| With the constructing of the highway and development of automobile technology, the speed of automobile is greatly improved. On the highway, the speed of many automobiles more than 100km/h. With the improvement of the speed of automobile, More and more factors can affect the normal driving of automobile. More and more people pay attention to the influence of crosswind on the automobile driving safety. The relative data shows that a part of accidents of the high speed automobile is caused by crosswind, crosswind causes sideslip of automobile,offset the original movement track. The driver’s reaction is not timely or lack of experience cause the automobile go out of control. In order to improve the automobile driving safety, to improve the above phenomenon, this paper adopt combined control system based on the four-wheel steeringt and differential braking to improve the crosswind stability of high-speed automobile.First of all, considering the action of crosswind,differential braking and four-wheel steering, deduced the nonlinear model of four degrees of freedom includes longitudinal, lateral, horizontal pendulum and the lateral movement. Considering the nonlinear tyre, used the "magic formula" tire model,which can express the nonlinearity of the tire.This model as the basis of crosswind stability study of high speed automobile.The second, analyzing the individual control of four-wheel steering and differential braking effects on the crosswind stability. Four-wheel steering imposes a rear wheel steering angle to improve vehicle’s motion,analyzed the characteristics of four-wheel steering control, established nonlinear dynamic model and the simulation diagram of the four-wheel steering system considerating the action of crosswind. Differential braking inflicts on each wheel braking force to improve the car’s motion. Establishing nonlinear dynamic model and the simulation diagram of the differential braking system considerating the action of crosswind, analyzed distribution strategy of the braking force.The simulation test of individual control of four-wheel steering and differential braking effects on the crosswind stability.At last, proposing a combined controller based on sliding mode variable structure control,combined control of four-wheel steering and differential braking, control the rear wheel steering angle and the braking force, make automobile of combined control under the influence of crosswind follow ideal model. The simulation experiment was carried out under different crosswind and different driving conditions, compared driving condition of combined control automobile, uncontrolled automobile, ideal model, differential brake automobile and four-wheel steering automobile. Verifying the established combined controller based on sliding mode variable structure control is effective. |
