2-stroke engine

Abstract

To solve a problem of the blowout of a two-stroke engine.SOLUTION: An engine 2 of this embodiment is a 4-stream scavenging engine. Four scavenging ports 34 include: left-and-right first scavenging ports 34(lef-1), 34(ref-1) which are located at a side relatively separating from an exhaust port 22, and also located while opposing each other with a cylinder 4 sandwiched therebetween; and left-and-right second scavenging ports 34(lef-2), 34(ref-2) which are located at the exhaust port 22 side rather than the left-and-right first scavenging ports 34(lef-1), 34(ref-1), and also located while opposing each other with the cylinder 4 sandwiched therebetween. The opening timing of the two scavenging ports of a first group Diag-No.1 constituted of the second left-side scavenging port and the first right-side scavenging port, and having a diagonal relationship with respect to each other differs from the opening timing of the two scavenging ports of a second group Diag-No.2 constituted of the first left-side scavenging port and the second right-side scavenging port, and having a diagonal relationship with respect to each other.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a two-stroke engine for a work machine, and more particularly to an exhaust gas control technology. [Background technology]

[0002] In a traditional two-stroke engine, the mixture precompressed in the crankcase is supplied to the combustion chamber through a scavenging port that opens into the cylinder during the scavenging stroke. A two-stroke engine includes at least two pairs of scavenging ports. The pair of scavenging ports are arranged opposite each other across the cylinder and are opened and closed by the piston.

[0003] Two-stroke engines have a problem called "blow-by." "Blow-by" is a phenomenon in which part of the mixture supplied to the combustion chamber escapes from the exhaust port together with the exhaust gas. This "blow-by" is a well-known and important issue with two-stroke engines.

[0004] In order to overcome emission regulations that are becoming stronger every year, there have been proposed a four-stroke scavenging engine in which the number of scavenging ports is increased to four (two pairs of scavenging ports), a six-stroke scavenging engine in which the number of scavenging ports is increased to six (three pairs of scavenging ports) (Patent Document 1), and a stratified scavenging engine in which leading air is supplied before the supply of the mixture to the combustion chamber during the scavenging stroke (Patent Document 2).

[0005] Patent Document 3 points out the following problem with two-stroke engines. In a two-stroke engine, the mixture supplied to the combustion chamber from a pair of scavenging ports facing each other across the cylinder strongly collides in the center of the cylinder. This collision causes a shortcut phenomenon in which part of the mixture flows toward the exhaust port. Patent Document 3 points out that this shortcut phenomenon is the cause of the "blow-through" problem. Patent Document 3 also proposes arranging a shielding member in each of the first and second scavenging passages constituting one set of scavenging passages out of two sets of scavenging passages diagonally across the cylinder in a four-stroke scavenging engine. Here, the shielding member has a plurality of holes. In the scavenging stroke, the flow velocity of the mixture discharged into the combustion chamber from a scavenging passage in which a porous shielding member is arranged is slower than the flow velocity of the mixture discharged into the combustion chamber from a scavenging passage without a shielding member.

[0006] In a typical four-flow scavenging engine, the mixture gas supplied to the combustion chamber from two pairs of scavenging ports facing each other collides at the center of the cylinder. Unlike this typical four-flow scavenging engine, in the four-flow scavenging engine of Patent Document 3, a porous shielding member is arranged in two diagonally opposite scavenging ports among the four scavenging ports, thereby weakening the flow velocity of the mixture gas discharged from the scavenging ports. As a result, the collision of the mixture gas discharged from the two opposing scavenging ports is weakened, and the collision position is offset from the center of the cylinder. This can suppress the problem of "blow-by". However, even with this configuration, the mixture gas discharged from the two opposing scavenging ports still collides and reverses at a relatively early stage of the scavenging stroke, which causes the emission of unburned gas. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP Patent Publication No. 60-222521 [Patent Document 2] US 6,718,917 B2 [Patent Document 3] JP Patent No. 5060459 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a two-stroke engine that can overcome further emission regulations by suppressing the "blow-by" problem that is a problem with two-stroke engines. [Means for solving the problem]

[0009] The above technical problem is solved by the present invention. In a two-stroke engine, fresh air precompressed in the crankcase is supplied to the combustion chamber through the scavenging port during the scavenging stroke to perform scavenging. having at least four scavenge ports; The four scavenging ports include left and right first scavenging ports that are located relatively away from the exhaust port and opposed to each other across the cylinder, and left and right second scavenging ports that are located closer to the exhaust port than the left and right first scavenging ports and opposed to each other across the cylinder, This is achieved by providing a two-stroke engine characterized in that the opening timing of a first set of two scavenging ports in a diagonal relationship with each other, which are formed by the second left side scavenging port and the first right side scavenging port, is different from the opening timing of a second set of two scavenging ports in a diagonal relationship with each other, which are formed by the first left side scavenging port and the second right side scavenging port.

[0010] The effects and other objects of the present invention will become apparent from the following detailed description of the preferred embodiment of the present invention and its modified examples. [Brief description of the drawings]

[0011] [Figure 1] 1 is a vertical sectional view of a two-stroke engine of a first embodiment. FIG. [Diagram 2]FIG. 2 is a cross-sectional view of the four-stroke scavenging two-stroke engine of the first embodiment taken along line II-II in FIG. [Diagram 3] FIG. 3 is a cross-sectional view of the two-stroke engine of the first embodiment taken along line III-III in FIG. 2. [Figure 4] FIG. 2 is a diagram for explaining the concepts of "opposite" and "diagonal" used in the description of the present invention. [Diagram 5] FIG. 2 is a planar development view of four scavenging ports included in the four-stroke scavenging engine of the first embodiment. [Figure 6] FIG. 7 is an explanatory diagram of the operation of the two-stroke engine of the first embodiment, and is a diagram for explaining the state of the mixture (fresh air) entering the combustion chamber immediately after the first set of diagonal scavenging ports are opened ((II) in FIG. 6). [Figure 7] FIG. 7 is an explanatory diagram of the operation of the two-stroke engine of the first embodiment, and is a diagram for explaining the state of the mixture (fresh air) in the combustion chamber immediately after the first set of diagonal scavenging ports are opened and then the second set of diagonal scavenging ports are opened (FIG. 7(II)). [Figure 8] FIG. 8 is an explanatory diagram of the operation of the two-stroke engine of the first embodiment, and is a diagram for explaining the state of the mixture (fresh air) in the combustion chamber when the first set of diagonal scavenging ports and the second set of diagonal scavenging ports are both open and immediately before they are closed ((II) in FIG. 8). [Figure 9] FIG. 11 is a diagram for explaining modified examples of opening and closing timings of a first set of diagonal scavenging ports and a second set of diagonal scavenging ports. [Figure 10] FIG. 11 is a diagram for explaining a second modified example of the opening timing and closing timing of the first set of diagonal scavenging ports and the second set of diagonal scavenging ports. [Figure 11] FIG. 13 is a diagram for explaining a third modified example of the opening timing and closing timing of the first set of diagonal scavenging ports and the second set of diagonal scavenging ports. [Figure 12] FIG. 1 is a vertical sectional view of a two-stroke engine according to a second embodiment in which the present invention is applied to a stratified scavenging engine. [Figure 13]FIG. 13 is a diagram for explaining the positional relationship between the air port 102 and the mixture port 104 when the piston is located at the bottom dead center in the stratified scavenging engine of FIG. 12. [Figure 14] FIG. 11 is a vertical sectional view of a two-stroke engine according to a third embodiment in which a fuel injection valve is disposed in an intake passage instead of a carburetor. [Figure 15] FIG. 11 is a vertical sectional view of a two-stroke engine according to a fourth embodiment in which a fuel injection valve is arranged facing a crank chamber instead of a carburetor. [Figure 16] FIG. 2 is a diagram for explaining the diagonal relationship of six scavenging passages when the present invention is applied to a six-flow scavenging engine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figures 1 to 11 are diagrams for explaining a two-stroke engine 2 of a first embodiment and related modifications.

[0013] Figure 1 is a vertical cross-sectional view of a two-stroke engine 2, and Figure 2 is a cross-sectional view taken along line II-II in Figure 1. The illustrated two-stroke engine 2 is a small engine mounted in portable work machines such as brush cutters, chain saws, and blowers, and is an air-cooled single-cylinder engine.

[0014] Reference numeral 4 denotes a cylinder, and 6 denotes a spark plug (FIG. 1). A piston 8 is inserted into the cylinder 4 so as to be able to reciprocate freely, and a combustion chamber 10 is defined by the piston 8. The reciprocating motion of the piston 8 is transmitted to a crankshaft 14 by a connecting rod 12. The crankshaft 14 converts the reciprocating motion of the piston 8 into rotational motion and outputs it. As is well known, the crankshaft 14 is housed in a crank chamber 16.

[0015] With reference to Fig. 1, reference numeral 20 denotes an intake port, and reference numeral 22 denotes an exhaust port. The intake port 20 and the exhaust port 22 are opened and closed by a piston 8. An intake passage 24 is connected to the intake port 20. The intake passage 24 has an air cleaner 26 at its upstream end, and a carburetor 28 next to it. The carburetor 28 draws up fuel F from a fuel tank 30 to generate an air-fuel mixture, and supplies the generated air-fuel mixture to the intake port 20.

[0016] The air-fuel mixture is supplied to the crank chamber 16 through the intake port 20. The air-fuel mixture (fresh air) in the crank chamber 16 is pre-compressed by the downward movement of the piston 8. The air-fuel mixture (fresh air) pre-compressed in the crank chamber 16 is supplied to the combustion chamber 10 through a scavenging passage 32 (FIG. 2) during the scavenging stroke.

[0017] 2, the scavenging passage 32 is configured as a passage extending in the vertical direction. A lower end 32a of the scavenging passage 32 opens to the crank chamber 16. An upper end of the scavenging passage 32 forms a scavenging port 34, which communicates with the combustion chamber 10. The scavenging port 34 is opened and closed by the piston 8. The structures of the scavenging passage 32 and the piston-opening / closing type scavenging port 34 are well known, so a detailed description thereof will be omitted.

[0018] Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. The two-stroke engine 2 of the first embodiment is a four-flow scavenging engine having four scavenging ports 34, and is a well-known Schnirle engine. When the cylinder 4 is viewed in plan, two scavenging ports 34 are located on one side of a virtual cylinder center line iL connecting the intake port 20 and the exhaust port 22, and two scavenging ports 34 are located on the other side.

[0019] In order to explain the present invention, it is necessary to identify each of the four scavenging ports 34. Each scavenging port 34 is identified as follows. The two scavenging ports 34 located on one side of the cylinder center line iL are called "right scavenging ports" and (rig) is added to the reference symbol 34. Among the two right scavenging ports 34 (rig), the scavenging port located on the side away from the exhaust port 22, i.e., the side of the intake port 20, is called "first right scavenging port" and (rig-1) is added to the reference symbol 34. Among the two right scavenging ports 34 (rig), the scavenging port located on the side of the exhaust port 22 is called "second right scavenging port" and (rig-2) is added to the reference symbol 34.

[0020] Similarly, the two scavenging ports 34 located on the other side of the cylinder center line iL are called "left scavenging ports" and (lef) is added to the reference symbol 34. Of the two left scavenging ports 34(lef), the scavenging port located on the side away from the exhaust port 22, i.e., on the side of the intake port 20, is called the "first left scavenging port" and (lef-1) is added to the reference symbol 34. Of the two left scavenging ports 34(lef), the scavenging port located on the side of the exhaust port 22 is called the "second left scavenging port" and (lef-2) is added to the reference symbol 34.

[0021] The first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) are positioned opposite each other across the cylinder 4. The second right scavenging port 34 (rig-2) and the second left scavenging port 34 (lef-2) are positioned opposite each other across the cylinder 4.

[0022] As described above, the two-stroke engine 2 of the first embodiment is a four-flow scavenging engine with reference to Fig. 4. A first right scavenging port 34 (rig-1) and a first left scavenging port 34 (lef-1) are located on the side away from the exhaust port 22, i.e., on the intake port 20 side. Also, a second right scavenging port 34 (rig-2) and a second left scavenging port 34 (lef-2) are located on the exhaust port 22 side.

[0023] 1 and 3, the first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) facing each other have the same rectangular shape when viewed from the front. The second right scavenging port 34 (rig-2) and the second left scavenging port 34 (lef-2) also have the same rectangular shape when viewed from the front.

[0024] The shapes of the first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) in front view and the shapes of the second right scavenging port 34 (rig-2) and the second left scavenging port 34 (lef-2) in front view are not limited to rectangular and may be arbitrary. In addition, the shapes of the first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) when cross-sectionally formed may be substantially rectangular or substantially triangular. Similarly, the shapes of the second right scavenging port 34 (rig-2) and the second left scavenging port 34 (lef-2) when cross-sectionally formed may be substantially rectangular or substantially triangular.

[0025] Regarding the cross-sectional shape of the first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) and / or the second right scavenging port 34 (rig-2) and the second left scavenging port 34 (lef-2), the fact that the shape may be substantially triangular as described above has two meanings. One is a triangle with the apex on the cylinder 4 side, and the other is a triangle with the base on the cylinder 4 side.

[0026] In the four-flow scavenging engine 2 of this embodiment, the first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) facing each other are basically configured to have the same shape, and the mixture discharged from the first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) is directed in a direction away from the exhaust port 20.

[0027] In the four-flow scavenging engine 2 of this embodiment, the opening timing of the first right scavenging port 34 (rig-1) and the opening timing of the first left scavenging port 34 (lef-1) facing each other are different, but in the past, the opening timing of the first left and right scavenging ports 34 (rig-1), 34 (lef-1) were synchronized. In this conventional example, as the piston 8 descends, the first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) gradually open, and as the opening degree increases, the mixture starts to be discharged from both of these scavenging ports 34 (rig-1), 34 (lef-1) simultaneously. In this conventional example, similarly to the four-flow scavenging engine 2 of the present embodiment, when the opposing right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) are provided substantially symmetrically with respect to the cylinder center line iL, the direction of the first mixture discharged from the first right scavenging port 34 (rig-1) which changes with the descent of the piston 8 and the direction of the second mixture discharged from the first left scavenging port 34 (lef-1) are line-symmetric, so that the first mixture and the second mixture collide in the first region on the cylinder center line iL described above. In addition, even if the first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) facing each other are not exactly symmetrical with respect to the cylinder center line iL, if the opening timings of the first left and right scavenging ports 34 (rig-1) and 34 (lef-1) are synchronized, the mixture discharged from both scavenging ports collides at a position slightly shifted from the cylinder center line iL. The mixture colliding at either position reverses its direction from the collision position and short-circuits to the exhaust port 22, which is the cause of the conventional unburned gas emission.

[0028] The same is true for the second right scavenging port 34 (rig-2) and the second left scavenging port 34 (lef-2) facing each other, and the direction of the third mixture discharged from the second right scavenging port 34 (rig-2) and the direction of the fourth mixture discharged from the second left scavenging port 34 (lef-2), which change with the downward movement of the piston 8, are symmetrical with respect to the cylinder center line iL described above. Therefore, it is basically set so that the third mixture and the fourth mixture collide in a second region different from the above-mentioned first region.

[0029] 3, the orientations of the first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) may be set so as to collide with each other at the center of the cylinder 4, but as shown in FIG 3, the orientations of the first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) may be slightly different from each other so as not to collide with each other at the center of the cylinder 4. Similarly, the orientations of the second right scavenging port 34 (rig-2) and the second left scavenging port 34 (lef-2) may be slightly different from each other so as not to collide with each other at the center of the cylinder 4, as shown in FIG 3.

[0030] The above is the basic design guideline for the four scavenging ports 34 of a general and traditional four-flow scavenging engine. Also, it is a basic design guideline that the timing at which the two scavenging ports 34 of a pair facing each other open is the same.

[0031] The two-stroke engine 2 of the first embodiment respects the basic design guidelines of the traditional four-stroke scavenging engine described above, and in particular, changes the settings of the opening timing of each scavenging port 34 under the classification of the first and second sets of opposing scavenging ports (Opos-No.1), (Opos-No.2).

[0032] As described above, the two-stroke engine 2 of the first embodiment is a four-flow scavenging engine, and with reference to FIG. 4, there are two sets of scavenging ports 34 opposed to each other as follows: (1) The first pair of opposing scavenging ports (Opos-No.1): The first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1) form a first set of opposed scavenging ports Opos-No. 1. (2) The second pair of opposing scavenging ports (Opos-No.2): The second right scavenging port 34 (rig-2) and the second left scavenging port 34 (lef-2) form a second set of opposed scavenging ports Opos-No. 2.

[0033] The concept of "diagonal" necessary for explaining the present invention will be specifically explained. There are two sets of scavenging ports 34 that are diagonally related to each other as follows. (1) The first pair of diagonal scavenging ports (Diag-No.1): The second left scavenging port 34 (lef-2) and the first right scavenging port 34 (rig-1) form a first set of diagonal scavenging ports Diag-No. 1. (2) The second pair of diagonal scavenging ports (Diag-No.2): The first left scavenging port 34 (lef-1) and the second right scavenging port 34 (rig-2) form a second set of diagonal scavenging ports Diag-No. 2.

[0034] FIG. 5 is a diagram showing the four scavenging ports 34 by developing the cylinder 4 in a plane, and is a diagram for explaining the opening and closing timing of the first set of diagonal scavenging ports Diag-No.1 and the second set of diagonal scavenging ports Diag-No.2. "Up" in FIG. 5 indicates the direction toward the piston top dead center, and "Down" indicates the direction toward the piston bottom dead center. As can be seen from FIG. 5, the first set of diagonal scavenging ports Diag-No.1 opens earlier than the second set of diagonal scavenging ports Diag-No.2.

[0035] As described above, the two-stroke engine 2 of the first embodiment has four scavenging ports 34, which are generally rectangular in front view. Referring to the second left scavenging port 34 (lef-2) in Fig. 5 as an example, the second left scavenging port 34 (lef-2) has an upper edge 34a and a lower edge 34b that both extend in a generally horizontal direction, and the second left scavenging port 34 (lef-2) is opened and closed by the piston 8 passing over the upper edge 34a and the lower edge 34b.

[0036] The upper edge 34a of the first group of scavenging ports Diag-No.1 is located at a height level Δt above the upper edge 34a of the second group of scavenging ports Diag-No.2. Therefore, as described above, the first group of scavenging ports Diag-No.1 opens at an earlier timing than the second group of scavenging ports Diag-No.2. By making the opening timings of the first group Diag-No.1 and the second group Diag-No.2 different in this way, the first pressure of the mixture (fresh air) when the first group Diag-No.1 opens and fresh air enters the combustion chamber 10 from the first group Diag-No.1 can be made different from the second pressure of the mixture (fresh air) when the second group Diag-No.2 opens and fresh air enters the combustion chamber 10 from the second group Diag-No.2.

[0037] In addition, with respect to the upper edges 34a extending in the horizontal direction of the four rectangular scavenging ports 34, the upper edges 34a of the second left scavenging port 34 (lef-2) and the first right scavenging port 34 (rig-1) constituting the first set of scavenging ports Diag-No.1 are located at the same height level. Therefore, the opening timing of the first set of scavenging ports 34 (lef-2), 34 (rig-1) is the same, and therefore the first set of scavenging ports Diag-No.1 opens synchronously.

[0038] Similarly, the first left-side scavenging port 34 (lef-1) and the second right-side scavenging port 34 (rig-2) constituting the second set of scavenging ports Diag-No.2 have their upper edges 34a located at the same height level, so the opening timings of these second set of scavenging ports 34 (lef-1), 34 (rig-2) are the same, and therefore the second set of scavenging ports Diag-No.2 open synchronously.

[0039] As a variant, when the first set of scavenging ports Diag-No.1 are opened synchronously, the opening timings of the second set of scavenging ports 34(lef-1), 34(rig-2) do not have to be perfectly synchronized. Similarly, when the second set of scavenging ports Diag-No.2 are opened synchronously, the opening timings of the first set of scavenging ports 34(lef-2), 34(rig-1) do not have to be perfectly synchronized.

[0040] The timing of closing the four scavenging ports 34 will be described. With reference to Fig. 5, the lower edges 34b of the scavenging ports of the first and second sets Diag-No.1 and Diag-No.2, i.e., the four scavenging ports 34, are set to the same height level. Therefore, the four scavenging ports 34 included in the two-stroke engine 2 of the first embodiment are set to close synchronously. Therefore, the opening height of the two scavenging ports of the first set Diag-No.1 is (Opening top and bottom length dimensions) is the opening height of the two scavenging ports of the second set of scavenging ports Diag-No.2 (Opening top and bottom length dimensions) than long .

[0041] In the example shown in FIG. 5, the second left scavenging port 34 (lef-2) and the first right scavenging port 34 (rig-1) are defined as the first set of scavenging ports Diag-No. 1, but this may be defined as a second set, and the second right scavenging port 34 (rig-2) and the first left scavenging port 34 (lef-1) may be defined as the first set of scavenging ports Diag-No. 1.

[0042] The term "synchronization" mentioned above is not limited to perfect synchronization in this specification. In the case of perfect synchronization, the term "perfect synchronization" is used. The meaning that the scavenging ports Diag-No.1 of the first set open synchronously includes the meaning that the scavenging ports Diag-No.1 of the first set open completely synchronously and the meaning that they open at approximately the same timing. The meaning that the scavenging ports Diag-No.2 of the second set open synchronously includes the meaning that the scavenging ports Diag-No.2 of the second set open completely synchronously and the meaning that they open at approximately the same timing. Here, the meaning that the opening timing of the first set and the opening timing of the second set are different from each other within a range where the opening timing can be distinguished and does not cause confusion in this distinction. It should be understood that the above explanation also applies to the "synchronization" used in the closing timing of the scavenging ports Diag-No.1 of the first set and the closing timing of the scavenging ports Diag-No.2 of the second set.

[0043] The operation of the two-stroke engine 2 of the embodiment will be described with reference to Figs. 6 to 8. Fig. 6 shows the timing when the scavenging ports 34 start to open during the downward movement of the piston 8 (II), and the operation at that time is shown in (I). In Fig. 6 (II), the line Ln(1) indicates the upper edge position of the piston 8. In the scavenging stroke, the first diagonally positioned right scavenging port 34 (rig-1) and the second diagonally positioned left scavenging port 34 (lef-2) start to open first. In other words, the first diagonally positioned scavenging port 34 (rig-1) and the first diagonally positioned scavenging port 34 (lef-2) start to open. The second diagonally positioned right scavenging port 34 (rig-2) and the first diagonally positioned left scavenging port 34 (lef-1) remain closed.

[0044] As shown in FIG. 6(I), the first mixture discharged from the first right scavenging port 34 (rig-1) and the second mixture discharged from the second left scavenging port 34 (lef-2) flow into the first inflow area first area offset from the center of the cylinder 4. The first right scavenging port 34 (rig-1) and the second left scavenging port 34 (lef-2) are not opposed to each other across the cylinder 4. Since they are diagonally positioned, the distances that they each take to reach the first inflow area first area can be lengthened. Here, the initial inflow area is the first inflow area first area offset from the center line iL of the cylinder 4. Since the first mixture from the first right scavenging port 34 (rig-1) and the second mixture from the second left scavenging port 34 (lef-2) in a diagonal relationship flow into this first inflow area first area, these first and second mixtures do not collide, and the first inflow area first area appears at a position offset from the center of the cylinder 4 as described above. In this first inflow area first area, the first mixture discharged from the first right scavenging port 34 (rig-1) and the second mixture discharged from the second left scavenging port 34 (lef-2) do not collide at the beginning of scavenging because the distances they take to reach each other are long. When the first mixture and the second mixture face each other, the mixtures from the two scavenging ports located apart from each other merge gently, generating a tumble flow in the combustion chamber, and the combustion chamber can be scavenged evenly. In addition, since the collision position is offset from the center, even if the flow is reversed at that position, a short circuit to the exhaust port does not occur.

[0045] At this time, the first left scavenging port 34 (lef-1) and the second right scavenging port 34 (rig-2) are not open, so the scavenging flow that flows in first can flow in while maintaining the designed desired directivity without being affected by the scavenging flow from the adjacent scavenging ports. In detail, in FIG. 6(I), if the first left scavenging port 34 (lef-1) is also opened in synchronization with the second left scavenging port 34 (lef-2), the scavenging flow that flows in from the second left scavenging port 34 (lef-2) cannot approach or reach the wall surface on the intake side due to the presence of the scavenging flow from the first left scavenging port 34 (lef-1). In addition, the scavenging flow from the first left scavenging port 34 (lef-1) comes into contact with the second left scavenging port 34 (lef-2) and is deflected toward the exhaust side, causing a short circuit to the exhaust port. In this embodiment, the adjacent scavenging ports on the left and right sides open at different timings, so that the directivity of the second left scavenging port 34 (lef-2) and the first right scavenging port 34 (rig-1), which are introduced first into the cylinder, is maintained, and there is no influence of deflection caused by contact between adjacent scavenging flows, so that it is possible to more reliably prevent unburned gas from short-circuiting to the exhaust port 22.

[0046] FIG. 7 shows a state when the piston 8 has descended a predetermined distance from the state shown in FIG. 6, and shows a state when the second right scavenging port 34 (rig-2) and the first left scavenging port 34 (lef-1) located at the second diagonal start to open. The line Ln(2) shows the upper edge position of the piston 8. In this state, all of the four scavenging ports 34 are open. That is, the first and second pairs Opos-No.1 and Opos-No.2 facing each other are open. The first and third mixtures discharged from the first facing pair Opos-No.1 (the first right scavenging port 34 (rig-1) and the first left scavenging port 34 (lef-1)) intersect in the second inflow area ((I) in FIG. 7), but since it is not yet the beginning of the scavenging stroke, even if a collision occurs, the collision speed is slow, and reversal from the collision position and short circuit to the exhaust port 22 are unlikely to occur. In addition, since the first mixture gas discharged from the first right-side scavenging port 34 (rig-1) has already flowed into the second inflow area, the second inflow area is generated at a position offset from the center of the cylinder 4.

[0047] In addition, the second and fourth mixture gases discharged from the second opposing pair Opos-No.2 (the second right scavenging port 34 (rig-2) and the second left scavenging port 34 (lef-2)) intersect in the third inflow area (FIG. 7(I)). However, since the second mixture gas discharged from the second left scavenging port 34 (lef-2) has already flowed in, the third inflow area (third area) occurs at a position offset from the center of the cylinder 4. Furthermore, the collision in the third inflow area (third area) is weak because it is not at the beginning of the scavenging stroke.

[0048] In this way, the mixture introduced from the second opposing pair also merges gently with the mixture from the two distant scavenging ports at a position offset from the center. In addition, collision between the first and second pairs is avoided, so that tumble flows with a time difference are constantly generated in the combustion chamber during the scavenging stroke, and the combustion chamber can be scavenged evenly. By synchronizing the opening timing of the opposing scavenging ports and separating the opening timings in the first and second pairs, it is possible to prevent unburned gas from short-circuiting to the exhaust port at the beginning of scavenging, and to generate tumble flows in the combustion chamber one after another, scavenging the burnt gas in the entire combustion chamber evenly and replacing it with fresh air sufficiently.

[0049] Figure 8 shows a state where the piston 8 has further descended from the state shown in Figure 7 and the four scavenging ports 34 are about to close. The line Ln(3) shows the upper edge position of the piston 8. In this state, all four scavenging ports 34 are open, and the air-fuel mixture is discharged from each scavenging port 34 into the combustion chamber.

[0050] The air-fuel mixture discharged from each scavenging port 34 is shown by an arrow, and when looking at this figure, it looks like the air-fuel mixture discharged from the scavenging ports 34 (rig-1) and 34 (lef-1) of the first opposing pair Opos-No.1 that are opposed to each other mixes. Similarly, the air-fuel mixture discharged from the scavenging ports 34 (rig-2) and 34 (lef-2) of the second opposing pair Opos-No.2 that are opposed to each other mixes. However, one of the scavenging ports of the first opposing pair Opos-No.1 that are opposed to each other opens first. This time difference creates a difference in the flow speed of the air-fuel mixture (fresh air) discharged from the two scavenging ports of the first opposing pair Opos-No.1. Therefore, the air-fuel mixture discharged from the two scavenging ports of the first opposing pair Opos-No.1 does not merge at the center of the cylinder 4. Similarly, one of the scavenging ports of the second opposing group Opos-No.2 opens first, and the other opens later. This time difference creates a difference in the flow speed of the mixture (fresh air) discharged from the two scavenging ports of the second opposing group Opos-No.2. Therefore, the mixture discharged from the two scavenging ports of the second opposing group Opos-No.2 does not merge in the center of the cylinder 4. In this way, even when the four scavenging ports are open at the same time, there is no collision or merger of the opposing scavenging flows in the center of the cylinder 4, and no interference with each other's directivity due to adjacent scavenging flows.

[0051] Of the two scavenging ports constituting the first pair Opos-No.1 facing each other, one opens early and the other opens late. The flow velocity of the mixture (fresh air) discharged from the scavenging port 34 that opens relatively early into the combustion chamber 10 is fast. The flow velocity of the mixture (fresh air) discharged from the scavenging port 34 that opens late is relatively slow. Next, as the opening area of ​​the two scavenging ports 34 constituting the first pair Opos-No.1 increases, the pressure of the mixture discharged from the scavenging port 34 decreases, and therefore the flow velocity of the mixture discharged from the two scavenging ports 34 slows down.

[0052] Similarly, one of the two scavenging ports constituting the second opposing pair Opos-No.2 opens earlier and the other opens later. The flow velocity of the mixture (fresh air) discharged from the scavenging port 34 that opens earlier into the combustion chamber 10 is fast. The flow velocity of the mixture (fresh air) discharged from the scavenging port 34 that opens later is relatively slow. Next, when the opening area of ​​the two scavenging ports 34 constituting the second opposing pair Opos-No.2 increases, the pressure of the mixture discharged from the scavenging port 34 decreases, and therefore the flow velocity of the mixture discharged from the two scavenging ports 34 slows down.

[0053] As described above, in the two sets of diagonal scavenging ports 34, the flow velocity of the mixture discharged from the diagonal scavenging ports 34 of the second diagonal set Diag-No2, which starts to open later, is slower than the flow velocity of the mixture discharged from the first diagonal set Diag-No1, which starts to open earlier. Due to the relative speed difference between the flow velocities of the mixture (fresh air) discharged from the first and second diagonal sets Diag-No1 and Diag-No2, it is possible to prevent the mixture (fresh air) discharged from the four scavenging ports 34 from strongly colliding with each other at the center of the cylinder 4.

[0054] As described with reference to Fig. 5, the height levels of the lower edges 34b of the four scavenging ports 34 are the same. In other words, the opening height of the diagonal scavenging ports 34 of the second diagonal set Diag-No2, which starts to open later, is smaller than the opening height of the scavenging ports 34 of the first diagonal set Diag-No1, which starts to open earlier. As a result, the pressure of the mixture discharged from the diagonal scavenging ports 34 of the second diagonal set Diag-No2, which starts to open later, can be maintained at a relatively high value, so that the flow velocity of the mixture discharged from the scavenging ports 34 of the second diagonal set Diag-No2 can be maintained at a relatively high level.

[0055] Due to the above-mentioned action, according to the two-stroke engine 2 of the embodiment, the horizontal angle and flow velocity of the mixture (fresh air) entering the combustion chamber 10 when each scavenging port 34 is opened are different, and this makes it possible to suppress the occurrence of a shortcut phenomenon in which a part of the mixture (fresh air) flows toward the exhaust port 22 due to collision of the mixture (fresh air) entering the combustion chamber 10 from the four scavenging ports 34. Then, the burnt gas in the cylinder 4 can be scavenged by the mixture (fresh air) entering the combustion chamber 10 from the four scavenging ports 34. Note that since there are four scavenging ports, it is not necessary to provide four scavenging passages corresponding to the scavenging ports. The same action can be obtained as long as the mixtures are joined by fewer than four passages on the crankcase side and four ports are provided at the opening position to the cylinder.

[0056] We actually built a prototype of a two-stroke engine 2 and evaluated its performance, and obtained the following results. (1) Amount of HC in exhaust gas: A reduction effect of approximately 3.1% to approximately 5.9% was confirmed compared to our company's general and traditional four-stroke scavenging engine. (2)Improved power output: Reducing the amount of blow-by increases power output. Compared to our company's general and traditional four-stroke scavenging engines, we were able to confirm an improved power output of approximately 2.1% to 2.8%.

[0057] In addition, an analysis of the flow of the mixture discharged from the scavenging port confirmed that a tumble flow was generated within the combustion chamber 10.

[0058] 9 to 12 show modified examples of the opening and closing timings of the first set of diagonally related scavenging ports Diag-No.1, and also show modified examples of the opening and closing timings of the second set of diagonally related scavenging ports Diag-No.2.

[0059] As can be seen from Fig. 9, the opening timing of the second diagonal scavenging port Diag-No.2 may be synchronized with the closing timing of the first diagonal scavenging port Diag-No.1. That is, when the first right scavenging port 34 (rig-1) and the second left scavenging port 34 (left-2) of the first diagonal set Diag-No.1 are closed, the second right scavenging port 34 (rig-2) and the first left scavenging port 34 (left-1) of the second diagonal set Diag-No.2 may be opened.

[0060] 10, the closing timing of the scavenging port Diag-No.2 of the second diagonal group may be delayed from the closing timing of the scavenging port Diag-No.1 of the first diagonal group. That is, after the first right scavenging port 34 (rig-1) and the second left scavenging port 34 (left-2) of the first diagonal group Diag-No.1 are closed, the second right scavenging port 34 (rig-2) and the first left scavenging port 34 (left-1) of the second diagonal group Diag-No.2 may be closed.

[0061] 11, the closing timing of the diagonal scavenging port Diag-No.2 of the second set may be earlier than the closing timing of the diagonal scavenging port Diag-No.1 of the first set. That is, the second right scavenging port 34 (rig-2) and the first left scavenging port 34 (left-1) of the second diagonal set Diag-No.2 may be closed before the first right scavenging port 34 (rig-1) and the second left scavenging port 34 (left-2) of the first diagonal set Diag-No.1 are closed.

[0062] While the engine 2 in which the present invention is applied to a traditional two-stroke engine has been described as the first embodiment, the present invention is not limited to this.

[0063] 12 and 13 show a second embodiment in which the present invention is applied to a stratified scavenging engine. In the description of the stratified scavenging engine 100 of the second embodiment, the same elements as those of the two-stroke engine 2 of the first embodiment are given the same reference numerals, and the description thereof will be omitted.

[0064] The stratified scavenging engine 100 includes an air port 102 and a mixture port 104 in the cylinder 4. Fig. 13 is a diagram for explaining the positional relationship between the air port 102 and the mixture port 104 when the piston 8 is located at the bottom dead center. Air is supplied to the air port 102 from the intake system, and the air supplied to the air port 102 is supplied as leading air to the upper part of the scavenging passage 34 (Fig. 2) through a piston groove 8a formed on the circumferential surface of the piston 8. On the other hand, the mixture is supplied to the mixture port 104 from the intake system, and the mixture is supplied to the crank chamber 16 through the mixture port 104.

[0065] The intake system of the stratified scavenging engine 100 includes a carburetor 28 connected to an air filter 26, and an intake pipe 106 connected to the carburetor 28. The carburetor 28 includes a throttle valve 110 and a choke valve 112, both of which are butterfly valves. When the throttle valve 110 and the choke valve 112 are both fully open in the carburetor 28, an air passage 114 and a mixture generation passage 116 are formed within the carburetor 28.

[0066] The intake pipe 106 has a partition wall 120, which defines an air passage 122 and a mixture passage 124. The air passage 114 in the carburetor 28 communicates with the air passage 122 of the intake pipe 106. Air filtered by the air filter 26 is supplied to the air port 102 through the air passage 114 and the air passage 122.

[0067] On the other hand, the upstream end of the mixture passing passage 124 of the intake pipe 106 communicates with the mixture generating passage 116 in the carburetor 28, and the downstream end of the mixture passing passage 124 communicates with the crank chamber 16. The mixture generated in the mixture generating passage 116 in the carburetor 28 is supplied to the crank chamber 16.

[0068] In the scavenging stroke of the stratified scavenging engine 100, first, lead air is supplied to the combustion chamber 10 from the scavenging port 34, and then the mixture precompressed in the crank chamber 16 is supplied to the combustion chamber 10.

[0069] Two-stroke engines 200, 300 of the third and fourth embodiments shown in Figures 14 and 15 are equipped with a fuel injection valve 202 instead of the carburetor 28. In the two-stroke engine 200 of the third embodiment shown in Figure 14, the fuel injection valve 202 is incorporated in the intake passage 24. In the two-stroke engine 300 of the third embodiment shown in Figure 15, the fuel injection valve 202 is incorporated in the crank chamber 16. Although Figures 14 and 15 are shown as modified examples of the two-stroke engine 2 shown in Figure 1, the stratified scavenging engine 100 shown in Figure 12 may be equipped with a fuel injection valve 202 instead of the carburetor 28.

[0070] As described above, the present invention can be applied not only to traditional two-stroke engines, but also to stratified scavenging engines, and can also be applied to two-stroke engines incorporating a fuel injection valve instead of a carburetor. For this reason, in two-stroke engines, the mixture or leading air supplied to the combustion chamber 10 during the scavenging stroke is generally called "fresh air". In particular, when applied to a stratified scavenging engine, in addition to the above-mentioned effect of avoiding collision and interference during mixture scavenging, the following effect is obtained. In terms of the order of steps, first, air is introduced at the very beginning of the scavenging stroke by the first diagonal scavenging port group (Diag-No.1; 34(rig-1), 34(lef-2)) which opens first. At this time, the second diagonal scavenging port group (Diag-No.2; 34(rig-2), 34(lef-1)) remains closed. As the piston 8 descends, air begins to be introduced from the second scavenging port group (Diag-No.2), and then the mixture is introduced from the first scavenging port group (Diag-No.1). At this time, the mixture is introduced from the first scavenging port group (Diag-No.1) and air is introduced from the second scavenging port group (Diag-No.2), so that the inside of the cylinder 4 is filled with the mixture and air. When the piston descends further and the scavenging is at the end of the scavenging, the mixture is finally introduced from both the first scavenging port group (Diag-No.1) and the second scavenging port group (Diag-No.2). In this way, if the present invention is applied to a stratified scavenging engine, the time for introducing air can be set long while maintaining the total amount of introduced air. In addition, complete air without mixture is introduced at the very beginning of scavenging, a lean mixture is introduced in the middle, and the mixture is introduced at the end, thereby reducing the blow-by at the beginning of scavenging and eliminating disadvantages such as a decrease in power output and insufficient acceleration due to a lack of mixture.

[0071] In addition, the engines 2, 200, and 300 of the embodiment in which the present invention is applied to a four-stroke scavenging engine have been described as a typical example of the present invention, but the present invention can be applied to a two-stroke engine including four or more scavenging ports 34. For example, the present invention can be applied to a six-stroke scavenging engine disclosed in Patent Document 1. In a six-stroke scavenging engine, a specific example of the "diagonal" as used in the present invention is shown in FIG. 16. For example, the first right scavenging port 34 (rig-1) and the third left scavenging port 34 (lef-3) constitute the scavenging ports having a diagonal relationship of the first group Diag-No.1. For example, the third right scavenging port 34 (rig-3) and the first left scavenging port 34 (lef-1) constitute the scavenging ports having a diagonal relationship of the third group Diag-No.3. It is preferable to synchronize the opening timings of the scavenging ports constituting each of the first and third diagonal groups Diag-No.1 and Diag-No.3, while making the opening timings of the first and third diagonal groups Diag-No.1 and Diag-No.3 different. In the example of Fig. 16, the second right scavenging port 34 (rig-2) and the second left scavenging port 34 (lef-2) facing each other are opened in synchronization, and the opening timings are set to be different from the opening timings of the scavenging ports constituting each of the first and third diagonal groups.

[0072] Combinations in which the opening timings of the first to third diagonal pairs Diag-No. 1 to Diag-No. 3 are relatively different from one another are listed below as examples. (1) The first and second right scavenging ports 34 (rig-1), 34 (rig-2) and the third left scavenging port 34 (lef-3) may be set as a first group of scavenging ports diagonally arranged to each other, and the third right scavenging port 34 (rig-3) and the first and second left scavenging ports 34 (lef-1), 34 (lef-2) may be set as a second group of scavenging ports diagonally arranged to each other, and a plurality of scavenging ports constituting the first group may be opened at a first synchronization timing, and a plurality of scavenging ports constituting the second group may be opened at a second synchronization timing different from the first synchronization timing.

[0073] (1) The first and second right-side scavenging ports 34 (rig-1), 34 (rig-2) and the third left-side scavenging port 34 (lef-3) may be set as a first group of scavenging ports diagonally related to each other, and the third right-side scavenging port 34 (rig-3) and the first and second left-side scavenging ports 34 (lef-1), 34 (lef-2) may be set as a second group of scavenging ports diagonally related to each other, and a plurality of scavenging ports constituting the first diagonal group may be opened at a first synchronization timing, and a plurality of scavenging ports constituting the second diagonal group may be opened at a second synchronization timing different from the first synchronization timing. (2) The first left scavenging port 34 (lefg-1) and the second and third right scavenging ports 34 (rig-2), 34 (rig-3) may be set as a first group of scavenging ports diagonally related to each other, and the first right scavenging port 34 (rig-1) and the second and third left scavenging ports 34 (lef-2), 34 (lef-3) may be set as a second group of scavenging ports diagonally related to each other, and a plurality of scavenging ports constituting the first diagonal group may be opened at a first synchronization timing, and a plurality of scavenging ports constituting the second diagonal group may be opened at a second synchronization timing different from the first synchronization timing.

[0074] (3) The first right scavenging port 34 (rig-1) and the third left scavenging port 34 (lef-3) may be set as a first set of scavenging ports diagonally arranged, the first left scavenging port 34 (lef-1) and the second right scavenging port 34 (rig-2) may be set as a second set of scavenging ports diagonally arranged, and the second left scavenging port 34 (lef-2) and the third right scavenging port 34 (rig-3) may be set as a third set of scavenging ports diagonally arranged. The opening timings of the scavenging ports constituting each of the first to third sets may be synchronized, while the opening timings of the first to third sets may be made different.

[0075] As can be seen from the above example, by making the opening timing of each diagonal group or group different while synchronizing the opening timing of the scavenging ports constituting each group or group, the six-stroke scavenging engine can also achieve the same effects as the above-mentioned four-stroke scavenging engine. [Explanation of symbols]

[0076] 2. First embodiment of two-stroke engine (four-stroke scavenging type) 100 Second embodiment of two-stroke engine (stratified scavenging type) 200 Third embodiment of two-stroke engine (fuel injection valve arranged in intake passage) 300 Fourth embodiment of two-stroke engine (fuel injection valve arranged in crankcase) 4 cylinders 8 Piston 10 Combustion chamber 16 Crankcase 20 Intake port 22 Exhaust port 24 Intake passage 28 Carburetor 32 Scavenging passage 34 Scavenging port 34a Upper edge of rectangular scavenging port 34b Lower edge of rectangular scavenging port iL Cylinder centerline (imaginary line connecting the intake port and exhaust port) Diag-No.1 The first set of two diagonally arranged scavenging ports Diag-No.2 The second set of two diagonal scavenging ports 202 Fuel injection valve

Claims

1. In a two-stroke engine, fresh air precompressed in a crankcase is supplied to a combustion chamber through a scavenging port during a scavenging stroke to perform scavenging. having at least four scavenge ports; The four scavenging ports include left and right first scavenging ports that are located relatively farther from the exhaust port and opposed to each other across the cylinder, and left and right second scavenging ports that are located closer to the exhaust port than the left and right first scavenging ports and opposed to each other across the cylinder, the opening timings of two scavenging ports in a first set diagonally arranged with respect to each other and consisting of the second left scavenging port and the first right scavenging port are the same; the opening timings of two scavenging ports of a second set diagonally arranged with respect to each other and consisting of the first left scavenging port and the second right scavenging port are the same; A two-stroke engine, characterized in that the opening timing of the two scavenging ports of the first set is different from the opening timing of the two scavenging ports of the second set.

2. Each of the four scavenging ports has an upper edge, and the upper edge defines an opening timing of the scavenging port; 2. The two-stroke engine according to claim 1, wherein the height levels of the upper edges of the two scavenging ports of the first set are different from the height levels of the upper edges of the two scavenging ports of the second set.

3. The left and right first scavenging ports and the left and right second scavenging ports opposed to each other across the cylinder are directed in a direction away from the exhaust port, 2. The two-stroke engine according to claim 1, wherein the first scavenging port and the second scavenging port are oriented in a different direction.

4. 4. The two-stroke engine according to claim 3, wherein the four scavenging ports are generally rectangular in front view, and a vertical length dimension of an opening of the two scavenging ports in the first set is different from a vertical length dimension of an opening of the two scavenging ports in the second set.

5. The two-stroke engine is a stratified scavenging engine, 5. The two-stroke engine according to claim 1, wherein in a scavenging stroke, leading air is supplied to the combustion chamber before the mixture precompressed in the crank chamber is supplied to the combustion chamber through the scavenging port.

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