JP2009144927A - Dynamic pressure bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To refeed lubricating oil led to flow into a circulation groove to a radial bearing clearance by an asymmetric dynamic pressure groove. <P>SOLUTION: A bearing member 1 made of oil-impregnated sintered metal is fixed to the inner periphery of the bottomed cylindrical housing 9, and a shaft member 7 is supported in a non-contact manner by dynamic pressure of oil generated in the radial bearing clearance or a thrust bearing clearance. The shaft member is formed with a flange portion opposed to one end surface of the bearing member, dynamic pressure of lubricating oil is generated in the thrust bearing clearance formed between the end surface of the bearing member and the end surface of the flange portion, and the dynamic pressure groove is asymmetrically formed in order to push the lubricating oil into the thrust bearing clearance. Thereby, the lubricating oil is led to flow into the circulation groove. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing device that supports a shaft in a non-contact manner with a fluid dynamic pressure generated in a bearing gap.

  The hydrodynamic bearing device supports the shaft in a non-contact manner, and thus has characteristics such as high rotational accuracy, high speed rotation, low noise, and low cost. In recent years, these characteristics have led to magnetic disks such as HDDs, It is expected to be used as a spindle support bearing in spindle motors for optical disks such as DVDs, magneto-optical disks such as MOs, polygon scanner motors for laser beam printers, and the like.

  This dynamic pressure type bearing device fixes a sleeve-shaped bearing member to the inner periphery of a bottomed cylindrical housing, and connects a shaft inserted into the inner periphery of the bearing member to a radial bearing gap, or a radial bearing gap and a thrust bearing gap. It is a structure which supports by the dynamic pressure which arose in both. In general, in this type of bearing, the space sandwiched between the thrust receiving surface formed at the bottom of the housing and the end surface of the bearing member facing this has a sealed structure. Therefore, in order to open this sealed space to the outside air, the bearing An axial groove (circulation groove) is formed on the outer periphery of the member so as to open at both end faces thereof.

JP 2001-152174 A

  By the way, in the manufacturing process of a bearing member, a bearing member is shape | molded by the predetermined dimension by putting sleeve-shaped sintered metal in a die and sizing. After sizing, springback occurs with mold removal, and the outer periphery of the bearing member swells to the outer diameter side, but the circulation groove part during sizing is not in contact with the die and is not compressed to the inner diameter side, The amount of springback after demolding is smaller than in other places. Therefore, after sizing, as shown in FIG. 8, the outer periphery and inner periphery of the bearing member 21 are not perfect circles, but have a modified cross-sectional shape with a small diameter near the circulation groove 23. Conventionally, the circulation groove 23 is often formed at two locations on the outer periphery of the bearing member 21 (180 ° facing position). In this case, the cross-sectional shape after sizing is an ellipse having the circulation groove 23 portion as a short axis.

  However, with such an elliptical shape, a narrow part (short axis direction) and a wide part (major axis direction) are formed in the radial bearing gap between the inner periphery of the bearing member 21 and the outer periphery of the shaft 25. In this case, the floating effect of the shaft due to the fluid dynamic pressure is reduced at the wide radial bearing gap, so the bearing rigidity in the elliptical long axis direction is reduced, causing the shaft to run around, and there is concern that NRRO etc. may be adversely affected. Is done.

  Therefore, an object of the present invention is to provide a hydrodynamic bearing device having high rotational accuracy by eliminating a bearing rigidity difference in each direction due to deformation after springback.

In order to achieve the above object, in the present invention, a shaft member, a bearing member made of an oil-impregnated sintered metal, opposed to the outer periphery of the shaft member via a radial bearing gap, and a housing in which the bearing member is fixed to the inner periphery are provided. The shaft member is supported in a non-contact manner by generating a dynamic pressure of the lubricating oil in the radial bearing gap by the relative rotation of the shaft member and the bearing member, and the outer periphery of the bearing member is opened at both end faces. in the dynamic pressure type bearing device to form a circular groove lubricating oil flows Te, the circulation grooves possess three or more, the flange portion of one end face facing the bearing member provided on the shaft member, the end face of the bearing member and the flange portion By generating a dynamic pressure of the lubricating oil in the thrust bearing gap formed between the end face of the cylinder and the aforesaid dynamic pressure groove having an asymmetric shape that pushes the lubricating oil into the thrust bearing gap. It was decided to flow into the circulation groove .

By providing the shaft member with a flange portion facing one end surface of the bearing member, and generating dynamic pressure of the lubricating oil in the thrust bearing gap formed between the end surface of the bearing member and the end surface of the flange portion, The member can be supported in a non-contact manner in the thrust direction. In this case, the lubricating oil in the thrust bearing gap flows more into the groove due to the influence of centrifugal force. However, if there are three or more circulating grooves, the lubricating oil can be reliably absorbed.

The dynamic pressure groove on the bearing surface has an asymmetric shape that pushes the lubricating oil into the thrust bearing gap, so the amount of lubricating oil flowing into the circulation groove further increases, but even in this case, the lubricating oil is absorbed with a margin. can do. In this case, the opening of the housing is sealed by the seal member, a gap is formed between the bearing member and the seal member, and the circulation groove is communicated with the inner periphery of the seal member through the gap.

  By providing three or more circulation grooves, the bearing rigidity in each direction is increased, so that the rotation accuracy of the bearing can be increased.

As described above, according to the present invention, the lubricating oil flowing into the circulation groove by the asymmetrical dynamic pressure groove can be re-supplied to the radial bearing gap.
Further, since three or more circulation grooves are formed on the outer periphery of the bearing member, it is possible to prevent instability of the bearing rigidity due to the springback deformation of the bearing member after sizing, and further increase the rotation accuracy of the bearing. Can be increased.

1 is a longitudinal sectional view of a hydrodynamic bearing device according to the present invention. It is a perspective view of a bearing member. It is a figure which shows the dimensionless rigidity in various bearings. It is a cross-sectional view of a 3-arc bearing. It is a cross-sectional view of a 4-arc bearing. It is a cross-sectional view explaining the eccentricity. It is a longitudinal cross-sectional view of the dynamic pressure type bearing device which formed the axial bearing asymmetrical radial bearing surface. It is a cross-sectional view of a two-arc bearing.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 8.

  As shown in FIG. 1, the hydrodynamic bearing device according to the present embodiment includes a sleeve-shaped bearing member 1, a shaft member 7, and a bottomed cylindrical housing 9 as main components.

  The bearing member 1 is formed of an oil-impregnated sintered metal in which a sintered metal is impregnated with lubricating oil or lubricating grease so that the oil is retained in the pores. As the sintered metal, for example, a copper-based or iron-based material, or a material containing both of them as a main component can be used. Preferably, the sintered metal is formed using 20 to 95% of copper. The bearing member 1 is manufactured through the steps of compacting, sintering, sizing, and oil impregnation, as in the prior art, and the bearing member 1 thus obtained has an inner peripheral surface and one end surface 1a. Then, a dynamic pressure generating groove 3 (dynamic pressure groove) described later is formed by means such as press working.

  On the inner periphery of the bearing member 1, radial bearing surfaces 5a and 5b having a plurality of dynamic pressure grooves 3 as dynamic pressure generating means are formed. In the illustrated example, the case where the two radial bearing surfaces 5a and 5b are formed apart from each other in the axial direction is illustrated, but the number of the radial bearing surfaces 5a and 5b is not limited to two, but one or three. It can also be set as above. The dynamic pressure grooves 3 on the radial bearing surfaces 5a and 5b need only be inclined with respect to the axial direction, and may be arranged in a spiral shape as well as in a herringbone shape as shown. In addition, it is also possible to use a non-circular radial bearing surface having no dynamic pressure groove such as a harmonic waveform.

  The shaft member 7 is formed of a metal material such as stainless steel, and includes a straight shaft portion 7a and a disk-shaped flange portion 7b provided at an end of the shaft portion 7a. The shaft portion 7a and the flange portion 7b can be formed by separate press-fitted parts, or can be integrally formed by means such as forging.

  The housing 9 is formed in a bottomed cylindrical shape with one end opened and the other end closed. The bearing member 1 is fixed to the inner periphery of the housing 9 by means such as press fitting or adhesion. At this time, the shaft portion 7 a of the shaft member 7 is disposed on the inner periphery of the bearing member 1, and the flange portion 7 b is disposed in the space between the bottom portion 9 a of the housing 9 and one end surface 1 a of the bearing member 1. The housing bottom 9a can be integrally formed with the cylindrical housing main body 9b as shown, or can be formed as a separate part from the housing main body 9b and assembled by fitting them together. The opening of the housing main body 9b is sealed by a seal member 10 to prevent the oil as a lubricating fluid from flowing out, and is maintained between the seal member 10 and the end surface 1b of the bearing member 1 facing the seal member 10. In order to enhance the oil effect, a slight gap in the axial direction is formed.

  In this state, both end surfaces 7b1 and 7b2 of the flange portion 7b are opposed to one end surface 1a of the bearing member 1 and the thrust receiving surface 9a1 of the housing bottom portion 9a. Thrust bearing surfaces 11a and 11b having a plurality of dynamic pressure grooves (not shown) are formed as dynamic pressure generating means on the end surface 1a of the bearing member 1 and the thrust receiving surface 9a1 facing the flange portion 7b. The dynamic pressure groove shape of the thrust bearing surfaces 11a and 11b is arbitrary, and, like the radial bearing surfaces 5a and 5b, in addition to forming herringbone and spiral dynamic pressure grooves, a step-type thrust bearing surface is formed. You can also. The dynamic pressure grooves can be formed on both end surfaces 7b1 and 7b2 of the flange portion 7b instead of the bearing member end surface 1a and the thrust receiving surface 9a1. In this case, the thrust grooves are formed on both end surfaces 7b1 and 7b2 of the flange portion 7b. A bearing surface is formed.

  A minute gap (radial bearing gap) between the radial bearing surfaces 5a, 5b and the outer peripheral surface of the shaft portion 7a, and the thrust bearing surfaces 11a, 11b and opposite surfaces (in the illustrated example, both end surfaces 7b1, 7b1 of the flange portion 7b) 7b2) is filled with oil as a lubricating fluid. During relative rotation of the shaft member 7 and the bearing member 1 (when the shaft member 7 is rotated in the present embodiment), oil acts on the radial bearing gap and the thrust bearing gap by the action of the bearing surfaces 5a, 5b, 11a, and 11b. A dynamic pressure is generated, and the shaft member 7 is supported in a non-contact manner relative to the bearing member 1 in both the radial direction and the thrust direction.

  On the outer periphery of the bearing member 1, as in the prior art, grooves opened on both end faces 1 a and 1 b, that is, circulation grooves 12 are formed in the axial direction. The circulation groove 12 communicates the sealed space between the bottom portion 9a of the housing 9 and the end surface 1a of the bearing member 1 with the outside of the bearing, and serves as a passage through which oil flows in the axial direction. The oil in the circulation groove 12 is absorbed by the bearing member 1 and further oozes out from the surface of the bearing member 1 and is resupplied to each bearing gap. In the present invention, three or more, preferably three circulation grooves 12 are provided at equal intervals in the circumferential direction for the reason described later (see FIG. 2).

  When three circulation grooves 12 are formed in this way, after sizing, the bearing member 1 has three large diameters as shown in FIG. 4 due to the difference in the spring back amount between the circulation groove 12 and other portions. The cross section is deformed into a substantially triangular cross section formed by the arc 13 (hereinafter, the deformed bearing member is referred to as a three-arc bearing). In addition, when four circulation grooves 12 are formed, the bearing member after sizing is deformed into a substantially rectangular cross section composed of four large-diameter arcs 13 as shown in FIG. Called). Although illustration is omitted, even when five or more circulation grooves 12 are provided, the cross section is deformed into a polygonal cross section (5 arc bearing, 6 arc bearing, etc.) having the same number of large-diameter arcs as the circulation grooves 12. 4 and 5 depict the degree of deformation with respect to a perfect circle exaggerated for easy understanding, but such a clear deformation cannot be confirmed with the naked eye.

  FIG. 3 shows the analysis result of the dimensionless rigidity of the oil film in the two-arc bearing, the three-arc bearing, and the four-arc bearing, which are conventional journal bearings. This is obtained by expressing the fluid pressure in the bearing clearance as a second-order differential equation called Reynolds equation and solving it numerically by a computer. In the region where the pressure is negative, the Reynolds condition is used as the pressure boundary condition. The lay nozzle condition here is a condition in which the pressure gradient becomes 0 at the oil film breaking portion and the flow rate is continuous.

  The two-arc bearing, the three-arc bearing, and the four-arc bearing here are bearings provided with two, three, and four circulation grooves 12 each having a width of 10 ° in the circumferential direction. In any bearing, the ratio (L / D) between the axial length L and the outer diameter D of the bearing member 1 is set to 0.5. Further, the eccentricity ε of the shaft member 7 is based on ε = 0.1 (the eccentricity in the case of the two-arc bearing is ε = 0.0868). Note that ε = 0 indicates a state in which the shaft centers of the bearing member 1 and the shaft member 7 coincide with each other as shown by a broken line in FIG. 6, and ε = 1 indicates that the shaft member 7 has a bearing member as indicated by a two-dot chain line in FIG. 1 represents the inscribed state (the width of the radial bearing gap in FIG. 6 is exaggerated).

In the figure, Kxx, Kyy, Kxy, and Kyx represent the elastic constants of the oil film, and numerically solved pressure part distributions are integrated on the bearing surface, and the obtained loads in the x and y directions are x and y directions. It is obtained by differentiating numerically with each displacement . These are expressed dimensionlessly, and if the four dimensionless stiffnesses are represented by Kij, the dimensional stiffness kij is represented by the following equation.

kij = (W / Cp) Kij
Here, W represents a bearing load, and Cp represents a bearing radius gap.

  The subscript xx is the displacement in the X direction that generates a force in the X direction (short axis direction of the ellipse), yy is the displacement in the Y direction that generates a force in the Y direction (long axis direction of the ellipse), and xy is the displacement in the X direction. Yx represents a displacement in the Y direction that generates a force, and yx represents a displacement in the X direction that generates a force in the Y direction. The subscripts xy and yx are coupled terms indicating the force generated with respect to the displacement received from other motions that are not self, and when this is large, the instability of the whirling vibration of the shaft member 7 increases. It will be. From FIG. 3, Kxx and Kyy are not balanced in the two-arc bearing, and the difference in bearing rigidity depending on the load direction is large, whereas both values are balanced in the three-arc bearing and the four-arc bearing. It can be understood that there is no such inconvenience. From the above, it is preferable that the number of the circulation grooves 12 be three or more so that the cross-sectional shape of the bearing member 1 after the spring back approximates to a three-arc bearing or a four-arc bearing.

  On the other hand, when considering the clearance management of the radial bearing gap in the case of mass production, the difference in the inner diameter dimension becomes larger depending on the measurement direction in the four-arc bearing (see the arrow in FIG. 5), Such a difference is small (see arrow in FIG. 4). Therefore, compared with the 4-arc bearing, the 3-arc bearing can loosen the tolerance range of the inner diameter dimension, and can be manufactured at a lower cost. Further, according to FIG. 3, the absolute values of the coupled terms Kxy and Kyx are smaller in the three-arc bearing, so that the three-arc bearing is also preferable in this respect. On the other hand, in bearings with 5 or more arcs, the cross-sectional shape after spring back deformation is close to a perfect circle bearing, so there is a concern that unstable self-excited vibration called whirl occurs in the shaft member 7, and the cost of grooving is also high. Increase. For the above reasons, it is most preferable to form three circulation grooves so that the cross-sectional shape after deformation of the spring back approximates that of a three-arc bearing.

  FIG. 7 shows that, of the two radial bearing surfaces 5a and 5b, the bearing surface 5a on the closed side of the housing 9 is formed asymmetrically in the axial direction, and oil is pushed into the housing closed side (downward in the drawing) by the dynamic pressure groove It is a structure with enhanced power. In this case, since the oil film formation region is shifted toward the housing closing side, the amount of oil flowing into the circulation groove 12 increases, and the conventional two circulation grooves (23: see FIG. 8) sufficiently absorb the oil flow rate. Although there is a concern that it cannot be performed, such a problem can be avoided by providing three or more circulation grooves 12 as described above. Although the number of circulation grooves can be determined according to the flow of oil, it is most preferable to form the three circulation grooves 12 as described above in view of rotational accuracy.

1 Bearing member 1a End face (housing closed side)
1b End face (housing opening side)
3 Dynamic pressure groove 5a Radial bearing surface (housing closed side)
5b Radial bearing surface (housing opening side)
7 Shaft member 7a Shaft portion 7b Flange portion 9 Housing 9a Housing bottom portion 9a1 Thrust receiving surface 9b Housing body 10 Seal member 11a Thrust bearing surface (housing opening side)
11b Thrust bearing surface (housing closed side)
12 Circulating groove 13 Large-diameter arc

Claims (3)

A shaft member, comprising a bearing member made of oil-impregnated sintered metal and opposed to the outer periphery of the shaft member via a radial bearing gap, and a housing having the bearing member fixed to the inner periphery, the shaft member and the bearing member being relatively rotated. the radial bearing gap, by generating dynamic pressure of the lubricating oil at the dynamic pressure grooves and the non-contact support the shaft member, and the outer periphery of the bearing member, to form a circular groove lubricating oil flows is opened on both end faces thereof kinematic In the pressure bearing device,
The circulating grooves possess three or more, the flange portion of one end face facing the bearing member provided on the shaft member, the thrust bearing gap formed between said end face and the end face of the flange portion of the bearing member of the lubricating oil A dynamic pressure bearing device , wherein dynamic pressure is generated, and the dynamic pressure groove is formed in an asymmetric shape so as to push the lubricating oil into the thrust bearing gap, thereby causing the lubricating oil to flow into the circulation groove . 2. The hydrodynamic bearing device according to claim 1, wherein the lubricating oil flowing into the circulation groove is resupplied to the radial bearing gap. The movement according to claim 1 or 2, wherein the opening of the housing is sealed by a seal member, a gap is formed between the bearing member and the seal member, and the circulation groove is communicated with the inner periphery of the seal member through the gap. Pressure bearing device.

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