Optimal vehicle suspension characteristics for increased structural fatigue life

Abstract

The designers of heavy, off-road vehicle suspension systems face unique challenges. The ride comfort versus handling compromise in these vehicles has been frequently investigated using mathematical optimisation. Further challenges exist due to the large variations in vehicle sprung mass. The suspension system must provide adequate isolation from road load inputs throughout its payload operating range. This is imperative if good vehicle structural life is to be ensured. A passive suspension system can only provide optimal isolation at a single payload. The designer of such a suspension system must therefore make a compromise between designing for a fully-laden or unladen payload state. This work deals with suspension optimisation for vehicle structural life. The work mainly addresses two questions: 1) What are the suspension characteristics required to ensure optimal isolation of the vehicle structure from road loads? and 2) If such optimal suspension characteristics can be found, how sensitive are they to changes in vehicle payload? The study aims to answer these questions by examining a Land Rover Defender 110 as case study. An experimentally validated mathematical model of the test vehicle is constructed for the use in sensitivity studies. Mathematical optimisation is performed using the model in order to find the suspension characteristics for optimal structural life of the vehicle under consideration. Sensitivity studies are conducted to determine the robustness of the optimal characteristics and their sensitivity to vehicle payload variation. Recommendations are made for suspension characteristic selection for optimal structural life. AFRIKAANS : Ontwerpers van swaar, veldvoertuig suspensie stelsels staar unieke uitdagings in die gesig. Die ritgemak teenoor hantering kompromie in hierdie voertuie is reeds telkemale ondersoek, ook met wiskundige optimering. Verdere uitdagings bestaan as gevolg van die groot veranderinge in geveerde massa by hierdie voertuie. Die suspensiestelsel moet gepaste isolasie van pad insette oor `n wye reeks van bedryfstoestande lewer. Dit is veral belangrik indien daar verseker wil word dat die voertuig goeie struktuurleeftyd het. `n Passiewe suspensiestelsel kan egter slegs optimale isolasie by `n enkele vragtoestand lewer. Die ontwerper van `n passiewe suspensie stelsel moet dus `n kompromie aangaan tussen ontwerp vir `n vol of leë vragtoestand. Hierdie studie handel oor suspensie optimering vir struktuur leeftyd. Die werk spreek hoofsaaklik twee vraagstukke aan: 1) Watter suspensie karakteristieke word benodig om die voertuig struktuur optimaal van padinsette te isoleer? en 2) Indien sulke optimale karakteristieke gevind kan word, wat is hulle sensitiwiteit vir veranderinge in voertuig vrag? Die studie mik om hierdie vraagstukke aan te spreek deur ondersoeke op `n Land Rover Defender 110 toetsvoertuig. `n Eksperimenteel gevalideerde, wiskundige model van die toetsvoertuig word saamgestel met die oog op sensitiwiteitstudies. Wiskundige optimering word met die model uitgevoer om sodoende die suspensie karakteristieke vir optimale struktuurleeftyd vir die betrokke toetsvoertuig te bepaal. Sensitiwiteitsanalises word gedoen om die robuustheid van die optimale karakteristieke, met betrekking tot veranderinge in voertuig vrag, vas te stel. Aanbevelings word gemaak oor die keuse van suspensie karakteristieke vir optimale struktuur leeftyd. Copyright