JP4301630B2 - 2-cycle internal combustion engine - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a two-cycle internal combustion engine, and more specifically, an air layer is formed upstream of an exhaust gas layer in a scavenging stroke, and the exhaust gas layer is pushed out from an exhaust port by the air layer 2 The present invention relates to a cycle internal combustion engine.
[Prior art]
A two-cycle internal combustion engine supplies an air-fuel mixture precompressed in a crank chamber or the like to the combustion chamber side of the cylinder block, compresses it by the upward movement of the piston, and burns it by electric ignition or the like. Gas is discharged to the exhaust port. In the two-cycle engine, there is a so-called blow-out problem that a part of the air-fuel mixture is mixed with the combustion waste gas and discharged to the outside as unburned gas, and the fuel consumption is deteriorated. Conventionally, there is known a two-cycle internal combustion engine in which an air layer is formed upstream of an exhaust gas layer in the scavenging stroke, and the exhaust gas layer is pushed out from an exhaust port by the air layer.
For example, Japanese Patent Laid-Open No. 9-41977 discloses a two-cycle internal combustion engine in which an air intake hole communicating with the outside through a check valve is provided in a scavenging passage leading to a scavenging port. In the two-cycle internal combustion engine, when the pressure in the crank chamber becomes negative due to the upward movement of the piston, the check valve opens, and external air flows into the scavenging passage from the air intake hole to form an air layer. Stay. The air layer is compressed by the downward movement of the piston. The piston is further lowered to open the exhaust port, and the exhaust gas is discharged to the outside through the exhaust port. Further, when the piston descends and the scavenging port opens, first, the air layer pre-compressed and staying in the scavenging passage is discharged to the combustion chamber side through the scavenging port and remains in the combustion chamber. Exhaust gas exhausted is pushed out and exhausted from the exhaust port. Thereafter, following the air layer, an air-fuel mixture flows into the combustion chamber via the scavenging port, scavenging remaining exhaust gas and air, and forming an air-fuel mixture layer in the combustion chamber. It is configured.
[0002]
JP-A-9-125966 discloses a stratified scavenging two-cycle internal combustion engine having an air supply path for taking in air through an air cleaner, and directly connecting the air supply path to a scavenging flow path from a crankcase to a cylinder. An engine is disclosed. The two-cycle internal combustion engine opens the exhaust port and the scavenging port by the downward movement of the piston, exhausts the exhaust gas from the exhaust port, and ejects the air accumulated in the scavenging passage from the scavenging port into the combustion chamber. Exhaust gas is forcibly discharged from the exhaust port. Subsequently, the air-fuel mixture is configured to enter the combustion chamber through the scavenging port after the air.
Further, the two-cycle engine described in JP-A-5-33657 has an air volume connected to an air cleaner via an air passage, and the air volume communicates with the crank chamber via the air passage. And communicated with the scavenging passage through another air passage. When the piston starts to descend, the crank chamber becomes positive pressure, the exhaust port opens and exhaust gas is discharged, and then the scavenging port opens and the air filled in the air volume passes through the scavenging passage, It flows into the combustion chamber from the scavenging port.
[Problems to be solved by the invention]
An object of the present invention relates to a two-cycle internal combustion engine in which an air layer is formed on the upstream side of an exhaust gas layer in the scavenging stroke, and the exhaust gas layer is pushed out from an exhaust port by the air layer. Another object of the present invention is to provide a two-cycle internal combustion engine that can suck and deliver air with a simple and compact structure and can more reliably prevent the air layer and the air-fuel mixture from mixing with each other.
[0003]
[Means for Solving the Problems]
The object of the present invention is to form an air layer (A) on the upstream side of the exhaust gas layer (E) in the scavenging stroke, and to remove the exhaust gas layer (E) from the exhaust port (46) by the air layer (A). ) Is a two-cycle internal combustion engine (4) that is pushed out of the air by the pressure fluctuation caused by the up-and-down movement of the piston (22) and moves it toward the combustion chamber (56) in the cylinder block (44). And an air chamber (38) for pressure-feeding, the air chamber (38) having a recess (36) formed in the crankcase (24) opened to the crank chamber (28), a crankshaft (14), A two-cycle internal combustion engine characterized in that it is defined by an outer surface (16a) of a disk-shaped crank web (16, 18) that rotates integrally with the crank chamber (28). By It can be achieved to.
The two-cycle internal combustion engine according to the present invention operates as follows. When the piston moves upward, the crank chamber becomes negative pressure, and due to the negative pressure, external air is sucked into the air chamber and an air-fuel mixture is sucked into the crank chamber from a carburetor. Since the air chamber is partitioned from the crank chamber side by the side surface of the disc-shaped crank web, the air sucked into the air chamber and the air-fuel mixture do not mix with each other. Next, when the compressed air-fuel mixture in the combustion chamber explodes and the piston moves downward, the scavenging port is first opened, and the exhaust gas forming the exhaust gas layer (E) begins to flow out therefrom. Subsequently, air flows into the combustion chamber from the air chamber by a positive pressure generated by the downward movement of the piston, and forms an air layer (A) on the upstream side of the exhaust gas layer (E). The exhaust gas layer (E) is pushed out from the exhaust port by the air layer (A). Also, the air-fuel mixture flows into the combustion chamber from the crank chamber due to the positive pressure in the crank chamber, but is substantially separated from the exhaust gas layer (E) by the air layer (A). Mixing is prevented.
[0004]
According to the present invention, the air chamber is partitioned from the crank chamber by a recess formed in the crankcase so as to open to the crank chamber and a side surface of the disc-shaped crank web that rotates integrally with the crankshaft. Since it is defined, a two-cycle internal combustion engine having a simple structure and a small size can be provided. Further, since air is sucked and delivered by utilizing pressure fluctuations generated in the crank chamber, it is not necessary to provide a special means such as a pump, and a lightweight and small two-cycle internal combustion engine can be provided. Further, since the air chamber is partitioned by the crank chamber and the disc-shaped crank web, it is possible to prevent air-fuel mixture and air from being mixed. Further, since the exhaust gas is pushed out by the air and the mixture of the air-fuel mixture and the exhaust gas is effectively prevented by the air layer (A), the air-fuel mixture is prevented from being blown into the exhaust port, and the unburned gas Emissions can be prevented and fuel consumption can be prevented from deteriorating.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a two-cycle internal combustion engine according to the present invention will be described with reference to the accompanying drawings.
The two-cycle internal combustion engine according to the present embodiment is of a forced air cooling type and is suitable as a drive source for various devices. Here, a case where it is mounted on a chain saw will be described as an example.
FIG. 1 is a horizontal sectional view along a crankshaft of a chainsaw equipped with a two-cycle internal combustion engine according to the present embodiment. 2 is a cross-sectional view taken along arrow II-II shown in FIG.
As shown in FIG. 1, a chain saw 2 is provided at the rear, a two-cycle internal combustion engine 4 according to this embodiment, a drive unit 6 on which the two-cycle internal combustion engine 4 is mounted, and a front. And a cutting portion 8 having a cutter chain driven by the two-cycle internal combustion engine 4, and handle portions 10 and 12 held by hands.
Details of the two-cycle internal combustion engine 4 will be described with reference to FIGS. 1 and 2. The two-cycle internal combustion engine 4 includes a crankshaft 14 extending left and right (upper and lower in FIG. 1) and a pair of left and right discs mounted concentrically on the crankshaft 14 and spaced apart from each other by a distance d. Crank webs 16, 18, a crank pin 21 that is eccentrically provided between the pair of disc-shaped crank webs 16, 18 and supports the large end 20 a of the connecting rod 20, and swings around the crank pin 21. The connecting rod 20 is freely connected, and the piston 22 is swingably connected to a small end 20b of the connecting rod 20. The crankshaft 14 is supported by a crankcase 24 that defines a crank chamber 28 via a pair of left and right bearings 26 and 26. A space 32 defined by being closed by an air cleaner 30 is provided in front of the crank chamber 28 of the crankcase 24, and a diaphragm carburetor 37 is disposed in the space.
[0006]
As can be seen from FIG. 1 and FIG. 2, the inner wall surface 24a defining the crank chamber 28 is close to the pair of disc-shaped crank webs 16 and 18 with a very small gap therebetween. It is arranged. That is, the crank chamber 28 includes a substantially circular inner wall surface 24a adjacent to the outer surfaces 16a and 18a of the pair of disc-shaped crank webs 16 and 18, and a circumference of the pair of disc-shaped crank webs 16 and 18. It is comprised from the curved inner wall part 24a extended curvedly along a surface. The curved inner wall surface 24a substantially closes the space between the pair of disk-like crank webs 16 and 18, and an air-fuel mixture chamber 34 is formed between them. Thus, the air-fuel mixture chamber 34 having a relatively small volume is provided in the crank chamber 28 so that a larger pressure fluctuation can be obtained by the up-and-down movement of the piston 22. The curved inner wall surface 24a has two flat strip portions 24c that extend straight along the peripheral surfaces of the pair of disc-shaped crank webs 16 and 18 in a horizontal section along the crankshaft 14 shown in FIG. , 24c and a ridge 24b having a width slightly narrower than the distance d between them and projecting inward of the gas mixture chamber 34. The air-fuel mixture chamber 34 and the vaporizer 37 disposed in front of the air-fuel mixture chamber 34 communicate with each other through an air-fuel mixture intake hole 35 formed so as to penetrate the protruding strip portion 24b. In the air-fuel mixture intake hole 35, a reed type first that allows the air-fuel mixture to flow from the carburetor 37 into the air-fuel mixture chamber 34 due to the negative pressure in the crank chamber 28 due to the upward movement of the piston 22. A check valve 33 is provided.
Further, the crankcase 24 is formed with an annular recess 36 that extends around the bearing 26 (the bearing 26 on the left side in FIG. 1) and opens to the crank chamber 28. On the open side of the annular recess 36, an outer side surface 16a of the left disc-like crank web 16 is disposed adjacent to the annular recess 36, and the annular recess 36 is substantially closed by the outer side surface 16a. The air chamber 38 is formed. An air intake hole 40 that communicates the air chamber 38 and the space 32 is formed in front of the air chamber 38. The air intake hole 40 has a second check valve that allows air to flow from the space 32 into the air chamber 38 due to a negative pressure in the crank chamber 28 due to the upward movement of the piston 22. 42 is provided.
[0007]
FIG. 3 is a partial cross-sectional view of a cylinder block of the two-cycle internal combustion engine shown in FIG.
Referring to FIG. 3, the cylinder block 44 has an exhaust port 46 that opens to the combustion chamber 56 side on the lower surface side of the rear end portion of the chain saw 2, that is, on the right side in the axial direction of the crankshaft 14 in FIG. 1. Is formed. The cylinder block 44 is formed with an air passage 50 serving as an air port 50b having one end 50a opened to the air chamber 38 and the other end opened to the combustion chamber 56 side. The air ports 50 b are disposed in the combustion chamber 56 so as to face the exhaust ports 46, that is, at an angle of 180 ° with respect to each other in a cross section (not shown) of the cylinder block 44. . Further, an axis O′-O connecting the exhaust port 46 and the air port 50b between the exhaust port 46 and the air port 50b in the combustion chamber 56, that is, in a cross section of the cylinder block 44, is provided. A pair of scavenging ports 52a, 52a, 54a, and 54a are formed adjacent to each other on both sides of '(the longitudinal direction of the crankshaft 14). These scavenging ports 52a, 52a, 54a, 54a are directed in a direction away from the exhaust port 46 (upstream side of exhaust gas). Further, as can be seen from FIG. 3, each of the scavenging ports 52a, 52a, 54a, 54a is connected to the mixture chamber 34 via the mixture passages 52, 52, 54, 54 extending forward in the horizontal direction therefrom. Communicated with.
[0008]
As shown in FIGS. 1 and 3, the distance between the exhaust port 46, the air port 50b, and the scavenging ports 52a, 52a, 54a, 54a (the opening of each port from the central axis OO of the crankshaft 14). The relationship between the distance to the rear edge) should satisfy the following conditions.
Lex> Lair > Lsc
Lex: distance of the exhaust port 46 Lair: distance of the air port 50b Lsc: distance of the scavenging ports 52a, 54a, that is, when the piston 22 moves downward, the exhaust port 46 first opens, and then the air port 50b Then, the scavenging ports 52a, 52a, 54a, 54a are opened. Although the two-cycle internal combustion engine 4 according to the present embodiment is configured as described above, the air port 50b and the scavenging ports 52a, 52a, 54a, 54a may be opened simultaneously.
[0009]
4 and 5 schematically show the relationship between the exhaust gas layer E, the air layer A, and the air-fuel mixture layer 3 when the piston moves downward.
The two-cycle internal combustion engine 4 according to the present embodiment operates as follows.
When the piston 22 moves upward, the inside of the crank chamber 28 becomes negative pressure. Due to the negative pressure, the air-fuel mixture is sucked into the air-fuel mixture chamber 34 from the vaporizer 37 through the first check valve 33. At the same time, the negative pressure causes air to be sucked into the air chamber 38 via the air cleaner 30, the space 32, and the second check valve 42. The air chamber 38 is separated from the air-fuel mixture chamber 34 by the outer surface 16a of the disc-like crank web 16, and the gap between the disc-like crank webs 16, 18 is as follows. Since the protrusion 24b is substantially closed, the air-fuel mixture does not flow into the air chamber 38 through the gap around the disc-shaped crank web 16. That is, the air-fuel mixture chamber 34 and the air chamber 38 constitute an independent space, and the air-fuel mixture and the air do not mix with each other, but the pressure fluctuation in the crank chamber 28 reaches.
Next, when the compressed air-fuel mixture in the combustion chamber 56 explodes and the piston 22 moves downward, the exhaust port 46 is opened first, and the exhaust gas forming the exhaust gas layer E passes through the muffler 60 from there. It begins to flow out to the outside. Subsequently, air is exhausted by the positive pressure generated by the downward movement of the piston 22 and flows from the air chamber 38 to the combustion chamber 56 side through the air port 50b of the air flow path 50, and the exhaust gas layer E An air layer A is created on the upstream side (see FIG. 4). The exhaust gas layer E is pushed from the upstream side (the opposite side in the cross section of the combustion chamber 56) by the air layer A and flows out to the muffler 60 through the exhaust port 46. The exhaust gas is almost exhausted by the air layer A. Further, due to the positive pressure in the crank chamber 28 due to the downward movement of the piston 22, the air-fuel mixture in the air-fuel mixture chamber 34 passes through the air-fuel mixture passages 52, 52, 54, 54 and the combustion chamber 56. Flows into the side. Since each of the air-fuel mixture ports 52a, 52a, 54a, 54a is directed backward and away from the exhaust port 46, the inflowing air-fuel mixture is reversed after colliding with the top surface of the combustion chamber 56. Furthermore, the air-fuel mixture layer S is formed by flowing upstream of the air layer A (see FIG. 5). As a result, the remaining exhaust gas layer and the air layer A are pushed out to the exhaust port 46 from the downstream side thereof. The air-fuel mixture in the combustion chamber 56 is separated from the exhaust gas by the air layer A. This process is repeated thereafter.
[0010]
According to the present embodiment, the air chamber 38 has the annular recess 36 formed in the crankcase 24 that is a basic component of the two-cycle internal combustion engine 4, as well as the two-cycle internal combustion engine 4. Since it is defined by the outer surface 16a of the disc-like crank web 16 which is a basic component, a simple and small structure can be achieved.
In addition, according to the present embodiment, since air is sucked and discharged by utilizing the pressure fluctuation in the crank chamber 28, it is not necessary to provide a special means such as a pump, and the structure is light and simple. can do.
Further, since the air chamber 38 is formed in an annular shape around the bearing 26, it is possible to secure a sufficient volume for accommodating the air, and to increase the size of the device 2 without increasing the size thereof. Can be structured.
Further, since the crank web 16 has a disk shape, the air chamber 38 is always a space partitioned from the air-fuel mixture chamber 34 during the up-and-down movement of the piston 22, and mixing of the air and the air-fuel mixture is performed. Is prevented.
Further, since the gap between the pair of disc-shaped crank webs 16 is closed by the protruding ridges 24b projecting inward of the air-fuel mixture chamber 34, the circumference of the disc-shaped crank web 16 is increased. The air-fuel mixture does not flow into the air chamber 34 and the air does not flow into the air-fuel mixture chamber 34 through the gap, and the mixing of air and the air-fuel mixture is more reliably prevented.
[0011]
Furthermore, since the air-fuel mixture chamber 34 having a relatively small volume is provided in the crank chamber 28, a large pressure fluctuation can be obtained by the up-and-down movement of the piston 22.
Further, the air-fuel mixture flows from the vaporizer 37 into the air-fuel mixture chamber 34 through the first check valve 33 and further into the combustion chamber 56 through the scavenging ports 52 and 54. On the other hand, air is sucked into the air chamber 38 via the air cleaner 30, the space 32, and the second check valve 42, and further from the air port 50 b via the air flow path 50. It flows into the combustion chamber 56 side. As described above, since the flow path of the air-fuel mixture and the flow path of the air are separately independent, it is possible to effectively prevent the air-fuel mixture and air from being mixed in the process of being introduced to the combustion chamber 56 side. Can be prevented. Therefore, the exhaust gas layer E and the air-fuel mixture layer S can be separated better by the air layer A.
In addition, since the air port 50b is provided separately from the scavenging ports 52a and 54a, the timing for opening them can be set for each, and the air-fuel mixture is mixed after the exhaust gas is substantially pushed out by the air. So that the timing of introducing the air into the combustion chamber 56 and the timing of introducing the air-fuel mixture can be determined as appropriate. As a result, it is possible to more surely eliminate the exhaust gas by the air and to more reliably reduce the air-fuel mixture through the exhaust port 46.
[0012]
Furthermore, since air is introduced into the cylinder before the air-fuel mixture, carbon accumulation in the combustion chamber 56, the spark plug electrode portion 61, and the exhaust port 46 can be effectively prevented. Further, cooling of the piston 22 and the cylinder block 44 can be improved.
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say.
For example, in the present embodiment, the air port 50b and the scavenging ports 52a and 54a are provided separately and independently on the combustion chamber 56 side. These are desirable for reliably preventing mixing with the air-fuel mixture in the process of sending air to the combustion chamber 56 side. However, the air is sent from the air chamber 38 to the scavenging ports 52a and 54a. It may be.
[0013]
In the present embodiment, the air-fuel mixture chamber 34 having a relatively small volume is provided in the crank chamber 28. The air-fuel mixture chamber 34 is indispensable for preventing mixing of air-fuel mixture and air. The air chamber 38 may be partitioned from the crank chamber 28 by the outer surface 16a of the disc-shaped crank web 16.
Furthermore, although the air chamber 38 is annular, it may have other shapes as long as it has a volume sufficient to accommodate a required amount of air.
Furthermore, in the present embodiment, in order to more reliably partition the air chamber 38, it is desirable that the protruding strip portion 24b that protrudes into the air-fuel mixture chamber 34 is provided. However, if the flow of the air-fuel mixture and air between them is at a level that does not impede practically, it is not necessary to provide the ridges 24b, and the inner wall of the crank chamber 28 facing the air-fuel mixture chamber 34. May be flat in the axial direction of the crankshaft 14.
Further, in the present embodiment, the air port 50b is disposed at an angle of 180 ° with respect to the position facing the exhaust port 46, that is, in the cross section of the combustion chamber 56. The air port 50b only needs to be positioned upstream of the exhaust port 46 with respect to the scavenging ports 52a and 54a in the cross section.
[0014]
【The invention's effect】
The present invention relates to a two-cycle internal combustion engine in which an air layer A is formed on the upstream side of an exhaust gas layer in the scavenging stroke so that the exhaust gas layer is pushed out from the exhaust port by the air layer. It is possible to provide a two-cycle internal combustion engine that can suck and deliver air with a simple structure and can more reliably prevent the air layer and the air-fuel mixture layer from being mixed.
[Brief description of the drawings]
FIG. 1 is a horizontal sectional view including a crankshaft of a chainsaw equipped with a two-cycle internal combustion engine according to an embodiment of the present invention.
2 is a cross-sectional view taken along arrow II-II shown in FIG.
FIG. 3 is a partial sectional view of a cylinder block of the two-cycle internal combustion engine shown in FIG.
FIG. 4 shows a relationship among an exhaust gas layer, an air layer, and an air-fuel mixture layer when the piston moves downward.
FIG. 5 shows a relationship among an exhaust gas layer, an air layer, and an air-fuel mixture layer when the piston further moves downward.
[Explanation of symbols]
4 Two-cycle internal combustion engine 14 Crankshaft 16 Disc-like crank web 16a Outer side 18 Disc-like crank web 22 Piston 24 Crankcase 24a Inner wall surface 24b Projection strip 28 Crank chamber 34 Mixing chamber 36 Annular recess 37 Vaporizer 38 Air Chamber 42 Check valve 44 Cylinder block 46 Exhaust port 50b Air port 52a Scavenging port 54a Scavenging port 56 Combustion chamber E Exhaust gas layer A Air layer

Claims (5)

In the scavenging stroke, an air layer (A) is formed on the upstream side of the exhaust gas layer (E), and the exhaust gas layer (E) is pushed out from the exhaust port (46) by the air layer (A). A cycle internal combustion engine (4),
It has an air chamber (38) that takes in air by pressure fluctuation caused by the up-and-down movement of the piston (22) and pumps the air toward the combustion chamber (56) side in the cylinder block (44). ) Is a recess (36) formed in the crankcase (24) so as to open to the crank chamber (28), and a disc-shaped crank web (16, 18) rotating integrally with the crankshaft (14). A two-cycle internal combustion engine characterized in that it is defined by a side surface (16a) and separated from the crank chamber (28). The air in the air chamber (38) is supplied to the combustion chamber (56) side via an air port (50b) provided separately from the scavenging ports (52a, 54a). Item 2. A two-cycle internal combustion engine according to item 1. Two disc-shaped crank webs (16, 18) are provided on the crankshaft (14) at an interval in the axial direction, and the inner wall surface (24a) of the crank chamber (28) An air-fuel mixture that is disposed in the vicinity of the disc-shaped crank web (16, 18) and receives the air-fuel mixture from the vaporizer (37) between the pair of disc-shaped crank webs (16, 18). A chamber (34) is defined, and the inner wall surface (24a) of the crank chamber (28) is provided with a ridge (24b) projecting inwardly around the mixture chamber (34). The two-cycle internal combustion engine according to claim 1, wherein the two-cycle internal combustion engine is formed. The air port (50b) is located upstream in the exhaust gas flow direction with respect to the scavenging ports (52a, 54a) in a cross section across the cylinder of the cylinder block (44). The two-cycle internal combustion engine according to any one of claims 1 to 3. 5. The apparatus according to claim 4, wherein when the piston (22) moves downward, the exhaust port (46), the air port (50b), and the scavenging port (52a, 54a) are opened in this order. Cycle internal combustion engine.

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