Prediction of the Variation on Steering Wheel Shimmy due to Tangential and Radial Force Variation of the Tyres

The objective of this work is to develop a process that predicts the amount of steering wheel shimmy in a vehicle due to the tangential and radial force variation in the Tyre/Wheel assembly and also other components affecting shimmy. Steering wheel shimmy is defined as the torsional oscillation of the steering wheel due to excitation at the wheels. The tangential and radial force variation was modelled based on test data and applied on the wheels as excitation. Variation of these forces with the vehicle velocity was considered. The various factors that affect shimmy were then established. These factors were then divided into two categories - Geometric and Non-Geometric. A DOE was done, while considering the manufacturing variations, to study the sensitivity of those factors on shimmy. The DOE results were used to fit a regression model that predicts the shimmy velocity while considering the factors as inputs. The regression model was then considered for a Montecarlo simulation to estimate the distribution of shimmy velocity. A Normal or Weibull distribution was considered for the MonteCarlo Simulation for each of the factors in the DOE study. This distribution was then compared against a target. The target was used to design the suspension such that it is robust enough to withstand the manufacturing variations of the factors effecting shimmy.