JP2014194164A - Engine and portable work machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine which inhibits the deterioration of a function for keeping an unburnt gas in a combustion chamber.SOLUTION: In an engine 12, a combustion chamber 18 is provided in a cylinder 19 and an exhaust port 32 connected with the combustion chamber 18 is opened and closed by a piston 22 which reciprocates in the cylinder 19. The engine 12 includes: a first exhaust passage 31 which is provided at the cylinder 19 and is connected with the exhaust port 32; an opening part 31a which is formed at a downstream end of the first exhaust passage 31 in an exhaust direction of the combustion gas exhausted from the exhaust port 32; and a second exhaust passage 36 which is connected with the opening part 31a through a connection passage 41. The center E of the connection passage 41 when viewed in an operation direction of the piston 22 and the center C of the opening part 31a when viewed in the operation direction of the piston 22 are disposed at different positions in the operation direction of the piston 22.

Description

  The present invention relates to an engine used as a power source in a portable work machine such as a chain saw and a cutter, and a portable work machine including the engine.

  Many portable work machines represented by chain saws, cutters, and the like require the use of a two-cycle engine as a power source because high output, miniaturization, and weight reduction of the engine serving as a power source are required. In this two-cycle engine, unburned gas is discharged from the exhaust port of the combustion chamber during the exhaust / scavenging stroke of the engine, and the exhaust gas characteristics deteriorate. Therefore, in order to suppress the deterioration of exhaust gas characteristics in the two-cycle engine, a catalyst system, an air leading scavenging system, an exhaust pulsation system, and the like are employed.

  The catalyst system purifies exhaust gas by arranging a catalyst in the exhaust gas discharge path. The air leading method is a method in which air in the scavenging passage is led to the combustion chamber before the unburned gas is discharged from the combustion chamber during the exhaust / scavenging stroke of the engine. The exhaust pulsation system is a system in which uncombusted gas remains in the combustion chamber by propagating the pressure wave of the combustion gas discharged from the exhaust port to the exhaust port in the second half of the exhaust process of the engine. Among these methods, Patent Document 1 describes an example of an engine having a structure that suppresses deterioration of exhaust gas characteristics by an exhaust pulsation method, and a portable work machine including the engine.

  The engine described in Patent Document 1 has an exhaust pi provided downstream of the exhaust port and a branch pipe branched from the exhaust pipe. The downstream end of the exhaust pipe is connected to the outside of the muffler via an expansion chamber. In the engine described in Patent Document 1, the exhaust gas is discharged from the combustion chamber to the exhaust pipe, and immediately before the exhaust stroke is completed, the pressure in the expansion chamber is propagated to the vicinity of the exhaust port via the exhaust pipe. The pressure reflected inside is propagated to the vicinity of the exhaust port via the exhaust pipe. For this reason, the pressure near the exhaust port immediately before the end of the exhaust stroke increases, unburned gas is retained in the combustion chamber, and deterioration of exhaust gas characteristics can be suppressed, and engine output can be improved.

JP 2012-67668 A

  However, in order to suppress the outflow of exhaust gas, it is necessary to further enhance the effect of pressure wave propagation.

  An object of the present invention is to provide an engine that can further improve the function of retaining unburned gas in a combustion chamber, and a portable work machine including the engine.

  An engine according to an embodiment is an engine in which a combustion chamber is provided in a cylinder, and an exhaust port connected to the combustion chamber is opened and closed by a piston that reciprocates in the cylinder. The engine is provided in the cylinder. A first exhaust passage connected to the exhaust port, an opening formed at the downstream end of the first exhaust passage in the discharge direction of the combustion gas discharged from the exhaust port, and a connection passage to the opening A center of the connection passage in the direction of movement of the piston and a center of the opening in the direction of movement of the piston are different in the direction of movement of the piston. Placed in position.

  A portable work machine according to another embodiment includes the engine according to one embodiment and an operation member that operates by transmitting power of the engine.

  According to the engine of the present invention, the pressure wave propagated from the second exhaust passage through the connection passage to the exhaust port is easily propagated toward the exhaust port, and the function of retaining unburned gas in the combustion chamber is reduced. Can be suppressed.

It is front sectional drawing which shows the portable working machine which has an engine of this invention. It is an expanded sectional view which shows the structural example of the engine of this invention. It is an external view of the engine shown in FIG. It is an exploded view which shows a part of cylinder and muffler of the engine shown in FIG. It is a schematic diagram which shows operation | movement of the engine of this invention. It is a schematic diagram which shows operation | movement of the engine of this invention. It is a schematic diagram which shows operation | movement of the engine of this invention. It is a schematic diagram which shows operation | movement of the engine of this invention. It is a schematic diagram which shows operation | movement of the engine of this invention. It is an expanded sectional view which shows the other structural example of the engine of this invention. It is an expanded sectional view which shows the other structural example of the engine of this invention. It is an expanded sectional view which shows the other structural example of the engine of this invention. It is an expanded sectional view which shows the other structural example of the engine of this invention.

  An embodiment of an engine of the present invention and an embodiment of a portable work machine including the engine will be described in detail with reference to FIGS. FIG. 1 shows a cutting machine 10 as a portable working machine. The cutting machine 10 includes a main body case 11, an engine 12 provided inside the main body case 11, and a cutting blade provided outside the main body case 11. 13. The cutting blade 13 corresponds to the operating member of the present invention. The cutting blade 13 is rotatably supported, and a cover 14 that covers the cutting blade 13 is provided. A front handle 15 and a rear handle 16 are attached to the outside of the main body case 11, and an operator can lift the cutting machine 10 by grasping the front handle 15 and the rear handle 16. The rear handle 16 is provided with a throttle lever 17. The throttle lever 17 is provided for the operator to adjust the rotational speed of the engine 12.

  The engine 12 is an internal combustion engine that generates power by burning an air-fuel mixture in which fuel and air are mixed in a combustion chamber 18. The engine 12 includes a cylinder 19, a muffler 20, and a fuel supply device 21, and a piston 22 is provided inside the cylinder 19 so as to be capable of reciprocating in a direction along the center line A. The direction along the center line A is the operation direction of the piston in the present invention. 1 and 2, the combustion chamber 18 is formed above the piston 22 inside the cylinder 19. The cylinder 19 is provided with a spark plug 23 exposed to the combustion chamber 18. Further, a scavenging port 24 is formed on the inner surface of the cylinder 19, and the scavenging port 24 is connected to the crank chamber 25 via a scavenging passage.

  On the other hand, a crankcase 26 is provided below the cylinder 19, and a crank chamber 25 is formed in the crankcase 26. A crankshaft 27 is rotatably provided in the crank chamber 25, and a connecting rod 28 is provided from the inside of the cylinder 19 to the crank chamber 25. One end of the connecting rod 28 is connected to the crankshaft 27, and the other end of the connecting rod 28 is connected to the piston 22.

  An intake pipe 29 is attached to the cylinder 19, and an intake passage 30 provided inside the intake pipe 29 is connected to the crank chamber 25. The fuel supply device 21 is provided upstream of the intake passage 30 in the flow direction of the air supplied to the intake passage 30, and a mixture of fuel and air flows into the crank chamber 25 via the intake passage 30. Have been supplied. A first exhaust passage 31 that penetrates the cylinder 19 from the inner surface toward the outer surface is provided, and an exhaust port 32 that connects the first exhaust passage 31 and the inside of the cylinder 19 is provided.

  The exhaust port 32 is opened and closed by the operation of the piston 22. In FIG. 1, when the piston 22 moves in the first movement direction along the center line A, that is, ascends in the cylinder 19, the exhaust port 32 is closed by the piston 22. On the other hand, when the piston 22 moves in the second operation direction along the center line A in FIG.

  The muffler 20 has an exhaust pipe 33, a branch pipe 34, a first expansion chamber 35, and a second expansion chamber 44, and a second exhaust passage 36 is formed inside the exhaust pipe 33. A second exhaust passage 36 is connected to the downstream end of the first exhaust passage 31 in the flow direction of the exhaust gas discharged from the exhaust port 32 to the first exhaust passage 31. The cross-sectional area of the first exhaust passage 31 becomes wider as it approaches the second exhaust passage 36 in the exhaust gas flow direction. When the first exhaust passage 31 is viewed from the side as shown in FIG. 4, the opening shape is a shape that approximates a quadrangle.

  Further, the first exhaust passage 31 is extended so that the vertical center line B of the first exhaust passage 31 intersects the center line A at a non-right angle. As the exhaust gas flows in the first exhaust passage 31 and approaches the second exhaust passage 36, the center line B is inclined in a direction away from the horizontal line. Specifically, the center C of the downstream end of the first exhaust passage 31 is at a position lower than the center D of the exhaust port 32 in a state where the center line A of the piston 22 extends along the vertical line. .

  On the other hand, the second exhaust passage 36 extends substantially horizontally from the uppermost stream end toward the downstream in the flow direction of the exhaust gas, and then extends downward through the curved portion to provide the second exhaust gas. The most downstream end of the passage 36 is connected to the first expansion chamber 35. The cross-sectional area of the second exhaust passage 36 becomes wider as it approaches the first expansion chamber 35 in the exhaust gas flow direction. Further, the first expansion chamber 35 is a space surrounded by the wall member 37 and the partition wall 38. A third exhaust passage 39 is provided in the partition wall 38. The third exhaust passage 39 connects the first expansion chamber 35 and the second expansion chamber 44, and the second expansion chamber 44 is connected to the outside of the muffler 20 via the fourth exhaust passage 45.

  The engine 12 of the present invention is characterized by the structure of the connecting portion between the cylinder 19 and the muffler 20, and hereinafter, the structure of the characteristic part of the engine 12 will be sequentially described.

(Embodiment 1)
A first embodiment of the engine 12 will be described with reference to FIG. First, an opening 31 a is formed at the downstream end of the first exhaust passage 31. A gasket 40 is interposed between the wall member 37 and the cylinder 19. An opening 41 that penetrates the wall member 37 in the thickness direction is provided, and an opening 42 that penetrates the gasket 40 in the thickness direction is provided. The opening 41 corresponds to the connection passage of the present invention, and the first exhaust passage 31 is connected to the second exhaust passage 36 via the two openings 42 and 41. An opening 36 a is formed at the upstream end of the second exhaust passage 36. The cross-sectional area of the opening 41 is wider than the maximum value of the cross-sectional area of the branch passage 34a. In the present specification, upstream and downstream mean upstream and downstream in the discharge direction of the combustion gas discharged from the exhaust port 32.

  Further, a part of the exhaust pipe 33 is disposed in the first expansion chamber 35, and a flange 43 is provided at an end of the outer peripheral surface of the exhaust pipe 33 on the first exhaust passage 31 side. The flange 43 is an annular body projecting outward from the outer peripheral surface of the exhaust pipe 33, and the gasket 40 and the wall member 37 are interposed between the flange 43 and the cylinder 19. A screw member is inserted into a hole formed in the flange 43, and the screw member is tightened to fix the exhaust pipe 33, the wall member 37, and the gasket 40.

  The shape of the opening 31a of the first exhaust passage 31, the shape of the opening 42 of the gasket 40, and the shape of the opening 36a of the second exhaust passage 36 are substantially quadrangular, and the four corners of the opening are curved. And opening part 31a, 36a, 42 has the same opening width. Here, the opening width is the width of the piston 22 in the operation direction, that is, the direction along the center line A. Further, in the direction along the center line A, the upper and lower edges forming the openings 31a, 36a, 42 are at the same position. On the other hand, the opening width of the opening 41 provided in the wall member 37 is narrower than the opening width of the openings 31a, 36a, and 42.

  Further, in the direction along the center line A, the upper edge that forms the opening 41 is at the same position as the upper edge that forms the openings 31a, 36a, and 42. Furthermore, in the direction along the center line A, the lower edge 41b that forms the opening 41 is located at a position different from the lower edges that form the openings 31a, 36a, and 42.

  That is, the lower edge 41b of the opening 41 protrudes a predetermined amount upward from the lower edge 31c of the opening 31a and the lower edge of the second exhaust passage 36. In the direction along the center line A, the center E of the opening 41 and the center C of the opening 31a are arranged at different positions. Specifically, in the direction along the center line A, the length from the center E to the upper edge 32a of the exhaust port 32 is shorter than the length from the center C to the upper edge 32a. The upper edge 32a of the exhaust port 32 is the upper end of the location where the exhaust port 32 is open when the piston 22 operates toward top dead center. Thus, in the direction along the center line A, the center E is disposed at a position closer to the combustion chamber 18 than the center C.

  Further, a branch passage 34a is provided inside the branch pipe 34, and from the opening 36a of the second exhaust passage 36 to a location where the second exhaust passage 36 and the branch passage 34a are connected in the exhaust gas flow direction. In this range, the second exhaust passage 36 is substantially horizontal, and the center line F of the second exhaust passage 36 in the range is at the same height as the center C of the opening 31 a of the first exhaust passage 31. That is, the center line B and the center line F intersect at the center C. The center line F is at a position lower than the center E of the opening 41.

  The branch passage 34a is branched from the second exhaust passage 36, and extends upward from the branch point. Next, the branch passage 34a extends substantially horizontally, and further extends downward, and the end opposite to the second exhaust passage 36 is closed. The cross-sectional area of the branch passage 34a is constant from the second exhaust passage 36 toward the closed end in the exhaust gas flow direction. Note that the end of the branch passage 34a opposite to the second exhaust passage 36 may be closed, or may be connected to the first expansion chamber 35 through a small-diameter hole. In other words, the branch passage 34 a may have a structure that can reflect the pressure wave of the exhaust gas propagated from the second exhaust passage 36 to the second exhaust passage 36.

  When the engine 12 configured as described above is operated at a normal rotation speed, for example, 9000 rpm, the flow of exhaust gas in the engine 12 and the muffler 20 and the propagation state of the pressure wave of the exhaust gas are shown in FIG. 2, FIG. 5 to FIG. As shown in FIG. 5, when the piston 22 rises toward the top dead center and both the scavenging port 24 and the exhaust port 32 are closed, the pressure in the combustion chamber 18 rises, and the ignition plug is at a predetermined timing. The ignition control by the engine 23 is performed, and the air-fuel mixture burns, that is, explodes in the combustion chamber 18.

  Due to the explosion stroke, the inside of the combustion chamber 18 becomes high temperature and high pressure, and the piston 22 descends. When the piston 22 descends and the exhaust port 32 opens as shown in FIG. 6, the combustion gas in the combustion chamber 18 is discharged to the second exhaust passage 36 through the exhaust port 32 and the first exhaust passage 31. In this exhaust stroke, a positive pressure wave propagates through the second exhaust passage 36 and the branch passage 34a as indicated by an arrow G. When the positive pressure wave propagating from the second exhaust passage 36 toward the first expansion chamber 35 reaches the most downstream end of the second exhaust passage 36, the positive pressure wave is reversed to the negative pressure wave and reversely directed, that is, the second exhaust passage. It propagates in the direction of the arrow H that flows back through the inside of the pipe 36.

  On the other hand, the positive pressure wave propagated in the branch passage 34a reaches the downstream end of the branch passage 34a and is reflected, and the positive pressure wave is propagated in the direction of arrow J returning to the second exhaust passage 36 in the branch passage 34a. The During the above operation, the scavenging port 24 is closed by the piston 22.

  When the piston 22 further descends and the scavenging port 24 opens as shown in FIG. 7, the air-fuel mixture in the crank chamber 25 is drawn into the combustion chamber 18 via the scavenging port 24 and the combustion in the combustion chamber 18 is performed. The gas is discharged to the first exhaust passage 31. That is, the intake stroke and the scavenging stroke are generated in parallel. At the initial stage when the scavenging port 24 is opened, the negative pressure wave in the direction of the arrow H propagated by being reversed in the second exhaust passage 36 and the positive pressure in the direction of the arrow J reflected and propagated in the branch passage 34a. A pressure wave is synthesized. As a result, the back pressure of the exhaust port 32 and the first exhaust passage 31 decreases.

  Note that the combustion gas in the combustion chamber 18 passes through the exhaust port 32, the first exhaust passage 31, and the second exhaust passage 36 until the piston 22 reaches bottom dead center after the exhaust port 32 is opened. Further, the combustion gas is discharged from the first expansion chamber 35 to the outside of the muffler 20 via the second expansion chamber 44.

  On the other hand, when the piston 22 reaches the bottom dead center and the direction of operation is reversed, and the piston 22 moves up and the scavenging port 24 is closed, as shown by an arrow K in FIG. The positive pressure wave of the accumulated combustion gas is propagated to the second exhaust passage 36. Then, the positive pressure wave propagated in the second exhaust passage 36 passes through a branch point between the second exhaust passage 36 and the branch passage 34a, and a part of the positive pressure wave propagates into the branch passage 34a, and the others are the first exhaust passage. Propagate toward 31. For this reason, the pressure in the first exhaust passage 31 and the exhaust port 32 increases.

  The positive pressure wave propagated into the branch passage 34 a is reflected at the downstream end of the branch passage 34 a and returns to the second exhaust passage 36. Then, during the period from when the scavenging port 24 is closed due to the rise of the piston 22 to when the exhaust port 32 is closed, a part of the positive pressure wave reflected in the branch passage 34a is first shown in FIG. 1 is propagated to the exhaust passage 31. For this reason, the first exhaust passage 31 and the exhaust port 32 are maintained in a high pressure state.

  Further, when the piston 22 rises and the exhaust port 32 is closed, the air-fuel mixture in the combustion chamber 18 is compressed and then returns to the explosion stroke described above. Thereafter, the explosion stroke, the exhaust stroke, the scavenging / suction process are repeated, and the power that the piston 22 reciprocates is converted into the rotational force of the crankshaft 27. The engine 12 in the present embodiment is a so-called two-stroke one-cycle engine (two-cycle engine) in which one cycle of an intake / scavenging stroke, a compression stroke, an explosion stroke, and an exhaust stroke is performed in a process in which the piston 22 makes two strokes. is there. The torque of the crankshaft 27 is transmitted to the cutting blade 13 via the power transmission mechanism, and the cutting blade 13 rotates.

  As described above, according to the engine 12 of the present embodiment, the second exhaust from the first expansion chamber 35 is performed after the piston 22 is raised and the scavenging port 24 is closed until the exhaust port 32 is closed. Both the positive pressure wave propagated to the passage 36 and the positive pressure wave reflected in the branch passage 34 a and propagated to the second exhaust passage 36 are propagated to the first exhaust passage 31 and the exhaust port 32, and the exhaust port 32. Can be maintained at a high state.

  For this reason, it is possible to push back fresh air that is about to flow out from the combustion chamber 18 through the exhaust port 32 into the first exhaust passage 31, that is, unburned gas, into the combustion chamber 18. In other words, the pressure pulsation of the exhaust gas inside the muffler 20 is used to suppress unburned gas blow-through. Therefore, it is possible to suppress the deterioration of the exhaust gas characteristics in the engine 12 and improve the engine output.

  In particular, the engine 12 of the present embodiment is provided with an opening 41 between the first exhaust passage 31 and the second exhaust passage 36, and the center E of the opening 41 in the direction along the center line A. Is located closer to the upper edge 32a of the exhaust port 32 than to the center C of the opening 31a. That is, when the piston 22 moves toward the top dead center, the distance between the portion where the exhaust port 32 is open and the center E of the opening 41 can be shortened as much as possible.

  For this reason, the direction of the pressure wave propagated from the second exhaust passage 36 to the first exhaust passage 31 can be easily deflected or directed toward the open portion of the exhaust port 32. That is, the lower edge 41 b that forms the opening 41 functions as a weir for making it easier to concentrate the pressure wave on the exhaust port 32. Therefore, the engine 12 is further improved in the performance of retaining unburned gas in the combustion chamber 18.

  The cross-sectional area of the opening 41 provided in the wall member 37 can be set to 0.7 to 1.3 times the maximum value of the cross-sectional area of the exhaust port 32. The maximum value of the cross-sectional area of the exhaust port 32 means the maximum value of the cross-sectional area between the time when the scavenging port 24 is closed and the time when the exhaust port 32 is closed in the process of raising the piston 22. When the exhaust stroke of the engine 12, that is, when the piston 22 descends and the exhaust port 32 opens, the cross-sectional area of the exhaust port 32 becomes wider as the piston 22 descends. For this reason, even if the cross-sectional area of the opening 41 is 1.0 or less with respect to the maximum value of the cross-sectional area of the exhaust port 32, it is possible to suppress an increase in flow resistance when the combustion gas passes through the opening 41. .

  The distance from the exhaust port 32 to the lower edge 41b in the direction along the center line B of the first exhaust passage 31 and the center line F of the second exhaust passage 36 can be set between 20 mm and 50 mm. . This is because the pressure wave propagated from the second exhaust passage 36 to the first exhaust passage 31 flows intensively toward the exhaust port 32.

  Further, the wall member 37 as a single component forms the first expansion chamber 35 and the opening 41. For this reason, it can suppress that the number of parts of the engine 12 increases, can suppress the raise of the manufacturing cost of the engine 12, and can provide the cheap engine 12.

  Further, since the branch passage 34a is connected in the middle of the length direction of the second exhaust passage 36 in the exhaust gas flow direction, the entire muffler 20 can be reduced in size. That is, in order to reduce the size and weight of the engine 12 of this embodiment, the length of the exhaust pipe 33 and the length of the branch pipe 34 are shortened, the cross-sectional area and volume of the second exhaust passage 36 are reduced, Even when designing to reduce the cross-sectional area and the volume of the branch passage 34a, unburned gas can remain in the combustion chamber 18. In other words, both the effect of preventing the exhaust gas characteristics of the engine 12 from deteriorating and the effect of reducing the size and weight of the engine 12 can be achieved.

  In addition, when the engine speed is a predetermined normal speed, the pressure stored in the first expansion chamber 35 causes the first exhaust passage 31 to pass immediately before the piston 22 rises and the exhaust port 32 is closed. It is also possible to set the effective length of the second exhaust passage 36 and the effective length of the branch passage 34 a so as to be propagated to the exhaust port 32 via the passage.

  Further, the cross-sectional area of the opening 41 is preferably larger than the cross-sectional area of the most upstream end of the branch passage 34a. If comprised in this way, when the pressure wave reflected and returned by the branch channel | path 34a is propagated to the exhaust port 32 through the opening part 41, it can suppress that a pressure loss arises by distribution resistance. Therefore, the engine 12 is further improved in the performance of retaining unburned gas in the combustion chamber 18.

(Embodiment 2)
Next, a second embodiment of the engine 12 will be described with reference to FIG. In the engine 12 of FIG. 10, the opening 42 corresponds to the connection passage of the present invention, and the opening 31 a of the first exhaust passage 31 is connected to the opening 36 a of the second exhaust passage 36 via the openings 42 and 41. It is connected. In the engine 12 shown in FIG. 10, the center M of the opening 42 of the gasket 40 is arranged at a position different from the center C of the opening 31a in the direction along the center line A. More specifically, the length from the center M of the opening 42 of the gasket 40 to the upper edge 32a of the exhaust port 32 in the direction along the center line A is from the center C of the opening 31a to the top of the exhaust port 32. It is shorter than the length to the edge 32a.

  That is, in the direction along the center line A, the length from the center M to the open portion of the exhaust port 32 is shorter than the length from the center C to the open portion of the exhaust port 32. Thus, in the direction along the center line A, the center M is disposed at a position closer to the combustion chamber 18 than the center C. In the engine 12 of FIG. 10, the center of the opening 41 and the center C of the opening 31a are in the same position in the direction along the center line A. The other structure in the engine 12 of FIG. 10 is the same as the engine 12 of FIGS.

  The operation of the engine 12 in FIG. 10 is the same as the operation of the engine 12 described with reference to FIGS. Further, in the engine 12 of FIG. 10, the length from the center M of the opening 42 to the upper edge 32a of the exhaust port 32 in the direction along the center line A is from the center C to the upper edge 32a of the exhaust port 32. Shorter than length.

  Accordingly, the pressure wave propagated to the exhaust port 32 through the second exhaust passage 36 from when the piston 22 rises and the scavenging port 24 is closed to when the exhaust port 32 is closed, It is possible to concentrate on the open portion, and the same effect as that of the first embodiment of the engine 12 can be obtained. Moreover, in the engine 12 of FIG. 10, it can prevent that the characteristic of exhaust gas deteriorates by designing the opening width of the opening part 42 provided in the gasket 40, and the position of a height direction. Therefore, it is not necessary to provide a dedicated part, and the number of parts can be prevented from increasing. In the engine 12 of FIG. 10, the structure other than the position and opening width of the opening 42 of the gasket 40 can be designed in the same manner as the engine 12 of FIG. 2, and the same effect as the engine 12 of FIG. can get.

(Embodiment 3)
Next, a third embodiment of the engine 12 will be described with reference to FIG. In the engine 12 shown in FIG. 11, the lower edges of the openings 31a, 41, and 42 are in the same position in the direction along the center line A, and the lower edge of the flange 43 is the lower edges of the openings 31a, 41, and 42. It is in the position which protruded upwards from. Further, the end of the exhaust pipe 33 on the first exhaust passage 31 side is bent so as to ride on the lower edge of the flange 43. That is, the cross-sectional area of the opening 36a formed at the upstream end of the second exhaust passage 36 is narrower than the cross-sectional area of each of the openings 31a, 41, and 42. The opening 36a corresponds to the connection passage of the present invention.

  In the direction along the center line A, the center N of the opening 36a is arranged at a position different from the center C of the opening 31a. More specifically, the length from the center N of the opening 36a to the upper edge 32a of the exhaust port 32 in the direction along the center line A is the upper edge of the exhaust port 32 from the center C of the opening 31a. It is shorter than the length up to 32a. Thus, in the direction along the center line A, the center N is disposed closer to the combustion chamber 18 than the center C. The other structure in the engine 12 of FIG. 11 is the same as the engine 12 of FIGS.

  The operation of the engine 12 in FIG. 11 is the same as the operation of the engine 12 described in FIGS. In the engine 12 of FIG. 11, the length from the center N of the opening 36a to the upper edge 32a of the exhaust port 32 in the direction along the center line A is from the center C of the opening 31a to the top of the exhaust port 32. It is shorter than the length to the edge 32a. That is, in the direction along the center line A, the distance between the opened exhaust port 32 and the center N is made as short as possible.

  Therefore, the pressure wave propagated to the exhaust port 32 through the opening 36a of the second exhaust passage 36 from when the piston 22 rises and the scavenging port 24 is closed until the exhaust port 32 is closed. The exhaust port 32 can be concentrated and the same effect as that of the first embodiment of the engine 12 can be obtained. Moreover, in the engine 12 of FIG. 11, it can prevent that the characteristic of exhaust gas deteriorates by designing the opening width of the opening part 36a, and the position of a height direction. Therefore, it is not necessary to provide a dedicated part, and the number of parts can be prevented from increasing. In the engine 12 of FIG. 11, the structure other than the position of the opening 36 a and the opening width can be designed in the same manner as the engine 12 of FIG. 2, and the same effect as the engine 12 of FIG. 2 can be obtained.

(Embodiment 4)
Next, a fourth embodiment of the engine 12 will be described with reference to FIG. In the engine 12 shown in FIG. 12, the lower edges of the openings 31a, 41, and 42 are in the same position in the direction along the center line A, and the lower edge of the flange 43 is the lower edges of the openings 31a, 41, and 42. It is in the position which protruded upwards from. Further, the end of the exhaust pipe 33 on the first exhaust passage 31 side rides on the lower edge of the flange 43. In the engine 12 of FIG. 12, the opening 36a corresponds to a connection passage in the present invention. In the direction along the center line A, the center N of the opening 36a is arranged at a position different from the center C of the opening 31a. Specifically, in the direction along the center line A, the length from the opening 36a to the upper edge 32a of the exhaust port 32 is larger than the length from the center N of the opening 31a to the upper edge 32a of the exhaust port 32. Also short.

  Moreover, the upper wall 36b is extended substantially horizontally and the lower wall 36c is inclined and extended from the location where the flange 43 is attached among the exhaust pipes 33 downstream. The lower wall 36c is inclined in such a direction that the distance from the upper wall 36b becomes narrower as the opening 36a is approached. More specifically, the inner surface of the lower wall 36c is parallel to the center line B. The other structure in the engine 12 of FIG. 12 is the same as the engine 12 of FIGS.

  The operation of the engine 12 in FIG. 12 is the same as the operation of the engine 12 described in FIGS. In the engine 12 of FIG. 12, the center N of the opening 36a is in a position different from the opening 31a in the direction along the center line A. That is, in the direction along the center line A, the distance between the opened exhaust port 32 and the center N is made as short as possible. Thus, in the direction along the center line A, the center N is disposed closer to the combustion chamber 18 than the center C. Therefore, the pressure wave propagated to the exhaust port 32 through the opening 36a of the second exhaust passage 36 from when the piston 22 rises and the scavenging port 24 is closed until the exhaust port 32 is closed. The exhaust port 32 can be concentrated and the same effect as that of the first embodiment of the engine 12 can be obtained.

  Further, in the engine 12 of FIG. 12, the inner surface of the upper wall 36b is horizontal, and the lower wall 36c is inclined in such a direction that the distance between the upper wall 36b and the lower wall 36c becomes narrower as the opening 36a is approached. Therefore, the pressure wave propagated to the exhaust port 32 through the opening 36 a of the second exhaust passage 36 can be further concentrated near the exhaust port 32.

  Further, in the engine 12 of FIG. 12, the shape of the flange 43 and the structure of the exhaust pipe 33 are designed, the opening width of the opening 36a and the position in the height direction are adjusted, and the exhaust gas characteristics deteriorate. Can be prevented. Therefore, it is not necessary to provide a dedicated part, and the number of parts can be prevented from increasing. In the engine 12 of FIG. 12, the structure other than the position and opening width of the opening 36a can be designed in the same way as the engine 12 in FIG. 2, and the same effect as the engine 12 in FIG. 2 can be obtained.

(Embodiment 5)
Next, a fifth embodiment of the engine 12 will be described with reference to FIG. In the engine 12 shown in FIG. 13, the lower edges of the openings 31 a, 36 a, and 42 are in the same position in the direction along the center line A, and a part of the wall member 37 is the lower edge of the openings 31 a, 36 a, 42. In addition, an overhanging portion 37b that protrudes to a position closer to the center line F and extends from the position toward the first exhaust passage 31 via the curved portion 37a is provided.

  The overhang portion 37b is disposed across the openings 31a and 42, and the opening 41 is formed above the overhang portion 37b. A curved surface 37c that is continuous with the inner surface of the opening 41 is formed in the curved portion 37a. The overhanging portion 37b is located below the center C of the opening 31a, and the center P of the opening 41 is higher than the center C. In the engine 12 of FIG. 13, the opening 41 corresponds to the connection passage of the present invention. The other structure of the engine 12 of FIG. 13 is the same as that of the engine 12 of FIGS.

  The operation of the engine 12 in FIG. 13 is the same as the operation of the engine 12 described with reference to FIGS. In the engine 12 of FIG. 13, the center P of the opening 41 is in a position different from the center C of the opening 31 a in the direction along the center line A. That is, before the piston 22 operates and the exhaust port 32 is closed, the length from the center P to the open portion of the exhaust port 32 in the direction along the center line A is from the center C to the exhaust. It is shorter than the length of the port 32 up to the open portion. Thus, in the direction along the center line A, the center P is disposed closer to the combustion chamber 18 than the center C. Therefore, the pressure wave propagated to the exhaust port 32 through the opening 36a of the second exhaust passage 36 from when the piston 22 rises and the scavenging port 24 is closed until the exhaust port 32 is closed. The exhaust port 32 can be concentrated and the same effect as that of the first embodiment of the engine 12 can be obtained.

  Further, in the engine 12 of FIG. 13, a curved portion 37 a is provided on the wall member 37, and the pressure wave is propagated along the surface of the curved portion 37 a in a curved surface shape or an arc shape. Accordingly, it is possible to suppress the occurrence of pressure loss when the pressure wave is propagated to the exhaust port 32 through the opening 36a of the second exhaust passage 36.

  13 designs the shape of the wall member 37, adjusts the opening width of the opening 41, the position of the center P of the opening 41 in the direction along the center line A, and the exhaust gas characteristics. Can be prevented from deteriorating. Therefore, it is not necessary to provide a dedicated part, and the number of parts can be prevented from increasing. In the engine 12 of FIG. 13, the structure other than the shape of the wall member 37 can be designed in the same manner as the engine 12 of FIG. 2, and the same effect as the engine 12 of FIG. 2 can be obtained.

  The engine and portable work machine of the present invention are not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. For example, the engine of the present invention includes an engine in which the center line A is inclined with respect to the vertical line in addition to the structure in which the center line A is arranged along the vertical line. The engine of the present invention includes an engine having a structure in which the center line A and the center line B intersect at a substantially right angle, in addition to an engine having a structure in which the center line A and the center line B intersect at a substantially right angle. In the present invention, the cross-sectional shape of the opening and the cross-sectional shape of the connection passage include an ellipse and a circle.

  The portable work machine according to the present invention is an engine tool that transmits the power of the engine as a power source to the operating member. Etc. The operating member in the mower is a cutting blade. The operating member in the chain saw is a chain-like blade. The operating member in the blower is an impeller. The operating member in the cultivator is a tilling blade. The operating member in the hedge trimmer is a blade. The operating member in the drill is a drilling blade. The motion member in the present invention includes a motion member that rotates, a motion member that reciprocates, and a member that circulates.

  DESCRIPTION OF SYMBOLS 12 ... Engine, 13 ... Cutting blade, 18 ... Combustion chamber, 19 ... Cylinder, 22 ... Piston, 31 ... 1st exhaust passage, 31a, 36a, 41, 42 ... Opening part, 32 ... Exhaust port, 33 ... Exhaust pipe, 34a ... branch passage, 35 ... first expansion chamber, 36 ... second exhaust passage, 37 ... wall member, 37c ... curved surface, 40 ... gasket, 43 ... flange, C, E, M, N, P ... center.

Claims (11)

A combustion chamber is provided in the cylinder, and an exhaust port connected to the combustion chamber is opened and closed by a piston that reciprocates in the cylinder.
A first exhaust passage provided in the cylinder and connected to the exhaust port;
An opening formed at a downstream end of the first exhaust passage in a discharge direction of the combustion gas discharged from the exhaust port;
A second exhaust passage connected to the opening through a connection passage;
Have
The engine, wherein a center of the connection passage in the operation direction of the piston and a center of the opening in the operation direction of the piston are arranged at different positions in the operation direction of the piston.   2. The engine according to claim 1, wherein a center of the connection passage is disposed closer to the combustion chamber than a center of the opening in an operation direction of the piston.   The engine according to claim 1, further comprising a branch passage branched from the second exhaust passage.   The engine according to claim 3, wherein a cross-sectional area of the connection passage is wider than a cross-sectional area of the branch passage. An exhaust pipe having the second exhaust passage;
An expansion chamber from which combustion gas is discharged from the second exhaust passage;
A wall member forming the expansion chamber;
Have
The engine according to any one of claims 1 to 4, wherein the connection passage is formed at a location of the wall member interposed between the cylinder and an end of the exhaust pipe.   The engine according to claim 5, wherein a curved surface that is continuous with an inner surface of the connection passage is formed on the wall member. An exhaust pipe having the second exhaust passage;
A gasket interposed between an end of the exhaust pipe and the cylinder;
Have
The engine according to claim 1, wherein the connection passage is provided in the gasket. An exhaust pipe having the second exhaust passage;
A flange provided on the exhaust pipe and fixed to the cylinder;
Have
The engine according to any one of claims 1 to 4, wherein a part of the flange is extended in an operation direction of the piston to form the connection passage.   The engine according to any one of claims 1 to 8, wherein a cross-sectional area of the connection passage is 0.7 to 1.3 times a maximum value of a cross-sectional area of the exhaust port.   The engine according to any one of claims 1 to 9, wherein the connection passage is provided between 20 mm and 60 mm from the exhaust port in a length direction of the first exhaust passage. An engine according to any one of claims 1 to 10;
An operation member that operates by transmitting power from the engine;
Having a portable work machine.

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