Opposed-piston engine

Abstract

To provide an opposed-piston engine that can achieve high combustion efficiency.SOLUTION: An opposed-piston engine comprises: a cylinder; a scavenging-side piston; an exhaust-side piston; and a first fuel injection device and a second fuel injection device which are disposed offset in a circumferential direction so as to face each other across a central axis of the cylinder 2, and which inject fuel between the scavenging-side piston and the exhaust-side piston. A cavity of the scavenging-side piston and the exhaust-side piston includes: a first cavity part including a first widening portion in which the width increases from a central part of each of the scavenging-side piston and the exhaust-side piston toward the side where the first fuel injection device is disposed; and a second cavity part including a second widening portion in which the width increases from the central part of each of the scavenging-side piston and the exhaust-side piston toward the side where the second fuel injection device is disposed. The first widening portion and the second widening portion each have the smallest width at a connection portion between the first widening portion and the second widening portion.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to an opposed piston engine.

Background Art

[0002] There is an opposed piston engine in a two-stroke diesel engine in which two pistons are arranged to face each other inside one cylinder, and a combustion chamber is formed between the two pistons (for example, Patent Document 1). In the opposed piston engine, an exhaust stroke in which combustion gas in the cylinder is discharged from an exhaust port formed in the cylinder wall while the piston makes one reciprocation, and a scavenging stroke in which air is taken into the cylinder from a scavenging port formed in the cylinder wall are performed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 discloses that a donut-shaped combustion space is formed by the opposing top surfaces of two pistons, and fuel is injected into this combustion space from a fuel injection device provided on the cylinder wall. The fuel injection device injects fuel along the radial direction of the cylinder in a cross-section along the axial direction of the cylinder.

[0005] In the combustion space described in Patent Document 1, when fuel is injected from a plurality of fuel injection devices, the fuel may interfere with each other, leading to a decrease in thermal efficiency. Further, in the combustion space described in Patent Document 1, since the spray does not reach the outside in the radial direction compared to the donut-shaped combustion space, the space utilization rate of the fuel is low, and there is a risk that the combustion gas temperature will rise and cause a decrease in thermal efficiency.

[0006] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide an opposed piston engine capable of achieving high combustion efficiency.

Means for Solving the Problems

[0007] The opposed piston engine according to at least one embodiment of the present disclosure includes a cylinder in which a scavenging port is formed on one side in the axial direction and an exhaust port is formed on the other side in the axial direction, a scavenging side piston disposed on the one side in the axial direction inside the cylinder, an exhaust side piston disposed on the other side in the axial direction inside the cylinder, a first fuel injection device configured to inject fuel between the scavenging side piston and the exhaust side piston inside the cylinder, a second fuel injection device configured to inject fuel between the scavenging side piston and the exhaust side piston inside the cylinder, and the second fuel injection device is circumferentially displaced so as to face the first fuel injection device across the central axis of the cylinder when viewed from one side in the axial direction. The cavities formed on the top surfaces of the scavenging side piston and the exhaust side piston respectively include a first cavity portion including a first widened portion whose width increases as it goes from the central portion of each of the scavenging side piston and the exhaust side piston toward the side where the first fuel injection device is disposed, a second cavity portion including a second widened portion whose width increases as it goes from the central portion of each of the scavenging side piston and the exhaust side piston toward the side where the second fuel injection device is disposed. Each of the first widened portion and the second widened portion is configured such that the width is minimized at the connection portion between the first widened portion and the second widened portion.

Advantages of the Invention

[0008] According to at least one embodiment of the present disclosure, an opposed piston engine capable of achieving high combustion efficiency is provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0010] Hereinafter, some embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as embodiments or shown in the drawings are not intended to limit the scope of the present disclosure, but are merely illustrative examples.

[0011] (Opposed piston engine) FIG. 1 is a schematic cross-sectional view of an opposed piston engine according to an embodiment of the present disclosure. As shown in FIG. 1, an opposed piston engine 1 according to some embodiments includes a cylinder 2, a scavenging side piston 3, an exhaust side piston 4, a first fuel injection device 5, and a second fuel injection device 6.

[0012] An internal space 20 extending along the axial direction of the cylinder 2 is formed inside the cylinder 2. The cylinder 2 has an outer surface 21 and an inner surface 22 that forms the internal space 20 inside the cylinder 2 in the radial direction of the cylinder 2 relative to the outer surface 21. In the illustrated embodiment, the cylinder 2 is formed in a cylindrical shape extending along the axial direction of the cylinder 2. Each of the outer surface 21 and the inner surface 22 of the cylinder 2 is formed in a circular cross-sectional shape perpendicular to the axial direction of the cylinder 2.

[0013] Hereinafter, the above one side (the upper side in FIG. 1) in the axial direction of the cylinder 2 is defined as the scavenging side, and the other side (the lower side in FIG. 1) in the axial direction of the cylinder 2 is defined as the exhaust side. The scavenging side piston 3 is arranged to be reciprocally movable along the axial direction of the cylinder 2 on the scavenging side of the internal space 20. The exhaust side piston 4 is arranged to be reciprocally movable along the axial direction of the cylinder 2 on the exhaust side of the internal space 20.

[0014] The scavenging-side piston 3 has a top surface 31 which is the end surface on the exhaust side of the scavenging-side piston 3, and an outer peripheral surface 32. The exhaust-side piston 4 has a top surface 41 which is the end surface on the scavenging side of the exhaust-side piston 4, and an outer peripheral surface 42. In the cylinder 2, a combustion chamber 11 is formed between the top surface 31 of the scavenging-side piston 3 and the top surface 41 of the exhaust-side piston 4 in the internal space 20. In other words, the top surface 31 of the scavenging-side piston 3 faces the top surface 41 of the exhaust-side piston 4 across the combustion chamber 11 in the axial direction of the cylinder 2.

[0015] On the inner surface 22 on the scavenging side of the cylinder 2, at least one (a plurality in the illustrated example) of scavenging ports 23 is formed. The plurality of scavenging ports 23 are provided at intervals in the circumferential direction of the cylinder 2. Each of the plurality of scavenging ports 23 forms a flow path for guiding combustion gas CG (compressed air in the illustrated example) from the outside of the cylinder 2 to the internal space 20. The combustion gas CG is guided from the outside of the cylinder 2 into the internal space 20 through the scavenging port 23 and flows toward the exhaust side in the internal space 20.

[0016] On the inner surface 22 on the exhaust side of the cylinder 2, at least one (a plurality in the illustrated example) of exhaust ports 24 is formed. The plurality of exhaust ports 24 are provided at intervals in the circumferential direction of the cylinder 2. Each of the plurality of exhaust ports 24 forms a flow path for discharging exhaust gas EG from the internal space 20 to the outside of the cylinder 2. The exhaust gas EG present in the internal space 20 is discharged to the outside of the cylinder 2 through the exhaust port 24.

[0017] In FIG. 1, the scavenging-side piston 3 and the exhaust-side piston 4 at the bottom dead center are shown by solid lines, and the top surface 31 of the scavenging-side piston 3 at the top dead center and the top surface 41 of the exhaust-side piston 4 at the top dead center are each shown by a two-dot chain line.

[0018] The scavenging-side piston 3 and the exhaust-side piston 4 reciprocate synchronously inside the cylinder 2 along the axial direction of the cylinder 2. The scavenging-side piston 3 is configured to be reciprocable between the top dead center (the position closest to the exhaust-side piston 4) and the bottom dead center (the position farthest from the exhaust-side piston 4) of the scavenging-side piston 3. The exhaust-side piston 4 is configured to be reciprocable between the top dead center (the position closest to the scavenging-side piston 3) and the bottom dead center (the position farthest from the scavenging-side piston 3) of the exhaust-side piston 4. The scavenging-side piston 3 and the exhaust-side piston 4 may reach the top dead center or the bottom dead center at the same time, or may be out of sync when reaching the top dead center or the bottom dead center.

[0019] In the illustrated embodiment, as shown in FIG. 1, the scavenging-side piston 3 is connected to one end of the scavenging-side connecting rod 14 via the scavenging-side piston pin 12, and the other end of the scavenging-side connecting rod 14 is connected to the crankshaft 16. The exhaust-side piston 4 is connected to one end of the exhaust-side connecting rod 15 via the exhaust-side piston pin 13, and the other end of the exhaust-side connecting rod 15 is connected to the above-mentioned crankshaft 16. When the crankshaft 16 rotates about the rotation axis 17, the scavenging-side piston 3 and the exhaust-side piston 4 reciprocate inside the cylinder 2 synchronously with each other and with their sliding directions on opposite sides of the axial direction of the cylinder 2.

[0020] Each of the first fuel injection device 5 and the second fuel injection device 6 is configured to inject fuel between the scavenging-side piston 3 and the exhaust-side piston 4 in the internal space 20 of the cylinder 2. Each of the first fuel injection device 5 and the second fuel injection device 6 injects fuel into the combustion chamber 11 when the crank angle (the rotation angle of the crankshaft 16) reaches a predetermined angle (for example, when the scavenging-side piston 3 or the exhaust-side piston 4 reaches the top dead center).

[0021] The opposed piston engine 1 compresses and heats the combustion gas CG introduced into the cylinder 2 through the scavenging port 23 to a temperature above the ignition point of the fuel F by the scavenging side piston 3 and the exhaust side piston 4. The first fuel injection device 5 and the second fuel injection device 6 respectively inject the fuel F into the compressed and heated combustion gas CG, causing the fuel F to self-ignite. A combustion flame is formed by the self-ignition of the fuel F. Due to the expansion of the combustion gas generated by the self-ignition, the scavenging side piston 3 and the exhaust side piston 4 are pushed in a direction away from each other. Then, the reciprocating motion of the scavenging side piston 3 and the exhaust side piston 4 is transmitted to the crankshaft 16 and converted into rotational force (power) by the crankshaft 16.

[0022] Each of the plurality of scavenging ports 23 is formed on the scavenging side of the top surface 31 of the scavenging side piston 3 at top dead center and on the exhaust side of the top surface 31 of the scavenging side piston 3 at bottom dead center. Each of the plurality of exhaust ports 24 is formed on the exhaust side of the top surface 41 of the exhaust side piston 4 at top dead center and on the scavenging side of the top surface 41 of the exhaust side piston 4 at bottom dead center.

[0023] When the top surface 31 of the scavenging side piston 3 slides to the scavenging side of each scavenging port 23, the combustion gas CG can be supplied to the internal space 20 through each scavenging port 23. When the top surface 41 of the exhaust side piston 4 slides to the exhaust side of each exhaust port 24, the exhaust gas EG can be discharged from the internal space 20 through each exhaust port 24. Since the combustion gas CG supplied to the internal space 20 is compressed by a supercharger (not shown), due to the pressure difference between the scavenging port 23 and the exhaust port 24, the combustion gas CG is supplied to the internal space 20 and the exhaust gas EG is discharged from the internal space 20.

[0024] (First Embodiment) FIG. 2 is a schematic cross-sectional view schematically showing the vicinity of the combustion chamber 11 of the opposed piston engine 1 according to the first embodiment of the present disclosure. FIG. 3 is an explanatory view for explaining the cavity shape of the scavenging side piston 3 in the first embodiment of the present disclosure. FIG. 4 is an explanatory view for explaining the cavity shape of the exhaust side piston 4 in the first embodiment of the present disclosure. FIG. 5 is a schematic cross-sectional view taken along the line A-B of the opposed piston engine 1 shown in FIG. 3. In FIG. 3, a schematic view of the scavenging side piston 3, the first fuel injection device 5, and the second fuel injection device 6 of the opposed piston engine 1 viewed from the exhaust side is shown. In FIG. 4, a schematic view of the exhaust side piston 4, the first fuel injection device 5, and the second fuel injection device 6 of the opposed piston engine 1 viewed from the scavenging side is shown.

[0025] When viewed from one axial side (scavenging side or exhaust side) as shown in FIGS. 3 and 4, the second fuel injection device 6 is displaced in the circumferential direction of the cylinder 2 so as to face the first fuel injection device 5 with the central axis (radial central axis) CA of the cylinder 2 interposed therebetween. In one embodiment, the second fuel injection device 6 is displaced within a range of 180° ± 5° in the circumferential direction centered on the central axis CA of the cylinder 2 with respect to the first fuel injection device 5.

[0026] In the illustrated embodiment, the first fuel injection device 5 is inserted through a first through hole 25 penetrating from the outer surface 21 to the inner surface 22 of the cylinder 2, and a part including the injection hole 51 is disposed in the internal space 20. The second fuel injection device 6 is inserted through a second through hole 26 penetrating from the outer surface 21 to the inner surface 22 of the cylinder 2, and a part including the injection hole 61 is disposed in the internal space 20.

[0027] (Scavenging side cavity) As shown in FIG. 3, a scavenging side cavity 7 having a predetermined cavity volume is formed on the top surface 31 of the scavenging side piston 3. In the embodiment shown in FIG. 3, the top surface 31 of the scavenging side piston 3 includes a flat surface 31A extending along a direction orthogonal to the axial direction of the cylinder 2, and the scavenging side cavity 7 has a concave shape recessed more on the scavenging side than the flat surface 31A.

[0028] As shown in FIGS. 2 and 3, the scavenging-side cavity 7 includes a scavenging-side first cavity portion (first cavity portion) 71 and a scavenging-side second cavity portion (second cavity portion) 72 formed on the side where the second fuel injection device 6 is disposed with respect to the scavenging-side first cavity portion 71. The scavenging-side second cavity portion 72 is connected at the center portion 30 of the scavenging-side piston 3 such that the edge on the side where the first fuel injection device 5 is disposed is connected to the edge on the side where the second fuel injection device 6 of the scavenging-side first cavity portion 71 is disposed.

[0029] As viewed from one axial side (exhaust side) as shown in FIG. 3, a straight line passing through the central axis CA of the cylinder 2 and the first fuel injection device 5 (specifically, the center of the outlet opening of the injection hole 51) is defined as a first reference line BL1. Then, when the length position of the intersection point P1 of the outer peripheral edge of the top surface 31 of the scavenging-side piston 3 with the first reference line BL1 on the side where the first fuel injection device 5 is disposed is defined as 0%, and the length position of the intersection point P2 of the outer peripheral edge of the top surface 31 of the scavenging-side piston 3 with the first reference line BL1 on the side where the second fuel injection device 6 is disposed is defined as 100%, the central portion 30 of the scavenging-side piston 3 is in the range of 40% or more and 60% or less in length position. In the illustrated embodiment, at the 50% length position, the inner end in the radial direction of the scavenging-side second widened portion 721 (scavenging-side second cavity portion 72) is connected to the inner end in the radial direction of the scavenging-side first widened portion 711 (scavenging-side first cavity portion 71).

[0030] As shown in FIG. 3, the scavenging-side first cavity portion 71 includes at least a part of a scavenging-side first widened portion (first widened portion) 711 whose width increases as it goes from the central portion 30 of the scavenging-side piston 3 toward the side where the first fuel injection device 5 is disposed. A part of the scavenging-side first widened portion 711 may be formed at the central portion 30 of the scavenging-side piston 3. In the illustrated embodiment, the scavenging-side first widened portion 711 has a constant rate of increase in width in the direction toward the side where the first fuel injection device 5 is disposed, but the rate of increase in width may increase or decrease, or a part of the scavenging-side first widened portion 711 may include a portion with a constant width.

[0031] As shown in FIG. 3, the scavenging side piston 3 has a wall surface 712 on one side in the width direction of the scavenging side first cavity portion 71, a wall surface 713 on the other side in the width direction of the scavenging side first cavity portion 71, a wall surface (scavenging side second wall surface) 714 on the outer side in the radial direction of the scavenging side first cavity portion 71, and a bottom surface 715 of the scavenging side first cavity portion 71. Each of the wall surfaces 712, 713, and 714 has one end in the axial direction connected to the bottom surface 715 and the other end in the axial direction connected to the flat surface 31A. One end of the wall surface 714 in the circumferential direction is connected to the wall surface 712, and the other end in the circumferential direction is connected to the wall surface 713. The scavenging side first cavity portion 71 has a cavity shape defined by the wall surfaces 712, 713, 714, and the bottom surface 715.

[0032] As shown in FIG. 3, the scavenging side second cavity portion 72 includes at least a part of a scavenging side second widening portion (second widening portion) 721 whose width increases as it goes from the central portion 30 of the scavenging side piston 3 toward the side where the second fuel injection device 6 is disposed. A part of the scavenging side second widening portion 721 may be formed in the central portion 30 of the scavenging side piston 3. In the illustrated embodiment, the scavenging side second widening portion 721 has a constant rate of increase in width in the direction toward the side where the second fuel injection device 6 is disposed, but the rate of increase in width may increase or decrease, or a part of the scavenging side second widening portion 721 may include a portion with a constant width.

[0033] As shown in FIG. 3, the scavenging side piston 3 has a wall surface 722 on one side in the width direction of the scavenging side second cavity portion 72, a wall surface 723 on the other side in the width direction of the scavenging side first cavity portion 72, a wall surface (scavenging side first wall surface) 724 on the outer side in the radial direction of the scavenging side second cavity portion 72, and a bottom surface 725 of the scavenging side second cavity portion 72. Each of the wall surfaces 722, 723, and 724 has one end in the axial direction connected to the bottom surface 725 and the other end in the axial direction connected to the flat surface 31A. One end of the wall surface 724 in the circumferential direction is connected to the wall surface 722, and the other end in the circumferential direction is connected to the wall surface 723. The scavenging side second cavity portion 72 has a cavity shape defined by the wall surfaces 722, 723, 724, and the bottom surface 725.

[0034] In the illustrated embodiment, as shown in FIG. 3, the scavenging-side piston 3 includes a scavenging-side first protrusion 34 that forms a scavenging-side first wall surface 724, a scavenging-side second protrusion 33 that forms a scavenging-side second wall surface 714, a scavenging-side third protrusion 35 that forms wall surfaces 712 and 722 on one side in the width direction of the scavenging-side cavity 7, and a scavenging-side fourth protrusion 36 that forms wall surfaces 713 and 723 on the other side in the width direction of the scavenging-side cavity 7.

[0035] Each of the scavenging-side first widened portion 711 and the scavenging-side second widened portion 721 of the scavenging-side cavity 7 is configured such that the width is minimized at the connection portion 73 between the scavenging-side first widened portion 711 and the scavenging-side second widened portion 721.

[0036] (Exhaust-side cavity) On the top surface 41 of the exhaust-side piston 4, as shown in FIG. 4, an exhaust-side cavity 8 having a predetermined cavity volume is formed. In the embodiment shown in FIG. 4, the top surface 41 of the exhaust-side piston 4 includes a flat surface 41A extending along a direction orthogonal to the axial direction of the cylinder 2, and the exhaust-side cavity 8 has a concave shape that is recessed more on the exhaust side than the flat surface 41A.

[0037] As shown in FIGS. 2 and 4, the exhaust-side cavity 8 includes an exhaust-side first cavity portion (first cavity portion) 81 and an exhaust-side second cavity portion (second cavity portion) 82 formed on the side where the second fuel injection device 6 is disposed rather than the exhaust-side first cavity portion 81. In the central portion 40 of the exhaust-side piston 4, the edge on the side where the first fuel injection device 5 is disposed of the exhaust-side second cavity portion 82 is connected to the edge on the side where the second fuel injection device 6 is disposed of the exhaust-side first cavity portion 81.

[0038] The combustion chamber 11 includes a combustion chamber 11A on the side where the first fuel injection device 5 is arranged with respect to the central axis CA of the cylinder 2, and a combustion chamber 11B on the side where the second fuel injection device 6 is arranged with respect to the central axis CA of the cylinder 2. The exhaust-side first cavity portion 81 faces the scavenging-side first cavity portion 71 across the combustion chamber 11A in the axial direction of the cylinder 2. The exhaust-side second cavity portion 82 faces the scavenging-side second cavity portion 72 across the combustion chamber 11B in the axial direction of the cylinder 2.

[0039] As shown in FIG. 4, when viewed from one axial side (scavenging side), a straight line passing through the central axis CA of the cylinder 2 and the first fuel injection device 5 (specifically, the center of the outlet opening of the injection hole 51) is defined as the second reference line BL2. Then, when the length position of the intersection point P3 of the outer peripheral edge of the top surface 41 of the exhaust-side piston 4 with the second reference line BL2 on the side where the first fuel injection device 5 is arranged is defined as 0%, and the length position of the intersection point P4 of the outer peripheral edge of the top surface 41 of the exhaust-side piston 4 with the second reference line BL2 on the side where the second fuel injection device 6 is arranged is defined as 100%, the central portion 40 of the exhaust-side piston 4 is in the range of a length position of 40% or more and 60% or less. In the illustrated embodiment, at the 50% length position, the inner end in the radial direction of the exhaust-side second widened portion 821 (exhaust-side second cavity portion 82) is connected to the inner end in the radial direction of the exhaust-side first widened portion 811 (exhaust-side first cavity portion 81).

[0040] As shown in FIG. 4, the exhaust-side first cavity portion 81 includes at least a part of an exhaust-side first widened portion (first widened portion) 811 whose width increases as it goes from the central portion 40 of the exhaust-side piston 4 toward the side where the first fuel injection device 5 is arranged. A part of the exhaust-side first widened portion 811 may be formed in the central portion 40 of the exhaust-side piston 4. In the illustrated embodiment, the exhaust-side first widened portion 811 has a constant rate of increase in width in the direction toward the side where the first fuel injection device 5 is arranged, but the rate of increase in width may increase or decrease, or a part of the exhaust-side first widened portion 811 may include a portion with a constant width.

[0041] As shown in FIG. 4, the exhaust-side piston 4 has a wall surface 812 on one side in the width direction of the exhaust-side first cavity portion 81, a wall surface 813 on the other side in the width direction of the exhaust-side first cavity portion 81, a wall surface (exhaust-side first wall surface) 814 on the outer side in the radial direction of the exhaust-side first cavity portion 81, and a bottom surface 815 of the exhaust-side first cavity portion 81. Each of the wall surfaces 812, 813, and 814 has one end in the axial direction connected to the bottom surface 815 and the other end in the axial direction connected to the flat surface 41A. One end of the wall surface 814 in the circumferential direction is connected to the wall surface 812, and the other end in the circumferential direction is connected to the wall surface 813. The cavity shape of the exhaust-side first cavity portion 81 is defined by the wall surfaces 812, 813, 814, and the bottom surface 815.

[0042] As shown in FIG. 4, the exhaust-side second cavity portion 82 includes at least a part of an exhaust-side second widened portion (second widened portion) 821 whose width increases as it goes from the central portion 40 of the exhaust-side piston 4 toward the side where the second fuel injection device 6 is disposed. A part of the exhaust-side second widened portion 821 may be formed in the central portion 40 of the exhaust-side piston 4. In the illustrated embodiment, the exhaust-side second widened portion 821 has a constant width increase rate in the direction toward the side where the second fuel injection device 6 is disposed, but the width increase rate may increase or decrease, or a part of the exhaust-side second widened portion 821 may include a portion with a constant width.

[0043] As shown in FIG. 4, the exhaust-side piston 4 has a wall surface 822 on one side in the width direction of the exhaust-side second cavity portion 82, a wall surface 823 on the other side in the width direction of the exhaust-side first cavity portion 82, a wall surface (scavenging-side second wall surface) 824 on the outer side in the radial direction of the exhaust-side second cavity portion 82, and a bottom surface 825 of the exhaust-side second cavity portion 82. Each of the wall surfaces 822, 823, and 824 has one end in the axial direction connected to the bottom surface 825 and the other end in the axial direction connected to the flat surface 41A. One end of the wall surface 824 in the circumferential direction is connected to the wall surface 822, and the other end in the circumferential direction is connected to the wall surface 823. The cavity shape of the exhaust-side second cavity portion 82 is defined by the wall surfaces 822, 823, 824, and the bottom surface 825.

[0044] In the illustrated embodiment, as shown in FIG. 4, the exhaust-side piston 4 includes an exhaust-side first protrusion 43 that forms an exhaust-side first wall surface 814, an exhaust-side second protrusion 44 that forms an exhaust-side second wall surface 824, an exhaust-side third protrusion 45 that forms wall surfaces 812 and 822 on one side in the width direction of the exhaust-side cavity 8, and an exhaust-side fourth protrusion 46 that forms wall surfaces 813 and 823 on the other side in the width direction of the exhaust-side cavity 8.

[0045] Each of the exhaust-side first widened portion 811 and the exhaust-side second widened portion 821 of the exhaust-side cavity 8 is configured such that the width is minimized at the connection portion 83 between the exhaust-side first widened portion 811 and the exhaust-side second widened portion 821.

[0046] Reference numeral 50 in FIG. 2 indicates the flow of the spray injected from the first fuel injection device 5 and the spray flame generated by the combustion of the spray. Reference numeral 60 in FIG. 2 indicates the flow of the spray injected from the second fuel injection device 6 and the spray flame generated by the combustion of the spray. The spray injected from the first fuel injection device 5 flows in the combustion chamber 11 along the bottom surfaces 715 and 725 of the scavenging-side cavity 7 toward the side where the second fuel injection device 6 is disposed. The spray injected from the second fuel injection device 6 flows in the combustion chamber 11 along the bottom surfaces 815 and 825 of the exhaust-side cavity 8 toward the side where the first fuel injection device 5 is disposed.

[0047] The combustion chamber 11B on the second fuel injection device 6 side has a relatively large volume due to the scavenging-side second cavity portion 72 and the exhaust-side second cavity portion 82. By burning the spray injected from the first fuel injection device 5 in the combustion chamber 11B on the second fuel injection device 6 side where the spread of the spray injected from the second fuel injection device 6 is small, the combustion gas present in the combustion chamber 11B on the second fuel injection device 6 side can be utilized for the combustion of the spray flame.

[0048] The combustion chamber 11A on the side of the first fuel injection device 5 has a relatively large volume due to the scavenging-side first cavity portion 71 and the exhaust-side first cavity portion 81. By burning the spray injected from the second fuel injection device 6 in the combustion chamber 11A on the side of the first fuel injection device 5 where the spread of the spray injected from the first fuel injection device 5 is small, the combustion gas present in the combustion chamber 11A on the side of the first fuel injection device 5 can be utilized for the combustion of the spray flame. Thereby, high combustion efficiency with less unburned components can be achieved.

[0049] By making the widths at the connection portions 73 and 83 between the first widened portions 711 and 811 and the second widened portions 721 and 821 of the scavenging-side cavity 7 and the exhaust-side cavity 8 small, it is possible to suppress the spray flame of the first fuel injection device 5 from entering the combustion chamber 11A on the side of the first fuel injection device 5 from the combustion chamber 11B on the side of the second fuel injection device 6. Also, it is possible to suppress the spray flame of the second fuel injection device 6 from entering the combustion chamber 11B on the side of the second fuel injection device 6 from the combustion chamber 11A on the side of the first fuel injection device 5. Thereby, the interference between the spray flame of the first fuel injection device 5 and the spray flame of the second fuel injection device 6 can be suppressed, and further higher combustion efficiency can be achieved.

[0050] In some embodiments, each of the above-described scavenging-side first widened portion 711, scavenging-side second widened portion 721, exhaust-side first widened portion 811, and exhaust-side second widened portion 821 has a minimum width that is half or less of the maximum width.

[0051] When each of the scavenging-side first widened portion 711, scavenging-side second widened portion 721, exhaust-side first widened portion 811, and exhaust-side second widened portion 821 satisfies the condition that the minimum width is half or less of the maximum width, the outer volume in the radial direction of each of the combustion chamber 11A on the side of the first fuel injection device 5 and the combustion chamber 11B on the side of the second fuel injection device 6 can be made relatively large. Therefore, the combustion gas present in these combustion chambers 11A and 11B can be utilized for the combustion of the spray flame. Also, since the connection portions 73 and 83 with the first widened portions 711 and 811 and the second widened portions 721 and 821 can be made relatively small, the interference between the spray flame of the first fuel injection device 5 and the spray flame of the second fuel injection device 6 can be effectively suppressed.

[0052] In some embodiments, as shown in FIG. 2, at least a part of each of the above-described scavenging-side first wall surface 724 and the exhaust-side first wall surface 814 extends along the axial direction of the cylinder 2.

[0053] As shown in FIG. 2, when the inclination angle of the scavenging-side first wall surface 724 with respect to the axial direction of the cylinder 2 is defined as θ2, the scavenging-side first wall surface 724 includes a portion where the inclination angle θ2 satisfies the condition of -5° ≤ θ2 ≤ 5°. When the inclination angle of the exhaust-side first wall surface 814 with respect to the axial direction of the cylinder 2 is defined as θ3, the exhaust-side first wall surface 814 includes a portion where the inclination angle θ3 satisfies the condition of -5° ≤ θ3 ≤ 5°. Each of the scavenging-side first wall surface 724 and the exhaust-side first wall surface 814 may be formed in a concave arc shape having a predetermined curvature in a cross section along the axial direction of the cylinder 2 as shown in FIG. 2, or may be formed in a concave arc shape where the curvature gradually increases or decreases.

[0054] By guiding the spray flame flowing along the scavenging-side second cavity portion 72 by the scavenging-side first wall surface 724 to the exhaust-side second cavity portion 82, the combustion gas present in the exhaust-side second cavity portion 82 can be utilized for the combustion of the spray flame. Also, by guiding the spray flame flowing along the exhaust-side first cavity portion 81 by the exhaust-side first wall surface 814 to the scavenging-side first cavity portion 71, the combustion gas present in the scavenging-side first cavity portion 71 can be utilized for the combustion of the spray flame.

[0055] In some embodiments, as shown in FIG. 2, at least a part of each of the above-described scavenging-side second wall surface 714 and the exhaust-side second wall surface 824 extends along the axial direction of the cylinder 2.

[0056] As shown in FIG. 2, when the inclination angle of the scavenging-side second wall surface 714 with respect to the axial direction of the cylinder 2 is defined as θ1, the scavenging-side second wall surface 714 includes a portion where the inclination angle θ1 satisfies the condition of -5° ≤ θ1 ≤ 5°. When the inclination angle of the exhaust-side second wall surface 824 with respect to the axial direction of the cylinder 2 is defined as θ4, the exhaust-side second wall surface 824 includes a portion where the inclination angle θ4 satisfies the condition of -5° ≤ θ4 ≤ 5°. Each of the scavenging-side second wall surface 714 and the exhaust-side second wall surface 824 may be formed in a concave arc shape having a predetermined curvature in a cross section along the axial direction of the cylinder 2 as shown in FIG. 2, or may be formed in a concave arc shape where the curvature gradually increases or decreases.

[0057] By guiding the spray flame guided to the scavenging-side first cavity portion 71 along the axial direction of the cylinder 2 by the scavenging-side second wall surface 714 to the inner side in the radial direction (the side where the second fuel injection device 6 is disposed), the combustion gas existing inside the scavenging-side first cavity portion 71 in the radial direction can be utilized for the combustion of the spray flame. Further, by guiding the spray flame guided to the exhaust-side second cavity portion 82 along the axial direction of the cylinder 2 by the exhaust-side second wall surface 824 to the inner side in the radial direction (the side where the first fuel injection device 5 is disposed), the combustion gas existing inside the exhaust-side second cavity portion 82 in the radial direction can be utilized for the combustion of the spray flame.

[0058] In some embodiments, as shown in FIG. 2, the above-described first fuel injection device 5 has an injection central axis 52 inclined toward the scavenging side toward the inner side in the radial direction of the cylinder 2, and the above-described second fuel injection device 6 has an injection central axis 62 inclined toward the exhaust side toward the inner side in the radial direction of the cylinder 2. The first fuel injection device 5 injects fuel into the combustion chamber 11 along the extension direction of the injection central axis 52 which is the central axis of the injection hole 51. In the illustrated embodiment, the injection central axis 52 is directed toward the central portion of the scavenging-side cavity 7. The second fuel injection device 6 injects fuel into the combustion chamber 11 along the extension direction of the injection central axis 62 which is the central axis of the injection hole 61. In the illustrated embodiment, the injection central axis 62 is directed toward the central portion of the exhaust-side cavity 8.

[0059] In the illustrated embodiment, the second fuel injection device 6 is arranged at an axial position similar to that of the first fuel injection device 5 in the axial direction of the cylinder 2. Specifically, at least a part of the second fuel injection device 6 is present within the axial range where the first fuel injection device 5 exists in the axial direction of the cylinder 2. In the embodiment shown in FIG. 2, the first fuel injection device 5 and the second fuel injection device 6 are located on the exhaust side of the flat surface 31A and on the scavenging side of the flat surface 41A.

[0060] By inclining the injection center axes 52 and 62 of the first fuel injection device 5 and the second fuel injection device 6 in different directions in the axial direction of the cylinder 2, interference between the spray flame of the first fuel injection device 5 and the spray flame of the second fuel injection device 6 can be suppressed, so that a further higher combustion efficiency can be achieved.

[0061] (Second Embodiment) FIG. 6 is a schematic cross-sectional view schematically showing the vicinity of the combustion chamber 11 of the opposed piston engine 1 according to the second embodiment of the present disclosure. FIG. 7 is an explanatory view for explaining the cavity shape of the scavenging side piston 3 in the second embodiment of the present disclosure. FIG. 8 is an explanatory view for explaining the cavity shape of the exhaust side piston 4 in the second embodiment of the present disclosure. As shown in FIGS. 6 and 7, the scavenging side piston 3 in the second embodiment is different from the scavenging side piston 3 in the first embodiment in that it does not include the scavenging side second protrusion 33 that forms the scavenging side second wall surface 714. That is, in the scavenging side piston 3 in the second embodiment, the outer peripheral edge 716 of the bottom surface 715 of the scavenging side first cavity portion 71 is continuous with the outer peripheral surface 32 of the scavenging side piston 3.

[0062] As shown in FIGS. 6 and 8, the exhaust side piston 4 in the second embodiment is different from the exhaust side piston 4 in the first embodiment in that it does not include the exhaust side second protrusion 44 that forms the exhaust side second wall surface 824. That is, in the exhaust side piston 4 in the second embodiment, the outer peripheral edge 826 of the bottom surface 825 of the exhaust side second cavity portion 82 is continuous with the outer peripheral surface 42 of the exhaust side piston 4.

[0063] By forming the scavenging-side piston 3 such that the outer peripheral edge 716 of the bottom surface 715 of the scavenging-side first cavity portion 71 is continuous with the outer peripheral surface 32, the volume of the combustion chamber 11A on the side of the first fuel injection device 5 can be made relatively large. Thereby, the combustion gas present in the combustion chamber 11A on the side of the first fuel injection device 5 can be utilized for the combustion of the spray flame. Also, by forming the exhaust-side piston 4 such that the outer peripheral edge 826 of the bottom surface 825 of the exhaust-side second cavity portion 82 is continuous with the outer peripheral surface 42, the volume of the combustion chamber 11B on the side of the second fuel injection device 6 can be made relatively large. Thereby, the combustion gas present in the combustion chamber 11B on the side of the second fuel injection device 6 can be utilized for the combustion of the spray flame.

[0064] In some embodiments, as shown in FIG. 6, the above-described first fuel injection device 5 is disposed on one side (scavenging side) in the axial direction of the cylinder 2 with respect to the second fuel injection device 6. In the illustrated embodiment, the first fuel injection device 5 is at least partially within the axial range in which the scavenging-side first wall surface 724 in the axial direction of the cylinder 2 exists. The second fuel injection device 6 is at least partially within the axial range in which the exhaust-side first wall surface 814 in the axial direction of the cylinder 2 exists.

[0065] By arranging the first fuel injection device 5 and the second fuel injection device 6 at positions offset from each other in the axial direction of the cylinder 2, interference between the spray flame of the first fuel injection device 5 and the spray flame of the second fuel injection device 6 can be suppressed, and thus further higher combustion efficiency can be achieved.

[0066] In some embodiments, as shown in FIG. 6, the above-described first fuel injection device 5 has an injection central axis 52 along a direction orthogonal to the axial direction of the cylinder 2 and toward the inner side in the radial direction of the cylinder 2, and the above-described second fuel injection device 6 has an injection central axis 62 along a direction orthogonal to the axial direction of the cylinder 2 and toward the inner side in the radial direction of the cylinder 2. In the illustrated embodiment, the injection central axis 52 is directed toward the scavenging-side first wall surface 724. The second fuel injection device 6 is directed toward the exhaust-side first wall surface 814.

[0067] By arranging the injection center axes 52 and 62 of the first fuel injection device 5 and the second fuel injection device 6, which are arranged at positions shifted from each other in the axial direction of the cylinder 2, along a direction orthogonal to the axial direction, interference between the spray flame of the first fuel injection device 5 and the spray flame of the second fuel injection device 6 can be suppressed, so that a further high combustion efficiency can be achieved. In the second embodiment, compared with the first embodiment, since the spray and spray fire from the first fuel injection device 5 flow a relatively long distance along the scavenging side cavity 7, generation of a rotational flow (tumble flow) in the axial direction of the cylinder 2 on the scavenging side first wall surface 724 is promoted. Further, in the second embodiment, compared with the first embodiment, since the spray and spray fire from the second fuel injection device 6 flow a relatively long distance along the exhaust side cavity 8, generation of a rotational flow (tumble flow) in the axial direction of the cylinder 2 on the exhaust side first wall surface 814 is promoted. Thereby, a further high combustion efficiency can be achieved.

[0068] Note that the positions of the first fuel injection device 5 and the second fuel injection device 6 and the injection center axes 52 and 62 in the second embodiment may be adopted for the opposed piston engine 1 according to the first embodiment. In this case, it is preferable to provide holes and grooves for allowing the spray from the first fuel injection device 5 to pass through in the scavenging side second protrusion 33. Further, it is preferable to provide holes and grooves for allowing the spray from the second fuel injection device 6 to pass through in the exhaust side second protrusion 44. Also, the positions of the first fuel injection device 5 and the second fuel injection device 6 and the injection center axes 52 and 62 in the first embodiment may be adopted for the opposed piston engine 1 according to the second embodiment.

[0069] FIG. 9 is an explanatory diagram for explaining the scavenging port 23 of the opposed piston engine 1 according to an embodiment of the present disclosure. FIG. 10 is a schematic cross-sectional view along a direction orthogonal to the axial direction of the opposed piston engine 1 shown in FIG. 9. The scavenging port 23 in several of the above-described embodiments has a central axis CB extending along the radial direction toward the inside in the radial direction of the cylinder 2 as shown in FIG. 10.

[0070] The plurality of scavenging ports 23 are arranged at similar axial positions to each other in the axial direction of the cylinder 2. When a reference plane BF, which is a plane orthogonal to the axial direction of the cylinder 2 and includes the central axis line CB of one of the plurality of scavenging ports 23, is defined, the other scavenging ports 23 are present on the reference plane BF.

[0071] The combustion gas introduced into the cylinder 2 through the scavenging port 23 forms a rotational flow (tumble flow) that swirls in the axial direction of the cylinder 2 inside the cylinder 2. In this case, since the diffusion of the sprays from the first fuel injection device 5 and the second fuel injection device 6 depends mainly on the momentum of the sprays regardless of the swirl ratio, robust combustion that is less affected by the flow state of the combustion gas and thus the operating conditions of the opposed piston engine 1 becomes possible. In particular, in the opposed piston engine 1 according to the second embodiment, since the top surface 31 of the scavenging side piston 3 has a distribution in the axial direction of the cylinder 2, a time difference occurs in the timing of the inflow of the combustion gas into the internal space 20 through the scavenging port 23, thereby promoting the formation of the above-described tumble flow.

[0072] In this specification, expressions indicating relative or absolute arrangements such as "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric", or "coaxial" not only strictly represent such arrangements, but also represent states in which there are tolerances or relative displacements with angles and distances such that the same function can be obtained. For example, expressions indicating that things such as "identical", "equal", and "homogeneous" are in an equal state not only strictly represent an equal state, but also represent states in which there are tolerances or differences such that the same function can be obtained. Also, in this specification, expressions indicating shapes such as a rectangular shape or a cylindrical shape not only represent the shapes such as a rectangular shape or a cylindrical shape in a geometrically strict sense, but also represent shapes including concave and convex portions, chamfered portions, etc. within a range where the same effect can be obtained. Also, in this specification, the expressions "comprising", "including", or "having" for a component are not exclusive expressions that exclude the existence of other components.

[0073] The present disclosure is not limited to the above-described embodiments, and includes forms obtained by modifying the above-described embodiments and forms obtained by appropriately combining these forms.

[0074] The content described in some of the above-described embodiments is understood as follows, for example.

[0075] 1) The opposed piston engine (1) according to at least one embodiment of the present disclosure is a cylinder (2) in which a scavenging port (23) is formed on one side in the axial direction and an exhaust port (24) is formed on the other side in the axial direction, a scavenging side piston (3) disposed on the one side in the axial direction inside the cylinder (2), an exhaust side piston (4) disposed on the other side in the axial direction inside the cylinder (2), a first fuel injection device (5) configured to inject fuel between the scavenging side piston (3) and the exhaust side piston (4) inside the cylinder (2), a second fuel injection device (6) configured to inject fuel between the scavenging side piston (3) and the exhaust side piston (4) inside the cylinder (2), the second fuel injection device (6) being circumferentially displaced so as to face the first fuel injection device (5) across the central axis (CA) of the cylinder (2) when viewed from one side in the axial direction, the cavities (scavenging side cavity 7, exhaust side cavity 8) formed on the respective top surfaces (31, 41) of the scavenging side piston (3) and the exhaust side piston (4) are a first cavity portion (71, 81) including a first widening portion (711, 811) whose width increases as it goes from the central portion of each of the scavenging side piston (3) and the exhaust side piston (4) toward the side where the first fuel injection device (5) is disposed, A second cavity portion (72, 82) including second widening portions (721, 821) that increase in width as they extend from the central portions of the scavenging-side piston (3) and the exhaust-side piston (4) toward the side where the second fuel injection device (6) is disposed. Each of the first widening portions (711, 811) and the second widening portions (721, 821) of the cavities (7, 8) is configured such that the width is minimized at the connection portions (73, 83) between the first widening portions (711, 811) and the second widening portions (721, 821).

[0076] According to the configuration of 1) above, by burning the spray injected from the first fuel injection device (5) in the combustion chamber (11B) on the side of the second fuel injection device (6) where the spread of the spray injected from the second fuel injection device (6) is small, the combustion gas present in the combustion chamber (11B) on the side of the second fuel injection device (6) can be utilized for the combustion of the spray flame. Also, by burning the spray injected from the second fuel injection device (6) in the combustion chamber (11A) on the side of the first fuel injection device (5) where the spread of the spray injected from the first fuel injection device (5) is small, the combustion gas present in the combustion chamber (11A) on the side of the first fuel injection device (5) can be utilized for the combustion of the spray flame. Thereby, high combustion efficiency with less unburned components can be achieved.

[0077] Also, according to the configuration of 1) above, by making the width at the connection portion (73, 83) between the first widening portion (711, 811) and the second widening portion (721, 821) small, it is possible to suppress the spray flame of the first fuel injection device (5) from entering the combustion chamber (11A) on the side of the first fuel injection device (5). Also, it is possible to suppress the spray flame of the second fuel injection device (6) from entering the combustion chamber (11B) on the side of the second fuel injection device (6). Thereby, interference between the spray flame of the first fuel injection device (5) and the spray flame of the second fuel injection device (6) can be suppressed, and further high combustion efficiency can be achieved.

[0078] 2) In some embodiments, the opposed-piston engine (1) described in 1) above, The scavenging-side piston (3) On the outer side in the radial direction of the second cavity portion (72) of the scavenging-side piston (3), a scavenging-side first protrusion (34) protrudes toward the other side in the axial direction to form a scavenging-side first wall surface (724) which is the outer wall surface in the radial direction of the second cavity portion (72), The exhaust-side piston (4) On the outer side in the radial direction of the first cavity portion (82) of the exhaust-side piston (4), a exhaust-side first protrusion (43) protrudes toward the one side in the axial direction to form a exhaust-side first wall surface (814) which is the outer wall surface in the radial direction of the first cavity portion (82), Each of the scavenging-side first wall surface (724) and the exhaust-side first wall surface (814) has at least a part in the axial direction extending along the axial direction.

[0079] According to the configuration of 2) above, the scavenging-side first wall surface (724) guides the spray flame flowing along the second cavity portion (72) of the scavenging-side piston (3) to the second cavity portion (82) of the exhaust-side piston (4), so that the combustion gas existing in the second cavity portion (82) can be utilized for the combustion of the spray flame. Further, the exhaust-side first wall surface (814) guides the spray flame flowing along the first cavity portion (81) of the exhaust-side piston (4) to the first cavity portion (71) of the scavenging-side piston (3), so that the combustion gas existing in the first cavity portion (71) can be utilized for the combustion of the spray flame.

[0080] 3) In some embodiments, it is the opposed-piston engine (1) described in 2) above, The scavenging-side piston (3) On the outer side in the radial direction of the first cavity portion (71) of the scavenging-side piston (3), a scavenging-side second protrusion (33) protrudes toward the other side in the axial direction to form a scavenging-side second wall surface (714) which is the outer wall surface in the radial direction of the first cavity portion (71), The exhaust-side piston (4) On the outer side in the radial direction of the second cavity portion (82) of the exhaust-side piston (4), a second exhaust-side protrusion (44) that protrudes toward one side in the axial direction and forms an exhaust-side second wall surface (824) which is the outer wall surface in the radial direction of the second cavity portion (82) is included. Each of the scavenging-side second wall surface (714) and the exhaust-side second wall surface (824) has at least a part in the axial direction extending along the axial direction.

[0081] According to the configuration of 3) above, the scavenging-side second wall surface (714) guides the spray flame guided to the first cavity portion (71) of the scavenging-side piston (3) along the axial direction of the piston (2) to the inner side in the radial direction, so that the combustion gas existing inside the first cavity portion (71) in the radial direction can be utilized for the combustion of the spray flame. Further, the exhaust-side second wall surface (824) guides the spray flame guided to the second cavity portion (82) of the exhaust-side piston (4) along the axial direction of the piston (2) to the inner side in the radial direction, so that the combustion gas existing inside the second cavity portion (82) in the radial direction can be utilized for the combustion of the spray flame.

[0082] 4) In some embodiments, it is the opposed-piston engine (1) described in 2) above, wherein the scavenging-side piston (3) has the outer peripheral edge of the bottom surface of the first cavity portion (71) continuous with the outer peripheral surface (32) of the scavenging-side piston (3), and the exhaust-side piston (4) has the outer peripheral edge of the bottom surface of the second cavity portion (82) continuous with the outer peripheral surface (42) of the exhaust-side piston (4).

[0083] According to the configuration of 4) above, by forming the scavenging side piston (3) such that the outer peripheral edge of the bottom surface of the first cavity portion (71) is continuous with the outer peripheral surface (32), the volume of the combustion chamber (11A) on the side of the first fuel injection device (5) can be made relatively large. Thereby, the combustion gas present in the combustion chamber (11A) on the side of the first fuel injection device (5) can be utilized for the combustion of the spray flame. Further, by forming the exhaust side piston (4) such that the outer peripheral edge of the bottom surface of the second cavity portion (82) is continuous with the outer peripheral surface (42), the volume of the combustion chamber (11B) on the side of the second fuel injection device (6) can be made relatively large. Thereby, the combustion gas present in the combustion chamber (11B) on the side of the second fuel injection device (6) can be utilized for the combustion of the spray flame.

[0084] 5) In some embodiments, it is the opposed piston engine (1) described in any one of 1) to 4) above, wherein the first fuel injection device (5) has an injection center axis inclined toward the one side in the axial direction toward the inner side in the radial direction of the cylinder (2), and the second fuel injection device (6) has an injection center axis inclined toward the other side in the axial direction toward the inner side in the radial direction of the cylinder (2).

[0085] According to the configuration of 5) above, by inclining the injection center axes of the first fuel injection device (5) and the second fuel injection device (6) in different directions in the axial direction of the cylinder (2), interference between the spray flame of the first fuel injection device (5) and the spray flame of the second fuel injection device (6) can be suppressed, so that further higher combustion efficiency can be achieved.

[0086] 6) In some embodiments, it is the opposed piston engine (1) described in 4) above, wherein the first fuel injection device (5) is arranged on the one side in the axial direction rather than the second fuel injection device (6).

[0087] According to the configuration of 6) above, by arranging the first fuel injection device (5) and the second fuel injection device (6) at positions shifted from each other in the axial direction of the cylinder (2), interference between the spray flame of the first fuel injection device (5) and the spray flame of the second fuel injection device (6) can be suppressed, so that further higher combustion efficiency can be achieved.

[0088] 7) In some embodiments, the opposed piston engine (1) described in 6) above, wherein the first fuel injection device (5) has an injection central axis along a direction orthogonal to the axial direction toward the inner side in the radial direction of the cylinder (2), and the second fuel injection device (6) has an injection central axis along a direction orthogonal to the axial direction toward the inner side in the radial direction of the cylinder (2).

[0089] According to the configuration of 7) above, by arranging the injection central axes of the first fuel injection device (5) and the second fuel injection device (6) arranged at positions shifted from each other in the axial direction of the cylinder (2) along a direction orthogonal to the axial direction, interference between the spray flame of the first fuel injection device (5) and the spray flame of the second fuel injection device (6) can be suppressed, so that further higher combustion efficiency can be achieved.

[0090] 8) In some embodiments, the opposed piston engine (1) described in any one of 1) to 7) above, wherein the scavenging port (23) has a central axis (CB) along the radial direction toward the inner side in the radial direction of the cylinder (2).

[0091] According to the configuration of 8) above, the combustion gas introduced into the cylinder (2) through the scavenging port (23) forms a rotating flow (tumble flow) that rotates in the axial direction of the cylinder (2) inside the cylinder (2). In this case, since the diffusion of the sprays from the first fuel injection device (5) and the second fuel injection device (6) depends mainly on the momentum of the sprays rather than the swirl ratio, robust combustion that is less affected by the flow state of the combustion gas and thus the operating conditions of the opposed piston engine (1) becomes possible.

[0092] 9) In some embodiments, there is provided an opposed piston engine (1) according to any one of 1) to 8) above, each of the first widening portions (711, 811) and the second widening portions (721, 821) of the cavities (7, 8) has a minimum width that is half or less of the maximum width.

[0093] According to the configuration of 9) above, when each of the first widening portions (711, 811) and the second widening portions (721, 821) of the cavities (7, 8) satisfies the condition that the minimum width is half or less of the maximum width, the outer volumes in the radial direction of each of the combustion chambers (11A) on the first fuel injection device (5) side and the combustion chambers (11B) on the second fuel injection device (6) side can be made relatively large. Therefore, the combustion gas present in these combustion chambers (11A, 11B) can be utilized for the combustion of the spray flames. Also, since the connection portions (73, 83) with the first widening portions (711, 811) and the second widening portions (721, 821) can be made relatively small, interference between the spray flame of the first fuel injection device (5) and the spray flame of the second fuel injection device (6) can be effectively suppressed.

Explanation of Reference Numerals

[0094] 1 Opposed piston engine 2 Cylinder 3 Scavenging side piston 4 Exhaust side piston 5 Scavenging side fuel injection device 6 Exhaust side fuel injection device 7 Scavenging side cavity 8 Exhaust side cavity 11 Combustion chamber 12 Scavenging side piston pin 13 Exhaust side piston pin 14 Scavenging side connecting rod 15 Exhaust side connecting rod 16 Crankshaft 17 Rotating shaft 20 Internal space 21 Outer surface 22 Inner surface 23 Scavenging port 24 Exhaust port 31,41 Top surface 32,42 Outer peripheral surface

Claims

1. A cylinder having a scavenging port formed on one side in the axial direction and an exhaust port formed on the other side in the axial direction, A scavenging-side piston disposed on the one side in the axial direction inside the cylinder, An exhaust-side piston disposed on the other side in the axial direction inside the cylinder, A first fuel injection device configured to inject fuel between the scavenging-side piston and the exhaust-side piston inside the cylinder, A second fuel injection device configured to inject fuel between the scavenging-side piston and the exhaust-side piston inside the cylinder, the second fuel injection device being circumferentially displaced so as to face the first fuel injection device across the central axis of the cylinder when viewed from one side in the axial direction, The cavities formed on the top surfaces of the scavenging-side piston and the exhaust-side piston respectively, A first cavity portion including a first widening portion whose width increases as it goes from the central portion of each of the scavenging-side piston and the exhaust-side piston toward the side where the first fuel injection device is disposed, A second cavity portion including a second widening portion whose width increases as it goes from the central portion of each of the scavenging-side piston and the exhaust-side piston toward the side where the second fuel injection device is disposed, Each of the first widening portion and the second widening portion is configured such that the width is minimized at the connection portion between the first widening portion and the second widening portion, An opposed-piston engine.

2. The scavenging-side piston, Includes a scavenging-side first protruding portion that protrudes toward the other side in the axial direction outside the second cavity portion of the scavenging-side piston in the radial direction, and forms a scavenging-side first wall surface that is the outer wall surface of the second cavity portion in the radial direction, The exhaust-side piston, Includes an exhaust-side first protruding portion that protrudes toward the one side in the axial direction outside the first cavity portion of the exhaust-side piston in the radial direction, and forms an exhaust-side first wall surface that is the outer wall surface of the first cavity portion in the radial direction, Each of the scavenging-side first wall surface and the exhaust-side first wall surface has at least a part in the axial direction extending along the axial direction, The opposed-piston engine according to Claim 1.

3. The scavenging-side piston, On the outer side in the radial direction of the first cavity portion of the scavenging-side piston, a scavenging-side second protrusion is provided which protrudes toward the other side in the axial direction and forms a scavenging-side second wall surface which is the outer wall surface in the radial direction of the first cavity portion. The exhaust-side piston On the outer side in the radial direction of the second cavity portion of the exhaust-side piston, an exhaust-side second protrusion is provided which protrudes toward the one side in the axial direction and forms an exhaust-side second wall surface which is the outer wall surface in the radial direction of the second cavity portion. Each of the scavenging-side second wall surface and the exhaust-side second wall surface has at least a part in the axial direction extending along the axial direction. The opposed-piston engine according to claim 2.

4. The scavenging-side piston The outer peripheral edge of the bottom surface of the first cavity portion is continuous with the outer peripheral surface of the scavenging-side piston. The exhaust-side piston The outer peripheral edge of the bottom surface of the second cavity portion is continuous with the outer peripheral surface of the exhaust-side piston. The opposed-piston engine according to claim 2.

5. The first fuel injection device has an injection center axis inclined toward the one side in the axial direction toward the inner side in the radial direction of the cylinder. The second fuel injection device has an injection center axis inclined toward the other side in the axial direction toward the inner side in the radial direction of the cylinder. The opposed-piston engine according to any one of claims 1 to 4.

6. The first fuel injection device is arranged on the one side in the axial direction with respect to the second fuel injection device. The opposed-piston engine according to claim 4.

7. The first fuel injection device has an injection center axis along a direction orthogonal to the axial direction toward the inner side in the radial direction of the cylinder. The second fuel injection device has an injection center axis along a direction orthogonal to the axial direction toward the inner side in the radial direction of the cylinder. The opposed-piston engine according to claim 6.

8. The scavenging port has a central axis along the radial direction toward the inner side in the radial direction of the cylinder. The opposed-piston engine according to any one of claims 1 to 4.

9. Each of the first widened portion and the second widened portion of the cavity has a minimum width that is half or less of the maximum width. The opposed-piston engine according to any one of claims 1 to 4.

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