Rotary electric machine

Abstract

To provide a rotary electric machine in which a liquid coolant is jetted to end surfaces of a rotor, where the coolant is made to be difficult to invade to a gap between the rotor and a stator.SOLUTION: Cylindrical projections 36, 39 projecting outwardly in axial directions are provided on the outer peripheral sides of end plates 35, 38 arranged on both side end surfaces of a rotor core 31. Cooling oil 71, 72 supplied from oil supply holes 4c, 5c of end brackets 4, 5 of a rotary electric machine 1 hits end surfaces of a rotor 30 like arrows 71a, 72a of the rotor 30 and flows on the outer peripheral sides, is moved by the projections 36, 39 to positions (Zrf, Zrr) separated from the rotor core 31 in the axial directions like arrows 71c, 72c before being guided to the stator core 11 side. Therefor, the rotary electric machine 1 is formed so that absolute values of coordinate Zsf, Zsr of minimum inner diameters of resins 24, 26 are larger than absolute values of coordinates of the Zrf, Zrr, respectively.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a rotating electric machine in which a liquid refrigerant is sprayed onto the end face of the rotor in the direction of the rotation axis to cool the rotor and stator, and in particular to improvements in the shape of the end face of the rotor and the shape of the coil end portion of the stator. [Background technology]

[0002] With the backdrop of global warming and the depletion of fossil fuels, the electrification and energy conservation of various power sources is accelerating. Motors, which are key components, are required to have specifications that maximize the system performance, including the load machinery and the inverter, which is the drive circuit. In particular, high motor speed is a specification that is in high demand for various applications. For motors used in EVs (Electric Vehicles) and HEVs (Hybrid Electric Vehicles), the motor size (∝torque) is reduced by increasing the speed to increase the motor output (∝rotation speed x torque). Although the gear reduction ratio increases, the total system can be made smaller. For air compressor motors used as a utility device for gears, the compression mechanism (air end), which was previously driven by increasing the speed with a gear, is now directly driven by the air compressor on the rotating shaft of the motor without going through a speed-increasing gear, improving system efficiency.

[0003] On the other hand, increasing the motor speed leads to increased losses in the rotor core and permanent magnets due to increased frequency and current harmonics, so it is necessary to strengthen the cooling of the rotor. Various rotor cooling methods using cooling oil have already been proposed. In relatively low-speed motors, a method is used in which the rotor scoops up the cooling oil stored inside the rotating electric machine, but this is difficult to apply at high speeds because of increased fluid friction loss. In response to this, there is a method in which a flow path is provided inside the rotating shaft and the cooling oil flows through it. If the shaft core is simply cooled only, it is far from the heat source and does not provide a sufficient heat dissipation effect, so many of these flow paths are extended to the outer periphery of the rotor. In addition, some of these spray the cooling oil to the coil end portion to also cool the stator side. However, in order to use the inside of the rotating shaft as a flow path for the cooling oil, it is necessary to pump the cooling oil to the end of the rotating shaft, which requires an oil seal. If a flow path is formed up to the rotor side, the structure becomes even more complicated, leading to increased costs. Therefore, a method has been devised in which the cooling oil is sprayed on the end face of the rotor.

[0004] Patent Document 1 discloses a method in which a cooling oil flow path is formed so as to penetrate the front and rear end faces (e.g., end brackets) of a motor housing, and cooling oil is sprayed toward the end face of the rotor through this flow path. For this purpose, a cooling oil flow path is formed in the end bracket of the motor, cooling oil pressurized by an oil pump is supplied to the flow path, and the outlet part (nozzle) of the flow path is arranged so as to face the end face of the rotor, and the cooling oil is sprayed toward the end face of the rotor. This method is low cost because it does not require an oil seal in the rotating part or the formation of a complex flow path in the rotor. Furthermore, since the cooling oil is supplied close to the heat source of the rotor, a high heat dissipation effect can be expected. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-6091 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the cooling mechanism described in Patent Document 1, the cooling oil adhering to the rotor end surface is subject to the circumferential velocity component in the rotation direction and the radial velocity component due to centrifugal force, and is scattered toward the stator side, moves toward the center position of the rotor as viewed in the direction of the rotation axis, and may enter the gap (air gap or gap) between the rotor and the stator. When the cooling oil, which has a higher viscosity than air, enters the gap between the rotor and the stator, fluid friction loss increases. Since the fluid friction loss is proportional to the rotation speed, it is a factor that significantly reduces the efficiency of the rotating electric machine, especially at high speeds.

[0007] The present invention has been made in consideration of the above-mentioned background, and its object is to achieve high heat dissipation from the rotor while maintaining the efficiency of the rotating electric machine in a rotating electric machine having a cooling mechanism that sprays liquid refrigerant onto the end face of the rotor. Another object of the present invention is to provide a rotating electric machine that is configured so that liquid refrigerant is unlikely to enter the gap between the rotor and the stator. [Means for solving the problem]

[0008] Representative features of the invention disclosed in this application are as follows. According to one feature of the present invention, there is provided a rotating electrical machine including a rotating shaft, a rotor, and a stator. In the rotor, permanent magnets are provided on a rotor core fixed to the rotating shaft. The stator has a stator core and coils, and coil end portions are formed outside from end portions of the stator core in the rotating shaft direction. A cooling mechanism is provided on an axial end face of the rotor, into which a liquid refrigerant supplied from outside the rotating electrical machine is directly injected. Coordinates Zr of end portions of the rotor, viewed from the center position in the axial direction of the rotor in both directions in the rotating shaft direction, and coordinates Zs of a tip on the + side or - side, viewed in the rotating shaft direction, of the innermost peripheral portion of the coil end portion are such that the absolute values thereof satisfy |Zs| ≦ |Zr|, and the shapes of the stator and the rotor are set accordingly. The relationship of |Zs| ≦ |Zr| preferably holds over the entire circumference of the stator, but it is sufficient if this relationship holds at least at one location in the circumferential direction. Further, a circumferentially continuous protrusion is provided on the axial end face of the rotor located on the outer diameter side from an end portion of the cooling mechanism, and the absolute value |Zr| of the coordinate of the axial end portion of the protrusion is made equal to or greater than |Zs|, or the stack thickness (length in the rotating shaft direction) of the rotor core is made greater than the stack thickness (length in the rotating shaft direction) of the stator core.

[0009] According to another feature of the present invention, an end plate is provided on an axial end face of the rotor core, and a protrusion that is cylindrical and protrudes in the rotating shaft direction is provided near the outer periphery of the end plate. By setting the absolute value of the tip coordinate of the protrusion, viewed in the rotating shaft direction, to be Zr, the relationship of |Zs| ≦ |Zr| is satisfied. It is preferable to provide an inclined portion on the inner periphery of the protrusion such that the inner diameter expands linearly, curvilinearly, or stepwise toward the outer diameter direction. Further, depending on the difference in the shapes of the output side and the non-output side of the coil end portion of the stator, the shapes of the protrusions on the output side and the non-output side may be the same or different. A plurality of permanent magnets are held in the rotor core of the rotor, and the protrusion is formed such that the radius Rm of the innermost diameter portion of the permanent magnet and the radius Rt of the innermost diameter portion of the protrusion satisfy the relationship of Rm < Rt.

[0010] According to yet another feature of the present invention, a rotary electric machine is provided with plate-shaped end plates on both end faces in the direction of the rotation axis of a cylindrical rotor core, and liquid refrigerant is directly sprayed onto the end plates from outside the housing through a dedicated refrigerant path, and a circumferentially continuous cylindrical protrusion is formed on the outer periphery of the end plate radially outward from the center point of spray of the liquid refrigerant to guide the sprayed liquid refrigerant away from the end plate toward the outside in the direction of the rotation axis. Effect of the Invention

[0011] According to the present invention, the splash position of the liquid refrigerant splashing from the rotor to the stator side is away from the gap, and the liquid refrigerant adhering to the stator moves in the opposite direction to the gap side, thereby suppressing an increase in fluid friction loss due to the liquid refrigerant, and providing a rotating electric machine that achieves both high heat dissipation of the rotor and high efficiency of the rotating electric machine. Problems, configurations and effects other than those described above will become apparent from the following description. [Brief description of the drawings]

[0012] [Figure 1] 1 is a perspective view showing the appearance of a rotating electric machine 1 according to a first embodiment of the present invention. [Diagram 2] 2 is a cross-sectional perspective view showing the internal structure of the rotating electric machine 1 of FIG. [Diagram 3] 3 is a vertical sectional view of the rotating electric machine 1 of FIG. 2 taken along line AA. [Figure 4] 1 is a schematic partial cross-sectional view for illustrating the configuration of a rotating electric machine 1 according to a first embodiment of the present invention. [Diagram 5] FIG. 11 is a schematic partial cross-sectional view illustrating the configuration of a rotating electric machine 1A according to a modified example of the first embodiment of the present invention. [Figure 6] FIG. 11 is a schematic partial cross-sectional view for illustrating the configuration of a rotating electric machine 1B according to a second embodiment of the present invention. [Figure 7] FIG. 11 is a schematic partial cross-sectional view for illustrating the configuration of a rotating electric machine 1C according to a third embodiment of the present invention. [Figure 8]FIG. 11 is a schematic partial cross-sectional view for illustrating the configuration of a rotating electric machine 1D according to a fourth embodiment of the present invention. [Figure 9] 9A and 9B are cross-sectional views of molding dies 300, 300A and stators 10, 110 when molding stator 10, with FIG. 9A showing the die structure in this embodiment and FIG. 9B showing the die structure in a conventional example. [Figure 10] FIG. 1 is a schematic partial cross-sectional view for explaining the configuration of a rotating electric machine 101 of a conventional example. [Figure 11] FIG. 11 is a schematic partial cross-sectional view for explaining the configuration of a rotating electric machine 101A of a conventional example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the same parts are given the same reference numerals, and repeated explanations will be omitted. In addition, in this specification, the front, back, left, right, and up and down directions will be described as directions shown in the drawings.

[0014] FIG. 1 is a perspective view showing the appearance of a rotating electric machine 1 according to an embodiment of the present invention. The rotating electric machine 1 is, for example, an electric motor, and is configured by accommodating a rotating shaft 40, a rotor 30 (see FIG. 2 described later), and a stator 10 (see FIG. 2 described later) inside a housing 2. The housing 2 is formed in a divided shape, and is formed here by a cylindrical portion 3 and disk-shaped end brackets 4 and 5 provided so as to close the openings at both ends of the cylindrical portion 3. The cylindrical portion 3 is configured in a two-part shape with a cavity (reference numeral 51 in FIG. 2 described later) through which cooling oil flows. The end brackets 4 and 5 are formed with through holes 4a (see FIG. 2 described later), 5a, through which the rotating shaft 40 passes. The rotating shaft 40 extends far forward from the front end bracket 4, and is connected to a load portion (not shown) directly or via a power transmission mechanism. The rear end bracket 5 may have a structure without the through hole 5a. A plurality of connection parts for connecting piping to supply liquid refrigerant are formed in the cylindrical portion 3 and the end brackets 4 and 5 of the housing 2. The piping connection part 57 is a connection part for piping that supplies cooling oil to the rear end face of the rotor 30 (described later in FIG. 2).

[0015] FIG. 2 is a cross-sectional perspective view showing the internal structure of the rotating electric machine 1 of FIG. 1. The rotating electric machine 1 includes an annular stator 10 and a rotor 30 arranged inside the stator 10. The outer peripheral portion of the stator 10 is fixed to the inner peripheral wall of the cylindrical portion 3 of the housing 2, and the rotor 30 is fixed to the rotating shaft 40. The cylindrical portion 3 is formed of a front portion 3a and a rear portion 3b, and the space formed at the joint between these becomes a first cooling path 51. A cylindrical bearing holder 4b extending rearward is formed on the outer peripheral portion of the through hole 4a of the end bracket 4, and a bearing 41 is provided inside the bearing holder 4b. Similarly, a cylindrical bearing holder 5b extending forward is formed from the outer peripheral portion of the through hole 5a of the end bracket 5, and a bearing 42 is provided inside the bearing holder 5b. The rotating shaft 40 is rotatably supported by the two bearings 41 and 42.

[0016] Stator 10 is mainly composed of stator core 11 and coils wound in slots (described later in FIG. 3) of stator core 11. Coil ends 20 protrude from the front side of stator core 11, and coil ends 22 protrude from the rear side. Both coil ends 20, 22 are molded with resin (described in detail in FIG. 4 and subsequent figures). Lead wires (not visible in the figure) extend from coil ends 22 and are wired in a star connection or delta connection on connection plate 46.

[0017] The housing 2 is provided with four cooling paths through which a refrigerant flows to cool heat-generating parts. A liquid refrigerant is used, for example, cooling oil. The main objects to be cooled in the cooling paths are the stator 10, the rotor 30, and the bearings 41 and 42. The first cooling path 51 is on the outer periphery side of the stator 10, and mainly cools the stator core 11 and the coils (20, 22, etc.) by flowing cooling oil in a hollow portion (first cooling path 51) formed in the cylindrical part 3. The first cooling path 51 is connected to an inlet and an outlet (both not visible in the figure) for the cooling oil, and the cooling oil circulates in the circumferential direction. The first cooling path 51 is for indirect cooling in which the cooling oil does not directly come into contact with the objects to be cooled.

[0018] The cylindrical portion 3 is formed with a cooling oil supply port 52 for cooling the coil end 20 of the stator 10 and a cooling oil supply port 53 for cooling the coil end 22. The cooling oil supplied from an external pipe is directly supplied to the outer circumferential surface of the coil end 20 from the cooling oil supply port 52. The cooling oil supplied to the outer circumferential surface of the coil end 20 flows mainly in the circumferential direction on the outer circumferential surface of the coil end 20 toward the bottom surface of the housing 2, and is discharged to the outside from the discharge port 6. Similarly, the cooling oil is directly supplied to the outer circumferential surface of the coil end 22 from the cooling oil supply port 53. The cooling oil supplied to the outer circumferential surface of the coil end 22 flows mainly in the circumferential direction on the outer circumferential surface of the coil end 22 toward the bottom surface of the housing 2, and is discharged to the outside from the discharge port 7. The flow paths that supply the refrigerant to the front and rear sides of the stator 10 are the second cooling paths 52 and 53, which are direct cooling paths.

[0019] A third cooling path 54 for flowing cooling oil from the outside is formed in the end bracket 4. The cooling path 54 extends from the radial outside to near the center of the end bracket 4, turns 90 degrees, and extends rearward inside the bearing holder 4b to directly supply cooling oil for lubrication and cooling to the bearing 41. Similarly, a third cooling path 55 for flowing cooling oil from the outside is formed in the end bracket 5. The cooling path 55 extends from the radial outside to near the center of the end bracket 5, turns 90 degrees, and extends forward inside the bearing holder 5b to directly supply cooling oil to the bearing 42. The cooling paths 54 and 55 are direct cooling paths.

[0020] The end bracket 4 is further provided with a fourth cooling path that supplies cooling oil from the outside to the front end face and the rear end face of the rotor 30. The fourth cooling path is a mechanism for cooling the rotor 30, and directly injects cooling oil onto the end plates 35 and 38 located at the end faces of the rotor 30. The inlet of the cooling path that injects cooling oil onto the end plate 38 is a pipe connection part 57. Note that a pipe connection part 56 (see FIG. 3 described later), which serves as the inlet of the cooling path that supplies cooling oil to the front end face (end plate 35) of the rotor 30 among the fourth cooling paths, is separately provided on the right side surface of the cylindrical part 3 of the housing 2. The rotor cooling mechanism is provided with a pipe and a nozzle (not shown in the figure) attached to the inner wall surface of the housing 2 toward the end face of the rotor 30, and cooling oil is injected from the nozzle near the rotor 30 toward the end plates 35 and 38 in a direction substantially parallel to the rotation axis Z. An oil pump (not shown) and oil piping for pumping cooling oil (not shown) to the first to fourth flow paths are connected to the outside of the housing 2 of the rotating electrical machine 1. The cooling oil supplied to the inside of the housing 2 by the fourth cooling path is discharged from the outlets 6 and 7 to the outside of the housing 2 together with the cooling oil supplied by the second and third cooling paths.

[0021] FIG. 3 shows a vertical cross-sectional view of the AA portion of the rotating electric machine 1 in FIG. 1. This cross-sectional view is perpendicular to the rotation axis Z. The stator core 11 of the stator 10 is composed of teeth 12 made of amorphous metal and a back yoke 13 made of electromagnetic steel. However, the form of the stator 10 is arbitrary, and the teeth 12 and the back yoke 13 may be integrally formed. The space between the adjacent teeth 12 is a slot, and a plurality of coils 14 of rectangular wire are arranged in the radial direction in the slot via bobbins 15. Although not shown here, the coil 14 of rectangular wire is divided into one side (front side) and the other side (rear side) near the center of the stator 10 in the direction of the rotation axis Z, and the coils 14 are fitted together at concave and convex connecting parts (terminal parts) formed at the tip of the divided surfaces to form a closed circuit. The rotor 30 is based on a rotor core 31 formed by laminating a large number of thin, annular electromagnetic steel sheets in the direction of the rotation axis Z, and a plate-shaped permanent magnet 33 made of sintered neodymium is disposed in each of a large number of slots 32 for accommodating magnets formed near the outer edge of the rotor core 31. A piping connection part 56 for a fourth cooling mechanism is formed on the right side surface of the cylindrical part 3 of the housing 2, close to the front end bracket 4 (see FIG. 2). Note that the cross sections of the rotor 30 and stator 10 in FIG. 3 are not hatched.

[0022] Before describing the fourth cooling mechanism of the rotating electric machine 1 of the present invention, i.e., the configuration for injecting cooling oil onto the rotor 30, the flow of cooling oil in a conventional rotating electric machine 101 will be described with reference to Figures 10 and 11. Figure 10 is a partial cross-sectional view for explaining the shapes of the rotor 130 and the stator 110 in the conventional rotating electric machine 101, and the flow of cooling oils 81, 82.

[0023] The shapes of the stator core 131 and magnet 133 of the rotor 130 in FIG. 10 are the same as those of the rotor 30 shown in FIG. 2 and FIG. 3. Note that this figure is a schematic illustration for explaining the outline of the configuration, and the rotor core 131 and the stator core 111 are not hatched. The stator core 111 is a laminated core formed by laminating a large number of thin electromagnetic steel sheets in the direction of the rotation axis Z. Coils are wound around the slots of the stator core 111. The coils exposed on the front side from the stator core 111 are the coil ends 120, and the coil ends 122 extending rearward from the stator core 111 are formed on the rear side. In such a rotating electric machine 101, the cooling oil 81 is sprayed onto the front surface of the front end plate 135 of the rotor 130 from the oil supply hole 4c provided in the end bracket 4 on the front side. Similarly, cooling oil 82 is sprayed onto the rear surface of the rear end plate 138 of the rotor 130 from an opening 5 c provided in the rear end bracket 5 .

[0024] The cooling oil 81 injected from the oil supply hole 4c is injected toward the rear in a direction parallel to the rotation axis Z, toward an injection center point 191, as shown by an arrow 81a. This injection may be linear or may be shaped to diffuse in a cone. Similarly, the cooling oil 82 injected from the opening 5c ​​is injected toward the front side in a direction parallel to the rotation axis Z, toward an injection center point 192, as shown by an arrow 82a. Although not shown here, an extension pipe and a nozzle may be provided at the inner opening of the oil supply holes 4c and 5c so that the cooling oils 81 and 82 are injected in a predetermined direction with a predetermined degree of diffusion. Even when a nozzle not shown is provided, the injection centers are set to 191 and 192. The injection centers 191 and 192 are set to be radially outward from the bearings 41 and 42 and to be inner than the outer edge of the rotor 130. The injection centers 191 and 192 are set at one circumferential location on the front end face of the rotor 130 and one circumferential location on the rear end face of the rotor 130.

[0025] Cooling oil 81 that hits front end plate 135 of rotating rotor 130 flows radially outward around end plate 135 as indicated by arrow 81b due to centrifugal force while rotating in the circumferential direction, leaves the outer circumferential end of end plate 135, and arrives at the inner circumferential surface of coil end 120. Most of cooling oil 81 then flows along the inner circumferential surface and vertical surface of coil end 120 as indicated by arrows 81c and 81d, drops to the bottom surface of cylindrical portion 3, and is discharged from discharge port 6 formed in the bottom surface area as indicated by arrow 81e.

[0026] The flow of cooling oil 82 is similar, being sprayed as indicated by arrow 82a, and the cooling oil 82 that hits the rear end plate 138 flows radially outward as indicated by arrow 82b due to centrifugal force while being rotated in the circumferential direction by the rear end plate 138 of the rotating rotor 130, leaves the outer circumferential end of the end plate 138, flows along the inner circumferential surface and vertical surface of the coil end 122 as indicated by arrows 82c and 82d, drops on the bottom surface of the cylindrical portion 3, and is discharged as indicated by arrow 82e from a discharge port 7 formed in the bottom area. The discharged cooling oil 82 is recovered together with cooling oil 81 by a cooling oil recovery line (not shown), and is reused after being cooled.

[0027] The cooling oils 81 and 82 near the arrows 81b and 82b are accelerated in the circumferential and radial directions and splash near the bases of the coil ends 120 and 122, and may enter the gap 128 as indicated by the arrows 81f and 82f. Furthermore, depending on the shape of the coil ends 120 and 122 on the stator 110 side, the cooling oils 81 and 82 splashed on the stator 110 side may enter the gap 128 due to gravity or the like. For example, in FIG. 10, the coil ends 120 and 122 are inclined so that the inner diameter becomes larger toward the center position of the rotor 130 when viewed in the Z-axis direction (front-back direction in this case) in order to avoid interference between the wires. This type of shape is often used in distributed winding coils using round wires. When such an inclination is present, the cooling oils 81 and 82 splashed near the gap 128 are more likely to enter the gap 128.

[0028] FIG. 11 is a cross-sectional view of a rotating electric machine 101A in which coil ends 120 and 122 are molded with resins 124 and 126. The front coil end portion is formed with the coil end 120 and the resin 124, and the rear coil end portion is formed with the coil end 122 and the resin 126. In this way, the entire coil including the coil ends 120 and 122 may be molded in anticipation of improved coil retention strength and improved heat dissipation due to high thermal conductivity. When molding the coil ends 120 and 122, as shown in FIG. 9A, it is necessary to provide draft tapers 311a and 311b in a mold die (hereinafter, core die 310) that forms the inner diameter side. When molding from the output side to the anti-output side with a single core die 310, the inclination direction of the inner circumferential surface of the resin 126 needs to be the same on the output side and the anti-output side. In this structure, the inner circumferential surface (the side closer to the rotation axis Z) of the mold 126 on the non-output side needs to have a tapered shape 126a such that the inner diameter decreases toward the rear end (-Z direction), and this shape makes it easier for the scattered cooling oil to enter the gap 128 as shown by the arrow 84f. In addition, in the case of a rotating electric machine 101A in which the coil ends 120, 122 are molded with resins 124, 126, the cooling oil does not flow out from the gaps in the coils, so there is an even greater risk of the cooling oil entering the gap 128. In rotating electric machines with distributed winding and wave winding using rectangular wires, which are used in many vehicle-mounted motors, the coil ends rise almost vertically from the end faces, so the coil shape is not as shown in FIG. 10, but when molded, problems similar to those in FIG. 11 become apparent.

[0029] Next, the configuration of a rotating electric machine 1 according to a first embodiment of the present invention will be described with reference to Fig. 4. Fig. 4 is a schematic partial cross-sectional view showing the configuration of the rotating electric machine 1. Hereinafter, in this specification, the positions of the ends of the rotor 30 will be described based on the size in the forward direction (+Z direction) and the size in the rearward direction (-Z direction) with the center position of the rotor 30 as the reference (coordinate 0) when viewed in the direction of the rotation axis Z.

[0030] End plates 35, 38, which are metal members separate from the rotor core 31, are provided on the end faces of the rotor core 31 in the ±Z direction of the rotation axis. The end plates 35, 38 are often provided for reasons such as adjusting the rotation balance of the rotor 30 and preventing the permanent magnets 33 from moving in the ±Z direction of the rotation axis. In the front end plate 35, cooling oil 71 flowing in from the oil supply hole 4c of the end bracket 4 is sprayed in the -Z direction toward the surface (front surface) of the end plate 35 as indicated by the arrow 71a. The spray of cooling oil 71 indicated by the arrow 71a is sprayed straight or diffusely toward the spray center point 91 of the end plate 35, and has, for example, a conical spread. Similarly, in the rear end plate 38, cooling oil 72 flowing in from the oil supply hole 5c of the end bracket 5 is sprayed straight or diffusely toward the surface (rear surface) of the end plate 38 as indicated by the arrow 72a in the +Z direction.

[0031] The disk-shaped end plates 35, 38, each having a through hole formed in the center through which the rotating shaft 40 passes, are provided with a protrusion 36 protruding forward from the surface of the end plate 35 (the surface that does not contact the rotor core 31) and a protrusion 39 protruding rearward from the surface of the end plate 38, in a portion located radially outward (outer diameter side) from the injection center points 91, 92 of the cooling oil 71, 72 near the outer periphery. The protrusions 36, 39 are cylindrical members having a constant cross-sectional shape in the circumferential direction and are continuous, but the protrusion 36 on the output side and the protrusion 39 on the anti-output side are formed in different shapes. In FIG. 4, the end plate 35 and the protrusion 36, and the end plate 38 and the protrusion 39 are formed integrally, but the protrusions 36, 39 may be manufactured as separate parts from the end plates 35, 38 instead of being integral. The end plates 35, 38 and the protrusions 36, 39 are preferably made of highly thermally conductive materials in terms of improving heat dissipation, and non-magnetic materials are preferable in terms of reducing leakage flux from the rotor 30, so they may be made of aluminum alloy, non-magnetic stainless steel, or the like.

[0032] The front coil end 20 and the rear coil end 22 of the stator 10 are molded with resins 24 and 26. Here, the front and rear coil end portions are formed including the resin 24 and 26 portions, but the coil end portions may be formed only with the coil ends 20 and 22 without using the resins 24 and 26. Taper portions 24a and 26a are formed on the inner peripheral surfaces of the molded resins 24 and 26 such that the inner diameter expands in a direction away from the center position on both the output side and the anti-output side. The taper portion 24a on the output side has a shape in which the inner diameter simply increases from the boundary with the stator core 11. On the other hand, for the taper portion 26a on the anti-output side, since the lead wire 23 drawn from the coil end 22 protrudes largely radially inward, a taper portion 26b is formed in which the inner diameter largely decreases once rearward from the stator core 11, and then it becomes a taper portion 26a having an increasing shape. Note that the reason why the lead wire 23 protrudes largely toward the inner diameter side is to transmit the axial load also to the fitting portion of the lead wire when fitting the axially divided coils.

[0033] The inner position of the protrusion 36 (the portion close to the rotation axis Z) is located radially outside the inner position of the permanent magnet 33 (the inner peripheral position close to the rotation axis Z) when viewed in the radial direction R. That is, the permanent magnet 33 is arranged on the rotor core 31 such that the radius Rm of the innermost diameter portion of the permanent magnet 33 and the radius Rt of the innermost diameter portion of the protrusion 36 satisfy Rm < Rt. Further, the protruding tip position of the protrusion 36 (+Z coordinate of the front rotor 30) is +Zrf, and its inner position is located radially outside the inner position of the permanent magnet 33 (the inner peripheral position close to the rotation axis Z). Also, the protruding tip position of the protrusion 36 is located on the front side of the position where the diameter of the coil end portion on the stator 10 side is the smallest (= the position of the front end face on the front side of the stator core 11) +Zsf. That is, the relationship |Zsf| ≦ |Zrf| is satisfied.

[0034] The inner position of the protrusion 39 is located radially outward from the inner position of the permanent magnet 33 (the inner peripheral position close to the rotation axis Z). The protrusion tip position of the protrusion 39 (the distance from the end plate 38 in the rotation axis -Z direction) is -Zrr, and the position is located rearward from the position of the rear end face of the stator core 11 of the stator 10. The amount of protrusion of the protrusion 36 toward the front side in the rotation axis direction and the amount of protrusion of the protrusion 39 toward the rear side in the rotation axis direction are not the same. This is because the amount of protrusion of the protrusions 36, 39 in the rotation axis Z direction is determined in accordance with the shape of the stator 10 side, particularly the minimum inner diameter position of the resins 24, 26. The outer diameter of the protrusion 39 is formed slightly smaller than the outer diameter of the protrusion 36 in order to avoid the inward convex portion of the resin 26 (the mountain-shaped portion formed by the tapered portions 26a and 26b, which is the minimum inner diameter portion). The inner diameter of the protrusion 36 is formed slightly larger than the inner diameter of the protrusion 39. Furthermore, the innermost portion of the coil end of the protrusion 36, here the position between the tapered portions 26a and 26b, is located rearward of the position +Zsr where the diameter of the resin 24 on the stator 10 side is smallest. In other words, these absolute values ​​have the relationship |Zsr|≦|Zrr|.

[0035] The positional relationship between the protrusions 36, 39 and the coil ends 20, 22 is configured to satisfy |Zsf|≦|Zrf| on the front side (output side) and |Zsr|≦|Zrr| on the rear side (opposite output side). In other words, the relationship |Zs|≦|Zr| holds in either direction, except for the final suffixes "f" and "r" indicating the front and rear. In the shape of the resin 24 in FIG. 4, the coordinate Zsf coincides with the coordinate of the end face of the rotor core 31. On the other hand, in the coil end 22 on the opposite output side, the punched taper portion 26b from molding remains on the inner peripheral side except for the outer peripheral side, so the coordinate -Zsr is a position further rearward than the rear end face of the stator core 11, and is the boundary position between the taper portions 26b and 26a.

[0036] Next, the operation of the rotating electric machine 1 will be described. A DC magnetic field is generated by the permanent magnets 33 on the outer diameter side of the rotor 30. Meanwhile, a three-phase electric power converted to a predetermined frequency is generated by an inverter (not shown), and is fed to the coils 14 (see FIG. 3) of the stator 10, forming a rotating magnetic field in the radial direction of the stator 10. By passing an excitation current through the coils 14 in accordance with the magnetic pole positions of the stator 10, a predetermined torque is generated in the rotor 30 due to attraction and repulsion between the rotating magnetic field and the DC magnetic field, and the rotating shaft 40 can be rotated in a predetermined direction (rotation direction). When the rotating electric machine 1 is driven, cooling oil is pumped to each of the first to fourth flow paths by an oil pump (not shown). In this way, the cooling oil flows through the direct cooling flow path and the indirect cooling flow path in the housing 2, thereby cooling the heat-generating parts of the rotating electric machine 1.

[0037] The cooling oils 71, 72 sprayed from the fourth rotor cooling mechanism may be directly supplied to the front and rear end faces of the rotor 30, and the nozzle and piping structure may be arbitrary. The cooling oils may be supplied from the end brackets 4, 5 of the housing 2 using piping and nozzles, or a portion of the cooling oil supplied to the bearings 41, 42 may be branched off and sprayed from the branched flow path onto the end faces of the rotor 30. The cooling oils 71, 72 sprayed onto the front end face (end plate 35) and rear end face (end plate 38) of the rotor 30 as indicated by arrows 71a, 72a hit the end plates 35, 38, and move radially outward as indicated by arrows 71b, 72b while rotating circumferentially on the surfaces of the end plates 35, 38 due to surface tension.

[0038] The cooling oil 71, 72 that has reached the inner circumferential surfaces of the protrusions 36, 39 is prevented from moving radially outward by the protrusions 36, 39, so it moves in the direction of the arrows 71c, 72c that are in the direction of the rotation axis Z and away from the end plates 35, 38, and flows radially outward along the front end face of the protrusion 36 and the rear end face of the protrusion 39. The cooling oil that flows radially outward along the front end face of the protrusion 36 and the rear end face of the protrusion 39 and splashes from the rotor 30 to the stator 10 side splashes toward the coil ends 20, 22 at a position spaced apart from the gap 28. At this time, the cooling oil splashes to a position spaced apart from the front opening face and the rear opening face of the gap 28 by the height of the protrusions 36, 39 (the length in the direction of the rotation axis Z). This makes it possible to effectively suppress the amount of cooling oil that enters the gap 28 due to, for example, the rebound of the cooling oil 71, 72 when it adheres to the inner circumferential surfaces of the coil ends 20, 22.

[0039] Furthermore, since the resins 24, 26 at the positions where the cooling oils 71, 72 are applied are formed with the tapered portions 24a, 26a whose inner diameters expand toward the end brackets 4, 5, the cooling oils 71, 72 can be prevented from flowing in a direction approaching the gap 28 due to the kinetic energy and gravity of the cooling oils 71, 72 when they enter the tapered portions 24a, 26a. This can prevent an increase in fluid friction loss due to the cooling oils 71, 72 entering the gap 28. In addition, since the cooling oils 71, 72 also move in the direction of the rotation axis along the protrusions 36, 39 as indicated by the arrows 71c, 72c, the contact area between the cooling oils 71, 72 and the end plates 35, 38 of the rotor 30 increases, and the amount of heat dissipated from the rotor core 31 to the cooling oils 71, 72 increases. In particular, flow paths for cooling oils 71, 72 are formed near the front and rear end faces of permanent magnet 33, which is the main heat source, as indicated by arrows 71c, 72c, so that permanent magnet 33 can be actively cooled. As a result, it is possible to improve the heat dissipation of rotor 30 and increase the efficiency of rotating electric machine 1 at the same time.

[0040] In this embodiment, in order to avoid interference between the coil end 26 protruding toward the inner diameter side and the protrusion 39 and to splash the cooling oil 72 toward the tapered portion 26a side where the inner diameter is expanded, the outer diameter of the protrusion 39 on the anti-output side is made slightly smaller than the outer diameter of the rotor core 31 and the length in the rotation axis -Z direction (protrusion height of the protrusion 36) is increased. As a result, the shapes of the protrusions 36, 39 on the output side and the anti-output side are different and asymmetrical, but a symmetrical shape may be used as long as the relationship between the positions +Zsf, -Zsr in the rotation axis Z direction of the innermost portion of the coil end portion (here, the inner peripheral portion of the resins 24, 26) and the positions +Zrf, -Zrr of the end faces of the protrusions 36, 39 close to the end brackets 4, 5, respectively, satisfies the conditions |Zsf|≦|Zrf| and |Zsr|≦|Zrr| in absolute coordinates, or the shape of the coil end may be changed to another shape different from that shown in FIG. 4.

[0041] FIG. 5 is a schematic partial cross-sectional view for explaining the configuration of a rotating electric machine 1A according to a modified example of the first embodiment. The difference from the rotating electric machine 1 in FIG. 4 is the shape of the lead wire 23A from the rear coil end 22, and accordingly, the shape of the resin 27 and the shape of the protrusion 39A are different. The lead wire 23A is drawn out linearly from the stator core 11 in a direction substantially parallel to the rotation axis Z, and the shape of the inner circumference side of the resin 27 (tapered portion 27) is formed as a tapered portion 27a that is plane symmetrical with the resin 24 with respect to the center position. The shapes of the resins 24 and 27 can be formed by a conventional molding method shown in FIG. 9B. In FIG. 9B, molding is performed using two divided cores of core dies 310A and 310B.

[0042] In FIG. 5, cylindrical projections 36, 39A are provided on the outer periphery of the end plate radially outward from the center of injection of the liquid refrigerant onto the end plate, and are continuous in the circumferential direction to guide the injected liquid refrigerant away from the end plate in the direction of the rotation axis (front and rear). In addition, by changing the shape of the resin 27, the inner and outer diameters of the front projection 36 and the rear projection 39A are made the same for the projections 36, 39A, and the size in the direction of the rotation axis Z (the height of the projection) can also be made the same. The relationship between the absolute positions +Zsf, -Zsr of the innermost portion of the coil end portion (here, the innermost portion of the resin 24, 27) in the direction of the rotation axis Z and the absolute positions +Zrf, -Zrr of the end faces of the projections 36, 39A close to the end brackets 4, 5, respectively, satisfies the conditions |Zsf|≦|Zrf| and |Zsr|≦|Zrr|. As a result, the end plates 35, 38A, which are integrally manufactured with the protrusions 36, 39A, can be made common parts, and the number of types of components of the rotor 30A can be reduced. EXAMPLES

[0043] Next, a rotating electric machine 1B according to a second embodiment of the present invention will be described with reference to FIG. 6. The same reference numbers are used for parts that overlap with those of the first embodiment shown in FIG. 4 and FIG. 5, and therefore repeated description will be omitted. In the rotating electric machine 1B, the inner peripheral surfaces of the protrusions 36B and 39B of the rotor 30B are formed as inclined surfaces. The inclined surfaces when viewed in a cross section including the rotation axis Z as shown in FIG. 6 have a cross-sectional shape in which the inner diameter increases linearly as it moves away from the end plates 35B and 38B in the direction of the rotation axis Z. However, as long as the inclination is smooth, the cross-sectional shape may be formed as a curved inclined surface rather than a linear one. In FIG. 6, the inclined surfaces of the protrusions 36B and 39B are shaped symmetrically with respect to the center position of the rotor 30B in the direction of the rotation axis Z. In the second embodiment as well, the relationship between the absolute position |Zsf| of the innermost portion of resin 24 in the direction of rotation axis Z and the absolute position |Zrf| of the end face of protrusion 36B close to end bracket 4 satisfies the condition |Zsf|≦|Zrf|. Moreover, the relationship between the absolute position |Zsr| of the innermost portion of resin 27 in the direction of rotation axis Z and the absolute position |Zrr| of the end face of protrusion 39B close to end bracket 5 satisfies the condition |Zsr|≦|Zrr|.

[0044] Cooling oil 75, 76 supplied from oil supply holes 4c, 5c of end brackets 4, 5 is sprayed toward spray center points 91, 92 as indicated by arrows 75a, 76a, flows as indicated by arrows 75b-75f, 76b-76f, and is discharged to the outside from discharge ports 6, 7. At this time, the cooling oil 75, 76 flows smoothly in the axial and radial directions as indicated by arrows 75c, 76c on the tapered inner peripheral surfaces of protrusions 36B, 39B. By forming the inner peripheral surfaces of protrusions 36B, 39B into a tapered shape in this way, the cooling oil scattering from protrusions 36B, 39B is given an axial velocity component approaching the end brackets 4, 5 in addition to circumferential and radial velocity components. As a result, the faster the rotational speed of the rotor 30B, the further the cooling oils 75, 76 are scattered from the gap 28 in the direction of the rotation axis A1, thereby suppressing the occurrence of fluid friction loss due to the cooling oil entering the gap 28. EXAMPLES

[0045] A third embodiment of the present invention will be described with reference to FIG. 7. In the rotating electric machine 1C of the third embodiment, an end plate 35C having a protrusion 36C and an end plate 38C having a protrusion 39C are arranged on both end faces of a rotor 30C. The shape of the inner peripheral portion of the protrusions 36C and 39C is different from that of the second embodiment shown in FIG. 6, and is configured to have a so-called stepped or stepped shape in which the inner diameter changes stepwise rather than a continuous slope. As shown in FIG. 7, the step when viewed in a cross section including the rotation axis Z increases in two steps as the inner diameter moves away from the end plates 35C and 38C in the +Z direction or the -Z direction. The stepped portions of the end plates 35C and 38C are shaped symmetrically with respect to the center position of the rotor 30C in the rotation axis Z direction. In the third embodiment as well, the relationship between the absolute position |Zsf| in the direction of the rotation axis Z of the innermost portion of the front coil end portion (here, the innermost portion of the resin 24) and the absolute position |Zrf| of the end face of protrusion 39C close to end bracket 4 satisfies the condition |Zsf|≦|Zrf|. Moreover, the relationship between the absolute position |Zsr| in the direction of the rotation axis Z of the innermost portion of the rear coil end portion (the innermost portion of the resin 27) and the absolute position |Zrr| of the end face of protrusion 39C close to end bracket 5 satisfies the condition |Zsr|≦|Zrr|.

[0046] Cooling oil 77, 78 supplied from oil supply holes 4c, 5c of end brackets 4, 5 is sprayed as indicated by arrows 77a, 78a toward spray center points 91, 92, flows as indicated by arrows 77b to 77f, 78b to 78f, and is discharged to the outside from discharge ports 6, 7. At this time, the cooling oil 77, 78 flows while bending in the axial and radial directions as indicated by arrows 77c, 78c on the tapered surfaces on the inner circumferences of protrusions 36C, 39C. By forming the inner surface of the protrusions 36C, 39C in this manner, the cooling oil scattering from the protrusions 36C, 39C is given an axial velocity component toward the end brackets 4, 5 in addition to circumferential and radial velocity components. Furthermore, the contact time between the protrusions 36C, 39C and the cooling oil 77, 78 is longer. Therefore, the faster the rotational speed of the rotor 30C, the further the cooling oil 77, 78 will be scattered from the gap 28, thereby suppressing the occurrence of fluid friction loss due to the cooling oil 77, 78 entering the gap 28. EXAMPLES

[0047] FIG. 8 is a schematic partial cross-sectional view for explaining the configuration of a rotating electric machine 1D according to a fourth embodiment of the present invention. In the first to third embodiments, the projections 36, 39, etc. are used to configure the absolute positions |Zsf|, |Zsr| of the innermost circumferential portion of the coil end portion (the innermost circumferential portion of the resin 24, 26) in the direction of the rotation axis Z and the absolute positions |Zrf|, |Zrr| of the end faces of the projections 36, 39 close to the end brackets 4, 5, respectively, to satisfy the conditions of |Zsf|≦|Zrf| and |Zsr|≦|Zrr|. These conditions can be satisfied by extending the axial length of the rotor core 31D without forming the projections 36, 39. As shown in FIG. 8, the axial length (lamination thickness) L2 of the rotor core 31D is made larger by Lo on both the output side and the counter-output side than the axial length (lamination thickness) L1 of the stator core 11 of the stator 10. In other words, the relationship is L2=L1+2Lo. As a result, the front end face position of the permanent magnet 33D is located forward of +Zsf, and the rear end face position is located rearward of -Zsr, so that the permanent magnet 33D can be formed large. In addition, the relationship of |Zsf|≦|Zrf| and |Zsr|≦|Zrr| is satisfied, and the portions of the resins 24, 27 reached by the cooling oils 79, 80 flowing radially outward from the end plates 35D, 38D as indicated by arrows 79b, 80b are located approximately in the axial center of the tapered portions 24a, 27a whose inner diameters increase toward the end brackets 4, 5, and the distance between the end faces of the rotor core 11 and the portions is relatively large, so that the cooling oils 79, 80 can be effectively prevented from entering the gaps 28D.

[0048] In the fourth embodiment, the length of the rotor 30D in the direction of the rotation axis Z (mainly the lamination thickness of the rotor core 31D) is increased with a simple rotor structure, and the length of the permanent magnets 33D in the direction of the axis can be increased. As a result, the amount of magnetic flux of the rotor 30D increases, and it is possible to improve the characteristics of the rotating electric machine 1D, such as increasing the torque, output, and improving efficiency. Note that in this embodiment, the requirements |Zsf|≦|Zrf| and |Zsr|≦|Zrr| are realized by increasing the size of the rotor core 31D, but it is also possible to realize these relationships by increasing the thickness of the end plates 35D, 38D.

[0049] Although the present invention has been described above based on four embodiments, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0050] 1, 1A~1D Rotating motor 2. Housing 3. Cylindrical section 4,5 End bracket 4a, 5a through hole 4b, 5b Bearing holder 4c, 5c Oil supply hole 6, 7 Outlet 10 Stator 11 Stator core 12 Teeth 13 Back Yoke 14 Coil 15 Bobbin 20 Coil end (front side) 22 Coil end (rear side) 23, 23A leader line 24, 26, 27 Resin 24a, 26a, 26b, 27a Tapered section 28, 28D Gap 30, 30A~30D rotor 31, 31D rotor core 32 Slots 33, 33D Permanent magnet 35, 35B, 35C end plate 36 Protrusion 38, 38A~38C end plate 39, 39A~39C protrusion 40 Rotational Axis 41, 42 Bearings 46 Wiring board 51 First cooling path 52, 53 Cooling oil supply port (second cooling path) 54, 55 Third cooling path 56, 57 Piping connection (fourth cooling path) 71~82 Cooling oil (refrigerant) 91, 92 Injection center point 101, 101A Rotating Electric Machine 110 Stator 111 Stator core 120, 122 coil end 124, 126, 126C resin 128 Gap 130 Rotor 135, 138 end plate 191, 192 Injection center point 300, 300A mold tool 310, 310B core mold 320 upper mold 330 Outer diameter type 340 Lower mold 410 Stator 420, 422 coil end 424, 426 Resin Z rotation axis Zs Z coordinate of the innermost part of the coil end Zr Z coordinate of the outer surface of the rotor end plate

Claims

1. a rotor having a rotor core and fixed to the rotary shaft; a stator including a stator core and a coil, the stator core having a coil end portion formed on an outer side from an end portion in a rotation axis direction of the stator core, the stator being disposed on an outer circumferential side of the rotor with a gap therebetween; a cooling mechanism that injects a liquid refrigerant onto an axial end surface of the rotor, A rotating electric machine characterized in that the lengths of the stator and the rotor in the rotational axis direction are set so that the coordinates Zrf, Zrr of the end of the rotor as viewed in the rotational axis direction from the axial center position of the rotor and the coordinates Zsf, Zsr of the innermost part of the coil end portion as viewed in the rotational axis direction satisfy |Zsf|≦|Zrf| and |Zsr|≦|Zrr| at least at one point in the circumferential direction.

2. 2. The rotating electric machine according to claim 1, A rotating electric machine characterized in that an end plate is provided on the end face in the rotational axis direction of the rotor core, and a cylindrical protrusion protruding in the rotational axis direction is provided near the outer periphery of the end plate, and the tip coordinate of the protrusion as viewed in the rotational axis direction is Zr, thereby satisfying the relationships |Zsf|≦|Zrf| and |Zsr|≦|Zrr|.

3. 3. The rotating electric machine according to claim 2, A rotating electric machine, characterized in that an inclined portion is provided on an inner periphery of the protrusion so that the inner diameter expands linearly, curvedly, or in a stepped manner toward the outer diameter side.

4. 3. The rotating electric machine according to claim 2, A rotating electric machine characterized in that the shapes of the protrusions on the output side and the anti-output side are formed to be different in accordance with the difference in shape between the output side and the anti-output side of the coil end portion of the stator.

5. A rotating electric machine according to any one of claims 2 to 4, The rotor comprises a permanent magnet held in the rotor core, and the permanent magnet is arranged in the rotor core so that a radius Rm of an innermost portion of the permanent magnet and a radius Rt of an innermost portion of the protrusion satisfy Rm < Rt.

6. 2. The rotating electric machine according to claim 1, a length of said rotor core in the axial direction of said rotational axis being greater than a length of said stator core in the axial direction of said rotational axis of said rotating electric machine;

7. A rotating electric machine according to any one of claims 1 to 4, The coil end portion includes a coil end and a resin that molds the coil end, A rotating electric machine characterized in that a tapered portion whose inner diameter expands from the stator core toward the tip side of the coil end is formed on the inner surface of the resin, and the apex where the inner diameter of the tapered portion is the smallest is formed of Zr.

8. A rotating electric machine according to claim 7, a tapered portion provided between wires drawn from the coils;

9. A rotation axis; a rotor having a cylindrical rotor core fixed to the rotating shaft, a plurality of permanent magnets disposed within the rotor core, and an end plate provided on an end surface of the rotor core in a rotation axis direction; a stator including a stator core and a coil, the stator core having a coil end portion formed on an outer side from an end portion in a rotation axis direction of the stator core; A rotating electric machine having a cooling mechanism that injects a liquid refrigerant onto the end plate of the rotor core, A rotating electric machine characterized in that a circumferentially continuous cylindrical protrusion is formed on the outer periphery of the end plate, which is radially outward of the center point of injection of the liquid refrigerant onto the end plate, for guiding the injected liquid refrigerant away from the end plate toward the outside in the direction of the rotation axis.

10. 10. A rotating electric machine according to claim 9, A rotating electric machine characterized in that the positions of the stator and the protrusion in the rotational axis direction are set so that the coordinate Zr of the end of the protrusion of the rotor when viewed from the axial center position of the rotor along the rotational axis and the coordinate Zs in the rotational axis direction of the innermost portion of the coil end portion satisfy |Zs|≦|Zr|.

11. A rotating electric machine according to claim 10, A rotating electric machine, characterized in that an inner peripheral surface of the protrusion is provided with an inclined portion so that the inner diameter expands linearly, curvedly, or stepped toward the outer diameter side.

12. A rotating electric machine according to claim 10, A rotating electric machine characterized in that the shape of the end plate of the rotor is made different on the output side and the anti-output side in accordance with the difference in shape between the output side and the anti-output side of the coil end portion of the stator.

13. A rotating electric machine according to any one of claims 9 to 12, The rotor comprises a permanent magnet held in the rotor core, and the permanent magnet is arranged in the rotor core so that a radius Rm of an innermost portion of the permanent magnet and a radius Rt of an innermost portion of the protrusion satisfy Rm < Rt.

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