Dynamic Simulation of Vehicle Suspension Systems for Durability Analysis

Abstract

Optimisation for fatigue life is currently carried out manually, which is time consuming and may not achieve the best design. To shorten the design process, software for automated durability optimisation is being developed at the University of Leeds and is initially aimed at the automotive industry. A key aspect of the optimisation process is to obtain accurate load histories for the particular component to be optimised. If this is to be done early in the design process, before a rolling chassis prototype is available, then simulation must be relied upon to obtain these load histories. In the case of suspension components either a quarter vehicle model (QVM) or a full vehicle model (FVM) can be used as the basis for the multi-body system (MBS) simulation. This paper compares the suitability of the QVM and FVM for durability analysis. Results are presented for both a simplified vehicle suspension and for a more realistic suspension. Step inputs representing a kerb and a simplified pothole were applied to one wheel only. For the simplified suspension case, the local displacement of the body was less for the FVM than for the QVM. This indicates that the dynamic response at the other wheel stations contributes to the behaviour of the wheel station directly subjected to the step or pothole input. The study was repeated with a more realistic suspension model in the QVM and at one wheel station of the FVM, with similar results to the simplified suspension case. This study has shown that coupling exists between the four wheel stations of the FVM even when the suspension is independent. This coupling can affect the load histories applied to a particular suspension component, which may then affect its calculated durability. The strength of this coupling is such that the use of the QVM for durability analysis becomes questionable and the FVM should be used as the default.