| Compare with the traditional electric vehicle,the four wheel independent driving wheel motor vehicle has its unique advantage,and it is a new characteristic development direction of the electric vehicle.The four wheel drive vehicle compared with the two wheel drive vehicle can make better use of the ground adhesion.Through the reasonable adjustment of the driving forces of each tire,the energy loss can be reduced and is also good for the vehicle anti-skid control.Therefore,how to control the output driving force of each wheel is the key technologies for the research of four wheel independent drive hub motor electric vehicle.This paper focus on the technical advantages of the four wheel independent drive hub motor electric vehicle,study deeply on the longitudinal motion control of the electric vehicle.The following aspects are mainly carried out:(1)Through the analysis of the principle of vehicle longitudinal motion and motor drag control.The simulation models of vehicle model,control model and motor model are built.A simple driver model based on speed feedback is established.The experimental results show that the model can transform the expected speed of driver's input into the final output torque.The advantages and disadvantages of each wheel motor drive control strategies are compared laterally,and a double loop control system is designed,and its feasibility and effectiveness are verified by Simulink simulation experiment.(2)In order to solve the problem of vehicle instability caused by the change of the front and rear axle load during the longitudinal driving of the vehicle,a control algorithm for the dynamic adjustment of the axial distribution torque is designed.The longitudinal driving is divided into the starting condition,the medium and low speed acceleration condition and the high speed acceleration condition.When the vehicle is in the starting and medium and low speed acceleration condition,the adjustment ratio is a fixed value.In the high speed acceleration condition,the axle load will transfer to the backward axis because of the increase of air resistance.The simulation results show the torque dynamic adjustment ratio is guaranteed under the starting and the medium and low speed acceleration conditions,and the output torque is allocated according to the real time loadchange in the high speed acceleration condition.(3)In view of the slippery turning phenomenon of the wheels which may be encountered in a straight line or in the acceleration condition,a kind of fuzzy control strategy based on the state parameters of motor and wheel is put forward.The principle of vehicle slip state estimation based on wheel angular acceleration information is analyzed and a slip state judgement algorithm is designed.It is found that the ratio between the driving force of the wheel and the derivative of the driving force of the driving motor can help us judge the slip state of the vehicle.Using fuzzy control theory,the output torque of the hub motor is regulated under the combined effect of the obtained parameters and the wheel angular acceleration.The fuzzy control algorithm designed in this paper is compared with the classic model tracking control algorithm,and it is found that the fuzzy control algorithm designed in this paper is not only the same as the model tracking control in the anti slip control effect,but also can give consideration to the dynamic performance of the vehicle.(4)A CarSim/Simulink joint simulation experiment platform is build for the longitudinal motion control algorithm of vehicle.The final result accords with the established control target.It has a better anti skid control effect in the starting and low speed acceleration conditions,and ensures the output torque of the forward wheel in accordance with the given torque dynamic adjustment.Under high speed and acceleration condition,the load distribution of front and rear axle controls the output torque of front and rear wheels,and also ensures good driving and skid control effect. |
PDF Full Text Request