Electric motors are an important driving force of modern technology, from household appliances to industrial machinery. Among the many motor designs, internal rotor motors (also known as internal rotor motors) are one of the most widely used types due to their high efficiency, compactness, and high performance. Unlike an outer rotor motor, where the rotor surrounds the stator, the rotor of an inner rotor motor rotates inside the stator. This structure has the advantages of good heat dissipation performance, high speed and superior torque characteristics.
The Working Principle of the Internal Rotor Motor
By the core definition, an internal rotor motor is a type of motor in which the rotor (rotating part) is placed inside the stator (fixed part). This design is the oldest and most traditional structure in electrical engineering, dating back to the early days of electromagnetism. Unlike an external rotor motor, where the rotor wraps around the stator, the inner rotor structure places the rotating element at the core of the motor, which is surrounded and driven by the magnetic field generated by the stator.
Characteristics of Internal Rotor Motors
The internal rotor motor has a unique structure that is “built into the rotating core”, in which the rotor (rotating part) is surrounded by a stator (stationary part). This design is commonly used in:
- Brushed/brushless DC motor
- AC induction motor
- Synchronous motors
Core Features:
- Concentric rotating structure: to achieve better dynamic balance performance
- High-speed running capacity:30-50% reduction in moment of inertia
- Efficient heat dissipation design: The stator is externally positioned to form a natural heat dissipation channel
- Compact and lightweight: the power is increased by more than 35%.
The Structure of an Internal Rotor Motor
The internal rotor motor is made up of several key components that work together to ensure efficient operation:
1. Rotor (Rotating Part)
As the motion core of the motor, the brushless DC motor uses a permanent magnet structure, while the induction motor uses conductive windings. The rotor is mounted on the central shaft and transmits the mechanical energy to the load end. Its lightweight, balanced design ensures smooth operation at high speeds.
2. Stator (Stationary Part)
It is composed of laminated silicon steel sheets and copper windings, and when energized, a magnetic field is generated to drive the rotor to rotate. The external layout effectively improves heat dissipation efficiency and prolongs the life of the motor.
3. Bearings
The rotor shaft is supported for frictionless rotation, ball bearings are mostly used for high-speed applications, and plain bearings are used for silent scenarios.
4. Motor Housing
Protects internal components from dust, moisture, and mechanical damage, often with heat sink fins or vent slots for enhanced thermal management.
5. Commutation System
There are two implementations based on the type:
Brushed Motor: change the current direction of the rotor winding through carbon brushes and commutators, the structure is simple but requires regular maintenance
Brushless Motor (BLDC): It adopts electronic controller commutation, which has the advantages of high efficiency, long life and maintenance-free.
The Core Advantages of Internal Rotor Motors
Compared to other motor types, internal rotor motors offer several significant advantages:
(1) High Performance
Superior high-speed performance is its primary feature. Due to the smaller rotor diameter and lower inertia, this type of motor can achieve speeds far exceeding those of external rotor motors, which are especially suitable for scenarios that require fast dynamic response, such as CNC spindles and drone propulsion systems.
(2)Fast Heat Dissipation
Excellent heat dissipation is another advantage. The external design of the stator allows the operating heat to be quickly transmitted to the housing to dissipate, which can effectively prevent overheating and ensure long-term stable operation. At the same time, its compact and lightweight structure makes it useful in space-constrained fields such as electric vehicles and robots.
(3)High Torque
The high torque-inertia ratio gives it the ability to respond quickly to load/speed changes, which is essential for servo motors and precision motion control systems. In addition, it is compatible with AC/DC/EC power supply, and can be customized to meet the needs of different applications.
Application Scenarios of Internal Rotor Motors:
The versatility and reliability of internal rotor motors make them a core component in countless industries. Here are examples of how they power everything from everyday equipment to cutting-edge technology:
(1) Electric Vehicles and New Energy Mobility:
In the field of new energy, internal rotor motors are at the heart of electric vehicles (EVs) and new energy mobility solutions:
Electric Vehicles: High-power brushless internal rotor motor as drive motor. Delivers instant torque for fast acceleration and high revs for high-speed driving. Companies like Tesla rely on these motors for high efficiency (up to 4 miles per kWh) and high performance (0-60 mph in less than 3 seconds).
E-bikes and Scooters: Compact in-rotor motors are often integrated into the hub or frame to provide power for assisted riding or throttle drive. Its lightweight design ensures that the e-bike remains flexible, while efficient heat dissipation allows it to be used for long periods of time in hilly terrain
(2) Industrial Automation
In manufacturing and logistics, internal rotor motors are the key to increased precision and productivity:
CNC Machines: High-speed internal rotor spindles enable fast material removal in milling and turning operations for ultra-fine machining.
Robotic Arms: Servo motors with an internal rotor design enable robots to perform repetitive tasks, such as pick-and-place operations or welding, for example, on automotive assembly lines, where they ensure that each part is placed with a placement error of less than one hundredth of a millimeter.
(3)Aviation & Drones
In the aerospace sector, internal rotor motors are favored for their power-to-weight ratio and speed:
Drones and unmanned aerial vehicles (UAVs): Multi-rotor drones typically use small, high-speed internal rotor motors (often paired with reduction gears) to generate lift.
Epilogue:
From the early days of electric motors to today’s cutting-edge technology, internal rotor design has proven itself to be the backbone of reliability, efficiency and innovation. With the rotor at the core and the stator outward, the internal rotor motor provides high speed, precise control, and powerful heat dissipation, characteristics that shape a wide range of industries, from automotive to aerospace.
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What is a Internal Rotor Motor?