JP2009019639A - Manufacturing process of roller cam follower for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing process of a roller cam follower for an engine with a long life. <P>SOLUTION: The manufacturing process of a roller cam follower is a manufacturing process of a roller cam follower comprising a roller rollingly contacting with a cam of an engine, a roller shaft disposed inside the roller and fixed to a cam follower body, and a bearing interposed between the roller and the roller shaft. At least either one member out of the roller, roller shaft and bearing is manufactured thereby, after steel is subjected to carbonitriding treatment at a carbonitriding treatment temperature exceeding A<SB>1</SB>transformation point, is cooled to a temperature below the A<SB>1</SB>transformation point, thereafter is re-heated to a quenching temperature range which is the A<SB>1</SB>transformation point or above and below the carbonitriding treatment temperature, and is quenched. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a cam follower with a roller of an engine used for opening and closing an intake valve and an exhaust valve of an automobile engine. More specifically, the present invention relates to a method of manufacturing a cam follower with a roller of an engine that has improved durability and realized a long life. Is.

  Many of the recent rolling bearings are used for high-speed and high-load applications even though they are full-roller types, such as bearings used in cam follower bearings with rollers for engines. In a full-roller type bearing without a cage, the rollers may interfere with each other or the lubricant may not be supplied well into the bearing. For this reason, surface damage occurs at high speeds, and the roller position is not controlled smoothly and skew 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 a cam follower with a roller of an engine, there have been many improvements mainly for the purpose of improving the outer diameter of the outer ring. For example, compression 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 made mainly to improve the outer diameter of the outer ring that is in rolling contact with the mating cam. It was.

  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 are imparted by carbonitriding treatment, and hardness is increased as shown below There is an example in which the life of the bearing is extended by, for example. The conventional techniques related to the life enhancement related to the cam follower with a roller of the engine so far are as follows.

  (D1) A bearing for a cam follower device for a valve operating mechanism of an engine having a calculation life of 1000 hours or more at a rated engine speed (Patent Document 1).

  (D2) Carbide ratio: 10 to 25%, decomposition ratio with respect to initial value of retained austenite: 1/10 to 3/10, end face hardness: HV830 to 960, average surface roughness wavelength: 25 μm or less for cam follower device A bearing steel that has been subjected to carbonitriding and hard shot peening to realize a bearing shaft (Patent Document 2).

  (D3) A cam follower shaft in which a solid lubricating film such as a polymer compound is formed on the shaft to improve the shaft wear resistance (Patent Document 3).

  (D4) A cam follower shaft formed 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 4).

  (D5) A bearing for a cam follower device for a valve mechanism of an engine in which a bending stress with respect to a shaft is 150 MPa or less (Patent Document 5).

  (D6) A cam follower for a valve operating mechanism of an engine in which a phosphate coating excellent in lubricating oil retention is attached to a rolling surface of a bearing component (Patent Document 6).

  (D7) A cam follower for a valve mechanism of an engine in which crowning is provided in the roller rolling region of the shaft (Patent Document 7).

  (D8) Carburized shaft with high-concentration carburizing treatment or carbonitriding treatment in which the carbon concentration in the surface of the rolling surface of the shaft is 1.2% to 1.7% C, and the internal hardness is HV300 (Patent Document 8) .

  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 9).
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 JP 63-185917 A JP 2002-194438 A JP-A-5-179350

  In the future, in the case of cam followers with rollers for engines, it is expected that, as with ordinary bearings, the speed and load during use will increase and the viscosity of lubricating oil will decrease. In addition to the usual load-dependent rolling fatigue life, the life of the rolling contact life under these conditions is longer than the surface damage life due to metal contact caused by slipping or oil film breakage. There is a need for. However, no technology has been made to extend both lifetimes significantly. 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, this technique alone is effective in extending the service life of inner rings and rollers of full-roller bearings, although it is effective in extending the life of applications where bending acts like an outer ring. I couldn't.

  An object of this invention is to provide the manufacturing method of the cam follower with a roller of the engine which aimed at lifetime improvement.

  A method of manufacturing a cam follower with a roller according to the present invention includes a roller that is in rolling contact with a cam of an engine, a roller shaft that is positioned inside the roller and is fixed to the cam follower body, and a bearing that is interposed between the roller and the roller shaft. Is a manufacturing method of a cam follower with a roller. After carbonitriding the steel at a carbonitriding temperature exceeding the A1 transformation point, the steel is cooled to a temperature below the A1 transformation point, and then reheated to a quenching temperature range above the A1 transformation point and below the carbonitriding temperature, By performing quenching, at least one member of a roller, a roller shaft, and a bearing is manufactured.

  The cam follower with a roller of the engine of the present invention includes a roller that is in rolling contact with the cam shaft of the engine, a roller shaft that is positioned inside the roller and is fixed to the cam follower body, and a bearing that is interposed between the roller and the roller shaft. In the cam follower with a roller, at least one member of the roller, the roller shaft, and the bearing is provided with a nitrogen-enriched layer, and at least the austenite crystal grains in the surface layer portion are refined so that the grain size number exceeds 10 .

  By reducing the grain size number of the austenite grains of the above-mentioned member to exceed 10, the rolling fatigue life can be greatly improved. 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. 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 above-mentioned austenite crystal grain size is preferably as fine as possible, and more preferably austenite crystal grain size number 11 or more. The average crystal grain size may be 6 μm or less. The austenite grain size number may be satisfied in the nitrogen-enriched layer. However, in the usual case, the above-mentioned standard for austenite grain refinement is also satisfied in the steel body inside the nitrogen-enriched 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. The austenite crystal grain may be a grain boundary that can be observed by performing a process of revealing the grain boundary, such as etching, on the gold phase sample of the target member. In the sense that it is a grain boundary at the time of heating just before low-temperature quenching, it may be referred to as prior austenite grains. The measurement may be obtained by converting the average value of the JIS standard particle size number to the average particle size as described above, or while the random direction straight line superimposed on the metal phase structure by the intercept method or the like is associated with the grain boundary. An average value of the interval lengths may be taken, and a two-dimensional to three-dimensional interval length may be obtained by applying a correction coefficient.

  The nitrogen-enriched layer is formed by carbonitriding as will be described later, but the nitrogen-enriched layer may be enriched with carbon or may not be enriched. .

  In the cam follower with a roller of another engine of the present invention, at least one of the roller, the roller shaft, and the bearing has a nitrogen-enriched layer, and the fracture stress value of the member is 2650 MPa or more.

  The inventors of the present application have found that the fracture stress value of a steel having a carbonitriding layer can be increased to 2650 MPa or more, which has not been obtained conventionally, by a heat treatment method described later. Thereby, a high-strength rolling bearing can be obtained and excellent durability can be obtained with respect to the load form in the cam follower with roller.

  In the cam follower with a roller of still another engine of the present invention, at least one of the roller, the roller shaft, and the bearing has a nitrogen-enriched layer, and the hydrogen content of the member is 0.5 ppm or less.

  The above-mentioned heat treatment method (low-temperature secondary quenching method) and the hydrogen content contained in the member before being incorporated into the cam follower can be lowered. For this reason, it is possible to lengthen the time required for hydrogen entering the steel to reach the critical value for crack generation, and as a result, the durability can be enhanced by overlapping with unexplained reasons.

  A lower hydrogen content is desirable. However, in order to reduce it to less than 0.3 ppm, heating for a long time is required, the austenite grain size becomes coarse and the toughness deteriorates. For this reason, the more desirable amount of hydrogen is in the range of 0.3 to 0.5 ppm. More desirably, it is in the range of 0.35 to 0.45 ppm.

  Note that the above hydrogen content does not measure diffusible hydrogen, but only measures non-diffusible hydrogen released from steel at a predetermined temperature or higher. The amount of diffusible hydrogen is excluded from the measurement because it is released from the sample and dissipates even at room temperature if the sample size is small. Non-diffusible hydrogen is trapped in a defective portion or the like in steel and is released from a sample only after a predetermined heating temperature or higher. Even when limited to this non-diffusible hydrogen, the hydrogen content varies greatly depending on the measurement method. The above hydrogen content range is a range determined by a measurement method using a thermal conductivity method. Furthermore, as will be described later, it is desirable to measure using a DH-103 type hydrogen analyzer manufactured by LECO or a measuring device according to it.

  (C1) The cam follower body is rotatably attached to a rotating shaft located between one end and the other end, and an end of an engine opening / closing valve is attached to one end thereof. The other end may have a bifurcated roller support, and the roller shaft may be fixed to the bifurcated roller support.

  (C2) The cam follower body is provided between one end and the other end, and a roller shaft is fixed to a roller hole extending between the two side walls, and the engine follower is connected to one end. The end of the opening / closing valve may be in contact with the other end, and the pivot may be in contact with the other end.

  (C3) Further, the cam follower body is rotatably attached to a rotating shaft located between one end portion and the other end portion, and an end of an opening / closing valve for the engine is attached to the one end portion. The other end is in contact with the cam follower body side end of the interlocking rod that transmits the stress from the camshaft, and the roller shaft is on the cam end that is the other end of the interlocking rod. It may be attached and contact the cam.

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

  In the cam follower with a roller of the engine described above, the bearing may be a full roller type needle bearing. Further, the hardness of the end portion of the roller shaft may be lower than that of the central portion. In this way, the center part of the roller shaft has the necessary hardness as a rolling surface and is soft at the end part, so that it is possible to perform caulking processing while ensuring durability such as rolling fatigue life. . As a result, in all the rolling bearings described above, the end of the roller shaft may be crimped.

  Moreover, the cam follower main body may be press-molded. Production efficiency can be improved by press molding.

  The steel member of the present invention is a steel member that abuts against the rocker arm, and has a nitrogen-enriched layer in the surface layer portion that abuts against the rocker arm of the steel member, and the austenite grain size in the nitrogen-enriched layer is No. 11 That's it.

  With this configuration, it is possible to realize a long life by suppressing surface damage such as surface-origin separation and internal origin delamination in the surface layer portion of the cam contacting the steel member, for example, a cam follower roller. The steel member may be anything as long as it abuts on any part of the rocker arm, and may be a steel member such as a valve member that abuts an adjustment screw.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic front view showing a configuration of a cam follower with a roller of an engine according to an embodiment of the present invention, and FIG. 2 is a view corresponding to a cross section taken along line II-II of FIG. Referring to FIGS. 1 and 2, a rocker arm 1 that is a rotating member is rotatably supported on a rocker arm shaft 5 via a bearing metal or the like at a central portion.

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

  The rocker arm 1 is provided with a cam follower body 50 at one end 1a, and the cam follower body 50 integrally includes a roller support portion 14 formed in a bifurcated shape. Both ends of the roller shaft 2 corresponding to the inner ring are fixed to the bifurcated roller 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 via a roller 3 so as to be rotatable. The roller 3 constitutes a bearing interposed between the roller shaft 2 and the roller 4. In other words, the bearing interposed between the roller shaft 2 and the roller 4 can be rephrased as a roller. The axial direction of the roller 3 is arranged in parallel to the axis of the roller shaft. 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. There is no particular distinction between one and the other, and there is only a meaning that one end is an end that will be described earlier in the order of description.

  Here, a roller bearing composed of a roller shaft 2, a rolling element made of rollers 3 and an outer ring made of rollers 4 is used as a rocker arm full roller bearing. Generally, when a cage is not used, it is called a full roller bearing. Since the rocker arm full roller bearing rotates while contacting the cam 6, the pressing force and impact force of the cam 6 act on the outer ring 4. A cam follower with a roller of an engine according to an embodiment of the present invention is a member that includes the rocker arm full roller bearing and the cam follower main body.

  FIG. 3 is a view showing a cam follower with a roller of an engine according to another embodiment of the present invention. In this cam follower, the cam follower body 50 is fixed between the roller shaft 2 in a roller hole (not shown) opened between one end 1b and the other end 1a of the rocker arm 1 and extending between the two side walls. The end of the engine opening / closing valve 9 contacts one end, and a pivot (not shown) contacts the other end. The cam follower body 50 provided with the pivot hole 15 is biased by the spring 10 in a predetermined direction around the pivot, receives the driving force transmitted from the cam 6 by the roller 4, and resists the biasing force of the spring. Move 9

  FIG. 4 is a view showing a cam follower with a roller of an engine 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. In FIG. 4, the rotation shaft 5 is disposed at the center of the rocker arm 1, and the rocker arm 1 rotates around the rotation shaft 5. The end 1b of one arm of the rocker arm 1 contacts the end of the engine valve 9, and the end 1a of the other arm contacts the end of the interlocking rod 16. The adjustment screw 8 has a function of adjusting a contact position between the end 1a of the rocker arm and the interlocking rod 16.

  A cam follower body 50 is provided at a hollow bearing mounting portion 16 a located at the lower end of the interlocking rod 16, and a rocker arm full roller bearing is mounted by the mounting member 17. The cam 6 abuts against the roller 4 of the full roller bearing and transmits the driving force to the connecting rod.

  Among the members constituting the roller bearing of the engine cam follower with the roller, 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. Fine austenite grains.

  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 the embodiment of the present invention. Moreover, FIG. 7 is a figure explaining the modification of the heat processing method in embodiment of this invention. FIG. 6 is a heat treatment pattern showing a method of performing primary quenching and secondary quenching. FIG. 7 shows a method of cooling the material to below the A1 transformation point temperature during quenching, and then reheating and finally quenching. It is the heat processing pattern shown. Both are exemplary embodiments of the present invention. In these figures, in the treatment T1, carbon and nitrogen are diffused in the steel base and the carbon is sufficiently dissolved, and then cooled to below the A1 transformation point. Next, in process T2 in the figure, reheating is performed at a temperature lower than that of process T1, and oil quenching is performed therefrom.

  Any of the above heat treatments can be applied to the roller, roller shaft, rolling element (roller) and cam of the bearing component.

  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.

  In either of the two heat treatments described above, a nitrogen-enriched layer that is a “carbonitriding layer” is formed by carbonitriding in it. Since the carbon concentration of steel used as a material in the carbonitriding process is high, carbon may not easily enter the steel surface from the normal carbonitriding process atmosphere. For example, in the case of steel with a high carbon concentration (steel of about 1 wt%), a carburized layer with a higher carbon concentration may be generated, or a carburized layer with a higher carbon concentration may be difficult to generate. However, although the nitrogen concentration depends on the Cr concentration and the like, it is as low as about 0.025 wt% or less in normal steel, so a nitrogen-enriched layer is clearly generated regardless of the carbon concentration of the raw steel. . Needless to say, the nitrogen-enriched layer may be enriched with carbon.

  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. 7 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.

Next, examples of the present invention will be described.
(Example 1)
Bearings of the materials shown in Table 1 were prepared. These bearings are full-roller needle bearings included in cam followers with rollers of engines. The inner ring (roller shaft) has an outer diameter of 14.64 mm × width of 17.3 mm, and the outer ring has an inner diameter of 18.64 mm × outer diameter of 24 mm × width of 6.9 mm. Twenty-six rollers having an outer diameter of 2 mm and a length of 6.8 mm were used for the rollers, and the configuration was a full-roller type without using a cage. The basic dynamic load rating of this bearing is 8.6 kN, and the basic static load rating is 12.9 kN. Here, all the bearings are based on the same combination of materials, but some bearings may be manufactured by combining several materials or adding processing. Table 1 shows a list of manufactured bearings.

The breakdown of the samples shown in Table 1 is as follows.
No. 1: A bearing steel that has been subjected to strong cold working in advance and refined the crystal grains after heat treatment and then carbonitrided.
No. 2: The bearing steel was subjected to secondary quenching at a temperature lower than the carbonitriding temperature after carbonitriding.
No. 3: Carburized steel subjected to carbonitriding after carburizing treatment and subjected to secondary quenching at a lower temperature, that is, applied with low-temperature secondary quenching after carburizing treatment.

The austenite grain size of Nos. 1 to 3 is No. 1. 11 or more. In order to form a compressive stress on the surface layer based on these materials, the following samples were prepared as processed materials.
No. 4: No. Shot peening is applied to the inner and outer rings of 1, and barrel processing is applied to the rollers.
No. 5: No. Shot peening is applied to the inner and outer rings of No. 2 and barrel processing is applied to the rollers.
No. 6: No. Shot peening is applied to the inner and outer rings of 3, and barrel processing is applied to the rollers.

Moreover, the following were prepared as samples with increased surface hardness.
No. 7: No. Sub-zero (-196 ° C) treatment added to 1 inner and outer rings.
No. 8: No. Sub-zero (-196 ° C) treatment was added to the inner and outer rings of No. 1, shot peening was applied to the inner and outer rings, and the rollers were barrel processed.

Furthermore, the following samples were prepared assuming that the above method was applied to each element of the inner and outer rings and rollers, particularly the inner ring where the rolling life is a problem.
No. 9: After carbonitriding the inner ring and the rollers, those subjected to secondary quenching at a temperature lower than the carbonitriding temperature, and those using standard heat treatment for the outer ring were used.
No. 10: Carburized steel is used for the inner and outer rings, and after carburizing and cooling, carbonitriding and cooling, and then subjected to secondary quenching at a lower temperature, the roller is subjected to carbonitriding for bearing steel. gave.

As comparative examples, five types of sample Nos. 11 to 15 shown in the lower column of Table 1 were manufactured.
No. 11: Both inner and outer rings and rollers are standard heat-treated products of bearing steel.
No. 12: Carbonitrided products of bearing steel for both inner and outer rings and rollers.
No. 13: Standard carburized steel of carburized steel is used for inner and outer rings, and rollers are standard heat treated products of bearing steel.
No. 14: Secondary quenching of carburized steel.
No. 15: No. 11 samples with inner and outer ring shot peening and roller barrel processing.

  With respect to these samples, crystal grain size, hardness, and tempering hardness at 500 ° C. (heat resistance index) were measured. The results are shown in Table 1.

First, each test of rolling life evaluation and surface damage strength evaluation will be described.
(Rolling life evaluation): Outer ring (inner diameter 18.64 mm × outer diameter 24 mm × width 6.9 mm), 26 rollers (outer diameter 2 mm × length 6.8 mm), roller shaft (outer diameter 14.64 mm) X width 17.3 mm) and a rolling fatigue test was performed at a load of 2.58 kN. The test apparatus is shown in FIG. The test conditions are shown in Table 2. This test is an outer ring rotation test. Referring to FIG. 10, a configuration in which a plurality of needle rollers 53 (3) are arranged so as to roll between a roller shaft 52 (2) and an outer ring 54 (4) incorporated in the testing machine. A life test was performed by rotating the outer ring 54 at a predetermined speed while applying a radial load by the members 55 and 56. At this time, the test was performed at a load of 30% with a basic dynamic load rating of 8.6 kN. The test results are shown in Table 3.

  In the test results shown in Table 3, the roller or inner ring peeled off. In No. 9, some outer ring peeling was also observed. From Table 2, it was found that the examples of the present invention had a longer life than the comparative examples, and all of them exhibited a life that was about 3 times that of the standard product and about 1.5 times that of the carbonitrided product.

  (Peeling test): Table 4 shows a list of test samples including the peeling test and the test results, and Table 5 shows the test conditions of the peeling test. No. of the example of the present invention. 1 to 3 and those subjected to shot peening and sub-zero treatment, a total of 8 types (Nos. 1 to 8) and 5 types (Nos. 11 to 15) as comparative examples were subjected to a peeling test.

  Thirteen kinds of test samples having a diameter of 40 mm (mirror finish) were brought into rolling contact with SUJ rough surface test pieces under certain conditions, and peeling (microscopic) generated on the sample (mirror surface) test pieces after a certain period of time. The area ratio of the peeled aggregate) was measured. Here, the reciprocal of the area ratio is defined as the peeling strength, and the comparative example No. It was expressed as a ratio when the peeling strength of 11 was 1.

  The results are shown in Table 4. The specimens of the examples of the present invention have a peeling strength 1.5 times or more that of the comparative examples. It can be said that fine austenite crystal grains having a grain size number of 10 and moderate retained austenite increase toughness and increase resistance to crack initiation and propagation. Moreover, as for the thing (No. 4-8) which gave the compressive residual stress by the subzero process or the process, intensity | strength has improved all. It is considered that high hardness and compressive residual stress effectively act to suppress the generation and propagation of peeling cracks.

  (Smearing test): Using a test piece of the same material as the peeling test piece (see Table 4), the smearing strength was examined. Table 6 shows the test conditions. The test piece and the counterpart test piece were tested with the same material combination.

  The results are as shown in Table 4. Here, the evaluation represents the rotational speed of the mating test piece when smearing occurs as a ratio with the standard product (Comparative Example No. 11). Regarding smearing, the example of the present invention has a generated strength (rotational speed until generation) of 1.5 times or more compared to the standard product of the comparative example, which is higher than those of the other comparative examples. It can be said that the compositional grain size of the surface layer under a large sliding condition is suppressed and the seizure resistance is improved by the balance between the fineness of the crystal grains having the grain size number 11 or more, the appropriate amount of retained austenite and the presence of fine carbides. The one that has been processed is slightly stronger than the one that has not been processed.

  (Static crack strength test) About the test body shown in Table 4, the load was applied to the outer ring (inner diameter 18.64 mm x outer diameter 24 mm x width 6.9 mm) alone with an Amsler tester, and the crack strength was measured. The results are shown in Table 4. The crack starting point is the ring inner surface (rolling surface) surface. According to Table 4, when carbonitriding is generally performed, the comparative example No. As shown in FIG. 12, the static crack strength is lowered. On the other hand, Invention Example No. 1-3 are the same or slightly improved as the standard heat-treated products, and no reduction in static crack strength is observed. Invention Example No. in which these were processed. In the case of 4-6, the cracking strength is uniformly improved. In addition, Invention Example No. No. 7 sub-zero treated product, no. Although the static cracking strength is slightly lower than that in the case of No. 1 sub-zero treatment, the invention example No. In 8, the static crack strength is improved.

  Comparative Example No. The decrease in strength of 12 is due to the fact that the austenite crystal grains become coarse as a result of long-time heating in the carbonitriding process, and the amount of retained austenite increases, resulting in the formation of a locally low tensile strength structure. It is thought that it is. Comparative Example No. No. 13 has a reduced strength for the same reason.

(Crack fatigue strength test): In order to investigate the crack fatigue strength, a load was repeatedly applied to the outer ring of the test body of Table 4 under the conditions of Table 7 to determine the crack fatigue strength. That is, the outer ring was subjected to a repeated load within a range of a lower limit of 98 N and an upper limit of 3000 to 5000 N, and the number of repetitions until cracking was compared. Here, an SN diagram with different load conditions was obtained, and a load that could withstand 10 ⁵ repetitions was obtained.

  The results are shown in Table 4. Although the test result of the crack fatigue strength test was expressed as a ratio to the strength of the standard heat-treated product of the comparative example, the crack fatigue strength of each of the examples of the present invention was significantly improved compared to the comparative example. Regarding crack fatigue strength, the present invention example No. based on carburized steel. Example No. 6 of the present invention combining No. 3 and this with compressive residual stress gives good results.

  (Roller shaft end softening treatment): For induction annealing of both ends of the roller shaft, only one end of the roller shaft material after appropriate processing is brought close to the end opening of the high frequency coil, or The end portion is held in a slightly inserted state, the end portion is heated for a very short time by a high-frequency induced current, and then allowed to cool. Alternatively, after high-frequency heating, a method of rapid cooling by pouring water on the surface or charging the material into the water after cooling for a short time may be used. The hardness distribution obtained by this method is shown in FIG.

  As shown in FIG. 11 and Table 8, appropriate high strength is obtained in the A portion which is the central portion through which the rolling elements pass and the B portion at the end thereof. On the other hand, the hardness of the C part on the end face side of the outer peripheral surface and the D part which is the end face, which are important when performing caulking, is ensured to be soft enough for caulking.

  From the above results, it was confirmed that the durability of the rolling bearing for rocker arm was improved because the lubrication conditions were poor and the short life due to roller skew and roller interference was likely to occur. The above-mentioned improvement in durability is brought about by improving the surface damage (surface-origin type peeling such as peeling and smearing) life and internal origin peeling life by using a material with fine grain size and heat resistance. It was done. Specifically, the formation of a carbonitriding structure that secures an austenite grain size of a certain value or more by processing or heat treatment pattern of the material greatly increases the generation of cracks and the resistance to extension. As a result, it has been found that the generation of surface cracks due to surface layer heat generation and tangential force due to slipping can be suppressed, and that the life can be extended considerably even against cracks caused by external origin peeling. Based on these, further processing or heat treatment can be applied to impart compressive residual stress to the surface layer or increase the hardness, thereby further extending the life. These heat treatments and processings include techniques such as shot peening, barrel processing, rolling processing, burnishing, carburizing and carbonitriding, carbonitriding and subzero processing, carbonitriding, secondary quenching and subzero processing.

  In addition, when caulking is performed, the roller shaft serving as an inner ring as a bearing element has a limit that allows the outer peripheral edge of the roller shaft end and the edge of the outer peripheral surface of the roller shaft to be plastically deformed together. It is required to be soft. On the other hand, the roller shaft that is caulked and fixed to the roller support member may be loosened during long-term use of the cam follower and may fall out of the shaft hole due to rattling. Durability that can be caulked by adjusting the end surface hardness by adjusting the heating and cooling conditions of induction annealing on both ends of the roller shaft on the roller shaft with the characteristics obtained by the heat treatment and processing described above. An excellent roller shaft is possible. That is, since the above heat treatment and processing do not impair the cracking strength unlike conventional carbonitriding, a high-strength, long-life all-roller rolling bearing can be obtained. The shaft can be crimped by subjecting both end faces to induction annealing and adjusting the hardness.

  As a result, in bearings for rocker arms used for opening and closing of intake valves and exhaust valves of automobile engines, for example, with increased durability compared to bearings with small full-roller specifications with a bearing width of 5 mm to 12 mm. , And caulking can be performed.

(Example 2)
Example 2 of the present invention was performed using JIS standard SUJ2 material (1.0 wt% C-0.25 wt% Si-0.4 wt% Mn-1.5 wt% Cr). The manufacturing history of each sample shown in Table 9 is shown below.

  (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 due to insufficient quenching.

  (Samples E and F; Comparative Examples): The carbonitriding treatment was performed with the same history as the inventive examples A to D, and the secondary quenching temperature was 850 ° C. to 870 ° C., which is a carburizing nitrogen treatment temperature of 850 ° C. or more.

  (Conventional carbonitriding product; comparative example): Carbonitriding 850 ° C., holding time 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.

  (Normally hardened product; comparative example): It was heated to 850 ° C. and quenched without performing carbonitriding. Secondary quenching was not performed.

  (1) Measurement of hydrogen content, (2) Measurement of crystal grain size, (3) Charpy impact test, (4) Measurement of fracture stress value, (5) Rolling fatigue test Was done. Next, these test methods will be described.

I Test Method of Example 2 (1) Measurement of hydrogen amount The amount of hydrogen was analyzed for 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 g (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, the sample is taken out from the sampler and heated in a resistance heating furnace, and non-diffusible hydrogen is guided to the 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 JISZ2242. 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. 12 is a view showing a test piece of 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. 12, You may use the test piece of another shape.

Assuming that the fiber stress on the convex surface of the test piece of FIG. 12 is σ ₁ and the fiber stress on the concave surface is σ ₂ , σ ₁ and σ ₂ are obtained by the following formulas (Mechanical Engineering Handbook A4 Knitting Material Dynamics 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 / (ρ _o + η)} dA
(5) Rolling fatigue test Table 10 shows the test conditions for the rolling fatigue life test. FIG. 13 is a schematic view of a rolling fatigue life tester. FIG. 13A is a front view, and FIG. 13B is a side view. 13 (a) and 13 (b), the rolling fatigue life test piece 31 is driven by the drive roll 21 and rotates in contact with the ball 23. The ball 23 is a (3/4) ″ ball, which is guided by a guide roll and rolls while exerting a high surface pressure with the rolling fatigue life test piece 31.

II Test Results of Example 2 (1) Measurement of Hydrogen Content The conventional carbonitrided product that has been carbonitrided has 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 amount of hydrogen 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) Measurement of crystal grain size When the secondary quenching temperature is lower than the quenching (primary quenching) temperature during the carbonitriding process, that is, in the case of Samples B to D, the austenite grains have grain size numbers 11 to 11. 12 is 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 9, the Charpy impact value of the samples B to D of the example of the present invention 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. Charpy impact value of the normal quenched product is high and 6.70J / cm ^2.

(4) Measurement of fracture stress value The fracture stress value corresponds to the crack resistance strength. According to Table 9, 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 normally quenched product is 2770 MPa, which is equivalent to the fracture stress values of Samples B to F. Such improved cracking resistance strengths of Samples B to D are presumed 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 9, 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 3)
Next, a third embodiment of the present invention will be described. A series of tests were performed on the following A material, B material, and C 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 material for heat treatment, which is common to materials A to C. did. The manufacturing histories of the A material to the C material are as follows.
(A material: comparative example): Only normal quenching (without carbonitriding).
(B 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.
(C 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 10 and FIG. 13 as described above. The rolling fatigue life test results are shown in Table 11.

According to Table 11, the B material of the comparative example shows 3.1 times the L ₁₀ life of the A material which 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 C material of the present invention example has a long life of 1.74 times that of the B material and 5.4 times that of the A 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 12.

  The Charpy impact value of the B material (comparative example) subjected to carbonitriding was not higher than that of the normally quenched A material (comparative example), but the C material had the same value as the A material.

(3) Test of Static Fracture Toughness Value FIG. 14 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 (KIc value). The test results are shown in Table 13.
KI _c = (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 pre-crack depth is greater than the nitrogen-enriched layer depth, there is no difference between the A material and B material of the comparative example. However, the C 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 had the shape shown in FIG. 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 14.

  The B material subjected to the carbonitriding process has a slightly lower value than the A material subjected to normal quenching. However, the C material of the present invention has higher static crushing strength than the B material, and a level comparable to that of the A 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 15 together with the surface hardness and the amount of retained austenite (0.1 mm depth).

  It can be seen that the C material of the example of the present invention is suppressed to half or less compared to the dimensional change rate of the B 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 under the lubrication mixed with a foreign matter in which a predetermined amount of standard foreign matter was mixed was evaluated. The test conditions are shown in Table 16, and the test results are shown in Table 17.

  Compared to the A material, the B material subjected to the conventional carbonitriding treatment was about 2.5 times longer, and the C material of the example of the present invention had a long life of about 2.3 times. Although the C material of the present invention has less retained austenite than the B material of the comparative example, it has a substantially equivalent long life due to the intrusion of nitrogen and the influence of the refined microstructure.

  From the above results, the material C of the example of the present invention, that is, the bearing part produced by the heat treatment method of the present invention, has a long rolling fatigue life, which is difficult with the conventional carbonitriding process, and an 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. For example, the bearing is not limited to a full roller type needle bearing, and may be a ring-shaped sliding bearing. 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.

  By using the cam follower with a roller of the engine of the present invention and a steel member, the carbonitrided layer and the microstructure of the austenite grain size of the bearing parts that are refined in a range exceeding the particle size number of 10 are used. Fatigue life is greatly improved, and excellent crack strength and aging resistance can be obtained. Furthermore, by making both ends soft, it is possible to perform caulking molding, and the same effect can be obtained for a bearing including a member whose fracture strength or hydrogen content is in a range far from the conventional range. For this reason, it is expected to be widely used for parts in this field.

It is a figure which shows the cam follower with a roller of the engine in embodiment of this invention. It is sectional drawing which follows the II-II line in FIG. It is a figure which shows the cam follower with a roller of the engine in another embodiment of this invention. It is a figure which shows the cam follower with a roller of the engine in another embodiment of this invention. It is an enlarged view of the part of the full roller bearing which contacts the cam of the cam follower with a roller of the engine of FIG. It is a figure explaining the heat processing method in embodiment of this invention. It is a figure explaining the modification of the heat processing method in 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 hardness distribution at the time of softening the both ends of a roller shaft by high frequency heating. 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 End of cam follower body 2 Roller shaft (inner ring) 3 Roller (rolling element) 4 Roller (outer ring) 5 Cam follower shaft 6 Cam 7 Adjust screw 8 Lock nut 9 Valve 10 springs, 14 roller support parts, 15 pivots, 16 interlocking rods, 16a bearing mounting parts, 17 mounting members, 21 driving rolls, 22 guide rolls, 23 (3/4) "balls, 31 rolling fatigue life test pieces, 50 Cam follower body, 52 Roller shaft, 53 Rolling element, 54 Outer ring, 55, 56 Test machine member, T1 carbonitriding temperature, T2 quenching heating temperature.

Claims (1)

A roller in rolling contact with the engine cam;
A roller shaft located inside the roller and fixed to the cam follower body;
A method for producing a cam follower with a roller comprising a bearing interposed between the roller and a roller shaft,
After carbonitriding the steel at a carbonitriding temperature exceeding the A1 transformation point, cooling the steel to a temperature below the A1 transformation point, and then re-entering the quenching temperature range above the A1 transformation point and below the carbonitriding temperature. A method of manufacturing a cam follower with a roller, wherein at least one member of the roller, the roller shaft, and the bearing is manufactured by heating and quenching.

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