JPH10184451A - Piston for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify work for the dispersion of stress by installing a notch in each peripheral edge part in both longitudinal and vertical directions of a piston hole within the surface of the peripheral edge part of a combustion chamber, in case of a piston installed juste under this combustion chamber. SOLUTION: A piston is provided with two notches 15 and 15 by processing each peripheral edge part in both longitudinal and vertical directions of a piston hole 14 within the surface of a peripheral edge part 13 of a combustion chamber 12. This piston is deformed in the vertical direction to the piston hole 14 with the longitudinal direction of this piston hole 14 as the axis as it receives the influence of inertial force of a connecting rod and gas pressure into the combustion chamber 12. Here, if a stress distribution of the peripheral edge part 13 is varied, the total of stresses being loaded on this peripheral part 13 remains unchanged, so that two notches 15 and 15 are formed in the longitudinal direction of the piston hole 14 where a deformed amount is the smallest, enlarging the stress to be loaded on these notches 15 and 15. With this constitution, the stress to be loaded on a longitudinal part of the piston bole 14 of the peripheral part 13, where the deformed amount is the largest, is can be lessened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston for an internal combustion engine, and more particularly to a piston for an internal combustion engine having a combustion chamber on a top surface and injecting fuel directly into the combustion chamber.

[0002]

2. Description of the Related Art Generally, a piston for a direct injection engine in which a combustion chamber is formed in a concave shape with respect to the piston top surface has a very high pressure compared to a piston of an engine having a combustion chamber separately from the piston. Subject to heat load. In particular, in a piston for a direct injection diesel engine, the peripheral portions of the piston head portion and the combustion chamber portion have a thinner base material than other portions and are thermally weak. Here, a peripheral portion, which is a connection portion between the combustion chamber and the piston head, is a portion where the base material is thinner than other portions, and is very severe in heat. The crack generation mechanism at the peripheral portion will be described with reference to FIG.

[0003] Since the thermal load on the piston is high, the base material of the piston is in a heat-annealed state and softened. A high pressure is applied to the piston combustion chamber 121 as compared to other parts of the piston head, and the peripheral portion 131, the ring groove, and the piston head tend to spread outward. However, when the piston pin is connected to the piston pin hole 141, deformation of the piston in the direction of the piston pin hole 141 is suppressed due to the rigidity of the piston pin. Therefore, the deformation of the peripheral portion 131 due to the increase in the pressure of the combustion chamber 121 is performed in a direction perpendicular to the piston pin hole.

Therefore, the peripheral portion receives the maximum tensile stress in the direction of the piston pin hole 141 shown by the hatched portion in FIG. The piston is made of an aluminum alloy or cast iron, and these materials have a brittle property that is strong against compression and weak against tension.

Therefore, a technique for minimizing damage to the peripheral portion 131 has been conventionally considered.

The prior art is disclosed in Japanese Patent Laid-Open No. 4-27245.
The technique disclosed in No. 4 discloses a method in which a peripheral portion 8 made of a ceramic material having excellent heat resistance is connected to a piston head body 2 via a ring joint 7 made of a functionally graded material having a different coefficient of thermal expansion.
And the outer ring 6 is made of a material having a larger coefficient of thermal expansion than the metallic material of the piston head body 2. When the temperature rises, the outer peripheral ring 6 is deformed by a coefficient of thermal expansion smaller than the coefficient of thermal expansion determined by the coefficient of thermal expansion of its physical properties. Therefore, the outer ring 6 acts as an interference with the piston head main body 2 by an amount corresponding to the suppression of the thermal expansion when the temperature rises, and the ring coupling body 7 is strongly held by the piston head main body 2. According to this technique, the difference in thermal expansion between the peripheral portion and the piston head body can be absorbed by the ring assembly, and adverse effects such as damage to the peripheral portion are eliminated.

[0007] As a conventional technique, Japanese Patent Laid-Open No. 7-11958 is disclosed.
There is a technology disclosed in the issue. FIG. 3 shows a plan view of a piston top surface in this technique. This technique discloses a piston 1 having notches 7, 8 provided only in a direction substantially 45 degrees from a piston axis 8 of a peripheral edge 4 of a cavity opening of a combustion chamber 2 with respect to a longitudinal direction of a piston pin hole 6. ing. The dotted line 3 indicates the maximum diameter of the combustion chamber 2. By providing the notches 7 and 8, the rigidity of the notches 7 and 8 is lower than that of the other peripheral edge 4 of the cavity opening. Therefore, the durability of the piston is reduced by reducing the force applied in the longitudinal direction of the piston pin and the direction perpendicular to the longitudinal direction of the piston pin, which are the positions most susceptible to the inertial force and the pressure of the combustion gas due to the reciprocating motion of the piston. It is to improve.

[0008]

[Problems to be solved by the present invention]
In the technique of No. 54, the peripheral portion can be strengthened, but since only the peripheral portion is formed of ceramic, there is a problem that the manufacturing method is difficult and the cost increases.

In the technique disclosed in Japanese Patent Application Laid-Open No. 7-11958, the stress is minimized in the direction perpendicular to the longitudinal direction of the piston pin. Due to the backlash of the connection part with the piston and the variation in the shape of the combustion chamber of the piston, the stress in the longitudinal direction of the piston pin is not always the largest, and the stress is not necessarily the smallest in the direction perpendicular to the longitudinal direction of the piston pin. Absent. That is, when the stress distribution is ideal, the stress can be dispersed by providing the notch only in a direction approximately 45 degrees with respect to the center of the cavity opening as shown in FIG. If not ideal, the area between the notches is not necessarily the area where the maximum stress or the minimum stress is applied.
In the related art, it is difficult to disperse the stress even when the position where the large deformation amount varies even a little.

In order to solve the above-mentioned problems, the present invention has a simple manufacturing method, is inexpensive, and even when there is a variation in the dispersion of stress, the variation is allowed and the generation of cracks is allowed. It is an object of the present invention to provide a piston for an internal combustion engine, which prevents the occurrence of an internal combustion engine.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the invention according to claim 1 is characterized in that a peripheral portion formed to be concave with respect to the piston top surface and opened to the piston top surface is substantially true. A piston for an internal combustion engine, comprising: a combustion chamber having a circular shape; and a piston pin hole provided immediately below the combustion chamber, wherein a peripheral edge in a direction perpendicular to a longitudinal direction of the piston pin hole in a peripheral portion surface of the combustion chamber. Notches were provided in the parts.

According to the first aspect, since the notch is provided only in the peripheral portion in the direction perpendicular to the longitudinal direction of the piston pin hole, machining for dispersing stress is performed as compared with the conventional piston for an internal combustion engine. A simple and low-cost piston for an internal combustion engine can be provided.

According to a second aspect of the present invention, in the piston for an internal combustion engine of the first aspect, the notch is formed continuously and smoothly along a peripheral portion.

According to the second aspect, in addition to the effect of the first aspect, even if the dispersion of the stress varies, the variation can be allowed to prevent the occurrence of cracks in the peripheral portion.

[0015]

An embodiment according to the present invention will be described with reference to the drawings. 1 and 2 are views showing a piston for an internal combustion engine according to the present embodiment. In the present embodiment, a piston for a diesel engine will be described.

The configuration will be described. The piston of the present embodiment is formed in a concave shape with respect to the piston top surface 10,
The combustion chamber 12 includes a combustion chamber 12 in which a peripheral edge portion 13 opening to the piston top surface 10 has a substantially perfect circular shape, and a piston pin hole 14 provided immediately below the combustion chamber 12. In the plane of the part 13, the piston pin hole 14
Notch 1 by processing the peripheral part in the direction perpendicular to the longitudinal direction of
5 and 15 are provided.

The operation will be described. Piston intake,
It reciprocates while repeating four cycles of compression, combustion, and exhaust. At this time, the piston receives an inertial force due to the reciprocating motion. In the vicinity of the end of the compression stroke, the injected fuel self-ignites and burns, and the piston receives the pressure of the combustion gas generated at that time under load. The piston is connected to a connecting rod (not shown) by passing a piston pin (not shown) through the piston pin hole 14.
Therefore, under the influence of the inertia force of the connecting rod and the pressure of gas into the combustion chamber 1, the piston is perpendicular to the piston pin hole 14 with the longitudinal direction of the piston pin hole 14 as an axis as shown in FIG. Deform in the direction.

However, since the notches 15 are provided in the peripheral portion 13 in the direction perpendicular to the longitudinal direction of the piston pin hole 14 in the peripheral portion 13 of the combustion chamber, the stress at this portion is dispersed. . Here, since the total stress applied to the peripheral portion 13 does not change even if the stress distribution of the peripheral portion 13 changes, the notch 15 in the direction perpendicular to the longitudinal direction of the piston pin hole 14 with the least amount of deformation, 15, the stress applied to the notches 15, 15 is increased. This makes it possible to reduce the stress applied to the longitudinal portion of the piston pin hole 14 in the peripheral portion where the deformation amount is the largest.

The notches 15, 15 are formed continuously and smoothly along the peripheral portion 13, so that even if the stress distribution is uneven, the position where the maximum stress occurs is determined by the notches 15, 15. Is included in the range of
This variation can be allowed to prevent the occurrence of cracks in the peripheral portion 13.

[0020]

According to the first aspect, since the notch is provided only in the peripheral portion in the direction perpendicular to the longitudinal direction of the piston pin hole, machining for dispersing stress is performed as compared with the conventional piston for an internal combustion engine. A simple and low-cost piston for an internal combustion engine can be provided.

According to the second aspect, in addition to the effect of the first aspect, even if there is a variation in the dispersion of stress, it is possible to allow the variation and prevent the occurrence of cracks in the peripheral portion.

[Brief description of the drawings]

FIG. 1 is a plan view of a piston for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a sectional view taken on a plane perpendicular to a piston pin hole of FIG. 1;

FIG. 3 is a plan view of a conventional piston for an internal combustion engine.

FIG. 4 is an explanatory diagram of a crack generation mechanism in a peripheral portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Piston top surface 12 ... Combustion chamber 13 ... Peripheral part 14 ... Piston pin hole 15 ... Notch

Claims (2)

[Claims] Claims: 1. A piston is formed concavely with respect to a piston top surface,
A combustion chamber having a substantially circular shape in a peripheral portion opening to the piston top surface; and a piston pin hole provided immediately below the combustion chamber. A piston for an internal combustion engine, wherein a notch is provided in a peripheral portion of the peripheral portion in a direction perpendicular to a longitudinal direction of the piston pin hole. 2. The notch is formed continuously and smoothly along the peripheral portion.
Pistons for internal combustion engines.