A theoretical consideration to negative damping of hunting of wheelset

Abstract

This paper considers ways to increase stability of wheelset hunting. The aim of this study is to introduce formulas which represent the damped natural frequency and its damping. This has been done by analytical and not by numerical calculation. These formulas are functions of mass, creep coefficient and other wheelset parameters. These formulas are obtained with a 2 degree of freedom wheelset model whose radius of gyration of yaw equals to a half of gauge and whose creep coefficient is isotropic, in the first part of this paper. In the second part, based on one of these formulas, ways to increase damping of wheelset hunting are discussed. First, it is shown that a longer wavelength of geometrical hunting is effective in reducing hunting at all vehicle speeds. Secondly, it is shown that at speeds slower than a certain speed, the damping is increased when the ratio of the wheelset mass to the creep coefficient is larger. Further, a symbolic formula for this boundary speed is obtained. Thirdly, if it is assumed that the wheelset mass is proportional to the square of the wheel radius, then at speeds higher than a certain speed, the damping is increased when the wheel radius is larger. Moreover a symbolic formula for this boundary speed is also obtained.