Air leading-type stratified scavenging two-stroke internal-combustion engine

Abstract

The efficiency of charging air to a scavenging channel is enhanced by generating a gas flow in a piston groove simultaneously with the piston groove coming into communication with an air port. A piston groove 8 formed in a peripheral surface of a piston includes a pressure transmission through hole 10, and the pressure transmission through hole 10 consistently communicates with a crankcase. In the course of the piston moving up, upon a pressure in the crankcase becoming negative, the negative pressure in the crankcase affects the piston groove 8 through the pressure transmission through hole 10. Consequently, a pressure in the piston groove 8 is released to the crankcase through the pressure transmission through hole 10. Upon the piston moving up and the piston groove 8 being thereby brought into communication with the air port 4a, air enters the piston groove 8 through the air port 4a ((III) of FIG. 1).

Claims

1. An air leading-type stratified scavenging two-stroke internal-combustion engine comprising: an air port that opens in a cylinder wall and is opened/closed by a piston; a scavenging channel including a scavenging port that opens in the cylinder wall and is opened/closed by the piston, the scavenging channel directly communicating with a crankcase; and a piston groove formed in a peripheral surface of the piston to supply air received directly from the air port to the scavenging port in a scavenging process, the piston groove directly communicating with the scavenging port when the piston groove enables the air port and the scavenging port to communicate with each other to charge air into the scavenging channel through the air port, wherein the piston groove includes a pressure transmission through hole that directly communicates with the crankcase, wherein when a pressure in the crankcase becomes negative in the course of the piston moving up from the bottom dead center toward the top dead center, the negative pressure in the crankcase affects the piston groove through the pressure transmission through hole to release a pressure in the piston groove to the crankcase through the pressure transmission through hole prior to charging air into the scavenging channel, wherein the piston groove extends in a circumferential direction of the piston; and wherein the pressure transmission through hole is disposed in an end portion on the side of the piston groove, the side being opposite to the air port across a vertical line running across a piston pin hole in the piston, and wherein in a course of the piston moving up toward the top dead center, there is a period in which the piston groove is in communication with the air port but not in communication with the scavenging port.

2. The air leading-type stratified scavenging two-stroke internal-combustion engine according to claim 1, wherein the pressure transmission through hole is disposed on a downstream side in an air flow direction of the piston groove.

3. The air leading-type stratified scavenging two-stroke internal-combustion engine according to claim 1, wherein a plurality of the scavenging ports are disposed on a side of the engine; and wherein at a position adjacent to a scavenging port that is furthest from the air port from the plurality of scavenging ports, the pressure transmission through hole is disposed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram for describing a configuration and operation of a main concept of the present invention: (I) illustrates a state in which a piston starts moving up from the bottom dead center toward the top dead center; (II) illustrates a state in which the piston further moves up toward the top dead center; (III) illustrates a state in which the piston further moves up and a piston groove is thereby brought into communication with an air port; and (IV) illustrates a state in which the piston further moves up and the piston groove that is in communication with the air port is thereby brought into communication with a scavenging port.

(2) FIG. 2 is a perspective view of a piston included in an air leading-type stratified scavenging two-stroke internal-combustion engine according to an embodiment of the present invention.

(3) FIG. 3 is a diagram for describing a configuration of a cylinder included in an air leading-type stratified scavenging two-stroke internal-combustion engine according to the embodiment of the present invention.

(4) FIG. 4 is a horizontal cross-sectional view of the air leading-type stratified scavenging two-stroke internal-combustion engine according to the embodiment of the present invention, cut along a level of a height of an exhaust channel thereof.

(5) FIG. 5 is a front view of a piston groove included in the piston illustrated in FIG. 2.

(6) FIG. 6 is a diagram for describing states in the course of piston upward movement toward the top dead center in a two-stroke engine according to the embodiment including a piston with a piston groove having a relatively-large vertical width: (I) illustrates a state in which the piston is positioned at the bottom dead center; (II) illustrates a state in which the piston moves up from the bottom dead center toward the top dead center; (III) illustrates a state in which the piston further moves up and piston grooves are thereby brought into communication with an air port; (IV) illustrates a state in which the piston further moves up toward the top dead center; and (V) illustrates a state in which the piston is positioned at the top dead center.

(7) FIG. 7 is a diagram for describing states in the course of piston upward movement toward the top dead center in a two-stroke engine according to the embodiment including a piston with a piston groove having a relatively-small vertical width: (I) illustrates a state when a piston is positioned at the bottom dead; (II) illustrates a state in which the piston moves up from the bottom dead center toward the top dead center; (III) illustrates a state immediately after the piston further moves up and a piston groove comes into communication with an air port; (IV) illustrates a state in which the piston further moves up toward the top dead center and the piston groove comes into communication with an air port; and (V) illustrates a state in which the piston is positioned at the top dead center.

(8) FIG. 8 is a diagram for describing states in the course of piston upward movement toward the top dead center in a conventional air leading-type stratified scavenging two-stroke engine: (I) indicates a state immediately before a piston groove comes into communication with an air port; (II) indicates a state in which a piston moves up and the piston groove is thereby brought into communication with the air port; and (III) indicates a state in which the piston further moves up and the piston groove that is in communication with the air port is thereby brought into communication with a scavenging port.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

(9) A preferable embodiment of the present invention will be described below with reference to the attached drawings.

(10) FIG. 2 illustrates a piston included in an air leading-type stratified scavenging two-stroke internal-combustion engine according to an embodiment of the present invention. With reference to FIG. 2, a piston 20 includes piston grooves 22 in a peripheral surface thereof. The piston 20 includes a piston pin hole 24, and a piston pin (not shown) inserted through the piston pin hole 24 is connected to a connecting rod (not shown).

(11) The piston 20 is fitted in a cylinder 26, which is illustrated in FIG. 3, so as to be vertically and reciprocatably movable. The cylinder 26 includes first and second scavenging channels 30 and 32 in each of the left and the right sides in plan view, and the first and second scavenging channels 30 and 32 communicate with a crankcase 34. In the cylinder wall 28, first and second scavenging ports 30a and 32a open. The first scavenging ports 30a communicate with the respective first scavenging channels 30. The second scavenging ports 32a communicate with the respective second scavenging channels 32. In other words, the engine according the embodiment is a four-flow scavenging engine.

(12) In the figure, reference numeral 36 denotes an exhaust channel. Also, reference numeral 38 denotes an air channel. Also, reference numeral 40 denotes an air-fuel mixture channel. Air is supplied to the air channel 38. Air-fuel mixture produced by a carburetor (not shown) is supplied to the air-fuel mixture channel 40. Reference numeral 42 denotes a spark plug.

(13) FIG. 4 is a horizontal cross-sectional view of an air leading-type stratified scavenging two-stroke internal-combustion engine 50 according to the embodiment of the present invention. Referring to FIG. 4, a first scavenging port 30a and a second scavenging port 32a positioned in each of the left and the right sides are oriented in a direction opposite to the exhaust channel 36. In other words, the two-stroke internal-combustion engine 50 according to the embodiment is a loop scavenging engine.

(14) Referring back to FIG. 2, the piston grooves 22 extend in a circumferential direction of the piston 20. FIG. 5 is a front view of a piston groove 22. Referring to FIGS. 2 and 5, the piston grooves 22 each includes a pressure transmission through hole 52.

(15) The pressure transmission through holes 52 may have a diameter of 0.1 to 3.0 mm, preferably a diameter of 0.5 to 2.5 mm, most preferably a diameter of 1.0 to 2.0 mm. In the embodiment, the pressure transmission through holes 52 are arranged in respective downstream ends in an air flow direction of the respective piston grooves 22, that is, left ends (ends on the exhaust port side) in FIG. 5, and positioned in the lower side of the respective piston grooves 22 in front view of the piston grooves 22.

(16) Although each pressure transmission through hole 52 may be arranged at an arbitrary position in the relevant piston groove 22, it is effective to arrange the pressure transmission through holes 52 on the downstream side in the air flow direction of the piston grooves 22. With reference to FIG. 5, the alternate long and short dash line is a vertical line VL running across the piston pin hole 24. More specifically, arrangement of the pressure transmission through holes 52 on the downstream side relative to the vertical line VL running across the piston pin hole 24 (the left side in FIG. 5) is effective for generating an initial gas flow inside the piston grooves 22.

(17) In other words, the piston grooves 22 extend in the circumferential direction of the piston 20. The pressure transmission through holes 52 are disposed at respective positions adjacent to the respective first scavenging ports 30a positioned on the exhaust port side.

(18) FIGS. 6 and 7 each indicate a specific example in which in the course of the piston moving up toward the top dead center, air is supplied to the scavenging channels 30 and 32 through the piston grooves 22. In the figures, reference numeral 44 denotes a crankshaft. An engine 50A, which is illustrated in FIG. 6, has a configuration in which the piston grooves 22 are enlarged upward in order to increase respective volumes thereof. In an engine 50B, which is illustrated in FIG. 7, the piston grooves 22 are positioned below the piston pin hole 24. A vertical width of the piston grooves 22 is smaller than that of the piston grooves 22 illustrated in FIG. 6.

(19) The engine 50A illustrated in FIG. 6, which includes piston grooves 22 each having a relatively-large vertical width, will be described. (I) of FIG. 6 illustrates the piston 20 positioned at the bottom dead center. Upon the piston 20 moving up from the bottom dead center toward the top dead center, a pressure in the crankcase 34 becomes negative. The negative pressure in the crankcase 34 affects the piston grooves 22 through the pressure transmission through holes 52 ((II) of FIG. 6). The piston 20 further moves up toward the top dead center and the piston grooves 22 is thereby brought into communication with an air port 38a. Then, air in the air channel 38 is drawn into the piston grooves 22 ((III) of FIG. 6). In other words, upon the piston grooves 22 coming into communication with the air port 38a, a gas flow is generated in each of the piston grooves 22. This state continues until the piston grooves 22 come into communication with the first and second scavenging ports 30a and 32a ((IV) of FIG. 6).

(20) Upon the piston 20 further moving up toward the top dead center after the above period in which the piston grooves 22 come into communication with the air port 38a, the piston grooves 22 that are in communication with the air port 38a are thereby brought into communication with the first and second scavenging ports 30a and 32a. Consequently, the air already charged in each of the piston grooves 22 is supplied to the relevant first and second scavenging channels 30 and 32. Also, air is supplied from the air channel 38 to the first and second scavenging channels 30 and 32 through the piston grooves 22. This state in which the air port 38a communicates with the first and second scavenging ports 30a and 32a via the piston grooves 22 continues until the piston 20 reaches the top dead center ((V) of FIG. 6).

(21) The engine 50B in FIG. 7, which includes piston grooves 22 each having a relatively-small vertical width, will be described. (I) of FIG. 7 illustrates the piston 20 positioned at the bottom dead center. Upon the piston 20 moving up from the bottom dead center toward the top dead center, a pressure in the crankcase 34 becomes negative. The negative pressure in the crankcase 34 affects the piston grooves 22 through the pressure transmission through holes 52 ((II) of FIG. 7). This state continues until the piston 20 further moves up toward the top dead center and the piston grooves 22 are thereby brought into communication with the air port 38a ((III) of FIG. 7).

(22) Upon the piston 20 further moving up toward the top dead center and the piston grooves 22 being thereby brought into communication with the air port 38a, air in the air channel 38 is drawn into the piston grooves 22. In other words, upon the piston grooves 22 coming into communication with the air port 38a, a gas flow is generated in each of the piston grooves 22. This state is continued until the piston grooves 22 come into communication with the first and second scavenging ports 30a and 32a ((IV) of FIG. 7). Then, upon the piston 20 further moving up toward the top dead center and the piston grooves 22 are thereby brought into communication with the first and second scavenging ports 30a and 32a, the air already charged in each of the piston grooves 22 is supplied to the relevant first and second scavenging channels 30 and 32. Also, air in the air channel 38 is supplied to the first and second scavenging channels 30 and 32 through the piston grooves 22. This state in which the air port 38a communicates with the first and second scavenging ports 30a and 32a via the piston grooves 22 continues until the piston 20 reaches the top dead center ((V) of FIG. 7).

(23) In the engines 50A (FIG. 6) and 50B (FIG. 7) according to the embodiment of the present invention, at a stage prior to the piston grooves 22 coming into communication with the first and second scavenging ports 30a and 32a, the negative pressure in the crankcase 34 affects the piston grooves 22 through the pressure transmission through holes 52. Consequently, a gas flow is generated in each of the piston grooves 22. Then, this gas flow induces the action of air being sucked into the piston grooves 22 when the piston grooves 22 come into communication with the air port 38a. Consequently, simultaneously with the piston grooves 22 coming into communication with the air port 38a, air is drawn into the piston grooves 22 from the air port 38a. After this period in which the piston grooves 22 come into communication with the air port 38a, upon the piston grooves 22 that are in communication with the air port 38a come into communication with the scavenging ports 30a and 32a, air is immediately charged into the scavenging channels 30 and 32 through the piston grooves 22. Consequently, the efficiency of charging air to the scavenging channels 30 and 32 can be enhanced.

(24) In other words, an engine according to the embodiment enables induction of an initial action of supplying air to scavenging ports 30a and 32a through piston grooves 22 that are in communication with an air port 38a. Consequently, the certainty of charging air to scavenging channels 30 and 32 in each cycle can be enhanced.

(25) This means that the enhancement contributes to optimization of a timing for bringing the piston grooves and the scavenging ports into communication with each other and a timing for bringing the piston grooves and the air port into communication with each other. Consequently, an air leading-type stratified scavenging two-stroke internal-combustion engine with an output enhanced while exhaust gas emission characteristics are improved can be provided.

(26) Although the embodiment has been described in terms of an engine with two scavenging ports 30a and 32a on each side and the two scavenging ports 30a and the two scavenging ports 32a on the opposite sides are symmetrically arranged, respectively, as a typical example, it should be understood that the present invention is not limited to this example. The present invention includes, for example, the following alterations:

(27) (1) Engine including one scavenging port on each side;

(28) (2) Engine with one or more scavenging ports on the respective sides arranged asymmetrically; and

(29) (3) Engine with a plurality of scavenging ports on each side, the scavenging ports being connected to, for example, one scavenging channel extending in a Y shape while a plurality of scavenging ports 30a and 32a on each side, the scavenging ports 30a and 32a being connected to independent scavenging channels 30 and 32 in the embodiment, are provided.

(30) The present invention is applicable to an air leading-type stratified scavenging two-stroke internal-combustion engine. The present invention is favorable for use in a single-cylinder air-cooled engine to be mounted on a portable work machine such as a brush cutter or a chain saw. 20 piston 22 piston groove 24 piston pin hole VL vertical line running across piston pin hole 26 cylinder 28 cylinder wall 30 first scavenging channel 30a first scavenging port 32 second scavenging channel 32a second scavenging port 34 crankcase 36 exhaust channel 38 air channel 38a air port 40 air-fuel mixture channel 50 air leading-type stratified scavenging two-stroke internal-combustion engine 52 pressure transmission through hole