Dynamics of the Wheelset

As the wheelset is the basic guidance element of the railway vehicle it is appropriate to consider the dynamics of the wheelset as a preliminary to a discussion of the behaviour of a complete vehicle. In the simple two-axle vehicle of Figure 2.22, attention is now concentrated on a single wheelset which is connected by means of a mass-less suspension to the vehicle body which moves forward at constant velocity with negligible lateral and vertical motion. The vehicle body is assumed to apply a constant vertical force through the vertical suspension so that the total axle load is W. As discussed in Chapter 2, the system has three degrees of freedom, with the corresponding generalised coordinates lateral translation y of the centre of mass, angle of yaw ψ about a vertical axis and the rate of rotation of the wheelset Ω. The importance of this rather simple system lies in the fact that for a wide range of practical values of the parameters, the body of the vehicle does not strongly participate in the lateral motions of its wheelsets at high speeds, as will be discussed later, so that the elastically restrained wheelset exhibits behaviour which is typical of complete vehicles. Moreover, it is a system which lends itself to experimentation using a roller rig [1-4]. In addition, alternatives to wheelset guidance such as the peg-in-slot system, exhibit some contrasting aspects of the behaviour of guided wheeled systems, and will be briefly discussed.