Bearing devices and motors

Abstract

To provide a bearing device and a motor that can restrain reduction in a life of bearings.SOLUTION: A bearing device 1, 1A, or 1B comprises: a shaft 10 comprising a first end part 11 and a second end part 12; a sleeve 20 comprising a protruding part 22 protruding from an inner peripheral surface 23 opposed to an outer peripheral surface 13 of the shaft 10; a first bearing 30 on a side of the first end part 11 comprising an inner ring 31, an outer ring 32, and rolling bodies 33; and a second bearing 40 on a side of the second end part 12 comprising an inner ring 41, an outer ring 42, and rolling bodies 43. In the direction of an axis x, the protruding part 22 is arranged between the first bearing 30 and the second bearing 40, the outer ring 32 or 42 of one of the first bearing 30 and the second bearing 40 is in contact with the protruding part 22, and the outer ring 42 or 32 of the other of the first bearing 30 and the second bearing 40 is arranged separately from the protruding part 22. In the direction of the axis x, the inner ring 31 of the first bearing 30 is arranged closer to the side of the first end part 11 than the outer ring 32, and the inner ring 41 of the second bearing 40 is arranged closer to the side of the second end part 12 than the outer ring 42.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a bearing device and a motor including the bearing device.

Background Art

[0002] For example, as disclosed in Patent Document 1, there is known a blower including a shaft, a cylindrical sleeve around the axis of the shaft, a pair of bearings fixed to the inner peripheral surface of the sleeve to rotatably support the shaft, and springs for applying preload to each of the bearings.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such a blower, when the shaft rotates at high speed, the sleeve thermally expands due to frictional heat in the bearing. When the sleeve extends along the axis due to thermal expansion, the preload applied to the bearing may fluctuate. For example, if the preload increases excessively, the life of the bearing is shortened.

[0005] Therefore, an example of an object of the present invention is to provide a bearing device and a motor capable of suppressing a decrease in the life of the bearing.

Means for Solving the Problems

[0006] A bearing device according to one aspect of the present invention comprises a shaft having a first end and a second end; a sleeve having a projection that protrudes from an inner circumferential surface facing the outer circumferential surface of the shaft; a first bearing having an inner ring, an outer ring, and rolling elements, supported between the outer circumferential surface of the shaft and the inner circumferential surface of the sleeve at the first end; and a second bearing having an inner ring, an outer ring, and rolling elements, supported between the outer circumferential surface of the shaft and the inner circumferential surface of the sleeve at the second end, wherein the projection is positioned between the first bearing and the second bearing in the axial direction of the shaft; in the axial direction, the outer ring of one of the first bearings and the second bearing is in contact with the projection, and the outer ring of the other bearing is spaced apart from the projection; in the axial direction, the inner ring of the first bearing is positioned closer to the first end than the outer ring of the first bearing; and in the axial direction, the inner ring of the second bearing is positioned closer to the second end than the outer ring of the second bearing. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic end view showing the structure of a bearing device 1 according to the first embodiment of the present invention. [Figure 2] This is an end view schematicly showing the structure of a motor 100 according to one specific example. [Figure 3] This is an end view schematicly showing the thermal expansion of a motor 100 according to one specific example. [Figure 4] This is a schematic end view showing the structure of a bearing device 1A according to one modified example of the first embodiment of the present invention. [Figure 5] This is an end view schematicly illustrating the thermal expansion of motor 100A in another specific example. [Figure 6] This is a schematic end view showing the structure of a bearing device 1B according to a second embodiment of the present invention. [Figure 7] This is an end view schematicly showing the thermal expansion of motor 100B in another specific example. [Figure 8]This is a schematic end view showing the structure of a motor 100C according to another specific example, which includes a bearing device 1C according to the third embodiment of the present invention. [Figure 9] This is an end view schematicly showing the thermal expansion of motor 100C in another specific example. [Figure 10] This is an end view schematicly showing the structure of motor 100D related to another specific example. [Figure 11] This is an end view schematicly showing the structure of motor 100E related to another specific example. [Modes for carrying out the invention]

[0008] [First Embodiment] One embodiment of the present invention will be described below with reference to the attached drawings. Figure 1 is a schematic end view showing the structure of a bearing device 1 according to the first embodiment of the present invention. This end view is an end view along a virtual plane containing the axis x of the shaft 10 of the bearing device 1. The bearing device 1 comprises a shaft 10, a sleeve 20, and a pair of first bearings 30 and second bearings 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.

[0009] The shaft 10 has a first end 11, which is one end in the axial x direction, and a second end 12, which is the other end opposite to the first end 11 in the axial x direction. In the bearing device 1, in the axial x direction, the direction from the second end 12 toward the first end 11 is defined as the first direction FD, while the direction from the first end 11 toward the second end 12 is defined as the second direction SD. Furthermore, in the radial direction perpendicular to the axis x, the direction toward the axis x is defined as the inner circumference side, and the direction away from the axis x is defined as the outer circumference side.

[0010] An outer circumferential surface 13 is formed on the shaft 10 between the first end 11 and the second end 12. The outer circumferential surface 13 extends in a cylindrical shape with axis x as its central axis. The shaft 10 is formed from, for example, a metal material. The coefficient of linear expansion of the shaft 10 is, for example, 10 to 13 × 10 -6 The temperature range is / °C. In this embodiment, the shaft 10 has the same diameter between the first end 11 and the second end 12. However, the shaft 10 may have a partially different diameter between the first end 11 and the second end 12.

[0011] The sleeve 20 comprises a cylindrical portion 21 and a protruding portion 22. The cylindrical portion 21 defines an inner circumferential surface 23 that extends cylindrically with axis x as its central axis. The inner circumferential surface 23 faces the outer circumferential surface 13 of the shaft 10 in the radial direction. The protruding portion 22 protrudes radially inward from the inner circumferential surface 23 of the cylindrical portion 21 between both ends of the cylindrical portion 21 in the axial x direction. The protruding portion 22 is formed in an annular shape around the entire circumference of axis x. The inner circumferential surface 24 of the protruding portion 22 faces the outer circumferential surface 13 of the shaft 10. Note that the protruding portion 22 may be formed from multiple portions spaced apart from each other in the circumferential direction around axis x. In this embodiment, both ends of the cylindrical portion 21 in the axial x direction are open.

[0012] The cylindrical portion 21 and the protruding portion 22 are integrally formed from, for example, a metal material. In this embodiment, the coefficient of thermal expansion of the sleeve 20 is different from that of the shaft 10 and the first bearing 30 and second bearing 40 described later. Specifically, the coefficient of thermal expansion of the sleeve 20 is, for example, 15 to 25 × 10 -6 The range is / ℃, preferably 16-20 × 10 -6 The range is / ℃, more preferably 17~18×10 -6 The range is / °C. In other words, the coefficient of linear expansion of the sleeve 20 is set to be greater than the coefficients of linear expansion of the shaft 10 and the first bearing 30 and the second bearing 40.

[0013] A pair of first bearing 30 and second bearing 40 are supported between the outer peripheral surface 13 of the shaft 10 and the inner peripheral surface 23 of the sleeve 20. In the axial direction of the axis x, the first bearing 30 is arranged on the first end 11 side rather than the protruding portion 22, while the second bearing 40 is arranged on the second end 12 side rather than the protruding portion 22. That is, in the axial direction of the axis x, the protruding portion 22 is arranged between the first bearing 30 and the second bearing 40.

[0014] The first bearing 30 includes an inner ring 31, an outer ring 32 arranged on the outer peripheral side of the inner ring 31, and a plurality of rolling elements 33 arranged between the inner ring 31 and the outer ring 32. The inner ring 31 and the outer ring 32 are annular members centered on the axis x. That is, the axis x is also the axis of the first bearing 30. An inner ring raceway 34 is formed on the outer peripheral surface of the inner ring 31, while an outer ring raceway 35 is formed on the inner peripheral surface of the outer ring 32. A plurality of rolling elements 33 are arranged in the circumferential direction around the axis x between these inner ring raceway 34 and outer ring raceway 35. The rolling element 33 is a sphere, and thus the first bearing 30 is a ball bearing. Incidentally, the plurality of rolling elements 33 are held by, for example, an annular cage (not shown).

[0015] The inner ring 31 is supported by the outer peripheral surface of the shaft 10 at its inner peripheral surface. The outer ring 32 is supported by the inner peripheral surface of the sleeve 20 at its outer peripheral surface. 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 fitted into the sleeve 20 with a clearance and fixed to the sleeve 20 with an adhesive. Further, as will be described later, in the axial direction of the axis x, by arranging the inner ring 31 offset to the first end 11 side, that is, the first direction FD, with respect to the outer ring 32, a preload is applied to the first bearing 30. Incidentally, in the drawing, the offset arrangement of the inner ring 31 and the outer ring 32 in the axial direction of the axis x is exaggeratedly shown.

[0016] On the one hand, similar to the first bearing 30, the second bearing 40 includes an inner ring 41, an outer ring 42 disposed on the outer peripheral 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 having 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 peripheral surface of the inner ring 41, while an outer ring raceway 45 is formed on the inner peripheral surface of the outer ring 42. A plurality of rolling elements 43 are arranged circumferentially around the axis x between these inner ring raceway 44 and outer ring raceway 45. The rolling elements 43 are spherical bodies, and thus the second bearing 40 is a ball bearing. Note that the plurality of rolling elements 43 are held by, for example, an annular cage (not shown).

[0017] The inner ring 41 is supported by the outer peripheral surface 13 of the shaft 10 on its inner peripheral surface. The outer ring 42 is supported by the inner peripheral surface 23 of the sleeve 20 on its outer peripheral surface. In this embodiment, the inner ring 41 is fixed to the shaft 10 by press-fitting. On the other hand, the outer ring 42 is fitted into the sleeve 20 with a clearance and fixed to the sleeve 20 by an adhesive. Also, as will be described later, in the direction of the axis x, by arranging the inner ring 41 offset toward the second end portion 12 side, that is, in the second direction SD, with respect to the outer ring 42, a preload is applied to the second bearing 40. Note that in the drawings, the offset arrangement of the inner ring 41 and the outer ring 42 in the direction of the axis x is shown exaggeratedly.

[0018] As is clear from FIG. 1, the end face 32a of the outer ring 32 of the first bearing 30 facing the second direction SD is disposed at a distance from the end face 22a of the protruding portion 22 facing the first direction FD. On the other hand, in the direction of the axis x, the end face 42a of the outer ring 42 of the second bearing 40 facing the first direction FD is disposed in contact with the end face 22b of the protruding portion 22 facing the second direction SD. Also, due to the offset arrangement of the inner rings 31, 41 and the outer rings 32, 42 in the direction of the axis x, the interval S1 between the inner ring 31 of the first bearing 30 and the inner ring 41 of the second bearing 40 in the direction of the axis 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.

[0019] The inner ring 31, outer ring 32, and rolling elements 33 of the first bearing 30, and the inner ring 41, outer ring 42, and rolling elements 43 of the second bearing 40 are formed from a metallic material. The coefficient of linear expansion of the inner ring 31 and outer ring 41 of the first bearing 30 and the inner ring 41 and outer ring 42 of the second bearing 40 is, for example, 10 to 13 × 10 -6 The range is / °C. That is, the coefficients of linear expansion of the first bearing 30 and the second bearing 40 are different from the coefficient of linear expansion of the sleeve 20. Specifically, the coefficients of linear expansion of the inner ring 31 and outer ring 41 of the first bearing 30 and the inner ring 41 and outer ring 42 of the second bearing 40 are set to be smaller than the coefficient of linear expansion of the sleeve 20.

[0020] Next, the assembly method of the bearing device 1 according to this embodiment will be described below. First, the second bearing 40 is attached to the shaft 10 and the sleeve 20. Specifically, the inner ring 41 of the second bearing 40 is press-fitted from the second end 12 side to a predetermined position on the shaft 10. Meanwhile, the outer ring 42 of the second bearing 40 is fitted into the sleeve 20 by clearance fit. The end face 42a of the outer ring 42 contacts the end face 22b of the protrusion 22. In this state, the outer circumferential surface of the outer ring 42 is fixed to the inner circumferential surface 23 of the sleeve 20 with adhesive.

[0021] Subsequently, the first bearing 30 is attached to the shaft 10 and the sleeve 20. Specifically, the inner ring 31 of the first bearing 30 is press-fitted from the first end 11 side to a predetermined position on the shaft 10. The predetermined position is the position where the distance between the inner ring 31 and the inner ring 41 in the axial x direction is the aforementioned distance S1. At the same time, the outer ring 32 of the first bearing 30 is fitted into the sleeve 20 by clearance fit. The end face 32a of the outer ring 32 facing the second direction SD is positioned spaced apart from the end face 22a of the projection 22 in the axial x direction.

[0022] At this time, with the sleeve 20 fixed, a load is applied to the outer ring 32 of the first bearing 30 in the second direction SD, for example, by a preload spring (not shown). The outer ring 32 moves in the second direction SD. As a result, the outer ring 32 is positioned offset relative to the inner ring 31 in the second direction SD. In this way, the first bearing 30 is preloaded by the offset arrangement between the inner ring 31 and the outer ring 32 in the axial x direction.

[0023] Since the inner ring 31 is press-fitted onto the shaft 10, when the outer ring 32 moves in the second direction SD, it also causes the inner ring 31 to move in the second direction SD. As a result, the shaft 10 moves in the second direction SD. Since the inner ring 41 of the second bearing 40 is press-fitted onto the shaft 10, the movement of the shaft 10 in the second direction SD causes the inner ring 41 to be positioned offset from the outer ring 42 in the second direction SD. As a result, preload is applied to the second bearing 40.

[0024] At this time, the distance between the outer ring 32 of the first bearing 30 and the outer ring 42 of the second bearing 40 is set to distance S2. The end face 32a of the outer ring 32 of the first bearing 30 and the end face 22a of the projection 22 are spaced apart from each other. In this state, the outer circumferential surface of the outer ring 32 of the first bearing 30 is fixed to the inner circumferential surface 23 of the sleeve 20 with adhesive. The preloading spring is removed after the outer ring 32 is fixed to the sleeve 20. Thus the bearing device 1 is assembled.

[0025] Next, an example of how the bearing device 1 according to this embodiment is used will be described below. Figure 2 is a schematic end view showing the structure of a motor 100 according to one specific example. The motor 100 according to this specific example comprises the aforementioned bearing device 1, a member 101, a magnet 102, a stator core 103, and a coil 104. This motor 100 is capable of rotating the member 101 at high speed around the axis x at, for example, 30,000 rpm or more.

[0026] Member 101 is fixed to the shaft 10 on the side of the first end 11, which is further from the first bearing 30. In this example, member 101 is fixed to the first end 11. On the other hand, magnet 102 is fixed to the shaft 10 on the side of the second end 12, which is further from the second bearing 40. In this example, magnet 102 is fixed to the second end 12. Magnet 102 is, for example, a cylindrical permanent magnet. This magnet 102 constitutes the rotor of the motor 100. Thus, on the shaft 10, a relatively large member 101 with weight × diameter is positioned on the side of the first end 11, which is further from the second end 12, and a load is applied to the rotor. For example, when member 101 oscillates around axis x, a load (load) is generated that has a component in the rotational direction and a component in the direction of the rotational axis. Here, member 101 can be, for example, a belt or a gear.

[0027] The inner surface of a cylindrical stator core 103 faces the outer surface of the magnet 102. Multiple coils 104 are wound around each tooth of the stator core 103. The stator core 103 is formed from, for example, a laminate of magnetic material. The stator core 103 and the coils 104 constitute the stator of the motor 100. As is well known, the magnetic interaction between the magnetic field generated by the stator core 103 and the magnetic field of the magnet 102 causes the shaft 10, i.e., the member 101, to rotate around the axis x.

[0028] When the shaft 10, or member 101, rotates at a high speed of, for example, 30,000 rpm or more, frictional heat is generated in the first bearing 30 and the second bearing 40 between the inner rings 31, 41 and the outer rings 32, 42 and the rolling elements 33, 43. This frictional heat is conducted to the sleeve 20. As a result, the sleeve 20 expands due to heat. Figure 3 is a schematic end view showing the thermal expansion in a motor 100 according to one specific example. Here, we will focus particularly on the thermal expansion of the sleeve 20 in the x-axis direction.

[0029] As shown in Figure 3, when the sleeve 20 expands due to heat in the axial x direction, the outer ring 42 of the second bearing 40, which is in contact with the end face 22b of the projection 22 in the axial x direction, moves toward the second direction SD due to the thermal expansion of the projection 22 in the axial x direction (arrow a). On the other hand, the outer ring 32 of the first bearing 30 is not in contact with the end face 22a of the projection 22 in the axial x direction, and is therefore not affected by the thermal expansion of the projection 22 in the axial x direction. Furthermore, since the outer rings 32 and 42 are fixed to the inner circumferential surface 23 of the cylindrical portion 21 by adhesive, the thermal expansion of the cylindrical portion 21 is absorbed by the adhesive.

[0030] As described above, in the second bearing 40, the outer ring 42 moves toward the second direction SD due to the thermal expansion of the protrusion 22 in the axial x direction. That is, the outer ring 42 moves in a direction that eliminates the offset arrangement of the inner ring 41 and the outer ring 42. As a result, the preload decreases in the second bearing 40. On the other hand, in the first bearing 30, the position of both the inner ring 31 and the outer ring 32 does not change because they are not affected by the thermal expansion of the protrusion 22. As a result, the preload is maintained in the first bearing 30.

[0031] With the bearing device 1 and motor 100 described above, in the first bearing 30 and the second bearing 40, the distance S1 between the inner rings 31 and 41 is set to be larger than the distance S2 between the outer rings 32 and 42, and the outer ring 42 of the second bearing 40 is in contact with the projection 22 in the axial x direction. With this configuration, when the shaft 10 rotates at high speed, for example, the preload is maintained in the first bearing 30, while the preload decreases in the second bearing 40. An increase in preload can be avoided in both the first bearing 30 and the second bearing 40. A reduction in the lifespan of the first bearing 30 and the second bearing 40 can be suppressed.

[0032] Figure 4 is a schematic end view showing the structure of a modified bearing device 1A. The following describes the configuration that differs from the bearing device 1 described above. Components that are the same as those in the bearing device 1 described above are given the same reference numerals, and redundant explanations are omitted. As shown in Figure 4, in this bearing device 1A, the outer ring 32 of the first bearing 30 is clearance-fitted to the inner circumferential surface 23 of the sleeve 20. No adhesive is applied between the outer circumferential surface of the outer ring 32 and the inner circumferential surface 23 of the sleeve 20. That is, the outer ring 32 can move relative to the sleeve 20 in the axial x direction.

[0033] The bearing device 1A comprises an elastic member 50 and a retaining member 51. The retaining member 51 is attached to the end of the cylindrical portion 21 of the sleeve 20 on the FD side in the first direction. The retaining member 51 is an annular member with axis x as its central axis. The elastic member 50 is held on the inner surface of the retaining member 51 facing the second direction SD. The elastic member 50 is an annular member with axis x as its central axis. The elastic member 50 includes, for example, a coil spring or a leaf spring. The elastic member 50 is positioned between the outer ring 32 of the first bearing 30 and the retaining member 51, and applies a load to the outer ring 32 in the second direction SD.

[0034] As shown in Figure 5, the bearing device 1A is incorporated into the motor 100A. The configuration of the motor 100A is the same as that of the motor 100, except that the bearing device 1A is incorporated in place of the bearing device 1. When the shaft 10, i.e., the member 101, rotates at high speed, for example, 30,000 rpm or more, the sleeve 20 undergoes thermal expansion. The behavior of the second bearing 40 is the same as described above. On the other hand, in the first bearing 30, the outer ring 32 is not fixed to the cylindrical portion 21, and a load is applied to the outer ring 32 from the elastic member 50, so the thermal expansion of the cylindrical portion 21 is absorbed by the elastic member 50.

[0035] In the above case, similar to the motor 100 described above, in the second bearing 40, the outer ring 42 moves in a direction that eliminates the offset between the inner ring 41 and the outer ring 42 due to the thermal expansion of the protrusion 22, so the preload in the second bearing 40 decreases. Also, in the first bearing 30, since it is not affected by the thermal expansion of the protrusion 22, the positions of both the inner ring 31 and the outer ring 32 do not change. As a result, the preload in the first bearing 30 is maintained.

[0036] [Second Embodiment] Figure 6 is a schematic end view showing the structure of a bearing device 1B according to a second embodiment of the present invention. The following describes the configuration that differs from the bearing device 1 described above. Components that are the same as those in the bearing device 1 described above are denoted by the same reference numerals, and redundant explanations are omitted. In this bearing device 1B, the end face 22a of the projection 22 is in contact with the end face 32a of the outer ring 32 of the first bearing 30 in the axial x direction. On the other hand, the end face 42a of the outer ring 42 of the second bearing 40 is spaced apart from the end face 22b of the projection 22 in the axial x direction. Similar to the bearing device 1, the inner rings 31 and 41 are press-fitted onto the outer circumferential surface 13 of the shaft 10, while the outer rings 32 and 42 are clearance-fitted onto the inner circumferential surface 23 of the sleeve 20 and fixed with adhesive.

[0037] As shown in Figure 7, the bearing device 1B is incorporated into the motor 100B. In this example, member 101 is an impeller, and therefore motor 100B is a fan motor. When the shaft 10, i.e., member 101, rotates at high speed, for example, 30,000 rpm or more, the sleeve 20 expands due to thermal expansion. The outer ring 32 of the first bearing 30, which contacts the projection 22 in the axial x direction, moves toward the first direction FD due to the thermal expansion of the projection 22 (arrow a). On the other hand, the outer ring 42 of the second bearing 40, which does not contact the projection 22 in the axial x direction, is not affected by the thermal expansion of the projection 22. Furthermore, since the outer rings 32 and 42 are fixed to the inner circumferential surface 23 of the cylindrical portion 21 by adhesive, the thermal expansion of the cylindrical portion 21 is absorbed by the adhesive.

[0038] Furthermore, as shown in Figure 7, in the motor 100B, thrust toward the first direction FD is generated by the high-speed rotation of member 101, i.e., the impeller. When this thrust from the impeller exceeds 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 this movement of the shaft 10 toward the first direction FD, the inner ring 31 of the first bearing 30 and the inner ring 41 of the second bearing 40, which are fixed to the shaft 10, move toward the first direction FD (arrows b and c).

[0039] In the above case, in the first bearing 30, both the inner ring 31 and the outer ring 32 move toward the first direction FD, so the preload is maintained in the first bearing 30. Also, in the second bearing 40, the inner ring 41 moves in a direction that eliminates the offset between the inner ring 41 and the outer ring 42, so the preload decreases in the second bearing 40. Therefore, an increase in preload can be avoided in the first bearing 30 and the second bearing 40. The reduction in the lifespan of the first bearing 30 and the second bearing 40 can be suppressed.

[0040] [Third Embodiment] Figure 8 is a schematic end view showing the structure of a motor 100C incorporating a bearing device 1C according to the third embodiment of the present invention. The configurations that differ from the bearing device 1 are described below. Components similar to those described above are given the same reference numerals, and redundant explanations are omitted. In the bearing device 1C, the outer ring 32 of the first bearing 30 is in contact with the end face 22a of the projection 22 at the end face 32a facing the second direction SD. Furthermore, the inner ring 31 is positioned offset from the outer ring 32 in the second direction SD, thereby applying preload to the first bearing 30. The inner ring 31 is supported by press-fitting onto the shaft 10, and the outer ring 32 is supported by clearance fitting onto the inner circumferential surface 23 of the sleeve 20.

[0041] On the other hand, the outer ring 42 of the second bearing 40 is in contact with the end face 22b of the projection 22 at the end face 42a facing the first direction FD. Furthermore, the inner ring 41 is positioned offset from the outer ring 42 in the second direction SD, thereby providing preload to the second bearing 40. The inner ring 41 is supported by press-fitting onto the shaft 10, and the outer ring 42 is supported by clearance fitting on the inner circumferential surface 23 of the sleeve 20. In this example, the amount of offset of the inner ring 31 relative to the outer ring 32 in the first bearing 30 is set to be equal to the amount of offset of the inner ring 41 relative to the outer ring 42 in the second bearing 40.

[0042] In the motor 100C, the position of the magnet 102 fixed to the shaft 10 in the axial x direction is adjusted. Specifically, when the shaft 10 is stationary, the center position C1 of the magnet 102, defined in the axial x direction, is offset toward the first direction FD side relative to the center position C2 of the stator core 103, which is similarly defined in the axial x direction. This amount of offset is set so that when the shaft 10 rotates at high speed and moves to its maximum extent toward the first direction FD, the position of the end face 102a of the magnet 102 on the first direction FD side falls within a maximum distance MD that is 1.1 times the length L from the center position C2 of the stator core 103 to the end face 103a of the stator core 103 on the first direction FD side.

[0043] Next, let's consider a scenario where the shaft 10, or member 101, rotates at high speed, for example, 30,000 rpm or more. In this example, member 101 is an impeller, and motor 100C is a fan motor. When the thrust from the high-speed rotation of member 101 exceeds the magnetic attraction between the stator core 103 and the magnet 102, the shaft 10 is pulled in the first direction FD. In response to this 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 move toward the first direction FD (arrows a and b). As the inner rings 41 and 31 move relative to the outer rings 42 and 32, respectively, the preload in the second bearing 40 and the first bearing 30 decreases.

[0044] Figure 9 is a schematic end view showing the structure of the motor 100C when member 101 rotates at its maximum rotational speed. As shown in Figure 9, when member 101 rotates at a maximum rotational speed of, for example, 30,000 rpm or more, member 101, i.e., shaft 10, moves in the first direction FD against the magnetic attractive force between the stator core 103 and the magnet 102. At this time, the position of the end face 102a of the magnet 102 on the first direction FD side falls within a maximum distance MD that is 1.1 times the length L from the center position C2 of the stator core 103 to the end face 103a of the stator core 103 on the first direction FD side. At this time, the preload in the first bearing 30 and the second bearing 40 remains reduced.

[0045] With the bearing device 1C and motor 100C described above, when member 101 is rotating at a low speed, the magnet 102 is sufficiently opposed to the stator core 103 in the axial x direction. Therefore, the thrust of member 101 is less than the magnetic attractive force between the stator core 103 and the magnet 102. As a result, the shaft 10 does not move toward the first direction FD. That is, the magnet 102 can continue to sufficiently oppose the stator core 103, so the torque constant is maximized.

[0046] On the other hand, when member 101 rotates at high speed, if the thrust of member 101 exceeds the magnetic attraction force between the stator core 103 and the magnet 102, the shaft 10 moves toward the first direction FD. The area of ​​the magnet 102 facing the stator core 103 decreases. As a result, the torque constant decreases, making it easier for the shaft 10 to rotate at high speed. Furthermore, when no preload is generated in the first bearing 30 and the second bearing 40, the shaft 1 can rotate most stably. As a result, power consumption can be reduced.

[0047] Figure 10 is an end view schematicly showing the structure of motor 100D according to another specific example. As shown in Figure 10, this motor 100D incorporates a bearing device 1C, similar to motor 100C. The difference from motor 100C is that the magnet 102 comprises a first portion 102a located on the first direction FD side and a second portion 102b located on the second direction SD side than the first portion 102a. In this example, the lengths of the first portion 102a and the second portion 102b defined in the axial x direction are set so that the second portion 102b is greater than the first portion 102a.

[0048] Figure 11 is a schematic end view showing the structure of motor 100E according to another specific example. As shown in Figure 11, this motor 100E incorporates a bearing device 1C, similar to motors 100C and 100D. The difference from motor 100C is that motor 100C includes a first magnet 105 attached to member 101, i.e., the impeller, a second magnet 106 facing the first magnet 105 in the axial x direction, and a housing 107. The housing 107 houses, for example, the rotor and stator of motor 100E. Note that Figure 11 shows the state in which the shaft 10 has moved to its maximum extent in the first direction FD during high-speed rotation.

[0049] The second magnet 106 is fixed, for example, to the housing 107 of the motor 100E. The first magnet 105 and the second magnet 106, which face each other, have the same magnetic poles facing each other so that a repulsive force is generated between them. Specifically, the repulsive force is generated when the thrust of member 101 exceeds the magnetic attractive force between the magnet 102 and the stator core 103, and the shaft 10 moves in the first direction FD, as shown in Figure 11. Note that components similar to those described above are given the same reference numerals, and redundant explanations are omitted.

[0050] In the motor 100E described above, a repulsive force is generated between the first magnet 105 and the second magnet 106 when the shaft 10 moves in the first direction FD, thereby restricting further movement of the shaft 10 in the first direction FD. As a result, it is possible to prevent preload in the first bearing 30 and the second bearing 40 from acting in the opposite direction to the initial setting. Therefore, it is possible to reliably prevent damage to the first bearing 30 and the second bearing 40 due to so-called shoulder load.

[0051] Although the present invention has been described above through the embodiments described above, the technical scope of the present invention is not limited to the scope described in the embodiments above. It will be obvious to those skilled in the art that various modifications or improvements can be made to the embodiments described above. It will be clear from the claims that such modified or improved forms may also be included in the technical scope of the present invention.

[0052] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The components of the above embodiments, as well as their arrangement, materials, conditions, shapes, and sizes, are not limited to those exemplified and can be modified as appropriate. Furthermore, components shown in different embodiments can be partially substituted or combined to the extent that they do not contradict the technical context. [Explanation of symbols]

[0053] 1, 1A, 1B, 1C Bearing device, 10 Shaft, 11 First end, 12 Second end, 13 Outer surface, 20 Sleeve, 21 Cylindrical part, 22 Protrusion, 23 Inner surface, 24 Inner surface, 30 First bearing, 31 Inner ring, 32 Outer ring, 32a End face, 33 Rolling element, 34 Inner ring raceway, 35 Outer ring raceway, 40 Second bearing, 41 Inner ring, 42 Outer ring, 42a End face, 43 Rolling element, 44 Inner ring raceway, 45 Outer ring raceway, 100, 100A, 100B, 100C, 100D, 100E Motor, 101 Component (Impeller), 102 Magnet, 102a First part, 102b Second part, 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 Spacing, S2 Spacing

Claims

1. A shaft having a first end and a second end, A sleeve having a protrusion that extends from the inner circumferential surface opposite the outer circumferential surface of the shaft, A first bearing having an inner ring, an outer ring, and spheres as rolling elements, is supported at the first end side between the outer circumferential surface of the shaft and the inner circumferential surface of the sleeve, The second bearing comprises an inner ring, an outer ring, and spherical elements as rolling elements, which are supported between the outer circumferential surface of the shaft and the inner circumferential surface of the sleeve at the second end side, In the axial direction of the shaft, the protrusion is positioned between the first bearing and the second bearing. In the axial direction, the outer ring of the second bearing is in contact with the protrusion, and the outer ring of the first bearing is spaced apart from the protrusion. In the axial direction, the inner ring of the first bearing is positioned closer to the first end than the outer ring of the first bearing. In the axial direction, the inner ring of the second bearing is positioned closer to the second end than the outer ring of the second bearing. In the axial direction, the end face on the second end side of the inner ring of the first bearing is open. In the axial direction, the end face of the inner ring of the second bearing on the first end side is open. The shaft has the same diameter between the first end and the second end. The inner rings of the first and second bearings are press-fitted onto the outer surface of the shaft. The outer rings of the first and second bearings are clearance-fitted to the inner circumferential surface of the sleeve. The outer ring of at least one of the first bearing and the second bearing is fixed to the inner circumferential surface of the sleeve with adhesive. Bearing device.

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

3. Bearing device and A component comprising, The bearing device is A shaft having a first end and a second end, A sleeve having a protrusion that extends from the inner circumferential surface opposite the outer circumferential surface of the shaft, A first bearing having an inner ring, an outer ring, and spheres as rolling elements, is supported at the first end side between the outer circumferential surface of the shaft and the inner circumferential surface of the sleeve, The second bearing comprises an inner ring, an outer ring, and spherical elements as rolling elements, which are supported between the outer circumferential surface of the shaft and the inner circumferential surface of the sleeve at the second end side, The member is fixed to the portion of the shaft that is on the first end side of the first bearing, In the axial direction of the shaft, the protrusion is positioned between the first bearing and the second bearing. In the axial direction, the outer ring of the second bearing is in contact with the protrusion, and the outer ring of the first bearing is spaced apart from the protrusion. In the axial direction, the inner ring of the first bearing is positioned closer to the first end than the outer ring of the first bearing. In the axial direction, the inner ring of the second bearing is positioned closer to the second end than the outer ring of the second bearing. In the axial direction, the end face on the second end side of the inner ring of the first bearing is open. In the axial direction, the end face of the inner ring of the second bearing on the first end side is open. The shaft has the same diameter between the first end and the second end. The aforementioned member is a belt or a gear. Motor.

4. Bearing device and Equipped with an impeller, The bearing device is A shaft having a first end and a second end, A sleeve having a protrusion that extends from the inner circumferential surface opposite the outer circumferential surface of the shaft, A first bearing having an inner ring, an outer ring, and spheres as rolling elements, is supported at the first end side between the outer circumferential surface of the shaft and the inner circumferential surface of the sleeve, The second bearing comprises an inner ring, an outer ring, and spherical elements as rolling elements, which are supported between the outer circumferential surface of the shaft and the inner circumferential surface of the sleeve at the second end side, The impeller is fixed to the shaft at the first end side of the first bearing, In the axial direction of the shaft, the protrusion is positioned between the first bearing and the second bearing. In the axial direction, the outer ring of the second bearing is in contact with the protrusion, and the outer ring of the first bearing is spaced apart from the protrusion. In the axial direction, the inner ring of the first bearing is positioned closer to the first end than the outer ring of the first bearing. In the axial direction, the inner ring of the second bearing is positioned closer to the second end than the outer ring of the second bearing. In the axial direction, the end face on the second end side of the inner ring of the first bearing is open. In the axial direction, the end face of the inner ring of the second bearing on the first end side is open. The shaft has the same diameter between the first end and the second end. Motor.

5. The motor according to claim 4, wherein the inner ring of the first bearing and the inner ring of the second bearing move in a direction toward the first end.

6. The motor according to claim 5, further comprising a rotor fixed to the shaft on the second end side of the second bearing.

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