Rotor including specific magnet structure and motor provided with same

Provided is a rotor for use in an inner rotor-type motor, comprising a plurality of magnets arranged in a circumferential direction around the center axis, and a rotor core formed of a magnetic material. The rotor core has an inner core part and a plurality of outer core parts. The plurality of outer core parts and the plurality of magnets are alternately arranged in a circumferential direction at a radially outer side of the inner core part. The magnet has a pair of circumferential end surfaces which are magnetic pole surface, and at least one of them is a protruded surface. Also, the magnet has a portion of which circumferential width is wider than a circumferential width of an outer end surface. For this reason, the volume of the magnet can be increased and the magnetic force of the rotor can be increased, without the need to increase the diameter of the rotor. As a result, when such rotor is incorporated into a motor, the torque of the motor can be improved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotor and a motor.

2. Description of the Related Art

Conventionally, a rotor was disposed at the inner side of an armature, that is, a so-called inner rotor type motor has been known in the past. The rotor used in an inner rotor type motor can be mainly classified into an SPM (Surface Permanent Magnet) type rotor wherein a plurality of magnets can be attached to an outer circumferential surface of the rotor core, and an IPM (Interior Permanent Magnet) type rotor wherein a magnet is filled inside the rotor core.

In a typical IPM type rotor, as in the SPM type rotor, each magnet is disposed so that a pair of magnetic pole surfaces are directed towards a radially outer side and a radially inner side. For this reason, only the magnetic pole surface on a radially outer side is used to operate the motor. Therefore, in recent years, in order to effectively utilize the magnetic pole surface of the magnet, each of a pair of magnetic pole surfaces of the magnet is arranged in a circumferential direction, thereby proposing a so-called spoke type rotor structure.

A conventional rotor in which a pair of magnetic pole surfaces of the magnet are disposed to face towards a circumferential direction is disclosed in Japanese Unexamined Patent Application Publication No. 2010-63285, for example. The rotor disclosed in Japanese Unexamined Patent Application Publication No. 2010-63285 is provided with a magnet having an approximately rectangular parallelepiped shape, disposed at regular intervals in the periphery of the axial part. Also, each magnet is disposed so that a pair of magnetic pole surfaces face towards a circumferential direction, and the neighboring magnets are arranged so that identical poles face each other.

As described in Japanese Unexamined Patent Application Publication No. 2010-63285, a magnetic pole surface is effectively utilized in a spoke type rotor structure. For this reason, comparing the spoke type rotor structure with an SPM type rotor or an IPM type rotor (other than the spoke type), given that they are configured to generate the same magnetic force, the spoke type rotor structure is the one capable of designing a smaller diameter for the rotor.

However, in the recent years, not only the miniaturization of a motor but also the improvement of a torque is being required. That is, it is required to increase the magnetic force of the rotor without increasing the diameter of the rotor.

SUMMARY OF THE INVENTION

An exemplary first invention of the present application relates to a rotor which can be used in an inner rotor type motor, and has a plurality of magnets arranged in a circumferential direction and a rotor core formed of a magnetic material disposed in the periphery of a vertically extending center axis. The rotor core exists at a radially inner side than the magnet, and has an inner core part axially extending in a cylindrical shape and a plurality of outer core parts arranged in a circumferential direction with respect to a radially outer side of the inner core part. The plurality of outer core parts and the plurality of magnets are arranged alternately in a circumferential direction. The magnet has a pair of circumferential end surfaces which are magnetic pole surfaces. The magnetic pole surfaces having identical polarity of the plurality of magnets are configured to face one another in a circumferential direction, and at least one of the pair of circumferential end surfaces is a protruded surface which is more circumferentially protruded than a plane connecting an inner and an outer end thereof, and has an apex part which is most distant from the plane. The magnet is a rotor having a portion of which circumferential width is wider than a circumferential width of an outer end surface.

According to an exemplary invention of the present application, the volume of the magnet can be increased without the need to increase the diameter of the rotor. For this reason, the magnetic force of the rotor can be increased without the need to increase the diameter of the rotor. As a result, when the rotor is incorporated into the motor, the torque of the motor can be improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary preferred embodiments of the invention will be described below with reference to the drawings. Meanwhile, in the present application, a direction parallel to a center axis of a motor is referred to as an “axial direction”, a direction orthogonal to the center axis of the motor is referred to as a “radial direction”, and a direction along a circular arc having a center on the center axis of the motor is referred to as a “circumferential direction”. Also in the present application, the axial direction is also referred to as a vertical direction to describe the shapes or relative positions of each part, a rotor side being the upper side with respect to a base part. However, there is no intention to limit the direction at the time of manufacture and use of a motor according to the invention by this definition of the vertical direction.

Also, the description of “a parallel direction” in the present application also includes an approximately parallel direction.

1. First Preferred Embodiment

FIG. 1is a cross-sectional view of a rotor31A of a motor related to a first preferred embodiment. As shown inFIG. 1, the rotor31A has a substantially cylindrical shape, and has a center on a center axis9A which extends vertically. The rotor31A is a rotor which can be used in an inner rotor type motor, and rotates on the center axis9A.

As shown inFIG. 1, the rotor31A has a rotor core4A, and a plurality of magnets5A arranged around the center axis9A in a circumferential direction.

The rotor core4A has an inner core part41A and a plurality of outer core parts42A, and is formed of formed of a magnetic material. The inner core part41A exists at a radially inner side than the magnet5A, and axially extends in a cylindrical shape. The plurality of outer core parts42A exist at a radially outer side than the inner core part41A, and is arranged in a circumferential direction. Further, the plurality of outer core parts42A and the plurality of magnets5A are alternately arranged in a circumferential direction.

The magnet5A has a pair of circumferential end surfaces which are magnetic pole surfaces. In the present preferred embodiment, one of the pair of circumferential end surfaces of the magnet5A is a protruded surface51A, and the other is a flat surface52A. The protruded surface51A is more circumferentially protruded than a plane50A connecting an inner end and an outer end thereof. The protruded surface51A has an apex part510A which is most distant from the plane50A. Also, the flat surface52A is positioned over a substantially identical surface as the plane50A connecting an inner end and an outer end thereof.

Manufacturing costs of a magnet5A, of which only one of the magnetic pole surfaces is a flat surface52A are lower than those of a magnet, of which both of the magnetic pole surfaces are protruded surfaces. In this regard, by using a magnet5A, of which one of the magnetic pole surfaces is a protruded surface51A and the other is a flat surface52A, manufacturing costs can be reduced, and still increase the volume of the magnet.

The magnet5A has a wide part55A with the largest circumferential width. In the present preferred embodiment, a circumferential width of an inner end surface53A of the magnet5A is substantially identical to a circumferential width of an outer end surface54A. For this reason, a circumferential width of the wide part55A is wider than a circumferential width of the outer end surface54A. Meanwhile, in the present preferred embodiment, one of the circumferential end parts of the wide part55A overlaps with the apex part510A of the protruded surface51A.

According to the features described above, the magnet5A has a portion with a wider circumferential width than the outer end surface54A. For this reason, it is possible to increase the volume of the magnet5A without the need to increase the diameter of the rotor31A. That is, the magnetic force of the rotor31A can be increased without the need to increase the diameter of the rotor31A. As a result, the torque of the motor can be improved when the rotor31A is incorporated into the motor.

Here, when the rotor31A rotates, a centrifugal force directed towards a radially outer side is applied to the magnet5A, and the magnet5A tries to jump out towards an outer side of the rotor core4A. However, the magnet5A of this rotor31A has a wide part55A which has a wider circumferential width than that of the outer end surface54A. That is, in an outer end of the outer core part42A adjacent to both circumferential sides of the magnet5A, the intervals between the outer core parts42A are narrower than the wide part55A. For this reason, the magnet5A can be inhibited from falling out to a radially outer side.

The plurality of magnets5A are disposed so that the magnetic pole surfaces having identical polarity face each other in a circumferential direction. Also, as shown inFIG. 1, the plurality of magnets5A according to the present preferred embodiment are disposed so that the protruded surface51A and the flat surface52A face each other in a circumferential direction. That is, a magnet5A having an N-pole protruded surface511A and an S-pole flat surface522A, and a magnet5A having an S-pole protruded surface512A and an N-pole flat surface521A are disposed alternately in a circumferential direction.

Accordingly, the N-pole protruded surface511A of a magnet5A, and the N-pole flat surface521A of its neighboring magnet5A face each other in a circumferential direction across an outer core part42A. Likewise, the S-pole protruded surface512A of a magnet5A, and the S-pole flat surface522A of its neighboring magnet face each other in a circumferential direction across an outer core part42A.

By configuring the protruded surface51A and the flat surface to face each other in a circumferential direction as described above, the shapes of the plurality of outer core parts42A become identical. For this reason, the force applied to each outer core part42A becomes identical when the rotor31A rotates.

2. Second Preferred Embodiment

2-1. Entire Structure of Motor

Subsequently, a second preferred embodiment of the present invention will be described.FIG. 2is a vertical sectional view of a motor1. The motor1is used in an engine cooling fan of a vehicle, for example. However, the motor1of the present invention can also be used in other parts of a vehicle, or may be used in equipment other than vehicles. For example, the motor1of the present invention cam be used in OA equipment, medical equipment, large-sized industrial facilities, and the like.

The motor1has a rotor31A disposed at a radially inner side of an armature24, which is a so-called inner rotor type motor. As shown inFIG. 2, the motor1has a stationary part2and a rotating part3. The stationary part2is fixed to a frame body of equipment such as a vehicle. The rotating part3is rotatably supported with respect to the stationary part2.

The stationary part2of the present preferred embodiment has a shaft21, a base part22, a motor frame23, an armature24, and a circuit board25.

The shaft21is a columnar member vertically extending along a center axis9. The lower end part of the shaft21is fixed to the base part22.

The base part22exists at a lower side of the rotating part3, and expands in a radial direction. The base part22is a metallic material such as aluminum, etc. The motor frame23has a cylindrical part231having a cylindrical shape and having a center on the center axis9. The base part22and a lower end part of the motor frame23are fixed by a locking screw.

The armature24generates a magnetic flux in response to a drive current. The armature24exists at an upper side of the base part22, and is disposed on a radially outer side of the rotor31. The armature24has a stator core241, an insulator242, and a plurality of coils243. The stator241is formed of, for example, a laminated steel plate obtained by a plurality of electromagnetic steel plates laminated in an axial direction. The stator core241has a core back71having a ring shape, and a plurality of teeth72protruding from the core back71towards a radially inner side. The core back71is fixed to an inner peripheral surface of the cylindrical part231of the motor frame23. The plurality of teeth72are circumferentially arranged at substantially regular intervals.

The insulator242is formed of a resin which is an insulating material. The upper surface, the lower surface, and both circumferential end surfaces of each tooth72are covered by the insulator242. The coil243is composed of conductive wires wound around the insulator242. By being interposed between the teeth72and the coil243, the insulator242prevents the teeth72and the coil243from being electrically short-circuited. Meanwhile, insulation coating can be performed on the surface of the teeth, instead of employing an insulator242.

The circuit board25is disposed on the lower side of the base part22. An electronic component for driving the motor1is installed to the circuit board25. An end part of the conductive wire which forms the coil243is soldered or welded to the circuit board25, and electrically connected to the electronic component on the circuit board. Electric current, which is supplied from an outside power source, flows to the coil243through the circuit board25.

The rotating part3has a rotor31and a rotor holder32, and is rotatably supported with respect to the shaft21. A bearing mechanism12is interposed between the shaft21, and the rotor31and the rotor32. The bearing mechanism12of the present preferred embodiment uses a ball bearing wherein a sphere is interposed to relatively rotate an outer ring and an inner ring. However, other types of bearing such as a slide bearing or liquid bearing, etc. can also be used.

The rotor31is disposed on a radially inner side of the armature24, and rotates on the center axis9. The outer peripheral surface of the rotor31faces the inner end surface of the plurality of teeth72of the armature24in a radial direction. The rotor holder32is a resin member which holds the rotor31. The rotor holder32is formed, for example, by insert molding, the rotor31being an insert part. The rotor holder32is connected to, for example, a driving part such as an impeller, etc. of a fan by a locking screw.

In a motor1described above, when a drive current is supplied to the coil243of the stationary part2, a radial magnetic flux is generated at the plurality of teeth72of the stator core241. Further, by the action of magnetic flux between the teeth72and the rotor31, a radial torque is generated. As a result, the rotating part3rotates on the center axis9with respect to the stationary part2.

2-2. Structure of Rotor

Subsequently, a detailed structure of the rotor31will be described.FIG. 3is a cross-sectional view of the rotor31.FIG. 4is a partial cross-sectional view of the rotor31.

The rotor31has a substantially cylindrical shape, and has a center on the center axis9. The rotor31has a rotor core4, and a plurality of magnets5circumferentially arranged around the center axis9.

The rotor core4is a cylindrical member surrounding the shaft21. The rotor core4of the present preferred embodiment is formed of a laminated steel plate obtained by a plurality of electromagnetic steel plates laminated in an axial direction. The rotor core4has an inner core part41and a plurality of outer core parts42.

The inner core part41exists at a radially inner side than the magnet5, and axially extends in a cylindrical shape. A shaft hole43which axially penetrates the inner core part41is provided at the approximate center of the inner core part41. The shaft21is inserted into the shaft hole43.

The plurality of outer core parts42exist at a radially outer side than the inner core part41, and is arranged in a circumferential direction. The inner end of the outer core part42is connected to the inner core part41. Also, the plurality of outer core parts42, and the plurality of magnets5are alternately arranged in a circumferential direction. Meanwhile, the adjacent surfaces of the neighboring outer core part42and magnet5are in contact facing each other in a circumferential direction. Detailed structure of the rotor core4will be described later.

Each magnet5has a pair of circumferential end surfaces which are magnetic pole surfaces. The plurality of magnets5are disposed so that the magnetic pole surfaces having identical polarity face each other in a circumferential direction. In the present preferred embodiment, the pair of circumferential end surfaces of each magnet5are protruded surfaces51. As shown inFIG. 3, in the present preferred embodiment, N-pole protruded surfaces511face each other across the outer core part42in a circumferential direction, and S-pole protruded surfaces512face each other across the outer core part42in a circumferential direction.

The protruded surface51is more circumferentially protruded than a plane50connecting an inner end and an outer end thereof. The protruded surface51has an apex part510which is most distant from the plane50.

Also, the protruded surface51of the present preferred embodiment is a smoothly curved surface. That is, the surface heading towards the apex part510from the inner end of the protruded surface51is a curved surface. Also, the surface heading towards the apex part510from the outer end of the protruded surface51is a curved surface. For this reason, the normal of the protruded surface51heads towards a radially outer side along a radially outer direction, unlike when compared to a case in which the surface heading towards the apex part510from the outer end of the protruded surface51is a flat surface. As a result, in the outer core part42, a magnetic flux from the protruded surface51can be easily directed to a radially outer side. Accordingly, when the rotor is incorporated into the motor, the torque of the motor1can be further improved.

As to each magnet5, a circumferential width of the inner end surface and a circumferential width of the outer end surface54are substantially identical. As to each protruded surface51, the distance between the apex part510and the inner end of the protruded part51, and the distance between the apex part510and the outer end of the protruded part51are substantially identical. For this reason, both end parts of a wide part55, which has the largest circumferential width of the magnet5, overlap with each apex part510of the pair of protruded surfaces51.

The wide part55has a wider circumferential width than the inner end surface53and the outer end surface54. For this reason, the intervals between the outer end surfaces of the outer core parts42adjacent to both circumferential sides of the magnet5are narrower than the wide part55. Accordingly, the magnet5can be inhibited from falling out to a radially outer side to a radially outer side. Likewise, the magnet5can be inhibited from moving towards a radially inner side.

As described above, the magnet5has a portion of which width is wider than a circumferential width of the outer end surface54. For this reason, the volume of the magnet5can be increased without the need to increase the diameter of the rotor31. That is, the magnetic force of the rotor31can be increased without the need to increase the diameter of the rotor31. As a result, when the rotor31is incorporated into the motor1, the torque of the motor1can be improved. In the present preferred embodiment, the volume of the magnet5can be increased by the configuration in which both sides of the pair of circumferential end surfaces of the magnet5are protruded surfaces. Accordingly, the torque of the motor1can be further improved.

Also, the magnet5has a portion of which circumferential width is wider than a circumferential width of the inner end surface53. For this reason, a circumferential width of the inner end surface53does not need to be increased. That is, it is easy to secure the width of the region which connects the outer core part42and the inner core part41. Accordingly, it is easy to manufacture the rotor core4.

Meanwhile, the magnet5of the present preferred embodiment is a ferritic magnet. In recent years, the price of rare earth magnet has been increasing. For this reason, in order to lower the costs, a ferritic magnet is used, which is cheaper in comparison to a rare earth magnet. However, a technical requirement of lowering the costs and yet obtaining a higher torque in comparison to conventional motors still exists. When the structure of rotor31according to the present preferred embodiment is employed, it is not only possible to use a ferritic magnet, but it is also possible to increase the volume of the magnet5, and improve the torque of the motor1. As described above, the present invention is especially valuable in a rotor using a ferrite magnet.

However, a magnet other than a ferritic magnet can also be used in the rotor of the present invention. For example, a neodymium magnet can be used. In such case, the diameter of the rotor can be further reduced in order to lower the amount of magnet usage. Also, by using a magnet which is configured to have a pair of circumferential end surface which are magnetic pole surfaces, one side being a protruded surface and the other side a flat surface, it is possible to provide a rotor which satisfies the requirement of low cost as much as possible.

Here, as shown inFIG. 3, each magnet5of the present preferred embodiment is formed of two magnet pieces, a first magnet piece61and a second magnet piece. The first magnet piece61and the second magnet piece62are circumferentially adjacent to each other.

The first magnet piece61and the second magnet piece62respectively have a pair of circumferential end surfaces which are magnetic pole surfaces. One of the circumferential end surfaces of the first magnet piece61forms the N-pole protruded surface511of the magnet5. One of the circumferential end surfaces of the first magnet piece61is an S-pole flat magnetic pole surface, and an S-pole adsorption surface611which absorbs the second magnet piece62. Likewise, one of the circumferential end surfaces of the second magnet piece62is an N-pole flat magnetic pole surface, and an N-pole adsorption surface621which absorbs the first magnet piece61. One of the circumferential end surfaces of the second magnet piece62forms the S-pole protruded surface512of the magnet5. The S-pole adsorption surface611of the first magnet piece61and the N-pole adsorption surface621of the second magnet piece62absorb each other by magnetic force.

As described above, each magnet5is formed of two magnet pieces61,62having magnetic pole surface, one of which is a protruded surface and the other is a flat surface. The manufacturing cost of a magnet wherein one of the magnetic pole surfaces is a flat surface is lower than a magnet wherein both of the magnetic pole surfaces are protruded surfaces. In this regard, when compared to a case in which each magnet5is formed of a single type of magnet wherein both of the magnetic pole surfaces are protruded surfaces, the manufacturing cost can be reduced.

Also, since each magnet5is formed of a plurality of magnet pieces, eddy-current loss can be suppressed. For this reason, when the rotor31is incorporated into the motor1, the torque of the motor1can be improved.

Meanwhile, in the present preferred embodiment, each magnet5is formed of two magnet: pieces; however, the present invention is not limited thereto. Each magnet5can be formed of a single magnet piece. Also, each magnet5can be formed of three or more magnet pieces circumferentially adjacent to one another. In such case, as to the magnet pieces on both circumferential ends of the three or more magnet pieces, the surfaces which are circumferentially adjacent to the outer core part42become protruded surfaces51.

Subsequently, a detailed structure of the rotor core41will be described.

Each outer core part42is provided with a through hole44which axially penetrates the outer core part42. For this reason, the weight of the rotor31can be reduced. Meanwhile, in the present preferred embodiment, the through hole44is provided to every outer core part42; however, the present invention is not limited thereto. The plurality of core parts42do not need to be provided with the through hole44. Also, the through hole44can be provided to any one of a plurality of outer core parts42, or to two or more outer core parts42.

As shown inFIG. 4, in the present preferred embodiment, the through hole44has a so-called tear shape. Specifically, the through hole44is surrounded by two substantially planar parts441which parts away from each other as heading towards a radially outer side, an inner connection part442which connects the inner end of the two substantially planar parts441, and an outer connection part443which connects the outer end of the two substantially planar parts441.

Here, among the circumferential end surfaces of the outer core parts42, a point at which the tangent with respect to a cross section orthogonal to the center axis9is parallel with the substantially planar part441is defined as a parallel point421. In a peripheral part422of the parallel point421of the outer core part42, the circumferential intervals between the substantially planar part441and the circumferential end surface of the outer core part42are substantially regular. In the present preferred embodiment, the peripheral part422exists between an inner end vicinity of the substantially planar part441and a circumferential end surface of the outer core part42. That is, in the inner end vicinity of the through hole44, the circumferential intervals between the edge of the through hole44and the circumferential end surface of the outer core part42are substantially regular.

Also, in a radially outer side than the peripheral part422, the circumferential intervals between the edge of the through hole44and the circumferential end surface of the outer core part42expand in a radially outward direction. For this reason, the flow of magnetic flux which heads towards an outer end surface of the outer core part42, which is the magnetic pole surface of the rotor core4, from the magnet5can be efficiently guided. Accordingly, it is possible to suppress the degrading of the torque of the motor1which can be caused by the through hole44, unlike when compared to a rotor having a through hole of which circumferential intervals between the edge of the through hole and the circumferential end surface of the outer core part do not expand in a radially outward direction.

As shown inFIG. 3, a non-magnetic layer45interposed between an inner end surface53of each magnet5, and an inner circumferential surface of the inner core part41. For this reason, the short circuiting of the magnetic flux in a radially inner side of each magnet5can be suppressed. In the present preferred embodiment, the non-magnetic layer45is a resin which composes the rotor holder32. Meanwhile, the non-magnetic layer45can be another type of a non-magnetic material. Also, a gap can be interposed between the inner end surface53of each magnet5and the outer circumferential surface of the inner core part41, instead of a non-magnetic layer45.

The rotor core4protrudes from the outer circumferential surface of the inner core part41into the non-magnetic layer45, and has a projection46. The projection46is in contact with the inner end surface53of the magnet5. For this reason, it is possible to suppress the occurrence of positional difference of the magnets5at a radially inner side.

Meanwhile, the projection46of the present preferred embodiment is protruded from the outer circumferential surface of the inner core part41into the non-magnetic layer45; however, the present invention is not limited thereto. The projection46can be circumferentially protruded into the non-magnetic layer45from a side surface of the outer core part42, and can be in contact with the inner end surface of the magnet5.

Also, the outer core part42of the present preferred embodiment does not radially overlap with the outer end surface54of the magnet5. For this reason, the short circuiting of the magnetic flux in a radially outer side of the magnet5can be suppressed. Accordingly, the torque of the motor1can be prevented from being degraded.

Here, as described above, if a fixture extended along the outer end surface54of the magnet5from the circumferential end part of the outer end surface of the outer core part42is installed in order to inhibit the magnet5from falling out to a radially outer side, the fixtures of two neighboring outer core parts42will face each other along the outer end surface54of the magnet5, and thereby form a magnetic path. Then, with respect to a radially outer side of each magnet5, the magnetic flux from the N-pole to the S-pole of the magnet5will be short-circuited by the fixture of the outer core part42on the N-pole side and the fixture of the outer core part42on the S-pole side. In such case, the effective magnetic flux of the rotor31will be degraded, and therefore the torque of the motor1will also be degraded.

As to the rotor31of the present preferred embodiment, the magnet5has a portion of which circumferential width is wider than the outer end surface54in order to inhibit the magnet from falling out to a radially outer side. In this regard, it is unnecessary to install a fixture.

The exemplary preferred embodiments of the invention have been described above; however, the present invention is not limited thereto.

FIG. 5is a cross-sectional view of a rotor31B which relates to a first modified example. As shown inFIG. 5, one of a pair of circumferential end surfaces of each magnet5B is a protruded surface51B, and the other is a flat surface52B.

A plurality of magnets5B are disposed so that the magnetic pole surfaces having identical polarity face each other in a circumferential direction. Also, in the example ofFIG. 5, the plurality of magnets5B are disposed so that their protruded surfaces51B face each other in a circumferential direction. That is, the plurality of magnets5B are disposed so that their flat surfaces52B face each other in a circumferential direction.

Accordingly, a plurality of outer core parts42B are either arranged so that both of the pair of circumferential end surfaces are in contact with the protruded surface51B, or so that both of the pair of circumferential end surfaces are in contact with the flat surface52B. For this reason, during a non-operation status of the motor, the flow of magnetic flux from neighboring magnets5B at both circumferential of the outer core part42B is symmetrical. Such rotor31B is efficient when used in a forward-reverse two-way rotation motor.

FIG. 6is a cross-sectional view of a rotor31C according to another modified example. According to the example shown inFIG. 6, a pair of circumferential end surfaces of each magnet5C are protruded surfaces51C. The protruded surface51C is more circumferentially protruded than a plane50C connecting an inner end and an outer end thereof. The protruded surface51C has an apex510C which has the largest distance from the plane50C.

In the example shown inFIG. 6, a distance between the inner end of the protruded surface51C and the apex part510C is smaller than the distance between the outer end of the protruded surface51C and the apex part510C. For this reason, a portion near the outer end surface of the outer core part42C can be expanded widely. Accordingly, the magnetic flux which started from the surface of the magnet5C can be easily directed to the outer end surface of the outer core part42C.

FIG. 7is a cross-sectional view of a rotor31D which relates to another modified example. In the example shown inFIG. 7, a pair of circumferential end surfaces of each magnet5D are protruded surfaces51D. The protruded surface51D is more protruded than a plane50D connecting an inner end and an outer end thereof. The protruded surface51D has an apex part510D which is most distant from the plane50D.

In the example shown inFIG. 7, the apex part510D is a planar surface which has a width in a radial direction, and parallel with the plane5D. That is, the apex part510D is an axially extending planar surface. As described above, the apex part510D does not need to be a point on a cross-section perpendicular to the center axis, but can be a line having a width in a radial direction. For this reason, a portion having a wide circumferential width of the magnet5D can be enlarged. Accordingly, the volume of the magnet5D can be further increased. As a result, when the rotor31D is incorporated into the motor, the torque of the motor can be further improved.

Meanwhile, in the above preferred embodiment, the protruded surface is a smooth, curved surface; however, the present invention is not limited thereto. In the example shown inFIG. 7, as to the protruded surface51D, a surface heading towards the apex part510D from the outer end and a surface heading towards the apex part510D from the inner end are curved surfaces. Also, the apex part510D is a planar surface. As described above, the protruded surface51D can be configured with curved surfaces and planar surface.

FIG. 8is a cross-sectional view of a rotor31E which relates to another modified example. In the example shown inFIG. 8, a pair of circumferential end surfaces of each magnet5E are protruded surfaces51E. The protruded surface51E is more circumferentially protruded than a plane50E connecting an inner end and an outer end thereof. The protruded surface51E has an apex part510E which is most distant from the plane50E.

In the example ofFIG. 8, in the protruded surface51E, the surface which heads towards the apex part510E from the inner end is a planar surface. Also, in the protruded surface51E, the surface which heads towards the apex part510E from the outer end is a planar surface. For this reason, a portion near the outer end surface of the outer core part42E is expanded widely, unlike when compared to a case in which the surface heading towards the apex part510E from the outer end of the protruded surface51E is a curved surface. Accordingly, it is easy for the magnetic flux from the protruded surface51E to head towards the outer end surface of the outer core part42E.

Meanwhile, in the example shown inFIG. 8, both the surface heading towards the apex part510E from the outer end of the protruded surface51E and the surface heading towards the apex part510E from the inner end are planar surfaces; however, the present invention is not limited thereto. The protruded surface51E can be composed of a combination of curved surfaces and planar surfaces.

FIG. 9is a cross-sectional view of a rotor31F which relates to another modified example. In the example shown inFIG. 9, as to a magnet5F, the width of a wide part55F which has the widest circumferential width is wider than an inner end surface53F.

That is, the magnet5F has a portion of which circumferential width is wider than a circumferential width of the inner end surface53F. For this reason, it is possible to suppress the occurrence of positional difference of the magnets5F at a radially inner side.

A non-magnetic layer45F is interposed between the inner end surface53F of each magnet5F and the circumferential surface of an inner core part41F. For this reason, the short circuiting of the magnetic flux in a radially inner side of each magnet5F can be suppressed. Accordingly, when the rotor31F is incorporated into the motor, the torque of the motor can be improved.

Also, in the example shown inFIG. 9, the entire inner end surface53F of the magnet5F is adjacent to the non-magnetic layer45F. That is, in the above-described preferred embodiment, a rotor core has a projection which is in contact with the inner end surface of the magnet; however, in the example ofFIG. 9, the rotor core4F does not have a projection. For this reason, the short circuiting of the magnetic flux in a radially inner side of each magnet5F can be suppressed. Accordingly, when the rotor31F is incorporated into the motor, the torque of the motor can also be improved.

Furthermore, the detailed shapes of the respective member may be different from the shapes shown in the respective drawings of this specification. Moreover, the respective elements shown in the preferred embodiments and the modification may be appropriately combined with each other so that contradiction does not occur.

Finally, a difference in surface magnetic flux density will be described, depending on whether or not the magnet has a protruded surface.FIG. 10is a sectional view of a rotor31G having a conventional magnet5G in a substantially rectangular shape.FIG. 11is a drawing which shows a simulation result of surface magnetic flux density of the rotor31G and the rotor31B.

A simulation was performed to measure a surface magnetic flux density of the rotor31G illustrated inFIG. 10, which has a magnet5G of which the pair of circumferential end surfaces are flat surfaces52G, the surfaces being magnetic pole surfaces. The rotor31G has identical shape and size as the rotor31B, except for the shape of the magnet and both circumferential end surfaces of the outer core part42G.

Specifically, on a circle423G having the center axis9G as the center, and passing through the most protruded points422G, starting from one of the most protruded points422G, the magnetic flux density was calculated by performing simulation with 0.5 degree intervals around the center axis9G. Here, the most protruded point422G refers to a point among the outer end surface of the outer core part42G having the largest distance from the center axis9G. Here, a root-mean-square of the magnetic flux at each position is defined as the surface magnetic flux density.

Also, likewise, a simulation to calculate the surface magnetic flux density was performed with a rotor31B as shown inFIG. 5, which has a magnet5B wherein one of a pair of circumferential end surfaces which are magnetic pole surfaces is a protruded surface51B, and the other is a flat surface52B.

Specifically, on a circle423B having the center axis9B as the center, and passing through the most protruded points422B, starting from one of the most protruded points422B, the magnetic flux density was calculated by performing simulation with 0.5 degree intervals around the center axis9G. Here, the most protruded point422B refers to a point among the outer end surface of the outer core part42B having the largest distance from the center axis9B. Here, as with rotor31G, a root-mean-square of the magnetic flux at each position is defined as the surface magnetic flux density.

As shown inFIG. 11, the surface magnetic flux density of the rotor31B is bigger than the surface magnetic flux density of the rotor31G by approximately 7.6%.

That is, the rotor31B which has a magnet5B wherein one of a pair of circumferential end surfaces is a protruded surface has a bigger surface magnetic flux density when compared to the rotor31G which has a magnet5G wherein both of a pair of circumferential end surfaces are flat surfaces.

From such result, the rotor31B which has a magnet5B comprising the features of the present invention is capable of increasing the magnetic force of the rotor without the need to increase the diameter of the rotor when compared to the rotor31G which as a conventional magnet5G.

Meanwhile, the numerical value of the surface magnetic flux density shown inFIG. 11can be changed by altering a variety of conditions, for example, the material of the magnet, or the material of the core, etc. Even under such circumstances, when compared under identical conditions, the surface magnetic flux density of a conventional rotor and the surface magnetic flux density of a rotor having the features of the present invention will not be reversed. That is, when compared to a conventional rotor, the numerical value of the surface magnetic flux density of a rotor having the features of the present invention is increased.

The present invention can be used in a rotor and a motor.