JP2005180468A - Hydrodynamic bearing motor with levitation booster - Google Patents

Abstract

【Task】
Realizes a hydrodynamic bearing motor that has a floating booster, enables rapid floating from low-speed rotation, reduces sliding wear, and enables precise control of flying height.
[Solution]
A radial bearing is used as an unbalanced herringbone groove to provide a floating booster that pumps a lubricating fluid to the shaft end and cooperates with an orifice in the circulation path to generate most of the load capacity of the rotating part support. The gap in the radial direction is small and easy to manage, so it is energy efficient and powerful, enabling precise control of the flying height in cooperation with a spiral groove with a small shaft diameter.
Since the flow speed of the lubricating fluid can be set to the minimum, the possibility of leakage of the lubricating fluid is reduced, the axial loss is reduced, and a thin and low power consumption magnetic disk device is enabled by using the hydrodynamic bearing motor. .
[Selection] Figure 6

Description

  The present invention relates to a hydrodynamic bearing motor, and more particularly to a hydrodynamic bearing motor suitable for a high-speed rotation and thin magnetic disk drive (HDD).

  Since conventional hydrodynamic bearings for HDDs need to strictly control the axial position while maintaining the attitude of the rotating part, the rotating part is configured with a radial bearing, and the axial position is shared with a thrust bearing. In addition, it had a thrust bearing part larger in diameter than the shaft.

  With the trend toward miniaturization of HDDs, hydrodynamic bearing motors are also becoming smaller and thinner. In order to ensure radial bearing span, the present inventors have gradually developed a single thrust structure in which the thrust bearing previously invented is formed on the rear surface of the hub. Has become dominant. This contributes to reducing the axial loss by reducing the area where the lubricating fluid flows and friction, and further improving the assembly.

  However, the presence of a thrust bearing or thrust plate larger than the remaining shaft diameter has a region where the lubricating fluid flows at high speed only for the purpose of regulating the axial position of the rotating part. It always left a threat of leakage and a difficulty in reducing axial loss.

  The above problems can be improved by realizing a hydrodynamic bearing that precisely supports the rotating part with only a shaft and a sleeve without a thrust bearing or thrust plate, but such a configuration is dominated by today's bearing configuration. Various developments were attempted before becoming. They consist of a structure that always slides in contact with the center of the shaft end, a structure that floats with a small spiral groove at the shaft end, a structure that floats and supports the rotating part by magnetic repulsion or magnetic attraction, and lubricating fluid for radial bearings. For example, the load capacity in the axial direction is obtained by pumping.

  The first configuration that slides and rotates the shaft end has become quite realistic today when the weight of the rotating part has decreased, but it still has a point in which axial damping is difficult to work against and impact has been added. Considering the influence of the indentation due to, it is not suitable for use in HDD.

  The second configuration having a small spiral groove at the shaft end is proposed in, for example, Japanese Examined Patent Publication No. 46-8046. However, in the case of a small shaft diameter, a sufficient load capacity cannot be obtained at low speed rotation, so the flying height is small. It has a weak point that the sliding distance at the start and stop of rotation becomes large.

  The third configuration that supports the rotating part using the magnetic repulsive force or attractive force cannot achieve the positional accuracy in the axial direction, and has problems such as an increase in the number of parts, which is practical for small HDD applications. Not.

  In a fourth configuration using the lubricating fluid pumping capability of the radial bearing, the lubricating fluid is pumped into a gap formed by the bottom of the bottomed sleeve and the shaft end to obtain an axial load capacity. The lubrication fluid pumping of radial bearings is efficient and powerful enough to support the rotating body, but there are difficulties in precise control of flying height. There are two types of realistic proposals. One is a structure that controls the flying height by forming a variable opening along with the position of the shaft end that has a circulation path opening on the sleeve peripheral wall, and the shaft end and sleeve It is the structure which controls the flying height by forming an orifice between them.

  The former of the fourth configuration is proposed in Japanese Patent Publication No. 48-4498, and is formed by a shaft and a circulation path opening provided in the peripheral wall of the sleeve. It is difficult to ensure the accuracy of the above, and it is difficult to obtain a uniform flying height on the order of several micrometers as a HDD bearing.

  The latter configuration of the fourth configuration is proposed in Japanese Patent Laid-Open Nos. 58-24615, 58-24616, 58-54223, etc. to improve the flying height accuracy. It is difficult to control the flying height larger than the directional gap. In the current hydrodynamic bearing motor for HDD, the radial clearance is about 2 microns, and the flying height in the axial direction is about 5 microns, so it is difficult to apply to products because it wants to secure a margin for shock and vibration.

  For the reasons described above, any of the above-described methods proposed heretofore is difficult to adopt in current HDDs. However, since the radial bearing has a narrow radial gap, it is efficient and powerful, so there is a possibility of realizing high-precision control of the flying height of the rotating part by improving the second structure.

Japanese Patent Publication No.46-8046 "Fluid sliding bearing device"

Japanese Patent Publication No. 48-4498 "Hydrodynamic sliding bearings for axial and axial loads" Japanese Patent Application Laid-Open No. 58-24615 “Hydrodynamic Fluid Bearing Device” Japanese Patent Laid-Open No. 58-24616 "Hydrodynamic Fluid Bearing Device" Japanese Patent Laid-Open No. 58-54223 “Dynamic Pressure Spindle Device”

  Therefore, the object of the present invention is to have a levitation booster, which allows rapid levitation from low speed rotation, reduces sliding wear, and precisely controls the floating amount of the rotating part to achieve high speed rotation, thinning, low axial loss, The realization of a hydrodynamic bearing motor that can reduce costs, etc., and a thin, low power consumption magnetic disk drive.

  The basic concept of the hydrodynamic bearing motor according to the present invention consists of a cylindrical shaft and a bottomed sleeve that are relatively rotatably fitted, a lubricating fluid in the gap between the shaft and the sleeve, and a magnetic field between the rotating portion and the fixed portion. In a hydrodynamic bearing motor configured with magnetic means for generating an attractive force, the shaft surface or the inner peripheral surface of the sleeve has an unbalanced herringbone groove having a pumping ability in the sleeve bottom direction and the shaft There is a circulation path in the shaft or in the sleeve that connects the vicinity of the end and the side far from the shaft end of the unbalanced herringbone groove, and the flow path cross-sectional area is smaller than the flow path cross-sectional area formed by the gap between the shaft and the sleeve. A first axial load capacity generating means by an orifice is provided in the circulation path, and a spiral groove is provided at the end of the shaft, and a second axial load capacity generating means depending on the flying height is provided. The lube generates radial bearing dynamic pressure to maintain the rotating part posture and pumps the lubricating fluid to the bottom of the sleeve to balance the first and second axial load capacities with the magnetic attractive force and the rotating part weight. The rotating unit is controlled to a predetermined flying height.

  A force between [magnetic attraction force−rotation part weight] and [magnetic attraction force + rotation part weight] is applied to the thrust bearing of the HDD used as upright, inverted, or horizontally placed. If the first axial load capacity due to the lubricating fluid pumped by the radial bearing and the orifice is greater than the minimum value [magnetic attractive force-rotating part weight] applied to this thrust bearing, the flying height can be controlled. There will be no cases. That is, the flying height is not determined when the HDD is inverted. In the present invention, the first axial load capacity is obtained by the orifice provided in the circulation path and the unbalanced herringbone groove, and the second axial load capacity is obtained by providing the spiral groove at the shaft end or the sleeve bottom. As a result, the first axial load capacity is set to a value equal to or less than the value obtained by subtracting the weight of the rotating part from the magnetic attraction force, so that the hydrodynamic bearing motor can be used in any posture of the HDD. The first axial load capacity due to the lubricating fluid pumped by the radial bearing and the orifice bears most of the load applied to the thrust bearing, and the second axial load capacity due to the spiral groove only has to bear the remainder. Therefore, it becomes possible to support the rotating part with a small spiral groove corresponding to the shaft diameter.

  Further, when the access hole for the lubricating fluid which is connected to the circulation path in the sleeve and is gradually communicated with the air and communicated with the atmosphere at the end face of the sleeve is provided so that the lubricating fluid forms an interface with the air, the access hole on the end face of the sleeve is provided. This makes it easy to monitor the interface level of the lubricating fluid and to inject the lubricating fluid. Further, when bubbles are mixed in the lubricating fluid, the bubbles are stochastically released from the interface with the atmosphere in the access hole in the process of circulating the lubricating fluid and bubbles in the circulation path, and the lubricating fluid is The bubbles inside can be removed.

  A radial bearing is used as an unbalanced herringbone groove, and a floating fluid is pumped to the end of the shaft by a lubricating fluid to cooperate with the orifice in the circulation path to generate a large part of the load capacity of the rotating part support. The gap in the radial direction is small and easy to manage, so it is energy efficient, powerful, and capable of precise flying height control in cooperation with a spiral groove with a small shaft diameter.

  In addition, the structure with an access hole that has an interface with the atmosphere continuously in the circulation path in the sleeve makes it easy to inject oil and control the level under atmospheric pressure, simplifying the assembly process of the bearing and further reducing the cost. To.

  By using the above-mentioned hydrodynamic bearing motor, it is possible to realize a magnetic disk device having the characteristics of thinning, high track density recording by small shaft touch, and low power consumption by low axial loss.

  In the following, embodiments, principles and actions of a hydrodynamic bearing motor according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a longitudinal section and a view of a shaft end surface of a fluid dynamic bearing motor for HDD according to a first embodiment of the present invention. In the figure, a hydrodynamic bearing is mainly composed of a shaft 11, a sleeve 12, a counter plate 13, a lubricating fluid filled in a gap, and the shaft 11 is connected to a hub 14 having a disk mounting surface and further to the hub 14. The rotor magnet 16 is fixed to form a rotating portion, and the sleeve 12 includes a base plate 15, and the base plate 15 includes a rotating driving stator core 17, a coil 18, and the like to form a fixed portion. Reference numeral 19 denotes a magnetic piece that is fixed to the base plate 15 so as to face the rotor magnet 16 and generates a magnetic attractive force that attracts the rotating portion in the axial direction. Reference numeral 1k is a retainer for restricting the axial displacement of the rotating part.

  The bearing part is composed of a shaft 11, a sleeve 12, a counter plate 13, and a lubricating fluid in the gap between them. The sleeve 12 has an unbalanced herringbone groove 1a, 1b on the inner peripheral surface and a pump-out on the end surface of the shaft 11. It has a spiral groove 1c. The shaft 11 has a small hole 1d that opens to the center of the shaft end, a small hole 1g that communicates from the small hole 1d to the unbalanced herringbone grooves 1a and 1b, and a vent hole 1j that communicates from the small hole 1d to the seal portion 1m. The orifice forming member 1e is fixed in the small hole 1d to form the orifice 1f. The orifice forming member 1e has a tapered shape and has a lubricating fluid interface having a portion in which the gap gradually increases from the small hole 1d toward the small hole 1j.

  The shaft 11 and the sleeve 12 are opposed to each other with a minute gap of about 2 microns, and the gap has a lubricating fluid, but the shaft 11 is reduced in diameter so that the gap becomes large at the upper end of the minute gap. Part 1m. The lubricating fluid is substantially sealed in the seal portion 1m and the small hole 1d with an interface with air due to surface tension.

  The herringbone groove is composed of a combination of two spiral grooves that pump the lubricating fluid in the opposite direction as it rotates, but the unbalanced herringbone groove 1a, 1b is constructed by shortening the length of the spiral groove on the bottom side of the sleeve 12. , The lubricating fluid is pumped toward the bottom of the sleeve 12 during rotation. The shape of the unbalanced herringbone grooves 1a and 1b provided on the sleeve 12 will be described with reference to FIG. FIG. 2 is a perspective view of the sleeve 12 divided vertically and shows upper and lower herringbone grooves 1a and 1b formed on the inner peripheral surface. The shape and size of the dynamic pressure generating groove varies depending on the gap, the viscosity of the lubricating fluid, the target performance, etc., but the upper and lower herringbone grooves 1a and 1b are usually formed to a depth of about 6 microns. The lower herringbone groove 1b is composed of spiral grooves having axial lengths L1 and L2, and L1 is set to be larger than L2 as shown in FIG. Reference numeral 21 indicates the rotation direction of the shaft 11.

  The magnetic piece 19 is made of a magnetic material such as a silicon steel plate, ferrite, or permalloy, and generates a magnetic attractive force between the rotating portion and the fixed portion in cooperation with the rotor magnet 16. It is set to about 3 to 5 times the weight of the rotating part including the magnetic disk, hub 14, rotor magnet 16, shaft 11 and the like. When the magnetic attractive force is insufficient only by the magnetic piece 19, the positions of the stator core 17 and the rotor magnet 16 are displaced in the axial direction to generate the magnetic attractive force, or the counter plate 13 is magnetized by embedding a magnet at the tip of the shaft 11. Supplement the magnetic attraction as a body.

  The shaft end slides in contact with the counter plate 13 at the time of starting and stopping the rotation, but in order to avoid damage, the surface of the counter plate 13 is coated with a solid lubricant mainly composed of molybdenum disulfide of about 10 microns. Even if DLC is formed to a few micrometers in addition to diverted molybdenum, sliding resistance is reduced and it is effective for wear prevention.

  The unbalanced herringbone groove 1b pumps the lubricating fluid in the axial direction during rotation, and the flow passage cross-sectional area of the orifice 1f portion from the flow cross-sectional area formed by the gap between the shaft 11 and the sleeve 12 and the outer peripheral length of the shaft 11 Is set to a small value to increase the pressure of the lubricating fluid in the vicinity of the shaft end during rotation to generate the first axial load capacity.

  The spiral groove 1c at the shaft end generates a second axial load capacity that decreases with the flying height. In the first embodiment of the present invention, the weight of the rotating part is subtracted from the first axial load capacity as the magnetic attraction force. Set below the specified value. The purpose and operating principle will be described with reference to FIG.

  When stationary, the shaft 11 is in contact with the counter plate 13 mainly by magnetic attraction. The lubricating fluid pumped by the unbalanced herringbone groove 1b as it starts rotating passes between the shaft end and the counter plate 13 and circulates through the orifice 1f to the far side from the shaft end of the unbalanced herringbone groove 1b. On the other hand, the unbalanced herringbone groove 1a also pumps the lubricating fluid in the axial direction and supplies it to the unbalanced herringbone groove 1b to help quick ascent at start-up. The lubricating fluid interface is moved to the extent that it is eliminated.

  FIG. 3 illustrates the operating principle in which the position control of the rotating part is performed with the flying height FH on the horizontal axis and the axial load capacity LC on the vertical axis. In the figure, numeral 31 indicates a first axial load capacity generated by the unbalanced herringbone groove 1b and the orifice 1f. Reference numeral 32 denotes a second axial load capacity by the spiral groove 1c at the shaft end and the unbalanced herringbone groove 1b, and reference numeral 33 denotes a sum of the first and second axial load capacity.

  The HDD is used in the upright position shown in FIG. 1 or upside down, or in the horizontal position, and in mobile applications, vibration may be further applied. This is a point that differs greatly from the usage conditions of polygon scanners, VCRs, and the like, and it is a point that must be considered with respect to design specifications. The force applied between the rotating part and the fixed part varies depending on the posture. If it is upright as shown in FIG. 1, the value obtained by adding the weight of the rotating part to the magnetic attraction force is reversed. The value obtained by subtracting the rotating part weight from the force corresponds.

  Reference numeral 34 indicates a value obtained by adding the rotating part weight to the magnetic attractive force, and reference numeral 35 indicates a value obtained by subtracting the rotating part weight from the magnetic attractive force. Therefore, the flying height f1 at the position where the number 34 and the number 33 intersect in the upright position is the flying height f2 at the position where the number 35 and the number 33 intersect in the inverted position.

  If the first axial load capacity 31 is larger than the value 35 obtained by subtracting the weight of the rotating part from the magnetic attractive force, the second axial load capacity 32 by the spiral groove 1c when the HDD is used in an inverted state. Even if it becomes zero, the force to lift the rotating part works and the rotating part continues to float up to the limit regulated by the stopper 1k. In the present invention, since the first axial load capacity 31 is set smaller than the value obtained by subtracting the weight of the rotating part from the magnetic attractive force (indicated by reference numeral 35), the rotating part always depends on the second axial load capacity 32. As a result, the flying position can be controlled with respect to any posture of the HDD.

  During rotation, the unbalanced herringbone groove 1b constantly circulates the lubricating fluid through the orifice 1f and the small hole 1g, and the circulation path is connected to the small hole 1j and is opened to the atmosphere. Even if it is mixed, in the process of circulating through the circulation path, the bubbles probabilistically escape to the atmosphere from the small holes 1j, and the bubbles are excluded from the lubricating fluid. Therefore, the lubricating fluid injection in the assembly process can be performed under atmospheric pressure.

  The sealing portion 1m and the small hole 1d effectively seal the lubricating fluid by surface tension, but an oil repellent agent is applied to the surface constituting the sealing portion 1m to stop the stain due to the migration of the lubricating fluid. In the retaining portion 1k, sliding friction between the rotating portion and the fixed portion does not normally occur, but there is a possibility of contact when an excessive vibration shock is applied. In this case, it is not preferable that abrasion powder is generated. As a countermeasure, it is desirable that one member is formed of a hard member or a solid lubricant such as DLC or molybdenum disulfide is applied.

  The first embodiment of the present invention has a structure having a small-diameter thrust bearing at the end of the shaft and assisting the insufficient axial load capacity by an orifice in the circulation path. With this structure, it was possible to achieve an appropriate flying height of the rotating part without having a thrust bearing larger than the shaft diameter, and to realize a reliable hydrodynamic bearing motor.

  However, the first axial load capacity due to the orifice indicated by reference numeral 31 in FIG. 3 is a value when the steady rotational speed is reached. The same conditions apply to high-speed rotation models, and as a result, the first axial load capacity during low-speed rotation is small, and the sliding distance between the counter plate facing the shaft end is long immediately after starting and immediately before stopping. As a result, the service life and reliability are impaired. The second embodiment is an example of a structure in which this point is improved and the sliding speed between the shaft end and the counter plate can be shortened by setting the rotational speed at which the rotating part starts to rise.

  4 and 5 show the structure of the second embodiment, FIG. 4 shows a sectional view of the hydrodynamic bearing motor, and FIG. 5 shows a diagram for showing the operation of the orifice in the circulation path. The structure shown in this figure is based on the structure of the hydrodynamic bearing motor in the first embodiment shown in FIG. 1, and the circulation path in the shaft is moved into the sleeve, and the pump-out spiral provided at the shaft end. The groove 1c is replaced with a pump-in spiral groove 44. Since the shape has changed, the shaft, sleeve and counter plate are indicated by different numbers 41, 42 and 43, respectively.

  The sleeve 42 and the counter plate 43 have circulation paths 4 a, 45, 46 and an access hole 47. The end face of the shaft 41 has a pump-in spiral groove 44. The circulation holes 45 and 46 are small holes having a diameter of about 0.4 mm, and the access hole 47 opens to the upper end surface of the sleeve 42 while increasing the diameter continuously with the circulation hole 45. The circulation hole 46 is a small hole that communicates between the unbalanced herringbone grooves 1a and 1b, and the recess channel 4a that communicates with the shaft end and the circulation hole 45 form a circulation path for the lubricating fluid.

  The recessed channel 4a is precisely formed on the surface of the counter plate 43 by an etching technique. Its width is about 0.5 millimeters and the depth is about 0.1 millimeters. In addition, electric discharge machining, electrolytic machining, ion milling, precision cutting, etc. can be used.

  The orifice is composed of a recessed channel 4a formed by engraving the counter plate 43 and an orifice plate 49 formed of an elastic body provided in the middle of the circulation paths 45 and 46. The lower part of FIG. 4 shows a plan view of the shaft 41 and the sleeve 42.

  The orifice plate 49 has a minute hole 4b at the center, and is made of an elastic material such as oil-resistant resin or rubber. FIG. 5 shows an enlarged view of the structure near the orifice plate 49, FIG. 5 (a) shows a state during stationary to low-speed rotation, and FIG. 5 (b) shows a state during high-speed rotation. When the shaft 41 starts to rotate, the unbalanced herringbone groove 1b starts to feed the lubricating fluid in the direction of the counter plate 43. However, since the minute hole 4b of the orifice plate 49 has a small diameter, the flow of the lubricating fluid is stopped and the orifice plate 49 is stopped. The lubricating fluid pressure at the front shaft end is quickly increased to assist the floating part including the shaft 41. As the rotational speed further increases and the amount of lubricating fluid pumped by the unbalanced herringbone groove 1b increases, the pressure applied to the orifice plate 49 increases, and the orifice plate 49 made of an elastic body is pressed as shown in FIG. It is deformed to increase the opening diameter of the minute hole 4b. In FIG. 5B, the state after the deformation of the orifice plate 49 and the minute holes 4b is indicated by numerals 49 'and 4b', respectively. As shown in FIG. 5B, the support structure of the orifice plate 49 is provided with a deformable gap.

  As described above, the microhole 4b of the orifice plate 49 shown in FIG. 4 can have a small opening area during low speed rotation and a large opening area during high speed rotation. It is possible to reduce the sliding distance between the shaft end and the counter plate 43 at the time of starting or stopping by reducing the rising start rotation speed of the rotating portion including the shaft 41. Since the relationship between the first axial load capacity caused by the orifice plate 49 and the second axial load capacity caused by the spiral groove 44 at the shaft end is the same as that of the first embodiment shown in FIG. To do.

  In this embodiment, the access hole 47 that is continuous with the circulation hole 45 is provided and an interface of the lubricating fluid is provided. The unbalanced herringbone groove 1a pumps the lubricating fluid in the axial direction during rotation and accommodates the lubricating fluid in the shaft end portion whose volume has increased with the rotation and floating, and accordingly, the unbalanced herringbone groove 1a. The interface of the lubricating fluid is moved to a position where the imbalance is eliminated. In this case, the lubricating fluid that has caused excess or deficiency at the shaft end is adjusted by the lubricating fluid in the access hole 47. The access hole 47 is not essential, but has an important role in adjusting the lubricating fluid, and has a role of facilitating manufacture by reducing the dimensional tolerance of each part.

  During the rotation, the unbalanced herringbone groove 1b constantly circulates the lubricating fluid through the circulation path, and the circulation path is connected to the access hole 47 and opened to the atmosphere. In the process of circulating through the circulation path, the bubbles probabilistically escape from the access hole 47 to the atmosphere, and the bubbles are excluded from the lubricating fluid. Therefore, the lubricating fluid injection in the assembly process can be performed under atmospheric pressure, and the interface 48 of the lubricating fluid can be monitored from the access hole 47 or the lubricating fluid can be additionally injected after the assembly.

  If a small hole for observation is provided in the hub 14 corresponding to the access hole 47, the lubricating fluid can be monitored at any time even after completion, and if the access hole 47 is modified to be provided on the bottom side opposite to FIG. The lubricating fluid can be monitored from the outside of the HDD.

  Special attention should be paid to the minimum gap in the access hole 47 and the circulation paths 45 and 46. The interface of the lubricating fluid with the atmosphere has the same curvature at rest with the seal portion 1m and the access hole 47, and reaches equilibrium. Therefore, if the minimum gap in the access hole 47 is too large, the lubricating fluid is likely to leak. A gap adjusting member can be arranged in the access hole 47 to adjust the minimum gap, but the third embodiment facilitates this point.

  FIG. 6 shows the structure of the third embodiment of the present invention. The structure of the elastic orifice plate 49 in FIG. 4 is changed, and the sleeve is made into a double structure of the inner cylinder 61 and the outer cylinder 62, and the circulation path and Ventilation hole formation is facilitated.

  In FIG. 6, the sleeve has a double structure of an inner cylinder 61 and an outer cylinder 62, and a part of the outer peripheral surface of the inner cylinder 61 is flattened to create a crescent-shaped gap between the inner cylinder 61 and the outer cylinder 62. The function of the circulation path 45 and the access hole 47 in FIG. In other words, the cross section of the gap is a crescent shape, with narrow gap portions 64 at both ends, and a wide gap portion 65 of about 0.3 millimeters or more at the center. When one end of the gap is in contact with the lubricating fluid, the lubricating fluid concentrates in the narrow gap 64 at both ends due to surface tension, and the central wide gap 65 becomes an air passage. In FIG. 6, the circulation path 46 circulating to the unbalanced herringbone groove 1 b is formed from the narrow gap portion 64, so that the lubricating fluid passes through the recessed channel 4 a, the narrow gap portion 64, and the circulation path 46, and is unbalanced herringbone groove 1 b. To recirculate.

  In the lower part of FIG. 6, a sleeve end face constituted by an inner cylinder 61 and an outer cylinder 62 is shown, and a narrow gap portion 64 and a wide gap portion 65 are shown.

  Since the narrow gap portion 64 continues to the upper end surface of the sleeve, there is a possibility that the lubricating fluid may ooze out from the upper end surface of the sleeve. If the amount is of concern, it can be avoided by applying an oil repellent agent near the upper end of the sleeve of the narrow gap portion 64, or filling the narrow gap portion 64 near the upper end of the sleeve with a relatively high viscosity adhesive. For further completeness, a sealing plate 63 is used.

  The sealing plate 63 is a transparent thin plate and is disposed so as to cover the gap between the inner cylinder 61 and the outer cylinder 62 at the upper end surface of the sleeve. 7, the sealing plate 63 has a circular hole 71 having a diameter of about 0.3 mm or more at a position corresponding to the wide gap portion 65 of the gap portion. The circular hole 71 forms a seal portion due to surface tension to prevent the lubricating fluid from bleeding out. Since the sealing plate 63 is a transparent plate, the lubricating fluid in the narrow gap portion 64 can be visually recognized, and the amount of the lubricating fluid can be known from the position of the boundary.

  The management of the minimum gap of the access hole 47 in the second embodiment is important from the viewpoint of lubricating fluid sealing, and there is a possibility that a member for adjusting the gap is required. If a gap is provided between the inner cylinder 61 and the outer cylinder 62 as in the present embodiment, the minimum gap in the gap can be easily set and managed to about 0.1 to 0.2 mm, and lubrication can be achieved. The fluid sealing ability can be improved.

  The structure in which the sleeve is formed as a double cylinder as described above and the circulation path and the vent hole are formed as a gap therebetween facilitates the size control of the gap portion, but the outer diameter of the inner cylinder 61 and the inner diameter of the outer cylinder 62 are controlled. It requires precision and can increase costs. The outer cylinder 62 is made of resin, and the inner cylinder 61 and the outer cylinder are made smaller by making the inner diameter of the outer cylinder 62 slightly smaller than the outer diameter of the inner cylinder 61 and utilizing the elasticity of the outer cylinder 62 or the temperature expansion difference therebetween. It can be improved by assembling 62. In that case, instead of forming a gap portion by making a part of the outer peripheral surface of the inner cylinder 61 flat, the gap portion may be formed on the inner peripheral surface of the outer cylinder 62 by molding.

  8 (a) and 8 (b) are cross-sectional views showing the structure of the recessed channel 4a on the counter plate 43. The counter plate 43 and the elastic orifice 66 and its peripheral shaft 41, the inner cylinder of the sleeve 61, the outer cylinder 62, etc. are shown. As shown in these figures, the recess channel 4a is precisely formed on the counter plate 43 as a part of the circulation path by a technique such as pressing or electrolytic processing, but an opening is formed so as to face the outer periphery of the end of the shaft 41. The elastic orifice 66 is embedded in the recessed channel 4a including the opening. The elastic orifice 4a may be formed by disposing and fixing oil-resistant rubber or resin, or by applying semi-polymerized resin.

  The difference between FIG. 8A and FIG. 8B is that the former is stationary and the latter is close to steady rotation. That is, in a stationary state, the elastic orifice 66 almost completely closes the opening of the recessed channel 4a and increases the flow resistance of the circulation path, so that the shaft of the lubricating fluid pumped by the second herringbone groove 1b at the start of rotation is used. The pressure rise in the vicinity of the end portion is assisted to promptly lift the shaft 41. The elastic orifice 66 'is deformed by the lubricating fluid pressure that increases in the vicinity of the shaft end during the steady rotation shown in FIG. 8B, and the lubricating fluid is released by increasing the cross-sectional area of the flow path near the opening of the recessed channel 4a. Thus, an upper limit is set for the pressure increase near the shaft end. Therefore, even if the flow resistance at the elastic orifice 66 portion is set to be large at the time of low-speed rotation, the first axial load capacity 31 that is the gist of the present invention described with reference to FIG. It is easy to satisfy the condition at the time of steady rotation that is set smaller than the value obtained by subtracting the weight (indicated by reference numeral 35).

  Thus, the elastic orifice 66 provided in the recessed channel 4a, which is a part of the circulation path, quickly raises the rotating part including the shaft 41 and reduces the sliding distance between the shaft 41 and the counter plate 43, thereby causing wear. There is an effect to suppress. The depth of the recessed channel 4a is around 0.2 millimeters, and the width is about 1 millimeter, so that there is no difficulty in processing and embedding the elastic orifice 66.

  The principle of operation as a hydrodynamic bearing motor is the same as that of the embodiment shown in FIGS.

  9 and 10 show a fourth embodiment of the present invention, FIG. 9 shows a longitudinal section, and FIG. 10 shows a plan view and a partial section of the counter plate 91, respectively.

  In FIG. 9, the sleeve is composed of an inner cylinder 61 and an outer cylinder 62, and it is the same that a narrow gap portion 64, a wide gap portion 65 and a circulation hole 46 are provided between them. The counter plate 91 is made thicker than the counter plate 43 of FIG. The counter plate 91 is formed with a circular concave portion 92 that accommodates the shaft 41 as an extension of the inner peripheral surface of the sleeve inner cylinder 61, and a concave channel 93 is formed so as to be connected to the circular concave portion 92 and the narrow gap portion 64. . In FIG. 9, the recessed channel 93 is formed in two places. In the lower part of FIG. 9, reference numeral 94 denotes a boundary between the inner cylinder 61 and the outer cylinder 62, reference numeral 64 denotes a narrow gap portion, and reference numeral 65 denotes a position where the wide gap portion contacts the surface of the counter plate 91.

  10A is a plan view of the counter plate 91, and FIG. 10B is a sectional view of the opening of the recessed channel 93 indicated by A-A 'in FIG. 10A. Reference numeral 101 denotes an opening of the recess channel 93, reference numeral 102 denotes a cross-sectional shape of the opening 101, and reference numeral 103 denotes a bottom surface level of the circular recess 92.

  When the rotating part including the shaft 41 starts to rotate, the unbalanced herringbone groove 1b pumps the lubricating fluid in the axial direction. At that time, the opening 101 is above the bottom surface level 102 of the circular recess 92, so Closed, the lubricating fluid pressure in the vicinity of the shaft end is quickly increased to float the rotating part. When the shaft 41 floats and the flow area of the opening 101 is substantially increased, most of the lubricating fluid pumped by the unbalanced herringbone group 1b passes through the recessed channel 93 and the circulation paths 64 and 46 from the opening 101. As a result, it flows back to the unbalanced herringbone groove 1b and contributes little to the increase of the lubricating fluid pressure at the shaft end. However, at that time, the rotational speed is sufficiently high, and the axial load capacity by the spiral groove 44 is also large enough to support the rotating portion.

  In the description of the above embodiment, the circulation path opening is arranged at the center of the shaft end in the first embodiment, the shaft end groove is a pump-out spiral groove, and in other embodiments the circulation path opening is the shaft end. The groove at the end of the shaft arranged on the outer periphery of the part was composed of a pump-in spiral groove. This is a configuration in which mutual interference is reduced so that the spiral groove at the end of the shaft exhibits its maximum capability and load capacity control by an orifice or a variable opening in the circulation path is facilitated.

  From the first embodiment to the fourth embodiment, all the hydrodynamic fluid bearing motors have been described with respect to specific structural examples and operating principles of the present invention by taking the shaft rotation structure as an example. However, it is apparent that the present invention can be applied to a structure in which the shaft is fixed and the sleeve side is rotationally driven within the scope of the present invention. However, if there is a circulation path on the sleeve side, centrifugal force is applied to the lubricating fluid in the circulation path, and the possibility of lubricating fluid leakage is higher than that of the shaft rotation structure.

  Further, in the above embodiment, the thrust bearing is described as a spiral groove at the end of the shaft, and the operation principle and effect have been described. However, it is clear that the thrust bearing can be applied to other structures such as a structure in which the thrust bearing is formed on the sleeve end surface. It is effective to reduce sliding wear quickly.

  Although the entire structure of the magnetic disk drive using the hydrodynamic bearing motor of the above embodiment was not shown, the vertical cross-sectional structure of the hydrodynamic bearing motor that almost determines the vertical cross-sectional structure of the magnetic disk drive was shown. Thus, the thin structure of the magnetic disk device is defined. Thus, in the present embodiment, it was shown that the floating rotation of the rotating part including the magnetic disk can be supported with high accuracy without having a thrust bearing larger than the shaft diameter. By using the hydrodynamic bearing motor, a thin and low power consumption magnetic disk device can be realized.

  The operation principle and structure of the present invention have been described with reference to the embodiments. In the above embodiment, only a few examples are given to explain the operation principle of the present invention, and it is needless to say that the materials and structures can be modified without departing from the spirit of the present invention. For example, since air bubbles in the lubricating fluid can be removed at the air vent part following the circulation hole adopted in the above embodiment, the lubricating fluid is injected at atmospheric pressure and deaerated by rotating for a predetermined time. It is also possible to adopt such a process. Furthermore, it is possible to extend the time during which the hydrodynamic fluid bearing motor and the magnetic disk device can be moved by exchanging the lubricating fluid during use and adding the lubricating fluid by using these access holes.

  According to the hydrodynamic bearing motor of the present invention, it is possible to realize a hydrodynamic bearing motor capable of precisely controlling the flying height of the rotating portion without having a thrust bearing larger than the shaft diameter. Since the flow rate of the lubricating fluid can be kept to a minimum, the possibility of lubricating fluid leakage is reduced and axial loss is reduced. Furthermore, in the present invention, since the bubbles in the lubricating fluid can be removed during rotation, the assembling process is simplified and the cost can be reduced. It is particularly suitable for a thin and low current consumption magnetic disk device.

The longitudinal cross-section and shaft end surface of the hydrodynamic bearing motor which is a 1st Example are shown. The sleeve 12 in FIG. 1 is divided vertically and shown as a perspective view. The figure for demonstrating the floating position of a rotation part in a 1st Example is shown. The longitudinal cross-section and sleeve end surface of the hydrodynamic bearing motor which is a 2nd Example are shown. FIG. 5 shows an orifice plate configuration and operation in FIG. 4. The longitudinal cross-section and sleeve end surface of the hydrodynamic bearing motor which is a 3rd Example are shown. The structure of the sealing board 63 in FIG. 6 is shown. FIG. 6 shows the configuration and operation of the elastic orifice in FIG. The longitudinal cross-section and counterplate of the hydrodynamic bearing motor which are the 4th Example are shown. The details of the shape of the counter plate in FIG. 9 are shown.

Explanation of symbols

11 ... shaft, 12 ... sleeve,
13 ... Counter plate, 14 ... Hub,
15 ... Base plate, 16 ... Rotor magnet,
17 ... stator core, 18 ... coil,
19: Magnetic piece,
1a, 1b .. unbalanced herringbone groove,
1c... Spiral groove, 1d, 1g, 1j .. small hole,
1e: Orifice member, 1f: Orifice,
1k ... retainer, 1m ... seal part,
21 ... Rotation direction of the shaft 11,
31 ... first axial load capacity, 32 ... second axial load capacity,
33 ... sum of first and second axial load capacities,
34: Value obtained by adding the rotating part weight to the magnetic attractive force,
35 ... value obtained by subtracting the weight of the rotating part from the magnetic attractive force,
41 ... shaft, 42 ... sleeve,
43 ... counter plate, 44 ... spiral groove,
45, 46 .. circulation hole, 47 ... access hole,
48: Lubricating fluid interface, 49, 49 '.. Orifice plate,
4a... Recessed channel, 4b, 4b '.. micropore,
61 ... Inner cylinder, 62 ... Outer cylinder,
63 ... sealing plate, 64 ... narrow gap,
65 ... Wide gap part, 66, 66 '.. Elastic body orifice,
71 ... round hole,
91 ... counter plate, 92 ... circular recess,
93 ... concave channel, 94 ... boundary between the inner cylinder 61 and the outer cylinder 62,
101 ... opening, 102 ... cross-sectional shape of the opening,
103 ... the bottom level of the circular recess,

Claims (9)

A cylindrical shaft and a bottomed sleeve that are relatively rotatably fitted, a lubricating fluid filled in a gap between the shaft and the sleeve, and a magnetic means for generating a magnetic attractive force between the shaft and the sleeve. The hydrodynamic bearing motor constructed as described above has at least a thrust bearing groove and an unbalanced herringbone groove having a pumping capability of lubricating fluid in the axial direction on the shaft surface or inner peripheral wall of the sleeve. The sleeve has a circulation path connecting between the vicinity of the shaft end and the side farther from the shaft end of the unbalanced herringbone groove, and the circulation path is at least more than a flow path cross-sectional area formed by a radial gap between the shaft and the sleeve. It is assumed that it has an orifice with a small channel cross-sectional area when stationary, and the unbalanced herringbone groove generates a radial bearing dynamic pressure to maintain the rotating part posture during rotation. At the same time, the first axial load capacity that supports the rotating part in the axial direction by the lubricating fluid pressure that is pumped in the axial direction and increased by the pumped lubricating fluid and the orifice in the circulation path is The thrust bearing groove increases the lubricating fluid pressure during rotation to obtain a second axial load capacity for supporting the rotating portion in the axial direction, The rotating part is controlled to a predetermined flying height by balancing the sum of one axial load capacity and the second axial load capacity with the magnetic attraction force and the gravity applied to the rotating part. The hydrodynamic bearing motor is characterized in that the rotating part is surely floated and rotated in any position, and the sliding distance when starting and stopping is small. 2. The hydrodynamic bearing motor according to claim 1, wherein the thrust bearing groove is a spiral groove formed on the shaft end or the bottom surface of the sleeve, and when the circulation path opening is near the outer periphery of the shaft end, A hydrodynamic bearing motor characterized by a pump-out spiral groove when the path opening is near the shaft end center. 2. The hydrodynamic bearing motor according to claim 1, wherein a part or all of the orifice in the circulation path is made of an elastic body, and the orifice flow path is substantially cut off under a condition that the pressure of the lubricating fluid at the start and stop is small. An unbalanced herringbone that has a small area, a large cross-sectional area of the flow path due to deformation of the elastic body under the condition that the pressure of the lubricating fluid during steady rotation is large, and a large flow path resistance during low-speed rotation and a pumping capacity in the axial direction. A hydrodynamic bearing motor characterized by realizing a rapid pressure increase with the groove, setting an upper limit value of the pressure during steady rotation, and reducing the sliding distance when starting and stopping 4. The hydrodynamic bearing motor according to claim 3, wherein a part of the circulation path is a recessed channel provided in the counter plate, and the opening is provided in a portion facing the vicinity of the outer periphery of the shaft end. A hydrodynamic bearing motor characterized in that an orifice is formed that changes the flow path resistance in response to the lubricating fluid pressure in the vicinity of the outer periphery of the shaft end by being filled with an elastic body. 2. The hydrodynamic bearing motor according to claim 1, wherein the circulation path opening is configured so that a substantial opening cross-sectional area varies with the rising movement of the shaft end, and at least when stationary, the flow path breakage at the circulation path opening is established. A hydrodynamic bearing motor characterized by having a small area and enabling a quick increase in lubricating fluid pressure at the start of rotation and a small sliding distance when starting and stopping. 2. The hydrodynamic bearing motor according to claim 1, wherein the lubricating fluid is connected to the circulation path so that the lubricating fluid gradually forms a gap so as to form an interface with the air, and the lubricating fluid in the gap between the shaft and the sleeve is held. A hydrodynamic bearing characterized by having a vent hole that has a taper seal portion and communicated with the atmosphere, and that bubbles in the lubricating fluid are released to the atmosphere by the vent hole in the process of circulating the lubricating fluid in the circulation path. motor 7. The hydrodynamic bearing motor according to claim 6, wherein the lubricating fluid is connected to a circulation path in the sleeve, and a vent hole outlet is provided at the sleeve end face to provide an access hole for the lubricating fluid. Hydrodynamic bearing motor capable of level monitoring and lubrication fluid injection 8. The hydrodynamic bearing motor according to claim 7, wherein the sleeve has a double cylinder configuration of an inner cylinder and an outer cylinder, and the outer peripheral surface of the inner cylinder is partially flat, or the inner peripheral surface of the outer cylinder is provided with a recess. As a result, an axial gap is formed between the outer peripheral surface of the inner cylinder and the inner peripheral surface of the outer cylinder. The narrow gap portion in the gap cross section is circulated and the wide gap portion in the gap cross section is vented. Hydrodynamic bearing motor characterized in that it has an access hole to the lubricating fluid as a part 9. The hydrodynamic bearing motor according to claim 8, wherein the sleeve is exposed to the end face of the sleeve by a sealing plate having a circular opening having a diameter equal to or smaller than the gap of the wide gap portion formed between the inner cylinder and the outer cylinder of the sleeve. The hydrodynamic bearing motor is characterized in that the gap is sealed to prevent leakage of the lubricating fluid.

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