1. Field of the Invention
The invention relates to a piston used in an internal combustion engine, and particularly relates to the configuration of a crown surface of the piston.
2. Description of the Related Art
With regard to internal combustion engines, an internal combustion engine has been proposed in which a top surface of a piston has a pair of substantially symmetric peak portions with a center portion of the piston interposed between the pair of peak portions as described in Japanese Patent Application Publication No. 10-8968 (JP-A-10-8968). Each of the peak portions has a ridgeline that extends in a direction parallel to an axial direction of a crankshaft. Further, a recessed portion is formed on the top surface of the piston by a cylindrically curved surface whose center axis arranged in parallel to the axial direction of the crankshaft. A radius of curvature R of the cylindrically curved surface of the recessed portion is set to one-half of a bore diameter B.
Further, Japanese Patent Application Publication No. 2001-98947 (JP-A-2001-98947) describes the configuration of a piston in which a cavity combustion chamber is provided in a center portion of a crown surface of a piston so as to extend from the intake valve side to the exhaust valve side, and a sectional shape of the cavity combustion chamber has a large radius of curvature R2 in the intake valve side and a small radius of curvature R1 in the exhaust valve side.
A tumble flow is produced in each cylinder of an internal combustion engine. However, a distribution of strength of the tumble flow in the cylinder tends to be non-uniform. More specifically, the speed of flow of the air sucked through the intake valve tends to be fast around the center portion of a combustion chamber, and tends to be slow near a bore wall: Therefore, the distribution of the strength of the tumble flow tends to be non-uniform, and if the distribution of the strength of the tumble flow is non-uniform, the air and fuel do not mix well, so that the air-fuel mixture becomes inhomogeneous. Accordingly, desired effects intended by producing the tumble flow cannot be achieved, resulting in making it difficult to improve combustion. Further, it is not possible to sufficiently solve such problem even by the inventions described in JP-A-10-8968 and JP-A-2001-98947.
The invention provides a piston for an internal combustion engine in which strength of a tumble flow is made uniform and the uniformity of an air-fuel mixture is therefore improved.
A piston for an internal combustion engine according to a first aspect of the invention includes: a cavity defined by a curved recessed portion formed on a crown surface in a manner such that a surface of the curved recessed portion extends along a tumble flow produced during an intake stroke; and a weakening portion that is disposed in the cavity and reduces a strength of at least a part of the tumble flow. With this configuration, it is possible to make the strength of the tumble flow (that is, strength of turbulence) in the combustion chamber more uniform, and as a result, it is possible to produce more homogeneous air-fuel mixture and thus facilitate improvement of combustion.
The weakening portion provided on the piston for an internal combustion engine may be disposed in the portion of the recessed portion in which the strength of the tumble flow is stronger than the strength of the tumble flow in a surrounding portion. If the piston is not provided with the weakening portion, the strength of the tumble flow in the combustion chamber differs depending on positions in the combustion chamber. For example, when two intake valves are provided for each cylinder, the strength of the tumble flow produced by the gas taken in when the intake valves are opened is in some cases strong in the area where the gas flows from the two intake valves are merged. In this way, depending on the arrangement of the intake valves and the direction in which the intake valves are arranged, the distribution of the strength of the tumble flow in the combustion chamber becomes sometimes non-uniform. In other words, the strength of the tumble flow varies depending on the positions in the combustion chamber. Therefore, in consideration of such distribution of the strength of the tumble flow, if to the weakening portion is provided in a portion where the tumble flow is stronger (that may be simply referred to as “strong-flow portion”) than its surrounding portion, the strength of the tumble flow in the strong-flow portion is reduced, thereby reducing the difference in the strength between the strong-flow portion and its surrounding portion. Accordingly, it is possible to make the strength of the tumble flow in the combustion chamber more uniform.
In the piston according to the aspect described above, the weakening portion may include a weakening surface whose radius of curvature is larger than a radius of curvature of the recessed portion. When the tumble flow hits the weakening surface, the strength of the tumble flow is reduced. Accordingly, it is possible to make the strength of the tumble flow that hits the weakening portion closer to the strength of the tumble flow around the weakening portion. The weakening portion may include a flat surface. The weakening portion may be formed as a projection.
The weakening portion provided on the crown surface of the piston may be configured in a manner such that the effect of reducing the strength of the tumble flow is strong. The weakening portion may include a weakening surface whose radius of curvature is smaller than a radius of curvature of the recessed portion, and a length from the edge of the weakening surface on the intake valve side to the edge of the weakening surface on the exhaust valve side may differ between a center portion of the weakening portion and the peripheral portion of the weakening portion that is distant from the center portion in the axial direction of a crankshaft.
In consideration of the desired effect as described above, the length from the edge of the weakening surface on the intake valve side to the edge of the weakening surface on the exhaust valve side may be longer in the center portion than in the peripheral portion.
Further, the weakening portion may have the weakening surface that has a circular shape, or the weakening surface that is elliptically shaped. If the to weakening surface has a circular shape, the length in the center portion is longer than the length in the peripheral portion. If the weakening surface is elliptically shaped, the arrangement of the short axis and the long axis of the elliptical weakening surface may be appropriately determined.
Further, the weakening portion may be formed as a projection in the recessed portion. In this case, a top surface of the weakening portion is more gradually and smoothly connected to the recessed portion in the peripheral portion, compared to the center portion. For example, an angle formed between a sidewall of the weakening portion and the top surface of the weakening portion may be set larger in the peripheral portion than in the center portion. Alternatively, a connection portion that connects between a sidewall of the weakening portion and the recessed portion may be rounded, and a radius of curvature of the connection portion may be increased from the center portion to the peripheral portion.
Further, the weakening portion may be configured to be a recess in the recessed portion, and configured so that a depth of the weakening portion becomes shallower in the peripheral portion than in the center portion. It is conceivable that when the weakening portion is formed to be a recess, the deeper the depth of the weakening portion is, the stronger the effect of reducing the strength of the tumble flow by virtue of, for example, separation of the tumble flow is. Therefore, the depth of the weakening portion in the center portion may be set deeper than in the peripheral portion so as to strengthen the effect of reducing the strength of the tumble flow in the center portion.
Further, the weakening portion may be formed as a recess in the recessed portion, a bottom surface of the weakening portion may be more gradually and smoothly connected to the recessed portion in the peripheral portion, compared to the center portion. For example, an angle formed between a sidewall of the recessed portion and the bottom surface of the weakening portion may be larger in the peripheral portion than in the center portion. Alternatively, a connection portion that connects between the sidewall of the recessed portion and the bottom surface of the weakening portion may be rounded in the peripheral portion, and a radius of curvature of the connection portion may be increased from the center portion to the peripheral portion.
Further, the radius of curvature of the recessed portion in which the weakening portion is provided may be changed. For example, the radius of curvature of the recessed portion may be larger in the peripheral portion than in the center portion. With this configuration, it is possible to make the strength of the tumble flow in the combustion chamber more uniform.
The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:
Embodiments of the invention will be described in detail below with reference to the attached drawings.
First, a configuration around a combustion chamber in an internal combustion engine in which a piston 1 for an internal combustion engine (hereinafter simply referred to as “piston 1”) according to a first embodiment of the invention is installed will be described with reference to
The piston 1 according to the first embodiment is disposed in each of the cylinders in which the tumble flow as described above is produced, and makes the distribution of the strength of the tumble flow in the cylinder uniform. Next, a configuration of a crown surface of such a piston will be described.
The piston 1 includes a cavity 5 defined by a curved recessed portion 5a. The recessed portion 5a is formed on the crown surface so that the surface of the curved recessed portion 5a extends along the tumble flow produced during the intake stroke. The cavity 5 is formed in a manner such that a longitudinal direction of the cavity 5 is set along the axial direction of the crankshaft. As shown in the
A weakening portion 6 is provided in the cavity 5 thus configured. The weakening portion 6 is disposed so as to occupy a portion of the crown surface of the piston 1, the portion including a center portion of the crown surface. The weakening portion 6 reduces the strength of the tumble flow produced by the gas flowing into the combustion chamber when the intake valves 4 are opened. The distribution of the strength of the tumble flow varies depending on the arrangement of the intake valves 4 and the direction in which the intake valves 4 are arranged and therefore, the arrangement of the weakening portion 6 may be appropriately changed. The strength of the tumble flow tends to be strong in the center portion of the combustion chamber, and gradually decreased from the center portion to a portion near the bore wall. Therefore, the weakening portion provided on the crown surface of the piston is preferably configured in a manner such that the effect of reducing the strength of the tumble flow is strong in the center portion of the combustion chamber. In the first embodiment, the weakening portion 6 is disposed in the portion of the crown surface of the piston 1, the portion including the center portion of the crown surface where the strength of the tumble flow is stronger than its surrounding portion as described above.
A weakening surface 6a, which is a top surface of the weakening portion 6, is formed to be a circular, flat surface as shown in
The effect of reducing and uniforming the strength of the tumble flow that the thus-configured piston 1 exhibits will be described with reference to
As described above, the weakening portion 6 according to the first embodiment impedes the tumble flow and reduces the strength of the tumble flow in accordance with the strength of the tumble flow, that is, more strongly in the area in which the strength of the tumble flow is stronger. The configuration and size of the weakening portion 6 may be modified as appropriate so as to achieve desired reduction of the strength of the tumble flow. Therefore, the configuration shown in
The weakening surface 6a preferably has a larger radius of curvature than that of the recessed portion 5a. However, the weakening surface 6a may have a smaller radius of curvature than that of the recessed portion 5a.
Next, a second embodiment of the invention will be described with reference to
The weakening surface 52a (top surface) of the weakening portion 52 is more gradually and smoothly connected to the recessed portion 5a in a portion distant from the center portion of the weakening portion 52, compared to the center portion of the weakening portion 52.
Further, other structural elements in the configuration of the piston 51 are the same as the corresponding structural elements in the configuration of the piston 1 according to the first embodiment. Therefore, the corresponding structural elements are denoted by the same reference numerals in the drawings, and the detailed description thereof will be omitted.
A modification of the second embodiment may be configured so that the connection portion that connects between the recessed portion 5a and the sidewall surface 52b of the weakening portion 52 in the center portion of the piston 51 (shown in the sectional view taken along the line IXB-IXB) is not rounded, and only the connection portion that connects between the recessed portion 5a and the sidewall surface 52b of the weakening portion 52 in the peripheral portion of the piston 51 is rounded. Further, the curvature of the connection portion may be changed in a stepwise manner instead of in a continuous manner.
Next, a third embodiment of the invention will be described with reference to
As described above, if the recessed weakening portion 102 is provided in the recessed portion 5a, it is possible to adjust the reduction effect on the strength of the tumble flow by changing an angle 0 shown in
Further, the sidewall 102b may be curved so that the reduction effect on the strength of the tumble flow is adjusted by changing a roundness R of the curved sidewall 102b. More specifically, if the radius R of the curved sidewall 102b is set larger so that the tumble flow is produced along the curved sidewall 102b so as to suppress separation of the tumble flow, it is possible to weaken the reduction effect on the strength of the tumble flow in the portion distant from the center portion of the piston 101. As a result, in addition to the weakening of the effect to reduce the strength, the strength of the tumble flow in the center portion of the piston 101 is reduced, and it is possible to make the distribution of the strength of the tumble flow in the cylinder more uniform.
While the invention has been described with reference to exemplary embodiments thereof, it should be understood that the invention is not limited to the exemplary embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. It is apparent that the invention can be implemented in various other embodiments within the scope of the invention. The weakening portion provided for the piston according to the invention may have any configuration as long as it is possible to reduce the strength of the tumble flow. For example, a configuration may be adopted in which the portion of the crown surface of the piston that the strong tumble flow hits has a rougher surface than its surrounding portion.
Further, the weakening portion may be configured so that the length from the edge of the weakening portion on the intake valve side to the edge on the exhaust valve side is longer in the center portion of the weakening surface than the corresponding length in the portion distant from the center portion. For example, the weakening portion may be configured as shown in
Number | Date | Country | Kind |
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2007-210812 | Aug 2007 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB08/02124 | 8/12/2008 | WO | 00 | 2/12/2010 |