ROTOR OF BRUSHLESS MOTOR

Abstract: A rotor (31) of a brushless motor, wherein a rotary shaft (32) and a main yoke (33) fitted to the rotary shaft (32) in a body are provided, and in this main yoke (33) at least two magnetic pole heads (34a), (34b) radially projecting from the rotary shaft (32) are provided. Seats (35a), (35b) for receiving field permanent magnets (36a), (36b) are provided between the mutually adjacent magnetic pole heads (34a), (34b), and the permanent magnets (36a), (36b) are so mounted on the seats (35a), (35b) that the magnetic poles of identical polarity face each other with the center of the rotary shaft (32) between. Sub-yokes (38a),(38b) are installed on the outer surfaces of the field permanent magnets (36a), (36b), and a cylindrical sleeve (40) made of a non-magnetic material is installed on the outer circumferential surfaces of the magnetic pole heads (34a), (34b) and the sub-yokes (38a), (38b). Thus, the structure of the rotor (31) for brushless motors is simplified and the magnetic fluxes of the field permanent magnets (36a), (36b) are utilized effectively.

Description: 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. 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. 3 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 5 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 the rear end plate 5 and at the other end in a bearing 12 carried by 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. 4 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. 5 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 25 are inserted into the respective slots 24 so that N- and S-poles alternately look outward. With a 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. 5, 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 manufacturing process, on the other hand. Disclosure of the Invention The object set forth above is achieved, in accordance with a first aspect of the invention, by a rotor for brushless motor having the features of the claim. With this permanent magnet rotor constructed in accordance with the invention, the resinous molded material or the die cast material is used to connect the auxiliary yokes each defining the outer end of the magnetic pole with the main yoke defining the bases of the respective magnetic poles so that the entire magnetic flux generated from the field permanent magnets pass through the external space around the rotor and then reaches the adjacent magnetic poles. Consequently, the entire magnetic flux generated from the field permanent magnets intersects the stator provided around the rotor and interacts with electric current flowing through the excitation coils, effectively contributing to the rotation of the rotor. Further, the permanent magnet rotor according to the invention has the main yoke, field permanent magnets and auxiliary yokes mounted as piled, so that the field permanent magnets are not required to be inserted into a narrow slot, thereby capable of completely preventing the permanent magnets from being damaged during inserting. Brief Description of the Drawings: Fig. 1 is a perspective view showing an embodiment of the permanent magnet rotor constructed in accordance with the invention; Fig. 2 is a fragmentary sectional view showing this rotor in an enlarged scale; Fig. 3 is an axial sectional view showing a brushless motor of prior art; Fig. 4 is a perspective view showing a rotor of prior art; and Fig. 5 is a fragmentary sectional view showing the rotor of prior art in an enlarged scale. Preferred Embodiment of the Invention: The invention will be readily understood from the following description made with reference to the attached drawings. Fig. 1 shows a permanent magnet rotor constructed in accordance with the invention. A permanent magnet rotor 51 centrally has a main yoke 53 comprising a plurality of integrally laminated silicon steel sheets 52. Each of these silicon steel sheets 52 has a plurality of rectangular recesses 54 formed by pressing process so that these silicon steel sheets may be caulked together by forcing the recesses 54 into engagement with one another and thereby integrated into the main yoke 53. The main yoke 53 is centrally formed with an opening 55 axially extending therethrough to receive a rotatable shaft 56 which has, in turn, a key by means of which the rotatable shaft 56 is rotated integrally with the main yoke 53. The main yoke 53 has along its outer periphery a pair of magnetic poles 57 projecting radially outward and a pair of magnet seats 58. The magnet seats 58 are formed symmetrically with respect to the rotatable shaft 56 and carry thereon a pair of field permanent magnets 59, respectively, with their magnetic poles of the same polarity being opposed to each other. In this specific embodiment, the field permanent magnets 59 are shaped in flat boards and mounted on the magnet seats with their N-poles being opposed to each other. There are provided on the S-pole sides of these field permanent magnets 59 auxiliary yokes 61 each functioning as a magnetic pole 60. A space defined between each pair of the adjacent magnetic poles 57, 60 is filled with resinous molded member or die cast member to form a molded portion 62 which integrally assembles the main yoke 53, the field permanent magnet 59 and the auxiliary yoke 61. Outer peripheries of the respective molded portions 62 are formed in continuity with the magnetic pole surface of the magnetic poles 57, 60 so as to form together a cylindrical outer periphery of the permanent magnet rotor 51. Fig. 2 is a fragmentary sectional view showing the permanent magnet rotor 51 in an enlarged scale. The main yoke 53 has joint surfaces 63 destined to be in contact with the respective molded portions 62 between the magnetic poles 57 and the magnet seats 58, respectively. Each joint surface 63 is formed with a dovetail 64 adapted to be engaged with the associated molded portion 62. On the other hand, each auxiliary yoke 61 has, between its magnetic pole surface and its surface contacting the associated field permanent magnet 59, a joint surface 65 destined to be in contact with the associated molded portion 62. Each joint surface 65 is formed with a dovetail 66 adapted to be engaged with the associated molded portion 62. In the course of manufacturing the permanent magnet rotor 51. liquefied material to be molded is poured into a space defined between the main yoke 53 and the auxiliary yokes 61 and simultaneously into the grooves of the respective dovetails 64, 66. Once the liquefied material has been solidified and the molded portions 62 have been obtained, the main yoke 53 and the auxiliary yokes 61 are engaged with the molded portions 62 along the respective dovetails 64, 66 so as to hold the field permanent magnets 59 therebetween. Such a construction is effective to prevent the field permanent magnets 59 as well as the auxiliary yokes 61 from centrifugally flying off during its operation. As described above, the field permanent magnets 59 are arranged with their N-poles being opposed to each other and, in consequence, the magnetic flux generated from these field permanent magnets 59 describes, under the mutual repulsing effect of the opposing magnetic poles, lines extending from the magnetic poles of the main yoke 53 through the external space around the permanent magnet rotor 51 to the magnetic poles 60 of the auxiliary yokes 61. The opposite end surfaces of each field permanent magnet 59 extending between the both poles thereof are contiguous to the molded portions 62 of low magnetic permeability and, consequently, no magnetic flux is short-circuited through the molded portions 62 to the S-poles. Namely, the entire magnetic flux generated from the field permanent magnets 59 intersects the stator (not shown) provided around the permanent magnet rotor 51 and effectively contributes to rotation of the rotor 51. While the invention has been described in connection with the specific embodiment so constructed that the field permanent magnets are arranged with their magnetic poles of the same polarity being opposed to each other and mutual repulsion of these magnetic poles generates the magnetic poles along the outer periphery of the permanent magnet rotor, the number of which corresponds to twice the number of the permanent magnets, the invention is not limited to such a permanent magnet rotor but applicable also to the conventional permanent magnet rotor having the same number of field permanent magnets as the number of magnetic poles. While this embodiment of permanent magnet rotor has four magnetic poles, the invention is obviously applicable also to the permanent magnet rotor having any number of magnetic poles. According to the invention as has been described above, no part of the magnetic flux exiting one magnetic pole is short-circuited through the bridges to the other magnetic pole of each permanent magnet, since the bridges conventionally utilized to connect the main yoke with the auxiliary yokes are eliminated. In other words, the entire magnetic flux generated from the field permanent magnets passes through the external space around the permanent magnet rotor, then intersects the excitation coils of the stator and reaches the adjacent permanent magnet. The entire magnetic flux interacts with said excitation coils and thereby effectively contributes to the rotation of the rotor, thus providing the motor of high efficiency. In addition, it is unnecessary for the permanent magnet rotor of the invention to insert the permanent magnets of elongate configuration into the narrow slots and, as a result, damage of the permanent magnets possibly encountered by the prior art during the insertion of the permanent magnets can be perfectly avoided. Correspondingly, manufacturing of the permanent magnet rotor can be facilitated. Industrial Usefulness: As will be appreciated from the foregoing description, a structure-simplified but efficient brushless motor which is suitable for high speed rotation can be realized by adopting the permanent magnet rotor of the invention.

Claims: A rotor of a brushless motor comprising a rotatable shaft (56), a main yoke (53) mounted on said rotatable shaft (56) having at least a pair of magnetic poles (57) projecting therefrom radially outwardly and provided with magnet seats (58), at least two field permanent magnets (59) being provided on the respective magnet seats (58) with their magnetic poles of a same polarity being opposed to the rotatable shaft (56), at least two auxiliary yokes (60, 61) being mounted on outer surfaces of the field permanent magnets (60, 61) and functioning as a magnetic pole (60), characterised in that the main yoke (53) has joint surfaces (63) being formed with a dovetail (64), each auxiliary yoke (60, 61) has between its magnetic pole surface and its surface contacting the associated field permanent magnet (59) joint surfaces (65) together forming a dovetail (66), and a space defined between each pair of magnetic poles (57, 60) is filled with a connector member (62) of nonmagnetic material engaging said dovetails (64, 66), so that the field permanent magnets are held between the main yoke (53) and the auxiliary yokes (61) against the effect of centrifugal force in operation.

Inventors: ENDO KENICHI, KOIKE YOSHIKAZU, NAGATE TAKASHI, SETO TAKESHI, YAMAGISHI YOSHIHIKO, ENDO, KENICHI, KOIKE, YOSHIKAZU, NAGATE, TAKASHI, SETO, TAKESHI, YAMAGISHI, YOSHIHIKO, ENDO, KENICHI, SEIKO EPSON CORPORATION, KOIKE, YOSHIKAZU, SEIKO EPSON CORPORATION, NAGATE, TAKASHI, SEIKO EPSON CORPORATION, SETO, TAKESHI, SEIKO EPSON CORPORATION, YAMAGISHI, YOSHIHIKO, SEIKO EPSON CORPORATION
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1991
Main classification: H02K1
IPC codes: H02K1