General information

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Fig 1: Identifying Starter Motor

Courtesy of VOLVO CARS OF NORTH AMERICA.

This document describes the principle design and function of a starter motor, regardless of the make.

The starter motor (6/25) cranks the engine to make starting possible. The starter motor is located on the transmission side of the engine block. The exact location depends on engine type. A solenoid causes a pinion to mesh with the crown wheel on the engine's flywheel/carrier. When the engine has started and engine speed exceeds starter motor speed, the pinion disengages. This prevents overcranking of the starter motor.

This type of starter motor is equipped with permanent magnets instead of field windings (except for the V8 engine, which has field windings).

The starter motor gives the greatest torque at low RPM at the same time as the voltage current through the starter motor is greatest.

NOTE:

The engagement time for the starter motor must not exceed 20-30 seconds. Longer engagement time results in the starter motor overheating and becoming damaged.

The starter motor solenoid is controlled by a starter motor relay (2/35). The relay, in turn, is controlled by the ignition switch (3/1) together with either the central electronic module (CEM) (4/56) or the engine control module (ECM). The engine management system of the vehicle determines whether the starter motor relay is regulated by the central electronic module (CEM) or the engine control module (ECM).