Piston for internal combustion engine

Abstract

An intake guide part (5) that guides a tumble flow to a piston top surface (2) is formed, and lateral flat surfaces (6) are formed on both sides in a crankshaft axial direction of the intake guide part (5). Stepped parts (7) each extending in an intake / exhaust direction and facing a piston outer circumferential side are formed between the intake guide part (5) and the lateral flat surfaces (6), and the intake guide part (5) is set to a position higher than the lateral flat surfaces (6), thereby forming a compact combustion chamber (9) that excludes the lateral flat surfaces (6). A projection (11) is formed on a central flat surface (10) of the intake guide part (5), and a tumble flow is branched to both sides of the projection (11) in the vicinity of a compression dead point and caused to circulate through a pair of narrow passages (14) formed between the projection (11) and the lateral flat surfaces (6) on both sides.

Description

[Technical field]

[0001] The present invention relates to a piston for an internal combustion engine. [Background technology]

[0002] As a conventional piston for an internal combustion engine, for example, Patent Document 1 discloses a piston in which the intake air introduced into the cylinder during the intake stroke is guided by a cavity on the piston top surface to form a tumble flow. In this piston, a convex or concave damping portion is formed near the center of the piston top surface to equalize the tumble strength inside the cylinder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4379503 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a tumble flow is formed in a cylinder, the flow velocity in the vicinity of the electrode of the ignition plug increases, which makes it easy for sparks to fly off, so there is a demand for ensuring combustion stability. In addition, there is a demand for increasing the combustion speed in order to improve the thermal efficiency of the internal combustion engine. However, the technology of Patent Document 1, which aims to make the tumble strength in the cylinder uniform, cannot satisfy these demands, and more drastic measures are required.

[0005] The present invention has been made to solve these problems, and its object is to provide a piston for an internal combustion engine which can reduce the flow velocity near the electrode of the spark plug to ensure good combustion stability, while realizing rapid combustion and improving the thermal efficiency of the internal combustion engine. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the piston for an internal combustion engine of the present invention comprises an intake guide portion formed to protrude from the top surface of the piston and guiding a tumble flow formed in the cylinder during the intake stroke of the internal combustion engine, a protrusion formed on the intake guide portion, a pair of step portions formed on both sides in the crankshaft direction of the intake guide portion, each extending in the intake and exhaust directions and facing the outer periphery of the piston, and side flat surfaces formed on both sides in the crankshaft direction of the step portions, and the intake guide portion is characterized in that it is raised from the side flat surfaces via the step portions.

[0007] With the piston for an internal combustion engine constructed in this way, the intake air flowing into the cylinder of the internal combustion engine is guided by the intake guide portion on the top surface of the piston to form a tumble flow. Near the top dead center of compression, the tumble flow is split to both sides of the protrusion and flows through a pair of passages formed between the protrusion and each step portion. As a result, the flow speed of the tumble flow decreases above the protrusion located between the two passages, and the flow speed in the vicinity of the electrode of the spark plug also decreases, preventing the blowing off of sparks.

[0008] The tumble flows that are split off on either side of the protrusion pass through each passage, then make a U-turn and pass through each passage in the opposite direction again. At this time, the tumble flows generate shear forces that generate micro-scale vortices, and the vortices are crushed between the cylinder head and the flow, increasing the intensity of the turbulence. The step raises the position of the intake guide, making it easier for the vortices to be crushed, further increasing the intensity of the turbulence, which in turn increases the combustion speed.

[0009] In another aspect, each of the stepped portions may be formed as a leg of a trapezoid in a cross section in the crankshaft direction, and each step may be substantially linear from the intake side to the exhaust side. With an internal combustion engine piston configured in this manner, each step portion is approximately straight, thereby narrowing the width of the passage between each step portion and the protrusion, strengthening the shear force generated in the tumble flow, and shortening the path length of the forward and return paths.

[0010] In another aspect, the projection may be located below an electrode of the spark plug. With an internal combustion engine piston configured in this manner, the flow velocity of the tumble flow decreases on the protrusion located between the two passages, and therefore the flow velocity of the tumble flow in the vicinity of the electrode of the spark plug located directly above the protrusion also decreases.

[0011] In another aspect, the intake guide portion may have a flat central flat surface, a sloping intake side guide surface formed on the intake side of the central flat surface, and a sloping exhaust side guide surface formed on the exhaust side of the central flat surface, and the protrusion may be formed on the central flat surface.

[0012] In the piston for an internal combustion engine configured in this manner, the intake air that flows into the cylinder is guided to the central flat surface via the exhaust-side guide surface, and then passes through the intake-side guide surface and turns around upward to form a tumble flow. By forming a protrusion on the central flat surface, a flat area of ​​the central flat surface is interposed between the exhaust-side guide surface and the protrusion. Therefore, the tumble flow from the exhaust-side guide surface is smoothly diverted to both sides of the protrusion without passing over the protrusion.

[0013] In another aspect, the step portions may be disposed so as to be spaced apart from each other from the exhaust side toward the intake side. With an internal combustion engine piston configured in this manner, the step portions are spaced apart from each other as they move from the exhaust side to the intake side, so that the radius of curvature of the tumble flow when it makes a U-turn on the intake side becomes larger, enabling the tumble flow to be smoothly guided to the exhaust side while maintaining high kinetic energy.

[0014] In another aspect, an end of each of the stepped portions may be located more inward in the crankshaft direction than an end of a valve recess formed in the piston top surface. According to the internal combustion engine piston thus constructed, the tumble flow is smoothly guided from the ends of each step portion to the valve recess as the piston rises, reliably forming a desired flow in each passage. Effect of the Invention

[0015] According to the piston for an internal combustion engine of the present invention, the flow velocity in the vicinity of the electrode of the ignition plug is reduced to ensure good combustion stability, and rapid combustion is realized to improve the thermal efficiency of the internal combustion engine. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a plan view showing a top surface of the piston for an internal combustion engine according to the embodiment. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 2 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Diagram 5] FIG. 2 is a perspective view showing the flow of a tumble flow on a piston top surface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a piston for an internal combustion engine according to the present invention will now be described. 1 is a plan view showing the top surface of a piston for an internal combustion engine according to the present embodiment, FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1, FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1, and FIG. 4 is a cross-sectional view taken along line IV-IV in FIG.

[0018] An internal combustion engine (not shown) to which the piston 1 of this embodiment is applied is configured as, for example, an in-line four-cylinder engine, with each cylinder having four intake and exhaust valves. The crankshaft of the internal combustion engine extends in the vertical direction of Fig. 1, with a pair of intake valves disposed on the right side of Fig. 1 and a pair of exhaust valves disposed on the left side of Fig. 1. In the following description, the direction along the crankshaft is referred to as the crankshaft direction, and the direction perpendicular to this in which the intake and exhaust valves are disposed is referred to as the intake and exhaust direction.

[0019] In FIG. 1, a pair of intake valve recesses 3 having a substantially semicircular shape corresponding to each intake valve are recessed on the right side of the piston top surface 2, and a pair of exhaust valve recesses 4 having a substantially semicircular shape corresponding to each exhaust valve are recessed on the left side of the piston top surface 2. Since the outer diameter of the intake valve head is larger than that of the exhaust valve head, the intake valve recess 3 has a circular arc with a larger curvature than the exhaust valve recess 4. An intake guide portion 5 is formed between the intake valve recess 3 and the exhaust valve recess 4 on the piston top surface 2, and flat side surfaces 6 facing upward are formed on both sides of the intake guide portion 5 in the crankshaft direction. During the intake stroke of an internal combustion engine, a tumble flow is formed in the cylinder, and the shape of the intake guide portion 5 is set so as to be able to appropriately guide this tumble flow, the details of which will be described below.

[0020] Between the intake guide portion 5 and the side flat surfaces 6 on both sides, there are formed step portions 7 that extend in the intake / exhaust direction and face the outer periphery of the piston. As a result, the intake guide portion 5 is formed at a position higher than the side flat surfaces 6, in other words, it has a shape that is raised above the side flat surfaces 6 on both sides. For this reason, as shown in Figure 4, the area of ​​the side flat surfaces 6 does not form a combustion chamber with the cylinder head 8, and the area of ​​the piston top surface 2 excluding the side flat surfaces 6 forms a so-called compact combustion chamber 9.

[0021] In a plan view, each step portion 7 is linear and is disposed so as to be spaced apart from the other as it moves from the exhaust side to the intake side. The intake side end 7a (corresponding to the "end of the step portion" of the present invention) of each step portion 7 is located near the outer end 3a (corresponding to the "end of the valve recess" of the present invention) of the corresponding intake valve recess 3, and is curved inwardly so as to approach each other following the arc of the intake valve recess 3. Therefore, the intake side end 7a of each step portion 7 is located more inwardly in the crankshaft direction than the outer end 3a of the corresponding intake valve recess 3. Similarly, the exhaust side end 7b (corresponding to the "end of the step portion" of the present invention) of each step portion 7 is located near the outer end 4a (corresponding to the "end of the valve recess" of the present invention) of the corresponding exhaust valve recess 4, and is curved inwardly so as to approach each other following the arc of the exhaust valve recess 4. Therefore, the exhaust side end 7b of each step portion 7 is located more inwardly in the crankshaft direction than the outer end 4a of the corresponding exhaust valve recess 4.

[0022] The intake guide portion 5 consists of a central flat surface 10 located in the center of the piston top surface 2, a protrusion 11 formed on this central flat surface 10, an intake side guide surface 12 formed on the intake side of the central flat surface 10, and an exhaust side guide surface 13 formed on the exhaust side of the central flat surface 10.

[0023] The central flat surface 10 is flat and faces upward, and in plan view, has an isosceles trapezoid shape with each step portion 7 serving as a leg of the trapezoid connecting the intake side edge and the exhaust side edge. The intake side guide surface 12 is formed in a slope shape that starts from the intake side edge of the central flat surface 10 and extends obliquely upward toward the intake valve recess 3, and has approximately the same cross section at every point in the crankshaft direction. Similarly, the exhaust side guide surface 13 is formed in a slope shape that starts from the exhaust side edge of the central flat surface 10 and extends obliquely upward toward the exhaust valve recess 4, and has approximately the same cross section at every point in the crankshaft direction.

[0024] The protrusion 11 is formed by rising from the central flat surface 10 at the same height, has a flat upper surface, and in a plan view has a circular shape with its center approximately coinciding with the piston top surface 2. The outer diameter D of the protrusion 11 is smaller than the width L of the central flat surface 10 in the intake / exhaust direction, and flat areas of the central flat surface 10 are formed on both sides of the protrusion 11 in the intake / exhaust direction.

[0025] The piston 1 having the top surface 2 as described above is assembled into an internal combustion engine, and as shown in Fig. 4, a combustion chamber 9 is formed between the piston top surface 2 and a recess 8a formed in the underside of a cylinder head 8. Although not shown, in a plan view, the spark plug is surrounded by the intake and exhaust valves and is positioned approximately in the center of the combustion chamber 9, and a protrusion 11 on the piston top surface 2 is located directly below the electrode of the spark plug.

[0026] When the intake valve opens during the intake stroke while the internal combustion engine is running, the air-fuel mixture flows into the cylinder through each intake port as the piston 1 descends. The air-fuel mixture flows in an oblique direction (toward the exhaust side and downward) along the intake port, and when it reaches the piston top surface 2 inside the cylinder, it is guided to the central flat surface 10 through the exhaust-side guide surface 13, and then turns around and flows upward through the intake-side guide surface 12 to form a tumble flow. When the engine moves to the compression stroke, the piston 1 moves up while compressing the tumble flow up and down, and when the ignition timing is reached near the top dead center of the compression stroke, the air-fuel mixture is ignited by the spark plug and combustion begins, followed by the expansion stroke.

[0027] FIG. 5 is a perspective view showing the flow of the tumble flow on the top surface of the piston. To explain the flow of the tumble flow in the compression stroke in more detail, the tumble flow is guided from the exhaust-side guide surface 13 to the central flat surface 10, and in the region of the tumble flow corresponding to the protrusion 11 in the crankshaft direction, the flow is obstructed by the protrusion 11, and the flow velocity decreases. As the piston 1 rises, the flow path of the tumble flow is gradually restricted up and down, and the tumble flow is compressed up and down accordingly. When it reaches the vicinity of the compression top dead center, most of the tumble flow is diverted to both sides of the protrusion 11 without going over the protrusion 11. In addition, since the compact combustion chamber 9 does not include the side flat surface 6, the tumble flow does not spread to the region of the side flat surface 6. As a result, the path on the piston top surface 2 through which the tumble flow can flow near the compression top dead center is mainly restricted to a pair of narrow passages 14 formed between the protrusion 11 and each side flat surface 6 (in other words, each step portion 7), and the flow velocity of the tumble flow further decreases on the protrusion 11 located between both passages 14.

[0028] This region in the crankshaft direction where the tumble flow velocity is reduced is also the position of the spark plug electrode located directly above the projection 11. Therefore, the flow velocity of the tumble flow in the vicinity of the electrode is reduced, preventing sparks from being blown away, thereby ensuring reliable ignition of the air-fuel mixture and ensuring good combustion stability.

[0029] Meanwhile, the tumble flows that are branched to both sides of the protrusion 11 near the compression top dead center first flow through each passage 14 from the exhaust side to the intake side as shown by arrow A in Fig. 5 (hereinafter, this flow will be referred to as outward route A). Then, the tumble flows make a U-turn toward the outer end 3a along the arc portion of the intake valve recess 3, and again flow in the opposite direction, from the intake side to the exhaust side, through each passage 14 as shown by arrow B in Fig. 5 (hereinafter, this flow will be referred to as return route B).

[0030] As the tumble flow flows in the opposite directions in the outward path A and the return path B through such a narrow passage 14, the tumble flow generates a shearing force that generates micro-scale vortices, which are crushed between the cylinder head 8 as the piston 1 rises, improving the turbulence intensity. In particular, the position of the central flat surface 10 is elevated above the side flat surfaces 6 via the step portion 7, and is closer to the cylinder head 8, making it easier for the vortices to be crushed, further improving the turbulence intensity. Furthermore, as the combustion speed increases with the improvement in turbulence intensity, rapid combustion is achieved, and the thermal efficiency of the internal combustion engine can be improved.

[0031] In addition, the compact combustion chamber 9 suppresses the spread of the tumble flow onto the side flat surface 6, thereby reducing the cooling loss caused by the tumble flow coming into contact with the cylinder wall, which also contributes to improving thermal efficiency.

[0032] Furthermore, in this embodiment, since each step portion 7 is linear, the width of the passage 14 formed between each step portion 7 and the protrusion 11 is narrower. As a result, the outgoing path A and the returning path B of the tumble flow flowing through the passage 14 approach each other, strengthening the shear force and shortening the path lengths of the outgoing path A and the returning path B. As a result, finer micro-scale vortices can be generated and further reduction in cooling loss can be achieved.

[0033] Furthermore, the protrusions 11 are formed on the flat central flat surface 10 without protruding onto the sloping exhaust-side guide surface 13. If the protrusions 11 were directly connected to the exhaust-side guide surface 13, there would be a possibility that the tumble flow would overcome the protrusions 11 without reducing the flow rate. By providing a flat area of ​​the central flat surface 10 between the exhaust-side guide surface 13 and the protrusions 11, the phenomenon of the tumble flow overriding the protrusions 11 can be prevented. This allows the tumble flow to be smoothly diverted to both sides of the protrusions 11, generating finer micro-scale vortices.

[0034] Moreover, in addition to being linear, the steps 7 are arranged so as to be spaced apart from each other as they approach the intake side. As a result, the radius of curvature when the tumble flow flowing along the outgoing path A makes a U-turn becomes large. If the radius of curvature is small, the kinetic energy of the tumble flow is lost, but this situation can be prevented and the tumble flow can be smoothly guided to the return path B while maintaining high kinetic energy.

[0035] Moreover, the intake side end 7a of each step 7 is located inward in the crankshaft direction from the outer end 3a of the corresponding intake valve recess 3, and the exhaust side end 7b is located inward in the crankshaft direction from the outer end 4a of the corresponding exhaust valve recess 4. Therefore, the tumble flow, which is prevented from spreading to the side flat surface 6 as the piston 1 rises, is smoothly guided from the intake side end 7a of each step 7 to the intake valve recess 3, and from the exhaust side end 7b to the exhaust valve recess 4. As a result, in each passage 14, a desired flow consisting of an outward path A and a return path B is reliably formed. In this way, smooth guidance of the tumble flow while maintaining its kinetic energy also contributes to the generation of finer micro-scale vortices.

[0036] Although the description of the embodiment is finished above, the aspects of the present invention are not limited to this embodiment. For example, the shape of the intake guide portion 5 that guides the tumble flow may be changed, or the shape of the protrusion 11 that divides the tumble flow may be changed. [Explanation of symbols]

[0037] 1 piston 2 Piston top surface 3 Intake valve recess 3a,4a Outer end (end) 4 Exhaust valve recess 5. Intake guide section 7 Step 7a Intake end 7b Exhaust end 10 Central flat surface 11 Protrusions 12 Intake side guide surface 13 Exhaust side guide surface

Claims

1. an intake guide portion formed on the piston top surface to protrude and guide a tumble flow formed in the cylinder during the intake stroke of the internal combustion engine; A protrusion formed on the intake guide portion; a pair of step portions formed on both sides of the intake guide portion in the crankshaft direction, each step portion extending in an intake / exhaust direction and facing an outer periphery of a piston; a side flat surface formed on both sides of the step portion in the crankshaft direction; Equipped with The intake guide portion is raised from the side flat surface via the step portion. A piston for an internal combustion engine.

2. Each of the stepped portions is a leg of a trapezoid in a cross section in the crankshaft direction, and is generally linear from the intake side to the exhaust side.

2. The piston for an internal combustion engine according to claim 1.

3. The projection is located below the electrode of the spark plug.

3. A piston for an internal combustion engine according to claim 1 or 2.

4. the intake guide portion has a flat central flat surface, a sloping intake side guide surface formed on the intake side of the central flat surface, and a sloping exhaust side guide surface formed on the exhaust side of the central flat surface, The protrusion is formed on the central flat surface.

4. A piston for an internal combustion engine according to claim 1, wherein the piston is a piston having a diameter of 10 mm or less.

5. The steps are disposed so as to be spaced apart from each other from the exhaust side to the intake side.

5. A piston for an internal combustion engine according to claim 1 .

6. An end of each of the stepped portions is located inward in the crankshaft direction from an end of a valve recess formed in the piston top surface.

6. A piston for an internal combustion engine according to claim 1 .

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