Steering Stability Control For A Four In-Wheel Motor Drive Electric Vehicle

The electronic stability control(ESC)is a key problem on vehicle handling stability and safty,which also has significant meaning and realistic values in four in-wheel motor independent-drive electric vehicle(4IMDEV)steering flexibility and controllability.Focusing on the understeer and oversteer problem,a stability control strategy is proposed to improve the vehicle stability by controlling the traction/regenerative braking torques of the in-wheel motor traction units.By analyzing the 4IMDEV steering dynamics,and building the traction system of 4IMDEV with front-wheel-steering,the direct yaw-moment control(DYC)stability control strategy is used.After analyzing the influence of yaw rate and side-slip angle on stability,and the actuator constraints of the in-wheel motor traction unit,an ESC is proposed with vehicle reference model-yaw-moment and speed tracking upper level controller-lower level control allocation controller.The reference model generates the reference yaw rate and sideslip angle according to the driver's input and vehicle state.The upper level controller consists PID speed tracing controller and yaw moment controller.The yaw moment controller consists the fuzzy PID yaw rate yaw moment controller and sidelslip yaw moment controller and yaw moment sum controller.The yaw moment sum controller generates the weighted factors of yaw moment controllers' outputs based on the fuzzy rules according to the influence of yaw rate and side-slip angle on stability.The lower level control allocation controller allocates the control commands of traction/regenerative braking torques of in-wheel motor traction units.During the design of yaw moment sum controller,a weighted factor fuzzy control rule is designed based on the yaw rate and side-slip angle;in the lower level control allocator design,a multiple objective(maximize tire adhesion margin and minimize energy consumption)optimal torque allocation strategy and a hierarchical structure based on friction circle constraint.The dynamics model is built in Carsim and the control strategy model in Simulink to validate the proposed stability control strategy.By compared with servo control and ordinary continuous control strategies in step angle input and double lane change simulation maneuvers,the proposed stability strategy can improve the statbility better expecially in extreme conditions,like low adhesion and joint road surface,and decrease the energy consumption.The proposed stability control strategy is partly validated by steering wheel step angle input vehicle test on the 4IMDEV stability test platform.