A torque motor ( torque (English ) = torque) is a low-, electric direct drive from the group of slow runners. Torque motors have very high torque at relatively low speeds.


A torque motor can be viewed on high torques optimized, large servo motor with hollow shaft simply as a. They are usually built as a brushless DC motor. Partial but also switched reluctance motors are called torque motor. Since no conceptual standardization exists, the designation Torque (or High Torque ) is colloquially often used for other forms of low-speed or high torque drives.

Torque motors are an external rotor (stator inside the rotor ( " runners " ) on the outside ) and as a conventional internal rotor (rotor inside the stator outside) to produce. External rotor are more common in torque motors, because in them due to the below shown correlations with the same size a larger torque is available.

Special forms are, for example, swing motors, which perform no 360 ° rotation. As a modification of the torque motor, the linear motor can be considered, which represents a development of a torque motor and is used for linear motors.


In its basic principle of the conventional electric motors, torque motor. There are largely the basis for calculating multi-pole servo motors. The increased torque receives the torque motor is mainly due to the high number of pole pairs and the resulting short paths for the magnetic return circuit and windings, resulting in low copper losses and a deep performance combination of mass due to torque.

In addition, torque motors have a large diameter. Because torque is at a given force F effect on the relationship

Depending on the radius r. The force generated when the electric motor in the air gap between rotor and stator. Therefore, external rotor can by the larger air gap radius for the same size higher moments produce an internal rotor.


The large drive torque of torque motors enables high accelerations and result in high dynamics of the system. Torque motors have a higher stiffness than drive classic motor-gear units and no backlash. In order to better control characteristics result from reduced interference ( see: cascade control ) and increased repeatability.

Powerful torque motors have some very large dimensions, but due to the attributable mechanical elements such as timing belt and gears, they are compact. The motor is arranged coaxially to the shaft to be driven.

Torque motors are characterized by the elimination of mechanical elements noise and low maintenance. In the engine there is virtually no wear. The heat generation is greater than in conventional servo motors, an exposed location of this heat source is due to of the lost gear is often not possible. This water cooling of the motor is required in many cases.

In the acquisition torque drives are cheap intense - compared to conventional motor-gear units by a factor of 1.5 to 2.5 more expensive. Cost savings are in maintenance and energy consumption. For although torque motors usually have a lower maximum efficiency than high-speed engines, the entire system can be made more efficient by eliminating gearboxes and transmission elements.


Today, in many areas, for example for machine tools made ​​requests that can be satisfied only with modern drives. Motors with gearboxes here are often at a disadvantage because transmission can be built with little play only with great effort and the effective moment of inertia of a high-speed motor in the square of the gear ratio on the slow side is transmitted.

Torque motors are used for rapid and precise move and positioning and everywhere in application where high dynamic, low-backlash or high-torque drives are required.

  • In machine tools, rotary tables, rotary tables and other actuators are equipped with torque motors to achieve high positioning accuracy and wide dynamic range.
  • In servo presses torque motors replace the conventional engine flywheel combination to speed through the hub to be able to dynamically control.
  • In servo valves pivoting torque motors are used for the controlled opening and closing.
  • In the inland waterways are torque motors since 2010 constituents of diesel-electric drive systems and are built directly on the propeller shaft.