Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1993-05-19
1994-12-06
Skudy, R.
Electrical generator or motor structure
Dynamoelectric
Rotary
310261, 310271, H02K 2112
Patent
active
053714261
DESCRIPTION:
BRIEF SUMMARY
SPECIFICATION
1. Technical Field
This invention relates to a brushless motor which is of high efficiency and can be easily manufactured, and particularly to a rotor of such a brushless motor.
2. Prior Art
The brushless motor generally comprises a cylindrical rotor and permanent magnets made of ferrite or the like arranged on the outer peripheral surface thereof.
As shown in FIG. 6 of the attached drawing, a typical brushless motor 1 of prior art has a motor casing (i.e., stator) 2 comprising a cylindrical side wall 3, and front end plate 4 and a rear plate 9 both serving to block up opposite ends of the side wall 3, respectively. Inside the side wall 3, there are provided a plurality of excitation coils 6 arranged to define a cylindrical array and fixed to the inner surface of the side wall 3. A rotor 7 is concentrically provided with a rotatable shaft 8 fixed thereto. The rotatable shaft 8 projects from opposite ends of the rotor 7 so as to be rotatably supported at one end in a bearing 10 carried by an opening a of the rear end plate 5 and at the other end in a bearing 12 carried by an opening 11 of the front plate 4 of the motor casing 2. There is provided inside the side wall 3 of the motor casing 2 an annular member 13 adapted to hold a plurality of magnetic pole sensors 14 so that these sensors 14 are properly positioned closely adjacent one end surface of the rotor 7.
The rotor including permanent magnets for brushless motor generally comprises a yoke provided with slots serving to receive field permanent magnets.
Referring to FIG. 7 of the attached drawing, a conventional rotor 20 provided with the permanent magnets is isometrically shown with a yoke 22 formed from a plurality of integrally laminated silicon steel sheets 21. The yoke 22 has four magnetic poles 23 projecting radially outward and slots 24 adjacent outer ends of the respective magnetic poles to receive the respective field permanent magnets 25. The respective magnetic poles 23 are magnetized by these field permanent magnets 25. FIG. 8 of the attached drawing is a fragmentary sectional view showing the permanent magnet rotor 20 in an enlarged scale. As shown, the field permanent magnets 29 are inserted into the respective slots 24 so that N- and S-poles alternately look outward. With consequence, the field permanent magnets 25 generate magnetic flux extending from the respective N-poles through the yoke 22 and the external space surrounding the permanent magnet rotor 20, respectively, to the respective S-poles. The magnetic flux passing through the external space surrounding the permanent magnet rotor 20 intersects the stator provided around the rotor and interacts with electric current flowing through excitation coils of the stator to drive the permanent magnet rotor.
The yoke of the conventional permanent magnet rotor is formed with bridges 26 adapted to connect the outer ends with the bases of the respective magnetic poles. More specifically, as seen in FIG. 8, portions of the yoke 22 define the bridges 26 connecting the outer ends with the bases of the respective magnetic poles 23. A part of the magnetic flux which exits from each field permanent magnet 25 passes through the bridges 26 and reaches the S-pole of the same field permanent magnet 25. This magnetic flux passing through the bridges 26 does not contribute to rotational drive of the rotor and an efficiency of the field permanent magnets is correspondingly deteriorated.
Furthermore, with the conventional permanent magnet rotor, each field permanent magnet 25 of elongate configuration must be inserted into the relatively narrow slot and therefore the field permanent magnet 25 has sometimes been liable to be damaged during this inserting operation.
Accordingly, it is an object of the invention to provide a permanent magnet rotor of a simplified structure which is able to utilize the entire magnetic flux generated from the field permanent magnets for rotational driving, thereby improving the motor efficiency, on one hand, and facilitating assembling operation in the course of
REFERENCES:
patent: 4393320 (1983-07-01), Anderson
patent: 4445062 (1984-04-01), Glaser
patent: 4506181 (1985-03-01), Jones
patent: 4674178 (1987-06-01), Patel
patent: 5191256 (1993-03-01), Reiter, Jr. et al.
Endo Ken-ichi
Koike Yoshikazu
Nagate Takashi
Seto Takeshi
Yamagishi Yoshihiko
Seiko Epson Corporation
Skudy R.
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