Abstract: A brushless DC motor of the kind that includes a relatively large rotor permanent magnet magnetized radially in segments around its circumference to provide alternate segments oppositely magnetized has a stator magnetic structure with two dissimilar pole pieces in flux conducting relation to a pair of windings. A first of the pole pieces presents a face to the outer surface of the annular magnet across an air gap. A second pole piece, which may be somewhat further from the outer surface of the annular magnet, at the opposite end of the windings, presents only a narrow edge surface facing generally in the direction of the magnet. The modified pole piece is L-shaped or U-shaped, having one or two legs respectively, projecting from the coil support structure generally circumferentially with respect to the magnet.

Abstract: A simplified fan and brushless DC motor employs an annular permanent magnet magnetized in segments about its circumference. Each segment is oppositely radially magnetized with respect to the preceding segment as one proceeds around the magnet. Fan blades are located within the annular magnet. A coil and electromagnet structure defining two pole pieces reside outside the permanent magnet annulus. A Hall effect device switches the coil off and on in response to passage of the segments of the rotor magnet. Thus commutated, the single coil affects rotation of the rotor and the fan blades. A permanent magnet supported on the stator structure serves to magnetically detent the permanent magnet of the rotor, bringing the rotor to rest correctly for restarting.