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How Does a Starter Motor Work?

Starter Motors

David Taylor

15th Dec 2017

    To many people, starting a car may seem like pure magic. Turn the key, the engine starts and off you drive. Magic. However, turning on a car involves a lot more engineering than you may have originally thought.
    An engine in a car has two main jobs, these are:
    1. Suck in air.
    2. Combust fuel with said air.
    The problem for the engine is that it has to turn over to start the combustion process. If your engine isn’t turning over, there’s no air. If you have no air, then the fuel can’t combust. If the fuel can’t combust, then the engine won’t work.
    To solve this problem, engineers invented the starter motor. This is the initial tool responsible for turning over the engine and allowing all the other mechanics within your car to operate.
    TL:DR – Starter Motors
    A good way to understand the role of a starter motor is to imagine kick-starting a motorbike.  Instead of your foot kicking the engine into gear, a small electric component kicks the engine into gear.

    Starter Motor Jargon

    Before we start getting into the mechanics of how a starter motor operates, we think it’s important to clarify some of the car jargon you may stumble upon when reading this article. Refer back to this list further on in the article, if you need to.
Turning Over
    – If an engine is ‘turning over’, this means that the starter motor is working, engaging the flywheel and rotating the crankshaft.
    – Interchangeable with ‘turning over’, a common mistake is to believe that ‘turning over’ and ‘cranking’ are two separate functions.
Internal Combustion Engine
    – Typical car engine. This engine uses heat to combust petrol/diesel with an oxidizer in a combustion chamber.
Ignition Switch
    – Often key operated, the ignition switch sends a signal to the car battery.
    – Energy storage unit that is used to keep an engine running smooth when in neutral or when there is no acceleration.
    – Part of an engine that is attached to the flywheel. Sometimes referred to as the ‘crank’, a crankshaft changes the up and down motion of the pistons into rotation.
Trigger Wire
    – Generates an electrical signal which is initiated by the ignition switch.
Car Battery
    – A battery that is inside a car.
Starter Solenoid
    – Provides a current to the starter motor.
Pinion Gear
    – A type of small gear wheel which engages with the flywheel.

    How Does a Starter Motor Actually Work?

    Believe it or not, in the second it takes you to turn the ignition in your car, the mechanics of the vehicle will go through five steps to ignite your engine. These five steps are be listed below by the part that operates that step. Remember to refer back to the Starter Motor Jargon buster if you need help understanding the terms used in this article.
Step 1 – Triggering Switch
    When you turn the key in your car this sends a signal to the car battery. When the car battery receives this signal, it will operate the triggering switch which will then facilitate the transfer of energy from the battery to the starter solenoid. This is why you can’t start a car on a dead battery, but you can run a car on a dead battery.
Step 2 – Starter Solenoid
    Housed above the starter motor, the starter solenoid will receive a small electrical current sent from the car battery. This then closes a pair of heavy contacts within the solenoid that will relay a larger electrical current into the starter motor. All starter motors rely on a starter solenoid to operate.
Step 3 – Starter Motor
    After the solenoid has sent the larger electrical current to the starter motor, the electromagnet housed within the starter motor will switch on. This creates a magnetic field which will operate the pinion gear.
Step 4 – Pinion Gear
    When the electromagnet is turned on, the pinion gear senses the magnetic field and is forced out of the starter motor. Imagine a tiny, miniature gear on a bike, this pops out of the starter motor and fits snuggly onto the much larger flywheel.
Step 5 – Flywheel
    The final step before an engine starts involves the flywheel. This large mechanical gear is attached to the crankshaft and is operated by the pinion gear. When the pinion gear starts the flywheel, the gear starts to turn over and operate the pistons. As the pistons move up and down air is dragged into the engine. In turn, the engine computer unit (ECU) senses the air moving into the combustion chamber and starts to feed fuel into the engine. This combustion process can then take place and the engine will start.
    Are you replacing a broken or faulty starter motor? Don’t forget that we will buy your old core. Find out how you can contact us via the bottom of the homepage.
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