CN-114508411-B - Two-stroke engine

CN114508411BCN 114508411 BCN114508411 BCN 114508411BCN-114508411-B

Abstract

A two-stroke engine improves scavenging efficiency in an air cylinder. The scavenging passage connected to at least one scavenging port (16) among the plurality of scavenging passages (14) included in the cylinder constitutes a variable scavenging passage (14) (ch). The upper end of the variable scavenging passage (14 (ch)) has a guide surface (50) that defines the direction of discharge of the scavenging gas discharged from the variable scavenging port (16 (ch)) connected thereto in the horizontal plane. The guide surface (50) includes at least a first guide portion (50 (H)) defining a first discharge direction of the scavenging gas, and a second guide portion (50 (L)) defining a second discharge direction of the scavenging gas. In the scavenging stroke, the scavenging gas discharge direction is changed from the first discharge direction to the second discharge direction on the horizontal plane by the first guide portion (50 (H)) and the second guide portion (50 (L)).

Inventors

TAKUMI NONAKA
Bai Jingjian
Koza Koichiro
HOSHI TAKUYA

Assignees

株式会社山彦

Dates

Publication Date: 20260512
Application Date: 20211115
Priority Date: 20201116

Claims (12)

1. A two-stroke engine comprising: a piston disposed in the cylinder, reciprocating between a top dead center and a bottom dead center, and defining a combustion chamber; An exhaust port that opens to the cylinder and is opened or closed by the piston, and that is used to discharge burned gas in the combustion chamber; A crank chamber receiving fresh air, the fresh air being precompressed by a descending motion of the piston, and A plurality of scavenging passages that communicate the combustion chamber with the crank chamber in a scavenging stroke and that include a scavenging port for discharging fresh air precompressed in the crank chamber to the combustion chamber as scavenging gas, the scavenging port being opened or closed by the piston, The scavenging passage connected to at least one of the scavenging ports among the plurality of scavenging passages constitutes a variable scavenging passage, The upper end portion of the variable scavenging passage has a guide surface that defines a discharge direction of the scavenging gas discharged from the variable scavenging port connected to the upper end portion of the variable scavenging passage in a horizontal plane that is a surface that spreads in a lateral direction orthogonal to a surface that spreads along the up-and-down motion of the piston, The guide surface includes at least a first guide portion defining a first discharge direction of the scavenging gas, and a second guide portion defining a second discharge direction of the scavenging gas, The scavenging gas discharge direction is changed from the first discharge direction to the second discharge direction on the horizontal plane by the first guide portion and the second guide portion as the scavenging stroke proceeds, The first discharge direction is directed away from the exhaust side of the air cylinder and is tangential to the inner wall of the air cylinder, The second discharge direction is directed in a direction opposite to the exhaust port, i.e., a direction away from a tangential direction of an inner wall of the cylinder and shifted to a central portion of the cylinder.
2. A two-stroke engine according to claim 1, wherein, The guide surface has an upper guide portion and a lower guide portion, The upper guide portion forms the first guide portion, The lower guide portion forms the second guide portion, A step part is arranged between the upper guide part and the lower guide part, The first discharge direction is defined by the upper guide portion, The second discharge direction is defined by the lower guide portion, The step portion constituting a boundary of the upper guide portion and the lower guide portion is located at an intermediate portion in the up-down direction of the variable scavenging port.
3. A two-stroke engine according to claim 2, wherein, The guide surface has an intermediate guide portion that defines a third discharge direction of the scavenging gas between the upper guide portion and the lower guide portion.
4. A two-stroke engine according to claim 1, wherein, The guide surface is constituted by a guide portion having a plurality of stages in the up-down direction.
5. A two-stroke engine according to claim 1, wherein, The scavenging passage connected to one of the scavenging ports is a variable scavenging passage.
6. A two-stroke engine according to claim 1, wherein, The engine has four scavenging ports, The scavenging passage connected to at least one of the four scavenging ports is the variable scavenging passage.
7. A two-stroke engine according to claim 1, wherein, The scavenging passage connected to a scavenging port other than at least one scavenging port among the plurality of scavenging ports is the variable scavenging passage.
8. A two-stroke engine according to claim 6 or 7, wherein, The direction of the scavenging gas discharged from the variable scavenging ports facing each other is set so as not to collide with the scavenging gas discharged from the variable scavenging port facing each other among the plurality of variable scavenging ports.
9. A two-stroke engine according to claim 1, wherein, All the scavenging ports comprised by the engine are open at the same timing.
10. A two-stroke engine according to claim 1, wherein, The guide surface of at least the variable scavenging passage of the plurality of scavenging passages included in the engine is formed by a scavenging passage forming cover later attached to a cylinder block.
11. A two-stroke engine according to claim 1, wherein, The two-stroke engine is a reverse scavenged engine.
12. A two-stroke engine according to claim 1, wherein, The two-stroke engine is a stratified scavenging engine.

Description

Two-stroke engine Technical Field The present invention relates to a two-stroke engine. Background Conventionally, in a general two-stroke engine, scavenging in an air cylinder is performed using a mixture gas precompressed in a crank chamber in a scavenging stroke. The two-stroke engine includes a scavenging passage that communicates the crank chamber with the combustion chamber. The upper end opening of the scavenging passage, i.e. the scavenging port, is opened or closed by the piston reciprocating between the top dead center and the bottom dead center. Further, the exhaust port is opened or closed by the action of the piston. When the piston is lowered in the combustion stroke, the exhaust port and the scavenging port are opened near the bottom dead center of the piston, and scavenging in the cylinder is started while the scavenging port is opened. The scavenging port communicates with the crank chamber via a scavenging passage, and the pre-compressed mixture gas is discharged as scavenging gas from the scavenging port into the cylinder while the scavenging port is opened. In a conventionally known two-stroke engine in which a mixture gas is precompressed in a crank chamber, there is a problem of "blow-off of the mixture gas" occurring in a scavenging stroke. The "blow-off of the mixture gas" is a phenomenon in which the mixture gas discharged from the scavenging port, that is, the scavenging gas does not contribute to the scavenging, but is directly discharged from the exhaust port. In the blow-off phenomenon, since the unburned mixed gas is discharged, not only the environment is polluted, but also the gas supply efficiency (ηtr) is lowered to deteriorate the combustion consumption rate. In order to cope with the problem of blowoff of the mixture gas, as a method of scavenging, a "reverse scavenging" has been proposed, and has become the mainstream of the current two-stroke engine. The "reverse scavenging" is performed by directing the scavenging gas, which is the mixture gas discharged from the scavenging port, to the cylinder wall surface on the intake side, which is the side opposite to the exhaust port. A reverse-scavenging two-stroke engine is disclosed in patent document 1, for example. Patent document 1 discloses that the scavenging gas discharged from the scavenging port is sent to the cylinder wall surface on the intake side. The scavenging gas then reverses in the cylinder and proceeds toward the exhaust port. Here, patent document 1 proposes that the scavenging gas discharged from the scavenging port is directed to the cylinder wall surface on the intake side by forming the cross-sectional shape of the upper end portion of the scavenging passage into a substantially triangular shape with the scavenging port as one side. In the course of calling for environmental problems, the exhaust gas restriction becomes strict. In order to cope with this, various proposals have been made for preventing the blowing-off of the mixed gas. The scavenging port is opened with the descending motion of the piston, and then the effective opening area is made larger. Patent documents 2 and 3 disclose inventions for changing the direction of the scavenging gas, which is the mixture gas discharged from the scavenging port, in the above-described process. For convenience of explanation, a surface that spreads along the up-and-down motion of the piston is referred to as a "vertical surface", and a surface that spreads in the lateral direction orthogonal to the vertical surface is referred to as a "horizontal surface". Patent document 2 discloses an invention in which the ceiling wall surface of the portion near the exhaust port, which is the upper end portion of the scavenging passage, is three-dimensionally shaped, and the discharge direction of the scavenging gas is changed in the vertical plane by the ceiling wall surface of the three-dimensional shape. According to the above invention, the scavenging gas is directed upward when the scavenging port starts to open. Then, as the effective opening area of the piston descending scavenging port expands, the scavenging gas gradually points downward. Patent document 3 discloses an invention in which the top plate wall surface of the upper end portion of the scavenging passage, that is, the portion in the vicinity of the scavenging port is divided into a first surface on the intake side and a second surface on the exhaust side of the cylinder, and the first surface on the intake side has a relatively large inclination angle for directing the scavenging gas upward as compared with the second surface on the exhaust side. The upper edge of the scavenging port is given a stepped shape in association with the shape of the scavenging passage, and at the upper edge of the scavenging port, the first half upper edge on the intake side is located above the second half upper edge on the exhaust side. According to the invention of patent document 3, when the piston descends and reach