Steering performance dependence on front suspension design

Abstract

Steering performance parameters are the measures defined in this thesis to quantify the steering behavior of vehicles. The parameters are important for the earlier stages of the design process and therefore a good understanding on how these parameters may change when designing the suspension is vital. The objective of this work is to establish a general frame that describes the relation between the steering performance parameters and the suspension design factors regardless of the suspension type. The work was done by studying one steering performance parameter, namely forces in the steering rack under a simulated driving condition. A population of different suspension configurations with different design factors was studied. A model of a McPherson suspension, including both kinematics and steering forces, was developed in Matlab to simulate these scenarios and gather all the necessary data for the study. Different suspension configurations with different design factors were simulated in this environment and the output forces and other steering parameters were statistically post processed to find trends and confidence intervals to find the relations. The objective of the statistical analysis was to find a model that isolated the effect of each suspension design factor on the different steering performance parameters. Linear regression models were used to fit the data and variability of the estimators was specially studied. The result of the study evidenced the difficulty of this problem. There is only statistically significant relation between castor trail and castor angle with all the steering performance parameters studied. The statistical study also reveals a close relation of the suspension design factors between themselves and the same for the steering performance parameters.