JP7106922B2 - Engine exhaust gas state estimation method, catalyst abnormality determination method, and engine catalyst abnormality determination device - Google Patents

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 NOx catalyst that is provided in an exhaust passage of an engine and reduces NOx with a supplied reducing agent, and a reduction that can supply ammonia or a precursor of ammonia as a reducing agent to the selective reduction NOx catalyst Engines are known which are equipped with an agent supply means.

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

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

JP 2014-109224 A

However, according to studies by the inventors of the present application, the amount of ammonia discharged into a passage downstream of the selective reduction NOx catalyst (hereinafter sometimes referred to as the slip amount of ammonia) was determined by the balance between the adsorption and desorption kinetics of That is, when the ammonia adsorption reaction rate is higher than the desorption reaction rate, the ammonia adsorption reaction appears to be dominant and the ammonia slip amount decreases, while the ammonia desorption reaction rate is higher than the adsorption reaction rate. When it is higher than the speed, the desorption reaction of ammonia apparently becomes dominant, and the slip amount of ammonia increases. For this reason, it is necessary to consider a parameter that affects at least one of the ammonia adsorption reaction rate and the ammonia desorption reaction rate for the slip amount of ammonia.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and its object is to provide an engine having a selective reduction NOx catalyst, in which a passage to a passage downstream of the selective reduction NOx catalyst in the exhaust passage is provided. An object of the present invention is to improve the accuracy of estimating ammonia emissions.

In order to achieve the above object, the present invention provides a selective reduction NOx catalyst that is provided in an exhaust passage of an engine and reduces NOx with a supplied reducing agent; A method for estimating the exhaust gas state of an engine having a reducing agent supply means capable of supplying ammonia or a precursor of ammonia, the oxygen concentration for obtaining the oxygen concentration in the exhaust gas introduced into the selective reduction NOx catalyst Based on the obtaining step and the oxygen concentration obtained in the oxygen concentration obtaining step, an ammonia slip amount, which is the amount of ammonia discharged into a passage downstream of the selective reduction NOx catalyst in the exhaust passage, is estimated. a slip amount estimation step; an ammonia adsorption amount estimation step of estimating the ammonia adsorption amount of the selective reduction NOx catalyst; and an ammonia concentration acquisition step of acquiring the ammonia concentration in the exhaust gas introduced into the selective reduction NOx catalyst. , the slip amount estimating step includes, in addition to the oxygen concentration acquired in the oxygen concentration acquiring step, the estimated ammonia adsorption amount estimated in the ammonia adsorption amount estimating step, and the ammonia concentration acquired in the ammonia concentration acquiring step A step of estimating the slip amount based on the concentration of ammonia, and in the slip amount estimating step, when the oxygen concentration is low, the slip amount is estimated to be larger than when the oxygen concentration is high. did.

That is, the oxygen concentration in the exhaust gas introduced into the selective reduction NOx catalyst is a parameter that affects the adsorption reaction rate of ammonia in the selective reduction NOx catalyst. If the concentration is low, the adsorption reaction rate will be low and the slip amount of ammonia will increase. Therefore, by considering the oxygen concentration, the slip amount of ammonia can be accurately estimated.

In one embodiment of the engine exhaust gas state estimation method, in the slip amount estimation step, the slip amount is estimated so that the change in the slip amount becomes linear with respect to the change in the oxygen concentration.

In particular, in the slip amount estimating step, it is preferable to estimate the slip amount so that the change in the slip amount is linear with respect to the change in the oxygen concentration from the minimum oxygen concentration to the maximum oxygen concentration.

By estimating the slip amount so that the change in the slip amount becomes linear with respect to the change in the oxygen concentration, the slip amount of ammonia can be easily estimated, and the slip amount can be estimated more accurately. can be done.

Another embodiment of the engine exhaust gas state estimation method further comprises a catalyst temperature detection step of detecting the temperature of the selective reduction NOx catalyst, wherein the slip amount estimation step further includes the catalyst temperature detection. This is a step of estimating the slip amount based on the detected catalyst temperature detected in the step.

That is , the temperature of the NOx selective reduction catalyst is a parameter that affects the desorption reaction rate of ammonia in the NOx selective reduction catalyst. Therefore, by estimating the ammonia slip amount based on the estimated ammonia adsorption amount, the detected catalyst temperature, and the oxygen concentration, the ammonia slip amount can be estimated more accurately.

In the other embodiment, in the slip amount estimating step, when the oxygen concentration is low, the slip amount is estimated larger than when the oxygen concentration is high, and the same oxygen concentration and the same 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 oxygen concentration and the same estimated ammonia It is preferable that when the detected catalyst temperature is high, the slip amount is estimated to be larger than when the detected catalyst temperature is low, when the adsorption amount is compared.

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

In estimating the slip amount in this manner, the slip amount estimating step corrects the provisional slip amount estimated based on the estimated ammonia adsorption amount and the detected catalyst temperature based on the oxygen concentration. and estimating the slip amount.

As a result, the study of the slip amount based on the estimated ammonia adsorption amount and the detected catalyst temperature and the study of the slip amount based on the oxygen concentration can be performed separately, thereby reducing the man-hours required for development. Also, the estimation accuracy of the ammonia slip amount can be ensured.

In the other embodiment, the engine is disposed upstream of the selective reduction NOx catalyst in the exhaust passage, and is capable of absorbing NOx in the exhaust gas and reducing the absorbed NOx. a catalyst; and NOx catalyst regeneration control means for making the air-fuel ratio of the exhaust gas close to the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio in order to reduce the NOx stored in the storage reduction type NOx catalyst. Ammonia generation during reduction for estimating the amount of ammonia discharged into the exhaust gas from the storage reduction type NOx catalyst when the NOx stored in the storage reduction type NOx catalyst is reduced by the NOx catalyst regeneration control means An amount estimating step is further provided, wherein the ammonia adsorption amount estimating step includes the amount of ammonia supplied by the reducing agent supply means or the amount of ammonia precursor and the amount of ammonia estimated in the ammonia generation amount estimating step during reduction. and estimating the ammonia adsorption amount of the selective reduction NOx catalyst.

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

In another aspect of the present invention, the engine catalyst abnormality determination method using the engine exhaust gas state estimation method is targeted, and the engine is provided downstream of the selective reduction NOx catalyst in the exhaust passage. and a NOx sensor whose output value changes according to the amount of NOx and ammonia 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 NOx catalyst 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. shall include

According to this configuration, the output value of the NOx sensor changes according to the amount of NOx and the amount of ammonia in the exhaust gas. It is assumed that the amount of NOx inside is large. Therefore, when determining whether or not there is an abnormality in the selective reduction NOx catalyst based on the output value of the NOx sensor, even if the amount of NOx in the exhaust gas is small, the selective reduction NOx catalyst If there is an abnormality in the Therefore, when the slip amount of ammonia estimated in the slip amount estimating step is equal to or greater than the predetermined slip amount, the abnormality determination is limited so that the selective reduction NOx catalyst is abnormal when the amount of NOx in the exhaust gas is small. It is possible to suppress erroneous determination when there is

In still another aspect of the present invention, a selective reduction NOx catalyst provided in an exhaust passage of an engine for reducing NOx with a supplied reducing agent; oxygen concentration acquisition means for acquiring the oxygen concentration in the exhaust gas introduced into the selective reduction NOx catalyst; slip amount estimating means for estimating a slip amount of ammonia, which is an amount of ammonia discharged into a passage downstream of the selective reduction NOx catalyst in the exhaust passage, based on the oxygen concentration acquired by the oxygen concentration acquiring means; a NOx sensor provided downstream of the selective reduction NOx catalyst in the exhaust passage and having an output value that changes according to the amount of NOx and ammonia in the exhaust gas; an abnormality determination means for determining whether or not there is an abnormality in the selective reduction type NOx catalyst; an abnormality determination limiting means for limiting the abnormality determination of the means ; an ammonia adsorption amount estimation means for estimating an ammonia adsorption amount of the selective reduction NOx catalyst; and an ammonia concentration in exhaust gas introduced into the selective reduction NOx catalyst. the slip amount estimating means, in addition to the oxygen concentration acquired by the oxygen concentration acquiring means, the estimated ammonia adsorption amount estimated by the ammonia adsorption amount estimating means; and The slip amount is estimated based on the ammonia concentration acquired by the ammonia concentration acquiring means, and the slip amount estimating means increases the slip amount when the oxygen concentration is low compared to when the oxygen concentration is high. It shall be configured to estimate

Also in this configuration, since the output value of the NOx sensor changes according to the amount of NOx and the amount of ammonia in the exhaust gas, the abnormality determination means is a selective reduction type sensor even when the amount of NOx in the exhaust gas is small. There is a possibility that an erroneous determination may be made if there is an abnormality in the NOx catalyst. Therefore, when the slip amount of ammonia estimated by the slip amount estimating means is equal to or greater than the predetermined slip amount, the abnormality determination is restricted so that when the amount of NOx in the exhaust gas is small, the selective reduction NOx catalyst is abnormal. It is possible to suppress erroneous determination when there is Further, the slip amount estimating means can accurately estimate the slip amount of ammonia.

As described above, according to the present invention, the amount of ammonia is determined based on the oxygen concentration in the exhaust gas introduced into the selective reduction NOx catalyst, which is a parameter that affects the adsorption reaction rate of ammonia in the selective reduction NOx catalyst. By estimating the slip amount, it becomes possible to accurately estimate the slip amount of ammonia.

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; FIG. 2 is a block diagram showing a control system of the engine system; FIG. FIG. 4 is a diagram showing control maps for passive DeNOx control and active DeNOx control; 4 is a flow chart when selecting a catalyst for purifying exhaust gas. It is a part of the flowchart when performing DeNOx control. It is the remainder of the flowchart when executing the DeNOx control. It is a schematic diagram which shows the NOx detection principle of a NOx sensor. 4 is a flowchart showing a processing operation for estimating a slip amount of ammonia from an SCR catalyst; 4 is a map showing the slip amount of ammonia based on the ammonia adsorption amount of the SCR catalyst and the temperature of the SCR catalyst; FIG. 10 is a map showing the ammonia slip amount with respect to the ammonia adsorption amount of the SCR catalyst in the map shown in FIG. 9; FIG. FIG. 11 is an enlarged map of a region where the slip amount of ammonia is small in the map shown in FIG. 10. FIG. 4 is a map showing the relationship between the concentration of ammonia in the exhaust gas introduced into the SCR catalyst and the correction coefficient based thereon; 4 is a flow chart showing a processing operation for determining abnormality of an SCR catalyst; 4 is a time chart schematically showing changes over time of each parameter in abnormality determination of the SCR catalyst; 4 is a map showing the relationship between the concentration of oxygen in the exhaust gas introduced into the SCR catalyst and the correction coefficient based thereon;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail based on 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 an EX that discharges exhaust gas from the engine E. , and sensors 100 - 119 that detect various conditions relating to the engine system 200 . The engine system 200 includes a PCM (Power-train Control Module) 60 (see FIG. 2) for controlling the engine system 200, and a DCU (Dosing Control Unit) 70 for controlling the urea injector 51, which will be described later. is provided. This engine system 200 is an engine system provided in a vehicle, and an engine E is used as a driving source of the vehicle.

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

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

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

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

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

The exhaust system EX has an exhaust passage 41 through which exhaust gas passes. The exhaust gas passage 41 includes, from the upstream side, the turbine of the second turbocharger 6, the turbine of the first turbocharger 5, the NOx storage reduction catalyst 45, and the DPF (Diesel particulate filter) 46. , a urea injector 51 for injecting urea into the exhaust passage 41 on the downstream side of the DPF 46; a selective catalytic reduction (SCR) catalyst 47 for purifying NOx using the urea injected from the urea injector 51; and a slip catalyst 48 that oxidizes and purifies the unreacted ammonia. Further, the exhaust passage 41 is provided with an exhaust bypass passage 41a that bypasses the turbine of the second turbocharger 6, and an exhaust bypass valve 6b that opens and closes the exhaust bypass passage 41a. Further, the exhaust passage 41 is provided with a waste gate passage 41b that bypasses the turbine of the first turbocharger 5, and a waste gate valve 5a that opens and closes the waste gate passage 41b.

The storage-reduction type NOx catalyst 45 stores NOx in the exhaust gas in a lean state (excess air ratio λ>1) where the air-fuel ratio of the exhaust gas is larger than the stoichiometric air-fuel ratio, and converts the stored NOx into the exhaust gas. NOx storage reduction type catalyst (NSC: NOx Storage Catalyst) that reduces in a state where the air-fuel ratio is close to the theoretical air-fuel ratio (λ≈1) or in a rich state (λ<1) smaller than the theoretical air-fuel ratio. In addition, the storage reduction type NOx catalyst 45 not only functions as an NSC, but also uses oxygen in the exhaust gas to oxidize hydrocarbons (HC), carbon monoxide (CO), etc. to water and carbon dioxide. It is configured to also function as a diesel catalyst (DOC: Diesel Oxidation Catalyst). Specifically, the storage-reduction NOx catalyst 45 is formed by coating the surface of the DOC catalyst layer with the NSC catalyst material.

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

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

Both the storage reduction type NOx catalyst 45 and the SCR catalyst 47 are catalysts capable of purifying NOx, but the temperatures at which the NOx purification rate (NOx storage rate) increases are different from each other. Specifically, the NOx purification rate of the storage reduction type NOx catalyst 45 increases when the temperature of the storage reduction type NOx catalyst 45 is relatively low, while the NOx purification rate of the SCR catalyst 47 increases when the temperature of the SCR catalyst 47 (hereinafter referred to as , 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. . A first O2 sensor 111 that detects the concentration of oxygen in the exhaust gas is provided in the exhaust passage 41 immediately downstream of the first turbocharger 5 . Around the NOx storage reduction catalyst 45 in the exhaust passage 41 , a second exhaust temperature sensor 112 for detecting the temperature of the exhaust gas in the passage immediately upstream of the NOx storage reduction catalyst 45 , and the NOx storage reduction catalyst 45 . A third exhaust temperature sensor 113 that detects the temperature of the exhaust gas in the passage between the DOC 46, a differential pressure sensor 114 that detects the pressure difference between the passage immediately upstream of the DPF 46 and the passage immediately downstream of the DPF 46, A second O2 sensor 115 that detects the concentration of oxygen in the exhaust gas introduced into the SCR catalyst 47, and a first NOx sensor that detects the concentration of NOx in a passage immediately downstream of the DPF 46 and upstream of the urea injector 51. 116 and are provided. A catalyst temperature sensor 117 that detects the temperature of the SCR catalyst 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 is Furthermore, the exhaust passage 41 is provided with a PM sensor 119 that detects PM in the exhaust gas in the passage immediately upstream of the slip catalyst 48 . Although details will be described later, at least the second NOx sensor 118 is a NOx sensor whose output value changes depending not only on the amount of NOx in the exhaust gas but also on the amount of ammonia.

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

The engine system 200 of this embodiment is mainly controlled by the PCM 60 mounted on the vehicle. The PCM 60 is a microprocessor comprising a CPU, ROM, RAM, I/O bus, and the like. The CPU is a central processing unit that executes computer programs (including basic control programs such as an OS, and application programs that are started on the OS and implement specific functions). The ROM is a memory that stores various computer programs, data, and maps to be described later. 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 . Also, to the PCM 60, an accelerator opening sensor 150 for detecting the accelerator opening corresponding to the operation amount of the accelerator pedal (not shown) of the vehicle and a vehicle speed sensor 151 for detecting the vehicle speed of the vehicle are output. A detection signal is input. The PCM 60 mainly controls the operations of the throttle valve 7, the fuel injection valve 20, the glow plug 21, the first EGR valve 43c and the second EGR valve 43e based on the input signal. The PCM 60 also controls the operation of the urea injector 51 via the DCU 70 by sending an output signal to the DCU 70 . The DCU 70 also has the same configuration as the PCM 60 . PCM 60 may directly control the operation of urea injector 51 without going through DCU 70 .

Although details will be described later, the PCM 60 includes an ammonia adsorption amount estimator 61 that estimates the ammonia adsorption amount of the SCR catalyst 47, and an ammonia amount in the exhaust gas in the passage downstream of the SCR catalyst 47 in the exhaust passage 41. An abnormality determination unit 63 that determines whether or not there is an abnormality in the engine system 200 based on an abnormality determination condition based on the estimated slip amount estimation unit 62 and 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 an oxygen concentration acquisition unit 65 (oxygen concentration acquisition means) that acquires the oxygen concentration in the exhaust gas introduced into the SCR catalyst 47 are provided. In this embodiment, the oxygen concentration acquisition unit 65 acquires the oxygen concentration by detection by the second O2 sensor 115 . The oxygen concentration acquisition unit 65 may estimate and acquire the oxygen concentration. In this case, the oxygen concentration acquisition unit 65 estimates the oxygen concentration from the detection result of the first O2 sensor 111, for example.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

When the operating region of the engine E is in an operating region other than the first and second operating regions R1 and R2, and the NOx storage amount is equal to or greater than the first predetermined storage amount, most NOx is stored in the storage reduction NOx catalyst 45. not purified. However, in this embodiment, since the SCR catalyst 47 is provided downstream of the NOx storage reduction catalyst 45, the SCR catalyst 47 purifies the 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 based on whether or not the SCR catalyst 47 can purify NOx in addition to the operating range of the engine E described above. . This is because if the NOx in the exhaust gas can be properly purified by the SCR catalyst 47, there is no need to perform the DeNOx control to ensure the NOx purification performance of the storage reduction NOx catalyst 45. . As described above, the NOx purification rate of the storage reduction type NOx catalyst 45 is high when the temperature of the exhaust gas is relatively low, while the NOx purification rate of the SCR catalyst 47 is high when the temperature of the exhaust gas is relatively high. get higher Therefore, in this embodiment, as shown in the flowchart of FIG. to purify NOx.

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

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

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

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

In step S<b>105 , the PCM 60 executes the DeNOx control to cause the storage reduction type NOx catalyst 45 to purify NOx, and also causes the SCR catalyst 47 to purify NOx. That is, in this step S105, the PCM 60 causes the urea injector 51 to supply urea. After step S105, the process returns.

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

In step S<b>107 , NOx is purified only by the SCR catalyst 47 without using the NOx storage reduction catalyst 45 . The PCM 60 causes the urea injector 51 to supply urea to the SCR catalyst 47 also in this step S107. In this step S107, the execution of the DeNOx control is prohibited, and the NOx storage amount of the NOx storage reduction catalyst 45 is set to the adsorption limit, so that the NOx storage reduction catalyst 45 is prevented from purifying NOx. After step S107, the process returns. If the NOx storage amount of the storage reduction NOx catalyst 45 has not reached the limit, the storage reduction NOx catalyst 45 can store NOx. NOx may be purified (stored) at 45 . In other words, "do not purify NOx with the storage-reduction type NOx catalyst 45" here means "prohibit execution of DeNOx control".

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The ammonia slip amount based on the ammonia adsorption reaction and the ammonia desorption reaction within the SCR catalyst 47 is mainly determined by the balance between the ammonia adsorption reaction speed and the ammonia desorption reaction speed within the SCR catalyst 47 . The adsorption reaction rate and the desorption reaction rate are represented by Equations 2 and 3 below.

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

The adsorption reaction of ammonia to the SCR catalyst 47 is a reaction in which ammonia is only adsorbed to the acid points of the SCR catalyst 47, while the desorption reaction of ammonia from the SCR catalyst 47 is to remove the adsorbed ammonia from the SCR catalyst 47. is a reaction that separates from the acid site of Therefore, the activation energy Ed of the desorption reaction is considerably larger than the activation energy Ea of the adsorption reaction. That is, while the adsorption reaction rate is less affected by the SCR catalyst temperature, the desorption reaction rate is more likely to be affected by the SCR catalyst temperature.

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

Therefore, while the adsorption reaction rate mainly depends on the ammonia coverage of the SCR catalyst 47 (that is, the ammonia adsorption amount of the SCR catalyst 47) and the oxygen concentration in the exhaust gas introduced into the SCR catalyst 47, 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, which is determined by the balance between the adsorption reaction speed and the desorption reaction speed, must mainly consider the ammonia adsorption amount of the SCR catalyst 47, the SCR catalyst temperature, and the oxygen concentration. 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 catalyst temperature sensor 117 detects the SCR catalyst temperature, and the oxygen concentration acquisition unit 65 detects the second O2 sensor. 115 to acquire the oxygen concentration, and the slip amount estimating unit 62 calculates the ammonia adsorption amount estimated by the ammonia adsorption amount estimating unit 61, the SCR catalyst temperature detected by the catalyst temperature sensor 117, and the oxygen concentration acquiring unit. Based on the oxygen concentration acquired by 65, the slip amount of ammonia, which is the amount of ammonia discharged into the passage downstream of the SCR catalyst 47 of the exhaust passage 41, is estimated.

Here, in the present embodiment, the ammonia adsorption amount estimator 61, 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 estimator 61 first calculates the amount of ammonia that has flowed 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 the ammonia discharged into the exhaust gas from the NOx storage reduction catalyst 45 when the NOx stored in the NOx catalyst 45 is reduced. and HC supplied by post-injection. Therefore, ammonia generated by DeNOx control can be estimated from the NOx storage amount of the storage reduction NOx catalyst 45 and the post-injection amount. Next, the ammonia adsorption amount estimator 61 calculates the amount of ammonia consumed from the SCR catalyst 47 based on the amount of NOx flowing into 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 produced by the DeNOx control. The purification efficiency of the SCR catalyst 47 is obtained by reading a map stored in the memory of the PCM 60 with a theoretical value calculated in advance based on the SCR catalyst temperature, the flow rate of the exhaust gas introduced into the SCR catalyst 47, and the like. . Then, the ammonia adsorption amount estimator 61 estimates the current ammonia adsorption amount of the SCR catalyst 47 from the difference between the integrated value of the amount of ammonia flowing into the SCR catalyst 47 and the integrated value of the amount of ammonia consumed from the SCR catalyst 47. 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.

Note that when the DeNOx control is not being executed, the ammonia adsorption amount estimator 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 ammonia slip amount from the SCR catalyst 47 . The ammonia adsorption amount of the SCR catalyst 47 is estimated by an ammonia adsorption amount estimating section 61 , and the slip amount of ammonia from the SCR catalyst 47 is estimated by a slip amount estimating section 62 .

First, in step S301, the PCM 60 reads information from various sensors 100-119, 150, and 151. FIG. In this step S301, in particular, the catalyst temperature sensor 117 detects the SCR catalyst temperature. Also, in step S301, the oxygen concentration acquisition unit 65 acquires the oxygen concentration by reading information from the second O2 sensor 115. FIG.

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

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

In step S<b>304 described above, the PCM 60 estimates the ammonia adsorption amount of the SCR catalyst 47 . In step S304, when step S303 is passed through, the ammonia adsorption amount of the SCR catalyst 47 is estimated in consideration of the amount of ammonia generated by the DeNOx control. The amount of ammonia adsorbed by the SCR catalyst 47 is estimated without considering the amount of ammonia generated by .

Next, in step S305, the PCM 60 (slip amount estimating unit 62) acquires the estimated ammonia adsorption amount estimated in step S304, the SCR catalyst temperature detected by the catalyst temperature sensor 117 in step S301, and the SCR catalyst temperature obtained in step S301. The slip amount of ammonia from the SCR catalyst 47 is estimated based on the oxygen concentration. Specifically, the estimated ammonia adsorption amount and the SCR catalyst temperature are applied to the map shown in FIG. 9 and the map shown in FIG. 10 to estimate the ammonia slip amount (provisional slip amount) from the SCR catalyst 47, This provisional slip amount is corrected based on the oxygen concentration to estimate the slip amount. After step S306, the process returns.

FIG. 9 shows a map (stored in the memory of the PCM 60) obtained by experimenting to determine the ammonia slip amount while varying the ammonia adsorption amount of the SCR catalyst 47 and the SCR catalyst temperature. Although the details will be described later, a correction coefficient, which will be described later, is set to 1 based on the concentrations of ammonia and oxygen in the exhaust gas. In FIG. 9, the vertical axis is the ammonia adsorption amount of the SCR catalyst 47, and the horizontal axis is the SCR catalyst temperature. The lower limit of the vertical axis is 0, and the upper limit of the vertical axis is the ammonia adsorption limit of the SCR catalyst 47 . The horizontal axis is set to the temperature range in which the SCR catalyst 47 can be used, with the minimum temperature set at 160°C and the maximum temperature set at 400°C. "Small", "Medium", and "Large" in FIG. 9 represent the ammonia slip amount, and the ammonia slip amount increases in the order of "Small", "Medium", and "Large". Here, when the ammonia slip amount is equal to or greater than a predetermined slip amount, more specifically, an amount equal to or greater than an amount that affects the NOx concentration detection by the second NOx sensor 118, "small" or "medium" is selected according to the amount. and "large". "0" in FIG. 9 indicates that there is no slip of ammonia or that the amount of slip of ammonia is small enough not to affect detection of NOx concentration by the second NOx sensor 118 .

The maximum temperature at which the SCR catalyst 47 can be used means the maximum 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 speed, high load range. 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, when the SCR temperature is at the maximum temperature, even if the ammonia adsorption amount of the SCR catalyst 47 is small, ammonia slip occurs.

Furthermore, as shown in FIG. 9, when the ammonia adsorption amount of the SCR catalyst 47 is near the adsorption limit, 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 becomes equal to or greater than the predetermined slip amount is about 200.degree. In other words, when the ammonia adsorption amount of the SCR catalyst 47 is maximum, the ammonia slip amount exceeds the predetermined slip amount when the SCR catalyst temperature is the second predetermined temperature (for example, 250° C.).

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 . Curves L1 to L4 in FIG. 10 have different SCR catalyst temperatures. Specifically, L1 is the curve at the maximum temperature (400° C.) of the SCR catalyst 47, and L4 is the curve at the minimum temperature (160° C.) of the SCR catalyst 47. L2 and L3 are curves at the temperature between the maximum temperature and the minimum temperature of the SCR catalyst 47, and the higher temperature ( 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, under the condition that the SCR catalyst temperature is the same (here, the oxygen concentration and the ammonia concentration are also the same (hereinafter the same)), the It can be seen that when the ammonia adsorption amount of the SCR catalyst 47 is large, the ammonia slip amount increases compared to 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 ammonia coverage θ of the SCR catalyst 47 increases and the adsorption reaction rate decreases, while the desorption reaction rate increases. Therefore, in the present embodiment, the slip amount estimator 62 determines that the estimated ammonia adsorption 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 estimator 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 oxygen concentration and the ammonia concentration are also the same (the same applies hereinafter). )) condition, when the temperature of the SCR catalyst 47 is high, the ammonia slip amount is greater than when the temperature of the SCR catalyst 47 is low. This is because the higher the SCR catalyst temperature, the smaller the value of exp(-Ed/RT) in Equation 3 and the higher the desorption reaction rate. Therefore, in the present embodiment, the slip amount estimator 62 determines that the SCR catalyst 47 can be used in a temperature range in which the SCR catalyst 47 When the temperature is high, the slip amount of ammonia is estimated to be larger than when the SCR catalyst temperature is low.

Furthermore, as shown in FIG. 10, under the condition that the SCR catalyst temperature is the same within the temperature range in which the SCR catalyst 47 can be used, when the ammonia adsorption amount of the SCR catalyst 47 is large, the ammonia adsorption amount of the SCR catalyst 47 is It can be seen that the change in ammonia slip amount (that is, the slope of the curve in FIG. 10) with respect to the change in the ammonia adsorption amount of the SCR catalyst 47 increases compared to when the SCR catalyst 47 is small. Therefore, in the present embodiment, the slip amount estimator 62 determines that the estimated ammonia adsorption The ammonia slip amount is estimated such that when the amount is large, the change in the ammonia slip amount with respect to the change in the estimated ammonia adsorption amount is greater 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 1/3 of the adsorption limit. It can be seen that the change in ammonia slip amount with respect to the change in the ammonia adsorption amount of the SCR catalyst 47 is greater than when it is less than 3. Therefore, in this embodiment, when the SCR catalyst temperature is equal to or higher than the second predetermined temperature, the slip amount estimator 62, when compared with the same ammonia concentration, the same oxygen concentration, and the same SCR catalyst temperature, When the estimated ammonia adsorption amount is ⅓ or more of the adsorption limit, the change in the ammonia slip amount relative to the change in the estimated ammonia adsorption amount is greater than when the estimated ammonia adsorption amount is less than ⅓ of the adsorption limit. It is configured to estimate the slip amount of ammonia so as to increase.

Further, as shown in FIG. 10, in the temperature range in which the SCR catalyst 47 can be used, under the condition that the ammonia adsorption amount of the SCR catalyst 47 is the same, when the SCR catalyst temperature is high, when the SCR catalyst temperature is low, In comparison, it can be seen that the change in the slip amount of ammonia becomes greater with respect to the change in the SCR catalyst temperature. In particular, it can be seen that the above-described tendency is conspicuous in a region in which the ammonia adsorption amount of the SCR catalyst 47 is half or less of the adsorption limit of the SCR catalyst 47 . As described above, the activation energy required for the elimination reaction is relatively large. Therefore, when the SCR catalyst temperature is low, the value of exp(-Ed/RT) in Equation 3 itself is small, and even if the SCR catalyst temperature rises, the desorption reaction rate does not easily increase. On the other hand, when the SCR catalyst temperature is high, the value of exp(-Ed/RT) in Equation 3 is large, so the desorption reaction rate tends to increase as the SCR catalyst temperature rises. For this reason, the above changes occur. Therefore, in the present embodiment, the slip amount estimator 62 determines that the SCR catalyst 47 can be used in a temperature range in which the SCR catalyst 47 When the temperature is high, compared to when the SCR catalyst temperature is low, 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 greater.

FIG. 11 is an enlarged map of 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 smaller the ammonia adsorption amount of the SCR catalyst 47, and the more ammonia slip occurs. This is because the higher the SCR catalyst temperature, the larger the value of exp(-Ed/RT) in Equation 3, and even in a state where the SCR catalyst 47 adsorbs a small amount of ammonia, the desorption reaction rate is lower than the adsorption reaction rate. This is thought to be because it is faster. Therefore, in the present embodiment, the slip amount estimator 62 is configured to estimate that the higher the SCR catalyst temperature is, the smaller the ammonia adsorption amount at which ammonia slip begins to occur within the temperature range in which the SCR catalyst 47 can be used. It is

In the present embodiment, the slip amount estimator 62 considers the influence of the oxygen concentration in the exhaust gas introduced into the SCR catalyst 47 by , the slip amount is estimated by correcting it based on the oxygen concentration. Specifically, the slip amount estimator 62 multiplies the values of the map in FIG. 9 by a correction coefficient (different from C2 in Equation 2) based on the oxygen concentration to estimate the slip amount.

FIG. 15 is an example of a map (stored in the memory of the PCM 60) showing the relationship between the oxygen concentration in the exhaust gas introduced into the SCR catalyst 47 and the correction coefficient based thereon. The correction coefficient based on the oxygen concentration in the exhaust gas is a correction coefficient that increases as the oxygen concentration decreases. Therefore, when the oxygen concentration is low, the slip amount estimator 62 estimates the slip amount more than when the oxygen concentration is high.

In the present embodiment, when the oxygen concentration is the maximum oxygen concentration (same as the oxygen concentration in air), the correction coefficient based on the oxygen concentration is 1, and as the oxygen concentration decreases from here, the correction coefficient The coefficient is larger than 1. If the correction coefficient is 1, the ammonia slip amount considering the oxygen concentration is the same as the numerical values in the map of FIG.

The map in FIG. 15 is represented by a straight line from the minimum oxygen concentration (0) to the maximum oxygen concentration on a two-dimensional orthogonal graph in which the oxygen concentration is on the horizontal axis and the correction coefficient is on the vertical axis. . As a result, the slip amount estimator 62 estimates the slip amount so that the change in the slip amount becomes linear with respect to the change in the oxygen concentration from the minimum oxygen concentration (0) to the maximum oxygen concentration. become. In addition, the map is not limited to this, and may be represented by a straight line in a part between the minimum oxygen concentration (0) and the maximum oxygen concentration, and from the minimum oxygen concentration (0) to the maximum oxygen concentration It may be represented by a curve.

Strictly speaking, the adsorption reaction rate also changes depending on the concentration of ammonia in the exhaust gas introduced into the SCR catalyst 47, as shown in Equation 2 above. Therefore, in order to more accurately estimate the ammonia slip amount, it is preferable to consider the concentration of ammonia in the exhaust gas. Therefore, in the present embodiment, the slip amount estimator 62 adds a correction coefficient based on the oxygen concentration to the numerical values (provisional slip amount) of the map in FIG. A correction coefficient (different from C1 in Equation 2) based on the ammonia concentration is also multiplied.

FIG. 12 is an example of a map (stored in the memory of the PCM 60) showing the relationship between the concentration of ammonia 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 concentration of ammonia in the exhaust gas is low, the adsorption reaction is suppressed, so the adsorption reaction speed is low (that is, the slip amount increases). Therefore, as shown in FIG. 12, the correction coefficient based on the ammonia concentration in the exhaust gas is a correction coefficient that increases as the ammonia concentration decreases. In the present embodiment, the correction coefficient is set to 1 at an ammonia concentration D1 intermediate between the maximum ammonia concentration that the engine system 200 can take and 0, and when the ammonia concentration is higher than D1, the correction coefficient is set to be smaller than 1, When the ammonia concentration is lower than D1, the correction coefficient is made smaller than one. This correction factor varies over a range greater than zero and less than two. Note that the PCM 60 estimates the ammonia concentration in the exhaust gas 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. Also, the value of D1 is set according to an actual engine system through experiments or the like.

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

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

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

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

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

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

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

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

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

Changes in each parameter (estimated slip amount, etc.) when the PCM 60 executes abnormality determination will be described with reference to the time chart of FIG. 14, the ammonia adsorption amount is a value estimated by the ammonia adsorption amount estimating section 61 of the PCM 60, and the slip amount of ammonia is a value estimated by the slip amount estimating section 62 of the PCM 60. FIG. As for the output values of the NOx sensor, the dashed 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, the PCM 60 is executing normal fuel injection control, and the SCR catalyst 47 is in an inactive state. If the DeNOx control is executed from this initial state, the ammonia adsorption amount of the SCR catalyst 47 increases because ammonia is generated with the DeNOx control. After that, when the SCR catalyst temperature is lower than the first predetermined temperature, that is, when the SCR catalyst 47 does not purify NOx and the DeNOx control is executed, ammonia is not consumed from the SCR catalyst 47 and the SCR catalyst The ammonia adsorption amount of 47 increases.

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

When the temperature of the SCR catalyst 47 rises, ammonia slip occurs. As a result, the output value of the second NOx sensor 118 increases. Then, when the ammonia slip reaches or exceeds a predetermined slip amount, the PCM 60 stops the abnormality determination of the SCR catalyst 47 . As a result, as shown in FIG. 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. FIG. The PCM 60 restarts the abnormality determination of the SCR catalyst 47 when the ammonia slip becomes less than the predetermined slip amount.

Further, as shown in FIG. 14, when ammonia slip occurs, the PCM 60 estimates the ammonia adsorption amount to be smaller than when there is no ammonia slip. This is because when ammonia slip occurs, the desorption reaction of ammonia from the SCR catalyst 47 is dominant, so the amount of ammonia adsorbed by the SCR catalyst 47 can be considered smaller than when there is no ammonia slip. This improves the accuracy of estimating the amount of ammonia adsorbed by the SCR catalyst 47, which in turn improves the accuracy of estimating the slip amount of ammonia.

Therefore, in the present embodiment, when the oxygen concentration in the exhaust gas introduced into the SCR catalyst 47 is low, the slip amount estimator 62 determines that the slip amount of ammonia from the SCR catalyst 47 is lower than when the oxygen concentration is high. is estimated, the accuracy of estimating the slip amount can be improved.

Further, in the present embodiment, the slip amount estimator 62 estimates the slip amount based on the estimated ammonia adsorption amount and the detected catalyst temperature in addition to the oxygen concentration. By taking into consideration the parameters in 47 that have a relatively large effect on the adsorption reaction rate and desorption reaction rate of ammonia, the estimation accuracy of the slip amount can be further improved.

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

For example, in the above-described embodiment, the numerical value (provisional slip amount) of the map in FIG. Although the slip amount of ammonia was finally estimated, even if the numerical value of the map in FIG. good. Further, the flow rate of the exhaust gas introduced into the SCR catalyst 47 (as the flow rate of the exhaust gas increases, the frequency coefficient Aa decreases and the frequency coefficient Ad increases), and/or the degree of deterioration of the SCR catalyst 47 (degree of deterioration increases, the ammonia adsorption limit of the SCR catalyst 47 decreases and the coverage θ increases). In addition to the correction coefficient, a correction coefficient based on the flow rate of the exhaust gas and/or a correction coefficient based on the degree of deterioration of the SCR catalyst 47 may be further multiplied to finally estimate the ammonia slip amount. 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 degree of deterioration can be the heat load applied to the SCR catalyst 47 and/or the amount of HC poisoning of the SCR catalyst 47. The heat load is, for example, the heat energy applied to the SCR catalyst 47. It can be an integrated value. This integrated value of thermal energy can be substituted by, for example, a value obtained by adding the values for each SCR catalyst temperature obtained by multiplying the SCR catalyst temperature by the time during which the SCR catalyst temperature is maintained. 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 by experiment 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). The correction coefficient based on the degree of deterioration of the SCR catalyst 47 is smaller when the degree of deterioration is large than when the degree of deterioration is small.

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

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

Furthermore, in the above 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. It may be used for determining the purification rate of In other words, the estimation of the slip amount of ammonia from the SCR catalyst 47 can be used for purposes other than the abnormality determination of the SCR catalyst 47 .

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

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

The present invention comprises a selective reduction NOx catalyst that reduces NOx with 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 NOx catalyst. It is useful when estimating the exhaust gas state of an engine with

E engine 41 exhaust passage 45 storage reduction NOx 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 estimator (slip amount estimator)
63 Abnormality determination unit (abnormality determination means)
64 Abnormality judgment limiting unit (abnormality judgment limiting means)
65 oxygen concentration acquisition unit (oxygen concentration acquisition 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 ammonia in the exhaust gas)

Claims (9)

A selective reduction NOx catalyst that is provided in an exhaust passage of an engine and reduces NOx with a supplied reducing agent, and a reducing agent capable of supplying ammonia as the reducing agent or a precursor of ammonia to the selective reduction NOx catalyst. A method for estimating the exhaust gas state of an engine having supply means,
an oxygen concentration acquisition step of acquiring the oxygen concentration in the exhaust gas introduced into the selective reduction NOx catalyst;
A slip amount estimating step of estimating a slip amount of ammonia, which is an amount of ammonia discharged into a passage downstream of the selective reduction NOx catalyst in the exhaust passage, based on the oxygen concentration obtained in the oxygen concentration obtaining step. When,
an ammonia adsorption amount estimation step of estimating the ammonia adsorption amount of the selective reduction NOx catalyst;
an ammonia concentration acquisition step of acquiring the ammonia concentration in the exhaust gas introduced into the selective reduction NOx catalyst;
The slip amount estimating step is based on the oxygen concentration obtained in the oxygen concentration obtaining step, the estimated ammonia adsorption amount estimated in the ammonia adsorption amount estimating step, and the ammonia concentration obtained in the ammonia concentration obtaining step. is a step of estimating the slip amount,
A method for estimating the exhaust gas state of an engine, wherein in the slip amount estimating step, the slip amount is estimated to be larger when the oxygen concentration is low than when the oxygen concentration is high. In the method for estimating the exhaust gas state of an engine according to claim 1,
A method for estimating the exhaust gas state of an engine, wherein in the slip amount estimating step, the slip amount is estimated so that the change in the slip amount becomes linear with respect to the change in the oxygen concentration. In the engine exhaust gas state estimation method according to claim 2,
In the slip amount estimating step, the slip amount is estimated so that the change in the slip amount is linear with respect to the change in the oxygen concentration from the minimum oxygen concentration to the maximum oxygen concentration. State estimation method. In the engine exhaust gas state estimation method according to any one of claims 1 to 3,
a catalyst temperature detection step of detecting the temperature of the selective reduction NOx catalyst;
The method for estimating the exhaust gas state of an engine, wherein the slip amount estimating step is a step of estimating the slip amount based on the catalyst temperature detected in the catalyst temperature detecting step. In the engine exhaust gas state estimation method according to claim 4,
In the slip amount estimating step, when the oxygen concentration is low, the slip amount is estimated to be larger than when the oxygen concentration is high, and when compared with the same oxygen concentration and the same detected catalyst temperature. When the estimated ammonia adsorption amount is large, the slip amount is estimated to be larger than when the estimated ammonia adsorption amount is small. A method for estimating the exhaust gas state of an engine, wherein when the detected catalyst temperature is high, the slip amount is estimated more than when the detected catalyst temperature is low. In the engine exhaust gas state estimation method according to claim 5,
The slip amount estimating step is a step of estimating the slip amount by correcting a provisional slip amount estimated based on the estimated ammonia adsorption amount and the detected catalyst temperature based on the oxygen concentration. A method for estimating the exhaust gas state of an engine, characterized by: In the engine exhaust gas state estimation method according to any one of claims 4 to 6,
The above engine
a storage reduction NOx catalyst disposed upstream of the selective reduction NOx catalyst in the exhaust passage, capable of storing NOx in the exhaust gas and reducing the stored NOx;
NOx catalyst regeneration control means for reducing the NOx stored in the NOx storage reduction type NOx catalyst so that the air-fuel ratio of the exhaust gas is close to the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio;
further having
A step of estimating the amount of ammonia generated during reduction for estimating the amount of ammonia discharged into the exhaust gas from the storage-reduction type NOx catalyst when the NOx stored in the storage-reduction-type NOx catalyst is reduced by the NOx catalyst regeneration control means. further comprising
In the ammonia adsorption amount estimation step, the selection is performed based on the amount of ammonia or the amount of ammonia precursor supplied by the reducing agent supply means and the amount of ammonia estimated in the step of estimating the amount of ammonia generated during reduction. A method for estimating the exhaust gas state of an engine, comprising: 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 7,
The engine further includes a NOx sensor provided downstream of the selective reduction NOx catalyst in the exhaust passage and having an output value that changes according to the amount of NOx and the amount of ammonia in the exhaust gas,
an abnormality determination step of determining whether or not there is an abnormality in the selective reduction NOx catalyst based on the output value of the NOx sensor;
The abnormality determination step includes an abnormality determination restriction step for 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 NOx catalyst provided in an exhaust passage of an engine for reducing NOx with a supplied reducing agent, and a reducing agent capable of supplying ammonia as the reducing agent or a precursor of ammonia to the selective reduction NOx catalyst. A catalyst abnormality determination device for an engine having supply means,
oxygen concentration acquisition means for acquiring the oxygen concentration in the exhaust gas introduced into the selective reduction NOx catalyst;
Slip amount estimating means for estimating a slip amount of ammonia, which is an amount of ammonia discharged into a passage downstream of the selective reduction NOx catalyst in the exhaust passage, based on the oxygen concentration acquired by the oxygen concentration acquiring means. When,
a NOx sensor provided downstream of the selective reduction NOx catalyst in the exhaust passage and having an output value that changes according to the amount of NOx and the amount of ammonia in the exhaust gas;
Abnormality determination means for determining whether or not there is an abnormality in the selective reduction NOx catalyst based on the output value of the NOx sensor;
and abnormality determination limiting means for limiting the abnormality determination of the abnormality determining means when the ammonia slip amount estimated by the slip amount estimating means is equal to or greater than a predetermined slip amount. ,
ammonia adsorption amount estimating means for estimating the ammonia adsorption amount of the selective reduction NOx catalyst;
an ammonia concentration acquisition means for acquiring the ammonia concentration in the exhaust gas introduced into the selective reduction NOx catalyst;
The slip amount estimating means is based on the estimated ammonia adsorption amount estimated by the ammonia adsorption amount estimating means and the ammonia concentration acquired by the ammonia concentration acquiring means in addition to the oxygen concentration acquired by the oxygen concentration acquiring means. to estimate the above slip amount,
The slip amount estimating means is configured to estimate the slip amount more when the oxygen concentration is low than when the oxygen concentration is high. Abnormality determination device.

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