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Internal rotor motors

Innenläufermotor als Aufzugsantrieb

What is an internal rotor motor?

An internal rotor motor is a type of electric motor. An internal rotor motor consists of a movable rotor located inside the machine and an external fixed assembly, the stator. When current is supplied, the stator windings create an electromagnetic field of rotation, which causes the rotor to rotate through interaction with its rotor magnetic field.

Different technologies and motor types can be designed as internal rotors, e.g. EC motors or AC motors.

 Proven quality from ZIEHL-ABEGG: Motors for ventilation systems or elevator drives designed as internal rotors.

How does an internal rotor motor work?

A magnetic field is generated in the internal rotor of the internal rotor motor. Depending on the technology, the rotor field is generated by alternately poled permanent magnets (EC internal rotor) or by a wound sheet metal package with the addition of electrical current (AC internal rotor). The surrounding stator contains circular windings that create an electromagnetic field of rotation when current is supplied.
The rotor is set in motion by attracting different polarities while simultaneously rejecting identical polarities. The internal rotor moves with the stator's moving field of rotation or is driven by it.
The speed range required for the respective application can be configured electronically by means of integrated control electronics (EC internal rotor) or a connected frequency inverter (AC internal rotor).

How are internal rotor motors constructed?

An internal rotor motor typically consists of the following components:

  • Housing with power connection
  • Internal rotor with alternately poled permanent magnets (EC internal rotor) or wound sheet metal package (AC internal rotor), which are mounted on a shaft extending from the housing
  • Stator lamination pack surrounded by multiple windings for generating the rotating magnetic field

​ Maximum efficiency from ZIEHL-ABEGG: Designed as an internal rotor, the ZAtop is the new benchmark in elevator technology.

Housing with electrical junction box

Stator lamination pack with windings

Rotor stack with permanent magnets (EC internal rotor) or rotor windings (AC internal rotor)

Motor shaft

What are the advantages of internal rotor motors?

  • High output density: The small diameter of the rotor enables a high output density so that the required level of torque can be achieved even in a small installation space.
  • High speed: Due to their design, internal rotor motors achieve high speeds, which is advantage in model construction or servo motors, for example.
  • Low moment of inertia: Changes in speed or direction of rotation can be implemented in fractions of a second if required.
  • Additional flexibility: Two usable shaft ends allow an additional system or functional elements to be installed. This means that the internal rotor can be used in a wide variety of ways and integrated into all types of systems.
  • Type-specific advantages: If, for example, a BLDC motor is designed as an internal rotor, it exhibits very low mechanical wear due to the electrical commutation. This generally distinguishes brushless electric motors from conventional brush motors, which experience wear on the slide or sliding contacts due to material abrasion and spark formation (“brush fire”) .
  • Precisely adjustable speed range
  • Low noise and low vibration

Where are internal rotor motors used?

Due to their specific performance characteristics and advantages, internal rotor motors are often used in the following applications and areas:

Differences: Internal and external rotor motors

In an internal rotor motor, the moving rotor is located inside the machine and is surrounded by an immovable stator. Due to the small diameter of the rotor, motors of this type achieve a very high output density with low inertia. This makes it possible to change speed and direction of rotation within milliseconds, making this type of electric motor particularly attractive for the medical technology sector, for example, where maximum possible precision is important.
In an external rotor motor, on the other hand, the stator is installed inside the machine and is surrounded by an external rotor that transmits the torque. Due to the large area of interaction between the rotor and stator, an external rotor motor achieves high torque with comparatively low energy consumption.

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