JP2016128695A - Control device for nox purification device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect abnormalities of NOx, NH, temperature sensors, etc. provided in an exhaust passage and maintain performance of an NOx purification device by making a reducing agent supply amount appropriate even when an abnormality occurs in the sensor in the NOx purification device in which a device for supplying an exhaust gas reducing agent is arranged upstream of a reduction catalyst provided in the exhaust passage of an internal combustion engine.SOLUTION: An NOx purification device includes: NOx purification performance calculation means 33 for calculating NOx purification performance of a NOx catalyst on the basis of a signal from a NOx sensor 21 located downstream of the NOx catalyst; means for setting target catalyst NOx purification performance of a reduction catalyst in any operating state; and determination means 39 for determining an abnormality of the NOx sensor on the basis of a comparison between a purification performance value calculated by the NOx purification performance calculation means 33 when inlet ammonia supply amount corresponding to the target catalyst NOx purification performance is supplied with a set target catalyst NOx purification performance value. When an abnormality is determined, the reducing agent supply amount is calculated based on the target catalyst NOx purification performance value.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a control device for a NOx purification device that purifies NOx in exhaust gas of an internal combustion engine, and more particularly, to a NOx purification device that includes an exhaust gas reducing agent supply device upstream of a reduction catalyst provided in an exhaust system. The present invention relates to a control device.

The exhaust gas discharged from an internal combustion engine such as a diesel engine contains NOx (nitrogen oxides such as NO and NO ₂ ) that may cause environmental pollution. As an exhaust purification device used for reducing NOx to purify exhaust gas, an exhaust purification device using a liquid reducing agent derived from ammonia such as an aqueous urea solution is known.

  This exhaust purification device injects urea aqueous solution or the like into the exhaust passage on the upstream side of the reduction catalyst, adsorbs ammonia produced by the hydrolysis of urea to the reduction catalyst, and removes NOx flowing into the reduction catalyst. It is decomposed and released into nitrogen and water by ammonia.

The required injection amount of the reducing agent is obtained by calculation based on a plurality of parameter values including the NOx flow rate discharged from the internal combustion engine, the temperature of the reduction catalyst, the adsorption amount of ammonia adsorbed on the reduction catalyst, and the like.
In order to obtain a more efficient NOx purification performance, the actual injection amount of the reducing agent is corrected using a sensor that is sensitive to NOx and ammonia in addition to the calculated injection amount.

  In addition, JP 2010-133354 A (Patent Document 1) is provided with a specific gas concentration sensor that is sensitive to NOx and ammonia on the downstream side of the reduction catalyst in order to optimize the injection amount of the reducing agent. A sensor value detected by the sensor is compared with a predetermined threshold value to determine an abnormality in the actual injection amount of the reducing agent, and when an abnormality occurs, the injection amount calculation parameter value in the injection amount calculation unit is corrected. It is shown.

JP 2010-133354 A

  However, in order to obtain high-efficiency NOx purification performance, the actual injection amount of the reducing agent is corrected using a sensor that is sensitive to NOx and ammonia in addition to the calculated injection amount. In the case of determining abnormality in the actual injection amount of the reducing agent based on the sensor value detected by the specific gas concentration sensor sensitive to NOx and ammonia, and correcting the injection amount calculation parameter value in the injection amount calculation unit It is assumed that the sensors that are sensitive to NOx and ammonia are operating normally. If these sensors themselves are abnormal, it is difficult to obtain a desired effect.

In addition, when the injection amount of the reducing agent is determined by the NOx sensor, NH ₃ sensor, temperature sensor, etc. installed on the upstream or downstream side or downstream side of the reduction catalyst, sensor malfunction or noise is added to the signal. In this case, the reducing agent injection amount may be set excessively. In this case, the following problem occurs.
(1) Side reactions other than generating NH ₃ from the reducing agent may occur, and solid precipitates may be formed around the reducing agent injection nozzle due to decomposition of the reducing agent, thereby blocking the piping.
(2) Similarly, the reduction catalyst may be clogged or the catalyst may be damaged due to flying solid precipitates formed on the upstream side.
(3) There is a possibility that the amount of so-called ammonia slip, which not only wastes the reducing agent but also discharges a large amount of NH ₃ to the downstream of the reduction catalyst, increases.

Therefore, the present invention has been made in view of these problems, and is provided in an exhaust passage in a NOx purifying apparatus having an exhaust gas reducing agent supply device upstream of a reduction catalyst provided in an exhaust passage of an internal combustion engine. Provided is a control device for a NOx purification device capable of detecting abnormalities in a NOx sensor, NH ₃ sensor _, temperature sensor, etc. and maintaining the performance of the NOx purification device by optimizing the reducing agent supply amount even when the sensor is abnormal. The purpose is to do.

  In order to solve the above-described problems, the present invention provides a control device for a NOx purifying apparatus including an exhaust gas reducing agent supply device upstream of a reduction catalyst provided in an exhaust passage of an internal combustion engine, wherein the reduction of the exhaust passage is performed. A NOx sensor disposed on the downstream side of the catalyst, NOx purification performance calculating means for calculating NOx purification performance by the reduction catalyst based on a signal from the NOx sensor, and a target catalyst by the reduction catalyst in an arbitrary operation state A means for setting the NOx purification performance, a means for setting the inlet ammonia supply amount according to the target catalyst NOx purification performance, and a purification performance by the NOx purification performance calculating means when the set inlet ammonia supply amount is supplied Determining means for determining whether or not the NOx sensor is abnormal based on a comparison between a value and the set target catalyst NOx purification performance value; A reducing agent supply amount that calculates a supply amount of the exhaust gas reducing agent based on an inlet ammonia supply amount that is set according to the target catalyst NOx purification performance value. A control means is provided.

  According to this invention, the abnormality of the NOx sensor installed on the downstream side of the reduction catalyst is detected using a map or an arithmetic expression based on information such as the exhaust gas temperature and the NOx emission amount from the internal combustion engine without using the NOx sensor. A determination is made by comparing the calculated purification capability of the reduction catalyst with the purification capability of the reduction catalyst calculated based on the NOx sensor signal. For example, when the deviation or contrast value of these purification capacities is larger than a predetermined value, the NOx sensor is determined to be abnormal.

  And when it determines with it being abnormal, since the supply amount of the said exhaust gas reducing agent is calculated based on the target catalyst NOx purification performance value of a reduction catalyst, it can suppress excessive reducing agent spray by malfunction of a NOx sensor. it can. As a result, it is possible to suppress the formation of solid precipitates due to the decomposition of the reducing agent around the reducing agent injection nozzle, and to prevent the catalyst from being damaged due to the blockage of the piping and the arrival of the solid precipitate formed on the upstream side, It is possible to prevent wasteful reducing agent from being sprayed and suppress discharge to the downstream of the reducing catalyst.

  In the present invention, it is preferable that the reducing agent supply amount control means corrects the exhaust gas reducing agent amount calculated from the target catalyst NOx purification performance value by a safety factor of less than 0.5 to 1 as a safety factor. Multiply by a coefficient.

  As described above, when the supply amount of the exhaust gas reducing agent is calculated based on the target catalyst NOx purification performance value of the reduction catalyst calculated based on the information such as the NOx emission amount discharged from the internal combustion engine and the exhaust gas temperature. In order to prevent overspraying, multiplication of a correction factor (coefficient less than 0.5 to 1) as a safety factor ensures overspray suppression.

  In the present invention, preferably, a reducing agent concentration sensor for detecting the concentration of the exhaust gas reducing agent is provided, and the exhaust gas reducing agent concentration is appropriate by comparing the set value of the reducing agent concentration with the detection value of the reducing agent concentration sensor. In some cases, the determination by the determination means may be executed.

  When the reducing agent concentration sensor installed in the reducing agent tank detects the reducing agent concentration and the reducing agent stored in the reducing agent tank does not deviate significantly from the standard concentration as the reducing agent, it is judged whether the NOx sensor is abnormal. By performing this, it is possible to improve the accuracy of the NOx sensor abnormality determination.

  In the present invention, it is preferable that the reduction catalyst calculated based on the exhaust gas temperature detected by a temperature sensor installed on at least one of the upstream side and the downstream side of the reduction catalyst in order to estimate the temperature of the reduction catalyst. The temperature sensor is abnormal by comparing the temperature with the exhaust gas temperature detected by the exhaust gas temperature sensor other than the temperature sensor or the exhaust gas temperature calculated from the operating state of the internal combustion engine. It may be provided with a temperature sensor abnormality determination means for determining whether or not.

  By determining abnormality of the temperature sensor for estimating the temperature of the reduction catalyst, the NOx purification of the reduction catalyst is derived by deriving the catalyst temperature and the ammonia adsorption amount in the reduction catalyst based on the data such as the NOx emission amount from the internal combustion engine. The accuracy of the second NOx purification performance calculating means for calculating the performance can be increased, and as a result, the accuracy of the NOx sensor abnormality determination can be increased.

  Further, when the temperature sensor abnormality determining means determines that the temperature sensor is abnormal, it is based on the exhaust gas temperature detected by the exhaust gas temperature sensor other than the temperature sensor or the exhaust gas temperature calculated from the operating state of the internal combustion engine. By estimating the temperature of the reduction catalyst, appropriate control of the exhaust gas reducing agent can be performed even when the temperature sensor is abnormal, and excessive supply can be suppressed.

According to the present invention, the abnormality of the NOx sensor installed on the downstream side of the reduction catalyst is calculated using a map or an arithmetic expression based on the exhaust gas temperature and the NOx emission amount from the internal combustion engine without using the NOx sensor. The determination is made by comparing the purification capability of the reduction catalyst with the purification capability of the reduction catalyst calculated based on the NOx sensor signal.
And when it determines with it being abnormal, since the supply amount of the said exhaust gas reducing agent is calculated based on the target catalyst NOx purification performance value of a reduction catalyst, it can suppress excessive reducing agent spray by malfunction of a NOx sensor. it can.
As a result, it is possible to detect the abnormality of the NOx, temperature sensor, etc. provided in the exhaust passage and to optimize the reducing agent supply amount even when the sensor is abnormal to maintain the performance of the NOx purification device.

1 is an overall configuration diagram of the present invention. It is a block diagram of the configuration of the control device of the NOx purification device. It is a control flowchart of the control apparatus of 1st Embodiment. 3 is a flowchart subsequent to FIG. 3-1. It is a control flowchart of the control apparatus of 2nd Embodiment. It is a control flowchart of the control apparatus of 3rd Embodiment. It is a characteristic line figure which shows the relationship between the ammonia adsorption amount of a NOx catalyst used for a NOx purification apparatus, and a NOx purification rate. It is a characteristic line figure which shows the relationship between the catalyst temperature of the NOx catalyst used for a NOx purification apparatus, and a NOx purification rate. It is a characteristic diagram which shows the relationship between the catalyst temperature of the NOx catalyst used for a NOx purification apparatus, and the ammonia adsorption amount.

  Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention to that unless otherwise specified.

With reference to FIG. 1, the whole structure of the NOx purification apparatus which concerns on this invention is demonstrated.
An exhaust passage 3 of a diesel engine 1 mounted on a vehicle (not shown) has an oxidation catalyst (hereinafter abbreviated as DOC) 5 and particulate matter contained in exhaust gas (abbreviated as particulate matter, PM) from the exhaust upstream side. A diesel particulate filter (hereinafter abbreviated as DPF) 7 and a urea SCR system 9 are provided.
The urea SCR system 9 is a urea water injection means (reducing agent injection means) having a NOx catalyst 11 as a reduction catalyst and a spray nozzle 12 for injecting urea water as a reducing agent into the exhaust passage 3 upstream of the NOx catalyst 11. 13 and a urea water tank 15 for supplying urea water to the urea water injection means 13.

  In this way, the exhaust gas discharged from the engine 1 is oxidized in the exhaust passage 3 by oxidizing the fuel in the exhaust gas with the DOC 5, the exhaust gas temperature is raised, and the PM accumulated in the DPF 7 is heated through the DPF 7. An exhaust gas aftertreatment device is provided which is configured to denitrate nitrogen oxides in the exhaust gas by the urea SCR system 9 by burning with the exhaust gas.

The urea SCR system 9 sprays urea water into the exhaust passage 3 by the urea water injection means 13, and the sprayed urea water is heated as shown in the equation (1) by heat and moisture in the exhaust passage 3. Decompose and hydrolyze to release NH ₃ .
(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂ (1)
Thereafter, the generated ammonia flows in the exhaust passage 3 together with the exhaust gas and reaches the NOx catalyst 11. A part of the urea water does not become ammonia but reaches the NOx catalyst 11 as the urea water. Therefore, ammonia is generated from the urea water also in the NOx catalyst 11 by the reaction of the formula (1). The ammonia that has reached the NOx catalyst 11 reacts with nitrogen oxides contained in the exhaust gas, removes oxygen from the nitrogen oxides, and is reduced to nitrogen. Specifically, nitrogen oxides are reduced by the reactions shown in the following formulas (2) to (4) to generate N ₂ .
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (2)
2NH ₃ + NO + NO ₂ → 2N ₂ + 3H ₂ O (3)
8NH ₃ + 6NO ₂ → 7N ₂ + 12H ₂ O (4)

The control device 20 in the NOx purification device configured as described above will be described.
The control device 20 includes a signal from a NOx sensor 21 disposed downstream of the NOx catalyst 11, a signal from a downstream temperature sensor 25 disposed downstream of the NOx catalyst 11, and an upstream of the urea water spray nozzle 12. The signal from the upstream temperature sensor 27 disposed on the downstream side of the DPF 7, the signal from the DPF inlet temperature sensor 29 disposed on the inlet side of the DPF 7, and the signal disposed from the DOC inlet side A signal from the DOC inlet temperature sensor 31 is input.
Furthermore, signals such as the engine speed, engine load, and fuel injection amount relating to the operating state are input from the engine 1.

(First embodiment)
A first embodiment of the control device 20 will be described with reference to the block diagram of FIG. 2 and the flowcharts of FIGS. 3-1 and 3-2.
As shown in FIG. 2, the first NOx purification performance calculating means (NOx purification performance calculating means) 33 for calculating the NOx purification performance based on the signal from the NOx sensor 21 and the engine operating state calculating means 35 are used for NOx emission. And a second NOx purification performance calculating means 37 for calculating the exhaust gas temperature and calculating the NOx purification performance based on the exhaust gas temperature.
Further, a determination unit 39 that compares the calculation results from the first NOx purification performance calculation unit 33 and the second NOx purification performance calculation unit 37 to determine whether the NOx sensor 21 is abnormal is provided. Yes.

  Furthermore, based on the result of the determination means 39, it is controlled whether the calculation result from the first NOx purification performance calculation means 33 or the calculation result from the second NOx purification performance calculation means 37 is used, and urea water is used. A reducing agent supply amount control means 43 for controlling the urea water supply amount to the injection means 13 is provided. Specifically, when it is determined that the determination unit 39 is abnormal, the result of calculating the supply amount of the exhaust gas reducing agent based on the purification performance calculated by the second NOx purification performance calculation unit 37 is the urea water injection Output to means 13.

Further, signals from the downstream temperature sensor 25 and the upstream temperature sensor 27 of the NOx catalyst 11 are input to the second NOx purification performance calculating means 37, and the upstream temperature sensor 27 and the downstream temperature sensor 25 A temperature sensor abnormality determining means 45 for determining abnormality is connected. The determination means 39 receives a signal from a urea water concentration sensor (reducing agent concentration sensor) 47 that detects the concentration of the urea water injected into the urea water tank 15 and determines the concentration of the urea water. ing.
The signal processing from the upstream temperature sensor 27 and the downstream temperature sensor 25 will be described later in the third embodiment, and the signal processing from the urea water concentration sensor 47 will be described later in the second embodiment.

Next, with reference to the flowcharts of FIGS. 3A and 3B, the abnormality determination of the NOx sensor 21 according to the first embodiment and the control corresponding to the abnormality will be described.
First, in step S1, an engine operating state is input. Signals such as engine speed (Ne), engine load (Le), fuel injection amount (Qf) and the like are captured.

  In step S2, the exhaust gas temperature (TEX) exhausted from the engine 1 and the NOx exhaust flow rate (NOx catalyst inlet NOx flow rate) exhausted from the engine 1 (FNOxIN) based on the information on these engine operating states are used. ) Is calculated. If there is an oxidation catalyst (DOC), diesel particulate filter (DPF), etc. upstream of the NOx catalyst, the NOx emission amount taking into account the NOx reaction in the DOC or DPF relative to the engine exhaust NOx amount can be set as FNOxIN. good.

In step S3, the catalyst temperature (Tcat) of the NOx catalyst 11 is estimated based on the exhaust gas temperature (TEX) discharged from the engine 1 obtained in step S2.
The estimation is performed by using a correlation equation considering factors such as the length of the exhaust passage 3 from the outlet of the engine 1 to the NOx catalyst 11 and heat radiation. Factors to consider include temperature drop due to heat release in exhaust passage 3, response delay due to heat capacity at DOC5, temperature rise due to oxidation reaction of unburned fuel (CO, HC) at DOC5, response delay due to heat capacity at DPF7 The temperature rise due to the oxidation reaction of unburned fuel (CO, HC) in the DPF 7 and the response delay due to the heat capacity in the NOx catalyst 11 can be considered.

In step S3, the NH ₃ adsorption amount (Zcat) is calculated. The NH ₃ adsorption amount is calculated by using a preset relationship map (relational expression) between the catalyst temperature and the ammonia adsorption amount as shown in FIG.
As shown in FIG. 6, the NOx purification rate increases as the ammonia adsorption amount increases, and as shown in FIG. 7, the higher the catalyst temperature, the higher the purification rate. For this reason, it is preferable to control the ammonia adsorption amount high, but there is a limit to the ammonia adsorption amount that can be adsorbed to the NOx catalyst. When operating for a long time at a certain temperature, exhaust gas flow rate, exhaust gas concentration, etc., the ammonia adsorption amount reaches the limit, but if there is a change in the operating state, ammonia adsorption reaction and desorption on the catalyst. The amount of NH ₃ adsorbed on the catalyst is estimated from the reaction rate.

In step S4, the target catalyst NOx purification performance (ηtg) is set. This target catalyst NOx purification performance (ηtg) is the purification performance that is desired to be obtained at a certain operating state point. That is, the target maximum NOx purification performance of the catalyst determined from the maximum NH ₃ adsorption amount, the catalyst temperature, the catalyst amount, the exhaust gas flow rate, and the reducing agent supply amount at a certain operating state point is set.
The target catalyst NOx purification performance (ηtg) is obtained based on the NH ₃ adsorption amount characteristic map as shown in FIG. 8 and the catalyst temperature (Tcat) estimated in step S3, and the target catalyst NOx purification performance (ηtg) is set. .

In step S5, an inlet NH ₃ supply flow rate (FNH3IN) is set. From the target catalyst NOx purification performance (ηtg) set in step S4, the inlet NH ₃ supply flow rate (FNH3IN) corresponding to the target catalyst NOx purification performance (ηtg) is calculated and set. If the supply amount of NH ₃ is determined, the urea water supply amount is also determined by the reaction formula (1).

In step S6, the estimated catalyst NOx purification performance (ηa) is calculated. The estimated catalyst NOx purification performance (ηa) is for estimating the NOx purification performance of the catalyst in its operating state. From the inlet NH ₃ supply flow rate (FNH3IN) determined in step S5, the catalyst temperature (Tcat) in the operating state determined in step S3, and the NH ₃ adsorption amount (Zcat), the NOx purification performance in the operating state is estimated. To do.

In step S7, by using the estimated catalyst NOx purification performance calculated in step S6 (ηa), calculates the outlet NOx concentration at the outlet side of the NOx catalyst 11 (CNOxout), and an outlet NH ₃ concentrations (CNH3out), respectively.

In step S8, the reducing agent is sprayed so as to have the ammonia amount set in step S5.
In step S9, the outlet NOx concentration (SNOxout) is calculated based on the signal from the NOx sensor 21 installed on the downstream side of the NOx catalyst 11.

In step 10, the catalyst NOx purification performance (ηb) is calculated from the NOx concentration based on the signal from the NOx sensor 21 in step S9.
Then, in step S11, the target catalyst NOx purification performance (ηtg) set in step S4 is compared with the catalyst NOx purification performance (ηb) calculated in step S10, and the actually measured purification performance is greater than the target value purification performance. When it is small, the determination becomes NO, and the process proceeds to step S15 to correct the increase in the ammonia flow rate.

Further, when the actual purification performance is greater than the target purification performance, the determination becomes Yes, the process proceeds to step S12, the outlet NOx concentration (CNOxout) calculated from the engine operating state data in step S7, and the NOx in step S9. The outlet NOx concentration (SNOxout) calculated from the signal from the sensor 21 is compared, and it is determined whether or not the concentration ratio SNOxout / CNOxout is less than a predetermined threshold value α.
It may be determined whether the absolute value | CNOxout−SNOxout | of the concentration deviation is less than the predetermined threshold value α ′ instead of the concentration ratio.

If Yes in step S12, that is, if it is less than the threshold value α, the NOx sensor 21 is determined to be normal, and the ammonia flow rate is reduced in step S13.
In step S14, it is determined again whether the target catalyst NOx purification performance (ηtg) set in step S4 is equal to the catalyst NOx purification performance (ηb) calculated in step S10. If they are not equal, the process returns to step S11 and the same procedure is repeated.

Further, if NO in step S12, that is, if the threshold value α is equal to or larger than the threshold value α, it is determined in step S16 that the NOx sensor 21 is abnormal, and in step S17, the inlet NH ₃ supply flow rate (FNH3IN) is changed from the engine operating state. An ammonia flow rate is set for the target catalyst NOx purification performance (ηtg) calculated based on the calculated NOx discharge flow rate (FNOxIN), and further, a correction coefficient β, which is a safety coefficient, is multiplied.
In this way, the overspray is reliably suppressed by multiplying the correction coefficient β (coefficient less than 0.5 to 1) as a safety coefficient.

  Further, when it is determined in step S16 that the NOx sensor 21 is abnormal, the urea water spray itself is stopped instead of decreasing the ammonia flow rate setting value to suppress the urea water spray as described above. Also good. As described above, when the NOx sensor 21 is abnormal, by stopping the supply of the urea water, it is possible to reliably prevent wasteful consumption of the urea water and discharge of a large amount of ammonia downstream of the NOx catalyst.

The threshold value α in the determination in step S12 may be a constant value or may be changed. For example, the NOx emission amount (NOx catalyst inlet NOx flow rate) calculated from the engine speed and torque (FNOxIN) ) May be changed in accordance with (), and the threshold value α may be increased in accordance with an increase in NOx emission (an increase in engine speed and load).
As the NOx emission from the engine increases, the NOx emission at the NOx catalyst outlet may also increase. Therefore, by changing α to improve the estimation accuracy, NOx, which is a harmful substance, is avoided as much as possible. .
Further, as the NOx emission amount increases, the NOx emission amount at the NOx catalyst outlet may also increase. Therefore, in the transient operation state, the detection of the NOx sensor is based on the NOx emission amount calculated from the engine speed and torque. In such a case, the determination accuracy is improved by preventing NO in step S12 and erroneously determining that the NOx sensor is abnormal in step S16.

  According to the first embodiment described above, an abnormality of the NOx sensor 21 installed on the downstream side of the NOx catalyst 11 is mapped or calculated based on the NOx emission amount and the exhaust gas temperature from the internal combustion engine without using the NOx sensor 21. The outlet NOx concentration (CNOxout) that is the purification capability of the NOx catalyst 11 calculated using the equation, and the outlet NOx concentration (SNOxout) that is the purification capability of the NOx catalyst 11 calculated based on the signal from the NOx sensor 21. Specifically, since the determination is made based on whether or not the contrast value SNOxout / CNOxout is less than the predetermined threshold value α, the abnormality of the NOx sensor 21 can be reliably determined.

  As a result, excessive reducing agent spray due to the malfunction of the NOx sensor 21 can be suppressed. In addition, it is possible to suppress the formation of solid precipitates due to decomposition of the reducing agent around the reducing agent injection nozzle, to prevent the damage of the catalyst due to blockage of the piping and the arrival of solid precipitates formed on the upstream side. In addition to preventing spraying of the reducing agent, it is possible to suppress discharge to the downstream of the reduction catalyst.

Instead of comparing the outlet NOx concentration (CNOxout) calculated from the catalyst purification performance based on the engine operating state determined in step S12 and the outlet NOx concentration (SNOxout) based on the signal from the NOx sensor 21, the engine operating state is set. The abnormality determination of the ammonia sensor is also possible based on the outlet NH ₃ concentration calculated from the catalyst purification performance based on this and the signal from the ammonia sensor.

(Second Embodiment)
Next, a second embodiment of the control device 20 will be described with reference to the configuration block diagram of FIG. 2 and the flowchart of FIG.
In the second embodiment, the urea water concentration sensor 47 is provided in FIG. 2 to detect the urea water concentration, and the set value of the urea water concentration and the detection value of the urea water concentration sensor 47 are compared. When the ratio is smaller than the predetermined value, it is determined that the urea water concentration is appropriate, and the determination by the determination means 39 is executed. In FIG. 4, a portion P is added to the first embodiment. In other configurations, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In FIG. 4, if the determination in step S <b> 12 is NO, that is, if it is equal to or greater than the threshold value α, it is determined in step S <b> 16 that the NOx sensor 21 is abnormal, but before that determination, the reduction is performed in step S <b> 21. It is determined whether the concentration of urea water as the agent is at a specified concentration. That is, it is determined whether or not the absolute value of the deviation between the reducing agent set concentration Ua and the reducing agent measured concentration Ub is equal to or less than the threshold δ. Or you may determine by calculating a ratio instead of a deviation.

If it is greater than or equal to the threshold value δ in step S21, the process proceeds to step S22 to output a system abnormality and issue an alarm or an alarm lamp. Further, an alarm may be issued and the urea water supply may be stopped to stop the engine. Other configurations are the same as those of the first embodiment.
According to the second embodiment, the urea water concentration sensor 47 installed in the urea water tank 15 detects the urea water concentration, and the urea water as the reducing agent stored in the urea water tank 15 deviates from the standard concentration. Since the abnormality determination of the NOx sensor 21 is executed when the concentration is not, the accuracy of the abnormality determination of the NOx sensor 21 in the first embodiment can be improved.

(Third embodiment)
Next, a third embodiment of the control device 20 will be described with reference to the configuration block diagram of FIG. 2 and the flowchart of FIG.
In FIG. 2, the third embodiment includes an upstream temperature sensor 27 and a downstream temperature sensor 25 installed on the upstream and downstream sides of the NOx catalyst 11, and the temperature of the NOx catalyst 11 is estimated based on these signals. ing. Based on the signals from these temperature sensors, it is determined whether the temperature sensor is abnormal. This determination is performed by the temperature sensor abnormality determination unit 45 and the result is input to the second NOx purification performance calculation unit 37.
In FIG. 5, R1 and R2 are added to the first embodiment. In other configurations, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

As shown in FIG. 5, in step S31, at least one of the catalyst inlet gas temperature (TIN) and the catalyst outlet gas temperature (TOUT) is detected by the upstream temperature sensor 27 and the downstream temperature sensor 25, respectively.
In step S32, the catalyst temperature (Tcat) is calculated from at least one of the catalyst inlet gas temperature (TIN) and the catalyst outlet gas temperature (TOUT) detected in step S31. This calculation is performed by a predetermined relational expression or a correlation between the catalyst temperature obtained in advance by a test, the catalyst inlet gas temperature (TIN), and the catalyst outlet gas temperature (TOUT). Thereafter, in step S3, the subsequent calculation proceeds using the catalyst temperature calculated in step S32.

Steps S3 to S10 are the same as in the first embodiment.
In the third embodiment, in step S33, a signal (TDPF) from the temperature sensor other than the upstream temperature sensor 27 and the downstream temperature sensor 25, for example, the DPF inlet temperature sensor 29 disposed on the inlet side of the DPF 7, the DOC5 A signal from a DOC inlet temperature sensor 31 arranged on the inlet side is input (TDOC), and further, based on the information on the engine operating state, a catalyst using the exhaust gas temperature (TEX) discharged from the engine 1 using a data map. The temperature (T′cat) is calculated using the necessary relational expressions. This relational expression is calculated from a predetermined relational expression set in consideration of, for example, the length of the exhaust passage 3 and the amount of heat radiation.

Next, in step S34, it is determined whether the deviation is less than a predetermined threshold γ based on the deviation between the catalyst temperature (Tcat) obtained in step S32 and the catalyst temperature (T′cat) obtained in step S33. To do.
In the case of Yes, the process proceeds to [1] in FIG. 3-2. In the case of NO, since the deviation is equal to or greater than the predetermined threshold γ, it is determined that the upstream temperature sensor 27 and the downstream temperature sensor 25 are abnormal. To do.
In step S36, the catalyst temperature (T′cat) obtained in step S33 is set as the catalyst temperature Tcat in step S32, and the process returns to [3].

  According to the third embodiment described above, the second NOx purification performance calculation is performed by determining the abnormality of the upstream temperature sensor 27 and the downstream temperature sensor 25 of the NOx catalyst 11 for estimating the temperature of the NOx catalyst 11. The determination accuracy of the means 37 can be increased. That is, the calculation accuracy and reliability of the catalyst temperature in step S3 of FIG. 5 can be improved, and as a result, the accuracy of abnormality determination of the NOx sensor 21 can be increased.

  When it is determined that the upstream temperature sensor 27 and the downstream temperature sensor 25 are abnormal, the exhaust gas temperature detected by another exhaust gas temperature sensor other than the upstream temperature sensor 27 and the downstream temperature sensor 25 or the internal combustion engine By controlling the temperature of the NOx catalyst estimated based on the exhaust gas temperature calculated from the operating state as the catalyst temperature, the controller 20 controls the upstream temperature sensor 27 and the downstream temperature sensor 25 even when the upstream temperature sensor 27 and the downstream temperature sensor 25 are abnormal. An excessive supply of urea water can be suppressed.

  In addition, of course, you may implement combining 2nd Embodiment and 3rd Embodiment with respect to 1st Embodiment, respectively, and the effect demonstrated in each embodiment is acquired.

According to the present invention, in a NOx purification device provided with an exhaust gas reducing agent supply device upstream of a reduction catalyst provided in an exhaust passage of an internal combustion engine, such as NOx, NH3 _, temperature sensor, etc. provided in the exhaust passage. It is suitable for use in a control device for a NOx purification device that can detect an abnormality and optimize the amount of reducing agent supplied even when the sensor is abnormal to maintain the performance of the NOx purification device.

1 Diesel engine (internal combustion engine)
3 Exhaust passage 5 DOC (oxidation catalyst)
7 DPF (diesel particulate filter)
9 Urea SCR system 11 NOx catalyst (reduction catalyst)
13 Urea water injection means (reducing agent injection means)
DESCRIPTION OF SYMBOLS 15 Urea water tank 20 Control apparatus of NOx purification apparatus 21 NOx sensor 25 Downstream temperature sensor 27 Upstream temperature sensor 29 DPF inlet temperature sensor 31 DOC inlet temperature sensor 33 First NOx purification performance calculation means 35 Engine operation state calculation means 37 Second NOx purification performance calculation means 39 Determination means 43 Reducing agent supply amount control means 45 Temperature sensor abnormality determination means 47 Urea water concentration sensor (reducing agent concentration sensor)

Claims (5)

In a control device for a NOx purification device comprising an exhaust gas reducing agent supply device upstream of a reduction catalyst provided in an exhaust passage of an internal combustion engine,
A NOx sensor disposed downstream of the reduction catalyst in the exhaust passage;
NOx purification performance calculating means for calculating NOx purification performance by the reduction catalyst based on a signal from the NOx sensor;
Means for setting a target catalyst NOx purification performance by the reduction catalyst in an arbitrary operation state;
Means for setting an inlet ammonia supply amount in accordance with the target catalyst NOx purification performance;
Whether or not the NOx sensor is abnormal based on a comparison between the purification performance value by the NOx purification performance calculating means when the set inlet ammonia supply amount is supplied and the set target catalyst NOx purification performance value Determining means for determining
A reducing agent supply amount control means for calculating a supply amount of the exhaust gas reducing agent on the basis of an inlet ammonia supply amount set according to the target catalyst NOx purification performance value when the determination means determines that the abnormality is present; A control device for a NOx purification device, comprising:   2. The reducing agent supply amount control means multiplies the exhaust gas reducing agent amount calculated from the target catalyst NOx purification performance value by a correction coefficient of 0.5 to less than 1 as a safety coefficient. The control apparatus of the NOx purification apparatus as described.   A reducing agent concentration sensor for detecting the concentration of the exhaust gas reducing agent is provided. When the exhaust gas reducing agent concentration is appropriate by comparing the set value of the reducing agent concentration with the detection value of the reducing agent concentration sensor, the determination by the determining means The control device for the NOx purification device according to claim 1, wherein:   In order to estimate the temperature of the reduction catalyst, a reduction catalyst temperature calculated based on an exhaust gas temperature detected by a temperature sensor installed at least on one of the upstream side and the downstream side of the reduction catalyst, and other than the temperature sensor A temperature sensor that compares the exhaust gas temperature detected by another exhaust gas temperature sensor or the temperature of the reduction catalyst estimated based on the exhaust gas temperature calculated from the operating state of the internal combustion engine to determine whether or not the temperature sensor is abnormal The control device for the NOx purification device according to claim 1, further comprising abnormality determination means.   When the temperature sensor abnormality determining means determines that the temperature sensor is abnormal, reduction based on the exhaust gas temperature detected by the exhaust gas temperature sensor other than the temperature sensor or the exhaust gas temperature calculated from the operating state of the internal combustion engine The control device for the NOx purification device according to claim 4, wherein the temperature of the catalyst is estimated.

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