JP7197353B2 - Diagnostic device and exhaust purification device for internal combustion engine - Google Patents

Description

The present invention relates to a diagnostic device and an exhaust purification device for an internal combustion engine.

NO _X storage catalysts and NO _X selective reduction catalysts are known as members for reducing nitrogen oxides (NO _X ) contained in the exhaust gas of internal combustion engines such as diesel engines to purify the exhaust gas. The _NOx storage catalyst stores _NOx in the exhaust gas when the air-fuel mixture burned in the internal combustion engine is in a fuel-lean state with respect to the stoichiometric air-fuel ratio (stoichiometric). When in a rich state, _NOx is released and reacted with unburned hydrocarbons (HC: Hydrocarbon) in the exhaust, thereby reducing _NOx to nitrogen ( _N2 ). The NO _X selective reduction catalyst has a function of adsorbing ammonia (NH ₃ ) as a reducing component of NO _X , and reduces NO _X to N ₂ by reacting NO _X in the inflowing exhaust gas with NH ₃ . do.

For example, Patent Literature 1 discloses an exhaust purification device provided with both an NO _X storage catalyst and a NO _X selective reduction catalyst as one aspect of an exhaust purification device for purifying exhaust gas from an internal combustion engine. Specifically, in the exhaust purification device disclosed in Patent Document 1, the NO _X storage catalyst and the NO _X selective reduction catalyst are arranged in this order from the upstream side of the exhaust passage. In such an exhaust purification device, when NH ₃ is produced by the reaction between NO _X and HC in the NO _X storage catalyst, the NO _X selective reduction catalyst adsorbs the NH ₃ . Then, when NO _X flows out from the NO _X storage catalyst, the NO _X selective reduction catalyst reduces NO _X using NH ₃ .

Japanese Patent Publication No. 2006-522257

Here, in the exhaust purification device disclosed in Patent Document 1, when the deterioration of the NO _X selective reduction catalyst progresses or when the NO _X selective reduction catalyst is missing (not installed), NO _X and NH ₃ emissions may increase. Therefore, it would be significant if there was a diagnostic function capable of detecting the lack or deterioration of the _NOx selective reduction catalyst.

For example, using the fact that the NO _X selective reduction catalyst has a heat capacity, a temperature sensor is provided downstream of the NO _X selective reduction catalyst, and a temperature model and temperature sensor are created taking into consideration the heat capacity of the NO _X selective reduction catalyst. It is conceivable to determine the lack of the NO _X selective reduction catalyst by comparing the temperature detected by .

However, in the case of the method of comparing the temperature model and the detected temperature, in order to improve the accuracy of the diagnosis result, it is necessary to execute the diagnosis in an operating state in which the temperature change of the exhaust gas is relatively small. is limited. In addition, even if the NO _X selective reduction catalyst deteriorates, the change in heat capacity is _{small .} It is difficult to detect deterioration of the selective reduction catalyst.

The present invention has been made in view of the above problems, and an object of the present invention is to solve problems such as missing or deterioration of the NO _X selective reduction catalyst provided in the exhaust passage on the downstream side of the NO _X storage catalyst. An object of the present invention is to provide a diagnosis device and an exhaust emission control device for an internal combustion engine that can improve the detection accuracy of abnormality.

In order to solve the above problems, according to one aspect of the present invention, there is provided a NO _X selective reduction catalyst in an exhaust gas purification system having an NO _X storage catalyst and a NO _X selective reduction catalyst in order from the upstream side in an exhaust passage of an internal combustion engine. a downstream NO _X concentration estimation unit that calculates a downstream NO _X concentration estimated value that is an estimated value of the NO _X concentration in the exhaust passage downstream of the NO _X selective reduction catalyst; a sensor value detection unit that acquires a sensor value of an NO _X concentration sensor provided in an exhaust passage downstream of the NO _{X selective} reduction catalyst _; an upstream ammonia concentration estimator that obtains an estimated upstream ammonia concentration that is an estimated value of the ammonia concentration in the upstream exhaust passage _; and a determination unit that determines lack or deterioration of the NO _X selective reduction catalyst.

Further, in order to solve the above problems, according to another aspect of the present invention, an NO _X storage catalyst provided in an exhaust passage of an internal combustion engine and an NO _X storage catalyst provided in an exhaust passage downstream of the NO X storage catalyst An exhaust of an internal combustion engine provided with a NO _X selective reduction catalyst, a NO _X concentration sensor provided in an exhaust passage downstream of the NO _X selective reduction catalyst, and a diagnostic device for diagnosing abnormality of the NO _X selective reduction catalyst. In the purification device, the diagnosis device includes a downstream NO _X concentration estimation unit that calculates a downstream NO _X concentration estimated value, which is an estimated value of the NO _X concentration in the exhaust passage downstream of the NO _X selective reduction catalyst; a sensor value detection unit that acquires a sensor value of an NO _X concentration sensor provided in an exhaust passage downstream of the _{X selective} reduction catalyst _; an upstream ammonia concentration estimating unit that obtains an estimated upstream ammonia concentration value that is an estimated value of the ammonia concentration in the exhaust passage on the upstream side _; and a determination unit that determines lack or deterioration of the _X selective reduction catalyst.

As described above, according to the present invention, it is possible to improve the accuracy of detecting an abnormality such as missing or deterioration of the NO _X selective reduction catalyst provided in the exhaust passage downstream of the NO _X storage catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the structural example of the exhaust gas purification apparatus which concerns on this embodiment. It is a block diagram which shows the structural example of a diagnostic apparatus (control apparatus). FIG. 4 is an explanatory diagram showing changes in the integrated value of the downstream side NO _X concentration detection value; It is a flowchart which shows the operation example of a diagnostic apparatus (control apparatus).

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

<1. Overall Configuration of Exhaust Purification Device for Internal Combustion Engine>
A configuration example of an exhaust emission control system for an internal combustion engine according to this embodiment will be described. FIG. 1 is a schematic diagram showing a configuration example of an exhaust purification device 10. As shown in FIG.

The exhaust purification device 10 is provided in an exhaust system of an internal combustion engine 5 typified by a diesel engine or the like. In this embodiment, an example in which the internal combustion engine 5 is a diesel engine will be described. The internal combustion engine 5 includes a fuel injection system that injects fuel supplied to each cylinder. The fuel injection system may be, for example, a common rail system including a common rail holding high pressure fuel and a plurality of fuel injectors connected to the common rail. However, the internal combustion engine 5 is not limited to the above configuration example.

The operating state of the internal combustion engine 5 is controlled by the control device 100 . In the internal combustion engine 5, the air-fuel ratio of the air-fuel mixture to be combusted is switched to a stoichiometric state, a fuel-lean state, or a fuel-rich state according to operating conditions. Exhaust gas from the internal combustion engine 5 contains NO _x , particulate matter (PM), carbon monoxide (CO), HC, and the like.

The exhaust purification device 10 includes an oxidation catalyst 19 arranged in an exhaust pipe 11 of the internal combustion engine 5, an NO _X storage catalyst 15, a particulate filter 17, an NO _X selective reduction catalyst 13, and an NO _X concentration sensor 23. Prepare. The oxidation catalyst 19, the NO _X storage catalyst 15, the particulate filter 17, and the NO _X selective reduction catalyst 13 are arranged in the exhaust pipe 11 in this order from the upstream side of the exhaust flow.

The oxidation catalyst 19 oxidizes HC, CO, NO, or the like contained in the exhaust. For example, HC, CO or NO _are oxidized to _H2O , _CO2 or NO2. The particulate filter 17 is a filter that collects PM in the exhaust. The PM captured by the particulate filter 17 is combusted at appropriate times. For example, by increasing the amount of unburned HC contained in the exhaust gas of the internal combustion engine 5 and oxidizing the HC in the oxidation catalyst 19, the temperature of the exhaust gas is raised by increasing the temperature of the exhaust gas, thereby increasing the PM trapped in the particulate filter 17. to burn. In addition, the method of burning PM collected by the particulate filter 17 is not limited to the above example.

The _NOx storage catalyst 15 converts _NOx into _N2 by reacting _NOx in the exhaust gas with HC and CO. Specifically, the NO _X storage catalyst 15 stores NO _X in the exhaust when the internal combustion engine 5 is in a fuel-lean state, and releases the stored NO _X when the internal combustion engine 5 is in a fuel-rich state. HC and CO in the exhaust convert _NOx to _N2 . NH ₃ is also produced when NO _X is purified in the NO _X storage catalyst 15 .

The NO _X selective reduction catalyst 13 reduces NO _X to N ₂ by reacting NO _X in the exhaust gas with NH ₃ . Specifically, the NO _X selective reduction catalyst 13 adsorbs NH ₃ produced by the NO _X storage catalyst 15 and reduces NO _X in the inflowing exhaust gas to N ₂ by NH ₃ . The NO _X selective reduction catalyst 13 has a characteristic that the higher the catalyst temperature, the smaller the amount of NH ₃ that can be adsorbed. In addition, the NO _X selective reduction catalyst 13 has a characteristic that the NO _X reduction efficiency increases as the NH ₃ adsorption amount increases.

The NO _X concentration sensor 23 is provided in the exhaust pipe 11 downstream of the NO _X selective reduction catalyst 13 and is mainly used to detect the NO _X concentration in the exhaust flowing out from the NO _X selective reduction catalyst 13 . A sensor signal S_nox from the NO _X concentration sensor 23 is transmitted to the control device 100 . Information of the sensor signal S_nox of the NO _X concentration sensor 23 is used for abnormality diagnosis of the NO _X selective reduction catalyst 13 .

The _NOx concentration sensor 23 is known to respond not only to _NOx but also to _NH3 . However, when the NO _X selective reduction catalyst 13 is functioning normally, the outflow of NH ₃ to the downstream side of the NO _X selective reduction catalyst 13 is almost zero or extremely small. Therefore, in the exhaust purification device 10 according to the present embodiment, the sensor signal S_nox of the NO _X concentration sensor 23 is constructed so as to basically indicate the NO _X concentration in the exhaust gas.

In addition, one or more exhaust temperature sensors may be provided at appropriate positions on the exhaust pipe 11 to detect the exhaust temperature. A sensor signal S_tg of the exhaust temperature sensor is transmitted to the control device 100 . Information on the exhaust temperature at the position where the exhaust temperature sensor is provided can be used to estimate the temperature of the NO _X storage catalyst 15 or the NO _X selective reduction catalyst 13 .

<2. Diagnosis device (control device)>
Next, a configuration example of the control device 100 functioning as a diagnostic device according to this embodiment will be described. FIG. 2 is a block diagram showing a configuration example of the control device 100. As shown in FIG. The illustrated control device 100 is a control device 100 that controls the operating state of the internal combustion engine 5 . Note that the control device 100 may be configured by one control device, or may be configured by connecting a plurality of control devices so as to be able to communicate with each other.

Each control device 100 is configured to include a processor such as a CPU (Central Processing Unit) or MPU (Micro Processing Unit), an electric circuit, and the like, and is a device in which various functions are realized by the processor executing a computer program. you can Note that part or all of the control device 100 may be configured by, for example, a microcomputer, a microprocessor unit, or the like, or may be configured by an updatable device such as firmware, or may be configured by a CPU or the like. It may be a program module or the like that is executed by a command from.

The control device 100 includes an upstream NO _X concentration acquiring section 112 , an upstream ammonia concentration estimating section 113 , a downstream NO _X concentration estimating section 114 , a sensor value detecting section 116 and a determining section 118 . Each of these units may be a function realized by execution of a computer program by a processor. The control device 100 also includes a storage unit (not shown) including one or more storage elements such as RAM (Random Access Memory) or ROM (Read Only Memory). The storage unit stores computer programs executed by the processor, control parameters used for calculation, calculation results by the processor, acquired sensor values, and the like. The storage unit may include an HDD (Hard Disk Drive), a storage device, or the like.

(Upstream side NO _X concentration acquisition unit)
The upstream NO _X concentration acquisition unit 112 obtains an estimated value of the NO _X concentration in the exhaust passage on the downstream side of the NO _X storage catalyst 15 and on the upstream side of the NO _X selective reduction catalyst 13 (upstream NO _X concentration estimation value). value) N_us_mod. NO _X contained in the exhaust upstream of the NO _X selective reduction catalyst 13 is NO _X that has flowed out without being purified by the NO _X storage catalyst 15 .

The NO _X conversion efficiency may vary depending on the temperature of the NO _X storage catalyst 15 and the state of the exhaust gas. For this reason, the upstream NO _X concentration acquisition unit 112 refers to, for example, a map stored in advance in the storage unit, and based on the temperature of the NO _X storage catalyst 15 and the operating conditions of the internal combustion engine 5, determines the NO _X storage amount used for calculation. The conversion efficiency of NO _x in the catalyst 15 is set. The temperature of the NO _X storage catalyst 15 can be estimated based on the exhaust temperature, for example.

Specifically, the upstream NO _X concentration acquisition unit 112 obtains the temperature of the NO _X storage catalyst 15, the NO _X storage amount in the NO _X storage catalyst 15 when the internal combustion engine 5 is switched to the fuel-rich state, The upstream side NO _X concentration N_us_mod is calculated based on information such as the rich degree (air-fuel ratio) in the fuel-rich state and the rich combustion time of the internal combustion engine 5 . The NO _X storage amount, rich degree, and rich combustion time in the fuel-rich state of the internal combustion engine 5 can be estimated based on the operating conditions of the internal combustion engine 5 .

Note that when a _NOx concentration sensor for detecting the _NOx concentration in the exhaust passage on the downstream side of the _NOx storage catalyst 15 and on the upstream side of the _NOx selective reduction catalyst 13 is provided, the upstream _NOx concentration acquisition unit 112 may acquire the upstream _NOx concentration N_us_mod based on the sensor signal of the _NOx concentration sensor.

(Upstream ammonia concentration estimator)
The upstream ammonia concentration estimation unit 113 obtains an estimated value of the NH ₃ concentration in the exhaust passage downstream of the NO _X storage catalyst 15 and upstream of the NO _X selective reduction catalyst 13 (upstream NH ₃ concentration estimated value ) calculate _{NH3_us_mod} .

NH ₃ contained in the exhaust upstream of the NO _X selective reduction catalyst 13 is NH ₃ produced in the NO _X storage catalyst 15 . In the _NOx storage catalyst 15, _NH3 is produced according to the following reaction formula (1).
3.5H ₂ +NO ₂ →NH ₃ +2H ₂ O (1)

For example, the upstream ammonia concentration estimator 113 determines the temperature of the NO _X storage catalyst 15, the NO _X storage amount when the internal combustion engine 5 is switched to the rich combustion state, the rich degree of the internal combustion engine 5 in the rich combustion state (empty fuel ratio) and information such as the rich combustion time of the internal combustion engine 5, the upstream side NH ₃ concentration NH ₃ _us_mod is calculated. The temperature of the NO _X storage catalyst 15 can be estimated based on the exhaust temperature, for example. The NO _X storage amount, rich degree, and rich combustion time in the rich combustion state of the internal combustion engine 5 can be estimated based on the operating conditions of the internal combustion engine 5, for example.

Note that when an ammonia concentration sensor that detects the NH ₃ concentration in the exhaust passage on the downstream side of the NO _X storage catalyst 15 and on the upstream side of the NO _X selective reduction catalyst 13 is provided, the upstream ammonia concentration estimation unit 113 is , the upstream NH ₃ concentration NH ₃ _us_mod may be obtained based on the sensor signal of the ammonia concentration sensor.

(Downstream side NO _X concentration estimator)
The downstream NO _X concentration estimator 114 calculates an estimated value of the NO _X concentration in the exhaust passage on the downstream side of the NO _X selective reduction catalyst 13 (downstream NO _X concentration estimated value) N_ds_mod. The NO _X contained in the exhaust downstream of the NO _X selective reduction catalyst 13 flows out of the NO _X that has flowed out without being purified by the NO _X storage catalyst 15 without being reduced in the NO _X selective reduction catalyst 13 as well. NO _X When the NO _X selective reduction catalyst 13 is functioning normally, the amount of NO _X flowing out from the NO _X selective reduction catalyst 13 is extremely small. Therefore, the downstream NO _X concentration estimated value N_ds_mod is a relatively small value.

As described above, the maximum adsorption amount of NH ₃ in the NO _X selective reduction catalyst 13 decreases as the temperature of the NO _X selective reduction catalyst 13 increases. In addition, the NO _X reduction efficiency of the NO _X selective reduction catalyst 13 increases as the adsorption rate increases. Therefore, the downstream NO _x concentration estimation unit 114 refers to, for example, a map stored in advance in the storage unit, and selects NO _x to be used for calculation based on the temperature of the NO _x selective reduction catalyst 13 and the adsorption rate of NH ₃ . The NO _X reduction efficiency of the reduction catalyst 13 is set. The temperature of the NO _X selective reduction catalyst 13 can be estimated based on the exhaust temperature, for example. The NH ₃ adsorption rate can be estimated based on the upstream NO _X concentration N_us_mod, the upstream NH ₃ concentration NH ₃ _us_mod, the exhaust flow rate, and the temperature of the NO _X selective reduction catalyst 13 .

The adsorption rate of _NH3 can be estimated as follows, for example.
In the NO _X selective reduction catalyst 13, a reduction reaction of NO _X occurs according to the following reaction formula (2).
4NH ₃ +3NO ₂ →3.5N ₂ +6H ₂ O (2)
The downstream NO _X concentration estimation unit 114 uses the NO _X amount and the NH ₃ amount flowing into the NO _X selective reduction catalyst 13 and the temperature of the NO _X selective reduction catalyst 13 to estimate the amount of NH ₃ in the NO _X selective reduction catalyst 13. The amount of adsorption can be calculated.

The NO _X amount and NH ₃ amount flowing into the NO _X selective reduction catalyst can be obtained by multiplying the upstream NO _X concentration N_us_mod and the upstream ammonia concentration NH ₃ _us by the exhaust flow rate, respectively. The downstream NO _X concentration estimator 114 calculates the NO _X amount and the NH ₃ amount that flow into the NO _X selective reduction catalyst 13 during each calculation cycle for each predetermined calculation cycle. Then, the downstream NO _x concentration estimating unit 114 subtracts the NH ₃ amount required to reduce the NO _x of the calculated NO _x amount from the calculated NH ₃ amount, and integrates the obtained value for each calculation cycle. keep doing As a result, the downstream NO _X concentration estimator 114 can see changes in the amount of NH ₃ adsorbed in the NO _X selective reduction catalyst 13 .

When the NH ₃ adsorption amount is calculated in this manner, the NH ₃ adsorption rate with respect to the maximum adsorption amount corresponding to the temperature of the NO _X selective reduction catalyst 13 is obtained. The downstream NO _X concentration estimation unit 114 multiplies the upstream NO _X concentration N_us_mod by the NO _X reduction efficiency of the NO _X selective reduction catalyst 13 corresponding to the adsorption rate of NH ₃ to obtain the downstream NO _X concentration estimated value N_ds_mod can be calculated.

(Sensor value detector)
Sensor value detection unit 116 detects downstream NO _X concentration (downstream NO _X concentration detection value) N_ds_det as a sensor value based on sensor signal S_nox from NO _X concentration sensor 23 . The downstream NO _X concentration detection value N_ds_det basically indicates the NO _X concentration value, but indicates the NH ₃ concentration value when NH ₃ is flowing out to the downstream side of the NO _X selective reduction catalyst 13. It will be.

(Judgment part)
The determination unit 118 determines abnormality of the NO _X selective reduction catalyst 13 based on at least the downstream NO _X concentration estimated value N_ds_mod and the downstream NO _X concentration detected value N_ds_det. In this embodiment, the determination unit 118 selects NO _X based on the upstream NO _X concentration N_us_mod, the upstream NH ₃ concentration NH ₃ _us_mod, the downstream NO _X concentration estimated value N_ds_mod, and the downstream NO _X concentration detected value N_ds_det. Defects and deterioration of the reduction catalyst 13 are determined.

When the NO _X selective reduction catalyst 13 has no abnormality such as missing or deterioration, the downstream NO _X concentration detection value N_ds_det obtained based on the sensor signal S_nox of the NO _X concentration sensor 23 is calculated by the downstream NO _X concentration estimation unit 114. Approximate the estimated downstream _NOx concentration N_ds_mod. On the other hand, if the NO _X selective reduction catalyst 13 has an abnormality such as missing or deterioration, the maximum adsorption amount of NH ₃ in the NO _X selective reduction catalyst 13 _decreases . of NH ₃ increases.

Therefore, when the NO _X selective reduction catalyst 13 is abnormal, the downstream NO _X concentration detection value N_ds_det detected using the NO _X concentration sensor 23 becomes a larger value than the downstream NO _X concentration estimated value N_ds_mod. Using such a phenomenon, the determination unit 118 determines whether or not the NO _X selective reduction catalyst 13 is abnormal by comparing the downstream NO _X concentration detection value N_ds_det and the downstream NO _X concentration estimated value N_ds_mod. can do.

Further, there is a difference in the value of the downstream NO _X concentration detection value N_ds_det between when the NO _X selective reduction catalyst 13 is missing and when it is deteriorated. In this embodiment, the determination unit 118 determines whether the NO _X selective reduction catalyst 13 is deteriorated or missing. Specifically, when the NO _X selective reduction catalyst 13 is missing, the amount of NH ₃ adsorbed to the NO _X selective reduction catalyst 13 is zero, and all NH ₃ is at the installation position of the NO _X concentration sensor 23. reach. On the other hand, when the NO _X selective reduction catalyst 13 has deteriorated, part of the NH ₃ flowing into the NO _X selective reduction catalyst 13 is adsorbed by the NO _X selective reduction catalyst 13 or used for the NO _X reduction reaction.

Therefore, the downstream NO _X concentration detection value N_ds_det detected using the NO _X concentration sensor 23 when the NO _X selective reduction catalyst 13 is missing is the same as the downstream NO _X concentration detection value N_ds_det detected when the NO _X selective reduction catalyst 13 deteriorates. It becomes a large value compared to the value N_ds_det. When the NO _X selective reduction catalyst 13 is abnormal, the determination unit 118 determines whether the NO _X selective reduction catalyst 13 is missing or deteriorated based on the deviation width of the downstream NO _X concentration detection value N_ds_det from the downstream NO _X concentration estimated value N_ds_mod. can judge.

At this time, the determination unit 118 may compare the integrated value of the downstream NO _X concentration detection value N_ds_det and the integrated value of the downstream NO _X concentration estimated value N_ds_mod in the predetermined period. By comparing the respective integrated values, it becomes easier to determine the amount of deviation between the downstream NO _X concentration detected value N_ds_det and the downstream NO _X concentration estimated value N_ds_mod.

FIG. 3 is an explanatory diagram showing differences in the downstream NO _X concentration detection value N_ds_det when the NO _X selective reduction catalyst 13 is normal, missing, and deteriorated. FIG. 3 shows an example of integrated values of the downstream NO _X concentration detected value N_ds_det and the downstream NO _X concentration estimated value N_ds_mod in the period from time t1 to time t2.

When the NO _X selective reduction catalyst 13 is functioning normally, the downstream NO _X concentration detected value N_ds_det approximates the downstream NO _X concentration estimated value NH ₃ _ds_mod. Therefore, when the NO _X selective reduction catalyst 13 is normal, the integrated value of the downstream NO _X concentration detected value N_ds_det transitions in substantially the same manner as the integrated value of the downstream NO _X concentration estimated value N_ds_mod.

On the other hand, when the NO _X selective reduction catalyst 13 is missing, the NO _X concentration sensor 23 detects NH ₃ produced by the NO _X storage catalyst 15, so the downstream NO _X concentration detection value N_ds_det is It becomes a larger value than the NO _X concentration estimated value N_ds_mod. Therefore, when the NO _X selective reduction catalyst 13 is missing, the integrated value of the downstream NO _X concentration detection value N_ds_det changes while greatly exceeding the integrated value of the downstream NO _X concentration estimated value N_ds_mod.

Further, when the NO _X selective reduction catalyst 13 is degraded, part of the NH ₃ produced by the NO _X storage catalyst 15 flows out to the downstream side of the NO _X selective reduction catalyst 13, so the downstream NO _X concentration The detected value N_ds_det becomes a larger value than the downstream NO _X concentration estimated value N_ds_mod. However, the downstream NO _X concentration detection value N_ds_det at this time becomes a smaller value than the value when the NO _X selective reduction catalyst 13 is missing. Therefore, when the NO _X selective reduction catalyst 13 deteriorates, the integrated value of the downstream NO _X concentration detection value N_ds_det transitions between the integrated value when the NO _X selective reduction catalyst 13 is normal and the integrated value when the NO X selective reduction catalyst 13 is defective. do.

In this way, when the difference between the integrated value of the downstream NO _X concentration detection value N_ds_det and the integrated value of the downstream NO _X concentration estimated value N_ds_mod at time t2 is small, the determination unit 118 determines that the NO _X selective reduction catalyst 13 can be determined to be functioning normally. Further, when the difference between the integrated value of the downstream NO _X concentration detection value N_ds_det and the integrated value of the downstream NO _X concentration estimated value N_ds_mod at time t2 is large, the determination unit 118 determines that the NO _X selective reduction catalyst 13 is abnormal. It is determined that

Furthermore, determination unit 118 determines that the ratio (Y/X) of the integrated value (Y) of downstream NO _X concentration detected value N_ds_det to the integrated value (X) of downstream NO _X concentration estimated value N_ds_mod at time t2, for example, is set in advance. If the set threshold value β is exceeded, it may be determined that the NO _X selective reduction catalyst 13 is lacking. The threshold value β can be, for example, the ratio (Z/X) of the integrated value (Z) of the upstream side NH ₃ concentration estimated value NH ₃ _us_mod to the integrated value (X) of the downstream side NO _X concentration estimated value N_ds_mod.

When the NO _X selective reduction catalyst 13 is missing, the NO _X flowing out from the NO _X storage catalyst 15 together with the NH ₃ produced in the NO _X storage catalyst 15 reaches the installation position of the NO _X concentration sensor 23 . do. Therefore, when the NO _X selective reduction catalyst 13 is missing, the detected value of the NO _X concentration sensor 23 (downstream NO _X concentration detected value N_ds_mod) exceeds at least the upstream NH ₃ concentration estimated value NH ₃ _us_mod. Therefore, by setting the threshold value β to the ratio (Z/X) of the integrated value (Z) of the upstream NH ₃ concentration estimated value NH ₃ _us_mod to the integrated value (X) of the downstream NO _X concentration estimated value N_ds_mod, NO Deficiency of the _X- selective reduction catalyst 13 can be determined.

When the NO _X selective reduction catalyst 13 is missing, it is conceivable that the NO _X selective reduction catalyst 13 has been intentionally removed. may Further, when the NO _X selective reduction catalyst 13 deteriorates, the determination unit 118 may urge the driver or the like to replace the NO _X selective reduction catalyst 13 by, for example, turning on a warning lamp or sounding an alarm. good.

<3. Operation example of the diagnostic device>
Next, an operation example of the control device 100 functioning as a diagnostic device will be described with reference to the flowchart of FIG.

First, the upstream ammonia concentration estimating unit 113, the downstream NO _X concentration estimating unit 114, and the sensor value detecting unit 116 of the control device 100 obtain the upstream NH ₃ concentration estimated value NH ₃ _us_mod, the downstream NO _X concentration estimated value N_ds_mod, And the integration of the downstream NO _X concentration detection value N_ds_det is started (step S11). For example, each unit may start the integration when the internal combustion engine 5 is switched from the fuel-lean state to the fuel-rich state. As a result, diagnosis can be performed using the period during which NH ₃ is produced in the NO _X storage catalyst 15, and the reliability of the diagnosis result can be improved.

Next, the upstream ammonia concentration estimating unit 113 and the downstream NO _x concentration estimating unit 114 respectively calculate the upstream NH ₃ concentration estimated value NH ₃ _us_mod and the downstream NO _x concentration estimated value N_ds_mod, and the sensor value detecting unit 116 A downstream NO _X concentration detection value N_ds_det is detected (step S13).

Next, the upstream ammonia concentration estimating unit 113, the downstream NO _X concentration estimating unit 114, and the sensor value detecting unit 116 obtain the upstream NH ₃ concentration estimated value NH ₃ _us_mod and the downstream NO _X concentration estimated value NH 3 _us_mod obtained in step S13, respectively. The value N_ds_mod and the downstream NO _X concentration detection value N_ds_det are integrated (step S15).

Next, the upstream ammonia concentration estimating unit 113, the downstream NO _X concentration estimating unit 114, and the sensor value detecting unit 116 determine whether or not the elapsed time from the start of integration has passed a predetermined time. It is determined (step S17). The predetermined time may be set to an appropriate time in consideration of the allowable range of reliability of the diagnostic result and the like.

If the elapsed time has not passed the predetermined time (S17/No), the upstream ammonia concentration estimating unit 113, the downstream NO _x concentration estimating unit 114, and the sensor value detecting unit 116 return to step S13, and the upstream NH ₃ Calculation or detection of concentration estimated value NH ₃ _us_mod, downstream side NO _X concentration estimated value N_ds_mod, and downstream side NO _X concentration detected value N_ds_det, and integration are repeated.

On the other hand, if the elapsed time has passed the predetermined time (S17/Yes), the determination unit 118 of the control device 100 calculates the integrated value ∫N_ds_det of the downstream NO _X concentration detected value N_ds_det and the downstream NO _X concentration estimated value NH ₃ _ds_mod NH ₃ _ds_mod exceeds the threshold α (step S19). The threshold value α can be set to an appropriate value in consideration of the error of the downstream NO _X concentration estimated value N_ds_mod, the length of the predetermined time for integration, and the like.

When the difference |∫N_ds_det−∫N_ds_mod| is equal to or less than the threshold value α (S19/No), the determination unit 118 determines that the NO _X selective reduction catalyst 13 is functioning normally (no abnormality) (step S27), End this routine. On the other hand, if the difference | _{∫N_ds_det} − _{∫N_ds_mod} | It is determined whether or not the ratio of the integrated value ∫N_ds_det exceeds the threshold value β (step S21). The threshold value β may be, for example, the ratio of the integrated value ∫NH ₃ _us_mod of the upstream side NH ₃ concentration estimated value NH ₃ _us_mod to the integrated value ∫N_ds_mod of the downstream side NO _X concentration estimated value N_ds_mod.

When the ratio of the integrated value ∫N_ds_det of the downstream NO _X concentration detected value N_ds_det to the integrated value ∫N_ds_mod of the downstream NO _X concentration estimated value N_ds_mod exceeds the threshold value β (S21/Yes), the determination unit 118 performs NO _X selective reduction. It is determined that the catalyst 13 is lacking (step S23), and the routine ends. On the other hand, when the ratio of the integrated value ∫N_us_det of the downstream NO _X concentration detected value N_ds_det to the integrated value ∫N_ds_mod of the downstream NO _X concentration estimated value _{N_ds_mod} is equal to or less than the threshold β (S21/No), the determination unit 118 It is determined that the selective reduction catalyst 13 has deteriorated (step S25), and the routine ends.

As described above, the exhaust purification device 10 for the internal combustion engine 5 according to the present embodiment includes the NO _X storage catalyst 15 and the NO _X selective reduction catalyst 13 in order from the upstream side of the exhaust passage, and the NO _X selective reduction catalyst 13 A NO _X concentration sensor 23 is provided on the downstream side. The control device 100, which functions as a diagnostic device for diagnosing an abnormality of the NO _X selective reduction catalyst 13 of the exhaust purification device 10, selects NO _X based on the downstream NO _X concentration estimated value N_ds_mod and the downstream NO _X concentration detected value N_ds_det. The presence or absence of abnormality in the reduction catalyst 13 is determined. Therefore, the control device 100 can detect an abnormal state in which the NO _X selective reduction catalyst 13 does not function normally.

Further, in the present embodiment, when the NO _X selective reduction catalyst 13 is abnormal, the control device 100 further controls the upstream side NH ₃ concentration estimated value NH ₃ _us_mod, the downstream side NO _X concentration estimated value N_ds_mod, and the downstream side NO _X concentration detected value Lack or deterioration of the NO _X selective reduction catalyst 13 is determined based on N_ds_det. Therefore, the control device 100 can execute processing according to the abnormal state of the NO _X selective reduction catalyst 13 .

Further, in the present embodiment, the control device 100 detects the integrated value ∫NH ₃ _us_mod of the upstream NH ₃ concentration estimated value NH ₃ _us_mod, the integrated value ∫N_ds_mod of the downstream NO _X concentration estimated value N_ds_mod, and the downstream NO _X concentration detection The abnormality of the NO _X selective reduction catalyst 13 is determined using the integrated value ∫N_ds_det of the value N_ds_det. Therefore, the difference between the downstream NO _X concentration detected value N_ds_det and the upstream NH ₃ concentration estimated value NH ₃ _us_mod or the downstream NO _X concentration estimated value N_ds_mod becomes easier to discriminate, and the NO _X selective reduction catalyst 13 malfunctions. The reliability of diagnostic results can be improved.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

For example, in the above embodiment, the upstream NH ₃ concentration estimated value NH ₃ _us_mod, the downstream NO _X concentration estimated value N_ds_mod, and the downstream NO _X concentration detected value N_ds_det do not necessarily need to be integrated in consecutive periods. The above integration is performed after the internal combustion engine 5 is switched from the fuel-lean state to the fuel-rich state, is temporarily interrupted when the state is switched to the fuel-lean state, and is resumed when the state is switched to the fuel-lean state again. may be

In the above embodiment, the control device 100 not only determines whether the NO _X selective reduction catalyst 13 is abnormal, but also determines whether the NO _X selective reduction catalyst 13 is missing or deteriorated. is not limited to such examples. The control device 100 may determine only whether the NO _X selective reduction catalyst 13 is abnormal.

5 Internal combustion engine 10 Exhaust purification device 11 Exhaust pipe 13 NO _X selective reduction catalyst 15 NO _X storage catalyst 23 Ammonia concentration sensor 100 ... control device (diagnostic device), 112 ... upstream NO _x concentration acquiring unit, 113 ... upstream ammonia concentration estimating unit, 114 ... downstream NO _x concentration estimating unit, 116 ... sensor value detector, 118 ... decision unit

Claims (4)

A diagnostic device for diagnosing an abnormality of the NO _X selective reduction catalyst in an exhaust gas purification system having an NO _X storage catalyst and an NO _X selective reduction catalyst in order from the upstream side in an exhaust passage of an internal combustion engine,
a downstream NO _X concentration estimating unit that calculates a downstream NO _X concentration estimated value, which is an estimated value of the NO _X concentration in the exhaust passage downstream of the NO _X selective reduction catalyst;
a sensor value detection unit that acquires a sensor value of an NO _X concentration sensor provided in an exhaust passage on the downstream side of the NO _X selective reduction catalyst;
an upstream ammonia concentration estimating unit that calculates an upstream ammonia concentration estimated value that is an estimated value of ammonia concentration in an exhaust passage downstream of the NO _X storage catalyst and upstream of the NO _X selective reduction catalyst;
a determination unit that determines lack or deterioration of the NO _X selective reduction catalyst based on the estimated upstream ammonia concentration value, the estimated downstream NO _X concentration value, and the sensor value;
A diagnostic device comprising: The determination unit determines lack and deterioration of the NO _X selective reduction catalyst using the integrated value of the upstream ammonia concentration estimated value, the integrated value of the downstream NO _X concentration estimated value, and the integrated value of the sensor value. 2. The diagnostic device of claim 1 , wherein: The determination unit uses the upstream ammonia concentration estimated value, the downstream NO _X concentration estimated value, and the sensor value during a period in which ammonia flows out from the NO _X storage catalyst to determine whether the NO _X selective reduction catalyst is missing or deteriorated. 3. The diagnostic device according to claim 1 or 2 , which determines a NO _X storage catalyst provided in an exhaust passage of an internal combustion engine;
an NO _X selective reduction catalyst provided in an exhaust passage downstream of the NO _X storage catalyst;
an NO _X concentration sensor provided in an exhaust passage downstream of the NO _X selective reduction catalyst;
and a diagnostic device for diagnosing abnormality of the NO _X selective reduction catalyst,
The diagnostic device
a downstream NO _X concentration estimating unit that calculates a downstream NO _X concentration estimated value, which is an estimated value of the NO _X concentration in the exhaust passage downstream of the NO _X selective reduction catalyst;
a sensor value detection unit that acquires a sensor value of an NO _X concentration sensor provided in an exhaust passage downstream of the NO _X selective reduction catalyst;
an upstream ammonia concentration estimating unit that obtains an upstream ammonia concentration estimated value that is an estimated value of ammonia concentration in an exhaust passage downstream of the NO _X storage catalyst and upstream of the NO _X selective reduction catalyst;
a determination unit that determines lack or deterioration of the NO _X selective reduction catalyst based on the estimated upstream ammonia concentration value, the estimated downstream NO _X concentration value, and the sensor value;
An exhaust purification device for an internal combustion engine.

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