Research On Control Strategy Of Cooperative Braking Force Distribution Of Three Wheels Based On The Brake-by-wire System

With the development of science and technology,the brake-by-wire system has been paid more and more attention to by the automobile industry due to its high efficiency,energy conservation and redundancy.Due to its inherent redundancy of the brake-by-wire system,the braking force can be reallocated to the rest of the wheels when braking failure occurs in single or multiple wheels to ensure that the braking system can still realize the greatest braking performance when the fault occurs,thus improving driving comfort and safety for occupants.Based on the National Natural Science Fund Project,the following research was conducted on the brake-by-wire system:The dynamic analysis of the normal braking vehicle was carried out.An optimal braking force allocation strategy for four wheels based on tire load ratio and its calculation method were proposed.The vehicle dynamics model with the braking failure of a single wheel at different positions was established respectively,and the influence of single-wheel braking failure at different positions on the braking performance of the vehicle was qualitatively analyzed.A co-simulation experiment established by Simulink and CarSim was carried out to quantitatively analyze the influence of different braking conditions on the braking performance of the vehicle in the case of single wheel braking failure.Cooperative optimal braking force distribution and control strategy of three wheels was proposed focusing on the braking force reconstruction in the case of single wheel braking failure: the braking force of the remaining three wheels was redistributed initially by making full use of the ground adhesion coefficient to meet the driver's desired deceleration as closely as possible;the front steering controller was designed by sliding mode control method in order to correct the yaw rate and the side slip angle to prevent the vehicle from deflection and spin caused by the braking force reconstruction;considering the influence of the front steer on the longitudinal force of the tire,the mathematical model of tire lateral force based on the magic formula was established.The braking force was optimized in real time at the target of tire load rate in the side slippery condition by Quadratic Programming.A co-simulation experiment established by Simulink and CarSim was carried out to analyze the strategy.The simulation results show that the proposed method of cooperative optimal braking force distribution is effective in different braking conditions,realizing the vehicle stability after single wheel brake failure.