Internal combustion engine

Abstract

This internal combustion engine includes, in a cavity (CA), a bottom wall (510) that extends radially outward from a center axis (A) while gradually trending away from a cylinder head, a plurality of recess walls (520) that are in communication with the bottom wall (510) and are curved so as to protrude radially outward, and step sections (550) that are provided between the bottom wall (510) and the recess walls (520), wherein the step sections (550) are arc-shaped in planar view. As a result, a spray flame (B2) that flows along the bottom wall (510) flows along the step sections (550), and thus the spray flame (B2) is drawn away (the areas surrounded by dashed lines (VII) in the diagram) from the bottom wall (510) and moves toward the center of the cavity (CA), and mixing of a fuel and residual air is further promoted, making it possible to improve combustion efficiency.

Description

internal combustion engine

[0001] The present invention relates to an internal combustion engine.

[0002] For example, Japanese Patent Publication No. 2011-502226 (Patent Document 1) discloses an internal combustion engine including a cylinder, a piston, a cylinder head, and a fuel injection device. A piston bowl is provided on the upper surface of the piston. The piston bowl has an outer bowl portion that opens upward and protrusions that are evenly distributed around the circumference of the outer bowl portion.

[0003] Special Publication No. 2011-502226

[0004] In the internal combustion engine described in Patent Document 1, flames that collide with adjacent portions of the outer bowl section in the circumferential direction across the protrusion tend to be directed toward the center of the combustion chamber by the protrusion. At this time, adjacent flames across the protrusion may interfere with each other, causing the flames to stagnate near the outer bowl section. In this case, utilization of air in the center of the combustion chamber is not promoted, resulting in reduced combustion efficiency.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide an internal combustion engine that allows for improved combustion in the combustion chamber.

[0006] an intake valve that opens and closes the intake port; an exhaust valve that opens and closes the exhaust port; a piston that is movable relative to the cylinder liner in a central axial direction of the cylinder liner and has a cavity that forms a combustion chamber at a position facing the cylinder head; and an injector that injects fuel from the cylinder head toward the cavity, wherein the injector injects the fuel from a center of the combustion chamber to a radially outer side of the cylinder liner, and the cavity includes a bottom wall that extends radially outward from the central axis and gradually moves away from the cylinder head, a plurality of recessed walls that communicate with the bottom wall and are curved so as to be convex outward in the radial direction, and a step portion provided between the bottom wall and the recessed walls, the step portion having an arc shape in a plan view.

[0007] According to the present invention, it is possible to provide an internal combustion engine that is capable of improving combustion in the combustion chamber.

[0008] FIG. 1 is a plan view schematically showing an internal combustion engine in an embodiment. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1. FIG. 3 is a perspective view of a cavity of a piston. FIG. 4 is a plan view schematically showing a cavity. FIG. 5 is a cross-sectional view showing the side shape of a step portion of a cavity in an embodiment. FIG. 6 is a schematic cross-sectional view showing the flow of a spray flame according to the side shape of a cavity in a comparative example. FIG. 7 is a schematic cross-sectional view showing the flow of a spray flame according to the side shape of a step portion of a cavity in an embodiment. FIG. 8 is a cross-sectional view showing another form of a step portion of a cavity in an embodiment. FIG. 9 is a cross-sectional view showing another form of a step portion of a cavity in an embodiment. FIG. 10 is a plan view showing the arrangement of the step portion of a cavity in an embodiment. FIG. 11 is a plan view showing another arrangement of the step portion of a cavity in an embodiment.

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the accompanying drawings, in which the same or equivalent components are designated by the same reference numerals.

[0010] (Internal combustion engine 1) A schematic configuration of an internal combustion engine 1 according to one embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a plan view showing the internal combustion engine 1, and Figure 2 is a cross-sectional view taken along line II-II in Figure 1.

[0011] The internal combustion engine 1 includes a cylinder liner 100, a cylinder head 200, an intake valve 300, an exhaust valve 400, a piston 500, and an injector 600. Although only one cylinder is shown in Figures 1 and 2, the internal combustion engine 1 can also be applied to a multi-cylinder type. The cylinder liner 100 is formed in a cylindrical shape.

[0012] The cylinder head 200 is connected to an end of the cylinder liner 100. The cylinder head 200 is formed in a disk shape. The cylinder head 200 has an intake port h1 and an exhaust port h2. The intake valve 300 opens and closes the intake port h1. The intake valve 300 is held by the cylinder head 200. The exhaust valve 400 opens and closes the exhaust port h2. The exhaust valve 400 is held by the cylinder head 200.

[0013] The piston 500 is movable relative to the cylinder liner 100 along the central axis of the cylinder liner 100 (central axis A in the vertical direction in FIG. 2 ). As shown in FIG. 2 , the piston 500 has a cavity CA formed in a position facing the cylinder head 200. The cavity CA has a shape that is recessed from a top surface 504 of the piston 500 in a direction away from the cylinder head 200 (downward in FIG. 2 ).

[0014] Specifically, the piston 500 has a bottom wall 510 that extends radially outward from the central axis A and gradually moves away from the cylinder head 200. A combustion chamber is formed between the piston 500, including the cavity CA, and the cylinder head 200. The piston 500 forms a partition wall 502 that defines the cavity CA.

[0015] The injector 600 is provided in the cylinder head 200 at a position facing the central axis A of the cylinder liner 100. The injector 600 injects fuel from the cylinder head 200 toward the cavity CA. More specifically, the injector 600 injects fuel from the center of the combustion chamber toward the outside in the radial direction of the cylinder liner 100.

[0016] The partition wall 502 of the piston 500 will be described in detail with reference to Figures 3 and 4. Figure 3 is a perspective view of the cavity of the piston, and Figure 4 is a plan view schematically showing the cavity. With reference to Figures 2 to 4, the partition wall 502 has a bottom wall 510, a plurality of recessed walls 520 arranged at a predetermined pitch along the circumference, and protruding walls 530 extending inward between adjacent recessed walls 520.

[0017] The bottom wall 510 faces the injector 600 in the direction of the central axis A of the cylinder liner 100. As shown in Fig. 2, the bottom wall 510 has a shape that is gradually inclined so as to be gradually separated from the cylinder head 200 from the central portion facing the injector 600 in the direction of the central axis A toward the outer side in the radial direction.

[0018] When viewed along the bottom wall 510, the recess wall 520 has an elliptical shape resembling a track. The recess wall 520 has a shape that is curved so as to be convex outward in the radial direction. A plurality of recess walls 520 are arranged annularly in the circumferential direction of the cylinder liner 100 at a predetermined pitch. The recess walls 520 are formed at positions where they collide with the spray flame B formed by ignition of the fuel injected from the injector 600. In this embodiment, nine recess walls 520 are arranged annularly in the circumferential direction of the cylinder liner 100, but the number can be set as appropriate and is not limited to the number in this embodiment.

[0019] Each protruding wall 530 has a shape that protrudes toward the center of the combustion chamber between adjacent recessed walls 520. In this embodiment, the number of protruding walls 530 is nine, which is the same as the number of recessed walls 520.

[0020] Next, the relationship between the recess wall 520 and the bottom wall 510 will be described with reference to Fig. 5 to Fig. 7. Fig. 5 is a cross-sectional view showing the side shape of a step portion 550 in the cavity CA, Fig. 6 is a cross-sectional schematic view showing the flow of a spray flame according to the side shape of the cavity CA in a comparative example, and Fig. 7 is a cross-sectional schematic view showing the flow of a spray flame according to the side shape of the step portion 550 in the cavity CA.

[0021] Referring to FIG. 5 , a step portion 550 is provided between the bottom wall 510 (region indicated by S1) and the recess wall 520 (region indicated by S2). The step portion 550 is formed by a straight line portion D1 extending from the bottom wall 510 in a direction further away from the cylinder head 200. Therefore, an apex P1, which serves as an inflection point, is provided at the connection between the bottom wall 510 and the step portion 550. At the connection between the step portion 550 and the recess wall 520 (opposite the apex P1), the straight line portion D1 extends in the tangential direction of the recess wall 520. As a result, the step portion 550 forms an inclined surface extending from the outside toward the inside of the cylinder head 200 (extending upward). A curved lip portion R1 extending inward is provided on the opposite side of the step portion 550 of the recess wall 520 (on the cylinder head 200 side).

[0022] 5, when viewed along a cross section on an imaginary plane including the central axis A, the ratio of the lengths of a first horizontal distance L1 from the central axis A to the step portion 550 of the recess wall 520 and a second horizontal distance L2 including the step portion 550 to the outermost portion P2 of the bottom surface of the recess wall 520 may be approximately 2:1. Alternatively, the dimensional ratio is preferably such that the second horizontal distance L2 is smaller than the ratio of approximately 2:1.

[0023] The flow of the spray flame will now be described by comparing Figures 6 and 7. Figure 6 shows the flow of spray flame B according to the side shape within cavity CA when a conventional step portion is not provided. Spray flame B, formed by ignition of fuel injected from injector 600, collides with recess wall 520 and separates at lip R1 into spray flame B1, which flows to the outside of cylinder liner 100 (squish region), and spray flame B2, which flows along the bottom surface of recess wall 520 and bottom wall 510. Spray flame B2 flowing along bottom wall 510 flows toward the center of cavity CA while contacting bottom wall 510, which inhibits mixing with air and causes heat loss by the piston, thereby hindering improvement of combustion efficiency.

[0024] 7, in the case where the stepped portion 550 according to the present embodiment is provided, the spray flame B2 flowing along the bottom wall 510 flows along the stepped portion 550, and therefore the spray flame B2 is peeled off from the bottom wall 510 (the area surrounded by the dashed line VII in the figure) and heads toward the center of the cavity CA. As a result, mixing of the fuel and the remaining air is further promoted, which makes it possible to improve the degree of constant volume, reduce cooling loss, reduce smoke, and otherwise improve combustion efficiency.

[0025] Other embodiments of the step portion 550 will be described with reference to Figures 8 and 9. Figures 8 and 9 are cross-sectional views showing other embodiments of the step portion in the cavity CA. The step portion 550A shown in Figure 8 is a substantially triangular step portion having a steep sidewall 500w on the bottom wall 510 side between the bottom wall 510 and the recess wall 520. Even in this embodiment, the same effects as those of the step portion 550 described above can be obtained.

[0026] 9 has a generally tower-like shape that extends upward and has a first side wall 550x that stands on the bottom wall 510 side and a second side wall 550y that drops into the recess wall 520. Even in this configuration, the same effects as those of the above-described step portion 550 can be obtained.

[0027] Next, the arrangement of the step portion when viewed from above will be described with reference to Fig. 10 to Fig. 12. Fig. 10 is a plan view showing the arrangement of the step portion 550 in the cavity CA, and Figs. 11 and 12 are plan views showing other arrangements of the step portion in the cavity CA.

[0028] 7 is provided on the bottom wall 510 side along the arrangement of the recess walls 520, and is therefore arranged in an arc shape on the circumference, separated at a predetermined pitch, as shown in Fig. 10. For example, as shown in Fig. 11, by providing a step 550 on the bottom wall 510 side of the protruding wall 530 as well, and providing an annular step 550C in a plan view, it is possible to further promote mixing of the fuel and remaining air and improve combustion efficiency.

[0029] As another embodiment, as shown in FIG. 12 , by providing a step portion 550D inside the step portion 550 so as to fill in the gaps between the step portions 550 that are arranged at a predetermined pitch on the circumference, it is possible to further promote mixing of the fuel and remaining air and improve combustion efficiency.

[0030] Aspects It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0031] an intake valve that opens and closes the intake port; an exhaust valve that opens and closes the exhaust port; a piston that is movable relative to the cylinder liner in a central axial direction of the cylinder liner and has a cavity that forms a combustion chamber at a position facing the cylinder head; and an injector that injects fuel from the cylinder head toward the cavity, wherein the injector injects the fuel from a center of the combustion chamber to the outside in the radial direction of the cylinder liner, and the cavity includes: a bottom wall that extends radially outward from the central axis and gradually moves away from the cylinder head, a plurality of recessed walls that are connected to the bottom wall and curved so as to be convex outward in the radial direction, and a step portion provided between the bottom wall and the recessed walls, wherein the step portion has an arc shape in a plan view.

[0032] (Aspect 2) The internal combustion engine according to aspect 1, wherein the step portion has a linear portion extending from the bottom wall in a direction further away from the cylinder head.

[0033] (Aspect 3) The internal combustion engine according to Aspect 1 or Aspect 2, wherein the recess wall has an elliptical shape like a track when viewed along the bottom wall, a plurality of the recess walls are arranged at a predetermined pitch along the circumference, a partition wall is provided between adjacent recess walls, and the step portion is provided for each of the plurality of recess walls.

[0034] (Aspect 4) The internal combustion engine according to any one of Aspects 1 to 3, wherein a length ratio of a first horizontal distance from the central axis to the step portion of the recess wall to a second horizontal distance including the step portion to an outermost portion of a bottom surface of the recess wall is smaller than a ratio of approximately 2:1.

[0035] It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the description of the above embodiments, and further includes all modifications within the meaning and scope of the claims.

[0036] 1 internal combustion engine, 100 cylinder liner, 200 cylinder head, 300 intake valve, 400 exhaust valve, 500 piston, 550, 550A, 550B, 550C, 550D step portion, 500w side wall, 502 partition wall, 504 top surface, 510 bottom wall, 520 recess wall, 530 protruding wall, 550x first side wall, 550y second side wall, 600 injector.

Claims

1. a cylinder liner having a cylindrical inner circumferential surface; a cylinder head connected to the cylinder liner and having an intake port and an exhaust port; an intake valve that opens and closes the intake port; an exhaust valve that opens and closes the exhaust port; a piston that is movable relative to the cylinder liner in a central axis direction of the cylinder liner and has a cavity that forms a combustion chamber at a position facing the cylinder head; an injector that injects fuel from the cylinder head toward the cavity; Equipped with the injector injects the fuel from a center portion of the combustion chamber outward in a radial direction of the cylinder liner, The cavity is a bottom wall extending radially outward from a central axis and gradually moving away from the cylinder head; a plurality of recessed walls that are connected to the bottom wall and curved so as to be convex outward in the radial direction; a step portion provided between the bottom wall and the recess wall, The step portion has an arc shape when viewed in a plan view. Internal combustion engine.

2. The step portion has a linear portion extending from the bottom wall in a direction further away from the cylinder head.

2. The internal combustion engine according to claim 1.

3. When the recess wall is viewed along the bottom wall, it has an elliptical shape like a track; The recessed portion wall is arranged at a predetermined pitch along the circumference, A partition wall is provided between adjacent recessed wall portions, The step portion is provided for each of the plurality of recess walls.

2. The internal combustion engine according to claim 1.

4. a first horizontal distance from the central axis to the step portion of the recess wall and a second horizontal distance to the outermost portion of the bottom surface of the recess wall including the step portion, the second horizontal distance being smaller than a ratio of approximately 2:1; 2. The internal combustion engine according to claim 1.