JP2012036837A - Diagnostic device for exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide diagnostic device for an exhaust emission control device, which correctly diagnoses a decrease in urea water concentration and which discriminates between catalyst degradation and the decrease of the urea water concentration.SOLUTION: The diagnostic device for the exhaust emission control device is applied to a urea SCR system including: an oxidation catalyst 2 with oxidation capacity for components in exhaust gas; a urea water adding device 11 for adding urea water into the exhaust gas; and a selective reduction catalyst 5 for reducing nitrogen oxides in the exhaust gas to nitrogen, from the upstream side of an exhaust passage 16. An exhaust sensor 9 for detecting the concentration of the nitrogen oxides on a downstream side with respect to the selective reduction catalyst 5, and a ratio detecting means 14 for detecting the ratio of the amount of substance of nitrogen dioxide to the amount of substance of nitrogen monoxide contained in the exhaust gas at the downstream side of the oxidation catalyst 2 are provided. Additionally, a determining means 8d for determining whether the urea water concentration is proper, on the basis of the ratio detected by the ratio detecting means 14 and the concentration of the nitrogen oxides detected by the exhaust sensor 9, is provided.

Description

  The present invention relates to a diagnostic device for diagnosing the concentration of urea water in an exhaust purification device that purifies engine exhaust by adding urea water.

Conventionally, an exhaust purification system using a urea addition type selective reduction catalyst (urea SCR (Selective Catalytic Reduction) catalyst) as a catalyst for removing nitrogen oxide (NOx) contained in vehicle exhaust gas has been known. Yes. That is, an aqueous urea solution as a reducing agent is injected into the exhaust passage upstream of the selective reduction catalyst, ammonia (NH ₃ ) is generated by hydrolysis of urea, and NOx is reduced to nitrogen and water with NH _3. is there. A system using a selective reduction catalyst is effective for purifying NOx in an atmosphere having a relatively high oxygen concentration, such as exhaust from a diesel engine, or at a low temperature.

In a general urea SCR system, an amount of urea water having an equivalent ratio of 1 with respect to the amount of NOx discharged from the engine is supplied. On the other hand, the amount of NH ₃ produced by hydrolysis of urea water depends on the concentration of urea water, so if the concentration of urea water is lower than the normal concentration, the intended amount of NOx cannot be purified. . Thus, a system has been developed in which a urea identification sensor for confirming the concentration of urea water is provided in a tank for storing urea water. However, such a urea identification sensor is expensive, and there is a problem that the cost of the entire system increases.

  In order to solve such a problem, a technique for confirming the concentration of urea water using a NOx sensor instead of a urea identification sensor has been proposed. For example, in Patent Document 1, when the NOx purification rate is calculated based on the NOx concentration detected by the NOx sensor and the NOx purification rate decreases after the urea water is replenished, the urea water concentration in the urea water tank is reduced. A technique for presuming that it has decreased is disclosed. In this technique, the remaining amount of urea water and the presence or absence of replenishment are determined using a level sensor provided in the urea water tank.

JP 2009-79584 A

However, the cause of the decrease in the NOx purification rate is not always the decrease in the urea water concentration. For example, the NOx purification rate may decrease due to catalyst deterioration. Therefore, in the conventional technique as described in Patent Document 1, there is a problem that the reliability of the estimation that the urea water concentration has decreased is poor, and it is difficult to grasp the true cause of the decrease in the NOx purification rate. . In addition, it is difficult to distinguish between such deterioration of the catalyst and a decrease in urea water concentration.
Moreover, in the technique of Patent Document 1, since it is necessary to provide a level sensor in the urea water tank, even if the urea identification sensor is omitted, the cost may increase.

This case has been devised in view of the above problems, and it is possible to correctly diagnose a decrease in urea water concentration and to diagnose exhaust gas purification devices that can distinguish between catalyst deterioration and urea water concentration decrease. An object is to provide an apparatus.
The present invention is not limited to this purpose, and is a function and effect derived from each configuration shown in the embodiments for carrying out the invention described later, and other effects of the present invention are to obtain a function and effect that cannot be obtained by conventional techniques. Can be positioned.

(1) A diagnostic device for an exhaust emission control device disclosed herein is provided in an exhaust passage of an engine, has an oxidation catalyst having an oxidizing ability for components in exhaust, and is provided downstream of the oxidation catalyst. Applied to a urea SCR system provided with a urea water addition device for adding urea water, and a selective reduction catalyst that is provided downstream of the urea water addition device and reduces nitrogen oxides in exhaust to nitrogen .
In the above system, an exhaust sensor that detects the concentration of the nitrogen oxide downstream of the selective reduction catalyst, and a nitrogen dioxide substance amount relative to a nitrogen monoxide substance amount contained in the exhaust gas downstream of the oxidation catalyst And ratio detecting means for detecting the ratio of
Whether the concentration of the urea water added from the urea water addition device is appropriate based on the ratio detected by the ratio detection unit and the concentration of the nitrogen oxide detected by the exhaust sensor. A determination means for determining whether or not is provided.

The number ratio here is a molar ratio (ratio of the number of molecules per unit volume), which corresponds to the molar fraction (concentration) ratio.
The ratio detection means may be configured to detect the ratio of the amount of nitrogen dioxide to the amount of nitrogen oxide (total of nitrogen monoxide and nitrogen dioxide) contained in the exhaust gas downstream of the oxidation catalyst.

(2) In the determination unit, the ratio detected by the ratio detection unit is approximately one-to-one, the urea water is added from the urea water addition device, and is detected by the exhaust sensor. When the concentration of the nitrogen oxide is less than a predetermined concentration, it is determined that the concentration of the urea water is appropriate.
In this case, it is a condition for determining that the concentration of the urea water is appropriate that the number of moles of nitric oxide and the number of moles of nitrogen dioxide are substantially the same. The predetermined concentration of nitrogen oxide is a minute concentration close to zero.
In an environment where the ratio of the number of nitrogen monoxide and nitrogen dioxide is almost one-to-one, the reduction reaction of nitrogen oxides in the selective reduction catalyst is promoted and the nitrogen oxide purification rate is improved compared to other environments. In addition, it is less susceptible to the deterioration of the selective reduction catalyst.

(3) The ratio detection means includes exhaust temperature estimation means for estimating the exhaust temperature inside the oxidation catalyst, and the exhaust temperature estimated by the exhaust temperature estimation means is a predetermined thermal dissociation temperature (NO It is preferable to detect that the ratio is approximately one to one when ₂ → NO thermal dissociation temperature.
(4) The thermal dissociation temperature is preferably in the range of 350 to 450 ° C.

(5) The apparatus further comprises oxygen concentration detection means for detecting the oxygen concentration inside the oxidation catalyst and exhaust pressure detection means for detecting the exhaust pressure inside the oxidation catalyst, wherein the ratio detection means comprises the oxygen concentration The thermal dissociation temperature is preferably calculated based on the exhaust pressure and the exhaust temperature.
(6) Further, the ratio detection means, when the exhaust temperature estimated by the exhaust temperature estimation means falls from the state higher than the thermal dissociation temperature to become the thermal dissociation temperature, It is preferable to detect that the ratio is approximately one to one.

(7) A catalyst filter provided downstream of the oxidation catalyst and upstream of the selective reduction catalyst for collecting particulates contained in exhaust gas and burning the collected particulates. Prepare.
When the exhaust gas temperature estimated by the exhaust gas temperature estimating unit decreases from the state where the exhaust gas temperature is equal to or higher than the combustion temperature of the particulates in the catalytic filter and reaches the thermal dissociation temperature, Detect that the ratio is approximately one to one.
That is, the determination of the urea water concentration is performed immediately after the regeneration control of the catalyst filter.
(8) In addition, it is preferable to provide the alerting | reporting means which alert | reports the result of determination by the said determination means to a passenger | crew.

(1) According to the disclosed exhaust gas purifying apparatus diagnosis apparatus, it is possible to identify an environment for determining whether or not the concentration of urea water is appropriate by grasping the exhaust gas component ratio. Can be correctly diagnosed. Further, it is possible to diagnose a decrease in urea water concentration in an environment that does not depend on catalyst deterioration, that is, it is possible to distinguish between catalyst deterioration and urea water concentration decrease.
Further, a sensor for detecting the component and concentration of urea water is not necessary, and the configuration of the exhaust system can be simplified. Furthermore, the exhaust sensor that originally detects the concentration of nitrogen oxides can be given a function as a sensor for determining the concentration of urea, and the cost of the exhaust purification system can be reduced.

  (2) The determination in an environment where nitrogen oxides are likely to be reduced makes it possible to reliably grasp that the concentration of urea water is inappropriate (the concentration of urea water is low), and the determination accuracy of the urea water concentration Can be improved. Also, for example, by observing the reduction reaction of nitrogen oxides in a temperature range that is not affected even if the oxidation catalyst that generates nitrogen dioxide deteriorates, the deterioration of the oxidation catalyst and the decrease in urea water concentration are discriminated. be able to.

(3) By estimating the ratio based on the NO ₂ → NO thermal dissociation temperature, it is possible to easily and accurately grasp the environment in which nitrogen oxides are likely to be reduced, and the determination accuracy of urea water concentration is further improved. Can be made.
(4) It is possible to easily grasp an environment in which the ratio of nitrogen monoxide and nitrogen dioxide is approximately one to one, and the control configuration can be simplified.

(5) By using oxygen concentration, exhaust pressure and exhaust temperature, the thermal dissociation temperature can be calculated accurately, and the environment in which the ratio of nitrogen monoxide and nitrogen dioxide is almost one to one can be accurately grasped. It becomes possible. Thereby, the determination accuracy of the urea water concentration can be further improved.
(6) By making the target of determination control only when the exhaust gas temperature decreases, the thermal dissociation temperature can be accurately estimated.

(7) By burning the particulates on the catalyst filter immediately before the determination of the urea water concentration, it is possible to determine the urea water concentration without consuming nitrogen oxides upstream of the selective reduction catalyst, The determination accuracy can be further improved. In addition, since the ammonia adsorbed on the selective reduction catalyst can be consumed by the regeneration control of the catalyst filter, the influence of only the urea water concentration can be observed, and the determination accuracy of the urea water concentration is further improved. be able to.
(8) When it is determined that the urea water concentration is not appropriate, a notification to that effect is given to the occupant, thereby prompting maintenance or replacement of the urea water.

It is a figure which illustrates typically the whole structure of the diagnostic device of the exhaust-air-purification device concerning one embodiment. It is a graph for demonstrating the characteristic of the oxidation catalyst which concerns on the diagnostic apparatus of FIG. 2 is a graph illustrating the relationship between the catalyst temperature of the selective reduction catalyst of FIG. 1 and the maximum ammonia adsorption amount. It is a graph showing the relationship between the NO ₂ ratio of the diagnostic device of FIG. 1 and the exhaust temperature. Is a graph illustrating the relationship between the deterioration and the NO ₂ ratio of the oxidation catalyst according to the diagnostic device of FIG. 2 is a graph illustrating the relationship between the operating state of the engine of FIG. 1 and the concentration of nitrogen oxides contained in exhaust gas. It is a flowchart which illustrates the control content in the diagnostic apparatus of FIG. 2A and 2B are graphs for explaining control by the diagnostic device of FIG. 1, in which FIG.

  Hereinafter, a diagnostic device for an exhaust emission control device will be described with reference to the drawings. Note that the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described in the following embodiment.

[1. Constitution]
[1-1. overall structure]
The exhaust gas purifying apparatus diagnosis apparatus 10 of this embodiment is applied to the vehicle intake and exhaust system illustrated in FIG. An engine 20 in FIG. 1 is a diesel engine using light oil as a fuel, and an exhaust passage 16 and an intake passage 17 are connected to the engine 20. Intake air is introduced into the combustion chamber of each cylinder of the engine 20 via the intake passage 17, and exhaust gas after combustion is discharged to the outside via the exhaust passage 16.

  A turbocharger 18, a DPF (Diesel Particulate Filter) device 1, and an SCR (Selective Catalytic Reduction) device 4 are interposed in the exhaust passage 16 in order from the upstream side of the exhaust flow. The DPF device 1 is a continuous regeneration type filtration device, and the SCR device 4 is a purification device for removing NOx contained in the exhaust gas.

  The turbocharger 18 is a supercharger interposed so as to straddle the exhaust passage 16 and the intake passage 17. The turbocharger 18 rotates the turbine with the exhaust pressure of the exhaust gas flowing through the exhaust passage 16 and uses the rotational force. By driving the compressor, the intake air from the intake passage 17 is compressed and the engine 20 is supercharged.

A urea injector 11 is provided between the DPF device 1 and the SCR device 4 on the exhaust passage 16. The urea injector 11 is a nozzle that sprays an aqueous solution of urea [CO (NH ₂ ) ₂ ] into the exhaust gas. Here, urea added to the exhaust gas is thermally decomposed and hydrolyzed to NH ₃ by exhaust heat.

An exhaust pressure sensor 12, an oxygen concentration sensor 13, and a temperature sensor 14 are provided upstream of the DPF device 1. The exhaust pressure sensor 12 is a pressure sensor that detects the pressure P _E (exhaust pressure) of the exhaust flowing into the DPF device 1. The oxygen concentration sensor 13 detects the oxygen concentration _CE of the exhaust flowing into the DPF device 1, and the temperature sensor 14 detects the exhaust temperature T ₁ flowing into the DPF device 1. The detected pressure P _E , oxygen concentration C _E and exhaust temperature T ₁ are input to the controller 7 described later.

An air flow sensor 22 is provided at an arbitrary position on the intake passage 17 (for example, upstream of the throttle valve). The air flow sensor 22 is a flow rate sensor that detects an intake air amount Q introduced into the cylinder of the engine 20. An accelerator opening sensor 23 is provided at an arbitrary position of the intake / exhaust system. The accelerator opening sensor 23 detects an operation amount θ _AC (accelerator opening) of the accelerator pedal by the driver. The engine 20 is controlled to have an output corresponding to the accelerator opening θ _AC by the action of an engine ECU (not shown). Therefore, the accelerator opening θ _AC is an index of the torque (load) of the engine 20.

Further, in the vicinity of the crankshaft 21 of the engine 20, an engine speed sensor 24 for detecting an engine speed N _e is provided. The detected intake air amount Q by the air flow sensor 22, the detected accelerator opening theta _AC accelerator opening sensor 23, an engine speed N _e detected by the engine speed sensor 24 is inputted to the controller 7 which will be described later ing.

[1-2. DPF device]
The DPF device 1 includes a DOC (Diesel Oxidation Catalyst) catalyst 2 disposed on the upstream side and a filter 3 disposed on the downstream side. This DPF device 1 has both a function of collecting PM (Particulate Matter, particulate matter) contained in exhaust gas and a function of continuously oxidizing and removing the collected PM. In addition, PM is a particulate substance in which fuel, lubricating oil components, sulfur compounds, and the like that remain unburned around black smoke (soot) made of carbon adhere.

The DOC catalyst 2 is an oxidation catalyst having an oxidizing ability with respect to components in exhaust gas, and is a catalyst in which a catalyst material is supported on a honeycomb-shaped carrier made of metal, ceramics or the like. Examples of components in the exhaust gas oxidized by the DOC catalyst 2 include nitrogen monoxide (NO) and hydrocarbons in unburned fuel. For example, when NO is oxidized by the DOC catalyst 2, nitrogen dioxide (NO ₂ ) is generated. The chemical reaction formula of the oxidation reaction of NO in the DOC catalyst 2 is illustrated below.
2NO + O ₂ → 2NO ₂ (Formula 1)

The DOC catalyst 2 has catalytic characteristics indicated by a solid line in FIG. The horizontal axis represents the exhaust temperature in the vicinity of the catalyst (also simply referred to as catalyst temperature), and the vertical axis represents the ratio of the NO ₂ concentration produced by the DOC catalyst 2 to the NO concentration in the exhaust. The DOC catalyst 2 hardly exhibits the ability to oxidize NO when the catalyst temperature is extremely low, and increases the amount of NO ₂ generated as the catalyst temperature increases. Further, when the catalyst temperature becomes a predetermined first activation temperature T _A or more areas, and generates the NO ₂ at a substantially constant rate with respect to the NO concentration. Note that the first activation temperature T _A is a value corresponding to such kind and amount of catalyst supported, for example, 200 [° C.] about.

A graph indicated by a broken line in FIG. 2 shows a change in catalyst characteristics when the DOC catalyst 2 deteriorates. When the DOC catalyst 2 is deteriorated or poisoned, the amount of NO ₂ generated at a low temperature decreases, and the increasing gradient of the NO ₂ generation rate with respect to the increase in the catalyst temperature decreases. As indicated by the white arrow in FIG. 2, the graph moves to the right as the deterioration progresses, and the catalyst temperature for obtaining the same NO ₂ production rate increases.

  The filter 3 is a porous filter (for example, a ceramic filter) that collects PM. The interior of the filter 3 is divided into a plurality along the flow direction of the exhaust gas by a porous wall. A large number of pores having a size commensurate with the particulates of PM are formed in the wall. When exhaust passes near or inside the wall, PM is collected on the wall and on the wall surface, and the exhaust is filtered.

In addition, as the filter 3 of the DPF device 1, a filter having a catalytic noble metal supported on the surface thereof may be used. In this case, exhaust particulates are incinerated using nitrogen dioxide or the like in the exhaust as an oxidizing agent. Thereby, PM collected by the filter 3 is removed, and the filter 3 is regenerated and purified. The chemical reaction formula of the PM combustion reaction in the filter 3 is illustrated below.
C + 2NO ₂ → 2NO + CO ₂ (Formula 2)
C + O ₂ → CO ₂ ... (Formula 3)

In this embodiment, the filter 3 is regenerated and purified by a continuous regeneration method in which PM is burned with NO ₂ during normal driving of the vehicle, and the filter 3 is regenerated and purified by a forced regeneration method in which PM is burned with O _{2 as} necessary. Is done. The reaction shown in Formula 2 is a PM combustion reaction at a low temperature, and proceeds mainly during regeneration control by the continuous regeneration system. Moreover, the reaction shown in Formula 3 is a PM combustion reaction at a high temperature, and proceeds mainly during regeneration control by the forced regeneration method. The exhaust temperature necessary for burning PM on the filter 3 during forced regeneration is referred to as regeneration temperature T _F (for example, 550 to 600 [° C.]).

[1-3. SCR device]
The SCR device 4 incorporates an SCR catalyst 5 (selective reduction catalyst) disposed on the upstream side and a CUC (Clean Up Catalyst) catalyst 6 disposed on the downstream side thereof.
The SCR catalyst 5 is a urea-added nitrogen oxide selective reduction catalyst that adsorbs NH ₃ supplied from the upstream side and reduces the NOx in the exhaust to nitrogen using the adsorbed NH ₃ as a reducing agent. It is.

As shown in FIG. 3, the maximum value of the adsorption amount of NH ₃ on the SCR catalyst 5 increases as the catalyst temperature of the SCR catalyst 5 is lower, and decreases as the temperature is higher. Further, when the catalyst temperature is equal to or higher than a predetermined consumption temperature T _C (for example, about 400 ° C. or higher), NH ₃ is almost completely consumed. The function of adsorbing NH ₃ is not an essential function for the SCR catalyst 5. The type of the catalyst is arbitrary, and for example, it is conceivable to use a catalyst such as zeolite or vanadium.

Reduction reaction of NOx in the SCR catalyst 5, catalyst temperature of SCR catalyst 5 is higher than a predetermined second activation temperature T _B (e.g., above about 200 ° C.) occurs when a reaction rate higher catalyst temperature is a high temperature Rises. The chemical reaction formula for the decomposition reaction of urea is exemplified below.
CO (NH ₂ ) ₂ → HNCO + NH ₃ (Formula 4)
HNCO + H ₂ O → NH ₃ + CO ₂ (Formula 5)

The chemical reaction formula of the NOx reduction reaction in the SCR catalyst 5 is exemplified below. In the SCR catalyst 5, three types of reactions occur. Among these reactions, the reaction of Formula 8 in which NO and NO ₂ react in equimolar ratios is faster than the reactions of Formulas 6 and 7 from the temperature range where the catalyst temperature is 200 ° C. or lower. proceed. The reaction of the formula 6 has the slowest reaction rate. In the present diagnostic apparatus 10, it is determined whether or not the concentration of urea water is appropriate by referring to the NOx concentration in an environment where the reaction of Formula 8 is likely to occur.
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (Formula 6)
8NH ₃ + 6NO ₂ → 7N ₂ + 12H ₂ O (Formula 7)
NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (Formula 8)

The CUC catalyst 6 is an oxidation catalyst for removing excess NH ₃ (slip NH ₃ ) in the reduction reaction of the SCR catalyst 5. A chemical reaction formula of the oxidation reaction of NH ₃ in the CUC catalyst 6 is illustrated below.
4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O (Formula 9)

[1-4. NO ₂ ratio]
Here, in relation to the NOx reduction reaction at the SCR catalyst 5, the molar fraction (molar concentration, substance) of NOx contained in the exhaust gas flowing into the SCR catalyst 5 (that is, the exhaust gas downstream from the DPF device 1). The mole fraction of NO ₂ with respect to (amount) is called the NO ₂ ratio. For example, NO ₂ ratio of the exhaust gas NO ₂ is not present is 0, NO ₂ ratio of the exhaust gas present in NO and NO ₂ transgression equimolar is 0.5.
Note that a molar ratio (amount of substance) of NO and NO ₂ may be used instead of the NO ₂ ratio. These values can be converted to each other. For example, it is synonymous that the NO ₂ ratio is 0.5 and that the ratio of the number of NO and NO ₂ (physical quantity) is 1: 1.

FIG. 4 shows the relationship between the upper limit value of the NO ₂ ratio and the exhaust temperature when a typical vehicle exhaust system is assumed. The upper limit of the NO ₂ ratio is 1.0 when the exhaust gas temperature is low. For example, the exhaust temperature of the DOC catalyst 2 vicinity when it is about the first activation temperature T _A is substantially all of the produced NO ₂ is shown to be present in the exhaust.

On the other hand, the higher the exhaust gas temperature, the more active NO ₂ changes to stable NO (thermal dissociation), and the NO ₂ ratio decreases. The amount of NO _{2 that} thermally dissociates is determined by temperature and the like, and the ratio is always constant. For example, placing the temperature at which the NO ₂ ratio 0 shown in FIG. 4 with a predetermined temperature T _D, since the exhaust gas temperature is NO ₂ when a predetermined temperature T _D is not present in the exhaust, if NO in DOC catalyst 2 _{Even if 2} is produced, NO ₂ immediately thermally dissociates into NO due to chemical equilibrium.

As shown in FIG. 5, the relationship between the exhaust NO ₂ ratio and the exhaust temperature on the downstream side of the DOC catalyst 2 can be expressed as a superposition of the graphs of FIGS. 2 and 4. Here, when the exhaust gas temperature is _lower than the first activation temperature T _A , the NO ₂ ratio is defined by the catalyst characteristics (NO ₂ generation capability) of the DOC catalyst 2, and when the exhaust temperature is equal to or higher than the first activation temperature T _A , ₂ ratio is defined by the equilibrium action of NO and NO _2.

Further, when the DOC catalyst 2 deteriorates, the graph shifts to the high temperature side as shown by the white arrow in FIG. 5, and the NO ₂ ratio changes as shown by the broken line. At this time, the NO ₂ ratio defined by the former decreases, whereas the NO ₂ ratio defined by the latter does not change. For example, when the exhaust temperature NO ₂ ratio defined by the latter of 0.5 is T _E, regardless of the degree of deterioration of the DOC catalyst 2, NO ₂ ratio when the exhaust temperature is T _E is 0.5. Hereinafter, NO ₂ ratio by thermal dissociation of NO ₂ (equilibrium during dissociation from NO ₂ to NO) is referred to as 0.5 and comprising thermal dissociation temperature T _E to a exhaust temperature (NO ₂ → NO heat dissociation temperature).

It should be noted that the relationship between the NO ₂ ratio and temperature defined by the latter varies depending on the chemical equilibrium reaction between NO and NO ₂ . That is, the shape and thermal dissociation temperature T _E in the graph of FIG. 4 is changed according to the state of the exhaust gas NO and NO ₂ is present.
More precisely, the NO ₂ ratio is described as a function of the exhaust temperature T ₁ , the exhaust pressure P _E and the oxygen concentration C _E. Therefore, the controller 7 of the diagnostic apparatus 10 accurately grasps the environment in which the reaction of the above formula 8 is likely to occur, that is, the environment where the NO ₂ ratio is 0.5, and refers to the NOx concentration in the environment. To control the concentration of urea water. The configuration of the controller 7 will be described in detail below.

[2. controller]
The controller 7 [ECU, Engine (electronic) Control Unit] is an electronic control unit that comprehensively manages the intake / exhaust system including the engine 20, and is an LSI device in which a microprocessor, ROM, RAM, and the like are integrated. In the controller 7, in addition to the regeneration control of the filter 3, the urea water injection control from the urea injector 11, the diagnostic control of the urea water concentration, the intake air related to the air-fuel ratio of the mixture of the engine 20 and the combustion reaction in the cylinder The amount, fuel injection amount, fuel injection timing, ignition timing, exhaust temperature, etc. are controlled.

  The NOx sensor 9, exhaust pressure sensor 12, oxygen concentration sensor 13, temperature sensor 14, air flow sensor 22, accelerator opening sensor 23, and engine speed sensor 24 are connected to the input side of the controller 7. Further, a urea injector 11, a control device (engine ECU) for the engine 20, and a notification device 15 (notification means) are connected to the output side of the controller 7. The notification device 15 is an output device including a display device such as a display and a lamp and an acoustic device such as a speaker and a buzzer, and is attached to, for example, an instrument panel in the passenger compartment.

In the present embodiment, among the functions implemented in the controller 7, mainly three types of control, namely filter regeneration control, urea water addition control, and urea water concentration diagnostic control will be described.
The filter regeneration control is control for purifying the filter 3 by forcibly burning the PM collected by the filter 3. The starting conditions for this control are, for example, that the vehicle travel distance has exceeded a predetermined distance (for example, 500 [km]) since the previous filter regeneration control was performed, and that the estimated amount of PM accumulated on the filter 3 Is over a predetermined amount.

The environmental conditions necessary for obtaining a predetermined PM combustion efficiency by the filter regeneration control are that the exhaust gas temperature flowing into the filter 3 is equal to or higher than the predetermined regeneration temperature T _F , and the state is a predetermined time (for example, several 10 seconds) and so on. Therefore, in the filter regeneration control, the exhaust gas temperature is adjusted so that the temperature of the filter 3 is maintained at the regeneration temperature T _F or higher for a predetermined time. In the filter regeneration control, the higher the oxygen concentration in the exhaust, the better the PM combustion state.

The urea water addition control is control for appropriately injecting urea water from the urea injector 11 so that NH ₃ is always adsorbed on the SCR catalyst 5. The adsorption amount of NH _{3 on} the SCR catalyst 5 is calculated based on the amount of urea water injected, the catalyst temperature of the SCR catalyst 5, the estimated value of the NOx amount flowing into the SCR catalyst 5, and the like. The starting condition of this control is, for example, that a predetermined time has elapsed since the previous urea water addition control was performed, or that the NH ₃ adsorption amount became less than a predetermined minimum value.

The urea water concentration diagnostic control is a control for diagnosing whether or not the concentration of the urea water injected from the urea injector 11 is an appropriate concentration, and informing the passenger when the concentration is considered to be low. . Here, it is determined that the urea water concentration is low when all of the following conditions are satisfied.
[Condition A] Exhaust temperature is decreasing after filter regeneration control is performed [Condition B] Exhaust state in which the NO ₂ ratio is approximately 0.5 [Condition C] A predetermined time has elapsed after the addition of urea water [Condition D] The detected value C _{1 of the} NOx sensor is less than the predetermined value C ₀

  As shown in FIG. 1, since the NOx sensor 9 is provided on the most downstream side of the exhaust passage 16, even if the NOx value detected by the NOx sensor 9 simply increases and the NOx purification rate decreases, It is important to judge the cause separately from the deterioration of the DOC catalyst 2. The controller 7 of the present embodiment increases the NOx value (decreases the NOx purification rate) by providing additional conditions such as [Condition A], [Condition B], and [Condition C] with respect to [Condition D]. Identify the cause of

[3. Controller functions]
Functions programmed as software or hardware circuits inside the controller 7 are schematically shown in FIG. In the case of software, the function described below is realized by recording the software in a memory or storage device (not shown) and reading it to a CPU (Central Processing Unit) (not shown) as needed.

The controller 7 is provided with a regeneration control unit 7a, a urea water addition control unit 7b, and a concentration determination control unit 8.
The regeneration control unit 7a performs filter regeneration control. The regeneration control unit 7a determines a filter regeneration control start condition based on information transmitted from a timer, an engine ECU, or the like (not shown), and raises the exhaust temperature discharged from the engine 20 when the start condition is satisfied. Thereby, the exhaust gas temperature introduced into the filter 3 rises, and the PM collected by the filter 3 burns.

The urea water addition control unit 7b performs urea water addition control, and includes an engine exhaust NOx amount estimation unit 7c and an NH ₃ adsorption amount calculation unit 7d. The engine exhaust NOx amount estimation unit 7b estimates and calculates the NOx amount (that is, the engine out NOx amount) contained in the exhaust immediately after being exhausted from the engine 20.
As shown in FIG. 6, the engine exhaust NOx amount estimation unit 7c stores a map describing the correspondence between the operating state of the engine 20 and the NOx amount (NOx concentration) exhausted from the engine 20 at that time. Yes. The engine exhaust NOx amount estimation unit 7c calculates the engine out NOx amount based on the intake air amount Q, the accelerator opening degree θ _AC , the engine speed _Ne, and this map.

The engine out NOx amount tends to increase as the load acting on the engine 20 increases (the torque generated by the engine 20 increases). Further, as shown by a broken line in FIG. 6, when conveniently divided into three regions according to the operating state to the magnitude of the engine speed N _e, in the operating state of low rotation region and the high rotation speed region, the middle There is a tendency for the NOx concentration in the exhaust to increase compared to the operating state in the middle rotation region. Such a tendency becomes more prominent as the load acting on the engine 20 is larger.

NH ₃ adsorption amount calculating portion 7d is for calculating the amount of adsorption of NH ₃ adsorbed on the SCR catalyst 5. The adsorption amount of NH ₃ decreases as the amount of NOx reduced by the SCR catalyst 5 increases, and recovers when urea water is added from the urea injector 11. Note that the maximum value of the adsorption amount of NH ₃ depends on the catalyst temperature of the SCR catalyst 5.

This NH ₃ adsorption amount calculation unit 7d assumes that the amount of NH ₃ required to reduce all of the engine-out NOx amount calculated by the engine exhaust NOx amount estimation unit 7c is consumed on the SCR catalyst 5. The amount of NH ₃ is subtracted from the amount of adsorption at that time, and the amount of adsorption of NH ₃ is updated. Thereby, when urea water is not injected from the urea injector 11, the estimated value of the adsorption amount of NH ₃ on the SCR catalyst 5 gradually decreases.

When the maximum value of the adsorption amount becomes smaller than the adsorption amount at that time due to the decrease in the catalyst temperature of the SCR catalyst 5, the adsorption amount is updated to the maximum value at that time. In this case, a part of the adsorbed NH ₃ slips downstream. The slipped NH ₃ is purified by the CUC catalyst 6.

When the adsorption amount X becomes less than a preset minimum value, the NH ₃ adsorption amount calculation unit 7d outputs a control signal to the urea injector 11 to inject urea water. Thus, the adsorbed NH ₃ amount calculation unit 7d, the control for injecting the urea water as the amount of adsorption of NH ₃ is automatically replenished this Decreasing carried out.
In the present embodiment, after the filter regeneration control is performed, the NH ₃ adsorption amount calculation unit 7d is also operated when the exhaust temperature _TG reaches a predetermined injection temperature T _H higher than a thermal dissociation temperature T _E described later. A control signal is output to the injector 11 to inject urea water. The predetermined injection temperature T _H is, for example, a temperature that is about 50 ° C. higher than the thermal dissociation temperature T _E.

The concentration determination control unit 8 performs urea water concentration diagnosis control, and includes a ratio detection unit 8a and a determination unit 8d. The ratio detection unit 8 a detects the NO ₂ ratio of the exhaust gas downstream of the DOC catalyst 2. Further, the determination unit 8d determines whether the concentration of urea water injected from the urea injector 11 is appropriate based on the NO ₂ ratio detected by the ratio detection unit 8a and the NOx concentration C ₁ detected by the NOx sensor 9. It is to determine whether or not.

The ratio detection unit 8a includes an exhaust temperature estimation unit 8b and a thermal dissociation temperature estimation unit 8c. The exhaust gas temperature estimation unit 8b estimates the exhaust gas temperature T _G (the catalyst temperature of the DOC catalyst 2) inside the DOC catalyst 2 based on the exhaust gas temperature T ₁ detected by the temperature sensor 14. Note that the estimation method of the catalyst temperature _TG of the DOC catalyst 2 is not limited to this, and for example, an estimation method using the exhaust temperature on the downstream side of the DOC catalyst 2 or taking this into account may be used.

The thermal dissociation temperature estimation unit 8c calculates a thermal dissociation temperature T _E , and here, the thermal dissociation temperature T _E is detected by the exhaust pressure sensor 12 and the oxygen concentration sensor 13 detects the oxygen pressure P _E. Calculation is performed based on the concentration _CE and the exhaust temperature T ₁ detected by the temperature sensor 14.
The equilibrium constant Kp related to the calculation of the thermal dissociation temperature T _E is a function of the exhaust temperature T ₁ . For example, the equilibrium constant Kp _(298K) of the exhaust having a temperature of 25 [° C.] (that is, 298 [K]) can be obtained as follows. However, R means a gas constant and ΔG means Gibbs energy.

Further, the equilibrium constant Kp _(T1) of exhaust at a temperature T ₁ other than 25 [° C.] can be obtained as follows. ΔH means enthalpy.

Using the above equilibrium constant Kp _(T1) , the molar fraction of NO ₂ when NO and NO ₂ are in equilibrium is expressed as follows. Where A, B and C ′ are the molar fractions of NO, O ₂ and NO ₂ at equilibrium, respectively, and P is the total exhaust pressure.

From Equations 10 to 12, the molar fraction (oxygen concentration C _E ) of exhaust temperature T ₁ , O ₂ , the molar fraction (concentration) of NO in equilibrium from the exhaust pressure P _E, and the molar fraction (concentration) of NO ₂ Is required. The thermal dissociation temperature estimation unit 8c such operation, NO ₂ ratio to calculate the thermal dissociation temperature T _E of 0.5.

The determination unit 8d determines an abnormality in urea water concentration (being lower than the normal concentration) based on a predetermined abnormality determination condition. Here, when all of the above-mentioned [Condition A] to [Condition D] are satisfied, it is determined that the urea aqueous solution concentration is low, and the notification device 15 is controlled to notify the passenger of the abnormality.
The exhaust state of [Condition B] is determined by comparing the thermal dissociation temperature T _E estimated by the thermal dissociation temperature estimation unit 8c and the exhaust temperature T _G estimated by the exhaust temperature estimation unit 8b. Since the exhaust gas temperature T _G is NO ₂ ratio is 0.5 when they match a thermal dissociation temperature T _E, the difference between the exhaust temperature T _G and the thermal dissociation temperature T _E is less than the predetermined value, NO ₂ ratio is 0.5 Can be considered.

If the exhaust temperature _TG is within a range of, for example, ± 50 [° C.] with the thermal dissociation temperature _TE as a median value, it is considered that the NO ₂ ratio can be regarded as 0.5.
The predetermined density C _{0 according} to the above [Condition D] is 0 or a minute value close to 0. The specific value varies depending on the performance of the NOx sensor 9, the type of the engine 20, the structure of the exhaust passage 16, etc., but may be set within a range of, for example, about 0 to 100 [ppm].

[4. flowchart]
FIG. 7 is a flowchart for explaining an example of control in the exhaust purification device 10. This flow is repeatedly performed inside the controller 7. In this flow, a control flag F is used. The flag F indicates whether or not the exhaust state is suitable for diagnosis of urea water concentration, and is normally set to F = 0. Further, when [Condition A] and [Condition B] are satisfied, F = 1 is set.

  In Step A10, it is determined whether or not the control flag F is F = 0. If F = 0, the process proceeds to step A20. If F = 1, the process proceeds to step A70. In Step A20, it is determined whether or not the filter regeneration control is performed in the regeneration control unit 7a.

Here, when the filter regeneration control is not performed or during execution of the filter regeneration control, [Condition A] is not yet satisfied, and thus the flow is finished as it is. Even in this case, since this flow is repeatedly performed, when the completion of the filter regeneration control is detected in the next and subsequent control cycles, the process proceeds to step A30.
The conditions for proceeding to step A30 can be changed. For example, the process may proceed to step A30 when, for example, the exhaust temperature T ₁ becomes equal to or higher than a predetermined regeneration temperature (for example, 550 [° C.]).

In step A30, the exhaust gas temperature estimation unit 8b estimates the exhaust gas temperature T _G (catalyst temperature) inside the DOC catalyst 2 based on the exhaust gas temperature T ₁ detected by the temperature sensor 14. The exhaust temperature _TG estimated here immediately after completion of the regeneration control is a high temperature close to the regeneration temperature _TF , and the exhaust temperature _TG decreases with time. In the subsequent step A40, the thermal dissociation temperature estimation unit 8c calculates the thermal dissociation temperature T _E based on the exhaust pressure P _E , the oxygen concentration C _E, and the exhaust temperature T ₁ . The thermal dissociation temperature T _E is elevated higher oxygen concentration C _E in the exhaust gas, it decreases the lower the oxygen concentration C _E. Further, exhaust pressure P _E is raised higher, the exhaust pressure P _E is decreased as low.

In the subsequent step A41, it is determined whether or not the exhaust gas temperature T _G estimated by the exhaust gas temperature estimation unit 8b is equal to or lower than a predetermined injection temperature T _H higher than the thermal dissociation temperature T _E obtained in the previous step. If T _G > T _H , the process returns to step A30, and the exhaust gas temperature T _G estimation calculation is continued. If T _G ≦ T _H , the process proceeds to step A42.
In Step A42, a control signal is output from the NH ₃ adsorption amount calculation unit 7d to the urea injector 11, and urea water is injected into the exhaust gas.

In step A50, the exhaust gas temperature T _G is whether a temperature close to the obtained thermal dissociation temperature T _E at Step A40 is determined. Here, for example, whether or not the exhaust gas temperature T _G is included in a predetermined temperature range having the thermal dissociation temperature T _E as a median value (that is, whether (T _E −α) ≦ T _G ≦ (T _E + α) holds). NO] is determined. Here, if the exhaust temperature T _G is substantially equal to the thermal dissociation temperature T _E, the process proceeds to step A60, the flag F is set to F = 1. Further, when the exhaust temperature T _G is not yet dropped to the vicinity of the thermal dissociation temperature T _E returns to step A30, to continue the estimation calculation of the exhaust temperature T _G.

In step A50, the above [Condition B] is determined. Until [Condition B] is satisfied, the NO ₂ ratio is relatively low and the amount of NO ₂ contained in the exhaust gas is small. Therefore, in the SCR catalyst 5, the reaction of the above equation 6 becomes the dominant environment. On the other hand, when [Condition B] is satisfied, the NO ₂ ratio becomes 0.5, and the reaction of the above equation 8 becomes the dominant environment. When the exhaust gas temperature _TG further decreases and the NO ₂ ratio increases, the reaction of the above equation 7 becomes the dominant environment.

In step A70, the urea water addition control unit 7b determines whether the urea water addition control has been performed within a predetermined time before this. The urea water addition control of the present embodiment is performed according to the increase or decrease of the NH ₃ adsorption amount on the SCR catalyst 5. Here, when urea water addition control is implemented, it progresses to step A80, and when not implemented, it progresses to step A150.

In step A150, it is determined whether or not the exhaust gas temperature T _G has dropped to a predetermined lower limit temperature T _MIN or less (for example, 300 [° C.] or less) where the NO ₂ ratio greatly deviates from 0.5. Here, if it is determined that the exhaust gas temperature T _G ≦ the lower limit temperature T _MIN , the flag F is set to F = 0 because it is considered inappropriate as an environment for diagnosing the urea water concentration ( Step A160), the flow ends. If it is determined that the exhaust gas temperature T _G > the lower limit temperature T _MIN , the flow ends without changing the flag F. In this case, when urea water addition control is performed in the next and subsequent control cycles, the control proceeds from step A70 to step A80.

In step A <b> 80, the concentration C ₁ detected by the NOx sensor 9 is input to the controller 7. Here, the integrated value of the NOx amount may be calculated based on the exhaust gas flow rate estimated from the concentration C ₁ and the intake air amount Q. In the subsequent step A90, it is determined whether or not a predetermined time has elapsed since the urea water addition control was performed. Here, for example, the elapsed time from step A42 is determined. The predetermined time set in this step is a time for preventing misdiagnosis immediately after the urea water addition control is performed, and may be set arbitrarily (for example, 0 to several tens of seconds). Until the predetermined time elapses, step A80 is repeatedly executed, and when the predetermined time elapses, the control proceeds to step A100.

At step A100, the determining unit 8d, the concentration C ₁ of the NOx is equal to or less than the predetermined concentration C ₀ is determined. The predetermined density C ₀ is a minute value close to 0. Here, if C ₁ <C ₀ , the process proceeds to step A110, and it is determined that the concentration of urea water is appropriate.
The flow after Step A90 is a flow executed in an exhaust environment where all of the above [Condition A], [Condition B] and [Condition C] are satisfied. At this time, in the SCR catalyst 5, the NOx reduction reaction of the above formula 8 is dominant, and NOx is purified at a high reaction rate. Thereby, the NOx purification rate in the SCR catalyst 5 is improved, and the detected NOx concentration C ₁ is less than the predetermined concentration C ₀ unless the concentration of urea water is lower than the normal concentration.

On the other hand, when the determination result in step A100 is C ₁ ≧ C ₀ , the NOx purification action in the SCR catalyst 5 is weakened. Therefore, control proceeds to step A120, and it is determined that the concentration of urea water is not appropriate. In subsequent step A130, the notification device 15 is controlled by the controller 7, and the fact that an abnormality has been detected in the concentration of urea water is displayed on a display device such as a display or a lamp. In addition, sound devices such as speakers and buzzers make announcements and warning sounds that prompt the passenger to replace and check urea water.

[5. Action, effect]
FIG. 8 (a) shows the variation over time of the exhaust gas temperature _TG during a running test of a vehicle equipped with the exhaust gas purification device diagnosis device 10, and FIG. 8 (b) shows the calculated value of the engine out NOx and the NOx sensor. 9 is a graph showing the variation with time of the NOx concentration C ₁ detected in FIG.

Time t ₁ in FIG. 8 (a) is a time when the filter regeneration control is started by the reproduction control unit 7a. The filter regeneration control is continued until time t ₂ , and the exhaust temperature _TG estimated by the exhaust temperature estimator 8 b is increased to the regeneration temperature _{TF of the} filter 3 or higher.
In the filter regeneration control, PM adsorbed on the filter 3 is burned, and NO ₂ in the exhaust is consumed. Furthermore, with increasing exhaust temperature T _G reduces the maximum value of the adsorption amount of the SCR catalyst 5 NH _3, the amount of adsorption of NH ₃ gradually decreases.

On the other hand, the filter regeneration control is reduced and the exhaust temperature T _G gradually completed time t _2, the a state of satisfied [condition A]. At this time, the thermal dissociation temperature estimation unit 8c of the controller 7 calculates the equilibrium constant Kp _(T1) according to the exhaust temperature T ₁ according to the above equations 10 to 12, and calculates the exhaust pressure P _E and the oxygen concentration C _E. A corresponding thermal dissociation temperature _TE is calculated.

Further, when the exhaust gas temperature T ₁ becomes the injection temperature T _H at time t ₃ , urea water is injected into the exhaust gas, and NH ₃ is replenished. Also, the determining unit 8d of the controller 7, the exhaust temperature T _G at time t ₄ is a state when it is determined that substantially equal to the thermal dissociation temperature T _E of [Condition B] is satisfied, in the exhaust NO and NO ₂ The ratio becomes 1 to 1. For example, if the injection temperature T _H is 50 [° C.] higher than the thermal dissociation temperature T _E , [Condition B] is satisfied when the exhaust temperature T ₁ decreases by 50 [° C.] from time t _3. become. Thereafter, the NOx concentration C ₁ detected by the NOx sensor 9 is determined at a time t ₅ when a predetermined time has elapsed from the injection time t _{3 of} urea water.

As shown in FIG. 8 (b), above [Condition A], between times t ₅ ~t ₆ is a state in which satisfied [Condition B] and [Condition C] is efficient NOx is in the SCR catalyst 5 As long as the concentration of urea water is not low, a NOx purification rate close to 100% can be obtained. Even if urea water addition control is not performed at time t ₃ , if it is performed before time t ₆ , the NOx concentration C ₁ detected by the NOx sensor 9 is subsequently determined.

Thus, by grasping the exhaust gas component ratio, it is possible to specify an environment for determining whether or not the concentration of urea water is appropriate, and to accurately determine whether or not the concentration of urea water is appropriate. Can be determined.
Further, it is possible to diagnose a decrease in urea water concentration in an environment that does not depend on catalyst deterioration, that is, it is possible to distinguish between catalyst deterioration and urea water concentration decrease.
Further, a urea quality sensor for detecting the components and concentration of urea water is not necessary, and the configuration of the exhaust system can be simplified. Furthermore, it is possible to provide a function as a conventional urea quality sensor to an exhaust sensor that originally detects the concentration of nitrogen oxides, thereby reducing the cost of the exhaust purification device.

In the above control, the urea water concentration is determined in an environment where the ratio of the number of NO and NO ₂ is approximately one-to-one. In such an environment, the NOx reduction reaction (for example, the chemical reaction shown in Formula 8) in the SCR catalyst 5 is promoted compared with other environments, and the NOx purification rate is improved. In this way, the determination in an environment where NOx is likely to be reduced makes it possible to reliably grasp that the concentration of urea water is inappropriate (the concentration of urea is low) and improve the determination accuracy of the urea water concentration Can be made.

Further, as shown in FIG. 5, the thermal dissociation temperature T _{E at} which the NO ₂ ratio becomes 0.5 is a temperature that is not affected even if the DOC catalyst 2 that generates NO ₂ deteriorates. That is, in the state exhaust temperature T _G is equal to the thermal dissociation temperature T _E, the ratio of NO and NO ₂ in the inevitably exhaust is a one-to-one by chemical equilibrium effects. For example, unless the DOC catalyst 2 that deteriorates so severely that the broken line in FIG. 5 crosses the solid line graph below 0.5 is used (that is, unless the NO ₂ generation capability of the DOC catalyst 2 is extremely reduced). , NO and NO ₂ mole fractions are approximately equal.
By determining the concentration of the urea water in such an environment, it is possible to distinguish between the deterioration of the DOC catalyst 2 and the decrease in the urea water concentration.

Further, the diagnostic apparatus 10 described above, the ratio of NO and NO ₂ with the inside of the exhaust temperature T _G of DOC catalyst 2 is determined whether or not an environmental as a one-to-one. In this way, it is possible to accurately and easily detect that the environment is rich in NOx reduction with a simple configuration using the temperature sensor 14 provided in the DOC catalyst 2, and to determine the urea water concentration. The accuracy can be further improved.

Further, in the diagnostic device 10 described above, the thermal dissociation temperature T _E is calculated based on the oxygen concentration C _E and the exhaust pressure P _E in the exhaust passage 16. In other words, it is possible to calculate the exact value of the thermal dissociation temperature T _E in accordance with the combustion state of the engine 20, the ratio of NO and NO ₂ it is possible to accurately grasp the environment to be one-to-one . Thereby, the determination accuracy of the urea water concentration can be further improved.

The ratio of NO and NO ₂ is the temperature at which one-to-one, as shown in FIG. 5, there are actually binary between the temperature T _X and the thermal dissociation temperature T _E. Therefore, even when the exhaust gas temperature is equal to the temperature T _X , the ratio of NO to NO ₂ becomes one-to-one, and the concentration of urea water can be determined. However, since the value of the temperature T _X varies with the deterioration of the DOC catalyst 2 as indicated by the broken line in FIG. 5, it is difficult to distinguish between the deterioration of the catalyst and the decrease in the urea water concentration.

In contrast, in the diagnostic apparatus 10 described above is judged urea water concentration in the process of controlling the internal exhaust temperature T _G of DOC catalyst 2 the temperature is lowered from the state is higher than the thermal dissociation temperature T _E. Accordingly, among the two temperature the ratio is one-to-one NO and NO _2, it is possible to refer to the thermal dissociation temperature T _E of the chemical equilibrium NO and NO _2, the catalyst degradation and the urea water concentration A distinction from decline is ensured. In this way, the thermal dissociation temperature T _E can be accurately estimated by making the determination control only when the exhaust gas temperature decreases.

In particular, in the diagnostic device 10 described above, the exhaust temperature _TG inside the DOC catalyst 2 is not increased forcibly, but is increased using filter regeneration control. As a result, the fuel consumption associated with the temperature rise of the DOC catalyst 2 can be reduced, and the PM deposited on the filter 3 immediately before the diagnosis is removed, so that the diagnostic accuracy can be further improved. Further, since NH ₃ adsorbed on the SCR catalyst 5 is consumed with the filter regeneration control, the influence of only the urea water injected from the urea injector 11 can be observed at the time of diagnosis. Also in this respect, there is an advantage that diagnostic accuracy can be further improved.

  Further, when it is diagnosed that the urea water concentration is low, the notification device 15 notifies the passenger of that fact, so even if urea water having a different concentration is accidentally injected into the tank, Thus, it is possible to promptly prompt the occupant to replace and adjust the urea water, and it is possible to make the vehicle intake / exhaust system healthy.

[6. Modified example]
Regardless of the embodiment described above, various modifications can be made without departing from the spirit of the invention. Each structure of this embodiment can be selected as needed, or may be combined appropriately.

In the above embodiment, the concentration C ₁ of the NOx is determined whether is less than the predetermined concentration C ₀ at step A100 of FIG. That is, here, the NOx value detected by the NOx sensor 9 is directly compared with a predetermined threshold, but instead of such a configuration, the NOx amount in the exhaust discharged to the downstream side of the SCR device 4 The integrated value may be compared with a predetermined threshold value. Alternatively, the NOx purification rate is calculated by comparing the estimated value of the NOx amount discharged from the engine 20 and the integrated value of the NOx amount downstream of the SCR catalyst 4, and the NOx purification rate is compared with a predetermined threshold value. It is good.

Further, in the above-described embodiment, an example of calculating the thermal dissociation temperature T _E inside the controller 7 is illustrated, but the fluctuation range of the exhaust pressure P _E and the oxygen concentration C _E is known, for example, due to the characteristics of the engine 20 or the like. in this case, it is possible to advance the expected variation range of thermal dissociation temperature T _E. Therefore, a control configuration may be adopted in which the NO ₂ ratio is considered to be 0.5 because the exhaust temperature _TG of the DOC catalyst 2 is within a predetermined temperature range. In this case, for example, when the exhaust temperature _TG is around 400 [° C.], it can be considered that the NO ₂ ratio is considered to be 0.5. Alternatively, when the exhaust gas temperature _TG is around 350 to 450 [° C.], the NO ₂ ratio may be regarded as 0.5.
With such a configuration, it is possible to easily grasp the environment in which the ratio of NO to NO ₂ in the exhaust gas is one to one, and the exhaust pressure sensor 12 and the oxygen concentration sensor 13 are omitted from the configuration of the above-described embodiment. The apparatus configuration and the control configuration can be further simplified.

Further, in the above-described embodiment, an example of grasping the exhaust state in which the NO ₂ ratio becomes 0.5 based on the exhaust temperature _TG is illustrated, but the detection method of the NO ₂ ratio is not limited to this. For example, the NO ₂ ratio may be estimated and calculated using a NO sensor that detects the concentration of only NO and a NOx sensor that detects both the concentrations of NO and NO ₂ . Or it may be configured to grasp the NO ₂ ratio with NO ₂ analyzer. By grasping the NO ₂ ratio in the exhaust, it is possible to obtain the same effect as in the above-described embodiment.

In the above-described embodiment, the description has been given by taking as an example the diagnosis of the decrease in the urea water concentration and the deterioration of the DOC catalyst 2, but the deterioration of the catalyst that is determined by the diagnosis according to the present invention is the DOC catalyst 2. However, the present invention is not limited to this, and can be applied to separation from deterioration of other catalysts.
In addition, although the exhaust purification apparatus 10 of the above-mentioned embodiment illustrated what connected the DPF apparatus 1 and the SCR apparatus 4 in series on the exhaust passage 16, at least DOC catalyst 2, urea injector 11, SCR catalyst 4, and NOx sensor If it is an intake and exhaust system provided with 9, it is possible to realize a device having the above technical effects.
Moreover, although what applied this invention to the exhaust system of the diesel engine illustrated in the above-mentioned embodiment, the application to the exhaust system of a gasoline engine is also possible.

[7. Addendum]
The following supplementary notes are further disclosed with respect to the above embodiments and modifications.

(Appendix 1)
An oxidation catalyst provided in the exhaust passage of the engine and capable of oxidizing components in the exhaust;
A urea water addition device that is provided downstream of the oxidation catalyst and adds urea water into the exhaust;
A selective reduction catalyst that is provided downstream of the urea water addition device and reduces nitrogen oxides in the exhaust gas to nitrogen;
An exhaust sensor that detects the concentration of the nitrogen oxides downstream of the selective reduction catalyst;
A ratio detection means for detecting a ratio of the amount of nitrogen dioxide to the total amount of nitrogen oxide contained in the exhaust gas downstream of the oxidation catalyst;
Whether or not the concentration of the urea water added from the urea water addition device is appropriate based on the ratio detected by the ratio detection means and the concentration of the nitrogen oxide detected by the exhaust sensor A diagnostic device for an exhaust gas purification apparatus, comprising: a determination means for determining

(Appendix 2)
The determination means includes
The ratio detected by the ratio detection means is approximately 0.5, the urea water is added from the urea water addition device, and the concentration of the nitrogen oxides detected by the exhaust sensor is less than a predetermined concentration When it is, it determines with the density | concentration of the said urea water being appropriate, The diagnostic apparatus of the exhaust gas purification apparatus of Claim 1 characterized by the above-mentioned.

(Appendix 3)
The ratio detection means includes exhaust temperature estimation means for estimating the exhaust temperature inside the oxidation catalyst, and the ratio is calculated when the exhaust temperature estimated by the exhaust temperature estimation means is a predetermined thermal dissociation temperature. The diagnostic apparatus for an exhaust gas purification apparatus according to appendix 2, wherein it is detected that the ratio is approximately 0.5.

(Appendix 4)
The ratio detection means is configured such that the ratio is approximately 0.5 when the exhaust temperature estimated by the exhaust temperature estimation means decreases from the temperature higher than the thermal dissociation temperature to the thermal dissociation temperature. The diagnostic apparatus for an exhaust gas purification apparatus according to appendix 3, wherein the presence of the exhaust gas purification apparatus is detected.

(Appendix 5)
Provided on the downstream side of the oxidation catalyst and the upstream side of the selective reduction catalyst, and includes a catalyst filter that collects the particulates contained in the exhaust and burns the collected particulates,
When the exhaust gas temperature estimated by the exhaust gas temperature estimating unit decreases from the state where the exhaust gas temperature is equal to or higher than the combustion temperature of the particulates in the catalytic filter and reaches the thermal dissociation temperature, The diagnostic apparatus for an exhaust emission control device according to appendix 4, wherein the ratio is detected to be approximately 0.5.

1 DPF device 2 DOC catalyst 3 filter 4 SCR device 5 SCR catalyst 6 CUC catalyst 7 controllers 7a reproduction control unit 7b urea water addition control unit 7c engine emissions NOx amount estimating unit 7d NH ₃ adsorption amount calculating unit 8 concentration determination control unit 8a Ratio Detection unit 8b Exhaust temperature estimation unit 8c Thermal dissociation temperature estimation unit 8d Determination unit 9 NOx sensor 10 Exhaust purification device diagnostic device 11 Urea injector 12 Exhaust pressure sensor 13 Oxygen concentration sensor 14 Temperature sensor 15 Notification device 20 Engine

Claims (8)

An oxidation catalyst provided in the exhaust passage of the engine and capable of oxidizing components in the exhaust;
A urea water addition device that is provided downstream of the oxidation catalyst and adds urea water into the exhaust;
A selective reduction catalyst that is provided downstream of the urea water addition device and reduces nitrogen oxides in the exhaust gas to nitrogen;
An exhaust sensor that detects the concentration of the nitrogen oxides downstream of the selective reduction catalyst;
A ratio detecting means for detecting a ratio of the amount of nitrogen dioxide to the amount of nitrogen monoxide contained in the exhaust gas downstream of the oxidation catalyst;
Whether or not the concentration of the urea water added from the urea water addition device is appropriate based on the ratio detected by the ratio detection means and the concentration of the nitrogen oxide detected by the exhaust sensor A diagnostic device for an exhaust gas purification apparatus, comprising: a determination means for determining The determination means includes
The ratio detected by the ratio detecting means is approximately one-to-one, the urea water is added from the urea water adding device, and the concentration of the nitrogen oxide detected by the exhaust sensor is a predetermined concentration 2. The diagnostic apparatus for an exhaust gas purification apparatus according to claim 1, wherein when it is less than, the concentration of the urea water is determined to be appropriate. The ratio detection means includes exhaust temperature estimation means for estimating the exhaust temperature inside the oxidation catalyst, and the ratio is calculated when the exhaust temperature estimated by the exhaust temperature estimation means is a predetermined thermal dissociation temperature. 3. The exhaust gas purifying apparatus diagnosis apparatus according to claim 2, wherein it is detected that the ratio is approximately one to one. The diagnostic apparatus for an exhaust gas purification apparatus according to claim 3, wherein the thermal dissociation temperature is in a range of 350 to 450 ° C. Oxygen concentration detection means for detecting the oxygen concentration inside the oxidation catalyst;
An exhaust pressure detecting means for detecting an exhaust pressure inside the oxidation catalyst,
The exhaust gas purifying apparatus diagnosis apparatus according to claim 3 or 4, wherein the ratio detection means calculates the thermal dissociation temperature based on the oxygen concentration, the exhaust pressure, and the exhaust temperature. The ratio detection means is configured such that the ratio is approximately 1: 1 when the exhaust temperature estimated by the exhaust temperature estimation means decreases from a temperature higher than the thermal dissociation temperature to the thermal dissociation temperature. 6. The exhaust gas purifying apparatus diagnosis apparatus according to claim 3, wherein the exhaust gas purifying apparatus according to claim 3 is detected. Provided on the downstream side of the oxidation catalyst and the upstream side of the selective reduction catalyst, and includes a catalyst filter that collects the particulates contained in the exhaust and burns the collected particulates,
When the exhaust gas temperature estimated by the exhaust gas temperature estimating unit decreases from the state where the exhaust gas temperature is equal to or higher than the combustion temperature of the particulates in the catalytic filter and reaches the thermal dissociation temperature, The exhaust gas purifying apparatus diagnosis apparatus according to claim 6, wherein it is detected that the ratio is approximately 1: 1. The diagnostic apparatus for an exhaust gas purification apparatus according to any one of claims 1 to 7, further comprising a notification unit that notifies a passenger of a result of the determination by the determination unit.

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