JP4862604B2 - Exhaust gas recirculation device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine that recirculates part of the exhaust gas of the internal combustion engine to an intake system.

As a technique for reducing the amount of nitrogen oxide (hereinafter also referred to as “NOx”) contained in the exhaust gas of an internal combustion engine, exhaust gas recirculation (hereinafter also referred to as “EGR”) in which a part of the exhaust gas is recirculated to the intake system. The device is known.

  Also, as a technology that enables EGR in a wider operating range, a low-pressure EGR passage that recirculates the exhaust gas downstream of the turbocharger turbine to the intake air passage upstream of the compressor is provided. A technique is known in which exhaust gas is recirculated using an EGR passage (see, for example, Patent Document 1).

On the other hand, in order to purify NOx and particulate matter in the exhaust gas of an internal combustion engine, a technique for providing an NOx storage reduction catalyst or a particulate filter (hereinafter referred to as “filter”) in the exhaust system of the internal combustion engine is known. Yes. When performing NOx reduction processing, SOx poisoning recovery processing, or filter PM regeneration processing of the NOx storage reduction catalyst, the reducing agent is added to the exhaust gas by adding the reducing agent into the exhaust gas. In this case, it is known that mixing of the reducing agent and the exhaust gas can be promoted by using the stirring action of the turbine by adding the reducing agent to the exhaust gas upstream of the turbocharger turbine. Yes.

However, in an internal combustion engine having a low pressure EGR passage, when the reducing agent is added to the exhaust upstream of the turbocharger turbine, the reducing agent added to the exhaust is recirculated to the intake passage by the low pressure EGR passage, In some cases, combustion in an internal combustion engine is affected.
JP-A-2005-76456 JP 2006-022808 A Japanese Patent Laid-Open No. 2004-076595 JP 2002-021539 A JP 2003-090212 A JP 2002-364212 A

  The present invention has been made in view of the above circumstances, and in particular, in an internal combustion engine that operates a plurality of superchargers using the energy of exhaust from a plurality of cylinder groups, exhaust gas is recirculated by a low-pressure EGR passage. The present invention relates to an exhaust gas recirculation device. And the objective is to suppress that the reducing agent added to exhaust_gas | exhaustion in the upstream of a supercharger goes around to an intake system by a low pressure EGR channel | path for regeneration of the purification | cleaning capability of an exhaust gas purification device.

  To achieve the above object, the present invention provides an exhaust gas recirculation device for an internal combustion engine in which the cylinders of the internal combustion engine are divided into a plurality of cylinder groups and each cylinder group has an exhaust passage and a supercharger. In the plurality of exhaust passages corresponding to the above, the greatest feature is that the exhaust passage having the low-pressure EGR passage and the exhaust passage for adding the reducing agent on the upstream side of the supercharger are separated.

More specifically, two or more cylinder groups formed by a collection of cylinders in an internal combustion engine having a plurality of cylinders;
An exhaust passage provided for each of the cylinder groups, through which exhaust from the cylinder groups passes;
A turbocharger provided for each of the cylinder groups, a turbine disposed in each of the exhaust passages, and a compressor disposed in an intake passage of the internal combustion engine;
An exhaust purification device that purifies exhaust gas that passes through the exhaust passage on the downstream side of the turbine, and that regenerates purification capacity by supplying a reducing agent;
When regenerating the purification capacity of the exhaust purification device, which is disposed upstream of the turbine in the exhaust passage, the reducing agent is added to the exhaust purification device by adding a reducing agent to the exhaust gas passing through the exhaust passage. A turbo pre-reducing agent addition means to be supplied;
A low-pressure EGR passage that is provided in a part of the exhaust passage, and has one end connected to the downstream side of the turbine in the exhaust passage and the other end connected to the upstream side of the compressor in the intake passage;
A low pressure EGR flow control device for controlling the amount of exhaust gas passing through the low pressure EGR passage;
With
The turbo pre-reducing agent addition means is provided in an exhaust passage where the low-pressure EGR passage is not provided.

  That is, the internal combustion engine in the present invention has a plurality of cylinders, and the plurality of cylinders are grouped into two or more cylinder groups. An exhaust passage is provided for each cylinder group, and a turbocharger turbine is disposed in each exhaust passage. That is, in the present invention, as many turbochargers are provided as the number of the cylinder groups. And the intake air introduced into the internal-combustion engine flows through the intake passage connected to the compressor of each supercharger.

  Further, a part of the exhaust passage is provided with a low pressure EGR passage which is connected to the downstream side of the turbine in the exhaust passage and the upstream side of the compressor of the intake passage and communicates with the low pressure EGR passage. Is provided with a low pressure EGR flow rate control device for controlling the flow rate of the exhaust gas recirculated through the low pressure EGR passage.

  Further, upstream of the turbine in a part of the exhaust passage is provided with a turbo pre-reducing agent adding means for adding a reducing agent to the exhaust when the purification ability of the exhaust purification device is regenerated. The low-pressure EGR passage is provided in an exhaust passage not provided with the turbo pre-reducing agent addition means, and the low-pressure EGR passage and the exhaust passage provided with the turbo pre-reducing agent addition means are separated. It was.

  With such a configuration, it is possible to suppress the reducing agent added to the exhaust gas from the turbo pre-reducing agent adding means from entering the intake passage of the internal combustion engine through the low pressure EGR passage.

  Further, in the present invention, all of the exhaust passages merge at the downstream side of the turbine in each exhaust passage to form a downstream exhaust passage, and one end of the low pressure EGR passage is exhausted upstream of the downstream exhaust passage. The exhaust purification device connected to the passage may be provided in the downstream exhaust passage.

  That is, all the exhaust passages join together to form a downstream exhaust passage, and a common exhaust purification device is provided in the downstream exhaust passage. The low pressure EGR passage is provided in a part of the exhaust passage before joining.

By so doing, when the purification capability of the exhaust purification device is regenerated, the purification capability of the common exhaust purification device can be more reliably regenerated by adding the reducing agent to the exhaust from the turbo pre-reducing agent addition means. Further, even if all the exhaust passages merge on the downstream side, the low pressure EGR passage,
Since it is provided in a different exhaust passage upstream from the turbo pre-reducing agent addition means, it is avoided that the reducing agent added from the turbo pre-reducing agent addition means is introduced into the low-pressure EGR passage and goes around the intake passage. it can.

  Further, in the conventional configuration in which the low pressure EGR passage is connected to the downstream side of the exhaust passage provided with the turbo pre-reducing agent addition means, the reducing agent added to the exhaust from the turbo pre-reduction agent addition means is low pressure. In order to avoid inflow into the EGR passage as it is, the connection portion between the low pressure EGR passage and the exhaust passage needs to be arranged on the downstream side of the exhaust purification catalyst.

  On the other hand, in the present invention, the low pressure EGR passage and the exhaust passage provided with the turbo pre-reducing agent addition means are separated, so the low pressure EGR passage and the exhaust passage are connected upstream of the exhaust purification device. It is possible to make it. As a result, exhaust having a relatively high pressure can be caused to flow into the low pressure EGR passage, and the controllability of exhaust gas recirculation can be improved.

  Further, in the present invention, the amount of exhaust gas passing through the high pressure EGR passage and the high pressure EGR passage having one end connected to the upstream side of the turbine in the exhaust passage and the other end connected to the downstream side of the compressor in the intake passage is controlled. The high-pressure EGR flow rate control device is provided in the exhaust passage where the turbo pre-reducing agent addition means is disposed, and the connection portion between the high-pressure EGR passage and the exhaust passage is located upstream of the turbo pre-reducing agent addition means. It may be.

  That is, in the present invention, both the high-pressure EGR passage and the low-pressure EGR passage may be provided, and the high-pressure EGR and the low-pressure EGR may be switched or used together depending on the operation state of the internal combustion engine so that the exhaust gas from the internal combustion engine can be recirculated. . The high-pressure EGR passage may recirculate the exhaust gas upstream of the turbo pre-reducing agent adding means downstream of the compressor in the intake passage.

  Then, as the internal combustion engine, the high pressure EGR and the low pressure EGR can be switched or used together, and the exhaust gas can be recirculated suitably in a wider operating state of the internal combustion engine. Further, since the high pressure EGR passage is connected to the exhaust passage on the upstream side of the turbo pre-reducing agent adding means, it is possible to suppress the reducing agent added from the turbo pre-reducing agent adding means from entering the intake passage by the high pressure EGR passage. .

  In the present invention, the reducing agent is added to the exhaust gas passing through the exhaust passage on the downstream side of the turbine in the exhaust passage provided with the low pressure EGR passage and upstream of the exhaust purification device. The turbo post-reducing agent adding means for supplying the reducing agent is further provided, and the connecting portion between the low pressure EGR passage and the exhaust passage is downstream of the turbine in the exhaust passage and upstream of the turbo post-reducing agent adding means. It may be located.

  In other words, in the present invention, the exhaust passage provided with the low pressure EGR passage may be provided with a turbo after-reductant addition means downstream of the turbocharger turbine. The low-pressure EGR passage may communicate with the upstream side of the turbo post-reductant addition means and the upstream side of the compressor in the intake passage, which is downstream of the turbine in the exhaust passage. As a result, it is possible to regenerate the purification ability of the exhaust emission control device while suppressing the reducing agent added from the post-turbo reducing agent addition means from flowing into the intake passage through the low pressure EGR passage.

  In the present invention, the post-turbo reducing agent addition means may be provided on the upstream side of the exhaust purification device in the downstream side exhaust passage. This also makes it possible to regenerate the purification ability of the exhaust emission control device while suppressing the reducing agent added from the turbo after-reducing agent addition means from flowing into the intake passage by the low pressure EGR passage.

Further, according to the present invention, when the reducing agent is supplied to the exhaust gas purification device during regeneration of the purification performance of the exhaust gas purification device, if the operating state of the internal combustion engine belongs to a predetermined low / medium load region, the turbo When the reducing agent is added from the pre-reducing agent adding unit and the operating state of the internal combustion engine belongs to a predetermined high load region, the reducing agent is added from both the turbo pre-reducing agent adding unit and the turbo post-reducing agent adding unit. You may do it.

  Then, in the low / medium load range where the exhaust flow rate is relatively small, the reducing agent added from the turbo pre-reducing agent addition means can promote atomization by the supercharger, and the purification capability of the exhaust purification device. The reproduction efficiency at the time of reproduction can be improved. Further, in a high load region that requires a relatively large amount of reducing agent, the amount of reducing agent required can be satisfied by adding the reducing agent from the turbo after-reducing agent addition means. In this high load region, since the exhaust flow rate is relatively large, atomization can be promoted for the reducing agent added from the post-turbo reducing agent addition means.

  Here, the predetermined low / medium load region is a range of operating states in which the purification ability of the exhaust purification device can be regenerated by adding the reducing agent only from the turbo pre-reducing agent addition means, Required experimentally. In addition, the predetermined high load region means that after adding the reducing agent only from the turbo pre-reducing agent addition means, it is difficult to regenerate the purification capacity of the exhaust purification device, and the exhaust flow rate is large, so the post-turbo reduction is performed. The reducing agent added from the agent addition means is within the range of operating conditions in which atomization can be sufficiently performed. The range of this operating state is obtained experimentally in advance.

  Further, in the present invention, the supercharger has a variable nozzle that can adjust the flow rate of the exhaust gas that rotates the turbine by changing the opening, and the opening of the variable nozzle in each supercharger is: The back pressure in the exhaust passage provided with the low pressure EGR passage and the exhaust passage other than that may be adjusted to be the same.

  That is, it is conceivable that the flow rate of the exhaust gas flowing through the exhaust passage differs between the exhaust passage provided with the low-pressure EGR passage and the exhaust passage not provided with the low-pressure EGR passage. Then, the back pressure differs for each cylinder group to which each exhaust passage is connected, and the influence on the operating performance of the internal combustion engine may vary for each cylinder group. Therefore, in the present invention, the variable nozzles of the supercharger provided in each exhaust passage are adjusted so that the back pressure in the exhaust passage provided with the low pressure EGR passage is equal to the back pressure in the other exhaust passage. If it does so, the back pressure of the exhaust passage connected to each cylinder group can be equalized, and the operation performance in each cylinder group can be equalized.

  In the present invention, a throttle valve for controlling the flow rate of the intake air passing through the intake passage is provided in the intake passage where the compressor of each supercharger is disposed. The opening of the throttle valve is determined by the low pressure EGR passage. You may adjust so that the back pressure in the exhaust passage provided and the exhaust passage which is not so may be made the same.

  As described above, in the present invention, the variable nozzles of the supercharger provided in each exhaust passage are adjusted so that the back pressure in the exhaust passage provided with the low pressure EGR passage and the exhaust passage other than that are equal. did. However, even in this case, the back pressure of the exhaust passage connected to each cylinder group cannot be sufficiently equalized, and the operation performance in each cylinder group may not be sufficiently equalized.

In the present invention, in such a case, the load on the compressor side of the turbocharger is adjusted by further adjusting the opening of the throttle valve in each intake passage, and the exhaust passage provided with the low pressure EGR passage and the exhaust that is not so. The back pressure in the passage may be the same. By doing so, the back pressure for each cylinder group to which each exhaust passage is connected can be equalized more reliably, and the operating performance of the internal combustion engine in each cylinder group can be made uniform.

  In the present invention, when the amount of exhaust gas recirculated through the low pressure EGR passage is equal to or greater than a predetermined allowable value in a transient state of the internal combustion engine, the high pressure EGR is cut (valve closed). The rotational speed of the supercharger related to the exhaust passage provided with the high pressure EGR passage may be increased, and the rotational speed of the supercharger related to the exhaust passage provided with the low pressure EGR passage may be decreased.

  Here, let us consider a transient state of the internal combustion engine, for example, a case where the accelerator pedal is once lowered and the accelerator is depressed again to accelerate rapidly. In such a case, EGR gas based on low pressure EGR having relatively low responsiveness is excessively introduced into the internal combustion engine, which may cause a problem such as misfire.

  In the present invention, in order to properly maintain the EGR rate of the intake air introduced into the internal combustion engine in such a transient state of the internal combustion engine, the rotational speed of the supercharger related to the high-pressure EGR with high responsiveness is increased, The rotational speed of the supercharger related to the low-pressure EGR with low responsiveness was reduced.

  Specifically, the rotational speed of the supercharger may be reduced by opening a variable nozzle of the supercharger related to the exhaust passage provided with the low pressure EGR passage. Further, the rotational speed may be increased by closing the variable nozzle of the supercharger related to the exhaust passage provided with the high pressure EGR passage. Further, by the control such as reducing the amount of exhaust passing through the high pressure EGR passage by the high pressure EGR flow control device or increasing the amount of intake air introduced into the supercharger related to the exhaust passage provided with the high pressure EGR passage. The supercharger according to the high pressure EGR may be operated under a condition with good supercharging efficiency.

  By doing so, it is possible to increase the flow rate of EGR gas by the high-pressure EGR with high responsiveness and decrease the flow rate of EGR gas by the low-pressure EGR with low responsiveness, and improve the responsiveness as a whole of the EGR in a transient state. Can do. As a result, inconveniences such as misfire caused by excessive introduction of EGR gas into the internal combustion engine in a transient state can be suppressed.

  Here, the predetermined permissible value is that in the transient state of the internal combustion engine, if the amount of exhaust gas recirculated by the low-pressure EGR having low responsiveness is more than this, there is a possibility that inconvenience such as misfire may occur. The amount of EGR gas as a threshold value to be determined, and may be obtained experimentally in advance.

  The means for solving the problems in the present invention can be used in combination as much as possible.

  In the present invention, in an internal combustion engine that operates a plurality of superchargers using the energy of exhaust from a plurality of cylinder groups, exhaust gas is exhausted upstream of the supercharger in order to regenerate the purification capability of the exhaust purification device. It is possible to suppress the reducing agent added to the air from entering the intake system by the low pressure EGR passage.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine, an intake / exhaust system, and a control system to which the present invention is applied. The internal combustion engine shown in FIG. 1 is a V-type 8-cylinder internal combustion engine having a right bank 1 and a left bank 51 and having four cylinders 2 and 52 in each bank 1 and 51. Here, the four cylinders 2 and 52 formed in each bank 1 and 51 correspond to each cylinder group in the present embodiment.

  A common intake manifold 3 is connected to the left and right banks 1 and 51 of the internal combustion engine, and each branch pipe of the intake manifold 3 is connected to the combustion chambers of the cylinders 2 and 52 of the left and right banks 1 and 51 via an intake port. It is communicated. The intake manifold 3 is connected to a common intake pipe 5 upstream. A surge tank 6 is provided in the common intake pipe 5. An intercooler 7 for cooling the intake air before flowing into the common intake pipe 5 is provided further upstream of the common intake pipe 5.

  The common intake pipe 5 branches into a right intake pipe 8 and a left intake pipe 58 upstream of the intercooler 7. The right intake pipe 8 is provided with a right throttle valve 9 that can change the cross-sectional area of the right intake pipe 8. The right throttle valve 9 is connected to an ECU 35, which will be described later, via an electrical wiring, and the flow rate of the intake air flowing through the right intake pipe 8 is adjusted by controlling the valve opening degree based on a control signal from the ECU 35. I can do things. A compressor 10 a of the right supercharger 10 that operates using exhaust energy as a drive source is provided upstream of the throttle valve 9. The right intake pipe 8 further upstream of the compressor 10a is provided with an air flow meter and an air cleaner (not shown).

  On the other hand, the left intake pipe 58 is provided with a compressor 60a of the left supercharger 60 that operates using exhaust energy as a drive source. A left throttle valve 59 capable of changing the cross-sectional area of the left intake pipe 58 is provided upstream of the compressor 60a. The left throttle valve 59 is also connected to the ECU 35 via electric wiring, and the flow rate of the intake air flowing through the left intake pipe 58 can be adjusted by controlling the valve opening degree based on a control signal from the ECU 35. it can.

  Next, the exhaust system of the internal combustion engine will be described. A right exhaust manifold 4 is connected to the right bank 1 of the internal combustion engine, and each branch pipe of the right exhaust manifold 4 communicates with a combustion chamber of each cylinder 2 of the right bank 1 through an exhaust port. A turbine 10 b of the right supercharger 10 is connected to the right exhaust manifold 4. A right exhaust pipe 12 is connected to an opening through which the exhaust of the turbine 10b flows.

  A left exhaust manifold 54 is connected to the left bank 51 of the internal combustion engine, and each branch pipe of the left exhaust manifold 54 communicates with the combustion chamber of each cylinder 2 of the left bank 51 through an exhaust port. The left exhaust manifold 54 is connected to the turbine 60b of the left supercharger 60. A left exhaust pipe 62 is connected to an opening through which the exhaust of the turbine 60b flows out.

The right exhaust pipe 12 and the left exhaust pipe 62 merge downstream to form the collective exhaust pipe 15. The collective exhaust pipe 15 is provided with a DPNR 20 for purifying NOx and particulate matter in exhaust gas passing therethrough. On the downstream side of the DPNR 20, the collective exhaust pipe 15 is open to the atmosphere. The collective exhaust pipe 15 corresponds to a downstream exhaust passage in the present embodiment. In this embodiment, in order to purify NOx and particulate matter in the exhaust gas passing through the collective exhaust pipe 15, the DPNR 20
The NOx storage reduction catalyst and the filter for collecting the particulate matter may be arranged in series.

Here, the right exhaust manifold 4 and the downstream side of the right throttle valve 9 of the right intake pipe 8 are communicated with each other through a high pressure EGR passage 22. The high-pressure EGR passage 22 is provided with a high-pressure EGR valve 23 that controls the flow rate of exhaust gas that passes through the high-pressure EGR passage 22. The high pressure EGR valve 23 is connected to the ECU 35 via an electrical wiring, and the amount of exhaust flowing through the high pressure EGR passage 22 may be adjusted by controlling the valve opening degree based on a control signal from the ECU 35. it can. The high pressure EGR passage 22 and the high pressure EGR valve 23 constitute a high pressure EGR device 30. (Hereinafter, the exhaust gas flowing through the high pressure EGR passage 22 is referred to as “high pressure EGR gas”, and the amount thereof is referred to as “high pressure EGR gas amount”).

  On the other hand, the left exhaust pipe 62 and a portion of the left intake pipe 58 between the left compressor 60a and the left throttle valve 59 are communicated with each other through a low pressure EGR passage 72. The low pressure EGR passage 72 passes through the low pressure EGR passage 72. A low pressure EGR valve 73 for controlling the exhaust flow rate is provided. The low pressure EGR valve 73 is also connected to the ECU 35 via electric wiring, and the amount of exhaust flowing through the low pressure EGR passage 72 may be adjusted by controlling the valve opening degree based on a control signal from the ECU 35. it can. The low pressure EGR passage 72 and the low pressure EGR valve 73 constitute a low pressure EGR device 80. (Hereinafter, the exhaust gas flowing through the low pressure EGR passage 72 is referred to as “low pressure EGR gas”, and the amount thereof is referred to as “low pressure EGR gas amount”).

  Further, the right exhaust manifold 4 is provided with a pre-turbo fuel addition valve 25 that adds a reducing agent to the exhaust when the purification ability of the DPNR 20 is regenerated. On the other hand, on the upstream side of the DPNR 20 in the collective exhaust pipe 15, there is also provided a post-turbo fuel addition valve 26 that adds a reducing agent to the exhaust when the purification ability of the DPNR 20 is regenerated. The pre-turbo fuel addition valve 25 corresponds to a pre-turbo reducing agent addition unit in the present embodiment, and the post-turbo fuel addition valve 26 corresponds to a post-turbo reducing agent addition unit.

  The internal combustion engine is also provided with an ECU 35 that is an electronic control computer. The ECU 35 includes a ROM, a RAM, a CPU, an input port, an output port, and the like (not shown), and performs known control such as fuel injection according to the operation state of the internal combustion engine 1 detected by various sensors and requests from the driver. The opening degree command signal is output to the high pressure EGR valve 23, the low pressure EGR valve 73, the right throttle valve 9, and the left throttle valve 59.

  In the above configuration, the air introduced into the right intake pipe 8 and the left intake pipe 58 is supercharged by the right compressor 10a and the left compressor 60a, and via the intercooler 7, the surge tank 6, and the intake manifold 3. It is introduced into each cylinder 2 and 52 of the right bank 1 and the left bank 51 of the internal combustion engine.

  Exhaust gas discharged from the cylinders 2 and 52 passes through the right exhaust manifold 4 and the left exhaust manifold 54 and flows into the right turbine 10b and the left turbine 60b to drive the turbine. After that, after passing through the right exhaust pipe 12 and the left exhaust pipe 62 and joining in the collective exhaust pipe 15, the particulate matter and NOx in the exhaust are collected in the DPNR 20, and finally discharged into the atmosphere.

  Here, when the low pressure EGR valve 73 is opened, the low pressure EGR passage 72 becomes conductive, and a part of the exhaust gas passing through the left exhaust pipe 62 flows into the left intake pipe 58 via the low pressure EGR passage 72. . The low-pressure EGR gas flowing into the left intake pipe 58 is supercharged by the left compressor 60a, and is introduced into the cylinders 2 and 52 of the banks 1 and 51 of the internal combustion engine via the intercooler 7, the surge tank 6, and the intake manifold 3. The

  When the high-pressure EGR valve 23 is opened, the high-pressure EGR passage 22 becomes conductive, and a part of the exhaust gas flowing through the right exhaust manifold 4 flows into the right intake pipe 8 via the high-pressure EGR passage 22 and the intercooler 7 Then, they are recirculated to the cylinders 2 and 52 of the banks 1 and 51 of the internal combustion engine via the surge tank 6 and the intake manifold 3.

  By recirculating a part of the exhaust gas to the cylinders 2 and 52 of the internal combustion engine by the high pressure EGR passage 22 and / or the low pressure EGR passage 72, the combustion temperature in the combustion chamber is lowered and the amount of NOx generated in the combustion process is lowered. Can be made.

  In this embodiment, the high pressure EGR valve 23 corresponds to a high pressure EGR flow rate control device. The low pressure EGR valve 73 corresponds to a low pressure EGR flow control device.

  Thus, in the present embodiment, a part of the exhaust discharged from the right bank 1 of the internal combustion engine is recirculated by the high pressure EGR device 30 and a part of the exhaust discharged from the left bank 51 is low pressure EGR device 80. The exhaust gas can be recirculated by either one of the high pressure EGR device 30 and the low pressure EGR device 80 for each bank.

<Reducing agent (fuel) addition control>
Next, the control when performing the NOx reduction process of DPNR 20 in the present embodiment will be described. In this embodiment, when the operation state of the internal combustion engine when performing the NOx reduction process of the DPNR 20 is a low to medium load operation state, it passes through the right exhaust manifold 4 from the pre-turbo fuel addition valve 25. Add fuel to the exhaust. The fuel added to the exhaust gas is supplied to the DPNR 20 after passing through the right exhaust pipe 12 and the collective exhaust pipe 15 after passing through the turbine 10 b of the right supercharger 10.

Here, as described above, in this embodiment, the right bank 1 side is provided with the high pressure EGR passage 22, the high pressure EGR valve 23, and the pre-turbo fuel addition valve 25, and the left bank 2 side is provided with the low pressure EGR passage 72. And a low-pressure EGR valve 73 is provided. The high pressure EGR passage 22 is provided on the upstream side of the pre-turbo fuel addition valve 25. Therefore, even if fuel is added from the pre-turbo fuel addition valve 25 during the NOx reduction process of the DPNR 20, there is no possibility that the added fuel will enter the high-pressure EGR passage 22 or the low-pressure EGR passage 72 and be introduced into the internal combustion engine. .

  In addition, when fuel is added from the pre-turbo fuel addition valve 25, if there is a possibility that the added fuel may enter the low-pressure EGR passage 72 and be introduced into the internal combustion engine, the low-pressure EGR passage 72 is connected to the DPNR 20. It is necessary to connect to the collective exhaust pipe 15 on the downstream side. This is because the fuel added from the pre-turbo fuel addition valve 25 is oxidized and removed by the catalyst and is not introduced into the low-pressure EGR passage 72. However, in the present embodiment, since the fuel from the pre-turbo fuel addition valve 25 is not introduced into the low pressure EGR passage 72, the low pressure EGR passage 72 is connected to the collecting exhaust pipe 15 on the upstream side of the DPNR 20. May be.

  As a result, the exhaust gas can be passed through the low pressure EGR passage 72 in a state where the exhaust gas pressure is higher, and the controllability of the low pressure EGR gas amount can be improved.

In general, since the exhaust gas flow rate is small in the low to medium load operating state, there is a possibility that the fuel added to the exhaust gas and the exhaust gas are not sufficiently mixed during the NOx reduction process. On the other hand, in the present embodiment, since the fuel is added from the pre-turbo fuel addition valve 25, the exhaust gas and the fuel are agitated by the turbine 10b of the right supercharger 10, and both can be sufficiently mixed.

Further, in this embodiment, when the NOx reduction process of the DPNR 20 is performed in a high load operation state, if the amount of added fuel is insufficient with the amount added from the pre-turbo fuel addition valve 25, the post-turbo fuel addition valve From 26, fuel was added.

  By doing so, sufficient fuel can be supplied to the DPNR 20 even in a high-load operation state in which the amount of added fuel tends to be insufficient. Further, the exhaust flow rate is large in a high-load operation state, and the fuel and the exhaust gas can be sufficiently mixed by adding fuel from the post-turbo fuel addition valve 26. Further, in this embodiment, the low pressure EGR passage 72 is connected to the left exhaust pipe 62 on the upstream side of the post-turbo fuel addition valve 26, so that the fuel added to the low pressure EGR passage 72 from the post-turbo fuel addition valve 26 There is no risk of sneaking around.

<Back pressure control>
Next, in the present embodiment, control for equalizing back pressure in the right bank 1 and the left bank 51 will be described. In the present embodiment, as described above, the exhaust system of the right bank 1 is provided with the high pressure EGR device 30, and the exhaust system of the left bank 51 is provided with the low pressure EGR device 80. Then, since the paths differ between the exhaust system related to the right bank 1 and the exhaust system related to the left bank 51, the right supercharger 10 and the left supercharger 60 may have different exhaust flow rates. Then, the back pressure in the right bank 1 and the left bank 51 is different, and there is a possibility that the driving performance is different for each bank.

  Therefore, in this embodiment, the turbine 10b of the right supercharger 10 and the turbine 60b of the left supercharger 60 are provided with variable nozzles (not shown). And the opening degree of the variable nozzle in the right supercharger 10 and the left supercharger 60 is controlled independently, so that the back pressure in the right bank 1 and the left bank 51 is equalized. Here, for example, an exhaust pressure sensor (not shown) is provided in the right exhaust manifold 4 and the left exhaust manifold 54, and the opening of the variable nozzle is set so that the output values of the exhaust pressure sensors in the right exhaust manifold 4 and the left exhaust manifold 54 are the same. You may control. Or you may control the opening degree of each variable nozzle so that the rotation speed of the turbine 10b of the right supercharger 10 and the turbine 60b of the left supercharger 60 may become the same.

  If it does so, the back pressure in the right bank 1 and the left bank 51 can be equalized, and the driving | operation performance as the whole internal combustion engine can be improved.

  By the way, as described above, even if the opening degrees of the variable nozzles of the right supercharger 10 and the left supercharger 60 are controlled, it is difficult to equalize the back pressure in the right bank 1 and the left bank 51. There is a case. In such a case, the left supercharging is controlled by controlling the opening degree of the right throttle valve 9 and the left throttle valve 59 and independently controlling the amount of fresh air flowing into the right intake pipe 8 and the left intake pipe 58. The supercharging pressure and the transient EGR amount of the machine 10 and the right supercharger 60 may be controlled. If it does so, the driving performance in the right bank 1 and the left bank 51 can be made uniform more reliably, and the driving performance as the whole internal combustion engine can be improved.

<Control of EGR gas amount in transient state>
Next, control of the amount of EGR gas in an excessive state of the internal combustion engine according to this embodiment will be described.

  Here, consider a transient state of the internal combustion engine, for example, a case where the amount of depression of an accelerator pedal (not shown) is once decreased and then the accelerator pedal is depressed again to accelerate rapidly. In such a case, the amount of low-pressure EGR gas recirculated by the low-pressure EGR device 80 with relatively low responsiveness cannot follow the change in the operating state of the internal combustion engine, and is excessively introduced into the internal combustion engine, causing misfires, etc. There was a risk of problems.

  Therefore, in the present embodiment, in the transient state as described above, the variable nozzle of the left supercharger 60 is opened to reduce the rotational speed of the turbine 60b, and the right supercharger 10 is closed with the variable nozzle closed. Increase the rotational speed of 10b. Then, introduction of fresh air from the right intake pipe 8 can be promoted, and introduction of low-pressure EGR gas from the left intake pipe 58 can be suppressed.

  Thereby, the amount of low-pressure EGR gas introduced into the internal combustion engine can be suppressed, and an excessive amount of low-pressure EGR gas in a transient state can be eliminated. Moreover, since the ratio of the amount of high-pressure EGR gas can be relatively increased and the ratio of the amount of low-pressure EGR gas can be relatively decreased, the responsiveness of the entire EGR gas can be improved.

  In this case, it is desirable to change the opening degree of the high pressure EGR valve 23 in the valve closing direction. The throttle valve 9 is preferably changed in the valve opening direction. By doing so, fresh air can be introduced into the internal combustion engine from the right intake pipe 8 more efficiently, and the amount of low-pressure EGR gas introduced into the internal combustion engine can be suppressed more efficiently.

  In the above configuration, in order to prevent the high pressure EGR valve 23 and the low pressure EGR valve 73 from being clogged, the upstream side of the high pressure EGR valve 23 in the high pressure EGR passage 22 and the upstream side of the low pressure EGR valve 73 in the low pressure EGR passage 72. An oxidation catalyst may be provided on the side.

  Further, in the above configuration, the high pressure EGR passage 22 may be directly connected to the surge tank 6 instead of being connected to the right intake pipe 8.

  In the present embodiment, the example in which the right exhaust pipe 12 and the left exhaust pipe 62 merge on the downstream side of the supercharger to form the collective exhaust pipe 15 and the collective exhaust pipe 15 is provided with the DPNR 20 has been described. However, the present invention may be applied to a configuration in which the right exhaust pipe 12 and the left exhaust pipe 62 do not merge and the two exhaust pipes are independently provided with DPNR.

Even in this case, the exhaust pipe provided with the pre-turbo fuel addition valve and the exhaust pipe provided with the low pressure EGR passage are separated from each other in the NOx reduction process of DPNR in each exhaust pipe. Even if fuel is added, there is no possibility that the added fuel will enter the low-pressure EGR passage and be introduced into the internal combustion engine.

  In addition, as described above, since the exhaust pipe provided with the pre-turbo fuel addition valve and the exhaust pipe provided with the low-pressure EGR passage are separated from each other, the present invention has a feature. May be applied to an internal combustion engine that is not provided with a high pressure EGR passage and is provided with only a low pressure EGR passage.

  In the above embodiment, the internal combustion engine is a V-type internal combustion engine, and the four cylinders 2 and 52 provided in the banks 1 and 51 correspond to the cylinder group, respectively, but the present invention is applied. Is not limited to a V-type internal combustion engine. For example, three cylinders of an in-line 6-cylinder internal combustion engine may be divided into two cylinder groups, and a low pressure EGR device and a pre-turbo fuel addition valve may be assigned to each cylinder group.

Further, in the above embodiment, the fuel addition control in the NOx reduction process of the DPNR 20 has been described, but it is needless to say that the same idea may be applied to the SOx poisoning recovery process and the PM regeneration process of the DPNR 20.

It is a figure which shows schematic structure of the internal combustion engine in the Example of this invention, its intake / exhaust system, and a control system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Right bank 2 ... Cylinder 3 ... Intake manifold 4 ... Right exhaust manifold 5 ... Common intake pipe 6 ... Surge tank 7 ... Intercooler 8 ... Right intake pipe 9 ... Right throttle valve 10 ... Right supercharger 12 ... Right exhaust pipe 15 ... Collective exhaust pipe 20 ... DPNR
30 ... High pressure EGR device 51 ... Left bank 52 ... Cylinder 54 ... Left exhaust manifold 58 ... Left intake pipe 59 ... Left throttle valve 60 ... Left supercharger 62 ...・ Left exhaust pipe 72 ... Low pressure EGR passage 73 ... Low pressure EGR valve 80 ... Low pressure EGR device 35 ... ECU

Claims (8)

Two or more cylinder groups formed by a collection of cylinders in an internal combustion engine having a plurality of cylinders;
An exhaust passage provided for each of the cylinder groups, through which exhaust from the cylinder groups passes;
A turbocharger provided for each of the cylinder groups, a turbine disposed in each of the exhaust passages, and a compressor disposed in an intake passage of the internal combustion engine;
An exhaust purification device that purifies exhaust gas that passes through the exhaust passage on the downstream side of the turbine, and that regenerates purification capacity by supplying a reducing agent;
When regenerating the purification capacity of the exhaust purification device, which is disposed upstream of the turbine in the exhaust passage, the reducing agent is added to the exhaust purification device by adding a reducing agent to the exhaust gas passing through the exhaust passage. A turbo pre-reducing agent addition means to be supplied;
A low-pressure EGR passage that is provided in a part of the exhaust passage, and has one end connected to the downstream side of the turbine in the exhaust passage and the other end connected to the upstream side of the compressor in the intake passage;
A low pressure EGR flow control device for controlling the amount of exhaust gas passing through the low pressure EGR passage;
With
The turbo pre-reducing agent addition means is provided in an exhaust passage where the low-pressure EGR passage is not provided,
All of the exhaust passages merge on the downstream side of the turbine in each exhaust passage to form a downstream exhaust passage,
One end of the low-pressure EGR passage is connected to the exhaust passage upstream of the downstream exhaust passage,
The exhaust gas recirculation device for an internal combustion engine, wherein the exhaust gas purification device is provided in the downstream exhaust passage . A high pressure EGR passage provided in an exhaust passage in which the turbo pre-reducing agent addition means is disposed, one end connected to the upstream side of the turbine in the exhaust passage and the other end connected to the downstream side of the compressor in the intake passage. When,
A high pressure EGR flow control device for controlling the amount of exhaust gas passing through the high pressure EGR passage;
Further comprising
2. The exhaust gas recirculation device for an internal combustion engine according to claim 1 , wherein a connection portion between the high-pressure EGR passage and the exhaust passage is located upstream of the turbo pre-reducing agent adding means in the exhaust passage. A reducing agent is added to the exhaust gas purification device by adding a reducing agent to the exhaust gas passing through the exhaust gas passage on the downstream side of the turbine in the exhaust gas passage provided with the low pressure EGR passage and upstream of the exhaust gas purification device. Further comprising a turbo after-reducing agent addition means for supplying
Connection portion between the exhaust passage and the low-pressure EGR passage, in claim 1 or 2, characterized in that a downstream side of the turbine in the exhaust passage located upstream of the turbo after reducing agent addition means An exhaust gas recirculation device for an internal combustion engine as described. The post-turbo reducing agent addition that is provided on the upstream side of the exhaust purification device in the downstream exhaust passage and supplies the reducing agent to the exhaust purification device by adding the reducing agent to the exhaust that passes through the downstream exhaust passage. The exhaust gas recirculation device for an internal combustion engine according to claim 1 , further comprising means. When the reducing agent is supplied to the exhaust gas purification device during regeneration of the purification capacity of the exhaust gas purification device, if the operating state of the internal combustion engine belongs to a predetermined low / medium load region, the turbo prereductant When the reducing agent is added from the adding means and the operating state of the internal combustion engine belongs to a predetermined high load region, the reducing agent is added from both the pre-turbo reducing agent adding means and the post-turbo reducing agent adding means. The exhaust gas recirculation device for an internal combustion engine according to claim 4 . The supercharger has a variable nozzle that can adjust the flow rate of exhaust gas that rotates the turbine by changing the opening degree,
The opening degree of the variable nozzle in each supercharger claim 1, wherein said exhaust passage pressure EGR passage is provided, to be adjusted in order to back pressure the same in an exhaust passage otherwise The exhaust gas recirculation device for an internal combustion engine according to any one of claims 1 to 5 . In the intake passage where the compressor of each supercharger is arranged, a throttle valve for controlling the flow rate of the intake air passing through the intake passage is provided,
7. The internal combustion engine according to claim 6 , wherein the opening degree of the throttle valve is adjusted so that back pressures in the exhaust passage provided with the low pressure EGR passage and the exhaust passage other than the exhaust passage are the same. Exhaust gas recirculation device. In the transient state of the internal combustion engine, when the amount of exhaust gas that passes through the low pressure EGR passage and is recirculated to the internal combustion engine is equal to or greater than a predetermined allowable value,
Claims wherein with the high-pressure EGR passage increases the rotational speed of the supercharger according to an exhaust passage provided, wherein said that the low-pressure EGR passage to reduce the rotational speed of the supercharger according to an exhaust passage provided Item 3. An exhaust gas recirculation device for an internal combustion engine according to Item 2 .

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