The present invention relates to a rotating electrical machine such as a motor and generator and, more particularly to, a rotating electrical machine provided with a magnet holder having a comb-shaped arm.
A permanent magnetic field has been used in many small-size motors and generators. At the time of use of the permanent magnetic field, a magnet is often fixed to a rotor or stator by using an adhesive. Further, as disclosed in Patent Documents 1 and 2, a method in which a magnet is provided on the outer periphery of a rotor core or rotary shaft and the magnet is mold-fixed by a non-magnetic member is known. Patent Document 1 discloses a method of filling the gaps between the magnets with nonmagnetic member through die cast molding, and Patent Document 2 discloses a method of integrally molding a magnet on the outer periphery of a rotor core using a synthetic resin. In these methods, the magnet can be fixed to the rotor core or the like without a use of an adhesive.
As the method not requiring an adhesive, there is often used a method using a magnet holder having a comb-shaped arm as disclosed in Patent Documents 3 and 4.
Jpn. Pat. Appln. Laid-Open Publication No. 05-153745
Jpn. Pat. Appln. Laid-Open Publication No. 09-19091
Jpn. Pat. Appln. Laid-Open Publication No. 2004-129369
Jpn. Pat. Appln. Laid-Open Publication No. 2005-45978
Jpn. Pat. Appln. No. 2004-210085
However, in the case where the magnet holder 101 having the configuration as shown in
When the arm end portions 103b spread and thereby the holding force applied to the magnet 106 in the radial direction is reduced as described above, the end portion side of the magnet 106 may be lifted up to cause backlash in the magnet 106. In particular, in the case where a configuration in which a plurality of magnets 106 (106a, 106b) are inserted in the axial direction is adopted, the backlash easily occurs in the magnet 106b on the axial direction end side. When the backlash in the radial direction occurs in the magnet 106, performance (occurrence of cogging, etc.) and reliability of the rotating electrical machine are lowered. In particular, the backlash greatly affects a rotating electrical machine requiring low cogging characteristics and high reliability, such as a motor for electric power steering apparatus and, therefore, elimination of backlash has been required.
Secondly, when the gap size of the arm base portions 103a is small, there may be case where the magnet 106 cannot be pushed all the way to the back of the holder arms 103 as shown in
An object of the present invention is to provide a rotating electrical machine capable of suppressing backlash of a magnet in the radial direction and suppressing an axial variation in the fitting position of the magnet.
According to the present invention, there is provided a rotating electrical machine having: a magnet holder including a base portion fixed to a rotary shaft and a plurality of arm members projecting from the base portion in the extending direction of the rotary shaft so as to be able to contain and hold a magnet between the adjacent arm members, characterized in that each of the arm members has an arm main body fixed to the outer periphery of a rotor core and extending in the extending direction of the rotary shaft and also has a bridge portion for connecting the base portion and the arm main body and formed to have a circumferential width set smaller than width of the arm main body.
In the rotating electrical machine according to the present invention, since each of the arm members projecting from a base portion in the extending direction of the rotary shaft has an arm main body and a bridge portion for connecting the base portion and the arm main body and formed to have a circumferential width set smaller than width of the arm main body, the rigidity of the base portion of each arm members is set lower than that of conventional magnet holders, and magnets are held by elasticity of the arm members. This prevents arm member end portions from spreading at the fitting time of the magnets to prevent a magnet holding force from being reduced due to the spread-open of the arm member end portions, thereby suppressing backlash of the magnet. In particular, in the case where a plurality of magnets are disposed in the axial direction, backlash easily occurs in the magnet on the end portion side as described above. However, in the rotating electrical machine according to the present invention, the magnet on the end portion side is held by the elasticity of the arm members without backlash. Further, in this case, the magnet may be held between the adjacent arm members while the bridge portion is elastically deformed in the circumferential direction.
In the rotating electrical machine, the base portion may have, between the adjacent arm members, a contact surface with which the axial direction end portion of the magnet is brought into contact, and the end portion of the arm main body on the base portion side may be positioned away from the contact surface in the axial direction. This makes it easy to insert the magnet since the magnet is not nipped between the bases of the arm members, thereby increasing workability. Further, insertion of the magnet is not blocked by the bases of the arm members, so that the magnet can be inserted all the way to the back of the arm members, thereby suppressing a variation in the fitting position of the magnet. Further, in this case, a void portion into which the magnet can be moved may be formed between the end surface of the arm main body on the base portion side and the contact surface. Furthermore, in the void portion, the distance between the bridge portions adjacently disposed may be set larger than the circumferential direction dimension of the magnet.
The rotating electrical machine according to the present invention has: a rotor core fixed to a rotary shaft; a plurality of magnets fitted to the rotor core on the outer periphery thereof along the circumferential direction; and a magnet holder including a base portion fixed to the rotary shaft and a plurality of arm members projecting from the base portion in the extending direction of the rotary shaft so as to contain and hold the magnet between the adjacent arm members. Each of the arm members has an arm main body fixed to the outer periphery of the rotor core and extending in the extending direction of the rotary shaft and also has a bridge portion for connecting the base portion and the arm main body and formed to have a circumferential width set smaller than width of the arm main body. With this configuration, the rigidity of the base portion of each arm members can be set lower than that of conventional magnet holders, allowing the magnets to be held by elasticity of the arm members. This prevents arm member end portions from spreading at the fitting time of the magnets to prevent a magnet holding force from being reduced due to the spread-open of the arm member end portions. As a result, it is possible to suppress backlash of the magnet due to the reduction of the holding force, increasing the performance and reliability of the rotating electrical machine.
An embodiment of the present invention will be described below with reference to the accompanying drawings.
The motor 1 is roughly constituted by a motor section 4 and a sensor section 5. The motor section 4 includes a stator 6 and a rotor 7. Hall elements (magnetic detection elements) 8 are disposed in the sensor section 5. The rotor 7 is rotatably disposed inside the stator 6, that is, the motor 1 is configured to be a brushless motor of an inner rotor type.
The stator 6 includes a stator core 12 around which a drive coil 11 is wound and a metal-made yoke 13 for containing the stator core 12. The stator core 12 is formed by laminating metal plates made of a magnetic material. A salient pole projects at the inner peripheral side of the stator core 12 and a drive coil 11 is wound around the salient pole to form a winding. The yoke 13 has a bottomed cylindrical shape and is made of a magnetic material. A bracket 14 formed by aluminum die casting (or synthetic resin) is fitted to the open end side of the yoke 13.
A rotor shaft 2 is arranged in the rotor 7. The rotor shaft 2 is supported by bearings 15a, 15b fitted respectively to the yoke 13 and bracket 14 so as to be freely rotated. A rotor core 16 is fixed to the rotor shaft 2. The rotor core 16 is formed by laminating metal plates made of a magnetic material. Segment-shaped rotor magnets 17 are fitted to the outer periphery of the rotor core 16. A set of two rotor magnets 17 (17a, 17b) (hereinafter, abbreviated as “magnet 17”) is fitted in the axial direction, and a total of six sets of two magnets 17 are fitted in the circumferential direction. A side plate 18 is fitted to the axial direction end of the rotor core 16.
Additionally, a magnet holder 19 made of a synthetic resin is fixed to the rotor shaft 2.
Each of the holder arms 32 is a cantilever structure extending in the axial direction from the holder base 31. Each of the holder arms 32 has an arm main body 41 extending in the axial direction and a bridge portion 51 connecting the arm main body 41 and holder base 31.
As shown in
As shown in
An engagement projection 44 is formed on the inner peripheral side of the arm main body 41. The engagement projection 44 is to be engaged with a holder anchoring groove 45 formed on the outer peripheral part of the rotor core 16. The holder anchoring groove 45 extends along the axial direction of the rotary shaft. A total of six holder anchoring grooves 45 are provided in the circumferential direction of the rotor core 16. The opening part 45a of each of the holder anchoring grooves 45 is made narrower than the bottom part 45b thereof. The engagement projection 44 is made to show a matching profile and hence has a substantially trapezoidal cross section. When the engagement projection 44 is put into the holder anchoring groove 45 in the axial direction, the engagement projection 44 having substantially a trapezoidal cross section becomes tightly engaged with the holder anchoring groove 45 and holder arm 32 is fixed to the outer peripheral surface 16a of the rotor core 16 and prevented from being released in the radial direction.
As shown in
The magnets 17 are fitted to the rotor core 16 fixed to the rotor shaft 2 and the magnet holder 19 from the free end side (the right end side in
When the magnet 17a is press-inserted between the holder arms 32, an axial direction end portion 17c of the magnet 17 faces the inner end surface 53a of the side wall portion 53. When the press insertion of the magnet 17 is continued, the axial direction end portion 17c abuts the projections 55 formed in the inner end surface 53a. In the motor 1, the insertion of the magnets 17a and 17b is continued after the magnet 17a has been brought into contact with the projections 55 while crushing the projections 55 by the axial direction end portion 17c of the magnet 17a until the rear end surfaces (right end surface in
Meanwhile, the magnet 17 and rotor core 16 have dimensional tolerance, respectively. In particular, in the case where a plurality of magnets are disposed in the axial direction, the dimensional tolerance is accumulated to easily cause backlash in the axial direction. In the case of the motor 1 in which the magnet 17 is fitted while the projection 55 are pressed and crushed, the dimensional tolerance is absorbed by the crushing amount of the projection 55. Therefore, even in the case of a motor having a longer axial direction length, i.e., even when a plurality of magnets 17 are disposed in the axial direction, the axial direction backlash does not occur in the magnet 17, preventing the magnet 17 from being damaged due to vibration. Further, the fitting positions of the magnets 17 in the circumferential direction can be aligned to each other, and displacement of the magnet 17 in the axial direction can be prevented, whereby motor characteristics become stable. Furthermore, the accumulated tolerance is absorbed by the projection 55, so that the processing accuracy of the magnet 17 and rotor core 16 can be reduced and the manufacturing cost can be lowered.
In the case of the conventional magnet holder 101 as shown in
Further, as shown in
The magnet 17 press-fitted into the corresponding magnet housing section 43 is held in it by the elastic resilience of the magnet holder pieces 42 and the arm main body 41. In this condition, the radial movement of the magnet 17 is limited by the corresponding first contact sections 46 whereas the circumferential movement of the magnet 17 is limited by the corresponding second contact sections 47. In other words, the magnet 17 is rigidly held to the outer peripheral surface 16a of the rotor core 16 by the elastic resilience of the magnet holder 19 without any adhesive. Thus, the magnet is free from the tensile force that is produced due to the difference in the thermal deformation rate of the components operating on the magnet 17 when adhesive is used and hence from the risk of being broken due to the difference in the coefficient of linear expansion.
Additionally, the magnet 17 is supported by the first and second contact sections 46, 47 and a non-contact area 48 is arranged between them, so that if the ambient temperature rises when the motor is in operation and the magnet 17 thermally expands, the magnet 17 is not constrained firmly by the holder arms 32. Therefore, the stress that is produced in the magnet 17 due to deformation and constraint can be alleviated to prevent the magnet from being broken.
Furthermore, since no adhesive is used, there arises no problem due to the dispersion of bonding strength according to the bonding conditions and the quantity of the applied adhesive and the degradation of the adhesive agent in a hot environment so that the product quality will be improved. Since the holder arms 32 are aligned by the holder anchoring grooves 45, it is possible to accurately align and anchor the magnets and stabilize the product characteristics. No anti-rotation mechanism is required when aligning the magnets, so that the apparatus structure can be simplified and the assembling man-hours can be reduced. Additionally, since the motor is assembled only by means of an assembling operation of press-fitting the magnets 17, neither the adhesive applying operation nor the time for hardening the adhesive in the assembling process is required to reduce the number of manufacturing facilities, the man-hours and hence the manufacturing cost including the cost of the adhesive can be reduced.
Meanwhile, the magnet 17 generally requires a large dimensional tolerance and, when rare earth magnets are used for the magnet 17, the magnet can rust when the surfaces of the magnets are scarred. Thus, it is necessary to avoid excessive press-fitting force while a sufficient level of pressure is secured to hold the magnet 17 there. In view of these circumstances, in a magnet fixing structure according to the present invention, since the cross sectional shape of the magnet housing section 43 is differentiated from that of the magnet 17 and the first and second contact sections 46, 47 support the magnet 17 at the two points and the non-contact area 48 is arranged between them, the change in the press-fitting force due to the dimensional tolerance is alleviated. Accordingly, even if the magnet 17 shows a dimensional variation, it is possible to press-fit the magnet 17 into the magnet housing section 43 flexibly with a constant pushing force, so that the magnets are prevented from being broken in the assembling process.
A ring-shaped sensor magnet 20 is fitted to the sensor magnet fitting portion 33. The sensor magnet fitting portion 33 is formed at the leading end of the holder base 31 (left end in
The magnet holder 19 is covered by a magnet cover 21 from the outside. The magnet cover 21 is made of a non-magnetic material such as stainless steel or aluminum and formed by deep drawing. The magnet cover 21 is provided with a small diameter portion 21a for covering the sensor magnet 20 and a large diameter portion 21b for covering the magnets 17. A tapered section 21c is arranged between the small diameter section 21a and the large diameter section 21b.
The magnet cover 21 is fitted to the magnet holder 19 carrying the magnets 17 and the sensor magnet 20 from the side of the holder base 31. The opening end portion (right end side in
In other words, when the magnets 17 are fitted to the respective magnet housing sections 43, the outer peripheral ends of the holder arms 32 are located radially outside the outer peripheral ends of the magnets 17. Therefore, a gap 49 is formed between the top portion of each of the magnets 17 and the inner peripheral surface of the magnet cover 21 as shown in
In the motor 1, the magnets 17 are anchored to the magnet holder 19 without the magnet cover 21. However, the magnet cover 21 is arranged at the outside of the magnets 17 from the viewpoint of reliability so as to prevent the motor from falling into a locked condition when any of the magnets 17 comes off or is broken. When the magnet cover 21 is put in position by a sort of press-fitting, the magnet holder pieces 42 are pressed further against the corresponding magnets 17, whereby the magnets 17 are held and fixed more rigidly.
Hall elements 8 are arranged radially outside of the sensor magnet 20 at the side of the sensor section 5. A total of three Hall elements 8 for the U-, V- and W-phases are provided. The Hall elements 8 are arranged vis-à-vis the sensor magnet 20 at regular intervals. The magnetic polarities of the sensor magnet 20 correspond to those of the magnets 17, the number of poles of the sensor magnet 20 being same as those of the magnets 17, and are arranged at positions same as those of the magnets 17 as viewed in the peripheral direction. Then, the sensor magnet 20 is rigidly held by the magnet cover 21. In the motor 1, the magnets 17 have six poles structure and the sensor magnet 20 is magnetized to six poles corresponding to the magnets 17. The Hall elements 8 send out signals according to the magnetic polarity changes of the sensor magnets 20, so that the rotary position of the rotor 7 is detected according to those signals.
The Hall elements 8 are arranged in the circumferential direction at the leading end of the sensor holder 22 fitted to the bracket 14. A printed board 24 is fitted to the outside of the sensor holder 22. Both the sensor holder 22 and the printed board 24 are fixed to the bracket 14 by screws 23. An end cap 25 is fitted to the outer end of the bracket 14 to protect the parts of the printed board 24 and other elements contained in the bracket 14 from the external atmosphere. A power supply cable 26 is also connected to the bracket 14 in order to supply a power to the drive coil 11. The power supply cable 26 is lead out of the motor by way of a rubber grommet 27 fitted to the lateral side of the bracket 14.
While the sensor magnet 20 and Hall elements 8 are used to detect the rotary position of the rotor 7 in the above-described first embodiment, they may be replaced by a resolver rotor and a resolver. In this case, the resolver rotor is fitted to the position similar to the sensor magnet 20. The resolver rotor is fixed to the rotor shaft 2. Then, sensor magnet fitting section 33, the small diameter section 21a and the tapered section 21c are taken away from the magnet holder 19 and the magnet cover 21. The resolver is arranged at the position of the Hall elements 8 on the bracket 14.
The present invention is by no means limited to the above-described embodiments, which may be modified and altered in various different ways without departing from the spirit and scope of the present invention.
For example, the present invention is applied to an inner rotor type brushless motor in the above-described embodiment, it can also be applied to a motor with brushes and an electric generator. While rotor magnets 17 can be fixed to a rotor core 16 without using any adhesive according to the present invention, a small amount of adhesive may be used to bond the rotor magnets 17 to the rotor core 16.
Number | Date | Country | Kind |
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2006-002846 | Jan 2006 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2007/050160 | 1/10/2007 | WO | 00 | 7/10/2008 |