1. Railway dynamics

Defining the general characteristics of a traction unit, i.e. defining its performance, requires a thorough knowledge of the traction program it will be used for: types of trains to be towed and their mass, gradients to be climbed, desired accelerations, maximum speed, degraded traction speeds, etc.

In this section, we first set out to establish the fundamental equation of dynamics that enables us to calculate the necessary running forces that a traction unit must develop in order to tow a train. We will then see that the maximum effort a wheel can develop on a rail is quickly limited by the phenomenon of adhesion; a loss of adhesion results in the wheel spinning, which can compromise a start.

Finally, knowledge of these various values enables the designer to establish what is known as the effort/speed characteristic of the prime mover,...