JPH09170621A - Pivot thrust bearing system and motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the displacement of a rotary shaft in the axial direction at a low cost and obtain a stable mixed lubrication state, in response to the request of the high precision, high speed rotation or low cost of a spindle motor. SOLUTION: In a pivot thrust bearing system in which the end surface of a rotary shaft 1 consisting of a steel material slides on a bearing material through a lubrication oil composition, by installing a lubrication oil flow in passage 2 installed along the axial center and opened to the axial center part of a rotary shaft 1 end surface and a lubrication oil discharge passage 3 connected to the lubrication oil flow in passage 2 and installed in the radial direction, by making a connection part a start point and opened on the rotary shaft side surface on the rotary shaft 1, the displacement of the rotary shaft in the axial direction is restrained and a stable wear resistance effect is obtained with the lapse of time in a mixed lubrication state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention finds application in pivot thrust bearing systems, such as spindle motors.

[0002]

2. Description of the Related Art In recent years, a spindle motor of high precision and high speed has been demanded from the background of high speed recording of a magnetic disk device and high density recording. With higher precision and higher speed rotation, it is necessary to suppress axial displacement of the rotary shaft of the spindle motor in particular over time.

Conventionally, as a thrust bearing, a pivot bearing system has been widely used in which a rotating shaft having an end face curved is slid on a bearing material through a lubricating oil composition. Since it is a mixed lubrication state in which there is a solid contact state in part with the lubrication state, wear progresses as the axial load increases due to an increase in magnetic recording media, or the sliding speed increases due to an increase in rotation speed. However, it is disadvantageous in that the axial displacement of the rotary shaft increases.

Therefore, a method of supporting the rotary shaft by a fluid radial bearing portion is adopted, and even when it is supported by a thrust bearing portion, in order to suppress axial displacement of the rotary shaft over time, for example, Japanese Patent Laid-Open No. 6-38442. As disclosed in Japanese Patent Laid-Open Publication No. 2003-242242, an attempt is made to generate a dynamic pressure by the fluid force of the lubricating oil due to the rotation of the rotating shaft and aim for a non-contact sliding state.

[0005]

SUMMARY OF THE INVENTION For example, JP-A-6-38
As described in Japanese Patent No. 442, it can be said that the fluid thrust bearing system that generates a stable dynamic pressure by the fluid force of the lubricating oil due to the rotation of the rotating shaft and basically maintains the non-contact sliding state is advantageous in reducing wear.

However, the fluid thrust bearing system has high processing accuracy such as processing accuracy of the end surface of the rotating shaft, processing accuracy of the spiral groove provided on the bearing material, and assembly accuracy for aligning the rotating shaft center with the center of the spiral groove. It has a drawback that the cost is high because the assembling accuracy is required.

In this respect, the pivot thrust bearing system has a simple structure and is therefore advantageous in terms of cost. However, as described above, there is a concern that wear will increase as the load increases.

[0008]

According to the present invention, in order to meet the demand for high precision, high speed rotation, or cost reduction of, for example, a spindle motor for driving a magnetic disk device, the axial displacement of the rotary shaft can be reduced at low cost. It is intended to suppress the above and obtain a stable mixed lubrication state.

According to the present invention, in a pivot thrust bearing system in which an end surface of a rotary shaft made of a steel material slides on a bearing material through a lubricating oil composition, the rotary shaft includes a shaft center portion of the rotary shaft end face and the rotary shaft. A pivot thrust bearing system is characterized in that a lubricating oil flow path having an opening on a side surface is provided.

The lubricating oil composition interposed between the rotating shaft and the bearing material of the present invention is a mineral oil-based or synthetic oil-based hydrocarbon base oil, a viscosity index improver, an extreme pressure additive, and an antioxidant. , Pour point improver, antifoaming agent, and other additives commonly used in bearing oils are added for convenience. In addition, greases, powders with stratified lattices such as graphite, MoS ₂ , BN,
Alternatively, coexistence or combination use with a metal thin film of In, Cu, Pd or the like is not a problem. The specific composition of the lubricating oil composition that controls the mixed lubrication state is as follows:
It is decided according to actual load conditions.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

In FIG. 1, reference numeral 1 is a rotary shaft, 2 is a shaft provided along the shaft center, and a lubricating oil inflow passage opened at the shaft center of the end surface of the rotating shaft is connected to the lubricating oil inflow passage 2. , A lubricating oil discharge passage that is provided in the radial direction starting from the connecting portion and opens to the side surface of the rotating shaft 1, and that the lubricating oil inflow passage 2 is provided.
The lubricating oil discharge passage 3 forms a lubricating oil passage.

As shown in FIG. 2, the rotating shaft 1 is rotatably supported by a bearing member 5 in the radial direction by a fluid radial bearing portion 4 and in the axial direction by a lubricating oil composition 6. When the rotating shaft 1 rotates in the direction of arrow e, the lubricating oil 6 in the lubricating oil discharge passage 3 moves in the direction of arrow a due to the centrifugal force caused by the rotation of the rotating shaft and is discharged from the opening on the side surface of the rotating shaft. It At the same time, negative pressure is generated in the lubricating oil inflow passage 2 and the lubricating oil discharge passage 3, and the lubricating oil 6 is guided to the lubricating oil inflow passage 2 through the opening of the end surface of the rotating shaft (arrow b).

Therefore, with the rotation of the rotary shaft 1, a flow of the lubricating oil 6 is generated in the direction of arrow a → arrow c → arrow b → arrow a → ... The lubricating oil 6 is efficiently supplied, and the lubricating oil required to obtain a good lubricating state is secured.

Therefore, the sliding state between the end surface of the rotary shaft and the bearing material shifts from the mixed lubrication state to the fluid lubrication state side, so that wear is reduced.

As described above, according to the present invention, when the end surface of the rotating shaft made of a steel material slides on the bearing material through the lubricating oil composition, the axial displacement of the rotating shaft is suppressed and stable resistance is maintained. Abrasion effect is exhibited.

[0017]

【Example】

(Example 1) [Preparation of sample] In the present embodiment, stainless steel with an outer diameter of 3 mm whose end face is curved to a radius of 4 mm is used, and a lubricating oil with a diameter of 0.5 mm and a length of 1 mm as shown in FIG. A rotary shaft was provided with an inflow passage and a lubricating oil discharge passage having a diameter of 0.5 mm, which was connected at a right angle to the lubricating oil inflow passage.

As a conventional example, a stainless steel having an outer diameter of 3 mm whose end face is curved to a radius of 4 mm, and as a comparative example,
The conventional example further provided with a spiral groove used in a fluid bearing as shown in FIG. 3 was used as the rotating shaft. The surface roughness of the end face of the rotary shaft was adjusted to Rmax <0.2 μm.

As a backing plate material, a plate-shaped carbon tool steel (SK
2) was used. The surface roughness of the sliding surface was adjusted to Rmax <0.2 μm.

As the lubricating oil composition, di-2-ethylhexyl sebacate (Mw 426, η ₄₀ 11.3 cps) containing 3% by weight of butyl ester of stearic acid was used.

[Sliding experiment] Axial load 60 gf,
Fig. 4 shows the axial displacement of the rotating shaft when a spindle motor with a rotation speed of 5400 rpm is driven in a mixed lubrication state.
Shown in

As is apparent from FIG. 4, the present invention shows that when a plate carbon tool steel (SK2) is used as the bearing material, the conventional example,
Compared to the comparative example, the amount of wear is small over time, and in the mixed lubrication state, the axial displacement of the rotating shaft is suppressed, and a stable wear resistance effect over time can be exhibited.

The case where the number of lubricating oil discharge paths provided on the rotary shaft is 2 and the connection angle between the lubricating oil inflow path and the lubricating oil discharge path is 90 ° has been described here. The connection angle is conveniently determined by the actual load conditions of the motor and the properties of the lubricating oil composition.

[0024]

As described above, according to the present invention, the end surface of the rotary shaft made of a steel material slides under a mixed lubrication state in which a bearing material and a boundary lubrication state or a solid contact state are mixed with each other through a lubricating oil composition. In this configuration, by utilizing the circulation of lubricating oil, the end surface of the rotating shaft is configured to positively supply the lubricating oil to the sliding surface. There is an effect that a dynamic state is realized, a rapid change in motor operation is suppressed at a low cost, and a high quality is achieved.

Although the embodiment of the high speed rotating spindle motor mounted on the magnetic disk device has been described here, the pivot thrust bearing system of the present invention can be widely applied to a spindle motor for driving a polygon mirror of a printer. Is.

[Brief description of the drawings]

FIG. 1 is an end face shape diagram of a rotating shaft using a pivot thrust bearing system of the present invention.

FIG. 2 is an explanatory view of a pivot thrust bearing system of the present invention.

FIG. 3 is a front view of a rotary shaft end face shape using a pivot thrust bearing system of a comparative example.

FIG. 4 is a comparison diagram of wear characteristics of the present invention and a conventional example and a comparative example.

[Explanation of symbols]

 1 Rotating shaft 2 Lubricating oil inflow path 3 Lubricating oil discharge path 4 Fluid radial bearing 5 Bearing material 6 Lubricating oil composition

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Fumitoshi Yamashita 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A pivot thrust bearing system in which an end surface of a rotary shaft made of a steel material slides on a bearing material through a lubricating oil composition, in a rotary shaft, a shaft center portion of the rotary shaft end face and a rotary shaft side surface. A pivot thrust bearing system comprising a lubricating oil passage having an opening. 2. A motor using the pivot thrust bearing system according to claim 1 for a thrust bearing.