JPH0617609A - Manufacture of engine tappet - Google Patents

Abstract

PURPOSE:To secure the wear resistance of an abutting part of a tappet and a valve stem end, and reduce the complicated manufacturing process in a manufacturing method of a seamless mechanical lash adjuster(MLA) tappet to be used in a valve driving system of direct-driven type for an engine valve operating device. CONSTITUTION:In a manufacturing of method of a steel tappet 1 where a sliding part 1b to be brought into slidable contact with a cam 8, and an abutting part 1a which abuts on a valve stem 2, at least an area around the sliding part 1b and the abutting part 1a of the tappet is carburized or carbo-nitrided, then the height is adjusted by polishing the abutting part 1a, and the local quenching treatment of the surface to be worked is executed by using laser beam or the like. Non-hardened carburized layer which has not been hardened during the carburizing or the carbo-nitriding process is hardened by this local quenching, forming a newly effective hardened layer in the abutting part 1a. This treatment allows a wider range of the machining margin of the abutting part 1a, and the ranking of the tappet height (h) can be executed over the wide range without difficulty after carburizing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a tappet which constitutes a part of a valve train in an engine of an automobile or the like, and particularly facilitates a weightless shimless tappet classified into many tappet heights. It relates to a method of manufacturing.

[0002]

2. Description of the Related Art With the increase in engine output and fuel efficiency, weight reduction of the valve train system has been attracting attention. Above all, in engines having a direct drive type valve drive system with high rotational speed, tappet Since the structure of the structure greatly affects the weight reduction, at present, HLA (Hydraulic L
ash Adjuster) and outer shim MLA (M
The transition from the mechanical Lash Adjuster) to the inner shim MLA is progressing.

That is, the above-mentioned HLA tappet adjusts the tappet clearance (clearance between the top of the tappet and the cam) to an appropriate amount by a hydraulic mechanism, and its own weight is large, which is an obstacle to weight reduction. As described in Japanese Utility Model Laid-Open No. 62-106, it is necessary to cover the entire area of the sliding surface with the cam, so a large shim must be attached, which is also inconvenient for weight reduction. is there.

On the other hand, the inner shim MLA tappets are classified into a disc type and a cap type. As shown in FIG. 6 or 7, tappet 1, intake / exhaust valve stem 2, valve spring 3, valve spring 3 and valve spring are used. Three
Is provided with a retainer 4 for receiving the load of the above, a cotter 5 for connecting the retainer 4 and the valve stem 2, and a disc type shim 6 (FIG. 6) or a cap between the contact portion 1a and the valve stem end 2a for adjusting the tappet clearance. The mold shim 7 (FIG. 7) is assembled. Reference numeral 8 represents a cam of a cam shaft that rotates in synchronization with the crankshaft of the engine, and 9 represents a cylinder head. Such inner shim M
When the LA tappet is used, there is an advantage that the shape of the shim itself is small and the weight increase is small, but there are the following problems.

(A) In the disc type, in order to position the shim 6, a flange portion 4a is separately provided on the retainer 4, or
Alternatively, it is necessary to provide a similar positioning portion on the tappet 1 side, which increases the weight of the retainer 4 or the tappet 1. (B) In the cap type, since the contact surface between the contact portion 1a side of the tappet and the valve stem end 2a side of the tappet is difficult to be parallel in manufacturing, inclination is likely to occur, which promotes variations in tappet clearance. Further, the inclination of the shim 7 causes a local increase in surface pressure, which promotes local wear. (C) In both the disc type and the cap type, since the number of constituent parts increases due to the presence of the shim, assembly variation easily occurs, which increases variation in tappet clearance.

(D) The shim height is finely divided into ranks (for example, the height difference between ranks = 25 μm, 36 ranks), and the management of its manufacture, particularly the carburizing and quenching process, is extremely complicated. As an example, looking at the manufacturing process of the disc-type inner shim, as shown in FIG. 8, the bar material is cut (first rank classification) and first divided into four ranks. Next, each of the 4 ranks is divided into 3 ranks by rough polishing (second rank classification), and the total is 12 ranks. Each of the 12 ranks is divided into 3 ranks by carburizing and quenching and further polishing (3rd rank division), and a 36 rank shim is manufactured as a whole. Here, the effective hardened layer by the carburizing and quenching process is 0.2 to
Since it is as thin as 0.5 mm, if the polishing allowance after carburizing and quenching is large, the non-hardened layer may be exposed, and it is not possible to carry out excessively large polishing (three ranks in this example), and it is close to the completed shape to some extent. It is necessary to carburize and quench after shaping. Therefore, in this example, the carburizing and quenching is carried out in the state of 12 ranks.

[0007]

Among the problems associated with such inner shim MLA tappets, in order to solve the above problems (a) to (c), as shown in FIG. , Without using a shim, prepare various types of tappets having different tappet heights h (height between the sliding contact portion 1b with the cam and the contact portion 1a with the valve stem end) of the tappet 1, which may be used at the time of assembly. It is conceivable to selectively use the same, that is, to employ the shimless MLA tappet. However, in this case, in order to make the tappet clearance a proper amount, it is necessary to rank the tappet heights h by as many ranks as the shim heights. However, it must be said that the problem in the shim manufacturing process described in (d) above may occur also in manufacturing the shimless MLA tappet.

This will be described more specifically with reference to the manufacturing process of the conventional inner shim or outer shim MLA tappet shown in FIG. 9. In the conventional tappet, first, the bar material is cut and then cooled. It is manufactured by hot forging, turning, carburizing and quenching, and finish polishing, but following the conventional manufacturing process, the shimless M with tappet height h divided into many ranks.
In order to obtain the LA tappet, it is necessary to rank in any of the above steps. Specifically, it is appropriate to divide the ranks in the turning process (process) before carburizing and quenching or the finish polishing process (process), but it was necessary to consider the following problems respectively.

(E) Before carburizing and quenching, if the contact portion 1a is turned to be divided into a large number of ranks, it is difficult to obtain the accuracy of the tappet height h, and the finishing process becomes complicated. The complexity of the process control of carburizing and quenching described in d) cannot be eliminated. (F) When the abutting portion 1a is subjected to finish polishing to be ranked after carburizing and quenching, an effective hardened layer (0.2 to 0.5 mm) is deleted, and wear of the contact portion 1a cannot be prevented.

In view of the above, the present invention provides a shimless MLA tappet manufacturing method capable of reducing the weight of a tappet and reducing the number of parts in a direct-acting valve drive system, in which a contact portion 1a with a valve stem end is resistant. The purpose of the present invention is to obtain a method capable of ensuring abrasion resistance and, at the same time, reducing the complexity of the manufacturing process.

[0011]

Therefore, the present invention is directed to a method of manufacturing a steel tappet, which comprises a sliding contact portion which is in sliding contact with a cam of a cam shaft, and an abutting portion which is in contact with a valve stem of an intake / exhaust valve. After carburizing or carbonitriding quenching at least the sliding contact portion and the contact portion of the tappet,
The contact portion is processed to adjust the height, and then the processed surface is subjected to a quenching treatment. As a preferred embodiment,
It is characterized in that the quenching treatment of the machined surface is performed by high-density energy irradiation such as laser beam or electron beam.

The present invention also provides a method for manufacturing a steel tappet, comprising: a sliding contact portion that is in sliding contact with a cam of a cam shaft; and a contact portion that is in contact with a valve stem of an intake / exhaust valve.
It is also possible to carry out quenching treatment only on the machined surface of the tappet with a large machining allowance, after carburizing or carbonitriding quenching at least around the sliding contact part and contact part of the tappet, then processing the contact part to adjust the height. It is a feature.

[0013]

As described above, the present invention is characterized in that the machined surface is locally quenched again. The operation will be described below with reference to the schematic diagrams shown in FIGS. 2 (a) to 2 (c). . FIG. 2A is a schematic sectional view showing only the vicinity of the contact portion 1a of the tappet 1 with the valve stem end, and shows a state after carburizing or carbonitriding (both are collectively referred to as carburizing) quenching. It is a thing. Usually, an effective hardened layer (hardened layer of a practical level) obtained by oil quenching after carburization is obtained only in a part of the carburized layer, and as can be seen here, under the effective hardened layer 10, hardening by quenching is performed. Carburized layer 1
1 is present. And this invention is such a carburized layer 1
1 is hardened by local quenching so as to have wear resistance.

For example, when the height of the contact portion 1a is adjusted by polishing the contact portion 1a and the machining allowance is larger than the thickness of the effective hardened layer 10 (when the contact portion 1a is ground to the position shown by the arrow A), the hardness of the contact portion 1a is increased. Wear resistance to the valve stem end is temporarily lost, but by locally quenching the machined surface, the hardness is restored and wear resistance is resumed. The reason is that the remaining carburized layer 11 is quench-hardened by the next local quenching. A schematic cross-sectional view explaining this is shown in FIG.

Even when the machining allowance of the abutting portion 1a is further large and the carburized layer 11 is also deleted (when it is ground up to the position shown by the arrow B), it is subjected to local quenching so that the outer peripheral region 1s of the abutting portion 1a is affected. Has a wide range of wear resistance. That is, the carburized layer 1 existing around the contact portion
1 is exposed to the abutting portion 1a by polishing, and this is hardened by local quenching, forming a ring-shaped effective hardened layer in the outer peripheral region 1s of the abutting portion 1a, which is effective for edge loading of the valve stem end. It has excellent wear resistance.
A quenching layer 12 having a hardness lower than that of the outer peripheral region 1s is formed on the surface portion of the contact portion 1a other than the outer peripheral region 1s by the quenching treatment. A schematic sectional view for explaining it is shown in FIG.

The machining allowance is small and the effective hardened layer 1 of the contact portion 1a
When 0 remains (when it is polished up to the position indicated by arrow C), local quenching to the worked surface is not necessary as long as it is determined that the remaining effective hardened layer 10 is sufficient from the viewpoint of wear resistance. Absent. However, when it is determined that the remaining amount of the effective hardened layer 10 is insufficient, local quenching should be performed, and even if the remaining effective hardened layer 10 is sufficient from the viewpoint of wear resistance, Process convenience, for example,
When it is recognized that it is complicated to place the one to be locally hardened and the one not to be locally hardened on separate lines, the local hardening can be uniformly performed.

As described above, according to the method of the present invention, the working margin of the abutting portion can be widened, and the ranking after carburizing and quenching can be performed over a wide range without any trouble. Conversely speaking, the ranking before carburizing and quenching is not necessary or required, and the complexity of carburizing and quenching is reduced.

[0018]

EXAMPLE In order to confirm the effect of the present invention, a tappet was manufactured according to the process shown in FIG. 3 and a hardness test of a contact portion of a valve stem end was conducted. That is, (20) SCM415H
Cold forging the material into a tappet shape with a shaft diameter of 7 mm
(21) This is formed into a shape before finish grinding by turning, (22) carburized at 920 ° C., (23) cooled to 830 ° C. and oil-quenched, (24) low-temperature tempered at 250 ° C. for 1.5 hours, and then, (25) The end surface of the contact portion was ground to a depth of 1 mm, which was used as a comparative example. It should be noted that the 1 mm grinding is as shown in
In the case of (a), it corresponds to grinding up to the position of the arrow B, and the carburized layer from the contact portion side is substantially completely removed. Further, (26) the beam diameter φ7.
Laser hardening was performed under the conditions of 0, output 900 w, and scanning speed 0.1 m / min, and (27) finish polishing was performed.

FIG. 4 shows the result of examining the hardness of the contact portion (end face diameter φ7.0) of the tappets of Examples and Comparative Examples.
In the comparative example in which the contact portion was not laser-quenched, the effective hardened layer (the layer exhibiting a hardness of Hv513 or more) was only up to the distance of 0.3 mm from the outer peripheral surface, and the area ratio to the entire end surface was 16.4%. It only occupies. However, in the embodiment in which the contact portion is laser-quenched, the effective hardened layer expands to a distance of 0.9 mm from the outer peripheral surface, and the area ratio of the effective hardened layer occupies 44.8%. It was possible to give abrasion resistance to the edge load of the end. The portion bordered by fine dots on the tappet shown in FIG. 1 is a portion corresponding to the effective hardening layer formed by the carburizing and laser hardening in the example.

Next, an example of the manufacturing process when manufacturing the Shimless MLA tappet divided into many ranks using the method of the present invention will be described with reference to the block diagram shown in FIG. First, prepare (30) bar material, and (31)
This is cut and cold forged into a (32) tappet shape,
(33) Molded into a shape before finishing by turning or the like, and divided into 4 ranks (first rank classification). next,
(34) After carburizing and quenching the surface portion, (35) the sliding contact portion 1b with the cam and the outer peripheral surface 1c in sliding contact with the cylinder head.
And the contact portion 1a with the valve stem end is rough-polished, and each of the 4 ranks is divided into 3 ranks, so that the total is 12 ranks (second rank classification). The finish forming of the sliding contact surface 1b and the outer peripheral surface 1c does not have to be performed in this process order, and may be performed after the finish processing of the contact portion 1a. Next, (36) the contact portion 1a is polished, and each of the 12 ranks is divided into 3 ranks, and the whole is divided into 36 ranks (third rank classification). (37) Among the tappets classified according to the rank in the previous step, those that require local quenching are locally quenched at the contact portion 1a with a high-energy beam, and (38) after finishing processing, (3)
9) It is sent to the inspection process. If local quenching is not required, it can be sent directly from the step 16 to the inspection step.

[0021]

According to the present invention, it is possible to secure the wear resistance, particularly the pitting resistance, of the contact portion of the shimless MLA tappet used in the direct drive type valve drive system with the valve stem end. It is possible to reduce complexity in the manufacturing process of the shimless MLA tappet, which is ranked according to a large number of tappet heights.

[Brief description of drawings]

FIG. 1 is a sectional view of a valve train using a shimless MLA tappet.

FIG. 2 is a schematic diagram for explaining the effect of local quenching.

FIG. 3 is a block diagram showing a process of manufacturing a shimless MLA tappet for use in a hardness test.

FIG. 4 is a diagram showing a hardness test result of a valve stem end contact portion of a shimless MLA tappet.

FIG. 5 is a diagram showing a process for manufacturing a shimless MLA tappet ranked according to a number of tappet heights.

FIG. 6 is a sectional view of a valve train using a disc-type inner shim MLA tappet.

FIG. 7 is a cross-sectional view of a valve train using a cap type inner shim MLA tappet.

FIG. 8 is a block diagram illustrating a manufacturing process of a disc type shim.

FIG. 9 is a block diagram illustrating a manufacturing process of an inner or outer shim MLA tappet.

[Explanation of symbols]

 1 Tappet 1a Contact part with valve stem end 1b Contact part with cam 1c Outer part of tappet 2 Valve stem 3 Valve spring 4 Retainer 5 Cotter 6 Disc type shim 7 Cap type shim 8 Cam 9 Cylinder head 10 Effective hardening layer 11 Carburized (nitrided) layer

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[Procedure amendment]

[Submission date] March 2, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] Figure 9

[Correction method] Added

[Correction content]

[Figure 9]

Claims (3)

[Claims] 1. A method for manufacturing a steel tappet, comprising: a sliding contact portion that is in sliding contact with a cam of a cam shaft; and a contact portion that is in contact with a valve stem of an intake / exhaust valve. After carburizing or carbonitriding quenching around the part, process the contact part and adjust the height,
Next, a method for manufacturing an engine tappet, characterized by quenching the processed surface. 2. The method for producing a tappet for an engine according to claim 1, wherein the quenching treatment of the machined surface is performed by high-density energy irradiation. 3. A method of manufacturing a steel tappet, comprising: a sliding contact portion that is in sliding contact with a cam of a cam shaft; and a contact portion that is in contact with a valve stem of an intake / exhaust valve. After carburizing or carbonitriding quenching around the part, process the contact part and adjust the height,
A method for manufacturing engine tappets, characterized by quenching only the machined surface of tappets with large machining allowances.