Internal combustion engine

Abstract

It promotes the mixing of fuel and air in the cavity. [Solution] The internal combustion engine 1 comprises a piston 30 with a cavity 40 formed in the center of its top surface, and an injector 22 for injecting fuel into the cavity 40. The cavity 40 has a raised portion 42 in the center, a projection 45 provided on the outside of the raised portion 42 along the circumferential direction of the piston 30, and a connecting portion 50 connecting the projection 45 and the raised portion 42. The connecting portion 50 includes a curved surface 52 connected to the projection 45, a flat surface 54 connected to the curved surface 52 on the radially inward side, and a stepped portion 56 formed between the flat surface 54 and the raised portion 42. The flat surface 54 is inclined from the connection point with the curved surface 52 to the stepped portion 56 such that it becomes lower towards the radially outward side.

Description

Technical Field

[0001] The present invention relates to an internal combustion engine having a piston with a cavity formed therein.

Background Art

[0002] In the cavity of the piston of Patent Document 1 below, a stepped portion is provided for separating fuel flowing along a curved portion toward a central raised portion in order to mix fuel (unburned fuel) and air.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above technology, the fuel separated at the stepped portion is likely to contact the raised portion before mixing with the surrounding air, resulting in insufficient air intake and no promotion of the mixing of fuel and air.

[0005] Therefore, the present invention has been made in view of these points, and an object thereof is to promote the mixing of fuel and air in the cavity.

Means for Solving the Problems

[0006] In one aspect of the present invention, an internal combustion engine is provided, comprising a piston having a cavity formed in the center of its top surface, and an injector for injecting fuel into the cavity, wherein the cavity has a raised portion provided in the radial center of the piston, a projection provided on the outside of the raised portion in the radial direction along the circumferential direction of the piston, and a connecting portion provided so as to surround the raised portion and connecting the projection portion and the raised portion, wherein the connecting portion includes a curved surface connected to the projection portion, a flat surface connected to the curved surface on the radially inward side, and a stepped portion formed between the flat surface and the raised portion, and the flat surface is inclined between the curved surface and the stepped portion such that it becomes lower towards the radially outward side.

[0007] Furthermore, a virtual line extending radially inward from the flat surface along the surface of the flat surface may pass between the apex of the raised portion and the injector.

[0008] Furthermore, the raised portion may have an inclined surface that slopes radially outward from the apex of the raised portion, and the stepped portion may be formed between the inclined surface and the flat surface.

[0009] Furthermore, the stepped portion may have a stepped surface that is inclined with respect to the flat surface, an upper end connecting the stepped surface and the flat surface, and a lower end connecting the stepped surface and the inclined surface, wherein the lower end is located below the upper end in the vertical direction.

[0010] Furthermore, the flat surface may be parallel to the inclined surface. Furthermore, the flat surface and the stepped portion may be provided along the circumferential direction.

[0011] Furthermore, the flat surface and the stepped portion may be provided in multiple locations at predetermined intervals in the circumferential direction.

[0012] Furthermore, the radial width of the flat surface may be greater than the radial width of the curved surface. [Effects of the Invention]

[0013] According to the present invention, the mixing of fuel and air in the cavity can be promoted. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram showing the configuration of an internal combustion engine 1 according to one embodiment. [Figure 2] This is a schematic diagram showing the cross-sectional configuration of cavity 40. [Figure 3] This is a schematic diagram showing the state in which the injector 22 injects fuel into the projection 45. [Figure 4] This is a schematic diagram showing the state in which fuel flows along a flat surface 54. [Figure 5] This is a schematic diagram showing the state in which the fuel has separated at the tip of the flat surface 54. [Figure 6] This is a schematic diagram showing a modified cross-sectional configuration of cavity 40. [Modes for carrying out the invention]

[0015] <Configuration of an internal combustion engine> Figure 1 is a schematic diagram showing the configuration of an internal combustion engine 1 according to one embodiment. In this example, the internal combustion engine 1 is mounted on a vehicle such as a truck, but it is not limited to this and may be mounted on a ship, for example.

[0016] The internal combustion engine 1 is, for example, a diesel engine. The internal combustion engine 1 is a power source that generates power to move a vehicle by burning and expanding a mixture of intake air and fuel in the combustion chamber 2. The internal combustion engine 1 has a cylinder block 10, a cylinder head 20, a piston 30, and a crankshaft 60.

[0017] The cylinder block 10 has a cylinder 12 that reciprocally accommodates the piston 30, and a crankcase 16 that accommodates the crankshaft 60. An oil pan 18 for storing lubricating oil is attached to the crankcase 16.

[0018] The cylinder head 20 is provided on the upper part of the cylinder block 10. The cylinder head 20 has an injector 22, an intake valve 25, and an exhaust valve 26. The injector 22 injects fuel into the combustion chamber 2 defined by the top surface of the piston 30, the inner wall surface 13 of the cylinder 12, and the cylinder head 20. The intake valve 25 introduces intake air (air) from the intake port 23 into the combustion chamber 2 by opening and closing operations. The exhaust valve 26 discharges exhaust gas from the combustion chamber 2 to the exhaust port 24 by opening and closing operations.

[0019] The piston 30 reciprocates within the cylinder 12. When the piston 30 reciprocates between the top dead center and the bottom dead center, it slides on the inner wall surface 13 of the cylinder 12. Lubricating oil is supplied to the inner wall surface 13, and an oil film is formed. By forming an oil film on the inner wall surface 13, the frictional force when the piston 30 slides on the inner wall surface 13 can be reduced.

[0020] A cavity 40 (see FIG. 2) is formed on the top surface 31 of the piston 30. The cavity 40 is formed by recessing the top surface 31 and forms part of the combustion chamber 2. For example, when the piston 30 is positioned near the top dead center, the injector 22 injects fuel into the cavity 40. The fuel injected into the cavity 40 mixes with air in the cavity 40 and burns. The detailed configuration of the piston 30 will be described later.

[0021] The crankshaft 60 is connected to the piston 30 via a connecting rod (hereinafter referred to as a conrod) 62. The crankshaft 60 converts the reciprocating motion of the piston 30 into a rotational motion.

[0022] <Detailed Configuration of Cavity> Figure 2 is a schematic diagram showing the cross-sectional configuration of the cavity 40. The vertical direction shown in Figure 2 is parallel to the axial direction of the piston 30. Figure 2 also shows the piston 30 located near top dead center.

[0023] The cavity 40 is formed by recessing the central part of the top surface 31 of the piston 30. As shown in Figure 2, the cavity 40 has a raised portion 42, a projection 45, and a connecting portion 50.

[0024] The raised portion 42 is a part that rises from the bottom of the cavity 40 toward the injector 22. The raised portion 42 is, for example, conical in shape. The raised portion 42 is located in the radial center of the piston 30. The raised portion 42 faces the injector 22 when the piston 30 is at top dead center. The apex of the raised portion 42 is located on the central axis C of the piston 30 and the injector 22.

[0025] The raised portion 42 has an inclined surface 43. The inclined surface 43 slopes downward in the vertical direction from the apex of the raised portion 42 radially outward. The inclined surface 43 is, for example, a flat surface inclined at a predetermined angle. However, it is not limited to this, and the inclined surface 43 may be a curved surface.

[0026] The projection 45 is a portion that protrudes upward in the vertical direction from the outside of the raised portion 42 in the radial direction of the piston 30. The uppermost part of the projection 45 is located closer to the top surface 31 of the piston 30 than the raised portion 42 in the cavity 40. Specifically, the uppermost part of the projection 45 is located above the apex of the raised portion 42 in the vertical direction. The vertical relationship between the projection 45 and the raised portion 42 can be appropriately changed according to the specifications required for the internal combustion engine 1. The projection 45 is provided along the circumferential direction of the piston 30. Here, the projection 45 is provided continuously around the entire circumference so as to surround the raised portion 42 in the circumferential direction.

[0027] As shown in Figure 2, the injector 22 injects fuel toward the projection 45. The injector 22 has a plurality of injection holes provided at predetermined intervals in the circumferential direction, and each injection hole injects fuel. In Figure 2, for the sake of explanation, only the direction of fuel injection from one injection hole is shown. The fuel injected by the injector 22 branches at the projection 45. A portion of the branched fuel flows toward the connection 50 as indicated by arrow A1 in Figure 2, and the remaining fuel flows toward the radially outward side of the cavity 40 as indicated by arrow A2.

[0028] The connecting portion 50 is located between the raised portion 42 and the projection portion 45 in the radial direction of the piston 30, and is the part that connects the projection portion 45 and the raised portion 42. In the vertical direction, the connecting portion 50 is located below the projection portion 45. In the circumferential direction, the connecting portion 50 is provided at a position corresponding to the projection portion 45. The projection portion 45 is provided so as to surround the raised portion 42 in the circumferential direction, and the connecting portion 50 is also provided so as to surround the raised portion 42. Here, the connecting portion 50 is provided along the circumferential direction of the piston 30. A portion of the fuel (unburned fuel) branched off from the projection portion 45 flows along the connecting portion 50 and heads toward the center of the cavity 40.

[0029] As shown in Figure 2, the connecting portion 50 has a curved surface 52, a flat surface 54, and a stepped portion 56. The curved surface 52 is located radially outward of the piston 30 at the connection portion 50 and is connected to the projection 45. The curved surface 52 is a guide surface that guides the fuel branched off at the projection 45 toward the center of the cavity 40. The curved surface 52 is curved with a predetermined curvature here to facilitate the guidance of the fuel toward the center of the cavity 40.

[0030] The curved surface 52 is provided along the circumferential direction. The curved surface 52 is formed continuously around the circumferential direction, surrounding the raised portion 42. As a result, even if the fuel that has been diverted at the projection 45 spreads out in the circumferential direction, the fuel can easily flow along the curved surface 52, thus guiding the fuel to the center of the cavity 40.

[0031] The flat surface 54 is located inward (towards the center) of the piston 30 in the radial direction of the piston 30 compared to the curved surface 52. Specifically, the flat surface 54 is located between the curved surface 52 and the stepped portion 56 in the radial direction of the piston 30. One end of the flat surface 54 is connected to the curved surface 52, and the other end of the flat surface 54 is connected to the stepped portion 56. The flat surface 54, like the curved surface 52, is provided along the circumferential direction. The flat surface 54, like the curved surface 52, is provided continuously around the circumference. Following the curved surface 52, the flat surface 54 guides the fuel toward the center of the cavity 40.

[0032] The flat surface 54 is inclined at a predetermined angle in the radial direction. The flat surface 54 is inclined such that the connection point with the curved surface 52 (one end of the flat surface 54) is located lower in the vertical direction than the connection point with the stepped portion 56 (the other end of the flat surface 54). Between the curved surface 52 and the stepped portion 56, the flat surface 54 is inclined such that it becomes lower towards the radial outer side. In this case, the flat surface 54 is parallel to the inclined surface 43 of the raised portion 42. However, it is not limited to the above, and the flat surface 54 does not have to be parallel to the inclined surface 43. The inclination of the flat surface 54 as described above makes it easier for the fuel flowing along the flat surface 54 to travel straight toward the radial center and upward in the vertical direction.

[0033] The stepped portion 56 is the part that forms a step between the raised portion 42 and the connecting portion 50. The stepped portion 56 is formed between the raised portion 42 and the flat surface 54. Specifically, the stepped portion 56 is formed between the inclined surface 43 of the raised portion 42 and the flat surface 54. The stepped portion 56 is provided along the circumferential direction. The stepped portion 56 is provided continuously over one full turn in the circumferential direction. By providing the stepped portion 56, fuel flowing straight along the flat surface 54 is more likely to separate at the stepped portion 56. Fuel flowing straight along the flat surface 54 is more likely to separate at the stepped portion 56 from the surface that forms the cavity 40.

[0034] The stepped portion 56 has a stepped surface 57, an upper end portion 64, and a lower end portion 65. The stepped surface 57 is a surface that is inclined with respect to the flat surface 54, and as an example, it is a flat surface perpendicular to the flat surface 54. The upper end portion 64 is the part that connects the stepped surface 57 and the flat surface 54 at one end (upper end) of the stepped surface 57. The upper end portion 65 is the part that connects the stepped surface 57 and the inclined surface 43 at the other end (lower end) of the stepped surface 57. Fuel flowing on the flat surface 54 separates from the surface that forms the cavity 40 at the upper end portion 64. Fuel that has flowed along the connection portion 50 travels straight toward the center in the radial direction and upward in the vertical direction as it flows on the flat surface 54. Fuel that has flowed on the flat surface 54 continues to travel straight without changing direction even after passing the upper end portion of the stepped surface 57. Therefore, the fuel flowing on the flat surface 54 separates from the surface forming the cavity 40 at the upper end 64 where the flat surface 54 and the stepped surface 57 are connected.

[0035] The lower end portion 65, which is connected to the inclined surface 43 of the stepped portion 56, is located below the upper end portion 64, which is connected to the flat surface 54 of the stepped portion 56, in the vertical direction. In the above description, it is assumed that the stepped surface 57 is a flat surface, but it is not limited to this, and the stepped surface 57 may be a curved surface.

[0036] Incidentally, the flat surface 54 is provided such that the imaginary line B extending from the flat surface 54, as shown in Figure 2, passes above the apex of the raised portion 42. The imaginary line B is an imaginary line extending along the surface of the flat surface 54 toward the radially inward (center side) of the piston 30. Specifically, the imaginary line B extending from the flat surface 54 passes between the apex of the raised portion 42 and the injector 22. As a result, the separated fuel can flow away from the inclined surface 43 of the raised portion 42, making it easier to take in air from around the inclined surface 43, and thus promoting the mixing of fuel and air. Note that the imaginary line B extending from the flat surface 54 may also pass through the injector 22 when the piston 30 is at top dead center.

[0037] Here, the flow of fuel injected by the injector 22 within the cavity 40 will be explained with reference to Figures 3 to 5. Figure 3 is a schematic diagram showing the state immediately after the injector 22 injects fuel into the projection 45. Figure 4 is a schematic diagram showing the state in which the fuel flows along the flat surface 54. Figure 5 is a schematic diagram showing the state in which the fuel has separated from the surface forming the cavity 40 at the upper end 64. Figure 3 shows the piston 30 located near top dead center, and Figures 4 and 5 show the state in which the piston 30 is moving toward bottom dead center.

[0038] Here, we assume that the injector 22 injects fuel when the piston 30 is near top dead center. As shown in Figure 3, the injector 22 injects fuel toward the projection 45. The injected fuel collides with the projection 45 and branches. Some of the branched fuel flows over the projection 45 and radially outward, while the remaining fuel flows toward the curved surface 52 of the connection part 50.

[0039] After the injector 22 injects fuel, the piston 30 moves toward bottom dead center. At this time, as shown in Figure 4, the fuel that flows from the projection 45 to the curved surface 52 then flows along the flat surface 54. As the fuel flows along the flat surface 54, the direction of fuel flow becomes straight. Specifically, it flows straight along the flat surface 54 toward the center in the radial direction and toward the upward in the vertical direction.

[0040] As the piston 30 moves further toward the bottom dead center, as shown in Figure 5, the fuel flowing on the flat surface 54 separates from the surface forming the cavity 40 at the upper end 64 where it connects to the stepped surface 57 of the flat surface 54. In particular, the straight flow of the fuel due to the flat surface 54 makes fuel separation easier. Unlike this embodiment, if there is no flat surface 54 and the curved surface 52 is connected to the stepped surface 57, the direction of fuel flow is not straight, making fuel separation difficult. Also, even if separation occurs, the non-straight flow of the fuel makes it more likely to come into contact with the raised portion 42.

[0041] The separated fuel does not come into contact with the raised portion 42 (specifically, the inclined surface 43) and flows away from the inclined surface 43. At this time, the fuel takes in the surrounding air and burns. In particular, the space between the flowing fuel and the inclined surface 43 makes it easier for air to be taken into the fuel from this space, thus promoting the combustion of the fuel.

[0042] <Variation> Figure 6 is a schematic diagram showing a modified cross-sectional configuration of the cavity 40. In this modified configuration, the radial width L1 of the flat surface 54 is greater than the radial width L2 of the curved surface 52. This increase in the width L1 of the flat surface 54 makes it easier to form a straight flow of fuel along the flat surface 54, thus making fuel separation more likely at the upper end 64.

[0043] Furthermore, in the modified example shown in Figure 6, the radial width L1 of the flat surface 54 is increased, thereby reducing the radial width of the inclined surface 43. Also, in the modified example, the length between the upper end 64 and the lower end 65 of the stepped surface 57 is shortened, so the inclination angle of the inclined surface 43 connected to the lower end 65 is reduced. As a result, the volume of the cavity 40, which is a recess, can be reduced, and the compression ratio during the compression stroke of the internal combustion engine 1 can be increased.

[0044] In the above description, the stepped portion 56 and the flat surface 54 are assumed to be continuously provided around the raised portion 42 in the circumferential direction, but the invention is not limited to this. For example, multiple stepped portions 56 and flat surfaces 54 are provided at predetermined intervals in the circumferential direction. Specifically, the stepped portions 56 and flat surfaces 54 are provided in accordance with the positions of multiple injection holes of the injector 22 in the circumferential direction. Even in this case, the fuel injected from each injection hole of the injector 22 and flowing along the connection portion 50 is more likely to separate at the upper end portion 64.

[0045] <Effects of this embodiment> The cavity 40 of the piston 30 in the above-described embodiment has a raised portion 42 provided in the radial center of the piston 30, a projection 45 provided circumferentially on the outside of the raised portion 42, and a connecting portion 50 provided so as to surround the raised portion 42 and connecting the projection 45 and the raised portion 42. The connecting portion 50 includes a curved surface 52 connected to the projection 45, a flat surface 54 connected to the curved surface 52 on the radially inward side, and a stepped portion 56 formed between the flat surface 54 and the raised portion 42. The flat surface 54 is inclined between the curved surface 52 and the stepped portion 56 such that it becomes lower towards the radially outward side. By providing the flat surface 54 described above, the fuel that has flowed from the curved surface 52 to the flat surface 54 is more easily separated at the upper end portion 64 connecting the flat surface 54 and the stepped portion 56. In addition, because the flat surface 54 is inclined away from the bottom of the cavity 40, the separated fuel is less likely to come into contact with the raised portion 42, and it becomes easier to take in surrounding air. As a result, the mixing of the separated fuel and air is promoted, and combustion efficiency is increased.

[0046] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of its gist. For example, all or part of the apparatus can be configured by functionally or physically distributing and integrating in any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of the new embodiments resulting from the combinations are combined with the effects of the original embodiments. [Explanation of symbols]

[0047] 1. Internal combustion engine 22 Injectors 30 pistons 40 Cavity 42 Ridge 43 Slope 45 Protrusion 50 Connection part 52 Curved surface 54 Flat surface 56 Stepped section

Claims

1. A piston with a cavity formed in the center of its top surface, An injector that injects fuel into the cavity, Equipped with, The aforementioned cavity is A raised portion provided in the radial center of the piston, A projection is provided on the outer side of the raised portion in the radial direction, along the circumferential direction of the piston, It is provided so as to surround the aforementioned raised portion and has a connecting portion that connects the projection and the aforementioned raised portion, The connecting portion includes a curved surface connected to the projection, a flat surface connected to the curved surface on the radially inward side, and a stepped portion formed between the flat surface and the raised portion. The flat surface is inclined such that it becomes lower towards the radially outer side between the curved surface and the stepped portion. Internal combustion engine.

2. A virtual line extending radially inward from the flat surface along the surface of the flat surface passes between the apex of the raised portion and the injector. The internal combustion engine according to claim 1.

3. The raised portion has an inclined surface that slopes outward in the radial direction from the apex of the raised portion. The stepped portion is formed between the inclined surface and the flat surface. The internal combustion engine according to claim 1.

4. The stepped portion has a stepped surface that is inclined with respect to the flat surface, an upper end connecting the stepped surface and the flat surface, and a lower end connecting the stepped surface and the inclined surface. The lower end is located below the upper end in the vertical direction. The internal combustion engine according to claim 3.

5. The flat surface is parallel to the inclined surface. The internal combustion engine according to claim 3.

6. The flat surface and the stepped portion are provided along the circumferential direction. The internal combustion engine according to claim 1.

7. The flat surfaces and stepped portions are provided in multiple locations at predetermined intervals in the circumferential direction. The internal combustion engine according to claim 1.

8. The radial width of the flat surface is greater than the radial width of the curved surface. The internal combustion engine according to claim 1.

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