JP2011214557A - Cylinder injection type spark ignition internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylinder injection type spark ignition internal combustion engine, capable of forming air-fuel mixture allowing stable stratified burning in the vicinity of a spark plug and suppressing discharge of smoke and unburnt hydrocarbon in stratified burning.SOLUTION: The cylinder injection type spark ignition internal combustion engine includes a concave spherical cavity provided at the center of the top face of a piston, the cavity having an opening formed substantially concentrically with the piston. The opening of the cavity is formed by an intake valve-side peripheral edge portion located on the intake valve side and an exhaust valve-side peripheral edge portion located on the exhaust valve side. One of the intake valve-side peripheral edge portion and the exhaust valve-side peripheral edge portion is formed by a curved surface having a large curvature radius, compared with the other.

Description

  The present invention relates to a direct injection spark ignition internal combustion engine.

  As is well known, an in-cylinder spark-ignition internal combustion engine is an internal combustion engine in which fuel is directly injected into a cylinder of the internal combustion engine, and a combustible mixture is ignited and burned by spark discharge by an ignition plug. In this in-cylinder spark ignition internal combustion engine, by injecting fuel into the cylinder in the compression stroke, a combustible air-fuel mixture is formed only near the spark plug at the time of ignition, and the entire in-cylinder is lean. There is a type in which stratified combustion that enables combustion of an air-fuel mixture is performed.

  However, in the case of stratified combustion, if the formation position of the combustible mixture deviates from the spark plug, ignition fluctuations, misfires, and combustion fluctuations due to ignition timing delays occur, so in order to perform good stratified combustion, in the vicinity of the spark plug It is important to stably form a combustible mixture.

  On the other hand, in a conventional in-cylinder spark ignition internal combustion engine, an ignition plug is arranged at the substantially central portion of the combustion chamber top portion and a fuel injection valve is arranged at the peripheral portion of the combustion chamber top portion. A concave groove extending from the lower side of the valve to the lower side of the spark plug is formed on the piston top surface, descends along the cylinder inner wall surface below the intake valve, changes direction on the piston top surface, and then turns up below the exhaust valve A flow (tumble flow) is generated in the combustion chamber, and the fuel injected from the fuel injection valve into the concave groove is guided by the bottom wall surface of the concave groove and directed toward the vicinity of the spark plug. A technique for forming stratified combustion in the vicinity has been proposed (see, for example, Patent Document 1).

  Further, conventionally, there is a cavity that is concave on the crown surface of the piston and has a ridge that is raised at the periphery, and the center of the cavity is offset with respect to the center of the piston, and the corner within the cavity that is set optimally A technique has been proposed in which the stratified mixture is smoothly transported to the vicinity of the spark plug and the stratified combustion is performed by the R of the part (see, for example, Patent Document 2).

JP-A-10-54247 Japanese Patent Laid-Open No. 11-182336

  FIG. 7 is an explanatory diagram showing the behavior of the air-fuel mixture in the latter half of the compression stroke in the conventional in-cylinder injection spark ignition internal combustion engine. As shown in FIG. 7, the conventional in-cylinder spark ignition internal combustion engine has a concave groove (cavity) 31 formed at a position offset toward the intake valve 33 side with respect to the center 32 of the piston 36. In the latter half of the compression stroke, a squish flow 37 generated from the squish portion between the cylinder head 35 and the piston 36 on the exhaust valve 34 side toward the cavity 31 causes the bottom wall surface of the cavity 31 and the cavity after the fuel injection. Since the air-fuel mixture 39 guided to the vicinity of the spark plug 38 by the rounded portion R in the corner portion 31 is swept away from the vicinity of the spark plug 38, the air-fuel mixture concentration at the ignition position becomes lean and ignition occurs. There is a problem that it becomes difficult to realize stable stratified combustion, such as deterioration of flame propagation.

  In particular, when the in-cylinder injection spark ignition internal combustion engine is set to a high compression ratio in order to improve the thermal efficiency and the fuel consumption rate, the aforementioned squish portion becomes narrower and is pushed out into the cavity 31 in the later stage of the compression stroke. Since the amount of gas increases and the strength of the squish flow 37 increases, the air-fuel mixture 39 in the vicinity of the spark plug 38 is pushed away to a place further away from the spark plug 38 and stratified combustion becomes unstable.

  On the other hand, the fuel injected to the cavity 31 at the top of the piston and adhering to the inner wall surface of the cavity is vaporized by receiving heat from the piston wall surface and receiving heat from the gas heated by compression of the combustion chamber. In the latter half of the compression stroke, as the combustion chamber is flattened due to the rise of the piston, the tumble flow formed in the combustion chamber in the intake stroke is crushed and abruptly attenuated. As a result, an air-fuel mixture with a high fuel concentration accumulates in the vicinity of the cavity wall surface, which causes a large amount of smoke and unburned hydrocarbons during stratified combustion.

  The present invention has been made in order to solve the problems in the conventional in-cylinder injection spark-ignition internal combustion engine as described above. In-cylinder spark-ignition internal combustion engine that can form a stable air-fuel mixture in the vicinity of the spark plug even under conditions where the air-fuel mixture is strong and difficult to stabilize, and can suppress the generation of smoke and unburned hydrocarbons during stratified combustion It is intended to provide.

A cylinder injection spark ignition internal combustion engine according to the present invention includes a cylinder housing a piston, a cylinder head fixed to the cylinder, and a combustion chamber formed between a top surface of the piston and an inner surface of the cylinder head. A fuel injection valve that directly injects fuel into the cylinder, an intake valve provided in the intake port of the cylinder, an exhaust valve provided in the exhaust port of the cylinder, and a substantially central portion of the top of the combustion chamber. An in-cylinder having an ignition plug fixed to the cylinder head and configured to perform stratified combustion by igniting the fuel injected from the fuel injection valve into the combustion chamber during the compression stroke by the ignition plug An injection-type spark ignition internal combustion engine, wherein the piston includes a concave spherical cavity having an opening formed substantially concentrically with the piston at a central portion of a top surface thereof. The opening of the cavity is formed by an intake valve side peripheral edge portion positioned on the intake valve side and an exhaust valve side peripheral edge portion positioned on the exhaust valve side, and the intake valve side peripheral edge portion and the exhaust valve One of the side peripheral edge portions is formed by a curved surface having a larger radius of curvature than the other.
It is characterized by this.

  In the cylinder injection type spark ignition internal combustion engine according to the present invention, the squish flow that has drifted to the piston top surface side due to the piston ascending causes one of the intake valve side peripheral edge portion and the exhaust valve side peripheral edge portion to On the other side of the intake valve side peripheral edge portion and the exhaust valve side peripheral edge portion, the squish flow is separated at the peripheral edge portion while being guided by the curved surface to be formed and flowing along the inner wall surface of the cavity. Then, since it flows toward the upper part of the cavity as it is, a tumble flow is formed inside the cavity by the interaction of the pair of squish flows having almost the same strength.

  As a result, the air-fuel mixture collected from the outer periphery of the combustion chamber to the center of the cavity by the squish flow generated in the latter half of the compression stroke is then firmly held in the center of the cavity by riding on the tumble flow in the cavity. Therefore, a stable air-fuel mixture is formed over a long period in the vicinity of the spark plug provided at the upper center of the cavity.

  Further, the tumble flow formed inside the cavity improves the heat transfer between the fuel adhering to the inner wall surface of the cavity and the compressed hot gas during the compression stroke injection. Since the fuel concentration is homogenized by transporting and stirring without allowing it to stay in the vicinity of the wall surface and promoting mixing with air, the emission of smoke and unburned hydrocarbons is suppressed during stratified combustion.

  According to the in-cylinder spark-ignition internal combustion engine according to the present invention, the piston includes a concave spherical cavity having an opening formed substantially concentrically with the piston at the center of the top surface of the piston. The portion is formed by an intake valve side peripheral edge portion positioned on the intake valve side and an exhaust valve side peripheral edge portion positioned on the exhaust valve side, and the intake valve side peripheral edge portion and the exhaust valve side peripheral edge portion Since one of these is formed by a curved surface having a larger radius of curvature than the other, the squish flow generated in the latter half of the compression stroke is a flow from the outer periphery of the combustion chamber toward the center of the cavity, and the cavity Since the strength of the squish flow facing the center balances almost equally, the air-fuel mixture formed in the combustion chamber by the compression stroke injection is in the latter half of the compression stroke. Reliably gathered toward the center of the cavity by quiche stream, thereby forming a stable mixture in the vicinity of the spark plug, the stratified combustion smoke, it is possible to suppress the generation of unburned hydrocarbons.

1 is a longitudinal sectional view of a direct injection spark ignition internal combustion engine according to Embodiment 1 of the present invention. FIG. 1 is a top view of a piston in a direct injection spark ignition internal combustion engine according to Embodiment 1 of the present invention. FIG. FIG. 6 is an explanatory diagram showing fuel spray behavior when a compression stroke injection is performed in the direct injection spark ignition internal combustion engine according to the first embodiment of the present invention. FIG. 3 is an explanatory view showing a mixture behavior formed after completion of compression stroke injection in a direct injection spark ignition internal combustion engine according to Embodiment 1 of the present invention; FIG. 5 is an explanatory diagram showing a squish flow and an air-fuel mixture behavior formed in the latter half of the compression stroke in the direct injection spark ignition internal combustion engine according to the first embodiment of the present invention. FIG. 5 is an explanatory diagram showing tumble flow and air-fuel mixture behavior formed in the latter half of the compression stroke in the direct injection spark ignition internal combustion engine according to Embodiment 1 of the present invention. It is explanatory drawing which shows the air-fuel | gaseous mixture behavior in the latter half of the compression stroke in the conventional cylinder injection type spark ignition internal combustion engine.

Embodiment 1 FIG.
Hereinafter, a direct injection spark ignition internal combustion engine according to Embodiment 1 of the present invention will be described with reference to the drawings. 1 is a longitudinal sectional view of a direct injection spark ignition internal combustion engine according to Embodiment 1 of the present invention. FIG. 2 is a top view of the piston in the direct injection spark ignition internal combustion engine according to the first embodiment of the present invention. 1 and 2, a piston 2 is fitted in a cylindrical cylinder 1. A so-called pent roof type cylinder head 3 is fixed on the cylinder 1, and a combustion chamber 4 is formed between the top surface of the piston 2 and the lower surface of the cylinder head 3.

  The cylinder head 3 is provided with two intake ports 5 (only one is shown in FIG. 1) and two exhaust ports 6 (only one is shown in FIG. 1). The intake port 5 communicates with the combustion chamber 4 via the intake valve 7, and the exhaust port 6 communicates with the combustion chamber 4 via the exhaust valve 8. The cylinder head 3 is provided with a combustion injection valve 9 for directly injecting fuel into the combustion chamber 4 so that its central axis is directed obliquely downward, and a spark plug 10 is provided at the center of the cylinder head 3. Is installed.

  As shown in FIG. 1, the pent roof type cylinder head 3 includes two inclined surfaces formed on the intake valve 7 side and the exhaust valve 8 side, respectively. The top surface of the piston 2 has an intake valve side inclined surface 11 inclined substantially parallel to the inclined surface on the intake valve 7 side of the cylinder head 3 and an exhaust gas inclined substantially parallel to an inclined surface on the exhaust valve 8 side of the cylinder head 3. And a valve-side inclined surface 12. Further, as shown in FIGS. 1 and 2, a circular concave spherical cavity 14 having an opening having the same center as the center 13 of the piston outer circle is provided at the center of the top surface of the piston 2. ing.

  Of the peripheral edge portions of the opening of the cavity 14 on the top surface of the piston 2, the exhaust valve side peripheral edge portion 141 located on the exhaust valve side inclined surface 12 is spherical with the exhaust valve side inclined surface 12. It is formed in a curved surface having a large curvature radius that smoothly connects the inner wall surface of the cavity 14. On the other hand, among the peripheral edge portions of the opening of the cavity 14, the intake valve side peripheral edge portion 142 located on the intake valve side inclined surface 11 is not formed on a curved surface. Even when the intake valve side peripheral edge portion 142 is formed of a curved surface, the radius of curvature thereof is smaller than the curvature radius of the curved surface forming the exhaust valve side peripheral edge portion 141. Exhaust valve side edge portion 141 and intake valve side peripheral edge portion 142 are connected to the exhaust valve side so that there is no step that causes fluctuations in combustion chamber flow fluctuations and accumulated fuel accumulation at two connection portions 16. The radius of curvature of the curved surface of the peripheral edge portion 141 is formed so as to gradually decrease toward the intake valve side peripheral edge portion 142.

  Next, the operation of the direct injection spark ignition internal combustion engine according to the first embodiment of the present invention configured as described above will be described. FIG. 3 is an explanatory view showing the fuel spray behavior when the compression stroke injection is performed in the direct injection spark ignition internal combustion engine according to the first embodiment of the present invention. In the execution of stratified combustion, as shown in FIG. 3, the combustion chamber has a fuel injection amount (injection period) corresponding to operating conditions such as the load and rotation speed of the internal combustion engine and the fuel injection timing. The fuel spray 20 is injected toward the inside 4.

  The injected fuel spray 20 is vaporized by receiving heat from the gas in the combustion chamber 4 to form an air-fuel mixture in the combustion chamber 4, while in the compression stroke injection in stratified combustion, as shown in FIG. The purpose is to inject fuel into the narrow combustion chamber 4 whose volume decreases every moment even during the fuel injection period, and generally to promote fuel vaporization by atomizing the fuel spray 20. Since the fuel is injected at a high pressure, the fuel is injected at a relatively strong momentum as compared with the gas flow in the combustion chamber 4. For this reason, although depending on the operating conditions such as the fuel injection amount, the fuel injection timing, and the piston ascending speed depending on the rotational speed of the internal combustion engine, a part of the fuel spray 20 is sufficiently vaporized in many operating conditions of the internal combustion engine. The fuel liquid film 21 is formed on the top surface of the piston 2, mainly on the inner wall surface of the cavity 14 provided on the top surface of the piston 2.

  FIG. 4 is an explanatory diagram showing the mixture behavior formed after the compression stroke injection is completed in the direct injection spark ignition internal combustion engine according to the first embodiment of the present invention. After the fuel injection is completed, the air-fuel mixture formed in the combustion chamber 4 diffuses into the combustion chamber 4 due to flow in the combustion chamber 4 and concentration diffusion due to a difference in fuel concentration with the surrounding gas. On the other hand, since the fuel liquid film 21 formed on the top surface of the piston 2 is vaporized by heat reception from the piston 2 or heat reception from a gas whose temperature has been increased by compression of the combustion chamber 4, generally, FIG. As shown, an air-fuel mixture 22 is formed in the combustion chamber 4 in which the fuel concentration near the inner wall surface of the cavity 4 is high and the fuel concentration decreases toward the outer periphery of the combustion chamber 4.

  At this time, generally, in the combustion chamber 4 having the cavity 14 on the top surface of the piston 2, the cavity having a large volume from the squish portion which is the outer peripheral portion of the cavity whose volume is greatly decreased in the combustion chamber 4 in the latter half of the compression stroke. The flow which pushes gas toward 14, that is, a so-called squish flow is generated.

  In the in-cylinder spark ignition internal combustion engine according to Embodiment 1 of the present invention, as shown in FIG. 2, a concave cavity 14 is provided at the center of the top surface of the piston 2 and has an opening concentric with the piston outer circle. Therefore, the volume of the combustion chamber 4 outside the cavity 14 is symmetric with respect to the center of the cavity 14.

  FIG. 5 is an explanatory diagram showing a squish flow formed in the latter half of the compression stroke and a mixture behavior in the direct injection spark ignition internal combustion engine according to the first embodiment of the present invention. As shown in FIG. 5, according to the in-cylinder spark ignition internal combustion engine according to the first embodiment of the present invention, the intake valve side squish flow 17 generated in the combustion chamber 4 in the latter half of the compression stroke, and the exhaust valve side squish. The flow 18 is all directed from the outer periphery of the combustion chamber 4 toward the center of the cavity 14, and the strength of the intake valve-side squish flow 17 and the exhaust valve-side squish flow 18 facing the center of the cavity 14. Are approximately equal and balance at the center of the cavity 14.

  As a result, the air-fuel mixture 22 shown in FIG. 4 formed in the combustion chamber 4 by the compression stroke injection, when the compression of the combustion chamber 4 proceeds and in the latter stage of the compression stroke, as shown in FIG. The flow 17 and the exhaust valve side squish flow 18 are surely collected toward the center of the cavity 14. Here, in the in-cylinder injection spark ignition internal combustion engine according to the first embodiment of the present invention, as shown in FIG. 1, a high compression composed of a pent roof type cylinder head 3 and a top surface of a pent roof type piston 2. Due to the ratio type combustion chamber 4, a strong exhaust valve side squish flow 18 and intake valve side squish flow 17 can be generated in the latter half of the compression stroke, and the air-fuel mixture is surely mixed at the center of the cavity 14. 22 can be collected.

  FIG. 6 is an explanatory diagram showing tumble flow and air-fuel mixture behavior formed in the latter half of the compression stroke in the direct injection spark ignition internal combustion engine according to Embodiment 1 of the present invention. As shown in FIG. 6, in the direct injection spark ignition internal combustion engine according to the first embodiment of the present invention, the exhaust valve side peripheral edge portion 141 of the cavity 14 has a spherical shape with the exhaust valve side inclined surface 12. Since it is formed by a curved surface having a large curvature radius so as to smoothly connect the inner wall surface of the cavity 14, the exhaust valve side squish flow 18 flowing from the exhaust valve side inclined surface 12 toward the center of the cavity 14 is Ascending, it drifts toward the top surface side of the piston 2 and is guided by the exhaust valve side peripheral edge portion 141 formed by a curved surface, and flows along the inner wall surface of the cavity 14.

  On the other hand, the intake valve side squish flow 17 that flows along the top surface of the piston 2 at the intake valve side peripheral edge portion 142 that is not formed on a curved surface having a large radius of curvature is an acute intake valve side peripheral edge portion 142. Is peeled off from the intake valve-side inclined surface 11 and flows toward the upper portion of the cavity 14 as shown in FIG.

  As a result, in the direct injection spark ignition internal combustion engine according to the first embodiment of the present invention, the exhaust valve side squish flow 18 that flows along the inner wall surface of the cavity 14 and the intake valve side that flows toward the top of the cavity 14 A tumble flow 19 as shown in FIG. 6 is formed in the cavity 14 by the interaction of a pair of substantially equal strength flows with the squish flow 17.

  Therefore, in the in-cylinder spark ignition internal combustion engine according to the first embodiment of the present invention, the air-fuel mixture 22 collected from the outer peripheral portion of the combustion chamber 4 to the central portion of the cavity 14 by the squish flow generated in the latter half of the compression stroke is Then, since it is sufficiently held at the center of the cavity 14 by riding on the tumble flow 19 formed in the cavity 14, stable mixing is performed in the vicinity of the spark plug 10 provided at the upper center of the cavity 14. It is possible to form the gas 23 over a long period of time.

  Therefore, according to the direct injection spark ignition internal combustion engine according to the first embodiment of the present invention, the air-fuel mixture 22 formed in the combustion chamber 4 by the compression stroke injection as shown in FIG. 4 is shown in FIG. As shown in FIG. 6, the squish flow generated in the latter half of the compression stroke is surely collected from the outer periphery of the combustion chamber 4 to the center of the cavity 14 and rides on the tumble flow 19 in the cavity 14 as shown in FIG. Therefore, a stable air-fuel mixture 23 can be formed in the vicinity of the spark plug 10 provided at the upper center of the cavity 14 over a long period of time. Stable stratified combustion without fluctuations in combustion can be realized even under operating conditions.

  In the cylinder injection spark ignition internal combustion engine according to the first embodiment of the present invention, in the latter half of the compression stroke, the gas that has become hot due to the compression of the combustion chamber 4 becomes the exhaust valve side squish flow 18 in the cavity 14. Since it flows along the wall surface, the heat transfer between the fuel liquid film 21 adhering to the inner wall surface of the cavity 14 and the compressed high-temperature gas during the compression stroke injection is improved, and the vaporization of the fuel liquid film 21 is promoted. The fuel vaporized by the formed tumble flow 19 is transported and agitated without staying in the vicinity of the wall surface of the cavity 14, and the fuel concentration is homogenized by promoting mixing with air. And the emission of unburned hydrocarbons.

  In addition, according to the in-cylinder injection spark ignition internal combustion engine according to the first embodiment of the present invention, the fuel liquid film 21 which is not vaporized by the ignition timing is reduced and injected by the promotion of vaporization of the fuel liquid film 21. As the fuel is effectively used, the combustion efficiency is improved, the output of the internal combustion engine and the fuel consumption rate can be improved, and the formation of deposits on the piston top surface, which is one of the causes of combustion fluctuations, is suppressed. You can also.

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Piston 3 Cylinder head 4 Combustion chamber 5 Intake port 6 Exhaust port 7 Intake valve 8 Exhaust valve 9 Fuel injection valve 10 Spark plug 11 Piston intake valve side inclined surface 12 Piston exhaust valve side inclined surface 13 Piston center 14 Recessed spherical cavity 15 Curved surface 17 Intake valve side squish flow 18 Exhaust valve side squish flow 19 Tumble flow 20 Fuel spray 21 Fuel liquid film 22 Mixture formed by compression stroke injection 23 Mixture 141 held in the center of the cavity Exhaust valve side peripheral edge 142 Intake valve side peripheral edge

Claims (3)

A cylinder housing a piston; a cylinder head fixed to the cylinder; a fuel injection valve that directly injects fuel into a combustion chamber formed between a top surface of the piston and an inner surface of the cylinder head; and the cylinder An intake valve provided at the intake port of the engine, an exhaust valve provided at the exhaust port of the cylinder, and an ignition plug fixed to the cylinder head at a substantially central portion of the top of the combustion chamber. A cylinder-injected spark ignition internal combustion engine configured to perform stratified combustion by igniting the fuel injected into the combustion chamber from the fuel injection valve during the compression stroke by the ignition plug;
The piston includes a concave spherical cavity having an opening formed substantially concentrically with the piston at the center of the top surface thereof.
The opening of the cavity is formed by an intake valve side peripheral edge portion positioned on the intake valve side and an exhaust valve side peripheral edge portion positioned on the exhaust valve side,
One of the intake valve side peripheral edge portion and the exhaust valve side peripheral edge portion is formed by a curved surface having a larger curvature radius than the other.
An in-cylinder injection spark ignition internal combustion engine. The cylinder head includes a pair of inclined surfaces inclined toward the top of the cylinder on the inner surface thereof,
The piston includes an intake valve side inclined surface and an exhaust valve side inclined surface which are inclined substantially parallel to the pair of inclined surfaces formed on the inner surface of the cylinder head on the top surface,
The intake valve side peripheral edge part is formed on the intake valve side inclined surface,
The exhaust valve side peripheral edge portion is formed on the exhaust valve side inclined surface,
2. The in-cylinder injection spark ignition internal combustion engine according to claim 1, wherein   The curved surface is formed so that a radius of curvature gradually decreases toward a connection portion between the intake valve side peripheral edge portion and the exhaust valve side peripheral edge portion. In-cylinder injection spark ignition internal combustion engine.

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