JP5155705B2 - Fluid dynamic bearing device, spindle motor, and fluid dynamic bearing device manufacturing method - Google Patents

Description

  The present invention relates to a fluid dynamic bearing device that can suppress variation in performance.

  In the fluid dynamic pressure bearing device, a configuration is known in which a groove (dynamic pressure groove) for generating dynamic pressure is provided on the shaft member or the bearing member side. This technique is described in Patent Documents 1 to 5, for example.

Japanese Utility Model Publication No. 62-63415 (FIG. 1) JP-A-4-285111 (Abstract) Japanese Patent Laid-Open No. 61-127918 (FIG. 9) JP-A-10-141358 (abstract) Japanese Patent No. 3150878 (FIGS. 4, 5, and 8)

  By the way, due to the relative movement between the shaft member and the bearing member, a sudden negative pressure state is generated in the lubricating fluid, thereby generating bubbles in the lubricating fluid (this phenomenon is called cavitation). There are things to do. When bubbles are generated in the lubricating fluid, leakage of the lubricating fluid to the outside, a decrease in dynamic pressure generation effect, and vibration occur. For this reason, the structure which suppresses this cavitation becomes important. In order to suppress cavitation, the dynamic pressure groove is bent into a shape like a so-called herringbone dynamic pressure groove, and the end of the bent dynamic pressure groove is opened to a larger gap space. Is effective. In this specification, the dynamic pressure groove having such a structure is referred to as a breakthrough herringbone dynamic pressure groove.

  However, when the conventional breakthrough / herringbone dynamic pressure groove is used, as shown in FIG. 9, in which the end of the herringbone dynamic pressure groove is simply extended to a large gap space, it corresponds to the gap and the enlarged gap. From the bending point of the breakthrough herringbone dynamic pressure groove due to the processing error when processing the shape to the inner peripheral surface of the bearing member or the outer peripheral surface of the shaft member and the processing error when forming the dynamic pressure groove As a result, the dimension to the end varies, and as a result, the performance of the hydrodynamic bearing device varies. Hereinafter, this point will be described in detail. The formation of the dynamic pressure groove is preferably performed by electrolytic processing (Electro Chemical Machining) from the viewpoint of ease of processing, low cost, and reduction of processing waste.

Hereinafter, this problem will be described by taking as an example the case where the above breakthrough / herringbone dynamic pressure groove is formed on the inner peripheral surface of the bearing member by electrolytic processing. The following factors can be considered as factors that cause variations in the dimension from the bending point to the end of the breakthrough herringbone dynamic pressure groove.
1) Variation in axial dimension of member shape forming gap and enlarged gap 2) Variation in axial dimension of electrode tool for forming dynamic pressure groove by electrolytic processing 3) Position of electrode tool in axial direction Axial variation in the hydrodynamic groove forming position caused by minute foreign matter or the like biting between the end face of the electrode tool and the end face of the bearing member, which is the reference position for positioning.

  As a result of the occurrence of the above factors alone or in duplicate, a gap is formed so as to be continuous with the enlarged gap portion with respect to the gap portion and the enlarged gap portion formed between the inner peripheral surface of the bearing member and the outer peripheral surface of the shaft portion. The position of the dynamic pressure groove formed in the portion shifts in the axial direction, and the axial dimension from the bending point to the end of the breakthrough herringbone dynamic pressure groove varies.

  In addition, the occurrence of the axial displacement described above causes a flow of lubricating fluid that is not intended in the original design, which causes variations in shaft rigidity, rotational torque, etc. The problem of performance variation arises.

  That is, in the invention described in Patent Document 1, due to the processing accuracy, if the relative positional relationship between the shaft member and the bearing member is shifted in the axial direction, the gap between the facing surface where no groove is formed is formed. The opposing area of the narrowed portion changes. This is a factor that increases the bearing resistance. That is, the invention described in Patent Document 1 cannot solve the problem of increased bearing resistance due to machining accuracy.

  In the invention described in Patent Document 2, since one end of the dynamic pressure groove is closed, the effect of preventing the generation of bubbles due to axial vibration or the like is poor. In the invention described in Patent Document 3, when an axial dimension error occurs, the end of the dynamic pressure groove is not opened in one axial direction, and the effect of suppressing the generation of bubbles is reduced. That is, there is a possibility that bubbles are likely to be generated due to dimensional errors. Further, when the end portion of the dynamic pressure groove is not opened, a narrow gap is formed between the shaft member and the bearing member, so that the bearing resistance increases.

  In the invention described in Patent Document 4, redundancy is secured in the formation position of the dynamic pressure groove, but when the formation position is shifted in the axial direction, the end of the dynamic pressure groove is continuous with the expanded diameter region. It is no longer the structure. For this reason, the structure which suppresses generation | occurrence | production of the bubble which arises at the time of a vibration etc. originates in the formation error of a dynamic-pressure groove | channel easily.

  Patent Document 5 describes a structure in which a dynamic pressure groove is continuous with an oil reservoir having a larger gap. However, as shown in FIG. 8 of the document, since the edge of the oil reservoir is adjacent to the narrow gap portion, if there is an error in the formation position of the groove portion constituting the oil reservoir, The width of the narrow part changes. That is, in this structure, the width of the narrow gap portion is likely to vary from product to product. On the other hand, this narrow gap portion has a great influence on the frictional force acting between the shaft member and the bearing member. Therefore, when the technique described in Patent Document 5 is adopted, the frictional resistance of the bearing tends to vary from product to product.

  In the technical background as described above, the present invention is a fluid dynamic pressure bearing device in which it is difficult for the disadvantage that the action of the dynamic pressure groove is hindered due to errors in machining accuracy, and further, variation in bearing resistance is difficult to occur. For the purpose of provision.

The invention according to claim 1 is a bearing member, a shaft member mounted on the bearing member in a relatively rotatable state, a lid member that closes one end side of the bearing member, the bearing member, and the shaft member. A lubricating fluid continuously filled in a gap between the bearing member or the shaft member, a pair of annular grooves formed at positions separated in the axial direction of the shaft member, and a member formed with the pair of annular grooves And each of the pair of annular grooves extends in the axial direction in the state having the same depth as the dynamic pressure groove, and includes a bent dynamic pressure groove that connects the pair of annular grooves. A fluid dynamic pressure bearing characterized in that it is continuous with an enlarged gap portion having a gap larger than a gap between an inner peripheral surface of the bearing member and an outer peripheral surface of the shaft member in a portion where a dynamic pressure groove is formed. Device.

  According to the first aspect of the present invention, in the structure including the dynamic pressure groove having the bent pattern that connects the pair of annular grooves separated in the axial direction, the outer edge of each annular groove, that is, the annular grooves are separated from each other. The edge portion located on the direction side is continuous with a portion (enlarged gap portion) where the interval between the bearing member / shaft member is wider than the portion of the dynamic pressure groove.

  According to this structure, since both ends of the dynamic pressure groove are connected to the two annular grooves and the ends thereof are opened, even if a relative movement between the bearing member and the shaft member suddenly occurs, the lubricating fluid The occurrence of a sudden negative pressure state in the inside is suppressed. For this reason, generation | occurrence | production of the bubble resulting from generation | occurrence | production of this negative pressure state is suppressed. Further, even if the position of the groove in the axial direction is shifted due to the processing accuracy when forming the dynamic pressure groove and the annular groove, the structure in which both ends of the dynamic pressure groove are connected to the two annular grooves is maintained. The axial dimension from the bend to the end of the groove is also maintained. For this reason, even if the position shift due to processing accuracy occurs, the function of suppressing the generation of the above-described bubbles is maintained.

  Further, according to this structure, the two annular grooves formed at the positions sandwiching the portion where the dynamic pressure groove is formed are larger than the dimension of the annular groove on the outer side in the axial direction (between the shaft member and the bearing member). The dimension of the gap) is continuous with the enlarged gap. For this reason, even if the position of the groove in the axial direction is shifted when forming the dynamic pressure groove and the annular groove, an unintended narrow gap is prevented from being formed between the inner periphery of the bearing member and the outer periphery of the shaft member. The That is, in the portion where the dynamic pressure groove is formed, when viewed along the circumference of the inner peripheral surface, the groove portion and the hill portion are alternately formed, and between the surface of the groove portion and the outer peripheral surface of the shaft member. If the gap between the surface of the hill portion and the outer peripheral surface of the shaft member is narrower than the gap of the shaft, and if such a narrow gap is formed at an unintended position due to the displacement of the dynamic pressure groove in the axial direction, the bearing Although the performance is impaired, such a problem can be avoided by connecting the pair of annular grooves with bent dynamic pressure grooves. In addition, since the bearing resistance is large in such a narrow gap, the rotational torque of the dynamic pressure bearing is increased, resulting in an increase in the power consumption of the spindle motor. Therefore, the narrow gap is formed as much as possible in the portion where no dynamic pressure is generated. It is preferable to use a structure that does not. By providing annular grooves at both ends of the dynamic pressure groove, a narrow gap (hill surface that does not generate dynamic pressure between the end of the dynamic pressure groove and the enlarged gap part over the entire circumference corresponding to the annular groove. And the outer peripheral surface of the shaft member are not formed, so that the rotational torque is reduced as compared with the conventional structure having no pair of annular grooves. In addition, a structure in which the end of the herringbone dynamic pressure groove is opened to a gap space with a larger interval is reliably ensured, and furthermore, due to a sudden relative movement between the shaft member and the bearing member due to impact, vibration, etc. Thus, it is possible to prevent a sudden negative pressure state from being generated in the lubricating fluid, and thereby bubbles from being generated in the lubricating fluid.

  In the first aspect of the present invention, the dynamic pressure groove and the annular groove may be provided on the shaft member side or on the bearing member side. In addition, the shape for constituting the enlarged gap portion is provided on the member side where the dynamic pressure groove and the annular groove are formed.

  The invention described in claim 2 is characterized in that, in the invention described in claim 1, the enlarged gap portion is constituted by a chamfered portion, a seal portion, a recess portion, or an undercut portion. According to the second aspect of the present invention, the enlarged gap portion is configured by using a portion existing in the conventional structure. For this reason, an increase in cost and an increase in size can be avoided.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the dynamic pressure groove has an asymmetric pattern in the axial direction with the bent portion as a boundary. By adopting an asymmetric pattern in the axial direction with the bent part as the boundary as the dynamic pressure groove, it is possible to effectively pressurize the lubricating fluid in the bearing device, the position accuracy of the dynamic pressure groove, the inner circumference of the bearing member It is possible to prevent negative pressure that may be generated due to deterioration of the dimensional accuracy of the surface.

  According to the invention described in claim 4, in the invention described in any one of claims 1 to 3, the dynamic pressure groove includes a pair of annular conductive portions and a bent conductive portion connecting the pair of annular conductive portions. It is formed simultaneously by the electrolytic processing using the electrode tool formed integrally. Electrolytic machining is advantageous in that it can be easily processed into a bearing member having an opening diameter, the machining cost is low, and machining waste is not generated. According to the invention described in claim 4, since the advantage of such electrolytic processing can be obtained, and the annular groove and the dynamic pressure groove are simultaneously formed with the same electrode tool, the annular groove and the dynamic pressure groove are formed. Even if the groove formation position shifts in the axial direction sometimes, the axial dimension from the bending point of the dynamic pressure groove to the end continuous with the annular groove does not change, so that variation in the performance of the fluid dynamic bearing device can be prevented. .

  The invention according to claim 5 is characterized in that, in the invention according to any one of claims 1 to 4, a pair of annular grooves is formed at a position partially overlapping with the enlarged gap portion. According to the fifth aspect of the present invention, even if the position of the annular groove in the axial direction is shifted due to processing accuracy, an overlap margin is secured, so the annular groove is continuous with the enlarged gap portion. The structure is preserved. Therefore, it is possible to avoid an inconvenience that an unintended narrow gap is formed between the outer peripheral surface of the shaft member and the inner peripheral surface of the bearing member due to this positional deviation. Further, when the annular groove and the dynamic pressure groove are formed simultaneously with the same electrode tool, even if the groove formation position shifts in the axial direction when forming the annular groove and the dynamic pressure groove, the annular groove overlaps the enlarged gap portion. Since the axial dimension from the bending point of the dynamic pressure groove to the end continuous with the annular groove does not change only by changing the width, it is possible to prevent variations in the performance of the fluid dynamic pressure bearing device.

  A sixth aspect of the present invention is a spindle motor using the fluid dynamic pressure bearing device according to any one of the first to fifth aspects.

The invention according to claim 7 is a bearing member, a shaft member mounted on the bearing member in a relatively rotatable state, a lid member closing one end side of the bearing member, the bearing member, and the shaft member. and a lubricating fluid filled in the gap between the a pair of annular grooves formed in a position away in the axial direction of the bearing member or the shaft member, the pair of annular grooves are formed in the member which is formed , and a bent dynamic pressure grooves connecting said pair of annular grooves, each of said pair of annular grooves extending in the axial direction in a state having the same depth as the dynamic pressure groove, the dynamic pressure grooves A method of manufacturing a fluid dynamic bearing device having a structure that is continuous with an enlarged gap portion having a gap larger than a gap between an inner circumferential surface of the bearing member and an outer circumferential surface of the shaft member in a portion where a gap is formed And the bearing member or the front in the shape constituting the enlarged gap portion A first step of processing the shaft member, and an electrode tool in which at least a pair of annular conductive portions and a bent conductive portion connecting the annular conductive portions are integrally formed in the portion processed in the first step. Te, possess an electrolytic machining process to simultaneously form a bent dynamic pressure grooves connecting said pair of annular grooves and annular grooves, it said in the electrolytic machining process, the axial direction and the said pair of annular grooves enlarged clearance Is a method of manufacturing a fluid dynamic bearing device, characterized in that a part of the fluid dynamic pressure bearing device is set.

  In the invention according to claim 7, after forming a shape (for example, a taper shape of a stepped portion, a seal portion or a tapered portion of a recess portion) to be a base of the enlarged gap portion, a part of the enlarged gap portion is overlapped. An annular groove is formed. As a result, even if a shift in the axial direction occurs in the position of the annular groove, it is possible to obtain a structure in which the annular groove continues to the enlarged gap portion, and the shaft from the bending point of the dynamic pressure groove to the end portion continuous to the annular groove. Directional dimensions do not change. For this reason, even if an error in the groove forming position occurs in the formation of the dynamic pressure groove and the annular groove, the effect of suppressing the generation of bubbles is not lost, and the resistance of the fluid dynamic pressure bearing device may increase unintentionally. This prevents the variation in the axial dimension from the bending point to the end of the dynamic pressure groove, thereby reducing the variation in the performance of the fluid dynamic bearing device. Therefore, the invention described in claim 7 is useful in the case of using electrolytic processing in which an error in the groove forming position is likely to occur.

  According to the present invention, bubbles are not easily generated due to negative pressure, and errors in the machining position when forming the dynamic pressure groove are absorbed by a simple structure, and movement due to the machining error in the formation position of the dynamic pressure groove. It is possible to provide a fluid dynamic pressure bearing device and a spindle motor with high bearing performance that are unlikely to cause an inconvenience that the action of the pressure groove is hindered, and that are not likely to cause variations in bearing performance.

(1) First embodiment (structure and manufacturing method)
Hereinafter, an example of a fluid dynamic bearing device using the present invention will be described. Drawing 1 is an example of the bearing member which constitutes the fluid dynamic pressure bearing device of an embodiment, and is a sectional side view showing the state in the middle of the processing. FIG. 2 is a side sectional view (A) showing a state in which electrolytic processing is performed on the bearing member shown in FIG. 1, and a partial enlarged view (B) in which a portion indicated by reference numeral B in (A) is enlarged. FIG. 3 is a side view showing a state in which a shaft member is mounted on the bearing member shown in FIG.

  FIG. 1 shows a bearing member 101 being processed. A shaft hole 102 into which the shaft member is inserted is formed in the bearing member 101 at the center. In FIG. 1, the code | symbol 103 is a cover attachment part in which the cover member mentioned later is engage | inserted. Continuing from the lid attachment portion 103, a heel housing portion 104 having an inner diameter smaller than that of the lid attachment portion 103 is provided. A shaft member-side flange member (flange portion), which will be described later, is supported by the flange housing portion 104. A groove forming portion 105 having a diameter smaller than that of the heel housing portion 104 is provided through the chamfered portion 106 continuously from the heel housing portion 104. The groove forming portion 105 is formed with a radial dynamic pressure groove and an annular groove, which will be described later. FIG. 1 shows a state in which the radial dynamic pressure groove and the annular groove are not formed in the groove forming portion 105. A chamfered portion 106 is formed at a portion that transitions from the heel housing portion 104 to the groove forming portion 105. The chamfered portion 106 has a shape cut obliquely with respect to the axial direction. The chamfered portion 106 is a portion that gradually increases in diameter from the groove forming portion 105 toward the flange housing portion 104, and in an assembled state as a bearing device, an example of an enlarged gap portion is formed in this portion.

  A recess 107 having an inner diameter larger than that of the groove forming portion 105 is formed continuously with the groove forming portion 105. The recess 107 is provided with the intention of reducing the rotational torque of the bearing and securing an oil reservoir of lubricating oil as a lubricating fluid. A tapered portion 108 is provided at the lower edge of the recess 107 so that the recess 107 having a relatively increased inner diameter is continuously connected to the groove forming portion 105 having a relatively smaller inner diameter. It has been. This structure is similarly provided as a taper portion 109 at the upper edge of the recess portion 107. The taper portion 108 is a portion that gradually increases in diameter from the groove forming portion 105, and an example of an enlarged gap portion is formed in this portion when assembled as a bearing device. The taper portion 109 has a similar function in terms of the shape constituting the enlarged gap portion.

  A groove forming portion 110 having an inner diameter reduced from the recess portion 107 is formed continuously from the recess portion 107. The groove forming portion 110 is formed with a dynamic pressure groove and an annular groove which will be described later. FIG. 1 shows a state in which the dynamic pressure groove and the annular groove are not formed in the groove forming portion 110. The inner diameter of the groove forming portion 110 is the same as that of the groove forming portion 105.

  A seal portion 111 is formed continuously with the groove forming portion 110. The seal portion 111 has a taper cross-sectional shape in which the inner surface has an angle of 15 ° with respect to the axial direction from the edge of the groove forming portion 110 toward the opening direction of the shaft hole 102 (upward direction in the figure). ing. The seal portion 111 has a function (capillary seal function) that prevents the lubricating oil from leaking out of the shaft hole 102 by utilizing the capillary force of the lubricating oil. The seal portion 111 is a portion that gradually increases in diameter from the groove forming portion 110, and an example of an enlarged gap portion is formed in this portion when assembled as a bearing device.

  Hereafter, the outline of the process of obtaining said structure is demonstrated easily. First, a metal material as a starting material for the bearing member 101 is prepared. Next, the base hole of the cylindrical shaft hole 102 is formed in this metal material. And the shape shown in FIG. 1 is obtained by cutting the inner surface.

  FIG. 2 shows a state in which dynamic pressure grooves and annular grooves are formed in the groove forming portions 105 and 110. That is, an annular groove 112, a dynamic pressure groove 113, and an annular groove 114 are formed in the groove forming portion 105. The annular groove 112 has a shape in which the inner surface is dug down into an annular shape that goes around the inner surface of the shaft hole 102. The annular groove 112 is continuous with the chamfered portion 106 that continues from the rod housing portion 104.

  The dynamic pressure groove 113 has a band shape, has a bent portion 113a bent at the center, and has a mountain shape when viewed in the circumferential direction. Such a shape of the dynamic pressure groove is generally known as a herringbone dynamic pressure groove. One end of the dynamic pressure groove 113 is continuous with the annular groove 112, and the other end is continuous with the annular groove 114. The dynamic pressure groove 113 has a symmetrical shape in the vertical direction in the figure with the bent portion 113a as a boundary.

  The annular groove 114 is continuous with the recess 107. That is, the annular groove 114 is continuous with the tapered portion 108 of the recess portion 107. The annular groove 114 has the same structure as the annular groove 112 except for the width. In this example, the width of the annular groove 114 is set wider than the width of the annular groove 112 (dimension in the axial direction), but this is not restrictive. What is necessary is just to select the width | variety of a cyclic | annular groove | channel as needed so that the edge part and expansion | swelling clearance gap part may be connected continuously. In addition, the annular groove 112, the dynamic pressure groove 113, and the annular groove 114 have the same depth in this example. In the annular grooves 112 and 114, the main flow direction of the lubricating oil is the circumferential direction, so no dynamic pressure is generated. Therefore, the depth dimension of the annular groove 112 and the annular groove 114 may be the same as or deeper than that of the dynamic pressure groove 113, but at least the dynamic pressure groove and the pair of annular grooves corresponding to it are formed by one electrode tool. In order to be able to process simultaneously, it is preferable to make both into the same depth dimension.

  As shown in FIG. 2, the groove forming portion 110 is formed with an annular groove 115, a dynamic pressure groove 116, and an annular groove 117. The annular groove 115 has a shape in which the inner surface is dug into an annular shape that goes around the inner surface of the shaft hole 102. The annular groove 115 is continuous with the tapered portion 109 of the recess portion 107. The annular groove 115, the dynamic pressure groove 116 and the annular groove 117 have the same depth as the annular groove 112, the dynamic pressure groove 113 and the annular groove 114.

  The dynamic pressure groove 116 has a belt-like shape and has a bent portion 116a bent at a position shifted from the center toward the inner side of the bearing (the lower side in the figure), and has a mountain shape that is asymmetric on both sides when viewed in the circumferential direction. have. One end of the dynamic pressure groove 116 is continuous with the annular groove 115, and the other end is continuous with the annular groove 117. The dynamic pressure groove 116 is also one of the herringbone dynamic pressure grooves. The reason why the dynamic pressure groove 116 is asymmetrical with respect to the bent portion 116a is that the lubricating fluid in the fluid dynamic pressure bearing device is effectively pressurized and the accuracy of the dynamic pressure groove and the bearing inner surface portion is increased. This is to prevent negative pressure that may occur. In this embodiment, since the length from the bending point of the dynamic pressure groove 116 to the upper end portion of the groove is longer than the length from the bending point to the lower end portion of the groove, the inside of the bearing device is pressurized. This prevents negative pressure inside the bearing.

  Hereinafter, the process of forming the annular groove 112, the dynamic pressure groove 113, the annular groove 114, the annular groove 115, the dynamic pressure groove 116, and the annular groove 117 will be described. In this example, these grooves are simultaneously formed by electrolytic processing. First, the bearing member 101 in the state shown in FIG. 1 is prepared. Next, the annular groove 112, the dynamic pressure groove 113, the annular groove 114, the annular groove 115, the dynamic pressure groove 116, and the annular groove 117 shown in FIG. 2 are simultaneously formed by electrolytic processing using the electrode tool 800 of FIG. The electrode tool 800 of FIG. 8 includes a pair of annular conductive portions 801 and 802 corresponding to the annular groove 112, the annular groove 114, and the dynamic pressure groove 113, respectively, and a bent motion that connects the pair of annular conductive portions 801 and 802. The pressure groove conductive portion 803 is integrally formed. Further, the electrode tool 800 includes a pair of annular conductive portions 804 and 805 corresponding to the annular groove 115, the annular groove 117, and the dynamic pressure groove 116, respectively, and a bent motion that connects the pair of annular conductive portions 804 and 805. A pressure groove conductive portion 806 is integrally formed. Further, the portion other than the conductive portion of the electrode tool 800 is covered with an insulating film. With these configurations, the grooves on the bearing member 101 side can be simultaneously formed using the electrode tool 800.

  At this time, the width of the annular groove 112 and the formation position thereof are set so that the edge of the annular groove 112 (the lower edge in the figure) partially overlaps the chamfered portion 106. Further, the width of the annular groove 114 and the formation position thereof are set so that the edge of the annular groove 114 (the upper edge in the drawing) partially overlaps the tapered portion 108. Further, the width of the annular groove 115 and the formation position thereof are set so that the edge of the annular groove 115 (the lower edge in the figure) partially overlaps the tapered portion 109. Further, the width of the annular groove 117 and the formation position thereof are set so that the edge of the annular groove 117 (the upper edge in the figure) partially overlaps the seal portion 111.

  By doing so, the annular groove 112 continues to the chamfered portion 106 even if a deviation occurs in the axial positioning of the electrode tool when the dynamic pressure grooves 113 and 116 and the annular grooves 112, 114, 115 and 117 are formed. It is possible to obtain a structure in which the groove 114 is continuous with the tapered portion 108, the annular groove 115 is continuous with the tapered portion 109, and the annular groove 117 is continuous with the seal portion 111. As an example, FIG. 2B shows how the annular groove 117 and the seal portion 111 overlap. That is, by setting the edge of the annular groove 117 so as to overlap the portion where the enlarged gap portion such as the taper portion is formed by the width w, the annular groove 117 is formed even if the position of the annular groove 117 is shifted in the axial direction. It is possible to secure a margin for the width w to obtain a structure continuous to the enlarged gap portion.

  In addition, since the dynamic pressure groove and the annular groove are formed at the same time, both ends of the dynamic pressure groove 113 are continuous (connected) to the annular grooves 112 and 114 even if the formation position is displaced in the axial direction. A structure in which both ends of the dynamic pressure groove 116 are continuous (connected) to the annular grooves 115 and 117 can be obtained. Further, even if the groove forming position is displaced in the axial direction due to the machining error of the bearing member 101 or the electrode tool, the length from the bending point to the end of each of the dynamic pressure grooves 113 and 116 is as designed. Since it is formed with dimensions, desired dynamic pressure characteristics are ensured. Therefore, it becomes easy to process the dynamic pressure grooves without affecting the dynamic pressure characteristics.

  Note that the dynamic pressure groove is also formed on the flange housing portion end surface 104a of the bearing member 101 simultaneously with or before or after the formation of the dynamic pressure groove and the annular groove. An outline of the dynamic pressure groove pattern is shown in FIG. In FIG. 4A, reference numeral 31 denotes a dynamic pressure groove formed in the heel housing portion end surface 104a. Thus, the bearing member 101 in the state shown in FIG. 2 is obtained.

  Hereinafter, the assembly procedure of the fluid dynamic bearing device shown in the present embodiment will be described. When the bearing member 101 in the state shown in FIG. 2 is obtained, the shaft member 120 shown in FIG. 3 is prepared. The shaft member 120 has a cylindrical shape in which a portion entering the shaft hole 102 (see FIG. 2) has no step, and an annular flange member 121 is fixed to the tip thereof.

  When the shaft member 120 is prepared, the shaft member 120 is inserted into the shaft hole 102 (see FIG. 1 or FIG. 2). The shaft member 120 is attached to the shaft hole 102 (see FIG. 1 or 2) of the bearing member 101 from the lower side of the drawing.

  When the shaft member 120 is mounted on the bearing member 101, the lid member 122 is fitted into the lid mounting portion 103 and fixed with an adhesive. Thrust dynamic pressure grooves are formed in the lid member inner end surface 122a of the lid member 122 facing the flange member 121 and the flange housing portion end surface 104a of the bearing member 101, respectively. An outline of the dynamic pressure groove pattern is shown in FIG. 4A, reference numeral 31 denotes a dynamic pressure groove formed on the heel housing portion end face 104a, and in FIG. 4B, reference numeral 32 denotes a dynamic pressure groove formed on the lid member inner end face 122a. After fixing the lid member 122, a predetermined amount of lubricating fluid is filled in the minute gap between the bearing member and the shaft member. In this way, as shown in FIG. 3, a fluid dynamic bearing device in which one end side is opened and the other end side is closed is obtained. As the lubricating fluid, for example, ester-based lubricating oil can be used. In FIG. 3, the groove forming portions on the inner peripheral surface of the bearing member 101 are two locations, that is, the groove forming portions 110 and 105. However, the groove forming portions may be one location or three or more locations.

(Function of the embodiment)
Hereinafter, the function of the bearing structure shown in FIG. 3 will be described. In the structure shown in FIG. 3, the shaft member 120 can rotate relative to the bearing member 101. During this rotation, radial dynamic pressure is generated in the lubricating fluid existing in the gap in the vicinity by the action of the radial dynamic pressure grooves 113 and 116. The dynamic pressure forms a balanced gap in the radial direction between the shaft member 120 and the bearing member 101, and the shaft member 120 with reduced friction can be rotated. Further, the thrust dynamic pressure grooves 31 and 32 formed on the flange housing portion end surface 104a of the bearing member 101 and the lid member inner end surface 122a of the lid member 122 generate dynamic pressure in the thrust direction on the shaft member 120. Then, the shaft member 120 is not in contact with the heel housing portion end surface 104a and the lid member inner end surface 122a, and the shaft member 120 is held in the axial direction.

(Advantages of the embodiment)
As shown in FIG. 2, since both ends of the dynamic pressure groove 116 are connected to the annular grooves 115 and 117, even if the shaft member 120 (see FIG. 3) vibrates or displaces with respect to the bearing member 101, the lubricating fluid Abrupt pressure fluctuations are mitigated by the annular grooves 115 and 117. For this reason, the generation of a sudden negative pressure in the lubricating fluid is suppressed, and the generation of bubbles is prevented. As a result, the function of generating dynamic pressure when vibration or a sudden force is applied to the shaft member 120 is not impaired, and stable bearing performance can be obtained. This also applies to the dynamic pressure groove 113.

  Further, since the edges of the annular grooves 112, 114, 115, and 117 overlap with the chamfered portion 106, the tapered portions 108 and 109 that are part of the recess portion 107, and the seal portion 111, the annular groove is formed. Even if some errors occur in the position, it is possible to maintain a structure in which the annular groove continues to the enlarged gap portion (for example, the gap portion formed in the chamfered portion 106). For this reason, formation of an unintended narrow gap due to an error in the formation position of the annular groove is prevented, and deterioration of bearing performance due to the formation of this narrow gap can be prevented.

(Spindle motor using the bearing of the embodiment)
Hereinafter, an example of a spindle motor using the bearing structure shown in FIG. 3 will be described. FIG. 5 is a cross-sectional view showing an example of a spindle motor. In FIG. 5, the same reference numerals as those in FIGS.

  FIG. 5 shows a shaft rotation type spindle motor 500. The spindle motor 500 is used as a drive source for a rotating device of a magnetic disk storage device such as a hard disk device or an optical disk storage device. The spindle motor 500 includes a shaft member 120 serving as a rotation shaft. The shaft member 120 is rotatably held by the bearing member 101, and a rotor 501 is fixed to one end portion of the shaft member 120. A rotating member (not shown) driven by the spindle motor 500 is fixed to the rotor 501 using a screw hole 502. A yoke 503 is fixed to the rotor 501, and an annular permanent magnet 504 is fixed to the yoke 503.

  As described with reference to FIG. 3, the shaft member 120 is supported by the bearing member 101 by a bearing mechanism using fluid dynamic pressure. The bearing member 101 is fixed to the stator housing 505. A stator core 506 made of a magnetic material is fixed to the stator housing 505. A coil 507 is wound around the stator core 506 to form a stator 508. The stator 508 faces the permanent magnet 504 on the rotor 501 side.

  From the winding start and winding end of the coil 507, wiring not shown is drawn. The stator housing 505 is provided with an insulating hole 509, through which the coil wiring is drawn and connected to the flexible printed wiring board by the solder 510. A drive current is supplied to the coil 507 from a drive circuit (not shown) via this wiring. By switching the drive current, a magnetic force whose polarity is periodically reversed is generated between the stator 508 and the permanent magnet 504 on the rotor 501 side, whereby the rotor 501 rotates with respect to the stator housing 505.

(2) Second Embodiment Hereinafter, an example in which a dynamic pressure groove and an annular groove are provided on the shaft member side will be described with reference to FIGS. In this case, in the configuration shown in FIGS. 1 to 3, the groove forming portion 105, the recess portion 107, the groove forming portion 110, and the seal portion 111 are not formed on the inner surface of the shaft hole 102 of the bearing member 101. Becomes the cylindrical inner surface without unevenness. Instead, the corresponding portions of the shaft member 120 are processed to form the first groove forming portion, the recess portion, the second groove forming portion, and the seal portion.

  FIG. 6 is a side view showing an outline of the shaft member subjected to the above-described processing. FIG. 6 shows the shaft member 601. A tip portion (lower end in the figure) of the shaft member 601 is a flange portion 602 having an enlarged diameter. The flange 602 is an integral part of the shaft member 601 and is formed by cutting. Reference numeral 603 denotes an undercut portion formed when the flange portion 602 is formed. The undercut portion 603 has an annular groove structure that is partially reduced in diameter.

  An annular groove 604 is formed continuously with the undercut portion 603. The annular groove 604 corresponds to the annular groove 112 of FIG. One end of the dynamic pressure groove 605 is connected to the annular groove 604 (continuous). An annular groove 606 is connected to the other end of the dynamic pressure groove 605. The annular groove 604, the dynamic pressure groove 605, and the annular groove 606 have the same depth. A groove forming portion 607 is configured by the annular groove 604, the dynamic pressure groove 605, and the annular groove 606.

  The annular groove 606 is continuous with the tapered portion 610 that constitutes the edge of the recess portion 608. The recess portion 608 has a structure with a diameter smaller than that of the groove forming portion 607, and the role thereof is the same as that of the recess portion 107 shown in FIG.

  The other edge of the recess 608 is a tapered portion 611, from which an annular groove 612 is continuous. One end of the dynamic pressure groove 613 is connected to the annular groove 612, and the other end of the dynamic pressure groove 613 is connected to the annular groove 614. The annular groove 612, the dynamic pressure groove 613, and the annular groove 614 constitute a groove forming portion 615. The annular groove 612, the dynamic pressure groove 613, and the annular groove 614 have the same depth dimension. A seal portion 616 is provided continuously to the annular groove 614. The seal portion 616 has a shape that is gradually reduced in diameter toward the top of the figure.

  Hereinafter, an example of the manufacturing method of the said structure is demonstrated. First, a shape in which the groove forming portions 607 and 615 are not formed is obtained. Next, groove forming portions 607 and 615 are formed by electrolytic processing. At this time, a part of the annular groove 604 overlaps the undercut part 603, a part of the annular groove 606 overlaps the taper part 610, a part of the annular groove 612 overlaps the taper part 611, and a part of the annular groove 614 The width of each annular groove and the formation position are adjusted so as to overlap the seal portion 616.

  As described above, the shaft member 601 shown in FIG. 6 is obtained. When the shaft member 601 is obtained, a bearing member 620 (see FIG. 7) in which no groove forming portion, recess portion, or seal portion is formed is prepared, and the shaft member 601 is mounted. Then, the lid member 621 (corresponding to the reference numeral 122 in FIG. 3) is fitted and fixed, and the gap between the bearing member and the shaft member is filled with lubricating oil, whereby the fluid dynamic bearing device in FIG. 7 is obtained.

  The present invention can be used for a fluid dynamic pressure bearing device and a spindle motor using the device.

It is a sectional side view which shows the outline | summary of the bearing member in the middle of a process. They are a sectional side view (A) and a partial enlarged view (B) which show the bearing member of a 1st embodiment. It is sectional drawing which shows 1st Embodiment. It is a front view which shows an example of the shape of a thrust dynamic pressure groove. It is sectional drawing which shows the outline | summary of a spindle motor. It is a side view which shows the outline | summary of a shaft member. It is sectional drawing which shows 2nd Embodiment. It is a side view which shows the outline | summary of an electrode tool. It is a side view which shows the conventional breakthrough herringbone dynamic pressure groove.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Bearing member, 102 ... Shaft hole, 103 ... Cover attaching part, 104 ... Saddle accommodating part, 105 ... Groove forming part, 106 ... Chamfering part, 107 ... Recessed part, 108 ... Tapered part, 109 ... Tapered part, 110 ... Groove forming part, 111 ... seal part, 112 ... annular groove, 113 ... dynamic pressure groove, 114 ... annular groove, 115 ... annular groove, 116 ... dynamic pressure groove, 117 ... annular groove, 120 ... shaft member, 121 ... collar member 122: Lid member, 500: Spindle motor, 501 ... Rotor, 502 ... Screw hole, 503 ... Yoke, 504 ... Permanent magnet, 505 ... Stator housing, 506 ... Stator core, 507 ... Coil, 508 ... Stator.

Claims (7)

A bearing member;
A shaft member mounted in a relatively rotatable state on the bearing member;
A lid member for closing one end side of the bearing member;
A lubricating fluid continuously filled in a gap between the bearing member and the shaft member;
A pair of annular grooves formed at positions separated in the axial direction of the bearing member or the shaft member;
Formed in a member in which the pair of annular grooves are formed, and a bent dynamic pressure groove connecting the pair of annular grooves,
Each of the pair of annular grooves extends in the axial direction in a state having the same depth as the dynamic pressure groove, and the inner peripheral surface of the bearing member and the shaft member in a portion where the dynamic pressure groove is formed. A fluid dynamic bearing device, characterized in that the fluid dynamic bearing device is continuous with an enlarged gap portion having a gap larger than a gap between the outer peripheral surface of the first and second outer peripheral surfaces.   The fluid dynamic bearing device according to claim 1, wherein the enlarged gap portion includes a chamfered portion, a seal portion, a recess portion, or an undercut portion.   3. The fluid dynamic bearing device according to claim 1, wherein the dynamic pressure groove has an asymmetric pattern in an axial direction with a bent portion as a boundary.   The dynamic pressure groove is simultaneously formed by electrolytic processing using an electrode tool in which at least a pair of annular conductive portions and a bent conductive portion connecting the pair of annular conductive portions are integrally formed. The fluid dynamic pressure bearing device according to any one of claims 1 to 3.   5. The fluid dynamic bearing device according to claim 1, wherein each of the pair of annular grooves is formed at a position partially overlapping with the enlarged gap portion.   A spindle motor using the fluid dynamic bearing device according to any one of claims 1 to 5. A bearing member;
A shaft member mounted in a relatively rotatable state on the bearing member;
A lid member for closing one end side of the bearing member;
A lubricating fluid filled in a gap between the bearing member and the shaft member;
A pair of annular grooves formed at positions separated in the axial direction of the bearing member or the shaft member;
Formed in a member in which the pair of annular grooves are formed, and a bent dynamic pressure groove connecting the pair of annular grooves,
Each of the pair of annular grooves extends in the axial direction in a state having the same depth as the dynamic pressure groove, and the inner peripheral surface of the bearing member and the shaft member in a portion where the dynamic pressure groove is formed. A method of manufacturing a fluid dynamic bearing device having a structure continuous to an enlarged gap portion having a gap larger than a gap between the outer peripheral surface of
A first step of processing the bearing member or the shaft member into a shape constituting the enlarged gap portion;
Using the electrode tool in which at least a pair of annular conductive portions and a bent conductive portion connecting the annular conductive portions are integrally formed on the portion processed in the first step, the pair of annular grooves and the annular grooves possess an electrolytic machining process for simultaneously forming a bent dynamic pressure grooves connecting,
In the electrolytic processing step, the pair of annular grooves and the enlarged gap portion are set so as to partially overlap in the axial direction .

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