Coordinated Control Strategy Of Semi-active Suspension Including Vehicle Transient Dynamics

Nowadays,the automobile industry is changing driving by the pressure of environment pollution and the innovation of vehicle technology.To master the core technology of low-carbon and intellectualization,the government and the major automobile manufacturers have spent lot of money in new energy vehicles and autonomous vehicle.The development of low-carbon and intellectualization requires the suspension to isolate the vibration effectively and ensures the grasping ability of the tires.Due to the low energy consumption and excellent performance,the semi-active suspension which can effectively coordinate the movement of the body and the wheels has attracted lot of attention.At present,most researches of semi-active suspension are lacking of consideration on vehicle transient behavior,which influences the vehicle state observation,tire force distribution and steady boundary solution.What’s more,it becomes the key obstacle of the semi-active suspension coordinated control with consideration of both the handling and the ride comfort.The relaxation effect of tyre and the suspension K&C characteristics will bring the vehicle system response delay.The actuator saturation will constrain the system control input,the vehicle dynamic of each direction couple together.the handling and the ride comfort vary from the road input and driving condition.In this paper,we will combine the theory with numerical simulation to study the transient dynamic respone of vehicle and its coordinated control.We will establish a simple and accurate method to describe the real-time transient characteristics of automobile and explore a coordinated control strategy of semi-active suspension to solve the time-delay,dynamic coupling and actuator saturation constraints of the vehicle transient performance.This paper is orginized as follows:1.Accurate vehicle dynamics modelingFirstly,we established the lateral and vertical dynamics model together with the transient tire model,modified suspension K&C characteristics.Secondly,we established the random road of the four wheels based on the correlation function and time delay between the four wheels.Finally,we verified this model by the joint simulation of CarSim and Simulink.2.Transient dynamic analysis of vehicleBased on the simulation,we analysised the effects of the K&C characteristics and transient tire model on the vehicle transient dynamic response.Besides,we also studied the influence of rough road on the handling stability.The simulation results show that the response time of the yaw rate and lateral acceleration was reduced with the consideration of suspension K&C characteristic,besides,the overshoot was also reduced.The response time of the yaw rate and lateral acceleration increased with the consideration of tire relaxation effect and the overshoot was basically unchanged.the effect of suspension K&C characteristics on ride comfort varied with the vehicle speed and road level.Rough pavement change wheel vertical load distribution and the wheel side slip angle increases.3.Online acquisition of road information and vehicle stateFirstly,we introduced a class of nonlinear systems’ s observation algorithm.We used this algorithm to estimate vehicle state and road roughness.Based on the simulation(front wheel angle 2 degrees and B class random road with 70km/h),we found that when considering the suspension K&C,the observation accuracy of the state could increase 3%~6%.Secondly,basised on the effective mean square method,we identified the input frequency of the road.Also,we identified the road grade referenced the ISO8608 pavement classification standard.Finally,the recursive least square method was used to identify the sprung mass,then built the load adaptive logic.4.Coordinated control strategy of semi-active suspensionFirstly,we consideried the load,working condition and road vertical input,then estabilished the coordinated control strategy of semi-active suspension including vehicle transient dynamics.Secondly,we introduced the state feedback and feedforward to the two degree of freedom vehicle model to acquire the optimal additional yaw moment according to the ITAE index,according to the principle of the load rate of the tire,we distributied the optimal wheel driving torque.The average load rate and the maximum load rate of tire is reduced with the consideration of the transient characteristics of the vehicle.Finally,the control objective was established by integrating the vehicle state and road surface information,and the MPC was used to solve the optimal suspension damping force under the dynamic coupling and actuator saturation constraints.