How does a car starter disengage after engine starts?

When you turn the key in your car's ignition, you are completing a circuit that allows electricity to flow from the battery to the starter motor. The starter motor then engages with the flywheel on the engine and turns it over. Once the engine starts, the starter motor is no longer needed and must be disengaged from the flywheel.

This is done by a component called a solenoid. The solenoid is an electromagnet that is mounted on the starter motor. When electricity flows through the solenoid, it creates a magnetic field that pulls in a plunger. The plunger is connected to a lever that disengages the starter motor from the flywheel.

When the key is released, the solenoid loses power and the plunger is released. This allows the starter motor to spring back into its original position and disengage from the flywheel.

The solenoid also plays a role in preventing the starter motor from engaging with the flywheel while the engine is running. When the engine is running, the alternator generates electricity that flows through the solenoid. This creates a magnetic field that holds the plunger in the retracted position, preventing the starter motor from engaging.

If the solenoid fails, the starter motor will not be able to disengage from the flywheel and the engine will continue to turn over even after the key is released. This can cause damage to the starter motor and the flywheel.