Disk drive in-hub radial-gap spindle motor with coils generating axial fields

• US 5,633,545 A
• Filed: 12/06/1995
• Issued: 05/27/1997
• Est. Priority Date: 12/06/1995
• Status: Expired due to Term

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: International Business Machines Corporation
• Inventors: Moser, Michael A., Albrecht, David W.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): Nguyen, Tran N.
• Application Number:
  US08/569,404
• Time in Patent Office: 538 Days
• Field of Search: 310/68 R, 310/67 R, 310/268, 310/156, 310/266
• US Class Current: 310/67.00R
• CPC Class Codes: H02K 1/148 Sectional cores H02K1/141 takes precedence
• CPC Class Codes: H02K 21/22 with magnets rotating around the armatures, e.g. flywheel magnetos
• CPC Class Codes: H02K 2201/12 Transversal flux machines
• CPC Class Codes: H02K 29/03 with a magnetic circuit specially adapted for avoiding torque ripples or self-starting problems

Abstract

An in-hub brushless permanent magnet DC motor has a radial working gap but uses coils wound in the axial direction of the motor. The coils generate fields that interact with the permanent magnet fields across the radial gap. The stator includes a plurality of angularly spaced stator teeth that have faces radially spaced across the gap from the permanent magnet. The stator teeth are connected to the base and extend axially into a cavity within the hub. The permanent magnet is a magnetically-segmented ring magnet located on an outer rim of the hub radially outwardly from the stator teeth. The magnetic flux from the permanent magnet is directed radially across the gap and into the stator teeth. Each stator tooth has an axially oriented post around which is wound a coil that generates an axial field. The axially-oriented part of each coil forms part of the magnetic circuit. The magnetic flux directed radially into each stator tooth is turned axially into the post and through the coil. The axially directed magnetic flux through the coil and post on each stator tooth is redirected from the axial direction to the circumferential direction by a ring magnetic flux guide. The ring flux guide interconnects the stator teeth and forms part of the magnetic circuit. Because the coils are wrapped around axial posts instead of the stator teeth a larger coil volume is obtained which results in higher motor efficiency and reduced heating of the bearing system. The angular spacing between adjacent teeth can be made very small or even eliminated since there is no need to locate a winding device between them as is required in conventional radial-gap motors. This results in a reduction in the motor cogging torque, which in turn allows a higher tooth/pole symmetry leading to better force balance and lower acoustic noise.

Claims

1. A brushless direct current motor comprising:

a base;

a shaft having a central axis extending from and fixedly attached to the base;

a lower ring bearing having radially inner and outer races with its inner race fixedly attached to the shaft;

an upper ring bearing having radially inner and outer races with its inner race fixedly attached to the shaft, the upper and lower bearings being spaced apart a fixed distance along said central axis;

a hub mounted to the outer races of the lower and upper bearings and rotatable about a central rotational axis generally coincident with said central axis of the shaft, the hub having a radially outer hub rim, the outer hub rim, the shaft and the spaced-apart lower and upper bearings defining a generally annularly shaped cavity located between the shaft, the outer hub rim and the spaced-apart bearings;

a magnetically segmented ring magnet attached to and located radially inwardly of the outer hub rim within said cavity for generating magnetic fields in a generally radial direction;

a plurality of stator teeth circumferentially spaced around the rotational axis, each stator tooth having a radially outer face spaced from and located radially inwardly of the ring magnet so as to define a radial gap;

a like plurality of magnetically permeable posts, each post extending in an axial direction generally parallel to the rotational axis and being connected to a corresponding stator tooth;

a like plurality of conductive coils, each coil being wound around a corresponding post for generating a magnetic field in an axial direction through its corresponding post and its corresponding stator tooth when conducting electrical current;

a ring flux guide of magnetically permeable material interconnecting adjacent posts in a generally circumferential direction; and

a support disk attached to the shaft, the support disk being attached to and supporting said interconnected stator teeth, posts, coils and ring flux guide within said cavity;

whereby magnetic flux from the ring magnet is directed radially inwardly across the radial gap to the face of a first stator tooth, axially through the post and coil on said first stator tooth, circumferentially by the ring flux guide to the post and coil on a second stator tooth adjacent said first stator tooth, axially through the post and coil on said second stator tooth, radially outwardly from the face of said second stator tooth across the radial gap to the ring magnet.

2. The motor according to claim 1 wherein the central planes of the ring magnet and each of the stator teeth are substantially coplanar.

3. The motor according to claim 1 further comprising a protective sleeve surrounding the coils for containing contaminants in the region of the coils.

4. The motor according to claim 1 wherein the support disk has radially directed fingers located between each of the stator teeth, the stator teeth being attached to and thereby supported by the fingers.

5. The motor according to claim 1 wherein the stator teeth are formed as a single piece structure with the teeth being connected to one another near their radially outer faces.

6. The motor according to claim 1 further comprising a magnetically permeable backing rim attached to an inner circumferential wall of the outer hub rim within said cavity, and wherein the magnetically segmented ring magnet is attached to and located radially inwardly of the backing rim;

whereby the backing rim provides a magnetic flux path between adjacent magnet segments.

7. A data disk drive motor assembly comprising:

the motor according to claim 1; and

a data disk mounted to the hub.