JPH10281145A - Fluid bearing device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve the bending rigidity of a shaft, reduce whirling of a rotating body, and reduce dynamic torque at low temperatures. The shaft has a diameter of 2 to 5 mm, and has a kinematic viscosity of 20 to 200 at 40 ° C. as a lubricant for a radial bearing clearance.
A hydrodynamic bearing device is characterized in that cSt fluorine oil is used and the radial bearing clearance is 3.5 to 10 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrodynamic bearing device, and more particularly to a hydrodynamic bearing device for a spindle motor for information equipment and audio / video equipment.
The present invention relates to a hydrodynamic bearing device for a spindle motor which is optimal for an optical disk device or a magnetic disk device.

[0002]

2. Description of the Related Art In recent years, a fluid bearing device for a spindle motor of an optical disk device and a magnetic disk device has been increasingly rotated at a high speed due to a demand for high-speed data transfer.
For this reason, the influence of the centrifugal force due to the unbalance of the rotating part accompanying the high-speed rotation is increasing more and more on the support bearing of the spindle motor.

FIG. 2 is a sectional view of a conventional bearing device. The rotating member includes a shaft 30, a disc mounting flange 31, and a rotor 33. The shaft 30 is press-fitted into the disk mounting flange 31, and the rotor 33 is fixedly installed on the lower surface of the disk mounting flange 31.

[0004] A support member for supporting the shaft 30 is composed of a stator 34, a base 35, a bearing member 36 and a steel ball 37. A groove for generating dynamic pressure for functioning as a radial dynamic pressure bearing is provided on a cylindrical radial bearing surface 36 a provided on the bearing member 36, and the bearing member 36 is pressed into the base 35. A steel ball 37 is press-fitted into the lower end of the bearing member 36, and the steel ball 37 functions as a thrust bearing. The stator 34 is press-fitted into a bearing member 36 and fixed.

Next, as an operation, when a current is applied to the stator 34, a rotating magnetic field is generated, whereby the rotor 33 rotates together with the shaft 30 and the disk mounting flange 31.
As a result, the pressure of the lubricant in the radial bearing clearance is increased by the pumping action of the groove for generating dynamic pressure provided on the radial bearing surface 36a, and the contact between the initial radial bearing surface 36a and the radial receiving surface 30b is changed to the non-contact state. I do.

At the same time, also in the thrust bearing, the thrust bearing surface 30a and the thrust receiving surface 37a provided on the end face of the shaft 30 are in point contact with each other to form a sliding bearing. This thrust bearing also has a thrust bearing surface 30a and a thrust receiving surface 3
Lubricant is contained between 7a and rotates in a state of point contact via the lubricant.

Further, a synthetic oil having good boundary lubrication properties was studied as a lubricant. In particular, the load capacity of the above-described radial bearing and thrust bearing is proportional to the viscosity of the lubricant used. Synthetic oil has a large viscosity change due to temperature change, so oil that satisfies the required load capacity at high temperature has a large increase in viscosity at low temperature and large dynamic torque of the bearing. If an oil having such a viscosity as to obtain is selected, the viscosity decreases at a high temperature and the load capacity becomes insufficient. Synthetic oil basically has poor temperature-viscosity characteristics, so the diameter of the shaft is reduced to 1.5 mm in order to reduce the torque of the bearing device, or the radial bearing surface 36a and the radial receiving surface 30b are used to secure the load capacity. And the distance between the radial bearing clearances was as small as about 3 μm.

However, when the bearing device rotates at a high speed, there arises a problem that the centrifugal force is increased due to imbalance when the disk is mounted, the bending rigidity of the shaft is insufficient, and the swiveling of the rotating body is increased. I have. Further, the bearing device is also required to have a low torque at a low temperature due to a demand for power saving of the device.

[0009]

SUMMARY OF THE INVENTION According to the first aspect of the present invention, the bending rigidity of the shaft is improved, the problem that the rotating body oscillates is increased, and the dynamic torque at low temperatures is reduced. It is an object of the present invention to provide a hydrodynamic bearing device that achieves the above.

[0010]

According to the first aspect of the present invention,
A cylindrical radial bearing surface provided on the bearing member is opposed to a radial receiving surface provided on the shaft via a radial bearing clearance, and a groove for generating dynamic pressure is provided on at least one of the radial receiving surface and the radial bearing surface. In the fluid dynamic bearing device, the diameter of the shaft is set to 2 to 5 mm, fluorinated oil having a kinematic viscosity of 20 to 200 cSt at 40 ° C. is used as a lubricant for the radial bearing clearance, and the radial bearing clearance is set to 3.5 to 10 μm. An object of the present invention is to provide a fluid dynamic bearing device.

The shaft has a diameter of 2 to 5 mm to improve the bending rigidity of the shaft. Within this range, it is possible to reduce the whirling of the rotating member that is the rotating body. In this case, when the diameter of the shaft is larger than 5 mm, the dynamic torque becomes too large.

As the lubricant, a fluorine oil which causes little increase in torque at low temperatures is used. In particular, by using a fluorine oil having a kinematic viscosity of 20 to 200 cSt at 40 ° C. having good temperature viscosity characteristics and a radial bearing clearance of 3.5 to 10 μm between the radial bearing surface and the radial receiving surface, at low temperatures. Appropriate dynamic torque can be obtained.

This makes it possible to meet the demand for labor saving of the bearing device. At low temperatures, unlike the viscosity characteristics of lubricating oil at room temperature, the increase in viscosity requires an increase in the energy for operating the bearing device, and there is a demand for energy that is not required at room temperature. The present invention makes it possible to drive the bearing device without using such extra energy.

The characteristics of fluorine oil as a lubricant include 40
When the temperature is lower than 20 cSt at 40 ° C., the dynamic torque becomes small, but the load capacity at high temperature becomes insufficient.
If it exceeds cSt, the load capacity increases, but the dynamic torque at low temperatures becomes too large. Therefore, in order to sufficiently exhibit the effects of the present invention, as described above, 40
It is desirable to use in the range of 20 to 200 cSt at ℃.

[0015] If the fluorine oil, which is a lubricant, is provided with 0.1 to 10% by weight of perfluoropolyether having a carboxylic acid at a terminal, boundary lubricity and leakage of the lubricant are obtained. Even better.

However, if the perfluoropolyether having a carboxylic acid at the terminal is less than 0.1% by weight and the fluorine oil is provided, the boundary lubrication property and the leakage property of the lubricant will be inferior. Further, when the fluoro oil has more than 10% by weight of perfluoropolyether having a carboxylic acid at the terminal, the physical properties of the fluoro oil are inferior, and it is difficult to obtain an appropriate dynamic torque at a low temperature.

If the radial bearing clearance between the radial bearing surface and the radial receiving surface is smaller than 3.5 μm, the dynamic torque increases at low temperatures, and if it is larger than 10 μm, the dynamic torque decreases but increases at high temperatures. The load capacity will be insufficient. Therefore, in order to sufficiently exhibit the effects of the present invention, the radial bearing clearance is desirably set to 3.5 to 10 μm as described above.

Further, the radial bearing clearance is set to 3.5 to 1
By setting the thickness within the range of 0 μm, there is an effect that the shaft can be easily inserted into the bearing member even when the lubricant is injected into the bearing member without providing an air vent hole in the bearing member.

A cylindrical radial bearing surface provided on the bearing member is opposed to a radial receiving surface provided on the shaft via a radial bearing clearance, and a thrust receiving surface provided on the end surface of the shaft is provided on the bearing member. May be opposed to the thrust bearing surface.

Further, it is sufficient that at least one of the radial bearing surface and the radial receiving surface of the hydrodynamic bearing device is provided with a groove for generating dynamic pressure, and in particular, is limited to either the radial bearing surface or the radial receiving surface. is not.

When the thrust bearing surface and the thrust bearing surface are in point contact, the contact area can be greatly reduced, and the dynamic torque can be reduced. Since the thrust receiving surface and the thrust bearing surface face each other via the lubricant, improvement in boundary lubricity can be expected, and wear between the contact surfaces can be reduced. In particular, when a convex spherical surface is provided on the thrust bearing surface, the step of press-fitting the steel ball constituting the thrust bearing into the bearing member can be omitted, and the assembling workability is improved.

The bearing member having the radial bearing surface and the thrust bearing surface may be integrally formed of synthetic resin. However, instead of being integrally formed, the bearing member having the radial bearing surface is formed of a copper-based metal such as free-cutting brass or phosphor bronze. Alternatively, the thrust receiving member having the thrust bearing surface may be formed of a plate made of wear-resistant metal or ceramic, and the thrust receiving member may be fixed to the bearing member. By adopting such a configuration, the bending strength of the bearing member can be maintained, and the phenomenon of wear of the thrust receiving member can be suppressed.

[0023]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a sectional view of the bearing device of the present invention. The rotating member includes a shaft 1, a disk mounting flange 6, and a rotor 3. The supporting member that supports the rotating member includes a stator 4, a base 2, and a bearing member 5.

The basic structure of the rotating member is the same as that of the conventional bearing device shown in FIG. As the material of the shaft 1 in the bearing device of the present invention, generally used heat-treated SUS440C stainless steel is used. However, the material of the shaft 1 used in the bearing device of the present invention is not particularly limited as long as the condition of the shaft diameter of 2 to 5 mm, which is a constituent requirement of the present invention, is satisfied.

The basic structure of the supporting member for supporting the rotating member is the same as that of the conventional bearing device shown in FIG. 2. However, since the shape and the like of the bearing member are different from those of the conventional bearing device, this point will be mainly described. explain.

In the bearing device of the present invention, the bearing member 5 has the flange 5c provided below the cylindrical portion of the bearing member 5. In other words, the axial position of the bearing member is different from that of the dynamic pressure generating groove and the flange. With such a structure, it is possible to prevent the accuracy of the groove for generating dynamic pressure from deteriorating due to the influence of the flange 5c during the injection molding of the bearing member made of synthetic resin.

Further, in the prior art, a thrust bearing surface of a thrust bearing is formed by press-fitting a steel ball as a thrust receiving member into a bearing member, but in the present invention, the thrust bearing surface is provided on the bearing member 5. The thrust bearing surface has a convex spherical surface 5d at the center.

By adopting such a structure, a convex portion can be simultaneously formed on the bearing member at the time of injection molding of the synthetic resin bearing member, and the step of press-fitting a steel ball as a thrust receiving member into the bearing member is omitted. Thus, it is possible to improve the assembling workability.

Further, the base 2 is made of a metal such as aluminum die-cast or zinc die-cast, and the cylindrical portion 5e of the bearing member 5 is press-fitted into the cylindrical portion 2a of the base 2 as shown in FIG. The bending composition of the bearing member 5 made of synthetic resin is reinforced. In this case, in particular, the cylindrical portion 2a of the base is made longer so as to be along the cylindrical portion 5e of the bearing member, and the bending rigidity of the bearing member 5 made of synthetic resin is reinforced.

In the bearing device of the present invention, in order to increase the bending rigidity of the bearing member of the fluid bearing, the cylindrical portion 5e having the radial bearing surface of the bearing member is made of a copper-based metal such as a free-cutting yellow body, phosphor bronze, and the like. A thrust receiving member having a bearing surface may be fixed to the bearing member. It is also possible to adopt a structure in which the thrust receiving member is a thrust plate made of ceramic or the like. In the case of such a structure, the strength of the bending rigidity of the bearing member 5 can be secured without making the cylindrical portion 2a of the base 2 long.

The cylindrical portion 5e of the bearing member and the cylindrical portion 2a of the base
When the adhesive is filled during the period, the bending rigidity of the bearing member 5 is further increased. The supporting member for supporting the rotating member is completed by incorporating the stator 4 into the cylindrical portion 2a of the base by press fitting or the like.

Next, the structure of the cylindrical portion 2a of the bearing member will be described. On the inner peripheral surface of the cylindrical portion 2a of the bearing member, cylindrical radial bearing surfaces 5a are provided at two locations spaced apart in the axial direction, and these radial bearing surfaces 5a are used for generating a herringbone-shaped dynamic pressure. A groove is provided for each. The shaft 1 disposed on the inner periphery of the bearing member 5 has a cylindrical radial receiving surface 1a which faces the radial bearing surface 5a via a lubricant in the radial bearing clearance 7 via a lubricant.

The radial bearing clearance 7 is set so as to satisfy the condition of 3.5 to 10 μm which is a component of the present invention. In particular, when it is out of this range, the load capacity decreases and the dynamic torque increases.

The lower end surface of the shaft 1 has a thrust receiving surface 5b opposed to the thrust bearing surface 1b via a lubricant, and this thrust receiving surface 5b is formed as a convex spherical surface to reduce the contact area with the thrust bearing surface 1b. It is in the state of contact.

The kinematic viscosity between the radial bearing surface 5a and the radial receiving surface 1a and between the thrust bearing surface 1b and the thrust receiving surface 5b is 20 to 200 cS at 40 ° C. as a lubricant.
t is filled with fluoro oil.

Next, the operation of the bearing device of the present invention will be described. However, since the basic operation is the same as that of the conventional bearing device, only the outline of the operation will be described. That is, when the stator 4 is energized, a rotating magnetic field is generated, and the rotor 3 rotates together with the shaft 1 and the disc mounting flange 6. When the rotating member including the shaft 1 and the rotor 3 rotates, the thrust bearing surface 1b is moved to the thrust receiving surface 5b.
It rotates in a state of point contact with the lubricant via a lubricant.

As described above, the thrust bearing surface 1b and the thrust receiving surface 5b are in point contact with each other to form a sliding bearing. However, lubricant is present in the thrust bearing clearance 8 between the thrust bearing surface 1b and the thrust receiving surface 5b. The contact points are opposed to each other and point contact is made, so that the boundary lubricity is improved, and the abrasion between the thrust bearing surface 1b and the thrust receiving surface 5b is reduced.

The thrust bearing surface 5b rotates in contact with the thrust bearing surface 1b as described above, and the radial bearing surface 5a and the radial bearing surface 1a are rotated by the pumping action of the groove for generating dynamic pressure. The pressure of the lubricant in the bearing clearance 7 increases, and the radial bearing surface 5a rotates without contact with the radial receiving surface 1a. Even if the rotation operation starts in this way, the structure of the bearing device of the present invention can secure the bending rigidity of the shaft and suppress the increase in torque at low temperatures.

Further, in order to improve boundary lubricity and leakage of the lubricant, the fluoro oil should be provided with a perfluoropolyether having a carboxylic acid at a terminal in a proportion of 0.1 to 10% by weight. Is achieved by

In the bearing device of the present invention, stainless steel is used as the material of the shaft and plastic is used as the bearing member in consideration of the insufficient rust-preventing ability of the fluoro oil. Further, considering the improvement of the slidability at the time of starting and stopping, PPS (polyphenylene sulfide resin) containing carbon fiber and Teflon can be used as the material of the bearing member. This invention reverses the hydrodynamic bearing device,
The bearing member 5 rotates, and the shaft member 1 can support the bearing member 5.

[0041]

According to the present invention, the bending rigidity of the shaft can be improved, and the dynamic torque at low temperatures can be reduced. Furthermore, when the bearing member has a radial bearing surface and a thrust bearing surface, the structure of the thrust bearing can be simplified, thereby improving the assembling workability and reducing the number of parts. As a result, the cost of the entire product can be significantly reduced, and an economically advantageous effect can be obtained.

The radial bearing clearance is set to 3.5 to 10
By setting it to μm, it is not necessary to provide an air vent hole on the bottom surface of the bearing member, and it is possible to simplify bearing processing.

[Brief description of the drawings]

FIG. 1 is a sectional view of a bearing device according to the present invention.

FIG. 2 is a sectional view of a conventional bearing device.

[Explanation of symbols]

 1 shaft 1a radial receiving surface 1b thrust bearing surface 2 base 3 rotor 4 stator 5 bearing member 5a radial bearing surface 5b thrust receiving surface 5c flange 5d convex spherical surface 5e cylindrical portion 7 radial bearing clearance

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Katsuhiko Tanaka 1-50-50 Kugenuma Shinmei, Fujisawa City, Kanagawa Prefecture Nippon Seiko Co., Ltd.

Claims (1)

[Claims] A cylindrical radial bearing surface provided on a bearing member faces a radial receiving surface provided on a shaft via a radial bearing clearance, and a dynamic pressure is generated on at least one of the radial bearing surface and the radial receiving surface. Fluid dynamic bearing device provided with a groove for use, a shaft having a diameter of 2 to 5 mm, and a kinematic viscosity of 20 to 200 cSt at 40 ° C. as a lubricant for the radial bearing clearance.
With a radial bearing clearance of 3.5 to 3.5
A hydrodynamic bearing device having a thickness of 10 μm.