Parts for Internal Combustion Engine Such as Piston and Cylinder Head

1. Technical Field

The present invention relates to parts for internal combustion engines such as pistons and cylinder heads and methods of manufacturing the same.

2. Background Art

It is a general practice to use solid ceramics such as silicon nitride, zirconia, mullite, and aluminum titanate for a thermal insulator of parts for internal engines such as pistons and cylinder heads. One problem here is that, even though these ceramics are of sufficiently high strength, they tend to degrade volumetric efficiency of the engine because of their high thermal conductivities.

Ceramic materials having a small thermal conductivity, on the other hand, are available in the form of foamed ceramics and laminates made from ceramic fibers. However, since their strength is no more than several tens of kgf/cm.sup.2, they cannot withstand the firing pressures that are generated by the combustion of fuel.

Subsequently, heat insulating composites made from inorganic fibers and/or hollow particles with a coating material prepared from a metallic alkoxide as the binder have been devised to correct these drawbacks, but a deficiency with these materials is that they need to be dried for a long period of time prior to the baking process.

This invention has been created in order to overcome these difficulties found with the conventional materials and manufacturing method, and has, as its first purpose, to provide parts for internal combustion engines such as pistons and cylinder heads that are not only strong enough to withstand the firing pressures, but also of a low thermal conductivity in order to realize a high volumetirc efficiency.

The second purpose is to provide a method of manufacturing these parts in which time for drying prior to baking is shortened.

An inorganic coating material made mainly from silica and titania (for example, the "Glasca E 1101" of Nippon Gosei Gomu Kabushiki Kaisha (Japan Synthetic Rubber Co., Ltd.)), whose solid components are reckoned to be 100 in weight, was added to potassium titanate fibers whose weight is 15 with respect to 100 of the solid components of the inorganic coating material, silicon nitride whiskers of 20 in weight, and glass balloons (which are hollow particles of glass) of 5, and all of them were mixed up well in a kneading machine. Then, calcium oxide of 0.8 in weight with respect to this mixture was added and they were poured under pressure into an enclosed mold of a preselected form.

As this slurry started hardening about three hours after pouring, the core was removed, a lid was placed to enclose the article completely, and it was left standing to dry. Here, complete enclosure is important because otherwise deformation or even cracking of the article may occur since the drying condition differs between the part that is directly exposed to the atmosphere and the part that is not.

The drying was continued with the article completely enclosed for more than 12 hours, then the article was baked 1,100.degree. C. for 30 minutes, obtaining the product thermal insulator, whose thermal conductivity was 1.5 kcal/m. h. .degree.C. and the compressive strength was more than 560 kgf/cm.sup.2.

It was found that addition of potassium titanate fibers and silicon nitride whiskers less than 5 and 10 in weight respectively with respect to 100 of the solid components of the inorganic coating material brought about insufficient thermal conductivities, while addition of them more than 40 and more than 50 respectively brought about insufficient strength. Addition of glass balloons of more than 15% resulted in similar failure.

Most inorganic coating materials that are commercially available can be used in the present invention.

The present invention is not limited to the above-described embodiment. For example, the CaO to be mixed may have weight parts of between 1 and 10 with respect 100 parts of the inorganic coating material, and the glass balloons to be mixed may have weight parts of zero with respect to 100 weight parts of the inorganic coating material.