Direct-Current Motors

Direct-current Motors







Good starting and control characteristics are standard features of direct-current motors. The rotor speed depends directly on the extent of the supply voltage and is therefore extremely easy to regulate.

The typical design of a direct-current motor includes a permanent magnet for the stator, while the operating voltage is supplied to the rotor coil via carbon brushes. When the motor is switched on, the rotor rotates until the rotor magnetic field is aligned with the stator magnetic field. In order for the rotor to continue rotating, the polarity and therefore the direction of the magnetic field in the rotor must be changed via the commutator. In the above example, the polarity is changed every 180° to ensure the rotor continues rotating.

On the 2 pole and 4-pole motors, a significant imbalance is generated during operation so a much larger number of poles is required in practice. The commutator generates the correct polarity so that the rotor can continue to rotate.







The different driving situations that arise in hybrid driving mode such as:
- alternating load
- frequently fluctuating speed
- operation as motor and generator
- relatively high performance

require a much more complicated design than the one illustrated. In order to reverse the rotation direction or operate the generator, for example, the power electronics must ensure varied switching of the rotor and stator coil. Even if the direct current from the high-voltage battery in the vehicle cannot be converted to an alternating or three-phase current, the voltage must still be adapted in order to achieve different speeds and torques.

However, additional problems caused by wear and friction on brushes and slip rings are encountered in driving mode.
In conclusion, the use of direct-current motors in hybrid vehicles is not an option for precisely the reasons stated above.

Installation locations for direct-current motors used in motor vehicles include:
- Wiper motors
- Fan motors
- Drive links
- Starter motor

Due to their high starting torques and simple speed control via the operating voltage, direct-current motors are typically installed as drive motors for rail vehicles or used in applications where only direct current energy is available and requirements are not demanding enough to justify converting the DC current into an alternating/three-phase current.

Brushless direct-current motors

Brushless direct-current motors are identical in design to synchronous motors (see below), but require integral control electronics to convert the direct current into a suitable alternating current or three-phase alternating current. The three-phase synchronous motor with power electronics used in hybrid technology can also be classed as a "brushless direct-current motor".