Engine piston

Abstract

To provide a piston excellent in a tumble flow producing function and flame propagating performance.SOLUTION: On a crown surface of a piston 5 are formed a center recess 21 long in a front-rear direction (crank shaft line direction) and squish surfaces 25 and 26 located on right and left sides thereof. The recess 21 is constituted of cross-sectional identical shape parts 22 with the same curvature radius R in a front-rear direction view, and cross-sectional shape changed parts 23 that are located on both front and rear ends thereof, and whose depths are changed in the front-rear direction. The curvature radius R of the cross-sectional shape identical part 22 is set to 1 to 3 times the diameter of a cylinder bore. Since a tumble flow 33 is guided across the full length of the cross-sectional shape identical part 22, the producing functionality of the tumble flow 33 is high. Since flame runs at high speed in the front-rear direction without being radiated to the piston 5, an unburned phenomenon cannot be eliminated. Therefore, the piston can contribute to improvement of thermal efficiency and fuel consumption, and prevention of deterioration of exhaust gas components.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a piston of an engine (internal combustion engine).

Background Art

[0002] In a gasoline engine, it is essential to completely burn the fuel in order to prevent deterioration of the exhaust gas components and improve fuel efficiency. Also, from the viewpoints of preventing knocking due to auto-ignition and improving the output by increasing the combustion pressure, it is required to increase the combustion speed. In this regard, it is beneficial to generate a tumble flow or a swirl flow in the cylinder bore, and by imparting a tumble flow or a swirl flow to the air-fuel mixture, the mixing property of the fuel and the intake air can be enhanced while the combustion speed can be improved by turbulization.

[0003] And it has been proposed to form a recess on the crown surface of the piston and guide the flow of the air-fuel mixture by the recess to promote the generation of a tumble flow or a swirl flow. As an example, in Patent Documents 1 and 2, it is disclosed to form a recess on the crown surface of the piston that is long in the front-rear direction, which is the crankshaft axis direction, and whose both front and rear end faces bulge in a plan view (viewed from the cylinder axis).[[ID=I7]]

[0004] Also, Patent Document 2 discloses that, for the purpose of equalizing the tumble flow, the recess is formed in a long form in the front-rear direction (crankshaft axis direction), and a circular flat portion is formed at the central portion of the recess. Further, Patent Document 3 discloses that, aiming at improving the swirl ratio and the tumble ratio, while forming the recess in a bowl shape, the curvature radius of the bottom surface and the outer diameter (diameter) of the piston are set in a specific relationship.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] Now, while generating tumble flow is particularly effective in creating turbulence in the air-fuel mixture, in order to rapidly and completely combust the mixture, it is necessary to burn the entire mixture filling the combustion chamber, which is composed of the cylinder head and piston, all at once. And while generating tumble flow is effective in creating turbulence in the mixture, even if the mixture is turbulent, if the initial flame generated by the spark plug does not propagate rapidly throughout the entire combustion chamber, unburned material will remain, making knocking more likely.

[0007] Upon examining each patent document, it appears that, when viewed locally, each document can promote turbulence in the fuel-air mixture. However, when viewed as a whole, it is questionable whether it can rapidly propagate the initial flame throughout the combustion chamber and prevent the generation of unburned fuel.

[0008] The present invention was made against this backdrop, and aims to disclose a piston structure that can achieve complete combustion of the fuel-air mixture. [Means for solving the problem]

[0009] The invention of claim 1 is, " This is for use in port injection engines. On the crown surface facing the cylinder head, A flat reference plane perpendicular to the cylinder bore axis, A center recess is formed that is elongated in the front-to-back direction, which is the direction of the crank axis, and squish surfaces are formed on the intake side and exhaust side, flanking the center recess. There, The center recess is formed in a recessed state relative to the reference surface, and the squish surface is higher than the reference surface. " This is the basic configuration, and in the above basic configuration, "the aforementioned center recess The aforementioned reference planes exist on both the front and rear sides and on both the left and right sides, The aforementioned center recess comprises a portion with the same cross-sectional shape where the bottom surface has the same radius of curvature when viewed from the front-rear direction and is continuous in the front-rear direction, and located on both the front and rear sides of the portion with the same cross-sectional shape. It should become shallower towards both the front and back ends. It has a section with a changing cross-sectional shape where the depth changes, The radius of curvature of the bottom surface in the same cross-sectional area is equal to the diameter of the cylinder bore. 1 to 3 times It is set to " That The configuration is added Yes, they are.

[0010] Claim 2 is an independent claim, " On the crown surface facing the cylinder head, a center recess is formed that is elongated in the front-to-back direction, which is the direction of the crank axis, and squish surfaces are formed on the intake side and exhaust side, flanking the center recess. In this basic configuration, "The center recess has a portion with a uniform cross-sectional shape where the bottom surface has the same radius of curvature when viewed from the front-rear direction and is continuous in the front-rear direction, and portions with a changed cross-sectional shape located on both the front and rear sides of the portion with a uniform cross-sectional shape where the depth changes in the front-rear direction, and the radius of curvature of the bottom surface in the portion with a uniform cross-sectional shape is set to 1 to 3 times the diameter of the cylinder bore." Furthermore, The apex of the intake and exhaust squish surfaces is set back from the center recess in the left-right direction, and its height is greater than the outer edge of the center recess, and a relief surface is formed from the apex of the squish surface toward the center recess." This is the structure. [Effects of the Invention]

[0011] In the present invention, the center recess extends for a long distance in the front-to-back direction, which is the direction of the crank axis. However, in the section with the same cross-sectional shape, the bottom surface is arc-shaped when viewed in the front-to-back direction. Therefore, the tumble flow can be smoothly guided along the entire length of that section with the same cross-sectional shape. Consequently, the front-to-back width of the tumble flow can be made as large as possible. In other words, a strong tumble flow can be generated.

[0012] On the other hand, since the piston is circular, the front-to-back length and left-to-right width of the cross-sectional shape of the center recess are inversely related, and there is a natural limit to the left-to-right width of the center recess in relation to the valve recesses provided to allow the intake and exhaust valves to move during the intake and exhaust strokes. However, in the present invention, the radius of curvature of the cross-sectional shape of the center recess is set to the diameter of the cylinder bore. 1 to 3 times By setting it this way, the length of the front-to-back portion of the cross-sectional shape can be made as large as possible, while the depth can be smoothly changed at the cross-sectional shape change section. Therefore, the area of ​​the portion of the cross-sectional shape can be made as large as possible, ensuring an improvement in the tumble flow generation function.

[0013] In addition, if the portion with the same cross-sectional shape is too deep, the portion with the same cross-sectional shape may act as a resistance to the flow of the tumble flow, making it likely for the air-fuel mixture to stagnate. Conversely, if the portion with the same cross-sectional shape is too shallow, the tumble flow generation function may become insufficient. However, as in the present invention, when the radius of curvature of the bottom surface in the portion with the same cross-sectional shape is 1 to 3 times set to that of the diameter of the cylinder bore (or the outer diameter of the piston), the portion with the same cross-sectional shape will have an appropriate depth, and in the compression stroke, it can promote the generation of the tumble flow without hindering the flow of the air-fuel mixture.

[0014] Also, although the tumble flow is broken down in the compression stroke and changes into a collection of fine turbulent flows, in the present invention, since the portion with the same cross-sectional shape has a long shape in the front-rear direction and an appropriate depth, the tumble flow can be made turbulent over a large area.

[0015] The center recess of the piston and the recess of the cylinder head jointly form the combustion chamber. However, when the radius of curvature of the bottom surface of the portion with the same cross-sectional shape is 1 to 3 times set to that of the diameter of the cylinder bore, it is possible to generate the initial flame mass formed by the spark of the ignition plug in a state where it does not contact the bottom surface of the portion with the same cross-sectional shape. Therefore, it is possible to prevent the heat of the initial flame from escaping to the piston and to propagate the high-temperature flame at high speed to the entire air-fuel mixture.

[0016] Also, when the initial flame propagates to the air-fuel mixture in the center recess, since the portion with the same cross-sectional shape is long in the front-rear direction, it is possible to prevent the flame from contacting the bottom surface of the center recess and to propagate without reducing the fire intensity to both ends in the front and rear of the center recess. In this regard as well, it has excellent flame propagation performance.

[0017] [[ID=第十九]] Thus, in the present invention, it is excellent in the tumble flow generation function and the turbulent flow generation function of the tumble flow, and in the combustion stroke, it is excellent in the high-speed flame propagation performance. These combined can prevent the afterburning phenomenon and burn the entire air-fuel mixture at once. As a result, it can contribute to preventing knocking, achieving complete combustion, improving the thermal efficiency and fuel consumption, and preventing the deterioration of the exhaust gas components.

[0018] By adopting the configuration of claim 2, the air-fuel mixture can be concentrated at the central recess, improving the flame propagation to the mixture. Furthermore, the upward pushing action of the squish surface during the compression stroke promotes turbulence in the tumble flow. These factors work together to enhance the effect of rapidly burning the air-fuel mixture. [Brief explanation of the drawing]

[0019] [Figure 1] In the figure illustrating the embodiment, (A) is a perspective view and (B) is a plan view. [Figure 2] (A) is a cross-sectional view of the engine as seen from the IIA-IIA direction in Figure 1(B), and (B) is a cross-sectional view of the engine as seen from the IIB-IIB direction in Figure 1(B). [Figure 3] (A) is a cross-sectional view of the engine as seen from the IIIA-IIIA direction in Figure 1(B), and (B) is a cross-sectional view of the same location in Figure 2(B) during the combustion stroke. [Modes for carrying out the invention]

[0020] Next, embodiments of the present invention will be described based on the drawings. This embodiment is applied to a multi-cylinder engine for an automobile. Hereafter, the terms front-rear and left-right will be used to specify directions, but the front-rear direction is the direction of the crank axis as defined in the claims, and the left-right direction is the direction perpendicular to the crank axis and the cylinder bore axis.

[0021] (1) Description of structure The basic structure of the engine is the same as in conventional engines. As shown in Figures 2 and 3, it has a cylinder block 2 in which a cylinder bore 1 is formed, and a cylinder head 4 fixed to the upper surface of the cylinder block 2 via a gasket 3. A piston 5 is slidably fitted into the cylinder bore 1. The piston 5 is connected to a connecting rod by a piston pin (neither shown), and the connecting rod is connected to a crank pin (not shown).

[0022] The cylinder head 4 has a downward-facing recess 6 for the combustion chamber that opens toward the cylinder bore 1. The downward-facing recess 6 is formed in a pent-roof shape with a tapered surface, and when viewed from below, it has a long shape in the front-to-back direction.

[0023] As shown in Figure 2(A), the cylinder head 4 has a pair of intake ports 7 and exhaust ports 8, one front and one rear, opening toward a downward recess 6, and these are arranged on the left and right sides. An intake valve 9 for opening and closing the intake port 7 and an exhaust valve 10 for opening and closing the exhaust port 8 are slidably mounted on the cylinder head 4. A spark plug 11 is mounted on the top surface of the downward recess 6. The spark plug 11 has a center electrode 12 and a ground electrode 13. The engine uses port injection.

[0024] Figure 1(A) shows the entire piston 5. The basic structure of the piston 5 is the same as in the conventional design, and it has a cylindrical portion 16 with three annular grooves 15 formed therein, and left and right longitudinal support portions (skirt portions) 17 that protrude downward from the cylindrical portion 16, and a piston pin insertion hole 18 that penetrates in the front-to-back direction is provided in the support portions 17. An oil ring 19 and a piston ring 20 are fitted into the annular grooves 15.

[0025] One of the features of this embodiment is that, first, a longitudinal center recess 21 is formed on the crown surface (top surface) of the piston 5. The longitudinal center line of the center recess 21 coincides with the longitudinal center line O1 of the piston 5, and its longitudinal length is close to the diameter of the piston 5.

[0026] Furthermore, the center recess 21 has a portion 22 with the same cross-sectional shape where the radius of curvature R of the bottom surface is constant when viewed in the front-rear direction, and is continuous with both the front and rear ends of the portion 22 with the same cross-sectional shape and has a depth It should become shallower towards both the front and back ends. It consists of a section 23 with a changing cross-sectional shape. The radius of curvature R of the bottom surface in the section 22 with the same cross-sectional shape is set to approximately twice the diameter of the cylinder bore 1 (or the outer diameter of the piston 5). As clearly shown in Figure 1(B), the section 23 with a changing cross-sectional shape bulges toward the intake side in a plan view. Top surface of piston 5 The center recess 21 has a flat reference surface perpendicular to the axis of the cylinder bore and the axis of the piston. The first reference surface 24 remains on the outer side of the center recess 21 in the front-rear direction, and the second reference surfaces 28 remain on both the left and right sides of the center recess 21. Therefore, the center recess 21 is recessed from the reference surfaces 24 and 28.

[0027] In the intake side area flanking the center recess 21, an intake side squish surface 25 is formed, which is higher in height toward the center recess 21. In the exhaust side area flanking the center recess 21, an exhaust side squish surface 26 is formed, which is higher in height toward the center recess 21. These squish surfaces 25 and 26 widen and become lower as they move away from the center recess 21, forming a ginkgo leaf shape in plan view.

[0028] Furthermore, the squish surfaces 25 and 26 are located a certain distance away from the longitudinal edges of the center recess 21, and the ridges 25a and 26a that form the vertices of the squish surfaces 25 and 26 are first Reference plane It is higher than 24. Therefore, a relief surface 27 is formed on the crown surface of the piston 5, inclined from the ridges 25a and 26a toward the center recess 21. The relief surface 27 narrows in length toward the center recess 21 and is continuous with the same radius of curvature R as the part 22 that has the same cross-sectional shape as the center recess 21.

[0029] As previously mentioned, On the crown surface of the piston 5, on both the left and right sides flanking the center recess 21, the first Reference plane The second one, at the same height as 24 Reference plane 28 is formed, and the first Reference plane 24 and 2 Reference plane 28 is continuous in a point-contact manner. Furthermore, in the areas to the left and right of the squish surfaces 25 and 26, there are third surfaces at the same height as the first and second reference surfaces 24 and 28. Reference plane 29 is formed. Therefore, the squish surfaces 25 and 26 are higher than the third reference surface 29. Third Reference plane Number 29 is arc-shaped in plan view. In Figure 1, each Reference plane Parallel diagonal lines are drawn on points 24, 28, and 29.

[0030] The left and right squish surfaces 25 and 26 are formed symmetrically on either side of the longitudinal center line O2 that divides the piston 5 into front and rear halves, and valve recesses 30 and 31 are provided on both the front and rear sides of the squish surfaces 25 and 26 to accommodate the valves 9 and 10. It is formed in a recessed state from the reference surfaces 28 and 29.The valve recesses 30 and 31 are composed of multiple inclined surfaces. The outer edge of the piston 5 is chamfered to a small extent, except for the areas of the valve recesses 30 and 31 (the chamfered portion is indicated by reference numeral 32).

[0031] The positions of the valve recesses 30 and 31 are determined by the valves 9 and 10, and therefore their positions are difficult to move. Consequently, the width of the center recess 21 is determined by the dimensions of the left and right valve recesses 30 and 31. In this embodiment, however, the width of the center recess 21 is one-third of the outer diameter of the piston 5, or slightly larger.

[0032] Furthermore, the cross-sectional shape change portion 23 of the center recess 21 requires a certain front-to-back width in order to smoothly change its depth. As a result, the front-to-back length of the portion 22 with the same cross-sectional shape in the center recess 21 is approximately 75% or slightly larger than the outer diameter of the piston 5. Therefore, the flat area of ​​the portion 22 with the same cross-sectional shape in the center recess 21 is approximately 1 / 3 of the crown surface area of ​​the piston 5.

[0033] (2) Summary In the above configuration, as shown by arrow 33 in Figure 2, during the intake and compression strokes, a tumble flow 33, which is a swirling flow in the left-right direction, is generated in the cylinder bore 1 due to the straightness of the intake airflow. In this case, since there is a front-to-back pair of intake ports 7, the air-fuel mixture has a front-to-back width. However, in this embodiment, the bottom surface of the portion 22 with the same cross-sectional shape, which represents most of the center recess 21 in the piston 5, is curved when viewed in the front-to-back direction. Therefore, the air-fuel mixture can be guided to curve upward over approximately the entire front-to-back length of the piston 5. Consequently, it has excellent tumble flow generation capabilities (it can generate a tumble flow 33 with a large front-to-back width).

[0034] Now, if the radius of curvature R of the section 22 with the same cross-sectional shape is small, the depth of the section 22 with the same cross-sectional shape becomes deeper, which necessitates increasing the front-to-back width of the section 23 with a change in cross-sectional shape. This shortens the front-to-back length of the section 22 with the same cross-sectional shape, potentially reducing the generation of tumble flow 33 and turbulence generation functions. Furthermore, it may prevent the tumble flow 33 from reaching the bottom of the section 22 with the same cross-sectional shape, causing the mixture to stagnate at the bottom of the section 22 with the same cross-sectional shape. Conversely, if the radius of curvature R of the section 22 with the same cross-sectional shape is too large, the depth of the section 22 with the same cross-sectional shape becomes shallower, reducing the guiding function of the tumble flow 33.

[0035] In this regard, if the radius of curvature R of the section 22 with the same cross-sectional shape is set to about twice the diameter of the cylinder bore 1, as in the embodiment, the front-to-back width of the section 23 with a changing cross-sectional shape is made as small as possible, increasing the front-to-back length of the section 22 with the same cross-sectional shape, while allowing the tumble flow 33 to smoothly contact the bottom surface of the section 22 with the same cross-sectional shape, thereby ensuring the generation of the tumble flow 33. If the radius of curvature R is set to 1 to 3 times the diameter of the cylinder bore 1, the same effects as in this embodiment can be enjoyed.

[0036] The tumble flow 33 is compressed during the compression stroke and transformed into a collection of fine turbulence, but because the section with the same cross-sectional shape 22 is long in the front-to-back direction, the density of the turbulence can be made uniform throughout the entire section with the same cross-sectional shape 22. As shown by the shading in Figure 3(B), during the combustion stroke, the spark from the spark plug 11 generates an initial flame 34, and the initial flame 34 spreads throughout the combustion chamber. In this embodiment, however, because the section with the same cross-sectional shape 22 has an appropriate depth, the initial flame 34 does not come into contact with the bottom surface of the section with the same cross-sectional shape 22, thus preventing heat from escaping from the initial flame.

[0037] Furthermore, as shown by the dashed arrow in Figure 1(B), the initial flame 34 spreads throughout the combustion chamber, but because the section with the same cross-sectional shape 22 is long in the front-to-back direction, the flame can travel in the front-to-back direction without contacting the bottom surface of the section with the same cross-sectional shape 22. This allows the entire mixture to be burned at once without reducing the flame intensity. Therefore, a strong flame can be propagated into the turbulent flow filling the entire combustion chamber, achieving both a high combustion speed and uniform dispersion of flame propagation.

[0038] In conclusion, this embodiment fully utilizes the effects of the tumble flow 33. Furthermore, since residual tumble flow 33 remains even at the end of the compression stroke, the initial flame 34 is generated slightly shifted towards the exhaust side.

[0039] As in this embodiment, by forming squish surfaces 25 and 26 with high peak heights in the intermediate front-to-rear portions of the intake and exhaust areas, the air-fuel mixture is sent to the portion 22 with the same cross-sectional shape by the squish surfaces 25 and 26 at the end of the compression stroke, thereby promoting turbulence of the air-fuel mixture and further contributing to improved combustion efficiency.

[0040] Furthermore, as described above, since residual tumble flow 33 remains even at the end of the compression stroke, the air-fuel mixture tends to move from the intake side to the exhaust side in the center recess 21. However, since the initial flame 34 is generated shifted to the exhaust side, the flame is propagated in the direction of the air-fuel mixture flow, thereby improving combustibility.

[0041] Furthermore, if the section with a change in cross-sectional shape 23 is formed in a state where the intake side is bulging, as shown by the arrow 35 in Figure 1(B), the turbulent mixture is guided by the residual flow of the tumble flow 33 toward the section with the same cross-sectional shape 22, which has the advantage of effectively preventing unburned fuel at the section with a change in cross-sectional shape 23.

[0042] Although embodiments of the present invention have been described above, the present invention can be implemented in various other ways. For example, the center recess can be positioned slightly off-center on the intake side or exhaust side. Valve recesses may not be necessary on the intake side, exhaust side, or both, in which case the size and position of the center recess can be freely determined. [Industrial applicability]

[0043] The present invention can be implemented in an engine piston. Therefore, it can be used industrially. [Explanation of Symbols]

[0044] 1 Cylinder bore 2 Cylinder Blocks 4 Cylinder head 5 pistons 6. Downward recess on the cylinder head 7 Intake port 8 exhaust ports 9 Intake valve 10 Exhaust valve 11 Spark plugs 21 Center recess 22 Same cross-sectional shape 23 Section with changing cross-sectional shape twenty four, 28,29 Reference plane 25, 26 Squish surface 27 Relief side 30,31 valve recesses 33 Tumble Flow 34 Initial flame

Claims

1. For use in a port injection engine, On the crown surface facing the cylinder head, a flat reference surface perpendicular to the cylinder bore axis, a center recess elongated in the front-to-back direction of the crank axis, and squish surfaces located on the intake side and exhaust side, flanking the center recess, are formed. The engine piston has a center recess formed in a recessed state from the reference surface, and the squish surface is higher than the reference surface. The reference planes exist on both the front and rear sides and on both the left and right sides of the center recess, and the center recess has a portion with a uniform cross-sectional shape where the bottom surface with the same radius of curvature is continuous in the front-to-rear direction when viewed from the front-to-rear direction, and portions with a changed cross-sectional shape located on both the front and rear sides of the portion with a uniform cross-sectional shape, where the depth changes so that it becomes shallower toward both the front and rear ends. The radius of curvature of the bottom surface in the same cross-sectional area is set to be 1 to 3 times the diameter of the cylinder bore. Engine piston.

2. A piston having a center recess that is elongated in the front-to-back direction, which is the direction of the crank axis, and squish surfaces located on the intake side and exhaust side, with the center recess in between, on the crown surface facing the cylinder head, The aforementioned center recess has a portion with a uniform cross-sectional shape where the bottom surface has the same radius of curvature when viewed from the front-rear direction and is continuous in the front-rear direction, and portions with a changed cross-sectional shape located on both the front and rear sides of the portion with a uniform cross-sectional shape where the depth changes in the front-rear direction, and the radius of curvature of the bottom surface in the portion with a uniform cross-sectional shape is set to 1 to 3 times the diameter of the cylinder bore. Furthermore, the apex of the intake and exhaust squish surfaces is set back from the center recess in the left-right direction, and its height is higher than the outer edge of the center recess, and a relief surface is formed from the apex of the squish surface toward the center recess. Engine piston.

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