JPS5825862B2 - Piston for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piston used in an internal combustion engine.

Conventionally, the profile (outer shape) of a piston has been designed by comprehensively considering the material of the piston, its thermal expansion, and furthermore, the movement within the cylinder. In order for the moving piston to always have an appropriate clearance, that is, to ensure that the piston touches the cylinder smoothly, and to maintain an appropriate gap between the piston ring and the ring groove, and in addition to this, the function of the piston ring is to ensure combustion. Care has been taken to seal the gas.

For example, in a very general piston 1 as shown in FIG. The profile has a diameter that gradually decreases toward the upper end 15 (from the upper end 15 of the piston to the top of the ring groove shown in Figure 1).

This is because the land portion 11 is directly exposed to combustion gas, so the diameter of the land portion 11 is made small in consideration of thermal expansion, and heat is gradually dissipated toward the bottom, which is why such a profile is used. .

As is clear from FIG. 1, the piston 1
The profile is symmetrical with respect to the vertical axis (piston axis) A-A of the piston 1.

Further, the cross-sectional shape of the piston 1 is not a perfect circle, but a shape close to an ellipse, as shown in FIG.

This is because a pin boss part 14 is formed on the piston 1 in order to maintain the strength of the pin hole 13 into which the piston pin 2 is inserted, so the thermal expansion of this part is smaller than that of other parts. Then, an axis (minor axis) Y-Y passes through the piston axis A-A and is parallel to the axis Y'Y' of the pin hole 13.
The axis passing through the piston axis A-A at right angles to the upper diameter (
This means that the diameter is smaller than that on the long axis (long axis) X-X.

In this case as well, the profile of the piston 1 is generally symmetrical with respect to the major axis XX and the minor axis YY.

Despite these various considerations,
The piston 1 reciprocating within the cylinder 3 is under rotational conditions.
Because load conditions, cooling conditions, etc. are not constant, not only does it not always hit the cylinder smoothly as originally intended, but the gap between piston 1 and cylinder 3 constantly changes, resulting in a seal failure and combustion gas blowing through. The reality is that

In many cases, the contact between the left side thrust side T of the piston 1 shown in FIG. 1 and the right side: anti-thrust side U (when the crankshaft not shown in the figure rotates clockwise) is different.

This is particularly true for piston pin 2 relative to piston axis A-A.
When the center O of the piston pin hole 13 is eccentric, when the combustion chamber center is eccentric from the axis of the piston 1, when the piston length is extremely short, when supercharging, etc. This is particularly noticeable, and the installation of the ejection nozzle is also strongly influenced by the position.

All of these are due to the moment around the piston pin that the piston receives within the cylinder.

For example, the center O of the piston pin 2 is the piston axis A-A
In the case where the piston 1 is eccentrically disposed on the thrust side T by about 0.5 to 2.5 degrees and is eccentric from the center of gravity G of the piston 1, the piston 1 will be located near the top dead center of the compression stroke as shown in Fig. 3. As shown in FIG. 3A, at the beginning of the expansion stroke, a clockwise moment M acts on the piston 1 about the center 0 of the piston pin 2, as shown in FIG.

Note that this moment l-M has a value shown by the following formula.

Compression stroke; M=Fg-x-Fi-y Expansion stroke; M=Fg-X-Fi-y Fg; Gas force Fl; Piston inertia force 8; Distance between piston pin hole center and cylinder center y; Piston pin hole center and the horizontal distance h from the center of gravity of the piston; the vertical distance R between the center of the piston pin hole and the center of gravity of the piston; receives gas force Fg due to this, and a reaction force R acts in the anti-thrust direction.

The inertial force Fi acts upward against the gas force Fg,
Since gas force Fg is larger than inertia force Fi, piston 1
A clockwise moment M acts around the center 0.

Therefore, due to the reaction force (side pressure) R and the moment M, the piston 1 is located on the anti-thrust side U of the cylinder 3, and
The land portion 17 on the anti-thrust side U comes into contact with the cylinder 3.

When the piston 1 approaches the top dead center further and fuel is supplied and explodes, the gas force Fg increases by 1.5 to 2 times, and the third
The engine moves to the expansion stroke as shown in the figure.

As long as fuel continues to be supplied after top dead center, the gas force Fg further increases, and the direction of the reaction force R reverses, causing a force in the thrust direction to act on the piston 1. Become.

The movement of the piston near the top dead center is explained as above, but the movement of the piston 1 in the thrust direction due to the increased moment l-M due to the gas force Fg and the reaction force R occurs instantaneously. , the lower end 18 of the skirt on the thrust side T collides with the cylinder 3, and the land portion 17 on the anti-thrust side U comes to press against the cylinder 3,
As shown in the figure, the piston 1 shifts to the downward stroke in a rightward tilted state.

For this reason, the gap between the land portion 19 on the thrust side T and the cylinder 3 increases, resulting in a poor seal and the combustion gas GA.
Gas leaks into the crankcase and dilutes the oil, and the same gas GA also enters the ring groove and deposits carbon, further increasing the temperature near the ring groove and carbonizing the oil.
This may lead to seizure of the piston ring.

In view of the above points, the present invention aims to provide a piston for an internal combustion engine that prevents combustion gas from leaking out.

The present invention will be explained below with reference to embodiments shown in FIGS. 4 and 5.

Note that the same - signal is attached to parts that are the same as those in the conventional example.

In FIGS. 4 and 5, 1 is a piston, 11 is a land portion thereof, and 12 is a skirt portion thereof.
Similar to the conventional piston shown in FIGS. 1 and 2, the diameter of the land portion 11 is smaller than that of the lower part of the skirt portion 12, and the pin boss portion 14 is provided along the piston axis A-A. The diameter on the minor axis Y-Y, which is parallel to the axis Y'-Y' of the pin hole 13
The diameter is smaller than the diameter on the major axis line XX passing through A.

Further, the cross-sectional profile of the skirt portion 12 is also substantially the same as that of a conventional piston.

The piston 1 of the present invention is characterized by the cross-sectional profile of the land portion 11, that is, the center O of the piston pin hole 13 is located at the thrust side T in the major axis X-X direction with respect to the piston axis A-A. Or, it is eccentric to the anti-thrust side U (the center O of the piston pin hole 13 is the axis A-A).
In the piston 1 (separated from the top), the land portion 11
The cross section of is defined by the length of the land portion on the side where the center O of the piston pin hole 13 is located, with respect to the minor axis Y-Y which passes through the piston axis A-A and is parallel to the piston pin hole axis y/y/. The length W of the land portion on the opposite side is made longer than the length W of the conventional land portion, and the profile of the land portion 11 is made asymmetric between the thrust side T and the anti-thrust side U with respect to the short axis YY, and the short axis The profile is approximately elliptical and symmetrical with respect to the major axis XX which is perpendicular to Y-Y and passes through the piston axis AA.

To explain the movement of the piston 1 in the cylinder 3 according to the present invention, the center O of the piston pin hole 13 is eccentric to the thrust side T and eccentric from the center of gravity G, as in the case of the conventional example. If so, in the vicinity of the top dead center of the compression stroke, the movement will be exactly the same as that shown in FIG. 3a.

Also, regarding the expansion stroke, the movement is roughly the same as shown in Figure 3, but as mentioned above, the length of the land part on the thrust side where the center O of the piston pin hole 13 is located is the same as the conventional one on the anti-thrust side. Since the land portion has a substantially elliptical shape that is longer than the length W of the land portion, when the piston 1 is inclined to the right with respect to the cylinder 3, the land portion 19 on the thrust side T and the cylinder 3 are connected as shown in FIG. The gap is the land portion 11
The length of the land part on the thrust side (■) is made narrower by the length W of the land part on the anti-thrust side, which prevents the flow of the gas GA that tries to flow down and improves the sealing performance. , the blow-through of combustion gas is reduced, the dilution of oil is reduced, and the amount of carbon that enters the ring groove is also reduced, which eliminates the problem of oil carbonization and seizure from the FP of the ring. .

The cross-sectional shape of the land portion is such that the length V of one side in the direction of the major axis X-X with respect to the minor axis Y-Y is longer than the length W of the other land portion on the opposite side. Although the shape is generally referred to as an elliptical shape, it goes without saying that the above shape may be formed by a combination of a true circle and an ellipse or an ellipse and an ellipse.

In addition, in this operation explanation, the piston 1 was mainly described in which the center O of the piston pin hole 13 was eccentrically moved toward the thrust side T with respect to the piston axis A-A. The piston 1 that is eccentric to the anti-thrust side U with respect to A moves in the exact opposite manner to the above explanation, and the land portion 1 of this piston 1
The cross-sectional shape of No. 1 is such that the length ■ of the land portion on the anti-thrust side U where the center O of the piston pin hole 13 exists is longer than the land portion W on the opposite thrust side with respect to the minor axis Y-Y. By making it approximately elliptical, the same effect as described above can be obtained.

Furthermore, the piston pin hole 13 shown in FIGS. 7 and 8
Even if the center O of the piston 1 is not eccentric, that is, the center O is on the histone axis A-A, and the piston pin axis Y'-Y' is aligned with the minor axis Y-Y parallel to this. Problems caused by blow-through of combustion gas have actually been confirmed due to the eccentricity of the combustion chamber mentioned above, the weight distribution of the piston itself to the piston pin, etc. It goes without saying that the present invention can be applied to these as well. Even in series engines, the eccentric direction of the center O of 13 varies, such as the thrust side T or the anti-thrust side U.
Furthermore, the force acting on piston 1 is different between the left and right banks.
This is especially true between mold machines, and the piston pin hole 13
The relationship between the eccentric direction of the center O and the lengths V and W of the land portions on the thrust side T and anti-thrust side U of the land portion 11 may be determined to be optimal for the engine on the other side.

[Brief explanation of drawings]

Figure 1 is a front view showing the shape of a conventional piston, Figure 2 is a sectional view of Figure 1, and Figure 3 is an explanatory diagram of the operation of a conventional piston from compression to expansion stroke, and a is top dead center. 4 is a front view showing an embodiment of the piston according to the present invention, FIG. 5 is a sectional view taken along the arrow E in FIG. 4, and FIG. 6 is a view showing the piston according to the present invention. FIG. 7 is a front view showing another embodiment of the piston according to the present invention, and FIG. 8 is a sectional view taken along the arrow E in FIG. 7. 1: Piston, 3 Niji cylinder, 11: Piston land part, 12: Piston skirt part, T Ni thrust side, U: Anti-thrust side, A-A: Piston axis, Y-Y: Minor axis (piston pin passes through the piston axis) (axis parallel to the hole axis), X-X: major axis (axis passing through the piston pin axis and perpendicular to the piston pin hole axis), V, W: length of the land portion.

Claims (1)

[Scope of Claims] 1. A cross section of an approximately ellipse in which the diameter on the minor axis passing through the piston axis and parallel to the piston pin hole axis is smaller than the diameter on the major axis passing through the piston axis at right angles to the minor axis. In a piston for an internal combustion engine having a surface, the cross-sectional shape of the land portion is such that the length of the land portion on the major axis is longer than the other with respect to the minor axis, and the length of the land portion on the major axis is longer than the other, and A piston for an internal combustion engine has a substantially elliptical shape that is symmetrical to the other. 2. It has a substantially elliptical cross section in which the diameter on the minor axis passing through the piston axis and parallel to the piston pin hole axis is smaller than the diameter on the major axis passing through the piston axis at right angles to the minor axis;
In a piston for an internal combustion engine in which the center of the piston pin hole is eccentric in the direction of the major axis with respect to the piston axis, the cross-sectional shape of the land portion is such that the length of the land portion on the major axis is relative to the minor axis, A piston for an internal combustion engine having a substantially elliptical shape in which the side where the center of the piston pin hole is located is longer than the opposite side and is symmetrical with respect to the major axis.