4. Power transmission

4.1 The need for transmission

The mechanical energy available on the crankshaft of an internal combustion engine is characterized by the engine torque curve (N · m) as a function of speed (rpm) (figure 3 a). Maximum torque is delivered at maximum speed, so at speeds close to idle, torque is minimal. Comparing this characteristic with that of hook force (tractive effort in kN) as a function of speed (km/h) for a rail vehicle (the same applies to a motor vehicle, figure 3 b), it is easy to see that the requirement is exactly the opposite:...