JP2006322334A - Direct injection type internal combustion engine and combustion method of the internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct injection type internal combustion engine or a combustion method of the internal combustion engine capable of developing excellent ignition performance by deviating the concentration of a mixture lump from a cavity on the discharge electrode part of an ignition plug by squish to avoid the excessive concentration of an air/fuel ratio at the discharge electrode part when ignition and burning are started at a rather delay time for promoting warmup to prevent the ignition plug from being fouled, worn, or smoked. <P>SOLUTION: In this direct injection type internal combustion engine having a fuel injection nozzle 8 jetting and feeding a fuel toward the cavity formed in a piston 24 and the spark plug 9, the flow of the mixture lump M formed by a jet fuel into the cavity flowing to the discharge electrode part 9a of the spark plug is deviated by the squish S, and the ignition and combustion are started while avoiding that the mixture concentration near the discharge electrode part is excessively increased. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an improvement in a spark ignition direct injection internal combustion engine or a combustion method thereof.

  In an internal combustion engine equipped with an exhaust purification catalyst, in order to improve exhaust emission performance after cold start, there is a problem of how quickly the temperature of the catalyst is raised to the activation temperature after start. In response to this problem, in a spark ignition type direct injection internal combustion engine, taking advantage of the feature that the fuel supply into the cylinder can be controlled relatively freely, it is possible to supply exhaust by secondary additional fuel supply or retard combustion. There has been proposed one that promotes catalyst activation by increasing the temperature.

For example, Patent Document 1 discloses an apparatus in which additional fuel is supplied in the middle to late stages of the expansion stroke to increase the exhaust temperature so that the thermal energy of the additional fuel is not lost as expansion work.
JP 2000-145511

  According to the applicant's knowledge, in a direct injection engine in which a stratified mixture is formed by the fuel injected toward the cavity provided on the piston crown surface, the fuel spray or mixture mass reversed in the cavity is present. There are cases where ignition and combustion under a rich atmosphere are concentrated on the discharge electrode portion of the spark plug. As a result, particularly under low temperature operation conditions that should promote the activity of the catalyst, problems such as smoldering and consumption of spark plugs due to a rich atmosphere and the occurrence of smoke are likely to occur.

The present invention is based on a direct injection internal combustion engine provided with a fuel injection valve for supplying fuel to a cavity formed on the piston crown surface and an ignition plug so as to face the combustion chamber. Or the combustion method is the gist.
A driving state detecting device for detecting an engine operating state, and a control device for controlling a fuel injection timing by the fuel injection valve, a fuel injection amount, and an ignition timing by the spark plug based on the detected operating state, Visually, the discharge electrode portion of the spark plug is unevenly distributed with respect to the center of the air-fuel mixture formed in the cavity, and mixed from the discharge electrode portion near the piston compression top dead center in the combustion chamber A squish area that causes squish toward the center of the air mass is provided.
・ A squish deflects the flow of the air-fuel mixture formed by the fuel injected into the cavity toward the discharge electrode portion of the spark plug to avoid over-concentration of the air-fuel mixture in the vicinity of the discharge electrode portion. In this state, ignition combustion is started.

  According to the direct injection internal combustion engine or the combustion method according to the present invention, for example, when ignition combustion is started at a relatively late time for promoting warm-up, the air-fuel mixture from the cavity becomes a discharge electrode portion of the spark plug. It is possible to deflect the concentration to be concentrated by squish and to avoid over-concentration of the air-fuel ratio of the discharge electrode part, so that good ignition performance can be exhibited, thus preventing the smoldering and consumption of spark plugs and the occurrence of smoke Can do.

  Japanese Patent Laid-Open No. 9-158736 discloses a technique for controlling the air-fuel mixture in the cavity using squish. However, this is aimed at avoiding misfire and extinguishing by holding the air-fuel mixture in the cavity by squish and preventing the air-fuel mixture from scattering, and the discharge electrode part of the spark plug has a rich atmosphere. It is not intended to address the problems caused by this, and thus does not disclose a solution.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, common parts are denoted by the same reference numerals. FIG. 1 shows a schematic configuration of an internal combustion engine to which the present invention is applicable. In the figure, 1 is an internal combustion engine body, 2 is an intake passage, 3 is a throttle valve, 4 is an exhaust passage, 5 is a catalytic converter, 6 is an intake valve, 7 is an exhaust valve, 8 is a fuel injection valve, and 9 is a spark plug. is there. 10 is a control unit, 11 is an intake air amount sensor, 12 is an accelerator opening sensor, 13 is a crank angle sensor, 14 is a coolant temperature sensor, and 15 is an exhaust oxygen sensor. Reference numeral 17 denotes a fuel pump that pumps fuel to the fuel injection valve 8 by cam driving, and 16 is a pressure sensor that detects the fuel pressure. Reference numeral 21 denotes a combustion chamber, and 24 denotes a piston.

  The control unit 10 corresponds to a control device according to the present invention, and is constituted by a microcomputer including a CPU and its peripheral devices. The control unit 10 is an internal combustion engine based on inputs from various sensors 11 to 16 as the operating state detection device. The operation state of the engine is judged, and the operation of the fuel pump 17, the fuel injection nozzle 8 and the spark plug 9 is controlled so that the fuel injection timing, the injection amount, and the ignition timing respectively match predetermined target values.

  This internal combustion engine is a four-valve type provided with two intake valves 6 and two exhaust valves 7, and a fuel injection valve 8 and a spark plug 9 are respectively disposed near the center of the combustion chamber surrounded by the four valves. is there. The fuel injection valve 8 is attached so that the center of the fuel spray is substantially parallel to the cylinder axis.

  As shown in FIG. 2-1 or FIG. 2-2, a circular concave cavity 31 is formed on the crown surface of the piston 24 so as to face the fuel injection valve 8. The center of the cavity 31 and the center (Cm) of the fuel spray by the fuel injection valve 8 are set so as to substantially coincide with each other, so that the fuel spray from the fuel injection valve 8 is substantially at the center of the bottom surface of the cavity 31. To collide with. The fuel injection valve 8 is a multi-hole nozzle or an outward type nozzle that injects fuel along a virtual conical surface with the nozzle portion at the top. The fuel injection valve having such spray characteristics has an advantage that the stagnation or shape change of the spray mass is small even when the cylinder pressure rises in the latter half of the compression stroke.

  The cavity 31 and the spark plug 9 are positioned so that the center Cm of the cavity 31 and the center Cg of the discharge electrode portion 9a of the spark plug are offset from each other. In this case, the cavity 31 is formed in the shape of a right cylindrical surface with its side wall portion 31a rising substantially perpendicular to the bottom surface, and the edge of the cavity region defined by the side wall portion 31 or the outside thereof. The discharge electrode portion center Cg is positioned at the center. Thus, when the combustion chamber is viewed from the cylinder center line direction, the discharge electrode portion 9a of the spark plug is unevenly distributed with respect to the center (Cm) of the air-fuel mixture M formed in the cavity 31. Yes.

  In the combustion chamber 21, as shown in FIG. 2B, a squish area As that generates a squish S from the discharge electrode portion 9a toward the center of the air-fuel mixture M near the piston compression top dead center. Is provided. The squish S is for deflecting the air-fuel mixture M so that it does not approach the discharge electrode portion 9a of the spark plug, as will be described later. More preferably, the squish S is seen from the side as shown in the figure. The squish area As is formed so that S is directed to the discharge electrode portion 9a.

  Next, an embodiment of a combustion system under the above configuration will be described. In general, in a direct injection internal combustion engine, fuel is injected and supplied during the compression stroke to stratify the mixture, and a stratified combustion operation mode in which operation is performed at a lean air-fuel ratio, and fuel is injected and supplied during the intake stroke. The mode of the homogeneous combustion operation in which the operation with the relatively rich premixed gas near the air-fuel ratio is performed is switched according to the operation state. The operation mode according to the present embodiment is basically a stratified combustion operation in which fuel injection is performed at or after the compression stroke, and in order to increase the exhaust temperature, particularly in the cold state before the exhaust purification catalyst 5 is activated. Ignition combustion is started at a later time. In the configuration shown in FIG. 1, the control unit 10 makes a determination based on a signal from the cooling water temperature sensor 14, and when the actual cooling water temperature is lower than a predetermined reference temperature, the cooling unit state is determined. And the combustion control is applied.

  FIG. 3 is a basic timing chart based on the control. In the drawing, Pf is an injection pulse signal output from the controller 10 to the fuel injection device, Pi is an ignition secondary current supplied from the ignition coil to the ignition plug 9 based on the ignition pulse signal to the ignition device, and A is an ignition plug. An air fuel ratio in the vicinity of the discharge electrode portion 9a, Ba represents an ignitable air fuel ratio width in the air fuel ratio range. The injection pulse signal Pf indicates that the rising edge of the pulse opens the nozzle of the fuel injection valve 8 to start fuel injection, and the falling edge closes the nozzle to end fuel injection. It is injected into the combustion chamber. In this case, the output timing of the injection pulse Pf, that is, the fuel injection timing is in the latter half of the compression stroke or later, and the ignition timing is in the vicinity of or after the compression top dead center immediately after the fuel injection. When combustion is started at the timing of such fuel injection and ignition, retard combustion occurs at a time when the combustion period is late, so much of the combustion energy is supplied to the exhaust gas to increase its temperature, and the temperature of the catalyst is increased. It can be raised quickly.

  Next, the details of the mixture formation and the combustion action under the control will be described. As described above, the fuel injected and supplied from the fuel injection valve 8 at the timing of the latter half of the compression stroke collides with the substantially central portion of the cavity 31 and then moves upward along the peripheral side wall portion 31a. While mixing with air, a substantially annular air-fuel mass M is formed in the circular cavity region. A part of the air-fuel mixture M moves toward the discharge electrode portion 9 a of the spark plug 9 as the air-fuel mixture M rises and the piston 24 moves. On the other hand, when the piston 24 reaches the vicinity of the top dead center, the gas in the squish area As is compressed and ejected as the squish S toward the discharge electrode portion 9a. By the flow of the squish S, the air-fuel mixture mass M that has been directed to the discharge electrode portion 9a is pushed away in the squish downstream direction. In particular, in this embodiment, since the discharge electrode portion 9a is positioned at the edge of the cavity 31 or the air mass M, the mixture concentration in the vicinity of the discharge electrode portion 9a is excessive due to the action of the squish S. You can definitely avoid the inconvenience of being rich. As a result, as shown in FIG. 4, the mixture concentration around the discharge electrode portion 9a can be set to an appropriate ignitable mixture concentration in the vicinity of the ignition timing. By starting the ignition combustion, good ignitability can be exhibited, and the smoldering and consumption of the spark plug 9 and the occurrence of smoke can be prevented.

  In addition, in this embodiment, since the cavity 31 has a circular shape and the center thereof coincides with the center of the fuel spray, the injected fuel is diffused in an isotropic manner in a cylindrical or annular shape in the combustion chamber. For this reason, an excessively rich or lean region is not generated in the air-fuel mixture, and it is possible to more reliably suppress the occurrence of defective combustion or smoke caused by the uneven air-fuel mixture concentration.

  FIGS. 4A and 4B show a second embodiment of the present invention. This is provided with means for generating an intake flow in substantially the same direction as the squish S. The intake flow is, for example, a vertical intake flow, that is, a tumble T as shown in the drawing. This is a suction port shape or a suction port having a directivity called a tumble port (not shown), but is partially formed by a valve. Realized by closing.

  A fuel injection valve 8 and a spark plug 9 are arranged in parallel with the two intake valves 6 or the exhaust valve 7 in a substantially central portion of the combustion chamber 21, and are provided in a direction orthogonal to a line segment connecting them. A squish is generated by the squish areas As1 and As2. However, in this case, as shown in FIG. 4B, the tumble T is formed so as to flow in the vicinity of the discharge electrode portion 9a of the spark plug from the intake side to the exhaust side. Thus, the squish area As1 on the intake valve side is made larger than the squish area As2 on the exhaust valve side so that the main flow S of squish occurs. Therefore, according to this embodiment, the synergistic action of the squish S and the tumble T generated in the combustion chamber 21 enables the fuel-rich air-fuel mixture mass from the cavity 31 to be more reliably moved away from the discharge electrode portion 9a. it can. In addition, as the intake air flow that promotes such an action, not only the tumble T as described above but also a swirl can be applied.

FIG. 5 shows a third embodiment of the present invention. This is another embodiment for the cavity 31. In this embodiment, at least a part of the cavity side wall 31a has a reentrant portion 31b inclined inward from the bottom of the cavity, and the discharge electrode portion of the spark plug is substantially above the reentrant portion 31b. 9a is located. According to this embodiment, when a part of the air-fuel mixture mass M by the fuel injected and supplied to the cavity 31 rises upward from the cavity 31 toward the upper side of the combustion chamber, the reentrant portion 31b causes the spark plug to It is biased in a direction away from the discharge electrode portion 9a (leftward in the figure). Therefore, in combination with the action of the squish S, it is possible to more reliably avoid the inconvenience that the fuel-rich mixture M reaches the discharge electrode portion 9a.

1 is an overall configuration diagram of an embodiment of a direct injection internal combustion engine to which the present invention is applied. 1 is a schematic longitudinal sectional view of a combustion chamber according to a first embodiment of the present invention. 1 is a schematic bottom view of a combustion chamber according to a first embodiment of the present invention. 2 is a timing chart showing the relationship between fuel injection timing, ignition timing, and air-fuel mixture concentration according to the embodiment. The schematic bottom view of the combustion chamber which concerns on the 2nd Embodiment of this invention. The schematic longitudinal cross-sectional view of the combustion chamber seen from A arrow direction of FIGS. The schematic longitudinal cross-sectional view of the combustion chamber which concerns on the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main body of direct injection type internal combustion engine 2 Intake passage 3 Throttle valve 4 Exhaust passage 5 Catalytic converter 6 Intake valve 7 Exhaust valve 8 Fuel injection valve 9 Spark plug 9a Discharge electrode part of spark plug 10 Control unit 21 Combustion chamber 24 Piston 31 Cavity As, As1, As2 Squish area S Squish T Tumble (intake flow)

Claims (12)

A fuel injection valve for injecting fuel toward a cavity formed on the piston crown surface and an ignition plug are provided so as to face the combustion chamber, and an operation state detection device for detecting an engine operation state, and based on the detected operation state In a direct injection internal combustion engine comprising a control device for controlling the fuel injection timing by the fuel injection valve, the fuel injection amount, and the ignition timing by the spark plug,
As seen from the cylinder centerline direction, the discharge electrode portion of the spark plug is unevenly distributed with respect to the center of the air-fuel mixture formed in the cavity,
A direct injection internal combustion engine characterized in that a squish area is provided in the combustion chamber in the vicinity of a piston compression top dead center to generate a squish from the discharge electrode portion toward the center of the air-fuel mixture.   When the cavity and the spark plug are viewed from the cylinder center line direction, the discharge electrode of the spark plug is near the edge of the cavity region defined by the side wall of the cavity or upstream of the squish from the edge. The direct injection internal combustion engine according to claim 1, wherein the direct injection internal combustion engine is disposed so that the portions are located.   2. The direct side according to claim 1, wherein the side wall portion of the cavity has a reentrant portion inclined inward from the bottom side of the cavity, and the discharge electrode portion of the spark plug is positioned substantially above the reentrant portion. Injection-type internal combustion engine.   The direct injection internal combustion engine according to claim 1, wherein the cavity has a circular concave shape.   2. The direct injection internal combustion engine according to claim 1, wherein the fuel injection valve is provided such that the center of fuel spray is substantially parallel to a cylinder center line.   2. The direct injection internal combustion engine according to claim 1, wherein the fuel injection valve is provided at a position substantially coincident with a center of the cavity when viewed from a cylinder center line direction.   2. The direct injection internal combustion engine according to claim 1, wherein the control device sets a fuel injection timing at or after a compression stroke and an ignition timing at or near a compression top dead center in a predetermined operation state.   The direct injection internal combustion engine according to claim 7, wherein the predetermined operating state is a low temperature operation.   2. The direct injection internal combustion engine according to claim 1, wherein the ignition timing is set near the end timing of fuel injection.   2. The direct injection internal combustion engine according to claim 1, wherein the squish area is formed so that the squish faces the spark plug electrode portion when viewed from the side.   The direct injection internal combustion engine according to claim 1, further comprising means for generating an intake air flow in substantially the same direction as the squish. A combustion method for a direct injection internal combustion engine comprising a fuel injection valve for injecting fuel toward a cavity formed on a piston crown and an ignition plug so as to face a combustion chamber,
The flow of the air-fuel mixture formed by the fuel injected into the cavity toward the discharge electrode portion of the spark plug is deflected by squish to avoid excessive concentration of the air-fuel mixture in the vicinity of the discharge electrode portion. A combustion method for a direct injection internal combustion engine, characterized by starting ignition combustion in a state.

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