JP2009121423A - Exhaust control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust control device for an internal combustion engine capable of improving exhaust emission characteristics as a whole of the internal combustion engine, by reducing the variation of air/fuel ratios between cylinders. <P>SOLUTION: By using acquired air/fuel ratios of respective cylinders, difference between the air/fuel ratios of the cylinders is calculated (a step 102). When the difference between the calculated air/fuel ratios of the cylinders is less than a reference value, external EGR ratio control is performed (a step 106). In the step 106, the ratio of an external EGR taken out from an exhaust manifold to which the cylinder having relatively a rich air/fuel ratio is connected is made higher than the ratio of the external EGR taken out from another exhaust manifold. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust control device for an internal combustion engine having a split exhaust manifold.

  A variable valve mechanism that can change the valve lift amount and valve timing of an intake valve or an exhaust valve of an internal combustion engine is known (see, for example, Patent Document 1). In order to improve the output (particularly, the output at low speed) of an internal combustion engine equipped with such a variable valve mechanism, it is effective to avoid exhaust interference using a split exhaust manifold.

JP 2004-1000055 A JP-A-9-151805 JP 2006-37907 A

  However, there may be variations in the air-fuel ratio between the cylinders mainly due to variations in the external EGR amount between the cylinders. In this case, since the air-fuel ratio is enriched in the specific cylinder, smoke and unburned HC may be deteriorated. If it does so, there exists a possibility that exhaust emission characteristics cannot fully be improved as the whole internal combustion engine.

  The present invention has been made to solve the above-described problems, and is capable of improving exhaust emission characteristics of the internal combustion engine as a whole by reducing variations in the air-fuel ratio between the cylinders. An object is to provide an apparatus.

In order to achieve the above object, a first invention is an exhaust control device for an internal combustion engine having a plurality of cylinder groups and a split exhaust manifold,
A plurality of exhaust manifolds connected to the plurality of cylinder groups;
A plurality of EGR passages connected to the plurality of exhaust manifolds;
Air-fuel ratio acquisition means for acquiring the air-fuel ratio of each cylinder of the plurality of cylinder groups;
An external EGR ratio control means for controlling the ratio of the external EGR extracted from one exhaust manifold to which a cylinder having a relatively rich air-fuel ratio is connected to be higher than the ratio of the external EGR extracted from another manifold; It is provided with.

The second invention is the first invention, wherein
A variable valve mechanism that can change the opening timing of the exhaust valve of each cylinder;
Exhaust valve opening timing control for controlling the opening timing of the exhaust valves of other cylinders using the variable valve mechanism so that the exhaust pressure of the cylinder having a relatively rich air-fuel ratio becomes lower than a predetermined value. And means.

The third invention is the second invention, wherein
Further comprising an inter-cylinder difference calculating means for calculating an inter-cylinder difference in the air-fuel ratio acquired by the air-fuel ratio acquiring means,
When the inter-cylinder difference calculated by the inter-cylinder difference calculating means is greater than or equal to a reference value, the control by the external EGR ratio control means is executed with priority over the control by the exhaust valve opening timing control means. It is characterized by.

  In the first invention, the air-fuel ratio of each cylinder is acquired by the air-fuel ratio acquisition means. Then, the ratio of the external EGR extracted from one exhaust manifold to which the cylinder having a relatively rich air-fuel ratio is connected by the external EGR ratio control means is larger than the ratio of the external EGR extracted from the other exhaust manifold. And high controlled. When the ratio of the external EGR is increased, the exhaust pressure is decreased. Therefore, the internal EGR amount (residual gas amount) of the cylinder having a relatively rich air-fuel ratio can be reduced, and the air-fuel ratio of the cylinder can be made lean. Therefore, variation in the air-fuel ratio between the cylinders can be reduced, so that the exhaust emission characteristics can be improved as a whole internal combustion engine.

  In the second invention, the exhaust valve opening timing of the other cylinders is controlled by the exhaust valve opening timing control means so that the exhaust pressure of the cylinder having a relatively rich air-fuel ratio becomes lower than a predetermined value. The That is, by controlling the exhaust valve opening timing of the other cylinders, the timing of the exhaust pulsation from the other cylinders is shifted in the cylinders having a relatively rich air-fuel ratio, and the cylinders having a relatively rich air-fuel ratio are shifted. The exhaust pressure is made lower than a predetermined value. Therefore, the internal EGR amount (residual gas amount) of the cylinder having a relatively rich air-fuel ratio can be reduced, and the air-fuel ratio of the cylinder can be made lean. Therefore, variation in the air-fuel ratio between the cylinders can be reduced, so that the exhaust emission characteristics can be improved as a whole internal combustion engine.

  In the third aspect of the invention, when the air-fuel ratio difference between the cylinders is greater than or equal to the reference value, the control by the external EGR ratio control means is executed with priority over the control by the exhaust valve opening timing control means. Therefore, it is possible to prevent the exhaust valve opening timing of other cylinders from being significantly changed by the exhaust valve opening timing control means. Therefore, variation in the air-fuel ratio between cylinders can be reduced while suppressing deterioration in fuel consumption.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

[Description of system configuration]
FIG. 1 is a diagram for explaining the configuration of a system according to an embodiment of the present invention. The system shown in FIG. 1 is a diesel engine system having a supercharger. The present invention can also be applied to a gasoline engine system.

  The system shown in FIG. 1 includes an engine 1 having a plurality of cylinders 2. Reference numerals “# 1” to “# 4” in FIG. 1 represent the first to fourth cylinders. The pistons of the cylinders 2 are connected to a common crankshaft 4 via a crank mechanism. A crank angle sensor 5 is provided in the vicinity of the crankshaft 4. The crank angle sensor 5 is configured to detect the rotation angle of the crankshaft 4 (hereinafter referred to as “crank angle CA”).

  The engine 1 has an injector 6 corresponding to each cylinder 2. The injector 6 is configured to inject high pressure fuel directly into the cylinder 2. Each injector 6 is connected to a common delivery pipe 7. The delivery pipe 7 communicates with the fuel tank 9 via the fuel pump 8.

  The engine 1 has an intake port 10 corresponding to each cylinder 2. Each intake port 10 is provided with a plurality of intake valves 12. Connected to the intake valve 12 is a variable valve mechanism 13 capable of independently changing the valve opening characteristics (opening / closing timing and lift amount) of the intake valve 12. As the variable valve mechanism 13, a known electromagnetically driven valve mechanism, a mechanical or hydraulic variable valve mechanism, or the like can be used.

  Each intake port 10 is connected to a common intake manifold 14. The intake manifold 14 is provided with a supercharging pressure sensor 15. The supercharging pressure sensor 15 is configured to detect a pressure of air (hereinafter referred to as “supercharging air”) supercharged by a compressor 24a described later, that is, a supercharging pressure PIM.

  An intake passage 16 is connected to the intake manifold 14. A throttle valve 18 is provided in the middle of the intake passage 16. The throttle valve 18 is an electronically controlled valve that is driven by a throttle motor 19. The throttle valve 18 is driven based on the supercharging pressure PIM, the accelerator opening AA, or the like. The accelerator opening AA is detected by the accelerator opening sensor 21. In the vicinity of the throttle valve 18, a throttle opening sensor 20 for detecting the throttle opening TA is provided. An intercooler 22 for cooling the supercharged air is provided upstream of the throttle valve 18.

  A compressor 24 a of the supercharger 24 is provided upstream of the intercooler 22. The compressor 24a is connected to the turbine 24b via a connecting shaft (not shown). The turbine 24b is provided in an exhaust passage 38 to be described later. The turbine 24b is rotationally driven by exhaust dynamic pressure (exhaust energy), whereby the compressor 24a is rotationally driven.

  An air flow meter 26 is provided upstream of the compressor 24a. The air flow meter 26 is configured to detect an intake air amount Ga. An air cleaner 28 is provided upstream of the air flow meter 26. The upstream of the air cleaner 28 is open to the atmosphere.

  The engine 1 has an exhaust port 30 corresponding to each cylinder 2. A plurality of exhaust valves 32 are provided in the exhaust port 30. The exhaust valve 32 is connected to a variable valve mechanism 33 that can independently change the valve opening characteristics (opening / closing timing and lift amount) of the exhaust valve 32. As the variable valve mechanism 33, similarly to the variable valve mechanism 13 of the intake system, a known electromagnetically driven valve mechanism, a mechanical or hydraulic variable valve mechanism, or the like can be used.

  The system shown in FIG. 1 has split exhaust manifolds 34 and 35 to avoid exhaust interference. The first exhaust manifold 34 has a plurality of branch pipes 34A and 34B. One branch pipe 34A is connected to the exhaust port 30 of the first cylinder # 1, and the other branch pipe 34B is connected to the exhaust port 30 of the fourth cylinder # 4. That is, a first cylinder group including the first and fourth cylinders # 1 and # 4 is connected to the first exhaust manifold 34.

  The second exhaust manifold 35 has a plurality of branch pipes 35A and 35B. One branch pipe 35A is connected to the exhaust port 30 of the second cylinder # 2, and the other branch pipe 35B is connected to the exhaust port 30 of the third cylinder # 3. That is, a second cylinder group including the second and third cylinders # 2 and # 3 is connected to the second exhaust manifold 35.

  The downstream ends of the first and second exhaust manifolds 34 and 35 are connected to the exhaust collecting portion 36. An exhaust passage 38 is connected to the exhaust collecting portion 36. In the exhaust passage 38, the above-described turbine 24b of the supercharger 24 is disposed. The turbine 24 b is configured to be rotationally driven by the energy of the exhaust gas flowing through the exhaust passage 38.

A NOx catalyst 40 is provided in the exhaust passage 38 downstream of the turbine 24b. An air-fuel ratio sensor 42 that detects the air-fuel ratio is provided in the exhaust passage 38 upstream of the NOx catalyst 40.
The NOx catalyst 40 can be composed of, for example, a NOx storage reduction catalyst. The NOx catalyst 40 has a function of occluding NOx contained in exhaust gas leaner than the stoichiometric air-fuel ratio, and when exhaust gas richer than the stoichiometric air-fuel ratio flows or is reduced from the exhaust fuel addition valve 36. When the agent is added, it has a function of reducing and purifying the stored NOx and releasing it. The NOx catalyst 40 may have only a function of storing and reducing NOx, or may be a DPNR (Diesel Particulate-NOx-Reduction system) having a function of collecting soot in exhaust gas.

  The first exhaust manifold 34 is provided with a first EGR outlet 44. Specifically, the first EGR outlet 44 is provided downstream of the junction of the branch pipe 34A and the branch pipe 34B. The first EGR outlet 44 is connected to one end of the first EGR passage 46.

  Similarly, the second exhaust manifold 35 is provided with a second EGR outlet 48. Specifically, the second EGR outlet 48 is provided downstream of the junction of the branch pipe 35A and the branch pipe 35B. The second EGR outlet 48 is connected to one end of the second EGR passage 50.

  The other end of the first EGR passage 46 and the other end of the second EGR passage 50 merge to form an EGR passage 52. The EGR passage 52 is connected to the intake passage 16. An EGR cooler 54 is provided in the vicinity of the junction of the EGR passages 46 and 48. An EGR valve 56 is provided in the EGR passage 52 downstream of the EGR cooler 54 (on the intake passage 16 side).

The system according to the present embodiment includes an ECU (Electronic Control Unit) 60 that is a control device. A crank angle sensor 5, a supercharging pressure sensor 15, a throttle opening sensor 20, an accelerator opening sensor 21, an air flow meter 26, and the like are connected to the input side of the ECU 60. Further, an injector 6, a fuel pump 8, variable valve mechanisms 13 and 33, a throttle motor 19, an EGR valve 56, and the like are connected to the output side of the ECU 60.
The ECU 60 calculates the engine speed NE based on the crank angle CA. Further, the ECU 60 calculates the fuel injection amount based on the accelerator opening AA and the like. Further, the ECU 60 calculates the engine torque based on the fuel injection amount.
Although details will be described later, the ECU 60 controls the external EGR ratio by controlling the opening degree of the EGR valve 56.

[Features of the embodiment]
The system includes a split type first exhaust manifold 34 and a second exhaust manifold 35. Thereby, since exhaust interference can be prevented, engine torque can be improved.

Further, since the exhaust pressure is higher than the intake pressure, when the EGR valve 56 is opened in the exhaust stroke of the first and fourth cylinders # 1 and # 4, the first and fourth cylinders # 1 and # 4. The exhaust gas discharged from the first exhaust manifold 34 to the first exhaust manifold 34 is taken out from the first EGR outlet 44 to the first EGR passage 46. The exhaust gas taken out to the first EGR passage 46 is cooled by the EGR cooler 54 and then returned to the intake passage 16 via the EGR passage 52.
Similarly, when the EGR valve 56 is opened in the exhaust stroke of the second and third cylinders # 2 and # 3, the exhaust discharged from the second and third cylinders # 2 and # 3 to the second exhaust manifold 35. The gas is taken out from the second EGR outlet 48 to the second EGR passage 50. The exhaust gas taken out to the second EGR passage 50 is cooled by the EGR cooler 54 and then returned to the intake passage 16 through the EGR passage 52.
Thus, since exhaust gas can be taken out from both the exhaust manifolds 34 and 35 as external EGR, a sufficient amount of EGR can be ensured.

  By the way, as shown in FIG. 2, the air-fuel ratio may vary among the cylinders. FIG. 2 is a diagram showing the variation in the air-fuel ratio between cylinders. Specifically, FIG. 2A shows the air-fuel ratio variation in the first operating region (engine speed: 1400 rpm, engine torque: 25 Nm), and FIG. 2B shows the second operating region (engine speed). FIG. 2C shows the air-fuel ratio variation between cylinders in the third operating region (engine speed: 2000 rpm, engine torque: 180 Nm). Each is shown.

  As shown in FIG. 2 (A), in the first operating region, the cylinder having a relatively rich air-fuel ratio (hereinafter also referred to as “rich cylinder”) is the third cylinder # 3, and the air-fuel ratio is relatively high. The cylinder in which is lean (hereinafter also referred to as “lean cylinder”) is the fourth cylinder # 4. Further, as shown in FIG. 2B, in the second operating region, the rich cylinder is the second cylinder # 2, and the lean cylinder is the fourth cylinder # 4. Further, as shown in FIG. 2C, in the third operation region, the rich cylinders are the third and fourth cylinders # 3 and # 4, and the lean cylinders are the first and second cylinders # 1 and # 2. is there.

  As shown in FIG. 2, when the engine operating region is different, the rich cylinder and the lean cylinder are different. Therefore, it is not possible to reduce the variation in the air-fuel ratio between the cylinders in all engine operation regions only by taking measures against a specific cylinder.

  One of the factors that cause the variation in the air-fuel ratio between the cylinders as described above is the variation in the fuel injection amount. The main factor is the variation in the external EGR amount between the cylinders. The external EGR amount is affected by the supercharging pressure, the exhaust pressure, and the like. For this reason, when the variation between the cylinders of the external EGR amount occurs according to the engine operation region, the variation between the cylinders of the air-fuel ratio occurs.

  When the air-fuel ratio variation between the cylinders is large, there is a possibility that the exhaust emission characteristics cannot be sufficiently improved as a whole engine. Here, in order to reduce the NOx emission amount, it is effective to increase the external EGR amount. However, since the smoke and HC emissions from the rich cylinder increase, the external EGR amount cannot be increased. As a result, the amount of NOx emission cannot be reduced, and the exhaust emission characteristics of the engine as a whole cannot be sufficiently improved.

  Therefore, in order to sufficiently improve the exhaust emission characteristics of the engine as a whole, it is necessary to make the air-fuel ratio of the rich cylinder lean and reduce the air-fuel ratio variation between cylinders. Therefore, in the present embodiment, the control described below is executed in order to reduce the air-fuel ratio variation between cylinders.

[External EGR ratio control]
In the present embodiment, by controlling the opening degree of the EGR valve 56, the ratio of the external EGR extracted from the exhaust manifold to which the rich cylinder is connected (hereinafter referred to as “external EGR ratio”) is connected to the rich cylinder. Make it higher than the external EGR ratio to be taken out from other exhaust manifolds.

  FIG. 3 is a diagram for explaining external EGR ratio control according to the present embodiment. As shown in FIG. 3, the rich cylinders are the second and third cylinders # 2 and # 3. In this case, the external EGR ratio taken out from the second EGR outlet 48 of the second exhaust manifold 35 to which the second and third cylinders # 2 and # 3 are connected is taken out from the first EGR outlet 44 of the first exhaust manifold 34. The opening degree of the EGR valve 56 is controlled to be higher than the external EGR ratio. That is, the external EGR amount taken out from the second exhaust manifold 35 is made larger than the external EGR amount taken out from the first exhaust manifold 34. As a result, the exhaust pressure of the first exhaust manifold 34 is lowered, so that the internal EGR amounts of the second and third cylinders # 2 and # 3, which are rich cylinders, are reduced and the air-fuel ratio is made lean. Therefore, the variation in air-fuel ratio between cylinders is reduced.

FIG. 4 is a diagram for explaining the NOx reduction effect obtained by the external EGR ratio control. The triangle mark in FIG. 4 represents the NOx emission amount when the external EGR ratio control is not performed, and the circle mark represents the NOx emission amount when the external EGR ratio is implemented.
As described above, by executing the external EGR ratio control, the air-fuel ratio of the rich cylinder can be made lean. If it does so, smoke and HC discharge | emission amount can be reduced. Since the external EGR amount can be increased as much as the air-fuel ratio of the rich cylinder is made leaner, the NOx emission amount can be reduced as a whole as shown in FIG. Therefore, the exhaust emission characteristics of the engine as a whole can be sufficiently improved.

[Exhaust valve opening timing control]
By controlling the variable valve mechanisms 13 and 33, a valve overlap period in which both the intake valve 12 and the exhaust valve 32 are opened can be formed. During this valve overlap period, if the exhaust pressure is higher than the intake pressure, internal EGR occurs. Therefore, the internal EGR amount increases as the exhaust pressure increases. The exhaust pressure is greatly affected by exhaust pulsation from other cylinders.

  Therefore, in this embodiment, the timing of exhaust pulsation from the specific cylinder in the rich cylinder is shifted by controlling the exhaust valve opening timing of the specific cylinder. That is, by driving the variable valve mechanism 33 to control the exhaust valve opening timing of the specific cylinder, the timing of exhaust pulsation from the specific cylinder in the rich cylinder becomes a valley. The specific cylinder is a cylinder other than the rich cylinder, and the exhaust valve is opened while the exhaust valve 32 of the rich cylinder is open. For example, when the first cylinder # 1 is a rich cylinder, the third cylinder # 3 is a specific cylinder.

FIG. 5 is a diagram for explaining exhaust valve opening timing control according to the present embodiment.
For example, when the first cylinder # 1 is a rich cylinder, the exhaust valve opening timing of the third cylinder # 3, which is a specific cylinder, is retarded from the normal opening timing as shown in FIG. The Specifically, the exhaust valve of the third cylinder # 3 is opened more slowly than usual so that the timing of the exhaust pulsation from the third cylinder # 3 shifts in the first cylinder # 1 (so that it becomes a valley). .
By performing the exhaust valve opening timing control described above, the exhaust gas absolute value of the rich cylinder (for example, the first cylinder # 1) can be made lower than a predetermined value, so that the internal EGR amount of the rich cylinder is reduced. be able to. As a result, the air-fuel ratio of the rich cylinder can be made lean, and variations in the air-fuel ratio between the cylinders can be reduced.
Therefore, similarly to the external EGR ratio control, the smoke and HC emission amount can be reduced, and the external EGR amount can be increased as much as the air-fuel ratio of the rich cylinder is made leaner. As a whole, the amount of NOx emission can be reduced. Therefore, the exhaust emission characteristics of the engine as a whole can be sufficiently improved.

By the way, as a method of shifting the timing of exhaust pulsation, not only a method of delaying the exhaust valve opening timing but also a method of making the exhaust valve opening timing earlier than the normal timing as shown in FIG. However, if the exhaust valve opening timing is made earlier than the normal timing, the exhaust valve 32 is opened with a high in-cylinder pressure. Then, there is a possibility that the exhaust pressure absolute value cannot be made lower than a predetermined value in spite of shifting the exhaust pulsation timing.
On the other hand, according to the method of delaying the exhaust valve opening timing from the normal timing as described above, the exhaust valve 32 is opened while the in-cylinder pressure is low. For this reason, by shifting the timing of the exhaust pulsation, the exhaust pressure absolute value can be surely made lower than the predetermined value. Therefore, a method of delaying the exhaust valve opening timing from the normal timing is preferable.

When the air-fuel ratio variation between cylinders is large, it is necessary to use both the above-mentioned “external EGR ratio control” and “exhaust valve opening timing control”.
Here, if the exhaust valve opening timing control is prioritized over the external EGR ratio control, the exhaust valve opening timing is excessively advanced (rapidly opened) or retarded (slowly opened) from the normal timing. Become. If the exhaust valve opening timing is excessively advanced (rapidly opened), the expansion work is greatly reduced, resulting in deterioration of fuel consumption. On the other hand, even if the exhaust valve opening timing is retarded excessively (slow opening), the pump loss increases, resulting in deterioration of fuel consumption.
Therefore, in the present embodiment, the external EGR ratio control is performed with priority over the exhaust valve opening timing control. That is, after performing the external EGR ratio control, the exhaust valve opening timing control is performed. As a result, it is possible to avoid a significant increase in the retard amount or the advance amount of the exhaust valve opening timing, and thus it is possible to reduce the variation in the air-fuel ratio while preventing the deterioration of fuel consumption. .

[Specific processing in the embodiment]
FIG. 6 is a flowchart showing a routine executed by the ECU 60 in the present embodiment.
According to the routine shown in FIG. 6, first, the air-fuel ratio of each cylinder is acquired (step 100). In this step 100, the air-fuel ratio of each cylinder detected by the air-fuel ratio sensor 42 is read. The air / fuel ratio of each cylinder may be estimated by a model from the intake pressure, exhaust pressure, intake manifold shape, EGR passage, valve shape, etc., and the estimated air / fuel ratio may be read.

  Next, the inter-cylinder difference in air-fuel ratio acquired in step 100, that is, the air-fuel ratio variation between cylinders is calculated (step 102). Then, it is determined whether or not the difference between the air-fuel ratios calculated in step 102 is greater than or equal to a reference value (step 104). In step 104, it is determined whether or not both the external EGR ratio control and the exhaust valve opening timing control need to be performed in order to reduce the air-fuel ratio variation between cylinders.

If it is determined in step 104 that the air-fuel ratio difference between the cylinders is less than the reference value, it is determined that one of external EGR ratio control and exhaust valve opening timing control may be performed. In this case, external EGR ratio control is performed (step 106). In this step 106, the external EGR ratio taken out from the exhaust manifold including the rich cylinder is made higher than the external EGR ratio taken out from other exhaust manifolds.
In this step 106, the exhaust valve opening timing control may be performed instead of the external EGR ratio control, but it is preferable to perform the external EGR ratio control because there is a possibility of deterioration of fuel consumption. Thereafter, this routine is terminated.

  On the other hand, if it is determined in step 104 that the air-fuel ratio difference between the cylinders is greater than or equal to the reference value, it is determined that both external EGR ratio control and exhaust valve opening timing control need to be performed. In this case, first, the external EGR ratio control is performed with priority (step 106A). In step 106A, the same processing as in step 106 is performed. Thereafter, exhaust valve opening timing control is performed (step 108). In this step 108, the exhaust valve opening timing of the specific cylinder is delayed from the normal timing by the control of the variable valve mechanism 33 (ExVVT control) so that the exhaust pulsation timing of the rich cylinder shifts. Since the processing of step 106 is performed prior to the processing of step 108, the retard amount or the advance amount of the exhaust valve opening timing in step 108 is not significantly increased, and deterioration of fuel consumption can be suppressed. . Thereafter, this routine is terminated.

Incidentally, in the above embodiment, the air-fuel ratio of each cylinder is detected by using one air-fuel ratio sensor 42 provided in the exhaust passage 38 upstream of the NOx catalyst 40, but each exhaust manifold 34, 35 has an empty air-fuel ratio. An air-fuel ratio sensor may be provided, and the air-fuel ratio of each cylinder may be detected using these air-fuel ratio sensors.
In the above embodiment, the system including the two exhaust manifolds 34 and 35 has been described. However, the present invention can also be applied to a system including three or more exhaust manifolds.

In the present embodiment, the first and second exhaust manifolds 34 and 35 are the “plurality of exhaust manifolds” in the first invention, and the first and second EGR passages 46 and 50 are the “plurality of exhaust manifolds” in the first invention. In the EGR passage, the air-fuel ratio sensor 42 is the “air-fuel ratio acquisition means” in the first invention, the exhaust valve 32 is the “exhaust valve” in the second invention, and the variable valve mechanism 33 is the second invention. It corresponds to each “variable valve mechanism”.
In the present embodiment, the ECU 60 executes the process of step 100, so that the “air-fuel ratio obtaining means” in the first invention executes the process of step 102, and the “cylinder” in the third invention is executed. The "external difference calculating means" executes the processing of step 106, so that the "external EGR ratio control means" in the first invention executes the processing of step 106A, and the "external EGR ratio control means in the third invention" ”, The“ exhaust valve opening timing control means ”in the second and third inventions is realized by executing the processing of step 108.

It is a figure for demonstrating the structure of the system by embodiment of this invention. It is a figure which shows the variation between cylinders of an air fuel ratio. It is a figure for demonstrating the external EGR ratio control by embodiment of this invention. It is a figure for demonstrating the NOx reduction effect obtained by external EGR ratio control. It is a figure for demonstrating the exhaust valve opening timing control by embodiment of this invention. 4 is a flowchart showing a routine executed by ECU 60 in the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 32 Exhaust valve 33 Variable valve mechanism 34 1st exhaust manifold 35 2nd exhaust manifold 42 Air-fuel ratio sensor 46 1st EGR passage 50 2nd EGR passage 60 ECU

Claims (3)

An exhaust control device for an internal combustion engine having a plurality of cylinder groups and a split exhaust manifold,
A plurality of exhaust manifolds connected to the plurality of cylinder groups;
A plurality of EGR passages connected to the plurality of exhaust manifolds;
Air-fuel ratio acquisition means for acquiring the air-fuel ratio of each cylinder of the plurality of cylinder groups;
An external EGR ratio control means for controlling the ratio of the external EGR extracted from one exhaust manifold to which a cylinder having a relatively rich air-fuel ratio is connected to be higher than the ratio of the external EGR extracted from another manifold; An exhaust control device for an internal combustion engine, comprising: The exhaust control device for an internal combustion engine according to claim 1,
A variable valve mechanism that can change the opening timing of the exhaust valve of each cylinder;
Exhaust valve opening timing control for controlling the opening timing of the exhaust valves of other cylinders using the variable valve mechanism so that the exhaust pressure of the cylinder having a relatively rich air-fuel ratio becomes lower than a predetermined value. And an exhaust control device for an internal combustion engine. The exhaust control device for an internal combustion engine according to claim 2,
Further comprising an inter-cylinder difference calculating means for calculating an inter-cylinder difference in the air-fuel ratio acquired by the air-fuel ratio acquiring means,
When the inter-cylinder difference calculated by the inter-cylinder difference calculating means is greater than or equal to a reference value, the control by the external EGR ratio control means is executed with priority over the control by the exhaust valve opening timing control means. An exhaust control device for an internal combustion engine.

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