JP2012021467A - Piston of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such problems in an engine using a tumble flow that in a piston which has a recessed portion on the top face thereof, and in which the recessed portion comprises a cylindrical inner face having a center line approximately parallel to a crankshaft line and a flat portion located in a middle portion in the width direction of the cylindrical inner face, disturbance of a mixture gas obtained by collapsing a generated tumble flow is reduced in a short period of time, and thereby, the time period for exerting an influence on the combustion performance is short and may not be enough to promote combustion.SOLUTION: The piston has a recessed portion having an inclined inner face on the top face, and has an elliptic flat face provided approximately at the center of the recessed portion.

Description

  The present invention relates to a piston of an internal combustion engine that causes a tumble flow in a cylinder.

  2. Description of the Related Art Conventionally, in an internal combustion engine, a tumble flow that is an airflow swirling in a reciprocating direction of a piston is generated in a cylinder in order to promote the propagation of a flame generated during mixing of intake air and fuel or combustion of the air-fuel mixture. In particular, in a cylinder injection internal combustion engine that directly injects fuel into a cylinder, a tumble flow is generated when homogeneous combustion is performed.

  In order to generate such a tumble flow, it is known that a recess is formed on the top surface of a piston. For example, Patent Document 1 discloses a piston including a concave portion on the top surface, and a cylindrical inner surface having a central line substantially parallel to the crank axis, and a flat portion located at a central portion in the width direction of the cylindrical inner surface. is doing. In Patent Document 1, a tumble flow is formed by the cylindrical inner surface in the intake stroke and the first half of the compression stroke, and the tumble flow once formed is collapsed by the flat portion before top dead center in the latter half of the compression stroke. As a result, the turbulence of the air-fuel mixture, which is a collection of small tumble flows, increases its strength and promotes the propagation of combustion.

  However, in the thing of this patent document 1, disturbance of air-fuel | gaseous mixture reduces with a raise of a piston. In other words, the air-fuel mixture is disturbed by the flat part, but even if the turbulent state is maintained and ignited, the period of influence on the combustion performance is shortened because the disturbance is reduced within a short time. It does not lead to promotion of combustion.

JP 2007-32539 A

  Therefore, the present invention focuses on the above points and aims to improve the quality of the combustion state by balancing the collapse and maintenance of the tumble flow.

  That is, the piston of the internal combustion engine of the present invention is characterized in that a concave portion having an inclined inner surface is provided on the top surface, and an elliptical flat surface is provided in the approximate center of the concave portion.

  The inclined inner side surface is a concept including a concave curved surface that is recessed toward the outside of the flat surface and the concave portion. Specifically, it is a concept including a surface having a shape such as an inner surface of a reverse cone or a reverse elliptical cone, a paraboloid, or the like.

  The oval shape is a concept including a shape obtained by connecting an ellipse and two semicircles located at a distance or opposite ends of the semi-ellipse with a straight line or a quadratic curve.

  According to such a configuration, the sucked air-fuel mixture generates a tumble flow by the concave portion, and then the tumble flow is disrupted by the flat surface located substantially at the center of the concave portion, thereby generating turbulence of the air-fuel mixture. Since the flat surface is only at the center of the recess, the turbulence of the air-fuel mixture can be maintained by the tumble flow that is maintained even after the turbulence of the air-fuel mixture is generated.

  The present invention is configured as described above, and the turbulence of the mixture can be maintained by the tumble flow that is maintained even after the generation of the turbulence of the mixture. Therefore, a highly efficient combustion state is maintained for a long time. be able to.

Sectional drawing which shows schematic structure of the principal part of the engine of embodiment of this invention. The front view of the piston of the embodiment. The top view of the piston of the embodiment. Sectional drawing along the II line | wire of FIG.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the engine 100 of this embodiment is an in-cylinder injection type in which fuel is directly injected into a cylinder. The engine 100 includes a fuel injection valve 3 that injects fuel into the cylinder bore 1, particularly toward the combustion chamber 2, two intake valves 4, two exhaust valves 5, and a spark plug 6 in a cylinder head 7. A piston 9 is provided in a cylinder bore 1 of a cylinder block fixed to the head 7 via a gasket 8 so as to be reciprocally operable. As these configurations of the engine 100 per se, excluding the piston 9, those well known in this field can be widely applied.

  The piston 9 has a feature in the shape of its top surface. As shown in FIG. 2, the piston 9 has a concave portion 11 formed on almost the entire surface of the top surface when the direction in which the through hole 10 into which the piston pin is inserted is directed, and the front surface of the top surface. An intake valve recess 12 for avoiding contact with the piston 9 when the intake valve 4 is open is provided on the left hand, and an exhaust valve recess 13 is provided on the front right hand. Flat portions 14 and 15 are formed between the intake valve recess 12 and the exhaust valve recess 13, respectively.

  As shown in FIG. 3, the recess 11 is formed between the intake valve recess 12 and the exhaust valve recess 13 when the top surface of the piston 9 is viewed from above, and has a substantially elliptical shape. Therefore, the concave portion 11 has a major axis direction that is the same as that of the through hole 10 of the piston pin, and a minor axis direction that coincides with the direction of the line segment that connects the intake valve 4 and the exhaust valve 5. An oblique squish forming surface 16 for a squish area formed between the periphery of the recess 11 and the periphery of the combustion chamber 2 when the piston 9 is almost at the top dead center is provided.

  The recess 11 includes an inclined inner surface 17 and an oval flat surface 18. As shown in FIG. 4, the inner side surface 17 is a concave curved surface formed of a part of a paraboloid, for example, and is concave while being inclined from the center side of the concave portion 11, that is, the inner side of the concave portion 11. The inner surface 17 is formed over the entire circumference of the recess 11. A flat portion 18 is formed continuously with such an inner surface 17. The boundary portion between the inner surface 17 and the flat portion 18 is smoothly continued so that no corners are formed.

  The flat portion 18 is formed inside the annular inner surface 17 so as to be surrounded by the inner surface 17. In this embodiment, the flat portion 18 has an elliptical shape, and the major axis direction of the ellipse is made to coincide with the major axis direction of the recess 11. When the size of the flat portion 18 is schematically shown, the major axis is, for example, 40% to 60% of the cylinder bore diameter, and the minor axis is, for example, 1.2 to 1.5 times the spark plug diameter. In the engine 100 including the two intake valves 4 as in this embodiment, the major axis of the flat portion 18 is set to a dimension that is approximately equal to the distance between the extended lines of the line passing through the center of the intake port 19. That's fine. The flat portion 18 is configured by a plane perpendicular to the reciprocating direction of the piston 9.

  When the engine 100 is operated in such a piston 9, air is taken into the cylinder bore 1 through the intake port 19. The inhaled air is generated in a tumble flow while being mixed with fuel. That is, the air sucked into the cylinder bore 1 flows toward the concave portion 11 of the piston 9 and is mixed with the fuel in the meantime, and the air-fuel mixture of the intake air and the fuel is guided to the concave portion 11 of the piston 9 in the cylinder bore 1. It becomes a tumble style.

  In the compression stroke, the generated tumble flow increases its strength when the piston 9 rises toward the compression top dead center, and near the 80 ° crank angle (hereinafter referred to as CA) before the compression top dead center. Is maintained. The tumble flow at this time has a diameter substantially equal to the cylinder bore diameter.

  The generated tumble flow gradually collapses by the flat portion 18 of the recess 11 from the time when the piston 9 reaches around 30 ° CA before the compression top dead center. As a result, many turbulences of the air-fuel mixture are generated in the space between the piston 9 and the ceiling of the combustion chamber 2.

  At this time, in the piston 9 of this embodiment, since the inner side surface 17 which inclines as shown in FIG. 4 exists in the both ends of the major axis direction of the recessed part 11, the both ends of the major axis direction of the recessed part 11 exist. The generation of the tumble flow is maintained by the inner surface 17. That is, although the tumble flow is converted into turbulence of the air-fuel mixture by the flat portion 18 of the concave portion 11, the generation of the tumble flow is maintained in the space portions on both ends in the major axis direction of the flat portion 18. The turbulence is agitated by the tumble flow, and the mixture can be prevented from being attenuated.

  Accordingly, even when the piston 9 has almost reached the position of the compression top dead center, the mixture is disturbed in the combustion chamber 2, particularly in the space surrounding the spark plug 6, so that ignition is promoted. Combustion is propagated efficiently. As a result, a good combustion state in which the air-fuel mixture burns without waste can be maintained for a long time.

  In addition, this invention is not limited to the above-mentioned embodiment.

  For example, the shape of the flat portion 18 constituting the recess 11 may be an ellipse. Such an ellipse may have a shape obtained by connecting both ends of the major axis in a semicircle or semi-ellipse and connecting corresponding ends of the opposing semi-circle or semi-ellipse with a straight line. In this case, instead of a straight line, an arc such as an arc of a quadratic curve expanding outward may be used. Even in the case where the flat portion is formed by an ellipse having such a shape, the boundary portion with the inner surface is assumed to be smoothly continuous.

  Further, the inner side wall 17 provided along the outer edge of the flat portion 18 has a shape of an inner surface of an inverted cone or an inner surface of an inverted elliptical cone other than a concave curved surface formed of a part of a paraboloid as in the above-described embodiment. There may be. Even in this case, the boundary portion between the inner wall and the flat portion is made to continue smoothly as in the above-described embodiment.

  In the above embodiment, the in-cylinder spark ignition engine has been described. However, as another embodiment, a port injection spark ignition engine (a gasoline engine) that injects fuel toward the intake port. ) May be applied.

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  As an application example of the present invention, an in-cylinder engine that directly injects fuel into the cylinder can be cited.

9 ... Piston 11 ... Recess 17 ... Inner surface 18 ... Flat part

Claims (1)

A concave portion having an inclined inner surface is provided on the top surface,
Piston for an internal combustion engine having an oval flat surface at substantially the center of the recess

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