JP2004183767A - Dynamic pressure bearing, spindle motor with dynamic pressure bearing, and disc driving device using spindle motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To discharge bubbles collected between a thrust bearing part and a radial bearing part. <P>SOLUTION: Pump-in type spiral grooves are formed on the thrust bearing part as dynamic pressure generating grooves, an axially unbalanced herringbone groove row is formed on the radial bearing part as the dynamic pressure generating grooves, and the oil is continuously held between the thrust bearing part and the radial bearing part. A groove for segmentalizing the bubbles intruded in the oil in operation is formed on a boundary part of the thrust bearing part and the radial bearing part. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a dynamic pressure bearing, a spindle motor provided with the dynamic pressure bearing, and a disk drive using the spindle motor.
[0002]
[Prior art]
Conventionally, as a bearing for a spindle motor used in a disk drive device for driving a recording disk such as a hard disk, a lubricating fluid such as oil interposed between the shaft and the sleeve to support the shaft and the sleeve so as to be relatively rotatable. Various dynamic pressure bearings utilizing the above fluid pressure have been proposed.
[0003]
In recent years, a disk drive device using such a spindle motor has started to be applied to a small device such as a portable information terminal, and a demand for further thinning is increasing.
[0004]
For this reason, the applicant of the present application has made it possible to eliminate the need for a thrust plate for forming the thrust bearing portion, to reduce the size and thickness of the motor, and to increase the distance between the radial bearing portions as much as possible. A spindle motor for a disk drive device capable of obtaining rigidity has been proposed (see Patent Document 1).
[0005]
FIG. 1 shows a spindle motor using such a dynamic pressure bearing. The spindle motor illustrated in FIG. 1A forms a thrust bearing portion S for generating a floating force of the rotor a between a bottom surface of the rotor a and an upper end surface of the sleeve b, and is integrated with the rotor a. Upper radial bearing portion for acting on the alignment of the rotor a and preventing the rotor a from collapsing through an air interposed portion d communicating with the outside air between the outer peripheral surface of the shaft c and the inner peripheral surface of the sleeve b provided at R1 and a lower radial bearing portion R2. A stator f is mounted on a base member e to which the sleeve b is fixed, and a rotor magnet g is fixed to the rotor a so as to face the stator f.
[0006]
The schematic configuration of the thrust bearing portion S and the upper radial bearing portion R1 in the spindle motor will be described with reference to FIGS. 1 (b) and 1 (c). As shown in FIG. 1B in an enlarged manner, a thrust bearing S formed between the bottom surface of the rotor a and the upper end surface of the sleeve b has a radially inward direction indicated by an arrow A in FIG. A pump-in type spiral groove SG for inducing the flow of oil toward one side is provided, so that a supporting force in the floating direction of the rotor a is obtained. The specific shape of the spiral groove SG provided in the thrust bearing S is illustrated in FIG. In addition, the upper radial bearing portion R1 disposed radially inward of the thrust bearing portion S has a position closer to the air interposition portion d than the spiral groove portion RS1 located on the thrust bearing portion S side as shown in FIG. Is provided with a herringbone groove HG1 having an axially unbalanced shape in which the spiral groove portion RS2 having a longer dimension in the axial direction is provided, and thereby the radial support on the upper end portion side of the shaft c is provided. Power is gained. At this time, since the pumping force of the spiral groove portion RS2 against the oil exceeds the pumping force of the spiral groove portion RS1 by the difference in the axial dimension, the dynamic pressure of the upper radial bearing portion R1 toward the thrust bearing portion S is increased. Occurs.
[0007]
Although the shape of the dynamic pressure generating groove is not particularly illustrated, the lower radial bearing portion R2 has a pair of spiral grooves having substantially the same axial dimension, and a herring with a shape symmetrical in the axial direction. The bone groove HG2 is provided, so that a radial supporting force on the lower end side of the shaft c is obtained. Further, a ring-shaped member h made of a ferromagnetic material is disposed at a position of the base member e opposed to the rotor magnet g in the axial direction, and a magnetic attraction acting between the rotor magnet g and the ring-shaped member h. The support force in the direction of suppressing the floating of the rotor a is obtained by the force. The levitation force generated by the dynamic pressure generated in the thrust bearing portion S and the magnetic attraction force acting between the rotor magnet g and the ring-shaped member h are balanced to support the axial load applied to the rotor a.
[0008]
By having the dynamic pressure bearing having the above configuration, in the spindle motor shown in FIG. 1A, the structure of the motor can be simplified and the cost can be reduced without significantly reducing the bearing rigidity. It has the advantage of becoming.
[0009]
[Patent Document 1]
JP-A-2000-197309 (pages 4 to 6, FIG. 2)
[0010]
[Problems to be solved by the invention]
By the way, in the spindle motor shown in FIG. 1, the bottom surface of the rotor a and the sleeve b in a region radially inward of the thrust bearing S (shown as a region P surrounded by a dashed line in FIG. 1B). Is set so that the gap size between the upper end surface of the first and second thrust bearings is substantially equal to that of the thrust bearing portion S.
[0011]
Normally, the gap size of the region P that does not contribute to the generation of the dynamic pressure is set to several times larger than the gap size of the thrust bearing portion S, more specifically, the gap size of the bearing portion is set to several μm. On the other hand, in the region P, by setting the gap size to be as large as about several tens of μm, it is possible to reduce the loss at the time of rotation caused by the viscosity of the oil and to improve the efficiency. By providing a region having such a large gap size adjacent to the bearing portion, when disturbance such as shock or vibration is applied when the motor without dynamic pressure is stationary, vibration in the axial direction of the rotor a due to the disturbance increases. This is newly found. Such non-operational vibration is caused by the fact that the oil held by the thrust bearing portion S escapes to the region P with a large gap when the rotor a is pressed against the sleeve b by a disturbance, so that the damping effect by the oil is reduced. It is believed to be due to
[0012]
As described above, even when the rotor a is not operated, the vibration of the rotor a is increased, and the vibration of the disk mounted on the rotor a is also increased. . Therefore, in order to avoid this, the region P located on the radially inner side of the thrust bearing S is also set to have substantially the same gap size as the bearing.
[0013]
When bubbles are mixed in the oil, the bubbles are formed by the pumping action of the herringbone groove HG1 provided in the upper radial bearing portion R1 and the spiral groove SG provided in the thrust bearing portion S. It will be collected in the area P located inward in the radial direction of S. However, since the region P is a minute gap having substantially the same gap size as that of the bearing portion and has no dynamic pressure groove formed therein, the bubbles collected in this region P have a circumferential shape even when the rotor a rotates. Only the flow in the direction occurs, and the stagnation occurs at the place.
[0014]
Bubbles staying in the region P on the radially inner side of the thrust bearing portion S are aggregated while flowing in the circumferential direction with the rotation of the motor, and eventually form one circumferential air band. When an air band is generated in the oil in the region P in this manner, abnormal vibration during operation, deterioration of NRRO (non-repetitive runout component), or radial direction of the oil due to the spiral groove SG provided in the thrust bearing S is performed. There is a possibility that the inflow to the inside is hindered and a predetermined levitation force cannot be obtained, resulting in an abnormal levitation of the rotor a. The cause of the air bubbles entering the oil may be, for example, carelessness of an operator in the oil injection process, or unbalanced pumping of the herringbone groove HG1 during rotation of the motor, resulting in the spiral groove portion located on the air interposed portion d side. It is conceivable that the oil interface is disturbed due to the lower end of the RS 2 being exposed to the air, whereby the air is caught in the oil and appears as bubbles.
[0015]
An object of the present invention is to eliminate even if bubbles enter the oil continuously held between the thrust bearing portion and the upper radial bearing portion due to a problem of a worker, a processing error, or the like. It is to provide a simple dynamic pressure bearing.
[0016]
Another object of the present invention is to provide a highly reliable spindle motor and a disk drive device using the spindle motor by providing the above-described dynamic pressure bearing as a bearing means, thereby avoiding problems caused by bubbles. That is.
[0017]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a thrust bearing for generating a dynamic pressure acting in one axial direction on oil held in a minute gap, and a radially inner side of the thrust bearing. A radial bearing portion, which is arranged and generates a dynamic pressure acting in a radial direction on the oil held in the minute gap, wherein the thrust bearing portion has a dynamic pressure generating groove as the dynamic pressure generating groove. A dynamic pressure generating groove row is formed in the circumferential direction by a pump-in type spiral groove that induces a flow toward the radially inward side with respect to the radial bearing portion. A dynamic pressure generating groove row is formed in the circumferential direction by a herringbone groove having an unbalanced shape in the axial direction so that the maximum pressure of the dynamic pressure generated with respect to the thrust bearing part side is displaced and appears. Sura Between the thrust bearing portion and the radial bearing portion, the oil is held continuously without interruption in each minute gap, and at the boundary between the thrust bearing portion and the radial bearing portion. A groove is provided for dividing air bubbles that have entered the oil during operation.
[0018]
According to the above configuration, at the boundary between the thrust bearing portion and the radial bearing portion, the oil is agitated at the time of operation by providing a groove for agitating and dividing the air bubbles, and in a circumferential direction. Pressure fluctuations will appear intermittently and randomly while maintaining positive pressure. By entrapping air bubbles in such circumferential pressure fluctuations, the air bubbles are fragmented until they become smaller than the gap size of the minute gap in the bearing portion, so that the air bubbles can be easily discharged.
[0019]
According to a second aspect of the present invention, in the dynamic pressure bearing according to the first aspect, the dynamic pressure bearing has a shaft and a sleeve, and the groove for dividing the bubble is provided on a surface of the shaft. It is characterized by a notched groove.
[0020]
According to a third aspect of the present invention, in the dynamic pressure bearing according to the first aspect, the dynamic pressure bearing has a shaft and a sleeve, and the groove for dividing the bubble is formed on a surface of the shaft by knurling. It is characterized by being formed by processing.
[0021]
According to a fourth aspect of the present invention, in the dynamic pressure bearing according to the second or third aspect, a chamfered portion is provided on a surface of the sleeve located at a boundary between the thrust bearing portion and the radial bearing portion. In addition, the chamfered portion is provided with a groove for discharging the air bubbles to the thrust bearing portion side by electrolytic processing.
[0022]
According to a fifth aspect of the present invention, in the dynamic pressure bearing according to the fourth aspect, the groove provided in the chamfered portion of the sleeve for discharging bubbles to the thrust bearing portion side has a dynamic pressure of the thrust bearing portion. It is characterized in that at least one of the spiral grooves forming the generating groove row is provided so as to extend radially inward from the other spiral grooves.
[0023]
According to a sixth aspect of the present invention, there is provided a shaft, a sleeve having a through hole through which the shaft is freely rotatably inserted, and an axially opposed upper end surface of the sleeve. A rotor having a circular top plate integrally formed with a shaft, wherein a minute gap for holding oil is provided between an upper end surface of the sleeve and a bottom surface of the top plate. A thrust bearing portion is formed by forming a dynamic pressure generating groove for inducing fluid dynamic pressure in oil held in the minute gap in accordance with the rotation of the rotor, and a thrust bearing portion is formed. A minute gap for holding oil is formed between the outer circumference of the shaft and a dynamic pressure generating groove for inducing fluid dynamic pressure in the oil held in the minute gap in accordance with the rotation of the rotor. Provided A radial gap is formed between the upper end surface of the sleeve and the bottom surface of the top plate where the thrust bearing portion is formed. The dynamic pressure bearing according to any one of claims 1 to 5, wherein the dynamic pressure bearing is formed so as to have substantially the same gap dimension up to the side, and includes the thrust bearing portion and the radial bearing portion. It is characterized by.
[0024]
Further, the invention according to claim 7 includes a shaft, a pair of annular thrust plates projecting radially outward from an outer peripheral surface of the shaft, and one axial surface of the pair of thrust plates. A hollow cylindrical sleeve having a pair of thrust surfaces facing each other through a minute gap and an outer peripheral surface of the shaft continuous with the thrust surface and a radial inner peripheral surface facing the radial direction through the minute gap. A spindle motor, wherein oil is held in a minute gap formed between one surface in the axial direction of the pair of thrust plates and the pair of thrust surfaces, and induces dynamic pressure in the oil. Thrust bearing portions are respectively formed by providing the dynamic pressure generating grooves, and a minute gap formed between the outer peripheral surface of the shaft and the radial inner peripheral surface of the sleeve is formed. And a pair of radial bearing portions are axially separated by providing a dynamic pressure generating groove for inducing dynamic pressure in the oil, and the pair of thrust plates forming the thrust bearing portion. The small gap formed between one surface of the small gap and a pair of thrust surfaces of the sleeve is formed to have substantially the same gap size from the inner diameter end side to the outer diameter end side of the minute gap. The pair of thrust bearings and the pair of radial bearings constitute a pair of hydrodynamic bearings each including a pair of thrust bearings and a radial bearing, and the pair of hydrodynamic bearings are respectively claimed. A dynamic pressure bearing according to any one of 1 to 5.
[0025]
In addition, the invention according to claim 8 is a disk drive device in which a recording disk capable of recording information is rotationally driven, a housing, a spindle motor fixed inside the housing and rotating the recording disk, A disk drive having information access means for writing or reading information at a required position on a disk, wherein the spindle motor is a spindle motor according to claim 6 or 7.
[0026]
By the way, the inventions described in the claims other than claim 1 relate to the configuration according to the embodiment of the present invention. Regarding the function and effect of the configuration of the invention according to each claim and the principle thereof, the following invention is described. The embodiment and the effects of the invention will be described in detail.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a dynamic pressure bearing according to the present invention will be described together with a spindle motor using the same, and each embodiment of a disk drive device using the spindle motor will be described with reference to the drawings. It is not limited to the embodiment shown.
[0028]
An embodiment of the present invention will be described with reference to FIG. In this embodiment, the structure is substantially the same as that of the dynamic pressure bearing used for the spindle motor shown in FIG. 1 described above. Only the differences from the dynamic pressure bearing of the spindle motor will be described.
[0029]
FIG. 2A is a partially enlarged cross-sectional view illustrating a schematic configuration near the boundary between the upper radial bearing portion R1 and the thrust bearing portion S in a partially enlarged manner, and FIGS. 2B and 2C. FIG. 3 is a front view illustrating a surface near an upper end of a shaft c, and a plan view illustrating a modification thereof. As shown in FIGS. 2A and 2B, in the dynamic pressure bearing according to the embodiment of the present invention, the outer circumferential surface of the shaft c corresponding to the boundary between the upper radial bearing portion R <b> 1 and the thrust bearing portion S has a substantially cross section. It differs from the dynamic pressure bearing shown in FIG. 1 in that a rectangular cutout groove G is provided.
[0030]
Thus, by providing the notch groove G on the surface of the shaft c located between the upper radial bearing portion R1 and the thrust bearing portion S, the oil is agitated at the time of rotation of the rotor a, so that the oil is stirred in the circumferential direction. Pressure fluctuations appear intermittently and randomly while maintaining the positive pressure. By entrapping air bubbles in such circumferential pressure fluctuations, the air bubbles are fragmented until they become smaller than the gap size of the minute gap in the bearing portion, so that the air bubbles can be easily discharged. In this embodiment, the notch groove G is partially provided on the surface of the shaft c as shown in FIG. 2B, but as shown in FIG. By performing knurling, it is also possible to form a notch groove G 'provided in a circumferential shape.
[0031]
As described above, the air bubbles subdivided by the notch groove G (or G ′) into a smaller state than the minute gap of the bearing portion can easily move in the minute gap, and naturally the pressure is reduced. It moves to the lower interface side and is eventually discharged. However, as shown in FIG. 3, by forming some of the spiral grooves SG1 provided in the thrust bearing portion S as spiral grooves SG1A extending to the radially inner side, the notch grooves G are formed. This makes it possible to mechanically control the discharge of the fragmented air bubbles, thereby increasing the stability.
[0032]
That is, as shown in FIG. 3, the spiral groove SG1A provided in the thrust bearing portion S is provided with a spiral groove SG1A extending radially inward from the other grooves, thereby rotating the rotor a. At this time, the spiral grooves SG1 and SG1A cause the oil to flow radially inward and radially outward. The bubbles collected in the region P by multiplying such a radial flow sequentially start moving outward in the radial direction, and eventually the interface of the oil end located on the radial outside of the thrust bearing portion S. Released from the air.
[0033]
At this time, the radial inner end of the spiral groove SG1A extending inward in the radial direction is a chamfered portion b1 provided at the corner between the upper end of the inner peripheral surface of the sleeve b and the radial inner end of the upper end surface. (See FIG. 2 (a).), The air bubbles can be more easily and reliably discharged. The portion of the spiral groove SG1A located at the chamfered portion b1 of the sleeve b does not necessarily need to be provided continuously with the spiral groove SG1A, but can be provided independently of the spiral groove SG1A. It is also possible to provide more than the number of formed.
[0034]
With the above configuration, the gap formed between the bottom surface of the rotor a and the upper end surface of the sleeve b is made almost the same as the thrust bearing portion S over the entirety, so that the rotor a It is possible to solve various problems such as abnormal vibration due to stagnation of bubbles, deterioration of NRRO, and abnormal floating of the rotor a while suppressing vibration during non-operation.
[0035]
Note that there is no particular limitation on how many spiral grooves SG1 provided in the thrust bearing portion S are formed so as to extend inward in the radial direction, as long as they can be arranged at equal intervals in the circumferential direction. good.
[0036]
Further, such a dynamic pressure bearing is applicable not only to a spindle motor having a configuration as shown in FIG. 1A but also to a spindle motor having another configuration. Next, an example of applying such a dynamic pressure bearing to a spindle motor having another configuration will be described with reference to FIG.
[0037]
The spindle motor shown in FIG. 4 includes a bracket 2, a shaft 4 having one end externally fixed in a central opening provided in the bracket 2, and a rotatable relative to the shaft 4. Rotor 6. The rotor 6 has a rotor hub 6a on which a recording disk (shown as a disk plate 53 in FIG. 5) is mounted on an outer peripheral portion, and a shaft 4 which is located on the inner peripheral side of the rotor hub 6a via a minute gap for holding oil. And a sleeve 6b that is axially supported by the shaft. A rotor magnet 10 is fixed to the inner peripheral portion of the rotor hub 6a by means of adhesion or the like, and a stator 12 is mounted on the bracket 2 so as to face the rotor magnet 10 in the radial direction.
[0038]
At a substantially central portion of the sleeve 6b, a through hole 6b1 is formed through the sleeve 6b in the axial direction so that an inner peripheral surface forms a minute gap for retaining oil between the inner peripheral surface and the outer peripheral surface of the shaft 4. An annular upper thrust plate 14 and a lower thrust plate 16 projecting radially outward are attached to the upper and lower portions, respectively.
[0039]
At both ends in the axial direction of the sleeve 6b, corresponding to the upper thrust plate 14 and the lower thrust plate 16, the upper thrust surface 6b2 and the lower thrust surface 6b3 having a diameter larger than the outer diameter of the upper and lower thrust plates 14, 16. Is formed. An annular and hollow cylindrical upper bush member 18 and lower bush member 20 are mounted on the outer peripheral portions of the upper thrust surface 6b2 and the lower thrust surface 6b3. Open ends of the upper and lower bush members 18 and 20 are closed by an upper seal cap 22 and a lower seal cap 24.
[0040]
An annular projection 6b4 projecting outward in the radial direction is formed between the upper and lower thrust surfaces 6b2 and 6b3 on the outer periphery of the sleeve 6b, and the outer periphery of the annular projection 6b4 and the rotor hub are formed. The inner peripheral surface 6a is fastened by, for example, press fitting.
[0041]
A minute gap for retaining oil is formed between the upper thrust surface 6b2 and the lower surface (the inner side surface in the axial direction) of the upper thrust plate 14, and the upper thrust bearing 26 is formed.
[0042]
In addition, a small gap for retaining oil is formed between the lower thrust surface 6b3 and the upper surface (the inner side surface in the axial direction) of the lower thrust plate 16, and a lower thrust bearing portion 28 is formed.
[0043]
Further, an upper radial bearing portion 30 and a lower radial bearing portion 32 are formed between the inner peripheral surface of the through hole 6b1 and the outer peripheral surface of the shaft 4.
[0044]
The upper and lower radial bearing portions 30 and 32 serve as dynamic pressure generating grooves so as to generate dynamic pressure toward the adjacent thrust bearing portions 26 and 28, respectively, in the axial direction as shown in FIG. 2 is provided with an unbalanced herringbone groove HG1, and the configuration of the upper and lower thrust bearings 26 and 28 is the same as that of the thrust bearing S shown in FIG. A pump-in type spiral groove SG1 is provided, and a spiral groove SG1A extending inward in the radial direction is provided. That is, the rotor 6 is supported by upper and lower portions of the shaft 4 with the same shape of the bearing by forming a pair of the combination of the radial bearing portion R1 and the thrust bearing portion S on the upper and lower portions of the shaft shown in FIG. Therefore, it is possible to stably support even a high-load spindle motor that rotationally drives a plurality of recording disks, for example, and avoid the occurrence of various problems due to the retention of bubbles. It becomes possible to do.
[0045]
Therefore, it is possible to suppress the vibration of the rotor 6 when the rotor 6 is not operating due to the application of the disturbance, and at the same time, it is possible to discharge the air bubbles mixed in the oil held in the dynamic pressure bearing, thereby improving the reliability. And a spindle motor having a high speed can be obtained.
[0046]
Next, a disk drive device according to an embodiment of the present invention will be described.
[0047]
FIG. 5 is a schematic diagram showing the internal configuration of a general disk drive device 50. The inside of the housing 51 forms a clean space with extremely small amount of dust and the like, and a spindle motor 52 having a disk-shaped disk plate 53 for storing information installed therein is installed therein. In addition, inside the housing 51, a head moving mechanism 57 for reading and writing information from and to the disk plate 53 is arranged. The head moving mechanism 57 supports a head 56 for reading and writing information on the disk plate 53, and supports the head. The actuator 55 is configured to move the arm 55, the head 56, and the arm 55 to a required position on the disk plate 53.
[0048]
By using the spindle motor of each of the above embodiments as the spindle motor 52 of such a disk drive device 50, a highly reliable disk drive device can be obtained.
[0049]
As described above, the dynamic pressure bearing according to the present invention, the spindle motor including the dynamic pressure bearing, and the disk drive device according to one embodiment have been described. However, the present invention is not limited to the embodiment, and the scope of the present invention is not limited to the embodiment. Various changes and modifications are possible without departing from the scope of the invention.
[0050]
【The invention's effect】
ADVANTAGE OF THE INVENTION The dynamic pressure bearing of this invention enables discharge | release of the air bubble mixed in the oil, and it becomes possible to maintain stable performance.
[0051]
Further, in the spindle motor of the present invention, it is possible to suppress the vibration of the rotor when it is not operating and to avoid the problem caused by the accumulation of bubbles, so that a highly reliable spindle motor can be obtained. Become.
[0052]
Further, in the disk drive device of the present invention, the destruction of the head due to the contact with the disk due to the vibration of the spindle motor during non-operation is prevented, and at the same time, the problem caused by the bubbles staying in the bearing portion of the spindle motor is reduced. Since the occurrence is also avoided, it is possible to provide a very stable and highly reliable disk drive.
[Brief description of the drawings]
1 (a) and 1 (b) are cross-sectional views showing a schematic configuration of a part of a conventional spindle motor and a bearing portion thereof which are a prerequisite configuration of the present invention, and FIG. It is a top view which shows the shape of the spiral groove provided in the thrust bearing part.
FIG. 2A is a partially enlarged cross-sectional view showing a schematic configuration in the vicinity of a boundary between an upper radial bearing portion and a thrust bearing portion in a partially enlarged manner, and FIGS. (C) is a surface view illustrating a surface near the upper end of the shaft, and a plan view illustrating a modification thereof.
FIG. 3 is a plan view showing a shape of a spiral groove according to the embodiment of the present invention.
FIG. 4 is a sectional view showing an application example of the dynamic pressure bearing of the present invention to another spindle motor.
FIG. 5 is a cross-sectional view schematically showing an internal configuration of the disk drive device.
[Explanation of symbols]
26, 28, S Thrust bearings 30, 32, R1 Radial bearings G, G 'Notch grooves SG, SG1, SG1A Spiral groove HG1 Herringbone groove

Claims (8)

A thrust bearing that generates dynamic pressure acting in one axial direction on oil held in the minute gap; and a thrust bearing disposed radially inward of the thrust bearing and held in the minute gap. A radial bearing that generates dynamic pressure acting radially on the applied oil,
The thrust bearing portion is provided with a dynamic pressure generation groove row in the circumferential direction as a dynamic pressure generation groove by a pump-in type spiral groove that induces a flow of the oil toward a radially inward side,
In the radial bearing portion, a dynamic pressure is generated by a herringbone groove having an unbalanced shape in the axial direction such that a maximum pressure of a dynamic pressure generated on the oil as a dynamic pressure generating groove is biased toward the thrust bearing portion side. The generation groove row is provided in the circumferential direction,
Between the thrust bearing portion and the radial bearing portion, the oil is continuously held in each minute gap without interruption, and at a boundary portion between the thrust bearing portion and the radial bearing portion. Is a dynamic pressure bearing provided with grooves for subdividing bubbles that have entered the oil during operation. 2. The dynamic pressure bearing according to claim 1, wherein the dynamic pressure bearing has a shaft and a sleeve, and the groove for dividing the air bubbles is a notch-shaped groove provided on a surface of the shaft. Dynamic pressure bearing. 2. The dynamic pressure bearing according to claim 1, wherein the dynamic pressure bearing has a shaft and a sleeve, and the groove for dividing the bubble is formed by knurling the surface of the shaft. Pressure bearing. A chamfered portion is provided on the surface of the sleeve located at the boundary between the thrust bearing portion and the radial bearing portion, and the bubbles are discharged to the thrust bearing portion side by electrolytic machining in the chamfered portion. The dynamic pressure bearing according to claim 2, wherein a groove is provided for the dynamic pressure bearing. Grooves provided in the chamfered portion of the sleeve for discharging bubbles to the thrust bearing portion side, at least one of the spiral grooves forming the dynamic pressure generating groove row of the thrust bearing portion, other, The dynamic pressure bearing according to claim 4, wherein the bearing is formed so as to extend radially inward of the spiral groove. A shaft, a sleeve having a through-hole through which the shaft is freely rotatably inserted, and a circular ceiling in which the shaft is opposed to the upper end surface of the sleeve in the axial direction and the shaft is integrally formed with the rotation axis. A spindle motor comprising a rotor having a plate,
A minute gap for holding the oil is formed between the upper end surface of the sleeve and the bottom surface of the top plate, and a fluid dynamic pressure is induced in the oil held in the minute gap according to the rotation of the rotor. The thrust bearing portion is constituted by providing the dynamic pressure generating groove
A minute gap for holding oil is formed between the inner peripheral surface of the through hole of the sleeve and the outer peripheral surface of the shaft, and the oil retained in the minute gap in response to the rotation of the rotor. A radial bearing portion is configured by providing a dynamic pressure generating groove for inducing fluid dynamic pressure,
The minute gap formed between the upper end surface of the sleeve and the bottom surface of the top plate where the thrust bearing portion is formed has substantially the same gap size from the inner diameter end side to the outer diameter end side of the minute gap. Is formed as
6. A spindle motor according to claim 1, wherein a dynamic pressure bearing comprising said thrust bearing portion and said radial bearing portion is the dynamic pressure bearing according to any one of claims 1 to 5. A shaft, a pair of annular thrust plates protruding radially outward from the outer peripheral surface of the shaft, and a pair of thrusts respectively opposed to one axial surface of the pair of thrust plates via a minute gap; A spindle motor comprising: a hollow cylindrical sleeve having a surface and a radial inner peripheral surface which is continuous with the thrust surface and which radially opposes the outer peripheral surface of the shaft and the radial direction via a minute gap,
Oil is held in a minute gap formed between one surface of the pair of thrust plates in the axial direction and the pair of thrust surfaces, and a dynamic pressure generating groove for inducing a dynamic pressure in the oil is provided. Each constitutes a thrust bearing part,
Oil is held in a minute gap formed between the outer peripheral surface of the shaft and the radial inner peripheral surface of the sleeve, and a dynamic pressure generating groove for inducing a dynamic pressure in the oil is provided. Are paired apart from each other in the axial direction,
The minute gap formed between one surface of the pair of thrust plates constituting the thrust bearing portion and the pair of thrust surfaces of the sleeve extends from an inner diameter end to an outer diameter end of the minute gap. , Are formed to have substantially the same gap size,
2. The pair of thrust bearings and the pair of radial bearings constitute a pair of hydrodynamic bearings each including a pair of thrust bearings and a radial bearing, and the pair of hydrodynamic bearings are respectively. A spindle motor, which is the dynamic pressure bearing according to any one of claims 1 to 5. In a disk drive device in which a recording disk capable of recording information is driven to rotate, a housing, a spindle motor fixed inside the housing and rotating the recording disk, and a device for writing or reading information at a required position on the recording disk 8. A disk drive device comprising: an information access unit according to claim 1, wherein said spindle motor is the spindle motor according to claim 6 or 7.

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