Opposed-piston engine

Abstract

An opposed-piston engine includes: 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 part 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 part 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 part and the second widening part each have the smallest width at a connection part between the first widening part and the second widening part.

Description

opposed-piston engine

[0001] This application claims priority from Japanese Patent Application No. 2024-004625, filed with the Japan Patent Office on January 16, 2024, the contents of which are incorporated herein by reference.

[0002] Two-stroke diesel engines include opposed-piston engines, which have two pistons arranged opposite each other inside a single cylinder, forming a combustion chamber between the two pistons (see, for example, Patent Document 1). In opposed-piston engines, each time the piston reciprocates, an exhaust stroke is performed in which combustion gas inside the cylinder is discharged through an exhaust port formed in the cylinder wall, and a scavenging stroke is performed in which air is taken into the cylinder through a scavenging port formed in the cylinder wall.

[0003] Patent No. 5782109

[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 taken along the axial direction of the cylinder.

[0005] In the combustion space described in Patent Document 1, when fuel is injected from multiple fuel injection devices, the fuels may interfere with each other, resulting in a decrease in thermal efficiency. Also, in the combustion space described in Patent Document 1, the fuel spray does not reach the outside of the doughnut-shaped combustion space in the radial direction, resulting in a low fuel space utilization rate and a rise in the combustion gas temperature, which may cause a decrease in thermal efficiency.

[0006] In view of the above circumstances, an object of at least one embodiment of the present disclosure is to provide an opposed-piston engine that can achieve high combustion efficiency.

[0007] an opposed-piston engine according to at least one embodiment of the present disclosure, comprising: a cylinder having a scavenging port formed on one side in an axial direction and an exhaust port formed on the other side in the axial direction; a scavenging-side piston arranged on the one side in the axial direction inside the cylinder; an exhaust-side piston arranged 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; and 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 arranged offset in the circumferential direction to face the first fuel injection device across the central axis of the cylinder when viewed from the one side in the axial direction, wherein cavities formed on top surfaces of the scavenging-side piston and the exhaust-side piston each include: a first cavity portion including a first widening portion whose width increases from a central portion of the scavenging-side piston and the exhaust-side piston toward the side where the first fuel injection device is arranged; a second cavity portion including a second widened portion whose width increases 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, and each of the first widened portion and the second widened portion is configured so that the width is smallest at a connection portion between the first widened portion and the second widened portion.

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

[0009] FIG. 9 is a schematic cross-sectional view of an opposed-piston engine according to an embodiment of the present disclosure. FIG. 9 is a schematic cross-sectional view schematically showing the vicinity of a combustion chamber of an opposed-piston engine according to a first embodiment of the present disclosure. FIG. 9 is an explanatory view for explaining the cavity shape of a scavenging-side piston in the first embodiment of the present disclosure. FIG. 9 is an explanatory view for explaining the cavity shape of an exhaust-side piston in the first embodiment of the present disclosure. FIG. 9 is a schematic cross-sectional view of the opposed-piston engine shown in FIG. 3, taken along the arrows A-B. FIG. 9 is a schematic cross-sectional view schematically showing the vicinity of a combustion chamber of an opposed-piston engine according to a second embodiment of the present disclosure. FIG. 9 is an explanatory view for explaining the cavity shape of a scavenging-side piston in the second embodiment of the present disclosure. FIG. 9 is an explanatory view for explaining the cavity shape of an exhaust-side piston in the second embodiment of the present disclosure. FIG. 9 is an explanatory view for explaining scavenging ports of an opposed-piston engine according to an embodiment of the present disclosure. FIG. 9 is a schematic cross-sectional view taken along a direction perpendicular to the axial direction of the opposed-piston engine shown in FIG.

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

[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 injector 5, and a second fuel injector 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 radially inward of the outer surface 21 of the cylinder 2. 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 so that the cross section perpendicular to the axial direction of the cylinder 2 has a circular shape.

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

[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 circumferential 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 circumferential 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 in the axial direction of the cylinder 2, with the combustion chamber 11 between them.

[0015] At least one scavenging port 23 (in the illustrated example, multiple scavenging ports) is formed in the inner surface 22 on the scavenging side of the cylinder 2. The multiple scavenging ports 23 are provided at intervals in the circumferential direction of the cylinder 2. Each of the multiple 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 through the scavenging port 23 to the internal space 20 and flows through the internal space 20 toward the exhaust side.

[0016] At least one exhaust port 24 (in the illustrated example, multiple exhaust ports) is formed in the inner surface 22 on the exhaust side of the cylinder 2. The multiple exhaust ports 24 are provided at intervals around the circumference of the cylinder 2. Each of the multiple 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 bottom dead center are indicated by solid lines, and the top surface 31 of the scavenging side piston 3 at top dead center and the top surface 41 of the exhaust side piston 4 at top dead center are indicated by two-dot chain lines.

[0018] The scavenging-side piston 3 and the exhaust-side piston 4 reciprocate in synchronization with each other inside the cylinder 2 along the axial direction of the cylinder 2. The scavenging-side piston 3 is configured to be able to reciprocate between the top dead center of the scavenging-side piston 3 (the position closest to the exhaust-side piston 4) and the bottom dead center (the position farthest from the exhaust-side piston 4). The exhaust-side piston 4 is configured to be able to reciprocate between the top dead center of the exhaust-side piston 4 (the position closest to the scavenging-side piston 3) and the bottom dead center (the position farthest from the scavenging-side piston 3). 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 reach the top dead center or the bottom dead center at different times.

[0019] 1 , the scavenging side piston 3 is connected to one end of a scavenging side connecting rod 14 via a scavenging side piston pin 12, and the other end of the scavenging side connecting rod 14 is connected to a crankshaft 16. The exhaust side piston 4 is connected to one end of an exhaust side connecting rod 15 via an exhaust side piston pin 13, and the other end of the exhaust side connecting rod 15 is connected to the crankshaft 16. When the crankshaft 16 rotates around a rotation axis 17, the scavenging side piston 3 and the exhaust side piston 4 reciprocate inside the cylinder 2 in synchronization with each other, 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 top dead center).

[0021] In the opposed-piston engine 1, the scavenging-side piston 3 and the exhaust-side piston 4 compress and heat the combustion gas CG introduced into the cylinder 2 through the scavenging ports 23 to a temperature above the ignition point of the fuel F. The first fuel injector 5 and the second fuel injector 6 inject fuel F into this 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. The expansion of the combustion gas generated by the self-ignition pushes the scavenging-side piston 3 and the exhaust-side piston 4 in directions away from each other. The reciprocating motion of the scavenging-side piston 3 and the exhaust-side piston 4 is then transmitted to the crankshaft 16, which converts it into rotational force (power).

[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] The top surface 31 of the scavenging-side piston 3 slides closer to the scavenging side than each scavenging port 23, thereby enabling the supply of combustion gas CG to the internal space 20 via each scavenging port 23. The top surface 41 of the exhaust-side piston 4 slides closer to the exhaust side than each exhaust port 24, thereby enabling the exhaust gas EG to be discharged from the internal space 20 via each exhaust port 24. Since the combustion gas CG supplied to the internal space 20 is compressed by a turbocharger (not shown), the pressure difference between the scavenging ports 23 and the exhaust port 24 allows the supply of combustion gas CG to the internal space 20 and the discharge of exhaust gas EG from the internal space 20.

[0024] (First embodiment) Fig. 2 is a schematic cross-sectional view 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 diagram for explaining the cavity shape of the scavenging-side piston 3 in the first embodiment of the present disclosure. Fig. 4 is an explanatory diagram 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 of the opposed-piston engine 1 shown in Fig. 3, taken along the arrows A-B. Fig. 3 shows 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. Fig. 4 shows 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.

[0025] 3 and 4 , the second fuel injection device 6 is arranged offset in the circumferential direction of the cylinder 2 relative to the first fuel injection device 5 so as to face the cylinder 2 across the central axis (radial central axis) CA of the cylinder 2. In one embodiment, the second fuel injection device 6 is arranged offset within a range of 180°±5° relative to the first fuel injection device 5 in the circumferential direction about the central axis CA of the cylinder 2.

[0026] In the illustrated embodiment, the first fuel injection device 5 is inserted through a first through-hole 25 that penetrates from the outer surface 21 to the inner surface 22 of the cylinder 2, and a portion thereof, including an injection hole 51, is disposed in the internal space 20. The second fuel injection device 6 is inserted through a second through-hole 26 that penetrates from the outer surface 21 to the inner surface 22 of the cylinder 2, and a portion thereof, including an 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 in 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 perpendicular to the axial direction of the cylinder 2, and the scavenging-side cavity 7 has a concave shape that is recessed toward the scavenging side from the flat surface 31A.

[0028] 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 arranged relative to the scavenging-side first cavity portion 71. In the scavenging-side second cavity portion 72, an edge on the side where the first fuel injection device 5 is arranged is connected to an edge of the scavenging-side first cavity portion 71 on the side where the second fuel injection device 6 is arranged, in the central portion 30 of the scavenging-side piston 3.

[0029] 3 , when viewed from one axial side (exhaust 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 a first reference line BL1. When the length position of an intersection P1 of the outer circumferential 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 an intersection P2 of the outer circumferential 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 has a length position in the range of 40% to 60%. In the illustrated embodiment, at the 50% length position, the radially inner end of the scavenging-side second widened portion 721 (scavenging-side second cavity portion 72) is connected to the radially inner end of the scavenging-side first widened portion 711 (scavenging-side first cavity portion 71).

[0030] 3 , the scavenging-side first cavity portion 71 includes, at least in part, a scavenging-side first widened portion (first widened portion) 711 whose width increases from the central portion 30 of the scavenging-side piston 3 toward the side where the first fuel injector 5 is disposed. A part of the scavenging-side first widened portion 711 may be formed in 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 injector 5 is disposed, but the rate of increase in width may increase or decrease, or the scavenging-side first widened portion 711 may include a part with a constant width.

[0031] 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 radial outer side of the scavenging-side first cavity portion 71, and a bottom surface 715 of the scavenging-side first cavity portion 71. One axial end of each of the wall surfaces 712, 713, and 714 is connected to the bottom surface 715, and the other axial end is connected to the flat surface 31A. One circumferential end of the wall surface 714 is connected to the wall surface 712, and the other circumferential end 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, and 714 and the bottom surface 715.

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

[0033] 3 , the scavenging-side piston 3 has a wall surface 722 on one side in the width direction of the scavenging-side second cavity 72, a wall surface 723 on the other side in the width direction of the scavenging-side first cavity 72, a radially outer wall surface (scavenging-side first wall surface) 724 of the scavenging-side second cavity 72, and a bottom surface 725 of the scavenging-side second cavity 72. One axial end of each of the wall surfaces 722, 723, and 724 is connected to the bottom surface 725, and the other axial end is connected to the flat surface 31A. One circumferential end of the wall surface 724 is connected to the wall surface 722, and the other circumferential end is connected to the wall surface 723. The scavenging-side second cavity 72 has a cavity shape defined by the wall surfaces 722, 723, and 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 protruding portion 34 that forms a scavenging-side first wall surface 724, a scavenging-side second protruding portion 33 that forms a scavenging-side second wall surface 714, a scavenging-side third protruding portion 35 that forms a wall surface 712 and a wall surface 722 on one side in the width direction of the scavenging-side cavity 7, and a scavenging-side fourth protruding portion 36 that forms a wall surface 713 and a wall surface 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 so that the width is minimized at a connection portion 73 between the scavenging side first widened portion 711 and the scavenging side second widened portion 721.

[0036] (Exhaust-side cavity) As shown in Fig. 4, an exhaust-side cavity 8 having a predetermined cavity volume is formed in the top surface 41 of the exhaust-side piston 4. In the embodiment shown in Fig. 4, the top surface 41 of the exhaust-side piston 4 includes a flat surface 41A extending in a direction perpendicular to the axial direction of the cylinder 2, and the exhaust-side cavity 8 has a concave shape that is recessed toward the exhaust side from the flat surface 41A.

[0037] 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 relative to the exhaust-side first cavity portion 81. In the exhaust-side second cavity portion 82, the edge on the side where the first fuel injection device 5 is disposed is connected to the edge of the exhaust-side first cavity portion 81 on the side where the second fuel injection device 6 is disposed, in the center portion 40 of the exhaust-side piston 4.

[0038] The combustion chamber 11 includes a combustion chamber 11A on the side where the first fuel injection device 5 is disposed relative 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 disposed relative to the central axis CA of the cylinder 2. The exhaust-side first cavity 81 faces the scavenging-side first cavity 71 across the combustion chamber 11A in the axial direction of the cylinder 2. The exhaust-side second cavity 82 faces the scavenging-side second cavity 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 center 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 second reference line BL2. The length position of an intersection P3 of the outer circumferential 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 disposed is defined as 0%. The length position of an intersection P4 of the outer circumferential 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 disposed is defined as 100%. In this case, the central portion 40 of the exhaust-side piston 4 has a length position in the range of 40% to 60%. In the illustrated embodiment, at the 50% length position, the radially inner end of the exhaust-side second widened portion 821 (exhaust-side second cavity portion 82) is connected to the radially inner end of the exhaust-side first widened portion 811 (exhaust-side first cavity portion 81).

[0040] 4 , the exhaust-side first cavity portion 81 includes at least a first exhaust-side widened portion (first widened portion) 811 whose width increases from the central portion 40 of the exhaust-side piston 4 toward the side where the first fuel injector 5 is disposed. A portion 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 injector 5 is disposed, but the rate of increase in width may increase or decrease, or 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 widthwise side of the exhaust-side first cavity portion 81, a wall surface 813 on the other widthwise side of the exhaust-side first cavity portion 81, a radially outer wall surface (exhaust-side first wall surface) 814 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 axial end connected to the bottom surface 815 and the other axial end connected to the flat surface 41A. The wall surface 814 has one circumferential end connected to the wall surface 812 and the other circumferential end connected to the wall surface 813. The wall surfaces 812, 813, and 814 and the bottom surface 815 define a cavity shape for the exhaust-side first cavity portion 81.

[0042] 4 , the exhaust-side second cavity portion 82 includes at least a second exhaust-side widened portion (second widened portion) 821 in a portion thereof, the width of which increases from the central portion 40 of the exhaust-side piston 4 toward the side where the second fuel injector 6 is disposed. A portion 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 rate of increase in width of the exhaust-side second widened portion 821 is constant in the direction toward the side where the second fuel injector 6 is disposed, but the rate of increase in width may increase or decrease, or 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 radially outer wall surface (scavenging-side second wall surface) 824 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 axial end connected to the bottom surface 825 and the other axial end connected to the flat surface 41A. The wall surface 824 has one circumferential end connected to the wall surface 822 and the other circumferential end connected to the wall surface 823. The wall surfaces 822, 823, and 824 and the bottom surface 825 define a cavity shape of the exhaust-side second cavity portion 82.

[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 widening portion 811 and the exhaust side second widening portion 821 of the exhaust side cavity 8 is configured so that the width is smallest at the connection portion 83 between the exhaust side first widening portion 811 and the exhaust side second widening portion 821.

[0046] Reference numeral 50 in Fig. 2 indicates the flow of the spray injected from the first fuel injector 5 and the spray flame generated by combustion of the spray. Reference numeral 60 in Fig. 2 indicates the flow of the spray injected from the second fuel injector 6 and the spray flame generated by combustion of the spray. The spray injected from the first fuel injector 5 flows within the combustion chamber 11 along the bottom surfaces 715, 725 of the scavenging-side cavity 7 toward the side where the second fuel injector 6 is disposed. The spray injected from the second fuel injector 6 flows within the combustion chamber 11 along the bottom surfaces 815, 825 of the exhaust-side cavity 8 toward the side where the first fuel injector 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 72 and the exhaust-side second cavity 82. By combusting 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 spray injected from the second fuel injection device 6 spreads less, the combustion gas present in the combustion chamber 11B on the second fuel injection device 6 side can be utilized for combustion of the spray flame.

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

[0049] By narrowing the widths of the connecting portions 73, 83 between the first widened portions 711, 811 and the second widened portions 721, 821 of the scavenging-side cavity 7 and the exhaust-side cavity 8, it is possible to prevent the spray flame of the first fuel injection device 5 from entering the combustion chamber 11A on the first fuel injection device 5 side from the combustion chamber 11B on the second fuel injection device 6 side. It is also possible to prevent the spray flame of the second fuel injection device 6 from entering the combustion chamber 11B on the second fuel injection device 6 side from the combustion chamber 11A on the first fuel injection device 5 side. This makes it possible to prevent interference between the spray flame of the first fuel injection device 5 and the spray flame of the second fuel injection device 6, thereby achieving even higher combustion efficiency.

[0050] In some embodiments, the minimum width of each of the above-mentioned scavenging side first widening portion 711, scavenging side second widening portion 721, exhaust side first widening portion 811 and exhaust side second widening portion 821 is equal to or less than half of the maximum width.

[0051] When each of the scavenging-side first widened portion 711, the scavenging-side second widened portion 721, the exhaust-side first widened portion 811, and the exhaust-side second widened portion 821 satisfies the condition that the minimum width is equal to or less than half of the maximum width, the radial outer volumes of the combustion chamber 11A on the first fuel injection device 5 side and the combustion chamber 11B on the second fuel injection device 6 side can be made relatively large, so that the combustion gas present in these combustion chambers 11A, 11B can be utilized for combustion of the spray flame. In addition, the connection portions 73, 83 between the first widened portions 711, 811 and the second widened portions 721, 821 can be made relatively small, so that 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 portion of each of the scavenging side first wall surface 724 and the exhaust side first wall surface 814 in the axial direction of the cylinder 2 extends along the axial direction.

[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] The scavenging-side first wall surface 724 guides the spray flame flowing along the scavenging-side second cavity 72 to the exhaust-side second cavity 82, thereby making it possible to utilize the combustion gas present in the exhaust-side second cavity 82 for combustion of the spray flame. Furthermore, the exhaust-side first wall surface 814 guides the spray flame flowing along the exhaust-side first cavity 81 to the scavenging-side first cavity 71, thereby making it possible to utilize the combustion gas present in the scavenging-side first cavity 71 for combustion of the spray flame.

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

[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] The scavenging-side second wall surface 714 guides the spray flame, which has been guided to the scavenging-side first cavity 71 along the axial direction of the cylinder 2, radially inward (to the side where the second fuel injection device 6 is arranged), thereby making it possible to utilize the combustion gas present radially inside the scavenging-side first cavity 71 for combustion of the spray flame. Furthermore, the exhaust-side second wall surface 824 guides the spray flame, which has been guided to the exhaust-side second cavity 82 along the axial direction of the cylinder 2, radially inward (to the side where the first fuel injection device 5 is arranged), thereby making it possible to utilize the combustion gas present radially inside the exhaust-side second cavity 82 for combustion of the spray flame.

[0058] In some embodiments, as shown in FIG. 2 , the first fuel injection device 5 has an injection central axis 52 inclined toward the scavenging side toward the inside in the radial direction of the cylinder 2, and the second fuel injection device 6 has an injection central axis 62 inclined toward the exhaust side toward the inside 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 center 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 center of the exhaust-side cavity 8.

[0059] In the illustrated embodiment, the second fuel injector 6 is disposed at the same axial position as the first fuel injector 5 in the axial direction of the cylinder 2. Specifically, at least a portion of the second fuel injector 6 is located within the axial range in which the first fuel injector 5 is located in the axial direction of the cylinder 2. In the embodiment shown in Fig. 2, the first fuel injector 5 and the second fuel injector 6 are located on the exhaust side of the flat surface 31A and on the scavenging side of the flat surface 41A.

[0060] By tilting the injection center axes 52, 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, thereby achieving even higher combustion efficiency.

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

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

[0063] By shaping the scavenging-side piston 3 so 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 first fuel injection device 5 side can be made relatively large. This allows the combustion gas present in the combustion chamber 11A on the first fuel injection device 5 side to be utilized for combustion of the spray flame. Furthermore, by shaping the exhaust-side piston 4 so 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 second fuel injection device 6 side can be made relatively large. This allows the combustion gas present in the combustion chamber 11B on the second fuel injection device 6 side to be utilized for combustion of the spray flame.

[0064] 6 , the first fuel injection device 5 is disposed on one side (scavenging side) of the second fuel injection device 6 in the axial direction of the cylinder 2. In the illustrated embodiment, at least a portion of the first fuel injection device 5 is located within an axial range in which the scavenging-side first wall surface 724 of the cylinder 2 is located in the axial direction. At least a portion of the second fuel injection device 6 is located within an axial range in which the exhaust-side first wall surface 814 of the cylinder 2 is located in the axial direction.

[0065] By positioning 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, thereby achieving even higher combustion efficiency.

[0066] 6 , the first fuel injection device 5 has an injection center axis 52 extending radially inward of the cylinder 2 and perpendicular to the axial direction of the cylinder 2, and the second fuel injection device 6 has an injection center axis 62 extending radially inward of the cylinder 2 and perpendicular to the axial direction of the cylinder 2. In the illustrated embodiment, the injection center 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 aligning the injection central axes 52, 62 of the first fuel injector 5 and the second fuel injector 6, which are arranged at positions offset from each other in the axial direction of the cylinder 2, along a direction perpendicular to the axial direction, interference between the spray flame of the first fuel injector 5 and the spray flame of the second fuel injector 6 can be suppressed, thereby achieving even higher combustion efficiency. In the second embodiment, compared to the first embodiment, the spray and spray flame from the first fuel injector 5 flow a relatively long distance along the scavenging-side cavity 7, thereby promoting the generation of a rotational flow (tumble flow) toward the axial direction of the cylinder 2 on the scavenging-side first wall surface 724. Furthermore, in the second embodiment, compared to the first embodiment, the spray and spray flame from the second fuel injector 6 flow a relatively long distance along the exhaust-side cavity 8, thereby promoting the generation of a rotational flow (tumble flow) toward the axial direction of the cylinder 2 on the exhaust-side first wall surface 814. This allows even higher combustion efficiency to be achieved.

[0068] The positions and injection central axes 52, 62 of the first fuel injection device 5 and the second fuel injection device 6 in the second embodiment may be adopted in the opposed-piston engine 1 according to the first embodiment. In this case, it is preferable to provide the scavenging-side second protruding portion 33 with a hole or a groove for passing the spray from the first fuel injection device 5. It is also preferable to provide the exhaust-side second protruding portion 44 with a hole or a groove for passing the spray from the second fuel injection device 6. It is also preferable to use the positions and injection central axes 52, 62 of the first embodiment in the opposed-piston engine 1 according to the second embodiment.

[0069] Fig. 9 is an explanatory diagram for explaining a scavenging port 23 of an opposed-piston engine 1 according to one embodiment of the present disclosure. Fig. 10 is a schematic cross-sectional view taken along a direction perpendicular to the axial direction of the opposed-piston engine 1 shown in Fig. 9. As shown in Fig. 10, the scavenging port 23 in some of the embodiments described above has a central axis CB that extends radially inward of the cylinder 2 in the radial direction.

[0070] The plurality of scavenging ports 23 are arranged at similar axial positions to one another in the axial direction of the cylinder 2. When a reference plane BF is defined as a plane that includes a central axis CB of one of the plurality of scavenging ports 23 and is perpendicular to the axial direction of the cylinder 2, the other scavenging ports 23 exist on the reference plane BF.

[0071] The combustion gas introduced into the cylinder 2 through the scavenging ports 23 forms a rotating flow (tumble flow) that swirls in the axial direction of the cylinder 2 inside the cylinder 2. In this case, the diffusion of the sprays from the first fuel injector 5 and the second fuel injector 6 is not dependent on the swirl ratio but is mainly dependent on the momentum of the spray, enabling robust combustion that is less affected by the flow state of the combustion gas and, in turn, the operating conditions of the opposed-piston engine 1. In particular, in the opposed-piston engine 1 according to the second embodiment, the top surface 31 of the scavenging-side piston 3 has a distribution in the axial direction of the cylinder 2, which causes a time lag in the timing at which the combustion gas flows into the internal space 20 through the scavenging ports 23, thereby promoting the formation of the above-mentioned tumble flow.

[0072] In this specification, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0073] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0074] The contents of the above-described embodiments can be understood, for example, as follows.

[0075] 1) An opposed-piston engine (1) according to at least one embodiment of the present disclosure includes: a cylinder (2) having a scavenging port (23) formed on one side in an axial direction and an exhaust port (24) formed on the other side in the axial direction; a scavenging-side piston (3) arranged on the one side in the axial direction inside the cylinder (2); an exhaust-side piston (4) arranged 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); and 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 arranged circumferentially offset from the first fuel injection device (5) so as to face opposite to the first fuel injection device (5) across a central axis (CA) of the cylinder (2) when viewed from the one side in the axial direction. The cavities (scavenging side cavity 7, exhaust side cavity 8) formed in the top surfaces (31, 41) of the scavenging side piston (3) and the exhaust side piston (4) respectively include: a first cavity portion (71, 81) including a first widened portion (711, 811) whose width increases from a central portion of the scavenging side piston (3) and the exhaust side piston (4) respectively toward a side where the first fuel injection device (5) is disposed; and a second cavity portion (72, 82) including a second widened portion (721, 821) whose width increases from the central portion of the scavenging side piston (3) and the exhaust side piston (4) respectively toward a side where the second fuel injection device (6) is disposed. Each of the first widened portion (711, 811) and the second widened portion (721, 821) of the cavity (7, 8) is configured so that the width is smallest at the connection portion (73, 83) between the first widened portion (711, 811) and the second widened portion (721, 821).

[0076] According to the configuration of 1), the spray injected from the first fuel injection device (5) is combusted 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, so that the combustion gas present in the combustion chamber (11B) on the second fuel injection device (6) side can be utilized for combustion of the spray flame. Also, the spray injected from the second fuel injection device (6) is combusted in the combustion chamber (11A) on the first fuel injection device (5) side, where the spread of the spray injected from the first fuel injection device (5) is small, so that the combustion gas present in the combustion chamber (11A) on the first fuel injection device (5) side can be utilized for combustion of the spray flame. This allows for high combustion efficiency with little unburned fuel.

[0077] Furthermore, according to the configuration 1), by reducing the width of the connection portion (73, 83) between the first widened portion (711, 811) and the second widened portion (721, 821), it is possible to suppress the spray flame of the first fuel injection device (5) from entering the combustion chamber (11A) on the first fuel injection device (5) side. Also, it is possible to suppress the spray flame of the second fuel injection device (6) from entering the combustion chamber (11B) on the second fuel injection device (6) side. This suppresses interference between the spray flame of the first fuel injection device (5) and the spray flame of the second fuel injection device (6), thereby achieving even higher combustion efficiency.

[0078] 2) In some embodiments, in the opposed-piston engine (1) described in 1) above, the scavenging-side piston (3) includes a scavenging-side first protruding portion (34) that protrudes toward the other side in the axial direction from a radially outer side of the second cavity portion (72) of the scavenging-side piston (3) and forms a scavenging-side first wall surface (724) that is the radially outer wall surface of the second cavity portion (72), and the exhaust-side piston (4) includes an exhaust-side first protruding portion (43) that protrudes toward the one side in the axial direction from a radially outer side of the first cavity portion (82) of the exhaust-side piston (4) and forms an exhaust-side first wall surface (814) that is the radially outer wall surface of the first cavity portion (82), and at least a portion in the axial direction of each of the scavenging-side first wall surface (724) and the exhaust-side first wall surface (814) extends 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), thereby making it possible to utilize the combustion gas present in the second cavity portion (82) for combustion of the spray flame. Also, 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), thereby making it possible to utilize the combustion gas present in the first cavity portion (71) for combustion of the spray flame.

[0080] 3) In some embodiments, in the opposed-piston engine (1) described in 2) above, the scavenging-side piston (3) includes a scavenging-side second protruding portion (33) that protrudes toward the other axial direction from a radially outer side of the first cavity portion (71) of the scavenging-side piston (3) and forms a scavenging-side second wall surface (714) that is the radially outer wall surface of the first cavity portion (71), and the exhaust-side piston (4) includes an exhaust-side second protruding portion (44) that protrudes toward the one axial direction from a radially outer side of the second cavity portion (82) of the exhaust-side piston (4) and forms an exhaust-side second wall surface (824) that is the radially outer wall surface of the second cavity portion (82), and at least a portion in the axial direction of each of the scavenging-side second wall surface (714) and the exhaust-side second wall surface (824) extends along the axial direction.

[0081] According to the configuration of 3), the scavenging-side second wall surface (714) guides the spray flame, which has been guided to the first cavity portion (71) of the scavenging-side piston (3) along the axial direction of the piston (2), radially inward, thereby making it possible to utilize the combustion gas present on the radially inner side of the first cavity portion (71) for combustion of the spray flame. Also, the exhaust-side second wall surface (824) guides the spray flame, which has been guided to the second cavity portion (82) of the exhaust-side piston (4) along the axial direction of the piston (2), radially inward, thereby making it possible to utilize the combustion gas present on the radially inner side of the second cavity portion (82) for combustion of the spray flame.

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

[0083] According to the configuration 4) above, by forming the scavenging-side piston (3) in a shape 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 first fuel injection device (5) side can be made relatively large. As a result, the combustion gas present in the combustion chamber (11A) on the first fuel injection device (5) side can be utilized for combustion of the spray flame. Furthermore, by forming the exhaust-side piston (4) in a shape 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 second fuel injection device (6) side can be made relatively large. As a result, the combustion gas present in the combustion chamber (11B) on the second fuel injection device (6) side can be utilized for combustion of the spray flame.

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

[0085] According to the configuration of 5), by inclining the injection central 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), it is possible to suppress interference between the spray flame of the first fuel injection device (5) and the spray flame of the second fuel injection device (6), thereby achieving even higher combustion efficiency.

[0086] 6) In some embodiments, 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 relative to the second fuel injection device (6).

[0087] According to the configuration of 6), the first fuel injection device (5) and the second fuel injection device (6) are disposed at positions offset from each other in the axial direction of the cylinder (2), thereby making it possible to suppress interference between the spray flame of the first fuel injection device (5) and the spray flame of the second fuel injection device (6), thereby achieving even higher combustion efficiency.

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

[0089] According to the configuration of 7) above, the respective injection central axes of the first fuel injection device (5) and the second fuel injection device (6), which are arranged at positions offset from each other in the axial direction of the cylinder (2), are aligned along a direction perpendicular to the axial direction, thereby making it possible to suppress interference between the spray flame of the first fuel injection device (5) and the spray flame of the second fuel injection device (6), thereby achieving even higher combustion efficiency.

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

[0091] According to the configuration 8), the combustion gas introduced into the cylinder (2) through the scavenging port (23) forms a rotating flow (tumble flow) swirling in the axial direction of the cylinder (2) inside the cylinder (2). In this case, the diffusion of the sprays from the first fuel injection device (5) and the second fuel injection device (6) is not dependent on the swirl ratio but is mainly dependent on the momentum of the sprays, thereby enabling robust combustion that is less susceptible to the flow state of the combustion gas and, ultimately, the operating conditions of the opposed-piston engine (1).

[0092] 9) In some embodiments, in the opposed-piston engine (1) described in any one of 1) to 8) above, the first widened portion (711, 811) and the second widened portion (721, 821) of the cavity (7, 8) each have a minimum width that is equal to or less than half of the maximum width.

[0093] According to the configuration of 9), when the first widened portion (711, 811) and the second widened portion (721, 821) of the cavity (7, 8) each satisfy the condition that the minimum width is equal to or less than half of the maximum width, the radial outer volumes of the combustion chamber (11A) on the first fuel injection device (5) side and the combustion chamber (11B) on the second fuel injection device (6) side can be made relatively large, so that the combustion gas present in these combustion chambers (11A, 11B) can be utilized for combustion of the spray flame. Furthermore, the connection portion (73, 83) between the first widened portion (711, 811) and the second widened portion (721, 821) can be made relatively small, so that 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.

[0094] REFERENCE SIGNS LIST 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 circumferential 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; and 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 include 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, and 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 to have the minimum width at the connection portion between the first widening portion and the second widening portion. 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 on the outer side in the radial direction of the second cavity portion of the scavenging side piston and forms a scavenging side first wall surface that is the outer wall surface in the radial direction of the second cavity portion. The exhaust side piston includes an exhaust side first protruding portion that protrudes toward the one side in the axial direction on the outer side in the radial direction of the first cavity portion of the exhaust side piston and forms an exhaust side first wall surface that is the outer wall surface in the radial direction of the first cavity portion. 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. Opposed piston engine according to claim 1.

3. The scavenging-side piston includes a scavenging-side second protrusion that protrudes toward the other side in the axial direction on the outer side in the radial direction of the first cavity portion of the scavenging-side piston, and forms a scavenging-side second wall surface that is the outer wall surface in the radial direction of the first cavity portion. The exhaust-side piston includes an exhaust-side second protrusion that protrudes toward the one side in the axial direction on the outer side in the radial direction of the second cavity portion of the exhaust-side piston, and forms an exhaust-side second wall surface that 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 has an outer peripheral edge of a bottom surface of the first cavity portion continuous with an outer peripheral surface of the scavenging-side piston. The exhaust-side piston has an outer peripheral edge of a bottom surface of the second cavity portion continuous with an 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 central 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 central 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 central 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 central 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 width portion and the second width portion of the cavity has a minimum width that is not more than half of the maximum width. The opposed-piston engine according to any one of claims 1 to 4.

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