JP2005016393A - Exhaust-emission control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain capacity for oxidation of an EGR catalyst by oxidatively removing PM deposited on the EGR catalyst, and prevent melting loss of the EGR catalyst in an exhaust-emission control system of an internal combustion engine provided with an EGR system having the EGR catalyst. <P>SOLUTION: The exhaust-emission control system is provided with an exhaust-emission control means for trapping particulates contained in exhaust gas, an EGR passage, an EGR cooler, the EGR catalyst, and an EGR valve. In the combustion cycle of the internal combustion engine, a secondary injection of an additional fuel-injection is carried out at a specified timing after a primary injection in order to oxidatively remove particulates trapped by the exhaust-emission control means, and at the same time exhaust gas is allowed to flow to the EGR catalyst through the EGR passage by opening the EGR valve (S107-S112) in a specified period during the secondary injection is being carried out. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust purification system that performs exhaust purification of an internal combustion engine.
[0002]
[Prior art]
As a technique for suppressing NOx in exhaust gas discharged from an internal combustion engine, there is a so-called EGR device that recirculates a part of the exhaust gas to an intake passage of the internal combustion engine. The EGR device introduces exhaust gas into a combustion chamber of an internal combustion engine, thereby lowering the combustion temperature in the combustion chamber and reducing the amount of NOx produced.
[0003]
The EGR device includes devices such as an EGR passage through which recirculated exhaust flows, an EGR cooler for cooling the exhaust flowing through the EGR passage, and an EGR valve that adjusts the amount of exhaust flowing through the EGR passage. Here, if HC or particulate matter (hereinafter referred to as “PM”) contained in the recirculated exhaust gas adheres to and accumulates on these EGR coolers and EGR valves, the exhaust cooling capacity decreases due to clogging of the EGR cooler. In addition, the EGR valve is stuck, and it becomes difficult to perform the exhaust gas recirculation control well.
[0004]
Therefore, an EGR catalyst that oxidizes substances in exhaust gas is provided on the upstream side of the EGR cooler to purify HC, PM, etc. in the exhaust gas flowing into the EGR cooler, etc., and to prevent adverse effects caused by these. Is disclosed (for example, see Patent Document 1). Further, when soot contained in the exhaust adheres to the EGR cooler and its cooling capacity is reduced, the temperature of the exhaust is raised and the attached soot is burned to remove the soot by oxidation. (See, for example, Patent Document 2).
[0005]
Further, the exhaust gas discharged from the internal combustion engine contains PM, and exhaust purification means for collecting the PM in the exhaust gas and suppressing the release of the PM into the outside air in the exhaust passage of the internal combustion engine. Provided. However, when the amount of PM collected by the exhaust purification means increases, the flow of exhaust in the exhaust passage is hindered, and the back pressure in the exhaust passage increases, which may adversely affect the operation of the internal combustion engine. In view of this, a technique has been disclosed in which the amount of fuel injected and the timing of injection are controlled or fuel is added to the exhaust to supply HC to the exhaust and oxidize and remove the PM collected in the exhaust purification means ( For example, see Patent Document 3.)
[0006]
[Patent Document 1]
JP 2000-45881 A
[Patent Document 2]
JP 2002-174148 A
[Patent Document 3]
JP 2002-180816 A
[Patent Document 4]
JP-A-9-13945
[Patent Document 5]
JP-A-8-338320
[Patent Document 6]
JP 2001-140703 A
[Patent Document 7]
JP 2002-371874 A
[0007]
[Problems to be solved by the invention]
In an internal combustion engine equipped with an EGR device, an EGR catalyst for preventing adverse effects on the EGR device by HC, PM, etc. by oxidizing and removing HC, PM, etc. contained in the exhaust gas flowing through the EGR device, When the EGR device is provided, if the PM in the exhaust gas accumulates on the EGR catalyst, the oxidation ability of the EGR catalyst decreases, and it becomes difficult to prevent the exhaust flow and to perform good exhaust gas recirculation control.
[0008]
Furthermore, after the oxidation state in the EGR catalyst does not proceed well and the operating state of the internal combustion engine in which PM discharged from the internal combustion engine accumulates on the EGR catalyst lasts for a relatively long time, it flows into the EGR catalyst. When the exhaust gas temperature rises, the PM deposited on the EGR catalyst burns all at once, and the temperature of the EGR catalyst increases excessively, and the EGR catalyst itself may be melted.
[0009]
The present invention has been made in view of the above situation, and is an exhaust gas purification system for an internal combustion engine having an EGR device equipped with an EGR catalyst. The EGR catalyst removes PM deposited on the EGR catalyst by oxidation by a simpler method. It is an object of the present invention to provide an exhaust purification system for an internal combustion engine that maintains the oxidation ability of the EGR catalyst and avoids EGR catalyst erosion caused by the accumulation of the EGR catalyst.
[0010]
[Means for Solving the Problems]
The present invention focuses on sub-injection, which is fuel injection performed at a predetermined time after main injection, for oxidizing and removing PM accumulated in the exhaust purification unit of the exhaust purification system of the internal combustion engine. This is because the fuel when the sub-injection is performed is exposed to high-temperature combustion gas in the combustion chamber, so that the molecular weight of HC by the fuel becomes smaller and the fuel becomes more active. In addition, by using the sub-injection originally performed to oxidize and remove the PM deposited on the exhaust gas purification means for oxidizing and removing the PM accumulated on the EGR catalyst, an exhaust gas purification system for an internal combustion engine without requiring a special device. It is because it becomes possible to comprise more simply.
[0011]
Therefore, in an exhaust gas purification system for an internal combustion engine, an exhaust gas purification unit that is provided in an exhaust passage of the internal combustion engine, oxidizes substances in the exhaust gas discharged from the internal combustion engine, and collects PM contained in the exhaust gas; An EGR passage that recirculates a part of the exhaust discharged from the internal combustion engine from the exhaust passage upstream of the exhaust gas purification means to the intake passage of the internal combustion engine, and the EGR passage are provided in the EGR passage. An EGR cooler that cools the exhaust, an EGR passage that is provided upstream of the EGR cooler, oxidizes a substance in the exhaust that flows through the EGR passage, and an EGR passage that is downstream of the EGR catalyst. An EGR valve for controlling the flow of exhaust gas flowing through the EGR passage, and fuel injection again at a predetermined time after the main injection in the combustion cycle of the internal combustion engine. Between the sub-injection means that oxidizes and removes PM collected by the exhaust purification means, and the PM that is collected by the exhaust purification means by sub-injection of the sub-injection means. EGR valve control means for opening the EGR valve during a predetermined period to cause the exhaust gas to flow into the EGR catalyst via the EGR passage.
[0012]
In the exhaust gas purification system of the internal combustion engine, the PM contained in the exhaust gas is collected by the exhaust gas purification means, thereby suppressing the PM from being released to the outside air. However, as the collected PM increases, the exhaust flow in the exhaust passage is hindered, and the back pressure in the exhaust passage increases, which may adversely affect the operation of the internal combustion engine.
[0013]
Therefore, by performing the sub-injection by the sub-injection means, a lot of HC is included in the exhaust gas from the internal combustion engine. The predetermined time at which the sub-injection is performed refers to a time after the main injection in the combustion cycle of the internal combustion engine and the fuel injected by the sub-injection does not contribute to the engine output of the internal combustion engine. Any time in the period from to the exhaust stroke. Therefore, since the fuel injected by the sub-injection is injected into the high-temperature combustion gas generated by the main injection, the molecular weight of the fuel becomes smaller and the fuel becomes more active.
[0014]
Then, the HC in the exhaust gas is oxidized by the oxidation function of the exhaust gas purification means to raise the exhaust gas temperature, and PM trapped in the exhaust gas purification means is oxidized and removed. Here, the exhaust purification means is configured to include a filter that collects PM in the exhaust downstream of the oxidation catalyst that oxidizes substances in the exhaust, and the oxidation catalyst is supported on the filter. But you can.
[0015]
In the exhaust gas purification system for an internal combustion engine, exhaust gas recirculation control is performed in which a part of the exhaust gas discharged from the internal combustion engine is recirculated to the intake passage of the internal combustion engine via the EGR passage. NOx is reduced. Here, the EGR catalyst provided in the EGR passage oxidizes and purifies substances such as HC and PM contained in the exhaust gas flowing through the EGR passage, and HC and PM are added to the EGR cooler and EGR valve existing in the downstream EGR passage. Suppresses adhesion and deposition.
[0016]
However, when the amount of PM that exceeds the oxidation ability of the EGR catalyst is contained in the exhaust gas, there is a possibility that a relatively large amount of PM is deposited on the EGR catalyst. For this reason, the oxidation ability of the EGR catalyst is reduced, and the accumulated PM is exposed to high-temperature exhaust gas, so that the amount of the accumulated amount is relatively large, so that the temperature of the EGR catalyst is excessively increased and the EGR catalyst is melted. There is a fear.
[0017]
Therefore, by opening the EGR valve by the EGR valve control means, the HC supplied into the exhaust gas by the sub-injection by the sub-fuel injection means in order to oxidize and remove PM originally collected by the exhaust purification means, The EGR catalyst is also supplied and the exhaust temperature is raised by the oxidation ability of the EGR catalyst to oxidize and remove the deposited PM. At this time, the period during which the EGR valve is opened is a period during which the sub-injection by the sub-fuel injection means for oxidizing and removing the PM collected by the exhaust gas purification means is being performed, and is deposited on the EGR catalyst. The period may be sufficient to oxidize and remove the remaining PM. Naturally, the EGR valve may be opened while the PM collected by the exhaust gas purification means is oxidized and removed.
[0018]
In general, the exhaust gas temperature flowing into the EGR catalyst is higher than the exhaust gas temperature flowing into the exhaust gas purification means provided in the exhaust passage, so the amount of PM deposited on the EGR catalyst is less than the amount of PM trapped in the exhaust gas purification means. Further, the exhaust gas purification means has a structure originally intended to collect particulates in the exhaust gas. On the other hand, the EGR catalyst is intended to oxidize substances in the exhaust gas, and does not have a structure mainly for collecting PM. Therefore, also from a structural point of view, the amount of PM deposited on the EGR catalyst is smaller than the amount of PM collected on the exhaust purification means. Therefore, while the sub-injection by the sub fuel injection means for oxidizing and removing the PM collected by the exhaust purification means is being executed, the PM deposited on the EGR catalyst can be almost oxidized and removed.
[0019]
As a result, it is possible to oxidize and remove PM accumulated on the EGR catalyst at the same time as oxidizing and removing PM collected by the exhaust gas purification means by a simpler method of controlling the opening of the EGR valve, It becomes possible. As a result, it is possible to avoid melting of the EGR catalyst caused by PM accumulation on the EGR catalyst.
[0020]
Here, the sub-injected fuel is injected at a time when the engine output of the internal combustion engine is not reached. Therefore, if the temperature of the combustion gas in the combustion chamber immediately before the sub-injection is low, vaporization of the fuel injected by the sub-injection is not sufficiently promoted and the molecular weight of the fuel becomes large. For this reason, the oxidation reaction in the exhaust gas purification means and the EGR catalyst is not efficiently performed, and there is a possibility that the exhaust gas will adhere to the exhaust passage and the EGR passage of the internal combustion engine.
[0021]
Therefore, the exhaust gas purification system for the internal combustion engine further includes a temperature increase control means for increasing the combustion gas temperature of the internal combustion engine when the combustion gas temperature of the internal combustion engine is lower than a predetermined combustion gas temperature. And when the combustion gas temperature of the internal combustion engine is lower than a predetermined combustion gas temperature, the auxiliary injection means raises the combustion gas temperature of the internal combustion engine to the predetermined combustion gas temperature by the temperature increase control means. Sub-injection is performed.
[0022]
Here, the predetermined combustion gas temperature is a combustion gas temperature at which the vaporization of the fuel injected by the sub-injection can be sufficiently promoted. The combustion gas temperature can be estimated from the temperature of the exhaust discharged from the combustion chamber of the internal combustion engine, the temperature of the exhaust gas flowing into the EGR catalyst, the exhaust purification means, and the like. Thus, by controlling the timing at which the sub-injection is performed, the vaporization of the fuel injected by the sub-injection is promoted, and the oxidation reaction by the exhaust purification means and the EGR catalyst by the fuel is performed more efficiently. obtain.
[0023]
Further, if the exhaust gas temperature flowing into the EGR catalyst is high, the EGR catalyst itself may be thermally deteriorated. In particular, since the exhaust gas temperature flowing into the EGR catalyst is relatively higher than the exhaust gas temperature flowing into the exhaust gas purification means, there is a high possibility that the EGR catalyst will be thermally deteriorated. Therefore, the exhaust gas purification system for an internal combustion engine described above further includes a deposit amount estimating means for estimating the amount of PM deposited on the EGR catalyst. The EGR valve control means adjusts the opening time of the EGR valve based on the accumulation amount estimated by the accumulation amount estimation means.
[0024]
The amount of PM accumulated on the EGR catalyst can be estimated based on the amount of fuel supplied to the combustion of the internal combustion engine. Further, when the exhaust temperature of the internal combustion engine is relatively high, that is, when the engine load of the internal combustion engine belongs to the middle and high load region, PM accumulated on the EGR catalyst is gradually oxidized by the exhaust heat. The amount of deposition is reduced. On the other hand, when the exhaust temperature of the internal combustion engine is relatively low, that is, when the engine load of the internal combustion engine belongs to the low load region, the PM temperature on the EGR catalyst gradually decreases without decreasing because the exhaust temperature is low. To increase. Therefore, based on the operating state of these internal combustion engines, it is possible to estimate the PM accumulation amount on the EGR catalyst more accurately.
[0025]
And by adjusting the valve opening time of the EGR valve according to the PM accumulation amount of the EGR catalyst, when the accumulation amount is small, the valve opening time of the EGR valve is suppressed unnecessarily. Is possible. As a result, since the time during which the EGR catalyst is exposed to high-temperature exhaust gas is shortened, it is possible to more reliably suppress thermal degradation of the EGR catalyst.
[0026]
In order to suppress thermal degradation of the EGR catalyst, it is also useful to reduce the frequency of opening the EGR valve by the EGR valve control means. That is, instead of adjusting the valve opening time of the EGR valve based on the PM accumulation amount on the EGR catalyst described above, the EGR valve control means captures the exhaust purification means by sub-injection of the sub-injection means. Every time the collected PM is removed by oxidation a predetermined number of times, the EGR valve is opened to allow exhaust to flow into the EGR catalyst through the EGR passage.
[0027]
As described above, generally, the amount of PM deposited on the EGR catalyst is smaller than the amount of PM collected on the exhaust purification means. Therefore, the PM that has accumulated on the EGR catalyst is not oxidized and removed by opening the EGR valve every time the PM in the exhaust gas purification means is oxidized and removed by the sub-injection, that is, the exhaust gas purification means. The EGR valve is opened once every time oxidation removal of PM is performed a predetermined number of times.
[0028]
Thus, even if the opening frequency of the EGR valve during the sub-injection is lowered, it is possible to oxidize and remove PM deposited on the EGR catalyst. And the thermal deterioration of an EGR catalyst is suppressed because the inflow frequency of the exhaust_gas | exhaustion to an EGR catalyst falls. Here, the predetermined number, which is the opening frequency of the EGR valve at the time of the sub-injection, may be obtained in advance through experiments or the like. Therefore, the control for suppressing the thermal degradation of the EGR catalyst becomes simple, and the thermal degradation can be easily suppressed.
[0029]
In the exhaust gas purification system for an internal combustion engine as described above, the oxidation removal of PM collected by the exhaust gas purification means is performed by HC supplied to the exhaust gas by sub-injection. However, since the amount of fuel injected by the sub-injection is limited by the state in the combustion chamber of the internal combustion engine, the amount of HC that can reach the exhaust purification unit is limited. Therefore, it is difficult to quickly raise the temperature of the exhaust gas purification unit, and the time required for oxidizing and removing the PM collected by the exhaust gas purification unit becomes long.
[0030]
Therefore, in the exhaust gas purification system for an internal combustion engine as described above, a fuel addition means that is provided in an exhaust passage of the internal combustion engine upstream of the exhaust gas purification means and adds fuel to the exhaust gas flowing into the exhaust gas purification means, Prepare. The fuel is added to the exhaust gas flowing through the exhaust passage by the fuel addition unit when the PM collected by the exhaust gas purification unit by the sub-injection of the sub-injection unit is executed.
[0031]
By doing in this way, HC supplied for the oxidation removal of PM collected by the exhaust gas purification means is supplied by the sub-injection and also supplied by the fuel addition means. As a result, the temperature of the exhaust gas purification means rises quickly, the PM oxidation removal by the exhaust gas purification means is promoted, and the time required for the PM oxidation removal is shortened.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
Here, an embodiment of an exhaust gas purification system for an internal combustion engine according to the present invention will be described based on the drawings. FIG. 1 is a block diagram showing a schematic configuration of an exhaust purification system to which the present invention is applied, a compression ignition type internal combustion engine 1 including the exhaust purification system, and a control system thereof.
[0033]
The internal combustion engine 1 is an internal combustion engine having four cylinders 2. Further, a fuel injection valve 3 for directly injecting fuel into the combustion chamber of the cylinder 2 is provided. The fuel injection valve 3 is connected to a pressure accumulation chamber 4 that accumulates fuel at a predetermined pressure. The pressure accumulating chamber 4 communicates with the fuel pump 6 through the fuel supply pipe 5.
[0034]
Next, an intake branch pipe 7 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 7 communicates with a combustion chamber of the cylinder 2 via an intake port. Here, the communication between the combustion chamber of the cylinder 2 and the intake port is performed by opening and closing the intake valve. The intake branch pipe 7 is connected to the intake pipe 8. An air flow meter 9 that outputs an electrical signal corresponding to the mass of the intake air flowing through the intake pipe 8 is attached to the intake pipe 8. An intake throttle valve 10 for adjusting the flow rate of the intake air flowing through the intake pipe 8 is provided at a portion of the intake pipe 8 located immediately upstream of the intake branch pipe 7. The intake throttle valve 10 is provided with an intake throttle actuator 11 that is configured by a step motor or the like and that opens and closes the intake throttle valve 10.
[0035]
Here, the intake pipe 8 located between the air flow meter 9 and the intake throttle valve 10 is provided with a compressor housing 17a of a centrifugal supercharger (turbocharger) 17 that operates using exhaust energy as a drive source. The intake pipe 8 downstream of the housing 17a is provided with an intercooler 16 for cooling the intake air that has been compressed in the compressor housing 17a and has reached a high temperature.
[0036]
On the other hand, an exhaust branch pipe 12 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 12 communicates with the combustion chamber of the cylinder 2 through an exhaust port. Here, the communication between the combustion chamber of the cylinder 2 and the exhaust port is performed by opening and closing the exhaust valve. Further, the internal combustion engine 1 is provided with an EGR device 21. The EGR device 21 recirculates part of the exhaust from the exhaust branch pipe 12 to the intake branch pipe 7. The EGR device 21 includes an EGR passage 22 extending from the exhaust branch pipe 12 (upstream side) to the intake branch pipe 7 (downstream side), an EGR catalyst 23 provided on the EGR passage 22 in order from the upstream side, and an EGR cooler. 24 and an EGR valve 25.
[0037]
The EGR catalyst 23 is a catalyst having a function of purifying exhaust gas by oxidizing HC, PM and the like in the exhaust gas flowing through the EGR passage 22. The EGR cooler 24 cools the exhaust gas flowing through the EGR passage 22, and the EGR valve 25 adjusts the flow rate of the exhaust gas flowing through the EGR passage 22. When the EGR valve 25 is opened, a part of the exhaust gas in the exhaust branch pipe 12 flows into the EGR passage 22, and HC, PM, etc. in the exhaust gas are oxidized by the EGR catalyst 23, and the EGR cooler 24, EGR valve 25. Then, the air is recirculated to the intake branch pipe 7.
[0038]
The exhaust branch pipe 7 is connected to the turbine housing 17 b of the centrifugal supercharger 17. The turbine housing 17b is connected to an exhaust pipe 13, and the exhaust pipe 13 is connected to a muffler downstream. In the middle of the exhaust pipe 13, an oxidation catalyst 14 having a function of oxidizing substances in the exhaust from the internal combustion engine and a filter 15 having a function of collecting PM in the exhaust are provided downstream of the oxidation catalyst 14. It has been. Exhaust gas from the internal combustion engine 1 flows into the oxidation catalyst 14, HC in the exhaust gas is oxidized by the oxidation catalyst 14, and the temperature of the exhaust gas flowing into the filter 15 is raised by the oxidation heat. Further, PM in the exhaust gas is collected by the filter 15 and PM is prevented from being released to the outside air. Further, a fuel addition valve 30 is provided in the exhaust pipe 13 upstream of the oxidation catalyst 14 to add fuel to the exhaust gas flowing through the exhaust pipe 13.
[0039]
Here, the fuel injection valve 3 and the fuel addition valve 30 are opened and closed by a control signal from an electronic control unit (hereinafter referred to as ECU: Electronic Control Unit) 20. That is, in accordance with a command from the ECU 20, the fuel injection timing and the fuel injection amount in the fuel injection valve 3 and the fuel addition valve 30 are controlled for each valve. The EGR valve 25 is also controlled to open according to a command from the ECU 20.
[0040]
Further, an accelerator opening sensor 35 is electrically connected to the ECU 20, and the ECU 20 receives a signal corresponding to the accelerator opening and calculates an engine torque required for the internal combustion engine 1 based on the signal. In addition, the crank position sensor 32 is electrically connected to the ECU 20, and the ECU 20 receives a signal corresponding to the rotation angle of the output shaft of the internal combustion engine 1 and calculates the engine rotational speed and the like of the internal combustion engine 1.
[0041]
The exhaust pipe 13 between the oxidation catalyst 14 and the filter 15 is provided with an exhaust temperature sensor 34 that detects the temperature of the exhaust gas flowing into the filter 15. Further, an exhaust air / fuel ratio sensor 31 for detecting the air / fuel ratio of the exhaust gas flowing out from the filter 15 is provided in the exhaust pipe 13 downstream of the filter 15. The exhaust temperature sensor 34 and the exhaust air / fuel ratio sensor 31 are electrically connected to the ECU 20 respectively. The exhaust temperature sensor 34 transmits a voltage corresponding to the exhaust temperature to the ECU 20 to detect the exhaust temperature, and the exhaust air / fuel ratio sensor 31 The air-fuel ratio of the exhaust is detected by transmitting a voltage corresponding to the concentration of oxygen in the exhaust to the ECU 20.
[0042]
Furthermore, one end of an upstream introduction pipe 33a that introduces exhaust gas is connected to the exhaust pipe 13 upstream of the oxidation catalyst 14, and one end of a downstream introduction pipe 33b that introduces exhaust gas to the exhaust pipe 13 downstream of the filter 15. Is connected. The other ends of the upstream introduction pipe 33 a and the downstream introduction pipe 33 b are connected to the differential pressure sensor 33. The differential pressure sensor 33 detects the differential pressure by transmitting to the ECU 20 a voltage corresponding to the differential pressure of the exhaust gas introduced from the upstream side introduction pipe 33a and the downstream side introduction pipe 33b.
[0043]
Exhaust gas discharged from the internal combustion engine 1 is purified by an exhaust gas purification system including these sensors, the oxidation catalyst 14, the filter 15, the fuel addition valve 3, the fuel addition valve 30, and the like. Therefore, PM contained in the exhaust gas is collected by the filter 15, but if the amount of collection increases, the operating state of the internal combustion engine 1 is adversely affected. Therefore, it is necessary to remove the collected PM. . At this time, since the differential pressure detected by the differential pressure sensor 33 increases as PM is collected by the filter 15, the PM collected by the filter 15 when the differential pressure exceeds a predetermined pressure. Oxidation removal is performed.
[0044]
The oxidation removal of the PM collected by the filter 15 is after the main injection in which the fuel injection from the fuel injection valve 3 is performed near the compression top dead center, and the time when the injected fuel does not contribute to the engine output of the internal combustion engine For example, this is performed by sub-injection in which fuel is injected at 90 ° after compression top dead center. The fuel by the sub-injection is exposed to the combustion gas in the combustion chamber to become a more active state and is oxidized by the downstream oxidation catalyst 14, thereby raising the temperature of the exhaust gas flowing into the filter 15. The PM collected in the catalyst is oxidized and removed. Also, it is possible to oxidize and remove PM collected by the filter 15 by directly adding fuel to the exhaust gas by the fuel addition valve 30, but the exhaust temperature at the time of fuel addition is somewhat lowered. The added fuel is difficult to vaporize. The opening timing and opening time of the fuel injection valve 3 or the fuel addition valve 30 for the sub-injection are based on the temperature of the exhaust gas flowing into the filter 15 based on signals from the exhaust temperature sensor 34 and the exhaust air / fuel ratio sensor 31. Is controlled by the ECU 20 so that the temperature becomes an appropriate temperature.
[0045]
Here, in order to suppress the production amount of NOx due to combustion, the EGR valve 25 is opened and the exhaust gas is recirculated. Then, the exhaust gas flows into the EGR catalyst 23, and HC and PM in the exhaust gas are oxidized in the EGR catalyst 23. However, depending on the operating state of the internal combustion engine 1, the exhaust gas temperature may be low, so the amount of PM in the exhaust gas may also increase. If such a state continues for a long time, PM accumulates on the EGR catalyst 23. After that, when the high-temperature exhaust gas flows into the EGR catalyst 23, the accumulated PM is oxidized, and the EGR catalyst 23 is excessively heated and may be melted. Therefore, control for removing PM deposited on the EGR catalyst 23 will be described with reference to FIG. FIG. 2 is a flowchart of PM removal control for oxidizing and removing PM deposited on the EGR catalyst 23. The control is executed by the ECU 20.
[0046]
First, in S101, when starting this control, control parameters such as the amount of PM trapped by the filter 15 and timer used in this control are initialized. When the process of S101 ends, the process proceeds to S102.
[0047]
In S102, the PM collection amount Sf at the filter 15 is calculated. Specifically, the PM collection amount Sf is calculated according to the differential pressure detected by the differential pressure sensor 33. Further, the PM collection amount Sf may be calculated according to the integrated value of the fuel injection amount injected from the fuel injection valve 3 after the previous main control. When the process of S102 ends, the process proceeds to S103.
[0048]
In S103, it is determined whether or not the PM collection amount Sf calculated in S102 is larger than a predetermined PM collection amount Sf0. Here, the predetermined amount of collected PM Sf0 is judged to be that the collected PM should be removed by oxidation because the amount of collected PM in the filter 15 increases and adversely affects the combustion state in the internal combustion engine 1. It is a threshold for Accordingly, when it is determined in S103 that the PM collection amount Sf is larger than the predetermined PM collection amount Sf0, the processing after S104 is performed to oxidize and remove the PM collected by the filter 15. On the other hand, when it is determined in S103 that the PM collection amount Sf is less than or equal to the predetermined PM collection amount Sf0, it means that the filter 15 still has the ability to collect PM, and S102 The subsequent processing is performed again.
[0049]
In S104, the temperature of the combustion gas in the internal combustion engine 1 is raised. In this control, the oxidation removal of the PM collected by the filter 15 is caused by oxidizing the HC contained in the exhaust gas by the sub-injection described later by the oxidation catalyst 14 and raising the exhaust gas temperature by the oxidation heat. Done in At this time, when the temperature of the combustion gas in the internal combustion engine 1 is low, the vaporization of the fuel injected by the sub-injection is not sufficiently promoted, so that the temperature of the exhaust gas in the oxidation catalyst 14 becomes insufficient and the filter 15 The collected PM is not efficiently oxidized and removed. Therefore, the temperature of the combustion gas in the internal combustion engine 1 is raised in order to promote the vaporization of the fuel and bring it into an active state. Specifically, in the vicinity of the time when fuel injection from the fuel injection valve 3 (hereinafter referred to as “main injection”) performed in the vicinity of the compression stroke top dead center ends, for example, at the time of 30 ° after the compression top dead center. Again, fuel injection with a relatively small fuel injection amount (hereinafter referred to as “auxiliary injection”) is performed. The fuel injected by the auxiliary injection is exposed to the high-temperature combustion gas generated by the combustion of the main injection fuel and burns. As a result, the temperature of the combustion gas further increases as compared with the case of only the main injection. When the process of S104 ends, the process proceeds to S105.
[0050]
In S105, it is determined whether or not the combustion gas temperature is higher than a predetermined temperature T0. The predetermined temperature is a threshold value at which it is determined that the combustion gas temperature has risen to an extent sufficient for performing sub-injection. Further, in the present embodiment, the detection of the combustion gas temperature is estimated from the exhaust gas temperature detected by the exhaust gas temperature sensor 34. The relationship between the temperature detected by the exhaust temperature sensor 34 and the combustion gas temperature may be obtained in advance through experiments or the like. In order to detect the temperature of the combustion gas more directly, a temperature sensor may be provided in a portion communicating with the exhaust port, particularly the exhaust port, to detect the temperature of the combustion gas immediately after being discharged through the exhaust port. . When it is determined in S105 that the combustion gas temperature is higher than the predetermined temperature T0, the process proceeds to S106. On the other hand, when it is determined in S105 that the combustion gas temperature is equal to or lower than the predetermined temperature T0, the combustion gas temperature is raised to the extent that sub-injection for oxidizing and removing the PM collected by the filter 15 is performed. Therefore, the processing after S104 is performed again.
[0051]
In S106, sub-injection is performed to oxidize and remove PM collected by the filter 15. The fuel injected by the sub-injection is performed at a timing that does not contribute to the engine output of the internal combustion engine 1. Therefore, for example, when the auxiliary injection in S104 is performed at a timing of 30 ° after the compression stroke top dead center, the sub-injection is performed at a timing of 90 ° after the compression stroke top dead center. In addition, the timing of the sub-injection may be determined in consideration of the combustion gas temperature in the internal combustion engine 1 and the position of the piston in each cylinder in the expansion stroke and the exhaust stroke, without being limited to this timing.
[0052]
By performing the sub-injection of S106, a large amount of HC is contained in the exhaust gas flowing into the oxidation catalyst 14 located upstream of the filter 15. Then, HC in the exhaust is oxidized in the oxidation catalyst 14, and the exhaust temperature flowing into the filter 15 is further raised by the oxidation heat, and the PM collected in the filter 15 is oxidized and removed. When the process of S106 ends, the process proceeds to S107.
[0053]
In S107, the EGR valve 25 is opened. As a result, the exhaust gas containing a large amount of HC originally in the active state supplied to the filter 15 also flows into the EGR catalyst 23. Then, HC contained in the exhaust is oxidized in the EGR catalyst 23, and PM deposited on the EGR catalyst 23 is oxidized and removed by the oxidation heat. When the process of S107 ends, the process proceeds to S108.
[0054]
In S108, it is determined whether or not the temperature of the filter 15 is a predetermined temperature. Here, the predetermined temperature refers to the temperature of the filter 15 sufficient to oxidize and remove the PM collected by the filter 15. The temperature of the filter 15 is estimated from the exhaust temperature detected by the exhaust temperature sensor 34. It should be noted that the relationship between the temperature detected by the exhaust temperature sensor 34 and the temperature of the filter 15 may be obtained in advance through experiments or the like. When it is determined in S108 that the temperature of the filter 15 is the predetermined temperature, the process proceeds to S109. On the other hand, when it is determined in S108 that the temperature of the filter 15 is not the predetermined temperature, the process of S108 is repeated until the temperature of the filter 15 reaches the predetermined temperature.
[0055]
In S109, the timer Tm is started, and the process proceeds to S110. In S110, the process waits for the next process until the timer Tm exceeds the predetermined time Tm0. If Tm exceeds the predetermined time Tm0 in S110, the process proceeds to the next S111.
[0056]
In S111, the sub-injection started in S106 is terminated. Therefore, the sub-injection is continued for a predetermined time Tm0 after the temperature of the filter 15 reaches the predetermined temperature. Therefore, the predetermined time Tm0 represents a time for continuously performing the sub-injection necessary for oxidizing and removing the PM collected by the filter 15. When the process of S111 ends, the process proceeds to S112.
[0057]
In S112, the EGR valve 25 opened in S107 is closed, and the flow of exhaust gas into the EGR catalyst 23 is stopped. After the process of S112, this control is terminated.
[0058]
In this control, when the PM collected in the filter 15 by the sub-injection is oxidized and removed, the EGR valve 25 is opened, so that exhaust containing a large amount of HC that is originally in an active state to be supplied to the filter 15 is generated. The EGR catalyst 23 is also supplied. As a result, PM deposited on the EGR catalyst 23 is oxidized and removed. Therefore, the PM accumulated on the EGR catalyst 23 is removed by oxidation by a simple method of controlling the opening timing of the EGR valve 25 to maintain the oxidation ability of the EGR catalyst 23, and the accumulation of the EGR catalyst 23 is the cause. It becomes possible to avoid the melting loss of the EGR catalyst 23.
[0059]
In general, the exhaust temperature flowing into the EGR catalyst 23 is higher than the exhaust temperature flowing into the filter 25, and the structure of the EGR catalyst 23 is a structure that oxidizes substances in the exhaust, and mainly collects PM. Since the target structure is not provided, the PM accumulation amount on the EGR catalyst 23 is smaller than the PM collection amount on the filter 15. Therefore, it is possible to sufficiently oxidize and remove the PM accumulated on the EGR catalyst 23 by opening the EGR valve 25 in the time for oxidizing and removing the PM collected by the filter 15 by the sub-injection.
[0060]
Moreover, in this control, in order to oxidize and remove PM collected by the filter 15, the time for continuing the sub-injection after the temperature of the filter 15 reaches a predetermined temperature is controlled by a timer. Here, instead of the control by the timer, the time during which the sub-injection is continued may be controlled by making the differential pressure detected by the differential pressure sensor 33 smaller than a predetermined pressure.
[0061]
<Second Embodiment>
Here, in the PM removal control according to the first embodiment, the EGR valve 25 is opened while the sub-injection for oxidizing and removing the PM collected by the filter 15 is performed. The PM deposited on the EGR catalyst 23 is removed by oxidation. However, the amount of PM deposited on the EGR catalyst 23 is generally smaller than the amount of PM collected by the filter 15 as described above. Therefore, in the first embodiment, the valve opening time of the EGR valve 25 may be excessively long to oxidize and remove the PM deposited on the EGR catalyst 23. Further, since the opening time of the EGR valve 25 becomes longer, the time during which the high-temperature exhaust gas flows into the EGR catalyst 23 becomes longer, so that the EGR catalyst 23 may be further deteriorated by heat.
[0062]
Therefore, PM removal control for removing PM deposited on the EGR catalyst 23 and suppressing thermal degradation of the EGR catalyst 23 as much as possible will be described with reference to FIG. FIG. 3 is a flowchart of the PM removal control. The control is executed by the ECU 20. In the PM removal control flowchart shown in FIG. 3, the same processes as those in the PM removal control flowchart shown in FIG. 2 are denoted by the same reference numerals as those in FIG.
[0063]
In the PM removal control flowchart of FIG. 3, the processes from S201 to S212 are added to the PM removal control flowchart shown in FIG. The most characteristic process in this control is that the valve opening time of the EGR valve 25 is controlled according to the amount of PM accumulated on the EGR catalyst 23.
[0064]
In this control, when the process S102 ends, the process proceeds to S201. In S201, the PM deposition amount Se deposited on the EGR catalyst 23 is calculated. In calculating the PM accumulation amount Se, the accumulated value of the fuel injection amount injected from the fuel injection valve 3 and the accumulated time when the EGR valve 25 is opened when this control is not executed are determined. The PM deposition amount Se is calculated.
[0065]
At this time, the temperature of the exhaust gas flowing into the EGR catalyst 23 fluctuates depending on the operating state of the internal combustion engine 1. Especially when the exhaust gas temperature becomes low, PM tends to accumulate on the EGR catalyst 23, and as the exhaust gas temperature increases, The PM deposited on the EGR catalyst 23 is oxidized and the amount of deposition is reduced. Therefore, in consideration of the operation state of the internal combustion engine 1, that is, the exhaust temperature flowing into the EGR catalyst 23 is estimated from the operation state (engine load, engine speed, etc.) of the internal combustion engine 1, and the PM accumulation amount on the EGR catalyst 23 is estimated. By reflecting in the above, it becomes possible to calculate the PM deposition amount more accurately. When the process of S201 is completed, the processes of S103 to S106 are performed.
[0066]
Then, when the process of S106 ends, the process proceeds to S202. In S202, the valve opening time Topen of the EGR valve 25 is calculated based on the PM accumulation amount Se in the EGR catalyst 23 calculated in S201. The EGR valve opening time Topen is a time required for oxidizing and removing PM accumulated on the EGR catalyst 23 by opening the EGR valve 25. Therefore, the EGR valve opening time Topen becomes shorter as the PM accumulation amount on the EGR catalyst 23 becomes smaller. The relationship between the PM accumulation amount Se and the EGR valve opening time Topen is obtained in advance by experiments or the like and stored in the ROM in the ECU 20 in the form of a map. In S202, the EGR valve opening time Topen is calculated by accessing the map. When the process of S202 ends, the process proceeds to S203.
[0067]
In S203, as in S107 described above, the EGR valve 25 is opened, and the exhaust gas flows into the EGR catalyst 23. When the process of S203 ends, the process proceeds to S204. In S204, the EGR timer Tem is started. The EGR timer Tem is a timer for controlling the valve opening time of the EGR valve 25. When the process of S204 ends, the process proceeds to S205.
[0068]
In S205, it is determined whether or not the EGR timer Tem has exceeded the EGR valve opening time Topen, that is, whether or not the EGR valve 25 has been opened for the time necessary for oxidizing and removing the PM deposited on the EGR catalyst 23. To be judged. If it is determined in S205 that the EGR timer Tem has exceeded the EGR valve opening time Topen, the process proceeds to S207. On the other hand, when it is determined that the EGR timer Tem does not exceed the EGR valve opening time Topen, the process proceeds to S108. In this control, when it is determined in S108 that the filter temperature is not the predetermined temperature, the processing after S205 is performed again.
[0069]
Moreover, in this control, S206 which performs the process similar to S205 is provided between S109 and S110. If it is determined in S206 that the EGR timer Tem has exceeded the EGR valve opening time Topen, the process proceeds to S210. On the other hand, when it is determined in S206 that the EGR timer Tem does not exceed the EGR valve opening time Topen, the process proceeds to S110. In this control, when it is determined in S110 that the timer Tm does not exceed the predetermined time Tm0, the processing after S206 is performed.
[0070]
If it is determined in S205 and S206 that the EGR timer Tem has exceeded the EGR valve opening time Topen, the process proceeds to S207 and S210, respectively, and the EGR valve 25 is closed. By doing so, the EGR valve 25 is not maintained in the open state while the sub-injection for the oxidation removal of the collected PM amount by the filter 15 is performed, but the EGR catalyst 23 The valve is opened only for the time necessary to oxidize and remove the PM deposited on the substrate. When the process of S207 is completed, the processes of S208 and S209 that perform the same processes as S108 and S109 are performed.
[0071]
Then, when the processes of S209 and S210 are completed, the processes of S211 and S212 that perform the same processes as S110 and S111 are performed. After the process of S212, this control is terminated.
[0072]
In this control, as in the first embodiment, the PM accumulated on the EGR catalyst 23 is removed by oxidation by the simple technique of controlling the valve opening timing of the EGR valve 25, and the oxidation capacity of the EGR catalyst 23 is controlled. While maintaining, it is possible to avoid melting of the EGR catalyst 23 caused by the accumulation of the EGR catalyst 23. Further, by controlling the valve opening time of the EGR valve 25 based on the PM accumulation amount accumulated on the EGR catalyst, it is possible to shorten the time during which high-temperature exhaust gas flows into the EGR catalyst 23 as much as possible. Thus, thermal degradation of the EGR catalyst 23 is suppressed.
[0073]
<Third Embodiment>
Here, PM removal control that removes PM deposited on the EGR catalyst 23 and suppresses thermal degradation of the EGR catalyst 23 as much as possible, instead of the first embodiment described above, will be described with reference to FIG. FIG. 4 is a flowchart of the PM removal control. The control is executed by the ECU 20. In the PM removal control flowchart shown in FIG. 4, the same processes as those in the PM removal control flowchart shown in FIG. 2 are denoted by the same reference numerals as those in FIG.
[0074]
In the PM removal control flowchart of FIG. 4, the processes from S301 to S306 are added to the PM removal control flowchart shown in FIG. The most characteristic process in this control is that the frequency of opening the EGR valve 25 is made lower than the frequency of oxidizing and removing PM deposited on the filter 15 by sub-injection.
[0075]
In this control, first, S301 is performed instead of S101 in the flowchart of FIG. In S301, when starting this control, control parameters such as the amount of PM trapped by the filter 15 used in this control and a timer are initialized. However, the sub-injection counter described later is not initialized. When the process of S301 ends, the processes of S102 to S106 are performed thereafter. When the process of S106 ends, the process proceeds to S302.
[0076]
In S302, the auxiliary injection counter is counted to calculate the auxiliary injection number Ns. The sub-injection counter is a parameter that is counted every time sub-injection is started in the process S106, and represents the number of times PM collected by the filter 15 is removed by oxidation. When the process of S302 ends, the process proceeds to S303.
[0077]
In S303, it is determined whether or not the sub injection number Ns is equal to or greater than a predetermined injection number N0. If it is determined in S303 that the sub-injection number Ns is equal to or greater than the predetermined injection number N0, the process proceeds to S304. On the other hand, if it is determined in S303 that the sub injection number Ns is less than the predetermined injection number N0, the process proceeds to S108.
[0078]
In S304, the EGR valve 25 is opened as in S107 described above. Thereby, PM deposited on the EGR catalyst 23 is oxidized and removed. Therefore, the oxidation removal of the PM deposited on the EGR catalyst 23 is performed once every N0 oxidation removal of the PM collected by the filter 15 by the sub-injection. Therefore, the predetermined number of injections N0 described above indicates the ratio at which the PM removed from the EGR catalyst 23 is oxidized and removed with respect to the oxidation removal of the PM collected by the filter 15 by the sub-injection.
[0079]
As described above, the amount of PM deposited on the EGR catalyst 23 is generally smaller than the amount of PM collected by the filter 15. Therefore, the predetermined number of injections N0 may be determined in consideration of the degree of PM accumulation in the EGR catalyst 23. Further, since the degree of accumulation of PM varies depending on the operation state of the internal combustion engine 1, when the predetermined operation state of the internal combustion engine 1 continues, for example, when the engine load of the internal combustion engine 1 continues to be a low load state, In the case where the load state continues, the predetermined number of injections N0 itself may be changed based on the operating state of the internal combustion engine 1, and the predetermined number of injections N0 corresponding to each operating state may be set. When the process of S304 ends, the process proceeds to S305.
[0080]
In S305, the auxiliary injection counter is initialized. That is, the sub injection number Ns is set to zero. When the process of S305 is completed, the process proceeds to S108, and the processes from S108 to S112 are performed thereafter. In this control, a process S306 is provided between the processes S111 and S112, and it is determined whether or not the EGR valve 25 is opened, and it is determined that the EGR valve 25 is opened. When the process is performed, the process of S112 is performed.
[0081]
In this control, similarly to the first embodiment, the PM accumulated on the EGR catalyst 23 is removed by oxidation by the simple technique of controlling the valve opening timing of the EGR valve 25, and the oxidation capacity of the EGR catalyst 23 is controlled. It is possible to prevent the EGR catalyst 23 from being melted due to PM accumulation on the EGR catalyst 23 while maintaining it. Furthermore, the time during which high-temperature exhaust gas flows into the EGR catalyst 23 can be reduced by a simpler control method in which the frequency of opening the EGR valve 25 is reduced below the frequency at which PM collected by the filter 15 is oxidized and removed. It becomes possible to make it as short as possible, and thus thermal degradation of the EGR catalyst 23 is suppressed.
[0082]
<Fourth embodiment>
In the above-described embodiments, the PM collected by the filter 15 is removed by sub-injection. However, since the supply of HC to the exhaust by sub-injection is limited by the state in the combustion chamber of the internal combustion engine 1, the amount of HC that can reach the filter 15 is limited. For this reason, it is difficult to quickly raise the temperature of the filter 15, and the time required for oxidizing and removing the PM collected by the filter 15 becomes longer.
[0083]
Therefore, in the above-described embodiments, fuel is added from the fuel addition valve 30 to the exhaust when the sub-injection is performed. As a result, the amount of HC contained in the exhaust gas flowing into the oxidation catalyst 14 is increased, so that more oxidation heat is generated in the oxidation catalyst 14 due to the oxidation of HC, and the temperature of the exhaust gas flowing into the filter 15 rises. . As a result, the temperature of the filter 15 is quickly raised to a temperature necessary for oxidizing and removing the collected PM. Note that after the filter 15 rises to a temperature necessary for oxidizing and removing the collected PM, the collected PM is oxidized in the filter 15 to generate oxidation heat. However, the fuel addition by the fuel addition valve 30 may be stopped within a range in which the temperature of the filter 15 does not decrease excessively by stopping the fuel addition by the fuel addition valve 30.
[0084]
【The invention's effect】
As described above, the exhaust gas purification system for an internal combustion engine according to the present invention is an exhaust gas purification system for an internal combustion engine having an EGR device including an EGR catalyst, and collects PM in exhaust gas discharged from the internal combustion engine. The exhaust gas purifying means oxidizes and removes PM accumulated on the EGR catalyst by a simple method of opening the EGR valve and allowing the exhaust gas to flow into the EGR catalyst when the collected PM is oxidized and removed by sub-injection. Thus, it is possible to maintain the oxidation ability of the EGR catalyst and to avoid the EGR catalyst from being damaged due to PM deposition on the EGR catalyst.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of an exhaust purification system according to an embodiment of the present invention, an internal combustion engine including the exhaust purification system, and a control system thereof.
FIG. 2 is a flowchart showing PM removal control for oxidizing and removing particulate matter (PM) deposited on an EGR catalyst in the exhaust purification system according to the embodiment of the present invention.
FIG. 3 is a second flowchart showing PM removal control for oxidizing and removing particulate matter (PM) deposited on the EGR catalyst in the exhaust purification system according to the embodiment of the present invention.
FIG. 4 is a third flowchart showing PM removal control for oxidizing and removing particulate matter (PM) deposited on the EGR catalyst in the exhaust purification system according to the embodiment of the present invention.
[Explanation of symbols]
1 ... Internal combustion engine
3. Fuel injection valve
7. Intake branch pipe
8. Intake pipe
12 .... Exhaust branch pipe
13. Exhaust pipe
14 ... Oxidation catalyst
15 ... Filter
20 .... ECU
21... EGR device
22 ... EGR passage
23... EGR catalyst
24 ... EGR cooler
25 ... EGR valve
30 ... Fuel addition valve
31 ... Exhaust air-fuel ratio sensor
32 ... Crank position sensor
33... Differential pressure sensor
34 ... Exhaust temperature sensor

Claims (5)

An exhaust purification means that is provided in an exhaust passage of the internal combustion engine, oxidizes a substance in the exhaust discharged from the internal combustion engine, and collects particulate matter contained in the exhaust;
An EGR passage for recirculating a part of the exhaust discharged from the internal combustion engine from the exhaust passage upstream of the exhaust purification means to the intake passage of the internal combustion engine;
An EGR cooler that is provided in the EGR passage and cools the exhaust gas flowing through the EGR passage;
An EGR catalyst that is provided in the EGR passage on the upstream side of the EGR cooler and oxidizes a substance in the exhaust gas flowing through the EGR passage;
An EGR valve that is provided in the EGR passage on the downstream side of the EGR catalyst and controls the flow of exhaust gas flowing through the EGR passage;
Sub-injection means for performing sub-injection, which is fuel injection again at a predetermined time after main injection in the combustion cycle of the internal combustion engine, to oxidize and remove particulate matter collected by the exhaust gas purification means;
The EGR valve is opened to exhaust the EGR catalyst through the EGR passage during a predetermined period of time during which the particulate matter trapped in the exhaust purification unit is oxidized and removed by the sub-injection of the sub-injection unit. An exhaust gas purification system for an internal combustion engine, comprising: When the combustion gas temperature of the internal combustion engine is lower than a predetermined combustion gas temperature, further comprising a temperature increase control means for increasing the combustion gas temperature of the internal combustion engine,
When the combustion gas temperature of the internal combustion engine is lower than a predetermined combustion gas temperature, the sub injection means raises the combustion gas temperature of the internal combustion engine to the predetermined combustion gas temperature by the temperature increase control means, The exhaust gas purification system for an internal combustion engine according to claim 1, wherein injection is performed. A deposition amount estimating means for estimating a deposition amount of particulate matter deposited on the EGR catalyst;
3. The exhaust gas of the internal combustion engine according to claim 1, wherein the EGR valve control means adjusts a valve opening time of the EGR valve based on the accumulation amount estimated by the accumulation amount estimation means. Purification system. The EGR valve control means opens the EGR valve by opening the EGR valve every time the oxidation removal of the particulate matter collected by the exhaust gas purification means by the sub injection of the sub injection means is executed a predetermined number of times. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2, wherein exhaust gas is caused to flow into the EGR catalyst via a passage. A fuel addition unit that is provided in the exhaust passage upstream of the exhaust purification unit and that adds fuel to the exhaust gas flowing into the exhaust purification unit;
The fuel addition means adds fuel to the exhaust gas flowing through the exhaust passage when the particulate matter collected by the exhaust gas purification means by the sub-injection of the sub-injection means is removed by oxidation. An exhaust purification system for an internal combustion engine according to any one of claims 1 to 4.

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