JP2004270468A - Abnormality determining device for nox sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abnormality determining device for an NOx sensor capable of reliably determining an abnormality of the NOx sensor so as to effect the proper regeneration of an NOx occluded catalyst. <P>SOLUTION: The abnormality determining device for the NOx sensor is provided in the exhaust gas passage of an internal combustion engine with an NOx occluded catalyst to occlude NOx in exhaust gas during lean operation and discharge and reduce occluded NOx by performing rich operation and the Ox sensor is situated on the side situated downstream of the exhaust gas of the NOx occlusion catalyst, and comprises an NOx discharging means (S202) to forcibly create a state wherein NOx in the NOx occluded catalyst is discharged; a real NOx reduction rate computing means (S203) to compute the actual NOx reduction rate of the NOx occlusion catalyst in a state that NOx is discharged by the NOx discharging means; a reference NOx reduction rate setting means (S205) to preset a reference NOx reduction rate based on an engine operating state; and an abnormality determining means (S206) to compare the actual NOx reduction rate with the reference NOx reduction rate and determine the abnormality of the NOx sensor. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an abnormality determination device for a NOx sensor, and more particularly, to an abnormality determination device for a NOx sensor applied to estimating the amount of NOx stored in a NOx storage catalyst.
[0002]
[Prior art]
In general, the NOx storage catalyst stores NOx (nitrogen oxide) in exhaust gas when the exhaust air-fuel ratio is lean, and releases and reduces the stored NOx when the exhaust air-fuel ratio is rich. It is a storage type NOx catalyst.
Specifically, it has a characteristic of storing NOx in exhaust gas as a nitrate in an oxygen excess state (oxidizing atmosphere) and reducing the stored NOx to nitrogen in a carbon monoxide excess state (reducing atmosphere).
[0003]
Here, FIG. 5A is a diagram showing the performance of the NOx storage catalyst. As shown in the figure, when the NOx storage amount is small, the NOx reduction rate (corresponding to the NOx purification rate of the NOx storage catalyst), which is an index of the NOx purification performance, increases when the NOx storage amount is small, whereas the NOx storage amount is large. Then, the NOx reduction rate has a performance of rapidly decreasing. Therefore, in the internal combustion engine (hereinafter, the engine), the operation is switched to the rich operation in which the excess air ratio is low (low λ) such that the exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio or a value close to the stoichiometric air-fuel ratio before the NOx storage amount is saturated. In this way, a rich spike for periodically switching between the rich operation and the lean operation is performed. As a result, although the fuel efficiency is increased, the stored NOx is released and reduced to regenerate the NOx storage catalyst, and the exhaust gas is purified well. It is known that a NOx sensor disposed downstream of the NOx storage catalyst is used to detect the NOx storage amount.
[0004]
As described above, the regeneration is indispensable for the NOx storage catalyst, and in the regeneration, it is important to suppress the rich operation to a necessary minimum in order to suppress an increase in fuel consumption. In order to suppress the rich operation to the necessary minimum, it is necessary to accurately detect the NOx occlusion amount by the NOx sensor, and the NOx sensor is required to prevent damage or abnormal output. Required.
[0005]
Therefore, there has been proposed a technology of an exhaust gas purifying apparatus for correcting a shift in sensor output due to deterioration of a NOx sensor that detects the concentration of NOx in exhaust gas (for example, see Patent Document 1).
In this device, the correction is performed to eliminate the deviation between the sensor output when the concentration of NOx on the downstream side of the NOx storage catalyst becomes substantially zero and the actual sensor output, thereby improving the detection accuracy of NOx. It is planned.
[0006]
[Patent Document 1]
JP-A-2000-282942 (paragraph number 0010, FIG. 5, etc.)
[0007]
[Problems to be solved by the invention]
By the way, in the technology of the exhaust gas purifying device, the operating state in which the NOx concentration in the exhaust gas passing through the NOx storage catalyst becomes almost zero, such as a light load operation or a fuel cut operation at the time of idling, is detected, and the NOx concentration is detected. The correction is made as if the drift of the sensor output was reset.
[0008]
However, as described above, the NOx reduction rate fluctuates with respect to the NOx storage amount so that the purification performance suddenly decreases as the NOx storage amount increases, and the NOx sensor determines whether the NOx sensor is abnormal. In order to judge more accurately, it is necessary to consider that the NOx reduction rate changes according to the NOx storage amount.
That is, according to the conventional technique, when the NOx reduction rate is maintained constant without fluctuating, for example, when the NOx reduction rate is high, the NOx storage amount at that time does not change. Even if the above correction is performed without grasping the NOx concentration, the detection accuracy of the NOx concentration can be improved, but, for example, after the NOx storage amount increases and the NOx reduction rate starts to fluctuate, Even if the light load operation is performed, there is a possibility that the NOx concentration downstream of the NOx storage catalyst does not always become zero, and the detection accuracy of the NOx concentration can be improved even if the above correction is performed in such a situation. That is, there is a problem that the range in which the abnormality determination of the NOx sensor is possible is limited.
[0009]
In other words, in the conventional technique, the drift amount of the sensor output cannot be corrected unless the engine operation state in which the concentration of NOx in the exhaust gas that has passed through the NOx storage catalyst becomes almost zero is not reached. However, there is a problem that the abnormality determination time is limited, and the abnormality of the NOx sensor is easily overlooked.
FIG. 5B is a timing chart of the rich operation in the conventional device.
[0010]
As shown in the figure, the output of the NOx sensor disposed downstream of the NOx storage catalyst shows a small amount of NOx concentration along with the NOx storage amount during normal operation indicated by the solid line until switching from the lean operation to the rich operation. When the output is increased and then the operation is returned from the rich operation to the lean operation, the sensor output is output in a decreasing trend due to the reduction of NOx.
[0011]
Here, as described above, when the abnormality of the NOx sensor is overlooked, for example, when the output of the NOx sensor is abnormally indicated by a dashed line such that the output of the NOx sensor is detected lower, the NOx reduction rate is actually low, that is, NOx Although the storage amount is large and the regeneration of the NOx storage catalyst is required immediately, the NOx reduction rate is detected by the abnormality of the NOx sensor, that is, it is detected as if the NOx storage amount is still small, and the regeneration of the NOx storage catalyst is performed. Is erroneously determined to be unnecessary.
[0012]
That is, in order to properly regenerate the NOx storage catalyst based on the information from the NOx sensor, it is necessary to be able to appropriately determine the abnormality of the NOx sensor. However, there still remains a problem in that abnormality of the NOx sensor is reliably determined.
The present invention has been made in view of such a problem, and provides an abnormality determination device for a NOx sensor that can reliably determine an abnormality of a NOx sensor in order to appropriately reproduce a NOx storage catalyst. Aim.
[0013]
[Means for Solving the Problems]
To achieve the above object, an abnormality determination device for a NOx sensor according to claim 1 is provided in an exhaust passage of an internal combustion engine to store NOx in exhaust gas during a lean operation and perform rich operation of the stored NOx. A NOx storage catalyst that releases and reduces the NOx, a NOx sensor that is provided downstream of the NOx storage catalyst and detects the amount of NOx, and a NOx release unit that forcibly generates a state where NOx in the NOx storage catalyst is released. An actual NOx reduction rate calculating means for calculating an actual NOx reduction rate of the NOx storage catalyst in a state where NOx is released by the NOx releasing means, and a reference NOx reduction for presetting a reference NOx reduction rate according to an engine operating state. Rate setting means, and abnormality determination means for comparing the actual NOx reduction rate with a reference NOx reduction rate and determining an abnormality of the NOx sensor. It is characterized by a door.
[0014]
Therefore, according to the abnormality determination device for a NOx sensor according to the first aspect, in order to intentionally generate a fresh state in which the NOx storage catalyst hardly stores NOx, the condition in which the abnormality determination of the sensor can be performed is forcibly set. The abnormality determination of the NOx sensor is performed by comparing the actual NOx reduction rate with the reference NOx reduction rate in this state, so that the NOx reduction rate as the purification performance of the NOx storage catalyst is any value. However, a situation in which an abnormality can be determined can be created, and the abnormality can be determined over a wide range from a point in time when the NOx reduction rate is high to a point in time when the NOx reduction rate is low, without being restricted by the range in which the abnormality can be determined. Since the abnormality determination is always possible, the accuracy of the abnormality determination is further improved, whereby the NOx occlusion amount is more accurately grasped. Specifically, an increase in fuel efficiency due to an increase in the frequency of the rich operation and a decrease in the NOx reduction rate due to the fact that the rich operation is not performed are reliably suppressed.
[0015]
Further, the invention according to claim 2 is characterized in that the NOx releasing means performs the rich operation a plurality of times at short intervals and forcibly generates a state in which NOx in the NOx storage catalyst is released.
As a result, the heat load due to combustion is reduced as compared with the case where the rich operation is continued at a low λ, and even if a situation in which the heat load due to combustion can be increased by long-term NOx release processing occurs, black smoke is generated. Deterioration is prevented, and NOx in the NOx storage catalyst is almost certainly released.
[0016]
Further, the invention according to claim 3 is characterized in that the reference NOx reduction rate setting means presets a reference NOx reduction rate based on the catalyst temperature.
This makes it possible to accurately set the reference NOx reduction rate. Further, when the abnormality determination unit determines that the abnormality is abnormal, the NOx storage amount is estimated from the reference NOx reduction rate. An increase in fuel efficiency and a decrease in the NOx reduction rate are more reliably suppressed.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Referring to FIG. 1, there is shown an engine system configuration diagram including a diesel engine (hereinafter, simply referred to as an engine) 1 to which an abnormality determination device for a NOx sensor according to an embodiment of the present invention is applied. The configuration of the abnormality determination device for a NOx sensor according to the present invention will be described based on FIG.
[0018]
As shown in FIG. 1, a fuel supply system 16 having a fuel injection device and an intake passage for introducing fresh air (intake air) into the combustion chamber 4 by opening an intake valve 6 are provided in each cylinder 2 of the engine 1. 8 and an exhaust passage 20 through which exhaust gas from the combustion chamber 4 is led out by opening the exhaust valve 18.
An upstream side of the intake passage 8 is provided with a supercharger 14, and an air cleaner (not shown) is connected to a distal end of the intake passage 8. The intake passage 8 is provided with an air supply throttle 10 and an intercooler 12. The intercooler 12 cools fresh air passing through the intake passage 8 to increase its volumetric efficiency.
[0019]
On the other hand, a NOx storage catalyst 22 is connected downstream of the exhaust passage 20. The NOx storage catalyst 22 stores NOx in the exhaust gas when the exhaust air-fuel ratio is lean, and releases and reduces the stored NOx when the exhaust air-fuel ratio is rich and HC or CO is present in the exhaust gas. The NOx storage catalyst has a known configuration.
An exhaust gas circulation passage (EGR passage) 24 branches off and extends from the exhaust passage 20, and the tip of the EGR passage 24 is provided at the intake passage 8 on the downstream side of the position where the air supply throttle 10 is provided. It is connected to the passage 8. The EGR passage 24 recirculates a part of the exhaust gas (EGR gas) into the intake passage 8 to suppress the emission of NOx. The EGR passage 24 is provided with an EGR cooler 26 for cooling the EGR gas and an EGR valve 28 electrically connected to the ECU 36. The EGR valve 28 regulates the flow area of the EGR passage 24.
[0020]
The air supply throttle 10 is also electrically connected to the ECU 36, and the flow path area of the intake passage 8 is adjusted to adjust the amount of EGR gas at the time of in-cylinder rich operation. The air supply amount after merging with the passage 8 is adjusted.
Fresh air from the air cleaner enters the intake passage 8 via the supercharger 14, reaches the intercooler 12, is adjusted by the air supply throttle 10, and then joins with the EGR gas to form air supply to each cylinder 2 Is guided into the combustion chamber 4. Then, the combustion of the fuel supplied from the fuel supply system 16 causes the crankshaft 34 and the flywheel 35 to operate. When the combustion is completed, the exhaust gas is discharged to the exhaust passage 20 and sent to the NOx storage catalyst 22.
[0021]
Here, a NOx sensor 30 for detecting a NOx concentration, that is, a NOx amount based on an output voltage is disposed at an appropriate position downstream of the NOx storage catalyst 22 in the exhaust passage 20, and is electrically connected to the ECU 36. Have been. In the present embodiment, no NOx sensor is provided upstream of the NOx storage catalyst 22. This is because the NOx concentration on the inlet side of the NOx storage catalyst 22 is provided in the electronic control unit (ECU) 36 and is set based on a map previously obtained from engine operating conditions. However, the present invention is not necessarily limited to this embodiment. In order to detect the concentration of NOx on the inlet side of the NOx storage catalyst 22, a separate NOx sensor may be provided upstream of the NOx storage catalyst 22.
[0022]
In addition to the NOx sensor 30 described above, various sensors for detecting the operating state of the engine 1, such as the crank angle sensor 32, are electrically connected to the input side of the ECU. On the other hand, on the output side of the ECU 36, various actuators such as the fuel supply system 16, the air supply throttle 10, and the EGR valve 28 are electrically connected. Further, alarm means 42 for notifying the driver of the abnormality of the NOx sensor 30 is also connected.
[0023]
Then, the ECU 36 stores NOx in the exhaust gas in the oxidizing atmosphere in the NOx storage catalyst 22 while periodically performing the rich operation. That is, the NOx storage catalyst 22 is regenerated by periodically keeping the engine 1 constant in the low λ state and releasing and reducing the stored NOx in a reducing atmosphere. As the rich operation in the present embodiment, a large amount of EGR is performed, that is, the condition of the rich operation is created by using the EGR valve 28 and the air supply throttle 10 and in-cylinder rich utilizing the emission of carbon monoxide due to incomplete combustion. If this condition is satisfied, NOx is released and reduced.
[0024]
Here, the ECU 36 includes a NOx releasing section (NOx releasing means) 38 for forcibly generating a state in which NOx in the NOx storage catalyst 22 is released as much as possible, and a state in which NOx is released by the NOx releasing section 38. An actual NOx reduction rate calculation unit for calculating an actual NOx reduction rate of the NOx storage catalyst 22, and a reference NOx reduction rate setting for presetting a reference NOx reduction rate from the catalyst temperature of the NOx storage catalyst 22 and the exhaust gas flow rate (SV). And an abnormality determination unit (abnormality determination unit) 40 that compares the actual NOx reduction rate with the reference NOx reduction rate and determines whether the NOx sensor 30 is abnormal. When it is determined that 30 is abnormal, the abnormal NOx storage amount estimating unit estimates the NOx storage amount from the reference NOx reduction ratio by the reference NOx reduction ratio setting unit. It is equipped with a door.
[0025]
FIG. 2 shows a flowchart of abnormality determination control in the NOx sensor abnormality determination device. Hereinafter, a control procedure of the NOx sensor abnormality determination device configured as described above will be described.
As shown in the drawing, in step S201, it is determined whether or not the traveling distance of the vehicle equipped with the engine 1 exceeds a predetermined specified distance. This is to determine the time when the abnormality determination of the NOx sensor 30 is performed, and the determination may be made based on the travel time in addition to the determination based on the travel distance. When it is determined that the traveling distance of the vehicle exceeds a predetermined specified distance that requires the determination of an abnormality of the NOx sensor 30, that is, when the determination is YES, the process proceeds to step S202. If it is determined that there is no such distance, the above determination is repeated until the distance exceeds the predetermined distance.
[0026]
In step S202, the NOx releasing unit 38 continuously performs the rich operation with a short interval between the rich operations a plurality of times to completely release and reduce the NOx stored in the NOx storage catalyst 22. In other words, the NOx storage catalyst 22 is forcibly made to be in a fresh state so as to positively create a situation where an abnormality can be determined.
FIG. 3 shows a time chart in a case where the rich operation is performed at the time of abnormality determination in the NOx releasing unit 38.
[0027]
As described above, during the general regeneration of the NOx storage catalyst 22, the rich operation is performed on the engine 1 while the low λ state is kept constant, whereas the rich operation when the NOx emission unit 38 determines that there is an abnormality is performed. As shown in the figure, when the abnormality of the NOx sensor 30 is determined, the intermittent rich operation with a short interval is performed, that is, the low λ state and the high λ state other than the low λ state are frequently repeated with respect to the engine 1. To make it work.
[0028]
More specifically, the rich operation at the time of abnormality determination of the NOx sensor 30 in the NOx releasing unit 38 is performed by dividing a period in which the rich operation is performed once during the general regeneration of the NOx storage catalyst 22 into substantially equal intervals, and dividing the period. The NOx storage catalyst 22 is regenerated by repeatedly performing the rich operation at a short interval as described above a plurality of times. For example, as shown in the figure, the period in which the rich operation at the time of the general regeneration is performed once is divided into 11 at substantially equal intervals, and the rich operation with the short interval is performed six times in order to reduce the NOx storage catalyst 22. Play it.
[0029]
In this way, even when a long-term rich operation is required to cause the abnormality determination state of the NOx sensor 30, a case where the rich operation is continued in the low λ state is performed. As a result, the heat load due to combustion is reduced, and while preventing the deterioration of black smoke, the NOx storage amount is gradually reduced to forcibly bring the NOx storage catalyst 22 into a fresh state, thereby actively creating a situation in which abnormality can be determined. You can do so.
[0030]
In step S203, the actual NOx reduction rate calculation unit calculates the actual NOx reduction rate from the upstream and downstream NOx concentrations in the fresh NOx storage catalyst 22 under the normal lean operating conditions of the engine 1. η (actual value) is calculated as in the following equation (1), and the process proceeds to step S204.
η = (NOx concentration on the inlet side−NOx concentration on the outlet side) / NOx concentration on the inlet side ... (1)
Here, the NOx concentration on the inlet side is set based on the map value stored in the ECU 36, and the NOx concentration on the outlet side is detected by the NOx sensor 30.
[0031]
In step S204, the catalyst temperature of the NOx storage catalyst 22 and the exhaust gas flow rate (SV) are read. In step S205, the reference NOx reduction rate setting unit sets the reference NOx reduction rate based on the catalyst temperature of the NOx storage catalyst 22 and SV. (Reference value) is set using a reference value setting map.
FIG. 4 is a diagram showing a reference value setting map in the reference NOx reduction rate setting section.
[0032]
As described above, the reference NOx reduction rate, which is the reference value, is set in advance in the reference value setting map provided in the ECU 36 based on the catalyst temperature of the NOx storage catalyst 22 and the SV. That is, when the catalyst temperature and the SV are detected from the operating state of the engine 1, the reference NOx reduction rate setting section sets a point on a curved surface of a three-dimensional reference value setting map as a reference value.
[0033]
The reference value may be set in advance from the exhaust gas temperature in the exhaust passage 20 and the SV, instead of the catalyst temperature of the NOx storage catalyst 22.
In step S206, the abnormality determination unit 40 compares the actual value with the reference value, specifically, determines whether or not the actual value is equal to the reference value. Then, when it is determined that the actual value does not greatly deviate from the reference value as the reference curved surface and the actual value is equal to the reference value, that is, when the determination is YES, the process proceeds to step S207, and the NOx sensor 30 is determined to be normal. Make a judgment and prepare for the next abnormality judgment.
[0034]
On the other hand, if it is determined in step S206 that the actual value greatly deviates from the reference value and the actual value is not equal to the reference value, the process proceeds to step S208, where the NOx sensor 30 is determined to be abnormal, Proceed to step S209. The abnormality of the NOx sensor 30 includes a case where the actual value is larger than the reference value and a case where the actual value is smaller than the reference value. If the actual value is larger than the reference value, it is determined that the NOx sensor 30 is output lower, whereas if the actual value is smaller than the reference value, it is determined that the NOx sensor 30 is output higher. I do.
[0035]
In step S209, the abnormality determination unit 40 outputs a signal to the alarm unit 42 to notify the driver of the abnormality of the NOx sensor 30, and the process proceeds to step S210.
In step S210, since there is an abnormality in the NOx sensor 30, the abnormality determining unit 40 uses the above-described reference value for estimating the NOx occlusion amount with respect to the abnormal-time NOx occlusion amount estimating unit. Command not to use the value and prepare for the next abnormality judgment.
[0036]
As described above, in the present invention, since the NOx releasing unit 38 that forcibly generates a fresh state in which NOx is not stored in the NOx storage catalyst 22 is provided, the NOx storing catalyst 22 is not restricted by the range in which abnormality can be determined. The abnormality determination of the NOx sensor 30 can be always performed in response to the abnormality determination request.
In addition, when the NOx release unit 38 determines that the NOx sensor 30 is abnormal, the NOx release unit 38 performs a plurality of rich operations that cause the engine 1 to frequently repeat the low λ state and the high λ state. Even if a long-term rich operation is necessary in the occurrence of the abnormality determination situation, the deterioration of black smoke can be prevented as compared to a case where the rich operation is continued in the low λ state.
[0037]
In addition, since a reference NOx reduction rate setting unit that presets a reference NOx reduction rate from the catalyst temperature and SV of the NOx storage catalyst 22 is provided, an accurate reference value can be set.
Further, when the abnormality determination unit 40 determines that the NOx sensor 30 is abnormal, the abnormal operation NOx storage amount estimation unit that estimates the NOx storage amount from the reference value is provided. Can be reliably prevented.
[0038]
Further, when the abnormality determination unit 40 determines that the NOx sensor 30 is abnormal, the alarm means 42 for notifying the abnormality of the NOx sensor 30 is provided. Can respond.
Thereby, it is possible to perform appropriate regeneration of the NOx storage catalyst 22 based on the information from the NOx sensor 30.
[0039]
The description of one embodiment of the present invention is finished above, but the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention.
For example, in the method of enrichment, rich operation is performed by a large amount of EGR as in the present embodiment, and in-cylinder rich utilizing the emission of carbon monoxide due to incomplete combustion, and unburned fuel (HC) during the exhaust stroke. The in-cylinder rich supplied by post injection or the out-of-cylinder rich supplied HC to the NOx storage catalyst may be used.
[0040]
Further, a diesel engine is preferable, but the present invention is not limited to this. The NOx sensor abnormality determination device of the present invention can be applied to all engine systems that include a NOx storage catalyst in an exhaust passage and can perform a rich operation. it can.
[0041]
【The invention's effect】
As can be understood from the above description, according to the abnormality determination device for a NOx sensor of the present invention described in claim 1, in order to intentionally generate a fresh state in which the NOx storage catalyst hardly stores NOx. Since a situation in which the sensor abnormality determination is performed is forcibly generated, and in this state, the actual NOx reduction rate is compared with the reference NOx reduction rate to determine the abnormality of the NOx sensor, the purification performance of the NOx storage catalyst is determined. It is possible to create a situation in which an abnormality can be determined regardless of the value of the NOx reduction rate, and the abnormality determination can be performed over a wide range from a time point when the NOx reduction rate is high to a time point when the NOx reduction rate is low, without being restricted by the range in which the abnormality can be determined. It can be performed.
[0042]
Therefore, the abnormality determination accuracy can be further improved because the abnormality determination can always be performed, and as a result, the NOx storage amount can be grasped more accurately. Specifically, it is possible to reliably suppress an increase in fuel efficiency due to an increase in the frequency of the rich operation and a decrease in the NOx reduction rate due to the fact that the rich operation is not performed.
Further, according to the second aspect of the present invention, the heat load due to combustion is reduced as compared with the case where the rich operation is continued at a low λ, and the heat load due to combustion can be increased, for example, due to the long-term rich operation. Even if a situation arises, the deterioration of black smoke can be prevented.
[0043]
Furthermore, according to the third aspect of the present invention, it is possible to accurately set the reference NOx reduction rate, and when the abnormality determination means determines that there is an abnormality, the reference NOx reduction rate is calculated from the reference NOx reduction rate. By estimating the NOx storage amount, it is possible to more reliably suppress the increase in the fuel efficiency and the decrease in the NOx reduction rate.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an engine system to which an abnormality determination device for a NOx sensor according to an embodiment of the present invention is applied.
FIG. 2 is a control flowchart in the NOx sensor abnormality determination device of FIG. 1;
FIG. 3 is a timing chart of the rich operation at the time of abnormality determination in the abnormality determination device of the NOx sensor of FIG. 1;
FIG. 4 is a diagram showing a reference value setting in the abnormality determination device for the NOx sensor of FIG. 1;
FIG. 5A is a diagram showing the performance of a NOx storage catalyst, and FIG. 5B is a timing chart of a rich operation in a conventional device.
[Explanation of symbols]
22 NOx storage catalyst 30 NOx sensor 36 Electronic control unit (ECU)
38 NOx emission part (NOx emission means)
40 abnormality judgment unit (abnormality judgment means)

Claims (3)

A NOx storage catalyst that is provided in an exhaust passage of the internal combustion engine and stores NOx in exhaust gas during a lean operation and releases and reduces the stored NOx by performing a rich operation;
A NOx sensor that is provided downstream of the NOx storage catalyst and that detects the amount of NOx;
NOx releasing means for forcibly generating a state of releasing NOx in the NOx storage catalyst;
Actual NOx reduction rate calculation means for calculating an actual NOx reduction rate of the NOx storage catalyst in a state where NOx is released by the NOx release means;
Reference NOx reduction rate setting means for presetting a reference NOx reduction rate according to an engine operating state;
Abnormality determining means for comparing the actual NOx reduction rate with the reference NOx reduction rate and determining an abnormality of the NOx sensor;
An abnormality determination device for a NOx sensor, comprising: 2. The NOx sensor abnormality determination device according to claim 1, wherein the NOx releasing means performs the rich operation a plurality of times at short intervals to forcibly generate a state in which NOx in the NOx storage catalyst is released. . 3. The NOx sensor abnormality determination device according to claim 1, wherein the reference NOx reduction rate setting means sets the reference NOx reduction rate in advance based on a catalyst temperature.

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