JPH10227312A - Fluid bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in a fluid bearing device by which a rotary shaft is journaled by fluid pressure, that the bearing clearance of a land part for supporting the rotary shaft by dynamic pressure is narrow, thereby exothermic action occurs at the time of high speed rotation, the rotary shaft and a bearing member are locally thermally expanded in this land part, and finally seizure occurs. SOLUTION: Bearing clearances d1, d2 are so arranged that the bearing clearance d1 between a dynamic pressure generating land part 14 and a rotary shaft 20 is set larger than the bearing clearance d2 leading from static pressure pockets 6, 7 to a drain groove 10. Preferably, the bearing clearance d1 is set to be from 1.3 to twice the bearing clearance d2. Hereby, an exothermic action amount in the land part 14 can be suppressed even at high speed rotation, therefore seizure can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid bearing device for bearing a rotating shaft such as a main shaft of a machine tool, particularly a rotating shaft rotated at high speed, through a pressurized fluid such as bearing oil.

[0002]

2. Description of the Related Art Generally, a fluid bearing is provided with a bearing pocket and a land on an inner peripheral surface of a bearing member having a certain bearing clearance between the bearing and a rotating shaft. The rotating shaft is supported by the fluid pressure (static pressure, dynamic pressure) of the pressurized fluid supplied to the bearing gap of the motor.

[0003] Such a fluid bearing is provided with a pair of concave grooves provided in the inner peripheral surface of the bearing member and extending in the axial direction so as to be spaced apart in the axial direction, and provided in the axial direction so as to communicate with the pair of concave grooves. There is a case in which a plurality of sets of U-shaped bearing pockets are provided by concave grooves. In this device, a static pressure is generated by a U-shaped bearing pocket, and in a land portion surrounded by the U-shaped bearing pocket, a dynamic pressure is applied to a minute gap between the rotating shaft and the rotating shaft as the rotating shaft approaches and displaces. Is generated to support the rotating shaft.

[0004] One having a U-shaped bearing pocket as described above is disclosed in JP-B-60-37329. In this case, the dynamic rigidity is improved by making the bearing gap of the land 17 narrower than the bearing gap of the bearing pockets 15, 16, 18.

[0005]

Recently, with the demand for high-speed grinding at a high peripheral speed, for example, a peripheral speed of the grinding wheel of 180 m / sec, a bearing supporting the grinding wheel shaft has been adapted to a high speed. In the state of the art at the time of the above prior art, 4
The peripheral speed of the grindstone is about 5 to 60 m / sec, which is a very low peripheral speed in view of the current technical level.

According to experiments by the inventor of the present invention, when high-speed grinding (peripheral speed: 180 m / sec) is performed using this conventional technique, the amount of heat generated in the bearing portion becomes excessive. It was found that due to thermal expansion, the bearing gap became small and the desired bearing performance could not be obtained.
In particular, it has been found that the amount of heat generated at the lands where the dynamic pressure is generated increases, and the bearing clearance locally decreases.

To solve this problem, it is conceivable to increase the bearing clearance. However, if such a solution is adopted, the required bearing rigidity cannot be achieved, and further, the bearing clearance cannot be achieved. Since the consumption of the supplied oil increases in proportion to the cube of, the oil supply device increases in size and the power loss also increases. In addition, it is difficult to put the tank to practical use because the tank for collecting the discharged oil also becomes large.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and a means according to a first aspect of the present invention comprises a rotating shaft and a bearing member for rotatably supporting the rotating shaft. A plurality of static pressure pockets provided on the inner peripheral surface of the bearing member, a dynamic pressure land portion surrounded by the static pressure pockets to generate dynamic pressure, and a supply hole for supplying a fluid to the static pressure pockets; A fluid bearing device having an annular drain groove formed on an inner peripheral surface of the bearing member and configured to discharge a fluid supplied to the static pressure pocket through a bearing gap between the rotating shaft and the bearing member. The gap between the dynamic pressure land and the rotary shaft is larger than the gap between the static pressure pocket and the drain groove.

According to a second aspect of the present invention, in addition to the first aspect, the dynamic pressure land portion and the rotating shaft are disposed between the static pressure pocket and the drain groove in a bearing gap between the static pressure pocket and the drain groove. It is characterized in that the bearing gap between them is increased from 1.3 times to 2 times.

[0010]

Embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1 and FIG. 2, a discharge passage 2 is provided at a lower portion of a bearing housing 1 which preferably forms a grindstone base of a grinding machine.
A cylindrical bearing member 5 having a bearing surface 4 on the inner peripheral surface is fitted in the bearing housing 1. As shown in FIG. 2, a rotary shaft 20 is rotatably supported on the bearing member 5 by fluid pressure.

A plurality of pairs of a pair of axially spaced static pressure pockets 6 and 7 are recessed in the circumferential direction on an inner peripheral bearing surface 4 of the bearing member 5. , 7 are connected by an axially extending supply groove 8 at one end in the circumferential direction, and together with the supply groove 8, form a substantially U-shaped static pressure pocket. Due to the formation of the static pressure pockets 6, 7 and the supply groove 8, a dynamic pressure land portion 14 for generating a dynamic pressure having the same inner peripheral surface height as the bearing surface 4 is formed in a portion surrounded by a U-shape.

A supply port 9 for supplying oil to the supply groove 8 and the static pressure pockets 6 and 7 is opened in the supply groove 8.
It communicates with an annular groove 12 provided on the outer periphery of the bearing member 5 through a communication hole 15 which acts as a throttle. (See FIG. 3) An oil supply passage 13 is formed in the bearing housing 1 at a position corresponding to the annular groove 12, and when pressure oil is supplied from an oil supply pump (not shown), the annular groove 12, the communication hole 15 are formed. The pressure oil is supplied into the supply groove 8 and the static pressure pockets 6 and 7 through the supply port 9.

In order to make the formation state of the static pressure pockets 6 and 7, the supply groove 8 and the dynamic pressure land portion 14 easy to understand,
This will be described below with reference to the perspective view of FIG. In the bearing member 5, annular drain grooves 10 are recessed at both axial ends of the static pressure pockets 6,7. The drain groove 10 is connected to the bearing housing 1 via a discharge passage 11 formed in the bearing member 5.
The oil flowing into the drain groove 10 is collected in an oil tank (not shown).

The bearing member 5 has a rotating shaft 2 as shown in FIG.
0 has a slight clearance (bearing clearance) with the bearing surface 4, and the diameter D 1 of the portion of the rotating shaft 20 facing the dynamic pressure land portion 14 is the diameter of the portion facing the drain groove 10. D
It is formed smaller than 2. As a result, the bearing gap d1 between the dynamic pressure land 14 and the rotary shaft 20 is set to be larger than the bearing gap d2 from the static pressure pockets 6, 7 to the drain groove 10. Preferably, the bearing gap d1 is set to be 1.3 to 2 times d2. Further, the bearing gap d2 is set to a conventional interval.

The operation of the embodiment having the above configuration will be described below. From supply pump (not shown) to bearing housing 1
When the pressure oil is supplied to the oil supply path 13, the pressure oil is supplied from the annular groove 12 on the outer periphery of the bearing member 5 to the supply groove 8 of the bearing surface 4 through the communication hole 15 which performs a throttle action. When the pressure oil is filled in the static pressure pockets 6 and 7 through the supply groove 8, the pressure oil flows out to the dynamic pressure land portion 14 and the drain groove 10 through the bearing gaps d1 and d2. At this time, the outflow resistance works in accordance with the bearing gap, so that the
7. A static pressure is generated in the supply groove 8, and the rotating shaft 20 is statically supported by the static pressure.

In the bearing gap d1 between the dynamic pressure land 14 at the center and the rotating shaft 20, static pressure pockets 6, 7,.
The pressure oil flowing from the supply groove 8 generates the same static pressure as the static pressure pockets 6 and 7 and the supply groove 8. Rotary axis 2
When a load is applied to the shaft and the center shaft is eccentric, as shown in FIG. 4, a wedge-shaped clearance in which the bearing gap gradually narrows toward the eccentric side due to the difference between the diameter D1 of the rotating shaft 20 and the inner diameter of the dynamic pressure land portion. P is made. The pressure oil is swept around the surface of the rotary shaft 20 and is drawn into the wedge-shaped clearance P to generate a dynamic pressure, and the rotary shaft 20 is supported by the dynamic pressure.

At this time, as compared with the prior art, the bearing clearance d2
Since the bearing gap d1 of the dynamic pressure land portion 14 is sufficiently large, the amount of heat generated can be suppressed even when the rotating shaft 20 rotates at high speed. FIG. 5 shows a temperature rise graph showing the results of this experiment. Here, the thin broken line indicates the temperature of the discharged oil in the conventional hydrodynamic bearing device in which all the bearing gaps are constant, and is about 45 ° C., whereas the fluid bearing of the present invention shown by the bold solid line According to the device (the bearing clearance d1 was set to 1.4 times d2), the temperature was about 33 ° C, and the calorific value could be suppressed by 10 ° C or more. Further, when the bearing gap d1 is 1.6 times d2, it becomes as indicated by a thick broken line, and the amount of generated heat can be further suppressed.

Here, the thin solid line represents the temperature of the supplied oil which is common to the experimental results of the prior art and the present invention (Experiment 1 and Experiment 2). From the experimental results, as described above, it is desirable that the bearing gap d1 is preferably 1.3 to 2 times as large as d2. By doing so, not only the optimal dynamic pressure effect and static pressure effect can be obtained, but also the amount of heat generation can be greatly reduced.

In the above embodiment, the diameter of the rotary shaft 20 is reduced to increase the bearing gap d1 at the dynamic pressure land portion 14. However, the inner diameter of the bearing surface 4 may be changed. For example, as shown in FIG. 6, the rotating shaft 20 has a uniform diameter and the inner diameter C of the dynamic pressure land portion 14 of the bearing member 5.
1 and the inner diameter C2 of the portion from the static pressure pockets 6 and 7 to the drain groove 10 are changed so that the bearing clearance c1 is preferably c2
1.3 times to 2 times. Thereby, the same effect as in the above embodiment can be obtained.

As an application example, FIGS. 7 and 8 show a third example.
An embodiment of the present invention will be described. In this device, a convex portion 30 is provided in each of the static pressure pockets 6 and 7, and a discharge port connected to the discharge passages 2 and 3 is provided at the center of the convex portion 30 similarly to Japanese Patent Publication No. 60-33729 shown in the prior art. 31 are provided. At this time, in order to obtain the same effect as in the first and second embodiments, the bearing gap d3 between the projection 30 and the rotating shaft 20 is the same as d2, that is, d1 is 1.3 to 2 times d3. Double it.

If the dynamic pressure land portion 14 is tapered as shown in FIG. 9 or stepped with a step as shown in FIG. 10, fluid flows into the wedge-shaped clearance P when the rotating shaft 20 is eccentric. Since it is easily introduced, the stability of dynamic pressure rigidity and the load capacity can be further improved.

[0022]

According to the first aspect of the present invention, the bearing clearance between the rotating shaft and the dynamic pressure land for generating the dynamic pressure is made larger than the bearing clearance from the static pressure pocket to the drain groove. Thus, the amount of heat generated at the dynamic pressure land can be suppressed even when the rotating shaft is rotated at a high speed. Therefore, seizure can be prevented. In addition, since the bearing gap from the static pressure pocket to the drain groove has a conventional interval, the supply oil does not increase. Therefore, conventional oil supply devices and recovery tanks may be used.

The bearing clearance between the dynamic pressure land portion and the rotary shaft is set to be 1.3 to 2 times the bearing clearance reaching the drain groove.
By making the size twice as large, the amount of heat generation can be greatly reduced as shown in the graph of the experimental data, and the optimum bearing rigidity can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view of the bearing unit of the embodiment.

FIG. 3 is a sectional perspective view of a bearing unit according to the embodiment.

FIG. 4 is a sectional view of the present embodiment as viewed from the circumferential direction.

FIG. 5 is a diagram illustrating a rise in oil temperature in the present embodiment.

FIG. 6 is a sectional view illustrating a second embodiment.

FIG. 7 is a sectional view illustrating a third embodiment.

FIG. 8 is a partial sectional view showing a third embodiment.

FIG. 9 is a partial sectional view illustrating a fourth embodiment.

FIG. 10 is a partial sectional view showing a fifth embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 bearing housing 2, 3 discharge path 4 bearing surface 5 bearing member 6, 7 static pressure pocket 8 supply groove 9 supply port 10 drain groove 11 discharge path 12 annular groove 13 oil supply path 14 dynamic pressure land 15 communication hole 20 rotary shaft D1, D2, d1, d2, d3 Bearing clearance

Claims (2)

[Claims] 1. A rotating shaft, a bearing member rotatably supporting the rotating shaft, a plurality of static pressure pockets provided on an inner peripheral surface of the bearing member, and a dynamic pressure generated by the static pressure pocket. A dynamic pressure land portion, a supply hole for supplying a fluid to the static pressure pocket, and a bearing formed on an inner peripheral surface of the bearing member, the bearing provided between the rotating shaft and the bearing member for supplying the fluid supplied to the static pressure pocket to the bearing. In a fluid dynamic bearing device having an annular drain groove that is discharged through a gap, the gap between the dynamic pressure land portion and the rotating shaft is larger than the gap between the static pressure pocket and the drain groove. A hydrodynamic bearing device characterized by being enlarged. 2. The hydrodynamic bearing device according to claim 1, wherein a bearing gap between the dynamic pressure land portion and the rotating shaft is set to 1.3 with respect to a bearing gap from a static pressure pocket to a drain groove.
A hydrodynamic bearing device characterized in that the number is doubled to doubled.