JP2763931B2 - Tappet manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for manufacturing a tappet used for manufacturing a tappet constituting a valve train of an engine. 2. Description of the Related Art Various structures are employed in a valve train of an engine. For example, a camshaft is rotated in synchronization with the rotation of a crankshaft of the engine, and the tappet is rotated by the rotation of the camshaft. There is a structure in which the engine valve is reciprocated through a plunger end of a hydraulic mechanism portion of the tappet. FIG. 10 partially shows an example of a valve train of an engine, and shows a valve train using a hydraulic tappet. In FIG. 10, reference numeral 11 denotes a camshaft in which a plurality of cams 11b are formed in the middle of a shaft 11a, and reference numeral 12 denotes a tappet crown surface 12a, a tappet shaft portion 12b, and a plunger end 12c of a tappet hydraulic mechanism, which come into contact with the cam 11b. Tappets, 13
Is a tappet guide, and 14 is an engine valve (stem). In such a valve operating mechanism, the power transmission at the time of opening and closing the valve is such that the rotation of the camshaft 11 is transmitted from the cam 11b to the tappet crown surface 12a, and the engine valve (stem) is transmitted through the plunger end 12c of the tappet hydraulic mechanism. It goes to 14. In this case, the cam 11b of the camshaft 11 usually has
An inclination angle α of about ７7 ′ is provided, and is in contact with the tappet crown surface 12a that has been subjected to spherical finishing. Therefore, the contact position A between the inclined cam 11b and the spherical tappet spherical surface 12a is offset by an offset amount D with respect to the tappet center C, and the tappet 12 rotates with the rotation of the camshaft 11, and the tappet 12 rotates. The wear of the crown surface 12a is made uniform. Conventionally, when manufacturing such a tappet 12,
The tappet material is subjected to cold forging and machining to form a tappet coarse material having a tappet shape. The tappet coarse material is subjected to high-concentration carburizing or carbonitriding treatment and quenching and tempering treatment, and the tappet shaft portion is formed. After finishing the inner and outer surfaces of 12b, the spherical surface of the tappet crown surface 12a is polished, and the hydraulic tappet hydraulic mechanism is assembled together with the plunger end 12c to form a hydraulic tappet. In addition, in many cases, the surface finish polishing is not performed on the tappet crown surface 12a but the surface finish polishing is performed, but in this case, the degree of the material used is more excellent in consideration of the disadvantage of wear due to not rotating. It is common to do. (Problems to be Solved by the Invention) However, in such a conventional method for manufacturing a tappet, a spherical finish polishing for making the tappet crown surface spherical is performed, and in the case where the spherical surface is not made spherical. Even if there is a surface finish polishing, distortion during heat treatment is also added, and at least about 30 μm will be scraped off by the polishing allowance, carbon diffused from the surface and carbide with excellent wear resistance Since the layer was scraped off, it was inevitable that the tappet had a reduced abrasion resistance. Therefore, when using under high surface pressure,
There is a problem that scuffing wear and pitching wear are likely to occur. Further, in terms of manufacturing, spherical finish polishing and flat finish polishing have a problem that the cost is increased because a hard layer on which carbides are precipitated is polished. (Object of the Invention) The present invention has been made in view of such conventional problems, and utilizes a large amount of carbide precipitation layer on a tappet crown surface formed by high concentration carburizing or carbonitriding. It is formed by heat treatment, while reducing the occurrence of scuffing wear and pitting wear as superior wear resistance, avoiding a decrease in wear resistance and increasing costs due to performing spherical finish polishing or flat surface finish polishing. The contact position with the other cam is offset with respect to the center of the tappet by making contact with the other cam at the convex shape portion of the tappet crown surface, and wear of the tappet crown surface is caused by causing the tappet to rotate with the rotation of the cam. To be able to average and at the same time to make the lubrication oil circulation more sufficient It is an object of the present invention to provide a method for manufacturing a tappet, which can manufacture a tappet having a reduced thickness.

Configuration of the Invention

(Means for Solving the Problems) According to a method for manufacturing a tappet according to the present invention, a high-concentration carburizing or carbonitriding treatment is performed on a tappet rough material having a tappet shape to reduce the amount of precipitated carbide on the tappet crown surface by 30%. More preferably, the amount of precipitated carbides is set to 38% or more and the amount of precipitated carbides is gradually reduced from the tappet crown surface toward the inside, and the amount of precipitated carbides on the tappet crown surface is maintained without performing the surface polishing and the spherical polishing of the tappet crown surface. The method of manufacturing such a tappet is characterized in that it is formed on the abrasion-resistant tappet crown surface and that a convex portion is formed by heat treatment to offset a contact position with a mating cam from the tappet center. Is a means for solving the above-mentioned conventional problem. The tappet manufactured by the tappet manufacturing method according to the present invention includes a mushroom type, a cap type, and the like, but is not particularly limited, and a tappet applied to a hydraulic tappet structure is naturally manufactured. included. As the material of the tappet used in the tappet manufacturing method according to the present invention, a material suitable for high-concentration carburizing or carbonitriding treatment is used. For example, chromium steel (SCr), chromium molybdenum steel (SCM) bearing steel (SUJ) ) Etc. are used. Then, using such tappet material, a tappet-shaped rough material is formed by appropriate processing means such as cold forging, cutting, and finishing. For high concentration carburizing or carbonitriding, methane (CH ₄ ), propane (C ₃ H ₈ ), butane (C
₄ H ₁₀₎ those using an endothermic type gas as such or ammonia (such as to perform a nitriding process using NH _3), etc. may be employed as the enriched gas after carburization. By performing such carburizing or carbonitriding treatment, the amount of precipitated carbide on the tappet crown surface is reduced by 30%.
% Or more, preferably 38% or more, and the amount of precipitated carbide is gradually reduced from the tappet crown surface toward the inside. In this case, if the amount of the precipitated carbide on the tappet crown surface is less than 30%, the wear resistance becomes insufficient, and scuffing wear and pitting wear are generated, which is not preferable. Thus, while precipitating carbide on the tappet crown surface and assuming that the amount of precipitated carbide gradually decreases from the tappet crown surface toward the inside, the amount of precipitated carbide on the tappet crown surface is reduced without performing flat polishing and spherical polishing on the tappet crown surface. Formed on the crown surface of the tappet with excellent abrasion resistance maintained. At the same time, a convex portion for offsetting the contact position with the mating cam from the center of the tappet is intentionally formed by heat treatment. The convex portion in this case is formed after the heat treatment by combining the shape, thickness, heat treatment conditions, and the like of the rough tappet material after the mechanical processing and before the heat treatment. It was found that the cooling rate during quenching was greatly affected by the heating rate and the carburizing time during the quenching, but not so much. (Effect of the Invention) Since the tappet manufacturing method according to the present invention has the above-described configuration, the high-concentration carbide precipitation layer formed on the tappet crown surface by high-concentration carburizing or carbonitriding treatment is utilized as it is. Since the tappet crown surface has less scuffing wear and pitching wear, and the convex portion formed by the heat treatment comes into contact with the mating cam, the contact position with the mating cam is offset with respect to the tappet center. The tappet rotates with the rotation, the lubricating oil's throwing power becomes even better, the contact area increases, and the wear resistance improves,
Even if normal abrasion occurs, there is an effect that the abrasion on the tappet crown surface is averaged. (Example) Example 1 In Example 1, as a mushroom-type hydraulic tappet material, 0.17 wt% C-0.5 wt% Si-2.2 wt% Cr
A chromium-molybdenum case hardening steel wire having a composition of -0.4% by weight of Mo and the balance of Fe was used. Then, the tappet material was subjected to cold forging and machining to produce a tappet coarse material (see FIG. 1) having a tappet shape. At this time, the roughness of the tappet crown surface was set to within 0.2a. Next, when performing high-concentration carburizing treatment on the tappet coarse material, 850 to 9 to avoid coarsening of precipitated carbides.
Performed at 00 ° C. In addition, butane (C ₄
Using endothermic gas to H ₁₀₎ as a raw material, butane (C ₄ H ₁₀₎
After carburizing at the carbon potential (1.4 wt% C) of the sooting generation limit due to the enrichment of
A quenching treatment of heating to 20 ° C. followed by oil cooling and a tempering treatment of heating to 160 ° C. followed by cooling were performed. Next, after performing a heat treatment including such a surface hardening treatment and a refining treatment, the inside and outside of the tappet shaft portion are machined, thereby forming a mushroom type for a hydraulic tappet as partially shown in FIG. I got a tappet. As shown in FIG. 1, the tappet 1 is formed near the peripheral portion of the tappet crown surface 1a after the surface hardening treatment and the tempering treatment by combining the shape, thickness, heat treatment conditions, and the like of the tappet coarse material. It has a convex portion 1b formed, a convex portion 1c formed at the center of the tappet crown 1a, and further has a tappet shaft 1d continuous with the tappet crown 1a. In the tappet 1 shown in FIG. 1, the contact position A between the inclined cam 2a of the camshaft 2 and the convex portion 1b near the peripheral portion is offset by an offset amount D with respect to the tappet center C. The tappet 1 rotates on its own axis with the rotation of the camshaft 2 so that the lubricating oil can easily move around and the wear of the tappet crown surface 1a can be averaged. I have. Next, tappet crown surface of tappet 1 thus obtained
Examination of the structure in 1a showed the results shown in FIG. As shown in FIG. 2, the amount of precipitated carbide on the surface was 30
7070%, the average is about 50%, and the amount of the precipitated carbide is gradually reduced toward the inside. The extent is about 20% in the portion where the conventional spherical polishing allowance (at least about 30 μm) is included. %. In addition, when the hardness distribution was examined, the results are shown in FIG. 3, and the hardness of the outermost surface was about Hv800. Further, the height of the convex portion 1b formed in the vicinity of the peripheral portion of the tappet crown 1a by the heat treatment has a maximum of 9 μm and a minimum of 5 μm.
μm, and the height of the convex portion 1c formed at the center of the tappet crown surface 1a is a maximum of 12 μm and a minimum of 7 μm, and the cam 2a is inclined at an inclination angle α = 2 to 7 ′. The offset amount D with respect to the tappet center C at the contact position A was 9.8 mm, and the tappet 1 was easy to rotate with the rotation of the cam 2a. Furthermore, the minimum radius of curvature of the convex portions 1b and 1c was 500 mm, and the surface pressure difference was not so large as compared with the conventional spherically polished one. Further, after assembling the tappet 1 together with the internal hydraulic mechanism parts, the tappet 1 was attached to the engine, and the scuffing wear and the pitching wear in the convex portion 1b of the tappet crown surface 1a were examined. The results shown in FIGS. 4 and 5, respectively. Met. Of these, the scuffing wear amount shown in FIG. 4 shows the results when the engine speed was 4000 rpm, the load surface pressure was 110 kgf / mm ² , and the durability time was 80 H. The mark ○ indicates the case where a 30 μm deep grinder was polished, the mark indicates the case where a lapping was performed, ●
Indicates a case where polishing was not performed. In addition, the pitching wear amount shown in FIG.
It shows the results when the test was performed under the conditions of load surface pressure: 110 kgf / mm ² and durability time: 80H. As shown in FIG. 4 and FIG.
%, And no finish polishing is performed at all, and the tappet wrapped to the extent that sooting on the surface is removed has extremely excellent wear resistance. As shown in FIG. 4, the scuffing wear amount is small. The average was very slight, about 2 μm, and as shown in FIG. 5, pitting wear did not substantially occur. On the other hand, a tappet having an amount of precipitated carbide of 50% and having not polished the surface showed normal wear of about 3.6 μm on average and no pitting wear. As described above, in the tappet according to the present invention, the scuffing wear is smaller than that obtained by the conventional polishing, and the amount of surface carbide is preferably 30% or more, preferably.
It is clear that when the content is 38% or more, both the scuffing wear amount shown in FIG. 4 and the pitching wear amount shown in FIG. 5 are reduced, and the wear resistance is excellent. And, the reason why the wear resistance is excellent is that the amount of the precipitated carbide is large, and if the amount of the precipitated carbide is less than 30%, scuffing and pitting are likely to occur, but the amount of the precipitated carbide is 30% or more. In this case, it was recognized that the amount of wear was small. Such improvement in wear resistance is apparent from the comparison between FIG. 6 showing the metal structure of the tappet crown before the test and FIG. 7 showing the metal structure of the tappet crown after the test, as shown in FIG.・ It is thought that this is because the crystal grain boundaries and the irregularities formed in the grains due to the refining treatment increased the retention of lubricating oil. Was observed. Furthermore, the convex portion 1b formed by the heat treatment and the cam
The offset amount D with respect to the tappet center C at the contact position A with 2a is 9.8 mm on average, which is larger than the conventional offset amount of 2-3 mm when spherical polishing is performed. It was confirmed that the rotation of the lubricating oil and the increase of the contact area due to the rotation also contributed to the improvement of the wear resistance. Example 2 In Example 2, as a cap type tappet material,
A bearing steel having a composition of 0.99 wt% C-0.24 wt% Si-1.44 wt% Cr-Fe was used. Then, the tappet material was subjected to cold forging and machining to prepare a tappet material having a tappet shape (see FIG. 8). Next, the tappet material is subjected to high-concentration carburization at 900 ° C. in the same atmosphere as in Example 1, and then the temperature is lowered to 800 ° C. to perform a nitriding treatment with 0.5 to 5% NH ₃ enriched gas. After oil quenching from the same temperature, tempering was performed at 160 ° C. × 2H × 2 times. Next, after such surface treatment and tempering treatment, the inside and outside of the tappet shaft were machined to obtain a cap-type tappet partially shown in FIG. As shown in FIG. 8, this tappet 1 is formed in the vicinity of the peripheral portion of the tappet crown surface 1a after the surface hardening treatment and the tempering treatment by combining the shape, thickness, heat treatment conditions and the like of the tappet coarse material. And a tappet shaft 1d continuous with the tappet crown 1a. In the tappet 1 shown in FIG. 8, the contact position A between the inclined cam 2b of the camshaft 2 and the convex portion 1b near the peripheral portion is offset from the tappet center C by the offset amount D. The tappet 1 rotates on its own axis with the rotation of the camshaft 2 so that the lubricating oil can easily move around and the wear of the tappet crown surface 1a can be averaged. I have. Next, tappet crown surface of tappet 1 thus obtained
Examination of the microstructure at 1a showed that the amount of precipitated carbide on the surface was
38%, the amount of precipitated carbide in the inside 30μm from the surface (the part corresponding to the conventional minimum polishing allowance) is 15%
Thus, the precipitated carbide had a round shape and fine crystal grains. When the hardness distribution was examined, the result was shown in FIG. 9, and the hardness of the outermost surface was about Hv800. Furthermore, the height of the convex portion 1b formed in the vicinity of the peripheral portion of the tappet crown 1a is a maximum of 3.1 μm, a minimum of 2.2 μm, and an average of 2.6 μm.
μm, the minimum radius of curvature is 620 mm, and the offset amount with respect to the tappet center C at the contact position A between the convex portion 1 b and the cam 2 b is 9 mm, which is larger than the offset amount when general spherical polishing is performed. Had become. Further, after assembling the tappet 1 with the internal hydraulic mechanism parts, the tappet 1 was assembled to the valve operating mechanism of the engine, and scuffing wear and pitching wear were examined. The results are shown in the following table. As is clear from the table, in the case of the example, scuffing wear did not occur, and normal wear slightly occurred on average by 3.2 μm, but pitting wear did not occur. Admitted. It was also confirmed that all the tappets were rotating. Also, in the second embodiment, compared with the conventional polished one, the tappet crown surface 1a has an increased amount of precipitated carbide to improve hardness, increase tempering resistance, and is easy to rotate, and lubricating oil is removed. In combination with the fact that the circumference became better, the wear was clearly small and the wear resistance was excellent.

【The invention's effect】

In the tappet manufacturing method according to the present invention, the tappet coarse material having a tappet shape is subjected to a high-concentration carburizing or carbonitriding treatment to reduce the amount of precipitated carbide on the tappet crown surface to 30% or more, preferably 38% or more. A wear-resistant tappet crown in which the amount of precipitated carbide on the tappet crown is maintained without subjecting the tappet crown to planar polishing and spherical polishing, assuming that the amount of precipitated carbide gradually decreases from the tappet crown toward the inside. And a heat treatment to form a convex portion that offsets the contact position with the mating cam from the center of the tappet, so that a carbide-rich precipitation layer on the tappet crown surface formed by high-concentration carburizing or carbonitriding. The scuffing abrasion after the abrasion resistance becomes even better And the occurrence of pitting wear can be reduced, and it is possible to avoid a decrease in wear resistance and an increase in cost due to performing spherical finish polishing or plane finish polishing, and a tappet crown surface formed by heat treatment. By contacting the mating cam with the mating cam at the convex part of the tappet, the contact position with the mating cam is offset with respect to the center of the tappet, so that the tappet can rotate with the rotation of the cam. And eliminates the need for a polished finish,
The extremely excellent effect that the wear resistance can be further improved by increasing the lubricating oil's throwing power and the contact area is brought about.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a main part of a valve operating mechanism using a tappet manufactured according to an embodiment of the present invention, and FIG. 2 is a metallographic photograph showing a metal structure on a tappet crown surface of the tappet in FIG. FIG. 3 is a graph showing the result of examining the hardness distribution of the tappet crown surface in the tappet of FIG. 1, and FIG. 4 is a graph showing the relationship between the amount of surface carbide and the amount of scuffing wear on the tappet crown surface of each tappet. FIG. 5 is a graph illustrating the relationship between the amount of surface carbide and the amount of pitting wear on the tappet crown surface of each tappet, and FIGS. 6 and 7 are wear tests. Metallographic photographs showing the metallographic structure of the tappet crown surface before (FIG. 6) and after the wear test (FIG. 7)
FIG. 8 is an explanatory view showing a main part of a valve operating mechanism using a tappet manufactured according to another embodiment of the present invention. FIG. 9 is a diagram showing the hardness of the tappet crown surface in the tappet of FIG. FIG. 10 is a graph showing the result of examining the distribution, and FIG. 10 is an explanatory diagram showing a main part of a valve operating mechanism using a conventional tappet. 1 ... tappet, 1a ... tappet crown surface, 1b ... convex portion, 2 ... camshaft, 2b ... cam, A ... contact position between tappet and cam, C ... tappet center, D ... Offset amount.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Makoto Kano 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture Inside Nissan Motor Co., Ltd. (72) Inventor Kunio Namiki 2-30 Datongcho, Minami-ku, Nagoya-shi, Aichi Daido Special Steel Inside (72) Inventor Takeshi Appearance Takeshi 2958, Ishikawa, Fujisawa-shi, Kanagawa Prefecture Inside Fuji Valve Co., Ltd. (72) Inventor Toshihiko Iwano 785, Minowa-cho, Minowa-cho, Kohoku-ku, Yokohama, Kanagawa Prefecture 56) References JP-A-62-253910 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F01L 1/14 C23C 8/32

Claims (2)

(57) [Claims] A rough tappet material having a tappet shape is subjected to a high-concentration carburizing or carbonitriding treatment so that the amount of carbide deposited on the tappet crown surface is 30% or more, and the tappet is deposited from the tappet crown surface toward the inside. Along with forming the wear-resistant tappet crown surface in which the amount of carbides precipitated on the tappet crown surface is maintained without subjecting the tappet crown surface to flat polishing and spherical polishing as the amount of carbide gradually decreases, and heat treatment with the mating cam. Forming a convex portion that offsets the contact position of the tappet from the center of the tappet. 2. The amount of carbide precipitated on the tappet crown surface is 38%.
The method for manufacturing a tappet according to claim 1, wherein