JP2020029835A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

To improve diagnosis accuracy for deterioration of an SCR converter.SOLUTION: An exhaust emission control system of an internal combustion engine is configured to determine that an SCR converter deteriorates in a case where an outflowing ammonia concentration AC at the time when a specified period ε has elapsed since an ammonia slip has been confirmed is equal to or higher than a deterioration determination concentration ζ (S200: YES), in addition to a case where a lapse time T1 from the start of ammonia supply (S120) to the confirmation of the ammonia slip (S150: YES) is shorter than a deterioration determination time γ (S170: YES).SELECTED DRAWING: Figure 2

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine that purifies nitrogen oxides in exhaust gas by selective catalytic reduction using ammonia as a reducing agent.

  2. Description of the Related Art As an exhaust gas purification system for an internal combustion engine, there is a system that purifies nitrogen oxides (NOx) in exhaust gas by selective catalytic reduction (SCR) using ammonia as a reducing agent. Some of such exhaust gas purification systems include an SCR converter that performs the above-described selective catalytic reduction, and an ammonia supply device that supplies ammonia to the SCR converter. The SCR converter has an SCR catalyst carried on a carrier made of a monolithic porous material having a large number of channels through which exhaust gas passes. In a diesel engine mounted on a vehicle, urea water is added to exhaust gas flowing in a portion of the exhaust passage upstream of the SCR converter, and ammonia generated by hydrolyzing the urea water at a high temperature is converted into an SCR converter. , A so-called urea SCR type exhaust gas purification system is adopted.

  Conventionally, as disclosed in Patent Document 1, there is known an exhaust purification system of a selective catalytic reduction system having a function of diagnosing deterioration of an SCR converter. In the exhaust gas purification system described in Patent Literature 1, deterioration diagnosis is performed by determining whether or not the SCR converter has deteriorated in the following manner.

  The SCR converter adsorbs ammonia in the exhaust gas when the temperature exceeds a certain temperature (adsorption start temperature). There is a limit to the amount of ammonia that can be adsorbed by the SCR converter, and the limit amount (saturated adsorption amount) decreases with the progress of deterioration. On the other hand, the minimum temperature (purification start temperature) of the SCR converter capable of selective catalytic reduction of NOx is higher than the adsorption start temperature. Therefore, when the SCR converter is in a temperature range equal to or higher than the adsorption start temperature and lower than the purification start temperature, the SCR converter adsorbs the ammonia in the inflowing exhaust gas, but is in a state in which the adsorbed ammonia is hardly consumed.

  In the exhaust gas purification system described in the above document, when the deterioration of the SCR converter is diagnosed, the supply of ammonia to the SCR converter in which almost no ammonia is adsorbed is started within the above temperature range. At this time, the supply amount of ammonia is set to an amount capable of adsorbing most of the supplied ammonia in the case of an SCR converter in which the ammonia adsorption amount is sufficiently smaller than the saturated adsorption amount. Therefore, the outflow amount of ammonia from the SCR converter at this time is maintained at almost 0 until the ammonia adsorption amount reaches the saturated adsorption amount. On the other hand, when the ammonia adsorption amount reaches the saturated adsorption amount, the outflow of ammonia (ammonia slip) cannot be suppressed. Therefore, the total amount of ammonia supplied during the period from the start of the ammonia supply to the confirmation of the ammonia slip is an amount corresponding to the saturated adsorption amount of the SCR converter. Therefore, in the exhaust gas purification system described in the above document, it is determined whether or not the saturated adsorption amount is lower than the original amount, that is, whether or not the SCR converter has deteriorated, based on the total amount of ammonia supplied in the above period. By making the determination, the deterioration diagnosis of the SCR converter is performed.

JP 2009-127496 A

  In the SCR converter, ammonia is adsorbed on the wall of each channel. Therefore, the sum of the saturated adsorption amounts of the respective channels is the saturated adsorption amount of the entire SCR converter. In the following description, the ammonia adsorption amount and the saturated adsorption amount in each channel are referred to as an individual adsorption amount and an individual saturated adsorption amount, respectively. In addition, the ammonia adsorption amount and the saturated adsorption amount of the entire SCR converter are referred to as a total adsorption amount and a total saturated adsorption amount, respectively.

  By the way, a part of the channel of the SCR converter may be closed by foreign matter such as soot. In the SCR converter in which such partial blockage occurs, exhaust gas flows intensively in an unblocked channel. Therefore, the progress of the adsorption of ammonia is faster in the unblocked channel when the partial blockage occurs than in the channel without the partial blockage. Therefore, when the above-described deterioration diagnosis is performed in a state where the partial occlusion has occurred, the individual adsorption amount of the unblocked channel becomes individual saturation earlier than the total adsorption amount reaches the total saturation adsorption amount. The adsorption amount is reached, and ammonia flows out through the channel. Therefore, when partial blockage has occurred, the total amount of ammonia supply during the period from the start of supply to the confirmation of ammonia slip is reduced even if the SCR converter has not deteriorated, as in the case where it has deteriorated. However, there is a risk that the battery is erroneously determined to be deteriorated.

  An exhaust gas purification system for an internal combustion engine that solves the above problems is provided in an SCR converter installed in an exhaust passage of the internal combustion engine and purifying nitrogen oxides by selective catalytic reduction using ammonia as a reducing agent. An ammonia supply device for supplying ammonia, an ammonia concentration sensor for detecting the concentration of ammonia in the exhaust gas flowing out of the SCR converter, and an outflow of ammonia from the SCR converter after the supply of ammonia by the ammonia supply device is started. And a deterioration determination unit that determines that the SCR converter has deteriorated on condition that the slip start time, which is the time until, is less than a specified deterioration determination time. Further, the deterioration determination unit in the exhaust gas purification system determines that the slip start time is shorter than the deterioration determination time, and furthermore, the rate of increase of the ammonia concentration after the outflow of ammonia from the SCR converter is confirmed. When the speed is equal to or higher than the deterioration determination speed, it is determined that the SCR converter has deteriorated, and the presence or absence of deterioration of the SCR converter is determined.

  When the supply of ammonia is started, the supplied ammonia is adsorbed on the SCR converter. When the amount of ammonia adsorbed by the SCR converter reaches the saturated adsorption amount, ammonia can no longer be adsorbed, so that ammonia flows out of the SCR converter. The outflow of ammonia (ammonia slip) at this time can be confirmed from the detection result of the ammonia concentration in the exhaust gas flowing out of the SCR converter by the ammonia concentration sensor. Since the saturated adsorption amount of ammonia in the SCR converter decreases with the progress of deterioration, when the SCR converter has deteriorated, the outflow of ammonia from the SCR converter is confirmed after starting the supply of ammonia. The slip start time, which is the time until, is shorter than the case where the slip has not deteriorated.

  On the other hand, when a partial blockage occurs in which the exhaust gas flow in the SCR converter is partially blocked by foreign matter such as soot, the exhaust gas flow, and thus the adsorption of ammonia, is concentrated in the unblocked region. Even if it has not deteriorated, the slip start time becomes short. However, the SCR converter at this time still has room for adsorbing ammonia, and continues to adsorb a certain amount of ammonia for a while after the start of the ammonia slip. Therefore, when the ammonia slip occurs before the ammonia adsorption amount reaches the saturated adsorption amount due to the partial blockage, the SCR converter after the start of the ammonia slip is compared with the case where the ammonia slip occurs after reaching the saturated adsorption amount. The rate of increase of the amount of ammonia discharged from the fuel becomes low.

  Thus, there is a difference in the rate of increase in the amount of ammonia discharged from the SCR converter after the start of the ammonia slip between the time of deterioration and the time of partial blockage. The difference in the increasing rate of the ammonia discharge amount appears as a difference in the increasing rate of the ammonia concentration in the exhaust gas discharged from the SCR converter. Therefore, in the case of the exhaust gas purification system that performs the deterioration determination based on the increasing speed of the ammonia concentration in addition to the slip start time, it is possible to separately determine the deterioration of the SCR converter and the partial blockage. Therefore, the exhaust gas purification system for an internal combustion engine can diagnose the deterioration of the SCR converter with high accuracy.

  The increasing rate of the ammonia concentration is obtained as a quotient obtained by dividing the amount of change in the ammonia concentration in a certain time by the time. Therefore, the deterioration determination unit in the exhaust gas purification system for the internal combustion engine determines that the ammonia concentration at the time when the slip start time is less than the specified deterioration determination time and the specified period has elapsed since the outflow of ammonia was confirmed. It can be configured that the SCR converter is determined to be deteriorated when the density is equal to or higher than the specified deterioration determination concentration.

  There is some variation in the increasing rate of the ammonia concentration after the start of the ammonia slip when the SCR converter is deteriorated. In order to reliably separate the deterioration and the partial blockage, including the case where the increasing rate of the ammonia concentration is the lowest within the range of such variation, it is necessary to set a certain long period as the specified period. However, in such a case, the time required to complete the deterioration determination naturally increases. On the other hand, when the increasing rate of the ammonia concentration is high within the above-mentioned range of variation, it is possible to distinguish between deterioration and partial blockage even if a shorter period is set as the specified period. Therefore, the deterioration determination unit in the exhaust gas purification system may be configured as follows. That is, the specified period is defined as a first period, and the specified deterioration determination concentration is defined as a first deterioration determination concentration. At this time, the deterioration determination unit determines that the ammonia concentration at the time when the slip start time is shorter than the deterioration determination time and the second period shorter than the first period has elapsed since the outflow of ammonia has been confirmed has passed the specified second deterioration. The configuration may be such that the SCR converter is determined to be degraded even when the density is equal to or higher than the determination density. When the deterioration determination unit is configured as described above, the determination can be completed in a short time if the determination can be made early within a range in which erroneous determination due to partial blockage can be avoided.

  As described above, when the deterioration determination unit determines whether or not the SCR converter has deteriorated, the slip start time is shorter than the deterioration determination time, and the time when the above-described determination time has elapsed since the outflow of ammonia was confirmed. If the increase rate of the ammonia concentration is lower than the deterioration determination rate, it is considered that there is a high possibility that the SCR converter is partially blocked. Therefore, in such a case, it is preferable to provide a blockage elimination control unit that performs blockage elimination control for eliminating partial blockage of the SCR converter. As the blockage elimination control unit, for example, a unit that performs blockage elimination control through a temperature raising process of raising the temperature of the SCR converter can be adopted. In an exhaust gas purification system including a compressed gas injector that blows compressed gas into an exhaust inlet of an SCR converter, a blockage removal control unit that performs blockage removal control by performing injection of compressed gas by the compressed gas injector is used. It is possible to adopt as.

FIG. 1 is a schematic diagram showing a configuration of a first embodiment of an exhaust gas purification system for an internal combustion engine. 4 is a flowchart of a deterioration determination routine performed by a deterioration determination unit provided in the exhaust gas purification system. 5 is a graph showing a relationship between an SCR temperature and a saturated adsorption amount. 4 is a time chart showing an embodiment of determining deterioration of the SCR converter in the exhaust gas purification system of the first embodiment. The graph which shows transition of the outflow ammonia density | concentration after the confirmation of the ammonia slip in each of the time of deterioration and the time of partial blockage. 9 is a time chart illustrating an embodiment of determining deterioration of an SCR converter in the exhaust gas purification system according to the second embodiment. 4 is a flowchart showing a part of a process of a deterioration determination routine performed by a deterioration determination unit provided in the exhaust gas purification system of the embodiment. The schematic diagram which shows the structure of the compressed gas injector used in an example of the blockage elimination control which the blockage elimination control part provided in the exhaust gas purification system of 3rd Embodiment implements. 9 is a flowchart illustrating a part of a process of a deterioration determination routine performed by a deterioration determination unit provided in the exhaust gas purification system according to the fourth embodiment.

(1st Embodiment)
Hereinafter, a first embodiment of an exhaust gas purification system for an internal combustion engine will be described in detail with reference to FIGS.

  First, the configuration of the exhaust gas purification system of the present embodiment will be described with reference to FIG. The exhaust gas purification system of the present embodiment is applied to a vehicle-mounted compression ignition type internal combustion engine 10. The internal combustion engine 10 includes a plurality of cylinders 11, an intake passage 20 that is a passage for introducing intake air to each cylinder 11, and an exhaust passage 30 that is a discharge passage for exhaust gas from each cylinder 11.

  An air cleaner 21 that filters dust and the like in the intake air, an air flow meter 22 that detects an amount of intake air, a compressor 23 of an exhaust turbocharger, an intercooler 24 that cools intake air, an intake air A throttle valve 25 for adjusting the amount of air is provided. Further, each cylinder 11 is provided with a fuel injection valve 26 for injecting fuel. Further, the exhaust passage 30 is provided with a turbine 31 of an exhaust turbo supercharger.

  An oxidation catalytic converter 32 for purifying unburned fuel components in exhaust gas such as HC and a DPF for collecting particulate matter (PM) in exhaust gas are provided in a portion of the exhaust passage 30 downstream of the turbine 31. (Diesel Particulate Filter) 33. A portion of the exhaust passage 30 downstream of the DPF 33 is provided with an SCR converter 34 for purifying nitrogen oxides (NOx) in the exhaust gas by selective catalytic reduction (SCR) using ammonia as a reducing agent. Further, an ASC (Ammonia Slip Catalyst) device 35 which is a small-sized oxidation catalyst converter for purifying ammonia flowing out of the SCR converter 34 is provided in a portion of the exhaust passage 30 downstream of the SCR converter 34. .

  A urea addition valve 36 is provided in a portion of the exhaust passage 30 downstream of the DPF 33 and upstream of the SCR converter 34. A urea water pump 38 is connected to the urea addition valve 36. The urea water pump 38 pumps out the urea water stored in the urea water tank 37 and supplies it to the urea addition valve 36. The urea addition valve 36 adds urea to the exhaust gas by injecting the urea water into the exhaust gas. In the exhaust gas purification system of the present embodiment, ammonia generated by hydrolyzing urea added to exhaust gas at high temperature is supplied to the SCR converter 34. That is, in the present embodiment, the urea addition valve 36, the urea water tank 37, and the urea water pump 38 constitute an ammonia supply device that supplies ammonia to the SCR converter 34.

  The SCR converter 34 has a catalyst (SCR catalyst) for NOx selective catalytic reduction carried on a carrier made of a porous material having a monolithic structure having a large number of channels through which exhaust gas passes. The SCR catalyst carried by the SCR converter 34 adsorbs ammonia in the exhaust gas when the temperature exceeds a certain temperature (adsorption start temperature). When the temperature of the SCR catalyst becomes equal to or higher than a certain temperature (purification start temperature) higher than the adsorption start temperature, the SCR catalyst starts reduction and purification of NOx in exhaust gas by selective catalytic reduction using the adsorbed ammonia as a reducing agent.

  Note that the SCR converter 34 is provided with an SCR temperature sensor 39 for detecting the temperature of the SCR catalyst (SCR temperature THS). In a portion of the exhaust passage 30 downstream of the SCR converter 34 and upstream of the ASC device 35, the concentration of ammonia in exhaust gas flowing out of the SCR converter 34 (hereinafter referred to as outflow ammonia concentration) is set. An ammonia concentration sensor 40 for detecting is provided.

  The internal combustion engine 10 is controlled by an electronic control unit 41. The electronic control unit 41 includes an arithmetic processing unit that executes arithmetic processing, and a memory that stores control programs and data. The electronic control unit 41 executes various processes related to the control of the internal combustion engine 10 by the arithmetic processing device reading a program from a memory and executing the program. Into the electronic control unit 41, detection signals of various sensors for detecting various state quantities related to the operation state of the internal combustion engine 10, such as the above-described air flow meter 22, the SCR temperature sensor 39, and the ammonia concentration sensor 40, are input. . The electronic control unit 41 controls the operation of the internal combustion engine 10 by controlling the opening degree of the throttle valve 25 and the amount and timing of fuel injection of the fuel injection valve 26 based on the detection results of these sensors. . Further, the electronic control unit 41 controls the amount of urea added to the exhaust gas by the urea addition valve 36 described above.

  The internal combustion engine 10 configured as described above includes the oxidation catalytic converter 32, the DPF 33, the SCR converter 34, and the ASC device 35 provided in the exhaust passage 30 as components of an exhaust gas purification system that purifies exhaust gas. . Further, an ammonia supply device (urea addition valve 36, urea water tank 37, urea water pump 38) for supplying ammonia to the SCR converter 34, an electronic control unit 41 for controlling the urea addition of the urea addition valve 36, and the control thereof. The sensors used (SCR temperature sensor 39, ammonia concentration sensor 40, etc.) are also components of such an exhaust gas purification system.

  The SCR converter 34 provided in such an exhaust gas purification system deteriorates with use over time, and the NOx purification performance decreases. Therefore, in the exhaust gas purification system of the present embodiment, the deterioration of the SCR converter 34 is determined. The deterioration determination of the SCR converter 34 is performed by the deterioration determination unit 43 provided in the electronic control unit 41.

  FIG. 2 shows a flowchart of a deterioration determination routine performed by the deterioration determination unit 43 for determining deterioration of the SCR converter 34. The deterioration determination unit 43 starts the processing of this routine from when the internal combustion engine 10 is started. The deterioration determination of the SCR converter 34 according to this routine is performed so that it is completed before the SCR temperature THS rises to a temperature equal to or higher than the NOx purification start temperature. Therefore, the deterioration determination in the present embodiment is performed in a state where the ammonia adsorbed on the SCR converter 34 is not consumed for purifying NOx.

  When the internal combustion engine 10 is started and the processing of this routine is started, first, in step S100, reading of the detection value of the SCR temperature THS by the SCR temperature sensor 39 is started. Thereafter, when it is confirmed that the SCR temperature THS has become equal to or higher than the adsorption start temperature (S110: YES), in step S120, urea is added to the exhaust gas by the urea addition valve 36, that is, ammonia is supplied to the SCR converter 34. Supply is started. At this time, reading of the detected value of the outflow ammonia concentration AC by the ammonia concentration sensor 40 is started in step S130, and measurement of the elapsed time T1 from the start of urea addition (ammonia supply) is started in step S140. You.

  In the present embodiment, the urea addition at this time is performed while the urea addition amount per unit time is constant. At this time, the amount of urea added to the SCR converter 34 per unit time is larger than the amount of ammonia (ammonia adsorption speed) that can be adsorbed per unit time by the SCR converter 34 in a state where sufficient room for adsorbing ammonia is left. Is set so that the amount of ammonia flowing into the tank becomes small. In the present embodiment, after the internal combustion engine 10 is started, the urea addition is started when the SCR temperature THS first reaches the adsorption start temperature, and the SCR converter 34 at this point hardly adsorbs ammonia. It is in a state.

  Thereafter, when it is confirmed that the outflowing ammonia concentration AC is equal to or higher than the specified slip determination concentration β (S150: YES), the process proceeds to step S160. The slip determination concentration β is set as a lower limit value of the outflow ammonia concentration AC at which it is recognized that the outflow of ammonia (ammonia slip) from the SCR converter 34 has started.

  When the process proceeds to step S160, in step S160, a calculation of the deterioration determination time γ based on the SCR temperature THS is performed. The calculation of the deterioration determination time γ here is performed in the following manner.

  FIG. 3 shows the relationship between the SCR temperature THS and the saturated adsorption amount in the unused SCR converter 34 (hereinafter referred to as “new contact”) by a solid line. The saturated adsorption amount with respect to the SCR temperature THS tends to gradually increase as the SCR temperature THS increases from the adsorption start temperature. On the other hand, as the SCR converter 34 deteriorates, the saturated adsorption amount tends to decrease as the deterioration progresses. In the present embodiment, a state in which the saturated adsorption amount with respect to a new touch becomes a fixed ratio A (0 <A <1) or less is defined as a state in which the SCR converter 34 is deteriorated. That is, the saturated adsorption amount of the SCR converter 34 in a deteriorated state is a value in a region (degraded region) indicated by hatching in FIG. In the following description, the saturated adsorption amount, which is indicated by a broken line in the drawing and is the upper limit of the deterioration region, is described as a boundary saturated adsorption amount. In the memory of the electronic control unit 41, the relationship between the SCR temperature THS and the boundary saturated adsorption amount is stored in advance as a map. When calculating the deterioration determination time γ, the boundary saturated adsorption amount at the current SCR temperature THS is obtained with reference to this map, and the quotient obtained by dividing the boundary saturated adsorption amount by the ammonia supply amount per unit time is obtained. , The deterioration determination time γ.

  Subsequently, in step S170, it is determined whether or not an elapsed time T1 (hereinafter, referred to as a slip start time) from the urea addition (ammonia supply) to the present, that is, until the ammonia slip is confirmed, is less than the deterioration determination time γ. Is determined. Here, if the slip start time is equal to or longer than the deterioration determination time γ (S170: NO), it is determined that the SCR converter 34 has not deteriorated, and after the urea addition is stopped in step S220, the present routine of this routine is executed. The process ends.

  On the other hand, when the slip start time (elapsed time T1) is shorter than the deterioration determination time γ (S170: YES), after the ammonia slip is confirmed in step S180 while urea addition is continued. Of the elapsed time T2 is started. Then, when the elapsed time T2 after the confirmation of the ammonia slip reaches the specified period ε (S190: YES), in step S200, whether the outflowing ammonia concentration AC at that time is equal to or more than the specified deterioration determination concentration 判定. It is determined whether or not. The details of the deterioration determination density ζ will be described later.

  If the outflow ammonia concentration AC at this time is lower than the deterioration determination concentration （(S200: NO), it is determined that the SCR converter 34 has not deteriorated, and after the urea addition is stopped in step S220 described above, This routine is terminated. On the other hand, if the outflow ammonia concentration AC at this time is equal to or higher than the deterioration determination concentration （(S200: YES), it is determined that the SCR converter 34 has deteriorated. Then, the deterioration determination process is performed in step S210, and after the urea addition is stopped in step S220, the current process of this routine ends.

  In the processing at the time of deterioration determination in step S210, notification of deterioration of the SCR converter 34 and NOx reduction processing are performed. The notification of deterioration is given by, for example, turning on a warning light (MIL) provided on an instrument panel or the like in a driver's seat. In some vehicles, a display panel for displaying the remaining amount of urea water or the like is provided near the urea water tank 37. On such a display panel, a display indicating that the SCR converter 34 is deteriorated is provided. May be performed. In addition, as the NOx reduction treatment, for example, in the high load operation region of the internal combustion engine 10 in which the generation amount of NOx by combustion increases, the opening degree of the throttle valve 25 is reduced to reduce the amount of oxygen used for combustion, thereby reducing the combustion temperature Is performed. Further, in the case of the internal combustion engine 10 having an exhaust gas recirculation (EGR) device for recirculating a part of exhaust gas during intake, as a NOx reduction measure, the amount of exhaust gas recirculation (EGR amount) is increased to increase the combustion temperature. Can be taken.

The operation and effect of the present embodiment will be described.
FIG. 4 shows the transition of the ammonia adsorption amount and the outflowing ammonia concentration when the deterioration determination is performed on the SCR converter 34 at the time of the new contact with a solid line. Here, for the sake of simplicity, it is assumed that the SCR temperature THS during execution of the deterioration determination, and thus the saturated adsorption amount of the SCR converter 34, is constant.

  When the supply of ammonia is started at time t0, the ammonia adsorption amount of the SCR converter 34 thereafter increases with time. Until the ammonia adsorption amount reaches the saturated adsorption amount, most of the supplied ammonia is adsorbed by the SCR converter 34, so that the outflowing ammonia concentration is maintained at almost zero. Thereafter, when the ammonia adsorption amount reaches the saturated adsorption amount at time t2, the SCR converter 34 generates an ammonia slip. The occurrence of ammonia slip at this time can be confirmed by the fact that the outflowing ammonia concentration AC has increased from a value near zero. Note that the outflow ammonia concentration at this time quickly increases to the ammonia concentration of the exhaust gas flowing into the SCR converter 34.

  Further, in FIG. 4, transition of the ammonia adsorption amount and the outflowing ammonia concentration when the deterioration determination is performed on the deteriorated SCR converter 34 is indicated by a two-dot chain line. In the deteriorated SCR converter 34, since the saturated adsorption amount is smaller than that at the time of a new touch, ammonia slip occurs at a time earlier than the time of the new touch (time t1 in the figure). Thus, there is a difference in the time from the start of urea addition (ammonia supply) to the occurrence of ammonia slip (ammonia slip start time) between the time of new contact and the time of deterioration. Therefore, normally, it can be determined that the SCR converter 34 has deteriorated when the slip start time is shorter than the specified deterioration determination time γ.

  Incidentally, there is a case where a part of the channel of the SCR converter 34 is blocked by a foreign substance such as soot (hereinafter, referred to as a partially blocked). In FIG. 4, the transition of the outflowing ammonia concentration when the deterioration determination is performed on the SCR converter 34 at the time of the new contact in the state where the partial blockage has occurred is indicated by a broken line. When partial occlusion occurs, exhaust gas flows intensively into unoccluded channels, and ammonia adsorption proceeds at a higher speed in such channels than when no partial occlusion occurs. Therefore, in the unblocked channel, the ammonia adsorption amount is saturated earlier than the ammonia adsorption amount of the entire SCR converter 34 reaches the saturated adsorption amount, and ammonia slip occurs through the channel. Therefore, when the partial blockage occurs, the slip start time is shortened even if the SCR converter 34 is not deteriorated. Therefore, it may not be possible to distinguish between deterioration and partial blockage based only on the slip start time.

  FIG. 5 shows the transition of the outflowing ammonia concentration after the confirmation of the ammonia slip at the time of deterioration and at the time of partial blockage, that is, after the outflowing ammonia concentration reaches the slip determination concentration β. At the time of deterioration, ammonia slip occurs when the ammonia adsorption amount of the entire SCR converter 34 reaches the saturated adsorption amount. Therefore, the outflowing ammonia concentration AC after confirming the ammonia slip at this time quickly increases to approximately the same as the ammonia concentration of the exhaust gas flowing into the SCR converter 34. On the other hand, at the time of partial blockage, ammonia slip occurs in a state where room for adsorbing ammonia is still left in the SCR converter 34. Therefore, at this time, the SCR converter 34 continues to adsorb a certain amount of ammonia for a while after the start of the ammonia slip. Therefore, when the ammonia slip occurs before the ammonia adsorption amount reaches the saturated adsorption amount due to partial blockage, the increasing speed of the outflowing ammonia concentration AC after the start of the ammonia slip becomes lower than that at the time of deterioration.

  In the present embodiment, the elapsed time from the time of confirming the ammonia slip until the distinct difference in the outflow ammonia concentration AC between the time of deterioration and the time of partial occlusion is set as the value of the specified period ε is set. I have. In addition, the outflow ammonia concentration AC at the time of partial blockage at the same time as the outflow ammonia concentration AC at the time of deterioration when the specified period ε has elapsed since the ammonia slip was confirmed is smaller than the lower limit of the possible value range. A value larger than the upper limit of the range of possible values is set as the value of the above-mentioned deterioration determination density ζ. Therefore, in the present embodiment, deterioration of the SCR converter 34 can be determined with high accuracy by distinguishing between deterioration and partial blockage.

  The increasing rate of the ammonia concentration is obtained as a quotient obtained by dividing the amount of change in the ammonia concentration in a certain time by the time. The value of the outflow ammonia concentration AC at the time when the specified period ε has elapsed since the confirmation of the ammonia slip is a value corresponding to the increasing speed of the outflow ammonia concentration AC from the time when the ammonia slip was confirmed. As described above, in the present embodiment, the presence or absence of deterioration of the SCR converter 34 is determined based on the increasing speed of the outflowing ammonia concentration AC after the ammonia slip is confirmed.

(2nd Embodiment)
Next, a second embodiment of the exhaust gas purification system for an internal combustion engine will be described in detail with reference to FIGS. Note that, in the present embodiment and each of the embodiments described later, the same reference numerals are given to configurations common to the above-described embodiments, and detailed description thereof will be omitted.

  In the first embodiment, it is determined whether the SCR converter 34 is deteriorated or partially blocked based on the outflowing ammonia concentration AC at a point in time when the specified period ε has elapsed since the ammonia slip was confirmed. Was. It should be noted that there is some variation in the increase rate of the outflow ammonia concentration AC after the start of the ammonia slip when the SCR converter 34 is deteriorated, and the specified period ε and the deterioration determination concentration ζ are considered in consideration of such variations. A value must be set.

  FIG. 6 shows the transition of the outflow ammonia concentration AC when the increase speed after the ammonia slip at the time of deterioration of the SCR converter 34 is confirmed is relatively high within the range of the variation, by a two-dot chain line L1. . In addition, in FIG. 5, the transition of the outflowing ammonia concentration AC when the increasing speed is the lowest within the range of the variation is indicated by a two-dot chain line L2. Further, in this figure, the transition of the outflowing ammonia concentration AC at the time of partial blockage is shown by a chain line.

  In order to surely distinguish between deterioration and partial blockage including the case where the outflow ammonia concentration AC is increasing at the lowest rate within the range of the variation, it is necessary to set a certain long period as the specified period ε. However, in such a case, the time required to complete the deterioration determination naturally increases. On the other hand, when the increasing rate of the outflowing ammonia concentration AC is high within the range of the above-described variation, it is possible to distinguish between deterioration and partial blockage even if a shorter period is set as the specified period ε.

  Therefore, in the present embodiment, the determination based on the outflowing ammonia concentration AC after confirming the ammonia slip for distinguishing the deterioration from the partial blockage is performed in two stages as described below. That is, first, it is determined whether or not the outflowing ammonia concentration AC at the time when the specified first period ε1 has elapsed since the confirmation of the ammonia slip is equal to or higher than the specified first deterioration determination concentration ζ1. At this point, even in the case of the two-dot chain line L2, that is, when the increase rate of the outflow ammonia concentration AC is the lowest within the range of variation, a clear difference occurs in the outflow ammonia concentration AC from that at the time of the partial occlusion.

  In addition, in the present embodiment, even when the second period ε2 shorter than the first period ε1 has elapsed since the confirmation of the ammonia slip, it is determined whether or not the outflowing ammonia concentration AC is equal to or higher than the specified second deterioration determination concentration. Judgment is being performed. Also at this point, in the case of the two-dot chain line L1, that is, when the increase rate of the outflow ammonia concentration AC is relatively high, it is possible to distinguish between deterioration and partial blockage based on the outflow ammonia concentration AC. . Therefore, if the determination can be made early as long as erroneous determination due to partial blockage can be avoided, the determination can be completed in a short time.

  In the present embodiment, a value lower than the first deterioration determination density # 1 is set as the value of the second deterioration determination density # 2. However, these values are appropriate values, and depending on the setting of the first period ε1 and the second period ε2 and the specifications of the SCR converter to be applied, the value of the second deterioration determination concentration ζ2 is higher than the first deterioration determination concentration ζ1. In some cases, it is desirable to set a high density or to set the same value for the first deterioration determination density # 1 and the second deterioration determination density # 2.

  FIG. 7 shows a processing procedure of a deterioration determination routine in such a case. This routine replaces the processing of steps S200 and S210 in the deterioration determination routine of the first embodiment shown in FIG. 2 with the processing of steps S300 to S330 shown in FIG. Are the same as in the first embodiment. It should be noted that the illustration of the processing from step S100 to step S150 is omitted in FIG.

  As described above, also in the present embodiment, after the confirmation of the ammonia slip (S170: YES), the measurement of the elapsed time T2 after the confirmation is started (S180), as in the case of the first embodiment. Processing proceeds. However, in the case of the present embodiment, the subsequent processing proceeds as follows.

  That is, in the case of the present embodiment, when the elapsed time T2 becomes equal to or longer than the second period ε2 after the start of the measurement of the elapsed time T2 (S300: YES), in step S310, the effluent ammonia concentration at that time is determined. It is determined whether or not AC is equal to or higher than the second deterioration determination concentration # 2. If the outflow ammonia concentration AC at this time is equal to or higher than the second deterioration determination concentration ζ2 (S310: YES), it is determined that the SCR converter 34 has deteriorated at that time. Then, the deterioration determination process is performed in step S210, and after the urea addition is stopped in step S220, the current process of this routine ends.

  On the other hand, if it is determined that the outflowing ammonia concentration AC is less than the second deterioration determination concentration ζ2 (S310: NO), the elapsed time T2 becomes equal to or longer than the first period ε1 thereafter. (S320: YES) In step S330, it is determined whether or not the outflowing ammonia concentration AC at that time is equal to or higher than the first deterioration determination concentration ζ1. If the outflow ammonia concentration AC is equal to or higher than the first deterioration determination concentration ζ1 (S330: YES), it is determined that the SCR converter 34 is deteriorated. Then, the deterioration determination process is performed in step S210, and after the urea addition is stopped in step S220, the current process of this routine ends. On the other hand, if the outflow ammonia concentration AC is less than the first deterioration determination concentration ζ1 (S330: NO), it is determined that the SCR converter 34 has not deteriorated, and the urea addition is stopped in step S220 described above. Thereafter, the current routine ends. In this case, it is determined that the SCR converter 34 is partially blocked.

(Third embodiment)
In the exhaust gas purification systems of the first embodiment and the second embodiment, the deterioration and the partial blockage are distinguished based on the increasing speed of the outflow ammonia concentration AC after the ammonia slip is confirmed. Although the partial blockage of the SCR converter 34 may be naturally resolved thereafter, the SCR converter 34 up to the removal is in a state where the NOx purification ability is reduced, and therefore it is desired that the SCR converter 34 be quickly resolved. Therefore, in the exhaust gas purification system of the present embodiment, when the occurrence of the partial blockage is confirmed, the electronic control unit 41 is provided with the blockage removal control unit 44 that performs the blockage removal control for removing the partial blockage. (See FIG. 1). That is, the blockage elimination control unit 44 when performing the deterioration determination in the mode of the first embodiment determines whether the outflowing ammonia concentration AC is less than the deterioration determination concentration ζ in step S200 in the deterioration determination routine of FIG. Execute blockage elimination control. In addition, when performing the deterioration determination in the mode of the second embodiment, the blockage elimination control unit 44 determines that the outflowing ammonia concentration AC is less than the first deterioration determination concentration ζ1 in step S330 in the deterioration determination routine of FIG. In this case, blockage elimination control is performed.

  The blockage elimination control is performed by performing a temperature raising process for raising the temperature of the SCR converter 34 and burning foreign substances such as soot clogged in the channels of the SCR converter 34. The temperature increase process can be performed, for example, by instructing the fuel injection valve 26 to perform post-injection, which is fuel injection after the completion of combustion in the cylinder 11. The fuel injected by the post injection is discharged to the exhaust passage 30 without being burned in the cylinder 11. The fuel burns inside the oxidation catalytic converter 32 or the like, so that the temperature of the exhaust gas flowing into the SCR converter 34 is increased. Thus, by raising the temperature of the SCR converter 34 to a temperature necessary for burning foreign matter, partial blockage can be eliminated. In the case of an internal combustion engine provided with a fuel addition valve for adding fuel to a portion of the exhaust passage 30 upstream of the oxidation catalytic converter 32, the fuel addition of the fuel addition valve is performed instead of the post injection. The same temperature raising process can be performed. Further, when the SCR converter 34 is provided with a combustion-type or electrothermal-type heater, it is possible to perform the temperature increasing process by directly heating the heater.

  Further, as shown in FIG. 8, a compressed gas injector 50 for blowing compressed gas is provided at the exhaust inlet of the SCR converter 34, and the blockage elimination control unit 44 performs the injection of compressed gas by the compressed gas injector 50. By doing so, it is also possible to perform blockage elimination control. The compressed gas injector 50 includes a pump 51 for compressing gas (for example, air), and an injection nozzle 52 for injecting the gas compressed by the pump 51 toward an exhaust inlet of the SCR converter 34. The compressed gas injected from the injection nozzle 52 blows out foreign substances clogged in the channel of the SCR converter 34, thereby eliminating partial blockage. Incidentally, by performing such spraying of the compressed gas in combination with the above-described temperature raising process, it is possible to more effectively eliminate partial blockage.

(Fourth embodiment)
In the exhaust gas purification system of the third embodiment, even if the blockage elimination control unit 44 performs the blockage elimination control, there are cases where the partial blockage of the SCR converter 34 cannot be eliminated. 34 must be repaired or replaced. Therefore, in the present embodiment, after the blockage elimination control is performed, a determination is made as to whether or not the partial blockage cannot be eliminated by the control (hereinafter, referred to as an unrecoverable determination).

  FIG. 9 shows a processing procedure of a deterioration determination routine when such an unrecoverable determination is made. This routine proceeds to the process of step S160 after the affirmative determination in step S150 in the degradation determination routine of the first embodiment shown in FIG. 2 or the degradation determination routine of the second embodiment shown in FIG. By the time, the processing of steps S400 to S450 is additionally performed. Although FIG. 5 does not show the processing from step S100 to step S140 and the processing after step S160, the contents of the processing of these omitted parts are described in the first embodiment or the second embodiment. The same as in.

  In this routine, when an affirmative determination is made in step S150, that is, when an ammonia slip is confirmed, the process proceeds to step S400. When the process proceeds to step S400, it is determined in step S400 whether the execution flag of the blockage elimination control is set. This flag is set when the blockage elimination control unit 44 performs the blockage elimination control. As described later, when the execution flag of the blockage elimination control is set here, the execution flag is cleared during execution of this routine (S440). Therefore, the case where the execution flag is set is a case where the partial blockage of the SCR converter 34 is confirmed in the previous deterioration determination and the blockage elimination control is performed.

  Here, if the execution flag of the blockage elimination control is not set (S400: NO), in step S450, the value of the current elapsed time T1, that is, the slip start time in the current deterioration determination is changed to the previous slip start. After setting the time value, the process proceeds to step S160. The value of the previous slip start time is not cleared even when the internal combustion engine 10 is stopped.

  On the other hand, if the execution flag of the blockage elimination control is set (S400: YES), the value of the previous slip start time is read in step S410. In the value of the previous slip start time read at this time, the slip start time in the previous deterioration determination is set.

  Subsequently, in step S420, it is determined whether or not the value of the previous slip start time is less than the current elapsed time T1. The value of the elapsed time T1 at this time represents the slip start time in the current deterioration determination. On the other hand, as described above, the determination here is performed only when the execution flag of the blockage elimination control is set, that is, when the blockage elimination control is performed after the previous deterioration determination. Therefore, the determination here is to determine whether or not the slip start time has been reduced as a result of the blockage elimination control. If the partial occlusion is reduced, the slip start time becomes shorter. Therefore, if the slip start time is reduced after the execution of the blockage elimination control, it can be determined that the current partial blockage occurring in the SCR converter 34 can be eliminated by the blockage elimination control. On the other hand, if the slip start time is not shortened after the execution of the blockage elimination control, it can be determined that the current partial blockage occurring in the SCR converter 34 cannot be eliminated by the blockage elimination control.

  Here, when the slip start time is shortened (S420: YES), the execution flag of the blockage elimination control is cleared in step S440, and the process proceeds to step S450 described above. In this case, even if the partial blockage of the SCR converter 34 has not been completely eliminated, it is determined that the partial blockage has occurred again in the subsequent routine, and the blockage elimination control is performed. Eventually, the partial occlusion will be resolved.

  On the other hand, if the slip start time has not been shortened (S420: NO), the process proceeds to step S440 after performing the recovery impossible determination time process in step S430. In the non-recoverable process, a process of notifying the SCR converter 34 that an unrecoverable partial blockage has occurred is performed by turning on a warning light provided on the instrument panel or the display panel. Note that even when an unrecoverable partial blockage occurs, the point at which the SCR converter 34 needs to be repaired or replaced is the same as the case where the SCR converter 34 has deteriorated. The notification may be common.

  Further, the content of the notification may be changed according to the transition of the state as follows. For example, a warning light that indicates each of a state in which partial occlusion has not been confirmed, a state in which partial occlusion has been confirmed, and a state in which the partial occlusion has been determined to be unrecoverable is provided, and a warning light that lights according to the state is provided. Try to switch. Also, the light emission color is green when partial occlusion has not been confirmed, the light emission color is yellow when partial occlusion has been confirmed but not determined to be unrecoverable, and the light emission color has been determined when non-recovery has been determined. The change of the state may be notified by changing the emission color of the warning light such as red.

Each of the above embodiments can be modified and implemented as follows. The above embodiments and the following modified examples can be implemented in combination with each other within a technically consistent range.
In the above embodiment, the SCR temperature is directly measured by the SCR temperature sensor 39. However, the SCR temperature is measured by measuring the temperature of the exhaust gas flowing out of the SCR converter 34 and estimating the SCR temperature from the temperature. May be estimated and obtained.

  In the above embodiment, the deterioration determination of the SCR converter 34 is performed in a state where the SCR temperature THS is lower than the NOx purification start temperature. When the deterioration determination is performed in a state where the SCR temperature THS is equal to or higher than the purification start temperature, it is necessary to set the deterioration determination time γ in consideration of the consumption of ammonia for NOx purification. That is, the amount of ammonia adsorbed by the SCR converter 34 decreases by the amount of ammonia consumed for NOx purification. Therefore, when the SCR temperature THS is equal to or higher than the purification start temperature, even if the supply amount of ammonia per unit time to the SCR converter 34 is the same, the larger the amount of ammonia consumed for NOx purification, the larger the ammonia adsorption amount. Until the amount reaches the saturated adsorption amount, that is, the slip start time becomes longer. Therefore, when performing the deterioration determination at the SCR temperature THS equal to or higher than the purification start temperature, the deterioration determination time γ may be set as follows. First, the amount of ammonia consumed per unit time is estimated based on the flow rate of exhaust gas and the SCR temperature THS. Further, by accumulating the estimated values, the amount of consumption of ammonia in the SCR converter 34 during a period from the start of the ammonia supply to the confirmation of the ammonia slip is calculated. Then, a quotient obtained by dividing the sum of the consumption amount of the ammonia and the boundary saturated adsorption amount at the current SCR temperature THS by the ammonia supply amount per unit time is set as the value of the deterioration determination time γ.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Cylinder, 20 ... Intake passage, 21 ... Air cleaner, 22 ... Air flow meter, 23 ... Compressor, 24 ... Intercooler, 25 ... Throttle valve, 26 ... Fuel injection valve, 30 ... Exhaust passage, 31 ... Turbine, 32 oxidation catalyst converter, 33 DPF, 34 SCR converter, 35 ASC device, 36 urea addition valve, 37 urea water tank, 38 urea water pump, 39 SCR temperature sensor, 40 ammonia concentration Sensors, 41: Electronic control unit, 43: Deterioration determination unit, 44: Blockage elimination control unit, 50: Compressed gas injector, 51: Pump, 52: Injection nozzle.

Claims (6)

An SCR converter installed in an exhaust passage of an internal combustion engine for purifying nitrogen oxides by selective catalytic reduction using ammonia as a reducing agent, an ammonia supply device for supplying ammonia to the SCR converter, and an outflow from the SCR converter An ammonia concentration sensor for detecting the ammonia concentration in the exhaust gas, and a slip start time, which is a time period from the start of the supply of the ammonia by the ammonia supply device until the outflow of the ammonia from the SCR converter is confirmed. A deterioration determination unit that determines that the SCR converter is deteriorated on condition that the time is less than the deterioration determination time of the internal combustion engine.
In addition to the slip start time being shorter than the deterioration determination time, the deterioration determining unit may further increase the ammonia concentration after the outflow of ammonia from the SCR converter is confirmed to be equal to or greater than a specified deterioration determination speed. An exhaust gas purification system for an internal combustion engine that determines whether or not the SCR converter has deteriorated as having deteriorated. The deterioration determination unit is configured such that the slip start time is less than a specified deterioration determination time, and the ammonia concentration at a time when a specified period has elapsed since the outflow of the ammonia was confirmed is equal to or greater than a specified deterioration determination concentration. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein it is determined that the SCR converter has deteriorated in some cases. When the specified period is a first period and the specified deterioration determination concentration is a first deterioration determination concentration, the deterioration determination unit determines that the slip start time is shorter than the deterioration determination time and the ammonia is discharged. It is determined that the SCR converter is deteriorated also when the ammonia concentration at the time when a second period shorter than the first period has elapsed after the confirmation is made is equal to or higher than a specified second deterioration determination concentration. 3. The exhaust gas purification system for an internal combustion engine according to 2. When the deterioration determination unit determines whether the SCR converter has deteriorated, the slip start time is shorter than the deterioration determination time, and the rate of increase in the ammonia concentration after the outflow of ammonia is confirmed is determined by the deterioration determination. The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 3, further comprising a blockage elimination control unit that performs blockage elimination control for eliminating partial blockage of the SCR converter when the speed is lower than the speed. The exhaust gas purification system for an internal combustion engine according to claim 4, wherein the blockage elimination control unit performs the blockage elimination control through a temperature increasing process for increasing the temperature of the SCR converter. A compressed gas injector for blowing compressed gas into an exhaust inlet of the SCR converter;
The exhaust gas purification system for an internal combustion engine according to claim 4, wherein the blockage elimination control unit performs the blockage elimination control by performing injection of compressed gas by the compressed gas injector.