JP6942002B2 - 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 can be used for various motors mounted on various electric devices, for example, for spindle motors incorporated in disk drive devices such as HDDs, fan motors incorporated in PCs, or laser beam printers. It is suitably used as a bearing device for a built-in polygon scanner motor.

For example, in Patent Documents 1 to 3 below, a radial bearing gap formed by a housing, a bearing sleeve fixed to the inner circumference of the housing, and an inner peripheral surface of the bearing sleeve and in which a fluid (for example, lubricating oil) is interposed. A radial bearing portion that non-contactly supports a shaft (a shaft member inserted into the inner circumference of the bearing sleeve) that should be supported by the dynamic pressure generated in the fluid in the radial bearing gap so as to be relatively rotatable in the radial direction. Various forms of hydrodynamic bearing devices are disclosed.

Japanese Unexamined Patent Publication No. 2004-116667 Japanese Unexamined Patent Publication No. 2010-96202 JP-A-2010-255777

In the above hydrodynamic bearing device, the inner peripheral surface accuracy (roundness, cylindricity, etc.) of the bearing sleeve greatly affects the clearance width accuracy of the radial bearing gap and the bearing performance (load bearing capacity) of the radial bearing. do. For example, when press-fitting is selected as the method for fixing the bearing sleeve to the housing, the bearing sleeve is deformed by the tightening force due to the press-fitting, and the accuracy of the inner peripheral surface of the bearing sleeve is likely to be adversely affected.

Therefore, the bearing sleeve is often fixed to the inner circumference of the housing by so-called gap adhesion. Gap adhesion here means that the bearing sleeve is crevice-fitted on the inner circumference of the housing (see JIS B 0401-1) so that the inner peripheral surface of the housing facing each other and the outer peripheral surface of the bearing sleeve are in the radial direction. This is a method of fixing both by forming a gap and curing the adhesive interposed in the radial gap. It has been considered that such a fixing method can prevent a decrease in accuracy of the inner peripheral surface of the bearing sleeve because the bearing sleeve does not receive a tightening force from the housing. However, according to the verification by the present inventor, it has been found that the accuracy of the inner peripheral surface of the bearing sleeve may be lowered even when the bearing sleeve is gap-bonded to the inner circumference of the housing.

In view of the above circumstances, the present invention improves the accuracy of the inner peripheral surface of the bearing sleeve in the fluid dynamic bearing device in which the bearing sleeve is fixed to the inner circumference of the housing by so-called gap adhesion, thereby improving the bearing performance of the radial bearing portion. The purpose is to further enhance it.

According to the verification of the present inventor, the above-mentioned problem of deterioration of the inner peripheral surface accuracy of the bearing sleeve is solved.
(1) The amount of deformation of the housing and the bearing sleeve due to a temperature change (particularly, when a heat-curable adhesive is used as the adhesive, a heat treatment performed to cure the adhesive) is different from each other.
(2) The adhesive (adhesive layer) between the housing and the bearing sleeve may expand or contract under the influence of temperature changes.
It turned out that it was caused by such things. It is considered that the problem (1) above can be solved by, for example, forming the housing and the bearing sleeve with the same material or a material having an approximate coefficient of linear expansion. However, the required characteristics for the housing and the bearing sleeve are different from each other, and as the material for forming the housing and the bearing sleeve, a material that can satisfy the required characteristics for each is usually selected. Therefore, it is not a good idea to change the housing and / or bearing sleeve forming material unnecessarily. Therefore, as a result of diligent studies by the present inventor, he has found a technical means capable of solving the above (2) as much as possible, and has come up with the present invention.

That is, the present invention, which was devised to achieve the above object, has a bearing sleeve having a radial bearing surface forming a radial bearing gap between the inner peripheral surface and the outer peripheral surface of the shaft member to be supported, and a bearing. The bearing sleeve is provided with a housing in which the sleeve is fixed to the inner circumference and a radial bearing portion that non-contactly supports the shaft member and the bearing sleeve in the radial direction by the dynamic pressure action of the fluid generated in the radial bearing gap. In a hydrodynamic bearing device fixed to the inner circumference of a housing via an adhesive layer formed in a radial gap between the outer peripheral surface and the inner peripheral surface of the housing, the housings facing each other via the radial gap. A cylindrical non-adhesive portion without an adhesive layer is provided between the inner peripheral surface of the bearing and the outer peripheral surface of the bearing sleeve. Of these, it is characterized in that it is provided so as to overlap in the axial direction with the maximum pressure generation region where the fluid dynamic pressure is maximum. The "maximum pressure generation region" referred to here is, for example, a radial bearing when a dynamic pressure generating portion for generating a dynamic pressure action on the fluid in the radial bearing gap is adopted as shown in FIG. It is a region facing the annular hill portion Ac in the portion (radial bearing gap).

The bearing performance (load bearing capacity) of a radial bearing that supports the shaft member and the bearing sleeve in a non-contact manner so that they can rotate relative to each other in the radial direction by the dynamic pressure of the fluid generated in the radial bearing gap, that is, the radial bearing that consists of a so-called dynamic bearing. ) Is a form of a dynamic pressure generating portion provided on at least one of the outer peripheral surface of the shaft member facing each other and the inner peripheral surface (radial bearing surface) of the bearing sleeve in order to generate a dynamic pressure action on the fluid in the radial bearing gap. It differs in various places in the axial direction according to the above, and is the highest in the maximum pressure generation region where the fluid dynamic pressure is maximum among the radial bearing portions. Therefore, in order to improve the bearing performance of the radial bearing portion made of a dynamic pressure bearing, it is most effective to improve the clearance width accuracy of the radial bearing gap in the maximum pressure generation region of the radial bearing portion.

As described above, if a cylindrical non-adhesive portion is provided between the inner peripheral surface of the housing facing each other via the radial gap and the outer peripheral surface of the bearing sleeve so that the adhesive layer does not intervene, the bearing sleeve can be formed. Of the inner peripheral surface, the cylindrical region that overlaps the non-adhesive portion in the axial direction is less affected by the expansion / contraction of the adhesive layer. Therefore, if at least a part of the non-adhesive portion in the axial direction is provided so as to overlap with the maximum pressure generation region of the radial bearing portion in the axial direction, the radial bearing is provided in at least a part of the maximum pressure generation region. The clearance width accuracy of the gap is less likely to fluctuate (decrease). This makes it possible to effectively improve the bearing performance of the radial bearing portion.

The non-adhesive portion can be provided, for example, so that the entire axial direction overlaps the maximum pressure generation region in the axial direction (see FIG. 5). Such a configuration can be preferably adopted when, for example, a bearing sleeve formed of a porous body having a relative density of 80% or more and less than 90% is used. The "relative density" here is also called the true density ratio, and is calculated from the following relational expression.
Relative density = (overall bearing sleeve density / true density) x 100 [%]
The "true density" in the above equation means the theoretical density of a material such as a molten material that does not have pores inside, and the "density of the entire bearing sleeve" is measured by, for example, the method specified in JIS Z2501. Can be done.

The non-adhesive portion may be provided so that its axial one-side and other-side ends are located axially outside the axial one-side and other-side ends of the maximum pressure generation region, respectively []. See FIG. 7 (a)]. In this way, the axial formation range of the non-adhesive portion is expanded as compared with the case where the entire axial direction of the non-adhesive portion overlaps with the maximum pressure generation region in the axial direction, so that the accuracy of the radial bearing surface is reduced. It is advantageous in preventing the above. Such a configuration can be preferably adopted when, for example, a bearing sleeve formed of a porous body having a relative density of 90% or more and 95% or less is adopted.

When a bearing sleeve made of a porous body having a relative density of 90% or more and 95% or less is adopted, it is preferable to use a bearing sleeve in which at least the surface perforations on the outer peripheral surface are sealed. The sealing portion that seals the surface opening can be formed, for example, by plastically deforming the surface layer portion of the bearing sleeve.

Bearing sleeves made of a porous body of sintered metal containing copper can be manufactured (mass-produced) at a relatively low cost, but the shape accuracy of each part (particularly the radial bearing surface) and the slidability of the radial bearing surface are excellent. It is good. Therefore, such a bearing sleeve can be preferably adopted in realizing a fluid dynamic bearing device having excellent bearing performance of the radial bearing portion.

In the above configuration, the non-adhesive portion can be formed of an annular recess having a radial dimension larger than the clearance width of the radial gap. In this way, even when the adhesive is filled in the annular recess in the process of filling and curing the adhesive in the radial gap (the process of forming the adhesive layer), the adhesive in the annular recess is made into a capillary tube. It can be moved to the radial gap side by force. Therefore, the above-mentioned non-adhesive portion can be reliably provided, and the effect of improving the accuracy of the inner peripheral surface of the bearing sleeve can be appropriately enjoyed through this. In addition, in order to appropriately move the adhesive to the radial gap side by the capillary force, a diameter-reduced portion gradually reduced in diameter toward the outside in the axial direction is provided in the annular recess, and the diameter of this reduced portion is reduced. It is preferable to arrange them adjacent to the directional gap in the axial direction.

The adhesive layer can be formed with a thermosetting adhesive. If it is a thermosetting adhesive, the housing and the bearing sleeve can be reliably adhered and fixed by performing heat treatment under predetermined conditions. A heat treatment for curing a thermosetting adhesive is indispensable, but its viscosity temporarily decreases as the temperature rises during the heat treatment. Therefore, in particular, if the non-adhesive portion is composed of the above-mentioned annular recess, even if the annular recess is filled with an adhesive (thermosetting adhesive) in the process of forming the adhesive layer, the inside of the annular recess There is an advantage that the adhesive can be smoothly and surely moved to the radial gap side.

Since the hydrodynamic bearing device according to the present invention has a feature that the bearing performance of the radial bearing portion is excellent, various motors having a rotor magnet and a stator coil, specifically, a disk drive device (particularly HDD) It can be suitably used by being incorporated into a spindle motor for PC, a fan motor for PC, a polygon scanner motor for LBP, and the like.

Based on the above, according to the present invention, it is possible to improve the accuracy of the inner peripheral surface of the bearing sleeve that is directly involved in the formation of the radial bearing gap, so that a fluid dynamic bearing device having improved bearing performance of the radial bearing portion is provided. be able to.

It is sectional drawing which shows an example of a spindle motor conceptually. It is sectional drawing which shows the fluid dynamic pressure bearing apparatus which concerns on 1st Embodiment of this invention. It is sectional drawing of the assembly which fixed the bearing sleeve to the inner circumference of a housing. It is a top view of the lower end surface of a bearing sleeve. It is a partially enlarged view of the assembly shown in FIG. (A) is a diagram showing an initial stage in the assembling process of the housing and the bearing sleeve, (b) is a diagram showing an intermediate stage in the assembling process, and (c) is a diagram showing an intermediate stage in the assembling process. It is a figure which shows the insertion completion stage of a sleeve. (A) is a partially enlarged cross-sectional view of an assembly in which a high-density bearing sleeve is fixed to the inner circumference of a housing, and (b) is a partially enlarged view of FIG. (A). It is sectional drawing which shows the fluid dynamic pressure bearing apparatus which concerns on 2nd Embodiment of this invention. It is sectional drawing which shows the fluid dynamic pressure bearing apparatus which concerns on 3rd Embodiment of this invention. Both the figure (a) and the figure (b) are enlarged views showing a modified example of the non-adhesive portion. It is a figure which shows the result of having confirmed how much the inner diameter dimension of a bearing sleeve changes before and after adhesive fixing. It is a figure which shows the confirmation result of the adhesive strength of a housing and a bearing sleeve.

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 spindle motor. The spindle motor shown in the figure is used for a disk drive device such as an HDD, and has a fluid dynamic pressure bearing device 1, a disk hub 3 fixed to a shaft member 2 of the fluid dynamic pressure bearing device 1, and a radius. It includes a stator coil 4 and a rotor magnet 5 that face each other with a directional gap, and a motor base 6 in which a housing 7 of a fluid dynamic bearing device 1 is fixed to the inner circumference. The rotor magnet 5 is fixed to the disc hub 3, and the stator coil 4 is fixed to the motor base 6. A predetermined number of discs (two in the illustrated example) are held in the disc hub 3. In a spindle motor having such a configuration, when the stator coil 4 is energized, the rotor magnet 5 is rotated by an electromagnetic force between the stator coil 4 and the rotor magnet 5, and the shaft member 2, the disk hub 3, and the disk hub 3 and the rotor magnet 5 are rotated accordingly. The disk D rotates integrally.

FIG. 2 shows the fluid dynamic bearing device 1 according to the first embodiment of the present invention. The fluid dynamic bearing device 1 includes a shaft member 2, a housing 7 having openings on one and other ends in the axial direction, a bearing sleeve 8 fixed to the inner circumference of the housing 7, and the axial direction of the housing 7. A lid member 10 for closing the end opening on the other side is provided, and the internal space of the housing 7 is filled with lubricating oil (indicated by dense scattering point hatching) as a fluid. In the following, for convenience of explanation, the side on which the lid member 10 is arranged is referred to as the lower side, and the side opposite to this is referred to as the upper side, but the usage mode of the fluid dynamic bearing device 1 is not limited.

The shaft member 2 has a shaft portion 2a and a flange portion 2b provided integrally or separately at the lower end of the shaft portion 2a, and the shaft portion 2a and the flange portion 2b are formed of a metal material such as stainless steel. Will be done. The shaft portion 2a is inserted into the inner circumference of the bearing sleeve 8, and the flange portion 2b is arranged in a space defined between the housing 7, the bearing sleeve 8 and the lid member 10.

The housing 7 is formed of a metal material (molten material) such as brass or stainless steel, or a resin material in a substantially cylindrical shape, and has a cylindrical tubular portion 7a and a short cylindrical shape protruding radially inward from the tubular portion 7a. The seal portion 7b of the above is integrally provided. The inner peripheral surface of the tubular portion 7a has a relatively small diameter small diameter inner peripheral surface 7a1 and a relatively large diameter large diameter inner peripheral surface 7a2 arranged below the small diameter inner peripheral surface 7a1.

The inner peripheral surface 7b1 of the seal portion 7b is formed in a tapered surface shape whose diameter is gradually reduced downward, and the diameter is gradually reduced downward between the inner peripheral surface 7b1 and the cylindrical outer peripheral surface 2a1 of the opposing shaft portion 2a. A wedge-shaped seal space S is formed. The seal space S has a buffer function of absorbing the amount of volume change due to the temperature change of the lubricating oil filled in the internal space of the housing 7, and always seals the oil level of the lubricating oil within the range of the assumed temperature change. It is held within the axial range of the space S. Although not shown, the wedge-shaped seal space S has an inner peripheral surface 7b1 of a sealing portion 7b formed in a cylindrical surface shape having a constant diameter and a shaft formed in a tapered surface shape whose diameter gradually decreases upward. It can also be formed by the outer peripheral surface 2a1 of the portion 2a.

The lid member 10 is formed of a metal material such as brass or stainless steel or a resin material in a disk shape, and is fixed to the large-diameter inner peripheral surface 7a2 of the tubular portion 7a of the housing 7. The upper end surface 10a of the lid member 10 has an annular thrust bearing surface, and the thrust bearing surface has a dynamic pressure generating portion for generating a dynamic pressure action on the lubricating oil in the thrust bearing gap of the thrust bearing portion T2. (Thrust dynamic pressure generating portion) C is formed. Although not shown, the thrust dynamic pressure generating portion C is, for example, a spiral-shaped dynamic pressure groove and a convex shape for partitioning the dynamic pressure groove, similarly to the thrust dynamic pressure generating portion B (see FIG. 4) described later. It is composed of hills and hills arranged alternately in the circumferential direction.

The bearing sleeve 8 has a cylindrical shape, and a cylindrical radial bearing surface is provided on the inner peripheral surface 8a at two positions separated in the axial direction. As shown in FIG. 3, the two radial bearing surfaces have dynamic pressure generating portions (radial dynamic pressure generating portions) for generating a dynamic pressure action on the lubricating oil in the radial bearing gaps of the radial bearing portions R1 and R2, respectively. ) A1 and A2 are formed. The radial dynamic pressure generating portions A1 and A2 in the illustrated example are opposite to the plurality of upper dynamic pressure grooves Aa1 which are inclined with respect to the axial direction and are provided apart from each other in the circumferential direction and the upper dynamic pressure grooves Aa1. It is composed of a plurality of lower dynamic pressure grooves Aa2 that are inclined in the direction and are provided apart from each other in the circumferential direction, and a convex hill portion (indicated by cross-hatching in the figure) that divides both dynamic pressure grooves Aa1 and Aa2. The hill is formed in the shape of a herringbone as a whole. That is, the hill portion is composed of an inclined hill portion Ab provided between adjacent dynamic pressure grooves in the circumferential direction and an annular hill portion Ac provided between the upper and lower dynamic pressure grooves Aa1 and Aa2. In the radial dynamic pressure generating portion A1, the upper dynamic pressure groove Aa1 has a larger axial dimension than the lower dynamic pressure groove Aa2, and the axial directions of both dynamic pressure grooves Aa1 and Aa2 constituting the radial dynamic pressure generating portion A2. The dimensions are the same as the axial dimensions of the lower dynamic pressure groove Aa2 of the radial dynamic pressure generating portion A1.

A thrust bearing surface is provided on the lower end surface 8b of the bearing sleeve 8, and as shown in FIG. 4, the thrust bearing surface is used to generate a dynamic pressure action on the lubricating oil in the thrust bearing gap of the thrust bearing portion T1. The dynamic pressure generating portion (thrust dynamic pressure generating portion) B of the above is formed. In the thrust dynamic pressure generating portion B of the illustrated example, a spiral-shaped dynamic pressure groove Ba and a convex hill portion Bb (indicated by cross-hatching in the figure) for partitioning the dynamic pressure groove Ba are alternately arranged in the circumferential direction. It is composed of.

As shown in FIGS. 2 and 3, the upper end surface 8c of the bearing sleeve 8 has an annular groove 8c1 and radial outer and inner ends are opened in the annular groove 8c1 and the upper end inner peripheral chamfer of the bearing sleeve 8, respectively. A radial groove 8c2 is formed. Further, one or more (three in this embodiment) axial grooves 8d1 are formed on the outer peripheral surface 8d of the bearing sleeve 8.

The bearing sleeve 8 having the above configuration is formed of a porous body, here, a porous body of a sintered metal containing copper and iron as main components. That is, the bearing sleeve 8 of the present embodiment is copper formed by heating and sintering a green compact of a raw material powder containing, for example, copper powder (copper powder) and iron powder (iron powder) as main components. It is made of an iron-based sintered body, and here, one having a relative density of 80% or more and less than 90% is used in consideration of oil retention capacity and mechanical strength. The radial dynamic pressure generating portions A1 and A2 provided on the inner peripheral surface 8a of the bearing sleeve 8 are molded at the same time as the sintered body is subjected to dimensional correction processing (sizing). Thrust dynamic pressure generation B provided on the lower end surface 8b of the bearing sleeve 8, annular groove 8c1 and radial groove 8c2 provided on the upper end surface 8c of the bearing sleeve 8, and axial groove 8d1 provided on the outer peripheral surface 8d of the bearing sleeve 8. Is molded at the same time as, for example, compression molding of the green compact or at the same time as sizing the sintered body.

The bearing sleeve 8 is fixed to the inner circumference of the tubular portion 7a of the housing 7 in a state where the upper end surface 8c is in contact with the lower end of the seal portion 7b. More specifically, as shown in FIG. 5, the bearing sleeve 8 is squeezed into the inner circumference of the tubular portion 7a so that the outer peripheral surface 8d of the bearing sleeve 8 and the small diameter inner peripheral surface 7a1 of the tubular portion 7a are opposed to each other. The bearing sleeve 8 is fixed to the inner circumference of the tubular portion 7a by forming a radial gap 11 between the two and curing the adhesive interposed in the radial gap 11. In short, the bearing sleeve 8 is fixed to the inner circumference of the tubular portion 7a of the housing 7 via an adhesive layer 12 (shown by cross-hatching in FIG. 5) formed in the radial gap 11. As the adhesive constituting the adhesive layer 12, a thermosetting adhesive typified by an epoxy resin adhesive is used here. Specific examples of the thermosetting adhesive that can be used include AE-780 manufactured by Ajinomoto Fine-Techno Co., Ltd., which gels (starts curing) at about 90 ° C. and completely cures at about 100 ° C.

As shown in FIGS. 3 and 5, an adhesive layer 12 is formed between the outer peripheral surface 8d of the bearing sleeve 8 facing each other via the radial gap 11 and the small diameter inner peripheral surface 7a1 of the tubular portion 7a of the housing 7. A cylindrical (short cylindrical) non-adhesive portion 13 that does not intervene, that is, a portion in which the bearing sleeve 8 and the tubular portion 7a of the housing 7 are not adhesively fixed over the entire circumference is provided at two upper and lower positions. There is. The non-adhesive portion 13 is composed of an annular recess 14 having a radial dimension larger than the clearance width δ1 of the radial gap 11, and the annular recess 14 is an annular groove having a groove depth δ on the small diameter inner peripheral surface 7a1 of the tubular portion 7a. It is formed by providing 7c. Each annular recess 14 has a cylindrical portion 14a having a constant diameter, and diameter-reduced portions 14b, 14c provided on both sides of the cylindrical portion 14a in the axial direction and gradually reduced in diameter toward the outside in the axial direction. Therefore, the reduced diameter portions 14b and 14c of each annular recess 14 are arranged axially adjacent to the radial gap 11 in which the adhesive layer 12 is formed.

As shown in FIGS. 2 and 3, the non-adhesive portion 13 (annular recess 14) has the maximum fluid dynamic pressure among the radial bearing portions R1 and R2 in which at least a part of the axial direction thereof is composed of a dynamic pressure bearing. It is provided so as to overlap in the axial direction with the maximum pressure generation region V _MAX. As shown in an enlarged view in FIG. 5, the non-adhesive portion 13 of the present embodiment is provided so that the entire _{axial direction overlaps the maximum pressure generation region VMAX} in the axial direction. Maximum pressure generating region V _MAX of the radial bearing portion R1, R2 in this embodiment, respectively, which is a counter area of the annular land portions Ac constituting the radial dynamic pressure generating portions A1, A2. Therefore, as shown in FIG. 5, assuming that the axial dimension (groove width of the annular groove 7c) of the non-adhesive portion 13 (annular recess 14) is L and the axial dimension of the annular hill portion Ac is L1, L ≦ L1. The relational expression is established, and the upper end and the lower end of the non-adhesive portion 13 are located axially inside the upper end and the lower end of the annular hill Ac, respectively (the axis of the annular hill Ac). (To be located within the directional range).

Hereinafter, a method of assembling the fluid dynamic bearing device 1 having the above configuration will be described focusing on a method of adhesively fixing the bearing sleeve 8 to the inner circumference of the housing 7.

First, as shown in FIG. 6A, in the small-diameter inner peripheral surface 7a1 of the housing 7 provided at two locations where the annular grooves 7c are vertically separated from each other, in the region below the lower annular groove 7c. After applying the adhesive (thermosetting adhesive) 12'over the entire circumference, the bearing sleeve 8 is inserted into the inner circumference of the tubular portion 7a via the lower end opening of the housing 7. When the insertion of the bearing sleeve 8 progresses to some extent, the bearing sleeve 8 comes into contact with the adhesive 12', and the adhesive 12'attaches to the vicinity of the outer peripheral edge of the upper end of the bearing sleeve 8. After that, as the insertion of the bearing sleeve 8 progresses, the adhesive 12'adhering to the bearing sleeve 8 moves relative to the rear side in the insertion direction of the bearing sleeve 8, and the outer peripheral surface 8d of the bearing sleeve 8 facing each other and the housing The adhesive 12'is filled in the radial gap 11 between the small diameter inner peripheral surface 7a1 of 7 [see FIGS. 6 (b) and 6 (c) above].

When the upper end outer peripheral edge of the bearing sleeve 8 comes into contact with the adhesive 12'applied to the small diameter inner peripheral surface 7a1 of the housing 7 in the embodiment shown in FIG. 6 (a), a relatively large amount is applied to the upper end outer peripheral edge of the bearing sleeve 8. Adhesive 12'is attached. At this time, if the annular groove 7c does not exist on the front side (upper side) of the bearing sleeve 8 in the insertion direction from the coating portion of the adhesive 12', most of the adhesive 12'attached to the outer peripheral edge of the upper end of the bearing sleeve 8. Moves together with the bearing sleeve 8 to the front side in the insertion direction of the bearing sleeve 8. Therefore, the required amount of the adhesive 12'cannot be interposed in the radial gap 11, and there is a possibility that the desired adhesive strength cannot be secured between the housing 7 and the bearing sleeve 8. Further, the excess adhesive 12'may wrap around the inner circumference of the bearing sleeve 8 via the upper end surface 8c of the bearing sleeve 8 and adversely affect the bearing performance of the radial bearing portion R1.

On the other hand, as described above, the adhesive 12'is previously applied to the small-diameter inner peripheral surface 7a1 on the rear side of the bearing sleeve 8 in the insertion direction (particularly, on the lower side of the lower annular groove 7c) than the annular groove 7c. If it is applied, the adhesive 12'adhered to the vicinity of the outer peripheral edge of the upper end of the bearing sleeve 8 is captured by the annular grooves 7c at the upper and lower positions as the bearing sleeve 8 is inserted, so that the above problems may occur. The sex is reduced as much as possible. Therefore, after the insertion of the bearing sleeve 8 is completed, the adhesive 12'can be interposed in substantially the entire radial gap 11 [axial region indicated by reference numeral Y in FIG. 6 (c)].

As described above, after the assembly in which the bearing sleeve 8 is temporarily fixed to the inner circumference of the housing 7 is manufactured, the adhesive 12'is cured by applying heat treatment to this assembly, and the bearing sleeve 8 is attached to the housing 7. On the other hand, it is adhesively fixed. When the above-mentioned AE-780 manufactured by Ajinomoto Fine-Techno Co., Ltd. is used as the adhesive 12', the heat treatment for the assembly is performed by, for example, the following procedure.
(A) The above assembly is placed in a heating container whose internal temperature is maintained at about room temperature (25 ° C.). (B) The internal temperature of the heating container is gradually raised until the temperature at which the adhesive 12'can be completely cured (about 100 ° C.) is reached.
(C) The temperature inside the container is maintained at about 100 ° C. for a predetermined time.

In step (B) above, as the internal temperature of the heating container rises, the viscosity of the adhesive 12'gradually decreases, and immediately before the internal temperature of the heating container reaches the gelling temperature of the adhesive 12'. At the stage, the viscosity of the adhesive 12'is almost zero. Along with this, the adhesive 12'interspersed in the annular recess 14 formed by the annular groove 7c of the housing 7 is drawn into the radial gap 11 having a relatively small radial dimension by the capillary force, and then cured. In particular, in the present embodiment, the annular recess 14 has diameter-reduced portions 14b and 14c whose diameters are gradually reduced toward the outside in the axial direction, and the diameter-reduced portions 14b and 14c are arranged adjacent to the radial gap 11 in the axial direction. Therefore, as the viscosity of the adhesive 12'decreases, the adhesive 12'intervened in the annular recess 14 (annular groove 7c) is smoothly drawn into the radial gap 11.

As described above, in the embodiment shown in FIGS. 3 and 5, the bearing sleeve 8 is adhesively fixed to the inner circumference of the housing 7, that is, the inner circumference of the housing 7 is provided via the adhesive layer 12 formed in the radial gap 11. The bearing sleeve 8 is fixed to the assembly, and the adhesive layer 12 does not intervene between the small-diameter inner peripheral surface 7a1 of the housing 7 facing each other via the radial gap 11 and the outer peripheral surface 8d of the bearing sleeve 8. An assembly provided with a cylindrical non-adhesive portion 13 is obtained.

Of the assemblies obtained as described above, after inserting the shaft portion 2a of the shaft member 2 into the inner circumference of the bearing sleeve 8, the lid member 10 is attached to the large-diameter inner peripheral surface 7a2 of the tubular portion 7a of the housing 7. Fix it. Specifically, first, the upper end surface 2b1 of the flange portion 2b of the shaft member 2 is brought into contact with the lower end surface 8b of the bearing sleeve 8, and the upper end surface 10a of the lid member 10 is brought into contact with the lower end surface 2b2 of the flange portion 2b. Then, the clearance width of the thrust bearing gaps of the thrust bearing portions T1 and T2 is set to zero. After that, the lid member 10 is moved downward with respect to the housing 7 by moving the shaft member 2 downward by the total amount of the gap widths of the gaps between the two thrust bearings, and the housing 7 and the lid member 10 are fixed at that position. Then, the internal space of the housing 7 is filled with lubricating oil, including the internal pores of the sintered metal bearing sleeve 8, by a method such as so-called vacuum impregnation. With the above, the fluid dynamic bearing device 1 shown in FIG. 2 is completed.

In the hydrodynamic bearing device 1 having the above configuration, when the shaft member 2 and the bearing sleeve 8 rotate relative to each other (the shaft member 2 rotates in the present embodiment), the upper and lower 2 provided on the inner peripheral surface 8a of the bearing sleeve 8 A radial bearing gap is formed between each of the radial bearing surfaces and the outer peripheral surface 2a1 of the shaft portion 2a facing the radial bearing surface. Then, as the shaft member 2 rotates, the pressure of the oil film formed in the gap between both radial bearings is increased by the dynamic pressure action of the radial dynamic pressure generating portions A1 and A2, and the shaft member 2 is supported in the radial direction in a non-contact manner. The bearing portions R1 and R2 are formed so as to be separated from each other in the vertical direction. At the same time, thrust between the thrust bearing surface provided on the lower end surface 8b of the bearing sleeve 8 and the upper end surface 2b1 of the flange portion 2b, and between the upper end surface 10a of the lid member 10 and the lower end surface 2b2 of the flange portion 2b. Bearing gaps are formed respectively. Then, as the shaft member 2 rotates, the pressure of the oil film formed in the gap between the two thrust bearings is increased by the dynamic pressure action of the thrust dynamic pressure generating portions B and C, and the shaft member 2 is moved in one thrust direction and the other thrust direction. Thrust bearing portions T1 and T2 that support non-contact are formed.

When the shaft member 2 rotates, the outer peripheral surface 2a1 of the shaft portion 2a and the inner circumference of the bearing sleeve 8 due to the axial dimensional difference between the upper dynamic pressure groove Aa1 and the lower dynamic pressure groove Aa2 constituting the radial dynamic pressure generating portion A1. Lubricating oil intervening in the radial gap (radial bearing gap of the radial bearing portion R1) between the surface 8a is pushed downward, and the thrust bearing gap of the first thrust bearing portion T1 → the axial groove 8d1 of the bearing sleeve 8. Radial circulation through the path of the axial fluid passage formed → the annular space formed by the upper end outer peripheral chamfer of the bearing sleeve 8 → the fluid passage formed by the annular groove 8c1 and the radial groove 8c2 of the bearing sleeve 8. It is pulled back into the radial bearing gap of the bearing portion R1. As a result, the pressure balance of the lubricating oil that fills the internal space of the housing 7 is maintained, and at the same time, bubbles are generated due to the generation of local negative pressure, leakage of the lubricating oil and vibration due to the generation of bubbles, etc. Can solve the problem.

As described above, in the fluid dynamic bearing device 1 according to the present invention, the small-diameter inner peripheral surface 7a1 and the bearing sleeve 8 of the housing 7 facing each other through the radial gap 11 in which the adhesive layer 12 is formed are formed. A cylindrical (short cylindrical) non-adhesive portion 13 in which the adhesive layer 12 does not intervene is provided between the outer peripheral surface 8d and the outer peripheral surface 8d. If such a non-adhesive portion 13 is provided, the adhesive layer 12 is provided in the cylindrical region of the inner peripheral surface 8a (radial bearing surface) of the bearing sleeve 8 that overlaps the non-adhesive portion 13 in the axial direction. The influence of expansion and contraction of the bearing becomes difficult. Therefore, at least a part of the non-adhesive portion 13 in the axial direction (in the present embodiment, the entire axial direction) should be provided so as to overlap _{the maximum pressure generation region V MAX of the radial bearing portions R1 and R2 in the axial direction.} For example, in at least a part of the maximum pressure generation region V _MAX , the clearance width accuracy of the radial bearing gaps of the radial bearing portions R1 and R2 is less likely to fluctuate. This makes it possible to effectively improve the bearing performance of the radial bearing portions R1 and R2.

As described above, the bearing performance of the radial bearing portions R1 and R2 is affected by the clearance width accuracy of the radial bearing gap. Therefore, in order to improve the bearing performance of the radial bearing portions R1 and R2, the axial direction of the non-adhesive portion 13 It is also considered advantageous to expand the formation range (axial dimension L: see FIG. 5). However, as the axial formation range of the non-adhesive portion 13 is expanded, the axial formation range of the adhesive layer 12 is reduced, so that the adhesive strength of the bearing sleeve 8 to the housing 7 is likely to be weakened. In particular, as described above, when the bearing sleeve 8 made of sintered metal having a relative density of 80% or more and less than 90% is used, in the process of forming the adhesive layer 12, adhesion is interposed in the radial gap 11. The agent 12'is easily sucked into the internal pores of the bearing sleeve 8 by the capillary force. Therefore, if the axial formation range of the non-adhesive portion 13 is unnecessarily expanded, it becomes impossible to secure a desired adhesive strength between the housing 7 and the bearing sleeve 8. When the desired adhesive strength is not secured between the housing 7 and the bearing sleeve 8, for example, when a large impact load is applied to the hydrodynamic bearing device 1, the position of the bearing sleeve 8 relative to the housing 7 or the like is changed. The deviation occurs, and the bearing performance of the hydrodynamic bearing device 1 deteriorates.

If the bearing sleeve 8 is formed of a non-porous material such as brass, it is possible to prevent a decrease in adhesive strength due to suction of the adhesive 12', and thus the axial formation range of the non-adhesive portion 13 is expanded. be able to. However, since the bearing sleeve 8 made of sintered metal can hold the lubricating oil in the internal pores, the oil film runs out in the radial bearing gaps of the radial bearing portions R1 and R2 and the thrust bearing gap of the thrust bearing portion T1. It is advantageous in preventing the above as much as possible and making it possible to stably exhibit the bearing performance of the radial bearing portions R1 and R2 and the thrust bearing portion T1.

Therefore, in order to expand the axial formation range of the non-adhesive portion 13 without impairing the above-mentioned action and effect that can be enjoyed when the bearing sleeve 8 is formed of sintered metal, for example, the relative density is 90%. It is effective to use the bearing sleeve 8 made of the above-enhanced high-density sintered metal. However, if the relative density of the bearing sleeve 8 is increased too much, the amount of oil retained in the internal pores of the bearing sleeve 8 decreases, which may impair the effect of preventing the oil film from running out in the bearing gap. Therefore, the relative density of the sintered bearing sleeve 8 is preferably 95% or less.

FIG. 7 (a) is a partially enlarged cross-sectional view of an assembly in which a bearing sleeve 8 made of a sintered metal (copper iron-based sintered metal) having a relative density increased to 90% or more is fixed to the inner circumference of the housing 7. ). The bearing sleeve 8 shown in the figure has the relative density increased to 90% or more, and at least has a sealing portion 15 for sealing the surface opening of the outer peripheral surface 8d. The configuration is different from that of the sleeve 8. The sealing portion 15 can also be formed by impregnating and curing a sealing material such as a resin material in the internal pores of the surface layer portion of the bearing sleeve 8, but in the present embodiment, the sealing portion 15 (with the base material of the bearing sleeve 8) is formed. A sealed body 15 is formed by subjecting a sintered body to a sizing process as a plastic working process.

That is, although detailed illustration is omitted, the sealing portion 15 is formed by using a sizing mold having a shaft-shaped core, a cylindrical die, and upper and lower punches coaxially arranged so as to be relatively movable in the axial direction. can do. Specifically, first, the bearing sleeve 8 is placed on the upper end surface of the lower punch, then the core is lowered, and the core is inserted (gap-fitted) into the inner circumference of the bearing sleeve 8. Next, the upper punch is moved downward, the bearing sleeve 8 is sandwiched in the axial direction by the upper and lower punches, and then the core, the upper punch, and the lower punch are integrally lowered to press-fit the bearing sleeve 8 into the inner circumference of the die. The press-fitting allowance of the outer peripheral surface 8d of the bearing sleeve 8 with respect to the inner peripheral surface of the die is changed according to the size of the bearing sleeve 8. For example, the wall thickness in the radial direction (between the inner peripheral surface 8a and the outer peripheral surface 8d). In the case of a bearing sleeve 8 having a diameter difference of 2 mm or less, the diameter difference is 100 μm or more.

When the bearing sleeve 8 is press-fitted into the inner circumference of the die and then the upper punch is further lowered to compress the bearing sleeve 8 in the axial direction, the bearing sleeve 8 expands and deforms in the radial direction, and the outer peripheral surface 8d of the bearing sleeve 8 becomes the die. It is strongly pressed against the inner peripheral surface of. As a result, the outer diameter side surface layer portion (particularly the outer peripheral surface 8d) of the bearing sleeve 8 is plastically deformed, and a sealing portion 15 for sealing the surface opening of the outer peripheral surface 8d is formed. When the bearing sleeve 8 is made of a copper-iron-based sintered metal as in the present embodiment, the sealing portion 15 has an Fe structure and a Cu structure of the bearing sleeve 8 as schematically shown in FIG. 7 (b). Of these, it is mainly formed by partially plastically deforming a relatively soft Cu structure. Therefore, as shown in the figure, the sealing portion 15 formed in the bearing sleeve 8 by subjecting the bearing sleeve 8 to a sizing process has a deformed portion 16 in which a part of the Cu structure is plastically deformed.

Use a bearing sleeve 8 made of a sintered metal (copper-iron-based sintered metal) having a relative density increased to 90% or more and having a sealing portion 15 for sealing the surface opening of the outer peripheral surface 8d. As a result, it becomes difficult for the adhesive 12'to be sucked into the internal pores of the bearing sleeve 8 in the process of forming the adhesive layer 12. Therefore, as shown in FIG. 7A, the forming range (axis) of the non-adhesive portion 13 in the axial direction. Even if the directional dimension L) is enlarged, the adhesive strength of the bearing sleeve 8 to the housing 7 can be increased. In the illustrated example, the relational expression of L> L1 is satisfied, and the upper end portion and the lower end portion of the non-adhesive portion 13 (annular recess 14) are the upper end portions of the annular hill portion Ac of the radial dynamic pressure generating portion A1 (A2), respectively. The non-adhesive portion 13 is provided so as to be located on the outer side in the axial direction from the lower end portion. Although it is possible to increase the adhesive strength of the bearing sleeve 8 to the housing 7 (adhesive strength per unit area) by adopting the bearing sleeve 8 having the above configuration, the axial dimension L of the non-adhesive portion 13 can be increased. If it is expanded excessively, the adhesive strength of the bearing sleeve 8 to the housing 7 will rather decrease. Therefore, it is preferable that the axial dimension L of the non-adhesive portion 13 is less than 6 times (L <6L1) the axial dimension L1 of the annular hill portion Ac.

Although the fluid dynamic bearing device 1 according to the first embodiment of the present invention has been described above, the fluid dynamic bearing device to which the present invention can be applied is not limited to the above embodiment. Hereinafter, the fluid dynamic pressure bearing device according to another embodiment to which the present invention can be applied will be described with reference to the drawings, but for simplification of the description, the configuration common to the above-mentioned fluid dynamic pressure bearing device 1 will be described. Omits a detailed description.

FIG. 8 shows the fluid dynamic bearing device 21 according to the second embodiment of the present invention. The main difference between the fluid dynamic bearing device 21 and the fluid dynamic bearing device 1 shown in FIG. 2 and the like is that the housing includes a cylindrical tubular portion 7a and a bottom portion 7d (lid) that closes the lower end opening of the tubular portion 7a. The point that the bottomed cylindrical housing 17 integrally provided with the member 10) and the seal portion 9 forming the seal space S on the inner peripheral surface 9a are separate members from the housing 17. The point is that the housing 17 is fixed to the inner circumference of the upper end portion by an appropriate means such as press fitting or bonding. Therefore, the thrust bearing gap of the thrust bearing portion T2 made of the dynamic pressure bearing is formed between the lower end surface 2b2 of the flange portion 2b and the upper end surface 17d1 of the bottom portion 17d of the housing 17.

FIG. 9 shows the fluid dynamic bearing device 31 according to the third embodiment of the present invention. The main difference between the fluid dynamic bearing device 31 and the fluid dynamic bearing device 1 shown in FIG. 2 and the like is.
-As a housing, a cylindrical tubular portion 7a in which a bearing sleeve 8 is gap-bonded to the inner circumference, and a large-diameter tubular portion 7e whose inner diameter and outer diameter dimensions are larger than the inner diameter and outer diameter dimensions of the cylinder 7a, respectively. The point that the housing 27 provided integrally with and is used,
A sealing member 19 having an inverted L-shaped cross section integrally having a disk portion 19a and a cylindrical portion 19b is fixed to the upper end of the bearing sleeve 8, and the tapered inner peripheral surface 19a1 of the disk portion 19a and the cylindrical outer peripheral surface of the shaft portion 2a are fixed. A wedge-shaped first seal space S1 whose diameter is gradually reduced downward is formed between 2a1 and the cylindrical outer peripheral surface 19b2 of the cylindrical portion 19b and the tapered inner peripheral surface of the large-diameter tubular portion 7e of the housing 27. A point forming a wedge-shaped second seal space S2 with a diameter gradually reduced downward with 7e1.
And so on.

Both the first seal space S1 and the second seal space S2 hold the oil level of the lubricating oil, and both the seal spaces S1 and S2 are formed by the radial groove 19a3 provided on the lower end surface 19a2 of the disk portion 19a. Through the fluid passage formed by the fluid passage, the fluid passage formed by the axial groove 8d1 provided on the outer peripheral surface 8d of the bearing sleeve 8, and the axial gap between the lower end surface of the cylindrical portion 19b and the stepped surface 7a4 of the housing 27. Communicate with each other.

Further, in the fluid dynamic bearing device 31 of the present embodiment, only a part of the axial direction of the outer peripheral surface 8d of the bearing sleeve 8 is gap-bonded to the small-diameter inner peripheral surface 7a1 of the tubular portion 7a of the housing 27 (both sides 8d, 7a1). It is fixed via the adhesive layer 12 formed in the radial gap 11 between them). Therefore, of the inner peripheral surface 8a of the bearing sleeve 8, the accuracy of the axial region P in which the outer peripheral surface 8d of the bearing sleeve 8 is not fixed to the small diameter inner peripheral surface 7a1 of the tubular portion 7a is such that the bearing sleeve 8 is the housing 7. It does not change even if it is fixed to the inner circumference of. In particular, in the form of illustrated example, the axial region P described above, since the axial substantially entire region of the maximum pressure generation region V _MAX of the radial bearing portion R1 are overlapped in the axial direction, of the radial bearing portion R1 The bearing performance is not significantly affected by the fixing mode of the housing 7 and the bearing sleeve 8. Accordingly, in the present embodiment, the non-adhesive portion 13 is provided so as to overlap at a maximum pressure generation region V _MAX and the axial direction of the radial bearing portion R2.

In the present embodiment, only a part of the outer peripheral surface 8d of the bearing sleeve 8 in the axial direction is adhesively fixed to the inner peripheral surface of the housing. Therefore, assuming that the bearing sleeve 8 having the same axial dimensions is used, the bearing sleeve The adhesive strength of the bearing sleeve 8 to the housing is lower than that in the case where the entire axial direction of the outer peripheral surface 8d of 8 is adhesively fixed to the inner peripheral surface of the housing (for example, FIG. 2). Therefore, in the present embodiment, as shown in the enlarged view of FIG. 8, a large-diameter inner peripheral surface 7f having a diameter larger than that of the small-diameter inner peripheral surface 7a1 is provided at the upper end of the small-diameter inner peripheral surface 7a1 of the tubular portion 7a. An adhesive layer 12 having a larger radial wall thickness than the adhesive layer 12 formed in the radial gap 11 is formed between the large-diameter inner peripheral surface 7f and the outer peripheral surface 8d of the bearing sleeve 8. The part that was done) is provided.

The fluid dynamic bearing devices 1, 21, 31 according to the embodiment of the present invention have been described above, but these fluid dynamic bearing devices can be appropriately modified without departing from the gist of the present invention. Is.

For example, as shown in FIG. 10A, the annular recess 14 constituting the non-adhesive portion 13 is provided with an annular groove 7c having a groove bottom shape having a V-shaped cross section on the small diameter inner peripheral surface 7a1 of the housing 7. In addition to being formed, as shown in FIG. 10B, it can also be formed by providing an annular groove 7c in which a part of the bottom surface of the groove has an arcuate surface shape on the small diameter inner peripheral surface 7a1 of the housing 7. In the case of the form shown in FIG. 10A, the annular recess 14 is composed of only the reduced diameter portions 14b and 14c without the cylindrical portion 14a being omitted. Further, in the above embodiment, the non-adhesive portion 13 (annular recess 14) is formed by providing the annular groove 7c on the inner peripheral surface 7a1 of the housing 7, but the non-adhesive portion 13 has a radial gap. It can be formed by providing an annular groove on the outer peripheral surface 8d of the bearing sleeve 8 facing the inner peripheral surface 7a1 of the housing 7 via 11, and also the inner peripheral surface of the housing 7 facing through the radial gap 11. It can also be formed by providing an annular groove on both the outer peripheral surface 8d of the 7a1 and the bearing sleeve 8.

Further, in the above embodiment, a heat-curable adhesive is used as the adhesive 12'for adhering and fixing the bearing sleeve 8 to the inner circumference of the housing (gap adhesion), but the present invention uses the heat-curable adhesive. It can also be preferably applied to a hydrodynamic bearing device in which the bearing sleeve 8 is adhesively fixed to the inner circumference of the housing by using an adhesive other than the above, for example, an anaerobic adhesive. However, in the case of a thermosetting adhesive, since the viscosity drops once in the process of curing the adhesive, between the inner peripheral surface of the housing and the outer peripheral surface of the bearing sleeve 8 facing each other via the radial gap 11. There is an advantage that the desired adhesive layer 12 and the non-adhesive portion 13 can be easily formed.

Further, in the above embodiments, the bearing sleeve 8 made of a porous body of a copper-iron-based sintered metal is used, but the present invention relates to other sintered metals containing copper (for example, copper-sintered steel-based). When using a bearing sleeve 8 made of a sintered metal or a copper-iron-sintered steel-based sintered metal, or a bearing sleeve 8 made of a porous body other than the sintered metal, for example, a porous resin. Can also be preferably applied when using. The present invention can also be applied to the case where a bearing sleeve 8 made of a non-porous material such as a soft metal such as brass or a resin material is used.

Further, the shapes of the radial dynamic pressure generating portions A1 and A2 are not limited to those shown above, and of course, they are appropriately changed according to the required characteristics and the like. Further, the radial dynamic pressure generating portions A1 and A2 may be provided on the outer peripheral surface 2a1 of the shaft portion 2a facing the inner peripheral surface 8a of the bearing sleeve 8.

Further, the present invention includes not only a fluid dynamic bearing device in which the shaft member 2 is on the rotating side and the bearing sleeve 8 is on the stationary side, but also a fluid dynamic bearing device in which the shaft member 2 is on the stationary side and the bearing sleeve 8 is on the rotating side. It can also be preferably applied to.

Further, the present invention can be preferably applied to a rotor having blades for blowing air, or a fluid dynamic bearing device in which a polygon mirror is provided on the shaft member 2. That is, the present invention is a fluid incorporated not only in the spindle motor for the disk drive shown in FIG. 1, but also in other motors for electric devices such as fan motors for PCs and polygon scanner motors for laser beam printers (LBPs). It can also be preferably applied to a hydraulic bearing device.

In order to demonstrate the usefulness of the present invention, two types of confirmation tests (first and second confirmation tests) described below were carried out.

[First confirmation test]
In the first confirmation test, there are three types in which the inner peripheral surface shape, specifically, the groove width (axial dimension of the annular recess 14) L and the groove depth δ (see FIG. 5) of the annular groove 7c are different from each other. Ten housings (here, the housing 27 shown in FIG. 8) were prepared. Next, a bearing sleeve 8 in which the radial dynamic pressure generating portions A1 and A2 shown in FIG. 3 are formed on the inner peripheral surface of each housing by using the thermosetting adhesive AE-780 manufactured by Ajinomoto Fine-Techno. Was gap-bonded in the manner shown in FIG. and,
(A) Amount of change in inner diameter dimension of the bearing sleeve before and after bonding (more specifically, amount of change in inner diameter dimension in the formation region of the annular hill portion Ac constituting the radial dynamic pressure generating portion A2).
(B) The adhesive strength of the bearing sleeve to the housing was confirmed. The above adhesive strength was evaluated by an axial load (pulling force) when an axial load was applied to the bearing sleeve and the adhesive layer was broken (the bearing sleeve fell off from the housing).

The three types of housings (first to third housings) and bearing sleeves prepared for carrying out the first confirmation test are as follows.
・ First housing: No annular groove (L = 0 mm, δ = 0 mm)
-Second housing: L = 1 mm, δ = 0.05 mm
-Third housing: L = 2.5 mm, δ = 0.05 mm
-Bearing sleeve: Axial dimension L1 of annular hill Ac (see FIG. 3) = 0.6 mm
-Gap width δ1 (see FIG. 5) of the radial gap formed between the inner peripheral surface of the housing and the outer peripheral surface of the bearing sleeve = 0.005 mm

The confirmation results of the above (a) and (b) are shown in FIGS. 11 and 12, respectively. “Sample 1” to “Sample 3” in FIGS. 11 and 12 are assemblies formed by adhering the bearing sleeves to the inner circumferences of the first to third housings, respectively.

As shown in FIG. 11, the inner diameter dimension of the bearing sleeve (inner diameter dimension in the formation region of the annular hill Ac) is reduced by about 1.05 μm on average in sample 1, and is reduced by 0.4 μm on average in sample 2, and is also reduced. In sample 3, it increased by about 0.15 μm on average. From this confirmation result, it can be seen that the absolute value of the amount of change in the inner diameter dimension of the bearing sleeve becomes smaller as the groove width L of the annular groove becomes larger. Therefore, in order to improve the accuracy of the inner peripheral surface of the bearing sleeve 8 (particularly the accuracy of the radial bearing surface), as shown in FIG. 5, the outer peripheral surface 8d of the bearing sleeve 8 and the housing facing each other through the radial gap 11 and the housing. It is advantageous to provide an annular non-adhesive portion 13 in which the adhesive layer 12 does not intervene between the inner peripheral surface 7a1 of 7 and further, it is further advantageous to expand the axial dimension of the non-adhesive portion 13. It can be said that.

On the other hand, as shown in FIG. 12, the adhesive strength of the bearing sleeve to the housing decreases as the axial dimension of the annular groove 7c (non-adhesive portion 13) increases, and the decrease in adhesive strength is particularly remarkable in Sample 3. rice field.

From the above, in reality, the axial dimensions of the non-adhesive portion may be determined according to the required adhesive strength, etc., but in order to improve the bearing performance of the radial bearing portion, the non-adhesive portion should be radial. It can be said that it is preferable to provide the bearing portion so as to overlap with the maximum pressure generation region (the entire axial direction) in the axial direction.

[Second confirmation test]
In the second confirmation test, the relative density of the bearing sleeve made of a porous body and the presence or absence of a sealing portion for sealing the surface opening of the outer peripheral surface of the bearing sleeve determine the adhesive strength between the housing and the bearing sleeve. It was confirmed whether it would affect the degree. Specifically, the adhesive strength (average value of 10 samples) when the bearing sleeve having the following configurations (1) and (2) is gap-bonded to the inner circumference of the copper housing shown in FIG. confirmed. The adhesive used to fix the two is a thermosetting adhesive AE-780 manufactured by Ajinomoto Fine-Techno Co., Ltd., as in the first confirmation test.
(1) A bearing sleeve made of a copper-iron-based sintered metal having a relative density of 80% or more and less than 90% (87%) and having no sealing portion on the outer peripheral surface (see FIG. 5).
(2) A bearing sleeve made of a copper-iron-based sintered metal having a relative density of 90% or more (93%) and having a sealing portion on the outer peripheral surface [see FIG. 7 (a)].

When the bearing sleeve 8 of the above (1) was used, the average value of the pulling force was 985N, whereas when the bearing sleeve 8 of the above (2) was used, the average value of the pulling force was 3202N. ..

From the above, when using a bearing sleeve made of a porous body, it is necessary to increase the relative density of the bearing sleeve (use a high-density bearing sleeve) and to provide a sealing portion on the outer peripheral surface of the bearing sleeve for the housing. It can be said that it is preferable for increasing the adhesive strength of the bearing sleeve and realizing a highly reliable hydrodynamic bearing device.

1 Fluid dynamic bearing device 2 Shaft member 7 Housing 7a Cylindrical part 7a1 Small diameter Inner peripheral surface 7c Circular groove 8 Bearing sleeve 8d Outer peripheral surface 11 Radial gap 12 Adhesive layer 12'Adhesive 13 Non-adhesive part 14 Annular recess 14b Reduced diameter Part 14c Reduced diameter part 15 Sealed part A1, A2 Radial dynamic pressure generating part Ac Circular hill part L Axial dimension of non-adhesive part (annular recess) L1 Axial dimension of annular hill R1, R2 Radial bearing part T Thrust bearing Part V _MAX Maximum pressure generation region δ Groove depth of annular groove δ1 Gap width of radial gap

Claims (7)

A bearing sleeve having a radial bearing surface forming a radial bearing gap between the inner peripheral surface and the outer peripheral surface of a shaft member to be supported, a housing in which the bearing sleeve is fixed to the inner circumference, and a fluid generated in the radial bearing gap. The shaft member and the bearing sleeve are provided with a radial bearing portion that rotatably and non-contactly supports the bearing sleeve in the radial direction by the dynamic pressure action of the bearing sleeve, and the bearing sleeve is provided between the outer peripheral surface thereof and the inner peripheral surface of the housing. In a hydrodynamic bearing device fixed to the inner circumference of the housing via an adhesive layer formed in a radial gap,
A cylindrical non-adhesive portion is provided between the inner peripheral surface of the housing facing each other via the radial gap and the outer peripheral surface of the bearing sleeve without the adhesive layer intervening, and the non-adhesive portion is the non-adhesive portion thereof. The axial length is substantially equal to the axial length of the maximum pressure generating region where the fluid dynamic pressure is maximum in the radial bearing portion, and is provided at substantially the same position as the maximum pressure generating region in the axial direction. A hydrodynamic bearing device characterized by the above. The fluid dynamic bearing device according to claim 1 , wherein the bearing sleeve is made of a porous body having a relative density of 80% or more and less than 90%. The fluid dynamic bearing device according to claim 1 or 2 , wherein the bearing sleeve is made of a porous body of a sintered metal containing copper. The fluid dynamic bearing device according to any one of claims 1 to 3 , wherein the non-adhesive portion is formed of a tubular recess having a radial dimension larger than the clearance width of the radial gap. The fluid dynamic pressure according to claim 4 , wherein the tubular recess has a reduced diameter portion whose diameter is gradually reduced toward the outside in the axial direction, and the reduced diameter portion is arranged adjacent to the radial gap in the axial direction. Bearing device. The fluid dynamic bearing device according to any one of claims 1 to 5 , wherein the adhesive layer is formed of a thermosetting adhesive. A motor having the fluid dynamic bearing device according to any one of claims 1 to 6, a rotor magnet, and a stator coil.

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