Rotor

Abstract

A rotor according to the present invention comprises a shaft part and a surrounding part. A recess is provided in the outer circumferential surface of the surrounding part. The recess wall surface extends linearly between one end and the other end in the circumferential direction. The recess wall surface also extends linearly between one end and the other end in the rotation axis direction.

Description

rotor

[0001] The present disclosure relates to a rotor rotatable about an axis of rotation.

[0002] For example, there is a rotor that is provided in a device such as a turbocharger and rotates about a rotation axis. In such a rotor, a portion of the outer circumferential surface of the rotor is removed in order to adjust the rotational balance. Such a method of removing a portion of the outer circumferential surface of the rotor in order to adjust the rotational balance is described, for example, in Patent Document 1.

[0003] International Publication No. 2021 / 095118

[0004] As described above, when the outer peripheral surface of the rotor is scraped away to adjust the rotational balance, a recess is formed on the outer peripheral surface of the rotor. If such a recess has corners, stress concentration occurs at the corners when the rotor rotates, increasing the stress in the recess. If the stress in the recess becomes too high, deformation or other problems may occur in the area where the recess is provided.

[0005] Therefore, the present disclosure describes a rotor that can adjust the rotational balance by using the recesses while suppressing the concentration of stress in the recesses.

[0006] A rotor according to one aspect of the present disclosure comprises a shaft portion rotatable around a rotation axis and an enclosing portion surrounding the outer surface of the shaft portion, wherein a recess is provided on the outer surface of the enclosing portion, wherein one circumferential end of the recess wall surface forming the recess is continuous with the outer surface of the enclosing portion, and the other circumferential end of the recess wall surface is continuous with the outer surface of the enclosing portion, the recess wall surface extends in a straight line between the one circumferential end and the other end, one end of the recess wall surface in the direction of the rotation axis is continuous with one end face of the enclosing portion in the direction of the rotation axis, and the other end of the recess wall surface in the direction of the rotation axis is continuous with the outer surface of the enclosing portion, and the recess wall surface extends in a straight line between the one end and the other end in the direction of the rotation axis.

[0007] According to various aspects of the present disclosure, it is possible to adjust the rotational balance by using the recess while suppressing the concentration of stress on the recess.

[0008] Fig. 1 is a cross-sectional view showing a schematic configuration of an electric motor including a rotor according to a first embodiment. Fig. 2 is a cross-sectional view showing the configuration of a shaft portion at room temperature. Fig. 3 is a front view of the rotor of Fig. 1. Fig. 4 is a side view of the rotor of Fig. 1, seen from the end on the side where a recess is provided. Fig. 5 is a top view showing the periphery of the recess of the rotor of Fig. 1. Fig. 6 is a front view of a rotor according to a second embodiment. Fig. 7 is a side view of the rotor of Fig. 6, seen from the end on the side where the recess is provided.

[0009] A rotor according to one aspect of the present disclosure comprises a shaft portion rotatable around a rotation axis and an enclosing portion surrounding the outer surface of the shaft portion, wherein a recess is provided on the outer surface of the enclosing portion, wherein one circumferential end of the recess wall surface forming the recess is continuous with the outer surface of the enclosing portion, and the other circumferential end of the recess wall surface is continuous with the outer surface of the enclosing portion, the recess wall surface extends in a straight line between the one circumferential end and the other end, one end of the recess wall surface in the direction of the rotation axis is continuous with one end face of the enclosing portion in the direction of the rotation axis, and the other end of the recess wall surface in the direction of the rotation axis is continuous with the outer surface of the enclosing portion, and the recess wall surface extends in a straight line between the one end and the other end in the direction of the rotation axis.

[0010] In this rotor, the recess wall surface forming the recess extends linearly between one end and the other end in the circumferential direction. The recess wall surface also extends linearly between one end and the other end in the rotation axis direction. That is, the recess has a shape formed by removing a portion of the outer periphery of the surrounding portion. The recess wall surface is also flat and has no corners. Therefore, in a rotor with this recess, stress concentration in the recess is suppressed even when the rotor rotates. In this way, the rotor can adjust the rotational balance by using the recess while suppressing stress concentration in the recess.

[0011] A rotor according to another aspect of the present disclosure comprises a shaft portion rotatable about a rotation axis and an enclosing portion surrounding the outer surface of the shaft portion, wherein a recess is provided on the outer surface of the enclosing portion, and wherein one circumferential end of the recess wall surface forming the recess is continuous with the outer surface of the enclosing portion and the other circumferential end of the recess wall surface is continuous with the outer surface of the enclosing portion, the recess wall surface is convexly curved radially outward between the one circumferential end and the other end, one end of the recess wall surface in the direction of the rotation axis is continuous with one end face of the enclosing portion in the direction of the rotation axis, and the other end of the recess wall surface in the direction of the rotation axis is continuous with the outer surface of the enclosing portion, and the recess wall surface extends linearly between the one end and the other end in the direction of the rotation axis.

[0012] In this rotor, the recess wall surface forming the recess is convexly curved radially outward between one end and the other end in the circumferential direction. The recess wall surface extends linearly between one end and the other end in the rotation axis direction. In other words, the recess has a shape formed by removing a portion of the outer periphery of the surrounding portion. The recess wall surface does not have corners. Therefore, in a rotor with this recess, stress concentration in the recess is suppressed even when the rotor rotates. In this way, the rotor can adjust the rotational balance by using the recess while suppressing stress concentration in the recess.

[0013] In the rotor described above, the maximum length of the recess in the direction of the rotation axis may be longer than the maximum depth of the recess in the radial direction perpendicular to the rotation axis. In this case, even when a large-volume recess is provided in the rotor, the thickness of the surrounding portion can be prevented from becoming thin. This prevents the strength of the surrounding portion from decreasing.

[0014] In the rotor described above, the shaft portion may include a shaft body rotatable about a rotation axis and a magnet, the surrounding portion may include a cylindrical armor ring that covers the shaft portion, and the outer peripheral surface of the surrounding portion may be formed by the outer peripheral surface of the armor ring. In this case, the rotor can be used as a motor rotor for an electric motor. Furthermore, even if the rotor is a motor rotor that rotates at high speed, the rotational balance can be adjusted by the recesses while suppressing stress concentration in the recesses for adjusting the balance.

[0015] In the rotor described above, the armour may be press-fitted onto the outer circumferential surface of the shaft portion, in which case the magnets can be easily held in the rotor by the armour.

[0016] Hereinafter, an embodiment in which a rotor according to the present disclosure is applied to an electric motor will be described with reference to the drawings. In each drawing, the same or corresponding elements are denoted by the same reference numerals, and redundant description will be omitted.

[0017] (First embodiment) A first embodiment of a rotor will be described. An electric motor 100 shown in FIG. 1 functions as a drive source for various electric motors. For example, the electric motor 100 may be used as a drive source for driving the impeller of an electric turbocharger. The electric motor 100 includes a rotor 1 and a stator 3 arranged to surround the rotor 1. The rotor 1 includes a shaft portion 10 that is rotatable about a rotation axis L, and an armoring (enclosing portion) 20 that surrounds an outer circumferential surface 10a of the shaft portion 10. For example, an impeller of an electric turbocharger is attached to the shaft portion 10.

[0018] In the following description, the circumferential direction refers to the direction along a ring centered on the rotation axis L. The radial direction refers to the direction perpendicular to the rotation axis L. The rotation axis direction refers to the direction along the rotation axis L (the extension direction of the rotation axis L). Hereinafter, the circumferential direction will also be referred to as the "circumferential direction S" (see FIG. 4, etc.). The radial direction will also be referred to as the "radial direction K" (see FIG. 4, etc.). The rotation axis direction will also be referred to as the "rotation axis direction L1" (see FIG. 1, etc.).

[0019] The stator 3 includes a core 31 disposed to surround the rotor 1, and a coil 32 formed by winding a conductor around the core 31. The core 31 is cylindrical with the rotation axis L as its central axis. The rotor 1 is disposed inside the core 31. When an alternating current is supplied to the coil 32 of the stator 3, the stator 3 generates a rotating magnetic field inside the core 31. This rotating magnetic field generates torque in the rotor 1. As a result, the rotor 1 rotates around the rotation axis L.

[0020] The rotor 1 will now be described in detail. The shaft portion 10 of the rotor 1 includes a first shaft body (shaft body) 11, a second shaft body (shaft body) 12, and a magnet 13. The first shaft body 11, the second shaft body 12, and the magnet 13 are each rotatable around a rotation axis L. The magnet 13 is sandwiched between the first shaft body 11 and the second shaft body 12 in the rotation axis direction L1. The first shaft body 11, the second shaft body 12, and the magnet 13 each have a cylindrical shape with the rotation axis L as the central axis.

[0021] The armor ring 20 has a cylindrical (tubular) shape with the rotation axis L as its central axis. The shaft portion 10 passes through the inside of the armor ring 20. The armor ring 20 surrounds the magnet 13. The armor ring 20 also surrounds a portion of the first shaft body 11 and the magnet 13 in the rotation axis direction L1, straddling the connection portion between the first shaft body 11 and the magnet 13. The armor ring 20 also surrounds a portion of the second shaft body 12 and the magnet 13 in the rotation axis direction L1, straddling the connection portion between the second shaft body 12 and the magnet 13. The armor ring 20 holds the first shaft body 11, the second shaft body 12, and the magnet 13. The cylindrical armor ring 20 covers the shaft portion 10 while accommodating the magnet 13 inside.

[0022] The armor 20 is made of, for example, a metal material. The armor 20 is press-fitted onto the outer peripheral surface 10a of the shaft portion 10. Here, "press-fit" refers to the armor 20 being attached in a state where it presses against the outer peripheral surface 10a of the shaft portion 10. Furthermore, the temperature of the rotor 1 increases during operation of the electric motor 100. For example, the linear expansion coefficients of the first shaft body 11 and the second shaft body 12 and the magnet 13 may differ from each other. In this case, when the temperature of the rotor 1 increases, steps may occur in the radial direction at the connection portions between the first shaft body 11 and the magnet 13 and the connection portions between the second shaft body 12 and the magnet 13. If steps occur on the outer peripheral surface 10a of the shaft portion 10 during operation of the electric motor 100, differences in interference with the press-fit armor 20 may occur, and stress on the armor 20 may increase near the steps.

[0023] For this reason, as shown in FIG. 2 , in this embodiment, the radial size of the first shaft body 11 and the second shaft body 12 at room temperature is different from the radial size of the magnet 13 at room temperature. Here, the radial size of the first shaft body 11, the second shaft body 12, or the magnet 13, whichever has a higher linear expansion coefficient, is made smaller than the radial size of the other one with a lower linear expansion coefficient. In the example shown in FIG. 2 , the first shaft body 11 and the second shaft body 12 have a higher linear expansion coefficient than the magnet 13. Therefore, the radial size of the first shaft body 11 and the second shaft body 12 is smaller than the magnet 13. As a result, when the temperature of the shaft portion 10 rises during operation of the electric motor 100, the difference in radial size between the first shaft body 11 and the magnet 13 and the difference in radial size between the second shaft body 12 and the magnet 13 can be reduced.

[0024] Furthermore, for example, during operation of the electric motor 100, temperature differences may occur at various positions in the shaft portion 10 along the rotation axis L. In such a case, even if the linear expansion coefficients of the first shaft body 11, the second shaft body 12, and the magnet 13 are approximately the same, radial steps may occur at the connection between the first shaft body 11 and the magnet 13 and at the connection between the second shaft body 12 and the magnet 13. For this reason, as described above, even in this case, the radial sizes of the first shaft body 11 and the second shaft body 12 at room temperature may be different from the radial size of the magnet 13 at room temperature. In this case, the radial sizes of the first shaft body 11, the second shaft body 12, and the magnet 13, which are located in areas where the temperature is high during operation, are made smaller than the radial sizes of the members which are located in areas where the temperature is low.

[0025] As a result, even if a step occurs on the outer peripheral surface 10a of the shaft portion 10 at room temperature as shown in Figure 2, the step on the outer peripheral surface 10a of the shaft portion 10 becomes smaller when the electric motor 100 is in operation as shown in Figure 1. Therefore, when the electric motor 100 is in operation, the step on the outer peripheral surface 10a of the shaft portion 10 is suppressed, and an increase in stress on the armoring 20 can be suppressed.

[0026] Furthermore, a recess 21 is provided in the armor outer peripheral surface (surrounding portion outer peripheral surface) 20a, which is the outer peripheral surface of the armor 20. In this manner, the rotor 1 is provided with the armor 20 as a surrounding portion that surrounds the outer peripheral surface 10a of the shaft portion 10. The outer peripheral surface of the surrounding portion is formed by the armor outer peripheral surface 20a of the armor 20. A recess 21 is provided in the outer peripheral surface of the surrounding portion (armor outer peripheral surface 20a) formed by the armor 20.

[0027] The recess 21 will be described in detail below. As shown in Figures 3 to 5, the recess 21 is recessed from the armor outer peripheral surface 20a of the armor 20 toward the rotation axis L. The recess 21 has a recess wall surface 21a that is a wall surface that forms the recess 21. In this way, the outer diameter surface of the armor 20 includes the cylindrical armor outer peripheral surface 20a and the recess wall surface 21a that forms the recess 21. The outer diameter surface is the surface that faces outward in the radial direction K.

[0028] One end H11 of the recess wall surface 21a in the circumferential direction S is continuous with the armor outer peripheral surface 20a. Here, "the end H11 is continuous with the armor outer peripheral surface 20a" means that the end H11 is located at the position of the armor outer peripheral surface 20a. The same applies to other descriptions of "continuous." The other end H12 of the recess wall surface 21a in the circumferential direction S is continuous with the armor outer peripheral surface 20a. The recess wall surface 21a extends linearly between one end H11 and the other end H12 in the circumferential direction S.

[0029] One end H21 of the recess wall surface 21a in the rotational axis direction L1 is continuous with one end face 20b of the armoring 20 in the rotational axis direction L1. The other end H22 of the recess wall surface 21a in the rotational axis direction L1 is continuous with the armoring outer peripheral surface 20a. The recess wall surface 21a extends linearly between the one end H21 and the other end H22 in the rotational axis direction L1.

[0030] That is, the recess wall surface 21a is flat. In the radial direction K, the recess wall surface 21a is located closer to the rotation axis L than the cylindrical armoring outer peripheral surface 20a. Furthermore, the recess 21 is formed by the flat recess wall surface 21a. The recess 21 does not have a wall portion that rises radially outward from the recess wall surface 21a. Therefore, the recess 21 does not have a corner (recessed corner). In other words, in this embodiment, the recess 21 does not have a corner (recessed corner) in any direction along the recess wall surface 21a. A corner is a concave corner formed when two surfaces face inward. Furthermore, the recess wall surface 21a does not have a corner in either the circumferential direction S or the rotation axis direction L1.

[0031] 3 , the maximum length A1 of the recess 21 in the rotational axis direction L1 is longer than the maximum depth A2 of the recess 21 in the radial direction K. For example, the recess 21 may be formed by a method such as machining the outer circumferential surface 20 a of the armor 20. The recess 21 is provided to achieve rotational balance of the rotor 1. The position in the circumferential direction S where the recess 21 is provided and the size (volume) thereof are appropriately adjusted so that the rotational balance of the rotor 1 can be achieved.

[0032] As described above, in this rotor 1, the recess wall surface 21a forming the recess 21 extends linearly between one end H11 and the other end H12 in the circumferential direction S. Furthermore, the recess wall surface 21a also extends linearly between one end H21 and the other end H22 in the rotational axis direction L1. In other words, the recess 21 has a shape formed by scraping away a portion of the outer periphery of the armoring 20. Furthermore, the recess wall surface 21a is flat and has no corners. Therefore, in the rotor 1 having this recess 21, stress concentration in the recess 21 is suppressed even when the rotor 1 rotates. In this way, the rotor 1 can adjust the rotational balance using the recess 21 while suppressing stress concentration in the recess 21.

[0033] The maximum length A1 of the recess 21 in the rotational axis direction L1 is longer than the maximum depth A2 of the recess 21 in the radial direction K. In this case, even when the rotor 1 is provided with a recess 21 having a large volume, it is possible to prevent the thickness of the armor 20 from becoming thin. As a result, it is possible to prevent the strength of the armor 20 from decreasing.

[0034] The shaft portion 10 includes a magnet 13. The armoring 20 surrounds the magnet 13. In this case, the shaft portion 10 can be used as a motor rotor for an electric motor. Even when the rotor 1 including the armoring 20 is used as a motor rotor that rotates at high speed, the rotational balance can be adjusted by the recesses 21, while suppressing stress concentration in the recesses 21 used for adjusting the balance.

[0035] The armoring 20 is press-fitted onto the outer peripheral surface 10a of the shaft portion 10. In this case, the armoring 20 allows the rotor 1 to easily hold the magnets 13.

[0036] Second Embodiment A second embodiment of the rotor will be described. Similar to the first embodiment, the rotor according to the second embodiment is also used as a motor rotor for an electric motor. The rotor according to the second embodiment will be described below, focusing on the differences from the rotor 1 according to the first embodiment. As shown in FIGS. 6 and 7 , the rotor 1A according to the second embodiment includes a shaft portion 10 and an armoring 20A. The armoring 20A has a recess 22 with a different configuration instead of the recess 21 of the armoring 20 according to the first embodiment.

[0037] A recess 22 is provided in an armor outer peripheral surface (enclosure outer peripheral surface) 20a, which is the outer peripheral surface of the armor 20A. The recess 22 is recessed from the armor outer peripheral surface 20a of the armor 20A toward the rotation axis L. The recess 22 has a recess wall surface 22a, which is a wall surface that forms the recess 22. In this way, the outer diameter surface of the armor 20A includes the cylindrical armor outer peripheral surface 20a and the recess wall surface 22a that forms the recess 22.

[0038] One end H11A of the recess wall surface 22a in the circumferential direction S is continuous with the armor outer peripheral surface 20a. The other end H12A of the recess wall surface 22a in the circumferential direction S is continuous with the armor outer peripheral surface 20a. The recess wall surface 22a is curved convexly radially outward between the one end H11A and the other end H12A in the circumferential direction S.

[0039] The recess wall surface 22 a being convexly curved radially outward may be curved in an arc shape or a curve other than an arc. The recess wall surface 22 a being convexly curved radially outward may be curved in a convex shape without forming a corner between one end H11A and the other end H12A in the circumferential direction S.

[0040] One end H21A of the recess wall surface 22a in the rotational axis direction L1 is continuous with one end face 20b of the armoring 20A in the rotational axis direction L1. The other end H22A of the recess wall surface 22a in the rotational axis direction L1 is continuous with the armoring outer peripheral surface 20a. The recess wall surface 22a extends linearly between the one end H21A and the other end H22A in the rotational axis direction L1.

[0041] In the radial direction K, the recess wall surface 22a is located closer to the rotation axis L than the cylindrical armoring outer peripheral surface 20a. Furthermore, the recess 22 does not have a wall portion that rises outward in the radial direction K from the recess wall surface 22a. Therefore, the recess 22 does not have a corner (recessed corner). Furthermore, the recess wall surface 22a does not have a corner in either the circumferential direction S or the rotation axis direction L1.

[0042] 6, the maximum length A3 of the recess 22 in the rotational axis direction L1 is longer than the maximum depth A4 of the recess 22 in the radial direction K. For example, the recess 22 may be formed by a method such as machining the outer circumferential surface 20a of the armor 20A. The recess 22 is provided to achieve rotational balance of the rotor 1A.

[0043] As described above, in this rotor 1A, the recess wall surface 22a forming the recess 22 is convexly curved outward in the radial direction K between one end H11A and the other end H12A in the circumferential direction S. Furthermore, the recess wall surface 22a extends linearly between one end H21A and the other end H22A in the rotational axis direction L1. In other words, the recess 22 has a shape formed by removing a portion of the outer periphery of the armoring 20A. Furthermore, the recess wall surface 22a does not have corners. Therefore, in the rotor 1A having this recess 22, stress concentration in the recess 22 is suppressed even when the rotor 1A rotates. In this way, the rotor 1A can adjust the rotational balance using the recess 22 while suppressing stress concentration in the recess 22.

[0044] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments. For example, the shaft portion 10 is not limited to being composed of the first shaft body 11, the magnet 13, and the second shaft body 12 aligned along the rotation axis direction L1. For example, the shaft portion may include a shaft body that can rotate about the rotation axis and a cylindrical magnet that surrounds the outer peripheral surface of the shaft body. The outer peripheral surface of the cylindrical magnet may then be surrounded by an armoring.

[0045] The armoring 20, 20A is not limited to being attached by being press-fitted onto the outer circumferential surface of the shaft portion 10. Furthermore, the rotor 1, 1A is not limited to being used as a motor rotor for an electric motor. In this case, the rotor does not need to be equipped with the magnet 13.

[0046] The gist of the present disclosure is as follows: [1] A rotor comprising: a shaft portion rotatable about a rotation axis; and an enclosing portion surrounding an outer peripheral surface of the shaft portion, wherein a recess is provided on the outer peripheral surface of the enclosing portion, wherein a recess wall surface forming the recess has one circumferential end portion continuous with the outer peripheral surface of the enclosing portion and another circumferential end portion continuous with the outer peripheral surface of the enclosing portion, wherein the recess wall surface extends linearly between the one circumferential end portion and the other circumferential end portion, wherein one end portion of the recess wall surface in the direction of the rotation axis is continuous with one end face of the enclosing portion in the direction of the rotation axis and the other end portion of the recess wall surface in the direction of the rotation axis is continuous with the outer peripheral surface of the enclosing portion, and wherein the recess wall surface extends linearly between the one circumferential end portion and the other circumferential end portion. [2] A rotor comprising: a shaft portion rotatable about a rotation axis; and an enclosing portion surrounding the outer peripheral surface of the shaft portion, wherein a recess is provided on the outer peripheral surface of the enclosing portion, wherein one circumferential end of the recess wall surface forming the recess is continuous with the outer peripheral surface of the enclosing portion, and the other circumferential end of the recess wall surface is continuous with the outer peripheral surface of the enclosing portion, the recess wall surface is convexly curved radially outward between the one circumferential end and the other circumferential end, one end of the recess wall surface in the rotation axis direction is continuous with one end face of the enclosing portion in the rotation axis direction, and the other end of the recess wall surface in the rotation axis direction is continuous with the outer peripheral surface of the enclosing portion, and the recess wall surface extends linearly between the one end and the other end in the rotation axis direction. [3] The rotor according to [1] or [2] above, wherein the maximum length of the recess in the rotation axis direction is longer than the maximum depth of the recess in the radial direction perpendicular to the rotation axis. [4] The rotor according to any one of the above [1] to [3], wherein the shaft portion includes a shaft body rotatable about a rotation axis and a magnet, the surrounding portion includes a cylindrical armor that covers the shaft portion, and the outer peripheral surface of the surrounding portion is formed by the outer peripheral surface of the armor. [5] The rotor according to the above [4], wherein the armor is press-fitted onto the outer peripheral surface of the shaft portion.

[0047] DESCRIPTION OF SYMBOLS 1, 1A Rotor 10 Shaft portion 10a Outer circumferential surface 11 First shaft body (shaft body) 12 Second shaft body (shaft body) 13 Magnet 20, 20A Armouring (encircling portion) 20a Armouring outer circumferential surface (encircling portion outer circumferential surface) 20b End surface (one end surface of encircling portion in the rotation axis direction) 21, 22 Recess 21a, 22a Recess wall surface H11, H11A End (one end in the circumferential direction of recess wall surface) H12, H12A End (other end in the circumferential direction of recess wall surface) H21, H21A End (one end in the rotation axis direction of recess wall surface) H22, H22A End (other end in the rotation axis direction of recess wall surface) L Rotation axis

Claims

1. A rotor comprising: a shaft portion rotatable about a rotation axis; and an enclosing portion surrounding the outer peripheral surface of the shaft portion; a recess is provided on the outer peripheral surface of the enclosing portion; a recess wall surface forming the recess has one circumferential end of the recess wall surface continuous with the outer peripheral surface of the enclosing portion and the other circumferential end of the recess wall surface continuous with the outer peripheral surface of the enclosing portion; the recess wall surface extends linearly between one of the circumferential ends and the other of the circumferential ends; one end of the recess wall surface in the direction of the rotation axis is continuous with one end face of the enclosing portion in the direction of the rotation axis, and the other end of the recess wall surface in the direction of the rotation axis is continuous with the outer peripheral surface of the enclosing portion; and the recess wall surface extends linearly between one of the end faces in the direction of the rotation axis and the other end.

2. A rotor comprising: a shaft portion rotatable about a rotation axis; and an enclosing portion surrounding the outer peripheral surface of the shaft portion, wherein a recess is provided on the outer peripheral surface of the enclosing portion; one circumferential end of the recess wall surface forming the recess is continuous with the outer peripheral surface of the enclosing portion, and the other circumferential end of the recess wall surface is continuous with the outer peripheral surface of the enclosing portion; the recess wall surface is convexly curved radially outward between the one circumferential end and the other circumferential end; one end of the recess wall surface in the direction of the rotation axis is continuous with one end face of the enclosing portion in the direction of the rotation axis, and the other end of the recess wall surface in the direction of the rotation axis is continuous with the outer peripheral surface of the enclosing portion; and the recess wall surface extends linearly between the one end and the other end in the direction of the rotation axis.

3. A rotor according to claim 1 or 2, wherein the maximum length of said recess in the direction of said rotation axis is longer than the maximum depth of said recess in the radial direction perpendicular to said rotation axis.

4. A rotor as described in claim 1 or 2, wherein the shaft portion comprises a shaft body rotatable around the rotation axis and a magnet, the surrounding portion comprises a cylindrical armor ring that covers the shaft portion, and the outer peripheral surface of the surrounding portion is formed by the outer peripheral surface of the armor ring.

5. A rotor according to claim 4, wherein said armoring is press-fitted onto the outer peripheral surface of said shaft portion.

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