JP2006037794A - Cylinder direct injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent worsening of HC and smoke due to adhesion of fuel liquid droplet to a piston 3. <P>SOLUTION: In the warm-up completion state in which the cooling water temperature of an internal combustion engine exceeds 80°C, normal stratified combustion operation and homogeneous combustion operation are performed. In the cool-down state in which the cooling water temperature is 80°C or less, in order to accelerate the activation of a catalytic converter and reduce the quantity of HC discharged, the top dead center injection operation is performed. In the top dead center injection operation, the injection start timing is before the compression top dead center, the injection end timing is after the compression top dead center, and fuel injection is performed extending over the compression top dead center. The ignition timing is after the compression top dead center delayed from the injection start timing by 15° to 20°CA. At the compression top dead center, a piston 3 approaches a fuel injection valve 15, and atomized fuel F collides with the base 16a in the oblique direction still in the high-energy state without little decreasing the speed, so that it is repelled by the base 16a and reflected toward the ignition plug 10 side. The quantity of liquid drops adhering to the base 16a becomes very small so that HC and smoke can be reduced. <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.
JP 2001-336467 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 the above prior art, when the engine is cooled, the fuel injection is performed during the halfway compression stroke in which the piston is in the middle of the stroke, so that the fuel spray easily adheres to the top of the piston as a droplet, causing HC and smoke. It becomes.

  In the present invention, a fuel injection valve for directly injecting fuel into a cylinder is arranged at a side portion of the combustion chamber, and is configured to inject fuel obliquely downward toward the top of the piston. In a direct injection type spark ignition internal combustion engine having a plug, fuel injection is performed in a predetermined operating state so that the injection start timing is before the compression top dead center and the injection end timing is after the compression top dead center. In addition, the ignition is performed after the compression top dead center delayed from the injection start timing, and the fuel spray injected near the compression top dead center is reflected by the surface of the piston top. Thus, the spray direction is set.

  Desirably, the fuel spray impinges on the surface of the top of the piston at an angle of 10 ° to 50 °. If it collides with the surface at a smaller angle, the fuel droplets are reflected without adhering to the surface.

  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.

  In the present invention, the fuel pressure may be corrected to be high when fuel injection is performed during the period across the compression top dead center as described above. As a result, the fuel droplets collide more strongly with the top surface of the piston and are more reliably reflected.

  In the present invention, an oil-repellent coating may be applied to the surface of the piston top where the fuel spray injected near the compression top dead center collides. This reduces the adhesion of fuel droplets. For example, polytetrafluoroethylene (PTFE) is used as the coating material.

  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.

  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.

  In other words, 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 are many minute disturbances that activate the combustion, It is a very stable place against the movement of the piston. Therefore, 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.

  In the vicinity of the compression top dead center where the fuel is injected as described above, the piston is close to the top dead center and is close to the fuel injection valve. Therefore, the fuel spray injected from the fuel injection valve collides with the surface of the top of the piston from an oblique direction while being in a high energy state with almost no damping, and is bounced and reflected here. That is, since the speed of fuel spraying is high, the amount of droplets that adhere is small and most of the light is reflected. Therefore, deterioration of HC and smoke due to the adhesion of fuel droplets is suppressed.

  According to this invention, the fuel injection period is set so as to straddle the compression top dead center, and the fuel spray is strongly and obliquely collided with the surface of the piston near the top dead center. Adhesion can be suppressed, and HC and smoke resulting from this can be reduced. At the same time, stable combustion can be obtained with the ignition timing significantly retarded from the compression top dead center.For example, when the internal combustion engine is cold, the amount of HC emission is reduced in combination with the suppression of fuel droplet adhesion. The catalyst can be greatly reduced, and the exhaust gas temperature can be raised to activate the catalyst early.

  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 a known swirl control valve may be provided instead.

  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 disposed 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. 5, it is arranged obliquely downward, but 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.

  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 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 piston 3 and the fuel spray F when fuel is injected from the fuel injection valve 15 near the compression top dead center. As shown in the figure, the piston 3 has risen to the vicinity of the top dead center, and is in a state closest to the injection hole of the fuel injection valve 15. At this time, the injection hole of the fuel injection valve 15 faces the bottom surface 16a of the recess 16 at the top of the piston 3, and the fuel spray F injected from the fuel injection valve 15 is in a high energy state with almost no attenuation of the velocity. It collides with the bottom surface 16a from an oblique direction. Accordingly, relatively large fuel droplets with high straightness are bounced off the bottom surface 16a and reflected toward the spark plug 10, and the amount of droplets adhering to the bottom surface 16a is very small. That is, when the distance to the piston 3 is shortened, the speed of the fuel spray F is increased, and the fuel spray F is easily repelled without adhering to the surface. Moreover, since the piston 3 is in the raised position, the fuel spray F collides with a position relatively close to the intake valve 6 in the concave portion 16 curved in a substantially arc shape, and the spray F on the bottom surface 16a The inclination angle becomes smaller. Therefore, rather than injecting in the middle of the compression stroke, the amount of attached droplets is reduced, and deterioration of HC and smoke due to the attachment of fuel droplets is suppressed. Here, it is desirable that the inclination angle θ (see FIG. 9) of the spray F with respect to the bottom surface 16a at the location where the fuel spray F collides with the bottom surface 16a is within a range of 10 ° to 50 °. If the fuel pressure regulated by the pressure regulator 32 is applied relatively higher during the top dead center injection operation than during the normal stratified combustion operation or homogeneous combustion operation, the piston 3 is given. The proportion of fuel adhering is less.

  Thus, by performing fuel injection across the compression top dead center when the internal combustion engine is not warmed up, adhesion of fuel droplets to the piston 3 which is a problem during cold operation is suppressed, and the fuel liquid Deterioration of HC and smoke due to droplet adhesion is avoided. At the same time, the fuel is injected into a place where a large gas flow collapses and is in a very stable state, so that it is possible to achieve both a large retardation of the ignition timing and securing of combustion stability. A sufficient increase in the exhaust gas temperature and a further reduction in the HC emissions can be achieved.

  Next, FIG. 10 shows an embodiment in which a coating 41 having oil repellency is applied to the bottom surface 16a of the recess 16 where the fuel spray injected near the top dead center collides. As the coating material, for example, a fluorine-based material such as polytetrafluoroethylene (PTFE) can be used. The coating 41 may be applied to the entire bottom surface 16a, but as shown in the drawing, it is also possible to coat only the range near the intake valve 6 where the fuel spray injected near the top dead center collides. By applying the oil-repellent coating 41 in this way, collision of fuel droplets that have collided is reduced.

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 relationship between the fuel spray injected in the compression top dead center vicinity, and a piston. Explanatory drawing of inclination-angle (theta) of spraying. The top view of the piston which shows the Example which gave the coating to the bottom face of a recessed part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Piston 5 ... Combustion chamber 10 ... Spark plug 16 ... Recessed part 16a ... Bottom 15 ... Fuel injection valve 41 ... Coating

Claims (5)

  A fuel injection valve that directly injects fuel into the cylinder is arranged at the side of the combustion chamber, and is configured to inject fuel obliquely downward toward the top of the piston. In the in-cylinder direct injection spark ignition internal combustion engine, in a predetermined operating state, the fuel injection is performed so that the injection start timing is before the compression top dead center and the injection end timing is after the compression top dead center. In a period spanning the point, ignition is performed after the compression top dead center delayed from the injection start timing, and the fuel spray injected near the compression top dead center is reflected on the surface of the piston top, An in-cylinder direct injection spark ignition internal combustion engine characterized in that the spray direction is set.   The in-cylinder direct injection spark ignition internal combustion engine according to claim 1, 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 is reflected. organ.   The in-cylinder direct injection spark ignition internal combustion engine according to claim 1 or 2, wherein the fuel pressure is corrected to be high when fuel injection is performed in a period over the compression top dead center as described above.   The in-cylinder direct injection spark according to any one of claims 1 to 3, wherein a coating having oil repellency is applied to a surface of a piston top where a fuel spray injected near the compression top dead center collides. Ignition internal combustion engine. The in-cylinder direct injection spark ignition internal combustion engine according to any one of claims 1 to 4, wherein the fuel spray collides with the surface of the top of the piston at an angle of 10 ° to 50 °.

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