Abstract

Design and synthesis of a vehicle suspension is a complex task due to constraints imposed by multiple widely conflicting kinematic and dynamic performance measures, which are further influenced by the suspension damper nonlinearity. In addition, synthesis of suspension for hybrid vehicles may involve additional design compromises among different measures in view of the limited lateral packaging space due to larger sub-frame requirements for placing the batteries. In this dissertation research, a coupled kineto-dynamic analysis method is proposed for synthesis of vehicle suspension system, including its geometry and joint coordinates, and asymmetric damping properties. Quarter-car and two-dimensional roll plane kineto-dynamic models of linkage suspensions are proposed for coupled kinematic and dynamic analyses, and optimal suspension geometry and damper syntheses.
The kinematic responses of quadra-link and double wishbone types of suspensions are evaluated using the single-wheel kinematic models. Laboratory measurements were performed and the data were applied to demonstrate validity of the 3- dimensional kinematic model. A sensitivity analysis method is proposed to study influences of various joint coordinates on kinematic responses and to identify a desirable synthesis. A kineto-dynamic quarter car model comprising linkage kinematics of a double wishbone type of suspension together with a linear, and single- and two-stage asymmetric damper is subsequently proposed for coupled kinematic and dynamic analyses. The coupling between the various kinematic and dynamic responses, and their significance are
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discussed for suspension synthesis. The effects of damping asymmetry on coupled responses are thoroughly evaluated under idealized bump/pothole and random road excitations, which revealed conflicting design requirements under different excitations. A constrained optimization problem is formulated and solved to seek design guidance for synthesis of a two-stage asymmetric damper that would yield an acceptable compromise among the kinematic and dynamic performance measures under selected excitations and range of forward speeds.
The coupled kinematic and dynamic responses in the roll plane are further analyzed through development and analysis of a kineto-dynamic roll-plane vehicle model comprising double wishbone type of suspensions, asymmetric damping and an antiroll bar. The results are discussed to illustrate conflicting kinematic responses such as bump/roll camber and wheel track variations, and an optimal geometry synthesis is derived considering the conflicting kinematic measures together with the lateral space constraint. A full-vehicle model comprising double wishbone type of suspensions is also developed in the ADAMS/car platform to study influences of faults in suspension bushings and linkages on the dynamic responses. The results of the study suggest that an optimal vehicle suspension synthesis necessitates considerations of the coupled kinematic and dynamic response analyses