JPS6350452Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a ceramic piston in which a ceramic piston head is integrally cast with a piston body.

Ceramic has excellent heat resistance and heat insulation properties, making it suitable for forming pistons for internal combustion engines. A ceramic piston is obtained by making the piston head part from ceramic and joining it to the piston body. There are various joining methods, but the ceramic piston according to the present invention is obtained by integrally casting a ceramic piston head with a piston body. During casting, ceramic heads can crack due to the clamping force caused by the solidification of molten metal, so a proposal has been made to insert a metal ring around the outer periphery of the head, which receives the clamping force, to prevent the ceramic from cracking. being done.

Furthermore, ceramic piston heads obtained by sintering silicon nitride, silicon carbide, alumina, etc. are generally finished by lathe grinding, and then the above-mentioned casting is performed; Ceramic is extremely hard, so even if it is ground using a diamond grindstone, it will inevitably become tapered or stepped due to relief. That is, when grinding a ceramic piston head 1 with a diamond grindstone 100 as shown in FIG. 1, the method shown on the left side of the figure creates a taper at an angle θ in the radial direction. According to the method shown, a step 101 can be created. When a metal ring with perpendicular end faces is fitted onto a tapered surface (or stepped surface) in this way, an outwardly open space is created between the rings, which allows molten metal to flow during casting. As shown in FIG. 2 (corresponding approximately to the cross-sectional view taken along the line B--B in FIG. 3), the molten metal flows particularly in the pouring direction indicated by A in the same figure. When the wedge shape 102 approaches the space, it pushes up the ceramic head when it solidifies, resulting in frequent cracking of the head as shown by the dashed line 103 in the figure.

This idea was created in view of the above problems.
The purpose is to reduce cracks in ceramic pistons formed by castings, thereby improving product yield.

The structure of the ceramic piston according to the present invention is that a ceramic piston head consisting of a substantially disc-shaped part and a cylindrical part protruding concentrically from the disc-shaped part is attached to a metal ring along the outer periphery of the cylindrical part. In the ceramic piston which is fitted and integrally cast with the piston body, the end face of the metal ring facing the disc-shaped part is inclined so that the outer peripheral part is higher. shall be.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a partial sectional view showing an example of a ceramic piston to which the present invention is applied. The ceramic piston 10 is composed of a ceramic piston head 1, a retaining ring 2, and an aluminum alloy piston body 3. The piston head 1 has a disc-shaped part 4 arranged facing the combustion chamber. A disk-shaped portion 5 having a smaller outer diameter is integrally formed below the disk-shaped portion 4 concentrically with the disk-shaped portion 4, and is integrated with the piston body 3. An annular recess 6 is formed on the outer periphery of the annular portion 5 to prevent the piston head portion 1 and the piston body 3 from coming off in the axial direction, and an annular recess 6 is formed at the bottom of the annular portion 5 to prevent rotation between them. A groove 7 is formed. As mentioned above, if the ceramic head part 1 is directly cast into the piston body 3, the circular part 5 may be corrugated by the clamping force during solidification of the molten metal.

A protection ring 2 is interposed to prevent this destruction. The protection ring 2 is made of a metal with a small coefficient of thermal expansion, such as invar, and the rigidity of the protection ring 2 relieves the tightening force during solidification of the molten metal. Therefore, the inner peripheral shape of the protection ring 2 is similar to the cylindrical portion 5 of the ceramic piston head portion 1.
An annular recess 8 is formed on the outer periphery of the protection ring 2 in order to prevent it from coming off from the piston body 3, corresponding to the outer peripheral shape including the annular recess 6. In order to attach the guard ring 2 having such a shape to the piston head portion 1, the guard ring 2 is formed as two pairs of substantially semicircular bodies. However, the shape of the semicircular body 2 is not limited to the above-mentioned example, and the important thing is that it is interposed on the outer periphery of the circular part 5 to relieve the clamping force when the molten metal solidifies. It is to have.

It is desirable that the upper end surface of the protection ring 2 and the lower surface of the disk-shaped portion 4 of the piston head portion 1 are in plane contact with each other, but as explained in the example of FIG. It is practically unavoidable that the lower surface of the disc-shaped portion 4 is tapered or stepped. Although the angle θ shown in FIG. 1 is approximately within 1 degree,
As already mentioned, an outwardly open space is created between the ceramic piston head 1 and the lower surface of the disc-shaped portion 4, and molten metal enters into this space, contributing to the destruction of the ceramic piston head 1. That's right.

In order to prevent such destruction, the upper end face of the protecting ring 2, that is, the end face facing the disc-shaped portion 4 of the ceramic piston head portion 1, is provided with an outer peripheral portion as shown in FIG. is high and slopes θ' toward the center. This inclination angle θ' is made larger than the inclination angle θ created during the grinding process of the ceramic piston head 1, so that as shown in FIG. The molten metal is always in circumferential contact with the lower surface of the piston head 1 and the molten metal does not penetrate into the space between the ceramic piston head 1 and the retaining ring 2 from here. or,
As shown in FIG. 6, even when the ceramic piston head 1 is stepped,
By providing the upper end surface of the protection ring 2 with an inclination such that the outer circumferential portion thereof becomes higher, this outer circumferential portion and the lower surface of the disc-shaped portion 4 can be kept in contact with each other at all times.

As explained above, according to the present invention, it is possible to further enhance the function of the retaining ring, and the destruction of the ceramic head due to the solidification of metal burrs during slow cooling in the casting process is prevented, thereby preventing the ceramic piston from being destroyed. This has the effect of improving manufacturing yield.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the grinding process of a ceramic piston head, Fig. 2 is a schematic diagram illustrating the process in which molten metal infiltrates in a wedge shape during casting, and Fig. 3 is a diagram of a ceramic piston head to which the present invention is applied. 4 is a sectional view of a protection ring to which the present invention is applied; FIG. 5 is a sectional view showing the state of contact with the protection ring when the lower surface of the ceramic piston head is inclined; FIG. 6 is a cross-sectional view of the stepped case. 1... Ceramic piston head part, 2...
Protection ring, 3... Piston body, 4... Disk-shaped part, 5... Cylindrical part.

Claims (1)

[Scope of utility model registration request] A ceramic piston head consisting of a substantially disc-shaped part and a cylindrical part protruding concentrically from the disc-shaped part is connected to the piston body by interposing a metal ring along the outer periphery of the cylindrical part. 1. An integrally cast ceramic piston, characterized in that the end face of the metal ring facing the disc-shaped portion is inclined so that the outer peripheral part thereof is higher.