Simulation and Modelling of Steering Ripple and Shudder

Abstract

Vehicle dynamics simulation is very common nowadays at any stage of chassis development which saves development time and cost. An Advanced Steering System Model has been developed and implemented in virtual environment to simulate steering characteristics and handling performance. In the vehicle measurement, it was found that the steering friction decreases when driven on an uneven road. As steering friction is an important steering characteristics related to steering centre feel, the Advanced Steering System Model should be able to produce accurate results for such phenomenon. The objective of this study is to validate the Advanced Steering System Model at different levels of road excitation. A steering system test bench was built up to realize the hardware-in-the-loop tests. In order to investigate the influence of the road excitation to the steering system friction, left and right rack forces were recorded on the test bench when the vehicle was driven on an uneven road. These two signals were imposed to the steering rack force to simulate the random road excitation in vehicle measurements. The measurements were used to validate the Advanced Steering Model. The Advanced Steering Model comprises mechanical module and power assist module. The advanced friction element in the mechanical module consists of an Exponential-Spring-Friction-Element and a parallel Maxwell-Element. It represents the frequency and amplitude dependency of the steering system accurately with appropriately identified parameters. The current parameters for the friction model were identified implicitly in this paper. The imposed noise was generated on a predefined uneven road. Further effort should be made to characterize this effect with constant frequency and amplitude force inputs on the test bench. The Advanced Steering Model is capable of representing the system response to the random road excitation, typically the friction reduction of the system due to the random noise input.

F2012-G06-013