JP7360596B2 - Engine exhaust purification device and method for estimating adhesion reducing agent - Google Patents

Description

The present invention provides a reducing agent injector that injects a reducing agent into an exhaust passage, a selective reduction NOx catalyst that uses the reducing agent to reduce NOx, and a NOx injector provided downstream of the selective reduction NOx catalyst. The present invention relates to an engine exhaust purification device including a sensor and a processing device that uses the NOx sensor to determine abnormality of a selective reduction NOx catalyst, and a method for estimating a deposited reducing agent carried out in the engine exhaust purification device. .

Conventionally, a urea injector injects urea as a reducing agent into an exhaust passage, and ammonia generated from the urea injected from this urea injector is adsorbed, and the adsorbed ammonia is reacted (reduced) with NOx in the exhaust gas. ) An engine exhaust purification device is known that includes an SCR (Selective Catalytic Reduction) catalyst as a selective reduction type NOx catalyst. Furthermore, in such an engine exhaust purification device, a technique is known in which an NOx sensor provided on the downstream side of the SCR catalyst is used to determine an abnormality of the SCR catalyst (for example, Patent Document 1). This Patent Document 1 discloses a technique for estimating the amount of ammonia flowing out from the SCR catalyst and restricting abnormality determination of the SCR catalyst when the amount of ammonia is large.

Japanese Patent Application Publication No. 2014-109224

By the way, it is conceivable to purify NOx using the SCR catalyst in a situation where the engine and the SCR catalyst are at a relatively low temperature (for example, when cold). When urea is injected from the urea injector under such relatively low temperature conditions, urea tends to adhere to the wall surface of the exhaust passage (the inner wall surface of the piping forming the exhaust passage). The urea that adheres to the wall of the exhaust passage solidifies when the temperature of the exhaust gas and pipes decreases, for example, when the engine is stopped (note that the solidified urea becomes a deposit). Then, the solidified urea is thermally decomposed into ammonia at once when the temperature of the exhaust gas or pipes becomes high.

Ammonia, which is generated all at once from the solidified urea by thermal decomposition, tends to be locally introduced into the SCR catalyst. As a result, the SCR catalyst may become locally saturated, and ammonia may be released (slip) from the SCR catalyst to the downstream side. In this case, if the NOx sensor on the downstream side of the SCR catalyst is used to determine the abnormality of the SCR catalyst as described above, the output value of the NOx sensor (corresponding to the amount (concentration) of nitrogen compounds in the exhaust gas) will be If it becomes large, there is a possibility that it will be erroneously determined that the SCR catalyst is abnormal. Note that ammonia slip due to local saturation of the SCR catalyst is likely to occur particularly when a relatively small SCR catalyst is used.

The present invention has been made in order to solve the problems of the prior art described above, and by appropriately taking into account the solidification of the reducing agent that adheres to the wall surface of the exhaust passage by the injection of the reducing agent injector, selective reduction can be achieved. It is an object of the present invention to provide an engine exhaust purification device and a method for estimating a deposited reducing agent that can reliably suppress erroneous determinations regarding abnormality determinations of NOx type catalysts.

In order to achieve the above object, the present invention uses a reducing agent injector that injects ammonia or a precursor of ammonia as a reducing agent into an exhaust passage of an engine, and a reducing agent injected by the reducing agent injector. , a selective reduction type NOx catalyst that reduces NOx in exhaust gas, and is installed on the exhaust passage downstream of the selective reduction type NOx catalyst, and the output value changes depending on the amount of NOx and ammonia in the exhaust gas. An engine exhaust purification device comprising a NOx sensor and a processing device that determines an abnormality with respect to a selective reduction NOx catalyst based on an output value of the NOx sensor, the processing device cleaning the exhaust passage by injecting a reducing agent injector. The amount of attached reducing agent, which is the amount of reducing agent attached to the wall surface, is determined, and the reducing agent attached to the wall surface of the exhaust passage is solidified based on the amount of attached reducing agent and the temperature of the piping of the exhaust passage and/or the temperature of the exhaust gas. When it is determined that the reducing agent has solidified, the processing device is configured to limit the execution of the abnormality determination, and when the pipe temperature is higher than a predetermined temperature, the processing device The system is characterized in that it is configured to determine whether the reducing agent adhered to the wall of the exhaust passage is solidified based on the relationship between the pipe temperature and the solidification rate, in which the lower the pipe temperature, the higher the solidification rate of the reducing agent. do.

In the present invention configured in this way, the processing device is configured, for example, by a circuit, and the amount of the attached reducing agent is the amount of reducing agent (attached reducing agent) attached to the wall surface of the exhaust passage by injection from the reducing agent injector. Based on the amount of the deposited reducing agent and the pipe temperature and exhaust gas temperature, it is determined whether the deposited reducing agent is solidified or not. When it is determined that the deposited reducing agent is solidified, selective reduction is performed. Restricts the execution of abnormality determination for type NOx catalysts.
According to the present invention described above, it is possible to accurately determine the solidification of the deposited reducing agent based on the amount of the deposited reducing agent, the piping temperature, and the exhaust gas temperature. Based on the accurate determination regarding the solidification of the attached reducing agent, it is possible to appropriately restrict the execution of abnormality determination for the selective reduction NOx catalyst, and as a result, it is possible to ensure that false determinations regarding abnormality determination for the selective reduction NOx catalyst are avoided. can be suppressed to Further, according to the present invention, since it is determined whether or not to perform abnormality determination of the selective reduction type NOx catalyst based on the accurate determination result regarding solidification of the reducing agent, unnecessary restrictions on abnormality determination can be suppressed, and abnormality determination This makes it possible to appropriately secure opportunities for implementation.

When the pipe temperature of the exhaust passage is relatively high, a phenomenon occurs in which the higher the pipe temperature, the lower the evaporation rate of the reducing agent (which relates to the evaporation of water contained in the reducing agent and is synonymous with the evaporation rate). Specifically, the surface of the reducing agent in contact with the piping evaporates, forming a thin vapor film, which prevents the reducing agent from coming into direct contact with the piping (i.e., the surface of the reducing agent under the reducing agent). As a result of the formation of a vapor film that inhibits heat conduction between the reducing agent and the piping, the reducing agent becomes difficult to evaporate.
Therefore, in the above-mentioned present invention, the processing device takes into account the characteristics related to evaporation of the reducing agent, and when the pipe temperature is a predetermined temperature or higher, the lower the pipe temperature, the faster the solidification rate of the reducing agent (basically Regarding the evaporation rate and solidification rate of the reducing agent, solidification of the reducing agent is determined based on the relationship that the higher the evaporation rate, the higher the solidification rate). Thereby, solidification of the deposit reducing agent can be determined more accurately.

In another aspect, the present invention provides a reducing agent injector that injects ammonia or a precursor of ammonia as a reducing agent into an exhaust passage of an engine, and a reducing agent injected by the reducing agent injector into the exhaust gas. a selective reduction NOx catalyst that reduces NOx; a NOx sensor that is provided on the exhaust passage downstream of the selective reduction NOx catalyst and whose output value changes depending on the amount of NOx and the amount of ammonia in the exhaust gas; An engine exhaust purification device comprising a processing device that determines an abnormality with respect to a selective reduction NOx catalyst based on an output value of a NOx sensor, the processing device having a reducing agent attached to a wall surface of an exhaust passage by injection from a reducing agent injector. The amount of adhering reducing agent, which is the amount of reducing agent that has been removed, is determined, and based on the amount of adhering reducing agent and the piping temperature of the exhaust passage and/or the temperature of the exhaust gas, it is determined whether the reducing agent adhering to the wall of the exhaust passage is solidified or not. The processing device is configured to limit the execution of abnormality determination when it is determined that the reducing agent is solidified, and when the pipe temperature is lower than a predetermined temperature, the processing device determines whether the pipe temperature is high. The system is configured to determine whether the reducing agent adhered to the wall surface of the exhaust passage is solidified based on the relationship between the pipe temperature and the solidification rate, in which the solidification rate of the reducing agent increases as the temperature increases.
According to the present invention configured as described above, in the processing apparatus, when the pipe temperature is relatively low, the phenomenon that the evaporation rate decreases as the temperature increases due to the presence of the vapor film as described above hardly occurs. By taking into account the usual characteristic that the higher the temperature, the higher the evaporation rate, solidification of the deposited reducing agent can be determined more accurately.
In another aspect, the present invention provides a reducing agent injector that injects ammonia or a precursor of ammonia as a reducing agent into an exhaust passage of an engine, and a reducing agent injected by the reducing agent injector into the exhaust gas. a selective reduction NOx catalyst that reduces NOx; a NOx sensor that is provided on the exhaust passage downstream of the selective reduction NOx catalyst and whose output value changes depending on the amount of NOx and the amount of ammonia in the exhaust gas; An engine exhaust purification device comprising a processing device that determines an abnormality with respect to a selective reduction NOx catalyst based on an output value of a NOx sensor, the processing device having a reducing agent attached to a wall surface of an exhaust passage by injection from a reducing agent injector. The amount of adhering reducing agent, which is the amount of reducing agent that has been removed, is determined, and based on the amount of adhering reducing agent and the piping temperature of the exhaust passage and/or the temperature of the exhaust gas, it is determined whether the reducing agent adhering to the wall of the exhaust passage is solidified or not. The processing device is configured to limit the execution of the abnormality determination when it is determined that the reducing agent is solidified, and the processing device Based on the injection rate of the reducing agent, determine the concentration of the reducing agent attached to the wall of the exhaust passage, and based on the amount of attached reducing agent and the concentration of the reducing agent, determine the amount of water in the reducing agent attached to the wall of the exhaust passage, and then The present invention is characterized in that it is configured to determine that the reducing agent attached to the wall surface of the exhaust passage is solidified when the moisture content of the agent is 0.
According to the present invention configured in this way, the processing device determines the concentration of the reducing agent based on the exhaust gas temperature, the exhaust gas flow rate, and the injection rate of the reducing agent by the reducing agent injector, and calculates the concentration of the reducing agent based on the reducing agent concentration. By determining the amount of water in the reducing agent based on this amount, solidification of the attached reducing agent can be determined more accurately based on this amount of water.
In another aspect, the present invention provides a reducing agent injector that injects ammonia or a precursor of ammonia as a reducing agent into an exhaust passage of an engine, and a reducing agent injected by the reducing agent injector into the exhaust gas. a selective reduction NOx catalyst that reduces NOx; a NOx sensor that is provided on the exhaust passage downstream of the selective reduction NOx catalyst and whose output value changes depending on the amount of NOx and the amount of ammonia in the exhaust gas; An engine exhaust purification device comprising: a processing device that determines an abnormality with respect to a selective reduction NOx catalyst based on an output value of a NOx sensor; The amount of adhering reducing agent, which is the amount of reducing agent that has been removed, is determined, and based on the amount of adhering reducing agent and the piping temperature of the exhaust passage and/or the temperature of the exhaust gas, it is determined whether the reducing agent adhering to the wall of the exhaust passage is solidified or not. The processing device is configured to limit the execution of abnormality determination when it is determined that the reducing agent is solidified, and the processing device is configured to limit the execution of abnormality determination when it is determined that the reducing agent is solidified. Based on the injection rate of the reducing agent, determine the concentration of the reducing agent attached to the wall of the exhaust passage. Based on the amount of attached reducing agent and the concentration of the reducing agent, determine the amount of water in the reducing agent attached to the wall of the exhaust passage. Based on the temperature, calculate the amount of evaporation of the reducing agent attached to the wall of the exhaust passage. The method is characterized in that it is configured to determine that the liquid is solidified.
According to the present invention configured in this way, the processing device determines the concentration of the reducing agent based on the exhaust gas temperature, the exhaust gas flow rate, and the injection rate of the reducing agent by the reducing agent injector, and calculates the concentration of the reducing agent based on the reducing agent concentration. By determining the amount of water in the reducing agent based on the water content and the amount of evaporation of the reducing agent based on the pipe temperature, solidification of the attached reducing agent can be determined more accurately based on the amount of water and the amount of evaporation.

In the present invention, preferably, when the predetermined temperature is a first predetermined temperature and the pipe temperature is a second predetermined temperature or higher that is higher than the first predetermined temperature, the higher the pipe temperature is, the more the reducing agent solidifies. The system is configured to determine whether the reducing agent adhered to the wall surface of the exhaust passage is solidified based on the relationship between the pipe temperature and the solidification rate, which indicates that the speed increases.
According to the present invention configured in this manner, when the piping temperature is considerably high, the evaporation rate decreases as the temperature increases, rather than the characteristic that the evaporation rate decreases as the temperature increases due to the presence of a vapor film as described above. By taking into account that the characteristic of increasing evaporation rate is dominant, it is possible to more accurately determine the solidification of the deposited reducing agent.

In the present invention, preferably, the absolute value of the rate of change in the solidification rate of the reducing agent with respect to the change in the pipe temperature when the pipe temperature is less than a predetermined temperature is higher than the absolute value of the rate of change in the solidification rate of the reducing agent.
Also according to the present invention configured in this manner, it is possible to more accurately determine the solidification of the deposited reducing agent.

According to the engine exhaust purification device and method for estimating adhering reducing agent according to the present invention, selective reduction type NOx Misjudgments regarding catalyst abnormality determinations can be reliably suppressed.

1 is a schematic configuration diagram of an engine to which an engine exhaust purification device and a method for estimating a deposited reducing agent according to an embodiment of the present invention are applied. 1 is a block diagram showing a control system of an engine to which an engine exhaust purification device and a method for estimating a deposited reducing agent according to an embodiment of the present invention are applied. FIG. 3 is an explanatory diagram of adhesion of urea water injected from a urea injector to piping, formation of a deposit of the adhered urea water, and decomposition of the deposited urea. 5 is a flowchart showing SCR catalyst abnormality determination processing according to an embodiment of the present invention. 5 is a flowchart showing urea deposit determination processing according to an embodiment of the present invention. FIG. 2 is a block diagram showing a method for calculating the total amount of adhered urea water according to an embodiment of the present invention. FIG. 3 is a diagram showing the relationship between pipe temperature and evaporation rate of adhered urea water, which is used when determining the amount of scattered urea water in the embodiment of the present invention. FIG. 2 is a block diagram illustrating a urea deposit determination method according to an embodiment of the present invention. FIG. 2 is a block diagram showing a method for calculating the amount of urea deposit decomposition according to an embodiment of the present invention. 5 is a time chart showing the results of urea deposit determination according to an embodiment of the present invention. 12 is a time chart showing the results of urea deposit determination according to a modified example of the embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an engine exhaust purification device and a method for estimating a deposited reducing agent according to an embodiment of the present invention will be described with reference to the accompanying drawings.

<Device configuration>
First, with reference to FIG. 1, a device configuration related to an engine exhaust purification device and a method for estimating a deposited reducing agent according to an embodiment of the present invention will be described. FIG. 1 is a schematic configuration diagram of an engine to which an engine exhaust purification device and a method for estimating a deposited reducing agent according to an embodiment of the present invention are applied.

The engine shown in FIG. 1 is a four-stroke diesel vehicle engine mounted on a vehicle as a driving power source, and includes an engine body 1 and an intake system 3S that supplies air necessary for combustion in the engine body 1. , an exhaust system 4S that purifies exhaust gas discharged from the engine body 1 and discharges it to the outside; a supercharging device 50 that compresses air (intake air) supplied by the intake system 3S and sends it out to the engine body 1; It includes an EGR device 70 that recirculates a part of the exhaust gas flowing through the system 4S to the intake system 3S.

The engine body 1 is of an in-line multi-cylinder type having a plurality of cylinders 2 arranged in a row (only one cylinder 2 is shown in FIG. 1), and a cylinder block 3 in which the plurality of cylinders 2 are formed. , has a cylinder head 4 attached to the upper surface of a cylinder block 3 so as to close the upper opening of each cylinder 2, and a plurality of pistons 5 inserted into each cylinder 2 so as to be able to reciprocate.

A combustion chamber 6 is defined above the piston 5. Fuel whose main component is light oil is supplied to the combustion chamber 6 by injection from a fuel injection valve 15, which will be described later. Then, the supplied fuel is combusted by compression ignition (diffusion combustion), and the piston 5, which is pushed down by the expansion force caused by the combustion, reciprocates in the vertical direction. A crankshaft 7, which is an output shaft of the engine body 1, is provided below the piston 5. The crankshaft 7 is connected to the piston 5 via a connecting rod 8, and is driven to rotate around a central axis in accordance with the reciprocating motion (up and down motion) of the piston 5.

The cylinder block 3 is provided with a crank angle sensor SN1 that detects the angle (crank angle) of the crankshaft 7 and the rotational speed of the crankshaft 7 (engine rotational speed). The cylinder head 4 is provided with a water temperature sensor SN2 that detects the temperature of cooling water flowing inside the engine body 1 (cylinder block 3 and cylinder head 4). The cylinder head 4 includes an intake port 9 and an exhaust port 10 that open into the combustion chamber 6, an intake valve 11 that opens and closes the intake port 9, an exhaust valve 12 that opens and closes the exhaust port 10, and an intake valve 11 and an exhaust valve 12. Valve mechanisms 13 and 14 are provided that open and close the valves in conjunction with the rotation of the crankshaft 7. The cylinder head 4 is further provided with a fuel injection valve 15 that injects fuel (light oil) into the combustion chamber 6. The fuel injection valve 15 is, for example, a multi-hole injection valve that injects fuel radially from the center of the ceiling surface of the combustion chamber 6.

The intake system 3S includes an intake passage 30 through which intake air introduced into the engine body 1 flows. A downstream end (intake manifold) of the intake passage 30 is connected to one side of the cylinder head 4 so as to communicate with the intake port 9. The intake passage 30 includes, in order from the upstream side, an air cleaner 31 that removes foreign matter in the intake air, an intercooler 32 that cools the intake air compressed by the supercharging device 50, and a throttle valve that can be opened and closed to adjust the flow rate of the intake air. 33, and a surge tank 34 for ensuring that intake air is evenly taken into each cylinder 2. An air flow sensor SN3 that detects the flow rate of air (fresh air) introduced into the engine body 1 through the intake passage 30 is provided in a portion of the intake passage 30 on the downstream side of the air cleaner 31. Further, the surge tank 34 is provided with an intake pressure sensor SN4 that detects the pressure of intake air inside the surge tank 34.

The exhaust system 4S includes an exhaust passage 40 through which exhaust gas discharged from the engine body 1 flows. An upstream end (exhaust manifold) of the exhaust passage 40 is connected to the other side surface of the cylinder head 4 so as to communicate with the exhaust port 10. The exhaust passage 40 is provided with a plurality of catalysts 41 to 44 for purifying various harmful components contained in the exhaust gas. In this embodiment, an oxidation catalyst 41, a DPF (Diesel Particulate Filter) 42, an SCR (Selective Catalytic Reduction) catalyst 43, and a slip catalyst 44 are provided in order from the upstream side in the exhaust passage 40. Further, a urea injector 45 and a mixing plate 47 are provided in a portion of the exhaust passage 40 between the DPF 42 and the SCR catalyst 43.

The oxidation catalyst 41 is a catalyst for oxidizing and detoxifying CO and HC in exhaust gas (converting them into CO ₂ and H ₂ O), and includes, for example, a porous carrier and a catalyst supported on the carrier. catalytic materials such as platinum and palladium. The DPF 42 is a filter for collecting soot in exhaust gas. This DPF 42 contains a catalyst material such as platinum for burning soot under high temperature conditions during filter regeneration.

The urea injector 45 is an injection valve that supplies urea water, which is obtained by dissolving high-purity urea with pure water, into the exhaust passage 40 . The urea injector 45 is connected to the downstream end of a supply pipe 46a that supplies urea water. A urea tank 46 that stores urea water is connected to the upstream end of the supply pipe 46a. Furthermore, a pump 46P that supplies urea water to the urea injector 45 is incorporated in the supply pipe 46a. When urea water is injected into the exhaust passage 40 from the urea injector 45, the urea contained in the urea water is converted into ammonia (NH ₃ ) by hydrolysis under high temperature, and then sent to the SCR catalyst 43 on the downstream side. It is adsorbed. The pump 46P is a pressurizing pump, and by generating pressurizing force, supplies the urea water stored in the urea tank 46 to the urea injector 45 through the supply pipe 46a.

The mixing plate 47 is a plate-shaped member that partitions the exhaust passage 40 into front and rear parts, and is provided in a portion of the exhaust passage 40 between the urea injector 45 and the SCR catalyst 43. The mixing plate 47 is formed with a plurality of openings for stirring the flow of exhaust gas. Such a mixing plate 47 plays a role of uniformly dispersing urea contained in the urea water injected from the urea injector 45 and sending it to the downstream side (SCR catalyst 43).

The SCR catalyst 43 is provided in the exhaust passage 40 on the downstream side of the urea injector 45, and is a catalyst for reducing and purifying NOx in the exhaust gas (converting it into N ₂ and H ₂ O). The SCR catalyst 43 includes, for example, a porous carrier and a catalyst material such as vanadium, tungsten, or zeolite supported on the carrier. As described above, the SCR catalyst 43 adsorbs ammonia generated from the urea water injected by the urea injector 45. The SCR catalyst 43 converts NOx in the exhaust gas into N ₂ and H ₂ O through a chemical reaction using this ammonia as a reducing agent (reducing action of ammonia). For example, in this embodiment, a relatively small SCR catalyst 43 is used in order to reduce costs.

The slip catalyst 44 is an oxidation catalyst for oxidizing ammonia that has slipped without being adsorbed by the SCR catalyst 43 (that is, has flowed downstream without being used for NOx reduction). As this slip catalyst 44, for example, one having a structure similar to that of the oxidation catalyst 41 can be used.

A first NOx sensor SN6 that detects the concentration of NOx contained in the exhaust gas is provided between the DPF 42 and the SCR catalyst 43 in the exhaust passage 40. A second NOx sensor SN7 that detects the concentration of NOx contained in the exhaust gas is provided at the portion. Furthermore, an exhaust gas temperature sensor SN5 that detects the temperature of exhaust gas is provided in the exhaust passage 40 at a portion downstream of the first NOx sensor SN6 and located immediately upstream of the SCR catalyst 43.

The supercharging device 50 is a so-called two-stage supercharging device, and includes a first supercharger 51 and a second supercharger 52 arranged in series. The first supercharger 51 is a so-called turbo supercharger, and is rotatably provided in conjunction with a turbine 62 that is rotatably driven by exhaust gas flowing through the exhaust passage 40 and flows through the intake passage 30. The first compressor 61 compresses the intake air. The exhaust passage 40 is provided with a bypass passage 63 for bypassing the turbine 62, and this bypass passage 63 is provided with a wastegate valve 64 that can be opened and closed. The second supercharger 52 is a so-called electric supercharger, and includes an electric drive motor 66 and a second compressor 67 that is rotationally driven by the drive motor 66 to compress intake air. The intake passage 30 is provided with a bypass passage 68 for bypassing the second compressor 67, and this bypass passage 68 is provided with a bypass valve 69 that can be opened and closed.

The EGR device 70 includes an EGR passage 71 that connects the exhaust passage 40 and the intake passage 30, and an EGR cooler 72 and an EGR valve 73 provided in the EGR passage 71. The EGR passage 71 connects a portion of the exhaust passage 40 upstream of the turbine 62 and a portion of the intake passage 30 between the throttle valve 33 and the surge tank 34. The EGR cooler 72 cools exhaust gas (EGR gas) that is recirculated from the exhaust passage 40 to the intake passage 30 through the EGR passage 71. The EGR valve 73 is provided in a portion of the EGR passage 71 downstream of the EGR cooler 72, and adjusts the flow rate of exhaust gas flowing through the EGR passage 71.

<Control configuration>
Next, with reference to FIG. 2, a control configuration regarding an engine exhaust purification device and a method for estimating a deposited reducing agent according to an embodiment of the present invention will be described. FIG. 2 is a block diagram showing a control system of an engine to which an engine exhaust purification device and a method for estimating a deposited reducing agent according to an embodiment of the present invention are applied.

As shown in FIG. 2, a vehicle equipped with the engine of this embodiment includes a controller 100 that controls the engine in an integrated manner. The controller 100 is composed of a circuit and is a controller based on a well-known microcomputer. The controller 100 is configured with one or more microprocessors 100a as a central processing unit (CPU) that executes programs, and RAM (Random Access Memory) or ROM (Read Only Memory), and stores programs and data. It is equipped with a memory 100b for storing information, and an input/output bus for inputting and outputting electrical signals. The controller 100 is an example of a "processing device" in the present invention.

Note that the controller 100 does not need to be a single processor, and may include a plurality of electrically connected processors. For example, the controller 100 mainly includes a first processor (typically a "PCM (Power-train Control Module)") for controlling the engine body 1, and a dosing control for the urea injector 45, pump 46P, etc. A second processor (typically a "DCU (Dosing Control Unit)").

Detection information from various sensors is input to the controller 100 . Specifically, the controller 100 is electrically connected to the above-described crank angle sensor SN1, water temperature sensor SN2, air flow sensor SN3, intake pressure sensor SN4, exhaust temperature sensor SN5, first NOx sensor SN6, and second NOx sensor SN7. ing. Various information detected by these sensors, such as crank angle, engine speed, engine water temperature, intake air flow rate, intake pressure (supercharging pressure), exhaust gas temperature, and NOx concentration in the exhaust gas, are It is input to the controller 100.

In addition to the above, the vehicle includes a vehicle speed sensor SN8 that detects the traveling speed (vehicle speed) of the vehicle, an accelerator sensor SN9 that detects the opening degree of the accelerator pedal operated by the driver driving the vehicle, and an accelerator sensor SN9 that detects the outside temperature. An outside temperature sensor SN10 is provided to detect the outside temperature. Information detected by these vehicle speed sensor SN8, accelerator sensor SN9, and outside temperature sensor SN10 is also input to the controller 100.

The controller 100 controls each part of the engine while executing various judgments, calculations, etc. based on input information from each of the sensors SN1 to SN10. That is, the controller 100 is electrically connected to the fuel injection valve 15, throttle valve 33, urea injector 45, pump 46P, wastegate valve 64, drive motor 66, bypass valve 69, EGR valve 73, etc. Control signals are output to each of these devices based on the calculation results.

In this embodiment, the controller 100 determines the NOx purification rate of the SCR catalyst 43 based on the output values of the first and second NOx sensors SN6 and SN7, and executes abnormality determination of the SCR catalyst 43 based on this purification rate. In particular, in this embodiment, although the details will be described later, the controller 100 takes into consideration the urea that has adhered to the wall surface of the exhaust passage 40 due to injection from the urea injector 45 (hereinafter referred to as "adhered urea"). Execution of abnormality determination of the SCR catalyst 43 is restricted.

<Basic concept of this embodiment>
Next, with reference to FIG. 3, the basic concept of the processing content performed by the controller 100 in the embodiment of the present invention will be explained. FIG. 3 is a diagram for explaining the problem to be solved in the embodiment of the present invention. Specifically, FIG. 3 is an explanatory diagram of the adhesion of urea water injected from the urea injector 45 to the piping, the formation of a deposit of the adhered urea water, and the decomposition of the deposited urea.

First, as shown in the upper part of FIG. The inner wall surface of the pipe 40a forming the passage 40 is reached (arrow A12). A part of the urea water that has reached the pipe 40a in this way is thrown off by the wall of the pipe 40a, evaporated, or thermally decomposed, and is flowed downstream without adhering to the pipe 40a. (arrow A13), but the remaining urea water remains in liquid form and adheres to the pipe 40a of the exhaust passage 40 (arrow A14). Such adhesion of urea water occurs when urea water is injected from the urea injector 45 in order to purify NOx by the SCR catalyst 43 when the engine and the SCR catalyst 43 are at a relatively low temperature (for example, when cold). tends to occur.

Next, as shown in the middle part of FIG. 3, the urea water adhering to the pipe 40a of the exhaust passage 40 as described above typically solidifies (in other words, turns white) when the exhaust gas temperature or the pipe temperature becomes low. Then, it becomes a deposit (arrow A15). For example, if the engine is stopped with urea water attached to the pipe 40a, the urea water becomes deposited while the engine is stopped (in one example, during soaking). In the following, the deposited urea will be referred to as a "urea deposit."

Next, as shown in the lower part of FIG. 3, when the exhaust gas temperature or the pipe temperature increases (for example, when the engine is restarted) while the urea deposit is attached to the pipe 40a, the urea deposit ((NH ₂ ) ₂ CO) is decomposed into ammonia (NH ₃ ), indicated by the symbol 201, and isocyanic acid (HNCO), indicated by the symbol 202, according to the chemical formula below, and flows downstream (arrow A16). Further, as indicated by the reference numeral 203, urea ((NH ₂ ) ₂ CO) may flow downstream as it is.
(NH ₂ ) ₂ CO → NH ₃ +HNCO

Basically, isocyanic acid 202 and urea 203 pass through the SCR catalyst 43 (arrow A17), but ammonia 201 is adsorbed by the SCR catalyst 43. However, the ammonia 201 decomposed from the urea deposit is locally introduced into the SCR catalyst 43, causing the SCR catalyst 43 to become locally saturated, and as a result, the ammonia 201 slips from the SCR catalyst 43 ( Arrow A18). Slip of the ammonia 201 due to such a local saturation state of the SCR catalyst 43 is likely to occur particularly when a relatively small SCR catalyst 43 is used.

When ammonia 201 and the like flow downstream of the SCR catalyst 43 in this way, the output value of the second NOx sensor SN7 downstream of the SCR catalyst 43 increases. This is because the output value of the second NOx sensor SN7 corresponds to the amount (concentration) of nitrogen compounds including ammonia 201, isocyanic acid 202, and urea 203. As a result, in the abnormality determination of the SCR catalyst 43 using the output value of the second NOx sensor SN7, there is a possibility that the normal SCR catalyst 43 will be erroneously determined to be abnormal (deteriorated).

From the above, in the present embodiment, the controller 100 takes into consideration the urea attached to the wall surface of the exhaust passage 40 due to injection from the urea injector 45, in order to suppress erroneous determination regarding abnormality determination of the SCR catalyst 43. It is determined whether or not the abnormality determination in step 43 can be performed. Specifically, in the present embodiment, the controller 100 first determines the amount of adhering urea water adhering to the wall surface of the exhaust passage 40 due to injection from the urea injector 45, and based on this amount of adhering urea water, exhaust gas temperature, and piping temperature, It is determined whether or not the urea water adhering to the wall surface of the exhaust passage 40 is solidified, that is, whether or not a urea deposit is generated. As a result, the controller 100 prohibits execution of the abnormality determination of the SCR catalyst 43 when it is determined that a urea deposit is generated. Further, when it is determined that a urea deposit is generated, the controller 100 determines the amount of decomposed urea deposit, which is the amount of ammonia or the like that is decomposed from the urea deposit and discharged into the exhaust passage 40. Then, if it is determined that the urea deposit remains based on the decomposed amount of the urea deposit, the controller 100 continues to prohibit abnormality determination of the SCR catalyst 43, while determining that the urea deposit has disappeared. If so, the prohibition of abnormality determination of the SCR catalyst 43 is canceled.

<Abnormality determination of SCR catalyst>
Next, with reference to FIG. 4, the overall flow of abnormality determination of the SCR catalyst 43 according to the embodiment of the present invention will be described. FIG. 4 is a flowchart showing the SCR catalyst abnormality determination process according to the embodiment of the present invention. This flowchart is repeatedly executed by the controller 100 at predetermined intervals.

First, when the SCR catalyst abnormality determination process is started, in step S11, the controller 100 acquires various information from the above-mentioned sensors SW1 to SW10 (see FIG. 2) and the like. Typically, the controller 100 acquires detection information from an air flow sensor SN3, an exhaust temperature sensor SN5, a first NOx sensor SN6, a second NOx sensor SN7, a vehicle speed sensor SN8, and an outside temperature sensor SN10.

Next, in step S12, the controller 100 executes a urea deposit determination process to determine whether or not the urea water adhering to the wall surface of the exhaust passage 40 has solidified, that is, whether or not a urea deposit has been generated. . In this urea deposit determination process, if it is determined that a urea deposit is being generated, the urea deposit determination flag is set to on, and if it is determined that a urea deposit is not being generated, the urea deposit determination flag is set to on. The determination flag is set to off. The details of the urea deposit determination process will be described later (FIG. 5).

Next, in step S13, the controller 100 determines whether the urea deposit determination flag in the urea deposit determination process of step S12 is off, that is, whether or not a urea deposit is generated.

In step S13, if it is determined that the urea deposit determination flag is off (step S13: Yes), the controller 100 determines that the urea deposit is not generated and that the abnormality determination of the SCR catalyst 43 can be accurately performed. It is determined that there is an abnormality, and the execution of the abnormality determination in subsequent processing is permitted. In this case, first, in step S14, the controller 100 determines the NOx purification rate of the SCR catalyst 43 based on the output values of the first NOx sensor SN6 and the second NOx sensor SN7. Specifically, the controller 100 determines the NOx amount in the exhaust passage 40 on the upstream side of the SCR catalyst 43 (hereinafter referred to as "upstream NOx amount") from the output value of the first NOx sensor SN6, and The NOx amount in the exhaust passage 40 on the downstream side of the SCR catalyst 43 (hereinafter referred to as "downstream NOx amount") is determined from the output value of the NOx sensor SN7. Then, the controller 100 determines the NOx purification rate of the SCR catalyst 43 from the upstream NOx amount and downstream NOx amount using the following equation. Note that the amount of NOx detected by the first and second NOx sensors SN6 and SN7 (which uniquely corresponds to the NOx concentration) includes not only NOx itself but also the amount (concentration) of various nitrogen compounds.
NOx purification rate = 1 - (downstream NOx amount/upstream NOx amount)

Next, in step S15, the controller 100 determines whether the NOx purification rate obtained in step S14 is less than a predetermined value. As a result, if it is determined that the NOx purification rate is less than the predetermined value (step S15: Yes), the controller 100 proceeds to step S16. In this case, the controller 100 determines that the SCR catalyst 43 is abnormal because the NOx purification rate of the SCR catalyst 43 is low (step S16). The controller 100 then proceeds to step S17 and performs processing (for example, displaying an image or outputting a sound) to issue a warning indicating that the SCR catalyst 43 is abnormal. After this, the controller 100 ends the SCR catalyst abnormality determination process.

On the other hand, if it is not determined in step S15 that the NOx purification rate is less than the predetermined value (step S15: No), that is, if the NOx purification rate is greater than or equal to the predetermined value, the controller 100 proceeds to step S18. move on. In this case, the controller 100 determines that the SCR catalyst 43 is normal because the NOx purification rate of the SCR catalyst 43 is high (step S18). Then, the controller 100 ends the SCR catalyst abnormality determination process.

On the other hand, if it is not determined in step S13 that the urea deposit determination flag is off (step S13: No), that is, if the urea deposit determination flag is on, the controller 100 proceeds to step S19. In this case, the controller 100 determines that the abnormality determination of the SCR catalyst 43 cannot be accurately performed because urea deposits have been generated, and prohibits the execution of the abnormality determination of the SCR catalyst 43 ( Step S19). Then, the controller 100 ends the SCR catalyst abnormality determination process.

<Urea deposit judgment>
Next, urea deposit determination according to an embodiment of the present invention will be specifically described. First, an overview of urea deposit determination according to an embodiment of the present invention will be described with reference to FIG. FIG. 5 is a flowchart showing urea deposit determination processing according to an embodiment of the present invention. This flowchart is executed by the controller 100 in step S12 of the SCR catalyst abnormality determination process shown in FIG.

First, when the urea deposit determination process is started, in step S21, the controller 100 determines the amount of urea water deposited on the wall surface of the exhaust passage 40 by injection from the urea injector 45. Specifically, the controller 100 calculates the amount of urea water that adheres to the wall surface of the exhaust passage 40 per unit time due to the injection of the urea injector 45, and integrates the amount of urea water that adheres per unit time. The total amount of adhering urea water, which is the total amount of urea water adhering to the wall surface of the exhaust passage 40 by the injection, is determined. Specifically, the controller 100 controls the exhaust gas temperature, the exhaust gas flow rate, and the urea injection rate (in other words, the amount of urea injected per unit time) by the urea injector 45. Hereinafter, it will be referred to as "urea injection rate." ), the first proportion of urea that reaches the pipe 40a among the urea injected by the urea injector 45 is determined, and the first proportion of urea that reaches the pipe 40a among the urea that reaches the pipe 40a is determined based on the pipe temperature and the exhaust gas flow rate. A second proportion of the attached urea is determined, and the total amount of attached urea water is determined based on these first and second proportions. Further, the controller 100 determines the amount of scattered urea water from the pipe 40a based on the evaporation rate of the adhered urea water depending on the pipe temperature, and subtracts the amount of the adhered urea water to reduce the amount of adhered urea water. Calculate the total amount of urea water.

Note that the exhaust gas temperature, exhaust gas flow rate, urea injection rate, and pipe temperature used in the process of step S21 (the same applies to the process described later) are defined as follows. The controller 100 uses the temperature detected by the exhaust gas temperature sensor SN5 as the exhaust gas temperature. The controller 100 also determines the exhaust gas flow rate (exhaust gas flow rate and ). Further, the controller 100 determines the urea injection rate from the control signal supplied to the urea injector 45 (more specifically, the control signal supplied from the DCU to the urea injector 45). Furthermore, the controller 100 applies the exhaust gas temperature detected by the exhaust temperature sensor SN5, the outside temperature detected by the outside temperature sensor SN10, and the vehicle speed detected by the vehicle speed sensor SN8 to a predetermined piping temperature model. , the pipe temperature of the exhaust passage 40 (particularly the temperature of the pipe 40a between the urea injector 45 and the SCR catalyst 43) is determined. In this case, the controller 100 calculates the pipe temperature model using the vehicle speed detected by the vehicle speed sensor SN8 as the speed (wind speed) of the traveling wind hitting the pipe 40a.

Next, in step S22, the controller 100 determines whether or not the adhered urea water is solidified, that is, whether or not a urea deposit is generated, based on the total amount of adhered urea water, exhaust gas temperature, and pipe temperature determined in step S21. Determine whether Specifically, the controller 100 (1) determines the concentration of adhered urea water based on the exhaust gas temperature, exhaust gas flow rate, and urea injection rate, and (2) determines the adhered urea water concentration based on the total amount of adhered urea water and the concentration of urea water. (3) find the amount of evaporation of the adhered urea water based on the piping temperature, and (4) determine the amount of urea deposit when the amount obtained by subtracting the amount of evaporation of the adhered urea water from the moisture content of the adhered urea water is 0. is determined to be generated.

As a result of step S22, if it is determined that a urea deposit is generated (step S22: Yes), the controller 100 proceeds to step S23 and sets the urea deposit determination flag to ON. On the other hand, if it is not determined that a urea deposit is generated (step S22: No), the controller 100 ends the urea deposit determination process. In this case, since no urea deposit is generated, the controller 100 maintains the urea deposit determination flag off.

Next, in step S24, the controller 100 determines the amount of urea deposited. In this case, the controller 100 basically obtains the current total amount of deposited urea water obtained in step S21 as is as the urea deposit amount.

Next, in step S25, the controller 100 determines the amount of decomposed urea deposit, which is the amount of ammonia or the like that is decomposed from the urea deposit and discharged into the exhaust passage 40. Specifically, the controller 100 applies a rate constant for decomposition of the urea deposit, which is defined by the pipe temperature, exhaust gas temperature, and decomposition activation energy, to the urea deposit amount determined in step S24. Then, the decomposition rate of ammonia and isocyanic acid from the urea deposit is determined, and the decomposed amount of the urea deposit is determined from this decomposition rate.

Next, in step S26, the controller 100 determines whether the urea deposit has disappeared based on the urea deposit amount obtained in step S24 and the urea deposit decomposition amount obtained in step S25. If the amount obtained by subtracting the decomposed amount of urea deposit from the amount of urea deposit is 0 (this corresponds to the case where the current amount of urea deposit has decreased to 0), the controller 100 determines that the urea deposit has disappeared. It is determined (step S26: Yes) and the urea deposit determination flag is switched from on to off (step S27). Then, the controller 100 ends the urea deposit determination process. After this, the prohibition of abnormality determination of the SCR catalyst 43 is lifted.

On the other hand, if the amount obtained by subtracting the urea deposit decomposition amount obtained in step S25 from the urea deposit amount obtained in step S24 is greater than 0 (this means that the current urea deposit amount is greater than 0), ), it is determined that the urea deposit has not disappeared (step S26: No), and the urea deposit determination process is ended. In this case, the controller 100 maintains the urea deposit determination flag on. Therefore, the prohibition of abnormality determination of the SCR catalyst 43 continues.

Next, details of each process executed in the above-mentioned urea deposit determination in the embodiment of the present invention will be described with reference to FIGS. 6 to 10.

FIG. 6 is a block diagram showing a method for calculating the total amount of attached urea water according to the embodiment of the present invention. As shown in FIG. 6, the controller 100 first determines which of the urea injected by the urea injector 45 reaches the pipe 40a based on the exhaust gas temperature, the exhaust gas flow rate, and the urea injection rate of the urea injector 45. Find the first ratio. For example, the controller 100 may refer to a map (eg, stored in the memory 100b) regarding the first proportion of urea predefined by the exhaust gas temperature, the exhaust gas flow rate, and the urea injection rate to determine the current exhaust gas rate. A first ratio corresponding to temperature, exhaust gas flow rate, and urea injection rate is determined. Basically, the map is defined such that the lower the exhaust gas temperature, the lower the exhaust gas flow rate, and the higher the urea injection rate, the larger the first ratio becomes.

Further, the controller 100 determines a second proportion of urea that adheres to the pipe 40a among the urea that has reached the pipe 40a based on the pipe temperature and the exhaust gas flow rate. For example, the controller 100 corresponds to the current pipe temperature and exhaust gas flow rate with reference to a map (eg, stored in the memory 100b) regarding the second proportion of urea, which is predefined by the pipe temperature and the exhaust gas flow rate. Find the second proportion. Basically, the map is defined such that the second ratio increases as the pipe temperature decreases and as the exhaust gas flow rate decreases.

Then, the controller 100 multiplies the current urea injection rate of the urea injector 45 by the first ratio and the second ratio determined as described above, so that the injection from the urea injector 45 can be applied to the wall surface of the exhaust passage 40. Find the amount of urea water attached per unit time. Next, the controller 100 calculates the total amount of adhered urea water, which is the total amount of urea water that has adhered to the wall surface of the exhaust passage 40 due to injection from the urea injector 45, by integrating the amount of adhered urea water per unit time. Note that the total amount of adhering urea water determined in this way is a provisional amount (hereinafter also referred to as the "total amount of temporarily adhering urea water"), and various amounts determined as described below are subtracted from this total amount of temporarily adhering urea water. It is assumed that the total amount of deposited urea water after the process and the subtraction process is finally applied for the determination regarding the urea deposit.

Furthermore, as shown in FIG. 6, the controller 100 calculates the total amount of temporarily adhered urea water as described above, and at the same time calculates the amount of scattered urea water that adheres from the pipe 40a due to the exhaust gas flow. As described above, the controller 100 subtracts this scattered amount of adhered urea water from the total amount of temporarily adhered urea water to obtain the final total amount of adhered urea water to be applied for the determination regarding the urea deposit. When calculating the amount of scattered urea water, the controller 100 first calculates the evaporation rate (in other words, evaporation rate) from the pipe temperature. Here, the evaporation rate of adhered urea water will be explained with reference to FIG. 7.

FIG. 7 is a diagram showing the relationship between pipe temperature (horizontal axis) and evaporation rate (vertical axis) of adhered urea water, which is used when determining the amount of scattered urea water in the embodiment of the present invention. The evaporation rate of adhered urea water shown on the vertical axis corresponds to the solidification rate (depositing rate) of adhered urea water, and the relationship is such that the higher the evaporation rate, the higher the solidification rate, and the lower the evaporation rate, the lower the solidification rate. There is. As shown in FIG. 7, when the pipe temperature is lower than the first predetermined temperature T1 (for example, a temperature higher than the boiling point of the liquid, in one example, about 140°C), the higher the pipe temperature, the faster the evaporation rate of the attached urea water. becomes higher (arrow A21). This is a normal characteristic of liquid evaporation, in which the higher the temperature, the more easily the liquid evaporates.

On the other hand, when the pipe temperature is higher than the first predetermined temperature T1 and lower than the second predetermined temperature T2 (for example, about 300° C.), the higher the pipe temperature, the lower the evaporation rate of the attached urea water (arrow A22). This is the opposite of the normal characteristics described above. This characteristic is such that when the pipe temperature is high to a certain extent, the surface of the urea water in contact with the pipe 40a evaporates to form a thin vapor film, and this vapor film prevents the urea water from coming into direct contact with the pipe 40a. This is due to the phenomenon that the urea water becomes difficult to evaporate as a result (that is, a vapor film is formed under the urea water and heat conduction between the urea water and the pipe 40a is inhibited).

The magnitude (absolute value) of the rate of change in evaporation rate with respect to a change in pipe temperature when the pipe temperature is below the first predetermined temperature T1 is as follows: is higher than the magnitude (absolute value) of the rate of change in evaporation rate with respect to change in pipe temperature when This is because the normal property that the evaporation rate increases as the temperature increases has a stronger influence on liquid evaporation than the special property that the evaporation rate decreases as the temperature increases due to the presence of a vapor film. It is.

On the other hand, when the pipe temperature is equal to or higher than the second predetermined temperature T2, the higher the pipe temperature, the higher the evaporation rate of the adhered urea water (arrow A23). This is due to normal characteristics. In other words, when the pipe temperature becomes considerably high, the normal characteristic that the evaporation rate increases as the temperature increases becomes more dominant than the special characteristic that the evaporation rate decreases as the temperature increases due to the presence of a vapor film. Because it gives.

Here, the controller 100 calculates the evaporation rate of the adhered urea water corresponding to the current piping temperature based on the relationship between the piping temperature and the evaporation rate as shown in FIG. 7 (for example, stored in the memory 100b as a map). .

Returning to FIG. 6, the controller 100 calculates the evaporation rate of urea water, the exhaust gas flow rate, the exhaust gas flow rate change rate (in other words, the amount of change in the exhaust gas flow rate per unit time), and the adhesion rate determined as described above. Based on the total amount of urea water, the amount of scattered urea water per unit time due to the exhaust gas flow is determined. For example, the controller 100 refers to a map (for example, stored in the memory 100b) regarding predetermined coefficients predefined by the evaporation rate of urea water, the exhaust gas flow rate, and a change in the exhaust gas flow rate, and determines the current evaporation rate. By determining coefficients corresponding to the speed, exhaust gas flow rate, and changes in exhaust gas flow rate, and applying these coefficients to the current total amount of adhered urea water, the amount of scattered adhered urea water per unit time is determined. Basically, the map specifies that the higher the evaporation rate of urea water, the higher the exhaust gas flow rate, and the larger the change in exhaust gas flow rate, the larger the amount of adhering urea water scattered per unit time. has been done. The controller 100 integrates the thus determined amount of scattered urea water per unit time. Then, the controller 100 subtracts the accumulated scattered amount of adhered urea water from the total amount of temporarily adhered urea water to obtain the final total amount of adhered urea water to be applied for the determination regarding the urea deposit.

In this way, in this embodiment, by using the amount of scattered urea water that takes into consideration the evaporation rate of urea water that has the characteristics shown in FIG. 2. When the temperature is less than the predetermined temperature T2, the higher the pipe temperature, the larger the amount of adhered urea water (specifically, the amount of adhered urea water per unit time; the same applies hereinafter) is required. Furthermore, when the pipe temperature is less than the first predetermined temperature T1, the higher the pipe temperature, the smaller the amount of adhered urea water required. Further, when the pipe temperature is equal to or higher than the second predetermined temperature T2, the higher the pipe temperature is, the smaller the amount of adhered urea water is required.

Furthermore, as shown in FIG. 6, the controller 100 determines the amount of urea water that has changed from the urea deposit to urea water (that is, the amount of urea that has dissolved into the exhaust gas in the urea deposit), and calculates this amount of urea water as the total amount of temporarily deposited urea water. Subtract from. In addition, the controller 100 determines the amount of urea water thermally decomposed in the adhered urea water (that is, the amount of adhered urea decomposed into ammonia and isocyanic acid) based on the adhered urea water temperature and the total amount of adhered urea water, and Subtract it from the total amount of temporarily attached urea water. In this case, the controller 100 determines the temperature of the adhered urea water based on the pipe temperature and the exhaust gas temperature, and determines the amount of thermally decomposed urea water based on the adhered urea water temperature. The method for calculating the amount of thermally decomposed urea water is the same as the method for calculating the decomposed amount of urea deposit (FIG. 9), which will be described later.

As described above, the controller 100 calculates the amount of scattered urea water and the amount of urea water that has changed from the urea deposit to urea water from the total amount of temporarily attached urea water obtained by integrating the amount of urea water that has adhered per unit time. The amount obtained by subtracting the amount of urea water thermally decomposed in the adhered urea water is used as the final total amount of adhered urea water applied for the determination regarding the urea deposit.

Next, FIG. 8 is a block diagram showing a urea deposit determination method according to an embodiment of the present invention. As shown in FIG. 8, the controller 100 first uses a urea water evaporation amount calculation model from urea water injection to pipe adhesion based on the exhaust gas temperature, exhaust gas flow rate, and urea injection rate to Determine the concentration (%) of urea in the attached urea water. Basically, the lower the exhaust gas temperature, the lower the exhaust gas flow rate, and the higher the urea injection rate, the higher the concentration of adhered urea water tends to be. Then, the controller 100 calculates the water content of the adhered urea water using the following formula from the concentration (%) of the adhered urea water and the total amount of the adhered urea water determined by the calculation method shown in FIG.
Water content of attached urea water = Total amount of attached urea water × (1 - Concentration of attached urea water / 100)

On the other hand, the controller 100 determines the amount of evaporation of the adhered urea water at the same time as determining the water content of the adhered urea water as described above. Specifically, the controller 100 calculates the evaporation rate of the adhered urea water from the pipe temperature using a method similar to that shown in FIG. 7 above, and calculates the evaporation amount of the adhered urea water by integrating the evaporation rate. . Then, the controller 100 determines that a urea deposit is generated when the amount obtained by subtracting the evaporation amount of the adhered urea water from the moisture content of the adhered urea water (hereinafter appropriately referred to as "residual moisture amount") is 0. The controller 100 determines this and sets the urea deposit determination flag to ON. At this time, the controller 100 applies the current total amount of adhered urea water as it is as the urea deposit amount.

As described above, in this embodiment, by using the evaporation rate of adhered urea water having the characteristics shown in FIG. When this is the case, the urea deposit determination will be made based on the relationship that the lower the pipe temperature, the higher the deposition rate of the adhered urea water (meaning the solidification rate of the adhered urea water; hereinafter the same shall apply). . Further, when the pipe temperature is lower than the first predetermined temperature T1, the controller 100 performs the urea deposit determination based on the relationship that the higher the pipe temperature, the higher the deposition rate of the adhered urea water. Further, when the pipe temperature is equal to or higher than the second predetermined temperature T2, the controller 100 performs the urea deposit determination based on the relationship that the higher the pipe temperature, the higher the deposition rate of the adhered urea water.

Next, FIG. 9 is a block diagram showing a method for calculating the amount of urea deposit decomposition according to an embodiment of the present invention. As shown in FIG. 9, the controller 100 first determines the urea deposit temperature based on the pipe temperature and exhaust gas temperature. Then, the controller 100 sets the predetermined frequency factor to "A," the gas constant to "R," the urea deposit temperature to "T," and the activation energy for decomposition of urea (Arrhenius parameter) to "Ea." , the rate constant (in other words, the reaction constant) k regarding the decomposition of urea is determined using the equation expressed by the following exponential function. Note that the frequency factor A is a value indicating the frequency of contact between the urea deposit and the exhaust gas. Furthermore, the activation energy is a value determined through experiments (also described in specialized literature).
k=Aexp{-Ea/(RT)}

Next, the controller 100 determines the decomposition rate V of the urea deposit into ammonia and isocyanic acid from the rate coefficient k and the amount of urea deposit using the following formula. Note that "α" in the formula is a value determined from experiments and the like.
V=k×(urea deposit amount) ^α

Next, the controller 100 calculates the decomposition amount of the urea deposit by integrating the decomposition rates V of ammonia and isocyanic acid. After this, the controller 100 subtracts the decomposed amount of urea deposit from the urea deposit amount (corresponding to the total amount of adhered urea water when the urea deposit determination flag is set to ON) (hereinafter referred to as "residual deposit amount" as appropriate). ) to determine whether the urea deposit has disappeared. Specifically, if the remaining deposit amount is greater than 0, the controller 100 determines that the urea deposit has not disappeared, keeps the urea deposit determination flag on, and determines whether the SCR catalyst 43 is abnormal. Continue the ban. On the other hand, if the remaining deposit amount is 0, the controller 100 determines that the urea deposit has disappeared, switches the urea deposit determination flag from on to off, and determines whether the SCR catalyst 43 is abnormal. Lift the ban.

Next, FIG. 10 is a time chart showing an example of the results of urea deposit determination according to the embodiment of the present invention. FIG. 10 shows, from top to bottom, (1) engine operating status (specifically, whether the engine is on (operating) or off (stopped)), (2) urea water injection request ( (Basically corresponds to the request for the use of the SCR catalyst 43 for NOx purification), (3) total amount of adhered urea water, (4) residual moisture amount obtained by subtracting the evaporation amount of adhered urea water from the moisture amount of adhered urea water. , (5) urea deposit amount (particularly remaining deposit amount), (6) urea deposit determination flag, and (7) SCR catalyst abnormality determination execution flag indicating whether or not to execute abnormality determination of the SCR catalyst 43. .

First, the controller 100 continuously calculates the total amount of adhering urea water, the amount of remaining water, etc. during the operation of the engine after time t10. During this engine operation, the controller 100 turns off the urea deposit determination flag when the total amount of adhered urea water is greater than 0 (that is, when there is adhered urea), since the residual moisture amount is always greater than 0. maintain. Therefore, the controller 100 executes the abnormality determination in accordance with the request for abnormality determination of the SCR catalyst 43 (arrow A30).

Next, at time t11, the engine is stopped, and at time t12, during which the engine is stopped, the remaining moisture content becomes 0 (arrow A31). In other words, a urea deposit is generated. At this time, since the engine is stopped (for example, the ignition switch is off), the controller 100 does not determine that a urea deposit has been generated. Then, at time t12, the engine is started and the controller 100 also starts operating. At this time, since the residual water content is 0, the controller 100 determines that a urea deposit has been generated, turns on the urea deposit determination flag (arrow A32), and sets the current total amount of adhering urea water to the urea deposit. Set as an amount (arrow A33). In this case, the controller 100 sets the total amount of adhered urea water to 0 (arrow A34). Then, from time t13, the controller 100 calculates the amount of decomposed urea deposit and subtracts this amount of decomposed urea deposit from the amount of urea deposit corresponding to the total amount of adhered urea water when the urea deposit determination flag is set to on. Calculate the remaining deposit amount.

Next, after time 13, the controller 100 determines that the urea deposit remains while the remaining deposit amount is greater than 0, and maintains the urea deposit determination flag on. While the urea deposit determination flag is on, the controller 100 prohibits execution of abnormality determination even if a request for abnormality determination of the SCR catalyst 43 is issued (broken line arrow A36). After this, at time t14, the remaining deposit amount becomes 0, so the controller 100 determines that the urea deposit has disappeared, and switches the urea deposit determination flag from on to off. As a result, after time t14, the controller 100 executes abnormality determination in accordance with the request for abnormality determination of the SCR catalyst 43 (arrow A37).

<Action and effect>
Next, the operation and effects of the engine exhaust purification device and the method for estimating the deposited reducing agent according to the embodiment of the present invention will be described.

In the present embodiment, the controller 100 determines the amount of urea water that adheres to the wall surface of the exhaust passage 40 due to the injection of the urea injector 45 (including the amount of urea water that adheres per unit time and the total amount of urea water that adheres). In addition to the amount of adhered urea water, it is determined whether or not the adhered urea water has solidified based on the piping temperature and exhaust gas temperature, and when it is determined that the adhered urea water has solidified, it is determined that the SCR catalyst 43 is abnormal. Restrict execution. According to this embodiment, it is possible to accurately determine the solidification of adhered urea water based on the amount of adhered urea water and the like. Based on the accurate determination regarding solidification of the adhered urea water, execution of abnormality determination of the SCR catalyst 43 can be appropriately restricted, and as a result, erroneous determination regarding abnormality determination of the SCR catalyst 43 can be reliably suppressed. I can do it.

Here, as described above (see FIG. 7), when the pipe temperature is relatively high, the surface of the urea water in contact with the pipe 40a is vaporized and a thin vapor film is formed, and this vapor film allows the urea water to flow into the pipe. As a result of inhibiting direct contact with 40a, a phenomenon occurs in which urea water becomes difficult to evaporate. Therefore, in the present embodiment, the controller 100 takes into account the characteristics regarding the evaporation of urea water, and when the pipe temperature is equal to or higher than the first predetermined temperature T1, the lower the pipe temperature, the more the solidification rate of the attached urea ( Solidification of the adhered urea water is determined based on the relationship that the deposition rate) increases. Thereby, the solidification of the adhered urea water can be determined more accurately.

Furthermore, in the present embodiment, when the pipe temperature is lower than the first predetermined temperature T1, the controller 100 determines the solidification of the adhered urea water based on the relationship that the higher the pipe temperature, the higher the solidification rate of the urea water. do. Accordingly, when the pipe temperature is relatively low, the phenomenon that the evaporation rate decreases as the temperature increases due to the presence of the vapor film as described above hardly occurs, so that the evaporation rate increases as the temperature increases. By taking this normal characteristic into account, it is possible to more accurately determine the solidification of adhering urea water.

Further, in the present embodiment, the controller 100 operates based on the relationship that when the pipe temperature is equal to or higher than the second predetermined temperature T2 (>first predetermined temperature T1), the higher the pipe temperature, the higher the solidification rate of urea water. , determine the solidification of adhered urea water. As a result, when the pipe temperature is quite high, the controller 100 has a characteristic that the evaporation rate increases as the temperature increases, rather than the characteristic that the evaporation rate decreases as the temperature increases due to the presence of a vapor film as described above. By taking into consideration the fact that it is dominant, it is possible to more accurately determine the solidification of adhered urea water.

Further, in the present embodiment, the controller 100 determines that the magnitude of the rate of change in the solidification rate of urea water with respect to a change in the pipe temperature when the pipe temperature is less than the first predetermined temperature T1 is By taking into account the characteristic that the rate of change in the solidification rate of urea water with respect to the change in pipe temperature is higher than T1, it is possible to more accurately determine the solidification of adhered urea water.

Further, in the present embodiment, the controller 100 determines the concentration of the adhered urea water based on the exhaust gas temperature, the exhaust gas flow rate, and the urea injection rate by the urea injector 45, and calculates the concentration of the adhered urea water based on the concentration of the adhered urea water. By determining the water content, solidification of the adhered urea water can be determined more accurately based on this water content.

Further, in the present embodiment, the controller 100 determines the concentration of the adhered urea water based on the exhaust gas temperature, the exhaust gas flow rate, and the urea injection rate by the urea injector 45, and calculates the concentration of the adhered urea water based on the concentration of the adhered urea water. By determining the moisture content and the evaporation amount of the adhered urea water based on the pipe temperature, it is possible to more accurately determine whether the adhered urea water has solidified based on the moisture content and the evaporation amount.

<Modified example>
Next, a modification of the above-described embodiment will be described. Note that the various modifications shown below can be implemented in combination as appropriate.

(Modification 1)
In the embodiment described above, the controller 100 determines that a urea deposit is generated when the residual moisture content obtained by subtracting the evaporation amount of the adhered urea water from the moisture content of the adhered urea water is 0, and performs the urea deposit determination. The flag was set to on (see FIGS. 8 and 10). In a modified example, instead of using such a residual moisture amount, the controller 100 calculates whether the exhaust gas temperature or the pipe temperature is If the value is less than a predetermined threshold, it may be determined that a urea deposit is being generated. Then, when the exhaust gas temperature or the piping temperature becomes less than the threshold value, the controller 100 estimates that all the urea water equivalent to the total amount of adhered urea water has been deposited, and the amount of urea deposit corresponding to the total amount of adhered urea water It may be determined that the urea deposit has disappeared when the amount decreases to zero.

FIG. 11 is a time chart showing an example of the results of urea deposit determination according to a modification of the embodiment of the present invention. FIG. 11 shows, from top to bottom, (1) engine operating state, (2) urea water injection request, (3) pipe temperature (exhaust gas temperature may be used instead), and (4) attached urea water. (5) urea deposit amount (especially remaining deposit amount), (6) urea deposit determination flag, and (7) SCR catalyst abnormality determination execution flag. Here, explanations similar to those in FIG. 10 will be omitted as appropriate, and parts different from FIG. 10 will be mainly explained.

As shown in FIG. 11, at time t21 while the engine is stopped, the pipe temperature becomes less than the threshold Te (arrow A41). At this time, since the engine is stopped, the controller 100 does not determine that a urea deposit has been generated. Then, at time t22, the engine is started and the controller 100 also starts operating. At this time, since the pipe temperature is less than the threshold value Te, the controller 100 determines that a urea deposit has been generated, turns on the urea deposit determination flag (arrow A42), and removes all the current total amount of adhered urea water. Set as the urea deposit amount (arrow A43). In this case, the controller 100 sets the total amount of adhered urea water to 0 (arrow A44). Then, from time t22, the controller 100 calculates the amount of decomposed urea deposit and subtracts this amount of decomposed urea deposit from the amount of urea deposit corresponding to the total amount of adhered urea water when the urea deposit determination flag is set to on. Calculate the remaining deposit amount.

After time 22, the controller 100 determines that the urea deposit remains while the remaining deposit amount is greater than 0, and maintains the urea deposit determination flag on. While the urea deposit determination flag is on, the controller 100 prohibits execution of abnormality determination for the SCR catalyst 43 even if a request for abnormality determination is issued (broken line arrow A46). After this, at time t23, the remaining deposit amount becomes 0, so the controller 100 determines that the urea deposit has disappeared, and switches the urea deposit determination flag from on to off. As a result, after time t23, the controller 100 executes abnormality determination of the SCR catalyst 43 in accordance with the request for abnormality determination (arrow A47).

According to the modification described above, it is determined that urea deposits are generated when the exhaust gas temperature or piping temperature becomes less than the threshold value, so that it is possible to determine the generation of urea deposits by simple processing. can. Also, at this time, it is estimated that all the urea for the total amount of adhered urea water has been deposited, and when the amount of urea deposit corresponding to the total amount of adhered urea water has decreased to 0, it is determined that the urea deposit has disappeared. Therefore, the disappearance of the urea deposit can be determined by simple processing.

(Modification 2)
In the embodiment described above, execution of the abnormality determination of the SCR catalyst 43 is prohibited when it is determined that a urea deposit is generated, that is, when the urea deposit determination flag is on. It is not limited to prohibiting execution. In the modified example, when the urea deposit determination flag is on, the predetermined value for determining the NOx purification rate is set higher than when the urea deposit determination flag is off, without prohibiting the execution of the abnormality determination of the SCR catalyst 43. The value may be increased (see FIG. 4) to make it difficult for the SCR catalyst 43 to be determined to be abnormal. In short, when the urea deposit determination flag is on, abnormality determination of the SCR catalyst 43 may be more limited than when the urea deposit determination flag is off. Even with such a modification, it is possible to appropriately suppress erroneous determination regarding abnormality determination of the SCR catalyst 43.

(Modification 3)
In the embodiment described above, the amount of water and the amount of evaporation of adhering urea water are determined according to the concentration of adhering urea water, and the generation of a urea deposit is determined based on both the amount of water and the amount of evaporation. However, in a modified example, the generation of urea deposits may be determined based only on the amount of evaporation of adhering urea water. In this modification, it may be determined that a urea deposit is being generated, for example, when the amount of evaporation of the adhering urea water is equal to or greater than a predetermined amount.

(Modification 4)
In the embodiment described above, urea, which is a precursor of ammonia, is injected from the urea injector 45, but in a modified example, ammonia may be directly injected from a predetermined injector.

(Modification 5)
In the embodiment described above, both the first and second NOx sensors SN6 and SN7 were used to determine whether the SCR catalyst 43 was abnormal. Alternatively, only the second NOx sensor SN7 may be used. In this case, the upstream NOx amount is determined according to the operating state of the engine, and the NOx purification rate is determined from this upstream NOx amount and the downstream NOx amount corresponding to the output value of the second NOx sensor SN7. It is sufficient to perform an abnormality determination.

(Modification 6)
In a modified example, urea may be preheated with a heater before urea injection to promote evaporation of urea during the period from urea injection to attachment to the pipe 40a. In this modification, in addition to the exhaust gas temperature, exhaust gas flow rate, and urea injection rate, the heater temperature or urea temperature may be taken into consideration when calculating the first proportion of urea that reaches the pipe 40a described above. Specifically, by multiplying the first ratio obtained from the map defined by the exhaust gas temperature, exhaust gas flow rate, and urea injection rate by a correction coefficient defined by the heater temperature or urea temperature, The first ratio may be corrected. In this case, the higher the heater temperature or urea temperature is, the smaller the correction coefficient is applied, so that the higher the heater temperature or urea temperature is, the smaller the first proportion of urea reaching the pipe 40a is.

1 Engine body 40 Exhaust passage 40a Piping 43 SCR catalyst 44 Slip catalyst 45 Urea injector 100 Controller SN5 Exhaust temperature sensor SN6 1st NOx sensor SN7 2nd NOx sensor SN8 Vehicle speed sensor SN10 Outside temperature sensor

Claims (6)

a reducing agent injector that injects ammonia or an ammonia precursor as a reducing agent into an exhaust passage of an engine;
a selective reduction type NOx catalyst that reduces NOx in exhaust gas using the reducing agent injected by the reducing agent injector;
a NOx sensor that is provided on the exhaust passage downstream of the selective reduction NOx catalyst and whose output value changes depending on the amount of NOx and the amount of ammonia in the exhaust gas;
a processing device that determines an abnormality with respect to the selective reduction type NOx catalyst based on the output value of the NOx sensor;
An exhaust purification device for an engine having
The processing device includes:
Determining the amount of adhering reducing agent, which is the amount of the reducing agent adhering to the wall surface of the exhaust passage due to the injection of the reducing agent injector,
Determining whether the reducing agent attached to the wall surface of the exhaust passage is solidified based on the amount of the attached reducing agent and the piping temperature of the exhaust passage and/or the temperature of the exhaust gas,
configured to limit execution of the abnormality determination when it is determined that the reducing agent has solidified;
When the pipe temperature is equal to or higher than a predetermined temperature, the treatment device controls the wall surface of the exhaust passage based on the relationship between the pipe temperature and the solidification rate such that the lower the pipe temperature, the higher the solidification rate of the reducing agent. configured to determine solidification of the reducing agent attached to the
An engine exhaust purification device characterized by: a reducing agent injector that injects ammonia or an ammonia precursor as a reducing agent into an exhaust passage of an engine;
a selective reduction type NOx catalyst that reduces NOx in exhaust gas using the reducing agent injected by the reducing agent injector;
a NOx sensor that is provided on the exhaust passage downstream of the selective reduction NOx catalyst and whose output value changes depending on the amount of NOx and the amount of ammonia in the exhaust gas;
a processing device that determines an abnormality with respect to the selective reduction type NOx catalyst based on the output value of the NOx sensor;
An exhaust purification device for an engine having
The processing device includes:
Determining the amount of adhering reducing agent, which is the amount of the reducing agent adhering to the wall surface of the exhaust passage due to the injection of the reducing agent injector,
Determining whether the reducing agent attached to the wall surface of the exhaust passage is solidified based on the amount of the attached reducing agent and the piping temperature of the exhaust passage and/or the temperature of the exhaust gas,
configured to limit execution of the abnormality determination when it is determined that the reducing agent has solidified;
When the pipe temperature is lower than a predetermined temperature, the processing device controls the wall surface of the exhaust passage based on the relationship between the pipe temperature and the solidification rate such that the higher the pipe temperature, the higher the solidification rate of the reducing agent. configured to determine solidification of the reducing agent attached to the
An engine exhaust purification device characterized by: a reducing agent injector that injects ammonia or an ammonia precursor as a reducing agent into an exhaust passage of an engine;
a selective reduction type NOx catalyst that reduces NOx in exhaust gas using the reducing agent injected by the reducing agent injector;
a NOx sensor that is provided on the exhaust passage downstream of the selective reduction NOx catalyst and whose output value changes depending on the amount of NOx and the amount of ammonia in the exhaust gas;
a processing device that determines an abnormality with respect to the selective reduction type NOx catalyst based on the output value of the NOx sensor;
An exhaust purification device for an engine having
The processing device includes:
Determining the amount of adhering reducing agent, which is the amount of the reducing agent adhering to the wall surface of the exhaust passage due to the injection of the reducing agent injector,
Determining whether the reducing agent attached to the wall surface of the exhaust passage is solidified based on the amount of the attached reducing agent and the piping temperature of the exhaust passage and/or the temperature of the exhaust gas,
configured to limit execution of the abnormality determination when it is determined that the reducing agent has solidified;
The processing device includes:
Determining the concentration of the reducing agent attached to the wall surface of the exhaust passage based on the temperature of the exhaust gas, the flow rate of the exhaust gas, and the injection rate of the reducing agent by the reducing agent injector;
Based on the amount of the reducing agent attached and the concentration of the reducing agent, determine the amount of water in the reducing agent attached to the wall surface of the exhaust passage,
It is configured to determine that the reducing agent attached to the wall surface of the exhaust passage is solidified when the moisture content of the reducing agent is 0.
An engine exhaust purification device characterized by: a reducing agent injector that injects ammonia or an ammonia precursor as a reducing agent into an exhaust passage of an engine;
a selective reduction type NOx catalyst that reduces NOx in exhaust gas using the reducing agent injected by the reducing agent injector;
a NOx sensor that is provided on the exhaust passage downstream of the selective reduction NOx catalyst and whose output value changes depending on the amount of NOx and the amount of ammonia in the exhaust gas;
a processing device that determines an abnormality with respect to the selective reduction type NOx catalyst based on the output value of the NOx sensor;
An exhaust purification device for an engine having
The processing device includes:
Determining the amount of adhering reducing agent, which is the amount of the reducing agent adhering to the wall surface of the exhaust passage due to the injection of the reducing agent injector,
Determining whether the reducing agent attached to the wall surface of the exhaust passage is solidified based on the amount of the attached reducing agent and the piping temperature of the exhaust passage and/or the temperature of the exhaust gas,
configured to limit execution of the abnormality determination when it is determined that the reducing agent has solidified;
The processing device includes:
Determining the concentration of the reducing agent attached to the wall surface of the exhaust passage based on the temperature of the exhaust gas, the flow rate of the exhaust gas, and the injection rate of the reducing agent by the reducing agent injector;
Based on the amount of the reducing agent attached and the concentration of the reducing agent, determine the amount of water in the reducing agent attached to the wall surface of the exhaust passage,
Based on the piping temperature, determine the amount of evaporation of the reducing agent attached to the wall surface of the exhaust passage,
It is configured to determine that the reducing agent attached to the wall surface of the exhaust passage is solidified when the amount obtained by subtracting the evaporation amount of the reducing agent from the moisture content of the reducing agent is 0.
An engine exhaust purification device characterized by: When the predetermined temperature is a first predetermined temperature, and the pipe temperature is a second predetermined temperature or higher that is higher than the first predetermined temperature, the processing device is configured to increase the solidification rate of the reducing agent as the pipe temperature increases. The engine exhaust gas according to claim 1 or 2 , wherein the engine exhaust gas is configured to determine solidification of the reducing agent adhering to the wall surface of the exhaust passage based on the relationship between the pipe temperature and the solidification rate, which increase. Purification device. The absolute value of the rate of change in the solidification rate of the reducing agent with respect to a change in the pipe temperature when the pipe temperature is below the predetermined temperature is The engine exhaust gas purification device according to any one of claims 1, 2, and 5 , wherein the absolute value of the rate of change in the solidification rate of the reducing agent is higher than the absolute value.

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