JP2008002319A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for more efficiently recovering the performance of an exhaust emission control device in an internal combustion engine equipped with two superchargers. <P>SOLUTION: Two turbines (10a, 20a) of the two-stage superchargers are disposed in an exhaust system of the internal combustion engine and the exhaust system is provided with two bypass passages (11, 21) for bypassing the respective turbines. When recovering such performance of the exhaust emission control device 7 as NOx reduction treatment, SOx poisoning recovery treatment or PM regeneration treatment, the performance recovery treatment is performed more efficiently by changing a combination of the two turbines (10a, 20a) and the two bypass passages (11, 21) through which the exhaust gas passes. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system for purifying exhaust gas from an internal combustion engine, and more particularly to an exhaust gas purification system for an internal combustion engine equipped with a two-stage supercharger.

The exhaust gas of an internal combustion engine contains harmful substances such as NOx. In order to reduce the emission of these harmful substances, it is known to provide a NOx catalyst for purifying NOx in the exhaust gas in the exhaust system of the internal combustion engine. In this technology, for example, when a storage reduction type NOx catalyst is provided, the purification capacity decreases as the amount of stored NOx increases, so that a reducing agent is supplied to the storage reduction type NOx catalyst by performing rich spike control. The NOx occluded in the catalyst is reduced and released (hereinafter referred to as “NOx reduction treatment”).

Further, in order to eliminate SOx poisoning in which the SOx in the exhaust gas is occluded in the NOx catalyst and the purification ability is reduced, the bed temperature of the NOx catalyst is raised and a reducing agent is sometimes supplied (hereinafter referred to as “SOx regeneration” Processing "). In this SOx regeneration process, the reducing agent is also used to increase the bed temperature of the NOx catalyst.

  Further, the exhaust gas of the internal combustion engine contains particulate matter (PM) containing carbon as a main component. A technique for providing a particulate filter (hereinafter referred to as “filter”) for collecting particulate matter in an exhaust system of an internal combustion engine is known in order to prevent such particulate matter from being released into the atmosphere.

  In such a filter, when the amount of collected particulate matter increases, the back pressure in the exhaust gas increases due to clogging of the filter and the engine performance deteriorates. Therefore, the particulate matter collected by raising the temperature of the filter. Is oxidized and removed (hereinafter referred to as “PM regeneration process”). Also in this case, in order to raise the temperature of the filter, fuel as a reducing agent may be supplied to the filter.

  There is also known an internal combustion engine provided with an exhaust turbine drive supercharger (hereinafter simply referred to as “supercharger”) driven by exhaust gas on an exhaust passage in the internal combustion engine. This supercharger is a device that rotates the turbine using the energy of exhaust gas discharged from the cylinder, compresses the air by a compressor attached to the same rotating shaft as the turbine, and sends the compressed air into the cylinder It is. Furthermore, in order to achieve a higher supercharging pressure, a two-stage supercharging system including a two-stage supercharger may be employed.

Here, when performing the above-mentioned NOx reduction treatment, SOx recovery treatment, or PM regeneration treatment, when the reducing agent is supplied to the NOx storage reduction catalyst or filter by adding the reducing agent into the exhaust gas, or the occlusion In some cases, the temperature of the exhaust gas introduced into the reduced NOx catalyst or the filter is raised. In such a case, the state of the air-fuel ratio in the exhaust, the state of mixing of the reducing agent into the exhaust, the exhaust temperature, and the like may change depending on how the exhaust passes through the two-stage supercharger.

  In contrast, in a series two-stage supercharged engine, a catalyst is provided downstream of the two superchargers, a bypass passage that bypasses the turbocharger turbine is provided, and a temperature drop occurs when exhaust passes through the supercharger. The technique which suppresses is proposed (for example, refer patent document 1).

However, it has not been disclosed to actively control the state of the air-fuel ratio in the exhaust, the state of mixing of the reducing agent into the exhaust, the exhaust temperature, etc. by actively using the two-stage supercharger.
JP 2004-1000069 A JP-A 63-309727 JP 2005-344714 A

  The present invention has been made in view of the above prior art, and an object of the present invention is to perform a process for recovering the performance of the exhaust purification device more efficiently in an internal combustion engine having a two-stage supercharger. It is to provide technology that can be used.

  In order to achieve the above object, the present invention comprises two superchargers in which a turbine is disposed in an exhaust system of an internal combustion engine, and a bypass passage that bypasses each turbine independently. In the recovery process, the maximum characteristic is to promote the performance recovery process by controlling the amount of exhaust gas passing through each of the two turbines and the two bypass passages.

More specifically, the first turbine has a first turbine in the exhaust passage of the internal combustion engine and a first compressor in the intake passage, and is driven by exhaust passing through the exhaust passage to supercharge intake air to the internal combustion engine. A turbocharger,
The exhaust passage of the internal combustion engine has a second turbine downstream of the first turbine and a second compressor upstream of the first compressor in the intake passage, and is driven by exhaust gas passing through the exhaust passage. A second supercharger for supercharging intake air to the internal combustion engine;
A first bypass passage that communicates between the upstream side of the first turbine in the exhaust passage and between the first turbine and the second turbine to bypass the first turbine to exhaust from the internal combustion engine;
A second bypass passage that communicates between the first turbine and the second turbine in the exhaust passage and the downstream side of the second turbine to bypass the second turbine to exhaust from the internal combustion engine;
The exhaust passage is disposed further downstream than the junction with the second bypass passage on the downstream side of the second turbine, purifies the exhaust gas, raises the temperature, and / or is supplied with the reducing agent. An exhaust purification device that performs performance recovery processing to recover exhaust purification performance;
A reducing agent adding means disposed on the upstream side of the branch portion of the first bypass passage on the upstream side of the first turbine of the exhaust passage, and for adding a reducing agent to the exhaust gas passing through the exhaust passage;
Of the exhaust from the internal combustion engine, the amount of exhaust passing through the first turbine is larger than the amount of exhaust passing through the first bypass passage, and among the exhaust from the internal combustion engine A first exhaust control means capable of selecting any bypass state in which the amount of exhaust passing through the first bypass passage is larger than the amount of exhaust passing through the first turbine;
Of the exhaust from the internal combustion engine, the amount of exhaust that passes through the second turbine is larger than the amount of exhaust that passes through the second bypass passage, and among the exhaust from the internal combustion engine A second exhaust control means capable of selecting any bypass state in which the amount of exhaust passing through the second bypass passage is larger than the amount of exhaust passing through the second turbine;
Performance recovery promoting means for activating the first exhaust control means and / or the second exhaust control means to promote performance recovery of the exhaust emission control device when the performance recovery processing is performed. To do.

Here, in the performance recovery process of the exhaust purification device, the reducing agent may be supplied to the exhaust purification device by adding the reducing agent to the exhaust from the reducing agent adding means as described above. Also,
In some cases, the temperature of the exhaust gas purification device is raised by raising the temperature of the exhaust gas.

  In such a case, the degree of mixing of the exhaust gas and the reducing agent can be controlled by changing the amount of the exhaust gas that passes through the turbocharger turbine out of the exhaust gas from the internal combustion engine. In addition, it is possible to control the gradient of the air-fuel ratio change when the rich spike is performed. Furthermore, the exhaust loss in the internal combustion engine can be changed to control the exhaust temperature.

  Thus, exhaust gas purification is achieved by controlling the amount of exhaust gas that passes through the turbines of the two superchargers and the amount of exhaust gas that passes through the two bypass passages among the reducing agent and exhaust gas added to the exhaust gas. The performance recovery process of the apparatus can be performed more efficiently.

Next, in the present invention, as a first example of an exhaust purification system that promotes performance recovery of the exhaust purification device, the performance recovery promoting means includes the exhaust purification device including an NOx storage reduction catalyst, and the internal combustion engine When the NOx reduction process is performed when the operating state of the engine belongs to a predetermined low load region, a reducing agent is added from the reducing agent adding unit, and the performance recovery promoting unit is configured to perform the first exhaust control. An exhaust purification system in which either one of the means and the second exhaust control means is selected as a supercharging state and the other is selected as a bypass state.

Here, in the NOx reduction process for the NOx storage reduction catalyst (hereinafter simply referred to as “NOx catalyst”), it may be necessary to perform a deep rich spike process. In other words, this is a case where NOx in the NOx catalyst is released and reduced by temporarily supplying a low air-fuel ratio exhaust gas of a predetermined value or less to the NOx catalyst.

In such a case, when the exhaust gas to which the reducing agent is added passes through the supercharger, the rich exhaust portion is mixed with the exhaust gas before and after the exhaust gas to change the air-fuel ratio, thereby reducing the rich spike. May end up. Therefore, when performing the NOx reduction process in the low-load operation state, the performance recovery promoting means causes either the first exhaust control means or the second exhaust control means to select the supercharging state and the other to the bypass state. Was selected.

  Then, since the exhaust gas to which the reducing agent is added bypasses the turbine of any one of the turbochargers, the rich exhaust gas part is mixed with the exhaust gas before and after the exhaust gas, and the change of the air-fuel ratio is performed. This can be suppressed, and the thinning of the rich spike can be suppressed. A sufficiently rich rich spike can be supplied to the catalyst to increase the purification efficiency of the NOx catalyst.

  Further, the performance recovery promoting means in the present invention executes this control when the operating state of the internal combustion engine belongs to a predetermined low load region, so that the exhaust does not pass through any one of the turbocharger turbines. Can also prevent the required load from being satisfied. The operating state in the predetermined low load region is a range of operating states in which the required load can be satisfied even if the exhaust does not pass through any one of the turbocharger turbines. Also good.

  In the above case, the first supercharger is a high-pressure turbine in which the first turbine has a predetermined small-diameter impeller, and the first compressor is a high-pressure compressor having a predetermined small-diameter impeller. A supercharger, wherein the second supercharger is a low pressure turbine in which the second turbine has a predetermined large diameter impeller, and the second compressor is a low pressure compressor having a predetermined large diameter impeller. In the case of adopting the configuration of a two-stage supercharger such as a certain low-pressure supercharger, the performance recovery promoting means causes the first exhaust control means to select a supercharging state, and the second exhaust control means A bypass state may be selected.

Then, in the two-stage supercharger, in a low-load operation state, the exhaust can be passed through only to a high-pressure turbine that is relatively easy to obtain a supercharging effect, and the supercharging effect can be obtained more efficiently. it can. In the above, the diameter of the predetermined large-diameter impeller in the second turbine may be 1.2 to 1.8 times the diameter of the predetermined small-diameter impeller in the first turbine. The ratio of the diameter of the predetermined large diameter impeller in the second compressor to the diameter of the predetermined small diameter impeller in the first compressor may be the same.

  In the above, when the first exhaust control means selects the supercharging state, the first turbine is allowed to pass through substantially the entire amount of exhaust from the internal combustion engine, and the second exhaust control means is in the bypass state. When selecting, the second bypass passage may pass through substantially the entire amount of exhaust from the internal combustion engine.

  If it does so, in the 1st supercharger from which the supercharging state is selected, since the almost whole quantity of exhaust gas passes the 1st turbine, the supercharging effect can be acquired more efficiently. Further, in the second supercharger in which the bypass state is selected, since almost the entire amount of exhaust gas passes through the second bypass passage, it is possible to more reliably suppress the rich spike from becoming thinner.

  In the present invention, as a second example of the exhaust gas purification system for promoting the performance recovery of the exhaust gas purification device, the exhaust gas purification device includes an NOx storage reduction catalyst, and SOx poisoning recovery processing is performed. In this case, a reducing agent is added from the reducing agent adding means, and the performance recovery promoting means causes both the first exhaust control means and the second exhaust control means to select a supercharging state. Can be mentioned.

Here, when performing the SOx poisoning recovery process on the NOx catalyst, it is necessary to raise the temperature of the NOx catalyst. Also in this case, the reducing agent is added to the exhaust gas from the reducing agent addition means. In that case, when the mixing of the reducing agent and the exhaust is insufficient, the reducing agent cannot sufficiently react with the NOx catalyst, or the reducing agent that has reached the NOx catalyst as a droplet is carbonized, and this carbonized reducing agent As a result, the NOx catalyst may become clogged.

Therefore, in the present invention, the performance recovery promoting means causes both the first exhaust control means and the second exhaust control means to select a supercharging state. Thereby, the mixing degree of exhaust gas and a reducing agent can be raised by a two-stage turbine. As a result, the reaction of the reducing agent in the NOx catalyst can be promoted, and the temperature of the NOx catalyst can be raised more efficiently.

  Further, in the present invention, as a third example of the exhaust gas purification system that promotes the performance recovery of the exhaust gas purification device, an exhaust gas that applies the same configuration as the second example to the temperature raising process of the filter in the PM regeneration process Mention may be made of a purification system.

In the present invention, as a fourth example of the exhaust gas purification system for promoting the performance recovery of the exhaust gas purification device, the exhaust gas purification device includes an NOx storage reduction catalyst, and the operation state of the internal combustion engine is predetermined. When the NOx reduction process is performed in the case of belonging to the middle load region, a reducing agent is added from the reducing agent adding unit, and the performance recovery promoting unit includes the first exhaust control unit and the second exhaust unit. An exhaust purification system that allows both control means to select a supercharging state can be mentioned.

  Here, when the operating state of the internal combustion engine is equal to or higher than the medium load, the amount of NOx discharged by the combustion in the combustion chamber increases, so the amount of reducing agent required in the NOx reduction process also increases. In such a case, the rich spike is sufficiently dark, but since the amount of reducing agent added from the reducing agent addition valve is large, there is a possibility that the degree of mixing of the reducing agent and exhaust becomes insufficient.

Therefore, in the present invention, in the above case, the performance recovery promoting means causes both the first exhaust control means and the second exhaust control means to select the supercharging state, and the reducing agent is added. Two turbines were passed through the exhaust to improve the degree of mixing of the reducing agent and the exhaust.

  If it does so, reaction in the NOx catalyst of a reducing agent can be accelerated | stimulated and the efficiency of a NOx reduction process can be improved. In the above, the predetermined medium load operation state is an operation state that is not so high that NOx discharged from the internal combustion engine increases and the temperature of the exhaust gas is too high to reduce the efficiency of NOx reduction. Required experimentally.

Further, in the present invention, as a fifth example of the exhaust gas purification system for promoting the performance recovery of the exhaust gas purification device, the exhaust gas purification device includes an NOx storage reduction catalyst, and the operating state of the internal combustion engine is a predetermined high level. When the SOx poisoning recovery process is performed when belonging to the load region,
A reducing agent is added from the reducing agent adding means, and the performance recovery promoting means includes an exhaust purification system that allows both the first exhaust control means and the second exhaust control means to select a supercharging state. it can.

  Here, conventionally, in an internal combustion engine provided with a turbocharger having a two-stage configuration as described above, in a high-load operation state, the first bypass passage is bypassed by exhaust, particularly the first turbine on the upstream side. In many cases, the exhaust gas having a high flow rate is prevented from being throttled by the first turbine, thereby suppressing the fuel consumption from being lowered.

However, in the temperature increase control of the NOx catalyst in the SOx poisoning regeneration, if it takes time to increase the temperature of the NOx catalyst, there is a possibility that the fuel consumption may be deteriorated. Therefore, in the present invention, when the SOx poisoning recovery process is performed when the operating state of the internal combustion engine belongs to a predetermined high load region, a reducing agent is added from the reducing agent adding means, and the performance The recovery promoting means causes both the first exhaust control means and the second exhaust control means to select the supercharging state.

Then, the back pressure in the exhaust manifold of the internal combustion engine can be increased, and the exhaust loss can be increased. As a result, the load on the internal combustion engine body increases, and the exhaust temperature can be raised. Thereby, the temperature increase of the NOx catalyst can be accelerated. In addition, the two turbines can be passed through the exhaust gas to which the reducing agent is added, and the reaction of the catalyst is promoted by promoting the mixing of the reducing agent and the exhaust gas. This also accelerates the temperature rise. it can. As a result, the fuel consumption associated with the temperature rise of the NOx catalyst can be reduced.

  Further, in the present invention, as a sixth example of the exhaust gas purification system that promotes recovery of the performance of the exhaust gas purification device, an exhaust gas that applies the same configuration as the fifth example to the temperature raising process of the filter in the PM regeneration process Mention may be made of a purification system.

  The first supercharger is a high pressure turbocharger in which the first turbine is a high pressure turbine having a predetermined small diameter impeller, and the first compressor is a high pressure compressor having a predetermined small diameter impeller. And the second supercharger is a low pressure turbine in which the second turbine has a predetermined large diameter impeller, and the second compressor is a low pressure compressor having a predetermined large diameter impeller. The above-described invention may be applied when a two-stage turbocharger is used as a machine.

In particular, in the fifth and sixth examples, since a high-pressure turbine having a small-diameter impeller provided on the upstream side can be passed through a large amount of exhaust gas, the back pressure in the exhaust manifold can be further increased. And the temperature rise of the NOx catalyst and the filter can be accelerated more efficiently.

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

  In the present invention, in the internal combustion engine provided with two superchargers, the process for recovering the performance of the exhaust emission control device can be performed more efficiently.

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

  First, the internal combustion engine and the intake / exhaust system in this embodiment will be described with reference to FIG. An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1 in this embodiment. The flow of exhaust in the figure is indicated by arrows.

  The intake / exhaust system of the present embodiment is provided with two turbochargers, a first turbocharger 10 and a second turbocharger 20. The first turbine 10 a of the first turbocharger 10 is disposed in the exhaust passage 3. The second turbine 20 a of the second turbocharger 20 is disposed on the downstream side of the first turbine 10 a in the exhaust passage 3. The diameter of the impeller of the first turbine 10 a of the first turbocharger 10 is set smaller than the diameter of the impeller of the second turbine 20 a of the second turbocharger 20.

  The exhaust passage 3 is provided with a first bypass passage 11 that communicates the upstream side and the downstream side of the first turbine 10a and bypasses the first turbine 10a to the exhaust. Similarly, a second bypass passage 21 is provided for communicating the upstream side and the downstream side of the second turbine 20a to bypass the second turbine 20a in the exhaust gas. Here, the downstream side of the first bypass passage 11 and the upstream side of the second bypass passage 21 are connected to form a shared bypass passage 31. A three-way valve 13 is provided at the junction between the shared bypass passage 31 and the exhaust passage 3, and is provided on the downstream side of the first turbine 10 a, the shared bypass passage 31, and the upstream side of the second turbine 20 a. It is possible to control which one is connected.

  Further, the first bypass passage 11 is provided with a flow rate control valve 15, and by closing the flow rate control valve 15, the first turbine 10 a is allowed to pass through all of the exhaust discharged from the internal combustion engine 1. be able to.

  The exhaust passage 3 upstream of the first bypass passage 11 is provided with a fuel addition valve 5 that adds fuel as a reducing agent to the exhaust that passes through the exhaust passage 3. Furthermore, an exhaust purification device 7 for purifying exhaust gas is provided further downstream of the location where the second bypass passage 21 joins the exhaust passage 3 on the downstream side of the second turbine 20a.

  In this exhaust purification device 7, an NOx storage reduction catalyst (hereinafter simply referred to as NOx catalyst) 7a and a wall flow type particulate filter (hereinafter simply referred to as filter) 7b made of a porous base material are arranged in series. ing.

The internal combustion engine 1 and its exhaust system configured as described above are provided with an electronic control unit (ECU) 25 for controlling the internal combustion engine 1 and the exhaust system. The ECU 25 is a unit that controls the operation of the internal combustion engine 1 in accordance with the operating conditions of the internal combustion engine 1 and the request of the driver, and performs control related to the exhaust gas purification device 7 of the internal combustion engine 1.

  Sensors related to control of the operating state of the internal combustion engine 1 such as a crank position sensor (not shown), an accelerator position sensor, and an air flow meter that detects the intake air amount are connected to the ECU 25 via an electrical wiring, and an output signal is sent to the ECU 25. To be input. On the other hand, a fuel injection valve (not shown) in the internal combustion engine 1 is connected to the ECU 25 via an electric wiring, and the fuel addition valve 5, the flow control valve 15, and the three-way valve 13 in this embodiment are connected to the ECU 25 via an electric wiring. And are controlled by the ECU 25.

  The ECU 25 includes a CPU, a ROM, a RAM, and the like. The ROM stores a program for performing various controls of the internal combustion engine 1 and a map storing data.

  Here, control when performing a so-called NOx reduction process on the NOx catalyst 7a of the exhaust purification device 7 will be described.

  In this case, a rich spike process is first performed in which fuel is added from the fuel addition valve 5 into the exhaust gas. At that time, when the operation state of the internal combustion engine 1 is a low load operation state, the flow control valve 15 is closed and the three-way valve 13 is controlled to exhaust the upstream and downstream sides of the three-way valve 13. All of the passage 3 and the common bypass passage 31 are communicated. Thus, the first turbine 10a is allowed to pass through substantially the entire amount of exhaust gas to which fuel has been added. Then, the second bypass passage 21 having a low flow resistance is passed through substantially the entire amount of the exhaust gas that has passed through the first turbine 10a, thereby bypassing the second turbine 20a. Then, the exhaust gas in that state is introduced into the exhaust gas purification device 7.

  Here, when rich spike is executed and both the first turbine 10a and the second turbine 20a are passed through the exhaust with the fuel added by the fuel addition valve 5, the rich exhaust is performed at that time. The part is mixed with the exhaust before and after that, and the change of the air-fuel ratio is made. In other words, the rich spike may become thin. However, as described above, when performing a rich spike, the exhaust mixed with fuel bypasses at least one turbine, avoiding excessive mixing of the added fuel and exhaust, and a sufficiently rich rich spike. It is possible to introduce the exhaust gas having been subjected to the NOx catalyst 7 a of the exhaust gas purification device 7.

  As a result, the NOx reduction treatment of the NOx catalyst 7a can be performed more efficiently. In the present embodiment, since only the first turbine 10a having the small-diameter impeller of the two turbines is passed through the exhaust gas, a larger supercharging effect can be obtained even in a low-load operation state. Obtainable.

  In the above description, substantially the entire amount of exhaust from the internal combustion engine 1 passes through the first turbine 10a and passes through the second bypass passage 21, but the manner of passage of exhaust is not limited thereto. For example, more than half of the exhaust from the internal combustion engine 1 passes through the first turbine 10a, the rest passes through the first bypass passage 11, and more than half of the exhaust passes through the second bypass passage 21, and the rest passes through the first bypass passage 21. You may make it pass 2 turbine 20a. Even in this case, in principle, the same effect as in the present embodiment can be obtained. The same applies to the following embodiments.

  Next, the SOx recovery process of the NOx catalyst 7a of the exhaust purification device 7 and the temperature increase process in the PM regeneration process of the filter 7b will be described. The configurations of the internal combustion engine and the intake / exhaust system in the present embodiment are the same as those shown in FIG.

Here, when the SOx recovery processing of the NOx catalyst 7a of the exhaust purification device 7 and the PM regeneration processing of the filter 7b are performed, fuel as a reducing agent is added to the fuel addition valve 5 to increase the temperature of the exhaust purification device 7. May be added to the exhaust.

In this case, if the degree of mixing of the fuel and the exhaust is insufficient, the fuel may not be sufficiently oxidized by the NOx catalyst 7a of the exhaust purification device 7, or the NOx catalyst 7a may be clogged by the carbonized fuel. .

  On the other hand, in the present embodiment, when performing the temperature raising process of the exhaust purification device 7, first, fuel addition from the fuel addition valve 5 to the exhaust is performed. And the 1st turbine 10a is allowed to pass through to the whole quantity of exhaust gas by closing the flow control valve 15. In addition, the three-way valve 13 is controlled to connect the upstream and downstream exhaust passages 3b of the three-way valve 13 and the common bypass passage 31 is shut off, allowing the second turbine 20a to pass through substantially the entire amount of exhaust. Then, the exhaust gas is introduced into the exhaust gas purification device 7.

Then, since the exhaust gas to which fuel is added passes through the two turbines of the first turbine 10a and the second turbine 20a and is sufficiently mixed with the exhaust gas, it is oxidized by the NOx catalyst 7a in the exhaust purification device 7. It is easy and can raise temperature efficiently. As a result, the temperature of the filter 7b can also be raised efficiently. Further, the fuel introduced into the exhaust purification device 7 as droplets can be suppressed from being carbonized in the NOx catalyst 7a, and the exhaust purification device 7 can be prevented from being clogged.

Next, a third embodiment of the present invention will be described. In the present embodiment, an example will be described in which the degree of mixing of fuel and exhaust is improved when the NOx reduction process of the exhaust purification device is performed in an intermediate load operation state of the internal combustion engine. The configurations of the internal combustion engine and the intake / exhaust system in this embodiment are the same as those shown in FIG.

When NOx reduction processing is performed on the NOx catalyst 7a of the exhaust purification device 7, first, fuel is added to the exhaust from the fuel addition valve 5. Here, when the operation state of the internal combustion engine 1 is a medium load operation state, the combustion temperature of the combustion in the internal combustion engine 1 rises, so the amount of NOx discharged increases. Accordingly, the amount of fuel to be added from the fuel addition valve 5 is increased. As a result, in the exhaust gas introduced into the exhaust gas purification device 7, the degree of mixing of the exhaust gas and the fuel added to the exhaust gas may be insufficient.

On the other hand, in the present embodiment, when the NOx reduction process is performed in an operation state where the internal combustion engine 1 is at a medium load or higher, the flow rate control valve 15 is closed and the first turbine 10a is set to substantially the entire exhaust amount. Let it pass. Further, the three-way valve 13 is controlled to connect the upstream and downstream exhaust passages 3 of the three-way valve 13 and the common bypass passage 31 is shut off, allowing the second turbine 20a to pass through substantially the entire amount of exhaust. By doing so, the fuel added in an increased amount from the fuel addition valve 5 and the exhaust gas can be sufficiently mixed, and the NOx reduction treatment can be efficiently performed by the NOx catalyst 7a in the exhaust purification device 7.

At that time, the oxygen in the NOx catalyst 7a is efficiently consumed by the fuel, so that the reduction efficiency in the NOx catalyst 7a can also be increased.

  Next, Example 4 in the present example will be described. In the present embodiment, an example will be described in which the temperature of the exhaust emission control device is increased efficiently, particularly when the operating state of the internal combustion engine is a high-load operating state. The configurations of the internal combustion engine and the intake / exhaust system in this embodiment are the same as those shown in FIG.

  Here, conventionally, when the operation state of the internal combustion engine 1 is a high load operation state, the flow control valve 15 is opened to allow the exhaust gas to pass through the first bypass passage 11, and a large amount of exhaust gas is generated in the first turbine. In many cases, it is possible to prevent the fuel from being squeezed through 10a and to prevent the fuel consumption from deteriorating.

  However, during the SOx poisoning recovery process of the NOx catalyst 7a of the exhaust purification apparatus 7 or the PM regeneration process of the filter 7b in the present embodiment, the flow rate control valve 15 is closed to bring the first turbine 10a to substantially the entire exhaust amount. Pass through. Further, the three-way valve 13 is controlled to connect the upstream and downstream exhaust passages 3 of the three-way valve 13 and the common bypass passage 31 is shut off, allowing the second turbine 20a to pass through substantially the entire amount of exhaust.

Then, by passing a large amount of exhaust gas through the first turbine 10a having a small diameter impeller and having a small capacity, the back pressure in the exhaust manifold (not shown) upstream of the exhaust passage 3 can be increased, and the exhaust loss can be reduced. Can be increased. Then, since the load of the internal combustion engine 1 increases, the exhaust temperature can be raised, and the NOx catalyst 7a or the filter 7b of the exhaust purification device 7 can be heated more efficiently. As a result, the temperature raising time of the exhaust purification device 7 can be shortened, and the fuel consumption can be improved.

  In the above embodiment, the NOx reduction process, the SOx poisoning recovery process, and the PM regeneration process correspond to the performance recovery process. The flow control valve 15 constitutes first exhaust control means. The combination of the flow control valve 15 and the three-way valve 13 constitutes second exhaust control means. Further, the ECU 25 constitutes performance recovery promoting means.

It is a figure which shows schematic structure of the internal combustion engine and the intake / exhaust system which concern on the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake passage 3 ... Exhaust passage 5 ... Fuel addition valve 7 ... Exhaust gas purification device 7a ... NOx catalyst 7b ... Filter 10 ... First turbo Charger 10a ... First turbine 11 ... First bypass passage 13 ... Three-way valve 15 ... Flow control valve 20 ... Second turbocharger 20a ... Second turbine 25 ... ECU
31 ... Common bypass passage

Claims (11)

A first turbocharger having a first turbine in an exhaust passage of the internal combustion engine and a first compressor in an intake passage, which is driven by exhaust gas passing through the exhaust passage and supercharges intake air to the internal combustion engine; ,
The exhaust passage of the internal combustion engine has a second turbine downstream of the first turbine and a second compressor upstream of the first compressor in the intake passage, and is driven by exhaust gas passing through the exhaust passage. A second supercharger for supercharging intake air to the internal combustion engine;
A first bypass passage that communicates between the upstream side of the first turbine in the exhaust passage and between the first turbine and the second turbine to bypass the first turbine to exhaust from the internal combustion engine;
A second bypass passage that communicates between the first turbine and the second turbine in the exhaust passage and the downstream side of the second turbine to bypass the second turbine to exhaust from the internal combustion engine;
The exhaust passage is disposed further downstream than the junction with the second bypass passage on the downstream side of the second turbine, purifies the exhaust gas, raises the temperature, and / or is supplied with the reducing agent. An exhaust purification device that performs performance recovery processing to recover exhaust purification performance;
A reducing agent adding means disposed on the upstream side of the branch portion of the first bypass passage on the upstream side of the first turbine of the exhaust passage, and for adding a reducing agent to the exhaust gas passing through the exhaust passage;
Of the exhaust from the internal combustion engine, the amount of exhaust passing through the first turbine is larger than the amount of exhaust passing through the first bypass passage, and among the exhaust from the internal combustion engine A first exhaust control means capable of selecting any bypass state in which the amount of exhaust passing through the first bypass passage is larger than the amount of exhaust passing through the first turbine;
Of the exhaust from the internal combustion engine, the amount of exhaust that passes through the second turbine is larger than the amount of exhaust that passes through the second bypass passage, and among the exhaust from the internal combustion engine A second exhaust control means capable of selecting any bypass state in which the amount of exhaust passing through the second bypass passage is larger than the amount of exhaust passing through the second turbine;
Performance recovery promoting means for activating the first exhaust control means and / or the second exhaust control means to promote performance recovery of the exhaust emission control device when the performance recovery processing is performed. An exhaust purification system for an internal combustion engine. The exhaust purification device includes an NOx storage reduction catalyst,
The performance recovery process is a NOx reduction process for reducing and releasing NOx of the NOx storage reduction catalyst,
When the NOx reduction process is performed when the operating state of the internal combustion engine belongs to a predetermined low load region,
A reducing agent is added from the reducing agent addition means,
The said performance recovery promotion means makes either one of the said 1st exhaust control means or the said 2nd exhaust control means select a supercharging state, and makes the other select a bypass state, The Claim 1 characterized by the above-mentioned. An exhaust purification system for an internal combustion engine. The first supercharger is a high pressure turbocharger in which the first turbine is a high pressure turbine having a predetermined small diameter impeller, and the first compressor is a high pressure compressor having a predetermined small diameter impeller,
The second supercharger is a low pressure turbocharger in which the second turbine is a low pressure turbine having a predetermined large diameter impeller, and the second compressor is a low pressure compressor having a predetermined large diameter impeller. Yes,
The exhaust gas purification system for an internal combustion engine according to claim 2, wherein the performance recovery promoting means causes the first exhaust control means to select a supercharging state and causes the second exhaust control means to select a bypass state. . When the first exhaust control means selects the supercharging state, the first turbine is allowed to pass through substantially the entire amount of exhaust from the internal combustion engine,
The exhaust purification system for an internal combustion engine according to claim 3, wherein the second exhaust control means allows the exhaust gas from the internal combustion engine to pass through the second bypass passage when selecting the bypass state. . The exhaust purification device includes an NOx storage reduction catalyst,
The performance recovery process is a SOx poisoning recovery process for reducing and releasing SOx of the NOx storage reduction catalyst,
When the SOx poisoning recovery process is performed,
A reducing agent is added from the reducing agent addition means,
2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the performance recovery promoting unit causes both the first exhaust control unit and the second exhaust control unit to select a supercharging state. 3. The exhaust gas purification device includes a filter that collects particulate matter in the exhaust gas,
The performance recovery process is a PM regeneration process for oxidizing and removing particulate matter of the filter,
When the PM regeneration process is performed,
A reducing agent is added from the reducing agent addition means,
2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the performance recovery promoting unit causes both the first exhaust control unit and the second exhaust control unit to select a supercharging state. 3. The exhaust purification device includes an NOx storage reduction catalyst,
The performance recovery process is a NOx reduction process for reducing and releasing NOx of the NOx storage reduction catalyst,
When the NOx reduction process is performed when the operating state of the internal combustion engine belongs to a predetermined medium load region,
A reducing agent is added from the reducing agent addition means,
2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the performance recovery promoting unit causes both the first exhaust control unit and the second exhaust control unit to select a supercharging state. 3. When the SOx poisoning recovery process is performed when the operating state of the internal combustion engine belongs to a predetermined high load region,
A reducing agent is added from the reducing agent addition means,
6. The exhaust gas purification system for an internal combustion engine according to claim 5, wherein the performance recovery promoting means causes both the first exhaust control means and the second exhaust control means to select a supercharging state. When the PM regeneration process is performed when the operating state of the internal combustion engine belongs to a predetermined high load region,
A reducing agent is added from the reducing agent addition means,
The exhaust purification system for an internal combustion engine according to claim 6, wherein the performance recovery promoting means causes both the first exhaust control means and the second exhaust control means to select a supercharging state. The first supercharger is a high pressure turbocharger in which the first turbine is a high pressure turbine having a predetermined small diameter impeller, and the first compressor is a high pressure compressor having a predetermined small diameter impeller,
The second supercharger is a low pressure turbocharger in which the second turbine is a low pressure turbine having a predetermined large diameter impeller, and the second compressor is a low pressure compressor having a predetermined large diameter impeller. 10. The exhaust gas purification system for an internal combustion engine according to claim 5, wherein the exhaust gas purification system is an internal combustion engine. The first exhaust control means allows the first turbine to pass through substantially the entire amount of exhaust from the internal combustion engine when selecting the supercharging state,
The internal combustion engine according to any one of claims 5 to 9, wherein the second exhaust control means allows the second turbine to pass through substantially the entire amount of exhaust from the internal combustion engine when selecting the supercharging state. Engine exhaust purification system.

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