A laminar-scavenging two-cycle engine which has a high laminar-scavenging effect, includes a scavenging passage having a crankcase side portion extending along a crankcase, and a cylinder side portion extending along a cylinder and having a length larger than the sum of the diameter and stroke of the cylinder. An ambient air introducing passage for introducing leading air into the scavenging passage is connected to an intermediate portion of the scavenging passage. A notch for opening a scavenging port to the side of the crankcase when a piston is near the top dead center is formed in the piston.

A laminar-scavenging two-cycle engine which has a high laminar-scavenging effect, includes a scavenging passage having a crankcase side portion extending along a crankcase, and a cylinder side portion extending along a cylinder and having a length larger than the sum of the diameter and stroke of the cylinder. An ambient air introducing passage for introducing leading air into the scavenging passage is connected to an intermediate portion of the scavenging passage. A notch for opening a scavenging port to the side of the crankcase when a piston is near the top dead center is formed in the piston.

The disclosure provides a two-cycle engine and an engine work machine. When a piston is located on the side of a bottom dead center, at a part corresponding to a notch part in the piston, an inner surface of the crank case protrudes toward an interior side to form a crank case first protruding part penetrating through the notch part toward the interior side. Meanwhile, the crank case at a part corresponding to a part without the notch part in the piston is not in a shape protruding toward the interior side. By assembling the piston and the crank case in such shapes, the piston is able to reciprocally move up and down without interfering with the crank case. In this case, by disposing the crank case first protruding part, the volume in the crank case is able to be reduced.

Among multiple scavenging passages 14 included in a cylinder, a scavenging passage connected to at least one scavenging port 16 constitutes a variable scavenging passage 14(ch). An upper end portion of the variable scavenging passage 14(ch) has a guide surface 50 defining a discharge direction of a scavenging gas discharged from a variable scavenging port 16(ch) connected thereto on a 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. The discharge direction of the scavenging gas is changed from the first discharge direction to the second discharge direction on the horizontal plane by the first and second guide portions 50(H) and 50(L) in the scavenging stroke.

Among multiple scavenging passages 14 included in a cylinder, a scavenging passage connected to at least one scavenging port 16 constitutes a variable scavenging passage 14(ch). An upper end portion of the variable scavenging passage 14(ch) has a guide surface 50 defining a discharge direction of a scavenging gas discharged from a variable scavenging port 16(ch) connected thereto on a 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. The discharge direction of the scavenging gas is changed from the first discharge direction to the second discharge direction on the horizontal plane by the first and second guide portions 50(H) and 50(L) in the scavenging stroke.

A two-stroke engine according to the present invention includes: a separating wall which confines a tip end portion of an ignition device; an ignition promoting chamber which is formed by means of the separating wall, is independent of a combustion chamber, and encloses the tip end portion of the ignition device; and a plurality of communicating holes which are provided in the separating wall, each of which is provided with a first opening that opens in the combustion chamber and a second opening that opens in the ignition promoting chamber, and which provide communication between the combustion chamber and the ignition promoting chamber.

A two-stroke engine according to the present invention includes: a separating wall which confines a tip end portion of an ignition device; an ignition promoting chamber which is formed by means of the separating wall, is independent of a combustion chamber, and encloses the tip end portion of the ignition device; and a plurality of communicating holes which are provided in the separating wall, each of which is provided with a first opening that opens in the combustion chamber and a second opening that opens in the ignition promoting chamber, and which provide communication between the combustion chamber and the ignition promoting chamber.

An engine (2) is a four-flow scavenging type engine. Four scavenging ports (34) include: first right and left scavenging ports (34(lef-1) and 34(ref-1)) that lie on a side relatively away from an exhaust port (22) and that lie facing each other with a cylinder (4) in between; and second right and left scavenging ports (34(lef-2) and 34(ref-2)) that lie closer to the exhaust port (22) than first right and left scavenging ports do and that lie facing each other with the cylinder (4) in between. The second left scavenging port and the first right scavenging port that make up a first mutually diagonal set (Diag-No.1) have different opening timings from those of the first left scavenging port and the second right scavenging port that make up a second mutually diagonal set (Diag-No.2).

A two-stroke engine with valves near bottom dead center that are adapted to prevent intake charge from exiting exhaust ports, wherein the valves are actuated by air pressure difference.

A two-stroke engine with valves near bottom dead center that are adapted to prevent intake charge from exiting exhaust ports, wherein the valves are actuated by air pressure difference.