Rotor for rotating electric machine

Abstract

Rotor (2) for a rotating electric machine, comprising a rotor core (15) and a permanent magnet (60) arranged in the rotor core (15), wherein in each of a plurality of magnetic poles (P) the rotor core (15) has a plurality of holes (20) including a first hole (21) and a second hole (22), in each of which the permanent magnet (60), having a planar magnetic pole surface (F), is arranged, the first hole (21) and the second hole (22) being arranged separately on both sides in a circumferential direction (C) with respect to a magnetic pole centerline (90) extending in a radial direction (R) through a center of the magnetic pole (P) in the circumferential direction (C), such that a separation distance between the first hole (21) and the second hole (22) in the circumferential direction (C) increases towards an outer side in the radial direction (R), the rotor core (15) having a plurality of of bridge sections (41)which are formed between two of the holes (20) that are adjacent to each other in the circumferential direction (C), the plurality of bridge sections (41) has an offset bridge section (51) located at a position that is displaced in the circumferential direction (C) from the magnetic pole centerline (90), an extension direction (D1) of the offset bridge section (51) is inclined in a cross-section perpendicular to an axial direction (L) with respect to the magnetic pole centerline (90) so that it approaches the magnetic pole centerline (90) in the direction towards the outer side in the radial direction (R), the plurality of holes (20) in each of the plurality of magnetic poles (P) is arranged such that it forms a surrounding hole group (31) that surrounds a magnetic pole center (91) which is an intersection of the magnetic pole centerline (90) and an outer circumferential surface (15a) of the rotor core (15),and the extension direction (D1) of the offset bridge section (51) in the cross-section is defined perpendicular to the axial direction (L) along a direction to a centroid (G1) of a target section (81) which is surrounded by the surrounding hole group (31).

Description

TECHNICAL FIELDThe present invention relates to a rotor for a rotating electric machine, including a rotor core and permanent magnets disposed in the rotor core.BACKGROUNDAs an example of a rotor for a rotating electric machine, a rotor for a rotating electric machine described in Japanese Patent Application JP 2012-165 482 A (Patent Document 1) is known. A rotor ( 10) described in Patent Document 1 includes a pair of permanent magnets ( 26) and a magnetic flux suppression hole ( 28) in each of a plurality of magnetic poles ( 24). At a magnet insertion hole (32) where the permanent magnet (26) is inserted, a first hole (28a) is formed so as to communicate with the magnet insertion hole (32). In the structure illustrated in FIGS. 2 and 3 of Patent Document 1, the magnetic flux suppression hole ( 28) is structured by two first holes ( 28 a, 28 a) and one second hole ( 28 b). Bridge portions (36) are formed between one first hole (28a) and the second hole (28b) and between the other first hole (28a) and the second hole (28b). The second hole ( 28 b) is disposed in a region in a circumferential direction having a magnetic pole center line (C). The bridge portion ( 36) is an offset bridge portion formed at a position shifted in the circumferential direction from the magnetic pole center line (C).As described in paragraph 0039 of Patent Document 1 regarding a centrifugal resistance strength, it is necessary that the bridge portion such as an offset bridge portion be formed in such a size that the strength of a rotor core is a strength sufficient to resist a centrifugal force during rotation of the rotor. An output torque of the rotating electric machine generally decreases as the amount of magnetic flux passing through the bridge portion (amount of leakage flux) increases. From the viewpoint of improving the output torque of the rotating electric machine, it is desirable to minimize the width of the bridge portion. However, Patent Document 1 does not describe a technology for reducing the width of the offset bridge portion. JP 2011-223 742 A and WO 2014 / 041 507 A1 and US 2007 / 0 096 579 A1 disclose further rotors.Related DocumentsPatent DocumentsPatent Document 1: JP 2012-165 482 ASUMMARY OF THE INVENTIONProblem to be Solved by the InventionThere is a demand to obtain a rotor for a rotating electric machine in which the width of an offset bridge portion can be reduced while securing the strength of a rotor core against a centrifugal force properly.Means for Solving the ProblemIn view of the above, a first characteristic structure of a rotor for a rotating electric machine is set forth in claim 1.According to the first characteristic structure, the extending direction of the offset bridge portion in the cross section perpendicular to the axial direction is the direction inclined with respect to the magnetic pole center line so as to approach the magnetic pole center line toward the outer side in the radial direction. Therefore, stress concentration on the offset bridge portion during rotation of the rotor (rotor for a rotating electric machine) can be mitigated as compared to a case where the extending direction is set as a direction parallel to the magnetic pole center line. As a result, the width of the offset bridge portion can be reduced while the strength of the rotor core against the centrifugal force is suitably secured.To give a supplementary description, during the rotation of the rotor, the offset bridge portion supports, against the centrifugal force, a radially outer portion of the rotor core in the magnetic pole where the offset bridge portion is provided (which will be referred to as a "support target portion" in this portion hereinafter). When a consideration is made using a simplified model, the centrifugal force is applied to the center of gravity of an object. Therefore, a tensile load toward the center of gravity of the support target portion is applied to the offset bridge portion during the rotation of the rotor. The sectional shape perpendicular to the axial direction at a portion of the rotor core that structures a magnetic pole is a symmetric shape or a shape analogous to the symmetric shape over an axis of symmetry defined along the magnetic pole center line. Therefore, the center of gravity of the support target portion is generally located on an outer side in the radial direction and on a magnetic pole center side in the circumferential direction with respect to the offset bridge portion. In this regard, according to the first characteristic structure described above, the extending direction of the offset bridge portion in the cross section perpendicular to the axial direction is the direction approaching the magnetic pole center line toward the outer side in the radial direction. Thus, the extending direction of the offset bridge portion is made closer to the direction in which the tensile stress is applied, and bending stress generated in the offset bridge portion during the rotation of the rotor can be reduced as compared with the case where the extending direction is set as the direction parallel to the magnetic pole center line. Along with the reduction in the bending stress generated in the offset bridge portion, the stress concentration on the offset bridge portion during the rotation of the rotor can be mitigated. As a result, the width of the offset bridge portion can be reduced while securing the strength of the rotor core against the centrifugal force.As described above, according to the first characteristic structure, it is possible to obtain the rotor for a rotating electric machine in which the width of the offset bridge portion can be reduced while appropriately securing the strength of the rotor core against the centrifugal force.According to the first characteristic structure, the permanent magnet having the planar magnetic pole surface can be used as the permanent magnet disposed in each of the first hole and the second hole. Thus, there is an advantage in that a necessary remanent flux density is easily ensured while reducing costs as compared with a case of using a permanent magnet having a curved magnetic pole surface. Further, the first hole and the second hole are arranged such that the separation distance therebetween increases in the circumferential direction toward the outer side in the radial direction. Thus, there is an advantage in that reluctance torque can be used.In view of the above, a second characteristic structure of the rotor for a rotating electric machine is set forth in claim 2.According to the second characteristic structure, the extending direction of the offset bridge portion is set in the cross section perpendicular to the axial direction along the direction toward the center of gravity of the target portion surrounded by the surrounding hole group. Therefore, the stress concentration on the offset bridge portion during the rotation of the rotor can be mitigated as compared to the case where the extending direction is set as the direction parallel to the magnetic pole center line. As a result, the width of the offset bridge portion can be reduced while the strength of the rotor core against the centrifugal force is suitably secured.To provide a supplementary description, during rotation of the rotor, the offset bridge portion, against the centrifugal force, supports the target portion surrounded by the surrounding hole group. When a consideration is made using a simplified model, the centrifugal force is applied to the center of gravity of an object. Therefore, a tensile load toward the center of gravity of the target portion is applied to the offset bridge portion during the rotation of the rotor. In this regard, according to the second characteristic structure described above, the extending direction of the offset bridge portion is set in the cross section perpendicular to the axial direction along the direction toward the center of gravity of the target portion. Thus, the extending direction of the offset bridge portion coincides with the direction in which the tensile stress is applied, and the bending stress generated in the offset bridge portion during the rotation of the rotor can be reduced. Along with the reduction in the bending stress generated in the offset bridge portion, the stress concentration on the offset bridge portion during the rotation of the rotor can be mitigated. As a result, the width of the offset bridge portion can be reduced while securing the strength of the rotor core against the centrifugal force.As described above, according to the second characteristic structure, it is possible to obtain the rotor for a rotating electric machine in which the width of the offset bridge portion can be reduced while appropriately securing the strength of the rotor core against the centrifugal force.According to the second characteristic structure, the plurality of holes are arranged to form the surrounding hole group surrounding the magnetic pole center. Thus, there is an advantage in that the reluctance torque can be used.In view of the above, a third characteristic structure of the rotor for a rotating electric machine is set forth in claim 5.According to the third characteristic structure, in the cross section perpendicular to the axial direction, the offset bridge portion is formed to extend toward the center of gravity on the magnetic pole center line corresponding to the magnetic pole where the offset bridge portion is formed. Therefore, the stress concentration on the offset bridge portion during the rotation of the rotor (rotor for a rotating electric machine) can be mitigated as compared to a case where the offset bridge portion is not formed to extend toward the center of gravity. As a result, the width of the offset bridge portion can be reduced while the strength of the rotor core against the centrifugal force is suitably secured.To give a supplementary description, during the rotation of the rotor, the offset bridge portion supports, against the centrifugal force, the radially outer portion of the rotor core in the magnetic pole where the offset bridge portion is provided. When a consideration is made using a simplified model, the centrifugal force is applied to the center of gravity of an object. Therefore, a tensile load toward the center of gravity on the magnetic pole center line corresponding to each magnetic pole is applied to the offset bridge portion during the rotation of the rotor. In this regard, according to the third characteristic structure described above, in the cross section perpendicular to the axial direction, the offset bridge portion is formed to extend toward the center of gravity on the magnetic pole center line corresponding to each magnetic pole. Thus, the direction of the offset bridge portion coincides with the direction in which the tensile stress is applied, and the bending stress generated in the offset bridge portion during the rotation of the rotor can be reduced. Along with the reduction in the bending stress generated in the offset bridge portion, the stress concentration on the offset bridge portion during the rotation of the rotor can be mitigated. As a result, the width of the offset bridge portion can be reduced while securing the strength of the rotor core against the centrifugal force.As described above, according to the third characteristic structure, it is possible to obtain the rotor for a rotating electric machine in which the width of the offset bridge portion can be reduced while appropriately securing the strength of the rotor core against the centrifugal force.According to the third characteristic structure, the permanent magnet having the planar magnetic pole surface can be used as the permanent magnet disposed in each of the first hole and the second hole. Thus, there is an advantage in that a necessary remanent flux density is easily ensured while reducing costs as compared with the case of using the permanent magnet having the curved magnetic pole surface. Further, the first hole and the second hole are arranged such that the separation distance therebetween increases in the circumferential direction toward the outer side in the radial direction. Thus, there is an advantage in that the reluctance torque can be used.Other features and advantages of the rotor for a rotating electric machine will become apparent from the following description of embodiments with reference to the drawings.BRIEF DESCRIPTION OF THE DRAWINGS[FIG. 1 ] FIG. 1 is a view illustrating a rotating electric machine according to an embodiment.[FIG. 2 ] FIG. 2 is a sectional view perpendicular to an axial direction illustrating a part of a rotor according to the embodiment.[FIG. 3] FIG. 3 is an analytical chart illustrating a voltage distribution according to the embodiment.[FIG. 4] FIG. 4 is a sectional view perpendicular to the axial direction illustrating a part of a rotor according to a comparative example.[FIG. 5 ] FIG. 5 is an analytical chart illustrating a stress distribution according to the comparative example.[FIG. 6 ] FIG. 6 is a sectional view perpendicular to the axial direction illustrating a part of the rotor according to the embodiment.[FIG. 7 ] FIG. 7 is a sectional view perpendicular to the axial direction illustrating a part of the rotor according to the comparative example.MODES FOR CARRYING OUT THE INVENTIONAn embodiment of a rotor for a rotating electric machine will be described with reference to the drawings. In the following description, an "axial direction L", a "radial direction R", and a "circumferential direction C" are defined with respect to an axis A (see FIG. 1 ) of the rotor for a rotating electric machine (hereinafter referred to as "rotor 2"). The axis A is an imaginary axis, and the rotor 2 rotates about the axis A. As illustrated in FIG. 2, one side in the circumferential direction C is defined as a "first circumferential side C 1" and the other side in the circumferential direction C (side opposite to the first circumferential side C 1) is defined as a "second circumferential side C 2". Terms related to dimensions, arrangement directions, arrangement positions, and the like are used herein as concepts including a state having a difference caused by a deviation (deviation allowed in manufacturing).As illustrated in FIG. 1, the rotor 2 is a rotor for a rotating electric machine, and is used for a rotating electric machine 1 together with a stator 3. In an example illustrated in FIG. 1, the rotating electric machine 1 is accommodated in a housing 4, a stator core 10 that is a core of the stator 3 is fixed to the housing 4 (in this case, an inner surface of the housing 4), and the rotor 2 is supported so as to be rotatable relative to the housing 4. Specifically, the rotating electric machine 1 includes a rotor shaft 6 supported via bearings 5 so as to be rotatable relative to the housing 4, and a rotor core 15 that is a core of the rotor 2 is coupled to the rotor shaft 6 so as to rotate together with the rotor shaft 6.The rotor core 15 is disposed so as to oppose the stator core 10 in the radial direction R. Specifically, the rotor 2 is a rotor for an inner rotor type rotary electric machine, and the rotor core 15 is disposed on an inner side in the radial direction R with respect to the stator core 10 at a position where the rotor core 15 overlaps the stator core 10 as viewed in the radial direction R. The rotating electric machine 1 is a rotating field type rotating electric machine, and coils 13 are wound around the stator core 10. The rotor 2, which serves as a field system, rotates by a magnetic field generated from the stator 3. The "rotating electric machine" is used herein as a concept including any of a motor (electric motor), a generator (electric generator), and a motor / generator that functions as both the motor and the generator as needed.As illustrated in FIG. 2, the rotor 2 includes the rotor core 15 and permanent magnets 60 arranged (embedded) in the rotor core 15. That is, the rotor 2 is a rotor to be used for a rotating electric machine having an embedding magnetic structure (for example, a synchronous electric motor). For example, the rotor core 15 is formed by stacking a plurality of annular plate-shaped magnetic plates (for example, electromagnetic steel plates) in the axial direction L, or is formed by having a green compact obtained by press-forming magnetic powder, which is a powder of a magnetic material, as a main component. In each magnetic pole P, the rotor core 15 has a plurality of holes 20 extending in the axial direction L. Each hole 20 is formed to pass through the rotor core 15 in the axial direction L. In this embodiment, each hole 20 is formed to extend parallel to the axial direction L. In this embodiment, each hole 20 is formed such that its sectional shape perpendicular to the axial direction L is uniform (identical) along the axial direction L. In the rotor core 15, a plurality of magnetic poles P are formed along the circumferential direction C. Magnetic poles P adjacent to each other in the circumferential direction C have opposite polarities. FIG. 2 illustrates a region in the rotor core 15 where a magnetic pole P is formed.The plurality of holes 20 provided in one magnetic pole P include first holes 21 disposed on the first circumferential side C 1 with respect to a magnetic pole center line 90 and second holes 22 disposed on the second circumferential side C 2 with respect to the magnetic pole center line 90. The magnetic pole center line 90 is a line that extends in the radial direction R through the center of the magnetic pole P in the circumferential direction C. Specifically, the magnetic pole center line 90 is a straight line (imaginary line) extending through the center of the magnetic pole P in the circumferential direction C in a cross section of the rotor core 15 that is perpendicular to the axial direction L parallel to the radial direction R. In this embodiment, the plurality of holes 20 provided in one magnetic pole P further include third holes 23 arranged in a region in the circumferential direction C including the magnetic pole center line 90 (specifically, third holes 23 whose center positions in the circumferential direction C coincide with the center of the magnetic pole P in the circumferential direction C).In each of the plurality of magnetic poles P, the rotor core 15 has the plurality of holes 20 including magnet insertion holes where the permanent magnets 60 are arranged. In this embodiment, all of the first holes 21, the second holes 22, and the third holes 23 are the magnet insertion holes. In this embodiment, a permanent magnet having a flat plate shape is used as the permanent magnet 60. That is, the permanent magnet 60 is formed such that its sectional shape perpendicular to the axial direction L is uniform along the axial direction L. The sectional shape is rectangular. The permanent magnet 60 has magnetic pole surfaces F each having a flat plate shape (see FIG. 3 ). The magnetic pole surface F is an outer surface perpendicular to a magnetization direction (polarization direction), and is a surface where a magnetic flux of the permanent magnet 60 runs in and out. In this embodiment, the magnetic pole surfaces F are two surfaces defining the long sides of the rectangle among the outer circumferential surfaces of the permanent magnet 60 (four surfaces defining the outer edges of the cross section perpendicular to the axial direction L). In this embodiment, the plurality of holes 20 provided in each magnetic pole P include the first holes 21 and the second holes 22 in each of which the permanent magnet 60 having the planar magnetic pole surfaces F is disposed.In the cross section perpendicular to the axial direction L, a part or the whole of the region in the magnet insertion hole is a magnet arrangement region where the permanent magnet 60 is disposed. In this embodiment, only a part of the region in the magnet insertion hole in the cross section perpendicular to the axial direction L is the magnet arrangement region. Magneto-resistance portions 20 athat function as magneto-resistances (flux barriers) for the magnetic flux flowing through the rotor core 15 are formed at portions of the magnet insertion hole on both sides in a direction along the magnetic pole surface F with respect to the magnet arrangement region. The magneto-resistance portion 20 ais a cavity (air space) or is filled with a filler (for example, a resin) having a lower magnetic permeability than that of the rotor core 15 (for example, magnetic sheets such as electromagnetic steel sheets).As illustrated in FIG. 2, the plurality of holes 20 in each of the plurality of magnetic poles P are arranged to form a first surrounding hole group 31 surrounding a magnetic pole center 91 that is an intersection of the magnetic pole center line 90 and an outer circumferential surface 15 aof the rotor core 15. That is, the rotor core 15 has a plurality of holes 20 forming the first surrounding hole group 31 in each of the plurality of magnetic poles P. The plurality of holes 20 forming the first surrounding hole group 31 includes the first hole 21 and the second hole 22, and further includes the third hole 23 in this embodiment. Specifically, the first surrounding hole group 31 is formed by a first hole 21, a second hole 22, and a third hole 23. In this embodiment, the first surrounding hole group 31 corresponds to a "surrounding hole group".In this embodiment, the rotor core 15 has a plurality of holes 20 forming a second surrounding hole group 32 in each of the plurality of magnetic poles P in addition to the plurality of holes 20 forming the first surrounding hole group 31. In this embodiment, the rotor core 15 further includes a plurality of holes 20 forming a third surrounding hole group 33 in each of the plurality of magnetic poles P. The second surrounding hole group 32 is a hole group surrounding the magnetic pole center 91 on a side closer to the magnetic pole center 91 than the first surrounding hole group 31. A flux of a q-axis magnetic flux is formed between the first surrounding hole group 31 and the second surrounding hole group 32. The third surrounding hole group 33 is a hole group surrounding the magnetic pole center 91 on a side closer to the magnetic pole center 91 than the second surrounding hole group 32. A flux of q-axis magnetic flux is formed between the second surrounding hole group 32 and the third surrounding hole group 33. The plurality of holes 20 forming the second surrounding hole group 32 includes the first hole 21 and the second hole 22, and further includes the third hole 23 in this embodiment. Specifically, the second surrounding hole group 32 is formed by a first hole 21, a second hole 22, and a third hole 23. The plurality of holes 20 forming the third surrounding hole group 33 include the first hole 21 and the second hole 22, but does not include the third hole 23 in this embodiment. Specifically, the third surrounding hole group 33 is formed by a first hole 21 and a second hole 22.Focusing on a pair of the first hole 21 and the second hole 22, as illustrated in FIG. 2, the first hole 21 and the second hole 22 are separately disposed on both sides in the circumferential direction C with respect to the magnetic pole center line 90, so that a separation distance between the first hole 21 and the second hole 22 increases in the circumferential direction C toward an outer side in the radial direction R. The "pair of the first hole 21 and the second hole 22" denotes the first hole 21 and the second hole 22 belonging to the same surrounding hole group (in this embodiment, the first surrounding hole group 31, the second surrounding hole group 32, or the third surrounding hole group 33). In a case where the plurality of holes 20 forming a surrounding hole group includes a plurality of first holes 21 and a plurality of second holes 22, the "pair of the first hole 21 and the second hole 22" denotes a first hole 21 and a second hole 22 belonging to the same surrounding hole group and arranged at the same position in the radial direction R. As described above, the permanent magnet 60 in this embodiment is a permanent magnet having a flat plate shape, and therefore each of the first hole 21 and the second hole 22 is formed to linearly extend along the magnetic pole surface F having a flat plate shape in the permanent magnet 60 in the cross section perpendicular to the axial direction L. In this embodiment, the sectional shape perpendicular to the axial direction L at a portion of the rotor core 15 structuring a magnetic pole P is a symmetrical shape about an axis of symmetry defined along the magnetic pole center line 90. That is, the pair of the first hole 21 and the second hole 22 has a symmetrical shape over the symmetry axis defined along the magnetic pole center line 90 in the cross section perpendicular to the axial direction L. In this embodiment, the pair of the first hole 21 and the second hole 22 are arranged in a V shape such that the distance therebetween increases toward the outer side in the radial direction R in the cross section perpendicular to the axial direction L.The rotor core 15 has a plurality of first bridge portions 41 each formed between two holes 20 adjacent to each other in the circumferential direction C. The first bridge portion 41 is formed between the plurality of holes 20 forming the first surrounding hole group 31. That is, the rotor core 15 has a plurality of first bridge portions 41 each formed between the plurality of holes 20 forming the first surrounding hole group 31. As illustrated in FIG. 2, in this embodiment, the first bridge portions 41 are formed between the first hole 21 and the third hole 23 that are adjacent to each other in the circumferential direction C (in other words, adjacent to each other in an arrangement direction of the plurality of holes 20 that form the first surrounding hole group 31; the same applies hereinafter), and between the second hole 22 and the third hole 23 that are adjacent to each other in the circumferential direction C. In this embodiment, the magneto-resistance portions 20 aof two holes 20 forming the first surrounding hole group 31 are arranged adjacent to each other in the circumferential direction C, and the first bridge portion 41 is formed between the two magneto-resistance portions 20 aadjacent to each other in the circumferential direction C. An outer circumferential bridge portion is formed between the outer circumferential surface 15 aof the rotor core 15 and each of two holes 20 (in this embodiment, the first hole 21 and the second hole 22) disposed at both ends (both ends in the arrangement direction) out of the plurality of holes 20 forming the first surrounding hole group 31. In this embodiment, the first bridge portion 41 corresponds to a "bridge portion".In this embodiment, the rotor core 15 includes a plurality of second bridge portions 42 each formed between the plurality of holes 20 forming second surrounding hole group 32. In this embodiment, the second bridge portions 42 are formed between the first hole 21 and the third hole 23 adjacent to each other in the circumferential direction C (in other words, adjacent to each other in an arrangement direction of the plurality of holes 20 forming the second surrounding hole group 32; the same applies hereinafter), and between the second hole 22 and the third hole 23 adjacent to each other in the circumferential direction C. In this embodiment, the magneto-resistance portions 20 aof two holes 20 forming the second surrounding hole group 32 are arranged adjacent to each other in the circumferential direction C, and the second bridge portion 42 is formed between the two magneto-resistance portions 20 aadjacent to each other in the circumferential direction C. An outer circumferential bridge portion is formed between the outer circumferential surface 15 aof the rotor core 15 and each of two holes 20 (in this embodiment, the first hole 21 and the second hole 22) disposed at both ends (both ends in the arrangement direction) out of the plurality of holes 20 forming the second surrounding hole group 32.In this embodiment, the rotor core 15 has a third bridge portion 43 formed between the plurality of holes 20 forming the third surrounding hole group 33. In this embodiment, the rotor core 15 has only a third bridge portion 43. The one third bridge portion 43 is formed between the first hole 21 and the second hole 22 adjacent to each other in the circumferential direction C (in other words, adjacent to each other in an arrangement direction of the plurality of holes 20 forming the third surrounding hole group 33; the same applies hereinafter). In this embodiment, the magneto-resistance portions 20 aof two holes 20 forming the third surrounding hole group 33 are arranged adjacent to each other in the circumferential direction C, and the third bridge portion 43 is formed between the two magneto-resistance portions 20 aadjacent to each other in the circumferential direction C. An outer circumferential bridge portion is formed between the outer circumferential surface 15 aof the rotor core 15 and each of two holes 20 (in this embodiment, the first hole 21 and the second hole 22) disposed at both ends (both ends in the arrangement direction) out of the plurality of holes 20 forming the third surrounding hole group 33.As illustrated in FIG. 1, the plurality of first bridge portions 41 include first offset bridge portions 51 located at positions displaced in the circumferential direction C from the magnetic pole center line 90. Specifically, the first bridge portion 41 formed between the first hole 21 and the third hole 23 is a first offset bridge portion 51 located at a position shifted to the first circumferential side C 1 from the magnetic pole center line 90, and the first bridge portion 41 formed between the second hole 22 and the third hole 23 is a first offset bridge portion 51 located at a position shifted to the second circumferential side C 2 from the magnetic pole center line 90. In this embodiment, the first offset bridge portion 51 corresponds to a "offset bridge portion".In this embodiment, the plurality of second bridge portions 42 include second offset bridge portions 52 located at positions displaced in the circumferential direction C from the magnetic pole center line 90. Specifically, the second bridge portion 42 formed between the first hole 21 and the third hole 23 is a second offset bridge portion 52 located at a position shifted to the first circumferential side C 1 from the magnetic pole center line 90, and the second bridge portion 42 formed between the second hole 22 and the third hole 23 is a second offset bridge portion 52 located at a position shifted to the second circumferential side C 2 from the magnetic pole center line 90.An output torque of the rotating electric machine 1 generally decreases as the amount of magnetic flux passing through each bridge portion (in this embodiment, each of the first bridge portion 41, the second bridge portion 42, and the third bridge portion 43) (amount of leakage flux) increases. Therefore, it is desirable to minimize the width of each bridge portion within a range in which the strength of the rotor core 15 against a centrifugal force can be suitably secured. The width of the bridge portion is a width in a direction perpendicular to an extending direction of the bridge portion in the cross section perpendicular to the axial direction L (substantially a width in the circumferential direction C or a width in a direction perpendicular to the magnetic pole center line 90). In this regard, the rotor 2 disclosed herein has a structure described below, whereby the width of the offset bridge portion (in this embodiment, each of the first offset bridge portion 51 and the second offset bridge portion 52) can be reduced while the strength of the rotor core 15 against the centrifugal force is suitably secured.As illustrated in FIG. 2, a portion of the rotor core 15 surrounded by the first surrounding hole group 31 is defined as a first target portion 81. An outer edge of the first target portion 81 on an outer side in the radial direction R is formed along the outer circumferential surface 15 aof the rotor core 15, but is illustrated on an outer side in the radial direction R with respect to the outer circumferential surface 15 ain FIG. 2 for ease of understanding. The outer edges of the first target portion 81 on both sides in the circumferential direction C and the outer edge of the first target portion 81 on an inner side in the radial direction R are formed along the arrangement regions of the plurality of holes 20 forming the first surrounding hole group 31. That is, the outer edge of the first target portion 81 on the first circumferential side C 1 is formed along the arrangement range of the first hole 21 belonging to the first surrounding hole group 31 so as to extend in an extending direction of the first hole 21 (in this case, the radial direction R). The outer edge of the first target portion 81 on the inner side in the radial direction R is formed along the arrangement area of the third hole 23 belonging to the first surrounding hole group 31 so as to extend in an extending direction of the third hole 23 (in this case, the direction perpendicular to the magnetic pole center line 90). The outer edge of the first target portion 81 on the second circumferential side C 2 is formed along the arrangement range of the second hole 22 belonging to the first surrounding hole group 31 so as to extend in an extending direction of the second hole 22 (in this case, the radial direction R). FIG. 2 illustrates an exemplary case in which the first target portion 81 is set to include the plurality of holes 20 forming the first surrounding hole group 31, but the first target portion 81 may be set not to include the plurality of holes 20 forming the first surrounding hole group 31. In this embodiment, the first target portion 81 corresponds to a "target portion".During rotation of the rotor 2, the first offset bridge portions 51 support the first target portion 81 described above against the centrifugal force. When a consideration is made using a simplified model, the centrifugal force is applied to a first center of gravity G 1 that is the center of gravity of the first target portion 81. Therefore, a tensile load toward the first center of gravity G 1 is applied to the first offset bridge portions 51 during the rotation of the rotor 2. The first center of gravity G 1 is a center of gravity of the mass (center of mass) of the first target portion 81, and is a center of gravity in a state where the permanent magnets 60 are disposed in the holes 20 used as the magnet insertion holes. In view of the fact that the tensile load toward the first center of gravity G 1 is applied to the first offset bridge portions 51 as described above, as illustrated in FIG. 2, a first extending direction D 1 that is an extending direction of the first offset bridge portion 51 in the cross section perpendicular to the axial direction L is set as a direction inclined with respect to the magnetic pole center line 90 so as to approach the magnetic pole center line 90 toward the outer side in the radial direction R (from the first offset bridge portion 51). As illustrated in FIG. 2, the first center of gravity G 1 is located on an outer side in the radial direction R and on a magnetic pole center side in the circumferential direction C with respect to the first offset bridge portion 51. By setting the first extending direction D 1 as the direction described above, the first extending direction D 1 is made closer to the direction in which the tensile load is applied, and a bending stress generated in the first offset bridge portion 51 during the rotation of the rotor 2 can be reduced as compared with a case that the first extending direction D 1 is set as a direction parallel to the magnetic pole center line 90. In FIG. 2, the first extending direction D 1 is illustrated only for one first offset bridge portion 51 out of the pair of first offset bridge portions 51 that are separately disposed on both sides in the circumferential direction C with respect to the magnetic pole center line 90. The first extending directions D 1 of the pair of first offset bridge portions 51 are symmetrical directions about an axis of symmetry defined along the magnetic pole center line 90.In order to further reduce the bending stress generated in the first offset bridge portion 51 during the rotation of the rotor 2, this embodiment provides a structure in which the first extension direction D 1 is set along a direction toward the first center of gravity G 1 (from the first offset bridge portion 51), as illustrated in FIG. 2. By setting the first extending direction D 1 in this manner, the first extending direction D 1 coincides with the direction in which the tensile load is applied, and the bending stress generated in the first offset bridge portion 51 during the rotation of the rotor 2 can be further reduced. Along with the reduction in the bending stress generated in the first offset bridge portion 51, stress concentration on the first offset bridge portion 51 during the rotation of the rotor 2 can be mitigated. As a result, the width of the first offset bridge portion 51 can be reduced while securing the strength of the rotor core 15 against the centrifugal force. The "direction toward the first center of gravity G 1" is a concept including not only a case that the first center of gravity G 1 is located accurately on an extension line of the direction but also a case that the first center of gravity G 1 deviates from the extension line within a range in which the direction is regarded as the direction toward the first center of gravity G 1. The same applies to a "direction to a second center of gravity G 2" described later. In other words, the first center of gravity G 1 and the second center of gravity G 2 may be considered as areas that extend to some extent.This embodiment further has a structure in which a second extending direction D 2 that is an extending direction of the second offset bridge portion 52 in the cross section perpendicular to the axial direction L is set along a direction toward the second center of gravity G 2 that is the center of gravity of a second target portion 82 (from the second offset bridge portion 52). As illustrated in FIG. 2, the second target portion 82 is a portion of the rotor core 15 surrounded by the second surrounding hole group 32. The second target portion 82 is set similarly to the first target portion 81 except that the first surrounding hole group 31 is replaced with the second surrounding hole group 32, and therefore detailed description will be omitted. During the rotation of the rotor 2, the second offset bridge portions 52 support the second target portion 82 against the centrifugal force. When a consideration is made using a simplified model, a tensile load toward the second center of gravity G 2 is applied to the second offset bridge portions 52 during the rotation of the rotor 2. In this regard, the second extending direction D 2 coincides with the direction in which the tensile stress is applied, and bending stress generated in the second offset bridge portion 52 during the rotation of the rotor 2 can be reduced in this embodiment because the second extending direction D 2 is set along the direction toward the second center of gravity G 2 (from the second offset bridge portion 52) as described above. Along with the reduction in the bending stress generated in the second offset bridge portion 52, stress concentration on the second offset bridge portion 52 during the rotation of the rotor 2 can be mitigated. As a result, the width of the second offset bridge portion 52 can be reduced while securing the strength of the rotor core 15 against the centrifugal force. In FIG. 2, the second extending direction D 2 is illustrated only for one second offset bridge portion 52 out of the pair of second offset bridge portions 52 separately disposed on both sides in the circumferential direction with respect to the magnetic pole center line 90. The second extending directions D 2 of the pair of second offset bridge portions 52 are symmetrical directions about an axis of symmetry defined along the magnetic pole center line 90.FIG. 3 is an analytical graph illustrating a voltage distribution at the first offset bridge portion 51 during the rotation of the rotor 2. In FIG. 3, the stress distribution is represented by contour lines of level. That is, each broken line is a contour level line connecting points where the amounts of stress are equal. A contour line represented by "H1" is a first contour line H1 indicating that the stress is the highest. A level contour line represented by "H2" is a second level contour line H2 indicating that the stress is the second highest. In FIG. 3, regions where the stress is the greatest (regions surrounded by the first contour lines H 1) are hatched for facilitating understanding of the stress distribution. FIG. 5 is an analytical graph illustrating a voltage distribution at a first offset bridge portion 51 during rotation of the rotor 2 according to a comparative example illustrated in FIG. 4. The comparative example illustrated in FIGS. 4 and 5 is not an example of the rotor for a rotating electric machine disclosed herein, but the same reference symbols as those in FIGS. 2 and 3 are assigned for simplifying comparison. As illustrated in FIG. 4, in the comparative example, both the first extending direction D 1 that is the extending direction of the first offset bridge portion 51 in the cross section perpendicular to the axial direction L and the second extending direction D 2 that is the extending direction of the second offset bridge portion 52 in the cross section perpendicular to the axial direction L are parallel to the magnetic pole center line 90. As is apparent from the comparison of FIG. 3 with FIG. 5 regarding the profiles of the first level contour line H 1 and the second level contour line H 2, the stress concentration on the first offset bridge portion 51 in the rotor 2 according to this embodiment (FIG. 3 ) is mitigated as compared to the rotor 2 according to the comparative example (FIG. 5 ).As described above, this embodiment provides the structure in which the first extending direction D 1, which is the extending direction of the first offset bridge portion 51 in the cross section perpendicular to the axial direction L, is set along the direction toward the first center of gravity G 1 of the first offset bridge portion 51 (see FIG. 2 ). That is, in the cross section perpendicular to the axial direction L, the first offset bridge portion 51 is formed to extend toward the center of gravity on the magnetic pole center line 90 corresponding to the magnetic pole P where the first offset bridge portion 51 is formed. The "center of gravity corresponding to the magnetic pole P where the first offset bridge portion 51 is formed" is the center of gravity of a support target portion that is a portion of the rotor core 15 that structures the magnetic pole P and is supported (can be regarded as being supported) by the first offset bridge portion 51. In this embodiment, the support target portion of the first offset bridge portion 51 is the first target portion 81, and therefore, the first center of gravity G 1 that is the center of gravity of the first target portion 81 is the center of gravity corresponding to the magnetic pole P where the first offset bridge portion 51 is formed. That is, in the cross section perpendicular to the axial direction L, the first offset bridge portion 51 is formed to extend toward the first center of gravity G 1 on the magnetic pole center line 90.This embodiment further provides the structure in which the second extending direction D 2, which is the extending direction of the second offset bridge portion 52 in the cross section perpendicular to the axial direction L, is set along the direction toward the second center of gravity G 2 from the second offset bridge portion 52 (see FIG. 2 ). That is, in the cross section perpendicular to the axial direction L, the second offset bridge portion 52 is formed to extend toward the center of gravity on the magnetic pole center line 90 corresponding to the magnetic pole P where the second offset bridge portion 52 is formed. The "center of gravity corresponding to the magnetic pole P where the second offset bridge portion 52 is formed" is the center of gravity of a support target portion that is a portion of the rotor core 15 that structures the magnetic pole P and is supported (can be regarded as being supported) by the second offset bridge portion 52. In this embodiment, the support target portion of the second offset bridge portion 52 is the second target portion 82, and therefore, the second center of gravity G 2 that is the center of gravity of the second target portion 82 is the center of gravity corresponding to the magnetic pole P where the second offset bridge portion 52 is formed. That is, in the cross section perpendicular to the axial direction L, the second offset bridge portion 52 is formed to extend toward the second center of gravity G 2 on the magnetic pole center line 90.In this embodiment, each of the first offset bridge portion 51 and the second offset bridge portion 52 is formed in a certain region 70 where the distance between two holes 20 is shortest in the cross section perpendicular to the axial direction L. For example, the distance between two holes 20 may be a distance in the circumferential direction C or a distance in a magnetic pole perpendicular direction B described later. As illustrated in FIG. 6, the first offset bridge portion 51 is formed in a certain region 70 where the distance between the first hole 21 and the third hole 23 belonging to the first surrounding hole group 31 is the shortest. In FIG. 6, only the specific area formed between the first hole 21 and the third hole 23 belonging to the first surrounding hole group 31 is represented by the reference symbol "70", but the specific area 70 exists between two holes 20 in each combination of two holes 20 adjacent to each other in the circumferential direction C. For example, the second offset bridge portion 52 is formed in a certain area 70 where the distance between the first hole 21 and the third hole 23 belonging to the second surrounding hole group 32 is the shortest.In this embodiment, the first offset bridge portion 51 so as to extend in the cross section perpendicular to the axial direction L toward the first center of gravity G 1 on the magnetic pole center line 90 is formed with a structure in which the first offset bridge portion 51 is formed in the cross section perpendicular to the axial direction L in a region located between a third straight line T 3 and a fourth straight line T 4, and the first offset bridge portion 51 is inserted between the two holes 20 on both sides in the circumferential direction C, which two holes 20 are located completely outside the region located between the third straight line T 3 and the fourth straight line T 4. The second offset bridge portion 52 is formed to extend in the cross section perpendicular to the axial direction L toward the second center of gravity G 2 on the magnetic pole center line 90, with a structure in which the second offset bridge portion 52 is formed in the cross section perpendicular to the axial direction L in a region located between the third straight line T 3 and the fourth straight line T 4, and the second offset bridge portion 52 is inserted between the two holes 20 on both sides in the circumferential direction C, which two holes 20 are located completely outside the region located between the third straight line T 3 and the fourth straight line T 4. The third straight line T 3 is a straight line passing through the end of the specific region 70 on the first circumferential side C 1 and the center of gravity on the magnetic pole center line 90 in the cross section perpendicular to the axial direction L. The fourth straight line T 4 is a straight line passing through the end of the specific region 70 on the second circumferential side C 2 and the center of gravity on the magnetic pole center line 90 in the cross section perpendicular to the axial direction L. The center of gravity on the magnetic pole center line 90 is the first center of gravity G 1 for the first offset bridge portion 51 and is the second center of gravity G 2 for the second offset bridge portion 52.A detailed description will be given of the first offset bridge portion 51 formed between the first hole 21 and the third hole 23 belonging to the first surrounding hole group 31. As illustrated in FIG. 6, the third straight line T 3 is a straight line passing through the end of the specific area 70 on the first circumferential side C 1 and the first center of gravity G 1, and the fourth straight line T 4 is a straight line passing through the end of the specific area 70 on the second circumferential side C 2 and the first center of gravity G 1. The first offset bridge portion 51 is formed in the region located between the third straight line T 3 and the fourth straight line T 4. The first offset bridge portion 51 is inserted between the two holes 20 on both sides in the circumferential direction C, which two holes 20 are arranged completely (in this case, the whole of the first hole 21 and the whole of the third hole 23) outside the range located between the third straight line T 3 and the fourth straight line T 4. Thus, the first offset bridge portion 51 is formed to extend toward the first center of gravity G 1 on the magnetic pole center line 90 in the cross section perpendicular to the axial direction L. In the structure of the comparative example illustrated in FIG. 7 (structure similar to that in FIG. 4 ), the first offset bridge portion 51 is inserted between the two holes 20 on both sides in the circumferential direction C, in which a part of at least one of the two holes 20 (in FIG. 7, a part of the first hole 21 and a part of the third hole 23) is disposed within the range located between the third straight line T 3 and the fourth straight line T 4. In the structure of the comparative example, the first offset bridge portion 51 is not formed to extend toward the first center of gravity G 1 on the magnetic pole center line 90 in the cross section perpendicular to the axial direction L.A description will be given herein assuming an exemplary case that the third straight line T 3 and the fourth straight line T 4 are set such that the distance between the third straight line T 3 and the fourth straight line T 4 decreases toward the center of gravity on the magnetic pole center line 90 (in this case, the first center of gravity G 1 or the second center of gravity G 2). The third straight line T 3 and the fourth straight line T 4 may be set such that the distance between the third straight line T 3 and the fourth straight line T 4 is constant (i.e., the third straight line T 3 and the fourth straight line T 4 are parallel). That is, the third straight line T 3 passing through the end of the specific area 70 on the first circumferential side C 1 and the first center of gravity G 1 and the fourth straight line T 4 passing through the end of the specific area 70 on the second circumferential side C 2 and the first center of gravity G 1 may be set while the first center of gravity G 1 is regarded as an area expanding to some extent.Finally, a description will be given of a definition of the extending direction of the bridge portion in the cross section perpendicular to the axial direction L. The extending directions of the bridge portions may be similarly defined except for the difference in the combinations of the two holes 20 forming the bridge portions. Therefore, the first extending direction D 1, which is the extending direction of the first offset bridge portion 51 in the cross section perpendicular to the axial direction L, will be described herein with reference to FIG. 3. The two holes 20 forming the first offset bridge portion 51 are referred to herein simply as two holes 20.As illustrated in FIG. 3, portions forming the first offset bridge portion 51 at the outer edges of the two holes 20 (in this case, the first hole 21 and the third hole 23) are defined as bridge forming edges 20 b. A direction perpendicular to the magnetic pole center line 90 in the cross section perpendicular to the axial direction L is defined as the magnetic pole perpendicular direction B. For example, a region located between the outer edges of the two holes 20 on both sides in the magnetic pole perpendicular direction B (region between the two holes 20 in which a line parallel to the magnetic pole perpendicular direction B intersects the both outer edges of the two holes 20) is defined as a bridge formation region. Portions defining the bridge formation region at the outer edges of the two holes 20 may be defined as the bridge formation edges 20 b. From the viewpoint of relaxing stress concentration, it is preferable that the shape of the bridge formation edge 20 bin the cross section perpendicular to the axial direction L is a shape (arc shape) in which the curvature is constant and the center of curvature is located inside the hole 20, or a shape in which the curvature continuously changes and the center of curvature of each part is located inside the hole 20. In this embodiment, the shape of the bridge formation edge 20 bin the cross section perpendicular to the axial direction L is the latter shape. In this embodiment, the bridge formation edge 20 bis structured by a part of the outer edge of the magneto-resistance portion 20 a.As illustrated in FIG. 3, two common inner tangents to the bridge formation edge 20 bof one hole 20 and the bridge formation edge 20 bof the other hole 20 out of the two holes 20 are defined as a first straight line T 1 and a second straight line T 2 in the cross section perpendicular to the axial direction L. The common inner tangent is a tangent common to the two bridge forming edges 20 bvia which the two bridge forming edges 20 bare opposed to each other. In this embodiment, based on the first straight line T 1 and the second straight line T 2 defined as described above, the first extending direction D 1 is set as a direction along a line segment bisecting an angle between the first straight line T 1 and the second straight line T 2 and not intersecting the two holes 20.The first extending direction D 1 may be defined by a method other than the method described above. For example, the first extending direction D 1 may be set along a straight line defined based on center positions of the bridge formation region described above in the magnetic pole perpendicular direction B at a plurality of positions in a direction parallel to the magnetic pole center line 90 in the cross section perpendicular to the axial direction L (a straight line passing through a plurality of center positions or an approximate curve defined based on a plurality of center positions). In this case, the plurality of positions may include both ends of the bridge formation region in the direction parallel to the magnetic pole center line 90 and the center of the bridge formation region in the direction parallel to the magnetic pole center line 90. Further, the first extending direction D 1 may be set as a direction in which the distance between two parallel tangents to the two bridge forming edges 20 bis longest in the cross section perpendicular to the axial direction L (extending direction of the tangents).[Other Embodiments]Next, other embodiments of the rotor for a rotating electric machine will be described.(1) In the embodiment described above, description will be given assuming the exemplary structure in which the second extension direction D 2 is set along the direction toward the second center of gravity G 2 (from the second offset bridge portion 52). However, the present invention is not limited to this structure. A structure in which the second extending direction D 2 is not set along the direction toward the second center of gravity G 2 may be employed. Also in this case, it is preferable that the second extending direction D 2 is set as a direction inclined with respect to the magnetic pole center line 90 so as to approach the magnetic pole center line 90 toward the outer side in the radial direction R (from the second offset bridge portion 52). In this case, a straight line obtained by extending the second extending direction D 2 from the second offset bridge portion 52 intersects the magnetic pole center line 90 at a position different from the second center of gravity G 2. For example, a structure in which the second extending direction D 2 is set along the direction toward the first center of gravity G 1 (from the second offset bridge portion 52) may be employed.(2) In the embodiment described above, description will be given assuming the exemplary structure in which the first extending direction D 1 is set along the direction toward the first center of gravity G 1 (from the first offset bridge portion 51). However, the present invention is not limited to this structure. A structure may be employed in which the first extending direction D 1 is set as a direction inclined with respect to the magnetic pole center line 90 so as to approach the magnetic pole center line 90 toward the outer side in the radial direction R (from the first offset bridge portion 51) but not along the direction toward the first center of gravity G 1. In this case, a straight line obtained by extending the first extending direction D 1 from the first offset bridge portion 51 intersects the magnetic pole center line 90 at a position different from the first center of gravity G 1. For example, a structure in which the first extending direction D 1 is set along the direction toward the second center of gravity G 2 (from the first offset bridge portion 51) may be employed.(3) In the embodiment described above, description will be given assuming the exemplary structure in which the rotor core 15 has the second surrounding hole group 32 and the third surrounding hole group 33 in addition to the first surrounding hole group 31. However, the present invention is not limited to this structure. For example, a structure in which the rotor core 15 includes only the first surrounding hole group 31 and the second surrounding hole group 32, a structure in which the rotor core 15 includes only the first surrounding hole group 31 and the third surrounding hole group 33, or a structure in which the rotor core 15 includes only the first surrounding hole group 31 may be employed. Further, a structure may be employed in which the rotor core 15 has, in addition to at least the first surrounding hole group 31, a fourth surrounding hole group surrounding the magnetic pole center 91 on a side farther from the magnetic pole center 91 than the first surrounding hole group 31.(4) In the embodiment described above, a description will be given assuming the exemplary structure in which the plurality of holes 20 forming the first surrounding hole group 31 includes a first hole 21 and a second hole 22, and the plurality of holes 20 forming the second surrounding hole group 32 includes a first hole 21 and a second hole 22. However, the present invention is not limited to this structure. A structure in which the plurality of holes 20 forming the first surrounding hole group 31 includes a plurality of first holes 21 and a plurality of second holes 22, or a structure in which the plurality of holes 20 forming the second surrounding hole group 32 includes a plurality of first holes 21 and a plurality of second holes 22 may be employed. In this case, the first offset bridge portion 51 or the second offset bridge portion 52 is formed between two first holes 21 adjacent to each other in the circumferential direction C or between two second holes 22 adjacent to each other in the circumferential direction C.(5) In the embodiment described above, description will be given assuming the exemplary structure in which the plurality of holes 20 forming the first surrounding hole group 31 includes the third hole 23, and the plurality of holes 20 forming the second surrounding hole group 32 includes the third hole 23. However, the present invention is not limited to this structure. A structure in which the plurality of holes 20 forming the first surrounding hole group 31 do not have the third hole 23 (for example, a structure in which only a plurality of first holes 21 and a plurality of second holes 22 are included), or a structure in which the plurality of holes 20 forming the second surrounding hole group 32 do not have the third hole 23 (for example, a structure in which only a plurality of first holes 21 and a plurality of second holes 22 are included) may be employed.(6) In the embodiment described above, description will be given assuming the exemplary structure in which all of the first holes 21, the second holes 22, and the third holes 23 are magnet insertion holes. However, the present invention is not limited to this structure. For example, a structure in which no permanent magnet 60 is disposed in the third hole 23 may be employed. For example, a structure in which the whole of the third hole 23 is a cavity (air space), or a structure in which the whole of the third hole 23 is filled with a non-magnetic filler (for example, a resin) may be employed.(7) In the embodiment described above, description will be given assuming the exemplary structure in which the plurality of holes 20 provided in each magnetic pole P include the first holes 21 and the second holes 22 in each of which the permanent magnet 60 having the planar magnetic pole surfaces F is disposed. However, the present invention is not limited to this structure. A structure may be employed in which a permanent magnet having curved magnetic pole surfaces is disposed in each of the first holes 21 and the second holes 22.(8) The structures disclosed in the embodiments described above are also applicable in combination with the structures disclosed in the other embodiments without producing contradiction (including combinations of the embodiments described as other embodiments). Also with respect to other structures, the embodiments disclosed herein are merely illustrative in all respects. Thus, various modifications may be made as appropriate without departing from the spirit of the disclosure.[Summary of Embodiments]A summary of the rotor for a rotating electric machine described above will be described below.The rotor (2) for a rotating electric machine includes the rotor core (15) and the permanent magnets (60) disposed in the rotor core (15). In each of the plurality of magnetic poles (P), the rotor core (15) has the plurality of holes (20) including the first hole (21) and the second hole (22) in each of which the permanent magnet (60) having the planar magnetic pole surface (F) is disposed. The first hole ( 21) and the second hole ( 22) are separately disposed on both sides in the circumferential direction (C) with respect to the magnetic pole center line ( 90) extending through the center of the magnetic pole (P) in the circumferential direction (C) in the radial direction (R) such that the separation distance between the first hole ( 21) and the second hole ( 22) increases toward the outer side in the radial direction (R) in the circumferential direction (C). The rotor core (15) has the plurality of bridge portions (41) each formed between two of the holes (20) adjacent to each other in the circumferential direction (C). The plurality of bridge portions ( 41) include the offset bridge portion ( 51) located at the position shifted in the circumferential direction (C) from the magnetic pole center line ( 90). The extending direction (D 1) of the offset bridge portion ( 51) in the cross section perpendicular to the axial direction (L) is inclined with respect to the magnetic pole center line ( 90) so as to approach the magnetic pole center line ( 90) toward the outer side in the radial direction (R).According to this structure, the extending direction (D 1) of the offset bridge portion ( 51) in the cross section perpendicular to the axial direction (L) is the direction inclined with respect to the magnetic pole center line ( 90) so as to approach the magnetic pole center line ( 90) toward the outer side in the radial direction (R). Therefore, the stress concentration on the offset bridge portion ( 51) during the rotation of the rotor ( 2) can be mitigated as compared to the case where the extending direction (D 1) is set as the direction parallel to the magnetic pole center line ( 90). As a result, the width of the offset bridge portion ( 51) can be reduced while the strength of the rotor core ( 15) against the centrifugal force is suitably secured.To give a supplementary description, during the rotation of the rotor ( 2), the offset bridge portion ( 51) supports, against the centrifugal force, the radially outer portion of the rotor core ( 15) in the magnetic pole (P) where the offset bridge portion ( 51) is provided (which will be referred to as a "support target portion" in this portion hereinafter). When a consideration is made using a simplified model, the centrifugal force is applied to the center of gravity of an object. Therefore, a tensile load toward the center of gravity of the support target portion is applied to the offset bridge portion ( 51) during the rotation of the rotor ( 2). The sectional shape perpendicular to the axial direction (L) at the portion of the rotor core ( 15) that structures a magnetic pole is a symmetric shape or a shape analogous to the symmetric shape over the symmetry axis defined along the magnetic pole center line ( 90). Therefore, the center of gravity of the support target portion is generally located on the outer side in the radial direction (R) and on the magnetic pole center side in the circumferential direction (C) with respect to the offset bridge portion ( 51). In this regard, according to the structure described above, the extending direction (D 1) of the offset bridge portion ( 51) in the cross section perpendicular to the axial direction (L) is the direction approaching the magnetic pole center line ( 90) toward the outer side in the radial direction (R). Thus, the extending direction (D 1) of the offset bridge portion ( 51) is made closer to the direction in which the tensile load is applied, and the bending stress generated in the offset bridge portion ( 51) during the rotation of the rotor ( 2) can be reduced as compared with the case where the extending direction (D 1) is set as the direction parallel to the magnetic pole center line ( 90). Along with the reduction in the bending stress generated in the offset bridge portion ( 51), the stress concentration on the offset bridge portion ( 51) during the rotation of the rotor ( 2) can be mitigated. As a result, the width of the offset bridge portion ( 51) can be reduced while securing the strength of the rotor core ( 15) against the centrifugal force.As described above, according to the structure described above, it is possible to obtain a rotor ( 2) for a rotating electric machine in which the width of the offset bridge portion ( 51) can be reduced while securing the strength of the rotor core ( 15) against the centrifugal force appropriately.According to the structure described above, the permanent magnet ( 60) having the planar magnetic pole surface (F) can be used as the permanent magnet ( 60) disposed in each of the first hole ( 21) and the second hole ( 22). Thus, there is an advantage in that a necessary remanent flux density is easily ensured while reducing costs as compared with the case of using the permanent magnet having the curved magnetic pole surface. Further, the first hole ( 21) and the second hole ( 22) are arranged such that the separation distance therebetween increases in the circumferential direction (C) toward the outer side in the radial direction (R). Thus, there is an advantage in that reluctance torque can be used.It is preferable that the plurality of holes (20) in each of the plurality of magnetic poles (P) is arranged to form the surrounding hole group (31) that surrounds the magnetic pole center point (91), which is the intersection of the magnetic pole center line (90) and the outer circumferential surface (15a) of the rotor core (15), and the extending direction (D1) of the offset bridge portion (51) is set in the cross section perpendicular to the axial direction (L) along the direction to the center of gravity (G1) of the target portion (81) surrounded by the surrounding hole group (31).According to this structure, the extending direction (D 1) of the offset bridge portion ( 51) can be caused to coincide with the direction of the tensile load applied to the offset bridge portion ( 51) during the rotation of the rotor ( 2). Thus, the bending stress generated in the offset bridge portion ( 51) during the rotation of the rotor ( 2) is further reduced, whereby the stress concentration on the offset bridge portion ( 51) during the rotation of the rotor ( 2) can be further mitigated.The rotor (2) for a rotating electric machine includes the rotor core (15) and the permanent magnets (60) disposed in the rotor core (15). In each of the plurality of magnetic poles (P), the rotor core (15) has the plurality of holes (20) including the magnet insertion holes (21, 22) where the permanent magnets (60) are arranged. The plurality of holes ( 20) in each of the plurality of magnetic poles (P) are arranged to form the surrounding hole group ( 31) surrounding the magnetic pole center point ( 91) that is the intersection of the outer circumferential surface ( 15 a) of the rotor core ( 15) and the magnetic pole center line ( 90) extending in the radial direction (R) through the center of the magnetic pole (P) in the circumferential direction (C). The rotor core (15) has the plurality of bridge portions (41) each formed between two of the holes (20) adjacent to each other in the circumferential direction (C). The plurality of bridge portions ( 41) include the offset bridge portion ( 51) located at the position shifted in the circumferential direction (C) from the magnetic pole center line ( 90). The extending direction (D 1) of the offset bridge portion ( 51) in the cross section perpendicular to the axial direction (L) is set along the direction to the center of gravity (G 1) of the target portion ( 81) surrounded by the surrounding hole group ( 31).According to this structure, the extending direction (D 1) of the offset bridge portion ( 51) is set in the cross section perpendicular to the axial direction (L) along the direction to the center of gravity (G 1) of the target portion ( 81) surrounded by the surrounding hole group ( 31). Therefore, the stress concentration on the offset bridge portion ( 51) during the rotation of the rotor ( 2) can be mitigated as compared to the case where the extending direction (D 1) is set as the direction parallel to the magnetic pole center line ( 90). As a result, the width of the offset bridge portion ( 51) can be reduced while the strength of the rotor core ( 15) against the centrifugal force is suitably secured.To give a supplementary description, during the rotation of the rotor (2), the offset bridge portion (51), against the centrifugal force, supports the target portion (81) surrounded by the surrounding hole group (31). When a consideration is made using a simplified model, the centrifugal force is applied to the center of gravity of an object. Therefore, a tensile load toward the center of gravity (G1) of the target portion (81) is applied to the offset bridge portion (51) during the rotation of the rotor (2). In this regard, according to the structure described above, the extending direction (D 1) of the offset bridge portion ( 51) is set in the cross section perpendicular to the axial direction (L) along the direction toward the center of gravity (G 1) of the target portion ( 81). Thus, the extending direction (D 1) of the offset bridge portion ( 51) coincides with the direction in which the tensile load is applied, and the bending stress generated in the offset bridge portion ( 51) during the rotation of the rotor ( 2) can be reduced. Along with the reduction in the bending stress generated in the offset bridge portion ( 51), the stress concentration on the offset bridge portion ( 51) during the rotation of the rotor ( 2) can be mitigated. As a result, the width of the offset bridge portion ( 51) can be reduced while securing the strength of the rotor core ( 15) against the centrifugal force.As described above, according to the structure described above, it is possible to obtain the rotor ( 2) for a rotating electric machine in which the width of the offset bridge portion ( 51) can be reduced while securing the strength of the rotor core ( 15) against the centrifugal force appropriately.According to the structure described above, the plurality of holes ( 20) are arranged to form the surrounding hole group ( 31) surrounding the magnetic pole center ( 91). Thus, there is an advantage in that the reluctance torque can be used.In the structure in which the extending direction (D 1) of the offset bridge portion (51) is set in the cross section perpendicular to the axial direction (L) along the direction toward the center of gravity (G 1) of the target portion (81) as described above, it is preferable that the rotor core (15) has, in each of the plurality of magnetic poles (P), the plurality of holes (20) that form the second surrounding hole group (32) that surrounds the magnetic pole center point (91) on the side closer to the magnetic pole center point (91) than the surrounding hole group (31) and also has the plurality of second bridge portions (42) that are each formed between the plurality of holes (20) that form the second surrounding hole group (32), the plurality of second bridge portions (42) includes the second offset bridge portion (52) located at the position shifted in the circumferential direction (C) from the magnetic pole center line (90), and the extending direction (D 2) of the second offset bridge portion (52) is set in the cross section perpendicular to the axial direction (L) along the direction to the center of gravity (G 2) of the second target portion (82) surrounded by the second surrounding hole group (32).According to this structure, the extending direction (D 2) of the second offset bridge portion ( 52) is set in the cross section perpendicular to the axial direction (L) along the direction to the center of gravity (G 2) of the second target portion ( 82) surrounded by the second surrounding hole group ( 32). Therefore, the stress concentration on the second offset bridge portion ( 52) during the rotation of the rotor ( 2) can be mitigated as compared to a case where the extending direction (D 2) is set as the direction parallel to the magnetic pole center line ( 90). As a result, the width of the second offset bridge portion ( 52) can be reduced, and the width of the first offset bridge portion ( 51) can be reduced, while the strength of the rotor core ( 15) against the centrifugal force is suitably secured.To give a supplementary description, during the rotation of the rotor (2), the second offset bridge portion (52) supports, against the centrifugal force, the second target portion (82) surrounded by the second surrounding hole group (32). When a consideration is made using a simplified model, the centrifugal force is applied to the center of gravity of an object. Therefore, a tensile load toward the center of gravity (G 2) of the second target portion ( 82) is applied to the second offset bridge portion ( 52) during the rotation of the rotor ( 2). In this regard, according to the structure described above, the extending direction (D 2) of the second offset bridge portion ( 52) is set in the cross section perpendicular to the axial direction (L) along the direction toward the center of gravity (G 2) of the second target portion ( 82). Thus, the extending direction (D 2) of the second offset bridge portion ( 52) coincides with the direction in which the tensile load is applied, and the bending stress generated in the second offset bridge portion ( 52) during the rotation of the rotor ( 2) can be reduced. Along with the reduction in the bending stress generated in the second offset bridge portion ( 52), the stress concentration on the second offset bridge portion ( 52) during the rotation of the rotor ( 2) can be mitigated. As a result, the width of the second offset bridge portion ( 52) can be reduced while securing the strength of the rotor core ( 15) against the centrifugal force.In the rotor (2) for a rotating electric machine in each of the structures described above, it is preferable that the portions forming the offset bridge portion (51) at the outer edges of the two holes (20) are defined as the bridge forming edges (20b), the two common inner tangents to one of the bridge forming edges (20b) and the other of the bridge forming edges (20b) of the two holes (20) in the cross section perpendicular to the axial direction (L) are defined as the first straight line (T1) and the second straight line (T2), and the extending direction (D1) of the offset bridge portion (51) in the cross section perpendicular to the axial direction (L) is defined as the direction along the line segment, bisecting the angle between the first straight line (T1) and the second straight line (T2) and not intersecting the two holes (20).According to this structure, the extending direction (D 1) of the offset bridge portion ( 51) can be set appropriately.The rotor (2) for a rotating electric machine includes the rotor core (15) and the permanent magnets (60) disposed in the rotor core (15). In each of the plurality of magnetic poles (P), the rotor core (15) has the plurality of holes (20) including the first hole (21) and the second hole (22) in each of which the permanent magnet (60) having the planar magnetic pole surface (F) is disposed. The first hole (21) and the second hole (22) are separately disposed on both sides in the circumferential direction (C) with respect to the magnetic pole center line (90) extending in the radial direction (R) through the center of the magnetic pole (P) in the circumferential direction (C), so that the separation distance between the first hole (21) and the second hole (22) increases in the circumferential direction (C) toward the outer side in the radial direction (R). The rotor core (15) has the plurality of bridge portions (41) each formed between two of the holes (20) adjacent to each other in the circumferential direction (C). The plurality of bridge portions ( 41) include the offset bridge portion ( 51) located at the position shifted in the circumferential direction (C) from the magnetic pole center line ( 90). In the cross section perpendicular to the axial direction (L), the offset bridge portion ( 51) is formed to extend toward the center of gravity (G 1) on the magnetic pole center line ( 90) corresponding to the magnetic pole (P) where the offset bridge portion ( 51) is formed.According to this structure, in the cross section perpendicular to the axial direction (L), the offset bridge portion ( 51) is formed to extend toward the center of gravity (G 1) on the magnetic pole center line ( 90) corresponding to the magnetic pole (P) where the offset bridge portion ( 51) is formed. Therefore, the stress concentration on the offset bridge portion ( 51) during the rotation of the rotor ( 2) can be mitigated as compared to the case where the offset bridge portion ( 51) is not formed to extend toward the center of gravity (G 1). As a result, the width of the offset bridge portion ( 51) can be reduced while the strength of the rotor core ( 15) against the centrifugal force is suitably secured.To give a supplementary description, during the rotation of the rotor ( 2), the offset bridge portion ( 51) supports, against the centrifugal force, the radially outer portion of the rotor core ( 15) in the magnetic pole (P) where the offset bridge portion ( 51) is provided. When a consideration is made using a simplified model, the centrifugal force is applied to the center of gravity of an object. Therefore, a tensile load toward the center of gravity (G1) on the magnetic pole center line (90) corresponding to each magnetic pole (P) is applied to the offset bridge portion (51) during the rotation of the rotor (2). In this regard, according to the structure described above, in the cross section perpendicular to the axial direction (L), the offset bridge portion ( 51) is formed to extend toward the center of gravity (G 1) on the magnetic pole center line ( 90) corresponding to each magnetic pole (P). Thus, the direction of the offset bridge portion ( 51) coincides with the direction in which the tensile load is applied, and the bending stress generated in the offset bridge portion ( 51) during the rotation of the rotor ( 2) can be reduced. Along with the reduction in the bending stress generated in the offset bridge portion ( 51), the stress concentration on the offset bridge portion ( 51) during the rotation of the rotor ( 2) can be mitigated. As a result, the width of the offset bridge portion ( 51) can be reduced while securing the strength of the rotor core ( 15) against the centrifugal force.As described above, according to the structure described above, it is possible to obtain the rotor ( 2) for a rotating electric machine in which the width of the offset bridge portion ( 51) can be reduced while securing the strength of the rotor core ( 15) against the centrifugal force appropriately.According to the structure described above, the permanent magnet ( 60) having the planar magnetic pole surface (F) can be used as the permanent magnet ( 60) disposed in each of the first hole ( 21) and the second hole ( 22). Thus, there is an advantage in that a necessary remanent flux density is easily ensured while reducing costs as compared with the case of using the permanent magnet having the curved magnetic pole surface. Further, the first hole ( 21) and the second hole ( 22) are arranged such that the separation distance therebetween increases in the circumferential direction (C) toward the outer side in the radial direction (R). Thus, there is an advantage in that the reluctance torque can be used.It is preferable that the offset bridge portion ( 51) is formed in the cross section perpendicular to the axial direction (L) in the specific region ( 70) where the distance between the two holes ( 20) is the shortest.According to this structure, the offset bridge portion ( 51) that can alleviate stress concentration during rotation of the rotor ( 2) as described above can be formed in the specific region ( 70) where strength is likely to decrease due to the short distance between the two holes ( 20). Thus, the stress concentration on the specific region ( 70) during the rotation of the rotor ( 2) can be mitigated. As a result, the strength necessary for the specific region ( 70) can be easily secured.In the structure in which the offset bridge portion (51) is formed in the specific region (70) as described above, it is preferable that, in the cross section perpendicular to the axial direction (L), the straight line passing through the end of the specific region (70) on one side (C 1) in the circumferential direction (C) and the center of gravity (G 1) is defined as the third straight line (T 3) and the straight line passing through the end of the specific region (70) on the other side (C 2) in the circumferential direction (C) and the center of gravity (G 1) is defined as the fourth straight line (T 4), and the offset bridge portion (51) is formed in the cross section perpendicular to the axial direction (L) in the region, The third straight line (T3) and the fourth straight line (T4) are located between the third straight line (T3) and the offset bridge portion (51) is inserted between the two holes (20) on both sides in the circumferential direction (C), the two holes (20) being located completely outside the range located between the third straight line (T3) and the fourth straight line (T4).According to this structure, the offset bridge portion ( 51) may be formed to extend toward the center of gravity (G 1) from the specific region ( 70) in the cross section perpendicular to the axial direction (L). Thus, the stress concentration on the specific region ( 70) during the rotation of the rotor ( 2) can be further mitigated.The rotor for a rotating electric machine disclosed herein is sufficient if at least one of the effects described above can be obtained.Description of the Reference Numerals2 Rotor (rotor for rotating electric machine) 15 Rotor core 15 a Außenumfangs surface 20 Hole 20 bBridge formation edge 21 First hole (magnet insertion hole) 22 Second hole (magnet insertion hole) 23 Third hole (magnet insertion hole) 31 First surrounding hole group (surrounding hole group) 32 Second surrounding hole group 41 First bridge portion (bridge portion) 42 Second bridge portion 51 First offset bridge portion (offset bridge portion) 52 Second offset bridge portion 60 Permanent magnet 70 Specific area 81 First target portion (target portion) 82 Second target portion 90 Magnetic pole center line 91 Magnetic pole center point C Circumferential direction D 1 First extending direction (extending direction) D 2 Second extending direction (extending direction) F Magnetic pole surface G 1 First center of gravity (center of target portion, center of gravity, the magnetic pole corresponds to) G 2 of second center of gravity (center of gravity of second target portion) L of axial direction P of magnetic pole R of radial direction T 1 of first straight line T 2 of second straight line T 3 of third straight line T 4 of fourth straight line

Claims

A rotor (2) for a rotating electric machine, comprising a rotor core (15) and a permanent magnet (60) disposed in the rotor core (15), wherein in each of a plurality of magnetic poles (P), the rotor core (15) has a plurality of holes (20) including a first hole (21) and a second hole (22), in each of which the permanent magnet (60) having a planar magnetic pole surface (F) is disposed, the first hole (21) and the second hole (22) are separately disposed on both sides in a circumferential direction (C) with respect to a magnetic pole center line (90) extending in a radial direction (R) through a center of the magnetic pole (P) in the circumferential direction (C), such that a separation distance between the first hole (21) and the second hole (22) increases in the circumferential direction (C) toward an outer side in the radial direction (R), the rotor core (15) has a plurality of bridge portions (41) each formed between two of the holes (20) adjacent to each other in the circumferential direction (C), the plurality of bridge portions (41) has an offset bridge portion (51) located at a position shifted in the circumferential direction (C) from the magnetic pole center line (90), an extending direction (D1) of the offset bridge portion (51) is inclined in a cross section perpendicular to an axial direction (L) with respect to the magnetic pole center line (90), so as to approach the magnetic pole center line (90) toward the outer side in the radial direction (R), the plurality of holes (20) in each of the plurality of magnetic poles (P) are arranged so as to form a surrounding hole group (31) surrounding a magnetic pole center point (91) that is an intersection of the magnetic pole center line (90) and an outer circumferential surface (15a) of the rotor core (15), and the extending direction (D1) of the offset bridge portion (51) is set in the cross section perpendicular to the axial direction (L) along a direction toward a center of gravity (G1) of a target portion (81) surrounded by the surrounding hole group (31).A rotor (2) for a rotating electric machine, comprising a rotor core (15) and permanent magnets (60) arranged in the rotor core (15), wherein in each of a plurality of magnetic poles (P), the rotor core (15) has a plurality of holes (20) including magnet insertion holes (21, 22) where the permanent magnets (60) are arranged, the plurality of holes (20) in each of the plurality of magnetic poles (P) is arranged to form a surrounding hole group (31) surrounding a magnetic pole center point (91) that is an intersection of an outer circumferential surface (15a) of the rotor core (15) and a magnetic pole center line (90) extending in a radial direction (R) through a center of the magnetic pole (P) in a circumferential direction (C), the rotor core (15) has a plurality of bridge portions (41) each formed between two of the holes (20) adjacent to each other in the circumferential direction (C), the plurality of bridge portions (41) has an offset bridge portion (51) located at a position shifted in the circumferential direction (C) from the magnetic pole center line (90), and an extending direction (D 1) of the offset bridge portion (51) is set in a cross section perpendicular to an axial direction (L) along a direction toward a center of gravity (G 1) of a target portion (81) surrounded by the surrounding hole group (31).The rotor (2) for a rotating electric machine according to claim 1 or 2, wherein the rotor core (15) has, in each of the plurality of magnetic poles (P), the plurality of holes (20) that form a second surrounding hole group (32) that surrounds the magnetic pole center point (91) on a side closer to the magnetic pole center point (91) than the surrounding hole group (31), and also has a plurality of second bridge portions (42) that are respectively formed between the plurality of holes (20) that form the second surrounding hole group (32), the plurality of second bridge portions (42) has a second offset bridge portion (52) that is located at a position that is offset in the circumferential direction (C) from the magnetic pole center line (90), and an extending direction (D 2) of the second offset bridge portion ( 52) in the cross section perpendicular to the axial direction (L) is set along a direction toward a center of gravity (G 2) of a second target portion ( 82) surrounded by the second surrounding hole group ( 32).The rotor (2) for a rotating electric machine according to any one of claims 1 to 3, wherein portions forming the offset bridge portion (51) at outer edges of the two holes (20) are defined as bridge forming edges (20b), two common inner tangents to one of the bridge forming edges (20b) and the other of the bridge forming edges (20b) of the two holes (20) in the cross section perpendicular to the axial direction (L) are defined as a first straight line (T1) and a second straight line (T2), and the extending direction (D1) of the offset bridge portion (51) in the cross section perpendicular to the axial direction (L) is defined as a direction along a line segment, bisecting an angle between the first straight line (T1) and the second straight line (T2) and not intersecting the two holes (20).A rotor (2) for a rotating electric machine, comprising a rotor core (15) and a permanent magnet (60) disposed in the rotor core (15), wherein in each of the plurality of magnetic poles (P), the rotor core (15) has a plurality of holes (20) including a first hole (21) and a second hole (22), in each of which the permanent magnet (60) having a planar magnetic pole surface (F) is disposed, the first hole (21) and the second hole (22) are separately disposed on both sides in a circumferential direction (C) with respect to a magnetic pole center line (90) extending in a radial direction (R) through a center of the magnetic pole (P) in the circumferential direction (C), such that a separation distance between the first hole (21) and the second hole (22) increases in the circumferential direction (C) toward an outer side in the radial direction (R), the rotor core (15) has a plurality of bridge portions (41) each formed between two of the holes (20) adjacent to each other in the circumferential direction (C), the plurality of bridge portions (41) has an offset bridge portion (51) located at a position shifted in the circumferential direction (C) from the magnetic pole center line (90), and in a cross section perpendicular to an axial direction (L), the offset bridge portion (51) is formed to extend toward a center of gravity (G1) on the magnetic pole center line (90) corresponding to the magnetic pole (P), where the offset bridge section (51) is formed.The rotor (2) for a rotating electric machine according to claim 5, wherein the offset bridge portion (51) is formed in the cross section perpendicular to the axial direction (L) in a specific region (70) where a distance between the two holes (20) is the shortest.The rotor (2) for a rotating electric machine according to claim 6, wherein in the cross section perpendicular to the axial direction (L), a straight line passing through an end of the specific region (70) on one side (C1) in the circumferential direction (C) and the center of gravity (G1) is defined as a third straight line (T3), and a straight line passing through an end of the specific region (70) on the other side (C2) in the circumferential direction (C) and the center of gravity (G1) is defined as a fourth straight line (T4), and the offset bridge portion (51) in the cross section perpendicular to the axial direction (L) is formed in a region located between the third straight line (T3) and the fourth straight line (T4), and the offset bridge portion (51) is inserted between the two holes (20) on both sides in the circumferential direction (C), which two holes (20) are located completely outside the range located between the third straight line (T3) and the fourth straight line (T4).

Images