JP2006291714A - Degrading determination device for exhaust emission control catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a degrading determination device for an exhaust emission control catalyst capable of increasing the chances of determining the degraded state of an exhaust emission control catalyst. <P>SOLUTION: An electronic controller performs the determination of the degraded state by determining that, when predetermined requirements are fulfilled, the temperature of the exhaust emission control catalyst (catalyst floor temperature) can be increased and, when at least the fulfilled state of the requirements is continued for a predetermined time or longer, the requirements for determining the degraded state of the exhaust emission control catalyst are fulfilled. When the degraded state is determined, the continued time of the fulfillment of the requirements is counted with a requirement fulfilling counter according to the fulfillment of the requirements (steps 110, 120). When the requirements are not fulfilled, the continued time counted during the fulfillment of the requirements is deducted by deducting the requirement fulfilling counter (steps 110, 140). By taking the results of the deduction as an initial value when the requirements are fulfilled again, the count-up of the requirement fulfilling counter (timing of continued time) is re-started. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a deterioration determination device that determines a deterioration state of an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine.

  Generally, in an internal combustion engine, an exhaust purification catalyst is provided in an exhaust passage, and exhaust gas is purified by the exhaust purification catalyst. For example, in a diesel engine, a lean burn gasoline engine, or the like, a NOx catalyst is provided in the exhaust passage as an exhaust purification catalyst. Then, nitrogen oxide NOx in the exhaust gas is occluded in the catalyst in an oxidizing atmosphere, and then a reducing agent is supplied into the exhaust gas to form a reducing atmosphere, releasing the nitrogen oxide NOx that has been occluded and reducing. To purify it.

  The exhaust purification catalyst including the NOx catalyst deteriorates when used over a long period of time, and the purification performance is lowered. For example, in the case of a NOx catalyst, there is a possibility that the nitrogen oxide NOx cannot be sufficiently occluded or the nitrogen oxide NOx cannot be sufficiently reduced in a reducing atmosphere. For this reason, it is important to accurately grasp the deterioration state of the exhaust purification catalyst and deal with the above problems at an early stage.

  Various techniques for grasping such a deterioration state have been proposed in the past. For example, Patent Document 1 calculates a deterioration coefficient corresponding to the temperature of the exhaust purification catalyst every time a predetermined time elapses, and calculates the deterioration coefficient. A technique is described in which integration is performed and it is determined that the integrated value has deteriorated when the integrated value exceeds a predetermined value.

Here, the determination of the above-described deterioration state is effective in eliminating the erroneous determination and ensuring the determination accuracy to be performed in a state where the exhaust purification catalyst is heated and activated. Accordingly, a precondition for determining whether or not the temperature of the exhaust purification catalyst can rise is set, and the time when this precondition is satisfied is counted. Then, when the time duration of the established condition of the preconditions reaches a predetermined value or more, that is, when the established condition continues for a predetermined time or more, it is determined that the execution condition is satisfied, and the process proceeds to determination of the deterioration state of the exhaust purification catalyst. I have to. Note that when the precondition is switched to a state where the precondition is not satisfied, the temperature of the exhaust purification catalyst decreases and the execution condition is not satisfied, and thus the duration time is normally cleared to “0”. And when it switches to the condition where the precondition is satisfied again, the time measurement of the duration is resumed from this value (= 0).
Japanese Patent Laid-Open No. 7-119447

  By the way, when it switches to the condition where a precondition is not materialized, after that, the temperature of an exhaust-purification catalyst hardly falls rapidly, rather it falls gradually with time. When switching to a situation where the precondition is satisfied again, the temperature of the exhaust purification catalyst often remains slightly lower than when the precondition was switched to a previous situation. This temperature is higher than the temperature of the exhaust purification catalyst when the precondition is switched to the previous condition (when the exhaust purification catalyst starts to rise in temperature).

  However, as described above, in the past, when switching to a situation where the preconditions are not satisfied, the preconditions are based on the premise that the temperature of the exhaust purification catalyst suddenly decreases and returns to the temperature before the temperature increase. The time duration counted during the establishment of is cleared. That is, the duration (= 0) corresponding to the temperature of the exhaust purification catalyst that is lower than the actual temperature is set as the initial value when the precondition is switched again. Therefore, by restarting the time measurement from this initial value, the time when the duration time reaches the predetermined value is delayed. It takes time to determine that the deterioration state of the exhaust purification catalyst can be determined, and as a result, the opportunity to determine the deterioration state is reduced.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a deterioration determination device for an exhaust purification catalyst that can increase opportunities for determining the deterioration state of the exhaust purification catalyst.

In the following, means for achieving the above object and its effects are described.
In the first aspect of the present invention, it is assumed that the temperature of the exhaust purification catalyst provided in the exhaust passage of the internal combustion engine can rise when a predetermined precondition is satisfied, and at least the precondition is satisfied for a predetermined time. An exhaust purification catalyst deterioration determination device that performs the determination of the deterioration state on the assumption that the execution condition for determining the deterioration state of the exhaust purification catalyst is satisfied by continuing as described above. And a subtracting unit for subtracting the duration time measured by the time measuring unit until the precondition is no longer satisfied.

  According to the above configuration, when a predetermined precondition is satisfied prior to the determination of the deterioration state of the exhaust purification catalyst, the time duration of the state of establishment is counted by the time measuring means. Then, if the establishment state is continued for a predetermined time or longer (when the measured continuous time exceeds a predetermined value), it is determined that the execution condition for determining the deterioration state of the exhaust purification catalyst is satisfied, and the deterioration state is determined. Is done.

  When the precondition is not satisfied, the temperature of the exhaust purification catalyst is lowered, and the execution condition for determining the deterioration state is not satisfied. At this time, the temperature of the exhaust purification catalyst does not rapidly decrease but gradually decreases with time. Therefore, there is a case where the temperature of the exhaust purification catalyst does not decrease to the value when the precondition was satisfied last time (at the start of temperature increase) until the precondition is satisfied again.

  In this regard, according to the first aspect of the present invention, when the precondition is not satisfied, the duration time measured so far by the time measuring means is subtracted by the subtracting means. Then, when the precondition is satisfied again, the measurement of the duration of the satisfaction condition is restarted from the value after the subtraction.

  Therefore, even if the temperature of the exhaust purification catalyst does not decrease so much during the precondition failure period and does not decrease to the value when the precondition was satisfied previously (at the start of temperature rise), It becomes possible to restart the time measurement of the duration from a value corresponding to the temperature of the exhaust purification catalyst and larger than the case where the duration is measured from “0”. For this reason, when the precondition is satisfied after re-establishment, the predetermined time is reached in a shorter time than when the time measurement is restarted from “0”. As a result, it becomes possible to determine the deterioration state of the exhaust purification catalyst in a shorter time, and the determination opportunity increases.

  According to a second aspect of the present invention, in the first aspect of the invention, the subtracting unit subtracts the duration using a subtraction value corresponding to the amount of air taken into the internal combustion engine. And

  Here, the air in the exhaust takes away heat when passing through the exhaust purification catalyst. Therefore, during the period in which the precondition is not satisfied, the temperature of the exhaust purification catalyst decreases due to the removal of the heat. The degree of temperature decrease at this time varies depending on the amount of heat removed by air (the amount of air). Further, there is a correlation between the amount of air in the exhaust gas that passes through the exhaust purification catalyst and the amount of air taken into the internal combustion engine.

  For this reason, as in the second aspect of the invention, the subtracting unit subtracts the duration using a subtraction value corresponding to the amount of air sucked into the internal combustion engine, thereby reducing the duration of the exhaust at that time. The temperature can be made corresponding to the temperature of the purification catalyst. Therefore, when the precondition is satisfied again, it is possible to quickly and accurately grasp that the deterioration state of the exhaust purification catalyst can be judged by restarting the time measurement from the value after the subtraction. It becomes possible to do.

  According to a third aspect of the present invention, in the second aspect of the invention, the subtracting means subtracts the duration using a larger subtraction value than when the amount of air is small than when the amount of air is small. To do.

  The amount of heat taken away when the air in the exhaust gas passes through the exhaust purification catalyst is small when the amount of air is small, and increases as the amount of air increases. For this reason, as described in claim 3, when the amount of air is large, the duration is excessively subtracted when the amount of air is small by subtracting the duration using a larger subtraction value than when the amount of air is small. It is possible to suppress subtraction or insufficient subtraction when the amount of air is large. Therefore, regardless of the amount of air in the precondition failure period, the duration time is surely corresponding to the temperature of the exhaust purification catalyst until the time measurement is resumed according to the reestablishment of the precondition condition. It becomes possible to do.

  According to a fourth aspect of the present invention, in the first aspect of the invention, the subtracting unit subtracts the duration using a subtraction value corresponding to a degree of decrease in the temperature of the exhaust purification catalyst. To do.

  According to the above configuration, when the precondition is no longer satisfied, the temperature of the exhaust purification catalyst decreases, but the subtraction means subtracts the duration using a subtraction value corresponding to the temperature decrease degree, The duration can be made to correspond to the temperature of the exhaust purification catalyst at that time. Therefore, when the precondition is satisfied again, it is possible to quickly and accurately grasp that the deterioration state of the exhaust purification catalyst can be judged by restarting the time measurement from the value after the subtraction. It becomes possible to do.

  According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the subtracting means subtracts the duration using a larger subtraction value than when it is small when the degree of decrease is large. .

  According to the above configuration, when the temperature reduction degree of the exhaust purification catalyst is large, the duration time is subtracted using a larger subtraction value than when the temperature is small, so that the duration time is excessively subtracted when the degree of reduction is small. It is possible to suppress the subtraction from being insufficient when the degree of decrease is large. Therefore, regardless of the degree of decrease in the temperature of the exhaust purification catalyst during the period when the precondition is not satisfied, the continuation time of the exhaust purification catalyst is surely reached until the time measurement of the duration is resumed according to the reestablishment of the precondition. It becomes possible to make it correspond to the temperature.

According to a sixth aspect of the present invention, in the first aspect of the present invention, the subtracting means subtracts the duration using a subtraction value corresponding to a time when the precondition is not satisfied.
Here, the temperature of the exhaust purification catalyst decreases when the precondition is not satisfied, and increases when it is satisfied. There is a correlation between the amount of decrease when the temperature of the exhaust purification catalyst decreases and the precondition failure time. For this reason, as in the invention described in claim 6, the subtraction means subtracts the duration using a subtraction value corresponding to the pre-establishment time, so that the duration is determined as the temperature of the exhaust purification catalyst at that time. It can be made to correspond to. Therefore, when the precondition is satisfied again, it is possible to quickly and accurately grasp that the deterioration state of the exhaust purification catalyst can be judged by restarting the time measurement from the value after the subtraction. It becomes possible to do.

  According to a seventh aspect of the present invention, in the sixth aspect of the present invention, the subtracting means subtracts the duration using a larger subtraction value than when it is short when the failure time is long. .

  The amount of decrease in the temperature of the exhaust purification catalyst during the precondition failure period is small when the precondition failure time is short, and tends to increase as the precondition is long. Therefore, according to the seventh aspect of the invention, when the failure time is long, the duration time is subtracted using a larger subtraction value than when the failure time is short, so that the duration time is excessively subtracted when the failure time is short. It is possible to suppress the subtraction from being insufficient when the failure time is long. Therefore, regardless of the failure time, it is possible to ensure that the duration corresponds to the temperature of the exhaust purification catalyst before the time measurement of the duration is resumed according to the re-establishment of the precondition.

According to an eighth aspect of the present invention, in the first aspect of the present invention, the subtracting means subtracts the duration using a subtraction value corresponding to the temperature of the exhaust purification catalyst.
The degree of decrease in the temperature of the exhaust purification catalyst during the period in which the precondition is not satisfied differs depending on the temperature of the exhaust purification catalyst at that time, and it is considered that the degree of decrease is larger when the temperature is high than when it is low.

  For this reason, as in the invention described in claim 8, the subtraction means subtracts the duration using a subtraction value corresponding to the temperature of the exhaust purification catalyst, so that the duration is made the temperature of the exhaust purification catalyst at that time. It can be made compatible. Therefore, when the precondition is satisfied again, it is possible to quickly and accurately grasp that the deterioration state of the exhaust purification catalyst can be judged by restarting the time measurement from the value after the subtraction. It becomes possible to do.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a configuration of a multi-cylinder diesel engine (hereinafter simply referred to as an engine) 11 and its exhaust purification device 12 as an internal combustion engine to which the present embodiment is applied.

  The engine 11 is mainly configured to include an intake passage 13, a combustion chamber 14 for each cylinder 10, and an exhaust passage 15. An air cleaner 16 that purifies the air sucked into the intake passage 13 is provided at the most upstream portion of the intake passage 13. In the engine 11, an air flow meter 17 that detects the flow rate of air in the intake passage 13, a compressor 18 </ b> A of the turbocharger 18, an intercooler 19, and an intake throttle valve 21 are disposed in order from the air cleaner 16 toward the intake downstream side. Has been. The intake passage 13 is branched at an intake manifold 22 provided on the intake downstream side of the intake throttle valve 21, and is connected to the combustion chamber 14 of each cylinder 10 through this branched portion.

  The cylinder head 23 of the engine 11 is provided with a fuel injection valve 24 for each cylinder 10 for injecting fuel to be used for combustion in the combustion chamber 14. Each fuel injection valve 24 is supplied with fuel from a fuel tank 26 through a fuel supply path 25. The fuel supply path 25 is provided with a fuel pump 27 that sucks and pressurizes fuel from a fuel tank 26, and a common rail 28 that is a high-pressure fuel pipe that accumulates the discharged high-pressure fuel. The fuel injection valve 24 of each cylinder 10 is connected to the common rail 28.

  On the other hand, an exhaust port 29 is connected to each combustion chamber 14 in the exhaust passage 15. The exhaust passage 15 is provided with an exhaust manifold 31 for collecting exhaust discharged from each combustion chamber 14 through an exhaust port 29, and a turbine 18B of the turbocharger 18.

  Further, the engine 11 employs an exhaust gas recirculation (hereinafter referred to as “EGR”) device 32 that recirculates a part of the exhaust gas into the intake air. The EGR device 32 includes an EGR passage 33 that allows the intake passage 13 and the exhaust passage 15 to communicate with each other. The upstream side of the EGR passage 33 is connected between the exhaust manifold 31 of the exhaust passage 15 and the turbine 18B. In the middle of the EGR passage 33, an EGR cooler catalyst 34 that purifies the exhaust gas that is recirculated, an EGR cooler 35 that cools the exhaust gas that is recirculated, and an EGR that adjusts the flow rate of the exhaust gas that is recirculated. A valve 36 is provided. The downstream side of the EGR passage 33 is connected between the intake throttle valve 21 and the intake manifold 22 of the intake passage 13.

  In such an engine 11, the air taken into the intake passage 13 is purified by the air cleaner 16 and then introduced into the compressor 18 </ b> A of the turbocharger 18. In the compressor 18 </ b> A, the introduced air is compressed and discharged to the intercooler 19. Air that has become hot due to compression is cooled by the intercooler 19, and then distributed and supplied to the combustion chamber 14 of each cylinder 10 through the intake throttle valve 21 and the intake manifold 22. The flow rate of air in the intake passage 13 is adjusted through opening control of the intake throttle valve 21. The air flow rate (intake air amount) is detected by an air flow meter 17.

  In the combustion chamber 14 into which air has been introduced, fuel is injected from the fuel injection valve 24 in the compression stroke of each cylinder 10. Then, an air-fuel mixture of air introduced through the intake passage 13 and fuel injected from the fuel injection valve 24 is combusted in the combustion chamber 14. The piston 37 is reciprocated by the high-temperature and high-pressure combustion gas generated at this time, and the crankshaft 38 that is the output shaft is rotated to obtain the driving force (output torque) of the engine 11. The engine 11 is provided with a rotation speed sensor 39 that detects the rotation speed of the crankshaft 38 as the engine rotation speed.

  Exhaust gas generated by combustion in the combustion chamber 14 of each cylinder 10 is introduced into the turbine 18B of the turbocharger 18 through the exhaust manifold 31. When the turbine 18B is driven by the flow of the introduced exhaust, the compressor 18A provided in the intake passage 13 is driven in conjunction with the compression of the air.

  On the other hand, a part of the exhaust gas generated by the combustion is introduced into the EGR passage 33. The exhaust gas introduced into the EGR passage 33 is purified by the EGR cooler catalyst 34, cooled by the EGR cooler 35, and then recirculated into the air downstream of the intake throttle valve 21 in the intake passage 13. The flow rate of the exhaust gas thus recirculated is adjusted through the opening degree control of the EGR valve 36.

  The engine 11 is configured as described above. Next, the exhaust gas purification device 12 for purifying the exhaust gas discharged from the engine 11 will be described. The exhaust purification device 12 includes an addition valve 41 and a plurality (three) of catalytic converters (a first catalytic converter 42, a second catalytic converter 43, and a third catalytic converter 44) as an exhaust purification catalyst. ing.

  The most upstream first catalytic converter 42 is disposed on the exhaust downstream side of the turbine 18B, and is configured by supporting a NOx storage reduction catalyst on a carrier. In the first catalytic converter 42, nitrogen oxide NOx in the exhaust gas is occluded, and the occluded nitrogen oxide NOx is reduced and purified by supplying an unburned fuel component serving as a reducing agent. The second catalytic converter 43 is disposed on the exhaust downstream side of the first catalytic converter 42. The second catalytic converter 43 uses a porous material that allows the passage of gas components in the exhaust gas and prevents the passage of the particulate matter PM in the exhaust gas as a carrier, and supports the NOx catalyst of the occlusion reduction type on the carrier. It is comprised by. The third catalytic converter 44 is disposed on the exhaust downstream side of the second catalytic converter 43. The third catalytic converter 44 includes a carrier and an oxidation catalyst carried by the carrier, and purifies the exhaust gas through oxidation of hydrocarbon HC and carbon monoxide CO in the exhaust gas by the oxidation catalyst.

  The addition valve 41 is disposed upstream of the first catalytic converter 42 in the exhaust passage 15. The addition valve 41 is connected to the fuel pump 27 through a fuel passage 46, and the fuel supplied from the fuel pump 27 is injected into the exhaust gas as a reducing agent and added. The added fuel temporarily reduces the exhaust gas to a reducing atmosphere to reduce and purify the nitrogen oxides NOx stored in the first and second catalytic converters 42 and 43. Further, the second catalytic converter 43 simultaneously performs purification of the particulate matter PM.

  In the exhaust passage 15, the temperature between the first catalytic converter 42 and the second catalytic converter 43 is the temperature of the exhaust gas passing through the space (exhaust temperature), that is, the exhaust gas before flowing into the second catalytic converter 43. An exhaust gas temperature sensor 48 for detecting the temperature of the exhaust gas is provided. An exhaust temperature sensor 49 for detecting the temperature of the exhaust gas passing through the space, that is, the temperature of the exhaust gas immediately after passing through the second catalytic converter 43, is located in the space downstream of the second catalytic converter 43 in the exhaust passage 15. It is arranged. The exhaust passage 15 is provided with a differential pressure sensor 51 that detects a differential pressure between the exhaust pressure on the exhaust upstream side of the second catalytic converter 43 and the exhaust pressure on the exhaust downstream side. Further, oxygen sensors 52 and 53 for detecting the oxygen concentration in the exhaust gas are disposed upstream of the first catalytic converter 42 and between the second catalytic converter 43 and the third catalytic converter 44 in the exhaust passage 15. Each is arranged.

  The control of the engine 11 and the exhaust purification device 12 described above is performed by the electronic control device 61. The electronic control device 61 includes a CPU that executes various processes related to the control of the engine 11, a ROM that stores programs and data necessary for the control, a RAM that stores processing results of the CPU, and exchange of information with the outside. It is configured with an input / output port for performing

  In addition to the sensors described above, the input port of the electronic control device 61 includes an accelerator sensor 54 that detects the amount of accelerator depression by the driver, a common rail sensor 55 that detects the internal pressure (rail pressure) of the common rail 28, and an intake throttle valve 21. A throttle valve sensor 56 for detecting the opening is connected.

  Further, the intake throttle valve 21, the fuel injection valve 24, the fuel pump 27, the addition valve 41, the EGR valve 36, and the like are connected to the output port of the electronic control unit 61. The electronic control device 61 performs various operation controls of the engine 11 by controlling devices connected to the output ports based on the detection results of the sensors. Various operation controls include fuel injection control by the fuel injection valve 24, and also control related to combustion, control related to purification of exhaust gas, and the like.

  For example, in the fuel injection control, the electronic control unit 61 calculates the basic injection amount that is optimal for the operating state of the engine 11 based on the accelerator depression amount by the accelerator sensor 54 and the engine rotation speed by the rotation speed sensor 39. Further, the maximum injection amount is determined by adding corrections based on signals from various sensors to the basic maximum injection amount (the maximum amount that can be theoretically injected) determined by the engine speed. The basic injection amount and the maximum injection amount are compared, and the smaller injection amount is set as the target injection amount. Further, the basic injection timing is calculated based on the accelerator depression amount and the engine rotation speed, and is corrected by signals from various sensors, and the target injection timing optimum for the operating state of the engine 11 at that time is calculated. The energization of the fuel injection valve 24 is controlled based on the target injection amount and the target injection timing to open and close the fuel injection valve 24.

  In the control related to combustion, the electronic control unit 61 selects a mode corresponding to the operation state of the engine 11 from a plurality of preset combustion modes. The plurality of combustion modes include a normal combustion mode and a low temperature combustion mode. Here, in the engine 11 of the present embodiment to which the EGR device 32 is applied, the amount of inert gas in the combustion chamber 14, that is, recirculation when the fuel injection timing from the fuel injection valve 24 to the combustion chamber 14 is constant. As the amount of exhausted gas increases, the amount of soot generated in the combustion chamber 14 gradually increases. When the amount of exhaust gas recirculated reaches a predetermined value, the amount of soot generated peaks. When the amount of exhaust gas that is recirculated exceeds a predetermined value, the fuel in the combustion chamber 14 and the temperature around it decrease, and the amount of soot generated in the combustion chamber 14 decreases. In the low temperature combustion mode, fuel is combusted in the combustion chamber 14 while an amount of exhaust gas larger than the predetermined value is recirculated. In contrast, in the normal combustion mode, fuel is combusted in the combustion chamber 14 while an amount of exhaust gas smaller than the predetermined value is recirculated. Then, the electronic control unit 61 selects a combustion mode according to the operating state of the engine 11 at that time.

  Further, the electronic control unit 61 executes control on the exhaust purification catalyst as one of the controls related to exhaust purification. In this control, four catalyst control modes, ie, a catalyst regeneration control mode, a sulfur poisoning recovery control mode, a NOx reduction control mode, and a normal control mode, are set, and the electronic control device 61 is in a state of the catalytic converters 42 to 44. The catalyst control mode corresponding to is selected and executed.

  The catalyst regeneration control mode is a mode in which the particulate matter PM deposited in the second catalytic converter 43 is burned to emit carbon dioxide CO2 and water H2 O, and the fuel from the addition valve 41 is discharged. In this mode, the addition is continuously repeated to increase the temperature of the support (catalyst bed temperature) (600 to 700 ° C.).

  In the sulfur poisoning recovery control mode, the NOx catalyst in the first and second catalytic converters 42 and 43 is poisoned by the sulfur oxide SOx, and the sulfur oxide SOx is reduced when the NOx storage capacity decreases. This is a mode for controlling the release.

  The NOx reduction control mode is a mode in which the nitrogen oxides NOx stored in the NOx catalysts in the first and second catalytic converters 42 and 43 are reduced to nitrogen N2, carbon dioxide CO2 and water H2 O and released. . In this mode, the catalyst temperature becomes relatively low (for example, 250 to 500 ° C.) by intermittent fuel addition from the addition valve 41 with a relatively long time. The state other than this is the normal control mode, and the reducing agent is not added from the addition valve 41 in this mode.

  Furthermore, the electronic control unit 61 also performs control for determining the deterioration state of the NOx catalyst as one of the controls related to exhaust gas purification. This control is performed because the NOx catalyst is deteriorated by long-term use, and there is a possibility that the nitrogen oxide NOx cannot be sufficiently occluded or the nitrogen oxide NOx cannot be sufficiently reduced in a reducing atmosphere. This is because it is necessary to grasp the deterioration state in order to deal with the problem.

  The determination of the deterioration state is effectively performed in a situation where the NOx catalyst is heated and activated, in order to eliminate erroneous determination and ensure determination accuracy. Here, “temperature rise” refers to a phenomenon in which the NOx catalyst is activated by the reducing agent added from the addition valve 41 and the catalyst bed temperature rises. Therefore, in the present embodiment, a precondition is set for determining whether or not the catalyst bed temperature is in a situation where the catalyst bed temperature can be raised, and if the situation where this precondition is satisfied continues for a predetermined time or more, the NOx catalyst deteriorates. Assuming that the execution condition for determining the state is satisfied, the process proceeds to the same determination.

  The flowchart of FIG. 2 shows an “execution condition determination routine” for determining whether the execution condition is satisfied (established / not satisfied). A series of processing shown in this routine is executed by the electronic control device 61 as processing at predetermined time intervals. For this execution, a precondition establishment counter is used. The precondition fulfillment counter is for counting the duration of the situation where the precondition is met. The determination result is represented by the execution flag setting status (“ON” or “OFF”). If the execution condition is satisfied, the execution flag is set to “ON”, and if the execution condition is not satisfied, the execution flag is set to “OFF”.

  In this execution condition determination routine, the electronic control unit 61 first determines in step 110 whether a preset precondition is satisfied. Here, it is assumed that conditions A to H shown below are preconditions, and the catalyst bed temperature can be increased only when all of these conditions A to H are satisfied (preconditions: established). Yes. Accordingly, if any one of the conditions A to H is not satisfied, the precondition is not satisfied.

<Condition A>
The catalyst regeneration control mode or the sulfur poisoning recovery control mode is selected and executed as the catalyst control mode. This is because in these catalyst control modes, the addition of the reducing agent from the addition valve 41 is continuously repeated in order to increase the catalyst bed temperature and burn the particulate matter PM or release the sulfur oxide SOx. is there.

<Condition B>
The catalyst bed temperature must be above a certain value. This is because when the condition B is not satisfied, the NOx catalyst is not sufficiently activated, and even if the reducing agent is added from the addition valve 41, the catalyst bed temperature may not increase.

  As the catalyst bed temperature, it is desirable to use a value directly detected by a sensor or the like, but the exhaust gas temperature detected by the exhaust gas temperature sensors 48 and 49 may be used as an equivalent value of the catalyst bed temperature. In addition to this, based on the operating state of the engine 11 (for example, the engine speed, the fuel injection amount from the fuel injection valve 24, etc.), and further taking into account the response delay due to the heat capacity, the catalyst bed temperature is determined by the amount of heat given from the exhaust May be estimated.

<Condition C>
The exhaust temperature detected by the exhaust temperature sensor 49 is less than a certain value. However, this condition is such that when the catalyst bed temperature rises too much (when the catalyst bed temperature exceeds the predetermined value), the addition of the reducing agent from the addition valve 41 is stopped to raise the catalyst bed temperature. It is assumed that the exhaust emission control device 12 is not provided.

<Condition D>
The combustion mode can detect the deterioration state of the NOx catalyst. Examples of the combustion mode include combustion modes other than the low-temperature combustion mode. This is because, in the low-temperature combustion mode, when the air-fuel ratio is lowered to near the stoichiometric air-fuel ratio by the EGR device 32, the catalyst bed temperature of the NOx catalyst in the first catalytic converter 42 may greatly fluctuate. This is to prevent a decrease in accuracy.

<Condition E>
The addition valve 41 is operating. This is because if the reducing agent is not added from the addition valve 41, the catalyst bed temperature does not rise as intended.

<Condition F>
No abnormality is detected in the exhaust temperature sensors 48, 49. However, this condition is based on the premise of the exhaust purification device 12 in which processing for detecting abnormalities such as disconnection of the exhaust temperature sensors 48 and 49 is performed.

<Condition G>
The amount of fuel adhering to the exhaust manifold 31 is below a certain value. This is because, even if the reducing agent is added from the addition valve 41, if the amount adhering to the exhaust manifold 31 is large, the additive related to the temperature rise of the catalyst bed temperature decreases accordingly.

<Condition H>
The output voltage of the battery is above a certain value. This is because the detection accuracy of the exhaust temperature sensors 48 and 49 is lowered at a low voltage.

  If the determination condition in step 110 is satisfied (precondition: satisfied), it is considered that the catalyst bed temperature is likely to rise. Therefore, the process proceeds to step 120 and the precondition satisfaction counter is counted up. For example, by incrementing the counter by a predetermined value, the time is counted in units of the control cycle of this process. By this counting operation, the duration of the preconditions is established.

  Next, in step 150, it is determined whether or not the value of the precondition establishment counter is equal to or greater than a predetermined value α. If this determination condition is not satisfied, it is assumed that the catalyst bed temperature is not sufficiently high and that the deterioration state of the NOx catalyst has not yet been accurately determined, the execution flag is set to “OFF” in step 170. Set. After this setting process, the execution condition determination routine is temporarily terminated.

  If the preconditions continue to be established, step 120 is repeated during the establishment period, and the precondition establishment counter value increases. On the other hand, at this time, the catalyst bed temperature rises. Then, when the value of the condition establishment counter is equal to or greater than the predetermined value α and the determination condition of step 150 is satisfied, it is determined in step 160 that the deterioration state of the NOx catalyst can be accurately determined. Set the flag to “ON”. After this setting process, the execution condition determination routine is temporarily terminated.

  Note that the execution flag set as described above is used as at least one of indices for determining whether or not to determine the deterioration state of the NOx catalyst. When determining the deterioration, for example, the amount of deterioration is calculated based on the temperature of the NOx catalyst and the like, and this is integrated by a deterioration counter. Then, the deterioration counter is compared with a predetermined deterioration determination value, and when the deterioration counter value is equal to or greater than the deterioration determination value, it is determined that the deterioration is occurring.

  By the way, when the state where the precondition is satisfied is switched to the state where the precondition is not satisfied, the catalyst bed temperature is lowered and the execution condition for determining the deterioration state is not satisfied. As a situation in which the precondition is not satisfied, for example, when the load applied to the engine 11 is small, such as during deceleration or idling. On the other hand, in the execution condition determination routine, the determination condition in step 110 is not satisfied when the precondition is not satisfied. In this case, processing for setting the initial value of the precondition completion counter is performed in preparation for the case where the precondition is satisfied again.

  Here, when switching to a situation where the precondition is not satisfied, the catalyst bed temperature rapidly decreases as shown by a two-dot chain line in FIG. 3 as in the background art (see timing t2). It is assumed that the temperature has returned to the temperature at the time of switching to the previously established situation (at the start of raising the catalyst bed temperature, see timing t1). In this case, it is conceivable to clear (= 0) the value counted during the precondition fulfillment period (timed duration) as shown by the one-dot chain line in FIG.

  However, if the above value (= 0) is used as the initial value of the precondition completion counter when the precondition is switched again (see timing t3), a value that does not correspond to the actual catalyst bed temperature is obtained. May be set as an initial value. This is because the catalyst bed temperature gradually decreases with the passage of time as indicated by the solid line in FIG. 3 when switching to a situation where the precondition is not satisfied. And, depending on the period when the preconditions are not met, when switching to a situation where the preconditions are met again, the catalyst bed temperature is higher than when the preconditions were switched from the previously met condition to the not met condition. However, the temperature is only slightly decreased, and is often higher than the temperature at the time when the precondition was switched to the previous condition (at the start of temperature increase).

  Assuming that the value cleared as described above (= 0) is the initial value at the time when the precondition is switched again, the initial value is changed to the state where the precondition is again satisfied. When counting up is restarted from the value, the time to reach the predetermined value α is delayed. It takes time unnecessarily until it is determined that the deterioration state can be determined, and the opportunity for determination of deterioration is reduced.

  Therefore, if the determination condition of step 110 is not satisfied in order to eliminate such a problem, the process proceeds to step 130 to determine whether or not the precondition satisfying counter is greater than the minimum value (in this case, “0”). To do. When the precondition satisfaction counter is “0” and the determination condition of step 130 is not satisfied, the process proceeds to step 150 as described above.

  On the other hand, when the determination condition of step 130 is satisfied, the routine proceeds to step 140 where the precondition establishment counter is not cleared but is subtracted (decremented) by a predetermined value. By this subtraction process, the duration time measured during the precondition failure period is subtracted.

  As the subtraction value, it is desirable to use a value corresponding to the amount of decrease (reduction allowance) of the catalyst bed temperature. Here, the catalyst bed temperature is affected by the air passing through the NOx catalyst. That is, when the air in the exhaust gas passes through the NOx catalyst, the heat of the NOx catalyst is carried away by the air in the process of passing, and the catalyst bed temperature decreases. The degree of reduction at this time varies depending on the amount of heat removed by air (the amount of air). Further, there is a correlation between the amount of air in the exhaust gas that passes through the NOx catalyst and the amount of air taken into the combustion chamber 14 of the engine 11 (intake air amount). Considering this point, a constant value set based on the intake air amount is used as the subtraction value. Here, the case where the intake air amount reaches the maximum value that can be taken during the period when the preconditions are not satisfied (when the catalyst bed temperature drops the most) is used as a reference. To do.

  By the subtraction process in step 140, the value of the precondition satisfying counter becomes a value corresponding to or close to the catalyst bed temperature at that time. The process of step 140 is performed until immediately before switching to a situation where the precondition is satisfied again. Then, when switching to a situation in which the precondition is satisfied again, the value of the precondition forming counter immediately before the switch is made the initial value, and the count-up (step 120) is resumed.

After step 140, the process proceeds to step 150 described above, and is compared with a predetermined value α to set an execution flag.
The processing of steps 110 and 120 by the electronic control unit 61 in the execution condition determination routine corresponds to the time measuring means, and the processing of steps 110 and 140 corresponds to the subtraction means.

  When the processing is repeatedly performed according to the execution condition determination routine described above, the catalyst bed temperature and the precondition completion counter change as shown in FIG. This example shows a case where the precondition is not satisfied before the timing t1 and during the period from the timing t2 to t3, and the precondition is satisfied during the period from the timing t1 to t2 and the period after the timing t3.

  The precondition is not satisfied in the period before the timing t1, and the precondition completion counter holds a minimum value (= 0) that can be taken. Therefore, in the execution condition determination routine, processing is performed in the order of step 110 → 130 → 150 → 170 → return. Further, during this period, the catalyst bed temperature has not increased. That is, there is no difference in exhaust temperature between the exhaust upstream side and the exhaust downstream side of the second catalytic converter 43 in the exhaust passage 15.

  In the execution period of the execution condition determination routine, processing is performed in the order of step 110 → 120 → 150 → 170 (or 160) → return in the execution period of the preconditions at timings t1 to t2. As a result of the processing in step 120, the value of the precondition satisfaction counter increases. Based on the magnitude relationship between this value and the predetermined value α, the execution flag is set to “OFF” or “ON”. In this period, since the preconditions are satisfied, the catalyst bed temperature rises (temperature rises) as time passes.

  When the situation is switched to a situation where the precondition is not satisfied at the timing t2, the execution condition determination routine performs processing in the order of step 110 → 130 → 140 → 150 → 170 → return. By the process of step 140, the value of the precondition satisfaction counter is decreased. Since the subtraction value is a constant value, the precondition completion counter decreases with a constant change gradient during the precondition non-satisfaction period (timing t2 to t3). Further, during this period, the catalyst bed temperature gradually decreases.

  At the timing t3 when the precondition is switched again to the situation where the precondition is satisfied, the catalyst bed temperature is slightly lower than the catalyst bed temperature at the timing t2 when the precondition is switched to the previous condition. On the other hand, the value of the precondition satisfying counter is slightly smaller than the value at the timing t2 due to the processing of step 140 (subtraction processing). This value is larger than when the precondition establishment counter is cleared at timing t2 (see the alternate long and short dash line). In this way, at the timing t3 when the precondition is switched to the state where the precondition is satisfied again, the value of the precondition establishment counter becomes a value corresponding to the catalyst bed temperature at that time.

  After timing t3, in the execution condition determination routine, processing is performed in the same order as in the above-described period of timings t1 to t2. As for the precondition satisfying counter, the value at the timing t3 is set as an initial value, and counting up (step 120) is restarted from the value. The precondition completion counter increases with time. Further, during this period, the catalyst bed temperature rises as in the period from the timing t1 to t2.

According to the first embodiment described in detail above, the following effects can be obtained.
(1) By counting up the precondition establishment counter according to the precondition establishment, the duration of the precondition establishment condition is counted. When the precondition is no longer satisfied, the precondition completion counter is not cleared (= 0), but is subtracted, and the subtraction result is set as an initial value when the precondition is switched again.

  Therefore, even if the catalyst bed temperature does not decrease so much during the precondition failure period, and the precondition does not decrease to the value when the precondition is switched to the previous condition (at the start of temperature increase), the precondition is again When switching to the established condition, it is possible to restart counting up of the precondition satisfying counter from a larger value than when the initial value is “0”. Therefore, when the precondition is subsequently established, the value of the precondition establishment counter reaches the predetermined value α in a shorter time. As a result, it is possible to increase the determination opportunity by setting the deterioration state of the NOx catalyst in a shorter time.

  (2) A subtraction value (a constant value) is set in consideration of a decrease in the catalyst bed temperature due to the removal of heat from the air, and the precondition completion counter is subtracted using this subtraction value. Therefore, by this subtraction, a value corresponding to the catalyst bed temperature can be set as the initial value of the precondition establishment counter when switching to the situation where the precondition is established again. Accordingly, when the precondition is switched to a state where the precondition is satisfied again, the deterioration state of the NOx catalyst can be determined by restarting the precondition completion counter from the initial value set as described above. It becomes possible to quickly and accurately grasp this.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG.
In the second embodiment, in the execution condition determination routine, a value (variable value) corresponding to the intake air amount at that time is used as the subtraction value. This is because the amount of heat that is taken away when the air in the exhaust gas passes through the NOx catalyst is small when the amount of air is small and increases as the amount of air increases.

  Specifically, the electronic control unit 61 sets a precondition establishment counter in step 140 when the determination condition in step 110 of the execution condition determination routine (FIG. 2) is not satisfied and the determination condition in step 130 is satisfied. Subtract. In step 140, prior to subtraction, for example, a subtraction value is obtained by referring to a map stored in a memory. As shown in FIG. 4, the map defines the relationship between the intake air amount and the subtraction value so that the subtraction value becomes larger when the intake air amount is large than when it is small. Then, a subtraction value corresponding to the intake air amount at that time by the air flow meter 17 is obtained from the map, and the precondition satisfaction counter is subtracted using this value. After this processing, the routine proceeds to step 150.

  By performing the processing of step 140, for example, when the intake air amount is constant during the precondition failure period, the precondition satisfaction counter has a constant change gradient as shown in FIG. Each time the execution condition determination routine is executed, it decreases by a certain amount. On the other hand, if the intake air amount changes during the precondition failure period, the precondition counter is decreased with a change gradient corresponding to the intake air amount. When the intake air amount is small, the value of the precondition counter is decreased with a small decrease degree, and when the intake air amount is large, the value of the precondition satisfying counter is decreased. Then, when switching to a situation where the precondition is satisfied, counting up (step 120) is restarted with the value of the precondition establishment counter immediately before the switch is made as an initial value.

  Note that matters other than those described above, for example, each configuration of the engine 11 and the exhaust purification device 12, processing other than step 140 in the execution condition determination routine, and the like are the same as those in the first embodiment, and thus description thereof is omitted here. To do.

Therefore, according to the second embodiment, the following effects can be obtained in addition to the above (1) and (2).
(3) When the intake air amount is large, a larger subtraction value is set than when the intake air amount is small, and by subtracting the precondition establishment counter using this subtraction value, the duration of the precondition establishment condition is subtracted. Yes. For this reason, it can be suppressed that the precondition satisfying counter is excessively subtracted when the intake air amount is small, or the subtraction of the precondition satisfying counter is insufficient when the intake air amount is large. Regardless of the amount of intake air during the precondition failure period, it is possible to ensure that the precondition counter (duration) corresponds to the catalyst bed temperature before switching to a condition where the precondition is satisfied again. It becomes.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG.
In the execution condition determination routine, the third embodiment uses a value set in consideration of a decrease amount (decrease degree) of the catalyst bed temperature per unit time as a subtraction value. Here, the subtraction value may be a constant value, or may be a variable value that varies depending on the degree of decrease in the catalyst bed temperature.

  Specifically, the electronic control unit 61 sets a precondition establishment counter in step 140 when the determination condition in step 110 of the execution condition determination routine (FIG. 2) is not satisfied and the determination condition in step 130 is satisfied. Subtract. Here, when the subtraction value is a constant value, for example, the case where the degree of decrease in the catalyst bed temperature during the precondition failure period is the maximum value that can be taken is used as a reference. The value is the subtraction value. When the subtraction value is a variable value, prior to subtraction, for example, the subtraction value is set with reference to a map stored in the memory. In this map, as shown in FIG. 5, when the degree of decrease in the catalyst bed temperature is large, the relationship between the degree of decrease in the catalyst bed temperature and the subtraction value is defined so that the subtraction value becomes larger than when the degree is small. . And the fall degree of the catalyst bed temperature at that time is calculated | required. For example, regarding the execution condition determination routine, the difference between the catalyst bed temperature in the previous control cycle and the catalyst bed temperature in the current control cycle is obtained, and this is set as the degree of decrease. As the catalyst bed temperature, an actual measurement value (a value corresponding to the catalyst bed temperature) or an estimated value can be used as described above. A subtraction value corresponding to the degree of decrease is obtained from the map, and the precondition satisfaction counter is subtracted using the subtraction value. After this processing, the routine proceeds to step 150.

  By performing the processing of step 140, for example, when the subtraction value is a constant value, the precondition satisfaction counter is decreased by a constant amount with a constant change gradient, that is, every time the execution condition determination routine is executed. I will do it. On the other hand, when the subtraction value is a variable value, the value of the precondition satisfying counter decreases with a change gradient corresponding to the degree of decrease in the catalyst bed temperature. When the degree of decrease in the catalyst bed temperature is small, the value of the precondition establishment counter decreases with a small change gradient, and when the degree of decrease is large, the value of the precondition satisfying counter decreases.

  Note that matters other than those described above, for example, each configuration of the engine 11 and the exhaust purification device 12, processing other than step 140 in the execution condition determination routine, and the like are the same as those in the first embodiment, and thus description thereof is omitted here. To do.

Therefore, according to the third embodiment, in addition to the above (1), the following effects can be obtained.
(4) When the precondition is switched to a state where the precondition is not satisfied, the catalyst bed temperature is lowered, and the precondition completion counter is subtracted using a subtraction value corresponding to the degree of decrease in the catalyst bed temperature. . Therefore, by this subtraction, the precondition satisfaction counter can be made to correspond to the catalyst bed temperature at that time. Accordingly, when the precondition is switched to a state where the precondition is satisfied again, the deterioration condition of the NOx catalyst can be determined by restarting the countup of the precondition satisfying counter from the value set as described above. It becomes possible to grasp the situation quickly and accurately.

  (5) When the degree of decrease in the catalyst bed temperature is large, a larger subtraction value is set than when it is small, and by subtracting the precondition establishment counter using this subtraction value, the duration of the precondition establishment condition is subtracted. I am doing so. For this reason, it is possible to suppress the precondition satisfaction counter from being excessively subtracted when the catalyst bed temperature decrease degree is small, or the subtraction of the precondition satisfaction counter being insufficient when the catalyst bed temperature decrease degree is large. Regardless of the degree of decrease in the catalyst bed temperature during the period when the precondition is not met, the precondition fulfillment counter (duration) is sure to correspond to the catalyst bed temperature before switching to the situation where the precondition is met again. It becomes possible.

(Fourth embodiment)
Next, a fourth embodiment embodying the present invention will be described with reference to FIGS.
Here, the catalyst bed temperature decreases when the precondition is not satisfied, and increases when it is satisfied. There is a correlation between the amount of decrease when the catalyst bed temperature decreases and the period (non-establishment time) until the condition is changed to the condition where the precondition is not satisfied and then changed again. The decrease amount is small when the failure time is short, and increases as the failure time becomes longer. Therefore, in the fourth embodiment, in the execution condition determination routine, a value set in consideration of the non-establishment time is used as the subtraction value.

  The flowchart of FIG. 7 shows an “execution condition determination routine” corresponding to FIG. A series of processing shown in this routine is executed by the electronic control device 61 as processing at predetermined time intervals.

  In this execution condition determination routine, the electronic control unit 61 first determines in step 210 whether or not a precondition is satisfied. The contents of this precondition are the same as those described in the first embodiment.

  If the determination condition of step 210 is satisfied, it is determined in step 220 whether or not the precondition was satisfied when the execution condition determination routine was executed last time (previous control cycle). If this determination condition is satisfied (if the establishment condition continues), the routine proceeds to step 230 and the precondition establishment counter is counted up. Since the execution condition determination routine is executed at regular intervals and the precondition establishment counter is counted up at regular intervals, the duration of the establishment of the precondition is counted by the processing of step 230 above. Then, after the processing of step 230, the routine proceeds to step 260.

  When the precondition is no longer satisfied and the determination condition of step 210 is not satisfied, the elapsed time (non-establishment time) after switching to the situation (precondition: non-establishment) is counted in step 240. At this time, for example, the counter is used in the same manner as the above-described precondition establishment counter, and is incremented every time the process of step 240 is performed. Then, after the processing of step 240, the process proceeds to step 260. In this case, no operation is performed on the precondition establishment counter, and therefore, the value immediately before the precondition is switched to “not established” is held for the precondition establishment counter.

  On the other hand, if the determination condition of step 210 is satisfied and the determination condition of step 220 is not satisfied, that is, the precondition was not satisfied until the previous control cycle, the precondition is “ When it is switched from “not established” to “established”, the process proceeds to step 250, and a subtraction value used for subtraction of the precondition establishment counter is calculated. For this calculation, for example, a map stored in the memory is referred to. As shown in FIG. 6, the map defines the relationship between the failure time and the subtraction value so that the subtraction value becomes larger when the precondition failure time is long than when it is short. Then, a subtraction value corresponding to the pre-establishment failure time counted by the process of step 240 is obtained from the map, and the pre-condition satisfaction counter is subtracted using this value. After this processing, the routine proceeds to step 260. If the precondition is still satisfied in the next control cycle, the precondition completion counter is incremented (step 230) using the subtraction result as an initial value.

  In step 260 and subsequent steps, processing similar to that in steps 150 to 170 in FIG. 2 described above is performed. That is, in step 260, it is determined whether or not the value of the precondition establishment counter is greater than or equal to the predetermined value α. If the determination condition is satisfied, the execution flag is set to “ON” in step 270, while the condition is satisfied. If not, the execution flag is set to “OFF” in step 280. After the processing in step 270 or step 280, the execution condition determination routine is temporarily terminated.

  When the process is repeatedly performed according to the execution condition determination routine described above, the catalyst bed temperature and the precondition establishment counter change as shown in FIG. This example shows a case where the precondition is satisfied in the period before the timing t11 and the period after the timing t12, and the precondition is not satisfied in the period from the timing t11 to t12. The contents indicated by the alternate long and short dash line in FIG. 8 are the same as those in FIG.

  In the period before the timing t11 (precondition: establishment), in the execution condition determination routine, the determination conditions of steps 210 and 220 are both satisfied, so that steps 210 → 220 → 230 → 260 → 280 (or 270). By the process of step 230, the value of the precondition satisfaction counter increases. Based on the magnitude relationship between this value and the predetermined value α, the execution flag is set to “OFF” or “ON”. Further, in the above period, since the precondition is satisfied, the catalyst bed temperature rises (temperature rises) as time passes.

  In the execution condition determination routine, processing is performed in the order of step 210 → 240 → 260 → 280 → return when the precondition is switched to the situation where the precondition is not satisfied at timing t11. While the non-establishment time is counted by the processing of step 240, the precondition establishment counter is held.

  During a period from timing t11 to timing t12 when the precondition is again satisfied, the catalyst bed temperature gradually decreases. At the timing t12, the catalyst bed temperature is slightly lower than the catalyst bed temperature at the timing t11 when the precondition is switched to a situation where the previous condition is not satisfied. On the other hand, in the execution condition determination routine, since the determination condition of step 210 is satisfied but the determination condition of step 220 is not satisfied, processing is performed in the order of step 210 → 220 → 250 → 260 → 280 → return. At this time, the precondition completion counter is subtracted by the subtraction value corresponding to the failure time (step 240) by the processing of step 250. By this subtraction, the value of the precondition satisfying counter becomes smaller than the value at the timing t11 when the precondition was switched to the situation where the precondition was not met last time. This value is larger than when the precondition establishment counter is cleared at timing t11 (see the one-dot chain line in FIG. 8). In this way, at the timing t12 when the precondition is switched to the state where the precondition is satisfied again, the precondition completion counter has a value corresponding to the catalyst bed temperature at that time.

  After timing t12, in the execution condition determination routine, processing is performed in the same order as in the period before timing t11 described above. As for the precondition satisfying counter, the value after being subtracted by the process of step 250 at timing t12 is set as the initial value, and the count-up is restarted from that value. The precondition satisfying counter increases with time in response to an increase in the catalyst bed temperature. Further, after timing t12, the catalyst bed temperature rises because the precondition is satisfied.

Note that matters other than those described above, for example, the configuration of the engine 11, the exhaust purification device 12, and the like are the same as those in the first embodiment, and thus the description thereof is omitted here.
Therefore, according to the fourth embodiment, in addition to the above (1), the following effects can be obtained.

  (6) When the precondition is no longer satisfied, the catalyst bed temperature is lowered, and the measurement of the time when the precondition is not satisfied is started. And when it changes to the condition where the precondition is satisfied again, a subtraction value corresponding to the non-establishment time is set, and the precondition completion counter is subtracted using this subtraction value. Therefore, by this subtraction, when switching to a situation where the precondition is established again, the precondition establishment counter can be set to a value corresponding to the catalyst bed temperature. Therefore, when the precondition is subsequently established, it is possible to determine the deterioration state of the NOx catalyst by resuming the precondition establishment counter from the above value. It becomes possible to grasp quickly and accurately.

  (7) When the precondition failure time is long, a larger subtraction value is set than when it is short, and the precondition completion counter is subtracted by using this subtraction value to subtract the precondition completion time. . For this reason, it is possible to prevent the precondition establishment counter from being excessively subtracted when the non-establishment time is short, or the subtraction of the precondition establishment counter to be insufficient when the non-establishment time is long. Therefore, regardless of the failure time, the precondition fulfillment counter value (duration) is changed until the precondition fulfillment counter is again established and the precondition fulfillment counter counts up again (duration time measurement). Can be made to correspond to the catalyst bed temperature.

Note that the present invention can be embodied in another embodiment described below.
The degree of decrease in the catalyst bed temperature during the period in which the preconditions are not satisfied varies depending on the catalyst bed temperature at that time, and the degree of decrease is considered to be greater when the catalyst bed temperature is high than when it is low.

  Therefore, a subtraction value corresponding to the catalyst bed temperature is set. When the catalyst bed temperature is high, the subtraction value is set to a larger value than when the catalyst bed temperature is low. Then, by subtracting the precondition establishment counter using the set subtraction value, the initial value of the precondition establishment counter when the precondition is switched to the state where the precondition is established again is obtained. In this way, an initial value corresponding to the catalyst bed temperature can be set. Accordingly, when the precondition is switched again to the situation where the precondition is satisfied, the deterioration condition of the NOx catalyst can be determined by restarting the count up of the precondition establishment counter (the time counting of the duration) from the initial value. It becomes possible to quickly and accurately grasp this.

  -The contents of the preconditions in each of the above embodiments are merely examples. The contents of this precondition may be changed as appropriate on the condition that it is possible to grasp that the temperature of the NOx catalyst can rise.

The subtraction value in each of the above embodiments may be calculated based on a predetermined arithmetic expression instead of the map.
In the second embodiment, the map (see FIG. 4) used when calculating the subtraction value only needs to have a map structure in which the subtraction value becomes larger than when the intake air amount is large. Therefore, the map structure may be appropriately changed within a range satisfying this condition. For example, the range in which the intake air amount can be taken may be divided into two or more regions, and a subtraction value may be set for each region (the same subtraction value is used in the same region).

  For the maps (see FIGS. 5 and 6) used when calculating the subtraction value in the third and fourth embodiments, the map structure may be changed as described above. In the third embodiment, when the degree of decrease in the catalyst bed temperature is large, the map structure is such that the subtraction value is larger than when the catalyst bed temperature is small. In the fourth embodiment, when the precondition is long, the subtraction value is larger than when it is short. The map structure is as follows.

  In the second and third embodiments, the precondition establishment counter may be operated in the same manner as in the fourth embodiment. That is, instead of subtracting the precondition establishment counter every time the execution condition determination routine is executed, the precondition establishment counter is held during the precondition non-satisfaction period, and the precondition is established again. The precondition fulfillment counter may be subtracted at once when switching.

  For example, in the second embodiment, the intake air amount is integrated during a period in which the precondition is not satisfied. When switching to a situation where the precondition is again satisfied, a subtraction value corresponding to the integrated value of the intake air amount at that time is obtained, and this is a precondition establishment counter when switching to a situation where the precondition is not satisfied Subtract from

  In the third embodiment, the degree of decrease in the catalyst bed temperature (the amount of decrease per unit time) is integrated during the period in which the precondition is not satisfied. When switching to a situation where the precondition is again established, a subtraction value corresponding to the integrated value of the degree of decrease at that time is obtained, and this is obtained from the precondition establishment counter when switching to a situation where the precondition is not established. Subtract.

  The present invention is not limited to a diesel engine, but can also be applied to a case where a catalyst configuration similar to that of each of the above embodiments is employed for a lean combustion gasoline engine or the like.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the structure of an engine and an exhaust gas purification apparatus about 1st Embodiment which actualized this invention. The flowchart explaining the execution condition determination routine in 1st Embodiment. The timing chart which shows an example of the change condition of the establishment condition of a precondition, a catalyst bed temperature, and a precondition establishment counter in 1st Embodiment. The schematic diagram which shows the map structure of the map used for determination of a subtraction value in 2nd Embodiment. The schematic diagram which shows the map structure of the map used for determination of a subtraction value in 3rd Embodiment. The schematic diagram which shows the map structure of the map used for determination of a subtraction value in 4th Embodiment. The flowchart explaining the execution condition determination routine in 4th Embodiment. The timing chart which shows an example of the change condition of the satisfaction condition of a precondition, catalyst bed temperature, and a precondition establishment counter in 4th Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Diesel engine (internal combustion engine), 15 ... Exhaust passage, 42 ... 1st catalytic converter (exhaust purification catalyst), 43 ... 2nd catalytic converter (exhaust purification catalyst), 61 ... Electronic control unit (time measuring means, subtraction means) .

Claims (8)

When the predetermined precondition is satisfied, it is assumed that the temperature of the exhaust purification catalyst provided in the exhaust passage of the internal combustion engine can rise, and at least if the precondition is continued for a predetermined time or more, the exhaust purification An exhaust purification catalyst deterioration determination device configured to determine the deterioration state on the assumption that the execution condition for determining the deterioration state of the catalyst is satisfied,
Clocking means for timing the duration of the establishment of the preconditions;
An exhaust purification catalyst deterioration determining apparatus comprising: a subtracting unit that subtracts a duration time measured by the time measuring unit until the precondition is not satisfied. The exhaust gas purification catalyst deterioration determination device according to claim 1, wherein the subtraction means subtracts the duration using a subtraction value corresponding to an amount of air taken into the internal combustion engine. The exhaust gas purification catalyst deterioration determination device according to claim 2, wherein the subtraction means subtracts the duration using a larger subtraction value than when it is small when the amount of air is large. The exhaust gas purification catalyst deterioration determination device according to claim 1, wherein the subtraction means subtracts the duration using a subtraction value corresponding to a degree of temperature decrease of the exhaust gas purification catalyst. The exhaust gas purification catalyst deterioration determination device according to claim 4, wherein the subtraction means subtracts the duration using a larger subtraction value than when the decrease degree is large. 2. The exhaust gas purification catalyst deterioration determination device according to claim 1, wherein the subtraction unit subtracts the duration using a subtraction value corresponding to a time when the precondition is not satisfied. The exhaust gas purification catalyst deterioration determination device according to claim 6, wherein the subtraction means subtracts the duration time using a larger subtraction value than when it is short when the failure time is long. The exhaust gas purification catalyst deterioration determination device according to claim 1, wherein the subtracting means subtracts the duration using a subtraction value corresponding to a temperature of the exhaust gas purification catalyst.

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