JP6453702B2 - Abnormality diagnosis device for exhaust purification mechanism - Google Patents

Description

  The present invention relates to an abnormality diagnosis device for an exhaust purification mechanism.

  2. Description of the Related Art An exhaust gas purification mechanism for an internal combustion engine that includes a NOx purification catalyst for purifying nitrogen oxide (NOx) in exhaust gas in an exhaust passage is known. Such an exhaust purification mechanism includes an addition mechanism for adding a reducing agent such as urea water to the exhaust, and ammonia derived from the reducing agent added to the exhaust is adsorbed by the NOx purification catalyst. Then, NOx is reduced by ammonia adsorbed on the NOx purification catalyst.

  When the molar ratio of NO (nitrogen monoxide) and NO2 (nitrogen dioxide) in the exhaust gas is 1: 1 and the chemical reaction represented by the following formula (1) occurs as shown in Patent Document 1 and the like Compared with the reduction of NOx by other chemical reactions, the NOx purification efficiency of the NOx purification catalyst is increased.

NO + NO2 + 2NH3 → 2N2 + 3H2O (1)

Hereinafter, the ratio (molar ratio) occupied by NO2 in NOx contained in the exhaust is referred to as NO2 ratio [NO2 ratio (%) = NO2 / (NO + NO2) × 100].

  When the molar ratio of NO and NO2 in the exhaust gas is 1: 1, the NO2 ratio is 50%, and this NO2 ratio of 50% is an optimum value for realizing high purification efficiency in the NOx purification catalyst. It has become.

Here, since most of the NOx generated in the cylinder of the internal combustion engine is NO, the NO2 ratio of the exhaust gas flowing into the NOx purification catalyst cannot be set to the optimum value as it is.
Therefore, in the apparatus described in Patent Document 1, an oxidation catalyst is provided upstream of the exhaust of the NOx purification catalyst, and a part of NO contained in the exhaust is changed to NO2 by utilizing an oxidation reaction by the oxidation catalyst. The chemical reaction represented by the above formula (1) is promoted.

JP 2009-216019 A

  By the way, in an apparatus that performs abnormality diagnosis of NOx purification by the exhaust purification mechanism, the NOx purification rate is based on the NOx amount in the exhaust flowing into the NOx purification catalyst and the NOx amount in the exhaust after passing through the NOx purification catalyst. When the calculated NOx purification rate is equal to or less than a preset abnormality determination value, it is determined that there is an abnormality in NOx purification.

  Here, the NOx amount in the exhaust after passing through the NOx purification catalyst is detected by the NOx sensor, while the NOx amount in the exhaust flowing into the NOx purification catalyst uses a calculated value calculated based on the engine operating state or the like. Can be considered. However, in this case, the following inconvenience may occur.

  That is, when the oxidation catalyst provided upstream of the NOx purification catalyst is relatively new, NOx adsorption and desorption may occur in the oxidation catalyst. Therefore, when a phenomenon occurs in which NOx adsorbed on the oxidation catalyst is desorbed, an amount of NOx exceeding the calculated value of the NOx amount flows into the NOx purification catalyst. Therefore, the actual NOx amount before flowing into the NOx purification catalyst becomes larger than the calculated value, and the actual NOx amount in the exhaust gas after passing through the NOx purification catalyst due to the increase in the actually flowing NOx amount. Will also increase.

  As described above, when the actual NOx amount before flowing into the NOx purification catalyst becomes larger than the calculated value, and when the NOx amount in the exhaust gas after passing through the NOx purification catalyst increases, before the flow into the NOx purification catalyst. The NOx purification rate obtained from the calculated value of the NOx amount and the detected value of the NOx amount after passing through the NOx purification catalyst decreases. Here, if the reduced NOx purification rate is less than or equal to the abnormality determination value, such a decrease in the NOx purification rate is temporary due to the desorption phenomenon of the oxidation catalyst, and there is no abnormality in the exhaust purification mechanism itself. Nevertheless, it is erroneously determined that the NOx purification is abnormal.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an abnormality diagnosis device for an exhaust purification mechanism that can suppress erroneous determination that there is an abnormality in NOx purification.

  An abnormality diagnosis device for an exhaust purification mechanism that solves the above problems includes an oxidation catalyst provided in an exhaust passage of an internal combustion engine, an NOx purification catalyst that is provided in an exhaust passage downstream of the oxidation catalyst and purifies NOx, and A reducing agent addition mechanism for adding a reducing agent containing an ammonia component to the exhaust gas flowing into the NOx purification catalyst, and a NOx sensor provided in an exhaust passage downstream of the NOx purification catalyst. Then, the NOx amount in the exhaust gas flowing into the NOx purification catalyst is calculated, the NOx purification rate is calculated based on the calculated NOx amount and the NOx amount detected by the NOx sensor, and the calculated When the NOx purification rate is equal to or less than a preset abnormality determination value, it is determined that there is an abnormality in NOx purification. In this abnormality diagnosis device, when the condition that the NOx adsorbed on the oxidation catalyst is desorbed is satisfied and the condition that the ammonia adsorption amount of the NOx purification catalyst is equal to or less than a predetermined threshold is satisfied, The abnormality determination value is set lower than when both conditions are not satisfied.

  Even if the condition for desorbing NOx adsorbed on the oxidation catalyst is satisfied, if the amount of ammonia adsorbed on the NOx purification catalyst is sufficient, the NOx desorbed from the oxidation catalyst is purified by the NOx purification catalyst. Therefore, it is possible to suppress the NOx purification rate from being lowered to the abnormality determination value or less. On the other hand, if the amount of ammonia adsorbed on the NOx purification catalyst is not sufficient, NOx desorbed from the oxidation catalyst cannot be sufficiently purified by the NOx purification catalyst, so the NOx purification rate is below the abnormality determination value. There is a risk that it will drop to. Therefore, in the same configuration, when the condition that the NOx adsorbed on the oxidation catalyst is desorbed is satisfied and the condition that the ammonia adsorption amount of the NOx purification catalyst is equal to or less than a predetermined threshold is satisfied, the abnormality determination value is The value is made low. Therefore, when the NOx purification rate is temporarily lowered due to NOx desorption from the oxidation catalyst, it is possible to suppress the NOx purification rate from being equal to or lower than the abnormality determination value. Accordingly, it is possible to suppress erroneous determination that the NOx purification is abnormal even though the exhaust purification mechanism itself has no abnormality.

  The NOx adsorption and desorption phenomenon in the oxidation catalyst is likely to occur when the thermal deterioration of the oxidation catalyst is not progressing so much. Further, even if the thermal degradation of the oxidation catalyst is not progressing so much, if the temperature of the oxidation catalyst is below a certain temperature, NOx adsorption occurs, but desorption does not easily occur. Here, the degree of thermal deterioration of the oxidation catalyst increases as the total heat load value obtained by integrating the heat load of the oxidation catalyst increases. Further, such a heat load can be calculated using a detection value of an exhaust temperature sensor provided in an exhaust passage downstream of the oxidation catalyst. Whether or not the temperature of the oxidation catalyst is high enough to cause NOx desorption can be determined based on the detection value of the exhaust temperature sensor provided in the exhaust passage downstream of the oxidation catalyst.

  Therefore, in the abnormality diagnosis apparatus, an exhaust temperature sensor is provided in the exhaust passage downstream of the oxidation catalyst, and the total heat load value obtained by integrating the heat load of the oxidation catalyst is calculated using the detected value of the exhaust temperature sensor. In addition, when the condition that the total heat load value is equal to or smaller than a predetermined threshold value and the detected value of the exhaust temperature sensor is equal to or larger than the predetermined threshold value, NOx adsorbed on the oxidation catalyst is desorbed. It is preferable to determine that the condition to do is satisfied. According to this configuration, it is possible to appropriately determine whether or not a condition for desorbing NOx adsorbed on the oxidation catalyst is satisfied.

  In the abnormality diagnosis apparatus, when the abnormality determination value set when the condition that the ammonia adsorption amount is equal to or less than a predetermined threshold is not satisfied is set as a first determination value, the ammonia adsorption amount is equal to or less than the threshold. When the condition that there is, and the condition that NOx adsorbed to the oxidation catalyst is desorbed is not satisfied, a second determination value that is lower than the first determination value is set as the abnormality determination value. When the condition that the ammonia adsorption amount is equal to or less than the threshold value is satisfied and the condition that NOx adsorbed to the oxidation catalyst is desorbed is satisfied, the abnormality determination value is determined based on the second determination value. Alternatively, a third determination value that is a lower value may be set.

  According to this configuration, even when there is no abnormality in the exhaust purification mechanism itself, the amount of ammonia adsorbed on the NOx purification catalyst is less than the threshold value and the amount of NOx that can be purified is small, that is, the NOx purification rate is reduced. When it is easy to do, a second determination value that is lower than the first determination value is set as the abnormality determination value. Accordingly, it is possible to suppress the NOx purification rate from being equal to or less than the abnormality determination value, and it is possible to suppress erroneous determination that the NOx purification is abnormal even though the exhaust purification mechanism itself has no abnormality.

  Further, when the condition that the ammonia adsorption amount is equal to or less than the threshold value is satisfied and the condition for desorbing NOx adsorbed on the oxidation catalyst is satisfied, that is, when the NOx purification rate is likely to further decrease, As the determination value, a third determination value that is lower than the second determination value is set. Therefore, in this case as well, it is possible to suppress the NOx purification rate from becoming equal to or less than the abnormality determination value, and it is possible to erroneously determine that there is an abnormality in NOx purification even though there is no abnormality in the exhaust purification mechanism itself. Can be suppressed.

1 is a schematic diagram showing an internal combustion engine to which the abnormality diagnosis device for an exhaust gas purification mechanism according to an embodiment is applied and a peripheral configuration thereof. The graph which shows the fluctuation | variation of the NOx amount error accompanying the increase in the total heat load of an oxidation catalyst, and the fluctuation | variation of a NOx purification rate. 9 is a flowchart showing a procedure for processing for setting an abnormality determination value in the embodiment. The graph which shows the setting aspect of the abnormality determination value by the setting process of the embodiment. The graph which shows the setting aspect of the abnormality determination value in the modification of the embodiment.

Hereinafter, an embodiment in which an abnormality diagnosis device for an exhaust purification mechanism is applied to a diesel engine (hereinafter referred to as “engine”) mounted on a vehicle will be described with reference to FIGS.
As shown in FIG. 1, the engine 1 is provided with a plurality of cylinders # 1 to # 4. A plurality of fuel injection valves 4 a to 4 d are attached to the cylinder head 2. These fuel injection valves 4a to 4d inject fuel into the combustion chambers of the corresponding cylinders # 1 to # 4. Also, the cylinder head 2 is provided with intake ports for introducing fresh air into the cylinders and exhaust ports 6a to 6d for discharging combustion gas to the outside of the cylinders corresponding to the respective cylinders # 1 to # 4. It has been.

  The fuel injection valves 4a to 4d are connected to a common rail 9 that accumulates high-pressure fuel. The common rail 9 is connected to the supply pump 10. The supply pump 10 sucks fuel in the fuel tank and supplies high-pressure fuel to the common rail 9. The high-pressure fuel supplied to the common rail 9 is injected into the cylinder from the fuel injection valves 4a to 4d when the fuel injection valves 4a to 4d are opened.

  An intake manifold 7 is connected to the intake port. The intake manifold 7 is connected to the intake passage 3. An intake throttle valve 16 for adjusting the intake air amount is provided in the intake passage 3. The intake throttle valve 16 is adjusted in opening degree by an actuator 17.

An exhaust manifold 8 is connected to the exhaust ports 6a to 6d. The exhaust manifold 8 is connected to the exhaust passage 26.
In the middle of the exhaust passage 26, there is provided a turbocharger 11 for supercharging intake air introduced into the cylinder using exhaust pressure. An intercooler 18 is provided in the intake passage 3 between the intake side compressor of the turbocharger 11 and the intake throttle valve 16. The intercooler 18 cools the intake air whose temperature has risen due to supercharging of the turbocharger 11.

  A first purification member 30 that purifies the exhaust gas is provided in the middle of the exhaust passage 26 and downstream of the exhaust side turbine of the turbocharger 11. Inside the first purification member 30, an oxidation catalyst 31 and a filter 32 are arranged in series with respect to the flow direction of the exhaust gas.

  The oxidation catalyst 31 carries a catalyst for oxidizing HC in the exhaust. As the catalyst, strong basic alumina is used. The filter 32 is a member that collects PM (particulate matter) in the exhaust gas and is made of porous ceramic, and further supports a catalyst for promoting the oxidation of PM. The PM in the exhaust gas is collected when passing through the porous wall of the filter 32.

  Further, a fuel addition valve 5 for supplying fuel as an additive to the oxidation catalyst 31 and the filter 32 is provided in the vicinity of the collecting portion of the exhaust manifold 8. The fuel addition valve 5 is connected to the supply pump 10 through a fuel supply pipe 27. The position of the fuel addition valve 5 can be changed as appropriate as long as it is in the exhaust system and upstream of the first purification member 30. Instead of the fuel addition from the fuel addition valve 5, the engine fuel may be added to the exhaust by adjusting the fuel injection timing of each of the fuel injection valves 4a to 4d and performing the post injection.

  When the amount of PM collected by the filter 32 exceeds a predetermined value, the regeneration process of the filter 32 is started, and fuel is injected from the fuel addition valve 5 into the exhaust manifold 8. The fuel injected from the fuel addition valve 5 is oxidized when it reaches the oxidation catalyst 31, thereby increasing the exhaust temperature. The exhaust gas whose temperature has been raised by the oxidation catalyst 31 flows into the filter 32, whereby the temperature of the filter 32 is raised, whereby the PM deposited on the filter 32 is oxidized and the filter 32 is regenerated.

  A second purification member 40 that purifies the exhaust gas is provided in the middle of the exhaust passage 26 and downstream of the first purification member 30. Inside the second purification member 40, a selective reduction type NOx catalyst (hereinafter referred to as SCR catalyst) 41 is disposed as an exhaust purification catalyst that reduces and purifies NOx in exhaust using a reducing agent.

  Further, a third purification member 50 for purifying exhaust gas is provided in the middle of the exhaust passage 26 and downstream of the second purification member 40. Inside the third purification member 50, an ammonia oxidation catalyst 51 for purifying ammonia in the exhaust is disposed.

  The engine 1 is provided with a urea water supply mechanism 200 as a reducing agent supply mechanism for adding urea water, which is a reducing agent containing an ammonia component, to exhaust gas. The urea water supply mechanism 200 is connected to a tank 210 that stores urea water, a urea addition valve 230 that injects urea water into the exhaust passage 26, a urea addition valve 230, and the tank 210. Is supplied to the urea addition valve 230, and a pump 220 and the like provided in the middle of the urea water passage 240.

  The urea addition valve 230 is provided in the exhaust passage 26 between the first purification member 30 and the second purification member 40, and the injection hole is opened toward the SCR catalyst 41. When the valve portion of the urea addition valve 230 is opened, urea water is injected into the exhaust passage 26 via the urea water passage 240.

  The pump 220 is an electric pump, and at the time of forward rotation, the urea water is fed from the tank 210 toward the urea addition valve 230. On the other hand, during reverse rotation, urea water is sent from the urea addition valve 230 toward the tank 210. That is, during reverse rotation of the pump 220, urea water is collected from the urea addition valve 230 and the urea water passage 240 and returned to the tank 210.

  A dispersion plate 60 is provided in the exhaust passage 26 between the urea addition valve 230 and the SCR catalyst 41 to promote atomization of the urea water by dispersing the urea water injected from the urea addition valve 230. It has been.

  The urea water injected from the urea addition valve 230 is converted to ammonia by hydrolysis using exhaust heat and is adsorbed by the SCR catalyst 41. Then, NOx is reduced and purified by the ammonia adsorbed on the SCR catalyst 41.

  Here, when the exhaust discharged from the engine 1 passes through the oxidation catalyst 31, a part of NO contained in the exhaust is oxidized and changed to NO2. Therefore, the NO2 ratio of the exhaust after passing through the oxidation catalyst 31 is higher than the NO2 ratio of the exhaust before passing through the oxidation catalyst 31, and the NO2 ratio of the exhaust flowing into the SCR catalyst 41 is the optimum value ( 50%). Due to the oxidation of NO by the oxidation catalyst 31, the chemical reaction represented by the above formula (1) proceeds in the SCR catalyst 41, and the NOx purification efficiency is improved in the SCR catalyst 41.

  In addition, the engine 1 is provided with an exhaust gas recirculation device (hereinafter referred to as an EGR device). This EGR device is a device that reduces the combustion temperature in the cylinder by introducing a part of the exhaust gas into the intake air, thereby reducing the amount of NOx generated. This exhaust gas recirculation device includes an EGR passage 13 that communicates the intake passage 3 and the exhaust manifold 8, an EGR valve 15 provided in the EGR passage 13, an EGR cooler 14, and the like. By adjusting the opening degree of the EGR valve 15, the exhaust gas recirculation amount introduced into the intake passage 3 from the exhaust passage 26, that is, the so-called external EGR amount is adjusted. Further, the temperature of the exhaust gas flowing through the EGR passage 13 is lowered by the EGR cooler 14.

  Various sensors and switches for detecting the engine operating state are attached to the engine 1. For example, the air flow meter 19 detects the intake air amount GA in the intake passage 3. The throttle valve opening sensor 20 detects the opening of the intake throttle valve 16. The crank angle sensor 21 detects the rotation angle of the crankshaft, and the engine rotation speed NE is calculated based on the detection signal. The accelerator operation amount sensor 22 detects an amount of depression of an accelerator pedal (accelerator operation member), that is, an accelerator operation amount ACCP. The outside air temperature sensor 23 detects the outside air temperature THout. The vehicle speed sensor 24 detects the vehicle speed SPD of the vehicle on which the engine 1 is mounted. The ignition switch (IG) 25 is operated to start and stop the engine 1 by a driver of the vehicle.

  The first exhaust temperature sensor 100 provided upstream of the oxidation catalyst 31 detects the first exhaust temperature TH1 that is the exhaust temperature before flowing into the oxidation catalyst 31. Between the oxidation catalyst 31 and the filter 32, a second exhaust temperature sensor 120 that detects a second exhaust temperature TH2 that is an exhaust temperature before flowing into the filter 32 is provided. The differential pressure sensor 110 detects the pressure difference ΔP between the exhaust pressure upstream and downstream of the filter 32.

  A third exhaust temperature sensor 130 is provided in the exhaust passage 26 between the first purification member 30 and the second purification member 40 and upstream of the urea addition valve 230. The third exhaust temperature sensor 130 detects a third exhaust temperature TH3 that is the exhaust temperature before flowing into the SCR catalyst 41.

  In the exhaust passage 26 downstream of the third purification member 50, after passing through the SCR catalyst 41, the fourth exhaust temperature sensor 140 that detects the fourth exhaust temperature TH 4 that is the exhaust temperature after passing through the SCR catalyst 41. A NOx sensor 150 for detecting the amount of NOx in the exhaust gas is provided.

  Outputs from these various sensors are input to the control device 80. The control device 80 includes a central processing control device (CPU), a read-only memory (ROM) that stores various programs and maps in advance, a random access memory (RAM) that temporarily stores CPU calculation results, a timer counter, an input The microcomputer is mainly configured with an interface, an output interface, and the like.

  Then, the control device 80 controls, for example, the fuel injection amount control and fuel injection timing control of the fuel injection valves 4a to 4d and the fuel addition valve 5, the discharge pressure control of the supply pump 10, and the drive amount of the actuator 17 that opens and closes the intake throttle valve 16. Various controls of the engine 1 such as control and opening control of the EGR valve 15 are performed.

  Further, the control device 80 performs urea water addition control by the urea addition valve 230 as one of exhaust purification control. In this addition control, the control device 80 calculates a urea addition amount with no excess or deficiency in order to reduce NOx discharged from the engine 1 based on the engine operating state or the like. Then, the open state of the urea addition valve 230 is controlled so that the calculated urea addition amount is injected from the urea addition valve 230.

  In addition, the control device 80 constitutes an abnormality diagnosis device that determines whether or not there is an abnormality in the NOx purification performed by the exhaust purification mechanism including the SCR catalyst 41, the urea water supply mechanism 200, and the like.

  For such abnormality determination, the control device 80 sets the NOx amount in the exhaust gas flowing into the SCR catalyst 41 as the first NOx amount N1, and calculates this based on the engine operating state. That is, the amount of NOx generated in the cylinder of the engine 1 based on the fuel injection amount injected from the fuel injection valves 4a to 4d, the fuel injection timing, the engine rotational speed, the intake air amount GA related to the air-fuel ratio, and the like. The calculated value is set as the first NOx amount N1. Further, the NOx amount detected by the NOx sensor 150 provided in the exhaust passage 26 downstream of the SCR catalyst 41, that is, the NOx amount in the exhaust gas purified by the SCR catalyst 41 is defined as the second NOx amount N2, and the following equation (2 ) To calculate the NOx purification rate CF.

NOx purification rate CF = (first NOx amount N1−second NOx amount N2) / first NOx amount N1 × 100 (%) (2)

When the calculated NOx purification rate CF is equal to or less than the abnormality determination value α, it is determined that there is an abnormality in the NOx purification performed by the exhaust purification mechanism.

  By the way, in the oxidation catalyst 31 in which thermal deterioration does not progress so much, NOx is adsorbed on alumina in a region where the catalyst bed temperature is low. On the other hand, in the region where the catalyst bed temperature is high, the intermolecular movement of the adsorbed NOx becomes active, and the adsorbed NOx is desorbed from the oxidation catalyst 31.

  As shown in FIG. 2, when the value obtained by subtracting the actual NOx amount NR in the exhaust gas flowing into the SCR catalyst 41 from the first NOx amount N1 that is the calculated value is defined as NOx amount error ΔN1 (ΔN1 = N1−NR), When NOx adsorption or desorption occurs at the oxidation catalyst 31 described above, the NOx amount error ΔN1 fluctuates to the plus side or minus side with “0” as the center.

  That is, when the catalyst bed temperature is low and NOx adsorption is occurring in the oxidation catalyst 31, the actual NOx amount NR is smaller than the calculated first NOx amount N1, and therefore the NOx amount error ΔN1 is on the plus side. Value.

  On the other hand, when the catalyst bed temperature is high and NOx desorption occurs in the oxidation catalyst 31, the actual NOx amount NR is larger than the calculated first NOx amount N1, and therefore the NOx amount error ΔN1 is negative. Value.

The NOx purification rate CF also varies in synchronization with the variation of the NOx amount error ΔN1.
That is, when NOx adsorption occurs in the oxidation catalyst 31 and the NOx amount error ΔN1 becomes a positive value, the amount of NOx contained in the exhaust gas after passing through the SCR catalyst 41 is decreased as the actual NOx amount NR decreases. Less. Therefore, the NOx purification rate CF is higher than when the NOx amount error ΔN1 is “0”.

  On the other hand, when NOx desorption occurs in the oxidation catalyst 31 and the NOx amount error ΔN1 becomes a negative value, an increase in the actual NOx amount NR and a shortage of the ammonia amount adsorbed on the SCR catalyst 41 occur. If they overlap, the amount of NOx contained in the exhaust after passing through the SCR catalyst 41 increases. Therefore, the NOx purification rate CF is lower than when the NOx amount error ΔN1 is “0”. Here, as indicated by a circle E in FIG. 2, when the reduced NOx purification rate CF is equal to or less than the abnormality determination value α, such a decrease in the NOx purification rate CF is caused by the desorption phenomenon at the oxidation catalyst 31. Even if the exhaust purification mechanism itself is not abnormal, it is erroneously determined that the NOx purification is abnormal.

  Here, the degree of thermal degradation of the oxidation catalyst 31 increases as the total heat load value THL obtained by integrating the heat load (heat amount) applied to the oxidation catalyst 31 after the oxidation catalyst 31 is mounted on the engine 1 increases. To go. When the total thermal load value THL reaches a certain value (THLD) and reaches a certain value (A1), the fluctuation range of the NOx amount error ΔN1 and the NOx purification rate CF are thereafter increased. The fluctuation range becomes smaller and the erroneous determination is less likely to occur.

  Such a decrease in fluctuation width occurs because the NOx adsorption phenomenon and the desorption phenomenon hardly occur in the oxidation catalyst 31 when the thermal degradation of the oxidation catalyst 31 proceeds to a certain extent. The disappearance of the adsorption phenomenon and the desorption phenomenon is caused by the fact that the alumina is sintered and the surface area is reduced as the total heat load value THL of the oxidation catalyst 31 is increased, or sulfur is adsorbed at the base point. It is presumed that the NOx adsorption point decreases.

  Therefore, in this embodiment, although there is no abnormality in the exhaust purification mechanism itself, it is erroneously determined that there is an abnormality in NOx purification due to a temporary decrease in the NOx purification rate CF due to the above-described desorption phenomenon. In order to suppress this, the abnormality determination value α is appropriately variably set.

Hereinafter, the procedure for setting the abnormality determination value α will be described with reference to FIGS. This process is executed by the control device 80 at predetermined intervals.
When this process is started, first, it is determined whether or not the ammonia adsorption amount NH of the SCR catalyst 41 exceeds the adsorption amount determination value NHD (S100).

  The ammonia adsorption amount NH is calculated based on the urea addition amount, the exhaust temperature, and the like. Further, if the amount of ammonia adsorbed on the SCR catalyst 41 is temporarily reduced, NOx generated in the engine 1 cannot be sufficiently purified, and the NOx purification rate CF becomes equal to or less than the abnormality determination value α. There is a fear. Therefore, the adsorption amount determination value NHD is temporarily based on the fact that the ammonia adsorption amount NH is equal to or less than the adsorption amount determination value NHD, but the current ammonia adsorption amount NH is sufficient for the NOx generated in the engine 1. A value that can be determined to be an amount that cannot be purified is set.

  When the ammonia adsorption amount NH exceeds the adsorption amount determination value NHD (S100: YES), as shown in FIG. 4, the abnormality determination value α is the highest among the variable abnormality determination values α. 1 determination value α1 is set (S130). And this process is once complete | finished.

  On the other hand, when the ammonia adsorption amount NH is equal to or less than the adsorption amount determination value NHD (S100: YNO), it is determined whether or not the total heat load value THL of the oxidation catalyst 31 is equal to or less than the heat load determination value THLD (S110). ).

  The total heat load value THL is calculated using the detection value of the second exhaust temperature sensor 120 provided in the exhaust passage 26 downstream of the oxidation catalyst 31. For example, a temperature count value that is a detected value of the second exhaust temperature sensor 120 and that increases as the second exhaust temperature TH2 that is the temperature of the exhaust gas that has passed through the oxidation catalyst 31 is higher is prepared. Then, for each predetermined cycle, a temperature count value corresponding to the second exhaust temperature TH2 at that time is obtained, an integrated value of the temperature count value is calculated, and the integrated value is set as the current total heat load value THL. To do. The thermal load determination value THLD is set to a value that can be determined that NOx adsorption and desorption occurs in the oxidation catalyst 31 based on the total thermal load value THL being equal to or less than the thermal load determination value THLD. ing.

  When the total thermal load value THL exceeds the thermal load determination value THLD (S110: NO), as shown in FIG. 4, the abnormality determination value α is a value that is lower than the first determination value α1. 2 determination value α2 is set (S140). And this process is once complete | finished.

  On the other hand, when the total heat load value THL is equal to or lower than the heat load determination value THLD (S110: YES), it is determined whether or not the second exhaust temperature TH2 is equal to or higher than the temperature determination value THD (S120). The temperature determination value THD determines that the temperature of the oxidation catalyst 31 is a temperature at which NOx is desorbed from the oxidation catalyst 31 based on the second exhaust temperature TH2 being equal to or higher than the temperature determination value THD. A value that can be used is set.

  When the second exhaust temperature TH2 is lower than the temperature determination value THD (S120: NO), the second determination value α2 is set as the abnormality determination value α (S140). And this process is once complete | finished.

  On the other hand, when the second exhaust temperature TH2 is equal to or higher than the temperature determination value THD (S120: YES), as shown in FIG. 4, the abnormality determination value α is a third determination that is lower than the second determination value α2. The value α3 is set (S150). And this process is once complete | finished.

Next, the operation of the setting process will be described.
Even if the condition for desorbing NOx adsorbed on the oxidation catalyst 31 is satisfied, if the amount of ammonia adsorbed on the SCR catalyst 41 is sufficient, the NOx desorbed from the oxidation catalyst 31 is removed. Therefore, it is possible to suppress the NOx purification rate CF from being lowered to the abnormality determination value α or less. Conversely, if the amount of ammonia adsorbed on the SCR catalyst 41 is not sufficient, the NOx desorbed from the oxidation catalyst 31 cannot be sufficiently purified by the SCR catalyst 41, and therefore the NOx purification rate CF is abnormal. There is a possibility that the value falls below the determination value α.

  Therefore, in the setting process, the condition that the ammonia adsorption amount NH of the SCR catalyst 41 is equal to or less than the adsorption amount determination value NHD is satisfied (S100: YES), and the desorption condition of NOx adsorbed on the oxidation catalyst 31 is satisfied. Is established (S110: YES, S120: YES), the value of the abnormality determination value α is set to the lowest third determination value α3. Therefore, when the NOx purification rate CF temporarily decreases due to NOx desorption from the oxidation catalyst 31, the NOx purification rate CF can be suppressed from being equal to or less than the abnormality determination value α.

According to this embodiment described above, the following effects can be obtained.
(1) When the condition that the NOx adsorbed on the oxidation catalyst 31 is desorbed is satisfied and the condition that the ammonia adsorption amount NH is equal to or less than the adsorption amount determination value NHD is satisfied, neither of these conditions is satisfied. Compared to the time, the value of the abnormality determination value α is lowered. Therefore, when the NOx purification rate CF temporarily decreases due to NOx desorption from the oxidation catalyst 31, it is possible to suppress the NOx purification rate CF from being equal to or lower than the abnormality determination value α. Accordingly, it is possible to suppress erroneous determination that the NOx purification is abnormal even though the exhaust purification mechanism itself has no abnormality.

  (2) The NOx adsorption and desorption phenomenon in the oxidation catalyst 31 is likely to occur when the thermal degradation of the oxidation catalyst 31 is not progressing so much. Further, even when the thermal degradation of the oxidation catalyst 31 is not progressing so much, if the temperature of the oxidation catalyst 31 is equal to or lower than a certain temperature, adsorption of NOx occurs, but desorption does not easily occur. Here, the degree of thermal deterioration of the oxidation catalyst 31 increases as the total heat load value THL obtained by integrating the heat load of the oxidation catalyst 31 increases. Further, such a heat load can be calculated using a detection value of the second exhaust temperature sensor 120 provided in the exhaust passage 26 downstream of the oxidation catalyst 31. Whether or not the temperature of the oxidation catalyst 31 is high enough to cause NOx desorption can be determined based on the detection value of the second exhaust temperature sensor 120.

  Therefore, the total heat load value THL obtained by integrating the heat load of the oxidation catalyst 31 is calculated using the detection value of the second exhaust temperature sensor 120. Further, when the condition that the total heat load value THL is equal to or less than the heat load determination value THLD and the detection value of the second exhaust temperature sensor 120 is equal to or greater than the temperature determination value THD, NOx adsorbed on the oxidation catalyst 31 is satisfied. It is determined that the condition for desorbing is established. Therefore, it is possible to appropriately determine whether or not the condition for desorbing NOx adsorbed on the oxidation catalyst 31 is satisfied.

  (3) The abnormality determination value α that is set when the condition that the ammonia adsorption amount NH is equal to or less than the adsorption amount determination value NHD is not satisfied is defined as a first determination value α1. When the condition that the ammonia adsorption amount NH is equal to or less than the adsorption amount determination value NHD is satisfied (S100: NO), and the condition for desorbing NOx adsorbed on the oxidation catalyst 31 is not satisfied (S110: NO). ), The second determination value α2 that is lower than the first determination value α1 is set as the abnormality determination value α.

  Therefore, when there is no abnormality in the exhaust purification mechanism itself, the amount of ammonia adsorbed on the SCR catalyst 41 is less than the adsorption amount determination value NHD and the amount of NOx that can be purified is small, that is, the NOx purification rate CF. Is likely to decrease, a second determination value α2 that is lower than the first determination value α1 is set as the abnormality determination value α. Therefore, it is possible to suppress the NOx purification rate CF from being equal to or less than the abnormality determination value α, and to prevent erroneous determination that the NOx purification is abnormal even though there is no abnormality in the exhaust purification mechanism itself. it can.

  Further, when the condition that the ammonia adsorption amount NH is equal to or less than the adsorption amount determination value NHD is satisfied (S100: NO), and the condition that the NOx adsorbed on the oxidation catalyst 31 is desorbed is satisfied (S110: YES). And S120: YES), that is, when the NOx purification rate CF is more likely to decrease, the abnormality determination value α is set as follows. That is, the third determination value α3, which is lower than the second determination value α2, is set as the abnormality determination value α. Accordingly, in this case as well, it is possible to suppress the NOx purification rate CF from being equal to or less than the abnormality determination value α, and it is erroneously determined that there is an abnormality in NOx purification even though there is no abnormality in the exhaust purification mechanism itself. That can be suppressed.

In addition, the said embodiment can also be changed and implemented as follows.
In the above embodiment, the abnormality determination value α is changed to three levels, but may be changed to two levels.

  For example, as shown in FIG. 5, even if the ammonia adsorption amount NH is equal to or less than the adsorption amount determination value NHD, if the condition for desorbing NOx adsorbed on the oxidation catalyst 31 is not satisfied, the abnormality determination value α is set to ammonia. This is the same as the determination value αA set when the adsorption amount NH exceeds the adsorption amount determination value NHD. On the other hand, when the ammonia adsorption amount NH is equal to or smaller than the adsorption amount determination value NHD and the condition that the NOx adsorbed to the oxidation catalyst 31 is desorbed is satisfied, the abnormality determination value α is set to a determination value lower than the determination value αA. You may make it set to (alpha) B.

Further, the abnormality determination value α may be changed in four or more stages.
The total heat load value THL of the oxidation catalyst 31 tends to increase as the total travel distance of the vehicle equipped with the engine 1 increases. Therefore, more simply, the total heat load value THL may be obtained based on the total travel distance of the vehicle on which the engine 1 is mounted.

-The arrangement | positioning number of the oxidation catalyst 31, the filter 32, the SCR catalyst 41, and the ammonia oxidation catalyst 51 can be changed suitably.
The number of exhaust temperature sensors and NOx sensors can be changed as appropriate.

  Although urea water is used, other reducing agents may be used as long as the reducing agent contains an ammonia component.

  DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Cylinder head, 3 ... Intake passage, 4a-4d ... Fuel injection valve, 5 ... Fuel addition valve, 6a-6d ... Exhaust port, 7 ... Intake manifold, 8 ... Exhaust manifold, 9 ... Common rail, 10 DESCRIPTION OF SYMBOLS ... Supply pump, 11 ... Turbocharger, 13 ... EGR passage, 14 ... EGR cooler, 15 ... EGR valve, 16 ... Intake throttle valve, 17 ... Actuator, 18 ... Intercooler, 19 ... Air flow meter, 20 ... Throttle valve opening Sensors: 21 ... Crank angle sensor, 22: Accelerator operation amount sensor, 23 ... Outside air temperature sensor, 24 ... Vehicle speed sensor, 25 ... Ignition switch, 26 ... Exhaust passage, 27 ... Fuel supply pipe, 30 ... First purification member, 31 ... oxidation catalyst, 32 ... filter, 40 ... second purification member, 41 ... selective reduction type NOx catalyst (SCR catalyst), DESCRIPTION OF SYMBOLS 0 ... 3rd purification member, 51 ... Ammonia oxidation catalyst, 60 ... Dispersion plate, 80 ... Control apparatus, 100 ... 1st exhaust temperature sensor, 110 ... Differential pressure sensor, 120 ... 2nd exhaust temperature sensor, 130 ... 3rd exhaust Temperature sensor, 140, fourth exhaust temperature sensor, 150, NOx sensor, 200, urea water supply mechanism, 210, tank, 220, pump, 230, urea addition valve, 240, urea water passage.

Claims (3)

An oxidation catalyst provided in an exhaust passage of an internal combustion engine, a NOx purification catalyst provided in an exhaust passage downstream of the oxidation catalyst and purifying NOx, and a reducing agent containing an ammonia component in exhaust flowing into the NOx purification catalyst A reducing agent addition mechanism for adding NOx, and a NOx sensor provided in an exhaust passage downstream of the NOx purification catalyst, and calculates an amount of NOx in the exhaust gas flowing into the NOx purification catalyst, A NOx purification rate is calculated based on the calculated NOx amount and the NOx amount detected by the NOx sensor, and when the calculated NOx purification rate is equal to or less than a preset abnormality determination value, there is an abnormality in NOx purification. An abnormality diagnosis device for an exhaust purification mechanism for judging,
When the condition that the NOx adsorbed on the oxidation catalyst is desorbed is satisfied and the condition that the ammonia adsorption amount of the NOx purification catalyst is equal to or less than a predetermined threshold is satisfied, both of the above conditions are not satisfied An abnormality diagnosis device for an exhaust gas purification mechanism, wherein the abnormality determination value is made lower than that of the exhaust gas purification mechanism. An exhaust temperature sensor is provided in the exhaust passage downstream of the oxidation catalyst,
While calculating the total heat load value obtained by integrating the heat load of the oxidation catalyst using the detection value of the exhaust temperature sensor,
When the condition that the total heat load value is equal to or smaller than a predetermined threshold value and the detected value of the exhaust temperature sensor is equal to or larger than the predetermined threshold value is satisfied, the condition for desorbing NOx adsorbed on the oxidation catalyst is satisfied. The abnormality diagnosis device for an exhaust gas purification mechanism according to claim 1, wherein the abnormality diagnosis device is determined. When the abnormality determination value that is set when the condition that the ammonia adsorption amount is less than or equal to a predetermined threshold value is not satisfied is the first determination value, the condition that the ammonia adsorption amount is less than or equal to the threshold value is satisfied. And when the condition for desorbing NOx adsorbed on the oxidation catalyst is not satisfied, a second determination value that is lower than the first determination value is set as the abnormality determination value.
When the condition that the ammonia adsorption amount is equal to or less than the threshold value is satisfied and the condition that NOx adsorbed to the oxidation catalyst is desorbed is satisfied, the abnormality determination value is lower than the second determination value. The exhaust gas purification mechanism abnormality diagnosis apparatus according to claim 1 or 2, wherein a third determination value that is a value is set.