JP2020165533A - Fluid dynamic pressure bearing device - Google Patents

Abstract

To enable a shaft member to rotate in both normal or reverse directions to increase the area of a bearing, to obtain a sufficient dynamic pressure effect even in a case where a rotation speed is low.SOLUTION: A fluid dynamic pressure bearing device comprises: a shaft member; a bearing sleeve 18 with a shaft member inserted in its inner periphery; and a dynamic pressure groove 26 that supports the shaft member in a relative rotatable and non-contact manner by the pressure of an oil film generated in a radial bearing gap between the outer peripheral surface of the shaft member and an inner peripheral surface 24 of the bearing sleeve 18. The dynamic pressure groove 26 is composed of a large number of polygonal hill parts 27 patterned on the inner peripheral surface 24 of the bearing sleeve 18, and a polygonal groove part 28 formed so as to surround the polygonal hill parts 27.SELECTED DRAWING: Figure 3

Description

The present invention relates to a fluid dynamic bearing device.

The fluid dynamic bearing device supports the shaft member in a relative rotatably non-contact manner by the pressure generated in the fluid film (for example, an oil film) in the radial bearing gap between the outer peripheral surface of the shaft member and the inner peripheral surface of the bearing sleeve. Is what you do.

Due to its high rotational accuracy and quietness, hydrodynamic bearing devices include, for example, spindle motors for magnetic disk drive devices such as HDDs, polygon scanner motors for laser beam printers (LBPs), color wheel motors for projectors, and fan motors for electrical equipment. It is used by being incorporated in such as.

For example, in the hydraulic dynamic bearing device disclosed in Patent Document 1, the shaft member, the bearing sleeve in which the shaft member is inserted in the inner circumference, and the radial between the outer peripheral surface of the shaft member and the inner peripheral surface of the bearing sleeve. It is provided with a radial dynamic pressure generating portion that supports the shaft member relatively and non-contactly by the pressure of the oil film generated in the bearing gap.

FIG. 16 shows a bearing sleeve 1 constituting the fluid dynamic bearing device of Patent Document 1. As shown in FIG. 16, radial bearing surfaces 3 are formed on the inner peripheral surface 2 of the bearing sleeve 1 at two locations separated in the axial direction. A radial dynamic pressure generating portion is formed on the radial bearing surface 3. The white arrows in the figure indicate the flow of lubricating oil.

In the bearing sleeve 1 of Patent Document 1, a herringbone-shaped dynamic pressure groove 4 is formed as a radial dynamic pressure generating portion. The dynamic pressure groove 4 is composed of a hill portion 5 (a region indicated by a scattering point in the figure) and a groove portion 6 located between the hill portions 5. That is, the hill portion 5 has a structure that rises inward in the radial direction from the groove portion 6.

Japanese Unexamined Patent Publication No. 2011-196544

By the way, in the fluid dynamic bearing device described in Patent Document 1, the rotation direction of the shaft member (see the solid line arrow in FIG. 16) is limited to one direction. Therefore, when the bearing sleeve 1 is installed, the bearing sleeve 1 must be installed in a direction that matches the rotation direction of the shaft member, which complicates the assembly work and reduces workability.

Further, since the dynamic pressure groove 4 formed on the inner peripheral surface 2 of the bearing sleeve 1 has a herringbone shape, the bearing area (hill portion 5 of the dynamic pressure groove 4) is small. Therefore, the surface pressure applied to the radial bearing surface 3 of the bearing sleeve 1 increases, and the wear resistance decreases.

Further, in a region where the rotation speed of the shaft member is low, it becomes difficult to obtain a sufficient dynamic pressure effect, it becomes difficult to support the shaft member in a non-contact manner, and the shaft member is a radial bearing surface 3 of the bearing sleeve 1. May come into contact with.

Therefore, the present invention has been proposed in view of the above-mentioned problems, and an object of the present invention is that the rotation direction of the shaft member can correspond to both forward and reverse directions, the bearing area is increased, and the rotation speed is increased. An object of the present invention is to provide a fluid dynamic pressure bearing device capable of obtaining a sufficient dynamic pressure effect even in a low region.

The fluid dynamic bearing device according to the present invention is a fluid generated in a radial bearing gap between a shaft member, a bearing member having a shaft member inserted in the inner circumference, and an outer peripheral surface of the shaft member and an inner peripheral surface of the bearing member. It is provided with a radial dynamic pressure generating portion that supports the shaft member relatively and non-contactly by the pressure of the film.

As a technical means for achieving the above-mentioned object, the radial dynamic pressure generating portion in the present invention is a large number of polygonal hills arranged in a pattern on either the inner peripheral surface of the bearing member or the outer peripheral surface of the shaft member. It is characterized in that it is composed of a polygonal groove portion formed so as to surround the polygonal hill portion.

In the present invention, by forming a dynamic pressure groove composed of a polygonal hill portion and a polygonal groove portion as the radial dynamic pressure generating portion, it is possible to deal with any direction of rotation of the shaft member in the forward and reverse directions. .. Further, the bearing area of the bearing member (polygonal hill portion of the dynamic pressure groove) can be increased. Further, a sufficient dynamic pressure effect can be obtained even in a region where the rotation speed of the shaft member is low.

The radial dynamic pressure generating portion in the present invention preferably has a structure in which the surface opening ratio in the polygonal groove portion is larger than the surface opening ratio in the polygonal hill portion.

Adopting such a structure is effective in that lubricating oil can be efficiently supplied to the radial bearing surface of the bearing member.

The radial dynamic pressure generating portion in the present invention preferably has a structure in which a groove portion for supplying lubricating oil is formed in the center of the polygonal hill portion.

If such a structure is adopted, the lubricating oil is satisfactorily supplied to the radial bearing surface of the bearing member, which is effective in that the lubrication efficiency can be improved.

The radial dynamic pressure generating portion in the present invention preferably has a structure in which a hill portion that prevents the outflow of lubricating oil from the polygonal groove portion is formed.

If such a structure is adopted, it is possible to prevent the lubricating oil from flowing out from the polygonal groove portion, which is effective in that the lubrication efficiency can be improved.

It is desirable that the radial dynamic pressure generating portion in the present invention has a connecting groove portion for connecting adjacent polygonal groove portions, and the cross-sectional area of the connecting groove portion is larger than the cross-sectional area of the polygonal groove portion.

If such a structure is adopted, the amount of lubricating oil flowing through the connecting groove portion becomes larger than the amount of lubricating oil flowing through the polygonal groove portion, and the lubricating oil can be continuously supplied to the radial bearing gap.

The connecting groove portion in the present invention is composed of a first connecting groove portion that connects the polygonal groove portions that are vertically located in the axial direction and a second connecting groove portion that connects the polygonal groove portions in the circumferential direction. It is desirable to have a structure in which the cross-sectional area of is larger than the cross-sectional area of the second connecting groove.

If such a structure is adopted, even if the position of the center of gravity of the rotating shaft member deviates from the design point, the dynamic pressure for supporting the shaft member is constant within the smoothed range, and has robustness (robustness). be able to.

According to the present invention, by forming a dynamic pressure groove composed of a polygonal hill portion and a polygonal groove portion as a radial dynamic pressure generating portion, the shaft member can be rotated in either the forward or reverse direction. Can be done. Therefore, the work of assembling the bearing member is simplified and the workability can be improved.

Further, the bearing area of the bearing member (polygonal hill portion of the dynamic pressure groove) can be increased. Therefore, the surface pressure applied to the radial bearing surface of the bearing member is reduced, and the wear resistance can be improved.

Further, a sufficient dynamic pressure effect can be obtained even in a region where the rotation speed of the shaft member is low. Therefore, since the shaft member can be reliably supported without contact, it is possible to prevent the shaft member from coming into contact with the radial bearing surface of the bearing member.

It is sectional drawing which shows the schematic structure of the fan motor. It is sectional drawing which shows the fluid dynamic pressure bearing device incorporated in a fan motor. It is sectional drawing which shows an example of the bearing sleeve of a fluid dynamic pressure bearing apparatus. In the bearing sleeve of FIG. 3, (A) is a cross-sectional view showing the flow of lubricating oil during forward rotation, and (B) is a cross-sectional view showing the flow of lubricating oil during reverse rotation. It is sectional drawing which shows another example of a bearing sleeve. It is sectional drawing which shows another example of a bearing sleeve. It is sectional drawing which shows another example of a bearing sleeve. It is sectional drawing which shows another example of a bearing sleeve. It is a table for demonstrating the cross-sectional area of a connecting groove part. It is a table for explaining the surface area of the hill part of a dynamic pressure groove. It is sectional drawing which shows an example of the shaft member. It is sectional drawing which shows the other example of the shaft member. It is sectional drawing which shows the other example of the shaft member. It is sectional drawing which shows the other example of the shaft member. It is sectional drawing which shows the other example of the shaft member. It is sectional drawing which shows the bearing sleeve of the conventional fluid dynamic pressure bearing apparatus.

An embodiment of the hydrodynamic bearing device according to the present invention will be described in detail below with reference to the drawings. Before explaining the fluid dynamic bearing device, a fan motor in which the fluid dynamic bearing device is incorporated will be described.

FIG. 1 shows a schematic configuration of a cooling fan motor incorporated in an information device, for example, a mobile device such as a mobile phone or a tablet terminal.

As shown in FIG. 1, the main parts of the fan motor are the fluid dynamic bearing device 11 of the embodiment, the motor base 13 to which the housing 12 of the fluid dynamic bearing device 11 is fixed, and the fluid dynamic bearing device 11. A rotor 15 to which the shaft member 14 of the above is fixed is provided.

A stator coil 16 is attached to the motor base 13. Further, a rotor magnet 17 is attached to the rotor 15 so as to face the stator coil 16 via a radial gap.

When the stator coil 16 is energized, the rotor 15 and the shaft member 14 rotate integrally by the electromagnetic force generated between the stator coil 16 and the rotor magnet 17, and the blades (not shown) provided on the rotor 15 rotate in the axial direction or. A radial airflow is generated.

Next, the fluid dynamic bearing device 11 incorporated in the above-mentioned fan motor, that is, the fluid dynamic bearing device 11 of the embodiment will be described in detail below.

As shown in FIG. 2, the fluid dynamic bearing device 11 of the embodiment includes a shaft member 14, a bearing sleeve 18 which is a bearing member, a bottomed tubular housing 12, and a seal member 19. .. The internal space of the housing 12 is filled with a predetermined amount of lubricating oil (not shown).

A rotor 15 is attached to the shaft member 14 (see FIG. 1). A shaft member 14 is inserted into the inner circumference of the bearing sleeve 18. The housing 12 has an opening at the axial end and holds the bearing sleeve 18 on the inner circumference. The sealing member 19 is attached to the axial end of the housing 12 to close the opening of the housing 12.

The shaft member 14 is made of metal such as stainless steel and has a columnar shape. The outer diameter of the shaft member 14 is set smaller than the inner diameter of the bearing sleeve 18 and the seal member 19. A convex portion 20 is provided at the lower end of the shaft member 14. A rotor 15 is fixed to the upper end of the shaft member 14 (see FIG. 1).

The housing 12 is a metal or resin member in which a cylindrical side portion 21 and a bottom portion 22 are integrally formed. A resin receiving member 23 is arranged on the bottom 22 of the housing 12. The upper surface of the receiving member 23 functions as a thrust bearing surface that contacts and supports the convex portion 20 of the shaft member 14. The receiving member 23 may be omitted. In that case, the bottom surface of the housing 12 functions as a thrust bearing surface.

The bearing sleeve 18 has a cylindrical shape and is fixed to the inner peripheral surface of the side portion 21 of the housing 12 by an appropriate means such as press fitting. The bearing sleeve 18 is, for example, a porous body made of a copper-iron-based sintered metal containing copper and iron as main components. The internal pores of the bearing sleeve 18 are impregnated with lubricating oil. The material of the bearing sleeve 18 may be a porous body made of a soft metal such as brass or a resin, in addition to the sintered metal.

A radial dynamic pressure generating portion is formed on the inner peripheral surface 24 of the bearing sleeve 18 which is the radial bearing surface. The radial dynamic pressure generating portion makes the shaft member 14 relatively rotatable by the pressure of the fluid film (oil film) generated in the radial bearing gap between the outer peripheral surface 25 of the shaft member 14 and the inner peripheral surface 24 of the bearing sleeve 18. Support by contact.

In this embodiment, as shown in FIG. 3, a polygonal, for example, octagonal dynamic pressure groove 26 is formed as the radial dynamic pressure generating portion. Here, the octagonal dynamic pressure groove 26 is illustrated, but a polygonal dynamic pressure groove other than the octagon may be used.

The dynamic pressure groove 26 is composed of a large number of octagonal hills 27 arranged in a pattern on the inner peripheral surface 24 of the bearing sleeve 18 and an octagonal groove 28 formed so as to surround the octagonal hills 27. ing. The octagonal hill portion 27 has a structure that rises inward in the radial direction from the octagonal groove portion 28 (the region indicated by the scattered points in the figure).

The number and size of the octagonal hills 27 and the octagonal grooves 28 shown in FIG. 3 is an example, and the radial bearing gap between the outer peripheral surface 25 of the shaft member 14 and the inner peripheral surface 24 of the bearing sleeve 18. It may be set appropriately for forming an oil film on the bearing.

The dynamic pressure groove 26 has a shape symmetrical with respect to the axial center of the bearing sleeve 18. By arranging a large number of octagonal hills 27 and octagonal grooves 28 on the inner peripheral surface 24 of the bearing sleeve 18 in a pattern, a part of the octagonal groove 28 has a groove inclined with respect to the rotation direction of the shaft member 14. It will be arranged symmetrically with respect to the center of the axis.

The sealing member 19 is an annular member made of a soft metal such as brass or another metal or resin. The sealing member 19 is fixed to the upper end portion of the housing 12 in a state of being separated from the upper end surface of the bearing sleeve 18 (see FIG. 2).

As shown in FIG. 2, the inner peripheral surface 29 of the seal member 19 forms a non-contact seal (labyrinth seal) in the vicinity of the outer peripheral surface 25 of the shaft member 14. The shape and configuration of the seal member 19 may be other than the structure shown in FIG. 2, and may be arbitrary.

In the fluid dynamic bearing device 11 described above, when the shaft member 14 rotates, a radial bearing gap is formed between the inner peripheral surface 24 of the bearing sleeve 18 and the outer peripheral surface 25 of the shaft member 14. The dynamic pressure groove 26 of the bearing sleeve 18 causes a dynamic pressure action on the lubricating oil in the radial bearing gap.

When the shaft member 14 rotates at high speed, an oil film whose pressure is increased by the dynamic pressure action of the dynamic pressure groove 26 is formed in the radial bearing gap between the inner peripheral surface 24 of the bearing sleeve 18 and the outer peripheral surface 25 of the shaft member 14. Will be done. The oil film forms a radial bearing portion that non-contactly supports the shaft member 14. The thrust load applied to the shaft member 14 is contact-supported on the upper surface of the receiving member 23 which is the thrust bearing portion.

That is, the lubricating oil in the radial bearing gap is collected on the octagonal hill portion 27 side along the octagonal groove portion 28 of the dynamic pressure groove 26, and the pressure is applied between the octagonal hill portion 27 and the outer peripheral surface 25 of the shaft member 14. It becomes the maximum. As a result, a radial bearing portion that non-contactly supports the shaft member 14 is configured. The protrusion 20 of the shaft member 14 and the receiving member 23 slide to form a thrust bearing portion that contacts and supports the shaft member 14.

Here, the fluid dynamic pressure bearing device 11 is roughly classified into a dynamic pressure bearing and a perfect circular bearing. The dynamic pressure bearing is provided with a dynamic pressure groove 26 on the inner peripheral surface 24 of the bearing sleeve 18 for positively generating dynamic pressure in the oil film in the radial bearing gap. In a perfect circular bearing, the inner peripheral surface 24 of the bearing sleeve 18 is a cylindrical surface, and dynamic pressure is generated by the swing of the shaft member 14.

In the fan motor having the fluid dynamic pressure bearing device 11, the shaft member 14, the rotor 15, and the blades rotate with high rotational accuracy due to the pressure improving effect of the dynamic pressure groove 26 as the dynamic pressure bearing when used in a steady posture. However, abnormal noise is unlikely to occur due to contact between the shaft member 14 and the bearing sleeve 18.

Further, even when this fan motor is used in an unsteady state (for example, a swing state due to the swing of the shaft member 14) and the shaft member 14 is largely eccentric with respect to the bearing sleeve 18, the octagonal groove portion of the dynamic pressure groove 26 Since the ratio of the octagonal hill portion 27 to 28 is large, it is possible to exhibit a bearing capacity close to that of a perfect circular bearing.

In the fluid dynamic pressure bearing device 11 of the embodiment described above, the dynamic pressure groove 26 including the octagonal hill portion 27 and the octagonal groove portion 28 is formed as the radial dynamic pressure generating portion, whereby FIG. As shown in B), the rotation direction of the shaft member 14 can be either the forward direction or the reverse direction (see the solid line arrow in the figure).

That is, when the rotation direction of the shaft member 14 is the positive direction, the flow of the lubricating oil is the direction indicated by the white arrow in FIG. 4A. When the rotation direction of the shaft member 14 is opposite, the flow of the lubricating oil is the direction indicated by the white arrow in FIG. 4 (B).

As a result, when incorporating the bearing sleeve 18, there are no restrictions on the rotation direction of the shaft member 14, so that the bearing sleeve 18 can be incorporated without limitation. It can also be used in applications where the rotation direction of the shaft member 14 changes. As a result, the work of assembling the bearing sleeve 18 is simplified and the workability can be improved.

Further, the bearing area of the bearing sleeve 18 (octagonal hill portion 27 of the dynamic pressure groove 26) can be increased. Therefore, the surface pressure applied to the radial bearing surface of the bearing sleeve 18 is reduced, and the wear resistance can be improved. As a result, the life of the fluid dynamic bearing device 11 can be extended.

Further, a sufficient dynamic pressure effect can be obtained even in a region where the rotation speed of the shaft member 14 is low. In particular, the octagonal groove 28 functions as an oil sump during start / stop and low-speed rotation. As a result, the shaft member 14 can be reliably supported in a non-contact manner, so that the shaft member 14 can be prevented from coming into contact with the radial bearing surface of the bearing sleeve 18.

The bearing sleeve 18 of this embodiment is a porous body, and the surface opening ratio of the octagonal hill portion 27 is set to 20% or less, preferably 2 to 10%. Then, the surface opening ratio in the octagonal groove 28 is set larger than the surface opening ratio in the octagonal hill 27.

By adopting such a structure, lubricating oil can be efficiently supplied to the radial bearing surface of the bearing sleeve 18.

As shown in FIG. 5, a groove 30 (pocket) for supplying lubricating oil may be formed at the center of the octagonal hill portion 27 on the inner peripheral surface 24 of the bearing sleeve 18. The white arrows in FIG. 5 indicate the flow of lubricating oil from the groove 30.

By adopting such a structure, as shown by the white arrow in FIG. 5, the lubricating oil is satisfactorily supplied to the radial bearing surface of the bearing sleeve 18, so that the lubrication efficiency can be improved.

As shown in FIG. 6, on the inner peripheral surface 24 of the bearing sleeve 18, hills 31 for preventing the outflow of lubricating oil from the octagonal groove 28 are formed at both ends of the inner peripheral surface 24 of the bearing sleeve 18 in the axial direction. You may do so.

By adopting such a structure, it is possible to prevent the lubricating oil from flowing out from the octagonal groove 28 to the outside of the bearing sleeve 18, so that the lubrication efficiency can be improved.

On the inner peripheral surface 24 of the bearing sleeve 18 of the embodiment shown in FIGS. 3, 5 and 6, a connecting groove portion 32 for connecting adjacent octagonal groove portions 28 is formed. In the dynamic pressure groove 26, the cross-sectional area of the connecting groove portion 32 is made larger than the cross-sectional area of the octagonal groove portion 28. As a prerequisite, the cross-sectional area of the connecting groove portion 32 is made larger than twice the cross-sectional area of the octagonal groove portion 28.

For example, exemplifying the form of the inner diameter φ2 with three grooves in FIG. 9, when the depth of the octagonal groove 28 is 0.003 mm and the width W1 is 0.1607 mm, the cross-sectional area of the octagonal groove 28 is. It becomes 0.003 mm × 0.1607 mm = 0.0004821 mm ² . On the other hand, the depth of the connecting groove portion 32 is 0.003 mm, the width W2 thereof is 0.5315 mm, and the cross-sectional area of the connecting groove portion 32 is 0.003 mm × 0.9517 mm = 0.0028551 mm ² .

Here, if the cross-sectional area of the connecting groove portion 32 becomes too large, the dynamic pressure will decrease. Therefore, it is desirable that the cross-sectional area of the connecting groove portion 32 is 0.0028551 mm ² or less. Therefore, it is preferable to set the cross-sectional area of the connecting groove portion 32 after determining the cross-sectional area of the octagonal groove portion 28. Further, it is desirable that the depths of the octagonal groove 28 and the connecting groove 32 have the same dimensions as the radial bearing gap.

As described above, by making the cross-sectional area of the connecting groove portion 32 larger than the cross-sectional area of the octagonal groove portion 28, the amount of lubricating oil flowing through the connecting groove portion 32 becomes larger than the amount of lubricating oil flowing through the octagonal groove portion 28. Lubricating oil can be continuously supplied to the radial bearing gap. As a result, in the dynamic pressure groove 26, the dynamic pressure action can be effectively generated in the lubricating oil in the radial bearing gap.

If the cross-sectional area of the connecting groove portion 32 is smaller than the cross-sectional area of the octagonal groove portion 28, the amount of lubricating oil flowing through the connecting groove portion 32 is smaller than the amount of lubricating oil flowing through the octagonal groove portion 28, and the octagonal groove portion 28 Negative pressure is generated near the entrance, making it difficult to obtain a sufficient dynamic pressure effect.

As shown in FIG. 7, the connecting groove portion 32 described above (hereinafter referred to as the first connecting groove portion) connects two adjacent octagonal groove portions 28 located vertically in the axial direction of the bearing sleeve 18. ing. Further, a connecting groove portion 33 (hereinafter, referred to as a second connecting groove portion) is formed which connects each of the octagonal groove portions 28 located above and below in the circumferential direction.

The first connecting groove portion 32 has an oil pool function for suppressing a shortage of lubricating oil in the octagonal groove portion 28 and the second connecting groove portion 33. The octagonal groove 28 has a function of generating a dynamic pressure action and suppressing backflow due to the pressure generated in the second connecting groove 33.

The second connecting groove 33 has a function of smoothing the pressure peak of the dynamic pressure and suppressing eccentricity due to the displacement of the center of gravity of the shaft member 14. That is, even if the position of the center of gravity of the shaft member 14 deviates from the design point, the dynamic pressure for supporting the shaft member 14 is constant within the smoothed range, and robustness (robustness) can be obtained.

Here, it is preferable that the cross-sectional area of the first connecting groove portion 32 is large because lubricating oil is stored. However, if the cross-sectional area of the first connecting groove portion 32 is made too large, the flow path length of the octagonal groove portion 28 becomes long. It becomes shorter and it becomes difficult to generate the maximum dynamic pressure.

As a structure for increasing the cross-sectional area of the first connecting groove portion 32 without shortening the flow path length of the octagonal groove portion 28, the axial length of the first connecting groove portion 32 cannot be changed. As shown in 8, it is effective to form a recessed portion 34 in which the first connecting grooved portion 32 is expanded in the circumferential direction.

On the other hand, the generation of dynamic pressure can be increased by lengthening the flow path length of the octagonal groove 28, but if the flow path length of the octagonal groove 28 is too long, the first connecting groove 32 and the second connecting groove 32 and the second The cross-sectional area of the connecting groove portion 33 will be reduced, and the functions of the first connecting groove portion 32 and the second connecting groove portion 33 will be reduced.

Further, the second connecting groove 33 preferably has a large cross-sectional area because it smoothes the pressure peak of the dynamic pressure and suppresses the eccentricity due to the deviation of the center of gravity of the shaft member 14, but the second connecting groove 33 If the cross-sectional area of the groove portion 33 is made too large, the flow path length of the octagonal groove portion 28 becomes short as in the case of the first connecting groove portion 32, and it becomes difficult to generate the maximum dynamic pressure.

Therefore, the cross-sectional areas of the first connecting groove portion 32, the octagonal groove portion 28, and the second connecting groove portion 33 are defined as follows. Assuming that the cross-sectional area A of the first connecting groove portion 32, the cross-sectional area B of the octagonal groove portion 28, and the cross-sectional area C of the second connecting groove portion 33 are defined as A> C ≧ 2B (see FIG. 9).

Since the depths of the first connecting groove portion 32, the octagonal groove portion 28 and the second connecting groove portion 33 are the same, in FIG. 9, the first connecting groove portion 32, the octagonal groove portion 28 and the second connecting groove portion 33 are formed. Each cross-sectional area of is represented by each cross-sectional width. The "number" in the drawing means the number of the bearing sleeves 18 arranged in the circumferential direction, with the two octagonal hills 27 located vertically above and below the bearing sleeve 18 as one.

As shown in FIG. 9, the cross-sectional area ratio A / 2B of the first connecting groove portion 32 and the octagonal groove portion 28 is preferably 2.96 or more and 8.26 or less. When this cross-sectional area ratio is smaller than 2.96, a shortage of lubricating oil occurs in the octagonal groove 28 and the second connecting groove 33, and the dynamic pressure decreases. Further, if the cross-sectional area ratio is larger than 8.26, it becomes difficult to secure the flow path length of the octagonal groove 28, and the dynamic pressure decreases.

Further, the cross-sectional area ratio C / 2B of the second connecting groove portion 33 and the octagonal groove portion 28 is preferably 2.18 or more and 6.07 or less. If this cross-sectional area ratio is smaller than 2.18, it becomes difficult to smooth the maximum peak of dynamic pressure by the second connecting groove 33, and it becomes difficult to suppress eccentricity due to the deviation of the center of gravity of the shaft member 14. .. Further, if the cross-sectional area ratio is larger than 6.07, it becomes difficult to secure the flow path length of the octagonal groove portion 28, the dynamic pressure decreases, and the backflow of the lubricating oil to the first connecting groove portion 32 It becomes difficult to suppress the torque and the torque becomes high.

In this fluid dynamic pressure bearing device 11, the bearing area of the bearing sleeve 18, that is, the total sum of the hills is formed by forming the dynamic pressure groove 26 composed of the octagonal hill portion 27 and the octagonal groove portion 28 as the radial dynamic pressure generating portion. By increasing the surface area, it is possible to exert a bearing force close to that of a perfect circular bearing. Further, by increasing the surface area of the octagonal hill portion 27 of the dynamic pressure groove 26, a sufficient dynamic pressure effect can be obtained even in a region where the rotation speed of the shaft member 14 is low, and a bearing force close to that of a perfect circular bearing can be obtained. It can be demonstrated. Further, the dynamic pressure effect generated by the octagonal groove 28 is such that when the gap between the shaft member 14 and the bearing sleeve 18 is biased or tilted on the circumference, the gap between the shaft member 14 and the bearing sleeve 18 is smaller. However, the eccentricity of the shaft member 14 is suppressed by increasing the dynamic pressure as compared with the one having a larger gap between the shaft member 14 and the bearing sleeve 18.

As shown in FIG. 10, assuming that the total surface area of the inner peripheral surface 24 of the bearing sleeve 18 is D and the total surface area of the hills (total surface area of the hills) in the total surface area D is E, the total surface area of the hills with respect to the total surface area D. The ratio E / D of the surface area E is 76 to 78%. For this reason, it is preferable to increase the total surface area E of the hills of the dynamic pressure groove 26.

The inner peripheral surface 24 of the bearing sleeve 18 varies depending on the number of grooves along the axial direction. However, assuming that the surface area of the octagonal hills 27 per piece is F, the bearing sleeve 18 and the octagonal hills 27 per piece The surface area ratio F / D of is 2 to 6%.

When the surface area ratio F / D is smaller than 2%, the dynamic pressure generating force of the octagonal hills 27 per piece decreases, and when the surface area ratio F / D is larger than 6%, the first connecting groove 32 and the first connecting groove 32 and the second The dynamic pressure is reduced by reducing the size of the second connecting groove 33.

Further, in this embodiment, the angle of the octagonal groove 28 with respect to the circumferential direction of the bearing sleeve 18 may be about 15 ° to 45 °. The angle θ of the octagonal groove 28 shown in FIG. 10 is 40 ° (see FIG. 7).

In this embodiment, as shown in FIG. 7, the axial dimension L1 of the octagonal hill portion 27 located at the center in the axial direction is made longer than the axial dimension L2 of the octagonal hill portion 27 located vertically in the axial direction. Yes (L1> L2).

As a result, the lubricating oil flows out from the center line of the octagonal groove 28 into which the lubricating oil flows into the first connecting groove 32 and the second connecting groove 33, and from the first connecting groove 32 and the second connecting groove 33. The center line of the octagonal groove 28 is not in the same straight line, and when the center line is extended, both center lines do not intersect until they come into contact with the octagonal hill 27 located at the center in the axial direction ( See the alternate long and short dash line in FIG. 7).

With such a structure, the dynamic pressure release can be suppressed by preventing the lubricating oil from staying in the first connecting groove portion 32 and the second connecting groove portion 33, and the pressure in the octagonal groove portion 28 can be suppressed. Can be stabilized.

In the above embodiment, the case where the dynamic pressure groove 26 is provided on the inner peripheral surface 24 of the bearing sleeve 18 is illustrated, but as shown in FIGS. 11 to 15, the inner peripheral surface 24 of the bearing sleeve 18 is a smooth cylinder. The dynamic pressure groove 26 may be formed on the outer peripheral surface 25 of the shaft member 14 facing the surface.

The embodiment shown in FIG. 11 corresponds to the embodiment shown in FIG. The embodiment shown in FIG. 12 corresponds to the embodiment shown in FIG. The embodiment shown in FIG. 13 corresponds to the embodiment shown in FIG. The embodiment shown in FIG. 14 corresponds to the embodiment shown in FIG. 7. The embodiment shown in FIG. 15 corresponds to the embodiment shown in FIG.

In the above embodiment, the receiving member 23 of the thrust bearing portion touch-supports the convex portion 20 of the shaft member 14 (see FIG. 2), but the thrust bearing portion is the same as the radial bearing portion of the embodiment. , The shaft member 14 may be non-contactly supported by the pressure of the oil film.

Further, in the embodiment, a so-called shaft rotation type fluid dynamic bearing device 11 in which the bearing sleeve 18 is fixed and the shaft member 14 is rotated has been illustrated, but the present invention is not limited to this, and the shaft member 14 is fixed and the bearing sleeve 18 is used. The present invention may also be applied to a so-called fixed shaft type hydrodynamic bearing device that rotates.

The present invention is not limited to the above-described embodiments, and it goes without saying that the present invention can be implemented in various forms without departing from the gist of the present invention. Indicated by the scope of the claim and further includes the equal meaning described in the claims, and all modifications within the scope.

14 Shaft member 18 Bearing member (bearing sleeve)
24 Inner peripheral surface 25 Outer peripheral surface 26 Radial dynamic pressure generating part (dynamic pressure groove)
27 Polygonal hills (octagonal hills)
28 Polygonal groove (octagonal groove)
30 Groove 31 Hill 32 Connecting groove (first connecting groove)
33 Connecting groove (second connecting groove)

Claims (6)

The shaft member is relative to each other by the pressure of the fluid film generated in the radial bearing gap between the shaft member, the bearing member in which the shaft member is inserted in the inner circumference, and the outer peripheral surface of the shaft member and the inner peripheral surface of the bearing member. A fluid dynamic bearing device provided with a radial dynamic pressure generating part that is rotatably and non-contactly supported.
The radial dynamic pressure generating portion is formed so as to surround a large number of polygonal hills arranged in a pattern on either the inner peripheral surface of the bearing member or the outer peripheral surface of the shaft member, and the polygonal hills. A fluid dynamic bearing device characterized by being composed of a polygonal groove portion. The fluid dynamic pressure bearing device according to claim 1, wherein the radial dynamic pressure generating portion has a surface opening ratio in the polygonal groove portion larger than the surface opening ratio in the polygonal hill portion. The fluid dynamic pressure bearing device according to claim 1 or 2, wherein the radial dynamic pressure generating portion is formed with a groove portion for supplying lubricating oil at the center of the polygonal hill portion. The fluid dynamic pressure bearing device according to any one of claims 1 to 3, wherein the radial dynamic pressure generating portion is formed with a hill portion for preventing the outflow of lubricating oil from the polygonal groove portion. The radial dynamic pressure generating portion has a connecting groove portion that connects adjacent polygonal groove portions, and the cross-sectional area of the connecting groove portion is made larger than the cross-sectional area of the polygonal groove portion according to any one of claims 1 to 4. The hydrodynamic bearing device described. The connecting groove portion is composed of a first connecting groove portion that connects polygonal groove portions that are vertically located in the axial direction and a second connecting groove portion that connects the polygonal groove portions in the circumferential direction, and the first connecting groove portion. The fluid dynamic bearing device according to claim 5, wherein the cross-sectional area of is larger than the cross-sectional area of the second connecting groove portion.

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