Progressive Rate Coil Spring Design Analysis for Passenger Cars

In this paper, the governing equations on the progressive rate coil springs are derived and implemented as a software package. The spring is divided to conical elements and deformation of each element under gradually increasing load is determined, based on which the spring shape under an arbitrary load is extracted. Gradual load increase results in deactivation of the coils, which causes the stiffness variation. The stress calculations and fatigue life cycle estimation is performed based on SAE recommendations. The results are verified using FEM analysis and experiments.