JP2005249108A - Rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing capable of reducing a frictional coefficient of a rolling element and a retainer, and preventing the breakage of the retainer by improving the durability of the rolling bearing, and having superior transmitting efficiency and bearing service life. <P>SOLUTION: This rolling bearing 1 comprises an outer ring 2, an inner ring 3, a plurality of rolling elements 5 rotatably mounted between the outer ring 2 and the inner ring 3, and the metallic retainer 4 provided with a plurality of pockets 4a rotatably holding the rolling elements 5. The metallic retainer 4 has a nitride layer 6b having a thickness of 1-9% of a plate thickness of the metallic retainer 4, on inner faces of the pockets 4a kept into contact with the rolling elements 5. The surface roughness of the rolling element 5 is 0.003-0.01 μmRa. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rolling bearing used for a transmission bearing of an automobile, a belt type CVT (Continuously Variable Transmission) bearing, and the like.

Conventionally, an oil film parameter Λ representing the degree of oil film formation that greatly affects the quality of lubrication has been used as an index relating to the life of a rolling bearing (see, for example, Non-Patent Document 1). The oil film parameter Λ is obtained by the equation (1). In Equation (1), hmin is the minimum oil film thickness, hr1 and hr2 are the mean square roughness of the rolling contact surface between the inner or outer race and the rolling element, and σ ₁₂ is the centerline average roughness ( h≈1.12R), σ _c is the center line average roughness (h≈1.12R) of the rolling elements.

  It is known that the larger the value of the oil film parameter Λ, the thicker the oil film is formed and the longer the life of the rolling bearing. In the range of Λ ≦ 3, a so-called boundary lubrication state occurs, which may adversely affect the life of the rolling bearing. Therefore, conventionally, the rolling contact surface between the race and the rolling element has been processed to be as smooth as possible to sufficiently form an oil film. It should be noted that the ability to form an oil film is lower for a rotating wheel than a fixed wheel, and it was difficult to form an oil film on the rotating wheel, so it is desirable to reduce the surface roughness of the rotating wheel. It had been.

  Regarding the life extension of rolling bearings, the relationship between the surface roughness of the steel ball (rolling element) and the surface roughness of the rolling surface (track surface) is expressed as follows: 0.05 μm Ra <surface roughness of the steel ball <rolling surface The surface roughness of the steel ball is made close to the surface roughness of the rolling surface, and an oil film is formed between the surface of the steel ball and the rolling surface of the inner and outer rings to improve lubricity. Thus, it is known that the temperature increase of the steel ball is suppressed, the surface peeling of the steel ball is prevented, and the life is extended (for example, refer to Patent Document 1).

  Further, among the raceways of the outer ring and the inner race and the surface of the rolling element, at least the outer raceway surface is partitioned by a number of groove-like recesses having a depth of 0.0005 mm or more and 0.008 mm or less, and the groove-like recesses. In addition, by forming with a smooth portion having a roughness of 0.08 μm Ra or less after removing the groove-like recess, the outer ring raceway surface has an appropriate coefficient of friction to suppress the sliding motion of the rolling element, and the groove An oil reservoir function of the concave portion is also acted as a secondary function to prevent metal adhesion at the smooth portion and prevent seizure of the bearing (see, for example, Patent Document 2). .

On the other hand, a cage for a rolling bearing is a press cage obtained by subjecting a cold rolled steel sheet such as SPCC or SPCE to soft nitriding treatment such as pure nitriding (NH ₃ gas nitriding), gas soft nitriding, tuftride, ion nitriding, etc. Some have improved durability under severe lubrication conditions by using a metal corrugated cage. When the nitriding treatment is performed, it can be hardened more than the base material, and a surface layer having a surface hardness of about Hv 350 to 600 is formed and excellent durability is obtained. Usually, the thickness of the nitride layer is about 100 μm.
Rolling Bearing Engineering Editorial Committee, “Rolling Bearing Engineering”, Yokendo Publishing, July 10, 1975, first edition, p178 Japanese Examined Patent Publication No. 5-32602 (page 3-5, FIG. 1) Japanese Patent Publication No. 2508178 (page 3-5, FIG. 1)

  In recent years, there has been a strong demand for energy saving in automobiles, and in lubrication of automobile transmissions, for example, the amount of oil supply is reduced to 20 cc / min or less, or the viscosity resistance of an oil film is reduced by using a low-viscosity lubricating oil. Attempts have been made to improve fuel efficiency by such methods. In the belt type CVT, the CVT fluid has a low viscosity for the purpose of ensuring transmission efficiency, preventing noise generated during operation, and suppressing wear of the driving and driven pulleys and the endless belt. There is a tendency to use things.

  Rolling bearings made of standard bearing materials (for example, two types of bearing steel) are generally used for CVT, and lubrication of the bearings is also performed using CVT fluid. As a result of the combined action of the reduction in the amount of oil and the amount of lubrication and the axial vibration caused by belt fluctuation, sliding motion occurs between the bearing ring of the bearing and the rolling element, and wear occurs between the rolling element and the cage. Occurred and the surface roughness of the rolling element deteriorated, and there were cases where early peeling / wearing different from vibration and pressure mixing point type peeling due to contamination by foreign matters occurred. Under such use conditions, the surface damage prevention technology focusing on the oil film formation between the rolling elements and the raceway surface disclosed in Patent Document 1 and Patent Document 2 should sufficiently deal with the above problem. However, further measures are desired.

  Further, when the thickness of the nitride layer is set to 100 μm (for example, 10% of the nitride layer when the plate thickness of the cage is 1 mm) as in the conventional nitriding treatment of the cage, the overall strength of the cage is Although improved, conversely, the toughness is lowered and it becomes difficult to deform, so that it has been confirmed that the cage breaks due to metal fatigue.

  The present invention has been made in view of the above-described problems, and its purpose is to reduce the coefficient of friction between the rolling elements and the cage, and to improve the durability of the rolling bearing to break the cage (fatigue failure). It is an object of the present invention to provide a rolling bearing having excellent transmission efficiency and bearing life.

  In order to achieve the above-described object, the rolling bearing according to the present invention is characterized by the following (1) to (2).

(1) A metal cage in which an outer ring, an inner ring, a plurality of rolling elements rotatably disposed between the outer ring and the inner ring, and a plurality of pockets for holding the rolling elements in a freely rotatable manner are formed. A rolling bearing comprising:
The metal cage has a nitride layer having a thickness of 1% or more and 9% or less of the plate thickness of the metal cage on at least the inner surface of the pocket that contacts the rolling element.

  (2) In the rolling bearing according to (1), the surface roughness of the surface of the rolling element is 0.003 μmRa or more and 0.01 μmRa or less.

  According to the rolling bearing having the above-described configuration, the metal cage is formed on the inner surface of the pocket that contacts the rolling element, and the thickness of the metal cage is 1% or more and 9% or less, preferably 1% or more and 5% or less. A nitride layer having a thickness of 5 mm is formed, whereby the strength of the cage can be improved to prevent the cage from being damaged (fatigue failure, impact failure), and the rolling element and cage The friction coefficient between the two can be reduced. Therefore, even under the use conditions described above, it is possible to suppress wear on the pocket inner surface due to friction between the rolling elements and the cage, and to prevent deterioration of the surface roughness of the balls. Can prevent surface peeling damage caused by the outer ring raceway surface or the inner ring raceway surface and the ball entering between the balls.

  In general, the plate thickness of the cage is also determined according to the size of the bearing, and the load to be applied is different, and the frictional force acting on the cage and the rolling element varies depending on the load. Since the thickness of the nitride layer is also defined according to the frictional force, the thickness of the nitride layer formed on the inner surface of the pocket is not an absolute value (for example, 100 μm as in the prior art) but a cage. By defining the ratio with respect to the plate thickness, the optimum nitride layer thickness corresponding to rolling bearings having different dimensions (that is, cages having different plate thicknesses) can be defined.

  Further, by setting the surface roughness of the rolling element to 0.003 μmRa or more and 0.01 μmRa or less, the frictional resistance between the rolling element and the cage can be reduced. Even when metal contact is generated, it is possible to suppress the progress of wear and surface fatigue of the cage and to prevent the surface roughness of the rolling element from deteriorating.

  According to the rolling bearing of the present invention, it is possible to improve the durability of the rolling bearing by reducing the friction coefficient between the rolling elements and the cage and preventing the cage from being damaged (fatigue failure, impact failure). The transmission efficiency and life of the rolling bearing can be improved.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

  FIG. 1 is a partially broken perspective view of a rolling bearing according to an embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view of a main part showing a state in which balls as rolling elements are held in a cage in FIG.

  As shown in FIGS. 1 and 2, a rolling bearing 1 according to an embodiment of the present invention is rotatably held in an outer ring 2, an inner ring 3, a cage 4, and a pocket 4 a of the cage 4. And a plurality of balls 5 which are rolling elements. The plurality of balls 5 are rotatably held in the pocket 4 a of the cage 4 and are rotatably disposed between the outer ring raceway surface 2 a of the outer ring 2 and the inner ring raceway surface 3 a of the inner ring 3. In addition, the outer ring | wheel 2, the inner ring | wheel 3, and the ball | bowl 5 are formed, for example by 2 types of bearing steel which is bearing steel.

The cage 4 is, for example, a pair of corrugated plates 6 in which hemispherical recesses 6a are formed by pressing cold-rolled steel sheets (SPCC, SPCE) having a thickness t = 1 mm, and the hemispherical recesses 6a are arranged to face each other. Thus, the rivets 8 are integrally fixed. That is, it is a so-called metal corrugated cage in which a spherical space defined by a pair of opposed hemispherical recesses 6a, 6a is a pocket 4a. The cage 4 is soft-nitrided by an appropriate processing method such as pure nitriding (NH ₃ gas nitriding), gas soft nitriding, tuftride, ion nitriding, etc. ) 6a includes a thickness of 1% to 9%, preferably 1% to 5% of the thickness t of the cold-rolled steel sheet from at least the inner surface side (that is, the contact surface side with the ball 5). A nitride layer 6b having the structure is formed. Further, the surface of the ball 5 which is a rolling element is ground, and the surface roughness is set to 0.003 μmRa or more and 0.01 μmRa or less.

  According to the rolling bearing 1 of the present embodiment, the metal cage 4 is formed on the inner surface of the pocket 4a in contact with the rolling element 5 at 1% or more and 9% or less of the plate thickness t of the metal cage 4, preferably A nitride layer 6b having a thickness of 1% or more and 5% or less is formed, and the strength of the cage 4 can be improved to prevent the cage 4 from being damaged (fatigue failure, impact failure). The coefficient of friction between the rolling element 5 and the cage 4 can be reduced. Thus, the wear on the inner surface of the pocket 4a due to the sliding friction between the rolling element 5 and the cage 4 even under severe use conditions such as a high temperature environment exceeding 120 ° C. and the use of a low viscosity transmission lubricant. And the deterioration of the surface roughness of the balls 5 can be prevented. Furthermore, it is possible to suppress surface peeling damage caused by wear powder of the cage 4 entering between the outer ring raceway surface 2a or the inner ring raceway surface 3a and the ball 5. Further, according to the rolling bearing 1 of the present embodiment, since the surface roughness of the rolling element 5 is set to 0.003 μmRa to 0.01 μmRa, the friction resistance between the rolling element 5 and the cage 4 is reduced. Even when the metal contact is locally generated under the severe use conditions described above, the wear of the metal cage 4 and the progress of surface fatigue are suppressed, and the surface roughness of the ball 5 is reduced. Can be prevented. Thereby, the lifetime of the rolling bearing 1 can be prolonged.

  When the rolling bearing 1 of this embodiment is used in a belt type CVT, it is possible to use a low-viscosity CVT fluid, an excellent transmission efficiency, sufficient durability, and a low fuel consumption transmission. Units can be provided at low cost.

  In order to confirm the effect of the present invention, a life test conducted using an example according to the rolling bearing of the present invention and a comparative example for comparison with the example will be described.

The rolling bearing used for the life test is JIS nominal number 6206 (inner diameter 30 mm, outer diameter 62 mm, width 16 mm) in both the examples and the comparative examples, and the catalog allowable rotation speed is 13000 rpm. Rolling bearings are made of two types of bearing steel. The surface hardness of the inner and outer rings is HRC 58 to 66, the amount of retained austenite is 0.05 to 15%, the surface hardness of the rolling elements is HRC 62 to 67, and the surfaces of the inner and outer rings. The roughness σ _{12 used} was 0.03 to 0.05 μm Ra, and the rolling element surface roughness σ _c shown in Table 1 was used. The initial oil film parameter Λ is about Λ = 2.

The cage is a metal corrugated cage formed by pressing a steel plate having a thickness t = 1 mm. The pocket inner surface of the cage used in the examples and comparative examples is applied by the applicant of the present application. Applying the method disclosed in a Japanese Patent Application Laid-Open No. 2001-90734, pure nitriding treatment is performed in N ₂ (20%) + NH ₃ (80%) atmosphere gas at 560 ° C. to form dense nitride layers, respectively. Formed. The nitride layer thickness of each example and comparative example is formed in a ratio to the plate thickness t as shown in Table 1.

  The details of the life test are shown below.

(Test conditions)
The test conditions are as follows for both Examples and Comparative Examples.
Load: P (load load) / Cr (new dynamic load rating) = 0.20
Inner ring rotation speed: 15000-5000rpm range in 2 seconds, shifting slope: 2 / 1000rad
Lubricating oil: CVT fluid (viscosity: 35 cSt at 40 ° C, 7 cSt at 100 ° C)
Bearing temperature: 130 ° C (constant)
Test time: 250 hours Number of test bearings: 5 for each example and comparative example

(Evaluation methods)
The test is completed when 250 hours have elapsed from the start of the test, or when the vibration value reaches 5 times or more of the initial vibration value, and the rolling bearing is disassembled and evaluated by visually confirming whether there is any peeling or wear. did. The calculated life (basic rating life L ₁₀ ) of the rolling bearing subjected to the test is 208 hours.

(Test results)
The results are shown in Table 1.

  As shown in Table 1, in Examples 1, 2, and 3, the thickness of the nitride layer formed on the pocket inner surface is 1% or more and 5% or less of the plate thickness, and a test time of 250 hours elapses. Later, no peeling or peeling damage was observed in all of the five test bearings, and the good condition was maintained. Further, the surface roughness of the balls was the same level as before the test even after the test, and was as good as 0.01 μmRa or less. As a result of measuring the shape of the inner surface of the pocket, it is recognized that there is no trace of wear and no initial abnormality occurs.

  In Example 4, although cracks were observed in the cage of one test bearing when 250 hours had elapsed, no peeling damage was observed in all of the five rolling bearings. Regarding the occurrence of cracks in the cage, the cage of Example 4 is relatively hard because a deep nitrided layer is formed with a thickness of 9% with respect to the plate thickness t. It is considered that an unreasonable force was exerted by acceleration / deceleration at 1000 rad, resulting in a fatigue crack.

On the other hand, in Comparative Examples 1 and 2, when the L ₁₀ (reliability 90%) life reached 65 hours and 53 hours, the vibration value reached 5 times the initial vibration value, and each of the five test bearings. In all cases, peeling damage was observed on the balls or inner rings. Each of the above test times is 1/3 or less of the calculated life. For Comparative Example 1, the ball surface roughness before the test is good at 0.005 μmRa, but the nitrided layer is not formed on the cage, and the wear powder generated by the wear on the pocket inner surface is the ball and the raceway surface. Peeling damage occurred on the ball. In Comparative Example 2 as well, no nitride layer was formed on the cage, and wear powder generated by wear on the inner surface of the pocket entered between the balls and the raceway surface, causing peeling damage to the inner ring. In Comparative Example 2, the surface roughness of the ball before the test is 0.02 μmRa, which is about the same as the surface roughness of the raceway surface. When moving to the load zone, the ball's rotation axis changes variously, and the load on the entire surface of the ball reduces the fatigue of the ball surface, so peeling occurs on the inner ring, which is a rotating wheel. .

  In Comparative Example 3, two of the five pieces reached a vibration value of 5 times or more of the initial vibration value when 104 hours and 130 hours had elapsed, respectively, and peeling damage was observed on the balls. This is because the nitride layer formed on the inner surface of the pocket is as thin as 0.1% of the plate thickness, so that a slight amount of wear is observed on the inner surface of the pocket after the test, and the wear powder is between the ball and the raceway surface. Peeling damage occurred on the ball.

  In Comparative Example 4, one of the five pieces reached a vibration value of 5 times or more of the initial vibration value when 99 hours had elapsed, and seizure and breakage of the cage were observed. This is because the ball surface roughness before the test is as rough as 0.02 μmRa, so that the oil film formation is reduced (that is, the oil film parameter Λ is small), and the thickness of the nitride layer formed on the inner surface of the pocket of the cage As a result, the toughness of the cage is reduced because the thickness is 15% of the plate thickness. For this reason, after seizure occurs due to metal contact, the ball locks and the tensile stress acts repeatedly on the cage. The cage was torn.

  As apparent from the above results, a nitride layer having a thickness of 1% or more and 9% or less of the plate thickness is formed at least on the inner surface of the pocket of the cage, and the surface roughness of the balls (rolling elements) is 0.003 μmRa or more and 0. By setting it to 01 μmRa or less, the friction coefficient between the balls and the cage can be reduced, and wear of the balls and the cage can be suppressed. Preferably, the thickness of the nitrided layer is 1% or more and 5% or less of the cage thickness, so that the wear of the balls and the cage can be more reliably suppressed, and the strength and toughness of the cage can be balanced. The cage can be prevented from being damaged (fatigue damage, impact damage). As a result, even under harsh usage conditions (insufficient supply of transmission lubricant, use of low-viscosity transmission lubricant, high temperature environment, etc.), it is possible to prevent the bearing from peeling early and improve the bearing life. it can.

  Note that the present invention is not limited to the above-described embodiments and examples, and modifications, improvements, and the like can be made as appropriate. In addition, the material, shape, dimension, numerical value, form, number, arrangement location, and the like of each component in the above-described embodiments and examples are arbitrary and are not limited as long as the present invention can be achieved.

It is a partial fracture perspective view of the rolling bearing of the present invention. It is a principal part expanded sectional view which shows the state by which the ball | bowl was hold | maintained at the holder | retainer in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling bearing 2 Outer ring 3 Inner ring 4 Metal cage 4a Pocket 5 Ball (rolling element)
6b Nitride layer
t Thickness

Claims (2)

An outer ring, an inner ring, a plurality of rolling elements arranged between the outer ring and the inner ring so as to be freely rollable, and a metal cage formed with a plurality of pockets for holding the rolling elements so as to roll freely. A rolling bearing comprising:
The metal cage has a nitride layer having a thickness of 1% or more and 9% or less of the plate thickness of the metal cage on at least the inner surface of the pocket that contacts the rolling element. Rolling bearing.   The rolling bearing according to claim 1, wherein the rolling element has a surface roughness of 0.003 μmRa or more and 0.01 μmRa or less.

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