JP2005140006A - Cylinder direct injection internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylinder direct injection internal combustion engine with an injector installed with inclination to the center axis of a cylinder for actualizing stable stratified charge combustion in a wide load range. <P>SOLUTION: The cylinder direct injection internal combustion engine comprises the injector installed on an injector installation axis 15 inclined to the cylinder center axis 14. The crowned face of the piston 4 has a first approximately circular cavity 16a with its center located on the cylinder center axis 14 and a second approximately circular cavity 16b arranged inside the first cavity 16a with its center located different from the center of the first cavity 16a. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an in-cylinder direct injection internal combustion engine, and more particularly to an in-cylinder direct injection internal combustion engine in which a fuel injection direction from a fuel injection valve (injector) is inclined with respect to a cylinder central axis.

As a conventional in-cylinder direct injection internal combustion engine, for example, there is one described in Patent Document 1. This is a so-called center injection type, in which a cavity composed of a central deep dish part and a surrounding shallow dish part is formed on the upper surface (crown surface) of the piston, and the fuel injection timing is changed to change the fuel injection timing. The spray is injected into the deep dish part or the shallow dish part, and the stratified state of the fuel spray is made variable (by switching between stratified combustion and weakly stratified combustion) so as to realize combustion with good fuel efficiency.
JP 2000-265841 A

By the way, in the above-mentioned conventional one, the injector is disposed so as to be inclined with respect to the center axis of the cylinder (hereinafter referred to as the cylinder center axis), and the fuel is not provided unless the injector has a special structure for deflecting the fuel spray. The spray does not become an object of the axis with respect to the cylinder central axis, and causes any deviation.
Since this bias increases as the fuel spray diffuses, in the deep dish part and the shallow dish part that target (impact) fuel sprays with different degrees of diffusion (that is, different fuel injection timings), It is also necessary to change the positional relationship with respect to the injector.

  However, the above conventional ones do not define any positional relationship between the injector (inclination thereof) and the deep dish part and the shallow dish part, and there is room for improvement in this respect. That is, in the case of having a plurality of cavities intended for fuel sprays having different diffusion degrees, such as the deep dish part and the shallow dish part, in order to realize stable stratified combustion in a wide load range, an injector ( It is necessary to define in detail the positional relationship between each cavity and the inclination.

  The present invention has been made paying attention to such a problem, and provides an in-cylinder direct injection internal combustion engine capable of realizing a stratified fuel that is stable in a wide load range when the injector is inclined and disposed. With the goal.

  For this reason, the direct injection internal combustion engine according to the present invention is such that the direction of fuel injection from the injector is inclined with respect to the central axis of the cylinder, and the center of the cylinder is almost the cylinder surface of the piston. A substantially circular first cavity located on the central axis of the first cavity, and a substantially circular second cavity whose center is different from the center of the first cavity inside the first cavity. .

  According to the direct injection type internal combustion engine according to the present invention, the first cavity is provided at substantially the center position of the combustion chamber, and the second cavity is provided at a position corresponding to the fuel injection direction inclined with respect to the cylinder center axis. Therefore, even when the fuel injection direction from the injector is inclined with respect to the central axis of the cylinder, stratified combustion with good fuel efficiency using the first and second cavities can be realized.

  That is, for the first cavity used when a relatively large stratified mixture is generated (at high load) for a state where the fuel spray is spread when the piston position in the compression stroke is low, By locating at substantially the center, stratified combustion is performed at a position away from the wall surface, and stratified combustion with low fuel loss and good fuel efficiency is realized. On the other hand, for the second cavity used for generating a relatively small and strong stratified mixture (at low load), which is targeted for a state where the spread of the fuel spray is small near the compression top dead center, Rather than shifting the center to the position corresponding to the inclination of the fuel injection direction, the fuel spray is surely contained in the second cavity to reduce the generation of unburned HC (also realizing stratified combustion with good fuel efficiency) Become). Thereby, stable stratified combustion with good fuel efficiency can be realized in a wide load range from high load to low load.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a first embodiment of a direct injection type internal combustion engine (hereinafter simply referred to as an engine) according to the present invention. As shown in the figure, the combustion chamber 1 of this engine is composed of a cylinder head 2, a cylinder block 3, and a piston 4 that fits and slides in a cylinder 3a of the cylinder block 3.

  The cylinder head 2 is formed with an intake port 5 and an exhaust port 6 that open to the combustion chamber 1. An intake valve 7 and an exhaust valve 8 that open and close these ports 5 and 6 are driven by using an intake valve cam 9 and an exhaust valve cam 10, respectively, and intake into the combustion chamber 1 via the intake valve 7. Fresh air is introduced from the port 5, and the combustion exhaust is discharged from the combustion chamber 1 through the exhaust valve 8 to the exhaust port 6.

  The cylinder head 2 includes an injector 11 that directly injects fuel into the combustion chamber 1 toward the crown surface (upper surface) of the piston 4, and an ignition plug 12 that sparks and ignites the air-fuel mixture in the combustion chamber 1. In the state of facing the combustion chamber 1 from above 1, they are arranged close to each other in the vicinity of the cylinder center shaft 14. Here, a multi-hole type with high directivity is used as the injector 11 so that the change in the spray shape becomes small even when the in-cylinder pressure rises especially in the latter half of the compression stroke. The operation of 12 is controlled by an engine control unit (ECU) 13.

  Here, as shown in FIG. 1 (b), the injector 11 has an injection point 11 a at its tip offset from the cylinder central shaft 14 to the engine front side, and also to the engine front side with respect to the cylinder central shaft 14. It is installed on a shaft (hereinafter referred to as an injector installation shaft) 15 that is inclined to the right. Accordingly, the fuel injection direction from the injector 11 is also inclined with respect to the cylinder central axis 14. The offset direction of the injection point 11a of the injector 11 and the inclination direction of the injector installation shaft 15 may be the engine rear side, the intake side or the exhaust side.

The spark plug 12 has an ignition point (ignition gap) 12a at the tip thereof positioned on the cylinder center shaft 14 and is inclined with respect to the cylinder center shaft 14 opposite to the injector 11. Yes.
FIG. 2 shows the shape of the piston 4. As shown in FIG. 2A, a substantially circular cavity 16 is formed (recessed) on the crown surface of the piston 4 (as viewed from above). The cavity 16 has a double structure including an outer cavity 16a having a large diameter (corresponding to the first cavity of the present invention) 16a and an inner cavity 16b having a small diameter inside (corresponding to the second cavity of the present invention) 16b. However, the center of the outer cavity 16a and the center of the inner cavity 16b do not coincide with each other and are shifted by a predetermined amount in a predetermined direction.

  Specifically, the outer cavity 16a is formed so that the center thereof is located substantially on the cylinder center axis 14, while the inner cavity 16b is centered at the center when the piston 4 is near top dead center. It is formed so as to be offset from the center of the outer cavity 16a (that is, on the cylinder center shaft 14) toward the injector 11 so as to be positioned on the injector installation shaft 15 (FIG. 1B). 4 (c) etc.).

  Further, as shown in FIGS. 2B and 2C, the bottom surface of the outer cavity 16a, that is, the surface between the peripheral wall of the outer cavity 16a and the peripheral wall of the inner cavity 16b has a cavity depth toward the outer peripheral direction. The bottom surface of the inner cavity 16b is formed as a surface substantially perpendicular to the cylinder center axis 14. In addition to forming the entire bottom surface of the outer cavity 16a with the inclined surface, for example, a part thereof may be the inclined surface so as to be formed with the inclined surface and a surface substantially perpendicular to the cylinder center axis 14. .

The injector 11 performs fuel injection toward the outer cavity 16a under relatively high load conditions among the stratified operation conditions, and performs fuel injection toward the inner cavity 16b under relatively low load conditions.
Here, the behavior of the fuel spray and the air-fuel mixture of the present embodiment will be described.
FIG. 3 shows the behavior of fuel spray and air-fuel mixture under stratified high load operation conditions. Under the stratified high load operation condition, the injector 11 performs fuel injection when the fuel injection timing is controlled by the ECU 13 and the piston 4 is in a relatively low position in the compression stroke as shown in FIG. Then, the fuel spray spreads and first collides with the bottom surface of the outer cavity 16a. At this time, since the bottom surface of the outer cavity 16a is formed with the inclined surface, the fuel spray easily moves to the peripheral wall side of the outer cavity 16a, and the fuel spray moves to the peripheral wall side along the bottom surface. After that, as shown in FIG. 3B, it rises along the peripheral wall.

  Since the fuel spray that has risen has a strong penetration force of the fuel spray from the injector 11, as shown in FIG. 3C, the entire air-fuel mixture is space between the piston 4 and the lower surface of the cylinder head 2 by the spray flow. It has a circulating flow that turns like a vortex. By encircling the surrounding air by this circulating flow, a homogeneous and large stratified air-fuel mixture with little concentration unevenness is formed above the cavity 16.

Although not shown in the drawing, the fuel injection is performed for the second time toward the inner cavity 16b near the compression top dead center, thereby forming a homogeneous mixture in the outer cavity 16a and the inner cavity 16b. It is also possible to produce a more homogeneous stratified mixture.
Here, since the center of the outer cavity 16a is located on the cylinder center axis 14 and is arranged at the center of the combustion chamber, the flame during the combustion period is separated from the wall surface of the combustion chamber, and cooling loss is reduced. Less stratified combustion occurs. Further, since the ignition gap 12a of the spark plug 12 is positioned on the cylinder center shaft 14, the combustion is performed with respect to a relatively large stratified mixture generated at the center of the combustion chamber using (utilizing) the outer cavity 16a. Combustion from the center of the chamber (that is, the center of the stratified mixture) can be realized, and the combustion period can be shortened to further reduce the cooling loss.

  FIG. 4 shows the behavior of fuel spray and air-fuel mixture under stratified low load operation conditions. The air-fuel mixture formation under the stratified low load operation condition is substantially the same process as the stratified high load operation condition, except that the inner cavity 16b is used. That is, the injector 11 performs fuel injection when the fuel injection timing is controlled by the ECU 13 and the piston 4 in the compression stroke is at a high position (when it is near the top dead center) as shown in FIG. . Then, the fuel spray first collides with the bottom surface of the inner cavity 64b, and then passes through the bottom surface and the peripheral wall of the inner cavity 16b. A gas mixture is formed above the cavity 16 (see FIGS. 4B and 4C).

Here, the inner cavity 15b is formed so that its center is located on the injector installation shaft 15 when the piston 4 is located near the top dead center, so that the fuel spray accompanying the inclined installation of the injector 11 is formed. Spilling is effectively prevented.
FIG. 5 shows the shape of fuel spray from the injector 11 used in the present embodiment. As described above, a multi-hole type injector is used, but in this embodiment, the injector is positioned at the lowermost position when the injector is installed at an angle as compared to the normal multi-hole type injector shown in FIG. The one without the nozzle hole is used.

  Since the inner cavity 16b is formed with its center offset to the injector 11 side with respect to the center of the outer cavity 16a, the bottom surface of the outer cavity 16a is narrow and the inclination becomes steep. Circulation flow is unlikely to occur. For this reason, the injection hole located in the lowermost portion is eliminated, and fuel injection from the portion, that is, the predetermined region centered on the portion having the smallest distance from the peripheral wall of the outer cavity 16a to the inner cavity 16b is not performed. By doing so (see FIG. 5B), when using (utilizing) the outer cavity 16a, it is possible to suppress the formation of a non-uniform air-fuel mixture in advance and increase unburned HC and EGR resistance. The fuel spray is prevented from spilling from the cavity.

In addition, in this embodiment, although only the nozzle hole located in the said lowest part is eliminated, the nozzle hole which should be eliminated is set suitably (it may be one or more).
According to this embodiment, the injector 11 is installed on the injector installation shaft 15 in which the injection point 11a at the tip thereof is located away from the cylinder central shaft 14 and is inclined with respect to the cylinder central shaft 14, and the inner cavity ( Since the center of the second cavity 16b is located on the side of the injector 11 with respect to the cylinder central axis 14, even if the injector 11 cannot be installed on the cylinder central axis 14 due to layout restrictions, etc. The cavities 16b can be provided corresponding to the fuel injection direction, so that fuel spray spillage can be prevented and generation of unburned HC can be suppressed.

Further, when the piston 4 is in the vicinity of the top dead center, the center of the inner cavity (second cavity) 16b is located on the injector installation shaft 15, so that when the inner cavity 16b is used, more fuel spray is applied. The generation of unburned HC can be reduced effectively by being housed in the inner cavity 16b.
In addition, the injector 11 eliminates the nozzle hole located at the lowermost position when installed at an inclination, compared to a normal multi-hole type injector, and the inner cavity (second cavity) extends from the peripheral wall of the outer cavity (first cavity) 16a. Since the fuel is not injected into the portion where the distance to 16b is the smallest, that is, the portion where the circulating flow is difficult to occur, a non-uniform air-fuel mixture is formed when the outer cavity 16a is used (utilized). Can be prevented.

In addition, as the injector 11, a circulating flow utilizing the spray flow is effectively formed by using the multi-hole side having a strong penetrating force and little (spray) shape change even under back pressure. Thereby, for example, even when a large amount of EGR is introduced, a homogeneous air-fuel mixture can be generated, and stratified combustion with good fuel efficiency can be realized while suppressing the generation of NOx.
The injector 11 injects fuel toward the outer cavity (first cavity) 16a under the stratified high load operation condition, and injects fuel toward the inner cavity (second cavity) 16b under the stratified low load operation condition. By doing so, an appropriate large stratified air-fuel mixture is generated according to the load in the stratified operation region (controlling the fuel injection timing), and stratified combustion with good fuel efficiency can be realized regardless of the load.

  In addition, the injector 11 performs fuel injection twice in the compression stroke under the stratified high load operation condition, the first time toward the outer cavity (first cavity) 16a, and the second time the inner cavity (second cavite). By injecting fuel toward 16b, a uniform stratified air-fuel mixture can be generated in the entire cavity 16, and stratified combustion with higher fuel efficiency can be realized during high-load operation.

  In addition, since the spark gap 12a at the tip of the spark plug 12 is located on the cylinder center shaft 14, the spark plug 12 from the center of the combustion chamber against the large stratified mixture generated at the center of the combustion chamber using the outer cavity 16a. Combustion can be realized, and the combustion period can be shortened. Thereby, the further cooling loss reduction effect can be acquired especially in a stratified high load operation condition.

1 is a view showing an in-cylinder direct injection internal combustion engine according to an embodiment of the present invention. It is a figure which shows piston shape. It is a figure which shows the behavior of the fuel spray and the air-fuel | gaseous mixture in a stratified high load operation condition. It is a figure which shows the behavior of the fuel spray and the air-fuel | gaseous mixture in a stratified low load operation condition. It is a figure which shows the fuel spray shape from the injector of this embodiment. It is a figure which shows the fuel spray shape from normal (conventional) multi-hole type injection.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Combustion chamber, 2 ... Cylinder head, 3 ... Cylinder block, 3a ... Cylinder, 4 ... Piston, 7 ... Intake valve, 8 ... Exhaust valve, 11 ... Injector, 11a ... Injection point, 12 ... Spark plug, 12a ... Ignition Gap, 13 ... Engine control unit (ECU), 14 ... Cylinder center axis, 15 ... Injector installation axis (fuel injection direction), 16a ... Outer cavity, 16b ... Inner cavity

Claims (7)

An injector and a spark plug are disposed at the substantially upper center of a combustion chamber formed by a cylinder head, a cylinder of a cylinder block, and a piston sliding in the cylinder, and the fuel injection direction from the injector is the center of the cylinder. In a cylinder direct injection internal combustion engine inclined with respect to the shaft,
A substantially circular first cavity whose center is located on the center axis of the cylinder, and a center of the first cavity that is different from the center of the first cavity on the crown surface of the piston. An in-cylinder direct injection internal combustion engine comprising a substantially circular second cavity. The injector is installed on an injector installation axis, the injection point of which is located away from the center axis of the cylinder and inclined with respect to the center axis of the cylinder;
The in-cylinder direct injection internal combustion engine according to claim 1, wherein the center of the second cavity is located on the injector side with respect to the central axis of the cylinder.   The in-cylinder direct injection internal combustion engine according to claim 2, wherein the center of the second cavity is located on the injector installation shaft when the piston is near top dead center.   The injector includes a plurality of injection holes and is configured not to perform fuel injection to a portion where the distance from the peripheral wall of the first cavity to the second cavity is the smallest. The direct injection type internal combustion engine according to any one of 1 to 3.   The injector performs fuel injection toward the first cavity under a stratified high load operation condition and performs fuel injection toward the second cavity under a stratified low load operation condition. 4. The direct injection internal combustion engine according to any one of 4.   In the stratified high load operation condition, the injector performs fuel injection twice in the compression stroke, the first time is directed toward the first cavity, and the second time is directed toward the second cavity. The direct injection type internal combustion engine according to any one of claims 1 to 5, wherein   The direct injection internal combustion engine according to any one of claims 1 to 6, wherein an ignition gap at a tip of the spark plug is positioned on a central axis of the cylinder.

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