JPS61157744A - Piston for engine - Google Patents

Abstract

PURPOSE:To suppress a flow of blow-bye gas in an engine and ensure its safety operation, by forming a passage of pressure gas communicating with a peripheral sealed part from the top surface of a piston, in the case of the piston with at least its head part consisting of ceramic material. CONSTITUTION:A no-supercharge type engine 1 generates a negative pressure in a combustion chamber 2 as a piston 3 moves lowering, and the piston 3, easily generating the action of oil up, mounts to its bottom part an oil ring 4 for preventing the oil up. And the engine 1 forms the piston 3 and a cylinder liner 5, which form a no-cooling type heat insulating combustion chamber 2, by ceramics. The above piston provides pressure gas passages 6 in a tapered nozzle shape, facing to the diagonally upward between an upper sealed part 30 and a bottom sealed part 31 and forming the inflow side opening area of a piston top surface 3a larger than the delivery side opening area, and the piston 3 arranges in its peripheral part said pressure gas passage 6 in an equal space facing to a direction A in the drawing such that jetted gas turns in the counterclockwise direction as viewed from the piston top surface.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to engine pistons, and more particularly to ceramic pistons that do not require compression piston rings.

Conventional Technology Due to rapid advances in ceramic materials and ceramic molding technology, the combustion chamber of internal combustion engines has recently been engineered.
・Ceramic engines with a heat-insulating structure made of ceramics have been proposed.

In other words, since the frictional resistance between ceramics and ceramics is about two orders of magnitude smaller than that between metals, and even smaller than that between metals and ceramics, it is not possible to supply lubricating oil between the ceramic piston and the ceramic cylinder. It became possible to realize a lubricated engine. (As prior art, examples are disclosed in JP-A-59-1735361 "Piston for Engines", JP-A-59-1735361 "Piston for Engines", JP-A-59-1735361 "Piston for Engines", JP-A-59-1735361 "Japanese Patent Application Laid-open W3SS-47O4AAR Ceramic Engine", etc.) Problems to be solved] In these non-lubricated ceramic engines.

Ceramic piston rings cannot normally be installed due to the brittleness of the ceramic itself, unless the piston is of a split type that is joined at the piston ring groove. For this reason, a structure is often adopted in which a plurality of annular convex seals formed above the piston outer periphery are brought close to the circumferential surface of the cylinder lychee without providing a compression ring. Compared to the case where a piston ring with a surface that contacts the ring groove surface is used, the seal structure between the piston and litchi in the above-mentioned non-lubricated engine is still airtight in a diesel engine that requires a relatively high compression ratio. In addition, the amount of gas blow-by increases in various engines, which poses problems in terms of safe operation of the engine.

[Means for solving problems]

The engine piston of the present invention has at least a head portion made of a ceramic body.

The piston is characterized in that a pressure gas passage is formed that communicates with the outer seal portion from the top surface of the piston, and blow-by gas flow is suppressed by the pressure gas jetted out through the pressure gas passage. Therefore, with the above configuration, the present invention improves engine performance by creating a higher compression ratio within a range that does not cause knocking even in a non-lubricated engine that does not have a compression ring, and reduces the amount of blow-by gas to improve engine performance. The purpose is to ensure safe driving.

[Effect]

The frictional resistance between the ceramic piston and the ceramic cylinder litchi is two orders of magnitude lower than that between metals, and it has good sliding characteristics even without the supply of lubricating oil, making it especially suitable for non-cooled adiabatic engines. Demonstrates excellent heat resistance and wear resistance properties. In addition, the outer circumferential seal, which has an annular uneven shape on the upper surface of the piston, uses a labyrinth effect to throttle the high-temperature, high-pressure combustion gas, and through repeated expansion, blow-by gas flows from the lower part of the piston, that is, from the combustion chamber into the crankcase. This prevents leakage to a minimum. Generally, the leakage quantity ttrKg/S is determined by the following formula.

Kl is the order determined by the uneven shape. 1 is the area of the gap between the piston and the cylinder litchi, i%TO is the temperature at ignition, and l? o is the pressure generated at the time of ignition Kg/α - Tsuru is the number of grooves) This is the area of the gap between the piston and the cylinder litchi (1) The smaller the pressure generated at the time of ignition.

Further, the temperature decreases as the temperature at the time of ignition increases and the number of concavo-convex rings corresponding to the fins and grooves of the labyrinth increases. Therefore, by closing the clearance and providing a ring-shaped convex body as shown in FIG. 1, the fluid resistance increases, the pressure drop increases, and the amount of leakage decreases. For example, the pressure gas passage is like a tapered nozzle, from the maximum flow area of the inlet opening to the minimum flow area of the discharge side opening, where the high-pressure combustion gas is gradually expanded at a rate of A and discharged from the outlet at a high flow rate of . At the same time, by ejecting a gas flow that blows up toward the combustion chamber side that exceeds the momentum of the blow-by gas flow flowing down through the uneven outer seal portion, the normal pressure gas passage that exits to the crankcase is established.
If you use a tapered nozzle that curves toward the combustion chamber as shown in Figure g1 and Figure 2, friction will occur, and some of the frictional work will be converted into heat, even though the nozzle surface is extremely smooth and there is no heat exchange with the outside. This increases the temperature of the gas and is effectively used for acceleration, but the remainder is lost as friction loss called nozzle loss. However, the rate by which the nozzle exit velocity of the frictional gas stream is reduced relative to the adiabatic gas stream due to this nozzle loss is called the velocity coefficient, and in this case is estimated to be between 0.6 and 0.8. Also, regarding the nozzle ejection velocity and flow rate when the volope concentration changes with #14L of heat, calculation formulas are provided in the general fluid flow of industrial thermodynamics, so we will not explain them again here. In anticipation of age-related changes such as carbon adhesion on the nozzle, the nozzle discharge side opening that forms a flow rate constraint area is required as a condition for the momentum of the gas ejected from the tapered nozzle to exceed the momentum of the blowy gas that has been attenuated by the labyrinth effect. If the area is more negative than the gap area between the piston and the cylinder lychee (on the piston axis, 1゛, and on the confluence of 14), then l
/coaθ times to find the exit diameter of the tapered nozzle.

〔Example〕

An embodiment of a ceramic piston for an engine according to the present invention will be described below based on one drawing.

FIG. 1 is a longitudinal cross-sectional view of a main part of a combustion chamber incorporating a ceramic bimeton for a non-supercharged engine according to the present invention.

FIG. 2 is a longitudinal sectional view of a ceramic piston applicable to the supercharged engine, and FIG. 3 is a plan view of the piston showing the arrangement of the pressure gas passages.

First Embodiment> As shown in the first factor, the piston 3 of the non-supercharged engine to which the present invention is applied is such that the inside of the combustion chamber 2 becomes negative pressure as the piston 3 descends during the intake stroke. Since lubricating oil (inside the flank case) tends to rise, that is, an oil-up phenomenon occurs, an oil ring 4 is installed at the lower part of the flank case in order to suppress the oil-up to the minimum PL. As the engineering ceramics used for the piston 3 and cylinder liner 5 that form the thermal insulation layer combustion chamber 2 of the Sagi Cooling Rei, silicon carbide-clouded silicon nitride and Sialon, which have excellent heat resistance and high temperature strength, are used. In this embodiment, a silicon carbide sintered body having good wear resistance and a small coefficient of friction is used. The outer circumferential seal part 30 formed on the upper side of the piston has six ring-shaped unevenness formed at relatively small intervals, and the seal part 31 formed on the side part leading to the oil link number has a relatively small groove. Two ring-shaped irregularities are formed with a large distance between the targets. Pressure gas passages 6 in the shape of a gap between the inflow side of the piston top surface 3m are formed on the outer circumference of the piston 3 at equal intervals as shown in FIG. They are arranged facing the direction (indicated by the arrow).

The discharge side opening area of the pressure gas passage 6 above the piston is determined to be larger than the cross-sectional area of the gap between the piston 3 and the cylinder liner 5, as described above.

That is, when the piston outer diameter Do is 76.00'jfl, the cylinder liner inner diameter Di is 76.03φn, and the number n of pressure gas passages is 8, the cross-sectional area of the discharge side opening of the pressure gas passage 6 on the upper surface of the piston is estimated. Let's see* -
X (Di" - Do")≦ix〆×8 A claim characterized by an angle θ formed by the discharge side opening with respect to a plane including the turning direction (arrow view A) and a perpendicular line to the opening. The effective discharge side opening electrode is 1. from dv/cna a. It will be a five-fight battle. Other dimensions of the pressure gas passage 6 are determined based on this value.

Further, the ejected gas swirls and blows up blow-by gas into the combustion chamber 2, generating a swirl so that the injected fuel is completely combusted.

Second example! As shown in FIG. 2, the piston 23 of the supercharged engine 20 to which the present invention is applied is supplied with positive pressure fresh air during the air intake stroke, and the inside of the combustion chamber 22 is filled with the piston 23.
Because there is no negative pressure caused by the drop in the pressure, an oil-up phenomenon occurs.<<The oil link device is omitted. In order to stabilize piston behavior, a ring-shaped convex portion 24 is provided in place of the oil ring. Therefore, it is possible to enjoy the advantage of further reducing mechanical friction loss due to piston rings.

In this embodiment, the outer circumference from the top surface 23a of the piston is 10 J/m at the maximum (Journal of the Japan Society of Mechanical Engineers vol. 62 @ h
486・P, 5062~10751 Figure 8.90 For the engine speed and gas vent, refer to the amount) and estimate #), try calculating it under the condition that a larger amount of gas is ejected from the nozzle 6. . The relationship between the cross-sectional area a (#) of the discharge side opening of the nozzle and the outflow gas amount G (Kg/s) is expressed by a linear equation.

n-number of nozzles, ψc-・nozzle efficiency, Pl...maximum explosion pressure (Kg/IO1")・R...gas constant (29,
13)・T1-Temperature at explosion k] (1) B g , p e-Q, 6 is further multiplied by 1/coall Ca□45') to make the diameter of the discharge side opening of the nozzle 10-.

(2) Further 1/ at nm8 a we-0,8
■#C0■450) Multiply the nozzle discharge side opening diameter by 1
．． 7'a.

〔Effect of the invention〕

As described above, according to the ceramic piston for an engine of the present invention, the attachment of a conventional compression ring is omitted, and the outer circumferential seal portion is formed by a plurality of ring-shaped convex stripes instead of the ceramic piston. Because it is configured to operate within the cylinder litchi, it is possible to significantly reduce friction loss due to piston ring tension and increase net average effective pressure and output. Reduced sealing performance against prove-by gas compared to engines using

This prevents deterioration of engine performance, enjoys the benefits of a non-lubricated piston, and enables safe operation over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a main part of a combustion chamber incorporating a Selance piston for a non-supercharged engine according to the present invention. Fig. g2 is a longitudinal sectional view of a ceramic piston applicable to the supercharged engine, and Fig. 3 is a plan view of the piston showing the arrangement of the pressure gas passages. C code explanation) 2-Combustion chamber, 3.-Ceramic piston, 3m. 23m-piston top surface, 5-cylinder lychee, 6-pressure gas passage, ao, az-piston outer periphery seal. one or more one

Claims (1)

[Claims] 1. In a piston at least whose head portion is made of a ceramic body, a pressure gas passage is formed that communicates from the top surface of the piston to an outer peripheral seal, and blow-by is caused by the pressure gas ejected through the pressure gas passage. An engine piston characterized by suppressing gas flow. 2. The engine piston according to claim 1, wherein the pressure gas passage has a discharge side opening having a smaller diameter than an inflow side opening. 3. Claim 1, wherein the discharge side of the pressure gas passage is formed in a direction opposite to the flow direction of the blow-by gas.
Piston for the engine described in section.