JP2015040494A - Abnormality detection device for urea water addition valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abnormality detection device for a urea water addition valve, capable of detecting the occurrence of abnormality in the operation of the urea water addition valve with high reliability.SOLUTION: In abnormality diagnosis processing to be executed by the abnormality detection device, urea water is filled in a urea water pipe 18 by driving a urea water pump 17 while outputting a valve closing signal to a urea water addition valve 15. In the filling period, when a pump rotating speed Np detected by a pressure sensor 21 is a predetermined determination value Na or higher, the urea water addition valve 15 is determined to be opened and fixed. Furthermore, the temperature of the urea water addition valve 15 is estimated, and the determination value Na is corrected on the basis of an estimated temperature θ so that the determination value Na is higher as the estimated temperature θ is higher.

Description

  The present invention relates to a urea water addition valve abnormality detection device for adding urea water to exhaust gas.

  A urea SCR (Selective Catalytic Reduction) device is known as an exhaust gas purification device for a diesel engine. This urea SCR device includes a urea water addition valve that adds urea water to exhaust gas, and a pump that fills the supply passage to which the urea water addition valve is connected with urea water. In the urea SCR device, urea water is added to the exhaust gas from the urea water addition valve, and nitrogen oxide (NOx) in the exhaust gas is generated using ammonia generated by thermal decomposition and hydrolysis of urea by exhaust heat as a reducing agent. NOx is decomposed into water and nitrogen by performing a reduction reaction on the selective reduction catalyst.

  Further, in such a urea SCR device, when an abnormality occurs in the operation of the urea water addition valve, it is impossible to appropriately add urea water to the selective reduction catalyst. Therefore, in the apparatus described in Patent Document 1, the internal pressure of the supply passage is monitored by the pressure sensor, and the detected value of the pressure sensor when the pressure in the supply passage is reduced is below the threshold value. An abnormality is detected.

JP 2011-117440 A

  By the way, in the urea SCR device, when the pump pumps up the urea water, air is entrained, or the water of the urea water evaporates due to the heat of the supply passage and the urea water addition valve. Such gas is mixed. The gas mixed in the supply passage repeatedly expands and contracts in response to a change in the driving state of the pump, an opening / closing operation of the urea water addition valve, etc. As a result, the detected value of the pressure sensor vibrates. As a result, since the detected value of the pressure sensor includes a transient component caused by such vibration, the abnormality of the urea water addition valve based on the detected value of the pressure sensor as described in Patent Document 1 In detection, the reliability has to be low.

  The present invention has been made in view of such circumstances, and the problem to be solved is a urea water addition valve that can reliably detect that an abnormality has occurred in the operation of the urea water addition valve. An object of the present invention is to provide an abnormality detection device.

  An abnormality detection device for solving the above problem includes a sensor for detecting a rotation speed of a pump, and the rotation speed of the pump detected by the sensor reaches a determination value corrected based on an estimated temperature of a urea water addition valve. Based on the estimated temperature of the urea water addition valve, it detects the abnormality of the urea water addition valve based on the determination of whether or not, or the rotation speed of the pump detected by the sensor changes to reach a predetermined value The abnormality of the urea water addition valve is detected based on the determination as to whether or not the corrected determination time is exceeded.

  When the abnormality occurs in the urea water addition valve, the rotational speed of the pump changes in a manner different from that when the urea valve is normal. And even if the gas of a supply passage repeats expansion and contraction in a short time, the rotational speed of this pump is not easily affected. According to the above configuration, since the abnormality of the urea water addition valve is detected based on the rotation speed of such a pump, the abnormality of the urea water addition valve can be detected with high reliability. In addition, the temperature of the urea water addition valve is estimated, and the determination value and the determination time used when detecting an abnormality are corrected based on the estimated temperature. Even when taking different values depending on the temperature, such temperature dependence can be reflected in the abnormality detection, and the detection accuracy can be improved.

The block diagram which shows typically the whole structure of the exhaust gas purification apparatus by which a urea water addition valve is mounted. The flowchart which shows the execution procedure of the abnormality diagnosis process for detecting open sticking. The graph which shows the relationship between the judgment value for abnormality diagnosis, and the target pressure of urea water pressure. (A) is a driving state of the urea water pump, (b) is a rotation speed thereof, (c) is a urea water pressure, and (d) is a timing chart showing a transition of an open fixing flag when the abnormality diagnosis process is executed. The flowchart which shows the execution procedure of the abnormality diagnosis process for detecting closed fixation. (A) is the driving state of the urea water pump, (b) is its rotational speed, (c) is the urea water pressure, (d) is the driving state of the urea water addition valve, and (e) is closed when the abnormality diagnosis process is executed. The timing chart which shows transition of a sticking flag. The flowchart which shows the execution procedure of the abnormality diagnosis process for detecting the fall of a response speed. The graph which shows the relationship between the determination time for abnormality diagnosis, and the estimated temperature of a urea water addition valve. (A) is a driving state of the urea water pump, (b) is its rotational speed, and (c) is a timing chart showing transition of the responsiveness reduction flag when the abnormality diagnosis process is executed.

[First Embodiment]
Hereinafter, a first embodiment in which an abnormality detection device for a urea water addition valve according to the present invention is embodied will be described. Note that the urea water addition valve to be diagnosed by this abnormality detection device is mounted on an exhaust purification device of a diesel engine.

  As shown in FIG. 1, a diesel particulate filter (DPF: Diesel Particulate Filter) 12, an SCR catalyst unit 13, and an oxidation catalyst unit 14 are disposed in the exhaust passage 11 of the diesel engine 10 in order from the exhaust upstream. Has been. A urea water addition valve 15 that adds urea water to the exhaust gas is installed in a portion of the exhaust passage 11 between the DPF 12 and the SCR catalyst unit 13. The urea water addition valve 15 is opened and closed by electromagnetic force of a solenoid built in the main body.

  The SCR catalyst unit 13 is an exhaust purification unit that purifies NOx in exhaust by selective catalytic reduction, and carries a catalyst that promotes a NOx reduction reaction using ammonia as a reducing agent. Ammonia as a reducing agent is generated by the thermal decomposition and hydrolysis of the urea water added to the exhaust gas by the urea water addition valve 15 with the heat of the exhaust gas. The oxidation catalyst unit 14 has a function of decomposing ammonia that has passed through the SCR catalyst unit 13 by an oxidation reaction.

  The exhaust gas purification apparatus includes a urea water tank 16 that stores urea water, and a urea water pump 17 that pumps the urea water from the urea water tank 16. The urea water pump 17 is connected to the urea water addition valve 15 via the urea water pipe 18. The urea water pumped out by the urea water pump 17 is filled in the urea water pipe 18 and supplied to the urea water addition valve 15 using the urea water pipe 18 as a supply passage.

  A return pipe 19 is connected to the urea water pipe 18. The return pipe 19 is provided with a relief valve 20 that opens when the pressure of urea water filled in the urea water pipe 18 (hereinafter referred to as “urea water pressure Pu”) exceeds a predetermined pressure. When the relief valve 20 is opened, the urea water in the urea water pipe 18 is returned to the urea water tank 16 through the return pipe 19. In addition, a pressure sensor 21 that detects the urea water pressure Pu is installed in the urea water pipe 18.

  In addition to the pressure sensor 21 described above, the control unit 22 of the exhaust purification apparatus includes a rotation speed sensor 23 that detects the rotation speed of the urea water pump 17 (hereinafter referred to as “pump rotation speed Np”), and the bed temperature of the DPF 12. A floor temperature sensor 24 for detecting the outside air temperature, an outside air temperature sensor 25 for detecting the outside air temperature, and the like are electrically connected.

  The control unit 22 executes various processes while referring to the detection results of these sensors. For example, the control unit 22 controls the open / closed state of the urea water addition valve 15. Specifically, by outputting a valve opening signal to the urea water addition valve 15, the urea water addition valve 15 is opened while being energized, and a valve closing signal is output to the urea water addition valve 15. The urea water addition valve 15 is closed in a non-energized state.

  Further, the control unit 22 feedback-controls the pump rotation speed Np so that the urea water pressure Pu detected by the pressure sensor 21 matches a target pressure (hereinafter referred to as “target pressure Pt”). In addition, the control unit 22 performs an abnormality diagnosis process for detecting an abnormality that does not operate while the urea water addition valve 15 is open, that is, an open sticking. Details of the abnormality diagnosis process will be described below.

  In this abnormality diagnosis process, a pump detected by the pressure sensor 21 during a period in which the urea water pump 17 is driven and urea water pipe 18 is filled with urea water while outputting a valve closing signal to the urea water addition valve 15. When the rotation speed Np is equal to or higher than a predetermined determination value Na, it is determined that the urea water addition valve 15 is open and fixed. Further, the temperature of the urea water addition valve 15 is estimated, and the determination value Na is corrected based on the estimated temperature θ so that the determination value Na increases as the estimated temperature θ increases.

Specifically, the abnormality diagnosis process is executed according to the following procedure.
As shown in FIG. 2, in this abnormality diagnosis process, a valve closing signal is output to the urea water addition valve 15, and the driving of the urea water pump 17 is started (step S200, step S210). Next, the temperature of the urea water addition valve 15 is estimated based on the bed temperature and the outside air temperature of the DPF 12 (step S220). The estimated temperature θ of the urea water addition valve 15 becomes higher as the bed temperature of the DPF 12 is higher and the outside air temperature is higher.

  Next, a determination value Na is calculated based on the target pressure Pt of the urea water pressure Pu, and this determination value Na is further corrected based on the estimated temperature θ of the urea water addition valve 15 (step S230). Here, when feedback control for setting the urea water pressure Pu to the target pressure Pt is performed in a state where the urea water addition valve 15 is closed, the pump rotation speed Np converges to a predetermined convergence value. Na is a value obtained by adding a constant considering the individual difference of the urea water pump 17 to the convergence value. Therefore, even if the pump rotation speed Np during the feedback control varies due to individual differences of the urea water pump 17, if the urea water addition valve 15 is not fixed open, the pump rotation speed Np will not exceed the determination value Na. Absent.

  As shown in FIG. 3, the determination value Na increases as the target pressure Pt increases. Further, the determination value Na is corrected based on the estimated temperature θ so as to increase as the estimated temperature θ of the urea water addition valve 15 increases. Next, the pump rotational speed Np is feedback-controlled so that the urea water pressure Pu matches the target pressure Pt (step S240).

Next, it is determined whether or not both of the following two conditions are satisfied (step S250).

a: The urea water pressure Pu is not more than the target pressure Pt. b: The pump rotation speed Np is not less than the determination value Na.

If at least one of the condition a and the condition b is not satisfied (step S250: NO), the processes after step S240 are executed again. If the urea water pressure Pu has converged to the target pressure Pt when the processes in steps S240 and S250 are repeated, this series of processes is terminated.

  On the other hand, when both of the previous condition a and condition b are satisfied (step S250: YES), the open fixation flag Xo indicating that the urea water addition valve 15 is open and fixed is set to “ON” ( In step S260), this series of processing ends.

Next, an example of changes in the pump rotation speed Np and the urea water pressure Pu when the abnormality diagnosis process is executed will be described.
As shown in FIG. 4, when the driving of the urea water pump 17 is started (timing t1), the pump rotation speed Np and the urea water pressure Pu increase. When the urea water addition valve 15 is not open and fixed, the urea water pressure Pu is set to the target pressure Pt and the pump rotational speed Np is set to a predetermined value lower than the determination value Na, as indicated by a solid line in FIG. Converge (timing t3). Therefore, in this case, the open fixing flag Xo is not operated.

  On the other hand, when the urea water addition valve 15 is fixed open, the urea water filled in the urea water pipe 18 flows out from the urea water addition valve 15, so that it is indicated by a two-dot chain line in FIG. In addition, the increase in the urea water pressure Pu is delayed. As a result, the rotation resistance of the urea water pump 17 is reduced and the amount of increase in the pump rotation speed Np is increased as compared with the normal time. When the pump rotation speed Np becomes equal to or higher than the determination value Na, the open sticking flag Xo is set to “ON” (timing t2).

Next, the operation of the present embodiment will be described.
As described above, the urea water pressure Pu detected by the pressure sensor 21 always fluctuates as the gas mixed in the urea water pipe 18 repeats expansion and contraction. For example, when the relief valve 20 is opened and closed, the fluctuation caused by that becomes larger, and it takes a long time for the fluctuation to attenuate. On the other hand, the pump rotation speed Np detected by the rotation speed sensor 23 is not easily influenced even if the gas mixed in the urea water pipe 18 repeatedly expands and contracts, and the urea water pressure detected by the pressure sensor 21 is low. It is more stable than Pu.

  In the present embodiment, the pump rotational speed Np is monitored by the rotational speed sensor 23, and the pump rotational speed Np is compared with the determination value Na to detect the open adhesion of the urea water addition valve 15. The reliability of abnormality detection is improved.

  Even if the urea water addition valve 15 is not open and fixed, urea water may leak slightly from the urea water addition valve 15 in the closed state. The pump rotation speed Np during processing increases. Furthermore, when the temperature of the urea water addition valve 15 increases, the urea water is heated and the viscosity of the urea water leaking from the nozzle hole decreases. For this reason, the leakage amount of urea water increases, and the pump rotation speed Np during the abnormality diagnosis process further increases.

  In the present embodiment, the temperature of the urea water addition valve 15 is estimated, and this is corrected so that the determination value Na increases as the estimated temperature θ increases. That is, when the temperature of the urea water addition valve 15 is high, the pump rotation speed Np when open sticking is detected is higher than when the temperature is low. For this reason, it is possible to avoid erroneous detection that the urea water addition valve 15 is open and fixed due to the influence of leakage of urea water, and the detection accuracy can be improved.

As described above, according to the present embodiment, the following effects can be obtained.
(1) Based on the comparison between the pump rotation speed Np and the determination value Na, it can be detected with high reliability that the urea water addition valve 15 is fixed open. Even when the pump rotation speed Np at the time of abnormality diagnosis changes according to the temperature of the urea water addition valve 15 due to leakage of urea water from the urea water addition valve 15, abnormality diagnosis is performed in consideration of such temperature dependence. Therefore, the accuracy of detecting an abnormality can be increased.
[Second Embodiment]
Next, a second embodiment in which the urea water addition valve abnormality detection device according to the present invention is embodied will be described. In the present embodiment, in addition to the abnormality diagnosis process for detecting the open sticking described above, the abnormality diagnosis process for detecting the abnormality in which the urea water addition valve 15 does not operate while being closed, that is, the closed sticking is executed. . Details of the abnormality diagnosis process will be described below.

  In this abnormality diagnosis process, when the urea water addition valve 15 is not stuck open, the urea water pump 17 is driven while outputting the valve closing signal to the urea water addition valve 15, and urea water is supplied to the urea water pipe 18. Fill. If the rotation speed of the urea water pump 17 does not reach the determination value Nb even if a valve opening signal is output to the urea water addition valve 15 after the filling, it is determined that the urea water addition valve 15 is closed and fixed. I have to.

Specifically, the abnormality diagnosis process is executed according to the following procedure.
As shown in FIG. 5, in this abnormality diagnosis process, first, it is determined whether or not the open fixation flag Xo is “off”. If it is “on”, a series of processes is terminated (step S500: NO). On the other hand, when the open fixing flag Xo is “off” (step S500: YES), a valve closing signal is output to the urea water addition valve 15 and the urea water pump 17 is started to be driven (step S505, step S505). S510). Next, the pump rotational speed Np is feedback controlled so that the urea water pressure Pu matches the target pressure Pt (step S520). Then, in step S530, it is determined whether or not the urea water pressure Pu has converged to the target pressure Pt. If not converged (step S530: NO), the processing after step S520 is executed again.

  On the other hand, when the urea water pressure Pu has converged to the target pressure Pt (step S530: YES), a valve opening signal is output to the urea water addition valve 15 (step S540). Next, after waiting for a predetermined period to elapse after the valve opening signal is output to the urea water addition valve 15 (step S550), a determination value Nb used for abnormality diagnosis is calculated (step S560).

  Here, when feedback control for setting the urea water pressure Pu to the target pressure Pt is performed in a state where the urea water addition valve 15 is closed, the pump rotation speed Np converges to a predetermined convergence value. Nb is a value obtained by adding a constant considering the individual difference of the urea water pump 17 to the convergence value. Therefore, even if the pump rotation speed Np during feedback control varies due to individual differences of the urea water pump 17, if the urea water addition valve 15 is not closed and fixed, a valve closing signal output to the urea water addition valve 15 is generated. By switching to the valve opening signal, the pump rotation speed Np increases and becomes equal to or higher than the determination value Nb. This determination value Nb may be the same value as the determination value Na described in the first embodiment.

  Next, it is determined whether or not the pump rotation speed Np is less than the determination value Nb (step S570). If the pump rotation speed Np is equal to or higher than the determination value Nb (step S570: NO), this series of processes is terminated. On the other hand, when the pump rotation speed Np is less than the determination value Nb (step S570: YES), the closed fixation flag Xc indicating that the urea water addition valve 15 is closed and fixed is set to "ON" (step S570). S580), this series of processing is terminated.

Next, an example of changes in the pump rotation speed Np and the urea water pressure Pu when the abnormality diagnosis process is executed will be described.
As shown in FIG. 6, when the driving of the urea water pump 17 is started (timing t1), the pump rotation speed Np and the urea water pressure Pu increase. When the urea water pressure Pu converges to the target pressure Pt, the valve closing signal output to the urea water addition valve 15 is switched to the valve opening signal (timing t2). Here, when the urea water addition valve 15 is not closed and fixed, the urea water pressure Pu decreases from the target pressure Pt while the pump rotation speed Np increases from its convergence value, as shown by the solid line in FIG. Thus, the determination value Nb is exceeded (at timing t3). Therefore, in this case, the closed sticking flag Xc is not operated.

  On the other hand, when the urea water addition valve 15 is closed and fixed, the valve closing signal output to the urea water addition valve 15 at the timing t2 is switched to the valve opening signal as shown by a two-dot chain line in FIG. Even if this is done, neither the urea water pressure Pu nor the pump rotation speed Np will change. Then, when a predetermined period has elapsed from the timing t2, the closed sticking flag Xc is set to “ON” based on the fact that the pump rotation speed Np is less than the determination value Nb (timing t4).

Next, the operation of the present embodiment will be described.
When the urea water addition valve 15 is not closed and fixed, when the urea water addition valve 15 is opened, the urea water in the urea water pipe 18 flows out of the urea water addition valve 15 and the urea water pressure Pu decreases. Along with this, the rotational resistance of the urea water pump 17 decreases, and the pump rotational speed Np increases. On the other hand, when the urea water addition valve 15 is closed and fixed, the urea water addition valve 15 is not opened, and the urea water in the urea water pipe 18 does not flow out of the urea water addition valve 15. The pump rotation speed Np does not increase as the rotation resistance of the urea water pump 17 decreases. Therefore, it is possible to detect that the urea water addition valve 15 is closed and fixed based on the determination as to whether or not the pump rotation speed Np exceeds the determination value Nb.

As described above, according to this embodiment, in addition to the effect (1), the following effect can be achieved.
(2) It is possible to detect with high reliability that the urea water addition valve 15 is closed and fixed based on a comparison between the pump rotation speed Np and the determination value Nb.
[Third Embodiment]
Next, a third embodiment in which the urea water addition valve abnormality detection device according to the present invention is embodied will be described. In the present embodiment, in addition to the abnormality diagnosis processes for detecting the open sticking and the closed sticking described above, an abnormality diagnosis process for detecting a decrease in response speed when the urea water addition valve 15 is opened. Run. Details of the abnormality diagnosis process will be described below.

  In this abnormality diagnosis process, the valve closing signal output to the urea water addition valve 15 is switched to a valve opening signal and the urea water pump 17 is started to be driven until the pump rotation speed Np reaches a predetermined value Np1. When the time exceeds a predetermined determination time T, it is determined that the response speed when the urea water addition valve 15 opens is decreasing. Further, the temperature of the urea water addition valve 15 is estimated, and the determination time T is corrected based on the estimated temperature θ so that the determination time T becomes longer as the estimated temperature θ is lower.

Specifically, the abnormality diagnosis process is executed according to the following procedure.
As shown in FIG. 7, in this abnormality diagnosis process, first, it is determined whether or not the closed sticking flag Xc is “off”. If it is “on”, a series of processes is terminated (step S700: NO). On the other hand, when the closed fixation flag Xc is “OFF” (step S700: YES), a valve closing signal is output to the urea water addition valve 15, and the driving of the urea water pump 17 is stopped (step S705, S705). Step S710). Then, after waiting for the urea water pressure Pu to decrease to “0” (step S715), a valve opening signal is output to the urea water addition valve 15, and the driving of the urea water pump 17 is started (step S720). , Step S725).

  Next, the pump rotation speed Np is feedback-controlled using the predetermined value Np1 as a target value (step S730). Then, it is determined whether or not the pump rotation speed Np has converged to a predetermined value Np1 (step S740). When the pump rotation speed Np has not converged to the predetermined value Np1 (step S740: NO), the processes after step S730 are executed again.

  On the other hand, if the pump rotation speed Np has converged to the predetermined value Np1 (step S740: YES), then the temperature of the urea water addition valve 15 is estimated based on the floor temperature and the outside air temperature of the DPF 12 (step S750). . As described above, the estimated temperature θ increases as the bed temperature of the DPF 12 increases and as the outside air temperature increases.

  After calculating the estimated temperature θ in this way, a determination time T used for abnormality diagnosis is calculated (step S760). The determination time T is based on the time set based on the response speed when the temperature of the urea water addition valve 15 is the average temperature in the usage environment, and the reference value is further used as the urea water addition valve. This is a time corrected by 15 estimated temperature θ.

  As shown in FIG. 8, the determination time T becomes longer as the estimated temperature θ is lower. Next, it is determined whether or not the elapsed time since the start of the driving of the urea water pump 17 exceeds the determination time T (step S770). When the elapsed time since the start of the driving of the urea water pump 17 is equal to or shorter than the determination time T, this series of processing is ended (step S770: NO). On the other hand, when the determination time T is exceeded, the responsiveness reduction flag Xr indicating that the response speed when the urea water addition valve 15 is opened is set to “on”, and this series of The process ends (step S770: YES, step S780).

Next, an example of a change in the pump rotation speed Np when the abnormality diagnosis process is executed will be described.
As shown in FIG. 9, when the driving of the urea water pump 17 is started (timing t1), the pump rotational speed Np is feedback-controlled using the predetermined value Np1 as a target value. As a result, the pump rotation speed Np increases, and if the response speed when the urea water addition valve 15 opens is not decreased, it converges to the predetermined value Np1 before the determination time T elapses from the timing t1. (Timing t2). Therefore, in this case, the responsiveness reduction flag Xr is not operated.

  On the other hand, when the response speed when the urea water addition valve 15 opens is low, the pump rotation speed Np is still below the predetermined value Np1 even when the determination time T has elapsed (timing t3). Yes. Then, the pump rotation speed Np converges to a predetermined value Np1 after the determination time T has elapsed, and the responsiveness reduction flag Xr is set to “ON” (timing t4).

Next, the operation of the present embodiment will be described.
Even when the urea water addition valve 15 is not closed and fixed, the response speed when the urea water addition valve 15 is opened from the closed state decreases due to an increase in sliding resistance of the valve body. There is. And if the response speed of the urea water addition valve 15 decreases in this way, the urea water addition performance deteriorates as compared with the normal time, even if it cannot be said that it is a complete failure such as open fixation and closed fixation. It becomes.

  When the response speed when the urea water addition valve 15 is opened in this way decreases, the amount of urea water flowing out from the urea water addition valve 15 after outputting the valve opening signal to the urea water addition valve 15 is reduced. It becomes difficult to increase. For this reason, compared with the case where the response speed does not fall, the rotational resistance of the urea water pump 17 becomes large, and the pump rotational speed Np becomes difficult to increase. Therefore, according to the present embodiment, such a decrease in the responsiveness of the urea water addition valve 15 is detected based on the fact that the elapsed time until the pump rotation speed Np reaches the predetermined value Np1 exceeds the predetermined determination time T. can do.

  Further, when the temperature of the urea water addition valve 15 is low, the viscosity of the urea water becomes high and the sliding resistance of the valve body increases, so that the response even when the urea water addition valve 15 operates normally. The speed is reduced. In the present embodiment, since the determination time T is corrected based on the estimated temperature θ of the urea water addition valve 15, such temperature dependence of the response speed can be taken into consideration.

As described above, according to the present embodiment, in addition to the effects (1) and (2), the following effects can be achieved.
(3) While considering that the response speed of the urea water addition valve 15 changes according to the temperature of the urea water addition valve 15, it is possible to appropriately detect a decrease in responsiveness of the urea water addition valve 15.

As described above, the abnormality diagnosis process described in each embodiment can be modified as follows.
-On the premise that the abnormality diagnosis processing of the first embodiment and the second embodiment has been executed, the abnormality diagnosis processing for responsiveness reduction in the third embodiment is executed. The abnormality diagnosis process may be performed independently. Even in this case, the effect described in (3) can be achieved.

  In the third embodiment, the elapsed time from the start of driving the urea water pump 17 until the pump rotational speed Np converges to the predetermined value Np1 is compared with a plurality of determination times having different lengths. The responsiveness of the urea water addition valve 15 may be evaluated stepwise based on the comparison result. Specifically, it is determined that the longer the elapsed time is, the greater the degree of responsiveness reduction when the urea water addition valve 15 opens.

  As described above, the response speed increases as the temperature of the urea water addition valve 15 increases. However, when the temperature of the urea water addition valve 15 becomes extremely high, the energization resistance of the solenoid increases and the electromagnetic force increases. Since it falls, the response speed of the urea water addition valve 15 may fall. For this reason, when calculating the determination time T, the determination time T is determined in consideration of both the magnitude of the sliding resistance that changes according to the temperature of the urea water addition valve 15 and the electromagnetic force of the solenoid. May be.

  The temperature of the urea water addition valve 15 is estimated based on two parameters such as the floor temperature and the outside air temperature of the DPF 12, but in addition to these parameters, there is a correlation with the temperature of the urea water addition valve 15 such as the exhaust temperature. The temperature of the urea water addition valve 15 may be estimated by appropriately combining other parameters.

  DESCRIPTION OF SYMBOLS 10 ... Diesel engine, 11 ... Exhaust passage, 12 ... DPF, 13 ... SCR catalyst unit, 14 ... Oxidation catalyst unit, 15 ... Urea water addition valve, 16 ... Urea water tank, 17 ... Urea water pump, 18 ... Urea water piping , 19 ... return piping, 20 ... relief valve, 21 ... pressure sensor, 22 ... control unit, 23 ... rotational speed sensor, 24 ... floor temperature sensor, 25 ... outside air temperature sensor.

Claims (1)

An abnormality detection device for detecting an abnormality of a urea water addition valve for adding urea water filled in a supply passage by a pump to exhaust gas,
A sensor for detecting the rotation speed of the pump is provided. Based on the determination as to whether or not the rotation speed of the pump detected by the sensor reaches a determination value corrected based on the estimated temperature of the urea water addition valve, To determine whether or not the time until the abnormality is detected or the rotational speed of the pump detected by the sensor changes and reaches a predetermined value exceeds the determination time corrected based on the estimated temperature of the urea water addition valve An abnormality detection device for urea water addition valve that detects abnormality of urea water addition valve based on the above.