Claims
- 1. A brushless dc motor having a cylindrical type air gap, a slotted stator core and permanent magnet excitation, the air gap being defined between circumferentially facing faces of the slotted stator core and an opposing ring of permanent magnets formed to rotate with respect to the core, the core having a plurality of radially extending winding slots, and the motor including at least one winding forming electromagnetic poles defined in the sectors between slots of the stator core with a plurality of raised portions on each of the electromagnetic pole faces extending radially into the air gap, the circumferential width of the raised portions being small compared to the circumferential width of the pole pitch, the raised portions on each of the pole faces being located such that the distance measured in the direction of rotor rotation from the center of a stator slot defined between any given pair of stator poles to the center of one of said raised portions on the stator face adjacent said given pair of stator poles is equal to n times the rotor pole pitch, n being a whole number.
- 2. A motor according to claim 1, wherein the circumferential extent of the raised portion corresponds to from 0.5 to 1 times the circumferential width of the stator slot orifice.
- 3. A motor according to claim 2, wherein the air gap directly next to the raised portion as seen in the circumferential direction has the maximum dimension, which dimension decreases in the direction of the stator pole ends, preferably to a value equal to that above the cog.
- 4. A motor according to claim 3, wherein the height of the raised portion is from 0.1 to 0.3 mm with an effective air gap of from 0.3 to 0.6 mm.
- 5. A motor according to claim 3, wherein the reduction in air gap dimension is gradual and continuous.
- 6. A motor according to claim 5, wherein the air gap next to the raised portion soon decreases drastically in dimension, then increases again near the stator pole ends and finally decreases directly at the stator pole ends.
- 7. A motor according to claim 1, wherein the rotor is an internal rotor.
Priority Claims (2)
Number |
Date |
Country |
Kind |
3600737 |
Jan 1986 |
DEX |
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3723099 |
Jul 1987 |
DEX |
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Parent Case Info
This application is a continuation of Ser. No. 07/218,397, filed Jul. 13, 1988, now U.S. Pat. No. 4,998,032 which is a continuation-in-part of U.S. Ser. No. 07/140,976, filed Jan. 6, 1988, now abandoned, which is a continuation of U.S. Ser. No. 07/002,957, filed Jan. 13, 1987, now abandoned.
Foreign Referenced Citations (1)
Number |
Date |
Country |
0169569 |
Nov 1990 |
EPX |
Continuations (2)
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Number |
Date |
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Parent |
218397 |
Jul 1988 |
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Parent |
2957 |
Jan 1987 |
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Continuation in Parts (1)
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140976 |
Jan 1988 |
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