JP2008063986A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

In an exhaust emission control device for an internal combustion engine, a technique is provided that can start the supply of a reducing agent at an early stage when the supply of secondary air is started.
An exhaust passage of an internal combustion engine is provided with a reducing agent supply means, an exhaust purification catalyst, a secondary air supply means, and a catalyst having oxidation ability in order, and the secondary air supply means supplies secondary air from the secondary air supply means. When the supply amount of secondary air gradually increases after the start of supply, according to the supply amount of secondary air so that the air-fuel ratio of the exhaust gas flowing into the catalyst having oxidation ability becomes the target air-fuel ratio. The supply amount of the reducing agent from the reducing agent supply means is adjusted.
[Selection] Figure 3

Description

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

An NOx storage reduction catalyst (hereinafter referred to as NOx catalyst), a secondary air supply nozzle, and an oxidation catalyst may be provided in order from the upstream side of the exhaust passage (see, for example, Patent Document 1). By adopting such a configuration, even if the reducing agent supplied to the NOx catalyst passes through the NOx catalyst, the secondary air is supplied from the secondary air supply nozzle so that the reducing agent is used as the oxidation catalyst. Can be oxidized.
Japanese Patent Laid-Open No. 10-121952 JP 2002-155740 A

  By the way, in order to supply secondary air, the electric pump which discharges air may be used. This electric pump may be operated by supplying electric power only when supplying secondary air from the viewpoint of durability. Here, the electric pump gradually increases in rotational speed after supplying electric power, and the discharge amount of air increases. Even if a reducing agent is added while the rotational speed is increasing, the reducing agent that has passed through the NOx catalyst cannot be oxidized because oxygen is insufficient in the downstream oxidation catalyst. That is, the reducing agent cannot be supplied until power is supplied to the electric pump and the electric pump discharges a desired amount of air. In this way, if there is a period during which the reducing agent cannot be supplied, the period until the sulfur poisoning recovery of the NOx catalyst is completed is increased accordingly, so that the sulfur poisoning recovery is caused by a change in the operating state of the internal combustion engine during that period. There is a risk that it will not be possible. Similarly, during the NOx reduction, if the supply of the reducing agent is awaited, the reducing agent cannot be supplied at an optimal time, and the NOx purification rate may be reduced.

  The present invention has been made in view of the above-described problems, and provides a technique capable of starting the supply of the reducing agent at an early stage when the supply of secondary air is started in the exhaust gas purification apparatus for an internal combustion engine. For the purpose.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine;
Reducing agent supply means for supplying a reducing agent to an exhaust passage upstream of the exhaust purification catalyst;
A catalyst provided in an exhaust passage downstream of the exhaust purification catalyst and having an oxidizing ability;
Secondary air supply means for supplying secondary air to the exhaust passage downstream from the exhaust purification catalyst and upstream from the catalyst having the oxidation ability;
When the supply of secondary air is started from the secondary air supply means and the supply amount of the secondary air is gradually increasing, the air-fuel ratio of the exhaust gas flowing into the catalyst having the oxidation ability becomes the target air-fuel ratio. A secondary air supply start reducing agent amount adjusting means for adjusting the reducing agent supply amount from the reducing agent supply means according to the secondary air supply amount,
It is characterized by providing.

The exhaust purification catalyst purifies the exhaust gas by supplying a reducing agent or restores the exhaust gas purification capability. At this time, the reducing agent that has passed through the exhaust purification catalyst is oxidized by a catalyst having an oxidizing ability provided on the downstream side. Thereby, it is suppressed that a reducing agent is discharge | released in air | atmosphere.

  On the other hand, oxygen is required to oxidize the reducing agent with a catalyst having oxidation ability. For this reason, the secondary air supply means supplies oxygen to the catalyst having oxidation ability by supplying secondary air into the exhaust gas. The secondary air supply means starts supplying the secondary air when it becomes necessary to supply the reducing agent to the exhaust purification catalyst, for example. That is, the secondary air supply means does not always supply secondary air, but supplies secondary air as necessary.

  Here, a certain amount of time is required from when the secondary air supply means starts supplying the secondary air until the desired amount of secondary air can be supplied. That is, the secondary air gradually increases. The reducing agent supply means supplies the reducing agent while the secondary air is gradually increasing as described above, and the reducing agent supply amount at this time is adjusted by the reducing agent amount adjusting means at the start of the secondary air supply. Is done.

  In order for the reducing agent to be sufficiently oxidized by the catalyst having oxidation ability, the air-fuel ratio of the exhaust gas in the catalyst having oxidation ability must be relatively high (for example, the stoichiometric air-fuel ratio or more). . Therefore, the target air-fuel ratio is an air-fuel ratio that can oxidize the reducing agent with a catalyst having oxidation ability, and may be the lower limit value. That is, by supplying the reducing agent to the exhaust purification catalyst so that the air-fuel ratio of the exhaust gas flowing into the catalyst having oxidation ability becomes the target air-fuel ratio, the reducing agent can be oxidized by the catalyst having oxidation ability. . Here, since the air-fuel ratio of the exhaust gas flowing into the catalyst having oxidation ability changes according to the supply amount of secondary air, the oxidation ability is reduced by supplying the reducing agent according to the supply amount of secondary air. The air-fuel ratio of the exhaust gas flowing into the catalyst having the target air-fuel ratio can be set.

  Thus, the reducing agent can be supplied to the exhaust purification catalyst immediately after the supply of secondary air from the secondary air supply means is started. At this time, the reducing agent that has passed through the exhaust purification catalyst can be oxidized by the downstream catalyst.

  In the present invention, even if the reducing agent is supplied by the reducing agent supply means, the supply of the reducing agent can be prohibited if the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is larger than a predetermined value.

  Here, when the supply of secondary air is started and the supply amount of secondary air is gradually increasing, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst gradually decreases, so the supply of secondary air is started. Immediately after that, a desired air-fuel ratio may not be obtained with the exhaust purification catalyst. That is, even if the air-fuel ratio of the exhaust gas flowing into the catalyst having oxidation ability is an air-fuel ratio that can oxidize the reducing agent with the catalyst having oxidation ability, the exhaust purification catalyst can restore the exhaust purification ability. If it is not possible, the supplied reducing agent is wasted. Therefore, when the purification ability of the exhaust purification catalyst is not recovered, the consumption of the reducing agent can be reduced by prohibiting the supply of the reducing agent. That is, the predetermined value is an air-fuel ratio that can recover the purification ability of the exhaust purification catalyst, and may be a stoichiometric air-fuel ratio, for example.

  In the present invention, the secondary air supply means includes an electric pump that discharges air, and the secondary air supply start reducing agent amount adjusting means corresponds to the electric power supplied to the electric pump. Thus, the supply amount of the reducing agent can be adjusted.

When electric power is supplied to the electric pump, the motor in the electric pump starts to rotate, and then the rotational speed gradually increases. During this time, the amount of air discharged from the electric pump also gradually increases. And since there is a correlation between the electric power supplied to the electric pump and the amount of air discharged from the electric pump (the flow rate of air), by obtaining this relationship in advance, the electric pump is started when the electric pump is started. If the electric power supplied to the electric pump is detected, the flow rate of the secondary air discharged from the electric pump can be obtained. By adjusting the supply amount of the reducing agent based on this flow rate, the air-fuel ratio of the exhaust gas in the catalyst having oxidation ability can be made the target air-fuel ratio.

  In addition, the amount of secondary air discharged from the electric pump may be directly measured, and the relationship between the operating time of the electric pump and the amount of discharged air is obtained in advance and the operating time is measured. The amount of secondary air may be determined. Further, the air-fuel ratio of the exhaust before and after the supply of secondary air may be detected by a sensor, and the amount of secondary air may be obtained based on the difference between these air-fuel ratios.

  According to the present invention, the supply of the reducing agent can be started early when the supply of the secondary air is started.

  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 an exhaust system thereof. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine.

  An exhaust passage 2 is connected to the internal combustion engine 1, and each branch pipe of the exhaust passage 2 leads to a combustion chamber. In the middle of the exhaust passage 2, an NOx storage reduction catalyst 3 (hereinafter referred to as NOx catalyst 3) and an oxidation catalyst 4 are provided in order from the upstream side. The NOx catalyst 3 has a function of storing NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is reduced and a reducing agent is present. Have. In this embodiment, the NOx catalyst 3 corresponds to the exhaust purification catalyst in the present invention. In this embodiment, the oxidation catalyst 4 corresponds to a catalyst having oxidation ability in the present invention.

  Furthermore, in this embodiment, a fuel addition valve 5 is provided for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust passage 2 upstream of the NOx catalyst 3. Here, the fuel addition valve 5 is opened by a signal from the ECU 10 described later to inject fuel. The fuel injected from the fuel addition valve 5 into the exhaust passage 2 enriches the air-fuel ratio of the exhaust flowing from the upstream of the exhaust passage 2 and reduces the NOx stored in the NOx catalyst 3. . During this NOx reduction, so-called rich spike control is executed in which the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 3 is made rich in a spike (short time) in a relatively short cycle.

  Further, the NOx catalyst 3 also stores the sulfur component contained in the fuel in the same manner as NOx. The sulfur component occluded in this manner is less likely to be released than NOx and is accumulated in the NOx catalyst 3. This is called sulfur poisoning. Since the NOx purification rate in the NOx catalyst 3 is reduced by this sulfur poisoning, it is necessary to perform a sulfur poisoning recovery process for recovering from sulfur poisoning at an appropriate time. This sulfur poisoning recovery process is performed by raising the temperature of the NOx catalyst and flowing exhaust gas having a stoichiometric or rich air-fuel ratio to the NOx catalyst. Also at this time, the rich spike control is performed. In this embodiment, the fuel addition valve 5 corresponds to the reducing agent supply means in the present invention.

  Further, an exhaust temperature sensor 6 for detecting the temperature of the exhaust gas flowing through the exhaust passage 2 is attached to the exhaust passage 2 downstream of the NOx catalyst 3 and upstream of the oxidation catalyst 4. Based on the output signal of the exhaust temperature sensor 6, the temperature of the NOx catalyst 3 is detected.

  Further, a secondary air supply mechanism 7 is provided in the exhaust passage 2 downstream of the NOx catalyst 3 and upstream of the oxidation catalyst 4. The secondary air supply mechanism 7 includes a secondary air supply valve 71 that supplies secondary air into the exhaust passage 2, a secondary air supply pipe 72, and an air pump 73. The secondary air supply valve 71 is connected to an air pump 73 via a secondary air supply pipe 72. The air pump 73 includes an electric motor, and discharges air according to the number of rotations. Then, air is supplied to the exhaust passage 2 by operating the air pump 73 to discharge air. In this embodiment, the secondary air supply mechanism 7 corresponds to the secondary air supply means in the present invention. In the present invention, the air pump 73 corresponds to the electric pump in the present invention.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 is a unit that 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.

  An exhaust gas temperature sensor 6 is connected to the ECU 10 via an electric wiring, and an output signal of the exhaust gas temperature sensor 6 is input. On the other hand, the fuel addition valve 5 and the air pump 73 are connected to the ECU 10 via electric wiring, and these are controlled by the ECU 10.

  In this embodiment, when the sulfur poisoning recovery process is performed, the air pump 73 is operated to supply secondary air to the oxidation catalyst 4. Even if the air pump 73 starts to operate, the rotation speed does not increase immediately but gradually increases. Therefore, the supply amount of secondary air gradually increases. As described above, while the supply amount of the secondary air is gradually increasing, in this embodiment, the reducing agent is supplied in accordance with the supply amount of the secondary air. That is, the supply amount of the reducing agent is gradually increased, and the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 3 is gradually lowered.

  Here, FIG. 2 is a time chart showing the transition of the secondary air supply amount and the like at the start of the secondary air supply. The “S regeneration mode” is turned on when the sulfur poisoning recovery process is performed, and is turned off otherwise. Then, the S reproduction mode is switched from OFF to ON at the time indicated by (A). The “secondary air supply amount” is the amount of secondary air supplied from the air pump 73 to the NOx catalyst 3. The secondary air supply amount can be obtained, for example, by obtaining a relationship between the power supplied to the air pump 73 and the supply amount of the secondary air in advance and detecting the power. The “oxidation target air / fuel ratio” is a target value of the air / fuel ratio of the exhaust gas flowing into the oxidation catalyst 4. The “suppliable reducing agent amount” is an amount of reducing agent that can be oxidized by the oxidation catalyst 4 even when added from the fuel addition valve 5. “Addition target air-fuel ratio” is a target value of the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 3. “S regeneration addition” is turned on when fuel is added from the fuel addition valve 5, and is otherwise turned off. “Supply reducing agent amount” indicates the amount of reducing agent actually added from the fuel addition valve 5.

  When the S regeneration mode changes from OFF to ON, supply of power to the air pump 73 is started. Here, the secondary air supply amount from the air pump 73 changes from when the air pump 73 is started until the rotational speed becomes constant. This change in the secondary air supply amount continues until the rotational speed of the air pump 73 reaches a preset target value. In addition, the time when the rotation speed of the air pump 73 reaches the target value is indicated by (B). When the rotational speed of the air pump 73 reaches the target value, the rotational speed becomes constant thereafter, and the amount of secondary air from the air pump 73 and the power supplied to the air pump 73 become constant.

As described above, between (A) and (B), there is a correlation between the electric power supplied to the air pump 73 and the rotational speed of the air pump 73 or the discharge amount of air from the air pump 73. Therefore, by detecting the power supplied to the air pump 73, the air pump 73 is detected.
And the secondary air discharge amount (flow rate) can be obtained. This relationship can be obtained in advance through experiments or the like.

  Then, the fuel addition amount from the fuel addition valve 5 is adjusted so that the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 4 becomes the oxidation target air-fuel ratio, taking into account the secondary air amount at this time. The oxidation target air-fuel ratio is constant at the air-fuel ratio necessary for oxidizing the fuel by the oxidation catalyst 4, and may be, for example, not less than the theoretical air-fuel ratio or about 16. Since this oxidation target air-fuel ratio varies depending on the shape and capacity of the oxidation catalyst 4 and the type of the catalyst, an appropriate value is obtained in advance by experiments or the like. Thus, after the S regeneration mode is switched from OFF to ON, the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 4 is kept constant at the oxidation target air-fuel ratio regardless of the secondary air supply amount.

  If the secondary air supply amount and the oxidation target air-fuel ratio are known, the supplyable reducing agent amount can be obtained. The supplyable reducing agent amount increases as the secondary air supply amount increases because the oxidation target air-fuel ratio is constant.

  Then, the addition target air-fuel ratio is obtained based on the supplyable reducing agent amount. That is, the addition target air-fuel ratio is gradually lowered from when the S regeneration mode is switched from OFF to ON. That is, by gradually lowering the addition target air-fuel ratio, the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 4 is made constant at the oxidation target air-fuel ratio. Then, after the rotation speed of the air pump 73 becomes constant, the target addition air-fuel ratio is made constant.

  Incidentally, since the amount of reducible agent that can be supplied gradually increases, the amount of reducible agent that can be supplied is small immediately after the supply of secondary air is started. For this reason, the air-fuel ratio required for recovery of sulfur poisoning of the NOx catalyst 3 cannot be secured. On the other hand, in this embodiment, the supply of the reducing agent is started after the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 3 becomes the air-fuel ratio required for recovery of sulfur poisoning of the NOx catalyst 3. The time when the supply of the reducing agent is started is indicated by (C). That is, S regeneration addition is switched from OFF to ON at the time indicated by (C), and the supply of the reducing agent is actually started. In this embodiment, the air-fuel ratio of the exhaust at the time indicated by (C) corresponds to the “predetermined value” in the present invention.

  Next, the flow of the sulfur poisoning recovery process according to the present embodiment will be described. FIG. 3 is a flowchart showing a flow of the sulfur poisoning recovery process according to the present embodiment. This routine is repeatedly executed every predetermined time.

  In step S101, it is determined whether there is a sulfur poisoning recovery request. That is, it is determined whether or not the sulfur poisoning recovery process needs to be executed. For example, when the sulfur poisoning amount is a predetermined value (for example, 1.4 g) or more, it is determined that there is a sulfur poisoning recovery request. Since the sulfur poisoning amount has a correlation with the fuel consumption amount, the sulfur poisoning amount can be obtained based on the fuel consumption amount.

  If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, the process proceeds to step S110, and if the air pump 73 is operating, the air pump 73 is stopped (OFF). The

  In step S102, it is determined whether the sulfur poisoning recovery condition is satisfied. The sulfur poisoning recovery condition is a condition necessary for recovering sulfur poisoning.

  For example, whether the engine speed is between 1000 and 3000, the amount of fuel injected into the cylinder is between 10 and 30 (mm3 / st), or the temperature of the NOx catalyst 3 is 600 ° C. or higher. Or the like, and when both are satisfied, it is determined that the sulfur poisoning recovery condition is satisfied.

  If an affirmative determination is made in step S102, the process proceeds to step S103. On the other hand, if a negative determination is made, the process proceeds to step S110, and if the air pump 73 is operating, the air pump 73 is stopped (OFF). The

  In step S103, it is determined whether the fuel addition condition is satisfied. In this step, it is determined whether or not the fuel can be added from the fuel addition valve 5. If the fuel can be added, it is determined that the fuel addition condition is satisfied.

  For example, it is time when the temperature of the NOx catalyst 3 can be maintained within the target range even when fuel is added, or the temperature of the NOx catalyst 3 is lower than a temperature at which the NOx catalyst 3 may be overheated (for example, 700 ° C.), It is determined whether or not fuel is attached to the exhaust system to the extent that white smoke is generated (for example, whether the amount of fuel attached is less than 2 g), and it is determined that the fuel addition condition is satisfied when both are satisfied Is done.

  If an affirmative determination is made in step S103, the process proceeds to step S104. On the other hand, if a negative determination is made, the process proceeds to step S110, and if the air pump 73 is operating, the air pump 73 is stopped (OFF). The

  In step S104, the air pump 73 is turned on. That is, electric power is supplied to the air pump 73 and the air pump 73 starts to rotate.

  In step S105, the power supplied to the air pump 73 is read. The supplied power can be obtained, for example, by providing a wattmeter.

  In step S106, the flow rate of the air discharged from the air pump 73 is calculated based on the electric power read in step S105. It should be noted that the relationship between the electric power and the air flow rate is obtained in advance through experiments or the like and is mapped and stored in the ECU 10.

  In step S107, an addition target air-fuel ratio is calculated. The target addition air / fuel ratio is calculated so that the air / fuel ratio of the exhaust gas flowing into the oxidation catalyst 4 becomes the oxidation target air / fuel ratio.

Therefore, first, the oxidation target air-fuel ratio AFCCO is calculated. This oxidation target air-fuel ratio AFCCO is expressed by the following equation.
AFCCO = (GA + GAAI) / (GF + GFA)
However, GA is the flow rate of exhaust gas, GAAI is the flow rate of air calculated in step S106, GF is the fuel injection amount into the cylinder, and GFA is the fuel addition amount from the fuel addition valve 5. The flow rate GA of the exhaust gas can be obtained by, for example, an air flow meter assuming that it is equal to the intake air amount. A command value calculated by the ECU 10 is used as the fuel injection amount GF into the cylinder.

Based on the above equation, the fuel addition amount GFA necessary for the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 4 to become the oxidation target air-fuel ratio AFCCO can be obtained. Then, using this fuel addition amount GFA, the target addition air-fuel ratio AFNOx is expressed by the following equation.
AFNOx = GA / (GF + GFA)

  In step S108, it is determined whether or not the addition target air-fuel ratio AFNOx is equal to or less than a predetermined value. The predetermined value is an air-fuel ratio that can recover the sulfur poisoning of the NOx catalyst 3, and can be set to a value equal to or lower than the stoichiometric air-fuel ratio, for example. Since this value varies depending on the performance of the NOx catalyst 3, etc., an appropriate value is obtained in advance by experiments or the like.

  Here, if the sulfur poisoning of the NOx catalyst 3 cannot be recovered because the air-fuel ratio is not sufficiently lowered even if the fuel is added, the fuel consumption is deteriorated by adding the fuel. Therefore, in this step, it is determined whether or not the air-fuel ratio of the exhaust gas is lowered so that the sulfur poisoning recovery of the NOx catalyst 3 is possible when fuel is added.

  If an affirmative determination is made in step S108, the process proceeds to step S109. On the other hand, if a negative determination is made, the process returns to step S105.

  In step S109, fuel addition from the fuel addition valve 5 is executed. That is, by performing fuel addition according to the fuel addition amount GFA obtained in step S107, the NOx catalyst 3 can achieve an air-fuel ratio that can recover sulfur poisoning, and the oxidation catalyst 4 can oxidize the reducing agent. The air-fuel ratio can be set.

  In this embodiment, the ECU 10 that adjusts the fuel addition amount in this way corresponds to the reducing agent amount adjusting means at the start of secondary air supply in the present invention. Further, since the power supplied to the air pump 73 and the secondary air amount are correlated after the time shown in FIG. 2B, the power supplied to the air pump 73 after the time shown in FIG. The fuel addition amount may be obtained based on the above. Similarly, when the secondary air amount is detected by other means, the fuel addition amount can be obtained based on the secondary air amount.

  As described above, according to this embodiment, even when the rotational speed of the air pump 73 is increasing immediately after the start of the recovery from sulfur poisoning, fuel is added in accordance with the amount of air discharged from the air pump 73. Therefore, the fuel that passes through the NOx catalyst 3 can be oxidized by the oxidation catalyst 4 while recovering the sulfur poisoning of the NOx catalyst 3. That is, the fuel addition can be started early when the supply of secondary air is started.

  In the present embodiment, the case where sulfur poisoning recovery is performed has been described as an example, but the same applies to the case where fuel addition is performed while supplying secondary air from the air pump 73 (for example, during NOx reduction). be able to.

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 exhaust system. It is the time chart which showed transition of the supply amount etc. of secondary air at the time of secondary air supply start. It is the flowchart which showed the flow of the sulfur poisoning recovery process which concerns on an Example.

Explanation of symbols

1 Internal combustion engine 2 Exhaust passage 3 NOx storage reduction catalyst 4 Oxidation catalyst 5 Fuel addition valve 6 Exhaust temperature sensor 7 Secondary air supply mechanism 10 ECU
71 Secondary air supply valve 72 Secondary air supply pipe 73 Air pump

Claims (3)

An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine;
Reducing agent supply means for supplying a reducing agent to the exhaust passage upstream of the exhaust purification catalyst;
A catalyst provided in an exhaust passage downstream of the exhaust purification catalyst and having an oxidizing ability;
Secondary air supply means for supplying secondary air to the exhaust passage downstream from the exhaust purification catalyst and upstream from the catalyst having the oxidation ability;
When the supply of secondary air is started from the secondary air supply means and the supply amount of the secondary air is gradually increasing, the air-fuel ratio of the exhaust gas flowing into the catalyst having the oxidation ability becomes the target air-fuel ratio. A secondary air supply start reducing agent amount adjusting means for adjusting the reducing agent supply amount from the reducing agent supply means according to the secondary air supply amount,
An exhaust emission control device for an internal combustion engine, comprising:   2. The supply of the reducing agent is prohibited when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is larger than a predetermined value even if the reducing agent is supplied by the reducing agent supply means. An exhaust gas purification apparatus for an internal combustion engine as described.   The secondary air supply means includes an electric pump that discharges air, and the secondary air supply start reducing agent amount adjusting means adjusts the supply amount of the reducing agent according to the electric power supplied to the electric pump. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is adjusted.

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