Electric rotating machine

A magnetic resistance changing mechanism for changing a magnetic resistance of a stator magnetic path including a stator yoke portion and each tooth portion by mechanically changing the stator magnetic path is provided. A pair of side protruded portions are formed on circumferential sides of a rotor side end portion of each tooth portion. The rotor side end face of each tooth portion is shaped so that a gap between the rotor side end face of each tooth portion and an outer periphery of the rotor is increased continuously or stepwisely from a circumferential intermediate portion of the rotor facing end face toward circumferential end portions thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2012-178049 filed on Aug. 10, 2012, the entire disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to, inter alia, an electric rotating machine, and more specifically relates to an electric rotating machine preferably used as an electric motor as a driving source for various electric vehicles including electric motorcycles and various electric machines.

2. Description of the Related Art

The following description sets forth related art and problems therein and should not be construed as an admission of knowledge in the prior art.

Conventionally, electric vehicles, such as, e.g., electric motorcycles, are equipped with an electric motor as a driving source. Further, various electric devices, such as, e.g., DVDs, are also equipped with an electric motor as a driving source. An electric rotating machine such as an electric motor includes a rotor and a stator. The rotor includes a permanent magnet and is configured to rotate about a rotation axis. The stator includes stator windings and is arranged so as to face the rotor via a gap in a radial direction of the rotor.

In recent years, it has been desired that an electric motor used as a driving source of various electric vehicles including electric motorcycles may be small in size and high in performance. In the case of a vehicle equipped with an internal combustion engine, a transmission is normally used. In the case of electric motors of this kind, however, if the operational range from a high torque low speed revolution speed range to a low torque high speed revolution speed range is wide, a driving force appropriate for a vehicle operation can be obtained without using a transmission.

In an electric motor, however, due to the inherent characteristics, a high torque can be generated in a low revolution speed range. In an electric motor, however, the upper limit of the revolution speed will be limited in a high revolution speed range. That is, in an electric motor, a high torque can be generated in a low revolution speed range. However, as the revolution speed increases, the induced voltage (e.g., back electromotive force), which is to be generated at the stator winding arranged on the stator by magnetic flux of the permanent magnet provided at the rotor, increases. When the revolution speed increases and reaches a certain speed, the induced voltage induced at the stator winding becomes equal to the applied voltage of the electric motor, preventing the electric current flow in the stator winding. This in turn prevents a further increase of the revolution speed. To solve this problem, for example, a field weakening control, which decreases the induced voltage (e.g., back electromotive force), is employed.

In the field weakening control, a current to negate the induced voltage is supplied to the stator winding. In the case of an electric motor in which an electric power is supplied from the outside, the increased power consumption does not result in a shortened drivable time. Therefore, in such an electric motor, even if such a field weakening control is employed, there will be no problem. However, in the case of an electric motorcycle, no power is supplied thereto from the outside, and the electric motorcycle is driven only by a power supplied from a battery mounted thereon. In such a vehicle, the battery capacity is limited. Therefore, when the electric current is supplied to negate the induced voltage induced in the stator winding, the electric power consumption increases. This results in a shortened drivable time. For this reason, it is requested to decrease the power consumption as much as possible.

Herein is proposed a new stator structure capable of being replaced with a conventional field weakening control which induces additional power consumption (see Japanese Unexamined Laid-open Patent Application Publication No. 2006-191782). In this proposal, a tooth portion of a stator on which a winding is arranged is divided into at least two divided tooth portions. The at least two divided tooth portions are relatively movable. The relative movement of the at least two divided tooth portions causes magnetic flux flow changes, which decreases the influence on the stator winding by the flux of the permanent magnet of the rotor at the time of a high revolution speed. According to this proposal, the flux linkage of the stator winding at the time of a high revolution speed can be adjusted by a physical means. Therefore, the electrical power conventionally used for the field weakening control can be decreased or eliminated, which enabled to provide an electric rotating machine capable of decreasing power consumption.

In such an electric rotating machine of this type, it is desired to further enlarge the operational range from a high torque low revolution speed range to a low torque high revolution speed range.

SUMMARY OF THE INVENTION

The preferred embodiments of the present invention have been developed in view of the above-mentioned and/or other problems in the related art. The preferred embodiments of the present invention can significantly improve upon existing methods and/or apparatuses.

Among other potential advantages, some embodiments of the present invention can provide an electric rotating machine capable of further enlarging the operational range from a high torque low revolution speed range to a low torque high revolution speed range.

Among other potential advantages, some embodiments of the present invention can provide a radial gap type electric rotating machine in which, even if a permanent magnet having a strong magnetic force is used as a permanent magnet for a rotor, the operational range can be enlarged from a high torque low revolution speed range to a low torque high revolution speed range and the possible Joule loss can be reduced.

Other objects and advantages of the present invention will be apparent from the following preferred embodiments.

According to some embodiments of the present invention, an electric rotating machine is provided with a rotor having a plurality of permanent magnets arranged on an outer peripheral portion of a rotor main body and a stator arranged radially outward of the rotor main body.

The stator includes a plurality of tooth portions arranged at predetermined intervals in a circumferential direction of the rotor, a stator yoke portion arranged outside of the plurality of tooth portions, and a magnetic resistance changing mechanism configured to change a magnetic resistance of a stator magnetic path constituted by the stator yoke portion and each of the plurality of tooth portions by mechanically changing the stator magnetic path.

Each of the plurality of tooth portions includes a pair of side protruded portions protruded from both sides of a rotor side end portion of each of the plurality of tooth portions in the circumferential direction.

A magnetic resistance of a magnetic path formed by a gap between a pair of adjacent side protruded portions of a pair of adjacent tooth portions is set to have a value so that

a) when the magnetic resistance changing mechanism is in a first state in which the stator magnetic path is changed so that the magnetic resistance of the stator magnetic path is minimum or near minimum, a main magnetic path that extends from one of the magnetic poles of one of a pair of adjacent permanent magnets is formed by a magnetic path mainly passing through the pair of adjacent tooth portions corresponding to the pair of adjacent permanent magnets and the stator yoke portion, and

b) when the magnetic resistance changing mechanism is in a second state in which the stator magnetic path is changed so that the magnetic resistance of the stator magnetic path is maximum or near maximum, the main magnetic path is formed by a magnetic short-path mainly passing through a rotor side end portion of the tooth portion.

Furthermore, in a first relative position in which adjacent end portions of the pair of adjacent permanent magnets are positioned corresponding to a circumferential intermediate portion of the rotor side end portion of each tooth portion, a first magnetic short-circuit C1is defined as a magnetic short-circuit C constituting a magnetic short-path mainly passing through the circumferential intermediate portion.

In a second relative position in which adjacent end portions of the pair of adjacent permanent magnets are positioned corresponding to one of circumferential end portions of the rotor side end portion of each tooth portion, a second magnetic short-circuit C2is defined as a magnetic short-circuit C constituting a magnetic short-path mainly passing through the one of circumferential end portions.

In a third relative position in which adjacent end portions of the pair of adjacent permanent magnets are positioned corresponding to a pair of adjacent side protruded portions, a third magnetic short-circuit C3is defined as a magnetic short-circuit C constituting a magnetic short-path mainly passing through the gap between the pair of adjacent side protruded portions.

When the magnetic resistance changing mechanism is in the second state, the second magnetic short-circuit C2has a total magnetic resistance between a total magnetic resistance of the first magnetic short-circuit C1and a total magnetic resistance of the third magnetic short-circuit C3, and is configured to control a change ratio of the total magnetic resistance of the magnetic short-circuit C when the magnetic short-circuit C is changed from the second magnetic short-circuit C2to the third magnetic short-circuit C3and from the third magnetic short-circuit C3to the second magnetic short-circuit C2in accordance with a relative rotational movement of the rotor with respect to the stator.

In some exemplary embodiments of the electric rotating machine, it can be configured such that both end portions of a rotor facing end face of the rotor side end portion of each tooth portion in the circumferential direction are positioned between a first virtual curve A and a second virtual curve B. The first virtual curve A is a curve having a curvature radius R0centering on a rotation axis of the rotor and passing a rotor closest portion of the rotor facing end face which is closest to an outer periphery of the rotor. The second virtual curve B is a curve having a curvature having the same curvature radius R0as the curvature radius R0of the first virtual curve A and contacting the first virtual curve A at the rotor closest portion of the rotor facing end face, the second virtual curve B being convex toward the outer periphery of the rotor.

In some exemplary embodiments of the electric rotating machine, it can be configured such that the rotor facing end face of the rotor side end portion of each tooth portion is formed into a concave curve in cross-section which is concave toward the outer periphery of the rotor, the concave curve having a curvature radius larger than the curvature radius R0of the first virtual curve A.

In some exemplary embodiments of the electric rotating machine, it can be configured such that the rotor facing end face of the rotor side end portion of each tooth portion is formed into a cross-sectional shape in which a gap between the rotor facing end face of the rotor side end portion of each tooth portion and the outer periphery of the rotor is increased continuously or step-wisely from a circumferential intermediate portion of the rotor facing end face toward a circumferential end portion of the rotor facing end face.

In some exemplary embodiments of the electric rotating machine, it can be configured such that the rotor facing end face of the rotor side end portion of each tooth portion is formed into an angular cross-sectional shape having an obtuse angle, the cross-sectional shape being convex toward the outer periphery of the rotor.

In some exemplary embodiments of the electric rotating machine, it can be configured such that each tooth portion is divided into a plurality of divided tooth portions in the radial direction, the plurality of divided tooth portions including a first divided tooth portion arranged at an innermost portion in the radial direction and facing an outer peripheral portion of the rotor main body and a second divided tooth portion arranged at an outermost portion in the radial direction and connected to the stator yoke portion. At least one of the plurality of divided tooth portions in each tooth portion constitutes a movable divided tooth portion relatively movable in the circumferential direction with respect to the other divided tooth portion, and the movable divided tooth portion is movable between a first position and a second position, the first position and the second position being relatively different in magnetic resistance of a magnetic path formed by the plurality of divided tooth portions in each tooth portion.

In some exemplary embodiments of the electric rotating machine, it can be configured such that each tooth portion is divided into two divided tooth portions in the radial direction, the two divided tooth portions including a first divided tooth portion arranged so as to face the outer peripheral portion of the rotor main body and a second divided tooth portion arranged outside of the first divided tooth portion in the radial direction via a gap.

In some exemplary embodiments of the electric rotating machine, it can be configured such that the first position is defined as a magnetic resistance minimum position in which the plurality of divided tooth portions are aligned in the radial direction so that a magnetic resistance of a magnetic path constituted by the plurality of divided tooth portions becomes minimum. The second position is defined as a magnetic resistance maximum position in which the movable divided tooth portion is relatively moved with respect to the other divided tooth portion in the circumferential direction so that the magnetic resistance of the magnetic path constituted by the plurality of divided tooth portions becomes maximum. The movable divided tooth portion is relatively movable continuously or discontinuously within arbitrary positions between the magnetic resistance minimum position and the magnetic resistance maximum position.

In some exemplary embodiments of the electric rotating machine, it can be configured such that the permanent magnet is a neodymium magnet.

In some exemplary embodiments of the electric rotating machine, it can be configured such that the plurality of permanent magnets are arranged in the outer peripheral portion of the rotor main body in an embedded manner.

In some exemplary embodiments of the electric rotating machine, it can be configured such that the plurality of permanent magnets are arranged on the outer peripheral portion of the rotor main body in an outwardly exposed manner.

According to other embodiments of the present invention, a vehicle is equipped with the electric rotating machine as mentioned above.

According to still other embodiments of the present invention, an electronic product is equipped with the electric rotating machine as mentioned above.

According to some preferred embodiments of the present invention, when the magnetic resistance changing mechanism is in the second state in which the stator magnetic path is changed so that the magnetic resistance value of the stator magnetic path is the maximum value or close to it, the second magnetic short-circuit C2functions as a buffer circuit that controls the change ratio in the total magnetic resistance value of the magnetic short-circuit C in accordance with the revolution of the rotor. Therefore, it is possible to provide an electric rotating machine capable of controlling the peak value of the induced voltage induced on the stator winding and further enlarging the operational range by extending the upper limit of the revolution speed in a high revolution speed range even if the rotor rotates at a high speed in the second state.

Also, by employing the mechanical magnetic resistance changing mechanism, an electric rotating machine capable of decreasing or eliminating the electric power for a conventional field weakening control can be provided. Furthermore, even in the case of using a permanent magnet having a strong magnetic force, high torque can be obtained in a low revolution speed range, and the upper limit of the revolution speed in the high revolution speed range and the operational range can be enlarged.

In addition, because the change in magnetic flux of the rotor during high speed revolution in the second state can be controlled, it becomes possible to provide an electric rotating machine that can control the decrease in efficiency, the decrease in the magnetic coercive force and residual magnetic flux density of the permanent magnet caused by the heat generation due to the Joule loss, and the decrease in efficiency of the electric motor by decreasing the occurrence of a Joule loss generated in the permanent magnet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following paragraphs, some preferred embodiments of the present invention will be described with reference to the attached drawings by way of example and not limitation. It should be understood based on this disclosure that various other modifications can be made by those in the art based on these illustrated embodiments.

An electric motor as an electric rotating machine according to an embodiment of the present invention is suitably used for a main driving source or an auxiliary driving source in a variety of vehicles V including, e.g., electric motorcycles and other vehicles (seeFIG. 14). An electric motor of this kind typically has high torque at a low revolution speed and low torque at a high revolution speed. The electric rotating machine according to the present invention, however, is not limited for use in these vehicles, but can also suitably be used for, for example, an electric motor R as a driving force in electric products E including household electronics, such as, e.g., washing machines, etc., and office automation devices, such as, e.g., DVD players, etc. (seeFIG. 15).

Initially, the development process of the present invention will be explained. In the market, an even higher-performance electric rotating machine is desired. Therefore, it was attempted to further improve the performance by employing a permanent magnet piece having a stronger magnetic force, such as, e.g., a neodymium magnet. In detail, in a radial gap type electric rotating machine, a variety of research and studies were initially conducted to use a permanent magnet having a stronger magnetic force.

Specifically, an improved radial gap type electric rotating machine was proposed as shown inFIGS. 10A and 10B.

This radial gap type electric rotating machine includes a rotor102and a stator103. The rotor102includes a cylindrical rotor main body110configured to rotate about a rotation shaft101and a plurality of permanent magnet pieces MG embedded in an outer peripheral portion of the cylindrical rotor main body110and arranged at constant intervals in a circumferential direction of the rotor main body110. The stator103is formed into a cylindrical shape. The stator103is arranged radially outward of the rotor102so as to face an outer peripheral surface of the rotor102via a gap. More specifically, this electric rotating machine has the following structure.

The permanent magnet piece MG is formed into a rectangular cross-sectional plate shape extending in an axial direction. The permanent magnet piece MG is fixed to the outer peripheral portion of the rotor main body110in a state in which the permanent magnet piece MG is fitted in a slit S having a corresponding cross-sectional shape and formed radially inward of the outer peripheral surface of the rotor main body110so as to be positioned inwardly by a predetermined distance. Therefore, even if the rotor main body110rotates at a high revolution speed about the rotation shaft101, the permanent magnet piece MG does not break loose radially outward due to the centrifugal force.

The stator103is arranged radially outward of the rotor102and coaxially with the rotor102so as to face the outer periphery of the rotor102via a predetermined gap. The stator103includes a plurality of tooth portions130arranged at constant intervals in the circumferential direction of the rotor102in a state in which the stator103is arranged radially outward of the rotor102via the gap.

Each tooth portion130is divided into two divided tooth portions in a radial direction at a position of the tooth portion130closer to an end portion of the tooth portion130opposite to a rotor side end portion of the tooth portion130. In detail, each tooth portion130includes two divided tooth portions, e.g., a first tooth portion131arranged closer to the rotor side and a second tooth portion132arranged outside of the first tooth portion131. The first tooth portion131and the second tooth portion132are arranged in a relatively movable manner in the circumferential direction with a predetermined gap formed therebetween.

In each first tooth portion131, a rotor facing end face of the rotor side end portion is formed into an arc shape corresponding to the outer peripheral shape of the rotor102(e.g., formed to have a constant gap in the circumferential direction). Side protruded portions131aand131aextending in the circumferential direction are integrally formed on both circumferential side portions of the rotor side end portion. Each first tooth portion131is provided with a winding (not illustrated).

The second tooth portion132as a movable divided tooth portion is configured such that the relative position of the second tooth portion132relative to the first tooth portion131can be continuously changed between the first position shown inFIG. 10Aand the second position shown inFIG. 10B. The first position denotes a position in which the first tooth portion131and the second tooth portion132are arranged in a radially aligned manner as shown inFIG. 10A. The second position denotes a position in which the second tooth portion132is located at an intermediate position between the pair of adjacent first tooth portions131and131as shown inFIG. 10B.

When the second tooth portion132is in the first position shown inFIG. 10A, the magnetic flux from one of adjacent permanent magnet pieces MG reaches the other of adjacent permanent magnet pieces MG via the following path. That is, the magnetic flux from one of adjacent permanent magnet pieces MG reaches the other of adjacent permanent magnet pieces MG mainly through a magnetic circuit constituted by a pair of adjacent tooth portions130and the stator yoke portion150. This magnetic circuit is defined as a main magnetic circuit M.

On the other hand, as shown inFIG. 10B, when the second tooth portion132is in the second position, the magnetic flux from one of adjacent permanent magnet pieces MG reaches the other of adjacent permanent magnet pieces MG via the following path. That is, the magnetic flux from one of adjacent permanent magnet pieces MG reaches the other of adjacent permanent magnet pieces MG mainly through a magnetic circuit constituted by a gap between the adjacent side protruded portions131aand131aof the adjacent tooth portions130. This magnetic circuit is defined as a magnetic short-circuit C.

In a state in which the second tooth portion132is in the second position, the magnetic short-circuit C as a main magnet circuit is formed at the rotor side end portion of the stator103. Therefore, even if the rotor102rotates at a high revolution speed, it was thought that the induced voltage induced to the stator winding will be suppressed, which enables an increased number of revolution of the rotor102.

Under the circumstances, for the aforementioned electric motor, a simulation analysis was conducted while moving the second tooth portion132as a movable divided tooth portion in the circumferential direction to change its relative position relative to the first tooth portion131. As a result, it was confirmed that, by moving the second tooth portion132as a movable divided tooth portion relative to the first tooth portion131, the upper limit of the high revolution speed range can be increased, which in turn can enlarge the operational range without using an electric power associated with a conventional field weakening control.

For the purpose of further extending the upper limit of the high revolution speed range to enlarge the operational range, further experiments and research were conducted. The experiments and research focused attention on the shape of the rotor side end portion of each tooth portion130of the stator103. As a result, it was found that by changing the shape of the rotor side end portion of each tooth portion130of the stator103, the operational range can be enlarged by extending the upper limit of the high revolution speed range, and completed the present invention.

That is, in the improved electrical rotating machine according to the aforementioned proposal, when the magnetic resistance between the first tooth portion131and the second tooth portion132becomes large by moving the movable divided tooth portion132(second tooth portion) in the circumferential direction, the influence by the magnetic short-circuit C becomes large. In other words, the magnetic flux of the adjacent permanent magnet pieces MG mainly passes through the rotor side end portion of the stator103.

Therefore, it was thought that the cross-sectional shape of the rotor facing end face of the rotor side end portion of the first tooth portion131of the stator103was preferably formed into a cross-sectional shape corresponding to the shape of the outer periphery of the rotor main body110. That is, it was thought that the gap between the rotor facing end surface of the first tooth portion131and the outer periphery of the rotor main body110should be preferably formed to be constant in the circumferential direction and that the gap should be decreased as small as possible.

However, further experiments and research revealed that when the rotor side end portion of each tooth portion130of the stator103is formed into a shape as mentioned above, the upper limit of the high revolution speed range becomes rather restricted.

It is initially assumed that the magnetic resistance between the first tooth portion131and the second tooth portion132has become large by moving the movable divided tooth portion (second tooth portion)132in the circumferential direction as shown inFIG. 10B. In this state, as shown inFIG. 11(A), when the adjacent end portions of the adjacent permanent magnet pieces MG and MG of the rotor102are positioned at the intermediate portion of the first tooth portion131of the stator103in the circumferential direction, the magnetic short-circuit C1is constituted by a path mainly passing through the circumferential intermediate portion of the rotor side end portion of the tooth portion (first tooth portion131). From this state, it is assumed that the rotor102rotates in a counterclockwise direction and the adjacent end portions of the adjacent permanent magnet pieces MG and MG of the rotor102are positioned at the left end portion of the first tooth portion131of the stator103in the circumferential direction as shown inFIG. 11(B). Also in this state, in the same way as in the state shown inFIG. 11(A), the magnetic short-circuit C2is constituted by a path mainly passing through one end portion (side protruded portion) of the rotor side end portion of the tooth portion (first tooth portion131). Therefore, even if the state changes from the state shown inFIG. 11(A)to the state shown inFIG. 11(B), the gap G between the rotor side end portion of the tooth portion (first tooth portion131) of the stator103and the outer periphery of the rotor main body110is constant, and therefore there is no big change in the magnetic resistance between the magnetic short-circuit C1and the magnetic short-circuit C2.

However, when the rotor102further rotates in the counterclockwise direction from the state shown inFIG. 11(B), the magnetic short-circuit C3is constituted by a path mainly passing through the gap between the adjacent side protruded portions131aand131aof the adjacent first tooth portion131and131. In this state, because the gap between the adjacent side protruded portions131aconstitutes a part of the magnetic short-circuit C, the total magnetic resistance of the magnetic short-circuit C3becomes larger as compared with the states shown inFIG. 11(A)andFIG. 11(B).

When the rotor102further rotates in the counterclockwise direction from the state shown inFIG. 11(C), the magnetic short-circuit C is again constituted by a path passing through the rotor side end portion (side protruded portion131a) of the tooth portion131of the stator103. Therefore, the total magnetic resistance of the magnetic short-circuit C2becomes the same value as the state shown inFIG. 11(B), which is smaller as compared with the total magnetic resistance of the state shown inFIG. 11(C).

In this way, especially when the state changes from the state shown inFIG. 11(B)to the state shown inFIG. 11(C)and when the state changes from the state shown inFIG. 11(C)to the state shown inFIG. 11(D), the total magnetic resistance of the magnetic short-circuit C changes largely and suddenly. In accordance with the large and sudden change of the magnetic resistance of the magnetic short-circuit C, the number of magnetic flux of the permanent magnet pieces MG and MG of the rotor102interlinked with the stator winding changes largely and suddenly. Consequently, the peak value of the induced voltage induced to the stator winding increases in accordance with the large and sudden change in the interlinking magnetic flux number. This prevents further increase in number of revolution of the rotor102.

It was confirmed that decreasing the change ratio of the magnetic resistance of the magnetic short-circuit by devising the shape of the rotor side end portion of each tooth portion130of the stator103can decrease the induced voltage to be induced to the stator winding, which in turn can increase the number of revolution of the rotor102, and completed the present invention. Hereinafter, the present invention will be explained in detail based on specific embodiments.

First Embodiment

FIGS. 1 to 6schematically show a radial gap type electric motor preferably used as an electric motor for electric motorcycles according to a first embodiment of the present invention. As shown in these figures, the radial gap type motor includes a columnar rotor2, a cylindrical stator3and a rotating mechanism4as main components. The columnar rotor2has a plurality of permanent magnet pieces MG arranged at an outer peripheral portion at certain intervals in a circumferential direction and is configured to rotate about a rotation shaft1. The cylindrical stator3is arranged radially outward of the outer peripheral portion of the rotor2via a gap so as to face the outer peripheral portion. The rotating mechanism4is configured to relatively move a movable divided tooth portion32constituting the stator3, which will be explained later.

As shown inFIG. 2, the rotor2includes a cylindrical rotor main body10having the rotation shaft1arranged at the axial center thereof. A total of six plate shaped permanent magnet pieces MG each having a rectangular cross-sectional shape are arranged in the circumferential direction of the rotor2at constant intervals in the outer peripheral portion of the rotor main body10.

As the permanent magnet piece MG, a magnet, such as, e.g., a neodymium magnet, which creates a strong magnetic force, can be preferably used. It was found that especially when using a permanent magnet having a strong magnetic force, depending on the shape and/or arrangement of the permanent magnet piece MG, the rotor2, and the stator3, Joule losses occur in the permanent magnet piece MG to increase the temperature of the permanent magnet, piece MG which largely deteriorates the efficiency of the motor and furthermore the coercive force of the permanent magnet is decreased, which causes deterioration of the motor's performance. These problems are not limited in the case of using a permanent magnet having a strong magnetic force, and can occur in varying degrees in the case of using a conventional permanent magnet having a normal magnetic force. In the rotating electric motor according to some embodiments of the present invention, the aforementioned problems are solved by the newly proposed structure which will be mentioned later.

As shown inFIG. 2, the permanent magnet piece MG is formed into a plate shape rectangular in cross-section extending along the axial direction X. As shown inFIG. 3, each permanent magnet piece MG is embedded in and fixed to a slit S having a corresponding cross-sectional shape and formed in the outer peripheral portion of the rotor main body10at a position radially inward of the outer peripheral surface by a predetermined distance. Therefore, even if the rotor main body10rotates at a high revolution speed about the rotation shaft1, the permanent magnet piece MG does not break loose to the outside in the radial direction due to the centrifugal force since the permanent magnet piece MG is fixedly fitted in the slit S.

The width dimension of the slit S is, as shown inFIG. 4Afor example, formed to be slightly larger than the width dimension of the permanent magnet piece MG. In a state in which the permanent magnet piece MG is fitted in the slit S, an air gap S1is formed at both ends of the permanent magnet piece MG to constitute a flux barrier.

The rotor main body10is formed by, for example, bonding a plurality of thin silicon steel plates, each formed into a predetermined shape by a punching process, in the axial direction X, so that possible eddy-current loss to be generated due to changes in magnetic flux in the rotor main body10can be reduced. This is the same for the stator3and the stator yoke portion50which will be mentioned later.

The stator3is arranged coaxially with the rotor2and arranged radially outward of the rotor2via a predetermined gap so as to face the rotor2. As shown inFIG. 2, the stator3includes a cylindrical first stator portion3A coaxially arranged with the rotor2via a predetermined gap and arranged outside of the outer periphery of the rotor2, and a cylindrical second stator portion3B coaxially arranged with the rotor2and radially outward of the first stator portion3A via a predetermined gap in a state in which the second stator portion3B is movable in the circumferential direction relative to the first stator portion3A.

The stator3includes, as shown inFIG. 4A, a plurality of tooth portions30arranged at predetermined intervals along the circumferential direction of the rotor2in a state in which they are arranged radially outward of the rotor2with the gap therebetween. Each tooth portion30is divided, at a portion closer to an end portion opposite to a rotor side end portion, into two divided tooth portions in the radial direction, e.g., a first tooth portion31arranged closer to the rotor side and a second tooth portion32arranged outside of the first tooth portion31.

The first tooth portion31and the second tooth portion32are arranged via a predetermined gap so that both the tooth portions31and32can be relatively movable in the circumferential direction. The gap between the first tooth portion31and the second tooth portion32is set to be smaller than the gap between the rotor side end face of the first tooth portion31and the outer periphery of the rotor2. That is, as shown inFIG. 4A, in a state in which the first tooth portion31and the second tooth portion32are arranged in the radially aligned manner, the magnetic resistance Rk1between the first tooth portion31and the second tooth portion32is smaller than the minimum magnetic resistant Rh between the rotor side end face of the first tooth portion31and the outer periphery of the rotor2.

Each first tooth portion31is formed, as shown inFIG. 5in an enlarged manner, so that the rotor facing end face of the rotor side end portion is formed into a circular arc cross-sectional shape concaving toward the rotor2and having a curvature radius R1larger than the curvature radius of the outer periphery of the rotor2. Specifically, the rotor facing end face of the rotor side end portion of the first tooth portion31is positioned between a first virtual curve A and a second virtual curve B. The first virtual curve A is defined as a curve having a curvature radius R0centering on a rotation axis of the rotor2and passing a rotor closest portion of the rotor facing end face which is closest to an outer periphery of the rotor2. The second virtual curve B is defined as a curve having a curvature having the same curvature radius as the curvature radius R0of the first virtual curve A and contacting the first virtual curve A at the rotor closest portion of the rotor facing end face. The second virtual curve B is convex toward the outer periphery of the rotor2. At both side portions of the rotor side end portion of the first tooth portion31in the circumferential direction, side protruded portions31aand31aare integrally formed so as to extend in the circumferential direction.

The gap between the side protruded portions31aand31aof adjacent first tooth portions31and31is set to be larger than the gap between the first tooth portion31and the second tooth portion32, as shown inFIG. 4A. Specifically, the gap between the adjacent side protruded portions31aand31aof the adjacent tooth portions30and30is set so that the magnetic resistance Rj between the adjacent side protruded portions31aand31aof the adjacent first tooth portions31and31is larger than the magnetic resistance 2Rk1, which is two times the magnetic resistance Rk1between the first tooth portion31and the second tooth portion32in a state in which the first tooth portion31and the second tooth portion32are arranged in the radially aligned manner (seeFIG. 4A).

As shown inFIG. 1, each first tooth portion31is provided with a winding40. As shown inFIG. 2, a plurality of first tooth portions31having the winding40constitute a cylindrical first stator portion3A molded with resin. The winding40can be a single winding or a plurality of separate and independent windings. In this embodiment, a single winding is employed.

The second tooth portion32is, as shown inFIG. 4A, formed integrally with the stator yoke portion50in a manner such that the second tooth portion32is inwardly protruded from the inner peripheral surface of the cylindrical stator yoke portion50, and arranged corresponding to the first tooth portion31. In this embodiment, the second tooth portion32is an integral structure with the stator yoke portion50, but it can be configured such that the second tooth portion32is formed separately from the stator yoke portion50and connected and fixed to the stator yoke portion50. As shown inFIG. 2, the second tooth portion32and the stator yoke portion50constitute a cylindrical second stator portion3B.

On the outer peripheral surface of the stator yoke portion50constituting the second stator portion3B, as shown inFIG. 2, on the partial region of the outer peripheral surface in the circumferential direction, a gear portion51having a plurality of teeth is formed along the entire length in the longitudinal direction of the stator yoke portion50. As shown inFIG. 1, the gear portion51is engaged with a wheel gear4cwhich is rotary driven by a drive motor4aof the rotating mechanism4via the speed reduction mechanism4b.

The drive motor4ais configured to rotate in both opposite directions by a controller C. The rotational force of the drive motor4ais transmitted to the wheel gear4cvia the speed reduction mechanism4b. The rotation of the wheel gear4cis transmitted to the gear portion51of the stator yoke portion50(second stator portion3B) to cause a relative movement of the second stator portion3B with respect to the first stator portion3A in the circumferential direction. This in turn causes a relative movement of the second tooth portion32with respect to the first tooth portion31within a certain range in the circumferential direction. In this way, by controlling the drive motor4a, the relative position of the first tooth portion31and the second tooth portion32can be arbitrarily and continuously or discontinuously changed.

By controlling the drive motor4awith the controller C, the relative position of the second tooth portion32as a movable divided tooth portion with respect to the first tooth portion31can be freely changed continuously or discontinuously between a magnetic resistance minimum position as shown inFIG. 4Aand a magnetic resistance maximum position as shown inFIG. 4B. The magnetic resistance minimum position is defined as a position in which the first tooth portion31and the second tooth portion32are arranged in a radially aligned manner and the magnetic resistance Rk of the magnetic path formed by the first tooth portion31and the second tooth portion32becomes minimum Rk1. On the other hand, the magnetic resistance maximum position is defined as a position in which the second tooth portion32is positioned in between a pair of adjacent first tooth portions31and31and the magnetic resistance Rk of the magnetic path formed by the first tooth portion31and the second tooth portion32becomes maximum Rk2.

When the magnetic resistance minimum position as shown inFIG. 4Ais defined as a first position and the magnetic resistance maximum position as shown inFIG. 4Bis defined as a second position, the movable divided tooth portion (the second tooth portion32) is controlled by the controller C so that the movable divided tooth portion moves between the first position and the second position.

In the present invention, it is not the case that the first position and the second position exactly correspond to the magnetic resistance minimum position and the magnetic resistance maximum position, respectively. For example, in the present invention, it can be configured such that two arbitrary positions between the magnetic resistance minimum position and the magnetic resistance maximum position are defined as the first position and the second position, respectively, and that the movable divided tooth portion (second tooth portion)32is moved between the first position and the second position.

In this embodiment, a tooth portion30which is divided into two portions in the radial direction is exemplified, but the present invention is not limited to that. In the present invention, the tooth portion30can be divided into, for example, three or more portions in the radial direction. When the tooth portion30is divided into three or more portions, the divided tooth portion arranged closest to the rotor2is defined as the first tooth portion31, and the divided tooth portion arranged at the radially outermost side is defined as the second tooth portion32. In cases where the tooth portion is divided into three or more divided tooth portions, it can be configured such that at least one of the plurality of divided tooth portions constitutes a movable divided tooth portion relatively movable with respect to the other divided tooth portions so that the magnetic resistance of the magnetic path formed by the divided tooth portions is adjustable by the relative movement of the movable divided tooth portion.

In this embodiment, the explanation is made such that each tooth portion is divided into the first tooth portion31and the second tooth portion32, but the structure can be understood as follows. That is, it can be understood such that the first tooth portion31constitutes a tooth portion30; the second tooth portion32and the stator yoke portion50constitute a stator yoke portion; a concave portion50ais formed on the inner peripheral surface of the stator yoke portion50; and the stator yoke portion50is relatively movable with respect to the tooth portion (first tooth portion31) in the circumferential direction. In that case, it is understood that the tooth portion30has a structure in which the tooth portion30is not divided in the radial direction. The present invention can have any other structure as long as the stator magnetic path formed by a stator yoke portion50and tooth portions30and30is mechanically changed so that the magnetic resistance value of the stator magnetic path can be changed. For example, one example of a modified magnetic resistance changing mechanism includes a mechanism in which a magnetic gap is provided at a part of the stator yoke portion50so that the magnetic gap can be adjusted.

In the first state in which the second tooth portion32as a movable divided tooth portion is arranged in the first position, it is configured to satisfy the following relational expression (seeFIG. 4A):
(the total magnetic resistance (2Rh+2Rk1) of the main magnetic circuitM)<(the total magnetic resistance (2Rh+Rj) of the magnetic short-circuitC.

In the aforementioned relational expression, Rh denotes a magnetic resistance between the rotor facing end face of the first tooth portion31and the outer peripheral surface of the rotor2, Rk1denotes a magnetic resistance between the first tooth portion31and the second tooth portion32, and Rj is a magnetic resistance between the adjacent side protruded portions31aand31a.

Also, in a state in which the second tooth portion32as a movable divided tooth portion is arranged in the second position, it is configured to satisfy both the following relational expressions (seeFIG. 4B):
(total magnetic resistance of the third magnetic short-circuitC3)<(total magnetic resistance of the main magnetic circuitM), and
(the total magnetic resistance (2Rh+Rj) of the magnetic short-circuitC)<(the total magnetic resistance (2Rh+2Rk2) of the main magnetic circuitM).

In the aforementioned relational expression, Rh denotes a magnetic resistance between the rotor facing end face of the first tooth portion31and the outer peripheral surface of the rotor2, Rk2denotes a magnetic resistance between the first tooth portion31and the second tooth portion32, and Rj denotes a magnetic resistance between the adjacent side protruded portions31aand31a. The main magnetic circuit M and the magnetic short-circuit C are defined as follows.

As shown inFIG. 4A, the main magnetic circuit M is defined as a magnetic circuit having a main magnetic path which extends from one of magnetic poles (radially outward magnetic pole in the drawing) of one of adjacent permanent magnet pieces MG and MG and reaches the other of magnetic poles (radially inward magnetic pole in the drawing) of the one of adjacent permanent magnet pieces MG and MG via one of the tooth portions30of the adjacent tooth portions30and30, the stator yoke portion50, the other of one of the tooth portions30of the adjacent tooth portions30and30, and the other of adjacent permanent magnet pieces MG and MG.

On the other hand, when the movable divided tooth portion32is moved in a clockwise direction to take the second position between the adjacent first tooth portions31and31as shown inFIG. 4B, the main magnetic circuit M is defined as follows. That is, the main magnetic circuit M is a magnetic circuit having a main magnetic path which extends from one of magnetic poles of adjacent permanent magnet pieces MG and MG and reaches the other of magnetic poles of the adjacent permanent magnet pieces MG and MG via the following portions in turn. The main magnetic path extends through the first tooth portion31of one of adjacent tooth portions30and30, a stator yoke portion side end portion of the first tooth portion31, and then an end portion of the second tooth portion32corresponding to the stator yoke portion side end portion of the first tooth portion31. Thereafter, the main magnetic paths extends through the second tooth portion32, an opposite end portion of the second tooth portion32, a stator yoke portion side end portion of the first tooth portion31of the other of adjacent tooth portions30and30, the first tooth portion31of the other of adjacent tooth portions30and30, and then the other of the adjacent permanent magnet pieces MG and MG.

Needless to say, regardless of the position of the second tooth portion32, the magnetic flux of the permanent magnet piece MG passes various paths other than the aforementioned path, e.g., a path between adjacent first tooth portions31and31, as a leakage flux. In the present invention, a magnetic circuit is defined based on a main magnetic flux path. It should be understood that this interpretation is applied not only to the main magnetic circuit M but also to the magnetic short-circuit C.

As shown inFIGS. 4A and 4B, the magnetic short-circuit C is defined as a magnetic circuit having a main magnetic path which extends from one of magnetic poles of one of adjacent permanent magnet pieces MG and MG and reaches the other of magnetic poles of one of the adjacent permanent magnet pieces MG and MG, mainly via the rotor side end portion side of the tooth portion30.

As shown inFIGS. 4A and 4B, when adjacent end portions of the adjacent permanent magnet pieces MG and MG are in a position corresponding to the adjacent side protruded portions31aand31aof the adjacent first tooth portions31and31, the magnetic short-circuit C is defined as a magnetic circuit having a magnetic main path as follows. That is, the magnetic short-circuit C is defined as a magnetic circuit having a main magnetic path which extends from one of magnetic poles of one of adjacent permanent magnet pieces MG and MG and reaches the other of magnet poles of the one of adjacent permanent magnet pieces MG and MG via the following portions in turn. The main magnetic path extends through a rotor side end portion of the first tooth portion31of the one of adjacent tooth portions30and30, and then one of side protruded portions31aof the rotor side end portion of the first tooth portion31of the one of adjacent tooth portions30and30. Thereafter, the main magnetic path extends through a side protruded portion31aof a rotor side end portion of a first tooth portion31of the other of adjacent tooth portions30and30, which is adjacent to the one of side protruded portions31a, a rotor side end portion of the first tooth portion31of the other of adjacent tooth portions30and30, and then the other of adjacent permanent magnetics MG and MG.

As explained above, the magnetic path of the magnetic short-circuit C differs slightly depending on the relative position of the permanent magnet piece MG of the rotor2and the first tooth portion31of the stator3. As mentioned above, however, the magnetic short-circuit C is defined as a magnetic circuit having a main magnetic path which extends from one of magnetic poles of one of adjacent permanent magnet pieces MG and MG and reaches the other of magnetic poles of one of the adjacent permanent magnets via the other of adjacent permanent magnet pieces MG and MG, without passing through a radially outward portion of the tooth portion30excluding the rotor side end portion and the side protruded portions31aand31aof the first tooth portion31.

In the electric motor according to this embodiment, when the rotor2rotates, the flow of the magnetic flux from one of magnetic poles of the permanent magnet piece MG to the other of magnetic poles differs between when the second tooth portion32is in the first position in which the second tooth portion32as a movable divided tooth portion and the first tooth portion31are arranged in a radially aligned manner (seeFIG. 4A) and when the second tooth portion32is in the second position in which the second tooth portion32is moved relative to the first tooth portion31(seeFIG. 4B).

First, the flow of the magnetic flux which exits from one of magnetic poles of the permanent magnet piece MG and reaches the other of magnetic poles when the rotor2rotates in a state in which the second tooth portion32as a movable divided tooth portion is in the first position in which the second tooth portion32and the first tooth portion31are arranged in a radially aligned manner (seeFIG. 4A) will be explained.

In this state, as explained above, the following relational expression is satisfied: (the total magnetic resistance (2Rh+2Rk1) of the main magnetic circuit M)<(the total magnetic resistance (2Rh+Rj) of the magnetic short-circuit C). In this state, regardless of the rotational position of the rotor2, the total magnetic resistance (2Rh+2Rk1) of the main magnetic circuit MG is small. Therefore, the majority of the magnetic flux exited from one of magnetic poles (e.g., the upper magnetic pole inFIG. 4A) of the permanent magnet piece MG (the right permanent magnet piece MG shown inFIG. 4A) returns to the other of magnetic poles (the lower magnetic pole shown inFIG. 4A) via the following magnetic path.

Focusing attention on the right permanent magnet piece MG shown inFIG. 4A, the magnetic flux from one of magnetic poles (the upper magnetic pole inFIG. 4A) of the permanent magnet piece MG returns to the other of magnetic poles (the lower magnetic pole inFIG. 4A) via the first tooth portion31of one of adjacent tooth portions30and30(the tooth portion30positioned in the middle inFIG. 4A), the second tooth portion32radially outwardly aligned with the first tooth portion31, the stator yoke portion50, the second tooth portion32of the other of adjacent tooth portions30and30(the tooth portion30positioned on the left side inFIG. 4A), the first tooth portion31of the other of adjacent tooth portions30and30(the tooth portion30positioned on the left side inFIG. 4A) radially inwardly aligned with the second tooth portion32, and the permanent magnet pieces MG arranged on the left side.

Obviously, other than the aforementioned path, leakage flux exists between the adjacent tooth portions30and30, especially between the side protruded portions31aand31aof the adjacent first tooth portions31and31. However, the magnetic resistance between the adjacent tooth portions30and30and the magnetic resistance between the side protruded portions31aand31aare significantly larger than the magnetic resistance (2Rk1) of the main magnetic circuit, and therefore the leakage flux does not largely exert an influence on the flow of the magnetic flux of the main magnetic circuit M. Further, on each of both widthwise ends of the permanent magnet pieces MG, a connection wall9connecting the upper iron core portion and the lower iron core portion is integrally formed (for example, seeFIG. 5). Although magnetic flux flow always exists in the connection wall9, the magnetic flux flow is saturated and stable. Therefore, the magnetic flux flow does not largely exert an influence on the magnetic flux flow of the main magnetic circuit M.

Therefore, when the rotor2rotates in a state in which the second tooth portion32as a movable divided tooth portion is in the first position in which the second tooth portion32and the first tooth portion31are arranged in a radially aligned manner (seeFIG. 4A), the flow of the magnetic flux which exits from one of magnetic poles of the permanent magnet piece MG and reaches the other of magnetic poles is stable. Therefore, the change of the magnetic flux in the permanent magnet piece MG is small. As a result, Joule losses generated in the permanent magnet piece MG are also small.

Next, the flow of the magnetic flux which exits from one of magnetic poles of the permanent magnet piece MG and reaches the other of magnetic poles when the rotor2rotates in a state in which the second tooth portion32as a movable divided tooth portion is moved relative to the first tooth portion31and is in the second position (seeFIG. 4B) will be explained.

In this state, as explained above, the following relational expression is satisfied:
(the total magnetic resistance (2Rh+Rj) of the magnetic short-circuitM)<(the total magnetic resistance (2Rh+2Rk2) of the main magnetic circuitM).

In this second positional state, regardless of the rotational position of the rotor2, the total magnetic resistance (2Rh+Rj) of the magnetic short-circuit C is smaller than the total magnetic resistance (2Rh+2Rk2) of the main magnetic circuit M. Therefore, the majority of the magnetic flux exited from one of magnetic poles (the upper side magnetic pole inFIG. 4B) of the permanent magnet M (the center permanent magnet piece MG inFIG. 4B) returns to the other of magnetic poles (the lower side magnetic pole inFIG. 4B) via the path of the magnetic short-circuit C.

In this embodiment, as shown inFIG. 5, the rotor facing end face of the rotor side end portion of each tooth portion30(first tooth portion31) is formed into a concave shape facing the rotor main body and having a curvature radius R1. The curvature radius R1is larger than a curvature radius R0of a first virtual curved line A centering on the rotation axis of the rotor2and passing through the closest portion of the rotor facing end face positioned closest to the outer peripheral surface of the rotor2.

That is, in this shape, the gap between the tooth portion30(first tooth portion31) and the rotor2(rotor main body10) gradually increases continuously from the circumferential intermediate portion toward the circumferential end portions of the rotor facing end face of the tooth portion30. In other words, the magnetic resistance Rh between the tooth portion30and the rotor2is gradually increased continuously from the circumferential intermediate portion to the circumferential end portions. It should be noted that the shape of the rotor facing end face of the rotor side end portion of the tooth portion30(first tooth portion31) is not limited to be changed continuously and gradually as in this embodiment, and can be changed discontinuously or step-wisely.

In this embodiment, as shown inFIG. 4B, in the second state in which the magnetic resistance between the first tooth portion31and the second tooth portion32has become larger by moving the movable divided tooth portion (second tooth portion)32in the circumferential direction, when the adjacent end portions of the adjacent permanent magnet pieces MG and MG of the rotor2take a first relative position in which the adjacent end portions are positioned at the circumferential intermediate portion of the tooth portion30of the stator3as shown inFIG. 6A, the magnetic short-circuit C1is a path passing through the circumferential intermediate portion of the rotor side end portion of the tooth portion30(first tooth portion31). From this state, when the rotor2is rotated in the counterclockwise direction and the adjacent end portions of the adjacent permanent magnet pieces MG and MG of the rotor2take a second relative position in which the adjacent end portions are located at the circumferential left end portion of the tooth portion31of the stator3as shown inFIG. 6(B), in the same manner as in the state shown inFIG. 6(A), the magnetic short-circuit C2is constituted by a path mainly passing through one end portion (side protruded portion)31aof the rotor side end portion of the tooth portion30(first tooth portion31). Therefore, when it changes from the state shown inFIG. 6(A)to the state shown inFIG. 6(B), although the gap G between the rotor side end portion of the tooth portion30(first tooth portion31) of the stator3and the outer periphery of the rotor main body10slightly enlarges, there is no sudden and large change in the magnetic resistance between the magnetic short-circuit C1and the magnetic short-circuit C2.

Next, when the rotor2is further rotated in the counterclockwise direction from the state shown inFIG. 6(B), the magnetic short-circuit C3is constituted by a path mainly passing through the gap between the adjacent side protruded portions31aand31aof the adjacent first tooth portions31and31. In this third relative position, because the gap between the adjacent side protruded portions31aand31aconstitute a part of the magnetic short-circuit C3, the total magnetic resistance of the magnetic short-circuit C3becomes larger as compared with the states shown inFIG. 6(A)andFIG. 6(B).

In other words, the second magnetic short-circuit C2has a total magnetic resistance value between the total magnetic resistance value of the first magnetic short-circuit C1and the total magnetic resistance value of the third magnetic short-circuit C3. This functions as a buffer circuit for controlling the rate of change in the total magnetic resistance value of the magnetic short-circuit C at the time of changing the magnetic short-circuit C from the second magnetic short-circuit C2to the third magnetic short-circuit C3and from the third magnetic short-circuit C3to the second magnetic short-circuit C2in accordance with the relative rotational movement of the rotor2with respect the stator3.

That is, in the case of a comparative example in which the rotor facing end face of the rotor side end portion of each tooth portion30(first tooth portion31) has a curved surface corresponding to the outer peripheral surface of the rotor main body10in which the gap is formed to be constant along the circumferential direction (seeFIGS. 10A and 10B), there is no big difference in the total magnetic resistance between the first magnetic short-circuit C1and the magnetic short-circuit C2, but there is a big difference in the total magnetic resistance between the second magnetic short-circuit C2and third magnetic short-circuit C3. Therefore, when the rotor2rotates in the circumferential direction, due to the change in the relative position of the rotor2with respect to each tooth portion30, the magnetic short-circuit C changes from the first magnetic short-circuit C1to the second magnetic short-circuit C2, and to the third magnetic short-circuit C3. In accordance with the change, the magnetic resistance changes suddenly when the magnetic short-circuit changes from the second magnetic short-circuit C2to the magnetic short-circuit C3and from the third magnetic short-circuit C3to the second magnetic short-circuit C2. This in turn causes changes of the number of magnetic flux interlinked with the stator winding of the permanent magnet piece MG, resulting in an increased peak value of the induced voltage induced to the stator winding. For this reason, the upper limit of the number of revolutions of the rotor2is limited.

On the other hand, in this embodiment, as explained above, the rotor facing end face of the rotor side end portion of each tooth portion30(first tooth portion31) is formed into a curved surface having a curvature radius slightly larger than the curvature radius of a curved surface corresponding to the outer peripheral surface of the rotor main body10. Therefore, the total magnetic resistance of the second magnetic short-circuit C2is larger than the total magnetic resistance of the first magnetic short-circuit C1. Further, the second magnetic short-circuit C2has a total magnetic resistance value between the total magnetic resistance value of the first magnetic short-circuit C1and the total magnetic resistance of the third magnetic short-circuit C3. Therefore, when the magnetic short-circuit C changes from the second magnetic short-circuit C2to the third magnetic short-circuit C3and from the third magnetic short-circuit C3to the second magnetic short-circuit C2, the change ratio of the magnetic resistance becomes smaller than the aforementioned comparative example. This changes the number of magnetic flux interlinked with the stator winding of the permanent magnet piece MG, resulting in a reduced peak value of the induced voltage induced to the stator winding as compared with the comparative example. For this reason, as compared with the comparative example, the upper limit of the number of revolutions of the rotor2can further be increased.

In addition, in the first embodiment, both circumferential end portions of the rotor facing end face of the rotor side end portion of each tooth portion30are, as shown inFIG. 5, positioned between the first virtual curve A and the second virtual curve B in the cross-sectional view. The first virtual curve A has a curvature radius R0centering on a rotation axis of the rotor2and passing a rotor closest portion of the rotor facing end face which is closest to the outer periphery of the rotor2(circumferential intermediate portion in this embodiment). The second virtual curve B has the same curvature radius R0as the curvature radius R0of the first virtual curve A and contacts the first virtual curve A at the rotor closest portion of the rotor facing end face. The second virtual curve B is convex toward the outer periphery of the rotor (seeFIG. 5).

Second Embodiment

An electric rotating machine according to a second embodiment of the present invention is a radial gap type electric motor preferably used as an electric motor for an electric motorcycle, as similar to the first embodiment. This radial gap type electric motor of this second embodiment is almost the same in basic structure as the electric motor of the first embodiment.

In this second embodiment, as shown inFIG. 7, the rotor facing end face of the rotor side end portion of each tooth portion30(first tooth portion31) is formed into an arrow-like cross-sectional shape overall having an obtuse angle which is convex toward the outer periphery of the rotor2(rotor main body10). In this embodiment, the total magnetic resistance of the second magnetic short-circuit C2is larger than the total magnetic resistance of the first magnetic short-circuit C1. Also, the second magnetic short-circuit C2has a total magnetic resistance value between the total magnetic resistance of the first magnetic short-circuit C1and the total magnetic resistance of the third magnetic short-circuit C3. Therefore, in this embodiment, when the magnetic short-circuit C changes from the second magnetic short-circuit C2to the third magnetic short-circuit C3and from the third magnetic short-circuit C3to the second magnetic short-circuit C2, the change ratio of the magnetic resistance is smaller than in the comparative example. This changes the number of magnetic flux interlinked with the stator winding of the permanent magnet piece MG, resulting in a reduced peak value of the induced voltage induced to the stator winding as compared with the comparative example. Therefore, as compared with the comparative example, the upper limit of the number of revolutions of the rotor2can be further increased. Since the other structures are the same as those of the first embodiment, the explanations thereof will be omitted.

Also in this second embodiment, both circumferential end portions of the rotor facing end face of the rotor side end portion of each tooth portion30are positioned between the first virtual curve A and the second virtual curve B in the cross-sectional shape. The first virtual curve A has a curvature radius R0centering on a rotation axis of the rotor2and passing a rotor closest portion of the rotor facing end face which is closest to the outer periphery of the rotor2(circumferential intermediate portion in this embodiment). The second virtual curve B has the same curvature radius R0as the curvature radius R0of the first virtual curve A and contacts the first virtual curve A at the rotor closest portion of the rotor facing end face. The second virtual curve B is convex toward the outer periphery of the rotor (seeFIG. 7).

Third Embodiment

An electric rotating machine according to a third embodiment of the present invention is a radial gap type electric motor preferably used as an electric motor for an electric motorcycle, as similar to the first embodiment. This radial gap type electric motor of this third embodiment is almost the same in basic structure as the electric motor of the first embodiment.

In the third embodiment, as shown inFIG. 8, the rotor facing end face of the rotor side end portion of each tooth portion30(first tooth portion31) is formed into a convex shape facing the outer peripheral surface of the rotor2(rotor main body10) and continuously changing in cross-section and positioned between the first virtual curve A and the second virtual curve B. The first virtual curve A has a curvature radius R0centering on a rotation axis of the rotor2and passing a rotor closest portion of the rotor facing end face which is closest to the outer periphery of the rotor2(intermediate portion in the circumferential direction in this embodiment). The second virtual curve B has the same curvature radius R0as the curvature radius R0of the first virtual curve A and contacting the first virtual curve A at the rotor closest portion of the rotor facing end face of the tooth portion30(first tooth portion31). The second virtual curve B is convex toward the outer periphery of the rotor2(rotor main body10).

Also in this embodiment, the total magnetic resistance of the second magnetic short-circuit C2is larger than the total magnetic resistance of the first magnetic short-circuit C1. Further, the second magnetic short-circuit C2has a total magnetic resistance value between the total magnetic resistance of the first magnetic short-circuit C1and the total magnetic resistance of the third magnetic short-circuit C3. Therefore, also in this embodiment, when the magnetic short-circuit C changes from the second magnetic short-circuit C2to the third magnetic short-circuit C3and from the third magnetic short-circuit C3to the second magnetic short-circuit C2, the change ratio of the magnetic resistance is smaller than in the comparative example. This changes the the number of magnetic flux interlinked with the stator winding of the permanent magnet piece MG, resulting in a reduced peak value of the induced voltage induced to the stator winding as compared with the comparative example. Therefore, as compared with the comparative example, the upper limit of the number of revolutions of the rotor2can be further increased. Since the other structures are the same as those of the first embodiment, the explanations thereof will be omitted.

Also in this third embodiment, both circumferential end portions of the rotor facing end face of the rotor side end portion of each tooth portion30are positioned between the first virtual curve A and the second virtual curve B in the cross-sectional view. The first virtual curve A has a curvature radius R0centering on a rotation axis of the rotor2and passing a rotor closest portion of the rotor facing end face which is closest to the outer periphery of the rotor2(circumferential intermediate portion in this embodiment). The second virtual curve B has the same curvature radius R0as the curvature radius R0of the first virtual curve A and contacts the first virtual curve A at the rotor closest portion of the rotor facing end face. The second virtual curve B is convex toward the outer periphery of the rotor (seeFIG. 8).

Fourth Embodiment

An electric rotating machine according to a fourth embodiment of the present invention is a radial gap type electric motor preferably used as an electric motor for an electric motorcycle, as similar to the first embodiment. This radial gap type electric motor of this second embodiment is almost the same in basic structure as the electric motor of the first embodiment.

In the fourth embodiment, as shown inFIG. 9, the rotor facing end face of the rotor side end portion of each tooth portion30(first tooth portion31) is formed into a cross-sectional shape in which the distance from the outer peripheral surface of the rotor2(rotor main body10) is increased step-wisely from a circumferential intermediate portion toward circumferential end portions.

Also in this embodiment, the total magnetic resistance of the second magnetic short-circuit C2is larger than the total magnetic resistance of the first magnetic short-circuit C1. Further, the second magnetic short-circuit C2has a total magnetic resistance value between the total magnetic resistance of the first magnetic short-circuit C1and the total magnetic resistance of the third magnetic short-circuit C3. Therefore, also in this embodiment, when the magnetic short-circuit C changes from the second magnetic short-circuit C2to the third magnetic short-circuit C3and from the third magnetic short-circuit C3to the second magnetic short-circuit C2, the change ratio of the magnetic resistance is smaller than in the comparative example. This changes the number of magnetic flux interlinked with the stator winding of the permanent magnet piece MG, resulting in a reduced peak value of the induced voltage induced to the stator winding as compared with the comparative example. Therefore, as compared with the comparative example, the upper limit of the number of revolutions of the rotor2can be further increased. Since the other structures are the same as those of the first embodiment, the explanations thereof will be omitted.

Also in this fourth embodiment, both circumferential end portions of the rotor facing end face of the rotor side end portion of each tooth portion30are positioned between the first virtual curve A and the second virtual curve B in the cross-sectional shape. The first virtual curve A has a curvature radius R0centering on a rotation axis of the rotor2and passing a rotor closest portion of the rotor facing end face which is closest to the outer periphery of the rotor2(circumferential intermediate portion in this embodiment). The second virtual curve B has the same curvature radius R0as the curvature radius R0of the first virtual curve A and contacts the first virtual curve A at the rotor closest portion of the rotor facing end face. The second virtual curve B is convex toward the outer periphery of the rotor (seeFIG. 9).

An electric rotating machine (in which the rotor facing end face of the rotor side end portion of each tooth portion has a curvature radius R1larger than the curvature radius of the first virtual curve A having a curvature radius R0centering on a rotation axis of the rotor2and passing a rotor closest portion of the rotor facing end face which is closest to the outer periphery of the rotor2) was used. As shown inFIG. 16, a power supply equipped with a battery and a three-phase inverter circuit as a driving force was connected to the electric rotating machine. In the first state and the second state in which the second tooth portion32as a movable divided tooth portion was moved to the first position and the second position, respectively, the rotor2was rotated.

The magnetic flux interlinked with the stator winding of the U phase of the tooth portion30(first tooth portion31) and the terminal voltage on the battery side of the inverter circuit in each position were examined. As a comparative example, using the electric rotating machine as shown inFIGS. 10A and 10B, in the same manner as mentioned above, the magnetic flux interlinked with the stator winding of the U phase of the tooth portion30(first tooth portion31) and the terminal voltage on the battery side of the inverter circuit in each position were examined. These results are shown in the graphs ofFIG. 12AtoFIG. 12D. When the curvature of the rotor side end portion of the tooth portion30(first tooth portion31) in the comparative example was set to 1, in the first embodiment, the curvature of the rotor side end portion of the tooth portion30(first tooth portion31) was set to 0.4.

From these results, it is understood that, at the second position (second state) in which the movable divided tooth portion was moved in the circumferential direction and the magnetic resistance of the main magnetic circuit M was large, the local rate of change of the waveform of the magnetic flux interlinked with the stator winding was controlled and the waveform was smoothed, as shown inFIG. 12C. Therefore, as shown inFIG. 12D, the peak value of the induced voltage (battery side terminal voltage) induced to the terminal on the battery side of the inverter circuit was lower than the comparative example. In this way, it was confirmed that the peak value of the induced voltage induced to the stator winding could be suppressed and the upper limit of the number of revolutions of the rotor2could further be increased than the comparative example.

As shown inFIG. 7, using an electric rotating machine in which the rotor facing end face of the rotor side end portion of the tooth portion30(first tooth portion31) of the stator3was formed into an obtuse angle that was convex toward the rotor2and having the same other structures as those of the first embodiment, the rotor2was rotated in the first state and the second state by moving the second tooth portion32as a movable divided tooth portion to the first position and the second position in a state in which a power supply equipped with a battery and a three-phase inverter circuit as a driving force were connected as shown in Example 1 andFIG. 16. Then, the magnetic flux interlinked with the stator winding of the U phase of the tooth portion30(first tooth portion31) and the terminal voltage on the battery side of the inverter circuit in each position were examined. Also, as a comparative example, using the electrical rotating machine as shown inFIGS. 10A and 10B, the magnetic flux interlinked with the stator winding of the U phase of the tooth portion30(first tooth portion31) and the terminal voltage on the battery side of the inverter circuit in each position were examined. These results are shown in the graphs ofFIG. 13AtoFIG. 13D.

From these results, it is understood that, at the second position (second state) in which the movable divided tooth portion was moved in the circumferential direction and the magnetic resistance of the main magnetic circuit M was large, the local rate of change of the waveform of the magnetic flux interlinked with the stator winding was controlled and the waveform was smoothed, as shown inFIG. 13C. Therefore, as shown inFIG. 13D, the peak value of the induced voltage (battery side terminal voltage) induced to the terminal on the battery side of the inverter circuit was lower than the comparative example. In this way, it was confirmed that the peak value of the induced voltage induced to the stator winding could be suppressed and the upper limit of the number of revolutions of the rotor2could further be increased than the comparative example.

In all of the aforementioned embodiments, it was exemplified that the permanent magnet piece MG was formed into a rectangular cross-section and fitted in the slit formed in the peripheral portion of the rotor main body. However, the present invention is not limited to that, and allows a structure in which, for example, a permanent magnet piece is formed into a cross-sectional arc shape corresponding to the outer periphery of the rotor main body and fixed to the outer peripheral surface of the rotor main body. In this case, needless to say, the permanent magnet piece should be securely fixed to the rotor main body so that it does not break loose from the rotor main body due to the centrifugal force caused by the revolution of the rotor.

The present invention can be used in place of a conventional field weakening control, but does not prevent the combined use with the conventional field weakening control.

It should be understood that the terms and expressions used herein are used for explanation and have no intention to be used to construe in a limited manner, do not eliminate any equivalents of features shown and mentioned herein, and allow various modifications falling within the claimed scope of the present invention.

While illustrative embodiments of the invention have been described herein, the present invention is not limited to the various preferred embodiments described herein, but includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. For example, in the present disclosure, the term “preferably” is non-exclusive and means “preferably, but not limited to.”

INDUSTRIAL APPLICABILITY

The electric rotating machine of the present invention can be used as an electric motor as a driving source for, e.g., various electric vehicles including electric motorcycles, and various electric machines.