Internal combustion engine
The internal combustion engine's cavity design with grooves and slits on the piston top surface addresses uneven spray distribution, promoting homogeneous air-fuel mixing and enhancing combustion efficiency.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- MITSUBISHI MOTORS CORP
- Filing Date
- 2023-03-14
- Publication Date
- 2026-06-23
AI Technical Summary
Existing internal combustion engines with cavities on the piston top surface face issues with uneven distribution of spray, leading to inadequate mixing of air and fuel.
The engine design includes a cavity on the piston top surface with a central first surface, a surrounding second surface, grooves, and slits that facilitate the mixing of air and fuel by promoting swirl flows and homogeneous mixture formation.
The design enhances the mixing of air and fuel, resulting in a more homogeneous air-fuel mixture and improved combustion efficiency.
Smart Images
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Abstract
Description
Technical Field
[0001] This disclosure relates to internal combustion engines.
Background Art
[0002] Conventionally, an internal combustion engine having a cavity on the top surface of a piston has been known (see, for example, Patent Document 1). Patent Document 1 discloses an internal combustion engine having a cavity with a two-stage structure.
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 a cavity in which spray is applied to a wall between an upper stage and a lower stage, and the spray diffuses to a central portion and an outer peripheral portion of the piston top surface. In the case of such a cavity, there may be a situation where there is too much spray in the central portion of the top surface.
[0005] An object of the present disclosure is to provide an internal combustion engine that facilitates the mixing of spray and air.
Means for Solving the Problems
[0006] The internal combustion engine according to this disclosure comprises a cylinder head and a cavity formed on the top surface of a piston, which forms a combustion chamber between itself and the cylinder head, wherein the cavity has a first surface located in the center of the top surface of the piston, a second surface located around the first surface and positioned closer to the cylinder head than the first surface, a groove provided on the second surface and recessed toward the first surface, and a wall provided on the first surface side of the groove, which separates a first space formed on the first surface and a second space formed in the groove, the wall including a first slit connecting the first space and the second space.
[0007] In this internal combustion engine, air enters through the first slit during the compression stroke, and mixing is easily promoted within the groove. [Effects of the Invention]
[0008] According to this disclosure, it is possible to provide an internal combustion engine that facilitates the mixing of spray and air. [Brief explanation of the drawing]
[0009] [Figure 1] A cross-sectional view of an internal combustion engine according to an embodiment of the present disclosure. [Figure 2] A top view of the piston of an internal combustion engine according to an embodiment of the present disclosure. [Figure 3] Cross-sectional view AA in Figure 1. [Figure 4] Cross-sectional view of BB in Figure 1. [Figure 5] Cross-sectional view of CC in Figure 1. [Figure 6] Cross-sectional view of DD in Figure 3. [Figure 7] A schematic diagram showing the flow of the gas mixture in Figure 4. [Figure 8] Schematic diagrams showing the flow of the mixture in Figures 5 and 6. [Figure 9] A diagram showing the shape of the lid according to a second embodiment of this disclosure. [Figure 10] A diagram showing the groove and cover shapes according to a second embodiment of this disclosure. [Modes for carrying out the invention]
[0010] <First Embodiment> The first embodiment of this disclosure will be described below with reference to the drawings.
[0011] As shown in Figure 1, the internal combustion engine 1 comprises 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 injector 12. The internal combustion engine 1 in this embodiment is a direct-injection diesel engine in which the fuel injector 12 directly injects fuel into the 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 cylinder 21 is arranged in the vertical direction (arrow Z in Figure 1).
[0012] Furthermore, the internal combustion engine 1 is equipped with 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, which generates a swirl flow in which the intake air swirls along a plane perpendicular to the sliding direction of the piston 6 (up and down in this embodiment). The internal combustion engine 1 of this embodiment will be described using an example in which the swirl flow swirls clockwise (see arrow S in Figure 2). In addition, the swirl flow generating means may also be a shape such as the intake port of the cylinder head 4 that is formed 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. The cavity 61 forms a combustion chamber between itself and the cylinder head 4 when the piston 6 is at top dead center. Therefore, it is preferable that the air-fuel mixture supplied to the cavity 61 be as homogeneous as possible. In the case of the direct-injection diesel engine of this embodiment, it is preferable to diffuse the fuel spray injected into the cavity 61 to form a homogeneous air-fuel mixture.
[0014] As shown in FIGS. 2 and 3, the cavity 61 has a first surface 62, a central space (an example of the first space) 62a, a second surface 63, an upper space (an example of the third space) 63a, a third surface 64, a plurality of groove portions 65, a plurality of internal spaces (an example of the second space) 66, a plurality of lid portions 68, a plurality of wall portions 69, and a curved portion 70.
[0015] The first surface 62 is disposed at the central portion of the top surface of the piston 6.
[0016] The central space 62a is formed on the first surface 62. The central space 62a of the present embodiment is a space defined by the cylinder head 4, the cavity 61 of the piston 6, and the third surface 64 when the piston 6 is 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 (see FIG. 1) than the first surface 62. In the present embodiment, the second surface 63 is disposed above the first surface 62 (see FIG. 3).
[0018] The upper space 63a is formed on the second surface 63. The upper space 63a is also the space above the groove portion 65. The upper space 63a of the present embodiment is a space sandwiched between the cylinder head 4 and the second surface 63 of the cavity 61 when the piston 6 is at the top dead center.
[0019] As shown in FIG. 3, the third surface 64 connects the edge on the outer peripheral side of the piston 6 of the first surface 62 (in the direction of arrow О in FIG. 2) and the edge on the central side of the piston 6 of the second surface 63 (in the direction of arrow I in FIG. 2). The third surface 64 of the present embodiment is a standing wall extending along the height direction of the piston 6 (in the direction of arrow Z in FIG. 3).
[0020] As shown in FIG. 2, a plurality of groove portions 65 are provided on the second surface 63. The plurality of groove portions 65 are formed radially on the second surface 63. In the present embodiment, eight groove portions 65 are formed radially. The eight groove portions 65 are arranged at a predetermined interval along the circumferential direction of the piston 6. Therefore, the eight groove portions 65 are arranged every 45 degrees.
[0021] As shown in Figure 3, the multiple grooves 65 are recessed portions extending from the second surface 63 toward the first surface 62. In this embodiment, the depth h1 of the multiple grooves 65 is lower than the height h2 of the second surface 63 relative to the first surface 62. However, the depth h1 of the multiple grooves 65 may be the same as h2.
[0022] As shown in Figures 3 and 4, the groove 65 includes a bottom surface 65a, a vertical surface 65b, and a pair of side surfaces 65c.
[0023] As shown in Figure 3, the bottom surface 65a of this embodiment extends approximately parallel to the first surface 62 and the second surface 63, spaced a distance h1 from the second surface 63. However, the bottom surface 65a may also be inclined in the depth direction of the groove 65 (direction of arrow X in Figure 3). That is, the depth h1 of the groove 65 may change as it moves from the central side of the piston 6 (direction of arrow I in Figure 3) to the outer circumference side (direction of arrow O in Figure 3). In this case, the depth h1 of the groove 65 may be formed to become deeper as it moves towards the outer circumference of the piston 6.
[0024] The vertical surface 65b extends from the bottom surface 65a along the height direction of the piston 6 (direction of arrow Z in Figure 3). In this embodiment, the vertical surface 65b extends generally parallel to the third surface 64.
[0025] As shown in Figure 4, the side surface 65c extends from the bottom surface 65a along the height direction of the piston 6 (direction of arrow Z in Figure 4). The pair of side surfaces 65c are spaced apart from each other by the width w1 of the groove 65.
[0026] As shown in Figure 2, the width w1 of the groove 65 in this embodiment widens towards the outer circumference of the piston 6. The groove 65 has a roughly trapezoidal shape that widens towards the outer circumference of the piston 6. This makes it easy to adjust the amount of spray left on the first surface 62 and the amount of spray that is sprayed to the area around the top surface.
[0027] The internal space 66 is a space formed within the groove 65. As shown in Figures 3 and 4, the internal space 66 is a space partitioned by the bottom surface 65a, the vertical surface 65b, the pair of side surfaces 65c, the lid 68, and the wall 69 of the groove 65. In this embodiment, the internal space 66 increases towards the outer circumference of the piston 6, following the shape of the groove 65 shown in Figure 2.
[0028] The cover portion 68 covers the cylinder head 4 side (see Figure 1) of the groove portion 65. In this embodiment, the upper surface of the cover portion 68 is part of the second surface 63. The cover portion 68 is formed with a predetermined thickness h3. The cover portion 68 is positioned opposite the bottom surface 65a of the groove portion 65.
[0029] As shown in Figure 4, the lid portion 68 includes a lid slit (an example of a second slit) 68a. The lid slit 68a penetrates the lid portion 68 and connects the internal space 66 and the upper space 63a.
[0030] The lid slit 68a in this embodiment has a linear shape that extends along the direction from the center side to the outer circumference of the piston 6 (see Figure 2). The width w2 of the lid slit 68a is constant along the direction from the center side to the outer circumference of the piston 6.
[0031] Furthermore, the width w2 of the lid slit 68a is smaller than the width w1 of the groove 65. In this embodiment, the width w2 of the lid slit 68a is formed to be approximately one-third to one-half the size of the width w1 of the groove 65.
[0032] Furthermore, as shown in Figure 3, the end of the lid slit 68a is located on the central side of the piston 6, relative to the vertical surface 65b of the groove 65, when viewed from above. In other words, the length r1 of the lid slit 68a is smaller than the depth r2 of the groove 65.
[0033] As shown in Figure 5, the wall portion 69 covers the first surface 62 side of the groove portion 65 and is a wall separating the central space 62a from the internal space 66. The central surface of the wall portion 69 in this embodiment is part of the third surface 64. The wall portion 69 is formed with a predetermined thickness h4. The wall portion 69 is positioned opposite the vertical surface 65b of the groove portion 65. The thickness h4 of the wall portion 69 in this embodiment is approximately the same as the thickness h3 of the lid portion 68. However, the thickness h4 of the wall portion 69 may be formed to a different thickness from that of the lid portion 68.
[0034] The wall portion 69 includes a wall slit (an example of a first slit) 69a. As shown in Figures 5 and 6, the wall slit 69a is provided in the wall portion 69. The wall slit 69a penetrates the wall portion 69 and connects the internal space 66 and the central space 62a. In this embodiment, the wall slit 69a has a linear shape that extends in the vertical direction of the piston 6 (in the direction of arrow Z in Figure 5). The width w3 of the wall slit 69a is constant along the vertical direction of the piston 6.
[0035] Furthermore, the width w3 of the wall slit 69a is smaller than the width w1 of the groove 65. In this embodiment, the width w3 of the wall slit 69a is formed to be approximately one-third to one-half the size of the width w1 of the groove 65, similar to the lid slit 68a.
[0036] The width w2 of the lid slit 68a and the width w3 of the wall slit 69a may be formed to be the same size or to be different sizes. In this embodiment, the lid slit 68a and the wall slit 69a are formed to be approximately the same width.
[0037] Furthermore, the wall slit 69a in this embodiment extends to approximately the same height as the bottom surface 65a of the groove 65. That is, the vertical length of the wall slit 69a is approximately equal to the depth h1 of the groove 65.
[0038] As shown in Figure 5, the lid slit 68a and the wall slit 69a may be continuous. In this embodiment, the lid slit 68a and the wall slit 69a are connected at the point where the second surface 63 and the third surface 64 connect. The internal space 66 may be connected to the central space 62a (see Figure 6) and the upper space 63a on the second surface 63 and the third surface 64.
[0039] In other words, in this embodiment, the lid slit 68a and the wall slit 69a are provided as continuous, straight slits of a constant width from the second surface 63 to the third surface 64.
[0040] As a result, during the compression stroke of the internal combustion engine 1, air enters the internal space 66 through the lid slit 68a using the squish and mixes with the atomized fuel. Furthermore, during the expansion stroke, the mixture containing the ignited flame is ejected from the lid slit 68a and the wall slit 69a.
[0041] Furthermore, because the widths of the lid slit 68a and the wall slit 69a are constant, there is no step in the width direction at the connection point between the second surface 63 and the third surface 64. This prevents thermal stress from concentrating at that location and damaging the piston 6.
[0042] As shown in Figures 3, 4, and 6, the curved section 70 includes a first curved section 70a and a second curved section 70b.
[0043] As shown in Figure 4, the first curved portion 70a extends from the inner wall of the groove 65 toward the lid slit 68a. In this embodiment, the first curved portion 70a is a curved surface connecting the side surface 65c of the groove 65 to the edge of the lid slit 68a of the lid 68. The curved portion 70 may also include a third curved portion 70c. The third curved portion 70c may be a curved surface that smoothly connects the bottom surface 65a and the side surface 65c of the groove 65. Furthermore, the bottom surface 65a may be formed as the third curved portion 70c as part of a spherical surface. This results in the internal space 66 becoming a smooth oval shape when viewed in the Z direction. As a result, the mixture flows easily.
[0044] As shown in Figure 6, the second curved portion 70b extends from the side surface 65c of the groove 65 toward the wall slit 69a. In this embodiment, the second curved portion 70b is a curved surface that connects the side surface 65c of the groove 65 to the edge of the wall slit 69a. The curved portion 70 may also include a fourth curved portion 70d. The fourth curved portion 70d may be a curved surface that smoothly connects the vertical surface 65b and the side surface 65c of the groove 65. Furthermore, the fourth curved portion 70d may completely include the vertical surface 65b. This results in the internal space 66 becoming a smooth oval shape when viewed in the Y direction. As a result, the mixture flows easily.
[0045] Next, the flow of the mixed gas in the internal space 66 will be explained using Figures 1 and 7.
[0046] As shown in Figure 1, the fuel injector 12 primarily injects fuel toward the first surface 62 and the third surface 64. The fuel injector 12 in this embodiment injects fuel in eight directions. The fuel injector 12 in this embodiment injects fuel toward eight grooves 65 (see Figure 2). In other words, the fuel injector 12 forms a spray in the direction of the grooves 65. The second surface 63 and the grooves 65 may be formed to match the injection port of the fuel injector 12.
[0047] In the internal combustion engine 1 formed in this manner, when fuel is injected from the fuel injection valve 12, eight spray particles enter the groove 65.
[0048] As shown in Figure 7, the spray reaches the lid slit 68a while being diffused by the swirl flow. The thick arrows in Figure 7 indicate the flow of the mixture reaching the groove 65.
[0049] As shown in Figure 7(a), the air-mixture that reaches the vicinity of the groove 65 reaches the internal space 66 through the lid slit 68a. The width w2 of the lid slit 68a is smaller than the width w1 of the groove 65 (see Figure 4). Therefore, the flow velocity of the air-mixture decreases as it passes through the lid slit 68a and reaches the internal space 66. This causes the spray to diffuse and promotes the homogenization of the air-mixture.
[0050] Furthermore, as shown in Figure 7(b), the air-fuel mixture that reaches the internal space 66 is pressed against the bottom surface 65a, the vertical surface 65b (see Figure 3), and the pair of side surfaces 65c of the groove 65. This promotes mixing with the intake air. In this embodiment, the path of the air-fuel mixture that reaches the internal space 66 from the lid slit 68a is reversed towards the lid slit 68a by the third curved section 70c near the bottom surface 65a. As a result, the air-fuel mixture is mixed while swirling in small vortices inside the internal space 66. This results in a homogeneous mixture and good combustion.
[0051] As shown in Figure 7(c), the homogenized mixture in the internal space 66 reaches the upper space 63a through the lid slit 68a. Therefore, the flow velocity of the mixture decreases as it passes through the lid slit 68a and reaches the upper space 63a. This causes further diffusion of the spray and promotes homogenization of the mixture.
[0052] Next, using Figure 8, the flow of the mixed gas reaching the internal space 66 through the wall slit 69a will be explained. The spray reaches the wall slit 69a while being diffused by the swirl flow.
[0053] As shown in Figure 8(a), the air-fuel mixture that reaches the internal space 66 through the wall slit 69a (see the thick dashed arrow in Figure 8(a)) mixes with the air-fuel mixture that reaches the internal space 66 through the lid slit 68a (see Figure 7(a)) while forming a vortex in the internal space 66. On the other hand, because the entrance to the internal space 66 is restricted by the wall slit 69a, the swirl flow in the central space 62a is more likely to maintain its flow.
[0054] Furthermore, as shown in Figure 8(b), the air-fuel mixture that reaches the internal space 66 through the wall slit 69a (see the thick arrow in Figure 8(b)) is pressed against the vertical surface 65b of the groove 65. The path of the air-fuel mixture is then reversed towards the wall slit 69a by the second curved section 70b and the fourth curved section 70d. As a result, the air-fuel mixture mixes within the internal space 66 while swirling in small vortices. This results in a homogeneous mixture and improved combustion.
[0055] The homogenized mixture in the internal space 66 ignites during the expansion stroke and is ejected through the wall slits 69a into the central space 62a as a mixture containing flames. As a result, the flames that pass through the wall slits 69a burn the mixture in the central space 62a, promoting the homogenization of combustion.
[0056] <Second Embodiment> Next, a second embodiment of this disclosure will be described with reference to Figure 9. In this second embodiment, only the differences from the first embodiment will be described.
[0057] As shown in Figure 9, the cavity 261 in the second embodiment has a second surface 263, a second space 263a, a groove 265, an internal space 266, and a lid 268. In the second embodiment, the thickness d1 of the lid 268 is different from that of the first embodiment. The other configurations are the same as in the first embodiment, so their description is omitted.
[0058] The dashed line in Figure 9 shows the shape of the groove 65 in the first embodiment. The thickness d1 of the lid 268 in the second embodiment is smaller than the thickness d0 in the first embodiment. For example, the lid 268 may be a plate-like member that covers the second surface 263 side of the groove 265. This shortens the distance from the second surface 263 to the internal space 266. As a result, the mixed air flowing into the lid slit 268a quickly reaches the internal space 266. This can promote the mixing of the spray.
[0059] Figure 10 shows modified shapes of the groove 65(265) and the cover 68(268) in this embodiment. In Figures 10(a) to (i), the dashed lines represent the groove 65(265), and the solid lines represent the cover 68(268).
[0060] In the embodiments shown in Figures 10(a) to (i), the width w1 of the groove 65(265) and the width w2 of the lid slit 68a(268a) provided in the lid 268 vary along the radial direction of the piston 6 (see Figure 1). In these embodiments, the width w1 of the groove 65(265) and the width w2 of the lid slit 68a may differ between the central and outer sides of the piston 6. This makes the squish flow from the upper space 63a(263a) to the central space 62a (see Figure 2) and the reverse squish flow from the central space 62a (see Figure 2) to the upper space 63a(263a) more turbulent. As a result, mixing in the upper space 63a(263a) is also promoted.
[0061] In Figure 10(a), the width w1 of the groove 65(265) is constant along the radial direction of the piston 6 (direction Y of the arrow in Figure 10). Also, the width w2 of the lid slit 68a(268a) narrows towards the outer circumference in the radial direction of the piston 6.
[0062] In Figure 10(b), the width w1 of the groove 65(265) is constant, as in Figure 10(a). On the other hand, the width w2 of the lid slit 68a(268a) widens towards the radial outer circumference of the piston 6.
[0063] In Figure 10(c), the width w1 of the groove 65(265) is constant, as in Figures 10(a) and (b). On the other hand, the lid slit 68a(268a) is formed in an elliptical shape when viewed from above.
[0064] In Figure 10(d), the width w1 of the groove 65(265) widens toward the radial outer circumference of the piston 6. The width w2 of the cover slit 68a(268a) narrows toward the radial outer circumference of the piston 6, similar to Figure 10(a).
[0065] In Figure 10(e), the width w1 of the groove 65(265) widens towards the radial outer circumference of the piston 6, similar to Figure 10(d). Similarly, the width w2 of the lid slit 68a(268a) widens towards the outer circumference, and is formed to be the same width as the width w1 of the groove 65(265) at its outermost point.
[0066] In Figure 10(f), the width w1 of the groove 65(265) widens towards the radial outer circumference of the piston 6, similar to Figures 10(d) and (e). The lid slit 68a(268a) is formed in an elliptical shape in top view, similar to Figure 10(c).
[0067] In Figure 10(g), the width w1 of the groove 65(265) narrows toward the radial outer circumference of the piston 6. Similarly, the width w2 of the lid slit 68a(268a) also narrows toward the outer circumference, and is formed to be wider than the width w1 of the groove 65(265) at its outermost point.
[0068] In Figure 10(h), the width w1 of the groove 65(265) narrows toward the radial outer circumference of the piston 6, similar to Figure 10(g). The width w2 of the lid slit 68a(268a) widens toward the outer circumference, similar to Figure 10(b).
[0069] In Figure 10(i), the width w1 of the groove 65(265) narrows towards the radial outer circumference of the piston 6, similar to Figures 10(g) and (h). The lid slit 68a(268a) is formed in an elliptical shape in top view, similar to Figures 10(c) and (f).
[0070] The width w1 of the groove 65(265) in Figures 10(d) to (f) widens towards the radial outer circumference of the piston 6. As a result, the spray that reaches the internal space 66(266) (see Figures 3 and 9) tends to remain in the internal space 66(266). Therefore, the lid slit 68a(268a) can introduce more air into the internal space 66(266). As a result, the mixture becomes more homogeneous.
[0071] The width w1 of the groove 65(265) in Figures 10(g) to (i) narrows towards the radial outer circumference of the piston 6. As a result, the air-fuel mixture is quickly pushed back when it reaches the internal space 66(266). This promotes the flow of the air-fuel mixture. Consequently, the diffusion of the spray is promoted, and the air-fuel mixture becomes homogeneous.
[0072] As explained above, this disclosure provides an internal combustion engine 1 in which the spray is easily dispersed uniformly.
[0073] <Other Embodiments> Although this embodiment has been described above, this disclosure is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention. In particular, the various modifications described herein can be combined as needed. [Explanation of symbols]
[0074] 1: Internal combustion engine 2: Cylinder block 4: Cylinder head 6: Piston 8: Intake valve 10: Exhaust valve 12: Fuel Injector 21: Cylinder 61,261: Cavity 62,262: 1st page 62a: Central space (an example of the first space) 63,263:Second side 63a, 263a: Upper space (an example of the third space) 64:Side 3 65, 265: Groove 66, 266: Internal space (an example of a second space) 68: Lid 68a, 268a: Slit in the lid (an example of a second slit) 69:Wall 69a: Wall slit (an example of the first slit) 70: Music section 70a: 1st song part 70b: 2nd song part
Claims
1. Cylinder head and, A cavity formed on the top surface of the piston, which forms a combustion chamber between it and the cylinder head, Equipped with, The aforementioned cavity is The first surface is located at the center of the top surface of the piston, A second surface is arranged around the first surface and is positioned closer to the cylinder head than the first surface, A groove provided on the second surface and recessed toward the first surface, A wall portion is provided on the first surface side of the groove portion, separating the first space formed on the first surface from the second space formed in the groove portion. The cavity covers the cylinder head side of the groove and includes a cover portion that separates the second space from the third space formed in the upper part of the groove. It has, The wall portion includes a first slit connecting the first space and the second space, and a second slit connecting the second space and the third space. The first slit is connected to the second slit, Internal combustion engine.
2. The cavity has a curved portion extending from the inner wall of the groove toward the first slit. The internal combustion engine according to claim 1.
3. The first slit and the second slit have the same width. An internal combustion engine according to claim 1 or 2.