Excessive traction torque while starting on slippery roads and slopes causes the wheels to spin, consequently reducing the directional stability and the traction force. To solve this problem, researches on the traction control system(TCS) that controls the traction torque using various vehicle parts have been conducted. But these commercial TCSs use experiential methods such as lookup table and gain-scheduling to achieve proper performance under various road and vehicle conditions. To design a systematic controller using non-experiential method is the goal of this research.
At first, this research proposes a fundamental slip controller which maintain the slipratios of the driven wheels to prevent the excessive slip of driven wheels. The slip controller is composed of brake and throttle controller. To avoid measurement problems and get the simple structure, brake controller was designed using Lyapunov redesign method and throttle controller was designed using multiple sliding mode controller. Through the hybrid use of brake and throttle controllers, the vehicle was insensitive to the variation of vehicle mass, brake gain and road condition and could gain traction performance.
Extending the fundamental slip controller to provide directional stability in the cornering and lane change on the slippery roads requires yaw rate and lateral acceleration sensors to detect the vehicle dynamics. The control system monitors the course of the vehicle and compares it to the desired by the driver. These additional sensors are fundamental for directional stability but very expensive. So a new method to measure the mixture of yaw rate & lateral acceleration using the speed difference of non-driven wheels is proposed. Using this measurement, the controller impose additional pressure to the driven wheels. Course deviation is corrected by braking the individual driven wheels and directional stability is gained.
When a vehicle start off in the stiff slopes and traction torque is not sufficient, the vehicle is pushed back by the gravity. To prevent this phenomenon, a transition controller which use the locking of the non-driven wheels is proposed. After the vehicle move forward, the controller converts to the original slip controller mentioned.
The total controllers can be unified in a consistent structure. The control performance was verified using 7 DOF and 15 DOF vehicle model.
