A study on effect of track and vehicle factors on wheel load variation over short wavelength longitudinal irregularities

In order to maintain good track condition, and to keep safety and ride-comfort, managing wheel load variation is important especially for high-speed railway. And wheel load variation is strongly affected by vehicle’s unsprung mass, so reducing unsprung mass is very effective in reduction of wheel load variation. However, reducing unsprung mass drastically is not easy. This is because unsprung parts support the weight of the vehicle and are the most important safety components. Therefore, in this paper, the effects of track and vehicle factors on wheel load variation were evaluated in order to investigate methods to suppress wheel load variation effectively, other than reducing unsprung mass. In evaluating wheel load variations, we focused on wheel load variations when the vehicle runs over short-wavelength longitudinal irregularities of about 5 m wavelengths on the ballast truck. This is because 5 m wavelength longitudinal irregularities are outstanding on the Tokaido Shinkansen recently and large wheel loads are often observed at 5 m wavelength longitudinal irregularities. Therefore, it is considered important to suppress wheel load variations at short wavelengths longitudinal irregularities of about 5 m in order to maintain good track conditions. First, we modeled track and vehicle as a multibody dynamic simulation that can run over a set of rail irregularities. Next, by simulating hanging sleepers, it was shown that the characteristic wheel load waveform and peak values on longitudinal irregularities of about 5 m could be reproduced. This indicates that the hanging sleeper is the cause of the large wheel load variations on longitudinal irregularities of about 5 m. Finally, we changed track and vehicle factors and estimated the effect of those changes on wheel load variation. And we have shown that it is important to increase the bending stiffness of the rails and reduce the track support stiffness in order to reduce wheel load variations, not only to reduce unsprung mass weight on the longitudinal irregularities of about 5 m.