What is Starter Motor:Definition & Components

starter motor

Do you aware that an engine and its components will not function without a starting motor? You should be aware of this. A starting motor is a significant component used in an electrically driven internal combustion engine. A component is necessary to start the initial cycle since an engine cannot rotate on its own. The starting motor helps to start the engine, which then runs continuously on its power. We’ll look at the definition, starter motor function, types, components, importance, and pros and cons of starting motors today.

Importance of Starter Motors in Vehicle

Starter motors are large, powerful electrical devices. They are employed in a variety of practical applications such as driving mechanical loads, operating rotating machinery, water pumping, and so on. Starter motors are likewise quite expensive. As a result, the failure of a motor might result in a significant financial loss. If they put a motor immediately on a power source, it will consume a large amount of inrush current. This will have several negative consequences, including:

  • Due to the high current flow, significant heat could be generated in the motor coil and motor circuits.
  • High-current consumption might cause a voltage fluctuation in the incoming supply, affecting other communications directly with the same resource.
  • The motor windings and circuit wires may be scorched.

To avoid these serious impacts, a motor starter is necessary, which can safely start the motor by lowering the beginning currently.

What is a Starter Motor?

starter motor

The automobile engine as a whole mainly includes a crank connecting rod mechanism, a gas distribution mechanism, a fuel system, a cooling system, a lubrication system, an ignition system and a starting system. The starting system is to rotate the crankshaft to complete the engine starting process, and the starter is the core component of the starting system. When the engine starts, it is disconnected from the engine already working on the combustion process. The device is mounted on the gearbox housing of the engine, and the starter motor gear meshes with the flywheel teeth.Qualified starter motors will go through the acceptance of the six items on the table before leaving the factory.

No Acceptance items Heavy defect Light defect Acceptable Quality Level (AQL)
1 Exterior 4
2 Fastener Tightening Torque 1
3 Installation Size 0.4
4 Noise 4
5 load performance 0.4
6 Electromagnetic switch performance (23℃±5℃) 0.4

Acceptance Items & Qualified Quality Level Table

Components of a Starter Motor

The following are the components of starter motors, including field coils,bendix drive,armature,plunger, commutator etc.and about their functional areas:

Field Coils

The field coils are screwed into the housing because they are made from two or more coils linked in sequence. The battery powers these coils, which transform them into an electromagnet that rotates the armature. This results in the formation of a magnetic field surrounding the armature.

Bendix Drive

It is a gear mechanism that engages the starter motor with the engine flywheel. It has a one-way clutch that allows it to spin freely in one direction and engage the flywheel in the other.


The armature is a type of electromagnet that is installed on the crankshaft or bearings to offer guidance. It has a multilayer malleable iron core coated in multiple conductor coils or windings.


A plunger in a starting motor pushes ahead so that the pinion may be contacted.It is an integral part of the solenoid and is activated when the ignition switch is turned on. The plunger moves forward, engaging the drive gear with the engine’s flywheel, which turns the engine over.


A commutator is a part of the shaft at the back of the housing where brushes provide power. It is composed of two panels that are attached to that same axle of the armature and also provide links for such electromagnet coils.


The solenoid is made up of two wire coils that are coiled around the center. This solenoid operates like a switch, connecting and disconnecting the electrical connection between the starting motor as well as the vehicle’s charge.

Brushes Set

Brushes are components that travel on a segment of the commutator at the housing’s back. It brushes against the commutator, conducting power.

Lever Fork

The lever fork is linked to the plunger, causing both to move forward simultaneously to contact the pinion.Which is a part of the solenoid and is connected to the plunger. When the plunger moves forward, the lever fork moves with it, causing the pinion to engage with the engine’s flywheel.

Drive Pinion

A pinion is a tiny device that consists of a drive and forces. It connects instantly after starting the engine by spreading the gears to the flywheel teeth. The engine’s spinning is caused by the flywheel.


The function is to protect the internal components of the starter motor from damage and reduce the impact of the environment.

Types of Starter Motors

The listed below are the two types of starters , direct-drive starting motors and reduction-gear starter motors and their distinctions. Of the two, the direct drive starter motor is the most common type of starter motor. The gear reduction type starter motor is suitable for larger engines.

Direct Drive Starter Motor

Direct Drive Starter Motor

Direct-drive starting motors represent the most widely used and oldest types of starter motors offered. It has many applications and manufacturing designs, but it is a motor unit. Its operation, like those of other kinds, is straightforward.


  • Low Maintenance: Direct drive starter motors’ strong dependability translates to lower maintenance needs. In many circumstances, frameless motors can run for their entire lifetime without requiring maintenance cycles, resulting in decreased downtime and peak capacity, and reliability during the part’s total service lifespan.
  • Design: Because of their large spindle hole sizes and moderate axial height, direct drive motors provide substantial design benefits. Because direct drive motors are made up of only two parts of starter motors, the stator, and rotor, they could be designed to have incredibly small structures.
  • Affordable: Direct-drive starting motors are less costly than reduction-gear starter motors because they are easier to use,simpler and have fewer parts than reduction-gear starter motors. In addition, they are also more reliable and require less maintenance.


  • Less Powerful: Direct drive starter motor starts to take up to 50% more electrical current gear reduction starters to switch on the vehicle engine. This implies that direct drive takes greater current from the car’s battery, which necessitates longer battery cables and other components built to withstand high voltage.
  • Cost: Direct drive motors are sometimes considered to be more costly in general. Also, if a direct drive motor needs to be serviced or replaced, the prices will usually be greater than for a standard motor.
  • Electrical Components: The circuitry required for electric motors varies depending on the kind of motor and can scope from a simple AC motor, in which the recurrence of the grid determines how quickly the motor spins, to complete oriented control systems with positive feedback or various converting processes in an organized parallel manner for switched reluctance machines.

Gear Reduction Starter Motor

Gear Reduction Starter Motor

Gear reduction starting motors are also more effective than direct drive motors. This implies that less of the electrical energy turned to mechanical energy is wasted as heat. The majority of gear reduction starter motors are variable speed motors. However, the soothing design also creates most gear reduction starter motors to focus significantly more recently through the motor’s solenoid terminal than many other direct drive starter motors.


  • More Powerful: Gear reduction starter motors are more efficient than direct-drive starter motors. They can start huge engines as well as motors in tougher conditions.
  • Longer Lifespan: Since they contain extra features that can handle shock and wear and tear, gear reduction starter motors get a longer lifespan than direct drive starting motors.
  • Suitable for larger engines and harsher environments: The spherical gear reduction feature enables gear reduction starter motors highly appropriate for larger cars and motors in tougher situations.


  • More expensive: In general, gear-reduction starting motors are more costly than direct-drive starter motors. The extra materials and design complexity lead to a higher product price.
  • More complex design: Gear reduction starter motors are more sophisticated than direct drive starting motors due to the gear reduction arrangement. Because of their intricacy, they could be more challenging to resolve and operate.
  • Requires more maintenance: Gear reduction starts to have a greater part count, but structural wear is frequently less than direct drive starting since they employ bearings rather than bushings. The most frequent reason for delayed starting in hot motors with direct drive starters is misaligned or damaged bushings.


The vehicle’s starting motor serves a crucial purpose. Changing over and starting the engine, ensures that the automobile starts when you want it to. As detailed in this chapter, numerous components of the starting motor are used to guarantee appropriate torque and proper contact with the flywheel. These beginning motor components, however, deteriorate or break down with time, leading the starter to fail.

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