JP4636273B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly, to a deterioration determination technique for a catalytic converter.

In general, a catalytic converter for purifying exhaust gas is interposed in an exhaust passage of an internal combustion engine mounted on a vehicle. In this type of catalytic converter, the oxygen storage capacity of the catalyst has a high correlation with the catalyst performance, so as a catalyst deterioration detection method, the deterioration of the catalytic converter is judged by monitoring the change over time in this oxygen storage capacity. The method is widely adopted.
In such a catalyst deterioration detection method, when the air-fuel ratio of the exhaust gas flowing into the catalytic converter is modulated with a predetermined period (for example, a modulation period of air-fuel ratio feedback control) and a predetermined amplitude between the lean air-fuel ratio and the rich air-fuel ratio, If the storage capacity is high, oxygen is stored in the catalytic converter, so the amplitude of the exhaust air-fuel ratio downstream of the catalyst is small or the period is long, and if the oxygen storage capacity is low, oxygen is not stored in the catalytic converter so much. Therefore, the deterioration of the catalytic converter is judged using the characteristic that the amplitude and cycle of the exhaust air-fuel ratio downstream of the catalyst hardly change with respect to the upstream side of the catalyst. For example, when performing deterioration determination based on oxygen concentration output values from oxygen sensors (O ₂ sensors) provided upstream and downstream of the catalyst, an output cycle ratio between the upstream and downstream of the catalyst is detected, and this output cycle ratio is set to a predetermined value. By comparing with the reference value, a decrease in oxygen storage capacity, that is, deterioration of the catalytic converter is determined.

On the other hand, recently, vehicles capable of performing so-called fuel cut that stops fuel supply during deceleration of the vehicle have been developed. In such a vehicle, when the fuel is returned from the fuel cut, in order to suppress NOx emission, a large amount of fuel is used as a reducing agent in order to remove (purge) the oxygen stored in the catalytic converter by the oxygen storage function. The air-fuel ratio is temporarily enriched by supplying it. The end of the enrichment is determined when the output of the oxygen sensor (O ₂ sensor) provided downstream of the catalyst has changed from the lean air-fuel ratio side to the rich air-fuel ratio side.

In this case, the richness of the air-fuel ratio at the time of fuel recovery from the fuel cut is used to monitor the rise time difference (O ₂ purge time) between the oxygen sensor on the upstream side of the catalyst and the oxygen sensor on the downstream side of the catalyst after the start of the enrichment. By doing so, it is possible to detect a decrease in the oxygen storage capacity, and thus the deterioration of the catalytic converter. Therefore, in a vehicle capable of performing fuel cut, it is also possible to select to use enrichment of the air-fuel ratio at the time of fuel return from the fuel cut as a catalyst deterioration detection method.

For example, at the time of fuel recovery from a fuel cut, the area ratio between the output of the upstream exhaust sensor and the output of the downstream exhaust sensor measured for a predetermined time, and the response until the output voltage of these sensors exceeds a predetermined determination voltage An apparatus having a configuration for performing deterioration determination by looking at a time shift is known (see Patent Document 1).
JP-A-6-81635

  By the way, in recent years, there is an increase in exhaust purification systems in which a plurality of exhaust catalytic converters arranged in the exhaust passage are not limited to one but arranged in series. In such an exhaust purification system, it is required to individually perform deterioration determination for a plurality of exhaust catalytic converters. However, even if each of the above-described deterioration determination methods is applied as it is, for example, the following problems are encountered. is there.

  That is, in the case of the method of determining the catalyst deterioration by detecting the output cycle ratio between the upstream and downstream of the catalyst, the exhaust after passing through the upstream catalytic converter flows into the downstream catalytic converter provided on the downstream side of the exhaust. As a result, the amplitude of the air-fuel ratio of the exhaust gas flowing into the downstream catalytic converter becomes small. Therefore, the difference in the amplitude or cycle of the exhaust air-fuel ratio between upstream and downstream of the downstream catalytic converter is unlikely to occur, and even if the output cycle ratio between the upstream and downstream of the catalyst is detected, there is a possibility that deterioration of the downstream catalytic converter cannot be accurately determined. There is.

In addition, in the case of a method that uses the enrichment of the air-fuel ratio at the time of fuel recovery from a fuel cut, the purpose is to purge oxygen stored in the catalytic converter in order to suppress NOx emission in the first place. The amount of reducing agent (HC, CO) must be promptly supplied, and the rise time difference (O ₂₎ between the oxygen sensor upstream of the catalyst and the oxygen sensor downstream of the catalyst in any of the catalytic converters arranged in series. Purge time) is reduced. For this reason, even if the catalytic converter deteriorates, it is difficult for changes in the rise time difference to appear, and there is a possibility that deterioration of the downstream catalytic converter cannot be accurately determined. This also applies to the technique disclosed in Patent Document 1.

  The present invention has been made to solve such a problem, and the object of the present invention is only in the upstream side even when a plurality of catalytic converters are arranged in series in the exhaust passage. Another object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can accurately determine deterioration of a downstream catalytic converter.

In order to achieve the above-described object, an exhaust emission control device for an internal combustion engine according to claim 1 is provided on a first catalytic converter disposed in an exhaust passage of the internal combustion engine and on a downstream side of the first catalytic converter. A second catalytic converter; a first exhaust sensor that detects an exhaust air-fuel ratio provided downstream of the first catalytic converter and upstream of the second catalytic converter; and the second catalytic converter A second exhaust sensor for detecting an exhaust air-fuel ratio provided on the downstream side of the engine, fuel cut means for temporarily stopping fuel supply to the internal combustion engine, and fuel supply to the internal combustion engine by the fuel cut means The air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine to the rich air-fuel ratio side temporarily and then gradually returning it to the stoichiometric air-fuel ratio or the vicinity thereof when returning the fuel supply after stopping Air-fuel ratio When the air-fuel ratio of the internal combustion engine is controlled to the rich air-fuel ratio side by the control means, a rise time difference detection means for detecting a rise time difference between the output of the first exhaust sensor and the output of the second exhaust sensor to the rich air-fuel ratio side And a mode switching means for selectively switching between a deterioration determination mode for determining deterioration of the catalytic converter and a normal mode for which no deterioration determination is performed, and when the deterioration determination mode is selected by the mode switching means, the rise Deterioration determining means for determining deterioration of the catalytic converter based on the rise time difference detected by the time difference detecting means, and the air-fuel ratio control means, when the deterioration determining mode is selected by the mode switching means, The degree of enrichment of the air-fuel ratio of the internal combustion engine is controlled smaller than when the normal mode is selected. And wherein the changing at large gradient toward the air-fuel ratio from the rich air-fuel ratio side to the stoichiometric air-fuel ratio or near together.

Further, in the exhaust gas purification apparatus for an internal combustion engine according to claim 2, in the first aspect , the air-fuel ratio control means sets the air-fuel ratio of the internal combustion engine to rich air until at least the output of the first exhaust sensor rises to the rich air-fuel ratio side. A small controlled state is maintained on the fuel ratio side, and then the air-fuel ratio is changed with a large gradient from the rich air-fuel ratio side toward the theoretical air-fuel ratio or the vicinity thereof.

According to the exhaust gas purification apparatus for an internal combustion engine according to claim 1, the first and second catalytic converters are used to suppress NOx emission when the fuel supply is restored after the fuel supply to the internal combustion engine is stopped by the fuel cut means. In order to purge the oxygen stored in the air, the air-fuel ratio of the internal combustion engine is temporarily controlled to the rich air-fuel ratio side by the air-fuel ratio control means, and then controlled to gradually return to the theoretical air-fuel ratio or the vicinity thereof. At this time, when the deterioration determination mode is selected by the mode switching means, the richness of the air-fuel ratio of the internal combustion engine is controlled to be smaller than that when the normal mode is selected, and in this state, the rise time difference detection means detects The deterioration of the second catalytic converter is determined on the basis of the rise time difference between the output of the first exhaust sensor and the output of the second exhaust sensor to the rich air-fuel ratio side. As described above, when the deterioration determination is made, the richness of the air-fuel ratio is controlled to be small, so that the oxygen purge can be gradually advanced in the second catalytic converter to increase the rise time difference. It is possible to easily detect the change in the rise time difference caused by the deterioration of the two-catalyst converter. Further, the air-fuel ratio is changed with a large gradient from the rich air-fuel ratio side toward the stoichiometric air-fuel ratio or the vicinity thereof, and the change gradient from the rich air-fuel ratio side to the stoichiometric air-fuel ratio or the vicinity thereof is largely controlled, thereby The degree of enrichment of the air-fuel ratio of the engine can be easily controlled to be small as a whole.

Accordingly, it is possible to accurately determine the deterioration of not only the first catalytic converter but also the downstream second catalytic converter .

According to the exhaust gas purification apparatus for an internal combustion engine according to claim 2 , the air-fuel ratio control means controls the air-fuel ratio of the internal combustion engine to be reduced to the rich air-fuel ratio side until at least the output of the first exhaust sensor rises to the rich air-fuel ratio side. Then, the air-fuel ratio is changed with a large gradient from the rich air-fuel ratio side toward the theoretical air-fuel ratio or the vicinity thereof. Thus, the air-fuel ratio of the internal combustion engine can be quickly returned to the stoichiometric air-fuel ratio or the vicinity thereof when the oxygen purge of the first catalytic converter is completed and the oxygen purge of the second catalytic converter is started. Therefore, in particular, since the oxygen purge of the second catalytic converter can be slowly advanced to increase the rise time difference, the deterioration of the second catalytic converter can be determined with higher accuracy.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to the present invention mounted on a vehicle. Hereinafter, the configuration of the exhaust emission control device will be described with reference to this figure.
As shown in the figure, for example, an intake pipe injection (MPI) 4-cylinder gasoline engine is employed as an engine body (hereinafter simply referred to as an engine) 1 that is an internal combustion engine.

A spark plug 4 is attached to the cylinder head 2 of the engine 1 for each cylinder, and an ignition coil 8 that outputs a high voltage is connected to the spark plug 4.
In the cylinder head 2, an intake port is formed for each cylinder, and one end of the intake manifold 10 is connected so as to communicate with each intake port. An electromagnetic fuel injection valve (injection) 6 is attached to the intake manifold 10, and a fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe 7. Has been.

  An electromagnetic throttle valve 14 for adjusting the amount of intake air is provided on the upstream side of the fuel injection valve 6 of the intake manifold 10 and a throttle position sensor (TPS) for detecting the valve opening of the throttle valve 14 is also provided. ) 16 is provided. Further, an air flow sensor 18 for measuring the intake air amount is interposed upstream of the throttle valve 14. As the air flow sensor 18, a Karman vortex type or a hot film type air flow sensor is used.

The cylinder head 2 has an exhaust port for each cylinder, and one end of an exhaust manifold 12 is connected so as to communicate with each exhaust port.
In addition, since the structure itself of the MPI engine taken up in the present embodiment is a publicly known structure, a detailed description thereof will be omitted.
An exhaust pipe 20 is connected to the other end of the exhaust manifold 12, and a three-way catalyst (first catalytic converter), which is one of the exhaust purification catalyst devices, is provided at an intermediate part or a relatively upstream part of the exhaust pipe 20. 30 is interposed as an upstream catalytic converter.

The three-way catalyst 30 is a catalyst capable of oxidizing and removing HC and CO and reducing and removing NOx when the air-fuel ratio is stoichiometric (theoretical air-fuel ratio = value 14.7) or in the vicinity thereof. It contains any of copper (Cu), cobalt (Co), silver (Ag), platinum (Pt), rhodium (Rh), and palladium (Pd). Such a noble metal has an oxygen storage function (O ₂ storage function) not only when it contains an oxygen storage material such as cerium (Ce) or zirconia (Zr) but also when this kind of oxygen storage material is not included. is doing. Therefore, when the three-way catalyst 30 occludes O ₂ in an oxidizing atmosphere in which the exhaust air-fuel ratio (exhaust A / F) is a lean air-fuel ratio (lean A / F), the exhaust A / F becomes a rich air-fuel ratio (rich A / F) until the next reducing atmosphere retains its O ₂ as a storage O _2, dissociated O by releasing the storage O ₂ in the reducing atmosphere is removed, for example, the oxidation of HC and CO in a reducing atmosphere state It can be removed.

Since the three-way catalyst 30 is disposed at a position relatively close to the engine 1, it can be activated early upon receiving a supply of high-temperature exhaust gas.
In the downstream portion of the exhaust pipe 20, an HC trap catalyst (second catalyst converter) 40 and a three-way catalyst 50, which are one of the exhaust purification catalyst devices, are interposed as downstream catalyst converters.
The HC trap catalyst 40 has a function of desorbing the stored HC when it reaches a certain temperature after storing hydrocarbons (HC) exhausted due to incomplete combustion of the fuel mainly at the start of the engine 1. is there. However, the HC trap catalyst 40 has a small amount of the noble metal as described above in the carrier, and also has an O ₂ storage function like the three-way catalyst 30.

The three-way catalyst 50 mainly reduces and removes HC desorbed from the HC trap catalyst 40 on the downstream side, and has the same function as the three-way catalyst 30.
Then, upstream of the three-way catalyst 30 in the exhaust pipe 20, between the three-way catalyst 30 and the HC trap catalyst 40, and between the HC trap catalyst 40 and the three-way catalyst 50, the O ₂ concentration in the exhaust is set. An O ₂ sensor 22, an O ₂ sensor (first exhaust sensor) 24, and an O ₂ sensor (second exhaust sensor) 26 that detect exhaust A / F by detection are provided.

The ECU (electronic control unit) 60 includes an input / output device, a storage device (ROM, RAM, etc.), a central processing unit (CPU), a timer counter, and the like. The ECU 60 performs comprehensive control of the exhaust emission control device including the engine 1.
Various sensors such as a crank angle sensor 42 for detecting the crank angle of the engine 1 are connected to the input side of the ECU 60 in addition to the TPS 16, the air flow sensor 18, the O ₂ sensors 22, 24, and 26 described above. Detection information from the sensors is input. Based on the information from the crank angle sensor 42, the engine speed Ne can be detected.

On the other hand, various output devices such as the fuel injection valve 6, the ignition coil 8, and the throttle valve 14 are connected to the output side of the ECU 60, and these various output devices are operated based on detection information from various sensors. The fuel injection amount, fuel injection timing, ignition timing, etc., are output. Specifically, the combustion air-fuel ratio (combustion A / F) is set to an appropriate target air-fuel ratio (target A / F) based on detection information from various sensors, and usually the target A based on information from the O ₂ sensor 22. / F is feedback (A / F-F / B) controlled at or near stoichio, an amount of fuel corresponding to the target A / F is injected from the fuel injection valve 6 at an appropriate timing, and the throttle valve 14 is The opening degree is adjusted to an appropriate degree, and spark ignition is performed by the spark plug 4 at an appropriate timing.

In addition, the engine 1 is configured to be capable of stopping fuel supply and performing fuel cut (hereinafter also referred to as F / C for short) when the vehicle is decelerating (fuel cut means). That is, in this engine 1, when the driver stops the depression of an accelerator pedal (not shown) and the engine speed Ne is equal to or higher than the predetermined speed, the fuel injection from the fuel injection valve 6 is performed according to a command from the ECU 60. It stops and performs fuel cut appropriately. In the engine 1, after the fuel cut is performed, immediately after the engine rotational speed Ne becomes equal to or lower than the return rotational speed and the fuel supply is restored, that is, immediately after the fuel cut is restored, sufficient engine output is obtained or NOx. reduce and remove the storage _{O 2} which is heavily occluded precious metal of the three-way catalyst 30, HC trap catalyst 40 and the three way catalyst 50 by the fuel cut in order to suppress the occurrence _{(O 2} purge) Subeku, ECU 60 by the target a / F is temporarily set to rich A / F and controlled to the rich A / F side (air-fuel ratio control means). The fuel cut may be performed for all cylinders or only for some cylinders.

Furthermore, the exhaust gas purification apparatus according to the present invention is configured to be able to select a deterioration determination mode for determining deterioration of the catalyst and a normal mode other than that (no determination of deterioration) at the time of fuel cut recovery. (Mode switching means) In the ECU 60, by selecting the deterioration determination mode, the three-way catalyst 30 that is particularly susceptible to deterioration based on information from the O ₂ sensors 22, 24, 26 after the start of enrichment of the target A / F. In addition, the deterioration determination of the HC trap catalyst 40 is performed (deterioration determination means).

That is, when the target A / F is controlled to the rich A / F side, the storage O ₂ occluded in a large amount in the three-way catalyst 30 or the like by the HC and CO in the exhaust gas from the upstream three-way catalyst 30 located in the previous stage. Reduced and removed in order. Specifically, when the O ₂ purge of the previous three-way catalyst 30 is completed, the HC and CO in the exhaust flow to the downstream side of the three-way catalyst 30 and the O ₂ purge of the HC trap catalyst 40 located in the middle stage starts. Then, when the O ₂ purge of the HC trap catalyst 40 is completed, HC and CO in the exhaust gas flow out to the downstream side of the HC trap catalyst 40 and the O ₂ purge of the three-way catalyst 50 located at the subsequent stage is started. At this time, the ECU 60 detects each rising time difference (O ₂ purge time) between the upstream O ₂ sensors 22 and 24 of the three-way catalyst 30 and the HC trap catalyst 40 and the downstream O ₂ sensors 24 and 26, respectively. Then, the deterioration of the three-way catalyst 30 and the HC trap catalyst 40 is judged (rising time difference detection means).

Specifically, since the O ₂ storage capacity and deterioration of the catalytic converter have a correlation, and it can be determined that the catalytic converter has deteriorated when the O ₂ storage capacity decreases, the O ₂ sensor 22 on the upstream side of the three-way catalyst 30 and the downstream side. When the rise time difference from the O ₂ sensor 24 becomes shorter than a predetermined time, the three-way catalyst 30 determines that the O ₂ storage capacity is deteriorated and deteriorates, and the upstream side of the O ₂ sensor 24 and the downstream side of the HC trap catalyst 40. When the rise time difference with the O ₂ sensor 26 on the side becomes shorter than a predetermined time, the HC trap catalyst 40 determines that the O ₂ storage capacity has deteriorated and deteriorated.

Hereinafter, the control content and operation of the exhaust emission control device according to the present invention configured as described above will be described.
Referring to FIG. 2, the control routine of the catalyst deterioration determination control according to the present invention executed by the ECU 60 is shown in a flowchart. Referring to FIG. 3, the execution result of the control routine of FIG. , The combustion A / F, the O ₂ sensor voltage, and the O ₂ storage rate (= actual O ₂ storage amount / maximum O ₂ storage amount) are respectively shown in time charts. The contents of the catalyst deterioration determination control of the exhaust purification apparatus according to the present invention will be described below with reference to the flowchart of FIG. 2 with reference to FIG. Note that reference numerals (22), (24), (26), (30), and (40) in FIG. 3 are the O ₂ sensors 22, 24, and 26, the three-way catalyst 30, and the HC trap catalyst 40, respectively. Correspond.

First, in step S10, it is determined whether or not the fuel cut is completed and the fuel supply is restored, that is, whether or not the fuel cut is restored. If the determination result is false (No), the routine is exited. If the determination result is true (Yes), the process proceeds to step S12.
In step S12, it is determined whether or not a rich A / F control condition is satisfied. Specific conditions include (1) whether the throttle valve 14 is fully closed and the fuel cut is continued for a specified time or more, (2) whether a predetermined time has elapsed after the engine 1 is started, or (3) the engine speed Ne is It is less than a predetermined value (for example, less than the return rotation speed). If the determination result is false (No) in step S12, the routine is exited. On the other hand, if the determination result is true (Yes) (that is, all the rich A / F control conditions (1) to (3) described above, etc.). If established, the process proceeds to step S14.

In step S14, it is determined whether or not the deterioration determination mode is selected. If the determination result is false (No), and it is determined that the deterioration determination mode is not selected and the normal mode is selected, the process proceeds to step S30, and the rich A / F control at the normal time is started.
In step S30, phase 1 control of rich A / F control is executed. Unlike normal time when burned gas remains immediately after fuel cut return, there is only fresh air in the cylinder of each cylinder. Therefore, in phase 1, only the first cycle immediately after fuel cut return for each cylinder In particular, fuel injection is performed by increasing the fuel supply amount (for example, fuel injection amount correction coefficient 2.0). In this case, the target A / F is a value 12, for example.

  In step S32, it is determined whether or not phase 1 control has been completed. As described above, since the phase 1 is performed only for the first one cycle immediately after the fuel cut recovery of each cylinder, specifically, the first one cycle of each cylinder is completed based on the information from the crank angle sensor 42. It is determined whether or not. When the determination result is false (No), the control of the phase 1 is continued, and when the determination result is true (Yes), the process proceeds to step S34.

In step S34, normal phase 2 control is executed during normal operation in rich A / F control. In the normal phase 2 control, the fuel supply amount is set so as to maintain the target A / F (for example, value 12) in the phase 1 and fuel injection is performed (for example, the fuel injection amount correction coefficient 1.3). If the target A / F (for example, value 12) is maintained in this way, the O ₂ purge of the three-way catalyst 30 on the most upstream side is completed quickly, and the O ₂ sensor 24 on the downstream side of the three-way catalyst 30. Output rises to the rich A / F side early (see broken lines (24) and (30) in FIG. 3).

In step S36, it is determined whether or not the control of the normal phase 2 is finished. Specifically, it is determined whether or not the output of the O ₂ sensor 24 has risen to a predetermined value or more on the rich A / F side. When the determination result is false (No), the control of the normal phase 2 is continued, and when the determination result is true (Yes), the process proceeds to step S38.
In step S38, the normal phase 3 control in the normal state of the rich A / F control is executed. In the normal phase 3 control, the fuel supply amount is changed by gradually returning the target A / F (for example, the value 12) to stoichiometric or its vicinity. As described above, when the fuel supply amount is changed so that the target A / F is gradually returned to the stoichiometric or the vicinity thereof, the O ₂ purge is completed relatively quickly for the HC trap catalyst 40 located in the next stage. The output of the O ₂ sensor 26 on the downstream side of the catalyst 40 quickly rises to the rich A / F side (see broken lines (26) and (40) in FIG. 3). Furthermore, the O ₂ purge is also completed relatively quickly for the three-way catalyst 50 located at the subsequent stage.

In step S40, it is determined whether or not the control of the normal phase 3 is finished. Specifically, it is determined whether the target A / F has reached stoichio or its vicinity. When the determination result is false (No), the control of the normal phase 3 is continued. When the determination result is true (Yes), the process proceeds to step S42, the rich A / F control is terminated, and the feedback control is performed. Resume.
As described above, in the normal mode, the storage O ₂ stored in the three-way catalyst 30, the HC trap catalyst 40, and the three-way catalyst 50 is immediately removed, and after the fuel cut is restored, the three-way catalyst 30, the HC trap catalyst 40, and the like. The catalytic function of the three-way catalyst 50 can be quickly recovered.

On the other hand, if the determination result in step S14 is true (Yes) and it is determined that the deterioration determination mode is selected, the process proceeds to step S16, and rich A / F control at the time of deterioration determination is started.
In step S16, phase 1 control of rich A / F control is executed. The control in phase 1 is the same as the normal control, and a description thereof is omitted.

In step S18, it is determined whether or not the control of phase 1 has been completed in the same manner as in step S32. If the determination result is false (No), phase 1 is continued, and if the determination result is true (Yes), the process proceeds to step S20.
In step S20, determination phase 2 at the time of deterioration determination in the rich A / F control is executed. In the control in the determination phase 2, the target A / F is set so that the degree of enrichment of the target A / F is smaller than that in the normal phase 2 (the target A / F is large) (for example, value 13), Fuel injection is performed by setting a fuel supply amount smaller than that in the case of the normal phase 2 so as to achieve this target A / F (for example, fuel injection amount correction coefficient 1.15). Thus, when the target A / F (for example, value 13) is set and fuel injection is performed, the O ₂ purge speed of the three-way catalyst 30 on the most upstream side is lower than the normal time (that is, O). ₂ purge proceeds slowly), and the output of the O ₂ sensor 24 on the downstream side of the three-way catalyst 30 rises to the rich A / F side after a certain time with respect to the output of the upstream O ₂ sensor 22 (see FIG. 3 (see solid lines (24) and (30)).

That is, the rise time difference between the upstream O ₂ sensor 22 and the downstream O ₂ sensor 24 of the three-way catalyst 30 is larger than that in the normal state (O ₂ purge time is longer than that in the normal state).
In step S22, it is determined in the same manner as in step S36 whether or not the control of determination phase 2 has been completed. If the determination result is false (No), the control of the determination phase 2 is continued, and if the determination result is true (Yes), the process proceeds to step S24.

  In step S24, control of determination phase 3 at the time of deterioration determination in rich A / F control is executed. In the control in the determination phase 3, the fuel supply amount is changed so that the change gradient of the target A / F is made larger than that in the normal phase 3 and returned to the stoichiometric or the vicinity thereof (for example, 4 in the control of the normal phase 3). The feedback control is resumed after the change gradient is twice as large.

In this way, when the fuel supply amount is changed so that the target A / F is quickly returned to the stoichiometric or its vicinity, in addition to the control in the determination phase 2, the degree of enrichment becomes smaller as a whole, and the HC located in the next stage The O ₂ purge of the trap catalyst 40 proceeds slowly as in the case of the three-way catalyst 30, and the output of the O ₂ sensor 26 on the downstream side of the HC trap catalyst 40 is somewhat to the output of the upstream O ₂ sensor 24. It rises to the rich A / F side after a while (see solid lines (26) and (40) in FIG. 3).

In other words, as shown by the white arrow in FIG. 3, the rise time difference between the upstream O ₂ sensor 24 and the downstream O ₂ sensor 26 is larger than that in the normal case even for the HC trap catalyst 40 located on the downstream side ( O ₂ purge time is longer than normal).
Further, the O ₂ purge of the three-way catalyst 50 located at the subsequent stage also proceeds slowly as in the case of the three-way catalyst 30 and the HC trap catalyst 40.

In step S26, it is determined whether or not the control of determination phase 3 has been completed, as in the case of step S40. If the determination result is false (No), the control of determination phase 3 is continued, and if the determination result is true (Yes), the process proceeds to step S28.
In step S28, the deterioration of the three-way catalyst 30 and the HC trap catalyst 40 is determined. That is, as described above, the three-way rising time difference between the upstream side of the _{O 2} sensor 22 and the downstream side of the _{O 2} sensor 24 of the catalyst 30, the upstream side of the HC trap catalyst 40 _{O 2} sensor 24 and the downstream _{O 2} Degradation is determined based on the rise time difference from the sensor 26.

In this case, as described above, the rise time difference between the O ₂ sensor 22 and the O ₂ sensor 24 and the rise time difference between the O ₂ sensor 24 and the O ₂ sensor 26 are larger than the normal time. It is possible to easily detect the change in the rise time difference caused by the deterioration of the HC trap catalyst 40 with high sensitivity, and to determine the deterioration of the three-way catalyst 30 and the HC trap catalyst 40 with high accuracy.

As a result, when the rise time difference between the upstream O ₂ sensor 22 and the downstream O ₂ sensor 24 of the three-way catalyst 30 becomes shorter than a predetermined time, the three-way catalyst 30 has deteriorated due to a decrease in O ₂ storage capacity. When the rise time difference between the upstream O ₂ sensor 24 and the downstream O ₂ sensor 26 of the HC trap catalyst 40 becomes shorter than a predetermined time, the HC trap catalyst 40 has a reduced O ₂ storage capability. It can be accurately determined that it has deteriorated.

In particular, here, the target A / F is smaller than that in the normal phase 2 until the output of the O ₂ sensor 24 provided on the downstream side of the three-way catalyst 30 rises to the rich A / F side (the target A / F is less than the target A / F). After the output of the O ₂ sensor 24 rises to the rich A / F side, the target A / F is changed with a large gradient toward or near the stoichio. Thus, possible to return the target A / F immediately in stoichiometric or near when the O ₂ purge of the three-way catalyst 30 is finished to O ₂ purge the downstream side of the HC trap catalyst 40 is started, the determination phase In addition to the control of 2, the degree of enrichment can be easily reduced as a whole, and in particular, the O ₂ purge of the downstream HC trap catalyst 40 is gradually advanced to increase the rise time difference between the O ₂ sensor 24 and the O ₂ sensor 26. Is possible. Thereby, it is possible to accurately determine the deterioration of the HC trap catalyst 40 even though it is on the downstream side of the three-way catalyst 30.

Thus, the exhaust gas purification apparatus according to the present invention can accurately determine the deterioration of not only the upstream three-way catalyst 30 but also the downstream HC trap catalyst 40 at the time of fuel cut recovery.
When the deterioration determination is completed, the process proceeds to step S42 as in the normal mode, and the rich A / F control is ended.

As a result, the storage O ₂ stored in the three-way catalyst 30, the HC trap catalyst 40, and the three-way catalyst 50 is removed while accurately determining the deterioration of the three-way catalyst 30 and the HC trap catalyst 40, and the three-way catalyst 30. The catalytic functions of the HC trap catalyst 40 and the three-way catalyst 50 can be recovered satisfactorily.
Although the description of the embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention is finished above, the embodiment is not limited to the above.

For example, in the above-described embodiment, the most downstream three-way catalyst 50 located in the subsequent stage is not affected by heat because it is hardly affected by heat. However, a separate O ₂ sensor is not provided on the downstream side of the three-way catalyst 50. provided, the O ₂ obtains the rise time difference from the output of the upstream side of the O ₂ sensor 26 and the output of the three-way catalyst 50 of the sensor, it is carried out also the deterioration determination of the three-way catalyst 50 based on the rising time difference Good.

In the above embodiment, the three-way catalyst 30, the HC trap catalyst 40, and the three-way catalyst 50 are arranged in this order in the exhaust pipe 20. However, the present invention is not limited to this, and a plurality of O ₂ storage capabilities are provided. As long as the exhaust gas purification system in which the catalytic converters are arranged in series, the type, quantity, and arrangement order of the catalytic converters may be any.
Moreover, in the said embodiment, although the engine 1 was made into the intake pipe injection type gasoline engine, it is not restricted to this, The engine 1 may be a cylinder injection type gasoline engine etc., for example.

1 is a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to the present invention mounted on a vehicle. It is a flowchart which shows the control routine of the catalyst deterioration determination control which concerns on this invention. Execution result of the fuel injection quantity correction coefficient of the catalyst deterioration determination control, the combustion A / F, O ₂ sensor voltage is a time chart showing for each O ₂ storage rate.

Explanation of symbols

1 engine body 6 fuel injection valve 20 an exhaust pipe 22 O ₂ sensor 24 O ₂ sensor (first exhaust sensor)
26 O ₂ sensor (second exhaust sensor)
30 Three-way catalyst (first catalytic converter)
40 HC trap catalyst (second catalytic converter)
50 Three-way catalyst 60 ECU (electronic control unit)

Claims (2)

A first catalytic converter disposed in an exhaust passage of the internal combustion engine;
A second catalytic converter disposed downstream of the first catalytic converter;
A first exhaust sensor that detects an exhaust air-fuel ratio that is provided downstream of the first catalytic converter and upstream of the second catalytic converter;
A second exhaust sensor for detecting an exhaust air-fuel ratio provided on the downstream side of the second catalytic converter;
Fuel cut means for temporarily stopping fuel supply to the internal combustion engine;
When returning the fuel supply after stopping the fuel supply to the internal combustion engine by the fuel cut means, the air-fuel ratio of the internal combustion engine is temporarily controlled to the rich air-fuel ratio side and then gradually brought to the stoichiometric air-fuel ratio or its vicinity. Air-fuel ratio control means for controlling to return ,
When the air-fuel ratio of the internal combustion engine is controlled to the rich air-fuel ratio side by the air-fuel ratio control means, the rise time for detecting the rise time difference between the output of the first exhaust sensor and the output of the second exhaust sensor to the rich air-fuel ratio side Time difference detection means;
Mode switching means for selectively switching between a deterioration determination mode for determining deterioration of the catalytic converter and a normal mode for not performing deterioration determination;
Deterioration determining means for determining deterioration of the catalytic converter based on the rising time difference detected by the rising time difference detecting means when the deterioration determining mode is selected by the mode switching means;
The air-fuel ratio control means, when the deterioration determination mode is selected by said mode switching means, the air-fuel ratio controls reduce the enrichment degree of the air-fuel ratio of the internal combustion engine than when the normal mode is selected An exhaust gas purification apparatus for an internal combustion engine, wherein the exhaust gas is changed with a large gradient from the rich air-fuel ratio side toward the stoichiometric air-fuel ratio or the vicinity thereof . The air-fuel ratio control means maintains a state where the air-fuel ratio of the internal combustion engine is controlled to be small toward the rich air-fuel ratio until at least the output of the first exhaust sensor rises to the rich air-fuel ratio, and then the air-fuel ratio is reduced to the rich air-fuel ratio. 2. The exhaust emission control device for an internal combustion engine according to claim 1 , wherein the exhaust gas purification device is changed with a large gradient from the fuel ratio side toward the stoichiometric air fuel ratio or the vicinity thereof.

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