Dynamic pressure bearing, fluid dynamic pressure bearing device, and motor

Abstract

A dynamic pressure bearing (bearing sleeve (8)) has a first dynamic pressure generating portion (11) and a second dynamic pressure generating portion (12) provided separately in the axial direction on an inner peripheral surface (8a). Each dynamic pressure generating portion (11, 12) has a plurality of dynamic pressure grooves (11a, 11b, 12a, 12b) having different inclination directions arranged in a herringbone shape. The first dynamic pressure generating portion (11) has an annular hill portion (11c) between the axial directions of the plurality of dynamic pressure grooves (11a, 11b) having different inclination directions. The plurality of dynamic pressure grooves (12a, 12b) having different inclination directions of the second dynamic pressure generating portion (12) are continuous in the axial direction.

Description

TECHNICAL FIELD

[0001] The present application relates to a dynamic pressure bearing, a fluid dynamic pressure bearing device, and a motor. BACKGROUND

[0002] A fluid dynamic pressure bearing device increases the pressure of lubricating fluid of a bearing gap formed between a bearing and a shaft by relative rotation of the bearing and the shaft, and non-contact supports the shaft using the pressure. Since the fluid dynamic pressure bearing device has characteristics such as high-speed rotation, high rotation accuracy, low noise, and the like, it is widely used as a bearing for a motor of a spindle motor of a magnetic disk drive device such as an HDD, a polygonal scan motor of a laser beam printer, a fan motor provided to a PC or the like.

[0003] An inner peripheral surface of a bearing of a fluid dynamic pressure bearing device is mostly formed with a dynamic pressure generating portion such as a dynamic pressure groove that actively generates pressure of lubricating fluid of a bearing gap (hereinafter, a bearing in which a dynamic pressure generating portion is formed on an inner peripheral surface will be referred to as a "dynamic pressure bearing"). For example, various dynamic pressure groove specifications formed in a dynamic pressure bearing are shown in Patent Documents 1 to 4 described below.

[0004] In Patent Document 1, a dynamic pressure groove specification in which a herringbone-shaped dynamic pressure groove provided at two places in the axial direction is continuous in the axial direction is shown.

[0005] In Patent Document 2, a dynamic pressure groove specification in which a herringbone-shaped dynamic pressure groove is formed on one side in the axial direction of a bearing surface and a cylindrical-shaped or spiral-shaped dynamic pressure groove is formed on the other side in the axial direction of the bearing surface is shown.

[0006] In Patent Document 3, a dynamic pressure groove specification in which a ratio of a circumferential width of a hill portion to a circumferential width of a groove portion is defined in order to reduce the amount of wear of a bearing surface is shown.

[0007] In Patent Document 4, a dynamic pressure groove specification in which a width of a dynamic pressure groove is made different on the upper side and the lower side with a center line as a reference is shown.

[0008] PRIOR ART DOCUMENTS

[0009] PATENT DOCUMENTS

[0010] Patent Document 1: Japanese Patent Application Publication No. 2015-64019

[0011] Patent Document 2: Japanese Patent Application Publication No. 2007-192316

[0012] Patent Document 3: Japanese Patent Application Publication No. 2007-255457

[0013] Patent Document 4: Japanese Patent Application Publication No. 2015-143576 SUMMARY

[0014] PROBLEMS TO BE SOLVED BY THE INVENTION

[0015] As a market trend, there is a strong demand for thinner and thinner information devices such as laptops, which in turn requires thinner fan motors for cooling them. On the other hand, recently, in order to cope with the high functionality of information devices for 5G mobile communication systems, there has been a tendency for increased heat generation from circuits, thus further increasing the requirements for the cooling performance of fan motors. Therefore, when using hydrodynamic bearings to support the rotating shaft of the fan motor, the axial dimension of the hydrodynamic bearings decreases with the thinning of information devices, but the size of the impeller increases in order to improve cooling performance, thus increasing the torque load applied to the hydrodynamic bearings. Thus, in order to make the hydrodynamic bearings axially compact while improving the bearing rigidity (torque rigidity) relative to the torque load and suppressing shaft oscillation, it is sometimes impossible to meet the requirements with the hydrodynamic groove specifications shown in Patent Documents 1 to 4.

[0016] Based on the above, the present invention improves the bearing rigidity relative to torque load and suppresses shaft oscillation without increasing the axial dimension of the hydrodynamic bearing.

[0017] Methods for solving problems

[0018] Figure 9 A conventional hydrodynamic bearing 100 is shown. A first hydrodynamic generating portion 102 and a second hydrodynamic generating portion 103, arranged axially separately, are provided on the inner peripheral surface 101 of the hydrodynamic bearing 100. Each hydrodynamic generating portion 102, 103 has multiple hydrodynamic grooves 104 arranged in a herringbone shape with different inclination directions.

[0019] To improve the torque stiffness of such a hydrodynamic bearing 100, one could consider increasing the bearing span L, which is the axial distance between the maximum pressure portions of the two hydrodynamic pressure generating portions 102 and 103 (in the example shown, the axial center portion of each hydrodynamic pressure generating portion 102 and 103). However, if the bearing span L is increased without changing the shape of the hydrodynamic pressure generating portions 102 and 103, the axial dimension of the hydrodynamic bearing 100 will increase.

[0020] For example, such as Figure 10 As shown, if the axial widths Da and Db of the annular mounds 105 of the dynamic pressure generating parts 102 and 103 are increased, the high-pressure area expands, and an increase in torque stiffness can be expected (in Figure 10 In the middle, it is represented by a dashed line. Figure 9 (The shape of the dynamic pressure groove). However, if the axial widths Da and Db of the annular mound 105 are increased, the axial widths Da1, Da2, Db1, and Db2 of the dynamic pressure groove 104 are correspondingly reduced, and the length of each dynamic pressure groove 104 becomes shorter. Therefore, the amount of fluid concentrated on the annular mound 105 side through the dynamic pressure groove 104 is reduced, resulting in a decrease in bearing rigidity.

[0021] In addition, as shown in Figure 11 If the axial widths Da1, Da2, Db1, Db2 of the dynamic pressure grooves 104 are maintained while the axial widths Da, Db of the annular hill portions 105 are expanded, the bearing span L becomes smaller, resulting in a decrease in the moment rigidity (in the Figure 11 In the dynamic pressure groove shape shown in Figure 9 by a dashed line, and (L) indicates the bearing span of the dynamic pressure groove.

[0022] Accordingly, the inventors have conceived of a configuration in which the fluid dynamic pressure (bearing rigidity) generated by the dynamic pressure generation portion differs depending on the axial position, with the idea that the amount of whip rotation of the shaft when a moment load is applied differs depending on the axial position. Based on this idea, the present application provides a dynamic pressure bearing having a first dynamic pressure generation portion and a second dynamic pressure generation portion provided separately in the axial direction on an inner peripheral surface, wherein each dynamic pressure generation portion has a plurality of dynamic pressure grooves arranged in a herringbone shape with different inclination directions, the first dynamic pressure generation portion has an annular hill portion between the axial directions of the plurality of dynamic pressure grooves with different inclination directions, and the plurality of dynamic pressure grooves with different inclination directions of the second dynamic pressure generation portion are continuous in the axial direction.

[0023] In this dynamic pressure bearing, the bearing rigidity of the first dynamic pressure generation portion having the annular hill portion is higher than the bearing rigidity of the second dynamic pressure generation portion having no annular hill portion (i.e., the plurality of dynamic pressure grooves with different inclination directions are continuous in the axial direction). In this way, by not providing the annular hill portion in the second dynamic pressure generation portion, the axial width of the annular hill portion of the first dynamic pressure generation portion can be expanded accordingly. Thus, the bearing rigidity of the first dynamic pressure generation portion can be improved without causing an increase in the axial dimension of the dynamic pressure bearing or a decrease in the bearing span. By configuring the dynamic pressure bearing in a manner in which the first dynamic pressure generation portion having a higher bearing rigidity is disposed at an axial position in which the amount of whip rotation of the shaft is expected to increase, the whip rotation of the shaft when a moment load is applied can be efficiently suppressed.

[0024] It is preferable that the dynamic pressure bearing described above have the inclination angle of the dynamic pressure grooves of the first dynamic pressure generation portion with respect to the circumferential direction be smaller than the inclination angle of the dynamic pressure grooves of the second dynamic pressure generation portion with respect to the circumferential direction. Thus, the bearing rigidity of each dynamic pressure generation portion can be maximized.

[0025] A fluid dynamic pressure bearing device can efficiently suppress the whip rotation of a shaft when a moment load is applied without increasing the axial dimension, wherein the fluid dynamic pressure bearing device has: the dynamic pressure bearing described above; a shaft member inserted into the inner periphery of the dynamic pressure bearing; and a radial bearing portion that supports the relative rotation of the shaft member by the dynamic pressure action of lubricating fluid in a radial bearing gap formed between the inner peripheral surface of the dynamic pressure bearing and the outer peripheral surface of the shaft member.

[0026] The fluid dynamic pressure bearing device described above can be assembled in a motor having a rotor rotating integrally with a shaft member or a dynamic pressure bearing and a driving section rotating the rotor (for example, a fan motor having a rotor with an impeller). In such a motor, generally, the runout of the shaft member is largest at an axial position including the center of gravity of the entire rotating side of the rotor. Therefore, by disposing the first dynamic pressure generating section having a higher bearing rigidity than the second dynamic pressure generating section at an axial position closer to the center of gravity of the entire rotating side of the rotor than the second dynamic pressure generating section, the runout of the shaft member when a torque load is applied can be efficiently suppressed.

[0027] Effects of Invention

[0028] As described above, according to the dynamic pressure bearing of the present application, the runout of the shaft with respect to a torque load can be suppressed while the bearing rigidity is increased without enlarging the axial dimension. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a cross-sectional view of a fan motor.

[0030] Figure 2 is a cross-sectional view of a fluid dynamic pressure bearing device assembled in the main shaft motor described above.

[0031] Figure 3 is a cross-sectional view of a dynamic pressure bearing (bearing sleeve) of one embodiment of the present application assembled in the fluid dynamic pressure bearing device described above.

[0032] Figure 4 is a cross-sectional view of a fluid dynamic pressure bearing device of another embodiment.

[0033] Figure 5 is a cross-sectional view of a main shaft motor of an HDD.

[0034] Figure 6 is a graph showing simulation results of the runout of the shaft.

[0035] Figure 7 is a graph showing simulation results of the runout of the shaft.

[0036] Figure 8 is a graph showing simulation results of the runout of the shaft.

[0037] Figure 9 is a cross-sectional view of a conventional dynamic pressure bearing.

[0038] Figure 10 is a cross-sectional view of a modification of the dynamic pressure bearing of Figure 9

[0039] Figure 11 is a cross-sectional view of another modification of the dynamic pressure bearing of Figure 9 ​​DETAILED DESCRIPTION

[0040] Hereinafter, an embodiment of the present application will be described with reference to the drawings.

[0041] Figure 1 The motor shown is a cooling fan motor assembled in an information device, particularly a mobile information device such as a notebook computer. The fan motor has a hydrodynamic pressure bearing device 1, a rotor 3 mounted to a shaft member 2 of the hydrodynamic pressure bearing device 1, a driving portion composed of a stator coil 6a and a rotor magnet 6b opposed across a radial direction gap, and a housing 5 that houses the above-mentioned members. The stator coil 6a is mounted to the outer periphery of the hydrodynamic pressure bearing device 1, and the rotor magnet 6b is mounted to the inner periphery of the rotor 3. By energizing the stator coil 6a, the rotor 3 and the shaft member 2 rotate integrally, and an air current is generated by an impeller 4 provided to the rotor 3.

[0042] As shown in Figure 2 , the hydrodynamic pressure bearing device 1 has the shaft member 2, a housing 7, a bearing sleeve 8 that is a dynamic pressure bearing of one embodiment of the present application, a seal portion 9, and a thrust receiving portion 10. Hereinafter, for the sake of convenience, the opening side of the housing 7 will be referred to as the upper side, and the bottom 7b side of the housing 7 will be referred to as the lower side in the up-and-down direction (axial direction), but this is not intended to limit the use of the motor. Figure 2

[0043] The shaft member 2 is formed in a cylindrical shape from a metal material such as stainless steel. The shaft member 2 has a cylindrical outer peripheral surface 2a and a spherical convex portion 2b provided to the lower end.

[0044] The housing 7 has a substantially cylindrical side portion 7a and a bottom 7b that closes the opening portion of the lower side of the side portion 7a. In the illustrated example, the side portion 7a and the bottom 7b are integrally injection molded from resin. The housing 5 and the stator coil 6a are fixed to the outer peripheral surface 7a2 of the side portion 7a. The bearing sleeve 8 is fixed to the inner peripheral surface 7al of the side portion 7a. A shoulder surface 7b2 located at a position higher than the inner diameter portion is provided to the outer diameter end of the upper side end surface 7bl of the bottom 7b, and the lower side end surface 8c of the bearing sleeve 8 abuts against this shoulder surface 7b2. The thrust receiving portion 10 made of resin is disposed to the central portion of the upper side end surface 7bl of the bottom 7b.

[0045] The bearing sleeve 8 is fixed to the inner peripheral surface 7al of the side portion 7a of the housing 7 by an appropriate method such as gap bonding, press fitting, press-in bonding (press fitting with adhesive intervention), and the like. In the present embodiment, the inner diameter of the bearing sleeve 8 is 3 mm or less in diameter, the outer diameter is 6 mm or less in diameter, and the axial dimension is 6 mm or less. The bearing sleeve 8 is composed of, for example, a metal, specifically a sintered metal, particularly a copper-iron sintered metal containing copper and iron as main components.

[0046] As​Figure 3 As shown, the first dynamic pressure generating portion 11 and the second dynamic pressure generating portion 12 are provided on the inner peripheral surface 8a of the bearing sleeve 8, which becomes a radial bearing surface, in an axially separated manner. Each of the dynamic pressure generating portions 11, 12 has a plurality of dynamic pressure grooves 11a, 11b, 12a, 12b arranged in a herringbone shape. The inclination directions of the upper dynamic pressure grooves 11a, 12a and the lower dynamic pressure grooves 11b, 12b of each of the dynamic pressure generating portions 11, 12 are different. In the illustrated example, the upper dynamic pressure grooves 11a, 12a are inclined in a direction that shifts toward the side opposite to the rotation direction of the shaft member 2 (left side in the drawing) as it goes toward the one axial direction (upper side in the drawing), and the lower dynamic pressure grooves 11b, 12b are inclined in a direction that shifts toward the side opposite to the rotation direction of the shaft member 2 (left side in the drawing) as it goes toward the other axial direction (lower side in the drawing). The bottom surfaces of the dynamic pressure grooves 11a, 11b, 12a, 12b are provided on the same cylindrical surface. The bottom surface of the lower dynamic pressure groove 11b of the first dynamic pressure generating portion 11 and the bottom surface of the upper dynamic pressure groove 12a of the second dynamic pressure generating portion 12 are continuous with the cylindrical surface 13 provided between the two dynamic pressure generating portions 11, 12 in the axial direction.

[0047] In the illustrated example, the inclination angles θ1a, θ1b of the dynamic pressure grooves 11a, 11b of the first dynamic pressure generating portion 11 with respect to the circumferential direction are equal, and the axial widths Da1, Da2 of the dynamic pressure grooves 11a, 11b are equal. The inclination angles θ2a, θ2b of the dynamic pressure grooves 12a, 12b of the second dynamic pressure generating portion 12 with respect to the circumferential direction are equal, and the axial widths Db1, Db2 of the dynamic pressure grooves 12a, 12b are equal. That is, the first dynamic pressure generating portion 11 and the second dynamic pressure generating portion 12 each have an axially symmetrical shape. The inclination angles θ1a, θ1b of the dynamic pressure grooves 11a, 11b of the first dynamic pressure generating portion 11 are smaller than the inclination angles θ2a, θ2b of the dynamic pressure grooves 12a, 12b of the second dynamic pressure generating portion 12. The axial widths Da1, Da2 of the dynamic pressure grooves 11a, 11b of the first dynamic pressure generating portion 11 are equal to the axial widths Db1, Db2 of the dynamic pressure grooves 12a, 12b of the second dynamic pressure generating portion 12. The dynamic pressure grooves 11a, 11b, 12a, 12b are each arranged at equal intervals in the circumferential direction. The number of the dynamic pressure grooves 11a, 11b, 12a, 12b is equal, and in the illustrated example, six are provided for each. Alternatively, one or both of the dynamic pressure generating portions 11, 12 can be formed in an axially asymmetrical shape. In this case, by the axially asymmetrical dynamic pressure generating portion, the lubricating fluid of the radial bearing gap is pressed in the axial direction, and the lubricating fluid is forcibly circulated inside the housing 7.

[0048] The first dynamic pressure generating portion 11 has a ring-shaped hill portion 11c between the axial direction of the upper dynamic pressure groove 11a and the lower dynamic pressure groove 11b. The first dynamic pressure generating portion 11 has inclined hill portions 11d, 11e between the circumferential direction of the upper dynamic pressure groove 11a and the circumferential direction of the lower dynamic pressure groove 11b, respectively. The ring-shaped hill portion 11c and the inclined hill portions 11d, 11e are raised from the bottom surface of the dynamic pressure grooves 11a, 11b toward the inner diameter side (cross-hatched area). Figure 3 The inner diameter surface of the ring-shaped hill portion 11c and the inclined hill portions 11d, 11e are provided on the same cylindrical surface. The ring-shaped hill portion 11c and all of the inclined hill portions 11d, 11e are continuously provided.

[0049] The second dynamic pressure generating portion 12 does not have a ring-shaped hill portion between the axial direction of the upper dynamic pressure groove 12a and the lower dynamic pressure groove 12b, and the dynamic pressure grooves 12a, 12b are continuous in the axial direction. The second dynamic pressure generating portion 12 has inclined hill portions 12d, 12e between the circumferential direction of the upper dynamic pressure groove 12a and the circumferential direction of the lower dynamic pressure groove 12b, respectively. The inclined hill portions 12d, 12e are raised from the bottom surface of the dynamic pressure grooves 12a, 12b toward the inner diameter side (cross-hatched area). Figure 3 The inner diameter surface of the inclined hill portions 12d, 12e is provided on the same cylindrical surface. Each inclined hill portion 12d is continuously provided with each inclined hill portion 12e, and a substantially V-shaped hill portion formed by each one of the inclined hill portions 12d, 12e is disposed separately in the circumferential direction.

[0050] As described above, since the second dynamic pressure generating portion 12 does not have a ring-shaped hill portion, the bearing sleeve 8 can accordingly enlarge the axial width Da of the ring-shaped hill portion 11c of the first dynamic pressure generating portion 11. For example, the axial width Da of the ring-shaped hill portion 11c can be made larger than the axial widths Da1, Da2 of the dynamic pressure grooves 11a, 11b. In this case, compared to a dynamic pressure bearing in which a ring-shaped hill portion is provided in each dynamic pressure generating portion (refer to PTL 1), the axial dimension of the bearing sleeve 8 is not enlarged, or the bearing span L, the axial dimensions of the dynamic pressure grooves 11a, 11b, 12a, 12b are not reduced. Figure 9

[0051] A radial groove 8b1 is formed in the upper end surface 8b of the bearing sleeve 8. A radial groove 8c1 is formed in the lower end surface 8c of the bearing sleeve 8. An axial groove 8d1 is formed in the outer peripheral surface 8d of the bearing sleeve 8. The number of the radial grooves 8b1, 8c1 and the axial groove 8d1 is arbitrary, and for example, three portions are formed at equal intervals in the circumferential direction, respectively.

[0052] The seal portion 9 is formed in a ring shape by resin or metal, and is fixed to the upper end portion of the inner peripheral surface 7a1 of the side portion 7a of the housing 7 (refer to FIG. 1). Figure 2 ​The sealing part 9 abuts against the upper end face 8b of the bearing sleeve 8. The inner circumferential surface 9a of the sealing part 9 is opposite to the outer circumferential surface 2a of the shaft component 2 in the radial direction, and a radial gap is formed between them.

[0053] The aforementioned hydrodynamic bearing device 1 is assembled according to the following steps. First, the thrust bearing part 10 is fixed to the upper end face 7b1 of the bottom 7b of the housing 7. Then, the bearing sleeve 8, which has been pre-lubricated with internal pores, is inserted into the inner circumference of the side portion 7a of the housing 7, so that the lower end face 8c of the bearing sleeve 8 abuts against the shoulder face 7b2 of the bottom 7b. Afterward, the sealing part 9 is fixed to the upper end of the inner circumferential surface 7a1 of the side portion 7a of the housing 7.

[0054] Then, the shaft component 2 is inserted into the inner circumference of the bearing sleeve 8. At this time, the air between the bottom 7b of the housing 7 and the lower end (protrusion 2b) of the shaft component 2 is discharged to the outside through the radial groove 8c1 of the lower end face 8c of the bearing sleeve 8, the axial groove 8d1 of the outer circumferential surface 8d, and the radial groove 8b1 of the upper end face 8b, thus allowing the shaft component 2 to be inserted smoothly. Afterward, lubricating oil is injected into the space inside the housing 7. The lubricating oil at least fills the gap (radial bearing clearance) between the inner circumferential surface 8a of the bearing sleeve 8 and the outer circumferential surface 2a of the shaft component 2, and the space P between the lower end face 8c of the bearing sleeve 8 and the upper end face 7b1 of the bottom 7b of the housing 7. The hydrodynamic bearing device 1 of this embodiment is a so-called partially filled hydrodynamic bearing device in which the amount of lubricating oil is less than the volume of the entire space inside the housing 7. Thus, the assembly of the hydrodynamic bearing device 1 is completed.

[0055] Assemble the hydrodynamic bearing device 1 into Figure 1 In the state of the motor shown, the center of gravity G of the entire rotating side, including rotor 3 and shaft component 2, is set at... Figure 2 The positions shown are as follows. In the hydrodynamic pressure generating portions 11 and 12 of the bearing sleeve 8, the first hydrodynamic pressure generating portion 11, having an annular mound 11c, is positioned axially closer to the center of gravity G than the second hydrodynamic pressure generating portion 12, which does not have an annular mound. In the example shown, the center of gravity G on the rotational side is positioned above the axial center of the bearing sleeve 8; therefore, the bearing sleeve 8 is assembled to the hydrodynamic bearing assembly 1 with the first hydrodynamic pressure generating portion 11 positioned above and the second hydrodynamic pressure generating portion 12 positioned below.

[0056] In the hydrodynamic bearing device 1 with the above-described structure, when the shaft component 2 rotates, a radial bearing clearance is formed between the inner circumferential surface 8a of the bearing sleeve 8 and the outer circumferential surface 2a of the shaft component 2. Furthermore, the hydrodynamic pressure generating portions 11 and 12 formed on the inner circumferential surface 8a of the bearing sleeve 8 generate hydrodynamic pressure on the lubricating oil in the radial bearing clearance. Specifically, the lubricating oil in the radial bearing clearance concentrates along the hydrodynamic pressure grooves 11a, 11b, 12a, 12b at the axial central side of each hydrodynamic pressure generating portion 11 and 12, increasing the fluid pressure in this portion. Thus, radial bearing portions R1 and R2 are constructed that provide non-contact support to the shaft component 2 in the radial direction. Additionally, a thrust bearing portion T is constructed that supports the shaft component 2 in the thrust direction by sliding through contact between the protrusion 2b at the lower end of the shaft component 2 and the thrust bearing portion 10.

[0057] Since the first dynamic pressure generating section 11 has an annular mound 11c, the generated hydraulic pressure (i.e., bearing rigidity) is higher compared to the case without the annular mound. Furthermore, since the annular mound is not provided on the second dynamic pressure generating section 12, the axial width D of the annular mound 11c of the first dynamic pressure generating section 11 can be increased, thereby further improving the bearing rigidity based on the first dynamic pressure generating section 11.

[0058] like Figure 2 As shown, since the center of gravity G of the entire rotating side including the rotor 3 is located higher than the axial center of the bearing sleeve 8, the oscillation rotation of the shaft component 2 tends to be larger on the upper side. The bearing sleeve 8 is assembled to the motor with the first dynamic pressure generating part 11 having an annular mound 11c positioned on the upper side and the second dynamic pressure generating part 12 without an annular mound positioned on the lower side. As a result, the upper part of the shaft component 2 with a larger oscillation rotation is supported by the radial bearing part R1 based on the first dynamic pressure generating part 11, which has relatively high bearing rigidity. On the other hand, the lower part of the shaft component 2 with a relatively smaller oscillation rotation is supported by the radial bearing part R2 based on the second dynamic pressure generating part 12, which has relatively low bearing rigidity. As described above, by slightly sacrificing the bearing rigidity based on the second dynamic pressure generating part 12 to increase the bearing rigidity of the first dynamic pressure generating part 11, the first dynamic pressure generating part 11 is used to support the axial position of the shaft component 2 near the center of gravity G, thereby effectively suppressing the oscillation and rotation of the shaft component 2 caused by torque load.

[0059] The first dynamic pressure generating section 11, which has an annular mound 11c, can improve the generated hydraulic pressure, i.e., bearing rigidity, by minimizing the inclination angles θ1a and θ1b of the dynamic pressure grooves 11a and 11b relative to the circumference. On the other hand, if the second dynamic pressure generating section 12, which does not have an annular mound, excessively reduces the inclination angles θ2a and θ2b of the dynamic pressure grooves 12a and 12b relative to the circumference, the generated hydraulic pressure, i.e., bearing rigidity, will decrease. Therefore, it is preferable that the inclination angles θ1a and θ1b of the dynamic pressure grooves 11a and 11b of the first dynamic pressure generating section 11 relative to the circumference are smaller than the inclination angles θ2a and θ2b of the dynamic pressure grooves 12a and 12b of the second dynamic pressure generating section 12 relative to the circumference. For example, the tilt angles θ1a and θ1b of the dynamic pressure grooves 11a and 11b of the first dynamic pressure generating unit 11 are made less than 30°, and the tilt angles θ2a and θ2b of the dynamic pressure grooves 12a and 12b of the second dynamic pressure generating unit 12 are made 30° or more. This maximizes the hydraulic pressure generated by each dynamic pressure generating unit 11 and 12. Furthermore, if the bearing rigidity is sufficient, the tilt angles θ1a and θ1b of the dynamic pressure grooves 11a and 11b of the first dynamic pressure generating unit 11 can be greater than, or equal to, the tilt angles θ2a and θ2b of the dynamic pressure grooves 12a and 12b of the second dynamic pressure generating unit 12.

[0060] This invention is not limited to the embodiments described above. Hereinafter, another embodiment of the invention will be described, but repeated descriptions of points identical to those in the above embodiments will be omitted.

[0061] The hydrodynamic bearing device 1 can also be a fully filled type. For example, in Figure 4 In the illustrated embodiment, a tapered surface that expands in diameter as it faces upwards is provided on the inner circumferential surface 9a of the sealing portion 9. A wedge-shaped sealing space S, with a radially narrowing width, is formed between the tapered surface of the sealing portion 9 and the outer circumferential surface of the shaft component 2. An oil level is maintained within this sealing space S. The entire space within the housing 7 (the space further inward than the sealing space S) is filled with lubricating oil.

[0062] The hydrodynamic bearing device 1 may also have a thrust bearing section that supports the shaft component 2 along the thrust direction using the fluid pressure from the thrust bearing clearance. For example, in Figure 4In the illustrated embodiment, a flange portion 2b is provided at the lower end of the shaft member 2. A dynamic pressure groove is formed at the lower side end surface 8c of the bearing sleeve 8, instead of a radial direction groove. A dynamic pressure groove is formed at the upper side end surface 7bl of the bottom portion 7b of the housing 7. In the illustrated example, the side portion 7a and the bottom portion 7b of the housing 7 are formed by different members, and the side portion 7a of the housing 7 and the seal portion 9 are formed by one member. When the shaft member 2 is rotated, a thrust bearing gap is formed between the upper side end surface 2bl of the flange portion 2b of the shaft member 2 and the lower side end surface 8c of the bearing sleeve 8, and between the lower side end surface 2b2 of the flange portion 2b of the shaft member 2 and the upper side end surface 7bl of the bottom portion 7b of the housing 7, respectively. Further, by the dynamic pressure grooves formed at the lower side end surface 8c of the bearing sleeve 8 and the upper side end surface 7bl of the bottom portion 7b of the housing 7, the pressure of the lubricating fluid in the thrust bearing gaps is increased, thereby constituting thrust bearing portions Tl, T2 that support the shaft member 2 in both thrust directions.

[0063] The fluid dynamic pressure bearing device 1 is not limited to a fan motor, and can be assembled to other motors (for example, a spindle motor of a disk drive device, a polygonal scan motor, etc.). For example, Figure 5 The illustrated spindle motor is used for a disk drive device of an HDD, and has the fluid dynamic pressure bearing device 1, a rotor 3 (a disk hub) mounted to the shaft member 2, a stator coil 6a, and a rotor magnet 6b. A disk D such as a magnetic disk is held in a prescribed number (2 in the illustrated example) on the rotor 3. When the stator coil 6a is energized, the shaft member 2, the rotor 3, and the disk D rotate integrally.

[0064] In the above embodiment, the fluid dynamic pressure bearing device of the shaft rotating type in which the dynamic pressure bearing is the fixed side and the shaft member is the rotating side is shown, but the dynamic pressure bearing of the present application can also be applied to a fluid dynamic pressure bearing device of the shaft fixed type in which the shaft member is the fixed side and the dynamic pressure bearing is the rotating side.

[0065] [Example 1]

[0066] In order to confirm the effects of the present application, the following simulation was performed.

[0067] A dynamic pressure bearing model (Example 1) having a dynamic pressure groove of the shape shown in Figure 3 A dynamic pressure bearing model (Comparative Example) having a dynamic pressure groove of the shape shown in Figure 9 The dynamic pressure groove specifications of Example 1 and the Comparative Example are shown in Table 1 below.

[0068] [Table 1]

[0069]

[0070] The shaft component model is constructed taking into account the overall weight and center of gravity of the rotating side, including the rotor. Then, the shaft component model is inserted into the inner circumference of the hydrodynamic bearing model, and with the axial direction horizontal, the amount of oscillation rotation when the shaft component model rotates is calculated according to the following calculation conditions. Furthermore, the amount of oscillation rotation refers to the maximum displacement (offset) of the shaft component model's axis of rotation relative to the axis of the shaft component model when stationary, in the direction perpendicular to the axial direction.

[0071] Radial bearing clearance: 5μm

[0072] Rotation speed: 4900 rpm

[0073] Lubricating oil: Kinematic viscosity at 40℃ = 42.6 mm 2 / s, kinematic viscosity at 100℃ = 7.32mm 2 / s

[0074] like Figure 6 As shown, when comparing Example 1 and the Comparative Example, it can be seen that at an ambient temperature of 20°C, no significant difference was observed in the shaft's runout. However, as the temperature increases, the runout of the shaft in the present invention decreases compared to the Comparative Example (this is because the viscosity of the lubricating oil decreases with increasing temperature, resulting in a decrease in bearing rigidity). In particular, the runout of the shaft in the radial bearing section R1 (first dynamic pressure generating section 11) of the Comparative Example at 100°C is 4.7 μm relative to the radial bearing clearance of 5 μm. In this case, considering the shaft's shape and the roundness of the bearing's inner diameter, it is highly likely that the shaft would be practically unusable due to contact with the bearing. In contrast, the runout of the shaft in the radial bearing section R1 (first dynamic pressure generating section 11) of the present invention at 100°C is 2.8 μm relative to the radial bearing clearance of 5 μm, thus enabling its practical use. Thus, although no significant difference was observed in the amount of shaft oscillation in Example 1 and the comparative example near room temperature where the viscosity of the lubricating oil is relatively high, the oscillation at high temperatures can be suppressed by adopting the hydrodynamic groove specification of Example 1, thereby enabling use in more demanding environments without increasing the axial dimension of the hydrodynamic bearing.

[0075] Next, various dynamic pressure bearing models (Examples 2-6) with different inclination angles θ1 (=θ1a=θ1b) of the dynamic pressure grooves 11a and 11b of the first dynamic pressure generating part 11 having annular mounds were fabricated, and the same simulation as described above was performed. The specifications of the dynamic pressure grooves of Examples 2-6 are shown in Table 2 below.

[0076] Table 2

[0077]

[0078] like Figure 7As shown, the smaller the inclination angle θ1 of the dynamic pressure grooves 11a and 11b of the first dynamic pressure generating section 11, the smaller the amount of shaft oscillation rotation. Based on this result, it is preferable that the inclination angle of the dynamic pressure grooves of the first dynamic pressure generating section relative to the circumferential direction is as small as possible, for example, preferably less than 30°, more preferably less than 20°. On the other hand, if the inclination angle of the dynamic pressure grooves of the first dynamic pressure generating section is too small, it may cause problems in workability, so it is preferable that it is 1° or more, more preferably 5° or more.

[0079] Next, dynamic pressure bearing models (Examples 7-11) were fabricated with different inclination angles θ2 (=θ2a=θ2b) relative to the circumference of the dynamic pressure grooves 12a and 12b of the second dynamic pressure generating part 12 that does not have annular mounds, and the same simulation as described above was performed. The specifications of the dynamic pressure grooves of Examples 7-11 are shown in Table 3 below.

[0080] Table 3

[0081]

[0082] like Figure 8 As shown, when the inclination angle of the dynamic pressure groove in the second dynamic pressure generating section is 30°, the shaft's oscillation rotation becomes minimal; the further away from 30°, the greater the shaft's oscillation rotation becomes. In particular, when the inclination angle of the dynamic pressure groove in the second dynamic pressure generating section is less than 30°, the increase in shaft oscillation rotation is significant compared to the case where it is greater than 30°. Based on this result, the inclination angle of the dynamic pressure groove in the first dynamic pressure generating section relative to the circumference is preferably 20° or more, more preferably 30° or more. Furthermore, to suppress the shaft's oscillation rotation, the inclination angle of the dynamic pressure groove in the second dynamic pressure generating section relative to the circumference is preferably 50° or less, more preferably 40° or less.

[0083] Label Explanation

[0084] 1: Hydrodynamic bearing assembly; 2: Shaft component; 3: Rotor; 4: Impeller; 7: Housing; 8: Bearing sleeve (hydrodynamic bearing); 9: Sealing part; 11: First hydrodynamic generating part; 11a, 11b: Hydrodynamic groove; 11c: Annular mound; 11d: Inclined mound; 12: Second hydrodynamic generating part; 12a, 12b: Hydrodynamic groove; 12d: Inclined mound; 13: Cylindrical surface; G: Center of gravity of the entire rotating side; L: Bearing span; R1, R2: Radial bearing parts; T: Thrust bearing part.

Claims

1. A hydrodynamic bearing having a first hydrodynamic pressure generating portion and a second hydrodynamic pressure generating portion provided separately in an axial direction on an inner peripheral surface, wherein each of the hydrodynamic pressure generating portions has a plurality of hydrodynamic grooves having different inclination directions arranged in a herringbone shape, the first hydrodynamic pressure generating portion has a ring-shaped hill portion between the axial directions of the plurality of hydrodynamic grooves having different inclination directions, the second hydrodynamic pressure generating portion has the plurality of hydrodynamic grooves having different inclination directions continuous in the axial direction, an inclination angle of the hydrodynamic grooves of the first hydrodynamic pressure generating portion with respect to a circumferential direction is smaller than an inclination angle of the hydrodynamic grooves of the second hydrodynamic pressure generating portion with respect to the circumferential direction, the inclination angle of the hydrodynamic grooves of the first hydrodynamic pressure generating portion with respect to the circumferential direction is 20° or less, and the inclination angle of the hydrodynamic grooves of the second hydrodynamic pressure generating portion with respect to the circumferential direction is 20° or more and 40° or less.

2. A hydrodynamic bearing apparatus comprising: the hydrodynamic bearing according to claim 1; a shaft member inserted into an inner periphery of the hydrodynamic bearing; and a radial bearing portion that supports relative rotation of the shaft member by a hydrodynamic pressure of lubricating fluid in a radial bearing gap formed between an inner peripheral surface of the hydrodynamic bearing and an outer peripheral surface of the shaft member.

3. A motor comprising: the hydrodynamic bearing apparatus according to claim 2; a rotor that rotates integrally with the shaft member or the hydrodynamic bearing; and a driving portion that rotationally drives the rotor.

4. The motor according to claim 3, wherein the first hydrodynamic pressure generating portion is disposed at an axial position closer to a center of gravity of an entire rotation side including the rotor than the second hydrodynamic pressure generating portion.

5. The motor according to claim 3, wherein the rotor has an impeller. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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