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
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
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.
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
2
Hydraulic Hybrid Vehicle page i
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
Hydraulic Hybrid Vehicle page ii
Noise Reduction and Smoothness .............................................................................................. 30
Increased Brake Life................................................................................................................... 31
CONCLUSIONS/RECOMMENDATIONS .............................................................................. 34
Objectives Completed ................................................................................................................. 34
Lessons Learned .......................................................................................................................... 34
Future Work Considerations ..................................................................................................... 35
Appendices ................................................................................................................................... 37
Hydraulic Hybrid Vehicle page 1
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
Hydraulic Hybrid Vehicle page 2
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
Hydraulic Hybrid Vehicle page 3
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.
Hydraulic Hybrid Vehicle page 4
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.
Hydraulic Hybrid Vehicle page 5
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.
Hydraulic Hybrid Vehicle page 6
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.
Hydraulic Hybrid Vehicle page 7
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.
Hydraulic Hybrid Vehicle page 8
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.
Hydraulic Hybrid Vehicle page 9
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
Hydraulic Hybrid Vehicle page 10
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.
Hydraulic Hybrid Vehicle page 11
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
Hydraulic Hybrid Vehicle page 12
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
5µ
Filter
Hydraulic Hybrid Vehicle page 13
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
Hydraulic Hybrid Vehicle page 14
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.
Hydraulic Hybrid Vehicle page 15
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
Hydraulic Hybrid Vehicle page 16
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.
Hydraulic Hybrid Vehicle page 17
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.
Hydraulic Hybrid Vehicle page 18
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
Hydraulic Hybrid Vehicle page 19
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
Hydraulic Hybrid Vehicle page 20
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.
Hydraulic Hybrid Vehicle page 21
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
Hydraulic Hybrid Vehicle page 22
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
Hydraulic Hybrid Vehicle page 23
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
Hydraulic Hybrid Vehicle page 24
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
Hydraulic Hybrid Vehicle page 25
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
Hydraulic Hybrid Vehicle page 26
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
Hydraulic Hybrid Vehicle page 27
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)
Hydraulic Hybrid Vehicle page 28
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
Hydraulic Hybrid Vehicle page 29
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.
Hydraulic Hybrid Vehicle page 30
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.
Hydraulic Hybrid Vehicle page 31
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.
Hydraulic Hybrid Vehicle page 32
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
Hydraulic Hybrid Vehicle page 33
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
Hydraulic Hybrid Vehicle page 34
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.
Hydraulic Hybrid Vehicle page 35
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
Hydraulic Hybrid Vehicle page 36
Hydraulic Hybrid Vehicle page 37
Appendices
Appendix 1 DFMEA
Appendix 2 Feasibility Study
Appendix 3 Safety Procedures
Appendix 4 MathCAD Noise Modeling
Hydraulic Hybrid Vehicle page 38
Appendix 1
Hydraulic Hybrid Vehicle page 39
Appendix 2
Feasibility Study for Converting Refuse Vehicles to Hybrid
Hydraulics
Prepared by
CRISTY IZATT and ROBERT FEREBAUER
For
LATAH SANITATION
Hydraulic Hybrid Vehicle page 40
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.
Hydraulic Hybrid Vehicle page 41
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)
Hydraulic Hybrid Vehicle page 42
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.
Hydraulic Hybrid Vehicle page 43
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
Hydraulic Hybrid Vehicle page 44
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
Hydraulic Hybrid Vehicle page 45
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 %
Hydraulic Hybrid Vehicle page 46
REFERENCES
1. Bradbury N. E. Retrofitting Direct-Injection and a Turbocharger to a Two-Stroke Engine
for Snowmobile Applications. M.S. Thesis, University of Idaho, 2006.
2. Ogink, R. Determination of the On-Engine Performance of an Automotive Turbocharger.
Royal Institute of Technology, Internal Combustion Engines Master of Science Thesis,
Stockholm 2000.
3. Bell, A. Forced Induction Performance Tuning: A Practical Guide to Supercharging and
Turbocharging. Sparkford, UK: Hayes, 2002.
4. MacInnes, H., Turbochargers. Berkley, NY: HP Books, 1984.
5. Watson, N., and M. S. Janota. Turbocharging the Internal Combustion Engine. New
York: Macmillan, 1982.
6. Xiao, H. An Advanced Turbocharger Model for the Internal Combustion Engine. Ph.D.
Dissertation, Purdue University, August 2000.
7. Steve Packer, Manufacturer of Aerocharger Turbochargers, Personal Correspondence,
2005.
8. Heywood, J. B., and E. Sher. The Two-Stroke Cycle Engine, Its Development, Operation,
and Design. Warrendale, PA: SAE, 1999.
9. Wright, C. W., and J. J. White, “Development and Validation of a Snowmobile Engine
Emission Test Procedure,” SAE Paper 982017, Sept. 1998.
10. Blair G.P. Design and Simulation of Two-Stroke Engines. Warrendale, PA: SAE, 1996.
11. Strauss S., and Y. Zeng, “The Effect of Fuel Spray Momentum on Performance and
Emissions of Direct-Injected Two-Stroke Engines,” SAE Paper 2004-32-0013