Two-stroke engine

Abstract

A two-stroke engine improves scavenging efficiency in a cylinder. A variable scavenging passage 14(ch) is constituted by a scavenging passage 14 of a plurality of scavenging passages included in the cylinder, which is connected to at least one scavenging port 16. An upper end portion of the variable scavenging passage 14(ch) has a guide surface 50 that defines a discharge direction on a horizontal plane of scavenging gas discharged from the variable scavenging port 16(ch) connected thereto. The guide surface 50 includes at least a first guide portion 50(H) that defines a first discharge direction of the scavenging gas, and a second guide portion 50(L) that defines a second discharge direction of the scavenging gas. In a scavenging stroke, the discharge direction of the scavenging gas is changed on the horizontal plane from the first discharge direction to the second discharge direction by the first guide portion 50(H) and the second guide portion 50(L).

Description

Technical Field

[0001] This invention relates to a two-stroke engine. Background Technology

[0002] Traditionally, two-stroke engines use a pre-compressed gas-fuel mixture from the crankcase for scavenging during the scavenging stroke. A two-stroke engine includes a scavenging passage that connects the crankcase and the combustion chamber. The upper opening of the scavenging passage, the scavenging port, is opened or closed by a piston that reciprocates between top dead center and bottom dead center. Furthermore, the piston's movement also opens or closes the exhaust port.

[0003] If the piston descends during the combustion stroke, the exhaust port and scavenging port open near the piston's bottom dead center. Scavenging begins in the cylinder at the same time the scavenging port opens. The scavenging port is connected to the crankcase via the scavenging passage. At the same time the scavenging port opens, the pre-compressed mixture is discharged into the cylinder as scavenging gas from the scavenging port.

[0004] In conventional two-stroke engines where the air-fuel mixture is pre-compressed in the crankcase, there is a problem of "mixture dispersion" that occurs during the scavenging stroke. "Mixture dispersion" refers to the phenomenon where the air-fuel mixture is discharged directly from the exhaust port without contributing to the scavenging process. Because unburned air-fuel mixture is discharged, this dispersion not only pollutes the environment but also reduces the air supply efficiency (ηtr), resulting in a worse combustion rate.

[0005] To address the problem of air-fuel mixture dispersion, a "reverse scavenging" method has been proposed and has become the mainstream approach in current two-stroke engines. "Reverse scavenging" is achieved by directing the air-fuel mixture discharged from the scavenging port, i.e., the scavenging gas, towards the cylinder wall on the intake side, opposite to the exhaust port. A reverse scavenging two-stroke engine is disclosed, for example, in Patent Document 1. As shown in Patent Document 1, the scavenging gas discharged from the scavenging port is directed towards the intake-side cylinder wall. Then, the scavenging gas reverses direction within the cylinder and travels towards the exhaust port.

[0006] Here, Patent Document 1 proposes to form the cross-sectional shape of the upper end of the scavenging passage into an approximate triangle with the scavenging port as one side, so that the scavenging gas discharged from the scavenging port is directed toward the cylinder wall on the intake side.

[0007] In the process of addressing environmental concerns, exhaust gas restrictions have become stringent. To address this, various proposals have been developed to prevent the dispersion of the gas mixture. The scavenging port opens as the piston descends, thus increasing the effective opening area. Patent documents 2 and 3 disclose inventions that, in the aforementioned process, change the direction of the gas mixture, i.e., the scavenging gas, emitted from the scavenging port.

[0008] For ease of explanation, the surface that expands along the vertical movement of the piston is called the "vertical surface," and the surface that expands in the transverse direction orthogonal to the vertical surface is called the "horizontal surface."

[0009] Patent document 2 discloses an invention in which the top plate wall of the upper part of the scavenging passage, i.e., the part near the exhaust port, has a three-dimensional shape, and the direction of the scavenging gas discharge changes in the vertical plane through the three-dimensional shape of the top plate wall. According to the invention, when the scavenging port begins to open, the scavenging gas points upward. Then, as the piston descends, the effective opening area of ​​the scavenging port expands, and the scavenging gas gradually points downward.

[0010] Patent document 3 discloses an invention in which the top plate wall of the upper portion of the scavenging passage, i.e., the portion near the scavenging port, is divided into a first surface on the intake side and a second surface on the exhaust side of the air cylinder, and the first surface on the intake side has a relatively larger tilt angle than the second surface on the exhaust side, causing the scavenging gas to point upwards. Related to the shape of the scavenging passage, the upper edge of the scavenging port has a stepped shape, and at the upper edge of the scavenging port, the first half of the upper edge on the intake side is positioned higher than the second half of the upper edge on the exhaust side.

[0011] According to the invention in Patent Document 3, when the piston descends and reaches the upper edge of the first half of the intake side of the scavenging port to open the scavenging port, the mixed gas discharged from the scavenging port, i.e., the scavenging gas, points relatively upward. When the piston descends further and reaches the upper edge of the second half of the exhaust side of the scavenging port, the scavenging gas discharged from the scavenging port then points relatively downward through the aforementioned second surface with a relatively small tilt angle. That is, the invention disclosed in Patent Document 3, like Patent Document 2, discloses an invention that changes the discharge direction of the scavenging gas in a vertical plane.

[0012] Existing technical documents

[0013] Patent documents

[0014] Patent Document 1: Japanese Patent No. 5553552

[0015] Patent Document 2: Japanese Patent Application Publication No. 60-145417

[0016] Patent Document 3: Japanese Patent Application Publication No. 2001-182541

[0017] With increasingly stringent restrictions on exhaust gases, further improvements in air supply efficiency (ηtr) are needed to minimize the emission of unburned gases and increase engine output. If we consider the proposals in Patent Documents 2 and 3 from the above perspective, there is a possibility of dead zones that cannot be reached by the scavenging gas emitted from the scavenging port when viewing the combustion chamber from above; further improvements are expected. Summary of the Invention

[0018] The purpose of this invention is to provide a two-stroke engine that improves the scavenging efficiency within the cylinder. This invention is ideally applicable to reverse-scavenging engines.

[0019] In addition, in two-stroke engines, fuel injection devices are used instead of carburetors for more precise fuel control. Regarding the configuration of fuel injection devices in these engines, in addition to (1) configuring the fuel injection device in the engine's intake system, (2) configuring the fuel injection device in the crankcase, etc., (3) configuring the fuel injection device in the cylinder. Engines with the fuel injection device configured in the cylinder are called "in-cylinder direct injection engines". In an in-cylinder direct injection two-stroke engine, air is supplied to the crankcase, where it is pre-compressed. Then, the pre-compressed air is introduced into the cylinder as scavenging gas through the scavenging passage and scavenging port, and is used for scavenging in the cylinder.

[0020] In the description of this invention, the mixed gas supplied to the gas cylinder as scavenging gas through the scavenging passage and scavenging port is collectively referred to as "air," and the term "fresh gas" is used. That is, the term "fresh gas" includes any one of the mixed gas and air, or both of them, flowing into the gas cylinder sequentially.

[0021] To address the aforementioned technical problems, the present invention provides a two-stroke engine, comprising: a piston disposed within a cylinder, reciprocating between top dead center and bottom dead center and defining a combustion chamber; an exhaust port opening into the cylinder and opened or closed by the piston, for discharging combusted gas from the combustion chamber; a crankcase receiving fresh air and pre-compressing the fresh air by the downward movement of the piston; and a plurality of scavenging passages communicating between the combustion chamber and the crankcase during the scavenging stroke, each passage including a scavenging port for discharging the pre-compressed fresh air in the crankcase as scavenging gas into the combustion chamber, the scavenging port being opened or closed by the piston. The scavenging passage connected to at least one of the scavenging ports constitutes a variable scavenging passage. The upper end of the variable scavenging passage has a guide surface. The guide surface defines the discharge direction of the scavenging gas discharged from the variable scavenging port connected to the upper end of the variable scavenging passage in the horizontal plane. The guide surface includes at least: a first guide portion that defines a first discharge direction of the scavenging gas; and a second guide portion that defines a second discharge direction of the scavenging gas. During the scavenging stroke, the discharge direction of the scavenging gas changes from the first discharge direction to the second discharge direction in the horizontal plane through the first guide portion and the second guide portion.

[0022] According to the present invention, the generation of the aforementioned dead zone that may occur in the inventions of Patent Documents 2 and 3 can be suppressed, thereby enabling efficient gas exchange within the gas cylinder through the scavenging gas during the scavenging stroke.

[0023] This invention is typically applicable to reverse scavenging engines. In a preferred embodiment of the invention, the guide surface is composed of surfaces that form steps. The stepped surface can be two levels, three levels, or more than three levels. Furthermore, the guide surface can also be composed of curved, stepless surfaces.

[0024] In a preferred embodiment of the invention, when the guide surface at the upper end of the scavenging passage connected to the scavenging port is, for example, in two stages, the first discharge direction of the scavenging gas defined by the first guide portion formed in the upper part of the guide surface is more oriented towards the intake side than the second discharge direction of the scavenging gas defined by the second guide portion formed in the lower part. That is, on a horizontal plane, the first discharge direction is more oriented towards a direction relatively farther from the cylinder bore center than the second discharge direction. Preferably, the first discharge direction is tangential to the inner wall of the cylinder.

[0025] The effects and other objectives of the present invention will become clear from the following detailed description of preferred embodiments. Attached Figure Description

[0026] Figure 1 It is a schematic diagram of the single-cylinder two-stroke engine of the embodiment.

[0027] Figure 2 It is a schematic diagram of the intake system of the two-stroke engine including the engine of the embodiment.

[0028] Figure 3 It is along Figure 1 The sectional view along line A-A.

[0029] Figure 4 It is along Figure 1 The sectional view along line B-B.

[0030] Figure 5 It is a schematic diagram for explaining the guide surface formed at the upper end of the variable scavenging passage.

[0031] Figure 6 It is along Figure 5 The sectional view along line VI-VI.

[0032] Figure 7 It is a perspective view of the cylinder block of the engine of the embodiment.

[0033] Figure 8 It is along Figure 7 The sectional view along line VIII-VIII.

[0034] Figure 9 It is along Figure 7 The sectional view along line IX-IX.

[0035] Figure 10 It is for Figure 5 The schematic diagram for explaining the modified example of the guide surface shown, that is, the three-stage guide surface (Japanese: 3-dan no guide surface).

[0036] Figure 11 It is along Figure 10 The schematic view along line XI-XI.

[0037] Figure 12 It is for Figure 5 The schematic diagram for explaining the modified example of the guide surface shown, that is, the stepless guide surface (Japanese: mudan no guide surface).

[0038] Figure 13 It is along Figure 12 The sectional view along line XIII-XIII.

[0039] Figure 14 It is related to Figure 3The corresponding figure illustrates an example of applying the invention to the upper end of a scavenging passage, which is connected to a second scavenging port on the exhaust side and a first scavenging port on the opposite exhaust side of a four-flow scavenging cylinder.

[0040] Figure 15 This is a diagram illustrating an example of applying the invention to the upper end of a scavenging passage connected to a second scavenging port on the exhaust side and the upper end of a scavenging passage connected to a first scavenging port on the intake side.

[0041] Figure 16 This figure illustrates an example of applying the invention to the upper end of a scavenging passage connected to a second scavenging port on the exhaust side of a cylinder and to the upper end of a scavenging passage connected to a second scavenging port on the intake side.

[0042] Figure 17 This is a diagram illustrating an example of applying the invention to the upper end of a scavenging passage connected to a first scavenging port and a second scavenging port opposite to each other on the exhaust side of a gas cylinder.

[0043] Figure 18 This is a diagram illustrating an example of applying the invention to the upper end of a scavenging passage connected to three scavenging ports other than the scavenging passage connected to the first scavenging port on the intake side.

[0044] Figure 19 This is a diagram illustrating an example of applying the invention to the upper end of a scavenging passage connected to a scavenging port on one side of a dual-flow scavenging cylinder.

[0045] Figure 20 This is a diagram illustrating an example of applying the invention to the upper end of a scavenging passage connected to scavenging ports located on both sides of a dual-flow scavenging cylinder.

[0046] Figure 21 This diagram is used to illustrate an example of a guide surface formed by a first dividing surface and a second dividing surface, wherein the angle formed by the first dividing surface and the second dividing surface on the cylinder is an acute angle.

[0047] Figure 22 This diagram is used to illustrate an example of a guide surface formed by a first dividing surface and a second dividing surface, wherein the angle between the first dividing surface and the second dividing surface and the cylinder is an obtuse angle.

[0048] (Symbol Explanation)

[0049] 100 Single-cylinder two-stroke engine system;

[0050] 2. Engine of the embodiment;

[0051] 4 cylinders;

[0052] 6. Pistons;

[0053] 8. Combustion chamber;

[0054] 12. Crank chamber;

[0055] 14. Scavenging passage;

[0056] 14 (ch) Variable scavenging passage;

[0057] 16 Scavenging ports;

[0058] 16 (ch) Variable scavenging ports;

[0059] 22. Exhaust port;

[0060] 50 guide surfaces;

[0061] 50 (H) Upper guide section;

[0062] 50 (L) Lower guide section;

[0063] 52. Step section;

[0064] 54. The guiding surface of the first modified example;

[0065] 54 (H) Upper guide section;

[0066] 54 (M) Intermediate guide section;

[0067] 54 (L) Lower guide section;

[0068] 60-cylinder block;

[0069] 62. The scavenging passage forms a cover;

[0070] 64. Threaded hole. Detailed Implementation

[0071] [Example]

[0072] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a schematic diagram of engine 2, an embodiment included in a single-cylinder, two-stroke engine system 100. Engine 2 is ideally suited for portable work equipment such as chainsaws, blowers, and lawnmowers. (Refer to...) Figure 1 The engine 2 shown in the figure has a piston 6 inserted into a cylinder 4, which reciprocates between top dead center and bottom dead center. An ignition plug 10 is installed in the combustion chamber 8 defined by the piston 6.

[0073] Combustion chamber 8 and crankcase 12 are connected during the scavenging stroke via scavenging passage 14. Scavenging passage 14 has a rectangular scavenging port 16 at its upper end, which is opened or closed by piston 6. Engine 2 has four scavenging ports 16, and to synchronize the opening timing of the four scavenging ports, the upper edges of the rectangular scavenging ports 16 are positioned at the same horizontal height. The lower ends of each scavenging port 16 open towards crankcase 12, forming a scavenging gas inlet 18. A two-stroke engine including four scavenging ports 16 is called a "four-flow scavenging engine".

[0074] Reference numeral "20" indicates the intake port, through which the air-fuel mixture is supplied to the crankcase 12. Reference numeral "22" indicates the exhaust port. The exhaust port 22 is located on the side opposite to the intake port 20. The engine 2 is a piston-valve type engine. That is, the intake port 20 and the exhaust port 22 are opened or closed by the piston 6. Furthermore, the air-fuel mixture is supplied to the crankcase 12 through the intake port 20, while the combusted gas in the combustion chamber 8 is discharged through the exhaust port 22.

[0075] Figure 2 This is a schematic diagram of the intake system 24 included in the two-stroke engine system 100. The intake system 24 has an air filter 26 at its upstream end, through which purified air is supplied to the carburetor 28. Fuel is supplied from the fuel tank 30 to the carburetor 28, where a mixture is generated.

[0076] Engine 2 is a stratified scavenging engine. Carburetor 28 has: a first passage 28a, which generates a gas-fuel mixture; and a second passage 28b, through which air received from air filter 26 passes. The first passage 28a, as the gas-fuel mixture generation passage, forms part of a gas-fuel mixture passage 32 leading to crankcase 12. The gas-fuel mixture generated by carburetor 28 is supplied to crankcase 12 via gas-fuel mixture passage 32 and then pre-compressed in crankcase 12.

[0077] The second passage 28b through which air is supplied forms part of the pilot air passage 34 that supplies pilot air to the scavenging passage 14. The piston 6 has a piston groove 6a on its circumferential surface. Pilot air received from the air filter 26 is supplied to the upper end of the scavenging passage 14 via the piston groove 6a. The piston groove 6a is described in detail in US2016 / 0376979A1, therefore a description of the piston groove 6a is omitted. A reed valve may also be used instead of the piston groove 6a. A reed valve is described in detail in Japanese Patent Application Publication No. 2000-337154.

[0078] In the scavenging type engine 2, pilot air is supplied to the combustion chamber 8 at the beginning of the scavenging stroke, followed by the supply of the mixture from the crankcase 12 to the combustion chamber 8.

[0079] Figure 3 It is along Figure 1 A cross-sectional view along line AA. Figure 4 It is along Figure 1 A cross-sectional view along the BB line. From Figure 3 , Figure 4 It can be seen that engine 2 is a "reverse scavenging" type engine that directs the scavenging gas emitted from each of the four scavenging ports 16 toward the intake side of the air cylinder.

[0080] Reference Figure 3 , Figure 4 The four rectangular scavenging ports 16 are arranged in two on each side of the air cylinder. To identify each scavenging port 16, the scavenging port 16 located on the right side of the figure, which is located next to the exhaust port 22, is referred to as the "exhaust-side first scavenging port" and is labeled with the reference numeral "16 (ex1)". The scavenging port 16 located on the right side of the figure, which is located next to the intake port 20, is referred to as the "intake-side first scavenging port" and is labeled with the reference numeral "16 (in1)".

[0081] The scavenging port 16 located on the left side of the figure, which is situated next to exhaust port 22, is referred to as the "exhaust-side second scavenging port" and is labeled with the reference numeral "16 (ex2)". Similarly, the scavenging port 16 located on the left side of the figure, which is situated next to intake port 20, is referred to as the "intake-side second scavenging port" and is labeled with the reference numeral "16 (in2)".

[0082] Figure 3 , Figure 4 Arrow 40 indicates the direction of the scavenging gas emitted from each scavenging port 16. Figure 3 , Figure 4 It can be seen that the scavenging gas is discharged towards the intake side, which is opposite to the exhaust port 22. In other words, the upper ends of the rectangular scavenging ports 16 of the engine 2 and the scavenging passages 14 connected thereto are substantially the same in their basic structure as those of the scavenging ports and the upper ends of the scavenging passages connected thereto, as described in Japanese Patent Application Publication No. 2000-34927, which are included in known reverse scavenging engines.

[0083] This invention is applied to Figure 1The upper end of the scavenging passage 14, which is the only one of the four scavenging ports 16 included in the engine 2 illustrated in the figure, is associated with the exhaust-side second scavenging port 16 (ex2). Therefore, the upper end of the scavenging passage 14 associated with the exhaust-side first scavenging port 16 (ex1), the intake-side first scavenging port 16 (in1), and the intake-side second scavenging port 16 (in2), other than the exhaust-side second scavenging port 16 (ex2), is the same as in the past. The scavenging passage 14 and scavenging port 16 to which the present invention is applied are referred to as "variable scavenging passage 14 (ch)" and "variable scavenging port (16ch)".

[0084] Figure 5 This is a schematic diagram of the upper end of the variable scavenging passage 14 (ch). Figure 6 It is along Figure 5 A cross-sectional view along line VI-VI. At the upper end of the variable scavenging passage 14 (ch), the side wall of the gas cylinder on the intake side forms a guide surface 50. The guide surface 50 has the function of directing the scavenging gas towards the intake side. The guide surface 50 is composed of an upper guide portion 50 (H) and a lower guide portion 50 (L). Figure 6 The reference numeral "52" in the attached drawing indicates a stepped portion. The stepped portion 52 is formed between the upper guide portion 50 (H) and the lower guide portion 50 (L), and the stepped portion 52 is located in the middle of the vertical direction of the guide surface 50.

[0085] Reference Figure 5 , Figure 6 The stepped portion 52 preferably extends in a direction orthogonal to the axis of the cylinder 4, i.e., the direction of movement of the piston 6. In other words, the stepped portion 52 is preferably located on a horizontal plane. Therefore, during the process of the piston 6 descending to increase the opening of the variable scavenging port 16 (ch), when switching from the upper guide portion 50 (H) to the lower guide portion 50 (L), the scavenging gas discharged from the variable scavenging port 16 (ch) can be guided into the cylinder without turbulence. Furthermore, the stepped portion 52 shown in the figure is composed of a vertical wall, but it could also be composed of an inclined wall or a curved wall.

[0086] Reference Figure 3 It can be well understood that in the cross-sectional shape of the upper end of the variable scavenging passage 14 (ch), the upper guide portion 50 (H) essentially forms the hypotenuse of an approximate triangle with the variable scavenging end 16 (ch), i.e. the exhaust-side second scavenging port 16 (ex2), as one side. Figure 3 As mentioned earlier, it is along Figure 1 A cross-sectional view along line AA. From Figure 1 It can be seen that at the cut-off line of AA, the descending piston 6 is located slightly below the upper edge of the rectangular scavenging port 16. That is to say, Figure 3The cross-sectional shape of the upper end of the variable scavenging passage 14 (ch) after the start of the scavenging stroke is shown in the variable scavenging passage 14 (ch) leading to the variable scavenging port 16 (ch).

[0087] from Figure 3 As can be seen, the upper guide portion 50(H) is formed by a surface extending tangentially from the exhaust side to the intake side along the inner wall of the cylinder 4. That is, the upper guide portion 50(H) is formed by an inclined surface having an angle θ (ex-H). Through the upper guide portion 50(H) with an inclined angle θ (ex-H), the scavenging gas is directed tangentially to the inner wall of the cylinder 4. Here, the inclined angle θ refers to the angle of inclination of the guide surface 50 relative to a straight line parallel to the straight line L connecting the exhaust port 22 and the intake port 20 when the combustion chamber 6 is viewed from above.

[0088] Therefore, during the period from the initial stage of the scavenging stroke, after the descending piston 6 opens the scavenging port 16, until the middle portion of the scavenging port 16 in the vertical direction, the scavenging gas guided by the upper guide 50 (H) is directed in a direction away from the exhaust side of the cylinder and tangential to the inner wall of the cylinder 4. (Using blank arrow 42...) Figure 3 The scavenging gas is directed to a specific direction by the upper guide portion 50 (H). This structure prevents unburned gases, which are easily generated during the initial scavenging phase, from being blown towards the exhaust port 22. Furthermore, the cross-sectional shape of the upper end of the approximately triangular scavenging passage formed by the directionality of the upper guide portion 50 (H) increases the flow velocity of the scavenging gas exiting from the variable scavenging port 16 (ch), including the guide surface 50, compared to the scavenging gas exiting from other scavenging ports 16. Therefore, the flow of the scavenging gas can be controlled more diversely, utilizing both different directions and different flow velocities. Moreover, by applying this invention to a portion of multiple scavenging passages, it is possible to prevent scavenging gases exiting from opposing scavenging ports 16 from colliding with each other, thus preventing a portion of the scavenging gas from short-circuiting at the exhaust port 22, based on changes in directionality and velocity.

[0089] On the other hand, refer to Figure 4 Can understand it very well. Figure 4 The illustrated lower guide portion 50 (L) has a cross-sectional shape, for example, substantially the same as the exhaust-side first scavenging port 16 (ex1) in the shape of its upper end in the variable scavenging passage 14 (ch), which is connected to the variable scavenging port 16 (ch), i.e., the exhaust-side second scavenging port 16 (ex2). While not specifically defined, the lower guide portion 50 (L) is composed of an inclined surface having the same angle θ (ex-L) as before, and appears approximately parallelogram-shaped when viewed from above. Figure 3 and Figure 4The comparison shows that the absolute value of the tilt angle θ(ex-L) of the lower guide portion 50 (L) is greater than the absolute value of the tilt angle θ(ex-H) of the upper guide portion 50 (H).

[0090] As mentioned above, Figure 4 It is along Figure 1 A cross-sectional view along the BB line. From Figure 1 It can be seen that at the cut-off line of BB, the descending piston 6 is located slightly above the lower edge of the rectangular scavenging port 16. Figure 4 This illustrates the shape of the upper end of the variable scavenging passage 14 (ch) before the piston 6 closes the variable scavenging port 16 (ch), i.e., the second scavenging port 16 (ex2) on the exhaust side. In other words, Figure 4 This is equivalent to the piston 6 being positioned slightly below the middle of the rectangular scavenging port 16 in the vertical direction, i.e., from the middle to the latter half of the scavenging stroke. Since the period from the middle to the latter half of the scavenging stroke occurs after the exhaust port 22 has opened significantly and the combustion of the gas in the cylinder has fully expanded, the combustion chamber is filled with combusted gas. In this state, the gas in the cylinder... Figure 4 It can be seen that the lower guide portion 50 (L) is configured such that, during the period when the descending piston 6 moves from the middle part of the variable scavenging port 16 (ch) in the vertical direction to the lower edge, the scavenging gas guided by the lower guide portion 50 (L) is directed in the opposite direction to the exhaust port 22, that is, in the tangential direction away from the inner wall of the cylinder 4 and shifted to the central part of the cylinder 4.

[0091] During the middle to latter half of the scavenging stroke, the scavenging gas replaces the combusted gas that has diffused throughout the combustion chamber, including the central part. Furthermore, because its cross-sectional area is larger than that of the upper guide section 50(H), a relatively gentle flow is formed. Therefore, the scavenging gas exiting from each scavenging port 16 does not short-circuit to the exhaust port 22, but instead gently intersects with the scavenging gas exiting from the opposing scavenging ports 16, thereby replacing the gas throughout the combustion chamber. This allows for uniform scavenging throughout the entire area of ​​the gas cylinder.

[0092] As explained above, during the scavenging stroke, the direction of the scavenging gas discharged from the variable scavenging port 16 (ch), i.e., the exhaust-side second scavenging port 16 (ex2), changes. In the first phase, before the variable scavenging port 16 (ch) is partially open, the scavenging gas points tangentially to the inner wall of the cylinder 4. Then, in the second phase, from the exhaust-side second scavenging port 16 (ex2) being partially open until it is closed, the gas points tangentially away from the inner wall of the cylinder 4, i.e., closer to the central axis of the cylinder 4.

[0093] In this way, by changing the direction of the scavenging gas discharged from the variable scavenging port 16 (CH), i.e., the exhaust-side second scavenging port 16 (ex2), during the descent of the piston 6 in the horizontal plane observed from above the combustion chamber 8 from the initial to the later stages of scavenging, initial "spreading" can be prevented, and the scavenging gas can be blown to the entire area of ​​the combustion chamber 8, thereby improving scavenging efficiency. Furthermore, by making the flow direction of the scavenging gas different in only a portion of the multiple scavenging passages 14 (variable scavenging passages 14 (ch)), collisions between the scavenging gases discharged from the opposing scavenging ports 16 can be avoided. This prevents the scavenging gas from losing its directionality and short-circuiting to the exhaust port 22 after collision, ensuring that each scavenging gas discharged from the multiple scavenging ports 16, after scavenging in the combustion chamber 8 while maintaining its own flow path, flows towards the exhaust port 22. In the embodiment, the two-stroke engine 2 pre-compresses the gas mixture in the crankcase 12 and uses it as scavenging gas, thus preventing the gas mixture from being blown away and improving the gas supply efficiency (ηtr). This improvement in gas supply efficiency (ηtr) leads to improved combustion efficiency.

[0094] Engine system 100 relates to a laminar scavenging engine. In this engine, the scavenging passage 14 expels pilot air into the combustion chamber 8 before the air-fuel mixture at the beginning of the scavenging stroke. The four scavenging ports 16, including the exhaust-side second scavenging port 16 (ex2) to which this invention is applied, have a rectangular shape common to conventional laminar scavenging engines. The upper edges of the rectangular scavenging ports 16 are horizontally level, meaning the scavenging start timing is approximately the same. In other words, during the intake stroke, when pilot air is introduced from the pilot air passage 34 through the piston groove into each scavenging passage 14, a sufficiently large and approximately equal amount of pilot air can be filled into all scavenging passages 14, thereby improving scavenging efficiency without compromising the previously known laminar scavenging effect.

[0095] In addition, refer to Figure 3 , Figure 4 It is evident that if the cross-sectional shape of the upper end of the variable scavenging passage 14 (ch) formed by the upper guide portion 50 (H) is compared with the cross-sectional shape formed by the lower guide portion 50 (L), the effective cross-sectional area of ​​the passage is different. Based on this difference, the flow rate of the scavenging gas discharged from the variable scavenging port 16 (ch) becomes diverse, and from the perspective of directionality and timing, the discharged scavenging gases do not collide with each other and are blown to various locations within the combustion chamber 8. In this embodiment, the cross-sectional area of ​​the scavenging passage formed by the upper guide portion 50 (H) is set to 37% of the cross-sectional area of ​​the scavenging passage formed by the lower guide portion 50 (L), but the aforementioned "37%" value can be optimally achieved by adjusting it within a range of 20% to 70% to correspond to the balance between the engine exhaust volume and the required pilot air volume.

[0096] Figures 7 to 9 Indicates reference Figure 1 , Figures 3 to 5 A specific example of engine 2 will be explained. Figure 7 The cylinder block 60 constituting the engine 2 is shown. In the cylinder block 60, the upper portion corresponding to the four scavenging ports 16 and the scavenging passages 14 connected thereto is formed by a pair of scavenging passage forming covers 62 that are threadedly fastened to the cylinder block 60. Figure 7 The reference numeral "64" in the attached drawing indicates a threaded hole.

[0097] Figure 8 It is along Figure 7 A cross-sectional view cut off along line VIII-VIII, which is consistent with the above. Figure 3 The corresponding sectional view. Figure 9 It is along Figure 7 A cross-sectional view cut off along line IX-IX, which is consistent with the above. Figure 4 Corresponding cross-sectional view. As can be seen from the above figures, the guide surface 50 is formed by the scavenging passage forming cover 62. In addition, in the embodiment, the upper ends of all four scavenging passages are formed by the scavenging passage forming cover 62, but it is also possible to form only the variable scavenging passage 14 (ch) by the scavenging passage forming cover 62.

[0098] As described above, the upper end of the variable scavenging passage 14(ch), which is connected to the rectangular variable scavenging port 16(ch), has a guide surface 50 on the suction side of the air cylinder. The guide surface 50 directs the scavenging gas toward the suction side. Furthermore, during the scavenging stroke, the direction of the scavenging gas changes on the horizontal plane. Figures 10 to 13 It is used for Figure 5 The diagram illustrates a modified example of the guide surface 50. (The aforementioned...) Figure 5 The guide surface 50 shown in the figure consists of two levels of guide portions: an upper guide portion 50 (H) and a lower guide portion 50 (L). However, it can also be as follows: Figure 10 , Figure 11 The diagram shows a guide section consisting of three levels, upper and lower.

[0099] Figure 11 It is along Figure 10 A cross-sectional view along line XI-XI. (Refer to...) Figure 10 , Figure 11 Specifically, in the first modified example, the guide surface 54 has an intermediate guide portion 54 (M) between the upper guide portion 54 (H) and the lower guide portion 54 (L). The upper guide portion 54 (H) and the lower guide portion 54 (L) included in the first modified example are derived from the above-mentioned... Figure 5The guide surface 50 includes an upper guide portion 50 (H) and a lower guide surface 50 (L), each having the same inclination angle θ. The middle guide portion 54 (M) preferably has the same middle inclination angle θ as the upper guide portion 54 (H) and the lower guide portion 54 (L), but is not limited to this and may differ. Therefore, during the scavenging stroke, the direction of the scavenging gas can be changed in three levels on the horizontal plane.

[0100] As described above, the intermediate guide portion 54 (M) preferably has the same intermediate tilt angle θ as the upper guide portion 54 (H) and the lower guide portion 54 (L), but is not limited to this. For example, the tilt angle θ of the intermediate guide portion 54 (M) may also be set to the same as that of the upper guide portion 54 (H) and the lower guide portion 54 (L). Figure 5 The tilt angle θ of the lower guide portion 50 (L) included in the guide surface 50 is the same value. The tilt angle θ of the lower guide portion 54 (L) can also be set to a value different from the tilt angle θ of the middle guide portion 54 (M). In addition, the tilt angles of the upper guide portion 54 (H), the middle guide portion 54 (M) and the lower guide portion 54 (L) can each be set to different values ​​in a stepwise manner.

[0101] As another example, the tilt angle θ of the intermediate guide 54 (M) can also be set to be the same as that of the intermediate guide 54 (M). Figure 5 The tilt angle θ of the upper guide portion 50 (H) included in the guide surface 50 is the same value, and the tilt angle θ of the upper guide portion 54 (H) and the lower guide portion 54 (L) is set to, for example, the same as... Figure 5 The tilt angle θ of the lower guide portion 50 (L) included in the guide surface 50 is the same. Of course, the tilt angle of the upper guide portion 54 (H) can also be different from the tilt angle θ of the lower guide portion 54 (L).

[0102] As a further variation of the guide surface 50, it can also be constructed as a multi-stage guide section, such as four or five stages. Thus, during the scavenging stroke, the direction of the scavenging gas can be changed in multiple stages on the horizontal plane. Furthermore, as another variation 56 of the guide surface 50, it can also be as follows... Figure 12 , Figure 13 As shown in the diagram, it consists of curved, continuously variable guide surfaces. Figure 13 It is along Figure 12 A cross-sectional view along line XIII-XIII. Therefore, during the scavenging stroke, the direction of the scavenging gas can be changed steplessly on the horizontal plane.

[0103] The above describes an embodiment of applying the present invention to a stratified scavenging engine. However, the present invention can also be applied to a two-stroke engine in which the scavenging gas does not include pilot air, or to an engine in which the pre-compressed mixture in the crankcase 12 is used as the scavenging gas.

[0104] Furthermore, the present invention can be ideally applied to two-stroke engines that employ a fuel injection device instead of a carburetor 28. For example, in the case of applying the present invention to a direct-injection two-stroke engine, the pre-compressed air in the crankcase is used as the scavenging gas. By applying the present invention to the aforementioned direct-injection two-stroke engine, the scavenging efficiency within the cylinder can be improved.

[0105] The following is for reference Figures 14 to 18 The following describes a variation of the variable scavenging port 16 (ch) and the upper end of the variable scavenging passage 14 (ch) connected thereto, in which the present invention is applied. It goes without saying that these variations can also be applied to layered scavenging engines and engines that use a pre-compressed mixture in the crankcase 12 as the scavenging gas. Referring to the above… Figure 3 In the above embodiments, the present invention is applied to the upper end of the scavenging passage 14 connected to the second scavenging port 16 (ex2) on the exhaust side, but it can also be replaced by other methods, such as... Figure 14 As illustrated, the invention is applied to the upper end of the scavenging passage 14 (ch) connected to the first exhaust port 16 (ex1) on the exhaust side, which is opposite to the second scavenging port 16 (ex2) on the exhaust side. As a further variation, the invention can also be applied to the upper end of the scavenging passage 14 connected to the first scavenging port 16 (in1) or the second scavenging port 16 (in2) on the intake side, instead of the first scavenging port 16 (ex1) or the second scavenging port 16 (ex2) on the exhaust side.

[0106] Figure 15 An example is shown where the invention is applied to the upper end of the scavenging passage 14 (ch) connected to the second scavenging port 16 (ex2) on the exhaust side and the upper end of the scavenging passage 14 (ch) connected to the first scavenging port 16 (in1) on the intake side. As a variation, the invention can also be applied to the upper end of the scavenging passage 14 connected to the first scavenging port 16 (ex1) on the exhaust side and the upper end of the scavenging passage 14 connected to the second scavenging port 16 (in2) on the intake side.

[0107] Figure 16 An example is shown where the invention is applied to the upper end of a scavenging passage 14 (ch) connected to a second scavenging port 16 (ex2) on the exhaust side of a cylinder and to the upper end of a scavenging passage 14 (ch) connected to a second scavenging port 16 (in2) on the intake side. As a variation, the invention can also be applied to the upper end of a scavenging passage 14 connected to a first scavenging port 16 (ex1) on the exhaust side and to the upper end of a scavenging passage 14 connected to a first scavenging port 16 (in1) on the intake side.

[0108] Figure 17 An example is shown where the invention is applied to the upper end of a scavenging passage 14 (ch) connected to a first scavenging port 16 (ex1) and a second scavenging port 16 (ex2) opposite to each other on the exhaust side of the air cylinder. As a variation, the invention is applied to the upper end of a scavenging passage 14 connected to a first scavenging port 16 (in1) and a second scavenging port 16 (in2) opposite to each other on the intake side of the air cylinder.

[0109] The invention can also be applied to the upper end of each scavenging passage 14 that is connected to three of the four scavenging ports 64 included in the air cylinder, excluding one of them. Figure 18 An example is shown of applying the invention to the upper end of a scavenging passage 14 (ch) connected to three scavenging ports 16 (ch) other than the scavenging passage 14, which is exemplarily connected to the first scavenging port 16 (in1) on the intake side. A scavenging port 16 to which the invention is not applied may also be the second scavenging port 16 (in2) on the intake side, the first scavenging port 16 (ex1) on the exhaust side, or the second scavenging port 16 (ex2) on the exhaust side.

[0110] This invention can be ideally applied to a dual-flow scavenging engine that includes a scavenging port 16 on each side of the air cylinder. Figure 19 An example is shown of applying the invention to the upper end of a scavenging passage 14 connected to a scavenging port 16 (2) located on one side of the air cylinder. Figure 20 The invention is shown applied to the upper end of the scavenging passage 14, which is connected to the scavenging ports 16(1) and 16(2) located on both sides of the air cylinder.

[0111] exist Figure 17 , Figure 18 , Figure 20 In the illustrated example, the exhaust-side scavenging ports 16(ex1), 16(ex2), 16(1), and 16(2) that are opposite to each other are variable scavenging ports 16(ch) associated with the variable scavenging passage 14(ch) of the present invention, but if we consider... Figure 17Taking an example as an illustration, in order to prevent the scavenging gas flow 42 (1) discharged from the first scavenging port 16 (ex1) on the exhaust side from colliding with the scavenging gas flow 42 (2) discharged from the second scavenging port 16 (ex2) on the exhaust side, it is preferable to set the inclination angle θ (ex-H1) of the upper guide surface 50 (H) associated with the first scavenging port 16 (ex1) and the inclination angle θ (ex-H2) of the upper guide surface 50 (H) associated with the second scavenging port 16 (ex2) on the exhaust side to different values. With the above structure, the scavenging gases discharged from the scavenging ports 16 that are opposite to each other are prevented from colliding with each other and short-circuiting to the exhaust port 22. After scavenging in the combustion chamber while maintaining their respective flow paths, the scavenging gases discharged from each scavenging port 16 flow to the exhaust port 22.

[0112] Above, refer to Figure 15 , Figure 16 The above description relates to the upper guide section 50 (H), but the same applies to the lower guide section 50 (L).

[0113] As shown in the accompanying drawings, the aforementioned guide surfaces 50(H), 50(L), 54(H), 54(M), and 54(L) are composed of surfaces extending in a straight line, but they may also be composed of surfaces that are curved when viewed from above. Furthermore, the surface shape of at least one of the guide surfaces 50(H), 50(L), 54(H), 54(M), and 54(L) may also be a curved surface shape comprising multiple segmented surfaces. If we were to describe the curved surface shape marked with reference numeral "58" for the aforementioned segmented surfaces, then... Figure 21 , Figure 22 An example is shown consisting of two dividing faces 58(1) and 58(2), but it is merely an example and can also consist of more than three dividing faces.

[0114] Figure 21 An example is shown where the included angle α1 between the first dividing surface 58(1) and the second dividing surface 58(2), i.e., the angle formed by the first dividing surface 58(1) and the second dividing surface 58(2) towards the interior of the cylinder 4, is an acute angle. Figure 22 This illustrates an example where the included angle α2 between the first dividing surface 58(1) and the second dividing surface 58(2), i.e., the angle formed by the first dividing surface 58(1) and the second dividing surface 58(2) towards the interior of the cylinder 4, is an obtuse angle. Figure 21 , Figure 22 The guide surfaces 50(H), 50(L), 54(H), 54(M), and 54(L) formed by the first dividing surface 58(1) and the second dividing surface 58(2) are shown in the example. Figure 21 , Figure 22 As shown by the blank arrows 42(1) and 42(2) in the diagram, it can expel scavenging gas in both directions.

Claims

1. A two-stroke engine, comprising: A piston, which is disposed in a cylinder, reciprocates between top dead center and bottom dead center and divides the combustion chamber; An exhaust port, which opens into the cylinder and is opened or closed by the piston, is used to discharge the burned gas from the combustion chamber; The crank chamber receives fresh air and pre-compresses it through the downward movement of the piston; as well as Multiple scavenging passages, which communicate the combustion chamber and the crankcase during the scavenging stroke, include scavenging ports for discharging pre-compressed fresh air in the crankcase as scavenging gas into the combustion chamber, the scavenging ports being opened or closed by the piston. The scavenging passage among the plurality of scavenging passages, which is connected to at least one of the scavenging ports, constitutes a variable scavenging passage. The upper end of the variable scavenging passage has a guide surface that defines the discharge direction of the scavenging gas from the variable scavenging port connected to the upper end of the variable scavenging passage in a horizontal plane. The horizontal plane is a horizontally expanding plane orthogonal to the plane that expands along the up-and-down movement of the piston. The guiding surface includes at least: a first guiding portion, which defines a first discharge direction of the scavenging gas; And a second guide portion, which defines a second discharge direction for the scavenging gas. As the scavenging stroke proceeds, the first guide and the second guide cause the direction of the scavenging gas to change from a first discharge direction to a second discharge direction on the horizontal plane. The first discharge direction points away from the exhaust side of the cylinder and is tangential to the inner wall of the cylinder. The second discharge direction points in the opposite direction to the exhaust port, that is, away from the tangential direction of the inner wall of the cylinder and shifted to the central part of the cylinder.

2. The two-stroke engine as described in claim 1, characterized in that, The guide surface has an upper guide portion and a lower guide portion. The upper guide portion forms the first guide portion. The lower guide portion forms the second guide portion. There is a stepped section between the upper guide section and the lower guide section. The first ejection direction is defined by the upper guide portion. The second ejection direction is defined by the lower guide portion. The stepped portion that forms the boundary between the upper guide portion and the lower guide portion is located in the middle part of the variable scavenging port in the vertical direction.

3. The two-stroke engine as described in claim 2, characterized in that, The guiding surface has a middle guiding portion, which defines the third discharge direction of the scavenging gas between the upper guiding portion and the lower guiding portion.

4. The two-stroke engine as described in claim 1, characterized in that, The guide surface is composed of multiple levels of guide sections in the vertical direction.

5. The two-stroke engine as described in claim 1, characterized in that, The scavenging path connected to one of the scavenging ports is a variable scavenging path.

6. The two-stroke engine as described in claim 1, characterized in that, The engine has four scavenging ports. The scavenging passage connected to at least one of the four scavenging ports is the variable scavenging passage.

7. The two-stroke engine as claimed in claim 1, wherein, The scavenging passage connected to one of the plurality of scavenging ports, except for at least one scavenging port, is the variable scavenging passage.

8. The two-stroke engine as described in claim 6 or 7, characterized in that, In order to prevent the scavenging gases emitted from the variable scavenging ports that are opposite each other from colliding, the direction of the scavenging gases emitted from the variable scavenging ports that are opposite each other is set.

9. The two-stroke engine as described in claim 1, characterized in that, All scavenging ports of the engine open at the same timing.

10. The two-stroke engine as claimed in claim 1, characterized in that, The guide surface of at least one of the variable scavenging passages included in the engine is formed by a scavenging passage forming cover subsequently installed on the cylinder block.

11. The two-stroke engine as claimed in claim 1, characterized in that, The two-stroke engine is a reverse scavenging engine.

12. The two-stroke engine as claimed in claim 1, characterized in that, The two-stroke engine is a stratified scavenging engine.

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