Abstract
The certainty of supplying air to a scavenging channel through a piston groove is improved. In a cylinder wall 2, a gas venting port 10 is formed below and adjacent to a scavenging port 6a. The gas venting port 10 is independent from the scavenging port 6a, and is opened/closed by a piston as each of an air port 4a and the scavenging port 6a is. Upon a piston groove 8 being brought into communication with the gas venting port 10 as a result of the piston moving up (FIG. 1(II)), blown-back gas in a piston groove 8 can move to a crankcase through the gas venting port 10. Along with this, air can enter the piston groove 8 from the air port 4a.
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 communicating with a crankcase to induce an air-fuel mixture in the crankcase to flow directly into a combustion chamber in a scavenging stroke of the engine; a piston groove formed in a peripheral surface of the piston, the piston groove enabling the air port and the scavenging port to communicate with each other to charge a lead air to the scavenging channel before the scavenging stroke; and a gas venting port that communicates with the crankcase through the scavenging channel, and opens in the cylinder wall independently from the scavenging port and is opened/closed by the piston to generate a gas flow in the piston groove prior to the piston groove coming into communication with the scavenging port, wherein the gas venting port is positioned on the crankcase side that is lower than the scavenging port in a cylinder axis direction, wherein in a course of the piston moving up toward the top dead center, before the piston groove that is in communication with the air port comes into communication with the scavenging port, the piston groove that is in communication with the air port comes into communication with the gas venting port, wherein in a course of the piston moving from the bottom dead center to the top dead center, the piston groove is brought into communication with the gas venting port and then is brought into communication with the scavenging port, and wherein when the piston is at the top dead center, the piston groove is not in communication with the air port.
2. The air leading-type stratified scavenging two-stroke internal-combustion engine according to claim 1, wherein the gas venting port is disposed at a position that allows the gas venting port to communicate with an end portion of the piston groove, the end portion being on a side opposite to a side on which the air port is positioned.
3. The air leading-type stratified scavenging two-stroke internal-combustion engine according to claim 2, 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 among the plurality of scavenging ports, the gas venting port is disposed.
4. The air leading-type stratified scavenging two-stroke internal-combustion engine according to claim 3, wherein the piston groove includes a pressure transmission through hole that consistently communicates with the crankcase.
5. The air leading-type stratified scavenging two-stroke internal-combustion engine according to claim 2, wherein the piston groove includes a pressure transmission through hole that consistently communicates with the crankcase.
6. The air leading-type stratified scavenging two-stroke internal-combustion engine according to claim 1, wherein the piston groove has a height dimension, wherein the piston has a direction of movement with respect to the cylinder wall and the height dimension is determined in the direction of movement of the piston, that allows the piston groove to simultaneously communicate with the scavenging port and the gas venting port when the piston groove is in communication with the air port.
7. 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 among the plurality of scavenging ports, the gas venting port is disposed.
8. The air leading-type stratified scavenging two-stroke internal-combustion engine according to claim 1, wherein the piston groove includes a pressure transmission through hole that consistently communicates with the crankcase.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a diagram for describing a configuration and operation of the present invention: (I) illustrates a state immediately before a piston moves up from the bottom dead center toward the top dead center and a piston groove is thereby brought into communication with an air port; (II) illustrates a state in which the piston further move up toward the top dead center and the piston groove that is in communication with the air port is thereby brought into communication with a gas venting port; and (III) illustrates a state in which the piston further move up and the piston groove is thereby brought into communication with a scavenging port.
(2) FIG. 2 is a diagram illustrating an example piston groove included in the present invention in order to describe setting of a height dimension of a piston groove.
(3) FIG. 3 is a diagram illustrating another example piston groove included in the present invention in order to describe setting of a height dimension of a piston groove.
(4) FIG. 4 is a diagram for describing another configuration and operation included in 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 immediately before a piston groove comes into communication with an air port; (III) illustrates a state in which the piston further moves up toward the top dead center and the piston groove that is in communication with the air port is thereby brought into communication with a gas venting port; and (IV) illustrates a state in which the piston further moves up and the piston groove is thereby brought into communication with a scavenging port.
(5) FIG. 5 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.
(6) FIG. 6 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.
(7) FIG. 7 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.
(8) FIG. 8 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 an alteration of the embodiment of the present invention.
(9) FIG. 9 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 of the present invention 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; (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 and the piston grooves are thereby brought into communication with a gas venting port; and (V) illustrates a state in which the piston is positioned at the top dead center.
(10) FIG. 10 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 of the present invention including a piston with a piston groove having a relatively-small vertical width: (I) illustrates a state when a piston is positioned at a 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 and the piston groove comes into communication with a gas venting port; and (V) illustrates a state in which the piston is positioned at the top dead center.
(11) FIG. 11 is a perspective view of a piston included in an air leading-type stratified scavenging two-stroke internal-combustion engine according to an alteration of the embodiment.
(12) FIG. 12 is a front view of a piston groove in the piston illustrated in FIG. 11.
(13) FIG. 13 is a horizontal cross-sectional view of the engine including the piston illustrated in FIG. 11 cut along a level of a height of an exhaust channel thereof.
(14) FIG. 14 is a diagram for describing states in the course of piston upward movement toward the top dead center in a conventional 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 toward the top dead center 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 toward the top dead 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
(15) A preferable embodiment of the present invention will be described below with reference to the attached drawings.
(16) FIG. 5 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. 5, 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).
(17) The piston 20 is fitted in a cylinder 26, which is illustrated in FIG. 6, 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.
(18) In the figure, reference numeral 36 denotes an exhaust channel. Also, reference numeral 38 denotes an air channel, and reference numeral 38a denotes an air port. 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, and the air-fuel mixture is supplied to the crankcase 34. Reference numeral 42 denotes a spark plug.
(19) Also referring to FIG. 6, in the cylinder wall 28, gas venting ports 46 are formed as additional ports. The gas venting ports 46 communicate with the crankcase 34 via the respective first scavenging channels 30.
(20) FIG. 7 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. 7, the first scavenging ports 30a and the second scavenging ports 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 engine 50 according to the embodiment is a loop scavenging engine. Here, FIG. 7 illustrates a state in which the piston grooves 22 are in communication with the respective first and second scavenging ports 30a and 32a. In this state, air is supplied to the first and second scavenging channels 30 and 32 through the piston grooves 22.
(21) FIG. 8 illustrates a cylinder 52, which is an alteration of the cylinder 26 illustrated in FIG. 6. The cylinder 52 also includes first and second scavenging channels 30 and 32, and first and second scavenging ports 30a and 32a open in a cylinder wall 54. Also, in the cylinder wall 54, gas venting ports 46 open. The gas venting ports 46 communicate with a crankcase 34 through respective gas venting channels 56 that are independent from the first and second scavenging channels 30 and 32.
(22) Piston grooves 22 extend in a circumferential direction of the piston 20. The gas venting ports 46 are disposed at respective positions adjacent to the respective first scavenging ports 30a positioned on the exhaust port side.
(23) FIGS. 9 and 10 each indicate a specific example in which in the course of the piston moving up, air is supplied to the first and second scavenging channels 30 and 32 through the piston grooves 22 (In FIGS. 9 and 10, only the first and second scavenging ports 30a and 32a are illustrated). An engine 50A, which is illustrated in FIG. 9, 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. 10, positions where the piston grooves 22 are formed are arranged below the piston pin hole 24 (FIG. 5). A vertical width of the piston grooves 22 is smaller than that of the piston grooves 22 illustrated in FIG. 9.
(24) The engine 50A in FIG. 9, which includes piston grooves 22 each having a relatively-large vertical width, will be described. (I) of FIG. 9 illustrates the piston 20 positioned at the bottom dead center. Upon the piston 20 moving up toward the top dead center from the bottom dead center ((II) of FIG. 9), a pressure in the crankcase 34 becomes negative. Even if the piston 20 further moves up and the piston grooves 22 are thereby brought into communication with the air port 38a, gas inside the piston grooves 22 does not flow until the piston grooves 22 come into communication with the gas venting ports 46 ((III) of FIG. 9).
(25) Upon the piston 20 further moving up and the piston grooves 22 that are in communication with the air port 38a being thereby brought into communication with the gas venting ports 46, the gas in the piston grooves 22 is drawn into the crankcase 34 via the gas venting ports 46, and following this, air is drawn from the air port 38a to the piston grooves 22 ((IV) of FIG. 9). In other words, a gas flow is generated inside each of the piston grooves 22.
(26) Then, upon the piston 20 further moving up and reaching the top dead center, the first and second scavenging ports 30a and 32a come into communication with the piston grooves 22 while the gas venting ports 46 are closed by the piston 20 ((V) of FIG. 9). As an alteration, when the piston 20 is positioned at the top dead center, the gas venting ports 46 may open to the crankcase 34.
(27) In the state in (IV) of FIG. 9, upon a gas flow being generated inside each of the piston grooves 22, a state in which the first and second scavenging ports 30a and 32a communicate with the piston grooves 22 and air enters the first and second scavenging ports 30a and 32a is created immediately after the generation of the flow until the state in (V) of FIG. 9 (top dead center). Therefore, the certainty of drawing air from the air channel 38 into the piston grooves 22 through the air port 38a and charging the air into the first and second scavenging channels 30 and 32 from the first and second scavenging ports 30a and 32a can be enhanced.
(28) The engine 50B in FIG. 10, which includes piston grooves 22 each having a relatively-small vertical width, will be described. (I) of FIG. 10 illustrates the piston 20 positioned at the bottom dead center. Upon the piston 20 moving up toward the top dead center from the bottom dead center, a pressure in the crankcase 34 become negative, but gas inside the piston grooves 22 does not flow until the piston 20 further moves up and the piston grooves 22 are thereby brought into communication with the gas venting ports 46 ((II) and (III) of FIG. 10).
(29) Upon the piston 20 further moving up toward the top dead center and the piston grooves 22 being thereby brought into communication with the gas venting ports 46, the negative pressure in the crankcase 34 affects the piston grooves 22, whereby the gas in the piston grooves 22 are sucked into the first scavenging channels 30 through the gas venting ports 46. Also, air in the air channel 38 is drawn into the piston grooves 22 through the air port 38a. In other words, simultaneously with the piston grooves 22 coming into communication with the gas venting ports 46, a gas flow is generated in each of the piston grooves 22.
(30) Upon the piston 20 further moving up and reaching the top dead center, the first and second scavenging ports 30a and 32a come into communication with the piston grooves 22 while the gas venting ports 46 are closed by the piston 20 ((V) of FIG. 10). In the state in (V) of FIG. 10, upon a gas flow being generated in each of the piston grooves 22, a state in which the first and second scavenging ports 30a and 32a communicate with the piston grooves 22 and air enters the first and second scavenging ports 30a and 32a is created immediately after the generation of the air flow until the state in (V) of FIG. 10. Therefore, the certainty of drawing air into the piston grooves 22 from the air channel 38 through the air port 38a and charging the air into the first and second scavenging channels 30 and 32 from the first and second scavenging ports 30a and 32a can be enhanced.
(31) FIGS. 11 to 13 are diagrams relating to an alteration of the engine described above. The alteration illustrated in FIGS. 11 to 13 is related to FIG. 4 described above. In a piston 20 included in the engine illustrated in FIGS. 11 to 13, a pressure transmission through hole 60 is formed in each of piston grooves 22, and the pressure transmission through holes 60 consistently communicate with a crankcase 34. The pressure transmission through holes 60 illustrated in FIGS. 11 to 13 correspond to the pressure transmission through holes 12 described with reference to FIG. 4.
(32) Each pressure transmission through hole 60 may be arranged at an arbitrary position in the relevant piston groove 22. A test shows that it is effective to arrange the pressure transmission through holes 60 on the downstream side of the piston grooves 22. With reference to FIG. 12, the alternate long and short dash line is a vertical line VL running across a piston pin hole 24. Arrangement of the pressure transmission through holes 60 on the downstream side relative to the vertical line VL running across the piston pin hole 24 (the left side in FIG. 12) is effective for generating a preferable gas flow inside the piston grooves 22. In other words, it is preferable that the pressure transmission through holes 60 be disposed at respective positions adjacent to the respective first scavenging ports 30a (FIG. 6) positioned on the exhaust port side.
(33) The pressure transmission through holes 60 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 60 are arranged in respective downstream ends in a gas flow direction of the respective piston grooves 22, that is, left ends (ends on the exhaust port side) in FIG. 12, and positioned on the lower side (crankcase side) of the respective piston grooves 22 in front view of the piston grooves 22.
(34) An engine according to the embodiment enables enhancement of the certainty of charging air to the scavenging channels. 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.
(35) 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:
(36) (1) Engine including one scavenging port on each side;
(37) (2) Engine with one or more scavenging ports on the respective sides arranged asymmetrically; and
(38) (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.
(39) 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 46 gas venting port 12, 60 pressure transmission through hole
