Internal combustion engine

Abstract

To provide an internal combustion engine that can improve the space utilization rate of the combustion chamber and improve thermal efficiency. [Solution] The internal combustion engine comprises a cylinder, a piston disposed inside the cylinder and having a top surface facing other members with an axial gap between them, and a fuel injector that injects fuel into the axial gap, the fuel injector having an injection center axis inclined toward the radially inward side of the cylinder and toward the downstream side in the direction of swirl flow, wherein at least one cavity formed on the top surface of the piston has a ridge extending along the radial direction of the piston at the circumferential position of the piston where the fuel injector is located, and an inclined surface that is inclined such that the depth of the cavity increases as it moves away from the ridge toward the downstream side in the direction of swirl flow.

Description

Technical Field

[0001] This disclosure relates to internal combustion engines.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

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

[0006] In view of the circumstances described above, at least one embodiment of this disclosure aims to provide an internal combustion engine that can improve the space utilization rate of the combustion chamber and improve thermal efficiency. [Means for solving the problem]

[0007] An internal combustion engine according to at least one embodiment of this disclosure is, Cylinder and A piston is disposed inside the cylinder and has a top surface that faces another member with an axial gap between them, The system comprises at least one fuel injection device configured to inject fuel into the axial gap inside the cylinder, and having an injection center axis inclined toward the radially inward side of the cylinder toward the downstream side in the direction of swirl flow, At least one cavity formed on the top surface of the piston is At the circumferential position of the piston where the at least one fuel injector is located, a ridge portion extends along the radial direction of the piston, It has an inclined surface that slopes such that the depth of the cavity increases as it moves away from the peak portion downstream in the direction of the swirl flow. [Effects of the Invention]

[0008] According to at least one embodiment of the present disclosure, an internal combustion engine is provided that can improve the space utilization rate of the combustion chamber and improve thermal efficiency. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view of an internal combustion engine according to one embodiment of the present disclosure. [Figure 2] This is a schematic perspective view of a piston in one embodiment of the present disclosure. [Figure 3] This is an explanatory diagram illustrating the cavity shape of a piston in one embodiment of the present disclosure. [Figure 4] This is a schematic perspective view of the opposing piston in one embodiment of the present disclosure. [Figure 5] This is an explanatory diagram illustrating the cavity shape of the opposing piston in one embodiment of the present disclosure. [Figure 6] This is a schematic cross-sectional view showing the vicinity of the first combustion chamber of an internal combustion engine according to one embodiment of the present disclosure. [Figure 7] This is a schematic cross-sectional view showing the vicinity of the second combustion chamber of an internal combustion engine according to one embodiment of the present disclosure. [Figure 8] This is an explanatory diagram illustrating a scavenging port of an internal combustion engine according to one embodiment of the present disclosure. [Figure 9] This is an explanatory diagram illustrating the groove portion of a piston in one embodiment of the present disclosure. [Figure 10] This is an explanatory diagram illustrating the groove portion of a piston in one embodiment of the present disclosure. [Figure 11] This is a schematic cross-sectional view of an internal combustion engine according to one embodiment of the present disclosure. [Modes for carrying out the invention]

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

[0011] (Internal combustion engine) Figure 1 is a schematic cross-sectional view of an internal combustion engine 1 according to one embodiment of the present disclosure. The internal combustion engine 1 according to some embodiments comprises a cylinder 2, a piston 3, and at least one fuel injector 5.

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

[0013] The piston 3 is disposed inside the cylinder 2 (internal space 20) and has a top surface 31 facing the other member 100 with an axial gap therebetween and an outer peripheral surface 32. In the embodiment shown in FIG. 1, the internal combustion engine 1 is an opposed piston engine, and the other member 100 is the opposed piston 4 provided in the opposed piston engine. The opposed piston 4 is disposed on one side in the axial direction of the cylinder 2 relative to the piston 3 inside the cylinder 2 (internal space 20). The opposed piston 4 has an opposed side top surface 41 facing the top surface 31 of the piston 3 with an axial gap therebetween and an outer peripheral surface 42.

[0014] Hereinafter, the other side in the axial direction of the cylinder 2 (the upper side in FIG. 1) is defined as the scavenging side, and the above-mentioned one side in the axial direction of the cylinder 2 (the lower side in FIG. 1) is defined as the exhaust side. The piston 3 is a scavenging side piston and is disposed reciprocally along the axial direction of the cylinder 2 on the scavenging side of the internal space 20. The opposed piston 4 is an exhaust side piston and is disposed reciprocally along the axial direction of the cylinder 2 on the exhaust side of the internal space 20.

[0015] The top surface 31 is the end surface on the exhaust side of the piston 3. The opposed side top surface 41 is the end surface on the scavenging side of the opposed side piston 4. A combustion chamber 11 is formed between the top surface 31 and the opposed side top surface 41 in the internal space 20 of the cylinder 2. In other words, the top surface 31 is opposed to the opposed side top surface 41 across the combustion chamber 11 in the axial direction of the cylinder 2.

[0016] At least one (multiple in the illustrated example) scavenging port 23 is formed on the inner surface 22 on the scavenging side of cylinder 2. The multiple scavenging ports 23 are spaced apart in the circumferential direction of cylinder 2. Each of the multiple scavenging ports 23 forms a passage for guiding the combustion gas CG (compressed air in the illustrated example) from the outside of cylinder 2 into the internal space 20. The combustion gas CG is guided from the outside of cylinder 2 through the scavenging port 23 into the internal space 20 and flows through the internal space 20 toward the exhaust side.

[0017] At least one (multiple in the illustrated example) exhaust port 24 is formed on the inner surface 22 on the exhaust side of cylinder 2. The multiple exhaust ports 24 are spaced apart in the circumferential direction of cylinder 2. Each of the multiple exhaust ports 24 forms a passage for discharging exhaust gas EG from the internal space 20 to the outside of cylinder 2. The exhaust gas EG present in the internal space 20 is discharged to the outside of cylinder 2 through the exhaust port 24.

[0018] In Figure 1, the piston 3 and the opposing piston 4 at bottom dead center are shown by solid lines, while the top surface 31 and the opposing piston top surface 41 at top dead center are shown by dashed lines. Figure 1 also shows the cavity shapes of the piston 3 and the opposing piston 4 as cross-sectional shapes along the circumferential direction of these pistons.

[0019] Piston 3 and the opposing piston 4 reciprocate synchronously within the cylinder 2 along the axial direction of the cylinder 2. Piston 3 is configured to reciprocate between its top dead center (the position closest to the opposing piston 4) and its bottom dead center (the position furthest from the opposing piston 4). The opposing piston 4 is configured to reciprocate between its top dead center (the position closest to piston 3) and its bottom dead center (the position furthest from piston 3). The timing of when piston 3 and the opposing piston 4 reach their top dead center and bottom dead center may coincide, or they may reach their top dead center and bottom dead center at different times.

[0020] In the illustrated embodiment, as shown in Figure 1, 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. Opposing 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. As the crankshaft 16 rotates around the rotation axis 17, piston 3 and opposing piston 4 reciprocate within the cylinder 2 in sync with each other, so that their sliding directions are opposite to the axial direction of the cylinder 2.

[0021] In the embodiment shown in Figure 1, the at least one fuel injector 5 described above includes a first fuel injector 5A and a second fuel injector 5B. Each of the first fuel injector 5A and the second fuel injector 5B is configured to inject fuel into the space between the piston 3 and the opposing piston 4 (axial gap) inside the cylinder 2 (internal space 20). Each of the first fuel injector 5A and the second fuel injector 5B injects fuel into the combustion chamber 11 when the crank angle (rotation angle of the crankshaft 16) reaches a predetermined angle (for example, when the piston 3 or the opposing piston 4 reaches top dead center).

[0022] The internal combustion engine 1 compresses and heats the combustion gas CG, which is introduced into the cylinder 2 through the scavenging port 23, to a temperature above the ignition point of the fuel F by the piston 3 and the opposing piston 4. The fuel injectors 5 (5A, 5B) inject the fuel F into this compressed and heated combustion gas CG, causing the fuel F to self-ignite. The self-ignition of the fuel F forms a combustion flame. The expansion of the combustion gas produced by the self-ignition pushes the piston 3 and the opposing piston 4 apart from each other. The reciprocating motion of the piston 3 and the opposing piston 4 is then transmitted to the crankshaft 16, which converts it into rotational force (power).

[0023] Each of the multiple scavenging ports 23 is formed on the scavenging side of the top surface 31 at top dead center and on the exhaust side of the top surface 31 at bottom dead center. Each of the multiple exhaust ports 24 is formed on the exhaust side of the opposing top surface 41 at top dead center and on the scavenging side of the opposing top surface 41 at bottom dead center.

[0024] The top surface 31 of piston 3 slides toward the scavenging side of each scavenging port 23, enabling the supply of combustion gas CG to the internal space 20 via each scavenging port 23. The opposing top surface 41 of the opposing piston 4 slides toward the exhaust side of each exhaust port 24, enabling the discharge of exhaust gas EG from the internal space 20 via each exhaust port 24. The combustion gas CG supplied to the internal space 20 is compressed by a supercharger (not shown), and the pressure difference between the scavenging port 23 and the exhaust port 24 enables the supply of combustion gas CG to the internal space 20 and the discharge of exhaust gas EG from the internal space 20.

[0025] Figure 2 is a schematic perspective view of the piston 3 in one embodiment of the present disclosure. Figure 3 is an explanatory diagram illustrating the cavity shape of the piston 3 in one embodiment of the present disclosure. Figure 3 shows a schematic view of the piston 3, the first fuel injector 5A, and the second fuel injector 5B as seen from the exhaust side. Figure 4 is a schematic perspective view of the opposing piston 4 in one embodiment of the present disclosure. Figure 5 is an explanatory diagram illustrating the cavity shape of the opposing piston 4 in one embodiment of the present disclosure. Figure 5 shows a schematic view of the opposing piston 4, the first fuel injector 5A, and the second fuel injector 5B as seen from the scavenging side.

[0026] (Fuel injection device) The second fuel injector 5B is positioned offset in the circumferential direction of the cylinder 2 so as to face the first fuel injector 5A across the central axis (radial central axis) CA of the cylinder 2 when viewed from one axial side (scavenging side or exhaust side) as shown in Figure 3. In one embodiment, the second fuel injector 5B is positioned offset from the first fuel injector 5A within a range of 180° ± 5° in the circumferential direction around the central axis CA of the cylinder 2.

[0027] In the illustrated embodiment, the first fuel injector 5A is inserted through a first through-hole 25 (see Figure 6) that penetrates from the outer surface 21 to the inner surface 22 of the cylinder 2, and a portion including the injection hole 51 is located in the internal space 20. The first fuel injector 5A (and its injection hole 51) has an injection center axis 52 that is inclined toward the radially inward side of the cylinder 2 and toward the downstream side in the direction of the swirl flow. Here, the direction of the swirl flow is toward one of the circumferential directions of the cylinder 2 (clockwise direction in Figures 2 and 3, and counterclockwise direction in Figures 4 and 5).

[0028] In the illustrated embodiment, the second fuel injector 5B is inserted through a second through-hole 26 (see Figure 7) that penetrates from the outer surface 21 to the inner surface 22 of the cylinder 2, with a portion including the injection hole 53 located in the internal space 20. The second fuel injector 5B (and its injection hole 53) has an injection center axis 54 that is inclined toward the radially inward side of the cylinder and toward the downstream side in the direction of the swirl flow.

[0029] (Cavity) As shown in Figures 2 and 3, at least one cavity 6 is formed on the top surface 31 of the piston 3, extending along the circumferential direction of the piston 3. In the embodiments shown in Figures 2 and 3, the at least one cavity 6 described above includes a first cavity 6A into which fuel (spray) injected from the first fuel injector 5A is directed, and a second cavity 6B into which fuel (spray) injected from the second fuel injector 5B is directed. Each of the first cavity 6A and the second cavity 6B extends along the circumferential direction of the piston 3.

[0030] As shown in Figures 2 and 3, the first cavity 6A and the second cavity 6B each have a ridge portion 61 (61A, 61B) that extends radially along the piston 3 at the circumferential position of the piston 3 where the fuel injectors 5 (5A, 5B) are located, and an inclined surface 62 (62A, 62B) that slopes such that the depth of the cavity 6 increases as it moves downstream from the ridge portion 61 (61A, 61B) in the direction of the swirl flow.

[0031] In the internal combustion engine 1, the fuel (spray) and combustion flame injected from the fuel injector 5 flow mainly along the direction of the swirl flow and downstream in the direction of the swirl flow within the combustion chamber 11, which includes the cavity space of the cavity 6.

[0032] By providing a ridge 61 and an inclined surface 62 in the cavity 6, the cavity 6 near the fuel injector 5 takes on a constricted shape, thereby reducing the volume of the cavity 6 near the fuel injector 5. This enables compression and ejection of the fuel injected from the fuel injector 5. Furthermore, in the internal combustion engine 1, the inclined surface 62 widens the cavity 6 space as it moves downstream in the direction of the swirl flow, inducing a flow that moves outward in the radial direction of the piston 3 in the combustion chamber 11. This promotes the diffusion and mixing of the spray and combustion flame in the combustion chamber 11, improving the space utilization rate of the combustion chamber 11. By improving the space utilization rate of the combustion chamber 11, the temperature rise of the combustion gas can be suppressed, thus reducing heat loss and improving thermal efficiency. In the case where the other component 100 is an opposing piston 4, the internal combustion engine 1 can improve the space utilization rate of the combustion chamber 11 and improve the thermal efficiency of the internal combustion engine 1.

[0033] Each of the first cavity 6A and the second cavity 6B, as shown in Figures 2 and 3, further includes a downstream ridge portion 63 (63A, 63B) that extends radially along the piston 3 downstream of the inclined surface 62 (62A, 62B) in the direction of swirl flow, and a rising surface 64 (64A, 64B) that slopes such that the depth of the cavity 6 increases as it moves upstream from the downstream ridge portion 63 (63A, 63B) in the direction of swirl flow. In the embodiment shown in Figures 2 and 3, each of the first cavity 6A and the second cavity 6B further includes a bottom surface 65 (65A, 65B) with one end connected to the downstream end of the inclined surface 62 (62A, 62B) and the other end connected to the upstream end of the rising surface 64 (64A, 64B). The bottom surface 65 (65A, 65B) may have a constant depth (axial height).

[0034] In the embodiments shown in Figures 2 and 3, the peak portion 61A also serves as the downstream peak portion 63B, and the downstream peak portion 63A also serves as the peak portion 61B.

[0035] Figure 6 is a schematic cross-sectional view schematically showing the vicinity of the first combustion chamber 11A of an internal combustion engine 1 according to one embodiment of the present disclosure. Figure 7 is a schematic cross-sectional view schematically showing the vicinity of the second combustion chamber 11B of an internal combustion engine 1 according to one embodiment of the present disclosure. The first combustion chamber 11A is the space formed in the combustion chamber 11 between the first cavity 6A of the piston 3 and another member 100 (in the illustrated example, the first opposing cavity 7A of the opposing piston 4). The second combustion chamber 11B is the space formed in the combustion chamber 11 between the second cavity 6B of the piston 3 and another member 100 (in the illustrated example, the second opposing cavity 7B of the opposing piston 4). Figures 6 and 7 schematically show cross-sections of the piston 3 and the opposing piston 4 along the reference circle RC (a circle extending in the circumferential direction of the cylinder 2, see Figures 3 and 5).

[0036] In the embodiments shown in Figures 6 and 7, the inclined surfaces 62 (62A, 62B) described above have a smaller inclination in the direction of swirl flow than the rising surfaces 64 (64A, 64B) described above. In a cross-section along the direction of swirl flow as shown in Figures 6 and 7, if the inclination angle of the inclined surface 62 with respect to the axial direction of the cylinder 2 is defined as θ1 and the inclination angle of the rising surface 64 with respect to the axial direction of the cylinder 2 is defined as θ2, then the inclination angle θ1 is greater than the inclination angle θ2. The inclined surfaces 62 (62A, 62B) and the rising surfaces 64 (64A, 64B) may be formed in a concave arc shape with a predetermined curvature in a cross-section along the direction of swirl flow as shown in Figures 6 and 7, or they may be formed in a concave arc shape where the curvature gradually increases or decreases.

[0037] By making the slope of the inclined surface 62 in the direction of swirl flow relatively gentle, the cavity space of the cavity 6 can be gradually widened toward the downstream side in the direction of swirl flow. As a result, compared to the case where the slope of the inclined surface 62 in the direction of swirl flow is relatively steep, a flow toward the radially outward direction of the piston 3 can be effectively induced in the combustion chamber 11.

[0038] (outer periphery, protrusion) In the embodiments shown in Figures 2 and 3, the piston 3 described above has an outer peripheral portion 33 that covers the outer circumference of the cavity 6 (6A, 6B) described above, and a projection portion 35 that protrudes radially inward from the cavity 6 and beyond the bottom surface 65 of the cavity 6. The projection portion 35 has a circular cross-sectional shape perpendicular to the axial direction of the cylinder 2. The projection portion 35 may be cylindrical or may be a frustoconical shape with a diameter decreasing towards the tip. The ridge portion 61 and the downstream ridge portion 63 described above are connected at their outer peripheral ends to the outer peripheral portion 33 and at their inner peripheral ends to the projection portion 35. The first cavity 6A and the second cavity 6B are separated by the ridge portion 61, the downstream ridge portion 63, and the projection portion 35.

[0039] In the internal combustion engine 1, the outer surface of the protrusion 35 guides the flow in the combustion chamber 11 along the direction of the swirl flow. By promoting the flow along the direction of the swirl flow, the destination of the fuel (spray) injected from the fuel injector 5 can be extended to the downstream side in the direction of the swirl flow, improving the space utilization rate of the combustion chamber 11 and improving the thermal efficiency of the internal combustion engine 1. In addition, by providing the protrusion 35 on the piston 3, interference between the fuel (spray) and combustion flame injected from the fuel injectors 5, which are arranged to face each other, can be suppressed.

[0040] In some embodiments of the internal combustion engine 1, the above-described projection 35 has a flat surface 351 at its tip that extends along the radial direction of the cylinder 2. By providing the piston 3 with a projection 35 having a flat surface 351, the necessary depth can be secured in the cavity 6 (6A, 6B) which serves as the passage for the spray.

[0041] (Mizobe) In some embodiments of the internal combustion engine 1, as shown in Figures 2 and 3, the piston 3 described above has a groove 34 provided on the top surface 331 of the outer peripheral portion 33 that covers the outer circumference of the cavity 6, and which connects the radially inner and outer sides of the outer peripheral portion 33. The groove 34 is provided downstream of the inclined surface 62 in the direction of swirl flow. Also, the groove 34 is provided upstream of the rising surface 64 in the direction of swirl flow. In other words, the groove 34 is provided within the circumferential range in which the bottom surface 65 is formed in the direction of swirl flow.

[0042] In the embodiments shown in Figures 2 and 3, the groove 34 includes a first groove 34A provided within the circumferential range where the first cavity 6A (bottom surface 65A) is formed, and a second groove 34B provided within the circumferential range where the second cavity 6B (bottom surface 65B) is formed. In the embodiments shown in Figures 2 and 3, the bottom surface of the groove 34 is formed at the same height as the bottom surface 65 in the axial direction of the piston 3, but it may be formed at a height that protrudes more than the bottom surface 65 or at a height that is recessed more than the bottom surface 65. In the embodiments shown in Figures 2 and 3, the groove 34 extends along the radial direction of the piston 3, and the groove width is constant.

[0043] The internal combustion engine 1 can effectively induce a radially outward flow in the combustion chamber 11 by substantially widening the cavity space of the cavity 6 with the groove 34.

[0044] In some embodiments of the internal combustion engine 1, as shown in Figure 3, when the piston 3 described above is viewed from one side in the axial direction of the cylinder 2, and the circumferential position of the fuel injector 5 (5A, 5B) is set to 0°, and the circumferential angle θ is defined with the swirl flow direction as positive, the circumferential center of the groove 34 (34A, 34B) is located at a circumferential position where the circumferential angle θ is 90° or more. CP in Figures 3 and 9 is the central axis passing through the circumferential center of the groove 34 (34A, 34B).

[0045] If the circumferential center of the groove 34 is set at a circumferential position where the circumferential angle θ is less than 90°, there is a risk that an excessive outward flow in the radial direction of the piston 3 will be induced near the fuel injector 5 in the combustion chamber 11, resulting in insufficient flow along the direction of the swirl flow. By setting the circumferential center of the groove 34 at a circumferential position where the circumferential angle θ is 90° or more, it is possible to sufficiently ensure flow along the direction of the swirl flow in the combustion chamber 11 while inducing an outward flow in the radial direction of the piston 3 in the combustion chamber 11.

[0046] (Variation of groove) Figure 8 is an explanatory diagram illustrating a scavenging port 23 of an internal combustion engine 1 according to one embodiment of the present disclosure. Figures 9 and 10 are explanatory diagrams illustrating a groove 34 of a piston 3 in one embodiment of the present disclosure. Each of the plurality of scavenging ports 23 described above has a central axis CB inclined toward the radially inward side of the cylinder 2 and toward the downstream side in the direction of swirl flow. As a result, the combustion gas introduced into the combustion chamber 11 (internal space 20) through the scavenging port 23 is guided to flow outward in the radial direction of the piston 3.

[0047] In some embodiments of the internal combustion engine 1, as shown in Figure 9, the grooves 34 (34A, 34B) described above have a central axis CP that is inclined toward the radially inward side of the cylinder 2 and toward the downstream side in the direction of swirl flow.

[0048] By inclining the central axis CP of the groove 34 toward the downstream side in the direction of swirl flow with respect to the radial direction, the fluid flow from the combustion chamber 11 to the groove 34 is suppressed, thereby preventing excessive outward flow in the radial direction of the piston 3 from being induced in the combustion chamber 11. Furthermore, by inclining the central axis CP of the groove 34 toward the downstream side in the direction of swirl flow with respect to the radial direction, the swirl flow of the combustion gas introduced into the combustion chamber 11 through the scavenging port 23 and the groove 34 can be promoted.

[0049] In some embodiments of the internal combustion engine 1, as shown in Figure 10, the grooves 34 (34A, 34B) described above have a groove width at the outer end 342 in the radial direction that is greater than the groove width at the inner end 341. In the embodiment shown in Figure 10, the groove width gradually increases from the inner end 341 to the outer end 342.

[0050] By making the groove width at the inner end 341 of the groove 34 relatively small, the fluid flow from the combustion chamber 11 to the groove 34 is suppressed, thereby preventing excessive outward flow in the radial direction of the piston 3 from being induced in the combustion chamber 11. Furthermore, by making the groove width at the outer end 342 of the groove 34 relatively large, the amount of fluid introduced into the groove 34 from outside the groove 34 is increased, thereby promoting the swirl flow of the combustion gas guided into the combustion chamber 11 through the scavenging port 23 and the groove 34.

[0051] (Opposite side cavity) As shown in Figures 4 and 5, at least one opposing cavity 7 is formed on the opposing top surface 41 of the opposing piston 4. In the embodiment shown in Figures 4 and 5, the at least one opposing cavity 7 includes a first opposing cavity 7A to which fuel (spray) injected from the first fuel injector 5A is guided, and a second opposing cavity 7B to which fuel (spray) injected from the second fuel injector 5B is guided. Each of the first opposing cavity 7A and the second opposing cavity 7B extends along the circumferential direction of the opposing piston 4.

[0052] As shown in Figures 4 and 5, the first opposing cavity 7A and the second opposing cavity 7B each have an opposing ridge portion 71 (71A, 71B) that extends along the radial direction of the opposing piston 4 at the circumferential position of the opposing piston 4 where the fuel injectors 5 (5A, 5B) are located, and an opposing inclined surface 72 (72A, 72B) that is inclined such that the depth of the opposing cavity 7 increases as it moves downstream from the opposing ridge portion 71 (71A, 71B) in the direction of the swirl flow.

[0053] In the internal combustion engine 1, by providing an opposing side ridge 71 and an opposing side inclined surface 72 in the opposing side cavity 7, the opposing side cavity 7 near the fuel injector 5 becomes constricted, thus reducing the volume of the opposing side cavity 7 near the fuel injector 5. This enables compression and ejection of the fuel injected from the fuel injector 5. Furthermore, the internal combustion engine 1 widens the cavity space of the opposing side cavity 7 as it moves downstream in the direction of the swirl flow by the opposing side inclined surface 72, thereby inducing a flow outward in the radial direction of the piston 3 in the combustion chamber 11. This promotes the diffusion and mixing of the atomization and combustion flame in the combustion chamber 11, improving the space utilization rate of the combustion chamber 11. By improving the space utilization rate of the combustion chamber 11, the temperature rise of the combustion gas can be suppressed, thus reducing heat loss and improving the thermal efficiency of the internal combustion engine 1.

[0054] The first opposing cavity 7A and the second opposing cavity 7B, as shown in Figures 4 and 5, further have a downstream ridge portion 73 (73A, 73B) that extends radially along the opposing piston 4 downstream in the swirl flow direction from the opposing inclined surface 72 (72A, 72B), and a rising surface 74 (74A, 74B) that slopes such that the depth of the opposing cavity 7 increases as it moves upstream from the downstream ridge portion 73 (73A, 73B) in the swirl flow direction. The first opposing cavity 7A and the second opposing cavity 7B further have a bottom surface 75 (75A, 75B) with one end connected to the downstream end of the opposing inclined surface 72 (72A, 72B) and the other end connected to the upstream end of the rising surface 74 (74A, 74B). The bottom surface 75 (75A, 75B) may have a constant depth (axial height).

[0055] In the embodiments shown in Figures 4 and 5, the opposing peak portion 71A also serves as the downstream peak portion 73B, and the downstream peak portion 73A also serves as the opposing peak portion 71B.

[0056] As shown in Figures 6 and 7, the opposing inclined surfaces 72 (72A, 72B) have a smaller inclination in the direction of swirl flow than the rising surfaces 74 (74A, 74B). In a cross-section along the direction of swirl flow as shown in Figures 6 and 7, if the inclination angle of the opposing inclined surface 72 with respect to the axial direction of the cylinder 2 is defined as θ3 and the inclination angle of the rising surface 74 with respect to the axial direction of the cylinder 2 is defined as θ4, then the inclination angle θ3 is greater than the inclination angle θ4. The opposing inclined surfaces 72 (72A, 72B) and the rising surfaces 74 (74A, 74B) may be formed in a concave arc shape with a predetermined curvature in a cross-section along the direction of swirl flow as shown in Figures 6 and 7, or they may be formed in a concave arc shape where the curvature gradually increases or decreases.

[0057] (outer periphery, protrusion) The opposing piston 4 has an outer peripheral portion 43 that covers the outer circumference of the opposing cavity 7 (7A, 7B), and a protruding portion 45 that extends radially inward from the opposing cavity 7 and protrudes from the bottom surface 75 of the opposing cavity 7. The protruding portion 45 has a circular cross-sectional shape perpendicular to the axial direction of the cylinder 2. The protruding portion 45 may be cylindrical or may be a frustoconical shape with a diameter decreasing towards the tip. The protruding portion 45 has a flat surface 451 at its tip that extends along the radial direction of the cylinder 2.

[0058] The opposing ridge portion 71 and the downstream ridge portion 73 are each connected at their outer circumference to the outer circumference portion 43 and at their inner circumference to the projection portion 45. The first opposing cavity 7A and the second opposing cavity 7B are separated by the opposing ridge portion 71, the downstream ridge portion 73, and the projection portion 45.

[0059] (Mizobe) The opposing piston 4 has a groove 44 provided on the top surface 431 of the outer peripheral portion 43 that covers the outer circumference of the opposing cavity 7, and which connects the radially inner and outer sides of the outer peripheral portion 43. The groove 44 is provided downstream of the opposing inclined surface 72 in the direction of swirl flow. Also, the groove 44 is provided upstream of the rising surface 74 in the direction of swirl flow. In other words, the groove 44 is provided within the circumferential range in which the bottom surface 75 is formed in the direction of swirl flow.

[0060] In the embodiments shown in Figures 4 and 5, the groove 44 includes a third groove 44A provided within the circumferential range where the first opposing cavity 7A (bottom surface 75A) is formed, and a fourth groove 44B provided within the circumferential range where the second opposing cavity 7B (bottom surface 75B) is formed. In the embodiments shown in Figures 4 and 5, the bottom surface of the groove 44 is formed at the same height as the bottom surface 75 in the axial direction of the opposing piston 4, but it may also be formed at a height that protrudes more than the bottom surface 75 or at a height that is recessed more than the bottom surface 75. In the embodiments shown in Figures 4 and 5, the groove 44 extends along the radial direction of the opposing piston 4, and the groove width is constant. The groove 44 (44A, 44B) may have a central axis CP that is inclined toward the inside of the cylinder 2 in the radial direction and downstream in the direction of swirl flow, as shown in the groove 34 (34A, 34B) in Figure 9. Furthermore, the grooves 44 (44A, 44B) may have a groove width at the outer end in the radial direction greater than the groove width at the inner end, as shown in the grooves 34 (34A, 34B) in Figure 10, or the groove width may gradually increase from the inner end to the outer end.

[0061] In some embodiments of the internal combustion engine 1, as shown in Figure 5, when the opposing piston 4 described above is viewed from one side in the axial direction of the cylinder 2, and the circumferential position of the fuel injector 5 (5A, 5B) is set to 0°, and the circumferential angle θ is defined with the swirl flow direction as positive, the circumferential center of the groove 44 (44A, 44B) is located at a circumferential position where the circumferential angle θ is 90° or more. CP in Figure 4 is the central axis passing through the circumferential center of the groove 44 (44A, 44B).

[0062] The opposing piston 4 has opposing inclined surfaces 72A and 72B, each facing the corresponding inclined surfaces 62A and 62B via an axial gap. The grooves 44A and 44B may also face the corresponding grooves 34A and 34B via an axial gap.

[0063] In some embodiments of the internal combustion engine 1, as shown in Figure 6, the injection center axis 52 of the first fuel injector 5A is inclined toward the radially inward side of the cylinder 2 toward the scavenging side in the axial direction of the cylinder 2. The inclined surface 62A of the first cavity 6A, through which the fuel (spray) injected from the first fuel injector 5A is guided, has a greater inclination in the swirl flow direction than the opposing inclined surface 72A of the first opposing cavity 7A, through which the fuel (spray) injected from the first fuel injector 5A is guided. In other words, in a cross-section along the swirl flow direction as shown in Figure 6, the inclination angle θ1 of the inclined surface 62A is smaller than the inclination angle θ3 of the opposing inclined surface 72A. Preferably, the angle difference between the inclination angle θ1 of the inclined surface 62A and the inclination angle θ3 of the opposing inclined surface 72A is greater than the sum of the depression angle of the first fuel injector 5A and the cone angle of the spray.

[0064] By making the inclination of the inclined surface 62A in the direction of swirl flow greater than the inclination of the opposing inclined surface 72A in the direction of swirl flow, interference between the fuel (spray) and combustion flame injected from the first fuel injector 5A and the piston 3 can be suppressed. Furthermore, by making the inclination of the opposing inclined surface 72A in the direction of swirl flow smaller than the inclination of the inclined surface 62A in the direction of swirl flow, the cavity space of the opposing cavity 7 can be gradually widened toward the downstream side in the direction of swirl flow, thereby effectively inducing a flow toward the radially outward direction of the piston 3 in the combustion chamber 11.

[0065] In some other embodiments, the inclination angle θ1 of the inclined surface 62A and the inclination angle θ3 of the opposing inclined surface 72A in the cross-section shown in Figure 6 may be the same. Also, in some other embodiments, the injection center axis 52 of the first fuel injector 5A may be aligned with the radial direction of the cylinder 2.

[0066] In some embodiments of the internal combustion engine 1, as shown in Figure 7, the injection center axis 54 of the second fuel injector 5B is inclined toward the exhaust side in the axial direction of the cylinder 2 toward the radially inward direction of the cylinder 2. The opposing inclined surface 72B of the second opposing cavity 7B, through which the fuel (spray) injected from the second fuel injector 5B is guided, has a greater inclination in the swirl flow direction than the inclined surface 62B of the second cavity 6B, through which the fuel (spray) injected from the second fuel injector 5B is guided. In other words, in a cross-section along the swirl flow direction as shown in Figure 7, the inclination angle θ3 of the opposing inclined surface 72B is smaller than the inclination angle θ1 of the inclined surface 62B. Preferably, the angle difference between the inclination angle θ1 of the inclined surface 62B and the inclination angle θ3 of the opposing inclined surface 72B is greater than the sum of the depression angle of the second fuel injector 5B and the cone angle of the spray.

[0067] By making the inclination of the opposing inclined surface 72B in the direction of swirl flow greater than the inclination of the inclined surface 62B in the direction of swirl flow, interference between the fuel (spray) and combustion flame injected from the second fuel injector 5B and the opposing piston 4 can be suppressed. Furthermore, by making the inclination of the inclined surface 62B in the direction of swirl flow smaller than the inclination of the opposing inclined surface 72B in the direction of swirl flow, the cavity space of the cavity 6 can be gradually widened toward the downstream side in the direction of swirl flow, thereby effectively inducing a flow toward the radially outward direction of the piston 3 in the combustion chamber 11.

[0068] In some other embodiments, the inclination angle θ1 of the inclined surface 62B in the cross-section shown in Figure 7 and the inclination angle θ3 of the opposing inclined surface 72B may be the same. Also, in some other embodiments, the injection center axis 54 of the second fuel injector 5B may be aligned with the radial direction of the cylinder 2.

[0069] In some of the embodiments described above, the shape of the opposing piston 4 differed from the shape of the piston 3, but in some other embodiments, the shape of the opposing piston 4 may be the same as the shape of the piston 3. That is, two pistons 3 with the circumferential positions of their inclined surfaces 62 aligned may be arranged so that their top surfaces 31 face each other.

[0070] Figure 11 is a schematic cross-sectional view of an internal combustion engine 1 according to one embodiment of the present disclosure. In some embodiments described above, the other member 100 was an opposing piston 4, but the other member 100 is not limited to an opposing piston 4. In some embodiments, as shown in Figure 11, the other member 100 is a cylinder head 101 that covers one axial opening of the cylinder 2 described above. Although not shown, the scavenging port 23 and exhaust port 24 described above may be formed in the cylinder head 101.

[0071] The cylinder head 101 has an opposing surface 102 that faces the top surface 31 of the piston 3 with an axial gap (combustion chamber 11) in between. In the embodiment shown in Figure 11, the opposing surface 102 is a flat surface extending along the radial direction of the cylinder 2, but an opposing cavity 7 may be formed thereon, such as the top surface 41 of the opposing piston 4. In some embodiments, the top surface 41 of the opposing piston 4 described above may be a flat surface extending along the radial direction of the cylinder 2 without an opposing cavity 7 being formed thereon.

[0072] Even when the other component 100 is the cylinder head 101, the internal combustion engine 1 can improve the space utilization rate of the combustion chamber 11 and improve the thermal efficiency of the internal combustion engine 1.

[0073] In this specification, expressions describing relative or absolute arrangements such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" shall not only describe such arrangements strictly, but also describe states of relative displacement with tolerances or angles or distances that allow for the same function to be achieved. For example, expressions such as "identical," "equal," and "homogeneous" that describe things being in an equal state not only describe a state of being strictly equal, but also describe a state in which there is a tolerance or a difference that is sufficient to achieve the same function. Furthermore, in this specification, expressions describing shapes such as quadrilaterals and cylindrical shapes shall not only represent geometrically precise quadrilaterals and cylindrical shapes, but also shapes that include uneven surfaces, chamfered surfaces, etc., to the extent that the same effect can be achieved. Furthermore, in this specification, the expressions “equipment,” “includes,” or “possess” of a component are not exclusive expressions that exclude the existence of other components.

[0074] This disclosure is not limited to the embodiments described above, but also includes modified forms of the embodiments described above, as well as forms that combine these forms as appropriate.

[0075] The contents described in some of the embodiments above can be understood, for example, as follows:

[0076] 1) An internal combustion engine (1) according to at least one embodiment of the present disclosure is Cylinder (2) and, A piston (3) is disposed inside the cylinder (2) and has a top surface (31) that faces another member (100) with an axial gap between them, The system comprises at least one fuel injector (5) configured to inject fuel into the axial gap inside the cylinder (2), and having an injection center axis inclined toward the radially inward side of the cylinder toward the downstream side in the direction of swirl flow, At least one cavity (6) formed on the top surface (31) of the piston (3) is At the circumferential position of the piston (3) where the at least one fuel injector (5) is located, a ridge (61) extends along the radial direction of the piston (3), The device includes an inclined surface (62) that slopes such that the depth of the cavity (6) increases as it moves away from the ridge (61) to the downstream side in the direction of the swirl flow.

[0077] According to the configuration described in 1) above, the fuel (spray) and combustion flame injected from the fuel injector (5) flow mainly along the direction of the swirl flow in the combustion chamber (11) toward the downstream side in the direction of the swirl flow. By providing a ridge (61) and an inclined surface (62) in the cavity (6), the cavity (6) near the fuel injector (5) becomes constricted, thereby reducing the volume of the cavity (6) near the fuel injector (5). This enables compression and ejection of the fuel injected from the fuel injector (5). Furthermore, according to the configuration described in 1) above, the inclined surface (62) widens the cavity (6) space toward the downstream side in the direction of the swirl flow, thereby inducing a flow toward the radially outward direction of the piston (3) in the combustion chamber (11). This promotes the diffusion and mixing of the spray and combustion flame in the combustion chamber (11), and improves the space utilization rate of the combustion chamber (11). By improving the space utilization rate of the combustion chamber (11), the temperature rise of the combustion gas can be suppressed, thereby reducing heat loss and improving thermal efficiency.

[0078] 2) In some embodiments, the internal combustion engine (1) described in 1) above, The aforementioned at least one cavity (6) is A downstream ridge portion (63) extending along the radial direction of the piston (3) downstream of the inclined surface (62) in the flow direction of the swirl flow, The present invention further includes a rising surface (64) that slopes such that the depth of the cavity (6) increases as it moves away from the downstream ridge (63) to the upstream side in the flow direction of the swirl flow, The inclined surface (62) has a smaller inclination in the flow direction of the swirl flow than the rising surface (64).

[0079] According to the configuration described in 2) above, by making the slope of the inclined surface (62) in the direction of swirl flow relatively gentle, the cavity (6) space can be gradually widened toward the downstream side in the direction of swirl flow. As a result, compared to the case where the slope of the inclined surface in the direction of swirl flow is relatively steep, a flow toward the radially outward direction of the piston (3) can be effectively induced in the combustion chamber (11).

[0080] 3) In some embodiments, the internal combustion engine (1) described in 1) or 2) above, The piston (3) is A groove (34) is provided on the top surface (331) of the outer peripheral portion (33) that covers the outer circumference of the cavity (6), and connects the radially inner and outer sides of the outer peripheral portion (33), and the groove (34) is provided downstream of the inclined surface (62) in the flow direction of the swirl flow.

[0081] According to the configuration described in 3) above, the groove (34) substantially widens the cavity (6) space, thereby effectively inducing a radially outward flow from the piston (3) in the combustion chamber (11).

[0082] 4) In some embodiments, the internal combustion engine (1) described in 3) above, When the piston (3) is viewed from one side in the axial direction of the cylinder (2), and the circumferential position of the fuel injector (5) is set to 0°, and a circumferential angle θ is defined with the flow direction of the swirl flow being positive, the circumferential center of the groove (34) is provided at a circumferential position where the circumferential angle θ is 90° or more.

[0083] According to the configuration described in 4) above, if the circumferential center of the groove (34) is set at a circumferential position where the circumferential angle θ is less than 90°, there is a risk that an excessive outward flow in the radial direction of the piston (3) will be induced near the fuel injector (5) in the combustion chamber (11), resulting in insufficient flow along the direction of the swirl flow. By setting the circumferential center of the groove (34) at a circumferential position where the circumferential angle θ is 90° or more, it is possible to sufficiently ensure a flow along the direction of the swirl flow in the combustion chamber (11) while inducing an outward flow in the radial direction of the piston (3) in the combustion chamber (11).

[0084] 5) In some embodiments, the internal combustion engine (1) described in any of 1) to 4) above, The other member (100) is an opposing piston (4) located inside the cylinder (2) on one side in the axial direction of the cylinder (2) relative to the piston (3), and having an opposing top surface (41) that faces the top surface (31) of the piston (3) with an axial gap between them. A scavenging port (23) is formed on the scavenging side, which is the other side in the axial direction of the cylinder (2), and an exhaust port (24) is formed on the exhaust side, which is the one side in the axial direction of the cylinder (2).

[0085] According to the configuration in 5) above, the other component (100) is the opposing piston (4). That is, the internal combustion engine (1) is an opposed-piston engine comprising a piston (3) which is a scavenging piston and an opposing piston (4) which is an exhaust piston. When the other component (100) is the opposing piston (4), the internal combustion engine (1) can improve the space utilization rate of the combustion chamber (11) and improve the thermal efficiency of the internal combustion engine (1).

[0086] 6) In some embodiments, the internal combustion engine (1) described in 5) above, The piston (3) is A groove (34) is provided on the top surface (331) of the outer peripheral portion (33) that covers the outer circumference of the cavity (6), and connects the radially inner and outer sides of the outer peripheral portion (33), and the groove (34) is provided on the downstream side in the flow direction of the swirl flow from the inclined surface (61), The groove (34) has a central axis (CP) that is inclined toward the radially inward direction toward the downstream side in the flow direction of the swirl flow.

[0087] According to the configuration in 6) above, by inclining the central axis (CP) of the groove (34) toward the downstream side in the direction of the swirl flow with respect to the radial direction, it is possible to suppress the excessive induction of outward flow in the radial direction of the piston (3) in the combustion chamber (11). Furthermore, by inclining the central axis (CP) of the groove (34) toward the downstream side in the direction of the swirl flow with respect to the radial direction, it is possible to promote the swirl flow of the combustion gas introduced into the combustion chamber (11) through the scavenging port (23) and the groove (34).

[0088] 7) In some embodiments, the internal combustion engine (1) described in 5) above, The piston (3) is A groove (34) is provided on the top surface (331) of the outer peripheral portion (33) that covers the outer circumference of the cavity (6), and connects the radially inner and outer sides of the outer peripheral portion (33), and the groove (34) is provided on the downstream side in the flow direction of the swirl flow from the inclined surface (61), In the groove portion (34), the groove width at the outer end (342) in the radial direction is greater than the groove width at the inner end (341).

[0089] According to the configuration described in 7) above, by making the groove width at the inner end (341) of the groove (34) relatively small, it is possible to suppress the excessive induction of outward flow in the radial direction of the piston (3) in the combustion chamber (11). Furthermore, by making the groove width at the outer end (342) of the groove (34) relatively large, it is possible to promote the swirl flow of the combustion gas guided into the combustion chamber (11) through the scavenging port (23) and the groove (34).

[0090] 8) In some embodiments, the internal combustion engine (1) described in any of 5) to 7) above, At least one opposing cavity (7) formed on the opposing top surface (41) of the opposing piston (4) is, At the circumferential position of the opposing piston (4) where the at least one fuel injector (5) is located, the opposing side crest portion (71) extends along the radial direction of the opposing piston (4), The device includes an opposing side inclined surface (72) that slopes such that the depth of the opposing side cavity (7) increases as it moves away from the opposing side crest (71) to the downstream side in the flow direction of the swirl flow.

[0091] According to the configuration in 8) above, by providing an opposing side ridge (71) and an opposing side inclined surface (72) in the opposing side cavity (7), the opposing side cavity (7) near the fuel injector (5) becomes constricted, thereby reducing the volume of the opposing side cavity (7) near the fuel injector (5). This enables compression and ejection of the fuel injected from the fuel injector (5). Furthermore, according to the configuration in 8) above, the opposing side inclined surface (72) widens the space of the opposing side cavity (7) as it moves downstream in the direction of the swirl flow, thereby inducing an outward flow in the radial direction of the piston (3) in the combustion chamber (11). This promotes the diffusion and mixing of the atomization and combustion flame in the combustion chamber (11), improving the space utilization rate of the combustion chamber (11). By improving the space utilization rate of the combustion chamber (11), the temperature rise of the combustion gas can be suppressed, thus reducing heat loss and improving thermal efficiency.

[0092] 9) In some embodiments, the internal combustion engine (1) described in 8) above, The at least one fuel injector (5) is It includes a first fuel injection device (5A) having an injection center axis that is inclined toward the scavenging side in the axial direction toward the radially inward direction, The inclined surface (62) of the cavity (6) through which the fuel injected from the first fuel injector (5A) is guided has a greater inclination in the flow direction of the swirl flow than the opposing inclined surface (72) of the opposing cavity (7) through which the fuel injected from the first fuel injector (5A) is guided.

[0093] According to the configuration in 9) above, by making the inclination of the inclined surface (62) in the direction of swirl flow greater than the inclination of the opposing inclined surface (72) in the direction of swirl flow, interference between the fuel (spray) and combustion flame injected from the first fuel injector (5A) and the piston (3) can be suppressed. Furthermore, by making the inclination of the opposing inclined surface (72) in the direction of swirl flow smaller than the inclination of the inclined surface (62) in the direction of swirl flow, the opposing cavity (7) space can be gently widened toward the downstream side in the direction of swirl flow, thereby effectively inducing a flow toward the radially outward direction of the piston (3) in the combustion chamber (11).

[0094] 10) In some embodiments, the internal combustion engine (1) described in 9) above, The at least one fuel injector (5) is A second fuel injector (5B) is positioned circumferentially offset from the first fuel injector (5A) so as to be opposed to the central axis of the cylinder (2) when viewed from one side in the axial direction of the cylinder (2), and further includes a second fuel injector (5B) having an injection central axis that is inclined toward the exhaust side in the axial direction toward the radially inward direction, The opposing inclined surface (72) of the opposing cavity (7) through which the fuel injected from the second fuel injector (5B) is guided has a greater inclination in the flow direction of the swirl flow than the inclined surface (62) of the cavity (6) through which the fuel injected from the second fuel injector (5B) is guided.

[0095] According to the configuration described in 10) above, by making the inclination of the opposing inclined surface (72) in the direction of swirl flow greater than the inclination of the inclined surface (62) in the direction of swirl flow, interference between the fuel (spray) and combustion flame injected from the second fuel injector (5B) and the opposing piston (4) can be suppressed. Furthermore, by making the inclination of the inclined surface (62) in the direction of swirl flow smaller than the inclination of the opposing inclined surface (72) in the direction of swirl flow, the cavity (6) space can be gently widened toward the downstream side in the direction of swirl flow, thereby effectively inducing a flow toward the radially outward direction of the piston (3) in the combustion chamber (11).

[0096] 11) In some embodiments, an internal combustion engine (1) as described in any of 1) to 10) above, The piston (3) has a projection (35) that protrudes radially inward from the cavity (6) and beyond the bottom surface (65) of the cavity (6), and the inner circumferential end of the ridge (61) is connected to the projection (35).

[0097] According to the configuration described in 11) above, the flow along the direction of the swirl flow is promoted by being guided by the outer surface of the protrusion (35). By promoting the flow along the direction of the swirl flow, the destination of the fuel (spray) injected from the fuel injector (5) can be extended to the downstream side in the direction of the swirl flow, improving the space utilization rate of the combustion chamber (11) and improving the thermal efficiency of the internal combustion engine (1). In addition, by providing the protrusion (35), interference between the fuel (spray) and combustion flame injected from the fuel injectors (5) which are arranged to face each other can be suppressed.

[0098] 12) In some embodiments, the internal combustion engine (1) described in 11) above, The protruding portion (35) has a flat surface (351) at its tip that extends along the radial direction.

[0099] According to the configuration described in 12) above, by providing the piston (3) with a protruding portion (35) having a flat surface (351), the necessary depth can be secured in the cavity (6) which serves as the passage for the spray.

[0100] 13) In some embodiments, the internal combustion engine (1) described in any of 1) to 4) above, The other member (100) is a cylinder head (101) that covers the opening on one side in the axial direction of the cylinder (2).

[0101] According to the configuration described in 13) above, the internal combustion engine (1) can improve the space utilization rate of the combustion chamber (11) and improve the thermal efficiency of the internal combustion engine (1) even when the other component (100) is the cylinder head (101). [Explanation of Symbols]

[0102] 1. Internal combustion engine 2 liters 3 pistons 4. Opposing pistons 5 Fuel injection device 5A 1st fuel injection device 5B 2nd fuel injection device 6 Cavity 6A First Cavity 6B Second Cavity 7. Opposite side cavity 7A First opposing cavity 7B Second opposing cavity 11 Combustion chamber 11A First Combustion Chamber 11B Second Combustion Chamber 23 scavenging ports 24 exhaust ports 33,43 Outer perimeter 34,44 Groove section 51,53 injection hole 52,54 Injection center axis 61 Minebe 62 Slope 63,73 Downstream peak 64,74 Rising surface 65, 75 base 71 Opposite peak 72 Opposite side inclined surface 100 Other components 101 Cylinder head

Claims

1. Cylinder and A piston is disposed inside the cylinder and has a top surface that faces another member with an axial gap between them, The system comprises at least one fuel injection device configured to inject fuel into the axial gap inside the cylinder, and having an injection center axis inclined toward the radially inward side of the cylinder toward the downstream side in the direction of swirl flow, At least one cavity formed on the top surface of the piston is At the circumferential position of the piston where the at least one fuel injector is located, a ridge portion extends along the radial direction of the piston, The system includes an inclined surface that slopes such that the depth of the cavity increases as it moves away from the peak portion downstream in the direction of the swirl flow, Internal combustion engine.

2. The aforementioned at least one cavity is A downstream ridge portion extending along the radial direction of the piston, downstream of the inclined surface in the flow direction of the swirl flow, The present invention further comprises a rising surface that slopes such that the depth of the cavity increases as it moves away from the downstream ridge portion to the upstream side in the flow direction of the swirl flow, The inclined surface has a smaller inclination in the flow direction of the swirl flow than the rising surface. The internal combustion engine according to claim 1.

3. The aforementioned piston is A groove provided on the top surface of the outer peripheral portion covering the outer circumference of the cavity, which connects the radially inner and outer sides of the outer peripheral portion, and having a groove provided downstream of the inclined surface in the flow direction of the swirl flow, An internal combustion engine according to claim 1 or 2.

4. When the piston is viewed from one side in the axial direction of the cylinder, and the circumferential position of the fuel injection device is defined as 0°, and the circumferential angle θ is defined as the positive direction of the swirl flow, the circumferential center of the groove is provided at a circumferential position where the circumferential angle θ is 90° or more. The internal combustion engine according to claim 3.

5. The other member is an opposing piston located on one side of the cylinder in the axial direction relative to the piston inside the cylinder, and having an opposing top surface that faces the top surface of the piston with an axial gap between them. A scavenging port is formed on the scavenging side, which is the other side in the axial direction of the cylinder, and an exhaust port is formed on the exhaust side, which is the one side in the axial direction of the cylinder. An internal combustion engine according to claim 1 or 2.

6. The aforementioned piston is A groove provided on the top surface of the outer peripheral portion covering the outer circumference of the cavity, which connects the radially inner and outer sides of the outer peripheral portion, and having a groove provided downstream of the inclined surface in the flow direction of the swirl flow, The groove portion has a central axis that is inclined toward the radially inward direction toward the downstream side in the flow direction of the swirl flow. The internal combustion engine according to claim 5.

7. The aforementioned piston is A groove provided on the top surface of the outer peripheral portion covering the outer circumference of the cavity, which connects the radially inner and outer sides of the outer peripheral portion, and having a groove provided downstream of the inclined surface in the flow direction of the swirl flow, The groove portion is such that the groove width at the outer end in the radial direction is greater than the groove width at the inner end. The internal combustion engine according to claim 5.

8. At least one opposing cavity formed on the opposing top surface of the opposing piston is At the circumferential position of the opposing piston on which the at least one fuel injection device is located, the opposing side crest portion extends along the radial direction of the opposing piston, The system includes an opposing inclined surface that slopes such that the depth of the opposing cavity increases as it moves away from the opposing crest portion downstream in the flow direction of the swirl flow, The internal combustion engine according to claim 5.

9. The at least one fuel injection device is The first fuel injection device includes an injection center axis that is inclined toward the scavenging side in the axial direction toward the radially inward direction, The inclined surface of the cavity through which the fuel injected from the first fuel injector is guided has a greater inclination in the flow direction of the swirl flow than the opposing inclined surface of the opposing cavity through which the fuel injected from the first fuel injector is guided. The internal combustion engine according to claim 8.

10. The at least one fuel injection device is A second fuel injection device is positioned circumferentially offset from the first fuel injection device so as to face the central axis of the cylinder when viewed from one side in the axial direction of the cylinder, and further includes a second fuel injection device having an injection central axis inclined toward the exhaust side in the axial direction toward the radially inward direction, The opposing inclined surface of the opposing cavity through which the fuel injected from the second fuel injector is guided has a greater inclination in the flow direction of the swirl flow than the inclined surface of the cavity through which the fuel injected from the second fuel injector is guided. The internal combustion engine according to claim 9.

11. The piston has a projection that extends radially inward from the cavity and protrudes beyond the bottom surface of the cavity, and the inner circumferential end of the ridge portion is connected to the projection. An internal combustion engine according to claim 1 or 2.

12. The aforementioned projection has a flat surface at its tip that extends along the radial direction. The internal combustion engine according to claim 11.

13. The aforementioned other member is a cylinder head that covers the opening on one side in the axial direction of the cylinder. An internal combustion engine according to claim 1 or 2.

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