Starter - Planetary Gear Set Added

GROUP 12
Engine - Electrical



Bulletin Number
12 03 86 (2057)



Montvale, NJ
January 1987
Technical Dept.



SUBJECT:
Starter with Planetary Gear Set

MODELS:
All with M 20 Engines





A new and powerful starter with planetary gear set has been developed for the new M 20 engines. Its cold cranking speed is approximately 15 rpm higher than the previous version.



A planetary gear set between the armature and the pinion ensures ample torque in the runup phase. The gear set ratio is 1:4.36.

The armature shaft has teeth cut on it to act as this sun gear, which drives the three planet gears. These run in an internal gear that is insulated from the starter housing to prevent noise transmission.

The planet gear carrier is connected to the starter pinion, which is pushed into the flywheel ring gear by the engagement lever.



The engagement lever of the solenoid switch is made from plastic to save weight; the plastic material contains graphite to improve its sliding and locating properties.

A further advantage of the new starter apart from low weight is its increased efficiency. The use of 6 permanent magnets in place of 4 exciter windings enables the output rating to be increased by 0.3 kW (0.39 hp).

As a result of the four times higher armature speed and the change in the manner of rotation, the starter is louder than conventional types.

Operating principle

When the ignition switch is turned to energize the solenoid, its armature pushes the pinion towards the flywheel ring gear with the engagement lever.

As the pinion is pushed forward it is forced to rotate by the spiral splines on the pinion shaft. Shortly before the end of the solenoid armature travel is reached, the solenoid switch completes the main current circuit and the armature begins to rotate.

As a result of the spiral action of the splines, the pinion continues to move towards the flywheel ring gear until it reaches its travel limit on the pinion shaft and begins to turn the engine over.

To prevent the starter from being driven at an excessive speed because of the high reduction ratio between starter pinion and flywheel ring gear, an overrun device is incorporated in the pinion assembly.

As soon as the starter is switched off (by turning the ignition key back), the pinion returns to its rest position.

To ensure that the starter comes to a halt as soon as possible after being switched off, it incorporates an armature brake.