JP2008169808A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of suppressing deterioration of emission by surely oxidizing reducing component passed through an exhaust emission control device by an oxidation catalyst in the case that a regeneration process of performance of the exhaust emission control device is conducted by supplying a reducing agent to the exhaust emission control device. <P>SOLUTION: When conducting a PM regeneration process, a NOx reducing process and a SOx poisoning recovering process by supplying the reducing agent to the exhaust emission control device such as a filter and a NOx catalyst, secondary air is supplied to the oxidation catalyst in a downstream of the exhaust emission control device and oxidation of a reducing component passed through the exhaust emission control device in the oxidation catalyst is promoted. After completing supply of the reducing agent to the exhaust emission control device, secondary air is continuously be supplied to the oxidation catalyst for a predetermined period of time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

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

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

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

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

Here, in the NOx reduction processing and SOx poisoning recovery processing for the NOx catalyst and the PM regeneration processing for the filter, when the reducing component of the reducing agent supplied to the NOx catalyst and the filter passes downstream, the secondary air A technique is known in which the reducing component that has passed through the supply of oxygen and an oxidation catalyst is oxidized to suppress the emission of the reducing component into the atmosphere.

In this regard, a secondary air introduction pipe and a secondary air amount adjustment valve that communicate the exhaust system and the intake system are provided, and the reducing agent is supplied to the NOx catalyst only when the pressure of the intake system is higher than the pressure of the exhaust system. In addition, a technique for supplying air from the secondary air introduction pipe to the upstream side of the catalyst having an oxidation function has been proposed (for example, see Patent Document 1).

Further, when the engine is started or when the exhaust gas temperature is equal to or lower than a predetermined temperature, the intake air amount is reduced and the secondary air is supplied from the secondary air supply nozzle, so that NOx, HC and C in the exhaust gas are reduced.
A technique for reducing O has been proposed (see, for example, Patent Document 2).

When the reducing agent is supplied to the NOx catalyst as described above, for example, a part of the reducing agent supplied to the NOx catalyst passes through the NOx catalyst through the adsorption and desorption processes on the NOx catalyst. Even after the supply of the reducing agent is finished, the reducing component HC continues to be discharged from the NOx catalyst. Here, in the control for supplying the reducing agent to the NOx catalyst and supplying the air from the secondary air introduction pipe to the upstream side of the oxidation catalyst, the supply of the secondary air to the oxidation catalyst is performed simultaneously with the supply of the reducing agent to the NOx catalyst. Suppose that it was stopped. Then, even after the secondary air supply stops,
May continue to be discharged from the NOx catalyst, and may not be sufficiently oxidized by the oxidation catalyst, but may be diffused to the outside, resulting in a worse emission.
JP 2003-343245 A Japanese Patent Laid-Open No. 10-121952

  The present invention has been made in view of the above-described facts, and an object of the present invention is to provide an exhaust purification device when a reducing agent is supplied to the exhaust purification device and regeneration processing of the purification capability of the exhaust purification device is performed. It is to provide a technique that can more reliably oxidize a reducing component that has passed through an oxidation catalyst and suppress deterioration of emissions.

In order to achieve the above object, the present invention provides an exhaust gas purification apparatus when a reducing agent is supplied to an exhaust gas purification apparatus such as a filter or a NOx catalyst to perform PM regeneration processing, NOx reduction processing, SOx poisoning recovery processing, or the like. After supplying secondary air to the oxidation catalyst disposed downstream of the exhaust gas to promote oxidation of the reducing component that has passed through the exhaust purification device in the oxidation catalyst, and after the supply of the reducing agent to the exhaust purification device is completed, The main feature is that the supply of secondary air to the oxidation catalyst is continued for a predetermined period.

More specifically, an exhaust purification device that is provided in an exhaust passage of the internal combustion engine and purifies exhaust from the internal combustion engine;
Reducing agent addition means for adding a reducing agent to the exhaust gas passing upstream of the exhaust gas purification device in the exhaust passage;
An oxidation catalyst provided on the downstream side of the exhaust purification device in the exhaust passage and having an oxidizing ability;
Secondary air supply means for supplying secondary air to the oxidation catalyst by introducing secondary air between the exhaust gas purification device and the oxidation catalyst in the exhaust passage;
Regenerating means for supplying a reducing agent to the exhaust purification device by adding a reducing agent to the exhaust gas from the reducing agent adding means, and for performing a regeneration process of the purification ability of the exhaust purification device;
Reducing component oxidation promoting means for promoting the oxidation in the oxidation catalyst of the reducing component discharged from the exhaust gas purification device by supplying secondary air from the secondary air supply means to the oxidation catalyst during the regeneration process. When,
An exhaust gas purification system for an internal combustion engine comprising:
The reducing component oxidation promoting means continues supplying the secondary air from the secondary air supplying means for a predetermined period after the addition of the reducing agent from the reducing agent adding means in the regeneration process is completed. It is characterized by.

Here, as described above, when supplying the reducing agent to the filter and the NOx catalyst in the PM regeneration process, the NOx reduction process, and the SOx poisoning recovery process, the reducing component of the supplied reducing agent is H.
C and CO may pass through the filter and the NOx catalyst. Such a reducing component is suppressed from being oxidized by the oxidation catalyst provided downstream of the filter and the NOx catalyst and being directly diffused to the outside. At that time, the secondary air is supplied to the oxidation catalyst to promote the oxidation of the reducing component in the oxidation catalyst.

However, since the reducing agent supplied to the exhaust purification device such as the filter and the NOx catalyst is discharged from the exhaust purification device after being adsorbed and desorbed to the oxidation purification device, the reduction agent supplied to the exhaust purification device. There may be a time delay before the reducing component of the agent passes through the exhaust purification device and is discharged.

  Then, in the regeneration process such as the PM regeneration process, the NOx reduction process, and the SOx poisoning recovery process, the timing when the supply of the reducing agent to the exhaust purification device is terminated and the timing when the supply of the secondary air to the oxidation catalyst is terminated. When the same period is used, the reducing component that has passed through the exhaust purification device is supplied to the oxidation catalyst after the supply of the secondary air is completed, and the oxidation efficiency of the reducing component at that time decreases. was there. As a result, the reducing component that has not been sufficiently oxidized in the oxidation catalyst may be diffused to the outside, leading to a deterioration in emissions.

  Therefore, in the present invention, after the supply of the reducing agent to the exhaust gas purification device in the regeneration process such as the PM regeneration process, the NOx reduction process, the SOx poisoning recovery process, etc. is completed, it is possible to supply the oxidation catalyst for It was decided to continue supplying the next air.

  Then, after the supply of the reducing agent to the exhaust purification device is completed, the reducing component discharged through the adsorption and desorption processes in the exhaust purification device can be more reliably oxidized in the oxidation catalyst, Deterioration of emissions can be suppressed.

  In the above description, the predetermined period may be a period from the end of the supply of the reducing agent to the exhaust purification device to the almost complete end of the reduction component passing through the exhaust purification device.

  In the present invention, the predetermined period may be determined based on the amount of the reducing agent added from the reducing agent addition means and / or the temperature of the exhaust gas purification device in the regeneration process.

  Here, the amount of reducing agent discharged through the exhaust purification device increases as the amount of reducing agent added from the reducing agent addition means in the regeneration process increases. Then, the period during which the reducing component that has passed through the exhaust purification device is discharged from the exhaust purification device becomes longer as the amount of the reducing agent added from the reducing agent addition means in the regeneration process increases. Therefore, there is a high correlation between the period during which the reducing component that has passed through the exhaust purification device is discharged from the exhaust purification device and the amount of the reducing agent added from the reducing agent addition means in the regeneration process.

  Further, when the temperature of the exhaust purification device is high, the added fuel is highly evaporable and the catalytic reaction is also highly reactive, so that the amount of reducing components passing through the exhaust purification device is considered to be small. Conversely, when the temperature of the exhaust purification device is low, it is considered that the amount of reducing components passing through the exhaust purification device increases because the added fuel has low evaporability and low catalytic reaction. Therefore, there is a high correlation between the period during which the reducing component that has passed through the exhaust purification device is discharged from the exhaust purification device, and the temperature of the exhaust purification device.

  Therefore, in the present invention, the predetermined period may be determined based on the amount of the reducing agent added from the reducing agent addition means and / or the temperature of the exhaust purification device in the regeneration process. Specifically, when the amount of reducing agent added from the reducing agent addition means in the regeneration process is larger, the predetermined period may be longer. Further, when the temperature of the exhaust purification device is higher, the predetermined period may be shorter.

  In other words, the predetermined period when the amount of the reducing agent added from the reducing agent addition unit in the regeneration process is larger may be equal to or longer than the predetermined period when the amount of the reducing agent is smaller. In the regeneration process, the predetermined period when the temperature of the exhaust purification apparatus is higher may be equal to or less than the predetermined period when the temperature of the exhaust purification apparatus is lower.

According to this, the predetermined period is more accurately matched with the period from when the supply of the reducing agent to the exhaust purification device is completed until the discharge of the reducing component that has passed through the exhaust purification device is almost completed. Can do. As a result, after the supply of the secondary air is completed, it is possible to suppress the reduction component of the reducing agent from being discharged from the exhaust purification device, thereby deteriorating the emission and supplying the secondary air for a longer period than necessary. .

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

  In the present invention, when the reducing agent is supplied to the exhaust purification device and the purification performance of the exhaust purification device is regenerated, the reducing component that has passed through the exhaust purification device can be more reliably oxidized in the oxidation catalyst. It is possible to suppress the deterioration of emission more reliably.

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

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine according to the present embodiment, and its intake / exhaust system and control system. In FIG. 1, the inside of the internal combustion engine 1 is omitted. In FIG. 1, an intake pipe 6 for introducing fresh air is connected to the internal combustion engine 1. The intake pipe 6 is provided with an intake throttle valve 15 that controls the intake air amount and an air flow meter 16 that detects the flow rate of the intake air. On the other hand, an exhaust pipe 5 through which the exhaust discharged from the internal combustion engine 1 flows is connected to the internal combustion engine 1, and this exhaust pipe 5 is connected downstream to a muffler (not shown). Further, an exhaust gas purification device 10 that purifies the exhaust gas passing through the exhaust pipe 5 is disposed in the middle of the exhaust pipe 5.

Inside the exhaust purification device 10 in the present embodiment, NSR1 that is a NOx storage reduction catalyst is provided.
DPNR 10b, which is disposed downstream of NSR 10a and has both the function of a wall flow filter made of a porous base material and the function of an NOx storage reduction catalyst, and DPNR 10
and an oxidation catalyst 10c that is disposed downstream of b and has oxidation ability.

In the exhaust pipe 5, upstream of the exhaust purification device 10, during the NOx reduction process, the SOx poisoning recovery process for the NSR 10 a, the PM regeneration process, the NOx reduction process, and the SOx poisoning recovery process for the DPNR 10 b, A fuel addition valve 12 for supplying fuel as a reducing agent to 10 is disposed. The fuel addition valve 12 corresponds to a reducing agent addition means in this embodiment.

  Further, a temperature sensor 13 that detects the temperatures of the NSR 10a and the DPNR 10b is provided between the NSR 10a and the DPNR 10b in the exhaust purification device 10. In addition, a secondary air injection valve 14 for supplying secondary air to the oxidation catalyst 10c is provided between the DPNR 10b and the oxidation catalyst 10c. The secondary air injection valve 14 is in communication with an air tank (not shown) so that air can be injected into the exhaust purification device 10 at a predetermined air pressure. The secondary air injection valve 14 corresponds to secondary air supply means in this embodiment.

The internal combustion engine 1 configured as described above and its exhaust system are provided with an electronic control unit (ECU) 20 for controlling the internal combustion engine 1 and the exhaust system. The ECU 20 controls the exhaust gas purification device 10 of the internal combustion engine 1 in addition to controlling the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the driver's request.

In addition to a crank position sensor and an accelerator position sensor (not shown), sensors related to control of the operation state of the internal combustion engine 1 such as a temperature sensor 13 and an air flow meter 16 are connected to the ECU 20 via electric wiring, and an output signal is transmitted. It is input to the ECU 20. On the other hand, a fuel injection valve (not shown) in the internal combustion engine 1 is connected to the ECU 20 via an electrical wiring, and the fuel addition valve 12, the secondary air injection valve 14 and the intake throttle valve 15 in this embodiment are electrically connected. It is connected via wiring and is controlled by the ECU 20.

  The ECU 20 includes a CPU, a ROM, a RAM, and the like. The ROM stores a program for performing various controls of the internal combustion engine 1 and a map storing data. NOx reduction processing routine for reducing and releasing NOx occluded in NSR 10a, SOx poisoning recovery routine for SOx poisoning recovery, PM regeneration routine for oxidizing and removing particulate matter collected by DPNR 10b (whichever In addition, the secondary air injection extension control routine, which will be described later, is one of programs stored in the ROM of the ECU 20. Therefore, the ECU 20 corresponds to the regenerating means and reducing component oxidation promoting means in this embodiment.

Next, control when supplying the reducing agent and the secondary air to the exhaust purification device 10 will be described by taking the NOx reduction process for the NSR 10a and the DPNR 10b as an example. First, the NOx reduction process for the conventional NSR 10a will be described. NSR10a and DPNR10b
When NOx reduction treatment is performed, fuel as a reducing agent is added from the fuel addition valve 12 into the exhaust gas, and the fuel is supplied to the NSR 10a and the DPNR 10b.

  FIG. 2 is a graph showing the relationship between the air-fuel ratio of the exhaust gas introduced into the exhaust gas purification apparatus 10 at that time and the components contained in the exhaust gas discharged from the DPNR 10b.

  As shown in FIG. 2, when the air-fuel ratio of the exhaust gas introduced into the exhaust gas purification apparatus 10 is high, the released NOx is discharged without being reduced, and the amount of NOx discharged from the DPNR 10b increases. On the other hand, when the air-fuel ratio of the exhaust gas introduced into the exhaust gas purification apparatus 10 is low, the amount of HC in the exhaust gas increases because more reducing components pass without being oxidized in the NSR 10a and DPNR 10b.

Therefore, the exhaust purification device 1 during the NOx reduction process of the NSR 10a and the DPNR 10b
The air-fuel ratio of the exhaust gas introduced into 0 is desirably controlled within a range indicated by A in FIG. However, in reality, the air-fuel ratio of the exhaust gas becomes excessively rich due to an increase in the fuel injection characteristics of the fuel addition valve 12 or a variation in fuel properties (an increase in specific gravity, etc.), for example, in the range of B in FIG. was there. As a result, the amount of HC in the exhaust discharged from the DPNR 10b may increase.

  On the other hand, conventionally, HC discharged from the DPNR 10b is oxidized in the downstream oxidation catalyst 10c to suppress emission of HC to the outside. Further, when fuel is supplied to the exhaust purification device 10 in the NOx reduction process, secondary air is injected from the secondary air injection valve 14 at the same time as the fuel addition from the fuel addition valve 12 to the oxidation catalyst 10c. Secondary air has been supplied to promote the HC oxidation reaction in the oxidation catalyst 10c.

  However, in this case, since the fuel added from the fuel addition valve 12 is discharged after the adsorption and desorption processes in the NSR 10a and the DPNR 10b, the fuel is added from the DPNR 10b after the fuel addition from the fuel addition valve 12 is completed. HC may continue to be discharged. As a result, for the HC discharged from the DPNR 10b after the fuel addition from the fuel addition valve 12 is completed, the oxidation reaction in the oxidation catalyst 10c cannot be promoted by the supply of the secondary air from the secondary air injection valve 14. There was a case. As a result, the HC discharged from the DPNR 10b may not be sufficiently oxidized by the oxidation catalyst 10c and may be diffused to the outside.

  Therefore, in the present invention, after the fuel addition from the fuel addition valve 12 is completed, the secondary air injection from the secondary air injection valve 14 is continued for a predetermined period.

  FIG. 3 shows the control of the fuel addition valve 12 and the secondary air injection valve 14 and the change in the amount of HC component in the exhaust discharged from the exhaust purification device 10 in this embodiment.

  The two curves shown in the upper part of FIG. 3 show that during the exhaust from the exhaust purification device 10 when it is assumed that the fuel addition from the fuel addition valve 12 is ON / OFF and the oxidation catalyst 10c and the secondary air are not injected. This shows the change in the amount of HC. In this case, the amount of HC in the exhaust increases over a long period from the middle of fuel addition from the fuel addition valve 12 to after the fuel addition from the fuel addition valve 12 is turned off.

  The two curves shown in the middle stage of FIG. 3 are the cases where the oxidation catalyst 10c is provided, and the secondary air from the secondary air injection valve 14 is synchronized with the fuel addition from the fuel addition valve 12 shown in the upper stage. 6 shows the change in the amount of HC in the exhaust gas from the exhaust gas purification device 10 when the injection is performed. In this case, as described above, during the period in which the secondary air is injected from the secondary air injection valve 14, the amount of HC in the exhaust gas decreases and becomes substantially zero. After the fuel addition from 12 and the injection of secondary air from the secondary air injection valve 14 are turned off, the amount of HC in the exhaust gas increases.

  The two curves shown in the lower part of FIG. 3 are cases where secondary air injection from the secondary air injection valve 14 is performed in addition to fuel addition from the fuel addition valve 12 shown in the upper part. Even after the fuel addition from the valve 12 is turned off, during the exhaust from the exhaust purification device 10 when the secondary air injection from the secondary air injection valve 14 is extended over the secondary air injection extension time T1. This shows the change in the amount of HC. In this case, the amount of HC in the exhaust does not increase even after the fuel addition is turned off, and is substantially zero.

The secondary air injection extension time T1 is determined as in the following formula (1).
T1 = C1 × τ (1)
Here, τ is the amount of fuel added from the fuel addition valve 12 at the time of fuel addition, and is determined according to the operating state of the internal combustion engine 1. C1 is an extension time correction coefficient. This extension time correction coefficient is a coefficient determined according to the temperatures of the NSR 10a and the DPNR 10b.

  That is, under the conditions where the temperature of the NSR 10a and the DPNR 10b is high, the added fuel has good evaporability and the catalytic reaction is highly reactive, so that the amount of HC discharged through the NSR 10a and the DPNR 10b and downstream of the DPNR 10b is reduced. . On the other hand, when the temperature of the NSR 10a and the DPNR 10b is low, the added fuel is poorly evaporative and the reactivity of the catalytic reaction is low, so the amount of HC passing through the NSR 10a and the DPNR 10b and discharged downstream of the DPNR 10b increases. . Therefore, C1 has a relationship as shown in FIG. 4, for example, with respect to the temperatures of the NSR 10a and the DPNR 10b.

Thus, in this embodiment, the secondary air injection extension time T1 becomes shorter as the temperature of the NSR 10a and the DPNR 10b is higher so that the amount of fuel added from the fuel addition valve 12 in the NOx reduction process increases. Has been determined.

  Next, FIG. 5 shows a flowchart of a secondary air injection extension control routine in the present embodiment. This flow is a program stored in the ROM of the ECU 20, and is executed by the ECU 20 at predetermined intervals while the internal combustion engine 1 is in operation.

  When this routine is executed, it is first determined in S101 whether fuel is being added from the fuel addition valve 12 or not. Specifically, the determination may be made by reading a drive signal for the fuel addition valve 12 into the ECU 20. If a positive determination is made here, the process proceeds to S102, and if a negative determination is made, the process proceeds to S106.

  In S102, it is determined whether or not secondary air injection from the secondary air injection valve 14 is in progress. Specifically, the determination may be made by reading the drive signal of the secondary air injection valve 14 into the ECU 20. If it is determined here that the secondary air is being injected, this routine is immediately terminated. On the other hand, if it is determined that the secondary air is not being injected, the process proceeds to S103. In S103, the secondary air injection from the secondary air injection valve 14 is started. When the process of S103 ends, the process proceeds to S104.

  In S104, the secondary air injection extension control end flag is turned OFF. When the process of S104 ends, the process proceeds to S105.

  In S105, the secondary air injection extension time T1 is derived. Specifically, the value of the extended time correction coefficient C1 is read from the map in which the relationship shown in FIG. 4 is stored based on the temperatures of the NSR 10a and DPNR 10b obtained from the output signal of the temperature sensor 13. Then, based on the C1 and the fuel addition amount τ related to the fuel addition determined to be being implemented in S101, the calculation shown in Expression (1) is performed, and T1 is calculated. When the process of S105 ends, this routine is temporarily ended.

  The description returns to the case where a negative determination is made in S101. In this case, it progresses to S106 and it is determined whether secondary air injection extension control is complete | finished. Specifically, it is determined whether or not the secondary air injection extension control end flag is ON. When the secondary air injection extension control end flag is ON, it is determined that the secondary air injection extension control by the secondary air injection valve 14 has ended, and the secondary air injection has ended. The routine is temporarily terminated. On the other hand, if it is determined that the secondary air injection extension control end flag is OFF, the process proceeds to S107.

  In S107, it is determined whether or not the elapsed time since the last fuel addition from the fuel addition valve 12 has exceeded T1 calculated in S105. If it is determined that the elapsed time from the end of fuel addition is T1 or less, this routine is temporarily ended. On the other hand, if it is determined that the elapsed time from the end of fuel addition has exceeded T1, it can be determined that the period during which secondary air injection extension control should be performed has ended, and thus the process proceeds to S108.

  In S108, the injection of secondary air from the secondary air injection valve 14 is terminated. When the process of S108 ends, the process proceeds to S109.

  In S109, the secondary air injection extension control end flag is turned ON. When the process of S109 is completed, this routine is temporarily ended.

  As described above, in the present embodiment, in the NOx reduction process of the NSR 10a and the DPNR 10b, the secondary air injection is performed over the secondary air injection extended time T1 even after the fuel addition from the fuel addition valve 12 is completed. The secondary air injection from the valve 14 was continued.

Therefore, even after the fuel addition from the fuel addition valve 12 is completed, the HC component of the added fuel is introduced into the oxidation catalyst 10c after the adsorption and desorption processes in the NSR 10a and the DPNR 10b. Oxidation in the oxidation catalyst 10c can be promoted. Thereby, it can suppress more reliably that HC component is discharged | emitted from the exhaust gas purification apparatus 10, and is dissipated outside, and exhaust emission can be improved more reliably.

  In the above-described embodiment, the NSR 10a, the DPNR 10b, and the oxidation catalyst 10c are arranged in the case of the exhaust purification device 10, and the secondary air is supplied from the secondary air injection valve 14 to the DPNR 10b and the oxidation catalyst 10c in the exhaust purification device 10. The oxidation catalyst 10c is disposed in a case different from the NSR 10a and the DPNR 10b, and the secondary air is supplied from the secondary air injection valve 14 to the exhaust pipe 5 between the cases. May be injected.

  In the above embodiment, the temperature sensor 13 is arranged between the NSR 10a and the DPNR 10b in order to detect the temperatures of the NSR 10a and the DPNR 10b. However, the temperature of the NSR 10a and the temperature of the DPNR 10b are separately detected, and two temperatures are detected. In this relationship, the extension time correction coefficient C1 may be determined. Further, an average value of two temperatures may be calculated, and the extended time correction coefficient C1 may be determined in relation to this average value. Furthermore, without using the temperature sensor 13, the temperatures of the NSR 10a and the DPNR 10b may be estimated from the past operating state history.

In the above embodiment, the NOx reduction process for the NSR 10a and the DPNR 10b has been described as an example. Of course it is good.

  Further, in the above-described embodiment, when the reducing agent is supplied to the exhaust gas purification device 10, the fuel is added by injecting the fuel into the exhaust gas from the fuel addition valve 12. You may add by sub-injection.

  Further, in the above embodiment, the secondary air injection extension time T1 is determined by the formula (1), and is calculated one by one using both the fuel addition amount from the fuel addition valve 12 and the temperatures of the NSR 10a and the DPNR 10b as parameters. Yes. However, even if the secondary air injection extension time T1 is defined as a predetermined constant value, the effects of the present invention can be sufficiently achieved. Alternatively, only one of the fuel addition amount from the fuel addition valve 12 and the temperatures of the NSR 10a and the DPNR 10b may be determined as a parameter. Further, the exhaust flow velocity may be calculated one by one in addition to the parameter.

It is a figure which shows schematic structure of the internal combustion engine in the Example of this invention, its intake / exhaust system, and a control system. 5 is a graph showing the relationship between the air-fuel ratio of exhaust gas introduced into the NSR and the emission exhausted from the DPNR in the NOx reduction processing of NSR and DPNR according to an example of the present invention. 6 is a graph showing changes in the amount of HC in exhaust from the exhaust purification device with respect to the fuel addition period and the secondary air injection period in the NOx reduction treatment of NSR and DPNR according to an example of the present invention. It is a graph which shows the relationship between the temperature of NSR and DPNR in the Example of this invention, and the extended time correction coefficient of the injection time of secondary air. It is a flowchart which shows the secondary air injection extension control routine in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Exhaust pipe 6 ... Intake pipe 10 ... Exhaust gas purification apparatus 10a ... NSR
10b ... DPNR
DESCRIPTION OF SYMBOLS 10c ... Oxidation catalyst 12 ... Fuel addition valve 13 ... Temperature sensor 14 ... Secondary air injection valve 15 ... Intake throttle valve 16 ... Air flow meter 20 ... ECU

Claims (3)

An exhaust purification device that is provided in an exhaust passage of the internal combustion engine and purifies exhaust from the internal combustion engine;
Reducing agent addition means for adding a reducing agent to the exhaust gas passing upstream of the exhaust gas purification device in the exhaust passage;
An oxidation catalyst provided on the downstream side of the exhaust purification device in the exhaust passage and having an oxidizing ability;
Secondary air supply means for supplying secondary air to the oxidation catalyst by introducing secondary air between the exhaust gas purification device and the oxidation catalyst in the exhaust passage;
Regenerating means for supplying a reducing agent to the exhaust purification device by adding a reducing agent to the exhaust gas from the reducing agent adding means, and for performing a regeneration process of the purification ability of the exhaust purification device;
Reducing component oxidation promoting means for promoting the oxidation in the oxidation catalyst of the reducing component discharged from the exhaust gas purification device by supplying secondary air from the secondary air supply means to the oxidation catalyst during the regeneration process. When,
An exhaust gas purification system for an internal combustion engine comprising:
The reducing component oxidation promoting means continues supplying the secondary air from the secondary air supplying means for a predetermined period after the addition of the reducing agent from the reducing agent adding means in the regeneration process is completed. An exhaust gas purification system for an internal combustion engine.   The predetermined period when the amount of the reducing agent added from the reducing agent addition unit in the regeneration process is larger than the predetermined period when the amount of the reducing agent is smaller. 2. An exhaust gas purification system for an internal combustion engine according to 1. The predetermined period when the temperature of the exhaust gas purification device is higher in the regeneration process is set to be equal to or less than the predetermined time period when the temperature of the exhaust gas purification device is lower. An exhaust purification system for an internal combustion engine.

Images