Patent Application
20090276992
The present invention relates to a method for manufacturing a raceway member, a method for manufacturing a valve train, and the raceway member, and more particularly, relates to a raceway member fixed to an adjoining member through plastic deformation of a part thereof, a method for manufacturing the raceway member, and a method for manufacturing a valve train provided with a cam follower having the raceway member.
Generally, a rolling bearing is provided with a raceway member such as an outer ring and an inner ring, and a rolling element such as a ball or a roller arranged in contact with the raceway member. The rolling bearing is used in such a manner that at least one of the raceway members, the inner ring and the outer ring may be fixed to some other member adjoining the raceway member. The raceway member is fixed by fitting the raceway member into the other adjoining member, or also by plastic deformation such as caulking of a partial region of the raceway member.
Such fixing of the raceway member utilizing plastic deformation is more advantageous than fixing by fitting, in that it is possible, for example, to reduce the cost and the size because no additional member for fixing is needed. On the other hand, in order to fix the raceway member utilizing plastic deformation, hardness distribution in the raceway member should be carefully considered. That is, when fixing utilizing plastic deformation is carried out, the region to be plastically deformed in the raceway member needs to have a relatively low hardness, for example, a hardness not greater than 300 HV, from a viewpoint of suppressing generation of a crack at the time of plastic deformation. On the contrary, a raceway surface, which is a surface in contact with the rolling element in the raceway member, needs to have a high hardness, for example, a hardness not smaller than 653 HV (58 HRC), from a viewpoint of ensuring a sufficient rolling contact fatigue life.
In recent years, fixing of the raceway member utilizing plastic deformation is widely employed because of the above-described advantages. For example, a full-complement roller type (without a cage) radial roller bearing, which is a kind of a rolling bearing, may be employed as a cam follower with roller for a valve train activating an air-intake valve or an exhaust valve for an engine. In mounting this cam follower with roller as well, it is possible to plastically deform a partial region of the raceway member constituting the cam follower and fix the region to a retaining member in order to mount the cam follower on the retaining member. Therefore, there have been many studies regarding the rolling bearing which can be used as a cam follower with roller, for improving the lifetime and the like (Japanese Patent Laying-Open No. 2000-38907 (Patent Document 1), Japanese Patent Laying-Open No. 10-47334 (Patent Document 2), Japanese Patent Laying-Open No. 10-103339 (Patent Document 3), Japanese Patent Laying-Open No. 10-110720 (Patent Document 4), Japanese Patent Laying-Open No. 2000-38906 (Patent Document 5), Japanese Patent Laying-Open No. 2000-205284 (Patent Document 6), Japanese Patent Laying-Open No. 2002-31212 (Patent Document 7), Japanese Utility Model Laying-Open No. 63-185917 (Patent Document 8), and Japanese Patent Laying-Open No. 2002-194438 (Patent Document 9)), as well as some proposals for improving the lifetime and fixing utilizing plastic deformation at the same time (Japanese Patent Laying-Open No. 5-321616 (Patent Document 10), Japanese Patent Laying-Open No. 62-7908 (Patent Document 11), and Japanese Patent Laying-Open No. 2005-299914 (Patent Document 12)).
As described above, in the raceway member fixed to some other member through plastic deformation of a partial region thereof, it is required that a region including a raceway surface has a sufficient hardness, and at the same time, a region to be plastically deformed has a hardness permitting plastic deformation without generating a crack and the like. As described in above Patent Documents 10-12, however, the hardness of the region to be plastically deformed is not fully controlled simply by not quench hardening the region to be plastically deformed. The hardness of the region to be plastically deformed then varies depending on the shape of the raceway member or quantity of the raceway members that are simultaneously heat-treated, and it is impossible to keep the hardness of the region in a preferable range in a stable manner. As a result, in the actual mass production process, fixing utilizing plastic deformation may be difficult. On the other hand, as described in Patent Document 12, the hardness of the region to be plastically deformed can be fully controlled if high temperature tempering is performed after quench hardening of the entire raceway member. In this case, however, heat treatment steps increase in number and the manufacturing cost of the raceway member rises.
Therefore, it is an object of the present invention to provide a method for manufacturing a raceway member, in which a hardness of a region to be plastically deformed is controllable in a stable manner and a sufficient rolling contact fatigue life is ensured by making a hardness of a region including a raceway surface sufficiently high, while suppressing increase in the manufacturing cost. Moreover, it is another object of the present invention to provide a method for manufacturing a valve train having sufficient durability, on which a cam follower is easily mounted utilizing plastic deformation, while suppressing increase in the manufacturing cost. Moreover, it is yet another object of the present invention to provide a raceway member, in which a hardness of a region to be plastically deformed is controlled in a stable manner, and a sufficient rolling contact fatigue life is ensured with a sufficiently high hardness of a region including a raceway surface, while suppressing increase in the manufacturing cost.
A method for manufacturing a raceway member according to the present invention includes: a steel member preparation step of preparing a steel member which is a member formed of steel and generally shaped into a raceway member, a heat treatment step of heat-treating the steel member, and a finishing step of finishing the steel member heat-treated in the heat treatment step. The heat treatment step includes a carbonitriding step, a temperature holding step, and a induction hardening step. In the carbonitriding step, the steel member is heated to a carbonitriding temperature, which is a temperature not lower than A1 point, and carbonitrided. In the temperature holding step, the steel member carbonitrided in the carbonitriding step is cooled from the carbonitriding temperature to a temperature range between not lower than a temperature 100° C. below A1 point and lower than A1 point, and is held in the temperature range for not less than 60 minutes and not more than 180 minutes. In the induction hardening step, following the temperature holding step, a high hardness region in the steel member including a region to become a raceway surface of the raceway member is induction hardened, without quench hardening of a low hardness region which is a region other than the high hardness region.
Generally, the steel member is cooled continuously in the case where the carbonitrided steel member is not quench hardened immediately. In that case, however, even when the same heat treatment facility is used, the cooling rate of the steel member varies depending on the shape and the size of the steel member and the amount of the other steel members that are simultaneously treated together, and the like. Moreover, depending on a shape of the steel member, the cooling rate may be different from part to part of the steel member.
In the case where the steel member heated to the temperature not lower than A1 point is cooled without being quench hardened, the structure of steel forming the steel member basically transforms into pearlite. Here the hardness of the steel member can be suppressed, for example, to a hardness not greater than 300 HV by aggregation and coarsening of iron carbide (cementite; Fe3C; referred to as carbide hereinafter) constituting the pearlite structure (a steel structure consisting of a ferrite phase, which is alpha iron, and iron carbide). In order to aggregate and coarsen carbide, it is effective here to set the cooling rate (temperature lowering per unit time) low in cooling the steel member.
Considering the variation of the cooling rate resulting from the shape of the steel member and the like and difference in cooling rates from part to part of the steel member as described above, however, it is not easy to control the hardness of the region to be plastically deformed in the raceway member in a stable manner, since the required cooling condition varies depending on the shape of the steel member and the like. In addition, although the hardness of the region to be plastically deformed can be suppressed in a stable manner if the cooling rate is lowered without limitation, production efficiency lowers and the manufacturing cost increases because heat treatment requires a longer time.
On the contrary, the inventors examined a heat treatment history in detail, for making the hardness of the carbonitrided steel member stable regardless of the shape and the size of the steel member and the amount of the other steel members that are simultaneously treated together and the like. As a result, the following knowledge was acquired.
That is, when the carbonitrided steel member is cooled to a temperature lower than A1 point, coarsening and aggregation of carbide is not sufficient in the case where the steel member is cooled to a temperature range below the temperature lower by 100° C. than A1 point in a short period of time, and it may be difficult to plastically deform the steel member without generating a crack depending on shape and the like of the steel member. Moreover, in a case where the steel member is held in the temperature range between not lower than a temperature 100° C. below A1 point and lower than A1 point for less than 60 minutes, pearlite transformation of steel is not completed, and fine carbide and/or layered carbide may precipitate in steel and the hardness is increased, depending on the subsequent cooling rate, and plastic deformation is difficult without generating a crack. In that temperature range, on the other hand, pearlite transformation of steel is mostly completed within 180 minutes and plastic deformation is possible without generating a crack regardless of the subsequent cooling rate. Therefore, holding the steel member in that temperature range for more than 180 minutes is less advantageous, and rather results in reducing production efficiency of the raceway member.
As described above, according to the method for manufacturing the raceway member of the present invention, in the temperature holding step, the steel member carbonitrided in the carbonitriding step of the heat treatment step is cooled to the temperature range between not lower than a temperature 100° C. below A1 point and lower than A1 point, and is held in the range for not less than 60 minutes and not more than 180 minutes. Therefore, the steel member is held in an appropriate temperature range for a necessary and sufficient period of time, steel forming the steel member undergoes pearlite transformation by isothermal transformation or in a condition that the cooling rate is very low, and carbide is coarsened and aggregated at the time when the transformation is mostly completed. As a result, the steel member has the hardness allowing plastic deformation without generating a crack, in a stable manner. Then, in the induction hardening step, the high hardness region including the region to become a raceway surface of the raceway member is induction hardened and partially hardened, so that easy plastic working of the region which is not quench hardened and the rolling contact fatigue life in the raceway surface of the raceway member are obtained at the same time. As a result, according to the method for manufacturing the raceway member of the present invention, the hardness of the region to be plastically deformed can be controlled in a stable manner, and a sufficient rolling contact fatigue life is ensured by making the hardness of the region including the raceway surface sufficiently high, while increase in the manufacturing cost is suppressed.
A method for manufacturing a valve train according to the present invention is a method for manufacturing a valve train having a cam follower and a retaining member retaining the cam follower, and activating at least any one of an air-intake valve and an exhaust valve of an engine. The method for manufacturing the valve train includes a cam follower manufacturing step of manufacturing a cam follower, a retaining member manufacturing step of preparing a retaining member, and a mounting step of mounting the cam follower on the retaining member. In the cam follower manufacturing step, the raceway member constituting the cam follower is manufactured by the above-described method for manufacturing the raceway member. In the mounting step, the raceway member is fixed to the retaining member through plastic working of a low hardness region, whereby the cam follower is mounted on the retaining member.
According to the method for manufacturing the valve train of the present invention, since the raceway member constituting the cam follower is manufactured by the above-described method for manufacturing the raceway member, the hardness of the region to be plastically deformed can be controlled in a stable manner, and a sufficient rolling contact fatigue life can be ensured by making the hardness of the region including the raceway surface sufficiently high, while increase in the manufacturing cost of the raceway member is suppressed. The raceway member is fixed to the retaining member through plastic working of the low hardness region of the raceway member whose hardness is controlled in a stable manner, and the cam follower is mounted on the retaining member. Therefore, a method for manufacturing a valve train having sufficient durability, resulting from a sufficient rolling contact fatigue life of the raceway member, on which a cam follower is easily mounted utilizing plastic deformation, can be provided, while increase in the manufacturing cost is suppressed.
The raceway member according to the present invention is manufactured by the above-described method for manufacturing the raceway member. According to the raceway member of the present invention, because the raceway member is manufactured by the above-described method for manufacturing the raceway member of the present invention, a raceway member can be provided, in which the hardness of the region to be plastically deformed is controlled in a stable manner and a sufficient rolling contact fatigue life is ensured with a sufficiently high hardness of a region including a raceway surface, while increase in the manufacturing cost is suppressed.
According to the method for manufacturing the raceway member of the present invention, as clarified from the above description, the method for manufacturing the raceway member can be provided, in which the hardness of the region to be plastically deformed is controllable in a stable manner and a sufficient rolling contact fatigue life is ensured by making the hardness of the region including the raceway surface sufficiently high, while increase in the manufacturing cost is suppressed. Moreover, according to the method for manufacturing the valve train of the present invention, a method for manufacturing a valve train having sufficient durability, on which a cam follower is easily mounted utilizing plastic deformation, can be provided, while increase in the manufacturing cost is suppressed. Moreover, according to the raceway member of the present invention, a raceway member can be provided, in which the hardness of the region to be plastically deformed is controlled in a stable manner, and a sufficient rolling contact fatigue life is ensured with a sufficiently high hardness of a region including a raceway surface, while increase in the manufacturing cost is suppressed.
1 cam follower, 2 rocker arm, 2B one end, 2C other end, 2D through hole, 3 rocker arm shaft, 4 bearing metal, 5 cam, 5A cam shaft, 5B outer circumferential surface, 6 valve, 7 spring, 8 lock nut, 9 adjustment screw, 10 valve train, 11 roller, 11A roller raceway surface, 12 shaft, 12A shaft raceway surface, 12B high hardness region, 12C low hardness region, 13 roller, 13A roller rolling contact surface, 21 side wall, 21A through hole, 21B tapered portion, 22 pivot abutting portion, 30 shaft of cam follower, 31 raceway surface, 32 high hardness region, 40 rolling contact fatigue life tester, 41 rotation shaft, 42 driving roller, 42A outer circumferential surface, 43 outer ring, 44 roller, 45 bearing, 80 adjustment screw, 81 joint member, 82 lock nut, 90 push rod.
Embodiments of the present invention will be described hereinafter with reference to the drawings. Note that, in the following drawings, the same or corresponding elements have the same reference characters allotted and description thereof will not be repeated.
First, with reference to
Referring to
Cam follower 1 includes annular roller 11 as an outer ring, a hollow cylindrical shaft 12 penetrating roller 11, and a plurality of rollers 13 arranged between roller 11 and shaft 12. Rocker arm 2 is held at the central portion by a rocker arm shaft 3 with a bearing metal 4 and the like being interposed and pivotable around rocker arm shaft 3. Valve 6 is biased by elastic force of a spring 7 to the direction of an arrow 7A. Therefore, cam follower 1 is always pressed against outer circumferential surface 5B of cam 5 by elastic force of spring 7 with adjustment screw 9 and rocker arm 2. Cam 5 has an egg-like cross-sectional shape in a cross section perpendicular to an axial direction of shaft 12 which is an inner ring of cam follower 1. Cam 5 is formed integrally with cam shaft 5A and configured to be rotatable around cam shaft 5A.
With reference to
Furthermore, with reference to
Although a case with hollow shaft 12 employed for reducing the weight is shown in
Now the operation of valve train 10 in the first embodiment is described. With reference to
Now a method for manufacturing shaft 12 of cam follower 1 as a raceway member and valve train 10 in the first embodiment is described.
With reference to
Next, a heat treatment step is performed, in which the steel member prepared in the steel member preparation step is heat-treated. The heat treatment step includes a carbonitriding step, a temperature holding step, a induction hardening step, and a tempering step. The detail of this heat treatment step will be described later.
A finishing step is then performed, in which the steel member heat-treated in the heat treatment step is finished. Specifically, shaft 12 of cam follower 1 is completed by finishing, such as grinding and super-finishing, of the steel member for which the heat treatment has been completed.
Details of the heat treatment step included in the method for manufacturing the shaft of the cam follower according to the first embodiment are now described. In
In the heat treatment step, with reference to
The temperature holding step is then performed, in which the steel member carbonitrided in the carbonitriding step is cooled from the carbonitriding temperature to a temperature range between not lower than a temperature 100° C. below A1 point and lower than A1 point and is held in the temperature range for not less than 60 minutes and not more than 180 minutes.
At this time, steel forming the steel member starts pearlite transformation by being cooled to a temperature lower than A1 transformation point. Pearlite transformation proceeds as time passes, even if the temperature is not lowered. Therefore, the transformation of steel forming the steel member is mostly completed by being held in the above temperature range for not less than 60 minutes and not more than 180 minutes as described above, while the condition of isothermal transformation or such a condition that the cooling rate is very low is maintained. As a result, carbide in steel is sufficiently coarsened and aggregated, and the hardness is suppressed.
Moreover, it is possible to coarsen and aggregate carbide in a constant condition regardless of the shape and the size of the steel member and the amount of the other steel members that are simultaneously treated together, because the temperature of the steel member is held in the above temperature range during the period when pearlite transformation proceeds. Furthermore, it is possible to coarsen and aggregate carbide in a constant condition regardless of the part of the steel member because the cooling rate does not vary greatly from part to part. As a result, the hardness of low hardness region 12C of shaft 12 can be controlled in a stable manner, and shaft 12 having low hardness region 12C allowing plastic working without generating a crack can be manufactured in a stable manner. In addition, since the heat treatment step can be more simplified than the conventional step of performing quenching and high temperature tempering after carbonitriding, increase in the manufacturing cost can be suppressed.
As for the temperature at which the steel member should be held in the temperature holding step, a temperature not lower than 650° C. and not higher than 720° C. is specifically preferable, from the viewpoint of sufficiently proceeding with coarsening and aggregation of carbide. In more detail, the preferable temperature at which the steel member is held more or less varies depending on the kind of steel the steel member is formed of For example, a temperature not lower than 650° C. and not higher than 700° C. is preferable for JIS SUJ2, and a temperature not lower than 670° C. and not higher than 700° C. is preferable for SCM 420. Additionally, as for the period of time during which the steel member is held in the above-described temperature range in the temperature holding step, it is preferable to set the time duration to not less than 60 minutes and not more than 120 minutes, from the viewpoint of achieving improvement in production efficiency, sufficient progress of pearlite transformation and suppression of variation of the cooling rate, at the same time.
Next with reference to
Next, for the steel member, a induction hardening step is performed, in which high hardness region 12B including a region to become shaft raceway surface 12A of shaft 12 as the raceway member is induction hardened without quench hardening of low hardness region 12C (both ends) which is a region other than high hardness region 12B. Specifically, the steel member is set in a induction hardening apparatus such that a surface of high hardness region 12B is opposite to an induction coil, and high hardness region 12B is induction-heated to a temperature not lower than 800° C. and not higher than 1000° C., which is a temperature not lower than A1 point such as 900° C., by feeding high frequency current to the induction coil. Then the steel member is rapidly cooled, for example, by oil cooling or water cooling from the temperature range not lower than A1 point to a temperature lower than Ms point. High hardness region 12B is thereby quench hardened without quench hardening of low hardness region 12C. Now the surface part of the steel member including high hardness region 12B has been carbonitrided in the carbonitriding step. Therefore, by induction hardening high hardness region 12B in the induction hardening step, shaft raceway surface 12A is turned into a region with high resistance to rolling contact fatigue, and shaft 12 can be provided with an excellent rolling contact fatigue life property.
Moreover, the surface part directly under shaft raceway surface 12A comes to have a steel structure containing retained austenite of not less than 10 volume % and not more than 50 volume %, or not less than 15 volume % and not more than 35 volume %, which is a more preferable range, with austenite grain size being not smaller than No. 11 (the grain size number of prior austenite grain; JIS G 0551), by being induction hardened after being carbonitrided. Therefore, the rolling contact fatigue life property of shaft 12 is further improved. Note that a surface part means a region whose distance from the raceway surface is within 0.2 mm.
Here the above induction heating in the induction hardening step is implemented here by Joule's heat resulting from eddy current generated inside shaft 12 which is a workpiece, and the heat equivalent to work with hysteresis loss, and thus it is possible to heat only a desired part of shaft 12 locally by controlling the frequency of the high frequency current fed to the induction coil, the output of the power source, the heating time, and the like. Therefore, high hardness region 122B can be easily quench hardened without quench hardening of low hardness region 12C.
Next with reference to
According to the method for manufacturing shaft 12 as a raceway member in the above first embodiment, it is possible to make the hardness of high hardness region 12B including carbonitrided raceway surface 12A sufficiently high and to provide raceway surface 12A with a sufficient rolling contact fatigue life property, while suppressing increase in the manufacturing cost. It is also possible to make both ends of shaft 12 (low hardness region 12C) plastically deformable while avoiding generation of a crack, by controlling and suppressing the hardness of low hardness region 12C, that is both ends of shaft 12, in a stable manner, and to manufacture shaft 12 which is easily fixed through plastic deformation
Shaft 12 as a raceway member in the first embodiment of the present invention manufactured by the method for manufacturing the raceway member according to the above first embodiment serves as a raceway member with the hardness of the region including a raceway surface being sufficiently high to ensure a sufficient rolling contact fatigue life, and with the hardness of the region to be plastically deformed being controlled in a stable manner, while increase in the manufacturing cost is suppressed.
A1 point here means a point corresponding to a temperature where a steel structure starts transformation from ferrite to austenite when steel is heated, while Ms point means a point corresponding to a temperature where steel transformed into austenite starts transformation to martensite, when the steel is cooled.
A method for manufacturing valve train 10 according to the first embodiment will be described hereinafter. With reference to
In the cam follower manufacturing step here, shaft 12 as a raceway member constituting cam follower 1 is manufactured by the method for manufacturing the raceway member according to the above-described first embodiment.
Moreover, in the mounting step, with reference to
In the method for manufacturing valve train 10 according to the first embodiment, shaft 12 is manufactured by the above-described manufacturing method of the raceway member according to the first embodiment, shaft 12 is fixed to rocker arm 2 by being caulked, and cam follower 1 is mounted on rocker arm 2. Therefore, in the method for manufacturing valve train 10 according to the first embodiment, a method for manufacturing valve train 10 having sufficient durability because shaft 12 as a raceway member has a sufficient rolling contact fatigue life, on which a cam follower is easily mounted utilizing plastic deformation, can be provided, while increase in the manufacturing cost is suppressed.
Next with reference to
With reference to
That is, in valve train 10 according to the second embodiment, a pivot abutting portion 22, to which a not-shown pivot abuts is formed at one end 2B of rocker arm 2. Rocker arm 2 is then held rotatably with pivot abutting portion 22 serving as a fulcrum.
When cam 5 rotates together with cam shaft 5A around cam shaft 5A, the distance from cam shaft 5A to the contact portion of cam 5 and cam follower 1 changes periodically. Therefore, rocker arm 2 swings with pivot abutting portion 22 serving as a fulcrum. As a result, valve 6 reciprocates, and the air-intake valve or the exhaust valve of the engine opens and closes.
Note that shaft 12 as a raceway member and valve train 10 in the second embodiment have, basically the same configuration as shaft 12 and valve train 10 in the first embodiment as described above, and can be manufactured by a similar manufacturing method.
Next with reference to
With reference to
That is, push rod 90 having a bar shape is connected to one end 2B of rocker arm 2 with an adjustment screw 80 fixed to rocker arm 2 with a lock nut 82 and a joint member 81. On push rod 90 as a retaining member, cam follower 1 is mounted on an end which is opposite to the end to which rocker arm 2 is connected. Cam 5 is arranged in contact with the outer circumferential surface of roller 11 of cam follower 1 on outer circumferential surface 5B.
When cam 5 rotates together with cam shaft 5A around cam shaft 5A, the distance from cam shaft 5A to the contact portion of cam 5 and cam follower 1 changes periodically. Therefore, one end 2B of rocker arm 2 is pushed by push rod 90 and rocker arm 2 swings with rocker arm shaft 3 serving as a fulcrum. As a result, valve 6 reciprocates and the air-intake valve or the exhaust valve of the engine opens and closes.
Note that shaft 12 as a raceway member and valve train 10 in the third embodiment have basically the same configuration as shaft 12 and valve train 10 in the first embodiment as described above, and can be manufactured by a similar manufacturing method.
Example 1 of the present invention will be described hereinafter. The property of the raceway member manufactured by the method for manufacturing the raceway member according to the present invention was tested for evaluation. The procedure of the test was as follows.
First of all, the method for fabricating a test sample to be tested will be described. As an example of the present invention, a solid, columnar test sample (a shaft of a cam follower) with the outer diameter of 14.6 mm and the length of 17.3 mm was fabricated, by employing JIS SUJ2 bearing steel as a raw material, with a manufacturing method similar to the manufacturing method of shaft 12 as a raceway member in the first embodiment described based on
On the other hand, test samples as comparative examples outside the scope of the present invention (comparative examples A and B) were also fabricated, for which only the induction hardening step and the tempering step were performed, with the carbonitriding step and the temperature holding step of the heat treatment step being omitted, in the steps similar to the above-described steps for the test samples.
Next, the method for property evaluation will be described. The hardness of the outer circumferential surface, the amount of retained austenite on the raceway surface and the austenite grain size number of the above-described test sample were investigated. With reference to
The amount of retained austenite on raceway surface 31 was calculated by measuring diffraction intensity of martensite a (211) plane and austenite y (220) plane of raceway surface 31, using an X-ray diffraction meter (XRD). Moreover, the austenite grain size number was measured based on the measuring method of the grain size number of prior austenite grain described in JIS G 0551.
Table 1 shows the result of the property evaluation. With reference to Table 1, in examples A and B which were fabricated according to the method for manufacturing the example of the present invention, the hardness at measurement locations A and B, which were included in raceway surface 31 was 790-805 HV, in which improvement in a rolling contact fatigue life could be expected. Moreover, the hardness at measurement locations C and D in a region other than raceway surface 31 was 220-235 HV, which was not greater than 300 HV in the hardness range allowing plastic working such as caulking without generating a crack.
On the other hand, in comparative examples A and B fabricated by the conventional manufacturing method outside the scope of the present invention, the hardness at measurement locations A and B included in raceway surface 31 was 735-780 HV. It is contemplated that the hardness was lower than in examples A and B because the test sample in comparative examples A and B was not carbonitrided. Moreover, the hardness at measurement locations C and D in a region other than raceway surface 31 was 200-220 HV.
Moreover, in examples A and B, the amount of retained austenite on raceway surface 31 was 31.5-32.5 volume %. This is included in a preferable range of not less than 10 volume % and not more than 50 volume %, and in a more preferable range of not less than 15 volume % and not more than 35 volume %, for achieving both improvement in the rolling contact fatigue life, particularly the rolling contact fatigue life in a contaminated environment and the like where hard foreign substances are mixed into a lubricant and dimensional stability at the same time.
On the other hand, in comparative examples A and B, the amount of retained austenite on raceway surface 31 was 7.5-8.5 volume %. It is contemplated that the amount of retained austenite was lower than in examples A and B because the test sample in comparative examples A and B was not carbonitrided. As a result, the amount of retained austenite in comparative examples A and B was out of the preferable range, which was not less than 10 volume % and not more than 50 volume %, for achieving both improvement in the rolling contact fatigue life, particularly the rolling contact fatigue life in a contaminated environment and the like with foreign substances mixed in, and dimensional stability at the same time.
Moreover, in examples A and B, the grain size number of austenite grains on raceway surface 31 was 12, which was in a preferable range not smaller than 11, for improving the rolling contact fatigue life, toughness, and the like.
On the other hand, in comparative examples A and B, the grain size number of austenite grains on raceway surface 31 was 10.5-11. It is contemplated that the grain size number was smaller (prior austenite grain was greater) than in examples A and B because the test sample in comparative examples A and B was not carbonitrided and number density of carbide serving as a site where austenite grain is formed in induction hardening was smaller than number density in examples A and B.
As described above, the raceway member fabricated by the method for manufacturing the raceway member according to the present invention had a higher hardness and a greater austenitic grain size number on the raceway surface than the conventional raceway member, the amount of retained austenite was in the preferable range, and a region of which plastic working was easy was formed therein. Therefore, it was ensured that the raceway member fabricated by the method for manufacturing the raceway member according to the present invention had an excellent rolling contact fatigue life on the raceway surface and it was easy to fix the raceway member utilizing plastic working such as caulking.
Example 2 of the present invention will be described hereinafter. The rolling contact fatigue life of the raceway member manufactured by the method for manufacturing the raceway member according to the present invention was tested for investigation. The procedure of the test was as follows.
The rolling contact fatigue life test for an outer-ring rotation type was conducted with the shaft of the cam follower fabricated as the test sample shown in
With reference to
An annular, outer ring 43 is arranged such that its outer circumferential surface comes in contact with an outer circumferential surface 42A of the driving roller, and a plurality of rollers 44 are arranged such that their outer circumferential surfaces come in contact with an inner circumferential surface of outer ring 43. Furthermore, with reference to
When rotating shaft 41 rotates around the axis using the not-shown source of power, driving roller 42 rotates together with rotating shaft 41. Outer ring 43 then rotates, by being driven by driving roller 42. As a result, roller 44 rolls on raceway surface 31 of fixed shaft 30 of the cam follower. Now the test was performed under the condition that the load imposed on shaft 30 of the cam follower was set to 2200 N, the revolution rate of outer ring 43 was set to 7000 rpm, an engine oil was employed as the lubricant oil (SAE viscosity grades: 10W-30), and the oil temperature was set to 100° C. According to this condition, either surface damage or internally originating flaking occurs during the test. Therefore, a lifetime can be checked through the test for both surface damage and internally originating flaking. The period of time before flaking occurred at shaft 30 of the cam follower (rolling contact fatigue life) was investigated. Furthermore, the rolling contact fatigue life obtained as a result of the experiment was analyzed statistically, and the period of time before flaking occurred in 10% of the test samples (L10 lifetime) was calculated. Table 2 shows the test results.
In Table 2, the lifetime ratio of each test sample is shown assuming that the L10 lifetime of comparative example A as 1. With reference to Table 2, the shaft of the cam follower of examples A and B, which are the examples of the present invention, has a rolling contact fatigue life about three times longer than the rolling contact fatigue life of comparative examples A and B with the conventional shaft of the cam follower. It is contemplated that this is because carbonitriding treatment is performed for examples A and B as described above, whereby the austenite grain size was small and the amount of retained austenite was within the preferable range.
It was confirmed, based on the result of above Examples 1 and 2, that, according to the method for manufacturing the raceway member of the present invention, it was possible to allow the material of the region including the raceway surface to have a sufficiently high hardness and to be highly resistant to the rolling contact fatigue, by carbonitriding and induction hardening, and to control and suppress the hardness of a region other than the raceway surface in a stable manner, and a raceway member which was easily fixed utilizing plastic deformation could be manufactured, while suppressing increase in the manufacturing cost by not increasing the heat treatment steps in number.
The embodiments and examples disclosed herein are by way of example in all respects and should not be interpreted as restrictive. The scope of the present invention is determined not by the above description but by the appended claims, and intended to include all the modifications within the meaning and the scope equivalent to those of the claims.
The raceway member and the method for manufacturing the raceway member of the present invention can be applied particularly advantageously to the raceway member which is fixed to the adjoining member through plastic deformation of a part thereof, and to the manufacturing method. Moreover, the method for manufacturing the valve train of the present invention can be applied particularly advantageously to the manufacturing method of the valve train provided with the cam follower having the raceway member fixed to the adjoining member through plastic deformation of a part thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-192994 | Jul 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/061698 | 6/11/2007 | WO | 00 | 1/12/2009 |
