JP2018105146A - Deterioration diagnostic device for exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a deterioration diagnostic device for an exhaust emission control device that is used for diagnosing deterioration of the exhaust emission control device having an NOx occlusion reduction type catalyst and a selective reduction type catalyst provided in an exhaust passage of an internal combustion engine, is configured to enable a diagnosis to be made by using only one NOx sensor and can diagnose deterioration of each catalyst without depending on NHadsorption amount of the selective reduction type catalyst.SOLUTION: A deterioration diagnostic device 10 for an exhaust emission control device 24 includes: air-fuel ratio control means 12 for controlling an air-fuel ratio of exhaust gas flowing into an NOx occlusion reduction type catalyst 26; an NOx sensor 14 for detecting an NOx concentration of exhaust gas downstream of a selective reduction type catalyst 28; and a diagnosis section 16 for diagnosing deterioration of each catalyst. The diagnosis section 16 diagnoses deterioration of each catalyst on the basis of a first signal output by the NOx sensor 14 when the air-fuel ratio of the exhaust gas is controlled to a rich condition and a second signal output by the NOx sensor 14 when the air-fuel ratio of the exhaust gas is controlled to a lean condition.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a deterioration diagnosis device that diagnoses deterioration of an exhaust purification device provided in an exhaust passage of an internal combustion engine.

As a technique for purifying nitrogen oxide (NO _x ) contained in exhaust gas from an internal combustion engine such as an engine, a NOx occlusion reduction type catalyst (NSR catalyst) provided in an exhaust passage of the internal combustion engine, and exhaust gas downstream from the NSR catalyst An exhaust emission control device including a selective reduction catalyst (SCR catalyst) provided in a passage has been proposed. For example, Patent Document 1 discloses an exhaust gas exhaust treatment system for a diesel engine or a lean combustion gasoline engine, an ammonia generating component by an NSR catalyst or a lean NOx trap catalyst (LNT catalyst), and downstream of the NSR and LNT catalyst. And an SCR catalyst that includes a molecular sieve having a CHA crystal structure.

  Both the NSR catalyst and the SCR catalyst may deteriorate due to sulfur poisoning in the exhaust, high heat of the exhaust, or the like. A deterioration diagnosis device that diagnoses the deterioration of the NSR catalyst provided in the exhaust passage of the internal combustion engine or a deterioration diagnosis device that diagnoses the deterioration of the SCR catalyst provided in the exhaust passage of the internal combustion engine has been proposed.

  Patent Document 2 discloses an exhaust atmosphere changing means for changing the ratio of an oxidizing agent and a reducing agent in the exhaust gas of an internal combustion engine, an exhaust aftertreatment device disposed in an exhaust passage of the internal combustion engine, an upstream of the exhaust aftertreatment device, and A diagnostic apparatus for an exhaust aftertreatment device is disclosed that includes an exhaust atmosphere detection means provided downstream and first and second deterioration diagnosis means. In the diagnostic device disclosed in Patent Document 2, the first deterioration diagnosis means diagnoses deterioration of the exhaust aftertreatment device under operating conditions in which the exhaust atmosphere is switched to the rich side or lean side, and the second deterioration diagnosis means When it is determined by the first deterioration diagnosis means that the exhaust aftertreatment device has deteriorated, the operation shifts to a diagnostic operation mode to diagnose the deterioration of the exhaust aftertreatment device. Patent Document 2 discloses a configuration in which an NOx trap catalyst, a combination thereof with a diesel particulate trap (DPF), and an oxidation catalyst are disposed upstream of the combination as an exhaust aftertreatment device.

Patent Document 3 discloses an exhaust gas purification apparatus that includes a selective reduction catalyst provided in an exhaust passage of an internal combustion engine and a reducing agent supply device that injects a reducing agent into the exhaust passage upstream of the selective reduction catalyst. a deterioration diagnosis device of the selective reduction catalyst for diagnosing a deterioration state of the selective reduction catalyst, an upstream / downstream amount of NO _X detection means for obtaining respective amount of NO _X at the upstream side / downstream side of the selective reduction catalyst In addition, a deterioration diagnosis apparatus including a determination unit that determines a deterioration state of the selective reduction catalyst is disclosed. The deterioration diagnosis device disclosed in Patent Document 3, based on the consumption of the reducing agent from the stop injection of the reducing agent until the amount of NO _X at the upstream side and the downstream side of the NO _X amount becomes equal, determination A means determines the deterioration state of the selective reduction catalyst.

JP 2012-522636 A JP 2004-308455 A JP 2012-255397 A

  In an exhaust emission control device provided with an NSR catalyst and an SCR catalyst provided in an exhaust passage of an internal combustion engine, it is conceivable to provide a device for diagnosing the deterioration of each of the NSR catalyst and the SCR catalyst. However, in order to provide both the NSR catalyst diagnosis device disclosed in Patent Document 2 and the SCR catalyst deterioration diagnosis device disclosed in Patent Document 3, the upstream side of the NSR catalyst, Between the SCR catalyst, NOx sensors must be provided at least at three locations downstream of the SCR catalyst.

Further, since the NOx purification rate of the SCR catalyst varies depending on the amount of NH ₃ adsorbed by the SCR catalyst, the NH _{3 of} the SCR catalyst is used in order to accurately diagnose the deterioration of each catalyst in the exhaust gas purification apparatus including the NSR catalyst and the SCR catalyst. It is conceivable to calculate the amount of adsorption. However, since the NOx sensor cannot distinguish between NH ₃ and NOx in the exhaust gas, the NOx sensor provided between the NSR catalyst and the SCR catalyst cannot accurately measure the NH ₃ concentration flowing into the SCR catalyst. It is difficult to estimate the NH ₃ adsorption amount. Therefore, in Patent Document 3, when the injection of the reducing agent from the upstream side of the SCR catalyst is stopped and the adsorption amount of NH ₃ is made zero, the deterioration diagnosis of the SCR catalyst is performed. It is considered that exhaust emission deteriorates due to the stoppage of the engine.

An object of the present invention is to provide a deterioration diagnosis for diagnosing deterioration of an exhaust gas purification device provided in an exhaust passage of an internal combustion engine and comprising a NOx storage reduction catalyst and a selective reduction catalyst downstream of the NOx storage reduction catalyst. The apparatus can be configured so that only one NOx sensor is used for deterioration diagnosis, and the NOx occlusion reduction type catalyst and the selective reduction are not dependent on the NH ₃ adsorption amount of the selective reduction type catalyst. It is an object of the present invention to provide a deterioration diagnosis device for an exhaust gas purification device that can diagnose deterioration of a type catalyst.

  An exhaust gas purification apparatus deterioration diagnosis apparatus according to the present invention includes an exhaust gas provided with an NOx storage reduction catalyst provided in an exhaust passage of an internal combustion engine and a selective reduction catalyst located downstream of the NOx storage reduction catalyst. A deterioration diagnosis device for diagnosing deterioration of a purification device, wherein air-fuel ratio control means for controlling an air-fuel ratio of exhaust flowing into the NOx storage reduction catalyst, and detecting NOx concentration in exhaust downstream of the selective reduction catalyst A NOx sensor that outputs a signal corresponding to the detected NOx concentration, and a diagnosis unit that diagnoses deterioration of the NOx storage reduction catalyst and the selective reduction catalyst, the diagnosis unit comprising the air-fuel ratio control A first signal output from the NOx sensor when the air-fuel ratio is controlled to a rich condition by the means, and the NOx when the air-fuel ratio is controlled to a lean condition by the air-fuel ratio control means. Capacitors is based on the second signal output to diagnose the deterioration of the NOx storage reduction catalyst and the selective reduction catalyst.

  In a preferred aspect, the diagnostic unit integrates the first signal to calculate a first integrated value when the air-fuel ratio is controlled to a rich condition by the air-fuel ratio control means, and the air-fuel ratio control means When the air-fuel ratio is controlled to a lean condition, the second signal is integrated to calculate a second integrated value, the first integrated value exceeds a predetermined first threshold, and the second integrated value is calculated. When the value exceeds a predetermined second threshold, it is diagnosed that the selective catalytic reduction catalyst has deteriorated, the first integrated value does not exceed the first threshold, and the second integrated value If the NO exceeds the second threshold value, the NOx storage reduction catalyst is diagnosed as being deteriorated.

  In another preferred aspect, the period during which the first signal is accumulated is from the start of the control for setting the air-fuel ratio to the rich condition by the air-fuel ratio control means until the end of the control or a predetermined time after the end of the control. This is the period until

  In another preferred aspect, the apparatus further comprises NOx concentration acquisition means for acquiring the NOx concentration in the exhaust in the exhaust passage between the internal combustion engine and the NOx storage reduction catalyst.

  In another preferred aspect, the apparatus further includes NOx concentration acquisition means for acquiring the NOx concentration in the exhaust in the exhaust passage between the NOx storage reduction catalyst and the selective reduction catalyst.

  In another preferred aspect, the first heating means and the second heating means increase the catalyst bed temperatures of the NOx storage reduction catalyst and the selective reduction catalyst while the NOx sensor detects the NOx concentration of the exhaust gas, respectively. Is further provided.

According to the present invention, it is possible to diagnose deterioration of each of the NOx occlusion reduction type catalyst and the selective reduction type catalyst based only on the output signal from the NOx sensor that detects the NOx concentration in the exhaust downstream of the selective reduction type catalyst. Therefore, the deterioration diagnosis device for the exhaust gas purification device can be configured such that only one NOx sensor is used for the deterioration diagnosis, and the deterioration diagnosis does not depend on the NH ₃ adsorption amount of the selective catalytic reduction catalyst. Is possible. Furthermore, in order to diagnose the deterioration of each catalyst, it is not necessary to carry out a diagnostic operation mode or to stop or change the operation of various devices that may affect the exhaust properties. The impact on fuel consumption and exhaust gas can be suppressed.

It is a composition schematic diagram showing an example of a degradation diagnostic device concerning this embodiment. It is a structure schematic which shows the other example of the deterioration diagnostic apparatus which concerns on this embodiment. It is a graph which shows an example of the degradation diagnosis result by the degradation diagnostic apparatus shown in FIG. It is a graph which shows the output signal of a NOx sensor in the deterioration diagnosis by the deterioration diagnosis apparatus concerning this embodiment. It is a graph which shows the other example of the degradation diagnosis result by the degradation diagnostic apparatus shown in FIG. It is a graph which shows an example of the degradation diagnosis result by the degradation diagnostic apparatus shown in FIG. It is a structure schematic which shows the other example of the deterioration diagnostic apparatus which concerns on this embodiment. It is a graph which shows the other example of the degradation diagnosis result by the degradation diagnostic apparatus shown in FIG. It is a flowchart which shows the flow of the deterioration diagnosis by the deterioration diagnosis apparatus which concerns on this embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments described below.

  FIG. 1 is a schematic configuration diagram illustrating an example of the deterioration diagnosis device 10 of the exhaust purification device 24 according to the present embodiment. An exhaust purification device 24 is provided in the exhaust passage 22 connected to the internal combustion engine 20. The exhaust purification device 24 includes a NOx occlusion reduction type catalyst (NSR catalyst 26) and a selective reduction type catalyst (SCR catalyst 28) provided in order from the upstream side of the exhaust passage 22. The deterioration diagnosis apparatus 10 according to the present embodiment includes a NOx sensor 14, an air-fuel ratio control means 12, and a diagnosis unit 16. The diagnosis unit 16 diagnoses the deterioration of the NSR catalyst 26 and the SCR catalyst 28.

  The internal combustion engine 20 generates power by burning a mixture of fuel and air inside the cylinder and reciprocating the piston. The internal combustion engine 20 is a vehicular multi-cylinder engine, and may be a compression ignition engine such as a diesel engine or a spark ignition engine such as a gasoline engine.

Diesel engines and lean-burn gasoline engines that perform lean burn at a higher air-fuel ratio than the stoichiometric air-fuel ratio can reduce fuel consumption and gas-phase carbonization compared to stoichiometric gasoline engines that have the same stoichiometric air-fuel ratio. Emission of hydrogen (HC) and carbon monoxide (CO) can be reduced. On the other hand, relatively large amounts of nitrogen oxides (NOx) are emitted from diesel engines and lean burn gasoline engines. NOx includes, for example, NO (nitrogen monoxide), NO ₂ (nitrogen dioxide), N ₂ O (zincated nitrogen), and the like.

The NSR catalyst 26 is a catalyst used for purifying NOx contained in the exhaust gas of the internal combustion engine 20. For example, platinum as a catalyst component is formed on the surface of a base material made of oxide such as alumina (Al ₂ O ₃ ). Such a noble metal and a NOx occlusion component are supported. The NOx storage component is, for example, a compound containing an element selected from alkali metals, alkaline earth metals, rare earth elements, and the like.

The NSR catalyst 26 has a NOx absorption / release action of storing or releasing NOx depending on the air-fuel ratio of the inflowing exhaust gas. In a lean atmosphere where the air-fuel ratio of the exhaust flowing into the NSR catalyst 26 is higher than the stoichiometric air-fuel ratio, the NSR catalyst 26 stores NOx in the exhaust in the form of nitrate. On the other hand, in a rich atmosphere where the air-fuel ratio of the exhaust gas flowing into the NSR catalyst 26 is the same as or lower than the stoichiometric air-fuel ratio, the NOx stored in the NSR catalyst 26 is reduced by reducing components (HC, CO, H ₂ ) contained in the exhaust gas. It is reduced to nitrogen (N ₂ ).

  When the exhaust gas discharged from the internal combustion engine 20 and flowing into the NSR catalyst 26 is lean, the NSR catalyst 26 has a function of storing NOx in the exhaust gas and purifying the exhaust gas. However, if the NSR catalyst 26 continues to store NOx in the exhaust, the NOx storage amount of the NSR catalyst 26 eventually reaches the saturated storage amount, and the NSR catalyst 26 cannot store NOx. Therefore, the NOx occlusion capacity of the NSR catalyst 26 is released by releasing the occluded NOx from the NSR catalyst 26 by making the exhaust gas flowing into the NSR catalyst 26 rich before the NOx occlusion amount by the NSR catalyst 26 reaches the saturated occlusion amount. Can be recovered. As described above, the NSR catalyst 26 can continuously purify NOx discharged from the internal combustion engine 20 operating under the lean condition by repeatedly supplying the exhaust gas in a rich atmosphere (rich spike) repeatedly. it can.

However, it is known that when the exhaust gas flowing into the NSR catalyst 26 has a rich atmosphere, ammonia (NH ₃ ) is generated as a byproduct of the catalytic reaction of the NSR catalyst 26, for example, the reaction between the reducing component and the occluded NOx. It has been. Some NH ₃ produced by the NSR catalyst 26 reacts with NOx desorbed from the NSR catalyst 26 to become N ₂ , but most of the NH ₃ is considered to be discharged downstream from the NSR catalyst 26. As will be described later, NH ₃ discharged from the NSR catalyst 26 when the exhaust gas is rich is adsorbed by the SCR catalyst 28 provided on the downstream side of the NSR catalyst 26.

  The SCR catalyst 28 is a catalyst used for purifying NOx contained in the exhaust gas of the internal combustion engine 20. For example, a base metal oxide, zeolite, noble metal, or the like is supported as a catalyst component on a carrier such as ceramics or titanium oxide. It is configured. The SCR catalyst 28 adsorbs the reducing agent when the air-fuel ratio of the inflowing exhaust gas is a rich atmosphere, and reacts the adsorbed reducing agent with NOx when the air-fuel ratio is a lean atmosphere. Has the effect of purifying NOx.

Here, since there is an upper limit on the amount of reducing agent adsorbed on the SCR catalyst 28, it is necessary to periodically supply the reducing agent to the SCR catalyst 28 in order to continuously purify NOx in the lean exhaust gas. . In the exhaust purification device 24 according to the present embodiment, the NSR catalyst 26 is provided upstream of the SCR catalyst 28, and NH ₃ exhausted from the NSR catalyst 26 when the exhaust is in a rich atmosphere is supplied to the SCR catalyst 28. It is used as a reducing agent to be adsorbed. Accordingly, the reducing agent can be supplied to the SCR catalyst 28 without providing a reducing agent supply device that supplies the reducing agent (typically urea water) to the exhaust passage 22 upstream of the SCR catalyst 28.

As described above, in the exhaust purification device 24 including the NSR catalyst 26 and the SCR catalyst 28, when the exhaust gas flowing into the exhaust purification device 24 is in a lean condition, the NSR catalyst 26 stores NOx in the exhaust, NOx not occluded by the catalyst 26 reacts with NH ₃ on the SCR catalyst 28 in the SCR catalyst 28 and is reduced to N ₂ . By the action of these two catalysts, the NOx concentration in the exhaust under lean conditions can be remarkably reduced. On the other hand, in the case of rich conditions where the exhaust gas flowing into the exhaust gas purification device 24 is a rich atmosphere, NOx stored in the NSR catalyst 26 is reduced to N ₂ by HC, CO, etc. in the exhaust gas. At this time, NH ₃ is generated as a by-product in the NSR catalyst 26, but NH ₃ is adsorbed by the SCR catalyst 28, so that the amount of NH ₃ discharged from the exhaust purification device 24 can be kept low. Thus, in the exhaust rich condition, a reducing component HC, CO, can be kept lower the concentration of such NH _3, also can be reused as a reducing agent for the NH ₃ adsorbed to the SCR catalyst 28 It becomes.

  Both the NSR catalyst 26 and the SCR catalyst 28 used in the exhaust purification device 24 may be deteriorated by sulfur poisoning or high heat due to sulfur-containing components in the exhaust gas. When the NSR catalyst 26 deteriorates, the NOx purification rate of the NSR catalyst 26 may decrease due to a decrease in the saturated storage amount of NOx. When the SCR catalyst 28 deteriorates, the NOx purification rate of the SCR catalyst 28 may decrease due to a decrease in the saturated adsorption amount of the reducing agent.

  The deterioration diagnosis device 10 of the exhaust purification device 24 according to the present embodiment includes an air-fuel ratio control means 12, a NOx sensor 14, and a diagnosis unit 16. The diagnosis unit 16 determines whether or not each of the NSR catalyst 26 and the SCR catalyst 28 has deteriorated. Diagnose.

  The air-fuel ratio control means 12 controls the air-fuel ratio of the exhaust flowing into the NSR catalyst 26 of the exhaust purification device 24. When the NSR catalyst 26 is provided as the exhaust purification device 24, the air-fuel ratio control means 12 restores the NOx storage capability of the NSR catalyst 26 by performing a rich spike that makes the exhaust gas flowing into the NSR catalyst 26 a rich atmosphere. Any means may be used as long as it is a known means. Examples of the air-fuel ratio control means 12 include means capable of changing the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 20, for example, means for adjusting the amount of intake air supplied to the cylinder, a fuel injection device, and the like. When the fuel injection device is provided in the cylinder, a rich atmosphere of exhaust may be realized by injecting fuel in the late stage of the expansion stroke or in the exhaust stroke to increase the concentration of unburned fuel in the exhaust.

  The air-fuel ratio control means 12 may be a reducing agent supply means that is provided in the exhaust passage 22 upstream of the NSR catalyst 26 and supplies a reducing agent into the exhaust. By supplying the reducing agent into the exhaust gas by the reducing agent supply means, the exhaust gas flowing into the NSR catalyst 26 can be made rich. As the reducing agent in this case, for example, a gas such as hydrogen or carbon monoxide, a liquid or gaseous hydrocarbon, a liquid fuel such as gasoline or light oil, or the like can be used. The amount of reducing agent supplied by the reducing agent supply means may be determined based on the operating state of the internal combustion engine 20 (engine speed, fuel injection amount, etc.). The air-fuel ratio control means 12 operates according to an instruction from the diagnosis unit 16 described later. The air-fuel ratio control means 12 may perform air-fuel ratio feedback control by providing an air-fuel ratio sensor in the exhaust passage 22 upstream of the NSR catalyst 26 and measuring the air-fuel ratio of the exhaust.

The deterioration diagnosis device 10 according to this embodiment includes a NOx sensor 14 provided downstream of the SCR catalyst 28. The NOx sensor 14 detects the NOx concentration of the exhaust gas and outputs a signal corresponding to the detected NOx concentration. The NOx sensor 14 decomposes NOx in the exhaust into N ₂ and O ₂ and outputs a current proportional to the amount of oxygen ions based on the O ₂ . On the other hand, NH ₃ in the exhaust is oxidized inside the NOx sensor 14 and decomposed into NO and H ₂ O, and the decomposed NO outputs a current on the same principle as NOx in the exhaust. Therefore, the NOx sensor 14 outputs a signal proportional to the total concentration of NOx and NH ₃ , and cannot output the NOx concentration and the ammonia concentration separately. The deterioration diagnosis apparatus 10 according to the present embodiment may include a NOx sensor provided at a location other than the downstream side of the SCR catalyst 28.

  Note that “downstream of the SCR catalyst 28” where the NOx sensor 14 is provided means downstream of at least a part of the SCR catalyst 28. The NOx sensor 14 is preferably disposed, for example, in a region downstream of 30% with respect to the total length in the direction along the exhaust flow inside the SCR catalyst 28, and with respect to the total length inside the SCR catalyst 28. More preferably, it is arranged in the vicinity of 50% or in the downstream region. When the exhaust emission control device 24 includes a plurality of SCR catalysts 28, the “full length” means from the upstream end of the SCR catalyst 28 arranged on the most upstream side to the downstream end of the SCR catalyst 28 arranged on the most downstream side. It means length. In the deterioration diagnosis device 10 shown in FIG. 1, the NOx sensor 14 is provided in the exhaust passage 22 on the downstream side of the SCR catalyst 28. FIG. 2 is a schematic configuration diagram illustrating another example of the deterioration diagnosis apparatus 10 according to the present embodiment. In the deterioration diagnosis apparatus 10 illustrated in FIG. 2, the NOx sensor 14 is disposed inside the SCR catalyst 28 and is exhausted. It is provided at a position in the vicinity of 50% of the total length in the direction along the flow.

  Returning to FIG. 1, the deterioration diagnosis device 10 according to the present embodiment includes a diagnosis unit 16 that diagnoses deterioration of the NSR catalyst 26 and the SCR catalyst 28 included in the exhaust purification device 24. The diagnosis unit 16 outputs a first signal output from the NOx sensor 14 when the air-fuel ratio is controlled to a rich condition by the air-fuel ratio control means 12, and when the air-fuel ratio is controlled to a lean condition by the air-fuel ratio control means 12. The deterioration of the NSR catalyst 26 and the SCR catalyst 28 is diagnosed based on the second signal output from the NOx sensor 14.

  The diagnosis unit 16 is composed of, for example, a microcomputer, and transmits an instruction signal for instructing the air-fuel ratio control means 12 to operate, and receives a signal output from the NOx sensor 14. Based on the exhaust air-fuel ratio condition (rich or lean) controlled by the air-fuel ratio control means 12 and the output signal of the NOx sensor 14, the diagnosis unit 16 includes an NSR catalyst 26 and an SCR catalyst 28 included in the exhaust purification device 24. Diagnose the deterioration. The deterioration diagnosis in the diagnosis unit 16 is realized by executing a program by a microcomputer. Although not shown, the diagnosis unit 16 includes a storage unit including a storage element such as a RAM and a ROM, a drive circuit for energizing the air-fuel ratio control unit 12 and the like. In the storage means, a control program and information indicating a predetermined range (predetermined time, threshold value, etc.) are stored in advance, and a calculation result by the diagnosis unit 16 is written. When the diagnosis unit 16 determines that the NSR catalyst 26 or the SCR catalyst 28 is abnormally deteriorated as a result of the deterioration diagnosis, the diagnosis unit 16 outputs an abnormal signal to, for example, a diagnosis unit. Displays that abnormal deterioration has occurred.

  Deterioration diagnosis of the exhaust purification device 24 including the NSR catalyst 26 and the SCR catalyst 28 by the deterioration diagnosis device 10 according to the present embodiment will be specifically described with reference to FIG. FIG. 3 is a graph showing an example of the deterioration diagnosis result by the deterioration diagnosis apparatus 10 according to the present embodiment. In the graph of FIG. 3, the first integrated value (integrated value RI) obtained by integrating the first signal output from the NOx sensor 14 when the air-fuel ratio is controlled to the rich condition by the air-fuel ratio control means 12 is shown horizontally. The vertical axis represents the second integrated value (integrated value LI) obtained by integrating the second signal output from the NOx sensor 14 when the air-fuel ratio is controlled to the lean condition by the air-fuel ratio control means 12. Respectively.

  In the graph of FIG. 3, a circle (◯) in the region (A) surrounded by a broken line indicates NOx obtained using the exhaust purification device 24 in which neither the NSR catalyst 26 nor the SCR catalyst 28 has deteriorated. The integrated value RI of the sensor 14 output signal and the coordinates (RI, LI) of the integrated value LI are shown. Similarly, the triangular mark (Δ) in the region (B) surrounded by the broken line indicates the integrated value RI obtained using the exhaust purification device 24 in which the NSR catalyst 26 has deteriorated and the SCR catalyst 28 has not deteriorated. The square marks (□) in the region (C) surrounded by the broken line with the coordinates (RI, LI) of LI indicate that the SCR catalyst 28 has deteriorated and the NSR catalyst 26 has not deteriorated. The integrated values RI and LI coordinates (RI, LI) obtained by using them are respectively shown. Hereinafter, the reason why the distribution area of the coordinates (RI, LI) varies depending on whether the NSR catalyst 26 and the SCR catalyst 28 are deteriorated will be described.

[Area (A): NSR catalyst 26-normal, SCR catalyst 28-normal]
In the exhaust purification device 24 in which neither the NSR catalyst 26 nor the SCR catalyst 28 has deteriorated, as described above, the NOx occlusion in the NSR catalyst 26 and the NOx reduction reaction in the SCR catalyst 28 cause the The NOx concentration is significantly reduced. Further, when the exhaust gas is lean, NH ₃ adsorbed on the SCR catalyst 28 is consumed by the NOx reduction reaction, so that NH ₃ is hardly discharged into the exhaust gas. Therefore, when the exhaust gas flowing into the NSR catalyst 26 is lean, since the NOx concentration and the NH ₃ concentration detected by the NOx sensor 14 are both low, the integrated value LI of the output signal of the NOx sensor 14 is as shown in FIG. As shown in FIG.

On the other hand, when the exhaust gas flowing into the NSR catalyst 26 is rich, the NOx concentration in the exhaust gas is very low, and the NOx occluded in the NSR catalyst 26 is N ₂ due to the reducing agent components such as HC and CO in the exhaust gas. Therefore, almost no NOx is discharged from the NSR catalyst 26, and hence the SCR catalyst 28. As for NH ₃ , NH ₃ is produced as a by-product of the reaction in the NSR catalyst 26 under rich conditions, but most of it is adsorbed by the SCR catalyst 28. Therefore, even when the exhaust gas flowing into the NSR catalyst 26 is rich, since the NOx concentration and the NH ₃ concentration detected by the NOx sensor 14 are both low, the integrated value RI of the output signal of the NOx sensor 14 is As shown in FIG.

  As a result, in the exhaust purification device 24 in which neither the NSR catalyst 26 nor the SCR catalyst 28 has deteriorated, the coordinates (RI, LI) composed of the integrated values RI and LI in the graph of FIG. 3 are the lower left region (A). Will be distributed within.

[Area (B): NSR catalyst 26-deteriorated, SCR catalyst 28-normal]
When the NSR catalyst 26 deteriorates, the NOx saturated occlusion amount of the NSR catalyst 26 decreases. In the exhaust gas purification device 24 in which the NSR catalyst 26 has deteriorated and the SCR catalyst 28 has not deteriorated, when the exhaust gas is lean, the NOx occlusion amount in the NSR catalyst 26 is immediately saturated. descend. Further, if the NOx occlusion amount in the NSR catalyst 26 is small, the amount of NH ₃ discharged from the NSR catalyst 26 under a rich condition decreases, and the adsorption amount of NH ₃ adsorbed on the SCR catalyst 28 also decreases. Therefore, the amount of NOx reduced by the SCR catalyst 28 under lean conditions also decreases with a decrease in NH ₃ that is a reducing agent. The NH _3, NH ₃ adsorbed on the SCR catalyst 28 for consumption by the reduction of NOx, is hardly discharged. Therefore, when the exhaust gas flowing into the NSR catalyst 26 is lean, the NOx occlusion amount in the NSR catalyst 26 is reduced, and the NH ₃ adsorption amount in the SCR catalyst 28 is reduced. NOx emission amount increases, and the integrated value LI of the output signal of the NOx sensor 14 increases as compared with the region (A) as shown in FIG.

On the other hand, when the exhaust is rich, the NOx concentration in the exhaust flowing into the NSR catalyst 26 is very low, and the NOx occluded in the NSR catalyst 26 is reduced to N ₂ by the reducing agent component in the exhaust. Little NOx is discharged from the NSR catalyst 26 and the SCR catalyst 28. NH ₃ is produced as a by-product in the NSR catalyst 26, most of which is adsorbed on the SCR catalyst 28. Thus, the rich conditions, since NOx emissions and NH ₃ emissions from the entire exhaust gas purification device 24 are both at low concentrations, the integrated value RI of the output signal of the NOx sensor 14, as shown in FIG. 3 lower It can be suppressed.

  As a result, in the case of the exhaust purification device 24 in which the NSR catalyst 26 is deteriorated and the SCR catalyst 28 is not deteriorated, the coordinates (RI, LI) composed of the integrated values RI and LI in the graph of FIG. Are distributed in the region (B) moved upward.

[Region (C): NSR catalyst 26-normal, SCR catalyst 28-deteriorated]
When the SCR catalyst 28 deteriorates, the NH ₃ saturated adsorption amount of the SCR catalyst 28 decreases. In the exhaust purification device 24 in which the SCR catalyst 28 has deteriorated and the NSR catalyst 26 has not deteriorated, when the exhaust gas is lean, the NOx storage amount of the NSR catalyst 26 is not affected, so the NOx purification rate in the NSR catalyst 26 does not decrease. . In the SCR catalyst 28 with respect thereto, NH ₃ for adsorption amount is immediately saturated in rich conditions, NH ₃ adsorption amount used for the reduction of NOx under lean conditions reduces, NOx purification rate in the SCR catalyst 28 Decreases. The NH _3, NH ₃ adsorbed on the SCR catalyst 28 for consumption by the reduction of NOx, is hardly discharged. Therefore, when the exhaust gas flowing into the NSR catalyst 26 is lean, the amount of NH ₃ adsorbed by the SCR catalyst 28 decreases, so that the NOx emission amount from the entire exhaust purification device 24 increases, and the output signal of the NOx sensor 14 The integrated value LI increases as compared with the region (A) as shown in FIG.

On the other hand, when the exhaust is rich, the NOx concentration in the exhaust flowing into the NSR catalyst 26 is very low, and the NOx occluded in the NSR catalyst 26 is reduced to N ₂ by the reducing agent component in the exhaust. Little NOx is discharged from the NSR catalyst 26 and the SCR catalyst 28. The NH _3, would otherwise, NH ₃ generated as a by-product in the NSR catalyst 26 is for the most part should be adsorbed by the SCR catalyst 28. However, since the SCR catalyst 28 deteriorates and the NH ₃ saturated adsorption amount decreases, the NH ₃ adsorption amount in the SCR catalyst 28 immediately saturates, and thereafter, NH ₃ is discharged downstream from the SCR catalyst 28. Is done. The discharged NH ₃ is detected by the NOx sensor 14. Therefore, when the exhaust gas flowing into the NSR catalyst 26 is rich, the NH ₃ exhaust amount from the exhaust purification device 24 increases due to the decrease in the NH ₃ saturated adsorption amount at the SCR catalyst 28, and the output signal of the NOx sensor 14 The integrated value RI increases as shown in FIG.

  As a result, in the case of the exhaust purification device 24 in which the SCR catalyst 28 has deteriorated and the NSR catalyst 26 has not deteriorated, the coordinates (RI, LI) composed of the integrated values RI and LI in the graph of FIG. Are distributed in the region (C) that has moved upward and to the right.

  As described above, in the deterioration diagnosis of the exhaust gas purification device 24 according to the present embodiment, the coordinate positions of the integrated values RI and LI calculated in the actual deterioration diagnosis indicate which region of the coordinate plane (RI, LI) shown in FIG. Therefore, it can be easily and clearly determined whether or not abnormal deterioration has occurred for each of the NSR catalyst 26 and the SCR catalyst 28. As a specific method of determining which region the coordinate positions of the integrated values RI and LI correspond to, for example, a threshold for separating the regions (A) to (C) on the coordinate plane (RI, LI) is integrated. There is a method in which the integrated values RI and LI calculated in actual deterioration diagnosis are compared with the threshold values after the values RI and LI are determined in advance by experiments or the like.

More specifically, with respect to the integrated value LI, a threshold value LI ₀ that divides a case where both the NSR catalyst 26 and the SCR catalyst 28 are normal and a case where at least one of the NSR catalyst 26 and the SCR catalyst 28 deteriorates (see FIG. 3). ) And the integrated value RI, a threshold RI ₀ that separates the case where the NSR catalyst 26 is deteriorated and the SCR catalyst 28 is normal from the case where the NSR catalyst 26 is normal and the SCR catalyst 28 is deteriorated (see FIG. 3). ) Is determined in advance. Then, it carried out degradation diagnosis according to this embodiment, comparing the accumulated value LI and the calculated threshold LI _0. At this time, if LI ≦ LI ₀ , it is determined that both the NSR catalyst 26 and the SCR catalyst 28 on which the deterioration diagnosis has been performed are normal. Further, LI> when LI is _zero, the integrated value RI calculated by comparing the threshold value RI _0, it is determined that RI ≦ RI ₀ if the NSR catalyst 26 is deteriorated, RI> RI ₀ if SCR catalyst 28 Is determined to have deteriorated.

  As described above, the deterioration diagnosis device 10 according to the present embodiment includes only one NOx sensor 14 that detects the NOx concentration of the exhaust downstream of the SCR catalyst 28 as a device for measuring the exhaust properties from the internal combustion engine 20. The presence or absence of deterioration of each of the NSR catalyst 26 and the SCR catalyst 28 provided in the exhaust purification device 24 can be diagnosed. Therefore, in the deterioration diagnosis device 10 according to the present embodiment, the deterioration diagnosis of the NSR catalyst and the SCR catalyst can be performed with a simpler configuration as compared with the case where the device described in Patent Document 2 or 3 is applied.

  In addition, in the deterioration diagnosis of the exhaust gas purification device 24 by the deterioration diagnosis device 10 according to the present embodiment, it is necessary to implement a special diagnostic operation mode or to stop or change the operation of various devices that can affect the exhaust properties. And not. The detection of the NOx sensor 14 for the deterioration diagnosis may be performed when the air-fuel ratio of the exhaust is controlled to the rich condition or the lean condition using the air-fuel ratio control means 12, and the exhaust using the air-fuel ratio control means 12 is performed. The control of the air-fuel ratio is conventionally performed when the NSR catalyst 26 is used as the exhaust purification device 24. Therefore, the deterioration diagnosis device 10 according to the present embodiment can remarkably suppress the influence on the fuel consumption, exhaust gas and the like accompanying the deterioration diagnosis of the exhaust purification device 24.

Further, in the deterioration diagnosis apparatus 10 according to the present embodiment, the SCR catalyst 28 is adsorbed with NH ₃ , despite using the conventional NOx sensor 14 that detects the NOx concentration and the NH ₃ concentration in the exhaust gas without distinction. The presence or absence of deterioration of each of the NSR catalyst 26 and the SCR catalyst 28 can be diagnosed without depending on the amount.

The effect of the NH ₃ adsorption amount of the SCR catalyst 28 on the output of the NOx sensor 14 provided downstream of the SCR catalyst 28 will be described. In the graph of FIG. 3, the distribution of the same mark seen in each of the regions (A) to (C), that is, the difference in the position of the coordinates (RI, LI) is due to the difference in the initial adsorption amount of NH ₃ in the SCR catalyst 28. Is based. The initial amount of adsorption of NH ₃ in the SCR catalyst 28, an NH ₃ adsorption amount at the time of changing the air-fuel ratio of the exhaust gas flowing into the NSR catalyst 26 from lean condition to the rich condition (during the rich spike start). For example, in the region (B) (NSR catalyst 26-deteriorated, SCR catalyst 28-normal), the triangle marks (Δ) are distributed along the vertical axis direction. When the exhaust is rich, the NOx concentration and NH ₃ concentration of the exhaust downstream of the SCR catalyst do not change unless the SCR catalyst is saturated. On the other hand, when the exhaust gas is lean, since the amount of NH ₃ initial adsorption in the SCR catalyst 28 is large, a large amount of NOx is reduced in the SCR catalyst 28 and the NOx purification rate is improved, so the integrated value LI decreases. Therefore, in the region (B), the triangle mark (Δ) moves downward in the vertical axis direction as the amount of initial NH ₃ adsorption on the SCR catalyst 28 increases.

In the region (C) (NSR catalyst 26-normal, SCR catalyst 28-degraded), the amount of NH ₃ saturated adsorption of the SCR catalyst is decreased, so that the larger the initial amount of NH ₃ adsorption on the SCR catalyst 28, the more the adsorption is possible. The amount of NH ₃ decreases. Therefore, when the exhaust gas is rich, the NH ₃ concentration in the exhaust gas downstream from the SCR catalyst 28 increases and the integrated value RI increases as the NH ₃ initial adsorption amount in the SCR catalyst 28 increases. On the other hand, when the exhaust gas is lean, the NOx concentration of the exhaust gas flowing into the NSR catalyst 26 is high and the NH ₃ concentration is low. Since the NSR catalyst 26 is normal, the NOx purification rate is high and the NOx concentration in the exhaust gas flowing into the SCR catalyst 28 is low. Therefore, even if the NH ₃ adsorption amount changes, the integrated value LI does not change greatly. Therefore, in the region (C), the square mark (□) moves to the right in the horizontal axis direction as the amount of initial NH ₃ adsorption on the SCR catalyst 28 increases.

As shown in FIG. 3, the coordinates (RI, LI) of the NSR catalyst 26 and the SCR catalyst 28 are coordinated (RI, LI) depending on the NH ₃ initial adsorption amount of the SCR catalyst 28 for each region (A) to (C) where the presence or absence of deterioration is different. Distribution is seen. However, the regions (A) to (C) do not overlap each other, and as described above, the calculated integrated values RI and LI are compared with the threshold values RI ₀ and LI ₀ , so that the NSR catalyst 26 and the SCR catalyst 28 respectively. The presence or absence of deterioration can be determined.

In the exhaust purification device 24, it is also conceivable that both the NSR catalyst 26 and the SCR catalyst 28 deteriorate simultaneously. In this case, since the NOx occlusion amount of the NSR catalyst 26 is saturated immediately under lean conditions, the NOx purification rate in the NSR catalyst 26 is reduced, and the NH ₃ adsorption amount of the SCR catalyst 28 is reduced. The NOx purification rate at 28 also decreases. On the other hand, since NH ₃ adsorbed on the SCR catalyst 28 is consumed by the reduction of NOx, NH ₃ is hardly discharged. Therefore, when both the NSR catalyst 26 and the SCR catalyst 28 deteriorate at the same time, the integrated value LI of the output signal of the NOx sensor 14 under the lean condition is compared with the regions (A) to (C) in FIG. Increase significantly.

On the other hand, when the exhaust gas is rich, the NOx concentration in the exhaust gas flowing into the NSR catalyst 26 is very low, and the NOx occluded in the NSR catalyst 26 is reduced to N ₂ by the reducing agent component in the exhaust gas. NOx is hardly discharged from the NSR catalyst 26 and the SCR catalyst 28. On the other hand, a small amount of NH ₃ produced as a by-product in the NSR catalyst 26 is adsorbed by the SCR catalyst 28. However, the amount of NH ₃ adsorbed by the SCR catalyst 28 is immediately saturated, and is further downstream than the SCR catalyst 28. NH ₃ is discharged. Therefore, when both the NSR catalyst 26 and the SCR catalyst 28 deteriorate at the same time, the integrated value RI of the output signal of the NOx sensor 14 under the rich condition increases with respect to the regions (A) and (B) in FIG. However, it becomes almost the same as the region (C).

As a result, in the case of the exhaust gas purification device 24 in which both the NSR catalyst 26 and the SCR catalyst 28 have deteriorated, the coordinates (RI, LI) made up of the integrated values RI and LI are within the region moved further above the region (C). Will be distributed. In the deterioration diagnosis device 10 according to the present embodiment, for example, a threshold value that separates the region (C) from the region where the coordinates (RI, LI) are distributed when both the NSR catalyst 26 and the SCR catalyst 28 deteriorate. LI ₁ is determined in advance, and then the integrated value LI calculated by performing the deterioration diagnosis according to the present embodiment is compared with the threshold value LI ₁ so that the NSR catalyst 26 is normal and the SCR catalyst 28 is It is possible to determine when the deterioration has occurred and when both the NSR catalyst 26 and the SCR catalyst 28 have deteriorated.

The accumulation period of the output signal of the NOx sensor 14 will be described with reference to FIG. FIG. 4 is a graph showing an output signal of the NOx sensor 14 in the deterioration diagnosis by the deterioration diagnosis apparatus 10 according to the present embodiment. The graph shown in FIG. 4 is a simulation of the output signal of the NOx sensor 14 in the exhaust purification device 24 in which the NSR catalyst 26 is normal and the SCR catalyst 28 is deteriorated. FIG. 4 also shows the NOx concentration of the exhaust flowing into the NSR catalyst 26, the NOx concentration of the exhaust between the NSR catalyst 26 and the SCR catalyst 28, and the NH ₃ concentration, together with the output signal of the NOx sensor 14.

The period during which the diagnosis unit 16 integrates the first signal output from the NOx sensor 14 to calculate the integrated value RI is a period in which the air-fuel ratio of the exhaust gas is controlled to the rich condition by the air-fuel ratio control means 12. Good. The integration period of the first signal is preferably a period from the start of the control by the air-fuel ratio control means 12 to the end of the control, and after the control is started by the air-fuel ratio control means 12, It may be a period until a predetermined time TR elapses after the end of the control. As shown in FIG. 4, even after the air-fuel ratio of the exhaust gas is changed from the rich condition to the lean condition, the product under the rich condition such as NH ₃ is continuously discharged until the predetermined time TR elapses. Because. The predetermined time TR is, for example, not less than 0 seconds and not more than 5 seconds.

The period during which the second signal output from the NOx sensor 14 is integrated in order to calculate the integrated value LI may be a period in which the air-fuel ratio of the exhaust gas is controlled to the lean condition by the air-fuel ratio control means 12. It is desirable to start the integration of the second signal when a predetermined time TL has elapsed since the control by the control means 12 was started. This is because discharge of products under rich conditions such as NH ₃ is reduced, and the output signal of the NOx sensor 14 is stabilized. The predetermined time TL is longer than the predetermined time TR, for example, 5 seconds or longer. The end of the integration period of the second signal is not particularly limited. For example, the integration of the second signal may be ended when the air-fuel ratio of the exhaust gas is changed from the lean condition to the rich condition by the air-fuel ratio control means 12.

  The degradation diagnosis apparatus 10 shown in FIG. 1 includes first NOx concentration acquisition means 32, flow rate acquisition means 34, first temperature sensor 36, second temperature sensor 38, and second NOx concentration acquisition means 40. Each of these devices outputs a signal based on the acquired data to the diagnosis unit 16, and the diagnosis unit 16 confirms whether the deterioration diagnosis start condition is satisfied based on each received signal, or under appropriate conditions. Conduct deterioration diagnosis.

  The first NOx concentration acquisition means 32 acquires the NOx concentration in the exhaust in the exhaust passage 22 between the internal combustion engine 20 and the NSR catalyst 26. The first NOx concentration acquisition means 32 flows into the NSR catalyst 26 based on, for example, the operating state (rotational speed, fuel injection amount, etc.) of the internal combustion engine 20 and the air-fuel ratio of the exhaust controlled by the air-fuel ratio control means 12. You may be comprised so that the NOx density | concentration in exhaust_gas | exhaustion may be estimated. The first NOx concentration acquisition means 32 may be a NOx sensor provided between the internal combustion engine 20 and the NSR catalyst 26 in the exhaust passage 22.

  The flow rate acquisition unit 34 acquires the flow rate Q of the exhaust gas flowing through the exhaust passage 22. The flow rate acquisition means 34 may be a known flow meter, for example. The flow rate acquisition means 34 may be an intake air amount sensor of the internal combustion engine 20, in which case the flow rate Q is calculated based on the intake air amount of the internal combustion engine 20.

  The first temperature sensor 36 detects the temperature of the exhaust gas in the exhaust passage 22 downstream of the NSR catalyst 26, and the second temperature sensor 38 detects the temperature of the exhaust gas in the exhaust passage 22 downstream of the SCR catalyst 28. As the first temperature sensor 36 and the second temperature sensor 38, a thermocouple, a thermistor, an infrared temperature sensor, or the like is used. The first temperature sensor 36 and the second temperature sensor 38 output data indicating the detected temperatures in the exhaust gas to the diagnosis unit 16. The diagnosis unit 16 may estimate the bed temperature of the NSR catalyst 26 based on the output value of the first temperature sensor 36, and may estimate the bed temperature of the SCR catalyst 28 based on the output value of the second temperature sensor 38. it can.

  The second NOx concentration acquisition means 40 acquires the NOx concentration in the exhaust gas in the exhaust passage 22 between the NSR catalyst 26 and the SCR catalyst 28. The second NOx concentration acquisition means 40 is, for example, the bed temperature of the NSR catalyst 26 estimated based on the operating state of the internal combustion engine 20, the air-fuel ratio of the exhaust controlled by the air-fuel ratio control means 12, and the output value of the first temperature sensor 36. The NOx concentration of the exhaust gas between the NSR catalyst 26 and the SCR catalyst 28 may be estimated based on the NOx occlusion speed of the NSR catalyst 26 in the normal state acquired in advance. Further, the second NOx concentration acquisition means 40 may be a NOx sensor provided between the NSR catalyst 26 and the SCR catalyst 28.

  In the deterioration diagnosis device 10 according to the present embodiment, the diagnosis unit 16 detects the flow rate Q inside the exhaust passage 22 acquired by the flow rate acquisition unit 34 and the exhaust gas flowing into the NSR catalyst 26 acquired by the first NOx concentration acquisition unit 32. Based on the NOx concentration C1 and the NOx concentration C2 of the exhaust discharged from the NSR catalyst 26 acquired by the second NOx concentration acquisition means 40, the NOx storage amount St currently stored in the NSR catalyst 26 is estimated. The NOx occlusion amount St of the NSR catalyst 26 estimated thereby is, for example, control of the air-fuel ratio (rich spike) of the exhaust by the air-fuel ratio control means 12 for recovering the NOx occlusion capacity of the NSR catalyst 26, or described later This is used to determine whether or not to perform deterioration diagnosis for more appropriate deterioration diagnosis.

Using the deterioration diagnosis device 10 according to the present embodiment, the integrated values RI and LI of the output signal of the NOx sensor 14 are calculated, and the calculated integrated values RI and LI are compared with the threshold values RI ₀ and LI ₀ to thereby calculate the NSR catalyst 26. In the deterioration diagnosis method for diagnosing deterioration of the SCR catalyst 28, the operation time at the lean air-fuel ratio is short, and the integration of the first signal (the signal output from the NOx sensor 14 when the air-fuel ratio is controlled to the rich condition) is started. When the NOx occlusion amount St occluded by the NSR catalyst 26 at this time (hereinafter also referred to as “NOx occlusion amount Stf”) is small, it may be difficult to set the threshold LI ₀ . This is because if the NOx occlusion amount Stf is small, the amount of NH ₃ discharged from the NSR catalyst 26 when the air-fuel ratio is controlled to a rich condition decreases, and the amount of NH ₃ adsorbed by the SCR catalyst 28 also decreases. Then, even if both the NSR catalyst 26 and the SCR catalyst 28 are normal, the NOx purification rate in the SCR catalyst 28 decreases, and as a result, the integrated value LI increases. On the other hand, when the NSR catalyst 26 is abnormally deteriorated and the SCR catalyst 28 is normal, if the initial NH ₃ adsorption amount of the SCR catalyst 28 is saturated, NOx that the abnormally deteriorated NSR catalyst 26 could not occlude is Since it is purified by the SCR catalyst 28, the integrated value LI becomes small. As a result, the difference between the integrated value LI when the NSR catalyst 26 and the SCR catalyst 28 are both normal and the integrated value LI when the NSR catalyst 26 is abnormally deteriorated and the SCR catalyst 28 is normal is small. It is.

FIG. 5 is a graph showing the deterioration diagnosis result obtained by the deterioration diagnosis apparatus 10 shown in FIG. 1 and showing the deterioration diagnosis result when the integration period of the integrated value LI is short and the NOx occlusion amount Stf is small. FIG. 5 shows the integrated values RI and LI when the deterioration diagnosis is performed using the deterioration diagnosis device 10 shown in FIG. 1 with respect to the exhaust gas purification device 24 in which the presence or absence of deterioration of the NSR catalyst 26 and the SCR catalyst 28 is different. The distribution of is shown. As indicated by a region (X) in FIG. 5, the lower side of the distribution of triangle marks (Δ) where the NSR catalyst 26 is deteriorated and the SCR catalyst 28 is normal (the NH ₃ initial adsorption amount is large) is NSR. to close the distribution of circle is normal to both the catalyst and the SCR catalyst (○), the setting of the threshold LI ₀ is difficult.

Further, as indicated by a region (Y) in FIG. 5, the left side of the distribution of square marks (□) where the SCR catalyst 28 is deteriorated and the NSR catalyst 26 is normal (the NH ₃ initial adsorption amount is small) However, since the NSR catalyst 26 is deteriorated and the SCR catalyst 28 is close to the distribution of triangle marks (Δ), it is difficult to set the threshold value RI ₀ . This is because if the NOx occlusion amount Stf is small, the amount of NOx released from the NSR catalyst 26 under rich conditions, and hence the amount of NH ₃ produced as a by-product, is reduced, and adsorbed on the SCR catalyst 28 having a small initial amount of NH ₃ adsorption As a result, it is considered that the NH ₃ concentration in the exhaust gas when the NOx sensor 14 is detected becomes small, and the coordinates (RI, LI) move to the left.

On the other hand, in the embodiment shown in FIG. 2, the NOx sensor 14 is provided at a position near 50% with respect to the total length in the direction along the exhaust flow inside the SCR catalyst 28. In the deterioration diagnosis apparatus 10, when the NOx sensor 14 is provided inside the SCR catalyst 28 as shown in FIG. 2, it is more compared with the case where it is provided in the exhaust passage 22 on the downstream side of the SCR catalyst 28 as shown in FIG. The lower limit of the range of the NOx occlusion amount Stf at which appropriate deterioration diagnosis can be performed can be lowered. This is because by providing the NOx sensor 14 inside the SCR catalyst 28, the amount of the SCR catalyst 28 component existing between the upstream end of the SCR catalyst 28 and the NOx sensor 14 is reduced, and the NH ₃ saturated adsorption amount is reduced. It is caused by having made it.

FIG. 6 is a graph showing the deterioration diagnosis result obtained by the deterioration diagnosis apparatus 10 shown in FIG. 2 and the deterioration diagnosis result when the NOx occlusion amount Stf is small. FIG. 6 shows the integrated values RI and LI when the deterioration diagnosis is performed using the deterioration diagnosis device 10 shown in FIG. 2 for the exhaust purification device 24 in which the presence or absence of deterioration of the NSR catalyst 26 and the SCR catalyst 28 is different. The distribution of is shown. When the NO 3 sensor 14 is provided inside the SCR catalyst 28 and the amount of the SCR catalyst 28 component existing between the upstream end of the SCR catalyst 28 and the NO x sensor 14 is reduced, the NH ₃ saturated adsorption amount is reduced. Since the maximum value of the NH ₃ initial adsorption amount of the catalyst 28 also decreases, the lower end of the distribution indicated by the triangle (Δ) shown in FIG. 6 moves upward relative to the lower end of the distribution indicated by the triangle (Δ) shown in FIG. Will be. Thus, to avoid proximity region (A) and region (B), it will allow the setting of the threshold LI _0. Further, if the NH ₃ saturated adsorption amount of the SCR catalyst 28 is decreased, the SCR catalyst 28 is caused by NH ₃ generated from the NSR catalyst 26 under the rich condition even if the NH ₃ initial adsorption amount of the SCR catalyst 28 is small. Since it is saturated in a short time, the left end of the distribution of square marks (□) shown in FIG. 6 is moved to the right with respect to the left end of the distribution of square marks (□) shown in FIG. As a result, the threshold RI ₀ can be set while avoiding the proximity of the region (B) and the region (C).

  As described above, by providing the NOx sensor 14 inside the SCR catalyst 28, if the lower limit of the NOx occlusion amount Stf in which the deterioration diagnosis can be performed becomes low, a rich spike that reduces NOx occluded in the NSR catalyst 26 is generated. It is not necessary to pause for a long period of time, deterioration diagnosis can be performed at an appropriate timing, and further deterioration of exhaust gas from the exhaust system can be suppressed.

FIG. 7 is a schematic configuration diagram illustrating another example of the deterioration diagnosis apparatus 10 according to the present embodiment. 7 includes first heating means 42 and second heating means 44 that increase the catalyst bed temperatures of the NSR catalyst 26 and the SCR catalyst 28, respectively, while the NOx sensor 14 detects the NOx concentration of the exhaust gas. Prepare. The 1st heating means 42 and the 2nd heating means 44 should just be a well-known heater etc. which have the function to raise a catalyst bed temperature. When the catalyst bed temperature of the NSR catalyst 26 is increased by the first heating means 42, the NOx saturated occlusion amount of the NSR catalyst 26 is decreased accordingly. Further, when the catalyst bed temperature of the SCR catalyst 28 is increased by the second heating means 44, the NH ₃ saturated adsorption amount of the SCR catalyst 28 is decreased accordingly. Therefore, the deterioration diagnosis apparatus 10 shown in FIG. 7 increases the catalyst bed temperatures of the NSR catalyst 26 and the SCR catalyst 28 while the NOx sensor 14 detects the NOx concentration of the exhaust gas, so that the deterioration diagnosis apparatus 10 shown in FIG. Based on the same principle, the lower limit of the range of the NOx occlusion amount Stf in which more appropriate deterioration diagnosis can be performed can be made lower than that of the deterioration diagnosis device 10 shown in FIG. As a result, it is not necessary to suspend the rich spike that reduces NOx stored in the NSR catalyst 26 for a long period of time, and deterioration diagnosis can be performed at an appropriate timing. Further, deterioration of exhaust gas from the exhaust system can be reduced. It becomes possible to suppress.

  Returning to FIG. 1, the diagnosis unit 16 in the deterioration diagnosis apparatus 10 shown in FIG. 1 estimates the NOx occlusion amount St that the NSR catalyst 26 actually occludes, but the estimated value of the NOx occlusion amount St of the NSR catalyst 26. And the actual NOx occlusion amount Str may differ. FIG. 8 is a graph showing another example of the deterioration diagnosis result by the deterioration diagnosis apparatus 10 shown in FIG. FIG. 8 shows distributions of the integrated values RI and LI when the NOx storage amount St of the NSR catalyst 26 estimated by the diagnosis unit 16 is different from the actual NOx storage amount Str.

When the NOx occlusion amount Str is smaller than the NOx occlusion amount St (in FIG. 8, the asterisk (*) in the region (B) and the X mark (x) in the region (C)), the exhaust is in a rich condition. Since the amount of NH ₃ discharged from the NSR catalyst 26 when controlled is reduced, the integrated value RI (horizontal axis) of the NOx sensor 14 output signal tends to decrease. Further, regarding the integrated value LI (vertical axis) of the NOx sensor 14 output signal when the exhaust gas is controlled to the lean condition, in the region (B) where the NSR catalyst 26 has deteriorated, the NOx saturation occlusion amount decreases, and the NOx Although there are some that fluctuate with the difference between the storage amount St and the NOx storage amount Str, there is no significant change as a whole. Therefore, as shown in FIG. 8, when the NOx occlusion amount Str is smaller than the NOx occlusion amount St, the distribution region tends to move to the left side, but the regions (A) to (C) are all good. Therefore, the deterioration diagnosis for diagnosing the deterioration of the NSR catalyst 26 and the SCR catalyst 28 by comparing the integrated values RI and LI with the threshold values RI ₀ and LI ₀ is possible.

The same applies to the case where the NOx occlusion amount Str is larger than the NOx occlusion amount St (the black diamond (♦) in the region (B) and the black circle (●) in the region (C) in FIG. 8). Yes, as shown in FIG. 8, although the distribution region tends to move to the right side, the regions (A) to (C) are all well separated, so the integrated values RI and LI are set to the threshold values RI ₀ and LI. A deterioration diagnosis for diagnosing the deterioration of the NSR catalyst 26 and the SCR catalyst 28 in comparison with ₀ is possible. As described above, even when there is a difference between the NOx occlusion amount St of the NSR catalyst 26 estimated by the diagnosis unit 16 and the actual NOx occlusion amount Str, the degradation diagnosis device 10 according to this embodiment includes the NSR catalyst 26 and The presence or absence of deterioration in each of the SCR catalysts 28 can be determined.

  In the deterioration diagnosis using the deterioration diagnosis apparatus 10 according to the present embodiment, particularly when the NOx occlusion amount St of the NSR catalyst 26 estimated by the diagnosis unit 16 is used, the deterioration diagnosis is performed a plurality of times, and a plurality of deteriorations are performed. It is desirable to make a final determination as to whether or not the NSR catalyst 26 and the SCR catalyst 28 are deteriorated based on the average value of the diagnosis results.

  As long as the deterioration diagnosis using the deterioration diagnosis device 10 according to the present embodiment is not hindered, another device may be provided in the exhaust passage 22. For example, when the internal combustion engine 20 is a diesel engine, an oxidation catalyst that oxidizes HC and CO contained in the exhaust, and a particulate filter having a function of collecting particulates (PM) such as soot contained in the exhaust May be provided in the exhaust passage 22 upstream of the NSR catalyst 26.

  FIG. 9 is a flowchart showing a flow of deterioration diagnosis of the exhaust purification device 24 performed by the deterioration diagnosis device 10 according to the present embodiment. Hereinafter, each step of the flowchart of FIG. 9 will be described with reference to FIG. The deterioration diagnosis is performed every time a predetermined period elapses. Further, it is assumed that the exhaust gas flowing into the NSR catalyst 26 is controlled to the lean condition when the rich spike is not performed.

  In step S102, it is determined whether or not a deterioration diagnosis start condition for the exhaust purification device 24 is satisfied. The deterioration diagnosis start condition is, for example, that the bed temperatures of the NSR catalyst 26 and the SCR catalyst 28 are equal to or higher than the activation temperature, the intake air amount of the internal combustion engine 20 is within a predetermined range, For example, the operation state is a steady operation or a quasi-steady state that becomes steady in a short time. The bed temperature of the NSR catalyst 26 can be estimated based on the output value of the first temperature sensor 36. Further, the temperature of the SCR catalyst 28 can be estimated based on the output value of the second temperature sensor 38. If it is determined in step S102 that the start condition is satisfied, the process proceeds to step S104. If it is determined in step S102 that the start condition is not satisfied, the present process is terminated, and the deterioration diagnosis is performed again after a predetermined period.

  In step S104, a rich spike is started in which the air-fuel ratio control means 12 controls the air-fuel ratio of the exhaust gas flowing into the NSR catalyst 26 to a rich condition. As a result, the exhaust gas flowing into the NSR catalyst 26 becomes a rich atmosphere lower than the stoichiometric air-fuel ratio, and NOx stored in the NSR catalyst 26 is completely reduced.

  In step S106, it is determined whether or not the rich spike in step S104 has been completed, that is, whether or not the rich spike has continued for a predetermined period. In step S104, the duration of the rich spike is calculated from, for example, the fuel injection amount in the internal combustion engine 20, the estimated NOx storage amount of the NSR catalyst 26, and the like. If it is determined in step S106 that the rich spike has not been completed, the process of step S106 is repeated. That is, the rich spike is continued until a predetermined time has elapsed. If it is determined in step S106 that the rich spike has been completed, the air-fuel ratio of the exhaust gas flowing into the NSR catalyst 26 is controlled to a lean condition by the air-fuel ratio control means 12, and the process proceeds to step S108.

  In step S108, the NOx storage amount St stored in the NSR catalyst 26 when the air-fuel ratio of the exhaust is controlled to the lean condition is calculated. In order to calculate the NOx occlusion amount St, the flow rate acquisition means 34 acquires the flow rate Q inside the exhaust passage 22. Further, the estimated NOx concentration C1 upstream of the NSR catalyst 26 is acquired by the NOx concentration acquisition means based on the operating state of the internal combustion engine 20. Furthermore, based on the operating state of the internal combustion engine 20, the bed temperature of the NSR catalyst 26 estimated based on the output value of the first temperature sensor, and the NOx occlusion speed of the NSR catalyst 26 in the normal state acquired in advance, the NSR catalyst 26 A value of the estimated NOx concentration C2 downstream and upstream of the SCR catalyst 28 is acquired. Based on the difference between the estimated NOx concentration C1 upstream of the NSR catalyst 26 and the estimated NOx concentration C2 downstream of the NSR catalyst 26 and the flow rate Q, the NOx occlusion amount St of the NSR catalyst 26 is calculated. The estimated NOx concentrations C1 and C2 may be values from the first NOx concentration acquisition unit 32 and the second NOx concentration acquisition unit 40, respectively.

  In step S110, it is determined whether or not the NOx occlusion amount St of the NSR catalyst 26 is equal to or greater than a predetermined value St1. The predetermined value St1 is a value determined in advance by experiments or the like as the NOx occlusion amount that allows the deterioration diagnosis of the NSR catalyst 26 to be performed. Even if the NSR catalyst 26 deteriorates and the NOx saturation storage amount decreases, if the NOx storage amount St of the NSR catalyst 26 is small, the output signal of the NOx sensor 14 does not change and it is difficult to diagnose the deterioration of the NSR catalyst 26. Become. Therefore, in step S110, it is confirmed that the NOx occlusion amount St is equal to or greater than the predetermined value St1, and that the deterioration diagnosis of the NSR catalyst 26 is possible. If it is determined that the NOx occlusion amount St is smaller than the predetermined value St1, the lean operation is continued and step S108 is performed again. If it is determined that the NOx occlusion amount St is equal to or greater than the predetermined value St1, the process proceeds to step S112.

  In step S112, it is determined whether or not the NOx occlusion amount St of the NSR catalyst 26 is equal to or less than a predetermined value St2. As the predetermined value St2, for example, the NOx saturated occlusion amount of the NSR catalyst 26 or a value close to this can be determined. If it is determined that the NOx occlusion amount St is larger than the predetermined value St2, the present process is terminated, and the deterioration diagnosis is performed again after a predetermined period. This is because when the NOx occlusion amount St of the NSR catalyst 26 exceeds the predetermined value St2, there is a high possibility that some kind of error occurs in the process of calculating the NOx occlusion amount St of the NSR catalyst 26 and accurate deterioration diagnosis cannot be performed. If it is determined that the NOx occlusion amount St is equal to or less than the predetermined value St2, the process proceeds to step S114.

  In step S114, the integrated value of the output signal of the NOx sensor 14 is set to zero. In step S116, a rich spike is started in which the air-fuel ratio control means 12 controls the air-fuel ratio of the exhaust gas flowing into the NSR catalyst 26 to a rich condition. In step S118, the process of integrating the output signal of the monitored NOx sensor 14 every minute time is started. The start of integration of the output signal of the NOx sensor 14 in step S118 is, for example, simultaneously with the start of the rich spike.

  In step S120, it is determined whether or not the rich spike in step S116 has been completed, that is, whether or not the rich spike has continued for a predetermined period. If it is determined in step S120 that the rich spike has not been completed, the process of step S120 is repeated. That is, the rich spike is continued until a predetermined time elapses, during which the output signal of the NOx sensor 14 is integrated. If it is determined in step S120 that the rich spike has been completed, the air-fuel ratio of the exhaust gas flowing into the NSR catalyst 26 is controlled to a lean condition by the air-fuel ratio control means 12, and the process proceeds to step S122.

  In step S122, the integration of the output signal of the NOx sensor 14 is finished, and the first integrated value (integrated value RI) obtained by integrating the first signal output from the NOx sensor 14 when the exhaust is controlled to the rich condition. Is calculated. The completion of the integration of the output signal of the NOx sensor 14 in step S122 is, for example, at the same time as the completion of the rich spike or at the time when a predetermined time TR has elapsed from the completion of the rich spike.

  In step S124, the integrated value of the output signal of the NOx sensor 14 is set to zero. In step S126, the process of integrating the output signal of the monitored NOx sensor 14 every minute time is started. The start of integration of the output signal of the NOx sensor 14 in step S126 is, for example, a point in time when a predetermined time TL (where TL> TR) has elapsed since the end of the rich spike.

  In step S128, it is determined whether or not the operating time under lean conditions has exceeded a predetermined time T1. If it is determined in step S128 that the operation time under the lean condition does not exceed the predetermined time T1, the process of step S128 is repeated. That is, the operation under the lean condition is continued until the predetermined time T1 elapses, during which the output signal of the NOx sensor 14 is integrated. If it is determined in step S128 that the operating time under the lean condition has exceeded the predetermined time T1, the process proceeds to step S130.

In step S130, it is determined whether or not the operating time under lean conditions has exceeded a predetermined time T2. If it is determined in step S130 that the operation time under the lean condition does not exceed the predetermined time T2, the process proceeds to step S132. If it is determined that the operation time under the lean condition has exceeded the predetermined time T2, the present process is terminated, and the deterioration diagnosis is performed again after the predetermined period. When the operation time under lean conditions exceeds a predetermined time T2, NOx occlusion amount of the NSR catalyst 26 becomes NOx saturation occlusion amount, due to the adsorbed NH ₃ amount of the SCR catalyst 28 is reduced NOx purification rate This is because the exhaust gas is lowered and the exhaust gas is deteriorated, so that it is not suitable as an operation region.

  In step S132, the integration of the output signal of the NOx sensor 14 is finished, and the second integrated value (integrated value LI) obtained by integrating the second signal output from the NOx sensor 14 when the exhaust is controlled to the lean condition. Is calculated.

In step S134, the integrated value LI which is calculated in step S132 it is compared with a threshold LI ₀ determined in advance. If the integrated value LI does not exceed the threshold LI ₀ , the process proceeds to step S136, and it is determined that both the NSR catalyst 26 and the SCR catalyst 28 are normal. If the integrated value LI exceeds the threshold value LI ₀ , the process proceeds to step S138.

In step S138, the integrated value RI calculated in step S122 is compared with a threshold value RI ₀ determined in advance. If the integrated value RI does not exceed the threshold value RI ₀ , the process proceeds to step S140 and it is determined that the NSR catalyst 26 has deteriorated. On the other hand, if the integrated value RI exceeds the threshold value RI ₀ , the process proceeds to step S142 and it is determined that the SCR catalyst 28 has deteriorated.

According to the present embodiment, only the output signal from the NOx sensor 14 that detects the NOx concentration of the exhaust downstream of the SCR catalyst 28 for the exhaust purification device 24 that includes the NSR catalyst 26 and the SCR catalyst 28 provided in the exhaust passage 22. Based on the above, it is possible to diagnose whether each of the NSR catalyst 26 and the SCR catalyst 28 has deteriorated. Therefore, the deterioration diagnosis device 10 of the exhaust purification device 24 according to the present embodiment can perform the deterioration diagnosis of the NSR catalyst and the SCR catalyst while having a configuration in which only one NOx sensor is used. In addition, the deterioration diagnosis device 10 of the exhaust purification device 24 according to the present embodiment diagnoses the deterioration of the NSR catalyst 26 and the SCR catalyst 28 without depending on the NH ₃ adsorption amount of the SCR catalyst 28.

  Further, in the deterioration diagnosis device 10 of the exhaust purification device 24 according to the present embodiment, the NOx sensor when the air-fuel ratio of the exhaust gas flowing into the NSR catalyst 26 is controlled to the rich condition and the lean condition using the air-fuel ratio control means 12. If the output signal from 14 is acquired, the deterioration of each of the NSR catalyst 26 and the SCR catalyst 28 can be diagnosed. Therefore, when the deterioration diagnosis of the NSR catalyst 26 and the SCR catalyst 28 is performed, it is not necessary to perform a special diagnostic operation mode or to stop or change the operation of various devices that may affect the exhaust properties. It is possible to suppress the influence on the fuel consumption, exhaust gas, etc. associated with the deterioration diagnosis.

  DESCRIPTION OF SYMBOLS 10 Deterioration diagnostic apparatus, 12 Air fuel ratio control means, 14 NOx sensor, 16 Diagnosis part, 20 Internal combustion engine, 22 Exhaust passage, 24 Exhaust gas purification apparatus, 26 NSR catalyst, 28 SCR catalyst, 32 1st NOx concentration acquisition means, 34 Flow volume acquisition Means, 36 first temperature sensor, 38 second temperature sensor, 40 second NOx concentration acquisition means, 42 first heating means, 44 second heating means.

Claims (6)

A deterioration diagnosis device that diagnoses deterioration of an exhaust purification device that is provided in an exhaust passage of an internal combustion engine and includes a NOx storage reduction catalyst and a selective reduction catalyst that is downstream of the NOx storage reduction catalyst. ,
Air-fuel ratio control means for controlling the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst;
A NOx sensor that detects the NOx concentration in the exhaust downstream of the selective catalytic reduction catalyst and outputs a signal corresponding to the detected NOx concentration;
A diagnostic unit for diagnosing deterioration of the NOx storage reduction catalyst and the selective reduction catalyst;
The diagnostic unit has a first signal output from the NOx sensor when the air-fuel ratio is controlled to a rich condition by the air-fuel ratio control means, and the air-fuel ratio is controlled to a lean condition by the air-fuel ratio control means. A deterioration diagnosis device for an exhaust gas purification device that diagnoses deterioration of the NOx storage reduction catalyst and the selective reduction catalyst based on a second signal that is sometimes output by the NOx sensor. The diagnostic unit integrates the first signal to calculate a first integrated value when the air-fuel ratio is controlled to a rich condition by the air-fuel ratio control means, and the air-fuel ratio is made lean by the air-fuel ratio control means. When the condition is controlled, the second signal is integrated to calculate a second integrated value,
When the first integrated value exceeds a predetermined first threshold value and the second integrated value exceeds a predetermined second threshold value, it is diagnosed that the selective catalytic reduction catalyst has deteriorated. ,
The diagnosis is made that the NOx storage reduction catalyst is deteriorated when the first integrated value does not exceed the first threshold value and the second integrated value exceeds the second threshold value. The exhaust gas purification device deterioration diagnosis device according to claim 1.   The period for accumulating the first signal is a period from the start of the control that makes the air-fuel ratio rich by the air-fuel ratio control means to the end of the control or until a predetermined time elapses after the control ends. The deterioration diagnosis device for an exhaust gas purification device according to claim 2.   The exhaust emission control device according to any one of claims 1 to 3, further comprising NOx concentration acquisition means for acquiring NOx concentration in the exhaust gas in an exhaust passage between the internal combustion engine and the NOx storage reduction catalyst. Deterioration diagnostic device.   The exhaust gas purification according to any one of claims 1 to 4, further comprising NOx concentration acquisition means for acquiring a NOx concentration in the exhaust gas in an exhaust passage between the NOx storage reduction catalyst and the selective reduction catalyst. Equipment deterioration diagnosis device. The first heating means and the second heating means for increasing the catalyst bed temperatures of the NOx occlusion reduction catalyst and the selective reduction catalyst while the NOx sensor detects the NOx concentration of the exhaust gas, respectively. The deterioration diagnosis device for an exhaust gas purification device according to any one of?