ClassX Video Lessons Youtube Channel The Engineering Mindset Starter Motor Explained – How a car's electric starter motor works
Have you ever wondered how cars start so effortlessly with just a turn of a key or the push of a button? This convenience is all thanks to the starter motor, a crucial component in vehicles with combustion engines. Let’s dive into how this small yet powerful device works to get your car moving.
In the early days of automobiles, starting a car was a manual and often risky task. Drivers had to crank the engine by hand using a handle connected to the crankshaft. Thankfully, modern cars have replaced this cumbersome process with the electric starter motor, making starting your car as simple as turning a key or pressing a button.
The starter motor is an electric motor that converts electrical energy from the car’s battery into mechanical energy. This energy is used to kickstart the engine’s combustion process. When you start your car, the starter motor engages with the engine’s flywheel, a large wheel with teeth around its edge. The motor’s pinion gear temporarily connects with the flywheel, causing it to rotate. This rotation moves the crankshaft and pistons, initiating the combustion process that powers the engine. Once the engine is running, the starter motor disengages, and the engine continues to operate independently.
The starter motor comprises several essential parts:
When you turn the ignition key, a small current flows into the solenoid coil, which consists of two parts: the pulling coil and the holding coil. These coils generate a magnetic field that moves an iron piston within the solenoid. This movement connects the main electrical terminals, allowing a large current to flow into the motor, powering it up.
The motor’s electromagnetic field interacts with the stator’s magnetic field, causing the rotor to spin rapidly. This rotation is transferred through the shaft and pinion gear, turning the flywheel and starting the engine. As the engine begins to run faster than the starter motor, the overrunning clutch disengages, allowing the pinion gear to spin freely.
Once the engine is running, releasing the ignition key cuts power to the solenoid coil, allowing the spring to push the piston back. This action disengages the pinion gear from the flywheel, and the starter motor stops drawing power. The engine continues to run on its own, and the alternator takes over, recharging the battery for future starts.
Understanding how a starter motor works not only gives you insight into your car’s operation but also helps you diagnose potential issues, such as a faulty starter or a dead battery. For more fascinating insights into automotive engineering, explore additional resources and keep learning!
Try constructing a basic electric motor using household items like a battery, copper wire, and magnets. This hands-on activity will help you understand the principles of electromagnetism and how they apply to the starter motor’s operation.
Examine a detailed diagram of a starter motor. Identify and label each component, such as the solenoid, rotor, and pinion gear. Discuss with your classmates how each part contributes to the motor’s function.
In groups, role-play the starting process of a car. Assign roles for each component of the starter motor and simulate the sequence of events from turning the ignition key to the engine running independently.
Research how cars were started before the invention of the electric starter motor. Present your findings on manual cranking and discuss the evolution and advantages of modern starter motors.
Work through a case study where a car fails to start. Use your knowledge of the starter motor to diagnose potential issues, such as a dead battery or a faulty solenoid, and propose solutions.
Here’s a sanitized version of the provided YouTube transcript:
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This video explains how cars used to start by cranking the engine by hand, but now we simply turn a key or press a button. This advancement is made possible by the starter motor, and I will show you how it works.
Starter motors are found in combustion engine vehicles and are relatively small but powerful electric motors that convert the electrical energy from the battery into mechanical energy. Have you ever started a car with a dead battery or have tips for diagnosing a faulty starter motor? Let me know in the comments!
To start a car engine, we need to initiate the combustion process by moving the pistons, which are connected to the crankshaft. In early cars, a handle was connected to the crankshaft and turned by hand, which was inconvenient and somewhat dangerous. In modern engines, a flywheel with teeth around its perimeter is connected at the rear. The starter motor is positioned close to this flywheel, and when we start the car, it temporarily connects to the flywheel, forcing it to rotate. This action turns the crankshaft, moves the pistons, and starts the combustion process. After this, the starter motor disconnects from the flywheel, and the engine continues to run.
The pinion gear of the starter motor is small compared to the flywheel and must rotate at a high speed while requiring high torque to turn the crankshaft. Therefore, the starter motor draws a large current from the battery during startup. Once the engine is running, the alternator generates electricity and recharges the battery.
Let’s look at the main parts of the starter motor. At the top, we find the solenoid, which has electrical connections and a thick wire running down into the main case that houses the electric motor. There’s a removable plate on the rear of the main case. The drive end frame holds everything together and allows the motor to be mounted to the car. The front has a shield partially covering the pinion gear.
Inside the device, the shaft runs the entire length of the starter motor, and attached to the shaft is the rotor, often called the armature. This rotor rotates with the shaft and has channels cut into it with coils of thick enameled wire inserted into each channel. The ends of the wires connect to commutator plates, which are segments of copper insulated from each other and spaced around the rotor’s circumference.
At the end of the motor, spring-loaded brushes push against the commutator plates, allowing electricity to flow through the coils of wire in the rotor. Surrounding the rotor and attached to the case are permanent magnets that form the stator. Some starter motors use field windings, which are coils of wire that generate an electromagnetic field when powered.
When electricity flows to the rotor, it generates an electromagnetic field that interacts with the stator’s magnetic field, causing the rotor to rotate. The gaps in the commutator reset the magnetic field, preventing the rotor from aligning, which results in constant rotation. Typically, there are two pairs of brushes and multiple commutator plates activated simultaneously to ensure a strong magnetic field and smooth rotation.
The thick wire runs from the brushes to the solenoid. Inside the solenoid, there is an iron piston that moves back and forth, surrounded by a solenoid coil. When energized, the solenoid coil generates an electromagnetic field that attracts the iron piston, pulling it backward. A return spring allows the piston to return to its original position when the solenoid is de-energized.
The rear end of the piston has a conductive metal plate. As the piston moves back, it contacts the main electrical terminals on the rear of the solenoid, allowing a large electrical current to flow into the brushes and power the motor. When the coil is de-energized, it cuts power to the motor.
The front end of the piston connects to a lever, which pivots and transfers motion to the drive sleeve. An overrunning clutch sits ahead of this, with the pinion gear attached to the front of the shaft. The overrunning clutch protects the electrical motor. Inside the clutch are rollers that can move back and forth, locking the pinion gear in place when it starts to turn. Once the engine starts and the flywheel rotates faster than the pinion gear, the rollers unlock, allowing the pinion to rotate freely.
Some starter motors also use a planetary gear to increase torque, but we won’t go into detail on that here.
When the ignition key is turned, a small current flows into the solenoid coil, which consists of two coils known as the pulling coil and the holding coil. The pulling coil is connected to the main output terminal, and both coils create a strong magnetic field that pulls the piston back. As the contactor plate connects across the main terminals, the pulling coil turns off due to no voltage difference, while the holding coil continues to run.
As the piston moves back, it pulls on the lever, which pivots and transfers motion to the drive sleeve, pushing it forward. This action slightly rotates the pinion, allowing it to lock the rollers in the clutch and slide into the flywheel. Once the contactor plate connects across the terminals, a large current flows through the contactor plate, thick wire, and into the brushes, powering the motor.
The coil produces an electromagnetic field that interacts with the stator, causing the rotor to rotate rapidly with high torque. This rotation transfers through the shaft, clutch, and pinion gear, turning the flywheel and starting the combustion process. Eventually, the engine rotates the flywheel faster than the starter motor, unlocking the overrunning clutch, allowing the pinion gear to spin freely.
When the key is released, power to the solenoid coil is cut, releasing the piston. The spring pushes the lever back, removing the pinion gear from the flywheel, and the current to the starter motor is cut. The combustion engine continues to run on its own, and the alternator recharges the battery.
For more information on automotive engineering, check out the links in the video description. Don’t forget to follow us on social media!
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This version removes any promotional content and maintains a focus on the technical aspects of how starter motors work.
Starter Motor – An electric motor that initiates the engine’s operation by turning the crankshaft until the engine can sustain itself. – The starter motor is crucial for starting the car’s engine, especially in cold weather conditions.
Electrical Energy – Energy that is caused by the movement of electrons through a conductor, often used to power devices and machinery. – The electrical energy supplied to the circuit was converted into light and heat by the bulb.
Mechanical Energy – The sum of potential and kinetic energy in a system, used to perform work. – The wind turbine converts wind’s kinetic energy into mechanical energy to generate electricity.
Combustion Process – A chemical reaction between a fuel and an oxidant, producing heat and often light, used in engines to generate power. – The combustion process in the engine’s cylinders releases energy that propels the vehicle forward.
Flywheel – A heavy rotating disk used to store rotational energy and stabilize the speed of a machine. – The flywheel helps maintain a consistent engine speed by smoothing out fluctuations in power output.
Rotor – The rotating part of an electrical or mechanical device, such as in an electric motor or generator. – The rotor in the electric motor spins rapidly to convert electrical energy into mechanical motion.
Solenoid – A coil of wire that acts as a magnet when carrying electric current, often used to control a mechanical device. – The solenoid in the starter motor engages the pinion gear with the engine’s flywheel.
Magnetic Field – A region around a magnetic material or a moving electric charge within which the force of magnetism acts. – The magnetic field generated by the solenoid is used to activate the starter motor.
Pinion Gear – A small gear that engages with a larger gear or rack, often used in the starter motor to turn the engine’s flywheel. – The pinion gear meshes with the flywheel to crank the engine during startup.
Alternator – A device that converts mechanical energy into electrical energy, typically used in vehicles to charge the battery and power the electrical system. – The alternator ensures that the car’s battery remains charged while the engine is running.
