JP2015010589A - Abnormality diagnostic device for exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abnormality diagnostic device for an exhaust emission control device, in which the drop in diagnostic accuracy is suppressed.SOLUTION: In an abnormality diagnostic device for an exhaust emission control device for diagnosing an abnormality of an exhaust emission control device containing an SCR catalyst, a threshold value and a correction coefficient are set on the basis of an intermediate characteristic between a purification characteristic at the time when the exhaust emission control device is normal and a purification characteristic at the time when the exhaust emission control device is abnormal, and the NOpurification rate calculated by using the NOoutflow as a parameter is corrected by said correction coefficient. The abnormality diagnostic device of the exhaust emission control device compares the NOx purification rate after correction and said threshold value thereby diagnosing abnormality of the exhaust emission control device.

Description

  The present invention relates to a technique for diagnosing abnormality of an exhaust purification device disposed in an exhaust passage of an internal combustion engine.

As a method of diagnosing an abnormality in the exhaust purification device including the selective catalytic reduction catalyst, the NO _X purification rate (the ratio of the amount of NO _X purified by the exhaust purification device to the amount of NO _X flowing into the exhaust purification device) and A method for comparing the threshold value is known. In such a method, is determined in advance a threshold for each temperature of the exhaust purification device has been proposed a method using a threshold value corresponding to the temperature at which the NO _X purification rate was determined. Furthermore, a correction coefficient is obtained based on the temperature-based operation time of the exhaust purification device, NO _X purification rate has been proposed a method of correcting the threshold value using a correction coefficient corresponding to the temperature at which is calculated (e.g. , See Patent Document 1).

JP 2006-037770 A JP-A-10-311213 US Pat. No. 8,245,567

However, NO _X purification rate may exhibit properties that differ in the normal state and abnormal. For this reason, if the threshold value is set in accordance with either the normal or abnormal characteristics, there is a possibility that the diagnostic accuracy may be lowered.

  The present invention has been made in view of the above situation, and an object thereof is to suppress a decrease in diagnostic accuracy in an abnormality diagnosis device for an exhaust purification device.

The present invention employs the following means in order to solve the above-described problems. That is, the present invention provides an exhaust purification device disposed in an exhaust passage of an internal combustion engine,
Measuring means for measuring the amount of a specific component contained in the exhaust gas flowing out from the exhaust purification device;
Calculation means for calculating a performance value that is a numerical value correlated with the purification performance of the exhaust purification device using the measurement value of the measurement means;
Diagnosing means for diagnosing an abnormality of the exhaust purification device by comparing the performance value calculated by the calculating means with a threshold value;
In the exhaust gas purification apparatus abnormality diagnosis device comprising
Means for storing a purification characteristic which is data indicating a correlation between the performance value and an environmental parameter affecting the performance value, the normal characteristic being a purification characteristic when the exhaust purification device is normal; First storage means for storing an intermediate characteristic that is an intermediate purification characteristic with an abnormal characteristic that is a purification characteristic when the exhaust purification device is abnormal;
Second storage means for storing a performance value corresponding to a value of a specific environmental parameter in the intermediate characteristic as a specified value;
First acquisition means for acquiring a first correction coefficient that is a correction coefficient for correcting the intermediate characteristic such that a performance value in the intermediate characteristic becomes a constant value equal to the specified value;
Setting means for setting the threshold based on two purification characteristics obtained by correcting the normal characteristics and the abnormal characteristics with the first correction coefficient;
Second acquisition means for acquiring the value of the environmental parameter when the measurement means measures the amount of the specific component;
Third acquisition means for deriving a performance value corresponding to the value of the environmental parameter acquired by the second acquisition means from the intermediate characteristic, and acquiring a ratio of the specified value to the derived performance value as a second correction coefficient; ,
Further comprising
The diagnosis unit corrects the performance value by multiplying the performance value calculated by the calculation unit and the second correction coefficient, and compares the corrected performance value with a threshold set by the setting unit. By doing so, the abnormality of the exhaust emission control device is diagnosed.

  According to the abnormality diagnosis device for the exhaust gas purification apparatus configured as described above, the threshold value is set based on an intermediate characteristic between the normal time characteristic and the abnormal time characteristic of the exhaust purification device. Therefore, the accuracy of abnormality diagnosis can be improved as compared with the case where the threshold value is set based on either the normal characteristic or the abnormal characteristic of the exhaust purification device. In particular, it is possible to improve the abnormality diagnosis accuracy when the normal characteristic and the abnormal characteristic tend to be different.

  Further, the performance value calculated by the calculation means is corrected by a second correction coefficient that is a ratio between the intermediate characteristic and the specified value, and the abnormality value of the exhaust gas purification apparatus is diagnosed by comparing the corrected performance value with a threshold value. Accordingly, it is possible to suppress a decrease in diagnostic accuracy due to the influence of environmental parameters.

  By the way, an error may be included in the measured value of the measuring means. Therefore, the normal characteristic and the abnormal characteristic used when determining the intermediate characteristic and the threshold value may be a purification characteristic that takes into account the measurement error of the measuring means. For example, the normal characteristic may be data indicating the correlation between the minimum value that can be taken by the performance value within the range of the measurement error of the measuring means and the environmental parameter. On the other hand, the abnormal characteristic may be data indicating the correlation between the maximum value that can be taken by the performance value within the range of the measurement error of the measuring means and the environmental parameter. When the normal characteristic and the abnormal characteristic are determined in this way, it is possible to perform an accurate abnormality diagnosis even when an error is included in the measurement value of the measuring means.

The abnormality diagnosis device for an exhaust gas purification apparatus according to the present invention is suitable for diagnosing an abnormality in an exhaust gas purification apparatus that includes a selective catalytic reduction catalyst. As a measurement means in that case, a NO _X sensor that measures the amount of NO _X contained in the exhaust gas can be used. Further, the performance value calculated by the calculating means includes a NO _X purification rate (a ratio of the amount of NO _X purified by the selective reduction catalyst to the amount of NO _X flowing into the selective reduction catalyst), NO _X A purification amount (amount of NO _x purified by the selective reduction catalyst) can be used. (Proportion of NO ₂ in the NO _X in the exhaust gas) as the environmental parameters that affect the NO _X purification performance of the selective reduction catalyst, the temperature of the selective reduction catalyst, NO ₂ ratio of the exhaust gas flowing into the selective reduction catalyst, The amount of NO _X flowing into the selective reduction catalyst can be used. In particular, since the temperature of the selective reduction catalyst has a large influence to the NO _X purification performance of the selective reduction catalyst, it is preferable that a temperature of at least the selective reduction catalyst is used as the environmental parameter.

  ADVANTAGE OF THE INVENTION According to this invention, in the abnormality diagnostic apparatus of the exhaust gas purification apparatus which diagnoses abnormality of the exhaust gas purification apparatus arrange | positioned in the exhaust passage of an internal combustion engine, the fall of diagnostic accuracy can be suppressed.

It is a figure which shows schematic structure of the internal combustion engine to which this invention is applied, and its exhaust system. It is a figure which shows the intermediate characteristic of the characteristic at the time of normal time, and the characteristic at the time of abnormality, and the setting method of a regulation value. It is a figure which shows the method of correct | amending an intermediate characteristic using a 1st correction coefficient. It is a figure which shows the method of correct | amending the characteristic at the time of a normal time and the characteristic at the time of abnormality using a 1st correction coefficient, and the setting method of a threshold value. In consideration of the measurement error of the NO _X sensor is a diagram showing an example of setting the intermediate characteristic of the normal-state characteristic and abnormal characteristics. FIG. 6 is a diagram illustrating an example in which normal characteristics and abnormal characteristics shown in FIG. 5 are corrected by a first correction coefficient. It is a flowchart which shows the process routine performed by ECU when abnormality diagnosis processing is implemented. It is a figure which shows the characteristic at the time of abnormality when abnormality generate | occur | produces in an addition valve or a pump. NO _X purification performance of the SCR catalyst is a diagram showing an abnormal characteristics when deteriorated. It is a diagram showing a setting method of the intermediate characteristic in the case of using the NO ₂ ratio as an environment parameter. It is a figure which shows the example which correct | amended the normal time characteristic and the abnormal time characteristic shown in FIG. 10 with the 1st correction coefficient.

  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 internal combustion engine to which the present invention is applied and its exhaust system. An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) or a spark ignition type internal combustion engine (gasoline engine) capable of lean combustion (lean burn operation).

  An exhaust passage 2 is connected to the internal combustion engine 1. The exhaust passage 2 is a passage for circulating burned gas (exhaust gas) discharged from the cylinder of the internal combustion engine 1. In the middle of the exhaust passage 2, a first catalyst casing 3 and a second catalyst casing 4 are arranged in series from the upstream side.

  The first catalyst casing 3 includes, for example, an oxidation catalyst and a particulate filter inside a cylindrical casing. In that case, the oxidation catalyst may be carried on a catalyst carrier disposed upstream of the particulate filter, or may be carried on the particulate filter.

The second catalyst casing 4 accommodates a catalyst carrier on which a selective reduction catalyst (SCR (Selective Catalytic Reduction) catalyst) is supported in a cylindrical casing. The catalyst carrier is composed of, for example, an alumina-based or zeolite-based active component (support) on a monolith type substrate having a honeycomb-shaped cross section formed of cordierite, Fe-Cr-Al heat-resistant steel, or the like. It is a coated one. Note that a catalyst carrier on which an oxidation catalyst is supported may be disposed downstream of the SCR catalyst in the second catalyst casing 4. In this case, the oxidation catalyst is a catalyst that oxidizes an additive that has passed through the SCR catalyst among the additives supplied to the SCR catalyst from the addition valve 5 described later.

An addition valve 5 for adding (injecting) ammonia (NH ₃ ) or an additive that is a precursor of NH ₃ into the exhaust passage 2 between the first catalyst casing 3 and the second catalyst casing 4. Is arranged. The addition valve 5 is a valve device having a nozzle hole that is opened and closed by the movement of the needle. The addition valve 5 is connected to an additive tank 51 via a pump 50. The pump 50 sucks the additive stored in the additive tank 51 and pumps the sucked additive to the addition valve 5. The addition valve 5 injects the additive pumped from the pump 50 into the exhaust passage 2. The opening / closing timing of the addition valve 5 and the discharge pressure of the pump 50 are electrically controlled by an electronic control unit (ECU) 9.

Here, the additive stored in the additive tank 51 is NH ₃ gas or an aqueous solution such as urea or ammonium carbamate. In this embodiment, an aqueous urea solution is used as the additive.

When the urea aqueous solution is injected from the addition valve 5, the urea aqueous solution flows into the second catalyst casing 4 together with the exhaust gas. At that time, the urea aqueous solution is thermally decomposed by the heat of the exhaust or is hydrolyzed by the SCR catalyst. When the urea aqueous solution is thermally decomposed or hydrolyzed, NH ₃ is generated. The NH ₃ thus generated is adsorbed or occluded by the SCR catalyst. NH ₃ adsorbed or occluded by the SCR catalyst reacts with nitrogen oxide (NO _x ) contained in the exhaust gas to generate nitrogen (N ₂ ) or water (H ₂ O). That is, NH ₃ functions as a NO _X reducing agent.

  Here, the SCR system including the second catalyst casing 4, the addition valve 5, the pump 50, and the additive tank 51 corresponds to the exhaust purification apparatus according to the present invention.

The internal combustion engine 1 configured as described above is provided with an ECU 9. The ECU 9 is an electronic control unit that includes a CPU, ROM, RAM, backup RAM, and the like. Various sensors such as a first NO _X sensor 6, a second NO _X sensor 7, an exhaust temperature sensor 8, a crank position sensor 10, an accelerator position sensor 11, and an air flow meter 12 are electrically connected to the ECU 9.

The first NO _X sensor 6 is disposed in the exhaust passage 2 between the first catalyst casing 3 and the second catalyst casing 4, and the amount of NO _X contained in the exhaust gas flowing into the second catalyst casing 4 (hereinafter referred to as “NO NO”). _The electric signal correlated with the “ _X inflow amount” is output. Second NO _X sensor 7 is arranged from the second catalyst casing 4 in the exhaust passage 2 downstream, the amount of the NO _X flowing out from the second catalyst casing 4 (hereinafter, referred to as "NO _X outflow") correlates with Outputs electrical signals. The exhaust temperature sensor 8 is disposed in the exhaust passage 2 downstream from the second catalyst casing 4 and outputs an electrical signal correlated with the temperature of the exhaust gas flowing out from the second catalyst casing 4. The crank position sensor 10 outputs an electrical signal correlated with the rotational position of the output shaft (crankshaft) of the internal combustion engine 1. The accelerator position sensor 11 outputs an electrical signal that correlates with the operation amount of the accelerator pedal (accelerator opening). The air flow meter 12 outputs an electrical signal correlated with the amount (mass) of air taken into the internal combustion engine 1.

  The ECU 9 is electrically connected to various devices (for example, a fuel injection valve) attached to the internal combustion engine 1, the addition valve 5, the pump 50, and the like. The ECU 9 electrically controls various devices of the internal combustion engine 1, the addition valve 5, the pump 50, and the like based on the output signals of the various sensors described above. For example, the ECU 9 executes processing for diagnosing an abnormality of the SCR system (abnormality diagnosis processing) in addition to known control such as fuel injection control of the internal combustion engine 1 and addition control for intermittently injecting the additive from the addition valve 5. To do.

Hereinafter, an execution method of the abnormality diagnosis process in the present embodiment will be described.
First, the ROM of the ECU 9 stores a purification characteristic (intermediate characteristic) between a purification characteristic when the SCR system is normal (normal purification characteristic) and a purification characteristic when the SCR system is abnormal (abnormal purification characteristic). ) Is stored in advance.

The purification characteristics here are data (map or functional expression) indicating the correlation between a numerical value (performance value) correlated with the purification performance of the SCR catalyst and an environmental parameter that affects the purification performance of the SCR catalyst. is there. Performance value, NO _X purification rate of the SCR catalyst and (ratio of the amount of the NO _X which has been purified by the SCR catalyst with respect to the amount of the NO _X flowing into the SCR catalyst), the NO _X purification amount (SCR catalyst of the SCR catalyst Amount of purified NO _x ).

The environmental parameters include the bed temperature of the SCR catalyst, the flow rate of the exhaust gas flowing into the SCR catalyst, the amount of NO _X flowing into the SCR catalyst, the NO ₂ ratio of the exhaust gas flowing into the SCR catalyst (with respect to the amount of NO _X contained in the exhaust gas). The ratio of the amount of NO ₂ contained in the exhaust gas). In this embodiment, an example of using the NO _X purification rate as the performance value. Also, of the environmental parameters described above, likely environmental parameters most affected in the NO _X purification rate is the bed temperature of the SCR catalyst. Therefore, the bed temperature of the SCR catalyst is used as the environmental parameter.

FIG. 2 is a diagram illustrating an example of intermediate characteristics. The vertical axis in Figure 2 shows the NO _X purification rate Enox of the SCR catalyst, the horizontal axis in FIG. 2 shows a bed temperature of the SCR catalyst. Also, the solid line in FIG. 2 indicates the intermediate characteristic, the alternate long and short dash line indicates the normal characteristic, and the dotted line indicates the abnormal characteristic. Intermediate characteristic, as shown in FIG. 2, is determined as NO _X purification rate at each bed temperature is greater than the NO _X purification rate of small and abnormal properties than NO _X purification rate of the normal state characteristic. The ROM for storing such intermediate characteristics corresponds to the first storage means according to the present invention.

ECU9 of ROM stores NO _X purification rate corresponding to a particular bed temperature in the intermediate characteristic as defaults. In the example shown in FIG. 2, NO _X purification rate Enox1 when the bed temperature is a specific temperature T1 is stored as a specified value. The specific temperature T1 is an arbitrarily determined temperature and may be any temperature as long as the bed temperature of the SCR catalyst can be taken. The ROM that stores the specified value Enox1 corresponds to the second storage unit according to the present invention.

  A threshold value used for abnormality diagnosis processing is stored in advance in the ROM of the ECU 9. Here, a threshold value setting method will be described. It is assumed that the threshold is set before shipment of the vehicle on which the internal combustion engine 1 is mounted.

First, a correction coefficient (first correction coefficient) for correcting the intermediate characteristic is obtained so that the NO _X purification rate of the intermediate characteristic becomes a constant value equal to the specified value Enox1 (first acquisition means). The first correction coefficient, as NO _X purification rate Enox for each bed temperature of the intermediate characteristic is equal to the specified value Enox1, a coefficient for correcting the NO _X purification rate Enox each bed temperature, bed temperature Can be obtained by a function expression using as an argument. For example, as shown in FIG. 3, for NO _X purification rate Enox2 when bed temperature is T2 is smaller than the prescribed value Enox1, first correction coefficient when bed temperature is T2 "1" to a value greater than Become. Further, NO _X purification rate Enox3 when bed temperature is T3 because greater than the specified value Enox1, first correction coefficient when bed temperature is T3 becomes "1" smaller value. The first correction coefficient when the bed temperature is the specific temperature T1 is “1”.

When the first correction coefficient is obtained by the above procedure, the normal characteristic and the abnormal characteristic are corrected using the first correction coefficient. In the example shown in FIG. 3, the first correction coefficient is a value larger than “1” when the bed temperature is lower than T1, and is a value smaller than “1” when the bed temperature is higher than T1. Therefore, as shown in FIG. 4, the bed temperature is in the range below T1, NO _X purification rate and NO _X purification rate of abnormal properties of the normal-state characteristic is increased corrected. On the other hand, bed temperature in the range higher than T1, NO _X purification rate and NO _X purification rate of abnormal properties of the normal-state characteristic is reduced corrected. However, since the NO _X purification rate of the abnormal characteristic has a smaller absolute value than the NO _X purification rate of the normal characteristic, the correction amount of the abnormal characteristic is smaller than the correction amount of the normal characteristic. When the normal characteristic and the abnormal characteristic are corrected as indicated by the solid line in FIG. 4, a threshold value is set based on the corrected normal characteristic and the corrected abnormal characteristic (setting means). For example, to identify the differences is smallest bed temperature of the NO _X purification rate of the corrected abnormal characteristics and NO _X purification rate of the corrected normal time characteristic, NO _X purification rate of the normal-time characteristic after the correction of the bed temperature an intermediate value between the NO _X purification rate of the corrected abnormal characteristics (dashed line in FIG. 4) may be set as the threshold value.

By the way, an error may be included in the measured values of the first NO _X sensor 6 and the second NO _X sensor 7. Therefore, as shown in FIG. 5, the normal characteristics are determined using the minimum NO _X purification rate within the range of errors included in the measured values of the first NO _X sensor 6 and the second NO _X sensor 7. Is desirable (“minimum normal characteristic” in FIG. 5). On the other hand, the abnormal characteristics are preferably determined using the maximum NO _X purification rate within the range of errors included in the measured values of the first NO _X sensor 6 and the second NO _X sensor 7 (in FIG. 5). "Maximum abnormal characteristics"). With such normal time characteristics and abnormal characteristics defined, there is a case where NO _X purification rate equals the bed temperature of the NO _X purification rate and abnormal characteristics of the normal time characteristic (T0 in FIG. 5) is present . Intermediate characteristic of such cases, it is assumed that the bed temperature is defined as NO _X purification rate when a T0 becomes equal to the NO _X purification rate of the normal-time characteristic (NO _X purification rate of abnormal properties) .

When normal operation characteristics and abnormal characteristics as shown in FIG. 5 is corrected by the first correction coefficient, NO _X purification rate of abnormal characteristics after correction and NO _X purification rate of normal time characteristics after correction, As shown in FIG. 6, when the bed temperature is T0, it becomes equal to the specified value Enox1. Therefore, the threshold value may be set to a value equal to the specified value Enox1.

  Next, a method for executing the abnormality diagnosis process using the threshold value will be described with reference to FIG. FIG. 7 is a flowchart showing a processing routine executed by the ECU 9 when the abnormality diagnosis process of the SCR system is performed. The processing routine shown in FIG. 7 is stored in advance in the ROM of the ECU 9 and is periodically executed by the ECU 9 (CPU) during the operation of the internal combustion engine 1.

In the processing routine of FIG. 7, the ECU 9 determines whether or not an execution condition for the abnormality diagnosis processing is satisfied in the processing of S101. The execution conditions of the abnormality diagnosis process are conditions such that the internal combustion engine 1 is in a warm-up completion state, the SCR catalyst is in an active state, and the first NO _X sensor 6 and the second NO _X sensor 7 are in an active state. Can be illustrated. If a negative determination is made in the process of S101, the ECU 9 once ends the execution of this process routine. On the other hand, when an affirmative determination is made in the process of S101, the ECU 9 proceeds to the process of S102.

In the process of S102, the ECU 9 determines whether NO _X purification rate of the selective reduction catalyst is stable. Specifically, ECU 9 determines that the internal combustion engine 1 is not in a transient operating condition, such as an acceleration operating state or decelerating state, NO _X purification rate of the selective reduction catalyst is stable. If a negative determination is made in the processing of S102, the ECU 9 once ends the execution of this processing routine. On the other hand, when an affirmative determination is made in the process of S102, the ECU 9 proceeds to the process of S103.

In the process of S103, the ECU 9 is the measured value of the first NO _X sensor 6 (NO _X inflow) Anoxin, measurement of the second NO _X sensor 7 (NO _X outflow) Anoxout, and measurements of the exhaust gas temperature sensor 8 (Exhaust temperature) Tex is read.

In the process of S104, the ECU 9 calculates the NO _X purification rate Enox using the NO _X inflow amount Anoxin and the NO _X outflow amount Anoxout read in the process of S103. Specifically, the ECU 9 calculates the NO _X purification rate Enox by substituting the NO _X inflow amount Anoxin and the NO _X outflow amount Anoxout into the following equation (1).
Enox = 1− (Anoxout / Anoxin) (1)
It should be noted that the calculation means according to the present invention is realized by the ECU 9 executing the process of S104.

In the process of S105, the ECU 9 calculates the second correction coefficient C2. Specifically, ECU 9 is first to derive the NO _X purification rate corresponding to the bed temperature of the SCR catalyst in the intermediate characteristics stored in the ROM. Here, the bed temperature of the SCR catalyst is the bed temperature of the SCR catalyst when the NO _X inflow amount Anoxin and the NO _X outflow amount Anoxout are measured. Note that the bed temperature of the SCR catalyst correlates with the measured value of the exhaust temperature sensor 8. Therefore, ECU 9 derives NO _X purification rate corresponding to the exhaust temperature Tex read in the process of the S103. In this case, the ECU 9 executes the process of S103, thereby realizing the second acquisition unit according to the present invention. Then, ECU 9 reads the specified value Enox1 from ROM, and calculates a ratio of the prescribed value Enox1 for NO _X purification rate derived from the intermediate characteristic (second correction factor C2). The ECU 9 executes the process of S105, thereby realizing the third acquisition unit according to the present invention.

In the process of S106, the ECU 9, by multiplying the second correction factor C2 calculated in NO _X purification rate Enox and the S105 calculated in the processing of the S104, it corrects the NO _X purification rate.

In the process of S107, the ECU 9 reads the threshold value stored in ROM, NO _X purification rate Enox corrected in the processing of the S106 it is determined whether a threshold value or more. If an affirmative determination is made in step S107, the ECU 9 proceeds to step S108 and diagnoses that the SCR system is normal. On the other hand, when a negative determination is made in the process of S107, the ECU 9 proceeds to the process of S109 and diagnoses that the SCR system is abnormal.

  It should be noted that the diagnosis means according to the present invention is realized by the ECU 9 executing the processes of S106 to S109.

When the abnormality diagnosis process is executed by the method described above, the threshold is set based on an intermediate characteristic between the normal characteristic and the abnormal characteristic, and therefore the threshold is set based on either the normal characteristic or the abnormal characteristic. The accuracy of abnormality diagnosis can be increased compared to the case where it is set. In particular, it is possible to increase the accuracy of abnormality diagnosis when the normal characteristics and abnormal characteristics tend to be different. Further, the NO _X purification rate Enox corrected by the second correction coefficient, by performing abnormality diagnosis by comparing the NO _X purification rate Enox a threshold after correction, the influence of environmental parameters (e.g., the bed temperature of the SCR catalyst) It is also possible to suppress a decrease in diagnostic accuracy due to the above. Further, by determining the intermediate characteristic or the threshold in consideration of the measurement error of the first NO _X sensor 6 and the second NO _X sensor 7, the diagnostic accuracy of the measurement error of the first NO _X sensor 6 and the second NO _X sensor 7 It is also possible to suppress a decrease in the above.

  In addition, according to the abnormality diagnosis device for the exhaust gas purification device of the present embodiment, the diagnostic accuracy can be adjusted by arbitrarily setting the intermediate characteristic. For example, when the purification characteristic closer to the normal characteristic than the abnormal characteristic is determined as the intermediate characteristic, the abnormality diagnosis accuracy can be increased. On the other hand, when the purification characteristic closer to the abnormal characteristic than the normal characteristic is determined as the intermediate characteristic, the normal diagnosis accuracy can be increased. Further, by changing the setting method of the intermediate characteristic according to the bed temperature of the SCR catalyst, it is possible to obtain diagnostic accuracy corresponding to the temperature range.

Here, in the configuration in which the oxidation catalyst is disposed downstream of the SCR catalyst in the second catalyst casing 4, the abnormal characteristics may tend to vary depending on the type of abnormality. For example, when the amount of additive supplied from the addition valve 5 is smaller than the target amount due to an abnormality in the addition valve 5 or the pump 50, the abnormal characteristic tends to approximate the normal characteristic as shown in FIG. Indicates. In contrast, when the NO _X purifying ability of the SCR catalyst is decreased, as shown in FIG. 9, NO _X purification rate of abnormal properties increases at low region of the bed temperature. This, in the state where the NO _X purification performance of the SCR catalyst has deteriorated, attributable to when the temperature of the SCR catalyst and the oxidation catalyst is low, the NH ₃ and NO _X having passed through the SCR catalyst is reacted with the oxidation catalyst It is thought. Thus, when the NO _X purification rate corresponding to each bed temperature may take different values depending on the type of abnormality, using the highest NO _X purification rate of the plurality of the NO _X purification rate corresponding to each bed temperature What is necessary is just to set the characteristic at the time of abnormality.

In this embodiment, as the environmental parameters affecting the NO _X purification rate of the SCR catalyst, an example has been described using a bed temperature of the SCR catalyst, NO ₂ ratio of the exhaust gas flowing into the SCR catalyst, NO flows into the SCR catalyst _X The amount (NO _X inflow amount) or the flow rate of the exhaust gas flowing into the SCR catalyst may be used. For example, when the NO ₂ ratio is used as the environmental parameter, intermediate characteristics may be determined as shown in FIG. The vertical axis in Figure 10 indicates the NO _X purification rate Enox of the SCR catalyst, the horizontal axis in Figure 10 shows the NO ₂ ratio. Further, the solid line in FIG. 10 indicates the intermediate characteristic, the alternate long and short dash line indicates the normal characteristic, and the dotted line indicates the abnormal characteristic. Intermediate characteristic, as shown in FIG. 10, only to be determined as NO _X purification rate at each NO ₂ ratio is greater than the NO _X purification rate of small and abnormal properties than NO _X purification rate of the normal state characteristic. In that case, the NO _X purification rate (Enox1 in FIG. 10) corresponding to a specific NO ₂ ratio (Rno2 in FIG. 10) may be set to the specified value. Then, a first correction coefficient for correcting the intermediate characteristic as NO _X purification rate of the intermediate characteristic is a constant value equal to the specified value Enox1, normal state characteristics and abnormal characteristics by using the first correction coefficient (See FIG. 11), and the threshold value may be set based on the corrected normal characteristics and abnormal characteristics. Also, the environmental parameter is not limited to one, and two or more environmental parameters may be combined. In that case, it is possible to more reliably suppress a decrease in diagnostic accuracy due to the influence of environmental parameters.

1 Internal combustion engine 2 Exhaust passage 3 First catalyst casing 4 Second catalyst casing 5 Addition valve 6 First NO _X sensor 7 Second NO _X sensor 8 Exhaust temperature sensor 9 ECU
50 Pump 51 Additive tank

Claims (4)

An exhaust purification device disposed in an exhaust passage of the internal combustion engine;
Measuring means for measuring the amount of a specific component contained in the exhaust gas flowing out from the exhaust purification device;
Calculation means for calculating a performance value that is a numerical value correlated with the purification performance of the exhaust purification device using the measurement value of the measurement means;
Diagnosing means for diagnosing an abnormality of the exhaust purification device by comparing the performance value calculated by the calculating means with a threshold value;
In the exhaust gas purification apparatus abnormality diagnosis device comprising
Means for storing a purification characteristic which is data indicating a correlation between the performance value and an environmental parameter affecting the performance value, the normal characteristic being a purification characteristic when the exhaust purification device is normal; First storage means for storing an intermediate characteristic that is an intermediate purification characteristic with an abnormal characteristic that is a purification characteristic when the exhaust purification device is abnormal;
Second storage means for storing a performance value corresponding to a value of a specific environmental parameter in the intermediate characteristic as a specified value;
First acquisition means for acquiring a first correction coefficient that is a correction coefficient for correcting the intermediate characteristic such that a performance value in the intermediate characteristic becomes a constant value equal to the specified value;
Setting means for setting the threshold based on two purification characteristics obtained by correcting the normal characteristics and the abnormal characteristics with the first correction coefficient;
Second acquisition means for acquiring the value of the environmental parameter when the measurement means measures the amount of the specific component;
Third acquisition means for deriving a performance value corresponding to the value of the environmental parameter acquired by the second acquisition means from the intermediate characteristic, and acquiring a ratio of the specified value to the derived performance value as a second correction coefficient; ,
Further comprising
The diagnosis unit corrects the performance value by multiplying the performance value calculated by the calculation unit and the second correction coefficient, and compares the corrected performance value with a threshold set by the setting unit. An abnormality diagnosis device for an exhaust gas purification device, characterized by diagnosing an abnormality in the exhaust gas purification device. In claim 1, the normal characteristic is data indicating a correlation between the environmental parameter and a minimum value that can be taken by the performance value within a measurement error range of the measuring means,
The abnormality diagnosis device for an exhaust gas purification apparatus, wherein the abnormal characteristic is data indicating a correlation between a maximum value that the performance value can take within a measurement error range of the measurement means and the environmental parameter. In Claim 1 or 2, the exhaust emission control device includes a selective reduction catalyst,
The measuring means is a NO _X sensor that measures the amount of NO _X contained in the exhaust,
It said calculating means, the abnormality diagnosis device for an exhaust purification apparatus, characterized by calculating the NO _X purification rate as the performance value.   4. The exhaust gas diagnosis apparatus abnormality diagnosis device according to claim 3, wherein the environmental parameter is a temperature of the selective catalytic reduction catalyst.

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