A passive nonlinear damping design for a road race car application

A suspension system does not merely isolate a vehicle from the shocks and vibrations induced by the road surface. It also keeps the wheels in contact with the road, ensuring vehicle stability and control. In order to properly determine the stiffness and damping parameters of a Formula SAE, models for a quarter car and a seven degree-of-freedom car (DOF-7) were developed based upon Newton’s second law. These were built using MatLab/Simulink. The quarter car model was taken first, to study the effect of four (4) suspension parameters on the tires’ vertical load fluctuations. The results were then used to optimize suspension parameters for the 7-DOF model, taking the bounce, roll and pitch motions of the chassis into account in addition to its four-wheel hops. Track data was acquired and used as input to the model. Nonlinear damping was implemented in the 7-DOF model to study the car’s behavior. The simulation results show that very high damping helps control the slow motions of the chassis, while at higher wheel hop speeds, a low damping ratio minimizes the tires’ vertical load fluctuations.