JP7155566B2 - Engine catalyst abnormality determination method and engine catalyst abnormality determination device - Google Patents

Description

The technology disclosed herein belongs to a technical field related to an engine catalyst abnormality determination method and an engine catalyst abnormality determination device.

Conventionally, a selective reduction NOx catalyst that is provided in an exhaust passage and reduces NOx with a supplied reducing agent, and a reducing agent supply capable of supplying ammonia as a reducing agent or a precursor of ammonia to the selective reduction NOx catalyst An engine comprising means is known.

For example, Patent Document 1 describes a selective reduction NOx catalyst that is provided in an exhaust passage of an internal combustion engine (engine) and uses ammonia as a reducing agent, and ammonia or a precursor of ammonia in the exhaust that flows into the selective reduction NOx catalyst. and a NOx sensor disposed in a passage on the downstream side of the selective reduction type NOx catalyst and detecting ammonia in the exhaust gas as NOx. In the one that determines the deterioration of the NOx type NOx catalyst, the amount of ammonia flowing out from the selective reduction type NOx catalyst is estimated, and if the amount of ammonia flowing out is large, whether to limit the use of the detected value of the NOx sensor in the deterioration determination. , or prohibiting the deterioration determination itself.

Further, in Patent Document 1, when the temperature of the selective reduction NOx catalyst rises, the amount of ammonia adsorbed on the selective reduction NOx catalyst increases, and when the amount of ammonia adsorbed becomes excessive, the selective reduction type It is disclosed that the NOx catalyst is more likely to be discharged into the downstream passage.

JP 2014-109224 A

However, according to studies by the inventors of the present application, the amount of ammonia discharged into a passage downstream of the selective reduction NOx catalyst (hereinafter sometimes referred to as the slip amount of ammonia) was determined by the balance between the adsorption and desorption kinetics of That is, when the ammonia adsorption reaction rate is higher than the desorption reaction rate, the ammonia adsorption reaction appears to be dominant and the ammonia slip amount decreases, while the ammonia desorption reaction rate is higher than the adsorption reaction rate. When it is larger than the speed, the desorption reaction of ammonia apparently becomes dominant, and the slip amount of ammonia increases. Therefore, in order to improve the accuracy of estimating the slip amount of ammonia, not only the adsorption amount of ammonia to the selective reduction NOx catalyst as in Patent Document 1, but also the adsorption reaction rate and desorption reaction rate of ammonia Speed and need to be considered.

The technology disclosed herein has been made in view of this point, and its purpose is to reduce the amount of fuel to a passage downstream of the selective reduction NOx catalyst in an engine equipped with a selective reduction NOx catalyst. to improve the accuracy of estimating ammonia emissions.

In order to solve the above problems, the technology disclosed herein provides a selective reduction NOx catalyst that is provided in an exhaust passage of an engine and reduces NOx with a supplied reducing agent; A catalyst abnormality determination method for an engine including reducing agent supply means capable of supplying ammonia as a reducing agent or a precursor of ammonia, wherein the engine is positioned downstream of the selective reduction NOx catalyst in the exhaust passage. a step of detecting the state of the selective reduction type NOx catalyst, further comprising a NOx sensor whose output value changes according to the amount of NOx and the amount of ammonia in the exhaust gas; A dividing step of virtually dividing so as to line up in the flow direction of the region to set n (n is an integer of 2 or more) virtual regions, and based on the detected state of the selective reduction NOx catalyst, an adsorption reaction rate estimating step of estimating the adsorption reaction rate of ammonia in the selective reduction NOx catalyst for each of the virtual regions; a desorption reaction rate estimating step of estimating a desorption reaction rate for each virtual region; an estimated adsorption reaction rate estimated in the adsorption reaction rate estimating step; and an estimated desorption reaction estimated in the desorption reaction rate estimating step. a slip amount estimating step of estimating a slip amount of ammonia, which is an amount of ammonia discharged into a passage downstream of the selective reduction NOx catalyst of the exhaust passage, based on the speed; and the output value of the NOx sensor. and an abnormality determination step of determining whether or not there is an abnormality in the selective reduction NOx catalyst based on , the step of detecting the state of the selective reduction type NOx catalyst includes a catalyst temperature detection step of detecting the temperature of the selective reduction type NOx catalyst; setting the catalyst temperature of each of the virtual regions so that the catalyst temperature of each of the virtual regions increases, and the step of estimating the adsorption reaction rate is based on the catalyst temperature of each of the n virtual regions, and the n The desorption reaction rate estimating step estimates the desorption reaction rate for each virtual region based on the catalyst temperature for each of the n virtual regions, and In the slip amount estimation step, from the i-th virtual region (i is an integer from 1 to n−1) among the n virtual regions, (i+1) including an internal slip amount estimating step of estimating a slip amount of ammonia to the n-1th virtual region, and executing the internal slip amount estimating step in order from the first virtual region located on the most upstream side of the exhaust gas; After the internal slip amount estimating step is executed until the slip amount of ammonia from the virtual area to the n-th virtual area is estimated, the slip amount of ammonia to the exhaust passage is estimated from the n-th virtual area. and a step of estimating the estimated value as an ammonia slip amount of the selective reduction NOx catalyst, and the abnormality determination step is performed when the ammonia slip amount estimated in the slip amount estimating step is equal to or greater than a predetermined slip amount. , includes an abnormality determination limiting step for limiting the abnormality determination, and the state of the selective reduction NOx catalyst further includes an HC poisoning amount, which is an amount of HC adsorbed to the acid points of the selective reduction NOx catalyst. , the step of detecting the state of the selective reduction NOx catalyst further includes a step of estimating the HC poisoning amount for each of the virtual regions, and the adsorption reaction rate estimating step includes determining whether the estimated HC poisoning amount is The composition is such that the larger the value, the smaller the adsorption reaction rate is estimated .

According to this configuration, the slip amount of ammonia is estimated based on the estimated adsorption reaction speed and the estimated desorption reaction speed estimated based on the state of selective reduction type NOx. Therefore, the slip amount of ammonia can be estimated in consideration of the adsorption reaction rate and desorption reaction rate of ammonia in the selective reduction NOx catalyst. Thereby, the estimation accuracy of the slip amount of ammonia can be improved.

Further, when ammonia actually flows into the selective reduction NOx catalyst, part of it is adsorbed in the exhaust upstream side of the selective reduction NOx catalyst (hereinafter referred to as the upstream part), and the remainder is the selective reduction type It flows into a portion of the NOx catalyst on the exhaust downstream side (hereinafter referred to as a downstream portion). Ammonia desorbed from the upstream portion also flows into the downstream portion. That is, the total value of the remaining amount of ammonia and the amount of ammonia desorbed from the upstream portion is the slip amount of ammonia from the upstream portion to the downstream portion (hereinafter referred to as internal slip amount). Then, the total value of the amount of ammonia that could not be adsorbed by the downstream portion out of the ammonia that slipped to the downstream portion and the amount of ammonia that was desorbed from the downstream portion was obtained from the actual selective reduction NOx catalyst. is the slip amount of ammonia. Therefore, in order to improve the accuracy of estimating the slip amount of ammonia, the internal slip amount of ammonia is estimated, and based on the internal slip amount, from the downstream portion of the selective reduction type NOx catalyst to the outside of the selective reduction type NOx catalyst. It is preferable to estimate the amount of slip of ammonia into the .

Therefore, in the above-described embodiment, the selective reduction NOx catalyst is virtually divided so as to be aligned in the flow direction of the exhaust gas, n virtual regions are set, and the i-th virtual region to the (i+1)-th virtual region are set. Estimate the amount of internal slip to the virtual region of This estimation of the internal slip amount is repeated in order from the first virtual area until the internal slip amount of ammonia from the (n-1)th virtual area to the nth virtual area is estimated. After that, the slip amount of ammonia to the exhaust passage is estimated from the n-th virtual area. Then, the ammonia slip amount from the n-th virtual area to the exhaust passage is estimated as the ammonia slip amount from the selective reduction NOx catalyst. As a result, the adsorption reaction and desorption reaction in the actual selective reduction NOx catalyst are reflected, so the accuracy of estimating the slip amount of ammonia can be further improved.

In addition, since the output value of the NOx sensor changes according to the amount of NOx and the amount of ammonia in the exhaust gas, when the amount of ammonia in the exhaust gas is large, even when the amount of NOx is small, the NOx in the exhaust gas I consider it to be too much. Therefore, when determining whether or not there is an abnormality in the selective reduction NOx catalyst based on the output value of the NOx sensor, even if the amount of NOx in the exhaust gas is small, the selective reduction NOx catalyst If there is an abnormality in the Therefore, by limiting the abnormality determination when the ammonia slip amount estimated in the slip amount estimation step is equal to or greater than the predetermined slip amount, the selective reduction type NOx catalyst can It is possible to suppress erroneous determination that there is an abnormality.

In the catalyst abnormality determination method, the state of the selective reduction NOx catalyst includes an ammonia adsorption amount of the selective reduction NOx catalyst, and the step of detecting the state of the selective reduction NOx catalyst includes: may include an ammonia adsorption amount estimation step of estimating the ammonia adsorption amount of the

That is, the adsorption reaction rate and the desorption reaction rate mainly depend on the ammonia adsorption amount of the NOx selective reduction catalyst and the NOx selective reduction catalyst. That is, by estimating the ammonia adsorption amount of the selective reduction NOx catalyst and detecting the temperature of the selective reduction NOx catalyst, it is possible to improve the estimation accuracy of the adsorption reaction rate and the desorption reaction rate. Therefore, it is possible to further improve the accuracy of estimating the slip amount of ammonia.

In the catalyst abnormality determination method, the state of the selective reduction NOx catalyst includes an ammonia adsorption amount of the selective reduction NOx catalyst, and the step of detecting the state of the selective reduction NOx catalyst includes: In the ammonia adsorption amount estimation step, the adsorption amount of ammonia is estimated for each of the n virtual regions, and in the adsorption reaction rate estimation step, the The adsorption reaction rate is estimated for each of the n virtual regions based on the estimated ammonia adsorption amount for each of the n virtual regions, and in the desorption reaction speed estimation step, the estimated ammonia adsorption for each of the n virtual regions is calculated. estimating the desorption reaction rate for each of the virtual regions, and in the internal slip amount estimating step, based on the estimated adsorption reaction speed and the estimated desorption reaction speed in each of the virtual regions, the i-th virtual A slip amount of ammonia from the region to the (i+1)-th virtual region may be estimated.

That is, in the actual selective reduction NOx catalyst, the ammonia adsorption amount does not have a uniform distribution, except when the ammonia adsorption amount of the selective reduction NOx catalyst is near 0 or near the adsorption limit. not That is, the ammonia adsorption amount differs for each virtual region, and accordingly the adsorption reaction speed and desorption reaction speed also differ for each virtual region. Therefore, in the above embodiment, the ammonia adsorption amount is estimated for each virtual area, and the adsorption reaction rate and desorption reaction rate for each virtual area are estimated based on the estimated ammonia adsorption amount for each virtual area. ing. As a result, the adsorption reaction and desorption reaction in the actual selective reduction NOx catalyst are more accurately reflected, and the accuracy of estimating the slip amount of ammonia can be further improved.

In the catalyst abnormality determination method for estimating the ammonia slip amount by calculating the internal slip amount, an ammonia concentration estimation step of estimating the ammonia concentration of the exhaust gas introduced into the virtual region is performed for each of the n virtual regions. Further including, in the internal slip amount estimating step, the amount of ammonia from the i-th virtual region to the (i+1)-th virtual region in consideration of the ammonia concentration of the exhaust gas introduced into the i-th virtual region Each slip amount may be estimated.

That is, since the adsorption reaction rate also depends on the ammonia concentration in the exhaust gas, it is preferable to estimate the adsorption reaction rate in consideration of the ammonia concentration. Therefore, by taking into account the concentration of ammonia in the exhaust gas, the internal slip amount can be estimated with higher accuracy, and the accuracy of estimating the ammonia slip amount of the selective reduction NOx catalyst can be further improved. can.

In the catalyst abnormality determination method, the state of the selective reduction NOx catalyst includes the temperature of the selective reduction NOx catalyst, and the step of detecting the state of the selective reduction NOx catalyst includes the temperature of the selective reduction NOx catalyst. In the desorption reaction rate estimating step, the rate of change of the estimated desorption reaction rate with respect to the detected amount of change in catalyst temperature is The estimated desorption reaction rate may be estimated so as to be greater than the change rate of the estimated adsorption reaction rate.

That is, the adsorption reaction of ammonia to the selective reduction NOx catalyst is a reaction in which ammonia is only adsorbed to the acid sites of the selective reduction NOx catalyst, while the desorption reaction of ammonia from the selective reduction NOx catalyst is It is a reaction that separates the adsorbed ammonia from the acid site of the selective reduction NOx catalyst. Therefore, the activation energy of the desorption reaction is considerably larger than the activation energy of the adsorption reaction. In other words, while the adsorption reaction rate is less likely to be affected by the temperature of the selective reduction NOx catalyst, the desorption reaction rate is more likely to be affected by the temperature of the selective reduction NOx catalyst.

Therefore, with the above configuration, the difference in magnitude between the activation energy of the desorption reaction and the activation energy of the adsorption reaction is reflected, and the estimation accuracy of the desorption reaction rate and the adsorption reaction rate is improved. Thereby, the estimation accuracy of the ammonia slip amount can be further improved.

In the catalyst abnormality determination method, the engine is disposed upstream of the selective reduction NOx catalyst in the exhaust passage, and is capable of absorbing NOx in the exhaust gas and reducing the absorbed NOx. and NOx catalyst regeneration control means for making the air-fuel ratio of the exhaust gas close to or richer than the stoichiometric air-fuel ratio in order to reduce the NOx stored in the storage-reduction type NOx catalyst. estimating the amount of ammonia generated during reduction for estimating the amount of ammonia discharged from the storage reduction type NOx catalyst into the exhaust gas when the NOx stored in the storage reduction type NOx catalyst is reduced by the NOx catalyst regeneration control means; the step of detecting the state of the selective reduction NOx catalyst, wherein the state of the selective reduction NOx catalyst includes an ammonia adsorption amount of the selective reduction NOx catalyst; and an ammonia adsorption amount estimation step of estimating an adsorption amount, wherein the ammonia adsorption amount estimation step includes the amount of ammonia supplied by the reducing agent supply means or the amount of ammonia precursor, and the amount of ammonia generated during reduction. The ammonia adsorption amount may be estimated in consideration of the amount of ammonia estimated in the estimation step.

That is, by making the air-fuel ratio of the exhaust gas close to the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, the reaction to reduce the NOx occluded in the NOx storage reduction catalyst requires NOx and Includes reaction with HC. Therefore, in the process of reducing NOx stored in the storage-reduction type NOx catalyst, hydrogen in HC reacts with nitrogen in NOx to generate ammonia. In order to increase the accuracy of estimating the amount of ammonia adsorbed by the selective reduction NOx catalyst, it is preferable to consider the amount of ammonia generated by reducing the NOx stored in the NOx storage reduction catalyst. Therefore, with the configuration as described above, it is possible to improve the accuracy of estimating the ammonia adsorption amount of the selective reduction NOx catalyst in the ammonia adsorption amount estimating step. can be improved .

The technology according to the present disclosure also targets an engine catalyst abnormality determination device. Specifically, a selective reduction NOx catalyst that is provided in an exhaust passage of an engine and reduces NOx with a supplied reducing agent, and ammonia or a precursor of ammonia as the reducing agent is added to the selective reduction NOx catalyst. A device for detecting a catalyst abnormality of an engine including means for supplying a reducing agent capable of being supplied is targeted, and the means for detecting the state of the selective reduction type NOx catalyst and the selective reduction type NOx catalyst are arranged in the flow direction of the exhaust gas. and virtual dividing means for setting n (n is an integer equal to or greater than 2) virtual regions; and based on the detected state of the selective reduction NOx catalyst, the selective reduction NOx catalyst and a desorption reaction for estimating the desorption reaction rate of ammonia in the selective reduction NOx catalyst based on the detected state of the selective reduction NOx catalyst. and the selective reduction NOx catalyst in the exhaust passage based on the estimated adsorption reaction speed estimated by the adsorption reaction speed estimation means and the estimated desorption reaction speed estimated by the desorption reaction speed estimation means. slip amount estimating means for estimating a slip amount of ammonia, which is the amount of ammonia discharged into a passage downstream of the a NOx sensor whose output value changes according to the amount of NOx and the amount of ammonia; and abnormality determination means for determining whether or not there is an abnormality in the selective reduction NOx catalyst based on the output value of the NOx sensor. an abnormality determination limiting means for limiting the abnormality determination by the abnormality determining means when the ammonia slip amount estimated by the slip amount estimating means is equal to or greater than a predetermined slip amount; The means for detecting the state includes catalyst temperature detection means for detecting the temperature of the selective reduction NOx catalyst, and based on the temperature detected by the catalyst temperature detection means, the catalyst temperature increases in the virtual region on the upstream side. The catalyst temperature of each of the virtual regions is set to be higher, and the adsorption reaction rate estimating means estimates the adsorption reaction rate of each of the n virtual regions based on the catalyst temperature of each of the n virtual regions. The desorption reaction rate estimating means estimates the desorption reaction rate for each virtual region based on the catalyst temperature for each of the n virtual regions, and the slip amount estimating means estimates the n virtual regions. From the i-th virtual region (i is an integer from 1 to n-1) to the (i+1)-th virtual region estimating the internal slip amount, which is the ammonia slip amount, and estimating the internal slip amount in order from the first virtual region located on the most upstream side of the exhaust gas, and calculating the n-1th virtual region to the nth virtual region After estimating the internal slip amount of ammonia into the exhaust passage, the estimated value is estimated as the ammonia slip amount of the selective reduction NOx catalyst. The state of the selective reduction NOx catalyst further includes an HC poisoning amount, which is the amount of HC adsorbed to the acid sites of the selective reduction NOx catalyst, and the means for detecting the state of the selective reduction NOx catalyst is and means for estimating the HC poisoning amount for each of the virtual regions, wherein the adsorption reaction rate estimating means estimates a smaller adsorption reaction rate as the estimated HC poisoning amount increases .

Even in this configuration, the output value of the NOx sensor changes according to the amount of NOx and the amount of ammonia in the exhaust gas. If there is an abnormality in the catalyst, an erroneous judgment may be made. Therefore, when the slip amount of ammonia estimated by the slip amount estimating means is equal to or greater than the predetermined slip amount, the abnormality determination is restricted so that when the amount of NOx in the exhaust gas is small, the selective reduction NOx catalyst is abnormal. It is possible to suppress erroneous determination when there is

In one embodiment of the engine catalyst abnormality determination device, the state of the selective reduction NOx catalyst includes an ammonia adsorption amount of the selective reduction NOx catalyst and a temperature of the selective reduction NOx catalyst. The means for detecting the state of the NOx-type NOx catalyst includes ammonia adsorption amount estimation means for estimating the ammonia adsorption amount of the selective reduction-type NOx catalyst, and catalyst temperature detection means for detecting the temperature of the selective reduction-type NOx catalyst. .

As described above, the adsorption reaction rate and the desorption reaction rate mainly depend on the ammonia adsorption amount of the NOx selective reduction catalyst and the NOx selective reduction catalyst. That is, by estimating the ammonia adsorption amount of the selective reduction NOx catalyst and detecting the temperature of the selective reduction NOx catalyst, it is possible to improve the estimation accuracy of the adsorption reaction rate and the desorption reaction rate. Therefore, it is possible to further improve the accuracy of estimating the slip amount of ammonia .

As described above, according to the technology disclosed herein, the slip amount of ammonia can be estimated in consideration of the adsorption reaction rate and desorption reaction rate of ammonia in the selective reduction NOx catalyst. , the accuracy of estimating the slip amount of ammonia can be improved.

1 is a schematic configuration diagram of an engine system to which an engine catalyst abnormality determination device according to an exemplary embodiment is applied; FIG. 2 is a block diagram showing a control system of the engine system; FIG. FIG. 4 is a diagram showing control maps for passive DeNOx control and active DeNOx control; 4 is a flow chart when selecting a catalyst for purifying exhaust gas. It is a part of the flowchart when performing DeNOx control. It is the remainder of the flowchart when executing the DeNOx control. It is a schematic diagram which shows the NOx detection principle of a NOx sensor. FIG. 3 is a schematic diagram schematically showing the adsorption reaction and desorption reaction of ammonia within the SCR catalyst. FIG. 4 is a conceptual diagram showing a model for estimating the slip amount of ammonia from the SCR catalyst; 4 is a flowchart showing a processing operation for estimating a slip amount of ammonia from an SCR catalyst; 4 is a flow chart showing a processing operation for determining abnormality of an SCR catalyst; 4 is a time chart schematically showing changes over time of each parameter in abnormality determination of the SCR catalyst;

Exemplary embodiments are described in detail below with reference to the drawings.

FIG. 1 shows an engine system 200 to which an engine catalyst abnormality determination device according to the present embodiment is applied. The engine system 200 includes an engine E as a diesel engine, an intake system IN that supplies intake air to the engine E, a fuel supply system FS that supplies fuel to the engine E, and an EX that discharges exhaust gas from the engine E. , and sensors 100 - 119 that detect various conditions relating to the engine system 200 . Further, the engine system 200 includes a PCM (Power-train Control Module) 60 (see FIG. 2) for controlling the engine system 200, and a DCU (Dosing Control Unit) 70 for controlling the urea injector 51, which will be described later. is provided. This engine system 200 is an engine system provided in a vehicle, and an engine E is used as a driving source of the vehicle.

The intake system IN has an intake passage 1 through which intake air passes. In this intake passage 1, in order from the upstream side, there are an air cleaner 3, a compressor of the first turbocharger 5, a compressor of the second turbocharger 6, an intercooler 8, a throttle valve 7, and a surge tank. 12 are provided. The intake passage 1 is also provided with an intake bypass passage 1a that bypasses the compressor of the second turbocharger 6, and an intake bypass valve 6a that opens and closes the intake bypass passage 1a.

An air flow sensor 101 that detects the amount of intake air and a first intake temperature sensor 102 that detects the temperature of the intake air are provided in the intake passage 1 immediately downstream of the air cleaner 3 . A passage between the first turbocharger 5 and the second turbocharger 6 in the intake passage 1 is provided with a first intake pressure sensor 103 that detects the pressure of intake air. A second intake air temperature sensor 106 that detects the temperature of the intake air that has passed through the intercooler 8 is provided in the intake passage 1 immediately downstream of the intercooler 8 . The throttle valve 7 is provided with a position sensor 105 for detecting the opening degree of the throttle valve 7 . The surge tank 12 is provided with a second intake pressure sensor 108 that detects the pressure of intake air in the intake manifold.

The engine E includes an intake valve 15 for introducing intake air supplied from an intake manifold of the intake passage 1 into a combustion chamber 17, a fuel injection valve 20 for injecting fuel toward the combustion chamber 17, and heat generated by energization. A blow plug 21 having a heat generating portion in the combustion chamber 17, a piston 23 reciprocating due to combustion of the air-fuel mixture in the combustion chamber 17, and exhaust gas generated by combustion of the air-fuel mixture in the combustion chamber 17. and an exhaust valve 27 for discharging to passage 41 . Piston 23 is connected to crankshaft 25 via connecting rod 24 . The crankshaft 25 is rotated by the reciprocating motion of the piston 23 .

The engine E is provided with a crank angle sensor 100 that detects the rotation angle of the crankshaft. PCM 60 (see FIG. 2) acquires the engine speed based on the detection signal from crank angle sensor 100 .

The fuel system FS has a fuel tank 30 for storing fuel and a fuel supply passage 38 for supplying fuel from the fuel tank 30 to the fuel injection valves 20 . The fuel supply passage 38 is provided with a low-pressure fuel pump 31, a high-pressure fuel pump 33, and a common rail 35 in this order from the upstream side.

The exhaust system EX has an exhaust passage 41 through which exhaust gas passes. In the exhaust gas passage 41, from the upstream side, the turbine of the second turbocharger 6, the turbine of the first turbocharger 5, the NOx catalyst 45 (occlusion reduction type NOx catalyst), and the DPF (Diesel particulate filter) 46, a urea injector 51 that injects urea into the exhaust passage 41 on the downstream side of the DPF 46, an SCR (Selective Catalytic Reduction) catalyst 47 that purifies NOx using the urea injected from the urea injector 51, and an SCR. A slip catalyst 48 that oxidizes and purifies unreacted ammonia discharged from the catalyst 47 is provided. Further, the exhaust passage 41 is provided with an exhaust bypass passage 41a that bypasses the turbine of the second turbocharger 6, and an exhaust bypass valve 6b that opens and closes the exhaust bypass passage 41a. Further, the exhaust passage 41 is provided with a waste gate passage 41b that bypasses the turbine of the first turbocharger 5, and a waste gate valve 5a that opens and closes the waste gate passage 41b.

The NOx catalyst 45 absorbs NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio (the excess air ratio λ is λ>1), and converts the absorbed NOx into the air-fuel ratio of the exhaust gas. is in the vicinity of the stoichiometric air-fuel ratio (λ≈1) or in a rich state (λ<1) smaller than the stoichiometric air-fuel ratio. In addition, the NOx catalyst 45 functions not only as an NSC, but also as a diesel catalyst ( DOC: Diesel Oxidation Catalyst). Specifically, the NOx catalyst 45 is formed by coating the surface of the DOC catalyst layer with the NSC catalyst material.

The DPF 46 is a filter that collects particulate matter (PM) in the exhaust. The PM trapped in the DPF 46 is combusted by exposure to high temperatures and supplied with oxygen, and removed from the DPF 46 .

The SCR catalyst 47 adsorbs ammonia produced from urea injected from the urea injector 51 and reacts (reduces) the adsorbed ammonia with NOx in the exhaust gas to purify it. Therefore, the SCR catalyst 47 corresponds to a selective reduction type NOx catalyst that reduces NOx with the supplied reducing agent, and the urea injector 51 is a reducing agent capable of supplying urea, which is a precursor of ammonia, as a reducing agent. corresponds to the agent supply means. The SCR catalyst 47 is configured by supporting a catalyst metal that reduces NOx with ammonia on zeolite that traps ammonia.

Both the NOx catalyst 45 and the SCR catalyst 47 are catalysts capable of purifying NOx, but the temperatures at which the NOx purification rate (NOx storage rate) increases are different from each other. Specifically, the NOx purification rate of the NOx catalyst 45 is high when the temperature of the NOx catalyst 45 is relatively low, while the NOx purification rate of the SCR catalyst 47 is higher than the temperature of the SCR catalyst 47 (hereinafter referred to as SCR catalyst temperature). increases at relatively high temperatures. In this embodiment, both the NOx catalyst 45 and the SCR catalyst 47 are warmed up by heat supplied from the exhaust gas.

An exhaust pressure sensor 109 that detects the pressure of the exhaust gas and a first exhaust temperature sensor 110 that detects the temperature of the exhaust gas are provided in a passage upstream of the second turbocharger 6 in the exhaust passage 41. . An O2 sensor 111 that detects the oxygen concentration of the exhaust gas is provided in the exhaust passage 41 immediately downstream of the first turbocharger 5 . Around the NOx catalyst 45 in the exhaust passage 41, a second exhaust temperature sensor 112 for detecting the temperature of the exhaust gas in the passage immediately upstream of the NOx catalyst 45 and the exhaust gas in the passage between the NOx catalyst 45 and the DPF 46 are provided. A third exhaust temperature sensor 113 that detects the temperature of the exhaust gas, a differential pressure sensor 114 that detects the pressure difference between the passage immediately upstream of the DPF 46 and the passage immediately downstream of the DPF 46, A fourth exhaust temperature sensor 115 that detects the temperature of the gas, and a first NOx sensor 116 that detects the concentration of NOx at a position in the passage immediately downstream of the DPF 46 and upstream of the urea injector 51 are provided. . Further, in the vicinity of the SCR catalyst 47 in the exhaust passage 41, a catalyst temperature sensor 117 for detecting the SCR catalyst temperature, which is a parameter representing the state of the SCR catalyst 47, and a NOx concentration in the passage immediately downstream of the SCR catalyst 47 are installed. A second NOx sensor 118 is provided to detect. Furthermore, the exhaust passage 41 is provided with a PM sensor 119 that detects PM in the exhaust gas in the passage immediately upstream of the slip catalyst 48 . Catalyst temperature sensor 117 is an example of means for detecting the state of SCR catalyst 47 . Although details will be described later, at least the second NOx sensor 118 is a NOx sensor whose output value changes depending not only on the amount of NOx in the exhaust gas but also on the amount of ammonia.

The engine system 200 in this embodiment further has an EGR device 43 that recirculates part of the exhaust gas to the intake. The EGR device 43 includes an EGR passage 43a connecting a passage upstream of an upstream end of the exhaust bypass passage 41a in the exhaust passage 41 and a passage between the throttle valve 7 and the surge tank 12 in the intake passage 1; It has an EGR cooler 43b for cooling the exhaust gas passing through the passage 43a and a first EGR valve 43c for opening and closing the EGR passage 43a. The EGR device 43 also has an EGR cooler bypass passage 43d that bypasses the EGR cooler 43b, and a second EGR valve 43e that opens and closes the EGR cooler bypass passage.

The engine system 200 of this embodiment is mainly controlled by the PCM 60 mounted on the vehicle. The PCM 60 is a microprocessor comprising a CPU, ROM, RAM, I/O bus, and the like.

Detection signals from various sensors 100 to 119 are input to the PCM 60 . Also, to the PCM 60, an accelerator opening sensor 150 for detecting the accelerator opening corresponding to the operation amount of the accelerator pedal (not shown) of the vehicle and a vehicle speed sensor 151 for detecting the vehicle speed of the vehicle are output. A detection signal is input. The PCM 60 mainly controls the operations of the throttle valve 7, the fuel injection valve 20, the glow plug 21, the first EGR valve 43c and the second EGR valve 43e based on the input signal. The PCM 60 also controls the operation of the urea injector 51 via the DCU 70 by sending an output signal to the DCU 70 .

Although the details will be described later, the PCM 60 includes an ammonia adsorption amount estimator 61 for estimating the ammonia adsorption amount of the SCR catalyst 47, which is a parameter representing the state of the SCR catalyst 47, Abnormality determination for determining whether or not there is an abnormality in the engine system 200 based on a slip amount estimating unit 62 that estimates the amount of ammonia in the exhaust gas in the passage and an abnormality determination condition based on the output value of the second NOx sensor 118 and an abnormality determination limiter 64 that limits the abnormality determination by the abnormality determination unit 63 . The ammonia adsorption amount estimator 61 is an example of means for detecting the state of the SCR catalyst 47 .

<Normal fuel injection control>
The PCM 60 controls the fuel injection valve so that the air-fuel ratio of the air-fuel mixture in the combustion chamber 17 is leaner than the stoichiometric air-fuel ratio (λ>1) in normal fuel injection control that does not perform DeNOx control, which will be described later. 20. Also, in normal fuel injection control, the PCM 60 stops the post-injection performed in the DeNOx control and executes only the main injection.

In normal fuel injection control, the PCM 60 sets the injection amount of fuel in the main injection according to the operating state of the vehicle. Specifically, first, the PCM 60 acquires input signals from various sensors 100 to 119, 150, and 151. FIG. Next, the PCM 60 sets a target acceleration based on the acquired operating conditions of the vehicle including the operation of the accelerator pedal. The PCM 60 then determines the target torque of the engine E for achieving the determined target acceleration. Then, the PCM 60 calculates the injection amount to be injected from the fuel injection valve 20 based on the target torque and the engine speed so that the determined target torque is output from the engine E.

Also, in normal fuel injection control, the PCM 60 sets the injection timing of the main injection in accordance with the operating state of the vehicle.

After that, the PCM 60 controls the fuel injection valve 20 to achieve the set injection amount and injection timing.

<DeNOx control>
Next, the DeNOx control for releasing NOx stored in the NOx catalyst 45 (hereinafter sometimes referred to as stored NOx) from the NOx catalyst 45 will be described.

In this embodiment, the PCM 60 reduces the NOx stored in the NOx catalyst 45 to almost 0 when the NOx storage amount is equal to or greater than the first predetermined storage amount (for example, when the NOx storage amount is near the storage limit). DeNOx control is executed in order to Further, in the present embodiment, the PCM 60 ensures that even if the NOx storage amount is less than the first predetermined storage amount, the NOx storage amount is equal to or larger than the second predetermined storage amount, which is less than the first predetermined storage amount, and the vehicle is accelerated. DeNOx control may be executed when the air-fuel ratio of the exhaust gas changes to the rich side. In the following description, DeNOx control executed when the NOx storage amount is equal to or greater than the first predetermined storage amount is referred to as active DeNOx control. DeNOx control executed when the air-fuel ratio changes to the rich side is called passive DeNOx control. When these are not distinguished, they are simply referred to as DeNOx control.

As described above, the NOx catalyst 45 reduces the stored NOx in a state where the air-fuel ratio of the exhaust gas is close to the stoichiometric air-fuel ratio (λ≈1) or in a rich state (λ<1) smaller than the stoichiometric air-fuel ratio. be. Therefore, in the DeNOx control, it is necessary to lower the air-fuel ratio of the exhaust gas than during normal operation in order to reduce the stored NOx. Therefore, in the present embodiment, the post injection is executed in addition to the main injection to lower the air-fuel ratio of the exhaust gas and reduce the stored NOx. The excess air ratio λ during DeNOx control is, for example, λ=0.94 to 1.06.

The injection amount of fuel in the post injection (hereinafter simply referred to as post injection amount) is set based on the operating state of the engine E. As shown in FIG. Specifically, first, the PCM 60 determines at least the amount of intake air detected by the air flow sensor 101, the oxygen concentration of the exhaust gas detected by the O2 sensor 111, and the main injection calculated in the above fuel injection control. get the quantity. Furthermore, the PCM 60 also acquires the amount of exhaust gas (EGR amount) recirculated to the intake system IN by the EGR device 43, which is obtained by a predetermined model or the like.

Next, the PCM 60 calculates the amount of air to be introduced into the engine E based on the obtained fresh air amount and EGR gas amount. Then, the PCM 60 calculates the oxygen concentration of the air introduced into the engine E from the calculated air amount.

Next, the PCM 60 calculates the post-injection amount required to bring the air-fuel ratio of the exhaust gas to a target air-fuel ratio (hereinafter referred to as a target DeNOx air-fuel ratio) near or below the theoretical air-fuel ratio. That is, the PCM 60 determines how much fuel should be injected in the post injection in addition to the injection amount of the main injection in order to bring the air-fuel ratio of the exhaust gas to the target DeNOx air-fuel ratio. At this time, the PCM 60 calculates the post-injection amount in consideration of the difference between the oxygen concentration detected by the O2 sensor 111 and the oxygen concentration of the air introduced into the engine E.

In the present embodiment, the passive DeNOx control is executed when the air-fuel ratio of the exhaust gas changes to the rich side due to acceleration of the vehicle. The injection amount is smaller in passive DeNOx control than in active DeNOx control. Therefore, if the passive DeNOx control is performed as frequently as possible and the active DeNOx control is performed less frequently, it is possible to suppress deterioration in fuel consumption due to the DeNOx control.

As for the fuel injection timing in the post-injection, in the present embodiment, the injection timing is changed depending on the form of DeNOx control. Specifically, the PCM 60 sets the timing at which the post-injected fuel is combusted in the combustion chamber 17 of the engine E when executing the active DeNOx control. On the other hand, when the passive DeNOx control is executed, the timing is set such that the post-injected fuel is not burned in the combustion chamber 17 of the engine E and is discharged to the exhaust passage 41 as unburned fuel.

Here, operating conditions for executing active DeNOx control and passive DeNOx control will be described with reference to FIG. 3 . In FIG. 3, the horizontal axis indicates the engine speed, and the vertical axis indicates the engine load. Further, in FIG. 3, a curve L1 indicates the maximum torque line of the engine E. As shown in FIG.

In this embodiment, the PCM 60 is in a medium load range in which the engine load is greater than or equal to the first predetermined load Lo1 and less than the second predetermined load Lo2 (>the first predetermined load Lo1), and the engine speed is the first predetermined speed. Active DeNOx control is executed in the middle speed range of N1 or more and less than the second predetermined speed N2 (>first predetermined speed N1), that is, in the first operating region R1 shown in FIG. This is to suppress the generation of smoke and HC by allowing ignition to occur in a state in which air and fuel are appropriately mixed. For this reason, for example, the ignition of post-injected fuel may be effectively delayed by introducing an appropriate amount of EGR gas during active DeNOx control.

The reason for suppressing the generation of HC during active DeNOx control is that when EGR gas is introduced as described above, HC is also recirculated to the intake system IN as EGR gas, and this HC becomes a binder and combines with soot. This is to prevent the passage of EGR gas from being clogged due to the In addition, this is to prevent HC from being discharged without being purified when active DeNOx control is executed in a region where the temperature of the NOx catalyst 45 is low and HC purification performance is not ensured.

On the other hand, in the present embodiment, passive DeNOx control is executed when the engine load is in a region considerably higher than the first operating region R1, that is, in the second operating region R2 shown in FIG. This is because when the engine load is in the second operating region R2, the temperature of the NOx catalyst 45 is usually at a temperature at which the DOC, which constitutes the NOx catalyst 45, exhibits the HC purification performance. This is because the unburned fuel (HC) discharged into the exhaust passage 41 by passive DeNOx control is sufficiently purified by the NOx catalyst 45 .

Operating regions other than the first and second operating regions R1 and R2 will be explained. In a region in which the engine load is higher than the first operating region R1 but lower than the second operating region R2, the in-cylinder temperature of the engine E increases. Therefore, combustion occurs when the air and fuel are not properly mixed, and smoke and HC are likely to occur. In a region where the engine load is the same as in the first operating region R1 but the engine speed is higher than the first operating region R1, the time required for one stroke of the engine E is short, so air and fuel are properly mixed. Combustion occurs when it is not done, and smoke and HC are likely to occur. Furthermore, in a region where the engine load is lower than the first operating region R1, or a region where the engine load is the same as the first operating region R1 but the engine speed is lower than the first operating region R1, the temperature of the NOx catalyst 45 is likely to be lower than the temperature at which stored NOx can be reduced. For these reasons, in the present embodiment, the DeNOx control is not executed when the operating range of the engine E is in an operating range other than the first and second operating ranges R1 and R2.

When the operating region of the engine E is in an operating region other than the first and second operating regions R1 and R2, and the NOx storage amount is equal to or greater than the first predetermined storage amount, NOx is hardly purified by the NOx catalyst 45. However, in this embodiment, the SCR catalyst 47 is provided downstream of the NOx catalyst 45 , so the NOx not purified by the NOx catalyst 45 can be purified by the SCR catalyst 47 .

In the present embodiment, whether or not to execute the DeNOx control as described above is determined based on whether or not the SCR catalyst 47 can purify NOx in addition to the operating range of the engine E described above. . This is because if the NOx in the exhaust gas can be properly purified by the SCR catalyst 47, there is no need to perform the DeNOx control to ensure the NOx purification performance of the NOx catalyst 45. As described above, the NOx purification rate of the NOx catalyst 45 increases when the temperature of the exhaust gas is relatively low, while the NOx purification rate of the SCR catalyst 47 increases when the temperature of the exhaust gas is relatively high. Therefore, in this embodiment, as shown in the flowchart of FIG. I'm trying to choose whether to purify.

The processing of the PCM 60 when selecting a catalyst for purifying exhaust gas will be described with reference to the flowchart of FIG. While the engine E is operating, the PCM 60 always or at predetermined intervals executes processing based on this flow chart.

First, in step S101, the PCM 60 detects various sensors 100 to 119, 150
, 151, and in the next step S102, it is determined whether or not the SCR catalyst temperature is lower than the first predetermined temperature. When the determination in step S102 is YES, the process proceeds to step S103, while when the determination in step S102 is NO, the process proceeds to step S104. The first predetermined temperature is a temperature at which the SCR catalyst 47 can purify NOx but the NOx purification rate is less than a predetermined purification rate, and is 160° C., for example.

In step S<b>103 , the PCM 60 executes the DeNOx control to purify NOx only with the NOx catalyst 45 without purifying NOx with the SCR catalyst 47 . In this step S103, the PCM 60 restricts the supply of urea by the urea injector 51 so that the SCR catalyst 47 does not purify NOx. In other words, the phrase "NOx is not purified by the SCR catalyst 47" means "limiting the supply of urea by the urea injector 51". After step S103, the process returns.

In step S104, it is determined whether or not the SCR catalyst temperature is lower than the second predetermined temperature (>first predetermined temperature). When the determination in step S104 is YES, the process proceeds to step S105, while when the determination in step S104 is NO, the process proceeds to step S106. The second predetermined temperature is a temperature near the lower limit of the temperature range in which the NOx purification rate of the SCR catalyst 47 can be equal to or higher than the predetermined purification rate, and is, for example, 250.degree.

In step S105, the PCM 60 executes the DeNOx control to cause the NOx catalyst 45 to purify NOx and also causes the SCR catalyst 47 to purify NOx. That is, in this step S105, the PCM 60 causes the urea injector 51 to supply urea. After step S105, the process returns.

In step S106, it is determined whether or not the flow rate of the exhaust gas is less than a predetermined flow rate. When the determination in step S106 is YES, the process proceeds to step S107, while when the determination in step S106 is NO, the process proceeds to step S105. The reason why the flow rate of the exhaust gas is determined in step S106 is that even if the SCR catalyst temperature is equal to or higher than the second predetermined temperature, the operating state of the engine E is, for example, in the high-speed, high-load operating region. This is because, when the flow rate of the exhaust gas is large, the SCR catalyst 47 alone may not be able to purify NOx. That is, when the flow rate of the exhaust gas is NO, which is equal to or higher than the predetermined flow rate, it is preferable to purify NOx by both the NOx catalyst 45 and the SCR catalyst 47, and the process proceeds to step S105.

In step S107, the NOx catalyst 45 does not purify NOx, and only the SCR catalyst 47 purifies NOx. The PCM 60 causes the urea injector 51 to supply urea to the SCR catalyst 47 also in this step S107. In this step S107, the execution of the DeNOx control is prohibited, and the NOx storage amount of the NOx catalyst 45 is set to the storage limit, so that the NOx catalyst 45 is prevented from purifying NOx. After step S107, the process returns. If the NOx storage amount of the NOx catalyst 45 has not reached the storage limit, it is possible for the NOx catalyst 45 to store NOx. occluded). That is, the phrase "no purification of NOx by the NOx catalyst 45" means "prohibition of execution of the DeNOx control".

Next, the processing operation of the PCM 60 when executing the DeNOx control will be described with reference to FIGS. 5 and 6. FIG. When the PCM 60 is to execute the DeNOx control according to the flowchart shown in FIG. 4, it executes processing operations based on the flowcharts shown in FIGS.

First, in step S201, the PCM 60 reads information from various sensors 100 to 119, 150, 151, and in the next step S202, determines whether or not the NOx storage amount in the NOx catalyst 45 is equal to or greater than the first predetermined storage amount. judge. When the determination in step S202 is YES, the process proceeds to step S203, while when the determination in step S202 is NO, the process proceeds to step S211. The NOx storage amount is obtained by estimating the NOx amount in the exhaust gas based on, for example, the operating state of the engine E, the flow rate of the exhaust gas, the temperature of the exhaust gas, etc., and integrating the estimated NOx amount. be done.

In step S203, the PCM 60 determines whether or not the operating range of the engine E belongs to the first operating range R1. When the determination in step S203 is YES, the process proceeds to step S205 to execute the active DeNOx control, while when the determination in step S203 is NO, the process proceeds to step S212.

At step S204, the PCM 60 sets the post-injection amount. As described above, the post-injection amount is based on the oxygen concentration of the air introduced into the engine E, the injection amount of fuel in the main injection, and the like, and is the amount necessary for the air-fuel ratio of the exhaust gas to reach the target DeNOx air-fuel ratio. It is set to the injection amount.

In the next step S205, the PCM 60 sets the timing of post-injection. As described above, in the active DeNOx control, the post-injection timing is set to the timing at which the post-injected fuel is combusted in the combustion chamber 17 of the engine E.

Subsequently, in step S206, the PCM 60 determines whether or not the post-injection amount calculated in step S204 is less than the first predetermined injection amount. When the determination in step S206 is YES, the process proceeds to step S207, while when the determination in step S206 is NO, the process proceeds to step S208. By setting the first predetermined injection amount, deterioration of fuel consumption due to execution of DeNOx is suppressed.

At step S207, the PCM 60 controls the fuel injection valve 20 so as to post-inject the post-injection amount set at step S205. After step S207, the process proceeds to step S210.

On the other hand, in step S208, the throttle valve 7 is controlled to be closed, and in the next step S209, the fuel injection valve 20 is controlled so as to post-inject with the first predetermined injection amount. In steps S208 and S209, the throttle valve 7 is adjusted so that the air-fuel ratio of the exhaust gas reaches the target DeNOx air-fuel ratio by the post-injection amount not exceeding the first predetermined injection amount (actually, the value of the first predetermined injection amount itself). is throttled to lower the oxygen concentration of the air introduced into the engine E. After step S209, the process proceeds to step S210.

At step S210, the PCM 60 determines whether or not the NOx storage amount has become substantially zero. When the determination in step S210 is YES, the active DeNOx control is terminated and the process returns, while when the determination in step S210 is NO, the process returns to step S203. In step S210, whether or not the NOx storage amount has become substantially zero is determined by accumulating the post-injection amount, and determining whether the integrated value has reached a value sufficient to reduce the absorbed NOx amount equal to or greater than the first predetermined absorption amount to substantially zero. It is determined based on whether or not It should be noted that the fact that the NOx storage amount becomes substantially zero also includes the fact that the NOx storage amount becomes zero.

On the other hand, in step S211, which is followed when the determination in step S202 is NO, the PCM 60 determines whether or not the NOx storage amount in the NOx catalyst 45 is equal to or greater than the second predetermined storage amount. When the determination in step S211 is YES, the process proceeds to step S212. When the determination in step S211 is NO, there is no need to execute the active DeNOx control and the passive DeNOx control, so the process returns.

At step S212, the PCM 60 sets the post-injection amount. Similar to step S204, the post-injection amount is determined based on the oxygen concentration of the air introduced into the engine E, the injection amount of fuel in the main injection, etc., even though the air-fuel ratio of the exhaust gas reaches the target DeNOx air-fuel ratio. It is set to the required injection amount.

At step S213, the PCM 60 sets the timing of the post-injection. As described above, in the passive DeNOx control, the timing of post-injection is set to the timing at which the post-injected fuel is not burned in the cylinder and is discharged to the exhaust passage 41 as unburned fuel.

In the next step S214, the PCM 60 determines whether or not the post-injection amount calculated in step S212 is less than the second predetermined injection amount. When the determination in step S206 is YES, the process proceeds to step S207, while when the determination in step S206 is NO, the process proceeds to step S208. The second predetermined injection amount is set to a value that is set only when the operating range of the vehicle is in the second operating range, and is a value smaller than the first predetermined injection amount. That is, when the post-injection amount is less than the second predetermined injection amount, the operating range of the vehicle is in the second operating range R2 in which the passive DeNOx control can be executed.

Subsequently, in step S215, the PCM 60 controls the fuel injection valve 20 so as to perform post-injection with the post-injection amount set in step S215. After step S216, the passive DeNOx control is terminated and the process returns.

In step S216, the PCM 60 executes normal fuel injection control without executing passive DeNOx control. That is, the fuel injection valve 20 is controlled so that only main injection is performed without post injection. After step S216, the process returns to step S203.

As described above, by executing the DeNOx control, in the present embodiment, it is possible to appropriately purify NOx in the exhaust gas while suppressing deterioration in fuel consumption due to the DeNOx control.

<SCR catalyst abnormality determination>
Next, the abnormality determination of the SCR catalyst 47 will be explained.

The SCR catalyst 47 purifies NOx by causing a reaction (reduction) between ammonia adsorbed on the SCR catalyst 47 and NOx in the exhaust gas. Ammonia adsorbed on the SCR catalyst 47 is basically generated by a thermal decomposition reaction or a hydrolysis reaction in the exhaust passage 41 of urea ((NH2)2CO) injected from the urea injector 51 .

The injection amount of urea from the urea injector 51 (hereinafter simply referred to as urea injection amount) is controlled by the DCU 70 . Specifically, the DCU 70 sets the urea injection amount so that the ammonia adsorption amount of the SCR catalyst 47 reaches a preset target adsorption amount. More specifically, the DCU 70 estimates the current ammonia adsorption amount of the SCR catalyst 47 using a model, and sets the urea injection amount based on the difference between the target adsorption amount and the estimated value.

The current ammonia adsorption amount of the SCR catalyst 47 is estimated by a model from the urea injection amount, the ammonia amount generated by the DeNOx control, the NOx inflow amount, and the purification efficiency of the SCR catalyst 47, which will be described later in detail. Also, the target adsorption amount is set to be smaller when the SCR catalyst temperature is higher than when the SCR catalyst temperature is low. Furthermore, the target adsorption amount is set to a value smaller than the ammonia adsorption limit of the SCR catalyst 47 .

The abnormality determination of the SCR catalyst 47 is performed by the abnormality determination unit 63 of the PCM 60 based on the actual NOx purification rate of the SCR catalyst 47 . Specifically, first, the abnormality determination unit 63 calculates the NOx amount in the passage on the upstream side of the SCR catalyst 47 (hereinafter referred to as the upstream NOx amount) based on the detection result of the first NOx sensor 116, and calculates the SCR catalyst. The amount of NOx in the passage on the downstream side of 47 (hereinafter referred to as the amount of NOx on the downstream side) is calculated based on the detection result of second NOx sensor 118, and the actual purification rate of SCR catalyst 47 is calculated based on Equation 1 below. calculate.

Purification rate = 1 - (downstream NOx amount/upstream NOx amount) (Formula 1)
Next, when the purification rate calculated by Equation 1 is equal to or less than the predetermined purification rate, the abnormality determination unit 63 determines that there is a possibility that an abnormality has occurred in the SCR catalyst 47, and adds one to the failure count. Then, the abnormality determination unit 63 determines that the SCR catalyst 47 has an abnormality when the count number of the failure count reaches or exceeds a predetermined value. In other words, the failure determination condition of the failure determination unit 63 is that the purification rate is equal to or less than a predetermined purification rate and that the failure count is equal to or greater than a predetermined value.

Further, when the abnormality determination unit 63 determines that the SCR catalyst 47 is abnormal, it warns the occupants of the vehicle that the SCR catalyst 47 is abnormal. This warning is given, for example, by turning on a lamp provided at a position visible to the occupants of the vehicle.

In order to accurately determine the abnormality, it is particularly necessary to accurately calculate the downstream NOx amount based on the detection result of the second NOx sensor 118 . However, in general, the output value (detected value) of the NOx sensor changes not only with NOx in the exhaust gas but also with ammonia in the exhaust gas. The unit 63 may make an erroneous determination. The principle of NOx detection by the NOx sensor will be described below with reference to FIG.

FIG. 7 schematically shows the NOx detection principle. Although FIG. 7 illustrates the second NOx sensor 118, the first NOx sensor 116 has the same configuration. As shown in FIG. 7, the second NOx sensor 118 has a first cavity 118a connected to the exhaust passage 41 and a second cavity 118b connected to the first cavity 118a. In the exhaust gas that has flowed into the second NOx sensor 118, HC and CO in the exhaust gas are first oxidized in the first cavity 118a, and gases other than NOx are removed. NOx that has passed through the first cavity 118b is then reduced to nitrogen in the next second cavity 118b. At this time, oxygen derived from NOx is generated in the second cavity 118b. The second NOx sensor 118 detects the concentration of NOx by detecting the concentration of oxygen derived from NOx generated in the second cavity 118b.

Here, when ammonia is mixed in the exhaust gas that has flowed into the second NOx sensor 118, the ammonia in the exhaust gas is oxidized in the first cavity 118a as shown in FIG. It is decomposed into NOx and H2O. As shown in FIG. 7, this ammonia-derived NOx is reduced in the second cavity 118b and decomposed into nitrogen and oxygen. Therefore, the second NOx sensor 118 also detects NOx derived from ammonia as NOx in the exhaust gas. Therefore, the output value of the second NOx sensor 118 changes according to the NOx and ammonia in the exhaust gas.

The output value of the first NOx sensor 116 also changes according to the amount of ammonia in the exhaust gas. Although details will be described later, since ammonia is also generated by the DeNOx control, the first NOx sensor 116 may also detect ammonia as NOx. However, by estimating the amount of ammonia generated by the DeNOx control and calculating the upstream NOx amount based on the estimated value and the detection result of the first NOx sensor 116, the upstream NOx amount can be calculated with high accuracy. can be done.

Basically, by setting the target adsorption amount to an appropriate value by the DCU 70, the ammonia discharge amount (hereinafter referred to as ammonia slip amount) to the passage downstream of the SCR catalyst 47 in the exhaust passage 41 can be reduced. can be suppressed to some extent. However, in the SCR catalyst 47, the adsorption reaction and the desorption reaction of ammonia always occur. (Ammonia slip occurs). Therefore, it may not be possible to accurately calculate the downstream NOx amount from the detection result of the second NOx sensor 118 .

Therefore, in the present embodiment, the slip amount of ammonia is estimated, and the abnormality determination by the abnormality determination section 63 is limited based on this estimated slip amount. A method for estimating the slip amount of ammonia will be described in detail below.

The ammonia slip amount based on the ammonia adsorption reaction and the ammonia desorption reaction within the SCR catalyst 47 is mainly determined by the balance between the ammonia adsorption reaction speed and the ammonia desorption reaction speed within the SCR catalyst 47 . Therefore, in the present embodiment, the slip amount estimator 62 estimates the ammonia slip amount based on the adsorption reaction rate and the desorption reaction rate. The adsorption reaction rate and the desorption reaction rate are represented by Equations 2 and 3 below.

Adsorption reaction rate = Aa x (1-θ) x exp (-Ea/RT) x C1 x C2 (Formula 2)
Desorption reaction rate = Ad x exp (-Ed/RT) x adsorption amount (Equation 3)
In Equation 2, Aa is the frequency coefficient of the adsorption reaction, θ is the ammonia coverage of the SCR catalyst 47, Ea is the activation energy required for the adsorption reaction, R is the gas constant, T is the SCR catalyst temperature, and C1 is the exhaust gas. is a correction coefficient based on the concentration of ammonia, and C2 is a correction coefficient based on the concentration of oxygen in the exhaust gas. The activation energy Ea is a constant determined by experiments and simulations. The coverage θ is a value obtained by dividing the current ammonia adsorption amount of the SCR catalyst 47 by the ammonia adsorption limit of the SCR catalyst 47, and is a variable that can take a value of 0 or more and 1 or less. On the other hand, in Equation 3, Ad is the frequency coefficient of the desorption reaction, Ed is the activation energy required for the desorption reaction, R is the gas constant, and T is the SCR catalyst temperature. The activation energy Ed is a constant determined by experiments and simulations. The adsorption amount is the ammonia adsorption amount of the SCR catalyst 47 .

Although the correction coefficient C1 affects the final ammonia slip amount, it does not affect the adsorption reaction speed as much as the ammonia coverage of the SCR catalyst 47, that is, the ammonia adsorption amount of the SCR catalyst 47 does. Therefore, the adsorption reaction rate and the desorption reaction rate mainly depend on the ammonia adsorption amount of the SCR catalyst 47 and the SCR catalyst temperature.

Therefore, in order to estimate the ammonia slip amount based on the adsorption reaction rate and the desorption reaction rate, it is necessary to consider the state of the SCR catalyst 47, particularly the ammonia adsorption amount of the SCR catalyst 47 and the SCR catalyst temperature. . Therefore, in the present embodiment, the ammonia adsorption amount estimating unit 61 estimates the ammonia adsorption amount of the SCR catalyst 47, the catalyst temperature sensor 117 detects the SCR catalyst temperature, and the estimated ammonia adsorption estimated by the ammonia adsorption amount estimating unit 61 is detected. Based on the amount and the SCR catalyst temperature detected by the catalyst temperature sensor 117, the adsorption reaction speed estimator 65 and the desorption reaction speed estimator 66 estimate the adsorption reaction speed and the desorption reaction speed, respectively. Based on the estimated adsorption reaction speed estimated by the adsorption reaction speed estimation unit 65 and the estimated desorption reaction speed estimated by the desorption reaction speed estimation unit 66, the SCR catalyst of the exhaust passage 41 is calculated by the slip amount estimation unit 62. The slip amount of ammonia, which is the amount of ammonia discharged to the passage downstream of 47, is estimated.

Here, as shown in FIG. 8, when ammonia actually flows into the selective reduction NOx catalyst, part of it is adsorbed on the exhaust upstream side of the SCT catalyst 47 (hereinafter referred to as the upstream side portion). , and the remainder flows into the exhaust downstream side portion of the selective reduction NOx catalyst (hereinafter referred to as the downstream side portion). Ammonia desorbed from the upstream portion also flows into the downstream portion. That is, the total value of the remaining amount of ammonia and the amount of ammonia desorbed from the upstream portion is the slip amount of ammonia from the upstream portion to the downstream portion (hereinafter referred to as internal slip amount). Then, the sum of the amount of ammonia that could not be adsorbed by the downstream portion of the ammonia that slipped to the downstream portion and the amount of ammonia that was desorbed from the downstream portion is the actual amount of ammonia from the SCR catalyst 47. slip amount. Therefore, in order to improve the accuracy of estimating the ammonia slip amount, it is possible to estimate the ammonia internal slip amount and estimate the ammonia slip amount to the outside of the SCR catalyst 47 based on the estimated internal slip amount. preferable.

Therefore, in this embodiment, first, the SCR catalyst 47 is virtually divided so as to be aligned in the flow direction of the exhaust gas, and n (n is an integer equal to or greater than 2) virtual regions S are set. Specifically, as shown in FIG. 9, n strip-shaped imaginary regions S are set so as to be arranged in parallel at equal intervals in the flow direction of the exhaust gas. Next, the slip amount estimating unit 62 designates the n virtual regions S as 1 to n in order from the exhaust upstream side, and sets the i-th (i is an integer from 1 to n−1) among the n virtual regions. , the internal slip amount of ammonia to the (i+1)-th virtual region Si+1 is estimated.

When estimating the internal slip amount in the i-th virtual area Si, the slip amount estimator 62 considers the internal slip amount from the virtual area Si-1 one upstream side. That is, the slip amount estimating unit 62 adds the amount of ammonia desorbed from the i-th virtual area Si to the internal slip amount from the virtual area Si-1 on the one upstream side, and further adds the ammonia amount desorbed from the i-th virtual area Si. A value obtained by subtracting the amount of ammonia calculated is estimated as an internal slip amount in the i-th virtual area Si.

The slip amount estimator 62 estimates the internal slip amount in order from the first virtual region S1 located on the most upstream side of the exhaust gas, from the (n−1)th virtual region Sn−1 to the nth virtual region Sn. Repeat until the internal slip amount of ammonia is estimated. After that, the slip amount of ammonia to the exhaust passage 41 is estimated from the n-th virtual area Sn. Then, the slip amount estimator 62 estimates the ammonia slip amount from the n-th virtual area Sn to the exhaust passage 41 as the ammonia slip amount of the SCR catalyst 47 .

As a result, the actual adsorption reaction and desorption reaction in the SCR catalyst 47 are reflected, so the accuracy of estimating the slip amount of ammonia can be further improved. Note that the greater the number of virtual regions S (the number of n), the higher the estimation accuracy. However, if there are too many, the load on the slip amount estimating section 62 will increase, so it is preferable to set the number of virtual areas S to about 10 to 15. FIG.

Here, in the actual SCR catalyst 47, the ammonia adsorption amount does not have a uniform distribution, except when the ammonia adsorption amount of the SCR catalyst 47 is near 0 or near the adsorption limit. That is, the ammonia adsorption amount differs for each virtual region S, and the adsorption reaction speed and the desorption reaction speed also differ for each virtual region S accordingly. Therefore, in order to accurately estimate the internal slip amount of ammonia in the SCR catalyst 47, the ammonia adsorption amount in each virtual region S is estimated, and based on the estimated ammonia adsorption amount for each virtual region S, each virtual It is preferable to estimate the adsorption and desorption kinetics in region S, respectively.

Therefore, in the present embodiment, the ammonia adsorption amount estimator 61 estimates the ammonia adsorption amount for each of the n virtual regions S. The adsorption reaction rate estimator 65 estimates the adsorption reaction rate for each of the n virtual regions S based on the estimated ammonia adsorption amount for each of the n virtual regions S, and the desorption reaction rate estimator 66 estimates the n The desorption reaction rate is estimated for each of the n virtual regions S based on the estimated amount of adsorbed ammonia for each virtual region S of . Then, based on the estimated adsorption reaction rate and the estimated desorption reaction rate in each virtual area S, the slip amount estimation unit 62 calculates the slip amount of ammonia from the i-th virtual area Si to the (i+1)-th virtual area Si+1. Estimate each.

The ammonia adsorption amount estimating unit 61 determines each virtual area based on the urea injection amount by the urea injector 51, the ammonia amount generated by the DeNOx control, the NOx inflow amount to each virtual area S, and the purification efficiency of each virtual area. Estimate the ammonia adsorption amount of S. Specifically, the ammonia adsorption amount estimator 61 first calculates the amount of ammonia that has flowed into the first virtual region S1 based on the urea injection amount and the amount of ammonia generated by the DeNOx control. The ammonia generated by the DeNOx control is the ammonia that is discharged from the NOx catalyst 45 into the exhaust gas when the NOx stored in the NOx catalyst 45 is reduced. caused by the reaction of Therefore, ammonia generated by DeNOx control can be estimated from the NOx storage amount of the NOx catalyst 45 and the post-injection amount.

Next, the ammonia adsorption amount estimator 61 estimates the amount of ammonia adsorbed in the first virtual region S1 among the ammonia that has flowed into the first virtual region S1. Here, the ammonia adsorption amount estimator 61 assumes that the number obtained by dividing the adsorption limit amount of ammonia of the entire SCR catalyst 47 by the number of regions n is the adsorption limit of each virtual region S, and adsorbs to the first virtual region S1. Estimate the amount of ammonia produced. That is, when the amount of ammonia flowing into the first virtual region S1 is greater than the adsorption limit of the first virtual region S1, the first virtual region S1 adsorbs ammonia up to the adsorption limit, and the remaining While it is estimated that the ammonia is adsorbed in the downstream virtual region S, when the amount of ammonia that has flowed into the first virtual region S1 is less than the adsorption limit of the first virtual region S1, the first virtual region S1 assumes that all of the incoming ammonia has been adsorbed.

For the virtual regions S after the second virtual region S2, the amounts of ammonia adsorbed in the virtual regions S are similarly estimated. The amount of ammonia flowing into the virtual region S after the second virtual region S2 is the virtual region S upstream of itself (for example, if the third virtual region S3, the first and second virtual regions S1 and S2) Calculated by subtracting the amount of ammonia adsorbed on the

Next, the ammonia adsorption amount estimator 61 calculates the amount of ammonia consumed in each virtual area S based on the amount of NOx flowing into each virtual area S and the purification efficiency of each virtual area S. The amount of NOx flowing into the first virtual region S1 is calculated based on the detection result of the first NOx sensor 116 and the estimated value of ammonia produced by the DeNOx control. The amount of NOx flowing into the virtual regions after the second virtual region S2 is obtained by subtracting the amount of NOx reduced in the virtual region S upstream of itself from the amount of NOx flowing into the first virtual region S1. calculate. The purification efficiency of the SCR catalyst 47 is obtained by reading a map stored in the PCM 60 with a theoretical value calculated in advance based on the SCR catalyst temperature, exhaust gas flow rate, and the like.

Then, the ammonia adsorption amount estimator 61 calculates the current ammonia adsorption amount of each virtual region S from the difference between the integrated value of the amount of ammonia adsorbed in each virtual region S and the integrated value of the amount of ammonia consumed from the SCR catalyst 47. to estimate Note that when the DeNOx control is not being executed, the ammonia adsorption amount estimator 61 does not consider the amount of ammonia generated by the DeNOx control when calculating the amount of ammonia flowing into the first virtual region S1.

Further, in the present embodiment, the desorption reaction rate estimator 65 makes the rate of change of the estimated desorption reaction rate with respect to the amount of change in the SCR catalyst temperature greater than the rate of change of the estimated adsorption reaction rate with respect to the amount of change in the SCR catalyst temperature. The desorption reaction rate of each virtual region S is estimated so that In particular, in the temperature range in which the SCR catalyst 47 can be used, the desorption reaction rate estimator 65 determines that the change rate of the estimated desorption reaction rate with respect to the increment of the SCR catalyst temperature is equal to the estimated adsorption reaction rate with respect to the increment of the SCR catalyst temperature. The desorption reaction rate of each virtual region S is estimated so as to be greater than the rate of change of . That is, the adsorption reaction of ammonia to the SCR catalyst 47 is a reaction in which ammonia is only adsorbed to the acid points of the SCR catalyst 47, while the desorption reaction of ammonia from the SCR catalyst 47 is to convert the adsorbed ammonia into the SCR. It is a reaction that separates from the acid site of the catalyst 47 . Therefore, the activation energy Ed of the desorption reaction is considerably larger than the activation energy Ea of the adsorption reaction. In other words, while the adsorption reaction rate is hardly affected by the SCR catalyst temperature, the desorption reaction rate is easily affected by the SCR catalyst temperature. Therefore, by configuring as described above, the difference in magnitude between the activation energy Ed of the desorption reaction and the activation energy Ea of the adsorption reaction is reflected, and the estimation accuracy of the desorption reaction rate and the adsorption reaction rate is improved. improves. As a result, the estimation accuracy of the ammonia slip amount can be further improved.

Incidentally, in the actual SCR catalyst 47, the SCR catalyst temperature may also have a distribution. In the SCR catalyst 47 of the present embodiment, which is warmed up by the exhaust gas, the upstream portion of the SCR catalyst 47 is in contact with the high-temperature exhaust gas, while the downstream portion of the SCR catalyst 47 is Exhaust gas after heat absorption contacts the upstream portion. Therefore, when n virtual regions S are set, basically the first virtual region S1 has the highest temperature, and the temperature decreases toward the downstream side of the exhaust gas, and the nth virtual region S1 The distribution is such that Sn has the lowest temperature. Therefore, based on the SCR catalyst temperature detected by the catalyst temperature sensor 117, a temperature distribution is assumed such that the temperature decreases from the first virtual region S1 toward the n-th virtual region Sn. Based on this, the SCR catalyst temperature for each of the n virtual areas S may be estimated. Then, the ammonia adsorption amount estimating unit 61, the adsorption reaction speed estimating unit 65, and the desorption reaction speed estimating unit 66 determine the ammonia The adsorption amount, the adsorption reaction rate, and the desorption reaction rate may be estimated respectively. As a result, the estimation accuracy of the slip amount of ammonia in the SCR catalyst 47 can be further improved.

Here, the adsorption reaction speed of the SCR catalyst 47 is slightly affected by factors other than the ammonia adsorption amount of the SCR catalyst 47 and the SCR catalyst temperature. For example, like the correction coefficients C1 and C2 described in Equation 2 above, the adsorption reaction rate is affected by the concentration of ammonia and oxygen in the exhaust gas. In the present embodiment, in order to consider such factors affecting the adsorption reaction rate, the slip amount estimator 62 uses a provisional slip amount (internal slip) estimated based on the adsorption reaction rate and desorption reaction rate. ) is multiplied by a plurality of correction coefficients C1' to C5' to obtain the final slip amount (including the internal slip amount).

In this embodiment, the factors affecting the adsorption reaction rate are the concentration of ammonia in the exhaust gas, the concentration of oxygen in the exhaust gas, the flow rate of the exhaust gas, the number of acid points in the SCR catalyst 47, and the amount of HC poisoning in the SCR catalyst 47. I'm trying to take into account. In the following, the effects of these on the adsorption reaction rate will be described in detail.

The concentration of ammonia in the exhaust gas affects the correction coefficient C1 in Equation (2). Specifically, the higher the ammonia concentration, the easier the adsorption reaction proceeds. Therefore, basically, the higher the ammonia concentration in the exhaust gas, the larger the correction coefficient C1, the higher the adsorption reaction speed, and the smaller the slip amount. Therefore, in the present embodiment, the correction coefficient C1′ for an intermediate ammonia concentration between the maximum ammonia concentration that the engine system 200 can take and 0 is set to 1, and when the ammonia concentration is higher than the intermediate ammonia concentration, the correction coefficient C1 ' is made smaller than 1, and the correction coefficient is made smaller than 1 when the ammonia concentration is lower than the intermediate ammonia concentration.

The concentration of ammonia in the exhaust gas flowing into the first virtual region S1 is estimated from the flow rate of the exhaust gas, the amount of urea injected by the urea injector 51, and the amount of ammonia generated by the DeNOx control. The concentration of ammonia in the exhaust gas flowing into the virtual regions S after the second virtual region S2 is estimated from the flow rate of the exhaust gas and the internal slip amount of the virtual region S immediately before.

The oxygen concentration in the exhaust gas affects the correction coefficient C2 in Equation (2). Specifically, when the oxygen concentration is high, the adsorption reaction proceeds easily. That is, the higher the oxygen concentration in the exhaust gas, the larger the correction coefficient C2, the higher the adsorption reaction speed, and the smaller the slip amount. Therefore, in the present embodiment, the correction coefficient C2' is set to 1 when the oxygen concentration in the atmosphere (approximately 23% by weight) is 1, and the correction coefficient C2' becomes larger than 1 as the oxygen concentration in the exhaust gas decreases. to As for the oxygen concentration in the exhaust gas, for example, the detection result of the O2 sensor 111 can be used. Further, the correction coefficient C2' based on the oxygen concentration of the exhaust gas does not change for each virtual region S, and is set to the same value for all the virtual regions S.

The exhaust gas flow rate affects the frequency factor Aa in Equation (2). Specifically, when the flow rate of the exhaust gas is high, the flow velocity of the exhaust gas increases, and the contact frequency with the zeolite forming the SCR catalyst 47 decreases, so the frequency coefficient Aa decreases. Therefore, the higher the flow rate of the exhaust gas, the smaller the frequency coefficient Aa, the smaller the adsorption reaction speed, and the larger the slip amount. Therefore, in the present embodiment, the correction coefficient C3′ at a flow rate intermediate between 0 and the maximum flow rate that the engine system 200 can take (for example, the flow rate of the exhaust gas at high load and high speed) is set to 1, and the flow rate of the exhaust gas is is higher than the intermediate flow rate, the correction coefficient C3' is made smaller than 1, while the correction coefficient C3' is made smaller than 1 when the flow rate of the exhaust gas is lower than the intermediate flow rate. It should be noted that the correction coefficient C3' based on the flow rate of the exhaust gas does not change for each virtual region S and is set to the same value for all the virtual regions S.

The number of acid sites in the SCR catalyst 47 affects the coverage θ in Equation (2). Specifically, when the number of acid sites decreases, the adsorption limit of ammonia in the SCR catalyst 47 (the adsorption limit of ammonia in each imaginary region S) decreases, so the coverage θ tends to increase. Therefore, as the number of acid sites of the SCR catalyst 47 decreases, the coverage θ increases and the adsorption reaction speed decreases. If the number of acid sites of the SCR catalyst 47 decreases, the ammonia adsorption amount of the SCR catalyst 47 also decreases, and the desorption reaction rate may decrease. However, since the ammonia in the exhaust gas that has flowed into the SCR catalyst 47 is less likely to be adsorbed by the SCR catalyst 47, the amount of slip increases as a result. The number of acid sites in the SCR catalyst 47 is predetermined by the properties of the zeolite forming the SCR catalyst 47, but it is generally known that the number decreases when the SCR catalyst 47 is thermally loaded. Therefore, in the present embodiment, when the number of acid points of the SCR catalyst 47 is maximum, that is, when the SCR catalyst 47 is new, the correction coefficient C4' is set to 1, and the heat load applied to the SCR catalyst 47 is large. The correction coefficient C4' is set to be larger than 1 as the number increases. A heat load applied to the SCR catalyst 47 is estimated from an integrated value of heat energy applied to the SCR catalyst 47 . This thermal energy can be substituted by the product of the SCR catalyst temperature and the time the SCR catalyst temperature is maintained. Note that the correction coefficient C4 based on the number of acid points of the SCR catalyst 47 is not changed for each virtual region S, but is set to the same value for all the virtual regions S.

The HC poisoning amount of the SCR catalyst 47 affects the coverage θ in Equation (2). HC poisoning is adsorption of HC to acid sites of the SCR catalyst 47 where ammonia should be adsorbed. That is, when the amount of HC poisoning increases, the adsorption limit of ammonia in the SCR catalyst 47 (the adsorption limit of ammonia in each imaginary region S) decreases, so the coverage θ tends to increase. Therefore, as the HC poisoning amount of the SCR catalyst 47 increases, the coverage θ increases, the adsorption reaction speed decreases, and the slip amount increases. When the amount of HC is large, it becomes difficult for the adsorption reaction to proceed. This is because HC is adsorbed on the acid sites of the SCR catalyst 47 (that is, poisoning by HC occurs), and the number of acid sites capable of adsorbing ammonia decreases. That is, as the amount of HC in the exhaust gas increases, the adsorption reaction speed decreases and the slip amount increases. Therefore, in the present embodiment, the correction coefficient C5′ is set to 1 when the HC poisoning amount of the SCR catalyst 47 is 0, and the correction coefficient C5′ becomes larger than 1 as the HC poisoning amount of the SCR catalyst 47 increases. make it

The HC poisoning amount of the SCR catalyst 47 differs for each virtual area S. The amount of HC poisoning in each imaginary region S is estimated based on the amount of HC flowing into the SCR catalyst 47, which is estimated based on the rotational speed and load of the engine E, and an HC adsorption model set by experiment or the like.

In this embodiment, the PCM 60 stores maps for setting the correction coefficients C1' to C5' for each of the correction coefficients C1' to C5'. The PCM 60 applies detected or estimated parameters (ammonia concentration in the exhaust gas, etc.) to the map, and sets correction coefficients C1' to C5' for each virtual region S. These correction coefficients C1' to C5' may be set by the slip amount estimator 62, or the PCM 60 may be provided with another processor for setting the correction coefficients C1' to C5'.

Next, the processing operation of the PCM 60 when estimating the ammonia slip amount from the SCR catalyst 47 will be described with reference to FIG. Note that the ammonia adsorption amount in each virtual area S is estimated by the ammonia adsorption amount estimating unit 61, and the ammonia internal slip amount in each virtual area S and the final ammonia slip amount from the SCR catalyst 47 are estimated by slip amount estimation. The adsorption reaction speed of each virtual region S is estimated by the unit 62 , the adsorption reaction speed of each virtual region S is estimated by the adsorption reaction speed estimation unit 65 , and the desorption reaction speed of each virtual region S is estimated by the desorption reaction speed estimation unit 66 .

First, in step S301, the PCM 60 reads information from various sensors 100-119, 150, and 151. FIG. In this step S301, in particular, the catalyst temperature sensor 117 detects the SCR catalyst temperature.

In the next step S302, the PCM 60 determines whether DeNOx control is being performed. When the determination in step S302 is YES, the process proceeds to step S303, while when the determination in step S302 is NO, the process proceeds to step S304.

In the next step S303, the PCM 60 estimates the amount of ammonia generated by DeNOx control.

In the next step S304, the SCR catalyst 47 is virtually divided into n virtual regions S in the flow direction of the exhaust gas.

Subsequently, in step S305, the PCM 60 estimates the ammonia adsorption amount of the i-th virtual area Si (initially, the first virtual area S1).

Next, in step S306, the PCM 60 estimates the adsorption reaction rate and desorption reaction rate in the i-th virtual area Si (initially, the first virtual area S1).

Next, in step S307, the PCM 60 sets correction coefficients C1' to C5' in the i-th virtual area Si (initially, the first virtual area S1).

Next, in step S308, the PCM 60 performs The final internal slip amount is estimated by multiplying the internal slip amount of ammonia into the (i+1)th virtual area Si+1 by each of the correction coefficients C1′ to C5′.

Subsequently, in step S309, it is determined whether or not i is n-1, that is, whether or not the internal slip amount of ammonia from the (n-1)-th virtual region Sn-1 to the n-th virtual region Sn has been estimated. . When the determination in step S309 is YES, the process proceeds to step S311, while when the determination in step S309 is NO, the process proceeds to step S310.

In step S310, 1 is added to i, and the process returns to step S305. As a result, the estimation of the internal slip amount is repeated in order from the first virtual area S1 until the internal slip amount from the (n-1)th virtual area Sn-1 to the nth virtual area Sn is calculated.

On the other hand, in step S311, the ammonia adsorption amount of the n-th virtual area Sn is estimated, and in the next step S312, the adsorption reaction rate and the desorption reaction rate of the n-th virtual area Sn are estimated.

Next, in step S313, the PCM 60 sets each correction coefficient C1' to C5' in the n-th virtual area Sn.

Then, in step S314, the slip amount of ammonia from the n-th virtual area Sn to the exhaust passage 41 is estimated. The amount of ammonia discharged into the exhaust passage 41 in step S313 corresponds to the ammonia slip amount of the SCR catalyst 47 . After step S314, the process returns.

By estimating the slip amount of ammonia in the slip amount estimating unit 62 as described above, the parameters that affect the adsorption reaction rate and the desorption reaction rate of ammonia are considered. It is possible to improve the estimation accuracy of the slip amount.

The estimated slip amount of ammonia estimated by the slip amount estimating section 62 is input to the abnormality determination limiting section 64 of the PCM 60 . The abnormality determination limiter 64 determines that the estimated slip amount of ammonia is equal to or greater than a predetermined slip amount, more specifically, an amount that affects the NOx concentration detection by the second NOx sensor 118 to such an extent that the abnormality determination unit 63 makes an erroneous determination. When the above is the case, the abnormality determination of the SCR catalyst 47 by the abnormality determination unit 63 is restricted. Specifically, when the estimated slip amount of ammonia is equal to the predetermined slip amount, the abnormality determination limit unit 64 determines that even if the purification rate calculated by the abnormality determination unit 63 using Equation 1 is equal to or less than the predetermined purification rate, Determination is stopped so that the abnormality determination unit 63 is prevented from counting failures. As a result, the abnormality determination unit 63 does not determine that the SCR catalyst 47 is out of order even if it is determined that the purification rate of the SCR catalyst 47 is equal to or lower than the predetermined purification rate due to the ammonia slipping in the SCR catalyst 47. be able to. As a result, the abnormality determination unit 63 can determine the failure of the SCR catalyst 47 in a situation where the downstream NOx amount can be accurately calculated, so that erroneous determination by the abnormality determination unit 63 can be suppressed.

Next, the processing operation of the PCM 60 when executing the abnormality determination of the SCR catalyst 47 will be described with reference to FIG. In the processing operations to be described below, control related to abnormality determination of the SCR catalyst 47 is performed by the abnormality determination section 63 of the PCM 60, and control regarding restriction of the abnormality determination is performed by the abnormality determination restriction section 64. FIG. Abnormality determination based on this flowchart is performed at predetermined time intervals while the SCR catalyst 47 is usable (while the SCR catalyst temperature is equal to or higher than the first predetermined temperature).

First, in step S401, the PCM 60 reads information from various sensors 100 to 119, 150, and 151, and in the next step S402, calculates the NOx purification rate of the SCR catalyst 47. FIG.

In the next step S403, the PCM 60 determines whether or not the NOx purification rate of the SCR catalyst 47 calculated in step S402 is less than a predetermined purification rate. When the determination in step S403 is YES, the process proceeds to step S404, while when the determination in step S403 is NO, the SCR catalyst 47 is determined to be normal and the process returns.

In step S404, it is determined whether or not the estimated slip amount of ammonia is less than a predetermined slip amount. When the determination in step S404 is YES, the process proceeds to step S405, while when the determination in step S404 is NO, the process proceeds to step S409. The estimated slip amount of ammonia is estimated based on the flowchart shown in FIG.

In step S405, the PCM 60 increments the failure count by one, and in the next step S406, the PCM 60 determines whether or not the failure count has reached a predetermined value or more. When the determination in step S406 is YES, the process proceeds to step S407, while when the determination in step S406 is NO, the process returns as still in the determination period.

In step S407, it is determined that there is an abnormality in the SCR catalyst 47, and in the next step S408, the vehicle occupants are warned. After step S408, the process returns.

On the other hand, in step S409 to which the PCM 60 proceeds when the determination in step S404 is NO, the PCM 60 stops abnormality determination, and then returns.

Changes in each parameter (estimated slip amount, etc.) when the PCM 60 executes abnormality determination will be described with reference to the time chart of FIG. 12 . In FIG. 12 , the ammonia adsorption amount is a value estimated by the ammonia adsorption amount estimator 61 of the PCM 60 , and the ammonia slip amount is a value estimated by the slip amount estimator 62 of the PCM 60 . Here, the ammonia adsorption amount is the ammonia adsorption amount of the entire SCR catalyst 47, and the integrated value of the ammonia adsorption amount in each virtual region S is considered. The ammonia slip amount corresponds to the ammonia slip amount from the n-th virtual area Sn to the exhaust passage 41 . In FIG. 12, the output values of the NOx sensor are indicated by a dashed line for the output value of the first NOx sensor 116 and by a solid line for the output value of the second NOx sensor 118 .

First, in the initial state, the PCM 60 is executing normal fuel injection control, and the SCR catalyst 47 is in an inactive state. If the DeNOx control is executed from this initial state, the ammonia adsorption amount of the SCR catalyst 47 increases because ammonia is generated with the DeNOx control. After that, when the SCR catalyst temperature is lower than the first predetermined temperature, that is, when the SCR catalyst 47 does not purify NOx and the DeNOx control is executed, ammonia is not consumed from the SCR catalyst 47 and the SCR catalyst The ammonia adsorption amount of 47 increases.

When the SCR catalyst temperature reaches or exceeds the first predetermined temperature, the SCR catalyst 47 starts to purify NOx, so the ammonia adsorption amount of the SCR catalyst 47 starts to decrease. At the same time, abnormality diagnosis of the SCR catalyst 47 is started. Also, since NOx flows downstream of the NOx catalyst 45, the output value of the first NOx sensor 116 increases.

When the temperature of the SCR catalyst 47 rises, ammonia slip occurs. As a result, the output value of the second NOx sensor 118 increases. Then, when the ammonia slip reaches or exceeds a predetermined slip amount, the PCM 60 stops the abnormality determination of the SCR catalyst 47 . As a result, as shown in FIG. 12, it is possible to prevent the abnormality determination from being executed in a state in which the output value of the second NOx sensor 118 exceeds the output value of the first NOx sensor 116 . The PCM 60 restarts the abnormality determination of the SCR catalyst 47 when the ammonia slip becomes less than the predetermined slip amount.

Further, as shown in FIG. 12, when ammonia slip occurs, the PCM 60 estimates the ammonia adsorption amount to be smaller than when there is no ammonia slip. This is because when ammonia slip occurs, the desorption reaction of ammonia from the SCR catalyst 47 is dominant, so the amount of ammonia adsorbed by the SCR catalyst 47 can be considered smaller than when there is no ammonia slip. This improves the accuracy of estimating the amount of ammonia adsorbed by the SCR catalyst 47, which in turn improves the accuracy of estimating the slip amount of ammonia.

Therefore, in the present embodiment, the ammonia slip amount of the SCR catalyst 47 is estimated in consideration of the ammonia adsorption reaction rate and the ammonia desorption reaction rate of the SCR catalyst 47. Estimation accuracy can be improved.

The technology disclosed herein is not limited to the above embodiments, and substitutions are possible without departing from the scope of the claims.

For example, in the above-described embodiment, the ammonia adsorption amount, the adsorption reaction rate, and the desorption reaction rate are estimated for each virtual region S. Each of the adsorption reaction rate and the desorption reaction rate may be assumed to be the same value. In this case, the ammonia adsorption amount estimation unit 61 estimates the ammonia adsorption amount of the entire SCR catalyst 47, and the adsorption reaction speed estimation unit 65 and the desorption reaction speed estimation unit 66 estimate the total ammonia adsorption amount. Adsorption and desorption kinetics are estimated. Then, the slip amount estimating unit 62 assumes that the adsorption reaction rate and the desorption reaction rate of each virtual region S are the adsorption reaction rate and the desorption reaction rate that are respectively estimated based on the estimated ammonia adsorption amount of the whole. , the internal slip amount in each virtual area S is estimated.

Further, in the above-described embodiment, the estimated ammonia adsorption amount of the SCR catalyst 47 and the SCR catalyst temperature are used as parameters representing the state of the SCR catalyst 47, and based on these parameters, the adsorption reaction rate and the desorption reaction rate Although the speed is estimated, the state of the SCR catalyst 47 may be detected from the engine speed and the engine load. In this case, for example, a map corresponding to the engine speed and the engine load, which is for obtaining an ammonia slip characteristic value indicating the ease with which ammonia slips in the SCR catalyst 47, is stored in the PCM 60 in advance. . Then, an ammonia slip characteristic value corresponding to the operating state is calculated from the detected engine speed value, the detected engine load value, and the above map, and based on this ammonia slip characteristic value, the adsorption reaction rate and the desorption reaction rate are calculated. Estimate speed and.

Furthermore, in the above-described embodiment, the SCR catalyst 47 is virtually divided in the flow direction of the exhaust gas to estimate the internal slip amount. If the ammonia slip amount of the SCR catalyst 47 is estimated based on the desorption reaction rate and the desorption reaction rate, it is not necessary to set a model in which the SCR catalyst 47 is virtually divided as described above.

Further, in the above-described embodiment, the provisional slip amount estimated based on the estimated adsorption reaction rate and the estimated desorption reaction rate is multiplied by the correction coefficients C1′ to C5′ to obtain the final slip amount. However, not limited to this, correction coefficients other than the correction coefficients C1' to C5' may be further considered, and some of the correction coefficients C1' to C5' (correction coefficient C1' based on the concentration of ammonia, etc. ) may be considered.

Furthermore, in the above embodiment, urea, which is a precursor of ammonia, is supplied by the urea injector 51, but ammonia may be directly supplied.

Further, in the above embodiment, a case has been described in which the estimation of the slip amount of ammonia from the SCR catalyst 47 is used to determine whether the SCR catalyst 47 is abnormal. It may be used for determining the purification rate of In other words, the estimation of the slip amount of ammonia from the SCR catalyst 47 can be used for purposes other than the abnormality determination of the SCR catalyst 47 .

Furthermore, in the above-described embodiment, in the abnormality determination of the PCM 60, after determining whether or not the purification rate of the SCR catalyst 47 is less than the predetermined purification rate (step S403), the estimated ammonia slip amount is less than the predetermined slip amount. (step S404), but the present invention is not limited to this, and before the calculation of the purification rate of the SCR catalyst 47 and the determination based on the purification rate, the estimated slip amount of ammonia is equal to the predetermined slip amount. You may judge whether it is less than. In this case, the processing operation of the PCM 60 is such that when the estimated slip amount of ammonia is equal to or greater than the predetermined slip amount, the processing operation returns without calculating the purification rate of the SCR catalyst 47 or making a determination based on the purification rate. Become.

The above-described embodiments are merely examples, and should not be construed as limiting the scope of the present disclosure. The scope of the present disclosure is defined by the claims, and all modifications and changes within the equivalent range of the claims are within the scope of the present disclosure.

The technology disclosed herein comprises a selective reduction NOx catalyst that is provided in an exhaust passage of an engine and reduces NOx with a supplied reducing agent; It is useful in determining the exhaust gas condition of an engine with a reducing agent supply means capable of supplying a solid.

41 Exhaust passage 45 NOx catalyst (occlusion reduction type NOx catalyst)
47 SCR catalyst (selective reduction NOx catalyst)
51 urea injector (reducing agent supply means)
60 PCM
61 ammonia adsorption amount estimating unit (means for detecting the state of the selective reduction NOx catalyst, ammonia adsorption amount estimating means)
62 slip amount estimator (slip amount estimator)
63 Abnormality determination unit (abnormality determination means)
64 Abnormality judgment limiting unit (abnormality judgment limiting means)
65 adsorption reaction rate estimation unit (adsorption reaction rate estimation means)
66 desorption reaction rate estimating unit (desorption reaction rate estimating means)
117 catalyst temperature sensor (means for detecting the state of the selective reduction NOx catalyst, catalyst temperature detection means)
118 Second NOx sensor (NOx sensor whose output value changes according to the amount of NOx and ammonia in the exhaust gas)
Engine E

Claims (8)

A selective reduction NOx catalyst provided in an exhaust passage of an engine for reducing NOx with a supplied reducing agent, and a reducing agent capable of supplying ammonia as the reducing agent or a precursor of ammonia to the selective reduction NOx catalyst. A catalyst abnormality determination method for an engine comprising supply means,
The engine further comprises a NOx sensor provided downstream of the selective reduction NOx catalyst in the exhaust passage and having an output value that changes according to the amount of NOx and ammonia in the exhaust gas,
a step of detecting the state of the selective reduction NOx catalyst;
a dividing step of virtually dividing the selective reduction NOx catalyst so as to line up in the exhaust gas flow direction to set n virtual regions (where n is an integer equal to or greater than 2);
an adsorption reaction rate estimation step of estimating an adsorption reaction rate of ammonia in the selective reduction NOx catalyst for each virtual region based on the detected state of the selective reduction NOx catalyst;
a desorption reaction rate estimating step of estimating a desorption reaction rate of ammonia in the selective reduction NOx catalyst for each virtual region based on the detected state of the selective NOx catalyst;
Based on the estimated adsorption reaction speed estimated in the adsorption reaction speed estimation step and the estimated desorption reaction speed estimated in the desorption reaction speed estimation step, a slip amount estimation step of estimating a slip amount of ammonia, which is the amount of ammonia discharged into the passage;
an abnormality determination step of determining whether or not there is an abnormality in the selective reduction NOx catalyst based on the output value of the NOx sensor;
The state of the selective reduction NOx catalyst includes the temperature of the selective reduction NOx catalyst,
The step of detecting the state of the selective reduction NOx catalyst includes:
a catalyst temperature detection step of detecting the temperature of the selective reduction NOx catalyst;
a step of setting the catalyst temperature of each of the virtual regions based on the temperature detected in the catalyst temperature detecting step so that the catalyst temperature of the virtual region on the upstream side becomes higher;
including
The adsorption reaction rate estimating step estimates the adsorption reaction rate for each of the n virtual regions based on the catalyst temperature for each of the n virtual regions,
The desorption reaction rate estimating step estimates a desorption reaction rate for each virtual region based on the catalyst temperature for each of the n virtual regions,
The slip amount estimation step includes:
an internal slip amount estimating step of estimating the slip amount of ammonia from the i-th (i is an integer from 1 to n−1) virtual area to the (i+1)-th virtual area among the n virtual areas; ,
The internal slip amount estimating step is executed in order from the first virtual area located furthest upstream of the exhaust until the slip amount of ammonia from the (n−1)th virtual area to the nth virtual area is estimated. a step of estimating the slip amount of ammonia into the exhaust passage from the n-th virtual region after executing the slip amount estimating step, and estimating the estimated value as the ammonia slip amount of the selective reduction NOx catalyst; can be,
The abnormality determination step includes an abnormality determination restriction step of limiting the abnormality determination when the ammonia slip amount estimated in the slip amount estimation step is equal to or greater than a predetermined slip amount ,
The state of the selective reduction NOx catalyst further includes an HC poisoning amount, which is the amount of HC adsorbed to the acid sites of the selective reduction NOx catalyst,
The step of detecting the state of the selective reduction NOx catalyst further includes the step of estimating the HC poisoning amount for each virtual region,
The adsorption reaction rate estimating step estimates a smaller adsorption reaction rate as the estimated HC poisoning amount increases . In the engine catalyst abnormality determination method according to claim 1,
The state of the selective reduction NOx catalyst includes the ammonia adsorption amount of the selective reduction NOx catalyst,
The step of detecting the state of the selective reduction NOx catalyst includes:
A catalyst abnormality determination method for an engine, comprising an ammonia adsorption amount estimation step of estimating an ammonia adsorption amount of the selective reduction NOx catalyst. In the engine catalyst abnormality determination method according to claim 1,
The state of the selective reduction NOx catalyst includes the ammonia adsorption amount of the selective reduction NOx catalyst,
The step of detecting the state of the selective reduction NOx catalyst includes an ammonia adsorption amount estimation step of estimating the ammonia adsorption amount of the selective reduction NOx catalyst,
In the ammonia adsorption amount estimation step, the adsorption amount of ammonia is estimated for each of the n virtual regions,
In the adsorption reaction rate estimating step, the adsorption reaction rate is estimated for each of the n virtual regions based on the estimated ammonia adsorption amount for each of the n virtual regions,
In the desorption reaction rate estimating step, the desorption reaction rate is estimated for each of the virtual regions based on the estimated ammonia adsorption amount for each of the n virtual regions,
In the internal slip amount estimation step, based on the estimated adsorption reaction rate and the estimated desorption reaction rate in each virtual area, the slip amount of ammonia from the i-th virtual area to the (i+1)-th virtual area is calculated. An engine catalyst abnormality determination method, characterized by estimating. In the engine catalyst abnormality determination method according to claim 1 or 3,
further comprising an ammonia concentration estimation step of estimating the ammonia concentration of the exhaust gas introduced into the virtual region for each of the n virtual regions;
In the internal slip amount estimating step, the ammonia slip amount from the i-th virtual area to the (i+1)-th virtual area is calculated in consideration of the concentration of ammonia in the exhaust gas introduced into the i-th virtual area. A method for judging catalyst abnormality of an engine, characterized by estimating each. In the engine catalyst abnormality determination method according to any one of claims 1 to 4,
In the desorption reaction rate estimating step, the rate of change of the estimated desorption reaction rate with respect to the detected amount of change in catalyst temperature is greater than the rate of change of the estimated adsorption reaction rate with respect to the detected amount of change in catalyst temperature. A method for judging an abnormality of a catalyst in an engine, characterized by estimating the estimated desorption reaction rate as described above. In the engine catalyst abnormality determination method according to any one of claims 1 to 5,
The engine includes an occlusion reduction type NOx catalyst disposed upstream of the selective reduction type NOx catalyst in the exhaust passage and capable of absorbing NOx in the exhaust gas and reducing the absorbed NOx; NOx catalyst regeneration control means for reducing the NOx occluded in the NOx catalyst so that the air-fuel ratio of the exhaust gas is close to the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio;
A step of estimating the amount of ammonia generated during reduction for estimating the amount of ammonia discharged into the exhaust gas from the storage-reduction type NOx catalyst when the NOx stored in the storage-reduction-type NOx catalyst is reduced by the NOx catalyst regeneration control means. further comprising
The state of the selective reduction NOx catalyst includes the ammonia adsorption amount of the selective reduction NOx catalyst,
The step of detecting the state of the selective reduction NOx catalyst includes an ammonia adsorption amount estimation step of estimating the ammonia adsorption amount of the selective reduction NOx catalyst,
In the ammonia adsorption amount estimating step, the amount of ammonia supplied by the reducing agent supply means or the amount of the precursor of ammonia and the amount of ammonia estimated in the ammonia generation amount estimating step during reduction are considered to adsorb ammonia. A method for judging catalyst abnormality of an engine, characterized by estimating an amount. A selective reduction NOx catalyst provided in an exhaust passage of an engine for reducing NOx with a supplied reducing agent, and a reducing agent capable of supplying ammonia as the reducing agent or a precursor of ammonia to the selective reduction NOx catalyst. A catalyst abnormality determination device for an engine comprising supply means,
means for detecting the state of the selective reduction NOx catalyst;
virtual dividing means for virtually dividing the selective reduction NOx catalyst so as to line up in the exhaust gas flow direction to set n virtual regions (where n is an integer equal to or greater than 2);
adsorption reaction rate estimation means for estimating an adsorption reaction rate of ammonia in the selective reduction NOx catalyst based on the detected state of the selective reduction NOx catalyst;
desorption reaction rate estimating means for estimating a desorption reaction rate of ammonia in the selective reduction NOx catalyst based on the detected state of the selective reduction NOx catalyst;
Based on the estimated adsorption reaction speed estimated by the adsorption reaction speed estimation means and the estimated desorption reaction speed estimated by the desorption reaction speed estimation means, slip amount estimating means for estimating a slip amount of ammonia, which is the amount of ammonia discharged into the passage;
a NOx sensor provided downstream of the selective reduction NOx catalyst in the exhaust passage and having an output value that changes according to the amount of NOx and the amount of ammonia in the exhaust gas;
Abnormality determination means for determining whether or not there is an abnormality in the selective reduction NOx catalyst based on the output value of the NOx sensor;
an abnormality determination limiting means for limiting the abnormality determination of the abnormality determining means when the ammonia slip amount estimated by the slip amount estimating means is equal to or greater than a predetermined slip amount;
The means for detecting the state of the selective reduction NOx catalyst includes catalyst temperature detection means for detecting the temperature of the selective reduction NOx catalyst, and based on the temperature detected by the catalyst temperature detection means, setting the catalyst temperature of each of the virtual regions so that the catalyst temperature becomes higher in the virtual regions;
The adsorption reaction rate estimating means estimates the adsorption reaction rate for each of the n virtual regions based on the catalyst temperature for each of the n virtual regions,
The desorption reaction rate estimating means estimates the desorption reaction rate for each of the virtual regions based on the catalyst temperature for each of the n virtual regions,
The slip amount estimating means is
Estimate an internal slip amount, which is a slip amount of ammonia from the i-th (i is an integer from 1 to n−1) virtual region to the (i+1)-th virtual region among the n virtual regions,
After estimating the internal slip amount in order from the first virtual region located furthest upstream of the exhaust gas, and estimating the internal slip amount of ammonia from the (n−1)th virtual region to the nth virtual region, the n estimating the slip amount of ammonia into the exhaust passage from the second virtual region, estimating the estimated value as the slip amount of ammonia of the selective reduction NOx catalyst ;
The state of the selective reduction NOx catalyst further includes an HC poisoning amount, which is the amount of HC adsorbed to the acid sites of the selective reduction NOx catalyst,
the means for detecting the state of the selective reduction NOx catalyst further includes means for estimating the HC poisoning amount for each virtual region,
The adsorption reaction rate estimating means estimates a smaller adsorption reaction rate as the estimated HC poisoning amount increases . In the engine catalyst abnormality determination device according to claim 7 ,
The state of the selective reduction NOx catalyst includes the ammonia adsorption amount of the selective reduction NOx catalyst, and the means for detecting the state of the selective reduction NOx catalyst includes:
A catalyst abnormality determination device for an engine, comprising ammonia adsorption amount estimating means for estimating an ammonia adsorption amount of the selective reduction type NOx catalyst.

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