Research On Braking Ride Comfort Based On Integrated Control Of Suspension And Brake-By-Wire System

Complicated driving conditions arouse the emphasis of vehicle ride comfort. Generally speaking, vehicle ride comfort can be improved by the adjustment of suspension system. Moreover, the introduction of active suspension system even enhances the improvement potential of ride comfort.Nevertheless, in some specified driving conditions, e.g. braking scenario, ride comfort involves not only vertical motion but also longitudinal motion. Since suspension system mainly exerts influence on pitch, roll and vertical motion, it is reasonable to use braking system to control the longitudinal vibration. Thus, it is a relatively effective method that using integrated control of active suspension and Brake-By-Wire system solves the braking ride comfort problem,which is also one of the focused areas on recent studies.First, regarding to pitch motion during non-emergency braking, this paper proposes a PID controller based on Skyhook theory to control the pitch motion during braking. The PID controller realizes control of three dimensions of pitch motion. The simulation results indicate that the proposed PID algorithm can effectively attenuate the pitch angle vibration and maintain vehicle body attitude during braking. Besides, in order to insist with development of control algorithm, this paper designs a control algorithm verification test bench for active suspension. This test bench is designed based on adjusted single wheel model and using coil-motor as actuator. With the help of this test bench, control algorithm can be verified and iterated promptly, enhancing development efficiency.Furthermore, this paper redefines braking process in three phases, and points out that ride comfort is of most significance in the post-braking phase.Through analyzing the braking critical state in post-braking phase, it is found out that the low frequency tire mode transition leads to longitudinal vibration in this phase. To solve this problem, a longitudinal vibration based on MPC is proposed with optimization target of longitudinal acceleration by controlling the braking pressure. For the purpose of further developing the control algorithm,the control trigger condition, braking pressure rebuilding condition and decreasing pressure limit are discussed as well. The MPC method is simulated in MATLAB/Simulink and tested in the test vehicle and the result shows that the ride comfort in post-braking phase is improved significantly.At last, with respect to emergency braking which is safety-critical, active suspension is introduced into the ABS control. An upper controller is proposed to coordinate the integrated control of the two systems. Using the vehicle state variables to differentiate braking conditions, the priorities of safety and comfort would be adjusted accordingly by the upper controller. And during ABS control,a compensated active suspension force is added to change tire normal force. The simulation results show that with integrated ABS algorithm, both braking performance and ride comfort are enhanced respectively.