JPH0426930B2 - - Google Patents

Description

[Detailed Description of the Invention] 〓Field of Industrial Application〓 The present invention relates to a method of manufacturing a piston for an internal combustion engine, and particularly to a piston for an internal combustion engine in which a cooling cavity is formed in the head using a soluble core. Relating to a manufacturing method.

〓Background technology and its problems〓 The temperature of pistons used in high-load engines tends to rise, and as the temperature rises, ring stays and piston ring scuffs tend to occur. In order to prevent such ring sticks and piston ring scuffs, a cooling cavity 3 is formed inside the head 2 of the piston 1, as shown in FIG. 1, for example. By passing cooling oil through this cavity, the head 2 of the piston 1 can be cooled. In order to manufacture such a piston 1, a water-soluble soluble core made by pressing and sintering common salt or melting and casting common salt is used, and this core is Casting is carried out using a stator attached to the core of the mold that forms the piston 1, and after casting, the above-mentioned cooling cavity 3 is formed by dissolving and removing the above-mentioned soluble core with water. I try to do that.

The fixation of the soluble core made of salt or the like to form such a cooling cavity 3 is carried out using a boss 5 in which the pin hole 4 of the piston 1 is formed, as shown in FIG.
A support pin 6 was disposed at this portion, and the soluble core was supported by this pin 6. A hole in the piston 1 formed after removing the pin 6 is used to form an inlet and outlet for cooling oil. Another method is to use a pin boss 5 in which a pin hole 4 is formed, as shown in FIG.
The soluble core was supported by three support pins 6 placed near the ceiling of the inner surface of the piston 1 away from the piston 1.

However, when supporting the soluble core using the support pins 6 arranged as shown in FIG. 2 or 3, there were problems in both cases. That is, as shown in FIG. 2, when supporting by a pair of support pins 6 disposed at the pin boss 5, the soluble core 7 is supported at two points, so that the fourth
As shown by the arrow in the figure, the position of the core 7 becomes difficult to determine, causing the position of the cooling cavity 3 formed in the piston 1 to change in the direction of the arrow. However, there was a drawback that the cooling effect of the piston 1 varied in the direction of the arrow.

In addition, when the piston is supported by three support pins 6 as shown in FIG. During operation of piston 1, more than necessary flowed out, and as a result, piston 1 could not be cooled sufficiently.

In order to further reduce the weight of piston 1,
It is necessary to create a structure that removes unnecessary waste. Therefore, in such a case, an undercut portion may be formed inside the piston 1. In order to form the undercut, it is necessary to make the core of the piston casting mold separable. That is, as shown in FIG. 5, the core of the mold for casting the piston 1 must be formed from an entercore 8 and a pair of side cores 9 on both sides.

However, when such a mold is used, if the support pin 6 is arranged at the position shown in FIG. 2, the support pin 6 will get in the way when the side core 9 is moved toward the center. Therefore, after pulling out the seta core 8 downward, it is necessary to remove the support pin 6 downward before moving the side core 9 toward the center. Therefore, the support pin 6 that supports the soluble core 7 must be formed separately from the side core 9, and the structure must be such that the support pin 6 can be removed downward from the side core 9. However, with such a structure, the accuracy of supporting the core 7 for forming the cavity 3 may deteriorate, or burrs may occur due to wear between the support pin 6 and the side core 9, which may shorten the life of the mold. There is a problem with making it shorter.

Furthermore, if such a splittable mold core is used and the support pins 6 are arranged as shown in FIG. I can't make it bigger,
This makes the soluble core 7 easy to wobble.
Conversely, if the positional accuracy of the soluble core 7 is increased, it becomes impossible to use a mold divided into the center core 8 and the side cores 9, and it becomes impossible to form an undercut portion in the piston 1. Therefore, the piston 1 comes to have some waste.

〓Object of the Invention〓 The present invention has been made in view of the above-mentioned problems, and is designed to accurately support a soluble core for forming a cooling cavity, and also to support an undercut using a splittable mold. It is an object of the present invention to provide a method for manufacturing a pinton for an internal combustion engine in which the amount of waste material is reduced.

〓Summary of the Invention〓 The present invention provides a method for injecting a molten metal into the mold and solidifying the molten metal with the soluble core supported by the mold core, and melting the soluble core after solidification. In the method in which a cooling cavity is formed in the head, the core of the mold is formed from a core divided into a plurality of parts, and the soluble core is divided into two parts in a direction substantially orthogonal to the axial direction of the piston pin. A method of manufacturing a piston for an internal combustion engine, characterized in that the piston is supported by the divided center core of the mold core at points, and an undercut portion is formed by the side cores, In particular, by supporting the soluble core on the divided center core of the mold core at two points in a direction substantially orthogonal to the axial direction of the piston pin, it is possible to undercut the inside of the piston using a splittable mold. This is done by forming a section and removing unnecessary meat. In a further preferred embodiment, the support pin for supporting the soluble core on the center core has a cross-sectional shape of an approximately oval shape that is large in the circumferential direction of the piston and small in radius, and is supported at two points. The soluble core is held in position with high precision.

〓Example〓 The present invention will be described below with reference to an illustrated example.
FIG. 6 shows a mold core 15 used in a manufacturing method according to an embodiment of the present invention. and a side core 17. The center core 16 is integrally provided with a base 18 at its lower part, and the side core 17 is formed with a protrusion 19 on its upper end side, and this protrusion 19 forms an undercut part into a piston. It's becoming like that. A soluble core 21 is supported by the center core 16 via support pins 20.

The support pin 20 for supporting the soluble core 21 on the mold core 15 has a substantially elliptical cross-sectional shape that is large in the circumferential direction of the piston 23 and small in the radial direction, as shown in FIG. It has a shape in which the ratio of the radial dimension a to the circumferential dimension b is approximately 1:2. Furthermore, as is clear from FIG. 7, the pair of support pins 20 are arranged in a direction perpendicular to the axial direction of the piston pin 22 that connects the piston 23 to the connecting rod.

In this way, the soluble core 21 becomes the core 1 of the mold.
When a pin was cast from an aluminum alloy using this mold 15 while supported by the piston 5, a piston 23 as shown in FIG. 8 was obtained. This piston 23 has a cooling cavity 26 formed inside its head 24 and on the outer circumferential side of a combustion chamber 25 consisting of a recessed portion. The cooling cavity 26 is formed by dissolving the salt-soluble core 21 in water after the aluminum alloy injected into the mold is solidified.
A boss 28 having a pin hole 27 is formed on the lower side of the cavity 26.
An undercut portion 29 is formed on the upper side of the piston 8 by the protrusion 19 of the side core 17 of the mold 15, and this undercut portion 29 removes unnecessary material from the piston 23 to reduce the weight. I have to.

As described above, according to the method for manufacturing the piston 22 according to this embodiment, the soluble core 2 is attached to the center core 16 of the mold 15, which has become divisible, via the support pin 20.
1 is supported, there is no need to remove the support pin 20 before moving the side core 17 toward the center. That is, it is sufficient to directly pull out the support pin 20 downward together with the center core 16, and then move the side core 17 toward the center and then pull it out downward. Therefore, it is possible to eliminate the drawbacks such as a decrease in the positional accuracy of the cooling cavity 26 or the occurrence of burrs. Furthermore, piston 23
A pair of support pins 20 having a cross-sectional shape that is long in the circumferential direction and small in the radial direction are used to support the soluble core 21.
Since the soluble core 21 is supported at two points, it is possible to stably support the soluble core 21. This also makes it possible to improve the positional accuracy of the cooling cavity 26, and to improve the cooling temperature. It becomes possible to eliminate variations. Furthermore, since the soluble core 21 is supported by the pair of support pins 20, 3
More than one hole is not formed in the piston 23, and therefore cooling oil can be prevented from flowing out of the hole before sufficient cooling is achieved.

Although the present invention has been described above with reference to an illustrated embodiment,
The present invention is not limited to the above embodiments, and various modifications can be made based on the technical idea of the present invention. For example, in the above example, the number of mold cores is 3.
Although it is a split type, the same effect can be obtained even if the center core is further divided into three parts and the whole is divided into five parts. Further, the cross-sectional shape of the support pin 20 in the above embodiment is not necessarily limited to the shape shown in FIG. 7, but may be an ellipse or other various shapes.

<Effects of the Invention> As described above, in the present invention, the core of the mold is formed from a core divided into a plurality of parts, and the soluble core is attached to the mold at two points in a direction substantially perpendicular to the axial direction of the piston pin. The core is supported by a divided center core, and an undercut portion is formed by the side cores.

Therefore, the soluble core comes to be supported by the center core of the mold core, which has become divisible, and there is no need to remove the support means for supporting the soluble core before moving the side cores toward the center. In other words, it becomes possible to directly pull out the support means for supporting the soluble core downward together with the center core, then move the side cores laterally toward the center, and then pull them out downward.

In addition, the divided side core of the mold core allows an undercut portion to be formed inside the piston, and this undercut portion allows the piston to be made lighter by removing waste material. .

Further, according to an embodiment in which the cross-sectional shape of the support means is large in the circumferential direction of the piston and small in the radial direction, the soluble core can be reliably supported without wobbling, and the cooling cavity can be formed with high precision.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing a conventional piston for an internal combustion engine, and is a cross-sectional view taken along the line ~ in FIG. 2, FIG. 2 is a cross-sectional view taken along the ~ line in FIG. A sectional view similar to Fig. 2, Fig. 4 is an external perspective view showing a soluble core for forming a cooling cavity in this piston, and Fig. 5 is a core of a mold into which this soluble core can be divided. FIG. 6 is a vertical cross-sectional view showing a core of a mold used in a piston manufacturing method according to an embodiment of the present invention, and FIG. 7 is a vertical cross-sectional view showing a state in which it is supported by Figure 8 is a vertical cross-sectional view of a piston cast using this mold. In addition, in the symbols used in the drawings, 15...Mold core, 16...Center core, 17...Side core, 20...Support pin, 21...Soluble core, 2
2... Piston pin, 23... Piston, 24...
...Head, 26...Cooling cavity, 27...Pin hole,
29...This is an undercut portion.

Claims (1)

[Scope of Claims] 1. Molten metal is injected into the mold with the soluble core supported by the mold core and solidified, and after solidification, the soluble core is melted to form the head part. In the method, the core of the mold is formed from a plurality of divided cores, and the soluble core is formed at two points in a direction substantially perpendicular to the axial direction of the piston pin. A method for manufacturing a piston for an internal combustion engine, characterized in that the piston is supported by a divided center core of the mold core, and an undercut portion is formed by side cores. 2. The support pin for supporting the soluble core in the mold has a substantially elliptical cross-sectional shape that is larger in the circumferential direction of the piston and smaller in the radial direction. A method for manufacturing a piston for an internal combustion engine according to item 1.