JP2019167936A - Exhaust gas state estimation method for engine, catalyst abnormality determination method for engine, and catalyst abnormality determination device for engine - Google Patents

Abstract

To improve an estimation accuracy of an emission amount of ammonia into a passage downstream a selection reduction type NOx catalyst in an exhaust passage in an engine having the selection reduction type NOx catalyst.SOLUTION: A deterioration degree of the selection reduction type NOx catalyst is estimated. On the basis of this deterioration degree, a slip amount of ammonia, which is an emission amount of ammonia into a passage downstream the selection reduction type NOx catalyst in the exhaust passage, is estimated. In this estimation, when the deterioration degree gas is large, the slip amount is estimated larger compared to that in the case of the less deterioration degree.SELECTED DRAWING: Figure 15

Description

  The present invention belongs to a technical field related to an engine exhaust gas state estimation method, a catalyst abnormality determination method, and an engine catalyst abnormality determination device.

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

  For example, Patent Document 1 discloses a selective reduction type NOx catalyst provided in an exhaust passage of an internal combustion engine (engine) and using ammonia as a reducing agent, and ammonia or an ammonia precursor in exhaust gas flowing into the selective reduction type NOx catalyst. A reducing agent supply unit for supplying and a NOx sensor disposed in a passage downstream of the selective reduction type NOx catalyst and detecting ammonia in the exhaust as NOx are provided, and selective reduction is performed based on a detected value of the NOx sensor. In the case where the deterioration determination of the NOx catalyst is performed, the amount of ammonia flowing out from the selective reduction NOx catalyst is estimated, and if the amount of ammonia flowing out is large, is the use of the detected value of the NOx sensor limited in deterioration determination? Or prohibiting the deterioration determination itself.

  In Patent Document 1, when the temperature of the selective reduction type NOx catalyst rises, the amount of ammonia adsorbed on the selective reduction type NOx catalyst increases, and when the ammonia adsorption amount becomes excessive, the ammonia is reduced to the selective reduction type NOx catalyst. It is disclosed that it becomes easier to discharge into a passage downstream of the NOx catalyst.

JP 2014-109224 A

  However, according to the study by the present inventors, the amount of ammonia discharged into the passage downstream of the selective reduction type NOx catalyst (hereinafter sometimes referred to as ammonia slip amount) is the ammonia in the selective reduction type NOx catalyst. It was found to be determined by the balance between the adsorption reaction rate and the desorption reaction rate. That is, when the ammonia adsorption reaction rate is larger than the desorption reaction rate, the ammonia adsorption reaction apparently becomes dominant, and the ammonia slip amount decreases, while the ammonia desorption reaction rate decreases. When it is larger than the speed, the ammonia elimination reaction apparently becomes dominant, and the ammonia slip amount increases. For this reason, the ammonia slip amount needs to take into account a parameter that affects at least one of the adsorption reaction rate and the desorption reaction rate of ammonia.

  The present invention has been made in view of such a point, and an object of the present invention is to provide an engine having a selective reduction type NOx catalyst to a passage downstream of the selective reduction type NOx catalyst in the exhaust passage. The purpose is to improve the estimation accuracy of ammonia emission.

  In order to achieve the above object, in one aspect of the present invention, a selective reduction type NOx catalyst provided in an exhaust passage of an engine for reducing NOx by a supplied reducing agent, the selective reduction type NOx catalyst, Deterioration degree estimation step for estimating the deterioration degree of the selective reduction type NOx catalyst for an exhaust gas state estimation method for an engine having a reducing agent supply means capable of supplying ammonia or a precursor of ammonia as a reducing agent; Based on the degree of deterioration of the selective reduction NOx catalyst estimated in the deterioration degree estimation step, the ammonia slip amount, which is the amount of ammonia discharged into the passage downstream of the selective reduction NOx catalyst in the exhaust passage. A slip amount estimating step for estimating the slip amount, and in the slip amount estimating step, when the deterioration degree is large, compared to when the deterioration degree is small. Many estimates the slip amount and manner.

  That is, the ammonia coverage of the selective reduction type NOx catalyst is a parameter that affects the adsorption reaction rate of ammonia in the selective reduction type NOx catalyst. As the coverage increases, the adsorption reaction rate decreases and ammonia The amount of slip increases. The coverage is a value obtained by dividing the current ammonia adsorption amount of the selective reduction type NOx catalyst by the ammonia adsorption limit of the selective reduction type NOx catalyst. If the selective reduction type NOx catalyst adsorbs ammonia at the adsorption limit, no more ammonia can be adsorbed, and all of the ammonia introduced into the selective reduction type NOx catalyst slips.

  Here, the selective reduction type NOx catalyst deteriorates due to the heat load applied to the selective reduction type NOx catalyst, HC poisoning at the acid point, etc., and the deterioration causes the ammonia adsorption limit of the selective reduction type NOx catalyst. descend. For this reason, if the degree of deterioration of the selective reduction type NOx catalyst is increased, the above-described coverage is increased even if the ammonia adsorption amount is the same, and the slip amount of ammonia is increased.

  Therefore, in the slip amount estimation step, when the degree of deterioration is large, the slip amount of ammonia can be accurately estimated by estimating the slip amount more than when the degree of deterioration is small. .

  In one embodiment of the engine exhaust gas state estimation method, the deterioration degree estimation step includes at least one of a thermal load applied to the selective reduction type NOx catalyst and an HC poisoning amount of the selective reduction type NOx catalyst. Is the step of estimating the degree of deterioration.

  This makes it possible to accurately estimate the ammonia adsorption limit of the selective reduction type NOx catalyst, that is, the degree of deterioration that affects the coverage of the selective reduction type NOx catalyst, and to estimate the slip amount of ammonia accurately. can do.

  In another embodiment of the engine exhaust gas state estimation method, an ammonia adsorption amount estimation step of estimating the ammonia adsorption amount of the selective reduction NOx catalyst, and a catalyst temperature detection step of detecting the temperature of the selective reduction NOx catalyst In addition to the degree of deterioration of the selective reduction type NOx catalyst estimated in the deterioration degree estimation step, the slip amount estimation step includes an estimated ammonia adsorption amount estimated in the ammonia adsorption amount estimation step, and The slip amount is estimated based on the detected catalyst temperature detected in the catalyst temperature detecting step.

  That is, since the coverage also changes depending on the change in the ammonia adsorption amount of the selective reduction type NOx catalyst, the ammonia adsorption amount of the selective reduction type NOx catalyst also affects the ammonia adsorption reaction rate in the selective reduction type NOx catalyst. It is. The ammonia adsorption amount of the selective reduction type NOx catalyst is also a parameter that affects the desorption reaction rate of ammonia in the selective reduction type NOx catalyst. The temperature of the selective reduction type NOx catalyst is a parameter that affects the desorption reaction rate. Therefore, by estimating the ammonia slip amount based on the estimated ammonia adsorption amount, the detected catalyst temperature, and the degree of deterioration, the ammonia slip amount can be estimated more accurately.

  In the other embodiment, in the slip amount estimating step, when the degree of deterioration is large, the slip amount is estimated to be larger than when the degree of deterioration is small. When the estimated ammonia adsorption amount is large when compared with the detected catalyst temperature, the slip amount is estimated to be larger than when the estimated ammonia adsorption amount is small, while the same degradation degree and the same estimated ammonia are estimated. When the detected catalyst temperature is high when compared with the amount of adsorption, it is preferable to estimate the slip amount more than when the detected catalyst temperature is low.

  This makes it possible to estimate the ammonia slip amount with higher accuracy.

  Thus, when estimating the slip amount, the slip amount estimation step corrects the temporary slip amount estimated based on the estimated ammonia adsorption amount and the detected catalyst temperature based on the degree of deterioration. It is preferable that the slip amount is estimated.

  As a result, the number of man-hours for development can be reduced by separately examining the slip amount based on the estimated ammonia adsorption amount and the detected catalyst temperature and examining the slip amount based on the degree of deterioration. Moreover, the estimation accuracy of the slip amount of ammonia can be ensured.

  In the other embodiment, the engine is disposed upstream of the selective reduction type NOx catalyst in the exhaust passage and stores NOx in the exhaust gas and can store the stored NOx and reduce the stored NOx. A catalyst and NOx catalyst regeneration control means for setting the air-fuel ratio of the exhaust gas to be close to or richer than the stoichiometric air-fuel ratio in order to reduce NOx occluded in the NOx storage reduction catalyst. When reducing NOx stored in the NOx storage reduction catalyst by the NOx catalyst regeneration control means, the amount of ammonia generated during reduction is estimated to estimate the amount of ammonia discharged from the NOx storage reduction catalyst into the exhaust gas. An ammonia estimation amount estimation step, wherein the ammonia adsorption amount estimation step comprises the amount of ammonia supplied by the reducing agent supply means or the amount of precursor of ammonia; Based on the amount of ammonia is estimated by the reduction during the ammonia generation amount estimation step is a step of estimating the ammonia adsorption amount of the selective reduction type NOx catalyst, it is preferable.

  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 NOx occluded in the NOx storage reduction catalyst is reduced by the reaction between NOx and the exhaust gas. Reaction with HC is included. For this reason, in the process of reducing the NOx stored in the NOx storage reduction catalyst, the hydrogen of HC reacts with the nitrogen of NOx to generate ammonia. In order to increase the estimation accuracy of the ammonia adsorption amount of the selective reduction type NOx catalyst, it is preferable to consider the amount of ammonia generated by reducing the NOx stored in the storage reduction type NOx catalyst. Therefore, with the configuration as described above, the estimation accuracy of the ammonia adsorption amount of the selective reduction type NOx catalyst in the ammonia adsorption amount estimation step can be improved. This can be further improved.

  In another aspect of the present invention, the engine is provided on the downstream side of the selective reduction type NOx catalyst in the exhaust passage for an engine catalyst abnormality determination method using the exhaust gas state estimation method of the engine. And a NOx sensor whose output value changes according to the NOx amount and the ammonia amount in the exhaust gas, and based on the output value of the NOx sensor, whether or not there is an abnormality in the selective reduction type NOx catalyst. An abnormality determination step for determining the abnormality determination, and the abnormality determination step includes an abnormality determination limiting step for limiting the abnormality determination when the ammonia slip amount estimated in the slip amount estimation step is greater than or equal to a predetermined slip amount. Shall be included.

  According to this configuration, since the output value of the NOx sensor changes according to the NOx amount and the ammonia amount in the exhaust gas, when the ammonia amount in the exhaust gas is large, even if the NOx amount is small, the exhaust gas It is considered that the amount of NOx inside is large. For this reason, when it is determined whether there is an abnormality in the selective reduction type NOx catalyst based on the output value of the NOx sensor, even if the NOx amount in the exhaust gas is small, the selective reduction type NOx catalyst. If there is an abnormality, there is a risk of erroneous determination. Therefore, when the ammonia slip amount estimated in the slip amount estimation step is equal to or greater than the predetermined slip amount, the abnormality determination is restricted, so that when the NOx amount in the exhaust gas is small, the selective reduction type NOx catalyst is abnormal. It is possible to suppress erroneous determination that there is.

  In still another aspect of the present invention, a selective reduction type NOx catalyst that is provided in an exhaust passage of an engine and reduces NOx by a supplied reducing agent, and ammonia or ammonia as the reducing agent in the selective reduction type NOx catalyst. The deterioration degree estimating means for estimating the deterioration degree of the selective reduction type NOx catalyst and the deterioration degree estimating means for a catalyst abnormality determination device for an engine having a reducing agent supply means capable of supplying a precursor of In addition, based on the degree of deterioration of the selective reduction type NOx catalyst, a slip amount estimation means for estimating an ammonia slip amount, which is the amount of ammonia discharged into the passage downstream of the selective reduction type NOx catalyst in the exhaust passage. And provided downstream of the selective reduction type NOx catalyst in the exhaust passage, according to the amount of NOx and the amount of ammonia in the exhaust gas. Estimated by a NOx sensor whose force value changes, an abnormality determining means for determining whether or not the selective reduction type NOx catalyst is abnormal based on the output value of the NOx sensor, and the slip amount estimating means An abnormality determination limiting unit that limits the abnormality determination of the abnormality determination unit when the ammonia slip amount is greater than or equal to a predetermined slip amount, and the slip amount estimation unit It is assumed that the slip amount is estimated to be larger than when the degree of deterioration is small.

  Also in this configuration, since the output value of the NOx sensor changes in accordance with the NOx amount and the ammonia amount in the exhaust gas, the abnormality determination means is the selective reduction type even when the NOx amount in the exhaust gas is small. If the NOx catalyst is abnormal, there is a risk of erroneous determination. Therefore, when the slip amount of ammonia estimated by the slip amount estimation means is greater than or equal to the predetermined slip amount, the selective determination type NOx catalyst is abnormal when the NOx amount in the exhaust gas is small by limiting the abnormality determination. It is possible to suppress erroneous determination that there is. Further, the slip amount estimating means can accurately estimate the ammonia slip amount.

  As described above, according to the present invention, the slip amount of ammonia is estimated based on the degree of deterioration of the selective reduction NOx catalyst, which is a parameter affecting the adsorption reaction rate of ammonia in the selective reduction NOx catalyst. As a result, the ammonia slip amount can be accurately estimated.

1 is a schematic configuration diagram of an engine system to which an engine catalyst abnormality determination device according to an embodiment of the present invention is applied. It is a block diagram which shows the control system of an engine system. It is a figure which shows the control map of passive DeNOx control and active DeNOx control. It is a flowchart at the time of selecting the catalyst which purifies exhaust gas. It is a part of flowchart when performing DeNOx control. It is the remainder of the flowchart at the time of performing DeNOx control. It is a schematic diagram which shows the NOx detection principle of a NOx sensor. It is a flowchart which shows the processing operation which estimates the slip amount of ammonia from an SCR catalyst. It is a map which shows the slip amount of ammonia based on the ammonia adsorption amount of a SCR catalyst, and the temperature of a SCR catalyst. 10 is a map showing the slip amount of ammonia with respect to the ammonia adsorption amount of the SCR catalyst in the map shown in FIG. 9. It is the map which expanded the area | region where the slip amount of ammonia is small in the map shown in FIG. It is a map which shows the relationship between the ammonia concentration in the exhaust gas introduce | transduced into an SCR catalyst, and the correction coefficient based on it. It is a flowchart which shows the processing operation of abnormality determination of an SCR catalyst. It is a time chart which shows typically the time change of each parameter in abnormality determination of an SCR catalyst. It is a map which shows the relationship between the thermal load of an SCR catalyst, and the correction coefficient based on it. It is a map which shows the relationship between the HC poisoning amount of a SCR catalyst, and the correction coefficient based on it.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an engine system 200 to which an engine abnormality determination device according to an embodiment of the present invention 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 EX that discharges exhaust gas from the engine E. And sensors 100 to 119 for detecting various states 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 a urea injector 51 described later. Is provided. The engine system 200 is an engine system provided in a vehicle, and the engine E is used as a drive source for 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, 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, a surge tank 12 are provided. The intake passage 1 is 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 air temperature sensor 102 that detects the intake air temperature are provided in a passage immediately downstream of the air cleaner 3 in the intake passage 1. A first intake pressure sensor 103 that detects intake pressure is provided in a passage between the first turbocharger 5 and the second turbocharger 6 in the intake passage 1. 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 a passage immediately downstream of the intercooler 8 in the intake passage 1. The throttle valve 7 is provided with a position sensor 105 that detects the opening degree of the throttle valve 7. The surge tank 12 is provided with a second intake pressure sensor 108 that detects the intake pressure in the intake manifold.

  The engine E generates heat by energization with an intake valve 15 for introducing the intake air supplied from the intake manifold of the intake passage 1 into the combustion chamber 17, a fuel injection valve 20 for injecting fuel toward the combustion chamber 17. A blow plug 21 having a heat generating part in the combustion chamber 17, a piston 23 reciprocating by 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 are exhausted. And an exhaust valve 27 for discharging to the passage 41. The piston 23 is connected to the crankshaft 25 via a 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. The PCM 60 (see FIG. 2) acquires the engine speed based on the detection signal from the crank angle sensor 100.

  The fuel system FS includes 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 valve 20. In the fuel supply passage 38, a low-pressure fuel pump 31, a high-pressure fuel pump 33, and a common rail 35 are provided in 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, in order from the upstream side, the turbine of the second turbocharger 6, the turbine of the first turbocharger 5, the NOx storage reduction catalyst 45, a 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 urea injected from the urea injector 51, and an exhaust from the SCR catalyst 47 And a slip catalyst 48 that oxidizes and purifies the unreacted ammonia. 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 storage reduction catalyst 45 stores NOx in the exhaust gas in a lean state (excess air ratio λ> 1) in which the air-fuel ratio of the exhaust gas is larger than the stoichiometric air-fuel ratio, and the stored NOx is exhausted to the exhaust gas. Is a NOx storage reduction catalyst (NSC: NOx Storage Catalyst) that reduces in a state where the air-fuel ratio is near the stoichiometric air-fuel ratio (λ≈1) or a rich state where the air-fuel ratio is smaller than the stoichiometric air-fuel ratio (λ <1). The NOx storage reduction catalyst 45 not only functions as an NSC but also oxidizes hydrocarbons (HC), carbon monoxide (CO), and the like using oxygen in the exhaust gas to change them into water and carbon dioxide. It is comprised so that it may also have a function as a diesel catalyst (DOC: Diesel Oxidation Catalyst). Specifically, the NOx storage reduction catalyst 45 is formed by coating the surface of the DOC catalyst layer with an NSC catalyst material.

  The DPF 46 is a filter that collects particulate matter (PM) in the exhaust gas. The PM collected in the DPF 46 is exposed to a high temperature and combusted by being supplied with oxygen, and is removed from the DPF 46.

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

  The NOx storage reduction catalyst 45 and the SCR catalyst 47 are both catalysts capable of purifying NOx, but the temperatures at which the NOx purification rate (NOx occlusion rate) increases are different from each other. Specifically, the NOx purification rate of the NOx storage reduction catalyst 45 becomes high when the temperature of the NOx storage reduction catalyst 45 is relatively low, while the NOx purification rate of the SCR catalyst 47 is the temperature of the SCR catalyst 47 (hereinafter referred to as “NOx purification rate”). SCR catalyst temperature) is relatively high.

  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 O 2 sensor 111 that detects the oxygen concentration in the exhaust gas is provided in a passage immediately downstream of the first turbocharger 5 in the exhaust passage 41. In the vicinity of the NOx storage reduction catalyst 45 in the exhaust passage 41, there are a second exhaust temperature sensor 112 for detecting the temperature of the exhaust gas in the passage immediately upstream of the NOx storage reduction catalyst 45, the NOx storage reduction catalyst 45, A third exhaust temperature sensor 113 for detecting the temperature of the exhaust gas in the passage between the DOC 46 and a differential pressure sensor 114 for detecting a 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 exhaust gas in the passage immediately downstream of the DPF 46, and a first NOx that detects the concentration of NOx in the passage immediately downstream of the DPF 46 and upstream of the urea injector 51. Sensor 116 is provided. A catalyst temperature sensor 117 that detects the SCR catalyst temperature and a second NOx sensor 118 that detects the concentration of NOx in the passage immediately downstream of the SCR catalyst 47 are provided around the SCR catalyst 47 in the exhaust passage 41. It has been. Further, the exhaust passage 41 is provided with a PM sensor 119 for detecting PM in the exhaust gas in the passage immediately upstream of the slip catalyst 48. As will be described in detail later, at least the second NOx sensor 118 is a NOx sensor whose output value changes depending on not only the amount of NOx in the exhaust gas but also the amount of ammonia.

  The engine system 200 in this embodiment further includes an EGR device 43 that recirculates a part of the exhaust gas to the intake air. The EGR device 43 includes an EGR passage 43a that connects a passage upstream of the 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. Further, the EGR device 43 includes 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 that includes a CPU, a ROM, a RAM, an I / O bus, and the like. The CPU is a central processing unit that executes computer programs (including basic control programs such as an OS and application programs that are activated on the OS to realize specific functions). The ROM is a memory in which various computer programs and data and a map described later are stored. The RAM is a memory provided with a processing area used when the CPU performs a series of processes. The I / O bus is an input / output bus for inputting / outputting electrical signals to / from the PCM 60.

  Detection signals from various sensors 100 to 119 are input to the PCM 60. Further, the PCM 60 outputs an accelerator opening sensor 150 that detects an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) of the vehicle and a vehicle speed sensor 151 that detects a vehicle speed of the vehicle. A detection signal is input. The PCM 60 mainly controls the operation 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. Further, the PCM 60 controls the operation of the urea injector 51 via the DCU 70 by sending an output signal to the DCU 70. The DCU 70 has the same configuration as the PCM 60. The PCM 60 may directly control the operation of the urea injector 51 without going through the DCU 70.

  As will be described in detail later, the PCM 60 calculates the ammonia adsorption amount estimation unit 61 that estimates the ammonia adsorption amount of the SCR catalyst 47 and the ammonia amount in the exhaust gas in the passage downstream of the SCR catalyst 47 of the exhaust passage 41. A slip amount estimation unit 62 to be estimated, an abnormality determination unit 63 that determines whether there is an abnormality in the engine system 200 based on an abnormality determination condition based on the output value of the second NOx sensor 118, and the abnormality determination unit 63 An abnormality determination limiting unit 64 that limits abnormality determination, and a deterioration level estimation unit 65 (degradation level estimation means) that estimates the deterioration level of the SCR catalyst 47 are provided.

<Normal fuel injection control>
The PCM 60 uses a 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 without performing DeNOx control, which will be described later. 20 is controlled. In the normal fuel injection control, the PCM 60 stops the post injection performed in the DeNOx control and executes only the main injection.

  In the normal fuel injection control, the PCM 60 sets the fuel injection amount in the main injection according to the driving state of the vehicle. Specifically, first, the PCM 60 acquires input signals from the various sensors 100 to 119, 150, and 151. Next, the PCM 60 sets a target acceleration based on the obtained driving state of the vehicle including the operation of the accelerator pedal and the like. Next, the PCM 60 determines a target torque of the engine E for realizing the determined target acceleration. Then, the PCM 60 calculates an injection amount to be injected from the fuel injection valve 20 based on the target torque and the engine speed so as to output the determined target torque from the engine E.

  Further, in normal fuel injection control, the PCM 60 sets the injection timing of the main injection according to the driving state of the vehicle.

  Thereafter, the PCM 60 controls the fuel injection valve 20 so as to achieve the set injection amount and injection timing.

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

  In the present embodiment, when the NOx occlusion amount is equal to or greater than the first predetermined occlusion amount (for example, when the NOx occlusion amount is near the occlusion limit), the PCM 60 substantially reduces the NOx occluded in the occlusion reduction type NOx catalyst 45 to 0. DeNOx control is executed in order to reduce the pressure to about 1. In this embodiment, even if the NOx occlusion amount is less than the first predetermined occlusion amount, the PCM 60 has an NOx occlusion amount that is greater than or equal to the second predetermined occlusion amount that is smaller than the first predetermined occlusion amount and is accelerated by the vehicle. When the air-fuel ratio of the exhaust gas changes to the rich side, DeNOx control may be executed. In the following description, the DeNOx control that is executed when the NOx occlusion amount is greater than or equal to the first predetermined occlusion amount is referred to as active DeNOx control. DeNOx control that is executed when the air-fuel ratio changes to the rich side is referred to as passive DeNOx control. When these are not distinguished, they are simply called DeNOx control.

  As described above, the NOx storage reduction catalyst 45 stores NOx in a state where 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 where the stoichiometric air-fuel ratio is smaller (λ <1). Is reduced. For this reason, in 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 this embodiment, post-injection is executed in addition to main injection, thereby reducing the air-fuel ratio of the exhaust gas and reducing the stored NOx. The excess air ratio λ during DeNOx control is, for example, about λ = 0.94 to 1.06.

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

  Next, the PCM 60 calculates the amount of air introduced into the engine E based on the acquired 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 necessary for setting the air-fuel ratio of the exhaust gas to a target air-fuel ratio near the stoichiometric air-fuel ratio or lower than the stoichiometric air-fuel ratio (hereinafter referred to as a target DeNOx air-fuel ratio). That is, the PCM 60 determines how much fuel should be injected by post injection in addition to the injection amount of the main injection in order to set 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. Therefore, the fuel necessary for setting the air-fuel ratio of the exhaust gas to the target DeNOx air-fuel ratio. The amount of injection is smaller in passive DeNOx control than in active DeNOx control. For this reason, if passive DeNOx control is performed as frequently as possible and the frequency of active DeNOx control is reduced, deterioration of fuel efficiency due to DeNOx control can be suppressed.

  Regarding the fuel injection timing in the post-injection, in this embodiment, the injection timing is changed depending on the form of DeNOx control. Specifically, the PCM 60 sets the timing at which post-injected fuel is combusted in the combustion chamber 17 when executing 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 discharged into the exhaust passage 41 as unburned fuel without being burned in the cylinder.

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

  In the present embodiment, the PCM 60 is in the middle load region where the engine load is equal to or higher than the first predetermined load Lo1 and lower than the second predetermined load Lo2 (> first predetermined load Lo1), and the engine speed is the first predetermined speed. Active DeNOx control is executed when the engine speed is in the middle speed range that is equal to or greater than N1 and less than the second predetermined speed N2 (> the first predetermined speed N1), that is, in the first operation region R1 shown in FIG. This is to suppress the generation of smoke and HC by causing ignition in a state where air and fuel are appropriately mixed. For this purpose, 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 the 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 is combined with soot. This is to prevent the passage of the EGR gas from being blocked. In addition, in order to prevent HC from being discharged without being purified when active DeNOx control is executed in a region where the temperature of the NOx storage reduction catalyst 45 is low and HC purification performance cannot be ensured. is there.

  On the other hand, in this embodiment, passive DeNOx control is executed when the engine load is in a region that is considerably higher than the first operation region R1, that is, in the second operation region R2 shown in FIG. This is because when the engine load is in the second operation region R2, the temperature of the NOx storage reduction catalyst 45 is normally such that the HC purification performance by the DOC constituting the NOx storage reduction catalyst 45 is exhibited. Therefore, the unburned fuel (HC) discharged into the exhaust passage 41 by the passive DeNOx control is sufficiently purified by the NOx storage reduction catalyst 45.

  The operation region other than the first and second operation regions R1 and R2 will be described. In the region where the engine load is higher than the first operation region R1 but lower than the second operation region R2, the in-cylinder temperature of the engine E becomes high. Thus, combustion occurs in a state where air and fuel are not properly mixed, and smoke and HC are likely to be generated. Further, the engine load is the same as that in the first operation region R1, but in a region where the engine speed is higher than that in the first operation region R1, the time required for one stroke of the engine E is short, so that air and fuel are mixed appropriately. Combustion occurs in a state where it is not applied, and smoke and HC are likely to be generated. Further, in the region where the engine load is lower than the first operation region R1, or the region where the engine load is the same as the first operation region R1 but the engine speed is lower than the first operation region R1, the NOx storage reduction catalyst. The temperature of 45 tends to be lower than the temperature at which the stored NOx can be reduced. For these reasons, in the present embodiment, when the operation region of the engine E is in an operation region other than the first and second operation regions R1, R2, the DeNOx control is not executed.

  When the operating region of the engine E is in an operating region other than the first and second operating regions R1, R2, and when the NOx storage amount is equal to or greater than the first predetermined storage amount, NOx is almost not stored in the NOx storage reduction catalyst 45. Not purified. However, in this embodiment, since the SCR catalyst 47 is provided on the downstream side of the NOx storage reduction catalyst 45, the SCR catalyst 47 purifies NOx that has not been purified by the NOx storage reduction catalyst 45. be able to.

  In the present embodiment, whether or not to execute the DeNOx control as described above is determined according to whether or not the SCR catalyst 47 can purify NOx in addition to the operation region of the engine E described above. . This is because if NOx in the exhaust gas can be appropriately purified by the SCR catalyst 47, it is not necessary to deliberately perform DeNOx control to ensure NOx purification performance by the NOx storage reduction catalyst 45. . As described above, the NOx purification rate of the NOx storage reduction 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. Get higher. Therefore, in the present embodiment, as shown in the flowchart of FIG. 4, the PCM 60 executes DeNOx control according to the SCR catalyst temperature and purifies NOx with the NOx storage reduction catalyst 45 or the SCR catalyst 47. To select whether or not to purify NOx.

  With reference to the flowchart of FIG. 4, the process of PCM60 at the time of selecting the catalyst which purifies exhaust gas is demonstrated. The PCM 60 executes processing based on this flowchart all the time or every predetermined period while the engine E is operating.

  First, in step S101, the PCM 60 reads information from the various sensors 100 to 119, 150, and 151, and determines whether or not the SCR catalyst temperature is lower than the first predetermined temperature in the next step S102. 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 the predetermined purification rate, and is 160 ° C., for example.

  In step S103, the PCM 60 performs DeNOx control without purifying NOx with the SCR catalyst 47, and purifies NOx only with the NOx storage reduction catalyst 45. In this step S103, the PCM 60 limits the supply of urea by the urea injector 51 so that the SCR catalyst 47 does not purify NOx. In other words, “the SCR catalyst 47 does not purify NOx” here means “to restrict 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 a second predetermined temperature (> first predetermined temperature). When the determination at step S104 is YES, the process proceeds to step S105, while when the determination at 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 value, and is, for example, 250 ° C.

  In step S105, the PCM 60 executes DeNOx control to purify NOx by the NOx storage reduction catalyst 45, and also purifies NOx by the SCR catalyst 47. That is, in this step S105, the PCM 60 supplies urea from the urea injector 51. After step S105, the process returns.

  In step S106, it is determined whether or not the flow rate of the exhaust gas introduced into the SCR catalyst 47 is less than a predetermined flow rate. If the determination in step S106 is YES, the process proceeds to step S107. If the determination in step S106 is NO, the process proceeds to step S105. In step S106, the exhaust gas flow rate is determined even if the SCR catalyst temperature is equal to or higher than the second predetermined temperature. This is because when the flow rate of the exhaust gas is large, the SCR catalyst 47 alone may not completely purify NOx. That is, when the exhaust gas flow rate is higher than the predetermined flow rate, it is preferable to purify NOx by both the NOx storage reduction catalyst 45 and the SCR catalyst 47, and the process proceeds to step S105. The flow rate of the exhaust gas can be estimated from the operating state of the engine E (particularly the engine load and the engine speed).

  In step S107, the NOx is not purified by the NOx storage reduction catalyst 45, but NOx is purified only by the SCR catalyst 47. Also in this step S107, the PCM 60 supplies urea from the urea injector 51 to the SCR catalyst 47. In this step S107, execution of DeNOx control is prohibited, and the NOx occlusion amount of the NOx storage reduction catalyst 45 is set to the adsorption limit, so that NOx is not purified by the NOx storage reduction catalyst 45. After step S107, the process returns. If the NOx occlusion amount of the NOx storage reduction catalyst 45 has not reached the limit, the NOx storage occlusion can be stored by the NOx storage reduction catalyst 45. Therefore, also in this step S107, the NOx storage reduction catalyst. 45 may purify (occlude) NOx. That is, “the NOx storage reduction catalyst 45 does not purify NOx” here means “to prohibit execution of DeNOx control”.

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

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

  In step S203, the PCM 60 determines whether the operating region of the engine E belongs to the first operating region R1. When the determination in step S203 is YES, the process proceeds to step S205 to execute active DeNOx control, while when the determination in step S203 is NO, the process proceeds to step S212.

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

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

  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.

  In step S207, the PCM 60 controls the fuel injection valve 20 so that post injection is performed with the post injection amount set in 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 the closed side, and in the next step S209, the fuel injection valve 20 is controlled to perform post injection at the first predetermined injection amount. In step S208 and step S209, the throttle valve 7 is set so that the air-fuel ratio of the exhaust gas becomes the target DeNOx air-fuel ratio by the post-injection amount that does not exceed the first predetermined injection amount (actually the value of the first predetermined injection amount itself). To reduce the oxygen concentration of the air introduced into the engine E. After step S209, the process proceeds to step S210.

  In step S210, the PCM 60 determines whether or not the NOx occlusion amount has become substantially zero. When the determination in step S210 is YES, the active DeNOx control is terminated and the process returns. On the other hand, when the determination in step S210 is NO, the process returns to step S203. In step S210, whether or not the NOx occlusion amount has become substantially zero is determined by integrating the post injection amount, and the accumulated value has become a value that makes the occlusion NOx greater than or equal to the first predetermined occlusion amount substantially zero. Determine based on whether or not. In addition, that the NOx occlusion amount becomes substantially zero includes that the NOx occlusion amount becomes zero.

  On the other hand, in step S211, which proceeds when the determination in step S202 is NO, the PCM 60 determines whether the NOx occlusion amount in the NOx storage reduction catalyst 45 is equal to or greater than the second predetermined occlusion amount. When the determination in step S211 is YES, the process proceeds to step S212. On the other hand, when the determination in step S211 is NO, the process returns because there is no need to execute active DeNOx control and passive DeNOx control.

  In step S212, the PCM 60 sets the post injection amount. As with step S204 above, the post injection amount is such that the air-fuel ratio of the exhaust gas becomes the target DeNOx air-fuel ratio based on the oxygen concentration of the air introduced into the engine E, the fuel injection amount in the main injection, and the like. The required injection amount is set.

  In step S213, the PCM 60 sets the post injection timing. As described above, in the passive DeNOx control, the post injection timing is set to the timing at which the post-injected fuel is discharged into the exhaust passage 41 as unburned fuel without being burned in the cylinder.

  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 driving region of the vehicle is in the second driving region, 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 vehicle operating region is in the second operating region in which passive DeNOx control can be performed.

  In the subsequent step S215, the PCM 60 controls the fuel injection valve 20 so as to perform the post injection with the post injection amount set in the 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 performing post injection. After step S216, the process returns to step S203.

  As described above, by executing DeNOx control, in this embodiment, NOx in the exhaust gas can be appropriately purified while suppressing deterioration of fuel consumption due to DeNOx control.

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

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

  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 becomes 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.

  As will be described in detail later, 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 DeNOx control, the NOx inflow amount, and the purification efficiency of the SCR catalyst 47. The target adsorption amount is set so that the higher the SCR catalyst temperature, the smaller the target adsorption amount than when the SCR catalyst temperature is low. Further, the target adsorption amount is set to a value smaller than the ammonia adsorption limit in 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 purification rate of NOx in the SCR catalyst 47. Specifically, the abnormality determination unit 63 first calculates the NOx amount in the passage upstream of the SCR catalyst 47 (hereinafter referred to as upstream NOx amount) based on the detection result of the first NOx sensor 116, and the SCR catalyst. 47 is calculated based on the detection result of the second NOx sensor 118, and the actual purification rate of the SCR catalyst 47 is calculated based on the following equation (1). calculate.

Purification rate = 1− (downstream NOx amount / upstream NOx amount) (Equation 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 adds 1 to the failure count because there is a possibility that an abnormality has occurred in the SCR catalyst 47. Then, the abnormality determination unit 63 determines that the SCR catalyst 47 is abnormal when the failure count reaches or exceeds a predetermined value. That is, the fact that the purification rate is equal to or less than the predetermined purification rate and the count number of the failure count is equal to or greater than the predetermined value corresponds to the abnormality determination condition of the abnormality determination unit 63.

  Further, when it is determined that the SCR catalyst 47 is abnormal, the abnormality determination unit 63 gives a warning to the vehicle occupant that the SCR catalyst 47 is abnormal. This warning is performed, for example, by turning on a lamp provided at a position where the vehicle occupant can visually recognize.

  In order to accurately perform the abnormality determination, 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 NOx sensor changes the output value (detection value) not only with NOx in the exhaust gas but also with ammonia in the exhaust gas. The unit 63 may make an erroneous determination. Hereinafter, the principle of NOx detection by the NOx sensor will be described with reference to FIG.

  FIG. 7 schematically shows the principle of NOx detection. Although the second NOx sensor 118 is illustrated in FIG. 7, 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. The exhaust gas flowing into the second NOx sensor 118 is first oxidized in the first cavity 118a by oxidizing HC and CO in the exhaust gas and removing gases other than NOx. Next, the NOx that has passed through the first cavity 118b is 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 flowing into the second NOx sensor 118, the ammonia in the exhaust gas is oxidized in the first cavity 118a as shown in FIG. Decomposed into NOx and H ₂ O. The ammonia-derived NOx is reduced in the second cavity 118b and decomposed into nitrogen and oxygen as shown in FIG. For this reason, the second NOx sensor 118 detects NOx derived from ammonia as NOx in the exhaust gas. For this reason, the output value of the second NOx sensor 118 changes in accordance with NOx and ammonia in the exhaust gas.

  Note that the output value of the first NOx sensor 116 also changes according to the ammonia in the exhaust gas. Although details will be described later, since ammonia is also generated by DeNOx control, the first NOx sensor 116 may also detect ammonia as NOx. However, the upstream NOx amount can be accurately calculated 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. Can do.

  Basically, the amount of ammonia discharged into the passage downstream of the SCR catalyst 47 in the exhaust passage 41 (hereinafter referred to as ammonia slip amount) is set by the DCU 70 to an appropriate value for the target adsorption amount. It can be suppressed to some extent. However, in the SCR catalyst 47, ammonia adsorption reaction and desorption reaction always occur, and in a situation where the desorption reaction becomes dominant, ammonia is discharged into a passage downstream of the SCR catalyst 47. (Ammonia slip occurs). For this reason, the downstream NOx amount may not be accurately calculated from the detection result of the second NOx sensor 118.

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

  The amount of ammonia slip based on the ammonia adsorption reaction and desorption reaction in the SCR catalyst 47 is mainly determined by the balance between the ammonia adsorption reaction rate and the desorption reaction rate in the SCR catalyst 47. The adsorption reaction rate and the desorption reaction rate are represented by the following formulas 2 and 3.

Adsorption reaction rate = Aa × (1−θ) × exp (−Ea / RT) × C1 (Formula 2)
Desorption reaction rate = Ad × exp (−Ed / RT) × adsorption amount (Formula 3)
In the above 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 SCR. This is a correction coefficient based on the ammonia concentration in the exhaust gas introduced into the catalyst 47. The activation energy Ea is a constant determined by experiment or simulation. The coverage θ is a value obtained by dividing the current ammonia adsorption amount of the SCR catalyst 47 by the 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 the above formula 3, Ad is the frequency coefficient of the elimination reaction, Ed is the activation energy necessary for the elimination reaction, R is a gas constant, and T is the SCR catalyst temperature. The activation energy Ed is a constant determined by experiment or simulation. The adsorption amount is the ammonia adsorption amount of the SCR catalyst 47. The frequency coefficient Aa and the frequency coefficient Ad are obtained in advance through experiments and simulations.

  The ammonia adsorption reaction on the SCR catalyst 47 is a reaction in which ammonia is only adsorbed on the acid sites of the SCR catalyst 47, while the ammonia desorption reaction from the SCR catalyst 47 is performed by removing the adsorbed ammonia from the SCR catalyst 47. It is a reaction to cut off from the acid point. For this reason, the activation energy Ed of the desorption reaction is considerably larger than the activation energy Ea of the adsorption reaction. That is, the adsorption reaction rate is not easily influenced by the SCR catalyst temperature, while the desorption reaction rate is easily influenced by the SCR catalyst temperature.

  The ammonia concentration in the exhaust gas affects the final ammonia slip amount, but does not affect the adsorption reaction rate as much as the ammonia coverage of the SCR catalyst 47.

  Therefore, the adsorption reaction rate mainly depends on the ammonia coverage of the SCR catalyst 47, while the desorption reaction rate mainly depends on the ammonia adsorption amount of the SCR catalyst 47 and the SCR catalyst temperature. Therefore, the ammonia slip amount determined by the balance between the adsorption reaction rate and the desorption reaction rate mainly needs to consider the ammonia adsorption amount of the SCR catalyst 47, the SCR catalyst temperature, and the ammonia coverage. The ammonia adsorption limit of the SCR catalyst 47 that affects the ammonia coverage changes depending on the degree of deterioration of the SCR catalyst 47. Therefore, in the present embodiment, in the PCM 60, the ammonia adsorption amount estimation unit 61 estimates the ammonia adsorption amount of the SCR catalyst 47, the SCR catalyst temperature is detected by the catalyst temperature sensor 117, and the deterioration degree estimation unit 65 of the SCR catalyst 47. The degree of deterioration is estimated, and the slip amount estimation unit 62 is estimated by the ammonia adsorption amount estimated by the ammonia adsorption amount estimation unit 61, the SCR catalyst temperature detected by the catalyst temperature sensor 117, and the deterioration degree estimation unit 65. Based on the degree of deterioration, the slip amount of ammonia, which is the amount of ammonia discharged into the passage downstream of the SCR catalyst 47 in the exhaust passage 41, is estimated.

  Here, in the present embodiment, the ammonia adsorption amount estimation unit 61 is based on the urea injection amount, the ammonia amount generated by the DeNOx control, the NOx inflow amount to the SCR catalyst 47, and the purification efficiency of the SCR catalyst 47. The ammonia adsorption amount of the SCR catalyst 47 is estimated. Specifically, the ammonia adsorption amount estimation unit 61 first calculates the ammonia amount flowing into the SCR catalyst 47 based on the urea injection amount and the ammonia amount generated by the DeNOx control. The ammonia generated by the DeNOx control is ammonia that is exhausted into the exhaust gas from the NOx storage reduction catalyst 45 when the NOx storage NOx catalyst 45 is reduced, and the NOx storage NOx of the NOx storage catalyst 45 is stored. And HC supplied by post injection. For this reason, the ammonia generated by the DeNOx control can be estimated from the NOx occlusion amount of the NOx storage reduction catalyst 45 and the post injection amount. Next, the ammonia adsorption amount estimation unit 61 calculates the amount of ammonia consumed from the SCR catalyst 47 based on the NOx inflow amount to the SCR catalyst 47 and the purification efficiency of the SCR catalyst 47. The amount of NOx flowing into the SCR catalyst 47 is calculated based on the detection result of the first NOx sensor 116 and the estimated value of ammonia generated by DeNOx control. The purification efficiency of the SCR catalyst 47 is obtained by reading a map stored in the memory of the PCM 60 from a theoretical value calculated in advance based on the SCR catalyst temperature, the flow rate of exhaust gas introduced into the SCR catalyst 47, and the like. . Then, the ammonia adsorption amount estimation unit 61 estimates the current ammonia adsorption amount of the SCR catalyst 47 from the difference between the integrated value of the ammonia amount flowing into the SCR catalyst 47 and the integrated value of the ammonia amount consumed from the SCR catalyst 47. To do. Hereinafter, the ammonia adsorption amount of the SCR catalyst 47 estimated by the ammonia adsorption amount estimation unit 61 is referred to as an estimated ammonia adsorption amount.

  When the DeNOx control is not executed, the ammonia adsorption amount estimation unit 61 does not consider the ammonia amount generated by the DeNOx control in estimating the ammonia adsorption amount of the SCR catalyst 47.

  FIG. 8 shows the processing operation of the PCM 60 when estimating the slip amount of ammonia from the SCR catalyst 47. The ammonia adsorption amount of the SCR catalyst 47 is estimated by the ammonia adsorption amount estimation unit 61, and the ammonia slip amount from the SCR catalyst 47 is estimated by the slip amount estimation unit 62.

  First, in step S301, the PCM 60 reads information from the various sensors 100 to 119, 150, and 151. In this step S301, in particular, the SCR catalyst temperature is detected by the catalyst temperature sensor 117.

  In the next step S302, the PCM 60 determines whether or not DeNOx control is being performed. When the determination at step S302 is YES, the process proceeds to step S303, while when the determination at 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 step S304, the PCM 60 estimates the ammonia adsorption amount of the SCR catalyst 47. In this step S304, the ammonia adsorption amount of the SCR catalyst 47 is estimated in consideration of the ammonia amount generated by the DeNOx control when passing through the step S303, while the DeNOx control is performed when not passing through the step S303. The amount of ammonia adsorbed by the SCR catalyst 47 is estimated without considering the amount of ammonia generated by the above.

  In the next step S305, the PCM 60 (deterioration degree estimation unit 65) estimates the deterioration degree of the SCR catalyst 47.

  Next, in step S306, the PCM 60 (slip amount estimation unit 62) estimates the estimated ammonia adsorption amount estimated in step S304, the SCR catalyst temperature detected by the catalyst temperature sensor 117 in step S301, and estimated in step S305. Based on the degree of deterioration, the slip amount of ammonia from the SCR catalyst 47 is estimated. Specifically, the estimated ammonia adsorption amount and the SCR catalyst temperature are applied to the map shown in FIG. 9 or the map shown in FIG. 10 to estimate the slip amount of ammonia from the SCR catalyst 47 (temporary slip amount). The temporary slip amount is corrected based on the estimated degree of deterioration, and the slip amount is estimated. After step S306, the process returns.

  FIG. 9 shows a map (stored in the memory of the PCM 60) obtained by experiment to obtain the slip amount of ammonia by changing the ammonia adsorption amount of the SCR catalyst 47 and the SCR catalyst temperature. Although described later in detail, a correction coefficient described later based on the ammonia concentration in the exhaust gas and the degree of deterioration is set to 1. In FIG. 9, the vertical axis represents the ammonia adsorption amount of the SCR catalyst 47, and the horizontal axis represents the SCR catalyst temperature. The lower limit value on the vertical axis is 0, and the upper limit value on the vertical axis is the ammonia adsorption limit of the SCR catalyst 47. The horizontal axis is set to a temperature range in which the SCR catalyst 47 can be used. The minimum temperature is set to 160 ° C., and the maximum temperature is set to 400 ° C. “Small”, “Medium”, and “Large” in FIG. 9 represent the slip amount of ammonia, and the ammonia slip amount increases in the order of “Small”, “Medium”, and “Large”. Here, when the ammonia slip amount is equal to or larger than a predetermined slip amount, specifically, an amount that affects the detection of the NOx concentration by the second NOx sensor 118, “small”, “medium” depending on the amount. And “Large”. In addition, “0” in FIG. 9 indicates that there is no ammonia slip or that the ammonia slip amount is small enough not to affect the detection of the NOx concentration by the second NOx sensor 118.

  The maximum temperature at which the SCR catalyst 47 can be used means the highest temperature that the SCR catalyst 47 can take, and corresponds to the SCR catalyst temperature when the operating range of the engine E is in the high rotation and high load range. To do.

  As shown in FIG. 9, in the temperature range in which the SCR catalyst 47 can be used, the ammonia slip amount increases as the estimated ammonia adsorption amount increases and the SCR catalyst temperature increases. Further, as shown in FIG. 9, it can be seen that when the SCR temperature is at the maximum temperature, ammonia slip occurs even if the ammonia adsorption amount of the SCR catalyst 47 is small.

  Furthermore, as shown in FIG. 9, when the ammonia adsorption amount of the SCR catalyst 47 is in the vicinity of the adsorption limit, it can be seen that ammonia slip occurs even when the SCR catalyst temperature is low. In this embodiment, when the ammonia adsorption amount of the SCR catalyst 47 is at the adsorption limit, the temperature at which the ammonia slip amount is equal to or greater than the predetermined slip amount is about 200 ° C. That is, when the ammonia adsorption amount of the SCR catalyst 47 is the maximum, when the SCR catalyst temperature is the second predetermined temperature (for example, 250 ° C.), the ammonia slip amount exceeds the predetermined slip amount.

  FIG. 10 is a map showing in more detail the relationship between the ammonia adsorption amount of the SCR catalyst 47 and the ammonia slip amount in the map of FIG. The vertical axis represents the ammonia slip amount, and the horizontal axis represents the ammonia adsorption amount of the SCR catalyst 47. The lower limit of the horizontal axis is 0, and the upper limit is the adsorption limit of the SCR catalyst 47. Each of the curves L1 to L4 in FIG. 10 has a different SCR catalyst temperature. Specifically, L1 is a curve at the highest temperature (400 ° C.) of the SCR catalyst 47, and L4 is a curve at the lowest temperature (160 ° C.) of the SCR catalyst 47. L2 and L3 are curves in the temperature between the maximum temperature and the minimum temperature of the SCR catalyst 47, and the higher temperature (3 parts between the maximum temperature and the minimum temperature of the SCR catalyst 47). The curve at 320 ° C. is L2, and the curve at the lower temperature (240 ° C.) is L3.

  As shown in FIG. 10, in the temperature range in which the SCR catalyst 47 can be used, the SCR catalyst temperature is the same (here, the deterioration degree and the ammonia concentration are the same (hereinafter the same)), It can be seen that when the ammonia adsorption amount of the SCR catalyst 47 is large, the ammonia slip amount is larger than when the ammonia adsorption amount of the SCR catalyst 47 is small. This is because when the ammonia adsorption amount of the SCR catalyst 47 is large, the coverage rate θ of ammonia of the SCR catalyst 47 is increased and the adsorption reaction rate is lowered while the desorption reaction rate is increased. Therefore, in the present embodiment, the slip amount estimation unit 62 compares the estimated ammonia adsorption when compared with the same deterioration degree, the same ammonia concentration, and the same SCR catalyst temperature in the temperature range in which the SCR catalyst 47 can be used. When the amount is large, the ammonia slip amount is estimated to be larger than when the estimated ammonia adsorption amount is small. In particular, in the present embodiment, the slip amount estimation unit 62 is configured to estimate a larger ammonia slip amount as the estimated ammonia adsorption amount approaches the adsorption limit of the SCR catalyst 47.

  Further, as shown in FIG. 10, the ammonia adsorption amount of the SCR catalyst 47 is the same in the temperature range in which the SCR catalyst 47 can be used (here, the deterioration degree and the ammonia concentration are the same (hereinafter the same). )) Under the conditions, it can be seen that when the temperature of the SCR catalyst 47 is high, the slip amount of ammonia is larger than when the temperature of the SCR catalyst 47 is low. This is because, as the SCR catalyst temperature is higher, the value of exp (−Ed / RT) in Equation 3 becomes smaller and the elimination reaction rate increases. Therefore, in the present embodiment, the slip amount estimation unit 62 compares the SCR catalyst when compared with the same deterioration degree, the same ammonia concentration, and the same estimated ammonia adsorption amount in the temperature range in which the SCR catalyst 47 can be used. When the temperature is high, the ammonia slip amount is estimated to be larger than when the SCR catalyst temperature is low.

  Furthermore, as shown in FIG. 10, when the ammonia adsorption amount of the SCR catalyst 47 is large under the condition that the SCR catalyst temperature is the same in the temperature range where the SCR catalyst 47 can be used, the ammonia adsorption amount of the SCR catalyst 47. It can be seen that the change in the slip amount of ammonia with respect to the change in the ammonia adsorption amount of the SCR catalyst 47 (that is, the slope of the curve in FIG. 10) is larger than when the amount is small. Therefore, in the present embodiment, the slip amount estimation unit 62 compares the estimated ammonia adsorption when compared with the same deterioration degree, the same ammonia concentration, and the same SCR catalyst temperature in the temperature range in which the SCR catalyst 47 can be used. When the amount is large, the ammonia slip amount is estimated so that the change in the ammonia slip amount with respect to the change in the estimated ammonia adsorption amount becomes larger than when the estimated ammonia adsorption amount is small. .

  In particular, when the SCR catalyst temperature is equal to or higher than the second predetermined temperature, and under the condition that the SCR catalyst temperature is the same, when the ammonia adsorption amount is 1/3 or more of the adsorption limit, the ammonia adsorption amount is 1/2 of the adsorption limit. It can be seen that the change in the slip amount of ammonia with respect to the change in the ammonia adsorption amount of the SCR catalyst 47 is larger than when it is less than 3. Therefore, in the present embodiment, the slip amount estimation unit 62, particularly when the SCR catalyst temperature is equal to or higher than the second predetermined temperature, when compared at the same deterioration degree, the same ammonia concentration, and the same SCR catalyst temperature, When the estimated ammonia adsorption amount is 1/3 or more of the adsorption limit, the change in the ammonia slip amount with respect to the change in the estimated ammonia adsorption amount is larger than when the estimated ammonia adsorption amount is less than 1/3 of the adsorption limit. The ammonia slip amount is estimated so as to increase.

  Further, as shown in FIG. 10, when the SCR catalyst 47 has a high ammonia adsorption amount in the temperature range in which the SCR catalyst 47 can be used, when the SCR catalyst temperature is high, the SCR catalyst temperature is low. In comparison, it can be seen that the change in the slip amount of ammonia with respect to the change in the SCR catalyst temperature becomes large. In particular, it can be seen that the above-mentioned tendency appears remarkably in the region where the ammonia adsorption amount of the SCR catalyst 47 is less than half of the adsorption limit of the SCR catalyst 47. As described above, the activation energy required for the elimination reaction is relatively large. For this reason, when the SCR catalyst temperature is low, the value of exp (−Ed / RT) in Formula 3 itself is small, and even if the SCR catalyst temperature rises, the desorption reaction rate does not easily rise. On the other hand, when the SCR catalyst temperature is high, the value of exp (−Ed / RT) in Equation 3 increases, and therefore the desorption reaction rate tends to increase as the SCR catalyst temperature increases. For this reason, it becomes the above changes. Therefore, in the present embodiment, the slip amount estimation unit 62 compares the SCR catalyst when compared with the same deterioration degree, the same ammonia concentration, and the same estimated ammonia adsorption amount in the temperature range in which the SCR catalyst 47 can be used. When the temperature is high, the ammonia slip amount is estimated so that the change in the ammonia slip amount with respect to the change in the SCR catalyst temperature is larger than when the SCR catalyst temperature is low.

  FIG. 11 is a map obtained by enlarging a region where the slip amount of ammonia is relatively small in FIG. Referring to FIG. 11, it can be seen that the higher the SCR catalyst temperature, the more ammonia slip occurs from the time when the ammonia adsorption amount of the SCR catalyst 47 is smaller. This is because, as the SCR catalyst temperature is higher, the value of exp (−Ed / RT) in Equation 3 becomes larger, and the desorption reaction rate is higher than the adsorption reaction rate even when the ammonia adsorption amount of the SCR catalyst 47 is small. It is thought that this is because it becomes faster. Therefore, in the present embodiment, the slip amount estimation unit 62 is configured to estimate that in the temperature range in which the SCR catalyst 47 can be used, the ammonia adsorption amount at which ammonia slip begins to occur is smaller as the SCR catalyst temperature is higher. Has been.

  In the present embodiment, the deterioration degree estimation unit 65 estimates both the heat load applied to the SCR catalyst 47 and the HC poisoning amount of the SCR catalyst 47 as the deterioration degree.

  The heat load can be, for example, an integrated value of the thermal energy applied to the SCR catalyst 47. The integrated value of the thermal energy can be substituted with a value obtained by adding the values for each SCR catalyst temperature in a value obtained by multiplying the SCR catalyst temperature by the time during which the SCR catalyst temperature is maintained, for example. As the heat load increases, the ammonia adsorption limit of the SCR catalyst 47 decreases (that is, the slip amount increases).

  The HC poisoning amount of the SCR catalyst 47 is a value obtained by multiplying the integrated value of the HC generation amount estimated from the operating state of the engine E by a predetermined ratio. The predetermined ratio is a value obtained through experiments or the like. As the HC poisoning amount of the SCR catalyst 47 increases, the ammonia adsorption limit of the SCR catalyst 47 decreases (that is, the slip amount increases).

  In this embodiment, in order to consider the influence of the deterioration degree of the SCR catalyst 47, the numerical value (temporary slip amount) constituting the map of FIG. 9 is corrected based on the deterioration degree, and the slip amount is corrected. presume. Specifically, the slip amount is obtained by multiplying the numerical value of the map of FIG. 9 by a correction coefficient based on the degree of deterioration (specifically, the correction coefficient based on the thermal load and the correction coefficient based on the HC poisoning amount). Is estimated.

  FIG. 15 is an example of a map (stored in the memory of the PCM 60) showing the relationship between the thermal load and the correction coefficient based thereon. When the heat load is 0, the correction coefficient based on the heat load is 1, and the correction coefficient increases with respect to 1 as the heat load increases from here. If the correction coefficient is 1, the ammonia slip amount considering the heat load is the same as the numerical value in the map of FIG. The map of FIG. 15 is represented by a straight line on a two-dimensional orthogonal graph with the thermal load as the horizontal axis and the correction coefficient as the vertical axis.

  FIG. 16 is an example of a map (stored in the memory of the PCM 60) showing the relationship between the HC poisoning amount of the SCR catalyst 47 and the correction coefficient based thereon. When the HC poisoning amount is 0, the correction coefficient based on the HC poisoning amount is 1, and the correction coefficient increases with respect to 1 as the HC poisoning amount increases from here. If the correction coefficient is 1, the ammonia slip amount considering the HC poisoning amount is the same as the numerical value in the map of FIG. The map of FIG. 16 is represented by a straight line on a two-dimensional orthogonal graph with the HC poisoning amount on the horizontal axis and the correction coefficient on the vertical axis.

  Therefore, the slip amount estimation unit 62 estimates a larger amount of slip when the degree of deterioration (the thermal load and the amount of HC poisoning) is larger than when the degree of deterioration is small.

  Note that the deterioration level estimation unit 65 may estimate only one of the thermal load and the HC poisoning amount as the deterioration level, and the slip amount estimation unit 62 corresponds to the numerical values in the map of FIG. Thus, the slip amount may be estimated by multiplying only one of the correction coefficient based on the thermal load and the correction coefficient based on the HC poisoning amount.

  Here, as shown in the above equation 2, the adsorption reaction rate strictly varies depending on the ammonia concentration in the exhaust gas introduced into the SCR catalyst 47. For this reason, in order to estimate the ammonia slip amount more accurately, it is preferable to consider the ammonia concentration in the exhaust gas. Therefore, in the present embodiment, the slip amount estimation unit 62 adds to the numerical value (temporary slip amount) of the map of FIG. 9 in addition to the correction coefficient based on the degree of deterioration, and in the exhaust gas introduced into the SCR catalyst 47. A correction coefficient based on the ammonia concentration (different from C1 in Equation 2) is also multiplied.

  FIG. 12 is an example of a map (stored in the memory of the PCM 60) showing the relationship between the ammonia concentration in the exhaust gas introduced into the SCR catalyst 47 and the correction coefficient based thereon. As described above, the ammonia concentration in the exhaust gas is a parameter that affects the adsorption reaction rate. Specifically, when the ammonia concentration in the exhaust gas is low, the adsorption reaction is suppressed, so that the adsorption reaction rate is low (that is, the slip amount is increased). Therefore, the correction coefficient based on the ammonia concentration in the exhaust gas is a correction coefficient that increases as the ammonia concentration decreases, as shown in FIG. In the present embodiment, the correction coefficient in the ammonia concentration D1 between the maximum ammonia concentration that can be taken by the engine system 200 and 0 is 1, and when the ammonia concentration is higher than D1, the correction coefficient is made smaller than 1. When the ammonia concentration is lower than D1, the correction coefficient is made smaller than 1. This correction coefficient changes in a range larger than 0 and smaller than 2. The ammonia concentration in the exhaust gas is estimated by the PCM 60 based on the flow rate of the exhaust gas introduced into the SCR catalyst 47, the urea injection amount, and the ammonia amount generated by the DeNOx control. The value of D1 is set according to the actual engine system through experiments or the like.

  Since the slip amount estimation unit 62 estimates the ammonia slip amount as described above, the parameters affecting the ammonia adsorption reaction rate and the desorption reaction rate are taken into consideration. The estimation accuracy of the slip amount can be improved.

  The estimated slip amount of ammonia estimated by the slip amount estimation unit 62 is input to the abnormality determination limiting unit 64 of the PCM 60. When the estimated slip amount of ammonia is equal to or greater than the predetermined slip amount, specifically, the amount that affects the detection of the NOx concentration by the second NOx sensor 118, the abnormality determination limiting unit 64 detects the SCR catalyst 47 by the abnormality determination unit 63. Limits abnormal judgments. Specifically, when the estimated slip amount of ammonia is a predetermined slip amount, the abnormality determination limiting unit 64 determines that the abnormality determination unit 63 is abnormal even if the purification rate calculated by the above equation 1 is equal to or less than the predetermined purification rate. The determination is stopped so that the abnormality determination unit 63 does not count the failure. Accordingly, 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 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, and thus the erroneous determination of 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 operation described below, control relating to abnormality determination of the SCR catalyst 47 is executed by the abnormality determination unit 63 of the PCM 60, and control relating to restriction of the abnormality determination is executed by the abnormality determination restriction unit 64. The abnormality determination based on this flowchart is executed 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 the various sensors 100 to 119, 150, 151, and calculates the NOx purification rate of the SCR catalyst 47 in the next step S402.

  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. On the other hand, 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 the estimated slip amount of ammonia is less than a predetermined slip amount. If the determination in step S404 is YES, the process proceeds to step S405. If 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 adds one failure count, and in the next step S406, the PCM 60 determines whether or not the count number of the failure count has become a predetermined value or more. When the determination in step S406 is YES, the process proceeds to step S407. On the other hand, when the determination in step S406 is NO, the process returns as it is 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, a vehicle occupant is warned. After step S408, the process returns.

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

  A change in each parameter (estimated slip amount or the like) when the abnormality determination by the PCM 60 is executed will be described with reference to the time chart of FIG. In FIG. 14, the ammonia adsorption amount is a value estimated by the ammonia adsorption amount estimation unit 61 of the PCM 60, and the ammonia slip amount is a value estimated by the slip amount estimation unit 62 of the PCM 60. Further, regarding the output value of the NOx sensor, the broken line is the output value of the first NOx sensor 116, and the solid line is the output value of the second NOx sensor 118.

  First, in the initial state, it is assumed that the PCM 60 performs normal fuel injection control and the SCR catalyst 47 is in an inactive state. If the DeNOx control is executed from this initial state, ammonia is generated along with the DeNOx control, so that the ammonia adsorption amount of the SCR catalyst 47 increases. Thereafter, when DeNOx control is executed in a state where the SCR catalyst temperature is lower than the first predetermined temperature, that is, the NOx purification by the SCR catalyst 47 is not performed, ammonia is not consumed from the SCR catalyst 47, and the SCR catalyst is not consumed. The amount of ammonia adsorption of 47 increases.

  When the SCR catalyst temperature is equal to or higher than the first predetermined temperature, NOx purification is started by the SCR catalyst 47, so that 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. Further, since NOx flows downstream from the NOx storage reduction catalyst 45, the output value of the first NOx sensor 116 increases.

  As the temperature of the SCR catalyst 47 increases, ammonia slip occurs. As a result, the output value of the second NOx sensor 118 increases. When the ammonia slip exceeds the predetermined slip amount, the PCM 60 stops the abnormality determination of the SCR catalyst 47. Thereby, as shown in FIG. 14, it is possible to prevent the abnormality determination from being executed in a state where the output value of the second NOx sensor 118 exceeds the output value of the first NOx sensor 116. The PCM 60 restarts the determination of the abnormality of the SCR catalyst 47 when the ammonia slip becomes less than the predetermined slip amount.

  As shown in FIG. 14, the PCM 60 estimates that the ammonia adsorption amount is smaller when ammonia slip occurs than when there is no ammonia slip. This is because when ammonia slip occurs, the ammonia desorption reaction from the SCR catalyst 47 is dominant, and therefore, it can be considered that the ammonia adsorption amount of the SCR catalyst 47 is smaller than when there is no ammonia slip. Thereby, the estimation accuracy of the ammonia adsorption amount of the SCR catalyst 47 is improved, and further, the estimation accuracy of the ammonia slip amount is improved.

  Therefore, in the present embodiment, the slip amount estimation unit 62 estimates a larger amount of ammonia slip from the SCR catalyst 47 when the deterioration degree of the SCR catalyst 47 is larger than when the deterioration degree of the SCR catalyst 47 is small. As a result, the estimation accuracy of the slip amount can be improved.

  In the present embodiment, the slip amount estimation unit 62 estimates the slip amount based on the estimated ammonia adsorption amount and the detected catalyst temperature in addition to the deterioration degree. 47, the parameters that have a relatively large influence on the adsorption reaction rate and desorption reaction rate of ammonia are taken into consideration, so that the estimation accuracy of the slip amount can be further improved.

  The present invention is not limited to the embodiment described above, and can be substituted without departing from the spirit of the claims.

  For example, in the above-described embodiment, the numerical value (temporary slip amount) in the map of FIG. 9 is multiplied by the correction coefficient based on the deterioration degree of the SCR catalyst 47 and the correction coefficient based on the ammonia concentration in the exhaust gas. Although the ammonia slip amount is finally estimated, the ammonia slip amount may be finally estimated by multiplying the numerical value of the map of FIG. 9 by only the correction coefficient based on the degree of deterioration. Further, the flow rate of exhaust gas introduced into the SCR catalyst 47 (the greater the exhaust gas flow rate, the smaller the frequency coefficient Aa and the greater the frequency coefficient Ad) and / or the exhaust gas introduced into the SCR catalyst 47. In order to consider the influence of the oxygen concentration in the exhaust gas (which is not described in Equation 2 but strictly speaking, the adsorption reaction rate increases as the oxygen concentration in the exhaust gas increases) In addition to the correction coefficient based on the degree of deterioration, the numerical value is further multiplied by the correction coefficient based on the exhaust gas flow rate and / or the correction coefficient based on the oxygen concentration in the exhaust gas, and finally the ammonia The slip amount may be estimated. The correction coefficient based on the exhaust gas flow rate is larger when the exhaust gas flow rate is high than when the exhaust gas flow rate is low. The correction coefficient based on the oxygen concentration in the exhaust gas is larger when the oxygen concentration in the exhaust gas is low than when the oxygen concentration is high.

  Furthermore, instead of each of the correction coefficients, a correction amount may be obtained, and the correction amount may be added to or subtracted from the numerical values in the map of FIG.

  In the above embodiment, urea, which is a precursor of ammonia, is supplied by the urea injector 51. However, ammonia may be directly supplied.

  Further, in the above-described embodiment, the case where the estimation of the slip amount of ammonia from the SCR catalyst 47 is used for the abnormality determination of the SCR catalyst 47 has been described. For example, the urea injection amount calculation by the urea injector 51 and the slip catalyst 48 are performed. It may be used for the determination of the purification rate. That is, the estimation of the slip amount of ammonia from the SCR catalyst 47 can be used for other than the abnormality determination of the SCR catalyst 47.

  Further, in the above embodiment, after determining whether the purification rate of the SCR catalyst 47 is less than the predetermined purification rate (step S403) in the abnormality determination of the PCM 60, the estimated slip amount of ammonia is less than the predetermined slip amount. Although it has been determined whether or not there is (step S404), 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 less than the predetermined slip amount. It may be determined whether or not. In this case, when the estimated slip amount of ammonia is equal to or greater than the predetermined slip amount, the processing operation of the PCM 60 is a processing operation that returns as it is without calculating the purification rate of the SCR catalyst 47 and making a determination based on the purification rate. Become.

  The above-described embodiments are merely examples, and the scope of the present invention should not be interpreted in a limited manner. The scope of the present invention is defined by the scope of the claims, and all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  The present invention comprises a selective reduction type NOx catalyst that reduces NOx by a supplied reducing agent, and a reducing agent supply means capable of supplying ammonia or a precursor of ammonia as the reducing agent to the selective reduction type NOx catalyst. This is useful when estimating the exhaust gas state of an engine having the same.

E Engine 41 Exhaust passage 45 NOx storage reduction catalyst 47 SCR catalyst (selective reduction NOx catalyst)
51 Urea injector (reducing agent supply means)
60 PCM
61 Ammonia adsorption amount estimation unit (ammonia adsorption amount estimation means)
62 Slip amount estimating section (slip amount estimating means)
63 Abnormality determination unit (abnormality determination means)
64 Abnormality determination limiting unit (abnormality determination limiting means)
65 Degradation degree estimation unit (degradation degree estimation means)
117 catalyst temperature sensor (catalyst temperature detection means)
118 Second NOx sensor (NOx sensor whose output value changes according to the amount of NOx and the amount of ammonia in the exhaust gas)

Claims (8)

A selective reduction type NOx catalyst that is provided in an exhaust passage of an engine and that reduces NOx by a supplied reducing agent, and a reducing agent that can supply ammonia or a precursor of ammonia as the reducing agent to the selective reduction type NOx catalyst An exhaust gas state estimation method for an engine having a supply means,
A deterioration degree estimation step for estimating the deterioration degree of the selective reduction type NOx catalyst;
Based on the degree of deterioration of the selective reduction NOx catalyst estimated in the deterioration degree estimation step, the ammonia slip amount, which is the amount of ammonia discharged into the passage downstream of the selective reduction NOx catalyst in the exhaust passage. A slip amount estimating step for estimating
In the slip amount estimation step, when the deterioration degree is large, the slip amount is estimated to be larger than when the deterioration degree is small. The engine exhaust gas state estimation method according to claim 1,
The deterioration degree estimation step is a step of estimating at least one of a heat load applied to the selective reduction NOx catalyst and an HC poisoning amount of the selective reduction NOx catalyst as the deterioration degree. The engine exhaust gas state estimation method. The engine exhaust gas state estimation method according to claim 1 or 2,
An ammonia adsorption amount estimation step for estimating the ammonia adsorption amount of the selective reduction type NOx catalyst;
A catalyst temperature detecting step of detecting the temperature of the selective reduction type NOx catalyst,
The slip amount estimating step includes the estimated ammonia adsorption amount estimated in the ammonia adsorption amount estimation step and the catalyst temperature detection step in addition to the deterioration degree of the selective reduction type NOx catalyst estimated in the deterioration degree estimation step. An exhaust gas state estimation method for an engine, comprising the step of estimating the slip amount based on the detected catalyst temperature detected in step (1). The exhaust gas state estimation method for an engine according to claim 3,
In the slip amount estimation step, when the degree of deterioration is large, the slip amount is estimated more than when the degree of deterioration is small, and compared with the same degree of deterioration and the same detected catalyst temperature. When the estimated ammonia adsorption amount is large, the slip amount is estimated more than when the estimated ammonia adsorption amount is small, while when compared with the same deterioration degree and the same estimated ammonia adsorption amount, A method for estimating an exhaust gas state of an engine, wherein when the detected catalyst temperature is high, the slip amount is estimated to be larger than when the detected catalyst temperature is low. The method for estimating an exhaust gas state of an engine according to claim 4,
The slip amount estimating step is a step of estimating the slip amount by correcting the temporary slip amount estimated based on the estimated ammonia adsorption amount and the detected catalyst temperature based on the degree of deterioration. An exhaust gas state estimation method for an engine characterized by the above. The engine exhaust gas state estimation method according to any one of claims 3 to 5,
The above engine
An occlusion reduction type NOx catalyst that is disposed upstream of the selective reduction type NOx catalyst in the exhaust passage and occludes NOx in exhaust gas and can reduce the occluded NOx;
NOx catalyst regeneration control means for making the air-fuel ratio of the exhaust gas near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio in order to reduce the NOx occluded in the NOx storage reduction catalyst;
Further comprising
Reduction ammonia generation amount estimation step for estimating the amount of ammonia discharged into the exhaust gas from the NOx storage reduction catalyst when NOx stored in the NOx storage reduction catalyst is reduced by the NOx catalyst regeneration control means Further comprising
The ammonia adsorption amount estimation step is based on the amount of ammonia supplied by the reducing agent supply means or the amount of precursor of ammonia, and the amount of ammonia estimated in the reduction ammonia generation amount estimation step. An exhaust gas state estimation method for an engine, which is a step of estimating an ammonia adsorption amount of a reduced NOx catalyst. An engine catalyst abnormality determination method using the engine exhaust gas state estimation method according to any one of claims 1 to 6,
The engine further includes a NOx sensor that is provided on the downstream side of the selective reduction type NOx catalyst in the exhaust passage and whose output value changes according to the amount of NOx and the amount of ammonia in the exhaust gas,
Based on the output value of the NOx sensor, comprising an abnormality determination step for determining whether or not the selective reduction type NOx catalyst has an abnormality,
The abnormality determination step includes an abnormality determination limiting 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. Method. A selective reduction type NOx catalyst that is provided in an exhaust passage of an engine and that reduces NOx by a supplied reducing agent, and a reducing agent that can supply ammonia or a precursor of ammonia as the reducing agent to the selective reduction type NOx catalyst An engine abnormality determination device for an engine having a supply means,
A deterioration degree estimating means for estimating a deterioration degree of the selective reduction type NOx catalyst;
A slip of ammonia, which is the amount of ammonia discharged into the passage downstream of the selective reduction NOx catalyst in the exhaust passage, based on the deterioration degree of the selective reduction NOx catalyst estimated by the deterioration degree estimation means. Slip amount estimating means for estimating the amount;
A NOx sensor provided downstream of the selective reduction NOx catalyst in the exhaust passage and having an output value that changes in accordance with the amount of NOx and the amount of ammonia in the exhaust gas;
An abnormality determining means for determining whether or not the selective reduction NOx catalyst has an abnormality based on the output value of the NOx sensor;
An abnormality determination limiting unit that limits the abnormality determination of the abnormality determination unit when the ammonia slip amount estimated by the slip amount estimation unit is equal to or greater than a predetermined slip amount;
The engine catalyst abnormality determination device, wherein the slip amount estimating means is configured to estimate a larger amount of the slip amount when the deterioration degree is large than when the deterioration degree is small.

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