How an Engine Starter Motor Works

Summary

This video explains the functioning of a modern pre-engaged starter motor in vehicles. It covers how the solenoid and contactor work together to provide power to the starter motor, enabling the pinion to mesh with the engine's flywheel. The use of planetary gears to increase torque and the role of a one-way clutch to protect the motor from damage is also discussed. The video highlights the importance of these components in ensuring smooth engine cranking and preventing harm to the system during startup.

Takeaways

• 😀 The starter motor is a powerful electric motor used to crank an engine and initiate its operation.
• 😀 The starter motor contains a pinion gear that meshes with the engine's flywheel to turn the crankshaft.
• 😀 A pre-engaged type starter motor is commonly used in modern vehicles, which requires a solenoid to function.
• 😀 The solenoid is an electromagnet that gets energized by a small current, enabling the starter motor to operate.
• 😀 The solenoid moves a plunger that closes a contactor switch, completing the circuit from the battery to the motor.
• 😀 The starter motor requires heavy current to operate, making it impractical to connect directly to the ignition switch and battery.
• 😀 The use of the solenoid allows the ignition switch to be smaller and reduces the complexity of wiring in the system.
• 😀 The pinion gear slides towards the flywheel, rotating slightly to engage more smoothly due to its helical spline.
• 😀 A gear reduction system, including a planetary gear set, amplifies the torque from the motor, typically with a ratio of 7:1.
• 😀 The planetary gear system consists of a sun gear, ring gear, and planet gears, providing compact high-torque performance.
• 😀 A one-way clutch is used to prevent the motor from being damaged by excessive speed from the flywheel after the engine starts.

Q & A

What is the purpose of a starter motor in a vehicle?

A starter motor is a powerful electric motor used to crank the engine, initiating the process of starting the vehicle by turning the crankshaft.

How does the pre-engaged starter motor work?

In a pre-engaged starter motor, the solenoid is energized when the ignition switch is turned on, causing a plunger to slide and connect two copper terminals, completing the circuit and powering the motor to turn the engine.

Why is a solenoid used in the starter motor circuit instead of directly connecting the battery to the motor?

The solenoid is used because the motor requires a large amount of current, which would necessitate an unusually large ignition switch and thick wires. The solenoid only requires a small current to energize, making the system more efficient and manageable.

What role does the solenoid play beyond powering the motor?

In addition to energizing the motor, the solenoid helps engage the pinion with the flywheel by sliding the pinion toward the flywheel and rotating it slightly using a helical spline.

How does the gear reduction in the starter motor work?

The gear reduction is achieved through the use of a pinion and a flywheel, typically with a gear ratio between 15:1 and 20:1. This reduction increases torque but is still insufficient to crank the engine, which is why a planetary gear set is introduced.

What is the purpose of the planetary gear set in the starter motor?

The planetary gear set further increases the torque available to spin the engine. The gear set is lightweight and compact, offering a large gear reduction within limited space.

Can you describe the components of a planetary gear set?

A planetary gear set consists of a sun gear, a ring gear, a carrier, and a set of planet gears. In starters, the ring gear is fixed, the sun gear is the input, and the planet carrier is the output.

What happens when the engine is started and the pinion needs to disengage from the flywheel?

When the engine starts, the ignition switch is released, de-energizing the solenoid, which causes the pinion to return to its resting position, disengaging it from the flywheel.

What could happen if the ignition switch is not released promptly after the engine starts?

If the ignition switch is not released in time, the flywheel will continue to drive the pinion at a high speed, which could damage the motor due to excessive back-drive.

How does the one-way clutch prevent damage to the motor?

The one-way clutch uses a set of rollers between the outer and inner races. When the motor drives the pinion, the rollers engage, allowing power transfer. Once the engine drives the pinion at high speed, the rollers disengage, preventing back-drive to the motor.