Optimization of Front Bump Steer Using Design of Experiments

At the initial design stage of a new vehicle, chassis layout has the most important influence on overall vehicle performance. Most chassis designers have achieved target performances by trial and error as well as by individual know-how. Accordingly, a general procedure for automatically determining the optimum location of suspension hard points with respect to the kinematic characteristics needs to be created. In this paper, a method to optimize the toe angle in the double wishbone-type front suspension of a four-wheel-drive vehicle is presented using design of experiments, multibody dynamic simulation, and an optimum design program. The handling performances of two full vehicle models having the initial and the optimized toe angle are compared using a simulation of a single lane change maneuver. Front and rear suspensions are modeled as rigid bodies connected by kinematic joints using DADS. The derivatives of design variables with respect to the kinematic characteristics are obtained through experimental design sensitivity analysis using the perturbation method. An object function is defined in terms of the toe angle. Through design of experiments and regression analysis, the regression model function of the toe angle is obtained. The design variables having the optimized toe angle are obtained using the optimum design program DOT. A single lane change simulation and test of the full vehicle model are carried out to evaluate the handling performances of the vehicle with the toe angle optimized. The results of the lane change simulation show that the optimized vehicle has the improved handling performances compared with the initial vehicle.