2-stroke engine

Abstract

To provide a two-cycle engine which enables reduction of unburnt gas contained in exhaust gas and enables improvement of scavenging efficiency and combustion efficiency.SOLUTION: An engine 1 has a cylinder block 60 formed with a first communication passage 30A formed from a first scavenging port 20A in a radial direction of a cylinder 61a, and a first scavenging passage 10A which leads to a crank chamber 62a and in which an opening 11 is formed on a bottom surface 31 of the first communication passage 30A. A ceiling surface 34 of the first communication passage 30A inclines to the cylinder head 63 side in a direction from the first scavenging passage 10A side to the first scavenging port 20A side. The bottom surface 31 of the first communication passage 30A inclines to the crank chamber 62a side in a direction from the first scavenging passage 10A side to the first scavenging port 20A side.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a two-stroke engine for use in a small work machine. [Background technology]

[0002] The cylinder block of a two-stroke engine used in small work machines such as chainsaws, brush cutters, and blowers is formed with an intake passage leading to the crank chamber, an exhaust passage leading to the combustion chamber above the cylinder, and a scavenging passage connecting the crank chamber and the combustion chamber. In a two-stroke engine, the mixed gas flows from the intake passage into the crank chamber, then flows through the scavenging passage into the combustion chamber, and the piston reciprocates within the cylinder due to the expansion force generated when the mixed gas is burned in the combustion chamber (see, for example, Patent Document 1).

[0003] In the above-mentioned two-stroke engine, when the piston descends after the mixed gas is burned, the exhaust port of the exhaust passage opens to the top of the cylinder, and the burnt gas in the combustion chamber is exhausted to the exhaust passage (exhaust stroke). When the piston descends further, the scavenging port of the scavenging passage opens to the top of the cylinder, and the mixed gas in the crank chamber flows into the combustion chamber through the scavenging passage (scavenging stroke). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-002311 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the scavenging stroke of the two-stroke engine described above, since both the exhaust port and the scavenging port are open to the cylinder, the unburned gas that has flowed into the combustion chamber from the scavenging port is exhausted to the exhaust port together with the burned gas in the combustion chamber. When the amount of unburned gas contained in the exhaust gas increases, the amount of hydrocarbons (HC) contained in the exhaust gas increases.

[0006] An object of the present invention is to solve the above-mentioned problems and to provide a two-stroke engine capable of reducing the amount of unburned gas contained in the exhaust gas and improving the scavenging efficiency and combustion efficiency. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention is applied to a two-stroke engine including a cylinder block in which a cylinder and a crank chamber are formed, and a piston slidably mounted in the cylinder. The cylinder block is formed with an exhaust passage communicating with a combustion chamber in the cylinder through an exhaust port opening on an inner peripheral surface of the cylinder, and a scavenging port opening on the inner peripheral surface of the cylinder. The cylinder block is also formed with a communication passage formed from the scavenging port in the radial direction of the cylinder, and a scavenging passage formed in the axial direction of the cylinder, communicating with the crank chamber, and having an opening formed on the bottom surface of the communication passage. The ceiling surface of the communication passage is inclined toward the cylinder head as it moves from the scavenging passage side to the scavenging port side, and the bottom surface of the communication passage is inclined toward the crank chamber as it moves from the scavenging passage side to the scavenging port side. In a first aspect of the present invention, a protrusion is formed on the inner surface of the scavenging passage on the cylinder side at a portion on the communication passage side, the protrusion protruding radially outwardly of the cylinder further than the inner surface of the cylinder side at a portion on the crank chamber side, and the cross-sectional area of ​​the scavenging passage in the radial direction of the cylinder at the portion on the communication passage side is smaller than the cross-sectional area of ​​the scavenging passage in the radial direction of the cylinder at the portion on the crank chamber side. In a second configuration of the present invention, a plurality of the scavenging ports are formed in the cylinder block, and at least one of the communication passages is formed, and the communication passage is formed from the scavenging port arranged on the exhaust port side among the scavenging ports. Effect of the Invention

[0008] In the two-stroke engine of the present invention, the communication passage between the scavenging passage and the scavenging port expands in the axial direction of the cylinder as it moves from the scavenging passage side to the scavenging port side. In this configuration, the mixed gas compressed in the scavenging passage expands greatly in the communication passage and is ejected from the scavenging port into the combustion chamber, and the mixed gas is widely diffused in the combustion chamber, so that the scavenging efficiency and the combustion efficiency can be improved. In addition, the expansion of the scavenging flow (mixed gas) in the communication passage promotes atomization of the mixed gas, and the mixed gas is introduced into the combustion chamber while spreading in the axial direction of the cylinder. Then, the scavenging flow (mixed gas) flows evenly in the combustion chamber, so that the mixed gas is sufficiently replaced with new mixed gas in all areas in the cylinder. As a result, in the two-stroke engine of the present invention, the output and response are improved, and the amount of hydrocarbons (HC) contained in the exhaust gas can be significantly reduced. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing the intake / compression stroke of an engine according to an embodiment of the present invention, as viewed from the intake passage side. FIG. [Diagram 2] FIG. 1 is a side cross-sectional view showing the intake and compression strokes of an engine according to an embodiment of the present invention. [Diagram 3] 4 is a cross-sectional view showing a scavenging stroke of the engine according to the embodiment of the present invention as viewed from the intake passage side. FIG. [Figure 4] FIG. 2 is a side cross-sectional view showing a scavenging stroke of the engine according to the embodiment of the present invention. [Diagram 5] FIG. 5 is a cross-sectional view taken along line V-V of FIG. 4, showing a scavenging stroke of the engine according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the accompanying drawings. As shown in FIG. 1, the engine 1 of this embodiment is a two-stroke engine used in small working machines such as chainsaws, brush cutters, and blowers. Since the various power mechanisms in the engine 1 of this embodiment have the same configuration as known two-stroke engines, detailed explanations will be omitted except for the characteristic configurations constituting the present invention.

[0011] As shown in FIG. 2, the engine 1 includes a cylinder block 60 in which a cylinder 61a and a crank chamber 62a are formed, a piston 50 slidably mounted in the cylinder 61a, and a crankshaft 90 housed in the crank chamber 62a. The engine 1 also includes an intake passage 70 communicating with the crank chamber 62a, an exhaust passage 80 communicating with the combustion chamber 40, and a first scavenging passage 10A and a second scavenging passage 10B (see FIG. 5) that connect the crank chamber 62a and the combustion chamber 40.

[0012] In the engine 1 described above, when the piston 50 rises in the cylinder 61a, negative pressure is created in the crank chamber 62a, and a mixture of fuel and air produced in a carburetor (not shown) is filled into the crank chamber 62a through the intake passage 70. When the piston 50 reaches the top dead center, the mixed gas that has flowed into the cylinder 61a during the previous scavenging stroke is compressed in the combustion chamber 40. Then, when the mixed gas is ignited by the spark plug 41, the piston 50 is pushed down by the force of its expansion.

[0013] When the piston 50 descends, as shown in Fig. 4, the exhaust passage 80 is connected to the combustion chamber 40, and the burnt gas is exhausted to the exhaust passage 80. In addition, as shown in Fig. 3, the piston 50 descends, compressing the mixed gas filled in the crank chamber 62a. When the piston 50 reaches the bottom dead center, as shown in FIG. 5, the first scavenging passage 10A and the second scavenging passage 10B are connected to the combustion chamber 40, and the mixed gas flows into the combustion chamber 40 through the first scavenging passage 10A and the second scavenging passage 10B. As shown in FIG. 3, when piston 50 reaches bottom dead center, it is caused to rise again by the rotational force of crankshaft 90, and the intake and compression strokes are repeated.

[0014] 1, the cylinder block 60 is divided into an upper block 61 in which a cylinder head 63, a cylinder 61a, and an upper part of a crank chamber 62a are formed, and a lower case 62 in which a lower part of the crank chamber 62a is formed. The upper block 61 and the lower case 62 are assembled vertically.

[0015] The crankshaft 90 is formed with a crank journal 91 that is rotatably supported by the lower case 62, and a crank web 92 that is formed on the crank journal 91. The side wall portion 62b of the lower case 62 has an insertion hole 62c formed therein, and a bearing 62d is fitted into the inner circumferential surface of the insertion hole 62c. The crank journal 91 is inserted through the bearing 62 d , and its tip portion protrudes to the outside of the lower case 62 . The crank web 92 is connected to the piston 50 via the connecting rod 51 and configured to rotate around the axis of the crank journal 91 in conjunction with the reciprocating motion of the piston 50.

[0016] As shown in FIG. 2, the suction passage 70 is formed on the side of the upper block 61 (the right side in FIG. 2), with one end opening to the lower part of the cylinder 61a and the other end connected to a fuel supply passage (not shown). An opening 71 on the cylinder 61a side of the suction passage 70 is blocked by the side surface of the piston 50 when the piston 50 is at bottom dead center, as shown in FIG. 4, and opens to the lower part of the cylinder 61a and communicates with the crank chamber 62a when the piston 50 is at top dead center, as shown in FIG. 2.

[0017] The exhaust passage 80 is formed in a side portion (the left side portion in FIG. 2) of the upper block 61, at a position opposite to the suction passage 70. One end of the exhaust passage 80 is formed with an exhaust port 81 that opens to the inner circumferential surface of the cylinder 61a, and the other end is connected to a muffler (silencer) not shown. As shown in FIG. 4, exhaust port 81 is in communication with combustion chamber 40 when piston 50 is at bottom dead center, and as shown in FIG. 2, exhaust port 81 is blocked by the side surface of piston 50 when piston 50 is at top dead center.

[0018] As shown in FIG. 5, the first scavenging passage 10A and the second scavenging passage 10B are formed in the upper block 61 at positions on the sides of the cylinder 61a (top and bottom sides in FIG. 5) and along the axial direction of the cylinder 61a (see FIG. 1).

[0019] A pair of a first scavenging passage 10A and a second scavenging passage 10B are formed on the upper and lower sides of the cylinder 61a on the exhaust port 81 side of the center position P1 of the cylinder 61a in FIG. In this embodiment, a first scavenging passage 10A is formed on the upper side in FIG. 5, and a second scavenging passage 10B is formed on the lower side. Further, on the suction passage 70 side of the center position P1 of the cylinder 61a, a pair of second scavenging passages 10B, 10B are formed above and below the cylinder 61a in FIG.

[0020] 1, the lower end of the first scavenging passage 10A is connected to the crank chamber 62a. Also, an opening 11 that opens to a bottom surface 31 of a first communication passage 30A (described later) is formed at the upper end of the first scavenging passage 10A. In Fig. 1 and Fig. 3, in order to easily explain the configurations of the first scavenging passage 10A, the first communication passage 30A and the first scavenging port 20A, the first scavenging passage 10A, the first communication passage 30A and the first scavenging port 20A, are illustrated in a cross section taken at the center position of the cylinder block 60.

[0021] As shown in FIG. 1, similar to the first scavenging passage 10A, the second scavenging passage 10B has a lower end communicating with the crank chamber 62a (see FIG. 1) and an upper end formed with an opening 11 that opens into a bottom surface 31 of a second communication passage 30B described later. In Fig. 1 and Fig. 3, in order to easily explain the configurations of the second scavenging passage 10B, the second communication passage 30B and the second scavenging port 20B, the second scavenging passage 10B, the second communication passage 30B and the second scavenging port 20B, are illustrated in a cross section taken at the center position of the cylinder block 60.

[0022] 1, in the first scavenging passage 10A, the inner surface on the radially outer side of the cylinder 61a is formed linearly along the axial direction of the cylinder 61a. In addition, in the first scavenging passage 10A, the inner surface on the cylinder 61a side in the portion 12 on the first communication passage 30A side (the opening 11 side) is disposed radially outward of the cylinder 61a than the inner surface on the cylinder 61a side in the portion 13 on the crank chamber 62a side. That is, in the first scavenging passage 10A, the inner surface on the cylinder 61a side in the portion 12 on the first communication passage 30A side has a protruding portion that protrudes radially outward of the cylinder 61a than the inner surface on the cylinder 61a side in the portion 13 on the crank chamber 62a side. As a result, in the first scavenging passage 10A, the radial cross-sectional area of ​​the cylinder 61a at a portion 12 on the first communication passage 30A side (the opening 11 side) is smaller than the radial cross-sectional area of ​​the cylinder 61a at a portion 13 on the crank chamber 62a side.

[0023] The first scavenging port 20A and the second scavenging port 20B are openings with a rectangular cross section that open to the inner circumferential surface of the cylinder 61a (see FIG. 4). A first scavenging port 20A and a second scavenging port 20B are formed on both sides of the exhaust port 81 (both upper and lower sides in FIG. 5) of the exhaust port 81 closer to the exhaust port 81 than the center position P1 of the cylinder 61a, facing each other with the cylinder 61a in between. In this embodiment, a first scavenging port 20A is formed on the upper side in FIG. 5, and a second scavenging port 20B is formed on the lower side. Further, two second scavenging ports 20B, 20B are formed on both sides of the exhaust port 81 closer to the suction passage 70 than the center position P1 of the cylinder 61a, facing each other with the cylinder 61a therebetween.

[0024] As shown in FIG. 4, the first scavenging port 20A and the second scavenging port 20B open to the inner circumferential surface of the cylinder 61a at substantially the same height as the exhaust port 81. Therefore, when the piston 50 is located at the bottom dead center, the first scavenging port 20A and the second scavenging port 20B open to the upper part of the cylinder 61a and communicate with the combustion chamber 40. As shown in FIG. 2, when the piston 50 is located at the top dead center, the first scavenging port 20A and the second scavenging port 20B are blocked by the side surface of the piston 50.

[0025] As shown in FIG. 5, the first communication passage 30A and the second communication passage 30B are passages formed in the radial direction of the cylinder 61a. A first communication passage 30A and a second communication passage 30B are formed on the exhaust port 81 side of the center position P1 of the cylinder 61a at positions that are vertically symmetrical with respect to the cylinder 61a in Fig. 5. In this embodiment, the first communication passage 30A is formed on the upper side in Fig. 5, and the second communication passage 30B is formed on the lower side. Further, on the suction passage 70 side of the center position P1 of the cylinder 61a, two second communication passages 30B, 30B are formed as a pair, one above and one below, with the cylinder 61a in between in FIG.

[0026] The opening 11 of the first scavenging passage 10A opens in a bottom surface 31 of the first communication passage 30A. The first communication passage 30A is a passage that communicates between the opening 11 and the first scavenging port 20A. Between the opening 11 and the first scavenging port 20A, a shelf-shaped portion is formed by the bottom surface 31 of the first communication passage 30A, and functions as a guide surface for the lower part of the mixed gas (see FIG. 1).

[0027] The opening 11 of the second scavenging passage 10B opens in a bottom surface 31 of the second communication passage 30B. The second communication passage 30B is a passage that communicates between the opening 11 and the second scavenging port 20B. Between the opening 11 and the second scavenging port 20B, a shelf-shaped portion is formed by the bottom surface 31 of the second communication passage 30B, and functions as a guide surface for the lower part of the mixed gas (see FIG. 1).

[0028] The first communication passage 30A and the second communication passage 30B are formed from an opening 11 formed in the bottom surface 31 toward the anti-exhaust port side, which is the opposite side of the exhaust port 81 (the intake passage 70 side) within the combustion chamber 40 (cylinder 61a). The mixed gas that flows into the first communication passage 30A from the opening 11 of the first scavenging passage 10A is guided by the first communication passage 30A toward the side opposite the exhaust port, and is ejected from the first scavenging port 20A toward the side opposite the exhaust port in the combustion chamber 40. The mixed gas that flows into the second communication passage 30B from the opening 11 of the second scavenging passage 10B is guided by the second communication passage 30B toward the side opposite the exhaust port, and is ejected from the second scavenging port 20B toward the side opposite the exhaust port in the combustion chamber 40.

[0029] As shown in FIG. 4, the first communication passage 30A has a rectangular cross section formed with a bottom surface 31, both side surfaces 32 and 33, and a ceiling surface . 5, of both side surfaces 32, 33 forming the first communication passage 30A, the side surface 33 on the opposite exhaust port side is inclined away from the side surface 32 on the exhaust port 81 side from the radial outside of the cylinder 61a toward the first scavenging port 20A in the upper block 61. In other words, the side surface 33 on the opposite exhaust port side of the first communication passage 30A is formed to face the opposite exhaust port side in the combustion chamber 40 (cylinder 61a). In the first communication passage 30A, the opening width in the circumferential direction of the cylinder 61a increases from the opening 11 toward the first scavenging port 20A.

[0030] As shown in FIG. 1, a ceiling surface 34 of the first communication passage 30A is inclined toward the cylinder head 63 (upward in FIG. 1) from the opening 11 toward the first scavenging port 20A. A bottom surface 31 of the first communication passage 30A is inclined toward the crank chamber 62a (the lower side in FIG. 1) from the opening 11 toward the first scavenging port 20A. In this way, the height of the first communication passage 30A (the width in the axial direction of the cylinder 61a) increases from the radial outer side of the cylinder 61a toward the first scavenging port 20A. The inclination angle of the bottom surface 31 of the first communication passage 30A toward the crank chamber 62a is preferably set in the range of 70 to 100% of the inclination angle of the ceiling surface 34 of the first communication passage 30A toward the cylinder head 63.

[0031] Moreover, the maximum height (maximum width) of the first scavenging port 20A in the axial direction of the cylinder 61a is preferably at least twice the minimum height (minimum width) of the first communication passage 30A in the axial direction of the cylinder 61a. Furthermore, it is more preferable that the ratio of the minimum height of the first communication passage 30A in the axial direction of the cylinder 61a to the maximum height of the first scavenging port 20A in the axial direction of the cylinder 61a be set in the range of 1:2 to 1:4.

[0032] Moreover, the opening area of ​​the first scavenging port 20A is preferably four or more times the minimum cross-sectional area of ​​the first communication passage 30A in the axial direction of the cylinder 61a. Furthermore, it is more preferable that the ratio of the minimum cross-sectional area of ​​the first communication passage 30A in the axial direction of the cylinder 61a to the opening area of ​​the first scavenging port 20A is in the range of 1:4 to 1:8.

[0033] The bottom surface 31 of the first communication passage 30A and the inner wall surface of the first scavenging passage 10A in the radial direction of the cylinder 61a (the wall surface of the portion 12 of the first scavenging passage 10A on the first communication passage 30A side) are continuous with each other via a circular arc-shaped curved surface 35. Moreover, the ceiling surface 34 of the first communication passage 30A and the inner surface of the first scavenging passage 10A are continuous with each other via a circular arc-shaped curved surface 36.

[0034] The first communication passage 30A in this embodiment is formed in a divergent shape in which the cross-sectional area increases from the opening 11 toward the first scavenging port 20A. The axial cross-sectional area of ​​the cylinder 61a in the first communication passage 30A is larger than the radial cross-sectional area of ​​the cylinder 61a in a portion 12 on the first communication passage 30A side (opening 11 side) of the first scavenging passage 10A.

[0035] As shown in FIG. 4, the second communication passage 30B has a rectangular cross section with a bottom surface 31, both side surfaces 32, 33, and a ceiling surface 34, similar to the first communication passage 30A. As shown in FIG. 5, a side surface 33 of the second communication passage 30B on the side opposite the exhaust port is also formed so as to face the inside of the combustion chamber 40 on the side opposite the exhaust port. As shown in FIG. 1, the ceiling surface 34 of the second communication passage 30B also inclines toward the cylinder head 63 (upward in FIG. 1) from the opening 11 toward the second scavenging port 20B.

[0036] The second communication passage 30B is formed so that its cross-sectional area increases from the opening 11 toward the second scavenging port 20B, and the cross-sectional area in the axial direction of the cylinder 61a is formed larger than the cross-sectional area in the radial direction of the cylinder 61a at the opening 11 of the second scavenging passage 10B.

[0037] In the engine 1 of this embodiment, as shown in FIG. 3, when the piston 50 reaches the bottom dead center, the first scavenging port 20A and the second scavenging port 20B are in communication with the combustion chamber 40. As a result, the mixed gas that has filled the crank chamber 62a flows into the combustion chamber 40 through the first scavenging passage 10A, the first communication passage 30A, and the first scavenging port 20A. Furthermore, the mixed gas that has filled the crank chamber 62a flows into the combustion chamber 40 through the second scavenging passage 10B, the second communication passage 30B, and the second scavenging port 20B.

[0038] In the engine 1 of this embodiment, the ceiling surface 34 of the first communication passage 30A is inclined toward the cylinder head 63 from the first scavenging passage 10A toward the first scavenging port 20A. In addition, the bottom surface 31 of the first communication passage 30A is inclined toward the crank chamber 62a from the first scavenging passage 10A toward the first scavenging port 20A.

[0039] In this configuration, the mixed gas compressed in the first scavenging passage 10A expands significantly in the first communication passage 30A and is ejected from the first scavenging port 20A into the combustion chamber 40, and the mixed gas diffuses in the axial direction of the cylinder 61a in the combustion chamber 40. Also, compared to a configuration in which the width of the first communication passage 30A in the axial direction of the cylinder 61a is formed to be constant, atomization of the mixed gas is promoted when the mixed gas expands, and the homogeneity of the components of the mixed gas in the combustion chamber 40 is improved, so that the combustion of the mixed gas is stabilized.

[0040] By setting the inclination angle of the bottom surface 31 of the first communication passage 30A toward the crank chamber 62a side in the range of 70 to 100% of the inclination angle of the ceiling surface 34 of the first communication passage 30A toward the cylinder head 63 side and slightly extending the first communication passage 30A toward the combustion chamber 40, it is possible to effectively flow the mixed gas into the combustion chamber 40. Note that it is particularly preferable that the inclination angle of the bottom surface 31 of the first communication passage 30A toward the crank chamber 62a side be 90% of the inclination angle of the ceiling surface 34 of the first communication passage 30A toward the cylinder head 63 side.

[0041] As shown in FIG. 5, the opening width of the first communication passage 30A in the circumferential direction of the cylinder 61a increases from the opening 11 of the first scavenging passage 10A toward the first scavenging port 20A.

[0042] In the engine 1 of this embodiment, as shown in Fig. 3, the first communication passage 30A expands in the axial direction and circumferential direction of the cylinder 61a from the first scavenging passage 10A side toward the first scavenging port 20A side. In other words, the first communication passage 30A is formed in a divergent shape in which the cross-sectional area increases from the opening 11 toward the first scavenging port 20A. In this configuration, the cross-sectional area of ​​the first communication passage 30A expands not only in the axial direction of the cylinder 61a but also in the circumferential direction of the cylinder 61a. Therefore, the mixed gas compressed in the first scavenging passage 10A expands significantly in the first communication passage 30A and is ejected from the first scavenging port 20A into the combustion chamber 40. The mixed gas is diffused widely in the combustion chamber 40, thereby improving the scavenging efficiency and the combustion efficiency.

[0043] As shown in FIG. 1, the maximum height (maximum width) of the first scavenging port 20A in the axial direction of the cylinder 61a is preferably at least twice the minimum height (minimum width) of the first communication passage 30A in the axial direction of the cylinder 61a. Furthermore, it is more preferable that the ratio of the minimum height of the first communication passage 30A in the axial direction of the cylinder 61a to the maximum height of the first scavenging port 20A in the axial direction of the cylinder 61a be set in the range of 1:2 to 1:4. In this manner, by setting the maximum height of the first scavenging port 20A and the minimum height of the first communication passage 30A, it is possible to effectively improve the scavenging efficiency and the combustion efficiency.

[0044] Moreover, the opening area of ​​the first scavenging port 20A is preferably four or more times the minimum cross-sectional area of ​​the first communication passage 30A in the axial direction of the cylinder 61a. Furthermore, it is more preferable that the ratio of the minimum cross-sectional area of ​​the first communication passage 30A in the axial direction of the cylinder 61a to the opening area of ​​the first scavenging port 20A is in the range of 1:4 to 1:8. In this manner, by setting the minimum cross-sectional area of ​​the first communication passage 30A and the opening area of ​​the first scavenging port 20A, it is possible to effectively improve the scavenging efficiency and the combustion efficiency.

[0045] In the engine 1 of this embodiment, the inner surface of the cylinder 61a at the portion 12 of the first scavenging passage 10A on the first communication passage 30A side is disposed radially outward of the cylinder 61a than the inner surface of the cylinder 61a at the portion of the first scavenging passage 10A on the crank chamber 62a side. With this configuration, the lengths of the bottom surface 31 and the ceiling surface 34 of the first communication passage 30A, which are guide surfaces for the mixed gas, can be set sufficiently long, and the directivity of the mixed gas and the atomization promotion effect are improved. The radial cross-sectional area of ​​the cylinder 61a at the portion 12 of the first scavenging passage 10A on the first communication passage 30A side is formed smaller than the radial cross-sectional area of ​​the cylinder 61a at the portion 13 of the first scavenging passage 10A on the crank chamber 62a side.

[0046] As a result, the mixed gas flowing from the crank chamber 62a into the first scavenging passage 10A is compressed in the first scavenging passage 10A, and then flows into the cylinder 61a while expanding in the first communication passage 30A. In this way, the expansion of the mixed gas once compressed promotes atomization of the mixed gas, and since the mixed gas has directivity in the axial direction of the cylinder 61a, the inside of the cylinder 61a can be scavenged evenly. As a result, the mixed gas is introduced evenly into the entire area of ​​the cylinder 61a, and the burned gas from the previous combustion cycle is swept out and discharged, and is replaced with the mixed gas required for the current combustion cycle without waste. Therefore, the output and response of the engine 1 can be significantly improved, and the discharge of unburned gas can be reduced.

[0047] Further, the radial cross-sectional area of ​​the cylinder 61a at the portion 12 of the first scavenging passage 10A on the first communication passage 30A side is smaller than the axial cross-sectional area of ​​the cylinder 61a at the first communication passage 30A. As a result, the mixed gas that flows from the first scavenging passage 10A through the opening 11 into the first communication passage 30A is compressed once in the first scavenging passage 10A and then expands in the first communication passage 30A.

[0048] In the engine 1 of this embodiment, the inner surface of the first scavenging passage 10A and the bottom surface 31 of the first communication passage 30A are continuous with each other via a circular arc-shaped curved surface 35. In addition, the ceiling surface 34 of the first communication passage 30A and the inner surface of the first scavenging passage 10A are continuous with each other via a circular arc-shaped curved surface 36. This allows the mixed gas to flow smoothly along the curved surfaces 35, 36 when flowing from the first scavenging passage 10A into the first communication passage 30A.

[0049] 5, in the engine 1 of this embodiment, the side surface 33 of the first communication passage 30A and the second communication passage 30B on the side opposite to the exhaust port is formed so as to face the side opposite to the exhaust port in the combustion chamber 40. In addition, a plurality of scavenging ports 20A, 20B are formed in the cylinder block 60 of the engine 1 of this embodiment, and the first communication passage 30A is formed from the first scavenging port 20A arranged on the exhaust port 81 side among the scavenging ports 20A, 20B. As a result, the mixed gas flowing into the combustion chamber 40 from the first scavenging port 20A and the second scavenging port 20B is directed toward the side opposite the exhaust port, thereby significantly reducing the amount of unburned mixed gas exhausted to the exhaust port 81.

[0050] As described above, in the engine 1 of this embodiment, the amount of hydrocarbons (HC) contained in the exhaust gas can be significantly reduced. It has been confirmed that the engine 1 of this embodiment reduces the amount of hydrocarbons contained in the exhaust gas by approximately 30%, compared to a conventional engine in which the first communication passage 30A is not formed.

[0051] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit of the present invention. In the engine 1 of this embodiment, as shown in Fig. 5, one of the four communication passages is formed in the shape of the first communication passage 30A, but the number is not limited to this. For example, all of the four communication passages may be formed in the shape of the first communication passage 30A. It is preferable to apply the configuration of the present invention to one of the adjacent or facing scavenging ports. In this way, the mixed gases from the scavenging ports arranged in close positions flow into the cylinder 61a with different directivities and different speeds, so that the collision of the mixed gases can be avoided and the directivity of each mixed gas can be maintained. This makes it possible to effectively improve the scavenging efficiency and combustion efficiency of the engine 1.

[0052] In the engine 1 of this embodiment, four scavenging ports are formed, but the number is not limited to four. For example, two scavenging ports may be formed, one on each side of the exhaust port 81. [Explanation of symbols]

[0053] 1 Engine 10A First scavenging passage 10B Second scavenging passage 11 Opening 20A First scavenging port 20B Second scavenging port 30A first aisle 30B Second communication passage 31 Bottom 32 Side 33 Side 34 Ceiling surface 35 Curved Surface 36 Curved Surface 40 Combustion chamber 41 Spark plug 50 Piston 51 Connecting rod 60 Cylinder block 61a Cylinder 62a Crankcase 63 Cylinder head 70 Suction passage 71 Opening 80 Exhaust passage 81 Exhaust port 90 Crankshaft 91 Crank journal 92 Crank Web

Claims

1. a cylinder block in which a cylinder and a crank chamber are formed; a piston slidably mounted within the cylinder; The cylinder block includes: an exhaust passage communicating with a combustion chamber in the cylinder through an exhaust port that opens on an inner peripheral surface of the cylinder; A scavenging port opening to an inner peripheral surface of the cylinder; a communication passage formed in a radial direction of the cylinder from the scavenging port; a scavenging passage formed in an axial direction of the cylinder, communicating with the crank chamber, and having an opening formed in a bottom surface of the communication passage, A ceiling surface of the communication passage is inclined toward the cylinder head from the scavenging passage toward the scavenging port, a bottom surface of the communication passage inclined toward the crank chamber from the scavenging passage toward the scavenging port, a protrusion is formed on an inner surface of the scavenging passage on the cylinder side at a portion on the communication passage side, the protrusion protruding radially outwardly of the cylinder further than an inner surface of the cylinder side at a portion on the crank chamber side, a cross-sectional area of ​​the scavenging passage in a radial direction of the cylinder at a portion of the scavenging passage on the communication passage side is smaller than a cross-sectional area of ​​the scavenging passage in a radial direction of the cylinder at a portion of the scavenging passage on the crank chamber side.

2. 2. A two-stroke engine according to claim 1, The maximum width of the scavenging port in the axial direction of the cylinder is 2. A two-stroke engine comprising: a cylinder passage having a width greater than or equal to two times the minimum width of the communication passage in the axial direction of the cylinder;

3. 2. A two-stroke engine according to claim 1, a ratio of a minimum width of the communication passage in the axial direction of the cylinder to a maximum width of the scavenging port in the axial direction of the cylinder is set in a range of 1:2 to 1:

4.

4. A two-stroke engine according to any one of claims 1 to 3, The opening area of ​​the scavenging port is a minimum cross-sectional area of ​​the communication passage in the axial direction of the cylinder that is four or more times larger than the minimum cross-sectional area of ​​the communication passage.

5. A two-stroke engine according to any one of claims 1 to 4, A two-stroke engine, characterized in that a ratio of a minimum cross-sectional area of ​​the communication passage in an axial direction of the cylinder to an opening area of ​​the scavenging port is in a range of 1:4 to 1:

8.

6. A two-stroke engine according to any one of claims 1 to 5, a bottom surface of the communication passage having a slope angle toward the crank chamber that is set in a range of 70 to 100% of a ceiling surface of the communication passage having a slope angle toward the cylinder head.

7. A two-stroke engine according to any one of claims 1 to 6, a bottom surface of the communication passage and an inner surface of the scavenging passage that are continuous with each other via a curved surface having a circular arc shape.

8. A two-stroke engine according to any one of claims 1 to 7, a side surface of the communication passage on the side opposite the exhaust port, the side surface being formed so as to face the side of the combustion chamber opposite the exhaust port;

9. A two-stroke engine according to any one of claims 1 to 8, a scavenging port formed in the scavenging passage and having a circumferential width of the scavenging passage that is increased from an opening of the scavenging passage to a scavenging port;

10. A cylinder block in which a cylinder and a crank chamber are formed, a piston slidably mounted within the cylinder; The cylinder block includes: an exhaust passage communicating with a combustion chamber in the cylinder through an exhaust port that opens on an inner peripheral surface of the cylinder; A scavenging port opening to an inner peripheral surface of the cylinder; a communication passage formed in a radial direction of the cylinder from the scavenging port; a scavenging passage formed in an axial direction of the cylinder, communicating with the crank chamber, and having an opening formed in a bottom surface of the communication passage, A ceiling surface of the communication passage is inclined toward the cylinder head from the scavenging passage toward the scavenging port, a bottom surface of the communication passage inclined toward the crank chamber from the scavenging passage toward the scavenging port, The cylinder block includes: A plurality of the scavenging ports are formed, At least one of the communication passages is formed, The two-stroke engine, wherein the communication passage is formed from one of the scavenging ports that is disposed on the exhaust port side.

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