JP2008138804A - Rolling member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling member capable of separating a contact part by lubricating oil, even in an operation condition of frequently starting and stopping and an operation condition unable to expect supply of the lubricating oil from an external part to the contact part such as rocking motion or a low speed and high load. <P>SOLUTION: A dynamic pressure generating surface having a large number of very small dynamic pressure grooves 5 for generating the dynamic pressure action by the presence of the lubricating oil, is formed in a rolling contact part of the rolling member. A fluid lubricating state can be maintained even at a speed of not forming a sufficient oil film, by delivering the lubricating oil in the dynamic pressure grooves 5 from a deep lubricating oil storage pocket 4 by the thermal expansion, when starting relative motion, by dotting the lubricating oil storage pocket 4 deeper than the depth of the dynamic pressure grooves 5 on this dynamic pressure generating surface. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mechanical element such as a rolling bearing that realizes friction reduction by a relative motion mainly composed of rolling, and is particularly suitable for operating conditions such as frequent start and stop, swinging motion, or operating conditions such as low speed and high load. The present invention relates to a rolling member.

  In the rolling contact part of a rolling member such as a rolling bearing, a dynamic pressure effect is generated in the fluid interposed between the objects by the relative motion of the objects to achieve a fluid lubrication state, thereby preventing direct contact of the objects and friction. Wear can be reduced.

  However, when the amount of lubricating oil is small or when the speed is low, the dynamic pressure effect is small and the lubricating oil film is not formed, and there is a risk of causing solid contact. Particularly in recent years, low-viscosity lubricating oil has been used to reduce torque, and the amount of lubricating oil supplied from the outside has also decreased. For this reason, the possibility of becoming a solid contact state is further increased.

  Conventionally, even if the amount of lubricating oil in the vicinity of the contact portion is insufficient, lubrication is possible if the surface of the contact portion retains the lubricating oil. Therefore, a large number of fine recesses are provided on the surface, and lubrication is provided in the recesses. A technique for retaining oil is disclosed in Patent Document 1. This technique can improve boundary lubrication performance at low speeds.

  On the other hand, in a plain bearing, a technique is generally used in which lubricating performance is improved by forming a number of grooves having a depth of about the oil film thickness on a sliding surface. This utilizes the fact that a hydrodynamic dynamic pressure action occurs because the depth of the sliding surface changes due to the presence of the groove. An example in which this effect is applied to a rolling bearing is disclosed in Patent Document 2. The technique disclosed in Patent Document 2 attempts to prevent slippage by pressing a rolling element in which a slip occurs at a portion to which a relatively small load is applied against the raceway with a pressure by a dynamic pressure action. However, the technique of Patent Document 2 is based on the premise that sufficient lubricating oil is supplied to the contact portion from the outside of the contact portion, as in a general hydrodynamic bearing.

  Further, Non-Patent Document 1 discloses an example in which a deep concave portion is provided in a thrust flat plain bearing that supports high surface pressure. This is intended to improve the boundary lubrication performance by discharging the lubricating oil from the recess accompanying thermal expansion. However, this technique is not intended to generate hydrodynamic dynamic pressure effects.

Japanese Patent Laid-Open No. 02-168021 JP 2006-105361 A H.Kotera, A.Mori, N.Tagawa, PROPOSAL OF A SEIZURE PREVENTING METHOD IN HEAVILY LOADED SLIDING PAIRS, Synopses of the International Tribology Conference Kobe, 2005, D-04

  By the way, the hydrodynamic dynamic pressure action is generated by the viscosity of the fluid, the speed of the contact surface, and the wedge shape of the contact surface. In normal rolling contact, the contact portion of the member is inevitably in the shape of a wedge. Therefore, if a certain viscosity or speed is applied, an oil film is formed and the contact surface is separated.

  However, when trying to increase the dynamic pressure action at low speed, it is difficult to control the viscosity of the fluid, so it is necessary to improve the wedge shape. That is, it is conceivable to increase the dynamic pressure action at a low speed by providing a micro wedge shape on the surface in addition to the macro wedge shape.

  Although the purpose of the rolling bearing is different from that of the technique of Patent Document 2, it is considered that the oil film forming property at low speed is improved by providing a shallow concave portion that generates a dynamic pressure action. However, when the speed is low, supply of lubricating oil from the outside to the contact portion cannot be expected.

  Further, in the method of Patent Document 1, the fluid lubrication performance cannot be improved only with the lubricating oil held in the shallow concave portion.

  Therefore, the present invention provides the contact portion with lubricating oil even under operating conditions where frequent starting and stopping, swinging motion, or low speed and high load cannot be expected from the outside. It is intended to provide a rolling member that can be separated.

  In the present invention, a dynamic pressure generating surface having a large number of small dynamic pressure grooves that generate a dynamic pressure action due to the presence of lubricating oil is formed in the rolling contact portion of the rolling member, and the dynamic pressure generating surface is formed on the dynamic pressure generating surface. Lubricating oil storage pockets deeper than the groove depth were scattered.

The rolling member according to the present invention is sufficiently lubricated, for example, under the condition that the speed is low and the amount of lubricating oil flowing into the contact portion from the outside is small, that is, a large number of minute dynamic pressure grooves that generate dynamic pressure action. Even under conditions where there is no oil, the lubricating oil stored in the deep lubricating oil storage pocket is discharged to the contact surface by thermal expansion at the start of relative motion, so the lubricating oil is placed in a large number of minute dynamic pressure grooves. Is supplied and an oil film is easily formed by the dynamic pressure action. Therefore, the fluid lubrication state can be maintained even at a speed at which a sufficient oil film is not formed, and the contact portion can be separated by the lubricating oil.
Also, in the case of extremely low speed where oil film formation is essentially difficult, good lubricity as high as fluid lubrication cannot be expected, but due to thermal expansion due to frictional heat, it is mainly due to oil discharged from the surface through the lubricating oil storage pocket. The boundary lubricity prevents solid contact and prevents surface damage.

  As described above, the rolling member according to the present invention forms a dynamic pressure generating surface having a large number of dynamic pressure grooves that generate a dynamic pressure action in the rolling contact portion due to the presence of lubricating oil. Since the surface is interspersed with lubricant storage pockets that are deeper than the dynamic pressure grooves, the supply of lubricant from the deep lubricant storage pockets and the dynamic pressure action of a large number of shallow micro dynamic pressure grooves Even so, a sufficient lubricating oil film can be formed, and direct contact of the contact portion can be prevented. Further, surface damage can be prevented by boundary lubrication even at extremely low speeds.

FIG. 1 shows an example in which the present invention is applied to a roller 2 of a cylindrical roller bearing 1.
The rolling surface 3 of the roller 2 is formed on a dynamic pressure generating surface having a large number of minute dynamic pressure grooves 5 that generate a dynamic pressure action due to the presence of lubricating oil, as shown in FIG. 2 or FIG. 3 in an enlarged manner. In addition, the lubricating oil storage pockets 4 deeper than the depth of the dynamic pressure grooves 5 are scattered on the dynamic pressure generating surface. In FIG. 2 or FIG. 3, the lubricating oil storage pocket 4 is represented by a black circle.

In the example of FIG. 2 or FIG. 3, the shallow dynamic pressure grooves 5 are evenly disposed on the entire rolling surface 3 of the roller 2 so as to be orthogonal to the flow direction of the lubricating oil. 2 or 3, the lubricating oil storage pocket 4 is disposed between the dynamic pressure groove 5 and the dynamic pressure groove 5. However, the positional relationship between the dynamic pressure groove 5 and the lubricating oil storage pocket 4 is arbitrary. is there.
For example, as shown in FIG. 2, the deep lubricating oil storage pockets may be interspersed so as to be arranged in parallel at predetermined intervals in the rolling and sliding direction of the roller 2 (the direction of the arrow in FIG. 2). As shown in FIG. 3, the rollers 2 may be scattered in a staggered manner at predetermined intervals in the rolling and sliding direction (the direction of the arrow in FIG. 3). Since the lubricating oil 6 discharged from the deep lubricating oil storage pocket 4 moves backward in the traveling direction as the roller rolls, the lubricating oil storage pocket 4 is paralleled at a predetermined interval as shown in the example of FIG. When arranged so as to line up with each other, the distribution of the lubricating oil on the surface becomes parallel streaks as shown by a one-dot chain line in FIG. Further, when the lubricating oil storage pockets 4 are arranged in a staggered manner as in the example of FIG. 3, the streaks to the surface of the lubricating oil 6 are formed as shown by a one-dot chain line in FIG. 3, rather than the case of the example of FIG. 2. Distribution almost doubles.

  In the example of FIG. 2 or FIG. 3, the shape of the opening surface of the lubricating oil storage pocket 4 is all circular, but may be an ellipse or a polygon.

  Next, the cross-sectional shape of the hole of the dynamic pressure groove 5, that is, the bottom surface of the hole does not need to be parallel to the surface, and may be inclined. However, since the dynamic pressure action decreases when it is inclined deeper in the direction of fluid flow, as shown in FIGS. 4 and 5, at least the direction of fluid flow (as indicated by the arrows in FIGS. 4 and 5). It is desirable to incline so as to be shallow in the direction). In particular, as shown in FIG. 5, if the shape does not have a shoulder on one side of the hole, it is possible to reduce wear at the time of starting and stopping.

  Next, since the lubricating oil storage pocket 4 deeper than the dynamic pressure groove 5 is intended to store lubricating oil, the larger the volume, the better. However, since the dynamic pressure that contributes to the load support is not generated in the lubricating oil at the opening, it is desirable that the opening area is small. Therefore, the lubricating oil storage pocket 4 has a small diameter and a deep hole. Considering the current level of processing technology that can be mass-produced, the size is 20-30 μm in diameter and about 100 μm in depth.

  On the other hand, the dynamic pressure grooves 5 are intended to generate a dynamic pressure in a minute contact region, and are therefore relatively small with respect to the area of the contact portion, and it is desirable that there are many in the contact surface. Accordingly, assuming a normal rolling contact machine element represented by a rolling bearing, the groove width is set to 20 to 30 μm or less. In the case of a normal dynamic pressure bearing that is used in a state where there is sufficient lubricating oil, the depth of the groove that effectively generates the dynamic pressure action is about the oil film thickness. Expects a dynamic pressure effect under operating conditions where the oil film thickness is not sufficient. In the case of a general rolling bearing, the oil film thickness is at most several μm even when a sufficient oil film is generated. Therefore, the depth of the shallow dynamic pressure groove 5 is about 0.1 to 1 μm. The bottom surface of the dynamic pressure groove 5 does not necessarily have to be flat, but it is better that the shoulder portion is not bent as much as possible.

  The rolling bearing has a rotational speed of 0 at the start of operation or the dead center of the swinging motion, and gradually reaches a predetermined or maximum rotational speed. Immediately after starting the movement from the speed of 0, no lubricating oil is supplied from the outside, and since the speed of the contact surface is low, an oil film is not formed, and the solids are in contact with each other. When the movement is continued in the contact state, heat is generated due to high friction, and the lubricating oil held in the concave portion of the contact surface expands. The lubricating oil held in the dynamic pressure groove 5 is also discharged to the contact surface and is considered to contribute to lubrication. However, in the deep lubricating oil storage pocket 4, a relatively large amount of lubrication is caused by the difference in thermal expansion between the solid and the lubricating oil. Oil will be discharged onto the contact surface.

When the amount of lubricating oil in the rolling contact portion is extremely small, a dynamic pressure action cannot be generated in the dynamic pressure groove 5, but in the present invention, the dynamic pressure is increased by the lubricating oil discharged from the deep lubricating oil storage pocket 4. Lubricating oil is replenished to the groove 5, and an oil film due to a dynamic pressure action is easily formed on the rolling contact portion, and the contact surface is separated by the oil film.
Therefore, according to the present invention, solid contact on the contact surface is prevented even under operating conditions at a low speed, and the fluid lubrication state can be maintained.

  Further, in the case of extremely low speed where oil film formation is essentially difficult, solid contact is prevented by boundary lubricity due to oil discharged mainly from the deep lubricating oil reservoir pocket 4 due to thermal expansion due to frictional heat. .

Next, the lubricating oil stored in the deep lubricating oil storage pocket 4 is discharged mainly by thermal expansion caused by heat generation on the contact surface, but the roller member also thermally expands due to heat generation on the contact surface. Since the volume of the storage pocket 4 also increases, the discharge amount of the lubricating oil is the difference between the expansion of the volume of the lubricating oil stored in the lubricating oil storage pocket 4 and the increase of the volume of the lubricating oil storage pocket 4.
Therefore, the linear expansion coefficient of steel used for a normal rolling bearing is about 12 × 10 ⁻⁶ K ⁻¹ , whereas the thermal expansion coefficient of silicon nitride is about 3 × 10 ⁻⁶ K ⁻¹ . As described above, the smaller the coefficient of thermal expansion of the material of the roller, the higher the effect of discharging the lubricating oil. Therefore, when the roller is made of ceramic, particularly silicon nitride, it is advantageous to discharge the lubricating oil.

  In the above embodiment, the present invention is applied to the rolling surface of the roller of the cylindrical roller bearing. However, the present invention may be applied to an inner ring, an outer ring, a roller end face or a collar surface, and any other machine that performs rolling motion. Applicable to rolling contact part of element.

It is a conceptual diagram which shows the example which applied this invention to the roller of the cylindrical roller bearing. It is an enlarged plan view which shows the example of arrangement | positioning of the lubricating oil storage pocket 4 and the dynamic pressure groove 5 which are formed in the rolling contact part of the rolling member which concerns on this invention. It is an enlarged plan view which shows the example of arrangement | positioning of the lubricating oil storage pocket 4 and the dynamic pressure groove 5 which are formed in the rolling contact part of the rolling member which concerns on this invention. It is a longitudinal cross-sectional view which cuts an example of the cross-sectional shape of the lubricating oil storage pocket 4 and the dynamic pressure groove 5 which were formed in the rolling contact part of the rolling member which concerns on this invention in the direction of the AA line of FIG. It is a longitudinal cross-sectional view which cuts and shows the other example of the cross-sectional shape of the lubricating oil storage pocket 4 and the dynamic pressure groove 5 which were formed in the rolling contact part of the rolling member which concerns on this invention in the direction of the AA line of FIG. .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylindrical roller bearing 2 Roller 3 Rolling surface 4 Lubricant storage pocket 5 Dynamic pressure groove 6 Lubricant

Claims (4)

  A dynamic pressure generating surface having a large number of minute dynamic pressure grooves that generate dynamic pressure action due to the presence of lubricating oil is formed in the rolling contact portion, and lubrication deeper than the depth of the dynamic pressure grooves is formed on the dynamic pressure generation surface. A rolling member characterized by interspersed with oil storage pockets.   The rolling member according to claim 1, wherein deep lubricating oil storage pockets formed on the dynamic pressure generating surface are arranged in a staggered manner in the rolling direction.   The rolling member according to claim 1, wherein a bottom surface of the dynamic pressure groove is inclined so as to become shallower in a rolling direction.   The rolling member according to any one of claims 1 to 3, wherein the member forming the dynamic pressure groove and the lubricating oil storage pocket is formed of a ceramic such as silicon nitride.

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