JP4737960B2 - Roller bearing for rocker arm - Google Patents

Description

  The present invention relates to a rocker arm rolling bearing used for opening and closing an intake valve and an exhaust valve of an automobile engine, and more specifically to a rocker arm rolling bearing with a long life.

  Among the recent rolling bearings, there are bearings that are used for high-speed, high-load applications even though they are full-roller types, such as those used for rocker arms used to open and close engine intake valves and exhaust valves. Many. In particular, in a full-roller type bearing without a cage, the rollers are likely to be skewed due to interference between the rollers or because the roller position is not controlled smoothly. Moreover, if the lubricating oil is not supplied well into the bearing, a situation where the lubricating condition is poor is likely to occur. As a result, sliding heat generation and local surface pressure increase occurred, and surface damage (peeling, smearing, surface-origin separation) and internal origin-type delamination were likely to occur despite a large load capacity in the calculation. .

  In applications where the outer diameter of the outer ring is in rolling contact with the cam, such as bearings used for rocker arms used to open and close engine intake valves and exhaust valves, the conventional method has been mainly aimed at improving the outer diameter of the outer ring. There were many improvements. For example, compressive residual stress due to processing such as shot peening, and long life due to high hardness (machining effect) due to high-concentration carbonitriding have been performed mainly to improve the outer diameter of the outer ring that is in rolling contact with the mating cam. .

  In the conventional technology so far, the following measures have been taken.

  (1) A bearing component in which shot peening is applied to the bearing ring of the bearing component in order to improve the rolling fatigue life, and a reinforcing layer, a retained austenite-containing layer, and a hardened hardening layer are sequentially provided from the surface to the inside (Patent Document 1).

  (2) A technique for efficiently adjusting the size, area ratio, retained austenite amount and hardness of carbide in the martensite structure by shot peening (Patent Document 2).

  (3) Technology for matching the peak height and distribution of residual compressive stress due to shot peening to the maximum shear stress and depth of action acting during use in order to improve rolling fatigue life (Patent Document 3).

  (4) In carburized bearings, the combination of residual compressive stress σ (MPa) and residual austenite γ (%) on the surface after shot peening is performed to extend the life and final surface finishing is performed. A control method that satisfies 001σ + 0.3γ ≧ 1.0.

  (5) A cam follower device in which the hardness of the outer diameter of the cam follower outer ring is equal to that of the counterpart cam, and the hardness of the inner diameter of the outer ring is higher than the hardness of the outer diameter (Patent Document 4).

(6) In a component that is in rolling contact or rolling and sliding contact with other components facing each other, the maximum compressive stress of the surface layer portion having a depth of 0 to 50 μm from the surface is 50 to 110 kgf / mm ² , and the hardness is HV 830 to 960, The residual austenite is 7% or more, the average wavelength of the surface roughness is 25 μm or less, and these are achieved by shot peening (Patent Document 5).

  Although there are few improvements to extend the rolling life of the roller shaft, rollers, and the entire bearing corresponding to the inner ring, as shown below, heat resistance and microstructure stability by carbonitriding are given, and hardness is increased, as shown below There is an example in which the life of the bearing is extended by the above.

  (D1) A bearing for a cam follower device for a valve operating mechanism of an engine having a calculated service life of 1000 hours or more at a rated engine speed (Patent Document 6).

  (D2) Carbide ratio: 10 to 25%, decomposition ratio with respect to initial value of retained austenite: 1/10 to 3/10, end surface hardness: HV830 to 960, average wavelength of surface roughness: 25 μm or less Bearing steel is carbonitrided and hard shot peened to realize a bearing shaft (Patent Document 7).

  (D3) A cam follower shaft in which a solid lubricating film such as a polymer compound is formed on the shaft in order to improve the wear resistance of the shaft (Patent Document 8).

  (D4) A cam follower shaft made of tool steel or the like and made hard by ion nitriding or ion plating at a temperature lower than the tempering temperature (Patent Document 9).

  (D5) A bearing for a cam follower device for a valve operating mechanism of an engine in which a bending stress with respect to the shaft is 150 MPa or less (Patent Document 10).

  (D6) A cam follower for a valve operating mechanism of an engine in which a phosphate film having excellent lubricating oil retention is attached to the rolling surface of a bearing component (Patent Document 11).

  (D7) A cam follower for a valve operating mechanism of an engine having a crowned roller rolling region (Patent Document 12).

  (D8) Carburized shaft with high-concentration carburizing treatment or carbonitriding treatment in which the carbon concentration of the surface of the rolling surface of the shaft is 1.2% to 1.7% C, and the internal hardness is HV300 (Patent Document 13) .

  As another problem associated with the rocker arm, there is a case where both ends of the roller shaft are caulked to be caulked on the roller support member. In this case, the rolling surface of the roller shaft requires high hardness, but the end portion needs to be soft so that it can be crimped. Moreover, after caulking and fixing, strength (hardness) is required so as not to loosen during use. The following disclosure is made with respect to one that enables caulking to both ends of the roller shaft of the roller rocker.

(D9) A method in which the outer peripheral surface of the roller shaft is uniformly induction-hardened and tempered, and then both ends are subjected to induction annealing to soften both ends (Patent Document 14).
Japanese Patent Laid-Open No. 2-168022 JP 2001-65576 A Japanese Patent Laid-Open No. 3-199716 Japanese Utility Model Publication No. 3-119508 Japanese Patent No. 3125434 JP 2000-38907 A Japanese Patent Laid-Open No. 10-47334 Japanese Patent Laid-Open No. 10-103339 JP-A-10-110720 JP 2000-38906 A JP 2002-3212 A Japanese Utility Model Publication No. 63-185917 JP 2002-194438 A JP-A-5-179350

  In the future, as with ordinary bearings, rolling bearings for rocker arms used to open and close engine intake valves and exhaust valves are expected to increase in speed and load during use and to lower the viscosity of lubricating oil. Factors governing the life of bearings used under such conditions include life of surface damage due to metal contact caused by slipping and oil film breakage, in addition to the usual load-dependent rolling fatigue life. In order to extend the life of rolling bearings for rocker arms, it is necessary to extend these lifespans, but no technology has been established so far to significantly extend both lifespans. In addition, there is a problem that a short life due to roller interference and skew specific to the full roller bearing also occurs.

  Conventionally known techniques have mainly been those that improve the rolling life by high hardness and high compressive stress, and those that improve the rolling surface with the mating member. When these are actually evaluated as bearings, they are effective for fatigue strength in applications where bending acts like the outer ring and wear resistance of the outer surface of the outer ring, and although good results are obtained, it corresponds to the inner ring of the bearing This technology alone has not always been able to achieve a significant effect in extending the rolling fatigue life of shafts and rollers.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a rocker arm rolling bearing with a long life.

The rocker arm rolling bearing of the present invention includes an outer ring that is in rolling contact with the camshaft of the engine, an inner ring that is positioned inside the outer ring and is fixed to the rocker arm, and a plurality of rolling elements that are interposed between the outer ring and the inner ring. in the rolling bearing for the rocker arm with the door, the outer ring, inner ring, and at least the inner ring of the rolling element is cooled to the a ₁ transformation point temperature below after being carbonitrided at a carbonitriding temperature exceeding the a ₁ transformation point, further heated to a ₁ temperature lower than the transformation point than the carbonitriding temperature, has a nitriding layer by being quench-hardened, the range of grain size number of austenite crystal grains exceeds number 10, and spherical The area ratio of the activated carbide is 10% or more.

  The rolling fatigue life can be greatly improved by making the austenite grains of the above members finer as the particle size number exceeds 10. When the particle size number of the austenite particle size is 10 or less, the rolling fatigue life is not greatly improved. Usually, it should be 11 or more. The average crystal grain size may be 6 μm or less. Although it is desirable that the austenite particle size is finer, it is usually difficult to obtain a particle size number exceeding # 13.

  The austenite crystal grain size may be obtained by an ordinary method defined in JIS, or may be converted by obtaining an average grain size corresponding to the crystal grain size number by an intercept method or the like. The austenite grain size number may be satisfied in the carbonitriding layer. However, in the usual case, the above-mentioned standard for austenite grain refinement is also satisfied in the steel body inside the carbonitrided layer.

  The austenite crystal grains are austenite crystal grains that have undergone phase transformation during quenching and heating, and that remain as past history even after transformation to martensite by cooling. In the present specification, the “inner ring” includes a solid shaft and a hollow shaft.

  Moreover, the rolling fatigue life can be significantly improved by setting the area ratio of the spheroidized carbide of the member having the nitrogen-enriched layer to 10% or more. If the area ratio of the spheroidized carbide is less than 10%, the rolling fatigue life is not greatly improved, so the range is made 10% or more. The larger the area ratio of the spheroidized carbide, the better, but usually, if the area ratio exceeds 25%, the toughness of the material deteriorates due to carbide enlargement / aggregation, so it is preferably in the range of 10% to 25%. .

  The area ratio of the spheroidized carbide is a value at the surface layer of 50 μm of the rolling surface after grinding. After corrosion using a picric acid alcohol solution (picral), it can be observed with an optical microscope at a magnification of 400 times, for example. Here, although simply expressed as “spheroidized carbide”, “spheroidized carbide” is a combination of carbide and nitride.

  (C1) The rocker arm is rotatably attached to a rotary shaft located between one end and the other end, and the end of the valve for opening and closing the engine is in contact with one end, The rocker arm may have a bifurcated inner ring support at the other end, and the inner ring of the rocker arm rolling bearing of the present invention may be fixed to the bifurcated inner ring support.

  (C2) A rocker arm rolling bearing is provided between one end and the other end of the rocker arm, and the inner ring is fixed to the inner ring hole extending between the two side walls of the rocker arm. The end of the valve for opening and closing the engine may be in contact with one end, and the pivot may be in contact with the other end of the rocker arm.

  Further, (c3) the rocker arm includes a rocker arm main body and an interlocking rod that transmits stress from the cam shaft, and the rocker arm main body is formed between one end and the other end of the rocker arm main body. An end of the valve for engine opening / closing comes into contact with one end of the rocker arm main body, and one end of the interlocking rod contacts one end of the rocker arm main body. And the inner ring of the rolling bearing of the present invention may be fixed to the other end of the interlocking rod.

  The rocker arms (c1), (c2), and (c3) described above are common in that the driving force from the cam is transmitted to the engine valve, but the structure is different and can correspond to different engine types. It is like that.

  Further, the rocker arm rolling bearing may be a full roller type needle bearing.

  The rocker arm rolling bearing of the present invention has austenite grains refined so that the particle size number exceeds 10, and the area ratio of the spheroidized carbide is 10% or more, so the rolling fatigue life is greatly improved, Excellent crack strength and aging resistance can be obtained.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic front view showing a usage state of a rocker arm rolling bearing according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along line II-II in FIG. 1 and 2, the rocker arm 1 is rotatably supported by the rocker arm shaft 5 via a bearing metal or the like at the center.

  An adjustment screw 7 is screwed into one end 1 b of the rocker arm 1. The adjustment screw 7 is fixed by a lock nut 8 and is in contact with an upper end portion 9a of a valve 9 of an intake valve or an exhaust valve of the internal combustion engine at a lower end thereof. The valve 9 is biased by the elastic force of the spring 10.

  The rocker arm 1 integrally has an inner ring support portion 14 formed in a bifurcated shape at the other end 1a. Both ends of the roller shaft 2 corresponding to the inner ring are fixed to the bifurcated inner ring support portion 14 by press-fitting or retaining rings. A roller 4 constituting an outer ring is supported at the central portion of the outer peripheral surface of the roller shaft 2 through a plurality of rollers 3 as rolling elements. That is, a plurality of rollers 3 are interposed between the roller shaft 2 and the roller 4. The axial direction of the roller 3 is arranged parallel to the axis of the roller shaft 2. The outer peripheral surface of the roller 4 is in contact with the cam surface of the cam 6 provided on the cam shaft by the urging force of the spring 10. In other words, the cam 6 and the roller 4 are in rolling contact.

  When the cam 6 rotates, it is pushed by the cam 6 and the rocker arm 1 vibrates in the vertical direction. This vibration is transmitted to the valve 9 with the rocker arm shaft 5 as a fulcrum, and the valve 9 opens and closes. The rocker arm rolling bearing 50 according to the present embodiment is a full roller bearing in which no cage is used, and includes a roller shaft 2, a plurality of rollers 3, and a roller 4. The rocker arm rolling bearing 50 plays a role of reducing friction between the rocker arm 1 and the cam 6 and improving wear resistance. Since the rocker arm rolling bearing 50 rotates while being in contact with the cam 6, the pressing force and impact force of the cam 6 act on the roller 4.

  FIG. 3 is a schematic front view showing a usage state of a rocker arm rolling bearing according to another embodiment of the present invention. Referring to FIG. 3, a rocker arm rolling bearing 50 is provided between one end 1 b and the other end 1 a of the rocker arm 1. A roller hole (not shown) as an inner ring hole is formed between the two side walls 1 c of the rocker arm 1. The roller shaft 2 is fixed to the roller hole. Further, an upper end 9 a of an engine opening / closing valve 9 is in contact with one end 1 b of the rocker arm 1, and a pivot hole 15 is provided at the other end 1 a of the rocker arm 1. The pivot hole 15 abuts on a pivot (not shown). The rocker arm 1 provided with the pivot hole 15 is biased by a spring 10 in a predetermined direction around the pivot. The driving force transmitted from the cam 6 is received by the roller 4 to move the valve 9 against the urging force of the spring 10.

  FIG. 4 is a schematic front view showing a usage state of a rocker arm rolling bearing according to still another embodiment of the present invention. FIG. 5 is an enlarged view of a portion including the rocker arm rolling bearing of FIG.

  4 and 5, the rocker arm 1 has a rocker arm main body 11 and an interlocking bar 16 that transmits stress from the cam 6. A rocker arm shaft 5 is disposed between one end portion 11b and the other end portion 11a of the rocker arm main body 11, that is, at the central portion of the rocker arm main body 11, and the rocker arm main body 11 rotates around it. . The upper end portion 9 a of the valve 9 is in contact with one end portion 11 b of the rocker arm body 11, and the valve 9 is biased by the elastic force of the spring 10. Further, the upper end portion 16 b of the interlocking rod 16 is in contact with the other end portion 11 a of the rocker arm main body 11. The adjustment screw 7 has a function of adjusting the contact position between the rocker arm body 11 and the interlocking rod 16. The roller shaft 2 of the rocker arm rolling bearing 50 is attached to the hollow bearing mounting portion 16 a located at the lower end portion of the interlocking rod 16 by the mounting member 17. The cam 6 abuts against the roller 4 of the rocker arm rolling bearing 50 and transmits the driving force to the interlocking rod 16.

  1 to 5, there is no particular distinction between one and the other, and only an end that will be described earlier in the order of description is merely one end.

  Of the members constituting the rocker arm rolling bearing 50, at least one member of the roller 3, the roller shaft 2, and the outer ring roller 4 is subjected to a heat treatment of a low-temperature secondary quenching method to be described below. The particle size number of the austenite crystal grains is in the range exceeding 10 and the area ratio of the spheroidized carbide is 10% or more.

Next, heat treatment including carbonitriding performed on at least one bearing part of the outer ring (roller), inner ring (roller shaft) and rolling element of the rolling bearing will be described. FIG. 6 is a diagram for explaining a heat treatment method according to an embodiment of the present invention. Moreover, FIG. 7 is a figure explaining the modification of the heat processing method in one embodiment of this invention. FIG. 6 is a heat treatment pattern showing a method of performing the primary quenching and the secondary quenching, and FIG. 7 is a method in which the material is cooled to below the A ₁ transformation point temperature during quenching, and then reheated and finally quenched. It is the heat processing pattern which shows. Both are exemplary embodiments of the present invention. In these figures, in the treatment T ₁ , carbon and nitrogen are diffused in the steel base and the carbon is sufficiently dissolved, and then cooled to below the A ₁ transformation point. Next, in the process T ₂ of the in the figure, than the processing T ₁ is reheated to a low temperature, subjected to oil quenching from there.

  Rather than performing normal quenching, that is, carbonitriding once after the carbonitriding treatment, the crack strength can be improved and the aging change rate can be reduced while carbonitriding the surface layer portion. As described above, according to the above heat treatment method, it is possible to obtain a microstructure in which the grain size of austenite crystal grains is ½ or less of the conventional one. The bearing parts subjected to the above heat treatment have a long rolling fatigue characteristic, can improve the cracking strength, and can also reduce the rate of dimensional change over time.

  FIG. 8 is a view showing the microstructure of the bearing part, particularly austenite grains. FIG. 8A shows a bearing part of the present invention example, and FIG. 8B shows a conventional bearing part. That is, FIG. 8A shows the austenite grain size of the bearing steel to which the heat treatment pattern shown in FIG. 6 is applied. For comparison, FIG. 8B shows the austenite grain size of the bearing steel obtained by the conventional heat treatment method. FIGS. 9A and 9B are diagrams showing the austenite grain boundaries illustrated in FIGS. 8A and 8B. From the structure showing the austenite crystal grain size, the conventional austenite grain size is a JIS standard grain size number of 10 or less, and according to the heat treatment method of the present invention, the 12th fine grain can be obtained. Moreover, the average particle diameter of Fig.8 (a) was 5.6 micrometers as a result of measuring by the intercept method.

  Examples of the present invention will be described below.

(Example 1)
Using JIS standard SUJ2, a rocker arm rolling bearing for a rolling fatigue test was manufactured. The bearing is a full roller type needle bearing used for a rocker arm. The inner ring has an outer diameter φ14.64 mm × width L17.3 mm, and the outer ring has an inner diameter φ18.64 mm × outer diameter φ24 mm × width L6.9 mm. The rollers had an outer diameter of 2 mm and a length of L 6.8 mm, and 26 rollers were used. Moreover, it was set as the all roller type structure which does not use a holder | retainer. The basic dynamic load rating of this bearing is 8.6 kN, and the basic static load rating is 12.9 kN.

  The manufacturing history of each test bearing is as follows.

  Test bearing No. 1-No. 3 (Example of the present invention): Carbonitriding was performed under conditions of carbonitriding temperature of 850 ° C. and holding time of 150 minutes. During the carbonitriding process, an atmosphere of a mixed gas of RX gas and ammonia gas was used. At that time, test bearing No. 1-No. Each of No. 3 was subjected to carbonitriding by changing the mixing ratio of RX gas and ammonia gas. Thereafter, according to the heat treatment pattern shown in FIG. 6, primary quenching is performed from a carbonitriding temperature of 850 ° C., followed by secondary quenching by heating at a temperature 800 ° C. lower than the carbonitriding temperature, and then at 180 ° C. Tempering was performed for 90 minutes.

  Test bearing No. 4: Standard heat treatment was performed. That is, after heating in an RX gas atmosphere at a heating temperature of 840 ° C. and a holding time of 20 minutes, quenching was performed, followed by tempering at 180 ° C. for 90 minutes.

  Test bearing No. 5, 6: Carbonitriding was performed under conditions of carbonitriding temperature 850 ° C. and holding time 150 minutes. During the carbonitriding process, an atmosphere of a mixed gas of RX gas and ammonia gas was used. At that time, test bearing No. 5, no. 6 was subjected to carbonitriding by changing the mixing ratio of RX gas and ammonia gas. Thereafter, quenching was performed from 850 ° C., followed by tempering at 180 ° C. for 90 minutes.

  Test bearings No. 1 to No. 1 manufactured by the above manufacturing method. Table 1 shows the results of the material investigation and the function evaluation test of the inner ring 6.

  Next, a material investigation method and a function evaluation test method will be described.

  (1) Austenite crystal grain size: The austenite crystal grain size was measured based on the JIS G 0551 steel austenite grain size test method.

  (2) Amount of retained austenite: The amount of retained austenite was measured by comparing the diffraction intensities of martensite α (211) and retained austenite γ (220) by X-ray diffraction. As the amount of retained austenite, the value at the surface layer of 50 μm of the rolling surface after grinding was adopted.

  (3) Nitrogen content: The nitrogen content was measured using EPMA. For the nitrogen content, the value at the surface layer of 50 μm of the rolling surface after grinding was adopted.

  (4) Surface hardness: The surface hardness was measured using a Vickers hardness meter (1 kgf).

  (5) Area ratio of spheroidized carbide: The area ratio of spheroidized carbide was measured by observing with an optical microscope (400 times) after corrosion using a picric acid alcohol solution (picral). As the area ratio of the spheroidized carbide, the value at the surface layer of 50 μm of the rolling surface after grinding was adopted.

  (6) Rolling fatigue life test: FIG. 10 shows a rolling fatigue life test apparatus and Table 2 shows test conditions. This test apparatus is an outer ring rotation test apparatus. Referring to FIG. 10, a roller having a configuration in which a plurality of needle rollers 53 are arranged between a roller shaft 52 and a roller 54 incorporated in a testing machine so as to be able to roll is used. A rolling fatigue test was conducted by rotating at a predetermined speed while applying a radial load.

  (7) Static crack strength test: Using the outer ring of the test bearing, a static crack strength test was performed by applying a load with an Amsler tester alone.

  (8) Crack fatigue strength test: A crack fatigue strength test was performed under the test conditions shown in Table 3 using the outer ring of the test bearing.

  The results of (6) Rolling fatigue life test, (7) Static crack strength test, and (8) Crack fatigue strength test are the standard heat treatment product No. Assuming 4 as 1, the results of each test bearing were expressed as a ratio.

  Next, the test results shown in Table 1 will be described.

  (1) Austenite grain size: No. 1-No. No. 3 is remarkably refined with a crystal grain size number of 11-12. Standard heat treated product and conventional carbonitrided product No. 4-No. No. 6 is an austenite crystal grain having a crystal grain size number of 8 to 9 and coarser than the product of the present invention.

  (2) Residual austenite amount: No. 1-No. 3 is 12 to 24%, and moderate austenite exists. Standard heat treatment No. 4 is 8%, which is less than the invention. In addition, the conventional carbonitriding product No. 5, no. 6 is 29 to 36%, more than the invention. The amount of austenite of the invention is the amount of retained austenite between the standard heat treated product and the conventional carbonitrided product.

  (3) Nitrogen content: Product No. 1-No. 3 is 0.12 to 0.62%. Standard heat treatment No. Since No 4 was carbonitriding, the nitrogen content was 0%. In addition, the conventional carbonitriding product No. 5, no. 6 was 0.31 to 0.70%. The nitrogen content of the inventive product tended to be slightly lower than that of the conventional carbonitrided product. This is considered to be because the invention is subjected to secondary quenching at a temperature of 800 ° C. lower than the carbonitriding temperature after the conventional carbonitriding process.

  (4) Surface hardness: Product No. 1-No. 3 is HV730-780. Standard heat treatment No. 4 is HV740. In addition, the conventional carbonitriding product No. 5, no. No. 6 is HV760, HV650. Regarding No. 6, the amount of retained austenite is too large and the hardness is not obtained.

  (5) Area ratio of spheroidized carbide: No. 1-No. 3 is 11.4 to 13.6%. Standard heat treated product and conventional carbonitrided product No. 4-No. 6 is 7.9 to 9.6%. Inventive products have a larger area ratio of spheroidized carbides, are refined, and are larger than standard heat treated products and conventional carbonitrided products. This is considered because the invention is subjected to secondary quenching at a temperature of 800 ° C. lower than the carbonitriding temperature after conventional carbonitriding.

  (6) Rolling fatigue life test: No. 1-No. 3 is a standard heat treatment product No. Compared with No. 4, it has a rolling fatigue life of 3 times or more. 5, no. Compared to 6, it has a rolling fatigue life of 1.5 times or more. In addition, carbonitrided product No. 5, no. No. 6 is a standard heat treatment product No. Compared to 4, it has a rolling fatigue life slightly less than twice.

  (7) Static crack strength test: Product No. 1-No. 3 is a standard heat treatment product No. Compared to 4, it is equivalent or slightly improved. In addition, carbonitrided product No. 5, no. No. 6 is a standard heat treatment product No. Compared to 4, the static crack strength is reduced. This is considered to be caused by the coarsening of the nitrogen-enriched layer and austenite crystal grains in the surface layer portion.

  (8) Crack fatigue strength test: No. 1-No. 3 is a standard heat treatment product No. Compared to 4, it is improved by 20% or more. In addition, carbonitrided product No. 5, no. No. 6 is a standard heat treatment product no. Compared to 4, it is improved by 20% or more. This is considered to be caused by the formation of compressive residual stress in the surface layer due to the penetration of nitrogen into the surface.

  To summarize the above, the present invention product No. 1-No. 3 has a nitrogen-enriched layer in the surface layer, the austenite crystal is refined to a particle size number of 11 or more, the amount of retained austenite is moderately, it has an appropriate surface hardness, and the area of the spheroidized carbide Since the ratio is large, the normal load-dependent rolling fatigue life and crack fatigue strength are improved.

(Example 2)
Peeling and smearing specimens were manufactured using JIS standard SUJ2. The test piece has a size of outer diameter φ40 mm × width L12. The manufacturing history of each test bearing is as follows.

  Test bearing No. 1 (Example of the present invention): Carbonitriding was performed under conditions of carbonitriding temperature of 850 ° C. and holding time of 150 minutes. During the carbonitriding process, an atmosphere of a mixed gas of RX gas and ammonia gas was used. Thereafter, according to the heat treatment pattern shown in FIG. 6, primary quenching is performed from a carbonitriding temperature of 850 ° C., followed by secondary quenching by heating at a temperature 800 ° C. lower than the carbonitriding temperature, and then at 180 ° C. Tempering was performed for 90 minutes.

  Test bearing No. 2: Standard heat treatment was performed. That is, after heating in an RX gas atmosphere at a heating temperature of 840 ° C. and a holding time of 20 minutes, quenching was performed, followed by tempering at 180 ° C. for 90 minutes.

  Test bearing No. 3: Carbonitriding was performed under conditions of carbonitriding temperature of 850 ° C. and holding time of 150 minutes. During the carbonitriding process, an atmosphere of a mixed gas of RX gas and ammonia gas was used. Thereafter, quenching was performed from 850 ° C., followed by tempering at 180 ° C. for 90 minutes.

  Specimen No. manufactured by the above manufacturing method. 1-No. Table 4 shows the results of the material investigation, the peeling test, and the smearing test.

  Next, a peeling test method and a smearing test method will be described. The material investigation results were the same as in Example 1.

  (1) Peeling test: Generated on the test piece when the test piece and the counterpart test piece are brought into rolling contact under the test conditions shown in Table 5 with a standard heat treatment product of JIS standard SUJ2 having a rough surface as the counterpart test piece. The area ratio of peeling (aggregate of fine peeling) to be measured was measured as peeling strength. The peel strength ratio is the standard heat treatment product No. The result of each test bearing was represented by the reciprocal of the ratio, with 2 being 1.

  (2) Smearing test: Under the test conditions shown in Table 6, the test piece and the mating test piece are made of the same material, and the test pieces are brought into rolling contact with each other, and only the test piece is rotated at a constant rate. In this case, the relative rotation speed between the test pieces at the moment when the generated sound becomes larger than a certain value is defined as the smearing strength. The smearing strength ratio is the standard heat treatment product no. The result of each test bearing was expressed as a ratio with 2 being 1.

  Next, the test results shown in Table 4 will be described.

  (1) Peeling test: Product No. No. 1 is a standard heat treatment product No. Compared with No. 2, it has a peeling strength of 1.5 times or more. Compared to 3, it is the same or slightly improved. This has a nitrogen-enriched layer in the surface layer part, the austenite crystal is refined to a grain size number of 11 or more, the amount of retained austenite is moderately, it has an appropriate surface hardness, and the area of spheroidized carbide A large ratio is considered to have increased toughness and resistance to crack initiation and propagation.

  (2) Smearing test: Invention product No. No. 1 is a standard heat treatment product No. Compared with No. 2, it has a peeling strength of 1.5 times or more. Compared to 3, it is the same or slightly improved. This has a nitrogen-enriched layer in the surface layer part, the austenite crystal is refined to a grain size number of 11 or more, the amount of retained austenite is moderately, it has an appropriate surface hardness, and the area of spheroidized carbide It is thought that a high rate suppressed the plastic flow of the surface layer under large sliding conditions and improved the seizure resistance.

  In summary, the product No. No. 1 is better than the conventional bearing material in both peeling test and smearing test. In addition, the lubrication conditions are poor, the rollers interfere with each other, the roller position is not controlled smoothly, and the surface damage life due to roller skew is improved.

  The product of the present invention has a nitrogen-enriched layer in the surface layer part, the austenite crystal is refined to a particle size number of 11 or more, the amount of retained austenite is moderately, the surface hardness is appropriate, and the spheroidized carbide Therefore, the resistance to the occurrence and development of cracks is very large, and the generation of surface cracks due to surface heat generation and tangential force due to slip can be suppressed.

(Example 3)
Using JIS standard SUJ2 material (1.0 wt% C-0.25 wt% Si-0.4 wt% Mn-1.5 wt% Cr), (1) measurement of hydrogen content, (2) crystal grain size (3) Charpy impact test, (4) Fracture stress value measurement, and (5) Rolling fatigue test. Table 7 shows the results.

  The manufacturing history of each sample is as follows.

  Samples A to D (examples of the present invention): carbonitriding 850 ° C., holding time 150 minutes. The atmosphere was a mixed gas of RX gas and ammonia gas. In the heat treatment pattern shown in FIG. 6, primary quenching was performed from a carbonitriding temperature of 850 ° C., and then secondary quenching was performed by heating to a temperature range of 780 ° C. to 830 ° C. lower than the carbonitriding temperature. However, Sample A having a secondary quenching temperature of 780 ° C. was excluded from the test because of insufficient quenching.

  Samples E and F (comparative examples): The carbonitriding treatment was carried out with the same history as the invention examples A to D, and the secondary quenching temperature was 850 ° C. to 870 ° C., which is a carbonitriding temperature of 850 ° C.

  Conventional carbonitrided product (comparative example): carbonitrided at 850 ° C., holding time of 150 minutes. The atmosphere was a mixed gas of RX gas and ammonia gas. Quenching was performed as it was from the carbonitriding temperature, and secondary quenching was not performed.

  Normal quenching product (comparative example): without any carbonitriding treatment, it was quenched by heating to 850 ° C. Secondary quenching was not performed.

  Next, the test method will be described.

(1) Measurement of hydrogen amount The amount of hydrogen was determined by analyzing the amount of non-diffusible hydrogen in the steel using a DH-103 type hydrogen analyzer manufactured by LECO. The amount of diffusible hydrogen is not measured. The specification of this LECO DH-103 type hydrogen analyzer is shown below.

Analysis range: 0.01 to 50.00 ppm
Analysis accuracy: ± 0.1 ppm or ± 3% H (whichever is greater)
Analysis sensitivity: 0.01ppm
Detection method: thermal conductivity method Sample weight size: 10 mg to 35 mg (maximum: diameter 12 mm × length 100 mm)
Heating furnace temperature range: 50 ° C to 1100 ° C
Reagents: Anhydrone Mg (ClO ₄ ) ₂ , Ascarite NaOH
Carrier gas: nitrogen gas, gas dosing gas: hydrogen gas, both gases have a purity of 99.99% or more and a pressure of 40 psi (2.8 kgf / cm ² ).

  The outline of the measurement procedure is as follows. A sample collected with a dedicated sampler is inserted into the hydrogen analyzer together with the sampler. Internal diffusible hydrogen is directed to the thermal conductivity detector by a nitrogen carrier gas. This diffusible hydrogen is not measured in this example. Next, a sample is taken out from the sampler, heated in a resistance heating furnace, and non-diffusible hydrogen is guided to a thermal conductivity detector by nitrogen carrier gas. The amount of non-diffusible hydrogen can be known by measuring the thermal conductivity with a thermal conductivity detector.

(2) Measurement of crystal grain size The crystal grain size was measured based on the JIS G 0551 steel austenite grain size test method.

(3) Charpy impact test The Charpy impact test was performed based on the Charpy impact test method of the metal material of JIS Z2242. As a test piece, a U-notch test piece (JIS No. 3 test piece) shown in JIS Z 2202 was used.

(4) Measurement of Fracture Stress Value FIG. 11 is a diagram showing a test piece for a static crush strength test (measurement of a fracture stress value). The load until it is broken by applying a load in the P direction in the figure is measured. Thereafter, the obtained fracture load is converted into a stress value by the following bending beam stress calculation formula. In addition, a test piece is not restricted to the test piece shown in FIG. 11, You may use the test piece of another shape.

Sigma ₁ a fiber stress on the convex surface of the test piece of Figure 11, when the fiber stress and sigma ₂ in concave surface, sigma ₁ and sigma ₂ is determined by the following formula (Mechanical Engineering Handbook A4 Part material Mechanics A4-40) . Here, N is the axial force of the cross section including the axis of the annular test piece, A is the cross-sectional area, e ₁ is the outer radius, and e ₂ is the inner radius. Further, κ is a section modulus of the curved beam.

σ ₁ = (N / A) + {M / (Aρ _o )} [1 + e 1 / {κ (ρ _o + e ₁ )}]
σ ₂ = (N / A) + {M / (Aρ _o )} [1-e ₂ / {κ (ρ _o −e ₂ )}]
κ = − (1 / A) ∫ _A {η / (ρo + η)} dA
(5) Rolling fatigue life Table 8 shows the test conditions for the rolling fatigue life test. FIG. 12 is a schematic view of a rolling fatigue life tester. FIG. 12A is a front view, and FIG. 12B is a side view. Referring to FIGS. 12A and 12B, the rolling fatigue life test piece 121 is driven by the drive roll 111 and rotates in contact with the ball 113. The ball 113 is a 3/4 inch ball and is guided by the guide roll 112 to roll while exerting a high surface pressure with the rolling fatigue life test piece 121.

  The test results shown in Table 7 will be described as follows.

(1) Amount of hydrogen Conventional carbonitrided products that have undergone carbonitriding have a very high value of 0.72 ppm. This is presumably because ammonia (NH ₃ ) contained in the carbonitriding atmosphere decomposed and hydrogen entered the steel. On the other hand, in Samples B to D, the hydrogen amount is reduced to almost half of 0.37 to 0.40 ppm. This amount of hydrogen is at the same level as that of ordinary quenched products.

  By reducing the amount of hydrogen described above, embrittlement of steel due to hydrogen solid solution can be reduced. That is, the reduction in the amount of hydrogen greatly improves the Charpy impact value of Samples B to D of the present invention example.

(2) Crystal grain size When the secondary quenching temperature is lower than the quenching (primary quenching) temperature during carbonitriding, that is, in the case of Samples B to D, the austenite grains have grain size numbers 11 to 12 and Remarkably miniaturized. The austenite grains of Samples E and F, the conventional carbonitrided product, and the normal quenching product have a crystal grain size number 10 and are coarser than the samples B to D of the examples of the present invention.

(3) Charpy impact test According to Table 7, the Charpy impact value of the samples B to D of the present invention example is 6 compared to the Charpy impact value of the conventional carbonitrided product being 5.33 J / cm ^2. A high value of .30 to 6.65 J / cm ² is obtained. Among these, the lower the secondary quenching temperature, the higher the Charpy impact value tends to be. The normally hardened product has a Charpy impact value as high as 6.70 J / cm ² .

(4) Measurement of fracture stress value The fracture stress value corresponds to the crack resistance strength. According to Table 7, the conventional carbonitrided product has a fracture stress value of 2330 MPa. Compared to this, the fracture stress values of Samples B to D are improved to 2650 to 2840 MPa. The fracture stress value of the normal quenching product is 2770 MPa, and the improved cracking resistance strength of the samples B to D is estimated to have a great effect by reducing the hydrogen content, along with the refinement of austenite crystal grains.

(5) According to the rolling contact fatigue test table 7, usually sintered Irihin is reflecting that no has a nitriding layer on the surface layer portion, the rolling fatigue life L ₁₀ is the lowest. Compared to this, the rolling fatigue life of the conventional carbonitrided product is 3.1 times. The rolling fatigue life of Samples B to D is significantly improved as compared with the conventional carbonitrided product. Samples E and F of the present invention are substantially equivalent to conventional carbonitrided products.

  In summary, Samples B to D of the present invention have a reduced hydrogen content, an austenite crystal grain size of 11 or more, and improved Charpy impact value, crack resistance strength and rolling fatigue life. .

Example 4
Next, Example 4 will be described. A series of tests were performed on the following X material, Y material, and Z material. JIS standard SUJ2 material (1.0% by weight C-0.25% by weight Si-0.4% by weight Mn-1.5% by weight Cr) is used for the heat treatment material. did. The manufacturing history of the X material to the Z material is as follows.
(X material: comparative example): normal quenching only (not carbonitriding).
(Y material: comparative example): quenching as it is after carbonitriding (conventional carbonitriding quenching). Carbonitriding temperature 845 ° C, holding time 150 minutes. The atmosphere of the carbonitriding process was RX gas + ammonia gas.
(Z material: Example of the present invention): Bearing steel subjected to the heat treatment pattern of FIG. Carbonitriding temperature 845 ° C, holding time 150 minutes. The atmosphere of the carbonitriding process was RX gas + ammonia gas. The final quenching temperature was 800 ° C.

(1) Rolling fatigue life Test conditions and test equipment for the rolling fatigue life test are as shown in Table 8 and FIG. 12, as described above. The rolling fatigue life test results are shown in Table 9.

According to Table 9, the Y material of the comparative example shows 3.1 times the L ₁₀ life of the X material that has been subjected only to normal quenching in the comparative example (the life that one of the 10 test pieces breaks), The effect of extending the life by carbonitriding is recognized. On the other hand, the Z material of the example of the present invention has a long life of 1.74 times that of the Y material and 5.4 times that of the X material. The main reason for this improvement is thought to be the refinement of the microstructure.

(2) Charpy impact test The Charpy impact test was performed by the method according to the above-mentioned JISZ2242 using the U notch test piece. The test results are shown in Table 10.

  The Charpy impact value of the Y material (comparative example) subjected to carbonitriding was not higher than that of the normal quenching X material (comparative example), but the Z material obtained the same value as the X material.

(3) Test of Static Fracture Toughness Value FIG. 13 is a diagram showing a test piece of a static fracture toughness test. After introducing a precrack about 1 mm into the notch portion of this test piece, a static load by three-point bending was applied to determine the fracture load P. The following formula (I) was used for calculation of the fracture toughness value (K _Ic value). The test results are shown in Table 11.
K _Ic = (PL√a / BW ² ) {5.8−9.2 (a / W) +43.6 (a / W) ² −75.3 (a / W) ³ +77.5 (a / W ⁴ }… (I)

  Since the crack depth introduced in advance is larger than the depth of the nitrogen-enriched layer, there is no difference between the X material and the Y material of the comparative example. However, the Z material of the present invention example was able to obtain a value about 1.2 times that of the comparative example.

(4) Static crushing strength test (measurement of fracture stress value)
As described above, the static crushing strength test piece having the shape shown in FIG. 11 was used. In the figure, a static crushing strength test was performed by applying a load in the P direction. The test results are shown in Table 12.

  The Y material subjected to carbonitriding has a slightly lower value than the normal quenching X material. However, the Z material of the present invention has higher static crushing strength than the Y material, and a level comparable to that of the X material is obtained.

(5) Aged dimensional change rate The measurement results of the aged dimensional change rate at a holding temperature of 130 ° C. and a holding time of 500 hours are shown in Table 13 together with the surface hardness and the retained austenite amount (0.1 mm depth).

  It can be seen that the Z material of the example of the present invention is suppressed to half or less compared to the dimensional change rate of the Y material having a large amount of retained austenite.

(6) Life test under lubrication mixed with foreign matter Using a ball bearing 6206, the rolling fatigue life was evaluated under lubrication mixed with foreign matter in which a predetermined amount of standard foreign matter was mixed. Test conditions are shown in Table 14 and test results are shown in Table 15.

  Compared to the X material, the Y material subjected to the conventional carbonitriding treatment is about 2.5 times longer, and the Z material of the present invention example has a long life of about 2.3 times. Although the Z material of the present invention has less retained austenite than the Y material of the comparative example, it has a longer life than the Y material due to the intrusion of nitrogen and the influence of the refined microstructure.

  From the above results, the Z material of the example of the present invention, i.e., the bearing component manufactured by the heat treatment method of the present invention, has a long rolling fatigue life, which is difficult to achieve with conventional carbonitriding, and improved crack strength. It was found that the three items of reduction of the aging dimensional change rate can be satisfied simultaneously.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic front view which shows the use condition of the rolling bearing for rocker arms in one embodiment of this invention. It is sectional drawing which follows the II-II line in FIG. It is a schematic front view which shows the use condition of the rolling bearing for rocker arms in other embodiment of this invention. It is a schematic front view which shows the use condition of the rolling bearing for rocker arms in another embodiment of this invention. It is the figure which expanded the part containing the rolling bearing for rocker arms of FIG. It is a figure explaining the heat processing method in one embodiment of this invention. It is a figure explaining the modification of the heat processing method in one embodiment of this invention. It is a figure which shows the microstructure of a bearing component, especially an austenite grain. (a) is a bearing part of the example of the present invention, and (b) is a conventional bearing part. (A) shows the austenite grain boundary illustrated in FIG. 8 (a), and (b) shows the austenite grain boundary illustrated in FIG. 8 (b). It is a figure which shows the rolling fatigue testing machine of outer ring | wheel rotation. It is a figure which shows the test piece of a static crushing strength test (measurement of a fracture stress value). It is the schematic of a rolling fatigue life tester. (a) is a front view, (b) is a side view. It is a figure which shows the test piece of a static fracture toughness test.

Explanation of symbols

  1 rocker arm, 1a, 1b rocker arm end, 1c side wall, 2 roller shaft, 3 rollers, 4 rollers, 5 rocker arm shaft, 6 cam, 7 adjustment screw, 8 lock nut, 9 valve, 9a valve upper end, 10 Spring, 11 Rocker arm body, 11a, 11b Rocker arm body end, 14 Inner ring support, 15 Pivot hole, 16 Interlocking rod, 16a Bearing mounting portion, 16b Interlocking rod upper end, 17 Mounting member, 50 Roller bearing for rocker arm , 52 Roller shaft, 54 Roller, 55, 56 Member, 111 Drive roll, 112 Guide roll, 113 ball, 121 Rolling fatigue life test piece.

Claims (6)

An outer ring in rolling contact with the camshaft of the engine;
An inner ring located inside the outer ring and fixed to the rocker arm;
In a rocker arm rolling bearing comprising a plurality of rolling elements interposed between the outer ring and the inner ring,
The outer ring, the inner ring, and at least the inner ring is cooled to the A ₁ transformation point temperature below after being carbonitrided at a carbonitriding temperature exceeding the A ₁ transformation point, further wherein carburizing exceed A ₁ transformation point of the rolling element It is heated to a temperature lower than the nitriding temperature, and has a nitrogen-enriched layer by being hardened by quenching , the austenite grain size number is in the range exceeding 10 and the area ratio of spheroidized carbide is 10% der is, the amount of retained austenite in the surface layer 50μm is from 12 to 24% of the rolling surface, the nitrogen content of Ru 0.12 to 0.62% der rolling bearing rocker arm above. The rolling bearing for a rocker arm according to claim 1, wherein an area ratio of the spheroidized carbide of the inner ring is 10% or more and 25% or less. The rocker arm is rotatably attached to a rotary shaft which is located between the ends of the other side of the hand, the end portion of the opening and closing valve of the engine to an end of the one abuts the The rocker arm rolling bearing according to claim 1 or 2, wherein the rocker arm has a bifurcated inner ring support portion at the other end, and the inner ring is fixed to the bifurcated inner ring support portion. Provided between one end of the rocker arm and the other end;
The inner ring is fixed to an inner ring hole extending between two side walls of the rocker arm, the end of the opening / closing valve of the engine abuts on one end of the rocker arm, and the other end of the rocker arm The rolling bearing for a rocker arm according to claim 1, wherein the pivot abuts.   The rocker arm includes a rocker arm main body and an interlocking rod that transmits stress from the cam shaft, and the rocker arm main body is positioned between one end and the other end of the rocker arm main body. An end of a valve for opening and closing the engine is in contact with the one end of the rocker arm body, and the other end of the rocker arm body is connected to the interlocking rod. The rolling bearing for a rocker arm according to claim 1 or 2, wherein one end abuts and the inner ring is fixed to the other end of the interlocking rod.   The rocker arm rolling bearing according to any one of claims 1 to 5, wherein the roller bearing is a full roller type needle bearing.

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