Piston of engine

Abstract

To provide a piston of an engine which secures a combustion speed while securing flame propagation in squish parts.SOLUTION: A piston of an engine includes: a top surface; first valve recess parts each of which is formed along an outer peripheral edge of the top surface and releases a tip of one of a first valve or a second valve which introduces intake air into a combustion chamber or exhausts exhaust air from the combustion chamber; second valve recess parts each of which is formed along the outer peripheral edge of the top surface and releases a tip of the other of the first valve and the second valve; and squish parts which are formed between the outer peripheral edge of the top surface and the first and second valve recess parts. The first and second valve recess parts are separated from each other. The first valve recess part expands to the squish part side in a direction toward the second valve recess part side.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] There is an engine piston having two valve recesses formed on a top surface thereof that are connected to each other (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-113845 A Summary of the Invention [Problem to be solved by the invention]

[0004] It is believed that the deterioration of flame propagation in the squish portion is suppressed by connecting the two valve recesses as in the above patent document. This is because, if the two valve recesses are not connected, the flame heading toward the squish portion is suppressed from circling and propagating along the valve recess. However, by connecting the two valve recesses, the area of ​​the squish portion is reduced. As a result, the volume of the combustion chamber increases and the compression ratio decreases. In order to compensate for such a decrease in the compression ratio, for example, it is conceivable to form the bottom at the center of the top surface shallow. If the bottom becomes shallow, the vertical width of the combustion chamber is reduced, which may promote the attenuation of the tumble flow at the end of the compression stroke. As a result, the turbulence in the cylinder during combustion is reduced, which may decrease the combustion speed.

[0005] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an engine piston that ensures flame propagation in the squish portion while also ensuring combustion speed. [Means for solving the problem]

[0006] The above object can be achieved by a piston of an engine comprising: a top surface; a first valve recess portion formed along an outer peripheral edge of the top surface and allowing a tip end of one of first and second valves which introduce intake air into a combustion chamber or discharge exhaust gas from the combustion chamber to escape; a second valve recess portion formed along the outer peripheral edge of the top surface and allowing a tip end of the other of the first and second valves to escape; and a squish portion formed between the outer peripheral edge of the top surface and the first and second valve recess portions, wherein the first and second valve recess portions are spaced apart from each other, and the first valve recess portion expands towards the squish portion as it approaches the second valve recess portion. Effect of the Invention

[0007] According to the present invention, it is possible to provide an engine piston that ensures flame propagation in the squish portion while also ensuring combustion speed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram of the top surface of a piston of a comparative example. [Diagram 2] 2A and 2B are explanatory views of the top surface of the piston of this embodiment, and FIG. 2C is a cross-sectional view of a first modified example. [Diagram 3] 3A to 3C are explanatory diagrams of a second modified example. [Figure 4] FIG. 4A is a cross-sectional view of a third modified example, FIG. 4B is a cross-sectional view of a fourth modified example, and FIG. 4C is a cross-sectional view of a fifth modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Comparative Example] Before describing the top surface of the piston of this embodiment, a top surface 2x of a piston 1x of a comparative example will be described. Fig. 1 is an explanatory diagram of the top surface 2x of a piston 1x of a comparative example. In Fig. 1, an X-axis and a Y-axis that pass through the center of the top surface 2x and are perpendicular to each other are indicated by dotted lines. The piston 1x is used in an engine.

[0010] The top surface 2x is formed with a bottom portion 3, inclined portions 4i and 4e, squish portions 5i and 5e, and valve recess portions 6ix and 6ex. The bottom portion 3 is formed in the center of the top surface 2x. The inclined portions 4i and 4e are formed at positions symmetrical with respect to the Y axis. The two valve recess portions 6ix are formed at positions almost symmetrical with respect to the X axis. The two valve recess portions 6ex are formed at positions almost symmetrical with respect to the X axis. The valve recess portions 6ix and 6ex are formed at positions almost symmetrical with respect to the Y axis. The squish portions 5i and 5e are formed at positions symmetrical with respect to the Y axis. The squish portion 5i is located between the two valve recess portions 6ix, the inclined portion 4i, and the outer peripheral edge 2i on the intake valve side of the top surface 2x. The squish portion 5e is located between the two valve recess portions 6ex, the inclined portion 4e, and the outer peripheral edge 2e on the exhaust valve side of the top surface 2x.

[0011] In FIG. 1, two intake valve tips IV and two exhaust valve tips EV are indicated by dotted lines. In detail, the intake valve tip IV indicates the outer periphery of the tip of the intake valve that introduces intake air into the combustion chamber. The two intake valves correspond to the first and second valves. The exhaust valve tip EV indicates the outer periphery of the tip of the exhaust valve that discharges exhaust from the combustion chamber. The two exhaust valves correspond to the first and second valves. The valve recesses 6ix and 6ex are formed in a concave shape so as to allow the intake valve tip IV and the exhaust valve tip EV to escape, respectively. Here, the diameter of the intake valve tip IV is formed larger than the diameter of the exhaust valve tip EV. The valve recesses 6ix and 6ex are formed in an arc shape so as to allow a part of the outer periphery of the intake valve tip IV and the exhaust valve tip EV to escape, respectively. For this reason, the diameter of the valve recess 6ix is ​​formed larger than the diameter of the valve recess 6ex.

[0012] Flame propagation in a comparative example will be described. When the mixture in the combustion chamber is ignited by the spark plug, the mixture starts to burn and a flame is generated. Here, the spark plug is provided in the cylinder head so as to be located at approximately the center of the combustion chamber. Therefore, when the mixture is ignited by the spark plug, the flame propagates from near the intersection of the X-axis and the Y-axis to the intake valve side and the exhaust valve side along the X-axis. The flame propagated to the intake valve side proceeds along the X-axis to the squish portion 5i. In addition, a part of the flame that proceeds along the X-axis toward the squish portion 5i propagates so as to swirl along the valve recess portion 6ix. Similarly, the flame that propagates to the exhaust valve side proceeds along the X-axis to the squish portion 5e. In addition, a part of the flame that proceeds along the X-axis toward the squish portion 5e propagates so as to swirl along the valve recess portion 6ex.

[0013] As a result of the flame propagating in this manner, there is a risk that a flame non-propagation region S, where the flame does not propagate, may occur in the squish portion 5i between the valve recess portion 6ix and the outer peripheral edge 2i, or in the squish portion 5e between the valve recess portion 6ex and the outer peripheral edge 2e. In the flame non-propagation region S, the probability that fuel will remain unburned increases, which may cause a deterioration in emissions.

[0014] [This Example] 2A and 2B are explanatory diagrams of the top surface 2 of the piston 1 of this embodiment. In addition, the intake valve tip IV and the exhaust valve tip EV are omitted in FIG. 2A. As shown in FIG. 2A, the valve recesses 6i and 6e of the top surface 2 of the piston 1 of this embodiment are different in shape from the valve recesses 6ix and 6ex of the comparative example. Here, the two valve recesses 6i of this embodiment, like the comparative example, each of the two intake valve tips IV is released. Therefore, the two valve recesses 6i correspond to the first and second valve recesses. Similarly, the two valve recesses 6e correspond to the first and second valve recesses. The two valve recesses 6i extend closer to each other than the two valve recesses 6ix. However, the two valve recesses 6i are spaced apart from each other and are not connected.

[0015] The two valve recesses 6i expand toward the squish portion 5i as they approach each other. In other words, the width of the valve recess 6i along the X-axis expands. Such a shape of the valve recess 6i prevents the flame propagating along the X-axis toward the squish portion 5i from being separated by the valve recess 6i. As a result, the flame can be sufficiently propagated to the squish portion 5i, and flame propagation in the squish portion 5i is ensured. Note that although the number of exhaust valves is two here, even if there is one exhaust valve, flame propagation can be ensured by changing the shape of the intake side valve recess 6i.

[0016] In addition, the two valve recesses 6i are spaced apart from each other. This ensures the area of ​​the squish portion 5i. This allows the bottom 3 to be formed deep without reducing the compression ratio. This makes it possible to suppress the attenuation of the tumble flow and ensure the combustion speed. The same applies to the valve recesses 6e and the squish portions 5e.

[0017] FIG. 2B is a cross-sectional view taken along the line AA in FIG. 2A. The valve recess 6i includes a recess bottom surface 61 and recess side surfaces 62. The recess bottom surface 61 faces the bottom surface of the tip of the intake valve. The recess side surfaces 62 are continuous between the recess bottom surface 61 and the inclined portion 4i and the squish portion 5i. As shown in FIG. 2B, the recess side surfaces 62 and the inclined portion 4i are continuous at a gentle angle, not at a right angle. This prevents turbulence from occurring near the boundary between the inclined portion 4i and the recess side surfaces 62. This prevents the flame moving toward the squish portion 5i along the inclined portion 4i from being separated by the valve recess 6i. As a result, flame propagation in the squish portion 5i is ensured. The same is true for the valve recess 6e and the squish portion 5e.

[0018] [Variations] Next, several modified examples will be described. Fig. 2C is a cross-sectional view of a first modified example. Fig. 2C corresponds to Fig. 2B. The recess side surface 62a of the valve recess portion 6ia and the inclined portion 4ia are formed in a curved shape. This shape further suppresses the separation of the flame, and ensures the flame propagation in the squish portion 5i.

[0019] 3A to 3C are explanatory diagrams of the second modified example. FIG. 3A corresponds to FIG. 2A. FIG. 3B corresponds to FIG. 2B. FIG. 3C is a BB cross-sectional view of FIG. 3A. As shown in FIG. 3A, the two valve recesses 6i formed on the top surface 2b of the piston 1b expand toward the outer circumferential edge 2i as they approach each other. In detail, the width of the valve recess 6ib along the X-axis is almost constant and extends toward the other valve recess 6ib. Even with such a shape of the valve recess 6ib, the flame can be sufficiently propagated to the squish portion 5i, and the flame propagation in the squish portion 5i is ensured. The same is true for the valve recess 6eb.

[0020] As shown in Fig. 3B, the recess side surface 62b of the valve recess portion 6ib and the inclined portion 4i are continuous at a gentle angle rather than a right angle, thereby ensuring flame propagation in the squish portion 5i.

[0021] As shown in FIG. 3C, the recess side surface 62b smoothly connects between the recess bottom surface 61 and the squish portion 5i. In detail, the recess side surface 62b rises from the lowest point P to connect to the squish portion 5i. The lowest point P is the lowest point in the cross section of FIG. 3C. This allows the flame to be guided from the valve recess portion 6ib to the squish portion 5i. Therefore, flame propagation in the squish portion 5i is ensured. The same applies to the valve recess portion 6eb.

[0022] Fig. 4A is a cross-sectional view of the third modified example. Fig. 4A corresponds to Fig. 3C. A plane 64 is formed between the recess bottom surface 61 and the recess side surface 62c of the valve recess portion 6ic. The height position of the plane 64 is the same as the height of the lowest point P. As a result, the recess side surface 62c is located at a steeper angle toward the squish portion 5i than the recess side surface 62b in Fig. 3C. Therefore, attenuation of the flame is suppressed until it collides with the recess side surface 62c, and flame propagation in the squish portion 5i is ensured.

[0023] Fig. 4B is a cross-sectional view of a fourth modified example. Fig. 4B corresponds to Fig. 3C. Fig. 4C is a cross-sectional view of a fifth modified example. Fig. 4C corresponds to Fig. 4A. The squish portion 5id is inclined downward from the inside to the outside. For example, by making the shape of the combustion chamber of the cylinder head correspond to the squish portion 5id, it is possible to suppress the damping of the tumble flow. In this way, the shape of the squish portion is not limited to a flat surface.

[0024] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0025] 1 piston 2 Top surface 3 bottom 5i, 5e squish section 6i, 6e Valve recess

Claims

[Claim 1] The top surface and a first valve recess portion formed along an outer circumferential edge of the top surface, for allowing a tip portion of one of a first and a second valve that introduces intake air into the combustion chamber or discharges exhaust gas from the combustion chamber to escape; a second valve recess formed along an outer circumferential edge of the top surface to allow the other tip end of the first and second valves to escape; a squish portion formed between an outer peripheral edge of the top surface and the first and second valve recess portions, the first and second valve recesses are spaced apart from each other, A piston of an engine, wherein the first valve recess portion widens toward the squish portion as it approaches the second valve recess portion.

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