Dynamics of vehicles with semi-active suspensions exhibiting wheel hop

The present study investigates dynamic response of two degree of freedom qu arter-car models, subjected to road excitation. In these models, a semi-act ive control strategy is applied on the suspension dampers, which is based o n a switch of their damping coefficient between different values, so that t he resulting system approximates the performance of a vehicle involving sky -hook damping. An alternative control strategy is also applied, which is pa ssive and is based on selecting a different damping ratio when the wheel ve locity relative to the car body is positive or negative. Both of these cont rol strategies lead to oscillator models with parameter discontinuities. Si milar terms are also introduced into the equations of motion by considering wheel hop phenomena, where the vehicle wheel leaves the ground temporarily . Then, application of proper numerical techniques yields results in the fo rm of response diagrams, illustrating the effect of the system parameters o n its response and stability properties. Finally, some typical results are also presented for transient road excitation, determined by direct integrat ion of the equations of motion, in all cases, the results are compared to t hose obtained for vehicles with suspensions including passive shock absorbe rs. Moreover, special consideration is given to cases where wheel hop is po ssible to occur.