Abstract
This paper presents an optimization of a four-degrees-of-freedom quarter car seat and suspension system using genetic algorithms to
determine a set of parameters to achieve the best performance of the driver. Since the health of the driver is as important as the stability
of the car, the desired objective is proposed as the minimization of a multiobjective function formed by the combination of not only
suspension deflection and tire deflection but also the head acceleration and crest factor (CF), which is not practiced as usual by the
designers. The optimization results are compared through step and frequency responses of the seat and suspension system for the
optimum and currently used suspension systems. Comparatively better results are obtained from the optimized system in terms of
resonance peaks, CF, and vibration dose value. The concept and the ideas set forth in this work are directly applicable to both the car
suspension and seat design in industry.
r 2007 Elsevier B.V. All rights reserved.
Keywords: Quarter car; Suspension; Optimal seat design; Car-driver model
1. Introduction
Exposure to whole body vibration (WBV) associated
with a prolonged seating is an important risk factor for low
back pain (LBP) among drivers (Wilder, 1993; Pope et al.,
1998; Paddan and Griffin, 1998; Bovenzi and Hulshof,
1999; Griffin, 1998; Johnson and Neve, 2001). Both vehicle
suspension system and driver seat cushion designs have
attracted significant interest over the last several decades
with a significant effort being directed towards their
improvements. Vibration attenuation through the suspension
and seat will not only provide riding comfort but also
reduce the risk of LBP due to driving.
One of the early studies on the biomechanics of seated
drivers subject to vibration was realized by Suggs et al.
(1969), where the human body was modeled as a damped
spring-mass system to build a standardized vehicle seat
testing procedure. Muksian and Nash (1974) and Pope
et al. (1987) were investigated the response of seated
humans to sinusoidal vibration and impact. A detailed
experimental work on translational seat vibration was
performed by Griffin et al. (1982) to determine the effects
of level, frequency and direction of the seat vibration.
Dynamic response of a seated subject was investigated in
various aspects, for example, the effect of various cushions
(Pope et al., 1989), the effect of vibration frequency and
posture (Zimmermann and Cook, 1997; Wilder et al.,
1994), and the effect of backrest (Cho and Yoon, 2001;
Lewis and Griffin, 1996). Wan and Schimmels (1997)
established a seated human body model to design an
optimal seat suspension for isolation of the vertical WBV
based on the simulated subjective response. On the other
end of the spectrum, the effect of spinal forces due to WBV
(Fritz, 1997; Kumar et al., 1999; Verver et al., 2003) and
sitting biomechanics (Harrison et al., 2000) were considered
in some other studies.
Most of the studies on this subject treat the seat and
suspension designs separately. This study, however, integrates
both topics into a single problem through a
multiobjective optimization. The quarter car and the
seat with driver’s body are simply modeled together

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