JP2015203322A - Control device for exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an exhaust emission control system that is facilitated in identification of a part where anomaly is occurring, especially in detection of anomaly in urea water pressure detection means.SOLUTION: In the control device for an exhaust emission control system, a characteristic diagnosis part 35 compares a relationship between an actual rotation speed Rr of a motor 16 detected by a rotation speed sensor 32 and an actual urea water pressure Pr detected by a pressure sensor 33 with a characteristic map. The characteristic diagnosis part 35 diagnoses that anomaly is occurring in the pressure sensor 33 when the relationship between the actual rotation speed Rr and the actual urea water pressure Pr deviates from a setup range of the characteristic map.

Description

  The present invention relates to an exhaust purification system control device that purifies exhaust gas from an internal combustion engine.

  Conventionally, a urea SCR (Selective Catalytic Reduction) system using urea as post-processing for purifying exhaust gas of an internal combustion engine is known. In the urea SCR system, nitrogen oxide (NOx) contained in the exhaust is reduced by adding urea to the exhaust. Here, urea is added to the exhaust gas as urea water as an aqueous solution. If an abnormality occurs in the urea SCR system, urea water is not added to the exhaust gas, and there is a possibility that the exhaust gas treatment becomes insufficient. Therefore, a method for diagnosing abnormalities in the urea SCR system has been proposed (see Patent Document 1).

In Patent Document 1, a predetermined amount of urea water is added to the exhaust gas while the fuel supply to the internal combustion engine is stopped. And in patent document 1, the presence or absence of abnormality of the mechanism which injects urea water is diagnosed by detecting NOx density | concentration which changes with addition of urea water with a NOx sensor.
However, in the case of Patent Document 1, the presence or absence of abnormality depends on the NOx concentration detected by the NOx sensor. Therefore, in Patent Document 1, if an abnormality occurs in the concentration of NOx, the mechanism for injecting urea water is diagnosed as abnormal as a whole. As a result, there is a problem that it is difficult to specify which part of the mechanism for injecting urea water has an abnormality.

JP 2009-121413 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for an exhaust gas purification system that makes it easy to identify an abnormality component, particularly to identify an abnormality in urea water pressure detection means.

  In the invention according to claim 1 or 5, the storage means stores in advance the relationship between the rotational speed of the motor and the pressure of the urea water discharged from the urea water pump as a characteristic map. That is, the rotation speed of the motor is correlated with the pressure of urea water discharged from the urea water pump. Therefore, the storage means stores this correlated relationship as a characteristic map. The characteristic diagnosing means uses this characteristic map to show the relationship between the actual rotational speed that is the actual rotational speed of the motor detected by the rotational speed detecting means and the actual urea water pressure that is the actual pressure of urea water detected by the urea water pressure detecting means. Contrast with Thus, the characteristic diagnosis unit diagnoses that the urea water pressure detection unit has an abnormality when the relationship between the actual rotational speed and the actual urea water pressure is different from the characteristic map. Therefore, it is possible to easily grasp the abnormality of the urea water pressure detection means.

  In the invention according to claim 2, the characteristic diagnosis means diagnoses the characteristic of the urea water pressure detection means when the actual urea water pressure detected by the urea water pressure detection means is within the diagnosis pressure range. This diagnostic pressure range is set in advance. The urea water pressure detection means includes variations due to individual differences, for example. Further, the pressure of the urea water discharged from the urea water pump changes over time by repeating the time elapsed since the start of the urea water pump and the addition to the exhaust gas. Therefore, the characteristic diagnosis means executes diagnosis of the urea water pressure detection means when the pressure of the urea water is stable within a preset diagnostic pressure range. Accordingly, it is possible to improve the diagnosis accuracy of the abnormality of the urea water pressure detection means.

  In the invention according to claim 3, the characteristic diagnosing means diagnoses the characteristic of the urea water pressure detecting means when the actual rotational speed detected by the rotation detecting means is within the diagnostic rotational speed range. This diagnostic rotation speed range is set in advance. The motor that drives the urea water pump includes variations due to individual differences, for example. In addition, the rotation speed of the motor that drives the urea water pump changes with the passage of time from the start of the urea water pump or by repeated addition to the exhaust gas. Therefore, the characteristic diagnosis means performs diagnosis of the urea water pressure detection means when the pressure of the urea water is stable within a preset diagnostic rotation speed range. Accordingly, it is possible to improve the diagnosis accuracy of the abnormality of the urea water pressure detection means.

  In the invention according to claim 4, the rotation speed limiting means limits the rotation speed of the motor that drives the urea water pump to the rotation upper limit value or less. When there is an abnormality in the urea water pressure detection means, even if the rotation speed of the motor is controlled, the target urea water pressure may not be reached. At this time, the rotational speed and load of the motor may be excessive. Therefore, when the pressure of the urea water does not rise sufficiently even when the motor is driven, the rotation speed limiting means limits the rotation speed of the motor to the rotation upper limit value or less. Then, the characteristic diagnosis means performs diagnosis of the urea water detection means when the state where the rotation speed of the motor is limited continues for a set period. At this time, a large divergence occurs between the rotation speed of the motor and the pressure of the urea water. Therefore, it is possible to reliably diagnose abnormality of the urea water pressure detection means.

The block diagram which shows the control apparatus of the exhaust gas purification system by 1st Embodiment. The schematic diagram which shows the exhaust gas purification system by 1st Embodiment The schematic diagram which shows the characteristic map of the control apparatus by 1st Embodiment Schematic showing changes in urea water pressure and motor speed over time Schematic which shows the flow of a process in the control apparatus by 1st Embodiment. Schematic showing changes in urea water pressure and motor speed over time The block diagram which shows the control apparatus by 2nd Embodiment. Schematic which shows the flow of a process in the control apparatus by 2nd Embodiment. Schematic showing changes in urea water pressure and motor speed over time

Hereinafter, a control device for an exhaust gas purification system according to a plurality of embodiments will be described with reference to the drawings. Note that, in a plurality of embodiments, substantially the same components are denoted by the same reference numerals, and description thereof is omitted.
(First embodiment)
An exhaust purification system 10 shown in FIG. 2 constitutes an SCR system in which urea water is added to exhaust discharged from an internal combustion engine 11 mounted on a vehicle, for example, to reduce NOx contained in the exhaust. Exhaust gas from the internal combustion engine 11 is released to the atmosphere via an exhaust passage 13 formed by the exhaust pipe member 12. The internal combustion engine 11 is a diesel engine, for example. The exhaust purification system 10 may be applied not only to a diesel engine but also to a gasoline engine or a gas turbine engine. Further, the exhaust purification system 10 is not limited to the on-board internal combustion engine 11, but may be applied to a stationary internal combustion engine 11 such as a power generation unit, for example.

  The exhaust purification system 10 includes a urea water tank 14, a urea water pump 15, a motor 16, a urea water passage portion 17, and a reduction catalyst 18. The urea water tank 14 stores an aqueous solution of urea that is urea water. The urea water pump 15 is accommodated in the urea water tank 14. The motor 16 drives the urea water pump 15. The urea water pump 15 is driven by supplying electric power to the motor 16, pressurizes the urea water sucked from the urea water tank 14, and discharges it to the urea water passage portion 17. The urea water passage portion 17 forms a urea water passage 19. The reduction catalyst 18 is provided in the exhaust passage 13 formed by the exhaust pipe member 12.

  The exhaust purification system 10 includes an injector 21 in addition to the above. The urea water passage 19 is connected to the injector 21 at the end opposite to the urea water pump 15. The urea water discharged from the urea water pump 15 is supplied to the injector 21 via the urea water passage 19. The injector 21 is provided on the exhaust pipe member 12. The injector 21 penetrates the exhaust pipe member 12 and has a tip exposed to the exhaust passage 13. The urea water supplied to the injector 21 is injected into the exhaust gas flowing through the exhaust passage 13. Exhaust gas discharged from the internal combustion engine 11 and urea water injected from the injector 21 are mixed in the exhaust passage 13 and flow into the reduction catalyst 18. NOx contained in the exhaust is reduced by a chemical reaction with urea contained in the urea water in the reduction catalyst 18.

  The above-described exhaust purification system 10 is controlled by the control device 30. As shown in FIG. 1, the control device 30 includes a control unit 31, a rotation speed sensor 32, a pressure sensor 33, and a storage unit 34. The control unit 31 includes a microcomputer having a CPU, a ROM, and a RAM, and controls the exhaust purification system 10 by a computer program stored in the ROM. The rotation speed sensor 32 corresponds to rotation speed detection means, and detects the actual rotation speed of the motor 16 as the actual rotation speed. The rotation speed sensor 32 outputs the detected actual rotation speed of the motor 16 to the control unit 31 as an electric signal. The rotation speed sensor 32 may directly detect the rotation speed of the motor 16 or may indirectly detect it from an electric signal supplied to the motor 16. The pressure sensor 33 corresponds to urea water pressure detecting means, and is provided in the urea water passage 19 connecting the urea water pump 15 and the injector 21 as shown in FIG. The pressure sensor 33 detects the actual pressure of the urea water discharged from the urea water pump 15 as the actual urea water pressure in the urea water passage 19. The pressure sensor 33 outputs the detected actual urea water pressure to the control unit 31 as an electric signal.

  The storage unit 34 is configured by a non-volatile medium such as a flash memory. The storage unit 34 may be shared with the ROM and RAM of the control unit 31. The storage unit 34 stores a characteristic map as shown in FIG. The characteristic map shows the relationship between the rotation speed of the motor 16 and the pressure of the urea water discharged from the urea water pump 15. This characteristic map is set in advance as an ideal relationship between the rotation speed of the motor 16 and the pressure of the urea water, and is stored in the storage unit 34. There is an inversely proportional relationship between the rotation speed of the motor 16 and the pressure or torque of the urea water discharged from the urea water pump 15 as shown in FIG. That is, when the pressure of the urea water discharged from the urea water pump 15 is determined, the rotation speed of the motor 16 becomes a specific value. In the present embodiment, the relationship between the rotation speed of the motor 16 and the pressure of the urea water is created as an ideal value obtained experimentally and stored in the storage unit 34.

  The control device 30 executes the computer program to realize the characteristic diagnosis unit 35 as software as shown in FIG. The characteristic diagnosis unit 35 may be realized by hardware, or may be realized by cooperation of software and hardware. The characteristic diagnosis unit 35 diagnoses the characteristic of the pressure sensor 33, that is, the abnormality of the pressure sensor 33. Specifically, the characteristic diagnosis unit 35 acquires the actual rotation speed of the motor 16 from the rotation speed sensor 32 and acquires the actual urea water pressure of the urea water in the urea water passage 19 from the pressure sensor 33. And the characteristic diagnosis part 35 diagnoses the characteristic of the pressure sensor 33 from the acquired actual rotation speed and an actual urea water pressure. As described above, when the pressure of the urea water discharged from the urea water pump 15 is determined, if the pressure sensor 33 is normal, the rotational speed of the motor 16 is uniquely determined. However, when an abnormality occurs in the pressure sensor 33, the relationship between the acquired actual rotational speed and the actual urea water pressure deviates from the ideal relationship of the characteristic map shown in FIG. Therefore, if the deviation from the ideal relationship of this characteristic map becomes large, it is considered that some abnormality has occurred in the pressure sensor 33. Therefore, the characteristic diagnosis unit 35 diagnoses that an abnormality has occurred in the pressure sensor 33 when the relationship between the acquired actual rotational speed and the actual urea water pressure deviates from the characteristic map. In the case of the present embodiment, as shown in FIG. 3, the characteristic map has an upper limit value and a lower limit value with the ideal value as the median value. When the relationship between the acquired actual rotational speed and the actual urea water pressure deviates from the setting range set between the upper limit value and the lower limit value of the characteristic map, the characteristic diagnosis unit 35 Diagnose as abnormal. The upper limit value and the lower limit value are set according to the exhaust purification system 10 to be applied. As an example, the upper limit value and the lower limit value are set to about ± 10% to several tens% with respect to the ideal value.

  Further, the characteristic diagnosis unit 35 diagnoses an abnormality of the pressure sensor 33 when the actual urea water pressure is in a stable state. Specifically, the characteristic diagnosis unit 35 diagnoses the characteristic of the pressure sensor 33 when the actual urea water pressure acquired by the pressure sensor 33 is within the diagnostic pressure range. This diagnostic pressure range is arbitrarily set in advance according to the characteristics of the exhaust purification system 10 to be applied. The pressure sensor 33 includes variations due to individual differences, for example. Further, the pressure of the urea water discharged from the urea water pump 15 changes with time by repeating the elapsed time since the start of the urea water pump 15 and the addition of the urea water to the exhaust gas. As described above, when an individual difference or a change in pressure with time occurs, if the diagnosis of the pressure sensor 33 is executed, the reliability of the actual urea water pressure detected by the individual difference or change with time may be reduced. Therefore, the characteristic diagnosis unit 35 executes the diagnosis of the pressure sensor 33 when the pressure of the urea water is stable within a preset diagnosis pressure range.

  Moreover, the characteristic diagnosis part 35 is good also as a structure which diagnoses about the abnormality of the pressure sensor 33 on the condition that the rotation speed of the motor 16 exists in the stable state. The characteristic diagnosis unit 35 diagnoses the characteristic of the pressure sensor 33, for example, when the actual rotational speed of the motor 16 acquired by the rotational speed sensor 32 is in the diagnostic rotational speed range. The diagnostic rotational speed range is arbitrarily set in advance according to the characteristics of the exhaust purification system 10 to be applied. Similar to the pressure sensor 33, the motor 16 and the rotation speed sensor 32 include variations due to individual differences, for example. Further, the pressure of the urea water discharged from the urea water pump 15 changes with time by repeating the elapsed time since the start of the urea water pump 15 and the addition of the urea water to the exhaust gas. As described above, when an individual difference or a change in pressure over time occurs, if the diagnosis of the pressure sensor 33 is executed, the reliability of the actual rotational speed detected by the individual difference or change over time may be reduced. Therefore, the characteristic diagnosis unit 35 executes the diagnosis of the pressure sensor 33 when the rotational speed of the motor 16 is stable within a preset diagnostic rotational speed range.

  The control unit 31 controls the number of rotations of the motor 16 so as to constantly control the pressure of the urea water discharged from the urea water pump 15 to the target pressure Pt. The target pressure Pt has an upper limit value and a lower limit value determined in advance in consideration of errors. The control unit 31 controls the pressure of the urea water between an upper limit value and a lower limit value with the target pressure Pt as a median value. When the motor 16 is started, the urea water pump 15 starts discharging urea water. Therefore, the actual urea water pressure Pr detected by the pressure sensor 33 rises almost proportionally with time as shown in FIG. If the pressure sensor 33 is normal, the control unit 31, when the actual urea water pressure Pr detected by the pressure sensor 33 reaches the target pressure Pt, the motor 16 based on the actual urea water pressure Pr so as to maintain the target pressure Pt. The number of rotations is feedback controlled. That is, if the pressure sensor 33 is normal, the actual rotational speed Rr of the motor 16 is maintained within a set range between the upper limit value and the lower limit value of the characteristic map shown in FIG. At this time, the actual rotational speed Rr of the motor 16 is controlled within the normal rotational speed range as shown in FIG.

Next, the flow of diagnosis with the above configuration will be described with reference to FIG.
When the motor 16 is started (S101), the characteristic diagnosis unit 35 starts a process for controlling the pressure of the urea water (S102). At the same time, the characteristic diagnosis unit 35 acquires the actual urea water pressure Pr from the pressure sensor 33 (S103). Then, the characteristic diagnosis unit 35 compares the acquired actual urea water pressure Pr with the target pressure Pt, and determines whether or not the actual urea water pressure Pr is at the target pressure Pt (S104). At this time, the characteristic diagnosis unit 35 determines whether or not the actual urea water pressure Pr is between the upper limit value and the lower limit value of the target pressure Pt. When the actual urea water pressure Pr is not the target pressure Pt (S104: No), the characteristic diagnosis unit 35 returns to S102, repeats the process for controlling the urea water pressure, and waits until the actual urea water pressure Pr reaches the target pressure Pt. To do.

  On the other hand, when the actual urea water pressure Pr is the target pressure Pt (S104: Yes), the characteristic diagnosis unit 35 acquires the actual rotational speed Rr from the rotational speed sensor 32 (S105). Then, the characteristic diagnosis unit 35 compares the acquired actual rotational speed Rr and the lower limit rotational speed Rmin (S106). This lower limit rotational speed Rmin corresponds to the lower limit value in the characteristic map shown in FIG. That is, when the actual urea water pressure Pr is determined to be the value acquired in S103, if the pressure sensor 33 is normal, the actual rotational speed Rr of the motor 16 is determined from the characteristic map shown in FIG. It will be between Rmax. Therefore, the characteristic diagnosis unit 35 compares the actual rotational speed Rr and the lower limit rotational speed Rmin.

  When an abnormality occurs in the pressure sensor 33, there is a difference between the actual rotation speed Rr of the motor 16 acquired as shown in FIG. 6 and the actual urea water pressure Pr detected by the pressure sensor. That is, when the actual urea water pressure Pr is controlled to the target pressure Pt, compared to when the pressure sensor 33 is normal, (A) the rotational speed of the motor 16 is constant in a state higher than the normal rotational speed range. In such a case, there are cases where (B) the rotational speed of the motor 16 becomes constant in a state lower than the normal rotational speed range, or (C) the rotational speed of the motor 16 does not reach the normal rotational speed range. Therefore, when an abnormality occurs in the pressure sensor 33, the actual rotation speed Rr of the motor 16 deviates from a setting range set between the upper limit rotation speed Rmax and the lower limit rotation speed Rmin of the characteristic map.

  Therefore, when the actual rotational speed Rr is lower than the lower limit rotational speed Rmin (S106: Yes), the characteristic diagnosis unit 35 diagnoses that the pressure sensor 33 is abnormal (S107). Further, when the actual rotational speed is equal to or higher than the lower limit rotational speed Rmin (S106: No), the characteristic diagnosis unit 35 compares the actual rotational speed Rr with the upper limit rotational speed Rmax (S108). The characteristic diagnosis unit 35 diagnoses that the pressure sensor 33 is abnormal (S107) even when the actual rotational speed Rr is higher than the upper limit rotational speed Rmax (S108: No). On the other hand, when the actual rotational speed Rr is equal to or lower than the upper limit rotational speed Rmax (S108: Yes), the characteristic diagnosis unit 35 diagnoses that the pressure sensor 33 is normal (S109). That is, when the actual rotation speed Rr is equal to or lower than the upper limit rotation speed Rmax in S108, the actual rotation speed Rr is in a setting range set between the upper limit rotation speed Rmax and the lower limit rotation speed Rmin. Therefore, since the actual rotational speed Rr of the motor 16 is in a normal setting range, the characteristic diagnosis unit 35 diagnoses that the pressure sensor 33 is normal.

  As described above, in the first embodiment, the characteristic diagnosis unit 35 represents the relationship between the actual rotation speed Rr of the motor 16 detected by the rotation speed sensor 32 and the actual urea water pressure Pr detected by the pressure sensor 33, as a characteristic map. Contrast with The characteristic diagnosis unit 35 diagnoses that an abnormality has occurred in the pressure sensor 33 when the relationship between the actual rotational speed Rr and the actual urea water pressure Pr deviates from the setting range of the characteristic map. Therefore, the abnormality of the pressure sensor 33 can be easily grasped.

(Second Embodiment)
FIG. 7 shows an exhaust purification system control apparatus according to the second embodiment.
The control device 30 of the second embodiment includes a rotation speed limiting unit 36 in addition to the configuration of the first embodiment. The rotation speed limiter 36 is realized by software by executing a computer program in the control unit 31. The rotation speed limiter 36 may be realized in hardware, or may be realized by cooperation of software and hardware. The rotation speed limiter 36 limits the rotation speed of the motor 16 to a preset rotation upper limit value Mr or less. When the pressure sensor 33 is abnormal, the actual urea water pressure Pr may not reach the target pressure Pt even if the rotational speed of the motor 16 is controlled as shown in FIG. In this case, the actual urea water pressure Pr does not reach the target pressure Pt, and the processes of S102 and S103 are repeated. In this case, the abnormality of the pressure sensor 33 cannot be diagnosed, and an excessive load may be applied to the motor 16. Therefore, when the actual urea water pressure Pr does not reach the target pressure Pt and there is a possibility that the rotation speed of the motor 16 becomes excessive, the rotation speed limiter 36 limits the rotation speed of the motor 16 to the rotation upper limit value Mr or less. .

  When the rotation speed limiter 36 limits the rotation speed of the motor 16 in this way, the characteristic diagnosis unit 35 determines that if the period during which the rotation speed of the motor 16 is limited to the rotation upper limit value Mr or more exceeds the set period, The abnormality of the pressure sensor 33 is diagnosed by the rotational speed of the motor 16 at the time. This setting period is arbitrarily set according to the characteristics of the motor 16 and the like.

The flow of diagnosis according to the second embodiment will be described with reference to FIG. In addition, description is abbreviate | omitted about the process same as the flow of diagnosis in 1st Embodiment.
When the motor 16 is started (S201), the characteristic diagnosis unit 35 resets the count C of the timer provided in the control unit 31 (S202). That is, the characteristic diagnosis unit 35 sets the count C of the timer of the control unit 31 to C = 0. At the same time, the characteristic diagnosis unit 35 starts a process for controlling the pressure of the urea water (S203). When the pressure of the urea water is controlled, the characteristic diagnosis unit 35 acquires the actual urea water pressure Pr from the pressure sensor 33 (S204), and determines whether or not the actual urea water pressure Pr is at the target pressure Pt (S205). ).

  When the actual urea water pressure Pr is the target pressure Pt (S205: Yes), the characteristic diagnosis unit 35 acquires the actual rotational speed Rr from the rotational speed sensor 32 (S206). Then, the characteristic diagnosis unit 35 compares the acquired actual rotational speed Rr and the lower limit rotational speed Rmin (S207). When the actual rotational speed Rr is lower than the lower limit rotational speed Rmin (S207: Yes), the characteristic diagnosis unit 35 diagnoses that the pressure sensor 33 is abnormal (S208). Further, when the actual rotational speed is equal to or higher than the lower limit rotational speed Rmin (S207: No), the characteristic diagnosis unit 35 compares the actual rotational speed Rr with the upper limit rotational speed Rmax (S209). Then, the characteristic diagnosis unit 35 diagnoses that the pressure sensor 33 is abnormal when the actual rotational speed Rr is higher than the upper limit rotational speed Rmax (S209: Yes) (S208). On the other hand, when the actual rotational speed Rr is equal to or lower than the upper limit rotational speed Rmax (S209: No), the characteristic diagnosis unit 35 diagnoses that the pressure sensor 33 is normal (S210).

  By the way, when the characteristic diagnosis unit 35 determines in S205 that the actual urea water pressure Pr is not the target pressure Pt (S205: No), the characteristic diagnosis unit 35 acquires the actual rotation speed Rr from the rotation speed sensor 32 (S211). Then, the characteristic diagnosis unit 35 determines whether or not the actual rotation speed Rr acquired in S211 is equal to or less than the rotation upper limit value Mr (S212). The characteristic diagnosis unit 35 increments the count C by “1” when the actual rotation speed Rr of the motor 16 is equal to or less than the rotation upper limit value Mr (S212: Yes) (S213). That is, the characteristic diagnosis unit 35 sets the count C to “C = C + 1”. On the other hand, when the actual rotation speed Rr of the motor 16 is larger than the rotation upper limit value Mr (S212: No), the characteristic diagnosis unit 35 returns to S203 and repeats the process for controlling the pressure of the urea water. If the rotation speed limiter 36 is functioning, normally, it is not determined that the actual rotation speed Rr of the motor 16 is greater than the rotation upper limit value Mr in S212. That is, under normal circumstances, the actual rotation speed Rr of the motor 16 will not exceed the rotation upper limit value Mr in S212. However, when the load fluctuation is large, such as immediately after the urea water pump 15 is started, the actual rotational speed Rr of the motor 16 may temporarily exceed the rotation upper limit value Mr. In this case, the characteristic diagnosis unit 35 returns to S203 and continues the process of controlling the pressure of the urea water.

  The characteristic diagnosis unit 35 increments the count C in S213, and determines whether or not the count C has reached the set period T (S214). That is, the characteristic diagnosis unit 35 determines whether or not the state in which the rotation speed of the motor 16 is limited to the rotation upper limit value Mr or less by the rotation speed limit unit 36 is the set period T. When the characteristic diagnosis unit 35 determines that the count C has not reached the set period T (S214: No), the process returns to S203 and repeats the process of controlling the pressure of the urea water. On the other hand, when the characteristic diagnosis unit 35 determines that the count C has reached the set period T (S214: Yes), it determines whether or not the actual urea water pressure Pr acquired in S204 is smaller than the lower limit pressure Pmin (S215). As described above, when the pressure sensor 33 is abnormal, the actual urea water pressure Pr does not rise to a sufficient value. Therefore, the actual urea water pressure Pr does not reach the target pressure Pt as shown in FIG. Therefore, when the actual urea water pressure Pr has not reached the lower limit pressure Pmin lower than the target pressure Pt (S215: Yes), the characteristic diagnosis unit 35 diagnoses that the pressure sensor 33 is abnormal (S208). This lower limit pressure Pmin can be arbitrarily set as a value lower than the target pressure Pt. When the actual urea water pressure Pr is equal to or higher than the lower limit pressure Pmin (S215: No), the characteristic diagnosis unit 35 returns to S203 and repeats the process for controlling the pressure of the urea water.

  In the second embodiment, the rotation speed limiter 36 limits the rotation speed of the motor 16 that drives the urea water pump 15 to the rotation upper limit value Mr or less. When the pressure sensor 33 is abnormal, the pressure of the urea water may not reach the target pressure Pt even if the rotation speed of the motor 16 is controlled. At this time, the rotation speed and load of the motor 16 may be excessive. Therefore, when the pressure of the urea water does not rise sufficiently even when the motor 16 is driven, the rotation speed limiter 36 limits the rotation speed of the motor 16 to the rotation upper limit value Mr or less. And the characteristic diagnosis part 35 will perform the diagnosis of the pressure sensor 33, if the state where the rotation speed of this motor 16 is restrict | limited continues until the setting period T. FIG. At this time, the actual urea water pressure Pr detected by the pressure sensor 33 does not reach the lower limit pressure Pmin lower than the target pressure Pt. Therefore, the characteristic diagnosis unit 35 diagnoses that the pressure sensor 33 is abnormal when the actual urea water pressure Pr does not reach the lower limit pressure Pmin. Therefore, the abnormality of the pressure sensor 33 can be reliably diagnosed.

  The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

  In the drawings, 10 is an exhaust purification system, 14 is a urea water tank, 15 is a urea water pump, 16 is a motor, 30 is a control device, 32 is a rotation speed sensor (rotation speed detection means), and 33 is a pressure sensor (urea water pressure detection). Means), 34 is a storage section (storage means), 35 is a characteristic diagnosis section (characteristic diagnosis means), and 36 is a rotation speed limiting section (rotation speed limiting means).

Claims (5)

In the exhaust gas purification system (10) comprising a urea water pump (15) for discharging urea water stored in a urea water tank (14) and a motor (16) for driving the urea water pump (15), the exhaust gas A control device (30) for controlling the purification system (10),
Storage means (34) for storing a relationship between a preset rotation speed of the motor (16) and the pressure of urea water discharged from the urea water pump (15) as a characteristic map;
A rotational speed detection means (32) for detecting an actual rotational speed of the motor (16);
Urea water pressure detecting means (33) for detecting the actual urea water pressure discharged from the urea water pump (15);
The characteristic stored in the storage means (34) is the relationship between the actual rotational speed detected by the rotational speed detection means (32) and the actual urea water pressure detected by the urea water pressure detection means (33). In contrast to the map, characteristic diagnosis means (35) for diagnosing the characteristic of the urea water pressure detection means (33);
An exhaust purification system control apparatus comprising:   The characteristic diagnosis means (35) diagnoses the characteristic of the urea water pressure detection means (33) when the actual urea water pressure detected by the urea water pressure detection means (33) is within a preset diagnostic pressure range. The exhaust purification system control device according to claim 1.   The characteristic diagnosis means (35) diagnoses the characteristic of the urea water pressure detection means (33) when the actual rotation speed detected by the rotation speed detection means (32) is within a preset diagnosis rotation speed range. The exhaust purification system control device according to claim 1 or 2. A rotation speed limiting means (36) for controlling the rotation speed of the motor (16) to be equal to or lower than a preset rotation upper limit value;
When the period during which the actual rotational speed detected by the rotational speed detection means (32) is less than or equal to the upper limit of rotation exceeds a preset set period, the characteristic diagnosis means (35) detects the urea water pressure detection means ( 33. The exhaust purification system control device according to claim 1, wherein the control device diagnoses the characteristic of 33).   The characteristic diagnosing means (35) is configured so that a relationship between the actual rotational speed detected by the rotational speed detecting means (32) and the actual urea water pressure detected by the urea water pressure detecting means (33) The abnormality of the urea water pressure detecting means (33) is diagnosed when exceeding a preset range from the relationship between the rotation speed of the motor (16) and the pressure of the urea water. The control apparatus of the exhaust gas purification system described.

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