JPH0356143B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for obtaining a light alloy rocker arm for use in an overhead camshaft valve mechanism of an internal combustion engine by a die-casting method, and particularly relates to a method for obtaining a rocker arm made of a light alloy by a die-casting method. The present invention relates to a die-casting method for a rocker arm in which wear-resistant parts are integrated by means of rod wrapping.

BACKGROUND OF THE INVENTION A rocker arm used in an overhead camshaft valve mechanism of an internal combustion engine is formed, for example, in a shape as shown in FIG. That is, the rocker arm 01 has a thick cylindrical bearing part 02 in its center that fits with the rocker arm shaft, and a sliding surface 40 that slides on the valve drive cam is formed at the end of the arm 03.
A screw hole 06 for a valve clearance adjustment screw is formed at the end of the valve clearance adjustment screw. This Rotsuka arm 01
In addition to being made of ordinary cast iron, malleable cast iron, spheroidal graphite cast iron, etc., forged products are also available in recent years. In order to impart wear resistance to the sliding surface 04,
For cast products, the surface layer is hardened by chilling or flame hardening, and forged products are hardened by flame hardening, induction hardening, chrome plating, etc. Further, as another method for imparting wear resistance to the sliding contact surface 04, there is also an example of adhering a wear-resistant piece formed of a sintered material, a chilled cast plate, or the like.

On the other hand, in structural members for internal combustion engines, efforts are being made to reduce weight by adopting light alloy materials such as aluminum alloys and magnesium alloys.
Forming moving parts such as the rocker arm from a light alloy material is also effective in reducing inertial force. In particular, it is effective to form the rocker arm used in an overhead camshaft type valve mechanism suitable for high-speed engines from a light alloy material.

FIG. 2 shows a light alloy rocker arm 01A as an example. This Rotsuka Arm 01
A is obtained by die-casting, and a wear-resistant piece 03a made of iron-based sintered material, ceramics, etc. is integrated with the end of the arm 03 by casting. A sliding contact surface 04 with good wear resistance is obtained.

Problems to be Solved by the Invention When the rocker arm 01A shown in FIG.
The sprues will be placed in the positions indicated by the arrows, and the sprues will be oriented in the directions indicated by the arrows. By providing such a sprue, molten metal can be reliably supplied to the bearing portion 02, which requires a relatively large amount of molten metal, and to the end of the arm that is farthest from the sprue.

However, when sprue A is adopted, since the wear-resistant piece 03a is located on the side in the molten metal supply direction, the supply of hot water around the wear-resistant piece 03a having protrusions is delayed, resulting in poor adhesion. If a good cast-in structure cannot be obtained and sprue B is adopted, there will be no wear-resistant parts.
3a is located farthest from the sprue, the flow of the metal around the wear-resistant part 03a is poor, and similarly a good cast-in structure cannot be obtained. In either case, there is a risk that the wear-resistant piece 03a may be misaligned during pouring.

Furthermore, there is a possibility that cavities may be formed in the thick bearing portion 02.

Furthermore, in the device described in JP-A No. 61-3649, the sprue provided on the side where the wear-resistant piece is installed opens from the outside of the wear-resistant piece toward the surface of the wear-resistant piece. Therefore, when casting a wear-resistant part, the shape of the cast-in part becomes complicated, which delays the supply of hot water around the wear-resistant part, making it difficult to obtain a cast-in structure with good adhesion. Moreover, as a result of pouring the metal under high pressure, there was a risk that the wear-resistant piece having the protrusion on the back surface would be displaced during pouring.

Means and Effects for Solving the Problems The present invention relates to an improvement of a die-casting method for a rocker arm that overcomes the above-mentioned difficulties, and provides a rocker arm made of a light alloy for use in an overhead camshaft type valve mechanism of an internal combustion engine. In a die-casting method for a rocker arm, the rocker arm has a thick bearing portion that fits into the rocker arm shaft, and is integrally provided with a wear-resistant piece for cam sliding contact having a protrusion on the back surface. Using a mold in which a sprue is provided on the opposite side of the wear-resistant piece, with the rocker arm positioned toward the wear-resistant piece installation position, and the sprue is oriented in the direction of the wear-resistant piece installation position, This method is characterized in that molten metal is poured under pressure toward the back surface of the wear-resistant part.

Since the present invention is configured as described above,
As a result of the hot water being supplied directly from the sprue to the casting part without bypassing the wear-resistant part, the adhesion is good, and even though the hot metal is poured under high pressure, a pressing force acts on the mold. Prevents wear-resistant parts from shifting.

The present invention also provides a rocker arm made of a light alloy for use in an overhead camshaft valve mechanism of an internal combustion engine,
In a die-casting method for a rocker arm that has a thick bearing part that fits with the rocker arm shaft and is integrally equipped with a wear-resistant piece for cam sliding contact with a protrusion on the back surface, the sprue is oriented in the direction in which the wear-resistant piece is installed. After pouring metal under pressure toward the back surface of the wear-resistant part using a mold oriented in the positional direction, immediately before the molten metal solidifies, pour the metal into the thick bearing part using a pressurizing rod. Since a secondary pressing force is applied in the direction of the virtual rocker arm axis center line, even if the sprue is provided closer to the wear-resistant piece installation position than the bearing formation position, the thick bearing part will not be cast. The occurrence can be suppressed.

Embodiment Hereinafter, an embodiment of the die-casting method for a rocker arm for an internal combustion engine according to the present invention will be described with reference to the drawings shown in FIGS. 3 to 5.

Mold hole (cavity) 2 for rocker arm of mold 1
Inside, a wear-resistant piece 4 (made of iron-based sintered material, ceramics, etc.) having a protrusion 5 on its back surface is installed at a predetermined position. The sprue 3 is aligned with the virtual rocker arm axis center line L perpendicular to the plane of the paper in FIG.
The wear-resistant piece 4 is formed closer to the installation position, and the sprue 3 is oriented as shown by arrow C.
The wear-resistant pieces are oriented in four directions.

Also, a pressure rod (plunger) is hydraulically driven so that it can penetrate the wall of one of the mold elements 1A and 1B and enter the mold hole 2.
6 is provided. This pressure rod 6 is located on the virtual rocker arm axis center line L, and moves back and forth along the center line L (see FIG. 4).

When the mold 1 having such a structure is used and the light alloy is poured under pressure into the mold hole 2 through the sprue 3, the first molten metal is supplied around the wear-resistant piece 4, and after that area is filled, The molten metal is sequentially filled toward the concave portion 2a side that forms the bearing portion. Then, after the mold cavity 2 is completely filled with the molten metal and just before the molten metal in the concave portion 2a solidifies, the pressurizing rod 6 is advanced (double-dashed line in FIG. 4) to form a rocker arm to be obtained. Apply secondary pressure to the thick bearing part.

By pouring the metal toward the wear-resistant piece 4 in this way, the pressure of the molten metal can be actively used as an acting force for immovably fixing the wear-resistant piece 4 in a fixed position. It is possible to prevent the wear-resistant piece 4 from shifting, and to improve the adhesion between the molten metal and the wear-resistant piece 4.

The reason why the bearing part is subjected to secondary pressurization is to eliminate cavities that tend to occur in thick-walled parts where solidification is delayed. A fine and healthy crystal structure can be obtained, and excellent strength and wear resistance can be imparted to the bearing part, which is the part that fits with the rocker arm shaft.

Test example 1 Using JIS AC12 material, it was heated to a molten metal temperature of 670~
Molten metal was poured into mold 1 at 690° C. with a primary pressure of 600 kg/cm ² .

Obtained Rotsuka arm material 7 (see Figure 5)
This was then cut along a plane perpendicular to the virtual rocker arm axis center line L, and the gap between the main body 8 and the wear-resistant piece 4 was examined to check the adhesion between them, and it was found to be a maximum of 20 μm. On the other hand, when the gap was similarly examined for the rocker arm material cast with the mold sprue placed at the position of arrow B in FIG. 5, the gap was found to be at most 40 μm.

Test example 2 Using JIS AC12 material, it was heated to a molten metal temperature of 670~
Molten metal was poured into mold 1 at 690° C. with a primary pressure of 600 kg/cm ² .

Immediately before the bearing part solidified, the pressure rod 6 was advanced to apply a secondary pressing force of 2500 kg/cm ² to the thick bearing part of the rocker arm to be obtained.

The obtained Rotsuka arm material 7 (see Fig. 5).
(However, the drawing is shared with Test Example 1), this was cut along a plane perpendicular to the virtual rocker arm axis center line L, and the pin hole 10 was cut.
The bearing portion 9 in which the pores were formed was etched, and the size and number (N) of the pores were determined. The results are shown in FIG.

On the other hand, casting was carried out under the same conditions as above, except that secondary pressure was not applied, and the size and number of cavities (N) of the obtained rocker arm material were investigated in the same manner as described above. The result is the 7th
As shown in the figure.

<Evaluation of test results> It is clear that the secondary pressurization drastically reduces both the number and size of blowholes, and it is clear that a defect-free rocker arm of good quality can be obtained.

Furthermore, it can be seen that the cast-in property is improved by providing the sprue of the mold at a position close to the wear-resistant part and pouring the metal toward the wear-resistant part.

Effects of the Invention In the present invention, as described above, since the molten metal is poured under pressure toward the back surface of the wear-resistant piece, the molten metal flows smoothly onto the back surface of the wear-resistant piece and is brought into close contact with the back surface of the wear-resistant piece. As a result, both the cast-in properties of the wear-resistant piece and the casting quality of the rocker arm can be improved without causing any displacement of the wear-resistant piece.

Further, in the present invention, after performing the pressurized pouring and immediately before the molten metal solidifies, a pressure rod is used to apply a secondary pressing force in the direction of the center of the virtual rocker arm axis to the thick bearing portion. Therefore, even if the sprue is provided closer to the wear-resistant part installation position with respect to the bearing part formation position, the occurrence of casting cavities in the thick bearing part can be suppressed, and a uniform and fine crystal structure can be maintained in the same part. This makes it possible to improve the strength and wear resistance of the bearing part.

[Brief explanation of drawings]

1 and 2 are respectively front views of known rocker arms, FIG. 3 is a sectional view of essential parts of a mold used in the method of the present invention, FIG. 4 is a sectional view of the same mold, and FIG. 5 is a front view of the Rotsuka arm material obtained using the mold, FIG. 6 is a graph examining the number and size of cavities in the Rotsuka arm material, and FIG. 7 is a graph showing the number and size of cavities in the Rotsuka arm material as a comparative example. This is the graph I investigated. 1... Mold, 2... Mold hole, 2a... Concave portion, 3
... Sprue, 4... Wear-resistant piece, 5... Protrusion, 6...
...Pressure rod, 7...Rotsuka arm material, 8...Main body, 9...Bearing section, 10...Pin hole.

Claims (1)

[Scope of Claims] 1. A rocker arm made of light alloy used in an overhead camshaft type valve mechanism of an internal combustion engine, which has a thick bearing portion that fits with a rocker arm shaft, and a cam slide with a protrusion on the back surface. In a die-casting method for a rocker arm integrally provided with a contacting wear-resistant part, the rocker arm is placed on the side where the wear-resistant part is installed with respect to the bearing part formation position, and on the opposite side of the wear-resistant part with the rocker arm in between. A rocker arm for an internal combustion engine, characterized in that a mold is provided with a sprue and the sprue is oriented in the direction of the installation position of the wear-resistant part to pour molten metal under pressure toward the back surface of the wear-resistant part. die casting method. 2. A rocker arm made of light alloy used in an overhead camshaft type valve mechanism of an internal combustion engine, which has a thick bearing part that fits with the rocker arm shaft, and a wear-resistant piece for cam sliding contact with a protrusion on the back surface. In the die-casting method for a rocker arm, a sprue is provided closer to the wear-resistant part installation position with respect to the bearing part formation position, and the sprue is oriented in the direction of the wear-resistant part installation position. After pouring the molten metal under pressure toward the back surface of the wear-resistant part using the mold, immediately before the molten metal solidifies, a virtual rocker arm is poured onto the thick bearing part using a pressure rod. A die-casting method for a rocker arm for an internal combustion engine, characterized by applying a secondary pressing force in the direction of the shaft centerline.