Final Report Outline



Hydraulic Hybrid Vehicle Project

Final Report

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Team Dumpster Divers:

Michael Amato, Seneca Bertovich, Eric Hake,

Andrea Morey, Michael Shurtliff, & Joel Stobie

Latest Revision: May 10, 2005

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.

Table of Contents

1.0 Introduction 1

1.1 Project Goals and Scope of Report 1

1.2 Functional Requirements 1

1.3 Background Information 2

2.0 Methods and Materials 3

2.1 Current System Description 3

2.2 Objective 1: Safety Improvement 4

2.3 Objective 2: Achievability of Project 6

2.4 Objective 3: Fuel Mileage and Acceleration Improvement 7

2.5 Objective 4: Cost Effective 9

2.6 Objective 5: Increase of Reliability 10

2.7 Objective 6: Maintainability of System 12

2.8 Objective 7: Weight Reduction 14

2.9 Objective 8: Noise Reduction 15

2.10 Objective 9: Increase of Vehicle Brake Life 18

3.0 Results and Discussion 19

3.1 Safety Improvement Results 19

3.2 Achievability Results 20

3.3 Fuel Mileage and Acceleration Improvement Results 21

3.4 Cost Results 25

3.5 Increase of Reliability Results 26

3.6 Maintainability Results 27

3.7 Weight Reduction Results 28

3.8 Noise Reduction Results 29

3.9 Increase of Vehicle Brake Life Results 30

4.0 Conclusion 33

4.1 Objectives Completed 33

4.2 Lessons Learned 33

4.3 Future Work Considerations 33

Appendices A-1

Appendix A: DFMEA A-2

Appendix B: Feasibility Study A-3

Appendix C: Safety Procedures A-6

Appendix D: MathCAD Document of Noise Modeling A-7

1.0 Introduction

1 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. The secondary goal was to increase the efficiency of the hybrid vehicle by redesigning the previously installed system.

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.

1.3 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 |

1.4 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 was not a stand-alone system. Figure 1 shows the previous system mounted in the bed of the truck.

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Figure 1 - Photo of 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.

2.0 Methods and Materials

2.1 Current System Description

The figure below shows the layout of the new system installed on the vehicle. Using AmeSim modeling software helped develop the following schematic. Although the schematic is very detailed, it shows the basic layout of the combined system. 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. One may also note that the kidney loop installed cleans fluid as its running through the system.

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Figure 2 - Hydraulic system layout

2.2 Objective 1: Safety Improvement

DFMEA

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, |Replace Seals, |Tonneau Cover |

| |Reduce Length of Hose |Don’t pressurize Seals | |

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.

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. (See Figure 2 on next page) 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.

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Figure 3 - Solid works model of accumulator location

The table below 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.

Table III – Proposed Remedies of DFMEA Failures

|Failures |Remedies |No Pressurized Seals |New Accumulator |Steal Covers |Reduce Hose Length |Pressure |

|↓ |→ | |Mounting |on Nitrogen | |Transducers |

| | | | |Side of | | |

| | | | |Accumulators | | |

|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.

2.3 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.

Table IV – Team Schedule for School Year 2004-2005

|Phase |Phase Goals/Objectives |Applicable Dates |

|Phase One |Organize Area |Aug. 30, 2004 - Sept. 30, 2004 |

|Problem Definition | | |

| |Customer Interview | |

| |Review Reference Material | |

| |Understand Tools | |

| |Get to Know Team | |

| |Understand Hydraulics | |

|Phase Two |Make Schematic of Old Design |Oct. 1, 2004 – Oct. 25, 2004 |

|Research Old System | | |

| |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 |Redesign |Nov. 2, 2004 – Nov. 30, 2004 |

|Model Alternatives | | |

| |Compare Different Designs | |

| |Math Model New System | |

|Phase Five |Build Excel Model |Dec. 1, 2004 – Jan 31, 2005 |

|Design New System | | |

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

|Test New System | | |

| |Test on Roads | |

| |Acquire Data | |

|Phase Eight |Finalize Testing |April 9, 2005 – May 7, 2005 |

|Design Evaluation | | |

| |Analyze Data | |

| |Write Final Reports/Recommendations | |

2.4 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.

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.

When used as a motor, by the rotational speed determined the efficiency of the hydrostat. The motor was most efficient above 500 rpm, as seen in Figure 4. 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 determined to use the hydraulic system to assist the engine at ten mph and use until it depleted the energy.

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Figure 4 - Hydrostat motor performance

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.

2.5 Objective 4: Cost Effective

Feasibility Report

One of the requirements for this project was to make a system that was cost effective so that it can be a marketable hybrid solution. To answer this requirement, information was drawn from the feasibly 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.

2.6 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. This device, used to drain and fill the hydraulic system, had a ten-micron filter on it and. Figure 5 shows a picture of the fluid cart.

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Figure 5 - Fluid transfer cart with filter

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Figure 6 - 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.

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Figure 7 - Kidney loop filters

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Figure 8 - Kidney loop and case drain pumps

2.7 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.

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Figure 9 - Ball valve on high-pressure side

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. (See Figure 10 on next page.)

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Figure 10 - 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.

Shifting the transfer case into “neutral”, to prevented excessive wear on the hydrostat during extended highway trips. The below figure shows the transfer case.

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Figure 11 - Transfer case, left shaft drives the wheels, right shaft drive the hydrostat

2.8 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. Below is a table of 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 |

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.

2.9 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.

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% of the transmitted vibration.

Space constraints drove the design of the geometry of the mounts. The assembly is shown below in Figure 12.

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Figure 12 - 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 13 - Controls flow diagram

A Controls flow diagram shown in Figure 13 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 was created using the variables in the system (i.e. accumulator pressures, brake and throttle positions). This algorithm shown in Equation 1 controlled the swash plate angle in a calculated smooth response to the system variables.

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The graph shown in Figure 14 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.’

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Figure 14 - Graph of 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 computer program was refined to fix any problems and to increase the overall smoothness of the system.

2.10 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.

3.0 Results and Discussion

3.1 Safety Improvement Results

The new system design changes gave an 18% improvement in safety. 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, |Replace Seals, |Tonneau Cover |

| |Reduce Length of Hose |Don’t pressurize Seals | |

|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.

3.2 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 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 – |4 weeks |4 weeks |

|Problem Definition | | |

|Phase Two – |4 weeks |7 weeks |

|Research Old System | | |

|Phase Three – |1 week |2 weeks |

|Preliminary Testing | | |

|Phase Four – |4 weeks |3 weeks |

|Model Alternatives | | |

|Phase Five – |8 weeks |8 weeks |

|Design New System | | |

|Phase Six – |5 weeks |4 weeks |

|Fabrication | | |

|Phase Seven – |4 weeks |2 weeks |

|Test New System | | |

|Phase Eight – |4 weeks |2 weeks |

|Design Evaluation | | |

|TOTAL: |34 weeks |34 weeks |

3.3 Acceleration and Fuel Mileage

Table VIII – Acceleration 0-35 MPH

|Only diesel engine |With hydraulic assist |INCREASE |

|~15 seconds |~8.4 seconds |38% |

The table above shows the increase in acceleration of the vehicle from 0-35mph with and without using the hydraulic assist with similar throttle positions. See graphs below for data.

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Figure 15 - Acceleration data from 0-35

The graphs on the next page 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 graphs below 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 16 and 17 show the assist data.

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Figure 16 - Assist Pressure Graphs

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Figure 17 - Velocity and swash plate assist data

Figure 18 shows the test data for three assist cycles without using the diesel engine.

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Figure 18 - 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 (Equation (2)).

[pic] Where: [pic] (2)

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.

3.4 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

3.5 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 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% |

3.6 Objective 6: 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.

3.7 Objective 7: Weight Reduction

The new system weighed about one-third the previous system (See 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%.

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 |

3.8 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.

3.9 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% |

During this regen cycle, graphs shown below in Figures 19 and 20, 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 19 - Regen pressure data

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Figure 20 - Assist velocity and swash angle

4.0 Conclusion

4.1 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% |Yes |

|Increase Brake Life |Achieve 50% efficiency of system |Yes |

4.2 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.

4.3 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

Appendices

DFMEA A-2

Feasibility Study A-3

Safety Procedures A-6

MathCAD Noise Modeling A-7

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Final Report

May 3, 2004

Feasibility Study for Converting Refuse Vehicles to Hybrid Hydraulics

Prepared by

CRISTY IZATT and ROBERT FEREBAUER

For

LATAH SANITATION

Feasibility Study for Converting Refuse Vehicles to Hybrid Hydraulics

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% and brake expenditures by 75%.[1] The cost of brakes and the hydraulic hybrid system was adjusted with a 2.53% yearly inflation rate.[2] The cost of diesel fuel was adjusted with a 2.5% yearly inflation rate.[3] The salvage value of the hydraulic hybrid system is 50% 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.

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) |

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.

Safety Procedures

For working on the hydraulic system on 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

1. Turn on the engine.

2. Apply brake pedal.

3. Shift into drive(D).

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

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

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

7. Shift into Neutral(N).

8. *Run hydraulic assist through the control system.

9. Save the collected data on the used laptop.

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

*control system for testing on jack stands only

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[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. , p. 475, 3/28/04

[3] The cost of diesel fuel was calculated with data obtained from the Department of Energy.[4] Using the data from 1995 to 2002 a rate of increase equal to 2.5% was used. , 03/28/04

[5] The salvage value is based on numbers obtained from Wholesale Hydraulics.

[6] 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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System ON

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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