How a Starter Works

Rest Position -- No current supplied to starter, pinion demeshed. Tooth meets gap -- Favorable meshing position. Pull-in and hold-in windings are engergized. A pinion tooth meets a gap in the ring gear, and the pinion meshes immediately. The starter position just before the main current is switched on is shown. Tooth meets tooth -- Unfavorable meshing position. Pinion tooth meets ring-gear tooth. Engaging lever in end position, meshing spring compressed, pull-in winding not energized. Main current flows, armature rotates. Pinion attempts to mesh with ring gear. Engine is cranked -- End position. Engaging lever in end position, pull-in winding not engerized. Main current flows, pinion is fully meshed. Engine is cranked.

Axial travel

When the starter switch or the ignition/starter switch is operated, the pull-in and hold-in windings of the solenoid switch are also energized. The solenoid armature pulls in the engaging lever against the force of a return spring. The engaging lever, via guide rings and a meshing spring, pushes the driver with pinion against the ring gear on the engine flywheel; the driver and pinion simultaneously rotate due to the action of the helical spline. The starter motor armature does not yet turn in this phase, because the main current for the excitation and armature windings has not yet been switched on.

If the pinion can immediately engage the ring gear, the pinion moves forward until it reaches the end of its travel and the moving contact in the solenoid switch meets the solenoid contacts (Figure, Pos. 2). The starter motor is now switched on.

If a pinion tooth meets a ring-gear tooth, the pinion cannot immediately mesh with the ring gear. As a result, the meshing spring is compressed via the engaging lever and the guide rings until the moving contact in the solenoid switch meets the solenoid contacts (Figure, Pos. 3).

The starter motor is now switched on and begins to turn Initially, the pinion turns along the ring gear surface. At the first opening, the pinion gears respond to the pressure exerted by the engagement spring and, especially, the helical motion along the engagement axis by meshing with the teeth in the ring gear.

Helical travel

At the end of the solenoid travel, the solenoid switch contacts close -- independent of the pinion position -- and switch on the starter current. The starter armature now begins to rotate, and the helical spline forces the pinion, which is prevented from turning by the ring gear with which it has meshed, even further into the ring gear until it contacts the stop ring of the armature shaft.

When the starter circuit is closed the pull-in winding is simultaneously shorted. Now only the hold-in winding acts. However, its magnetic force is sufficient to hold the solenoid armature in its pulled-in position until the engine is started (Figure, Pos. 4).

Demeshing

After the engine starts and the speed of the starter pinion exceeds the no-load speed of the starter motor, the roller-type overrunning clutch described earlier breaks the connection between the pinion and the armature shaft. This keeps the armature from being rotated too fast and damaged. The pinion remains meshed as long as the engaging lever is held in the engaged position. The engaging lever, driver and pinion are returned to their initial positions by the return spring only when the starter is switched off. The return spring also ensures that the pinion remains in its rest position in spite of engine vibration until the starter is again operated.