Investigation of the effect of longitudinal creepage on wheel squeal

Wheel squeal is generally attributed to the lateral wheel vibration induced by lateral creepage. It should be noted, however, longitudinal creepage also exists at wheel/rail interface. Given the significance of longitudinal creepage in vehicle dynamics, a test rig that can introduce various longitudinal creepages by changing the teeth number of synchronous pulley is developed in this research, and measurement results show that squeal spectrum has three dominant peaks, whose sound pressure levels decrease with longitudinal creepage. In order to investigate the reason why longitudinal creepage can mitigate wheel squeal, a model of a wheel/rail system is developed in this research to analyse this phenomenon using complex eigenvalue method, and the results show the inner wheel tends to generate unstable vibration at three different vibration modes, correlating well with the dominant peaks of sound spectrum. Further analyses can illustrate the reason why longitudinal creepage can mitigate wheel squeal: the absolute value of effective damping ratio of each mode decreases with longitudinal creepage, so structural damping and frictional damping are less likely to be overcome by negative damping.