JP5051148B2 - Abnormality diagnosis device for exhaust purification system - Google Patents

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. The following configuration is known as a 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 on the exhaust upstream side. . In the system, urea water is stored in the tank at a predetermined urea concentration (for example, 32.5% or 33%), and is fed from the tank to the urea water addition valve by a pump.

  In the above system, by adding urea water into the exhaust pipe from the urea water addition valve, ammonia (NH3) produced by hydrolysis of urea water reacts with NOx in the exhaust gas on the NOx catalyst, and exhaust gas is discharged. NOx inside is selectively reduced and purified. Here, in order to increase the NOx purification rate in the NOx catalyst and suppress the excess ammonia in the NOx reduction reaction from being discharged from the exhaust pipe, it is necessary to supply ammonia to the NOx catalyst without excess or deficiency. It becomes.

  However, when the remaining amount of urea water in the tank becomes small or the concentration of urea water stored in the tank changes for some reason, an appropriate amount of ammonia cannot be supplied to the amount of NOx in the exhaust. It is possible. In view of this, conventionally, the remaining amount of urea water in the tank is detected, or abnormality diagnosis of the quality is performed (for example, see Patent Document 1).

  In Patent Document 1, a liquid level sensor and a concentration sensor (for example, a PH sensor) are provided in a urea water tank, and when the remaining amount of urea water becomes a specified amount or less due to a detection value of the liquid level sensor, It is disclosed that when it is detected from the detected value that urea water having a concentration other than the specified concentration is stored in the tank, an alarm is activated to notify the driver.

JP 2002-371831 A

  However, in Patent Document 1, the remaining amount of urea water in the tank is detected using a liquid level sensor, while the quality of urea water in the tank is detected using a concentration sensor. At least two sensors are required to detect the quality. Moreover, the quality abnormality diagnosis of urea water cannot be performed in the case of a failure of the concentration sensor or in a vehicle in which the concentration sensor is not mounted in the tank.

  The present invention has been made in order to solve the above-mentioned problems, and it is a main object of the present invention to provide an abnormality diagnosis device for an exhaust purification system capable of performing a quality abnormality diagnosis of a reducing agent solution with a relatively simple configuration. And

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

A first configuration includes a reducing agent tank for storing a reducing agent solution having a predetermined concentration, and a selective reduction catalyst that is provided in an exhaust passage of an internal combustion engine and selectively purifies NOx in exhaust gas by the reducing agent solution. And is applied to an exhaust gas purification system in which the reducing agent solution is added to the upstream side of the selective catalytic reduction catalyst by a reducing agent addition means. A liquid amount detecting means for detecting a liquid amount in the reducing agent tank; a liquid amount at the time of stop detected by the liquid amount detecting means when the internal combustion engine is stopped; and the liquid at the next start of the internal combustion engine. And an abnormality diagnosing unit that performs an abnormality diagnosis relating to the quality of the reducing agent solution based on a comparison result with the starting liquid amount detected by the amount detecting unit.

  If the quality of the reducing agent solution stored in the reducing agent tank deteriorates due to, for example, evaporation of the solvent or mixing of a liquid other than the reducing agent solution, exhaust purification may not be performed properly. Here, when quality abnormality of the reducing agent solution in the reducing agent tank occurs, it is conceivable that the amount of liquid in the reducing agent tank changes before and after the occurrence of the abnormality. That is, when the solvent evaporates, the amount of liquid in the reducing agent tank decreases, and when liquid other than the reducing agent solution is mixed in the tank, the amount of liquid in the tank increases. In addition, such a change in the liquid amount may occur during a standing period from the stop of the internal combustion engine to the next start.

In that respect, in the first configuration , the quality abnormality of the reducing agent solution is diagnosed based on the change in the amount of liquid in the reducing agent tank between when the internal combustion engine is stopped and at the next start. As a result, it is possible to detect an operation that is a previous stage of quality abnormality such as evaporation of the solvent or mixing of liquid other than the reducing agent solution, and accordingly, the quality abnormality diagnosis of the reducing agent solution can be suitably performed.

  Here, the time when the internal combustion engine is stopped is, for example, when the internal combustion engine is actually stopped or when it is estimated that the internal combustion engine is stopped, and specifically, when the ignition switch is switched from on to off, or The time when the rotational speed of the internal combustion engine becomes zero or close to it. The time when the internal combustion engine is started is, for example, the time when the internal combustion engine is started or a predetermined time after the start. Specifically, when the ignition switch is switched from OFF to ON, or the rotational speed of the internal combustion engine. Is the time when the rotation speed reaches a predetermined rotational speed.

As a case where the amount of liquid in the reducing agent tank decreases, it is conceivable that the solvent has evaporated due to, for example, standing for a long period of time. In such a case, the reducing agent solution is concentrated to increase the reducing agent concentration. In view of that, the second configuration is such that the abnormality diagnosing means is configured to reduce the reduction when the deviation from the stop-time liquid amount to the lower-side liquid amount is greater than a predetermined decrease determination value. It is determined that there is a concentration increase abnormality in which the reducing agent concentration of the reducing agent solution has shifted to an increasing side as an abnormality relating to the quality of the agent solution. According to the present invention, it is possible to specify that an abnormal increase in the reducing agent concentration has occurred among the abnormalities in the quality of the reducing agent solution, based on the change in the liquid amount from when the internal combustion engine is stopped to when it is started.

  Here, the divergence degree may be a difference expressed by subtracting the starting liquid amount from the stopping liquid amount, or may be a ratio of the starting liquid amount to the stopping liquid amount.

When it is diagnosed that there is an abnormal increase in the reducing agent concentration, it is desirable to correct the concentration to a normal reducing agent concentration. In view of this point, the third configuration is a replenishment amount calculation that calculates a replenishment amount of the solvent of the reducing agent solution to be replenished into the reducing agent tank based on the starting amount and the stopping amount. And means for notifying the user of the replenishment amount of the solvent calculated by the replenishment amount calculation unit when the abnormality diagnosis unit detects that the concentration increase is abnormal. The reductant concentration in the reductant tank is corrected to an appropriate value by replenishing the reductant tank with an amount of solvent corresponding to the amount of evaporation. As a result, an appropriate amount of reducing agent can be supplied to the amount of NOx in the exhaust gas, and thus NOx purification can be performed appropriately.

Possible causes of the decrease in the amount of liquid in the reducing agent tank include leakage abnormality due to damage to the reducing agent tank in addition to evaporation of the solvent. Here, when the amount of liquid in the tank decreases, the rate of decrease in the amount of liquid is relatively fast in the case of a leakage abnormality, whereas the rate is slow when the solvent evaporates. In view of this point, the fourth configuration includes means for measuring a leaving time of the vehicle on which the internal combustion engine is mounted, and the abnormality diagnosis means has the degree of deviation larger than a predetermined decrease determination value, and When the standing time is equal to or longer than a predetermined time, it is determined that the concentration increase abnormality has occurred as an abnormality relating to the quality of the reducing agent solution, the degree of deviation is greater than a predetermined decrease determination value, and the standing time is the predetermined time. If it is less than the time, it is determined that an abnormal leakage of urea water from the reducing agent tank has occurred. According to this configuration, the abnormality diagnosis is performed based on the liquid amount change and the vehicle leaving time, so when the liquid amount in the reducing agent tank decreases, whether the cause of the liquid amount decrease is due to the quality abnormality, It can be specified whether it is due to leakage abnormality.

  When the reducing agent solution is replenished into the reducing agent tank, for example, water may be mixed instead of the normal concentration reducing agent solution, or a reducing agent solution that is thinner than the normal concentration may be mixed. In such a case, it is considered that the amount of liquid in the tank increases as in the case where a normal concentration reducing agent solution is supplied. However, when water or the like is supplied into the tank, the concentration of the reducing agent solution deviates from the normal concentration, so that an amount of reducing agent corresponding to the amount of NOx in the exhaust gas cannot be supplied to the exhaust passage. There is a risk that NOx purification cannot be performed properly. That is, when water or a dilute concentration reducing agent solution is supplied into the tank, the amount of liquid in the tank increases, but it can be said that the NOx purification rate is different from the normal concentration.

In view of this, the fifth configuration includes means for detecting a decrease in the NOx purification rate in the selective reduction catalyst, and the abnormality diagnosis means is configured to increase the start-up liquid amount from the stop-time liquid amount. When the degree of divergence to is greater than a predetermined increase determination value and a decrease in the NOx purification rate is detected, the liquid different from the reducing agent solution as the abnormality related to the quality of the reducing agent solution or the It is determined that there is a replenishment abnormality in which a reducing agent solution other than the predetermined concentration is replenished. According to this invention, since the quality abnormality of the reducing agent solution is diagnosed on the basis of the change in the liquid amount from the stop of the internal combustion engine to the starting time and the NOx purification rate, Can specify that a replenishment abnormality in which a reductant solution other than a different liquid or normal concentration is replenished has occurred.

The sixth configuration includes means for calculating the amount of the reducing agent solution added by the reducing agent addition means based on the starting amount and the stopping amount. In this way, an amount of reducing agent solution corresponding to the concentration of reducing agent in the reducing agent tank can be supplied into the exhaust gas from the reducing agent addition means. Specifically, for example, when the concentration of the reducing agent is increased due to evaporation of the solvent (decrease in the amount of liquid), the amount of addition from the reducing agent addition means is less than when no reduction in the amount of liquid is observed, and the dilute reduction When the concentration of the reducing agent is reduced due to the mixing of the agent solution (increase in the amount of liquid), the amount of addition from the reducing agent addition means is made larger than when the increase in the amount of liquid is not observed. As a result, an appropriate amount of reducing agent can be supplied to the amount of NOx in the exhaust gas, and thus NOx purification can be performed appropriately.

The block diagram which shows the outline | summary of a urea SCR system. The flowchart which shows the process sequence of a water level detection process at the time of a stop. The flowchart which shows the process sequence of a quality abnormality diagnosis process.

  Hereinafter, an embodiment of an exhaust 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 has various actuators and various sensors for purifying exhaust, and ECU (Electronic Control Unit) 40, etc., for purifying exhaust discharged by a diesel engine (not shown) mounted on an automobile. Has been built.

  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, on the downstream side of the SCR catalyst 13, there is provided an exhaust sensor 16 in which a NOx detector (NOx sensor) and an exhaust temperature detector (exhaust temperature sensor) are both built. The exhaust sensor 16 detects the amount of NOx in the exhaust (NOx purification rate by the SCR catalyst 13) and the temperature of the exhaust on the downstream side of the SCR catalyst 13.

  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).

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 is additionally supplied with 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 CNH (for example, 32.5%) is stored therein. 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 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, and can rotate in either the forward or reverse direction. The urea water in the urea water tank 21 is sucked up by the normal 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 this embodiment, since the urea water pump 23 is provided outside the urea water tank 21, that is, without being immersed in the urea water, the urea water pump 23 is damaged due to freezing and expansion of the urea water in the urea water tank 21. Is suppressed.

  In the urea water supply pipe 22, a filter device 25 for filtering urea water is provided upstream of the urea water pump 23 (on the urea water tank 21 side). 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 driven to rotate in the forward rotation direction, whereby the urea water in the urea water tank 21 is pumped up, passes through the filter device 25, and is downstream. Flowing. Thereby, the foreign material etc. which are contained in urea water are removed. 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 regulating 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.

  On the other hand, 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 so that the urea water in the urea water supply pipe 22 is sucked back and flows into the urea water tank 21. Is done. In the present embodiment, this urea water sucking back operation is performed by the ECU 40 when the engine is stopped. In other words, it is avoided that the urea water remains in the urea water supply pipe 22 while the engine is stopped, thereby preventing the urea water supply pipe 22 from being damaged due to freezing and expansion of the urea water.

  As another configuration of the urea water supply system, a urea water level sensor 31 that detects the remaining amount of urea water (water level) stored in the urea water tank 21 is provided in the urea water tank 21. The urea water supply pipe 22 is provided with a urea water pressure sensor 32 that detects the pressure of the urea water in the urea water supply pipe 22 (line pressure PNH).

  In addition, this system is provided with a display panel 33 in front of the driver's seat for displaying various information relating to the vehicle such as the engine speed, engine water temperature, fuel remaining amount, urea water remaining amount, and the ECU 40 performs various display controls. Done.

  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 operates various actuators such as the urea water addition valve 15 in a desired mode based on detection values of various sensors, thereby performing various controls related to exhaust purification. To implement. Specifically, for example, detection signals are input from various sensors such as the exhaust sensor 16, the urea water level sensor 31, and the urea water pressure sensor 32 described above, and the energization time of the urea water addition valve 15 and the urea water pump are based on the input signals. 23 drive amount 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 system according to this embodiment, 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. Thus, urea water is added and supplied into the exhaust pipe 11. 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.

  The amount of urea added to the exhaust gas by the urea water addition valve 15 is calculated so as not to cause excess or deficiency of ammonia according to the amount of NOx in the exhaust gas detected by the exhaust sensor 16. However, if the concentration of urea water stored in the urea water tank 21 deviates from the specified concentration CNH or if a liquid other than urea water is mixed in the urea water tank 21, the amount of NOx in the exhaust gas is increased. On the other hand, it is conceivable that an appropriate amount of ammonia cannot be supplied, resulting in a decrease in the NOx purification rate and ammonia slip.

  That is, for example, when the engine is left in a stopped state for a long time, the water component of the urea water in the urea water tank 21 evaporates, and the concentration of the urea water may be higher than the specified concentration CNH. In such a case, there is a concern that the ammonia supply amount into the exhaust gas becomes excessive with respect to the NOx emission amount, and as a result, ammonia slip occurs. On the other hand, it is detected by the urea water level sensor 31 that the remaining amount of urea water in the urea water tank 21 has become small, and in response to this, the user replaces the urea water in the urea water tank 21 with water instead of the urea water having the specified concentration CNH. It is conceivable that the concentration of urea water will be lower than the prescribed concentration CNH when urea solution with a urea concentration lower than the defined concentration CNH is replenished. In such a case, there is a concern that the amount of ammonia supplied into the exhaust gas is insufficient, and as a result, the NOx purification rate in the exhaust gas decreases. Alternatively, when the user mistakenly or intentionally replenishes a liquid other than urea water (for example, light oil) when replenishing urea water into the urea water tank 21, the quality of the urea water is reduced due to the foreign matter, As a result, there is a concern that the NOx purification rate may decrease or a system failure may occur.

  The inventor paid attention to the fact that the quality of the urea water is considered abnormal when the remaining amount of the urea water in the urea water tank 21 changes. That is, when the water in the urea water tank 21 evaporates, the amount of liquid in the tank decreases, and when the liquid is replenished in the urea water tank 21, the amount of liquid in the tank increases. The change in the remaining amount of urea water in the urea water tank 21 is an event that occurs after the engine is stopped until the next engine start, and is tracked by the urea water level sensor 31 that is normally used for detecting the remaining amount of urea. We focused on what we can do.

  Therefore, in the present embodiment, the urea water level in the urea water tank 21 when the engine is stopped (stopped water level WLb) and the urea water level in the urea water tank 21 when the engine is next started (starting water level WLa). ) Are detected by the urea water level sensor 31 and, based on the comparison result, the quality abnormality of the urea water is diagnosed as an abnormality diagnosis after the engine is started. Hereinafter, the quality abnormality diagnosis process of this embodiment will be described with reference to the flowcharts of FIGS.

  First, the stop level water level detection process (stop time level detection process) will be described. FIG. 2 is a flowchart regarding the processing procedure of the water level detection processing at the time of stop. This process is repeatedly executed by the ECU 40 at a predetermined time period.

  In FIG. 2, first, in step S11, it is determined whether or not the engine has stopped. The engine stop determination is made, for example, by determining that the engine speed is zero or that the ignition switch is OFF. If it is after engine stop, it will progress to step S12 and it will be determined whether the urea water remaining in the urea water supply pipe 22 has already been sucked back. If the urea water sucking back is not completed, the process proceeds to step S13, and urea water sucking back control is executed. In the present embodiment, reverse rotation driving of the urea water pump 23 is performed for a predetermined time as urea water sucking back control.

  When a predetermined time has elapsed from the start of the reverse rotation driving of the urea water pump 23, it is determined in step S12 that the urea water has been sucked back, and the process proceeds to step S14, where the urea water level sensor 31 causes the urea water level in the urea water tank 21 to increase. Is detected, and the detected value is stored as a water level WLb at the time of stopping.

  Next, processing for diagnosing urea water quality abnormality (quality abnormality diagnosis processing) will be described with reference to FIG. FIG. 3 is a flowchart relating to the processing procedure of the quality abnormality diagnosis processing. This process is repeatedly executed by the ECU 40 at a predetermined time period.

  In FIG. 3, first, in step S21, it is determined whether or not the engine has been started. The engine start determination is performed, for example, by determining that the engine rotation speed is not zero or that the ignition switch is turned on. If the engine has been started, the process proceeds to step S22, where the urea water level sensor 31 detects the water level of the urea water in the urea water tank 21, and sets the detected value as the starting water level WLa. The detection of the starting water level WLa is preferably performed before the start of driving of the urea water pump 23, that is, before the start of feeding urea water from the urea water tank 21 to the urea water addition valve 15.

  In subsequent step S23, the stop water level WLb stored at the time of the previous engine stop is read, and a deviation WLd from the stop water level WLb at the start water level WLa is calculated. In the present embodiment, a value obtained by subtracting the stop time water level WLb from the start time water level WLa is defined as the deviation degree WLd.

  In step S24, whether the divergence degree WLd is positive or negative is determined. If the divergence degree WLd is a positive value, the process proceeds to step S25. In step S25, it is determined whether or not the divergence degree WLd is larger than the increase side determination value α (α> 0). When the divergence degree WLd is equal to or lower than the ascending-side determination value α, the process proceeds to step S26, and it is determined that the quality of the urea water in the urea water tank 21 is normal. On the other hand, if the divergence degree WLd is larger than the ascending-side determination value α, the process proceeds to step S27 to determine whether or not the NOx purification rate detected by the exhaust sensor 16 is an appropriate value. If the NOx purification rate is not appropriate, the process proceeds to step S28, and liquids other than urea water (for example, light oil) are replenished in the urea water tank 21 while the engine is stopped, among the abnormalities in urea water quality. Alternatively, it is determined that a supply abnormality has occurred that urea water or water having a concentration lower than the specified concentration CNH has been supplied, and for example, a warning is generated by sound generation or lamp lighting.

  Further, if the divergence degree WLd is a negative value, the process proceeds to step S29, and it is determined whether or not the absolute value of the divergence degree WLd is larger than the lower determination value β (β> 0). When the divergence degree WLd is equal to or lower than the lower-side determination value β, the process proceeds to step S30, and it is determined that the quality of the urea water in the urea water tank 21 is normal. On the other hand, when the divergence degree WLd is larger than the lower-side determination value β, the process proceeds to step S31, and among urea water quality abnormalities, the urea concentration of urea water increases due to water evaporation from the urea water tank 21. It is determined that a dry abnormality has occurred, and for example, a warning is generated by sound generation or lamp lighting.

  In the subsequent step S32, the amount of water to be replenished in the urea water tank 21 (water replenishment amount Qw) is calculated in order to make the urea concentration in the urea water tank 21 a specified concentration, and the water replenishment amount Qw is displayed on the display panel. 33. The water replenishment amount Qw is a decrease from the stop time water level WLb at the start time water level WLa, that is, the deviation WLd. By supplying the water for the water replenishment amount Qw into the urea water tank 21 by the driver, the urea water in the urea water tank 21 is maintained at an appropriate urea concentration.

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

  A comparison is made between the water level in the urea water tank 21 detected after the engine is stopped by the urea water level sensor 31 (water level WLb at the time of stopping) and the water level in the urea water tank 21 detected at the next engine start (the water level WLa at the time of starting). Since the abnormality diagnosis of the quality of urea water is performed based on the comparison result, the water level change in the reducing agent tank between the stop of the engine and the next start-up, that is, water evaporation and urea water It is possible to detect an operation that is a pre-stage of quality abnormality such as mixing of liquid other than the above, and thus it is possible to suitably perform quality abnormality diagnosis of urea water.

  When the starting water level WLa is lower than the lower-side determination value β with respect to the stopping water level WLb, it is determined that an abnormal concentration increase has occurred, and the starting water level WLa is the stopping water level. A configuration in which it is determined that a replenishment abnormality has occurred that the liquid replenished in the urea water tank 21 is a liquid different from the urea water having the specified concentration CNH when it rises above the ascending determination value α with respect to WLb. Therefore, it is possible to specify which of the quality abnormalities is occurring.

  Using a sensor provided in a normal urea SCR system such as the urea water level sensor 31 and diagnosing the quality abnormality of urea water based on the detected value, the quality abnormality can be implemented using an existing sensor. . That is, it is not necessary to separately provide a means for detecting a quality abnormality. Therefore, the quality abnormality diagnosis of urea water can be performed with a relatively simple configuration. Further, the remaining amount of urea water in the urea water tank 21 and its quality abnormality can be detected by one sensor.

  Since it is configured to calculate the water replenishment amount Qw from the starting water level WLa and the stop water level WLb and display the water replenishing amount Qw on the display panel 33 when it is diagnosed that the urea concentration rises abnormally, The driver can be encouraged to replenish water corresponding to the amount of water. As a result, the urea concentration in the urea water tank 21 can be corrected to an appropriate value, so that NOx purification can be appropriately performed.

  In order to diagnose the quality abnormality based on the deviation degree WLd and the NOx purification rate, when the water level in the tank rises between the engine stop and the next engine start, the rise in the water level is caused by the urea water having the specified concentration CNH. It can be specified whether it is due to replenishment or due to the supply of a liquid other than urea water or urea water other than the specified concentration CNH.

  Since the water level detected by the urea water level sensor 31 after the suction back control is set to the stop time water level WLb and the water level detected before the start of the driving of the urea water pump 23 is set to the start time water level WLa, the urea water supply By comparing the water levels in a state where no urea water is present in the tube 22, the abnormality diagnosis can be performed more accurately.

  In diagnosing quality abnormality based on the water level change of the starting water level WLa from the stopping water level WLb, the quality is determined when the deviation degree WLd (WLa−WLb) is larger than the rising side determination value α or the lowering side determination value β. Since it is determined that there is an abnormality, it is suitable for suppressing erroneous detection.

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

  A soak timer that detects the soak time (vehicle leaving time) after the ignition switch is turned off is provided in the ECU 40, for example. Then, when the divergence degree WLd is larger than the lower-side determination value β and the soak time is equal to or greater than the determination value, it is determined that the urea water quality is abnormal. On the other hand, when the divergence degree WLd is larger than the lower-side determination value β and the soak time is less than the determination value, it is determined that there is an abnormal leakage of urea water from the urea water tank 21. As a cause of the decrease in the urea water level in the urea water tank 21 while the engine is stopped, the urea water leaks out of the urea water tank 21 due to damage of the urea water tank 21 and the like in addition to the evaporation of the urea water. It is possible that Among these causes, in the case of urea water leakage from the urea water tank 21, the urea water level is lowered on the lower side determination value β in a relatively short time (for example, several hours or several days). On the other hand, in the case of water evaporation, the urea water level decreases over a relatively long time (for example, several weeks to several months). Therefore, it is possible to accurately specify that the quality abnormality of the urea water has occurred by determining the quality abnormality with the soak time as a requirement.

  -In the structure which determines the drying abnormality of urea water based on the comparison result of soak time and a judgment value, the judgment value is changed by environmental conditions, such as a season and a region. For example, the water component of urea water is more likely to evaporate in summer than in winter, and the water component of urea water is more likely to evaporate in warm regions than in cold regions. For this reason, in an environment where drying of urea water is likely to be promoted, such as in summer and warm regions, the decrease in urea water level is also likely to be promoted. Therefore, it is preferable to decrease the soak time determination value in an environment where drying of urea water is more easily promoted.

  The urea water addition amount from the urea water addition valve 15 is calculated based on the difference (deviation degree WLd) between the starting water level WLa and the stopping water level WLb, and the calculated addition amount is discharged from the urea water addition valve 15 to the exhaust pipe. 11 to be added. For example, when urea water addition amount control is performed on the assumption that the urea concentration is the specified concentration CNH in spite of the urea concentration of the urea water being increased due to evaporation of the urea water, An excessive amount of ammonia is supplied relative to the amount of NOx. In such a case, there is a concern about the occurrence of ammonia slip. Therefore, when the starting water level WLa is lower than the stopping water level WLb (when the divergence degree WLd is a negative value), the urea addition amount is decreased as the divergence degree WLd is larger. Thereby, an appropriate amount of ammonia can be supplied to the NOx in the exhaust gas.

  For example, an ammonia gas sensor is provided on the exhaust gas downstream side of the SCR catalyst 13 as means for detecting excessive ammonia discharge (ammonia slip) in the SCR catalyst 13. When the deviation degree WLd is larger than the rising side determination value α or is a positive value and excessive ammonia discharge is detected by the ammonia gas sensor, an abnormal quality of urea water is detected from the specified concentration CNH. It is determined that there is a replenishment abnormality that urea water with a higher concentration is replenished in the urea water tank 21. That is, when the deviation degree WLd is larger than the ascending determination value α, it is considered that some liquid has been replenished into the urea water tank 21 when the engine is stopped. Moreover, considering that the excess discharge of ammonia is detected, it is considered that the replenished liquid has a urea concentration of urea water higher than the specified concentration CNH. Therefore, based on the divergence degree WLd and the presence or absence of ammonia slip, the supply abnormality that the liquid (the urea water whose urea concentration is higher than the specified concentration CNH) that changes the urea concentration to the increasing side among the quality abnormalities of the urea water is supplied. Can be identified.

  In the configuration including the ammonia gas sensor, when the deviation degree WLd is larger than the lower-side determination value β and excessive ammonia discharge is detected by the ammonia gas sensor, urea water quality abnormality is detected. It is determined that there is a dry abnormality that the urea concentration has become higher than the specified concentration CNH due to evaporation of water in the water tank 21. When the cause of the decrease in the urea water level when the engine is stopped is the urea water leakage abnormality, the urea concentration in the urea water tank 21 does not change, so that ammonia is not excessively supplied at the time of subsequent engine startup (ammonia slip does not occur). it is conceivable that. Therefore, by performing abnormality determination based on the deviation degree WLd and the presence or absence of ammonia slip, it is possible to accurately identify that the quality abnormality of the urea water has occurred.

  In the above embodiment, when it is detected that there is an abnormality in concentration increase, the water supply amount Qw into the urea water tank 21 calculated from the starting water level WLa and the stopping water level WLb is displayed on the display panel 33. Thus, the urea concentration in the urea water tank 21 is corrected to the specified concentration CNH by water replenishment by the user, but the water replenishment to the urea water tank 21 is automatically controlled based on a command signal from the ECU 40. To do. Specifically, a water storage tank for replenishing water is mounted on the system, and water for the amount of water replenishment Qw is supplied from the water storage tank to the urea water tank 21.

  -It is configured to detect the water level WLb at the time of stop after it is determined that the engine is stopped and to detect the water level WLa at the time of start after the engine start is determined, but the detection timing of the water level WLb at the time of stop and the water level WLa at the time of start is Not limited. The stop water level WLb is detected before the engine is stopped, specifically, for example, when the engine speed reaches a predetermined low speed. Or it is set as the structure detected before the sucking-back control of urea water after an engine stop. Further, for example, the start-up water level WLa is detected when a predetermined low rotational speed is reached, or is detected when a predetermined time elapses after the ignition switch is turned on.

  The degree of deviation of the starting water level WLa from the stopping water level WLb is calculated by subtracting the stopping water level WLb from the starting water level WLa, but may be a ratio of the starting water level WLa to the stopping water level WLb. In this case, in step S24 of FIG. 3, instead of determining whether the divergence degree is positive or negative, it is determined whether or not the divergence degree is larger than value 1. If the divergence degree is larger than value 1, the process proceeds to step S25. If it is also smaller, the process proceeds to step S29. In step S29, it is determined whether or not the divergence degree is smaller than the lower side determination value β. If the degree of divergence is equal to or higher than the lower side determination value β, the process proceeds to step S30. Proceed to step S31.

  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.

  Instead of detecting a change in the amount of liquid in the reducing agent tank 21 as a change in water level based on the detected value of the urea water level sensor 31, a change in volume or weight of liquid in the reducing agent tank 21 is detected.

  -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 (selective reduction type catalyst), 15 ... Urea water addition valve (reducing agent addition means), 21 ... Urea water tank (reducing agent tank), 23 ... Urea water pump, 31 ... Urea water level sensor (liquid amount detection means), 32 ... Urea water pressure sensor, 40 ... ECU (abnormality diagnosis means, replenishment amount calculation means, addition amount correction means).

Claims (6)

A reducing agent tank for storing a reducing agent solution having a predetermined concentration; and a selective reduction catalyst that is provided in an exhaust passage of an internal combustion engine and selectively purifies NOx in exhaust gas by the reducing agent solution. Applied to the exhaust gas purification system in which the reducing agent solution is added to the exhaust gas upstream side of the catalyst by the reducing agent addition means,
A liquid amount detecting means for detecting a liquid amount in the reducing agent tank;
Based on the comparison result between the stop-time liquid amount detected by the liquid amount detection means when the internal combustion engine is stopped and the start-time liquid amount detected by the liquid amount detection means at the next start-up of the internal combustion engine. An abnormality diagnosis means for performing an abnormality diagnosis on the quality of the reducing agent solution;
Equipped with a,
The abnormality diagnosing means determines that the reducing agent solution has an abnormality related to the quality of the reducing agent solution when a deviation degree of the starting liquid amount from the stopping liquid amount to a lower side is larger than a predetermined decrease determination value. An abnormality diagnosis device for an exhaust gas purification system, characterized in that it is determined that there is a concentration increase abnormality in which the concentration of the reducing agent is shifted to an increasing side . Replenishment amount calculating means for calculating a replenishment amount of the solvent of the reducing agent solution to be replenished into the reducing agent tank based on the starting liquid amount and the stopping liquid amount;
Informing means for informing the user of the replenishment amount of the solvent calculated by the replenishment amount calculating means when the abnormality diagnosing means detects that there is a concentration increase abnormality,
An abnormality diagnosis device for an exhaust purification system according to claim 1 . Means for measuring the time for which the vehicle on which the internal combustion engine is mounted is measured;
The abnormality diagnosing means determines that the concentration increase abnormality has occurred as an abnormality relating to the quality of the reducing agent solution when the degree of divergence is greater than a predetermined decrease determination value and the standing time is equal to or longer than a predetermined time. The method according to claim 1 or 2 , wherein when the degree of divergence is greater than a predetermined decrease determination value and the leaving time is less than the predetermined time, it is determined that an abnormal leakage of urea water from the reducing agent tank has occurred. An abnormality diagnosis device for an exhaust purification system as described. Exhaust gas purification system according to any one of claims 1 to 3 comprising means for calculating the amount of the reducing agent solution by the reducing agent adding means in accordance with said stop fluid amount and the starting liquid volume Abnormality diagnosis device. A reducing agent tank for storing a reducing agent solution having a predetermined concentration; and a selective reduction catalyst that is provided in an exhaust passage of an internal combustion engine and selectively purifies NOx in exhaust gas by the reducing agent solution. Applied to the exhaust gas purification system in which the reducing agent solution is added to the exhaust gas upstream side of the catalyst by the reducing agent addition means,
A liquid amount detecting means for detecting a liquid amount in the reducing agent tank;
Based on the comparison result between the stop-time liquid amount detected by the liquid amount detection means when the internal combustion engine is stopped and the start-time liquid amount detected by the liquid amount detection means at the next start-up of the internal combustion engine. An abnormality diagnosis means for performing an abnormality diagnosis on the quality of the reducing agent solution;
Means for calculating the amount of the reducing agent solution added by the reducing agent addition means based on the starting liquid amount and the stopping liquid amount;
An abnormality diagnosis device for an exhaust purification system, comprising: Means for detecting a decrease in the NOx purification rate in the selective catalytic reduction catalyst,
The abnormality diagnosing means is a case where the degree of deviation of the starting liquid amount from the stopped liquid amount to the rising side is larger than a predetermined increase determination value and a decrease in the NOx purification rate is detected to, in any one of the reducing agent solution and the different liquids or the predetermined concentration other than the reducing agent solution is determined that supply abnormality is replenished claims 1 to 5 as the abnormality regarding the quality of the reducing agent solution An abnormality diagnosis device for an exhaust purification system as described.

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