Bearing device and motor

Abstract

A bearing device (1, 1A, 1B) is provided with: a shaft (10) having a first end (11) and a second end (12); a sleeve (20) having a protrusion (22) protruding from an inner peripheral surface (23) of the sleeve (20), the inner peripheral surface (23) facing the outer peripheral surface (13) of the shaft (10); a first bearing (30) on the first end (11) side, the first bearing (30) having an inner ring (31), an outer ring (32), and a rotating body (33); and a second bearing (40) on the second end portion (12) side, the second bearing (40) having an inner ring (41), an outer ring (42), and a rotating body (43). In the direction of the axis (x), the protruding portion (22) is disposed between the first bearing (30) and the second bearing (40), the outer ring (32, 42) of one of the first bearing (30) and the second bearing (40) is in contact with the protruding portion (22), and the outer ring (42, 32) of the other of the first bearing (30) and the second bearing (40) is disposed so as to be separated from the protruding portion (22). In the direction of the axis (x), the inner ring (31) of the first bearing (30) is disposed closer to the first end (11) side than the outer ring (32), and the inner ring (41) of the second bearing (40) is disposed closer to the second end (12) side than the outer ring (42).

Description

TECHNICAL FIELD

[0001] The present application relates to a bearing device and a motor provided with the bearing device. BACKGROUND

[0002] Known, for example, from Patent Literature 1 is a blower provided with: a shaft; a cylindrical sleeve surrounding an axis of the shaft; a pair of bearings fixed to an inner peripheral surface of the sleeve to support the shaft so as to be rotatable; and a spring to impart a pre-load to each of the bearings.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: International Publication No. 2019 / 111430 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] In such a blower, when the shaft rotates at high speed, the sleeve can thermally expand due to frictional heat within the bearings. When the sleeve elongates along the axis due to thermal expansion, the pre-load imparted to the bearings can vary. For example, when the pre-load excessively increases, the life of the bearings can be shortened.

[0008] Therefore, one example of a technical problem of the present application is to provide a bearing device and a motor capable of suppressing a decrease in the life of bearings.

[0009] SOLUTION TO THE PROBLEM

[0010] One aspect of the bearing device in the present application is provided with: a shaft having a first end portion and a second end portion; a sleeve having a protruding portion protruding from an inner peripheral surface of the sleeve opposite to an outer peripheral surface of the shaft; a first bearing supported between the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve on the first end portion side, having an inner ring, an outer ring, and a rolling element; and a second bearing supported between the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve on the second end portion side, having an inner ring, an outer ring, and a rolling element, in the axis direction of the shaft, the protruding portion is disposed between the first bearing and the second bearing, in the axis direction, the outer ring of one of the first bearing and the second bearing is in contact with the protruding portion, the outer ring of the other of the first bearing and the second bearing is disposed apart from the protruding portion, in the axis direction, the inner ring of the first bearing is disposed at a position closer to the first end portion side than the outer ring of the first bearing, and in the axis direction, the inner ring of the second bearing is disposed at a position closer to the second end portion side than the outer ring of the second bearing. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1is a cross-sectional view schematically showing the structure of a bearing device 1 of a first embodiment of the present application.

[0012] Figure 2 is a cross-sectional view schematically showing the structure of a motor 100 of one example.

[0013] Figure 3 is a cross-sectional view schematically showing the pattern of thermal expansion in the motor 100 of one example.

[0014] Figure 4 is a cross-sectional view schematically showing the structure of a bearing device 1A of a modification of the first embodiment of the present application.

[0015] Figure 5 is a cross-sectional view schematically showing the pattern of thermal expansion in the motor 100A of another example.

[0016] Figure 6 is a cross-sectional view schematically showing the structure of a bearing device 1B of a second embodiment of the present application.

[0017] Figure 7 is a cross-sectional view schematically showing the pattern of thermal expansion in the motor 100B of another example.

[0018] Figure 8 is a cross-sectional view schematically showing the structure of a motor 100C including a bearing device 1C of a third embodiment of the present application of another example.

[0019] Figure 9 is a cross-sectional view schematically showing the pattern of thermal expansion in the motor 100C of another example.

[0020] Figure 10 is a cross-sectional view schematically showing the structure of a motor 100D of another example.

[0021] Figure 11 is a cross-sectional view schematically showing the structure of a motor 100E of another example. DETAILED DESCRIPTION

[0022] [First Embodiment]

[0023] Hereinafter, one embodiment of the present application will be described with reference to the drawings. Figure 1is a sectional view schematically showing the structure of a bearing device 1 of a first embodiment of the present application. This sectional view is a sectional view along an imaginary plane including an axis x of a shaft 10 of the bearing device 1. The bearing device 1 is provided with the shaft 10, a sleeve 20, and a pair of a first bearing 30 and a second bearing 40. The shaft 10 is, for example, a cylindrical rotating shaft. At least a portion of the shaft 10 is housed in the sleeve 20. The first bearing 30 and the second bearing 40 are supported between the shaft 10 and the sleeve 20.

[0024] The shaft 10 defines one end portion in the axis x direction, that is, a first end portion 11, and the other end portion in the axis x direction opposite to the first end portion 11, that is, a second end portion 12. In the bearing device 1, a direction from the second end portion 12 toward the first end portion 11 in the axis x direction is defined as a first direction FD, and a direction from the first end portion 11 toward the second end portion 12 is defined as a second direction SD. Further, a direction in a radial direction orthogonal to the axis x and tending toward the axis x is defined as an inner peripheral side, and a direction away from the axis x is defined as an outer peripheral side.

[0025] Between the first end portion 11 and the second end portion 12, an outer peripheral surface 13 is formed in the shaft 10. The outer peripheral surface 13 extends in a cylindrical shape with the axis x as a center axis. The shaft 10 is formed of, for example, a metal material. The linear expansion coefficient of the shaft 10 is, for example, in the range of 10 to 13 x 10 -6 / °C. In the present embodiment, the shaft 10 has the same diameter between the first end portion 11 and the second end portion 12. However, the shaft 10 can have a locally different diameter between the first end portion 11 and the second end portion 12.

[0026] The sleeve 20 is provided with a cylindrical portion 21 as a barrel portion and a protruding portion 22. The cylindrical portion 21 defines an inner peripheral surface 23 that extends in a cylindrical shape with the axis x as a center axis. The inner peripheral surface 23 opposes the outer peripheral surface 13 of the shaft 10 in the radial direction. The protruding portion 22 protrudes from the inner peripheral surface 23 of the cylindrical portion 21 to the inner peripheral side in the radial direction between both end portions in the axis x direction of the cylindrical portion 21. The protruding portion 22 is formed in a ring shape around the axis x over the entire circumference. An inner peripheral surface 24 of the protruding portion 22 opposes the outer peripheral surface 13 of the shaft 10. Note that the protruding portion 22 can be formed of a plurality of portions separated from each other in the circumferential direction around the axis x. In the present embodiment, both end portions in the axis x direction of the cylindrical portion 21 are open.

[0027] The cylindrical portion 21 and the protruding portion 22 are formed integrally of, for example, a metal material. In the present embodiment, the linear expansion coefficient of the sleeve 20 is different from the linear expansion coefficients of the shaft 10 and the first bearing 30 and the second bearing 40 described later. Specifically, the linear expansion coefficient of the sleeve 20 is, for example, in the range of 15 to 25 x 10 -6 / °C, preferably in the range of 16 to 20 x 10 -6 / °C, more preferably in the range of 17 to 18 x 10-6 The linear expansion coefficient of the sleeve 20 is set to be greater than the linear expansion coefficients of the shaft 10 and the first bearing 30 and the second bearing 40. That is, the linear expansion coefficient of the sleeve 20 is set to be greater than the linear expansion coefficients of the shaft 10 and the first bearing 30 and the second bearing 40.

[0028] A pair of the first bearing 30 and the second bearing 40 are supported between the outer circumferential surface 13 of the shaft 10 and the inner circumferential surface 23 of the sleeve 20. In the axial direction x, the first bearing 30 is disposed at a position closer to the first end portion 11 than the protruding portion 22, and the second bearing 40 is disposed at a position closer to the second end portion 12 than the protruding portion 22. That is, in the axial direction x, the protruding portion 22 is disposed between the first bearing 30 and the second bearing 40.

[0029] The first bearing 30 has an inner ring 31, an outer ring 32 disposed on the outer circumferential side of the inner ring 31, and a plurality of rolling elements 33 disposed between the inner ring 31 and the outer ring 32. The inner ring 31 and the outer ring 32 are annular members with the axis x as the central axis. That is, the axis x is also the axis of the first bearing 30. An inner ring raceway 34 is formed on the outer circumferential surface of the inner ring 31, and an outer ring raceway 35 is formed on the inner circumferential surface of the outer ring 32. Between these inner ring raceway 34 and the outer ring raceway 35, the plurality of rolling elements 33 are arranged in the circumferential direction around the axis x. The rolling elements 33 are spherical, and thus the first bearing 30 is a rolling bearing. Note that the plurality of rolling elements 33 are held, for example, by an annular retainer (not shown).

[0030] The inner ring 31 is supported by the outer circumferential surface 13 of the shaft 10 via the inner circumferential surface thereof. The outer ring 32 is supported by the inner circumferential surface 23 of the sleeve 20 via the outer circumferential surface thereof. In the present embodiment, the inner ring 31 is fixed to the shaft 10 by press-fitting. On the other hand, the outer ring 32 is gap-fitted to the sleeve 20 and fixed to the sleeve 20 by an adhesive. Further, as described later, in the axial direction x, the inner ring 31 is disposed so as to be offset to the first end portion 11 side, that is, the first direction FD, with respect to the outer ring 32, whereby the first bearing 30 is given a pre-press. Note that in the drawings, the offset disposition of the inner ring 31 and the outer ring 32 in the axial direction x is exaggeratedly shown.

[0031] On the other hand, the second bearing 40, like the first bearing 30, has an inner ring 41, an outer ring 42 disposed on the outer circumferential side of the inner ring 41, and a plurality of rolling elements 43 disposed between the inner ring 41 and the outer ring 42. The inner ring 41 and the outer ring 42 are annular members with the axis x as the central axis. That is, the axis x is also the axis of the second bearing 40. An inner ring raceway 44 is formed on the outer circumferential surface of the inner ring 41, and an outer ring raceway 45 is formed on the inner circumferential surface of the outer ring 42. Between these inner ring raceway 44 and the outer ring raceway 45, the plurality of rolling elements 43 are arranged in the circumferential direction around the axis x. The rolling elements 43 are spherical, and thus the second bearing 40 is a rolling bearing. Note that the plurality of rolling elements 43 are held, for example, by an annular retainer (not shown).

[0032] The inner ring 41 is supported to the outer peripheral surface 13 of the shaft 10 by its inner peripheral surface. The outer ring 42 is supported to the inner peripheral surface 23 of the sleeve 20 by its outer peripheral surface. In the present embodiment, the inner ring 41 is fixed to the shaft 10 by press-fitting. On the other hand, the outer ring 42 is gap-fitted to the sleeve 20 and is fixed to the sleeve 20 by an adhesive. Further, as will be described later, in the axial direction x, the inner ring 41 is arranged to be offset to the second end portion 12 side, i.e., the second direction SD, with respect to the outer ring 42, whereby the second bearing 40 is given a pre-press. Note that, in the drawings, the offset arrangement of the inner ring 41 and the outer ring 42 in the axial direction x is exaggeratedly shown.

[0033] According to Figure 1 As is apparent, the end surface 32a of the outer ring 32 of the first bearing 30 facing the second direction SD is arranged to be separated from the end surface 22a of the protruding portion 22 facing the first direction FD. On the other hand, in the axial direction x, the end surface 42a of the outer ring 42 of the second bearing 40 facing the first direction FD is arranged to be in contact with the end surface 22b of the protruding portion 22 facing the second direction SD. Further, due to the offset arrangement of the inner rings 31, 41 and the outer rings 32, 42 in the axial direction x, the interval SI between the inner ring 31 of the first bearing 30 and the inner ring 41 of the second bearing 40 in the axial direction x is larger than the interval S2 between the outer ring 32 of the first bearing 30 and the outer ring 42 of the second bearing 40.

[0034] The inner rings 31, 41, the outer rings 32, 42, and the rotating bodies 33, 43 of the first bearing 30 and the second bearing 40 are formed of a metal material. The linear expansion coefficients of the inner rings 31, 41 and the outer rings 32, 42 of the first bearing 30 and the second bearing 40 are, for example, in the range of 10 to 13 x 10 -6 / °C. That is, the linear expansion coefficients of the first bearing 30 and the second bearing 40 are different from the linear expansion coefficient of the sleeve 20. Specifically, the linear expansion coefficients of the inner rings 31, 41 and the outer rings 32, 42 of the first bearing 30 and the second bearing 40 are set to be smaller than the linear expansion coefficient of the sleeve 20.

[0035] Next, the assembling method of the bearing device 1 of the present embodiment will be described. First, the second bearing 40 is assembled to the shaft 10 and the sleeve 20. Specifically, the inner ring 41 of the second bearing 40 is press-fitted to a prescribed position of the shaft 10 from the second end portion 12 side. On the other hand, the outer ring 42 of the second bearing 40 is fitted to the sleeve 20 by gap fitting. The end surface 42a of the outer ring 42 is in contact with the end surface 22b of the protruding portion 22. In this state, the outer peripheral surface of the outer ring 42 is fixed to the inner peripheral surface 23 of the sleeve 20 by an adhesive.

[0036] Subsequently, the first bearing 30 is assembled to the shaft 10 and the sleeve 20. Specifically, the inner ring 31 of the first bearing 30 is pressed into a prescribed position of the shaft 10 from the first end portion 11 side. The prescribed position is a position at which the interval between the inner ring 31 and the inner ring 41 in the axial direction x becomes the aforementioned interval S1. Meanwhile, the outer ring 32 of the first bearing 30 is fitted to the sleeve 20 in a clearance fit. The end face 32a of the outer ring 32 facing the second direction SD is disposed so as to be separated from the end face 22a of the protruding portion 22 in the axial direction x.

[0037] At this time, in a state in which the sleeve 20 is fixed, a load is imparted to the outer ring 32 of the first bearing 30 in the second direction SD, for example, by a pre-load spring (not shown). The outer ring 32 moves in the second direction SD. As a result, the outer ring 32 is disposed so as to be relatively offset in the second direction SD with respect to the inner ring 31. In this way, the first bearing 30 is imparted with a pre-load by the offset disposition between the inner ring 31 and the outer ring 32 in the axial direction x.

[0038] The inner ring 31 is pressed into the shaft 10, so when the outer ring 32 moves in the second direction SD, the inner ring 31 also moves in the second direction SD. As a result, the shaft 10 moves in the second direction SD. The inner ring 41 of the second bearing 40 is pressed into the shaft 10, so by the movement of the shaft 10 in the second direction SD, the inner ring 41 is disposed so as to be offset in the second direction SD with respect to the outer ring 42. As a result, the second bearing 40 is imparted with a pre-load.

[0039] At this time, the interval between the outer ring 32 of the first bearing 30 and the outer ring 42 of the second bearing 40 is set to the interval S2. The end face 32a of the outer ring 32 of the first bearing 30 and the end face 22a of the protruding portion 22 are separated from each other. In this state, the outer peripheral surface of the outer ring 32 of the first bearing 30 is fixed to the inner peripheral surface 23 of the sleeve 20 by an adhesive. The pre-load spring is removed after the outer ring 32 is fixed to the sleeve 20. In this way, the bearing device 1 is assembled.

[0040] Next, one example of a usage scheme of the bearing device 1 of the present embodiment will be described. Figure 2 is a cross-sectional view schematically showing the structure of a motor 100 of one embodiment. The motor 100 of this embodiment is provided with the aforementioned bearing device 1, a member 101, a magnet 102, a stator core 103, and a coil 104. The motor 100 is a motor that can rotate the member 101 at high speed, for example, at 30,000 rpm or more about the axial line x.

[0041] The member 101 is fixed to the shaft 10 at a position closer to the first end portion 11 than the first bearing 30. In this example, the member 101 is fixed to the first end portion 11. On the other hand, the magnet 102 is fixed to the shaft 10 at a position closer to the second end portion 12 than the second bearing 40. In this example, the magnet 102 is fixed to the second end portion 12. The magnet 102 is, for example, a cylindrical permanent magnet. This magnet 102 constitutes a rotor of the motor 100. Thus, on the shaft 10, the member 101, which is larger in weight and diameter, is disposed on the first end portion 11 side than on the second end portion 12 side, and a load is applied to the rotor. For example, in the case where the member 101 swings around the axis x, a rotational direction component and a rotational axis direction component are generated as the load (load). Here, as the member 101, for example, a belt, a gear, or the like can be cited.

[0042] The inner peripheral surface of the cylindrical stator core 103 opposes the outer peripheral surface of the magnet 102. The teeth of the stator core 103 are each wound with a plurality of coils 104. The stator core 103 is formed of, for example, a laminate of a magnetic material. The stator core 103 and the coils 104 constitute a stator of the motor 100. As is well known, the shaft 10, i.e., the member 101, is rotated around the axis x by magnetic interaction of a magnetic field generated in the stator core 103 and a magnetic field of the magnet 102.

[0043] When the shaft 10, i.e., the member 101, rotates at a high speed of, for example, 30,000 rpm or more, frictional heat is generated between the inner races 31, 41 and the outer races 32, 42 and the rotating body 33 in the first bearing 30 and the second bearing 40. This frictional heat is conducted to the sleeve 20. As a result, the sleeve 20 is thermally expanded. Figure 3 is a cross-sectional view schematically showing a pattern of thermal expansion in the motor 100 of one embodiment. Here, attention is particularly paid to thermal expansion in the axis x direction of the sleeve 20.

[0044] As shown in Figure 3 When the sleeve 20 is thermally expanded in the axis x direction, the outer race 42 of the second bearing 40, which is in contact with the end surface 22b of the protruding portion 22 in the axis x direction, moves toward the second direction SD (arrow a) due to thermal expansion of the protruding portion 22 in the axis x direction. On the other hand, the outer race 32 of the first bearing 30 is not in contact with the end surface 22a of the protruding portion 22 in the axis x direction, and thus is not affected by thermal expansion of the protruding portion 22 in the axis x direction. In addition, the outer race 32 and the outer race 42 are fixed to the inner peripheral surface 23 of the cylindrical portion 21 by the adhesive, and thus thermal expansion of the cylindrical portion 21 is absorbed by the adhesive.

[0045] As described above, the second bearing 40 is affected by thermal expansion in the axis x direction of the protrusion 22, and the outer ring 42 moves toward the second direction SD. That is, the outer ring 42 moves toward a direction in which the offset configuration of the inner ring 41 and the outer ring 42 is eliminated. As a result, the pre-press in the second bearing 40 is reduced. On the other hand, the first bearing 30 is not affected by thermal expansion of the protrusion 22, and thus neither the position of the inner ring 31 nor the position of the outer ring 32 is changed. As a result, the pre-press in the first bearing 30 is maintained.

[0046] According to the bearing device 1 and the motor 100 as described above, in the first bearing 30 and the second bearing 40, the interval S1 between the inner ring 31 and the inner ring 41 is set to be larger than the interval S2 between the outer ring 32 and the outer ring 42, and the outer ring 42 of the second bearing 40 is in contact with the protrusion 22 in the axis x direction. According to such a structure, in the case where the shaft 10 is rotated at high speed, for example, the pre-press in the first bearing 30 is maintained, and on the other hand, the pre-press in the second bearing 40 is reduced. An increase in the pre-press in both the first bearing 30 and the second bearing 40 can be avoided. A reduction in the life of the first bearing 30 and the second bearing 40 can be suppressed.

[0047] Figure 4 is a sectional view schematically showing a structure of a bearing device 1A of a modification example. Hereinafter, a structure different from the aforementioned bearing device 1 will be described. Note that the same reference numerals are attached to the same structures as those of the aforementioned bearing device 1, and the repeated description will be omitted. As shown in Figure 4 the bearing device 1A, the outer ring 32 of the first bearing 30 is clearance-fitted to the inner peripheral surface 23 of the sleeve 20. An adhesive is not applied between the outer peripheral surface of the outer ring 32 and the inner peripheral surface 23 of the sleeve 20. That is, the outer ring 32 can relatively move in the axis x direction with respect to the sleeve 20.

[0048] The bearing device 1A is provided with an elastic member 50 and a retaining member 51. The retaining member 51 is fitted to the end portion of the cylindrical portion 21 of the sleeve 20 on the first direction FD side. The retaining member 51 is a ring-shaped member with the axis x as a center axis. The elastic member 50 is retained to the inner surface of the retaining member 51 facing the second direction SD. The elastic member 50 is a ring-shaped member with the axis x as a center axis. The elastic member 50 includes, for example, a coil spring, a leaf spring. The elastic member 50 is disposed between the outer ring 32 of the first bearing 30 and the retaining member 51, and imparts a load to the outer ring 32 in the second direction SD.

[0049] As Figure 5As shown, bearing device 1A is incorporated into motor 100A. The structure of motor 100A is identical to that of motor 100, except that bearing device 1A is incorporated instead of bearing device 1. When shaft 10, or component 101, rotates at high speeds, for example, at 30,000 rpm or higher, sleeve 20 thermally expands. The behavior of second bearing 40 is similar to that described above. Meanwhile, in first bearing 30, outer ring 32 is not fixed to cylindrical portion 21. Furthermore, elastic member 50 applies a load to outer ring 32, so thermal expansion of cylindrical portion 21 is absorbed by elastic member 50.

[0050] In this situation, as in the case of motor 100 described above, the second bearing 40 is affected by the thermal expansion of the protrusion 22, causing the outer ring 42 to move in a direction that eliminates the offset between the inner ring 41 and outer ring 42. Consequently, the preload in the second bearing 40 is reduced. Furthermore, the first bearing 30 is not affected by the thermal expansion of the protrusion 22, so the positions of the inner ring 31 and outer ring 32 remain unchanged. As a result, the preload in the first bearing 30 is maintained.

[0051] [Second embodiment]

[0052] Figure 6 This is a cross-sectional view schematically illustrating the structure of a bearing device 1B according to a second embodiment of the present invention. The following describes the structures that differ from the previously described bearing device 1. Components identical to those of the previously described bearing device 1 are denoted by the same reference numerals, and duplicate descriptions are omitted. In this bearing device 1B, the end face 22a of the protrusion 22 contacts the end face 32a of the outer ring 32 of the first bearing 30 in the direction of the axis x. Meanwhile, the end face 42a of the outer ring 42 of the second bearing 40 is spaced apart from the end face 22b of the protrusion 22 in the direction of the axis x. As in the bearing device 1, the inner rings 31 and 41 are press-fitted onto the outer circumferential surface 13 of the shaft 10. Meanwhile, the outer rings 32 and 42 are clearance-fitted with the inner circumferential surface 23 of the sleeve 20 and secured to the inner circumferential surface 23 of the sleeve 20 using an adhesive.

[0053] like Figure 7 As shown, bearing device 1B is incorporated into motor 100B. In this example, component 101 is an impeller, meaning motor 100B is a fan motor. When shaft 10, or component 101, rotates at a high speed (e.g., 30,000 rpm or higher), sleeve 20 thermally expands. The outer ring 32 of first bearing 30, which contacts protrusion 22 in the axis x direction, moves in the first direction FD (arrow a) due to the thermal expansion of protrusion 22. On the other hand, outer ring 42 of second bearing 40, which does not contact protrusion 22 in the axis x direction, is unaffected by the thermal expansion of protrusion 22. Furthermore, outer rings 32 and 42 are fixed to inner circumferential surface 23 of cylindrical portion 21 with adhesive, so thermal expansion of cylindrical portion 21 is absorbed by the adhesive.

[0054] In addition, if Figure 7 As shown, in motor 100B, the high-speed rotation of component 101, i.e., the impeller, generates thrust in a first direction FD. When the thrust generated by the impeller exceeds the magnetic attraction between stator core 103 and magnet 102, shaft 10 is pulled in the first direction FD. In response to the movement of shaft 10 in the first direction FD, the inner race 31 of the first bearing 30 and the inner race 41 of the second bearing 40, which are fixed to shaft 10, move in the first direction FD (arrows b and c).

[0055] In this case, in the first bearing 30, both the inner ring 31 and the outer ring 32 move in the first direction FD, thereby maintaining the preload in the first bearing 30. Furthermore, in the second bearing 40, the inner ring 41 moves in a direction that eliminates the misalignment between the inner ring 41 and the outer ring 42, thereby reducing the preload in the second bearing 40. Consequently, an increase in the preload in the first and second bearings 30, 40 can be avoided, and a reduction in the service life of the first and second bearings 30, 40 can be suppressed.

[0056] [Third embodiment]

[0057] Figure 8 This is a cross-sectional view schematically showing the structure of a motor 100C incorporating a bearing device 1C according to a third embodiment of the present invention. The following describes structures that differ from the bearing device 1. It should be noted that structures identical to those previously described are denoted by the same reference numerals, and duplicate descriptions are omitted. In the bearing device 1C, the end face 32a of the outer ring 32 of the first bearing 30, which faces the second direction SD, contacts the end face 22a of the protrusion 22. Furthermore, the inner ring 31 is configured to be offset in the second direction SD relative to the outer ring 32, thereby imparting preload to the first bearing 30. It should be noted that the inner ring 31 is supported on the shaft 10 by press-fitting, and the outer ring 32 is supported on the inner circumferential surface 23 of the sleeve 20 by a clearance fit.

[0058] Meanwhile, the end face 42a of the outer ring 42 of the second bearing 40, facing in the first direction FD, contacts the end face 22b of the protrusion 22. Furthermore, the inner ring 41 is offset in the second direction SD relative to the outer ring 42, thereby applying a preload to the second bearing 40. It should be noted that the inner ring 41 is press-fitted to the shaft 10, while the outer ring 42 is loosely fitted to the inner circumferential surface 23 of the sleeve 20. Furthermore, in this example, the offset of the inner ring 31 relative to the outer ring 32 in the first bearing 30 is set to be equal to the offset of the inner ring 41 relative to the outer ring 42 in the second bearing 40.

[0059] In the motor 100C, the position of the magnet 102 in the axial direction x of the shaft 10 is adjusted. Specifically, when the shaft 10 is at rest, the center position Cl of the magnet 102 defined in the axial direction x is disposed so as to be biased toward the first direction FD side with respect to the center position C2 of the stator core 103 defined in the axial direction x. The amount of bias is set so that, when the shaft 10 is moved toward the first direction FD by the maximum amount at the time of high-speed rotation of the shaft 10, the position of the end surface 102a on the first direction FD side of the magnet 102 converges within the maximum distance MD that is 1.1 times the length L from the center position C2 of the stator core 103 to the end surface 103a on the first direction FD side of the stator core 103.

[0060] Next, a scenario in which the shaft 10, i.e., the member 101, is rotated at high speed of, for example, 30000 rpm or more is assumed. Note that in this example, the member 101 is an impeller, and the motor 100C is a fan motor. When the thrust force generated by the high-speed rotation of the member 101 is higher than the magnetic attraction force between the stator core 103 and the magnet 102, the shaft 10 is pulled toward the first direction FD. In response to the movement of the shaft 10 toward the first direction FD, the inner ring 41 of the second bearing 40 and the inner ring 31 of the first bearing 30 are moved toward the first direction FD (arrows a and b). In this way, the inner ring 41 and the inner ring 31 are moved with respect to the outer ring 42 and the outer ring 32, respectively, whereby the pre-pressures in the second bearing 40 and the first bearing 30 are reduced.

[0061] Figure 9 is a cross-sectional view schematically showing the structure of the motor 100C in the case where the member 101 is rotated at high speed at the maximum rotational speed. As shown in Figure 9 When the member 101 is rotated at high speed at the maximum rotational speed of, for example, 30000 rpm or more, the member 101, i.e., the shaft 10, is moved toward the first direction FD against the magnetic attraction force between the stator core 103 and the magnet 102. At this time, the position of the end surface 102a on the first direction FD side of the magnet 102 converges within the maximum distance MD that is 1.1 times the length L from the center position C2 of the stator core 103 to the end surface 103a on the first direction FD side of the stator core 103. At this time, the pre-pressures in the first bearing 30 and the second bearing 40 are maintained in the reduced state.

[0062] According to the bearing device 1C and the motor 100C as described above, when the member 101 is rotated at low speed, the magnet 102 is sufficiently opposed to the stator core 103 in the axial direction x. Therefore, the thrust force of the member 101 is lower than the magnetic attraction force between the stator core 103 and the magnet 102. As a result, the shaft 10 is not moved toward the first direction FD. That is, the magnet 102 can be continuously opposed to the stator core 103, and thus the torque constant becomes maximum.

[0063] On the other hand, when the thrust of the member 101 is higher than the magnetic attraction force between the stator core 103 and the magnet 102 while the member 101 is rotating at high speed, the shaft 10 moves toward the first direction FD. The opposing area of the magnet 102 with respect to the stator core 103 decreases. As a result, the constant torque decreases, and thus high-speed rotation of the shaft 10 becomes easy. In addition, if the state where no pre-pressing is generated in the first bearing 30 and the second bearing 40 is achieved, the shaft 1 can rotate most stably. As a result, reduction of power consumption can be achieved.

[0064] Figure 10 is a cross-sectional view schematically showing the structure of another embodiment of the motor 100D. As shown in Figure 10 , the motor 100D is incorporated in the bearing device 1C as with the motor 100C. The point of difference between the motor 100D and the motor 100C is that the magnet 102 has a first portion 102b disposed on the first direction FD side and a second portion 102c disposed at a position closer to the second direction SD side than the first portion 102b. In this example, the lengths of the first portion 102b and the second portion 102c in the axial direction x are set such that the second portion 102c is longer than the first portion 102b.

[0065] Figure 11 is a cross-sectional view schematically showing the structure of another embodiment of the motor 100E. As shown in Figure 11 , the motor 100E is incorporated in the bearing device 1C as with the motor 100C and the motor 100D. The point of difference between the motor 100E and the motor 100C is that the motor 100C has a first magnet 105 attached to the member 101, i.e., the impeller, a second magnet 106 opposing the first magnet 105 in the axial direction x, and a housing 107. The housing 107 accommodates, for example, the rotor and the stator of the motor 100E. Note that, Figure 11 is shown in a state where the shaft 10 has moved toward the first direction FD to the maximum extent at high-speed rotation.

[0066] The second magnet 106 is fixed to the housing 107 of the motor 100E, for example. The same magnetic poles of the first magnet 105 and the second magnet 106 opposing each other oppose to generate repulsive force that repels. Specifically, the repulsive force is set to be generated when the thrust of the member 101 is higher than the magnetic attraction force between the magnet 102 and the stator core 103, so that the shaft 10 moves toward the first direction FD as shown in Figure 11 . Note that the same reference numerals are attached to the same structures as the foregoing structure, and the overlapping description is omitted.

[0067] In the motor 100E described above, the repulsive force between the first magnet 105 and the second magnet 106 is generated when the shaft 10 is moved in the first direction FD, and thus further movement of the shaft 10 in the first direction FD is limited. As a result, it is possible to prevent the pre-pressing in the opposite direction to the initial setting from acting in the first bearing 30 and the second bearing 40. Therefore, it is possible to reliably prevent breakage in the first bearing 30 and the second bearing 40 caused by so-called shoulder riding.

[0068] The above-described embodiments have been described for the purpose of facilitating understanding of the present application, and are not intended to limit the present application. Each of the constituent elements included in the above-described embodiments, and the arrangement, material, condition, shape, and size thereof, etc. are not limited to the contents exemplified above, and can be appropriately changed. Furthermore, the constituent elements shown in different embodiments can be partially replaced or combined with each other within a range not contradictory in the technical field.

[0069] The above-described embodiments have been described for the purpose of facilitating understanding of the present application, and are not intended to limit the present application. Each of the constituent elements included in the above-described embodiments, and the arrangement, material, condition, shape, and size thereof, etc. are not limited to the contents exemplified above, and can be appropriately changed. Furthermore, the constituent elements shown in different embodiments can be partially replaced or combined with each other within a range not contradictory in the technical field.

[0070] Explanation of Reference Numerals

[0071] 1, 1A, 1B, 1C: bearing device; 10: shaft; 11: first end portion; 12: second end portion; 13: outer peripheral surface; 20: sleeve; 21: cylindrical portion; 22: protruding portion; 23: inner peripheral surface; 24: inner peripheral surface; 30: first bearing; 31: inner ring; 32: outer ring; 32a: end surface; 33: rolling element; 34: inner ring raceway; 35: outer ring raceway; 40: second bearing; 41: inner ring; 42: outer ring; 42a: end surface; 43: rolling element; 44: inner ring raceway; 45: outer ring raceway; 100, 100A, 100B, 100C, 100D, 100E: motor; 101: member (impeller); 102: magnet; 102a: end surface; 102b: first portion; 102c: second portion; 103: stator core; 104: coil; 107: housing; C1: center position; C2: center position; FD: first direction; L: length; MD: maximum distance; SD: second direction; S1: interval; S2: interval.

Claims

1. A bearing device comprising: a shaft having a first end and a second end; a sleeve having a protrusion protruding from an inner peripheral surface of the sleeve opposite to the outer peripheral surface of the shaft; a first bearing supported between the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve on the first end side, and including an inner ring, an outer ring, and a rotor; and The second bearing is supported between the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve on the second end side and includes an inner ring, an outer ring, and a rotor. In the axial direction of the shaft, the protrusion is arranged between the first bearing and the second bearing. In the axial direction, the outer ring of one of the first bearing and the second bearing is in contact with the protrusion, and the outer ring of the other of the first bearing and the second bearing is arranged to be separated from the protrusion. In the axial direction, the inner ring of the first bearing is arranged closer to the first end portion than the outer ring of the first bearing. In the axial direction, the inner ring of the second bearing is arranged closer to the second end portion than the outer ring of the second bearing.

2. The bearing device according to claim 1, The inner rings of the first bearing and the second bearing are press-fitted into the outer circumferential surface of the shaft, and the outer rings of the first bearing and the second bearing are clearance-fitted with the inner circumferential surface of the sleeve.

3. The bearing device according to claim 2, The outer ring of at least one of the first bearing and the second bearing is fixed to the inner peripheral surface of the sleeve by an adhesive.

4. The bearing device according to claim 1, The linear expansion coefficient of the shaft is different from the linear expansion coefficient of the sleeve.

5. A motor comprising: The bearing device according to any one of claims 1 to 4; and The impeller is fixed to the shaft at a position closer to the first end portion than the first bearing.

6. The motor according to claim 5, comprising: The rotor is fixed to the shaft at a position closer to the second end portion than the second bearing.

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