ABSTRACT Omni-directional electric vehicle built by our research group is an advanced electric vehicle whose four wheels can drive, steer and brake independently. The vehicle chassis system is composed of four in-wheel motors, four independent steer motors and electromagnetic brake system, and its control system is divided into logical control layer and underlying execution layer. The information exchange between these two layers is implemented by CAN bus. In this paper, the traction control logic for Omni-directional electric vehicle is developed. The study mainly involves two aspects: the vehicle states estimation and the traction control logic design. The vehicle states, including vehicle longitudinal velocity, lateral speed, side slip angle and yaw rate, etc, are estimated based on Extended Kalman Estimation and multiple degrees of freedom vehicle model. Longitudinal velocity is used to design the traction control logic; the other estimated states are the preconditions for the future study. To design the traction control logic, the slip ratio of each wheel is obtained according to the estimated velocity firstly. Through PID control, the single wheel slip ratio control is realized to make the slip ratio of each wheel below the optimum value. Then the vehicle traction control logic is introduced to eliminate the influence of the additional yaw moment to steer stability. Finally, the effectiveness of the estimation algorithm and the traction control logic are verified by the simulation in the environment of Matlab/simulink and Carsim. INTRODUCTION Omni-directional electric vehicle (EV) is a new concept vehicle, each wheel of the EV can drive, steer and brake independently. On this advanced platform, the flexible driving and turning mode can be implemented easily, such as zero radius turning, oblique driving and crab. The chassissystem widely uses x-by-wire technology. It includes the drive system housing four hub-motors in the wheels, the steering system turning by four torque motors, and the brake system using electromagnetic brakes. All these actuators can be controlled independently. Due to their rapid response and precise control, high performance of chassis control such as traction control, electronic differential control, direct yaw moment control and regenerative braking control systems can be employed easily at low cost. Omni-directional EV represents the development way of advanced civilian vehicle, military vehicle and wheel mobile robots in the future [ 1, 2]. Like traditional vehicles, the vehicle stability and safety are important for Omni-directional EV. Traction control system, as an important component to improve vehicle stability, can enhance a driver's ability to maneuver a vehicle moving in a low adhesion road or during starting. In these conditions, the wheel drive torque is likely to exceed the maximum adhesion force between the vehicle's tires and the road, which causes excessive slip [ 2, 10, 11]. While the wheel slip ratio is much larger than the optimal slip ratio of the corresponding road, the longitudinal adhesion force will decrease greatly and the wheel's steer-ability will be lose during cornering maneuvers. So the traction control system for Omni-directional EV is necessary to be studied. Because all wheels of Omni-directional EV are driven, the rotational speeds of the wheels cannot be used to estimate the speed of the vehicle. To solve this problem, many new methods [ 3, 4, 5, 6] are proposed. Some methods [ 3, 4, 5] can maximize the adhesion force without vehicle speed and road condition. They only need the rotating speed of the driving wheels and the motor torques. Other methods [ 6] use a specific observer to estimate vehicle states including speed information. Traction Control Logic Based on Extended Kalman Filter for Omni-directional Electric Vehicle2012-01-0251 Published 04/16/2012 Guoying Chen, Changfu Zong and Xueli Guo Jilin University Copyright © 2012 SAE International doi:10.4