WO2011108733A1

WO2011108733A1 - Rotor, method of manufacturing rotor, and motor

Info

Publication number: WO2011108733A1
Application number: PCT/JP2011/055155
Authority: WO
Inventors: Masanori Nakamura; Tsuyoshi Hirokawa
Original assignee: Nidec Corp
Current assignee: Nidec Corp
Priority date: 2010-03-03
Filing date: 2011-02-28
Publication date: 2011-09-09
Anticipated expiration: 2012-09-03
Also published as: JP2011182602A; CN102782991A; JP5629859B2; CN102782991B

Abstract

The method includes the step of: a) defining a base of the rotor cover; b) defining support regions each having a cross section in a shape of a minor arc, and arranged to project radially outward to match the convex surface of a separate one of the magnets; c) arranged the magnets on the outer circumferential surface of the rotor core, and fitting the rotor core with the magnets arranged thereon to the base, and d) deforming a portion of the base which surrounds an opening of the base to define a collar portion projecting radially inward. In step b), each support region is defined such that an inner surface thereof is arranged to have a radius of curvature smaller than that of the convex surface.

Description

DESCRIPTION

ROTOR, METHOD OF MANUFACTURING ROTOR, AND MOTOR

BACKGROUND OF THE INVENTION TECHNICAL FIELD

The present invention relates to a method of manufacturing a rotor, the rotor, and a motor.

BACKGROUND ART

Japanese Patent No. 4003694 discloses a scatter preventing cover which is arranged on a rotor and in which portions with a decreased diameter are defined at regular intervals, so that the scatter preventing cover is shaped substantially like flower petals.

JP-A 5-344669 discloses a structure in which a metal tube is fitted on an outer circumferential portion of a magnet of a rotor, and in which doughnut-shaped spacers are arranged at both axial end portions of the metal tube. Each end portion of the metal tube includes a bend portion and a collar portion defined by bending the end portion of the metal tube radially inward through a pressing process.

Furthermore, JP-A 2003-299279 discloses a motor in which a cylindrical cover of a rotor includes long narrow fold portions capable of elastic deformation defined therein, the fold portions extending along a plurality of permanent magnets and being embedded in gaps between the permanent magnets. After the rotor is inserted inside the cover, ends of the cover are bent radially inward through a swaging process.

[Patent Document 1] Japanese Patent No. 4003694 [Patent Document 2] JP-A 5-344669

[Patent Document 3] JP-A 2003-299279

DISCLOSURE OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

Excellent thermal resistance is required of manufacture of rotors for use in motors which are installed in vehicles, for example. Accordingly, such rotors are generally manufactured by the following method. That is, a plurality of magnets are arranged on an outer circumferential surface of a rotor core, and the rotor core with the magnets arranged thereon is inserted inside a rotor cover. Then, an adhesive which is to solidify at high temperature is arranged between the rotor core and the rotor cover to secure components of the rotor to one another in a unified manner.

The above method, however, requires two adhering processes . A first adhering process is performed when the rotor core and each magnet are adhered to each other through an adhesive applied therebetween, and a second adhering process is performed when the rotor core, the magnets, and the rotor cover are adhered to one another in a unified manner through an adhesive applied therebetween. Therefore, much time, effort, and cost have been required for the manufacture of this type of rotors, because each adhering process involves solidifying the adhesive using a high-temperature curing oven, and so on. Moreover, a 100% inspection needs to be carried out to confirm that the adhesive has been properly solidified, which leads to a large amount of effort and cost even after the manufacture.

In view of the above problems, the present invention has been conceived to provide a method of manufacturing a rotor which is able to construct the rotor in a unified manner without use of an adhesive, and so on. This method and so on are able to achieve improved productivity and reduced production cost.

SOLUTION TO THE PROBLEMS

A rotor according to a preferred embodiment of the present invention includes a rotor core including a through hole in which a shaft of a motor is inserted; a plurality of magnets arranged to extend in parallel with the through hole, and arranged on an outer circumferential surface of the rotor core at regular intervals in a circumferential direction; and a cylindrical rotor cover fitted to the rotor core with the magnets arranged therebetween. Each of the magnets includes a convex surface arranged to face radially outward and project so as to assume a minor arc in a cross-section. According to a preferred embodiment of the present invention, a method is provided of manufacturing the rotor including the magnets and having the above-described features, the method including the steps of: a) defining a base of the rotor cover, the base including a cylindrical circumferential wall and having an opening at at least one end thereof; b) depressing portions of the circumferential wall of the base radially inward to define a plurality of support regions, each support region having a cross section in a shape of a minor arc, and arranged to project radially outward to match the convex surface of a separate one of the magnets; c) arranging the magnets on the outer circumferential surface of the rotor core, and fitting the rotor core with the magnets arranged thereon to the base after step b) ; and d) deforming a portion of the base which surrounds the opening to define a collar portion projecting radially inward after step c) . In step b) , each support region is defined such that an inner surface thereof is arranged to have a radius of curvature smaller than that of the convex surface.

According to the above-described method, it is possible to arrange the inner surface of each support region defined in the rotor cover to have a radius of curvature smaller than that of the convex surface of the magnet. As a result, when the magnets and so on are fitted to predetermined positions inside the rotor cover, each support region is brought into contact with the convex surface of the corresponding magnet, and is deformed to come into surface contact with the convex surface. As a result, each magnet is circumferentially and radially retained by the corresponding support region.

The magnets and the rotor core are therefore properly held by the rotor cover without use of an adhesive .

EFFECT OF THE INVENTION

As described above, according to a preferred embodiment of the present invention, it is possible to construct the rotor in a unified manner without use of an adhesive. This makes it possible to achieve improved productivity and reduced production cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[Fig. 1] Fig. 1 is a cross-sectional view of a motor .

[Fig.2] Fig.2 is an exploded view of components of a rotor.

[Fig. 3] Fig. 3 is a cross-sectional view of a rotor cover as viewed from a direction indicated by line I-I of Fig. 2.

[Fig. 4] Figs. 4A and 4B are diagrams for explaining a relationship between a support region and a convex surface.

[Fig. 5] Fig. 5 is a diagram for explaining conditions required of the support region and so on.

[Fig.6] Fig.6 is another diagram for explaining conditions required of the support region and so on.

[Fig. 7] Fig. 7 is a diagram for explaining a support region defining step.

[Fig.8] Fig.8 is another diagram for explaining the support region defining step.

[Fig. 9] Fig. 9 is a cross-sectional view corresponding to Fig. 8 as viewed from a direction indicated by line II-II of Fig. 8.

[Fig. 10] Fig. 10 is a diagram for explaining a collar portion defining step.

[Fig. 11] Fig. 11 is another diagram for explaining the collar portion defining step.

[Fig. 12] Fig. 12 is yet another diagram for explaining the collar portion defining step.

DESCRIPTION OF THE REFERENCE CHARACTERS

1 motor

6 shaft

300 rotor

310 rotor core

311 through hole

320 magnets

321 convex surfaces

330 spacer

340 rotor cover

340a base

341 collar portion

347 support regions

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings . Note that the following description is meant to be merely illustrative, and should not be construed to restrict the scope of the present invention, applications thereof, or purposes thereof.

[Overall Structure of Motor]

Fig. 1 illustrates a motor 1 including a rotor 300 according to a preferred embodiment of the present invention. The motor 1 is an inner-rotor brushless motor to be installed in a vehicle, and is used to drive an electric power steering, for example. As illustrated in Fig. 1, the motor 1 includes a casing 2, a busbar unit 100, a stator 200, the rotor 300, a shaft 6, and so on.

The casing 2 includes a receptacle 2a which has a bottom and is substantially cylindrical, and a substantially disc-shaped lid 2b. The lid 2b is secured to a flange of the receptacle 2a. The flange of the receptacle 2a is arranged to project radially outward around a circumference of an opening of the receptacle 2a. The stator 200 and so on are contained inside the receptacle 2a. A through hole 3 is defined in a central portion of the lid 2b. A bearing portion 4 is arranged on a bottom surface of the receptacle 2a to be opposed to the through hole 3. Bearings 5 are arranged in the bearing portion 4 and inside the through hole 3. The shaft 6 is supported through the bearings 5 to be rotatable with respect to the casing 2. One end portion of the shaft 6 is arranged to project outward from the lid 2b through the through hole 3. The end portion of the shaft 6 is connected to the electric power steering through a speed reducer (not shown) .

The rotor 300 is fixed to a middle portion of the shaft 6 such that the rotor 300 is coaxial with the shaft 6. The stator 200 is fixed to an inner circumferential surface of the receptacle 2a such that the stator 200 surrounds the rotor 300. An inner circumferential surface of the stator 200 and an outer circumferential surface of the rotor 300 are arranged opposite each other with a slight gap therebetween so that the motor 1 can efficiently exhibit its performance. The busbar unit 100 is attached to an end portion of the stator 200. In Fig. 1, reference numeral 7" indicates a rotation angle sensor arranged to detect a rotation angle.

The motor 1 is provided with a variety of contrivances in order to achieve improved productivity, reduced production cost, and so on. Details thereof will now be described below.

[Structure of Rotor 300]

As illustrated in Figs. 1 and 2, the rotor 300 according to the present preferred embodiment includes a rotor core 310, magnets 320, a spacer 330, a rotor cover 340, and so on. The rotor core 310, the magnets 320, and the spacer 330 are securely united through the rotor cover 340 without use of an adhesive. Note that Fig. 2 shows the rotor cover 340 (i.e., a base 340a) before a collar portion 341 is defined therein.

The rotor core 310 is a columnar member having a cross section substantially in the shape of a regular octagon. The rotor core 310 includes a through hole 311 defined at its center. The through hole 311 is arranged to be substantially coaxial with a rotation axis S, and is arranged to have the shaft 6 secured therein. The rotor core 310 is defined by a plurality of metal sheets placed one upon another along the rotation axis S and united in a single body.

The rotor 300 according to the present preferred embodiment includes eight magnets 320 (i.e., eight poles) . Each magnet 320 is shaped like a band plate. Each magnet 320 includes a convex surface 321 arranged to proj ect so as to assume a minor arc in a cross-section . The magnets 320 are arranged to orient the convex surfaces 321 thereof radially outward. Moreover, each magnet 320 is arranged to have the convex surface 321 thereof extending in parallel with the through hole 311. The magnets 320 are therefore arranged on an outer circumferential surface of the rotor core 310 at regular intervals in a circumferential direction with a predetermined gap defined between adjacent ones of the magnets 320. The magnets 320 are polarized such that each of the magnets 320 defines a south or a north pole. The south and north poles of the magnets 320 are arranged to alternate with each other in the circumferential direction. The magnets 320 are held between the rotor core 310 and the rotor cover 340.

The spacer 330 is an annular member arranged to extend along an inner circumferential surface of the rotor cover 340. The spacer 330 is arranged to have an outside diameter slightly smaller than the inside diameter of the rotor cover 340. In addition, the spacer 330 is arranged to have an inside diameter greater than the diameter of the through hole 311. The outside diameter of the spacer 330 is at least arranged to be smaller than the outside diameter of the rotor core 310. Note that the spacer 330 may be made of either a metal or a resin, as long as it is made of a non-magnetic material.

The spacer 330 is arranged between end surfaces of the rotor core 310 and the magnets 320 fitted to the rotor cover 340 and the collar portion 341, which is defined by deforming an end portion of the base 340a . The spacer 330 is arranged to restrain an axial movement of the magnets 320 and the rotor core 310 in combination with the collar portion 341. Moreover, the spacer 330 contributes to facilitating processing of the collar portion 341, and also to preventing the magnets 320 and the rotor core 310 from being damaged during the processing. Details thereof will be described below.

The rotor cover 340 includes a cylindrical circumferential wall 342 and a bottom wall 343 arranged to close one end thereof. The rotor cover 340 is a metal article defined by subjecting the base 340a, which is cylindrical, has a bottom, and has an opening 344 at an opposite end, to press working or the like. The rotor core 310, the magnets 320, and the spacer 330 are placed inside the rotor cover 340 through the opening 344. The rotor core 310 and the magnets 320 are press fitted to the rotor cover 340. The rotor cover 340 is arranged to protect the rotor core 310 and the magnets 320, and properly position and unitedly hold the rotor core 310 and the magnets 320 without use of an adhesive.

The rotor cover 340 is essentially identical to the base 340a except that the rotor cover 340 includes the collar portion 341 defined therein, and that the circumferential wall 342 of the rotor cover 340 has an uneven shape. A portion (hereinafter also referred to as a "processed edge 345") of the base 340a which surrounds the opening 344 is deformed radially inward to define the collar portion 341 projecting radially inward, so that the rotor cover 340 is completed. The axial dimension of the base 340a is therefore designed to be greater than the axial dimension of the rotor core 310 and the magnets 320.

The outer surface of the circumferential wall 342 of the rotor cover 340 includes a plurality of recesses 346 defined therein. The recesses 346 are arranged to extend along the rotation axis S, correspondingly to the magnets 320. The recesses 346 are defined in an axial middle portion of the rotor cover 340, without extending over an axial end portion thereof on either side (in particular, an axial end portion closer to the opening 344) .

Each recess 346 includes a first end wall 346a arranged at an end thereof closer to the opening 344. The first end wall 346a is arranged to extend from an outer circumferential surface of the rotor cover 340 radially inward substantially perpendicularly. The first end walls 346a of the recesses 346 are arranged substantially in a straight line in the circumferential direction . Meanwhile, an end portion of each recess 346 at an end closer to the bottom wall 343 has a tapered shape . The end portion of each recess 346 at the end closer to the bottom wall 343 includes a second end wall 346b arranged to extend from the outer circumferential surface of the rotor cover 340 radially inward obliquely. Note that the shape of the second end wall 346b is a result of avoiding forced removal of the base 340a from a columnar jig 360 when defining the recesses 346.

Referring to Fig. 3, because of the recesses 346, the rotor cover 340 includes a plurality of support regions 347 each having a cross section in the shape of a minor arc. Each support region 347 is arranged to project radially outward to match the convex surface 321 of a separate one of the magnets 320 fitted inside the rotor cover 340. In other words, each magnet 320 is arranged such that the convex surface 321 thereof is arranged opposite a separate one of the support regions 347. Each magnet 320 is restrained from circumferential movement and retained at a predetermined position by the corresponding support region 347.

Between every two support regions 347 adjacent to each other in the circumferential direction, a recessed portion 348 extending in a line along the rotation axis S and being continuous with the two support regions 347 is defined. In contrast to the support regions 347, each recessed portion 348 is arranged to project radially inward to have a cross section in the shape of a minor arc. The recessed portion 348 is a small depression which is embedded in a gap defined between every two adjacent magnets 320. Each recessed portion 348 is arranged in a circumferential middle of a separate one of the recesses 346. In addition, the recessed portion 348 is arranged to extend from the first end wall 346a to a vicinity of the second end wall 346b. The recessed portions 348 contribute to securely preventing a contact between any magnets 320 adjacent to each other in the circumferential direction.

Each support region 347 is arranged in secure surface contact with the convex surface 321 of a separate one of the magnets 320. This contributes to properly holding the magnets 320.

Specifically, referring to Figs. 4A and 4B, an inner surface of the support region 347 is arranged to have a smaller radius of curvature than that of the convex surface 321. Dimensions of portions of the rotor cover 340 are designed such that both circumferential ends of the convex surface 321 of each magnet 320 are positioned circumferentially inward of both circumferential ends of the inner surface of the corresponding support region 347.

Referring to Fig. 4A, when no external force is applied to the support region 347 , the support region 347 has a smaller radius of curvature than that of the convex surface 321. Therefore, when the convex surface 321 is brought into contact with the inner surface of the support region 347, two separate portions of the support region 347 near both circumferential ends thereof are brought into contact with the convex surface 321, while a middle portion of the support region 347 is not in contact with the convex surface 321. Referring to Fig. 4B, after the rotor core 310 and so on are fitted to the rotor cover 340, forces are applied to the rotor cover 340 as if to increase the diameter of the rotor cover 340. As a result, both circumferential end portions of the support region 347 are pulled in mutually opposite directions. As a result, a force acting toward the rotation axis S is applied to the support region 347 to force the support region 347 onto the magnet 320. In this manner, the inner surface of the support region 347 is brought into surface contact with the convex surface 321 in its substantial entirety.

Moreover, when the support region 347 has been brought into close contact with the convex surface 321 to have the same radius of curvature as that of the convex surface 321, an arc having this radius of curvature and defined by the support region 347 is longer than an arc having this radius of curvature and defined by the convex surface 321. This contributes to securing the surface contact between the convex surface 321 and the support region 347. As a result, the magnet 320 is properly positioned circumferentially.

Referring to Figs. 5 and 6, mathematical equations for deriving the radius of curvature of the support region 347 and so on will now be described below . It is assumed that Ra denotes the radius of curvature (mm) of the support region 347 when no external force is acting on the support region 347, and that denotes the central angle (radian) thereof. It is similarly assumed that Rb denotes the radius of curvature of the recessed portion 348, and that β denotes the central angle thereof.

It is assumed that Ra' denotes the radius of curvature of the support region 347 when the support region 347 has been deformed after the magnets 320 and so on are fitted to the rotor cover 340, and that a' denotes the central angle thereof. It is similarly- assumed that Rb' denotes the radius of curvature of the recessed portion 348 when the recessed portion 348 has been deformed after the magnets 320 and so on are fitted to the rotor cover 340, and that β' denotes the central angle thereof. Note that Ra' is equal to the radius of curvature of the convex surface 321.

It is assumed that R denotes a maximum outside diameter (mm) of the rotor cover 340 when the magnets 320 and so on have been fitted to the rotor cover 340.

It is also assumed that Θ denotes the central angle of one pole of the rotor 300, that t denotes the thickness (mm) of the rotor cover 340, that L denotes the circumferential length (mm) of the rotor cover 340, and that E denotes the Young' s modulus of the rotor cover 340.

When the rotor cover 340 is constructed in the above-described manner, the following geometric equations hold. a' = θ + β' Eq. 1 (R - t - Ra')sin9 = (Ra' + Rb' + t)sinP' Eq.

2

Furthermore, when the magnets 320 and so on have been fitted to the rotor cover 340, pulling forces F are produced at the support region 347 and circumferential end portions of the recessed portions

348. The support region 347 and the recessed portions

348 are stretched thereby, so that the following equation holds.

a' Ra'-aRa _ β' Rb'-/3Rb _ F

Eq. 3

aRa PRb tEL

The pulling forces F produced at the support region 347 produce a radially inward force N (i.e., a supporting force) acting on the magnet 320. The supporting force N is represented by the following equation .

N = 2Fsin (α' /2) Eq. 4

Therefore, the proper holding of the magnets 320 is ensured by making the supporting force N calculated based on the above equations greater than a maximum centrifugal force applied to the magnets 320.

Specifically, the proper holding of the magnets

320 is ensured when the following inequality holds:

N > Mm-Rm-S² Eq. 5

where Mm denotes the mass of each magnet 320, Rm denotes the distance from the center of the through hole 311 to the center of gravity of the magnet 320, and S denotes a maximum angular velocity of the rotor 300 based on a design thereof.

[Method of Manufacturing Rotor 300]

Next, a method of manufacturing the rotor 300 according to the present preferred embodiment will now be described below.

As described above, the magnets 320 and so on are fitted to the rotor cover 340 without use of an adhesive to construct the rotor 300 in a unified manner. Specifically, a method of fitting the magnets 320 and so on to the rotor cover 340 to construct the rotor 300 in a unified manner includes a step of defining the base 340a of the rotor cover 340 (i.e., a base defining step) ; a step of defining the support regions 347 in the base 340a (i.e., a support region defining step) ; a step of fitting the rotor core 310 and the magnets 320 to the base 340a (i.e., a fitting step) ; a step of defining the collar portion 341 in the base 340a to complete the rotor cover 340 (i.e., a collar portion defining step) ; and so on.

(Base Defining Step)

The base 340a of the rotor cover 340 is defined in the base defining step . Specifically, a metal sheet is subjected, for example, to press working to define the base 340a as illustrated in Fig. 7 , which has a bottom and is substantially cylindrical and free of joints . The thickness of the metal sheet is preferably in the range of about 0.2 mm to about 0.3 mm, from the standpoint of durability and motor performance.

(Support Region Defining Step)

In the support region defining step, portions of the circumferential wall 342 of the base 340a are depressed radially inward so that the recesses 346 are defined therein. As a result, the support regions 347 are defined therein. In the present preferred embodiment, the recessed portions 348 are defined simultaneously with the support regions 347.

Referring to Figs. 7, 8, and 9, the columnar jig 360 and eight pressing bars 361 (i.e., pressing dies) are used in the support region defining step. The pressing bars 361 are arranged for the recesses 346. The axial dimension of the jig 360 is greater than the axial dimension of the base 340a. The outside diameter of the jig 360 is slightly smaller than the inside diameter of the base 340a. An outer circumferential surface of the jig 360 includes eight depressed portions 362 defined therein. The depressed portions 362 are arranged to correspond to the recesses 346 in cross-section, in other words, to the support regions 347 and the recessed portions 348 in cross-section. Each of the depressed portions 362 is arranged to extend from an axial middle portion to an upper edge of the outer circumferential surface of the jig 360. Each depressed portion 362 includes a closed end 362a, which is closed by an end surface spreading radially, and an open end 362b.

Each pressing bar 361 includes a pressing surface 361a. The pressing surface 361a is arranged to project in such a manner as to correspond to the recess 346 in cross-section. The pressing bars 361 are arranged around the jig 360 such that the pressing surfaces 361a thereof are arranged to face the depressed portions 362 of the jig 360. In addition, each pressing bar 361 is capable of being shifted in a radial direction. An axial end of the pressing surface 361a of each pressing bar 361 is aligned with the closed end 362a of a separate one of the depressed portions 362. The other axial end of the pressing surface 361a of each pressing bar 361 is positioned axially below an upper edge of the jig 360.

Referring to Fig. 7, in the support region defining step, the base 340a is first placed over the upper edge (i.e., a fitting edge) of the jig 360 and fitted to the jig 360, so that a state as illustrated in Fig. 9 is reached. Thereafter, the pressing bars 361 are pressed against the outer circumferential surface of the base 340a. Predetermined portions of the circumferential wall 342 of the rotor cover 340 are thereby deformed to shape the recesses 346 as illustrated in Fig. 2.

Each depressed portion 362 includes the open end 362b arranged at the upper edge of the jig 360. Therefore, after the pressing bars 361 are shifted backward, the base 340a can be easily removed from the jig 360 by simply pulling the base 340a off the jig 360, without the need for a forced removal.

(Fitting Step)

In the fitting step, which is performed after the support region defining step, the rotor core 310, the magnets 320, and the spacer 330 are fitted to the base 340a so that they are temporarily assembled in a unified manner.

For example, a supporting tool is used to support the rotor core 310 with the magnets 320 arranged at predetermined positions on the outer circumferential surface thereof. The base 340a is then placed over axial ends of the rotor core 310 and the magnets 320 and press fitted thereto so that the rotor core 310 and the magnets 320 reach predetermined positions . At this time, the rotor core 310 and the magnets 320 are circumferentially aligned with the base 340a such that both circumferential ends of the convex surface 321 of each magnet 320 are positioned circumferentially inward of both circumferential ends of the inner surface of the corresponding support region 347.

When the rotor core 310 and the magnets 320 are circumferentially aligned with the base 340a such that both circumferential ends of the convex surface 321 of each magnet 320 are positioned circumferentially inward of both circumferential ends of the inner surface of the corresponding support region 347, the convex surfaces 321 are arranged in surface contact with the corresponding support regions 347. The magnets 320 are thereby held securely in the circumferential direction. Moreover, the recessed portions 348 are embedded between every pair of adjacent magnets 320. This contributes to preventing a contact between the magnets 320.

Finally, the spacer 330 is placed on end surfaces, facing the opening 344, of the rotor core 310 and so on fitted to the base 340a. When the rotor core 310, the magnets 320, and the spacer 330 have been properly fitted to the base 340a, the end portion (i.e., the processed edge 345) of the base 340a closer to the opening 344 is arranged to protrude over an end surface of the spacer 330.

(Collar Portion Defining Step)

In the collar portion defining step, which is performed after the fitting step, the processed edge 345 of the base 340a is deformed to define the collar portion 341. The collar portion 341 is arranged to seal the magnets 320 and so on inside the rotor cover 340.

The collar portion defining step will now be described below with reference to Figs. 10, 11, and 12. In the collar portion defining step, a dedicated lathe apparatus 370 is used to define the collar portion 341 as illustrated in Figs .10 to 12. The lathe apparatus 370 includes a chuck 371 which is capable of being rotated about the rotation axis S, a tail stock 372, and so on. The tail stock 372 is arranged to be opposed to the chuck 371 along the rotation axis S, and is arranged to rotate in synchronism with the chuck 371 while supporting the spacer 330.

The lathe apparatus 370 further includes a small-diameter roller (i.e., a cam follower 373) arranged on a top thereof and being freely rotatable. The lathe apparatus 370 further includes a crimping tool 374. The crimping tool 374 is capable of being shifted in a radial direction with respect to the rotation axis S of the chuck 371 and so on. In addition, the crimping tool 374 is capable of being tilted at least within a range between the rotation axis S and an axis perpendicular to the rotation axis S. Furthermore, the lathe apparatus 370 further includes a touch probe 375 used to determine a reference position during processing. The lathe apparatus 370 further includes a control apparatus and so on (not shown) which are used to perform centralized control of the chuck 371, the tail stock 372, the cam follower 373, the crimping tool 374, and the touch probe 375. The lathe apparatus 370 is arranged to automatically perform a series of processes for defining the collar portion 341.

In the collar portion defining step, first, the base 340a having the rotor core 310 and so on fitted thereto is held by the chuck 371 such that the opening 344 of the base 340a is arranged to face outward. At this time, the chuck 371 and the base 340a are arranged to be substantially coaxial with each other to share the same rotation axis S. Referring to Fig. 10, once the lathe apparatus 370 is activated, the touch probe 375 is first driven. The touch probe 375 is then brought into contact with the end surface of the spacer 330. A reference surface to be used as a reference during the processing is set thereby. Note that performing the processing based on the reference surface contributes to coping with variations in the dimensions of different parts.

Referring to Fig. 11, the tail stock 372 starts operating based on the set reference surface . The tail stock 372 is then properly pressed against the spacer 330 toward the chuck 371. The base 340a is thereby held by the lathe apparatus 370. In addition, the base 340a is caused to rotate about the rotation axis S at a predetermined rotation rate, together with the chuck 371 and the tail stock 372.

Referring to Fig. 12, while the base 340a is rotating, the cam follower 373 is pressed against the processed edge 345 of the base 340a. Referring to Fig. 11, the cam follower 373 is then tilted in a stepwise manner, so that the processed edge 345 is deformed radially inward to define the collar portion 341. When the collar portion 341 has been defined, the spacer 330 is held between the collar portion 341 and an end portion of the rotor core 310.

The cam follower 373 is arranged to rotate as needed at this time. The rotation of the cam follower 373 contributes to preventing occurrence of an excessive frictional force (i.e., an aggressive wear) and an unwanted force between the processed edge 345 and the cam follower 373. Furthermore, the spacer 330 contributes to preventing a damage of any magnet 320 and the end portion of the rotor core 310. Furthermore, the spacer 330 also contributes to retaining the circular shape of the processed edge 345 against influence of the recesses 346. The spacer 330 thus facilitates the shaping of the collar portion 341.

The collar portion 341 is thereby so shaped as to extend evenly in the radial direction to have a fine finish. The collar portion 341 is arranged in close contact with the spacer 330 to restrain the movement of the spacer 330.

The collar portion 341 is preferably arranged to project radially inward from the circumferential wall 342 by more than about 1 mm. The projection of more than about 1 mm ensures that the collar portion 341 is reliably shaped to be flat without being corrugated, and also ensures secure retention of the spacer 330. Note that the collar portion 341 may not necessarily be arranged to extend uniformly along the entire circumference thereof. That is, a cut or cuts may be defined in a portion or portions of the collar portion 341.

The rotor cover 340 is completed when the collar portion 341 has been defined. The collar portion 341 and the spacer 330 combine to restrain the axial movement of the rotor core 310 and the magnets 320 fitted inside the rotor cover 340. As described above, the rotor 300 can be constructed without use of an adhesive, according to the present preferred embodiment. This leads to improved productivity and reduced production cost. Furthermore, it is possible to arrange the magnets at regular intervals in the circumferential direction without use of an intervening adhesive. This leads to an improvement in the degree of imbalance of the rotor.

Note that the present invention is not limited to the rotor 300 and so on according to the above-described preferred embodiment. It is to be understood by those skilled in the art that variations and modifications can be made without departing from the scope and spirit of the present invention.

For example, the shape of the cross section of the rotor core 310 is not limited to an octagon. The shape of the cross section of the rotor core 310 may be changed to a circle, any of a variety of other polygons, or the like suitably in accordance with the number of magnets 320 arranged on the rotor core 310 and the shape of each magnet 320. Also note that the rotor cover 340 may be arranged to have openings at both ends thereof. In this case, spacers 330 are arranged at both ends of the rotor cover 340. In addition, both end portions of the rotor cover 340 may be deformed to define a pair of collar portions 341.

Claims

1. A method of manufacturing a rotor including: a rotor core including a through hole in which a shaft of a motor is inserted;

a plurality of magnets arranged to extend in parallel with the through hole, and arranged on an outer circumferential surface of the rotor core at regular intervals in a circumferential direction, each of the magnets including a convex surface arranged to face radially outward and project so as to assume a minor arc in a cross-section; and

a cylindrical rotor cover fitted to the rotor core with the magnets arranged therebetween;

the method comprising the steps of:

a) defining a base of the rotor cover, the base including a cylindrical circumferential wall and having an opening at at least one end thereof;

b) depressing portions of the circumferential wall of the base radially inward to define a plurality of support regions, each support region having a cross section in a shape of a minor arc, and arranged to project radially outward to match the convex surface of a separate one of the magnets;

c) arranging the magnets on the outer circumferential surface of the rotor core, and fitting the rotor core with the magnets arranged thereon to the base after step b) ; and

d) deforming a portion of the base which surrounds the opening to define a collar portion projecting radially inward after step c) ; wherein

in step b) , each support region is defined such that an inner surface thereof is arranged to have a radius of curvature smaller than that of the convex surface .

2. The method according to claim 1, wherein step c) includes positioning both circumferential ends of the convex surface of each magnet circumferentially inward of both circumferential ends of the inner surface of the corresponding support region, and arranging the convex surface in surface contact with the corresponding support region.

3. The method according to any one of claims 1 and 2, wherein step b) includes defining recessed portions in portions of the circumferential wall of the base which are arranged between every two support regions adjacent to each other, each recessed portion being arranged to be embedded between a separate pair of adjacent ones of the magnets.

4. The method according to any one of claims 1 to

3, wherein

N > Mm-Rm-S²

where N is a radial component of a maximum supporting force applied to each magnet, Mm is a mass of each magnet, Rm is a distance from a center of the through hole to a center of gravity of the magnet, and S is a maximum angular velocity of the rotor.

5. The method according to any one of claims 1 to

4, wherein

the support regions are defined in an axial middle portion of the rotor cover excluding both end portions thereof;

step c) includes fitting an annular spacer to the base near the opening thereof such that an outer circumferential surface of the spacer is arranged to extend along an inner circumferential surface of the base; and

step d) includes arranging the spacer to be held between the collar portion and an end portion of the rotor core.

6. The method according to claim 5, wherein the collar portion is defined to project radially inward from the circumferential wall of the base by 1.0 mm or more .

7. The method according to any one of claims 5 and

6, wherein step d) includes rotating the base with the rotor core, the magnets, and the spacer fitted thereto about the through hole, and, while the base is rotating, tilting a cam follower while pressing the cam follower against the portion of the base which surrounds the opening to define the collar portion.

8. The method according to any one of claims 5 to

7, wherein

step b) includes fitting the base to a columnar jig through a fitting edge of the jig, and pressing a plurality of pressing dies against an outer circumferential surface of the base to define the support regions, the jig including a plurality of depressed portions corresponding to the support regions defined in an outer circumferential surface thereof; and

an end of each depressed portion closer to the fitting edge of the jig is arranged to extend up to the fitting edge.

9. A rotor manufactured by employing the method of any one of claims 1 to 8.

10. A motor comprising:

the rotor of claim 9; and

a cylindrical stator arranged outside an outer circumference of the rotor; wherein an inner circumferential surface of the stator is arranged in close proximity to an outer circumferential surface of the rotor.