Rotor sleeve and rotor

Abstract

The rotor sleeve includes a through-hole into which a shaft is fitted. The shaft comprises a small-diameter section and a large-diameter section, which have different outer diameters and are arranged side by side along one axis. The through-hole includes: a small-diameter section and a large-diameter section, spaced apart along the axis, into which the small-diameter section and the large-diameter section are each firmly fitted; and an intermediate section located between the small-diameter section and the large-diameter section.The small-diameter hole section and the large-diameter hole section each include a groove in an inner surface, extending from an intermediate position along the axis to the intermediate hole section. The rotor sleeve includes an oil pressure supply hole formed in an inner surface of the intermediate hole section or in an inner surface of the groove.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a rotor sleeve and a rotor. STATE OF THE ART

[0002] A rotor having a shaft with a stepped portion and a sleeve fitted onto the shaft is known (see, for example, PTL 1). The sleeve has a recess arranged to cover the stepped portion and has an oil pressure supply hole communicating with the cavity.

[0003] When assembling the rotor, the sleeve is shrunk onto the shaft. This secures the sleeve and shaft together with high contact pressure on both sides of the cavity in the direction of the axis. When disassembling the rotor, oil pressure is supplied to the inside of the recess via the oil pressure supply hole to expand the sleeve through elastic deformation in the radial direction. The sleeve is then removed from the shaft in the direction of the axis by the force exerted on the stepped portion of the shaft. LITERATURE LISTPATENT LITERATURE

[0004] PTL 1 Japanese Unexamined Patent Application, Publication No. S62-98444 SUMMARY OF THE INVENTION TECHNICAL TASK

[0005] When the rigidity of the sleeve is low, such as when the thickness and weight of the sleeve have been reduced, the sleeve will be deformed into a barrel shape when oil pressure is applied to the recess. Specifically, the amount of deformation at both ends of the sleeve in the axis direction is small, and the contact pressure between the sleeve and the shaft on both sides of the recess in the axis direction cannot be sufficiently reduced. Therefore, it is desirable to make it easier to remove the shaft from the sleeve, even when the rigidity of the sleeve is low. SOLUTION TO THE TASK

[0006] One aspect of the present disclosure is a rotor sleeve comprising a through hole into which a shaft is fitted, including a small-diameter shaft portion and a large-diameter shaft portion that have different outer diameters and are arranged side by side in a direction of an axis. The through hole includes: a small-diameter hole portion and a large-diameter hole portion that are spaced apart from each other in the direction of the axis, and into which the small-diameter shaft portion and the large-diameter shaft portion are respectively tightly fitted; and an intermediate hole portion disposed between the small-diameter hole portion and the large-diameter hole portion.The small-diameter hole portion and the large-diameter hole portion each include a groove in an inner surface thereof, extending from an intermediate position thereof in the axis direction to the intermediate hole portion. The rotor sleeve includes an oil pressure supply hole formed in an inner surface of the intermediate hole portion or an inner surface of the groove. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical sectional view of a rotor according to an embodiment of the present disclosure. Fig. 2 is a vertical sectional view of a sleeve according to the first embodiment of the present disclosure, which includes the rotor in Fig. 1 forms. Fig. 3 is a vertical sectional view for explaining the function of the rotor in Fig. 1 and the sleeve in Fig. 2. Fig. 4 is a front view of a main shaft supporting the rotor in Fig. 1 forms. Fig. Fig. 5 is a vertical sectional view showing a first modification of the sleeve in Fig. 2 shows. Fig. Fig. 6 is a vertical sectional view showing a second modification of the sleeve in Fig. 2 shows. Fig. Fig. 7 is a vertical sectional view showing a third modification of the sleeve in Fig. 2 shows. Fig. 8 is a vertical sectional view of a rotor according to a second embodiment of the present disclosure. Fig. 9 is a vertical sectional view showing a modification of the rotor in Fig. 8 shows. DESCRIPTION OF EMBODIMENTS

[0007] Hereinafter, a sleeve 4 and a rotor 1 according to a first embodiment of the present disclosure will be described with reference to the drawings.

[0008] The rotor 1 according to this embodiment is, for example, a rotor for a built-in motor in which a stator is incorporated in an industrial machine. As shown in Fig. 1, the rotor 1 comprises a main shaft (shaft) 2 and a cylindrical sleeve (rotor sleeve) 4 having a through hole 3 into which the main shaft 2 is fitted.

[0009] As in Fig. 1 and Fig. 4, the main shaft 2 comprises a small-diameter shaft portion 5 and a large-diameter shaft portion 6, which are arranged side by side in the direction of an axis O. The main shaft 2 comprises a bearing surface 7 against which an end face of the sleeve 4 on the side of the large-diameter shaft portion 6 bears in the direction of an axis.

[0010] The small-diameter shaft section 5 and the large-diameter shaft section 6 are each a smooth cylindrical surface, and the large-diameter shaft section 6 has a larger outer diameter than the small-diameter shaft section 5. Between the small-diameter shaft section 5 and the large-diameter shaft section 6, a step 8 is formed with a height corresponding to the difference in outer diameter (radius) between the small-diameter shaft section 5 and the large-diameter shaft section 6.

[0011] An iron core 9 is shrunk onto the outer surface of the sleeve 4. Side rings 10 are fixed to both ends of the iron core 9 in the direction of the axis O. The side rings 10 have a larger outer diameter than the iron core 9 to protect the inner surface of the stator so that the iron core 9 does not touch the inner surface of the stator when the rotor 1 is inserted into the stator. The side rings 10 have a plurality of screw holes (not shown) for fixing weights for balancing the rotor 1.

[0012] The side rings 10 are made of a non-magnetic material to block a magnetic path from the iron core 9. Since the linear expansion coefficient of a non-magnetic material is typically larger than that of a magnetic material forming the iron core 9, the side rings 10 are fixed by shrinking onto the outer surface of the sleeve 4 with an interference larger than that of the iron core 9.

[0013] The through-hole 3 in the sleeve 4 has, at one end thereof in the direction of the axis O, a large-diameter hole portion 11 into which the large-diameter shaft portion 6 of the main shaft 2 is to be tightly fitted. The through-hole 3 in the sleeve 4 also has, at its other end in the direction of the axis O, a small-diameter hole portion 12 into which the small-diameter shaft portion 5 of the main shaft 2 is to be tightly fitted. In this embodiment, the small-diameter hole portion 12 and the large-diameter hole portion 11 have substantially the same length in the direction of the axis O.

[0014] The through hole 3 in the sleeve 4 also has an intermediate hole portion 13 at a position between the small-diameter hole portion 12 and the large-diameter hole portion 11 in the direction of the axis O. In this embodiment, the intermediate hole portion 13 has a longer length in the direction of the axis O than the small-diameter hole portion 12 and the large-diameter hole portion 11, and a larger inner diameter than the large-diameter hole portion 11. An oil pressure supply hole 14 for supplying oil pressure from the outside is formed in the inner surface of the intermediate hole portion 13.

[0015] In this embodiment, as shown in Fig. 2, a spiral groove (groove) 15 is formed in the inner surface of each of the small-diameter hole portion 12 and the large-diameter hole portion 11 of the sleeve 4. The spiral groove 15 extends from an intermediate position of each of the small-diameter hole portion 12 and the large-diameter hole portion 11 in the direction of the axis O to a boundary position with the intermediate hole portion 13 and is continuous with the intermediate hole portion 13.

[0016] In the Fig. In the example shown in Figure 2, the spiral grooves 15 have a predetermined groove width, a predetermined pitch, and several turns along the direction of the axis O. The winding direction of the spiral grooves 15 can be arbitrary.

[0017] The width, pitch, and number of turns of the spiral grooves 15 are appropriately determined based on the magnitude of the radial force achieved by the applied oil pressure. The radial force achieved by the oil pressure can be increased by increasing the width, decreasing the pitch, and increasing the number of turns of the spiral grooves 15. This, in turn, reduces the contact area between the small-diameter hole portion 12 and the small-diameter shaft portion 5 and the contact area between the large-diameter hole portion 11 and the large-diameter shaft portion 6, thereby reducing the frictional force therebetween.

[0018] The width, pitch and number of turns of the spiral grooves 15 are therefore set to appropriate values ​​based on the relationship between the friction force and the magnitude of the radial force achieved by the oil pressure.

[0019] The function of the sleeve 4 and rotor 1 designed in this embodiment will be described below. To assemble the rotor 1 according to this embodiment, the iron core and the side rings 10 are preliminarily shrunk onto the outer surface of the sleeve 4.

[0020] Then the main shaft 2 is inserted into the through hole 3 in the sleeve 4 by shrinking from the left side to the right side in Fig. 1 relative to the assembly of the sleeve 4, the iron core 9, and the side rings 10. The main shaft 2 and the sleeve 4 can be positioned relative to each other in the direction of the axis O by the abutment surface 7 of the main shaft 2 abutting the end face of the sleeve 4 on the side of the large-diameter hole portion 11.

[0021] In this state, the small-diameter shaft portion 5 of the main shaft 2 is tightly fitted into the small-diameter hole portion 12 of the sleeve 4, and the large-diameter shaft portion 6 of the main shaft 2 is tightly fitted into the large-diameter hole portion 11 of the sleeve 4. Thus, the main shaft 2 and the sleeve 4 are fixed to each other. This defines a sealed space between the main shaft 2 and the sleeve 4.

[0022] At the position of the intermediate hole portion 13, a cylindrical first space A is defined between the intermediate hole portion 13 and the outer surface of the main shaft 2 facing the intermediate hole portion 13 in the radial direction. At the positions of the small-diameter hole portion 12 and the large-diameter hole portion 11, spiral-shaped second spaces B, each with one end as a dead end, are defined between the spiral grooves 15 and the outer surface of the main shaft 2 facing the spiral grooves 15. The spiral-shaped second spaces B each open into the first space A at their other ends.

[0023] To disassemble the rotor 1, high oil pressure is supplied to the first space A via the oil pressure supply hole 14. The oil pressure supplied to the first space A is also supplied to the spiral-shaped second spaces B, which are continuous with the first space A.

[0024] In the first room A, as indicated by arrows in Fig. 3, the oil pressure exerts a force to expand the sleeve 4 in the radial direction. As indicated by arrows, an axial force proportional to the cross-sectional area difference between the large-diameter shaft section 6 and the small-diameter shaft section 5 acts on the step 8 provided in the main shaft 2.

[0025] Furthermore, in this embodiment, by supplying the oil pressure from the first space A to the spiral second spaces B, the sleeve 4 is also expanded in the radial direction at the small diameter hole portion 12 and the large diameter hole portion 11 as indicated by arrows.

[0026] As a result, the contact pressure between the small-diameter shaft portion 5 and the small-diameter hole portion 12 and the contact pressure between the large-diameter shaft portion 6 and the large-diameter hole portion 11 decrease, which makes it possible to easily remove the main shaft 2 from the sleeve 4 with the axial force generated by the oil pressure.

[0027] In this case, since the intermediate hole portion 13 is longer in the direction of the axis O than the small diameter hole portion 12 and the large diameter hole portion 11, even a low oil pressure can generate a large force for expanding the sleeve 4 in the radial direction at the central portion of the sleeve 4 in the direction of the axis O.

[0028] Meanwhile, the side rings 10 are fitted at both ends of the sleeve 4 in the axis O direction with a large interference. Therefore, their expansion in the radial direction due to oil pressure is suppressed compared to that of the central portion in the axis O direction. Therefore, especially when the thickness and weight of the sleeve 4 are reduced, the sleeve 4 tends to elastically deform into a so-called barrel shape, which is large in the center in the axis O direction and small at both ends, when oil pressure is applied.

[0029] According to this embodiment, by providing the spiral grooves 15 in the inner surfaces of the small-diameter hole portion 12 and the large-diameter hole portion 11, it is possible to generate a force for expanding the sleeve 4 in the radial direction also at both ends in the direction of the axis O. Thus, the contact pressure between the small-diameter hole portion 12 and the small-diameter shaft portion 5 and between the large-diameter hole portion 11 and the large-diameter shaft portion 6 can be easily reduced.

[0030] In other words, there is an advantage that even if the thickness and weight of the sleeve 4 have been reduced, it is possible to alleviate the elastic deformation into a barrel shape due to the supply of oil pressure and to easily remove the main shaft 2 from the sleeve 4.

[0031] Therefore, with the sleeve 4 and the rotor 1 according to this embodiment, the thickness and weight of the sleeve 4 can be reduced, thereby enabling a reduction in the weight and cost of the rotor 1 and the motor and an increase in the diameter and rigidity of the main shaft 2.

[0032] Furthermore, in the sleeve 4 and the rotor 1 according to this embodiment, since the spiral grooves 15 are formed in the inner surfaces of the small-diameter hole portion 12 and the large-diameter hole portion 11, there is no need to machine grooves in the outer surface of the main shaft 2. With an assembled motor, a user prepares the main shaft 2. Therefore, eliminating the need to machine grooves in the outer surface of the main shaft 2 saves the user the trouble of performing special machining, which is advantageous.

[0033] Furthermore, according to this embodiment, the inner diameter of the intermediate hole portion 13 is set larger than that of the large-diameter hole portion 11. Thus, it is only necessary to prepare a main shaft 2 with a simple shape that has two cylindrical surfaces of different diameters, namely a small-diameter smooth shaft portion 5 and a large-diameter smooth shaft portion 6. This also eliminates the need for the user to perform special machining on the main shaft 2.

[0034] Furthermore, by making the inner diameter of the intermediate hole portion 13 larger than the inner diameter of the small-diameter hole portion 12, the small-diameter shaft portion 5 can be fitted into the small-diameter hole portion 12 without contacting the inner surface of the intermediate hole portion 13 when the main shaft 2 is inserted into the through hole 3 in the sleeve 4. Thus, the insertion of the main shaft 2 into the sleeve 4 is easy.

[0035] In the sleeve 4 and the rotor 1 according to this embodiment, the intermediate hole portion 13 is formed to have a longer length in the axis O direction than the small-diameter hole portion 12 and the large-diameter hole portion 11. There is a gap between the intermediate hole portion 13 and the outer surface of the main shaft 2 in the radial direction, and the main shaft 2 and the sleeve 4 do not fit together. Therefore, the requirements for surface roughness and surface accuracy are low.

[0036] Only the small-diameter hole portion 12 and the large-diameter hole portion 11 located at the ends of the sleeve 4 in the direction of the axis O, and the small-diameter shaft portion 5 and the large-diameter shaft portion 6 fitted therein require precise machining. Therefore, in the sleeve 4, the area requiring precise machining is not the entire length of the sleeve 4, but a limited portion in the direction of the axis O. This is advantageous in that machining costs can be reduced.

[0037] In addition, there is no need for precise machining of the entire area of ​​the small-diameter shaft portion 5 and the large-diameter shaft portion 6 in the main shaft 2. As shown in Fig. As shown in the hatched section in Figure 4, precise machining is required only in the area to be fitted into the small-diameter hole portion 12 and the large-diameter hole portion 11. This also saves effort for the user.

[0038] In this embodiment, the spiral grooves 15 formed in the small-diameter hole portion 12 and the large-diameter hole portion 11 wind around the axis O several times at a predetermined pitch. The spiral grooves 15 are grooves distributed in the circumferential direction in the small-diameter hole portion 12 and the large-diameter hole portion 11.

[0039] This allows the radial force generated by the oil pressure to be distributed substantially evenly in the direction of the O axis and the circumferential direction of the small-diameter hole portion 12 and the large-diameter hole portion 11. Thus, the small-diameter hole portion 12 and the large-diameter hole portion 11 can be expanded evenly in the circumferential direction to evenly reduce the contact pressure.

[0040] In the sleeve 4 and the rotor 1 according to this embodiment, the spiral grooves 15 are provided in the small-diameter hole portion 12 and the large-diameter hole portion 11. Instead, as shown in Fig. 5, a plurality of circumferential grooves 16 extending annularly in the circumferential direction may be provided at intervals along the axis O, and linear connecting grooves 17 extending along the axis O may be provided at any position along the circumferential direction. The connecting grooves 17 connect the plurality of circumferential grooves 16 to the intermediate hole portion 13.

[0041] Even with this structure, the circumferential grooves 16 are distributed along the axis O and the circumferential direction, allowing the oil pressure supplied to the first space A to be supplied to the circumferential grooves 16 via the connecting grooves 17. The annular circumferential grooves 16 and the linear connecting grooves 17 can be machined more easily than the spiral grooves 15.

[0042] In addition, as in Fig. 6, a plurality of linear grooves (grooves) 18 extending linearly in the direction of the axis O may be arranged at intervals in the circumferential direction. The linear grooves 18 extend from an intermediate position of each of the small-diameter hole portion 12 and the large-diameter hole portion 11 in the direction of the axis O to the boundary with the intermediate hole portion 13 and are continuous with the intermediate hole portion 13.

[0043] Even with this structure, the linear grooves 16 are distributed circumferentially, allowing the oil pressure supplied to the first space A to be supplied to the linear grooves 16. The linear grooves 16 can be machined more easily than the spiral grooves 15.

[0044] Furthermore, the plurality of linear grooves 18 formed at intervals in the circumferential direction may be wound around the axis O, as shown in Fig. 7 is shown.

[0045] In this embodiment, the intermediate hole portion 13 is formed to have a larger inner diameter than the large-diameter hole portion 11. However, the inner diameter of the intermediate hole portion 13 may be the same as that of the large-diameter hole portion 11, or may be larger than that of the small-diameter hole portion 12 and smaller than or equal to that of the large-diameter hole portion 11. If the inner diameter of the intermediate hole portion 13 is larger than that of the small-diameter hole portion 12, an axial force can be generated by the oil pressure. This facilitates the insertion of the main shaft 2 into the sleeve 4.

[0046] In this embodiment, the dimension of the intermediate hole portion 13 in the axis O direction is set larger than the dimension of the small diameter hole portion 12 and the large diameter hole portion 11 in the axis O direction. Instead, the dimension of the intermediate hole portion 13 in the axis O direction may be smaller than or equal to the dimension of the small diameter hole portion 12 and the large diameter hole portion 11 in the axis O direction.

[0047] Next, a rotor 20 according to a second embodiment of the present disclosure will be described below with reference to the drawings.

[0048] In the description of this Embodiment 1, the same reference numerals denote the same components as those of the rotor 1 according to the first embodiment described above, and their description is omitted.

[0049] As in Fig. 8, the rotor 20 according to this embodiment differs from the rotor 1 according to the first embodiment in that the spiral grooves 15 are not provided in the sleeve 4, but are formed in the small diameter shaft portion 5 and the large diameter shaft portion 6 of the main shaft 2.

[0050] One spiral groove 15 extends from an intermediate position in the direction of the axis O of the small-diameter shaft portion 5 facing the small-diameter hole portion 12 to a position beyond the boundary between the small-diameter hole portion 12 and the intermediate hole portion 13. The other spiral groove 15 extends from an intermediate position in the direction of the axis O of the large-diameter shaft portion 6 facing the large-diameter hole portion 11 to the boundary between the large-diameter hole portion 11 and the intermediate hole portion 13.

[0051] Also with this structure, when oil pressure is supplied to the first space A, the oil pressure is also supplied to the second spaces B in a spiral shape from the first space A. Therefore, a force for expanding the sleeve 4 in the radial direction can be generated not only in the intermediate hole portion 13 but also in the small-diameter hole portion 12 and the large-diameter hole portion 11.

[0052] In addition, instead of the spiral grooves 15, circumferential grooves 16 and connecting grooves 17 similar to those in Fig. 5 or linear grooves 18 similar to those in Fig. 6 may be formed in the small diameter shaft portion 5 and the large diameter shaft portion 6 of the main shaft 2.

[0053] In addition, as in Fig.9, a plurality of annular circumferential grooves 16 may be provided in the inner surfaces of the small-diameter hole portion 12 and the large-diameter hole portion 11, and linear connecting grooves 17 may be provided in the outer surface of the main shaft 2. Conversely, a plurality of annular circumferential grooves 16 may be provided in the outer surfaces of the small-diameter shaft portion 5 and the large-diameter shaft portion 6, and linear connecting grooves 17 may be provided in the inner surfaces of the small-diameter hole portion 12 and the large-diameter hole portion 11.

[0054] Furthermore, at least the spiral grooves 15, the circumferential grooves 16, the connecting grooves 17, and / or the linear grooves 18 may be provided in the small-diameter hole portion 12, the small-diameter shaft portion 5, the large-diameter hole portion 11, and the large-diameter shaft portion 6. In this embodiment, the oil pressure supply hole 14 is formed in the intermediate hole portion 13. Instead, the oil pressure supply hole 14 may be formed in any of the spiral grooves 15, the circumferential grooves 16, the connecting grooves 17, and the linear grooves 18 provided in the small-diameter hole portion 12 and the large-diameter hole portion 11.

[0055] Although the embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the above-described embodiments. Various additions, replacements, changes, partial deletions, and the like may be made to these embodiments without departing from the gist of the disclosure or without deviating from the spirit and essence of the present disclosure, which are derived from the contents described in the claims and their equivalents. For example, in the above-described embodiments, the order of operations and the order of processes shown as examples are not exhaustive. The same applies to the case where numerical values ​​or mathematical expressions are used in the description of the above-described embodiments. LIST OF REFERENCE SYMBOLS 1.20 rotor 2 Main shaft (shaft) 3 through holes 4 Sleeve (rotor sleeve) 5 Small diameter shaft section 6 Large diameter shaft section 11 Large diameter hole section 12 small diameter hole section 13 Intermediate hole section 14 Oil pressure supply hole 15 Spiral groove (groove) 16 circumferential groove 17 Connecting groove 18 Linear groove (groove) O axis QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 62-98444

[0004]

Claims

[1] Rotor sleeve, comprising: a through hole into which a shaft is fitted, comprising a small-diameter shaft portion and a large-diameter shaft portion having different outer diameters and arranged side by side in a direction of an axis, wherein the through hole comprises: a small-diameter hole portion and a large-diameter hole portion, which are spaced apart from each other in the direction of the axis and into which the small-diameter shaft portion and the large-diameter shaft portion are respectively tightly fitted; and an intermediate hole portion disposed between the small-diameter hole portion and the large-diameter hole portion, the small-diameter hole portion and the large-diameter hole portion each comprise in an inner surface thereof a groove extending from an intermediate position thereof in the direction of the axis to the intermediate hole portion, and the rotor sleeve has an oil pressure supply hole formed in an inner surface of the intermediate hole portion or an inner surface of the groove. [2] The rotor sleeve according to claim 1, wherein the intermediate hole portion has a longer length in the axis direction than the small diameter hole portion and the large diameter hole portion and a larger inner diameter than the small diameter hole portion. [3] The rotor sleeve according to claim 1 or 2, wherein the groove is distributed in a circumferential direction of the inner surface of each of the small diameter hole portion and the large diameter hole portion. [4] Rotor sleeve according to one of claims 1 to 3, wherein the groove is a spiral groove. [5] Rotor sleeve according to one of claims 1 to 3, wherein the groove comprises one or more circumferential grooves formed annularly over an entire circumference and a connecting groove connecting the circumferential grooves and the intermediate hole portion. [6] A rotor sleeve according to any one of claims 1 to 3, wherein the groove comprises a plurality of grooves provided at intervals in a circumferential direction. [7] Rotor, comprising: a shaft in which a small-diameter shaft section and a large-diameter shaft section with different outer diameters are arranged side by side in a direction of an axis; and a rotor sleeve comprising a through hole into which the shaft is fitted, wherein the through hole comprises: a small-diameter hole portion and a large-diameter hole portion, which are spaced apart from each other in the direction of the axis and into which the small-diameter shaft portion and the large-diameter shaft portion are respectively tightly fitted; and an intermediate hole portion disposed between the small-diameter hole portion and the large-diameter hole portion, at least inner surfaces of the small-diameter hole portion and the large-diameter hole portion and / or outer surfaces of the small-diameter shaft portion at a position to be fitted into the small-diameter hole portion and the large-diameter shaft portion at a position to be fitted into the large-diameter hole portion each comprise a groove extending from an intermediate position of each of the small-diameter hole portion and the large-diameter hole portion in the direction of the axis to the intermediate hole portion, and the rotor includes an oil pressure supply hole formed in an inner surface of the intermediate hole portion, the groove, or an outer surface of the shaft facing the intermediate hole portion in a radial direction. [8] A rotor according to claim 7, wherein the intermediate hole portion has a longer length in the axis direction than the small diameter hole portion and a larger inner diameter than the small diameter hole portion. [9] A rotor according to claim 7 or 8, wherein the groove is distributed in a circumferential direction of the inner surface of each of the small diameter hole portion and the large diameter hole portion. [10] A rotor according to any one of claims 7 to 9, wherein the groove is a spiral groove. [11] A rotor according to any one of claims 7 to 9, wherein the groove comprises one or more circumferential grooves formed in an annular manner over an entire circumference and a connecting groove connecting the circumferential grooves and the intermediate hole portion. [12] A rotor according to any one of claims 7 to 9, wherein the groove comprises a plurality of grooves provided at intervals in a circumferential direction.

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