JPS59173536A - Engine piston - Google Patents

Abstract

PURPOSE:To provide a non-lubrication type piston having a superior heat resistance, by forming ring-like grooves on an outer circumferential surface of an engine piston of ceramic sintered materials to be contacted with a cylinder liner and thereby eliminating provision of a piston ring. CONSTITUTION:In an engine piston 1 formed of ceramic sintered materials, ring- like grooves are formed on an outer circumferential surface of the piston 1 to be contacted with a cylinder liner 2. The grooves are formed, for example, to be a stepped shape as a whole. Such a shape of the grooves may be designed to a suitable sectional shape according to engine output, piston diameter, compression ratio and workability of ceramics. With this structure, no piston ring is required, and reduction of air tightness is suppressed by a labyrinth effect as exhibited by the grooves. Accordingly, it is possible to obtain a non-lubrication type engine piston having a superior wear resistance and heat resistance.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention aims to improve the efficiency of an engine by applying ceramic parts in place of conventional metal engine parts. Not regarding ceramic pistons.

[Prior art]

Recent developments in new ceramics are attracting attention as they meet requirements that could not be met with conventional metal materials. Engine parts are one example, and various attempts have been made to make them ceramic in order to meet the demand for improved durability of parts, particularly in order to achieve higher efficiency. Regarding the piston,
There are some that have only the top of the head made of ceramic and others that have the entire head made of ceramic, but in both cases, it is assumed that a piston ring will be installed for practical purposes. In addition to the conventional piston ring made of metal, there are also piston rings in which a ceramic layer is adhered to all metal parts.

The use of metal piston rings reduces the effect of ceramicizing the piston body by half, and those with a ceramic layer attached improve wear resistance, but it also dramatically improves the durability temperature. cannot be expected.

[Purpose of the invention]

It is an object of the present invention to solve these problems and at the same time to make it possible to realize a thermally insulated, non-lubricated engine by using it in combination with a ceramic cylinder liner.

[Summary of the Invention] The present invention relates to the structure of a ceramic piston that does not require the installation of a piston ring during use. is suppressed by the labyrinth effect induced by one or more grooves provided in the groove. The labyrinth effect referred to here is a phenomenon that is used as a labyrinth packing in which metal fins of white metal, brass, nickel, etc. are alternately implanted in the shaft and bearing part to create an airtight structure for the rotating shaft. Instead of implanting fins, grooves were provided on the outer periphery of the piston, and the shape of the grooves was designed to ensure airtightness. In addition, when following the conventional labyrinth packing, fins must be attached to the inner wall of the cylinder liner, and in this way,
In such a case, even if the piston can perform rotational movement, axial movement, so-called piston movement, will not be possible.

Therefore, in the present invention, the inner wall of the cylinder liner does not require any special measures, but simply has a smooth cylindrical inner hole having a clearance of D/1000 or more with respect to the piston diameter so that the piston can slide. Just configure it.

[Embodiments of the invention]

FIG. 1 shows a piston having a groove on its outer periphery and a state in which the piston is inserted into a cylinder liner according to the present invention. 1st
FIG. 1(a) shows the case where grooves are provided in a stepwise manner, and FIG. 1(b) shows the case where spiral grooves are provided. As already mentioned, the labyrinth effect is used in Patsukin, but I will explain the labyrinth effect here.

That is, when the piston is in operation, the pressure difference between the upper and lower parts of the piston reaches its maximum at the moment of ignition at the dead center, and becomes the minimum at the dead center. What controls the efficiency of piston movement is the amount of leakage of the upper pressure, and the amount of leakage ωLq / s is (1
) can be expressed by the formula.

Here, Kl and 2 are constants, A is the area of the gap between the piston and cylinder liner, 1-F7+2, To is the temperature at ignition °, and P is the pressure generated at ignition KSI 7 cm
”, n can be treated as the number of grooves.

Therefore, the leakage amount ω becomes T as AXPo becomes smaller.

And the larger n is, the smaller it is. In the ceramic engine, which is the object of the present invention, ω is higher than that in a metal engine, so ω becomes small without special consideration. Although reducing Po in particular poses a problem in ensuring the engine's functionality, it is advantageous for small engines because Pa becomes smaller. n is governed by the size of the piston, but can be increased arbitrarily within a considerable range. Strictly speaking, the number n of grooves in the one shown in Fig. 1 (6) is 1, but when applying this to a small engine, it is necessary to take into consideration the fact that Pa is relatively small, and also the cylinder liner and piston. It is advantageous in that it has a smaller sliding resistance. (1)
In the equation, the effect of the groove shape is a constant.

Various cross-sectional shapes as shown in FIG. 2 can be adopted depending on the engine output, piston diameter, compression ratio, and workability of the ceramic, although this will affect K2. The entrance and exit corners of the groove have sharp corners, and the larger the fluid resistance, the smaller the leakage amount ω. Figure 2(a).

(b) is an example in which a sharp entrance/exit angle is provided.In addition, in order to prevent the gas that has flowed in through the small gap between the piston and cylinder liner from leaking, it is necessary to It is desirable to generate a vortex flow of gas, and for this purpose, the shapes shown in FIGS. 2(C) to 2(f) can be selected at will depending on the engine output, pressure POX groove dn, etc.

Here, this light is applicable not only to ceramic pistons but also to metal pistons, but the effect is most enhanced in the case of a combination of a ceramic piston and a ceramic cylinder liner, regardless of the background of the invention. The reason for the lie is that the frictional resistance of ceramic-to-ceramic is two orders of magnitude lower than that of metal-to-metal, and even lower than that of ceramic-to-ceramic. This is one of the major reasons why no lubrication is possible.

There are no specific ceramics that can be used for non-inventive purposes, and all of the ceramics that are used as engineering ceramics can be used! Samurai exhibits its characteristics in a sintered body whose main component is silicon carbide, which has excellent high-temperature strength and contains a small amount of sintering aid.

In addition, although Figures 81 (a) and (b) show examples where the diameter of the piston skirt is close to the inner diameter of the cylinder liner, pistons with a diameter of the skirt portion of the piston that are considerably smaller than the inner diameter of the cylinder liner are also used. It is possible.

〔Effect of the invention〕

As stated above, the present invention provides a ceramic piston that does not require the installation of piston rings at all.
Its characteristics are particularly demonstrated in high-efficiency heat-insulated engines that use ceramic cylinder liners.

[Brief explanation of the drawing]

Fig. 1(a) is a schematic diagram of a piston having a stepped groove for maintaining airtightness with a labyrinth effect in the present invention, and a state in which the piston is inserted into a cylinder liner.
b) is a schematic diagram of a piston with a spiral groove, the second
Figures (a) to (f) are cross-sectional views of grooves formed on the outer circumference of the piston that are effective in producing a labyrinth effect.

Claims (1)

[Claims] (2) An engine piston made of a ceramic sintered body, characterized in that the piston is provided with a ring-shaped groove on its sliding surface with a cylinder liner.