A Continuously Variable Power-Split Transmission in A

Published on July 2016 | Categories: Documents | Downloads: 68 | Comments: 0 | Views: 428
of x
Download PDF   Embed   Report

Comments

Content

A Continuously Variable Power-Split Transmission in a Hybrid-Electric Sport Utility Vehicle

Miguel M. Gomez

Thesis submitted to the College of Engineering and Mineral Resources at West Virginia University in partial fulfillment of the requirements for the degree of

Master of Science in Mechanical Engineering

Victor H. Mucino, Ph.D., Chair James Smith, Ph.D. Nigel Clark, Ph.D.

Department of Mechanical and Aerospace Engineering

Morgantown, West Virginia 2003

Keywords: CVT, Power Split, Transmission, Hybrid, SUV Copyright 2003 Miguel M. Gomez

ABSTRACT A Continuously Variable Power-Split Transmission in a Hybrid-Electric Sport Utility Vehicle Miguel M. Gomez
Continuously variable transmissions (CVTs) have an infinitely variable ratio, which allows the engine to operate more time in the optimum range given an appropriate control of the engine valve throttle opening (VTO) and transmission ratio. In contrast, traditional automatic and manual transmissions have several fixed transmission ratios forcing the engine to operate outside the optimum range. Usually CVTs are used in small vehicles due to power limitations of the variable elements. Continuously variable power split transmissions (CVPST) were developed in order to reduce the fraction of power passing through the variable elements. This configuration includes a planetary gear train (PGT), which allows the power to be split and therefore increase the power envelope of the system. The PGT also provides a branch that can be used in a hybrid electric vehicle (HEV) operation through an electric motor. HEVs are receiving special attention nowadays because they require a smaller internal combustion (IC) engine than they do in normal vehicles and consequently represent savings in fuel. HEVs generally employ conventional automotive transmissions. In this thesis a conceptual design for a CVPST for a HEV is presented, with increased power envelope in the system for a sport utility vehicle (SUV) application. A LabVIEW® program has been developed, which according to the vehicle characteristics, driving resistance coefficients and power source data, provides engine-vehicle velocity relationships, CVT ratio, variable pulley radii, belt force and power trace following the ideal fuel consumption curve. This thesis aims at extending CVT applications in the automotive industry to bigger vehicles (and engines) such as pickup trucks and perhaps small buses.

ACKNOWLEDGMENTS
First of all I would like to thank God for giving me the capability to finish my thesis work. I would like to extend my deepest gratitude to my research advisor and committee chairman, Dr. Victor H. Mucino for his continuous guidance, encouragement, support and patience through all this work. I would also like to express my appreciation to my thesis committee members, Dr. James Smith and Dr. Nigel Clark for their helpful comments and suggestions regarding my work. I would also like to express a special thank you to the Mexican National Council of Science and Technology (CONACYT) for their financial support, without which, this work would not have been possible. Thank you very much to all the people at the Council of Science and Technology in the State of Queretaro (CONCYTEQ) for your help and support during the pre-process of my studies, especially to Dr. Alejandro Lozano Guzman and Mr. Juan Sanchez Ramirez. I would like to show my gratitude to Dr. Jacky Prucz for his support and help through my last year of my studies. I also would like to thank my parents and all my family members who were a great source of inspiration to me. Last but not the least I would like to thank all my friends at West Virginia University who helped me in my work, especially to Rohit Paramatmuni.

iii

TABLE OF CONTENTS
Abstract……………………………………………………………………………………ii Acknowledgments………………………………………………………………………..iii Table of contents……………………………………………………….…………………iv Keyword list………………………………………………..……………………………..vi Nomenclature…………………………………………………………………………….vii List of figures…………………………………………………………………….………..x List of tables……………………………………………………….………………..…..xiii Chapter 1 Introduction………………………………………………………………1

1.1 Overview… … … … … … … … … … … … … … … … … … … … … … … … … … ...1 1.2 Objective… … … … … … … … … … … … … … … … … … … … … … … … … … ...5 Chapter 2 Relevant literature review … … … … … … … … ...… … … … … … … … … .6

2.1 Continuously variable transmissions… … ..… … … … … … .… … … … … … … .6 2.1.1 Types of CVT… … … … … … … … … … … … … … … … … … … … ..7

2.2 Hybrid-electric vehicles… … … … … … … … … … … … ..… … … … … … … … 12 2.3 Power-split technology… … … … … … … … … … … … ..… … … … … … … … .18 2.4 Power-split hybrid electric vehicles… … … … … … … ...… … … … … … … … .20 2.5 Continuously variable transmission controller… … … … … ..… .… … … … … 24 Chapter 3 PS-CVT concepts and kinematic models… … … … ..… … … … … … … .26

3.1 CVTs and power-split concepts… … … ..… … … … … … … … … … … … … … .26 3.2 Power flow configurations… … … … ..… … … … … … … … … … … … … … … 31 Power-split case… … .… … … … … … … … … … … … … … … … … … … … … .31 Power recirculation case I… … .… … … … … … … … … … … … .… … … … … .32 Power recirculation case II… … … … … ..… … … … … … … … … … … … .… ...34 iv

Chapter 4

Hybrid-electric power-split CVT conceptual design… … ...… … … … .36

4.1 Design proposed… … … … … … … … … … … … … … … … … … … … … … … ...36 4.2 Operational modes… … … … … … … … … … … … … … … … … … … … … … ...41 4.3 Velocity relationship equations… … … … … … … … … … … … … … … … … … 49 4.4 Force equations… … .… … … … … … … … … … … … … … … … … … … … … ...51 Chapter 5 Example conceptual design… … … … ..… … … … … … … … … … … … ...54

5.1 Vehicle considerations… .… … … … … … … … … … … … … … … … … … … … 54 5.1 LabVIEW® plots… … … … … … … ..… … … … … … … … .… … … … … … … ..60 Chapter 6 Control simulation… … .… … … … … … … … … … … … … … … … … … ..71

6.1 Control method proposed… … … … … … … … … .… … … … … … … … … … … 71 6.2 Controllers needed in the design… … … … … … … … … … … … … … … … … ..73 6.3 LabVIEW® simulation… … … … … … … .… ..… … … … .… … … … … … … … 76 Chapter 7 Simulation tests and results… … ..… … … … … … … … … … … … … … ..83

7.1 Case I: Low speed… … … … … … … … … … … … … … … … … … … … … … … 83 7.2 Case II: Medium speed… … … … … … … … … … … … … … … … … … … … … 86 7.3 Case III: High speed… … … … … … … … … … … … … … … … … … … … … … .89 Chapter 8 Final Comments… … … … … … … … … … … … … … … … … … … … … ...92

8.1 Conclusions… … … … … … … … … … … … … … … … … … … … … … … … … ..92 8.2 Future work… … … … … .… … … … … … … … … … … … … … … … … … … … .94 Appendix: LabVIEW® diagram codes… … … ..… … … … .… … … … … … … … … … … ...96 References… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … 102 Vita… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … ...107

v

KEYWORD LIST
Acronyms: ACS = Advanced Control System CVT = Continuously Variable Transmission CVPST = Continuously Variable Power-Split Transmission GM = General Motors HEV = Hybrid-Electric Vehicle HMMWV = Hybrid Electric Powered High Mobility Multipurpose Wheeled Vehicle HP = Horse-Power IC = Internal Combustion MTU = Michigan Technological University MVB = Metal pushing V-belt OEM = Original Equipment Manufacture PC = Personal Computer PGT = Power Gear Train PNGV = Partnership for a New Generation of Vehicles SAE = Society of Automotive Engineers SUV = Sport Utility Vehicle VTO = Valve Throttle Opening WVU = West Virginia University ZF = Zahnradfabrik Friedrichshafen AG

vi

NOMENCLATURE
a = CVT input pulley a x = Acceleration in the forward direction A = Frontal area of the vehicle b = CVT belt c = Output pulley CVT C = Center distance between CVT pulleys CD = Drag coefficient d = Countershaft gear DA = Air resistance e = Idler gear f = Control gear fr = Tire and ground factor effect Fx = Tractive force on the ground Fb = CVT belt force Fctr/i = Fcs/i = Force from the idle gear to the control (or countershaft) gear Fs/p = Force from the planet gear to the sun gear Fp = Force on the planet gear Fr/p = Force from the planet gear to the ring gear g = gravitational acceleration

ιcvt = CVT ratio
Id = Rotational inertia of the drive shaft

I e = Engine rotational inertia

vii

I t = Rotational inertia of the transmission I w = Rotational inertial of the wheels and axles shafts L = Length of the CVT belt M = Mass of the vehicle Mr = Equivalent mass of the rotating components
N f = Numerical ratio of the final drive N tf = Combined ratio of transmission and final drive

Nr = Ring gear number of teeth Np = Planet gear number of teeth p = Planet gear
r = Radius of the vehicle wheel

rg = Ring gear ro = Countershaft gear radius rp = Planet gear radius rs = Sun gear radius rri = Ring gear radius rro = Control gear radius
rps = Driving variable pulley radius rpo = Driven variable pulley radius

P = Engine horsepower capacity Rx = Rolling resistance Rxf = Frontal tires rolling resistance Rxr = Rear tires rolling resistance viii

s = Sun gear Te = Engine torque at a given speed (from dynamometer data) Tin = IC engine input torque Tem = Electric motor input torque Tout = Total output torque V = Vehicle velocity W = Weight of the vehicle

ρ = Air density
η tf = Combined efficiency of transmission and final drive

ωin = ωa = Input angular velocity ωc = Input pulley angular velocity ωd = ωcs = Countershaft gear angular velocity ωf = Control gear angular velocity ωout = ωp = Planet gear angular velocity ωr = Ring gear angular velocity

γc = Ratio between the driven variable pulley and the driving variable pulley radii γg = Ratio between the sun gear and the ring gear radii γgc = Ratio between the counter-shaft gear and the control gear radii
φ = Angle between the x-axes and the line formed between the driving pulley center and
belt initial contact point θ = Road slope angle (in radians)
Γ(φ ) = CVT pulley radii function in terms of the φ angle

ix

LIST OF FIGURES
Figure 2.1 Figure 2.2 Figure 2.3 Figure 2.4 Figure 2.5 Figure 2.6 Figure 2.7 Figure 2.7 Figure 2.8 Figure 2.9 Figure 2.10 Figure 2.11 Figure 2.12 Figure 3.1 Toroidal CVT… … … … … … … … … … … … … … … … … ...… … … … … … 9 Metal push belt CVT… … … … … … .… … … … … … … … … … … … … … ...9 Variable diameter belt CVT… … … … ..… … … … … … … … … … … … … .10 Example of a commercial flat-belt CVT… ..… … … … … … … … … … … ..11 Electric car diagram… … … … … … … … … … … … … … … … … … … … ...14 Parallel hybrid diagram block… … … … … … … … … … … … … … … … … 14 Series hybrid diagram block… … … … … … … … … … … … … … … … … ..15 Series hybrid diagram block… … … … … … … … … … … … … … … … … ..16 Power-split mode… … … … … … … … … … … … … … .… … … … … … … ..20 Differential transmission and CVT system for motorcycles… … … … … ..22 Transmission configuration diagram proposed by John Anderson… … … 23 CVT belt type… … … … … … … … … … … … … … … .… … … … … … … … 25 CVT control schematic… … … … … .… … … … … … … … … … … … … … .25 Improved fuel economy plot; showing torque vs. engine speed of a 100kW IC engine with CVT ideal line… … … … … … … … … ..… … … … 27 Figure 3.2 Improved vehicle performance plot; tractive effort vs. vehicle speed for a CVT and a five-speed manual gearbox… … … … … … … .… … … … 27 Figure 3.3 Figure 3.4 Figure 3.5 Figure 3.6 Figure 3.7 Figure 3.8 Power-split diagram… … … … … ..… … … … … … … … … … … … … … … .28 Continuously variable power-split transmission… … … ...… … … … … … .29 Pulley system diagram… .… … … … … … … … … … … … … … … … … … ..30 Force analysis diagram for the power split mode… … ...… … … … … … ...31 Force analysis diagram for the power recirculation case-I… … .… ...… … 33 Force analysis diagram for the power recirculation case-II… .… … ..… … 34 x

Figure 4.1 Figure 4.2 Figure 4.3 Figure 4.4 Figure 4.5 Figure 4.6 Figure 4.7 Figure 4.8 Figure 4.9 Figure 4.10 Figure 4.11 Figure 5.1 Figure 5.2

Hybrid-electric CVPST diagram… … … ..… … … … … … … … … … … … ..36 Force analysis diagram for the proposed hybrid-electric CVPST… .… … 38 Power analysis diagram… … … … … … … … … … … … … … … … … … … .39 Electric mode… … … … … … … … … … … … … … … … … … … … … … … .43 Reverse mode… … … … … … … … … … … … … … … … .… … … … … … … 43 Engine start (P-split) / Battery recharge mode… … … ..… … … … … … … .44 Engine power-split mode… … … .… … … … … … … … … … … … … … … ..45 Hybrid-electric/ Maximum power mode… … … … … .… … … … … … … ..46 Idle-neutral (Case I) / Recharge battery mode… ..… … … … … … … … … .48 Idle-neutral mode (Case II)… .… … … … … … … … … … … … … … … … ...48 CVPST sketch with radii, gears and pulleys notation… … … … … … ...… .49 Loads acting on a vehicle… … … … … … … … … … … … … … … … … … ...54 (a) The LX5 DOHC V6 by General Motors; (b) Power and torque plot for this engine… … … … … … … … … … … … ..58

Figure 5.3 Figure 5.4 Figure 5.5 Figure 5.6 Figure 5.7 Figure 5.8 Figure 5.9 Figure 5.10 Figure 5.11

The Unique Mobility SR286… … … … … … … … … … … … … … … … … ..59 Engine speed vs. vehicle velocity plot… … … … … … … … … … … … … ...61 Variable pulley radii (CVT) vs. angle φ … … … … … ...… … … … … ...… .62 Angle φ for high and low speeds used for several plots… … … … … … ...62 CVT ratio vs. φ angle… … … … … … … … … .… … … … … … … … … … ...63 (a) Belt force vs. CVT ratio; (b) Belt force vs. φ angle...… … … … … … .64 Driving resistance curves – Torque vs. rpm’s… ..… … … … … … … … … .65 (a) Torque vs. CVT ratio; (b) Torque vs. angle φ … … ..… … … … ...… … 66 (a) Power vs. CVT ratio; (b) Torque vs. angle φ … … … … … ..… … … … 68

xi

Figure 5.12 Figure 6.1 Figure 6.2

Acceleration vs. vehicle velocity… … … … ...… … … … … … … … … … … 69 Basic block diagram… … ..… … … … … … … … … … … … … … … … … … .72 Control computer system configuration for the hybrid Toyota Prius (a)Starting and traveling at low speed; (b) Full acceleration… … … … … .73

Figure 6.3 Figure 6.4 Figure 6.5

Controller diagram proposed… … … … … … … … … … … … … … … … … .75 Specific-fuel consumption map for a V-8 engine 300 in3… … … … … … ..77 VTO vs. rpm’s ideal curve (line with dots) compared with parabolic equation developed (black line)… … … … … … … … … … … … .78

Figure 6.6

LabVIEW® environment for the hybrid-electric CVPST simulator for the SUV… … … … … … … … … … … … … … … … … … … … 82

Figure 7.1 Figure 7.2 Figure 7.3 Figure A.1

Hybrid-electric CVPST LabVIEW® simulation for case I… … .… ..… … 85 Hybrid-electric CVPST LabVIEW® simulation for case II… … … ....… ..88 Hybrid-electric CVPST LabVIEW® simulation for case III… … … .… ...90 LabV IEW® diagram code for the engine speed vs. vehicle velocity plot… … … ..… … … … … … … … … … … … … … … … … .97

Figure A.2 Figure A.3

LabVIEW® diagram code for the driving resistance curves… … … … … .98 LabVIEW® diagram code for the pulley radii, CVT ratio, belt force, torque and power plots… … … … … … … … … … … … … … … ..99

Figure A.4

LabVIEW® diagram code for the acceleration vs. vehicle velocity plot… … … … … … … … … … … … … … ..… … … … … ...100

Figure A.5

LabVIEW® diagram code for the hybrid-electric CVPST simulator… … … … … .… … … … … … … … … … … … … … … … 101

xii

LIST OF TABLES

Table 4.1

Operational modes for the hybrid-electric CVPST… … ..… … … … … … ..41

xiii

Chapter 1
1.1 Overview

Introduction

A car must meet certain minimum requirements, in order to be useful and reliable for the customer. In general, a vehicle should be able to: - Drive at least 300 miles between re-fueling - Be refueled quickly and easily - Be able to reach a velocity to keep up with the rest of the traffic on the road Gasoline cars usually meet these requirements however some of them produce a considerable amount of pollution and also gas mileage is nowadays an issue of concern. Vehicle pollution is an important issue particularly in large cities. An electric car, on the other hand, produces almost no pollution, but it can only go 50 to 100 miles between charges. And the problem has been that it is very slow and inconvenient to recharge. Usually drivers’ desire for quick acceleration causes cars to be much less efficient than they could be. It can be noticed that a car with a less powerful engine gets better gas mileage than an identical car with a more powerful engine. This is because most of the cars only use a small percentage of their horsepower for typical operations. In the scenario of driving along a flat road on the freeway at 60 mph, the car engine has to provide the power for three things: - Overcome the aerodynamic drag caused by pushing the car through the air. - Overcome all of the friction in the car' components like the tires, transmission, axles s and brakes. - Provide power for accessories such as air conditioning, power steering and headlights.

1

For most cars, it takes less than 20 horsepower to provide for the aforementioned items. So, the purpose of having the “extra power” is for what its called "floor it", which is the only time were all the power is being used. The rest of the time, it uses considerably less power than what is available. Most cars require a relatively big engine to produce enough power to accelerate the car quickly. In a small engine, however, the efficiency can be improved by using smaller, lighter parts, by reducing the number of cylinders and by operating the engine closer to its maximum load. There are several reasons why smaller engines are more efficient than big ones: - The big engine is heavier than the small engine, so the car uses extra energy every time it accelerates or drives up a hill. - The pistons and other internal components are heavier, requiring more energy each time they go up and down in the cylinder. - The displacement of the cylinders is larger; so more fuel is required to move them. - Bigger engines usually have more cylinders and each cylinder uses fuel every time the engine fires, even if the car is not moving. This explains why two of the same model cars with different engines can get different mileage. If both cars are driving along the freeway at the same speed, the one with the smaller engine uses less energy. Both engines have to output the same amount of power to drive the car, but the small engine uses less power to drive itself. Therefore, using small engines near their maximum power limit will result in less fuel consumption, and in addition, if a continuously variable transmission (CVT) is used, this

2

can improve efficiency since there are not gearshifts, preventing the operation in the least efficient regimes of the engine. A CVT offers the potential of allowing the engine to operate near the optimum efficiency curve throughout a continuous range of velocity ratios without disturbing the driver with discrete shifts. A disadvantage faced nowadays using CVTs, is the fact that shows power limitations since a belt is used instead of gears. This power limitation is the reason why CVTs are only used in small cars. The concept of a continuously variable power-split transmissions (CVPST) brought by Mucino, V. et al. (1997) for automotive applications features the allowance of increasing engine power while reducing the power losses associated with power transmission, specially at low-speed-high torque modes, providing CVT ratio capability. The main reason on the use of a CVPST with an electric-hybrid vehicle (HEV) is to increase the power envelope capability for a given CVT element in the vehicle, which enables the CVT concept for light duty applications such as pick up trucks and small buses. Internal combustion (IC) engines are nearing perfection, engineers continue to explore the outer limits of IC efficiency and performance, but advancements in fuel economy and emissions have effectively stalled. While many IC vehicles meet low emissions standards, these will give way to new stricter government regulations in big polluted cities in the very near future. As additional options for improvement, automobile manufacturers have begun development of alternative power vehicles. The use of CVTs in the automotive industry is found mostly (99 %) in Japan and Europe, and just 1 % in the U.S. including the Honda Civic and the Subaru Justy. The reason for low popularity is

3

that the torque capacity has been restricted to the production of cars with a small displacement engine, as it was stated before. Currently, there are no CVT applications in light duty vehicles. A new conceptual idea for a hybrid-electric CVPST is presented in this work, which includes analysis and development of velocity and force equations. Also a LabVIEW® simulation program and a transmission control system was designed.

4

1.2

Objective

Develop a new conceptual configuration for a hybrid-electric CVPST with special focus in a sport utility vehicle (SUV). This design would be generalized for most of light duty vehicle applications. Another special issue is the replacement of the driver who is in charge of the gas pedal or valve throttle opening (VTO) for a controller. This controller has the purpose of matching the gas required (VTO) with the torque needed in the output and the velocity that the operator (driver) requests. One more objective is to show changes in the behavior of the system in an enginetransmission model simulated in LabVIEW® for different scenarios that a vehicle normally faces. Once all these objectives are accomplished, the design that is being proposed is expected to deliver more power than needed for a normal light duty vehicle, even though a smaller engine is to be used. Also improved efficiency is expected due to the fact that there is a power-split; therefore less power flows through the variable transmission as compared to normal CVT vehicles where all the power passes through it. At the same time, it is going to improve gas consumption and subsequent reduction of emissions may potentially be expected as the idea of the HEV is taken into account as previously described, with a smaller engine for the application.

5

Chapter 2
2.1

Relevant literature review

Continuously variable transmissions

A continuously variable transmission (CVT) as mentioned previously, provides a continuously variable ratio between the power source (engine) and the output shaft (wheels). CVTs offer the potential to take advantage of engine power and reach peak efficiency without using shifting gears. A century ago rubber v-belt transmissions were used in Benz and Daimler gasolinepowered vehicles. One important development with this type of transmissions was the Variomatic in 1965 (Hendrix et. al., 1988) and since 1975 the Volvo model 66 cars have been equipped with this type of transmission (Volvo Co. website). As mentioned before, a limitation in CVT applications is power capacity, that is why different kinds of CVTs have been developed in the past two decades. The metal pushing block v-belt (MVB) was one of the most important developments. It had received very good compactness, power density values and had higher efficiency than other types of traction, hydraulic or electric CVTs (Hendriks et al., 1988). This type of CVT has been used in more than one million of Japanese and European automobiles since 1994. The problem faced with this shaft-toshaft CVT is that it does not offer enough torque capacity. This limitation in power, compared with gear transmissions, is another reason why CVTs are not widely used. In order to take advantage of the CVT and overcome its disadvantages, the belt CVT was combined with a gear train (Lemmens, 1972-1974, Takayama et al. 1991). This

development is known as the continuously variable power split transmission (CVPST), which combines a planetary gear train with a CVT v-belt (Cowan, 1992, Mucino et al.,

6

1997). The most important idea of this configuration is that the power flowing through the belt can be less than 50 % at low speeds and around 90 % at high speeds; additionally, the power split allows the system to improve its efficiency by around 10 %. This power-split capability expands CVT applications thus giving the opportunity for CVTs to be used in bigger vehicles. The metal pushing belt is currently used in CVTs for small engine vehicles. It is difficult to manufacture and consequently is very expensive. One of the ideas of CVPST is to use rubber belts in order to reduce the cost of the transmission. Reviewing the paper work presented by Mucino et al. (1997), there are several important issues involved with the design of a CVPST. In this process, it is appropriate to choose parameters to allow the input power split, one part through the belt and the other one through the planetary gear set. Since the inception of CVTs in automotive industry, it had undergone several changes in the past twenty years; the developments include gear, hydraulic, toroidal-traction, push belt, variable diameter belt and flat/v-belt.

2.1.1 Types of CVTs
CVT systems can be categorized into six main types, according to its functionality and way of operation. o GEAR CVT This kind of CVT provides the continuously variable speed ratio using gear trains. Gives a wide range of speed outputs, as well as high torque at low speed and vice versa. The gear CVT was created by Cook in 1975 and it was different than

7

automatic transmissions because it required a very complex fluid logic control. The power source, such as the engine, is connected through a clutch to the transmission input shaft and this in conjunction with the intermediate shaft, drove the output shaft. The highest gear ratio is reached at low speed and when the output torque reduces to a certain point, all the power is given by the planetary gear train (PGT). A different gear CVT was developed by Won (1989) where gear ratio changed by a combination of floating and differential gearing. A fully geared CVT was created by Epilogic Inc. (Fitz; Pires, 1991), which was used in electric vehicles. A servo driven actuator controlled the ratio adjustment, which varied linearly with the displacement of the control actuator. o HYDRAULIC CVT Since it uses a hydraulic motor, it can provide a continuously variable speed ratio with its adjustment, which includes the amount of hydraulic fluid in the closed circuit. In this kind of CVT, either the hydraulic pump or motor are of variable displacement (Kawahara et al., 1990). This type of CVT is not used in automotive applications because its space requirements: Moreover it is noisy, low efficient and costly. o TOROIDAL TRACTION CVT These transmissions use the high shear strength of viscous fluids to transmit torque between an input torus and an output torus. As the movable torus slides linearly, the angle of a roller changes relative to shaft position, as seen in figure 2.1. This results in a change in the gear ratio.

8

Input

Figure 2.1: Toroidal CVT (Machida; Murakami, 2000) o PUSH BELT CVT This most common type of CVT uses segmented steel blocks stacked on a steel ribbon, as shown in figure 2.2. This belt transmits power between two conical pulleys or sheaves, one fixed and one movable. In essence a sensor reads the engine output and then electronically increases or decreases the distance between pulleys and thus the tension of the drive belt. The continuously changing distance between the pulleys (their ratio to one another) is analogous to shifting gears. Push-belt CVTs were first developed decades ago, but new advances in belt design have recently drawn the attention of automakers worldwide.
Block Ring

Moveable Block

Fixed

Figure 2.2: Metal push belt CVT (Fujii et al., 1992,1993).

9

The standard pushing belt is applied in engine ranges from 550 cubic centimeter to 1.2 liters (Hendriks et. al. 1988) usually used in small cars, however, is very expensive due to the difficulty of manufacturing. o VARIABLE DIAMETER FLAT/V BELT CVT This type of CVT is represented in figure 2.3. The flat belt CVT uses two rotary disk assemblies, one of them is driven with an input shaft and the other one drives to an output shaft. All the power flows through the belt and the continuously variable speed ratio is produced by the variable diameter with respect to the center of each disk, which have a flat cross section like the belt. In the case of the v-belt CVT, the two pulleys have a “V” cross-section and each pulley connects to a conical pulley.

Figure 2.3: Variable diameter belt CVT (Vibrate Software web-page, 2003)

This transmission has the same fundamental operation as the flat and pushing belt where one pulley remains fixed and the other one movable. However the pulleys separate at high gear ratios and can lead to the problems with creep and slip that

10

have plagued CVTs for years. This inherent defect has directed research and development toward push belt CVTs.

Figure 2.4: Example of a commercial flat-belt CVT (Honda Multimatic, 1995).

The Honda Multimatic CVT shown in figure 2.4 consists of an oil-pressure variable input and output pulley, and a metal belt that connects the two. With an oil-system clutch on the "driven" side, the Multimatic acts as an automatic transmission. The two pulley widths adjusted by oil pressure react to the position of throttle, speed and other conditions. For instance, when the accelerator is depressed the driving pulley width increases. At the same time the driven pulley width decreases - the two combining for a "lower gear" effect. In addition, the metal belt is highly flexible and accommodates the ever-changing width of the pulleys and transfers power efficiently without any slippage.

11

2.2

Hybrid-electric vehicles

An American engineer, H. Piper, filed for a patent on his hybrid vehicles in November 23rd, 1905 (Wouk, Victor; 1997). His vehicle could accelerate to 25 mph in 10 seconds, a full 20 seconds faster than the average half-minute of its contemporaries. Piper achieved this by combining a gasoline engine with an electric motor, today recognized as a standard hybrid configuration. Three and a half years later, Piper finally received his patent but by this time engines had become powerful enough to achieve Piper’s performance on their own. Engine developments, along with equipment that allowed them to be started without a crank, led to the decline of electric and hybrid vehicles between 1910 and 1920. Fifty years went by before the oil crisis of the 1970’s led to the construction of several experimental hybrid vehicles. But it wasn’t until the 1990’s that major work commenced on hybrid technologies. This was helped in the US by the formation of the partnership for a new generation of vehicles (PNGV) consortium. It was comprised of the "big three" car manufacturers along with about 350 smaller companies and the aim being to develop a car capable of giving 80 miles per gallon of gasoline. This efficiency has to be achieved without sacrificing performance or safety while emitting around one eighth of the pollutants of conventional vehicles and not costing significantly more. The PNGV has not specified the type of vehicle powertrain that is to meet their requirements but the IC engine/electric motor hybrid is the most likely ahead of fuel cell and flywheel alternatives. The two main objectives of this kind of vehicles are fuel consumption improvement and emissions reduction. Currently Honda and Toyota have this technology and both

12

manufacturers have begun selling their models in the United States. In fact, most automobile manufacturers have announced plans to manufacture their own versions. Any vehicle is hybrid when it combines two or more sources of power. In fact, many people have probably owned a hybrid vehicle at some point. For example, a motorized pedal bike is a type of hybrid because it combines the power of a gasoline engine with the pedal power of its rider. Hybrid vehicle examples can be found everywhere. Most of the locomotives we see pulling trains are diesel-electric hybrids. They combine mechanical technology, like a two-stroke diesel engine, with heavy-duty electric motors and generators throwing in some computer technology for good measurement. Seattle has diesel-electric buses running in the streets, these can draw electric power from overhead wires or run on diesel when they are away from the wires. Mining trucks are often diesel-electric hybrids. A number of submarines are also hybrid vehicles some are nuclear-electric and some are diesel-electric. Any vehicle that combines two or more sources of power that can directly or indirectly provide propulsion power is considered hybrid (Nice, Karim; 2003). The case of interest for this study is the gasoline-electric hybrid car, which is just a combination between a gasoline-powered car and an electric car. With the next diagram in figure 2.5 the most noticeable differences can be explained.

13

Figure 2.5: Electric car diagram. A gasoline-powered car uses an engine as the power source of the automobile and needs fuel in order to be functional. An electric car uses a motor as the power source and batteries as the energy storage supply, which usually provides for a range between 50 and 100 miles. The two power sources found in a hybrid car can be combined in different ways. One way known as a parallel hybrid has a fuel tank, which supplies gasoline to the engine, but it also has a set of batteries that supplies power to an electric motor. Both the engine and the electric motor can turn the transmission at the same time and finally the transmission turns the wheels.

Figure 2.6: Parallel hybrid diagram block.

14

Figure 2.6 shows a typical parallel hybrid diagram block. You can notice that the electric motor and gas engine connect to the transmission. As a result in a parallel hybrid, both the electric motor and the gas engine can provide propulsion power. By contrast, in a series hybrid configuration (figure 2.7) the gasoline engine turns an alternator and the generator can either charge the batteries or power an electric motor that drives the transmission. Thus, the gasoline engine never directly powers the vehicle. In the diagram shown in figure 2.7 of the series hybrid, it can be seen that all of the components form a line that eventually connect with the transmission.

Figure 2.7: Series hybrid diagram block. Finally, having a power-split box these two arrangements can be combined and have a configuration that could work in either series or parallel. This configuration is known as the series-parallel configuration and it has as stated previously a power-split box, which allows the engine to either supply full power to the alternator or the transmission. This configuration is shown on figure 2.8.

15

Figure 2.8: Series-parallel hybrid diagram block. Hybrid-electric cars contain the following parts: ¾ Gasoline engine: The hybrid car has a gasoline engine just like the ones we can find on most cars. However the engine on a hybrid-vehicle will be smaller and will use advanced technologies to reduce emissions and increase efficiency. ¾ Fuel tank: The fuel tank in a hybrid is the energy storage device for the gasoline engine. Gasoline has much higher energy than batteries. For example, it takes about 1 000 pounds of batteries to store as much energy as 1 gallon of gasoline. ¾ Electric motor: The electric motor on a hybrid car is very sophisticated. Some advanced electronics allow it to act as a motor as well as a generator. For example, when it needs to, it can draw energy from the batteries to accelerate the car. But acting as a generator it can slow the car down and return energy to the batteries. ¾ Generator: The generator produces electrical power for the batteries.

16

¾ Batteries: The batteries in a hybrid car are the energy storage device for the electric motor. It can provide energy into the batteries as well as draw energy from them. ¾ Transmission: The transmission on a hybrid car performs the same basic function as the transmission on a conventional car. Currently automatic and manual transmissions are being used.

17

2.3

Power-split technology

Power-split transmissions use differentials or PGTs in combination with variable elements, such as a CVT. The power is split and a fraction of the power flows through the CVT element to the differential (or PGT) while the remaining power circulates directly through the differential. Power-split transmissions have the advantage of transferring power that is greater than the capacity of the variable element, which is the limiting reason in CVT applications. This kind of technology has been developed for automotive applications using metal push belts and hydrostatic drives for the variable element. It has also been used in farm tractors. In 1972 Lemmens described the combination of a PGT with a v-belt CVT in a transmission. The input shaft rotates the v-belt and the chain drive; this last one transmits rotation to the planetary carrier while the v-belt transmits power to the sun gear. The output shaft is connected to the ring gear. Most of the power flows through the PGT while the CVT it is used to control the speed of the sun gear and at the same time to get a variable range of speeds. Lemmens improved his invention in 1974 in order to provide an automatic CVT where the only setting required was neutral, forward and reverse. This arrangement can have a non-desirable configuration known as power recirculation, which is not a real power-split system. Takayama et al. in 1989 presented a power-split transmission, which consisted of a CVT with a v-belt and a two-way differential clutch. Most of the power is transmitted to the belt while the rest goes through the two-way differential clutch. When the CVT reaches the maximum gear ratio, the output speed in the two-way differential clutch becomes slower than the output gear where as the output pulley shaft gains the power

18

from the belt with the one from the differential clutch. With this it is possible to increase power and acceleration and at the same time reduce an amount of load carried by the belt. In 1991 Kumm et al. presented a combination of flat belt CVT and a normal PGT. With his configuration it is possible to have a reverse drive and improvement in efficiency using the flat belt. It showed two different modes, in the low speed mode the input torque was divided into two directions, one was through the PGT and the output shaft, while the other was through the PGT and the CVT back to the input shaft. Consequently in the high-speed mode the input power was transmitted directly through the CVT to the output shaft and reverse output speeds were available by changing the ratio control direction in the CVT. In this arrangement the power transmitted by the gear train was greater than the input power. Cowan proposed a variable speed transmission unit connected with a PGT (1992, 1993) in which the sun gear and the primary variator were mounted on the input shaft and the planetary carrier was connected to the output shaft. The variator transmitted some amount of the input power to a counter-shaft, which at the same time is connected to the control gear and finally passes the power to the ring gear. When the control gear was linked with the counter-shaft the input power was split into two directions. A percentage of the power flowed through the variator and the rest went directly through the sun gear. Splitting the input power, the amount of power flowing through the CVT was reduced making the system more efficient.

19

2.4

Power-split hybrid-electric vehicles

A power-split HEV has been already developed in many different configurations. Recent work has been done on the future truck competition for the Society of Automotive Engineers (SAE) with the purpose of creating a SUV to be green and efficient with performance, utility and affordability that customers expect. The vehicle presented by Michigan Technological University (MTU) has come first in this competition as they converted a production SUV to a HEV. The HEV drive system utilized a planetary power-split transmission, which had the ability to couple the advantages of a parallelhybrid with the advantages of a series hybrid. The drive system consists of a planetary gear set coupled to an alternator, motor and an IC engine and performs the power-split operation without the need of belt drives or clutching devices.

Figure 2.8: Power-split mode (Beard, John et al.; MTU Future Truck; 2001)

20

The system operates in four operational states and its configuration is shown in figure 2.8. When the engine is off and the electric motor alone propels the vehicle and regenerates braking power it is called the electric mode because the engine is left off line. The second mode is the engine start mode where the transition from electric to a hybrid vehicle takes place. In order to bring the engine up to operating speed, the alternator applies a torque in the forward direction of rotation. When the speed of the planet carrier becomes faster than the ring gear, the alternator stops providing power and begins to extract some of the engine power and at this point reaches the power-split mode. As the vehicle speed increases, the amount of power being transferred through the ring gear and chain drive increases with the speed of the ring gear. At highways where speed and load is constant, the engine power required decreases allowing the alternator speed to decrease and when it reaches zero we get to the final operational type called parallel mode. In this mode all the power is transferred via the ring gear, as opposed to using the recirculation loop made up of the alternator and motor, which has increased losses in energy conversion. These operational states met fuel efficiency and low emissions that SUV consumers expected and also maintained its manufacture feasible. This thesis has the goal of increasing power so that it can be used in bigger vehicles such as small buses and pick up trucks, and instead of using a chain drive it will be used a vbelt CVT. Kuen-Bao and Shen-Tarng (1999) have done some work on automatic hybrid transmissions for motorcycles using CVTs where they presented a systematic approach in designing an automatic transmission including a conceptual and kinematic design, efficiency analysis, engine and transmission matching. Their basic concept is to combine

21

a stepped and a stepless design into a hybrid transmission system. Four hybrid transmission systems consisting of two degrees of freedom PGTs and rubber v-belt drive units were synthesized. They also performed kinematic analysis and a kinematic design of the hybrid transmission to obtain the range of the relative speed ratio of the differential gear and provided the relationship between the major dimensions. In their results, the transmission efficiency is not better than that of the existing CVT since the parts of the prototype were roughly fabricated; nevertheless the overall results showed that their design was theoretically correct and practically feasible. Figure 2.9 shows the differential transmission with a CVT system used in their work.

Figure 2.9: Differential transmission and CVT system for motorcycles (Kuen-Bao; Shen-Tarng; 1999).

22

John Anderson’s thesis work (1999) also proposes a CVT transmission combined with a HEV for the design and model of a torque and speed control transmission. His study was conducted to determine the feasibility of creating a multiple input/output transmission. This transmission, which was the torque and speed control transmission, is combination of a PGT and a CVT. He studied six different operating modes for these transmission technologies. These six modes are conventional, electric vehicle, series HEV, parallel HEV, variate 1, parallel HEV, variate 2, and geared neutral. Each of these modes has specific efficiency benefits during vehicle operation. This type of operation allows for a transmission to be significantly more flexible than current automotive transmissions. The engine can send power to the drive wheels directly through the PGT and the CVT simultaneously. The results of his study showed a transmission that is capable of efficient operation under a wide variety of circumstances.

Figure 2.10: CVT configuration diagram proposed by John Anderson (1999).

23

From figure 2.10 it can be observed that this configuration requires all engine power from the engine to be transmitted through the CVT. Variation of the CVT ratio allows the overall range of gear ratios to match the engine output power required at the wheels. The motor speed is prescribed by the engine speed and the CVT ratio total power output is a function of engine speed, engine torque and motor torque.

2.5

Continuously variable transmission controller

The first electronic control system appeared on the market in the early seventies. These were simple transistor control units for actuating in and/or out valves and were capable only of determining shift points. At the beginning of the eighties first microcomputer controls were presented by Y. Taga. The first transmission with fully electronic microprocessor control of all major functions appeared on the market in 1983. This was the ZF’s 4 HP-22, a 4 speed automatic transmission with hydrodynamic torque converter and lock-up clutch for vehicles with rear wheel drive. The electronic control function was performed by a microcomputer enabling substantial functional improvements to be achieved. Of the numerous CVT concepts mechanical belt/chain type pulley-drive CVTs are the most advanced and have a small scale of production. The offset input and output shafts in their design makes them very compact and therefore ideal for front-wheel drive vehicles with limited installation space, although their overall power ratio is less than a planetary transmission.

24

Figure 2.11 shows a prototype. This system was used for performing basic tests on the transmission itself but also for developing the control and regulating strategy. It was therefore equipped with an all-electronic control system shown in figure 2.12.

Figure 2.11: CVT belt type (Schwab, Manfred; 1994).

Figure 2.12: CVT control schematic (Schwab, Manfred; 1994). 25

Chapter 3

CVPST Concepts and kinematic models

3.1

CVTs and power-split concepts

In recent years it has become important to decrease fuel consumption in motor vehicles and get the best vehicle performance possible in a given engine. Both of these issues can be improved by using a CVT as stated in previous chapters. To take full advantage of such a transmission, two requirements must be fulfilled: a) The efficiency of the CVT must be fairly high. b) Its speed ratio range must be large enough to allow the engine to operate as efficiently as possible. Most CVT designs do not fulfill both of these requirements; however this can be improved by a split-power CVT. Figure 3.1 shows the typical characteristic of torque vs. speed of an IC engine. Level lines for equal specific fuel consumption are included as well as hyperbolas for equal engine power. The dashed line marks the most efficient combinations of torque and speed that produce the required power determined by the speed and acceleration of the vehicle. Using a CVT the ideal line can be followed by always choosing a proper speed ratio. Thus the engine can operate at the most favorable speed for a certain power, which is independent from vehicle’s speed. The continuous change between different speed ratios provides a smooth jerk-free driving.

26

Figure 3.1: Improved fuel economy plot; showing torque vs. engine speed of a 100kW IC engine with CVT ideal line (Hedman, 1992).

Figure 3.2: Improved vehicle performance plot; tractive effort vs. vehicle speed for a CVT and a five-speed manual gearbox (Mattsson, 1993).

27

Figure 3.2 shows theoretically how the maximum engine power can be delivered to the driving wheels at all vehicle speeds; this gives improved vehicle performance as compared with using a manual gearbox with a finite number of discrete speed ratios. In practice, the performance improvement obtained from the maximum engine torque is smaller than in the loss-free case because a CVT generally has larger losses than a manual transmission. In some situations it is necessary to limit the engine power due to CVT restrictions. Combining a PGT with a CVT the power can be split into two branches as shown on figure 3.3. This kind of transmission is referred as the continuously variable power-split transmission (CVPST), where the power through the variator is aimed to be less than the input power.
Variator

Planetary gear arrangement

Figure 3.3: Power-split diagram (Mattsson, 1993).

The CVPST for automotive applications presented by Mucino (1997) consists of a pulley set (variator) coupling two of the three rotating elements of a PGT (sun and ring gears). The power-split appears when the input shaft delivers power to the sun gear as well as to the driving pulley, which in turn drives the ring gear of the PGT through the variator.

28

Since the input shaft delivers power in two directions, the variator carries only a fraction of the total power flowing through the input shaft and the planetary gear set collects the power flowing from the ring and the sun gear delivering the total output power. Figure 3.4 shows the diagram of the CVPST for automotive applications proposed by Mucino et al. (1997).

Figure 3.4: Continuously variable power-split transmission (Mucino et al., 1997).

Some important gear ratio relationships that should be consider from the previous figure are:

γg =

rs , rri

γ gc =

ro , rro

γc =

r po rps

(3. 1)

29

and the output-input relationship is (Mucino et al., 1997):

γ c (1 + γ g ) ϖ in = ϖ out γ cγ g + γ gc

(3. 2)

The pulleys are variable; therefore it is necessary to have a relationship between them according to figure 3.5 where C is the center distance between pulleys.

V-Belt Rps

M
Center Distance (C)

Rpo

Figure 3.5: Pulley system diagram (Mucino et al., 1997). In order to find a relationship between the pulleys it was necessary to define a function Γ of the angle φ (in radians) defined as:
Γ(φ ) = φ cos(φ ) − 1 − cos 2 (φ )

The pulley radius relationships are (Mucino et al., 1997):
rpo = 2CΓ(φ ) + L 2π

>
rpo = 2CΓ(φ ) + L + C cos(φ ) 2π

(3. 3)

(3. 4)

(3. 5)

30

Also a relationship for the total belt length in terms of both variable pulleys was developed in order to check that both radii were accurate. L = 2( C 2 − (rpo − r ps ) 2 + rpo (π − φ ) + rpsφ (3. 6)

3.2

Power flow configurations

The power flowing trough a CVT in combination with a PGT can show different configurations. The power-split mode is the most desirable mode since less amount of power flows through the belt, however some undesirable situations such as recirculation and inverse direction on the output shaft can appear and should be considered when the system is being designed. Force and power diagrams of these cases are shown next.

Power-split case: This is the most desirable case because just an amount of the total input power goes through the belt and the other amount goes to the sun gear. Since CVTs nowadays have power limitations this configuration gives the opportunity to expand its applications. The input power comes from the engine (HP) and splits, a percentage goes through the sun gear and the other one flows through the CVT. This last percentage is going to lose some efficiency. That power goes to the counter shaft then passes through the idler gear and finally reaches the control gear. This last power is added to the power coming from the sun gear flowing through the planet gear, which transmits the total power to the output shaft.

31

Where

Figure 3.6: Force analysis diagram for the power-split mode

F1 = Belt force from pulley 1 to 2 F2 = Belt force from pulley 2 to 1 F3 = Force from the counter shaft gear to the idler gear F4 = Force from the control gear to the idler gear F5 = Force from the idler gear to the counter shaft gear F6 = Force from the idler gear to the control gear F7 = Force from the planet gear to the sun gear F8 = Force from the planet gear to the ring gear F9 = Force from the sun gear to the planer gear F10 = Force from the ring gear to the planet gear F11 = Force from the output shaft to the planet gear F12 = Force from the planet gear to the output shaft

32

Power recirculation case-I: This is a non-desirable case known as the power recirculating transmission (first mode). Compared to the power-split case there is no idler gear, which changes the direction in the control gear. The input power comes from the engine (HP) and again splits, a percentage goes through the sun gear and the other part goes to the CVT and again the part that goes through the belt is going to lose some efficiency. That power goes directly to the counter shaft passing through the control gear. This power is added to the one coming from the sun gear flowing through the planet gear, which transmits the total power to the output shaft. As shown in figure 3.7 since there is no idler gear in this system the direction in the control gear can either rotate in the opposite direction or give no output power.

Figure 3.7: Force analysis diagram for the power recirculation case-I. Where F1 = Belt force from pulley 1 to 2 F2 = Belt force from pulley 2 to 1

33

F3 = Force from the counter shaft gear to the control gear F4 = Force from the control gear to the counter shaft gear F5 = Force from the planet gear to the sun gear F6 = Force from the planet gear to the ring gear F7 = Force from the sun gear to the planer gear F8 = Force from the ring gear to the planet gear F9 = Force from the output shaft to the planet gear F10 = Force from the planet gear to the output shaft Power recirculation case-II: The third and final possible case in a CVPST is where the power is recirculating through the system and the power flowing through the CVT can be higher than the input power. Since the power is recirculating through the variator and the PGT, the input power instead of splitting power through the CVT is adding power to the recirculating power. Also the direction of the output shaft is reversed, which is not desirable. Figure 3.8 shows a force diagram for this case.

Figure 3.8: Force analysis diagram for the power recirculation case-II.

34

Where F1 = Belt force from pulley 1 to 2 F2 = Belt force from pulley 2 to 1 F3 = Force from the counter shaft gear to the control gear F4 = Force from the control gear to the counter shaft gear F5 = Force from the planet gear to the sun gear F6 = Force from the planet gear to the ring gear F7 = Force from the output shaft to the planet gear F8 = Force from the sun gear to the planer gear F9 = Force from the ring gear to the planet gear F10 = Force from the planet gear to the output shaft

35

Chapter 4

Hybrid-electric power-split CVT conceptual design

4.1

Design proposed

This chapter’s objective is to show a conceptual design for a new hybrid-electric CVPST configuration, power analysis and the development of velocity and force equations. This design will allow the possibility to use a small IC engine which in addition to an electric motor will give a higher or at least the same amount of output torque in a more efficient way compared to nowadays light duty vehicles. The benefit of this design is the opportunity to show a configuration in which a CVPST can be used for light duty applications and at the same time improve efficiency, fuel consumption and help reduce pollution.

Figure 4.1: Hybrid-electric CVPST diagram.

36

Figure 4.1 shows the proposed system where the electric motor/generator is connected to the countershaft and can either give variable torque or not. The engine has a constant input torque and it is controlled by a clutch for idle modes. This torque given by the engine is split, an amount goes through the belt and the other amount goes directly to the sun gear. The amount of power flowing through the belt connects to a pulley rotating the countershaft. Depending on the circumstances, the electric motor (where its input shaft is connected to the countershaft) can either add power or not. The power flowing through the countershaft passes to an idler gear used in order to have the control gear rotate in the same direction as the input power shafts. This control gear is directly connected to the ring gear of the PGT. This power in the ring gear is added to the one from the sun gear and gives the output power to the planet gear, which connects to the differential shaft.

Force analysis: The following force analysis diagram (figure 4.2) shows that the system is always going to be in a power-split mode since the output velocity direction of the ring gear and the sun ring are always in the same direction. This way it can be assured that the nondesirable modes (power recirculation, high power circulation through the belt, etc.) are not going to be present. On the other hand many clutches and brakes have to be placed into the system in order to accomplish common vehicle performances, i.e. driving up hills (high torque required), highways (constant velocity, low torque required), highway pass (high torque reached in minimum amount of time), in the city (variable velocity, many stops, variable torque needed), etc. In order to achieve all these states of operation, a clutch is needed to decouple the IC engine another one for the electric motor, one more

37

for the output shaft and finally one for the countershaft gear that connects to the idler gear. These clutches are shown with more detail in figure 4.3.

Figure 4.2: Force analysis diagram for the proposed hybrid-electric CVPST Where • • • • • • • • • • F1 = Belt force from pulley 1 to 2 F2 = Belt force from pulley 2 to 1 F3 = Force from the counter shaft gear to the idler gear F4 = Force from the control gear to the idler gear F5 = Force from the idler gear to the counter shaft gear F6 = Force from the idler gear to the control gear F7 = Force from the planet gear to the sun gear F8 = Force from the planet gear to the ring gear F9 = Force from the sun gear to the planer gear F10 = Force from the ring gear to the planet gear 38

• •

F11 = Force from the output shaft to the planet gear F12 = Force from the planet gear to the output shaft

Force equations were developed and will be shown in the course of the chapter. Power analysis: As stated previously, there are two input powers, one through the engine and the other one by the electric motor. They can either work together (when a high amount of power is required) or separately depending on the circumstances and the environmental conditions. Figure 4.3 shows a sketch of the power flowing through the system for the maximum amount of power mode. The majority of the power comes from the IC engine, which has constant speed and it is designated with Pin1 in red color. This power splits in two directions, the one in blue goes through the belt and the one in gray goes directly to the sun gear.

Figure 4.3: Power analysis diagram.

39

Since a smaller engine is being used, when more power is required the electric motor starts running and supplies an amount. This power is designated with Pin2 in brown color, which is added to the split power coming from the blue arrow resulting in more power flowing through the countershaft gear and consequently to the idler and control gear. Both showed with a magenta color arrow. This last gear is connected to the ring gear of the PGT and transmits the power to the planet gear, which also receives the split power coming from the engine input by the sun gear. This total power at the planet gear is transmitted to the differential shaft designated by Pout in red color. This output power is increased since there is a power split and only an amount of the input power by the engine passes through the CVT, which makes it more efficient. It is necessary to add a small gearbox formed by two gears and a synchronizer in the transmission from the planet gear shaft to the differential shaft. This is for the purpose of reaching the desirable velocity ratios on the CVT. Since it is only a two-gear change it does not represent a big amount of losses. The sketch on figure 4.3 also shows the clutches and brakes required for the appropriate performance of a vehicle. Clutch A decouples the IC engine from the CVT input shaft; clutch B decouples the electric motor from the CVT output shaft/countershaft; clutch C decouples the output CVT pulley from the countershaft; clutch D decouples the countershaft from the gear that connects to the control gear; clutch E decouples the output shaft (for the idle or neutral mode); brake 1 stops the sun gear from the PGT as well as the shaft that connects it to the engine and brake 2 stops the ring gear from rotating.

40

4.2

Operational modes

Table 4.1 shows the six different stages in which the vehicle can operate (with two possible idle modes), depending on the amount of power required and the environmental conditions. This table specifies which clutches, gears and breaks are connected and which ones are not, having in total six stages. Modes Electric Reverse A B C D E B1 B2 G1 G2 Engine E. Motor /Generator Batteries ON ON O X O X X X O O X OFF ON O X O X X X O O X OFF ON
Engine / Battery recharge Engine / Power-split Hybridelectric/ Max. power Idle I / Battery recharge Idle II

X X X

X O X X X O O O/X X/O ON OFF

X X X X X

X X X

O X O O O X X O O OFF ON

O X O X O X ON ON / Generator ON/Charge

O O O X O O ON ON / Generator

O O O/X X/O ON ON

OFF

ON

ON/Charge

ON

Table 4.1: Operational modes for the hybrid-electric CVPST Table 4.1 is related to figure 4.3, where A, B, C, D and E are the five clutches needed for decoupling different components on the vehicle. Compared to nowadays-automatic 41

transmissions, which use at least four clutches, this does not represent a problem for the configuration proposed. B1 and B2 are brakes and finally G1 and G2 are the output gears that connect the output shaft from the planet gears to the differential. The first row indicates the six different modes of operation with two different idle modes and the first column has the different operational components from the vehicle. The following columns show which components are either open or close for clutches, brakes and gears. It also shows if the engine, electric motor and the battery pack are either on or off. O stands for open, X for closed; O/X or X/O are used for cases in which the component can have both possibilities (open or closed) for that particular mode. In some cases if there are two components with this notation, one of them has to be open while the other one has to be closed and vice versa. Next figures for each mode followed by an explanation are presented, components in red show the elements that are working and carrying power. STAGE 1: ELECTRIC MODE

The first stage is the electric mode where the IC engine is off, thus the electric motor alone propels the vehicle and regenerates braking power. The battery pack supplies energy to the electric motor, therefore clutches B, D and E are engaged. The power flows from the electric motor to the countershaft, then through the idle gear to the control gear. This last one is connected to the ring gear and finally passes the power through the planet gears and gearbox to finally reach the differential, as shown in figure 4.4. Break 1 is activated, consequently the sun gear remains stopped assuring that the planet gears rotate in the same direction as the ring gear. Gear 1 is used because more torque is required when the car is started. Since the engine is off, clutches A & C are disconnected; therefore there is no power flowing through the CVT.

42

Figure 4.4: Electric mode

STAGE 2:

REVERSE MODE

The second stage is the reverse mode, which operates just as the electric mode but with the difference that the electric motor operates in the reverse direction giving an opposite output direction, as shown in figure 4.5.

Figure 4.5: Reverse mode In this case, as the previous one, the engine is left off-line and all the power is supplied by the electric motor flowing through the countershaft to the ring gear, planet gear and 43

finally the output shaft to the differential. Clutches, brakes and gears are engaged just like the electric mode. STAGE 3: ENGINE START (P-SPLIT) / BATTERY RECHARGE MODE

The third stage is the engine start mode, at this point if all the power given by the engine is not necessary, then an amount is split through the CVT and goes to the electric motor that will work as a generator in order to recharge the battery pack. The other amount of power split on the input pulley of the CVT goes to the sun gear from the PGT. Then it is transmitted to the planet gears followed by the output shaft and the differential. As shown in figure 4.6 break 2 is activated, which stops the ring gear of the PGT so it can assure that the planet gears are rotating in the forward direction. Break 1 is released since the sun gear is transmitting the power to the output shaft. Clutches A, B, C and E are engaged so as gear 2, as it is assumed that the vehicle is still going in low speed.

Figure 4.6: Engine start (p-split) / Battery recharge mode. Clutch D is not engaged this is with the purpose of letting all the power split by the CVT to go to the electric motor-generator to charge the battery pack.

44

STAGE 4:

ENGINE POWER-SPLIT MODE

The fourth stage is the engine power-split mode where the input power from the IC engine is split into the sun gear of the PGT and the belt from the CVT just as the previous case. The amount of power flowing through the belt goes to the countershaft, idle and control gear, which is connected to the ring gear and finally its transmitted to the planet gears of the PGT, this power is added to the one coming from the sun gear and obviously increases the output power passing through the output shaft, gearbox and differential. The controller can adjust the speed ratio by changing the CVT ratio and the fuel valve throttle opening (VTO). In this case all the power given by the engine is used and since there is a power-split, more power can be gained and efficiency will increase (Bonthron, A.; Hsieh L. and Yan H, 1990) if it is compared with single shaft-to-shaft variable transmissions.

Figure 4.7: Engine power-split mode. As shown in figure 4.7 clutches A, C, D and E are engaged and allow the power from the IC engine to be split. Clutch B is left off line since the electric motor-generator is not either supplying or receiving power. Break 1 and 2 are not activated because power is

45

coming from two directions (ring and sun gear) and its added in the planet gears. Either gear 1 or gear 2 can be engaged depending on the velocity of the vehicle and the speed ratio on the CVT.

STAGE 5:

HYBRID-ELECTRIC / MAXIMUM POWER MODE

If more power than the one provided by the IC engine is necessary then the electric motor starts to operate and the transition from an IC engine vehicle to a hybrid-electric takes place. This is the fifth stage known as the hybrid-electric mode where the maximum amount of power is provided. There is a second input power coming from the electric motor, which is connected to the countershaft and is added to the split power coming from the engine through the CVT.

Figure 4.8: Hybrid-electric/ Maximum power mode.

This power flows through the control gear and ring gear reaching the planet gears that also receive power from the sun gear. Finally it passes by the gearbox and the output

46

shaft (differential). In this mode the maximum amount of power is provided because the two power sources are running. Figure 4.8 shows that all the clutches are engaged and both brakes are released since the maximum amount of power is provided and both input powers sources are running. Either gear 1 or gear 2 can be activated depending on the torque required by the vehicle. The amount of power given by the electric motor is limited by the energy that the battery pack can provide, when it runs out of energy the system can either go back to stage 3 for recharging batteries or stage 4 letting the engine run by itself. The stage chosen depends on the amount of power required and can be switched eventually.

STAGE 6:

IDLE-NEUTRAL / RECHARGE BATTERY MODE

The final stage is the idle or neutral mode, which can operate in two different ways. The first possibility is recharging batteries by having the engine operating by itself. So while the vehicle remains stopped the engine provides power to the electric motor-generator for recharging batteries. In this case, as shown in figure 4.9, all the power provided by the IC engine flows through the variator and supplies energy to the electric motor-generator. Clutches A, B and C remain engaged since all the power goes to the generator; and clutches D and E are disengaged giving a result of zero output power and velocity. Break 2 is activated stopping the ring gear, while break 1 is not activated and allows the ring gear to spin free. The second possibility for this idle-neutral mode is when the electric motor is running. This case may be necessary at some point while the vehicle operates in stage 1 (electric mode). The diagram for this second case is shown in figure 4.10.

47

Figure 4.9: Idle-neutral (case I) / Recharge battery mode.

Figure 4.10: Idle-neutral mode (case II). Here the electric motor spins freely without providing power. Clutches A, C, D and E are disengaged letting the output shaft without any velocity. Brakes 1 and 2 are activated stopping the ring and sun gear. Therefore just clutch B is engaged and prepared to switch to an electric mode if clutch D and E are connected. Comparing these two possibilities of idle-neutral mode, the first one is the more desirable since the battery pack is being recharged.

48

4.3

Velocity relationship equations

Assuming the following configuration the velocity relationships are going to be developed.

Figure 4.11: CVPST sketch with radii, gears and pulleys notation

Where: a = Input pulley CVT d = Countershaft gear rg = Ring gear rs = Sun gear radius rro = Control gear radius b = Belt e = Idler gear p = Planet gear rri = Ring gear radius rps = Input pulley radius c = Output pulley CVT f = Control gear s = Sun gear ro = Countershaft gear radius rpo = Output pulley radius

ωin = Input angular velocity ωc = Input pulley angular velocity ωd = ωcs = Countershaft gear angular velocity

49

The characteristic parameters, which define the geometric configuration, involve the overall radii of four gears and the pitch radius of the variable pulleys. Two clutches are shown in the previous figure that illustrates the connection between the transmission and the power sources (engine and electric motor). In this arrangement there are five gears (sun, planet, ring, control and countershaft) whose radii can be used to express the inputoutput velocity relationship. Consequently, the ratios are established by the following (previously defined by Mucino et al.)

γc =

ωc ωc = ω a ω in

γ gc =

ωf ωd

γg =−

ωp ωr

(4. 1)

rearranging this relationships can be written as

ω c = ω a γ c = ω in γ c
since then

;

ω f = ω d γ gc

(4. 2) (4. 3) (4. 4)

ωc = ωd
ω f = ω c γ gc = ω in γ c γ gc

for the angular velocity on the ring and sun gear

ω r = ω f = ω in γ c γ gc

and

ω s = ω in

(4. 5)

using the general equation for planetary gear trains

ω p −ωs N = − r = −γ g ωr −ωs Np
where N r and N s are the number of teeth for the ring and sun gears respectively rearranging

(4. 6)

ω p − ω s = γ g (ω s − ω r )

(4. 7)

50

and substituting ω s = ω in and ω r = ω inγ c γ gc can be written as

ω p − ω in = γ g (ω in − ω inγ c γ gc )

(4. 8)

then it is possible to find a velocity relationship between the input and the output shafts

ω out = 1 + γ g (1 − γ c γ gc ) ω in

(4. 9)

and one between the output and countershaft using ω r = ω d γ gc on the previous equations resulting in

ω out ω out 1 1 = = + γ g ( − γ gc ) ωd γc γc ω cs
The variable pulley relationships were previously shown in chapter 3.1.

(4. 10)

4.4

Force equations

Referring to figure 4.2 with the force analysis diagram for the hybrid-electric CVPST a useful relationship can be derived for the belt force based on the ratios described on the previous section. First the force equilibrium equations are developed
Tin = Fb rps + Fs / p rs Tout = F p rp = ( Fs / p + Fr / p )rp

(4. 11) (4. 12)

Where Fs / p is the force on the sun gear by the planet gear and Fr / p is the force on the ring gear by the planet gear. Deriving equation (4.12) it can be found that
Fb = Tin − Fs / p rs rps

(4. 13)

where Fb is the force by the belt. 51

From equation (4.12) Fs / p = and for Fr / p Tout − Fr / p rp (4. 14)

Fr / p = Fctr / i
since Fctr / i = Fcs / i .

rro r = Fcs / i ro ri ri

(4. 15)

Where Fctr / i is the force on the control gear by the idler gear and Fcs / i is the force on the countershaft gear by the idler. From equilibrium forces on the countershaft the following equation can be developed Fcs / i = Tem + Fb rpo ro (4. 16)

Here Tem is the torque generated by the electric motor. Combining equations (4.15) and (4.16) Fr / p = Combining equations (4.14) and (4.17) (Tem + Fb rpo ) rro ro ri (4. 17)

Fs / p =

Tout  (Tem + Fb rpo ) rro − rp  ro ri 

   

(4. 18)

Combining equations (4.13) and (4.18)
T  (Tem + Fb rpo ) rro   Fb rps = Tin −  out −   rs  r ro ri   p   

(4. 19)

52

Rearranging, the force on the belt can be found in terms of gear radii, input and output torque and CVT ratio, which is variable. A relationship between pulleys radii has been developed already and it was previously shown in chapter 3.1. Finally the force on the belt is
Fb = Tout ro rri rs − Tem rro rrs − Tin rp ro rri rpo rro rs − rps rp ro rri

(4. 20)

Where rp and rpo can be alternatively substitute by
rp = rri − rs 2

;

rpo = ι cvt r ps

(4. 21)

and ι cvt is the CVT ratio which is variable and directly proportional to the pulley radii defined by ι cvt =
rpo rps

.

53

Chapter 5

Example conceptual design

5.1

Vehicle considerations

Many considerations have to be taken into account for the analysis of the system designed. A vehicle consists of many components distributed within its exterior envelope. For braking, acceleration and its most turning analysis the whole vehicle is often treated as a lumped mass, excepting the wheels. Only the forward and longitudinal motions are sufficient to be considered for driving test purposes and for the vehicle used for this study. DYNAMIC LOADS The dynamic loads acting on a vehicle are traction forces, which push the vehicle to move through the x direction and the rest of the forces acting in that direction are the resistance forces. These forces are shown in figure 5.1.

Figure 5.1: Loads acting on a vehicle (Gillespie, 1992). The traction force is the one coming from the engine and its transferred to the wheels through the power train. The output torque given by the engine varies accordingly to the 54

VTO (gas pedal) and the engine speed. This VTO changes during the acceleration time and increases as more power is required, that is why the engine torque can not be easily defined as a function. If the control system defines the VTO as a function of the vehicle speed then the engine torque can be known. The traction force is defined as (Gillespie, 1992): Fx = where Te = Engine torque at a given speed (from dynamometer data)
N tf = Combined ratio of transmission and final drive

Te N tf η tf r

ax 2 2 − ( I e + I t ) N tf + I d N f + I w } 2 r

{

(5. 1)

η tf = Combined efficiency of transmission and final drive
r = Wheel radius

I e = Engine rotational inertia I t = Rotational inertia of the transmission I d = Rotational inertia of the drive shaft
N f = Numerical ratio of the final drive

I w = Rotational inertial of the wheels and axles shafts a x = Acceleration in the forward direction The aerodynamic drag should also be considered. It is the result of the air stream interacting with the vehicle and results in six components of forces and moments. These components are drag and rolling moment in the longitudinal direction, side force and pitching moment in the lateral direction and finally lift and yawing moment in the vertical

55

direction. From all of them, air resistance is the most considerable and important aerodynamic force. This air resistance coefficient varies depending on the shape of the vehicle and it is defined as (Gillespie, 1992):
DA = 1 ρV 2 C D A 2

(5. 2)

Where ρ is the air density, A the frontal area of the vehicle and C D the drag coefficient. Another important dynamic load is the rolling resistance, which is the total resistance force from the wheels. In calculations the dynamic weight of the vehicle including the effects of acceleration, trailer towing forces and the vertical component of air resistance should be considered. When calculating rolling resistance a coefficient must be defined. This coefficient

f r is a factor that reflects the effects of the complicated and

interdependent physical properties faced by the tire and the ground, which are the temperature, pressure load, vehicle velocity, tire material, slip, etc. At lower speeds the coefficient increases almost linearly with speed. This coefficient is defined as (Gillespie, 1992):
f r = 0.01(1 + V ) 160km / h

(5. 3)

Where V is in km/h and fr is dimensionless and the rolling resistance is defined as (Gillespie, 1992):
R x = R xf +R xr = f rW

(5. 4)

where W and Rx are in kg.m/s2 or Newtons.

56

POWER AND ACCELERATION EQUATIONS In the case of the acceleration of a vehicle two limitations can be present, engine power and traction on the drive wheels, which may depend on vehicle speed. For low speed tire traction may be a limiting factor, while at high speeds engine power may be considered as the limiting factor. Limitations in power involve examination of the engine characteristics and the power train. Engines can be characterized by the torque and power curves as a function of speed. Power and torque are related by speed. That is: Power (HP) = Torque (lb-ft) x speed (rpm’s) (5. 5)

The ratio between engine power and vehicle weight is an important consideration for acceleration performance. Taking into account the velocity, gravitational speed, engine horsepower and the vehicle’s weight, an acceleration equation can be developed from second Newton’s law.
ax = Fx g P = 550 M VW

( ft / sec 2 )

(5. 6)

For a more exact performance it requires the modeling of mechanical systems in which engine transmits power to the ground. The actual torque delivered to the drivetrain is reduced by the amount required to accelerate inertia of the rotating components. Considering the mass of the vehicle (M), the rolling resistance (Rx), the tractive force at the ground (Fx), the aerodynamic drag forces (DA) and the hitch (towing) forces (Rhx), an equation can be developed.

( M + M r )a =

Te N tf η tf W + Wr a= − R x − D A − Rhx − W sin θ g r

(5. 7)

57

Where M r stands for the equivalent mass of the rotating components, N tf the ratio of transmission and final drive, η tf the combined efficiency of transmission and final drive and θ is the road slope angle (radians). VEHICLE CONSIDERED As an example application for this thesis the Michigan Technological University (MTU) HEV used for the future truck competition was considered. Its dimensions were used for the calculations on the program created in LabVIEW®. This SUV has the body of a Chevrolet Suburban model 2000-2001 and it was considered because it is an example of a light duty application and is one of the most popular vehicles nowadays in America. An IC engine LX5 DOHC V6 by General Motors was selected and is shown in figure 5.2.

(a)

(b)

Figure 5.2: (a) The LX5 DOHC V6 by General Motors; (b) Power and torque plot for this engine (GM’ s website, 2003)

58

This engine uses gasoline as fuel; it has a capacity of 215 HP (160 kW) and weighs 375 lbs. (168 kg). Based on the well-known Cadillac NorthStar V8, the GM LX5 was introduced in 1999 Oldsmobile Intrigue and remained the OEM (Original Equipment Manufacture) engine for the Intrigue in 2000 and 2001. The under-square bore-to-square ratio exhibited by the LX5 provides high thermal efficiency and strong low-end torque, while four valves per cylinder provide good top-end aspiration. It has a 9.3:1 compression ratio and is near optimum for regular octane fuel and when combined with cam profile and intake tuning it enables the engine to produce an amazingly flat torque curve with 90 % of maximum torque available from 1600 to 5600 rpm. The resulting power curve is nearly linear and makes the engine particularly predictable and easy to control in a power-split configuration. The electric motor considered (figure 5.3) was a pair of Unique Mobility SR286, which also works as a generator. It weighs 102 kg (225 lbs.), is 336 mm. (13.2 in) long and its water-cooled. Its power capacity is 130 kW (175 hp).

Figure 5.3: The Unique Mobility SR286 (HMMWV PEI’ s website, 2003)

59

5.2

LabVIEW® plots

LabVIEW® version 6i software is a powerful instrumentation and analysis programming language for PCs. It uses icons instead of lines of text to create applications. In contrast to text-based programming languages where instructions determine program execution, LabVIEW® uses dataflow programming where data determine execution. LabVIEW® can generate charts, graphs and customized used-defined graphics in a friendly way. First a used interface is built by using a set of tools and objects. The user interface is known as the front panel. Code is added using graphical representations of functions to control the front panel objects. The block diagram contains this code. If organized properly, the block diagram resembles a flowchart. For this thesis purpose, a LabVIEW® program was created, which can be used to design the PGT and CVT as input values can be changed. It can also be used to see plot results on different data such as velocity, pulley variable radii, belt force behavior, torque and power.

1. Engine speed vs. vehicle velocity: Figure 5.4 shows the CVT gear ratio range in an engine speed (rpm’ s) with respect to vehicle velocity (km/h) plot. The inputs needed are the high and low CVT ratios, the differential ratio and the wheel radius. The area between both lines represents the variable ratios that the CVT follows. The highest ratio slope is shown with a black line and the lowest ratio with the red one. The LabVIEW® code that generates the previous plot can be found in the appendix at the end of the thesis.

60

Figure 5.4: Engine speed vs. vehicle velocity plot. According to the input data for the vehicle considered (SUV) another program was developed for the plots of the variable pulley radii, belt force, torque and power data. This program shows the following useful plots. 2. Variable pulley radii vs. driving pulley contact angle φ : On the left side of figure 5.5 the input data boxes are shown, which depend on the capacity of the IC engine, electric motor, gear ratios, distance between pulleys and the length of the belt. The plot shows the values for the variable pulley radii with respect to angle φ , which is the angle between the x-axis of the driving pulley and the line from the center to the contact point between the pulley and the belt, as shown in figure 5.6. This angle is changing depending on the CVT ratio. 61

Figure 5.5: Variable pulley radii (CVT) vs. angle φ . In figure 5.5 Rps= rps represents the driving pulley radius (black line), while Rpo= rpo represents the driven pulley radius (red line). It can be seen that the crossover takes place at 90° where the radii are equal. These radii are given in inches.

=
¡

High speed

Figure 5.6: Angle φ for high and low speeds used for several plots.

 

=

Low speed

62

3. CVT ratio vs. driving pulley contact angle φ : The plot on figure 5.7 shows the relationship between the CVT ratio and the angle φ (driving pulley contact angle). It can be seen that for this particular case and design, the CVT ratio has a range that goes from 1.45 to 0.30. This is the reason why the gearbox was added on the output shaft, so this ratio can increase to 2.6, which is what a vehicle usually needs. It was found comparable to commercial CVTs such as the Multitronic CVT used in the Audi A4 and A6 which range goes from 2.45 to 0.4 or the Honda Civic HX that goes from 2.47 to 0.45.

Figure 5.7: CVT ratio vs. φ angle.

It can be seen that at an angle of 90° the CVT ratio is 1 this means that both pulleys have the same diameter and are rotating at the same speed.

63

4. Belt force vs. CVT ratio and driving pulley contact angle φ : The following plots in figure 5.8 show the reaction force by the belt, this is useful in terms of design in assuring that the belt used for the CVT is going to handle the maximum amount of force. The first plot shows the relationship between the belt force (lb) and the CVT ratio, while the second one is between the belt force and the driving pulley contact angle φ . It can be seen in both plots that the maximum amount of force is when the CVT ratio is high and the angle is low, this means that the vehicle’ s speed is either zero or in low speed. While the vehicle gains speed the belt force decreases and less amount of power flows through the belt, which makes the system even more efficient.

(a)

(b)

Figure 5.8: (a) Belt force vs. CVT ratio; (b) Belt force vs. φ angle. 5. Driving resistance curves – Torque vs. rpm’s: It has to be taken into account the driving resistance loads as described at the beginning of the chapter. A small program was developed which shows the resistance

64

loads for the CVT ratio range. The input data needed includes the rolling resistance coefficient, the air resistance coefficient, the gross weight of the vehicle, the frontal area, the road grade and the CVT limit ratios. The curves are shown in figure 5.9 and it can be seen that as the rpm’ s increase the resistance torque also increase. The red line represents the lowest CVT ratio (or high speed) and the black one represents the highest CVT ratio (or low speed). This shows that as the vehicle gains speed the driving resistance loads increase considerably.

Figure 5.9: Driving resistance curves – Torque vs. rpm’ s

65

6. Torque vs. driving pulley contact angle φ and CVT ratio: The first plot in figure 5.10 shows the change of torque on each pulley with respect to the driving pulley contact angle φ . As the belt force plots, the maximum amount of torque takes place when the vehicle starts. This torque decreases as the vehicle gains speed. This is due to the fact that it has traction and breaking inertia forces when it starts. It can be seen that at an angle of 90° the crossover takes place and it happens when both pulleys have the same diameter. In the same way the second plot in figure 5.10 illustrates the torque vs. the CVT ratio, which also shows similar results. As the vehicle gains speed the torque reduces. It can also be seen that the crossover takes place when the CVT ratio is 1 and as the previous case this is when the pulleys have the same diameter.

(a) Figure 5.10: (a) Torque vs. CVT ratio (b) Torque vs. angle φ .

(b)

66

In the previous plots the black line represents the torque for Rps = rps, which is the driving pulley and the red line represents the torque for the driven pulley Rpo = rpo of the CVT.

7. Power vs. driving pulley contact angle φ and CVT ratio: Figure 5.11 shows the power plots for both pulleys with respect to the driving pulley angle φ . The power plots show a similar result as the torque plots, the maximum amount of torque is given when the car starts and its in low speed. As it gains speed the power decreases. Again it can be seen that the crossover between the pulleys takes place when the pulley contact angle φ is 90° and when the CVT ratio is 1. As stated before this is because both pulleys have the same diameter at that moment. It can be seen that for this particular design the maximum amount of power that passes through the driving pulley is 210 HP and as it was explained in previous chapters, the power is diverted. An amount of power goes toward the sun gear of the planetary gear train and the other amount flows through the belt. In this case the maximum amount of power flowing through the belt is 100 Hp, which is considerably lower than the power that commercial steel-push belts handle. It reduces more than 50 % of power with the power-split configuration (from 215 HP to 100 HP in this particular example). In the hybrid-electric configuration mode the power flowing through the driven pulley increases according to the power supplied by the electric motor, which can be variable. As the previous cases the driving pulley (Rps) is shown as the black line and the driven pulley (Rpo) with the red line.

67

(a)

(b)

Figure 5.11: (a) Power vs. CVT ratio; (b) Torque vs. angle φ .

8. Acceleration vs. vehicle velocity: The plot for the acceleration range for the CVT ratio vs. vehicle’ s velocity is shown in figure 5.12. The black line represents the highest CVT ratio and the red line is for the lowest ratio. There are many vehicle-input considerations that have to be taken into account such as the wheel radii, the vehicle’ s weight, frontal area, specific weight and the environment temperature. All this inputs depend on the vehicle considered and are easy to determine. As it is shown in figure 5.12 the acceleration decreases as the vehicle gains speed. When constant velocity is reached the acceleration is almost zero and that is what happens in a vehicle. Mostly, acceleration is needed in order to gain speed. This can vary according to driving conditions. If suddenly acceleration is needed, for instance when passing a car in an interstate highway, this plot would look 68

different. If the value for a particular CVT ratio wants to be known, the values for highest of lowest ratio can be changed and the correspondent line would show the plot for that particular ratio.

Figure 5.12: Acceleration vs. vehicle velocity.

This program can be connected to the CVT ratio controller and a single line would show how the vehicle acceleration behaves. This plot shows optimal conditions for the SUV considered.

69

All LabVIEW® codes and programming icons for these plots are shown in the appendix at the end of this thesis. There are four code diagrams the first one is for the engine vs. speed plot, the second one for the driving resistance curves, the third one includes the pulley radii, CVT ratio, belt force, torque and power plots and the last diagram code is for the acceleration vs. velocity plot. The inputs can be changed for any case giving the opportunity to be a useful tool for design.

70

Chapter 6

Control simulation

From the past demands concerning gearshift comfort, drivability and the need for interaction between transmission and other vehicle systems provide the reason for introducing electronic control systems for transmissions. The standard functions of such systems have proven their worth and contributed towards satisfying these demands. For this reason, despite the additional cost, most CVTs require to be computer-electronically controlled. The use of computer-electronically controlled systems in the driveline has increased rapidly. Apart from engine management and brake systems, electronic transmission control systems are the subject of intensive development work. This is not only with the objective of improving comfort and drivability but also for reducing fuel consumption and at the same time increasing efficiency. LabVIEW® software version 6i (as in chapter five for the plots) was used for the development of a vehicle-transmission simulation program, which shows how the control system proposed would work.

6.1

Control method proposed

The aim of this control system besides improving comfort and drivability is the replacement of the driver who is in charge of the gas pedal (VTO) for a controller. This controller has the purpose of following as close as possible the ideal operating schedule of the transmission in the fuel consumption map. Obviously this will reduce fuel consumption and at the same time will increase efficiency.

71

The behavior of the system will be shown in subchapter 6.3 and chapter 7 with a LabVIEW® simulation program, where the velocity can be set at any speed and the program shows simultaneously how the system is working with the CVPST in a hybridvehicle. The block diagram in figure 6.1 shows in general terms how the control system would operate. The input data would be the speed set by the operator and the torque sensor at the shaft connected to the differential and the wheels.

CONTROL SYSTEM Specific fuel consumption map (T vs rpms) Torque Signal Controller Optimum CVT ratio Valve Throttle VTO Opening CVT
Transmission

Estimated Shaft Torque

Vehicle Speed Speed (by Operator) sensor

E. MOTOR

Power

PGT

Diff

Torque Sensor

ENGINE

CVT ratio Power

Figure 6.1: Basic block diagram The torque signal coming from the output shaft is compared with the estimated shaft torque and follows the ideal line on the transmission for the specific fuel consumption map. The controller varies the torque and CVT ratio. By changing these two variables is how the engine follows the best efficient path. The output data coming from the controller is the VTO (amount of gas) to the IC engine, the CVT ratio and a torque signal to the electric motor in case more power is needed and/or when the hybrid-electric mode

72

is operating in the vehicle. Two controllers are going to be needed and it is explained with more detail in the next subchapter.

6.2

Controllers needed in the design

The control system for a hybrid-vehicle is complicated. Implementation of the control hardware is important for reliable execution of the control strategy proposed previously, and for the normal operation of the vehicle. Two different types of controllers are needed for the conceptual hybrid-electric CVPST configuration proposed in this work. • Hybrid-electric modes of operation controller: This control system has been developed already by many of the HEV automotive companies in the market, just to mention a few the Toyota Prius and the Honda Civic.

(a)

(b)

Figure 6.2: Control computer system configuration for the hybrid Toyota Prius (a)Starting and traveling at low speed (b) Full acceleration (Toyota Motor Sales Inc., USA; Romans, Brent; 2000).

In the case of the Toyota Prius it has an Advanced Control System (ACS) that monitors and controls the engine, generator, electric motor and battery pack.

73

The ACS acts as a sophisticated control center that makes important decisions like whether to have the engine on or off, whether to have the generator charge the battery or whether to have the motor drive the wheels or store energy during braking. Figure 6.2 shows two operational cases of the control system for the Toyota Prius. A controller like this one is going to be necessary, which as it was just explained, will be a smart machine and will decide when each component will be operating and will allow to have the different modes of operation shown in chapter 4. Since many of this type of controllers have already been developed and it is not the objective of this work, a control system for this purpose was not proposed in this thesis. However it is important to notice that is needed. This controller would give as an output data the electric motor and engine powers for the second controller. • Transmission and optimum VTO controller: The second controller needed for the hybrid-electric CVPST is proposed in this work. This new concept is for the control of the VTO and the CVT ratio, which will solve the problem addressed at the beginning of this thesis regarding the inefficient way of drivers operating their vehicles. The diagram shown in figure 6.3 explains graphically how this controller would operate. It will have two inputs; the torque in the output shaft coming from a sensor and the speed set by the driver, which will come from the accelerator pedal. The controller will determine the driving resistance torque from the sensor in the output shaft and according to the speed wanted it will determine how much torque is required to reach that speed in the least amount of time in the most efficient way.

74

Figure 6.3: Controller diagram proposed

Accordingly to the torque needed the controller changes the CVT ratio smoothly as it gains speed following the torque-CVT ratio curve. The CVT ratio and the torque supplied by the two sources are changed so the best efficient path in the fuel consumption map can be followed. Finally this controller will allow the VTO to have the smallest opening and will give an output signal to the IC engine’ s throttle. The second output signal would be the CVT ratio given directly to a hydraulic control valve, which will be changing the diameters of the pulleys dependently. The way of operation of this control system will be shown in a LabVIEW® simulator in the next subchapter and chapter 7. It will show how the variable pulleys of the CVT, driving resistance torque, belt force, velocity relationships, VTO and output power are changing. 75

6.3

LabVIEW® simulation

In a typical application the driver controls the VTO and the transmission ratio (with the shift stick). The vehicle responds with acceleration, which depends on the “excess torque” availability (from the engine) and the driving resistance from the road. Typically in an acceleration maneuver the gas pedal is maintained at a high constant VTO level (say 85 %) except when clutching and the operator controls “when” to shift gears. Anecdotal training makes drivers shift when no further speed gain (acceleration) is possible. In the case of a CVT operated vehicle the “controller” will control both the VTO and the transmission ratio. A controller that matches torque and VTO with the best efficient path would improve the overall efficiency considerably, leaving the driver with the only responsibility of controlling the vehicle’ s speed. A software controller simulation was developed for an increased power envelope. It was considered a light-duty hybrid vehicle application (SUV) as described in chapter 5, in which a CVPST can be used to bring the power from two sources (engine and electric motor). The software used for this simulation was LabVIEW® version 6i. Considerations for the development of the program: The pedal velocity is represented as a knob control, where the user can adjust to the velocity wanted. This velocity is simulated by a sub-program, which starting from a random number (close to zero) goes to a number of equations that follow a regular velocity curve. It has some noise to simulate the variation of speed. This noise vibration makes it look like a usual speedometer. The appendix has the program code and by clicking on the icons it opens the subprograms, which show the different equations used

76

for the velocity simulation. For training in LabVIEW® a tutorial manual is available at the following web site http://www.physics.utoledo.edu/~alukasz/labview_tutorial.PDF. Two more knob controls are set for the power adjustment, one for the IC Engine and the other one for the electric motor. According to the input torque by this two sources and the velocity set, an equation calculates the change on the CVT and changes the rpm’ s as the velocity is increasing; trying to maintain the revolutions at a speed of 3 100 rpm’ s at 65 mph (104.6 km/h). At this velocity, by controlling the break mean effective pressure, the VTO can spend most of the time within the ideal curve as shown in figure 6.4.

Figure 6.4: Specific-fuel consumption map for a V-8 engine 300 in3 (Gillespie, 1992) A number of input values are required to run the simulation. Depending on them the plots are going to change and some times show inaccurate results. The input values needed for the program are: • Vehicle characteristics: Wheel radius, differential ratio, gross weight and frontal area. The values considered for the example of the SUV were 16 in (406.4 mm), 4.0,

77

4760 lb. and 31.1 ft 2 respectively. The power knob controls goes from 0 to 225 HP for the IC Engine and from 0 to 175 HP for the electric motor. • Driving resistance coefficients: Such as the rolling resistance, air resistance and road grade coefficients. The values considered were 0.03, 0.41 and 0.02 respectively. • Planetary gear train characteristics: These values can be changed arbitrarily for design purposes and the results and behavior can be seen simultaneously in the plots. These input data includes the number of teeth and radii at the sun, ring, planet, counter-shaft and control gears. According to the total input torque and the rpm’ s, the CVT ratio will be increasing its ratio from an equation relationship and will be shown in a waveform chart.
1.2

1

y = 5E-08x - 0.0003x + 0.9854
0.8

2

VTO

0.6

0.4

0.2

0 0 1000 2000 3000 4000 5000 6000

rpm

Figure 6.5: VTO vs. rpm’ s ideal curve (line with dots) compared with parabolic equation developed (black line).

78

As the CVT ratio changes with the velocity and rpm’ s the VTO will follow the ideal curve for the fuel consumption chart as closely as possible. A second order equation was developed for the parabola that passes through the curve generated by the VTO vs. rpm’ s as closely as possible, where the break mean effective pressure is considered to increase constantly with the rpm’ s. This parabola is shown in figure 6.5. The value of the VTO is shown with respect of time in another waveform chart. With all the remaining input data equations for the input/output velocity relationship, belt force, variable radii pulleys and power were developed and introduced in the program. The results are shown in waveform charts and change as the velocity and power controls are adjusted to different values. The driving resistance forces are calculated and shown in the same plot of the total power out by the CVPST. Also it is shown how these driving resistance forces affect the output power on the transmission. Finally it is displayed a third curve in the same plot for the power left available in the system. When the output power by the CVPST is close to the driving resistance curve it means that more power is required. If more power is not available, that means that the maximum amount of power capacity by the vehicle has been reached. The knob control panels can always be changed to different limit values by just clicking on the numbers and changing them to the desired limits. This also allows the possibility to use any kind of IC engine or electric motor. Unfortunately this simulator was designed only for a SUV as an example of application. Therefore the torque-rpm’ s and VTO ideal curves were considered for this vehicle. Also the hybrid-electric CVPST was considered with two power sources input. In case a

79

different vehicle wants to be simulated with this configuration (hybrid-electric CVPST) the equations for the torque-rpm’ s and VTO ideal curves have to be changed.

Recommendations while using the software: The vehicle and driving resistance coefficients, which are input data, have to be real values from vehicle specification and technical papers. If some of these values are guessed, they may give imprecise results. Also if the PGT gear ratios and radii are unknown, it has to be considered that the number of teeth and radius of the ring gear is higher than the planet and sun gears. Also the number of teeth for any case has to make sense with the radius of the gear. If a very slow speed is maintained (close to zero) the output power and belt force increases considerably, this is because there are some equations that tend to go to infinity when it approaches zero. This is the only limitation with this program.

Program environment: When the program is accessed, on the upper left hand the knob controls for the velocity and power sources can be seen. On the right upper hand the different boxes for the vehicle and driving resistance coefficients are displayed. On the lowest part of the right side the indicators for the PGT ratios and radii can be seen. Once all the input data is given, the program can be run by going to the “ operate” tool bar on the top and clicking the first option “ run” . While the program is running the velocity and the two power sources can be changed as desired. The plots will be changing simultaneously as the controllers are being moved. The program can be stopped by either clicking the stop

80

indicator on the main screen or going to the “ operate” tool bar again and clicking the second option “ stop” . Figure 6.6 shown in the next page shows how the environment of the simulator looks like while it is running at 155 km/h for 170 HP at the IC engine and 125 HP at the electric motor. Different test and scenarios are considered to see how the program works. They are shown in the next chapter. This program could be a useful design tool for PGTs and CVTs since the values for the ratios and radii can be changed while the results can be seen simultaneously.

81

Figure 6.6: LabVIEW® environment for the hybrid-electric CVPST simulator for a SUV.

82

Chapter 7

Simulation tests and results

The aim of developing a software program for the hybrid-electric CVPST proposed was to see the results of this configuration and how it behaves under certain conditions. Three cases were considered, which are low, medium and high speed. On these cases it can be seen how the transmission works when there is low, medium and high torque and how the VTO tries to follow the ideal fuel consumption curve as close as possible. As explained in the previous chapter the driving resistance forces, angular velocity relationships, belt force, CVT ratio and power are shown in different plots as the velocity and input powers are being changed. For the three cases the program tries to reach the input velocity (provided by the operator) in the least amount of time.

7.1

Case I: Low speed

For this case the velocity was set at 17.8 mph (28.7 km/h), which corresponds to 800 rpm’ s to demonstrate a low speed when the vehicle starts running. In this event if enough battery is available the car can be propelled by the electric motor itself set to 100 HP and the IC engine can be left offline. From the waveform charts on figure 7.1 it can be seen that the CVT ratio has a high ratio value close to 2.4, which is the high ratio for conventional CVTs in the market. The output/input angular velocity relationship has a small value due to the low speed; this means that the output shaft is rotating very slow compared to the input shaft. The belt force is close to 70 lb. and the power available is high, this is because the engine has to overcome inertia, friction and resistance forces. The driving resistance forces are very small due to the fact that at low speed there is not

83

much air and rolling resistance. This forces increase as the vehicle gains velocity. At the variable pulley chart the driven pulley has a big diameter (8 in.) while the driving pulley has a small value (4 in.) and this makes sense with the angular velocity plot where the output shaft rotates slower than the input shaft. In this case a second arrangement possibility is that the IC engine supplies all the power instead of the electric motor. Since there is plenty of power left a big percentage of it can go to the electric motor/generator and recharge the batteries.

84

Figure 7.1: Hybrid-electric CVPST LabVIEW® simulation for case I. 85

7.2

Case II: Medium speed

In this case the velocity was set at 60 mph (96.7 km/h) to demonstrate a medium speed. For this example the hybrid-electric variable split mode can be used; the car is propelled by both input power sources (IC engine and electric motor) set to 100 HP each one. In this case less than half of the power capacity of the IC engine and more than half of the electric motor are being used. This configuration can vary depending on the battery level. If recharging is required, then the IC engine increases power and a portion goes to the electric motor/generator. These input power variations are controlled by the hybridelectric modes of operation controller as stated in previous chapters. From the waveform charts on figure 7.2 it can be seen that the CVT ratio decreases to 1.2, which is when both pulleys in the variator have almost the same diameter. The driving pulley has a slightly smaller diameter (4.7 in.) compared with the driving pulley (5.3 in.). Having both pulleys at the same diameter is the most desirable condition due to the fact that less friction losses are present and less power is transmitted through the variable transmission as the vehicle gains speed. Also there is less possibility of slippery between pulley and belt. One of the parameters taken into account for the controller design was that when the vehicle reaches 60 mph (which is usually the limit speed at interstate highways) the engine should be around 3000 rpm’ s and follow the best path for the VTO possible. This way fuel consumption reduces considerably and it spends most of the time in the ideal line. As it can be seen on the waveform chart in figure 7.2 at this velocity the VTO has a low value (close to 50 %), which is the objective of this controller.

86

The output/input angular velocity relationship increases its value to approximately 2.0. Compared to the previous case it can be seen that the belt force decreases considerably because of the gain in speed, however resistance forces start to increase. In this case if a hybrid-electric mode is to be avoided, the IC engine has to propel the vehicle at its maximum capacity so that the battery can be recharged. On the other hand if the batteries are charged already the electric motor can be used at its maximum capacity. But the most desirable configuration would be the hybrid-electric mode where both power sources supply an amount of their power. In that way the power-split mode can take place with less power flowing through he variator.

87

Figure 7.2: Hybrid-electric CVPST LabVIEW® simulation for case II.

88

7.3

Case III: High speed

For this last case the velocity was set at 113.7 mph (183 km/h) to signify high speed and demonstrate the use of the design at its maximum power capacity. In this example the hybrid-electric variable split mode has to be used. The car is propelled by both input power sources (IC engine and electric motor) at almost their maximum capacity 225 HP and 170 HP respectively. This configuration depends on the capacity of the battery, for instance when battery recharge is required the IC engine works by itself at its maximum capacity splitting an amount of its power to the electric motor/generator and the other amount to drive the vehicle. Consequently the vehicle’ s speed would have to be reduced. From the waveform charts on figure 7.3 it can be seen that the CVT ratio decreases to almost 0.5, which is the lowest ratio for commercial CVTs in the market. It can be seen that this design satisfies the higher and lower ratios that most of conventional CVTs have. Since at high speed the transmission is in overdrive the variable pulley diagram shows that the driving pulley has a bigger diameter (close to 5 in.) compared with the driven pulley (3 in.). This also can be shown with the output/input angular velocity relationship chart, which has a high value (above 2.5) signifying that the output shaft is rotating two and half times faster than the input shaft. The simulations for the three cases were considered to start from a zero velocity and reach either a low, medium or high speed in the least amount of time. For the VTO waveform chart it can be seen that it follows a “ U” curve reaching its efficient point at the bottom of the curve when the vehicle reaches 60 mph. Nevertheless it starts going up until it reaches more than 80 % of its opening, which is not a very efficient state and stays in a straight line at that percentage.

89

Figure 7.3: Hybrid-electric CVPST LabVIEW® simulation for case III

90

The belt force compared to the previous case it does not decrease much. Reduces to approximately 15 lb. This value does not change much when the vehicle has gained a medium speed. In the total power waveform chart from figure 7.3 it can be seen that driving resistance forces have increased to almost 300 HP; the resistance forces are an issue at this point. This is the reason why the vehicle has to use both of its power sources so that it can overcome all this forces and gain the desired speed following the most efficient fuel consumption path. Analyzing the chart in this example, almost all the power capacity was used and it has 100 HP extra. This amount of power can allow to either leave one of the input power sources drive the vehicle or it could help the vehicle to gain some more speed. When the battery runs out of power the speed has to reduce due to the fact that a power source (electric motor) is not going to be available and less power is left to drive the vehicle. Also in this third case the power is always going to be diverted because both power sources are going to be on line. At high speeds CVTs are known to be less efficient (Hsieh, Yan, 1990 and Bonthron A.), however not much of the power split in this configuration flows through the belt and it does not become an important issue.

91

Chapter 8

Final comments

8.1

Conclusions:

A new hybrid-electric CVPST system has been proposed. This design has the advantage of having the second power source (electric motor) connected to the output shaft of the CVT. Having this configuration, when the electric motor is working, less amount of power flows from the engine through the variable elements and therefore friction loses are reduced yielding a more efficient transmission, yet with variable ratio. The simulator shown previously provides the behavior of the system under three basic conditions (which depend on the desired speed). Results are consistent and illustrate that for a medium speed (or at a speed limit, which in the majority of interstate highways is 60 mph) the controller will have the throttle opening of the engine in almost its lowest percentage possible (around 50 %). Therefore Case II in Chapter 7 yields the most desirable condition for the vehicle to operate. This means that if the velocity remains constant, the engine will spend most of the time in its fuel consumption ideal range. If more speed is required, it can be seen that this VTO increases its level, however it still follows the ideal curve and does not go above 85 %. Due to the fact that fuel consumption is being reduced and less fuel is being burned and delivered to the environment, it is inferred that emissions would be less although this demonstration is left for future work. Since a variable transmission is being used, the contention can be made that the IC engine spends more time in its optimum operating range. Yet, from previous works (Hsieh, Yan, 1990 and Bonthron A.) it is also known that CVTs are less efficient as speed increases. 92

However, on the belt force simulation results, it can be seen that as the vehicle gains speed the belt force decreases significantly, which in turn reduces the power flow through the variable transmission and thus reduces the friction losses in the variable elements. This simulator is a very useful tool for design purposes. It provides basically all the data required for the analysis of a hybrid-electric CVPST in terms of velocity relationships, forces, power, variable pulleys and VTO. All this data can be simulated in real time by changing vehicle characteristics, resistance coefficients and PGT dimensions. The simulator helps on visualizing the range of the CVT and therefore on its design. It also helps on the design of a proper PGT dimensions. It is hoped that the work of this thesis will help demonstrate alternate applications for CVTs in automotive industry.

93

8.2

Future work:

The simulator proposed could have additional charts and information that could be useful for the designer. An acceleration and efficiency chart would be helpful on the analysis of how the system is behaving. Secondly, an IC engine map has to be developed for the one considered on the design and the ideal fuel consumption curve information has to be programmed into the simulator. In addition, a comprehensive design for the drivetrain has to be developed. This means that the detail engineering on the dimensions for the gears of the PGT, variable pulleys, belt, bearings, clutches, brakes, etc. has to be done. Then it is ready for some experimental tests. It has to be mentioned that all the results with this simulator and design were considered conceptually due to the fact that a vehicle and control instrumentation was not provided. These results can vary upon environmental conditions and external forces. The future work (after having the comprehensive design finished) would be to conduct experimental tests and prove the accuracy of this design with data acquisition (in real vehicles). It is also left for future work to synchronize the controller proposed in this work with the second controller needed, which is the operational mode controller. After having these two controllers synchronized the two power inputs for the hybrid-electric controller would be the output data from the operational modes controller and it would be left to the driver to just control the speed of the vehicle making it follow its best fuel consumption line. Finally this work could follow a study regarding emissions control. While the throttle opening, torque and CVT ratio are being controlled; fuel consumption is made to follow

94

its ideal line. Future work needs to prove the fact that saving fuel also represents reduction in emissions considering the different modes of operation of this design.

95

APPENDIX:
LabVIEW® diagram codes

96

Figure A.1: LabVIEW® diagram code for the engine speed vs. vehicle velocity plot.

97

Figure A.2: LabVIEW® diagram code for the driving resistance curves.

98

Figure A.3: LabVIEW® diagram code for the pulley radii, CVT ratio, belt force, torque and power plots. 99

Figure A.4: LabVIEW® diagram code for the acceleration vs. vehicle velocity plot.

100

Figure A.5: LabVIEW® diagram code for the hybrid-electric CVPST simulator. 101

REFERENCES
• Anderson, John; “ Designing and modeling a torque and speed control transmission” ;WVU, 1999 • Beard, John; Haapala, Karl; Thul, Aaron; Andrasko, Steve; Muehlfield, Christian; Brandon, Bloss; Richard, Nesbitt; “ Design and development of the 2001 Michigan Tech future truck: a power-split hybrid-electric vehicle” ; MTU, 2001 • Bonthron, Anders; “ CVT-efficiency measured under dynamic running

conditions” ; SAE Technical Paper No. 850569 • Cowan, Ben; “ Variable speed transmission” ; U.S. Patent No. 5167591; December 1992 • • Cowan, Ben; “ Variable speed transmission” ; U.S. Patent No. 5215323; June 1993 Fujii, Toru; Kusano, Takayuki; Takahashi, Mitsuhiko; Kiji, Takafumi; “ Study on forces transmitting between pulleys and blocks of a block-type CVT belt” ; SAE Technical Paper No. 921746 • Fujii, Toru; Kurokawa, T.; Kanehara S.; “ A study of a metal pushing v-belt type CVT-Part1: relation between transmitted torque and pulley thrust” ; SAE paper No. 930666 • Fujii, Toru; Kurokawa, T.; Kanehara S.; “ A study of a metal pushing v-belt type CVT-Part 2: compression force between metal blocks and ring tension” ; SAE paper No. 930667 • Gillespie, Thomas D.; “ Fundamentals of vehicle dynamics” ; SAE Chapters 1-4; 1992.

102



General Motors LX5 3.5L V6 Model 2000 engine’ s website; Pictures taken from http://www.gm.com/automotive/gmpowertrain/engines_cartruck/other/35_main.ht m



Hedman, A.;Jacobson, B.; Mattsson, P.; “ Frequency functions in driveline and vehicle performance simulation” ; VDI Berichte 1007, pp. 181-190; 1992.



Hendriks, Emery; ter Heegde, Paul; van Prooijen, Tom; “ Aspects of a metal pushing v-belt for automotive CVT applications” ; SAE Transactions Vol. 97; SAE Technical Paper No. 881734; 1988



Hybrid-electric powered high mobility multipurpose wheeled vehicle (HMMWV) developed by PEI Electronics, Inc.; Electric motor picture was taken from the link http://winnetou.lcd.lu/oinet001z/hoffmann/hybrid.html



Hsieh, L.; Yan, H.; “ On the mechanical efficiency of continuously variable transmissions” ; U.S. Patent No. 4967556; November 6, 1990.



Kawahara, Eiichiro; “ Hydraulically operated continuously variable transmission” ; U.S. Patent No. 4944154; July 31, 1990



Kaz; WongKN; “ The temple of VTEC Asia special focus on the Multimatic transmission” ; October 2000; Honda’ s Multimatic Technology Page

http://asia.vtec.net/article/mmt/ • Kuen-Bao; Shen-Tarng; Wen-Ming; Ting-Shan; Hong-Sen; “ New automatic hybrid transmission for motorcycles” ; Proc. Natl. Sci. Counc. ROC(A) Vol. 23; pp. 716-727; November 6, 1999.

103



Kumm; Emerson, L.,; “ Continuously variable transmission using planetary gearing with regenerative torque transfer and employing belt slip to measure and control pulley torque” ; U.S. Patent No. 5011458; April 30, 1991



Lemmens, John; “ Continuously variable automatic transmission” ; U.S. Patent No. 3850050; November 26, 1974



Lemmens, John; “ Variable speed transmission” ; U.S. Patent No. 3641843; February 15, 1972



Machida, Hisashi; Murakami, Yasuo; “ Development of the PowerToros unit half toroidal CVT” ; Research and development center NSK; October 2000.



Mattson, Per; “ Continuously variable split-power transmissions with several modes” ; Machine and vehicle design department in Chalmers University of Technology; 1993



Mucino, V. H.; Smith, J. E.; Cowan, B.; Kmicikiewicz, M.; “ A continuously variable power split transmission for automotive applications” ; SAE Technical Paper No. 970687; 1997



Nice, Karim; “ How hybrid-electric cars work” ; How stuff work electronic document; 2003; Web link: http://auto.howstuffworks.com/hybrid-car.htm/printable



National Instruments Corporation; “ LabVIEW® manual of contents” ; Part number 320998A-01; January 1996; Web link: http://www.physics.utoledo.edu/~alukasz/labview_tutorial.PDF



Nissan Motor Corporation Ltd.; Minoru, Shinohara; Takashi, Shibayama; Kunio, Ohtsuka; Katsumi, Nawata; Shigeru, Ishii; Hiroshi, Yoshizumi; “ Nissan

electronically controlled four-speed automatic transmission” ; SAE Technical Paper No. 890530

104



Nissan Motor Corporation Ltd.; Hiroshi, Yamaguchi; Yasushi, Narita; Hiroshi, Takahashi; Yuji, Katou; “ Automatic transmission shift schedule control using fuzzy logic” ; SAE Technical Paper No. 930674



Palmer, R. S. J.; Bear, J. H. F.; “ Mechanical efficiency of a variable speed fixed center v-belt drive” ; ASAE Transactions J of Engineering for Industry; pp. 771-779



Petersmann, Josef; Seidel, W.; Môllers; “ Porsche carrera 2 Tiptronic transmission” ; Porsche Entwicklungszentrum; SAE Technical Paper No. 901760



Romans, Brent; Hybrid Highlights “ Road test: 2001 Toyota Prius” ; Hybrid-electric configuration diagrams (Toyota Motors Sales, Inc. USA); December 12, 2000; Web link: http://www.edmunds.com/reviews/roadtests/roadtest/43877/page5photo.html



Schwab, Manfred; “ Electronically-controlled transmission systems – current position and future developments” ; Zahnradfabrik Friedrichshafen AG; SAE Technical Paper No. 901156; 1994



Shellenberger, Michael; “ Design considerations for variable power split hydraulic drives for industrial applications” ; WVU 1999



Takayama; “ Continuously variable transmission” ; U.S. Patent No. 5050457; September 24, 1991



Toyota Motor Corporation; Toyota Prius technical specifications; Web link: http://www.toyota.com



Vibrate Software Webpage; “ Continuously variable transmissions” ; March 2003; http://www.vibratesoftware.com/html_help/html/Diagnosis/Reference/CVT_Transmi ssions.htm#Saturn

105



Volvo Car Corporation; “ History web-electronic document” ; Web link: http://www2.car.volvo.se/cars/history/66.html



Wouk, Victor; “ Hybrid-electric vehicles history” ; Scientific American article; October 1997



Y., Taga; K., Nakamura; H., Ito; “ Toyota computer controlled four-speed automatic transmission” ; SAE Technical Paper No. 820740



Zhijian, Lu; “ Acceleration simulation of a vehicle with a continuously variable power split transmission” ; WVU July, 1998

106

VITA
Miguel M. Gomez was born on November 15th in Mexico City, Mexico. At an early age he moved to a nearby city called Queretaro. He did his undergraduate studies at Queretaro Institute of Technology for a B. S. degree in Mechanical Engineering. He worked as a design engineer in technology development at CIATEQ (Technology Development Center of Queretaro) for one and a half years in the areas of machine design and automation where he worked on several projects for different companies. He entered a Masters study program promoted by the Council of Science and Technology in the State of Queretaro (CONCYTEQ) and also was sponsored with a scholarship by the Mexican National Council of Science and Technology (CONACYT). This program’ s objective was to encourage students to study abroad. Miguel finally pursued his Masters studies in Mechanical Engineering at West Virginia University where he is about to graduate.

107

Sponsor Documents

Or use your account on DocShare.tips

Hide

Forgot your password?

Or register your new account on DocShare.tips

Hide

Lost your password? Please enter your email address. You will receive a link to create a new password.

Back to log-in

Close