Roll steer minimization of McPherson-strut suspension system using genetic algorithm method

In this research the roll steer of a front McPherson suspension system is studied and the design characteristics of mechanism are optimized using Genetic Algorithm method. The roll steer is defined as undesirable and uncontrollable changes in the steering angle of the steered wheels during the rolling action of the vehicle body due to cornering maneuver or asymmetric bumps. The roll steer affects handling and dynamic stability of the vehicle due to variation of the angles of the wheel and the suspension links (i.e. camber, caster and toe). However these changes cause other problems. In this paper, in conjunction with the study of three-dimensional kinematic model of McPherson mechanism, a set of mathematical equations are derived to determine the suspension behavior of a typical vehicle through the rolling. The kinematic analysis is followed by an optimization process using the genetic algorithm method to determine the optimum length and orientation of the mechanism's members to minimize the variations of the toe, the camber and the caster angles. However the variations cannot be expressed by closed form functions, thus a performance index is defined in the integral form which expresses the overall variations of the main parameters in the whole range of rolling of the body. It is shown that the genetic algorithm can be effectively used in optimization of three-dimensional behavior of such spatial linkages in which the performances indices have no closed form with many variables under the non-smooth constrains. The presented method not only can be used to design of optimum novel suspension systems, but also to improve the kinematic behavior of existing systems.