Opposed piston engine

Abstract

To provide an opposed piston engine capable of reducing thermal load of an exhaust-side piston.SOLUTION: An opposed piston engine includes: a cylinder provided with a scavenging port at one side in an axial direction and an exhaust port at the other side in the axial direction; a scavenging-side piston disposed at one side in the axial direction inside of the cylinder; an exhaust-side piston disposed at the other side in the axial direction inside of the cylinder; and at least one fuel injection device constituted to inject a fuel between the scavenging-side piston and the exhaust-side piston inside of the cylinder. A top face of the exhaust-side piston is formed into a flat shape, a top face of the scavenging-side piston is provided with a scavenging-side cavity having a prescribed cavity volume, and at least one fuel injection device includes at least one scavenging-side fuel injection device having a central axis inclined to one side in the axial direction toward the inside in a radial direction of the cylinder.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] There is an opposed piston engine in which two pistons are arranged oppositely inside one cylinder to form a combustion chamber between the two pistons in a two-stroke diesel engine (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. Sometimes, the scavenging port formed in the cylinder wall is inclined to form a swirl flow (swirling flow) in the air taken in from the scavenging port, thereby enhancing the effect of replacing scavenging and exhaust.

[0003] 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 in 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.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In an opposed piston engine, fuel is injected from a fuel injection device provided on the cylinder wall. The fuel injected into the cylinder may flow into a swirl flow formed in the cylinder and burn in the outer peripheral region of the fuel chamber. When the combustion flame spreads in the outer peripheral region of the combustion chamber, there is a risk of an increase in the heat load on the outer peripheral portion of the piston where the cooling action from the inside of the piston is difficult to reach. An increase in the heat load on the outer peripheral portion of the piston may cause problems such as poor sliding of the piston due to deterioration of piston lubrication (deterioration of lubricating oil) and damage to the piston due to thermal stress generated in the piston.

[0006] Of the two pistons of the opposed piston engine, the scavenging side piston, which is the piston close to the scavenging port, has its top surface cooled by low-temperature air (low-temperature gas) during the scavenging stroke, while the exhaust side piston, which is the piston close to the exhaust port, is also exposed to high-temperature exhaust gas during the exhaust stroke. FIG. 6 is an explanatory diagram for explaining the temperature distribution of the gas facing the top surface of the exhaust side piston of the opposed piston engine according to the comparative example. FIG. 7 is an explanatory diagram for explaining the temperature distribution of the gas facing the top surface of the scavenging side piston of the opposed piston engine according to the comparative example. In FIGS. 6 and 7, the scavenging side piston 03 and the exhaust side piston 04 have the same shape. As shown in FIGS. 6 and 7, the temperature of the gas facing the top surface 041 of the exhaust side piston 04 is higher than the temperature of the gas facing the top surface 031 of the scavenging side piston 03. For this reason, there is concern that the heat load on the outer peripheral portion 043 of the exhaust side piston 04 may lead to problems such as damage to the exhaust side piston.

[0007] In view of the above circumstances, an object of at least one embodiment of the present disclosure is to provide an opposed piston engine capable of reducing the heat load on the exhaust side piston.

Means for Solving the Problems

[0008] An opposed piston engine according to an embodiment of the present disclosure includes 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, and A scavenging-side piston disposed on 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, At least one fuel injection device configured to inject fuel between the scavenging-side piston and the exhaust-side piston inside the cylinder, The top surface of the exhaust-side piston is formed in a flat shape, A scavenging-side cavity having a predetermined cavity volume is formed on the top surface of the scavenging-side piston, The at least one fuel injection device includes at least one scavenging-side fuel injection device having a central axis inclined toward one side in the axial direction toward the inner side in the radial direction of the cylinder.

Advantages of the Invention

[0009] According to at least one embodiment of the present disclosure, a opposed-piston engine capable of reducing the thermal load of the exhaust-side piston is provided.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0011] 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 thereto, but are merely illustrative examples. For example, expressions representing 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 or distances that can obtain the same function. For example, expressions representing 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 that can obtain the same function. For example, expressions representing shapes such as a rectangular shape or a cylindrical shape not only represent 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. On the other hand, the expressions "comprising", "including", or "having" for one component are not exclusive expressions excluding the existence of other components. Note that the same reference numerals may be given to the same configurations and the description may be omitted.

[0012] (Opposed Piston Engine) FIG. 1 is a schematic cross-sectional view schematically showing the configuration 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 having a cylinder bore 21 formed therein that extends axially, a scavenging side piston 3 disposed on one side (the upper side in FIG. 1) of the cylinder 2 in the axial direction, an exhaust side piston 4 disposed on the other side (the lower side in FIG. 1) of the cylinder 2 in the axial direction, and at least one fuel injection device (fuel injection valve) 5 configured to inject fuel between the scavenging side piston 3 and the exhaust side piston 4 inside the cylinder 2. Hereinafter, one side (the upper side in FIG. 1) of the cylinder 2 in the axial direction is defined as the scavenging side, and the other side (the lower side in FIG. 1) of the cylinder 2 in the axial direction is defined as the exhaust side.

[0013] The cylinder 2 has an inner surface 22 that forms the cylinder bore 21. At least one (a plurality in the illustrated example) scavenging port 23 is formed in the inner surface 22 on the scavenging side of the cylinder 2. At least one (a plurality in the illustrated example) exhaust port 24 is formed in the inner surface 22 on the exhaust side of the cylinder 2. The plurality of scavenging ports 23 are provided at intervals in the circumferential direction of the cylinder 2. The plurality of exhaust ports 24 are provided at intervals in the circumferential direction of the cylinder 2.

[0014] Each of the plurality of scavenging ports 23 is shaped to guide combustion gas CG (compressed air in the illustrated example) from the outside to the inside of the cylinder 2 in a direction inclined toward one side in the circumferential direction with respect to the radial direction of the cylinder 2. In certain embodiments, each of the plurality of scavenging ports 23 extends in a direction inclined by a predetermined angle toward one side in the circumferential direction with respect to the radial direction of the cylinder 2. The combustion gas CG introduced into the inside of the cylinder 2 (i.e., the cylinder bore 21) through the scavenging port 23 forms a swirl flow SF (swirling flow) inside the cylinder 2. For this reason, the combustion gas CG introduced into the inside of the cylinder 2 through the scavenging port 23 flows toward the exhaust side while swirling. By forming the swirl flow SF inside the cylinder 2, it is possible to enhance the effect of replacing scavenging and exhaust in the cylinder bore 21 during the scavenging process and the exhaust process, and it is also possible to enhance the effect of promoting the combustion of the injected fuel.

[0015] The scavenging side piston 3 is disposed reciprocally along the axial direction of the cylinder 2 on the scavenging side of the cylinder bore 21. The exhaust side piston 4 is disposed reciprocally along the axial direction of the cylinder 2 on the exhaust side of the cylinder bore 21. 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 cylinder bore 21. In other words, the top surface 31 of the scavenging side piston 3 faces the top surface 41 of the exhaust side piston 4 with the combustion chamber 11 interposed therebetween.

[0016] 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.

[0017] The scavenging-side piston 3 and the exhaust-side piston 4 reciprocate inside the cylinder 2 in synchronization with each other. The scavenging-side piston 3 is configured to be able to reciprocate 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 able to reciprocate 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 the times at which they reach the top dead center or the bottom dead center may be offset.

[0018] 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. As 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 in synchronization with each other and with their sliding directions being on opposite sides of the axial direction of the cylinder 2.

[0019] The fuel injection device 5 is provided on the inner surface 22 of the cylinder 2. The fuel injection device 5 has at least one injection hole 51 for injecting fuel F into the cylinder bore 21. The fuel injection device 5 injects fuel into the cylinder bore 21 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).

[0020] 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. By injecting the fuel F from the fuel injector 5 into this compressed and heated combustion gas CG, the fuel F is caused 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 a rotational force (power) by the crankshaft 16.

[0021] 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.

[0022] When the top surface 31 of the scavenging side piston 3 slides on the scavenging side of each scavenging port 23, the supply of the combustion gas CG to the cylinder bore 21 through each scavenging port 23 becomes possible. When the top surface 41 of the exhaust side piston 4 slides on the exhaust side of each exhaust port 24, the discharge of the exhaust gas EG from the cylinder bore 21 through each exhaust port 24 becomes possible. Since the combustion gas CG supplied to the cylinder bore 21 is compressed by a supercharger (not shown), due to the pressure difference between the scavenging port 23 and the exhaust port 24, the supply of the combustion gas CG to the cylinder bore 21 and the discharge of the exhaust gas EG from the cylinder bore 21 are performed.

[0023] (First Embodiment) FIG. 2 is a schematic cross-sectional view schematically showing the vicinity of the combustion chamber of the opposed piston engine according to the first embodiment of the present disclosure. As shown in FIG. 2, the opposed piston engine 1 according to some embodiments includes the cylinder 2 described above, the scavenging side piston 3 described above, the exhaust side piston 4 described above, and the at least one fuel injection device 5 described above. The top surface 41 of the exhaust side piston 4 is formed in a flat shape. A scavenging side cavity 6 having a predetermined cavity volume is formed in the top surface 31 of the scavenging side piston 3. The at least one fuel injection device 5 described above includes a scavenging side fuel injection device 5A having a central axis CA1 inclined toward the scavenging side (the one side in the axial direction of the cylinder 2) inside the cylinder 2 in the radial direction.

[0024] In the illustrated embodiment, the scavenging side cavity 6 is formed to be recessed in the central portion of the top surface 31 of the scavenging side piston 3, and the top surface 31 of the scavenging side piston 3 includes a scavenging side outer peripheral edge portion 32 that extends toward the outer peripheral side (the outside in the radial direction of the cylinder 2) along a direction orthogonal to the axial direction of the cylinder 2 from the outer peripheral edge 61 of the scavenging side cavity 6. The outer peripheral end of the scavenging side outer peripheral edge portion 32 is continuous with one end of the outer peripheral portion 33 of the scavenging side piston 3 that extends along the axial direction of the cylinder 2. The scavenging side cavity 6 has a concave curved surface 62 whose depth from the outer peripheral edge 61 increases as it goes inward in the radial direction of the cylinder 2 from the outer peripheral edge 61.

[0025] In the illustrated embodiment, the top surface 41 of the exhaust side piston 4 includes a flat surface 41A that extends along a direction orthogonal to the axial direction of the cylinder 2. The outer peripheral end of the flat surface 41A is continuous with one end of the outer peripheral portion 43 of the exhaust side piston 4 that extends along the axial direction of the cylinder 2. The scavenging side fuel injection device 5A is provided on the inner surface 22 of the cylinder 2 with the central axis CA1 inclined with respect to the radial direction of the cylinder 2. The scavenging side fuel injection device 5A injects fuel into the cylinder bore 21 along the extension direction of the central axis CA1. The extension direction of the central axis CA1 points to the central portion of the scavenging side cavity 6.

[0026] According to the above configuration, the top surface 41 of the exhaust-side piston 4 is formed in a flat shape, and a scavenging-side cavity 6 having a predetermined cavity volume is formed in the top surface 31 of the scavenging-side piston 3. Therefore, the combustion chamber 11 formed between the scavenging-side piston 3 and the exhaust-side piston 4 has a larger volume on the scavenging side than on the exhaust side. The fuel injected from the scavenging-side fuel injection device 5A flows toward the scavenging side (one side in the axial direction) along the extension direction of the central axis CA1 of the scavenging-side fuel injection device 5A and burns in the scavenging-side cavity 6. By burning the fuel mainly on the scavenging side of the combustion chamber 11 in this way, the heat load on the exhaust-side piston 4 can be reduced.

[0027] FIG. 3 is an explanatory diagram for explaining the temperature distribution of the combustion gas facing the top surface of the exhaust-side piston in the first embodiment. As shown in FIGS. 3 and 6, the temperature of the combustion gas facing the top surface 41 of the exhaust-side piston 4 in the first embodiment is overall lower than the temperature of the combustion gas facing the top surface 041 of the exhaust-side piston 04 of the opposed-piston engine 01 according to the comparative example. That is, the exhaust-side piston 4 in the first embodiment has a reduced heat load compared to the exhaust-side piston 04 in the comparative example.

[0028] Also, according to the above configuration, by making the top surface 41 of the exhaust-side piston 4 flat, the heat input from the combustion chamber 11 to the top surface 41 of the exhaust-side piston 4 can be suppressed. Thereby, the heat loss of combustion in the combustion chamber 11 can be suppressed, and thus the decrease in the thermal efficiency of the opposed-piston engine 1 can be suppressed.

[0029] (Second Embodiment) FIG. 4 is a schematic cross-sectional view schematically showing the vicinity of the combustion chamber of the opposed-piston engine according to the second embodiment of the present disclosure. As shown in FIG. 4, the opposed-piston engine 1 according to some embodiments includes the cylinder 2 described above, the scavenging-side piston 3 described above, the exhaust-side piston 4 described above, and at least one fuel injection device 5 described above. An exhaust-side cavity 7 having a predetermined cavity volume is formed in the top surface 41 of the exhaust-side piston 4. A scavenging-side cavity 6 having a cavity volume larger than that of the exhaust-side cavity 7 is formed in the top surface 31 of the scavenging-side piston 3. The at least one fuel injection device 5 described above includes a scavenging-side fuel injection device 5A having a central axis CA1 inclined toward the scavenging side (the one side in the axial direction of the cylinder 2) toward the inside in the radial direction of the cylinder 2.

[0030] In the illustrated embodiment, the scavenging-side cavity 6 is formed to be recessed in the central portion of the top surface 31 of the scavenging-side piston 3. The top surface 31 of the scavenging-side piston 3 includes a scavenging-side outer peripheral edge portion 32 that extends outward in the radial direction of the cylinder 2 (the outer side in the radial direction of the cylinder 2) along a direction perpendicular to the axial direction of the cylinder 2 from the outer peripheral edge 61 of the scavenging-side cavity 6. The outer peripheral end of the scavenging-side outer peripheral edge portion 32 is continuous with one end of the outer peripheral portion 33 of the scavenging-side piston 3 that extends along the axial direction of the cylinder 2. The scavenging-side cavity 6 has a concave curved surface 62 whose depth from the outer peripheral edge 61 increases as it goes inward in the radial direction of the cylinder 2 from the outer peripheral edge 61.

[0031] In the illustrated embodiment, the exhaust-side cavity 7 is formed to be recessed in the central portion of the top surface 41 of the exhaust-side piston 4. The top surface 41 of the exhaust-side piston 4 includes an exhaust-side outer peripheral edge portion 42 that extends outward in the radial direction of the cylinder 2 (the outer side in the radial direction of the cylinder 2) along a direction perpendicular to the axial direction of the cylinder 2 from the outer peripheral edge 71 of the exhaust-side cavity 7. The outer peripheral end of the exhaust-side outer peripheral edge portion 42 is continuous with one end of the outer peripheral portion 43 of the exhaust-side piston 4 that extends along the axial direction of the cylinder 2. The exhaust-side cavity 7 has a concave curved surface 72 whose depth from the outer peripheral edge 71 increases as it goes inward in the radial direction of the cylinder 2 from the outer peripheral edge 71.

[0032] The volume of the solid formed by the virtual surface 63 that extends along a direction orthogonal to the axial direction of the cylinder 2 and has the outer peripheral edge 61 of the scavenging side cavity 6 as its outer peripheral edge and the concave curved surface 62 described above may be defined as the cavity volume of the scavenging side cavity 6 described above. Further, the volume of the solid formed by the virtual surface 73 that extends along a direction orthogonal to the axial direction of the cylinder 2 and has the outer peripheral edge 71 of the exhaust side cavity 7 as its outer peripheral edge and the concave curved surface 72 described above may be defined as the cavity volume of the exhaust side cavity 7 described above.

[0033] In certain embodiments, the cavity volume of the scavenging side cavity 6 is made larger than that of the exhaust side cavity 7 by making the depth (e.g., maximum depth or average depth) of the scavenging side cavity 6 deeper than that of the exhaust side cavity 7. Also, in certain embodiments, the cavity volume of the scavenging side cavity 6 is made larger than that of the exhaust side cavity 7 by making the diameter dimension of the outer peripheral edge 61 of the scavenging side cavity 6 larger than that of the outer peripheral edge 71 of the exhaust side cavity 7.

[0034] In the illustrated embodiment, the scavenging side fuel injection device 5A is provided on the inner surface 22 of the cylinder 2 with its central axis CA1 inclined with respect to the radial direction of the cylinder 2. The scavenging side fuel injection device 5A injects fuel into the cylinder bore 21 along the extension direction of the central axis CA1. The extension direction of the central axis CA1 is directed toward the central portion of the scavenging side cavity 6.

[0035] According to the above configuration, the cavity volume of the scavenging-side cavity 6 is larger than the cavity volume of the exhaust-side cavity 7. Therefore, the combustion chamber 11 formed between the scavenging-side piston 3 and the exhaust-side piston 4 has a larger volume on the scavenging side than on the exhaust side. The fuel injected from the scavenging-side fuel injection device 5A flows toward the scavenging side (one side in the axial direction) along the extension direction of the central axis CA1 of the scavenging-side fuel injection device 5A and burns in the scavenging-side cavity 6. By burning the fuel mainly on the scavenging side of the combustion chamber 11 in this way, the heat load on the exhaust-side piston 4 can be reduced. Further, by forming the exhaust-side cavity 7 on the top surface 41 of the exhaust-side piston 4, the fuel can be burned in a shorter period compared to the case where the top surface 41 of the exhaust-side piston 4 has a flat shape, so the isochoric ratio of the opposed-piston engine 1 can be increased. By increasing the isochoric ratio of the opposed-piston engine 1, a decrease in the thermal efficiency of the opposed-piston engine 1 can be suppressed.

[0036] In some embodiments, as shown in FIGS. 2 and 4, the top surface 31 of the scavenging-side piston 3 described above includes the scavenging-side cavity 6 described above and the scavenging-side outer peripheral edge portion 32 described above. According to the above configuration, the scavenging-side cavity 6 is formed in the central portion of the top surface 31 of the scavenging-side piston 3, and the scavenging-side outer peripheral edge portion 32 is formed on the outer peripheral side of the scavenging-side cavity 6. In this case, it is possible to suppress the combustion flame in the scavenging-side cavity 6 from reaching the outer peripheral portions 33 and 43 of the scavenging-side piston 3 and the exhaust-side piston 4 through the space facing the scavenging-side outer peripheral edge portion 32, so that the heat load on the outer peripheral portions 33 and 43 of the scavenging-side piston 3 and the exhaust-side piston 4 can be reduced.

[0037] In some embodiments, as shown in FIG. 4, the top surface 41 of the exhaust-side piston 4 described above includes the exhaust-side cavity 7 described above and the exhaust-side outer peripheral edge portion 42 described above. According to the above configuration, an exhaust-side cavity 7 is formed in the central portion of the top surface 41 of the exhaust-side piston 4, and an exhaust-side outer peripheral edge portion 42 is formed on the outer peripheral side of the exhaust-side cavity 7. In this case, it is possible to suppress the combustion flame in the exhaust-side cavity 7 from reaching the scavenging-side piston 3 and the outer peripheral portions 33, 43 of the exhaust-side piston 4 through the space facing the exhaust-side outer peripheral edge portion 42, so that the heat load on the outer peripheral portions 33, 43 of the scavenging-side piston 3 and the exhaust-side piston 4 can be reduced.

[0038] In some embodiments, as shown in FIG. 4, at least one of the fuel injection devices 5 described above includes the scavenging-side fuel injection device 5A described above and an exhaust-side fuel injection device 5B having a central axis CA2 that is inclined toward the exhaust side (the other side in the axial direction of the cylinder 2) toward the inside in the radial direction of the cylinder 2.

[0039] In the illustrated embodiment, the exhaust-side fuel injection device 5B is provided on the inner surface 22 of the cylinder 2 such that the central axis CA2 is inclined with respect to the radial direction of the cylinder 2. The exhaust-side fuel injection device 5B injects fuel into the cylinder bore 21 along the extension direction of the central axis CA2. The extension direction of the central axis CA2 is directed toward the central portion of the exhaust-side cavity 7.

[0040] FIG. 5 is an explanatory diagram for explaining the positional relationship between the scavenging-side fuel injection device and the exhaust-side fuel injection device. In the illustrated embodiment, the exhaust-side fuel injection device 5B is displaced in the circumferential direction of the cylinder 2 so as to face the scavenging-side fuel injection device 5A with the axis 25 of the cylinder 2 (the center of the cross section in the direction orthogonal to the axial direction of the inner surface 22 of the cylinder 2) interposed therebetween. In this case, since the interference between the combustion flame of the fuel injected from the scavenging-side fuel injection device 5A and the combustion flame of the fuel injected from the exhaust-side fuel injection device 5B can be suppressed, the fuel injected from the scavenging-side fuel injection device 5A and the exhaust-side fuel injection device 5B can be suitably burned. In a certain embodiment, the exhaust-side fuel injection device 5B is displaced within ±5° of 180° in the circumferential direction of the cylinder 2 with respect to the scavenging-side fuel injection device 5A.

[0041] According to the above configuration, the fuel injected from the exhaust-side fuel injection device 5B flows toward the exhaust side (the other side in the axial direction) along the extension direction of the central axis CA2 of the exhaust-side fuel injection device 5B and burns in the exhaust-side cavity 7. By burning the fuel not only on the scavenging side but also on the exhaust side of the combustion chamber 11 by the exhaust-side fuel injection device 5B, the fuel can be burned in a short period of time, so that the isochoric degree of the opposed piston engine 1 can be increased. By increasing the isochoric degree of the opposed piston engine 1, a decrease in the thermal efficiency of the opposed piston engine 1 can be suppressed.

[0042] In some embodiments, in the opposed piston engine 1 as shown in FIG. 4, the above-described scavenging-side fuel injection device 5A is configured to have a larger fuel injection amount than the above-described exhaust-side fuel injection device 5B.

[0043] The scavenging-side fuel injection device 5A and the exhaust-side fuel injection device 5B are configured to inject fuel by operating a valve mechanism (not shown) inside in response to the input of an electric signal, or by operating the valve mechanism (not shown) inside with fuel that has been pressurized by a mechanical injection pump. In one embodiment, the fuel injection amount of the scavenging-side fuel injection device 5A and the exhaust-side fuel injection device 5B is adjusted by adjusting the valve opening period of the valve mechanism of the scavenging-side fuel injection device 5A and the exhaust-side fuel injection device 5B. The adjustment of the valve opening period of the valve mechanism of the scavenging-side fuel injection device 5A and the exhaust-side fuel injection device 5B may be performed by the engine control unit 18 provided in the opposed piston engine 1. By increasing the valve opening period of the valve mechanism, the fuel injection amount can be increased.

[0044] In one embodiment, the engine control unit 18 controls the fuel pressure of the scavenging-side fuel injection device 5A and the exhaust-side fuel injection device 5B, rather than the valve opening period of the valve mechanism. By increasing the fuel pressure of the scavenging-side fuel injection device 5A compared to the fuel pressure of the exhaust-side fuel injection device 5B, the fuel injection amount of the scavenging-side fuel injection device 5A can be made larger than that of the exhaust-side fuel injection device 5B.

[0045] In one embodiment, by making the hole diameter of the injection hole 51A of the scavenging-side fuel injection device 5A larger than the hole diameter of the injection hole 51B of the exhaust-side fuel injection device 5B, the fuel injection amount of the scavenging-side fuel injection device 5A can be made larger than that of the exhaust-side fuel injection device 5B.

[0046] According to the above configuration, by injecting a larger amount of fuel into the scavenging side of the combustion chamber 11 than into the exhaust side of the combustion chamber 11 with the scavenging-side fuel injection device 5A and the exhaust-side fuel injection device 5B, the fuel can be mainly burned on the scavenging side of the combustion chamber 11, so that the heat load on the exhaust-side piston 4 can be reduced.

[0047] 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.

[0048] The content described in some of the above embodiments can be understood as follows, for example.

[0049] 1) The opposed piston engine (1) according to at least one embodiment of the present disclosure includes 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), and at least one fuel injection device (5) configured to inject fuel between the scavenging side piston (3) and the exhaust side piston (4) inside the cylinder (2). The top surface (41) of the exhaust side piston (4) is formed in a flat shape. A scavenging side cavity (6) having a predetermined cavity volume is formed in the top surface (31) of the scavenging side piston (3). The at least one fuel injection device (5) includes a scavenging side fuel injection device (5A) having a central axis (CA1) inclined toward the one side in the axial direction toward the inner side in the radial direction of the cylinder (2).

[0050] According to the configuration of 1) above, the top surface (41) of the exhaust-side piston (4) is formed in a flat shape, and a scavenging-side cavity (6) having a predetermined cavity volume is formed in the top surface (31) of the scavenging-side piston (3). Therefore, the combustion chamber (11) formed between the scavenging-side piston (3) and the exhaust-side piston (4) has a larger volume on the scavenging side than on the exhaust side. The fuel injected from the scavenging-side fuel injection device (5A) flows toward the scavenging side (one side in the axial direction) along the central axis (CA1) of the scavenging-side fuel injection device (5A) and burns in the scavenging-side cavity (6). By burning the fuel mainly on the scavenging side of the combustion chamber (11) in this way, the heat load on the exhaust-side piston (4) can be reduced. Also, by making the top surface (41) of the exhaust-side piston (4) flat, the heat input from the combustion chamber (11) to the top surface (41 ) of the exhaust-side piston (4) can be suppressed. As a result, the heat loss of combustion in the combustion chamber (11) can be suppressed, and thus the decrease in the thermal efficiency of the opposed-piston engine (1) can be suppressed.

[0051] 2) The opposed-piston engine (1) according to at least one embodiment of the present disclosure includes 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), and at least one fuel injection device (5) configured to inject fuel between the scavenging-side piston (3) and the exhaust-side piston (4) inside the cylinder (2). An exhaust-side cavity (7) having a predetermined cavity volume is formed in the top surface (41) of the exhaust-side piston (4), and a scavenging-side cavity (6) having a cavity volume larger than that of the exhaust-side cavity (7) is formed in the top surface (31) of the scavenging-side piston (3). The at least one fuel injection device (5) includes at least one scavenging-side fuel injection device (5A) having a central axis (CA1) inclined toward the one axial side in the radial inner side of the cylinder (2).

[0052] According to the configuration of 2) above, the cavity volume of the scavenging-side cavity (6) is larger than the cavity volume of the exhaust-side cavity (7). For this reason, the combustion chamber (11) formed between the scavenging-side piston (3) and the exhaust-side piston (4) has a larger volume on the scavenging side than on the exhaust side. The fuel injected from the scavenging-side fuel injection device (5A) flows along the central axis (CA1) of the scavenging-side fuel injection device (5A) toward the scavenging side (one axial side) and burns in the scavenging-side cavity (6). By burning the fuel mainly on the scavenging side of the combustion chamber (11) in this way, the heat load on the exhaust-side piston (4) can be reduced. Further, by forming the exhaust-side cavity (7) in the top surface (41) of the exhaust-side piston (4), the fuel can be burned in a shorter period compared to the case where the top surface (41) of the exhaust-side piston (4) has a flat shape, so that the isochoric degree of the opposed-piston engine (1) can be increased. By increasing the isochoric degree of the opposed-piston engine (1), a decrease in the thermal efficiency of the opposed-piston engine (1) can be suppressed.

[0053] 3) In some embodiments, the opposed-piston engine (1) described in 2) above, the exhaust-side cavity (7) is formed to be recessed in the central portion of the top surface (41) of the exhaust-side piston (4), the top surface (41) of the exhaust-side piston (4) includes an exhaust-side outer peripheral edge portion (42) extending toward the outer peripheral side along a direction orthogonal to the axial direction from the outer peripheral edge (71) of the exhaust-side cavity (7).

[0054] According to the configuration of 3) above, the top surface (41) of the exhaust piston (4) has an exhaust-side cavity (7) formed in the central portion, and an exhaust-side outer peripheral edge portion (42) is formed on the outer peripheral side of the exhaust-side cavity (7). In this case, it is possible to suppress the combustion flame in the exhaust-side cavity (7) from reaching the outer peripheral portions (33, 43) of the scavenging piston (3) and the exhaust piston (4) through the space facing the exhaust-side outer peripheral edge portion (42), so that the heat load on the outer peripheral portions (33, 43) of the scavenging piston (3) and the exhaust piston (4) can be reduced.

[0055] 4) In some embodiments, it is the opposed-piston engine (1) described in any one of 1) to 3) above, the scavenging-side cavity (6) is formed to be recessed in the central portion of the top surface (31) of the scavenging piston (3), the top surface (31) of the scavenging piston (3) includes a scavenging-side outer peripheral edge portion (32) that extends outward in the direction orthogonal to the axial direction from the outer peripheral edge (61) of the scavenging-side cavity (6).

[0056] According to the configuration of 4) above, the top surface (31) of the scavenging piston (3) has a scavenging-side cavity (6) formed in the central portion, and a scavenging-side outer peripheral edge portion (32) is formed on the outer peripheral side of the scavenging-side cavity (6). In this case, it is possible to suppress the combustion flame in the scavenging-side cavity (6) from reaching the outer peripheral portions (33, 43) of the scavenging piston (3) and the exhaust piston (4) through the space facing the scavenging-side outer peripheral edge portion (32), so that the heat load on the outer peripheral portions (33, 43) of the scavenging piston (3) and the exhaust piston (4) can be reduced.

[0057] 5) In some embodiments, it is the opposed-piston engine (1) described in any one of 1) to 4) above, the at least one fuel injection device (5) further includes at least one exhaust-side fuel injection device (5B) having a central axis (CA2) inclined toward the other side in the axial direction toward the inner side in the radial direction of the cylinder (2).

[0058] According to the configuration of 5) above, the fuel injected from the exhaust-side fuel injection device (5B) flows toward the exhaust side (the other side in the axial direction) along the extension direction of the central axis (CA2) of the exhaust-side fuel injection device (5B), and burns in the exhaust-side cavity (7). By burning the fuel not only on the scavenging side but also on the exhaust side of the combustion chamber (11) with the exhaust-side fuel injection device (5B), the fuel can be burned in a short period of time, so that the isochoric ratio of the opposed-piston engine (1) can be increased. By increasing the isochoric ratio of the opposed-piston engine (1), a decrease in the thermal efficiency of the opposed-piston engine (1) can be suppressed.

[0059] 6) In some embodiments, it is the opposed-piston engine (1) described in 5) above, the at least one scavenging-side fuel injection device (5A) is configured to have a larger fuel injection amount than the at least one exhaust-side fuel injection device (5B).

[0060] According to the configuration of 6) above, by injecting a larger amount of fuel to the scavenging side of the combustion chamber (11) than to the exhaust side of the combustion chamber (11) with the scavenging-side fuel injection device (5A) and the exhaust-side fuel injection device (5B), the fuel can be mainly burned on the scavenging side of the combustion chamber (11), so that the thermal load on the exhaust-side piston (4) can be reduced.

Explanation of reference numerals

[0061] 1,01 Opposed-piston engine 2 Cylinder 3,03 Scavenging-side piston 4,04 Exhaust-side piston 5 Fuel injection device 5A Scavenging-side fuel injection device 5B Exhaust-side fuel injection device 6 Scavenging-side cavity 7 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 18 Engine control unit 21 Cylinder bore 22 Inner surface 23 Scavenging port 24 Exhaust port 25 Axis 31,031,41,041 Top surface 32 Scavenging-side outer peripheral edge 33,43 Outer peripheral part 41A Flat surface 42 Exhaust-side outer peripheral edge 51,51A,51B Injection hole 61,71 Outer periphery 62,72 Concave curved surface 63,73 Virtual surface CA1,CA2 Central axis CG Combustion gas EG Exhaust gas F Fuel SF Swirl flow

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, At least one fuel injection device configured to inject fuel between the scavenging-side piston and the exhaust-side piston inside the cylinder, The top surface of the exhaust-side piston is formed in a flat shape, A scavenging-side cavity having a predetermined cavity volume is formed on the top surface of the scavenging-side piston, The at least one fuel injection device includes a scavenging-side fuel injection device having a central axis inclined toward the one side in the axial direction toward the inner side in the radial direction of the cylinder, The scavenging-side cavity is formed to be recessed at the central portion of the top surface of the scavenging-side piston, The top surface of the scavenging-side piston is a scavenging-side outer peripheral edge portion that extends toward the outer peripheral side along a direction orthogonal to the axial direction from the outer peripheral edge of the scavenging-side cavity, and includes a scavenging-side outer peripheral edge portion formed in an annular shape on the outer peripheral side of the scavenging-side cavity, The scavenging-side cavity is a concave curved surface whose depth from the outer peripheral edge increases as it goes toward the inner side in the radial direction of the cylinder from the outer peripheral edge of the scavenging-side cavity, and has a concave curved surface including the deepest portion of the scavenging-side cavity, An opposed-piston engine.

2. 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, At least one fuel injection device configured to inject fuel between the scavenging-side piston and the exhaust-side piston inside the cylinder, An exhaust-side cavity having a predetermined cavity volume is formed on the top surface of the exhaust-side piston, A scavenging-side cavity having a cavity volume larger than that of the exhaust-side cavity is formed on the top surface of the scavenging-side piston, The at least one fuel injection device includes a scavenging-side fuel injection device having a central axis inclined toward the one side in the axial direction toward the inner side in the radial direction of the cylinder, The scavenging-side cavity is formed to be recessed in the central portion of the top surface of the scavenging-side piston. The top surface of the scavenging-side piston is a scavenging-side outer peripheral edge portion that extends outward in the outer peripheral side along the direction orthogonal to the axial direction from the outer peripheral edge of the scavenging-side cavity, and includes a scavenging-side outer peripheral edge portion formed in an annular shape on the outer peripheral side of the scavenging-side cavity. The scavenging-side cavity is a concave curved surface whose depth from the outer peripheral edge increases as it goes inward in the radial direction of the cylinder from the outer peripheral edge of the scavenging-side cavity, and has a concave curved surface including the deepest part of the scavenging-side cavity. Opposed piston engine.

3. 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, At least one fuel injection device configured to inject fuel between the scavenging-side piston and the exhaust-side piston inside the cylinder. An exhaust-side cavity having a predetermined cavity volume is formed on the top surface of the exhaust-side piston. A scavenging-side cavity having a cavity volume larger than that of the exhaust-side cavity is formed on the top surface of the scavenging-side piston. The at least one fuel injection device includes a scavenging-side fuel injection device having a central axis inclined toward the one side in the axial direction toward the inner side in the radial direction of the cylinder. The scavenging-side cavity is formed to be recessed in the central portion of the top surface of the scavenging-side piston. The top surface of the scavenging-side piston is a scavenging-side outer peripheral edge portion that extends outward in the outer peripheral side along the direction orthogonal to the axial direction from the outer peripheral edge of the scavenging-side cavity, and includes a scavenging-side outer peripheral edge portion formed in an annular shape on the outer peripheral side of the scavenging-side cavity. The exhaust-side cavity is a concave curved surface whose depth from the outer peripheral edge increases as it goes inward in the radial direction of the cylinder from the outer peripheral edge of the exhaust-side cavity, and has a concave curved surface including the deepest part of the exhaust-side cavity. Opposed piston engine.

4. The scavenging-side cavity is a concave curved surface whose depth from the outer peripheral edge increases as it extends inward in the radial direction of the cylinder from the outer peripheral edge of the scavenging-side cavity, and has a concave curved surface including the deepest part of the scavenging-side cavity. The opposed-piston engine according to claim 3.

5. The exhaust-side cavity is formed to be recessed in the central part of the top surface of the exhaust-side piston. The top surface of the exhaust-side piston is an exhaust-side outer peripheral edge portion that extends outward in the direction perpendicular to the axial direction from the outer peripheral edge of the exhaust-side cavity, and includes an exhaust-side outer peripheral edge portion formed in an annular shape on the outer peripheral side of the exhaust-side cavity. The opposed-piston engine according to any one of claims 2 to 4.

6. The at least one fuel injection device further includes an exhaust-side fuel injection device having a central axis inclined toward the other side in the axial direction inward in the radial direction of the cylinder. The opposed-piston engine according to any one of claims 1 to 5.

7. The scavenging-side fuel injection device is configured to have a larger fuel injection amount than the exhaust-side fuel injection device. The opposed-piston engine according to claim 6.

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