JP2013104348A - Catalyst deterioration determination system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst deterioration determination system configured to use NHgenerated in a NOx catalyst in reduction of NOx, to determinate deterioration of the NOx catalyst properly.SOLUTION: The catalyst deterioration determination system is provided in an exhaust passage of an internal combustion engine to store NOx, and determines deterioration of an NOx storage and reduction catalyst which reduces the stored NOx with supplied reductant. When the amount of sulfur and deposited in a non-regenerable state on the NOx storage and reduction catalyst is less than a predetermined abnormal amount, and when an exhaust air-fuel ratio is a rich air/fuel ratio for a predetermined period of time, the system determines that the NOx storage and reduction catalyst is deteriorated if the amount of NHin exhaust discharged from the NOx storage and reduction catalyst is less than a predetermined amount.

Description

  The present invention relates to a catalyst deterioration determination system.

NOx in exhaust gas discharged during lean combustion of an internal combustion engine is occluded by an occlusion reduction type NOx catalyst (hereinafter also simply referred to as “NOx catalyst”), and then the air-fuel ratio is temporarily made rich so that the NOx catalyst it can be reduced to N ₂ with the release of NOx from. About this NOx catalyst, there exists a tendency for the reduction | restoration capability of a NOx catalyst to deteriorate by poisoning by the sulfur component contained in exhaust, abnormal heat generation, etc. as a factor. Therefore, various catalyst deterioration detection techniques have been developed in order to detect NOx catalyst deterioration and promote appropriate processing.

  For example, in the technology disclosed in Patent Document 1, a NOx sensor disposed downstream of the NOx catalyst is used to calculate the NOx reduction rate by the NOx catalyst and the change in the NOx occlusion capacity of the NOx catalyst. The catalyst is judged for deterioration. Specifically, when the calculated NOx storage capacity of the NOx catalyst is greatly reduced, it is determined that the NOx catalyst has been thermally deteriorated.

JP 2008-190507 A

To reduce the NOx occluded in the NOx catalyst, when the ambient atmosphere and the state of the rich air-fuel ratio, NOx reacts with HC or H ₂ contained in the reducing agent NH ₃ is generated. In general, a NOx sensor can detect NH _{3 as} well as NOx, but it is difficult to detect each of them separately. In order to distinguish and detect NOx and NH ₃ , it is necessary to provide sensors corresponding to each. Therefore, in order to determine the deterioration of the NOx catalyst using NH ₃ generated in the NOx catalyst, it is necessary to provide a sensor corresponding to the detection target in the conventional technology, and the deterioration determination system has to be large. .

In other words, whether the detecting the NH ₃ generated by the NOx catalyst to attempt the deterioration determination of the NOx catalyst during the reduction of NOx using a NOx sensor, the detected value is meant the detection of NH _3, Since it is difficult to distinguish whether it means detection of NOx, it is difficult to make an accurate deterioration determination.

The present invention has been made in view of the above-described problems, and provides a system capable of more accurately determining the deterioration of a NOx catalyst by using NH ₃ generated by the NOx catalyst during the reduction of NOx. With the goal.

In the present invention, in order to solve the above problem, in order to sufficiently reduce the NOx stored in the NOx catalyst in a state where the amount of sulfur constantly deposited on the NOx catalyst is assumed to be relatively small. After the reduction atmosphere is formed, the deterioration determination of the NOx catalyst is performed on the basis of the amount of NH ₃ detected on the downstream side of the NOx catalyst. By limiting the conditions for detecting the NH ₃ generation amount in this way, it is possible to accurately determine the deterioration of the NOx catalyst based on the amount of NH ₃ generated during NOx reduction.

Therefore, in detail, the present invention determines deterioration of a NOx storage reduction catalyst (NOx catalyst) that is provided in the exhaust passage of the internal combustion engine, stores NOx, and reduces the stored NOx by supplying a reducing agent. In the catalyst deterioration determination system, the reducing agent supply unit that adjusts the air-fuel ratio of the exhaust gas that passes through the NOx storage reduction catalyst by supplying the reducing agent to the NOx storage reduction catalyst, and the NOx storage reduction catalyst A detection unit that is arranged on the downstream side and can detect NH ₃ in the exhaust discharged from the NOx storage reduction catalyst, and when the reducing agent is supplied from the reducing agent supply unit, the air-fuel ratio of the exhaust is rich An air-fuel ratio control unit that adjusts the amount of reducing agent so that the amount of sulfur is assumed to be less than a predetermined abnormal amount in the NOx storage reduction catalyst in a state where poisoning regeneration is impossible In The NH ₃ generation amount detected by the detection unit is less than the predetermined generation amount when the exhaust air / fuel ratio is set to the rich air / fuel ratio for a predetermined period by the air / fuel ratio control unit. A degradation determination unit that determines that the reduced NOx catalyst is degraded.

  The catalyst deterioration determination system according to the present invention determines the deterioration of the NOx catalyst provided in the exhaust passage. Here, when the NOx catalyst is placed in a lean atmosphere by the exhaust gas flowing in, the NOx in the exhaust gas is occluded, and the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is adjusted to a rich air-fuel ratio by the air-fuel ratio control unit and reduced there By making the agent exist, the stored NOx is reduced. This reducing agent is supplied into the exhaust gas by the reducing agent supply unit under the control of the air-fuel ratio control unit. As an example, the reducing agent may be supplied into the exhaust gas via a supply valve or the like. Further, the amount of HC as the reducing agent contained in the exhaust gas from the internal combustion engine may be adjusted by controlling the combustion state of the internal combustion engine.

Here, the NOx catalyst is generally in a state where a noble metal such as platinum and a strongly basic metal such as Ba functioning as a NOx storage agent exist. In the state where platinum or the like coexists with a strongly basic metal, the basic metal functions as an electron acceptor, and platinum or the like functions as an electron acceptor. The state is a state in which the NOx catalyst can normally perform its original function (hereinafter referred to as “normal state”). When the NOx catalyst is in a normal state, when NOx stored is reduced and N ₂ is generated, NH ₃ is also generated by the reaction between the supplied reducing agent and NOx.

  On the other hand, when the NOx catalyst is exposed to the exhaust gas, the sulfur component contained in the exhaust gas is also stored in a basic metal such as Ba, which is a NOx storage agent, and a sulfur poisoning state is formed. This sulfur poisoning state can be basically regenerated by performing a predetermined treatment according to the prior art. However, when platinum or the like is sintered by heat stress, a part of the sulfur poisoning state formed is It becomes a non-renewable state and tends to reside in the NOx catalyst. In this specification, the state in which sulfur poisoning has become remarkably permanent in the NOx catalyst so as not to be regenerated is referred to as a state in which sulfur poisoning regeneration ability is reduced.

Here, the applicant of the present invention, in the NOx catalyst that has fallen into the state of reduced sulfur poisoning regeneration ability, the phenomenon in which NOx is reduced while the amount of NH ₃ produced is significantly suppressed during the reduction of NOx ( Hereinafter, it was referred to as “reduction event at the time of deterioration”). In the reduction event at the time of deterioration, the balance of the NOx catalyst in the normal state is lost, the function of the basic metal as the electron acceptor is relatively weakened, and the function of platinum or the like is strengthened. However, since the functions of platinum and the like are weakened to some extent by sintering as described above, the supplied reducing agent sufficiently generates NH ₃ that is generated by reaction with NOx under normal conditions. The intermediate product is not produced. This intermediate product has a function of selectively reducing NOx to N ₂ , and as a result, in the NOx catalyst in a state of reduced sulfur poisoning regeneration ability, the amount of NH ₃ produced is suppressed In addition, the above-described deterioration reduction event that NOx reduction is performed may occur.

Therefore, in the catalyst deterioration determination system according to the present invention, in a state where the amount of sulfur accumulated in a state in which poisoning regeneration is impossible on the NOx catalyst is assumed to be less than a predetermined abnormal amount, the air-fuel ratio control unit When the exhaust air-fuel ratio is in a rich air-fuel ratio for a predetermined period, the NOx catalyst deterioration determination is performed based on the NH ₃ generation amount detected by the detector. The predetermined abnormal amount here is a threshold value for determining whether or not the NOx catalyst is deteriorated due to sulfur accumulated in a state in which poisoning regeneration is impossible in the NOx catalyst. The predetermined period is a period during which the NOx catalyst is placed in a rich air-fuel ratio, which is necessary to release at least NOx stored in the NOx catalyst and reduce it.

If the amount of sulfur accumulated in the NOx catalyst is less than a predetermined abnormal amount, when the exhaust air-fuel ratio is in a rich air-fuel ratio for a predetermined period by the air-fuel ratio control unit, the supplied reducing agent, occluded NOx, This reaction should produce a relatively large amount of NH ₃ . However, in a state where the amount of accumulated sulfur is assumed to be smaller than the predetermined abnormal amount, when the NH ₃ generation amount when the rich air-fuel ratio state for the reduction of stored NOx is formed is smaller than the predetermined generation amount In this case, it is possible to determine that the NOx catalyst has deteriorated due to a reduction in the sulfur poisoning regeneration ability. Therefore, the predetermined generation amount is a threshold value regarding the NH ₃ generation amount at the time of NOx reduction for determining whether or not the NOx catalyst is deteriorated.

In the catalyst deterioration determination system configured in this way, when it is assumed that the amount of accumulated sulfur in the NOx catalyst is relatively small, the sulfur poisoning of the NOx catalyst is based on the amount of NH ₃ generated during NOx reduction. The determination of deterioration due to is performed. When the amount of NH ₃ produced during NOx reduction is lower than the predetermined production amount under the condition that the amount of sulfur deposited on the NOx catalyst is assumed to be relatively small, the deterioration of the NOx catalyst that has become noticeably permanent occurs. Means that Therefore, in the catalyst deterioration system according to the present invention, as described above, it is possible to accurately perform the deterioration determination based on the amount of NH ₃ generated during NOx reduction.

  Here, in the catalyst deterioration determination system, the NOx stored in the NOx storage reduction catalyst when the amount of sulfur accumulated in the NOx storage reduction catalyst is the predetermined abnormal amount during the predetermined period is reduced and purified. It may be a period necessary for the exhaust air-fuel ratio to be in the rich air-fuel ratio state or a period longer than the period in which the exhaust air-fuel ratio is in the rich air-fuel ratio state.

Thus, by setting the predetermined time, which is the rich air-fuel ratio formation time by the air-fuel ratio control unit performed when determining the deterioration of the NOx catalyst described above, based on the amount of sulfur accumulated in the NOx catalyst, the sulfur regeneration capacity is lowered. NOx reduction with a reducing agent in the NOx catalyst in the state, i.e., can be reflected in the determination by sufficiently degradation determination unit amount of NH ₃ produced by the reduction reaction of NOx while suppressing the generation of NH ₃ It becomes. In the NOx catalyst in a state where the sulfur regeneration ability is lowered, the reaction of the intermediate product from the reducing agent, that is, the consumption reaction of the reducing agent tends to proceed slowly due to the sintering of platinum or the like. Setting based on the amount of accumulated sulfur in the catalyst is useful for accurate deterioration determination.

In the catalyst deterioration determination system, the detection unit may be a NOx sensor capable of detecting NOx and NH ₃ in the exhaust gas. As described above, at the time of deterioration determination, when the exhaust air-fuel ratio is brought to a rich air-fuel ratio by the air-fuel ratio control unit and NOx is being reduced, NOx is reduced to N ₂ in principle. Or NH ₃ is produced by the reaction with the reducing agent. Therefore, NOx does not flow out downstream of the NOx catalyst, or even if it flows out, the amount is extremely small. Therefore, as described above, the catalyst deterioration determination based on the amount of NH ₃ generated during NOx reduction can be accurately performed even by the NOx sensor.

Here, in the catalyst deterioration determination system described above, in the case where the catalyst deterioration detection system further includes a catalyst temperature detection unit that detects the temperature of the NOx storage reduction catalyst, the deterioration determination unit indicates that the amount of accumulated sulfur in the NOx storage reduction catalyst is NH ₃ detected by the detection unit when the exhaust air-fuel ratio is in the rich air-fuel ratio state for the predetermined period by the air-fuel ratio control unit in a state assumed to be less than the predetermined abnormal amount. The generation amount is equal to or greater than the predetermined generation amount, and the catalyst temperature detected by the catalyst temperature detection unit is equal to or lower than a predetermined catalyst temperature that is a threshold for the NOx storage reduction catalyst to determine its active state. In some cases, the NOx storage reduction catalyst may be determined to be poisoned by the reducing agent.

In the catalyst deterioration determination system configured as described above, it is impossible to regenerate the NOx catalyst as described above because the NH ₃ generation amount detected by the detection unit exceeds the predetermined generation amount under a predetermined condition. This means that there is no deterioration state accompanied by a state of reduced sulfur poisoning regeneration ability. However, although the exhaust air-fuel ratio is set to the rich air-fuel ratio for determination of deterioration even if it is not in such a deteriorated state, the NOx catalyst temperature is below the predetermined catalyst temperature. A state in which a good oxidation reaction of the reducing agent is inhibited, in other words, platinum in the NOx catalyst is covered with the reducing agent and a good oxidation reaction is inhibited. Conceivable. Therefore, in such a case, it can be determined that the NOx catalyst is not in a deteriorated state accompanied by a reduced state of sulfur poisoning regeneration ability, but is in a state of being poisoned by the reducing agent.

The poisoning of the NOx catalyst by this reducing agent is different from the deteriorated state accompanied by the reduced state of sulfur poisoning regeneration ability in that it can be regenerated by removing the reducing agent covering the NOx catalyst. Therefore, the catalyst deterioration determination system may further include a poisoning regeneration unit that regenerates the reducing agent poisoning state when the storage reduction type NOx catalyst is poisoned by the reducing agent. Then, the deterioration determination unit is configured so that the poisoning regeneration unit covers the NOx storage reduction catalyst with the reducing agent in a state where the amount of sulfur accumulated in the storage reduction NOx catalyst is assumed to be less than the predetermined abnormal amount. After regenerating the poisonous state, when the exhaust air-fuel ratio is set to the rich air-fuel ratio for the predetermined period by the air-fuel ratio control unit, the NH ₃ generation amount detected by the detection unit is the predetermined generation If the catalyst temperature is not less than the amount and the catalyst temperature detected by the catalyst temperature detector is not more than the predetermined catalyst temperature, it may be determined that the amount of sulfur contained in the reducing agent is abnormal.

In the catalyst deterioration determination system configured as described above, the reduction amount is reduced by regenerating the poisoning state by the reducing agent by the poisoning regeneration unit in a state where the amount of accumulated sulfur in the NOx catalyst is assumed to be smaller than the predetermined abnormal amount. The problem of the NOx catalyst due to the poisoning of the agent is solved. In such a state, when the exhaust air / fuel ratio is set to the rich air / fuel ratio, the NH ₃ production amount detected by the detection unit is equal to or greater than the predetermined production amount. It means that there is no deterioration state with a possible reduced state of sulfur poisoning regeneration ability. However, even if it is not in such a deteriorated state, the temperature of the NOx catalyst is still below the predetermined catalyst temperature means that the amount of sulfur contained in the reducing agent is abnormal, that is, the reducing agent contains more sulfur than expected. I can reasonably think. This is because if the reducing agent contains more sulfur than expected, platinum or the like of the NOx catalyst is covered with a sulfur component and the temperature of the NOx catalyst does not rise sufficiently. Therefore, in such a case, it is preferable to determine that the abnormality is not related to the deterioration state of the NOx catalyst itself but to sulfur contained in the reducing agent used.

Here, in the catalyst deterioration determination system described above, in the case where a heat history acquisition unit that acquires the heat history of the NOx storage reduction catalyst is further provided, the deterioration determination unit is configured to determine the amount of sulfur accumulated in the NOx storage reduction catalyst. NH detected by the detection unit when the exhaust air-fuel ratio is in the rich air-fuel ratio state for the predetermined period by the air-fuel ratio control unit in a state where the air-fuel ratio control unit is assumed to be less than the predetermined abnormal amount. ₃ generation amount is not less than the predetermined generation amount,
In addition, when the thermal history of the NOx storage reduction catalyst acquired by the thermal history acquisition unit is a predetermined abnormal heat history indicating abnormal heat generation, the NOx storage reduction catalyst is in a deteriorated state due to abnormal heat generation. It may be determined that

In the catalyst deterioration determination system configured as described above, it is impossible to regenerate the NOx catalyst as described above because the NH ₃ generation amount detected by the detection unit exceeds the predetermined generation amount under a predetermined condition. This means that there is no deterioration state accompanied by a state of reduced sulfur poisoning regeneration ability. However, even if the exhaust air-fuel ratio is set to the rich air-fuel ratio for the deterioration determination even if it is not in such a deteriorated state, the heat history of the NOx catalyst is a predetermined abnormal heat history. It is reasonably considered that the NOx catalyst is in a deteriorated state due to the abnormal heat history. Therefore, in such a case, it is possible to determine that the NOx catalyst is not in a deteriorated state accompanied by a reduced state of sulfur poisoning regeneration ability but is in a deteriorated state due to an abnormal heat history.

According to the present invention, in the catalyst deterioration determination system, it is possible to perform more accurate determination of NOx catalyst deterioration by using NH ₃ generated by the NOx catalyst during NOx reduction.

It is a figure which shows schematic structure of the exhaust system of the internal combustion engine by which the catalyst degradation determination system which concerns on this invention is arrange | positioned. During NOx reduction in NOx catalyst in a normal state, a model diagram of _{N 2} and NH ₃ produced. During NOx reduction in NOx catalyst in the degradation (abnormal) state, it is a model diagram of _{N 2} and NH ₃ produced. It is a figure which shows the consumption condition of HC which is a reducing agent in a NOx catalyst. 6 is a time chart regarding NOx purification and NH ₃ generation when exhaust gas having a rich air-fuel ratio is supplied to a NOx catalyst that stores NOx to some extent. It is a figure which shows the correlation with the exhaust air-fuel ratio supplied to a NOx catalyst according to the deterioration state of a NOx catalyst, and the amount of unpurified NOx. According to the deteriorated state of the NOx catalyst, it is a diagram illustrating the exhaust air-fuel ratio to be supplied to the NOx catalyst, the correlation between NH ₃ generation amount during NOx reduction. It is a 1st control flowchart for determining the deterioration of a NOx catalyst performed in the catalyst deterioration determination system which concerns on this invention. It is a 2nd control flowchart for determining the deterioration of a NOx catalyst performed in the catalyst deterioration determination system which concerns on this invention. It is a figure which shows the detail of the HC poisoning reproduction | regeneration process included in the control shown to FIG. 9A. FIG. 10 is a diagram showing the correlation between the exhaust air / fuel ratio supplied to the NOx catalyst and the amount of unpurified NOx in accordance with the HC poisoning state of the NOx catalyst in relation to the deterioration determination control shown in FIGS. 9A and 9B. 9A and 9B are diagrams showing a correlation between the exhaust air-fuel ratio supplied to the NOx catalyst and the amount of NH ₃ generated during NOx reduction, according to the HC poisoning state of the NOx catalyst, with respect to the deterioration determination control shown in FIGS. 9A and 9B. . It is a 3rd control flowchart for determining the deterioration of a NOx catalyst performed in the catalyst deterioration determination system which concerns on this invention. FIG. 13 is a diagram showing the correlation between the exhaust air-fuel ratio supplied to the NOx catalyst and the amount of unpurified NOx according to the thermal deterioration state of the NOx catalyst, with respect to the deterioration determination control shown in FIG. FIG. 13 is a diagram showing the correlation between the exhaust air-fuel ratio supplied to the NOx catalyst and the amount of NH ₃ generated during NOx reduction, according to the thermal deterioration state of the NOx catalyst, with respect to the deterioration determination control shown in FIG.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram showing a schematic configuration of an exhaust system of an internal combustion engine equipped with a catalyst deterioration system according to an embodiment of the present invention. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders. An exhaust passage 2 is connected to the internal combustion engine 1. An occlusion reduction type NOx catalyst 4 (hereinafter referred to as NOx catalyst 4) is provided in the middle of the exhaust passage 2.

The NOx catalyst 4 is constituted by, for example, using alumina (Al ₂ O ₃ ) as a carrier, and carrying, for example, barium (Ba) and platinum (Pt) on the carrier. The NOx catalyst 4 occludes NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high (that is, when the exhaust air / fuel ratio is in a lean air / fuel ratio), and the oxygen concentration of the inflowing exhaust gas decreases and when the reducing agent is present (i.e., when the exhaust air-fuel ratio is in a state of rich air-fuel ratio) has a function of reducing NOx that has been occluded in N _2. An injection valve 5 for injecting a reducing agent into the exhaust gas is attached to the exhaust passage 2 upstream of the NOx catalyst 4. The injection valve 5 is opened by a signal from the ECU 10 described later, and injects the reducing agent into the exhaust. For example, the fuel (HC) of the internal combustion engine 1 is used as the reducing agent, but the reducing agent is not limited thereto.

  The fuel injected from the injection valve 5 into the exhaust passage 2 lowers the air-fuel ratio of the exhaust flowing from the upstream side of the exhaust passage 2. When NOx stored in the NOx catalyst 4 is reduced, so-called rich spike control is performed to reduce the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 4 in a relatively short cycle by injecting HC from the injection valve 5. Run. The amount of HC injected from the injection valve 5 is determined based on, for example, the operating state (engine speed and fuel injection amount) of the internal combustion engine 1. The relationship between the HC amount, the engine speed, and the engine load can be mapped in advance and stored in a memory in the ECU 10 to be described later. Further, an air-fuel ratio sensor may be attached to the exhaust passage 2, and the HC amount may be feedback controlled so that the air-fuel ratio detected by the air-fuel ratio sensor becomes a target value necessary for NOx reduction.

  The injection valve 5 corresponds to a reducing agent supply unit according to the present invention. Moreover, it replaces with the HC supply form by the injection valve 5, and the form which supplies HC by discharging | emitting exhaust gas containing unburned fuel from the internal combustion engine 1 is also employable. That is, an in-cylinder injection valve for injecting fuel into the cylinder is provided, and sub-injection (post-injection) for injecting fuel again during the expansion stroke or exhaust stroke after the main injection from the in-cylinder injection valve is performed. Alternatively, by delaying the fuel injection timing from the in-cylinder injection valve, the gas containing a large amount of HC can be discharged from the internal combustion engine 1.

An upstream NOx sensor 7 that measures the NOx concentration in the exhaust is attached to the exhaust passage 2 upstream of the injection valve 5. Further, a downstream NOx sensor 8 for measuring the NOx concentration in the exhaust and a temperature sensor 9 for measuring the temperature of the exhaust are attached to the exhaust passage 2 downstream of the NOx catalyst 4. In the present embodiment, the downstream NOx sensor 8 corresponds to the detection unit in the present invention, and can substantially detect NOx and NH ₃ in the exhaust gas. Note that NH ₃ in the exhaust gas is detected as NOx because it reacts with O ₂ and becomes NO in the downstream NOx sensor 8. Therefore, the downstream NOx sensor 8 can detect NH ₃ in the exhaust gas as NOx, but in that case, it is difficult to determine whether NH ₃ is detected or NOx is detected.

The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 controls the operation state of the internal combustion engine 1 according to the operation conditions of the internal combustion engine 1 and the request of the driver. In addition to the above sensors, the ECU 10 outputs an electric signal corresponding to the amount of depression of the accelerator pedal 11 by the driver to detect the engine load, and an accelerator position sensor 12 for detecting the engine speed. 13 are connected via electric wiring, and the output signals of these various sensors are input to the ECU 10.

  On the other hand, the injection valve 5 is connected to the ECU 10 via electric wiring, and the ECU 10 controls the opening and closing timing of the injection valve 5. In this embodiment, the ECU 10 that adjusts the amount of HC supplied from the injection valve 5 and controls the air-fuel ratio of the exhaust corresponds to the air-fuel ratio control unit in the present invention. The ECU 10 performs rich spike control with the exhaust air / fuel ratio targeted at a rich air / fuel ratio (for example, about 14), and performs a reduction process of NOx stored in the NOx catalyst 4.

Further, the ECU 10 performs a determination process related to catalyst deterioration of the NOx catalyst 4 based on a detection signal obtained from the downstream NOx sensor 8. Therefore, from this viewpoint, the ECU also corresponds to the deterioration determination unit in the present embodiment. Here, FIG. 2 shows a model of N ₂ and NH ₃ generation during NOx reduction in the NOx catalyst 4 in the normal state, and FIG. 3 shows NOx reduction in the NOx catalyst 4 in a deteriorated state that cannot be recovered. It shows the _{N 2} and NH ₃ generated model of the time. The non-recoverable deterioration state (the state shown in FIG. 3) is a large amount of sulfur component in a state where sintering of Pt contained in the NOx catalyst 4 due to thermal stress and poisoning regeneration due to the sintering is impossible. This is due to the accumulation of slag and is also referred to as an “abnormal condition” in this specification. The state shown in FIG. 2 is a state that is not the abnormal state, and is also referred to as a “normal state” in this specification.

The NOx catalyst 4 causes NO to react with O ₂ on Pt when the air-fuel ratio of the exhaust gas is lean, and occludes Ba as Ba (NO ₃ ) ₂ . On the other hand, when HC is supplied to make the exhaust air-fuel ratio rich, the NOx catalyst 4 in the normal state releases Ba (NO ₃ ) ₂ as NO ₂ and further reduces to N ₂ on Pt. . Here, in the NOx catalyst 4, Pt coexists with strongly basic Ba. In such a case, Ba functions as an electron acceptor and Pt functions as an electron acceptor. The oxide PtO ₂ is formed on Pt. Therefore, the Pt activity is balanced in a slightly lowered state, and the balanced state becomes a state in which the NOx catalyst 4 can normally perform its original function (corresponding to the normal state described above). When the NOx catalyst 4 is in the normal state as described above, the supplied HC (others, CO, H _2, etc.) is supplied when the stored NOx is reduced and N ₂ is generated as shown in FIG. NH ₃ is also produced by the reaction of NOx with NOx.

  On the other hand, the NOx catalyst 4 is exposed to exhaust gas, and thus continues to undergo thermal stress over time. As a result, sintering occurs in Pt contained in the NOx catalyst 4, and the ability to regenerate the sulfur poisoning state due to the sulfur component stored in Ba is reduced. As a result, sulfur components accumulate. The state in which sulfur poisoning has become remarkably permanent in the NOx catalyst 4 in this manner is referred to as a sulfur poisoning regeneration ability lowered state, which corresponds to the abnormal state described above (the state shown in FIG. 3).

In this abnormal state, the balance between Pt and Ba in the normal state of the NOx catalyst 4 is lost, and the function of Ba as an electron acceptor is relatively weakened, resulting in a stronger function of Pt. However, since the function of Pt is weakened to some extent by sintering as described above, the consumption reaction of HC as a reducing agent becomes slow in the abnormal NOx catalyst 4 as shown in FIG. FIG. 4 is a diagram showing the HC consumption state in the NOx catalyst 4, where the horizontal axis represents the axial distance of the NOx catalyst 4 and the vertical axis represents the amount of HC remaining in the NOx catalyst 4. In addition, the triangles in the figure indicate the HC consumption state in the NOx catalyst 4 in a normal state in which sintering and sulfur component deposition can be ignored in the NOx catalyst 4. Also, the black circles in the figure indicate the HC consumption status in the NOx catalyst 4 in an abnormal state.

Thus, in the NOx catalyst 4 in the abnormal state, the supplied HC does not sufficiently generate NH ₃ that is generated by the reaction with NOx in the normal state, and the intermediate product (NH Intermediate to ₃ and only produce amines, amides, etc.). This intermediate product has a function of selectively reducing NOx to N _2. As a result, in the NOx catalyst 4 in an abnormal state, the amount of NH ₃ produced is suppressed, and NOx That is, a reduction event occurs when the reduction is performed.

This deterioration reduction event will be described in detail with reference to FIGS. Here, the NOx catalyst 4 in the abnormal state has a significantly reduced storable NOx amount (NOx occlusion amount) compared to the NOx catalyst 4 in the normal state. This is because the NOx catalyst 4 in an abnormal state is in a state in which the sulfur poisoning regeneration ability is lowered, and a large amount of sulfur components are accumulated in a state in which regeneration is impossible. Further, as described above, when HC, which is a reducing agent, is supplied from the injection valve 5 to the NOx catalyst 4, the reduction of NOx stored in the NOx catalyst 4 is performed according to the model shown in FIG. Reaction occurs, the amount of unpurified (unreduced) NOx decreases, and NH ₃ is generated by the reaction of NOx and HC (see FIG. 5).

Here, the present applicant has found that the amount of NH ₃ produced during NOx reduction differs greatly between when the NOx catalyst 4 is in a normal state and when it is in an abnormal state. FIG. 6 shows the correlation between the exhaust air-fuel ratio supplied to the NOx catalyst 4 and the amount of unpurified NOx according to the deterioration state of the NOx catalyst 4, and FIG. 7 shows the NOx according to the deterioration state of the NOx catalyst 4. The correlation between the exhaust air-fuel ratio supplied to the catalyst 4 and the amount of NH ₃ produced during NOx reduction is shown. 6 and 7, the triangles and black circles in the figures correspond to the legend triangles and black circles shown in FIG. 4, respectively. In addition, the white squares in the figure indicate that the amount of sulfur deposited in a non-renewable state is comparatively small although the same degree of sintering as the NOx catalyst 4 in the abnormal state is formed, and still serves as a NOx catalyst. It represents the transition of the amount of unpurified NOx and the amount of NH ₃ produced in a state where the function is maintained and can be treated as a normal state (normal state 2).

As can be understood from FIGS. 6 and 7, regarding the amount of unpurified NOx, the NOx catalyst can be obtained if rich air-fuel ratio exhaust gas is supplied to the NOx catalyst 4 regardless of whether or not the NOx catalyst 4 is in a normal state. The outflow amount of unpurified NOx from 4 is almost negligible. However, when the NOx catalyst 4 is in an abnormal state, it can be found that the amount of NH ₃ produced during NOx reduction tends to be significantly lower than that in the normal state. In particular, when the transition of the NH ₃ generation amount according to the normal state 2 is compared with the transition of the NH ₃ generation amount according to the abnormal state, the amount of accumulated sulfur in spite of the same degree of sintering of Pt in the NOx catalyst 4. As a result of the increase, the amount of NH ₃ produced is significantly reduced. From this, paying attention to the amount of sulfur deposited in the NOx catalyst 4 in a non-renewable state, whether or not the NOx catalyst 4 is in an abnormal state by using the amount of NH ₃ generated during NOx reduction is determined. It can be seen that the deterioration state can be determined.

Based on the above, FIG. 8 shows a flow of deterioration determination control of the NOx catalyst 4 according to the present embodiment. The catalyst deterioration determination control is repeatedly executed as appropriate by the ECU 10. First, in S101, it is determined whether or not a precondition for determining deterioration of the NOx catalyst 4 is satisfied. For example, it is determined that the precondition is satisfied when the temperature of the NOx catalyst 4 is a temperature suitable for NOx reduction. Here, the temperature of the NOx catalyst 4 is detected by the temperature sensor 9. The temperature suitable for NOx reduction is, for example, based on the fact that if the NOx catalyst 4 is excessively low in temperature, the activity of the catalyst is deteriorated, and if it is excessively high in temperature, the storage capacity of Ba is decreased. It has a predetermined temperature range to be set. Therefore, when the temperature of the NOx catalyst 4 belongs to the predetermined temperature range, an affirmative determination is made in S101, and the process proceeds to S102.
If it does not belong, a negative determination is made and this control is terminated.

  Next, in S102, the sulfur poisoning regeneration (S regeneration) is completed in the NOx catalyst 4, and the sulfur deposition amount (S deposition amount) estimated after the completion is equal to or less than a predetermined deposition amount S0. Is determined. That is, it is determined whether or not the amount of sulfur accumulated in the NOx catalyst 4 in a state where poisoning regeneration is impossible is equal to or less than a predetermined accumulation amount S0 that is a threshold value. Since sulfur poisoning regeneration is a conventional technique, a detailed description thereof is omitted, but this is a process for removing sulfur stored in the NOx catalyst 4 in a state where poisoning regeneration is possible. In this process, the catalyst temperature of the NOx catalyst 4 is raised while HC is supplied. According to this sulfur poisoning regeneration process, it is possible to remove the sulfur content occluded in the NOx catalyst 4, but for the sulfur content deposited in a state in which poisoning regeneration is impossible, the NOx catalyst 4 can be removed. It is difficult to remove from. As described above, this is because Pt of the NOx catalyst 4 is deteriorated by sintering due to thermal stress over time. The amount of sulfur accumulated in the NOx catalyst 4 is estimated based on the operating state of the internal combustion engine 1 and the history of thermal stress (catalyst temperature history) received by the NOx catalyst 4.

  The predetermined accumulation amount S0 is set as a threshold value for determining whether or not the sulfur accumulation amount on the NOx catalyst 4 is a certain amount when the NOx catalyst 4 is in a normal state. Therefore, if an affirmative determination is made in S102, it means that the sulfur component of a degree that can be regarded as a normal state is deposited on the NOx catalyst 4, and the process proceeds to S103. On the other hand, if a negative determination is made in S102, it means that a sulfur component exceeding the amount that can be regarded as a normal state is deposited on the NOx catalyst 4, and in the present embodiment, this control is terminated.

  In S103, it is determined whether or not the NOx occlusion amount stored in the NOx catalyst 4 is equal to or greater than a predetermined NOx occlusion amount S1. The NOx occlusion amount stored in the NOx catalyst 4 is estimated based on the NOx amount in the exhaust detected by the upstream NOx sensor 7. The predetermined NOx occlusion amount S1 is set as the NOx amount that can be occluded to the maximum by the NOx catalyst 4 when it is assumed that the NOx catalyst 4 is in an abnormal state. Therefore, if an affirmative determination is made in S103, it means that if the NOx catalyst 4 is in an abnormal state, it is already in a state where NOx cannot be further occluded, and the process proceeds to S104. On the other hand, if a negative determination is made in S103, it means that the NOx catalyst 4 is still in a state where it can occlude NOx, and in the present embodiment, this control is terminated.

In S <b> 104, rich spike control for determining deterioration of the NOx catalyst 4 is performed via the injection valve 5. In the rich spike control, the exhaust rich air-fuel ratio (for example, the exhaust air-fuel ratio is about 14 ± 0.2) that can generate NH ₃ according to the model shown in FIG. 2 when the NOx catalyst 4 is in a normal state. ) Is formed, and the control continuation time of the NOx catalyst 4 in the abnormal state is determined based on the fact that the consumption reaction of the supplied HC is slow when the NOx catalyst 4 is in the abnormal state as shown in FIG. The injection valve 5 is controlled so as to be longer than a predetermined time set so as to sufficiently reduce the stored NOx. Therefore, when the process of S104 is performed, the NOx catalyst 4 performs NOx reduction according to the model shown in FIG. 2 or NOx reduction according to the model shown in FIG. When the process of S104 ends, the process proceeds to S105.

In S105, when the deterioration determination rich spike control according to S104 is executed, the amount of NH ₃ flowing out of the NOx catalyst 4, that is, the amount of NH ₃ generated during NOx reduction in the NOx catalyst 4, is greater than or equal to a predetermined NH ₃ generation amount S2. It is determined whether or not. The amount of NH ₃ produced during NOx reduction in the NOx catalyst 4 is detected using the peak output of the downstream side NOx sensor 8 or the like. As shown in FIGS. 6 and 7, during the NOx reduction, the amount of unpurified NOx flowing out from the NOx catalyst 4 is negligibly small, so that the downstream NOx sensor 8 when the process of S104 is performed is performed. The detected value may be understood to reflect the amount of NH ₃ generated according to the model shown in FIG. 2 or FIG.

The predetermined NH ₃ generation amount S2 is based on the fact that the amount of NH ₃ generated during NOx reduction differs depending on whether the NOx catalyst 4 shown in FIGS. 2 and 3 is in a normal state or an abnormal state. The threshold value for determining the deterioration state of the NOx catalyst 4 is set. Therefore, if an affirmative determination is made in S105, it means that the NOx catalyst 4 is performing NOx reduction according to the model shown in FIG. 2, and thus the process proceeds to S106, where it is determined that the NOx catalyst 4 is in a normal state. can do. On the other hand, if a negative determination is made in S105, it means that the NOx catalyst 4 is undergoing NOx reduction according to the model shown in FIG. 3, and thus the process proceeds to S107, where the NOx catalyst 4 is in an abnormal state. Can be determined.

In the catalyst deterioration determination control according to the above-described embodiment, the deterioration determination rich spike control according to S104 is executed under the condition that the NOx catalyst 4 is assumed to be in a normal state through the processing of S102 and S103. NH ₃ amount of production that is detected by the downstream side NOx sensor 8, or the NOx catalyst 4 is in an abnormal state, the deterioration is determined of the time. Thus, paying attention to the amount of sulfur component deposited on the NOx catalyst 4 in a state in which poisoning regeneration is impossible, the deterioration determination is performed based on the amount of NH ₃ generated at the time of NOx reduction, so that the downstream side NOx sensor 8 It is possible to effectively improve the accuracy of the catalyst deterioration determination using the.

  A second embodiment of the catalyst deterioration determination control executed in the catalyst deterioration determination system according to the present invention will be described with reference to FIGS. 9A, 9B, 10, and 11. FIG. Of the processes included in the catalyst deterioration determination control shown in FIG. 9A, those equivalent to the processes included in the catalyst deterioration determination control shown in FIG. 8 are given the same reference numerals, and the detailed description thereof is omitted. .

Therefore, in the catalyst deterioration determination control shown in FIG. 9A, when it is determined in S105 that the NH ₃ generation amount at the time of NOx reduction in the NOx catalyst 4 is equal to or greater than the predetermined NH ₃ generation amount S2, the process proceeds to S201. In S201, it is determined whether or not the catalyst temperature of the NOx catalyst 4 is equal to or higher than a predetermined temperature T0. The predetermined temperature T0 falls into a state covered with the HC supplied with the NOx catalyst 4 in consideration of the temperature rise caused by the supply of HC when the NOx catalyst 4 is in the active state. It is set as a threshold value for determining whether the oxidation function of Pt contained is lost, that is, whether the HC poisoning state has been reached.

Here, FIG. 10 shows the correlation between the exhaust air-fuel ratio supplied to the NOx catalyst 4 and the amount of unpurified NOx according to the HC poisoning state of the NOx catalyst 4, and FIG. 11 shows the HC poisoning state of the NOx catalyst 4. The correlation between the exhaust air-fuel ratio supplied to the NOx catalyst 4 and the amount of NH ₃ produced during NOx reduction is shown. 10 and 11, the black circles in the figure represent the transition of the amount of unpurified NOx and the amount of NH ₃ produced in the NOx catalyst 4 in the HC poisoning state, and the triangles in the figure are in the normal state. The transition of unpurified NOx amount and NH ₃ production amount in the NOx catalyst 4 is shown. As can be understood from FIGS. 10 and 11, when the NOx catalyst 4 is in the HC poisoning state, unpurified NOx flows out from the NOx catalyst 4, and a small amount of NH ₃ is also generated and flows out. Therefore, as a result of the downstream NOx sensor 8 detecting both unpurified NOx and generated NH ₃ without distinction, there is a high possibility that an affirmative determination is made in the determination process in S105.

In view of this point, if an affirmative determination is made in S <b> 201 after an affirmative determination in S <b> 105, it is reasonably considered that the NOx catalyst 4 retains the Pt oxidation function. 4 can be determined to be in a normal state. On the other hand, when a positive determination is made in S105 and a negative determination is made in S201, the NOx catalyst 4 is considered to be in an HC poisoning state. Therefore, in this embodiment, in that case, the HC poisoning regeneration process according to S202 is performed.

  FIG. 9B shows a flowchart of the HC poisoning regeneration process. If a negative determination is made in S201, it is determined in S203 that the NOx catalyst 4 is in an HC poisoning state in accordance with the above reason. Note that this HC poisoning state is caused by the NOx catalyst 4 being covered with HC, so that the HC poisoning can be regenerated unlike the above-described abnormal state. Therefore, in S204, a process for regenerating the HC poisoning in the NOx catalyst 4 is performed. In the regeneration process, HC adhering to the NOx catalyst 4 is removed by increasing the temperature of the exhaust discharged from the internal combustion engine 1.

  Thereafter, in S205, rich spike control is performed via the injection valve 5, and the exhaust air-fuel ratio flowing into the NOx catalyst 4 is brought to a rich air-fuel ratio state. The rich air-fuel ratio may be the same as the rich air-fuel ratio set in the above-described process S104. When the processing of S205 ends, the process proceeds to S206. In S206, it is determined whether or not the catalyst temperature of the NOx catalyst 4 is equal to or higher than a predetermined temperature T0 as in S201. If an affirmative determination is made in S206, this means that the Pt oxidation function in the NOx catalyst 4 has returned to a state where it can sufficiently exert its effect, and in S207, the regeneration of HC poisoning in the NOx catalyst 4 has been completed. Determined.

  On the other hand, if a negative determination is made in S206, it means that the Px oxidation function in the NOx catalyst 4 has not returned to a state where it can sufficiently be exhibited. As a case where the oxidation function of Pt does not recover in the NOx catalyst 4, there is a case where the amount of sulfur component contained in the fuel of the internal combustion engine 1 used as the reducing agent is abnormally large. When the amount of sulfur component contained in HC is large, the sulfur component is occluded and deposited in Ba, and it is also deposited on Pt and loses its function. In this case, since the Pt activity continues to be lost, NOx reduction by the NOx catalyst 4 becomes difficult, and a large amount of unpurified NOx is detected by the downstream NOx sensor 8. Therefore, in this case, an affirmative determination is made in S105 and a negative determination is made in S201 and S206.

  Based on the above, when a negative determination is made in S206, the process proceeds to S208, where it is determined that the fuel used in the internal combustion engine 1 is abnormal, that is, the amount of sulfur component contained in the fuel is abnormally large. . In this case, an abnormality warning is issued in S209 so as to refrain from using the fuel for the user. In the abnormality warning, information indicating a fuel abnormality is emitted from a display device (display), a sound device (speaker), or the like (not shown).

  As described above, in the catalyst deterioration determination control according to the second embodiment, in addition to the accurate abnormality determination of the NOx catalyst 4, the HC poisoning determination of the NOx catalyst 4 and its regeneration processing, and further the fuel used in the internal combustion engine 1 are determined. Abnormality determination is performed.

  A third embodiment of the catalyst deterioration determination control executed in the catalyst deterioration determination system according to the present invention will be described with reference to FIGS. 12, 13, and 14. FIG. Of the processes included in the catalyst deterioration determination control shown in FIG. 12, the same processes as those included in the catalyst deterioration determination control shown in FIG. 8 are denoted by the same reference numerals, and detailed description thereof is omitted. .

Therefore, in the catalyst deterioration determination control shown in FIG. 9A, when it is determined in S105 that the NH ₃ generation amount at the time of NOx reduction in the NOx catalyst 4 is equal to or greater than the predetermined NH ₃ generation amount S2, the process proceeds to S301. In S301, it is determined whether or not there is no heat history of abnormal heat generation in the NOx catalyst 4. This thermal history is determined based on the history of the catalyst temperature of the NOx catalyst 4 detected by the temperature sensor 9.

Here, FIG. 13 shows the correlation between the exhaust air-fuel ratio supplied to the NOx catalyst 4 and the amount of unpurified NOx in accordance with the thermal degradation state of the NOx catalyst 4, and FIG. 14 shows the thermal degradation state of the NOx catalyst 4. The correlation between the exhaust air / fuel ratio supplied to the NOx catalyst 4 and the amount of NH ₃ produced during NOx reduction is shown. 13 and 14, the white circles in the drawings represent the transition of the amount of unpurified NOx and the amount of NH ₃ generated in the NOx catalyst 4 in a normal state, and the black triangles in the drawings are uniformly heat It shows the transition of the amount of unpurified NOx and the amount of NH ₃ produced in the NOx catalyst 4 in a deteriorated state (a state exposed to thermal stress of about 800 degrees lower than the heat deterioration due to abnormal heat generation). Further, the white triangle in the figure represents the transition of the amount of unpurified NOx and the amount of NH ₃ produced in the NOx catalyst 4 in a state of thermal degradation due to abnormal heat generation, and the white square in the figure represents the NOx catalyst 4 in the abnormal state. Represents the transition of the amount of unpurified NOx and the amount of NH ₃ produced.

In the NOx catalyst 4, when abnormal heat generation occurs for some reason, the NOx catalyst 4 originally has the occlusion / reduction function lost. Therefore, as can be understood from FIGS. 13 and 14, in such a case, the amount of NOx that passes through the NOx catalyst 4 increases, and the amount of NOx that is occluded is small. ₃ amount is also small. Therefore, the downstream NOx sensor 8 detects both unpurified slip-through NOx and generated NH ₃ without distinction, and as a result, there is a high possibility that an affirmative determination is made in the determination process in S105. In view of this point, when an affirmative determination is made in S105 after an affirmative determination in S105, it is reasonably considered that the NOx catalyst 4 has not been thermally deteriorated due to abnormal heat generation. Can be determined to be in a normal state. On the other hand, when a negative determination is made in S301, it is determined in S302 that the NOx catalyst 4 is thermally deteriorated due to abnormal heat generation.

  As described above, in the catalyst deterioration determination control according to the third embodiment, in addition to the accurate abnormality determination of the NOx catalyst 4, the heat deterioration determination due to abnormal heat generation of the NOx catalyst 4 is performed.

<Other examples>
Determination of HC poisoning of the NOx catalyst 4 shown in the second embodiment and its regeneration process, determination of abnormality of the fuel used in the internal combustion engine 1, and abnormal heat generation of the NOx catalyst 4 shown in the third embodiment The thermal deterioration determination by may be performed in the same catalyst deterioration determination process. In this case, when the NOx catalyst 4 is thermally deteriorated due to abnormal heat generation, the determination as to S301 is made after an affirmative determination is made in S105, based on the fact that the function as the NOx catalyst has not been sufficiently achieved. It is preferable to perform the processing before the determination processing according to S201. In this case, if an affirmative determination is made in S301, the determination process related to S201 is performed.

1 Internal combustion engine 2 Exhaust passage 4 NOx storage reduction catalyst (NOx catalyst)
5 Injection Valve 7 Upstream NOx Sensor 8 Downstream NOx Sensor 9 Temperature Sensor 10 ECU
11 Accelerator pedal 12 Accelerator opening sensor 13 Crank position sensor

Claims (6)

In a catalyst deterioration determination system for determining deterioration of a NOx storage reduction catalyst that is provided in an exhaust passage of an internal combustion engine and stores NOx and reduces the stored NOx by supplying a reducing agent.
A reducing agent supply unit that adjusts an air-fuel ratio of exhaust gas passing through the NOx storage reduction catalyst by supplying a reducing agent to the NOx storage reduction catalyst;
A detection unit disposed downstream of the NOx storage reduction catalyst and capable of detecting NH ₃ in the exhaust discharged from the NOx storage reduction catalyst;
An air-fuel ratio control unit that adjusts the amount of the reducing agent so that the air-fuel ratio of the exhaust gas becomes a rich air-fuel ratio when the reducing agent is supplied from the reducing agent supply unit;
When it is assumed that the amount of sulfur deposited on the NOx storage reduction catalyst in a state where poisoning regeneration is impossible is less than a predetermined abnormal amount, the air-fuel ratio control unit controls the exhaust air-fuel ratio for a predetermined period. A deterioration determination unit that determines that the NOx storage reduction catalyst is deteriorated when the NH ₃ generation amount detected by the detection unit is less than a predetermined generation amount when the rich air-fuel ratio is set. When,
A catalyst deterioration determination system. In the predetermined period, an exhaust air-fuel ratio required for reducing and purifying NOx stored in the NOx storage reduction catalyst when the amount of accumulated sulfur in the NOx storage reduction catalyst is the predetermined abnormal amount is reduced. A period in which the rich air-fuel ratio is set, or a period in which the exhaust air-fuel ratio is longer than a period in which the rich air-fuel ratio is set,
The catalyst deterioration determination system according to claim 1. The detection unit is a NOx sensor capable of detecting NOx and NH ₃ in exhaust gas.
The catalyst deterioration determination system according to claim 1 or 2. A catalyst temperature detector for detecting the temperature of the NOx storage reduction catalyst;
The deterioration determination unit
When the exhaust air-fuel ratio is set to the rich air-fuel ratio for the predetermined period by the air-fuel ratio control unit in a state where the amount of accumulated sulfur in the NOx storage reduction catalyst is assumed to be smaller than the predetermined abnormal amount In addition, the amount of NH ₃ detected by the detection unit is equal to or greater than the predetermined generation amount, and the catalyst temperature detected by the catalyst temperature detection unit determines whether the NOx storage reduction catalyst is active. When the temperature is equal to or lower than a predetermined catalyst temperature that is a threshold value for determining, the NOx storage reduction catalyst is determined to be poisoned by a reducing agent.
The catalyst deterioration determination system according to any one of claims 1 to 3. A poisoning regeneration section for regenerating the reducing agent poisoning state when the NOx storage reduction catalyst is in a poisoning state by a reducing agent;
The deterioration determination unit
In a state where the amount of sulfur accumulated in the NOx storage reduction catalyst is assumed to be less than the predetermined abnormal amount, the poisoning regeneration unit regenerates the poisoning state of the NOx storage reduction catalyst with the reducing agent, When the air-fuel ratio control unit sets the exhaust air-fuel ratio to the rich air-fuel ratio for the predetermined period, the NH ₃ generation amount detected by the detection unit is not less than the predetermined generation amount, and When the catalyst temperature detected by the catalyst temperature detector is equal to or lower than the predetermined catalyst temperature, it is determined that the amount of sulfur contained in the reducing agent is abnormal.
The catalyst deterioration determination system according to claim 4. A heat history acquisition unit that acquires the heat history of the NOx storage reduction catalyst;
The deterioration determination unit
When the exhaust air-fuel ratio is set to the rich air-fuel ratio for the predetermined period by the air-fuel ratio control unit in a state where the amount of accumulated sulfur in the NOx storage reduction catalyst is assumed to be smaller than the predetermined abnormal amount Further, the NH ₃ production amount detected by the detection unit is equal to or greater than the predetermined production amount, and the thermal history of the NOx storage reduction catalyst acquired by the thermal history acquisition unit is a predetermined value indicating abnormal heat generation. In the case of the abnormal heat history, it is determined that the NOx storage reduction catalyst is in a deteriorated state due to abnormal heat generation.
The catalyst deterioration determination system according to any one of claims 1 to 5.

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