JP2004019512A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of accurately diagnosing degradation of NOx adsorption catalyst. <P>SOLUTION: The exhaust emission control device comprises the NOx adsorption catalyst 25 disposed in an exhaust passage 22 and for adsorbing or discharging NOx in response to oxygen concentration in exhaust gas, an NOx sensor 26 disposed on the downstream side of the NOx adsorption catalyst and having a metal cover, an oxygen concentration control means 32 for controlling the oxygen concentration to discharge NOx from the NOx adsorption catalyst when the NOx adsorption amount of the NOx adsorption catalyst reaches a predetermined amount, and a diagnosing means 32 that detects an NOx discharge state from the NOx adsorption catalyst based on an output from the NOx sensor in discharging NOx and diagnoses degradation of the NOx adsorption catalyst based on it. The oxygen concentration control means controls the oxygen concentration to be 0.3% or lower or 0.5% or higher during the degradation diagnosis. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device for removing NOx (nitrogen oxide) from exhaust gas of an engine or the like.
[0002]
[Prior art]
As an exhaust purification device for an automobile or the like that operates by lean burn, a NOx adsorption catalyst that adsorbs NOx when the oxygen concentration in the exhaust gas is high and releases the adsorbed NOx when the oxygen concentration in the exhaust gas becomes low is used. Apparatus equipped with are known. Since there is a limit to the amount of NOx adsorbed by the NOx adsorbing catalyst, in such a device, when the NOx adsorbing catalyst adsorbs NOx to the saturation amount, the engine shifts from an operation state by lean burn to an operation state near the stoichiometric air-fuel ratio. For example, a process of reducing the oxygen concentration in the exhaust gas to release NOx from the NOx adsorption catalyst and reducing and purifying the NOx is performed.
[0003]
In this process, the amount of NOx on the downstream side is detected by a NOx sensor provided on the downstream side of the NOx adsorption catalyst, and the deterioration state of the NOx adsorption catalyst is diagnosed based on the detection result. A device for diagnosing is known (JP-A-2000-337131).
[0004]
[Problems to be solved by the invention]
However, the inventor of the present invention has found that NOx detection by a NOx sensor is not properly performed in an oxygen concentration region where the deterioration state is diagnosed by the above-described device or the like, and as a result, the diagnosis becomes inaccurate. Was. As a result of studying this problem, the metal contained in the metal cover provided to protect the detector for detecting NOx acts as a catalyst in this oxygen concentration region, and the NOx to be detected is CO, H2 The reaction was caused by reacting with a reducing gas such as HC and reducing NOx reaching the detector.
[0005]
The present invention has been made in such a situation, and it is an object of the present invention to provide an exhaust gas purification device capable of accurately performing a deterioration diagnosis of a NOx adsorption catalyst.
[0006]
[Means for Solving the Problems]
According to the invention of the present application, a NOx adsorption catalyst that is disposed in an exhaust passage and adsorbs or releases NOx according to the oxygen concentration in exhaust gas, and a NOx that is disposed downstream of the NOx adsorption catalyst and has a metal cover A sensor, oxygen concentration control means for releasing the NOx from the NOx adsorption catalyst by controlling the oxygen concentration when the NOx adsorption amount of the NOx adsorption catalyst reaches a predetermined amount, and an oxygen concentration control means for releasing the NOx from the NOx sensor when the NOx is released. Diagnostic means for detecting a state of NOx release from the NOx adsorption catalyst based on the output, and performing a deterioration diagnosis of the NOx adsorption catalyst based on the detected state.The oxygen concentration control means includes: An exhaust emission control device is provided, wherein the oxygen concentration is controlled to a concentration of 0.3 or less or 0.5% or more.
[0007]
According to the exhaust gas purification apparatus having such a configuration, during the deterioration diagnosis, the oxygen concentration in the exhaust gas is set to a range in which the catalytic action of the metal included in the metal cover is unlikely to occur. The NOx concentration on the downstream side can be accurately measured. As a result, the deterioration diagnosis of the NOx adsorption catalyst based on the output of the NOx adsorption catalyst sensor is also accurately performed.
[0008]
According to a preferred aspect of the present invention, the oxygen concentration control means controls the oxygen concentration to 0.1 or less or 0.5% or more during the deterioration diagnosis. According to another preferred aspect of the present invention, the oxygen concentration control means controls the oxygen concentration to 0% during the deterioration diagnosis.
[0009]
According to another preferred embodiment of the present invention, the NOx adsorption catalyst adsorbs NOx at a high oxygen concentration and releases NOx adsorbed at a low oxygen concentration. A catalyst metal for purifying NOx released from the material; and the diagnosis unit diagnoses deterioration of at least one of the NOx adsorbent and the catalyst metal.
[0010]
According to another preferred aspect of the present invention, the oxygen concentration control means controls the oxygen concentration in a range of 0.1 to 0.6% for a predetermined period after the end of the deterioration diagnosis.
[0011]
According to another preferred embodiment of the present invention, the oxygen concentration control means controls the oxygen concentration in the exhaust gas within a range of 0.1 to 0.6% after the lapse of the predetermined period. According to such a configuration, after completion of the deterioration diagnosis, the operation state shifts to an operation state in which fuel efficiency is emphasized.
[0012]
According to another preferred aspect of the present invention, the oxygen concentration control means changes the content of the oxygen concentration control based on a diagnosis result by the diagnosis means. According to such a configuration, since the NOx release amount is controlled according to the degree of deterioration of the NOx adsorption catalyst, the NOx amount in the exhaust gas discharged to the outside of the exhaust system can be suppressed.
[0013]
According to another aspect of the present invention, a NOx adsorption catalyst that is disposed in an exhaust passage of an engine and adsorbs or releases NOx according to the oxygen concentration in exhaust gas, and a metal that is disposed downstream of the NOx adsorption catalyst A NOx sensor having a cover, oxygen concentration control means for controlling the oxygen concentration to release NOx from the NOx adsorption catalyst when the NOx adsorption amount of the NOx adsorption catalyst reaches a predetermined amount, and Diagnostic means for detecting a state of NOx release from the NOx adsorption catalyst based on an output from the NOx sensor, and performing deterioration diagnosis of the NOx adsorption catalyst based on the state; and During the deterioration diagnosis by the diagnosis means, the oxygen concentration is controlled to a first value at which the metal does not cause a catalytic action on NOx. Controlling the degree to higher second value than the first value, the exhaust gas purification device is provided, characterized in that.
[0014]
According to such a configuration, during deterioration diagnosis of the NOx adsorption catalyst, the metal forming the cover of the NOx sensor is less likely to cause a catalytic action, and the NOx sensor can accurately measure NOx in the exhaust gas.
[0015]
According to a preferred embodiment of the present invention, the second value is in the range of 0.1 to 0.6%.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a drawing schematically showing a configuration of a spark ignition type engine system 100 for an automobile equipped with an engine exhaust gas purification apparatus according to a preferred embodiment of the present invention.
[0017]
The engine system 100 includes an engine body 1. In this engine system, a lean burn operation in which the air-fuel ratio is set higher than 14.7 is performed in a predetermined operating state. The engine main body 1 includes a plurality of cylinders 2 (only one is shown) and a piston 3 reciprocally arranged in the cylinder 2, and a combustion chamber 4 is formed by the cylinder 2 and the piston 3. ing. An ignition plug 6 connected to an ignition circuit 5 is mounted above the combustion chamber 4 so as to face the combustion chamber 4, and an injector 7 for directly injecting fuel into the combustion chamber 4 is mounted.
[0018]
A fuel supply circuit having a high-pressure fuel pump, a pressure regulator, and the like is connected to the injector 7. The fuel from the fuel tank is adjusted to an appropriate pressure by the fuel supply circuit and supplied to the injector 7. The fuel supply circuit is provided with a fuel pressure sensor 8 for detecting a fuel pressure.
[0019]
The combustion chamber 4 communicates with an intake passage 10 via an intake port provided with an intake valve 9. The intake passage 10 is provided with an air cleaner 11 for filtering intake air, an air flow meter 12 for detecting an intake air amount, an electric throttle valve 13 for restricting the intake passage 10, and a surge tank 14 in this order from the upstream side. Has been. The electric throttle valve 13 is configured to be opened and closed by a motor 15. Further, a throttle opening sensor 16 for detecting the opening of the electric throttle valve 13 is disposed in the vicinity of the electric throttle valve 13, and an intake pressure sensor 17 for detecting an intake pressure is attached to the surge tank 14.
[0020]
In the intake passage 10, a portion downstream of the surge tank 14 is an independent passage branched for each cylinder. The downstream end of each independent passage is divided into two, each connected to an intake port of the same cylinder, and a swirl valve 18 is provided on one of them. This swirl valve 18 is driven by an actuator 19. When the swirl valve 18 is closed, intake air is supplied to the combustion chamber 4 only from the other branch passage, and strong intake swirl is generated in the combustion chamber 4. Further, a swirl valve opening sensor 20 for detecting the opening of the swirl valve 18 is provided near the swirl valve 18.
[0021]
An exhaust passage 22 is connected to the combustion chamber 4 via an exhaust port provided with an exhaust valve 21, and the exhaust passages 22 from the respective cylinders are joined on the downstream side. An oxygen concentration sensor (O 2) for detecting the oxygen concentration in the exhaust gas is sequentially provided to the merged exhaust passage 22 from the upstream side. ₂ Sensor) 24, a NOx adsorption catalyst 25 that adsorbs NOx, and a NOx sensor 26. The NOx adsorbing catalyst 25 adsorbs NOx when the oxygen concentration in the exhaust gas is high such as lean burn operation, and releases the adsorbed NOx when the oxygen concentration becomes low. This is a NOx absorption-reduction type NOx trap catalyst including a catalytic metal (noble metal) for reducing and purifying released NOx.
[0022]
The NOx adsorption catalyst 25 includes a cordierite honeycomb-structured carrier, and a wall of each through hole formed in the carrier is coated with an inner catalyst layer, and an outer catalyst layer is coated on the inner catalyst layer. I have.
[0023]
In the inner catalyst layer having the NOx absorption catalytic function, a noble metal such as platinum and a NOx absorbent such as Ba are supported on a porous support material such as alumina or ceria. In the outer catalyst layer having the NOx reduction function, a catalyst metal such as platinum and rhodium and, in some cases, a NOx absorbent such as Ba are supported on a support material such as zeolite which is a porous material. .
[0024]
The NOx adsorption amount of the NOx adsorption catalyst 25 has a limit. In the present embodiment, when the detected value of NOx in the exhaust gas by the NOx sensor 26 exceeds a predetermined threshold value, it is determined that the NOx adsorption of the NOx adsorption catalyst has reached saturation, and the oxygen concentration in the exhaust gas is increased. It is configured to perform a process of releasing NOx from the NOx adsorbent (rich spike process).
[0025]
FIG. 2 is a schematic sectional view showing the structure of the NOx sensor 26. As shown in FIG. 2, the NOx sensor 26 includes a detector 26c covered by a first cover 26a and a second cover 26b. The detector 26c generates an output according to the NOx concentration in the exhaust gas. The first cover 26a and the second cover 26b have a function of protecting the detector from thermal shock and impurities in exhaust gas, and are made of stainless steel such as SUS. Openings 26d and 26e offset from each other are formed in each of the first cover 26a and the second cover 26b so that exhaust gas is introduced into the detector 26c as indicated by an arrow A. It is configured.
[0026]
An upstream end of an EGR passage 27 that recirculates a part of the exhaust gas to the intake system is connected to the exhaust passage 22 at a position upstream of the oxygen concentration sensor 24. The downstream end of the EGR passage 27 is connected to the intake passage 10 between the throttle valve 13 and the surge tank 14. Further, the EGR passage 27 is provided with an EGR valve 28 whose opening can be electrically adjusted and a lift sensor 29 for detecting a lift amount of the EGR valve 28, and these constitute an exhaust gas recirculation means. .
[0027]
Further, a secondary air supply passage 30 that feeds a part of the intake air from the intake passage 10 to a position on the upstream side of the NOx adsorption catalyst 25 is connected to the exhaust passage 22. The secondary air supply passage 30 is provided with a controllable flow regulating valve 31.
[0028]
The engine system 100 further includes an ECU (electronic control unit) 32 for controlling the entire system. The ECU 34 receives signals from the air flow sensor 12, the throttle opening sensor 16, the intake pressure sensor 17, the swirl control valve opening sensor 20, the oxygen concentration sensor 24, and the lift sensor 29 of the EGR valve 28. The ECU 32 further includes a water temperature sensor 33 for detecting a cooling water temperature of the engine body 1, an intake air temperature sensor 34 for detecting an intake air temperature, an atmospheric pressure sensor 35 for detecting an atmospheric pressure, and a rotational speed sensor 36 for detecting an engine rotational speed. , And a signal from an accelerator opening sensor 37 for detecting the opening of the accelerator pedal (accelerator operation amount) is also input.
[0029]
The ECU 32 controls fuel injection to control the injection state of the fuel injected from the injector 7 according to the operation state of the engine, ignition timing control to control the ignition timing of the air-fuel mixture by the ignition plug 6, and NOx adsorption of the NOx adsorption catalyst 25. When the amount reaches a predetermined amount, rich spike control is performed to release the NOx from the NOx adsorption catalyst 25 by controlling the oxygen concentration in the exhaust gas, and the degree of deterioration of the NOx adsorption catalyst 25 is diagnosed from the NOx release state at the time of the rich spike. Perform deterioration diagnosis control and the like.
[0030]
The fuel injection control is configured to control the fuel injection according to the operating state of the engine. In the present embodiment, in the operation range of low load and low rotation to medium rotation and medium load, fuel is injected collectively from the injector 7 at a predetermined timing of the compression stroke to burn the mixture in the vicinity of the ignition plug 6 in a state where the mixture is unevenly distributed. Then, the combustion control for the stratified charge combustion mode in which the air-fuel ratio of the air-fuel mixture in the combustion chamber 4 is in a lean state of about 30 is executed. Further, in the region on the higher load side than the region in the stratified combustion mode, combustion control for a combustion mode with an air-fuel ratio near λ = 1 is performed in two fuel injections of the intake stroke and the compression stroke. Further, in the high-load, high-speed operation region, the combustion control for the uniform combustion mode in which the fuel is collectively injected from the injector 7 in the intake stroke to make the air-fuel ratio in the combustion chamber 4 rich is performed.
[0031]
NOx, which is largely generated by the combustion in the lean state, is adsorbed by the NOx adsorption catalyst 25 provided on the downstream side. In the present embodiment, the NOx adsorption amount of the NOx adsorption catalyst 25 is estimated based on the output signal of the NOx sensor 26, and if it is determined that the NOx adsorption of the NOx adsorption catalyst 25 is saturated, the air-fuel ratio control and the like are executed. As a result, the oxygen concentration in the exhaust gas is reduced to, for example, 0.3% or less, and control for releasing NOx from the NOx adsorption catalyst 25 (rich spike control) is performed. Further, based on the output signal from the NOx sensor 26 at this time, the deterioration determination of the NOx adsorption catalyst 25 is also performed. In the present embodiment, when the NOx adsorption catalyst 25 is diagnosed as being deteriorated, a display means 41 including a warning light or the like for notifying an occupant of the deterioration is provided.
[0032]
Next, an engine control process performed by the ECU 32 at the time of the rich spike process, which is a premise of the deterioration diagnosis control of the NOx adsorption catalyst 25, will be described with reference to the flowchart of FIG. This control is performed in the combustion by lean burn among the above-mentioned combustion states.
[0033]
First, in step S1, output signals from the air flow sensor 12, the oxygen concentration sensor 24, the NOx sensor 26, the water temperature sensor 33, the intake air temperature sensor 34, the atmospheric pressure sensor 35, the rotation speed sensor 36, the accelerator opening sensor 37, and the like are input. You.
[0034]
Next, in step S2, it is determined whether or not the output value NOxex of the NOx sensor 26 is larger than a predetermined threshold value NOexo. This threshold value NOexo is a value for determining whether the NOx adsorption amount of the NOx adsorption catalyst 25 is saturated. If YES in step S2, it indicates that the NOx sensor 26 has adsorbed NOx up to the saturation amount, and it is necessary to perform the process of releasing NOx, so the rich spike process of releasing NOx is started.
[0035]
First, in step S3, 1 is added to the value T of the timer, and then in step S4, the throttle valve opening Tv is set to the throttle valve opening Tvλ for rich spike control. In the rich spike control, the combustion is performed in a rich state, and the oxygen concentration in the exhaust gas is reduced. Therefore, the throttle valve opening Tvλ for the rich spike control has a smaller value than that during the lean burn.
[0036]
Next, in step S5, the throttle valve is driven so as to attain the throttle valve opening Tvλ for rich spike control. In step S6, it is determined whether the timer value T is less than T1. When the timer value T is less than T1, the process proceeds to step S7, and the fuel injection amount, fuel injection timing, and ignition timing for rich spike are set. In the present embodiment, at the time of rich spike control, split injection is performed in which fuel is injected in two stages, an intake stroke and a compression stroke. Therefore, the injection amount Qλs1 during the intake stroke and the injection amount Qλs2 during the compression stroke are set as the fuel injection amount. Further, as the fuel injection timing, an injection timing Iλs1 in the intake stroke and an injection timing Iλs2 in the compression stroke are set. Further, θλs is set as the ignition timing.
[0037]
At this time, in the present embodiment, the total injection amount corresponding to the air-fuel ratio of 14.5 or less, that is, the sum of the injection amounts Qλs1 and Qλs2, is set such that the oxygen concentration in the exhaust gas becomes 0.3% or less. . Further, it is preferable to set a fuel injection amount corresponding to an air-fuel ratio of 14.3 or less so that the oxygen concentration in the exhaust gas becomes 0.1% or less. It is more preferable to set a fuel injection amount corresponding to an air-fuel ratio of 14.3 or less so as to be equal to or less than%. Preferably, Qλs1 and Qλs2 are set to the same value.
[0038]
Next, the process proceeds to step S8, where fuel injection and ignition are executed based on the fuel injection amount, fuel injection timing, and ignition timing set in step S7. As a result, the combustion that has been lean burn shifts to combustion on the rich side, and the oxygen concentration in the exhaust gas is greatly reduced. As a result, NOx is released from the NOx adsorption catalyst 25. As described later, in the present embodiment, the deterioration diagnosis of the NOx adsorption catalyst 25 is performed based on the NOx release state.
[0039]
In the NOx sensor 26 of this embodiment having a cover made of stainless steel such as SUS, as shown in FIG. 4, even if the NOx concentration in the exhaust gas is the same, the output value depends on the oxygen concentration. Fluctuates. The output value of the NOx sensor ranges from 0% (corresponding to exhaust gas when the air-fuel ratio is about 14.0) to 0.6% (corresponding to exhaust gas when the air-fuel ratio is about 14.8). It decreases and becomes lowest near the oxygen concentration of 0.4% (corresponding to exhaust gas having an air-fuel ratio of about 14.6).
[0040]
As described above, in the present embodiment, during the rich spike control in which the deterioration diagnosis of the NOx adsorption catalyst 25 is performed, the oxygen concentration in the exhaust gas is 0.3% or less, preferably 0.1% or less, more preferably 0% or less. % Is set as the total fuel injection amount. As a result, the oxygen concentration in the exhaust gas decreases to a range where the output value of the NOx sensor 26 is not affected by the metal cover of the NOx sensor, so that the deterioration of the NOx adsorption catalyst 25 based on the output value of the NOx sensor 26 is reduced. The diagnosis will be made accurately.
[0041]
If YES in step S6, that is, if the processes in steps S7 and S8 have been continued during the predetermined period T1, the process proceeds to step S9, where the timer value T is set to the second predetermined period longer than the first predetermined period T1. It is determined whether it is less than T2. If YES in step S9, that is, if the predetermined period T1 has elapsed but the predetermined period T2 has not elapsed, the process proceeds to step S10, where the fuel injection amount, fuel injection timing, and ignition timing for the air-fuel ratio 14.7 (λ = 1) are set. Is set. In the present embodiment, also in the combustion at λ = 1 during the rich spike control, the split injection is performed in which the fuel is injected in two stages, the intake stroke and the compression stroke. Therefore, the injection amount Qλ1 in the intake stroke and the injection amount Qλ2 in the compression stroke are set as the fuel injection amount. Further, as the fuel injection timing, an injection timing Iλ1 in the intake stroke and an injection timing Iλ2 in the compression stroke are set. Further, θλ is set as the ignition timing. In this embodiment, during this control, the sum of the total injection quantity per cycle, that is, the injection quantity Qλ1 and Qλ2, is set so that the air-fuel ratio is 14.6 to 14.8, preferably 14.7. Is set. Preferably, Qλ1 and Qλ2 are set to the same value. If the air-fuel ratio is 14.6, the oxygen concentration in the exhaust gas is about 0.4%. If the air-fuel ratio is 14.7, the oxygen concentration in the exhaust gas is about 0.5% and the air-fuel ratio is 14.8. For example, the oxygen concentration in the exhaust gas is about 0.6%. Further, the air-fuel ratio may be set so that the oxygen concentration in the exhaust gas is 0.1 to 0.6%.
[0042]
Next, the process proceeds to step S8, where fuel injection and ignition are executed based on the fuel injection amount, fuel injection timing, and ignition timing set in step S10. As a result, combustion is performed near the air-fuel ratio of 14.7 (λ = 1), and the oxygen concentration in the exhaust gas becomes lower than in the lean operation. NOx is continuously released from the NOx adsorption catalyst 25. When NO is determined in the step S2, the process proceeds to a step S11, and it is determined whether or not the timer is counting. When YES is determined, the process proceeds to a step S3. If NO in step S11, the process proceeds to step S12, in which the throttle valve opening Tv is set to the throttle valve opening Tv for lean burn, and the throttle valve is driven based on the throttle valve opening Tv set in step S13. .
[0043]
Next, the routine proceeds to step S14, where the fuel injection amount Q for lean burn, the fuel injection timing I, and the ignition timing θ are set. In this embodiment, during lean burn control, stratified lean combustion is performed by batch injection in the compression stroke. Next, the process proceeds to step S8, where fuel injection and ignition are executed based on the fuel injection amount, fuel injection timing, and ignition timing set in step S14.
[0044]
As described above, when the output value of the NOx sensor 26 exceeds NOxexo during the lean burn operation, it is determined that the NOx adsorption amount of the NOx adsorption catalyst 25 has reached the saturation amount (FIG. 5 (a) )), During the first predetermined period T1, the air-fuel ratio is set to a value richer than 14.5 (preferably near 14.3), and after the first predetermined period T1 ends and the second predetermined period Until the period T2, control is performed to set the air-fuel ratio to a value near 14.7 (FIG. 5B). In the present embodiment, the deterioration state of the NOx adsorption catalyst 25 is diagnosed based on the NOx release state during the first predetermined period T1.
[0045]
Next, the details of the deterioration diagnosis of the NOx adsorption catalyst 25 performed by the ECU 32 will be described with reference to the flowchart of FIG.
[0046]
First, in step S21, it is determined whether the output value NOxex of the NOx sensor 26 is larger than a predetermined threshold value NOxexo. When YES is determined in the step S21, the rich spike control for releasing NOx as described above is started. Next, the process proceeds to step S22, and it is determined whether or not the value T of the timer set in step S3 is less than a predetermined period T1.
[0047]
If YES in step S22, that is, if T is less than T1, the process proceeds to step S23, where the output value NOxex of the NOx sensor 26 is stored and the process returns. If NO in step S22, that is, if the timer value T is equal to or greater than T1, the process proceeds to step S24 to extract the stored maximum value NOxmax of the output value NOxex (1,..., N) of the NOx sensor 26. . Further, in step S25, the integrated value NOxα of NOxex (1,..., N) is calculated.
[0048]
Next, the process proceeds to step S26, in which NOxβ is a threshold value for determining the deterioration of the NOx adsorbent such as Ba of the NOx adsorption catalyst 25, and NOxmax0 is a threshold value for determining the deterioration of the noble metal in the catalyst layer inside the NOx adsorption catalyst 25. And. Since the state of release of NOx from the NOx adsorption catalyst 25 is affected by the flow rate of the exhaust gas and the like, these thresholds are set according to the operating state. In the present embodiment, NOxβ and NOxmax0 are set according to the map of FIG. 7 in which NOxβ and NOxmax0 increase as the adsorbed air amount Ce or the engine speed Ne increases.
[0049]
Next, in step S27, it is determined whether or not the NOxα calculated in step S25 is larger than a threshold NOxβ for diagnosing deterioration of the noble metal contained in the NOx adsorption catalyst 25. When YES is determined in the step S27, it is diagnosed that the noble metal contained in the NOx adsorption catalyst is deteriorated, and the process proceeds to a step S28, where a warning is given by the display means 41 such as a warning lamp, and the process is ended.
[0050]
If NO in step S27, the process proceeds to step S29, in which it is determined whether the maximum value NOxmax of the NOx release amount extracted in step S24 is larger than a threshold NOxmax0 for diagnosing deterioration of the NOx adsorbent such as Ba. I do. When YES is determined in the step S29, it is diagnosed that the NOx adsorbent such as Ba is deteriorated, the process proceeds to a step S28, a warning is given by the display means 41 such as a warning lamp, and the process is ended.
[0051]
If NO in step S29, it is diagnosed that the NOx adsorption catalyst 25 has not deteriorated, and the stored values such as NOxmax, NOxα, NOxex (1,..., N) are cleared, and the process returns.
[0052]
If NO in step S21, the process proceeds to step S31 to determine whether the timer is counting. If YES, the process proceeds to step S22. If NO, the process returns.
[0053]
The present invention is not limited to the above embodiment, and various changes or modifications can be made within the scope of the technical matters described in the claims.
Further, control may be performed to change the period of the rich spike control, for example, the end time of T2, based on the result of the deterioration diagnosis.
[0054]
In the above-described embodiment, at the time of the rich spike control, the air-fuel ratio is changed to reduce the oxygen concentration in the exhaust gas. However, other methods, for example, the post-injection in the expansion stroke, A configuration for reducing the oxygen concentration may be used.
[0055]
In the above embodiment, the deterioration diagnosis of the NOx adsorption catalyst is performed based on the NOxex in the initial predetermined period T1 at the time of the rich spike. However, at the time of λ = 1 combustion after the passage of T1, the entire predetermined period T2, or lean after that, A configuration may be adopted in which the deterioration diagnosis of the NOx adsorption catalyst is performed based on NOxex during the operation period.
[0056]
Further, depending on the type of the NOx adsorption catalyst, even when the air-fuel ratio is controlled to 14.3 or less during the rich spike as in the above embodiment, immediately after the control is started, the oxygen concentration downstream of the NOx adsorption catalyst reaches a desired region. There may be a period in which the oxygen concentration in the exhaust gas is not reduced and is about 0.3 to 0.5%. Therefore, the rich spike control is started and the time when the oxygen concentration in the exhaust gas becomes lower than the range of, for example, 0.3 to 0.5% is defined as the start of T1, and at this time, the timer is started. The counting may be started.
[0057]
Furthermore, in the above-described embodiment, the device for diagnosing the deterioration of both the NOx adsorption catalyst and the noble metal of the NOx adsorption catalyst, but may be a device for diagnosing one of them.
[0058]
【The invention's effect】
As described above, according to the present invention, there is provided an exhaust gas purification apparatus capable of accurately performing deterioration diagnosis of a NOx adsorption catalyst.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an engine system including an exhaust gas purification device according to a preferred embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating a configuration of a NOx sensor according to an embodiment of the present invention.
FIG. 3 is a flowchart showing the contents of processing of engine control performed by an ECU during rich spike control.
FIG. 4 is a graph showing a relationship between an oxygen concentration and an output value of a NOx sensor at the same NOx concentration.
FIG. 5 is a time chart showing the relationship between the oxygen concentration in the exhaust gas and the amount of NOx released from the NOx adsorption catalyst.
FIG. 6 is a flowchart showing the contents of processing performed by an ECU at the time of deterioration diagnosis control of a NOx adsorption catalyst.
FIG. 7 is an example of a map for setting a threshold for deterioration determination.
[Explanation of symbols]
1: Engine body
24: Oxygen concentration sensor
25: NOx adsorption catalyst
26: NOx sensor
32: ECU

Claims (8)

A NOx adsorption catalyst arranged in the exhaust passage, for adsorbing or releasing NOx according to the oxygen concentration in the exhaust gas;
A NOx sensor having a metal cover disposed downstream of the NOx adsorption catalyst;
Oxygen concentration control means for controlling the oxygen concentration to release NOx from the NOx adsorption catalyst when the NOx adsorption amount of the NOx adsorption catalyst reaches a predetermined amount;
Diagnostic means for detecting a state of NOx release from the NOx adsorption catalyst based on an output from the NOx sensor at the time of the NOx release, and performing a deterioration diagnosis of the NOx adsorption catalyst based on the state;
The oxygen concentration control means controls the oxygen concentration to 0.3 or less or 0.5% or more during the deterioration diagnosis.
An exhaust purification device characterized by the above-mentioned. The oxygen concentration control means controls the oxygen concentration to 0.1 or less or 0.5% or more during the deterioration diagnosis.
The exhaust purification device according to claim 1. The oxygen concentration control means controls the oxygen concentration to 0% during the deterioration diagnosis.
The exhaust purification device according to claim 1. The NOx adsorption catalyst adsorbs NOx at a high oxygen concentration and releases NOx adsorbed at a low oxygen concentration, and a catalytic metal for purifying NOx released from the NOx adsorbent. With
The diagnosis means diagnoses deterioration of at least one of the NOx adsorbent and the catalyst metal;
The exhaust gas purification device according to claim 1. The oxygen concentration control means controls the oxygen concentration within a range of 0.1 to 0.6% for a predetermined period after the end of the deterioration diagnosis.
The exhaust gas purification device according to claim 1. The oxygen concentration control means changes the content of the oxygen concentration control based on a diagnosis result by the diagnosis means,
The exhaust gas purifying apparatus according to claim 1. A NOx adsorption catalyst that is disposed in an exhaust passage of the engine and that adsorbs or releases NOx according to the oxygen concentration in the exhaust gas;
A NOx sensor disposed downstream of the NOx adsorption catalyst and having a metal cover; and when the NOx adsorption amount of the NOx adsorption catalyst reaches a predetermined amount, the oxygen concentration is controlled to release NOx from the NOx adsorption catalyst. Oxygen concentration control means for causing
Diagnostic means for detecting a state of NOx release from the NOx adsorption catalyst based on an output from the NOx sensor at the time of the NOx release, and performing a deterioration diagnosis of the NOx adsorption catalyst based on the state;
The oxygen concentration control means controls the oxygen concentration to a first value at which the metal does not cause a catalytic action on NOx during the deterioration diagnosis by the diagnosis means, and thereafter reduces the oxygen concentration to the first value for a certain period of time. Controlling to a second value higher than the value,
An exhaust purification device characterized by the above-mentioned. The second value is in the range of 0.1-0.6%;
The exhaust purification device according to claim 7.

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