ABSTRACT
As discussed in Chapter 1, guidance is the ability of a vehicle to follow the geometric layout of the track, and is mainly determined by behaviour in curves. It has been seen in Chapter 3 that a wheelset will only be able to move outwards to the rolling line if either the radius of curvature or the flangeway clearance is sufficiently large, otherwise longitudinal creep forces are generated. In addition, the forces of cant deficiency must be reacted by lateral forces acting between wheel and rail so that lateral creep forces are generated. Moreover, for stability the wheelsets in a vehicle must be constrained by the suspension in some way. The forces imposed by the suspension must be reacted by further creep forces. If the vehicle has any dimensional misalignments then these will also be accommodated by further straining of the suspension and additional creep forces. It follows that the way in which the wheelsets are connected together, through the car body or otherwise, is fundamental to the mechanism of guidance. Consequently, the starting point for this Chapter is a general consideration of the way in which two wheelsets may be elastically connected. This is followed by a discussion of the conflict between stability and steering. Finally, the response of the complete vehicle to track curvature, cant deficiency, and misalignments is considered, the attitude of the vehicle and the forces acting being obtained by solving the equations of equilibrium. A two-axle vehicle with a single stage suspension (or a bogie or truck unrestrained by the car body) is considered. The symmetric two-axle vehicle is the simplest form of vehicle which embodies in a practical way wheelsets and their interconnections. The two-axle vehicle is important in its own right, for in addition to its widespread use in the past as both a passenger and freight vehicle, it is increasingly seen as the light weight vehicle of the future. Moreover, its study is an essential step to the understanding of the bogie vehicle and more complex configurations.
