The three interlinked steering system parameters viz, steering castor, castor trail and steering offset of single track vehicles influence their handling characteristics significantly. Traditionally, prototype vehicles with several combinations of these parameters are made, experimental testing in special test tracks is done with expert riders and the rider’s feel is used for optimisation of the design layout.
This study uses a multi-body computer simulation model of a motorcycle for this purpose. A non-linear computer model was used to simulate the test track driving conditions, made use for the experimental evaluation of prototype machines. A special handling test track simulating the low speed tight corner manoeuvres that are typical in the Indian driving conditions was simulated using the computer model. The non-linear simulation results are used for obtaining a linearised version of the bike model at various steady states. The linear model was used to analyse the system stability properties against small perturbations at various steady states and response gains, which are indicative of the handling quality of the bikes. Nine different combinations of the steering system parameters, for application of DOE (Design Of Experiments) technique, were analysed and the results obtained.
Prototype motorcycles with the nine different designs, were manufactured and subjected to special test track evaluation. The motorcycles were fully instrumented for measuring various parameters like steering torque, steer angle, yaw rate and roll rate. The data thus acquired was transformed into numerical measures of bike’s handling quality and the data was subjected to analysis of variance, using DOE technique.
The analysis results from the linear model are compared with the corresponding results obtained from the experimental work and found to have a very good degree of agreement. The results obtained are found to give a set of guidelines for optimisation of the steering system design. Thus a methodology is pioneered to use a virtual prototype for steering system design optimisation for motorcycles. Such a method can help immensely in cutting down product development time and cost, and the solutions thus obtained are expected to be of better quality.