaho

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HYDRAULIC HYBRID VEHICLE Final Report KLK348 N06-17 National Institute for Advanced Transportation Technology University of Idaho Robert Wiegers; Franklin Albrecht and Donald Blackketter with Cristy Izatt and Robert Ferebauer December 2006

Transcript of HYDRAULIC HYBRID VEHICLE - University of Idaho

Page 1: HYDRAULIC HYBRID VEHICLE - University of Idaho

HYDRAULIC HYBRID VEHICLE

Final Report KLK348 N06-17

National Institute for Advanced Transportation Technology

University of Idaho

Robert Wiegers; Franklin Albrecht and Donald Blackketter

with Cristy Izatt and Robert Ferebauer

December 2006

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DISCLAIMER

The contents of this report reflect the views of the authors,

who are responsible for the facts and the accuracy of the

information presented herein. This document is disseminated

under the sponsorship of the Department of Transportation,

University Transportation Centers Program, in the interest of

information exchange. The U.S. Government assumes no

liability for the contents or use thereof.

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1. Report No. 2. Government Accession No. 3. Recipient‟s Catalog No.

4. Title and Subtitle

Hydraulic Electric Vehicle

5. Report Date

December 2006

6. Performing Organization Code

KLK348

5.Author(s)

Robert Wiegers; Franklin Albrecht and Donald Blackketter

8. Performing Organization Report No.

N06-20

9. Performing Organization Name and Address

National Institute for Advanced Transportation Technology

University of Idaho

10. Work Unit No. (TRAIS)

PO Box 440901; 115 Engineering Physics Building

Moscow, ID 838440901

11. Contract or Grant No.

DTRS98-G-0027

12. Sponsoring Agency Name and Address

US Department of Transportation

Research and Special Programs Administration

13. Type of Report and Period Covered

Final Report: August 2004-September

2005

400 7th Street SW

Washington, DC 20509-0001

14. Sponsoring Agency Code

USDOT/RSPA/DIR-1

Supplementary Notes:

16. Abstract

Because there is a large demand for better fuel economy on vehicles, researching different hybrid methods is necessary. The main

goal of this project was to design, build, and test a complete hydraulic launch assist system on a Ford F350 diesel truck. The

system described in the report shows how each of the functional requirements was implemented using different modeling

techniques and solutions. These included Excel modeling, developing a complex control system, using DFMEA, and gathering

test data. As shown in the report, the team met each functional requirement successfully according to their allotted guidelines.

Large strides where made in making the system safe and reliability. In conclusion, this system proved the concept that makes a

hydraulic hybrid vehicle safer, lighter, and smoother for marketability.

17. Key Words

18. Distribution Statement

Unrestricted; Document is available to the public through the National

Technical Information Service; Springfield, VT.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

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TABLE OF CONTENTS

INTRODUCTION......................................................................................................................... 1

PROJECT GOALS AND SCOPE OF REPORT ..................................................................... 1

Project Objectives ......................................................................................................................... 2

Background Information and Research ..................................................................................... 2

DESCRIPTION OF PROBLEM ................................................................................................. 4

APPROACH/METHODOLOGY ................................................................................................. 5

Objective 1: Safety Improvement ................................................................................................ 5

Testing Safety ........................................................................................................................................................... 7

Objective 2: Achievability of Project .......................................................................................... 7

Scheduling and Time Management........................................................................................................................... 7

Objective 3: Fuel Mileage and Acceleration Improvement ...................................................... 8

Acceleration .............................................................................................................................................................. 8

Fuel Mileage ........................................................................................................................................................... 10

Objective 4: Cost Effective ......................................................................................................... 10

Feasibility Report .................................................................................................................................................... 10

Objective 5: Increase of Reliability ........................................................................................... 11

Objective 6: Maintainability of System..................................................................................... 13

Objective 7: Weight Reduction .................................................................................................. 15

Objective 8: Noise Reduction ..................................................................................................... 16

New Mounting ........................................................................................................................................................ 16

Controls System Smoothness .................................................................................................................................. 17

Objective 9: Increase of Vehicle Brake Life ............................................................................. 20

FINDINGS/RESULTS ................................................................................................................ 21

Safety Improvement Results ...................................................................................................... 21

Achievability Results .................................................................................................................. 21

Acceleration and Fuel Mileage .................................................................................................. 23

Cost Results ................................................................................................................................. 28

Reliability ..................................................................................................................................... 28

Objective 10: Improve Maintainability .................................................................................... 29

Objective 11: Weight Reduction ................................................................................................ 29

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Noise Reduction and Smoothness .............................................................................................. 30

Increased Brake Life................................................................................................................... 31

CONCLUSIONS/RECOMMENDATIONS .............................................................................. 34

Objectives Completed ................................................................................................................. 34

Lessons Learned .......................................................................................................................... 34

Future Work Considerations ..................................................................................................... 35

Appendices ................................................................................................................................... 37

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INTRODUCTION

Because there is a large demand for better fuel economy on vehicles, researching different hybrid

methods is necessary. The main goal of this project was to design, build, and test a complete

hydraulic launch assist system on a Ford F350 diesel truck. The system described in the report

shows how each of the functional requirements was implemented using different modeling

techniques and solutions. These included Excel modeling, developing a complex control system,

using DFMEA, and gathering test data. As shown in the report, the team met each functional

requirement successfully according to their allotted guidelines. Large strides where made in

making the system safe and reliability. In conclusion, this system proved the concept that makes

a hydraulic hybrid vehicle safer, lighter, and smoother for marketability.

PROJECT GOALS AND SCOPE OF REPORT

The main goal of this project was to design, build, and test a complete hydraulic launch assist

system on a Ford F350 diesel truck (Fig. 1). The secondary goal was to increase the efficiency of

the hybrid vehicle by redesigning the previously installed system.

Figure 1 – Ford F350 Diesel Truck

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Because there is a large demand for better fuel economy on vehicles, researching different hybrid

methods is necessary. The hybrid designed for this project used a hydraulic launch assist system

to capture energy during braking and reuse it during acceleration. The system described in the

report shows how each of the functional requirements was implemented using different modeling

techniques and solutions. In-depth research and data-collection was beyond the scope of this

report.

Project Objectives

Below is a table of the project‟s functional requirements in order of importance. Each

requirement had a measurable goal with which to compare the results.

Table I – Functional Requirements

Importance Functional Requirements Measurable Goal

1 Safety Improvement No DFMEA RPN‟s > 300

2 Achievability Design and Build by EXPO

3 Improve Fuel Mileage and Acceleration Increase by 25%

4 Cost effective Payoff Period less than 5 years

5 Increase Reliability Increase DFMEA RPN‟s by 100%

6 Maintainability More accessible components

7 Reduce Weight Reduce by 1000 lbs

8 Noise Reduction/Smoothness Reduce by 50%

9 Increase Brake Life Achieve 50% efficiency of system

Background Information and Research

One of the goals of this project was to increase the efficiency of the previous system installed on

the vehicle from a previous project. The system built on the Ford F350 truck, during the spring

of 2004, had three piston accumulators mounted horizontally in the bed of the truck. It had a

large sixty-five gallon reservoir and a vane pump, belt-driven by the engine that charged the low-

pressure accumulator. Mounted directly to the frame was the hydrostat, while all other

components mounted to the bed of the truck. The controls system used Field Point modules but

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was not a stand-alone system. Figure 2 shows the previous system mounted in the bed of the

truck.

Figure 2- Previous system

To improve upon the old design, the team researched several methods and different systems to

determine what would be the best way to meet each objective. Detail Design Review written

December 2004 outlined all the research and other methods considered. The main points the

research revealed that the best design for the team was to use bladder accumulators and change

the pre-charge pump to an electric pump rather than take torque off the engine with the vane

pump. Other improvements, such as upgrading the hydrostat and using high-pressure hose, were

beyond the scope of the project.

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DESCRIPTION OF PROBLEM

Figure 3 shows the basic layout of the combined system as installed on the vehicle (prepared

with AmeSim modeling software).

Figure 3 Hydraulic system layout

The electric pump pre-charges the low-pressure accumulator when the system is not running.

During regenerative braking, the hydrostat pumps fluid from the low-pressure accumulator to the

high-pressure accumulator. During hydraulic launch assist, the high-pressure releases the energy

captured through the hydrostat motor. The kidney loop installed cleans fluid as its running

through the system.

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APPROACH/METHODOLOGY

Objective 1: Safety Improvement

To improve the safety of the system, the team used the tool, Design Failure Modes Effects

Analysis (DFMEA). High risk factors included accumulators rupturing, system overpressure,

broken hoses, pinhole leaks, and contaminated fluid.

DFMEA analyzed three different aspects of failures: potential failure effects, the causes for each

of these failures, and the detection of each failure. Each aspect was assigned a number one to ten

based on certain criteria. Each failure mode had an effect severity, causal occurrence, and control

detection number. Multiplied together gave the Risk Assessment Number, or the RPN. The team

decided that any RPN below 300 was an acceptable risk factor for the project. The highest risks

of the system included the possibly of pinhole leaks and breaking hoses. See Appendix 1-A for a

complete table of the DFMEA.

Table II – Highest RPN of the DFMEA

Potential Failure Mode Broke High Pressure

Line or Hose

External

Leakage

Pin Hole

Leak

Potential Effect(s) of

Failure

System Inoperable/

Injury

System

Inoperable

Death/Injury/Property

Damage

Causes Under-inspected Seal failure Environmental

RPN 400 300 270

Recommended Actions Pressure Testing the

Fittings, Reduce

Length of Hose

Replace Seals,

Don‟t pressurize

Seals

Tonneau Cover

Implemented control measures reduced the possibility of system overpressure. The weakest high-

pressure hydraulic component allowed for a maximum pressure of 3500 psi, while the low-

pressure accumulator could handle up to 500 psi. Installed pressure transducers monitored the

system pressure in strategic locations, and the on-dash program interface has pressure readouts.

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A tonneau cover enclosed the bed adding an additional safety measure by protecting users and

by-standers from broken hoses and pinhole leaks.

Mounted inside of the vehicle frame rails were the accumulators to mitigate the possibility of the

accumulators rupturing in the event of an accident (Fig. 4). This allowed room for crush zones on

the sides and back of the vehicle that would keep the accumulators from being punctured or

crushed. On the accumulators, steel covers over the nitrogen gas valves added protection.

Figure 4 Solid works model of accumulator location

Table III illustrates the failures to be remedied using the above-mentioned design changes. As

one can see, the higher rated RPN had more remedies than other failures analyzed by the

DFMEA.

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Table III – Proposed Remedies of DFMEA Failures

Failures

Remedies

No

Pressurized

Seals

New

Accumulator

Mounting

Steal Covers

on Nitrogen

Side of

Accumulators

Reduce

Hose

Length

Pressure

Transducers

Tonneau

Cover

Accumulator Tank

Explodes

X X X X X

Broken High-

Pressure Hose

X X X X X

Relief Valve Fails X

Kidney Loop Failure X

Hydrostat Fails X

Bladder Rupture X

E-Pump Fails X

External Leakage X X X

Pin Hole Leak X X X

Testing Safety

The test used to test safety of the hydraulic system was in the shop on jack stands. The purpose

of this test was to verify that the hydraulic system was working safely at all operating pressures.

This test gave the opportunity to fix leaky fittings and compare the analog pressure readouts to

the digital readouts on the computer. Safety procedures for jack stand testing are located in

Appendix C.

Objective 2: Achievability of Project

Scheduling and Time Management

The following is the schedule of the team for the school year with eight specific phases. Each

phase had intermittent goals and objectives associated with its corresponding phase. The team

used Microsoft Project to keep an ongoing, updated status of the project for the year. The table

below simplifies the Gantt chart into a more readable format.

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Table IV – Team Schedule for School Year 2004-2005

Phase Phase Goals/Objectives Applicable Dates

Phase One

Problem Definition

Organize Area

Aug. 30, 2004 Sept. 30,

2004

Customer Interview

Review Reference Material

Understand Tools

Get to Know Team

Understand Hydraulics

Phase Two

Research Old System

Make Schematic of Old Design

Oct. 1, 2004 – Oct. 25,

2004

Make Math Models of Old Design

Understand Old Controls System

Schematic of Old Control System

Phase Three Preliminary

Testing

Check Results to Models Oct. 26, 2004 Nov. 1,

2004 Collect Data

Correct any Model Errors

Phase Four

Model Alternatives

Redesign Nov. 2, 2004 – Nov. 30,

2004 Compare Different Designs

Math Model New System

Phase Five

Design New System

Build Excel Model

Dec. 1, 2004 – Jan 31,

2005

Create Solid Model

Size Components

Order Parts

Finalize Design

Phase Six Fabrication

Take Apart Old System

Jan. 31, 2005 – March 7,

2005

Build All Components

Assemble All Components

Tune System

Phase Seven

Test New System

Test Using Jack-Stands March 8, 2005 –April 8,

2005 Test on Roads

Acquire Data

Phase Eight

Design Evaluation

Finalize Testing

April 9, 2005 – May 7,

2005

Analyze Data

Write Final

Reports/Recommendations

Objective 3: Fuel Mileage and Acceleration Improvement

Acceleration

Modeling the hydraulic system in Excel showed the contributing factors to acceleration and fuel

mileage. The pressure, the displacement per revolution, and the efficiency of the hydrostat were

all directly proportional to the acceleration. It then followed to increase each of these factors.

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Being able to change the hydrostat to a larger one proved to be beyond the scope of this project.

The only available hydrostat was twice as large, the placement and mounting of which was

determined to be too time intensive. With the same knowledge, however, it was determined to

use the maximum displacement as often as possible. The control system determines if the driver

actually requested the full available torque and adjusts the displacement accordingly.

The maximum pressure on the high-pressure side of the hydrostat was set to 3500 psi. The desire

to assure safety has limited this value, however with properly rated fittings; the high-pressure

accumulator could reach 5000 psi.

Figure 5 Hydrostat motor performance

When used as a motor, by the rotational speed determined the efficiency of the hydrostat. The

motor was most efficient above 500 rpm (Fig. 5). With the current transfer case, this translates to

approximately ten mph. As explained below, an engine was most inefficient when accelerating at

the lowest speeds. Therefore, it was desirous to assist the engine at the lowest speed possible. For

this reason, a different transfer case with a more advantageous gear ratio was considered, but

again would have been too time intensive to mount. For the most efficient operating range, it was

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determined to use the hydraulic system to assist the engine at ten mph and use until it depleted

the energy.

To testing of these objectives took place on relatively flat section of road. The purpose of this

test was to obtain data describing how the hydraulic system was working. The control system at

this time was user controlled, so the user could engage the hydraulic system at desired vehicle

speeds and rates. Several regen and assist cycles from various speeds and pressures comprised

this road test.

Fuel Mileage

The increase of fuel mileage correlated to the increase in acceleration. All the factors that helped

increase acceleration will also help the fuel mileage. With the available equipment, accurate

measurement of the fuel economy was unavailable. Using a fuel flow meter and odometer would

be the proper way to collect this data.

Instead, the test data was used to determine the average amount of kinetic energy increase during

an assist cycle and compare that to the energy needed to accelerate the vehicle to 35 mph. Then

the two numbers were compared to see how much energy would be conserved during this

acceleration. The percent change is an estimated amount of energy savings for this small part of

the drive cycle. However, when repeated, those small parts of the drive cycle could accumulate

to a savings in fuel usage.

Objective 4: Cost Effective

Feasibility Report

One of the requirements for this project was to make a system that was cost effective, and

therefore a marketable hybrid solution. To meet this requirement, information was drawn from

the feasibilityy report regarding the cost analysis of a hydraulic launch assist system on a refuse

vehicle. (See Appendix B). Although the system for the project is different then the one analyzed

in the feasibility report, the same concepts apply and it is a safe assumption that the system built

would have a similar payoff period and savings.

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Objective 5: Increase of Reliability

To improve the safety of the system, the team used DFMEA. Several strategies were used to

increase the reliability of the system, including: using a fluid cart to filter the oil during system

draining and filling, building a kidney loop into the system, using spin-off replaceable hydraulic

filters, and designing a reservoir with a removable lid for cleaning.

Research showed that hydraulic systems perform best when the fluid is clean, and that

contaminated fluid can lead to component breakdown. As a solution to this problem, the AVCT

(Advanced Vehicle Concepts Team) built a fluid transfer device with a donated pump (Fig. 6).

This device, used to drain and fill the hydraulic system, had a ten-micron filter

Figure 6 Fluid transfer cart with filter

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Figure 7 Kidney loop flow diagram

A kidney loop maintained the cleanliness of the fluid. The kidney loop was a hydraulic loop with

two filters placed in series. The loop used a small electric pump, a ten-micron filter for larger

particles, and a five-micron filter for smaller particles. The loop ran at any time, as it was

connected to the field point units, and pumps at about one gallon per minute. This can filter our

eleven-gallon reservoir in about eleven minutes. The reservoir breather cap has a forty-micron

filter, to protect against external contamination. This design allowed the circulation of fluid

through these filters at any time.

Figure 8 Kidney loop filters

Reservoir

Pump

10µ

Filter

Filter

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Figure 9 Kidney loop and case drain pumps

Objective 6: Maintainability of System

Installed manual ball valves allowed for discharge of the hydraulic accumulators and drainage of

the fluid from the system. The ball valves also served as a high point to remove air from the

system when charged with fluid. A fine mesh screen placed at the inlet to the reservoir tank

brought dissolved air out of the fluid. The dislodged air rose to the surface in the virtually static,

non-pressurized reservoir fluid and exited through a filler/breather cap.

Figure 10 Ball valve on high-pressure side

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Two fine particulate filters and the reservoir, which acted as a settling tank and coarse particulate

filter, minimized and controlled fluid contamination. An electric fuel pump provided flow to two

oil filters that cleaned reservoir fluid and returned it to the tank. To provide a sufficient low spot

in the reservoir where coarse particulates settled, the reservoir mounted parallel to the frame,

which titled from front to back. A removable lid on the reservoir provided access for cleaning,

maintenance, or inspection. Additionally, the filter cart built filtered the fluid before entry to the

system (see Section 2.6).

The diamond-plate aluminum control box featured a removable front panel and sliding shelves

for access to the field point modules and additional wiring and circuitry. Quick-disconnect

wiring harnesses allowed for removal of the control box from the vehicle for remote lab work.

Lexan windows in the control box allowed for visual inspection of the field point modules while

providing waterproof protection for the internal electronics (Fig. 11).

Figure 11 Control Box with removable panel on left

The modified pickup bed lifted about three feet vertically from the frame. It provided room to

work on the system with the bed still attached and provided room for observation of the system

when on display. Hydraulic rams powered by the low-pressure accumulator recharge pump

raised the bed when needed. The computer located inside the cab controlled the rams.

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Shifting the transfer case into neutral prevented excessive wear on the hydrostat during extended

highway trips (Fig. 12).

Figure 12 Transfer case, left shaft drives the wheels, right shaft drive the hydrostat

Objective 7: Weight Reduction

Design changes reduced the weight of the system by reducing the weight of specific components.

By concentrating on specific components such as the accumulators and reservoir tank, weight of

the entire system would decrease. Table V lists the major components that were changed.

Table V – Component Comparison

Component Old System New System

Low Pressure Accumulator steel, piston type Carbon fiber wrapped, bladder

High Pressure Accumulator(s) 2 steel Carbon fiber wrapped, bladder

Hydraulic Fluid 65 gallons 15 gallons

Accumulator Mounts Aluminum Steel

Reservoir Mount None Steel shelf

Reservoir 60 gallon reservoir 11 gallon reservoir

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The new accumulators, wrapped in carbon fiber, reduced the mass of the energy storage system.

The low pressure and high-pressure accumulators weighed approximately fifty and 200 lbs.,

respectively. Previous accumulators were constructed with steel and weighed nearly 300 lbs.

each, adding nearly 1000 lbs. to the vehicle.

Fluid requirements for the new design decreased from sixty-five gallons to eleven gallons. This

reduction decreased the total weight of the system by more than 400 lbs. due to a smaller

reservoir tank and nearly fifty less gallons of hydraulic fluid.

Design changes to the vehicle bed included a mounting apparatus and frame for a lift bed, which

added mass to the vehicle overall. This negated some of the other weight reductions, and

collectively the mounts for the reservoir and the accumulators plus the lift bed added

approximately 350-400 lbs. to the entire system.

Objective 8: Noise Reduction

New Mounting

The next functional requirement for this project was to reduce the noise of the system by 50%. In

testing, observers noted that most of the noise was machine born; the hydrostat, the central

machine, created most of it. Originally, the hydrostat mounted rigidly to the frame of the vehicle

and transmitted vibrations directly to the frame causing a significant portion of the noise.

The new mounting system prevented the hydrostat from transmitting vibrations directly to the

frame. Using a methodology for choosing the spring rate from Karman Rubber (See Appendix

D), an ideal material spring rate to isolate the 80% of the hydrostat‟s vibration from the vehicle

frame was found. Using an rpm of 2500 and a maximum torque from the hydrostat of 600 foot-

pounds, a dampener with a maximum spring rate of 9857 pounds force per inch was required to

get 80% isolation (see MathCAD sheet). Karman Rubber suggested using a mount with a spring

rate less than the maximum spring rate and a maximum allowable force greater than the force

applied to the mount.

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Since the hydrostat also had vibrations parallel to the axis of its center shaft, the use of an

isolation dampener isolated vibrations in all directions. The new dampener had a maximum

spring rate of 6125 pounds force per inch and a maximum loading capacity of 490 pounds force.

This gives a calculated isolation of 87.5 percent of the transmitted vibration.

Space constraints drove the design of the geometry of the mounts (Fig. 13).

Figure 3 New Hydrostat mount assembly drawing

Controls System Smoothness

Vibration and cavitation are the two main causes for noise in a hydraulic system. Proper control

of the system can limit this noise. As the hydraulic motor worked within its recommended and its

most efficient ranges, cavitation was reduced and hydraulic fluid and mechanical parts ran

smoothly. To control the system, it was important to understand the hydrostatic motor

efficiencies and pressures required to work properly. By use of software program Labview and

Compact FieldPoint Modules from National Instruments, the team created a control system.

Several factors came into play when balancing the control of the hydrostat with the speed of the

vehicle. These factors included the different pressures in the accumulators and the driver‟s torque

and brake request. By balancing these different factors, it was expected to be able to run the

hydrostat in its most efficient range all of the time with the proper pressures and thus reduce

noise causing cavitation and vibration.

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Figure 14 Controls flow diagram

A Controls flow diagram (Fig. 14) helped determine the steps needed in each phase of the

hydraulic cycle. With a good picture of what was required in each step of the controls flow

diagram, a control algorithm (Eq. 1) was created using the variables in the system (i.e.

accumulator pressures, brake and throttle positions). The algorithm controlled the swash plate

angle in a calculated smooth response to the system variables.

Buff

Which

Mode?

System ON

Assist Mode Regen Mode

Inputs

Correct

?

Inputs

Correct

?

Brake

pressure

Accumulator

Pressures,

Transmission,

Engine RPMs.

Brake Pressure

Accumulator

Pressures,

Transmission,

Velocity,

Throttle

Pressure

NO NO

Throttle

Pressure

Open Valve

YES

Open Valve

YES

Swash

Angle?

Swash

Angle?

Done? Done?

NO NO

Close Valve YES YES

Accumulator

Pressures,

Velocity,

Throttle

Pressure

Accumulator

Pressures,

Velocity,

Brake Pressure

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ValueAllowedMinimumMin

ValueAllowedMaximumMax

TimesponseFactorSkewSK

eSwashMax

MinMaxSK

)(Re

1001%

(1)

Figure 15 indicates the path of the swash plate angle over the range of values given by the

variables in the system. As variables approach either their maximum value or their minimum

value, the swash plate angle will taper off smoothly until there is no displacement of the fluid in

the hydrostat and the vehicle is „free-wheeling.‟

Figure 15 Swash plate control

To test the controls system, users monitored the system closely while driving the vehicle around

town using the computer program to control the system. The primary purpose of this test was to

validate the computer program and the smoothness of the system. After each driving cycle, the

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computer program was refined to fix any problems and to increase the overall smoothness of the

system.

Objective 9: Increase of Vehicle Brake Life

When decelerating, the hydraulic system provided the necessary resistive torque on the drive

shaft to slow the vehicle to a stop from thirty mph. Stopping from thirty miles per hour usually

filled the accumulator to the desired 3500 pound per square inch, but this could change based on

the incline or decline of the road. From thirty miles per hour, the potential energy stored in the

accumulator averaged about 250 kilojoules.

Due to the ability of the hydraulic system to decelerate the vehicle appropriately, using the

brakes heavily below thirty miles per hour was not necessary. This reduced the amount of use on

the brakes, and therefore extended the life of the brakes.

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FINDINGS/RESULTS

Safety Improvement Results

The new system design changes improved safety by 18 percent. Most of the RPNs that resulted

in a safety failure reduced between 100 points to 240 points (see the table below). These savings

results from the Tonneau cover which reduced the severity of the failure modes. To see a full

DFMEA of the full system, please refer to Appendix A.

Table VI – RPN Improvements

Potential Failure Mode Broke High Pressure

Line or Hose

External Leakage Pin Hole

Leak

Potential Effect(s) of

Failure

System Inoperable/

Injury

System

Inoperable

Death/Injury/Property

Damage

Causes Under-inspected Seal failure Environmental

Old RPN 400 300 270

Design Changes Pressure Testing the

Fittings, Reduce

Length of Hose

Replace Seals,

Don‟t pressurize

Seals

Tonneau Cover

New RPN 160 200 60

Qualitatively, the team took into account other immeasurable considerations to keep the system

safe. For example, when operating the system, regular stops occurred in order to observe the

system and make sure it was operating properly. When the system was in operation, users used

proper face shields to protect from broken hoses or other mechanical failures. To ensure all

components were within their rated pressures, system operation only occurred with a maximum

pressure of 3500 psi in the high-pressure accumulator tank.

Achievability Results

The team successfully completed the project by the main deadline of April 29, 2005 to present

the project by the University of Idaho Engineering Expo. However, some of the phases took

longer than expected, due to faulty scheduling or poor time-management of the team. As shown

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in the table below, some phases took longer than scheduled; therefore, other phases had to be cut

short and quality may have suffered. For example, Phase Two – Researching Old Design, took

three weeks longer than anticipated, and the shortened subsequent phases, which caused anxiety

among team members.

Table VII – Team Schedule Changes

Phase Weeks Allowed Actual Time to Completion

Phase One –

Problem Definition

4 weeks 4 weeks

Phase Two –

Research Old System

4 weeks 7 weeks

Phase Three –

Preliminary Testing

1 week 2 weeks

Phase Four –

Model Alternatives

4 weeks 3 weeks

Phase Five –

Design New System

8 weeks 8 weeks

Phase Six –

Fabrication

5 weeks 4 weeks

Phase Seven –

Test New System

4 weeks 2 weeks

Phase Eight –

Design Evaluation

4 weeks 2 weeks

TOTAL: 34 weeks 34 weeks

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Acceleration and Fuel Mileage

Table VIII – Acceleration 0-35 MPH

Only diesel engine With hydraulic assist INCREASE

~15 seconds ~8.4 seconds 38%

Table VIII shows the increase in acceleration of the vehicle from 0-35mph with and without

using the hydraulic assist with similar throttle positions. Figures 16A and 16B provide the data.

Figure 2A Acceleration data from 0-35 mph

Assist Comparison on Incline

0

5

10

15

20

25

30

35

40

45

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81 83 85 87 89 Time (5/sec) Speed (mi/hr)

Assist-Incline NoAssist-Incline

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Figure 3B Acceleration data from 0-35 mph

Figures 16A and B show test data of three assist tests under similar conditions. Interpretations of

these tell how the hydraulic system worked during assist. As the swash plate opened, hydraulic

fluid began to flow from the high-pressure to the low-pressure accumulator. The pressure

gradient across the hydrostat drove the fluid flow. As the fluid flowed, the high pressure

decreased as the low pressure increased. This produced a torque on the drive shaft connected to

the driveline of the vehicle, which then produced an acceleration shown by the change in

velocity.

All of the data are on the same time frame. Each set of test data shows the assist cycle that

occurred after a regen cycle that started at about 30 mph. Figures 17 and 18 show the assist data.

Assist Incline Throttle

0

0.5

1

1.5

2

2.5

3

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 Time (5/sec) Throttle Voltage (V)

NoAssist Throttle-Incline Assist Throttle-Incline

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Figure 17 Assist Pressures

High Pressure (Assist)

0

500

1000

1500

2000

2500

3000

3500

4000

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45

Time (half seconds)

Pressure (psi)

Test 1

Test 2

Test 3

Low Pressure (Assist)

0

100

200

300

400

500

600

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45

Time (half seconds)

Pressure (psi)

Test 1

Test 2

Test 3

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Figure 18 Velocity and swash plate assist data

Velocity (Assist)

0

2

4

6

8

10

12

14

16

18

20

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 Time (half second)

Velocity (mph)

Test 1 Test 2

Test 3

Swash Voltage (Assist)

0

0.5

1

1.5

2

2.5

3

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45

Time (half seconds)

Voltage (volts)

Test 1 Test 2

Test 3

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Figure 19 shows the test data for three assist cycles without using the diesel engine.

Figure 9 Assist torque graph

Hydraulic system specs @ 3500 psi

Max torque 185 ft-lb

Average assist torque 140 ft-lb for 15 seconds

The hydraulic system added a maximum of 185 pound-feet of torque to the drive shaft when

engaged at 3500 pounds per square inch. This torque assisted the diesel engine, which reduced

the load on the engine increased the overall vehicle output. This torque was calculated from the

test data using the equation for torque on a hydraulic pump (Eq. 2)

2

dispPT Where:

ntdisplacemepumpdisp

PPP

TorqueT

lowhigh

_

(2)

Hydraulic Assist Torque Curve

0

20

40 60

80

100

120

140

160

180

200

14:28:43 14:28:47 14:28:51 14:28:55 14:28:59 Time

Torque (ft-lbs)

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Table IX – Fuel Increase (0-35 MPH)

Energy needed to accelerate from 0-35mph 371.2 kJ

Energy available from hydraulic system (∆KE from

test data) from 11-19mph

72.7 kJ

Difference 298.5 kJ

Percent Decrease (energy required from engine) 20%

The above table shows how much less the engine has to work to accelerate from 0-35mph, based

upon the energy that the hydraulic system can add to the kinetic energy of the vehicle during

assist.

Cost Results

The feasibility report determined that by using a 1993 Mack Refuse truck, the system would

have a payback period of four years. The savings of fuel and brakes accumulated over $30,000

after ten years of operation. (See Table X).

Table X. Cost of Fuel and Brakes after Ten Years

System Brakes Fuel

Original Vehicle $2,800 $120,000

Hybrid Vehicle $700 $90,000

Savings $2,100 (75% savings) $30,000 (25% savings)

*Source: Feasibility Study for Converting Refuse Vehicles to Hybrid Hydraulics

Reliability

By using Design Failure Modes Effects and Analysis, the reliability of the system increased by

900%. This was due to the changes to the system that decreased the amount of contaminated

fluid of the system. The reason why the percentage is so high is that the changes implemented

decreased the occurrence number of the DFMEA from nine to one. Most hydraulic component

failures are due to contaminated fluid. Making sure that the fluid was clean decreased the chance

of a failure. The table below illustrates the pervious RPN calculated due to contaminated fluid

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and the new RPN calculated due to filtered fluid. In all four examples the RPN decrease almost

ninety percent.

Table XI – DFMEA Results for Reliability

Potential Failure RPN due to

Dirty Fluid

RPN due to

Clean Fluid

Percentage Decreased

(RPN)

Hydrostat Fails 216 24 89%

Tandem Valve Fails 216 24 89%

Relief Valve Fails 189 21 89%

E-Pump Fails 162 18 89%

Objective 10: Improve Maintainability

The time to remove the hydraulic system was reduced by seventy-five percent. To determine

maintainability quantitatively, the team measured the amount of time it took to remove both the

new and old functional system and have every component off the vehicle. The previous system

took three full working days to take completely apart. Comparatively, the new system took less

than six hours to remove all system components.

Success of this functional requirement could also be determined qualitatively as well. For

example, the lift bed system allowed greater access to most of the components. This allowed

users to be able to troubleshoot issues easier and more effectively. In addition, an access panel

installed on the reservoir improved the ability to access the hydraulic fluid as well as allowed for

a greater cleaning capability. Ball valves placed at high elevation points on the system allowed

for air removal when filling the system with hydraulic fluid.

Objective 11: Weight Reduction

The new system weighed about one-third the previous system (Table XII). Most of the weight

reduction savings occurred with the replacement of the accumulators and reservoir. Those

replacements alone reduced the weight by 46 percent.

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Table XII– Weight Comparison of New and Old System

Component Old System Weight

(lbs.)

New System Weight

(lbs.)

Low Pressure Accumulator ~300 ~50

High Pressure Accumulator(s) ~700 ~200

Hydraulic Fluid 450 100

Accumulator Mounts 25 75

Reservoir Mount --- 75

Reservoir 150 20

TOTAL 1625 520

Noise Reduction and Smoothness

The noise of the system increased the total vehicle noise by two decibels when the system was

on. When the system was not in operation, the vehicle noise, created mostly by the diesel engine

was eighty-nine decibels. While the system in operation, the noise was at ninety-one decibels.

This means that the system was only two decibels louder than just running the engine alone.

Although data of the old system was not collected, observers recall that the old system was

significantly louder than the new system.

The ride quality improved due to the increased of the smoothness of the system. Observers felt

very little vibration in comparison to the old system.

During testing, the controls system initially was very smooth as it transitioned through the

driving cycle. Occasional noise occurred as the controls system hiccupped and caused cavitation.

By fine-tuning the system, it no longer provided opportunity for noise and allowed a very smooth

transition.

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Increased Brake Life

Table XIII – Decrease in Brake Wear

Avg. energy stored in the accumulators during regen

from 30mph

250 kJ

Energy needed to be dissipated in brakes, stopping

from 45mph = 613kJ

613 kJ

Difference 363 kJ

Percent decrease in break wear 41 percent

During this regen cycle (Fig. 20 and 21), the vehicle swash plate was engaged at about thirty

miles per hour. As the fluid pumped from the low-pressure accumulator to the high-pressure

accumulator, the pressure decreased and increased in them respectively. As the pressure across

the hydrostat increased the torque on the driveshaft increased, which then caused a greater

deceleration rate.

This test data showed that the when hydraulic system was used, it could slow the vehicle in a

timely manner from thirty miles per hour to a stop. Therefore, the hydraulic system had the

capability to remove that kinetic energy from the vehicle, which then increased the brake life.

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Figure 20 Regen pressure data

High Pressure (Regen)

0

500

1000

1500

2000

2500

3000

3500

4000

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41

Time (half seconds)

Pressure (psi)

Series1

Series2 Series3

Low Pressure (Regen)

0

100

200

300

400

500

600

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41

Time (half seconds)

Pressure (psi)

Series1

Series2 Series3

Series1

Series2 Series3

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Figure 21 Assist velocity and swash angle

Velocity (Regen)

0

5

10

15

20

25

30

35

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41

Velocity (mph)

Test 1 Test 2

Test 3

Time (half seconds)

Voltage to Swash Plate (Regen)

0

0.5

1

1.5

2

2.5

3

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41

Time (half seconds)

Voltage (V)

Test 1 Test 2

Test 3

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CONCLUSIONS/RECOMMENDATIONS

Objectives Completed

As shown in Section 3.0 and all its subsections, most of the functional requirements were met,

indicating a successful project. The truck‟s completion met the deadline and was functional with

a vast improvement in safety, reliability, maintainability, weight, and noise. Due to the scope of

the project, not all of the requirements could be measured and compared to the goals. For

example, due to lack of time and resources, exact fuel mileage and brake life was not obtained.

Below is a table of the functional requirements that the project met.

Table XIV – Completed Functional Requirements

Functional Requirements Measurable Goal Completed

Safety Improvement No DFMEA RPN‟s > 300 Yes

Achievability Design and Build by EXPO Yes

Improve Fuel Mileage and Acceleration Increase by 25% Yes

Cost effective Payoff Period less than 5 years Yes

Increase Reliability Increase DFMEA RPN‟s by 100% Yes

Maintainability More accessible components Yes

Reduce Weight Reduce by 500 lbs Yes

Noise Reduction/Smoothness Reduce by 50 PERCENT Yes

Increase Brake Life Achieve 50% efficiency of system Yes

Lessons Learned

One of the most difficult tasks for the team to overcome was the ability to meet deadlines. The

team learned that failure to meet certain deadlines early proved to create more problems to

meeting subsequent deadlines. In addition, due to failure to meet deadlines, some desirable

design changes did not have time to be completed.

Another lesson the team learned was the value of communicating effectively. The team did not

use their time efficiently during team meetings because communication took too much time or

the right information was not conveyed. The team learned how to facilitate better meetings by

being prepared and concise when delivering information to the rest of the team.

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Future Work Considerations

Due to the scope of the project, some desirable changes could not be made to the system and can

be considered for future projects. These include but are not limited to:

Improving the hydrostat efficiency at lower vehicle speeds

Designing a new controls system using a printed circuit board

Applying hydraulic hybrid technology to the refuse disposal vehicle market

Implementing a jake-brake system for storing more energy and increasing brake life

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Appendices

Appendix 1 DFMEA

Appendix 2 Feasibility Study

Appendix 3 Safety Procedures

Appendix 4 MathCAD Noise Modeling

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Appendix 1

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Appendix 2

Feasibility Study for Converting Refuse Vehicles to Hybrid

Hydraulics

Prepared by

CRISTY IZATT and ROBERT FEREBAUER

For

LATAH SANITATION

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Objective

The objective of this study was to analyze the savings and payback period of installing hybrid

hydraulic technology to a 1993 Mack Refuse Truck currently used by Latah Sanitation in Latah

County, Idaho.

Assumptions

The hybrid hydraulic system will reduce the fuel expenditures by 25 percent and brake

expenditures by 75 percent.1 The cost of brakes and the hydraulic hybrid system was adjusted

with a 2.53 percent yearly inflation rate.2 The cost of diesel fuel was adjusted with a 2.5 percent

yearly inflation rate.3 The salvage value of the hydraulic hybrid system is 50 percent of original

value.4

Target Vehicle

The target vehicle is a 1993 Mack Refuge Truck. The truck has a Mack 300 horsepower engine,

and an Allison HT 740 automatic transmission. The truck has an empty weight of 34,420 pounds

(lbs). It collects nearly 10,000 lbs of refuse each day with an average of 250 stops, and a

maximum payload of 19,000 lbs.

1 The fuel efficiency rate came from the efficiency achieved by Eaton, Inc. with their hybrid

hydraulic system. The reduction of brake wear was calculated using 2003 Future Truck data.

2 The inflation rate was calculated from an average of the percent changes in the Consumer Price

Index (CPI) from 1992 through 2002. http://www.census.gov/prod/2004pubs/03statab/prices.pdf

, p. 475, 3/28/04

3 The cost of diesel fuel was calculated with data obtained from the Department of Energy.

3

Using the data from 1995 to 2002 a rate of increase equal to 2.5% was used.

http://www.eia.doe.gov/emeu/aer/txt/stb0522.xls , 03/28/04

4 The salvage value is based on numbers obtained from Wholesale Hydraulics.

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Hybrid Hydraulic Cost Analysis

The cost of a hydraulic hybrid system is estimated to be $24,000. Table 1 shows the costs

associated with the system, including capital costs.

Table 1. Hydraulic Hybrid Cost

Component Quantity Price Each Total

Hydrostat 1 $5,000.00 $5,000.00

Accumulators 7 $2,000.00 $14,000.00

Valves 1 $1,000.00 $1,000.00

Tank 1 $1,000.00 $1,000.00

Plumbing 1 $2,000.00 $2,000.00

Miscellaneous 1 $1,000.00 $1,000.00

Total $24,000.00

The operating cost is calculated for ten years into the future. The main operating costs are fuel

and brakes. Table 2 shows the cost of fuel and brakes after ten years of use.

Table 2. Cost of Fuel and Brakes after Ten Years

System Brakes Fuel

Original Vehicle $2,813.10 $119,841.28

Hybrid Vehicle $703.27 $89,880.96

Savings $2,109.83 (75% savings) $29,960.32 (25% savings)

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The hybrid system pays for itself after 4 years of operation.5 At ten years the total savings is

$32,070.14.

All of the components of the hydraulic hybrid system are salvageable and can be used on another

vehicle when the current vehicle is replaced. This would create a situation in which the only cost

of equipping a future vehicle with a hydraulic hybrid system is installation.

Results

The payback period for the hybrid hydraulic system is 4 years. The system provides a total

savings of $32,070.14 after ten years of operation. In addition to these savings, clean vehicle

technology will also contribute to environmental and social improvements. The conservation of

diesel fuel will reduce the amount of petroleum products that enter the Palouse and reduce the

emission of carbon dioxide and nitrogen oxides. Reducing brake wear will also benefit the

environment by decreasing the amount of brake dust released into the air. Also, because hybrid

operation reduces the engine load, there will be a decrease in noise emissions.

5 Payback period is equal to the time needed for the accumulated savings to equal the initial cost

of the hybrid hydraulic system minus the salvage value.

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Appendix 3

Safety Procedures

or working on the Hydraulic System

on the Ford F350

1. Cover exhaust and turn on the fan.

2. Check all hoses and fittings to make sure they are secure.

a. Note: If you suspect a leak, use a piece of wood rather than your hands to find it.

Pinhole leaks are very dangerous!!!

3. Wheels must be blocked.

4. When there is any high pressure in the system, stay out of line of sight from the tanks and

the hoses. If the system must be looked at with high pressure, wear a face shield as well

as eye protection.

Procedures for Experimentation

When truck is on Jack Stands

5. Turn on the engine.

6. Apply brake pedal.

7. Shift into drive(D).

8. Release brake pedal, allowing drive shaft and wheels to rotate freely.

9. Through the control system this will charge the accumulators to no more than 3000psi. *

10. Apply the brake pedal to stop wheels from rotating.

11. Shift into Neutral(N).

12. *Run hydraulic assist through the control system.

13. Save the collected data on the used laptop.

14. Repeat steps 2-7 until desired data has been achieved.

*control system for testing on jack stands only

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Appendix 4

Selecting The Correct Vibration InsulatorMethodology from: Karman Rubber www.karman.com/selectvibro.cfm

When selecting the proper vibration insulator for the application, we must know:

1. The maximum load to be supported

2. The number of mounts to support the load

3. The frequency of the vibration (if there is more than one, the lowest frequency will be the

determining frequency)

4. Any s ize restrictions

Step 1: Calculate the load on each mount.

Weight of hydrostat: P h 136 Torque from hydrostat: T h 600

Number of Mounts: N 4 Dis tance from center of hydrostat shaft to center of mount: l .5 ft

Load Per Mount: P m

P h

T h

l

NP m 334

Step 2: Calculate the lowest dis turbing frequency based on the operating speed in Hz

RPM 2500

f dRPM

60f d 41.667

Step 3: Calculate the natural frequency that the system needs for 80% isolation

f n

f d

2.45f n 17.007

Step 4: Calculate the required s tatic deflection to obtain the des ired natural frequency

d s9.8

f n2

d s 0.034

Step 5: Calculate the required spring rate k to obtain teh desired natural frequency

kP m

d s

k 9.857 103

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Step 6: Select a mount that has a maximum load rating greater than or equal to the

calculated load per mount and a spring rate k less than the calculated spring rate.

Actual Spring rate:

Dampener:

Maximum Load: P max 490

Maximum Deflection: d max .08

k a

P max

d max

k a 6.125 103

Step 7: Calculate the transmissibili ty based on the actual spring rate for the selected mount

Actual Deflection: dP m

k a

d 0.055

Actual Natural Frequency:f n_act

9.8

df n_act 13.406

Transmiss ibility: T1

f d

f n_act

2

1

T 0.115

Isolation: I 1 T( ) I 88.453 %

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