Research On Differential Relations Of Wheel-Driven Electric Vehicles

With the increasing attention and importance of new energy vehicles,potential distributed drive electric vehicles have become a research hotspot.The four-wheel independent drive characteristics of distributed drive electric vehicles improve the flexibility of vehicle control.But at the same time,it also adds technical difficulties to drive control.Among the control technologies,the differential problem of distributed drive is also an important research topic.This paper mainly analyzes and studies the differential speed problem of wheel-side fourwheel drive electric vehicle,and probes into the optimal differential torque of wheel side drive by means of vehicle dynamics simulation comparison,which mainly has the following work contents and research results:(1)There are two main modes of differential control for wheel-side drive electric vehicles: speed drive and torque drive.Differential speed control under speed control mode is based on the ideal Ackerman steering model to control the speed of each wheel.In the middle and high speed steering process,it is easy to cause four wheels over-constraints due to inappropriate target speed,which is not conducive to vehicle driving.Torque control mode is to control the differential speed of wheel-side drive vehicle by directly driving the wheel with torque.Through the analysis of the dynamic correlation between wheels of wheel-side-driven vehicles and the vehicle,it is concluded that wheels driven by torque can always achieve speed coordination without exceeding the ground adhesion limit,and the simulation of uniform speed steering is carried out with different proportion of torque distribution.The results show that the sliding rates of the four wheels are relatively small and the speed co-operation between wheels is achieved.It shows that torque drive is the best choice for differential control of wheelside vehicles.(2)Torque-driven differential control needs to distribute the wheels' torques under steering conditions.Better distribution of differential torques should ensure the driving stability of vehicles.In order to improve vehicle stability limit and reduce tire wear,this paper proposes two methods: differential torque allocation with minimum tire total load rate and differential torque allocation with minimum tire total energy dissipation rate.The former aims at minimum tire total load rate,while the latter aims at minimum tire total energy dissipation rate based on tire energy dissipation rate theory.Distribution of differential torque.The simulation results of steering condition show that the load rate distribution method can eliminate the additional yaw moment produced by the axle-load ratio distribution method,and has better driving efficiency than the traditional axle-load ratio distribution method.In the steering acceleration condition,the total tire load rate can be significantly reduced and the stability limit of the vehicle can be improved,but it is not conducive to tire wear.The energy dissipation rate distribution method can effectively reduce the total energy dissipation rate of tires.The larger the vehicle corners and the higher the vehicle speed,the more obvious the reduction of the total energy dissipation rate of tires is,the more beneficial it is to reduce tire wear,but it is not conducive to vehicle driving stability.In order to take into account the vehicle driving stability limit and tire wear,the steering driving condition is divided into 16 working conditions according to the stability limit grade.Combining with the different influence of the two distribution modes on the vehicle stability limit and tire wear under different steering conditions,the differential torque is coordinated allocated by using two distribution modes with different weights,which effectively guarantees the vehicle.Driving stability and reduced tire wear.(3)During the steering process,the real-time transfer of axle load and the combined action of longitudinal force and lateral force of tire can not effectively solve the problem of side slip instability under extreme conditions.In order to compensate for the shortcomings of sliding rate control,the paper uses tire force as the objective control,estimates the maximum tire longitudinal force that can be provided by the ground at each moment in steering condition,controls the driving moment of tire,determines and limits the critical speed of vehicle,and solves the problem of sideslip under extreme conditions.Through the above research work,the paper solves the problem of wheel speed coordination in medium and high speed steering conditions,and ensures the driving stability of vehicles under different steering conditions.At the same time,it reduces tire wear and improves the driving performance of vehicles under comprehensive steering conditions.