JP4609299B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

A technique is known in which an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst) is disposed in an exhaust passage of an internal combustion engine. The NOx catalyst occludes NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reduces the stored NOx when the oxygen concentration of the inflowing exhaust gas decreases and a reducing agent is present.

By the way, the NOx catalyst is sulfur oxide (S
Ox) is also occluded by the same mechanism as NOx. The stored SOx is less likely to be released than NOx and accumulates in the NOx catalyst. This is called sulfur poisoning. Since the NOx purification rate in the NOx catalyst is reduced by this sulfur poisoning, it is necessary to perform a poisoning recovery process for recovering from sulfur poisoning at an appropriate time. This poisoning recovery process is performed by causing the NOx catalyst to have a high temperature and the exhaust gas having a reduced oxygen concentration to flow through the NOx catalyst.

Thus, when the reduction of NOx and the recovery of sulfur poisoning are performed in a rich atmosphere, the reducing agent or H ₂ S may flow out downstream of the NOx catalyst. Here, a technique is known in which an oxidation catalyst is provided downstream of the NOx catalyst, air is supplied to the oxidation catalyst to form an oxygen-excess atmosphere, and a reducing agent and H ₂ S are oxidized (for example, Patent Documents). 1).
JP 2000-110552 A JP 2002-038939 A Japanese Patent Laying-Open No. 2005-076504 Japanese Patent Laid-Open No. 2004-076762 JP-A-6-129237

  By the way, during transient operation of the internal combustion engine, combustion may be performed with a rich air-fuel ratio in the cylinder of the internal combustion engine, and in this case, the air-fuel ratio of the exhaust gas from the internal combustion engine changes to the rich air-fuel ratio. In addition, when a reducing agent is added during exhaust, the reducing agent may adhere to the exhaust passage. The reducing agent adhering in this way evaporates all at once when the flow rate of the exhaust gas increases, such as during acceleration, or when the exhaust gas temperature rises, and the air-fuel ratio of the exhaust gas changes to the rich side. Let

  For this reason, if a certain amount of secondary air is supplied, the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst fluctuates, so that the lean air-fuel ratio exhaust gas may flow into the oxidation catalyst. Also, when the exhaust gas that has changed to the rich side reaches the oxidation catalyst, the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst does not change immediately even if the supply of the reducing agent is stopped or the supply amount is reduced. . Therefore, the oxidation catalyst becomes a rich atmosphere, and the oxidation ability is reduced. From the above, there is a risk that HC may slip through the oxidation catalyst or white smoke may be generated.

  The present invention has been made in view of the above-described problems, and in an exhaust gas purification apparatus for an internal combustion engine, a technique capable of maintaining an air-fuel ratio of exhaust gas flowing into a catalyst having an oxidation function at an appropriate value. The purpose is to provide.

In order to achieve the above object, the exhaust gas purification apparatus for an internal combustion engine of the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine of the present invention is
A catalyst provided in the exhaust passage of the internal combustion engine and having an oxidation function;
Secondary air supply means for supplying secondary air to the exhaust passage upstream of the catalyst having the oxidation function;
Air-fuel ratio fluctuation detecting means for detecting fluctuations in the air-fuel ratio of the exhaust gas flowing into the catalyst having the oxidation function;
With
The amount of secondary air supplied by the secondary air supply means is adjusted according to the change in the air-fuel ratio detected by the air-fuel ratio fluctuation detection means.

  In this way, even if the air-fuel ratio of the exhaust gas flowing upstream of the catalyst having oxidation ability is rich air fuel, the oxidation is performed by supplying air upstream of the catalyst having oxidation function by the secondary air supply means. Exhaust gas flowing into the catalyst can be set to a lean air-fuel ratio. Thereby, the oxidation capability of the catalyst can be improved. Then, if the air-fuel ratio fluctuation detecting means detects the fluctuation of the air-fuel ratio of the exhaust gas flowing into the catalyst, and the secondary air is supplied by the secondary air supply means in accordance with the fluctuation, the atmosphere of the catalyst is changed to a lean atmosphere. Can be. That is, even if the exhaust gas from the internal combustion engine is lean at the present time, if the rich gas is discharged in the past, the secondary air is also added when the rich gas reaches the catalyst having an oxidation function. Supply.

In this way, HC, CO, H ₂ S and the like can be oxidized by the catalyst. The air-fuel ratio fluctuation detecting means detects the fluctuation of the air-fuel ratio of the exhaust gas flowing into the catalyst having oxidation ability. This is because the fluctuation of the air-fuel ratio of the exhaust gas immediately before the catalyst having oxidation ability or the secondary air is detected. The fluctuation of the air-fuel ratio of the exhaust in the vicinity of the location where the secondary air is supplied by the supply means may be detected.

Further, in the present invention, a NOx catalyst that is provided upstream of the catalyst having the oxidation ability and reduces NOx in the presence of a reducing agent;
Reducing agent addition means for adding a reducing agent from upstream of the NOx catalyst;
Further comprising
The amount of secondary air supplied by the secondary air supply means can be adjusted according to the fluctuation of the air-fuel ratio detected by the air-fuel ratio fluctuation detection means after the reducing agent is added by the reducing agent addition means. .

When the reducing agent is added by the reducing agent addition means, a part of the reducing agent may adhere to the exhaust passage. The reducing agent adhering to the exhaust passage in this way evaporates from the exhaust passage and reaches the NOx catalyst and the catalyst having oxidation ability even after the addition of the reducing agent by the reducing agent adding means is completed. Thereby, even if the reducing agent is not added, the air-fuel ratio of the exhaust varies. Even in such a case, the air-fuel ratio fluctuation is detected by the air-fuel ratio fluctuation detecting means, and the air is supplied by the secondary air supply means in accordance with this. That is, even when no reducing agent is added from the reducing agent addition means at present, if the reducing agent has been added from the reducing agent addition means in the past, the reducing agent becomes a catalyst having an oxidation function. Supply secondary air when reaching. Thereby, the air-fuel ratio of the exhaust gas flowing into the catalyst having oxidation ability can be made the lean air-fuel ratio. Furthermore, the oxidation ability of the catalyst can be improved.

Further, in the present invention, the air-fuel ratio fluctuation detecting means includes a delay time that is a time from when unburned HC is discharged from the internal combustion engine to the catalyst having the oxidation capability, and / or the reducing agent. A variation in the air-fuel ratio is detected based on a delay time that is a time from when the reducing agent is added by the adding means to when the reducing agent adheres to the exhaust passage and then evaporates to reach the catalyst having the oxidation ability. it can.

  That is, even if unburned HC is discharged from the internal combustion engine, or even if a reducing agent adheres to the exhaust passage and then evaporates, there is a certain distance to the catalyst having oxidation ability, so they reach the catalyst. It takes time. Such a time is called a delay time. Then, when unburned HC is discharged from the internal combustion engine and / or when the elapsed time after the reducing agent adhering to the exhaust passage evaporates becomes a delay time, air is supplied by the secondary air supply means. By supplying, the air-fuel ratio of the exhaust gas flowing into the catalyst having oxidation ability can be made the lean air-fuel ratio.

  In the present invention, the delay time may be calculated based on the flow rate of exhaust gas and the volume of the exhaust passage.

  The volume of the exhaust passage refers to the location where the secondary air is supplied by the secondary air supply means from the location where the reducing agent added by the cylinder of the internal combustion engine or the reducing agent addition means adheres, or the oxidation capacity. The volume up to the catalyst. If the flow rate of the exhaust gas and the volume of the exhaust passage are determined, the time required for the unburned HC and the evaporated reducing agent to reach the catalyst having oxidation ability, that is, the delay time is also determined. That is, the delay time can be calculated based on the flow rate of the exhaust gas and the volume of the exhaust passage.

  In the present invention, the air-fuel ratio fluctuation detecting means may include an air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust.

  By directly measuring the air-fuel ratio of the exhaust with the air-fuel ratio sensor, it is possible to accurately detect fluctuations in the air-fuel ratio. The variation in the air-fuel ratio can also be obtained from the amount of reducing agent attached to the exhaust passage and the amount of evaporation, and the delay time.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention can maintain the air-fuel ratio of the exhaust gas flowing into the catalyst having an oxidation function at an appropriate value.

  Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which an exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied and its intake / exhaust passage. The internal combustion engine 1 shown in FIG. 1 is a four-cycle diesel engine having four cylinders 2.

  An intake branch pipe 3 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 3 communicates with a combustion chamber of each cylinder 2. The intake branch pipe 3 is connected to an intake pipe 4, and a compressor housing 5 a of a centrifugal supercharger (turbocharger) 5 that operates using the heat energy of exhaust gas as a drive source is provided in the middle of the intake pipe 4. Yes. An intake throttle valve 6 for adjusting the flow rate of the intake air flowing through the intake pipe 4 is provided at a portion of the intake pipe 4 located immediately upstream of the intake branch pipe 3.

On the other hand, an exhaust branch pipe 9 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 9 leads to a combustion chamber of each cylinder 2. The exhaust branch pipe 9 is connected to the turbine housing 5 b of the turbocharger 5. The turbine housing 5 b is connected to the exhaust pipe 10. A particulate filter (hereinafter simply referred to as a filter) 11 carrying an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst) is provided in the middle of the exhaust pipe 10. The filter 11 collects particulate matter (hereinafter referred to as PM) in the exhaust gas. The NOx catalyst stores NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reduces the stored NOx when the oxygen concentration of the inflowing exhaust gas decreases and a reducing agent is present. Have An oxidation catalyst 12 having oxidation ability is provided downstream of the filter 11. In addition, an air-fuel ratio sensor 13 that outputs an electrical signal corresponding to the air-fuel ratio of the exhaust gas flowing between the filter 11 and the oxidation catalyst 12 is attached.

  A secondary air supply nozzle 20 for supplying secondary air into the exhaust pipe 10 is attached to the exhaust pipe 10 between the filter 11 and the oxidation catalyst 12. One end of a secondary air supply pipe 21 is connected to the secondary air supply nozzle 20. The other end of the secondary air supply pipe 21 is connected to the air pump 22. The air pump 22 includes an electric motor, and discharges air according to the number of rotations.

  Then, when the secondary air supply nozzle 20 is opened, the air pump 22 and the exhaust pipe 10 are communicated with each other. At this time, the air pump 22 operates and discharges air, so that air flows into the secondary air supply pipe 21. Then, this air is supplied to the exhaust pipe 10 via the secondary air supply nozzle 20. The air supplied to the exhaust pipe 10 in this way flows into the oxidation catalyst 12 while being mixed with the exhaust gas flowing from the upstream side of the exhaust pipe 10. In this embodiment, the air pump 22 corresponds to the secondary air supply means in the present invention.

Further, in this embodiment, a reducing agent addition valve 14 is provided for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust branch pipe 9. The reducing agent addition valve 14 is opened by a signal from the ECU 10 described later to inject fuel. The fuel injected from the reducing agent addition valve 14 into the exhaust branch pipe 9 enriches the air-fuel ratio of the exhaust and reduces NOx stored in the NOx catalyst. During NOx reduction, so-called rich spike control is performed in which the air-fuel ratio of the exhaust gas flowing into the filter 11 is made rich in a spike (short time) with a relatively short cycle. In this embodiment, the reducing agent addition valve 14 corresponds to the reducing agent supply means in the present invention.

  The internal combustion engine 1 configured as described above is provided with an ECU 15 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 15 controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  Various sensors are connected to the ECU 15 via electric wiring, and output signals of the various sensors described above are input to the ECU 15. On the other hand, the intake throttle valve 6, the reducing agent addition valve 14, the secondary air supply nozzle 20, the air pump 22 and the like are connected to the ECU 15 through electrical wiring, and the ECU 15 can control them. . For example, the ECU 15 can adjust the valve opening amount of the secondary air supply nozzle 20 and thereby can control the supply amount of the secondary air. The ECU 15 stores various application programs and various control maps.

By the way, the NOx catalyst is sulfur oxide (S
Ox) is also occluded by the same mechanism as NOx. The stored SOx is less likely to be released than NOx and accumulates in the NOx catalyst. This is called sulfur poisoning. Since the NOx purification rate in the NOx catalyst is reduced by this sulfur poisoning, it is necessary to perform a poisoning recovery process for recovering from sulfur poisoning at an appropriate time. This poisoning recovery process is performed by causing the NOx catalyst to have a high temperature and the exhaust gas having a reduced oxygen concentration to flow through the NOx catalyst. In the sulfur poisoning recovery process, the ECU 15 executes fuel addition control (so-called rich spike control) in which the oxygen concentration in the exhaust gas flowing into the filter 11 is lowered in a spike manner with a relatively short period.

  In the fuel addition control, the ECU 15 controls the reducing agent addition valve 14 so as to inject fuel as a reducing agent in a spike manner from the reducing agent addition valve 14, thereby temporarily setting the air-fuel ratio of the exhaust gas flowing into the filter 11. A predetermined target rich air-fuel ratio is set. In the filter 11, SOx is released from the NOx catalyst as the temperature rises. This makes it possible to recover the sulfur poisoning of the NOx catalyst carried on the filter 11.

By the way, when fuel is supplied to the NOx catalyst in order to recover the sulfur poisoning of the NOx catalyst, SOx is released from the NOx catalyst as described above. This released SOx is H ₂ S in a rich atmosphere. It is easy to become. If the amount of fuel added is too large, reducing components such as HC and CO may flow downstream through the NOx catalyst.

  On the other hand, it is conceivable to provide an oxidation catalyst downstream to oxidize hydrocarbons (HC) and the like. However, since the atmosphere is reduced when sulfur poisoning is restored, the oxidation ability of the oxidation catalyst is significantly reduced.

Therefore, in this embodiment, the secondary air is supplied upstream of the oxidation catalyst 12 to make the exhaust gas flowing into the oxidation catalyst 12 an oxidizing atmosphere so that the oxidation ability of the oxidation catalyst 12 is enhanced. Thereby, it becomes possible to oxidize HC, CO, H ₂ S and the like by the oxidation catalyst 12.

  For this reason, in this embodiment, the time until the unburned HC discharged when the load on the internal combustion engine 1 increases reaches the oxidation catalyst 12 (hereinafter referred to as the unburned HC arrival time) is taken into consideration. Supply secondary air. Alternatively, the secondary air is supplied in consideration of the time required to reach the oxidation catalyst 12 after the fuel is added from the reducing agent addition valve 14 (hereinafter referred to as the attached fuel arrival time). In addition, when the distance between the secondary air supply nozzle 20 and the oxidation catalyst 12 is long, the time until the secondary air supply nozzle 20 is reached may be used instead of the time until the secondary air supply nozzle 20 is reached. In such a case, if the secondary air is supplied after the unburned HC or the like arrives at the oxidation catalyst 12, it flows into the oxidation catalyst 12 until the secondary air reaches the oxidation catalyst 12. This is because the exhaust gas to be exhausted has a rich air-fuel ratio. Therefore, in the present embodiment, the time until the secondary air supply nozzle 20 is reached is hereinafter referred to as unburned HC arrival time or attached fuel arrival time.

  The unburned HC arrival time can be obtained from the exhaust gas flow rate and the exhaust system volume. This unburned HC arrival time can also be calculated using conventional techniques. Here, the volume of the exhaust system indicates the volume of the location where the exhaust flows, such as the exhaust branch pipe 9, the turbocharger 5, the exhaust pipe 10, and the filter 11 from the exhaust port to the secondary air supply nozzle 20. Further, the air-fuel ratio of the exhaust from the internal combustion engine 1 is obtained based on the intake air amount and the fuel supply amount into the cylinder 2. From the air-fuel ratio of the exhaust gas and the flow rate of the exhaust gas, the amount of secondary air necessary to make the air-fuel ratio of the exhaust gas a lean air-fuel ratio can be obtained. Then, after the air-fuel ratio exhaust gas is discharged from the internal combustion engine 1, the necessary secondary air amount is supplied from the secondary air supply nozzle 20 when the unburned HC arrival time has elapsed. Thereby, the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 12 can be made the lean air-fuel ratio.

  The attached fuel arrival time can be calculated based on the volume of the exhaust system through which the added fuel flows and the flow rate of the exhaust. The amount of fuel adhering to the exhaust system and the amount of evaporation thereof can be calculated based on the wall temperature of the exhaust system and the flow rate of the exhaust. These can also be calculated using conventional techniques. Further, these relationships may be obtained in advance through experiments or the like and mapped.

  Then, when fuel is added from the reducing agent addition valve 14 and the load of the internal combustion engine is increased thereafter, the secondary air supply is performed when the attached fuel arrival time has elapsed after the load of the internal combustion engine 1 is increased. Secondary air is supplied from the nozzle 20. Here, the air-fuel ratio of the exhaust before supplying the secondary air is obtained based on the intake air amount of the internal combustion engine 1, the fuel supply amount into the cylinder 2, and the evaporation amount of the fuel adhering to the exhaust system. be able to. From the air-fuel ratio of the exhaust gas and the flow rate of the exhaust gas, the amount of secondary air required to make the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 12 lean can be obtained. Thereby, even after the supply of fuel from the reducing agent addition valve 14 is stopped, the supply of secondary air is performed.

  Further, in this embodiment, the secondary air amount is feedback-controlled so that the air-fuel ratio of the exhaust detected by the air-fuel ratio sensor 13 becomes the target lean air-fuel ratio. For example, even when there is a difference between the calculated unburned HC arrival time or adhering fuel arrival time and the actual arrival time, the secondary air supply amount can be corrected based on the detection value of the air-fuel ratio sensor 13. Therefore, the exhaust gas having a more appropriate air-fuel ratio can be supplied to the oxidation catalyst 12. Therefore, in this embodiment, the air-fuel ratio sensor 13 is attached upstream of the secondary air supply nozzle 20. The distance between the air-fuel ratio sensor 13 and the secondary air supply nozzle 20 is set so that feedback control of the secondary air amount can be performed. That is, after the air-fuel ratio of the exhaust gas is detected by the air-fuel ratio sensor 13, the time required to supply the secondary air into the detected exhaust gas is from the air-fuel ratio sensor 13 to the secondary air supply nozzle 20. It is set so as to be shorter than the time taken to flow.

Next, the flow of secondary air supply control according to the present embodiment will be described. FIG. 2 is a flowchart showing a flow of secondary air supply control according to the present embodiment. This routine is NOx
It is repeatedly executed at predetermined time intervals during reduction control or sulfur poisoning recovery control execution.

In step S101, it is determined whether rich control is being performed. In the NOx reduction control and the sulfur poisoning recovery control, the air-fuel ratio of the exhaust gas flowing into the filter 11 is temporarily set to a predetermined target rich air-fuel ratio. Since secondary air is required immediately after the period when the filter 11 is at the target rich air-fuel ratio and immediately after that, it is determined in this step whether or not this period is reached. If an affirmative determination is made in step S101, the process proceeds to step S102, whereas if a negative determination is made, this routine is temporarily terminated.

  In step S102, the change of the exhaust air / fuel ratio and the unburned HC arrival time accompanying the change of the load of the internal combustion engine 1 are calculated. That is, the air-fuel ratio of the exhaust gas and its change are calculated based on the intake air amount of the internal combustion engine 1 and the fuel supply amount into the cylinder 2, and the unburned HC arrival time is calculated from the exhaust gas flow rate and the exhaust system volume. . If the internal combustion engine 1 is in steady operation, this step is omitted.

  In step S103, the amount by which the fuel adhering to the exhaust system evaporates and the adhering fuel arrival time are calculated. These values are calculated as described above.

In step S104, the secondary air supply amount necessary for the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 12 to become the target lean air-fuel ratio is calculated. Here, the target lean air-fuel ratio includes an air-fuel ratio (for example, stoichiometric: 14.7 or more) required for oxidation of unburned HC and H ₂ S and an air-fuel ratio (for example, 16 for suppressing SO ₃ generation). The following is set in advance. The secondary air supply amount is obtained in consideration of the unburned HC from the internal combustion engine 1 and the fuel added by the reducing agent addition valve 14 and adhering to the exhaust system.

In step S105, the secondary air supply nozzle 20 is opened while the air pump 22 is operated to supply secondary air. That is, the opening degree of the secondary air supply nozzle 20 is adjusted so that the secondary air amount calculated in step S104 is obtained.

  In step S106, the opening degree of the secondary air supply nozzle 20 is feedback-controlled so that the air-fuel ratio obtained by the air-fuel ratio sensor 13 becomes the target lean air-fuel ratio.

In this way, oxygen can be supplied by supplying exhaust gas having a target lean air-fuel ratio to the oxidation catalyst 12, so that CO, HC, and H ₂ that flow out of the NOx catalyst during NOx reduction or sulfur poisoning recovery. S and the like can be oxidized.

  In the present embodiment, the ECU 15 that performs the processing of step S102, 103, or 106 corresponds to the air-fuel ratio fluctuation detecting means in the present embodiment.

It is a figure which shows schematic structure of the internal combustion engine which applies the exhaust gas purification apparatus of the internal combustion engine which concerns on an Example, and its intake and exhaust passage. It is the flowchart which showed the flow of the secondary air supply control which concerns on an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Intake branch pipe 4 Intake pipe 5 Turbocharger 6 Intake throttle valve 9 Exhaust branch pipe 10 Exhaust pipe 11 Filter (Occlusion reduction type NOx catalyst)
12 Oxidation catalyst 13 Air-fuel ratio sensor 14 Reducing agent addition valve 15 ECU
20 Secondary air supply nozzle 21 Secondary air supply pipe 22 Air pump

Claims (5)

A catalyst provided in the exhaust passage of the internal combustion engine and having an oxidation function;
Secondary air supply means for supplying secondary air to the exhaust passage upstream of the catalyst having the oxidation function;
Air-fuel ratio fluctuation detecting means for detecting fluctuations in the air-fuel ratio of the exhaust gas flowing into the catalyst having the oxidation function;
N which is provided upstream of the catalyst having oxidation ability and reduces NOx in the presence of a reducing agent
Ox catalyst,
Reducing agent addition means for adding a reducing agent from upstream of the NOx catalyst;
With
The amount of secondary air supplied by the secondary air supply means is adjusted in accordance with the fluctuation of the air-fuel ratio detected by the air-fuel ratio fluctuation detection means after the reducing agent is added by the reducing agent addition means. An exhaust purification device for an internal combustion engine. A catalyst provided in the exhaust passage of the internal combustion engine and having an oxidation function;
Secondary air supply means for supplying secondary air to the exhaust passage upstream of the catalyst having the oxidation function;
Air-fuel ratio fluctuation detecting means for detecting fluctuations in the air-fuel ratio of the exhaust gas flowing into the catalyst having the oxidation function;
With
Adjusting the amount of secondary air supplied by the secondary air supply means according to the air-fuel ratio fluctuation detected by the air-fuel ratio fluctuation detection means ;
The air-fuel ratio fluctuation detecting means includes a delay time which is a time from when unburned HC is discharged from the internal combustion engine to reach the catalyst having the oxidation ability, and / or a reducing agent is added by the reducing agent adding means. The exhaust of the internal combustion engine, wherein the fluctuation of the air-fuel ratio is detected based on a delay time that is a time from when it is attached to the exhaust passage and thereafter evaporating to reach the catalyst having the oxidation ability Purification equipment. The air-fuel ratio fluctuation detecting means includes a delay time which is a time from when unburned HC is discharged from the internal combustion engine to reach the catalyst having the oxidation ability, and / or a reducing agent is added by the reducing agent adding means. to claim 1, wherein the detecting a variation in air-fuel ratio based on the delay time, a time to reach to a catalyst having the oxidizing capability and evaporated thereafter attached to the exhaust passage after being An exhaust gas purification apparatus for an internal combustion engine as described. The exhaust purification device for an internal combustion engine according to claim 2 or 3 , wherein the delay time is calculated based on a flow rate of exhaust gas and a volume of the exhaust passage.   5. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio fluctuation detecting means includes an air-fuel ratio sensor that detects an air-fuel ratio of the exhaust gas.

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