JP2006242262A - Tapered roller bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of surface originating separation leading to a very short life resulting from metal contact of poor lubrication. <P>SOLUTION: This tapered roller bearing comprises a plurality of tapered rollers laid between the raceway surfaces of an inner ring and an outer ring and rollingly held by a cage. A roller coefficient γ is γ>0.94. A phosphoric acid metal salt coating is formed on at least either the raceway surface or the tapered roller. The total thickness of the coating on the raceway surface or the roller is 10 nm or greater. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a tapered roller bearing used, for example, in a shaft support portion of an automobile transmission.

  For example, a tapered roller bearing used for a shaft support portion of an automobile transmission has an outer ring having a conical raceway surface, a conical raceway surface, and a small flange portion at a small diameter side end of the raceway surface, The inner ring having a large flange at the end on the large-diameter side, a plurality of tapered rollers arranged to roll between the raceway surface of the outer ring and the raceway surface of the inner ring, and a tapered roller as a rolling element And a steel plate retainer that is held at equal intervals in the direction.

  This tapered roller bearing was assembled so as to maintain a non-contact state in which the cage does not contact the raceway surface of the outer ring, or a cage having a guide surface that abuts the raceway surface of the outer ring. There exists a thing (for example, refer patent document 1). The latter type in which the cage comes into contact with the outer ring is easier to secure the strength of the cage than the former type in which the cage does not come into contact with the outer ring. Since it can be increased, it is easy to reduce the maximum surface pressure on the raceway surface. However, in the type in which the cage is in contact with the outer ring, the outer circumferential surface of the cage may come into contact with the raceway surface of the outer ring to promote wear at the contact portion and cause an increase in drag torque.

  On the other hand, in a rolling bearing including a tapered roller bearing, as a means for preventing damage caused by poor lubrication such as peeling damage, the surface of the rolling element or the raceway surface of the inner and outer rings is formed on a random minute rough surface, and the minute rough surface is formed. Some have the surface roughness kept within a certain range (see, for example, Patent Documents 2 and 3). However, since the sound deteriorates, it is difficult to adopt means as disclosed in Patent Documents 2 and 3 for the ball bearing. In addition, a dedicated processing facility is required for forming the dimples, which increases the cost.

In addition, by forming a compound reaction film layer with a thickness of 0.05 to 0.5 μm under the surface of the rolling element or under the raceway surface of the inner and outer rings, the load resistance and seizure resistance can be sufficiently improved with low wear. There is a rolling bearing (see, for example, Patent Document 4). However, the effect of peeling life due to poor lubrication such as peeling damage is not clearly disclosed.
JP 2003-28165 A Japanese Patent Publication No. 5-87688 No. 6-20900 Japanese Patent No. 2969700

  By the way, in recent years, low-viscosity oil tends to be used for automobile transmissions for the purpose of AT / CVT missions and fuel efficiency reductions, and the use environment has been reduced due to the miniaturization and high output of missions. There is a tendency for high loads and high temperatures.

  Therefore, the bearing has changed to a harsh lubricating environment, and surface-origin separation with a very short life due to the occurrence of metal contact due to poor lubrication is becoming more likely to occur on the raceway surface of the inner and outer rings. is the current situation.

  Therefore, the present invention has been proposed in view of the above-mentioned problems, and its object is to prevent the occurrence of surface-origin separation in a very short life due to the occurrence of metal contact due to poor lubrication. It is an object of the present invention to provide a tapered roller bearing.

  As a technical means for achieving the above-mentioned object, it is effective to increase the oil film forming ability of the bearing raceway surface and reduce the occurrence rate of metal contact, and the difference in the maximum surface pressure of the raceway surface is the metal surface. In order to influence the incidence of contact, it is also effective to increase the filling rate of the tapered rollers in the bearing so that the maximum surface pressure of the raceway surface is lowered.

  Therefore, the present invention provides a tapered roller bearing in which a plurality of tapered rollers are interposed between both raceway surfaces of the inner ring and the outer ring so as to be freely rollable by a cage, and the roller coefficient γ is γ> 0.94. In addition, a metal phosphate salt film is formed on at least one of the raceway surface or the tapered roller, and the total film thickness of the raceway surface and the rolling element is 10 nm or more. The roller coefficient γ (roller filling rate) is defined by the equation: γ = (Z · DA) / (π · PCD). Here, Z: number of rollers, DA: roller average diameter, PCD: roller pitch circle diameter.

  In the present invention, by setting the roller coefficient γ to γ> 0.94, the maximum surface pressure of the raceway surface can be reduced, so that early damage due to excessive surface pressure of the raceway surface can be prevented. In addition, by forming a highly lipophilic metal phosphate salt film on the bearing surface of at least one of the raceway surfaces of the inner and outer rings or rolling elements, the ability to form an oil film on the bearing raceway surface in a dilute lubrication environment is increased. Since the occurrence rate of contact can be reduced, it is possible to prevent the occurrence of surface-origin separation in a very short lifetime due to the occurrence of metal contact due to poor lubrication. The total film thickness of the raceway surface and the rolling element needs to be 10 nm or more. If the total film thickness is less than 10 nm, it is difficult to increase the oil film forming ability of the bearing raceway surface in a dilute lubrication environment, and a desired effect cannot be exhibited.

  The aforementioned metal phosphate salt coating can be formed by immersing the inner and outer rings or rolling elements in a phosphate triester solution containing tricresyl phosphate. The phosphate triester solution containing tricresyl phosphate means that tricresyl phosphate is used as a representative example of the phosphate triester solution. Further, in the formation of the metal phosphate salt film, it is difficult to form a metal phosphate salt film having a thickness larger than 70 nm in consideration of the dimensional change of the bearing and the number of processing steps. The thickness of the coating is desirably 70 nm or less.

  According to the present invention, by setting the roller coefficient γ to γ> 0.94, the maximum surface pressure of the raceway surface can be reduced, so that early damage due to excessive surface pressure of the raceway surface can be prevented. In addition, a highly oleophilic metal phosphate film is formed on the raceway surfaces of the inner and outer rings or at least one bearing metal surface of the rolling element, and the total film thickness of the raceway surface and the rolling element is 10 nm or more. As a result, the oil film forming ability of the bearing raceway surface in a dilute lubrication environment can be increased and the incidence of metal contact can be reduced, so the surface with a very short life resulting from the occurrence of metal contact due to poor lubrication. It is possible to prevent the occurrence of starting point peeling. As a result, a highly reliable long-life rolling bearing can be provided.

  The tapered roller bearing in the embodiment of the present invention has an outer ring having a conical raceway surface, a conical raceway surface, a small flange portion at a small diameter side end portion of the raceway surface, and a large flange portion at a large diameter side end portion. A steel plate that holds inner rings each having a flange, a plurality of tapered rollers that are freely rollable between a raceway surface of the outer ring and a raceway surface of the inner ring, and tapered rollers that are rolling elements at equal intervals in the circumferential direction. And a cage made of metal. This tapered roller bearing is assembled to a shaft support portion of a transmission of an automobile, for example, by a shaft (not shown) being coaxially inserted into an inner ring and an outer ring being attached to the inner diameter of a housing (not shown).

  In the conventional tapered roller bearing, the roller coefficient γ is set to γ ≦ in order to secure the column width of the cage while avoiding contact between the outer ring and the cage, and to obtain appropriate cage column strength and smooth rotation. It was 0.94. Here, if the roller filling rate is simply increased without changing the diameter of the cage, the columns of the cage become thin, and it becomes difficult to ensure sufficient column strength. On the other hand, when the diameter of the cage is increased in the direction in which the clearance between the cage and the outer ring is reduced in order to ensure the column strength of the cage, the outer peripheral surface of the cage comes into contact with the raceway surface of the outer ring and the contact portion May accelerate wear and cause an increase in drag torque.

  Therefore, in the tapered roller bearing of this embodiment, the diameter of the cage is increased in the direction in which the clearance between the cage and the outer ring is reduced, and the cage does not always contact the raceway surface of the outer ring during operation. By setting the diameter to maintain a non-contact state, the roller coefficient γ (the roller filling rate) is set to γ> 0.94. Thereby, it is possible to secure the column strength of the cage and increase the filling rate of the rollers.

  On the other hand, the tapered roller bearing is not particularly limited in its material and type of radial bearing, thrust bearing, etc., but the inner and outer rings and the rolling elements are made of metal that can be treated with a phosphoric acid coating. Materials made of steel, case-hardened steel, stainless steel, plating, white metal containing lead and tin, and other bearing alloys are possible.

  In the tapered roller bearing described above, a highly lipophilic metal phosphate metal salt coating is formed on at least one of the bearing metal surfaces of the raceway surfaces of the inner and outer rings or the rolling elements. As a result, the oil film forming ability of the bearing raceway surface in a dilute lubrication environment can be increased and the incidence of metal contact can be lowered, so that the surface starting point with a very short life resulting from the occurrence of metal contact due to poor lubrication The occurrence of peeling can be prevented.

  Further, the total thickness of the metal phosphate coating formed on the raceway surface and the bearing metal surface of the rolling element is set to 10 nm or more. If the total film thickness is less than 10 nm, it is difficult to increase the oil film forming ability of the bearing raceway surface in a dilute lubrication environment, and a desired effect cannot be exhibited.

This metal phosphate film can be formed by immersing inner and outer rings or rolling elements in a phosphate triester solution containing tricresyl phosphate. This phosphate triester is an organic phosphate compound represented by (RO) ₃ P═O (wherein R represents an aryl group, an aliphatic hydrocarbon group, or an alicyclic hydrocarbon group). Commercially available industrial materials can be used as the agent. A typical example of these phosphate triesters is tricresyl phosphate (CH ₃ C ₆ H ₄ O) ₃ PO.

  Further, in the formation of the metal phosphate salt film, it is difficult to form a metal phosphate salt film having a thickness larger than 70 nm in consideration of the dimensional change of the bearing and the number of processing steps. The thickness of the coating is preferably 70 nm or less. Furthermore, when forming the metal phosphate salt film, heating may be performed to increase the reaction rate.

  The present applicant conducted a life test under severe lubrication and overload conditions on a conventional product with a roller coefficient γ ≦ γ4, a bearing A with a roller coefficient γ> 0.94, and the product of the present invention. . The test results are as shown in FIG. The bearing A uses a steel plate cage, and the outer ring and the cage are always in contact during operation. As is apparent from the figure, the product of the present invention did not cause any abnormality with respect to the conventional product and the bearing A, and a remarkable effect was obtained in terms of life time.

  Further, the present applicant dipped the inner and outer rings or rolling elements constituting the rolling bearing in a 100% stock solution of tricresyl phosphate to form a metal phosphate salt film on the surface of the bearing metal.

  Here, as disclosed in the above-mentioned Patent Document 4, when a compound reaction film layer of 0.05 to 0.5 μm is formed, load resistance and seizure resistance can be improved with low wear. However, in order to form such a thick film, it is necessary to immerse for a long time, and considering the product cost, it is not suitable for a rolling bearing for automobiles.

  Therefore, the processing temperature and processing time in the formation of the metal phosphate film are considered in consideration of the dimensional change of the bearing and the number of processing steps, and a bearing with a metal phosphate film that can be processed at an upper limit of 150 ° C. × 100 h is manufactured. The improvement effect on the surface-origin peeling was confirmed under severe lubrication environment. The maximum thickness of the metal phosphate coating film that can be formed when 150 ° C. × 100 h is the upper limit treatment condition was 70 nm.

  The thickness of the metal phosphate coating was measured by X-ray photoelectron spectroscopy (XPS analysis). In this XPS analysis, the sample surface is irradiated with X-rays, and the information (qualitative and quantitative) and the binding state of the elements on the sample surface are obtained by analyzing the energy of photoelectrons emitted from the outermost surface of the sample (about several angstroms). Furthermore, by performing measurement while sputtering the sample surface using an argon (Ar) ion gun, the depth direction of the element, that is, the distribution state under the sample surface can be analyzed.

  The present applicant changed the thickness of the metal phosphate coating formed as described above and conducted a life test under severe lubrication. The test data is as shown in FIG. As a result, if the total thickness of the raceway surfaces of the inner and outer rings and the metal phosphate coating on the rolling elements is 10 nm or more, it becomes possible to increase the oil film forming ability of the bearing raceway surface under severe lubrication environment. It has been confirmed that it is possible to prevent the occurrence of surface-origin peeling with a very short lifetime due to the occurrence of metal contact due to a defect.

It is a table | surface which shows the life test result under severe lubrication about a roller coefficient. It is a table | surface which shows the lifetime test result under severe lubrication about the thickness of a metal phosphate salt film.

Claims (3)

  In a tapered roller bearing in which a plurality of tapered rollers are interposed between both raceway surfaces of an inner ring and an outer ring so as to be freely rollable by a cage, the roller coefficient γ is γ> 0.94, and the raceway surface Alternatively, the tapered roller bearing is characterized in that a metal phosphate salt film is formed on at least one of the tapered rollers, and the total film thickness of the raceway surface and the rolling element is 10 nm or more.   2. The tapered roller bearing according to claim 1, wherein the metal phosphate salt film is formed by immersing inner and outer rings or rolling elements in a phosphate triester solution containing tricresyl phosphate.   The tapered roller bearing according to claim 1, wherein a thickness of the metal phosphate coating is 70 nm or less.

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