Combustion chamber structure of a spark-ignition internal combustion engine

Abstract

The initial flame generated at the ignition point P of the spark plug 28 may be pushed by the tumble flow and come into contact with the main exhaust wall surface 25, causing the flame to be extinguished. [Solution] When the intersection of a straight line L1 passing through the ignition point P and perpendicular to the exhaust-side main wall surface 23 and the tumble preservation surface 2 is defined as point A1, the midpoint between the ignition point P and point A1 is defined as the tumble center point C, and the intersection of a straight line L2 passing through this tumble center point C and along the cylinder axis direction and the tumble preservation surface 2 is defined as point A2, then in at least a portion of the crank angle range from ignition timing to top dead center, the lowest part of the tumble preservation surface 2, which is point B1, lies between points A1 and A2. As a result, the tumble flow T revolves around the tumble center point C and flows parallel to the exhaust-side main wall surface 25 near the spark plug 28. Therefore, the initial flame growing from the ignition point P of the spark plug 28 is less likely to come into contact with the exhaust-side main wall surface 25.

Description

Technical Field

[0001] The present invention relates to a combustion chamber structure of a spark ignition internal combustion engine configured by combining a cylinder head side combustion chamber and a piston crown surface, particularly to a combustion chamber structure of a spark ignition internal combustion engine that performs combustion using a tumble flow.

Background Art

[0002] As disclosed in Patent Document 1, a spark ignition internal combustion engine is known that generates a tumble flow in the cylinder during the intake stroke by the shape of the intake port itself or a tumble control valve arranged in the intake port, and performs combustion using the tumble flow stored in the cylinder after passing through the compression stroke.

[0003] Patent Document 1 discloses a combustion chamber structure in which a tumble storage surface smoothly recessed is formed on the piston crown surface and combined with a pentroof type combustion chamber on the cylinder head side.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a spark ignition internal combustion engine that uses a tumble flow, when the center of rotation of the tumble flow swirling vertically in the cylinder is close to the spark plug at the timing near the ignition timing, the tumble flow tends to enter the ignition point of the spark plug obliquely. As a result, an initial flame growing from the ignition point of the spark plug is pushed by the tumble flow and contacts the wall surface of the pentroof type combustion chamber, and a phenomenon of flameout easily occurs. Thereby, for example, the lean combustion limit of the spark ignition internal combustion engine is restricted.

Means for Solving the Problems

[0006] This invention relates to a combustion chamber structure for a spark-ignition internal combustion engine, which is formed by combining a cylinder head-side combustion chamber and a piston crown surface. The piston crown surface described above has a dish-shaped recessed central tumble preservation surface, The above-mentioned cylinder head side combustion chamber has a pent-roof type configuration, with a planar intake side main wall and an exhaust side main wall, respectively. When point A1 is the intersection of a straight line L1 passing through the spark plug ignition point P and perpendicular to the exhaust-side main wall surface with the piston crown surface, and point A2 is the intersection of a straight line L2 passing through the tumble center point C, which is the midpoint between the spark plug ignition point P and point A1, and along the cylinder axis direction with the piston crown surface, In at least a portion of the crank angle range between ignition timing and top dead center, The lowest point on the tumbled surface, point B1, lies between points A1 and A2.

[0007] With this configuration, the direction of the tumble flow near the spark plug follows the main wall surface on the exhaust side, reducing the contact between the initial flame generated at the ignition point P of the spark plug and the main wall surface on the exhaust side. [Effects of the Invention]

[0008] According to this invention, the initial flame growing from the ignition point of the spark plug is less likely to come into contact with the main wall surface on the exhaust side, thereby suppressing flame extinction. As a result, for example, the dilution combustion limit is widened and thermal efficiency is improved. [Brief explanation of the drawing]

[0009] [Figure 1] A cross-sectional view showing a first embodiment of the combustion chamber structure according to this invention. [Figure 2] A cross-sectional view showing the second embodiment. [Figure 3] A cross-sectional view showing the third embodiment. [Modes for carrying out the invention]

[0010] Hereinafter, an embodiment of this invention will be described in detail with reference to the drawings. Figure 1 shows a combustion chamber structure consisting of a piston 1 and a cylinder head-side combustion chamber 21 of the first embodiment. The combustion chamber structure of this embodiment is used in a spark-ignition internal combustion engine (a so-called gasoline engine) equipped with a pair of intake valves and a pair of exhaust valves in each cylinder. In particular, the internal combustion engine equipped with the combustion chamber structure shown is an in-cylinder injection type internal combustion engine in which fuel is injected directly into the cylinder by a fuel injection valve, and is configured to perform lean or high EGR-rate diluted combustion by utilizing the tumble flow generated in the cylinder by the shape of the intake port itself or by a tumble control valve placed in the intake port.

[0011] The crown surface of the piston 1 in the first embodiment includes a dish-shaped recessed central tumble preservation surface 2 and an outer circumferential squish surface 3 located on the outer circumference of the tumble preservation surface 2, which forms a minute squish gap between it and the squish surfaces 26 and 27 on the outer circumference of the cylinder head side combustion chamber 21, which will be described later.

[0012] The tumble preservation surface 2 is the portion that forms a substantial combustion space between it and the combustion chamber 21 on the cylinder head side, and its cross-sectional shape is a smoothly continuous curve to be suitable for preserving the tumble flow. This tumble preservation surface 2 is formed to occupy a relatively large area in the center of the piston 1, leaving an annular outer squish surface 3 on the outer circumference of the piston 1. In a preferred embodiment, this tumble preservation surface 2 has a rotationally symmetric shape about the centerline of the piston 1. That is, the tumble preservation surface 2 is surrounded by a circular ridge 5 that forms a perfect circle about the centerline of the piston 1, and the inner circumference of this circular ridge 5 is recessed in a dish shape consisting of a smoothly continuous curved surface.

[0013] The outer squish surface 3 is formed in an annular shape between the outer edge of the piston crown surface and the circular ridge 5. As shown in the figure, this outer squish surface 3 is formed in a gentle taper shape, gradually becoming higher towards the inner circumference from the outer edge toward the circular ridge 5, and in one embodiment, it has a rotationally symmetric shape around the center line of the piston 1. In other words, the outer squish surface 3 is a conical surface with a relatively large apex angle.

[0014] The combustion chamber 21 on the cylinder head side is roughly composed of an intake-side main wall surface 23 on which an intake valve (not shown) is located, an exhaust-side main wall surface 25 on which an exhaust valve (not shown) is located, an intake-side squish surface 26, and an exhaust-side squish surface 27, with a spark plug 28 and a fuel injection valve (not shown) located in the center. The intake-side main wall surface 23 and the exhaust-side main wall surface 25 are basically inclined planes, and these main wall surfaces 23 and 25, which are recessed from the bottom surface of the cylinder head, form a so-called pent-roof type combustion chamber that forms a combustion space with the tumble-preserving surface 2 of the piston 1. The intake-side squish surface 26 and the exhaust-side squish surface 27 have a shape that follows the cone surface corresponding to the outer peripheral squish surface 3 which is a cone surface on the piston 1 side.

[0015] Figure 1 illustrates the state when the piston 1 is at top dead center. At top dead center, a small squish gap 30 of a certain width is formed between the squish surfaces 26 and 27 on the cylinder head side and the outer circumferential squish surface 3 on the piston 1 side. The pent-roof type combustion chamber 21, consisting of the intake side main wall surface 23 and the exhaust side main wall surface 25, is combined with the tumble preservation surface 2 on the piston 1 side to form a combustion space that is close to a sphere, and the tumble generated inside the cylinder during the intake stroke is effectively preserved.

[0016] In the combustion chamber structure of the above embodiment, as shown in Figure 1, when point A1 is defined as the intersection of a straight line L1 passing through the ignition point P of the spark plug 28 and perpendicular to the exhaust-side main wall surface 25 with the tumble preservation surface 2 (i.e., the piston crown surface), and the midpoint between the ignition point P and point A1 is defined as the tumble center point C, and when point A2 is defined as the intersection of a straight line L2 passing through this tumble center point C and along the cylinder axis direction with the tumble preservation surface 2 (i.e., the piston crown surface), then point B1, which is the lowest part of the tumble preservation surface 2, lies between point A1 and point A2 in at least a portion of the crank angle range from ignition timing to top dead center.

[0017] With such a configuration, as shown in FIG. 1, the tumble flow T near the ignition timing generally swirls around the tumble center point C, and near the ignition plug 28, it flows parallel to the exhaust-side main wall surface 25. Therefore, the initial flame growing from the ignition point P of the ignition plug 28 is less likely to contact the exhaust-side main wall surface 25, and flameout is suppressed. As a result, for example, the dilution combustion limit (lean limit or EGR rate limit) is widened, and the thermal efficiency can be improved.

[0018] Note that if the above geometric relationship exists in at least a part of the crank angle range from the ignition timing to the top dead center, sufficient operational effects can be obtained.

[0019] Next, FIG. 2 shows a second embodiment of the present invention. In this second embodiment, the bottom of the tumble retention surface 2 on the piston 1 side forms a plane orthogonal to the piston 1 center line. In a preferred embodiment, the planar portion of this bottom forms concentric circles with respect to the outer peripheral edge of the piston 1 and the above circular ridge line 5. When the bottom is planar in this way, it can be considered that the center of the planar bottom (that is, the center of the tumble retention surface 2) is the point B1, which is the lowest part of the tumble retention surface 2. And regarding this point B1, similar to the first embodiment, in at least a part of the crank angle range from the ignition timing to the top dead center, the relationship that the point B1 is between the point A1 and the point A2 is established.

[0020] Also in this second embodiment, similar to the first embodiment, the tumble flow T flows parallel to the exhaust-side main wall surface 25 near the ignition plug 28.

[0021] Next, FIG. 3 shows a third embodiment of the present invention. In this third embodiment, a further recessed cavity 31 for the plug is provided in a part of the tumble storage surface 2 of the piston 1 corresponding to the ignition plug 28. This cavity 31 for the plug is provided to ensure an appropriate distance for flame formation between the crown surface of the piston 1 and the ignition plug 28. For example, as shown in the figure, it is locally recessed in the tumble storage surface 2 so as to have an arcuate cross-sectional shape. In a preferred embodiment, the cavity 31 for the plug has a shape that forms a part of a sphere.

[0022] In the crown surface of the piston 1 having the cavity 31 for the plug as described above, when the point B1, which is the lowest part of the tumble storage surface 2, is included in the formation range of the cavity 31 for the plug, as shown in FIG. 3, the above-mentioned point B1 is defined on the virtual contour of the tumble storage surface 2 in the formation range of the cavity 31 for the plug. That is, the point B1, which is the lowest part of the tumble storage surface 2 when it is assumed that the cavity 31 for the plug does not exist, is between the point A1 and the point A2.

[0023] Also in this third embodiment, similar to the first embodiment, the tumble flow T flows parallel to the exhaust side main wall surface 25 in the vicinity of the ignition plug 28. And by providing the cavity 31 for the plug, the growth of the initial flame is not hindered by the crown surface of the piston 1.

[0024] In a preferred embodiment, the point B2, which is the lowest part of the cavity 31 for the plug, is located on the exhaust side of the point B1, which is the lowest part of the above-mentioned tumble storage surface 2. Further, this point B2 is located on a straight line L3 passing through the ignition point P of the above-mentioned ignition plug 28 and along the cylinder axis direction.

[0025] Note that the cavity 31 for the plug may be an elliptical recess that extends elongated along the crankshaft axis direction.

[0026] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various modifications are possible. In the above embodiment, the tumble preservation surface 2 on the crown surface of the piston 1 is formed concentrically in the central part of the piston 1, but in this invention, the tumble preservation surface 2 may be located off-center from the center of the piston 1, or it may be an irregular shape other than a circle. Furthermore, the squish surfaces 3, 26, and 27 may be configured along a plane perpendicular to the centerline of the piston 1. [Explanation of symbols]

[0027] 1... Piston 2…Tumble storage surface 3…Outer squish surface 21...Cylinder head side combustion chamber 23…Main wall surface on the intake side 25... Main wall on the exhaust side 26... Intake side squish surface 27... Exhaust side squish surface 28... Spark plug

Claims

1. A combustion chamber structure for a spark-ignition internal combustion engine, which is formed by combining the cylinder head side combustion chamber and the piston crown surface, The piston crown surface described above has a dish-shaped recessed central tumble preservation surface, The above-mentioned cylinder head side combustion chamber has a pent-roof type configuration, with a planar intake side main wall and an exhaust side main wall, respectively. When point A1 is the intersection of a straight line L1 passing through the spark plug ignition point P and perpendicular to the exhaust-side main wall surface with the piston crown surface, and point A2 is the intersection of a straight line L2 passing through the tumble center point C, which is the midpoint between the spark plug ignition point P and point A1, and along the cylinder axis direction with the piston crown surface, In at least a portion of the crank angle range between ignition timing and top dead center, Point B1, which is the lowest point on the tumbled surface, is located between points A1 and A2. Combustion chamber structure of a spark-ignition internal combustion engine.

2. A recessed plug cavity is provided in a portion of the tumble storage surface mentioned above, to accommodate the spark plug. Point B1 is defined on the virtual contour of the tumble preservation surface within the formation range of the plug cavity. The combustion chamber structure of a spark-ignition internal combustion engine according to claim 1.

3. Point B2, which is the lowest point of the plug cavity mentioned above, is located closer to the exhaust than point B1. The combustion chamber structure of a spark-ignition internal combustion engine according to claim 2.

4. Point B2 is located on a straight line L3 that passes through the spark plug ignition point P and is aligned with the cylinder axis. The combustion chamber structure of a spark-ignition internal combustion engine according to claim 3.

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