Coordination Control Of Electro-hydraulic ESP For In-wheel Motor Driven Electric Vehicle Under Limit Working Conditions

Most foreign and domestic research of electric vehicle stability control mainly focuses on ESP or DYC single system,but rarely focuses on coordination control of ESP and DYC to improve vehicle stability.In consideration of ESP works in an extensive three-mode process(increasing pressure,maintaining pressure,reducing pressure),which makes hydraulic pressure unable to be adjusted precisely and resulting in response delay.While the torque of in-wheel motor can be precisely controlled,and its response of torque is rapid.As can be seen from the analysis above,the prominent advantage of in-wheel motor can be used to compensate for the inherent shortcoming of ESP in the process of vehicle stability control.Therefore,this paper proposes to combine hydraulic ESP with DYC system to generate an electro-hydraulic composite system to improve handling stability characteristics of in-wheel motor driven electric vehicle.Firstly,this paper analyzes the coupling optimization mechanism of electro-hydraulic ESP.From the aspects of the necessity and feasibility of electro-hydraulic coupling optimization under limit working conditions,this paper explains the effect of the stability of in-wheel motor driven electric vehicle with coupling optimization mechanism,which lays a theoretical foundation for the following coordination control research of electro-hydraulic ESP.Due to actual slip angle is hard to measure,this paper puts forward the estimation of slip angle based on extended kalman filter.Through simulation experiment,it is verified that the estimatior based on extended kalman filter which designed in this paper can achieve good estimation results even under limit working conditions.Secondly,this paper studies the coordination control strategy of electro-hydraulic ESP based on the slip angle and yaw rate as the controlled quantity.The coordination control strategy of electro-hydraulic ESP adopts hierarchical control in order to reducethe control target overlap and allocation redundancy of the system.Upper controller uses sliding mode variable structure control.Lower controller,according to the minimum tire utilization as the optimization goal,uses quadratic programming optimization allocation method to allocate motor differential driving and hydraulic differential braking in order to realize the required additional moment and longitudinal force of upper controller accurately.Thirdly,this paper uses CarSim and Simulink to establish the dynamic model of in-wheel motor driven electric vehicle and control system model of electro-hydraulic ESP,through two limit stability simulation experiments(steering wheel angle continuous sinusoidal input under low adhesion and emergency double lane change under low adhesion),comparing the control effects of coordination control of electro-hydraulic ESP,traditional ESP control and DYC control from vehicle trajectory,yaw rate,slip angle.The results show that under limit working conditions the proposed coordination control of electro-hydraulic ESP can reflect the driver's operation intention better than single system control and improves the handling stability of in-wheel motor driven electric vehicle.