JP4345714B2 - In-cylinder direct injection layer combustion engine - Google Patents

Description

  The present invention relates to an in-cylinder direct injection stratified combustion engine.

  In order to reduce NOx, it is effective to introduce EGR gas into the combustion chamber. Currently, in most automobile engines, EGR gas is introduced into the combustion chamber. For example, Patent Document 1 discloses that an EGR layer is formed in the center of a combustion chamber in order to suppress flame propagation to the center of the combustion chamber in a peripheral ignition type engine. In Cited Document 2, a vertical swirl containing EGR gas and a vertical swirl not containing EGR gas are formed in stripes in an intake port injection, central ignition engine, and an air layer not containing EGR gas is formed in the vicinity of the spark plug. It is disclosed. These are in a so-called port injection type engine in which fuel is injected into an intake port.

  On the other hand, there is a so-called in-cylinder direct injection stratified combustion engine in which fuel is directly injected into the cylinder to perform stratified combustion, and a part of them is put into practical use. Even in such an in-cylinder direct injection stratified combustion engine, EGR gas is introduced into the combustion chamber in order to reduce NOx. For example, there is one described in Patent Document 3.

  By the way, when EGR gas is introduced, the ratio of fresh air decreases, and the air-fuel ratio of the air-fuel mixture shifts to the rich side as a whole. Therefore, in a direct injection stratified combustion engine, the air-fuel ratio in the air-fuel mixture is not uniform. Since there are rich and lean regions, the originally rich region becomes richer when EGR gas is introduced, flame propagation becomes unstable, combustion fluctuation increases, HC increases, fuel consumption deteriorates, etc. Induce.

  In the apparatus described in Patent Document 3, air containing EGR gas is introduced into a cylinder, and a mixture of fuel and air is injected into the cylinder instead of fresh air. Flame propagation becomes unstable, which may cause an increase in combustion fluctuation, an increase in HC, a deterioration in fuel consumption, and the like.

JP-A-6-88553 Japanese Patent Application Laid-Open No. Hei 6-200765 JP 2004-150284 A

  In view of the above problems, an object of the present invention is to provide an in-cylinder direct injection stratified combustion engine that introduces EGR gas so that NOx can be reduced while suppressing instability of combustion.

According to the first aspect of the invention, the first intake port that guides air to the combustion chamber via the first intake valve, the second intake port that guides air to the combustion chamber via the second intake valve, and the first EGR gas introduction means for introducing EGR gas into the intake port, a fuel injection valve arranged to be able to inject fuel toward a substantially central portion when viewed from the cylinder axial direction of the combustion chamber, and a spark plug, The intake port is disposed so that one of the two lines defining the flow path wall when viewed from the cylinder axial direction is substantially tangent to the cylinder circle, and the second intake port is substantially parallel to the first intake port. arranged toward the center, a layer of air containing the EGR gas to the outside of the area as seen from the cylinder axis direction of the combustion chamber, containing no EGR gas inside the region when viewed from the cylinder axis direction of the combustion chamber air After the fuel layer is formed, the fuel is injected from the fuel injection valve. Injecting fuel toward a substantially central portion as viewed from the cylinder axis direction of the chamber, empty layer containing no inner EGR gas as viewed from the cylinder axis direction is rich compared to the layer containing the outer EGR gas An in-cylinder direct injection stratified combustion engine is provided in which an air-fuel mixture having a fuel ratio distribution is formed and the air-fuel mixture is ignited by the spark plug .

  According to the invention of claim 2, in the cylinder of claim 1, the flow rate adjusting valve for adjusting the air flow rate is provided in the second intake port, and the opening degree is changed according to the load. A combustion engine is provided.

  According to the invention of claim 3, in the cylinder of claim 1, the second intake valve includes variable lift means for changing the lift, and the lift of the second intake valve is changed according to the load. A direct injection stratified combustion engine is provided.

According to the invention of claim 4, the intake port for introducing air to the combustion chamber via the intake valve, the EGR gas introduction means for introducing EGR gas into the intake port, and the air when viewed from the cylinder axial direction of the combustion chamber are substantially omitted. Air injection means for injecting into the central portion, a fuel injection valve arranged to be able to inject fuel toward the substantially central portion when seen from the cylinder axial direction of the combustion chamber, and a spark plug, and via an intake valve air containing Te by injecting air into the substantially central portion as viewed from the cylinder axis direction of the combustion chamber from the air injection valve after introducing the air containing the EGR gas, the EGR gas to the outside when viewed from the cylinder axis direction of the combustion chamber the layers inside the allowed form a layer of air that does not contain the EGR gas when viewed from the cylinder axis direction of the combustion chamber, after which the fuel is injected in a substantially central portion as viewed from the cylinder axis direction of the combustion chamber from the fuel injection valve The Siri And the layer as seen from Da axial direction does not include the inside of the EGR gas than the layer containing the outer EGR gas to form a mixture having an air-fuel ratio distribution becomes rich, to ignite the fuel mixture by the spark plug An in-cylinder direct injection stratified combustion engine is provided.

  According to the invention described in each claim, air containing EGR gas is distributed in the outer region as viewed from the cylinder axis direction, and air not including EGR gas is distributed in the inner region as viewed from the cylinder axis direction. Is formed, fuel is injected from the fuel injection valve into the central portion when viewed from the cylinder axis direction, the air-fuel ratio in the inner region is relatively rich, and the air-fuel ratio in the outer region is relatively lean . The rich region that is likely to become unstable when the EGR rate is increased does not have EGR gas, and the lean portion that easily generates NOx is suppressed from generating NOx by the effect of EGR gas. In this way, NOx can be reduced while suppressing instability of combustion.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram showing the configuration of the first embodiment of the present invention, and is a view of a cylinder as viewed from above. In FIG. 1, 1 is a cylinder, 10 is a surge tank, 11 is a first intake port, 12 is a second intake port, 13 is a first intake valve, and 14 is a second intake valve. Reference numeral 15 is a first exhaust valve, 16 is a second exhaust valve, 17 is a first exhaust port, 18 is a second exhaust port, and the first exhaust port 17 and the second exhaust port 18 are gathered downstream to form an exhaust pipe. 19 is connected.

  22 is a fuel injection valve that injects fuel from the upper center of the cylinder 1, and 23 is a spark plug. The fuel injection valve 22 and the spark plug 23 are controlled by an electronic control unit (hereinafter referred to as ECU) 30. The ECU 30 is composed of a microcomputer, and an input port 31, an output port 32, a RAM 33, a ROM 34, a CPU 35, etc. are connected to each other by a common bus 36.

  Air that has passed through an air cleaner (not shown) from an intake port (not shown) passes through the first intake port 11 and the second intake port 12 via the surge tank 10 and passes through the first intake valve 13 and the second intake valve 13 to the cylinder. 1 is introduced. Here, as shown in the figure, the first intake port 11 is disposed so that one of the two lines defining the flow path wall as viewed from the cylinder axial direction is substantially tangent to the cylinder circle. The air introduced into the cylinder 1 from the first intake port 11 flows along the inner wall of the cylinder 1 and is distributed in a donut shape as indicated by a thick arrow.

  An EGR pipe 20 extending from the exhaust pipe 19 is attached to the first intake port 11 so that a part of the exhaust gas is recirculated into the first intake port 11 as EGR gas. Therefore, the air introduced into the cylinder 1 from the first intake valve 13 is air containing EGR gas. The amount of EGR gas is controlled by the EGR control valve 21.

  On the other hand, the second intake port 12 is disposed substantially parallel to the first intake port 11, and the streamline is directed toward the approximate center of the cylinder 1. The air introduced into the cylinder 1 from the second intake port 12 flows through the inside of the air introduced from the first intake port 11 distributed in a donut shape as indicated by a thin arrow, for example, and is in the combustion chamber. It is distributed in the central area. A flow rate adjusting valve 24 is attached to the second intake port 12 in order to adjust the flow rate of air introduced from the second intake port 12.

  As a result, in the stage before fuel injection in the compression stroke, air containing EGR gas is distributed in the outer region as viewed from the cylinder axis direction, and air not containing EGR gas is distributed in the central region. That is, an air distribution having two layers in the radial direction is formed.

When fuel is injected from the fuel injection valve 22 axisymmetrically with respect to the cylinder axis while the two-layer air distribution is formed in the radial direction as described above, the air-fuel ratio in the central region near the fuel injection valve 22 is relatively The air-fuel ratio in the outer region becomes relatively lean.
When the EGR rate is increased, the region that is likely to become unstable is a rich region as described above, but as described above, the rich region has no EGR gas and generates NOx. The easy lean portion suppresses the generation of NOx by the effect of EGR gas. In this way, NOx can be reduced while suppressing instability of combustion.

FIG. 2 is a cross-sectional view of the state after the fuel is injected as seen from the side of the cylinder 1.
FIG. 3 shows changes in the region including EGR gas and the region not including EGR gas depending on the degree of opening of the flow rate adjusting valve 24 provided in the second intake port 12, and (A) shows the flow rate adjusting valve. The case where the opening degree of 24 is large is shown, and (B) shows the case where the opening degree of the flow rate adjusting valve 24 is small. An image diagram of the air-fuel ratio distribution is appended to each.

Next, a modification of the first embodiment will be described. FIG. 4 is a diagram showing the configuration of this modification. Compared with the configuration of the first embodiment shown in FIG. 1, the flow rate adjustment valve 24 provided in the second intake port 12 is removed. Yes. Therefore, for example, the cam for driving the second intake valve 14 is a three-dimensional cam as shown in FIG. 5, and the lift amount of the second intake valve 14 is changed by shifting this cam in the cam shaft direction according to the load. The amount of air passing through the second intake port 14 is controlled.
Since this modification only changes the method for responding to a change in load, NOx can be reduced while suppressing instability of combustion, as in the first embodiment.

Next, a second embodiment will be described.
6A, 6B, and 6C are diagrams showing the configuration and operation of the second embodiment, in which an air injection valve 25 is provided in the central portion, and the air injection valve 25 is The air injection amount is changed by a signal from the ECU 30. Since the air injection valve 25 is thus provided, the air introduced into the first intake port 11 is formed so as to turn along the peripheral wall of the cylinder 1 as in the first embodiment, and the second intake air It is not necessary for the port 12 (not shown in FIG. 6) to go to the central portion. Further, the intake control valve provided in the second intake port 12 of the first embodiment and the variable lift mechanism of the valve in the modification of the first embodiment are unnecessary.

First, as shown in (A), air containing EGR gas is introduced into the entire region in the cylinder. And before fuel injection, as shown to (B), the air which does not contain EGR gas is introduce | transduced in the center of said (A) state. At this time, as in the first embodiment, air containing EGR gas is distributed outside, and air not containing EGR gas is distributed inside.
Then, fuel is injected into the central portion of the state (B), and ignition is performed when the state (C) is reached.

  Similarly to the first embodiment, in the second embodiment, air including EGR gas is distributed outside and air not including EGR gas is distributed inside as viewed from the cylinder axial direction. Therefore, as in the first embodiment, NOx can be reduced while suppressing unstable combustion.

  The present invention can be applied to an internal combustion engine, in particular, a direct injection stratified combustion engine in which direct fuel injection is performed in a cylinder for stratified combustion.

It is a figure which shows the structure of 1st Embodiment. It is the figure which looked at the state after fuel was injected from the side of a cylinder. The change of the area | region which contains EGR gas when the air flow rate of a 2nd intake port is changed, and the area | region which does not contain are shown, (A) shows the case where the area | region containing EGR gas is large, (B) The case where the area | region containing EGR gas is small is shown. It is a figure which shows the structure of the modification of 1st Embodiment. It is the solid cam used in the modification of 1st Embodiment. It is a figure explaining the structure and effect | action of 2nd Embodiment, Comprising: (A) The state which introduce | transduced the air containing EGR gas into the whole area | region in a cylinder is shown, (B) In the state of said (A) A state in which air that does not include EGR gas is introduced is shown in the center, and (C) a state in which fuel is injected into the central portion of the state in (B) above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder 11,12 1st, 2nd intake port 13,14 1st, 2nd intake valve 15,16 1st, 2nd exhaust valve 17,18 1st, 2nd exhaust port 19 Exhaust pipe 20 EGR pipe 21 EGR Control valve 22 Fuel injection valve 23 Spark plug 24 Flow rate adjustment valve 25 Air injection valve 30 Electronic control unit (ECU)

Claims (4)

A first intake port that guides air to the combustion chamber via the first intake valve; and a second intake port that guides air to the combustion chamber via the second intake valve;
EGR gas introduction means for introducing EGR gas into the first intake port;
A fuel injection valve arranged to be able to inject fuel toward a substantially central portion when viewed from the cylinder axial direction of the combustion chamber, and an ignition plug ;
The first intake port is disposed so that one of the two lines defining the flow path wall when viewed from the cylinder axial direction is substantially tangent to the cylinder circle, and the second intake port is substantially parallel to the first intake port. Placed so as to go to the center
A layer of air as viewed from the cylinder axis direction of the combustion chamber including the EGR gases to the outside of the area, after allowed a layer of air containing no EGR gas inside the region when viewed from the cylinder axis direction of the combustion chamber, The fuel is injected from the fuel injection valve toward the substantially central portion when viewed from the cylinder axial direction of the combustion chamber, and the layer not including the inner EGR gas as viewed from the cylinder axial direction is compared with the layer including the outer EGR gas. An in-cylinder direct injection stratified combustion engine characterized by forming an air-fuel mixture having a rich air-fuel ratio distribution and igniting the air-fuel mixture by the spark plug .   The in-cylinder direct injection stratified combustion engine according to claim 1, wherein a flow rate adjusting valve for adjusting an air flow rate is provided in the second intake port, and the opening degree is changed according to a load.   The in-cylinder direct injection stratified combustion engine according to claim 1, wherein the second intake valve includes variable lift means for changing a lift, and the lift of the second intake valve is changed according to a load. An intake port that directs air to the combustion chamber via an intake valve;
EGR gas introduction means for introducing EGR gas into the intake port;
Air injection means for injecting air into a substantially central portion when viewed from the cylinder axial direction of the combustion chamber;
A fuel injection valve disposed so as to be able to inject fuel toward the substantially central portion when viewed from the cylinder axial direction of the combustion chamber, and an ignition plug ;
By injecting air into the substantially central portion as viewed from the cylinder axis direction of the combustion chamber after introducing the air containing the EGR gas through the intake valve from the air injection valve, EGR outwardly as viewed from the cylinder axis direction of the combustion chamber A layer of air containing no gas is formed on the inner side when viewed from the cylinder axial direction of the combustion chamber.
Thereafter, fuel is injected from the fuel injection valve into a substantially central portion when viewed from the cylinder axis direction of the combustion chamber, and the layer not including the inner EGR gas as viewed from the cylinder axis direction is compared with the layer including the outer EGR gas. An in-cylinder direct injection stratified combustion engine characterized by forming an air-fuel mixture having a rich air-fuel ratio distribution and igniting the air-fuel mixture by the spark plug .

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