The present invention relates generally to an electronically commutated direct-current motor (ECM).
Motors of this kind are used, inter alia, to drive miniature fans (cf. EP-A1-0 908 630 and corresponding U.S. Pat. No. 6,013,966, FEHRENBACHER et al). For various reasons, it may be desirable to operate such a motor without a Hall generator, and for that purpose to commutate it with the voltage that is induced, during operation, by the rotor in the stator winding. This is known, for example, from U.S. Pat. No. 4,156,168, VOGEL, but in the case of this known motor the direction in which it will start after being switched on is not certain, and this known motor is therefore suitable only for specific applications in which rotation direction is not important.
One object or the invention is therefore to provide new electronically commutated motor whose startup rotation direction is certain. In accordance with the invention, the motor used is one having a rotor that, when the motor is currentless, has at least one mechanical preferred position. The current in the motor is controlled using a bistable multivibrator that has, at startup, an electrical preferred position which is adapted to the mechanical preferred position of the rotor. At startup, the result of the electrical preferred position is that the stator is excited in such a way that the rotor starts, from its mechanical preferred position, in the correct rotation direction. Because a separate rotor position sensor is eliminated, a motor of this kind has a simple configuration with good efficiency, since the power consumption for a rotor position sensor is eliminated. The invention is therefore particularly advantageous for miniature and subminiature motors in which the power consumption of a rotor position sensor, for example a Hall IC, would greatly reduce the electrical efficiency; and it is highly suitable, for example, for motors in which the electronic components are arranged separately from the actual motor (i.e. stator with stator winding, and rotor).
Further details and advantageous developments of the invention are evident from the exemplary embodiment described below and shown in the drawings, which is in no way to be understood as a limitation of the invention.