JP6981900B2 - Fluid dynamic bearing device and motor equipped with it - Google Patents

Description

The present invention relates to a fluid dynamic bearing device and a motor including the same.

As is well known, the fluid dynamic bearing device has features such as high speed rotation, high rotation accuracy and low noise. Therefore, the hydrodynamic bearing device is, for example, a bearing for a spindle motor incorporated in a disk drive device such as an HDD, a fan motor incorporated in a PC or the like, or a polygon scanner motor incorporated in a laser beam printer (LBP). It is used as a device.

The hydrodynamic bearing device is a full-fill type in which the entire internal space of the housing containing the bearing members is filled with lubricating oil, and the lubricating oil is interposed in a part of the internal space of the housing (lubricating oil in the internal space). There is a partial fill type (a mixture of air and air). For example, Patent Document 1 below discloses an example of a partial fill type hydraulic pressure bearing device.

The hydrodynamic bearing device of Patent Document 1 is made of an oil-impregnated sintered metal, and has a bearing member that forms a radial bearing gap with a shaft to be supported, and an end portion on one side in the axial direction is opened and the other end in the axial direction is opened. A bottomed tubular shape with a closed end on the side, a housing that houses the bearing member, a sealing member that forms a sealing gap to seal one end opening of the housing, and a shaft, bearing member, and bottom of the housing. It is provided with a ventilation path that opens the sealed space defined by the above to the outside air through a seal gap, and a part of the ventilation path is an annular shape provided between the outer peripheral portion of one end of the bearing member and the cylinder portion of the housing. It is open to the oil reservoir (oil holding space). Further, between one end surface of the bearing member and the other end surface of the seal member, the ends of the radial outer side and the radial inner side are opened in the oil retention space and the seal gap (the oil retention space and the seal gap are communicated with each other). An axial gap is formed.

In the hydrodynamic bearing device of Patent Document 1, by providing the above axial gap, the lubricating oil exuded from the bearing member during the operation of the bearing device is pushed up to the housing opening side through the ventilation path and held. Even if the oil collects in the oil space, the distance between the oil level of the lubricating oil accumulated in the oil holding space and the sealing member (the other end surface) can be increased, so the oil caused by the contact between the lubricating oil and the sealing member can be obtained. It is said that leakage can be prevented.

Japanese Patent No. 4481475

In the fluid dynamic bearing device of Patent Document 1, one end of the annular oil-retaining space in the axial direction (housing opening side) is connected to the outer end of the axial gap over the entire circumference. Therefore, when the fluid dynamic bearing device is used (operated) in an inclined posture or when an impact load is applied to the fluid dynamic bearing device during operation, the lubricating oil to be held in the oil retention space is It easily flows into the axial gap and easily reaches the seal gap connected to the oil holding space through the axial gap. In this case, it cannot be said that the risk of oil leakage can be reduced even if additional oil leakage prevention measures such as applying an oil repellent agent to at least one of the two facing surfaces forming the seal gap can be taken. In particular, during continuous operation of the bearing device, the lubricating oil expands thermally, the viscosity of the lubricating oil decreases, and the fluidity of the lubricating oil increases, so that the risk of oil leakage increases.

In view of such circumstances, the present invention provides a fluid dynamic pressure bearing device (partial fill type fluid dynamic pressure bearing device) capable of stably exhibiting desired bearing performance with a low risk of oil leakage. With the goal.

The present invention, which was devised to achieve the above object, comprises a bearing member made of a porous body impregnated with lubricating oil and forming a radial bearing gap between the outer peripheral surface of the shaft to be supported, and a bearing member in the axial direction. It has a bottomed tubular shape with one end open and the other end closed, and is defined by a housing that houses the bearing member, a seal gap that seals the opening of the housing, and the shaft, bearing member, and bottom of the housing. It has a ventilation path that opens the closed space to the outside air, and a tubular oil retention space that is provided between the outer peripheral portion of one end of the bearing member and the cylinder portion of the housing and can hold the oil level of the lubricating oil. A fluid formed by a path including a first passage opened in a closed space and an oil-retaining space, and an axial gap formed by one end surface of a bearing member and having a radial inner end connected to a sealing gap. In the hydraulic bearing device, an annular portion that is in contact with one end surface of the bearing member is provided, and an oil holding space and an axial gap are provided in at least one of one end surface of the bearing member and the other end surface of the annular portion that is in contact with the one end surface. It is characterized in that it communicates through a second passage formed by the groove portion.

According to the above configuration, the closed space and the seal gap are communicated with each other through a ventilation path having a first passage, a tubular oil retention space, a second passage, and an axial gap, and the oil retention of the ventilation passages. The space and the axial gap communicate with each other in a partial region in the circumferential direction via the second passage. In this case, for example, when the lubricating oil exuded from the bearing member is accumulated in the oil holding space during the operation of the fluid dynamic bearing device in an inclined posture, or when the lubricating oil is accumulated in the oil holding space, the fluid dynamic bearing is used. Even when an impact load is applied to the device, the amount of lubricating oil accumulated in the oil holding space flowing into the axial gap can be significantly reduced as compared with the conventional configuration. Therefore, the risk of oil leakage through the seal gap can be effectively reduced.

The oil-retaining space is provided with an enlarged diameter portion whose radial dimension gradually expands from the other side in the axial direction (bottom side of the housing) to the one side in the axial direction (opening side of the housing) to operate the hydraulic pressure bearing device. If the oil level of the lubricating oil inside is held in the axial range of the enlarged diameter portion, the lubricating oil interposed in the oil-retaining space can be drawn to the bottom side of the housing by the capillary force. As a result, the inflow amount of the lubricating oil from the oil holding space to the axial gap can be further reduced, and the risk of oil leakage through the seal gap can be further reduced.

The diameter-expanded portion to be provided in the oil-retaining space is, for example, provided on the inner peripheral surface of the cylinder portion of the housing with a diameter-expanded surface gradually increased from the other side in the axial direction to one side in the axial direction. It can be formed from the cylindrical outer peripheral surface of the bearing member.

When the groove portion (groove portion forming the second passage) is provided on one end surface of the bearing member made of a porous body, the surface opening ratio of the surface forming the groove portion is set to the groove portion of the one end surface of the bearing member. It can be made larger than the surface opening rate of the region excluding the surface to be formed. When such a configuration is adopted, when the internal temperature of the device rises, such as when the hydrodynamic bearing device is in operation, the lubricating oil impregnated in the bearing member tends to seep into the axial gap through the groove forming surface. For this reason, in particular, if the groove portion is provided with a radial groove or an annular groove in which the inner end portion in the radial direction is connected to the chamfer provided on the inner peripheral edge portion at one end of the bearing member, the groove portion seeps into the axial gap. Lubricating oil can be easily supplied to the radial bearing gap through the annular space formed by the chamfer. In this case, it is advantageous in preventing the oil film from running out in the radial bearing gap.

If the fluid dynamic pressure bearing device having the above configuration is further provided with a dynamic pressure generating portion (radial dynamic pressure generating portion) that generates a dynamic pressure action on the lubricating oil interposed in the radial bearing gap, the shaft can be moved in the radial direction. The supporting radial bearing portion can be composed of a dynamic pressure bearing having excellent bearing performance. At this time, if the dynamic pressure generating portion is formed in a shape that pushes the lubricating oil that is interposed in the radial bearing gap into the bottom side (the other side in the axial direction) of the housing, the lubricating oil that is interposed in the axial clearance is radial. Since it is easily pulled into the bearing gap, it is more advantageous in preventing the oil film from running out in the radial bearing gap.

If an oil-repellent film is formed on at least one of the two facing surfaces forming the seal gap, the risk of oil leakage through the seal gap can be further reduced.

If the bearing member is sandwiched between the lid member constituting the bottom of the housing and the annular portion from both sides in the axial direction, the bearing member can be easily and accurately positioned and fixed to the housing.

Since the hydrodynamic bearing device according to the present invention has the above-mentioned characteristics, it can be used as a motor for various electric devices such as a spindle motor for a disk drive device, a fan motor for a PC, and a polygon scanner motor for an LBP. It can be incorporated and used suitably.

From the above, according to the present invention, it is possible to provide a fluid dynamic bearing device capable of stably exhibiting desired bearing performance over a long period of time with a low risk of oil leakage.

It is sectional drawing which shows one structural example of a fan motor conceptually. It is a vertical sectional view of the fluid dynamic pressure bearing device which concerns on one Embodiment of this invention. It is a vertical sectional view of a bearing member. It is a top view which shows the upper end surface of a bearing member. It is a partially enlarged view of FIG. It is a partially enlarged sectional view of the fluid dynamic bearing apparatus which concerns on other embodiment. It is a partially enlarged sectional view of the fluid dynamic bearing apparatus which concerns on other embodiment. It is a top view of the upper end surface of the bearing member which concerns on other embodiment. (A) is a plan view of an upper end surface of a bearing member according to another embodiment, and (b) is a partial enlargement of a fluid dynamic pressure bearing device when the bearing member shown in (a) is adopted. It is a sectional view.

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

FIG. 1 conceptually shows an example of a configuration of a fan motor incorporating the fluid dynamic pressure bearing device 1 according to the embodiment of the present invention. The fan motor shown in the figure is a rotating member having a hydrodynamic bearing device 1, a motor base 6 constituting the stationary side of the motor, a stator coil 5 attached to the motor base 6, and blades (not shown). The rotor 3 is provided with a rotor magnet 4 attached to the rotor 3 and facing the stator coil 5 via a radial gap. The housing 7 of the fluid dynamic bearing device 1 is fixed to the inner circumference of the motor base 6, and the rotor 3 is fixed to one end of the shaft member 2 of the fluid dynamic bearing device 1. In the fan motor configured in this way, when the stator coil 5 is energized, the rotor magnet 4 is rotated by the electromagnetic force between the stator coil 5 and the rotor magnet 4, and the shaft member 2 and the shaft member 2 are accompanied by this rotation. The rotor 3 fixed to the rotor 3 rotates integrally.

When the rotor 3 rotates, wind is sent upward or downward in the figure depending on the form of the blades provided on the rotor 3. Therefore, during the rotation of the rotor 3, a downward or upward thrust in the figure acts on the shaft member 2 of the fluid dynamic pressure bearing device 1 as a reaction force of this blowing action. A magnetic force (repulsive force) in a direction that cancels this thrust is applied between the stator coil 5 and the rotor magnet 4, and the thrust load generated by the difference in magnitude between the thrust and the magnetic force is applied to the fluid dynamic bearing device 1. It is supported by the thrust bearing portion T of. The magnetic force in the direction of canceling the thrust can be generated, for example, by arranging the stator coil 5 and the rotor magnet 4 so as to be displaced in the axial direction (detailed illustration is omitted). Further, when the rotor 3 is rotated, a radial load acts on the shaft member 2 of the fluid dynamic bearing device 1. This radial load is supported by the radial bearing portions R1 and R2 of the fluid dynamic bearing device 1.

FIG. 2 shows a vertical cross-sectional view of the hydrodynamic bearing device 1 according to the embodiment of the present invention. The fluid dynamic bearing device 1 includes a bottomed tubular housing 7 in which one end in the axial direction is opened and the other end in the axial direction is closed, a bearing member 8 housed in the housing 7, and a bearing member 8. A shaft member 2 inserted into the inner circumference and a sealing member 9 for sealing an opening at one end of the housing 7 are provided. Hereinafter, for convenience of explanation, the side on which the seal member 9 is arranged (the opening side of the housing 7) is set as the upper side, and the side opposite to the axial direction thereof is set as the lower side, but the posture of the fluid dynamic bearing device 1 during operation is limited. I don't do it.

The housing 7 includes a cylindrical member 71a having a cylindrical tubular portion 71a and an annular portion 71b integrally protruding inward in the radial direction from the upper end portion of the tubular portion 71a, and a lid member 72 for closing the lower end opening of the tubular portion 71a. It is formed into a bottomed cylinder shape by connecting and integrating with and by appropriate means such as adhesion and press fitting. The lid member 72 has a bottomed tubular shape integrally having a short cylindrical portion 72a and a disc-shaped bottom portion 72b that closes the lower end opening of the short cylindrical portion 72a. In the present embodiment, the thrust plate 10 made of a resin material is arranged on the upper side of the bottom 72b of the lid member 72 made of a non-porous metal material, and the inner bottom surface of the housing 7 is arranged on the upper end surface 10a of the thrust plate 10. Consists of. The thrust plate 10 does not necessarily have to be provided and may be omitted.

Lubricating oil 11 (indicated by dense scattered point hatching in FIG. 2) is interposed in the internal space of the housing 7, and the amount thereof is measured in the radial direction of the shaft member 2 during the operation of the hydrodynamic bearing device 1. A sealed space 12 (shaft member 2) in which the radial bearing gap Gr (see FIG. 5) in which the radial bearing portions R1 and R2 that support non-contact are formed and the thrust bearing portion T that supports the shaft member 2 in one direction of the thrust are formed. , The space defined by the bottom of the bearing member 8 and the housing 7) is adjusted to the extent that it can be satisfied. That is, the lubricating oil 11 does not fill the entire internal space of the housing 7, and for example, the lubricating oil 11 may or may not intervene in the axial gap 22 described later.

The shaft member 2 is made of a highly rigid metal material such as stainless steel, and its outer peripheral surface 2a is formed on a smooth cylindrical surface without unevenness, and its lower end surface 2b is formed on a convex spherical surface. A rotor 3 having blades (see FIG. 1) is fixed to the upper end of the shaft member 2.

The bearing member 8 is formed in a cylindrical shape with a porous body, here, a porous body of a sintered metal containing copper and iron as main components, and the internal pores thereof are impregnated with the lubricating oil 11. The bearing member 8 can also be formed of a porous body other than the sintered metal, for example, a porous resin.

On the inner peripheral surface 8a of the bearing member 8, two cylindrical radial bearing surfaces forming a radial bearing gap Gr of the radial bearing portions R1 and R2 with the outer peripheral surface 2a of the opposing shaft member 2 are provided at two locations in the axial direction. It is provided apart from each other. As shown in FIG. 3, dynamic pressure generating portions (radial dynamic pressure generating portions) A1 and A2 for generating a dynamic pressure action on the lubricating oil 11 interposed in the radial bearing gap Gr are formed on each radial bearing surface, respectively. Will be done. The radial dynamic pressure generating portions A1 and A2 of the present embodiment are inclined in opposite directions to each other and are provided apart from each other in the axial direction, and both the upper dynamic pressure groove Aa1 and the lower dynamic pressure groove Aa2. It has a convex hill portion that divides the dynamic pressure grooves Aa1 and Aa2, and the hill portion exhibits a herringbone shape as a whole. That is, the hill portion is provided between the inclined hill portion Ab provided between the adjacent dynamic pressure grooves in the circumferential direction and the upper and lower dynamic pressure grooves Aa1 and Aa2, and the annular hill portion having substantially the same diameter as the inclined hill portion Ab. It consists of Ac.

In the upper dynamic pressure generating portion A1, the axial dimension X ₁ of the upper dynamic pressure groove Aa1 is set to be larger than _{the axial dimension X 2} of the lower dynamic pressure groove Aa2 _{(X 1} > X ₂ ), and the lower side. In the radial dynamic pressure generating portion A2 of the above, the axial dimensions of the upper dynamic pressure groove Aa1 and the lower dynamic pressure groove Aa2 are the axial dimensions X _{2 of the lower dynamic pressure groove Aa2 of the upper radial dynamic pressure generating portion A1.} It is set to be the same. Therefore, when the shaft member 2 is rotated, the lubricating oil 11 interposed in the radial gap (radial bearing gap Gr) between the outer peripheral surface 2a of the shaft member 2 and the inner peripheral surface 8a of the bearing member 8 is on the lower side (housing 7). It is pushed into the bottom 72b side).

The form of the radial dynamic pressure generating portions A1 and A2 is not limited to the above. For example, one or both of the radial dynamic pressure generating portions A1 and A2 may have a plurality of spiral-shaped dynamic pressure grooves arranged in the circumferential direction. Further, either one or both of the radial dynamic pressure generating portions A1 and A2 may be formed on the outer peripheral surface 2a of the opposing shaft member 2.

As shown in FIGS. 3 and 4, an annular groove 8c1 having a V-shaped cross section is provided at the radial center portion of the upper end surface 8c of the bearing member 8. Further, on the upper end surface 8c of the bearing member 8, the radial inner end portion is opened in the annular groove 8c1, and the radial outer end portion is opened in the chamfer 8e provided on the upper end outer peripheral edge portion of the bearing member 8. The radial grooves 8c2 are provided at a plurality of locations (three locations in the present embodiment) separated in the circumferential direction. Further, on the outer peripheral surface 8d of the bearing member 8, the upper end portion opens in the chamfer 8e, and the axial groove 8d1 having the lower end portion opened in the chamfer provided in the lower end outer peripheral edge portion of the bearing member 8 is separated in the circumferential direction. It is provided at a plurality of locations (three locations in the present embodiment). In the present embodiment, the axial groove 8d1 is arranged between two radial grooves 8c2 adjacent to each other in the circumferential direction.

The bearing member 8 having the above configuration has a housing in which the upper end portion thereof is in contact with the annular portion 71b of the housing 7, that is, the upper end surface 8c is in contact with the lower end surface 71b1 of the annular portion 71b of the housing 7. It is fixed to the inner circumference of 7.

The bearing member 8 can be fixed to the housing 7 by appropriate means such as press-fitting, bonding, and press-fitting (combined use of press-fitting and bonding), but in the present embodiment, the bearing member is formed by the annular portion 71b and the lid member 72. The bearing member 8 is fixed to the inner circumference of the housing 7 by sandwiching the 8 from both sides in the axial direction. Therefore, the lower end surface 8b of the bearing member 8 is in contact with the upper end surface 72a1 of the short cylindrical portion 72a, and the upper end surface 8c of the bearing member 8 is in contact with the lower end surface 71b1 of the annular portion 71b. By doing so, the housing 7 can be formed (the tubular member 71 and the lid member 72 are fixed), and at the same time, the bearing member 8 can be fixed to the housing 7, so that the labor required for assembling the members can be reduced. Can be mitigated. Further, for example, when the bearing member 8 is press-fitted into the inner circumference of the tubular portion 71a of the housing 7 with a large tightening allowance, the deformation of the bearing member 8 due to the press-fitting spreads to the inner peripheral surface 8a of the bearing member 8 and the radial bearing gap is formed. The width accuracy and, by extension, the bearing performance of the radial bearing portions R1 and R2 may be adversely affected. On the other hand, in the above fixing method, such an adverse effect is prevented as much as possible.

A cylinder capable of holding the oil level of the lubricating oil 11 between the outer peripheral portion of the upper end of the bearing member 8 and the cylinder portion 71a of the housing 7 during operation of the hydrodynamic bearing device 1 (when the shaft member 2 is rotating). An oil-retaining space 13 is provided. The oil retention space 13 can be formed by thinning the outer peripheral portion of the upper end of the bearing member 8 or by thinning the inner peripheral portion of the upper end of the tubular portion 71a of the housing 7, but the upper end of the bearing member 8 can be formed. If the outer peripheral portion is lightened, it becomes difficult to properly bring the upper end surface 8c of the bearing member 8 and the annular portion 71b of the housing 7 into contact with each other. Therefore, here, the oil-retaining space 13 is formed by removing the inner peripheral portion of the upper end of the tubular portion 71a of the housing 7.

As shown in FIGS. 2 and 5, the oil holding space 13 of the present embodiment is arranged adjacent to the enlarged diameter portion 13a whose radial dimension gradually expands from the lower side to the upper side and the upper side of the enlarged diameter portion 13a. Although it is provided with a cylindrical portion 13b having a constant diameter, it may be composed of only the enlarged diameter portion 13a. The enlarged diameter portion 13a is formed by providing an enlarged diameter surface (tapered surface) 71a2 gradually increasing in diameter from the lower side to the upper side on the inner peripheral surface 71a1 of the tubular portion 71a of the housing 7, and the cylindrical portion 13b. Is formed by providing a cylindrical large-diameter inner peripheral surface 71a3 on the inner peripheral surface 71a1 of the tubular portion 71a of the housing 7. In the present embodiment, the oil holding space 13 is formed so that the oil level of the lubricating oil 11 during operation of the fluid dynamic bearing device 1 is located within the axial range of the enlarged diameter portion 13a.

The sealing member 9 is formed in an annular shape from a metal material or a resin material, and is fixed to the inner circumference of the annular portion 71b of the housing 7 by an appropriate means. Explaining with reference to FIG. 5, the annular portion 71b of the present embodiment has a small diameter inner peripheral surface 71b2, a large diameter inner peripheral surface 71b3, and a stepped surface 71b4 connecting both inner peripheral surfaces 71b2 and 71b3, and is a sealing member. 9 is fixed to the large-diameter inner peripheral surface 71b3 in a state where the upper end surface 9c is in contact with the stepped surface 71b4. The lower end surface 9b of the seal member 9 forms an axial gap 22 with the upper end surface 8c of the facing bearing member 8, and the inner peripheral surface 9a of the seal member 9 is with the outer peripheral surface 2a of the opposite shaft member 2. A seal gap S is formed between the two. In the present embodiment, the gap width of the axial gap 22 is set to, for example, about 8 mm or less, and the gap width (radius value) of the seal gap S is set to, for example, about 0.3 mm or less.

In the hydrodynamic bearing device 1 having the above configuration, when the shaft member 2 and the bearing member 8 rotate relative to each other (in the present embodiment, the shaft member 2 rotates), the inner peripheral surface 8a of the bearing member 8 is rotated at two locations above and below. A radial bearing gap Gr is formed between the radial bearing surface provided apart from the bearing surface and the outer peripheral surface 2a of the shaft member 2 facing the radial bearing surface. Further, when the shaft member 2 rotates, the lubricating oil 11 impregnated into the internal pores of the bearing member 8 is bearing due to the generation of pressure (negative pressure) accompanying the rotation of the shaft member 2 and the thermal expansion of the lubricating oil 11 due to the temperature rise. It exudes one after another to the outside of the bearing member 8 through the surface opening of the member 8. The lubricating oil 11 (a part of) exuded from the bearing member 8 forms an oil film in the radial bearing gap Gr, and the pressure of this oil film is increased by the dynamic pressure action of the radial dynamic pressure generating portions A1 and A2. As a result, the radial bearing portions R1 and R2 that non-contactly support the shaft member 2 in the radial direction are formed at two positions apart from each other in the axial direction.

At the same time, a thrust bearing portion T that contacts and supports the shaft member 2 in one direction of the thrust is formed on the inner bottom surface of the housing 7 (the upper end surface 10a of the thrust plate 10). As described above, the shaft member 2 is subjected to a magnetic force for pressing the shaft member 2 downward (supporting the shaft member 2 in the thrust and other directions). Therefore, even when the pressure in the closed space 12 in which the thrust bearing portion T is formed increases with the rotation of the shaft member 2, it is possible to prevent the shaft member 2 from overfloating as much as possible. However, it is not always necessary to act the magnetic force as an external force for pressing the shaft member 2 downward, and it may be allowed to act as necessary. That is, when the thrust as a reaction force of the blowing action is sufficiently large and the shaft member 2 can be pressed downward only by this thrust, it is not necessary to apply the magnetic force to the shaft member 2.

The fluid dynamic pressure bearing device 1 described above usually has a procedure of assembling an assembly in which the housing 7, the bearing member 8 and the sealing member 9 are assembled, and then inserting the shaft member 2 into the inner circumference of the bearing member 8. It is assembled by stepping on it. When inserting the shaft member 2, the inner circumference of the bearing member 8 is provided with a predetermined amount of lubricating oil 11 for the purpose of improving the insertability of the shaft member 2 and interposing a predetermined amount of lubricating oil 11 in the closed space 12 in which the thrust bearing portion T is formed. A predetermined amount of lubricating oil 11 is pre-filled. At this time, with the insertion of the shaft member 2, the air interposed between the lower end surface 2b of the shaft member 2 and the lubricating oil 11 filled in the inner circumference of the bearing member 8 is compressed, but the bearing member 8 Since the clearance width of the radial clearance (radial bearing clearance Gr) between the inner peripheral surface 8a and the outer peripheral surface 2a of the shaft member 2 is set to a minute width of about several μm, the above air (compressed air) is used. It is difficult to discharge the material to the outside of the device through the radial gap between the shaft member 2 and the bearing member 8 and the seal gap S. If the compressed air cannot be discharged to the outside of the device due to the insertion of the shaft member 2, it becomes difficult to properly insert the shaft member 2.

The hydrodynamic bearing device 1 of the present embodiment is formed by an outer peripheral surface 8d or the like of the bearing member 8 and opens the closed space 12 to the outside air (communicate between the closed space 12 and the external space of the bearing device 1). Has 20. The ventilation passage 20 has a first passage 21, an oil retention space 13 and a second passage 23 formed between the housing 7 and the bearing member 8, and an axial gap 22 formed between the bearing member 8 and the seal member 9. And the seal gap S. By providing such a ventilation path 20, the compressed air can be appropriately discharged to the outside of the device when the shaft member 2 is inserted.

The first passage 21 is a passage that opens into the closed space 12 and the oil holding space 13 to communicate the two spaces 12 and 13, and is provided on the upper end surface 72a1 of the short cylindrical portion 72a of the lid member 72 in the present embodiment. It is formed by a radial passage formed by the radial groove 72a2, an annular passage formed by chamfering on the outer peripheral edge of the lower end of the bearing member 8, and an axial groove 8d1 provided on the outer peripheral surface 8d of the bearing member 8. It is composed of an axial passage. The radial passage may be any as long as it can communicate the closed space 12 and the annular passage, and may be formed, for example, by providing a radial groove on the lower end surface 8b of the bearing member 8. Further, the axial passage may be formed by providing an axial groove on the inner peripheral surface 71a1 of the tubular portion 71a of the housing 7.

The second passage 23 is a passage that opens into the oil-retaining space 13 and the axial gap 22 to communicate the oil-retaining space 13 and the axial gap 22 in a partial region in the circumferential direction. In the present embodiment, the bearing member It is formed by providing the above-mentioned annular groove 8c1 and radial groove 8c2 on the upper end surface 8c of 8. Therefore, here, the annular groove 8c1 and the radial groove 8c2 form the "groove portion" in the present invention.

As described above, during the operation of the hydrodynamic bearing device 1, the lubricating oil 11 impregnated into the internal pores of the bearing member 8 seeps out to the outside of the bearing member 8, so that the lubricating oil 11 is formed on the inner peripheral surface 8a of the bearing member 8. The amount of oil intervening in the radial gap (radial bearing gap Gr), the closed space 12 formed by the lower end surface 8b of the bearing member 8, and the like increases. Therefore, during the operation of the hydrodynamic bearing device 1, (a part of) the lubricating oil 11 interposed in the internal space of the housing 7 flows through the ventilation passage 20 and is pushed up to the opening side of the housing 7, and the oil holding space 13 is used. Accumulates within the axial range of. At this time, the oil-retaining space 13 formed in the outer peripheral portion of the upper end of the bearing member 8 and the axial gap 22 formed in the upper end surface 8c of the bearing member 8 are all formed as in the conventional hydrodynamic bearing device. If a configuration connected over the circumference is adopted, even if the oil retention space 13 and the axial gap 22 have sufficient volumes, the fluid dynamic bearing device 1 may be used in an inclined posture or may be operated. When an impact load is applied to the fluid dynamic bearing device 1 inside, the lubricating oil accumulated in the oil holding space 13 easily flows into the axial gap 22, and therefore, through the axial gap 22 and the seal gap S. There is a problem that the risk of oil leakage is high.

On the other hand, in the fluid dynamic bearing device 1 according to the present invention, the annular portion 71b that abuts on the upper end surface 8c of the bearing member 8 is provided, and the upper end surface 8c of the bearing member 8 and the lower end surface of the annular portion 71b that abuts on the upper end surface 8c are provided. The oil-retaining space 13 and the axial gap 22 are communicated with each other via a second passage 23 formed by a groove portion provided on at least one of 71b1 (in this embodiment, the annular groove 8c1 and the radial groove 8c2 on the upper end surface 8c). ing. According to such a configuration, the oil holding space 13 and the axial gap 22 communicate with each other in a partial region in the circumferential direction via the second passage 23 described above. In this case, for example, when the lubricating oil 11 exuded from the bearing member 8 is accumulated in the oil holding space 13 during the operation of the fluid dynamic bearing device 1 in an inclined posture, the lubricating oil 11 is accumulated in the oil holding space 13. Even when an impact load is applied to the hydrodynamic bearing device 1 in this state, the amount of inflow of the lubricating oil 11 accumulated in the oil holding space 13 into the axial gap 22 can be significantly reduced as compared with the conventional configuration. Therefore, the risk of oil leakage through the seal gap S can be effectively reduced.

Further, in the present embodiment, the oil holding space 13 is located so that the oil level of the lubricating oil 11 during operation of the hydrodynamic bearing device 1 is located within the axial range of the enlarged diameter portion 13a in the oil holding space 13. Is formed. In this case, since the pulling force to the bottom side of the housing 7 due to the capillary force acts on the lubricating oil 11 interposed in the oil holding space 13, the risk of oil leakage through the seal gap S is further effectively reduced. Can be done.

In addition, in order to enhance the effect of preventing oil leakage through the seal gap S, any of the two facing surfaces (in the present embodiment, the inner peripheral surface 9a of the seal member 9 and the outer peripheral surface 2a of the shaft member 2) forming the seal gap S. It is preferable to form an oil-repellent film on one or both of them. FIG. 6 shows an example thereof, in which an oil-repellent film 30 is formed on both the inner peripheral surface 9a of the seal member 9 and the outer peripheral surface 2a of the shaft member 2.

As described above, the fluid dynamic bearing device 1 according to the embodiment of the present invention, more specifically, the internal space of the housing 7 is partially filled with the lubricating oil 11 (the internal space of the housing 7 is partially filled with the lubricating oil 11 and air). The partial fill type hydrodynamic bearing device 1 has a feature that the risk of oil leakage is low and the desired bearing performance can be stably exhibited for a long period of time.

Although the fluid dynamic pressure bearing device 1 according to the embodiment of the present invention has been described above, various changes can be made to the fluid dynamic pressure bearing device 1 without departing from the gist of the present invention.

For example, the thrust bearing portion T that supports the lower end of the shaft member 2 can be formed of a so-called dynamic pressure bearing. Although detailed illustration is omitted, in this case, the lower end surface 2b of the shaft member 2 is formed on a flat surface in a direction orthogonal to the axis line. At this time, on either the lower end surface 2b of the shaft member 2 or the inner bottom surface of the housing 7 facing the lower end surface 2b, a dynamic pressure generating portion (thrust) composed of a plurality of dynamic pressure grooves and a convex hill portion for partitioning them is provided. Dynamic pressure generating part) is formed.

Further, in the above, the seal gap S is formed between the inner peripheral surface 9a of the seal member 9 fixed to the annular portion 71b of the housing 7 and the outer peripheral surface 2a of the shaft member 2, but as shown in FIG. 7, the seal is formed. The member 9 may be omitted. In this case, a seal gap S can be formed between the inner peripheral surface (small diameter inner peripheral surface) 71b2 of the annular portion 71b and the outer peripheral surface 2a of the shaft member 2. Further, in this case, the axial gap 22 is formed between the upper end surface 8c of the bearing member 8 and the lower end surface of the annular portion 71b facing the upper end surface 8c. Although not shown, it is preferable to form the oil repellent film 30 (see FIG. 6) on at least one of the two facing surfaces forming the seal gap S even when such a configuration is adopted.

Further, in the above, as shown in FIGS. 3 and 4, the second passage 23 for communicating the oil retention space 13 and the axial gap 22 is provided on the upper end surface 8c of the bearing member 8 with an annular groove 8c1 and a radial groove 8c2. However, the second passage 23 can be formed, for example, by providing only the radial groove 8c2 on the upper end surface 8c of the bearing member 8. An example thereof is shown in FIG. 8, and in the embodiment shown in the figure, the radial outer end portion is opened to the chamfer 8e provided on the upper end outer peripheral edge portion of the bearing member 8 and the radial inner end portion is provided. A radial groove 8c2 is provided so as to open in the chamfer 8f provided on the inner peripheral edge portion of the upper end of the bearing member 8.

Further, the second passage 23 can also be formed by providing the annular groove 8c1 and the radial groove 8c2 on the upper end surface 8c of the bearing member 8 in the embodiment shown in FIGS. 9A and 9B. That is, in this embodiment, at the point where the radially inner end of the annular groove 8c1 is connected to the chamfer 8f provided on the inner peripheral edge of the upper end of the bearing member 8 (the point where the groove width of the annular groove 8c1 is expanded). The configuration is different from the embodiment shown in FIGS. 2 to 6.

According to such a configuration, the gap width of the axial gap 22 formed by the upper end surface 8c of the bearing member 8 can be expanded as compared with the embodiment shown in FIG. The amount of oil can be increased. Therefore, even when the lubricating oil 11 flows into the axial gap 22, it is advantageous in preventing oil leakage through the seal gap S. Further, since the radially inner end of the annular groove 8c1 is connected to the chamfer 8f provided on the inner peripheral edge of the upper end of the bearing member 8, when the lubricating oil 11 intervenes in the annular groove 8c1, the lubricating oil 11 is used. It becomes easy to supply to the radial gap (radial bearing gap Gr) between the inner peripheral surface 8a of the bearing member 8 and the outer peripheral surface 2a of the shaft member 2. In particular, as shown in FIG. 3, when the radial dynamic pressure generating portion A1 having a shape of pushing the lubricating oil 11 interposed in the radial bearing gap Gr toward the bottom side of the housing 7 is provided, the radial bearing of the radial bearing portion R1 is provided. The lubricating oil 11 interposed above the gap Gr can be easily drawn into the radial bearing gap Gr of the radial bearing portion R1. Therefore, it is advantageous in preventing oil leakage through the seal gap S and in preventing the oil film from running out in the radial bearing gap Gr.

Further, although not particularly mentioned above, the surface opening ratio of the surface (groove forming surface) forming the annular groove 8c1 and / or the radial groove 8c2 provided on the upper end surface 8c of the sintered metal bearing member 8. Can be made larger than the surface opening rate of the region of the upper end surface 8c of the bearing member 8 excluding the groove forming surface. By doing so, when the fluid dynamic bearing device 1 is in operation or the like, the lubricating oil 11 impregnated into the internal pores of the bearing member 8 tends to seep into the annular groove 8c1 and / or the radial groove 8c2. Therefore, when the radial groove 8c2 is provided in the embodiment shown in FIG. 8 or when the annular groove 8c1 and the radial groove 8c2 are provided in the embodiment shown in FIG. 9A, the grooves 8c1 and 8c2 are exuded. It becomes easy to supply the lubricating oil 11 to the radial bearing gap Gr of the radial bearing portion R1. Therefore, it is advantageous in preventing deterioration of the bearing performance of the radial bearing portions R1 and R2 due to the oil film running out of the radial bearing gap Gr.

As described above, as a means for making the surface opening rate of the groove forming surface different from the surface opening rate of the region other than the groove forming surface, for example, the bearing member 8 can be manufactured by the following procedure. Conceivable. First, the green compact of the raw material powder containing the metal powder as the main component is compression-molded, and at the same time, the grooves 8c1 and 8c2 are molded on one end surface of the green compact, and then the green compact is heated and sintered. To obtain a sintered body. After that, the sintered body is put into a sizing mold and compressed in the axial direction to finish the sintered body into a finished product shape (radial dynamic pressure generating portions A1 and A2 are molded on the inner peripheral surface of the sintered body. At the same time, the dimensional accuracy of the sintered body is corrected), the surface on which the grooves 8c1 and 8c2 are formed is pressed by the pressure surface of the punch formed on the flat surface. In short, the formed surface of the grooves 8c1 and 8c2 is a non-molded surface that is not molded by the sizing mold, while the region other than the groove forming surface is a molded surface by the sizing mold. By doing so, while carrying out the minimum steps necessary for manufacturing the bearing member 8 made of sintered metal having the radial dynamic pressure generating portions A1 and A2, the surface opening rate of the groove forming surface and the surface opening rate are determined. It is possible to provide a difference from the surface opening rate of the region other than the groove forming surface.

When the surface opening ratio is different in the upper end surface 8c of the bearing member 8 as described above, if the groove depths of the grooves 8c1 and 8c2 are too shallow, the sintered body is axially moved by the sizing mold. The grooves 8c1 and 8c2 may disappear as the compression is performed. Therefore, it is preferable that the groove depths of the grooves 8c1 and 8c2 to be molded into the green compact are 0.05 mm or more. Further, if the occupied area of the grooves 8c1 and 8c2 on the upper end surface 8c of the bearing member 8 is too large, the sintered body cannot be appropriately compressed in the axial direction when the sintered body is compressed in the axial direction. The molding accuracy of the radial dynamic pressure generating portions A1 and A2 and the shape accuracy of the bearing member 8 may be adversely affected. Therefore, the area ratio of the grooves 8c1 and 8c2 to the upper end surface 8c of the bearing member 8 is preferably 50% or less.

The technical means for making a difference between the surface opening rate of the groove-forming surface and the surface opening rate of the region other than the groove-forming surface is not limited to the above, and for example, the sealing treatment is performed in the region other than the groove-forming surface. It is also possible to apply. However, in this case, a separate process for performing the hole sealing treatment is required, which increases the manufacturing cost of the bearing member 8. Therefore, as described above, while performing the minimum necessary steps (compression molding step, sintering step, and sizing step) for obtaining the bearing member 8 made of sintered metal, the inside of the upper end surface 8c of the bearing member 8 It is preferable to provide a difference in the surface opening rate.

Further, in the above, the second passage 23 is formed by providing the radial groove 8c2 and the annular groove 8c1 on the upper end surface 8c of the bearing member 8, but the second passage 23 is provided on the upper end surface 8c of the bearing member 8. It can be formed by replacing the radial groove 8c2 or the annular groove 8c1 or by providing a radial groove or the like in the annular portion 71b1 of the housing 7 that abuts on the upper end surface 8c of the bearing member 8.

Further, in the above, the case where the present invention is applied to the fluid dynamic pressure bearing device 1 in which the annular portion 71b in contact with the upper end surface 8c of the bearing member 8 is provided integrally with the tubular portion 71a of the housing 7 has been described. The present invention can also be applied when the annular portion 71b is provided separately from the tubular portion 71a of the housing 7. In this case, although not shown, for example, after arranging the bearing member 8 on the inner circumference of the bottomed tubular housing having the portion corresponding to the tubular portion 71a and the lid member 72, the bearing member 8 is arranged. At the upper end, the outer diameter side region of the lower end surface abuts on the upper end surface 8c of the bearing member 8 to form a second passage 23 with the bearing member 8, and the inner diameter side region of the lower end surface is the bearing member 8. If an annular member (for example, a seal member 9) that forms an axial gap 22 is fixed to the upper end surface 8c, the fluid dynamic bearing device 1 that can exert the same operation and effect as that of the embodiment described above can be obtained. can get.

Further, either one or both of the radial bearing portions R1 and R2 may be composed of other known dynamic pressure bearings such as so-called multi-arc bearings, step bearings, and corrugated bearings, and the dynamic pressure generating portion may be formed. It can also be configured with a so-called perfect circular bearing that does not exist. Further, the radial bearing portions may be provided at two locations separated in the axial direction as described above, or may be provided at one location in the axial direction or at three or more locations separated from each other in the axial direction.

Further, in the above, the case where the present invention is applied to the fluid dynamic pressure bearing device 1 in which the rotor 3 having blades is fixed to the shaft member 2 as the rotating member has been described, but the present invention has been described as the rotating member. It can also be preferably applied to a disc hub having a disc mounting surface or a fluid dynamic bearing device 1 in which a polygon mirror is fixed to a shaft member 2. That is, the present invention is not only a fan motor as shown in FIG. 1, but also a fluid motion incorporated in a spindle motor for a disk device, a polygon scanner motor for a laser beam printer (LBP), and other motors for electric devices. It can also be preferably applied to the pressure bearing device 1.

1 Fluid dynamic bearing device 2 Shaft member 7 Housing 8 Bearing member 8c Upper end surface (one end surface)
8c1 annular groove 8c2 radial groove 8e, 8f chamfer 9 Seal member 10 Thrust plate 11 Lubricating oil 12 Sealed space 13 Oil retention space 13a Expansion part 20 Ventilation passage 21 First passage 22 Axial gap 23 Second passage 30 Oil repellent film 71 Cylindrical member 71a Cylindrical portion 71b Circular portion 72 Lid member A1, A2 Radial dynamic pressure generating portion Gr Radial bearing gap R1, R2 Radial bearing portion T Thrust bearing portion

Claims (8)

A bearing member made of a porous body impregnated with lubricating oil and forming a radial bearing gap with the outer peripheral surface of the shaft to be supported, and a bottomed cylinder with one end in the axial direction open and the other end closed. A housing that has a shape and houses the bearing member, a seal gap that seals the opening of the housing, a ventilation path that opens the sealing space defined by the shaft, the bearing member, and the bottom of the housing to the outside air, and the bearing member. A first, which is provided between the outer peripheral portion of one end and the tubular portion of the housing, has a tubular oil-retaining space capable of holding the oil level of the lubricating oil, and has a ventilation path opened in the closed space and the oil-retaining space. In a hydrodynamic bearing device formed by a passage and one end surface of a bearing member and including an axial gap in which a radial inner end is connected to a seal gap.
An annular portion abutting on one end surface of the bearing member is provided, and an oil retention space and an axial gap are formed by a groove provided on at least one of one end surface of the bearing member and the other end surface of the annular portion abutting on the one end surface. It communicates through the second passage ,
The oil holding space has a diameter-expanded portion whose radial dimension gradually expands from the other side in the axial direction to one side in the axial direction, and the oil level of the lubricating oil during operation of the hydrodynamic bearing device expands in diameter. fluid dynamic bearing device according to claim Rukoto held in the axial extent of the parts. The inner peripheral surface of the tubular portion of the housing is provided with a diameter-expanded surface that gradually increases in diameter from the other side in the axial direction to one side in the axial direction. The fluid dynamic bearing device according to claim 1 , wherein the portion is formed. The groove is provided on one end surface of the bearing member, and the surface opening rate of the surface forming the groove is higher than the surface opening rate of the region of one end surface of the bearing member excluding the surface forming the groove. The hydrodynamic bearing device according to claim 1 or 2. The fluid dynamic pressure bearing device according to claim 3 , wherein the groove portion has a radial groove or an annular groove whose inner end portion is connected to a chamfer provided on the inner peripheral edge portion of one end of the bearing member. A claim having a dynamic pressure generating portion that causes a dynamic pressure action on the lubricating oil interposed in the radial bearing gap, and the dynamic pressure generating portion having a shape of pushing the lubricating oil interposed in the radial bearing gap toward the bottom side of the housing. Item 5. The hydrodynamic bearing device according to any one of Items 1 to 4. The fluid dynamic bearing device according to any one of claims 1 to 5, wherein an oil-repellent film is formed on at least one of two facing surfaces forming a seal gap. The fluid dynamic pressure bearing device according to any one of claims 1 to 6 , wherein the bearing member is sandwiched between the lid member constituting the bottom portion of the housing and the annular portion from both sides in the axial direction. A motor provided with the hydrodynamic bearing device according to any one of claims 1 to 7.

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