JP2010196522A - Abnormality diagnostic device for exhaust emission control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To discriminate between recoverable abnormality and unrecoverable abnormality when the abnormality of a filter device is diagnosed. <P>SOLUTION: An exhaust emission control system includes: a urea water tank 21 for storing urea water; a urea water adding valve 15 connected to the urea water tank 21 through a urea water supply pipe 22 and adding the urea water in the urea water tank 21 into an exhaust pipe 11; a urea water pump 23 arranged in the urea water supply pipe 22 and feeding the urea water to the urea water adding valve 15; and a urea water filter 25 provided in the urea water supply pipe 22. In this system, an ECU 40 detects a pressure difference between the upstream side of the urea water filter 25 and the downstream side thereof, and also diagnoses the abnormality of the urea water filter 25 based on a change on a depressurization side in the detected pressure difference during operation of the urea water pump 23. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an abnormality diagnosis device for an exhaust purification system, and in particular, exhaust purification employing a selective reduction catalyst (SCR) that selectively purifies nitrogen oxides (NOx) in exhaust with ammonia as a reducing agent. The present invention relates to a system abnormality diagnosis device.

  In recent years, urea SCR systems have been developed as exhaust gas purification systems for purifying NOx in exhaust gas at a high purification rate in engines (particularly diesel engines) applied to automobiles and the like, and some have been put into practical use. For example, the following configuration is known as the urea SCR system. That is, a selective reduction type NOx catalyst is provided in an exhaust pipe connected to the engine body, and a urea water addition valve for adding urea water (reducing agent solution) as a NOx reducing agent is provided upstream of the exhaust. Yes. In this system, urea water is added into the exhaust pipe by the urea water addition valve, so that ammonia (NH3) generated by hydrolysis of urea water reacts with NOx in the exhaust gas on the NOx catalyst. Thereby, NOx in the exhaust is selectively reduced and purified.

  The above system is further provided with a urea water tank for storing urea water and a urea water pump for pumping the urea water in the urea water tank, thereby supplying urea water to the urea water addition valve. A water supply system has been established. The urea water tank is connected to a urea water addition valve via a pipe, and a urea water pump is disposed in the pipe. Further, a filter is attached in the middle of the piping, and foreign matters such as dust mixed in the urea water are removed by this filter (see, for example, Patent Document 1).

JP 2009-7969 A

  If a large amount of foreign matter is collected by the filter, the foreign matter may cause clogging of the filter, and urea water may not be supplied to the urea water addition valve. Here, the urea water is easily frozen (the urea water having a concentration of 32.5% is frozen at minus 11 ° C.), and urea is likely to be precipitated by evaporation of the water. Therefore, when a filter abnormality occurs due to clogging, it is considered that the cause of the clogging is not due to dust mixed in the urea water but due to freezing or crystallization of the urea water. However, such clogging due to frozen objects etc. is a temporary abnormality that can be recovered, and if this temporary abnormality is diagnosed as an abnormality equivalent to clogging due to dust or the like, it is troublesome to recover the abnormality such as filter replacement. The user may be required to take corrective action.

  The present invention has been made in order to solve the above-described problem, and in an abnormality diagnosis relating to a filter device, it is possible to distinguish between an abnormality that can be recovered and an abnormality that is not, and thus appropriate countermeasures when an abnormality occurs in the filter device. An object of the present invention is to provide a control device for an exhaust gas purification system that can perform the above-mentioned.

  The present invention employs the following means in order to solve the above problems.

  The invention according to claim 1 is a reduction agent tank that stores a reducing agent solution, and a reduction agent that is connected to the reducing agent tank via a reducing agent passage and adds the reducing agent solution in the tank to an exhaust passage of the internal combustion engine. A reducing agent pump for supplying the reducing agent solution to the reducing agent addition device provided in the reducing agent passage, and a filter provided on the upstream side of the reducing agent pump in the reducing agent passage. And an exhaust purification system including the device. The present invention provides a differential pressure detection means for detecting a pressure difference between the upstream side and the downstream side of the filter device, and a pressure reduction side of the pressure difference detected by the differential pressure detection means during operation of the reducing agent pump. An abnormality diagnosis means for performing an abnormality diagnosis on the filter device based on the change.

  When the clogging of the filter device occurs, it is conceivable that the cause is due to a frozen substance or a precipitate of the reducing agent solution in addition to the cause due to foreign matters such as dust. Here, in the case of clogging due to foreign matter, a measure for removing the foreign matter (for example, replacement or cleaning of the filter device) is required. On the other hand, in the case of clogging due to the frozen material of the reducing agent solution, it can be thawed or dissolved in the reducing agent solution as time passes, without performing the above-mentioned measures for removing foreign matter. It is considered that the filter device can be returned to a normal state. That is, the subsequent countermeasures for bringing the filter device into a normal state are different between clogging due to foreign matters such as dust and clogging due to a frozen substance of the reducing agent solution.

  Therefore, the present invention performs abnormality diagnosis on the filter device by monitoring a change on the pressure reducing side in the pressure difference between the upstream side and the downstream side of the filter device. In this abnormality diagnosis, when the filter device is clogged with foreign matter such as dust, the pressure difference cannot be resolved unless the foreign matter is removed. On the other hand, when it is caused by the frozen material or precipitate of the reducing agent solution, the pressure difference is eliminated by thawing the frozen material or dissolving the precipitate. Therefore, by monitoring the pressure difference between the filters, when the filter device is clogged, it is possible to identify whether it is a temporary abnormality or a continuous abnormality. As a result, in the abnormality diagnosis relating to the filter device, it is possible to distinguish between an abnormality that can be restored to normal and an abnormality that is not, and accordingly, it is possible to take appropriate measures when an abnormality occurs in the filter device.

  When a large amount of foreign matter or the like is collected in the filter device, the pressure difference between the downstream side and the upstream side of the filter device increases. Therefore, an abnormality diagnosis related to clogging of the filter device can be performed by the differential pressure. However, the abnormality diagnosis cannot distinguish between clogging due to foreign matters such as dust and clogging due to frozen material of the reducing agent solution.

  In view of this, the invention according to claim 2 is characterized in that the abnormality diagnosing means diagnoses an abnormality related to the filter device by using the fact that the pressure difference is larger than a predetermined abnormality determination value as one of the abnormality determination conditions. After the pressure difference becomes larger than a predetermined abnormality determination value, when there is a change on the pressure reduction side of the pressure difference, it is diagnosed that there is no abnormality or temporary abnormality related to the filter device. According to this configuration, it is possible to detect a clogging abnormality of the filter device and to specify whether the abnormality content can be returned to a normal state or not.

  Here, as the predetermined abnormality determination value, for example, a value set in advance as a value for determining the replacement time or cleaning time of the filter device is used. In addition, in this system, if the abnormality diagnosis results in an abnormality being diagnosed, the abnormality content is notified to the user, and if there is no abnormality or a temporary abnormality is diagnosed, the abnormality content is not notified to the user. Good.

  It is conceivable that the frozen material or precipitate of the reducing agent solution may be present in the solution or on the filter when the temperature of the reducing agent solution or the outside air temperature is within a certain temperature range. In view of this point, the invention according to claim 3 includes temperature detection means for detecting the temperature of the reducing agent solution, and the abnormality diagnosis means detects the temperature of the reducing agent solution detected by the temperature detection means. When there is a change in the pressure difference detected by the differential pressure detecting means on the reduced pressure side when the temperature is within a predetermined temperature range, the filter device is diagnosed as having no abnormality or a temporary abnormality. According to this configuration, in order to determine whether or not the cause of the clogging abnormality of the filter device is due to the frozen material of the reducing agent solution in a situation where the frozen material or precipitate of the reducing agent solution may exist, It is possible to accurately identify the abnormality content related to the apparatus. Here, the temperature of the reducing agent solution may be directly measured by, for example, a sensor or the like, or may be estimated from the outside air temperature.

  Freezing of the reducing agent solution occurs in a low temperature range below the freezing point of the solution or in the vicinity thereof. In view of this, the invention according to claim 4 is the case where the abnormality detecting means is a case where the temperature of the reducing agent solution is in a predetermined low temperature range, and there is a change on the pressure reduction side of the pressure difference. In this case, a temporary abnormality due to freezing of the reducing agent solution is diagnosed. According to this configuration, it is possible to specify that the cause of the clogging of the filter device is due to the frozen material of the reducing agent solution, and thereafter appropriate measures for thawing the frozen material on the filter device can be performed. it can.

  The precipitation of the reducing agent occurs at a high temperature range where evaporation of the solvent (for example, water) is promoted. In view of this, the invention according to claim 5 is the case where the abnormality detecting means is a case where the temperature of the reducing agent solution is in a predetermined high temperature range, and there is a change on the pressure reduction side of the pressure difference. In this case, a temporary abnormality due to the precipitation of the reducing agent is diagnosed. According to this configuration, since it is possible to specify that the cause of the clogging abnormality of the filter device is due to the precipitation of the reducing agent, the precipitate (crystal) on the filter device is then dissolved in the reducing agent solution. Appropriate measures can be taken.

  It is conceivable that a frozen material or a precipitate of the reducing agent solution is generated while the internal combustion engine is stopped (while being left). In view of this point, in the invention described in claim 6, the abnormality diagnosis unit performs abnormality diagnosis on the filter device based on a change in the pressure difference on the pressure reducing side during a predetermined start-up period of the internal combustion engine. According to this configuration, since the abnormality diagnosis is performed during a period in which a frozen product of the reducing agent solution can exist in the reducing agent solution, it is determined whether the filter device is temporarily clogged. Can be suitably implemented.

The block diagram which shows the outline | summary of a urea SCR system. The figure which shows the line pressure at the time of the clogging abnormality of a urea water filter. The flowchart which shows the process sequence of a filter abnormality diagnosis process. The time chart which shows transition of the pressure between filters at the time of clogging of a urea water filter.

  Hereinafter, an embodiment of an exhaust gas purification system embodying the present invention will be described with reference to the drawings. The exhaust purification system of this embodiment purifies NOx in exhaust using a selective reduction catalyst, and is constructed as a urea SCR system. First, the configuration of this system will be described in detail with reference to FIG. FIG. 1 is a configuration diagram showing an outline of a urea SCR system according to the present embodiment. This system is constructed with various actuators and various sensors for purifying exhaust gas, which is exhausted by a diesel engine (not shown) mounted on a car, and ECU (electronic control unit) 40, etc. Has been.

  In the engine exhaust system of FIG. 1, an exhaust pipe 11 connected to the engine body and forming an exhaust passage is provided. In the exhaust pipe 11, a DPF (Diesel Particulate Filter) 12, a selective catalytic reduction catalyst in order from the exhaust upstream side. (Hereinafter referred to as SCR catalyst) 13 is provided. Further, a urea water addition valve 15 for adding and supplying urea water (urea aqueous solution) as a reducing agent solution into the exhaust pipe 11 is provided between the DPF 12 and the SCR catalyst 13 in the exhaust pipe 11.

  In the exhaust pipe 11, a NOx sensor 16 and an exhaust temperature sensor 17 are provided on the downstream side of the SCR catalyst 13. The NOx sensor 16 detects the amount of NOx in the exhaust (NOx purification rate by the SCR catalyst 13) on the downstream side of the SCR catalyst 13, and the exhaust temperature sensor 17 detects the exhaust on the downstream side of the SCR catalyst 13. Temperature is detected.

  An oxidation catalyst 19 as an ammonia removing device is provided further downstream of the SCR catalyst 13 in the exhaust pipe 11. The oxidation catalyst 19 removes ammonia (NH3) discharged from the SCR catalyst 13, that is, excess ammonia.

  Next, the configuration of each of the above parts constituting the system will be described.

  The DPF 12 is a PM removal filter that collects PM (particulate matter) in the exhaust gas. The DPF 12 carries a platinum-based oxidation catalyst and removes HC and CO together with a soluble organic component (SOF) that is one of the PM components. The PM collected in the DPF 12 can be removed by combustion by post-injection after the main fuel injection in the diesel engine or the like (corresponding to a regeneration process), and thus the DPF 12 can be used continuously.

The SCR catalyst 13 promotes a NOx reduction reaction (exhaust purification reaction).
4NO + 4NH3 + O2 → 4N2 + 6H2O (Formula 1)
6NO2 + 8NH3 → 7N2 + 12H2O (Formula 2)
NO + NO2 + 2NH3 → 2N2 + 3H2O (Formula 3)
Such a reaction is promoted to reduce NOx in the exhaust gas. A urea water addition valve 15 provided on the upstream side of the SCR catalyst 13 adds and supplies ammonia (NH 3) as a NOx reducing agent in these reactions.

  The urea water addition valve 15 has substantially the same configuration as an existing fuel injection valve (injector), and since a known configuration can be adopted, the configuration will be briefly described here. The urea water addition valve 15 is configured as an electromagnetic on-off valve provided with a drive unit composed of an electromagnetic solenoid or the like, and a valve body unit having a urea water passage through which urea water flows and a needle for opening and closing the tip jet port 15a. The valve is opened or closed based on a drive signal from the ECU 40. That is, when the electromagnetic solenoid is energized based on the drive signal, the needle moves in the valve opening direction along with the energization, and urea water is added (injected) from the tip ejection port 15a as the needle moves.

  Urea water is sequentially supplied from the urea water tank 21 to the urea water addition valve 15. Hereinafter, the configuration of the urea water supply system will be described. In the following description, for the sake of convenience, the urea water tank 21 side is on the upstream side and the urea water addition valve 15 side is on the downstream, based on the case where urea water is supplied from the urea water tank 21 to the urea water addition valve 15. List as side.

  The urea water tank 21 is configured by a sealed container with a liquid supply cap, and urea water having a predetermined specified concentration is stored therein. In this embodiment, the urea concentration is 32.5%, which is the concentration at which the freezing temperature (freezing point) is the lowest.

  The urea water tank 21 and the urea water addition valve 15 are connected by a urea water supply pipe 22, and a urea water passage (reducing agent passage) is formed in the urea water supply pipe 22. A suction port for sucking urea water is formed at the tip of the urea water supply pipe 22 on the urea water tank 21 side, and the suction port is in a state where urea water is stored in the urea water tank 21. In the state of being immersed in urea water.

  A urea water pump 23 is provided in the middle of the urea water supply pipe 22. The urea water pump 23 is an in-line electric pump that is rotationally driven by a drive signal from the ECU 40. In the present embodiment, the urea water pump 23 is provided without being immersed in the urea water in the urea water tank 21. Thereby, damage to the urea water pump 23 due to freezing and expansion of the urea water in the urea water tank 21 is suppressed.

  In the present embodiment, the urea water pump 23 can rotate in either the forward or reverse direction. That is, the urea water in the urea water tank 21 is sucked up by the forward rotation of the urea water pump 23, and the urea water is sucked back into the urea water tank 21 by the reverse rotation of the urea water pump 23.

  In the urea water supply pipe 22, a porous urea water filter 25 that filters urea water is provided on the upstream side (urea water tank 21 side) of the urea water pump 23. By removing the foreign matter in the urea water by the urea water filter 25, the foreign matter is prevented from entering the urea water addition valve 15 and the urea water tank 23. In the present embodiment, the urea water filter 25 is provided in a state where it is not immersed in the urea water in the urea water tank 21. Further, a pressure adjusting valve 26 for adjusting the pressure of the urea water is provided on the downstream side (the urea water addition valve 15 side) from the urea water pump 23.

  At the time of urea water pressure feeding to the urea water addition valve 15 side, the urea water pump 23 is rotationally driven in the normal rotation direction by energizing the urea water pump 23. As a result, urea water in the urea water tank 21 is pumped up, passes through the urea water filter 25, and flows downstream. At this time, foreign matter contained in the urea water is removed by the urea water filter 25. Then, urea water is discharged (pressure-fed) from the urea water pump 23, the urea water is adjusted to a predetermined supply pressure by the pressure adjustment valve 26, and then fed to the urea water addition valve 15. Further, the excess urea water as a result of the pressure adjustment is returned to the urea water tank 21 through the return pipe 27.

  When the urea water is sucked back into the urea water tank 21, the urea water pump 23 is driven to rotate in the reverse rotation direction. As a result, the urea water in the urea water supply pipe 22 is sucked back and flows into the urea water tank 21. In the present embodiment, this urea water sucking back operation is performed by the ECU 40 when the engine is stopped. That is, it is avoided that the urea water remains in the urea water supply pipe 22 while the vehicle is left after the engine is stopped, thereby preventing the urea water supply pipe 22 from being damaged due to freezing and expansion of the urea water.

  A urea water temperature sensor 31 that detects the temperature of the urea water stored in the urea water tank 21 is provided in the urea water tank 21. A urea water pressure sensor 32 that detects the pressure of the urea water in the urea water supply pipe 22 (line pressure PN) is provided in the middle of the urea water supply pipe 22. In the present embodiment, the urea water pressure sensor 32 (32P) is provided on the downstream side of the urea water pump 23 so that the line pressure PN can be detected. Further, as the urea water pressure sensor 32, particularly in this embodiment, the upstream sensor 32F that detects the line pressure upstream of the urea water filter 25 (filter upstream pressure PNF), and the urea water downstream of the urea water filter 25 and urea water. A downstream sensor 32B that detects a line pressure upstream of the pump 23 (filter downstream pressure PNB) is provided.

  In the system, the ECU 40 is a part that mainly performs control related to exhaust gas purification as an electronic control unit. The ECU 40 includes a known microcomputer (not shown), and performs various controls related to exhaust purification by operating various actuators such as the urea water addition valve 15 in a desired manner based on detection values of various sensors. carry out. Specifically, for example, detection signals are input from various sensors such as the NOx sensor 16, the exhaust temperature sensor 17, the urea water temperature sensor 31, and the urea water pressure sensor 32 described above, and the urea water addition valve 15 is energized based on the detection signals. Time, the driving amount of the urea water pump 23, and the like are controlled. Thereby, an appropriate amount of urea water is added and supplied into the exhaust pipe 11 at an appropriate time.

In the above system, during operation of the engine, the urea water in the urea water tank 21 is pumped to the urea water addition valve 15 through the urea water supply pipe 22 by driving the urea water pump 23, and the urea water addition valve 15 in the exhaust pipe 11 is driven. The urea water is added and supplied. Then, urea water is supplied to the SCR catalyst 13 in the exhaust pipe 11 together with the exhaust gas, and the exhaust gas is purified by the NOx reduction reaction in the SCR catalyst 13. When reducing NOx, for example,
(NH2) 2CO + H2O → 2NH3 + CO2 (Formula 4)
As a result, urea water is hydrolyzed at a high temperature due to exhaust heat. As a result, ammonia (NH 3) is generated and adsorbed on the SCR catalyst 13, and NOx in the exhaust gas is selectively reduced and removed by the ammonia in the SCR catalyst 13. That is, NOx is reduced and purified by performing a reduction reaction based on ammonia (the above reaction formulas (Formula 1) to (Formula 3)) on the SCR catalyst 13.

  By the way, when solid substances such as dust accumulate in the urea water filter 25 and the urea water filter 25 is clogged, the urea water in the urea water tank 21 is sufficiently fed downstream from the urea water filter 25. As a result, the urea water addition amount from the urea water addition valve 15 into the exhaust pipe 11 may be less than the required amount.

  FIG. 2 is a diagram showing the line pressure PN when the urea water filter 25 is clogged abnormally. In FIG. 2, the solid line indicates a normal time when the urea water filter 25 is not clogged abnormally, and the alternate long and short dash line indicates the abnormal time when the urea water filter 25 is clogged abnormally.

  When the discharge pressure of the urea water pump 23 is controlled to a constant value (for example, 9 atm), as shown in FIG. 2, the line pressure PNP on the downstream side (point A in the figure) of the urea water pump 23 is urea water. It is higher than the line pressure (filter downstream pressure PNB) on the upstream side of the pump 23 and downstream of the urea water filter 25 (point B in the figure) by the pump discharge pressure. The relationship between the filter downstream pressure PNB and the line pressure (filter upstream pressure PNF) on the upstream side (point C in the figure) of the urea water filter 25 is substantially the same when the urea water filter 25 is normal. That is, the pressure difference between the filter upstream pressure PNF and the filter downstream pressure PNB is substantially zero.

  On the other hand, when the urea water filter 25 is clogged, the relationship between the line pressures at the points A and B is the same as when the filter is normal. On the other hand, the relationship between the line pressures at point B and point C is such that a pressure difference occurs between the upstream side and the downstream side of the urea water filter 25, and as shown by the one-dot chain line in FIG. The line pressure at point C (filter upstream pressure PNF) is negative with respect to the pressure PNB).

  Therefore, in this system, diagnosis of clogging abnormality of the urea water filter 25 is performed based on the line pressure PN, and a warning is issued when it is diagnosed that there is clogging abnormality. In the present embodiment, among the urea water pressure sensors 32, the detected values of the upstream sensor 32F and the downstream sensor 32B are used, and the filter upstream pressure PNF detected by the upstream sensor 32F is calculated from the filter downstream pressure PNB detected by the downstream sensor 32B. When the subtracted filter pressure ΔPN (PNB−PNF) becomes larger than a predetermined determination value (filter abnormality determination value PNTH), an abnormality warning lamp is turned on because it is time to replace the urea water filter 25. I am going to do that.

  However, when the inter-filter pressure ΔPN becomes larger than the filter abnormality determination value PNTH and the urea water filter 25 is clogged, the cause of the clogging is not due to dust mixed in the urea water. It is considered that this is due to freezing or crystallization of urea water. That is, urea water is easy to freeze, and urea water with a concentration of 32.5% freezes at minus 11 ° C. Therefore, for example, in an automobile used in a cold region, when the outside air temperature is extremely low (for example, minus 10 ° C.) when the engine is started, it is conceivable that part or all of the urea water is frozen. In such a case, when urea water in the urea water tank 21 is sucked up by the operation of the urea water pump 23, the freezing of urea water present in the urea water tank 21 cannot pass through the urea water filter 25. It is conceivable that the urea water filter 25 accumulates as a residue. Further, the urea water held in the urea water filter 25 may freeze after the engine is stopped and before the next engine start to block the hole of the urea water filter 25.

  Further, urea water tends to precipitate urea crystals by evaporation of water as a solvent. For this reason, when the temperature is high, for example, in summer, the urea water held in the urea water filter 25 may be evaporated after the engine is stopped and until the next engine start. In this case, urea crystals may be deposited on the urea water filter 25 and the crystals may block the holes of the urea water filter 25.

  In particular, in this embodiment, since the urea water in the urea water supply pipe 22 is sucked back into the urea water tank 21 when the engine is stopped, the urea water that could not be returned by the sucking back process becomes droplets to supply the urea water. There is a risk of remaining in the tube 22. For this reason, it is conceivable that icing or crystalline substances of urea water are likely to be generated in the urea water supply pipe 22 due to freezing of the droplets or evaporation of moisture.

  However, the clogging due to the frozen or crystallized urea water is temporary and can be restored to the normal state after a while. That is, it is considered that the frozen or crystallized urea water is melted or dissolved by the passing urea water while the liquid urea water passes through the urea water filter 25. Therefore, if clogging is caused by icing or the like, it is conceivable that the clogging is eliminated by feeding urea water from the urea water tank 21 to the urea water addition valve 15. On the other hand, in the case of clogging due to dust or the like, the foreign matter remains attached to the urea water filter 25, so it is necessary to request the user to take a normal recovery action such as filter replacement. Therefore, if this temporary abnormality is diagnosed as an abnormality equivalent to clogging due to dust or the like, the user will be required to perform the treatment even though the treatment for returning to normality is originally unnecessary.

  Therefore, in this embodiment, the inter-filter pressure ΔPN is detected when the urea water pump 23 is operated, and an abnormality diagnosis relating to the urea water filter 25 is performed based on the change on the reduced pressure side of the detected inter-filter pressure ΔPN. Thereby, it is specified whether the clogging of the urea water filter 25 is due to dust or the like, or due to icing or crystalline substances of the urea water, and a warning is performed based on the abnormal content.

  Specifically, the filter pressure ΔPN is calculated by subtracting the filter upstream pressure PNF detected by the upstream sensor 32F from the filter downstream pressure PNB detected by the downstream sensor 32B. Determine if there is a change. When the inter-filter pressure ΔPN is changed to the reduced pressure side, the urea water pressure (inter-filter pressure ΔPN) generated between the upstream side and the downstream side of the urea water filter 25 is gradually eliminated. That is, it is assumed that the pressure difference between the filters is temporary and no warning is given.

  FIG. 3 is a flowchart showing a processing procedure of processing relating to abnormality diagnosis of the urea water filter 25 (filter abnormality diagnosis processing). This process is executed by the ECU 40 when the engine is started (for example, by turning on the ignition switch).

  In FIG. 3, in step S11, it is first determined whether or not the urea water pump 23 is operating. The process proceeds to step S12 on condition that the urea water pump 23 is operating, the upstream sensor 32F of the urea water pressure sensor 32 detects the filter upstream pressure PNF of the urea water filter 25, and the downstream sensor 32B detects the filter downstream pressure PNB. To do. In the subsequent step S13, the inter-filter pressure ΔPN is calculated as a pressure difference generated between the upstream side and the downstream side of the urea water filter 25 by subtracting the filter upstream pressure PNF from the filter downstream pressure PNB.

  In step S14, it is determined whether or not the inter-filter pressure ΔPN is greater than the filter abnormality determination value PNTH. If the inter-filter pressure ΔPN is equal to or less than the filter abnormality determination value PNTH, the process proceeds to step S15, and it is determined that the filter is normal. That is, it is determined that the pressure difference between the upstream side and the downstream side of the urea water filter 25 does not occur or is small, and the urea water filter 25 is not clogged abnormally. On the other hand, if the inter-filter pressure ΔPN is greater than the filter abnormality determination value PNTH, the process proceeds to step S16 and subsequent steps.

  In step S16, it is determined whether or not there is a change to the pressure reducing side in the inter-filter pressure ΔPN. Here, regarding the change on the pressure reduction side of the inter-filter pressure ΔPN, in this embodiment, the inter-filter pressure ΔPN is monitored for a predetermined abnormality determination time TA (for example, several minutes), and a continuous decrease in the inter-filter pressure ΔPN is observed. If it is determined that there is a change in the pressure reduction side of the inter-filter pressure ΔPN.

  If no change on the pressure reduction side of the inter-filter pressure ΔPN is observed, the process proceeds to step S17, where it is determined that foreign substances such as dust have accumulated in the urea water filter 25, that is, a filter abnormality has occurred, and the filter replacement time A warning is issued to notify that this is the case. On the other hand, if there is a change on the pressure reduction side of the inter-filter pressure ΔPN, the process proceeds to step S18, and no warning is given because it is an abnormality that can be restored to the normal state even if it is left as it is. That is, the clogging of the urea water filter 25 is due to the frozen or crystallized substance of the urea water, and is determined to be a temporary abnormality that is eliminated by passing the urea water through the urea water filter 25 as the pump operates. .

  Next, a temporal transition of the inter-filter pressure ΔPN will be described with reference to the drawings. FIG. 4 is a time chart showing the transition of the inter-filter pressure ΔPN when the engine is started. 4A shows a case where the urea water filter 25 is clogged with foreign matter such as dust, and FIG. 4B shows a case where the urea water filter 25 is caused by a frozen substance or a crystalline substance of urea water.

  When the ignition switch is turned on and the urea water pump 23 is operated, the urea water in the urea water tank 21 passes through the urea water supply pipe 22, thereby increasing the line pressure PN. At this time, when an abnormal clogging due to foreign matters such as dust occurs in the urea water filter 25, as shown in FIG. 4A, the inter-filter pressure ΔPN increases with the operation of the urea water pump 23, It is constant at a value higher than the filter abnormality determination value PNTH. In this case, since there is no change in the inter-filter pressure ΔPN within the abnormality determination time TA from the timing t1 when the filter abnormality determination value PNTH is exceeded, it is diagnosed that the urea water filter 25 is clogged abnormally at the diagnosis timing t2, and a warning is given. Is implemented.

  On the other hand, when the clogging in the urea water filter 25 is due to the frozen or crystallized urea water, the inter-filter pressure ΔPN increases with the operation of the urea water pump 23 as shown in FIG. Even if the filter abnormality determination value PNTH is exceeded at the timing t1, the inter-filter pressure ΔPN turns to the pressure reduction side and gradually decreases within the abnormality determination time TA from the timing t1. Then, since a change on the pressure reduction side of the inter-filter pressure ΔPN was observed within the abnormality determination time TA from the timing t1, it is diagnosed that the urea water filter 25 is not clogged abnormally (temporary abnormality) at the diagnostic timing t2. The warning is not implemented.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  The urea water filter 25 is clogged because the abnormality relating to the urea water filter 25 is diagnosed based on a change in the pressure difference between the upstream side and the downstream side of the urea water filter 25 (pressure between the filters ΔPN). If this is the case, it is possible to specify whether it is a temporary abnormality or a continuous abnormality. Thereby, in the abnormality diagnosis regarding the urea water filter 25, it is possible to distinguish between an abnormality that can be restored to normal and an abnormality that is not. As a result, appropriate measures can be taken when an abnormality occurs in the urea water filter 25.

  When the inter-filter pressure ΔPN is larger than the filter abnormality determination value PNTH and a change on the pressure-reducing side of the inter-filter pressure ΔPN is seen, no warning is given as a temporary abnormality of the urea water filter 25 Therefore, it is possible to suppress an excessive warning for an abnormality that can be restored to normal. Further, it is possible to avoid prompting the user to take inappropriate measures such as filter replacement for an abnormality that can be restored to normal.

  Since the abnormality determination process based on the inter-filter pressure ΔPN is performed at the time of starting the engine, the process can be performed in a situation where a frozen product or precipitate of urea water may exist.

  In this system, since urea water is sucked back after the engine is stopped, a frozen or crystallized product of urea water is likely to be generated between the time when the engine is stopped and the next time the engine is started. Where the urea water filter 25 is likely to be clogged, the abnormality diagnosis of the urea water filter 25 is performed based on the inter-filter pressure ΔPN, thereby specifying that the urea water filter 25 is clogged with a frozen substance or the like. be able to. Therefore, the abnormality diagnosis can be performed under a situation where there is a high need to distinguish between an abnormality that can be recovered and an abnormality that is not.

  Since the urea water filter 25 is provided in a state where it is not immersed in the urea water in the urea water tank 21, the urea water held in the urea water filter 25 is easily frozen by contact with the outside air (cold air). Since urea crystals are likely to precipitate due to evaporation of water from the retained urea water, the urea water filter 25 is subjected to an abnormal diagnosis of the urea water filter 25 based on the inter-filter pressure ΔPN. It is possible to specify that clogging has occurred. Therefore, the abnormality diagnosis can be performed under a situation where it is highly necessary to distinguish between an abnormality that can be recovered and an abnormality that is not.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  Based on the urea water temperature detected by the urea water temperature sensor 31, it is determined whether the urea water filter 25 is clogged with foreign matter such as dust or the frozen water of the urea water. Specifically, the urea water temperature sensor 31 takes into account that the urea water freezes below a predetermined frozen material generation temperature (for example, minus 11 ° C. + α) and the urea water crystallization occurs above a predetermined crystallization temperature. When the urea water temperature measured by the above is in a predetermined low temperature region or a predetermined high temperature region, and a change on the pressure reducing side of the inter-filter pressure ΔPN is observed, the urea water due to freezing of the urea water or the like It is specified that the filter 25 is temporarily clogged. The urea water temperature may be estimated based on the outside air temperature detected by the outside air temperature sensor in addition to the urea water temperature sensor 31 directly detecting the urea water temperature. In this case, the abnormal content related to the urea water filter 25 may be specified based on the outside air temperature detected by the outside air temperature sensor.

  When diagnosing the clogging abnormality of the urea water filter 25 based on the urea water temperature, whether the urea water is caused by freezing or crystallization of the urea water is specified according to the urea water temperature. As described above, freezing of urea water has a freezing point of minus 11 ° C. if urea water has a urea concentration of 32.5%. Therefore, when the urea water temperature measured by the urea water temperature sensor 31 is equal to or lower than the predetermined frozen material generation temperature and a change on the pressure reducing side of the inter-filter pressure ΔPN is observed, the urea water filter 25 is clogged. Specify that the cause is a frozen product of urea water. Moreover, since crystal precipitation from urea water is due to evaporation of water, the precipitation tends to occur as the temperature increases. Therefore, the urea water filter 25 is clogged when the urea water temperature measured by the urea water temperature sensor 31 is equal to or higher than a predetermined crystallization temperature and a change on the pressure reducing side of the inter-filter pressure ΔPN is observed. Is due to the crystallization of urea water. As described above, the abnormality diagnosis of the urea water filter 25 is performed based on the urea water temperature, so that the cause of the temporary clogging of the urea water filter 25 is due to the freezing of the urea water or the crystal of the urea water. It can be specified whether it is due to conversion. Therefore, after the abnormality diagnosis, an appropriate measure can be taken according to the cause of the clogging abnormality.

  When the inter-filter pressure ΔPN is larger than the filter abnormality determination value PNTH in step S14 in FIG. 3 and when a change on the decreasing side of the inter-filter pressure ΔPN is observed in step 16, the urea water filter In this configuration, it is determined that the clogging of 25 is temporary, but when this is changed, a change on the rising side of the pressure ΔPN between the filters is seen, and a change on the decreasing side is seen after the change on the rising side. In such a case, it may be determined that the urea water filter 25 is temporarily clogged.

  The pressure between filters ΔPN is calculated from the detection value of the upstream sensor 32F and the detection value of the downstream sensor 32B, and abnormality diagnosis is performed based on the calculated value. However, the detection value of the upstream sensor 32F is used as the pressure between filters. It is good also as a structure which implements abnormality diagnosis as (DELTA) PN. As shown in FIG. 2, if the line pressure at the point B (filter downstream pressure PNB) does not change, the line pressure at the point C (filter upstream pressure PNF) is monitored, so that the urea water filter 25 is normal and abnormal. It is possible to specify the time. Therefore, it is effective when the pressure on the downstream side of the urea water filter 25 does not fluctuate.

  A return means for returning the frozen or crystallized urea water accumulated in the urea water filter 25 into the urea water tank 21 is provided. For example, the return means is constructed by the ECU 40 and the urea water pump 23. In this configuration, in the time chart of FIG. 4B described above, when it is determined that there is a clogging abnormality due to a frozen substance or the like at the diagnosis timing t2 after the operation of the urea water pump 23, the operation of the urea water pump 23 is performed. Stop. As a result, the differential pressure between the filter downstream pressure PNB and the filter upstream pressure PNF is eliminated, and the frozen matter or the like adhering to the urea water filter 25 is returned into the urea water tank 21. Therefore, clogging of the urea water filter 25 can be eliminated as early as possible. Or you may provide the return mechanism which returns the frozen material etc. which adhered to the urea water filter 25 in the urea water tank 21 in the upstream of the urea water filter 25. FIG. As the return mechanism, for example, a pipe branched from the urea water supply pipe 22 is provided on the upstream side of the urea water filter 25, and a pressure adjusting valve is provided in the middle of the pipe. When it is determined at diagnosis timing t2 that there is a clogging abnormality due to a frozen substance or the like, the frozen substance or the like on the urea water filter 25 is returned into the urea water tank 21 by opening the pressure adjustment valve.

  A so-called in-line system in which the urea water pump 23 is provided in the middle of the urea water supply pipe 22 without being immersed in the urea water in the urea water tank 21 is applied to the present invention. A so-called in-tank system provided in a state of being immersed in urea water in 21 may be applied to the present invention. Specifically, as an in-tank system, a urea water pump 23 is provided in the urea water tank 21 while being immersed in urea water, and the urea water pump 23 is immersed in urea water in the suction port portion thereof. A urea water filter 25 is provided. Further, an upstream sensor 32F and a downstream sensor 32B for measuring the line pressure PN at each position are provided on the upstream side and the downstream side of the urea water filter 25. In this configuration, when a part of the urea water in the urea water tank 21 is frozen to generate icing, the icing cannot pass through the urea water filter 25 as in the above embodiment. The urea water filter 25 may be temporarily clogged. Therefore, in the present embodiment as well, as described above, the cause of the clogging abnormality of the urea water filter 25 is specified based on the inter-filter pressure ΔPN, and a warning is given when the cause is a frozen substance of the urea water. If you do not.

  The configuration in which the urea water filter 25 is arranged upstream of the urea water pump 23 in the urea water supply pipe 22 is applied, but this is changed and the urea water filter 25 is arranged downstream of the urea water pump 23. A configuration may be applied.

  The urea water pump 23 is configured to be able to rotate in the forward and reverse directions, and the pump 23 is driven to rotate in the reverse direction to recover the residual urea water in the urea water supply pipe 22 in the urea water tank 21. It may be changed. For example, a pump (a suction pump) separate from the urea water pump 23 is provided. Then, urea water is pumped by the urea water pump 23, and urea water is sucked back by the suction pump. At this time, the suction pump is provided in a pipe branched from the urea water supply pipe 22 on the downstream side of the urea water pump 23.

  -Besides being put into practical use as a urea SCR system for in-vehicle diesel engines, it can also be put into practical use as a urea SCR system for gasoline engines, particularly lean burn engines. In addition, the present invention can be similarly applied to an exhaust purification system using a reducing agent solution other than urea water. For example, it is conceivable to use an aqueous solution containing ammonia as the reducing agent solution.

  DESCRIPTION OF SYMBOLS 11 ... Exhaust pipe, 12 ... DPF, 13 ... SCR catalyst, 15 ... Urea water addition valve (reducing agent addition apparatus), 21 ... Urea water tank (reducing agent tank), 23 ... Urea water pump (reducing agent pump), 31 ... urea water temperature sensor (temperature detection means), 32 ... urea water pressure sensor (differential pressure detection means), 32F ... filter upstream sensor, 32B ... filter downstream sensor, 40 ... ECU (abnormality diagnosis means).

Claims (6)

A reducing agent tank for storing a reducing agent solution; a reducing agent addition device connected to the reducing agent tank via a reducing agent passage for adding the reducing agent solution in the tank to an exhaust passage of the internal combustion engine; and the reducing agent passage. Applied to an exhaust gas purification system comprising a reducing agent pump that supplies the reducing agent solution to the reducing agent addition device and a filter device provided in the reducing agent passage,
Differential pressure detecting means for detecting a pressure difference between the upstream side and the downstream side of the filter device;
An abnormality diagnosing means for performing an abnormality diagnosis on the filter device based on a change on the pressure reducing side of the pressure difference detected by the differential pressure detecting means during operation of the reducing agent pump;
An abnormality diagnosis device for an exhaust purification system, comprising: The abnormality diagnosing means is for diagnosing an abnormality related to the filter device as one of the abnormality determination conditions that the pressure difference is larger than a predetermined abnormality determination value.
2. The exhaust according to claim 1, wherein after the pressure difference becomes larger than a predetermined abnormality judgment value, if there is a change on the pressure reduction side of the pressure difference, the exhaust is diagnosed as no abnormality or temporary abnormality relating to the filter device. Abnormality diagnosis device for purification system. A temperature detecting means for detecting the temperature of the reducing agent solution;
The abnormality diagnosing means is a case where the temperature of the reducing agent solution detected by the temperature detecting means is in a predetermined temperature range, and a change on the pressure reducing side of the pressure difference detected by the differential pressure detecting means is detected. The abnormality diagnosis device for an exhaust purification system according to claim 1, wherein if there is any abnormality related to the filter device, the abnormality diagnosis device diagnoses that there is no abnormality or a temporary abnormality.   The abnormality detecting means is a temporary abnormality caused by freezing of the reducing agent solution when the temperature of the reducing agent solution is in a predetermined low temperature range and there is a change on the reduced pressure side of the pressure difference. The exhaust gas purification system abnormality diagnosis device according to claim 3 for diagnosing.   The abnormality detection means diagnoses a temporary abnormality due to the deposition of the reducing agent when the temperature of the reducing agent solution is in a predetermined high temperature range and there is a change on the reduced pressure side of the pressure difference. The abnormality diagnosis device for an exhaust purification system according to claim 3.   The exhaust gas purification according to any one of claims 1 to 5, wherein the abnormality diagnosis means performs an abnormality diagnosis on the filter device based on a change on the pressure reduction side of the pressure difference during a predetermined start period of the internal combustion engine. System abnormality diagnosis device.

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