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An algorithm was developed for a speed-dependent four-wheel steering system for a Formula SAE car. A linear bicycle model was implemented using the MATLAB and SIMULINK software packages. Various control laws were investigated for the rear steer angle with the objective of reducing the sideslip angle. A full 3D model of the vehicle incorporating weight transfer and tire non-linearity was then developed using the DADS software. An algorithm developed using the linear model with the aim of reducing vehicle sideslip angle was implemented in the nonlinear model. It is shown that this algorithm can improve the dynamic performance for both high-speed and low-speed maneuvers.

Though widely used in automobiles for many decades, independent suspension did not find much application in heavy vehicles until the early 1970's when it began to find a niche in the wheeled armoured vehicle market. Since then it has penetrated rather slowly in high performance applications, such as airport rescue and fire-fighting vehicles. A breakthrough came in the 1990's with its adoption on the Oshkosh MTVR truck, which is being produced in considerable volume. Independent front suspension has also, in the last decade, found increasing acceptance where performance benefits justify the higher cost, for example in touring coaches and motor homes. Significant efforts are being made to develop IFS for commercial heavy trucks but in this sector cost presents a very real obstacle to market acceptance. Independent rear suspensions for twin road wheel configurations present even more challenges for the designer.

This paper reports on the correlation of fatigue results with Finite Element Analysis (FEA) predictions for an axle housing designed as an integral part of an independent suspension for an off-road truck. The axle initially failed to meet the prescribed fatigue performance criteria and a description of the failures is given. Maximum permissible stress levels were estimated for the prescribed performance. Linear FEA was used to determine the stresses in the original axle housing that had failed the fatigue test. Analysis of the available fatigue data predicted component life that was in good agreement with the test results. Further FEA allowed the effectiveness of design modifications to be monitored, resulting in a new design having a high degree of probability of meeting the fatigue performance criterion, without increase in weight, and at a lesser cost than repeated testing.