Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1997-03-27
1998-10-06
Stephan, Steven L.
Electrical generator or motor structure
Dynamoelectric
Rotary
310162, 310261, H02K 127
Patent
active
058181393
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a brushless DC motor. More particularly, the present invention relates to a brushless DC motor including a stator and a rotor, which rotor includes permanent magnets each having a plate shape and a predetermined thickness therein so that the permanent magnets are parallel to a rotation axis of the rotor, and which rotor includes spaces for flux barrier each of which space elongates from an edge section of a permanent magnet housing space in a direction which is vertical to the rotation axis to a rotor surface.
BACKGROUND ART
From past, investigation and development are advanced for applying a brushless DC motor to various fields in view of advantage of possibility of improving of efficiency due to lack of secondary copper losses. A brushless DC motor is classified into two groups. One group has an arrangement that permanent magnets are mounted on a rotor surface (hereinafter, referred to as a surface DC motor). The other group has an arrangement that permanent magnets are built in and maintained in an interior of the rotor (hereinafter, referred to as a built in DC motor).
The built in DC motor includes a rotor in an interior of a stator, which rotor includes permanent magnets each having a plate shape and a predetermined thickness therein so that the permanent magnets are parallel to a rotation axis of the rotor, and which rotor includes spaces for flux barrier each of which elongates from an edge section of a permanent magnet housing space in a direction which is vertical to the rotation axis to an rotor surface, as is illustrated in Japanese Patent Laied-Open Gazette No. Hei 5-236686, and "Interior Permanent-Magnet Synchronous Motors for Adjustable-Speed Drives", IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. IA-22, NO. 4, JULY/AUGUST 1986, for example. A built in DC motor has advantages in comparison to a surface DC motor that driving in a wider range is possible, a higher torque is generated, and driving with higher efficiency is possible due to higher torque.
Further, a built in DC motor has permanent magnets within a rotor at predetermined positions which are near a rotation axis of the rotor so that a volume of each permanent magnet is smaller in comparison to a surface DC motor, therefore rare earth element permanent magnets having larger energy products are employed as permanent magnets.
In a built in DC motor having the above arrangement, a plate shaped permanent magnet is housed in an entirety of each permanent magnet housing space which elongates in a direction which is parallel to a rotation axis. Therefore, a negative magnetic field converges at edge sections of the permanent magnet (each edge section faces a space for flux barrier) so that an operating point of the permanent magnet exceeds an inflection point and demagnetization of the permanent magnet occurs (refer to points A and B and an arrow of characteristic curves of a rare earth element permanent magnet illustrated in FIG. 12, for example), when a negative magnetic field is applied to the permanent magnet which is built in and maintained in an interior of a rotor such that when the built in DC motor is started, when an inverter is in trouble, when the built in DC motor is driven by magnetic flux weakening control and the like. Specifically, lines of magnetic force under a condition that a negative magnetic field is applied to a permanent magnet are lines of magnetic force illustrated in FIG. 13. When the permanent magnet is virtually divided into a 2.times.16 number of small regions and a magnetic flux density of each region is measured, the measured magnetic flux densities are magnetic flux densities illustrated in FIG. 14 and magnetic flux densities at both regions which are located at edges are extremely smaller than that of other regions. Actually, the both edge regions exceed the inflection point so that magnetic flux densities of the both edge regions are 0. Further, each numeral illustrated in FIG. 14 represents a magnetic flux density at a central point of each region.
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REFERENCES:
patent: 3492520 (1970-01-01), Yates
patent: 4139790 (1979-02-01), Steen
patent: 4358696 (1982-11-01), Liu et al.
patent: 5548172 (1996-08-01), Kliman et al.
Kojima Hiroaki
Ooyama Kazunobu
Yamagiwa Akio
Daikin Industries Ltd.
Mullins B.
Stephan Steven L.
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