| Facing the double pressure of environment and energy, people began to pay more attention to electric cars than traditional cars. A bus is a social and public utility. Using electric buses will bring more benefit on energy, environment, and guiding the people awareness. And the study on electric cars is not much, especially on the electric buses. The active safety of electric buses should be paid more attention. Yaw moment control system belongs to the handling stability of vehicle. It can assure electric bus steering stably, prevent the occurrence of danger.Firstly, a controlled object should be established for the yaw moment control system. I establish a vehicle model with 7 degrees of freedom, including longitudinal, lateral, yaw, dynamic equations of four wheels, and some auxiliary model, the nonlinear tire model is Magic Formula. Establish driver control model with PID control and longitudinal velocity condition. The reference model is a vehicle model of two degrees of freedom, including lateral, yaw motion.Secondly, the controlled variable of control system is the vehicle yaw rate. It can show the yaw motion. I establish a fuzzy controller. The inputs of the controller are the deviation of the actual yaw rate and the reference yaw rate and the deviation's derivative. The output is the correction of yaw moment. Considering the characteristics of electric vehicles in changing the correction of yaw moment into the wheel torque variation in order to have little effect on the longitudinal motion, increase or decrease the driving torque, and consider the motor output torque margin.Finally, I establish the Simulink model and set the specific condition for simulation. The input of steering angle of the front wheel are angle step and sinusoidal. Simulate on good road and slippery road. I compare and analyze the changes of yaw rate with and without the yaw moment control system. The conclusion is the yaw moment control system can assure vehicles stable. |
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