Title page for ETD etd-07152008-102911
Els, Pieter Schalk Email
This thesis examines the classic ride comfort vs. handling compromise when designing a
vehicle suspension system. A controllable suspension system, that can, through the use of
suitable control algorithms, eliminate this compromise, is proposed and implemented.
It is a well known fact that if a vehicle suspension system is designed for best ride
comfort, then handling performance will suffer and vice versa. This is especially true for
the class of vehicle that need to perform well both on- and off-road such as Sports Utility
Vehicles (SUV�s) and wheeled military vehicles. These vehicles form the focus of this
The ride comfort and handling of a Land Rover Defender 110 Sports Utility Vehicle is
investigated using mathematical modelling and field tests. The full vehicle, non-linear
mathematical model, built in MSC ADAMS software, is verified against test data, with
favourable correlation between modelled and measured results. The model is
subsequently modified to incorporate hydropneumatic springs and used to obtain
optimised spring and damper characteristics for ride comfort and handling respectively.
Ride comfort is optimised by minimising vertical acceleration when driving in a straight
line over a rough, off-road terrain profile. Handling is optimised by minimising the body
roll angle through a double lane change manoeuvre. It is found that these optimised
results are at opposite corners of the design space, i.e. ride comfort requires a soft
suspension while handling requires a stiff suspension. It is shown that the ride comfort vs.
handling compromise can only be eliminated by having an active suspension system, or a
controllable suspension system that can switch between a soft and a stiff spring, as well as
low and high damping. This switching must occur rapidly and automatically without
A prototype 4 State Semi-active Suspension System (4S4) is designed, manufactured, tested and modelled mathematically. This system enables switching between low and
high damping, as well as between soft and stiff springs in less than 100 milliseconds.
A control strategy to switch the suspension system between the �ride� mode and the
�handling� mode is proposed, implemented on a test vehicle and evaluated during vehicle
tests over various on- and off-road terrains and for various handling manoeuvres. The
control strategy is found to be simple and cost effective to implement and works
extremely well. Improvements of the order of 50% can be achieved for both ride comfort
AFRIKAANS : In hierdie proefskrif word die klassieke kompromie wat getref moet word tussen ritgemak en hantering, tydens die ontwerp van �n voertuig suspensiestelsel ondersoek. �n
Beheerbare suspensiestelsel, wat die kompromie kan elimineer deur gebruik te maak van
toepaslike beheeralgoritmes, word voorgestel en ge�mplementeer.
Dit is �n bekende feit dat, wanneer die karakteristieke van �n voertuigsuspensiestelsel
ontwerp word vir die beste moontlike ritgemak, die hantering nie na wense is nie, en ook
omgekeerd. Dit is veral waar vir �n spesifieke kategorie van voertuie, soos veldvoertuie
en milit�re wielvoertuie, wat oor goeie ritgemak en hantering, beide op paaie en in die
veld, moet beskik. Die fokus van die huidige studie val op hierdie kategorie voertuie.
Die ritgemak en hantering van �n Land Rover Defender 110 veldvoertuig is ondersoek
deur gebruik te maak van wiskundige modellering en veldtoetse. Die volvoertuig, nieline�re
wiskundige model, soos ontwikkel met behulp van MSC ADAMS sagteware, is geverifieer teen eksperimentele data en goeie korrelasie is verkry. Die model is verander ten einde �n hidropneumatiese veer-en-demperstelsel te inkorporeer en verder gebruik om optimale veer- en demperkarakteristieke vir onderskeidelik ritgemak en hantering te verkry. Ritgemak is geoptimeer deur in �n reguit lyn oor �n rowwe veldterreinprofiel te ry, terwyl hantering geoptimeer is deur �n dubbelbaanveranderingsmaneuver uit te voer. Die
resultaat is dat die geoptimeerde karakteristieke op die twee uiterstes van die ontwerpsgebied l�. Beste ritgemak benodig �n sagte suspensie terwyl beste hantering �n harde suspensie benodig. Daar word aangedui dat die ritgemak vs. hantering kompromie slegs elimineer kan word deur gebruik van �n aktiewe suspensiestelsel, of �n beheerbare
suspensiestelsel wat kan skakel tussen �n sagte en stywe veer, asook ho� en lae demping.
Di� oorskakeling moet vinnig en outomaties geskied sonder enige ingryping van die
�n Prototipe 4 Stadium Semi-aktiewe Suspensie Stelsel (4S4) is ontwerp, vervaardig,getoets en wiskundig gemodelleer. Die stelsel skakel tussen ho� en lae demping, asook
tussen �n stywe en sagte veer binne 100 millisekondes.
�n Beheerstrategie wat die suspensiestelsel skakel tussen die �ritgemak� en �hantering�
modes is voorgestel, op �n toetsvoertuig ge�mplementeer en evalueer tydens
voertuigtoetse oor verskeie pad- en veldry toestande, asook tydens omrol- en
hanteringstoetse. Die beheerstrategie is koste-effektief en maklik om te implementeer en
werk besonder goed. Verbeterings in die orde van 50% kan behaal word vir beide ritgemak en hantering.
Els, PS 2006, The ride comfort vs. handling compromise for off-road vehicles, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-07152008-102911/ >