Epicyclic reduction gear unit

This motor can deliver considerable power despite its light weight. This advantage is achieved by combining a small armature, which can reach a very high rpm speed, with an epicyclic reduction gear which multiplies the torque delivered.

Epicyclic reduction gear unit

The driving gear is formed on the end of the armature. It meshes with 3 satellite gears, mounted on three pins on the satellite gear shaft, the end of which comprises the starter pinion for starting the engine. At the same time, the satellite gears mesh with a stator gear, fixed to the motor body, comprising internal teeth. The stator's reaction makes the satellite gear shaft rotate around the motor's axis at a slower speed than the armature.

The total rpm transmitted by the armature become transformed into revolutions of each satellite on its own axis, and rotations of the satellite gear shaft on the motor's axis.

1. Drive pinion with roller clutch
2. Satellite gear shaft
3. Stator (wheel with inner teeth)
4. Armature
5. Casing with windings and brushes
6. End bracket
7. Starter solenoid
8. Bracket

To renew the brushes only, break the old brushes with a hammer or crush them in a vice, then tin solder the winding terminals in the new brushes.

Diagram of Bosch starter motor connections