JPH0693840A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent excessive supply of secondary air and effectively purify the exhaust gas by estimating a quantity of unburnt gas adsorbed by an adsorbent, by calculating a required desorbing time from the result of the estimation, and introducing secondary air in accordance with the result of the calculation so as to desorb the unburnt gas. CONSTITUTION:In an engine body 1, a catalyst 6 is located in an exhaust gas passage 4, an adsorbent 8 for unburnt gas and a selector valve 9 are located in a bypass passage i3. Meanwhile, an air passage 13 incorporating an air pump 12 for feeding secondary air is connected to an exhaust manifold 2. A control unit 16 controls the selector valve 9 and the air pump 12 in accordance with detection signals from a catalyst temperature sensor 11, and engine operating condition detecting means 3, 10, 17 to 21. In this case, exhaust gas is introduced into the bypass passage 7 so as to be subjected predesorption during idle operation. Thereafter, a quantity of adsorbed unburnt gas is estimated in accordance with a variation in air-fuel ratio, and then a desorbing time is calculated, and thereafter, secondary air is introduced so as to carry out main desorption.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to an exhaust gas purifying apparatus mainly for reducing unburned gas such as unburned HC at low engine temperature.

[0002]

2. Description of the Related Art Conventionally, as an exhaust gas purification device for an internal combustion engine,
It is widely known that a catalyst is arranged in the exhaust passage, and the chemical adsorption of the catalyst promotes the oxidation reaction of unburned gas in the exhaust to purify the exhaust. However, in such an exhaust gas purification device, when the exhaust gas temperature is low such as when the engine is started, the catalyst does not rise to the activation temperature and the exhaust gas purification action is significantly reduced, so the exhaust gas is sufficiently purified. I can't.

Therefore, in a specific operation region where the exhaust gas purification capability of the catalyst is insufficient, unburned gas in the exhaust gas, for example, unburned HC is adsorbed by the adsorbent, so that the exhaust gas can be satisfactorily discharged regardless of the operating state. There has been proposed a technique for purifying the same (see, for example, JP-A-55-101715). In this technique, specifically, the exhaust passage on the upstream side of the catalyst is configured by the main passage and the bypass passage that are parallel to each other, and the adsorbent is arranged in the bypass passage. Further, a passage switching valve for switching the exhaust flow from the engine body to the bypass passage side or the main passage side according to the exhaust temperature, and a secondary air introduction passage connected to the adsorbent upstream side are provided.

In this technique, when the temperature of the exhaust gas is low after the engine is started (the adsorption temperature range in which the adsorption amount of the adsorbent is larger than the desorption amount:
At 100 ° C or lower), the unburned gas in the exhaust is adsorbed by the adsorbent by flowing the exhaust to the bypass passage side. When the exhaust gas temperature rises and exceeds the adsorption temperature range, the passage switching valve is switched to allow the exhaust gas to flow to the main passage side, thereby preventing desorption of the adsorbent. Furthermore, when the exhaust temperature rises to the catalyst activation temperature at which the purification action by the catalyst becomes active, the passage switching valve is switched again to introduce the exhaust gas to the bypass passage side while desorbing the unburned gas from the adsorbent. The desorbed unburned gas is purified by a catalyst to regenerate the adsorbent. Further, secondary air is introduced at the time of desorption of unburned gas to strengthen the oxidation reaction in the catalyst.

[0005]

However, in the conventional apparatus, the amount of unburned gas adsorbed by the adsorbent is not known, so unburned gas desorption processing is always performed when the catalyst is in the activated state. The need arises. Then, during the desorption process of the unburned gas, secondary air is introduced to prevent the desorbed unburned gas from causing the exhaust gas on the upstream side of the catalyst to become a rich atmosphere and to promote the oxidation reaction.

For this reason, when secondary air is introduced even though the amount of unburned gas desorbed is small, the upstream side of the catalyst is likely to be in an oxidizing atmosphere, and NO is converted in a reducing atmosphere.
There is a possibility that the conversion efficiency of the catalyst with respect to x will decrease and the NOx purification function will decrease. The present invention has been made in view of the above circumstances, and prevents the excessive supply of secondary air by estimating the adsorption amount of unburned gas in the adsorbent and desorbing the adsorbent for a proper time according to the estimated amount. It is an object of the present invention to provide an exhaust gas purification device for an internal combustion engine, which can effectively purify harmful components of exhaust gas.

[0007]

Therefore, according to the present invention, as shown in FIG. 1, an exhaust gas purification catalyst is provided in an exhaust passage, and an upstream exhaust passage of the catalyst is branched from the main passage. A bypass passage which joins again is provided, an adsorbent for adsorbing unburned gas is interposed in the bypass passage, and the exhaust flow is provided at least at one of a branch portion and a joining portion between the bypass passage and the main passage. A passage switching valve for selectively switching between the passage side and the bypass passage side, a secondary air introducing means for introducing secondary air into the exhaust passage upstream of the adsorbent, and a catalyst temperature detecting means for detecting the temperature of the catalyst. , A passage switching valve for introducing exhaust gas to the bypass passage side for a predetermined period from the engine start when the temperature is lower than the catalyst activation temperature, based on the catalyst temperature detecting means and the engine operating state detecting means. Switch control An unburned gas adsorption operation is performed, and when the temperature exceeds the catalyst activation temperature, the passage switching valve is switched and controlled so that the exhaust gas is introduced again into the bypass passage side, and the secondary air is introduced by the secondary air introducing means. In an exhaust gas purification device for an internal combustion engine configured to perform desorption operation of unburned gas, when the detection value of the catalyst temperature detection means becomes equal to or higher than the catalyst activation temperature after the adsorption operation, the operating state detection means is the first When the idle operation is detected, the pre-desorption processing means for driving and controlling the passage switching valve to the position where the exhaust gas is introduced to the bypass passage side for a predetermined time, and the pre-desorption processing means for the predetermined time, and the adsorbent downstream side An air-fuel ratio change detection unit that detects a change in the air-fuel ratio based on a detection value of an air-fuel ratio detection unit that is interposed in the exhaust passage and that detects the air-fuel ratio, and an air-fuel ratio change state detected by the air-fuel ratio change detection unit. Based Adsorption amount estimating means for estimating the adsorption amount of the unburned gas adsorbed by the adsorbent, desorption operation time calculating means for calculating the necessary desorption operation time based on the estimated value of the adsorption amount estimating means, The desorption operation time calculating means calculates the desorption operation time, and the desorption operation means performs the desorption operation accompanied by the secondary air introduction.

[0008]

In such a structure, when the first idle operation is detected when the catalyst temperature reaches the activation temperature after the unburned gas is adsorbed by the adsorbent at a low catalyst temperature after the engine is started, A pre-desorption process for estimating the adsorption amount is performed by driving the passage switching valve and introducing the exhaust gas into the bypass passage for a predetermined time. During this pre-desorption process period, changes in the air-fuel ratio during that period are detected. Then, the adsorption amount is estimated based on the detected change state of the air-fuel ratio. Here, it is estimated that the larger the change in the air-fuel ratio, the larger the adsorption amount. Further, the time required to desorb all unburned gas is calculated based on the estimated adsorption amount. Once the required desorption time has been calculated, 2
Next air is introduced to perform the original desorption process for the calculated required desorption time.

This makes it possible to prevent the introduction of an excessive amount of secondary air, and to prevent the NOx conversion efficiency of the catalyst from decreasing.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2 showing the system configuration of an embodiment of the present invention, the exhaust manifold 2 of the engine body 1 is provided with a first air-fuel ratio sensor 3 for controlling the fuel injection amount. Further, the exhaust passage 4 connected to the exhaust manifold 3
A pre-catalyst 5 for purifying exhaust gas and a main catalyst 6 are interposed between the two.

Exhaust passage 4 upstream of the main catalyst 6
Is composed of a bypass passage 7 that branches from the exhaust passage 4 and merges again, and a main passage 4A. In the bypass passage 7, an adsorbent 8 that adsorbs unburned gas, such as unburned HC, in the exhaust gas is provided. Intervened. At the confluence of the main passage 4A and the bypass passage 7, for example, an electromagnetic passage switching valve 9 that switches the passage so that the exhaust gas selectively flows through both passages is provided. This passage switching valve 9 is ON-OFF controlled, and when it is ON, the bypass passage 7 is opened, the main passage 4A is closed, and the entire amount of exhaust gas is allowed to flow into the bypass passage 7. At the time of OFF, the bypass passage 7 is closed and the main passage 4A is opened, and the entire amount of exhaust gas is flown into the main passage 4A.

A second air-fuel ratio sensor 10 is installed in the exhaust passage 4 between the passage switching valve 9 and the main catalyst 6 as an air-fuel ratio detecting means used for estimating the amount of adsorption during pre-desorption. There is. Further, a temperature sensor 11 as a catalyst temperature detecting means is provided in the exhaust passage 4 on the outlet side of the main catalyst 6. Further, the exhaust manifold 2 is connected to an air passage 13 for introducing secondary air into the exhaust passage 4 via the air pump 12 during the main desorption processing operation. The air pump 12 and the air passage 13 correspond to secondary air introducing means.

On the other hand, the intake passage 14 connected to the engine body 1
A throttle valve 15 is installed in the. Various detection signals are input to the control unit 16, and the passage switching valve 9 and the air pump 12 are drive-controlled on the basis of these various detection signals to perform an adsorption processing operation described later and a pre-desorption processing operation for estimating an adsorption amount. It also controls the main desorption processing operation and the like.

The various detection signals input to the control unit 16 are as follows. Throttle valve
The throttle opening signal from the throttle sensor 17 that detects the opening of the vehicle 15, the vehicle speed signal from the vehicle speed sensor 18, the engine speed signal based on the crank angle signal from the crank angle sensor 19, the start signal from the starter switch 20, the air flow There are an intake air flow rate signal from the meter 21, an engine cooling water temperature signal from the water temperature sensor 22, a catalyst outlet side temperature signal from the temperature sensor 11, and air-fuel ratio signals from the first and second air-fuel ratio sensors 3 and 10.

The control unit 16 includes a pre-desorption treatment means for estimating the amount of unburned gas adsorbed on the adsorbent, and a main catalyst during the pre-desorption treatment period, as shown in a flowchart described later. 6 Air-fuel ratio change detection means for detecting a change in the exhaust air-fuel ratio on the upstream side, adsorption amount estimation means for estimating the unburned gas adsorption amount based on the air-fuel ratio change state, and desorption required based on this estimated amount Each function of the desorption operation time calculation means for calculating the operation time and the main desorption processing means for performing the main desorption operation accompanied by the introduction of the secondary air for the desorption operation time is provided by software. .

Next, a schematic control operation of the exhaust emission control system of this embodiment will be described with reference to the flow chart of FIG. When the engine is started, first, in step 1 (abbreviated as S1 in the figure; hereinafter the same), the passage switching valve 9 is turned on to close the main passage 4A and introduce exhaust gas into the bypass passage 7 to adsorb the adsorbent. At 8, the adsorption processing of the unburned gas in the exhaust is executed. After that, when the exhaust temperature rises and exceeds the adsorption temperature range, the passage switching valve 9 is turned off to close the bypass passage 7 and open the main passage 4A side to introduce the exhaust gas to the main passage 4A side to raise the main catalyst 6. Get warm. The specific operation is shown in the flowchart of FIG. 4 described later.

In step 2, it is judged based on the signal from the temperature sensor 11 whether or not the exhaust temperature at the outlet side of the main catalyst 6 is 200 ° C. or higher. If it is 200 ° C. or higher, the process proceeds to step 3 to be described later. The pre-desorption processing operation for estimating the adsorption amount is executed according to the flowcharts shown in FIGS. When the required desorption time is calculated by this pre-desorption processing operation, the routine proceeds to step 4, where the main desorption processing operation shown in the flowchart of FIG. 8 is executed for the necessary desorption time to regenerate the adsorbent 8.

Next, the adsorption processing operation, the pre-desorption processing operation and the main desorption processing operation described above will be specifically described with reference to the flow charts of FIGS. First, the suction processing operation shown in FIG. 4 will be described. In step 11, it is determined whether or not the starter switch 20 is ON, and it is determined whether or not the engine is started. If YES, the process proceeds to step 12.

In step 12, it is judged from the signal from the water temperature sensor 22 whether the engine cooling water temperature is 40 ° C. or lower, and YES.
If it is (40 ° C or less), proceed to step 13 and set the adsorption end temperature.
Set to 60 ° C. If NO (higher than 40 ° C), the process proceeds to step 14 to determine whether the temperature is 70 ° C or lower, that is, whether the warm-up has been completed by hot restart. If YES (70 ° C or lower), the process proceeds to step 15 And set the adsorption end temperature to 70 ° C. If NO (higher than 70 ° C), the process proceeds to step 16 and the adsorption end temperature is set to 80 ° C.

As described above, the exhaust gas introduction period to the adsorbent 8 (specifically, the adsorption end set temperature) is set based on the cooling water temperature, so that the unburned gas is adsorbed and the temperature of the main catalyst 6 is raised. It can be effectively achieved. When the starter switch 20 is turned off after the engine is started, the routine proceeds to step 17, where it is judged whether the current cooling water temperature is below the set temperature set in step 13, step 15 or step 16, and if it is below the set temperature, it is unburned. In order to adsorb the gas, the passage switching valve 9 is turned on and the exhaust gas is introduced into the bypass passage 7. After that, when the temperature becomes higher than the set temperature, the process proceeds to step 19 to end the adsorption processing operation, the passage switching valve 9 is turned off, the bypass passage 7 is closed, and the exhaust gas is introduced into the main passage 4A side to raise the temperature of the main catalyst 6. I am trying.

Next, the pre-detachment processing operation of FIGS. 5 to 7 will be described. FIG. 5 shows a calculation routine of the required desorption time of the adsorbent 8. In step 21, it is determined whether or not all the unburned gas in the adsorbent 8 has been desorbed. This is determined by whether or not the count value of the necessary desorption time in the main desorption processing operation described later is 0. If all have been detached, proceed to step 22.

In step 22, it is determined whether or not the suction processing operation in the above-described suction processing operation has been performed. If so, proceed to step 23. In step 23, it is determined whether or not the adsorption amount has already been measured. This is because the measurement end flag in the air-fuel ratio change detection routine described later is O.
It is determined by whether or not N has been reached. Measurement end flag is ON
If not, it is determined that the measurement is not performed and the process proceeds to step 24.

At step 24, the adsorption measurement flag is set to ON, and the routine proceeds to step 25, where the pre-desorption control routine shown in FIG. 6 is executed. If the measurement end flag is determined to be OFF in step 23, it is determined that the adsorption amount measurement has already been completed, and the process proceeds to step 26. In step 26,
Flag determination whether or not the desorption time has been calculated,
If the calculation is completed, the flow ends. If not completed, go to step 27.

In step 27, the required desorption time and the secondary air introduction amount are calculated from the air-fuel ratio change state detected by the air-fuel ratio change detection routine of FIG. 7 based on the table of FIG. That is, the larger the amount of adsorption, the larger the amount of unburned gas desorbed in the pre-desorption processing operation and the larger the rate of change of the air-fuel ratio. Therefore, the larger the detected rate of change of the air-fuel ratio, the necessary desorption time and secondary air. Set a large introduction amount.

The pre-desorption control routine of FIG. 6 will be described. First, at step 31, it is judged whether the exhaust temperature on the outlet side of the main catalyst 6 is a temperature (200 ° C. or higher) at which the unburned gas can be desorbed, and if it is possible, the routine proceeds to step 32.
In step 32, it is determined based on the signal from the throttle sensor 17 whether the operating state is idle. This is because the amount of unburned gas desorbed from the adsorbent is the amount of inflowing air (the amount of exhaust).
The desorption amount is almost constant regardless of the temperature above the desorption temperature range of 200 ° C. Therefore, if the inflowing air amount to the adsorbent is constant, the desorption amount is almost constant. The amount of separation and the amount of adsorption are substantially proportional. Therefore, the adsorbed amount can be estimated by measuring the desorbed amount during idling when the air flowing into the adsorbent is substantially constant. If it is idle, proceed to step 33.

In step 33, it is judged whether or not the adsorption measurement flag in the necessary desorption time calculation routine of FIG. 5 is ON, and if it is ON, it is judged in step 34 whether the passage switching valve 9 is ON or OFF. If so, proceed to step 35,
The passage switching valve 9 is turned on to introduce the exhaust gas to the bypass passage 7 side to execute the pre-desorption operation and reset the timer for measuring the pre-desorption time to 0 before starting.

Then, the routine proceeds to step 36, where the air-fuel ratio change detection routine of FIG. 7 is executed. If it is in the non-idle state at step 32, the routine proceeds to step 37, where it is judged whether the passage switching valve 9 is ON or not. When the pre-detachment operation is completed, the pre-detachment time measurement timer is fixed.

Next, the air-fuel ratio change detection routine of FIG. 7 will be described. This routine is executed every 1 second. When the pre-desorption operation is started in the pre-desorption control routine of FIG. 6, in step 41, the air-fuel ratio detection signal from the second air-fuel ratio sensor 10 is read and the timer is counted up.

In step 42, it is judged whether or not the timer value has passed a preset time, and if the preset time has passed, it is determined that desorption of the unburned gas is unnecessary for further estimation of the adsorption amount. Go to 43 and turn on the measurement end flag
Then, the adsorption measurement flag is turned off, and the detection of the change in the air-fuel ratio is completed. In this way, by setting the pre-desorption time in advance, the air-fuel ratio detection error will be included if the time is too short, and if the time is too long, the desorption of the unburned gas will occur during the detection of the adsorption amount. It can be prevented that the amount increases and it becomes difficult to accurately detect the adsorption amount.

Next, the main desorption processing operation performed based on the required desorption time calculated as described above will be described with reference to the flowchart of FIG. In step 51, it is determined whether or not desorption has been performed for the desorption time longer than the necessary desorption time calculated by the necessary desorption time calculation routine of FIG. The determination is made based on the comparison with, and if NO, the process proceeds to step 52.

In step 52, the catalyst outlet side temperature is set to the activation temperature (for example, 300 ° C.) based on the signal from the temperature sensor 11.
℃) or above. If it is 300 ° C or higher, proceed to step 53. In step 53, the throttle valve opening signal from the throttle sensor 17, the vehicle speed signal from the vehicle speed sensor 18,
Based on the engine rotation speed signal from the crank angle sensor 19 or the like, it is determined whether or not the fuel cut operation during deceleration is performed. If NO, the routine proceeds to step 54, where it is determined whether or not the idle operation is performed depending on whether or not the ISC (idle speed control) valve is ON. That is, in step 53 and step 54, it is determined whether or not the operating state is such that even if the unburned gas is desorbed and the secondary air is introduced, the emission of NOx and the like is unlikely to increase.
NOx is not generated because the combustion is not performed at the time of fuel cut during deceleration, and the combustion temperature decreases at the time of idling, and the NOx generation amount decreases.

Therefore, when the determination at either step 53 or step 54 is YES, it is determined that the unburned gas can be desorbed and the routine proceeds to step 55. In step 55, it is determined whether or not the temperature decrease rate of the catalyst is less than or equal to a predetermined value (for example, 10 ° C./second). This is because even in the above-mentioned operating state in which the amount of NOx produced is small, if the temperature decrease rate of the main catalyst 6 is large in this operating state, the catalyst temperature decreases, the main catalyst 6 becomes inactive, and the conversion efficiency decreases. This is because there is a possibility. If the temperature decrease rate of the catalyst is smaller than the specified value, step
Continue to 56.

In step 56, the passage switching valve 9 is turned on to open the bypass passage 7 side and the air pump 12 is driven to introduce the exhaust gas into the adsorbent 8 and the secondary air to release the unburned gas. In addition, the oxidation reaction in the main catalyst 6 is strengthened, and a good effect of purifying exhaust harmful components is obtained.
In step 57, the timer for counting the necessary desorption time is counted up.

Both determinations in step 53 and step 54 are N.
When it is O or when the determination in step 55 is NO, the routine proceeds to steps 58 and 59, where the passage switching valve 9 is turned off to close the bypass passage 7 side and open the main passage 4A side to exhaust the exhaust gas to the main passage 4A. At the same time as the introduction, the drive of the air pump 12 is stopped, the introduction of the secondary air is stopped, and the desorption of unburned gas is stopped.

If the timer value for counting the required time matches the calculated value, it is determined that all the unburned gas adsorbed is desorbed, and the desorption operation is not performed until the adsorption operation is performed again. . In this way, by estimating the adsorption amount of the unburned gas adsorbed on the adsorbent 8 and setting the desorption processing time according to the estimated amount, it is possible to prevent the excessive supply of the secondary air. The NOx conversion efficiency of the catalyst 6 can be prevented from lowering, and the emission amount of exhaust harmful components can be effectively reduced.

In this embodiment, the adsorbed amount is estimated from the air-fuel ratio change rate during the pre-desorption process, but the present invention is not limited to this. For example, instead of the air-fuel ratio sensor, a lean or rich output is obtained. Using the oxygen sensor that reverses, set the air-fuel ratio to the lean side by about 5 to 10% in advance during pre-desorption, and start the pre-desorption with the output of the oxygen sensor fixed to the lean side. It is also possible to measure the time from the start to the time when the output of the oxygen sensor becomes rich and estimate the adsorption amount of the unburned gas by using the data obtained in advance based on this measurement time.

[0037]

As described above, according to the present invention, the unburned gas adsorption amount of the adsorbent is estimated, the necessary desorption treatment time is calculated based on the estimated amount, and the calculated desorption time is not calculated. Since the fuel gas desorption operation is performed, it is possible to prevent the excessive supply of the secondary air supply amount, prevent the reduction of the NOx conversion efficiency of the main catalyst, and prevent the increase of the NOx emission amount.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of an exhaust emission control device of the present invention.

FIG. 2 is a system diagram showing an embodiment of the present invention.

FIG. 3 is a flowchart for explaining the overall operation of the above embodiment.

FIG. 4 is a flowchart specifically illustrating a suction processing operation.

FIG. 5 is a flowchart for calculating a necessary desorption time in the pre-desorption processing operation.

FIG. 6 is a desorption control flowchart in a pre-desorption processing operation.

FIG. 7 is an air-fuel ratio detection flowchart in a shake desorption processing operation.

FIG. 8 is a flowchart specifically explaining the main desorption processing operation.

FIG. 9 is a diagram showing data used to calculate a required desorption time.

[Explanation of symbols]

 1 Engine Main Body 4 Exhaust Passage 4A Main Passage 6 Main Catalyst 7 Bypass Passage 8 Adsorbent 9 Passage Switching Valve 10 Second Air-Fuel Ratio Sensor 11 Temperature Sensor 15 Throttle Valve 16 Control Unit 17 Throttle Sensor 20 Starter Switch

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location F01N 3/24 F F02D 45/00 368 G 7536-3G

Claims (1)

[Claims] 1. An exhaust gas purification catalyst is provided in an exhaust passage, and a bypass passage is provided in an upstream exhaust passage of the catalyst to branch from the main passage and join again. An unburned gas is adsorbed in the bypass passage. A passage switching valve that interposes an adsorbent and that is provided in at least one of a branch portion and a merging portion between the bypass passage and the main passage and that selectively switches the flow of exhaust gas between the main passage side and the bypass passage side; 2 in the exhaust passage on the upstream side
A secondary air introducing means for introducing secondary air, a catalyst temperature detecting means for detecting the temperature of the catalyst, and an engine operating state detecting means are provided, and the catalyst is based on the catalyst temperature detecting means and the engine operating state detecting means. When the temperature is lower than the activation temperature, the passage switching valve is switched and controlled to introduce exhaust gas to the bypass passage for a predetermined period from the engine start, and the unburned gas adsorption operation is performed. In the exhaust gas purifying apparatus for an internal combustion engine, the passage switching valve is switch-controlled to introduce the exhaust gas to the passage side, and the secondary air is introduced by the secondary air introducing means to desorb the unburned gas. After the operation, when the detected value of the catalyst temperature detecting means becomes equal to or higher than the catalyst activation temperature, when the operating state detecting means detects the first idle operation, the exhaust gas is introduced to the bypass passage side for a predetermined time. Pre-desorption processing means for driving and controlling the passage switching valve to perform pre-desorption operation, and detection by the air-fuel ratio detection means interposed in the adsorbent downstream exhaust passage for the predetermined time to detect the air-fuel ratio Air-fuel ratio change detection means for detecting a change in the air-fuel ratio based on the value, and adsorption for estimating the adsorption amount of unburned gas adsorbed by the adsorbent based on the air-fuel ratio change state detected by the air-fuel ratio change detection means The amount estimation means, the desorption operation time calculation means for calculating the necessary desorption operation time based on the estimated value of the adsorption amount estimation means, and the desorption operation time calculated by the desorption operation time calculation means 2 An exhaust gas purification apparatus for an internal combustion engine, comprising: a main desorption processing means for performing a main desorption operation involving the introduction of secondary air.