JP5136450B2 - 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, in the urea SCR system, a selective reduction type NOx catalyst is provided in an exhaust pipe connected to the engine body, and urea water addition valve for adding urea water (reducing agent solution) as a NOx reducing agent to the exhaust upstream side thereof. Is provided. 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 concentration of urea water stored in the tank changes for some reason, it is considered that an appropriate amount of ammonia cannot be supplied with respect to the amount of NOx in the exhaust. Therefore, various methods for diagnosing abnormalities in the quality of urea water in the tank have been proposed (see, for example, Patent Document 1). In Patent Document 1, a concentration sensor that detects the concentration of urea water by using a heat transfer characteristic between two spaced apart heaters and a temperature sensor is used to diagnose an abnormal concentration of urea water in the tank. It is disclosed. In this concentration sensor, temperature sensors are arranged at two spaced apart positions, and a heater is incorporated in at least one of them. When the heater is activated, the other temperature sensor detects a temperature rise with characteristics corresponding to the thermal conductivity of the urea water. The concentration of urea water is detected according to this temperature rise characteristic.

JP 2005-127262 A

  However, in Patent Document 1, it is conceivable that an abnormal quality of urea water cannot be detected when the urea water is frozen. That is, when the heater of the concentration sensor is operated in a state where the urea water is frozen, the heat of the heater is used for melting the urea water, so it is considered that the temperature rise is not detected by the other temperature sensor. . Therefore, at the time of freezing urea water, quality abnormality cannot be diagnosed until urea water is thawed, and as a result, abnormality diagnosis cannot be performed promptly after engine startup.

  The present invention has been made to solve the above-described problem, and provides an abnormality diagnosis device for an exhaust purification system capable of performing abnormality diagnosis relating to the quality of a reducing agent solution regardless of the state of the reducing agent solution. Is the main purpose.

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

The first configuration includes a reducing agent tank that stores a reducing agent solution, a selective reduction catalyst that is provided in an exhaust passage of an internal combustion engine and selectively purifies nitrogen oxides in exhaust gas by the reducing agent solution, and the reduction The present invention is applied to an exhaust gas purification system including a reducing agent addition device that is connected to a reducing agent passage through a reducing agent passage and adds a reducing agent solution in the reducing agent tank to the exhaust upstream side of the selective catalytic reduction catalyst. A temperature detecting means for detecting the temperature of the reducing agent solution in the reducing agent tank; a state detecting means for detecting a frozen state of the reducing agent solution in the reducing agent tank; and a solution detected by the temperature detecting means. And an abnormality diagnosing unit that performs an abnormality diagnosis on the quality of the reducing agent solution based on the temperature and the frozen state detected by the state 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, the solutions having the same concentration of the reducing agent solution and not mixed with a liquid other than the reducing agent solution have the same melting point (freezing point). Therefore, although the temperature of the reducing agent solution stored in the reducing agent tank is a temperature indicating that it is in a frozen state (solid state) if the quality of the reducing agent solution is normal, it is actually frozen. If the temperature of the reducing agent solution stored in the reducing agent tank is not frozen (if it is in a liquid state), and if the quality of the reducing agent solution is normal, it is not frozen (liquid state) In the case where it is actually frozen (in a solid state) in spite of the temperature indicating the temperature, it is conceivable that a reducing agent solution having an abnormal quality (abnormal) is stored in the tank. In view of this point, in the first configuration , since the quality abnormality of the reducing agent solution is diagnosed based on the correspondence between the temperature of the reducing agent solution in the reducing agent tank and the frozen state, the reducing agent solution is frozen. Even so, an abnormality diagnosis relating to the quality of the reducing agent solution can be performed.

The change in the state of the reducing agent solution occurs when the internal combustion engine is stopped (being left) and after the internal combustion engine is started. That is, the change of the reducing agent solution from the liquid state to the solid state occurs while the internal combustion engine is stopped (while standing), and the change from the solid state to the liquid state occurs at or after the start of the internal combustion engine. In view of this point, the second configuration includes a heat supply means for supplying heat to the reducing agent solution in the reducing agent tank by starting the internal combustion engine, and the abnormality diagnosis means is provided after the internal combustion engine is started. An abnormality diagnosis relating to the quality of the reducing agent solution is performed during a predetermined start-up period. According to this configuration, since abnormality diagnosis is performed during a period in which the state change of the reducing agent solution is observed, it is possible to suppress the detection failure of quality abnormality. Further, since the abnormality diagnosis regarding the quality of the reducing agent solution is performed immediately after the internal combustion engine is started, the abnormality can be detected as early as possible.

When the temperature of the reducing agent solution stored in the reducing agent tank is lower than the melting point of the normal reducing agent solution, the reducing agent solution in the tank is not frozen. It is conceivable that a liquid other than the solution (for example, light oil) is mixed in the agent solution. In view of that, the third configuration is such that the abnormality diagnosing means is in a state where the solution temperature is lower than a predetermined specified temperature that is predetermined as the melting point of the reducing agent solution and the reducing agent solution is not frozen. In this case, it is determined that there is an abnormality in mixing that liquid other than the reducing agent solution is mixed as an abnormality related to the quality of the reducing agent solution. According to this configuration, it is determined based on the relationship between the temperature of the reducing agent solution and the frozen state that a mixing abnormality has occurred in which a liquid other than the solution is mixed among the quality abnormalities of the reducing agent solution. be able to.

In order to prevent freezing of the reducing agent solution, the concentration of the reducing agent solution having a normal quality may be set so that the melting point is the lowest in the solution. In such a case, when the reducing agent solution in the tank is frozen even though the temperature of the reducing agent solution in the reducing agent tank is higher than the melting point of the normal reducing agent solution, the reducing agent solution in the tank is frozen. It can be said that the concentration of is not consistent with the concentration (normal concentration) of a normal reducing agent solution. In view of this point, the fourth configuration is such that the reducing agent solution is set to a concentration that provides the lowest melting point as the lowest melting point in the aqueous solution containing the reducing agent, and the abnormality diagnosing means includes the solution temperature. Is higher than the minimum melting point and it is detected that the reducing agent solution is in a frozen state, it is determined that there is a concentration abnormality that is different from the normal concentration of the reducing agent as an abnormality related to the quality of the reducing agent solution. To do. According to this configuration, it is possible to specify that a concentration abnormality among the quality abnormalities of the reducing agent solution has occurred, based on the relationship between the temperature of the reducing agent solution and its frozen state.

A fifth configuration relates to the quality of the reducing agent solution at different temperatures within the same temperature range when the solution temperature is within a temperature range in the vicinity of a predetermined specified temperature that is predetermined as the melting point of the reducing agent solution. Carry out abnormality diagnosis. By so doing, abnormality diagnosis can be performed in a temperature range where a state change is observed in a normal quality reducing agent solution. Therefore, the abnormality diagnosis can be suitably performed while suppressing the frequency of abnormality diagnosis. The temperature range is preferably a temperature range including a predetermined specified temperature. In such a case, the different temperatures within the above temperature range are more preferably set to a higher temperature side and a lower temperature side than the specified temperature.

The sixth configuration further includes means for detecting a melting point of the solution stored in the reducing agent tank by detecting a temperature at which the reducing agent solution changes from a frozen state to a thawed state. According to this configuration, since the melting point of the liquid stored in the reducing agent tank is detected, the detected melting point is compared with the melting point of the reducing agent solution when the quality is normal. It is possible to know the degree of quality abnormality in the liquid stored in the tank.

The seventh configuration is applied to an exhaust gas purification system including a pump for feeding a reducing agent solution in the reducing agent tank to the reducing agent addition device, and the pump is disposed in the middle of the reducing agent passage. It is provided without being immersed in the reducing agent solution in the agent tank. According to this configuration, it is possible to suppress breakage of the pump when the reducing agent solution in the reducing agent tank is frozen and expanded.

The block diagram which shows the outline | summary of a urea SCR system. The figure which shows the relationship between the urea concentration of urea water, and a freezing point. The flowchart which shows the process sequence of a quality abnormality diagnosis process. The time chart which shows the time transition in the quality abnormality diagnosis of urea water.

  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, a NOx sensor 16 and an exhaust temperature sensor 17 are provided on the downstream side of the SCR catalyst 13. 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), and the exhaust temperature sensor 17 detects the temperature of the exhaust.

  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 in a state where it is not immersed in the urea water in the urea water tank 21, damage to the urea water pump 23 due to freezing and expansion of the urea water in the urea water tank 21 is suppressed. Is done.

  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.

  When 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, whereby 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. 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.

  Further, a cooling water passage 33 as a passage for engine cooling water is disposed in the urea water tank 21. That is, the engine coolant can be circulated from the engine main body → the urea water tank 21 → the engine main body by driving an engine-driven water pump (not shown). Thereby, the exhaust heat of the engine is used to prevent freezing of the urea water in the urea water tank 21 and to perform thawing at the time of freezing of the urea water. As a heat supply means of the present invention, a heating element such as a heater may be provided instead of the cooling water passage 33 in the urea water tank 21.

  As another configuration of the urea water supply system, a 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. The urea water supply pipe 22 is provided with a pressure sensor 32 that detects the pressure of the urea water in the urea water supply pipe 22 (line pressure PNH). The temperature sensor 31 preferably detects the temperature in the vicinity of the suction port of the urea water supply pipe 22.

  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 NOx sensor 16, the exhaust temperature sensor 17, the temperature sensor 31, and the pressure sensor 32, and the energization time of the urea water addition valve 15 is determined based on the input signals. The driving amount of the urea water pump 23 is 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 NOx sensor 16. However, if a liquid other than the urea water having the specified concentration CNH is stored in the urea water tank 21, the urea addition amount cannot be calculated to an appropriate value, resulting in a decrease in the NOx purification rate and ammonia slip. Conceivable.

  That is, for example, when the water component in the urea water in the urea water tank 21 evaporates or the urea water having a concentration higher than the specified concentration CNH is supplied into the urea water tank 21 due to being left for a long period of time, the urea The concentration of water becomes higher than the specified concentration CNH. For this reason, there is a concern that the ammonia supply amount into the exhaust gas becomes excessive and ammonia slip occurs. Further, when urea water or water having a concentration lower than the specified concentration CNH is supplied into the urea water tank 21, the concentration of urea water becomes lower than the specified concentration CNH. For this reason, there is a concern that the amount of ammonia supplied into the exhaust is insufficient, and the unpurified portion of NOx in the exhaust is discharged from the exhaust pipe 11. Alternatively, when a liquid other than urea water (for example, light oil) is accidentally or intentionally supplied into the urea water tank 21, the quality of the urea water is reduced due to the mixing of the liquid, and the NOx purification rate is reduced. There is a risk of failure.

  In view of this problem, the present inventor has paid attention to the fact that urea water maintained at a predetermined concentration has a freezing point (melting point) specific to the concentration. That is, in the urea water, the urea concentration and the freezing point have the relationship shown in FIG. 2, and in the concentration range below the predetermined concentration C0, the higher the concentration, the lower the freezing point, and the freezing point becomes the minimum value TE0 at the predetermined concentration C0. In addition, in the concentration range exceeding the predetermined concentration C0, the higher the concentration, the higher the freezing point. In this embodiment, the urea concentration at which the freezing point is lowest is set to the specified concentration CNH. For example, when the predetermined concentration C0 is 32.5% (specified concentration CNH), the freezing point is minus 11 ° C.

  Therefore, in this embodiment, the quality abnormality of the urea water is diagnosed based on the temperature of the urea water (urea water temperature TENH) and the frozen state of the urea water. Specifically, the detected value of the temperature sensor 31 (urea water temperature TENH) is compared with the freezing point (corresponding to the minimum value TE0) at the specified concentration CNH (predetermined concentration C0), and urea water estimated from the comparison result It is determined whether or not the frozen state and the actual frozen state of the urea water in the urea water tank 21 match. If the urea water frozen state estimated from the urea water temperature TENH does not match the actual frozen state, it is determined that there is a quality abnormality in the urea water in the urea water tank 21.

  FIG. 3 is a flowchart showing a processing procedure of processing relating to the quality abnormality diagnosis of urea water (quality abnormality diagnosis processing). This process is repeatedly performed every predetermined cycle (for example, every several seconds) by the ECU 40 during a predetermined engine start period after the ignition is turned on. Note that the predetermined engine start period is set based on, for example, the elapsed time since the ignition is turned on or the temperature of the engine coolant.

  In FIG. 3, first, in step S11, the urea water temperature TENH in the urea water tank 21 is detected by the temperature sensor 31, and in step S12, it is determined whether the urea water temperature TENH is less than the freezing point at the specified concentration CNH. In this embodiment, since the specified concentration CNH is C0, the freezing point at the specified concentration CNH is the minimum value TE0.

  When the urea water temperature TENH is equal to or higher than the minimum value TE0, the process proceeds to step S13, and the driving of the urea water pump 23 for feeding urea water from the urea water tank 21 to the urea water addition valve 15 is started, and step S14 is performed. It is determined whether or not the urea water is in a frozen state. In this embodiment, when the urea water pump 23 is driven, it is determined from the detected value of the pressure sensor 32 that the urea water is passing through the urea water supply pipe 22, that is, the pressure sensor 32 increases the pressure. When detected, it is determined that the urea water is not frozen.

  When the frozen urea water is thawed, the temperature of the urea water is considered in consideration of the time difference between the timing at which the urea water temperature TENH reaches the melting point and the timing at which the pressure sensor 32 detects a pressure increase. The frozen state (thaw state) of the urea water may be determined based on the line pressure PNH when a predetermined delay time TA (for example, 1 to 2 seconds) has elapsed since the time when TENH was detected.

  If the pressure sensor 32 detects an increase in pressure as the urea water pump 23 is driven and it is determined that the urea water is not frozen, the process proceeds to step S15 where the quality of the urea water is normal. It is determined that

  On the other hand, if the pressure increase is not detected by the pressure sensor 32 even if the urea water pump 23 is driven and it is determined that the urea water is in a frozen state, the process proceeds to step S16, and the urea water quality is abnormal. This is recognized and the contents of the abnormality are memorized and the check lamp is lit to inform the driver. That is, when the urea water is frozen despite the urea water temperature TENH detected by the temperature sensor 31 being higher than its melting point (minimum value TE0), the melting point of the liquid in the urea water tank 21 is the specified concentration CNH. Can be said to be higher. In such a case, it is conceivable that urea water having a concentration higher than the specified concentration CNH or urea water having a concentration lower than the specified concentration CNH is stored in the urea water tank 21 (see FIG. 2). Therefore, in this case, as one aspect of the urea water quality abnormality, it is determined that there is a concentration abnormality in which urea water other than the specified concentration CNH is supplied into the urea water tank 21.

  If the urea water temperature TEN is less than the minimum value TE0, an affirmative determination is made in step S12, and the process proceeds to step S17 to drive the urea water pump 23 in order to diagnose whether the urea water is in a frozen state. . The pump drive at this time may be equal to or smaller than the pump drive amount in the urea water feed pump drive to the urea water addition valve 15.

  Then, it progresses to step S18, and it is determined based on the detected value of the pressure sensor 32 at the time of the drive of the urea water pump 23 whether the urea water is the frozen state. When it is determined that the urea water is in a frozen state, the process proceeds to step S19, and it is determined that the quality of the urea water is normal.

  On the other hand, if the urea water is not frozen, the process proceeds to step S20, where it is recognized that there is a quality abnormality in the urea water, the abnormality content is stored, and a check lamp is lit to notify the driver. That is, when the urea water temperature TENH detected by the temperature sensor 31 is equal to or lower than its melting point (minimum value TE0), but the urea water is not frozen, the melting point of the liquid in the urea water tank 21 is higher than the specified concentration CNH. It can be said that it is low. In such a case, in the urea water tank 21, for example, light oil or the like is mixed with the urea water or stored alone, and it is considered that the melting point is lowered due to this. Therefore, in this case, as one aspect of the quality abnormality of urea water, it is determined that there is an abnormality in mixing that liquid other than urea water is mixed.

  When it is determined that the quality of the urea water is abnormal, the urea water addition from the urea water addition valve 15 into the exhaust gas may be stopped as a control for the subsequent urea water addition. Moreover, when the form of the quality abnormality of urea water shows mixing abnormality, addition of urea water may be stopped, and when concentration abnormality is shown, you may continue addition of urea water. Alternatively, as a configuration for selecting whether to stop or continue the addition of urea water according to the urea water temperature TENH at the time when it is determined that the liquid in the urea water tank 21 has changed from a frozen state to a non-freezing state. Also good.

  Next, a temporal transition of abnormality diagnosis related to the quality of urea water will be described using the time chart of FIG. In FIG. 4, it is assumed that the urea water temperature TENH is lower than the minimum value TE0 when the engine is started, that is, the urea water in the urea water tank 21 is frozen. 4A shows the case where the quality of the urea water is normal, FIG. 4B shows the case where the concentration abnormality occurs among the quality abnormalities of the urea water, and FIG. The case where it has occurred is shown. For convenience, FIG. 4 will be described without considering the time difference (delay time TA) between the timing at which the urea water temperature TENH reaches the melting point and the timing at which the pressure increase is detected by the pressure sensor 32.

  As the engine is started (ignition is turned on), circulation of engine cooling water is started, and pump driving for diagnosing quality abnormality is started. At this time, when the urea water of the specified concentration CNH is stored in the urea water tank 21, the urea water in the urea water tank 21 remains frozen before time t1, as shown in FIG. 4 (a). Therefore, even if the pump is driven, the line pressure PNH does not change and is maintained at zero pressure. Then, the urea water temperature TENH rises due to the circulation of the engine cooling water, and when the minimum value TE0 is reached at time t1, the urea water in the urea water tank 21 starts to melt, and the urea water that has melted melts into the urea water pump. The water is pumped up by 23 and passes through the urea water supply pipe 22. Further, at time t1 when the urea water temperature TENH reaches the minimum value TE0, the line pressure PNH starts to increase, and it is determined that the quality of the urea water is normal.

  On the other hand, when urea water having a concentration higher or lower than the specified concentration CNH is stored in the urea water tank 21, the melting point (freezing point) shifts to a higher temperature side than the minimum value TE0, and therefore FIG. As shown, the line pressure PNH does not increase when the urea water temperature TENH reaches the minimum value TE0, and the line pressure PNH increases when the temperature TE0 + ta is higher than the minimum value TE0. In this case, when the urea water temperature TENH reaches the minimum value TE0, it is determined that there is a quality abnormality (concentration abnormality) of the urea water.

  Further, when light oil is mixed in the urea water tank 21, the melting point (freezing point) shifts to a lower temperature side than the minimum value TE0, so that the urea water temperature TENH is the minimum value as shown in FIG. The line pressure PNH rises at a timing before reaching TE0, and when the pressure rises, it is determined that the urea water quality abnormality (mixing abnormality) is present.

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

  Since the urea water quality abnormality is diagnosed based on the urea water temperature TENH in the urea water tank 21 and the frozen state of the urea water, even if the urea water is in a frozen state, the abnormality related to the quality of the urea water Diagnosis can be performed.

  In order to diagnose the quality abnormality based on the detected value using the sensors provided in the normal urea SCR system, such as the temperature sensor 31 and the pressure sensor 32, the quality abnormality of the urea water is simply configured using the existing sensor and It can be detected with high accuracy.

  Since the quality abnormality diagnosis process is performed during a predetermined engine start-up period after the ignition is turned on, abnormality diagnosis is performed under circumstances where urea water may be frozen or when a change between a solid state and a liquid state appears. be able to. Therefore, it is possible to suppress the detection failure of the quality abnormality. Moreover, since the abnormality diagnosis regarding the quality of urea water is performed promptly after the engine is started, the abnormality can be detected as early as possible.

  When the urea water temperature TENH detected by the temperature sensor 31 is lower than the minimum value TE0 and the urea water is not frozen, it is determined that there is a mixing abnormality as a urea water quality abnormality, and the urea water temperature TENH is When the urea water is in a state of being higher than the minimum value TE0 and frozen, it is determined that there is a concentration abnormality as a quality abnormality of the urea water, so it is possible to specify which of the quality abnormalities has occurred.

  Since the configuration includes an in-line system in which the urea water pump 23 is arranged without being immersed in the urea water in the urea water tank 21, the urea water pump when the urea water in the urea water tank 21 is frozen and expanded. 23 can be prevented from being damaged.

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

  A predetermined temperature range (for example, minimum value TE0 ± β [° C.]) set so that the urea concentration is in the vicinity of the melting point (minimum value TE0) at the specified concentration CNH and includes the same melting point. Temperature range). When the quality of the urea water is normal, the urea water is frozen on the lower temperature side than the melting point, so there is a concern about the occurrence of seizure or the like due to idle rotation of the urea water pump 23. According to this configuration, The region where pump driving for abnormality diagnosis is performed on the low temperature side can be limited, and as a result, the load of the urea water pump 23 can be reduced.

  -In the above quality abnormality diagnosis process, the urea water is frozen by setting the temperature at a predetermined temperature (for example, the temperature every 1 ° C) from the starting temperature of the urea water detected when the engine is started (ignition is turned on). In this state, every time the detection value of the temperature sensor 31 reaches the diagnostic temperature, the frozen state of the urea water is determined. By doing so, the temperature at which the solution in the urea water tank 21 is melted can be detected. Further, by comparing the melting temperature and the melting point (minimum value TE0) at the time of normal quality, it is possible to know the degree of quality abnormality in the solution stored in the urea water tank 21.

  In the determination of the freezing of urea water, the urea water pump 23 is driven to determine the frozen state of the urea water every time the detected value of the temperature sensor 31 reaches the diagnostic temperature. That is, the urea water pump 23 is repeatedly turned on and off to diagnose the urea water quality abnormality.

  However, if the urea water pump 23 is repeatedly turned on and off at a temperature higher than the melting point of the urea water, the urea water supply to the urea water addition valve 15 may be hindered. Therefore, the determination of the frozen state by repeatedly turning the urea water pump 23 on and off may be performed in a temperature region on the lower temperature side than the melting point. This is because the time during which the urea water pump 23 is turned on in the temperature region lower than the melting point of the urea water is reduced, so that the load on the urea water pump 23 can be reduced. In addition, when the engine is started, an abnormality diagnosis is performed for each predetermined temperature as the temperature of the urea water increases due to the circulation of the engine cooling water, so that the melting temperature of the urea water can be detected.

  In the above quality abnormality diagnosis process, two points (for example, TE0 ± 1 [° C]) set near the freezing point (minimum value TE0 [° C]) at the specified concentration CNH and on the low temperature side and the high temperature side of the freezing point, respectively. Is the diagnosis temperature, and when the detected value of the temperature sensor 31 reaches the diagnosis temperature, the urea water pump 23 is driven for a predetermined short time to determine the frozen state of the urea water. According to this configuration, the quality abnormality diagnosis of urea water can be performed while minimizing the time during which the urea water pump 23 is turned on in the temperature region lower than the melting point. Further, the urea water freezing abnormality may be diagnosed using a temperature set near the freezing point (minimum value TE0) at the specified concentration CNH and set to the low temperature side or the high temperature side of the freezing point as a diagnosis temperature. According to such a configuration, it is possible to detect either a concentration abnormality or a mixing abnormality among quality abnormalities.

  In the above embodiment, the freezing determination is performed based on the detection value of the pressure sensor 32 when the urea water pump 23 is driven, but the freezing determination method is not limited to this. For example, the freezing determination is performed based on the detection value of the temperature sensor 31. Specifically, the determination is made based on the difference between the temperature at which the solid urea water starts to melt and the temperature at which it ends, or based on the length of the period during which the temperature is constant.

  A so-called in-line system in which the urea water pump 23 is not immersed in the urea water in the urea water tank 21 in the middle of the urea water supply pipe 22 is applied to the present invention. A so-called in-tank system provided in a state immersed in urea water in the tank 21 may be applied to the present invention.

  In addition to being put into practical use as a urea water SCR system for in-vehicle diesel engines, it can also be put into practical use as a urea water 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 apparatus), 21 ... Urea water tank (reducing agent tank), 22 ... Urea water supply pipe (Reducing agent passage), 23 ... urea water pump (pump), 31 ... temperature sensor (temperature detection means), 32 ... pressure sensor, 33 ... cooling water passage (heat supply means), 40 ... ECU (state detection means, abnormality) Diagnostic means).

Claims (9)

A reducing agent tank for storing a reducing agent solution; a selective reduction catalyst that is provided in an exhaust passage of an internal combustion engine and selectively purifies nitrogen oxides in exhaust gas by the reducing agent solution; and a reducing agent passage in the reducing agent tank. Is applied to an exhaust purification system including a reducing agent addition device that is connected to the reducing agent tank in the reducing agent tank and is added to the exhaust upstream side of the selective catalytic reduction catalyst.
Temperature detecting means for detecting the temperature of the reducing agent solution in the reducing agent tank;
State detecting means for detecting a frozen state of the reducing agent solution in the reducing agent tank;
An abnormality diagnosis means for performing an abnormality diagnosis on the quality of the reducing agent solution based on the solution temperature detected by the temperature detection means and the frozen state detected by the state detection means;
Heat supply means for supplying heat to the reducing agent solution in the reducing agent tank by starting the internal combustion engine ,
The abnormality diagnosis device for an exhaust gas purification system, wherein the abnormality diagnosis means performs an abnormality diagnosis on the quality of the reducing agent solution during a predetermined start period after the internal combustion engine is started . The abnormality diagnosing means relates to the quality of the reducing agent solution when the solution temperature is lower than a predetermined specified temperature that is predetermined as the melting point of the reducing agent solution and the reducing agent solution is not frozen. The abnormality diagnosis device for an exhaust purification system according to claim 1, wherein it is determined that there is an abnormality in mixing that liquid other than the reducing agent solution is mixed as an abnormality. A reducing agent tank for storing a reducing agent solution; a selective reduction catalyst that is provided in an exhaust passage of an internal combustion engine and selectively purifies nitrogen oxides in exhaust gas by the reducing agent solution; and a reducing agent passage in the reducing agent tank. Is applied to an exhaust purification system including a reducing agent addition device that is connected to the reducing agent tank in the reducing agent tank and is added to the exhaust upstream side of the selective catalytic reduction catalyst.
Temperature detecting means for detecting the temperature of the reducing agent solution in the reducing agent tank;
State detecting means for detecting a frozen state of the reducing agent solution in the reducing agent tank;
An abnormality diagnosis means for performing an abnormality diagnosis on the quality of the reducing agent solution based on the solution temperature detected by the temperature detection means and the frozen state detected by the state detection means ,
The abnormality diagnosing means relates to the quality of the reducing agent solution when the solution temperature is lower than a predetermined specified temperature that is predetermined as the melting point of the reducing agent solution and the reducing agent solution is not frozen. An abnormality diagnosis apparatus for an exhaust gas purification system, characterized in that it is determined that there is an abnormality in mixing that liquid other than the reducing agent solution is mixed as an abnormality. The reducing agent solution is set to a concentration that is the lowest melting point as the lowest melting point in the aqueous solution containing the reducing agent,
The abnormality diagnosing means, when it is detected that the solution temperature is higher than the minimum melting point and the reducing agent solution is frozen, the reducing agent concentration is normal as an abnormality relating to the quality of the reducing agent solution. The abnormality diagnosis device for an exhaust purification system according to any one of claims 1 to 3, wherein it is determined that there is a concentration abnormality different from the time. A reducing agent tank for storing a reducing agent solution; a selective reduction catalyst that is provided in an exhaust passage of an internal combustion engine and selectively purifies nitrogen oxides in exhaust gas by the reducing agent solution; and a reducing agent passage in the reducing agent tank. Is applied to an exhaust purification system including a reducing agent addition device that is connected to the reducing agent tank in the reducing agent tank and is added to the exhaust upstream side of the selective catalytic reduction catalyst.
Temperature detecting means for detecting the temperature of the reducing agent solution in the reducing agent tank;
State detecting means for detecting a frozen state of the reducing agent solution in the reducing agent tank;
An abnormality diagnosis means for performing an abnormality diagnosis on the quality of the reducing agent solution based on the solution temperature detected by the temperature detection means and the frozen state detected by the state detection means ,
The reducing agent solution is set to a concentration that is the lowest melting point as the lowest melting point in the aqueous solution containing the reducing agent,
The abnormality diagnosing means, when it is detected that the solution temperature is higher than the minimum melting point and the reducing agent solution is frozen, the reducing agent concentration is normal as an abnormality relating to the quality of the reducing agent solution. An abnormality diagnosis device for an exhaust purification system, characterized in that it is determined that there is a concentration abnormality different from the time . The abnormality diagnosis means relates to the quality of the reducing agent solution at different temperatures within the same temperature range when the solution temperature is within a temperature range in the vicinity of a predetermined specified temperature that is predetermined as the melting point of the reducing agent solution. The abnormality diagnosis device for an exhaust purification system according to any one of claims 1 to 5 , wherein abnormality diagnosis is performed. A reducing agent tank for storing a reducing agent solution; a selective reduction catalyst that is provided in an exhaust passage of an internal combustion engine and selectively purifies nitrogen oxides in exhaust gas by the reducing agent solution; and a reducing agent passage in the reducing agent tank. Is applied to an exhaust purification system including a reducing agent addition device that is connected to the reducing agent tank in the reducing agent tank and is added to the exhaust upstream side of the selective catalytic reduction catalyst.
Temperature detecting means for detecting the temperature of the reducing agent solution in the reducing agent tank;
State detecting means for detecting a frozen state of the reducing agent solution in the reducing agent tank;
An abnormality diagnosis means for performing an abnormality diagnosis on the quality of the reducing agent solution based on the solution temperature detected by the temperature detection means and the frozen state detected by the state detection means ,
The abnormality diagnosis means relates to the quality of the reducing agent solution at different temperatures within the same temperature range when the solution temperature is within a temperature range in the vicinity of a predetermined specified temperature that is predetermined as the melting point of the reducing agent solution. An abnormality diagnosis device for an exhaust purification system, characterized by performing abnormality diagnosis. 8. The apparatus according to claim 1, further comprising means for detecting a melting point of the solution stored in the reducing agent tank by detecting a temperature at which the reducing agent solution changes from a frozen state to a thawed state. An abnormality diagnosis device for an exhaust purification system according to claim 1. Applied to an exhaust purification system comprising a pump for feeding the reducing agent solution in the reducing agent tank to the reducing agent addition device;
The abnormality diagnosis device for an exhaust purification system according to any one of claims 1 to 8 , wherein the pump is provided in a state in which the pump is not immersed in the reducing agent solution in the reducing agent tank in the middle of the reducing agent passage.

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