Detailed Design Report of the Hybird Hydraulic Vehicle



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Hydraulic Hybrid Vehicle Project

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Team Dumpster Divers

Michael Amato

Seneca Bertovich

Eric Hake

Andrea Morey

Joel Stobie

Michael Shurtliff

NIATT – National Institute for Advanced Transportation Technology

University of Idaho

115 Engineering Physics Building

Moscow, ID 83344-0901

Last Revision: December 18, 2004 Revision #: 2.1

Table of Contents

Introduction 1

1.1 Document Revisions 1

1.2 Executive Summary 2

1.3 Problem Statement 2

1.4 Objectives and Goals 3

1.5 Functional Requirements 3

2.0 Methods and Materials 4

2.1 Current Platform 4

2.1.1 Hydraulic System 4

2.1.2 Control System 6

2.2 Literature Review 9

2.2.1 Hydraulics Research 9

2.2.2 Controls Research 11

2.3 Modeling of Requirements 12

2.4 Testing of Requirements 14

3.0 Results and Discussion 16

3.1 Results of the Modeling 16

3.2 Results from Testing 18

3.3 Deviations from Modeling and Testing 19

4.0 Design Considerations 20

4.1 Current System 20

4.2 HLA 20

4.3 SHEP 22

4.4 MuTT 23

4.5 Controls 23

5.0 Chosen Final Design 25

5.1 Hydraulic System 25

5.2 Hydraulic Components 27

5.3 Controls 27

5.4 Economic Analysis 29

6.0 Future Work 30

6.1 Project Schedule 30

6.2 Projected Issues 33

7.0 References 34

8.0 Appendices 35

Appendix A. Wiring of Current Controls System A-1

Appendix B. Flow Diagram/Equations of Excel Model B-1

Appendix C. Jack Stand Test Safety Procedures C-1

Appendix D. Road Test Safety Procedures D-1

Appendix E. Detailed Noise Modeling E-1

Appendix F. DFMEA of Current System F-1

Appendix G. DFMEA of MuTT System G-1

Appendix H. Excel Graphs of Modeling vs. Tests H-1

Introduction

1.1 Document Revisions

|Date |Author(s) |Revision |Rev. # |

|Dec. 14, 2004 |Joel Stobie and Andi Morey |Rough Draft – not complete |1.0 |

|Dec. 16, 2004 |Joel Stobie, Andi Morey, Michael|Rough Draft Complete |1.1 |

| |Amato, Michael Shurliff, and | | |

| |Eric Hake, Frank Albrecht. | | |

|Dec. 17, 2004 |Andi Morey |Final Draft for Submission Complete |2.0 |

|Dec. 18, 2004 |Michael Shurtliff |Final Draft second revision |2.1 |

1.2 Executive Summary

The purpose of this detail design report is to outline the methods and results of the research and design performed by the Dumpster Divers senior design team. The main objective for this project is to redesign the hydraulic hybrid system on a vehicle that was already installed onto a Ford F350 truck by a previous design team. The system uses the concept of regenerative braking, which takes energy off the drive shaft when braking and stores the energy. The energy is then used to assist the engine during acceleration by providing added torque to the drive shaft.

There were four different methods of research that was completed in order to design a new system. The current system was analyzed so that the team had more understanding with hydraulic hybrids and to find potential problems with the system. The team also modeled the different objectives and goals that are hoped to be achieved by this project. The current platform was tested for analysis of a hydraulic system, and the team also took into account different sources of literary research. With the results from the modeling and testing, as well as research into four different systems, a final design was chosen.

The system described in this report is a system created by the team in which different components and designs were utilized into one system. This report goes into details of this system and how the goals can be achieved through this system. It also describes the control system and the design of the new control system to go along with the new hydraulic system. This report will also go into a cost analysis as well as a project schedule which suggests that the project will not only be able to be completed on time but also within the allowed budget.

Any further details that are not included on this report is located on the teams website at: .

1.3 Problem Statement

Because of the large demand of improved fuel economy in all vehicles on the road and better emissions standard, there has been an increased interest in hybrid vehicle research. One of the options for hybrid vehicles is using hydraulic assist systems. The main goal for this project is to create a hydraulic launch assist system to place onto large sanitation vehicles that both improves their fuel economy while being a feasible and affordable design. Latah Sanitation is a hopeful customer who desires a system that can be an after-market add on package to their pre-made trucks to increase the brake life of their trucks as well as save them money on fuel. NIATT is the other customer who is hoping that the current project can be marketable to other vehicles such as bus transits systems and postal service vehicles. Other objectives included are to increase the efficiency of the current hydraulic system on the platform of a 1988 Ford F350, created by a previous project, to reduce component wear and tear on the system to increase brake life of the vehicle, to improve better noise control, to develop a new control system for hybrid operation, and to improve safety features.

1.4 Objectives and Goals

The main goal of this project is to take an existing hydraulic hybrid system that is currently on a 1988 Ford F350 truck and improve the efficiency of system. In order to do this, the overall efficiency was broken up into ten main goals for the project. These include, improving safety, design an achievable system, improve gas mileage and acceleration, keeping the project cost effective, increase the reliability of the system, have a system that is maintainability, use the controls system for smooth operation, reduce the weight of the system, reduce the noise on the current system, and to increase the brake life of the vehicle. These goals are organized in a fashion in which the team can make different methods and approaches to accomplish the goals. This is outlined in Section 2.3 with different modeling techniques.

1.5 Functional Requirements

These functional requirements are “achievable” goals with a numerical value in which the project can be measured. The following are seven functional requirements in which the project will strive to meet:

1. Safety - The vehicle must meet DFMEA requirements for road driving, which is to have a RPN score of less than 250.

2. Achievability – The project must be complete by the Engineering Expo on April 29th.

3. Cost Effective – The project must be complete within a budget of $10,000.

4. Acceleration – The new hydraulic system must give a vehicle a 125% increase in acceleration, without using the engine motor.

5. Gas Mileage – The new hydraulic system must have 60% increase of efficiency of the assist cycle. This will therefore increase the gas mileage of the vehicle.

6. Reduce Noise – The new system must reduce noise generation by 50%.

7. Brake Life – The new system must achieve 55% efficiency during the regenerative braking to increase the brake life of the vehicle.

2.0 Methods and Materials

2.1 Current Platform

2.1.1 Hydraulic System

2.1.1.1 System Description

The current platform for this project is a 1989 Ford F350 in which a previous team built a hydraulic hybrid system. This hydraulic system is currently on the vehicle and has been a base model for the project to build upon. The system uses the concept of regenerative braking, which takes energy off the drive shaft when braking and stores the energy as pressure in hydraulic cylinders. The energy is then used to assist the engine during acceleration by providing added torque to the drive shaft.

The system consists of seven major components: a hydrostatic transmission (also called a hydrostat), a low-pressure accumulator, a high-pressure accumulator, a tandem valve, a sixty gallon reservoir, and a charge pump. Hoses, lines and fittings connect these components together in the system.

2.1.1.1 Component Description

The charge pump is a Vickers model V20F vane pump which is belt driven under the hood by the diesel engine. The pump is necessary to circulate hydraulic fluid around the hydrostat to regulate the temperature. It is also used to supply fluid to the low-pressure accumulator and the hydrostat. The pump is supplied by the sixty-five gallon reservoir, which adds nearly five hundred pounds to the vehicle. This particular pump model is commonly used as a power steering pump on large vehicles and is capable of providing nine gallons per minute at 2000 psi.

The low-pressure accumulator is a cylindrical accumulator with a floating piston with nitrogen on one side and hydraulic fluid on the other. In operation, the charge pump pumps fluid into the low-pressure accumulator so that when the vehicle brakes are applied the hydrostat is supplied with inlet pressure provided by the low-pressure accumulator. The accumulators are charged with nitrogen to 90% of the calculated minimum operating pressure. Fabricated from steel, the burst pressures of the accumulators are constrained by threaded end caps at the nitrogen end of the cylinder, which are able to withstand approx. 25,000 psi based on calculations by last years design team. The accumulators will have a minimum safety factor of 5, depending on the operating pressure range.

The hydrostat is an Eaton 46 variable displacement in-line piston motor/pump. A swash plate controls the displacement of the hydrostat by adjusting the stroke length of the pistons. When not being used, the hydrostat is being driven by the drive shaft through a transfer case, but it is not pumping any fluid because the swash plate is closed. At the time the vehicle brakes are applied the hydrostat swash plate is opened and the hydrostat begins to pump fluid into the high-pressure accumulators using the energy from the drive shaft to drive the pump, which in turn slows the vehicle. When the vehicle comes to a stop the tandem valve then closes, containing the fluid in the high-pressure accumulators.

The tandem valve, International model # 07-8C-E-104 02, is used to switch the fluid flow path so that the hydrostat is always turning the same direction whether in a regenerative or assist cycle. This is important as the drive shaft is always turning the same way both during acceleration and deceleration. Two solenoids are used to slide a valve block into three positions: assist, neutral, and regenerative mode. The control system actuates one of the solenoids when the system is requested to go into either assist or regenerative mode, and the valve block self-centers itself when no voltage is applied to it from the controls.

When the vehicle is accelerating the hydrostat is used as a motor to add torque to the drive shaft. This torque is caused by the pressure differential across the hydrostat, the fluid exiting the hydrostat goes back into the reservoir.

2.1.1.3 Schematic (AMESim)

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Figure 1-A view of hydraulic schematic of the current Ford F-350

2.1.1.4 Flow Diagram

Shown on the next page is a flow diagram of the current platform installed on the F350 now. As one can see the charge pump is used to supply fluid to the low-pressure accumulator from the reservoir. Then when the hydrostat’s swash plate is opened, fluid travels from the low-pressure accumulator and is stored into the high-pressure accumulator. When energy needs to be released; it flows from the high-pressure accumulator, through the hydrostat into the reservoir.

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Figure 2 - Flow Diagram of the Current System

2.1.2 Control System

2.1.2.1 System Description

Given to the team was a basic control platform that a group of students had worked on the previous year. These students attempted to put a system together but basically ran out of time and did not have everything finalized. As the control system is usually one of the last implementations to a working system, it can be given that when the project was taken up by the current team, that there was not any form of program to run the system. The team however had a well-documented schematic of how the current system was wired up. With little time to connect the existing wires to the National Instruments field point modules and then adding some pressure transducers and thermocouple wires to help monitor the system, the current system was complete.

A simple program was created to monitor the three pressure transducers, the thermocouple wires and any other input and output signal available such as speed of the vehicle, throttle position, brake position, tandem valve position and swash plate angle. The program was created using LABVIEW and set up to be user controlled. Having never run the system before and having no information on the current system, the team was left to find out the unknowns. With a basic understanding of how the system needed to be controlled, the program was manually run and the user controlled the swash plate angle of the hydrostat by watching the pressure readout of the transducers. At the same time, measurements were taken of all data points and logged into a computer for analysis. This process was very inefficient but it allowed the team to get a better feel for the current system and see if the modeling was accurate.

2.1.2.2 Component Description

The main component of the system is the field point modules. The system consisted of five main modules, the analog input module, the analog output module, the thermocouple module, the relay module and the main module itself that reads the LABVIEW program. These are described in more detail in the research Section 2.2.2.

Attached to these modules were different sensors that sent voltages to the modules for the system to read and analyze. The signals that were needed include the break position, throttle position, pressures, speed, transmission, and others. Some of the sensors used basic circuit analysis method of using a potentiometer to send voltages back to the field points. For example, the brake position sensor is a 100mm linear motion potentiometer installed near the brake pedal. The throttle position sensor used a potentiometer that comes stock on the truck.

Other signals used different techniques to send information to the field points. For example, the pressure sensors were transducers that outputted a voltage linear to the pressure is was measuring. The speed sensor used a frequency to voltage converter attached to the rear anti-lock brakes to measure the speed of the vehicle. The transmission position sensor used a voltage regulator connected to the shift lever.

The valves and hydrostat came with their own circuitry in order to control them. The analog output module outputs 12 Volts to open and close the emergency dump valve, the tandem valve, and up to 2.8 Volts to change the swash plate angle of the hydrostat.

2.1.2.3 Wiring Schematic

See Appendix A. for full wiring schematic.

2.1.2.3 Flow Diagrams

Figure 3 - Regenerative Mode Flow Diagram

Figure 4 - Assist Mode Flow Diagram

2.2 Literature Review

2.2.1 Hydraulics Research

The bulk of the research done by the team was research on hydraulics and fluid mechanics. The research was separated into three main levels: component level, system level and vehicle level which focus on safety, prevention of failure, and design considerations.

2.2.1.1 Component Level

Hoses and couplings connect the different components of a hydraulic system. The configurations of hose systems are important as the failure of a hose or fitting typically results in a failure of the system. Hoses must be mounted and secured to reduce the connection points’ exposure to bending or shearing stresses (1 – See References), and a mount configuration subjecting a hose to five to seven degrees of twist will reduce the service life of the hose by 70% to 90%, respectively (2). The use of excessive couplings also causes a greater pressure drop between two hoses and increases the chance of the hose bearing the greater pressure to fail (1). The shank of a coupling that is crimped or pressed onto the end of hoses must be 1 ½ times the diameter of the hose to insure a secure connection (3).

To prevent injury or damage from a failed line, however, a steel whip-check cable or chain device should be installed on any high pressure fitting to control a hose from flailing in the event of a coupling failure (4). The safety factor of hoses is 4, which is an ASME standard (5). Pinhole leaks on high pressure lines can inject fluid into the skin and cause serious bodily injury (6). Additionally, safety precautions should be taken when working with a flammable fluid such as hydraulic fluid so it is routed away from any ignition source (6). Any hydraulic system should be shut down if fluid temp is above its specified limit (5).

Filters on the suction side of piston pumps are not recommended, as it may limit the flow rate of fluid entering the pump (5). Furthermore, filters aren’t suggested to be used in the case drain/oil cooling lines at the hydrostat because they may cause excessive pressure buildup (5). Ford found that bleeding air at high points in the system reduced aerated hydraulic fluid, and they experienced gas leakage into the hydraulic fluid with an in-line pulse suppressor (7). Antifoaming additive should be added to most hydraulic fluids to further help reduce aeration problems (8).

Two types of accumulators were studied and determined feasible with price and availability. Piston accumulators are pre-charged with nitrogen to 100 psi less than minimum operating pressure (9). Piston accumulators with capacities of greater than 5 gallons must typically be mounted vertically to avoid piston seal deformation and consequential gas leakage (10).

Bladder accumulators are the second type of feasible accumulator style. Ford’s EPA carbon accumulators utilized an elastomer foam in the nitrogen side of the bladder to minimize heat transfer between the gas and fluid during pressurization (7).

ASME standards call for a safety factor of 4 for production accumulators (11). However, the high pressure carbon fiber accumulators developed by the EPA for Ford utilize a safety factor of 3, which brings the burst pressure to 15000 psi (12). Flow control valves on the fluid side of accumulators can stop fluid flow when a high pressure line failure occurs, controlling the amount of fluid that drains from the system (12). Steel protective guards should be implemented over the gas fill valves to protect against breakage (11). Accumulator safety blocks are produced that control the pressure inside tanks and provide pressure relief when pressures become too high (13).

Ford determined that using a low pressure accumulator to function as a reservoir was more efficient than using a separate reservoir tank because a separate reservoir tank requires an extra pump to refresh the low pressure accumulator with fluid (7). However, if the reservoir is the low pressure accumulator, the fluid circulating through the hydrostat case is at the same pressure. Ford experienced leakage of the high pressure pump seals in their I-field pump by using a pressurized reservoir (7). This leakage occurs with case pressurization because excessive fluid pressure forces the lip of the shaft seal to slowly depress and wear a groove into the shaft, which eventually lets oil leak past the seal (2). When the reservoir was at its minimum pressure with Ford’s HLA setup, they experienced noise and aeration problems (7). Ford pre-charged their accumulators to 75 psi (7). Returning fluid in the reservoir should be controlled to enter with a fluid velocity of less than 2 ft/sec, and should return on a line that is higher than the suction line in the reservoir (8). Additionally, baffles and screens aide in de-aeration and controlling sloshing fluid (8).

Hydraulic fluid must be able to stand up to the conditions of a hydraulic device with adequate viscosity and lubrication properties. Fluid temperature is too hot when the fluid’s viscous properties falls below the system’s optimum level (2). Damage to seal materials begins to occur at 180 degrees Fahrenheit, and such operating temperatures should be avoided (2). An EPA test with hydraulic vehicles called for a fluid that could provide sufficient lubrication properties at continuous operations temperatures of 200 °F, and with extreme intermittent temperatures of 250 °F; they found that Poly-Alfa-Olefin or high-grade mineral oil (group III) bases were cost-effective and sufficient (12).

2.2.1.2 System Level

Cavitation occurs when a component in a system needs more fluid flow than can be provided by the system (2). When a component requests more fluid than is provided, the pressure difference between the inlet and outlet of the component increases; cavitation occurs when the pressure in the component reaches the evaporation pressure of the fluid. The fluid then boils and the bubbles formed during vaporization implode when pressurized, causing noise, erosion, and ultimately damage (8). Outgassing is a form of cavitation when a liquid gas, say air that is dissolved in a solution is brought below its saturation pressure and fills discontinuities in fluid with gas bubbles (14). However, the saturation pressure required for outgassing is higher than the pressure required to vaporize fluid, which implies that outgassing is a more probable cause of cavitation (15). The detection of cavitation is apparent with a 4-8 kHz hissing sound occurring at a component (8). It is the leading cause of noise in valves, followed by instability and impact (8). Instability, however, causes a single frequency squeal or whistle (8). To understand noise, it has been determined that it is proportional to flow and to the square of pressure (8). It can be reduced with a series of pressure drops in series or making sure enough flow is provided to each component in the system (8). Additionally, applying a vacuum to the system is effective in removing gas in solution and further reducing noise mechanisms (7).

Hydraulic shock is a major source of system leakage (8). It is defined as large pressure wave fronts that travel through the system (8). It typically occurs when valves are actuated rapidly, and is mitigated by using short lines, branches, cross sectional area changes, accumulators, and effective shock suppressors (8).

The safety of the entire system is highly based upon its self-containment of high pressures. Crush zones are passive safety systems that are already incorporated into most vehicles, and these zones protect the contents within a certain volume in vehicle (16). Large pickups are heavy vehicles that have long crush zones that aid in decelerating a vehicle more gradually in a collision (16).

2.2.1.3 Vehicle Level

Ford found that, by measuring noise inside the cab of the Navigator, that the I-field hydrostat and mounting system improved noise from previous loud hydraulic systems (7). Concentrating on the noise produced by the hydrostat is the most beneficial approach to noise problems because a hydraulic pump/motor contributes 95% of the noise in hydraulic machines (8). Sound waves are transmitted through air, fluid, and the structure, and fluidborne noise has about one thousand times more energy than airborne noise (8).

Fluidborne noises can be reduced by implementing in-line pulse suppressors (17). It is also suggested that fluids be operated at 110-130 °F to reduce noise in the system (8). Pumps and valves become eroded and produce more noise when water is in the system, and proper measures are needed to purge water from the system (8).

Any vehicle components near the hydrostat are potential noise radiators (8). The hydrostat displacement, pressure, and primarily speed affect the noise output of the system (8). To reduce the transmission of vibration from the pump to the vehicle, it is suggested by the “vibration isolation principle” that the natural frequency of the mounting hardware is much less than the applied load frequency produced by the hydrostat (8). Bushings for the mounts should be fabricated from Buna N or Neoprene to ensure longevity and oil resistance (8).

2.2.2 Controls Research

Research for the control system of the Hydraulic System can be divided two ways. An understanding of the current system, how it was supposed to work and how it was to be controlled, and then research of what the best and most efficient way to control this system and get the results that were wanted.

To understand the current system specifications were researched for voltage conditions of the tandem valve and the dump valve. Tests were run for the throttle position and the brake position and a strobe light was used for speed calibration. With all sensors working as expected, a deeper understanding of the swash plate was desired. With a nametag connected to the moog valve that controlled the hydrostat swash plate, we contacted the owner. HSD inc. out of Spokane created this particular moog valve and through several faxes and telephone conversations, a thorough understanding of how the moog valve controls the hydrostat was established.

With an understanding of the current system, research was directed to ways to improve what was given. The goal for this project was to make the system smooth and as efficient as possible. Aspects that were looked at were engine maps for the 7.3 L Diesel engine to evaluate prime times for assist and regeneration modes. Other hybrid control systems for both electric and hydraulic systems were found useful. The control for the Ford Explorer electric hybrid owned by NIATT was useful to understand the logic implemented to control the electric hybrid. Understanding of other aspects of the system such as flow rates, fluid shock, cavitation and pressure are helpful to avoid potential problems that can be avoided with the control system. A good analysis of how the average driver might react in all situations was looked at to help determine what would need to be handled.

2.3 Modeling of Requirements

2.3.1 Review/Goal of Modeling

In this project, modeling was very important because it allowed predictions of how the conceptual design will work without having to build the actual system. For each goal/objective of the project, a measuring process needed to be established. That way each variable affecting the goals, and therefore the system, can be predicted.

2.3.2 Modeling Approach

The modeling of the system will be approached several different ways. The functional requirements, stated previously, are not all things that can be measured through instrumentation, i.e. pressure transducers, flow meters, feedback sensors, etc. The modeling of these “non-measurable” requirements will be designed with knowledge from the research so that the stated requirement will be met.

The functional requirements are listed on Table 1, on the next page, in order of the importance with an explanation of how the requirement will be modeled.

Table 1 – Function Requirements and Modeling Techniques

|Importance |Goals and Need |Ways to Model |

|1 |Safety Improvement |DFMEA |

|2 |Achievability |Gantt Chart/Schedule |

|3 |Improve Gas Mileage and Acceleration |Using Excel and energy use, calculate over |

| | |driving cycle |

|4 |Cost effective |Economic Analysis |

|5 |Increase Reliability |DFMEA |

|6 |Maintainability |Access to components, access panel in reservoir,|

| | |user manuals with specs for all components |

|7 |Smoothness |Existence of Control system, accelerometer |

| | |readings |

|8 |Reduce Weight |Drawings, component specs |

|9 |Noise Reduction |Reference from noise book according to bushings |

| | |and shock suppressors |

|10 |Increase Brake Life |Using Excel, calculate over driving cycle |

Safety – Safety will be measured through an analysis called Design Failure Modes Effects and Analysis (DFMEA). This analysis gives a guideline to determine the severity, occurrence and detection of a failure mode happening. Then through analysis and design change, these measurers can be lessened thereby reducing the risk of a particular failure mode. This would then increase the safety of the system.

Achievability – This will be measured through our Gantt chart and schedule through the next several months. Being able to stay on track with the design is an important part of being able to finish the project.

Improve Gas Mileage – With an Excel math model that describes and gives numerical result predictions for the system, the energy saved will be determined by using a hydraulic system as well as determine the energy saved for any new system.

Improve Acceleration – Again using the Excel math model to determine how much the acceleration is achieved by the system.

Cost Effective – An economic analysis of a new design will be used to determine if building the system will be within budget.

Increased Reliability – Again through DFMEA analysis a new system design will be analyzed and any reliability issues designed out.

Increased Maintainability – This will be measured using 3D modeling, to determine if for a system layout the components will be easily accessible and therefore easier to maintain.

Smoothness – This will be measured by observation of the system in motion as well as comfort level of the driver and rider of the vehicle.

Reduced Weight – This will be measured by mathematical analysis of adding weights of components and comparing to a new system.

Reduced Noise of System – Through research and observation of the system, certain strategies will target different noise problems in the system.

Increase Brake Life –This will also be measured via the Excel math model to determine how much energy is being taken off of the drive shaft by the hydraulic system instead of the brakes.

2.3.2.1 System Modeling

The goal of the Excel math model was to be able to estimate what speed could be attained by using only the hydraulic assist, if the vehicle had been stopped from 30 mph. This would give an estimate of the efficiency of the system, in the form of how much energy could be recovered through this system. The reasoning behind this model was to be able to have some predicted numbers when testing began. It also shows conceptually how the system will react and behave under certain conditions, i.e. at a high pressure and a high displacement the torque on the driveshaft will be high as well.

The model is set up to be able to get results in both assist and regenerative modes. The inputs for assist and regenerative modes are initial pressure and initial velocity, respectively. Hydrostat displacement can also be an input for either mode. For regenerative mode, the spreadsheet will give a pressure obtained after slowing down from the input velocity. For assist, it will give a velocity obtained after releasing all the pressure in the accumulator. A flow diagram with the equations used in the model can be found in Appendix B.

2.4 Testing of Requirements

2.4.1 Goal of Testing

There were two different tests completed to gather sufficient amount of data. The system was first tested on jack stands, and when enough data was gathered, and the truck was deemed safe, the testing was taken to the road.

Jack Stand Test

The reason for this test was to become familiar with the current system and to make observations about how it worked, in a safe controllable environment. The observations were important to verify conceptually how a hydraulic system should work, and also to find potential problems with the system.

Road Test

Testing on the road was important to collect pressure, velocity and hydrostat displacement as each varied with time. This particular data was needed to verify the reliability of the Excel model used to describe the system, which in turn verifies the modeling discussed before.

2.4.2 Testing Procedure

Jack Stand Test

Many specifics of the test were directly affected because safety was the first concern. The first thing that needed to be done was to raise the rear axle of the F350, secure it on jack stands, and block the front wheels. The next step was to calibrate the sensors on the vehicle so that the control system could record the data so that it could be observed while system was in use. When actually running the system precise safety procedures were followed, to protect both the nearby observers and the system itself. These procedures can be found in Appendix C.

Road Test

The road test took place after testing on jack stands, when the team was more comfortable with the system and had more knowledge about how to run the controls. Several tests were completed using the engine to charge the accumulators. The testing was completed on a flat and long section of road in order to have plenty of room to complete the test. The truck was taken in to the regenerative mode and then the engine was used to accelerate. When the accumulators would reach the desired pressure the truck was taken to a complete stop and switched to assist mode. During this processes the controls would manually open the swash plate and the hydraulic system only was used to accelerate the vehicle. Varying accumulated pressures and varying swash plate angles were uses for several assist cycles.

The next step was to use the hydraulic system to slow the vehicle down. The starting velocity was around 22 mph and the swash plate was simply slowly open to steadily increase the stopping torque of the drive shaft to take the vehicle to a complete stop.

All of the data during the road tests were recorded via the control system and saved onto an Excel spread sheet to be analyzed at a later time. For protection, a detailed safety procedure outline was followed and can be found in Appendix D.

3.0 Results and Discussion

3.1 Results of the Modeling

Modeling each of the goals has provided several positive results. Through the research necessary to know how to model the goals, the team gained a lot of knowledge and learned a lot about vehicle modeling. The table below shows the results of the goal modeling that has been previously explained. Some of the results are numerical values that can be measured through instrumentation, whereas the others are subjective and the measurements of these are explained below.

Table 2 - Results of Modeling of the Goals

|Importance |Goals and Need |Results from Modeling |

|1 |Safety Improvement |Need a Threshold of 250 RPN |

|2 |Achievability |See Section 6.1 |

|3 |Improve Gas Mileage and Acceleration |Acceleration of 0.7 m/s2 |

|4 |Cost effective |See Section 5.4 |

|5 |Increase Reliability |Again, need a Threshold of 250 RPN |

|6 |Maintainability |No Access Panel for Cleaning/ Components are |

| | |closed off |

|7 |Smoothness |Improved with Controls System |

|8 |Reduce Weight |May be able to reduce by 50% from current |

| | |system. |

|9 |Noise Reduction |Current system will have a 100% noise set-point |

| | |according to observations. |

|10 |Increase Brake Life |De-acceleration of 0.73 m/s2 |

Safety – DFMEA of the current system showed several areas that scored quite high, and needed to be addressed. These failure modes included fluid contamination, relief valve failure, broken high-pressure hose or line, and control system malfunctions.

Achievability – In order to complete the project, hard milestones needed to be set. See Section 6.1 for project schedule.

Improve Acceleration – The results from the Excel model show that the current system has the potential to accelerate the vehicle at a rate of about 0.7 m/s2. This really is quite slow compared to an average vehicle (0.5 m/s2 would accelerate a vehicle to about 11 mph in 10 seconds, whereas a new Ford F350 reaches 60 mph in 10 seconds) (18).

Improve Gas Mileage – From above the Excel model shows a slow acceleration rate of the current system. This means that if driven on the road the engine would still need to be used to accelerate the vehicle. The system would still assist a small amount, but the less the engine had to work to achieve a reasonable acceleration the better the gas mileage of the engine would be.

Cost Effective – Finite budgeting will need to be considered greatly during the design processes of the new system and is described more accurately in Section 5.4.

Increase Reliability – The DFMEA analysis of the current system, as said before, showed many areas where system reliability could be improved.

Maintainability – Research has shown that it is very important to be able to maintain a hydraulic system. The current system has very few provisions for maintainability. There is no access panel on the reservoir for cleaning, and many other components are closed off so that maintaining them is very difficult.

Smoothness –The current system will be improved 100% by adding a functional control system. With a control system installed, it will be able to monitor pressures, speed, brake position, throttle position and many other sensors. From these indicators, the control system will allow assist and regenerative modes at appropriate times taking into effect the required times to adjust for fluid shock and vibration. As currently proven with a manually controlled system and the test results, a program installed to watch all possible reactions of the system and to adjust accordingly would improve the smoothness of the system.

Reduce Weight – Through the research it was found that the system does not need to have a sixty gallon reservoir to be completely functional. Designing a different reservoir that does not have as much fluid volume would result in reduced weight. Another observation when researching accumulators was that a carbon-fiber wrapped bladder accumulator will function as well as a floating piston accumulator that is on the current system, and weighs approximately half as much as the current accumulators. With just these two changes alone, it should be achievable to reduce the weight of the hydraulic system by 50%.

Noise Reduction – Through observation of the current system through both the jack stand and road tests, these noise problems occurred: structure borne pump noise, cavitation noise, airborne and fluidborne noise. See Appendix E.

Increase Brake Life – Similar to the acceleration, the deceleration rate due to the hydraulic system is 0.72 m/s2. This, again, is not as much as a normal vehicle. This causes the driver to still have to use the friction brakes to achieve a reasonable deceleration rate, therefore decreasing brake life. A better deceleration rate could be obtained by having a larger displacement hydrostat and having a higher minimum operating pressure of the high pressure accumulator.

3.2 Results from Testing

Jack Stand Test

The first test conducted took place in the shop area where the rear axle was propped up on jack stands and the hydraulic system was pressurized and then released.

Key Observations of Jack Stand Test

• As pressure climbed in the accumulators, during a regenerative cycle, the hydrostat needed more applied power to continue to raise the pressure.

• During the assist cycles, the greater the pressure difference across the hydrostat required more brake pressure to keep the wheels from spinning to fast.

• When switching from tandem valve from regenerative to assist mode, pressure could drop up to 200 psi.

Road Test

To compare the data accurately the Excel model had to be changed according to how the system was tested for each test run. The most significant differences were the starting pressures, starting velocities, and accumulator pre-charge pressure. The pre-charge pressure for the piston accumulators is designed to be 900 psi, but at the time of testing was 625 psi. Therefore in the tables below, the “ideal model” column shows the numerical results if the system was working as designed, as opposed to how it was tested. The “model as tested” column shows the numerical results modeled more closely to the test variables. The “test” column shows the numerical results from the data taken during the test.

Table 3 – Regenerative Mode Testing Results

|Regenerative Mode |Model as tested |Actual Test |

|Displacement |100% |Varying up to 100% |

|Start Pressure |1199 psi |1165 psi |

|Start Velocity |22 mph |22 mph |

|Time to come to stop |10.9 sec |21 sec |

|Pressure Obtained |1589 psi |1850 psi |

|Efficiency |36.70% |48.70% |

Table 4 – Assist Mode Testing Results

|Assist Mode |Model as tested |Actual Test |

|Displacement |100% |Varying up to 100% |

|Start Pressure |2295 psi |2316 psi |

|Start Velocity |0 mph |0 mph |

|Time to release pressure |34.5 sec |26 sec |

|Velocity Obtained |7.9 m/s |3.75 m/s |

|Efficiency |47.90% |13.60% |

3.3 Deviations from Modeling and Testing

Inconsistencies between the model and test numbers can be attributed to a number of things: when testing, it was very difficult to control the system to do all that was wanted, so some of the model inputs had to be changed to more accurately model the system as tested. The road where the test occurred was not completely flat, so for some of the tests the efficiency is better because the small slope of the road is helping the system do the work. The hydrostat displacement was being controlled manually through LABVIEW interface, which was susceptible to human error. All these things compound on each other and make for some deviations between the modeling and testing results.

Appendix H shows graphs of velocity and pressure for both regenerative and assist cycles comparing the test results and model results.

4.0 Design Considerations

4.1 Current System

4.1.1 System Description

The first and most obvious design consideration is the current system. The team could use the current system and make modifications to make the system meet the functional requirements. The system is current described in the above section of 2.1

4.1.2 Brief System Analysis

This system would be simple because it is currently functional on the vehicle. Because of this fact, the system would be fairly inexpensive to support because all of the major components are accounted for. However, the system as is, does not meet the DFMEA standards that were set. Also the system is very bulky, talking up most of the bed space, and is very heavy. As proven with the testing results, the truck is also very inefficient and noisy. With all of these combined it does not meet important functional requirements set forth by the team.

4.2 HLA – Hydraulic Launch Assist

4.2.1 System Description

The next system that would be considered is the Hydraulic Launch Assist that was installed on a donated Lincoln Navigator. This system has been proven to work well and to be efficient through the testing done by Ford and the documentation provided by them. The system is very similar conceptually to the current system in place on the Ford F350. The main difference is that the fluid flows back and forth between the high and low-pressure accumulators, making it more like a closed system. There is still a charge pump to circulate fluid out of the hydrostat case and to recharge the low-pressure accumulator when some of the fluid is lost due to hydrostat case leakage. The system also has a valve block that has the same function as a tandem valve, but uses poppet values to control direction instead. On Figure 5, on the next page, depicts the layout of the HLA.

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Figure 5 - HLA Diagram (source: Ford)

4.2.2 Brief System Analysis

As stated above the HLA system was proved to be efficient on the Navigator. According to Ford’s documentation, through the design the system was able to accelerate the vehicle to 22 miles per hour after stopping from 30 mph. This is plenty efficient for the project. Also, the system is lightweight. However, the major downfall to this system is that when the Navigator was donated, the controls system was removed. After observation of the system, it was shown that the controls system that would be needed would be very elaborate and difficult to implement. It is also assumed that because of the detailed needed for the controls system for the HLA, it would perhaps even be more costly to implement than with other systems.

4.3 SHEP – Stored Hydraulic Energy Propulsion

4.3.1 System Description

The SHEP system is a unitized system that was also donated by Ford. A unitized system has the accumulators, valves, and hydrostat in one large piece of equipment as opposed to the HLA and the current system where these parts are in different places and connected by hoses, lines, and fittings. The picture below, in Figure 6, shows the SHEP system that is currently in possession.

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Figure 6 - Picture of the SHEP system

4.3.2 Brief System Analysis

The biggest advantage to this system is that it is a unitized system, and therefore would be cheaper to implement. Also, the system would behave more like a closed system as well. However, the SHEP system is very large and very heavy. It weighs almost 900 lbs! The one major downfall to this system though, is that there is little known information on it and research would be difficult.

4.4 MuTT – Multiple Transportation Technologies

4.4.1 System Description

The MuTT system is a system designed by this team. As the name implies, the MuTT system is a conceptual design that incorporates ideas sparked from the research done by the team and puts it all into one system. It contains a kidney loop to filter fluid, a “Jake Brake” loop, and a new control system. This system will be explained in detail in the following section 5.0

4.4.2 Brief System Analysis

The main advantage to this system is that it can be designed from the top down by the team. It will contain a kidney loop to filter fluid which will help solve many fluid contamination problems brought up by the DFMEA. Also, it is hoped that a “Jake Brake” functionality could be designed and installed so that the system could be utilized more than just for stopping the vehicle.

Another main advantage is that the system will have a very similar system layout to the HLA. This will improve ease as well as cost of the system. A new control system will be developed with more ease on this system because the team can start over.

4.5 Controls

With every new design there are goals and desires that want to be accomplished. In the controls area, this is no different. There were several goals that needed to be accomplished with a design, but there were also desires to make the project look and function more technologically advanced.

In trying to meet the demands for the project, an alternative to the current set-up of the field point modules made by National Instrument was researched. There were a few different options. One of them was a microcontroller. If the system was to be mass produced, this would be the best pick. Microcontrollers are efficient and small and considerably much cheaper than the field point modules. The current set up is about $2500.00 and a microcontroller could be almost as low as $30.00. Fortunately, the field point was donated to the project by National Instruments, so cost of the field point for this project wasn’t a factor.

Some factors that needed to be considered were the software, space, and power. The software running the field point modules is LABVIEW which is a user friendly GUI programming language that is easy to learn and manipulate. Some design problems with the field point modules include space and power. Unfortunately field points were designed in a way that they take up a lot of space. Space is very important when you are trying to put it into a vehicle. The other issue is power, the field points require about 16 volts to function properly and a known problem with the modules is that if the power ever gets low enough, the internal circuitry is irreversibly damaged. In a standard 12 V vehicle, it is often difficult to supply 16 volts continuously and it is quite common for an alternator to go out or the battery to go bad so that it no longer sustains at least 12 Volts.

Also donated from previous projects was the newer Compact Field point Modules. These modules function almost identically to the older style except they have solved two of the biggest concerns; space and power. They are called compact because they have reduced the size considerably and yet they keep the same functionality. In the new compact field point, the low power problem was also solved so that accidents happen less and instruments are lost or damaged. Unfortunately, a supply of 16 volts is still needed but a boost converter can solve this problem. However, the cost of this new system is similar to the older field point modules so it wouldn’t be very feasible to mass produce this system.

5.0 Chosen Final Design

5.1 Hydraulic System – The MuTT system

The chosen design for this project is the MuTT system. It was chosen using a decision matrix shown in Table 5, below. The matrix scored each design by the objectives set out at the beginning of the semester. As one can see the HLA and MuTT system scored close to the HLA, so therefore the MuTT system will use the HLA parts, one of the major positive design features of the HLA system.

Table 5 – Design Decision Matrix

|Objectives |Weight Factor |Current |HLA |SHEP |MUTT |

|Achievability |2 |1 |9 |8 |5 |

|System Efficiency |3 |8 |3 |3 |5 |

|Cost |4 |3 |9 |7 |5 |

|Reliability |5 |7 |7 |5 |5 |

|Maintainability |6 |4 |4 |7 |3 |

|Smoothness |7 |7 |3 |3 |5 |

|Weight |8 |9 |3 |3 |5 |

|Noise |9 |7 |5 |5 |5 |

|Brake Wear |10 |5 |5 |7 |4 |

|Totals: |55 |6.200 |4.873 |5.109 |4.782 |

|Price |

|Sun. |Mon. |Tues. |Wed. |Thurs. |Fri. |Sat. |

|12 |13 |14 |15 |16 |17 |18 |

|Finals Week |  |  |  |Components Sized |DDR Due |  |

|------> | | | | | | |

|19 |20 |21 |22 |23 |24 |25 |

|Winter Break |  |  |  |  |  |  |

|------> | | | | | | |

|26 |27 |28 |29 |30 |31 |1 |

|Winter Break |  |  |  |  |  |  |

|------> | | | | | | |

|January |

|2 |3 |4 |5 |6 |7 |8 |

|Winter Break |  |  |  |  |  |  |

|------> | | | | | | |

|9 |10 |11 |12 |13 |14 |15 |

|  |  |  |School Starts |  |Solid Model |  |

| | | | | |Complete | |

|16 |17 |18 |19 |20 |21 |22 |

|  |No School |  |  |  |Parts Ordered/ |DESIGN PHASE DONE|

| | | | | |Finalized | |

|23 |24 |25 |26 |27 |28 |29 |

|Fabrication Phase |  |  |  |  |  |  |

|Begins: | | | | | | |

|February |

|30 |31 |1 |2 |3 |4 |5 |

|  |  |  |  |  |  |  |

|6 |7 |8 |9 |10 |11 |12 |

|  |Take Apart the F350|  |  |  |  |  |

|13 |14 |15 |16 |17 |18 |19 |

|  |  |  |  |  |  |  |

|20 |21 |22 |23 |24 |25 |26 |

|  |Components Built |  |  |  |  |  |

|March |

|27 |28 |1 |2 |3 |4 |5 |

|  |Components |  |  |  |  |  |

| |Assembled | | | | | |

|6 |7 |8 |9 |10 |11 |12 |

|FABRICA-TION |System Fully Tuned |Tesing Phase |  |  |  |  |

|COMPLETE | |Begins | | | | |

|13 |14 |15 |16 |17 |18 |19 |

|  |Testing on Jack |  |  |  |  |  |

| |Stands Complete | | | | | |

|20 |21 |22 |23 |24 |25 |26 |

|  |  |  |  |  |  |  |

|27 |28 |29 |30 |31 |1 |2 |

|TESTING COMPLETE |Road Tests Complete|Evaluation Phase |  |  |  |  |

| | |Begins | | | | |

|April |

|3 |4 |5 |6 |7 |8 |9 |

|  |  |  |  |  |  |  |

|10 |11 |12 |13 |14 |15 |16 |

|  |  |  |  |  |  |  |

|17 |18 |19 |20 |21 |22 |23 |

|  |  |  |  |  |  |  |

|24 |25 |26 |27 |28 |29 |30 |

|  |  |  |  |Data Analysis |EXPO!!! |EVALUA-TION |

| | | | |Complete | |COMPLETE |

|May |

|1 |2 |3 |4 |5 |6 |7 |

|Dead Week |  |  |  |  |  |DDR DUE! |

|------> | | | | | | |

|8 |9 |10 |11 |12 |13 |14 |

|Finals Week |  |  |  |  |  |Graduation! |

|------> | | | | | | |

6.2 Projected Issues

There are a few concerns that the team has regarding the project that should be address so that they may be dealt with appropriately. There are five main topics that will be briefly addressed: time management of the team, safety of the vehicle, smooth operation of the system, fabrication of the components and control systems development.

The first is time management. The team has had problems at the beginning of the semester with meeting deadlines and therefore careful consideration was taken into account when the second semester project schedule was developed. The deadlines are solid and should not be taken lightly. The second concern that should be addressed was safety of the vehicle and of the system. This is why the DFMEA was completed and safety was listed as the number one concern and there was a threshold of 250 RPN. (Please refer to Section 3.1)

The third concern was smooth operation of the system. Through the testing of the current system, observations noted that the system could be rough and not desirable form a riding stand point, both in comfort and in noise tolerance. Therefore the team will be concentrating on noise levels as well as trying to keep the system as smooth as possible by using the controls system.

Another concern is component fabrication. Both the mechanical and electrical engineers in the group have little experience using the allotted tools and computers for designing and making the parts that are needed. Much time will be spent learning and feeling comfortable with the processes.

The last concern for the team is the development of the controls system. Because it is mainly a software interface, bugs are inevitable for the designers; however, it is unpredictable if the bugs will be solved with ease or with difficulty. The team will use the problem solving skills that they have developed using other software and coding programs to help keep this concern to a minimum.

7.0 References

1. MSHA, Longwall: Hydraulic System Best Practices, 4/30/2002

2. Insider Secrets to Hydraulics, , 2003

3. Eaton, Boston Transfer Hose Products Master Catalog, Dec. 2003

4. Texas Workers’ Compensation Commission, Hydraulic Hose Fatality, May 12, 1999.

5.

6. hydraulics.

7. R.P. Kepner, Hydraulic Power Assist – a Demonstration of Hydraulic Hybrid Vehicle Regenerative Braking in a Road Vehicle Application, Society of Automotive Engineers, Inc., 2002.

8. S. Skaistis, Noise Control of Hydraulic Machinery, Marcel Dekker, Inc., 1988.

9.

10.

11.

12.

13.

14.

15. J. Roberson, Engineering Fluid Mechanics, 6th edition, John Wiley & Sons, Inc., 1997.

16.

17.

18.

8.0 Appendices

Appendix A. Wiring of Current Controls System

Appendix B. Flow Diagram/Equations of Excel Model

Appendix C. Jack Stand Test Safety Procedures

Appendix D. Road Test Safety Procedures

Appendix E. Detailed Noise Modeling

Appendix F. DMFEA on the Current System

Appendix G. DMFEA on the MuTT System

Appendix H. Excel Graphs of Modeling vs. Testing

Appendix A. – Wiring of Current Control System

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For Better View: See Team’s Website:

Appendix B. Flow Diagram/Equations of Excel Model

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REGEN

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other equations determined:

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ASSIST

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Other Equations to be Determined:

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Appendix C. Jack Stand Test Safety Procedures

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

System observers: set up

1. Set up video camera with real-time viewing if available. Do this before system is running.

2. Be sure rear wheels will be able to turn freely and there is nothing to hinder their movement.

3. Don not stand behind the vehicle when the system is in use, because of the danger of the filler valve breaking and becoming a projectile.

4. Avoid line of sight of the system while in use.

5. Use mirror to observe hydrostat.

6. If system must be observed by an individual wear a face shield

7. I fan observer does not have an active role in testing avoid standing within 15 feet of the system while it is being tested.

8. While system is in use be prepared to tell Controls person to dump the high pressure if something at all goes wrong.

System observers: while testing

1. Make note of anything observed from the system while in use. Including any movement or the parts or sounds. Make note of the mode (regen/assist) and also the system conditions (test pressure, displacement)

2. In case of emergency tell controls person to dump system, and if really bad….Run away.

Controls person: set up

1. Check controls- disconnect pedal input, make sure pressure and displacement can be controlled, check emergency controls.

2. Check data collection capability – pressures, temperatures and shaft rpm

3. Double check emergency controls

4. Set up controls in cab of truck for easy communication for person in Driver seat.

Controls person: testing

1. Set parameters for first run.

2. During cycle be continually watching data feedback in case of emergency.

3. During cycle be able to hear observers in case of emergency.

4. Start data collection.

5. Indicate for driver to start cycle, regen/assist

6. Run necessary amounts of tests.

Drivers seat: set up

1. Never shift from Drive to Park with truck on jackstands unless foot is firmly on brake pedal and wheels are not moving.

2. Always be able to hear controls person while testing. If in doubt shift into neutral and apply brake pedal.

Driver seat: for test cycle

1. Turn on engine.

2. Apply brake pedal

3. Tell Controls person to start regen mode.

4. Shift into drive

5. Apply accelerator to generate necessary torque to charge tanks.

6. Be listening carefully to controls person to know when to proceed to next step

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

8. Shift into neutral

9. Apply brake as needed to keep wheels from spinning out of control.

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

Appendix D. Road Test Safety Procedures

Safety Procedures

For working on the hydraulic system on F350

1. Make sure to have a long section of clear road, before testing is started.

2. Check accumulator precharge pressure to adjust model as necessary.

3. Make sure all necessary data is being collected.

4. Check, double check controls to make sure they are functioning properly.

Procedures for Experimentation

When truck is on Jack Stands

Driver:

REGEN

When ready to start regen cycle:

1. Accelerate to specified speed using diesel engine

2. Verify with Controls person that system is in regen mode.

3. Let foot off of gas pedal, Controls person will vary swash plate angle to start regen cycle.

4. IN CASE OF EMERGENCY do not hesitate to use brakes as necessary.

ASSIST

When ready to start assist cycle:

1. Come to a complete stop, with plenty of clear road ahead.

2. Shift into neutral

3. Verify with Controls person that system is in assist mode.

4. Let foot off of brake, Controls person will vary swash plate angle to start assist cycle.

5. IN CASE OF EMERGENCY do not hesitate to use brakes as necessary.

Controls Person:

REGEN

1. Always be in communication with driver.

2. When desired velocity has been reached, communicate with driver and begin to open swash plate. Start at about 25 to 50% then increase to max in a couple seconds to store as much fluid as possible.

ASSIST

1. When ready to begin assist control swash plate by starting at about 25 to 50% then increase to max in a couple seconds to accelerate as fast as possible.

Appendix E. Detailed Modeling for Noise Reduction

Purpose: Determine the level of noise reduction expected with the MUTT system.

Facts about hydaulic noise in general:

• Noise in hydraulic machines is caused by inadequate isolation of kinetic energy from piston and fluid movement. Among all the components in a hydraulic machine, 95% of noise is due to pumps and motors. ( A hydrostat is a pump and motor in a single component.)

• Parts that move in a variable displacement, in-line hydrostat are the cylinder block, pistons and shaft. The swash plate and the yoke that controls swash plate angle do not rotate. With a forcing function 2X the piston frequency, noise caused by piston movement is relatively low (approximately 2500 Hz at 30 mph on the F350).

• Fluid movement causes high noise when cavitation occurs or when fluid pressure is less than the saturation pressure of the dissolved air. Caused by pressure changes, air entrainment, high fluid velocity, and high temperatures, noise from cavitation is a hissing sound between 4 to 8 kHz.

• Noise transmits through fluid, structure, and air but pumps commonly generate 1000X more noise energy as structureborne or fluidborne. For a variable displacement, in-line hydrostat, forcing functions exist in 3 axis and their relative magnitude depends on the swashplate angle. The strongest structureborne noise is due to the force parallel to the shaft axis. Since all hydraulic components are connected by lines or hoses, structure and fluidborne noise are closely coupled. Airborne noise occurs when components or adjacent structures vibrate. All vehicle components near the pump are potential noise radiators. Long lengths and bends can cause hose to vibrate, because, with increasing pressure, hose expands radially and longitudinally.

• Noise can be reduced by isolating hydraulic components from the vehicle structure. The vibration isolation principle is to design the natural frequency of the mounts to be much lower than the forcing frequency of the load. When the forcing to natural frequency ratio approaches unity, the dynamic factor or transmissibility is infinite which means that the noise transmits through mount isolation material as if it did not exist.

Facts about the F350 system:

• Noise levels were not quantitatively measured during baseline testing but 7 observers did assess the noise qualitatively. Two considerations for this type of noise determination are: (1) sound at 4000 Hz is easiest to hear and (2) total loudness is determined primarily by the one or two of the loudest sounds rather than the sum of several smaller sounds.

• Predominant noise occurred during regenerative braking (regen); the low frequency noise sounded like a compression brake until very low speeds when a clunking noise was loudest. The frequency of the ‘compression brake’ noise was probably due to the hydrostat with a fundamental frequency equal to 2X the cylinder frequency. The noise appeared loudest at lower speeds probably because of the dynamic factor. The clunking noise at very low speeds was proportional to shaft speed (450 rpm at 10 mph) and sounded like driveshaft misalignment which could have been caused by deformation of the mounts. Although noise was more pronounced during regen, shaft torque was higher during assist; 200% higher peak value and 500% higher average value. The higher noise levels during regen were probably caused by cavitation.

• Cavitation was probable during regen, because of low inlet pressures, high fluid velocity, and high fluid temperatures. The system relied on the low pressure accumulator and an engine-driven pump to supply fluid under pressure during regen. The low pressure accumulator contained insufficient fluid under pressure to supply the hydrostat and the engine driven pump could not supply the demand. The low pressure accumulator did not contain fluid because it had a gas precharge pressure of 500 psi while the engine driven pump at 500 psi was attemping to fill it with fluid. Minimum inlet pressure for the hydrostat was 200 psi. The hydrostat had a maximum flow rate of 121 gpm while the engine driven pump was rated for 9 gpm. The small hose diameter from the engine-driven pump caused high fluid velocities and temperatures. With hose diameters of ½” from the engine-driven pump and 1.25” from the accumulator, fluid velocities were 6X higher through the hose from the engine.

• Mounts for the hydrostat consisted of ¼” rubber sandwiched between the hydrostat assembly and the frame. Because each mount was through-bolted, noise was not isolated. The two mounts for the hydrostat were in the vertical and horizontal planes with the horizontal mount cantilevered from the vehicle frame.

• The hydrostat was connected to the transfer case by a solid driveshaft. The transfer case was directly mounted to the frame without any noise isolation.

• The hydrostat and connecting lines were located directly below and within 6” of the pickup metal bed.

• All hydraulic components were connected by flexible hose. The longest length was from the engine-driven pump to the reservoir. Hoses connected to the tandem valve had multiple bends and in multiple planes.

Noise reduction design strategies:

• Give priority to reducing noise that produces the most energy (from the pump) and noise that is most perceptible (from cavitation).

• Mount the hydrostat and transfer case with complete isolation from the structure. For bolted mounts, insert isolation material against bolt heads, shanks, nuts and any structures or flanges. To uncouple the forcing function parallel to the shaft axis, use 45-degree angled mounts parallel to the shaft. Use the design formulas at to select mounts that will minimize the transmissibility of noise to the structure.

• Connect the hydrostat to the transfer case with tension cables. This will increase the mass thereby decreasing the natural frequency. A 50% increase in mass will lower the speed at which the dynamic factor is relevant by 20%.

• To totally eliminate the effects of the dynamic factor, decrease the swash plate angle at low speeds before the onset of objectionable noise.

• Use lines for bends and long lengths; use hoses in between. Support lines with rubber to dampen resonant vibrations and isolate noise from structure.

• Use a low pressure accumulator with volume and pressure that satisfies hydrostat inlet requirements.

• Connect the low pressure accumulator to the hydrostat with line that has the same diameter as the inlet port and with minimum number of restrictions from bends or connectors.

• Use a sound absorber/reflector between the hydrostat and surrounding vehicle components.

• Use a heat exchanger and thermostat to maintain fluid temperature between 110-130F.

NOISE REDUCTION TARGETS:

|STRATEGY |TARGET |

|Engineered mounts |Reduce structureborne pump noise |

|Tension cables |Postpone dynamic factor effects noise |

|Swash plate angle control |Eliminate dynamic factor effects |

|Composite lines and isolation support |Reduce structure and fluidborne noise |

|Redesigned low pressure accumulator |Eliminate cavitation noise |

|Sound absorber/reflector |Reduce airborne noise |

|Heat exchanger |Reduce fluidborne noise |

|TOTAL EXPECTED NOISE REDUCTION: 50% |

Reference: Skaistis, Noise Control of Hydraulic Machinery, Marcel Dekker, Inc., 1988.

Appendix F. DFMEA on the Current System

|Item # |Potential Failure Modes|Potential|Sever-ity |Causes |Occur-ance |

| | |Effect(s)| | | |

| | |of | | | |

| | |Failure | | | |

|1 |Accumulator Tank |500 |Install a pressure read-out on dash/ Fill |9 |3 |3 |81 |

| |Explodes | |valve protecting, end brackets and longitudal | | | | |

| | | |support | | | | |

|2 | |300 |Stain gauge detector | |3 |5 |135 |

|3 |Broken High Pressure |500 |Get rid of the nitrogen end hoses; cover the |8 |3 |10 |240 |

| |Line or Hose | |hoses by the tandem valves; install tunnel | | | | |

| | | |cover | | | | |

|7 | |720 |Build Fluid Cart/ Ports on system and use | |3 |4 |96 |

| | | |gauged filters on the cart | | | | |

|8 | |80 |  | |  |  |  |

|9 |Hydraulic Fluid |800 |Install an air filter in reservoir tank; |8 |4 |4 |128 |

| |Contamination | |install a control mechanism to detect bad | | | | |

| | | |filters, relocate filters | | | | |

|13 | |360 |  | |  |  |  |

|14 | |432 |  | |  |  |  |

Appendix G. DMFEA on MuTT System

|Item # |Potential Failure Modes|Potential|Sever-ity |Causes |Occur-ance |

| | |Effect(s)| | | |

| | |of | | | |

| | |Failure | | | |

|3 |Broken High Pressure |400 |Pressure Testing the Fittings/ Either by |8 |2 |10 |160 |

| |Line or Hose | |ourselves or professionally | | | | |

*Already Implemented in System - Recommended Actions already planned in design

Appendix H. Excel Graphs of Modeling vs. Testing

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Detail Design Report

Check Vehicle Speed

Check Transmission

Check Pressures

Turn off Brake Lights if on.

Read

Throttle

Loop Back to do checks – if any of the checks prove to be unsatisfactory, Set Tandem Valve to center and the controls will go into “stand-by” mode

Set Swash Plate Angle

Set Tandem Valve

Assist Mode

Driver Applies Throttle

Pressure

Loop Back to do checks – if any of the checks prove to be unsatisfactory, Set Tandem Valve to center and the controls will go into “stand-by” mode

Set Swash Plate Angle

Set Tandem Valve

Check Vehicle Speed

Check Transmission

Check Pressures

Turn on Brake Lights

Regenerative Mode

Driver Applies Brakes

Velocity

New Velocity

Deceleration Rate

Torque created by Hydrostat

Pressure across Hydrostat

Gas Pressure in Accumulator

Accumulator Gas Volume

Accumulator Fluid Volume

Flow Rate

Shaft Speed

Accumulator Pressure

Accumulator Gas Volume

Accumulator Fluid Volume

Flow Rate

Shaft Speed

Velocity

Acceleration Rate

Torque by Hydrostat

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