JP6142530B2 - Urea water consumption diagnostic device for urea SCR - Google Patents

Description

  The present invention relates to a urea SCR system that selectively reduces NOx in exhaust gas of an engine using urea water, and in particular, urea water consumption diagnosis for urea SCR that can accurately diagnose the amount of urea water injected by a dosing valve. It relates to the device.

  As an exhaust gas purification system for purifying NOx in the exhaust gas of a diesel engine, a selective catalytic reduction system (SCR system) using a selective reduction catalyst has been developed.

  This SCR system supplies urea water stored in a urea water tank upstream of the exhaust gas of the SCR device, hydrolyzes urea water with the heat of the exhaust gas, generates ammonia, and this ammonia generates a catalyst in the SCR device. NOx is reduced and purified. The urea water is supplied upstream of the exhaust gas of the SCR by being injected from a dosing valve provided on the upstream side of the SCR device.

  The urea water is supplied to the dosing valve by a supply module including a supply module pump (SM pump) and a urea water pressure sensor. The supply module is connected to the urea water tank through the suction line, and supplies urea water sucked up from the urea water tank through the suction line to the dosing valve through a pressure feed line connecting the supply module and the dosing valve. The dosing valve is controlled by a DCU (dosing control unit), and the dosing valve is controlled to open and close in accordance with the detected value of a NOx sensor provided downstream of the SCR device to adjust the urea injection amount.

The level of urea water in the urea water tank is detected by a urea water sensor provided in the urea water tank, and the remaining amount of urea water is detected from the level of urea water detected by the urea water sensor to replenish urea water. It is used as a guide (see, for example, Patent Documents 1 and 2) .

JP 2011-247137 A JP 2012-2061 A

  By the way, there is no means for detecting when the inside of the dosing valve for injecting urea water into the NOx catalyst and the inside of the pumping line reaching there are clogged with foreign substances. Further, there is a problem that there is no means for detecting the dosing valve even when the dosing valve is fixed in an open state due to adhesion of foreign matter or the like.

  About the consumption amount of this urea water, if the level change of the urea water sensor in a urea water tank is detected, the consumption amount can be estimated roughly.

  Therefore, the difference between the instructed injection amount of the urea water in the DCU and the actual injection amount in accordance with the instruction, that is, the consumption amount based on the detected value of the urea water sensor, is monitored, and the difference in the injection at the dosing valve is determined based on the difference. However, the detection accuracy of the urea water sensor detects the urea level step by step, and there is a problem that the detection accuracy is poor.

  The inventors of the present invention use the value when the consumption level changes more than the error range of the urea water sensor as the determination amount, and on the other hand, integrate the command injection amount with the DCU, and when the integrated command injection amount exceeds the determination amount In addition, the difference between the integrated command injection amount and the consumption amount due to the level change obtained from the urea water sensor is compared. Invented a diagnostic device that can determine the presence or absence of the above even if it is bad.

  If the urea water tank is replenished while the integrated consumption amount reaches the determination amount, it is necessary to add the replenishment amount to the calculated consumption amount. When detecting the replenishment amount, considering the rise in the liquid level due to the inclination of the vehicle, the design error of the sensor itself, etc., the time when there is a change greater than the value K1 between the two error ranges is recognized as replenishment It is necessary to add the replenishment amount to the consumption amount detected by the urea water sensor.

  However, if a replenishment amount smaller than the value K1 is performed, the amount becomes a detection error and is not regarded as a replenishment amount. If this is repeated, the error amount of the consumption amount actually consumed becomes large, resulting in an erroneous determination. Leave the problem to be.

  As a countermeasure, it is monitored whether or not the NOx value by the NOx sensor is normal. When the cumulative consumption is small with respect to the cumulative command injection amount and the deviation is large, if the NOx value is normal, a small amount is replenished. It has been proposed to determine that the urea water injection path is abnormal only when the NOx value is abnormal, and determine that there is an abnormality such as clogging of the urea water injection, without determining that it has been repeated.

  However, when the urea water sensor is fixed, there is a case where there is no change in the integrated consumption amount, and the deviation amount between the integrated instruction injection amount and the consumption amount becomes large.

  In this case, the NOx value is normal when the dosing valve is stuck in the open state and the urea water is continuously sprayed, and it is not possible to determine whether there is an abnormality based on the detected value of the NOx sensor. .

Accordingly, the object of the present invention is to solve the above-mentioned problems, and even if the change in the amount of urea water replenished to the urea water tank cannot be detected, and the actual consumption amount cannot be detected, the pumping line and the dosing valve are clogged or stuck with foreign matter. It is an object of the present invention to provide a urea water consumption diagnostic device for urea SCR capable of detecting a state or a state where urea water is continuously sprayed by a dosing valve.

In order to achieve the above object, the present invention provides a urea SCR for sucking urea water in a urea water tank with a supply pump and injecting the urea water from a dosing valve provided on the upstream side of the SCR device via a pressure feed line. In the urea water consumption diagnostic apparatus for use, a urea water sensor for detecting the level of urea water in the urea water tank, consumption calculation means for calculating an integrated consumption from a detection value input from the urea water sensor, An injection amount indicating means for instructing the amount of urea water to be injected from the dosing valve in accordance with NOx in the exhaust gas, and an instruction injection amount integration for calculating the integrated instruction injection amount by integrating the instruction injection amounts instructed by the injection amount instruction means Means, and abnormality diagnosis means for determining the presence or absence of a stack of the urea water sensor,
The abnormality diagnosing means determines the vehicle speed when the integrated command injection amount reaches a set value that corresponds to a value that causes a change in the urea water sensor output and is smaller than the determination amount before the cumulative command injection amount reaches the determination amount. The presence or absence of a stack of the urea water sensor by comparing the level change of the urea water sensor when traveling is not zero with a predetermined value,
The abnormality diagnosis unit is a urea water consumption diagnosis device for urea SCR, which determines that the urea water sensor is stuck when the level change of the urea water sensor is smaller than the predetermined value.

  A NOx sensor provided downstream of the SCR device;
  The abnormality diagnosis means determines that the urea water sensor is not stacked when the level change of the urea water sensor is equal to or greater than the predetermined value;
  When the abnormality diagnosis unit determines that the urea water sensor is not stacked, the abnormality diagnosis unit compares the integrated instruction injection amount when the integrated instruction injection amount reaches the determination amount and the integrated consumption amount, Determine whether the urea water injection by the dosing valve is normal or abnormal,
  The abnormality diagnosing means determines that urea water is replenished to the urea water tank little by little when the cumulative command injection amount exceeds a certain amount with respect to the cumulative consumption, and when the detected value of the NOx sensor is normal. When the urea water injection is determined to be normal and the detected value of the NOx sensor is abnormal, it is preferable to determine that the urea water injection is abnormal.

  Preferably, the abnormality diagnosing means determines that the urea water injection is abnormal regardless of the detected value of the NOx sensor when the integrated consumption exceeds a certain amount with respect to the integrated instruction injection amount.

  In another aspect of the present invention, urea water for urea SCR for sucking urea water in a urea water tank with a supply pump and injecting the urea water from a dosing valve provided on the upstream side of the SCR device via a pressure feed line. In the consumption diagnostic device,
A urea water sensor for detecting the level of urea water in the urea water tank; consumption calculation means for calculating an integrated consumption from a detection value input from the urea water sensor; and the dosing according to NOx in the exhaust gas. An injection amount instruction means for instructing the amount of urea water to be injected from the valve, an instruction injection amount integration means for calculating the integrated instruction injection amount by integrating the instruction injection amounts instructed by the injection amount instruction means, and a stack of the urea water sensor An abnormality diagnosis means for determining the presence or absence of
  The abnormality diagnosing means determines the vehicle speed when the integrated command injection amount reaches a set value that corresponds to a value that causes a change in the urea water sensor output and is smaller than the determination amount before the cumulative command injection amount reaches the determination amount. The presence or absence of a stack of the urea water sensor by comparing the level change of the urea water sensor when traveling is not zero with a predetermined value,
  The abnormality diagnosis means determines that the urea water sensor is not stacked when the level change of the urea water sensor is equal to or greater than the predetermined value;
  When the abnormality diagnosis unit determines that the urea water sensor is not stacked, the abnormality diagnosis unit compares the integrated instruction injection amount when the integrated instruction injection amount reaches the determination amount and the integrated consumption amount, A urea water consumption diagnostic device for urea SCR, which determines whether urea water injection by a dosing valve is normal or abnormal.

The present invention relates to urea water during traveling when the vehicle speed is not zero when the cumulative command injection amount reaches a set value that corresponds to a value at which the output of the urea water sensor changes before reaching the determination amount and is smaller than the determination amount. Compare the sensor level change with a predetermined value to determine whether there is a urea water sensor stack, and then compare the integrated command injection amount with the cumulative consumption when the integrated command injection amount reaches the determination amount By this, it becomes possible to detect the clogging of the dosing valve and the pressure feed line, and the failure to keep spraying due to the dosing valve open fixing.

It is the schematic of the SCR system in this invention. It is a figure which shows the flowchart of the consumption diagnosis of the urea water consumption diagnostic apparatus for urea SCR of this invention.

  A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 shows an outline of an SCR system. A SCR device 11 is connected to an exhaust pipe 10 of a diesel engine (not shown), and a dosing valve that injects urea water upstream of the SCR device 11. 12 is provided, and a NOx sensor 13 is provided downstream of the SCR device 11.

  The detected value of the NOx sensor 13 is input to a DCU (Dosing Control Unit) 14, and the dosing valve 12 is controlled to open and close by the DCU 14 so that the NOx purification rate falls within a predetermined range based on the detected value.

  The urea water U injected from the dosing valve 12 is stored in the urea water tank 15, sucked into the supply pump 18 of the supply module 17 from the suction line 16, foreign matter is removed from the supply pump 18 through the filter 19, and the pressure feed line 20. Is pumped to the dosing valve 12. Excess urea water U is returned from the pumping line 20 on the discharge side of the filter 19 into the urea water tank 15 through the return line 21.

  A urea water sensor 22 is provided in the urea water tank 15, and the urea water sensor 22 measures the level of the urea water in the urea water tank 15 and transmits it to the DCU 14. The pressure feed line 20 is provided with a urea water pressure sensor 23 for detecting the supply pressure of the urea water, and the detected pressure is transmitted to the DCU 14.

  The DCU 14 calculates the amount and timing of injecting urea water to the SCR device 11, drives the supply pump 18 to increase the urea water to a specified pressure, controls opening and closing of the dosing valve 12, and controls an appropriate amount at an appropriate timing. Spray.

  The NOx sensor 13 sends a measured value to the DCU 14 in order to monitor that the NOx value in the exhaust gas downstream of the SCR device 11 is steady due to the appropriate injection of urea water from the dosing valve 12. Send.

  The DCU 14 is connected to an ECM (engine control module) 26 that mainly performs fuel injection control. The ECM 26 receives vehicle speed, parking brake switch, and other driving information, and these are transmitted from the ECM 26 to the DCU 14.

  Further, the battery 24 is connected to the DCU 14 and the ON / OFF signal of the ignition key 25 is input.

  In this SCR system, the DCU 14 determines the injection amount of urea water to be injected from the dosing valve 12 based on the information of the ECM 26 so that the detected value of the NOx sensor 13 becomes steady, and the dosing valve 12 based on the determined value. Open / close control.

  First, in the abnormality diagnosis of urea water consumption, the injection amount instruction means 30 for instructing the DCU 14 the amount of urea water to be injected from the dosing valve 12 based on the information of the ECM 26 and the detected value of the NOx sensor 13, and the injection amount instruction means 30 From the command injection amount integration means 31 that integrates the command injection amount instructed in step, the consumption amount calculation means 32 that calculates the total consumption amount D from the detection value input from the urea water sensor 22, and the command injection amount integration means 31 Comparing the integrated instruction injection amount P with the integrated consumption amount D from the consumption calculation means 32, an abnormality diagnosis means 33 for determining whether the urea water injection by the dosing valve 12 is normal or abnormal is provided.

  When the abnormality diagnosis is started, the integrated command injection amount P of the command injection amount integration unit 31 is reset to zero, and at the same time, the consumption calculation unit 32 stores the level detected by the urea water sensor 22 as a level (S0). To do. Thereafter, when the vehicle travels and urea water is injected from the dosing valve 12, the command injection amount integration unit 31 sequentially integrates the command injection amount by the injection amount instruction unit 30 and stores the cumulative command injection amount P.

  In order to detect whether the urea water injection in the abnormality diagnosis means 33 is normal or abnormal, the detection accuracy does not increase unless the urea water is consumed to some extent (for example, the consumption amount is several tens to several tens of liters). Consumed when the vehicle travels several times, that is, when the ignition key 25 is repeatedly turned on and off, and the integrated command injection amount P in the command injection amount integration means 31 exceeds a determination amount L (for example, 15 L). The integrated consumption amount D in the amount calculation means 32 and the integrated instruction injection amount P are compared, and it is determined whether | D−P |> K1.

  In this determination, if urea water is properly injected, the integrated consumption amount D and the integrated instruction injection amount P are the same, and if the urea solution sensor 22 is less than the value K1 determined by the level measurement error range, It is diagnosed as normal, and if it is K1 or more, it is determined as abnormal. At this time, by comparing the absolute value of the difference between the two, D << P and DP are negative when there is no injection due to foreign matter or the like, and D >> P and D >> P when the dosing valve 12 continues to spray. -P becomes positive, and it can be determined from the plus or minus that clogging due to sticking and whether or not the dosing valve 12 remains sprayed.

  Further, since the urea water tank 15 is replenished with urea water, the consumption amount calculation means 32 detects the level of the level sensor by the urea water sensor 22 at the ON / OFF timing of the key switch, and the consumption amount calculating means 32 determines the replenishment amount. Judging. That is, the consumption calculating means 32 integrates the replenishment amount from the start of control to the time of diagnosis, and obtains the accumulated consumption amount D of urea water by adding the integrated replenishment amount to the actual level change.

  However, there are two cases where the output of the urea water sensor does not change even when the DCU command injection amount reaches a certain amount. One is when the detection unit (float) of the urea water sensor is fixed, and the other is when a small amount of replenishment that the DCU cannot recognize as replenishment is performed.

  The sticking of the urea water sensor 22 can be detected in Patent Document 1, but when the pumping line 20 is blocked or the dosing valve 12 remains in a sticking state, these cannot be detected. When a small amount is replenished, an occlusion cannot be detected.

  Therefore, in the present invention, first, the abnormality diagnosis unit 33 performs integration corresponding to a value (for example, 2 to 5 L) at which the level of the urea water sensor 22 is surely changed before the integrated instruction injection amount reaches the determination value. By setting the command injection amount as a set value A and determining the level change of the urea water sensor 22 when the set value A is reached, it is detected that the urea water sensor 22 is stuck and stuck.

  Next, in order to distinguish from the stack of urea water sensors 22, the abnormality diagnosis means 33 determines whether the output of the urea water sensor 22 shows a change greater than a certain value when the vehicle speed is not zero, that is, during traveling. To do. This change is the result of the level of the urea water U in the urea water tank 15 swaying. In this case, it is determined that there is no stack and a small amount of replenishment is performed and there is no change in the output of the level sensor. The presence or absence of abnormality is determined from the detected value of 13 and the NOx purification rate. In this case, when the value of the NOx sensor 13 (or NOx purification rate) is normal, it is not determined that the consumption is abnormal, and when the NOx value or the like is abnormal, it is determined that there is an abnormality.

As for the distinction between the case where urea water is replenished little by little and the case where the urea water sensor is stacked, the NOx purification rate by the NOx sensor 13 is monitored by the NOx purification rate determination means 34, and the NOx purification rate is within the normal range. When the cumulative consumption is small with respect to the cumulative command injection amount at or above the predetermined value Q, it is determined that a small amount of replenishment is repeated and that there is a difference between the DCU command injection amount and the urea water consumption by the urea water sensor. Therefore, it is determined that the consumption amount is abnormal only when the NOx value is less than the specified value Q and the integrated consumption amount exceeds the threshold with respect to the integrated instruction injection amount.

Moreover, integration dictates against consumption of accumulated consumption large deviation rate plus side abnormal injection amount, regardless of the NOx purification ratio, it is determined that the consumption anomaly only deviation accumulated instructed injection amount and the accumulated consumption .

  The determination of the purification rate of the NOx purification rate determination means 34 will be described.

  The injection amount instruction means 30 determines the instruction injection amount of urea water so that the detected value of the NOx sensor 13 falls within a steady range. However, even if the NOx sensor 13 can detect the NOx concentration on the downstream side of the SCR device 11, it cannot detect the NOx concentration in the exhaust gas flowing into the SCR device 11.

  The NOx purification rate determination means 34 obtains a purification rate from the commanded injection amount by the injection amount instruction means 30 and the NOx concentration detected by the NOx sensor 13, and determines whether or not the purification rate is equal to or greater than a specified value Q. Is.

That is, when 1 mol of urea ((NH ₂ ) ₂ CO) is hydrolyzed, 2 mol of ammonia (NH ₃ ) is generated, and this ammonia reacts with NOx (NO, NO ₂ ) to react with nitrogen and water. Therefore, there is a correlation between the amount of urea injected and the NOx concentration detected by the NOx sensor, and the NOx concentration on the inlet side of the SCR device 11 can be estimated from the injection amount. The NOx concentration on the inlet side and the outlet side can be estimated. The purification rate can be obtained from the NOx concentration. Therefore, the NOx purification rate determination means 34 obtains the NOx concentration on the inlet side from the commanded injection amount, and obtains the purification rate from the obtained inlet NOx concentration and the NOx concentration detected by the NOx sensor. In this case, although the inlet NOx concentration varies depending on the operating state of the engine, the NOx value released from the exhaust pipe 10 only needs to be equal to or less than the legal regulation value. Therefore, the specified value Q of the purification rate is matched to the engine characteristics. For example, it is set to 90% or more.

  This will be described with reference to the flowchart of FIG.

  When diagnosis is started in step S1 and the key switch is turned on (step S2), the initial level sensor position (S0) is read and stored by the urea water sensor (step S3). Next, in step S4, it is determined whether the vehicle speed is 0 km and the parking brake switch is ON. When the vehicle is stopped (Yes), the level sensor position (S0 ′) is repeatedly read, and urea water is replenished during the stop. If there is, the level S0 ′ is stored and updated with the maximum value (step S5). When the vehicle travels in this step S4 (No), the difference between the initially stored level S0 and the level S0 ′ stored during the stop (S0′−S0) is the detection accuracy of the urea water sensor. It is determined whether or not the value (K1) greater than or equal to the error range is larger (S0′−S0> K1). If it is determined in step S4 that the level is higher than the error range (Yes), S0′−S0 = Rp1 is set, and the replenishment amount is added to the integrated replenishment amount RΣ (step S7). The process proceeds to step S8 for starting the amount integration, and if the level S0 ′ is within the error range with respect to the first level S0 (No), the process proceeds to step S8. In step S8 for starting the command injection amount integration, the command injection amount is integrated until the key switch is turned off in step S9, and urea water is stored as level S0.

Next, in step S9, the cumulative command injection amount is determined, and when the cumulative command injection amount reaches the set value A corresponding to a value at which the urea water sensor 22 can change level reliably (Yes), step In S10, the input change amount of the urea water sensor is checked, and whether or not the urea water change amount is equal to or more than a value B obtained by adding the level change value to the first level S0, or the urea water sensor 22 shakes while traveling. If there is no change from the first level S0 or if the level change by the urea water sensor 22 cannot be detected (No), it is determined that the urea water sensor is stuck (step S11). Then, the integrated command injection amount is reset (step S12) and returned to the upstream of step S3. At this time, the driver is warned with a warning lamp or the like that the urea water sensor 22 is stuck.

  If it is determined in step S10 that there is no urea water sensor stack (Yes), the vehicle travels as it is, and the commanded injection amount integration is continued.

  Next, when the key switch is turned off in step S13, the level sensor position S1 after the first run from the start of control is read, and the accumulated consumption amount D (= S1-S0) of urea water at that time is stored. (Step S14).

  Next, when the key switch is turned on in step S15, it is determined in step S16 whether or not the cumulative command injection amount P by the previous travel has reached the determination amount L (P ≧ L). This determination amount L is set to, for example, 15 L in the range of several L to several tens of L, which is larger than the value A corresponding to the set value of the integrated instruction injection amount.

  If it is determined in step S16 that the cumulative instruction injection amount P of urea water has not reached the determination amount L (No), the process proceeds to step S17, and the level sensor position (S1 + n) is read and stored. Next, in step S18, the stored level (S1 + 1) is compared with level S1 before the key switch is turned on in step S15, and it is determined whether or not S1 + n−S1> K1, and urea water is replenished. If there is no replenishment (No), the process proceeds to step S21. If there is replenishment (Yes), S1 + n−S1 = R1 is calculated in step S19, and R1 is stored as a replenishment amount. In step S20, the replenishment amount R1 is added to the integrated replenishment amount RΣ, and the process proceeds to step S21. In step S21, the command injection amount integration is continued. Thereafter, if the key switch is turned off in step S22, the level sensor position (S2 + n) is read in step S23, and the integrated consumption D (= S2 + n-S1) is calculated and stored based on the level (S2 + n). Return to the upstream side of step S15.

Next, when the key switch is turned ON in step S15, it is determined again in step S16 whether or not the urea water cumulative command injection amount P has reached the determination amount L. When the integrated command injection amount P has not reached the determination amount L, the process returns from step S17 to S123 described above to step S15 and continues to integrate the command injection amount .

  If it is determined in step S16 that the cumulative command injection amount P has reached the determination amount L (Yes), it is determined in step S24 whether the cumulative replenishment amount RΣ = 0, or if there is no replenishment (Yes), in step S26. , | D−P |> K1, and when there is replenishment (No), in step S25, D is corrected at the time of replenishment (D = S2 + 1−S1 + RΣ), and the process returns to the determination in step S26.

  If the injection of urea water from the dosing valve is normal in the determination of step S26, the integrated consumption amount D and the integrated instruction injection amount P are substantially the same and 0, and are within the detection error value K1 (No ), It is determined in step S27 that the consumption is normal, and the control is terminated (step S32).

If the absolute value (| DP |) is compared with K1 in step S26 and the absolute value is larger than K1 (YES), a determination is made in step S28 as to whether or not the cumulative consumption amount D> the cumulative command injection amount P. .

  If the dosing valve is open and stuck in step S28, the cumulative consumption amount D is sufficiently larger than the cumulative command injection amount P (Yes), so it is determined in step S30 that the consumption amount is abnormal.

  When the cumulative consumption amount D is smaller than the cumulative command injection amount P, it is determined in step S29 whether the range of the NOx purification rate is equal to or greater than the specified value Q, and when the purification rate is less than the specified value Q (No). Since a dosing valve or the like is fixed, it is determined in step S30 that the consumption is abnormal.

In addition, when the determination in step S29 is equal to or greater than the specified value Q (Yes), it is a time when the replenishment amount has not been added to the integrated consumption amount D, and since there is no abnormality, the integrated instruction injection amount is reset (step S31). Thereafter, the control is terminated (step S32).

  In the above-described flow, the example in which the presence / absence of blockage is determined based on the NOx purification rate has been described. However, the presence / absence of blockage may be determined based on the detection value of the NOx sensor 13.

DESCRIPTION OF SYMBOLS 10 Exhaust pipe 11 SCR apparatus 12 Dosing valve 13 NOx sensor 15 Urea water tank 22 Urea water sensor 23 Urea water pressure sensor 30 Injection amount instruction means 31 Instruction injection amount integration means 32 Consumption amount calculation means 33 Abnormality diagnosis means 34 NOx purification rate determination means

Claims (4)

In the urea water consumption diagnostic device for urea SCR for sucking urea water in the urea water tank with a supply pump and injecting it from a dosing valve provided upstream of the SCR device via a pressure feed line,
A urea water sensor for detecting the level of urea water in the urea water tank; consumption calculation means for calculating an integrated consumption from a detection value input from the urea water sensor; and the dosing according to NOx in the exhaust gas. An injection amount instruction means for instructing the amount of urea water to be injected from the valve, an instruction injection amount integration means for calculating the integrated instruction injection amount by integrating the instruction injection amounts instructed by the injection amount instruction means, and a stack of the urea water sensor An abnormality diagnosis means for determining the presence or absence of
The abnormality diagnosing means determines the vehicle speed when the integrated command injection amount reaches a set value that corresponds to a value that causes a change in the urea water sensor output and is smaller than the determination amount before the cumulative command injection amount reaches the determination amount. The presence or absence of a stack of the urea water sensor by comparing the level change of the urea water sensor when traveling is not zero with a predetermined value,
The urea water consumption diagnosis apparatus for urea SCR, wherein the abnormality diagnosis means determines that the urea water sensor is stuck when the level change of the urea water sensor is smaller than the predetermined value. A NOx sensor provided downstream of the SCR device;
The abnormality diagnosis means determines that the urea water sensor is not stacked when the level change of the urea water sensor is equal to or greater than the predetermined value;
When the abnormality diagnosis unit determines that the urea water sensor is not stacked, the abnormality diagnosis unit compares the integrated instruction injection amount when the integrated instruction injection amount reaches the determination amount and the integrated consumption amount, Determine whether the urea water injection by the dosing valve is normal or abnormal,
The abnormality diagnosing means determines that urea water is replenished to the urea water tank little by little when the cumulative command injection amount exceeds a certain amount with respect to the cumulative consumption , and when the detected value of the NOx sensor is normal. and it is determined that the normal urea water injection, when the detection value of the NOx sensor is abnormal, abnormality is judged claim 1 urea SCR for urea water consumption diagnostic apparatus according urea water injection. The abnormality diagnosis means, when the accumulated consumption to the accumulated instructed injection amount exceeds a predetermined amount, for a urea SCR according to claim 2, wherein determining that abnormal depend not urea water injection to the detection value of the NOx sensor Urea water consumption diagnostic device.   In the urea water consumption diagnostic device for urea SCR for sucking urea water in the urea water tank with a supply pump and injecting it from a dosing valve provided upstream of the SCR device via a pressure feed line,
A urea water sensor for detecting the level of urea water in the urea water tank; consumption calculation means for calculating an integrated consumption from a detection value input from the urea water sensor; and the dosing according to NOx in the exhaust gas. An injection amount instruction means for instructing the amount of urea water to be injected from the valve, an instruction injection amount integration means for calculating the integrated instruction injection amount by integrating the instruction injection amounts instructed by the injection amount instruction means, and a stack of the urea water sensor An abnormality diagnosis means for determining the presence or absence of
  The abnormality diagnosing means determines the vehicle speed when the integrated command injection amount reaches a set value that corresponds to a value that causes a change in the urea water sensor output and is smaller than the determination amount before the cumulative command injection amount reaches the determination amount. The presence or absence of a stack of the urea water sensor by comparing the level change of the urea water sensor when traveling is not zero with a predetermined value,
  The abnormality diagnosis means determines that the urea water sensor is not stacked when the level change of the urea water sensor is equal to or greater than the predetermined value;
  When the abnormality diagnosis unit determines that the urea water sensor is not stacked, the abnormality diagnosis unit compares the integrated instruction injection amount when the integrated instruction injection amount reaches the determination amount and the integrated consumption amount, A urea water consumption diagnostic device for urea SCR, which determines whether urea water injection by a dosing valve is normal or abnormal.