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

Abstract

To provide a dynamic pressure bearing that can improve load capacity without enlarging an axial dimension and impairing versatility, and to provide a fluid dynamic pressure bearing device and a motor.SOLUTION: A dynamic pressure bearing includes: a bearing inner diameter surface opposite to an outer diameter surface of a shaft member; and a dynamic pressure generation part in the bearing inner diameter surface. The dynamic pressure generation part has a plurality of dynamic pressure grooves arranged in a herringbone pattern, and the dynamic pressure grooves include first and second groups of dynamic pressure grooves. An annular ridge part extending in the circumferential direction is provided between the first and second groups of dynamic pressure grooves. A recess for generating dynamic pressure is formed in a partial area of the annular ridge part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a dynamic pressure bearing, a fluid dynamic pressure bearing device, and a motor. [Background technology]

[0002] A fluid dynamic bearing device supports a shaft member in a non-contact manner, allowing relative rotation, by using pressure generated in a fluid film (e.g., an oil film) in the radial bearing gap between the outer circumferential surface of the shaft member and the inner circumferential surface of the bearing member. Due to their high rotational accuracy and quietness, fluid dynamic bearing devices are ideal for use in small motors such as spindle motors for information devices (e.g., magnetic disk drives such as HDDs, optical disk drives for CD-ROMs, CD-R / RWs, DVD-ROM / RAMs, and Blu-ray disks, and magneto-optical disk drives for MDs and MOs), polygon scanner motors for laser beam printers (LBPs), color wheels for projectors, and fan motors used in cooling fans for electrical equipment.

[0003] There is a strong demand for thinner portable information devices (so-called mobile devices) such as laptops and tablet PCs. Furthermore, in recent years, as information devices become more sophisticated to support 5G (five-grade G), the amount of heat generated from circuits increases, leading to higher demands for cooling performance. This has resulted in larger impellers attached to rotating shafts. This increases the load on the hydrodynamic bearing devices that support the rotating shafts of fan motors. 5G (fifth-generation G) refers to the "fifth-generation mobile communications system," and its three main features are "high speed and large capacity," "multiple simultaneous connections," and "ultra-low latency."

[0004] A conventional hydrodynamic bearing compatible with thin fan motors is described in Patent Document 1. The hydrodynamic bearing described in Patent Document 1 aims to increase bearing rigidity against moment loads and suppress shaft whirling without increasing the axial dimension. In this case, hydrodynamic pressure generating sections with different groove (hydrodynamic groove) specifications are arranged in two axial rows. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-54860 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the motor described in Patent Document 1, which uses a hydrodynamic bearing, it is necessary to change the groove specifications depending on the center of gravity position of the rotor, which can result in poor versatility and high costs. Furthermore, in this case, since the groove specifications for the top and bottom are different, if there is a motor with the same motor specifications but a different rotation direction, it cannot be used even if it is turned upside down.

[0007] In view of the above, the present invention provides a hydrodynamic bearing, a fluid dynamic bearing device, and a motor that can improve load capacity without increasing the axial dimension and without compromising versatility. [Means for solving the problem]

[0008] The hydrodynamic bearing of the present invention has an inner diameter surface facing the outer diameter surface of a shaft member, and is provided with a hydrodynamic pressure generating portion on the inner diameter surface of the bearing, the hydrodynamic pressure generating portion having a plurality of hydrodynamic pressure grooves arranged in a herringbone pattern, the hydrodynamic pressure grooves being provided with first and second hydrodynamic pressure groove groups spaced apart along the axial direction, with sloping hill portions formed between the hydrodynamic pressure grooves of the first and second hydrodynamic pressure groove groups, and annular hill portions being provided between the first and second hydrodynamic pressure groove groups and extending in the circumferential direction and connected to each of the sloping hill portions, and a recess for generating hydrodynamic pressure is formed in part of the annular hill portion.

[0009] According to the hydrodynamic bearing of the present invention, a step is formed between the inclined groove (hydrodynamic groove) in each hydrodynamic groove group and the annular hill portion, and pressure (hydrodynamic pressure) is generated at this step, and pressure (hydrodynamic pressure) is generated downstream in the direction of rotation from the recess in the annular hill portion. In other words, a recess is provided in the annular hill portion to generate pressure by a wedge effect, thereby improving load capacity.

[0010] It is preferable that a recess for generating the dynamic pressure is provided at the confluence of the annular hill portion and the inclined hill portion, the circumferential width of the recess is smaller than the circumferential width of the confluence, the number of dynamic pressure grooves in the first and second dynamic pressure groove groups is the same, the confluence of the inclined hill portion and the annular hill portion of the first dynamic pressure group coincides with the confluence of the inclined hill portion and the annular hill portion of the second dynamic pressure group, and the recess is provided at all confluences.

[0011] By providing recesses at all confluences between the annular hill and the inclined hill, the load capacity can be further increased.Furthermore, by making the circumferential width of the recesses smaller than the circumferential width of the confluences, the recesses can be set larger within the dimensions that do not contact the contours of the annular hill and the inclined hill, thereby further increasing the load capacity.

[0012] A pair of dynamic pressure generating portions having an upside-down shape and spaced apart in the axial direction may be formed on the inner diameter surface of the bearing. By configuring it in this way, it can be adapted to motors with the same specifications but different rotation directions by simply reversing the bearing upside down.

[0013] The fluid dynamic bearing device of the present invention comprises the dynamic bearing, a shaft member inserted into the inner circumference of the dynamic bearing, and a radial bearing portion that supports the relative rotation of the shaft member by the dynamic pressure action of the lubricating fluid in the radial bearing gap formed between the inner surface of the dynamic bearing and the outer surface of the shaft member.

[0014] The fluid dynamic bearing device of the present invention uses a dynamic bearing that can improve load capacity, so it is possible to support the load on the bearing even if the axial dimension of the bearing is reduced to make it thinner.

[0015] A motor according to the present invention includes the fluid dynamic bearing device, a rotor that rotates integrally with the shaft member or the dynamic bearing, and a drive unit that drives the rotor to rotate, impeller It has the following characteristics.

[0016] Even if the impeller size is increased, the load on the bearing can be sufficiently supported, and cooling performance can be improved. [Effects of the Invention]

[0017] The present invention improves load capacity, allowing the bearing to function satisfactorily even when miniaturized. In other words, it is possible to provide a bearing that improves load capacity without increasing the axial dimension. Furthermore, in motors using this hydrodynamic bearing, there is no need to change the groove specifications depending on the center of gravity of the rotor, and there is no risk of the bearing's versatility being compromised. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view of a hydrodynamic bearing according to the present invention. [Figure 2] FIG. 2 is an enlarged simplified view of the main part of FIG. [Figure 3] 1 is a cross-sectional view of a dynamic pressure bearing device using a dynamic pressure bearing according to the present invention. [Figure 4] FIG. 4 is a cross-sectional view of a motor equipped with the dynamic pressure bearing device shown in FIG. [Figure 5] FIG. [Figure 6] This shows the implementation product 1, where (a) is a groove specification diagram and (b) is a pressure distribution diagram. [Figure 7] This shows the comparative product 1, where (a) is a groove specification diagram and (b) is a pressure distribution diagram. [Figure 8] This shows comparative product 2, where (a) is a groove specification diagram and (b) is a pressure distribution diagram. [Figure 9] This shows conventional product 1, where (a) is the groove specification diagram and (b) is the pressure distribution diagram. [Figure 10] FIG. 10 is a cross-sectional view of a hydrodynamic bearing used in Example 2. [Figure 11] FIG. 1 is a cross-sectional view of a hydrodynamic bearing used in conventional product 2. DETAILED DESCRIPTION OF THE INVENTION

[0019] An embodiment of the present invention will now be described with reference to Figures 1 to 4. Figure 1 shows a dynamic pressure bearing according to this embodiment, Figure 2 shows an enlarged simplified view of the main parts of the dynamic pressure bearing, Figure 3 shows a fluid dynamic pressure bearing device using the dynamic pressure bearing according to the present invention, and Figure 4 shows a cooling fan motor using this fluid dynamic pressure bearing device. This fan motor is incorporated into, for example, information devices, particularly mobile devices such as mobile phones and tablet terminals.

[0020] This fan motor comprises a fluid dynamic bearing device 1 according to one embodiment of the present invention, a rotor 3 mounted on a shaft member 2 of the fluid dynamic bearing device 1, an impeller (vanes) 4 attached to the outer diameter end of the rotor 3, a stator coil 6a and a rotor magnet 6b opposed to each other with a radial gap between them, and a casing 5 that houses these. The stator coil 6a is attached to the outer periphery of the fluid dynamic bearing device 1, and the rotor magnet 6b is attached to the inner periphery of the rotor 3. When current is applied to the stator coil 6a, the rotor 3, impeller 4, and shaft member 2 rotate together, thereby generating an airflow in the axial or outer diameter direction.

[0021] As shown in Fig. 3, the fluid dynamic bearing device 1 comprises a shaft member 2, a housing 7, a bearing sleeve 8 as a dynamic bearing according to the present invention, a seal member 9, and a thrust bearing 10. In the following, the opening side of the housing 7 will be referred to as the upper side in the axial direction (the vertical direction in Fig. 2), and the side of the bottom 7b of the housing 7 will be referred to as the lower side.

[0022] The shaft member 2 is formed in a cylindrical shape from a metal material such as stainless steel, etc. The shaft member 2 has a cylindrical outer peripheral surface 2a and a spherical convex portion 2b provided at the lower end.

[0023] The housing 7 has a substantially cylindrical side portion 7a and a bottom portion 7b that closes the opening below the side portion 7a. In the illustrated example, the side portion 7a and the bottom portion 7b are integrally injection-molded from resin. The casing 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 7a1 of the side portion 7a. A shoulder surface 7b2 is provided at the outer diameter end of the upper end surface 7b1 of the bottom portion 7b, located above the inner diameter portion, and the lower end surface 8c of the bearing sleeve 8 abuts against this shoulder surface 7b2. A circumferential notch 7b4 is formed in the outer peripheral surface 7a2 of the side portion 7a, and the stator coil 6a is fitted into this circumferential notch 7b4. A resin thrust receiver 10 is disposed in the center of the upper end surface 7b1 of the bottom portion 7b. Instead of (or in addition to) providing the radial grooves 7b3 on the shoulder surface 7b2 of the housing 7, a radial groove may be formed on the lower end surface 8c of the bearing sleeve 8.

[0024] The bearing sleeve 8 is cylindrical and fixed to the inner peripheral surface 7a1 of the side portion 7a of the housing 7 by an appropriate means such as gap welding, press fitting, or press fitting adhesion (press fitting with an adhesive interposed therebetween). In this embodiment, the bearing sleeve 8 can be made of sintered metal processed by pressing, ingot material such as brass or stainless steel processed by cutting, or resin processed by injection molding.

[0025] A pair of dynamic pressure generating portions 20 (20A, 20B) are provided axially spaced apart on the inner peripheral surface 8a of the bearing sleeve 8, which serves as the radial bearing surface. Each of the dynamic pressure generating portions 20A, 20B has a plurality of dynamic pressure grooves 11a, 11b arranged in a herringbone pattern. The dynamic pressure grooves 11a, 11a on the axially outer side of the dynamic pressure generating portions 20A, 20B form a first dynamic pressure groove group 11A, 11A, and the dynamic pressure grooves 11b, 11b on the axially inner side of the dynamic pressure generating portion 20 form a second dynamic pressure groove group 11B, 11B. The pair of dynamic pressure generating portions 20A, 20B have an upside-down shape.

[0026] Furthermore, in each of the dynamic pressure generating portions 20A, 20B, the dynamic pressure grooves 11a, 11a on the axially outer side and the dynamic pressure grooves 11b, 11b on the axially inner side have different inclination directions. In the illustrated example, the dynamic pressure grooves 11a, 11a on the axially outer side are inclined from the axially outer side to the axially inner side along the rotation direction of the shaft member 2, while the dynamic pressure grooves 11b, 11b on the axially inner side are inclined from the axially inner side to the axially outward side along the rotation direction of the shaft member 2. The bottom surfaces of the dynamic pressure grooves 11a, 11b are provided on the same cylindrical surface. The bottom surface of the dynamic pressure groove 11b on the axially inner side is continuous with the cylindrical surface 13 provided axially between the two dynamic pressure generating portions 20 (20A, 20B).

[0027] Inclined hills 11c and 11d are provided between the dynamic pressure grooves 11a and 11b, respectively. Furthermore, in each dynamic pressure generating portion 20 (20A, 20B), annular hills 11e and 11e are provided between the first dynamic pressure groove group 11A and the second dynamic pressure groove group 11B. The inclined hills 11c and 11d and the annular hills 11e and 11e are indicated by cross-hatching. The annular hills 11e and 11e and the inclined hills 11c and 11d rise from the bottom surfaces of the dynamic pressure grooves 11a and 11b toward the inner diameter side. The inner diameter surfaces of the annular hills 11e and 11e and the inclined hills 11c and 11d are provided on the same cylindrical surface. The annular hills 11e and 11e and all of the inclined hills 11c and 11d are provided continuously.

[0028] Let A and B be the axial lengths (width dimensions) of the first dynamic pressure groove group 11A and the second dynamic pressure groove group 11B, and add them to the axial length (width dimension) C of the annular hill portion 11e, 11e, so that A = B > C. In each of the first dynamic pressure generating portions 20A and second dynamic pressure generating portions 20B, the inclination angle θa (see FIG. 2) of the dynamic pressure grooves 11a, 11a of the first dynamic pressure groove group 11A, 11A relative to the circumferential direction is set equal to the inclination angle θb (see FIG. 2) of the dynamic pressure grooves 11b, 11b of the second dynamic pressure groove group 11B, 11B relative to the circumferential direction.

[0029] The annular hill 11e is provided with a recess 11e1. In this case, the recess 11e1 is formed at the junction U of the inclined hills 11c and 11d and the annular hill 11e. In the illustrated example, the recess 11e1 is configured in a rectangular shape, and the depth dimension is equal to the height dimension of the annular hill 11e. That is, the bottom surface of the recess 11e1 is coincident with the cylindrical surface 13. The width dimension (axial length) of the recess 11e1 is also set to be approximately the same as the width dimension (axial length) of the annular hill portion 11e. In this case, the circumferential length of the recess 11e1 is set to a dimension that does not expose the recess 11e1 from the confluence portion U. That is, when the circumferential length of the confluence portion U is L and the circumferential length of the recess 11e1 is L1, L > L1 is satisfied. When the axial length of the confluence portion U is H and the axial length of the recess 11e1 in the bearing direction is H1, H ≥ H1 is satisfied.

[0030] Specifically, the bearing sleeve 8 is formed from a sintered metal, for example, a sintered metal containing 35 wt.% or more copper, particularly a sintered metal containing 35 wt.% or more each of copper and iron. The bearing sleeve 8 is manufactured by the following method. First, raw material powder is compressed to form a green compact (compacting process). The raw material powder contains, as the main component metal powder, either or both of copper-based powder (copper powder or copper alloy powder) and iron-based powder (iron powder or iron alloy powder). The raw material powder may also contain high-hardness powder such as stainless steel powder. In this embodiment, the raw material powder contains, as the main component metal powder, pure iron powder and pure copper powder. In addition to the main component metal powder, the raw material powder may also contain low-melting-point metal powder such as tin powder, carbon powder such as graphite powder, or a molding lubricant. The green compact is sintered at a predetermined sintering temperature to obtain a sintered body (sintering process). The sintered body is then sized to form dynamic pressure grooves 11, 11 on the inner circumferential surface (sizing process). In this embodiment, the inner peripheral surface of the sintered body is subjected to a sealing treatment such as rotary sizing, etc. The bearing sleeve 8 is completed by impregnating the internal pores of this sintered body with lubricating oil.

[0031] The bearing sleeve 8 has a density ratio of 80 to 95%. The bearing sleeve 8 has communicating pores that connect the interior and the surface; specifically, communicating pores with an oil content of 4% or more are formed. That is, the molding conditions of the bearing sleeve 8 (for example, the compression ratio in the compacting step and the sizing step) are set so that communicating pores with an oil content of 4% or more are formed. As a result of sizing, the surface opening ratio of the inner circumferential surface 8a (radial bearing surface) of the bearing sleeve 8 is set to be equal to or less than the porosity (= 100% - density ratio) of the bearing sleeve 8; specifically, it is set to be 10% or less, preferably 8% or less, and more preferably 5% or less. By setting the opening ratio to be 10% or less, it is possible to effectively prevent dynamic pressure from leaking from the inner diameter surface 8a.

[0032] Axial grooves 8d1 are formed on the outer peripheral surface of the bearing sleeve 8. The number of axial grooves 8d1 is arbitrary, and for example, they are formed in three locations at equal intervals in the circumferential direction.

[0033] The seal member 9 is formed in an annular shape from resin or metal and is fixed to the upper end of the inner circumferential surface 7a1 of the side portion 7a of the housing 7. The seal member 9 abuts against the upper end face 8b of the bearing sleeve 8. The inner circumferential surface 9a of the seal member 9 faces the outer circumferential surface 2a of the shaft member 2 in the radial direction, and a seal space S is formed therebetween. When the shaft member 2 rotates, the seal space S prevents the lubricating oil inside the bearing from leaking to the outside. A radial groove 9b1 is formed in the lower end face 9b of the seal member 9. Note that instead of (or in addition to) forming the radial groove 9b1 in the lower end face 9b of the seal member 9, a radial groove may be formed in the upper end face 8b of the bearing sleeve 8.

[0034] The hydrodynamic bearing device 1 is assembled as follows. First, the thrust receiver 10 is fixed to the upper end surface 7b1 of the bottom portion 7b of the housing 7. Next, the bearing sleeve 8, whose internal pores have been pre-impregnated with lubricating oil, is inserted into the inner periphery of the side portion 7a of the housing 7. With the lower end surface 8c of the bearing sleeve 8 abutting against the shoulder surface 7b2 of the bottom portion 7b, the outer periphery 8d of the bearing sleeve 8 is fixed to the inner periphery 7a1 of the side portion 7a. Next, the seal member 9 is fixed to the upper end of the inner periphery 7a1 of the side portion 7a of the housing 7. At this time, the seal member 9 is press-fitted into the side portion 7a of the housing 7, and the bearing sleeve 8 is sandwiched between the seal member 9 and the shoulder surface 7b2 of the bottom portion 7b of the housing 7 from both axial sides, thereby restraining the bearing sleeve 8 in the axial direction. Next, lubricating oil is dripped onto the inner periphery of the bearing sleeve 8, and the shaft member 2 is inserted, completing the assembly of the hydrodynamic bearing device 1. At this time, the internal space of the housing 7 sealed by the seal member 9 (including the internal cavity of the bearing sleeve 8) is filled with lubricating oil, and the oil level is maintained within the range of the seal space S.

[0035] In the fluid dynamic bearing device 1 configured as described above, when the shaft member 2 rotates, a radial bearing gap is formed between the inner circumferential surface 8a of the bearing sleeve 8 and the outer circumferential surface 2a of the shaft member 2. The dynamic pressure generating portions 20 (20A, 20B) formed on the inner circumferential surface 8a of the bearing sleeve 8 generate dynamic pressure in the lubricating oil in the radial bearing gap. Specifically, the lubricating oil in the radial bearing gap is collected toward the axial center of each dynamic pressure generating portion 20 (20A, 20B) along the dynamic pressure grooves 11a, 11b, increasing the fluid pressure in this area. This forms a radial bearing portion R (R1, R1) that supports the shaft member 2 in a non-contact manner in the radial direction. Furthermore, the protrusion 2b at the lower end of the shaft member 2 comes into contact with and slides against the thrust receiver 10, forming a thrust bearing portion T that supports the shaft member 2 in the thrust direction.

[0036] In the hydrodynamic bearing of the present invention, a step is formed between the inclined grooves (hydrodynamic grooves) 11a, 11b in each hydrodynamic groove group 20A, 20B and the annular hill portion 11e. This step generates pressure (dynamic pressure). Furthermore, the recess 11e1 of the annular hill portion 11e generates pressure (dynamic pressure) downstream of the recess 11e1 in the direction of rotation. This increases the pressure (dynamic pressure) generated on the annular hill portion 11e, improving the load capacity. This improved load capacity allows the bearing to function satisfactorily even when miniaturized. This means that a bearing with improved load capacity can be provided without increasing the axial dimension. Furthermore, in a motor using this hydrodynamic bearing, there is no need to change the groove specifications depending on the center of gravity of the rotor, and there is no risk of the bearing's versatility being compromised.

[0037] In addition, by providing recesses 11e1 at all confluences U between the annular hill portion 11e and the inclined hill portions 11c and 11d, the load capacity can be further increased.Furthermore, by making the circumferential width of the recesses 11e1 smaller than the circumferential width of the confluences U, the recesses 11e1 can be set larger within the dimensions that do not contact the contours of the annular hill portion 11e and the inclined hill portions 11c and 11d, thereby further increasing the load capacity.

[0038] Furthermore, the fluid dynamic bearing device of the present invention uses a dynamic bearing that can improve load capacity, so it is possible to support the load on the bearing even if the axial dimension of the bearing is reduced to make it thinner.

[0039] The motor according to the present invention can sufficiently support the load on the bearing even if the size of the impeller 4 is increased, and the cooling performance can be improved.

[0040] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. Various modifications are possible. In the above embodiment, the sintered oil-impregnated bearing 8 is fixed and the shaft member 2 rotates, but the present invention is not limited to this. A configuration in which the shaft member 2 is fixed and the sintered oil-impregnated bearing 8 rotates, or a configuration in which both the shaft member 2 and the sintered oil-impregnated bearing 8 rotate can also be adopted.

[0041] The hydrodynamic bearing device incorporating the sintered oil-impregnated bearing 8 according to the present invention is not limited to the spindle motor used in the disk drive device of the HDD, but can also be widely used in other small motors such as spindle motors incorporated in other information devices, polygon scanner motors of laser beam printers, color wheels of projectors, or fan motors for cooling.

[0042] In the embodiment, a pair of dynamic pressure generating portions 20A and 20B are provided, but one dynamic pressure generating portion 20 may be provided. Also, the inclination angles θa and θb of the respective dynamic pressure grooves 11a and 11b are not limited to those of the embodiment, and the number, arrangement pitch, groove width, etc. of the respective dynamic pressure grooves 11a and 11b can be arbitrarily set. Further, the depth of the dynamic pressure groove can also be variously changed as needed. In the embodiment, the depth of the dynamic pressure groove (inclined groove) and the depth of the recess 11e1 provided in the annular hill portion 11e are set to be the same, but they may be different. Note that by making the depths the same, productivity can be improved.

[0043] In the embodiment, when the axial lengths (width dimensions) of the first dynamic pressure groove group 11A and the second dynamic pressure groove group 11B are A and B, and the axial lengths (width dimensions) of the annular hill portions 11e and 11e are C, A = B > C is set, but A = B < C, A = B = C, or A ≠ B may also be possible. Also, as the shape of the recess 11e1, in the embodiment, it is a rectangular shape, but it may be a square shape, a polygon with five or more sides, or the like.

[0044] The bearing sleeve 8 is a cylindrical body with a porous structure, and is formed of sintered metal as in the embodiment, for example, but it can also be formed of a porous body made of a non-metallic material such as resin or ceramic. In addition to a porous body, it can also be formed of a structure that does not have internal pores or has pores of a size that do not allow lubricating oil to enter or exit. [Example]

[0045] For a bearing (Product 1) with the specifications shown in Table 1, the pressure distribution on the outer diameter surface of the shaft member and the forces acting on the outer diameter surface were calculated using thermal fluid analysis software (SIEMENS STAR-CCM+). STAR-CCM+ is integrated CAE software for multidisciplinary problems. Its core function is fluid analysis using the finite volume method. It also includes fluid physics functions, structural analysis using the finite element method, and particle analysis using the DEM method. STAR-CCM+ handles everything from CAD geometry creation to evaluation of calculation results in a single package, facilitating automation of the workflow. The workflow required for simulation setup, calculation execution, and result evaluation are all integrated into a single GUI, complete with all the necessary automation functions. STAR-CCM+'s extensive physical models and functions enable the analysis of a wide variety of phenomena. In addition to basic functions such as 2D / 3D, laminar / turbulent / inviscid, compressible / incompressible, buoyancy, translation / rotation, and porous regions, it also includes various turbulence models used in fluid analysis.

[0046] In this case, to shorten the analysis time, the dynamic pressure generating parts 20 were arranged in one row, as shown in Figure 5. The bearing specifications of the example 1 are shown in Table 1. The shaft (shaft member 2) used had an outer diameter (diameter) of 1.99 mm. [Table 1]

[0047] The inner diameter (diameter) of the bearing was 2 mm, the width (axial length of the bearing) was 1.80 mm, the groove depth was 10 μm, the hill-groove ratio was 1, the groove angle (θa, θb) was 20 degrees, the inclined groove width (axial length A of hydrodynamic groove groups 11A, 11B) was 0.7 mm, the annular hill width (axial length C of annular hill portion 11e) was 0.4 mm, the radial gap was 10 μm, and the eccentricity was 0. Here, the hill-groove ratio is H2 / H1, where H2 is the circumferential length of the hill portion and H1 is the circumferential length of the groove.

[0048] In this case, as shown in Figure 5 of Example 1, the axial length (width dimension) H of recess 11e1 was 0.4 mm, the circumferential length L1 of recess 11e1 was 0.32 mm, and recess 11e1 was arranged in a position not offset from the confluence part U. This was used as Example 1. Calculations were also carried out for two comparative examples 1 and 2, which had different positions and sizes of recess 11e1, and a conventional product without a recess. Therefore, the circumferential length of the ridge part of Comparative Example 1 was half that of Example 1, and the axial length of the ridge part of Comparative Example 2 was approximately 0.1 mm shorter than that of Example 1, and the ridge part was offset approximately 0.22 mm in the rotational direction. The rotation speed of shaft member 2 was set to 5,500 rpm.

[0049] Figure 6 shows the implementation product 1, where (a) is a groove specification diagram and (b) is a pressure distribution diagram; Figure 7 shows the comparison product 1, where (a) is a groove specification diagram and (b) is a pressure distribution diagram; Figure 8 shows the comparison product 2, where (a) is a groove specification diagram and (b) is a pressure distribution diagram; and Figure 11 shows the conventional product 1, where (a) is a groove specification diagram and (b) is a pressure distribution diagram.

[0050] As can be seen from each pressure distribution diagram, an increase in pressure was observed on the downstream side of the groove in the rotation direction in Example 1, Comparative Example 1, and Comparative Example 2, which were provided with recess 11e1. That is, the pressure on the outer diameter surface of the shaft member was 0.0049 N in Example 1, 0.0042 N in Comparative Example 1, 0.0042 N in Comparative Example 2, and 0.0039 N in Conventional Example 1. In this case, Example 1 had the highest pressure, 1.3 times that of the Conventional Example. [Example]

[0051] Next, a functional evaluation was carried out using Example Product 2 having the bearing specifications shown in Table 2. The shaft (shaft member 2) used had an outer diameter (diameter) of 1.99 mm. [Table 2]

[0052] The inner diameter (diameter) of the bearing (bearing sleeve 8) was 2 mm, the width (axial length of the bearing) was 2.35 mm, the groove depth was 3 μm, the hill-groove ratio was 1, the groove angle (θ1, θ2) was 20 degrees, the inclined groove width (axial length of the dynamic pressure groove) was 0.25 mm, the annular hill width (axial length of the annular hill 11e) was 0.2 mm, and the radial gap was 8 μm.

[0053] In this case, three items, No. 1 to No. 3, are produced as the implementation product 2, and No. 1 to No. 3 are produced as the conventional product 2. The three items shown in Figure 10 were used for No. 1 to No. 3 of the implementation product 2. The axial length (width) of the recess 11e1 was 0.2 mm, the circumferential length of the recess 11e1 was 0.25 mm, the recess 11e1 was disposed at a position where it would not be misaligned with the confluence U, the dimension L2 from the axial outer edge of the annular hill portion 11e of one dynamic pressure generating portion 20A to the other end face of the bearing (bearing sleeve 8) was 1.9 mm, and the dimension L3 from the axial outer edge of the annular hill portion of the other dynamic pressure generating portion 20B to the other end face of the bearing was 0.45 mm. In this case, Nos. 1 to 3 of Example 2 were identical in design.

[0054] In addition, as shown in FIG. 11, No. 1 to No. 3 of conventional product 2 are shown in FIG. In this case, No. 1 to No. 3 of conventional product 2 are identical in design. It was decided.

[0055] 11, a pair of dynamic pressure generating portions 120 (120A, 120B) are provided axially spaced apart on an inner peripheral surface 108a of a bearing sleeve 108, which serves as a radial bearing surface. Each of the dynamic pressure generating portions 120A, 120B has a plurality of dynamic pressure grooves 111a, 111b arranged in a herringbone pattern. The dynamic pressure grooves 111a, 111a on the axially outer sides of the dynamic pressure generating portions 120A, 120B form a first dynamic pressure groove group 111A, 111A, and the dynamic pressure grooves 111b, 111b on the axially inner sides of the dynamic pressure generating portion 120 form a second dynamic pressure groove group 111B, 111B. The pair of dynamic pressure generating portions 120A, 120B have an upside-down shape.

[0056] In each dynamic pressure generating portion 120A, 120B, the dynamic pressure grooves 111a, 111a on the axially outer side and the dynamic pressure grooves 111b, 111b on the axially inner side have different inclination directions. Sloped hill portions 111c, 111d are provided between the dynamic pressure grooves 111a, 111b, respectively. The sloped hill portions 11c, 11d and the annular hill portions 11e, 11e are indicated by cross-hatching.

[0057] The following Table 3 shows the results of the functional evaluation. In Table 3, a load (compression load) of 0.1 N was applied to the shaft (shaft member 2), and the shaft member 2 was rotated at a rotational speed of 100 to 1000 rpm for 60 seconds. The presence or absence of contact between the rotating shaft member 2 and the bearing (bearing sleeve 8) was measured. This measurement was performed using a publicly known electrical contact method. [Table 3]

[0058] The conventional products (No. 1 to No. 3) had contact between the shaft and bearing from 1000 rpm, and It can be seen that the number of contacts increases dramatically when the rotational speed is below 200 rpm. In contrast, for the test sample 2 (No. 1 to No. 3), almost no contact is observed up to 200 rpm, and the contact at 100 rpm is It can also be seen that the number of contacts was less than in the comparative example. The values ​​in Table 3 indicate the number of contacts, with larger values ​​indicating more contacts. In Table 3, >500 indicates that the shaft member and bearing came into contact with each other 500 times or more in 60 seconds.

[0059] The presence or absence of contact between the shaft (shaft member 2) and the bearing (bearing sleeve 8) was measured when the load (load) applied to the shaft (shaft member 2) was gradually increased. In this case, the test pieces 2 (No. 1 to No. 3) The rotation speed was 1000 rpm. The presence or absence of contact between the shaft (shaft member 2) and the bearing (bearing sleeve 8) was measured when the load (load) applied to the shaft member was gradually increased, and the results are shown in Table 4. This measurement was also performed using a known electrical contact method. In Table 4, "-" indicates that no measurement was performed at this load. This is because the number of contacts exceeded 500 at the load immediately before this load, and therefore the number of contacts at the subsequent load will also exceed 500. [Table 4]

[0060] As can be seen from Table 4, the load at which frequent contact between the shaft member and bearing was observed was 1.27 N for the conventional product, while it was 1.57 N (1.2 times) for the implemented product. Therefore, it was confirmed that the applied load of the implemented product 2 was higher than that of the conventional product 2. [Explanation of symbols]

[0061] 1. Fluid dynamic bearing device 2 Shaft member 3 rotors 4 impellers 5 Casing 8. Sintered oil-impregnated bearings (bearing sleeves) 8a Inner surface 11A, 11B dynamic pressure groove group 11a,11b dynamic pressure groove 11c Slope section 11e Circular Hill 11e1 recess 20(20A, 20B) Dynamic pressure generating part C Confluence R1 Radial bearing section

Claims

1. A dynamic pressure generating portion is provided on the inner diameter surface of the bearing, the inner diameter surface of the bearing facing the outer diameter surface of the shaft member. A pressure bearing, a hydrodynamic bearing characterized in that the hydrodynamic pressure generating portion has a plurality of hydrodynamic pressure grooves arranged in a herringbone pattern, the hydrodynamic pressure grooves are provided in first and second hydrodynamic pressure groove groups, and a sloping hill portion is formed between each of the hydrodynamic pressure grooves of the first and second hydrodynamic pressure groove groups, and an annular hill portion is provided between the first and second hydrodynamic pressure groove groups, connecting with each of the sloping hill portions and extending in the circumferential direction, and a recess for generating hydrodynamic pressure is formed in a part of the annular hill portion.

2. 2. A hydrodynamic bearing according to claim 1, characterized in that the circumferential width of the recess is smaller than the circumferential width of the confluence portion, the number of hydrodynamic grooves in the first and second hydrodynamic groove groups is the same, the confluence portion of the inclined hill portion and the annular hill portion in the first hydrodynamic groove group coincides with the confluence portion of the inclined hill portion and the annular hill portion in the second hydrodynamic groove group, and the recess is provided at all confluence portions.

3. 2. A hydrodynamic bearing according to claim 1, wherein a pair of hydrodynamic pressure generating portions having an upside-down shape and spaced apart in the axial direction are formed on the inner diameter surface of the bearing.

4. A fluid dynamic bearing device comprising: a dynamic pressure bearing according to any one of claims 1 to 3; a shaft member inserted into the inner periphery of the dynamic pressure bearing; and a radial bearing portion that supports relative rotation of the shaft member by the dynamic pressure action of a lubricating fluid in a radial bearing gap formed between the inner periphery of the dynamic pressure bearing and the outer periphery of the shaft member.

5. 5. A motor comprising: the fluid dynamic bearing device according to claim 4; a rotor that rotates integrally with the shaft member or the dynamic bearing; and a drive unit that drives the rotor to rotate, the rotor having an impeller.

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