JP2006299967A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate installation of an addition valve without changing the design of a cylinder head and to maximize the effectiveness of an additive agent, in an exhaust emission control system for an internal combustion engine 1 including a catalytic converter and the additive agent addition valve for recovering the cleanup capability of the catalytic converter. <P>SOLUTION: In the exhaust emission control system, the addition valve 10 is attached to the outer side of an exhaust manifold 41 upstream of the catalytic converter 8, the exhaust manifold 41 being one of exhaust passages 41, 42 and connected to exhaust ports 4 of the internal combustion engine 1. By thus externally providing the addition valve 10 on the exhaust manifold 41, it is unnecessary to change the design of the cylinder head as in the conventional system and it is possible to relatively easily install the addition valve. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust purification system used for an internal combustion engine mounted on a vehicle such as an automobile.

  Generally, an internal combustion engine purifies exhaust gas by a catalytic converter installed in an exhaust passage.

Particulate matter (PM) in exhaust gas (PM) under operating conditions in which the temperature of the combustion chamber and the exhaust temperature are low, such as cold operation, start-up operation, and low-speed low-load operation
In addition, the mixing amount of nitrogen oxides (NOx) tends to increase, and the catalyst bed temperature of the catalytic converter may become low, resulting in insufficient purification capacity.

  For this reason, there is a demand for recovering the catalytic converter by actively reducing NOx when the NOx absorption amount of the catalytic converter is saturated. In contrast, the following techniques have been conventionally considered.

  First, in a diesel engine having a catalytic converter using a NOx absorbent, hydrocarbons are obtained by thermally decomposing fuel by adding a NOx reducing agent (light oil) as needed upstream of the catalytic converter in the exhaust passage. This hydrocarbon is used as a reducing agent to promote the reduction of NOx absorbed by the NOx absorbent in the catalytic converter (see Patent Document 1). The reducing agent addition device is installed in the vicinity of the exhaust port of the cylinder head.

Further, in a diesel engine equipped with a catalytic converter such as a particulate filter capable of removing PM and equipped with a turbocharger, fuel (light oil) is added upstream of the catalytic converter in the exhaust passage as necessary. The fuel is pyrolyzed to generate hydrocarbons, and the hydrocarbons are reacted in the catalytic converter to raise the catalyst bed temperature of the catalytic converter (see Patent Document 2). The fuel addition device is installed in a region from the downstream of the turbine of the turbocharger to the upstream of the catalytic converter in the exhaust passage.
JP 2002-21539 A JP 2004-197635 A

  In any of the above conventional examples, although the purification ability of the catalytic converter can be positively recovered, there is room for improvement in the following points.

  In the conventional example according to Patent Document 1, the additive added to the exhaust port is blown back to the periphery of the exhaust port due to the influence of the exhaust pulsation, and the additive easily deposits and accumulates on the wall surface of the exhaust port. In order to install the reducing agent addition device in the engine, it is necessary to change the design of the cylinder head.

  In the conventional example according to Patent Document 2, since the distance from the fuel addition device to the catalytic converter is relatively short, the added fuel is less likely to atomize, and there is a concern that the effectiveness due to the addition of fuel becomes insufficient.

  The present invention provides an exhaust gas purification system for an internal combustion engine that includes a catalytic converter and an additive addition valve that recovers the purification ability of the catalytic converter, without changing the design of the cylinder head as in the conventional example. The purpose is to increase the effectiveness of the additive while making it relatively easy to install.

  An exhaust purification system for an internal combustion engine according to the present invention includes a catalytic converter that is provided in an exhaust passage of the internal combustion engine and purifies exhaust gas discharged to the exhaust passage, and an additive for recovering the purification capability of the catalytic converter. An addition valve for addition is provided, wherein the addition valve is attached outside the upstream portion of the catalytic converter in an exhaust manifold connected to an exhaust port of an internal combustion engine in the exhaust passage. Yes.

  The “additive” preferably contains a hydrocarbon (HC) component. For example, the type of fuel (light oil, gasoline, etc.) used in the target internal combustion engine, other dissimilar fuels, kerosene, etc. It can be.

The “catalytic converter” includes a type that uses a NOx absorbent and a type that captures particulate matter (PM) in exhaust gas as well as NOx purification.

  Here, in the former type of catalytic converter, the additive is thermally decomposed in the exhaust gas upstream of the catalytic converter by the addition of the additive, so that a large amount of hydrocarbon is generated. NOx that has already been absorbed is reduced, and the absorption capacity of the NOx absorbent is restored.

  In the latter type of catalytic converter, in addition to the above action, the additive is thermally decomposed in the exhaust gas upstream of the catalytic converter to generate a large amount of hydrocarbons. Reaction occurs in the catalytic converter, and the catalytic converter is heated by the reaction heat. As a result, PM already captured in the catalytic converter is incinerated, and the purification ability of the catalytic converter is restored.

  Since such an addition valve is externally installed on the exhaust manifold, it is possible to easily install the addition valve without changing the design of the cylinder head as in the conventional example when installing the addition valve.

  Furthermore, since the position of the addition valve is specified, it is difficult for the additive injected into the exhaust manifold to be blown back around the exhaust port due to the exhaust pulsation. Therefore, compared to the conventional example in which an additive is added to the exhaust port, the additive is less likely to adhere and deposit as a deposit on the wall surface of the exhaust port.

  By the way, in the exhaust purification system, the addition valve may be attached to the exhaust manifold in such a posture that the additive can be injected toward a collection portion of the exhaust manifold.

  According to this configuration, the additive is smoothly guided downstream from the exhaust manifold, which is further advantageous in suppressing the phenomenon in which the additive adheres to and accumulates on the exhaust port wall surface.

In the exhaust purification system, the addition valve may be attached to the exhaust manifold in a state of being supported by a holder separate from the exhaust manifold.

  According to this configuration, the addition valve can be easily attached to the exhaust manifold, and direct heat conduction from the exhaust manifold to the addition valve can be avoided by the holder, which is advantageous in suppressing the temperature increase of the addition valve. It becomes. As a result, thermal deterioration of the additive in the addition valve can be suppressed or prevented, and clogging of the addition valve is avoided.

  In the exhaust gas purification system, a heat insulating gasket may be interposed between the holder and the exhaust manifold.

  According to this configuration, heat conduction from the exhaust manifold to the addition valve can be reduced, so that thermal deterioration of the additive in the addition valve can be suppressed or prevented, and clogging of the addition valve is avoided. The

  In the exhaust gas purification system, the portion provided with the addition valve in the exhaust manifold is provided with a bulging portion that bulges outward, and the holder can be attached to the bulging portion by a flange connection. .

  According to this configuration, heat conduction from the exhaust manifold to the addition valve can be reduced, and a water jacket for cooling the addition valve can be installed in the holder. It becomes possible.

  The exhaust purification system further includes an exhaust gas recirculation device that returns a part of the exhaust gas discharged to the exhaust passage to the intake system of the internal combustion engine, and the addition valve is connected to the exhaust passage from the exhaust passage in the exhaust gas recirculation device. It can be arranged at a position farthest from the exhaust gas extraction site.

  According to this configuration, it is possible to suppress or prevent the additive from entering the intake system of the internal combustion engine by the exhaust gas recirculation device, so that the additive can be effectively used to recover the purification ability of the catalytic converter.

  The exhaust purification system includes a turbocharger that boosts intake air in an intake system of an internal combustion engine using exhaust gas discharged into the exhaust passage, and the addition valve is located upstream of the turbine of the turbocharger. Can be arranged.

  According to this configuration, the additive added to the exhaust passage is easily atomized by the stirring action and the temperature raising action by the turbine of the turbocharger, so that the purification ability recovery action for the catalytic converter is improved.

  According to the exhaust gas purification system for an internal combustion engine according to the present invention, the addition valve can be installed relatively easily without changing the design of the internal combustion engine, and the purification ability of the catalytic converter can be stably recovered. become.

  An embodiment of the present invention will be described below with reference to FIGS.

  Prior to the description of the exhaust purification system according to the present invention, a schematic configuration of an internal combustion engine to be used will be described with reference to FIG.

  An internal combustion engine 1 shown in FIG. 1 is an in-line four-cylinder diesel engine, and basically mixes air supplied from an intake system and fuel supplied from a fuel supply system at an appropriate air-fuel ratio. After the air-fuel mixture is injected into the combustion chamber 2 and burned, the exhaust gas in the combustion chamber 2 is released into the atmosphere from the exhaust system.

  In the intake system, an air cleaner 23, an air flow meter 24, and a throttle valve 25 are arranged in this order from the upstream side in an intake passage formed by connecting an intake pipe 22 to an intake manifold 21 connected to an intake port 3 of a cylinder head. It is. The air flow meter 24 outputs an electrical signal corresponding to the amount of air flowing into the intake pipe 22 via the air cleaner 23.

  The fuel supply system has a configuration in which a fuel tank 32, a supply pump 33, a common rail 34, a plurality of injectors 35,... The fuel in the fuel tank 32 is sucked out by the supply pump 33, supplied to the common rail 34, and injected from the common rail 34 to the combustion chamber 2 through the injectors 35. The supply pump 33 is driven by a crankshaft (not shown) of the internal combustion engine 1.

  The exhaust system includes an exhaust passage configured by connecting a muffler 42 to an exhaust manifold 41 connected to the exhaust port 4 of the cylinder head.

  The internal combustion engine 1 exemplified in this embodiment is equipped with a turbocharger 5, an intercooler 6, an EGR device 7 as an exhaust gas recirculation device, and a catalytic converter 8, and will be described below.

  The turbocharger 5 boosts intake air using exhaust gas, and includes a compressor 5a and a turbine 5b. The compressor 5 a is disposed downstream of the air flow meter 24 in the intake pipe 22, and the turbine 5 b is disposed between the collection portion of the exhaust manifold 41 and the muffler 42.

  The intercooler 6 cools the intake air whose pressure has been increased by the turbocharger 5, and is disposed between the compressor 5 a of the turbocharger 5 and the throttle valve 25.

  The EGR device 7 reduces NOx by returning a part of the exhaust gas (EGR gas) to the intake system and supplying it again to the combustion chamber 2, and enters the EGR passage 7a from the upstream side to the EGR catalytic converter 7b, EGR. The cooler 7c and the EGR valve 7d are arranged.

  The EGR passage 7a includes a bypass passage that bypasses the combustion chamber 2 and is connected from the exhaust system to the intake system. The EGR catalytic converter 7b removes unburned gas contained in the exhaust gas flowing into the EGR passage 7a to prevent the EGR cooler 7c from being clogged. The EGR cooler 7c includes a heat exchanger that lowers the temperature of the EGR gas by exchanging heat between the EGR gas and the coolant of the internal combustion engine 1, for example. The EGR valve 7d controls the amount of exhaust gas flowing in the EGR passage 7a from the exhaust system side to the intake system side.

  The catalytic converter 8 is interposed between an exhaust manifold 41 and a muffler 42 that constitute an exhaust passage. In this embodiment, the catalytic converter 8 is called a DPNR (Diesel Paticulate-Nox Reduction system).

The catalytic converter 8 made of DPNR reduces both particulate matter (PM) and nitrogen oxide (NOx) in the exhaust gas. As shown in FIG. 4, a honeycomb structure is formed in the case 8a. The body 8b is housed and arranged.

  The case 8a has a cylindrical shape at its intermediate portion, and has a tapered shape in which one end portion and the other end portion are gradually reduced in diameter toward the end edge. A honeycomb structure 8b is disposed in an intermediate portion of the case 8a.

Although not shown in detail, the honeycomb structure 8b has a configuration in which, for example, a NOx occlusion reduction type three-way catalyst is supported on a porous ceramic base material, and in principle, exhaust gas containing PM and NOx is exhausted. When flowing in as shown by the arrows in FIG. 5, PM is trapped in the micropores of the porous ceramic substrate, NOx is occluded when passing through the micropores of the porous ceramic substrate, and N ₂ and CO ₂ are discharged. It is like that.

Normally, the catalyst bed of the catalytic converter 8 absorbs NOx when the air-fuel ratio of the exhaust gas (hereinafter referred to as the exhaust air-fuel ratio) is leaner than the stoichiometric air-fuel ratio, and the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or higher. NOx absorbed as NO ₂ or NO is released when the oxygen concentration in the inflowing exhaust gas decreases as it becomes richer. N discharged from the catalyst bed of the catalytic converter 8
Ox (NO ₂ or NO) immediately reacts with unburned HC and CO in the exhaust gas and is reduced to N ₂ .

  Although explanations regarding various operations of the internal combustion engine 1 having the above-described configuration are omitted, the operations are basically controlled by the control device 9.

The control device 9 is an ECU (Electronic Control Unit), which is known from a central processing control device (CPU), a read-only memory (ROM), a random access memory (RAM) and the like connected to each other by a bidirectional bus as is well known. It is configured.

  Here, as necessary, the invention is devised to recover the purification ability of the catalytic converter 8 by supplying an additive (for example, diesel oil as a fuel for diesel engines) to the exhaust system. explain.

  Specifically, as shown in FIG. 1, an addition valve 10 that supplies an additive toward an assembly portion of the exhaust manifold 41 is attached to the outside of the exhaust manifold 41.

  The addition valve 10 is disposed in the exhaust introduction part to the combustion chamber 2 located at the left end in FIG. 1 among the four exhaust introduction parts of the exhaust manifold 41, and is out of the four exhaust introduction parts of the exhaust manifold 41. It is farthest from the EGR passage 7a connected to the exhaust introduction part of the combustion chamber 2 located at the right end of FIG.

  The addition valve 10 is connected to the supply pump 33 via the additive supply path 11. Specifically, the addition valve 10 is composed of a low-pressure injector, and is attached to the specific position of the exhaust manifold 41 via the holder 14 as shown in FIGS.

  The holder 14 is provided with a recess 14a that is fitted in a state where the nozzle 10a side of the addition valve 10 is buried. When the addition valve 10 is fitted and attached to the recess 14 a, the additive injected from the addition valve 10 is directed to the gathering portion of the exhaust manifold 41.

  Further, the holder 14 is provided with a water jacket 14b through which cooling water for cooling the nozzle portion (reference numeral omitted) of the addition valve 10 is passed.

  On the other hand, in the exhaust manifold 41, a bulging portion 41a bulging outward is provided at the place where the addition valve 10 is installed.

  As shown in FIGS. 2 and 3, the bulging portion 41 a has a passage 41 b that communicates with the exhaust manifold 41 and guides the additive injected from the addition valve 10 toward the collection portion of the exhaust manifold 41. Is provided.

  The holder 14 is attached to the bulging portion 41a of the exhaust manifold 41 by flange coupling. In order to reduce heat conduction from the exhaust manifold 41 to the addition valve 10, a heat insulating gasket 13 is interposed in the flange coupling portion between the bulging portion 41 a and the holder 14.

  In the first place, if the additive in the addition valve 10 is exposed to a high temperature because the state in which the addition valve 10 is closed becomes longer, there is a concern that the addition valve 10 may be clogged due to thermal degradation. As described above, if the heat conduction from the exhaust manifold 41 is reduced by the heat insulating gasket 13 and the addition valve 10 is cooled by the water jacket 14b of the holder 14, the additive in the addition valve 10 can be reduced. This is preferable because thermal deterioration can be suppressed or prevented and clogging of the addition valve 10 can be avoided.

  In addition, the addition valve 10, the additive supply path 11, the supply pump 33, and the control device 9 described above constitute an additive supply device, and regarding the supply timing and supply amount of the additive by this additive supply device, It is controlled by the control device 9.

  Next, the additive addition operation will be described.

  In the first place, in the case of a diesel engine, combustion is performed in a much leaner region than stoichiometric (theoretical air-fuel ratio), so NOx in the exhaust gas is absorbed by the catalyst bed of the catalytic converter 8 and the NOx emission amount from the catalytic converter 8 Is extremely low.

  However, as the operation time of the internal combustion engine 1 is accumulated, the NOx absorption capacity of the catalytic converter 8 is saturated.

  Therefore, the control device 9 estimates the NOx amount absorbed by the catalytic converter 8 based on the accumulated operation time of the internal combustion engine 1 and the history information of the operation state, and the estimated NOx amount is a predetermined value set in advance. When (appropriate value before the NOx absorption capacity of the catalytic converter 8 is saturated) is exceeded, a predetermined amount of additive is injected from the addition valve 10 into the exhaust gas for a predetermined time.

  Fuel as an additive injected from the addition valve 10 goes to the exhaust manifold 41 together with the exhaust gas discharged from the exhaust port 4 and is further atomized by the turbine 5b of the turbocharger 5.

This mist-like fuel is thermally decomposed in high-temperature exhaust gas upstream of the catalytic converter 8 to generate a large amount of hydrocarbons and reduce the oxygen concentration in the exhaust gas. The released NOx is released and reduced to N ₂ . As a result, the purification ability of the catalytic converter 8 is recovered.

  The control device 9 calculates the load of the internal combustion engine 1 based on an output signal of an accelerator opening sensor (not shown) (output voltage proportional to the opening of the throttle valve 25), and a crank (not shown) The rotational speed of the internal combustion engine 1 is calculated based on an output pulse from an angle sensor (which outputs a pulse every time the crankshaft rotates by a certain angle), and the operating state of the internal combustion engine 1 is determined based on these loads and rotational speed. .

  Other methods will be described.

  An exhaust temperature sensor 16 is provided upstream of the catalytic converter 8 in the muffler 42, and the exhaust temperature sensor 16 outputs an electrical signal corresponding to the temperature of the exhaust gas flowing into the catalytic converter 8 to the control device 9. To do.

  The control device 9 recognizes the ambient temperature upstream of the catalytic converter 8 based on the output from the exhaust temperature sensor 16 and estimates the catalyst bed temperature of the catalytic converter 8, so that the catalytic converter 8 has the desired purification capacity. Judge whether or not to demonstrate.

  In general, when the operating conditions are such that the temperature of the combustion chamber 2 and the exhaust gas temperature become low, such as cold operation, start-up operation or low-speed low-load operation of the internal combustion engine 1, the catalyst bed temperature of the catalytic converter 8 and its upstream side. Therefore, the purification ability of the catalytic converter 8 tends to be reduced.

  When the control device 9 determines that the catalyst bed temperature of the catalytic converter 8 is lower than a predetermined reference value based on the output of the exhaust temperature sensor 16, the control device 9 operates the additive valve 10 through the additive supply path 11. The high pressure fuel in the supplied supply pump 33 is injected into the exhaust manifold 41.

  Fuel as an additive injected from the addition valve 10 goes to the exhaust manifold 41 together with the exhaust gas discharged from the exhaust port 4 and is further atomized by the turbine 5b of the turbocharger 5.

  This mist-like fuel is thermally decomposed in high-temperature exhaust gas upstream of the catalytic converter 8 to generate a large amount of hydrocarbons, so that the hydrocarbons are reacted in the catalytic converter 8, and the reaction heat The temperature of the catalytic converter 8 is increased. Thereby, the purification capacity of the catalytic converter 8 is improved.

  As described above, in this embodiment, the addition valve 10 provided for recovering the purification capability of the catalytic converter 8 is installed externally to the exhaust manifold 41. Thereby, when installing the addition valve 10, it becomes possible to install simply without changing a design of a cylinder head like the conventional example, and it becomes possible to reduce an installation cost.

  Furthermore, since the arrangement position of the addition valve 10 is specified, a phenomenon in which the additive injected into the exhaust manifold 41 is blown back around the exhaust port 4 due to the influence of exhaust pulsation is less likely to occur. Therefore, compared to the conventional example in which an additive is added to the exhaust port 4, the additive is less likely to adhere and deposit as a deposit on the wall surface of the exhaust port 4.

  Further, in this embodiment, since the additive is injected upstream of the turbine 5b of the turbocharger 5 by the addition valve 10, the additive is fogged by the stirring action and the temperature raising action by the turbine 5b of the turbocharger 5. The effect for recovering the purification ability of the catalytic converter 8 is increased.

  Furthermore, in this embodiment, since the addition valve 10 is disposed away from the EGR passage 7a, the additive injected from the addition valve 10 can be prevented from flowing into the intake system via the EGR passage 7a. It is possible to avoid adversely affecting the driving of 1.

  Hereinafter, other embodiments of the present invention will be described.

  (1) In the above embodiment, the catalytic converter 8 can be a DPF (Diesel Paticulate Filter), a NOx storage reduction catalyst, an oxidation catalyst, or the like, for example. Further, when the internal combustion engine is a lean combustion type gasoline engine, the catalytic converter 8 can be a three-way catalytic converter.

  (2) In the above-described embodiment, an example in which the catalytic converter 8 is integrated is described. However, the present invention can be applied to two or three combined converters. As an example, for example, as shown in FIG. 6, in addition to the configuration shown in FIG. 1, the muffler 42 is provided with three catalytic converters 8A, 8B, 8C.

  In order from the upstream side of the muffler 42, the first catalytic converter 8A is, for example, an after turbo catalyst, the second catalytic converter 8B is, for example, an oxidation catalyst, and the third catalytic converter 8C is a DPF (Diesel Paticulate). Filter). Note that the after-turbo catalyst as the first catalytic converter 8A and the oxidation catalyst as the second catalytic converter 8B contribute to increase the DPF purification ability as the third catalytic converter 8C.

  The types of these catalytic converters 8A, 8B, and 8C are not particularly limited, and various types of catalytic converters can be used as appropriate.

  In such a configuration, when the additive addition operation described above is executed, the additive contributes to recover the purification ability of the three catalytic converters 8A, 8B, and 8C. Therefore, the exhaust gas purification performance can be improved as a whole.

  (3) FIG. 7 shows another embodiment of the present invention. In this embodiment, in addition to the configuration shown in FIG. 1, an exhaust throttle valve 18 for adjusting the exhaust flow rate is installed inside the muffler 42 on the downstream side of the catalytic converter 8. In this case, if necessary, by controlling the exhaust throttle valve 18 to the closed side, the catalyst bed temperature of the catalytic converter 8 and the ambient temperature around the catalytic converter 8 can be increased, so that the purification capacity of the catalytic converter 8 is increased. Is possible.

  For example, under operating conditions where the temperature of the combustion chamber 2 and the exhaust gas temperature are low, such as cold operation, start-up operation or low-speed low-load operation of the internal combustion engine 1, the catalyst bed temperature of the catalytic converter 8 and the atmosphere upstream and downstream thereof. As the temperature decreases, the purification capacity of the catalytic converter 8 tends to decrease. In such a case, the exhaust throttle valve 18 can be controlled to the closed side. Of course, the additive addition process described in the above embodiment may be executed together with the operation control of the exhaust throttle valve 18.

  (4) In each of the above embodiments, the turbocharger 5 and the EGR device 7 are provided as an example, but the present invention can be applied even if one or both of them are eliminated.

1 is a schematic configuration diagram showing an embodiment of an exhaust gas purification system for an internal combustion engine according to the present invention. It is an arrow view of the (2)-(2) line cross section of FIG. FIG. 3 is a cross-sectional view taken along line (3)-(3) in FIG. 2. It is a schematic block diagram which shows the catalytic converter of FIG. It is explanatory drawing which shows typically the purification principle by the catalytic converter of FIG. FIG. 6 is a view corresponding to FIG. 1 in another embodiment of the exhaust gas purification system for an internal combustion engine according to the present invention. FIG. 6 is a view corresponding to FIG. 1 in another embodiment of the exhaust gas purification system for an internal combustion engine according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Combustion chamber 4 Cylinder head exhaust port 5 Turbocharger 7 EGR device (exhaust gas recirculation device)
8 Catalytic converter 9 Control device 10 Addition valve 11 Additive supply path 16 Exhaust temperature sensor 33 Supply pump 41 Exhaust manifold (exhaust path)
42 Muffler (exhaust passage)

Claims (7)

An exhaust gas purification system for an internal combustion engine having a catalytic converter provided in an exhaust passage of the internal combustion engine for purifying exhaust gas discharged to the exhaust passage, and an addition valve for adding an additive for recovering the purification capability of the catalytic converter Because
The exhaust purification system for an internal combustion engine, wherein the addition valve is attached outside the upstream portion of the exhaust gas passage connected to the exhaust port of the internal combustion engine in the exhaust passage.   2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the addition valve is attached to the exhaust manifold in a posture capable of injecting the additive toward a collecting portion of the exhaust manifold.   The exhaust purification system for an internal combustion engine according to claim 1 or 2, wherein the addition valve is attached to the exhaust manifold in a state of being supported by a holder separate from the exhaust manifold.   The exhaust gas purification system for an internal combustion engine according to claim 3, wherein a heat insulating gasket is interposed between the holder and the exhaust manifold.   The portion provided with the addition valve in the exhaust manifold is provided with a bulging portion bulging outward, and the holder is attached to the bulging portion by flange connection. 5. An exhaust gas purification system for an internal combustion engine according to 3 or 4. An exhaust gas recirculation device for returning a part of the exhaust gas discharged to the exhaust passage to the intake system of the internal combustion engine;
The exhaust purification of an internal combustion engine according to any one of claims 1 to 5, wherein the addition valve is disposed at a position farthest from an exhaust gas extraction portion from the exhaust passage in the exhaust gas recirculation device. system. A turbocharger that boosts intake air in an intake system of an internal combustion engine using exhaust gas discharged into the exhaust passage;
The exhaust purification system for an internal combustion engine according to any one of claims 1 to 6, wherein the addition valve is disposed upstream of a turbine of the turbocharger.

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