Friction of a MacPherson suspension system at various load cases

In the current vehicle development process, the suspension friction is commonly treated as a constant force, while other suspension parameters, such as stiffness and damping, are quantified according to the actual kinetic state. Even though this simplification might be approximately true for many suspension variants, the theoretical background and the experiments conducted in this study indicate that the suspension friction of a MacPherson system is strongly subject to change depending on the forces and moments acting at the tyre contact patch. On the other hand, there is only a limited research basis quantifying to what extent suspension friction is affecting vehicle behaviour during various driving events. Therefore, assessments of whether an often-urged friction reduction is appropriate in the context of developmental efforts and benefits are equally limited. The first reasonable step is to accurately determine the actual amount of suspension friction regarding various boundary conditions and load situations, which currently is not constituted in literature. Hence, within the frame of the present study, the friction under various influences is investigated for a compact car, beginning at the full suspension and with special focus on lateral forces and combined wheel deflection states. While certain influences (engine state, excitation amplitude in a limited range) seem to be of minor importance, the suspension friction is strongly affected by various forces and moments at the tyres and by the wheel deflection level, whereas the lateral force dependence is mostly distinctive.