JP2007247885A - Hydrodynamic bearing type rotary device and recording and reproducing device with same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrodynamic bearing type rotary device which can maintain an appropriate life by considering the relationship of the life of the bearing with radial load, eccentricity, an oil shearing work function, a rotation rate and the like. <P>SOLUTION: This hydrodynamic bearing type rotary device has a shaft being inserted into a bearing hole of a sleeve so as to be relatively rotatable, and a radial bearing surface having hydrodynamic grooves formed on at least one of an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve. Given that an oil shearing work function represented by following expressions (1), (2), (3) is W, the hydrodynamic bearing type rotary device is formed such that a value of 1/W is 10000 or higher: expression (1) W=P×L×Ep, expression (2) Fs=(η×ω×D^2×L^2)/C^3, expression (3) Ep=P/(Fs×C), in which Fs is rigidity-equivalent function, Ep is eccentricity-equivalent function, P is load of one radial bearing, L is axial length of one radial bearing, C is radial clearance of radial bearing, η is absolute viscosity, ω is angular speed, and D is shaft diameter. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing type rotating device using a hydrodynamic bearing and a recording / reproducing apparatus including the hydrodynamic rotating device.

  In recent years, recording devices using rotating discs have increased their memory capacity and data transfer speeds have increased, so the bearings of the recording devices used for these devices always have a high precision disk load. Therefore, high performance and reliability for rotating the motor are required. Therefore, fluid bearing type rotating devices suitable for high-speed rotation are generally used as these rotating devices.

  The hydrodynamic bearing type rotary device rotates the shaft in a non-contact state with respect to the sleeve by interposing oil as a lubricant between the shaft and the sleeve and generating a pumping pressure during rotation by the dynamic pressure generating groove. Can be made. For this reason, since mechanical friction does not occur between the shaft and the sleeve during the rotation, it is possible to stably rotate at a high speed.

Hereinafter, an example of a conventional hydrodynamic bearing type rotating device will be described with reference to FIG.
As shown in FIG. 11, the conventional hydrodynamic bearing rotating device includes a sleeve 21, a shaft 22, a thrust plate 24, an oil 25, a base 26, a hub rotor 27, a stator 28 around which a coil is wound, and a rotor magnet 29. Yes.

  The shaft 22 is integrated with the flange 23 and is inserted into the bearing hole 21 </ b> C of the sleeve 21 in a rotatable state. The flange 23 is accommodated in the recess 21 </ b> D of the sleeve 21. Dynamic pressure generating grooves 21 </ b> A and 21 </ b> B are formed on at least one of the outer peripheral surface of the shaft 22 and the inner peripheral surface of the sleeve 21. On the other hand, dynamic pressure generating grooves 23 </ b> A and 23 </ b> B are formed on the surface of the flange 23 facing the sleeve 21 and the surface facing the flange 23 and the thrust plate 24. The thrust plate 24 is fixed to the sleeve 21 and the bearing gap is in a bag shape. The bearing gaps in the vicinity of the respective dynamic pressure generating grooves 21A, 21B, 23A, 23B are filled with at least oil 25, and the entire bag-shaped bearing gap formed by the sleeve 21 and the shaft 22 is also necessary. Accordingly, the oil 25 is filled.

A sleeve 21 is fixed to the base 26. The stator 28 is fixed to the base 26 so as to face the rotor magnet 29.
On the other hand, the hub rotor 27 is fixed to the shaft 22, and the rotor magnet 29, the disk 30, the spacer 32, the clamper 31, and the screw 33 are fixed.

Here, the operation of the conventional hydrodynamic bearing type rotating device configured as described above will be described as follows.
That is, in the conventional hydrodynamic bearing type rotating device, when a coil wound around the stator 28 is energized, a rotating magnetic field is generated, and a rotational force is applied to the rotor magnet 29. Thereby, the rotor magnet 29 starts rotating together with the hub rotor 27, the shaft 22, the flange 23, the disk 30, the spacer 32, the clamper 31, and the screw 33. When these members rotate, the dynamic pressure generating grooves 21A, 21B, 23A, and 23B collect the oil 25 filled in the bearing gap, and between the shaft 22 and the sleeve 21, and between the flange 23, the sleeve 21, and the thrust plate 24. During this period, a pumping pressure is generated.

Thus, the shaft 22 can be rotated in a non-contact state with respect to the sleeve 21 and the thrust plate 24, and data can be recorded / reproduced with respect to the rotating disk 30 by a magnetic head or an optical head (not shown). it can.
Japanese Patent No. 2506636 Japanese Patent No. 1748817 JP-A-1-120418 JP-A-62-1040271

However, the conventional hydrodynamic bearing type rotating device has the following problems.
That is, in FIG. 11, a minute gap of several μm is secured between the sleeve 21 and the shaft 22, while on the other hand, between the flange 23 and the sleeve 21 or the thrust plate 24, several μm to several A sufficient gap of 10 μm is secured. However, in the conventional hydrodynamic bearing type rotating device, when continuously rotating at a high speed for a long time under a high temperature condition (for example, 70 ° C.), the oil deteriorates due to the shearing force due to the bearing rotation. Otherwise, there is a risk of cosmetic damage and bearing burn-in.

Here, FIG. 12 shows an experimental result when the hydrodynamic bearing type rotating device designed for 10,000 rpm is continuously rotated at a double speed of 20,000 rpm.
Here, it can be seen that the life of the hydrodynamic bearing type rotating device is deteriorated by about 40% compared with 10,000 rotations.

FIG. 13 shows the experimental results when the hydrodynamic bearing type rotating device designed to have a radial load of 110 grams and operated continuously with the radial load doubled.
Here, this hydrodynamic bearing type rotating device does not cause a squeeze even when the radial bearing load is doubled, and the non-contact rotation is maintained. About 50 percent worse.

  As can be seen from the above experimental results, the radial fluid bearing of the conventional hydrodynamic bearing type rotating device is a bearing that deteriorates when the oil is deteriorated in the long term operation under a high temperature of about 70 ° C. under a high load. May break down. With regard to the life of these hydrodynamic bearing type rotating devices, it has already been proved that the relationship between the temperature and the bearing life has been shortened as the temperature increases according to Arrhenius reaction kinetics. However, the relationship between the radial load, the eccentricity, the oil shear work function, the rotational speed, etc., and the life of the bearing has not been theoretically clarified.

  An object of the present invention is to provide a fluid bearing type rotating device that can ensure a proper life in consideration of the relationship between the life of the bearing and the radial load, eccentricity, oil shear work function, rotational speed, etc. It is an object of the present invention to provide a bearing type rotating device and a recording / reproducing apparatus including the same.

  A hydrodynamic bearing type rotating device according to a first aspect of the present invention includes a sleeve having a bearing hole, a shaft inserted in a relatively rotatable state in the bearing hole of the sleeve, and the sleeve and the shaft attached to the rotating side. And a radial bearing surface having a dynamic pressure generating groove on at least one of the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve. When the oil (lubricant) shear work function expressed by the following formula (1) is W, the value of 1 / W is set to be 10,000 or more.

W = P × L × Ep (1)
Fs = (η × ω × D ^ 2 × L ^ 2) / C ^ 3 (2)
Ep = P / (Fs × C) (3)
W: oil (lubricant) shear work function Fs: stiffness equivalent function Ep: eccentricity equivalent function η: absolute viscosity at 70 ° C. [N · S / m ^ 2]
ω: angular velocity [rad / s (= 2 · π · f / 60)]
D: Shaft diameter [m]
f: Number of revolutions [rev / min]
L: Length per radial bearing [m]
C: Clearance in radial direction of radial bearing [m]
P: Load applied to the center of the bearing length for each radial bearing [N]
Here, the lubricant (for example, oil, etc., hereinafter referred to as oil) of the hydrodynamic bearing type rotating device has a high temperature (for example, about 70 ° C.). A relational expression indicating the reciprocal of the shear work function of the lubricant (hereinafter referred to as the oil shear work function) is provided so that the fluid bearing is not damaged in a short time because it becomes easy to evaporate or a sufficient oil film strength cannot be obtained. The lower limit (10000 or more) is set as a certain condition to be satisfied.

  Here, according to the graph showing the relationship between the reciprocal 1 / W of the oil shear work function W and the radial bearing life ratio, the reciprocal 1 / W of the oil shear work function W is 10000 or less set as the lower limit value. The oil shear work function becomes too large, and the radial bearing life ratio becomes 15000 or less. As a result, the shearing force that the oil receives due to the rotation of the bearing increases, so that the bearing is seized due to the evaporation of the oil and the deterioration of the oiliness, and the product life is shortened.

  Therefore, according to the hydrodynamic bearing type rotating device configured to satisfy the above conditional expression, it is possible to realize a long-life hydrodynamic bearing type rotating device even when continuously rotating at high speed under high temperature conditions. Play.

The hydrodynamic bearing type rotating device according to the second invention is the hydrodynamic bearing type rotating device according to the first invention, and is configured such that the value of 1 / W is 65000 or less.
Here, an upper limit value (65000 or less) is set as a constant condition to be satisfied by the relational expression indicating the reciprocal of the shear work function of oil.

  Here, in order to increase 1 / W, that is, to reduce the oil shear work function W, in order to maintain the rigidity and rotational accuracy of the fluid bearing while reducing the oil shear, the bearing clearance and the bearing area are increased. There is a need to. In this case, the current consumption of the motor increases under low temperature conditions due to the high viscosity resistance of the oil. Further, if the parts are enlarged and processed with high precision in order to maintain the rigidity and rotational accuracy of the bearing, the parts cost will increase.

Thereby, it can prevent that it becomes excessive quality regarding the lifetime of a bearing, and it can avoid that productivity, production cost, the performance in low temperature, etc. are impaired.
A hydrodynamic bearing type rotating device according to a third aspect of the present invention is a sleeve having a bearing hole, a shaft inserted in a relatively rotatable state in the bearing hole of the sleeve, and the sleeve and the shaft attached to the rotating side. And a radial bearing surface having a dynamic pressure generating groove on at least one of the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve. When the oil shear equivalent function expressed by the following equation (4) is E, the 1 / E value is 0.00001 or more.

E = Ep × ω × ω (4)
Fs = (η × ω × D ^ 2 × L ^ 2) / C ^ 3 (5)
Ep = P / (Fs × C) (6)
W: Oil (lubricant) shear work function Fs: Rigidity equivalent function Ep: Eccentricity equivalent function η: Absolute viscosity at 70 ° C. [N · S / m ^ 2]
ω: angular velocity [rad / s (= 2 · π · f / 60)]
D: Shaft diameter [m]
f: Number of revolutions [rev / min]
L: Length per radial bearing [m]
C: Clearance in radial direction of radial bearing [m]
P: Load applied to the center of the bearing length for each radial bearing [N]
Here, the lubricant (for example, oil, etc., hereinafter referred to as oil) of the hydrodynamic bearing type rotating device is subjected to shearing at a high temperature (for example, about 70 ° C.) at a high-speed continuous rotation, and the deterioration proceeds. As a certain condition that the relational expression showing the reciprocal of the oil shear work function should satisfy the lower limit ( 0.00001 or more) is set.

  Here, according to the graph showing the relationship between the reciprocal 1 / E of the oil shear equivalent function E and the radial bearing life ratio, the reciprocal 1 / E of the oil shear work function E is 0.00001 or less set as the lower limit value. In this case, the oil shear work function becomes too large, and the radial bearing life ratio becomes 15000 or less. As a result, the shearing force that the oil receives due to the rotation of the bearing increases, so that the bearing is seized due to the evaporation of the oil and the deterioration of the oiliness, and the product life is shortened.

  Therefore, according to the hydrodynamic bearing type rotating device configured to satisfy the above conditional expression, it is possible to realize a long-life hydrodynamic bearing type rotating device even when continuously rotating at high speed under high temperature conditions. Play.

A hydrodynamic bearing type rotating device according to a fourth aspect of the present invention is the hydrodynamic bearing type rotating device according to the third aspect of the present invention, wherein the value of 1 / E is 0.00013 or less.
Here, the upper limit value (0.00013) is set as a constant condition to be satisfied by the relational expression indicating the reciprocal of the shear work function of oil.

  Here, in order to increase 1 / E, that is, to reduce the oil shear work function E, the bearing clearance and the bearing area are increased in order to maintain the rigidity and rotational accuracy of the fluid bearing while reducing the oil shear. There is a need to. In this case, the current consumption of the motor increases under low temperature conditions due to the high viscosity resistance of the oil. Further, if the parts are enlarged and processed with high precision in order to maintain the rigidity and rotational accuracy of the bearing, the parts cost will increase.

Thereby, it can prevent that it becomes excessive quality regarding the lifetime of a bearing, and it can avoid that productivity, production cost, the performance in low temperature, etc. are impaired.
A hydrodynamic bearing type rotating device according to a fifth invention is the hydrodynamic bearing type rotating device according to the first to fourth inventions, wherein the gap in the radial direction formed between the radial bearing surface and the sleeve or the shaft is 1 μm or more and substantially constant.

Here, the lower limit is set for the size of the gap formed between the radial bearing surface and the srobe or shaft.
Here, when the size of the gap is less than 1 μm, depending on the processing accuracy and surface roughness of the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve, there is a risk of adversely affecting the life of the bearing. is there.

Accordingly, by further satisfying the above condition of 1 μm or more, it is possible to always ensure a stable life regardless of the processing accuracy and surface roughness of the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve. The hydrodynamic bearing type rotating device is a hydrodynamic bearing type rotating device according to any one of the first to fifth inventions, wherein a lubricant is held in a gap formed between the shaft and the sleeve, A lubricant reservoir is formed at a position adjacent to the radial bearing surface such that the gap between the opposing surfaces is larger than the radial bearing surface. The volume of the lubricant reservoir is 10% or more of the volume of the gap between the radial bearing surface and the sleeve or shaft.

  Here, the volume of the lubricant reservoir portion (hereinafter referred to as the oil reservoir portion) formed so as to be adjacent to the radial bearing surface between the shaft and the sleeve is defined between the radial bearing surface and the sleeve. It is specified by the volume of the gap.

  In general, in this type of hydrodynamic bearing device, the amount of accumulated lubricant such as oil or grease adjacent to the gap formed between the shaft and the sleeve has been secured to a large amount of 100% or more. On the other hand, in the hydrodynamic bearing type rotating device of the present invention, the oil shearing is reduced by reducing the oil shearing work. Therefore, if the oil pool amount is 10% or more, the reliability of the hydrodynamic bearing device is sufficiently guaranteed. can do. That is, in the hydrodynamic bearing type rotating device of the present invention, the oil reservoir portion is sufficiently reliable if the volume of the oil reservoir is within the range of 10% to 100% of the volume of the gap between the radial bearing surface and the sleeve or shaft. A hydrodynamic bearing type rotating device can be obtained.

  Thereby, the size of the oil reservoir volume was set within the above numerical range with respect to the volume of the gap between the radial bearing surface and the sleeve, so that the oil reservoir was continuously rotated at a high speed under a high temperature condition. Even in this case, a long-life hydrodynamic bearing type rotating device can be obtained.

A recording / reproducing apparatus according to a seventh aspect includes the fluid dynamic bearing type rotating apparatus according to any one of the first to sixth aspects.
According to this, it is possible to extend the life of the recording / reproducing apparatus while preventing deterioration in performance and quality.

  According to the hydrodynamic bearing type rotating device of the present invention, even when continuously rotating at a high speed under high temperature conditions, the lubricant such as oil is subject to shearing and deteriorates, so that the lubricant such as oil is likely to evaporate. In addition, it is possible to prevent the fluid bearing from being damaged in a short time due to the fact that a sufficient oil film strength cannot be obtained, and to obtain a long-life hydrodynamic bearing type rotating device with no oil film breakage.

A hydrodynamic bearing type rotating device 15 according to an embodiment of the present invention will be described below with reference to FIGS. 1 and 3.
[Configuration of Fluid Bearing Rotating Device 15]
As shown in FIG. 1, the hydrodynamic bearing type rotating device 15 according to the present embodiment includes a sleeve 1, a shaft 2, a thrust plate 4, an oil (lubricant) 5, a base 6, a hub rotor 7, and a stator around which a coil is wound. 8 and a rotor magnet 9 are provided.

The shaft 2 is integrated with the flange 3 and is inserted into the bearing hole 1C of the sleeve 1 in a rotatable state.
The flange 3 is attached to the lower end of the shaft 2 and is accommodated in the recess 1D of the sleeve 1.

  Further, dynamic pressure generating grooves 1 </ b> A and 1 </ b> B are formed on at least one of the outer peripheral surface of the shaft 2 and the inner peripheral surface of the sleeve 1. On the other hand, dynamic pressure generating grooves 3 </ b> A and 3 </ b> B are formed on the surface of the flange 3 facing the sleeve 1 and the surface facing the flange 3 and the thrust plate 4.

The thrust plate 4 is fixed to the sleeve 1 and the bearing gap is bag-shaped.
As shown in FIG. 3, an oil reservoir (lubricant reservoir) 1E provided by machining a circumferential groove with respect to the sleeve 1 or the shaft 2 is formed in the opening of the sleeve 1.

  The bearing gaps in the vicinity of the respective dynamic pressure generating grooves 1A, 1B, 3A, 3B shown in FIG. 1 are filled with at least oil 5, and the entire bag-like bearing gap consisting of the sleeve 1 and the shaft 2 and the oil The reservoir 1E is also filled with oil 5 as necessary.

  The hub rotor 7 is fixed to the shaft 2, and the rotor magnet 9, the disk 10, the spacer 12, the clamper 11, and the screw 13 are fixed. On the other hand, the sleeve 1 is fixed to the base 6, and the stator 8 is fixed to the base 6 so as to face the rotor magnet 9.

<Operation of Fluid Bearing Type Rotating Device 15>
Here, the operation of the hydrodynamic bearing type rotating device 15 having the above configuration will be described.
In the hydrodynamic bearing type rotating device 15 of this embodiment, when a coil wound around the stator 8 is energized, a rotating magnetic field is generated, and a rotational force is applied to the rotor magnet 9. The rotor magnet 9 starts rotating together with the hub rotor 7, the shaft 2, the flange 3, the disk 10, the spacer 12, the clamper 11, and the screw 13.

  In the dynamic pressure generating grooves 1A, 1B, 3A, 3B, the oil 5 is collected by this rotation, and a pumping pressure is generated between the shaft 2 and the sleeve 1, and between the flange 3, the sleeve 1, and the thrust plate 4.

  Thereby, the shaft 2 is rotated in a non-contact state with respect to the sleeve 1 and the thrust plate 4, and data can be recorded / reproduced with respect to the disk 10 by using a magnetic head or an optical head (not shown).

An embodiment of the hydrodynamic bearing type rotating device 15 having the above configuration will be described with reference to FIGS.
Here, in the hydrodynamic bearing type rotating device, under high temperature and high speed continuous rotation of the bearing, the oil filling the bearing gap is subjected to shearing and deterioration progresses, and the oil deteriorates and pulls oil molecules. It was hypothesized that the hydrodynamic bearing could be damaged in a short time due to being stripped off and evaporating or not having sufficient oil film strength.

  This is based on the hypothesis that the relationship between the oil shear work function (lubricant shear work function) and the bearing life is as shown in the graph of FIG. That is, it is a hypothesis that a hydrodynamic bearing type rotating device in which the shear work applied to oil is set within a certain range will have a long life even at high temperature and high speed continuous rotation.

  In order to prevent deterioration of oil due to shear work, firstly, it is conceivable to reduce the shear work amount for oil by elucidating the phenomenon of oil shearing and keeping the shear work below a certain value. Secondly, the radial shear clearance in the radial bearing, which has a large effect on the oil shear work function and is also affected by the machining accuracy of the parts, is specified to a certain value or more, so that the oil shear work function and mechanical wear are reduced. It is conceivable to reduce, and thirdly, to prevent the oil amount shortage by setting the oil amount (volume) of the oil reservoir to a certain level or more.

  Further, in this example, in the hydrodynamic bearing type rotating device 15 according to the above embodiment, the size of the radial bearing gap between the sleeve 1 and the shaft 2 and the actual life ratio (H) of the hydrodynamic bearing are shown in FIG. The relationship is as shown in the graph.

  That is, the smaller the gap in the radial direction between the radial bearing surface and the sleeve 1 (or the shaft 2), the higher the rigidity of the fluid bearing and the strength when an external force is applied, while the gap in the radial direction ( When C) is less than 1 μm, the processing accuracy of the outer peripheral surface of the shaft 2, the processing accuracy of the inner peripheral surface of the sleeve 1, and the surface roughness are adversely affected. Therefore, it is preferable that the radial bearing clearance is set to 1 μm or more in order to extend the life of the hydrodynamic bearing type rotating device.

  Here, the dynamic pressure generating groove 1A is formed in a sufficiently small gap formed by the sleeve 1 and the shaft 2 shown in FIGS. 3 and 4, and a substantially straight gap without a step portion is formed between the radial bearing surface and its opposing surface ( In the configuration formed between the sleeve 1 and the shaft 2), the size of the gap on the hub rotor 7 side (Lr in the figure) shown in FIG. 4 and the size of the oil reservoir 1E adjacent to the hub rotor 7 side (FIG. FIG. 6 shows the relationship between the ratio to the middle Lo) and the life of the hydrodynamic bearing type rotating device.

  According to the graph shown in FIG. 6, it is shown that the volume of the oil reservoir 1E on the hub rotor 7 side is good if it is approximately straight and is 10% or more of the volume of the radial bearing gap located on the hub rotor 7 side.

  Here, when no consideration is given to the setting of the oil shear work function and the radial bearing clearance as in the conventional hydrodynamic bearing type rotating device, the oil reservoir amount may require 100% or more. is there. However, when the setting of the oil shear work function and the radial bearing clearance is taken into consideration as in this embodiment, since the oil is not subjected to strong shearing, if there is a small oil reservoir as shown in FIG. It is enough. As described above, in the fluid dynamic bearing type rotating device of this embodiment, since a smaller amount of oil is required than in the prior art, even when an impact load is applied to the fluid dynamic bearing type rotating device, oil spills out. Can be avoided.

  As shown in FIG. 1, the radial bearing surface has one straight part and a bearing length of Lr. For example, as shown in FIG. When the groove 1B is divided into two by the small-diameter portion 2A of the shaft 2 and there are two straight portions, the oil amount shown in FIG. 6 corresponds to the radial bearing surface (Lr in the drawing) on the hub rotor 7 side. It means oil quantity.

Next, the conditions of the oil shear work function for reducing the shear work by setting the oil shear work function to a certain value or less were defined by mathematical expressions.
The first equation is a hypothesis that the oil shear work function W is affected by the heat generation amount and speed of the radial bearing portion or the bearing stiffness. The second equation is that the oil shear work function W is affected by the eccentricity of the bearing, and the third equation is that the oil shear work equivalent function W is the stiffness equivalent function of the third equation and the second equation. It is affected by each of the eccentricity equivalent functions.

These can be expressed in mathematical formulas.
Formula 1: Oil shear work function W = P × L × Ep
Second Formula: Eccentricity Equivalent Function Ep = P / (Fs × C)
Third equation: rigidity equivalent function Fs = (η × ω × D ^ 2 × L ^ 2) / C ^ 3
η: Absolute viscosity at 70 ° C. [N · S / m ^ 2]
ω: angular velocity [rad / s (= 2 · π · f / 60)]
f: Number of revolutions [rev / min]
D: Shaft diameter [m]
L: Length in the axial direction per radial bearing [m]
C: Clearance in radial direction of radial bearing [m]
P: Load applied to the center of the bearing length for each radial bearing [N]
Next, FIG. 7 shows the correlation between the reciprocal number (1 / W) of the oil shear work function (W) and the actual lifetime value (H) of the hydrodynamic bearing type rotating device. In addition, from FIG. 7, the reciprocal number (1 / W) and the life (H) of the hydrodynamic bearing type rotating device are in good agreement with the experimental results, and it has been proved that a correlation is recognized.

  From the above facts, as shown in FIG. 7, by setting the numerical value of the reciprocal (1 / W) of the oil shear work function (W) to be within the range of 10,000 to 65000, the oil is deteriorated by rotational shear. A hydrodynamic bearing type rotating device is obtained. From the viewpoint of bearing life, it is preferable that the numerical value of 1 / W is set so that the numerical value is as close as possible to 65000 within a range where excessive quality is not obtained.

  Here, as a basis for the lower limit value (10000) of the above numerical range, when the numerical value of 1 / W is smaller than 10000, the oil shear work function becomes too large and the life of the bearing is shortened. is there.

  Specifically, when 1 / W is less than the lower limit of 10,000, the oil is subjected to a large shearing force due to the rotation of the bearing, so that the oil evaporates or the oil property of the oil is lost and the bearing is seized. . As a result, in the hydrodynamic bearing type rotating device configured so that 1 / W is 10000 or more which is the lower limit value, continuous use is possible for about 50,000 hours (equivalent to about 5 years), whereas In the hydrodynamic bearing type rotating device with 1 / W of less than 10,000, the bearing portion is burned by continuous use for about 3000 to 8000 hours, and the life is shortened to about 1/10 to 1/5.

  On the other hand, the reason for the upper limit (65000) is that if the value of 1 / W is larger than 65000, it is an excessive life, and there is a possibility that productivity, cost, performance at low temperature, etc. may be impaired.

  Specifically, when 1 / W exceeds the upper limit of 65000, the life of the apparatus is sufficient. However, in order to reduce the oil shear work function W, that is, to maintain the rigidity and rotational accuracy of the fluid bearing while reducing the oil shear, the bearing area is increased and the bearing area is designed to be large. At low temperatures, the viscous resistance of the oil increases and the motor current consumption is about 1.2 to 2.0 times, and the required performance as a product is not satisfied. Furthermore, in order to reduce the oil shear work function W, to increase the bearing clearance and increase the bearing area and to secure equivalent bearing rigidity, high-precision bearing parts are processed and assembled with high precision. As a result, the cost of parts becomes high.

  Further, FIG. 8 shows the relationship between the radial friction equivalent function representing the magnitude of the friction torque of the radial bearing portion and the reciprocal (1 / W) of the oil shear work function (W). Here, if the reciprocal number (1 / W) is set too large, the radial bearing life becomes longer, but there is a disadvantage that the radial friction torque increases. The radial friction equivalent function is a function proportional to the bearing area and the rotational speed and inversely proportional to the size of the bearing gap, but detailed description thereof is omitted here.

Next, specific numerical values are given and the reciprocal number of the oil shear work function W is actually calculated.
In the hydrodynamic bearing type rotating device 15 shown in FIG.
Oil viscosity at 70 ° C. η = 0.004 [N · S / m ^ 2],
Angular velocity ω = 565.2 [rad / s (= 2 × π × 5400/60)],
Shaft diameter D = 0.000299 [m],
Length L per upper radial bearing L = 0.0023 [m],
Clearance C = 0.00000309 [m] in the radial direction of the radial bearing
Load P = 0.343 [N] applied to the center of the bearing length of the upper radial bearing
Then, from the above first to third formulas,
Rigidity equivalent function Fs = (η × ω × D ^ 2 × L ^ 2) / C ^ 3 = 3710000
Eccentricity equivalent function Ep = P / (Fs × C) = 0.0299
Oil shear work function W = P × L × Ep = 0.0000236
1 / W = 42400
It becomes.

When this calculation result is applied to the graph shown in FIG. 7, it is estimated that the hydrodynamic bearing type rotating device has a sufficient life of about 40,000 hours at 70.degree.
In this embodiment, stainless steel, high manganese chrome steel, or carbon steel is used as the material of the shaft 2. As the material of the sleeve 1, stainless steel, copper alloy, or a material obtained by electroless nickel plating or DLC coating on the surface thereof is used. Further, a material processed so that the surface roughness of the radial bearing surface is within a range of 0.01 to 1.60 μm is used.

  In addition, when a copper alloy that is not plated is used for the bearing material, the oil and the copper component cause a chemical reaction to accelerate deterioration, and the life of the hydrodynamic bearing device may be shortened by about 10%. However, these parameters are not considered in the oil shear work function W defined in the present invention.

  In the hydrodynamic bearing type rotating device shown in FIG. 4 described above, when the values of the radial loads applied to the upper and lower radial bearings are unknown, they can be obtained by the following method.

  That is, the shaft 2, the flange 3, the hub rotor 7, the rotor magnet 9, the disk 10, the spacer 12, the clamper 11, and the screw 13 that are the rotating body in the hydrodynamic bearing rotating device according to the present invention are taken out as a single unit, FIG. 10 shows a configuration in which a sufficiently thin thread is attached to Q and suspended in a natural state. By suspending the portion corresponding to the rotating body in this way, it is possible to obtain the position of the center of gravity that is the intersection of the axis center and the extension line of the yarn. In general, this method is called a thread fishing method.

Thereby, as shown in FIG. 10, the load Pu applied to the center part of the upper bearing length is
Pu = P × (S1 / (S1 + S2))
It can obtain | require based on the relational expression.

On the other hand, the load Pl applied to the central part of the lower bearing length is
Pl = P-Pu
It can obtain | require based on the relational expression.

  As described above, the radial load value applied to each of the upper and lower radial bearings can be obtained by obtaining the position of the center of gravity of the member serving as the rotating body. Thus, even when there are two radial bearing gaps as in the fluid bearing type rotating device shown in FIG. 4, the oil shear work function W is calculated by applying the value of Pl or Pu to P in the above first formula. Can do.

  As shown in FIG. 9, the rigidity equivalent function Fs defined above does not show a very strong correlation with the actual radial bearing life time H. On the other hand, as shown in FIG. 2, the reciprocal 1 / W of the oil shear work function W has a strong correlation with the bearing life H.

  In this embodiment, the viscosity of the oil injected into the gap between the shaft and the sleeve at 70 ° C. affects the life. In this embodiment, ester-based oil is used as the lubricant. However, when the main component of the oil is a lubricant of fluorine oil, silicon oil, or olefin oil, there is some influence on the life of the hydrodynamic bearing type rotating device. There is. However, since it has been confirmed by experiment separately that these effects are about 15% or less, these parameters are not taken into consideration for the oil shear work function W defined in this embodiment. As the lubricant, high fluidity grease can be used, and it is considered possible to use an ionic liquid.

  As described above, the gap in the radial direction of the radial bearing surface is 1.0 μm or more, and is a substantially straight gap without a step portion where the gap changes. A lubricant is held in a gap formed by the shaft and the sleeve, and an oil reservoir having a gap larger than that of the radial bearing surface is provided adjacent to the hub rotor 7 side of the radial bearing surface. In addition, the volume of the oil reservoir is configured to be 10% or more of the clearance volume of the radial bearing surface.

  Accordingly, by setting the numerical value of the reciprocal (1 / W) of the oil shear work function (W) of the radial fluid bearing within the range of 10,000 to 65000, the fluid bearing type rotating device with a long life in which the oil does not deteriorate due to rotational shearing. Can be obtained.

Another embodiment of the hydrodynamic bearing type rotating device 15 having the above configuration will be described with reference to FIGS. 1 to 6, 10, and 14 to 17 as in the first embodiment. It is.
In this example, the hypothesis was verified using an oil shear equivalent function (E) instead of the oil shear work function (W) described in Example 1.

  That is, it is hypothesized that the relationship between the oil shear equivalent function (E) and the bearing life is as shown in the graph shown in FIG. That is, it is a hypothesis that a hydrodynamic bearing type rotating device in which the shear work applied to oil is set within a certain range will have a long life even at high temperature and high speed continuous rotation.

  In order to prevent deterioration of oil due to shearing, firstly, it is conceivable to reduce the amount of shearing with respect to oil by elucidating the phenomenon that oil is sheared and keeping shear below a certain value. Second, the radial shear clearance in the radial bearing, which has a large effect on the oil shear equivalent function and is also affected by the machining accuracy of the parts, is defined to be a certain value or more, so that the oil shear work function and the mechanical elasticity are increased. It is conceivable to reduce, and thirdly, to prevent the oil amount shortage by setting the oil amount (volume) of the oil reservoir to a certain level or more.

  Also in this example, as in Example 1 above, in the hydrodynamic bearing type rotating device 15 according to the above embodiment, the size of the radial bearing gap between the sleeve 1 and the shaft 2 and the actual life ratio of the fluid bearing (H) has a relationship like the graph shown in FIG.

  That is, as described in the first embodiment, the smaller the gap in the radial direction between the radial bearing surface and the sleeve 1 (or the shaft 2), the higher the rigidity of the fluid bearing and the strength when an external force is applied. On the other hand, when the gap (C) in the radial direction is less than 1 μm, the processing accuracy of the outer peripheral surface of the shaft 2, the processing accuracy and the surface roughness of the inner peripheral surface of the sleeve 1 are adversely affected. Therefore, it is preferable that the radial bearing clearance is set to 1 μm or more in order to extend the life of the hydrodynamic bearing type rotating device.

  According to the graph shown in FIG. 6 described in the first embodiment, it is good if the volume of the oil reservoir 1E on the hub rotor 7 side is approximately straight and is 10% or more of the volume of the radial bearing gap located on the hub rotor 7 side. It is shown that.

  Here, when no consideration is given to the setting of the oil shear equivalent function and the radial bearing clearance as in the conventional fluid bearing type rotating device, the oil reservoir amount may require 100% or more. is there. However, when the setting of the oil shear equivalent function and the radial bearing clearance is taken into consideration as in this embodiment, since the oil is not subjected to strong shearing, if there is a small oil reservoir as shown in FIG. It is enough. As described above, in the fluid dynamic bearing type rotating device of this embodiment, since a smaller amount of oil is required than in the prior art, even when an impact load is applied to the fluid dynamic bearing type rotating device, oil spills out. Can be avoided.

  As shown in FIG. 1, the radial bearing surface has one straight part and a bearing length of Lr. For example, as shown in FIG. When the groove 1B is divided into two by the small-diameter portion 2A of the shaft 2 and there are two straight portions, the oil amount shown in FIG. 6 corresponds to the radial bearing surface (Lr in the drawing) on the hub rotor 7 side. The point that the oil amount is meant is the same as in the first embodiment.

Next, the conditions of the oil shear equivalent function for reducing the shear by setting the oil shear equivalent function to a certain value or less were defined by mathematical expressions.
The fourth equation is a hypothesis that the oil shear equivalent function E is affected by the eccentricity and speed of the radial bearing portion. The fifth equation is that the oil shear equivalent function E is affected by the bearing stiffness or the amount of heat generation, and the sixth equation is that the oil shear equivalent function E is affected by the oil shear or the amount of heat generation. It is.

These can be expressed in mathematical formulas.
Formula 4: Oil shear equivalent function E = Ep × ω × ω
Formula 5: Eccentricity equivalent function Ep = P / (Fs × C)
Sixth Formula: Rigidity equivalent function Fs = (η × ω × D ^ 2 × L ^ 2) / C ^ 3
η: Absolute viscosity at 70 ° C. [N · S / m ^ 2]
ω: angular velocity [rad / s (= 2 · π · f / 60)]
f: Number of revolutions [rev / min]
D: Shaft diameter [m]
L: Length in the axial direction per radial bearing [m]
C: Clearance in radial direction of radial bearing [m]
P: Load applied to the center of the bearing length for each radial bearing [N]
Next, FIG. 14 shows the correlation between the reciprocal (1 / E) of the oil shear equivalent function (E) and the actual lifetime value (H) of the hydrodynamic bearing type rotating device. In addition, from FIG. 14, the reciprocal number (1 / E) and the life (H) of the hydrodynamic bearing type rotating device are in good agreement with the experimental results, and it has been proved that a correlation is recognized.

  From the above fact, as shown in FIG. 14, by setting the numerical value of the reciprocal (1 / E) of the oil shear equivalent function (E) to be 0.00001 or more, the fluid in which the oil does not deteriorate due to rotational shearing. A bearing type rotating device is obtained. From the viewpoint of bearing life, it is preferable that the value of 1 / E is set so as to be as close as possible to 0.00013 or less in a range where excessive quality is not obtained.

  Here, as a basis for the lower limit (0.00001) of the numerical range of 1 / E, when the numerical value of 1 / E is smaller than 0.00001, the oil shear equivalent function becomes too large, and the bearing It is to shorten the life.

  Specifically, when 1 / E is less than the lower limit of 0.00001, the oil is subjected to a large shearing force due to the rotation of the bearing, so that the oil evaporates or the oil property of the oil is impaired. I will burn it. As a result, the hydrodynamic bearing type rotating device configured so that 1 / E is equal to or more than the lower limit value of 0.00001 can be continuously used for about 50,000 hours (equivalent to about five years). Thus, in the hydrodynamic bearing type rotating device with 1 / E less than 0.00001, the bearing portion is burned out by continuous use for about 3000 to 8000 hours, and the life is shortened to about 1/10 to 1/5. End up.

  In FIG. 14, when the value of 1 / E is 0.00001 or less, it changes rapidly. Under such conditions, too much shear is applied to the oil, and the molecular structure of the oil is stressed beyond the allowable value, and it is assumed that the oil has deteriorated in a short time. FIG. 17 shows an example in which the bearing life test was actually performed and the cumulative failure rate data was collected. The vertical axis in FIG. 17 is the cumulative failure rate of the hydrodynamic bearing type rotating device, and the horizontal axis is the total rotation time (H). Also in FIG. 17, when the value of 1 / E is 0.00001 or less, the graph is It is shown to be significantly (discontinuously) located on the left side. Based on these data, it has been found that the life of the hydrodynamic bearing type rotating device changes when the value of 1 / E is 0.00001.

  On the other hand, as a basis for the upper limit value (0.00013), when the value of 1 / E is larger than 0.00013, it is an excessive life, which may impair productivity, cost, performance at low temperature, and the like. There is.

  Specifically, when 1 / E exceeds the upper limit of 0.00013, the life of the apparatus is sufficient. However, in order to reduce the oil shear equivalent function E, that is, to maintain the rigidity and rotational accuracy of the fluid bearing while reducing the oil shear, the bearing area is increased and the bearing area is designed to be large. At low temperatures, the viscous resistance of the oil increases and the motor current consumption is about 1.2 to 2.0 times, and the required performance as a product is not satisfied.

  More specifically, in these hydrodynamic bearing type rotating devices, a current is supplied to the stator 8 by a driving LSI (integrated circuit) (not shown), a rotating magnetic field is generated and a rotating force is applied to the rotor magnet 9. When the value exceeds 0.00013, the capacity of the driving LSI (not shown) is exceeded, and the stator 8 current cannot be supplied, and a normal rotational speed may not be obtained.

  In addition, in order to reduce the oil shear equivalent function E, to increase the bearing clearance and increase the bearing area and to secure the same bearing rigidity, high-precision bearing parts are processed and assembled with high precision. As a result, the cost of parts becomes high.

  Further, FIG. 15 shows the relationship between the radial friction equivalent function representing the magnitude of the friction torque of the radial bearing portion and the reciprocal (1 / E) of the oil shear equivalent function (E). Here, if the reciprocal number (1 / E) is set too large, the radial bearing life becomes long, but there is a disadvantage that the radial friction torque becomes large. The radial friction equivalent function is a function proportional to the bearing area and the rotational speed and inversely proportional to the size of the bearing gap, but detailed description thereof is omitted here.

Next, specific numerical values are given and the reciprocal number of oil shear equivalent E is actually calculated.
In the hydrodynamic bearing type rotating device 15 shown in FIG.
Oil viscosity at 70 ° C. η = 0.0035 [N · S / m ^ 2],
Angular velocity ω = 439.6 [rad / s (= 2 × π × 4200/60)],
Shaft diameter D = 0.000299 [m],
Length L per radial bearing L = 0.00115 [m],
Clearance C = 0.00000309 [m] in the radial direction of the radial bearing
Load P = 0.196 [N] applied to the center of the bearing length of the upper radial bearing
Then, from the above fourth to sixth formulas,
Rigidity equivalent function Fs = (η × ω × D ^ 2 × L ^ 2) / C ^ 3 = 616000
Eccentricity equivalent function Ep = P / (Fs × C) = 0.103
Oil shear equivalent function E = P × L × Ep = 19900
1 / E = 0.00005
It becomes.

When this calculation result is applied to the graph shown in FIG. 14, it is estimated that the hydrodynamic bearing type rotating device has a sufficient life of about 40,000 hours at 70 ° C.
In this embodiment, as in the first embodiment, the shaft 2 is made of stainless steel, high manganese chrome steel, or carbon steel. As the material of the sleeve 1, stainless steel, copper alloy, or a material obtained by electroless nickel plating or DLC coating on the surface thereof is used. Further, a material processed so that the surface roughness of the radial bearing surface is within a range of 0.01 to 1.60 μm is used.

  In addition, when a copper alloy that is not plated is used for the bearing material, the oil and the copper component cause a chemical reaction to accelerate deterioration, and the life of the hydrodynamic bearing device may be shortened by about 10%. However, these parameters are not considered in the oil shear equivalent function E defined in the present invention.

  In the hydrodynamic bearing type rotating device shown in FIG. 4 described above, when the values of the respective radial loads applied to the upper and lower radial bearings are unknown, as in the first embodiment, the following method is used. Can be sought.

  That is, the shaft 2, the flange 3, the hub rotor 7, the rotor magnet 9, the disk 10, the spacer 12, the clamper 11, and the screw 13 that are the rotating body in the hydrodynamic bearing rotating device according to the present invention are taken out as a single unit, FIG. 10 shows a configuration in which a sufficiently thin thread is attached to Q and suspended in a natural state. By suspending the portion corresponding to the rotating body in this way, it is possible to obtain the position of the center of gravity that is the intersection of the axis center and the extension line of the yarn. In general, this method is called a thread fishing method.

Thereby, as shown in FIG. 10, the load Pu applied to the center part of the upper bearing length is
Pu = P × (S1 / (S1 + S2))
It can obtain | require based on the relational expression.

On the other hand, the load Pl applied to the central part of the lower bearing length is
Pl = P-Pu
It can obtain | require based on the relational expression.

  As described above, the radial load value applied to each of the upper and lower radial bearings can be obtained by obtaining the position of the center of gravity of the member serving as the rotating body. As a result, even when there are two radial bearing gaps as in the fluid bearing type rotating device shown in FIG. 4, the oil shear equivalent function E is calculated by applying the value of Pl or Pu to P in the above equation (4). be able to.

  As shown in FIG. 16, the rigidity equivalent function Fs defined above does not show a very strong correlation with the actual radial bearing life time H. On the other hand, as shown in FIG. 2, the inverse 1 / E of the oil shear equivalent function E has a strong correlation with the bearing life H.

  In this embodiment, the viscosity of the oil injected into the gap between the shaft and the sleeve at 70 ° C. affects the life. In this embodiment, ester-based oil is used as the lubricant. However, when the main component of the oil is a lubricant of fluorine oil, silicon oil, or olefin oil, there is some influence on the life of the hydrodynamic bearing type rotating device. There is. However, since it has been confirmed by experiments that these effects are about 15% or less, these parameters are not taken into consideration for the oil shear equivalent function E defined in this embodiment. As the lubricant, high fluidity grease can be used, and it is considered possible to use an ionic liquid.

  As described above, the gap in the radial direction of the radial bearing surface is 1.0 μm or more, and is a substantially straight gap without a step portion where the gap changes. A lubricant is held in a gap formed by the shaft and the sleeve, and an oil reservoir having a gap larger than that of the radial bearing surface is provided adjacent to the hub rotor 7 side of the radial bearing surface. In addition, the volume of the oil reservoir is configured to be 10% or more of the clearance volume of the radial bearing surface.

  Thus, by setting the numerical value of the reciprocal (1 / E) of the oil shear equivalent function (E) of the radial fluid bearing within the range of 0.00001 to 0.00013, the long-life fluid in which the oil does not deteriorate due to rotational shearing A bearing type rotating device can be obtained.

[Other Embodiments]
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the summary of invention.

(A)
In the said embodiment and Example, the structure of the bearing which the axis | shaft 2 rotated and the sleeve 1 was sealed in the bag shape was mentioned as an example, and was demonstrated. However, the present invention is not limited to this.

  For example, as shown in FIG. 1 of US Pat. No. 5,112,142 (HYDRODYNAMIC BEARING), the present invention can be applied to a bearing rotating device in which both ends of a shaft are fixed and a sleeve is rotatable.

  In this case, there is a substantially straight bearing gap that does not have a step portion, corresponding to the symbol Lr shown in FIGS. 1 and 4 of the above embodiment. Alternatively, it may be a fluid bearing rotating device having an oil reservoir connected to one of the lower portions.

(B)
In the said embodiment and Example, the structure of the bearing which the axis | shaft 2 rotated and the sleeve 1 was sealed in the bag shape was mentioned as an example, and was demonstrated. However, the present invention is not limited to this.

  For example, as shown in FIG. 2 of Japanese Patent No. 3155529 ("Motor with fluid dynamic pressure bearing and recording disk drive with this motor"), a hub rotor is fixed on the upper side of the shaft, and below the shaft. A ring-shaped member is attached, the periphery of the ring-shaped member has an oil sump adjacent to the radial bearing surface, and the lower surface of the hub rotor and the upper surface of the sleeve are opposed to form a thrust bearing surface. The present invention can also be applied to a bearing rotating device having a chamfered sleeve at the corner portion of the shaft and an oil reservoir adjacent to the radial bearing surface inside the thrust bearing surface.

(C)
In the above-described embodiments and examples, an oil reservoir is provided around the shaft 2 at the upper part of the radial bearing surface, and an oil sump extending upward in the axial direction is provided at the corner portion of the shaft 2 and the flange 3 at the lower part of the radial bearing surface. The structure was described as an example. However, the present invention is not limited to this.

  For example, as shown in Japanese Patent Application Laid-Open No. 2004-36892, the present invention can be applied even to a fluid bearing rotating device in which an oil sump extending in a direction substantially perpendicular to the shaft is provided on the radial bearing surface. .

  Further, as described in Japanese Patent Application Laid-Open No. 57-137820, the present invention can be similarly applied to a hydrodynamic bearing type rotating device in which a circulation hole is provided on a radial bearing surface. .

(D)
In the first embodiment, the relationship between the oil shear work function W of the radial bearing and the fluid bearing life H has been described. However, the present invention is not limited to this.
For example, it is considered possible to explain the thrust bearing part by constructing a similar hypothesis and theory.

(E)
In the second embodiment, the relationship between the oil shear equivalent function E of the radial bearing and the fluid bearing life H has been described. However, the present invention is not limited to this.
For example, it is considered possible to explain the thrust bearing part by constructing a similar hypothesis and theory.

(F)
In the said embodiment, the example which applied this invention to the hydrodynamic bearing type rotating device was given and demonstrated. However, the present invention is not limited to this.

  For example, as shown in FIG. 18, the fluid bearing mechanism 40 and the fluid bearing type rotating device 41 having the above-described configuration are mounted, and information recorded on the recording disk 10 is reproduced by the recording head 42, or the recording disk 10 The present invention can also be applied to the recording / reproducing apparatus 43 that records information on the recording medium.

  As a result, a highly reliable recording / reproducing apparatus can be obtained without degrading performance and quality.

  According to the present invention, it is possible to obtain a long-life hydrodynamic bearing type rotating device in which oil does not deteriorate due to rotational shearing. Therefore, the present invention can be widely applied to a hydrodynamic bearing type rotating device mounted on a disc type recording / reproducing device or the like. is there.

Sectional drawing which shows the structure of the hydrodynamic bearing type rotating apparatus which concerns on one Embodiment of this invention. The graph which shows the relationship between the bearing life and oil shear work function in a hydrodynamic bearing type rotating device. The enlarged view which shows the structure of the opening part vicinity of the hydrodynamic bearing type rotating apparatus of FIG. The enlarged view which shows the structure of the radial bearing clearance vicinity of the hydrodynamic bearing type rotating apparatus which concerns on other embodiment of this invention. The graph which shows the relationship between the radial bearing clearance of a fluid-bearing-type rotary apparatus, and a bearing life. The graph which shows the relationship between the oil sump ratio of a fluid bearing type | mold rotary apparatus, and a bearing life. The graph which shows the relationship between the reciprocal number of the oil shear work function in a fluid-type rotary bearing apparatus, and a bearing life. The graph which shows the relationship between the radial friction equivalent function and oil shear work function in a fluid-bearing rotary apparatus. The graph which shows the relationship between the rigidity equivalent function and bearing life of a hydrodynamic bearing type rotating device. The explanatory view showing the gravity center position of the hydrodynamic bearing type rotating device of Drawing 1. Sectional drawing which shows the structure of the conventional fluid dynamic bearing type rotating device. The graph which shows the relationship between the rotation speed and the bearing life in the conventional fluid dynamic bearing type rotating device of FIG. The graph which shows the relationship between the radial load and bearing life in the conventional fluid dynamic bearing type rotating apparatus of FIG. The graph which shows the relationship between the reciprocal number of the oil shear equivalent function in a fluid-type rotary bearing apparatus, and a bearing life. The graph which shows the relationship between the radial friction equivalent function and the oil shear equivalent function in a hydrodynamic bearing type rotating device. The graph which shows the relationship between the rigidity equivalent function and bearing life of a hydrodynamic bearing type rotating device. The graph which shows the relationship between the cumulative failure rate and time of the bearing of the hydrodynamic bearing type rotating device according to the present invention. The block diagram of the recording / reproducing apparatus provided with the fluid-bearing type rotating apparatus which concerns on this invention.

Explanation of symbols

1, 21 Sleeve 1A, 1B Dynamic pressure generating groove 1E Oil pool 2, 22 Shaft 3, 23 Flange 3A, 3B Dynamic pressure generating groove 4, 24 Thrust plate 5, 25 Oil 6, 26 Base 7, 27 Hub rotor 8, 28 Stator 9, 29 Rotor magnet 10, 30 Disc 11, 31 Clamper 12, 32 Spacer 13, 33 Screw 15 Fluid bearing type rotating device 21C Bearing hole 21D Recess 21A, 21B Dynamic pressure generating groove 23A, 23B Dynamic pressure generating groove 40 Fluid bearing mechanism 41 Fluid bearing type rotating device 42 Recording head 43 Recording / reproducing device E Oil shear equivalent function W Oil shear work function (lubricant shear work function)

Claims (7)

A sleeve having a bearing hole;
A shaft inserted in a relatively rotatable state in the bearing hole of the sleeve;
A hub rotor attached to a rotating side of the sleeve and the shaft;
A radial bearing surface in which a dynamic pressure generating groove is formed in at least one of the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve;
With
A hydrodynamic bearing type rotating device configured so that the value of 1 / W is 10,000 or more, where W is an oil (lubricant) shear work function represented by the following formula (1).
W = P × L × Ep (1)
Fs = (η × ω × D ^ 2 × L ^ 2) / C ^ 3 (2)
Ep = P / (Fs × C) (3)
W: Oil (lubricant) shear work function Fs: Rigidity equivalent function Ep: Eccentricity equivalent function η: Absolute viscosity at 70 ° C. [N · S / m ^ 2]
ω: Angular velocity [rad / S (= 2 · π · f / 60)]
D: Shaft diameter [m]
f: Number of revolutions [rev / min]
L: Length per radial bearing [m]
C: Clearance in radial direction of radial bearing [m]
P: Load applied to the center of the bearing length of each radial bearing [N] The 1 / W value is configured to be 65000 or less.
The hydrodynamic bearing type rotating device according to claim 1. A sleeve having a bearing hole;
A shaft inserted in a relatively rotatable state in the bearing hole of the sleeve;
A hub rotor attached to a rotating side of the sleeve and the shaft;
A radial bearing surface in which a dynamic pressure generating groove is formed in at least one of the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve;
With
A hydrodynamic bearing type rotating device configured such that the value of 1 / E is 0.00001 or more, where E is an oil (lubricant) shear equivalent function represented by the following equation (4).
E = Ep × ω × ω (4)
Fs = (η × ω × D ^ 2 × L ^ 2) / C ^ 3 (5)
Ep = P / (Fs × C) (6)
E: Oil (lubricant) shear equivalent function Fs: Rigidity equivalent function Ep: Eccentricity equivalent function η: Absolute viscosity at 70 ° C. [N · S / m ^ 2]
ω: angular velocity [rad / S (= 2 · π · f / 60)]
D: Shaft diameter [m]
f: Number of revolutions [rev / min]
L: Length per radial bearing [m]
C: Clearance in radial direction of radial bearing [m]
P: Load applied to the center of the bearing length of each radial bearing [N] The 1 / E value is configured to be 0.00013 or less.
The hydrodynamic bearing type rotating device according to claim 1. The radial gap formed between the radial bearing surface and the sleeve or the shaft is 1 μm or more and is substantially constant.
The hydrodynamic bearing type rotating device according to any one of claims 1 to 4. Lubricant is held in the gap formed between the shaft and the sleeve, and the lubricant reservoir is located at a position adjacent to the radial bearing surface so that the gap between the opposed surface is larger than the radial bearing surface. Is formed,
The volume of the lubricant reservoir is 10% or more of the volume of the gap between the radial bearing surface and the sleeve or the shaft.
The hydrodynamic bearing type rotating device according to any one of claims 1 to 5. A recording / reproducing apparatus comprising the hydrodynamic bearing type rotating device according to claim 1.

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