Starter Motor Operation (automotive)

Starter Motor Operation (automotive)


engagement is provided by operation of the ignition switch in the start position which activates a starter mounted solenoid whose plunger is engaged with the hooked end of opinion shift lever and operating fork solenoid operation moves the operating fork causing the pinion to engage with the ring gear and also causes the plunger contacts to bridge the main starter terminals the fork locates in a guide ring on opinion driver which is coupled to the pinion via a roller type over running clutch designed to transmit drive in one direction only the pinion driver is mounted on a helix machined on the armature shaft to form a very coarse thread this allows the pinion driver to rotate slightly when it has moved towards the ring gear and this feature together with a chamfer on the leading edge of the ring gear and pinion teeth is designed to assist meshing and easy engagement however if the pinion teeth butt against the ring gear teeth and engagement is prevented the guide ring continues its axial movement by sliding over the sleeve of the driver and compressing a meshing spring until the plunger contacts bridged the main terminals and the armature begins to turn slight armature rotation and the force from the meshing spring allows the pinion teeth to drop into mesh with the ring gear assisted by the screw action of the helix the helix forces the pinion further into the ring gear until opinion contacts a stop ring on the armature shaft this prevents further axial movement at the driver and pinion now locked to the shaft via the helix and over running clutch and transfer the armature rotation to the flywheel the pinion has only a small number of teeth compared to the ring gear and this means the armature will rotate several times for each revolution of the flywheel the gear reduction also multiplies the torque from the starter motor as soon as the engine starts its rotational speed will eventually exceed the speed of the armature at this instant the overrunning clutch breaks the connection between the pinion and the armature shaft and prevents over speeding and damage of the armature the pinion remains meshed as long as the engaging lever is held in the engaged position releasing the starter switch allows the solenoid plunger returned spring to return the engaging lever driver and pinion to their original position


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