JP2807797B2 - Camshaft and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sintered camshaft for an internal combustion engine and a method for manufacturing the same.

[Conventional technology]

As a lightweight camshaft having high abrasion resistance and withstanding a high surface pressure and a high load, there is a sintered camshaft in which a cam piece made of a sintered material is joined to a steel pipe.

In that case, to further improve the initial conformability and abrasion resistance of the cam portion, a relatively low temperature phosphate coating treatment,
A higher temperature nitriding or steam treatment is performed.

[Problems to be solved by the invention]

However, if the sintered camshaft contains a large amount of alloy components such as Cr for the purpose of improving the wear resistance, if a phosphate film treatment is performed, the film formation is hindered by these alloy components, and sufficient film formation is prevented. No effect can be expected.

On the other hand, when the nitriding treatment or the steam treatment is performed, it is necessary to perform the bending correction twice in the manufacturing process. In other words, after assembling a cam piece made of an iron-based sintered material into a steel pipe, the sintered camshaft is passed through a sintering furnace to simultaneously sinter the sintered material and simultaneously perform diffusion bonding between the pipe and the piece to form a camshaft material. I do. At this time, the pipe is deformed, that is, bent, because it passes through a high-temperature sintering furnace. Therefore, after passing through the sintering furnace, it is necessary to correct the bending of the camshaft material, especially the pipe. However, since internal stress remains in the camshaft material due to the bending correction, if the cam is polished and then subjected to high-temperature nitriding treatment or steam treatment, bending occurs again. Therefore, it is necessary to correct the bending again. The bending correction after the completion of the processing requires high precision, and if the correction is impossible, the completed camshaft, which requires a lot of man-hours, becomes defective and the production efficiency is remarkably reduced.

Japanese Patent Application Laid-Open No. 63-162852 discloses a method of performing a strain relief annealing to remove a processing stress of a camshaft and then performing a nitriding treatment. However, in the case of a sintered camshaft, when the nitriding treatment is performed, the cam surface often peels off during a high-load operation.

On the other hand, a method of forming a film of ferric oxide (Fe ₃ O ₄ ) on a camshaft using an iron-based alloy powder containing relatively large amounts of Cr and Cu is disclosed in Japanese Patent Application Laid-Open No. 58-3901. Have been.
In that case, a thin film of triiron tetroxide is sufficiently formed on the surface of the sintered body and the wall around the internal pores under reduced pressure, but if the triiron tetroxide is formed more than necessary, the cam will wear. It turned out to be easier.

In view of the above, an object of the present invention is to provide a sintered camshaft having good initial conformability and wear resistance, and a method for manufacturing the sintered camshaft with high production efficiency.

[Means to solve the problem]

In order to solve the above problems, according to the first invention, the component composition is 1.5 to 3.0% by weight, Si: 0.5 to 1.2%, and Mn: 1.
0% or less, Ni and Mo: 1 or 2 or less, 5.0 or less, Cr: 20.0% or less, W, Nb and V: 1 or 2 or more, 10% or less, P: 0.2 to
1.0%, S: 0.1% or less, Fe: the remainder, consisting of a sintered alloy cam piece with a surface layer of triiron tetroxide coating,
A camshaft joined to a steel pipe is provided. In this case, it is desirable that the triiron tetroxide film be formed in the area ratio of 60 to 80% on the cam piece surface.

Further, according to the present invention, the raw material powder is compressed to form a green compact for a cam piece, the green compact is assembled to a steel pipe, and the green compact is sintered and joined to the steel pipe to form a cam. A shaft material is formed, a bending correction is performed on the camshaft material, a strain relief annealing is performed to remove internal stress generated in the camshaft material by the bending correction, and a cam portion of the camshaft material is formed. A method for producing a camshaft, characterized in that polishing is performed by a polishing process and steam treatment is performed at a temperature lower than the strain relief annealing.

Furthermore, according to the present invention, the component composition after sintering is
In, C: 1.5-3.0%, Si: 0.5-1.2%, Mn: 1.0% or less, Ni
And Mo: 5.0 or less for one or two kinds, Cr: 20.0% or less, W, Nb and V: 10% or less for one or more kinds, P: 0.2 to 1.0%, S: 0.1
% Or less, Fe: the remainder, the cam piece of the green compact is assembled to a steel pipe and the camshaft material that has been sintered and bonded is bent, and then the strain relief annealing is performed to remove the internal stress due to the bending correction. And then performing a polishing process on the cam portion, and then performing a steam treatment at a temperature lower than the strain relief annealing.

[Action]

A large amount of carbides such as Cr, W, Nb, and V are formed in the cam piece, resulting in good wear resistance. In addition, a film of triiron tetroxide is formed by steam treatment. I have.

Also, by controlling the amount of carbide precipitation to keep the formation amount of the triiron tetroxide film within a certain range, it is possible to reduce the wear amount of both the camshaft itself and the mating material.

Further, after correcting the bending of the shaft due to sintering, if the internal stress generated by the bending is removed by strain relief annealing, then, even if it is exposed to a high temperature by steam treatment, if it is below the strain relief annealing temperature, it will bend. Does not occur, so that a highly accurate sintered camshaft can be manufactured.

[Examples] The reasons for limiting the range of the component composition of the cam piece will be described below.

C is 1.5 to 1.5 by weight in a sintered alloy cam piece.
3.0% included. In this range, a part is dissolved in the matrix to strengthen the matrix, and the other forms a carbide. However, if less than 1.5%, the effect cannot be obtained and the wear resistance and self-lubricating property are reduced. Also, if it exceeds 3.0%, carbides increase more than necessary,
Furthermore, it acts with P to generate an excessive liquid phase, and the shape as an assembled piece cannot be maintained.

Si is contained in the cam piece by 0.5 to 1.2% by weight. Si contributes to strengthening of the matrix, but if less than 0.5%, the effect cannot be obtained. If it exceeds 1.2%, the powder compactibility of the powder decreases, and the deformation during sintering increases. Further, since the formation of carbides is inhibited and graphite is precipitated, wear resistance is also reduced.

Mn is not more than 1.0% by weight in the cam piece. Mn is inevitably contained in the raw iron powder in the form of MnS, and is contained as an essential component even after sintering, but forms a solid solution in the matrix to promote the formation of a pearlite matrix structure. But 0.3%
If it exceeds, the progress of sintering is suppressed, coarse pores remain, and the compactibility tends to decrease. However, when it is necessary to enhance the effect of promoting pearlitization or improving hardenability, the upper limit of the addition is 1.0% at which the above tendency sharply increases.

Ni and Mo are one or two types in the sintered alloy cam piece.
The seeds contain less than 5.0% by weight. Both of them mainly have the effect of strengthening the matrix, but also contribute to the improvement of wear resistance due to the formation of carbides. One or two of these
The effect is expected to be less than 5.0% depending on the species, and if it exceeds this, the hardness will increase and the machinability will decrease. These are both contained as essential components.

Cr is contained by 20.0% or less by weight, and W, Nb, and V are 1%.
Species or two or more kinds are contained by 10% or less by weight ratio. these
Cr, W, Nb, and V are carbide forming elements. In the present invention, these elements are contained in a relatively large amount to enhance the wear resistance of the cam. Of these, Cr is the most effective and is essentially used, but other W, Nb, and V are selectively contained.

On the other hand, in the present invention, a film of triiron tetroxide is formed on the surface layer of the cam to improve the initial conformability, but if it is formed in a surface area ratio in the range of 60 to 80%, the cam shaft itself and the mating member are formed. Experiments have shown that the wear of both materials (rocker arm or tappet) can be reduced. The film of triiron tetroxide is formed on the matrix, and since the carbide does not contain iron, the film is not formed. Therefore, by adjusting the amount of addition of the above-mentioned carbide forming element and C to control the amount of carbide precipitation, it is possible to form an appropriate amount of triiron tetroxide film.

For this purpose, it is preferable to adjust Cr in a range of 20.0% or less and W, Nb, V in one or more kinds in a range of 10% or less. The lower limit of the total of these carbide forming elements is 3.0%, and when the lower limit is less, the area ratio of triiron tetroxide exceeds 80%,
The cam wear increases. On the other hand, the upper limit is 23%, and if it is more than 23%, the amount of carbide becomes excessive, and the area ratio becomes
Since it is less than 60%, the amount of wear of the mating material increases.

P is contained in an amount of 0.2 to 1.0% by weight. P generates Fe—C—P eutectic steadite and contributes to improvement of wear resistance. However, if it is less than 0.2%, there is no addition effect, and if it exceeds 1.0%,
The amount of the precipitated stadiite is also excessive, resulting in poor machinability and brittleness.

S is contained by 0.1% or less by weight. S is inevitably contained in the raw iron powder in the form of simple substance and MnS, but is suppressed to 0.1% or less to prevent embrittlement.

Next, a method of manufacturing a camshaft according to the present invention will be described. First, raw material powder for a sintered alloy cam piece is prepared. Here, the carbide forming elements Cr, W, Nb, V
The amount of carbides formed after sintering is adjusted by adjusting the addition amount of, and the ratio of each raw material powder is adjusted so that the coating amount of triiron tetroxide becomes a predetermined amount. Next, the raw material powder is compression-molded so as to have a desired cam piece shape to form a green compact for a cam piece. Next, the green compact for a cam piece is assembled to a steel pipe and sintered and joined in a sintering furnace to form a cam piece material in which the two are integrated.

By this sintering process, a sintered alloy cam piece is provided, and its component composition is C: 1.5 to 3.0% by weight, Si: 0.5 to
1.2%, Mn: 1.0% or less, Ni and Mo: 1 or 2 types, 5.0 or less,
Cr: 20.0% or less, W, Nb, and V: 1 or 2 or more, 10% or less, P: 0.2 to 1.0%, S: 0.1% or less, Fe: balance.

Also, at high temperatures in this sintering process, the camshaft material, especially the steel pipe, is deformed (bent, bent).
Occurs. Therefore, mechanical bending correction is performed to correct the bending. However, a new internal stress is generated in the camshaft material by the bending correction. Thereafter, the camshaft material is annealed to remove internal stress. That is, the internal distortion is removed. Next, the cam portion of the camshaft material is polished, and then subjected to steam treatment. Here, since the steam treatment is performed at an annealing temperature or less for strain relief, no new bending of the camshaft occurs in the steam treatment.

Next, a method of manufacturing a camshaft according to the present invention will be specifically described.

A cam piece made of a compact of an iron-based alloy powder and a journal piece made of a compact of a lower-grade iron-based alloy powder or steel are attached to a steel pipe.
After performing sinter joining by heating at 1200 ° C. for 1 to 2 hours, the mixture is cooled. As a result, the steel pipe bends, so that the bending is corrected.

Since internal stress is generated by pressurization for bending correction, strain relief annealing is performed to remove the internal stress. The austenite transformation temperature of the iron-based sintered material is around 700 ° C, and
Since the subsequent steam treatment is performed at around 580 ° C,
Hold at 650 ° C. for 1-2 hours and cool in furnace.

Thereafter, a polishing finish is performed, and then a steam treatment is performed at a lower temperature than the strain relief annealing for 1 to 3 hours. A treatment layer of triiron tetroxide is formed on the surface of the cam by the steam treatment, and the wear resistance is improved. In particular, the initial adaptation becomes good.

According to the above steps, as shown in the attached table, the camshafts of the present invention (Nos. 1 to 10) and the comparative camshafts (No.
~ 16) were manufactured. After measuring the surface hardness and the area ratio of ferric oxide, each was mounted on an engine and subjected to a wear test.

That is, using a 1.8-liter, in-line four-cylinder OHC engine, the camshaft slides with the rocker arm in motoring operation, and after 200 hours of operation at 2000 revolutions, wear of the cam and rocker arm (indicated as RA in the table) The amount and the presence or absence of scuffing on the cam were examined.

As the rocker arm, a high-Cr-based cast iron tip subjected to nitriding treatment was arranged on a sliding portion, and the rocker arm was used by casting with an aluminum base material.

As can be seen from the results shown in the table, when the amounts of the carbide forming elements such as Cr, W, Nb, and V were out of the component range of the present invention, the wear amount of the cam or the rocker arm, or both, increased. Scuffing also occurred more frequently.

Although the results were better than those of the comparative material, when the area ratio of triiron tetroxide was out of the range of 60 to 80% as in samples Nos. 9 and 10, the amount of wear of the cam or rocker arm also increased.

[Effects of the Invention] As described above, according to the present invention, a sintered camshaft having good initial conformability and high wear resistance is provided, and such a camshaft is subjected to bending correction after polishing. And can be produced efficiently.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22C 38/00 302 C22C 38/00 302E 38/48 38/48 F16H 53/02 F16H 53/02 B (58) Fields investigated (Int.Cl. . ^6, DB name) F01L 1/04 F16H 53/02 B22F 7/08 B22F 3/24

Claims (5)

(57) [Claims] (1) The composition of the component is expressed by weight%, C: 1.5-3.0%, Si:
0.5-1.2%, Mn: 1.0% or less, Ni and Mo: 1 or 2 types, 5.0
% Or less, Cr: 20.0% or less, W, Nb and V: 1 or more kinds and 10% or less, P: 0.2 to 1.0%, S: 0.1% or less, Fe: balance, 4% on the surface layer A camshaft in which a sintered alloy cam piece with an iron trioxide film formed is joined to a steel pipe. 2. The camshaft according to claim 1, wherein the triiron tetroxide coating is formed on the surface of the cam piece in an area ratio of 60 to 80%. 3. The composition of the cam piece, wherein Cr,
The camshaft according to claim 1, wherein the total weight ratio of W, Nb, and V is 3.0 to 23%. 4. A camshaft material comprising compressing a raw material powder to form a green compact for a cam piece, assembling the green compact into a steel pipe, and sintering and bonding the green compact to the steel pipe. The camshaft material is subjected to a bending correction, and the straightening annealing is performed to remove internal stress generated in the camshaft material by the bending correction, and the cam portion of the camshaft material is polished. A method of manufacturing a camshaft, comprising performing processing and performing steam treatment at a temperature lower than the strain relief annealing. 5. The composition after sintering, wherein the composition is expressed in weight%, and C: 1.5 to 3.0.
%, Si: 0.5 to 1.2%, Mn: 1.0% or less, Ni and Mo: 1 or 2
5.0 or less, Cr: 20.0% or less, W, Nb and V: 1 or 2
At least 10% or less, P: 0.2-1.0%, S: 0.1% or less, Fe: Remainder, the cam piece of the compact compacted to the steel pipe is bent and corrected. Then, after performing a strain relief annealing to remove internal stress due to bending correction, after further polishing the cam portion, a steam treatment at a temperature lower than the strain relief annealing of the camshaft, Production method.