Symposium on International Automotive Technology 2009 1Kensuke Itou, Takeshi Fujita, Ryota Shirato and Toru Akiba Nissan Motors Co. Ltd., JapanA Study of Novel Traction Control Method for Electric Motor Driven VehicleSAE Paper No. 2009-26-039 Copyright © 2009 The Automotive Research Association of India, Pune, India ABSTRACT Electric-motor-driven vehicles have attractive performance attributes not only for environmental solutions but also for vehicle motion control. An electric motor offers significant advantages such as fast torqueresponse, accurate estimation of torque output and the possibility of distributing motors independently in each wheel. These advantages effectively contribute toadvanced motion control. In this study, two feedback controllers were constructed for skid prevention during vehicle acceleration. A model-following controller wasused to consider the influence of back electromotive force and a slip ratio controller was used to consider the interaction between traction wheels. INTRODUCTION Electric-motor-driven vehicles, including Electric Vehicles (EVs) and Fuel Cell Vehicles (FCVs) have attractive performance attributes not only forenvironmental and energy solutions, but also with regard to vehicle motion control. Compared with an Internal Combustion Engine (ICE), an electric motor offers significant advantages such as fast torque response, accurate estimation of torque output, and the possibility of distributing motors independently in each wheel. These advantages can be used effectively toachieve advanced motion control. In this study, we focused on the advantage of fast torque response and constructed a feedback controller for skid prevention during vehicle acceleration. In general, the feedback controller can change the plantdynamics, so we can redesign the vehicle to be insensitive to disturbances. Such a feedback controller requires fast actuator response, and this requirement isbest met by using electric motors.MODEL OF WHEEL DYNAMICS Using a simple one-wheel model, as shown in Fig. 1, the equations of motion of the wheel and chassis can be given as equations [1, 2] ...(1) ...(2) where V, Vw are the chassis and the wheel velocity, and M, Mw are the vehicle weight and the mass equivalent to the wheel inertia respectively. Fm is the motor- generated force, which is equivalent to the value obtained by multiplying the motor output torque Tm by the wheel radius r. Fd is the driving force between the wheel and road surface. Figure 1 : One-Wheel Model Fd can also be expressed as ...(3)Symposium on International Automotive Technology 2009 2where /c109 is the friction coefficient between the wheel and road surface, N is the vertical load on the wheel, a is the slip ratio and is the local gradient of /c109/c32 /c47/c32 /c108/c44/c32 /c108 and a are given in equation 4 and 5 respectively, ...(4) ...(5) where V0 and Vw0 are the chassis and the wheel velocity at the operational point respectively. Considering the nonlinearity in the definition of /c108 and Fd, the transfer function from the motor output Fm to the wheel velocity Vw is ...(6) where ...(7) and s expresses a Laplace operator. Equation 6 shows the integral characteristics in a relatively low frequency region and its parameter is . So the simplest models of wheel dynamics can be derived as ...(8) where Padh(s) denotes the dynamics of the wheel in a gripping state and Pskid(s) denotes the dynamics of the wheel in a skidding state. These functions are approximated to obtain the most simplified models of vehicle-wheel dynamics. MODEL-FOLLOWING CONTROL EXPERIMENT By using these models of wheel dynamics, we constructed a model-following feedback system for avoiding wheel spin and installed it in an ExperimentalElectric Vehicle (EEV). This section describes the experimental conditions and results.OVER VIEW OF EEV : A small one-seat electric vehicle was built that is equipped with two electric motors, one in each rear wheel. The system config