Theoretical investigation of the effect of rail cleaning by wheels on locomotive tractive effort

The realistic modelling of a heavy haul locomotive’s behaviour requires the correct representation of friction contact conditions between each wheel and the rail. Recent discussion has raised the issue that, under traction or braking, a process of rail cleaning by leading wheels might be occurring that can lead to increased values of friction coefficient between following wheel treads and the crown of the head of the rails. Such a change can improve the tractive effort of a hauling locomotive, which is a key issue for freight rolling stock operations. In this paper, the change of friction coefficients under locomotive wheels due to the effect of rail cleaning are analysed based on expert opinions obtained through a literature review process. Also, some assumptions have been made in order to investigate the effect of variation in friction under individual wheels on locomotive dynamics. These assumptions adopt a progressive increase of the friction coefficient (but in progressively decreasing increments) from the leading to each subsequent following wheel on each side of the locomotive. For this study, the multibody model and a full electrical system of a heavy haul locomotive have been used for numerical experiments. The results obtained show that the variation of friction coefficients can have a significant influence on locomotive dynamics under traction.