2008:217 CIV MASTER'S THESIS Automotive Hybrid Technology Status, Function and Development Tools Gustaf Lagunoff Luleå University of Technology MSc Programmes in Engineering Mechanical Engineering Department of Applied Physics and Mechanical Engineering Division of Machine Elements 2008:217 CIV - ISSN: 1402-1617 - ISRN: LTU-EX--08/217--SE Abstract A diminishing oil reserve and increased environmental concern puts new demands on our vehicles. This thesis aims to identify the strengths and weaknesses of a conventional vehicle and explain the technology behind. Alternative energy sources are introduced and together with the knowledge learnt, their potentials are discussed. Unfortunately, none of them can be found to fulfil all future demands. Instead, hybrid vehicles are identified as a solution with high potential. Hybrid vehicles are consequently defined and the additional components are explained. The multiple energy sources of a hybrid vehicle bring increased drivetrain flexibility but also increased control complexity. With the goal to enhance the fuel economy and reduce emissions, optimum operating conditions are discussed for each drivetrain component and concrete control targets are extracted. Due to the complexity, computer modelling and simulation are expected to be an essential tool when it comes to hybrid vehicle development and optimization. As a result, cost efficient component models are suggested and finally a number of control optimization procedures are compared. The result of this thesis is a summary of relevant knowledge needed to reduce the development effort of hybrid vehicles. The key aspect is to understand the synergy effect of a hybrid drive train which enables the designer to approach the full potential of each component. [i] Acknowledgements It is funny, even though this thesis is the end of a long journey for me; it feels like the subject itself is the beginning of something new. I am very grateful for my time at Luleå University of Technology and I still hope that every day ahead gives me the opportunity to learn something new. I would like to thank senior teacher Elisabet Kassfeldt at LTU for her support on all levels and Professor Björn Kjellström at LTU for his feedback regarding internal combustion engines. From Haldex I would like to thank my supervisor Andreas Lindin for his support and department director Daniel Hervén for his support and for the opportunity to work with Haldex in the first place. Finally, many many thanks to my family for their pep ups and support throughout all of my education and a special thanks to my dear friend David Wiberg for his more or less constructive opinions. [ii] TABLE OF CONTENTS 1. INTRODUCTION 1 1.1 PROBLEM FRAMING 1 1.2 OBJECTIVES 2 1.3 DRIVING FORCES 3 1.4 SOURCE CRITICISM 9 1.5 MAIN RESULTS 9 1.6 OUTLINE 10 2. VEHICLE ENERGY EFFICIENCY 11 2.1 DEFINITION OF FUEL ECONOMY 11 2.2 CARBON FOOTPRINT 12 2.3 WHAT AFFECTS THE FUEL ECONOMY? 12 2.4 POSSIBLE ACTIONS AND THEIR POTENTIAL 13 3. DRIVETRAIN COMPONENTS IN A CONVENTIONAL VEHICLE 15 3.1 INTERNAL COMBUSTION ENGINE – THE PRIMARY FUEL CONVERTER 15 3.2 TRANSMISSION 35 3.3 DIFFERENTIALS 41 3.4 AUXILIARY SYSTEMS 41 4. VEHICLE PROPULSION ALTERNATIVES 42 4.1 CONVENTIONAL VEHICLES 42 4.2 ELECTRIC VEHICLES 44 4.3 FUEL CELL VEHICLES 44 4.4 HYBRIDS 45 4.5 THE CUSTOMER POINT OF VIEW 46 4.6 NOW, TOMORROW AND THE FUTURE 47 5. WHAT IS A HYBRID? 48 5.1 HYBRIDS IN HISTORY 48 5.2 HYBRID CARS 49 6. SOURCES OF HYBRID POWER AND ENERGY STORAGE 51 6.1 HUMAN 52 6.2 ENVIRONMENTAL 53 6.3 PNEUMATIC AND HYDRAULIC 55 6.4 FLYWHEEL 58 6.5 ELECTRICAL 61 [iii] 6.6 CHOOSING HYBRIDIZATION METHOD 66 7. DEGREE OF HYBRIDIZATION AND OPERATING MODES 68 7.1 MEASURING THE DEGREE OF HYBRIDIZATION 68 7.2 OPERATING MODES 71 7.3 DOH CLASSES 72 7.4 PHEV’S ELABORATED 77 7.5 CONCLUSIONS REGARDING THE DOH 77 8. DRIVETRAIN STRUCTURES 78 8.1 CONVENTIONAL 79 8.2 PARALLEL HYBRID 80 8.3 SERIES HYBRID 82 8.4 COMBINED (SPLIT) HYBRID 84 8.5 ALL WHEEL DRIVE, AWD 85 9. COMPONENTS OF A HYBRID ELECTRIC DRIVETRAIN 91 9.1 ELECTRICAL ENERGY STORAGE DEVICES 91 9.2 ELECTRICAL MACHINES 112 9.3 POWER ELECTRONICS 119 9.4 ELECTRIFIED AUXILIARY SYSTEMS 123 9.5 ADDITIONAL MECHANICAL DEVICES – POWER SPLIT 126 10. MODELLING 127 10.1 MODEL DEPTH AND FIDELITY LEVEL 127 10.2 ICE MODELLING 127 10.3 TRANSMISSION MODELS 130 10.4 VEHICLE DYNAMICS 132 10.5 VIRTUAL DRIVER AND DRIVING CYCLES 134 10.6 ELECTRICAL MACHINE MODELS 137 10.7 BATTERY MODELS 139 10.8 ULTRA CAPACITOR MODELS 141 10.9 POWER ELECTRONIC MODELS 141 10.10 AVAILABLE SIMULATION PLATFORMS 142 11. CONTROL 145 11.1 SYNERGY IS THE KEY 145 11.2 WHERE TO START 145 11.3 KEY COMPONENT CONTROL ASPECTS 146 11.4 PROCEDURES 149 11.5 REGENERATIVE BRAKING 156 12. FUTURE WORK 160 [iv] REFERENCES 161 APPENDIX A – PUGH MATRIX 167 APPENDIX B – NOMENCLATURE 168 [v] 1. Introduction This thesis is intended as a compilation of relevant knowledge to act as an incentive and basis for hybrid vehicle design and development. It consists of, among other things; the background and current status of hybrid vehicle technology as well as the fundamentals of important components. The text aims to be interesting and instructive to a wide range of readers and the main goal is to enlighten the potential and synergy-behavior of a hybrid vehicle drivetrain. 1.1 Problem framing If you are reading this text you have probably not missed the increased environmental concern and the lively debate regarding the increased oil price the last couple of years. On top of that, when the world’s largest oil consumer, i.e. the USA, reduces its car use by 5.4 % in August 2008 compared to the last year, it is evident that something is happening in the world of transport [Teknikens Värld]. In the end it all comes down to one thing, supply and demand. It is widely accepted that our crude oil resources will start to fall in a couple of years [EIA] while the total need for personal and freight transportation most likely will not. The result, all according to the supply and demand relationship, will keep on pushing the oil prices upwards. At the moment (2008-11-17) we are in the middle of a world-wide recession of the business cycle which in addition has hit the automotive industry especially hard. Together with a strengthened dollar, the oil price has dropped again [OPEC] but in the long term, supply and demand will rule. Extended to the next step, and as mentioned already noticed as a drop in US car use, the reaction to the increased transportation costs are strong and new alternatives are immediately sought for [Teknikens Värld]. Furthermore, as a reaction to proof of man kinds negative effect on the environment (which will be mentioned again later), an increased environmental interest has aroused worldwide [Johansson]. Due to the contribution from light and heavy vehicles, new legislation and emission targets are constituted around the world to limit our bad influence. As a result, new and tougher demands are put on vehicle manufacturers and in the end the customer. Once again ruled by supply and demand the new emission targets will, together with the diminishing fossil fuel reserve, act as a catalyst in the automotive industry and open new doors. There are many ways to reduce the use of fossil fuel and methods available to try and reach stringent emission demands. However, none of them offers a single solution to all problems. Instead it can be expected to be a combination of a few technical enhancements and energy sources etc. but one of those doors contains hybrid vehicle technology… [1] 1.2 Objectives The objective of this thesis can be divided into three parts, beginning with some useful information about the powers of the automotive industry together with a brief look at concerned parts of the environmental situation. By presenting the wide picture coupled with a concrete problem framing the reader is encouraged to gain interest in the challenging future of vehicle technology. The second part is devoted to the coherence and functionality of vehicular drivetrain components. Based on the drawbacks of a conventional vehicle and the general goals, this part tries to define, explain and compare alternative and enhanced technical solutions. From and including the latter half, the content is pervaded by the core subject, i.e. hybrid technology and hybrid electric vehicles in particular. Part three is aimed at applying the gathered knowledge into a future design process and exemplifies how it can be done in an effort-efficient way. Computer modeling and computer assisted control optimization is identified as powerful resources and an approach is suggested. Furthermore, some parts are directly intended to act as useful development tools related to the “Haldex eBAX” which is an internal hybrid vehicle project within the Haldex Traction AB corporation. [2] 1.3 Driving forces The main driving forces behind the development of hybrid vehicle technology, and hence this thesis, have already been briefly mentioned but let us take a closer look. 1.3.1 The oil price The oil price is governed by a number of geological, financial and political parameters etc. which nature is not in the scope of this thesis. Instead, a more important question is: how has the oil price changed throughout time and does it affect the automotive industry? Figure 1 - Crude oil prices 1920- 2007 [BP] Figure 1 visualizes the crude oil price between 1920 and 2007.