A Compliant Suspension Application to a Small Scale Car

Abstract

Compatibility of a compliant equivalent for a double wishbone suspension is assessed in this thesis. Reference rigid double wishbone suspension is taken from a small-scale model car. Rear left suspension of this model car is used as a reference to compare the compliant mechanism. Reference suspension mechanism is modeled using CATIA software. This 3D model is used for obtaining necessary dimensions and positions for kinematic analysis. After conducting the kinematic analysis of the reference suspension mechanism, a smaller equivalent rigid link mechanism needs to be designed as a sub step. The equivalent rigid link mechanism is designed to have the same kinematic properties such as camber, caster, toe variation etc. This sub step is performed because we cannot convert the reference suspension mechanism directly to its compliant equivalent. The reason for that is using pseudo rigid body method to convert a rigid link mechanism results in a bigger compliant equivalent than the mechanism itself. Therefore, converting the smaller rigid link equivalent mechanism to its compliant equivalent will result in a mechanism which has the same kinematic properties as the reference suspension mechanism and can be mounted in the same space on the vehicle. Compliant equivalent design was performed using fixed guided beams as compliant wishbone sections. After completing initial analyses, stress values on the compliant sections needed to be reduced. This is performed by introducing a novel approach by transforming the compliant lower wishbone to double layer formation. This approach keeps the pseudo joints of the compliant link and reduces the stress at the same time. Finite element analyses of the mechanism are performed on ANSYS software. Analyses are performed for static loading, maximum bump loading, maximum braking and curb hitting scenarios. Analytical approach is checked with finite element analysis and final compliant design is proven as an equivalent for the reference suspension mechanism.