JPH03115762A - Piston for internal combustion engine - Google Patents

Abstract

PURPOSE:To stabilize the position of a piston and prevent hammering by forming the elliptical degree of ellipses forming the cross-sectional configuration of a skirt part small at the upper part and large at the lower part around the axis of a piston pin, thereby reducing the contact area between the skirt part and a cylinder bore. CONSTITUTION:The skirt part 2 of a piston 1 is formed into approximately barrel shape in its cross-sectional configuration by changing the major axes of plural ellipses respectively along the axial direction of the piston 1. When the piston 1 is pressed to a cylinder bore, the skirt part 2 and the cylinder bore are brought into contact. The part, having the specified length h1 from the axis of a piston pin 3, of the skirt part 2 is brought into contact with the cylinder bore in a relatively large range because of the elliptical degree of the ellipse being set small. The part, having another length h2, of the skirt part 2 is brought into contact with the cylinder bore in a relatively narrow range because of the elliptical degree of the ellipse being set large. As a result, the whole contact area can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a piston for an internal combustion engine, and particularly to a technique for reducing friction in a skirt portion.

(Prior Art) In a conventional piston for an internal combustion engine, the cross-sectional shape of the skirt portion below the piston ring mounting groove is an elliptical shape with the short diameter in the axial direction of the piston pin, that is, in the direction of the center line. This is known (see Utility Model Application Publication No. 61-3947, Japanese Patent Application Publication No. 61-81558, etc.).

An example of such a piston is shown in FIGS. 6-8.

In these figures, the skirt portion 2 of the piston 1 is formed into a so-called barrel shape by changing the major diameters of the elliptical shapes X, Y, along the piston axis direction.

In this case, tapered surfaces 4 are formed on the surfaces of the outer peripheral surface of the skirt portion 2 on both sides facing each other in a direction orthogonal to the axial direction of the piston pin 3.

The length from the piston axis of the skirt shoulder 6 directly below the piston ring mounting groove 5 to the tapered surface 4 is the length of the piston 1.
η of the reference diameter φD, that is, smaller than the radius by a,
The length from the piston axis at the bottom of the skirt portion 2 to the tapered surface 4 is an ann smaller than the radius to form an oil film.
'(<an).

As described above, the long diameters of the ellipses X+ and Y+ change along the piston axis direction, so they change depending on the cross-sectional position as shown in FIGS. 7 and 8.

Further, the length of the piston pin hole 7 in the axial direction is 2×b shorter than the length of the hole in the direction perpendicular to the axial direction.

Although the dimensional differences between the various parts shown in FIGS. 6 to 8 are exaggerated to be larger than the actual size for convenience, they are actually quite small.

<Problems to be Solved by the Invention> However, the structure of the skirt portion 2 of the conventional piston 1 as described above has the following problems.

That is, since the ellipticity of the ellipses X, Y, of the skirt portion 2 shown in FIGS. 7 and 8 is constant in any part of the skirt portion 2, the contact area of the skirt portion 2 with the cylinder bore is It becomes like the part C shown in FIG. 9, which is a substantially constant large one.

As a result, a problem arises in that the friction of the skirt portion 2 increases.

If the above-mentioned contact area is reduced in order to solve this problem, the posture of the piston 1 during operation will become unstable, resulting in occurrence of hammering noise due to piston slap.

Therefore, in view of the above conventional problems, the present invention has a structure in which the ellipticity of the ellipse of the skirt portion is changed along the axial direction of the skirt portion, thereby reducing the contact area and improving the posture during piston operation. An object of the present invention is to provide a piston for an internal combustion engine that is designed to stabilize the piston.

<Means for Solving the Problems> For this reason, in the internal combustion engine piston of the present invention, the cross-sectional shape of the skirt portion below the piston ring mounting groove is an ellipse whose short axis is in the axial direction of the piston pin. In the piston for an internal combustion engine, the elliptical shape of the skirt portion has at least two types of ellipticity, the ellipticity being small above the axis of the piston pin and the ellipticity being large below the axis of the piston pin, and The structure is such that a portion with a small ellipticity and a portion with a large ellipticity are smoothly connected.

In this configuration, when the piston is pressed against the cylinder bore by side pressure due to combustion force, the skirt portion and the cylinder bore come into contact.

At this time, the skirt part above the axis of the piston pin is
Since the ellipticity of its cross-sectional shape is small, it contacts the cylinder bore over a rather wide range. Further, since the skirt portion below the axis of the piston pin has a large elliptic cross-sectional shape, it contacts the cylinder bore only in a narrow range.

Therefore, the contact area of the skirt portion with the cylinder bore becomes smaller than in the conventional case.

In this case, since the upper side of the skirt portion contacts the cylinder bore over a relatively large area, the piston posture is supported by this contact portion.

As a result of the above, it is possible to reduce the friction of the skirt portion, and at the same time, the posture during piston operation is stabilized, and the occurrence of hitting noise due to piston slap can be suppressed, making it possible to achieve both effects.

<Example> Embodiments of the present invention will be described below based on the drawings.

In the following figures, the same elements as in FIGS. 6 to 9 are given the same reference numerals to simplify the explanation.

1 to 3, the skirt portion 2 of the piston 1 is formed into a so-called barrel shape by changing the long diameters of the ellipse Xz and Yz along the piston axis direction, and the piston on the outer peripheral surface of the skirt portion 2 The structure in which the tapered surfaces 4 are formed on the surfaces of both sides facing each other in the direction orthogonal to the axial direction of the pin 3 is the same as in the conventional structure. In addition, in Fig. 1, aZ
>a.

As described above, the major axis of the elliptical shapes x, y changes along the piston axis direction, and thus changes depending on the cross-sectional position as shown in FIGS. 2 and 3.

In this case, the oval shape X2. Yz has at least two types of ellipticity, and is formed with a small ellipticity above the axis of the piston pin 3 and a large ellipticity below, and a portion with a small ellipticity and a portion with a large ellipticity. It is designed to connect smoothly.

For example, above the axis of the piston pin 3.

The cross-sectional shape of the skirt portion 2 at a portion having a length of is formed as shown in FIG. Further, the cross-sectional shape of the skirt portion 2 at a portion having a length h2 below the axis of the piston pin 3 is formed as shown in FIG.

As is clear in these figures, the ellipse X in Figure 2
2, the difference between the major axis and the minor axis is larger than that of ellipse Y2 in Fig. 3, and the ellipticity is larger (b
z>cz).

Further, the portion located above the axis of the piston pin 3 and above the length thereof is formed into an elliptical shape as shown in FIG.
The portion downward from this portion is formed into an elliptical shape as shown in FIG. 2, and both portions are formed so as to be smoothly connected.

A portion having a length h2 below the axis of the piston pin 3 is a portion having a piston reference diameter φD.

Furthermore, even if there are dimensional differences in each part shown in Figs. 1 to 3,
As with the conventional example, the figure is exaggerated to be larger than the actual size for convenience.

Next, the operation of this configuration will be explained.

As shown in FIG. 5, when the piston 1 is pressed against the cylinder bore 8 by the side pressure F due to the combustion force Fg, the skirt portion 2 and the cylinder bore 8 come into contact.

At this time, the skirt portion 2 at a length hl from the axis of the piston pin 3 comes into contact with the cylinder bore 8 over a somewhat wide range because the ellipticity of its cross-sectional shape Yt is small. Further, the skirt portion 2 at a length h2 from the axis of the piston pin 3 has a large ellipticity of its cross-sectional shape X2, so it contacts the cylinder bore 8 only in a narrow range.

Therefore, the contact area of the skirt portion 2 with the cylinder bore 8 becomes as shown in the portion D shown in FIG. 4, which is smaller than that of the conventional example shown in FIG.

In this case, the posture of the piston 1 is such that the upper side of the skirt portion 2 contacts the cylinder bore 8 over a relatively large area.
It is supported by this contact area.

As a result of the above, it is possible to reduce the friction of the skirt portion 2, and at the same time, the posture of the piston 1 during operation is stabilized, and the generation of hammering noise due to piston slap can be suppressed, making it possible to achieve both effects.

Here, in the above configuration, the elliptical shape Y2 of the skirt portion 2 in the upper part of the piston pin 3 is made smaller in ellipticity than the elliptical shape Xz of the skirt part 2 in the lower part. , The reason for this is as follows.

That is, considering the load distribution between the upper and lower parts from the piston pin axis of the skirt part 2, upper: lower - 6 = 4 (predicted from the state of piston wear), so in order to apply equal surface pressure, the area of the upper is better. needs to be made larger. Therefore, the fourth
The contact area shown in the figure is best for low friction.

In this case, as described above, the oval shape X2 of the skirt portion 2
．． Y, has at least two types of ellipticity, and may be formed such that the ellipticity is small above the axis of the piston pin 3 and the ellipticity is large below.

In addition, the contact points of the oval Xt and Yz portions of the skirt portion 2 with the cylinder bore are determined by ag+aZ in FIG.
You can change it by setting ゛.

Also, a! in Figure 1! +aZ゛ and s, c, in Figs. 2 and 3 are set in consideration of thermal expansion, and h+ and hz in Fig. 1 are determined at appropriate positions depending on the dimensions of each part of the piston 1. do.

<Effects of the Invention> As explained above, according to the piston for an internal combustion engine according to the present invention, the cross-sectional shape of the skirt portion is an ellipse whose minor axis is in the axial direction of the piston pin; Since the piston pin is formed with a small ellipticity above the axis and a large ellipticity below, the contact area of the skirt with the cylinder bore can be reduced while keeping the piston posture stable, resulting in low friction and piston. This is highly useful as it can both prevent the occurrence of hitting sounds due to slap.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of a piston for an internal combustion engine according to the present invention, FIG. 2 is a sectional view taken along At-A in FIG. 4 is a side view showing the contact portion of the piston skirt portion with the cylinder bore in the same embodiment as above; FIG. 5 is a sectional view illustrating the operation of the piston; and FIG. 6 is a view of a conventional piston for an internal combustion engine. Figure 7 is a sectional view taken along arrows A and -A in Figure 1, Figure 8 is a sectional view taken along arrows B and -B in Figure 1, and Figure 9 is a sectional view taken in the direction of arrows B and -B in Figure 1. It is a side view which shows the contact part with the cylinder bore of the piston skirt part in FIG. 1...Piston 2...Skirt portion 3...
Piston pin Xs, Yz...ellipse

Claims (1)

[Claims] In an internal combustion engine piston in which a cross-sectional shape of a skirt portion below a piston ring mounting groove is an ellipse whose minor axis is in the axial direction of the piston pin, the ellipse of the skirt portion has at least two types of ellipticity. The piston pin is characterized by having a small ellipticity above the axis of the piston pin and a large ellipticity below the axis of the piston pin, and a structure in which the part with the small ellipticity and the part with the large ellipticity are smoothly connected. Pistons for internal combustion engines.