58 IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 5, NO. 1, MARCH 2000 Mechatronic Design and Control of Hybrid Electric Vehicles Bernd M. Baumann, Gregory Washington, Bradley C. Glenn, and Giorgio Rizzoni, Member, IEEE Abstract—The work in this paper presents techniques for de- sign, development, and control of hybrid electric vehicles (HEV’s). Toward these ends, four issues are explored. First, the develop- ment of HEV’s is presented. This synopsis includes a novel defi- nition of degree of hybridization for automotive vehicles. Second, a load-leveling vehicle operation strategy is developed. In order to accomplish the strategy, a fuzzy logic controller is proposed. Fuzzy logic control is chosen because of the need for a controller for a nonlinear, multidomain, and time-varying plant with mul- tiple uncertainties. Third, a novel technique for system integration and component sizing is presented. Fourth, the system design and control strategy is both simulated and then implemented in an ac- tual vehicle. The controller examined in this study increased the fuel economy of a conventional full-sized vehicle from 40 to 55.7 mi/h and increased the average efficiency over the Federal Urban Driving Schedule from 23% to 35.4%. The paper concludes with a discussion of the implications of intelligent control and mecha- tronic systems as they apply to automobiles. Index Terms—Automotive control, hybrid vehicle control, intel- ligent control of automobiles. I. INTRODUCTION S INCE the oil crises of the 1970’s, fuel economy has been one of the dominant issues in automobile performance. Achieving the lowest possible fuel consumption helps to save natural resources and is more economical for consumers. It also translates directly into lower emissions. Often in contrast with these requirements, customers continue to demand increasing comfort and performance. In general, there are two methodolo- gies that can be employed to reduce the fuel consumption of an automobile [1]: 1) reducing losses such as aerodynamic drag, rolling resis- tance, and braking losses due to the vehicle inertia; 2) increasing the efficiency of energy conversion. While the first approach relates to design and structure of the vehicle’s body and, therefore, to the vehicle concept, the second approach relates to the power train. Three ways of developing more fuel-efficient power trains can also be identified: 1) optimization of existing power-train components [e.g., di- rect injection (DI) technology for internal combustion en- gines (ICE’s)]; Manuscript received July 17, 1998; revised May 10, 1999 and December 1, 1999. Recommended by Technical Editor H. Peng. This work was supported by the National Renewable Energy Laboratory. B. M. Baumann is with DaimlerChrysler Research and Technology, D-70546 Stuttgart, Germany. G. Washington, B. C. Glenn, and G. Rizzoni are with the Department of Me- chanical Engineering, The Ohio State University, Columbus, OH 43210 USA. Publisher Item Identifier S 1083-4435(00)02470-4. 2) development of new power train components (e.g., fuel cell technology, flywheels, and ultracapacitors); 3) combination of existing power-train components into hy- brid drivetrains. The work presented in this paper focuses on control issues arising from the implementation of hybrid drivetrains. In order to accomplish this task, the basic concepts of hybrid vehicles (HV’s) will be explained and a load-leveling strategy for a parallel hybrid electric vehicle (HEV) will be presented. An application-oriented overview of fuzzy logic control (FLC) will demonstrate its suitability for the control of HV’s. The implementation of a supervisory controller, which coordinates an ICE and an electric machine (EM), will also be presented. The system will then be compared to existing control strategies. Finally, the strategy will be demonstrated on an actual vehicle. The study of HV’s and their control is not new. Many re- searchers have engaged in the development of hybrids at var- ious levels since the 1970’s [11]–[25]. While the development of HEV’s is a rapidly advancing topic that has led to implemen- tation and simulation, the development of advanced control al- gorithms (at least, that reported in the open literature) has not kept pace with hybrid design [12]–[24]. Novelty in the work presented in this paper is evident in three areas: 1) this study represents the first reported usage of an intelligent controller, FLC, in an HEV; 2) this study defines and quantifies a mecha- tronics based term for classifying HV’s. This new terminology is called degree of hybridization (DOH); and 3) this study also defines a novel mechatronics-based technique for initial sizing of the ICE and the EM in a hybrid-electric power train. II. HEV’S The 1913 Webster Dictionary explains the word “hybrid” as “the offspring of the union of two distinct species” and as being “produced from the mixture of two species.” An HEV can, thus, be seen as a mixture of an ICE-powered automobile and an elec- tric vehicle (EV). When designing an HV, two major issues must be resolved. The first is: how does one size the EM and ICE? This is one of the most complicated issues in constructing the hybrid drivetrain. Traditionally, simulations have been used to find a good mix of ICE and EM. These simulations may be com- plex and time consuming. The second issue involves the choice of a proper operation strategy. These issues represent compo- nents of ongoing research but one possible solution can be found using the “synergy” principle of mechatronics. In other words, the overall system configuration and control strategy should make the final product better than just the addition of the in- dividual components themselves. 1083–4435/00$10.00 © 2000 IEEE