JP6149686B2 - HC catalyst poisoning detection system for SCR catalyst and HC catalyst poisoning detection method for SCR catalyst - Google Patents

Description

  The present invention relates to an SCR catalyst HC adsorption poisoning detection system and an SCR catalyst HC adsorption poisoning detection method capable of improving the detection accuracy of SCR catalyst poisoning of an SCR catalyst provided in an exhaust passage of an internal combustion engine.

In general, as one of NOx reduction catalysts for purifying NOx (nitrogen oxides) in exhaust gas of an internal combustion engine, there is a urea-based selective reduction catalyst (SCR: Selective Catalytic Reduction). In this SCR catalyst, urea ((NH ₂ ) ₂ CO) is supplied into the exhaust gas upstream of the SCR catalyst, and this urea is hydrolyzed to produce ammonia (NH ₃ ), which is adsorbed and held on the SCR catalyst. By reacting this adsorbed ammonia with NOx contained in the exhaust gas passing through the SCR catalyst, NOx is reduced to water (H ₂ O) and nitrogen (N ₂ ).

  As this SCR catalyst, a zeolite-based catalyst, in particular, an Fe-zeolite catalyst is put into practical use, and a diesel aftertreatment system using a combination of an oxidation catalyst, a urea water addition system, and an SCR catalyst is put into practical use. However, when HC in the exhaust gas is adsorbed on the SCR catalyst, ammonia, which is a reducing agent generated from urea, cannot be adsorbed on the SCR catalyst, and there is a problem of HC adsorption poisoning in which NOx purification performance is reduced ( (See FIG. 3).

  If an oxidation catalyst is arranged on the upstream side of the SCR catalyst and the oxidation catalyst is at or above the temperature showing HC oxidation activity, HC in the exhaust gas is oxidized and removed by this oxidation catalyst, so that HC does not flow into the SCR catalyst. So HC adsorption poisoning does not occur.

  However, when the engine is in an idle condition or the like and the exhaust gas temperature is low, the HC in the exhaust gas is not purified by the oxidation catalyst or DPF (diesel particulate filter), and the SCR catalyst May deteriorate due to HC adsorption poisoning.

  Therefore, HC adsorption, which is a process for desorbing HC by detecting the HC adsorption poisoning of the SCR catalyst appropriately and accurately and raising the temperature of the SCR catalyst above the temperature at which HC adsorbed on the SCR catalyst desorbs. It is necessary to carry out poisoning recovery treatment.

  In relation to this problem, the HC inflow amount to the SCR catalyst is estimated from the engine exhaust HC amount obtained from the engine operating conditions, the exhaust pipe injected fuel amount, the HC oxidation rate of the oxidation catalyst (DOC), or the SCR HC adsorption poisoning of the SCR catalyst is detected and estimated by estimating the amount of HC adhering to the SCR catalyst from the exhaust gas amount obtained from the HC concentration measured by the HC concentration sensor upstream of the catalyst and the intake air amount, etc. When the amount of HC adhering exceeds the allowable amount of adhering, a method for determining HC adsorption poisoning and raising the SCR catalyst temperature to perform HC desorption treatment and HC poisoning regeneration has been proposed. (For example, refer to Patent Document 1).

  In this detection method, in order to detect the amount of HC flowing into the SCR catalyst, the amount of HC flowing into the SCR catalyst is estimated from the engine operating conditions, or a new HC concentration sensor is disposed upstream of the SCR catalyst. It is necessary to install.

  When estimating the HC inflow amount from the engine operating conditions, etc., it is difficult to obtain the HC emission amount with a relatively large and accurate accuracy under the engine idle conditions, and the HC oxidation rate at the upstream oxidation catalyst. However, especially under low temperature exhaust gas conditions, temperature, exhaust gas flow rate, gas composition, etc. fluctuate, so it is difficult to obtain accurately and it is difficult to accurately estimate the amount of HC inflow into the SCR catalyst. is there.

  On the other hand, when an HC concentration sensor is provided, it is difficult to obtain sufficient detection accuracy with the current HC concentration sensor for exhaust gas measurement, and a new HC concentration sensor is required, which increases the cost. is there.

  Furthermore, even if the amount of HC inflow into the SCR catalyst can be accurately estimated, the HC in the exhaust gas is not composed of a single component but is composed of multi-component HC, and the composition ratio of HC increases depending on various conditions. fluctuate. In addition, if the HC species are different, the adhesion and adsorption characteristics and desorption characteristics to the SCR catalyst are different, and the larger the molecular weight, the larger the HC species adhesion amount to the SCR catalyst, and the greater the influence of ammonia adsorption inhibition. For example, the degree of influence on HC adsorption poisoning is different (see FIGS. 4 and 5, molecular weight of HC species 2> molecular weight of HC species 1). Therefore, the above detection method has a problem that it is difficult to appropriately detect the HC adsorption poisoning of the SCR catalyst.

JP 2009-41437 A

  The present invention has been made in view of the above, and an object of the present invention is to accurately measure the degree of deterioration due to HC adsorption poisoning of an SCR catalyst provided in an exhaust passage of an internal combustion engine without using an HC concentration sensor. It is an object to provide an SCR catalyst poisoning detection system for an SCR catalyst and a method for detecting HC adsorption poisoning of an SCR catalyst.

  To achieve the above object, an HC catalyst poisoning detection system for an SCR catalyst according to the present invention is an HC adsorption poisoning detection system for detecting HC adsorption poisoning of an SCR catalyst provided in an exhaust passage of an internal combustion engine. In order from the upstream side to the passage, an upstream side NOx amount detection device, a urea water addition device, the SCR catalyst, and a downstream ammonia-compatible NOx amount detection device having detection sensitivity for both NOx and ammonia are arranged, A temperature detection device for detecting an index temperature indicating the catalyst temperature of the SCR catalyst is provided, and further, a control device for controlling the urea water addition device and determining HC adsorption poisoning of the SCR catalyst is provided. However, when the index temperature detected by the temperature detecting device is between the first set temperature and the second set temperature set in advance, H for detecting HC adsorption poisoning of the SCR catalyst. In addition to performing adsorption poisoning detection control, in this HC adsorption poisoning detection control, control is performed to stop the addition of urea water from the urea water addition device, and after the urea water addition is stopped, the upstream NOx When the difference between the upstream NOx amount detected by the amount detection device and the downstream NOx amount detected by the downstream ammonia-compatible NOx amount detection device is equal to or less than a preset NOx purification end threshold, the urea water Whether or not the downstream NOx amount exceeds the upstream NOx amount after performing the control to resume the addition of urea water from the addition device and after the urea water addition has been resumed and a preset time has elapsed. When the downstream NOx amount exceeds the upstream NOx amount, it is determined that the SCR catalyst is HC adsorbed and the downstream NOx amount is the upstream NOx amount. Is If configured to perform determining and control the SCR catalyst does not have any HC adsorption poisoning.

  The temperature detection device that detects an index temperature that indicates the catalyst temperature of the SCR catalyst is a temperature detection device that is provided with a temperature sensor in the SCR catalyst and directly measures the catalyst temperature of the SCR catalyst. Although the catalyst temperature detected by this temperature sensor is a temperature indicating the temperature of the SCR catalyst, it is generally difficult to directly measure the catalyst temperature, and the temperature of the exhaust gas flowing into the SCR catalyst is substituted. In this case, the index temperature that indicates the catalyst temperature of the SCR catalyst is the temperature of the exhaust gas, and the temperature sensor that detects the temperature of the exhaust gas serves as the temperature detection device.

  The ammonia-compatible NOx amount detection device is a detection sensor having detection sensitivity for both NOx and ammonia, and has detection sensitivity not only for NOx but also for ammonia (see FIG. 6). The downstream NOx amount detected by the ammonia-compatible NOx amount detection device includes an amount corresponding to ammonia slip, and is detected as the sum of the NOx amount and the ammonia amount at the SCR catalyst outlet. By using this ammonia-compatible NOx amount detection device, the determination of HC adsorption poisoning of the SCR catalyst can be performed with higher accuracy.

  Next, the principle of HC adsorption poisoning detection in the SCR catalyst HC adsorption poisoning detection system and the SCR catalyst HC adsorption poisoning detection method will be described.

When the addition of urea water is stopped when the catalyst temperature of the SCR catalyst is within a certain range, ammonia (NH ₃ ) adsorbed and held by the SCR catalyst is used for NOx purification of exhaust gas passing through the SCR catalyst. Eventually, the amount of ammonia adsorbed and held on the SCR catalyst is reduced, and NOx purification hardly occurs. Therefore, the upstream NOx amount at the SCR catalyst inlet and the downstream NOx amount at the outlet are substantially equal. That is, the difference between the upstream NOx amount and the downstream NOx amount is equal to or less than a preset NOx purification end threshold.

  Under this situation, when the addition of urea water is resumed, the supply of ammonia to the SCR catalyst is resumed. However, since the ammonia is hardly adsorbed on the SCR catalyst, the SCR catalyst is not HC adsorbed and poisoned. In this case, ammonia is adsorbed on the SCR catalyst, the NOx purification reaction proceeds, ammonia slip does not occur, and the NOx of the exhaust gas is reduced, so that the downstream NOx amount becomes equal to or less than the upstream NOx amount. On the other hand, when the SCR catalyst is HC adsorbed and poisoned, almost no ammonia is adsorbed on the SCR catalyst, so the NOx purification reaction does not proceed, ammonia slip occurs, and NOx in the exhaust gas is not reduced. Therefore, the downstream NOx amount exceeds the upstream NOx amount. Therefore, based on the above, it can be determined whether or not the SCR catalyst is HC adsorbed.

  Further, the HC adsorption poisoning detection method for the SCR catalyst of the present invention for achieving the above object is an HC adsorption poisoning detection method for detecting the HC adsorption poisoning of the SCR catalyst provided in the exhaust passage of the internal combustion engine. In order from the upstream side to the exhaust passage, an upstream NOx amount detection device, a urea water addition device, the SCR catalyst, and a downstream ammonia-compatible NOx amount detection device having detection sensitivity for both NOx and ammonia are arranged. A temperature detecting device for detecting an index temperature indicating the catalyst temperature of the SCR catalyst is provided, and the index temperature detected by the temperature detecting device is between a preset first set temperature and a second set temperature. In addition, HC adsorption poisoning detection for detecting HC adsorption poisoning of the SCR catalyst is performed, and in this HC adsorption poisoning detection, addition of urea water from the urea water addition device is stopped, and this urea water is stopped. NOx purification end threshold in which the difference between the upstream NOx amount detected by the upstream NOx amount detection device and the downstream NOx amount detected by the downstream ammonia-compatible NOx amount detection device is preset after In the case of the following, after the urea water addition from the urea water addition device is restarted and the urea water addition is restarted and a preset set time has elapsed, the downstream NOx amount becomes the upstream It is determined whether or not the NOx amount is exceeded, and if the downstream NOx amount exceeds the upstream NOx amount, it is determined that the SCR catalyst is HC adsorbed and poisoned, and the downstream NOx amount is determined. When the amount is equal to or less than the upstream NOx amount, it is determined that the SCR catalyst is not subjected to HC adsorption poisoning.

  According to this method, an effect similar to that of the above-described HC catalyst poisoning detection system for the SCR catalyst can be obtained.

  According to the SCR catalyst poisoning detection system and the SCR catalyst poisoning detection method of the present invention, the HC catalyst poisoning of the SCR catalyst provided in the exhaust passage of the internal combustion engine without using the HC concentration sensor. The degree of deterioration due to can be detected with high accuracy. In particular, since it is not necessary to separately provide an HC concentration sensor in the exhaust passage, an increase in cost can be suppressed.

It is a figure which shows an example of a structure of HC adsorption poisoning detection system of the SCR catalyst of embodiment which concerns on this invention. It is a figure which shows an example of the control flow of the HC adsorption poisoning detection method of the SCR catalyst of embodiment which concerns on this invention. NH of the SCR catalyst ₃ is a diagram showing the relationship between adsorption amount and NOx purification rate. It is a figure which shows the difference in the amount of HC adsorption by HC kind of an SCR catalyst. NH by HC species into the SCR catalyst ₃ is a diagram showing a difference in effect on the adsorption. NOx in the NOx sensor is a diagram illustrating the sensitivity of the NH ₃ in the image manner.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an SCR catalyst HC adsorption poisoning detection system and an SCR catalyst HC adsorption poisoning detection method according to embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, an exhaust gas aftertreatment device 20 is provided in an exhaust passage 11 of an engine (internal combustion engine) 10 to constitute an exhaust gas purification system 2. The exhaust gas aftertreatment device 20 includes an oxidation catalyst (hereinafter referred to as DOC) 21, a PM collection filter (hereinafter referred to as DPF) 22, a urea water injector (urea water addition device) 31, An SCR catalyst 23 and an ammonia (NH ₃ ) slip catalyst 24 are disposed, and the DPF 22 purifies PM and the SCR catalyst 23 purifies NOx.

  The DOC 21 not only oxidizes and removes unburned HC and CO, but also oxidizes HC in the exhaust gas increased by fuel injection control of the engine 10 when regenerating the PM deposited on the DPF 22, It also plays the role of raising the temperature of the DPF 22 to a recyclable temperature. Further, the DPF 22 may be coated with an oxidation catalyst, and the effect of reducing the combustion temperature of PM and preventing CO and HC slip during regeneration can be obtained by providing the oxidation catalyst.

  Further, as the SCR catalyst 23, a zeolite catalyst such as Fe zeolite has been put into practical use and has a characteristic of adsorbing and holding ammonia generated by hydrolysis of urea, but HC adsorption to the zeolite SCR catalyst occurs. As a result, HC adsorption poisoning occurs in which the ammonia adsorption is inhibited and the NOx purification performance is lowered. The HC adsorption poisoning can be eliminated by raising the temperature of the SCR catalyst 23 to a temperature higher than the temperature at which the adsorbed HC is detached from the SCR catalyst 23, and can be regenerated. .

Further, as various sensors, an upstream NOx amount sensor (upstream NOx amount detection) that detects the NOx amount Nu of the exhaust gas G flowing into the SCR catalyst 23 between the DPF 22 and the urea water injector (urea water addition device) 31. The temperature sensor (temperature detection device) 32 for detecting the temperature Tg of the exhaust gas G flowing into the SCR catalyst 23 is disposed between the urea water injector (urea water addition device) 31 and the SCR catalyst 23. between 23 and NH ₃ slip catalyst 24, NOx and for both ammonia have sensitivity, downstream ammonia corresponding type NOx amount sensor for detecting the NOx amount Nd of the exhaust gas G flowing out from the SCR catalyst 23 (the downstream A side ammonia-compatible NOx amount detection device) 33 is provided.

  The ammonia-compatible NOx amount sensor 33 is a detection sensor having detection sensitivity for both NOx and ammonia, and has detection sensitivity not only for NOx but also for ammonia as illustrated in FIG. Therefore, the downstream NOx amount detected by the ammonia-compatible NOx amount detection device includes an amount corresponding to ammonia slip, and is detected as the sum of the NOx amount and the ammonia amount at the SCR catalyst outlet.

  That is, the upstream side NOx amount sensor 30, the urea water injector 31, the SCR catalyst 23, and the downstream side ammonia corresponding NOx amount sensor 33 are arranged in the exhaust passage 11 in order from the upstream side, and the temperature of the SCR catalyst 23 is indicated. A temperature sensor 32 is provided.

  When a temperature sensor is provided in the SCR catalyst 23 and the temperature Tc of the SCR catalyst 23 is directly measured, this temperature sensor becomes a temperature detection device, and the temperature detected by this temperature sensor is used as the temperature Tc of the SCR catalyst 23. In general, it is difficult to directly measure the temperature Tc of the SCR catalyst 23. Therefore, the temperature sensor (temperature) is used as the index temperature Ta for indicating the temperature Tc of the SCR catalyst 23. The temperature Tg of the exhaust gas G flowing into the SCR catalyst 23 detected by the detection device 32 is employed.

  In addition, a control device 41 that performs operation control of the urea water injector 31 and HC adsorption poisoning determination of the SCR catalyst 23 is provided. The control device 41 is usually configured to be incorporated in an overall system control device 40 that performs overall control of the engine 10 and overall control of a vehicle on which the engine 10 is mounted.

  In the HC adsorption / poisoning detection system 1 of the SCR catalyst 23 according to the present invention, the control device 41 detects that the temperature Tg detected by the temperature sensor 32 is between a first set temperature T1 and a second set temperature T2 that are set in advance. In some cases, HC adsorption poisoning detection control for detecting HC adsorption poisoning of the SCR catalyst 23 is performed. The first set temperature T1 is set to a lower limit temperature at which urea water hydrolysis proceeds, and the second set temperature T2 is a temperature at which the HC adsorbed on the SCR catalyst 23 does not desorb and the NOx purification reaction rate is below a certain level. Set to

  In this HC adsorption poisoning detection control, control is performed to stop the addition of urea water from the urea water injector 31, and after the addition of this urea water is stopped, the upstream NOx amount Nu detected by the upstream NOx amount sensor 30. And the downstream NOx amount (including ammonia) Nd detected by the downstream ammonia-capable NOx amount sensor 33 becomes equal to or less than a preset NOx purification end threshold N1 and NOx adsorption When the water is saturated, control is performed to resume the addition of urea water from the urea water addition device, and after the preset time t1 has elapsed after the urea water addition has been resumed, the downstream side It is determined whether the NOx amount Nd exceeds the upstream NOx amount Nu. If the downstream NOx amount Nd exceeds the upstream NOx amount Nu, the SCR catalyst 23 is HC adsorbed and poisoned. Constant, and if the downstream-side NOx amount Nd is less than the upstream side NOx amount Nu, configured to perform determining and control SCR catalyst 23 is not the HC adsorption poisoning.

  Next, an HC adsorption / poisoning detection method in the HC adsorption / poisoning detection system 1 for the SCR catalyst will be described with reference to an example of a control flow shown in FIG. This detection of HC adsorption and poisoning does not need to be performed regularly at all times. Under low-temperature exhaust gas conditions in which the DOC 21 or DPF 22 disposed in the exhaust passage 11 upstream of the SCR catalyst 23 does not exhibit HC purification performance, It is desirable to carry out when a certain period of time is integrated and the influence of HC adsorption poisoning of the SCR catalyst 23 can exceed a certain level.

  The control flow of FIG. 2 is called from the advanced control flow when the judgment that the HC adsorption poisoning detection is to be performed is made by the advanced control flow, and starts the operation control of the urea water injector 31 and the SCR. HC adsorption poisoning determination of the catalyst 23, HC adsorption poisoning recovery processing is carried out if necessary, returning to the advanced control flow, this is repeated, and when the engine 10 is shut down, Returning to the advanced control flow, it is shown to end with the end of the advanced control flow.

  When the control flow of FIG. 2 is called from the advanced control flow and starts, an index temperature Ta that indicates the catalyst temperature Tc of the SCR catalyst 23 is detected in step S11. Here, the temperature Tg of the exhaust gas G, which is the detection value of the temperature sensor 32, is set as the index temperature Ta.

  In the next step S12, it is determined whether or not the index temperature Ta is between the first set temperature T1 and the second set temperature T2. In other words, it is determined whether the temperature is in a preset temperature range (T1 <Ta <T2) that is higher than the first set temperature T1 and lower than the second set temperature T2. In this determination, when the index temperature Ta is not in the temperature range (NO), after the preset control time has elapsed, the process returns to step S11, and if repeated several times, it is determined that the HC adsorption poisoning determination cannot be performed, and the process returns. Go back to the advanced flow.

  On the other hand, if it is determined in step S12 that the index temperature Ta is in the set temperature range (YES), the process proceeds to step S13, the urea water addition from the urea water injector 31 is stopped, and then the process proceeds to step S14.

  In step S14, the upstream NOx amount sensor 30 detects the upstream NOx amount Nu, and the downstream ammonia-compatible NOx amount sensor 33 detects the downstream NOx amount (including ammonia) Nd, and the difference Ng (= Nu). After calculating -Nd), the process proceeds to step S15.

  In step S15, it is determined whether or not the difference Ng is equal to or less than the NOx purification end threshold value N1 set in advance by experiments or the like. In this determination, when the difference Ng is larger than the NOx purification end threshold N1 (NO), the process returns to step S14, and steps S14 to S15 are repeated until the difference Ng becomes equal to or less than the NOx purification end threshold N1.

  That is, by stopping the addition of urea water, ammonia adsorbed and held by the SCR catalyst 23 is used for NOx purification of the exhaust gas G passing through the SCR catalyst 23. Therefore, when time passes, the ammonia is adsorbed by the SCR catalyst 23. The ammonia that has been retained is reduced, and NOx purification hardly occurs. In order to detect this state, the upstream NOx amount Nu on the inlet side and the downstream NOx amount Nd on the outlet side in the SCR catalyst 23 are substantially equal, and the NOx difference Ng is preset in the NOx purification. It is determined whether or not the end threshold value N1 has been reached.

  If the difference Ng is equal to or smaller than the NOx purification end threshold value N1 in the determination in step S15 (YES), the process proceeds to step S16, the addition of urea water from the urea water injector 31 is resumed, and is set in advance by experiments or the like. After the set time t1 has elapsed, the process proceeds to step S17. Under this circumstance, even when the addition of urea water is resumed and the supply of ammonia to the SCR catalyst 23 is resumed, ammonia is hardly adsorbed on the SCR catalyst 23.

  In step S17, as in step S14, the upstream NOx amount Nu and the downstream NOx amount Nd are detected, and the process proceeds to step S18.

  In step S18, it is determined whether the downstream NOx amount Nd exceeds the upstream NOx amount Nu. When the downstream NOx amount Nd exceeds the upstream NOx amount Nu in step S18 (YES), the process proceeds to step S19, and it is determined that the SCR catalyst 23 is HC adsorbed and poisoned. That is, when the set time t1 elapses, when the SCR catalyst 23 is HC adsorbed and poisoned, ammonia is hardly adsorbed on the SCR catalyst 23, so that the NOx purification reaction does not proceed and ammonia slip occurs. The NOx of the exhaust gas G is not reduced. As a result, the downstream NOx amount Nd exceeds the upstream NOx amount Nu.

  If the downstream NOx amount Nd is equal to or smaller than the upstream NOx amount Nu in step S18 (NO), the process proceeds to step S21, and it is determined that the SCR catalyst 23 is not HC adsorbed. That is, when the set time t1 elapses, if the SCR catalyst 23 is not HC adsorbed and poisoned, ammonia is adsorbed on the SCR catalyst 23, the NOx purification reaction proceeds, no ammonia slip occurs, and the exhaust gas is exhausted. The NOx of the gas G is reduced. As a result, the downstream NOx amount Nd becomes equal to or less than the upstream NOx amount Nu.

  As shown in FIG. 6, the ammonia-compatible NOx amount sensor 33 has detection sensitivity not only for NOx but also for ammonia, so the downstream NOx amount Nd detected by the ammonia-compatible NOx amount sensor 33 includes: This includes not only the amount of NOx but also the amount of reaction with ammonia. Therefore, when ammonia slip occurs, the downstream NOx amount Nd detected as the sum of the NOx amount at the SCR catalyst 23 outlet and the amount corresponding to the ammonia slip becomes the upstream NOx amount Nu detected by the NOx amount at the SCR catalyst 23 inlet. Therefore, it is possible to judge more clearly. Therefore, the detection accuracy of the HC adsorption poisoning of the SCR catalyst 23 can be improved by employing the ammonia-compatible NOx amount sensor 33 that also reacts with the ammonia component.

  After the determination in step S19, the process proceeds to step S20, and the HC adsorption poisoning is eliminated by performing a regeneration process in which the SCR catalyst 23 is heated to perform the HC desorption process. After performing this HC adsorption poisoning recovery process, the process goes to return and returns to the advanced control flow. Further, after the determination in step 22, the process goes to return and returns to the advanced control flow. If the operation of the engine 10 is stopped while returning to the advanced control flow, the control flow is terminated together with the termination of the advanced control flow. Further, when the engine 10 is stopped in the middle of the control flow of FIG. 2, the process returns by an interruption to return to the advanced control flow, and this control flow is terminated together with the termination of this advanced control flow.

  With this control, the index temperature Ta detected by the temperature sensor 32 in the SCR catalyst HC adsorption poisoning detection method 1 in the SCR catalyst HC adsorption poisoning detection system 1 described above is set to the first set temperature T1 and the first preset temperature T1. When the temperature is between two set temperatures T2, HC adsorption poisoning detection for detecting HC adsorption poisoning of the SCR catalyst 23 can be performed.

  In this HC adsorption poisoning detection, the addition of urea water from the urea water injector 31 is stopped, and after the addition of this urea water is stopped, the upstream NOx amount Nu detected by the upstream NOx amount sensor 30 and the downstream side are detected. When the difference Ng from the downstream NOx amount Nd detected by the side ammonia corresponding NOx amount sensor 33 is equal to or less than the preset NOx purification end threshold N1, the addition of urea water from the urea water injector 31 is resumed, After the addition of the urea water is resumed and a preset time t1 has elapsed, it is determined whether or not the downstream NOx amount Nd exceeds the upstream NOx amount Nu, and the downstream NOx amount Nd is determined to be the upstream NOx. When the amount Nu is exceeded, it is determined that the SCR catalyst 23 is poisoned by HC, and when the downstream NOx amount Nd is equal to or less than the upstream NOx amount Nu, the SCR catalyst 23 is HC. It can be determined not to have the Chakuhidoku.

  According to the SCR catalyst HC adsorption poisoning detection system 1 and the SCR catalyst HC adsorption poisoning detection method, the HC adsorption of the SCR catalyst 23 provided in the exhaust passage 11 of the engine 10 without using the HC concentration sensor. The degree of deterioration due to poisoning can be accurately detected. In particular, since it is not necessary to separately provide an HC concentration sensor in the exhaust passage 11, an increase in cost can be suppressed.

1 HC catalyst poisoning detection system for SCR catalyst 2 Exhaust gas purification system 10 Engine (internal combustion engine)
11 Exhaust passage 20 Exhaust gas aftertreatment device 21 Oxidation catalyst (DOC)
22 PM collection filter (DPF)
23 SCR catalyst 24 NH ₃ slip catalyst 30 upstream NOx amount sensor (upstream NOx amount detection device)
31 Urea water injector (urea water addition device)
32 Temperature sensor (temperature detector)
33 NOx amount sensor for downstream ammonia type (downstream ammonia corresponding NOx amount detection device)
40 Overall system control device 41 Control device N1 NOx purification end threshold Nd Downstream NOx amount Ng Difference between upstream NOx amount and downstream NOx amount Nu Upstream NOx amount T1 First set temperature T2 Second set temperature Ta Index temperature Tc SCR Catalyst temperature Tg of catalyst Exhaust gas temperature t1 Setting time

Claims (2)

In an HC adsorption poisoning detection system for detecting HC adsorption poisoning of an SCR catalyst provided in an exhaust passage of an internal combustion engine,
In order from the upstream side to the exhaust passage, an upstream NOx amount detection device, a urea water addition device, the SCR catalyst, and a downstream ammonia-compatible NOx amount detection device having detection sensitivity for both NOx and ammonia are arranged. Providing a temperature detecting device for detecting an index temperature indicating the catalyst temperature of the SCR catalyst,
Furthermore, a control device for performing control of the urea water addition device and HC adsorption poisoning determination of the SCR catalyst is provided,
The control device
HC adsorption poisoning detection control for detecting HC adsorption poisoning of the SCR catalyst when the index temperature detected by the temperature detection device is between a preset first preset temperature and a second preset temperature. ,
In this HC adsorption poisoning detection control,
Perform control to stop the addition of urea water from the urea water addition device,
After stopping the addition of the urea water, a difference between the upstream NOx amount detected by the upstream NOx amount detection device and the downstream NOx amount detected by the downstream ammonia-compatible NOx amount detection device is preset. When the NOx purification end threshold value is reached, control is performed to resume the addition of urea water from the urea water addition device,
After restarting the addition of this urea water and elapse of a preset time,
Determining whether the downstream NOx amount exceeds the upstream NOx amount;
When the downstream NOx amount exceeds the upstream NOx amount, it is determined that the SCR catalyst is HC adsorbed and poisoned;
When the downstream NOx amount is less than or equal to the upstream NOx amount, control is performed to determine that the SCR catalyst is not HC adsorbed and poisoned. Poison detection system. In an HC adsorption poisoning detection method for detecting HC adsorption poisoning of an SCR catalyst provided in an exhaust passage of an internal combustion engine,
In order from the upstream side to the exhaust passage, an upstream NOx amount detection device, a urea water addition device, the SCR catalyst, and a downstream ammonia-compatible NOx amount detection device having detection sensitivity for both NOx and ammonia are arranged. A temperature detecting device for detecting an index temperature indicating the catalyst temperature of the SCR catalyst,
HC adsorption poisoning detection for detecting HC adsorption poisoning of the SCR catalyst when the index temperature detected by the temperature detection device is between a first preset temperature and a second preset temperature set in advance,
In this HC adsorption poisoning detection,
Stop adding urea water from the urea water addition device,
After stopping the addition of the urea water, a difference between the upstream NOx amount detected by the upstream NOx amount detection device and the downstream NOx amount detected by the downstream ammonia-compatible NOx amount detection device is preset. When the NOx purification end threshold value is reached, the urea water addition from the urea water addition device is resumed,
After restarting the addition of this urea water and elapse of a preset time,
Determining whether the downstream NOx amount exceeds the upstream NOx amount;
When the downstream NOx amount exceeds the upstream NOx amount, it is determined that the SCR catalyst is HC adsorbed and poisoned;
An SCR catalyst poisoning detection method for an SCR catalyst, wherein when the downstream NOx amount is equal to or less than the upstream NOx amount, it is determined that the SCR catalyst is not poisoned by HC.

Images