Disk drive spindle motor having split windings for each phase

Abstract

A reduced size brushless DC motor preferably for use as a disk drive spindle motor includes a rotor having two sets of permanent magnets, and a stator having separate portions corresponding to the two sets. An upper set of permanent magnets and the corresponding portion of the stator are located within the upper portion of the hub, which fits within the holes of the disks of a disk drive. A lower set of permanent magnets and corresponding portion of stator are located in the flange of the motor hub which supports the disks from below. In one embodiment, the stator core has all L-shaped cross-sectional area in the plane of the motor axis, one leg of the L driving the upper set of magnets in the rotor and the other leg driving the flange magnets. In a second embodiment, the stator core includes two separate pieces, one corresponding to each set of permanent magnets. In either embodiment, the separate coils or coil portions may be electrically connected in series or in parallel, or may be connected to switches enabling them to be driven in series or parallel selectively. Furthermore, the phases of the two sets of permanent magnets may be staggered to reduce the effects of transition from one magnetic pole to the next. Where the stator core includes two separate pieces, it is also possible to stagger the stator phases as well, reducing torque pulsations and wire interference.