ENGI 8936 – Term 8 Design Memorial University of Newfoundlanddicks/files/deliv/report1.pdf · The hydraulic hybrid design outlined in this report will incorporate a hydraulic system

ENGI 8936 – Term 8 Design

Memorial University of Newfoundland

Dr. Nick Krouglicof

PRELIMINARY DESIGN REPORT 1

Authors

Group 6: Jon Butler – 200325348 Matt Dicks – 200322964

Aimee Walsh – 200366250 Mike Vokey - 200346732

February 2, 2008

Preliminary Design Report 1

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Group 6 Page 2 February 2, 2008

Summary

It is well known that hydraulics can be used in vehicles to provide great amounts of torque and acceleration. This technology is commonly used in buses and trucks to aid in the fuel consumed by of city driving. Today there is a movement to reduce car emissions and to produce more fuel efficient, “green,” vehicles. Various technologies are being developed to improve fuel economy such as electric - internal combustion engine and flywheel hybrids, yet hydraulic technology has not been used to produce a fuel efficient passenger car.

Our goal is to determine the feasibility of using hydraulic technology to produce a fuel efficient passenger vehicle. The hydraulic hybrid design outlined in this report will incorporate a hydraulic system into a standard rear-wheel drive train configuration with the hydraulic system supplementing the gasoline engine during acceleration. In order to restore hydraulic pressure within the system, a hydraulic accumulator will be charged using regenerative braking when stopping and power from the engine when moving at constant speed. Also, a constant velocity transmission and reduced engine size will be incorporated in an attempt to improve efficiency even further.

Many advantages can be harnessed when using hydraulics in addition to outstanding torque and acceleration. First of all, the accumulator connects directly to the driveshaft which eliminates the need to convert mechanical energy from regenerative braking into electrical energy then back to mechanical energy, as is done in the electric – internal combustion hybrid. Hydraulic energy storage reduces energy losses through the transmission and also captures more energy from regenerative braking. Another advantage is that the system is lightweight and has the potential for greater reduction if using a smaller motor. Electric – internal combustion hybrids work on the principal of adding additional heavy batteries to store energy.

Analysis will be performed through the creation of an analytical model in Simulink and also testing from a physical model. A feasibility study will be performed by comparing efficiency, weight, output acceleration/torque, safety etc to other hybrid vehicles.


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Table of Contents SUMMARY...............................................................................................................................................2

1 STRATEGY.......................................................................................................................................4

1.1 OBJECTIVE..................................................................................................................................... 4 1.2 DELIVERABLES ................................................................................................................................ 4

2 HYBRID VEHICLES ..........................................................................................................................5

2.1 ELECTRIC-INTERNAL COMBUSTION ENGINE HYBRID ........................................................................... 5 2.2 HYDRAULIC HYBRID ...................................................................................................................... 10 2.3 FLYWHEEL HYBRID......................................................................................................................... 11

3 METHODOLOGY ..........................................................................................................................12

3.1 HYDRAULIC TECHNOLOGY DESCRIPTION ....................................................................................... 12 3.2 HYDRAULIC TECHNOLOGY ADVANTAGES ...................................................................................... 14 3.3 SIMULINK MODEL ......................................................................................................................... 15 3.4 PHYSICAL MODEL ........................................................................................................................ 15

4 OUTSTANDING RESEARCH..........................................................................................................16

5 CONCLUSION..............................................................................................................................16

6 REFERENCES.................................................................................................................................17

7 APPENDIX A – PROJECT MANAGEMENT PLAN .........................................................................18

Figures

FIGURE 1: DEGREES OF HYBRIDIZATION, REF. [1] ............................................................................................... 5 FIGURE 2: HYDRAULIC HYBRID PARALLEL CONFIGURATION, REF. [6] ................................................................. 10 FIGURE 3: HYDRAULIC HYBRID SERIES CONFIGURATION, REF. [6] ...................................................................... 11 FIGURE 4: ‘FLYBRID’ SYSTEM F1 RACING LAYOUT, REF. [2] ............................................................................... 11 FIGURE 5: DRIVE TRAIN OF BASIC MOTORIZED VEHICLE .................................................................................... 13 FIGURE 6: BASIC DESIGN SCHEMATIC .............................................................................................................. 14

Tables

TABLE 1: SERIES DRIVE TRAIN, REF. [1] ......................................................................................................... 7 TABLE 2: PARALLEL DRIVE TRAIN, REF. [1]..................................................................................................... 8 TABLE 3: SERIES-PARALLEL DRIVE TRAIN, REF. [1] ........................................................................................ 9 TABLE 4: SUZUKI G10 SPECIFICATIONS ........................................................................................................ 12 TABLE 5: SUZUKI G10 OUTPUT ..................................................................................................................... 13


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1 Strategy

1.1 Objective The objective of this project is to assess the feasibility of a hydraulic hybrid as a passenger vehicle.

System feasibility will be based on: � Performing a background study of available hydraulic systems � Modelling/adapting/optimizing a hydraulic system for use in a passenger vehicle � Comparing our design results with the effectiveness of the other hybrid systems � Designing/building/testing a physical model to assess efficiency

The feasibility assessment will be based on achievable efficiency improvements, if any, to a standard combustion vehicle being outfitted with a functional hydraulic hybrid design. The goal of this analysis is to develop a comprehensive analytical model of a hydraulic system being used with a reduced size combustion engine. With the use of a hydraulic accumulator system that is slowly pressurized by the engine and regenerative braking, the hydraulic motors can be engaged to accelerate from the stopped position and be used in conjunction with the engine for acceleration at higher speeds.

The intention of this design is to engage the more efficient hydraulic system when the combustion engine is outside of its peak efficiency RPM range, as well as, allowing for a smaller, more efficient engine without sacrificing performance.

1.2 Deliverables Project deliverables include the following:

� Technical Reports (x3) � Presentations (x3) � Project Website � Analytical Simulink Model � Physical Model


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2 Hybrid Vehicles

2.1 Electric-Internal Combustion Engine Hybrid

2.1.1 Degrees of Hybridization

According to HybridCenter.org, Ref. [1], not all Hybrid vehicles are created equal. The site uses a five step scale in which the addition of a new feature determines the degree of hybridization of the vehicle. It is important to note that ascending the scale of hybridization does not necessarily imply that the car is better in the greater scheme of vehicle performance; the system merely helps to categorize the different vehicle types.

Figure 1: Degrees of Hybridization, Ref. [1]

2.1.2 Mild Hybrid

As the name suggests, the “Mild Hybrid” is only a small modification of the conventional vehicle, oftentimes only improving the fuel economy by 10-20%. As can be seen in the above figure, the conventional vehicle has been improved by the addition of an electric motor which works in series, parallel or a combination of to supplement the power of the gas engine. Secondly, a regenerative braking system has been added to transform the kinetic energy which is typically lost during braking into power which recharges the battery. The power flow diagrams for series/parallel/combination systems, including regenerative braking systems, will be covered in the next section of the report.

The term “Mild Hybrid” is not a standardized industry term and is used more as a marketing term than a technical one. Although sometimes not recognized as an actual hybrid vehicle, the pairing of the gasoline and electric power sources create “low end torque”, in other words, better acceleration at low speeds.


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2.1.3 Full Hybrid

Otherwise known as the “Strong Hybrid”, experts and many consumers consider full hybrid vehicles have the base requirements in order to fit the hybrid classification. In other words, without the ability to drive a certain distance without ever employing power from the gasoline engine, a vehicle is not a true hybrid. The ability to do so has been developed through the addition of a large, high-capacity battery pack which is able to be recharged through coupling with power from the gas engine, as well as, the regenerative braking system.

Full Hybrid systems tend to rely on the Series-Parallel drive train which, although complex, offers substantial inter-conversion of power, mechanical and electrical, in order to obtain peak output from both power sources.

2.1.4 Plug-In Hybrid

A Plug-In Hybrid Electric Vehicle (PHEV) differs from the Full Hybrid in that it can be plugged into a clean energy source in order to charge the battery. The battery can then be used to drive the vehicle without supplementary power from the gasoline engine. Typical Plug-In Hybrid vehicles can run for approximately 10-20 miles without recharging the battery. Although this may seem like the more environmentally friendly option, since the battery is recharged through an available energy grid, the source of the energy determines how “green” the vehicle is; natural gas, coal, etcetera. PHEVs use either a Series or Parallel drive train.


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2.1.5 Hybrid Vehicle Drive Trains

The possible types of Electric – Internal Combustion Engine (E-ICE) hybrid drive trains are outlined in the following tables:

Table 1: Series Drive Train, Ref. [1]

Off • No power flow

Slow • Operates as fully electric car • Power drawn from battery alone

Accelerate

• Gas engine powers generator • Generator helps battery power the vehicle

Coast • Gas engine powers generator • Generator powers electric motor • Electric motor powers the vehicle and recharges the

battery (if necessary)

Brake • Kinetic energy created by braking is converted by the

motor • Motor charges the battery

• Eliminates the need for a complicated multi-speed transmission and clutch. Because series drive trains

• Performs best in stop-and-go driving • Used for buses and other urban work vehicles


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Table 2: Parallel Drive Train, Ref. [1]


Start (initial start or from idle) • No dedicated starting motor • Motor/Generator turns over gas engine using battery

power

Accelerate • Gas engine drives the wheels • Motor/Generator draws battery power when

necessary

Coast • Wheels driven by gas engine • Motor/Generator can draw extra power from the gas

engine to charge battery

Brake • Kinetic energy created by braking is converted by

the motor/generator • Motor/Generator charges the battery

• Eliminates the inefficiency of converting mechanical power to electricity and back o efficient on the highway o reduces city driving efficiency

� inefficient in stop-and-go driving


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Table 3: Series-Parallel Drive Train, Ref. [1]


Slow • Battery drives the electric motor which in turn drives

the wheels • Vehicle functions as though fully electric

Accelerate • Battery power drives the electric motor which powers

the wheels • Power Splitter routes gas engine power through the

generator to help battery

Coast • Gas engine powers the generator • Generator powers the electric motor and also powers

the battery (if necessary)

Brake • Kinetic energy created by braking is converted by the

electric motor • Electric Motor charges the battery

• At lower speeds it operates more as a series vehicle o Better city driving efficiency

• At high speeds, where the series drive train is less efficient, the engine takes over and energy loss is minimized.

• Incurs higher costs than a pure parallel hybrid since it needs a generator, a larger battery pack, and more computing power to control the dual system.

• Performs better than either of the systems alone


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2.2 Hydraulic Hybrid The Hydraulic Hybrid uses many of the same techniques as the E-ICE hybrid, however, the internal components which drive the system are entirely different. All Hydraulic Hybrids use a low-pressure reservoir, which holds the hydraulic fluid, a pump which moves the fluid throughout the system and an accumulator which contains pressure which is created by pumping fluid into it. An accumulator is a pressure storage tank in which a non-compressible hydraulic fluid is held under pressure by an external source, in the case of the vehicle, Nitrogen gas. The accumulator serves as the battery for the system, releasing pressure which in turn powers the driveshaft.

Unlike the E-ICE hybrid, the hydraulic hybrid does not require an electric motor in order to drive the wheels. By reducing the number of components under the hood we can significantly reduce the power lost while traversing the system. Like the E-ICE hybrid, however, the hydraulic hybrid uses regenerative braking in order to power the pump. As the vehicle slows down, the pump is activated and moves the hydraulic fluid from the reservoir back into the accumulator. As the vehicle accelerates, the pump moves the fluid back to the reservoir. With the fluid back in the reservoir, the cycle may repeat again. There are two possible layouts for the components required in a hydraulic hybrid. The two possibilities are a parallel hydraulic hybrid and a series hydraulic hybrid.

The parallel hydraulic hybrid simply connects the hybrid components to a conventional transmission and driveshaft. Although the accumulator is able to supplement the power supplied by the gasoline engine during acceleration, the engine is not able to idle-off like the conventional vehicle and all forms of the E-ICE hybrid; the Hydraulic Hybrid is always burning gas. Parallel systems boast a 40% increase in fuel economy according to the EPA and are able to be added to regular vehicles. Currently these systems exist only in heavy-duty vehicles like buses and delivery trucks.

Figure 2: Hydraulic Hybrid Parallel Configuration, Ref. [6]

In a similar layout to the Parallel system, the Series hydraulic hybrid skips the transmission and driveshaft and delivers the power almost directly to the wheels. The removal of these components not only improves vehicle efficiency but also allows the


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vehicle to idle-off like the E-ICE hybrid and conventional vehicle. The vehicle's gasoline engine can be shut off, resulting in even more fuel savings. Series hydraulic hybrids are estimated to improve fuel economy by 60 to 70 percent, and lessen emissions by as much.

Figure 3: Hydraulic Hybrid Series Configuration, Ref. [6]

2.3 Flywheel Hybrid Using Flywheels as a way to store and recover energy is an idea which has been implemented on several heavy-duty vehicle types such as buses and trams, however, the use of such a system in a smaller vehicle was considered dangerous due to gyroscopic forces inherent in the system. A company called Flybrid Systems have patented a system which they say overcomes the traditional problems of implementing the Flywheel Hybrid technology in small passenger vehicles. They have described their system thusly, Ref. [2], “The flywheel is connected to the transmission of the vehicle via a Continuously Variable Transmission (CVT) and manipulation of the CVT ratio achieves control of energy storage and recovery. When the ratio is changed so as to speed up the flywheel energy is stored and when the ratio is changed so as to slow down the flywheel energy is recovered.”

Figure 4: ‘Flybrid’ System F1 Racing Layout, Ref. [2]

Flybrid Systems acknowledge that this is not necessarily a novel idea, however, their implementation of it may be. With a super efficient regenerative braking system, recovering 70% of energy used, the system is certainly a viable option for automobile manufacturers. Flybrid Systems goes on to list the advantages of the Flywheel Hybrid, “The key advantage of flywheel hybrids is the power that can be transmitted between the flywheel and the vehicle wheels. The power transmission is only limited by the capability


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of the CVT and this capability is very impressive. Of course power is important in a racing car but in fact it is also very important in a road car. Even a mundane road car is capable of very high power transfer during braking and the key to hybrid system effectiveness is capturing as much of this normally wasted energy as possible.”

3 Methodology

3.1 Hydraulic Technology Description

3.1.1 General

The hybrid design outlined in this report will incorporate a hydraulic system, as discussed in Section 2.2, into a standard rear-wheel drive train configuration. The hydraulic system will be used to assist the engine during acceleration. In order to restore hydraulic pressure within the system, a hydraulic accumulator will be charged using regenerative braking when stopping and power from the engine when moving at constant speed.

3.1.2 Engine Selection

In order to reduce costs and gasoline emissions, the hydraulic hybrid system design is being combined with a small engine size. The design process discussed in this report will determine if the modified drive train will perform optimally with enhanced acceleration capabilities. It is also essential to analyse whether or not reducing engine size will affect the vehicle’s ability to reach and maintain the high speeds necessary to drive on the highway for extended periods of time.

Both issues need to be analysed in detail to verify the feasibility of the hybrid design. The proposed engine to be modelled using Simulink software is the Suzuki G10 1.0 L, inline-3. To augment the Simulink model, further testing will be conducted using a scale model with electric motor drive to determine proof of concept and system efficiency.

Table 4: Suzuki G10 Specifications

Description

Size 1.0 liter (993cc), inline 3-cylinder Piston/Cylinder 74 mm bore, 77 mm stroke

Compression Ratio 9.5:1 Material Aluminum alloy (for the block, cylinder head and pistons)

Weight 139 lbs.


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Table 5: Suzuki G10 Output

Carburated Model Fuel Injected Model

Power 48 hp (36 kW) at 5100 RPM 55 hp (41 kW) at 5700 rpm

Torque 57 ft·lbf (77 N·m) at 3200 rpm 58 ft·lbf (79 N·m) at 3300 rpm

3.1.3 The Drive Train

The basic operation of a motorized vehicle is controlled through the drive train, which consists of the engine, transmission, driveshaft, differential, and the wheel axle.

Figure 5: Drive Train of Basic Motorized Vehicle

The drive train in a vehicle can have two main configurations: two-wheel drive or four-wheel drive. For the two-wheel drive configuration, a vehicle can be powered by either front-wheel drive or rear-wheel drive. This design report will focus on rear-wheel driven cars only and will not include design considerations for any other drive train arrangement.

3.1.4 Hydraulic Hybrid Operation

The main purpose of the hydraulic hybrid design is to benefit from the high power conversion potential by using hydraulic mechanical advantage. With the use of a hydraulic system, as outlined in Section 2.2, it is possible for a vehicle to accelerate quickly without needing extra power from the engine. The proposed design will reduce engine size and maximize acceleration capabilities, therefore optimizing fuel consumption and reducing material weight and cost.

A Simulink and physical model will be designed based on the simple schematic shown in Figure 6.


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Figure 6: Basic Design Schematic

3.1.5 Design Model Description

The main components of the hydraulic system, shown in Figure 6, consist of:

• Variable Displacement Hydraulic Pump / Motor

• High Pressure Accumulator

• Regenerative Braking System

• Low Pressure Storage Tank

The variable displacement hydraulic pump/motor is the driving force of the entire system.

1) During braking and deceleration, it acts as a pump and charges the high pressure accumulator using the hydraulic fluid stored in the low pressure tank.

2) During acceleration, it is powered by high pressure fluid being forced from the high pressure accumulator through the pump/motor and assists the engine by adding additional torque to the drive shaft.

3) Finally, at high, constant speeds, the engine powers the pump/motor to act as a pump, slowly charging the high pressure accumulator. The accumulator is then prepared to power the pump/motor as a motor whenever the vehicle needs to accelerate to assist the engine. For example, if there is a need to pass another cars or if there is an incline in the road.

This system will optimize the efficiency of the drive train and reduce fuel emissions and brake pad-wear, especially in urban areas during stop and go traffic.

3.2 Hydraulic Technology Advantages Hydraulic systems have many potential advantages over existing hybrid technologies. They are known for their outstanding acceleration and torque capabilities, but have other fuel saving attributes that we want to investigate in the context of a passenger vehicle.


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First, the system is lightweight in comparison to the heavy additional batteries that are needed in the E-ICE system. Also, additional weight can be reduced by coupling the hydraulics with a smaller motor.

Second, having a system that is solely mechanical reduces transmission losses that occur through the conversion of energy. In the E-ICE system mechanical energy is produced from regenerative braking which is then used to charge the batteries. The energy is then converted from electrical to mechanical from the electric motor. In a hydraulic system, there is no need to convert the energy as it is stored as potential in the accumulator and sent directly to the driveshaft. Through this process more energy can be captured from the regenerative braking; modern systems have regained up to 70% of the input energy, Ref. [6]. Having a simple mechanical system also translates into easy maintenance and repair. Also, brakes are predicted to last longer with the use of regenerative breaking.

Hydraulic hybrids are environmentally friendly by increasing fuel economy by as much as 40% to 70% in parallel and series systems respectively, Ref. [6]. Also, the hydraulic fluid is clean and easy to dispose of compared to some of the toxic batteries used in E-ICE system.

Hydraulic systems also have some downfalls, as with any technology. The parallel system cannot have the motor turned off when using the hydraulic energy and is burning gas all the time. The series system does have the capability of turning off the motor but another issue arises concerning power for the cabin electronics which run off the battery. With the motor turned off the battery is not being recharged. This is only of concern if the motor is turned off for an extended period of time. Another issue that needs to be considered is limited space for the accumulator(s). To accelerate a car from stop to maximum speed, it requires a large accumulator.

3.3 Simulink Model Simulink is an environment for multidomain simulation and Model-Based Design for dynamic and embedded systems. It provides an interactive graphical environment and a customizable set of block libraries that let you design, simulate, implement, and test a variety of time-varying systems, including communications, controls, signal processing, video processing, and image processing.

Using the in-program block variables, we will model the governing equations for a series hydraulic system with regenerative braking. Using various results we will determine its feasibility in a passenger car.

3.4 Physical Model A physical model will be constructed from off the shelf parts found locally. We are using the model as a proof of concept and no optimization will be performed. Different flywheels will be used to model different vehicle weights and results will be used to determine the output torque and efficiency.


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4 Outstanding Research To successfully study the feasibility of the Hydraulic Hybrid as a passenger vehicle, we need to research some additional topics. All of these topics will be covered as we progress into the detailed design and modeling stages of this project. Before we can proceed with detailed design and the creation of an analytical model, we need to further research our system and determine the required sizes and details of the following components: vehicle, accumulator, motor and constant velocity transmission (CVT).

As a starting point we must choose a specific vehicle for which to base our calculations. Values such as curb weight, drag coefficient and rolling resistance are required in order to determine the amount of energy needed to reach and maintain maximum desired speed. The amount of energy needed to reach maximum speed will directly influence the type and size of accumulator required in our system. Consideration must be given to accumulator weight, pressure capacity and size. In addition to this research, a risk assessment will need to be performed on the use of accumulators in passenger vehicles. Motor size is determined by the energy needed to maintain maximum speed. Details about vehicle drag force, rolling resistance and passenger weight are needed to optimize our system by minimizing motor size.

Finally, to increase fuel efficiency, a Continuously Variable Transmission (CVT) will be used in our system. Additional research is required to choose an appropriate CVT that is efficient and to determine its gear ratio spread.

5 Conclusion The main purpose of this analysis is to determine the feasibility of using hydraulic technology to create a hybrid passenger vehicle. This vehicle should be able to operate like a normal passenger vehicle, using the accelerator/brake and be able to accelerate to maximum speed with four passengers on board.

Feasibility will be determined by comparing results taken from our analytical and physical models and comparing it against known outputs from existing hybrid vehicles. We will compare efficiency, total weight, fuel economy, predicted cost, complexity, output power/torque and safety.


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6 References

Ref. [1] Hybrid Center: http://www.hybridcenter.org/hybrid-center-how-hybrid-cars-work-under-the-hood.html

Ref. [2] Flybrid Systems: http://www.flybridsystems.com/Technology.html

Ref. [3] http://pr.caltech.edu/periodicals/EandS/articles/LXVII3/wouk.html

Ref. [4] http://www.businessweek.com/technology/content/sep2005/tc20050920_8040_tc_217.htm

Ref. [5] http://www.youmotorcar.com/?q=language:en,section:pages,mname:rmenu,pname:003-gasoline-vs-steam-and-electricity

Ref. [6] http://auto.howstuffworks.com/hydraulic-hybrid1.htm

Ref. [7] http://www.wikipedia.org

Ref. [8] http://auto.howstuffworks.com/fuel-cell.htm

Ref. [9] http://www1.eere.energy.gov/hydrogenandfuelcells/tech_validation/pdfs/fcm08r0.pdf


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7 Appendices


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APPENDIX A – Project Management Plan


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APPENDIX B – Gantt Chart

Documents

ENGI 8936 – Term 8 Design Memorial University of Newfoundlanddicks/files/deliv/report1.pdf · The hydraulic hybrid design outlined in this report will incorporate a hydraulic system