JPH0586815A - Manufacture of composite camshaft - Google Patents

Abstract

PURPOSE:To prevent a clearance from being formed between cam pieces and a shaft so as to provide a method for manufacturing a composite camshaft where the cam pieces can be firmly connected to the shaft. CONSTITUTION:A plurality of cam pieces 7 each provided with a projection and a through hole 8 having a tapered shape in the cam axial direction and having abrasion resistance, and a mold CB provided with a cavity 5 having a shape corresponding to a shape of a camshaft are manufactured. The cam pieces 7 are housed in predetermined positions inside the cavity 5 of the mold CB. The cavity 5 is filled with a molten aluminum alloy, and the camshaft where the cam piece 7 is inserted is cast. A pressure is applied to the cam piece 7 in the cam axial direction in such a manner as to enlarge the tapered shape of the through hole 8. The cam pieces 7 should be preferably caulked in a shaft in the vicinity of the end surface of the cam piece 7 as viewed in the cam axial direction.

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 composite camshaft.

[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 cam shaft, 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 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, and therefore a gap is generated between the cam piece and the shaft 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 increase the coupling strength between the cam piece and the shaft portion (see, for example, Japanese Patent Laid-Open Publication No. 2000-242242). (See JP-A-56-39356). However, even with such a manufacturing method, the amount of shrinkage of the shaft portion is still large, so that it is not possible to effectively prevent the formation of a gap between the cam piece and the shaft portion. The present invention has been made in order to solve the above-mentioned conventional problems, in a method for manufacturing a composite camshaft, in which a cam piece made of a wear-resistant material is cast with an aluminum alloy, a cam piece and a shaft portion are formed. It is an object of the present invention to provide a method for manufacturing a composite camshaft, which can prevent a gap from being generated between the cam piece and the shaft portion, and can firmly bond the cam piece and the shaft portion.

[0006]

In order to achieve the above object, a first aspect of the present invention provides a wear resistance in which a convex portion projecting inward is provided and a through hole having a taper shape is formed in a cam axis direction. And a plurality of cam pieces having a plurality of cam pieces and a molding die having a cavity portion capable of accommodating the cam pieces and having a shape corresponding to the shape of the cam shaft are manufactured. After arranging it in the position, fill the cavity with molten aluminum alloy and cast the cam piece, casting the cam shaft,
After that, each cam piece is pressed in such a direction that the tapered shape of the through hole expands in the cam axis direction, and a method for manufacturing a composite cam shaft is provided.

According to a second aspect of the present invention, in the method of manufacturing a composite camshaft according to the first aspect, after pressing each cam piece in such a direction that the tapered shape of the through hole expands, the cam piece is close to the end surface of the cam piece when viewed in the cam axis direction. Provided is a method for manufacturing a composite camshaft, characterized in that the shaft portion is crimped.

[0008]

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. The camshaft is manufactured by casting aluminum alloy. As shown in FIG. 1, the molding die CB used for manufacturing the camshaft S (see FIG. 3) is composed of an upper die 1 and a lower die 2, and the two dies 1 and 2 have a predetermined positional relationship. When assembled, a cavity 5 having a shape corresponding to the shape of the camshaft S is formed between the mold surface 3 (lower surface) of the upper mold 1 and the mold surface 4 (upper surface) of the lower mold 2. It is supposed to be done. Here, a plurality of cam piece accommodating portions 3a and a plurality of journal piece accommodating portions 3b are formed on the mold surface 3 of the upper mold 1. Further, a plurality of cam piece housing portions 4a and a plurality of journal piece housing portions 4b are also formed on the die surface 4 of the lower die 2.

An insulating layer 6 made of an electrically insulating material is provided in each of the cam piece accommodating portions 3a, 4a of the molds 1, 2 so that the cam piece 7 is inserted through the insulating layer 6 during casting. It is designed to be held within 2. As will be described later, since the cam piece 7 is electrically heated by using the current-carrying electrode 9 during casting, the insulating layer 6 is provided so that this current does not leak to the molds 1 and 2. .. In addition, at the time of casting, the journal piece housing portion 3
A cylindrical journal piece 11 having a hollow portion 12 is arranged in b and 4b, but since the journal piece 11 is not electrically heated, the journal piece accommodating portions 3b and 4b.
No insulating layer is provided on b.

As shown in FIGS. 2 (a) and 2 (b), the cam piece 7
Is a through hole 8 which penetrates this in the cam axis direction (the direction orthogonal to the paper surface in FIG. 2 (a) and the lateral direction in FIG. 2 (b)).
Is provided. A plurality of convex portions 15 and a plurality of concave portions 16 are formed on the peripheral surface of the through hole 8, that is, the inner peripheral surface of the cam piece 7, in order to enhance the bonding strength between the cam piece 7 and the casting during casting. .. The through hole 8 is formed so as to have a taper shape in the cam axis direction. Here, the taper angle θ, that is, the angle θ between the generatrix L ₂ of the through hole 8 and the cam axis direction L ₁ is set to, for example, tan ⁻¹ (1/10). The cam piece 7 is manufactured by a sintering method using an iron-based powder material having the following composition in order to improve wear resistance. After sintering, the outer peripheral surface of the cam piece 7 is hardened to improve wear resistance. <Cam piece material composition> C: 0.3 to 0.6 wt% 2. Mo: 0.5 to 1.5 wt% 3. Ni: 1.5 to 3.0 wt% (the balance is Fe)

A camshaft S (see FIG. 3) is manufactured by casting an aluminum alloy using the molding die CB, the cam piece 7 and the journal piece 11. The manufacturing method of the cam shaft S will be described below. To do. (1) As shown in FIG. 1, the lower half of the cam piece 7 is arranged in the cam piece housing portion 4a of the mold surface 4 of the lower mold 2 through the insulating layer 6, and the journal piece The lower half of the journal piece 11 is placed in the housing portion 4b. (2) The exposed portion of the cam piece 7 is housed in the cam piece housing portion 3a of the die surface 3 of the upper mold 1 through the insulating layer 6, and the exposed portion of the journal piece 11 is housed in the journal piece housing portion 3b. As described above, the upper die 1 and the lower die 2 are assembled. At this time, the electric heating electrode 9 is connected to the cam piece 7. (3) The cam piece 7 is energized through the electrode 9 for electric heating,
The cam piece 7 is heated to a temperature higher than a casting temperature of 740 ° C., which will be described later, for example, to 850 ° C. by electric heating to maintain this temperature. An electric heater may be used instead of the electric heating electrode 9 to heat the cam piece 7.

(4) Inside the cavity 5, aluminum alloy AC
Pouring and filling 4D molten metal. Here, the casting conditions are
For example, it is set as follows. <Casting conditions> 1. Pressure ………… 530kgf / cm²  2. Injection speed: 300 mm / sec 3. Casting temperature ... 740 ° C

(5) After the pouring, the molten aluminum alloy is solidified by air cooling to form a casting that surrounds the cam piece 7, that is, the camshaft S. At that time, the molten metal begins to solidify. Or, slightly later than this, for example, the energization heating of the cam piece 7 is stopped 5 to 10 seconds after the end of the pouring. Here, the molten metal solidified material in the cam part
(Shaft part) shrinks as it cools, but when the molten metal begins to solidify, the cam piece 7 has a high temperature (about 850
C.), the through hole 8
Has a larger diameter. Then, the molten metal solidified product contracts with reference to the through hole 8 having a large diameter, that is, the inner peripheral surface of the cam piece 7. Therefore, when the cooling is completed, the molten metal solidified product has a larger outer diameter than in the case where the cam piece 7 is not heated, but the cam piece 7 contracts as in the case where the cam piece 7 is not heated. Therefore, when cooling is completed, the shrinkage amount of the cam piece 7 and the molten metal solidification portion (shaft portion)
The difference between the contraction amount of the cam piece and the outer peripheral surface of the shaft becomes extremely small,
The joint strength between the cam piece 7 and the shaft portion is enhanced.

For comparison, the cam piece was heated to 850 ° C. in an atmospheric furnace and placed in a mold, and the cam shaft was cast under the other conditions in the same manner as described above. A gap of 10 to 20 μm was generated between the cam piece and the shaft portion. When the joining strength of this camshaft was examined, it was found that plastic deformation occurred due to a small torsional torque of 0.5 kgf · m or less, which was not practical as it was. Further, for comparison, when the cam shaft was cast without heating the cam piece at all, a gap of 20 to 50 μm was generated between the cam piece and the shaft portion in this cam shaft. And with this camshaft, 0.2kgf ・ m
It was found that the following extremely small torsional torque causes plastic deformation, which is not practical at all. Even with a camshaft having a large gap as in the above comparative example, the gap can be narrowed and the camshaft has sufficient durability by performing a pressurizing process in the taper expanding direction of the cam piece as described later. Of course it will be.

(6) The upper die 1 and the lower die 2 are removed, and the casting (camshaft S) is taken out. As shown in FIGS. 3 and 4, the cast product (cam shaft S) is composed of a cam piece 7 made of an iron diameter material and a shaft portion 17 made of an aluminum alloy around the cam portion. As described above, since the projection 15 and the recess 16 are formed in the through hole 8, the coupling strength between the cam piece 7 and the shaft portion 17 in the rotational direction is increased by this. (7) As shown by the arrow F in FIG.
The direction in which the tapered shape of the through hole 8 expands in the cam axis direction (see FIG.
Then, press or push to the left) to move about 0.2 to 0.3 mm. As a result, the cam piece 7 is pushed into the side where the diameter of the shaft portion 17 is large. As mentioned above,
Since the cam piece 7 is heated during casting,
Although the gap generated between the cam piece 7 and the shaft portion 17 is reduced, the gap between the cam piece 7 and the shaft portion 17 is completely filled by pressurizing or pressing the cam piece 7 in the F direction. The cam piece 7 and the shaft portion 17 are in close contact with each other, and the joint strength between them is significantly increased.
The durability of the camshaft S is improved.

(8) The shaft portion 17 is caulked at a position close to both end surfaces of the cam piece 7 in the cam axis direction. As a result, the cam piece 7 is moved to the shaft portion 17
On the other hand, it is fixed in the cam axis direction, and the joint strength (coupling strength) between the cam piece 7 and the shaft portion 17 is further increased. The caulking process may be performed only on the portion A near the end face where the taper shape of the cam piece 7 is narrowed, but it is preferable to perform the caulking process also on the portion B near the end face where the taper shape is widened. According to an experiment conducted by the inventors of the present application to confirm the effectiveness of the present invention, the joint strength of the cam portion of the cam shaft manufactured by the above manufacturing method is shown.
(Coupling strength) was very high, and the cam part had sufficient durability against cam grinding torque and torsion torque during operation.

[0017]

According to the first aspect of the invention, after the camshaft is cast, each cam piece is pressed in such a direction that the tapered shape of the through hole expands in the camshaft direction.
The cam piece is moved in this direction and is pushed into a portion of the shaft portion having a large diameter. As a result, the gap generated between the cam piece and the shaft portion is closed, and the cam piece and the shaft portion come into close contact with each other, so that the joining strength between the cam piece and the shaft portion is significantly increased, and the durability of the cam shaft is improved. To be enhanced.

According to the second invention, basically, the same operation and effect as those of the first invention can be obtained. Further, since the shaft portion is caulked at a position close to both end surfaces of the cam piece in the cam axial direction, the cam piece is fixed in the cam axial direction with respect to the shaft portion, and the gap between the cam piece and the shaft portion is fixed. The joint strength of is further improved.

[Brief description of drawings]

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

2 (a) and 2 (b) are a front elevational view and a side elevational view, respectively, of a cam piece.

FIG. 3 is a side view illustrating a camshaft manufactured by casting a cam piece with an aluminum alloy.

4 is a cross-sectional explanatory view of a cam portion of the cam shaft shown in FIG.

[Explanation of symbols]

 CB ... Mold S ... Cam shaft 5 ... Cavity part 7 ... Cam piece 8 ... Through hole 15 ... Convex part 17 ... Shaft part

Claims (2)

[Claims] 1. A plurality of wear-resistant cam pieces, each of which is provided with an inwardly projecting convex portion and is formed with a through hole having a tapered shape in a cam axis direction, and a cam which can accommodate the cam pieces and which can hold the cam pieces. Manufacture a mold equipped with a cavity that has a shape corresponding to the shaft shape,
Next, after placing each cam piece at a predetermined position in the cavity of the mold, the cavity is filled with molten aluminum alloy and the cam piece is cast to form a camshaft, after which each cam piece is moved in the cam axis direction. A method for manufacturing a composite camshaft, characterized in that pressure is applied in a direction in which the tapered shape of the through hole expands. 2. The method for manufacturing a composite camshaft according to claim 1, wherein each cam piece is pressed in a direction in which the tapered shape of the through hole expands, and then caulking is performed on the shaft portion near the end surface of the cam piece when viewed in the cam axis direction. A method for manufacturing a composite camshaft, characterized in that: