Study On Vehicle Front Wheel Alignment Parameters

In recent years, with the rapid development of vehicle industry in our country, the level of design was greatly improved, but the design and optimization of front wheel alignment parameters are still knotty problems. Formerly, the design of wheel alignment parameters relied on experience and tests, there is no mature design theory. The design theory of wheel alignment parameters was presented and an optimization scheme of wheel alignment parameters was proposed in this paper. The main research work in this paper is as follows:(1) The tire sideslip property and the interference effect of steering trapezium to front wheels steering movement were considered, the vertical, lateral and longitudinal force of tire were analyzed. In the calculation of vertical force and longitudinal force, the redistribution of front axle load was taken into account. In the calculation of lateral force, the tire side slip angle and camber were considered.(2) The influence of wheel alignment parameters on self-align moment was studied in this paper; the front wheel self-align moment produced by each directional force was calculated. Firstly, in the calculation of self-align moment produced by vertical force, the height variation of front wheel load, dynamic camber angle and dynamic castor trail were calculated by using coordinate transformation; and then self-align moment produced by load potential energy was calculated. Self-align moment produced by lateral and longitudinal force was calculated by using coordinate system transformation and torque produced by space force on axle. The influence of wheel alignment parameters on tire wear and shimmy was studied, the matching relation between toe-in angle and camber angle, and objective function measured tire wear during turning drive were obtained.(3) A whole vehicle model was assembled by using the subsystem of the vehicle in ADAMS/Car; the mathematical model of front wheels’ force and self-align moment was written to MATLAB, and the simulation of vehicle model was conducted combining with ADAMS/Car. The simulation shows that the mathematical model of the front wheels’ force and self-align moment has some certain correctness. In addition, the suspension simulation was conducted in ADAMS/Car, the correctness of the mathematical model of the height variation of front wheel load, dynamic camber angle and dynamic castor trail was verified.(4) An optimization scheme of wheel alignment parameters was proposed based on “fmincon” function in MATLAB optimization toolbox.