JP2005090693A - Rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prolong the life of a rolling bearing for a belt type continuously variable transmission by effectively preventing premature peeling resulting from hydrogen produced by tribochemical reaction. <P>SOLUTION: A surface layer part forming the raceway surface of a raceway ring or the rolling surfaces of rolling elements is formed as follows. The hardness is HRC 60 (Rockwell C hardness) or higher, a residual austenite amount is 15 to 45 vol.%, and a constant (K calculated by an equation (1) below) indicating the decomposing rate of residual austenite when it is held at a specified temperature for a specified time is 0.003 or below at the holding temperature of 170°C. (1) Equation: K=-In (γR<SB>t</SB>/γR<SB>0</SB>)/t, where t is the holding time at the specified temperature, γRt is a residual austenite amount (vol.%) after a time t<SB>i</SB>is passed, and γR<SB>0</SB>is a residual austenite amount (vol.%) at t=0. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rolling bearing. In particular, the present invention relates to a technique capable of extending the life of a rolling bearing even in applications where it is difficult to form a sufficient lubricating film on a raceway surface and the formed lubricating film is likely to be partially broken.

Rolling bearings for engine accessories such as a vehicle alternator (alternator), electromagnetic clutch, intermediate pulley, and tensioner are used at higher temperatures, higher vibrations, and higher loads than general bearings.
Therefore, it is difficult to form a sufficient lubricating film on the raceway surface, and the formed lubricating film is likely to be partially broken. Thereby, a track surface and a rolling element become easy to contact. In particular, since the raceway surface of the portion where the lubricating film is broken becomes an active new surface (a surface where the steel structure is exposed), this new surface becomes a catalyst, and the components of the lubricant and the lubricant are generated by a tribochemical reaction. The water contained in the water is decomposed and hydrogen ions are easily generated. The hydrogen ions are adsorbed on the new surface to form hydrogen atoms, and are accumulated in a high strain field (near the maximum shear stress position), whereby the tissue changes to a white tissue.

Since the rolling bearing for the above-mentioned use tends to cause early separation on the raceway surface due to such a structural change, the actual life may be extremely short compared to the calculated life.
On the other hand, a belt type continuously variable transmission of a vehicle has a mechanism for continuously changing a radius of a belt-driven pulley as a transmission mechanism of an automatic transmission.
For example, in the belt type continuously variable transmission described in Patent Document 1 below, as shown in FIG. 3, pulleys 7 and 8 are respectively connected to an input shaft (drive shaft) 5 and an output shaft (driven shaft) 6 arranged in parallel. A metal belt 9 is wound around these pulleys. This belt 9 has a structure in which a large number of thin (about 2 mm thick) friction pieces 92 are attached to two rings 91 having a structure in which about 10 thin plates having a thickness of about 0.2 mm are stacked. Power is transmitted by a pressing force when the friction pieces 92 are pressed against each other.

The driving force is transmitted from the input shaft pulley (primary pulley) 7 to the output shaft pulley (secondary pulley) 8 via the belt 9. Both pulleys 7 and 8 are composed of fixed conical plates 71 and 81 fixed to the respective shafts 5 and 6 and movable conical plates 72 and 82 movable in the axial direction by a hydraulic mechanism. A pulley groove is formed.
By moving the movable conical plates 72 and 82 of these pulleys 7 and 8 in the axial direction to change the groove width, and changing the position where the belt 9 contacts the pulleys 7 and 8 (effective rotation radius of the pulley), The gear ratio can be changed steplessly. For example, if the groove width of the input shaft pulley is reduced and the groove width of the output shaft pulley is increased, the effective rotation radius of the input shaft pulley decreases, the effective rotation radius of the output shaft pulley increases, and a large gear ratio is obtained. can get.

Shaft portions (pulley shafts) 71 a and 81 a in which fixed conical plates 71 and 81 of the pulleys 7 and 8 are integrated are supported by radial ball bearings 11 and 12.
Such a belt-type continuously variable transmission includes a ball bearing that supports the pulley shaft in order to smoothly operate a torque converter, a gear mechanism, a hydraulic mechanism, a wet clutch, and the like to transmit power. In addition, lubricating oils such as automatic transmission fluid (ATF) having a high traction coefficient (torque transmission capability) and continuously variable transmission fluid (CVTF) are used.

Here, the frequency (f: Hz) of vibration generated in the belt having the structure composed of the ring 91 and a large number of friction pieces 92 depends on the number of friction pieces (Zb) and the rotational speed (Nb: rpm) of the belt. It is represented by “f = Zb × (Nb / 60)”. Usually, the number of friction pieces is, for example, 250 to 400. In this case, when the rotational speed of the engine is changed from 600 min ⁻¹ to 7000 min ⁻¹ , the primary component of the vibration frequency generated in the primary pulley is 1000 to 1000 at the time of deceleration. 3000 Hz, 10000 to 35000 Hz when accelerated.

This frequency is higher than the frequency of vibration caused by gear engagement in a manual transmission (MT) or a normal (other than continuously variable transmission) automatic transmission (AT). This is probably because the number of gear teeth engaged with MT or AT is 50 or less, whereas the number of friction pieces of B-CVT is as large as 250 to 400.
Further, since acceleration and deceleration are repeated while the vehicle is running, the vibration of the belt and the vibration of the vehicle body may resonate. Since vibrations of various frequencies are generated in the vehicle body, resonance with the belt is likely to occur frequently. As a result, large vibrations are likely to occur in the rolling bearing for the belt type continuously variable transmission.

In addition, since the moment acting on each pulley during acceleration / deceleration fluctuates, or even a slight synchronization delay occurs in both pulleys due to sudden acceleration / deceleration, etc., the belt flutters. Bearings are susceptible to load fluctuations and slippage.
That is, the rolling bearing that supports the pulley shaft of the belt-type continuously variable transmission is prone to high-frequency vibrations, load fluctuations, slipping, and the like, and becomes hot due to the heat of friction between the belt and the pulley. Therefore, it is difficult to form a sufficient lubricating film on the raceway surface, and the formed lubricating film is likely to be partially broken. Therefore, early separation is likely to occur on the raceway surface by the same mechanism as the above-described rolling bearing for engine accessory. Furthermore, since there are sliding parts such as belts and pulleys in the belt-type continuously variable transmission, there is a concern that the service life may be shortened due to the inclusion of foreign matter.

  Here, SUJ2 is used to assemble a deep groove ball bearing with a nominal number of 6206 by using an inner ring, an outer ring, and balls produced by normal quenching and tempering, and rotate at 120 ° C. for 100 hours using CVTF as a lubricant. A rotation test was performed. When the hydrogen release rate from the ball was measured at each temperature before and after this test, the graph shown in FIG. 5 was obtained. From this graph, it was found that when CVTF was used as the lubricant, hydrogen ions were generated by the above-described tribochemical reaction, and this hydrogen was retained in the balls.

Considering this test result, in the rolling bearing that supports the pulley shaft of the belt type continuously variable transmission used in the harsh environment as described above, hydrogen is generated on the new raceway surface of the inner and outer rings and the rolling surface of the rolling element. The generation of ions is unavoidable and it is considered that early peeling is likely to occur.
In order to prevent premature peeling due to hydrogen generated by such a tribochemical reaction, the following Non-Patent Document 1 discloses that tribochemical is formed by forming a Ni film on the rolling surface of the rolling element by electroplating. It is described that hydrogen ions generated by the reaction are hardly adsorbed on the steel structure.
Japanese Patent Publication No.8-30526 Japan Society for Automotive Engineers, Academic Lecture Preprints, No. 30-02 (2002), 5-8 pages

However, in the rolling bearings for engine auxiliary machines and belt-type continuously variable transmissions used in harsh environments as described above, the Ni coating is comparatively formed even if the method described in Non-Patent Document 1 is adopted. Since it is soft and easily falls off due to wear, it is difficult to effectively suppress the adsorption of hydrogen ions to the steel structure.
The problem of the present invention is that a sufficient lubricating film is not easily formed on the raceway surface, and even if it is a rolling bearing used in an application where the formed lubricating film is likely to be partially broken, it is caused by hydrogen generated by a tribochemical reaction. This is to effectively prevent early peeling and to prolong the service life.

  In order to solve the above-described problems, the present invention provides a rolling bearing in which a plurality of rolling elements are rotatably disposed between an inner ring and an outer ring, and at least one of the inner ring, the outer ring, and the rolling element is The surface layer part of the raceway surface of the raceway or the rolling surface of the rolling element obtained by carburizing or carbonitriding and quenching and tempering after processing the material made of alloy steel into a predetermined shape is hard. Is an HRC (Rockwell C hardness) of 60 or more, the amount of retained austenite is 15 volume% or more and 45 volume% or less, and is a constant indicating the decomposition rate of retained austenite when held at a constant temperature for a predetermined time ((1) below) Provided is a rolling bearing characterized in that K) calculated by the equation is 0.003 or less at a holding temperature of 170 ° C.

K = −In (γR _t / γR ₀ ) / t (1)
In the formula, t is the holding time at a constant temperature, γR _t is the amount of retained austenite (volume%) after elapse of t time, and γR ₀ is the amount of retained austenite (volume%) at t = 0.
In order to set the constant K to 0.003 or less at a holding temperature of 170 ° C., for example, chromium (Cr in the steel matrix forming the surface layer portion (the portion excluding precipitates composed of carbides and other compounds from the structure) is used. ) Equivalent to 3.0 or more. That is, the heat treatment is performed after processing into a predetermined shape using an alloy steel having a chromium (Cr) equivalent of 3.0 or more. Moreover, it is preferable that the nickel (Ni) equivalent of the matrix of the structure | tissue which comprises the said surface layer part shall be 0.5 or more. The chromium (Cr) equivalent is represented by the following formula (2). The nickel (Ni) equivalent is represented by the following formula (3).

Cr equivalent = Cr + 2Si + 1.5Mo + 5V + 5.5Al + 1.75Nb + 1.5Ti + 0.75W (2)
Ni equivalent = Ni + Co + 0.5Mn + 0.3Cu (3)
The carburizing treatment and the carbonitriding treatment are performed, for example, at an ambient temperature of 900 to 960 ° C. for several hours in a furnace in which RX gas + enriched gas is introduced in the carburizing treatment and RX gas + enriched gas + ammonia gas is introduced in the carbonitriding treatment. This is done by holding.

  When quenching is performed immediately after the carburizing treatment or carbonitriding treatment, a structure mainly composed of retained austenite having a large particle size and lenticular martensite is obtained, but it is difficult to obtain a life improvement effect in this structure. Therefore, after carburizing treatment or carbonitriding treatment, after temporarily holding at a temperature below the Al transformation point or gradually cooling to room temperature, it is again heated to about 820 to 900 ° C. and quenched, and tempered at 160 to 200 ° C. It is preferable. Thereby, a fine structure in which fine and hard carbides or carbonitrides are uniformly dispersed in a matrix made of martensite and austenite can be obtained.

In order to ensure the hardness of the surface layer part and the amount of retained austenite, the carbon content of the surface layer part and the total content of carbon and nitrogen must be 1.0% by mass or more, and 1.2% by mass. The above is preferable. However, if the carbon content is too high, coarse carbides are formed and the rolling fatigue life is reduced, so the upper limit is set to 2.5 mass%, preferably 2.0 mass%.
The tempering temperature is preferably 180 to 240 ° C. from the viewpoint of stably forming retained austenite.

  According to the rolling bearing of the present invention, the hardness of the surface layer portion forming the raceway surface of the raceway or the rolling surface of the rolling element is set to HRC60 or more, and the retained austenite amount is set to 15% by volume or more and 45% by volume or less, The rolling fatigue strength and hardness of the surface layer portion are maintained in a good state. When the amount of retained austenite in the surface layer is less than 15% by volume, rolling fatigue is not sufficiently reduced. The amount of retained austenite in the surface layer portion is preferably 20% by volume or more. If the amount of retained austenite in the surface layer portion exceeds 45% by volume, the surface hardness may be reduced, or the race may be deformed when assembled.

Moreover, a high residual compressive stress is given to the said surface layer part by performing a carburizing process or a carbonitriding process.
The retained austenite existing in the surface layer has a function of capturing hydrogen ions generated by the above-described tribochemical reaction. Then, the hydrogen ions trapped in the austenite are in an equilibrium state between the adsorption rate to the surface layer part (austenite part of the structure constituting the surface layer part) and the release rate from the surface layer part when the bearing rotates. When stopped, it is easily released from the surface layer. Thereby, at the time of rotation of a bearing, it is suppressed that a hydrogen ion adsorb | sucks to the martensite part of the structure | tissue which comprises the said surface layer part.

Further, by setting the constant K to 0.003 or less at a holding temperature of 170 ° C., the retained austenite in the surface layer portion is not easily decomposed by heat or rolling fatigue, so that severe conditions (high-frequency vibration, load fluctuation, slippage) Even if it is used in a high temperature environment), the function of capturing hydrogen ions is exhibited.
The constant K at a holding temperature of 170 ° C. is preferably 0.002 or less, and more preferably 0.001 or less.

  The rolling bearing of the present invention is preferably used for supporting the rotating shaft of a pulley around which a belt of a belt type continuously variable transmission for a vehicle is wound (for example, radial ball bearings 11 and 12 in FIG. 3), and a vehicle AC. An application in which the rotating shaft is rotatably supported with respect to the stator side member between the rotating shaft to which the rotor of the generator is fixed and the stator side member to which the stator is fixed (for example, FIG. 4 radial ball bearings 20, 21).

  According to the present invention, it is difficult to form a sufficient lubricating film on the raceway surface, and even a rolling bearing used in an application in which the formed lubricating film is likely to be partially broken is caused by hydrogen generated by a tribochemical reaction. Early peeling is effectively prevented and the life is extended.

Hereinafter, embodiments of the present invention will be described.
As a test rolling bearing, a single row deep groove ball bearing corresponding to a nominal number 6206 was produced as follows.
For the inner ring and the outer ring, the materials shown in Table 1 below were prepared as ring-shaped materials, and after cutting into the shapes of the inner ring and the outer ring, the workpiece was heat-treated under various conditions. . For Nos. 1 to 3 and 6, first, carbonitriding was carried out using an atmosphere temperature of 930 ° C., an introduced gas: RX gas + enrich gas + ammonia gas (0.8 m ³ / h), and a treatment time of 3.5 hours. It went on condition of. Next, after cooling slowly to room temperature, it heated to each quenching temperature shown in Table 1, and quenched. Next, tempering was performed at 180 ° C.

Nos. 4 and 5 were tempered at 180 ° C. after heating to each quenching temperature shown in Table 1 and quenching.
For balls (rolling elements), first, a material composed of high-carbon chromium bearing steel type 2 (SUJ2) is cut and introduced with the same gas as described above, with an atmospheric temperature of 820 to 840 ° C. and a processing time of 1.5 hours. After the carbonitriding treatment, quenching was performed as it was, and tempering at 180 ° C. was further performed.
Next, by performing a finishing process by polishing, the surface roughness (Ra) of the inner ring and the outer ring is set to 0.01 to 0.03 μm, and the surface roughness (Ra) of the ball is set to 0.003 to 0.010 μm. .

For the inner ring and outer ring thus manufactured, the hardness (Rockwell C hardness: HRC) of the surface layer portion (the portion from the surface to a depth of 2% of the diameter of the ball) and the amount of retained austenite (γR) The total content of carbon and nitrogen (C + N) was measured. These measurement results are also shown in Table 1 below. The amount of retained austenite was measured by X-ray diffraction.
Further, each inner ring is held at 170 ° C., and the amount of retained austenite in the surface layer portion of the raceway surface is measured after 100 hours, 200 hours, 300 hours, 400 hours, and 500 hours. The constant K was calculated from the equation (1), and the average value was calculated. The results are also shown in Table 1 below.

Next, a rolling bearing composed of these inner rings, outer rings, and balls was attached to an oil bath lubrication type life tester shown in FIG. This life test was performed by preparing ten test bearings having the same configuration.
This testing machine includes an oil bath 14 and a load applying device 15, and the entire housing 2 to which the rolling bearing 1 is attached and a portion other than the base end portion 31 of the shaft 3 are arranged in the oil bath 14. ing. Lubricating oil 14 a is put in the oil bath 14 to a height at which the retaining ring 17 provided between the inner ring of the rolling bearing 1 and the shaft 3 is substantially buried. The load applying device 15 includes a load lever 15 a that applies a load to the rolling bearing 1 through the housing 2.

The lubricating oil, kinematic viscosity at 40 ° C. kinematic viscosity at 30.4mm ² / s, 100 ℃ was used traction oil is 5.2 mm ² / s. The test conditions were a test load: 9100 N, a rotation speed: 3000 mm ⁻¹ , and a temperature: 110 ° C.
Rotate the rolling bearing and measure the vibration generated in the bearing during the rotation test. When the vibration value during rotation reaches 5 times the initial vibration value, the test is interrupted and the raceway surface or ball of the inner ring or outer ring It was examined whether or not flaking occurred on the surface.

When the test was interrupted, the rotation time up to that point was defined as the life time. If the vibration value did not become five times the initial vibration value even when the rotation time was three times the calculated life, the rotation test was stopped at that time. Moreover, ten life time of the test bearing to organize the Weibull distribution function, seeking total rotation time of the 10% of the bearing from the short life side until flaking occurs and the L ₁₀ life. The ratio (L ₁₀ / L _cal ) of the L ₁₀ life to the calculated life L _cal was calculated.
These results are also shown in Table 1 below. Further, FIG. 2 is a graph showing the relationship between the retained austenite decomposition constant (K) and the life ratio (L ₁₀ / L _cal ) obtained from these results.

  As can be seen from these results, the inner ring and the outer ring are all within the scope of the present invention (the hardness of the raceway surface layer: HRC 60 or more, the retained austenite amount 15 to 45% by volume, K at 170 ° C. is 0.003 or less). The test bearings of No. 1 to No. 3 to be satisfied had a life longer than the calculated life. On the other hand, the life of the test bearings of Nos. 4 to 6 in which the inner ring and the outer ring all do not satisfy at least one of the ranges of the present invention was shorter than the calculated life. When the peeled part was observed, a white structure was confirmed in all the samples.

As described above, according to the No. 1 to 3 deep groove ball bearings in which the inner ring and the outer ring satisfy the scope of the present invention, it is difficult to form a sufficient lubricating film on the raceway surface, and the formed lubricating film is partially broken. Even if it is used in easy applications (supporting the rotating shaft of a pulley that wraps the belt of a belt type continuously variable transmission, for engine accessories, compressors, gas foot pumps, etc.), early peeling due to hydrogen generated by the tribochemical reaction Effectively preventing and extending the life.
The rolling bearing of the present invention is not limited to a ball bearing, and includes a cylindrical roller bearing, a tapered roller bearing, and a needle bearing.

It is a schematic block diagram which shows the oil bath lubrication type life tester used by the test as described in embodiment. Obtained from the test results of embodiment, it is a graph showing the relationship between the residual austenite decomposition constants (K) life ratio and (L ₁₀ / L _cal). It is a figure which shows an example of the belt type continuously variable transmission of a vehicle. It is a figure which shows an example of the alternating current generator for vehicles (alternator). It is a graph which shows the hydrogen discharge | release speed | velocity | rate from the ball | bowl at each temperature before and after performing the rotation test for the ball bearing which consists of an inner ring | wheel, an outer ring | wheel, and a ball | bowl made from SUJ2 using CVTF as a lubricant.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling bearing 2 Housing 3 Axis 31 The base end part of 11 Shaft 11 Radial ball bearing 12 Radial ball bearing 14 Oil bath 14a Lubricating oil 15 Load applying device 15a Load lever 17 Retaining ring 20 Radial ball bearing 21 Radial ball bearing 5 Input shaft (drive) axis)
6 Output shaft (driven shaft)
7 Input shaft pulley (primary pulley)
71 Fixed conical plate 72 Movable conical plate 8 Output shaft pulley (secondary pulley)
81 Fixed conical plate 82 Movable conical plate 9 Belt 91 Ring 92 Friction piece

Claims (3)

In a rolling bearing in which a plurality of rolling elements are arranged between an inner ring and an outer ring so as to freely roll,
At least one of the inner ring, the outer ring, and the rolling element is
After processing a material made of alloy steel into a predetermined shape, carburizing or carbonitriding, quenching and tempering, the surface layer part that forms the raceway surface of the raceway or the rolling surface of the rolling element has a hardness. HRC (Rockwell C hardness) of 60 or more, the amount of retained austenite is 15 volume% or more and 45 volume% or less, and is a constant indicating the decomposition rate of retained austenite when held at a constant temperature for a predetermined time (formula (1) below) The rolling bearing is characterized in that K) calculated by the above is 0.003 or less at a holding temperature of 170 ° C.
K = −In (γR _t / γR ₀ ) / t (1)
In the formula, t is the holding time at a constant temperature, γR _t is the amount of retained austenite (volume%) after elapse of t time, and γR ₀ is the amount of retained austenite (volume%) at t = 0.   The rolling bearing according to claim 1, which is used for supporting a rotating shaft of a pulley around which a belt of a belt type continuously variable transmission for a vehicle is wound.   For the purpose of supporting the rotary shaft rotatably with respect to the stator side member between the rotary shaft to which the rotor of the vehicle alternator is fixed and the stator side member to which the stator is fixed. The rolling bearing according to claim 1 used.

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