Abstract

This thesis deals with computer-aided modelling analysis and design of vehicle systems for ride and handling studies. Characteristics of vehicle multi-body models are identified and formalisms are developed for automatic computerized equation generation and solution. These are implemented using interactive graphics and applied to several vehicle dynamics studies. The method of velocity coefficients is proposed as a versatile tool to model and analyze suspension linkages for ride and handling. The velocity coefficients can be evaluated from a kinematic analysis and then used to characterize a linkage suspension as a linkage-free suspension of equivalent isolation and handling properties. Dynamic analysis can then be carried out without solving for the kinematics at each integration step, leading to efficient solution. When the suspensions are represented as force-generating elements, most vehicle models can be represented by free-multi-body systems or multi-body systems in tree configuration. For these systems, a computer-based modelling strategy is formulated which parallels the intuitive and customary techniques used by vehicle system dynamicists. In this scheme, each rigid body may have any number of degrees of freedom between 1 and 6. The implicit constraints are automatically taken care of in the formulation so that a minimal set of differential equations are generated. General purpose formulations are presented for the velocity coefficient and design sensitivity analysis of suspensions. A general analytical method has been derived to determine the vehicle roll stiffness and roll centre location, which has hitherto been done graphically. Some prevalent misconceptions regarding roll centre arising from the geographical construction, and compounded by an official SAE definition, have been clarified. Implementation of the formalisms developed is presented in the form of two pieces of software--GENKAD and CAMSYD. GENKAD is a comprehensive set of programs for the kinematic analysis and design of planar mechanisms, featuring automatic symbolic equation derivation. GENKAD can compute positions and velocity coefficients and determine their sensitivities to any of the system parameters, to be used for optimal design. CAMSYD is used for modelling and dynamic analysis of planar, lumped parameter mechanical systems. The system equations are generated symbolically and can be solved for a variety of analysis options. CAMSYD has interface to GENKAD to represent linkage suspensions. The theory as well as the software have been verified and validated through comparison with results from published literature. The software was also used for the modelling and dynamic analysis of a snowmobile. Displacement and acceleration time histories of the vehicle going over a bump obtained from simulation are compared with measurements made on an instrumented snowmobile