Modelling and Simulation of Vehicle Suspension System with Variable Stiffness Using Quasi-Zero Stiffness Mechanism

The dynamics and comfort of a vehicle closely depends on the stiffness of its suspension system. The suspension system of a vehicle always had to trade-off between comfort and performance of a vehicle; since for comfort a softer suspension is preferred which in turn decreases the aerodynamics and cornering performance and increases the ride height of the vehicle; whereas in stiffer suspension the ride height can be lowered, but forces due to bumps are transferred all the way up to the drivers cabin. This article aims to design a vehicle suspension model with variable stiffness using quasi-zero stiffness (QZS) mechanism and study its force-displacement characteristics and minimize the fundamental stiffness of the suspension system. The model developed uses the principle of negative stiffness to achieve low stiffness for the softer suspension system. The mechanism designed comprises of a pushrod suspension system with three parallel springs attached to one end of the rocker arm, one primary coil spring is mounted perpendicular to the rocker arm and the other two secondary plate springs are attached to the primary coil spring. In parallel, stiffness of all the three springs are added, giving stiffer suspension when required at low ride heights and higher cornering performance. For decreasing the stiffness, an actuator is used to position the secondary springs such that negative stiffness is produced, decreasing the stiffness of the system. The geometry stated above is modelled in Catia and simulated in MATLAB/Simulink. Graphs of force vs. displacement and stiffness vs. displacement are studied for both the conditions. A comparative study of conventional suspension and modelled suspension system is done.