Starter Motor: Description and Operation

Bosch starters have two types, direct drive and gear reduction. Direct drive starters incorporate an overrunning clutch type starter drive. A solenoid switch is mounted on the starter motor.
The other Bosch starter is a gear reduction starter. This starter uses six permanent magnets in place of conventional wound field magnets to save weight, eliminate field winding to case shorts, and improve cold start performance. The gear reduction system uses a planetary gear train to transmit armature rotation to the pinion shaft. A solenoid switch is mounted on the starter motor drive end shield.