JP2006046124A - Cylinder direct injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To satisfy both large delay of ignition timing and combustion stability and attain rise of exhaust gas temperature and reduction of HC emission when an engine is cold. <P>SOLUTION: In a warm-up completion condition that cooling water temperature exceeds 80°C, usual stratified combustion operation and homogeneous combustion operation are performed. In a cold engine condition below 80°C, top dead center injection operation is carried out for facilitating activation of a catalytic converter and for reducing HC emission. In this operation, injection starting timing is before compression top dead center, injection terminating timing is after the compression top dead center and fuel injection is carried out over the compression top dead center. Ignition timing is after the compression top dead center and is delayed by 15° to 20° CA from the injection starting timing. A geometric positional relation is set so that a centerline F of spray at the compression top dead center is reflected at a bottom 16a of a recessed portion 16 and is directed to an electrode portion 10a. At the compression top dead center, swirl and tumble are attenuated, minute turbulence actively occurs and positional change of a piston 3 is small so that stable combustion is attained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an in-cylinder direct injection spark ignition internal combustion engine that directly injects fuel into a cylinder, and more particularly to control of the injection timing and ignition timing.

  Patent Document 1 discloses that when an exhaust purification catalytic converter is in an unwarmed state lower than an activation temperature, fuel is injected during the compression stroke, and the ignition timing is retarded from the compression top dead center. Technology is disclosed.

Further, Patent Document 2 discloses a direct injection in a cylinder having a shape of the piston top so that fuel spray injected from the fuel injection valve during the compression stroke is reflected by the piston top and concentrated on the electrode portion of the spark plug. A spark ignition internal combustion engine is disclosed.
JP 2001-336467 A JP 2003-113717 A

  In order to raise the exhaust gas temperature and reduce HC in order to achieve early activation of the catalyst when the internal combustion engine is cold, it is desirable to retard the ignition timing as much as possible, but if the ignition timing is significantly retarded Since the combustion stability deteriorates, it cannot be retarded from a certain limit determined from the viewpoint of combustion stability. In the above-described conventional technology, it is difficult to ensure stable combustion, particularly under conditions such as cold, the ignition timing delay limit determined from the combustion stability is relatively advanced, and the ignition timing is sufficiently retarded. Cannot be realized.

  Further, in Patent Document 2, a concave portion is formed on the top of the piston along an elliptical shape in which the spark plug electrode portion becomes a focal point at a predetermined injection timing. However, during the compression stroke at the injection timing, the moving speed of the piston is increased. Therefore, in actuality, only a part of the injection period maintains the positional relationship in which the spark plug electrode portion is in focus. Therefore, the combustion stability is likely to change relatively greatly depending on the size of the injection period.

  The present invention relates to an in-cylinder direct injection spark ignition internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and that includes an ignition plug. When the gas temperature needs to be raised, fuel injection is performed in a period across the compression top dead center so that the injection start time is before the compression top dead center and the injection end time is after the compression top dead center, and The ignition is performed after the compression top dead center delayed from the injection start timing. Further, the shape of the piston top is configured such that when the piston is at the compression top dead center position, the fuel spray injected from the fuel injection valve toward the piston top is directed to the electrode portion of the ignition plug. .

  In one aspect of the present invention, the fuel injection valve is disposed on the side of the combustion chamber, and is configured to inject fuel obliquely downward toward the top of the piston, and ignites substantially the center of the combustion chamber. A plug is provided, and when the piston is at the compression top dead center position, the fuel spray injected from the fuel injection valve is reflected at the top of the piston and directed toward the electrode portion of the spark plug.

  For example, a concave portion having a gently curved bottom surface is provided at the top of the piston, and the fuel spray collides with the bottom surface of the concave portion and is reflected toward the spark plug. In other words, when the spray center line, which is the spray direction of spray, is geometrically reflected by the bottom surface of the recess, it is directed to the spark plug electrode portion, and is sprayed during the period across the compression top dead center. Most of the fuel is reflected to the spark plug side.

  Or the recessed part along the ellipse which each forms the nozzle hole part of a fuel injection valve and the electrode part of a spark plug when the piston exists in a compression top dead center position is formed in the said piston top part. Accordingly, the fuel spray that expands in a conical shape from the injection hole portion of the fuel injection valve that is one focus is reflected by the wall surface of the recess and is concentrated on the spark plug electrode portion that is the other focus. It should be noted that one cross section of the concave portion, for example, a cross section in a plane along the cylinder axis including the fuel injection nozzle hole portion and the spark plug electrode portion may be elliptical, and the spark plug electrode which is a focal point on the plane The fuel is concentrated in the area, but in a three-dimensional view, the recess is formed in a shape along the ellipsoid that rotates the ellipse so that all fuel spray concentrates on the spark plug electrode. Also good.

  Moreover, in one aspect of the present invention, the fuel injection valve is disposed at a side portion of the combustion chamber, and is configured to inject fuel obliquely downward toward the top of the piston. Is provided with a spark plug so that when the piston is at the compression top dead center position, the fuel spray injected from the fuel injection valve travels along the curved surface of the top of the piston and is guided to the electrode portion of the spark plug. It is configured. That is, in this case, the fuel spray does not collide with the surface of the piston top portion and is reflected, but proceeds along the curved surface and travels toward the spark plug electrode portion.

  FIG. 1 exemplifies the fuel injection period and ignition timing of the present invention together with the in-cylinder pressure change. The injection start timing ITS is before compression top dead center (TDC), and the injection end timing ITE is compression top dead center (TDC). Later. The length of the injection period T during that time corresponds to the injection amount. The ignition timing ADV is after compression top dead center (TDC), and is a timing delayed by a predetermined crank angle (for example, 15 ° CA to 20 ° CA) from the injection start timing ITS. This delay period D generally correlates with the distance from the fuel injection valve to the spark plug.

  The injection start timing ITS and the injection end timing ITE are controlled so that the period before the compression top dead center in the first half and the period after the compression top dead center in the second half are substantially equal with the compression top dead center (TDC) as the center. You may make it do.

  FIG. 2 shows the piston position change amount and the combustion chamber volume change amount due to the piston stroke in one cycle of the internal combustion engine. As shown in the figure, the amount of change per unit crank angle is the largest near the middle position of the stroke, and is very small near the bottom dead center (BDC) and near the top dead center (TDC). Therefore, in the vicinity of the compression top dead center where the fuel injection is performed in the present invention, the piston position change and volume change are very small, and a stable field that is not affected by the piston movement or the like can be formed.

  In the cylinder, a relatively large gas flow such as a swirl flow or a tumble flow is generated in the intake stroke and remains in the compression stroke. However, a large flow such as a swirl flow or a tumble flow is When the piston reaches near the compression top dead center and the combustion chamber becomes narrow, it collapses rapidly. FIG. 3 shows a change in flow velocity of a large flow in the combustion chamber under various engine speeds. As shown in the figure, a swirl flow or a tumble flow having a strength corresponding to the rotation speed is generated. Collapses rapidly before reaching compression top dead center (360 ° CA). Therefore, in the present invention, the fuel spray injected near the compression top dead center is not moved by a large flow such as a swirl flow or a tumble flow, and always forms a spray in a stable manner on the spark plug. Is possible.

  On the other hand, the energy of a relatively large flow such as the swirl flow or the tumble flow described above transitions to minute turbulence as the flow collapses. Therefore, the minute disturbance in the combustion chamber increases rapidly just before the compression top dead center. FIG. 4 shows the intensity of the minute turbulence caused by the collapse of the flow shown in FIG. 3 as a so-called turbulent flow rate converted to a flow velocity, and as shown in the figure, immediately before the compression top dead center. , Disturbances increase greatly. Such minute disturbances contribute to the activation of the combustion field, and a combustion improving action is obtained.

  Furthermore, in the present invention, the shape of the piston top is configured so that the fuel spray injected from the fuel injection valve toward the piston top when the piston is at the compression top dead center position is directed to the electrode portion of the spark plug. However, as described above, the piston position change amount per unit crank angle is very small near the compression top dead center where the fuel is injected, and the geometrical relationship between the fuel injection valve, the spark plug, and the piston top part is small. Changes in the positional relationship are slow. In particular, since the piston that has risen in the compression stroke is reversed and lowered at the top dead center, the width of the change in the piston position in the fuel injection period across the compression top dead center is further reduced. Accordingly, a larger portion of the injected fuel is directed to the spark plug electrode portion along the intended geometrical positional relationship, and a reliable air-fuel mixture is formed. Even if the fuel injection period increases or decreases, the change in the piston position relative to the fuel injection period is small, so that the combustion does not become unstable.

  Thus, in the present invention, the field in the combustion chamber near the compression top dead center where the fuel is injected does not have a large flow that moves the spray, and there is a minute disturbance that activates combustion. There are many, and it is a very stable field against the movement of the piston. In such a stable field, a combustible air-fuel mixture can be reliably formed in the vicinity of the spark plug by utilizing the intended geometric positional relationship among the fuel injection valve, the spark plug, and the piston top. Stable combustion is possible with the ignition timing retarded from the compression top dead center, and the retard limit of the ignition timing that is limited in terms of combustion stability is on the retard side. For this reason, the exhaust gas temperature can be significantly increased by a large retardation of the ignition timing, and the HC emission amount is reduced.

  According to the present invention, stable combustion can be obtained in a state where the ignition timing is significantly retarded from the compression top dead center. For example, when the internal combustion engine is cold, the exhaust gas temperature is raised and the catalyst is accelerated. Activation can be achieved and HC emissions can be reduced. In particular, since the geometric positional relationship between the fuel injection valve, the spark plug, and the piston top hardly changes during the injection period, a combustible air-fuel mixture can be stably formed in the vicinity of the spark plug, and more stable combustion can be realized. .

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

  5 to 7 show an embodiment of a direct injection type spark ignition internal combustion engine to which the present invention is applied. In particular, FIGS. 5 and 6 show the configuration of one cylinder. Indicates the system configuration of the entire organization.

  As shown in FIGS. 5 and 6, a piston 3 is slidably disposed in a cylinder 2 formed in the cylinder block 1, and a cylinder head 4 fixed to the upper surface of the cylinder block 1 and the piston 3 A combustion chamber 5 is formed between them. The cylinder head 4 is formed with an intake port 7 that is opened and closed by an intake valve 6 and an exhaust port 9 that is opened and closed by an exhaust valve 8. A pair of intake valves 6 and a pair of exhaust valves 8 are provided for one cylinder, and an ignition plug 10 is disposed at the center of the ceiling surface of the combustion chamber 5 surrounded by these four valves. . Further, in this embodiment, a partition wall 11 is provided in the intake port 7 so as to partition the intake port 7 into two upper and lower flow paths so that the tumble flow can be strengthened depending on the operation state. A tumble control valve 12 that opens and closes the lower flow path at the upstream end is provided. As can be easily understood by those skilled in the art, the tumble flow is strengthened when the lower flow path is closed by the tumble control valve 12, and the tumble flow is weakened when the tumble control valve 12 is opened. The tumble control valve 12 is not necessarily essential in the present invention, and can be omitted. Alternatively, a known swirl control valve may be provided.

  A fuel injection valve 15 for directly injecting fuel into the cylinder is disposed below the intake port 7 of the cylinder head 4, more specifically at a position between the pair of intake ports 7. That is, the fuel injection valve 15 is located on the side of the combustion chamber 5 on the intake valve 6 side, and is arranged so as to inject fuel along a direction orthogonal to a piston pin (not shown) on the plan view. In the cross-sectional view of FIG. However, the downward inclination angle is relatively small, that is, the fuel is injected in a direction close to the horizontal.

  On the other hand, the top portion of the piston 3 has a convex shape so as to enter the concave portion of the ceiling surface of the combustion chamber 5 having a pent roof type, and a concave portion 16 having a substantially rectangular shape in a plan view is formed at the center thereof. ing. The bottom surface 16a of the recess 16 forms a loose arc surface having a relatively large radius of curvature or a curved surface approximating an arc so as to follow the tumble flow. That is, the bottom surface 16a has a gently curved curve as shown in FIG. 5 in a cross section perpendicular to the piston pin including the spray center line of the fuel injection valve 15, and a straight line having a constant depth in the cross section in the piston pin axial direction. It becomes. Further, in the plan view, the fuel injection valve 15 faces one side of the substantially rectangular recess 16 and the spark plug 10 is positioned above the other side.

  Here, in this embodiment, when the piston 3 is at the top dead center position, when the spray center line from the fuel injection valve 15 is geometrically reflected by the bottom surface 16a of the recess 16, the spray center line is Is directed to the electrode portion 10a of the spark plug 10, that is, the geometrical relationship between the three, that is, the position and injection direction of the fuel injection valve 15, the position of the electrode portion 10a of the spark plug 10, and the bottom surface 16a of the piston 3. The height position, the curved shape, etc. are set.

  As shown in FIG. 7, the internal combustion engine of this embodiment is, for example, an in-line four-cylinder engine, and a catalytic converter 22 for purifying exhaust gas is provided in an exhaust passage 21 to which an exhaust port 9 of each cylinder is connected. An air-fuel ratio sensor 23 such as an oxygen sensor is disposed on the upstream side. The intake passage 24 to which the intake port 7 of each cylinder is connected is provided with an electronically controlled throttle valve 25 that is opened and closed by a control signal on the inlet side. An exhaust gas recirculation passage 26 is provided between the exhaust passage 21 and the intake air passage 24, and an exhaust gas recirculation control valve 27 is interposed in the middle. Further, the tumble control valves 12 of the respective cylinders are configured to be simultaneously opened and closed by a negative pressure type tumble control actuator 29 that is operated by a suction negative pressure introduced via a solenoid valve 28.

  The fuel injection valve 15 is supplied with the fuel adjusted to a predetermined pressure by the fuel pump 31 and the pressure regulator 32 via the fuel gallery 33. Therefore, when the fuel injection valve 15 of each cylinder is opened by the control pulse, an amount of fuel corresponding to the valve opening period is injected. The ignition plug 10 of each cylinder is connected to an ignition coil 34.

  The fuel injection timing, injection amount, ignition timing, etc. of the internal combustion engine are controlled by the control unit 35. The control unit 35 includes a detection signal of an accelerator opening sensor 30 that detects the amount of depression of an accelerator pedal, a detection signal of a crank angle sensor 36, a detection signal of an air-fuel ratio sensor 23, and a detection of a water temperature sensor 37 that detects a cooling water temperature. Signals, etc. are input.

  In the internal combustion engine configured as described above, when the warm-up is completed, for example, when the cooling water temperature exceeds 80 ° C., normal stratified combustion operation and homogeneous combustion operation are performed. That is, in a predetermined region on the low speed and low load side, as a normal stratified combustion operation, fuel injection is performed at an appropriate time in the compression stroke, with the tumble control valve 12 basically closed, and the compression is increased. Ignition is performed at the time before dead center. In this operation mode, fuel injection always ends before compression top dead center. The fuel injected toward the piston 3 during the compression stroke is collected in the vicinity of the spark plug 10 using a tumble flow swirling along the recess 16 and ignited there. Therefore, stratified combustion with an average air-fuel ratio lean is realized. In a predetermined region on the high speed and high load side, as a normal homogeneous combustion operation, fuel injection is performed during the intake stroke with the tumble control valve 12 basically open, and before compression top dead center. Ignition is performed at the MBT point. In this case, the fuel becomes a homogeneous air-fuel mixture in the cylinder and is basically operated near the stoichiometric air-fuel ratio.

  On the other hand, when the cooling water temperature of the internal combustion engine is 80 ° C. or lower, that is, when the warm-up is not completed, the top dead center is used to activate the catalytic converter 22, that is, to promote the temperature rise and reduce the HC emission amount. Let it be an injection operation. In the top dead center injection operation, as shown in FIG. 1 described above, the injection start timing ITS is before the compression top dead center (TDC), and the injection end timing ITE is after the compression top dead center (TDC). Fuel injection is performed across the points. The ignition timing ADV is after compression top dead center (TDC), and is ignited at a timing delayed by 15 ° CA to 20 ° CA from the injection start timing ITS. During this delay period, the fuel spray reflected by the piston 3 just reaches the vicinity of the spark plug 10 and forms a combustible air-fuel mixture in the vicinity of the spark plug 10, so that ignition combustion is surely performed and stratified combustion is performed. At this time, the fuel injection amount is controlled so that the average air-fuel ratio becomes the stoichiometric air-fuel ratio.

  In this embodiment, the fuel injection timing is controlled so that the injection start timing ITS becomes a predetermined crank angle, and the injection end timing ITE is determined by the injection start timing ITS and the fuel injection amount (injection time). . The injection start timing ITS and the injection end timing ITE are obtained based on the fuel injection amount so that the period before the compression top dead center and the period after the compression top dead center in the fuel injection period are equal. Is also possible.

  FIG. 8 shows the positional relationship between the fuel spray injected from the fuel injection valve 15 and the piston 3 or the electrode portion 10a when the piston 3 is at the compression top dead center position. As shown in the figure, the piston 3 is at the highest position in the cylinder 2, and the injection hole of the fuel injection valve 15 faces the bottom surface 16 a of the recess 16 at the top of the piston 3 from an oblique direction. At this time, the fuel spray injected from the fuel injection valve 15 collides with the bottom surface 16a from an oblique direction, is reflected, and travels toward the electrode portion 10a of the spark plug 10. Reference numeral F in the figure indicates a spray center line spreading in a conical shape, and the spray center line F is reflected by the bottom surface 16a and reaches the electrode portion 10a. In this embodiment, when seen on a plan view as shown in FIG. 6, the spray spreads in a thin fan shape and travels toward the electrode portion 10a.

  As described above, by performing fuel injection across the compression top dead center, the position of the piston 3 hardly changes during the fuel injection period, so that the positional relationship shown in FIG. 8 is maintained without being extremely broken. The Therefore, the desired combustible air-fuel mixture can be reliably formed in the vicinity of the spark plug 10. Preferably, the injection start timing ITS and the injection end timing ITE are symmetrical with respect to the top dead center TDC, that is, the period before the compression top dead center and the period after the compression top dead center in the fuel injection period are equal. If the control is performed, the change in the position of the piston 3 during the fuel injection period is minimized.

  It should be noted that the fuel pressure regulated by the pressure regulator 32 may be applied relatively higher during the top dead center injection operation than during the normal stratified combustion operation or homogeneous combustion operation. In this case, the bottom surface 16a is more reliably reflected by the penetration force of the spray, and the ratio of the fuel adhering to the piston 3 is reduced. At the same time, the fuel injection period is shortened, and the change in the position of the piston 3 during that period is further reduced.

  Thus, by performing fuel injection across the compression top dead center when the internal combustion engine is not warmed up, the desired combustible air-fuel mixture is formed near the spark plug 10 using the shape of the top of the piston 3. Can be reliably formed. As described above, the field in the combustion chamber near the compression top dead center where the fuel is injected does not have a large flow that causes the spray to move due to the collapse of the large flow, and the large flow collapses. Along with this, there are many minute disturbances that activate the combustion, and the field becomes very stable against the movement of the piston. Therefore, by performing fuel injection across the compression top dead center and delaying the ignition timing from the compression top dead center, it is possible to achieve both a large retardation of the ignition timing and ensuring combustion stability. A sufficient increase in exhaust gas temperature and a reduction in HC emissions can be achieved.

  It should be noted that the curved shape of the bottom surface 16a of the concave portion 16 is along an elliptical shape in which the nozzle hole portion of the fuel injection valve 15 and the electrode portion 10a of the spark plug 10 are in focus when the piston 3 is at the top dead center position. In this case, the spray spreading outside the spray center line F is also reflected toward the electrode portion 10a. Furthermore, if the three-dimensional shape of the recess 16 is a shape along a so-called ellipsoid obtained by rotating the above ellipse, the spray spreading from the nozzle hole portion when viewed on a plan view, The light is reflected and concentrated on the electrode portion 10a.

  Next, FIG. 9 shows a different embodiment of the present invention. In this embodiment, the curved shape of the bottom surface 16a of the recess 16 is different from the above-described embodiment, and the fuel spray injected from the fuel injection valve 15 when the piston 3 is at the compression top dead center position is applied to the bottom surface 16a. It advances along smoothly and is configured to be guided to the electrode portion 10a of the spark plug 10. That is, in this embodiment, since the curved shape of the bottom surface 16a on the fuel injection valve side substantially coincides with the traveling direction of the fuel spray, the fuel spray f does not collide with the bottom surface 16a of the piston 3 and is reflected, It progresses along the curved shape of the bottom surface 16a, and goes to the electrode portion 10a. Even in such a configuration, by performing the fuel injection during the period across the compression top dead center, the positional relationship with the piston 3 becomes stable, so that the desired combustible air-fuel mixture can be reliably supplied in the vicinity of the spark plug 10. Can be formed.

The characteristic view which showed an example of the fuel-injection period and ignition timing of this invention. The characteristic figure of the piston position change amount and volume change amount during a cycle. The characteristic figure which shows the change in the cycle of a big flow. The characteristic view which shows the change in the cycle of a minute disturbance. Sectional drawing which shows one Example of a direct injection type spark ignition internal combustion engine. FIG. FIG. 2 is a configuration explanatory view showing the system configuration of the entire internal combustion engine. Explanatory drawing which shows the positional relationship of the fuel spray injected at the compression top dead center, a piston, etc. Explanatory drawing similar to FIG. 8 which shows a different Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Piston 5 ... Combustion chamber 10 ... Spark plug 15 ... Fuel injection valve 16 ... Recessed part 16a ... Bottom

Claims (7)

  An in-cylinder direct injection spark ignition internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and that has an ignition plug, injects fuel when the engine is in a predetermined operating state. Before the dead center, the injection end timing is after the compression top dead center, and the ignition is performed after the compression top dead center delayed from the injection start timing, and the piston is compressed. Directly in the cylinder, wherein the shape of the top of the piston is configured so that the fuel spray injected from the fuel injection valve toward the top of the piston is directed to the electrode portion of the spark plug when in the dead center position. Injection spark ignition internal combustion engine.   The fuel injection valve is disposed at a side portion of the combustion chamber, and is configured to inject fuel obliquely downward toward the top of the piston. The fuel injection valve includes an ignition plug at a substantially central portion of the combustion chamber. 2. The direct injection spark ignition internal combustion engine according to claim 1, wherein the fuel spray injected from the injection valve is reflected from the top of the piston and travels toward the electrode portion of the spark plug.   The in-cylinder direct according to claim 2, wherein a concave portion having a gently curved bottom surface is provided at the top of the piston, and fuel spray collides with the bottom surface of the concave portion and reflects toward the spark plug. Injection spark ignition internal combustion engine.   The top of the piston is formed with a concave portion along an ellipse that focuses on the injection hole portion of the fuel injection valve and the electrode portion of the spark plug when the piston is at the compression top dead center position. The in-cylinder direct injection spark ignition internal combustion engine according to claim 2.   The fuel injection valve is disposed at a side portion of the combustion chamber, and is configured to inject fuel obliquely downward toward the top of the piston. The fuel injection valve includes an ignition plug at a substantially central portion of the combustion chamber. The in-cylinder direct injection type according to claim 1, wherein the fuel spray injected from the injection valve travels along the curved surface of the piston top and is guided to the electrode portion of the spark plug. Spark ignition internal combustion engine.   6. In-cylinder direct injection according to any one of claims 1 to 5, wherein the fuel injection period and the ignition timing are controlled when a rise in exhaust gas temperature is required as a predetermined operating state. Type spark ignition internal combustion engine. The in-cylinder direct injection spark ignition internal combustion engine according to any one of claims 1 to 6, wherein a period before the compression top dead center and a period after the compression top dead center in the fuel injection period are substantially equal.

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