Collectorless D.C. motor - has rotor magnet poles with small pole gaps and varied air gap between poles and stator

摘要

The external rotor motor (1) has a two pole rotor (2) formed as a continuous magnetic ring and a double 'T' yoke stator (5) with upper and lower pole (6a,7a). Grooves (8a,9a) between the stator poles carry the two windings (10,11) which run starting from the positive pole (12) and have their ends connected to the transistor circuitry (16,17). A digital switching Hall I.C. (13) fed from the positive pole via a series resistor (18) is used as a rotational position detector, the output controlling the transistor (16) directly, and the second transistor (17) via an inverter stage. The rotor magnet poles exhibit a trapezoidal, sinusoidal or rectangular magnetisation with small pole groups (3,4) between the poles (6,7), and the air gap - seen in the direction of rotation - in the area between slot openings (8,9) starts off with its greatest depth at the slot opening (9). It then becomes smaller over an angle of some 30 to 70 degrees electrical, and runs to the next pole (8) with a constant gap. This design exhibits a current characteristic with practically no null value.