JPH0586814A - Composite camshaft and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a composite camshaft where a cam piece and a shaft are firmly connected to each-other without forming a clearance between the cam piece and a cam nose, or a manufacturing method thereof. CONSTITUTION:A plurality of cam pieces 6 each having abrasion resistance and a mold provided with a cavity formed into a shape corresponding to a shape of a camshaft are manufactured. The cam piece 6 is housed inside the cavity of the mold. The cavity is filled with a molten aluminum alloy, thus casting the camshaft where the cam piece 6 is inserted. An insertion member (press-fitting pin 19) is press-fitted into a cam nose 15 made of an aluminum alloy. Preferably, a hole 16 is formed in the cam nose 15 by casting or boring. After casting, the insertion member (press-fitting pin 19) having a diameter larger than that of the hole 16 and rigidity higher than that of a casting material is press-fitted into the hole 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite camshaft and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, in automobiles, in order to improve running performance, higher output (higher performance) and lighter weight of engine are required. In order to increase the output of the engine, a DOHC (double overhead cam) mechanism, a multi-valve intake / exhaust mechanism, a variable valve mechanism, etc. are often used in the valve operating system. The number of shafts increases, and the structure becomes larger and more complicated. Also,
In recent years, the number of cylinders (displacement amount) tends to increase in order to achieve higher engine output, but with 6 or more cylinders, V-type engines are often used to shorten the overall length, and in this case the number of camshafts increases further. However, the valve train becomes even larger.
For this reason, in general, in an engine designed for high output,
There is a problem that the weight of the valve train becomes large, which hinders the weight reduction of the engine.

In order to cope with this, for example, a shaft is bored in the axial direction using a gun drill or the like, and the shaft is hollow so that the weight of the cam shaft is reduced, or a core is used for casting. A camshaft has been proposed in which the shaft portion is hollowed out. Further, there has been proposed a camshaft which obtains a similar effect by connecting a cam piece made of steel or a sintered alloy to a steel pipe (pipe shaft) by brazing, bulging caulking, plastic joining or the like. However, in these camshafts whose weight is reduced by making the shaft portion hollow, the weight reduction is limited because the entire camshaft is made of an iron-based material.

[0004]

Therefore, a cam shaft is formed of a material having high wear resistance only around the sliding surface of the cam and the other portion is formed of a lightweight aluminum alloy, for example, a cam piece formed of an iron material. A composite camshaft made by casting aluminum with an aluminum alloy has been proposed (see, for example, Japanese Patent Laid-Open No. Sho 5).
No. 8-121354). In such a camshaft, in the cam portion, only around the cam sliding surface (cam outer peripheral portion) is formed of an iron-based material (cam piece), and the cam nose portion or shaft portion inside thereof is formed of an aluminum alloy. However, in this case, the coefficient of thermal expansion of the aluminum alloy is much higher than the coefficient of thermal expansion of the iron-based material, so a gap is generated between the cam piece and the cam nose portion due to the difference in the coefficient of thermal expansion during cooling after the casting. As a result, there is a problem that the coupling strength between the cam piece and the shaft portion becomes low, and the durability of the cam shaft becomes low.

In order to improve this, there has been proposed a camshaft manufacturing method in which a concavo-convex portion is formed on the inner peripheral surface of the cam piece so as to enhance the coupling strength between the cam piece and the cam nose portion (or shaft portion). (For example, JP-A-5
6-39356 gazette). However, even with such a manufacturing method, since the amount of shrinkage of the cam nose portion is still large, there is a problem that it is not possible to effectively prevent a gap from being formed between the cam piece and the cam nose portion. The present invention has been made to solve the above-mentioned conventional problems, and in a composite camshaft formed by casting a cam piece made of a wear resistant material with an aluminum alloy, a cam piece and a cam nose portion are provided. It is an object of the present invention to provide a highly durable composite camshaft in which a cam piece and a shaft portion are firmly connected to each other without forming a gap between them, or a manufacturing method thereof.

[0006]

In order to achieve the above object, a first aspect of the present invention is to provide a plurality of cam pieces which are made of a wear-resistant material and serve as a cam outer peripheral portion, and which can accommodate the cam pieces and which has a cam shaft. Make a mold with a cavity that has a shape corresponding to the shape, then place each cam piece at a predetermined position in the cavity of the mold and fill the cavity with molten aluminum alloy to form the cam piece. A method for manufacturing a composite camshaft, which comprises casting a cast camshaft and then press-fitting an insertion member into a cam nose portion made of an aluminum alloy.

According to a second aspect of the present invention, in the method for manufacturing a composite camshaft according to the first aspect, a hole is formed in the cam nose portion by casting when the camshaft is cast, and the hole is formed in the hole after casting. A method for manufacturing a composite camshaft, characterized in that an insertion member having a larger diameter and higher rigidity than a casting material is press-fitted.

According to a third aspect of the present invention, in the method for manufacturing the composite camshaft according to the first aspect, after the camshaft is cast, a hole is formed in the cam nose portion by machining, and then the hole portion is formed in the hole. A method for manufacturing a composite camshaft, characterized in that an insertion member having a large diameter and higher rigidity than a casting material is press-fitted.

According to a fourth aspect of the present invention, in the method for manufacturing a composite camshaft according to the first aspect, when the camshaft is cast, a wedge-shaped insert member having a rigidity higher than that of the casting material is made to project at the end on the thickness side. Cast into the cam nose,
Provided is a method of manufacturing a composite camshaft, characterized in that an insert member is driven into a cam nose portion after casting.

A fifth aspect of the present invention is a composite camshaft formed by casting a plurality of cam pieces, which are made of wear-resistant material and serve as a cam outer peripheral portion, around an aluminum alloy. The cam nose portion is made of the aluminum alloy. Further, there is provided a composite camshaft, wherein an insert member having a rigidity higher than that of a casting material is press-fitted.

[0011]

EXAMPLES Examples of the present invention will be specifically described below.
In the camshaft manufacturing method according to the present invention, basically, after arranging the cam piece and the journal piece in the molding die, the molten aluminum alloy is poured into the cavity of the molding die to form the cam piece and the journal piece. Camshafts are manufactured by casting aluminum alloy. As shown in FIG. 1, the camshaft S (see FIG.
The molding die CB used for manufacturing (see FIG. 2) is composed of an upper die 1 and a lower die 2, and when both dies 1, 2 are assembled in a predetermined positional relationship, the die surface of the upper die 1 is 3 (bottom)
And the mold surface 4 (upper surface) of the lower mold 2 between the camshaft S
The cavity portion 5 having a shape corresponding to the shape of is defined. Here, on the mold surface 3 of the upper mold 1, a cam piece housing portion 3a and a journal piece housing portion 3b are provided.
And are formed. Also, on the mold surface 4 of the lower mold 2,
A cam piece housing portion 4a and a journal piece housing portion 4b are formed. The lower die 2 is provided with a core pin accommodating portion 11 described later at a position overlapping with the cam piece accommodating portion 4a.

The cam piece 6 is a cylindrical body having a hollow portion 7 and having a substantially uniform wall thickness, and is manufactured by a casting method or a sintering method using an iron-based material having excellent wear resistance. The outer peripheral surface of the cam piece is hardened to improve wear resistance. This cam piece 6 includes a cam shaft S (see FIG.
(See) When completed, it will become the cam sliding part. The cam piece 6 may be made of ceramic instead of iron-based material. Further, the journal piece 8 is a cylindrical body having a hollow portion 9 and having a uniform wall thickness, and is made of substantially the same material as the cam piece 6. The journal piece 8 becomes a journal portion when the camshaft S is completed.

A camshaft S (see FIG. 4) is manufactured by aluminum alloy casting using the molding die CB, the cam piece 6 and the journal piece 8. The manufacturing method of the camshaft S will be described below. .. (1) As shown in FIG. 1, the cam nose side half of the cam piece 6 is arranged in the cam piece housing portion 4a of the mold surface 4 of the lower mold 2, and the journal is housed in the journal piece housing portion 4b. Place half of piece 8 (no orientation). Incidentally, it goes without saying that the cam pieces 6 and the journal pieces 8 are respectively arranged in plural in the molding die CB. (2) The cylindrical core pin 12 is arranged in the core pin accommodating portion 11 of the lower mold 2. The core pin 12 is formed of a material having a melting point higher than that of an aluminum alloy, which is a casting material, and a coefficient of thermal expansion higher than that of the aluminum alloy, such as pure aluminum, so as not to melt during pouring. Core pin 12
Will be removed from the casting (camshaft) after casting, but since it is made of a material with a large coefficient of thermal expansion like this, the core pin 12 shrinks more than the surrounding aluminum alloy after casting. However, this makes it easy to remove the core pin 12. If a release agent having high heat resistance is applied to the outer peripheral surface of the core pin 12, the core pin 12 can be removed more easily. Here, the core pin 12 is arranged at a portion of the hollow portion 7 of the cam piece 6 on the cam nose side, that is, a portion which is substantially the central portion of the cam nose portion 15 (see FIG. 3) after casting.

(3) The exposed portion of the cam piece 6 is housed in the cam piece housing portion 3a of the die surface 3 of the upper mold 1, and the exposed portion of the journal piece 8 is housed in the journal piece housing portion 3b. , Assemble the upper mold 1 and the lower mold 2. (4) After pouring and filling molten aluminum alloy into the cavity 5, the molten metal is solidified by air cooling. (5) The upper die 1 and the lower die 2 are removed to take out the casting (camshaft S), and the core pin 12 is removed from the casting.
Remove. As described above, since the core pin 12 has a large coefficient of thermal expansion and the mold release agent is applied, the core pin 12 can be easily removed from the casting. As shown in FIG. 2 and FIG. 3, the casting comprises, around the cam portion, a cam piece 6 that is cast around, a shaft portion 14 and a cam nose portion 15 made of a solidified aluminum alloy. After the core pin 12 is removed, a columnar pin press-fitting hole 16 that penetrates the cam nose portion 15 in the camshaft axial direction (longitudinal direction) is formed in the substantially central portion of the cam nose portion 15. Here, since the thermal expansion coefficient of the aluminum alloy, which is the casting material, is larger than that of the iron-based material (or ceramic), which is the material of the cam piece 6, the cam nose portion 15 will not be attached to the cam piece 6 during cooling after pouring. The contraction amount is larger than that of the cam piece 6, and the gap 1 between the inner peripheral surface of the cam piece 6 and the outer peripheral surface of the cam nose portion 15 is 20 to 50 μm.
8 results. A protrusion 17 is formed at a portion corresponding to the core pin accommodating portion 11.

(6) As shown in FIG. 2, a substantially columnar press-fitting pin 19 having a chamfered tip end is press-fitted into the pin press-fitting hole 16 in the direction of arrow P. The press-fitting pin 19 is made of an iron-based material having a rigidity significantly higher than that of an aluminum alloy which is a casting material. The press-fitting pin 19 may be made of ceramic. Here, the diameter of the press-fitting pin 19 is set to a value larger than the inner diameter of the pin press-fitting hole 16. Moreover, the difference between the diameter of the press-fitting pin 19 and the inner diameter of the pin press-fitting hole 16 is set to a value larger than the gap 18 (20 to 50 μm), for example, 40 to 100 μm. In addition,
The press-fitting pin 19 corresponds to the insertion member described in claims 1, 2, 3, and 5. As shown in FIG. 4, the pin press-fitting hole 16
When the press-fitting pin 19 having a larger diameter is press-fitted,
The cam nose portion 15 made of an aluminum alloy is plastically deformed in the direction toward the outer periphery thereof, that is, in the direction toward the joint surface with the cam piece 6, whereby the gap 18 is closed and the cam piece 6 and the cam nose portion 15 are in close contact with each other. Therefore, the coupling strength between the cam piece 6 and the cam nose portion 15 (shaft portion 14) is enhanced, and the durability of the cam shaft S is significantly enhanced. Further, since the press-fitting pin 19 has high rigidity, the rigidity or strength of the cam nose portion 15 is increased, and the durability of the camshaft S is further improved. According to an experiment conducted by the present inventors to confirm the effectiveness of the present invention, the joint strength (coupling strength) of the cam portion of the camshaft manufactured by the above manufacturing method is very high, and the cam portion It had sufficient durability against grinding torque and torsional torque during operation. For comparison, a camshaft having a gap of 20 to 50 μm was manufactured between the cam piece and the cam nose part, and the joint strength of the cam part was examined. As a result, it was confirmed that even a small torsion torque of 0.2 kgf-m or less The part was deformed, which proved to be impractical.

In the above embodiment, the core pin 12 is used to form the pin press-fitting hole 16 by casting at the time of casting, but the core pin 12 is not used and a drill or the like is used after casting. The pin press-fitting hole 16 may be formed in the cam nose portion 15 by machining. Further, at the time of casting, a wedge-shaped insertion member such as a split pin is cast around the cam nose portion 15 so that the head protrudes to the outside of the cam nose portion 15, and the split pin is driven into the cam nose portion 15 after the casting. Therefore, the cam nose portion 15 may be plastically deformed to obtain the same effect.

[0017]

According to the first aspect of the present invention, the cam nose portion is plastically deformed in the outer peripheral direction by the press-fitting of the insertion member, and the gap between the cam piece and the cam nose portion is closed by the plastic deformation of the cam nose portion. The joint strength of the cam nose part is increased, and the durability of the camshaft is increased.

According to the second invention, basically, the same operation and effect as those of the first invention can be obtained. Further, since a hole is formed in the cam nose part by casting and the insertion member is press-fitted into this hole, the press-fitting is easy. Also, since the insertion member is made of a material with high rigidity,
The strength of the cam nose is increased, and the durability of the camshaft is further increased.

According to the third invention, basically, the same operation and effect as those of the first invention can be obtained. Furthermore, since a hole is formed in the cam nose part by machining and the insertion member is press-fitted into this hole, the press-fitting is easy.
Further, since the insertion member is made of a material having high rigidity, the strength of the cam nose portion is increased and the durability of the cam shaft is further improved.

According to the fourth invention, basically, the same operation and effect as those of the first invention can be obtained. Further, since the insert member is preliminarily cast around the cam nose portion, the post-casting process is easy. Further, since the insertion member is made of a material having high rigidity, the strength of the cam nose portion is increased and the durability of the cam shaft is further improved.

According to the fifth aspect of the invention, since the cam nose portion is plastically deformed toward the outer peripheral direction by the insertion member, the gap between the cam piece and the cam nose portion is closed and the joining strength between the cam piece and the cam nose portion is reduced. And the durability of the camshaft is increased. Further, since the insertion member is made of a material having high rigidity, the strength of the cam nose portion is increased and the durability of the cam shaft is further improved.

[Brief description of drawings]

FIG. 1 is an elevational sectional explanatory view of a molding die for manufacturing a camshaft.

FIG. 2 is a vertical cross-sectional explanatory view around the cam portion of the cam shaft before the press-fitting pin is press-fitted.

FIG. 3 is a cross-sectional explanatory view around the cam portion of the cam shaft before the press-fitting pin is press-fitted.

FIG. 4 is a cross-sectional explanatory view around the cam portion of the cam shaft after the press-fitting pin is press-fitted.

[Explanation of symbols]

 CB ... Mold S ... Cam shaft 5 ... Cavity part 6 ... Cam piece 12 ... Core pin 14 ... Shaft part 15 ... Cam nose part 16 ... Pin press-fitting hole 18 ... Gap 19 ... Press-fitting pin

Claims (5)

[Claims] 1. A plurality of cam pieces, which are made of a wear-resistant material and serve as a cam outer peripheral portion, and a molding die having a cavity portion capable of accommodating the cam pieces and having a shape corresponding to a cam shaft shape are manufactured. Then, after placing each cam piece at a predetermined position in the cavity of the molding die, the cavity is filled with molten aluminum alloy and the cam piece is cast to form a camshaft, after which the cam nose made of aluminum alloy is cast. A method for manufacturing a composite camshaft, characterized in that an insertion member is press-fitted into the portion. 2. The method for manufacturing a composite camshaft according to claim 1, wherein during casting of the camshaft, a hole is formed in the cam nose portion by casting, and the hole has a diameter larger than that of the hole after casting. A method for manufacturing a composite camshaft, characterized in that an insertion member having a rigidity higher than that of a casting material is press-fitted. 3. The method of manufacturing a composite camshaft according to claim 1, wherein after the camshaft is cast, a hole is formed in the cam nose part by machining, and then the hole has a diameter larger than that of the hole and is cast. A method for manufacturing a composite camshaft, characterized in that an insertion member having higher rigidity than a material is press-fitted. 4. The method for manufacturing a composite camshaft according to claim 1, wherein when the camshaft is cast, a wedge-shaped insert member having a rigidity higher than that of the casting material is cast into the cam nose portion so that the end portion on the thickness side protrudes. A method for manufacturing a composite camshaft, wherein the insert member is driven into the cam nose portion after casting. 5. A composite camshaft formed by casting a plurality of cam pieces made of wear-resistant material and forming a cam outer peripheral portion of an aluminum alloy, wherein the cam nose portion made of the aluminum alloy has a casting material. A composite camshaft in which an insert member having higher rigidity is press-fitted.