JPH09280105A - Piston of 2-cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the bottom part of an exhaust port of a cylinder wall from being extremely worn and hold the sealing performance of a ring at the bottom end of a piston. SOLUTION: In a 2-cycle engine having a scavenging port 4 in the peripheral wall 2 of a cylinder 1, when a piston 3 is reciprocally moved in the range of its stroke, a distance L between the bottom end of a second ring 12 of a lower side of the top end of the piston 3 and the top end of a third ring 13 of an upper side of the bottom end of the piston 3 is made larger than a piston stroke S, whereby the moving range of the second ring 12 in the lower side of the top end of the piston 3 does not overlap with the moving range of the third ring 13 in the upper side of the bottom end of the piston 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston for a two-cycle engine in which a scavenging hole is provided on a peripheral wall of a cylinder.

[0002]

2. Description of the Related Art In a two-stroke engine, as shown in FIG. 2, a plurality of scavenging holes 24 are formed at an intermediate height position near a bottom dead center of a piston 23 in a cylinder liner which constitutes a peripheral wall 22 of a cylinder 21. , Fresh air pressurized by a scavenging pump (not shown) or other means is supplied to a scavenging chamber provided outside the scavenging hole 24, and when the piston 23 reaches near the bottom dead center after combustion, By introducing fresh air into the cylinder 21 as indicated by an arrow and discharging combustion gas from an exhaust port (uniflow type) provided in the cylinder head 26 or an exhaust port (Schneille type) provided in the cylinder liner 22, the inside of the cylinder 21 It is configured to replace the combustion gas with fresh air.

In the piston 23 of such a two-cycle engine, as disclosed in, for example, Japanese Utility Model Laid-Open No. 61-157146 and Japanese Utility Model Laid-Open No. 2-76144, a first ring and a second ring are provided on the outer periphery of the upper end portion. First and second piston rings) 31 and 32 are arranged, and a third ring (compression ring) 33 is arranged on the outer periphery of the lower end portion. Further, as disclosed in Japanese Utility Model Laid-Open No. 4-75147, The oil ring 34 may be disposed below the oil ring 34.

In this piston 23, when the piston 23 is located at the top dead center, the third ring 33 is located below the scavenging hole 24, and when the piston 23 is located at the bottom dead center, the upper surface of the piston 23 is located below the scavenging hole 24. It is designed to be as short as possible in order to minimize weight while satisfying the requirement of being located at.

[0005]

However, in the two-stroke engine having the above-described structure, when the piston 23 is located at the top dead center, the third ring 33 is immediately below the scavenging hole 24 as shown in FIG. When the piston 23 is located at the bottom dead center, the first ring 31 is located immediately below the scavenging hole 24, and the second ring 32 is located below the scavenging hole 24, as shown in FIG. 2B. The moving range A at the lower end of the second ring 32 and the moving range B at the upper end of the third ring 33 due to the reciprocating movement of the piston 23 overlap in the range C below the scavenging hole 24.

Therefore, there is a problem that the area C below the scavenging holes 24 of the cylinder liner which constitutes the peripheral wall 22 is heavily worn, and the scratches formed when the first ring 31 and the second ring 32 pass through the scavenging holes 24. The third ring 33 and the oil ring 3 through the cylinder liner 22.
However, there is a problem that the transfer to No. 4 causes an increase in leakage of scavenging air into the crank chamber.

In view of the above-mentioned conventional problems, the present invention provides a piston for a two-cycle engine which is capable of preventing significant wear of a lower region of a scavenging hole in a peripheral wall of a cylinder and maintaining a sealing property of a ring at a lower end of the piston. With the goal.

[0008]

According to the present invention, in a piston of a two-cycle engine having a scavenging hole in a peripheral wall of a cylinder, a lower ring lower end at a piston upper end portion and an upper ring upper end at a piston lower end portion are provided. By making the distance larger than the piston stroke, the moving range of the lower ring at the upper end of the piston and the moving range of the upper ring at the lower end of the piston do not overlap when the piston reciprocates within the stroke range. , As a result, the lower area of the scavenging hole on the cylinder peripheral wall is not significantly worn, and even if the scavenging hole damages the ring at the upper end of the piston, the damage does not transfer to the ring at the lower end of the piston.
The sealability of the ring is ensured to prevent scavenging gas from leaking into the crank chamber for a long period of time.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIG.

In FIG. 1, reference numeral 1 denotes a cylinder, and its peripheral wall 2 is constituted by a cylinder liner. In the peripheral wall 2 of the cylinder 1, a plurality of scavenging holes 4 are arranged at appropriate intervals in the circumferential direction at an intermediate height position near the bottom dead center of the piston 3 which reciprocates in the cylinder 1.
Is provided. The scavenging hole 4 is composed of a so-called swirl port formed so as to be tangential to the radial axis of the cylinder 1 or a so-called straight port along the radial axis of the cylinder 1, which are independent of each other. Or, they are arranged in combination.

A scavenging chamber (not shown) is provided around the scavenging hole 4, and fresh air pressurized by a scavenging pump (not shown) is fed to the scavenging chamber, whereby Fresh air is introduced into the cylinder 1 from the scavenging hole 4. 5
Is a cylinder head that covers the upper surface of the cylinder 1 and forms a combustion chamber with the upper surface of the piston 3. The cylinder head 6 is provided with one or a plurality of exhaust ports (not shown) for exhausting combustion gas and an exhaust valve for opening and closing the exhaust ports.

A first ring (first piston ring) 11 and a second ring (second piston ring) 12 are provided on the outer periphery of the upper end of the piston 3, and a third ring (compression ring) 13 is provided on the outer periphery of the lower end. An oil ring 14 is provided. The distance L between the lower end of the second ring 12 and the upper end of the third ring 13 is larger than the piston stroke S.
/ S is set to 1.01 to 1.05. That is, L
/ S needs to be 1.01 or more due to dimensional tolerance of cylinder liner or piston, assembly tolerance, clearance of each part, expansion / contraction difference due to heat or load, etc., and if greater than 1.05, the weight of piston 3 is unnecessary. Since it becomes extremely large, it is preferable to set it in the above range.

According to the above construction, when the piston 3 reciprocates with its stroke S, the moving range A (= S) of the second ring 12 at the upper end of the piston 3 is reached.
And the moving range B (= S) of the third ring 13 at the lower end of the piston 3 do not overlap. Therefore, unlike the conventional case, both the second ring 12 and the third ring 13 do not make sliding contact with each other in the lower region of the scavenging hole 4 of the peripheral wall 2 of the cylinder 1, and significant wear of the lower region of the scavenging hole 4 of the peripheral wall 2 is prevented. can do.

Further, since the first ring 11 and the second ring 12 pass through the scavenging holes 4 when the piston 3 reciprocates, these piston rings 1 and
1 and 12 are easily scratched, but even if these rings 11 and 12 are scratched, there is no fear that the scratches will be transferred to the third ring 13 and the oil ring 14 via the peripheral wall 2, and the third ring 13 and the oil ring Since the sealability of 14 can be secured, it is possible to prevent leakage of scavenging air into the crank chamber for a long period of time.

[0015]

As described above, according to the piston of the two-cycle engine of the present invention, the distance between the lower ring lower end at the piston upper end and the upper ring upper end at the piston lower end is larger than the piston stroke. Therefore, when the piston reciprocates within its stroke range, the moving range of the lower ring at the upper end of the piston and the moving range of the upper ring at the lower end of the piston do not overlap, and therefore the scavenging holes of the cylinder peripheral wall are It is possible to prevent significant wear of the lower region, and even if the scavenging hole damages the ring at the top of the piston, it is possible to prevent the damage from transferring to the ring at the bottom of the piston, so that the sealability of that ring can be secured. This has the effect of preventing leakage of scavenging air into the crank chamber for a long period of time.

[Brief description of drawings]

FIG. 1 shows a schematic configuration of a main part of a two-cycle engine according to an embodiment of the present invention, (a) is a vertical cross-sectional view showing a state in which a piston is located at a top dead center, and (b) is a bottom dead center of the piston. It is a longitudinal cross-sectional view of the state located in.

FIG. 2 shows a schematic configuration of a main part of a conventional two-cycle engine, in which (a) is a vertical cross-sectional view of a piston positioned at top dead center, and (b) is a piston positioned at bottom dead center. FIG.

[Explanation of symbols]

 1 cylinder 2 peripheral wall 3 piston 4 scavenging hole 11 first ring (first piston ring) 12 second ring (second piston ring) 13 third ring (compression ring) 14 oil ring

Claims (1)

[Claims] 1. In a piston of a two-cycle engine having a scavenging hole in the peripheral wall of a cylinder, the distance between the lower ring lower end at the piston upper end and the upper ring upper end at the piston lower end is greater than the piston stroke. The piston of the two-cycle engine characterized by doing.