SENR9977 13 Systems Operation Section The alternator is connected to the battery through the ignition switch. Therefore, alternator excitation occurs when the switch is in the ON position. Starting Motor g00956095 Illustration 9 24 Volt Starting Motor (1) Terminal for connection of the ignition switch (2) Terminal for connection of the battery cable The starting motor has a solenoid. When the ignition switch is activated, voltage from the electrical system will cause the solenoid to engage the pinion in the flywheel ring gear of the engine.
When the pinion gear is engaged in the flywheel ring gear, the electrical contacts in the solenoid close the circuit between the battery and the starting motor. This causes the starting motor to rotate. This type of activation is called a positive shift. When the engine begins to run, the overrunning clutch of the pinion drive prevents damage to the armature. Damage to the armature is caused by excessive speeds. The clutch prevents damage by stopping the mechanical connection. However, the pinion will stay meshed with the ring gear until the ignition switch is released. A spring in the overrunning clutch returns the clutch to the rest position.
g00954820 Illustration 10 12 Volt Starting Motor (1) Terminal for connection of the battery cable (2) Terminal for connection of the ignition switch The starting motor turns the engine flywheel. The rpm is high enough in order to initiate a sustained operation of the fuel ignition in the cylinders.