Flatness-based Integrated Control For Vehicle Steering Stability

When vehicle encounters emergency obstacle avoidance,runs in high speed steering,and steers on the low adhesion road,due to the limitation of ground adhesion and tire longitudinal/lateral forces hybrid sliding characteristics,the tires easily turn into nonlinear region.As the tire longitudinal and lateral forces couple and restrict each other,if the tire driving torque is too large,tire lateral force will be very small,so the vehicle may sideslip without overcoming the centrifugal force.If the driver overreacts at the limit condition and makes steering wheel angle turns an inappropriate value,then the vehicle may run out of the road even if it keeps its stability.So it is necessary for the vehicle steering angle and tire driving/braking torque coupled control to make the tires produce reasonably lateral and longitudinal forces under the tire-road friction limit and to make the vehicle turn a corner smoothly.According to the analysis and summary of the research status,this paper study the vehicle integrated control based on the differential flat theory,which includes the controller intervening extent under the different condition of variable speeds and roads with different alignment.The main contents are as follows:Based on the differential flatness theory,find out the flat-outputs of the vehicle model and thus prove that the vehicle system is flat differential system.Express the driving/braking torque and tire steering angel with the flat-outputs and the vehicle variables,thus provide theoretical basis for the design and implementation of the controller.Provide the reference vehicle variables according to the research status:the target longitudinal speed is designed follow the principle of slowing down when entering a curve and speeding up when deviating from a curve;the target yaw rate changes with the road curve radius based on the kinematics theory;the target lateral speed has a relationship with the yaw rate according to the nonlinear dynamics theory.The overall scheme and structure of vehicle driving/braking and steering integrated control is proposed,the controller is designed,the realization of control strategy is done.Moreover,the controller intervening extent under the different condition of variable speeds and roads with different alignment is researched.Both the driver open loop input simulation and closed loop simulation are studied,as well as the contrast of vehicle handing stability and trajectory tracking effect for different control strategy.By changing the parameters of expectation longitudinal speed,controller parameters,the robustness performance of the controller is simulated.