JP7094118B2 - Sintered metal dynamic pressure bearing - Google Patents

Description

The present invention relates to a sintered metal dynamic pressure bearing.

Sintered metal bearings are used, for example, by impregnating their internal pores with lubricating oil, and the lubricating oil impregnated in the internal pores with the relative rotation of the shaft portion inserted in the inner circumference is used as the shaft portion. An oil film is formed by exuding to the sliding portion of the bearing, and the shaft portion is rotationally supported through the oil film. Due to its excellent rotational accuracy and quietness, such sintered metal bearings are more specifically used as bearing devices for motors mounted on various electric devices such as information devices, such as HDDs, CDs, and DVDs. , It is suitably used as a spindle motor bearing application in a disk drive device for a Blu-ray disk, or as a bearing application for a polygon scanner motor, a fan motor, etc. of a laser beam printer (LBP).

In this type of sintered metal bearing, a dynamic pressure groove (radial pressure groove) as a dynamic pressure generating portion is formed on the inner peripheral surface and / or the axial end surface of the bearing with the aim of further improving quietness and extending the life. And / or thrust dynamic pressure grooves) are arranged in a predetermined manner. In this case, so-called dynamic pressure groove sizing has been proposed as a method for forming the dynamic pressure groove. In this sizing, for example, the sintered body, which is the bearing material, is press-fitted into the inner circumference of the die, and the sintered body is pressed in the axial direction with the upper and lower punches, so that the sintered body is inserted into the inner circumference of the sintered body in advance. The sintered body is made to bite into the mold around the sizing pin. As a result, the shape of the molding die, that is, the shape corresponding to the radial dynamic pressure groove is transferred to the inner peripheral surface of the sintered body, and the radial dynamic pressure groove is formed into a predetermined shape. Further, the groove depth of the radial dynamic pressure groove formed by this means is usually 2 to 4 μm (see, for example, Patent Document 1 and Patent Document 2).

Japanese Patent No. 3607492 Japanese Patent No. 3602318

In recent years, in order to reduce the power consumption of the various motors described above, it has been required to reduce the torque of the bearing. The bearing torque can be reduced, for example, by increasing the radial bearing clearance between the shaft and the shaft to be rotationally supported, but simply increasing the radial bearing clearance will result in bearing rigidity (bearing here). Rigidity refers to the difficulty of swinging the shaft portion to be rotationally supported in the radial direction.) On the other hand, regarding the bearing rigidity, it is considered that the bearing rigidity increases as the groove depth of the dynamic pressure groove (radial pressure groove) provided on the inner peripheral surface of the bearing approaches the size of the radial bearing gap. According to this idea, in order to reduce the torque of the bearing, it is necessary not only to widen the radial bearing gap but also to increase the groove depth of the radial dynamic groove facing the radial bearing gap more than ever.

Here, Patent Document 2 describes the result of experimentally obtaining the relationship between the true density ratio of the sintered metal bearing and the springback amount (diameter amount) after groove formation (Patent Document 2). See FIG. 8). In order to remove the bearing from the molding die without damaging the radial dynamic pressure groove, the radius of the springback amount must be larger than the groove depth of the radial dynamic pressure groove, but the springback amount is the true density of the bearing. It correlates with the ratio. Since the true density ratio of a bearing affects the strength of the bearing itself and the formability after sintering, the range that can be realistically determined is determined to some extent. Therefore, when the springback amount of the bearing is set within the range that can be realistically taken, the groove depth of the radial dynamic pressure groove that can be formed is about 4 μm at the maximum (or less depending on the size of the bearing), which is more than this. It was difficult to increase the groove depth.

In view of the above circumstances, in the present invention, it is possible to secure the bearing rigidity and reduce the bearing torque by forming the radial dynamic pressure groove having a groove depth larger than the current level without damaging the bearing. This is a technical issue to be solved.

The solution to the above problems is achieved by the sintered metal dynamic pressure bearing according to the present invention. That is, this bearing is a sintered metal dynamic pressure bearing formed of sintered metal and having a radial bearing surface on the inner circumference, and lubricates the radial bearing surface and the radial bearing gap between the supported portion. In a sintered metal dynamic pressure bearing in which the radial dynamic pressure groove that causes the dynamic pressure action of the fluid is formed by molding, the young ratio is 75 GPa or less and 40 GPa or more, and the groove depth of the radial pressure groove is 4 μm. Characterized by a larger point.

As described above, since the present invention is basically used in a non-contact state with the supported portion (shaft portion, etc.), the Young's modulus of a sintered metal dynamic pressure bearing, which has not been considered so far, has not been considered so much. Focusing on the rate, based on the finding that when the Young's modulus and the groove depth of the radial dynamic pressure groove satisfy a predetermined relationship, a deeper radial dynamic pressure groove can be obtained without damaging the bearing. It was made. That is, if the dynamic pressure bearing is made of sintered metal in which the Young's ratio is adjusted within a predetermined range and the groove depth of the radial dynamic pressure groove formed by die forming is made larger than 4 μm, the radial pressure groove is accurate. Even when the molding can be performed well and the groove depth exceeds 4 μm, the dynamic pressure bearing can be taken out from the molding die without damaging the radial dynamic pressure groove as much as possible. From the above, according to the sintered metal dynamic pressure bearing according to the present invention, it is possible to form a radial dynamic pressure groove having a groove depth larger than the current level without damaging the bearing. It is possible to compensate for the decrease in bearing rigidity due to the expansion of the radial bearing gap by increasing the depth of the radial dynamic groove while expanding the bearing torque. Therefore, it is possible to both secure the bearing rigidity and reduce the bearing torque.

Further, in the sintered metal dynamic pressure bearing according to the present invention, the groove depth of the radial dynamic pressure groove may be 5 μm or more.

In the case of a sintered metal dynamic pressure bearing having a Young ratio of 75 GPa or less and 40 GPa or more as in the present invention, even if the groove depth is 5 μm or more, the radial dynamic pressure groove can be formed as much as possible. The dynamic pressure bearing can be taken out from the molding die without damaging it. Therefore, by setting the groove depth of the radial dynamic pressure groove to 5 μm or more, the radial bearing gap can be widened from the current level by that amount, which makes it possible to further reduce the bearing torque. ..

Further, in the sintered metal dynamic pressure bearing according to the present invention, the ratio of the size of the radial bearing gap to the groove depth of the radial dynamic pressure groove may be 0.7 or more and 1.3 or less. ..

By setting the size of the radial bearing gap with a predetermined width according to the groove depth of the radial dynamic pressure groove in this way, for example, while taking into account the variation in the groove depth of the radial dynamic pressure groove in mass-produced products. It is possible to effectively reduce the bearing torque and suppress the decrease in bearing rigidity due to the expansion of the radial bearing gap.

Further, in the sintered metal dynamic pressure bearing according to the present invention, the true density ratio may be 80% or more and 95% or less. The "true density ratio" here is a value (percentage) obtained by dividing the density of a porous body made of a sintered metal dynamic pressure bearing by the density assuming that the porous body has no pores. means.

By setting the true density ratio of the sintered metal dynamic pressure bearing to 80% or more, the strength of the bearing can be increased and fluctuations in the bearing dimensions (particularly the inner diameter dimension) can be suppressed. In addition, by keeping the true density ratio to 95% or less, moldability after sintering is ensured, and the situation where the internal pores become independent pores is prevented as much as possible, and the required amount of lubricating oil is added to the internal pores. Can be impregnated. Further, by setting the true density ratio within the above range, it is possible to secure a springback amount sufficient to form a radial dynamic pressure groove having a groove depth exceeding 4 μm without damaging the bearing.

Further, in the sintered metal dynamic pressure bearing according to the present invention, a thrust dynamic pressure groove that causes a dynamic pressure action of the lubricating fluid is formed in the thrust bearing gap between the supported portion and the end face in the axial direction by molding. You may.

In the case of a sintered metal dynamic pressure bearing having a Young's modulus of 75 GPa or less and 40 GPa or more as in the present invention, not only the radial dynamic pressure groove but also the thrust dynamic pressure groove should be formed by molding with high accuracy. Can be done. Therefore, it is possible to obtain a dynamic pressure bearing having excellent both radial bearing performance and thrust bearing performance.

Further, the sintered metal dynamic pressure bearing according to the present invention may be formed of a copper-iron-based sintered metal containing copper and iron as main components.

By forming the bearing from a copper-iron-based sintered metal containing copper and iron as main components in this way, the good formability of copper (pure copper structure or copper alloy structure) and iron (pure iron structure or The high hardness of the iron alloy structure) can be imparted to the above bearing. Therefore, it is possible to improve the wear resistance of the radial bearing surface including the radial dynamic pressure groove while accurately forming the radial dynamic pressure groove by molding.

Further, in the sintered metal dynamic pressure bearing according to the present invention, the internal pores may be impregnated with lubricating oil as a lubricating fluid.

In this way, if the internal pores are impregnated with lubricating oil, the radial bearing gap and its surroundings can be filled with abundant lubricating oil due to the exudation of the lubricating oil from the surface openings of the bearing. .. Therefore, it is possible to stably maintain the radial bearing performance.

As described above, the sintered metal dynamic pressure bearing according to the above description can both secure the bearing rigidity and reduce the bearing torque. Therefore, for example, the sintered metal dynamic pressure bearing and the sintered metal dynamic pressure bearing are sintered. It can be suitably provided as a fluid dynamic bearing device provided with a shaft portion as a supported portion inserted inside the metal dynamic pressure bearing, and further as a motor provided with the fluid dynamic pressure bearing device.

Based on the above, according to the present invention, it is possible to secure bearing rigidity and reduce bearing torque by forming a radial dynamic pressure groove having a groove depth larger than the current level without damaging the bearing. Is possible.

It is sectional drawing of the motor which concerns on one Embodiment of this invention. It is sectional drawing of the fluid dynamic pressure bearing apparatus shown in FIG. It is sectional drawing of the dynamic pressure bearing shown in FIG. FIG. 3 is a cross-sectional view taken along the line XX of FIG. FIG. 3 is an axial end view of the dynamic pressure bearing shown in FIG. It is a figure for demonstrating the process of molding a radial dynamic pressure groove shown in FIG. 3, (a) is before inserting a signing pin, (b) is sintering at the start of press-fitting into a die of a sintered body. It is a cross-sectional view of a body. It is a figure for demonstrating the process of molding a radial dynamic pressure groove shown in FIG. It is a cross-sectional view at a time point.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of a configuration of a spindle motor according to the present embodiment. This spindle motor is used, for example, in a disk drive device of an HDD, and has a gap between a fluid dynamic pressure bearing device 1 and a disk hub 3 fixed to a shaft member 2 of the fluid dynamic pressure bearing device 1, for example, in a radial direction. It includes a drive unit 4 including a stator coil 4a and a rotor magnet 4b facing each other, and a bracket 5. The stator coil 4a is fixed to the bracket 5, and the rotor magnet 4b is fixed to the disc hub 3. The fluid dynamic bearing device 1 is fixed to the inner circumference of the bracket 5. A predetermined number of discs (two in FIG. 1) 6 are held in the disc hub 3. When the stator coil 4a is energized, the rotor magnet 4b rotates, and along with this, the disk 6 held by the disk hub 3 rotates integrally with the shaft member 2.

FIG. 2 shows a cross-sectional view of the hydrodynamic bearing device 1 according to the embodiment of the present invention. This fluid dynamic pressure bearing device 1 includes a dynamic pressure bearing 8 made of sintered metal, a shaft member 2 inserted in the inner circumference of the dynamic pressure bearing 8 and rotating with respect to the dynamic pressure bearing 8, and the dynamic pressure bearing 8. A bottomed tubular housing 7 held on the inner circumference and a sealing member 9 for sealing the opening of the housing 7 are provided. The internal space of the housing 7 is filled with lubricating oil (indicated by dense scattered spot hatching) as a lubricating fluid. In the following description, for convenience, the side on which the seal member 9 is provided is referred to as the lower side, and the side opposite to the axial direction thereof is referred to as the lower side.

The housing 7 has a bottomed tubular shape having a cylindrical tubular portion 7a and a bottom portion 7b that integrally closes the lower end opening of the tubular portion 7a. A stepped portion 7c is provided at the boundary between the tubular portion 7a and the bottom portion 7b, and the dynamic pressure bearing 8 with respect to the housing 7 is provided by abutting the lower end surface 8b of the dynamic pressure bearing 8 on the upper end surface of the stepped portion 7c. The axial position of is set.

The inner bottom surface 7b1 of the bottom portion 7b is provided with an annular thrust bearing surface that forms a thrust bearing gap of the thrust bearing portion T2 with the lower end surface 2b2 of the flange portion 2b of the facing shaft member 2. The thrust bearing surface is provided with a dynamic pressure generating portion (thrust dynamic pressure generating portion) for generating a dynamic pressure action on the lubricating oil in the thrust bearing gap of the thrust bearing portion T2. Although not shown, the thrust dynamic pressure generating portion has, for example, a spiral-shaped dynamic pressure groove and a convex hill portion for partitioning the dynamic pressure groove, similarly to the thrust dynamic pressure generating portion B described later. It is configured by alternately arranging it in the circumferential direction (see FIG. 5).

The seal member 9 is formed in an annular shape, and is fixed to, for example, the inner peripheral surface 7a1 of the tubular portion 7a of the housing 7 by an appropriate means. The inner peripheral surface 9a of the seal member 9 is formed in a tapered surface shape whose diameter is gradually reduced downward, and the radial dimension is gradually reduced downward between the inner peripheral surface 9a and the outer peripheral surface 2a1 of the opposing shaft member 2. The seal space S is formed. The seal space S has a buffer function of absorbing the amount of volume change due to the temperature change of the lubricating oil filled in the internal space of the housing 7, and always seals the oil level of the lubricating oil within the range of the assumed temperature change. It is kept within the axial range of the space S.

The shaft member 2 includes a shaft portion 2a and a flange portion 2b provided integrally or separately at the lower end of the shaft portion 2a. Of the outer peripheral surface 2a1 of the shaft portion 2a, the portion facing the inner peripheral surface 8a of the dynamic pressure bearing 8 is not uneven except that a cylindrical escape portion 2c having a relatively small diameter is provided. It is formed on a smooth cylindrical surface. Further, the upper end surface 2b1 and the lower end surface 2b2 of the flange portion 2b are formed in a smooth flat surface shape.

The dynamic pressure bearing 8 is formed of a porous body of sintered metal in a cylindrical shape. The metal structure constituting this porous body can be arbitrarily adopted as long as it satisfies the regulation of the Young ratio described later, and for example, a metal structure of pure copper (including industrial pure copper) or a copper alloy and pure iron (pure iron (including industrial pure copper)). A metal structure mainly containing the metal structure of an iron alloy such as (including industrial pure iron) or iron alloy such as stainless steel can be adopted. Further, the internal pores of the dynamic pressure bearing 8 may be impregnated with lubricating oil.

On the inner peripheral surface 8a of the hydraulic bearing 8, there are two cylindrical radial bearing surfaces forming radial bearing gaps of the radial bearing portions R1 and R2 between the inner peripheral surface 8a of the shaft portion 2a facing each other and the outer peripheral surface 2a1 of the shaft portion 2a. It is provided apart from each other. As shown in FIG. 3, radial dynamic pressure generating portions A1 and A2 for generating a dynamic pressure action on the lubricating oil in the radial bearing gap are formed on the two radial bearing surfaces, respectively. The radial dynamic pressure generating portions A1 and A2 each have a plurality of upper dynamic pressure grooves Aa1 inclined in the axial direction and a plurality of lower dynamic pressure grooves Aa2 inclined in the direction opposite to the upper dynamic pressure groove Aa1. It is composed of convex hills that partition the radial dynamic pressure grooves Aa1 and Aa2, and the radial dynamic pressure grooves Aa1 and Aa2 are arranged in a herringbone shape as a whole. The hills are provided between the inclined hills Ab provided between the adjacent dynamic pressure grooves in the circumferential direction and the upper and lower radial dynamic pressure grooves Aa1 and Aa2, and the annular hills Ac having substantially the same diameter as the inclined hills Ab. It consists of.

Here, as shown in FIG. 4, the groove depths d1 and d2 of the radial dynamic pressure grooves Aa1 and Aa2 provided on the inner peripheral surface 8a (radial bearing surface) of the dynamic pressure bearing 8 are both larger than 4 μm. Further, the size G (radial amount) of the radial bearing gap between the shaft portion 2a and the outer peripheral surface 2a1 shown by the two-dot chain line in FIG. 4 is the groove depths d1 and d2 of the radial dynamic pressure grooves Aa1 and Aa2. When it is 1, it is set to 0.7 or more and 1.3 or less, and preferably 0.8 or more and 1.2 or less. The groove depths d1 and d2 of the radial dynamic pressure grooves Aa1 and Aa2 are measured after measuring the roundness shape (closed loop-shaped curve) of the inner peripheral surface 8a using, for example, a roundness measuring machine. The circular shape is developed so that the inner peripheral surface 8a becomes a flat bearing surface, and the height difference between the inclined hill portion Ab adjacent to each other and the radial dynamic pressure groove Aa1 (Aa2) is read as the groove depth d1 (d2). Can be obtained by.

The lower end surface 8b of the dynamic pressure bearing 8 is provided with an annular thrust bearing surface that forms a thrust bearing gap of the thrust bearing portion T1 between the lower end surface 8b and the upper end surface 2b1 of the facing flange portion 2b. As shown in FIG. 5, a dynamic pressure generating portion (thrust dynamic pressure generating portion) B for generating a dynamic pressure action on the lubricating oil in the thrust bearing gap of the thrust bearing portion T1 is formed on the thrust bearing surface. ing. The thrust dynamic pressure generating portion B of the illustrated example is configured by alternately arranging a spiral-shaped thrust dynamic pressure groove Ba and a convex hill portion Bb for partitioning the thrust dynamic pressure groove Ba in the circumferential direction. ..

The dynamic pressure bearing 8 having the above configuration is manufactured so that the Young's modulus is 75 GPa or less and 40 GPa or more. Here, Young's modulus can be measured by the method specified in JPMA M 10-1997. Further, the true density ratio is manufactured so as to be 80% or more and 95% or less. Hereinafter, an example of a method for manufacturing the dynamic pressure bearing 8 having the above configuration will be described.

The dynamic pressure bearing 8 according to the present invention has a compaction forming step (S1) in which a raw material powder is compression-molded to obtain a green compact, and a sintering step (S1) in which the green compact is sintered to obtain a sintered body 8'. S2) and the dynamic pressure groove sizing step (S3) in which the sintered body 8'is sized to form radial dynamic pressure grooves Aa1 and Aa2 as dynamic pressure generating portions on at least the inner peripheral surface 8a of the sintered body 8'. ) And mainly. If necessary, a dimensional sizing step of sizing the sintered body 8'after the sintering step (S2) and before the dynamic pressure groove sizing step (S3), and an inner peripheral surface of the sintered body 8'. 8a may be provided with a rotation sizing step for applying rotation sizing.

(S1) Powder forming step First, a raw material powder used as a material for a dynamic pressure bearing 8 to be a final product is prepared, and this is compression-molded into a predetermined shape by die press forming. Specifically, although not shown, a lower punch, which is arranged between the die, the core pin inserted in the hole of the die, and the die and the core pin, and is configured to be able to move up and down with respect to the die. The raw material powder is compression-molded using a molding die composed of an upper punch configured to be relatively displaced (elevated) with respect to both the die and the lower punch. In this case, the raw material powder is filled in the space formed by the inner peripheral surface of the die, the outer peripheral surface of the core pin, and the upper end surface of the lower punch, and then the upper punch is lowered with the lower punch fixed. Then, the raw material powder in the filled state is pressurized in the axial direction. Then, the upper punch is lowered to a predetermined position while pressurizing, and the raw material powder is compressed to a predetermined axial dimension, whereby the green compact is formed.

Here, as the raw material powder, one containing one kind or two or more kinds of arbitrary metal powders is used. In this embodiment, a raw material powder mainly containing pure copper powder and stainless steel powder as an iron alloy powder is used. Of course, pure iron powder may be used instead of stainless steel powder, or iron alloy powder other than stainless steel may be used. Alternatively, a mixture powder of an iron alloy powder such as stainless steel powder and pure iron powder added to pure copper powder may be used as a raw material powder. Further, the compounding ratio of the metal powder described above can be arbitrarily set as long as the Young's modulus of the dynamic pressure bearing 8 is within the numerical range (75 GPa or less and 40 GPa or more) specified in the present invention. For example, when the raw material powder contains pure copper powder and stainless steel powder, it is preferable to set the blending ratio so that the pure copper powder: 30 to 85 wt% and the stainless steel powder: 15 to 70 wt%. Alternatively, when the raw material powder contains pure copper powder, stainless steel powder, and pure iron powder, the blending ratio is adjusted so that pure copper powder + pure iron powder: 30 to 85 wt% and stainless steel powder: 15 to 70 wt%. It is better to determine. Of course, a substance other than the above-mentioned metal powder may be blended in the raw material powder, and for example, graphite or an amide wax-based solid lubricant powder may be blended.

(S2) Sintering Step After obtaining the green compact as described above, the green compact is baked by sintering at a temperature corresponding to the composition of the raw material powder, particularly the metal powder contained in the raw material powder. Obtain a bundling 8'(see Figure 6). For example, when the raw material powder contains pure copper powder as described above, the temperature at the time of sintering is set to a temperature of 750 ° C. or higher and lower than the melting point of copper.

(S3) Dynamic Pressure Groove Sizing Step The inner peripheral surface of the sintered body 8'is formed by performing a predetermined mold forming (dynamic pressure groove sizing) on the sintered body 8'obtained through the above steps S1 and S2. The radial dynamic pressure grooves Aa1 and Aa2 arrangement regions forming the radial dynamic pressure generating portions A1 and A2 are formed in 8a. As shown in FIG. 6, the molding apparatus 20 used here includes a die 21 having a press-fitting hole 21a of the sintered body 8', a sizing pin 22 inserted into the press-fitting hole 21a of the die 21, and a die. The lower punch 23, which is arranged between the 21 and the sizing pin 22 and is configured to be able to move up and down relative to the die 21, and is configured to be able to move up and down to any of the die 21 and the lower punch 23. It also has an upper punch 24. In this case, the inner diameter of the press-fitting hole 21a of the die 21 is appropriately set according to the press-fitting allowance of the sintered body 8'to be sizing. Further, on the outer peripheral surface of the sizing pin 22, a first molding die 22a having a shape corresponding to the radial dynamic pressure grooves Aa1 and Aa2 arrangement regions of the inner peripheral surface 8a to be molded is provided (see FIG. 6), and the bottom The upper end surface 23a of the punch 23 is provided with a second molding die having a shape corresponding to the thrust dynamic pressure groove Ba arrangement region of the lower end surface 8b to be formed (not shown). Here, the first forming die 22a is composed of a convex forming portion 22a1 for forming the radial dynamic pressure grooves Aa1 and Aa2, and a concave forming portion 22a2 for forming the inclined hill portion Ab and the annular hill portion Ac. .. In this case, the outer diameter dimension of the convex molding portion 22a1 and the outer diameter dimension of the region other than the first molding die 22a on the outer peripheral surface of the sizing pin 22 are set to be the same. Further, the value of half of the outer diameter dimensional difference between the convex forming portion 22a1 and the concave forming portion 22a2 is, for example, the target value (for example, 5 to 7 μm) of the groove depths d1 and d2 of the radial dynamic pressure grooves Aa1 and Aa2 to be formed. It is preferable to set the outer diameter dimension of the convex forming portion 22a1 and the outer diameter dimension of the concave forming portion 22a2 so as to be larger than the above.

Next, one aspect of the dynamic pressure groove sizing using the molding apparatus 20 having the above configuration will be described. First, as shown in FIG. 6A, the upper punch 24 and the sizing pin 22 are lowered from above the sintered body 8'arranged on the upper end surface 21b of the die 21. As a result, the sizing pin 22 is inserted into the inner circumference of the sintered body 8', and the first molding die 22a provided on the outer periphery of the sizing pin 22 faces the inner peripheral surface 8a in the radial direction. Then, when the first molding die 22a reaches a predetermined position in the axial direction of the inner peripheral surface 8a, only the upper punch 24 is continuously lowered to press the upper end surface 8c of the sintered body 8'(FIG. 6B). reference). As a result, the sintered body 8'is pushed into the press-fitting hole 21a of the die 21, the outer peripheral surface 8d of the sintered body 8'is pressed, and the first molding mold 22a of the sizing pin 22 inserted in advance in the inner circumference is pressed. The inner peripheral surface 8a bites. Further, from this state, the upper punch 24 is further lowered, the sintered body 8'is sandwiched between the upper punch 24 and the lower punch 23, and the deformation in the outer diameter direction is restrained by the die 21. By pressing the body 8'in the axial direction, the inner peripheral surface 8a further bites into the first molding die 22a (see FIG. 7A). The sizing pin 22 descends as the sintered body 8'descends because the inner peripheral surface 8a of the sintered body 8'bites against the first molding die 22a. In this way, the shape of the first molding die 22a, specifically the shapes of the convex molding portion 22a1 and the concave molding portion 22a2, are transferred to the inner peripheral surface 8a, respectively, thereby forming the radial dynamic pressure grooves Aa1 and Aa2. The hills Ab and Ac are formed (see FIG. 7 (b)). At this time, the second molding die provided on the upper end surface 23a of the lower punch 23 bites into the lower end surface 8b of the sintered body 8', so that the shape of the second molding die is transferred to the lower end surface 8b, which corresponds to the corresponding shape. The thrust dynamic pressure groove Ba and the hill portion Bb are formed.

After forming the predetermined radial dynamic pressure groove Aa1 and Aa2 arrangement regions and the thrust dynamic pressure groove Ba arrangement region on the inner peripheral surface 8a and the lower end surface 8b of the sintered body 8'in this way, the die 21 is used as the lower punch 23. On the other hand, it is relatively lowered to release the restrained state of the sintered body 8'by the die 21 (FIG. 7 (b)). As a result, the sintered body 8'causes springback in the outer diameter direction, and the outer diameter dimension of the outer peripheral surface 8d and the inner diameter dimension of the inner peripheral surface 8a increase. Further, by raising the upper punch 24 to release the restrained state of the sintered body 8'in the axial direction by the upper punch 24 and the lower punch 23 (FIG. 7 (b)), the sintered body 8'has a shaft. Springback occurs in the direction, and the axial dimensions of the outer peripheral surface 8d and the inner peripheral surface 8a increase. In this way, after the die 21 descends, the sintered body 8'causes springback in the outer diameter direction, so that the inner peripheral surface 8a expands in diameter, so that interference with the radial dynamic pressure grooves Aa1 and Aa2 is possible. The sizing pin 22 can be removed from the sintered body 8'while avoiding it. As a result, it is possible to obtain a sintered body 8'in which radial dynamic pressure grooves Aa1 and Aa2 are formed on the inner peripheral surface 8a, that is, a dynamic pressure bearing 8 in the form shown in FIGS. 3 to 5. The dynamic pressure bearing 8 manufactured through the above sizing has, for example, an inner diameter dimension of 1 to 5 mm, an outer diameter dimension of 3 to 8 mm, and an axial dimension of 2 to 15 mm.

The dynamic pressure bearing 8 having the above configuration is fixed to the inner circumference of the housing 7 (inner peripheral surface of the tubular portion 7a) by, for example, press fitting or adhesion. Of course, other means may be adopted. For example, although not shown, the dynamic pressure bearing 8 is pushed in the axial direction while the seal member 9 is press-fitted into the housing 7, and the step portion 7c of the housing 7 and the seal member 9 are used. The dynamic pressure bearing 8 can also be held on the inner circumference of the housing 7 by sandwiching the dynamic pressure bearing 8 in the axial direction. At this time, a predetermined radial gap may be provided between the outer peripheral surface 8d of the dynamic pressure bearing 8 and the inner peripheral surface of the housing 7.

In the fluid dynamic bearing device 1 having the above configuration, two radial bearing surfaces provided on the inner peripheral surface 8a of the dynamic bearing 8 before the start of relative rotation between the shaft member 2 and the dynamic bearing 8 and facing them. Radial bearing gaps are formed between the shaft portion 2a and the outer peripheral surface 2a1. Then, as the relative rotation between the shaft member 2 and the dynamic pressure bearing 8 is started, the pressure of the oil film formed in the gap between both radial bearings is the movement of the radial dynamic pressure generating portions A1 and A2 (dynamic pressure grooves Aa1 and Aa2). It is enhanced by the pressure action, and as a result, the radial bearing portions R1 and R2 that non-contactly support the shaft member 2 in a relative rotatable manner in the radial direction are formed at two positions separated in the axial direction. At this time, by providing the middle relief portion 2c on the outer peripheral surface 2a1 of the shaft portion 2a, a cylindrical lubricating oil reservoir is formed between the two radial bearing gaps. Therefore, it is possible to prevent the oil film from running out in the radial bearing gap, that is, the deterioration of the bearing performance of the radial bearing portions R1 and R2 as much as possible.

Further, before the relative rotation of the shaft member 2 and the dynamic pressure bearing 8, between the thrust bearing surface provided on the lower end surface 8b of the dynamic pressure bearing 8 and the upper end surface 2b1 of the flange portion 2b facing the thrust bearing surface, and A thrust bearing gap is formed between the inner bottom surface 7b1 of the bottom portion 7b of the housing 7 and the lower end surface 2b2 of the flange portion 2b facing the inner bottom surface 7b1. Then, as the relative rotation of the shaft member 2 is started, the pressure of the oil film formed in the gap between the two thrust bearings is the thrust of the thrust dynamic pressure generating portion B (dynamic pressure groove Ba) of the lower end surface 8b and the thrust of the inner bottom surface 7b1. Each of them is enhanced by the dynamic pressure action of the dynamic pressure generating portion, and as a result, thrust bearing portions T1 and T2 that non-contactly support the shaft member 2 in relative rotatability in one direction and the other direction of the thrust are formed.

As described above, according to the sintered metal dynamic pressure bearing 8 according to the present invention, that is, the radial motion formed by adjusting the young ratio to be 75 GPa or less and 40 GPa or more and forming a mold. If the dynamic pressure bearing 8 made of sintered metal has the groove depths d1 and d2 of the pressure grooves Aa1 and Aa2 larger than 4 μm, the radial pressure grooves Aa1 and Aa2 can be formed with high accuracy, and the groove depths d1 and d2. The dynamic pressure bearing 8 can be taken out from the molding die (die 21 and sizing pin 22 in this embodiment) without damaging the radial dynamic pressure grooves Aa1 and Aa2 as much as possible even when the pressure exceeds 4 μm. .. From the above, according to the dynamic pressure bearing 8 according to the present invention, the radial dynamic pressure grooves Aa1 and Aa2 having a groove depth larger than the current level can be formed without damaging the bearing. To compensate for the decrease in bearing rigidity due to the expansion of the radial bearing gap G by increasing the groove depths d1 and d2 of the radial dynamic pressure grooves Aa1 and Aa2, while expanding the bearing torque beyond the level to reduce the bearing torque. Can be done. Therefore, it is possible to secure the bearing rigidity, reduce the bearing torque, and further reduce the power consumption of the motor.

Although one embodiment of the present invention has been described above, the sintered metal dynamic pressure bearing according to the present invention is not limited to the above-exemplified form, and any form can be adopted within the scope of the present invention.

For example, in the above embodiment, a case where a pair of radial dynamic pressure grooves Aa1 and Aa2 that are inclined in opposite directions and form a herringbone shape is provided on the inner peripheral surface 8a is illustrated, but of course, the radial dynamics having other shapes are illustrated. The present invention can also be applied when the pressure groove is provided on the inner peripheral surface 8a by molding.

Further, the fluid dynamic bearing device 1 according to the above description is not limited to the application shown in FIG. 1 (for a disk device such as an HDD), and can be applied to other applications. For example, although not shown, the fluid dynamic bearing device 1 can be incorporated into a motor such as a polygon scanner motor for a laser beam printer (LBP) or a fan motor for a PC. When used by incorporating it into a polygon scanner motor, for example, when a polygon mirror is integrally or separately provided on the shaft member 2, and when used by incorporating it into a fan motor, for example, a fan having blades is integrated with the shaft member 2. Or it is provided separately.

Hereinafter, experiments (examples) for verifying the action and effect of the present invention will be described in detail.

In this experiment, five types of sintered metal dynamic pressure bearings 8 having different Young ratios were manufactured, and radial pressure grooves Aa1 and Aa2 were used for each dynamic pressure bearing 8 using the common molding device 20 shown in FIG. The size of the groove depths d1 and d2 (see FIG. 4) of the radial dynamic pressure grooves Aa1 and Aa2 actually formed on the inner peripheral surface 8a of each bearing when the molding (see FIG. 3) was performed. Was measured. Here, the true density ratio of each dynamic pressure bearing 8 was adjusted to be 86 to 88%. The size of each dynamic bearing 8 was set to an inner diameter dimension of 4 mm, an outer diameter dimension of 7.5 mm, and an axial dimension of 9.2 mm. Further, for any of the dynamic pressure bearings 8 (Examples 1 and 2, Comparative Examples 1 to 3), the groove depth of the sizing pin 22 (that is, half the difference in outer diameter between the convex molded portion 22a1 and the concave molded portion 22a2). The radial dynamic pressure grooves Aa1 and Aa2 were molded using the molding apparatus 20 having a value of 8 μm. Table 1 shows the measurement results of Young's modulus and the measurement results of the groove depths d1 and d2 of the radial dynamic pressure grooves Aa1 and Aa2. The values of the groove depths d1 and d2 of the radial dynamic pressure grooves Aa1 and Aa2 in Table 1 indicate the average value of the measurement results of n = 10.

As shown in Table 1, when the dynamic pressure bearing 8 (Examples 1 and 2) having a Young's modulus of 75 GPa or less is subjected to dynamic pressure groove sizing, the size is close to the groove depth (8 μm) of the molding die, specifically. Radial dynamic pressure grooves Aa1 and Aa2 having groove depths d1 and d2 of 5.5 to 6.7 μm could be obtained. On the other hand, when the dynamic pressure groove sizing is applied to the dynamic pressure bearings 8 (Comparative Examples 1 to 3) having a Young's modulus of more than 75 GPa, the size and concreteness cannot be said to be close to the groove depth (8 μm) of the molding die. The target was only radial dynamic pressure grooves Aa1 and Aa2 with groove depths d1 and d2 of 3.5 to 5.1 μm. The Young's modulus does not change even if the ratio of copper (Cu) powder increases, and the Young's modulus decreases as the compounding ratio of stainless steel (SUS) powder increases. For example, the surface of stainless steel powder is oxidized. Due to the presence of the coating film, it is considered that one of the reasons is that at the general sintering temperature of copper, the sintering is less likely to proceed than that of copper powder or iron (Fe) powder.

1 Fluid dynamic bearing device 2 Shaft member 2a Shaft part 2b Flange part 3 Disc hub 4a Stator coil 4b Rotor magnet 5 Bracket 6 Disc 7 Housing 7a Cylindrical part 7b Bottom part 7c Step part 8 Dynamic bearing 8'Sintered body 8a Inner circumference Surface 9 Sealing member 20 Molding device 21 Die 22 Sizing pin 22a Molding mold 22a1 Convex molding part 22a2 Concave molding part A1, A2 Radial dynamic pressure generating part Aa1, Aa2 Radial dynamic pressure groove B Thrust dynamic pressure generation part Ba Thrust dynamic pressure groove G Radial bearing clearance size (radial amount)
R1, R2 Radial bearing T1, T2 Thrust bearing S Seal space

Claims (5)

A sintered metal dynamic pressure bearing formed of sintered metal and having a radial bearing surface on the inner circumference. The dynamic pressure action of a lubricating fluid on the radial bearing surface and in the radial bearing gap between the supported portion. In a sintered metal dynamic pressure bearing in which a radial pressure groove is formed by molding.
It is a copper-iron sintered metal whose main components are copper and iron, and is formed so that the true density ratio is 80% or more and 95% or less.
The Young's modulus is 75 GPa or less and 40 GPa or more, and the ratio of the size of the radial bearing gap to the groove depth of the radial dynamic pressure groove is 0.7 or more and 1.3 or less, and the radial. A sintered metal dynamic pressure bearing characterized in that the groove depth of the dynamic pressure groove is 5 μm or more . The sintered metal dynamic pressure bearing according to claim 1 , wherein a thrust dynamic pressure groove that causes a dynamic pressure action of the lubricating fluid is formed on an axial end surface in a thrust bearing gap between the supported portion and the supported portion. .. The sintered metal dynamic pressure bearing according to claim 1 or 2 , wherein the internal pores are impregnated with lubricating oil as the lubricating fluid. A fluid comprising the sintered metal dynamic pressure bearing according to any one of claims 1 to 3 and a shaft portion as a supported portion inserted into the inner circumference of the sintered metal dynamic pressure bearing. Dynamic pressure bearing device. A motor provided with the fluid dynamic bearing device according to claim 4 .

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