JP2001240948A - Cam shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cam shaft which can be manufactured in an extremely efficient manner and which is composed of a plurality of cams of different contact mode with a counter being formed of a sintered alloy having the characteristic according to the contact mode. SOLUTION: In the cam shaft having a first cam 3 in slidable contact with corresponding counter members 5, 6 and a second cam 4 in rolling contact therewith, the first cam 3 is formed of a wear-resistant sintered alloy with fine carbide precipitated in a base structure mainly consisting of pearlite, and the second cam 4 is formed of a pitting-resistant sintered alloy with fine carbide precipitated in a base structure mainly consisting of martensite and bainite.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camshaft employed in an internal combustion engine, and more particularly, to a camshaft having a slipper follower and a roller follower as a mating member in a different manner of contact with the mating member. The present invention relates to a camshaft in which a plurality of cams are formed of a sintered alloy having characteristics according to a contact mode thereof, and the cams can be sintered at a time and diffused and sintered on a camshaft.

[0002]

2. Description of the Related Art As a conventional camshaft for an internal combustion engine, a chill cast iron camshaft, a steel camshaft formed by forging or total cutting, or a sintered alloy cam is used as a camshaft. There is an assembled camshaft and the like joined together. In addition, the manufactured camshaft includes
If necessary, surface treatment or heat treatment is performed for the purpose of improving abrasion resistance and strength, and specific properties are imparted as a whole. Such a camshaft is generally a cam follower having the same type of operation as a mating member, and is intended for, for example, a rocker arm or tappet of a sliding contact type, or a rocker arm or tappet of a rolling contact type. It is.

[0003] Such a conventional camshaft is opposed to a rocker arm having a cam follower (for example, a slipper follower 5 of a sliding contact type or a roller follower 6 of a rolling contact type) having different types of operation as shown in FIG. When the camshaft 1 is used as a member, the contact forms between the mating member and the cams 3 and 4 mounted on the camshaft 1 are different from each other, so that the durability and reliability of the camshaft 1 may not be maintained.

That is, since the cam 3 having the slipper follower 5 as a mating member slides at a high temperature due to sliding with the mating member, the cam 3 has a scuffing resistance (slip resistance) that can withstand sliding contact. (A property that seizure wear due to friction is unlikely to occur) is required. On the other hand, the cam 4 having the roller follower 6 as a mating member has a small curvature of the surface in contact with the mating member, and the contact surface rolls and slides under a high surface pressure, so that the pitching resistance can withstand rolling contact. (The property that surface damage due to rolling fatigue is unlikely to occur) is required. However, conventional camshafts cannot simultaneously satisfy such demands.

In order to solve such a problem, there is an assembled sintered camshaft including a plurality of cams having different contact forms with a mating member. The camshaft includes a sintered alloy cam that is in rolling contact with a mating member and a sintered alloy cam that is in sliding contact with the mating member. Specifically, the cam that comes into rolling contact with the mating member has a large amount of precipitated carbide, is formed of a sintered alloy in which the matrix is strengthened by a martensitic structure, has high fatigue strength, and has a high slip strength on the mating member. The contacting cam is formed by applying a steam treatment to the contact portion of the sintered alloy made of the same material as described above for the purpose of imparting initial conformability during operation, and has been provided with initial scuffing suppression and wear resistance. Things.

[0006]

However, in the above-mentioned assembled camshaft, the same sintered alloy is used for both the cams which are in sliding contact and rolling contact with the mating member, so that it is more efficient in that respect. Although it is possible to achieve high production and cost reduction, it is manufactured through a steam treatment process after joining each cam to the cam shaft by diffusion bonding method or mechanical press-fitting method, so a long cam shaft with each cam joined Must be put into a steam treatment furnace.
Therefore, there is a problem that the number of camshafts that can be put into one process is limited, which causes an increase in cost. In addition, since the supplied camshaft has already been ground to a predetermined size, there is a problem that bending (distortion) is likely to occur after the steam treatment, and a post-process for correcting the bending is further required. . Furthermore, if a steam-treated film is formed on the surface of the cam that comes into rolling contact with the mating member, the pitting resistance is adversely affected. Therefore, the masking step before the steam treatment, the lapping or grinding after the steam treatment, It is necessary to add a step of shaving off the processing film.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. In a camshaft employed in an internal combustion engine, a plurality of cams having different contact modes with a mating member are provided with a characteristic corresponding to the contact mode. The present invention relates to a camshaft that can be formed with a sintered alloy having the following characteristics and that can be manufactured extremely efficiently.

[0008]

According to a first aspect of the present invention, there is provided a camshaft including a plurality of cams having different contact forms with a mating member.
In a camshaft having a first cam that comes into sliding contact with a corresponding mating member and a second cam that comes into rolling contact with the first cam, the first cam has wear resistance in which fine carbides are precipitated in a base structure mainly composed of pearlite. The second cam is characterized in that the second cam is made of a pitching-resistant sintered alloy in which fine carbides are precipitated in a base structure mainly composed of martensite and bainite.

According to the present invention, the first cam, which comes into sliding contact with the corresponding mating member, is formed from a sintered alloy having a base structure mainly composed of pearlite. Good scuffing resistance. In addition, since fine carbides are precipitated in the matrix structure of the sintered alloy, excellent abrasion resistance is exhibited while suppressing the aggressiveness of the counterpart. Further, the second cam which is in rolling contact with the corresponding mating member is formed of a sintered alloy having a base structure mainly composed of martensite and bainite, and fine carbides are contained in the base structure of the sintered alloy. Since it is precipitated, it exhibits excellent wear resistance and pitting resistance, and surface damage due to rolling fatigue is extremely unlikely to occur. Therefore, in the camshaft according to the present invention, since each cam is formed of a sintered alloy having characteristics according to the manner of contact with the mating member, the durability and reliability thereof can be further improved. Furthermore, since the first cam that comes into sliding contact does not require steam treatment as in the related art, it can be manufactured efficiently, and there is no problem such as occurrence of bending.

According to a second aspect of the present invention, in the camshaft according to the first aspect, the wear-resistant sintered alloy comprises C: 1.
5 to 4.2% by mass, Cr: 2.0 to 24.0% by mass, M
o: 0.5 to 3.0% by mass, Si: 0.2 to 1.0% by mass, P: 0.2 to 1.0% by mass, Ni: 0 to 1.0% by mass, balance: Fe and The pitting resistant sintered alloy having unavoidable impurities has a C content of 1.5 to 4.2% by mass,
r: 2.0 to 24.0% by mass, Mo: 0.5 to 3.0% by mass, Si: 0.2 to 1.0% by mass, P: 0.2 to 1.
0% by mass, Ni: 1.0 to 2.5% by mass, balance: Fe and inevitable impurities, the first cam made of the wear-resistant sintered alloy and the first cam made of the pitch-resistant sintered alloy It is characterized in that the two cams are joined to the shaft by a diffusion joining method.

According to the present invention, since the respective sintered alloys having the component compositions within the above ranges can be sintered at the same temperature, the respective cams can be simultaneously sintered in the same step. As a result, the camshaft can be manufactured very efficiently. Further, the Ni content affecting the base structure is 0 to 1.0% by mass in the wear resistant sintered alloy for the first cam,
The pitching resistance sintered alloy for the second cam is 1.0 to 1.0.
Since the content is 2.5% by mass, a base tissue exhibiting characteristics required for each cam can be developed. further,
In the present invention, since the first cam that comes into sliding contact with the corresponding mating member and the second cam that comes into rolling contact are simultaneously joined by the diffusion joining method, the first cam can be firmly joined to the cam shaft with high production efficiency. . In addition, since each of the above-described cams can be sintered simultaneously at the same temperature, sintering and diffusion bonding can be performed simultaneously at the same temperature. As a result, the camshaft can be manufactured more efficiently.

According to a third aspect of the present invention, there is provided a camshaft comprising a plurality of cams having different contact forms with a mating member, the second cam being in rolling contact with the first cam in sliding contact with the corresponding mating member. , The first cam is
It consists of a wear-resistant sintered alloy in which fine carbides are precipitated in a base structure mainly composed of pearlite, and the second cam is
It is characterized by being made of pitting-resistant steel that has been quenched and tempered.

According to the present invention, the first cam made of a wear-resistant sintered alloy in which fine carbides are precipitated in a base structure mainly composed of pearlite, and the pitting-resistant steel that has been quenched and tempered. Since the second cam is formed of a sintered alloy and steel each having characteristics according to the manner of contact with the mating member, the durability and reliability thereof can be further improved. Furthermore, since the first cam that comes into sliding contact does not require steam treatment as in the related art, it can be manufactured efficiently, and there is no problem such as occurrence of bending.

According to a fourth aspect of the present invention, in the camshaft according to the third aspect, the wear-resistant sintered alloy comprises C: 1.
5 to 4.2% by mass, Cr: 2.0 to 24.0% by mass, M
o: 0.5 to 3.0% by mass, Si: 0.2 to 1.0% by mass, P: 0.2 to 1.0% by mass, Ni: 0 to 1.0% by mass, balance: Fe and The first cam having unavoidable impurities and made of the wear-resistant sintered alloy and the second cam made of the pitting-resistant steel are joined to the shaft by a press-fitting method.

According to the present invention, since each of the cams has excellent mechanical properties such as tensile strength, a camshaft in which those cams are firmly mechanically joined (press-fitted) to a shaft (camshaft) is used. Can be manufactured. Therefore, when a conventional chill cast iron cam having a relatively small mechanical strength is used, there is no problem that the cam cannot be firmly mechanically joined to the cam shaft, and the displacement of the cam during operation does not occur. There is no risk of cracking.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A camshaft according to the present invention will be described with reference to the drawings.

FIG. 1 is an example of an overall view of a camshaft 1 of the present invention, and FIG. 2 is a perspective view showing an aspect in which cams 3 and 4 of the camshaft 1 of the present invention come into contact with a mating member. FIG. 3 is a photomicrograph (× 200) showing an example of the matrix structure of the first sintered alloy for a cam. FIG. 4 is a graph showing the Ni content (%) in the sintered alloy and the residual content in the matrix structure. FIG. 5 is a graph showing the relationship with the austenite amount (%), and FIG. 5 is a photomicrograph (× 200) showing an example of the base structure of the second sintered alloy for cams.

As shown in FIGS. 1 and 2, the camshaft 1 of the present invention includes a plurality of cams 3 and 4 having different contact forms with the mating members 5 and 6 on the camshaft 2. It has a first cam 3 that comes into sliding contact with the mating member 5 and a second cam 4 that comes into rolling contact with the corresponding mating member 6. The first cam 3 and the second cam 4 are joined to the camshaft 2 by a diffusion joining method or a mechanical press-fitting method. Further, an end piece and a journal piece are provided as needed. The cam is formed of a material having characteristics according to the contact mode for each contact mode with the mating member,
The lift member and the working angle of the mating member are appropriately designed so as to be different from each other, and are mounted on the camshaft 1. As the contact mode,
As shown in FIG. 2, there are sliding contact with the slipper follower 5 and rolling contact with the roller follower 6.

A first feature of the present invention is that the first cam 3 is
The second cam 4 was formed of a wear-resistant sintered alloy in which fine carbides were precipitated in a base structure mainly composed of pearlite, and fine carbides were precipitated in a matrix structure mainly composed of martensite and bainite. It is formed of a pitching-resistant sintered alloy. In the present invention, attention is paid to the fact that the matrix structure of the sintered alloy is greatly affected by the Ni content,
By changing the i content, the matrix structure after sintering is changed to a matrix structure mainly composed of pearlite or a matrix structure mainly composed of martensite and bainite. The characteristic of the obtained sintered alloy is that it is preferable for the first cam that comes into sliding contact or that it is preferable for the second cam that comes into rolling contact. As a result, by providing the cams 3 and 4 having the characteristics according to the contact mode, it is possible to obtain the camshaft 1 with further improved durability and reliability.
Furthermore, the first cam 3 that comes into sliding contact does not require steam treatment as in the related art, so that the camshaft can be efficiently manufactured without any problem such as occurrence of bending. .

A second feature of the present invention is that sintering of the first cam 3 and the second cam 4 and joining based on diffusion sintering to the cam shaft 2 can be performed simultaneously at the same temperature. It is in. As a result, there is an effect that the camshaft can be manufactured firmly on the camshaft and extremely efficiently.

(1) First cam The first cam 3 has good initial running-in and slipping properties with a mating member that makes sliding contact, and has excellent scuffing resistance (corresponding to the slipper follower 5). It is made of an abrasion-resistant sintered alloy containing fine precipitated carbides in a base structure mainly composed of pearlite so as to exhibit the characteristic that seizure wear due to sliding friction is extremely unlikely to occur even in sliding contact. .

The component composition of the wear-resistant sintered alloy is as follows: C (carbon): 1.5 to 4.2 mass%, Cr (chromium): 2.0
To 24.0% by mass, Mo (molybdenum): 0.5 to 3.
0% by mass, Si (silicon): 0.2 to 1.0% by mass, P
(Phosphorus): 0.2 to 1.0% by mass, Ni (nickel):
0 to 1.0% by mass, balance: Fe (iron) and unavoidable impurities.

As shown in FIG. 3, the base structure of the wear-resistant sintered alloy includes a base structure 31 mainly composed of pearlite having a good slip property and a carbide such as a Cr carbide or a Cr—Fe—Mo—P composite carbide. In this embodiment, No. 32 is deposited. Further, the ratio of retained austenite (amount of retained austenite) of the base structure 31 is 10% or less. Such a wear-resistant sintered alloy can suppress initial scuff and exhibit excellent initial adaptability when slidingly contacting a mating member, and can also exhibit counter-attack suppression and excellent wear resistance. . In addition, since the retained austenite having poor thermal conductivity does not remain much in the base structure 31, a decrease in scuffing resistance due to the retained austenite is suppressed.

In the first cam 3, N 2 in the sintered alloy
By setting the i content to 0 to 1.0% by mass, the amount of retained austenite in the base structure 31 is suppressed. FIG. 4 is a graph showing the relationship between the Ni content (% by mass) in the sintered alloy and the amount of retained austenite (%) in the matrix structure. As shown in FIG. 4, when the Ni content exceeds 1.0% by mass, the amount of retained austenite in the matrix increases rapidly. Such retained austenite is sometimes preferred for improving wear resistance, but is less preferred for scuffing resistance. For example, in a sintered alloy having a retained austenite amount exceeding 10%, scuffing is likely to occur in a counterpart member made of steel.
Even when Ni is not added, generation of residual austenite can be suppressed, and excellent wear resistance and pitting resistance can be exhibited.
The Ni content is limited to 0 to 1.0% by mass.

Next, the reason why each component element other than Ni contained in the wear-resistant sintered alloy is limited to the above range will be described below.

C is preferably contained in an amount of 1.5% by mass in order to form high-hardness fine carbides and exhibit sufficient wear characteristics and scuffing resistance. However, when the C content exceeds 4.2% by mass, coarse carbides (mainly Cr
Carbides) are formed in the sintered alloy, and the coarse carbides generate coarse pores during the liquid phase sintering and embrittle the matrix structure. For this reason, the C content is limited to 1.5 to 4.2% by mass. When the wear-resistant sintered alloy is used under a high load and a high surface pressure, the C content is set to 2.0 to 4.2% by mass.
And at the same time, the Cr content is 12.0 to 2
It is preferable to set it as high as 4.0% by mass.

Cr is adjusted in the range of 2.0 to 24.0% by mass in accordance with the mechanical characteristics of the mating member. However, when the Cr content exceeds 24.0% by mass, the degree of refining the Cr carbide becomes small, and the hardness becomes too large. If the Cr content is less than 2.0% by mass, the carbides of Cr become slightly coarse, so that fine carbides of high hardness cannot be sufficiently precipitated, and have sufficient wear resistance and scuffing resistance. Absent. For this reason, the Cr content is limited to 2.0 to 24.0% by mass. When used under a high load and a high surface pressure, it is preferable to set the above range in relation to the C content.

Mo is added as a solid solution in the matrix to increase the hardness and to improve the wear resistance. However, this effect hardly changes even if the Mo content exceeds 3.0% by mass. If the Mo content is less than 0.5% by mass, such effects cannot be sufficiently exerted. For this reason, the Mo content is limited to 0.5 to 3.0% by mass. Mo within this range does not affect the amount of retained austenite.

Si is a component that promotes the formation of a liquid phase when the contents of C and P are reduced. However, if the Si content is less than 0.2% by mass, the effect of promoting the liquid phase cannot be obtained. Further, Si is added as an oxygen scavenger at the time of powder production, so that some remains. 0.2% by mass as controllable range
Was set as the lower limit. On the other hand, if the Si content exceeds 1.0% by mass, the matrix becomes brittle, the powder compactability of the powder decreases, and the deformation of the sintered alloy after sintering increases. For this reason,
The Si content is limited to 0.2 to 1.0% by mass.

P causes the Fe—C—P eutectic steadite. Stedite has a very high hardness and a freezing point of 9
Since the temperature is as low as about 50 ° C., liquid phase sintering is promoted. But,
If the P content exceeds 1.0% by mass, excessive staedite is generated, resulting in poor machinability. If it is less than 0.2% by mass, the precipitation amount of the stadite is small, so that high abrasion resistance cannot be obtained and a liquid phase hardly occurs. For this reason,
The P content is limited to 0.2 to 1.0% by mass.

As the component compositions other than those described above, Mn,
One or more of B, V, Ti, Nb and W can be added in appropriate amounts as needed. The purpose of adding these elements is to promote the generation of a liquid phase and the formation of carbides during liquid phase sintering, but the amount of addition is 0.1 to 5.0 in consideration of the hardness of the mating member. It is desirable to appropriately add an appropriate amount within the range of mass%. Furthermore, 300 ppm or less of Ca can be added for the purpose of improving workability. Further, the addition of Mn of 1.0% by mass or less is effective in strengthening the matrix, but when the Mn content exceeds 1.0% by mass, the progress of sintering is suppressed, so that coarse pores remain. As a result, the compactibility and sinterability are reduced.

Next, a method of manufacturing a first cam made of a wear-resistant sintered alloy will be described.

The first cam 3 is provided with a predetermined amount of various metal powders in iron powder as a main component or iron-based alloy powder containing a predetermined element so that the final component composition is within the above range. The powder for wear-resistant sintered alloy was added and adjusted, and then, by a normal sintering method, first, the powder for sintered alloy was press-formed to form a green compact having a predetermined shape. It is manufactured by sintering a green compact by a liquid phase sintering method. It is preferable to add a lubricant such as zinc stearate to the powder for the sintered alloy in order to improve the compaction property and mold release property at the time of mold molding. The preferable processing temperature of the liquid phase sintering is 1100 to 1200C, more preferably 1110 to 1160C. The sintering time at this time is preferably about 60 to 90 minutes. Further, if necessary, a tempering process or the like can be performed to adjust the characteristics of the obtained first cam.

In manufacturing the first cam 3, the first cam 3 and the cam shaft 2 are firmly diffusion-bonded by the shrinkage and diffusion phenomenon when the green compact of the first cam is subjected to liquid phase sintering. be able to. Specifically, in the case of a camshaft in which a camshaft and a cam made of a sintered alloy are assembled, high-density sintering of the first cam 3 and the first cam 3 2 can be bonded to the camshaft firmly by simultaneously performing the bonding process of diffusion bonding.

(2) Second Cam The second cam 4 has a property (excellent pitting resistance) in which surface damage due to rolling fatigue is extremely unlikely to occur with a mating member in rolling contact, and an excellent resistance to pitting. It is formed of a material exhibiting abrasion properties. In the present invention, a pitting-resistant sintered alloy or a pitting-resistant steel that has been quenched and tempered can be preferably used.

First, the second cam made of a pitching-resistant sintered alloy will be described.

The pitting-resistant sintered alloy for forming the second cam 4 is made of a pitting-resistant sintered alloy containing fine precipitated carbides in a base structure mainly composed of martensite and bainite. is there. Its component composition is
C: 1.5 to 4.2% by mass, Cr: 2.0 to 24.0% by mass, Mo: 0.5 to 3.0% by mass, Si: 0.2 to
1.0% by mass, P: 0.2 to 1.0% by mass, Ni: 1.
0 to 2.5% by mass, balance: Fe and inevitable impurities.

As shown in FIG. 5, the base structure of the pitting resistant sintered alloy has a large number of precipitated carbides such as Cr carbide 42 and Cr-Fe-Mo-P composite carbide 43 in its base structure 41. Since the base structure 41 is reinforced by the base structure composed of martensite-bainite-retained austenite, the base structure 41 has high strength, high toughness, high wear resistance, and excellent pitting resistance. It should be noted that a sintered alloy having a base structure of pearlite-bainite-retained austenite also has similar characteristics and can be preferably used as the second cam.

The second cam 4 made of a sintered alloy is different from the first cam only in that the Ni content is 1.0 to 2.5% by mass. The sintered alloy having the Ni content in this range changes to a matrix structure as shown in FIG.
As shown in FIG. 4, there is much retained austenite in the base structure. Therefore, high toughness and excellent fatigue resistance and wear resistance can be exhibited. But N
Even if the i content exceeds 2.5% by mass, the effect does not change. When the Ni content is less than 1.0% by mass, the amount of retained austenite becomes 10% or less, and the excellent fatigue resistance and wear resistance required for the second cam 4 that comes into rolling contact cannot be sufficiently satisfied. Furthermore, since the base structure is also mainly composed of pearlite, the pitching resistance required for the second cam 4 in rolling contact cannot be sufficiently satisfied. Therefore, the Ni content is set to 1.0 to 2.5 mass%.
Limited to.

It is to be noted that the second cam 4 which is in rolling contact does not necessarily require no scuffing resistance. Therefore, if it is desired to slightly improve the scuffing resistance, the Ni content should be slightly lowered. Thus, it is possible to improve the pearlite ratio of the base structure and reduce the amount of retained austenite in the base structure, which is a cause of scuffing.
When the pitting resistance is more important, the Ni content may be slightly increased to form a base structure mainly composed of martensite and bainite, thereby providing high pitting resistance.

The action of each component element other than Ni contained in the pitting resistant sintered alloy and the reason that each component element is limited within the above range are as described above for the first wear resistant sintered alloy for cams. Is the same as Furthermore, regarding the manufacturing method of the second cam made of a pitting resistant sintered alloy,
This is the same as the case of the first cam 3 made of the sintered alloy described above.

Next, a description will be given of a second cam made of pitting-resistant steel that has been subjected to quenching and tempering.

The second cam 4 has improved mechanical properties, particularly fatigue resistance, by quenching and tempering S50C (carbon steel), SCr (chromium steel), SCM (chromium molybdenum steel) or the like. It can be made of steel. The conditions of the quenching and tempering are appropriately set by a usual method while taking into consideration the characteristics of the obtained cam. The obtained second cam exhibits excellent pitting resistance and can be preferably used as a rolling contact type cam.

(3) Manufacture of camshaft As shown in FIG. 1, the camshaft 1 of the present invention is mounted on a steel pipe camshaft 2 by attaching the first cam 3 and the second cam 4 described above.
Are joined at predetermined positions according to mating members having different contact forms so as to have a predetermined operation angle. As the joining method of the cam and the cam shaft, a method by diffusion joining and a method by mechanical press-fitting can be preferably applied.

In the diffusion bonding method, a wear-resistant sintered alloy for a first cam and a pitching-resistant sintered alloy for a second cam in a powdered state before sintering are fixed to a cam shaft. And the respective cams are liquid-phase-sintered by the liquid-phase sintering method and are diffusion-bonded to the camshaft.

In the present invention, the wear-resistant sintered alloy for the first cam and the pitting-resistant sintered alloy for the second cam having different component compositions can be sintered at the same temperature and at the same temperature. The feature is that it can be diffusion bonded. Therefore, since the sintering of each cam itself and the diffusion bonding between the cam shafts can be performed simultaneously at the same temperature, the camshaft can be manufactured extremely efficiently.

At this time, the optimum conditions for sintering and diffusion bonding at the same temperature while maintaining excellent characteristics of each cam are as follows:
And P. Specifically, the contents of C and P of the wear-resistant sintered alloy component for the first cam are made smaller than the contents of C and P of the pitching-resistant sintered alloy component for the second cam. By lowering each by 0.1 to 0.3% by mass, sintering / diffusion bonding can be performed stably and with good quality reproducibility. As described above, the contents of C and P are adjusted by controlling the Ni content contained in each sintered alloy.
It is based on the difference in content. That is, while the Ni content is small in the wear resistant sintered alloy for the first cam, the Ni content is large and the carbide precipitation amount is large in the pitching resistant sintered alloy for the second cam. The sintering temperature for maintaining the optimum properties of the pitching resistant sintered alloy for the second cam tends to be slightly higher. In order to keep the optimum sintering temperature consistent while maintaining the optimum characteristics of each cam as much as possible, in the present invention, C
By adjusting the contents of P and P, the sintering / diffusion bonding conditions are optimized. For example, the components of the wear-resistant sintered alloy for the first cam are as follows: C: 2.2% by mass, Cr: 8.
0% by mass, Mo: 1.0% by mass, Si: 0.8% by mass,
Ni: 0.3% by mass, P: 0.3% by mass, Fe: remaining,
And the component composition of the pitching resistant sintered alloy for the second cam is C: 2.4% by mass, Cr: 12.0% by mass, Mo:
Sintering and diffusion bonding can be performed at the same temperature, with 1.0 mass%, Si: 0.8 mass%, Ni: 1.5 mass%, P: 0.5 mass%, and Fe: remaining.

In the present invention, since there is no need to perform a surface treatment for imparting scuffing resistance such as a steam treatment after the diffusion bonding treatment, it is possible to manufacture a camshaft more efficiently and at lower cost than before. it can.

The press-fitting method is a method of joining a cam to a cam shaft by a method as disclosed in Japanese Patent Application Laid-Open No. Hei 5-10340. That is, a first cam 3 made of a wear-resistant sintered alloy, a pitching-resistant sintered alloy or a quenching and tempering process is applied to a steel pipe camshaft 2 having a raised portion formed at a predetermined position by rolling. The camshaft is manufactured by a method in which the obtained second cam 4 made of the pitting-resistant steel is sequentially pressed into a predetermined position at a predetermined angle and joined. The first cam made of the wear-resistant sintered alloy, the second cam made of the pitting-resistant sintered alloy, and the second cam made of the hardened and tempered pitting-resistant steel are all reinforced. As it is excellent in tensile strength and fatigue strength, it can be fitted more firmly by press-fitting, and those cams can be firmly joined to the cam shaft without the risk of cam displacement or cam cracking as in the past. .

As described above, the camshaft 1 of the present invention
A plurality of cams 3 and 4 having different contact modes with a mating member, such as a camshaft having a slipper follower 5 and a roller follower 6 as a mating member, are provided with a sintered alloy or Because it was formed by steel,
The durability and reliability of the camshaft 1 can be further improved, and the workability and cost are excellent.

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the camshaft of the present invention will be described more specifically.

(Example 1) The component composition after sintering was C:
2.4% by mass, Cr: 12.0% by mass, Mo: 1.0% by mass, Si: 0.8% by mass, Ni: 1.9% by mass, P:
Each element was added to iron powder so that 0.5 mass%, Fe: remaining, and the powder for sintering was adjusted. Further, zinc stearate was added and mixed as a lubricant. Then,
After press molding with a surface pressure of 7 t / cm ² to form a green compact, it is assembled on a steel pipe camshaft, and then put in a vacuum furnace at 1100 to 1100 cm 2.
After sintering at a temperature of 1200 ° C. (average 1160 ° C.), finishing was performed with a cam grinder to obtain a sintered alloy camshaft of Example 1.

Example 2 The component composition after sintering was C:
2.6% by mass, Cr: 8.0% by mass, Mo: 2.0% by mass, Si: 0.8% by mass, Ni: 1.9% by mass, P:
Each element was added to iron powder so that 0.5 mass%, Fe: remaining, and the powder for sintering was adjusted. In other respects, a camshaft made of the sintered alloy of Example 2 was obtained as in Example 1.

(Example 3) The component composition after sintering was C:
2.0% by mass, Cr: 4.0% by mass, Mo: 2.0% by mass, Si: 0.8% by mass, Ni: 1.9% by mass, P:
Each element was added to iron powder so that 0.5 mass%, Fe: remaining, and the powder for sintering was adjusted. Other than that, the camshaft made of the sintered alloy of Example 3 was obtained as in Example 1.

(Example 4) The component composition after sintering was C:
2.4% by mass, Cr: 12.0% by mass, Mo: 1.0% by mass, Si: 0.8% by mass, P: 0.5% by mass, Fe:
The powders for sintering were prepared by adding the respective elements to the iron powder so as to obtain the following. In other respects, a camshaft made of the sintered alloy of Example 4 was obtained as in Example 1.

(Example 5) The component composition after sintering was C:
2.2% by mass, Cr: 8.0% by mass, Mo: 2.0% by mass, Si: 0.8% by mass, Ni: 0.3% by mass, P:
Each element was added to iron powder so that 0.3 mass%, Fe: remaining, and the powder for sintering was adjusted. Other than that, the camshaft made of the sintered alloy of Example 5 was obtained as in Example 1.

Example 6 The composition after sintering was C:
2.0% by mass, Cr: 4.0% by mass, Mo: 1.0% by mass, Si: 0.8% by mass, Ni: 1.0% by mass, P:
Each element was added to iron powder so that 0.5 mass%, Fe: remaining, and the powder for sintering was adjusted. Other than that, the camshaft made of the sintered alloy of Example 6 was obtained as in Example 1.

(Embodiment 7) As a rolling contact type cam used in a mechanical press-fitting method, S50C material was subjected to induction hardening and tempering, and then joined to a steel pipe cam shaft by a press-fitting method. Finishing was performed with a grinder to obtain a hardened and tempered steel camshaft of Example 7 having a surface hardness of about Hv720.

(Comparative Example 1) The component composition was as follows: C: 3.4% by mass, Cr: 0.8% by mass, Mo: 2.0% by mass, Ni +
Cu: 2.0% by mass, Si: 2.0% by mass, B: 0.4
% By mass, Mn: 0.7% by mass, Fe: Remaining, each element was dissolved, poured into a mold provided with a chill, cooled, and then finished with a cam grinder. A cam shaft made of chill cast iron was obtained.

Comparative Example 2 The sintered alloy cam of Example 1 was treated in a steam treatment furnace at a temperature of 550 to 600 ° C. for 90 minutes to obtain a sintered alloy cam of Comparative Example 2.

(Evaluation Method) Examples 1 to 7 and Comparative Example 1
2 and a sliding contact type slipper follower and a rolling contact type roller follower were used as mating members of each cam. In the test, a motoring test device capable of freely adjusting the load (surface pressure) applied to the cam by changing the compression amount of the spring was used.

The scuffing resistance is 1000 r. p.
m. The load (surface pressure) when scuffing occurred by changing the load (surface pressure) was evaluated as the critical surface pressure. The pitting resistance is 3000 r.p. p.
m. At high speed and changing the load (surface pressure), the load (surface pressure) when pitching occurred was evaluated as the critical surface pressure. The determination of the occurrence of pitching was based on monitoring of abnormal noise occurring at the time of occurrence of pitching and observation of the sliding surface.

(Evaluation Results) FIG. 6 shows the results of evaluating the scuffing resistance and pitting resistance of the cams obtained in Examples 1 to 7 and Comparative Example 2 in comparison with the critical surface pressure of Comparative Example 1. It is a graph shown. In the figure, the criteria for scuffing resistance and pitting resistance required for the first cam in sliding contact and the criteria for scuffing resistance and pitting resistance required for the second cam in rolling contact are shown. Each is shown.

The sintered alloy cams of Examples 1 to 3 and the steel cam of Example 7 all have the following criteria regarding the scuffing resistance and the pitting resistance required for the second cam in rolling contact. Was exceeded. In particular, the pitting resistance was significantly superior to the conventional cam shown in Comparative Example 1.

The cams made of the sintered alloys of Examples 4 to 6 are based on the standard required for the first cam in sliding contact and the value of the conventional cam shown in Comparative Example 1 with respect to the scuffing resistance and the pitting resistance. Both were exceeded. In addition, the same characteristics as the cam subjected to the steam treatment shown in Comparative Example 2 were shown.

[0066]

As described above, according to the present invention,
The first cam is formed of a wear-resistant sintered alloy in which fine carbides are precipitated in a base structure mainly composed of pearlite, and the second cam is formed in a base structure mainly composed of martensite and bainite. Since it is formed of a pitting resistant sintered alloy in which a carbide is precipitated, by providing a cam having characteristics according to the contact mode, it is possible to further improve the durability and reliability of the camshaft. The first cam that comes into sliding contact does not require steam treatment as in the related art, so that the camshaft can be efficiently manufactured without any problem such as bending.

Further, since the sintering of the first cam and the second cam and the joining based on the diffusion sintering to the cam shaft can be performed simultaneously at the same temperature, the cam shaft is firmly and extremely manufactured. The camshaft can be manufactured efficiently.

Further, according to the present invention, a first cam made of a wear-resistant sintered alloy in which fine carbides are precipitated in a base structure mainly composed of pearlite; Since the second cams made of steel are all excellent in mechanical properties such as tensile strength, a camshaft in which those cams are firmly mechanically joined (press-fitted) to the camshaft can be manufactured. . Therefore, when using a conventional chill cast iron cam with relatively small mechanical strength,
There is no problem that the cam cannot be firmly mechanically joined to the camshaft, and there is no risk of cam displacement or cracking during operation.

[Brief description of the drawings]

FIG. 1 is an example of an overall view of a camshaft according to the present invention.

FIG. 2 is a perspective view showing an aspect in which a cam included in a camshaft according to the present invention contacts a mating member.

FIG. 3 is a micrograph showing an example of a matrix structure of a first sintered alloy for a cam.

FIG. 4 is a graph showing the relationship between the Ni content (%) in a sintered alloy and the retained austenite content (%) in a matrix structure.

FIG. 5 is a micrograph showing an example of a base structure of a second sintered alloy for cams.

6 is a graph showing the results of evaluating the scuffing resistance and the pitting resistance of the cams obtained in Examples 1 to 7 and Comparative Example 2 in comparison with the critical surface pressure of Comparative Example 1. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Camshaft 2 Camshaft 3 First cam 4 Second cam 5 Slipper follower 6 Roller follower 31, 41 Base structure 32 Carbide 42 Cr carbide 43 Cr-Fe-Mo-P composite carbide

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G016 AA19 BA25 BA34 CA52 EA03 EA10 EA24 FA11 FA13 FA16 FA17 FA19 FA33 GA02 3J030 EA01 EA14 EB01 EB09 EC04 EC07 4K018 AA32 BA04 BA09 BA14 BA20 DA13 KA02 KA70

Claims (4)

[Claims] 1. A camshaft comprising a plurality of cams having different contact forms with a mating member, the camshaft having a first cam slidingly contacting the corresponding mating member and a second cam rolling contacting with the corresponding mating member. Is made of a wear-resistant sintered alloy in which carbides are precipitated in a base structure mainly composed of pearlite, and the second cam has a pitting resistance in which carbides are precipitated in a matrix structure mainly composed of martensite and bainite. A camshaft comprising a sintered alloy. 2. The wear-resistant sintered alloy according to claim 1, wherein C: 1.5 to
4.2% by mass, Cr: 2.0 to 24.0% by mass, Mo:
0.5 to 3.0% by mass, Si: 0.2 to 1.0% by mass,
P: 0.2 to 1.0% by mass, Ni: 0 to 1.0% by mass,
The balance: Fe and unavoidable impurities, wherein the pitting resistant sintered alloy contains 1.5 to 4.2% by mass of C, 2.0 to 24.0% by mass of Cr, and 0.5 to 100% of Mo.
3.0% by mass, Si: 0.2 to 1.0% by mass, P: 0.
2 to 1.0% by mass, Ni: 1.0 to 2.5% by mass, balance: Fe and inevitable impurities, the first cam made of the wear-resistant sintered alloy and the pitting-resistant sintering bond The camshaft according to claim 1, wherein the second cam made of gold is joined to the shaft by a diffusion joining method. 3. A camshaft comprising a plurality of cams having different contact forms with a mating member, the camshaft having a first cam slidingly contacting the corresponding mating member and a second cam rolling contacting with the corresponding mating member. Is made of a wear-resistant sintered alloy in which carbides are precipitated in a base structure mainly composed of pearlite, and the second cam is made of a pitting-resistant steel that has been quenched and tempered. shaft. 4. The wear-resistant sintered alloy according to claim 1, wherein C: 1.5 to
4.2% by mass, Cr: 2.0 to 24.0% by mass, Mo:
0.5 to 3.0% by mass, Si: 0.2 to 1.0% by mass,
P: 0.2 to 1.0% by mass, Ni: 0 to 1.0% by mass,
The balance: Fe and unavoidable impurities, wherein the first cam made of the wear-resistant sintered alloy and the second cam made of the pitting-resistant steel are joined to the shaft by a press-fitting method. The camshaft according to claim 3, wherein