A starter motor is an electric motor that turns the engine on when you turn the ignition key. It is a device that rotates (cranks) an internal combustion engine so that the engine can operate under its power. You might be surprised to learn how much more work it takes to get it to crank.
When the engine turns over, it creates suction, which is necessary to get air into the engine. When your engine fails to turn over, it indicates a lack of air intake. Without air, fuel combustion is impossible.
In this reading, we’ll explore what a starter motor is, its function, diagram, parts, types, and how it works.
Let’s get started!
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What Is A Starter?
A starter, or starter motor, is an electrical device that is used to rotate (crank) internal combustion engines so as to initiate the engine’s operation under its own power. As soon as the engine begins to run, it gets disconnected from the engine, which now relies on the combustion process.
The component is mounted on the engine’s gearbox housing, and the starter motor gear meets the flywheel’s teeth. Being an electrical component, a starter consists of a powerful DC (direct current) electric motor and a solenoid. The solenoid receives positive power directly from the battery and heart current from the engine body.
In order to turn the engine, a 12-volt battery must be used to run the starter. This means the battery has to be sufficient to power the device. In most situations where the starter motor clicks but won’t start, the issue is either from the battery or the starter itself.
Function Of A Starter Motor
The primary function of a starter motor in an automobile engine is to start the engine so it can work on its power. This is achieved due to the high torque rotation from the starter motor, which is used to turn the engine at fast speeds. The starter motor gives the engine the first or second rotation it needs to start working on its own.
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Parts Of The Starter Motor
There are several components that make up the starter motor. Here are its main parts:
Armature
An armature is an electromagnet component that is mounted on the driveshaft or bearings for a guide. It is made of a laminated soft iron core that is wrapped with numerous conductor loops or windings.
Field Coils
The field coils are held in a housing with screws, as it consists of two or more coils connected in series. These coils receive power from the battery that converts them into an electromagnet that turns the armature. This creates a magnetic field around the armature.
Commutator
A commutator is a section of the shaft at the rear of the housing on which brushes run to conduct electricity. It is made of two plates mounted to the axle of the armature; the plates provide connections for the coil of the electromagnet.
Brushes
Brushes are parts that run on a section of the commutator at the rear of the housing. It rubs the commutator and conducts electricity.
Solenoid
The solenoid features two coils of wire that are wrapped around the core. This solenoid serves as a switch that connects and closes the electrical connection between the starter motor and the vehicle’s battery.
Plunger
The function of a plunger in a starter motor is to push forward so the pinion can be engaged.
Lever Fork
The lever fork is connected to the plunger, which makes them push forward together to engage the pinion.
Pinion
A pinion is a small mechanism containing gears and springs. It engages immediately after the engine starts by extending the gear to the flywheel teeth. The flywheel is the source of engine rotation.
Diagram Of A Starter Motor
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Types of Starter Motor
There are various types of starter motors in a car, each with its own design and function. Here are its main types:
Direct Drive Starter Motor DD
Direct drive is the most common and older type of starter motor available out there. It comes with different applications and construction designs, but it’s a solenoid-operated unit. Well, its working remains plain like other types.
When the ignition switch or key is depressed, the car battery energizes the solenoid. This presses the plunger to shift the lever that directs the pinion gear. The pinion gear then meshes with the engine flywheel. So, as the starter motor spins, the flywheel spins along, which then causes the engine’s combustion to run on its own.
Planetary Gear (PLGR)
The existence of these types of starter motors has vastly replaced direct-drive types. It is a permanent magnet that transmits power between the pinion shaft and the armature. The armature spins with more speed and torque. The essence of planetary gear is to reduce gear, which further reduces the requirement of high current.
There is a sun gear located at the end of the armature and three planetary carrier gears inside the ring gear, held stationary. In addition, planetary gears are able to attain a great amount of gear reduction as the ring gear is held and the sun gear is input while outputting the carrier.
Permanent Magnet Gear Reduction (PMGR)
The permanent magnet gear reduction is designed to offer less weight, easy construction, and less heat generation. It features four to six magnet field assemblies rather than field coil starters. It has three terminals on the 12V solenoid and is also heavy-duty, making it require less current. Because there are no field coils, the commutator and brushes transfer current directly to the armature.
Permanent Magnet Direct Drive PMDD
The PMDD types of starter motors are similar to direct drive in several ways. Their difference is that the field coil is replaced with permanent magnets in the permanent magnet direct drive type.
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Off-Set Gear Reduction (OSGR)
These starter motor types work at high speeds at low currents. They are lighter and more compact, which makes them easy to assemble. Off-set gear reduction starters are common among four-wheel-drive vehicles as they increase cranking torque.
Inertial Starter
Inertial starters are the electric types that achieve the features of all types of starter motors. It works perfectly fine during cranking and even ensures the motor part’s safety. It starts the engine strong and very fast, making it the best option for cracking speed. Furthermore, the amount of weight associated with the torque capacity of the starter is extremely minimal.
How A Starter Motor Works
When the ignition key is turned or the button is pressed, the transmission should be in the park or neutral state. The battery voltage goes through the starter control circuit to activate the solenoid. The solenoid powers the starter motor, which aids in pushing the starter gear forward to mesh with the engine flywheel.
This flywheel is mounted on the engine crankshaft, so as the starter motor spins, it turns the flywheel as well as the crankshaft. As soon as the engine starts, the system disengages from the flywheel. Starter motors in an automatic transmission can only be operated when the vehicle is in park or neutral. But in manual transmission, you have to press the clutch pedal.
Inside the starter motor, four field windings are connected to the housing from the inside. The armature (rotating parts) is connected through the carbon brushes in series with the field coils. However, in some starters, field coils are replaced with magnet fields. There is a small gear at the front of the armature attached with an overrunning clutch.
Starter Motor Video
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Conclusion
The starter motor plays a crucial role in the starting system of a vehicle by cranking the engine until it can run on its own power. Operating with the help of the battery and ignition switch, it converts electrical energy into mechanical rotation to initiate combustion.
A faulty starter motor can lead to no-start issues, clicking sounds, or slow engine cranking. Regular inspection of the starter, wiring, and related components helps ensure reliable vehicle operation and prevents unexpected breakdowns. Maintaining a healthy starter system is essential for dependable engine performance.
FAQs on Starter Motor
What is a starter motor?
A starter motor is an electric motor that cranks the engine to start the combustion process in an internal combustion engine.
What are common signs of a bad starter motor?
Clicking noise, slow cranking, intermittent starting, or complete failure to start are common symptoms.
What causes starter motor failure?
Common causes include worn-out brushes, electrical issues, a faulty solenoid, or damaged wiring.
Can I start a car with a bad starter motor?
Sometimes tapping the starter lightly or jump-starting the car may work temporarily, but replacement is usually necessary.
How long does a starter motor last?
Typically, a starter motor can last between 100,000 and 150,000 miles depending on usage and vehicle type.
Is the starter motor the same as the alternator?
No. The starter motor starts the engine, while the alternator charges the battery and powers electrical systems once the engine is running.