JP2019039401A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

To early detect expansion of an ammonia adsorption amount estimation error.SOLUTION: An exhaust emission control device for an internal combustion engine 1 includes: a selective reduction type NOx catalyst 24 provided in an exhaust passage 4; reducing agent injection valve 25 provided on the upstream side of the NOx catalyst; an estimation section 100 for calculating first and second estimated adsorption amounts that are estimated values of an ammonia adsorption amount of the NOx catalyst; a control section 100 for controlling the reducing agent injection amount injected on the basis of the first estimated adsorption amount; a detection section 100 for detecting an actual purification rate of the NOx catalyst; and a determination section for determining whether the first and second estimated adsorption amounts are normal on the basis of the actual purification rate. The determination section calculates a normal range of a purification rate on the basis of the actual purification rate, calculates a first purification rate on the basis of the first estimated adsorption amount, calculates a second purification rate on the basis of the second estimated adsorption amount, and determines whether the first and second estimated adsorption amount are normal by comparing the first and second purification rates with the normal range.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus provided with a selective reduction type NOx catalyst.

2. Description of the Related Art An exhaust gas purification device for an internal combustion engine is known that includes a selective reduction type NOx catalyst (so-called SCR) that reduces and purifies NOx in exhaust gas. On the upstream side of the NOx catalyst, urea water as a reducing agent is injected, and the urea water is hydrolyzed to generate ammonia (NH ₃ ). Ammonia reacts with NOx on the NOx catalyst to reduce and purify NOx.

  The NOx catalyst has an ammonia adsorption ability, and exhibits higher NOx purification performance as more ammonia is adsorbed. For this reason, the ammonia adsorption amount of the NOx catalyst is estimated, and the reducing agent injection amount is controlled based on the estimated ammonia adsorption amount (see, for example, Patent Document 1).

International Publication No. 2014/199777

  Incidentally, the estimated adsorption amount, which is an estimated value of the ammonia adsorption amount, may deviate relatively greatly from the true value due to various causes. That is, the ammonia adsorption amount estimation error may increase. If this is left as it is, the preferred reducing agent injection amount control is not executed, and NOx slips in which NOx flows out downstream of the NOx catalyst or ammonia slips in which ammonia flows out downstream of the NOx catalyst occur. Or the exhaust gas performance deteriorates.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can detect an expansion of an ammonia adsorption amount estimation error at an early stage.

According to one aspect of the invention,
A selective reduction type NOx catalyst provided in the exhaust passage;
A reducing agent injection valve provided in the exhaust passage upstream of the NOx catalyst;
An estimation unit for calculating a first estimated adsorption amount and a second estimated adsorption amount which are different estimated values of the ammonia adsorption amount of the NOx catalyst;
A control unit that controls the reducing agent injection amount injected from the reducing agent injection valve based on the first estimated adsorption amount calculated by the estimating unit;
A detection unit for detecting an actual purification rate of the NOx catalyst;
A determination unit that determines whether the first estimated adsorption amount and the second estimated adsorption amount calculated by the estimation unit are normal based on the actual purification rate detected by the detection unit;
With
The determination unit
Calculate the normal range of the purification rate based on the actual purification rate,
Calculating the first purification rate based on the first estimated adsorption amount and calculating the second purification rate based on the second estimated adsorption amount;
Comparing the first purification rate and the second purification rate with a normal range and determining whether or not the first estimated adsorption amount and the second estimated adsorption amount are normal are provided. Is done.

  Preferably, when one of the first purification rate and the second purification rate is out of the normal range, the exhaust purification device has a first estimated adsorption amount and a second estimated adsorption amount corresponding to the one purification rate before the determination. And a repair unit that performs a repair operation for repairing one of the values using the other value.

  Preferably, in the repair operation, the restoration unit changes the value of one estimated adsorption amount corresponding to one purification rate to the value of the other estimated adsorption amount corresponding to the other purification rate or a value obtained by correcting this value. Substitution and calculation of one estimated adsorption amount is executed.

  Preferably, the determination unit determines that one of the estimated adsorption amounts is abnormal when one of the purification rates is out of a normal range after performing the repair operation by the repair unit.

According to another aspect of the invention,
A selective reduction type NOx catalyst provided in the exhaust passage;
A reducing agent injection valve provided in the exhaust passage upstream of the NOx catalyst;
An estimation unit for calculating a first estimated adsorption amount and a second estimated adsorption amount which are different estimated values of the ammonia adsorption amount of the NOx catalyst;
A control unit that controls the reducing agent injection amount injected from the reducing agent injection valve based on the first estimated adsorption amount calculated by the estimating unit;
A detection unit for detecting an actual purification rate of the NOx catalyst;
A normal range of the purification rate is calculated based on the actual purification rate detected by the detection unit, a first purification rate is calculated based on the first estimated adsorption amount, and a second purification is performed based on the second estimated adsorption amount. A calculation unit for calculating a rate;
When one of the first purification rate and the second purification rate is outside the normal range, one value of the first estimated adsorption amount and the second estimated adsorption amount corresponding to the one purification rate is used by using the other value. A repair unit for performing a repair operation for repair;
An exhaust emission control device for an internal combustion engine is provided.

  Preferably, in the repair operation, the restoration unit changes the value of one estimated adsorption amount corresponding to one purification rate to the value of the other estimated adsorption amount corresponding to the other purification rate or a value obtained by correcting this value. Substitution and calculation of one estimated adsorption amount is executed.

  According to the present invention, the expansion of the ammonia adsorption amount estimation error can be detected at an early stage.

It is the schematic which shows the structure of an internal combustion engine. It is a graph which shows the ammonia adsorption | suction characteristic of a NOx catalyst. The map for calculating a correction coefficient is shown. It is a graph which shows the relationship of each quantity with respect to urea water injection quantity. It is the schematic for demonstrating the 1st determination method. It is a time chart for demonstrating the calculation method of an integrated value difference. It is a flowchart of the determination routine of a 1st determination method. It is the schematic for demonstrating the 2nd determination method. It is a flowchart of the determination routine of the 2nd determination method.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. However, it should be noted that the present invention is not limited to the following embodiments.

  FIG. 1 shows an internal combustion engine to which the exhaust emission control device of this embodiment is applied. An internal combustion engine (also referred to as an engine) 1 is a multi-cylinder engine mounted on a vehicle (not shown). In the present embodiment, the vehicle is a large vehicle such as a truck, and the engine 1 as a vehicle power source mounted on the vehicle is an in-line four-cylinder diesel engine. However, there are no particular limitations on the types, types, applications, and the like of the vehicle and the internal combustion engine. For example, the vehicle may be a small vehicle such as a passenger car, and the engine 1 may be a gasoline engine.

  The engine 1 includes an engine body 2, an intake passage 3 and an exhaust passage 4 connected to the engine body 2, a turbocharger 14, and a fuel injection device 5. The engine body 2 includes structural parts such as a cylinder head, a cylinder block, and a crankcase, and movable parts such as a piston, a crankshaft, and a valve housed therein.

  The fuel injection device 5 includes a common rail fuel injection device, and includes a fuel injection valve, that is, an injector 7 provided in each cylinder, and a common rail 8 connected to the injector 7. The injector 7 is an in-cylinder injector that directly injects fuel into the cylinder 9, that is, into the combustion chamber. The common rail 8 stores the fuel injected from the injector 7 in a high pressure state.

  The intake passage 3 is mainly defined by an intake manifold 10 connected to the engine body 2 (particularly a cylinder head) and an intake pipe 11 connected to the upstream end of the intake manifold 10. The intake manifold 10 distributes and supplies the intake air sent from the intake pipe 11 to the intake ports of each cylinder. The intake pipe 11 is provided with an air cleaner 12, an air flow meter 13, a compressor 14 </ b> C of the turbocharger 14, an intercooler 15, and an electronically controlled intake throttle valve 16 in order from the upstream side. The air flow meter 13 is a sensor for detecting an intake air amount per unit time of the engine 1, that is, an intake flow rate, and is also referred to as a mass air flow (MAF) sensor or the like.

  The exhaust passage 4 is mainly defined by an exhaust manifold 20 connected to the engine body 2 (particularly a cylinder head) and an exhaust pipe 21 connected to the downstream side of the exhaust manifold 20. The exhaust manifold 20 collects exhaust gas sent from the exhaust port of each cylinder. A turbine 14 </ b> T of the turbocharger 14 is provided between the exhaust pipe 21 or between the exhaust manifold 20 and the exhaust pipe 21. In the exhaust passage 4 on the downstream side of the turbine 14T, an oxidation catalyst 22, a filter 23, a selective reduction type NOx catalyst (SCR) 24, and an ammonia oxidation catalyst 26 are provided in this order from the upstream side. These form post-processing members that perform exhaust post-processing. The exhaust passage 4 between the filter 23 and the NOx catalyst 24 is provided with a urea injector 25 as a reducing agent injection valve that injects urea water as a reducing agent into the exhaust passage 4.

  The oxidation catalyst 22 oxidizes and purifies unburned components (hydrocarbon HC and carbon monoxide CO) in the exhaust, and heats the exhaust gas with the reaction heat at this time. The filter 23 is a so-called continuous regeneration type diesel particulate filter that collects particulate matter (also referred to as PM) contained in the exhaust gas and continuously removes the collected PM by reacting with the precious metal. To do. The filter 23 is a so-called wall flow type in which the openings at both ends of the honeycomb structure base material are alternately closed in a checkered pattern.

The NOx catalyst 24 reduces and purifies NOx by reacting ammonia obtained by hydrolyzing the urea water injected from the urea injector 25 with NOx in the exhaust gas. The NOx catalyst 24 is a material in which a noble metal such as Pt is supported on the surface of a base material such as zeolite or alumina, a material in which a transition metal such as Cu is ion-exchanged on the surface of the base material, and titania on the surface of the base material. / Vanadium catalyst (V ₂ O ₅ / WO ₃ / TiO ₂ ) supported and the like. The ammonia oxidation catalyst 26 oxidizes and purifies excess ammonia discharged from the NOx catalyst 24.

  The engine 1 also includes an EGR device 30. The EGR device 30 includes an EGR passage 31 for returning a part of exhaust gas (referred to as EGR gas) in the exhaust passage 4 (especially in the exhaust manifold 20) to the intake passage 3 (particularly in the intake manifold 10), and EGR. An EGR cooler 32 that cools the EGR gas flowing in the passage 31 and an EGR valve 33 for adjusting the flow rate of the EGR gas are provided. The EGR device 30 is for executing external EGR.

  Further, the present embodiment includes an electronically controlled exhaust throttle valve 37 and an exhaust injector 38 provided in the exhaust passage 4 respectively. In the present embodiment, these are provided in the exhaust passage 4 between the turbine 14 </ b> T and the oxidation catalyst 22, and an exhaust injector 38 is disposed downstream of the exhaust throttle valve 37. However, these installation positions can be changed. The exhaust throttle valve 37 is a valve for adjusting the exhaust flow rate. The exhaust injector 38 is an injector for injecting fuel into the exhaust passage 4 mainly when the filter 23 is regenerated.

  A control device for controlling the engine 1 is mounted on the vehicle. The control device has an electronic control unit (referred to as ECU) 100 that forms a control unit or a controller. ECU 100 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like. The ECU 100 is configured and programmed to control the in-cylinder injector 7, the intake throttle valve 16, the urea injector 25, the EGR valve 33, the exhaust throttle valve 37, and the exhaust injector 38. Unless otherwise specified, it is assumed that the intake throttle valve 16 and the exhaust throttle valve 37 are controlled to be fully opened.

  The control device also has the following sensors. Regarding these sensors, in addition to the air flow meter 13 described above, a rotational speed sensor 40 for detecting the rotational speed of the engine, specifically a rotational speed per minute (rpm), and an accelerator opening degree are detected. An accelerator opening sensor 41 is provided. Further, exhaust temperature sensors 42, 43, 44 for detecting the exhaust temperature are provided at upstream side inlet portions of the oxidation catalyst 22, the filter 23 and the NOx catalyst 24. An exhaust temperature sensor 46 for detecting the exhaust temperature is provided at the downstream outlet of the NOx catalyst 24. Further, a differential pressure sensor 45 for detecting a differential pressure between the exhaust pressure at the inlet and the outlet of the filter 23 is provided.

  Further, an upstream side NOx sensor 47 and a downstream side NOx sensor 48 for detecting NOx in the exhaust gas are provided at the upstream side inlet portion and the downstream side outlet portion of the NOx catalyst 24, respectively. These NOx sensors 47 and 48 emit an output correlated with the NOx concentration of the exhaust gas. However, the NOx sensors 47 and 48 can also detect ammonia. The upstream NOx sensor 47 is provided on the upstream side of the urea injector 25. Output signals from the above sensors are sent to the ECU 100.

  Next, the contents of control executed by the ECU 100 will be described.

  First, an outline of control of the urea water injection amount injected from the urea injector 25 will be described. The urea water injection amount M is generally expressed as a sum of a first injection amount MA, a second injection amount MB, and a third injection amount MC, which will be described later, and is expressed by an equation: M = MA + MB + MC. The ECU 100 calculates the urea water injection amount M and causes the urea injector 25 to inject an amount of urea water equal to the calculated urea water injection amount M.

  First, the first injection amount MA corresponding to the NOx amount (inflow NOx amount) flowing into the NOx catalyst 24 is calculated. The inflow NOx amount is represented by the product of the NOx concentration detected by the upstream NOx sensor 47 and the exhaust gas flow rate. The exhaust gas flow rate is calculated based on the value of the intake air amount detected by the air flow meter 13. For example, the exhaust gas flow rate is calculated as a value equal to the value of the intake air amount. A predetermined relationship between the inflow NOx amount and the first injection amount MA, specifically, a map (which may be a function, the same applies hereinafter) is stored in the ECU 100, and the ECU 100 refers to this map and the inflow NOx amount. The first injection amount MA corresponding to is calculated. Here, the minimum injection amount required to reduce and purify the inflow NOx, in other words, the injection amount with an equivalence ratio of 1 to the inflow NOx amount is calculated as the first injection amount MA.

  The upstream NOx sensor 47 may be provided at a position upstream of the exhaust passage 4. The inflow NOx amount may be estimated by the ECU 100 based on the engine operating state (for example, the engine speed and the fuel injection amount of the in-cylinder injector 7). Further, the exhaust gas flow rate may be directly detected by a flow sensor provided in the exhaust passage 4.

  Second, a second injection amount MB for calculating the ammonia adsorption amount of the NOx catalyst 24 to be close to the target adsorption amount is calculated. That is, the NOx catalyst 24 has ammonia adsorption ability, and exhibits higher NOx purification performance as more ammonia is adsorbed. Therefore, the ammonia adsorption amount of the NOx catalyst 24 is estimated, and the reducing agent injection amount is controlled based on the difference between the estimated adsorption amount and the target adsorption amount. The reason for estimating the ammonia adsorption amount is that it is difficult to actually measure it.

  FIG. 2 shows the ammonia adsorption characteristics of the NOx catalyst 24. The line a indicates the upper limit value or adsorption limit of the ammonia adsorption amount obtained through experiments or the like, and this upper limit value tends to decrease as the catalyst temperature of the NOx catalyst 24 increases. Note that if ammonia is supplied when the actual ammonia adsorption amount is the upper limit value, the ammonia cannot be adsorbed to the NOx catalyst 24, so it flows out downstream of the NOx catalyst 24 and causes ammonia slip.

  A target value on the low adsorption amount side by a predetermined margin from the line a is determined as a line b, and this line b is stored in the ECU 100 in the form of a map.

  The ECU 100 estimates the catalyst temperature of the NOx catalyst 24 based on the detected value of at least one of the exhaust temperature sensors 44 and 46. For example, any one of the detected values may be regarded as the catalyst temperature, or an average value of both the detected values may be regarded as the catalyst temperature. Then, a target value Wt (a value at point c in FIG. 2) of the ammonia adsorption amount corresponding to the estimated catalyst temperature (Tc1 in FIG. 2) is calculated from the map. The catalyst temperature may be detected directly. Estimation and detection are collectively referred to as acquisition.

  A difference ΔW between the target adsorption amount Wt and the estimated adsorption amount We is obtained by an expression: ΔW = Wt−We, and a second injection amount MB corresponding to the difference ΔW is calculated. The larger the difference ΔW is, the larger the second injection amount MB is calculated.

  For example, when the estimated amount of adsorption We is smaller than the target amount of adsorption Wt, as shown at point d in FIG. 2, the difference ΔW is positive, so a positive second injection amount MB on the injection amount increasing side is calculated. By injecting the two injection amounts MB, the estimated adsorption amount We increases and gradually approaches the target adsorption amount Wt. On the other hand, when the estimated adsorption amount We is larger than the target adsorption amount Wt, for example, as shown at point e in FIG. 2, the difference ΔW is negative, and therefore the zero or negative second injection amount MB is calculated. As a result, the ammonia adsorbed on the NOx catalyst 24 is consumed for the reduction of NOx, the estimated adsorption amount We decreases, and gradually approaches the target adsorption amount Wt.

  Regarding the estimation method of the ammonia adsorption amount, in this embodiment, a mathematical model is constructed based on a chemical reaction formula representing the reaction between ammonia and NOx in the NOx catalyst 24, and the ammonia adsorption amount is accurately estimated by the ECU 100 based on the model. It is supposed to be. At this time, the ECU 100 determines the urea water injection amount M, the catalyst temperature of the NOx catalyst 24, the exhaust gas flow rate, the detected values of the upstream and downstream NOx sensors 47 and 48, and engine parameters (engine speed, fuel injection amount) representing the engine operating state. Etc.), etc., and the ammonia adsorption amount is estimated.

  Third, a third injection amount MC commensurate with the amount of NOx flowing out from the NOx catalyst 24 (outflow NOx amount) is calculated. Specifically, when the output (sensor output) V of the downstream NOx sensor 48 is equal to or less than a predetermined upper limit value Vup, the third injection amount MC that is zero is calculated assuming that the outflow NOx amount is within the allowable range. On the other hand, when the sensor output V exceeds the upper limit value Vup, since the outflow NOx amount is outside the allowable range, the positive third injection amount MC is calculated in order to increase the urea water injection amount and suppress the outflow NOx amount. The

  At this time, a difference ΔV (= V−Vup) between the sensor output V and the upper limit value Vup is calculated, and a third injection amount MC corresponding to the difference ΔV is calculated. Thus, the urea water injection amount M is feedback-controlled or feedback-corrected based on the sensor output V.

  Here, in the present embodiment, the third injection amount MC is represented by a correction coefficient K (≧ 1). That is, in the case of the present embodiment, the previous equation M = MA + MB + MC is represented by M = K × MA + MB (= MA + MB + (K−1) × MA), and MC = (K−1) × MA. A map as shown in FIG. 3 is stored in the ECU 100, and a correction coefficient K greater than 1 is calculated as the difference ΔV increases from zero. When the difference ΔV becomes equal to or greater than the limit value ΔV1 (> 0), the increase of the correction coefficient K is suppressed and limited to the limit value K1 (> 1). The correction coefficient K is 1 when the difference ΔV is less than or equal to zero.

  When the sensor output V exceeds the upper limit value Vup, a correction coefficient K (> 1) corresponding to the difference ΔV is calculated, and the first injection amount MA that is the base injection amount is increased and corrected by the correction coefficient K. As a result, The urea water injection amount M is corrected to increase.

Although an example of simple feedback control is shown here, the feedback control may be more complicated using a known technique such as PID control. Alternatively, the third injection amount MC, which is an addition term irrelevant to the first injection amount MA, may be calculated according to the difference ΔV, and the urea water injection amount M may be calculated by the equation M = MA + MB + MC.
In addition, since the urea water injection amount M is corrected by other correction amounts (for example, urea water temperature correction amount, urea concentration correction amount, etc.), it approximates the sum of the first to third injection amounts MA to MC. do not do.

  By the way, the downstream side NOx sensor 48 can detect not only NOx but also ammonia, and cannot detect both of them separately. For this reason, the relationship between the NOx catalyst downstream NOx amount with respect to the urea water injection amount, the sensor output of the downstream NOx sensor 48, and the ammonia amount (outflow ammonia amount) flowing out downstream of the NOx catalyst is shown in FIG. As shown.

  As shown in the vicinity of the left end of the figure, when the urea water injection amount is relatively small and insufficient with respect to the inflow NOx amount, the NOx catalyst 24 cannot reduce all the inflow NOx. Occur. The amount of outflow NOx increases and the NOx sensor output also increases. As the urea water injection amount increases, the urea water injection amount gradually matches the inflow NOx amount, so the outflow NOx amount gradually decreases and the NOx sensor output also gradually decreases.

  However, when the urea water injection amount is further increased, the urea water injection amount becomes excessive with respect to the inflow NOx amount, and an ammonia slip in which excess ammonia flows out from the NOx catalyst 24 occurs. As the urea water injection amount increases, the outflow ammonia amount also increases. Since the NOx sensor 48 detects this ammonia, the NOx sensor output gradually increases as the urea water injection amount increases.

  A balance point at which the NOx slip and the ammonia slip are balanced, that is, the urea water injection amount that can minimize both the outflow NOx amount and the outflow ammonia amount as much as possible is indicated by Mh in the figure. A small injection amount side from Mh is defined as a NOx slip region, and a large injection amount side from Mh is defined as an ammonia slip region.

  The NOx sensor output draws a curve that has a minimum value at the balance point. Therefore, it is impossible to determine whether the NOx sensor output is in the NOx slip region (whether NOx slip is occurring) or in the ammonia slip region (whether ammonia slip is occurring) only by the NOx sensor output. . For this reason, conventionally, the urea water injection amount is forcibly increased or decreased, and it is detected which side the NOx sensor output changes in accordance with that, and based on the result, the NOx sensor output is assigned to which region. It is determined whether it exists.

  For example, if the NOx sensor output decreases when the urea water injection amount is increased, it is determined that the NOx slip region is present (NOx slip is occurring), and the NOx sensor output increases when the urea water injection amount is increased. If it is, it is determined that it is in the ammonia slip region (ammonia slip is occurring).

  As described above, the value of the estimated adsorption amount We calculated by the ECU 100 may deviate from the true value relatively large due to various causes. That is, the ammonia adsorption amount estimation error may increase. The causes include, for example, temporary fixation of the urea injector 25 and long-time operation of the engine in a low exhaust temperature range where the NOx purification rate is unstable. If such an estimation error expansion is left as it is, a suitable reducing agent injection amount control is not performed, and NOx slip occurs or ammonia slip occurs, and exhaust gas performance deteriorates.

  Therefore, in the present embodiment, the ECU 100 performs self-diagnosis (OBD: On-Board Diagnostics) as described below in order to detect an increase in the ammonia adsorption amount estimation error at an early stage.

[First determination method]
In this embodiment, in order to determine whether the estimated adsorption amount We is normal, two different determination methods are performed in parallel. Here, first, a first determination method that is not directly related to the present invention will be described, and then a second determination method according to an embodiment of the present invention will be described.

  Regarding the first determination method, the ECU 100 calculates a determination threshold Th to be compared with the estimated adsorption amount We by the following procedure. Then, the estimated adsorption amount We is compared with the calculated determination threshold Th, and it is determined whether the estimated adsorption amount We is normal or abnormal according to the comparison result.

  In calculating the determination threshold Th, first, a first ammonia amount U corresponding to the urea water injection amount M is calculated. The first ammonia amount U is an ammonia amount obtained from the urea water injection amount M, and is calculated based on the urea water injection amount M from a map in which the relationship between both is stored in advance.

  Next, a second ammonia amount UA corresponding to the first injection amount MA is calculated. The second ammonia amount UA is also the ammonia amount obtained from the first injection amount MA, and is calculated based on the first injection amount MA from a map in which the relationship between them is stored in advance.

  A difference ΔU (= U−UA) between the first ammonia amount U and the second ammonia amount UA is calculated, and the difference ΔU is integrated to calculate an integrated value S = ΣΔU. Based on this integrated value S, a determination threshold Th is calculated.

  As shown in FIG. 5, there are two types of determination threshold Th, a determination threshold ThH when urea water injection is executed and a determination threshold ThL when urea water injection is not executed (when stopped). The ECU 100 changes the determination threshold Th when the urea water injection is executed and when it is not executed, and uses the determination threshold ThH when the urea water injection is executed and uses the determination threshold ThL when the urea water injection is not executed.

  In particular, the ECU 100 uses the determination threshold value ThH as the upper limit value of the estimated adsorption amount when the urea water injection is performed, and uses the determination threshold value ThL as the lower limit value of the estimated adsorption amount when the urea water injection is not performed. Hereinafter, the determination threshold ThH is also referred to as an upper limit determination threshold, and the determination threshold ThL is also referred to as a lower limit determination threshold.

  The ECU 100 sets a value larger by a predetermined first margin value than the integrated value S when the urea water injection is performed as an upper limit determination threshold ThH, and a value smaller by a predetermined second margin value than the integrated value S when the reducing agent injection is not performed. Is the lower limit determination threshold ThL. The first margin value is represented by α1 that is greater than or equal to zero, and the upper limit determination threshold ThH is calculated from the formula: ThH = S + α1. The second margin value is represented by an absolute value of α2 that is less than or equal to zero, and the lower limit determination threshold ThL is calculated from the formula: ThL = S + α2.

  When the urea water injection is executed, the estimated adsorption amount We is compared with the upper limit determination threshold ThH. When the estimated adsorption amount We is equal to or less than the upper limit determination threshold ThH, the estimated adsorption amount We is determined to be normal, and when the estimated adsorption amount We is greater than the upper limit determination threshold ThH, the estimated adsorption amount We is determined to be abnormal.

  On the other hand, when urea water injection is not executed, the estimated adsorption amount We is compared with the lower limit determination threshold ThL. When the estimated adsorption amount We is equal to or greater than the lower limit determination threshold ThL, the estimated adsorption amount We is determined to be normal, and when the estimated adsorption amount We is smaller than the upper limit determination threshold ThH, the estimated adsorption amount We is determined to be abnormal.

  The above difference ΔU is a value obtained by subtracting the amount of ammonia used to reduce the inflow NOx from the total amount of ammonia supplied to the NOx catalyst 24. This is considered to mean the maximum value of the ammonia amount per unit time that can be adsorbed to the NOx catalyst 24 when the urea water injection is performed. On the other hand, when the urea water injection is performed, the estimated adsorption amount We and the integrated value S tend to increase. Therefore, the upper limit determination threshold ThH calculated based on the integrated value S is generally considered suitable as a value that determines the upper limit value of the estimated adsorption amount. Therefore, in the present embodiment, the upper limit determination threshold ThH is calculated based on the integrated value S, and the estimated adsorption amount We is compared with the upper limit determination threshold ThH. When the estimated adsorption amount We is greater than the upper limit determination threshold ThH, the estimated adsorption amount We is calculated. Is determined to be abnormal. Thereby, the expansion of the ammonia adsorption amount estimation error can be detected at an early stage.

  On the other hand, when urea water injection is not performed, the total amount of ammonia supplied to the NOx catalyst 24 is zero, so that the difference ΔU means the maximum value of the ammonia amount per unit time that can be desorbed from the NOx catalyst 24. Conceivable. When urea water injection is not executed, the estimated adsorption amount We and the integrated value S tend to decrease. Therefore, the lower limit determination threshold ThL calculated based on the integrated value S is generally considered suitable as a value for determining the lower limit value of the estimated adsorption amount. Therefore, in the present embodiment, the lower limit determination threshold ThL is calculated based on the integrated value S, and the estimated adsorption amount We is compared with the lower limit determination threshold ThL. When the estimated adsorption amount We is smaller than the lower limit determination threshold ThL, the estimated adsorption amount We is calculated. Is determined to be abnormal. Also by this, the expansion of the ammonia adsorption amount estimation error can be detected at an early stage.

  The first margin value α1 and the second margin value α2 are values determined to shift the determination threshold Th slightly toward the abnormal side with respect to the integrated value S, which is an absolute reference, in order to improve diagnosis stability. The first margin value α1 and the second margin value α2 may be constant values, but here are variably set according to each state quantity in order to increase the diagnostic accuracy.

  In FIG. 6, the solid line indicates a change in the integrated value S when the urea water injection is executed, and the broken line indicates a change in the integrated value S when the urea water injection is not executed. The horizontal axis represents time t, t = n indicates the current (current) calculation time, and t = n−1 indicates the previous (predetermined time) calculation time. τ represents an interval of calculation timing, that is, a calculation cycle (for example, 10 msec). For example, when the urea water injection is executed, the ECU 100 sets the first margin value α1 as follows.

As shown by the solid line in FIG. 6, firstly, the integrated value difference _{ΔS n = S n -S n-} 1 is the difference between the integrated value S _n-1 of this integrated value S _n and the previous is computed. The integrated value difference ΔS _n can be rephrased as the rate of increase or the rate of increase of the current integrated value S per unit time. Next, a correction coefficient F1 for correcting the integrated value difference ΔS _n is calculated based on parameters such as exhaust temperature and exhaust gas flow rate. A detected value of the exhaust temperature sensor 44 is used for the exhaust temperature, and a value calculated based on the value of the intake air amount is used for the exhaust gas flow rate. A map stored in the ECU 100 is used for calculating the correction coefficient F1. Finally, the first margin value α1 is calculated by multiplying the integrated value difference ΔS _n by the correction coefficient F1. The first margin value α1 is a positive value when the integrated value S is increasing, and is a value of 0 or more otherwise.

Instead of multiplying by the correction coefficient F1, the correction value may be added to correct the integrated value difference ΔS _n . Further, the integrated value difference ΔS _n may be a difference between the integrated values S at a time interval longer than the calculation cycle τ.

  Next, a method for setting the second margin value α2 when urea water injection is not performed will be described. This setting method is substantially the same as the setting method of the first margin value α1.

As shown by the broken line in FIG. 6, firstly, the integrated value difference _{ΔS n = S n -S n-} 1 is the difference between the integrated value S _n-1 of this integrated value S _n and the previous is computed. When the integrated value S is decreasing, a negative integrated value difference ΔS _n is calculated. Next, a correction coefficient F2 for correcting the integrated value difference ΔS _n is calculated in the same manner as described above. The second margin value α2 is calculated by multiplying the integrated value difference ΔS _n by the correction coefficient F2. The second margin value α2 is a negative value when the integrated value S is decreasing, and is a value of 0 or less in other cases.

Instead of multiplying by the correction coefficient F2, the integrated value difference ΔS _n may be corrected by adding a correction amount.

  Next, a determination routine of the first determination method will be described with reference to FIG. The illustrated routine is repeatedly executed by the ECU 100 at every predetermined calculation cycle τ (for example, 10 msec).

  In step S101, the first ammonia amount U corresponding to the urea water injection amount M is calculated. In step S102, the second ammonia amount UA corresponding to the first injection amount MA is calculated.

  In step S103, a difference ΔU (= U−UA) between the first ammonia amount U and the second ammonia amount UA is calculated. In step S104, the difference ΔU is integrated to calculate an integrated value S = ΣΔU.

  In step S105, it is determined whether or not urea water injection is being performed. If it is the time of execution, the process proceeds to step S106. If it is not the time of execution, that is, if it is not the time of execution, the process proceeds to step S110.

  In the case of execution, in step S106, an upper limit determination threshold ThH that is a determination threshold when urea water injection is executed is calculated from the formula: ThH = S + α1.

  In step S107, it is determined whether or not the estimated adsorption amount We is larger than the upper limit determination threshold ThH.

  When the estimated adsorption amount We is equal to or less than the upper limit determination threshold ThH (We ≦ ThH), the process proceeds to step S108, where the estimated adsorption amount We is determined to be normal, and the routine is terminated.

  On the other hand, when the estimated adsorption amount We is larger than the upper limit determination threshold ThH (We> ThH), the process proceeds to step S109, where the estimated adsorption amount We is determined to be abnormal, and the routine is terminated. If it is determined that there is an abnormality, for example, measures necessary to return the estimated adsorption amount We to a normal value are taken, or a warning device (check lamp, etc.) (not shown) is activated to prompt the user to perform maintenance. Is preferred. Thereby, deterioration of exhaust gas performance can be suppressed.

  On the other hand, when urea water injection is not performed, in step S110, a lower limit determination threshold ThL that is a determination threshold when urea water injection is not performed is calculated from the formula: ThL = S + α2.

  In step S111, it is determined whether or not the estimated adsorption amount We is smaller than the lower limit determination threshold ThL.

  When the estimated adsorption amount We is equal to or greater than the lower limit determination threshold ThL (We ≧ ThL), the process proceeds to step S112, where the estimated adsorption amount We is determined to be normal, and the routine is terminated.

  On the other hand, when the estimated adsorption amount We is smaller than the lower limit determination threshold ThL (We <ThL), the process proceeds to step S113, where the estimated adsorption amount We is determined to be abnormal, and the routine is terminated.

  As described above, in the first determination method, the first ammonia amount U corresponding to the urea water injection amount M and the second injection amount MA corresponding to the first injection amount MA necessary for the reduction of NOx flowing into the NOx catalyst 24 are used. Based on the integrated value S of the difference ΔU from the ammonia amount UA, the determination threshold values ThH and ThL are calculated, and the estimated adsorption amount We is compared with the determination threshold values ThH and ThL to determine whether or not the estimated adsorption amount We is normal. For this reason, the expansion of the ammonia adsorption amount estimation error can be detected at an early stage.

  In the first determination method, the determination threshold value is changed between when the urea water injection is performed and when it is not performed. Therefore, the determination threshold value can be appropriately set, and the diagnostic accuracy can be improved.

  In the first determination method, the upper limit determination threshold ThH calculated when urea water injection is performed is used as the upper limit value of the estimated adsorption amount, and the lower limit determination threshold ThL calculated when urea water injection is not performed is the lower limit value of the estimated adsorption amount. Used as For this reason, it is possible to appropriately set the upper limit value and the lower limit value according to the upward tendency and the downward tendency of the estimated adsorption amount, and accordingly, the determination threshold value can be appropriately set and the diagnostic accuracy can be improved.

  In the first determination method, when the urea water injection is executed, a value that is larger than the integrated value S by a predetermined first margin value α1 is set as the upper limit determination threshold ThH, and when the urea water injection is not executed, a predetermined second value is set from the integrated value S. A value that is smaller by the margin value | α2 | is set as the lower limit determination threshold ThL. For this reason, the stability of diagnosis can be improved and misdiagnosis can be suppressed.

  According to the conventional method, when the NOx sensor output increases, the urea water injection amount is forcibly increased or decreased, and either NOx slip or ammonia slip occurs depending on how the NOx sensor output changes accordingly. It is possible to determine whether it is present. Then, it is conceivable that an abnormality in the estimated adsorption amount is determined on the assumption that one of the slips occurring is caused by the expansion of the ammonia adsorption amount estimation error. However, with this method, since it takes a relatively long time to determine whether NOx slip or ammonia slip occurs, an abnormality in the estimated adsorption amount cannot be detected at an early stage. On the other hand, in the case of the first determination method, the calculation of the determination threshold value Th and the comparison of the estimated adsorption amount We and the determination threshold value Th are always performed. Is possible.

[Second determination method]
Next, a second determination method according to the embodiment of the present invention will be described.

  In the second determination method, the estimated adsorption amount We is used as the first estimated adsorption amount, and the integrated value S is used as the second estimated adsorption amount. The integrated value S can be used as the second estimated adsorption amount because it can be regarded as the ammonia adsorption amount of the NOx catalyst 24 calculated simply. The estimated adsorption amount We and the integrated value S are estimates of different (different types) ammonia adsorption amounts.

  Based on the estimated adsorption amount We, a first purification rate R1 that is a first NOx purification rate of the NOx catalyst 24 is calculated. The first purification rate R1 is calculated from a predetermined map based on the estimated adsorption amount We, the exhaust temperature detected by the exhaust temperature sensor 44, and the exhaust gas flow rate.

  Based on the integrated value S, a second purification rate R2 that is a second NOx purification rate of the NOx catalyst 24 is calculated. The second purification rate R2 is calculated from a predetermined map based on the integrated value S, the exhaust temperature detected by the exhaust temperature sensor 44, and the exhaust gas flow rate.

  On the other hand, an actual purification rate Rt that is an actual NOx purification rate of the NOx catalyst 24 is detected separately from these. At this time, the amount of NOx flowing into the NOx catalyst 24 (inflow NOx amount Nin) is calculated as the product of the NOx concentration detected by the upstream NOx sensor 47 and the exhaust gas flow rate. Further, the amount of NOx flowing out from the NOx catalyst 24 (outflow NOx amount Nout) is calculated as the product of the NOx concentration detected by the downstream NOx sensor 48 and the exhaust gas flow rate. Then, the actual purification rate Rt is calculated by the formula: Rt = 1−Nout / Nin.

  Next, as shown in FIG. 8, the normal range of the purification rate R is calculated based on the actual purification rate Rt. The normal range is a range of the purification rate R that satisfies Rt−β2 ≦ R ≦ Rt + β1 (where β1, β2> 0). β1 is an upper limit value that defines the upper limit of the normal range, and β2 is a lower limit value that defines the lower limit of the normal range. β1 and β2 may be predetermined constant values, or may be variably set similarly to the above-described margin values α1 and α2.

  The first purification rate R1 and the second purification rate R2 are compared with the normal range to determine whether or not the estimated adsorption amount We and the integrated value S are normal.

  For example, if both the first purification rate R1 and the second purification rate R2 are within the normal range, it is determined that both the estimated adsorption amount We and the integrated value S are normal. When the first purification rate R1 is outside the normal range and only the second purification rate R2 is within the normal range, it is determined that the estimated adsorption amount We is abnormal and the integrated value S is normal. Conversely, when only the first purification rate R1 is within the normal range and the second purification rate R2 is outside the normal range, it is determined that the estimated adsorption amount We is normal and the integrated value S is abnormal.

  When the first purification rate R1 or the second purification rate R2 is larger than the normal range, the first purification rate R1 or the second purification rate R2 is determined to be within the excessively abnormal range. Further, when the first purification rate R1 or the second purification rate R2 is a value smaller than the normal range, the first purification rate R1 or the second purification rate R2 is determined to be within the underabnormal range.

  By the way, in this embodiment, when one of the first purification rate R1 and the second purification rate R2 is outside the normal range, it is not immediately determined as abnormal, but before the determination, one of the one corresponding to the one purification rate R1. A restoration operation is performed to restore the value of the estimated adsorption amount (one of the estimated adsorption amount We and the integrated value S) using the value of the other estimated adsorption amount (the other of the estimated adsorption amount We and the integrated value S). . When one of the purification rates still does not fall within the normal range even after performing this repair operation, one of the estimated adsorption amounts is determined to be abnormal.

  Since the repair operation is performed before the determination, there is a possibility that one of the estimated adsorption amounts can be returned to a normal value by this repair operation. If it can be restored to the normal value, it is possible to save the trouble of making an abnormality determination and carrying out inspection and maintenance. Such a repair operation is very useful.

  In the repair operation, basically, one estimated adsorption amount (one of the estimated adsorption amount We and the integrated value S) corresponding to one purification rate outside the normal range and having a high possibility of abnormality is converted to the other within the normal range. This is performed by substituting with the other estimated adsorption amount (the other of the estimated adsorption amount We and the integrated value S) considered to be normal, corresponding to the purification rate. After the replacement, the calculation of one estimated adsorption amount is executed or continued. The calculation is continued without any change for the other estimated adsorption amount that seems to be normal.

  If this repair operation is successful, the value of one estimated adsorption amount will eventually return to a normal value, and the corresponding one of the purification rate values will also fall within the normal range. Thus, the normal state can be restored, and the abnormal state can be removed without performing the abnormality determination.

  With reference to FIG. 9, the determination routine of the second determination method will be described. The illustrated routine is repeatedly executed by the ECU 100 at every predetermined calculation cycle τ (for example, 10 msec).

  In step S201, the first purification rate R1 is calculated based on the estimated adsorption amount We.

  In step S202, the integrated value S is calculated according to the method of steps S101 to S104 described above. The integrated value S calculated in step S104 may be used in step S202. In step S203, the second purification rate R2 is calculated based on the integrated value S.

  In step S204, the actual purification rate Rt is calculated based on the detection values of the NOx sensors 47, 48 and the like.

  In step S205, the normal range of the purification rate R is calculated based on the actual purification rate Rt. That is, the normal range of the purification rate R that satisfies Rt−β2 ≦ R ≦ Rt + β1 is calculated.

  In step S206, it is determined whether or not both the first purification rate R1 and the second purification rate R2 are within the normal range. When it is determined that both are within the normal range, the process proceeds to step S207, where it is determined that both the estimated adsorption amount We and the integrated value S are normal, and the routine is terminated.

  If it is not determined in step S206 that both are within the normal range, for convenience, it is determined that one of the first purification rate R1 and the second purification rate R2 is within the normal range and the other is outside the normal range. Shall. In this case, the process proceeds to step S208, whether the first purification rate R1 is outside the normal range, that is, whether the second purification rate R2 is within the normal range, and whether the first purification rate R1 is outside the normal range. Is judged. If yes, then continue with step S209, otherwise, continue with step S212. Here, “outside of the normal range” includes both the case of being in the overabnormal range and the case of being in the underabnormal range.

  Note that the determination in step S208 is “Yes” when the second purification rate R2 is in the normal range and the first purification rate R1 is outside the normal range for a predetermined time, and “No” otherwise. preferable. By doing so, it is possible to make a yes only when the state continues to some extent, and the reliability of the determination can be improved.

  In step S209, the value of the estimated adsorption amount We is replaced with the value of the integrated value S, and thereafter the calculation of the estimated adsorption amount We proceeds as usual.

  Next, in step S210, whether or not the first purification rate R1 is outside the normal range, that is, whether or not the second purification rate R2 is within the normal range and whether the first purification rate R1 is outside the normal range. To be judged.

  This determination is made when the second purification rate R2 is still within the normal range and the first purification rate R1 is outside the normal range even when a predetermined time has elapsed after the value replacement (that is, when the state does not change). ) To yes, otherwise no. Even if the value is replaced and the repair operation is successful, the value of the estimated adsorption amount We returns to the normal value, and the result is reflected and it takes a certain time until the first purification rate R1 returns to the normal range. Cost. In order to wait for such a time, it is preferable to make a determination after a lapse of a predetermined time, and this makes it possible to improve the reliability of the determination.

  If the determination in step S210 is yes, the process proceeds to step S211 and it is determined that the estimated adsorption amount We is abnormal. If it is determined that there is an abnormality, it is preferable to activate a warning device (check lamp or the like) (not shown) to prompt the user to perform maintenance as in the case of the first determination method. Thereby, deterioration of exhaust gas performance can be suppressed.

  On the other hand, if the determination in step S210 is no, the routine ends without proceeding to step S211. That is, in this case, it means that the repair operation has been successful and the first purification rate R1 has returned to the normal range, so the routine of this time is suspended and terminated. In the routine after the next time, step S206 will be YES, and it will be judged normal.

  On the other hand, when the process proceeds to step S212, it is substantially determined that the first purification rate R1 is within the normal range and the second purification rate R2 is outside the normal range. In this case, in step S212, it is determined whether or not the second purification rate R2 is within the excessively abnormal range.

  In the case of yes, in step S213, the value of the integrated value S is replaced with a value We + γ1 obtained by correcting the value of the estimated adsorption amount We, and thereafter the calculation of the integrated value S is advanced as usual.

  Here, the reason for replacing the estimated adsorption amount We with the corrected value We + γ1 is that, in the first determination method, the integrated value S is the upper limit value or lower limit value of the estimated adsorption amount We. This is because the value prescribes If the value is replaced with the value of the estimated adsorption amount We, after the replacement, the value of the integrated value S coincides with or very close to the value of the estimated adsorption amount We, and it is determined that the estimated adsorption amount We is abnormal immediately after the replacement. Can occur. Therefore, in order to avoid such a situation and to separate the offset integrated value S from the estimated adsorption amount We to some extent (offset), the estimated adsorption amount We is replaced with a corrected value We + γ1. γ1 is called a first offset amount and has a positive value. The first offset amount γ1 is calculated from, for example, a predetermined map based on the urea water injection amount M, the actual purification rate Rt, the exhaust temperature (detected value of the exhaust temperature sensor 44), and the like. In addition, when there is no said problem, you may substitute to the value of the estimated adsorption amount We.

  Next, in step S214, whether or not the second purification rate R2 is in the excessively abnormal range, that is, whether or not the first purification rate R1 is in the normal range and whether the second purification rate R2 is in the excessively abnormal range. Is judged.

  Also in this determination, as in step S210, when the first purification rate R1 is still in the normal range and the second purification rate R2 is in the excessively abnormal range even after a predetermined time has elapsed after the value replacement ( In other words, it is preferable to answer “yes” when the state does not change and “no” otherwise.

  If the determination in step S214 is yes, the process proceeds to step S215, and the integrated value S is determined to be abnormal. In this case, as in step S211, it is preferable to activate the warning device.

  On the other hand, if the determination in step S214 is no, the routine is terminated without proceeding to step S215. That is, in this case, it means that the repair operation is successful and the second purification rate R2 has returned to the normal range, so the routine of this time is suspended and terminated. In the routine after the next time, step S206 will be YES, and it will be judged normal.

  On the other hand, if the determination in step S212 is no, this is because the second purification rate R2 is in the underabnormal range, that is, the first purification rate R1 is in the normal range, and the second purification rate R2 is underabnormal. Means within range.

  In this case, in step S216, the value of the integrated value S is replaced with a value We + γ2 obtained by correcting the value of the estimated adsorption amount We, and thereafter the calculation of the integrated value S is advanced as usual.

  The reason for replacing the estimated adsorption amount We with the corrected value We + γ2 is the same as in step S213. γ2 is called a second offset amount and has a negative value. The second offset amount γ2 is also calculated from a predetermined map, for example, based on the urea water injection amount M, the actual purification rate Rt, the exhaust temperature (detected value of the exhaust temperature sensor 44), and the like. In addition, when there is no above-mentioned problem, you may substitute to the value of the estimated adsorption amount We.

  Next, in step S217, whether or not the second purification rate R2 is in the underabnormal range, that is, whether the first purification rate R1 is in the normal range and whether the second purification rate R2 is in the underabnormal range. Is judged.

  Also in this determination, when the first purification rate R1 is still in the normal range and the second purification rate R2 is in the underabnormal range even after a predetermined time has elapsed after the replacement of the value in step S216 (that is, It is preferable that the answer is yes when the state does not change, and no otherwise.

  If the determination in step S217 is yes, the process proceeds to step S215, and the integrated value S is determined to be abnormal.

  On the other hand, if the determination in step S217 is no, the routine is terminated without proceeding to step S215. That is, in this case, it means that the repair operation is successful and the second purification rate R2 has returned to the normal range, so the routine of this time is suspended and terminated. In the routine after the next time, step S206 will be YES, and it will be judged normal.

  Here, the integrated value S is not a value directly used for urea water injection amount control, but is an index value for determining whether or not the value of the estimated adsorption amount We is almost correct. Therefore, even if the value of the integrated value S, which is the second estimated adsorption amount, deviates greatly from the true value, no direct influence on the exhaust emission occurs.

  However, if the integrated value S is greatly deviated, it is impossible to accurately determine whether the estimated adsorption amount We is normal or abnormal, which may cause erroneous determination or erroneous diagnosis. For example, if the estimated normal adsorption amount We is erroneously determined to be abnormal, useless inspection and maintenance must be performed, which increases the burden on the user. If the estimated adsorption amount We, which is originally abnormal, is erroneously determined to be normal, NOx slip or ammonia slip due to an error increase in the estimated adsorption amount We occurs, and exhaust gas performance deteriorates.

  In the present embodiment, when the second purification rate R2 is out of the normal range, the integrated value S is repaired on the assumption that there is a possibility that the integrated value S may be abnormal. The value of the integrated value S can be returned to a normal value by a repair operation, and the above-described erroneous determination and various problems caused by this can be solved. Further, the abnormality determination can accurately detect the abnormality of the integrated value S, and can solve the erroneous determination and various problems caused by the erroneous determination.

  As described above, in the present embodiment, the first purification rate R1 and the second purification rate R2 are compared with the normal range to determine whether or not the estimated adsorption amount We and the integrated value S are normal. Therefore, it can be suitably determined whether or not the estimated adsorption amount We, which is the main first estimated adsorption amount used for controlling the urea water injection amount, is normal, and the estimation error of the estimated adsorption amount We can be increased early. Can be detected. Further, it can be determined whether or not the integrated value S that is the auxiliary second estimated adsorption amount is normal, and an increase in the estimated error of the integrated value S can be detected at an early stage. Further, it is possible to prevent an erroneous determination related to the determination of whether the estimated adsorption amount We is using the integrated value S.

  In the present embodiment, when one of the first purification rate R1 and the second purification rate R2 is outside the normal range, one value of the estimated adsorption amount We and the integrated value S corresponding to the one purification rate is determined before the determination. Perform a repair operation to repair. For this reason, one value of the estimated adsorption amount We and the integrated value S can be returned to a normal value by a repair operation, and wasteful abnormality determination can be prevented in advance, and abnormality determination can be minimized. it can.

  In the present embodiment, in the repair operation, the value of one estimated adsorption amount corresponding to one purification rate is replaced with the value of the other estimated adsorption amount corresponding to the other purification rate or a value obtained by correcting this value. . That is, the value of one estimated adsorption amount that may be abnormal is replaced with the value of the other estimated adsorption amount that seems to be normal, and the calculation of one estimated adsorption amount is executed. Thereby, the possibility that the value of one estimated adsorption amount can be restored increases, and the restoration operation can be performed smoothly.

  Moreover, in this embodiment, when one purification rate is outside a normal range after performing a repair operation, one estimated adsorption amount is determined to be abnormal. In other words, the estimated adsorption amount is determined to be abnormal only when one of the purification rates does not fall within the normal range even after the repair operation is performed, so that the determination reliability can be improved.

  In the present embodiment (second determination method), an embodiment in which only the repair operation portion is extracted and the normal / abnormal determination portion is omitted is possible, and an invention corresponding to this can be grasped. In this case, steps S207, S210, S211, S214, S215, and S217 can be omitted from the routine of FIG.

  As can be understood from the above description, the ECU 100 of the present embodiment corresponds to an estimation unit, a control unit, a determination unit, a calculation unit, and a restoration unit in the claims. Further, the ECU 100, the upstream side NOx sensor 47, and the downstream side NOx sensor 48 of the present embodiment constitute a detection unit referred to in the claims.

  Although the embodiments of the present invention have been described in detail above, various other embodiments of the present invention are possible.

  (1) For example, an embodiment in which the above-described repair operation portion is omitted and only the normal / abnormal determination portion is left is possible. In this case, steps S209, S210, S213, S214, and S216 can be omitted from the routine of FIG.

  (2) If the estimated adsorption amount We is calculated based on the result of feedback control based on the sensor output of the downstream NOx sensor 48, instead of determining that the estimated adsorption amount We is abnormal, or In addition, it may be determined that the feedback control is abnormal.

  (3) The reducing agent may be other than urea water as long as it has an equivalent function.

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

1 Internal combustion engine
4 Exhaust passage 24 NOx catalyst 25 Urea injector 47 Upstream NOx sensor 48 Downstream NOx sensor 100 Electronic control unit (ECU)

Claims (6)

A selective reduction type NOx catalyst provided in the exhaust passage;
A reducing agent injection valve provided in the exhaust passage upstream of the NOx catalyst;
An estimation unit for calculating a first estimated adsorption amount and a second estimated adsorption amount which are different estimated values of the ammonia adsorption amount of the NOx catalyst;
A control unit that controls the reducing agent injection amount injected from the reducing agent injection valve based on the first estimated adsorption amount calculated by the estimating unit;
A detection unit for detecting an actual purification rate of the NOx catalyst;
A determination unit that determines whether the first estimated adsorption amount and the second estimated adsorption amount calculated by the estimation unit are normal based on the actual purification rate detected by the detection unit;
With
The determination unit
Calculate the normal range of the purification rate based on the actual purification rate,
Calculating the first purification rate based on the first estimated adsorption amount and calculating the second purification rate based on the second estimated adsorption amount;
An exhaust gas purification apparatus for an internal combustion engine, wherein the first purification rate and the second purification rate are compared with a normal range to determine whether or not the first estimated adsorption amount and the second estimated adsorption amount are normal. When one of the first purification rate and the second purification rate is out of the normal range, one value of the first estimated adsorption amount and the second estimated adsorption amount corresponding to the one purification rate is set to the other value before the determination. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, further comprising a repairing unit that performs a repairing operation for repairing using the engine. In the repair operation, the repair unit replaces one estimated adsorption amount value corresponding to one purification rate with the other estimated adsorption amount value corresponding to the other purification rate or a value obtained by correcting this value. The exhaust emission control device for an internal combustion engine according to claim 2, wherein calculation of one estimated adsorption amount is executed. The exhaust gas purification of an internal combustion engine according to claim 2 or 3, wherein the determination unit determines that one of the estimated adsorption amounts is abnormal when one of the purification rates is out of a normal range after performing the repair operation by the repair unit. apparatus. A selective reduction type NOx catalyst provided in the exhaust passage;
A reducing agent injection valve provided in the exhaust passage upstream of the NOx catalyst;
An estimation unit for calculating a first estimated adsorption amount and a second estimated adsorption amount which are different estimated values of the ammonia adsorption amount of the NOx catalyst;
A control unit that controls the reducing agent injection amount injected from the reducing agent injection valve based on the first estimated adsorption amount calculated by the estimating unit;
A detection unit for detecting an actual purification rate of the NOx catalyst;
A normal range of the purification rate is calculated based on the actual purification rate detected by the detection unit, a first purification rate is calculated based on the first estimated adsorption amount, and a second purification is performed based on the second estimated adsorption amount. A calculation unit for calculating a rate;
When one of the first purification rate and the second purification rate is outside the normal range, one value of the first estimated adsorption amount and the second estimated adsorption amount corresponding to the one purification rate is used by using the other value. A repair unit for performing a repair operation for repair;
An exhaust emission control device for an internal combustion engine, comprising: In the repair operation, the repair unit replaces one estimated adsorption amount value corresponding to one purification rate with the other estimated adsorption amount value corresponding to the other purification rate or a value obtained by correcting this value. The exhaust purification device for an internal combustion engine according to claim 5, wherein calculation of one estimated adsorption amount is executed.

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