Automotive Electricity: Electric Drive

Chapter 4

The Components of Electric-Powered Vehicles ¹

Electric motors

Advantage of electric motors in road-vehicle drive-train systems

Before we begin presenting a description of electric motors, electronic converters and batteries used on-board vehicles, we will firstly give some elements that help appreciate the advantage of using electric traction in drive-train systems.

Let us note first of all that the mechanical torque of the electric motor results from the action of a magnetic induction flux on an electric current. In an electric motor, the flux imposes the dimensions of the magnetic material (iron); the current imposes the diameter of the wire (generally made of copper) which constitute the coil-windings.

Thus, electric-motor dimensions depend largely on the torque characteristics which we want to obtain.

The motor power is equal to the product of the torque by the rotation speed, such that at a given power, the size of the motor is as small as its rotation speed is high.

In a DC motor the rotational speed is limited:

– mechanically by removing risks on binder windings and commutated segments;

– electrically by the commutation of the current between the commutator segments.

In practice the electric motors used in road-vehicle drive-train systems have unit powers lower than 50–60 kW and their supply voltage most of the time remains lower than 200 Vdc.

Under these conditions it is possible to manufacture engines with a DC motor, which turn at 5,000 rpm.

Motors with AC current, ...