JP3622233B2 - Piston for internal combustion engine - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an improvement in a piston of an internal combustion engine.
[0002]
[Prior art]
Conventionally, there are pistons for internal combustion engines as shown in FIGS. The combustion pressure received by the crown surface 2 of the piston 1 is transmitted to the connecting rod via a piston pin (not shown) accommodated in the pin boss 3, and the ring land portion 4 of the piston 1 is sealed with combustion gas, etc. A piston ring mounting groove 5 for receiving the piston ring is formed.
[0003]
Below the piston ring mounting groove 5 of the piston 1 is formed a skirt portion 6 which serves to maintain the posture of the piston 1, and the cross-sectional shape of the skirt portion 6 is in the direction of the piston pin, that is, the apron 7 portion. It has an elliptical shape with a short diameter (see Japanese Utility Model Laid-Open Nos. 61-3947, 61-81558, etc.).
[0004]
[Problems to be solved by the invention]
However, in such a piston 1, the elliptical skirt portion 6 becomes close to a perfect circle due to thermal expansion during operation, but the skirt against the thrust force and anti-thrust force generated in the piston 1 by combustion pressure and inertial force. There are a portion where the portion 6 has a strong contact with the cylinder wall and the surface pressure increases, and a portion where the surface pressure hardly occurs and is not involved in supporting the load.
[0005]
A lubricating oil film is formed between the skirt portion 6 and the cylinder wall by supplying the lubricating oil, so that a good slidability can be obtained at a portion where the surface pressure is large, but a portion where the half surface pressure is hardly generated. The distance between the cylinder wall and the cylinder wall is narrow, and a frictional force is generated in this portion.
[0006]
That is, the frictional force is increased by the viscous resistance of the lubricating oil interposed in the narrow gap between the portion where the surface pressure hardly occurs and the cylinder wall.
[0007]
Further, the surface pressure increases at the lateral portion of the piston pin, but when the thrust force is large, a strong hit may occur locally near the apron 7.
[0008]
An object of the present invention is to solve such problems.
[0009]
[Means for Solving the Problems]
A first aspect of the invention is an internal combustion engine piston in which the cross-sectional shape of the skirt portion below the piston ring mounting groove is an ellipse whose apron portion in the piston pin direction has a short diameter, and the piston ring mounting of the skirt portion is On the surface directly below the groove, a groove whose width increases as it goes from the center side of the long diameter part of the skirt to the left and right apron ends, and to the surface of the skirt bottom part at the center of the long diameter part, the width increases toward the top from below. and their respective have a groove shape is narrowed, the groove of the skirt hem part, the groove bottom edge was formed in such a manner that a predetermined amount above the bottom of the skirt hem.
[0010]
According to a second aspect of the present invention, the groove immediately below the piston ring mounting groove is formed so that the width thereof is rapidly expanded in the vicinity of the apron.
[0012]
In the third invention, the grooves are formed by casting.
[0013]
[Action]
The elliptical piston whose cross-sectional shape of the skirt section has the apron portion in the direction of the piston pin as the short diameter is the thrust force and anti-thrust in the lateral direction of the piston pin, that is, the central portion of the long diameter section of the skirt section directly under the piston ring mounting groove. Although the surface pressure due to the force is large, almost no surface pressure is generated in the part that expands toward the left and right apron ends from the center of the long diameter part where the surface pressure is large, and in the part that narrows upward from the bottom of the skirt hem at the center of the long diameter part. do not do.
[0014]
In the first invention, a groove is provided in a portion where the surface pressure is hardly generated, thereby increasing a gap with the cylinder wall and reducing a frictional force due to a viscous resistance of the lubricating oil interposed between the cylinder wall. . Further, when the groove of the skirt skirt is provided, the groove lower end is formed so as to be a predetermined amount above the lowest part of the skirt skirt. Therefore, a small gap between the lowermost part of the skirt skirt and the cylinder wall can be maintained to absorb the impact force to the cylinder wall that causes so-called slap noise.
[0015]
In addition, when the thrust force is large with respect to the center of the long diameter portion of the skirt portion directly below the piston ring mounting groove, a strong hit may occur locally near the apron. In the second invention, the piston ring mounting groove The groove is formed so as to expand rapidly near the apron. Therefore, local hitting can be avoided and the durability of the piston is improved.
[0017]
In the third invention, the grooves can be easily formed by casting.
[0018]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0019]
As shown in FIGS. 1 and 2, a piston ring mounting groove 22 such as a top ring, a second ring, or an oil ring is formed in the ring land portion 21 at the head of the piston 20. A skirt portion 23 is formed.
[0020]
The cross-sectional shape of the skirt portion 23 is formed in an elliptical shape having a short apron 24 portion in the piston pin direction, and a pin boss 25 in which the piston pin is accommodated is formed in the apron 24.
[0021]
Then, on the surface of the skirt portion 23 immediately below the piston ring mounting groove 22, relief grooves 27a and 27b having a shape in which the width increases from the center L side of the long diameter portion 26 of the skirt portion 23 toward the left and right apron 24 ends. It is formed.
[0022]
The escape grooves 27a and 27b are formed from a portion separated by a predetermined distance from the center L of the long diameter portion 26 to a slightly inner side of the end of the apron 24. The escape grooves 27a and 27b are shallow grooves, and the outer shape and edge are formed in a curved shape.
[0023]
Further, a relief groove 29 having a shape whose width becomes narrower from the lower side to the upper side is formed on the surface of the skirt skirt part 28 at the center L of the long diameter part 26.
[0024]
The escape groove 29 is formed so that the lower end of the groove extends to the lowest part of the skirt skirt 28. The escape groove 29 is a shallow groove, and its outer shape and edge are formed in a curved shape.
[0025]
The escape grooves 27a, 27b, and 29 are integrally formed on both sides of the elliptical skirt portion 23 by a cast structure when the piston 20 is cast.
[0026]
Thus, the part which formed escape groove 27a, 27b, 29, ie, the part which spreads toward the left and right apron 24 end from the long diameter part 26 center L side of the skirt part 23 directly under the piston ring mounting groove 22, and the long diameter part 26 center In the portion narrowed from the lower side to the upper side of the L skirt skirt portion 28, the surface pressure hardly generates against the thrust force and the anti-thrust force generated by the combustion pressure and inertial force received by the piston 20.
[0027]
This has been confirmed by simulation. Therefore, a good lubrication state by the lubricating oil can be secured in the central portion of the long diameter portion 26 of the skirt portion 23 directly below the piston ring mounting groove 22 where the surface pressure due to the thrust force or anti-thrust force is large. At the same time, the clearance with the cylinder wall can be widened by forming the relief grooves 27a, 27b, 29 in the portion where the surface pressure hardly occurs.
[0028]
Thereby, it is possible to prevent the frictional force from increasing due to the viscous resistance of the lubricating oil interposed in the narrow gap between the portion of the skirt portion 23 where the surface pressure hardly occurs and the cylinder wall.
[0029]
In this case, since the frictional force becomes smaller as the gap with the skirt portion 23 becomes wider, the frictional force can be sufficiently reduced by the escape grooves 27a, 27b, and 29.
[0030]
On the other hand, the relief grooves 27a and 27b immediately below the piston ring mounting groove 22 act to guide the lubricating oil scraped off by the oil ring downward, thereby preventing the lubricating oil from rising to the combustion chamber.
[0031]
In addition, the escape grooves 27a, 27b, 29 are formed by casting as compared with the case where the skirt portion is extremely provided with ellipticity, a step, and the like to prevent an increase in frictional force due to the viscous resistance of the lubricating oil. It is possible to reduce the manufacturing cost and the processing time.
[0032]
3 and 4 show another embodiment in which the size of the escape groove is changed.
[0033]
In this case, the escape grooves 30a and 30b from the center L side of the long diameter portion 26 of the skirt portion 23 directly below the piston ring mounting groove 22 toward the left and right apron 24 ends are formed so that the width is rapidly enlarged in the vicinity of the apron 24. .
[0034]
Further, the escape groove 31 of the skirt skirt portion 28 at the center L of the long diameter portion 26 is formed so that the lower end of the groove is a predetermined amount above the lowermost portion of the skirt skirt portion 28.
[0035]
Other shapes and configurations are the same as those in FIGS.
[0036]
Thus, if the relief grooves 30a and 30b immediately below the piston ring mounting groove 22 are formed so that the width is rapidly increased in the vicinity of the apron 24, local contact with the cylinder wall generated in the vicinity of the apron 24 can be avoided. .
[0037]
Here, FIG. 5 shows the result of the lubrication analysis simulation of the piston skirt portion where the grooves 30a and 30b are not provided. On the thrust side with a crank angle of 420 °, a strong hit locally occurs at the skirt end (near the apron). I understand that
[0038]
This is considered to be because the skirt is greatly deformed when the thrust force is large and the force concentrates on the apron portion having a relatively high rigidity. As a countermeasure, the clearance groove 30a whose width suddenly increases in the vicinity of the apron 24. , 30b, the frictional force can be reduced as in the above embodiment, and the local contact can be avoided, and therefore the durability of the piston 20 can be greatly improved.
[0039]
Further, if the groove lower end of the escape groove 31 of the skirt skirt 28 is formed so as to be a predetermined amount above the lowermost portion of the skirt skirt 28, a small gap between the lowermost portion of the skirt skirt 28 and the cylinder wall is maintained. Can do. That is, the impact force that the piston 20 strikes against the cylinder wall due to the gap can be absorbed, and so-called slap noise can be suppressed.
[0040]
【The invention's effect】
As described above, according to the first invention, in the piston for an internal combustion engine in which the cross-sectional shape of the skirt portion below the piston ring mounting groove is an ellipse whose apron portion in the piston pin direction has a short diameter, On the surface of the skirt part just below the piston ring mounting groove, a groove with a shape that expands from the center side of the long diameter part of the skirt toward the left and right apron ends is formed on the surface of the skirt bottom part at the center of the long diameter part from below. Since each groove has a shape whose width becomes narrower toward the upper side, the surface of the cylinder wall is hardly affected by the thrust force or anti-thrust force generated by the combustion pressure or inertia force applied to the piston. The frictional force due to the viscous resistance of the lubricating oil present in the gap, that is, the frictional force of the piston can be reduced. Further, it is possible to prevent the lubricating oil from rising to the combustion chamber. Further, by forming the groove of the skirt hem so that the lower end of the groove is a predetermined amount above the lowermost part of the skirt skirt, a small gap between the skirt hem and the cylinder wall can be maintained to the cylinder wall. Can absorb the impact force and suppress slap noise.
[0041]
According to the second aspect of the present invention, the groove immediately below the piston ring mounting groove is formed so that the width thereof suddenly expands in the vicinity of the apron, so that the local contact generated in the vicinity of the apron when the thrust force is large. Can be avoided, and the durability of the piston can be improved.
[0043]
According to the third invention, each groove can be easily formed by casting, and the manufacturing cost and the processing time can be reduced.
[Brief description of the drawings]
FIG. 1 is a front view of a piston.
FIG. 2 is a side view thereof.
FIG. 3 is a front view of a piston according to another embodiment.
FIG. 4 is a side view thereof.
FIG. 5 is a characteristic diagram of surface pressure.
FIG. 6 is a front view of a conventional piston.
FIG. 7 is a side view thereof.
[Explanation of symbols]
21 Ring land portion 22 Piston ring mounting groove 23 Skirt portion 24 Apron 25 Pin boss 26 Long diameter portion 27a, 27b Relief groove 28 Skirt skirt 29 Relief groove 30a, 30b Relief groove 31 Relief groove

Claims (3)

In the piston for an internal combustion engine in which the cross-sectional shape of the skirt portion below the piston ring mounting groove is an ellipse whose apron portion in the piston pin direction has a short diameter,
On the surface of the skirt portion just below the piston ring mounting groove, a groove having a shape that increases in width from the center side of the long diameter portion of the skirt portion toward the left and right apron ends is formed below the surface of the skirt bottom portion at the center of the long diameter portion. and their respective have a groove shape in which the width becomes narrower as more upward,
The groove of the skirt skirt is formed so that the lower end of the groove is a predetermined amount above the bottom of the skirt skirt,
A piston for an internal combustion engine. 2. The piston for an internal combustion engine according to claim 1, wherein the groove immediately below the piston ring mounting groove is formed so that a width thereof is rapidly expanded in the vicinity of the apron. The piston for an internal combustion engine according to claim 1 or 2, wherein each of the grooves is formed by casting.

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