WO2024057868A1

WO2024057868A1 - Hydrodynamic bearing, hydrodynamic bearing device, and motor

Info

Publication number: WO2024057868A1
Application number: PCT/JP2023/030575
Authority: WO
Inventors: 慎治小松原
Original assignee: Ntn株式会社
Priority date: 2022-09-16
Filing date: 2023-08-24
Publication date: 2024-03-21
Also published as: CN117722435A; JP2024043207A

Abstract

A hydrodynamic bearing (bearing sleeve 8) is equipped with a sintered body in which dynamic pressure-generating parts A1, A2 are die-formed on the inner-circumferential surface thereof. The dynamic pressure-generating parts A1, A2 have a plurality of dynamic pressure grooves G1 which extend in a direction which is angled relative to the circumferential direction, and a plurality of inclined hill sections G3 which are provided between the plurality of dynamic pressure grooves G1 in the circumferential direction. The circumferential direction width h[mm] of each inclined hill section G3 and the dynamic pressure groove G1 depth Hf[μm] adjacent to said hill section G3 on one side thereof in the circumferential direction satisfy 0.1<h/Hf<0.65, and the variation in the depth Hf of the plurality of dynamic pressure grooves G1 is no more than 1μm.

Description

Hydrodynamic bearings, hydrodynamic bearing devices and motors

The present invention relates to a hydrodynamic bearing.

A dynamic pressure bearing is a cylindrical bearing member with dynamic pressure grooves formed on its inner peripheral surface. When the hydrodynamic bearing and the shaft member inserted into its inner circumference rotate relative to each other, the pressure of the fluid film generated in the radial bearing gap between the outer circumference of the shaft member and the inner circumference of the hydrodynamic bearing is reduced by the hydrodynamic groove. This pressure (dynamic pressure effect) allows the shaft member to be relatively rotatably supported in a non-contact manner. Due to its excellent rotational accuracy and quietness, fluid dynamic bearing devices having the above-mentioned hydrodynamic bearings and shaft members are used in spindle motors of HDD disk drives, polygon scanner motors of laser beam printers, and electronic devices. It is suitably used to support the rotating shaft of a cooling fan motor, etc.

As a method for forming dynamic pressure grooves on the inner circumferential surface of a hydrodynamic bearing, so-called dynamic pressure groove sizing is known, in which dynamic pressure grooves are molded on the inner circumferential surface of a cylindrical sintered body. In this dynamic pressure groove sizing, a sizing pin is inserted into the inner circumference of the sintered compact, and the sintered compact is press-fitted into the inner circumference of the die while being compressed in the axial direction by an upper punch and a lower punch. The inner peripheral surface of the body is pressed against a mold formed on the outer peripheral surface of the sizing pin. As a result, the shape of the mold is transferred to the inner circumferential surface of the sintered body, and dynamic pressure grooves are formed (see, for example, Patent Document 1).

Patent No. 3782900

In hydrodynamic bearings, dimensional accuracy of the hydrodynamic grooves, particularly variations in the depth of the plurality of hydrodynamic grooves, is a problem. 14 and 15 are diagrams showing the shapes (profiles) of dynamic pressure grooves of dynamic pressure bearings formed under the same conditions. The maximum diameter difference between each dynamic pressure groove and the adjacent hill portion on one side in the circumferential direction is defined as the depth of each dynamic pressure groove (hereinafter also referred to as "groove depth") Hf1 to Hf6. As shown in Fig. 14, the groove depths Hf1 to Hf6 have small variations (the difference between the maximum groove depth and the minimum groove depth is about 0.3 μm), and as shown in Fig. 15, the groove depths Hf1 to Hf6 are small. There was one with a large variation in Hf6 (the difference between the maximum groove depth and the minimum groove depth was about 1.5 μm). If the variation in groove depth is large, the variation in dynamic pressure generated in the circumferential direction becomes large, resulting in a decrease in bearing rigidity. In particular, when a hydrodynamic bearing is incorporated into a motor that is used in various positions (for example, a cooling fan motor for a tablet device), if the bearing rigidity is low, the hydrodynamic bearing and the shaft may come into contact, causing abnormal noise. There is a risk that problems such as occurrence of malfunction may occur.

Therefore, an object of the present invention is to stably supply a hydrodynamic bearing with high bearing rigidity.

When molding the dynamic pressure grooves, as shown in FIGS. 7, 9 and 10, the inner peripheral surface of the sintered body 28 is pressed against a mold 35 formed on the outer peripheral surface of the core rod 31, and the sintering process is performed. The material (meat) of the body 28 is introduced into the recess 35a of the mold 35. At this time, if the ratio h'/Hf' between the circumferential width h' [mm] and the depth Hf' [μm] of the recess 35a is too small, that is, the circumferential width h' of the recess 35a is too small, If the depth Hf' of the recess 35a is too deep, it becomes difficult for the material of the sintered body 28 to enter the recess 35a. Therefore, it becomes difficult to fill the entire area of the recess 35a with the material of the sintered body 28, and the molding accuracy of the hill portion and, ultimately, the molding accuracy of the dynamic pressure groove decreases.

Therefore, in the present invention, the ratio (flatness) h'/Hf' between the circumferential width h' [mm] and the depth Hf' [μm] of the concave portion of the mold is made larger than 0.1. This makes it easier for the material of the sintered body to penetrate into the corners of the recesses, so we can stably supply products with variations in the height of multiple hills, that is, the depth of multiple dynamic pressure grooves, of 1 μm or less. can do. In this case, the shape of the concave part of the core rod is transferred to the hill part between the dynamic pressure grooves formed in the sintered body, so the circumferential width h [mm] and the height (the circumferential direction of the concave part) of each hill part are The ratio (flatness) h/Hf to the depth (depth) Hf [μm] of the dynamic pressure groove adjacent to one side (flatness) becomes larger than 0.1.

On the other hand, if the circumferential width h' of the concave part of the mold is too large, the volume of the sintered body to be inserted into the concave part will be large, and a large molding pressure will be required to reduce the diameter of the sintered body. This leads to larger size and higher cost. Furthermore, if the depth Hf' of the recessed part of the mold is too shallow, the dynamic pressure groove becomes shallow, and there is a risk that the dynamic pressure will be insufficient. Therefore, the ratio h'/Hf' between the circumferential width h' [mm] and the depth Hf' [μm] of the concave part of the mold, that is, the circumferential width h [mm] and the height of the hill part of the sintered body. It is preferable that the ratio h/Hf to the height Hf [μm] be smaller than a predetermined value, and specifically, it is preferable to be smaller than 0.65.

From the above, the present invention provides a hydrodynamic bearing including a sintered body in which a hydrodynamic pressure generating part is molded on the inner peripheral surface.
The dynamic pressure generating portion has a plurality of dynamic pressure grooves extending in a direction inclined with respect to the circumferential direction, and a plurality of inclined hill portions provided between the plurality of dynamic pressure grooves in the circumferential direction,
The ratio h/Hf of the circumferential width h [mm] of each inclined hill portion to the depth Hf [μm] of the dynamic pressure groove adjacent to one circumferential side of the inclined hill portion is 0.1<h /Hf<0.65,
It can be characterized as a hydrodynamic bearing in which the variation in depth Hf of the plurality of hydrodynamic grooves is 1 μm or less.

If the density of the sintered body is low, when forming dynamic pressure grooves by pressing the sintered body from the outside diameter side, it will be difficult to apply pressure to the inner peripheral surface of the sintered body, so the dynamic pressure grooves will not be formed. It becomes difficult to mold with high precision. Therefore, it is preferable to set the density of the sintered body to be high. Specifically, the density ratio of the sintered body (density of the sintered body/density assuming that the sintered body has no pores) is set to a high value. It is preferably 80% or more. On the other hand, if the density of the sintered body is too high, the pores formed inside the sintered body will be too small, impairing the circulation of lubricating fluid through the internal pores, so the density ratio of the sintered body will be 95% or less. It is preferable that

If there is a large variation in the density ratio in each part of the sintered body, there will be a large variation in the amount of springback when the sintered body is taken out from the die. In this case, when the core rod is pulled out from the inner periphery of the sintered body, the part of the sintered body with a small amount of springback interferes with the mold for the core rod, causing this hill to sag, causing the sintered body to collapse. The variation in the height of the hill, that is, the variation in groove depth increases. For this reason, it is preferable that the variation in the density ratio in the axial direction and the radial direction of the sintered body be 3% or less to make the amount of springback of the sintered body uniform.

When the core rod is pulled out from the inner circumference of the sintered body, the corner of the outer diameter end of the mold for the core rod interferes with the hill formed on the inner circumference of the sintered body, causing the hill of the sintered body to There is a risk of being destroyed. In order to avoid this, it is preferable to round off the corners of the outer diameter end of the mold for the core rod in advance. On the other hand, it is ideal that the cross-sectional shape of the dynamic pressure groove is a perfect rectangle, and the more the groove is out of the rectangle, the more the dynamic pressure decreases. Therefore, if the corners of the outer diameter end of the mold are rounded as described above, the bottom corners of the dynamic pressure groove formed with this mold will be rounded and will collapse from the rectangular shape, so a drop in dynamic pressure can be avoided. I can't do it.

Therefore, among the corners of the outer diameter end of the core rod mold, the corner on the side (one axial side) that interferes with the dynamic pressure groove when pulled out from the inner periphery of the sintered body is It is preferable to round off the corners of the other side). In this case, in the axial cross section of the sintered body, the corner on one axial side of the groove bottom of the dynamic pressure groove is rounded more than the corner on the other axial side. Thereby, it is possible to avoid interference between the molding die of the core rod and the hill portion of the sintered body while ensuring the dynamic pressure generated by the dynamic pressure groove.

As described above, according to the present invention, it is possible to stably supply a hydrodynamic bearing with small variations in groove depth and high bearing rigidity.

It is a sectional view of a fan motor. FIG. 2 is an axial cross-sectional view of the fluid dynamic bearing device incorporated in the fan motor of FIG. 1. FIG. 3 is an axial cross-sectional view of a bearing sleeve (dynamic bearing) of the fluid dynamic bearing device of FIG. 2. FIG. FIG. 4 is a cross-sectional view of the bearing sleeve taken along line XX in FIG. 3 in an axis orthogonal direction. FIG. 2 is an axial cross-sectional view of the sizing mold and the sintered body, showing a state before the sintered body is inserted into the inner periphery of the die. FIG. 6 is a side view of the core rod of the sizing mold of FIG. 5 viewed from the outer periphery. FIG. 6 is a cross-sectional view of the sintered body and core rod of FIG. 5 in an axis orthogonal direction. FIG. 2 is an axial cross-sectional view of the sizing mold and the sintered body, showing a state in which the sintered body is inserted into the inner periphery of the die. 9 is a cross-sectional view of the sintered body and the core rod of FIG. 8 in a direction perpendicular to the axis. FIG. 3 is a cross-sectional view of the sintered body and the core rod taken out from the inner periphery of the die in the direction orthogonal to the axis. FIG. 2 is an axial cross-sectional view showing an example of a sintered body and a core rod taken out from the inner periphery of the die. FIG. 6 is a side view showing a step of rounding the corners of the mold for the core rod. FIG. 7 is an axial cross-sectional view showing another example of the sintered body and core rod taken out from the inner periphery of the die. It is a figure showing the shape (profile) of the dynamic pressure groove of a dynamic pressure bearing. It is a figure showing the shape (profile) of the dynamic pressure groove of a dynamic pressure bearing.

Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 1 conceptually shows an example of a fan motor. The fan motor shown in the figure is built into, for example, a portable information device such as a notebook computer or a tablet terminal, and generates an airflow to cool a heat generating source such as a CPU. This fan motor includes a fluid dynamic pressure bearing device 1, a motor base 5 constituting the stationary side of the motor, a rotor 3 fixed to a shaft member 2 of the fluid dynamic pressure bearing device 1, and blades attached to the rotor 3. 4, and a stator 6a and a magnet 6b that are arranged opposite to each other with a radial gap therebetween. The stator 6a is attached to the housing 7 of the fluid dynamic bearing device 1, and the magnet 6b is attached to the rotor 3. By energizing the coil of the stator 6a and generating an excitation force, the magnet 6b and the rotor 3 rotate together. As the rotor 3 rotates, an airflow is generated in an axial direction or a radially outward direction depending on the shape of the blades 4 attached to the rotor 3.

As shown in FIG. 2, the fluid dynamic bearing device 1 includes a shaft member 2, a housing 7, a bearing sleeve 8 as a dynamic pressure bearing according to an embodiment of the present invention, and a seal member 9. The internal space of the housing 7 is filled with lubricating oil. In the following, for convenience of explanation, the side where the shaft member 2 protrudes from the housing 7 in the axial direction (the upper side in FIG. 2) will be referred to as the "upper side", and the opposite side (the lower side in FIG. 2) will be referred to as the "lower side". However, this is not intended to limit the posture in which the fluid dynamic bearing device 1 is used.

The shaft member 2 is made of a metal material such as stainless steel. At least a region of the outer circumferential surface 2a of the shaft member 2 that faces the inner circumferential surface of the bearing sleeve 8 in the radial direction is a cylindrical surface that is not provided with irregularities such as dynamic pressure grooves. A convex spherical surface 2b is provided at the lower end of the shaft member 2. A rotor 3 is fixed to the upper end of the shaft member 2.

The housing 7 has a cylindrical portion 7a and a bottom portion 7b that closes the lower end opening of the cylindrical portion 7a. In the illustrated example, the cylindrical portion 7a and the bottom portion 7b are integrally formed of resin or metal material. A shoulder surface 7b2 arranged above the center portion is provided at the outer diameter side end of the upper end surface (inner bottom surface 7b1) of the bottom portion 7b. A stator 6a and a motor base 5 are fixed to an outer circumferential surface 7a2 of the cylindrical portion 7a.

In the illustrated example, a thrust plate 10 is provided on the inner bottom surface 7b1 of the housing 7. The thrust plate 10 is formed into a disk shape from a material that has better sliding properties than the material from which the housing 7 is formed. The convex spherical surface 2b at the lower end of the shaft member 2 is supported in contact with the upper end surface of the thrust plate 10. Note that the thrust plate 10 may be omitted, and in that case, the convex spherical surface 2b of the shaft member 2 is supported in contact with the inner bottom surface 7b1 of the housing 7.

The seal member 9 is formed into an annular shape from a resin or metal material, and is fixed to the upper end of the inner circumferential surface 7a1 of the cylindrical portion 7a of the housing 7. The lower end surface 9b of the seal member 9 is in contact with the upper end surface 8b of the bearing sleeve 8. An annular seal space S is formed between the inner circumferential surface 9a of the seal member 9 and the outer circumferential surface 2a of the opposing shaft member 2.

Note that this fluid dynamic pressure bearing device 1 is a so-called partial fill type in which lubricating oil and air are mixed inside the housing 7, but the present invention is not limited to this. , a so-called full-fill type may be used. In the case of the full-fill type, the oil level of the lubricating oil is always maintained within the axial range of the seal space S.

The bearing sleeve 8 is made of a cylindrical sintered body formed by sintering a compression molded body of metal powder, such as a copper-based sintered body containing copper as the main component or an iron-based sintered body containing iron as the main component. or a copper-iron sintered body whose main components are copper and iron. The bearing sleeve 8 is fixed to the inner periphery of the housing 7 in an oil-impregnated state in which the internal pores of the sintered body are impregnated with lubricating oil. In the illustrated example, the bearing sleeve 8 is fixed to the inner periphery of the cylindrical portion 7a of the housing 7 with its lower end surface 8c in contact with the shoulder surface 7b2 of the bottom portion 7b of the housing 7. The bearing sleeve 8 is fixed to the inner circumferential surface 7a1 of the cylindrical portion 7a by press-fitting, adhesion, press-fitting adhesion (combination of press-fitting and adhesion), or the like. In addition, after the bearing sleeve 8 is loosely fitted to the inner circumference of the housing 7, the bearing sleeve 8 is fixed to the inner circumference of the housing 7 by sandwiching it between the seal member 9 and the shoulder surface 7b2 of the housing 7 from both sides in the axial direction. You can also.

A dynamic pressure generating portion is formed on the inner peripheral surface 8a of the bearing sleeve 8. In this embodiment, as shown in FIG. 3, dynamic pressure generating portions A1 and A2 are provided at two locations in the axial direction of the inner circumferential surface 8a of the sintered body. In each of the dynamic pressure generation parts A1 and A2, a plurality of dynamic pressure grooves G1 extending in a direction inclined with respect to the circumferential direction and arranged side by side in the circumferential direction are provided, and a plurality of dynamic pressure grooves G1 are provided between the plurality of dynamic pressure grooves G1 in the circumferential direction. , a plurality of hill portions (cross-hatched regions) that are raised on the inner diameter side from the groove bottom of the dynamic pressure groove G1 are provided. In the illustrated example, each of the dynamic pressure generating portions A1 and A2 includes a dynamic pressure groove G1 arranged in a herringbone shape, an annular hill portion G2, and a plurality of dynamic pressure grooves G1 extending from the annular hill portion G2 to both sides in the axial direction. A plurality of inclined hill portions G3 are provided circumferentially between. The inner diameter surfaces of the annular hill portion G2 and the inclined hill portion G3 are arranged on the same cylindrical surface. The groove bottoms of the dynamic pressure grooves G1 are arranged on the same cylindrical surface. The entire inner circumferential surface 8a of the bearing sleeve 8, including the bottom surface of the dynamic pressure groove G1, the inner diameter surfaces of the annular hill portion G2 and the inclined hill portion G3, is a molded surface formed by pressing a mold.

An axial groove 8d1 is formed on the outer peripheral surface 8d of the bearing sleeve 8. A radial groove 8b1 and an annular groove 8b2 are 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. The annular groove 8b2 is provided to identify the up-down direction (ie, rotational direction) when the bearing sleeve 8 is assembled into the housing 7. The axial groove 8d1 and the radial grooves 8b1 and 8c1 form a communication path that communicates the space faced by the bottom 7b of the housing 7 with the atmosphere in the fluid dynamic bearing device 1 (see FIG. 2). Note that if there is no particular need, any or all of the radial grooves 8b1 and 8c1, the annular groove 8b2, and the axial groove 8d1 may be omitted.

FIG. 4 is a cross-sectional view (cross-sectional view taken along line XX in FIG. 3) of the dynamic pressure groove G1 of the bearing sleeve 8 at the axial center, developed so that the circumferential direction is straight, and the radius It is a diagram with exaggerated dimensions in the direction (vertical direction in the figure). The circumferential width h [mm] of each inclined hill portion G3 formed on the inner circumferential surface 8a of the bearing sleeve 8, and the depth Hf [μm] of the dynamic pressure groove G1 adjacent to one circumferential side of the inclined hill portion G3. ] (flatness) h/Hf satisfies 0.1<h/Hf<0.65. The depth Hf of the dynamic pressure groove G1 is defined as the minimum diameter of the top surface (inner diameter surface) of each inclined hill portion G3 and the dynamic pressure groove adjacent to one circumferential side (left side in FIG. 4) of the inclined hill portion G3. This is the difference in diameter from the maximum diameter of the bottom surface of the pressure groove G1. On the other hand, the circumferential width h of the inclined hill portion G3 is determined by the least square line L between the dynamic pressure groove G1 and the inclined hill portion G3 (line L of all the dynamic pressure grooves G1 in the circumferential direction in the axis orthogonal cross section shown in FIG. This is the circumferential direction dimension on a line L) drawn so that the total area S1 on the outer diameter side than the line L is equal to the total area S2 on the inner diameter side of the line L of all the inclined hill portions G3 in the circumferential direction. The depths of all the dynamic pressure grooves G1 formed in the inner circumferential surface 8a of the bearing sleeve 8 are approximately uniform, and specifically, the variation in the depth Hf of each dynamic pressure groove G1 is set to be 1 μm or less. That is, the difference between the depth Hf (MAX) of the deepest dynamic pressure groove G1 and the depth Hf (MIN) of the shallowest dynamic pressure groove G1 among the plurality of dynamic pressure grooves G1 is 1 μm or less.

The density ratio of the bearing sleeve 8 is 80 to 95%. The density ratio of the bearing sleeve 8 is a value measured in a dry state in which the internal pores of the sintered body are not impregnated with oil. The variation in density ratio in the axial direction and the radial direction of the sintered body forming the bearing sleeve 8 is set to be 3% or less. Specifically, the difference in the density ratio between the three equal parts of the sintered body in the axial direction and the difference in the density ratio between the three equal parts in the radial direction of the sintered body are both 3%. The following shall apply.

In the fluid dynamic bearing device 1 having the above configuration, when the shaft member 2 rotates, a radial bearing gap is formed between the outer peripheral surface 2a of the shaft member 2 and the inner peripheral surface 8a of the bearing sleeve 8. The pressure of the oil film generated in the radial bearing gap is increased by the dynamic pressure generating portions A1 and A2 (dynamic pressure grooves G1) formed on the inner circumferential surface 8a of the bearing sleeve 8, and this pressure (dynamic pressure action) A radial bearing portion R is formed to support the member 2 in the radial direction (see FIG. 2). Further, the convex spherical surface 2b at the lower end of the shaft member 2 comes into sliding contact with the upper end surface of the thrust plate 10 placed on the bottom portion 7b of the housing 7, thereby supporting the shaft member 2 in the thrust direction (contact support). A bearing portion T is formed.

Hereinafter, a method for manufacturing the bearing sleeve 8 will be explained.

The bearing sleeve 8 is manufactured through a compression molding process, a sintering process, and a sizing process in this order.

In the compression molding process, a cylindrical green compact having approximately the same shape as the bearing sleeve 8 in FIG. 3 is formed by compression molding raw material powder whose main raw material is metal powder. The inner circumferential surface of the powder compact has a cylindrical shape with no irregularities. An axial groove 8d1, a radial groove 8b1, and a radial groove 8c1 are formed on the outer peripheral surface, upper end surface, and lower end surface of the powder compact, respectively. As the raw material powder, metal powder {for example, one or more of copper-based powder (copper powder or copper-based alloy powder), iron-based powder (iron powder or iron-based alloy powder), copper-iron alloy powder} is used. A mixed powder is used as the main raw material and mixed with various fillers such as molding aids and solid lubricants.

In the sintering process, the green compact is heated at a predetermined sintering temperature to obtain a sintered body in which adjacent metal powder particles are bonded to each other via sintering necks. The density ratio of the sintered body thus formed is 80 to 95%. Further, the variation in density ratio in the axial direction and the radial direction of the sintered body 28 is 3% or less. In other words, the compression ratio in the compression molding step, the sintering temperature and time in the sintering step, etc. are set so that the density ratio of the sintered body satisfies the above.

In the sizing process, dynamic pressure grooves are formed on the inner circumferential surface 28a of the sintered body 28 using a sizing mold 30 shown in FIG. The sizing mold 30 includes a core rod 31, an upper punch 32, a lower punch 33, and a die 34. A mold 35 is formed on the outer peripheral surface of the core rod 31 . As shown in FIG. 6, the mold 35 has a hill portion 35c, an annular recess 35b, and an inclined recess 35a. In the illustrated example, recesses 35a and 35b (scattering regions) are formed on the cylindrical outer peripheral surface of the core rod 31, and the region remaining between the inclined recesses 35a in the circumferential direction becomes a hill portion 35c. The hill portion 35c, the annular recess 35b, and the inclined recess 35a have shapes that are the inversions of the unevenness of the dynamic pressure groove G1, the annular hill G2, and the inclined hill G3 shown in FIG. 3, respectively. Each inclined recess 35a has a ratio (flatness) h'/Hf' of circumferential width h' [mm] to depth Hf' [μm] of 0.1<h'/Hf'<0.65. (See Figure 7). The depth Hf' of each inclined recess 35a is the maximum diameter between the bottom surface (outer diameter surface) of each inclined recess 35a and the outer diameter surface of the hill portion 35c adjacent to one side in the circumferential direction of the inclined recess 35a. It's the difference.

First, the core rod 31 is inserted into the inner circumference of the sintered body 28, and the axial width of the sintered body 28 is restrained by the upper and

lower punches

32, 33. At this time, since the inner diameter of the sintered body 28 is slightly larger than the outer diameter of the core rod 31, a minute radial gap is formed between the inner peripheral surface of the sintered body 28 and the outer peripheral surface of the core rod 31. (See Figure 7).

Next, as shown in FIG. 8, while maintaining the relative positions of the sintered body 28, core rod 31, and upper and

lower punches

32, 33 in the axial direction as shown in FIG. Press fit into. As a result, the sintered body 28 is pressed from both sides in the axial direction and from the outer circumference, and the inner circumferential surface 28a of the sintered body 28 is reduced in diameter and pressed against the mold 35 formed on the outer circumferential surface of the core rod 31 (FIG. 9 reference). As a result, the shape of the mold 35 is transferred to the inner peripheral surface 28a of the sintered body 28, and the dynamic pressure groove G1 and the hill portions G2 and G3 are formed.

When the inner circumferential surface 28a of the sintered body 28 is pressed against the mold 35 in this way, the flatness h'/Hf' of the inclined recess 35a is larger than 0.1, so that the material of the sintered body 28 is pressed against the inclined recess 35a. (Meat) can enter easily. As a result, the material of the sintered body 28 can be filled up to the corners of the inclined recess 35a, so that the height of the inclined hill G3 formed in the inclined recess 35a, that is, the dynamic pressure adjacent to the inclined hill G3 is increased. The accuracy of the depth Hf of the groove G1 can be improved. Therefore, as described above, the depths of the dynamic pressure grooves G1 molded on the inner circumferential surface of the sintered body 28 can be made approximately uniform, and specifically, the depth Hf of all the dynamic pressure grooves G1 can be made substantially uniform. The variation can be suppressed to 1 μm or less.

After that, the sintered body 28, the core rod 31, and the upper and

lower punches

32, 33 are raised, and the sintered body 28 and the core rod 31 are taken out from the inner periphery of the die 34. At this time, the inner peripheral surface 28a of the sintered body 28 expands in diameter due to springback, and is separated from the mold 35 on the outer peripheral surface of the core rod 31 (see FIG. 10). Thereafter, the core rod 31 is pulled out from the inner periphery of the sintered body 28 (that is, the bearing sleeve 8) in which the dynamic pressure groove G1, the annular hill portion G2, and the inclined hill portion G3 are formed on the inner circumferential surface.

In this embodiment, as described above, the density ratio of the sintered body 28 is set to be high (80 to 95%), and the density ratio is substantially uniform in the axial direction and the radial direction. The variation in the amount of springback is suppressed, and the diameter of the entire inner circumferential surface 28a of the sintered body 28 can be uniformly expanded. This makes it difficult for the hill portions G2 and G3 molded on the inner circumferential surface 28a of the sintered body 28 to interfere with the mold 35 provided on the outer circumferential surface of the core rod 31, so that the hill portions G2 and G3 are It is possible to avoid sagging and more reliably suppress variations in the depths Hf of all the dynamic pressure grooves G1 to 1 μm or less.

The present invention is not limited to the above embodiments. Other embodiments of the present invention will be described below, but descriptions of points similar to the above embodiments will be omitted.

For example, as shown in FIG. 11, when the corners e1 and e2 at the outer diameter end of the hill portion 35c of the mold 35 formed on the outer peripheral surface of the core rod 31 are sharp (pin angle), the dynamic pressure groove G1 When the core rod 31 is pulled out from the inner periphery of the sintered body 28 (bearing sleeve 8) in the axial direction (arrow direction in the figure), the corner e1 on the axial one side of the hill portion 35c is sintered. There is a risk that it will interfere with the ridges G2, G3 on the inner circumferential surface of the body 28, and the ridges G2, G3 may be damaged.

Therefore, the corners of the outer diameter end of the mold 35 of the core rod 31 may be rounded. Specifically, as shown in FIG. 12, by spraying the abrasive material 50 onto the workpiece (in this case, the core rod 31) using the spray device 55, the surface of the workpiece is polished by friction with the abrasive material 50, and the shape is formed. The outer diameter end corner of the hill portion 35c of the mold 35 is rounded. In particular, in the illustrated example, the core rod 31 is set to form a predetermined inclination angle with respect to the projection direction of the abrasive material 50. That is, when the projection direction of the abrasive material 50 is the X direction, and the direction perpendicular to the X direction is the Y direction, the axis of the core rod 31 is inclined at a predetermined angle α with respect to the Y direction. In the illustrated example, the end of the core rod 31 on one axial side (the opposite axial end, the right side in the figure) of the mold 35 is closer to the injection device than the end on the other axial side (the axial end, the left side in the figure). 55, the axis of the core rod 31 is inclined with respect to the Y direction perpendicular to the projection direction X of the abrasive material 50. In this way, by spraying the abrasive material 50 from an oblique direction onto the mold 35 of the core rod 31, as shown in FIG. The corner e1 on the middle right side is rounded more than the corner e2 on the other axial side of each hill 35c (upstream side in the direction in which the core rod 31 is pulled out, left side in the figure). In the dynamic pressure groove G1 formed by this mold 35, a corner f1 on one axial side of the groove bottom is rounded more than a corner f2 on the other axial side. To determine whether the corner f1 of the hydrodynamic groove G1 is rounder than the corner f2, obtain an axial groove shape chart (see FIG. 13) of the hydrodynamic bearing (bearing sleeve 8) using a shape measuring machine. This can be determined by analyzing and reading the curvatures of the corners f1 and f2 in a state where the size is the same both vertically and horizontally.

As described above, since the corner e1 on one axial side of each hill portion 35c is rounded, the core rod 31 can be pulled out from the inner circumference of the sintered body 28 in the axial direction (in the direction of the arrow in FIG. 13). When the corner portion e1 and the hill portions G2 and G3 interfere with each other, it is possible to prevent the hill portions G2 and G3 from being bent. Furthermore, since the corner e2 on the other side in the axial direction is not rounded, the shape of the hill portions G2 and G3, and ultimately the shape of the dynamic pressure groove G1, can be approximated to a rectangular shape. can be secured.

Note that the rounding of the corners of the mold 35 may be performed manually, in addition to using the above-mentioned injection device.

The shape of the dynamic pressure groove G1 formed on the inner circumferential surface of the dynamic pressure bearing (bearing sleeve 8) is not limited to the above. For example, by omitting the annular hill portion G2, the dynamic pressure groove G1 inclined on one side with respect to the circumferential direction and the dynamic pressure groove G1 inclined on the other side with respect to the circumferential direction are made to be continuous, and The inclined hill part G3 and the inclined hill part G3 inclined to the other side may be made to be continuous. Alternatively, the dynamic pressure generating parts A1 and A2 may be spaced apart in the axial direction, and a cylindrical surface may be provided between them.

Furthermore, a dynamic pressure generating portion (for example, a spiral-shaped dynamic pressure groove and a hill portion) may be formed on one end surface of the dynamic pressure bearing in the axial direction. In this case, the shaft member is provided with a flange portion, and the fluid film pressure generated in the thrust bearing gap between one axial end surface of the hydrodynamic bearing and the end surface of the flange portion of the shaft member is provided on the end surface of the hydrodynamic pressure bearing. The shaft member is supported in a non-contact manner in the thrust direction by this pressure.

In the above embodiments, the case where the hydrodynamic bearing is on the fixed side and the shaft member is on the rotating side is shown, but the present invention is not limited to this, and the shaft member may be on the fixed side and the hydrodynamic bearing on the rotating side.

The dynamic pressure bearing according to the present invention is not limited to the sintered oil-impregnated bearing in which the inside is impregnated with lubricating oil as described above, but can also be used in a dry state without impregnating lubricating oil. Furthermore, the fluid dynamic pressure bearing device 1 having a dynamic pressure bearing according to the present invention is applicable not only to a fan motor but also to a spindle motor of a disk drive device of an HDD and a polygon scanner motor of a laser beam printer.

1 Fluid dynamic pressure bearing device 2 Shaft member 3 Rotor 4 Vane 5 Motor base 6a Stator 6b Magnet 7 Housing 8 Bearing sleeve (dynamic pressure bearing)
9 Seal member 10 Thrust plate 28 Sintered body 30 Sizing mold 31 Core rod 32 Upper punch 33 Lower punch 34 Die 35 Molding die 35a Inclined recess

35b Annular recess

35c Hill portion 50 Abrasive material 55 Injector A1, A2 Dynamic pressure generating portion G1 Dynamic pressure groove G2 Annular hill portion G3 Inclined hill portion R Radial bearing portion S Seal space T Thrust bearing portion

Claims

In a dynamic pressure bearing equipped with a sintered body with a dynamic pressure generating part molded on the inner peripheral surface,
The dynamic pressure generating portion has a plurality of dynamic pressure grooves extending in a direction inclined with respect to the circumferential direction, and a plurality of inclined hill portions provided between the plurality of dynamic pressure grooves in the circumferential direction,
The ratio h/Hf of the circumferential width h [mm] of each inclined hill portion to the depth Hf [μm] of the dynamic pressure groove adjacent to one circumferential side of the inclined hill portion is 0.1<h /Hf<0.65,
A hydrodynamic bearing in which a variation in depth Hf of the plurality of hydrodynamic grooves is 1 μm or less.
The density ratio of the sintered body is 80 to 95%,
2. The hydrodynamic bearing according to claim 1, wherein the sintered body has a density ratio variation of 3% or less in the axial direction and the radial direction.
The dynamic pressure according to claim 1 or 2, wherein in an axial cross section of the sintered body, a corner on one axial side of the groove bottom of the dynamic pressure groove is rounded more than a corner on the other axial side. bearing.
A hydrodynamic bearing device comprising the hydrodynamic bearing according to claim 1 or 2 and a shaft member inserted into the inner periphery of the hydrodynamic bearing.
A motor comprising the hydrodynamic bearing device according to claim 4, a stator, and a magnet.