internal combustion engine

Abstract

To provide an internal combustion engine in which spray is easy to diffuse uniformly.SOLUTION: An internal combustion engine according to the present disclosure comprises a cylinder head, and a cavity formed in a top surface of a piston, and forming a combustion chamber between itself and the cylinder head. The cavity comprises: a first surface arranged in a top surface center part of the piston; a second surface arranged around the first surface, and arranged closer to the side of the cylinder head than the first surface; a first groove part provided in the second surface, and recessed toward the side of the first surface; and a second groove adjacent to the first groove, and extending toward a peripheral edge of the piston so as to be longer than the first groove part.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to internal combustion engines. [Background technology]

[0002] Conventionally, an internal combustion engine having a cavity on the top surface of a piston is known (see, for example, Patent Document 1). Patent Document 1 discloses an internal combustion engine having a star-shaped cavity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-105570 A Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses that the spray is directed onto the wall of a star-shaped cavity to diffuse the spray. In such a cavity, the spray may be too little at the center of the top surface.

[0005] An object of the present disclosure is to provide an internal combustion engine in which spray is likely to diffuse uniformly. [Means for solving the problem]

[0006] The internal combustion engine according to the present disclosure comprises a cylinder head and a cavity formed in a top surface of a piston to form a combustion chamber between the cylinder head and the cavity, the cavity having a first surface located in the center of the top surface of the piston, a second surface located around the first surface and closer to the cylinder head than the first surface, a first groove portion provided in the second surface and recessed toward the first surface, and a second groove portion adjacent to the first groove portion and extending further toward the periphery of the piston than the first groove portion.

[0007] In this internal combustion engine, the spray supplied to the first groove portion turns back and is supplied to the center portion, where it is dispersed. The spray supplied to the second groove portion remains on the peripheral edge of the piston and is dispersed toward the peripheral edge. As a result, the spray is dispersed uniformly. [Effects of the Invention]

[0008] According to the present disclosure, an internal combustion engine can be provided in which spray is likely to diffuse uniformly. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of an internal combustion engine according to an embodiment of the present disclosure. [Figure 2] FIG. 1 is a top view of a piston according to a first embodiment of the present disclosure. [Figure 3] Cross sections AA and BB in Figure 1. [Figure 4] FIG. 2 is a diagram showing a spraying state according to the first embodiment of the present disclosure. [Figure 5] FIG. 2 is a diagram showing the penetration force of a spray according to the first embodiment of the present disclosure. [Figure 6] FIG. 10 is a diagram showing a spraying state according to the second embodiment of the present disclosure. [Figure 7] FIG. 10 is a partially enlarged view showing a spraying state according to a second embodiment of the present disclosure. [Figure 8] FIG. 10 is a top view of a piston according to a third embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] First Embodiment Hereinafter, a first embodiment of the present disclosure will be described with reference to the drawings.

[0011] As shown in Fig. 1, the internal combustion engine 1 includes a cylinder block 2, a cylinder head 4, a piston 6, a plurality of intake valves 8, a plurality of exhaust valves 10, and a fuel injection valve 12. The internal combustion engine 1 of this embodiment is a direct injection diesel engine in which the fuel injection valve 12 directly injects fuel into a cylinder 21 of the cylinder block 2. In this embodiment, two intake valves 8 and two exhaust valves 10 are arranged in one cylinder 21. The internal combustion engine 1 of this embodiment will be described using an example in which the cylinders 21 are arranged in a vertical direction.

[0012] The internal combustion engine 1 also includes a swirl flow generating means. In this embodiment, the swirl flow generating means is two intake valves 8. In this embodiment, the lift heights of the two intake valves 8 are different, thereby generating a swirl flow in which the intake air swirls along a plane perpendicular to the sliding direction of the piston 6 (in this embodiment, the up-and-down direction). The internal combustion engine 1 of this embodiment will be described using an example in which the swirl flow swirls counterclockwise. Note that the swirl flow generating means may also be one in which the shape of the intake port of the cylinder head 4 or the like is formed so as to generate a swirl flow. Alternatively, a valve that generates a swirl flow may be provided.

[0013] The piston 6 has a cavity 61 on its top surface. When the piston 6 is at top dead center, the cavity 61 forms a combustion chamber between the piston 6 and the cylinder head 4. Therefore, it is preferable that the air-fuel mixture supplied to the cavity 61 is as homogeneous as possible. In the case of the direct injection diesel engine of this embodiment, it is preferable that the spray of fuel injected into the cavity 61 is diffused to form a homogeneous air-fuel mixture.

[0014] The cavity 61 has a first surface 62 , a second surface 63 , a third surface 64 , a first groove portion 65 , a second groove portion 66 , and a curved surface 67 .

[0015] The first surface 62 is disposed at the center of the top surface of the piston 6 .

[0016] The first space 62a (see FIG. 2) is formed on the first surface 62. In this embodiment, the first space 62a is a space defined by the cylinder head 4, the first surface 62, and the third surface 64 when the piston 6 is positioned at the top dead center.

[0017] The second surface 63 is disposed around the first surface 62. The second surface 63 is disposed closer to the cylinder head 4 than the first surface 62. In this embodiment, the second surface 63 is disposed above the first surface 62.

[0018] The second space 63a (see FIG. 3) is formed on the second surface 63. The second space 63a is a space above the first groove portion 65 and the second groove portion 66. In this embodiment, the second space 63a is a space sandwiched between the cylinder head 4 and the second surface 63 of the cavity 61 when the piston 6 is positioned at the top dead center.

[0019] The third surface 64 connects the edge of the first surface 62 on the outer periphery side of the piston 6 (the direction of arrow O in FIG. 2) to the edge of the second surface 63 on the central side of the piston 6 (the direction of arrow I in FIG. 2). The third surface 64 in this embodiment is a standing wall extending along the height direction of the piston 6 (the direction of arrow Z in FIG. 1).

[0020] 2, a plurality of first groove portions 65 are provided on the second surface 63. The plurality of first groove portions 65 are formed radially on the second surface 63. In this embodiment, the plurality of first groove portions 65 are arranged in groups of four at predetermined intervals along the circumferential direction of the piston 6. Therefore, the first groove portions 65 are arranged at 90-degree intervals.

[0021] 3(a), the first groove portion 65 is a portion recessed from the second surface 63 toward the first surface 62. In this embodiment, the first groove portion 65 extends by a depth d1 along the depth direction from the center side of the piston 6 toward the peripheral edge side.

[0022] Fig. 3(a) is a cross-sectional view showing the AA cross section of Fig. 1. As shown in Fig. 2 and Fig. 3(a), the first groove portion 65 includes a bottom surface 65a, a vertical surface 65b, and a pair of side surfaces 65c.

[0023] 3(a), the bottom surface 65a extends substantially parallel to the second surface 63. The bottom surface 65a is spaced apart from the second surface 63 by a depth h1.

[0024] The vertical surface 65b extends from the bottom surface 65a in the height direction of the piston 6 (the direction of arrow Z in FIG. 3(a)).

[0025] 2, the side surfaces 65c extend from the bottom surface 65a along the height direction of the piston 6. The pair of side surfaces 65c are spaced apart from each other by the width w1 of the first groove portion 65.

[0026] Similar to the first groove portions 65, a plurality of second groove portions 66 are provided on the second surface 63. The plurality of second groove portions 66 are formed radially on the second surface 63. In this embodiment, four second groove portions 66 are arranged at predetermined intervals along the circumferential direction of the piston 6. Therefore, the second groove portions 66 are arranged every 90 degrees.

[0027] The second groove portion 66 is disposed adjacent to the first groove portion 65. In this embodiment, the first groove portions 65 and the second groove portions 66 are disposed alternately at 45° intervals along the circumferential direction of the piston 6.

[0028] Figure 3(b) is a cross-sectional view showing the cross section BB of Figure 1. As shown in Figure 3(b), the second groove portion 66 is a portion recessed from the second surface 63 toward the first surface 62. The second groove portion 66 of this embodiment extends by a depth d2 along the depth direction from the center side of the piston 6 toward the peripheral edge side.

[0029] The depth d2 of the second groove portion 66 is longer than the depth d1 of the first groove portion 65. Furthermore, the depth d2 of the second groove portion 66 may be formed to be approximately two to five times the length of the depth d1 of the first groove portion 65. In this embodiment, the depth d2 of the second groove portion 66 is formed to be approximately twice the length of the depth d1 of the first groove portion 65.

[0030] As shown in FIGS. 2 and 3(b), the second groove portion 66 includes a bottom surface 66a, a vertical surface 66b, and a pair of side surfaces 66c.

[0031] 3(b), the bottom surface 66a extends substantially parallel to the second surface 63. The bottom surface 66a is spaced apart from the second surface 63 by a depth h2.

[0032] 3, the depth h2 of the second groove portion 66 is deeper than the depth h1 of the first groove portion 65. That is, the bottom surface 66a of the second groove portion 66 is located closer to the first surface 62 than the bottom surface 65a of the first groove portion 65. The depth h2 of the second groove portion 66 may be approximately two to four times the depth h1 of the first groove portion 65. In this embodiment, the depth h1 of the second groove portion 66 is formed to be approximately twice the depth h1 of the first groove portion 65.

[0033] 3(b), the vertical surface 66b extends from the bottom surface 66a along the height direction (direction of arrow Z) of the piston 6. In this embodiment, the vertical surface 66b extends generally parallel to the third surface 64.

[0034] 2, the side surfaces 66c extend from the bottom surface 66a along the height direction of the piston 6. The pair of side surfaces 66c are spaced apart from each other by the width w2 of the second groove portion 66.

[0035] The width w2 of the second groove portion 66 is approximately the same as the width w1 of the first groove portion 65. However, the width w2 of the second groove portion 66 may be formed to be different from the width w1 of the first groove portion 65.

[0036] The curved surface 67 is formed on the inner surface of the first groove portion 65 and the second groove portion 66 located on the peripheral edge side of the piston 6. The curved surface 67 is an R-curved surface whose center of curvature is located on the central side of the piston 6. The curved surface 67 includes a first curved surface 67a and a second curved surface 67b.

[0037] The first curved surface 67a is provided in the first groove portion 65. The first curved surface 67a is formed as part or all of the vertical surface 65b of the first groove portion 65. The radius of curvature r1 of the first curved surface 67a is half the width w1 of the first groove portion 65. Both ends of the first curved surface 67a smoothly connect to a pair of side surfaces 65c of the first groove portion 65.

[0038] The second curved surface 67b is provided in the second groove portion 66. The second curved surface 67b is formed as part or all of the vertical surface 66b of the second groove portion 66. The radius of curvature r2 of the second curved surface 67b is half the width w2 of the second groove portion 66. Both ends of the second curved surface 67b smoothly connect to a pair of side surfaces 66c of the second groove portion 66.

[0039] Next, the flow of the air-fuel mixture in the cavity 61 will be described with reference to Figures 4 and 5. As shown in Figures 4 and 5, the fuel injection valve 12 injects fuel mainly toward the first groove portion 65 and the second groove portion 66. The fuel injection valve 12 of this embodiment injects fuel in eight directions.

[0040] The fuel injection valve 12 has first injection holes 12a and second injection holes 12b. Four first injection holes 12a and four second injection holes 12b are formed in the fuel injection valve 12. The first injection holes 12a and the second injection holes 12b are provided in the fuel injection valve 12 alternately at 45-degree intervals.

[0041] Fuel is injected from the first injection hole 12a toward the first groove portion 65. As shown in FIG. 5(a), the spray injected from the first injection hole 12a (see the dotted portion in FIGS. 4 and 5(a)) is directed toward the vertical surface 65b of the first groove portion 65 and the first curved surface 67a disposed in the first groove portion 65. The spray is then pushed back by the first curved surface 67a, and its course is changed toward the center of the piston 6. As a result, the spray returns to the center while diffusing inside the first groove portion 65. The spray that has returned to the center is further diffused, promoting homogenization of the air-fuel mixture in the center. The spray injected from the first injection hole 12a may have a smaller spray angle and stronger penetration than the spray injected from the second injection hole 12b. This increases the amount of spray returning from the first groove portion 65 to the center of the piston 6.

[0042] Fuel is injected from the second injection hole 12b toward the second groove portion 66. As shown in FIG. 5(b), the spray injected from the second injection hole 12b (see the dotted portion in FIGS. 4 and 5(b)) is directed toward the vertical surface 66b of the second groove portion 66 and the second curved surface 67b disposed in the second groove portion 66. The spray is then pushed back by the second curved surface 67b, and its course is changed toward the center of the piston 6. This causes the spray to diffuse inside the second groove portion 66, promoting homogenization of the air-fuel mixture. The spray injected from the second injection hole 12b may have a larger spray angle and weaker penetration than the spray injected from the first injection hole 12a. This increases the amount of spray that diffuses into the second groove portion 66.

[0043] Second Embodiment Next, a second embodiment of the present disclosure will be described with reference to Figures 6 and 7. Note that in the second embodiment, only the differences from the first embodiment will be described.

[0044] In the second embodiment, the cavity 261 further has a wall portion 268. Also, the second embodiment differs from the first embodiment in that the fuel injection valve 212 has four injection holes 212c.

[0045] The wall portion 268 is a wall that separates the first groove portion 65 and the second groove portion 66. The wall portion 268 is provided as a part of the third surface 64. The wall portion 268 of this embodiment is a curved surface that is convex toward the center of the piston 6 and smoothly connects the first groove portion 65 and the second groove portion 66.

[0046] The injection holes 212c (an example of third injection holes) are provided at 90 degree intervals. The injection holes 212c inject fuel toward the wall portion 268.

[0047] 7(a) indicates the flow path of the spray injected from the injection hole 212c. Also, the white arrow in the figure indicates the direction of the swirl flow within the cavity 61.

[0048] In this embodiment, the injection hole 212c of the fuel injection valve 212 injects fuel toward the vicinity of the center of the wall portion 268 (dotted line in FIG. 7(a)). Furthermore, the injection hole 212c injects fuel toward the wall portion 268 in a positional relationship in which the first groove portion 65 is upstream and the second groove portion 66 is downstream with respect to the direction of the swirl flow. The injected fuel is affected by the swirl flow and flows toward the second groove portion 66. This makes it possible to increase the amount of spray supplied to the second groove portion 66 compared to the first groove portion 65. As a result, mixing can be promoted inside the second groove portion 66 while diffusing the spray.

[0049] Furthermore, the fuel injection valve 212 may change the injection pressure depending on the state of the swirl flow within the cavity 61 .

[0050] When the cavity 61 is in a low swirl state, the fluidity of the fuel decreases, especially near the center of the cavity 61. For this reason, the fuel injection valve 212 may adjust the injection pressure to a high pressure in order to increase the amount of spray that is pushed back from the first groove portion 65 and the second groove portion 66 and heads toward the center of the piston 6. This increases the penetration power of the spray.

[0051] On the other hand, when the cavity 61 is in a high swirl state, the fuel is likely to diffuse, especially near the center of the cavity 61. For this reason, the fuel injection valve 212 may adjust the injection pressure to a low pressure so that the spray diffuses inside the first groove portion 65 and the second groove portion 66. This weakens the penetration power of the spray.

[0052] The thick arrow in Fig. 7(b) indicates the flow path of the spray injected from the injection hole 212c. In Fig. 7(b), the injection hole 212c injects fuel toward a position displaced by a distance x from the center of the wall portion 268 (the dashed-dotted line in Fig. 7(b)) toward the second groove portion 66.

[0053] When the spray collides with the wall portion 268, it branches in directions toward the first groove portion 65 and the second groove portion 66. The amount of spray branching toward the second groove portion 66 is greater than that toward the first groove portion 65. This allows the amount of spray supplied to the second groove portion 66 to be greater than that to the first groove portion 65. As a result, mixing can be promoted inside the second groove portion 66 while diffusing the spray.

[0054] Third Embodiment Next, a third embodiment of the present disclosure will be described with reference to Fig. 8. Note that in the third embodiment, only the differences from the first and second embodiments will be described.

[0055] The third embodiment differs from the first and second embodiments in that the cavity 361 further includes a plurality of partition walls 369. The partition walls 369 are provided on a pair of side surfaces 65c of the first groove portion 65 or a pair of side surfaces 66c of the second groove portion 66. The partition walls 369 are also disposed near the end of the piston 6 on the central portion side.

[0056] Each partition wall 369 includes an inclined surface 369a and a return portion 369b. The inclined surface 369a is inclined toward the inside of the first groove portion 65 or the second groove portion 66. The return portion 369b is provided at the end of the partition wall 369 on the peripheral edge side of the piston 6. The return portion 369b extends approximately perpendicularly from a pair of side surfaces 65c of the first groove portion 65 or a pair of side surfaces 66c of the second groove portion 66.

[0057] In the embodiment of Fig. 8(a), the partition walls 369 are provided on a pair of side surfaces 66c of the second groove portion 66. One partition wall 369 is provided on each side surface 66c, that is, two partition walls 369 are provided for each second groove portion 66. That is, a total of eight partition walls 369 are provided.

[0058] As a result, the path of the spray injected from the fuel injection valve 12 toward the second groove portion 66 (see the thick arrow in FIG. 8(a)) is guided toward the inside of the second groove portion 66 by the inclined surface 369a of the partition wall 369 near the entrance of the second groove portion 66. Furthermore, when the spray is pushed back by the vertical surface 66b or the second curved surface 67b of the second groove portion 66, it is further pushed back by the returning portion 369b of the partition wall 369. As a result, mixing of the spray is promoted between the partition wall 369 and the vertical surface of the second groove portion 66 or the second curved surface 67b.

[0059] In the embodiment of FIG. 8(b), the partition wall 369 is provided on a side surface 66c downstream of the swirl flow (see the hollow arrow in FIG. 8(b)) of the second groove portion 66. One partition wall 369 is disposed for each second groove portion 66. That is, a total of four partition walls 369 are provided.

[0060] Furthermore, the injection hole 312a of the fuel injection valve 312 may inject fuel toward the wall portion 368. As a result, the spray supplied to the first groove portion 65 is pushed back by the vertical surface 65b of the first groove portion 65 and diffuses while moving toward the center of the piston 6. Meanwhile, the spray supplied to the second groove portion 66 is pushed back by the vertical surface 66b of the second groove portion 66, and then its course is further changed by the return portion 369b of the partition wall 369, and flows inside the second groove portion 66. This promotes homogenization of the air-fuel mixture.

[0061] As described above, according to the present disclosure, it is possible to provide an internal combustion engine 1 in which the spray is likely to diffuse uniformly.

[0062] <Other embodiments> Although the present embodiment has been described above, the present disclosure is not limited to the above embodiment, and various modifications are possible within the scope of the gist of the invention. In particular, the multiple modifications described in this specification can be arbitrarily combined as necessary.

[0063] (a) For example, in the first to third embodiments described above, four first groove portions 65 and four second groove portions 66 are provided, but the present disclosure is not limited to this. For example, the internal combustion engine 1 may be provided with eight first groove portions 65 and eight second groove portions 66. Furthermore, the numbers of first groove portions 65 and second groove portions 66 can be changed to various different numbers.

[0064] (b) Furthermore, in the third embodiment, the partition wall 369 is provided in the second groove portion 66, but the present disclosure is not limited to this. The partition wall 369 may be provided in the first groove portion 65, or may be provided in both the first groove portion 65 and the second groove portion 66. [Explanation of symbols]

[0065] 1: Internal combustion engine 2: Cylinder block 4: Cylinder head 6: Piston 8: Intake valve 10: Exhaust valve 12,212,312: Fuel injection valve 12a: 1st injection hole 12b: 2nd injection hole 312a: 3rd injection hole 21: Cylinder 61,261,361:Cavity 62: 1st page 63: 2nd side 65: First groove 66: Second groove 269: Bulkhead

Claims

1. A cylinder head, a cavity formed in a top surface of the piston, forming a combustion chamber between the piston and the cylinder head; Equipped with The cavity is a first surface disposed at a central portion of the top surface of the piston; a second surface disposed around the first surface and closer to the cylinder head than the first surface; a first groove portion provided on the second surface, recessed toward the first surface, and extending toward a periphery of the piston; a second groove portion provided on the second surface adjacent to the first groove portion, recessed toward the first surface, and extending longer than the first groove portion toward the periphery of the piston; having Internal combustion engine.

2. a curved surface is formed on the inner surface of the first groove portion and the second groove portion located on the peripheral edge side of the piston; 2. The internal combustion engine according to claim 1.

3. a depth from the second surface to a bottom surface of the first groove portion is shallower than a depth from the second surface to the second groove portion; 2. The internal combustion engine according to claim 1.

4. Further comprising a fuel injection valve; The fuel injection valve has a first injection hole for injecting fuel toward a first groove portion; a second injection hole that injects fuel toward the second groove portion; having An internal combustion engine according to any one of claims 1 to 3.

5. Further comprising a fuel injection valve; the cavity has a partition wall separating the first groove portion and the second groove portion, the fuel injection valve has a third injection hole that injects fuel toward the partition wall. An internal combustion engine according to any one of claims 1 to 3.

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