Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-03-29
2001-06-26
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S112000, C310S261100
Reexamination Certificate
active
06252323
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to revolving magnetic field type motors.
Japanese Unexamined Patent Publication No. 8-251847 describes a typical revolving field type motor. The motor includes an eight-pole rotor that has a pair of magnet sets each including eight permanent magnets. The motor also includes a stator that has twelve salient poles. A coil is wound around each salient pole. Specifically, the eight permanent magnets of each magnet set are aligned substantially along a circle about the rotational axis of the rotor. The circles defined by the magnet sets are adjacent to each other along the rotor's rotational axis. One magnet set is located offset relative to the other by a predetermined offset angle (7.5 degrees) with respect to the rotational axis of the rotor. This structure reduces cogging torque generated by the motor.
While the rotor of this motor has eight magnetic poles, the stator of the motor has twelve salient poles. The least common multiple between the number of the rotor magnetic poles and the number of the stator salient poles, which is the least common multiple between eight and twelve, is twenty four. If nine salient poles are provided in the motor, instead of twelve, the corresponding least common multiple is seventy two. The least common multiple between the number of the rotor magnetic poles and the number of the stator salient poles corresponds to cogging torque pulsation, or cogging torque frequency. The cogging torque frequency is inversely proportional to cogging torque. That is, if cogging torque frequency increases as the least common multiple increases, cogging torque decreases.
However, if nine salient poles are provided in the motor, the offset angle between the two magnet sets with respect to the rotor's rotational axis must be altered to optimally decrease the cogging torque.
Cogging torque should be reduced in motors other than those having nine salient poles, or motors in which the number of the rotor magnetic poles (P) and the number of the stator salient poles (T) satisfy the following equation:
P=8n and T=9n (n is an integer equal to or greater than one).
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide a revolving magnetic field type motor that reliably decreases cogging torque.
To achieve the above objective, a revolving magnetic field type motor is provided. The motor includes a rotor having a plurality of sets of permanent magnets. The permanent magnets defines a plurality of rotor magnetic poles. The number of the rotor magnetic poles is “P”. The rotor has a plurality of blocks aligned in the rotor's axial direction. The number of the blocks is “m”. Each block has a set of the rotor permanent magnets. One set of the permanent magnets is offset relative to an adjacent set of the permanent magnets by a predetermined offset angle in the rotor's rotational direction. A stator has a plurality of coils. The coils defines a plurality of stator magnetic poles around an axis of the stator. The number of the stator magnetic poles is “T”. The coils generates a magnetic field for rotating the rotor when supplied with an electric current. The predetermined offset angle is within a range from about zero degrees/((m−1)×n) to about 22.5 degrees/((m−1)×n). The number of the rotor magnetic poles “P” is 8n (n is an integer equal to or greater than one). The number of the stator magnetic poles “T” is 9n (n is an integer equal to or greater than one). The number of the blocks “m” is an integer equal to or greater than two.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
REFERENCES:
patent: 4642502 (1987-02-01), Carpenter et al.
patent: 4713569 (1987-12-01), Schwartz
patent: 4739201 (1988-04-01), Brigham et al.
patent: 5010266 (1991-04-01), Uchida
patent: 5397951 (1995-03-01), Uchida et al.
patent: 5731647 (1998-03-01), Schueller et al.
patent: 2-114848 (1990-04-01), None
patent: 08251847 (1996-09-01), None
Matsushita Mitsuhiko
Nishikawa Yoshihito
Ozawa Takanori
Suzuki Mikitsugu
Asmo Co. Ltd.
Mullins Burton
Sawyer Law Group LLP
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