PISTON-CLUTCH 1605894 - Caterpillar

Starting Motor
Illustration 1 g00285113
Cross section of the starting motor (typical example)
(1) Field windings
(2) Solenoid
(3) Clutch
(4) Pinion
(5) Commutator
(6) Brush assembly
(7) Armature
Illustration 2 g00285112
Typical schematic of a solenoid
Solenoid (2) is an electromagnetic switch that performs two basic operations.
The solenoid closes the high current starting motor circuit with a low current start switch circuit.
The solenoid engages the starting motor's pinion with the flywheel ring gear.When the start switch is activated, electricity flows through the windings of the solenoid. The solenoid's plunger moves a mechanical linkage in order to push pinion (4). This engages the pinion with the flywheel ring gear. The pinion engages the flywheel ring gear before the electric contacts in the solenoid close the circuit between the battery and the starting motor. When the circuit between the battery and the starting motor is complete, the pinion turns the flywheel ring gear and the crankshaft.Clutch (3) provides protection to the starting motor so that the engine cannot turn the starting motor too fast. When the start switch is released, solenoid (2) causes pinion (4) to move away from the flywheel ring gear.Starting Motor Protection
The starting motor is protected from damage in two ways:
The starting motor is protected from engagement with the engine when the engine is running. The control feature will not allow the starting motor to engage if the speed is above 0 rpm.
The starting motor is protected from continuous starting. For example, if an operator is holding the engine control switch in the Start position after the engine starts, the starting motor solenoid will disengage after engine speed reaches 300 rpm.