JP2012036858A - Device for diagnosing catalyst degradation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for diagnosing catalyst degradation, which accurately diagnoses the degree of catalyst degradation of a post-stage oxidation catalyst provided on the downstream side of a selective reduction catalyst.SOLUTION: An injection device 11 for emitting a jet of urea water, the selective reduction catalyst 5, and the post-stage oxidation catalyst 6 are provided in order from an upstream side on an exhaust passage of an engine 20. The selective reduction catalyst 5 has a catalyst for purifying nitrogen oxides by using ammonia, obtained by hydrolyzing the urea water, as a reducing agent, and the post-stage oxidation catalyst 6 has a catalyst for purifying slip ammonia. Additionally, an exhaust sensor 9 is provided on the downstream side of the post-stage oxidation catalyst 6; an injection quantity increasing means 7b for increasing the injection quantity of the urea water from the injection device 11, and a determination means 8 for determining the degree of the degradation of the post-stage oxidation catalyst 6 are provided. The determination means 8 determines the degree of the degradation of the post-stage oxidation catalyst 6 on the basis of the concentration of the nitrogen oxides, which is detected by the exhaust sensor 9 when the injection device 11 emits the jet of a larger quantity of urea water than the quantity of urea water required for reduction by the selective reduction catalyst 5.

Description

  The present invention relates to a catalyst deterioration diagnosis apparatus that determines the degree of deterioration of a post-stage oxidation catalyst provided on the downstream side of a selective reduction catalyst that uses urea water to reduce nitrogen oxides in exhaust gas.

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, urea water as a reducing agent is injected into the exhaust passage on the upstream side of the selective reduction catalyst, ammonia (NH ₃ ) is generated by hydrolysis of urea, and NOx is converted into water and nitrogen (N ₂ ) with NH _3. It is something to reduce. An exhaust purification 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.

Some SCR systems include a post-stage oxidation catalyst for removing NH ₃ slipped downstream of the selective reduction catalyst. The post-stage oxidation catalyst is called, for example, an ammonia slip catalyst, CUC (Clean-up Catalyst) or the like (see, for example, Patent Document 1). Note that the amount of urea added to the exhaust gas in a general SCR system is controlled to a necessary and sufficient amount for the reduction reaction with the selective reduction catalyst. Therefore, NH ₃ does not normally reach the post-stage oxidation catalyst, and the post-stage oxidation catalyst is used as a fail-safe device in the event that NH ₃ should slip from the selective reduction catalyst.

JP 2010-71255 A

When NH ₃ arrives at the latter stage oxidation catalyst, the NH ₃ is oxidized on the oxidation catalyst layer to generate NO and NO ₂ . Further, a post-stage oxidation catalyst having a reduction catalyst layer for further reducing these NOx to N ₂ has been developed. On the other hand, if the oxidation catalyst layer or the reduction catalyst layer is deteriorated, the purification action of NH ₃ is reduced, so the degree of deterioration needs to be accurately grasped.
Regarding catalyst deterioration determination, for example, exhaust temperature sensors may be provided on the upstream side and downstream side of the catalyst to measure the amount of reaction heat on the catalyst, and the presence or absence of deterioration may be determined based on the amount of reaction heat. In this method, the degree of deterioration cannot be determined.

The present case has been devised in view of the above-described problems, and provides a catalyst deterioration diagnosis device that can accurately diagnose the degree of catalyst deterioration of a post-stage oxidation catalyst provided downstream of a selective reduction catalyst. For the purpose.
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) The catalyst deterioration diagnosis device disclosed here includes an injection device, a selective reduction catalyst, and a post-stage oxidation catalyst. The injection device is provided in the exhaust passage of the engine and injects urea water into the exhaust. The selective reduction catalyst is provided downstream of the injection device, and reduces the nitrogen oxide in the exhaust gas to nitrogen using ammonia hydrolyzed by the urea water as a reducing agent. The post-stage oxidation catalyst is provided downstream of the selective reduction catalyst, and purifies the ammonia that has flowed downstream of the selective reduction catalyst.
Further, an exhaust sensor that is provided downstream of the post-stage oxidation catalyst and detects the concentration of nitrogen oxides in the exhaust, and an amount of the urea water that is greater than the amount required for reduction by the selective reduction catalyst And an injection amount increasing means for injecting from the injection device.
Furthermore, it has a determination means for determining the degree of deterioration of the post-stage oxidation catalyst based on the concentration detected by the exhaust sensor when the amount of the urea water is increased by the injection amount increasing means.
That is, the concentration of nitrogen oxide according to the determination by the determination means is a concentration generated as a result of oxidation of excess urea more than the amount necessary for the reduction with the selective reduction catalyst by the post-stage oxidation catalyst.

(2) The apparatus further comprises ratio detection means for detecting a ratio of the amount of nitrogen dioxide to the total amount of nitrogen oxides contained in the exhaust gas flowing into the selective reduction catalyst, and the determination means includes the ratio detection means. It is preferable to determine the degree of deterioration of the post-stage oxidation catalyst based on the ratio and the concentration detected in step (b).
(3) Further, it is preferable that the injection amount increasing means increases the amount of the urea water when the ratio detected by the ratio detecting means is approximately 0.5.
In this case, since the number of moles of nitrogen monoxide and the number of moles of nitrogen dioxide are substantially the same, the reduction reaction of nitrogen oxides with the selective reduction catalyst is promoted, and the purification rate of nitrogen oxides is improved.

(4) An exhaust temperature that is provided upstream of the selective reduction catalyst and has an oxidation catalyst capable of oxidizing components in exhaust gas, and the ratio detection means estimates an exhaust temperature inside the oxidation catalyst. It is preferable to have an estimation means. Further, the ratio detection means detects that the ratio is approximately 0.5 when the exhaust temperature estimated by the exhaust temperature estimation means is a predetermined thermal dissociation temperature (NO ₂ → NO thermal dissociation temperature). It is preferable.
In this case, an exhaust state in which the number of moles of nitric oxide and the number of moles of nitrogen dioxide is approximately the same is estimated by the temperature inside the oxidation catalyst. In addition, it is preferable that predetermined | prescribed thermal dissociation temperature is the temperature of the range of 350-450 degreeC, for example.

(5) Moreover, it is preferable that the said back | latter stage oxidation catalyst has a reduction layer which reduces the said nitrogen oxide to nitrogen.
(6) Further, it is preferable that the injection amount increasing means calculates an amount required for reduction by the selective reduction catalyst based on the engine speed and the engine load.
(7) Moreover, it is preferable to provide the alerting | reporting means which alert | reports the result of determination by the said determination means.

(1) According to the disclosed catalyst deterioration diagnosis apparatus, the deterioration degree of the rear-stage oxidation catalyst can be accurately determined by observing the oxidation ability of ammonia in the rear-stage oxidation catalyst.
(2) By referring to the ratio of the physical quantity of nitrogen dioxide to the total physical quantity of nitrogen oxides, it is possible to accurately correct the detection value of the exhaust sensor, and to accurately determine the degree of deterioration of the post-stage oxidation catalyst. it can.

  (3) Under conditions where the purification rate of nitrogen oxides at the selective reduction catalyst is high, excess nitrogen oxides due to unpurified nitrogen oxides are not detected by the exhaust sensor, and are generally converted from ammonia. Only the generated nitrogen oxide can be detected by the exhaust sensor. Therefore, it is not necessary to consider the influence of the state of the catalyst upstream of the rear-stage oxidation catalyst, and the degree of deterioration of the rear-stage oxidation catalyst can be accurately determined.

(4) It is possible to accurately detect the ratio based on the exhaust temperature inside the oxidation catalyst, and to accurately grasp the state in which the detected value of the exhaust sensor is only nitrogen oxide converted from ammonia. . Therefore, the reliability of the detection value in the exhaust sensor can be improved, and the deterioration degree of the post-stage oxidation catalyst can be accurately determined.
(5) By reducing the nitrogen oxides generated by the post-stage oxidation catalyst to nitrogen, it is possible to further improve the exhaust purification performance while determining the degree of deterioration of the post-stage oxidation catalyst.

(6) A sensor for detecting the concentration of nitrogen oxides discharged from the engine becomes unnecessary, and the cost can be reduced.
(7) By notifying the degree of deterioration of the rear-stage oxidation catalyst to, for example, a driver or an occupant, early maintenance can be promoted, and it is possible to easily maintain a high exhaust purification performance state.

It is a figure which illustrates typically the whole structure of the catalyst deterioration diagnostic apparatus concerning one embodiment. It is a graph for demonstrating the characteristic of the DOC catalyst which concerns on the catalyst deterioration diagnostic apparatus of FIG. 2 is a graph illustrating the relationship between the catalyst temperature of the SCR catalyst of FIG. 1 and the maximum NH ₃ adsorption amount. Is a graph for explaining the characteristics of CUC catalyst of Figure 1, (a) shows the relationship between the catalyst temperature and the NH ₃ purification rate, (b) shows the relationship between the catalyst temperature and the N ₂ generation rate, (C) shows the relationship between the catalyst temperature and the NO ₂ generation rate. ₂ is a graph showing the relationship between the NO ₂ ratio and the exhaust gas temperature according to the catalyst deterioration diagnosis device of FIG. 1. ₂ is a graph for explaining the relationship between the deterioration of a DOC catalyst and the NO ₂ ratio according to the catalyst deterioration diagnosis device of FIG. 1. 3 is a three-dimensional graph illustrating the relationship between the catalyst temperature of the SCR catalyst, the NO ₂ ratio, and the NOx purification rate of the SCR catalyst according to the catalyst deterioration diagnosis device of FIG. 1. 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 catalyst deterioration diagnostic apparatus of FIG. 2 is a graph illustrating the temporal variation of the urea water injection amount and the detected value of NOx concentration at the time of diagnosis by the catalyst deterioration diagnosis device of FIG. 1.

  Hereinafter, the disclosed catalyst deterioration diagnosis apparatus 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 catalyst deterioration diagnosis apparatus 10 of this embodiment is applied to the vehicle intake / 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 (injection device) 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. Further, a NOx sensor 9 (exhaust sensor) for detecting the concentration C ₁ of NOx contained in the exhaust is provided on the downstream side of the SCR device 4. The pressure P _E , oxygen concentration C _E , exhaust temperature T _1, and NOx concentration C ₁ detected by each of these sensors 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 produced at low temperatures decreases, and the increasing gradient of the NO ₂ production rate with respect to the increase in catalyst temperature becomes small. 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.
On the surface of the filter 3, exhaust particulates are continuously incinerated using NO ₂ or the like in the exhaust as an oxidizing agent. Such a PM removal method is called a continuous reproduction method. This method is suitable for use in purifying and regenerating the filter during normal driving of the vehicle. For the purpose of promoting the combustion reaction of PM, etc., a filter provided with a catalyst layer (coated DPF) has been developed.

Further, in the filter 3 of the present embodiment, not only continuous regeneration type regeneration control but also forced regeneration type regeneration control in which PM is forcibly burned by raising the temperature of the filter 3 is performed. The method for raising the temperature of the filter 3 is arbitrary. For example, a method for raising the exhaust temperature by supplying hydrocarbons (unburned fuel, HC) or the like to the DOC catalyst 2 to generate oxidation heat, or the filter 3 It is possible to employ a method of heating the substrate with a heater or the like. The exhaust temperature necessary for burning PM on the filter 3 during the regeneration control of the forced regeneration system is called a regeneration temperature T _F (for example, 550 to 600 [° C.]).

Such regeneration control of the filter 3 is controlled by a controller 7 described later. PM collected by the filter 3 is removed by the regeneration control, and the filter 3 is regenerated and purified. The chemical reaction formula of PM combustion reaction in the filter 3 is exemplified below. 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.
C + 2NO ₂ → 2NO + CO ₂ (Formula 2)
C + O ₂ → CO ₂ ... (Formula 3)

[1-3. SCR device]
The SCR device 4 incorporates an SCR catalyst 5 (selective reduction catalyst) disposed on the upstream side and a CUC catalyst 6 (post-stage oxidation catalyst) disposed on the downstream side thereof.
SCR catalyst 5 is nitrogen oxide selective reduction catalyst urea addition type, receives the urea water supplied from the urea injector 11 on the upstream side to generate NH _3, and thereby adsorbing the NH _3, the adsorbed NH _It has the function of reducing NOx in the exhaust gas to nitrogen using ₃ as a reducing agent.

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 temperature T _C (for example, about 400 ° C. or higher), NH ₃ adsorption is almost completely lost. 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 this catalyst deterioration diagnosis device 10, the degree of deterioration (deterioration degree) of the CUC catalyst 6 is determined with reference 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. The CUC catalyst 6 has an oxidation catalyst layer that oxidizes NH ₃ and a reduction catalyst layer (reduction layer) that reduces NOx generated by the oxidation of NH ₃ . The chemical reaction formula of the oxidation reaction of NH ₃ in the oxidation catalyst layer is exemplified below. Examples of the reduction reaction in the reduction catalyst layer include those shown in the above formulas 6 to 8. NOx generated in the oxidation catalyst layer of the CUC catalyst 6 reacts with NH _{3 in the} reduction catalyst layer to become N ₂ .
4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O (Formula 9)
4NH ₃ + 5O ₂ → 4NO + 6H ₂ O (Formula 10)
4NH ₃ + 7O ₂ → 4NO ₂ + 6H ₂ O (Formula 11)

The relationship between the catalyst temperature of the CUC catalyst 6 and the NH ₃ purification rate is shown in FIG. The NH ₃ purification rate increases as the catalyst temperature rises, and shows a substantially constant purification rate when the catalyst temperature is equal to or higher than a predetermined temperature. On the other hand, when the CUC catalyst 6 deteriorates, the oxidizing power of NH ₃ in the oxidation catalyst layer decreases, and the graph of the NH ₃ purification rate shifts to the high temperature side as shown by the white arrow in FIG. The catalyst temperature necessary to obtain the same NH ₃ purification rate increases due to the deterioration of the CUC catalyst 6. Even if the CUC catalyst 6 deteriorates, if the catalyst temperature becomes high, a constant purification rate equivalent to that before the deterioration can be obtained.

Subsequently, the relationship between the catalyst temperature of the CUC catalyst 6 and the N ₂ generation rate on the downstream side of the CUC catalyst 6 is shown in FIG. The N ₂ generation rate increases when the catalyst temperature is in a predetermined temperature range, and decreases when the catalyst temperature is lower or higher than the temperature range.
Here, the temperature of the catalyst that gives the highest N ₂ generation rate is T _J. When the CUC catalyst 6 deteriorates, if the catalyst temperature is lower than the predetermined temperature T _J , the amount of NH ₃ produced decreases and the N ₂ generation rate also decreases due to the reduction of the oxidizing power of NH ₃ in the oxidation catalyst layer. To do. At this time, the graph of N ₂ generation rate, as indicated by a white arrow in FIG. 4 (b), the shift to the decreasing side of the high temperature side and N ₂ generation rate.

On the other hand, when the catalyst temperature is higher than the predetermined temperature T _J , the N ₂ generation rate decreases due to a decrease in the reactivity between NOx and NH ₃ in the reduction catalyst layer. At this time, the graph of N ₂ generation rate, as indicated by the black arrow in FIG. 4 (b), the shift to the decreasing side of the low temperature side and N ₂ generation rate. As described above, when the CUC catalyst 6 deteriorates, the N ₂ generation rate decreases, and the catalyst temperature range in which N ₂ is generated is narrowed.
Thus, when the CUC catalyst 6 is deteriorated, when the catalyst temperature is low, both the oxidation reaction in the oxidation catalyst layer and the reduction reaction in the reduction catalyst layer are reduced. However, when the catalyst temperature is high, the oxidation reaction proceeds preferentially over the reduction reaction. Therefore, as the catalyst temperature is higher, the reduction to N ₂ cannot catch up with the NOx amount generated by the CUC catalyst 6, and the NOx amount relatively increases.

For example, the relationship between the catalyst temperature of the CUC catalyst 6 and the NOx generation rate on the downstream side of the CUC catalyst 6 is shown in FIG. The NOx generation rate increases as the catalyst temperature increases. The higher the catalyst temperature, the more the NH ₃ oxidation reaction proceeds preferentially over the NOx reduction reaction, and it becomes substantially constant when the catalyst temperature is equal to or higher than the predetermined temperature. On the other hand, when the CUC catalyst 6 deteriorates, the N ₂ generation amount decreases as described above, and the NOx generation rate increases. Therefore, the NOx concentration detected on the downstream side of the CUC catalyst 6 at the same catalyst temperature increases as the catalyst deteriorates. Further, the catalyst temperature at which the same NOx concentration is detected decreases as the catalyst deteriorates, and shifts to the low temperature side as indicated by the white arrow in FIG.
Thus, as the deterioration of the CUC catalyst 6 progresses, the reactivity between NOx and NH ₃ decreases, and the amount of NOx generated increases.

[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. 5 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. 5 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. 6, 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 5. 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. 6, 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. 5 will vary 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 catalyst deterioration diagnosis device 10 accurately grasps the environment in which the reaction of the above equation 8 is likely to occur, that is, the environment where the NO ₂ ratio is 0.5, and then determines the NOx concentration under the environment. The control which diagnoses the density | concentration of urea water with reference is implemented.

FIG. 7 shows an example of the relationship between the catalyst temperature of the SCR catalyst 5 (exhaust temperature on the downstream side of the DOC catalyst 2), the NO ₂ ratio, and the NOx purification rate in the SCR catalyst 5. This three-dimensional graph shows that when the NO ₂ ratio is near 0.5, a high NOx purification rate can be obtained regardless of the catalyst temperature of the SCR catalyst 5. That is, when the NO ₂ ratio of the exhaust gas flowing into the SCR catalyst 5 is approximately 0.5, almost all NOx discharged from the engine 20 is reduced to N ₂ by supplying an appropriate amount of urea water.

[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, regeneration control of the filter 3, urea water injection control from the urea injector 11, control for diagnosing catalyst deterioration of the CUC catalyst 6, and the like are performed.

  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, that is, filter regeneration control, urea water addition control, and deterioration diagnosis 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. In this control, the amount of urea water added is calculated based on the amount of NOx to be reduced by the SCR catalyst 5.
For example, when the amount of NOx discharged from the cylinder of the engine 20 is large due to the driving state of the vehicle, the amount of urea water added is increased, and conversely, when the amount of NOx discharged from the cylinder of the engine 20 is small, urea water is increased. The amount of added is reduced. That is, the injection amount of urea water is calculated according to the NOx amount discharged from the engine 20. The execution condition of the urea water addition control, it like the catalyst temperature of the SCR catalyst 5 is a second activation temperature T _B or the like.

The deterioration diagnosis control is control for diagnosing catalyst deterioration of the CUC catalyst 6. This control is performed in conjunction with the urea water addition control, and adds a small amount of diagnostic addition to the urea water addition calculated in the urea water addition control and injects it. It has a function of diagnosing the degree of catalyst deterioration of the CUC catalyst 6 by determining how much ammonia produced by the urea water is treated by the CUC catalyst 6. Here, it is determined that the CUC catalyst 6 has deteriorated 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 It is a predetermined value C ₀ or the detected value C ₁ of the [condition D] NOx sensor

  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 determine whether the CUC catalyst 6 is due to catalyst deterioration. 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]. It is specified that the cause of this is the catalyst deterioration of the CUC catalyst 6.

[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 includes a regeneration control unit 7a, a urea water addition control unit 7b, a ratio detection unit 7c, and a deterioration diagnosis control unit 8.

  The regeneration control unit 7a performs filter regeneration control. The regeneration control unit 7a has a function of determining a start condition of the filter regeneration control based on information transmitted from a timer, an engine ECU, or the like (not shown), and raising the exhaust temperature discharged from the engine 20 when the start condition is satisfied. Have. 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 (injection amount increasing means) performs urea water addition control. Urea water addition control unit 7b is, the amount of NOx contained in the exhaust gas immediately after being discharged from the engine 20 (i.e., the engine-out NOx amount) was estimated calculation, urea injector 11 urea water amount P ₁ in response thereto It has a function to inject from. The amount P _{1 of} urea water calculated here is an amount necessary for NOx reduction in the SCR catalyst 5.

As shown in FIG. 8, the urea water addition control unit 7b stores a map that describes the correspondence between the operating state of the engine 20 and the NOx amount (NOx concentration) discharged from the engine 20 at that time. . The urea water addition control unit 7b 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 the broken line in FIG. 8, 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.

The urea water addition control unit 7b has a function of slightly increasing the amount of urea water added before and after the above [Condition B] is satisfied. The increment ΔP of the urea water addition amount is used for deterioration determination in the CUC catalyst 6 and is very small compared to the amount P ₁ described above.

The ratio detection unit 7c (ratio detection means) detects the NO ₂ ratio of the exhaust on the downstream side of the DOC catalyst 2, and includes an exhaust temperature estimation unit 7d and a thermal dissociation temperature estimation unit 7e. The exhaust temperature estimation unit 7d (exhaust temperature estimation means) estimates the exhaust temperature T _G (the catalyst temperature of the DOC catalyst 2) inside the DOC catalyst 2 based on the exhaust temperature T ₁ detected by the temperature sensor 14. is there. Note that the estimation method of the catalyst temperature _TG of the DOC catalyst 2 is not limited to this. For example, the exhaust temperature on the downstream side of the DOC catalyst 2 may be used, or an estimation method that takes this into account may be used. .

The thermal dissociation temperature estimation unit 7e calculates a thermal dissociation temperature T _E. Here, the thermal dissociation temperature T _E is the exhaust pressure P _E detected by the exhaust pressure sensor 12, and the oxygen detected by the oxygen concentration sensor 13. 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 12 to 14, the exhaust gas temperature T ₁ , the molar fraction of O ₂ (oxygen concentration C _E ), the exhaust gas pressure P _E , the NO molar fraction (concentration) in equilibrium and the NO ₂ molar fraction (concentration) Relationship 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 deterioration diagnosis control unit 8 (determination means) performs deterioration diagnosis control and determines whether or not the catalyst of the CUC catalyst 6 has deteriorated. Here, when all of the above [Condition A] to [Condition D] are satisfied, it is determined that the CUC catalyst 6 has deteriorated, and the notification device 15 is controlled to notify the passenger of the deterioration.

The exhaust state of [Condition B] is determined by comparing the thermal dissociation temperature T _E estimated by the thermal dissociation temperature estimation unit 7e and the exhaust temperature T _G estimated by the exhaust temperature estimation unit 7d. 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 concentration C _{0 according} to the above [Condition D] is a determination threshold value of the NOx concentration obtained by oxidizing the ammonia produced by the hydrolysis of the ΔP urea water on the CUC catalyst 6. For example, in the exhaust state where the NOx purification rate of the SCR catalyst 5 is approximately 100 [%], the detected value C ₁ of the NOx concentration detected by the NOx sensor 9 is obtained only by the above-described ΔP urea water. 6 is a value corresponding to the NOx concentration generated above. In the present embodiment, the degree of catalyst deterioration of the CUC catalyst 6 is determined using such characteristics.

[4. flowchart]
FIG. 9 is a flowchart for explaining an example of control in the catalyst deterioration diagnosis 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 temperature estimation unit 7d estimates the exhaust temperature T _G (catalyst temperature) inside the DOC catalyst 2 based on the exhaust 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 7e 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 subsequent step A41, it is determined whether or not the exhaust gas temperature T _G estimated by the exhaust gas temperature estimation unit 7d 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. Here, if the exhaust gas temperature T _G > the injection temperature T _H , the process returns to Step A30, and the calculation of the exhaust gas temperature T _G is continued. If the exhaust gas temperature T _G ≦ the injection temperature T _H , the process proceeds to Step A42. The predetermined injection temperature T _H is, for example, a temperature that is about 50 ° C. higher than the thermal dissociation temperature T _E.

In step A42, for example, based on the map shown in FIG. 8, the urea water addition control unit 7b performs an estimation calculation of the engine-out NOx amount. Moreover, the subsequent step A43, the amount P ₁ of the urea water required for reducing NOx estimated amount in step A42 is calculated.
In the subsequent step A44, urea water addition control is performed. Here, since it is determined in step A41 that the exhaust gas temperature T _G ≦ the injection temperature T _H, it is assumed that the above condition B will be satisfied soon, and control for slightly increasing the amount of urea water added is performed. This is added to normal urea water addition control. For example, a control signal for injecting from the urea injector 11 an amount of urea water obtained by adding a predetermined increment ΔP to the amount P ₁ obtained in the previous step is output from the urea water addition control unit 7b, and the urea water is discharged into the exhaust gas. Be injected.

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. 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 A45 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. Here, if C ₁ <C ₀ , the process proceeds to step A110, where it is determined that no catalyst deterioration is observed in the CUC catalyst 6.

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. As a result, the NOx purification rate in the SCR catalyst 5 is improved, and a NOx purification rate close to 100 [%] is obtained. On the other hand, in step A45, a slightly larger amount (P ₁ + ΔP) of urea water than the amount P ₁ necessary for NOx purification is added, so that the exhaust gas flowing into the CUC catalyst 6 corresponds to ΔP urea water. The amount of NH ₃ will be included. Therefore, the NH ₃ purification rate and NOx purification rate in the CUC catalyst 6 can be calculated based on the NH ₃ amount corresponding to the urea water of ΔP. Further, as long as the catalyst deterioration of the CUC catalyst 6 has not occurred, the detected NOx concentration C ₁ is less than the predetermined concentration C ₀ .

On the other hand, when the determination result in step A100 is C ₁ ≧ C ₀ , the NH ₃ and NOx purification action in the CUC catalyst 6 is weakened. Therefore, control proceeds to step A120, and it is determined that catalyst deterioration has occurred in the CUC catalyst 6. In subsequent step A130, the notification device 15 is controlled by the controller 7, and the detection of catalyst deterioration 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 inspect the CUC catalyst 6.

[5. Action, effect]
FIG. 10 shows temporal variation of the urea water injection amount and the NOx concentration C ₁ at the time of diagnosis by the catalyst deterioration diagnosis device 10. Time t ₁ in the figure corresponds to the start time of urea water addition control in step A45 of the above flowchart. The thick solid line in the figure is the NOx concentration C ₁ detected by the NOx sensor 9 when the CUC catalyst 6 is not deteriorated, and the thin solid line is detected by the NOx sensor 9 when the CUC catalyst 6 is deteriorated. The NOx concentration is C ₁ .

When urea water injection control is performed at time t ₁ , the urea water is hydrolyzed to NH ₃ on the SCR catalyst 5. The amount of urea water added to the exhaust gas at this time includes not only the amount P ₁ required for NOx reduction but also an increment ΔP. Therefore, NH ₃ has NH ₃ in excess that is not consumed in the reduction of NOx in the exhaust gas flowing into the CUC catalyst 6.

The CUC catalyst 6 purifies excess NH ₃ . Therefore, the NOx concentration detected by the NOx sensor 9 is only the concentration of NOx generated in the process of the purification reaction of NH _{3 in} the CUC catalyst 6. Therefore, when no catalyst deterioration has occurred in the CUC catalyst 6, as shown by a thick solid line in FIG. 10, NH ₃ and NOx are appropriately purified, and at a time t ₂ when the fluctuation of the NOx concentration is stabilized A detection value C _X less than the concentration C ₀ is obtained. Note that the lower the degree of deterioration of the CUC catalyst 6 (closer to a new article), the smaller the detected value C _X becomes to zero. The predetermined time according to the determination in step A90 of the flow chart described above, the variation in the NOx concentration corresponds to the time until t ₂ stably from the time t ₁ in FIG. 10.

On the other hand, when catalyst deterioration occurs in the CUC catalyst 6, NOx generated as a result of oxidation of NH ₃ is detected by the NOx sensor 9, for example, as shown in Equations 10 and 11 above. As shown by a thin solid line in FIG. 10, a detection value C _Y having a predetermined density C ₀ or more is obtained at time t ₂ . The detection value _CY increases as the degree of deterioration of the CUC catalyst 6 is higher (the deterioration is more severe).
The maximum value of the detected values C _Y becomes an amount corresponding to the increment ΔP of the urea water. That is, even if the CUC catalyst 6 is in a deteriorated state, if the increment ΔP is set sufficiently small, the deterioration of the CUC catalyst 6 can be diagnosed with little influence on the exhaust performance.

As described above, according to the catalyst deterioration diagnosis device 10 described above, the CUC catalyst is supplied by supplying slightly more urea water when the SCR catalyst 5 is in an exhaust state where the NOx purification rate is approximately 100 [%]. Thus, the catalytic ability of NH ₃ at 6 can be appropriately observed, and the degree of catalyst deterioration of the CUC catalyst 6 can be accurately determined.

Further, in the catalyst deterioration diagnosis device 10 described above, the degree of catalyst deterioration is determined in the above [Condition B], that is, in an exhaust state where the NO ₂ ratio is approximately 0.5. In the exhaust state where the NO ₂ ratio is approximately 0.5, the amount of unpurified NOx flowing downstream from the SCR catalyst 5 is extremely small, and therefore the detected value at the NOx sensor 9 is generated only by the reaction at the CUC catalyst 6. It corresponds to the concentration of NOx. Therefore, it is not necessary to consider the influence of the state of the catalyst upstream of the CUC catalyst 6, and the degree of deterioration of the CUC catalyst 6 can be accurately determined.

Further, in the above-described catalyst deterioration diagnosis device 10, when grasping the “exhaust state where the NO ₂ ratio is approximately 0.5”, the inside of the oxidation catalyst 2 is considered in consideration of the thermal dissociation characteristic from NO ₂ to NO. Refers to the exhaust temperature. As described above, it is possible to accurately and easily detect an environment rich in NOx reduction with a simple configuration using the temperature sensor 14 provided in the DOC catalyst 2. In addition, it is not necessary to use expensive sensors such as NO sensor, NO ₂ sensor, and exhaust component analyzer, and it is possible to grasp an appropriate exhaust state at low cost.

That is, it is possible to accurately grasp the state in which the detected value at the NOx sensor 9 is only NOx converted from NH ₃ . Therefore, the reliability of the detected value in the NOx sensor 9 can be improved, and the degree of deterioration of the CUC catalyst 6 can be accurately determined.
Further, in the catalyst deterioration diagnosis device 10 described above, the CUC catalyst 6 includes an oxidation catalyst layer and a reduction catalyst layer. Thus, by reducing NOx that can be generated in the oxidation catalyst layer of the CUC catalyst 6 to N ₂ in the reduction catalyst layer, it is possible to further improve the exhaust purification performance while determining the degree of deterioration of the CUC catalyst 6. .

In particular, in the above-described catalyst deterioration diagnosis device 10, when determining the deterioration of the CUC catalyst 6, the exhaust temperature is not increased forcibly, but the temperature increased by filter regeneration control is used. As a result, the fuel consumption associated with the temperature rise 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. In addition, since NH ₃ stored in the SCR catalyst 5 is desorbed along 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.

Moreover, the catalyst deterioration diagnosis apparatus 10 described above, and calculates the equilibrium temperature T _E on the basis of 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 equilibrium 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 as a one-to-one. Thereby, the diagnostic accuracy of the CUC catalyst 6 can be further improved.
Moreover, the catalyst deterioration diagnosis apparatus 10 described above, the intake air amount Q, and calculates the engine-out NOx amount using a map based on the accelerator opening theta _AC and the engine speed N _e. As a result, for example, it is not necessary to separately provide a NOx sensor in the exhaust manifold of the engine 20, and the cost can be further reduced.
Further, when it is diagnosed that the CUC catalyst 6 has deteriorated, the notification device 15 notifies the passenger of that fact, so that the passenger can be promptly inspected and replaced the CUC catalyst 6, and the vehicle intake It is easy to make the 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-described embodiment, an example in which the catalyst deterioration of the CUC catalyst 6 is diagnosed only in the exhaust state where the NO ₂ ratio is approximately 0.5 is illustrated, but the environmental conditions for diagnosing the catalyst deterioration are not limited thereto. For example, if the correlation between the NOx purification rate, the NO ₂ ratio, and the catalyst temperature in the SCR catalyst 5 as shown in FIG. 7 is used, the SCR catalyst 5 can be used even in an exhaust state other than the exhaust state where the NO ₂ ratio is approximately 0.5. It is possible to grasp the amount of NOx flowing into the CUC catalyst 6 side without being purified.
As described above, by using the NO ₂ ratio to reduce the influence of the inflow from the SCR catalyst 5 side from the detection value of the NOx sensor 9, the catalytic reaction with only the CUC catalyst 6 can be observed. Accordingly, the detection value of the NOx sensor 9 can be accurately corrected, and the degree of deterioration of the CUC catalyst 6 can be accurately determined.

In the embodiment described above, 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.

In the above-described embodiment, an example in which the deterioration state of the CUC catalyst 6 is determined in a binary manner is illustrated. However, the actual deterioration of the CUC catalyst 6 is gradually performed as shown in FIGS. Therefore, a method may be applied in which the degree of deterioration is digitized and presented to the occupant.
For example, on the basis of the amount of a substance produced or consumed in a catalytic reaction using a new CUC catalyst 6, the reduction rate (percentage) when the production or consumption of the substance is reduced is expressed as the “degradation degree” of the catalyst. Is defined.

In this case, the maximum value of the NOx concentration C ₁ shown in FIG. 9 increases as the degree of deterioration increases. Therefore, the degree of deterioration may be diagnosed as the NOx concentration C ₁ detected by the NOx sensor 9 increases.
More precisely, the amount of NOx estimated from the NOx concentration C ₁ detected by the NOx sensor 9 remains without being purified out of the amount of NOx estimated from the amounts of NH ₃ and NOx flowing into the CUC catalyst 6. Is considered to be an amount. Therefore, the ratio (percentage) of the former to the latter can be considered to correspond to the degree of deterioration of the CUC catalyst 6, and the degree of deterioration obtained in this way may be used as the diagnosis result.

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 addition, although the catalyst deterioration diagnosis apparatus 10 of the above-described embodiment is exemplified by the DPF device 1 and the SCR device 4 arranged in series on the exhaust passage 16, at least the urea injector 9, the SCR catalyst 5, the CUC catalyst 6, and the NOx. If it is an intake / exhaust system provided with the sensor 9, it is possible to realize a device that exhibits the above technical effect.
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.

1 DPF equipment 2 DOC catalyst (oxidation catalyst)
3 Filter 4 SCR device 5 SCR catalyst (selective reduction catalyst)
6 CUC catalyst (back-end oxidation catalyst)
7 controller 7a regeneration control unit 7b urea water addition control unit (injection amount increasing means)
7c Ratio detection unit (ratio detection means)
7d Exhaust temperature estimation unit (exhaust temperature estimation means)
7e Thermal dissociation temperature estimation part 8 Deterioration diagnosis control part (determination means)
9 NOx sensor (exhaust sensor)
10 Catalyst deterioration diagnosis device 11 Urea injector (injection device)
15 Notification device (notification means)

Claims (7)

An injection device that is provided in an exhaust passage of the engine and injects urea water into the exhaust;
A selective reduction catalyst that is provided downstream of the injection device and reduces the nitrogen oxide in the exhaust gas to nitrogen using ammonia hydrolyzed by the urea water as a reducing agent;
A downstream oxidation catalyst that is provided downstream of the selective reduction catalyst and purifies the ammonia that has flowed downstream of the selective reduction catalyst;
An exhaust sensor that is provided downstream of the rear-stage oxidation catalyst and detects the concentration of nitrogen oxides in the exhaust;
An injection amount increasing means for injecting an amount of the urea water from the injection device that is larger than an amount necessary for reduction by the selective reduction catalyst;
Determination means for determining the degree of deterioration of the post-stage oxidation catalyst based on the concentration detected by the exhaust sensor when the amount of the urea water is increased by the injection amount increasing means. A catalyst deterioration diagnosis device characterized by Comprising a ratio detection means for detecting the ratio of the amount of nitrogen dioxide to the total amount of nitrogen oxide contained in the exhaust gas flowing into the selective reduction catalyst;
2. The catalyst deterioration diagnosis apparatus according to claim 1, wherein the determination unit determines a deterioration degree of the rear-stage oxidation catalyst based on the ratio and the concentration detected by the ratio detection unit. 3. The catalyst deterioration diagnosis device according to claim 2, wherein the injection amount increasing means increases the amount of the urea water when the ratio detected by the ratio detecting means is approximately 0.5. Provided on the upstream side of the selective reduction catalyst, comprising an oxidation catalyst having an oxidation ability for components in the exhaust,
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. 4. The catalyst deterioration diagnosis apparatus according to claim 3, wherein it is detected that the ratio is approximately 0.5. The catalyst deterioration diagnostic apparatus according to any one of claims 1 to 4, wherein the rear-stage oxidation catalyst has a reduction layer that reduces the nitrogen oxides to nitrogen. The said injection amount increase means calculates the quantity required for the reduction | restoration by the said selective reduction catalyst based on the rotation speed of the said engine, and the load of the said engine, The any one of Claims 1-5 characterized by the above-mentioned. The catalyst deterioration diagnostic apparatus according to 1. The catalyst deterioration diagnosis apparatus according to claim 1, further comprising a notification unit that notifies a result of determination by the determination unit.

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