JP6905910B2 - Diagnostic device and diagnostic method - Google Patents

Description

The present invention relates to a diagnostic apparatus and a diagnostic method for diagnosing the concentration of a liquid reducing agent used for purifying the exhaust gas of an internal combustion engine by using a concentration sensor.

The urea SCR (Selective Catalytic Reduction) system has been put into practical use as a device for decomposing _{NO X} (nitrogen oxides) contained in the exhaust gas of internal combustion engines such as diesel engines mounted on vehicles and purifying the exhaust gas. ing. In the urea SCR system, an aqueous urea solution is used as the reducing agent. Urea SCR systems degrades NO _X by reacting ammonia produced by the urea aqueous solution is decomposed with NO _X in the exhaust gas.

The urea SCR system includes a selective reduction catalyst disposed in the exhaust passage and a reducing agent supply device for injecting an aqueous urea solution into the exhaust passage on the upstream side of the selective reduction catalyst. The selective reduction catalyst adsorbs ammonia and promotes the reduction reaction between _{NO X and ammonia in the inflowing exhaust gas.} The reducing agent supply device includes a pump for pumping the urea aqueous solution stored in the storage tank and an injection valve for injecting the urea aqueous solution pumped by the pump, and the drive control is performed by the control device to supply the urea aqueous solution. Inject into the exhaust passage.

The control device calculates the injection amount of the urea aqueous solution based on the amount of ammonia required to purify _{NO X} contained in the exhaust gas discharged from the internal combustion engine and the amount of ammonia adsorbable to the selective reduction catalyst. If the amount of the urea aqueous solution injected is too small, NO _X cannot be properly purified. Further, if the amount of the urea aqueous solution injected is too large, the amount of ammonia that flows out (slip) downstream of the selective reduction catalyst increases. Therefore, in the urea SCR system, a urea aqueous solution having a predetermined reference concentration is used, and the control device sets a target injection amount of the urea aqueous solution corresponding to the required amount of ammonia and executes injection control.

In such a urea SCR system, if the concentration of the urea aqueous solution is different from the reference concentration, the amount of ammonia produced from the injected urea aqueous solution will be excessive or insufficient. Therefore, as described in Patent Document 1, the storage tank in which the urea aqueous solution is stored is provided with a concentration sensor (also referred to as “quality sensor”), and the concentration of the urea aqueous solution does not deviate significantly from the reference concentration. Is being diagnosed.

Japanese Unexamined Patent Publication No. 2008-248710

Here, when the urea aqueous solution contains bubbles, the bubbles can interfere with the detection of the concentration of the urea aqueous solution by the concentration sensor. Therefore, the reliability of the detection value of the concentration sensor in the state where the bubbles can be contained in the urea aqueous solution is reliable. The sex becomes low. In order to prevent erroneous determination that the concentration of the urea aqueous solution having an appropriate concentration is abnormal even in a state where bubbles may be contained in the urea aqueous solution, it is necessary to set a large allowable range of deviation at the time of diagnosis. However, if the permissible range of deviation at the time of diagnosis is increased, it becomes difficult to determine an abnormality even when the actual concentration of the urea aqueous solution deviates significantly from the reference concentration.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a diagnostic device and a diagnostic method capable of improving the reliability of the diagnostic result of the concentration of an aqueous urea solution using a concentration sensor. To do.

According to a certain aspect of the present invention, a diagnostic device that diagnoses the concentration of a liquid reducing agent used for purifying the exhaust of an internal combustion engine mounted on a vehicle by using a concentration sensor installed in a tank that stores the liquid reducing agent. In the first determination unit for executing the first determination for determining whether or not the deviation between the detection value of the concentration sensor and the reference concentration of the liquid reducing agent is equal to or less than the first threshold value, and the detection value of the concentration sensor. A second determination unit for executing a second determination for determining whether or not the deviation between the liquid reducing agent and the reference concentration of the liquid reducing agent is equal to or less than the second threshold value larger than the first threshold value. The determination unit starts executing the first determination after the diagnostic device is activated, and ends the execution of the first determination when the first condition for increasing the number of bubbles in the liquid reducing agent in the tank is satisfied. The second determination unit is provided with a diagnostic device that executes the second determination after at least the first condition is satisfied.

Further, according to another aspect of the present invention, the concentration of the liquid reducing agent used for purifying the exhaust of the internal combustion engine mounted on the vehicle is diagnosed by using the concentration sensor installed in the tank for storing the liquid reducing agent. In the diagnostic method to be performed, the deviation between the detection value of the concentration sensor and the reference concentration of the liquid reducing agent during the period from the start of the diagnostic device to the establishment of the first condition in which the bubbles in the liquid reducing agent in the tank increase. The detection value of the concentration sensor and the reference concentration of the liquid reducing agent are executed after the first determination is executed to determine whether or not is equal to or less than the first threshold value, and at least after the first condition is satisfied after the diagnostic device is started. A diagnostic method is provided that executes a second determination to determine whether or not the deviation from is greater than or equal to the first threshold and is less than or equal to the second threshold.

As described above, according to the present invention, it is possible to improve the reliability of the diagnostic result of the concentration of the urea aqueous solution using the concentration sensor.

It is a schematic diagram which shows the applicable urea SCR system provided with the diagnostic apparatus which concerns on embodiment of this invention. It is a block diagram which shows the structural example of the diagnostic apparatus which concerns on this embodiment. It is explanatory drawing which shows an example which the bubble is generated in the urea aqueous solution. It is explanatory drawing which shows the 1st threshold value and 2nd threshold value. It is explanatory drawing which shows the execution period of the 1st determination and the 2nd determination. It is a flowchart which shows the diagnostic process by the diagnostic apparatus which concerns on this embodiment. It is a flowchart which shows the modification of the diagnosis process.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

<1. Configuration example of urea SCR system>
A configuration example of the urea SCR system 10 including the reducing agent supply device 30 will be described with reference to FIG. FIG. 1 is a schematic diagram showing a configuration example of the urea SCR system 10.

The urea SCR system 10 is provided in the exhaust system of an internal combustion engine 5 such as a diesel engine. The urea SCR system 10 is mounted on a vehicle, a construction machine, an agricultural machine, or the like equipped with an internal combustion engine 5, and uses an aqueous urea solution as a reducing agent to decompose _{NO X in the exhaust gas discharged from the internal combustion engine 5 and exhaust it.} Purify. As the urea aqueous solution, for example, a urea aqueous solution having the lowest freezing temperature of about 32.5% concentration is used. The freezing temperature in this case is about -11 ° C. Since the freezing temperature rises when the concentration of such an aqueous urea solution changes, it has a property of being easily frozen by evaporating water as a solvent.

The urea SCR system 10 includes a selective reduction catalyst 13 arranged in the middle of the exhaust pipe 11 and a reducing agent supply device 30 that injects an aqueous urea solution into an exhaust passage upstream of the selective reduction catalyst 13.

_{The selective reduction catalyst 13 selectively reduces NO X} contained in the exhaust gas of the internal combustion engine 5 using ammonia. The selective reduction catalyst 13 adsorbs ammonia produced by the decomposition of the urea aqueous solution injected by the reducing agent supply device 30. Then, the selective reduction catalyst 13 _{reacts NO X} in the inflowing exhaust gas with ammonia to decompose it. The selective reduction catalyst 13 has a property that the adsorbable amount of ammonia decreases as the catalyst temperature increases. Further, the selective reduction catalyst 13 has a property that the larger the ratio of the actual adsorbed amount of ammonia to the adsorbable amount, the higher the reducing efficiency of _{NO X.}

The reducing agent supply device 30 injects an aqueous urea solution into the exhaust passage upstream of the selective reduction catalyst 13. The reducing agent supply device 30 is driven and controlled by the control device 100. The injection amount of the urea aqueous solution _{is controlled so that the concentration of NO X} flowing downstream of the selective reduction catalyst 13 and the concentration of ammonia are equal to or less than the reference value. The injection amount of the urea aqueous solution is, for example, the NO _X concentration of the exhaust gas discharged from the internal combustion engine 5, the adsorbable amount of ammonia according to the temperature of the selective reduction catalyst 13, and the current adsorption amount of ammonia on the selective reduction catalyst 13. Etc. are set based on.

Exhaust pipes 11 upstream and downstream of the selective reduction catalyst 13 are provided with exhaust temperature sensors 21 and 23 that detect the exhaust temperature at their respective positions. The sensor signals of the exhaust temperature sensors 21 and 23 are output to the control device 100. The exhaust temperature detected by the exhaust temperature sensors 21 and 23 is also used for estimating the temperature of the selective reduction catalyst 13. In addition to this, the exhaust pipe 11 _{may be provided with a NO X} concentration sensor, an ammonia sensor, or the like (not shown).

<2. Configuration example of reducing agent supply device>
Next, a configuration example of the reducing agent supply device 30 will be described in detail. The reducing agent supply device 30 includes an injection valve 31 and a pump 41. The injection valve 31 is fixed to the exhaust pipe 11 upstream of the selective reduction catalyst 13. The pump 41 sucks up the urea aqueous solution in the storage tank 50 and pumps it. The pump 41 and the injection valve 31 are driven and controlled by the control device 100.

A first reducing agent pipe 58 whose other end is located in the storage tank 50 is connected to the suction port of the pump 41. A second reducing agent pipe 57 whose other end is connected to the injection valve 31 is connected to the discharge port of the pump 41. The pump 41 sucks up the urea aqueous solution in the storage tank 50 through the first reducing agent pipe 58, and supplies the urea aqueous solution to the injection valve 31 through the second reducing agent pipe 57.

A return pipe 59 whose other end is connected to the storage tank 50 is connected to the second reducing agent pipe 57. The return pipe 59 is provided with an orifice or a one-way valve (not shown) so as to hold the pressure in the second reducing agent pipe 57. Further, the pressure sensor 43 is provided in the second reducing agent pipe 57. The pressure sensor 43 is a sensor that detects the pressure Pu of the urea aqueous solution supplied to the injection valve 31, and the sensor signal is output to the control device 100.

As the pump 41, for example, an electromagnetically driven diaphragm pump or a gear pump is used. The output of the pump 41 is controlled by the control device 100. In the present embodiment, the control device 100 controls the output of the pump 41 so that the pressure Pu of the urea aqueous solution supplied to the injection valve 31 is maintained at a predetermined target value Ptgt. For example, the control device 100 feedback-controls the output of the pump 41 based on the difference ΔP between the pressure Pu detected by the pressure sensor 43 and the target value Ptgt.

As the injection valve 31, for example, an electromagnetically driven injection valve whose opening and closing can be switched by energization control is used. The electromagnetically driven injection valve 31 includes an electromagnetic coil, and has a structure in which the valve body moves and opens due to the magnetic force generated by energizing the electromagnetic coil. In the present embodiment, the control device 100 controls the output of the pump 41 so that the pressure Pu of the urea aqueous solution supplied to the injection valve 31 becomes a predetermined target value Ptgt, and according to the target injection amount of the urea aqueous solution. Adjust the valve opening time. For example, the control device 100 controls the injection amount of the urea aqueous solution by adjusting the duty ratio, which is the ratio of the energization time to the total time of the injection cycle, for each constant injection cycle.

Further, the reducing agent supply device 30 includes means for collecting the urea aqueous solution in the device in the storage tank 50. Since the freezing temperature of the urea aqueous solution is about -11 ° C. at the lowest, the urea aqueous solution may freeze while the internal combustion engine 5 is stopped. When the urea aqueous solution freezes in the apparatus, the volume expands, which may damage the respective pipes, the pump 41, the injection valve 31, and the like. Therefore, when the internal combustion engine 5 is stopped, the urea aqueous solution in the apparatus is recovered in the storage tank 50.

For example, when the pump 41 is a pump that can rotate in the reverse direction, the pump 41 is used as a means for recovering the urea aqueous solution, and the urea aqueous solution in the apparatus is sucked back to the storage tank 50 side. Further, by switching the connection destinations of the suction port and the discharge port of the pump 41 to the first reducing agent pipe 58 or the second reducing agent pipe 57, the flow of the urea aqueous solution driven by the pump 41 is reversed. A path switching valve may be provided as a means for recovering the urea aqueous solution. The means for recovering the aqueous urea solution may be other than the means exemplified here.

The storage tank 50 for storing the urea aqueous solution is provided with a thawing means for thawing the frozen urea aqueous solution when the urea aqueous solution is frozen. For example, the thawing means may be an electric heating device such as a heating wire or a PTC (Positive Temperature Coefficient) heater. Alternatively, a cooling water pipe for circulating the cooling water of the internal combustion engine 5 is provided in the storage tank 50, and the cooling water of the internal combustion engine 5 is circulated in the cooling water pipe to thaw the urea aqueous solution in the storage tank 50. It may be.

Further, the storage tank 50 is provided with a concentration sensor 51 for detecting the concentration of the urea aqueous solution in the storage tank 50 and a tank temperature sensor 53 for detecting the temperature of the urea aqueous solution in the storage tank 50. The sensor signals of the concentration sensor 51 and the tank temperature sensor 53 are output to the control device 100. As the concentration sensor 51, for example, a known urea water concentration sensor such as an ultrasonic sensor, a heat transfer type sensor, or an infrared type sensor is used. Each concentration sensor 51 may have an error in the detected value if bubbles are contained in the urea aqueous solution.

FIG. 3 is an explanatory diagram showing an example of a case where bubbles are generated in the urea aqueous solution in the storage tank 50 in which the concentration sensor 51 is installed. As described above, in the reducing agent supply device 30 according to the present embodiment, when the internal combustion engine 5 is stopped, the urea aqueous solution in the device is recovered in the storage tank 50. Therefore, when the internal combustion engine 5 is started, the urea aqueous solution is filled in the apparatus by first driving the pump 41.

At this time, since the urea aqueous solution is filled while the inside of the apparatus is filled with air, when the urea aqueous solution is supplied to the second reducing agent pipe 57, a part of the air is connected to the return pipe 59 together with the urea aqueous solution. It flows into the storage tank 50 through the storage tank 50. As a result, air bubbles are mixed in the urea aqueous solution in the storage tank 50, and the air bubbles can interfere with the concentration detection by the concentration sensor 51. In addition to these examples, for example, when the rotation speed of the internal combustion engine 5 is high or the vehicle speed is high, the urea aqueous solution in the storage tank 50 fluctuates due to the vibration of the vehicle, and bubbles are generated in the urea aqueous solution. In some cases.

<3. Configuration example of control device (diagnostic device)>
Next, a configuration example of the control device 100 that functions as a diagnostic device for the concentration of the urea aqueous solution according to the present embodiment will be described. FIG. 2 is a block diagram functionally showing the configuration of the control device 100.

The control device 100 includes a processing unit 110, a storage unit 140, an injection valve drive unit 150, and a pump drive unit 160. The processing unit 110 may be composed of, for example, a microcomputer such as a CPU, a microprocessor unit, or the like, or may be configured by an updatable one such as firmware. Further, the processing unit 110 may be a program module or the like executed by a command from a CPU or the like.

The sensor signal S_cu of the concentration sensor 51, the sensor signal S_tu of the tank temperature sensor 53, the sensor signal S_pu of the pressure sensor 43, and the sensor signals S_tgu and S_tgd of the exhaust temperature sensors 21 and 23 are input to the control device 100. Further, the control device 100 is provided with information on the operating state of the internal combustion engine 5 such as the on / off signal S_key_swt of the key switch of the vehicle, the engine speed Ne, and the vehicle speed V, directly or via a communication means such as CAN (Controller Area Network). Is entered.

The storage unit 140 includes a storage element (not shown) such as a RAM (Random Access Memory) and a ROM (Read Only Memory). The storage unit 140 may include other storage media such as a CD-ROM and a storage device. The storage unit 140 stores a program executed by the processing unit 110, various parameters used in the arithmetic processing, an arithmetic result, a detection result, and the like.

The injection valve drive unit 150 and the pump drive unit 160 are composed of an electric circuit. The injection valve drive unit 150 operates based on a drive instruction signal from the processing unit 110 to drive the injection valve 31. The pump drive unit 160 operates based on a drive instruction signal from the processing unit 110 to drive the pump 41.

The processing unit 110 includes a pressure detection unit 112, a concentration detection unit 114, a first determination unit 115, a second determination unit 116, a defrost control unit 118, an injection valve control unit 120, and a pump control unit 122. And have. Each of these units is a function realized by the processing unit 110 executing a program.

The pressure detection unit 112 detects the pressure Pu of the urea aqueous solution supplied to the injection valve 31 based on the sensor signal S_pu of the pressure sensor 43.

The concentration detection unit 114 detects the concentration (hereinafter, also referred to as “detection concentration”) C_u of the urea aqueous solution in the storage tank 50 based on the sensor signal S_cu of the concentration sensor 51.

The thawing control unit 118 performs thawing control when the temperature Tu of the urea aqueous solution in the storage tank 50 detected based on the sensor signal S_tu of the tank temperature sensor 53 is equal to or lower than the reference temperature for determining the necessity of executing the thawing control. Execute. The frozen urea aqueous solution is thawed by operating a thaw means (not shown). For example, the thawing control unit 118 operates a heating device installed in the storage tank 50 to thaw the frozen urea aqueous solution. Alternatively, the thawing control unit 118 circulates the cooling water of the internal combustion engine 5 through the cooling water pipe arranged in the storage tank 50 to thaw the frozen urea aqueous solution.

The thawing control unit 118 may end the thawing control when, for example, the temperature Tu of the urea aqueous solution in the storage tank 50 exceeds the above-mentioned reference temperature. Alternatively, the decompression control unit 118 may end the decompression control when a preset time has elapsed.

The pump control unit 122 controls the output of the pump 41. The pump control unit 122 feedback-controls the output of the pump 41 so that the pressure Pu detected by the pressure detection unit 112 becomes a preset target value Ptgt. For example, the pump control unit 122 PID controls the output of the pump 41 based on the difference ΔP between the detected pressure Pu and the target value Ptgt. Since the pressure Pu of the urea aqueous solution tends to decrease as the injection amount of the urea aqueous solution from the injection valve 31 increases, the output of the pump 41 increases as the injection amount of the urea aqueous solution increases.

For example, the pump control unit 122 sets the duty ratio, which is the ratio of the energization time to the total time of the processing cycle, for each fixed processing cycle. In this case, the larger the duty ratio, the larger the output of the pump 41. The pump control unit 122 outputs a drive instruction signal to the pump drive unit 160 based on the set duty ratio. The pump drive unit 160 energizes the pump 41 according to the input drive instruction signal.

The injection valve control unit 120 controls the drive of the injection valve 31. As described above, since the pressure Pu of the urea aqueous solution supplied to the injection valve 31 is controlled to be the target value Ptgt, the injection valve control unit 120 has the pressure Pu of the urea aqueous solution set to the target value Ptgt. On the premise of this, the valve opening time of the injection valve 31 is controlled according to the indicated value of the injection amount.

For example, the injection valve control unit 120 obtains the amount of ammonia required to reduce _{NO X} in the exhaust gas discharged from the internal combustion engine 5. The amount of the NO _X in the exhaust gas, for example, the NO _X concentration detected by the NO _X concentration or NO _X sensor is estimated based on the operating state of the internal combustion engine 5, NO _X obtained by multiplying the flow rate of the exhaust gas The flow rate is used.

Further, the injection valve control unit 120 obtains an excess or deficiency of ammonia with respect to the target adsorption amount of ammonia in the selective reduction catalyst 13. As the target adsorption amount of ammonia in the selective reduction catalyst 13, for example, a value obtained by multiplying the adsorbable amount according to the temperature of the selective reduction catalyst 13 estimated based on the exhaust temperature Tgas by the target adsorption rate is used. The target adsorption rate may be, for example, 70 to 80%. If the target adsorption rate is 70 to 80%, the adsorption rate is maintained relatively high and the NO _X reduction efficiency is maintained high, while ammonia can be adsorbed even when the catalyst temperature rises sharply. The amount is less likely to fall below the actual amount of ammonia adsorbed. The injection valve control unit 120 obtains an excess or deficiency of ammonia amount based on the difference between the current ammonia adsorption amount and the target adsorption amount obtained by integration.

The injection valve control unit 120 _{adds the amount of ammonia required to reduce NO X} in the exhaust gas and the amount of ammonia in excess or deficiency with respect to the target adsorption amount of the selective reduction catalyst 13. The injection valve control unit 120 sets a target injection amount as the amount of the urea aqueous solution capable of generating the calculated amount of ammonia, and outputs a drive instruction signal to the injection valve drive unit 150. The injection valve drive unit 150 energizes the injection valve 31 according to the input drive instruction signal. For example, the injection valve control unit 120 sets a duty ratio, which is the ratio of the energization time to the total time of the injection cycle, based on the target injection amount for each constant injection cycle. The injection valve drive unit 150 switches the energization of the injection valve 31 to the electromagnetic coil on and off according to the set duty ratio.

The first determination unit 115 executes the first determination regarding the concentration of the aqueous urea solution. Specifically, the first determination unit 115 determines whether or not the deviation between the detection concentration C_u of the urea aqueous solution detected by the concentration detection unit 114 and the reference concentration C0 is equal to or less than the first threshold value thre_A. In the present embodiment, the reference concentration C0 of the urea aqueous solution is 32.5%. The detection concentration C_u of the urea aqueous solution used for the determination may be an average value of the detection concentrations C_u detected within a predetermined period. The first determination unit 115 starts executing the first determination after the control device 100 is activated, and when the condition for increasing the number of bubbles in the urea aqueous solution in the storage tank 50 (first condition) is satisfied, the first determination unit 115 is executed. Ends the execution of the judgment of.

The second determination unit 116 executes a second determination regarding the concentration of the aqueous urea solution. Specifically, in the second determination unit 116, the deviation between the detection concentration C_u of the urea aqueous solution detected by the concentration detection unit 114 and the reference concentration C0 is greater than the first threshold value thre_A and equal to or less than the second threshold value thre_B. Determine if it exists. Similar to the first determination, the detection concentration C_u of the urea aqueous solution used for the determination may be an average value of the detection concentrations C_u detected within a predetermined period. The second determination unit 116 executes the second determination after at least the first condition is satisfied. That is, the second determination is executed after at least the execution of the first determination is completed. For example, the second determination unit 116 may start executing the second determination after the control device 100 is activated, and may continue the second determination even after the first condition is satisfied.

Here, the first determination by the first determination unit 115 and the second determination by the second determination unit 116 will be described. FIG. 4 is an explanatory diagram showing a first threshold value thre_A and a second threshold value thre_B used in the first determination and the second determination, respectively. The second threshold value thre_B, which is the allowable range of the deviation (| C_u-C0 |) between the detection concentration C_u and the reference concentration C0 used in the second determination, is the detection concentration C_u and the reference concentration C0 used in the first determination. It is set to a value larger than the first threshold value thre_A, which is an allowable range of deviation from (| C_u-C0 |). When the reference concentration C0 of the urea aqueous solution is 32.5%, the first threshold value thr_A is set to, for example, about 2.5%, and the second threshold value thre_B is set to, for example, 10.0%.

Since the first determination by the first determination unit 115 is performed during the period when there are few bubbles in the urea aqueous solution, the reliability of the detection concentration C_u detected by the concentration sensor 51 during the execution of the first determination is high. I can say. Therefore, the first threshold value thr_A is set to a relatively small value, and in the first determination, it is diagnosed whether the actual concentration of the urea aqueous solution is close to the reference concentration C0. For example, when an abnormality is detected by the first determination, _{it is difficult to supply an aqueous urea solution in just proportion according to NO X} in the exhaust gas, so that the output of the engine is limited or the engine is used. You may stop the start of.

On the other hand, since the second determination by the second determination unit 116 is performed during the period including the period during which bubbles can be generated in the urea aqueous solution, the detection concentration detected by the concentration sensor 51 during the execution of the second determination is performed. It can be said that the reliability of C_u is low. Therefore, the second threshold value thr_B is set to a relatively large value, and in the second determination, it is erroneously determined to be abnormal even though the actual concentration of the urea aqueous solution is close to the reference concentration C0. Suppress that. For example, if an abnormality is detected by the second determination, it is possible that the concentration of the urea aqueous solution is not abnormal and the state of the urea aqueous solution is unintentionally changed. It may be limited to measures.

FIG. 5 is an explanatory diagram showing an execution period of the first determination by the first determination unit 115 and the second determination by the second determination unit 116. In the example shown in FIG. 5, when the control device (diagnostic device) 100 is activated, both the first determination and the second determination are started to be executed. Urea into the reducing agent supply device 30 after the start of the control device 100, for example, until the thawing control of the urea aqueous solution in the storage tank 50 is completed, or until the catalyst temperature rises and the selective reduction catalyst 13 is activated. Filling of the aqueous solution is not started. Therefore, there are few bubbles in the urea aqueous solution in the storage tank 50.

Therefore, not only the second determination but also the first determination is executed in the period until the first condition that the bubbles in the urea aqueous solution in the storage tank 50 can increase is satisfied. As a result, the certainty that an abnormality in the concentration of the urea aqueous solution is detected is improved, and relatively strict measures such as output limitation of the internal combustion engine can be taken. On the other hand, after the first condition is satisfied, air bubbles may be contained in the urea aqueous solution in the storage tank 50, so that the first determination is not performed and only the second determination is continued. As a result, when it cannot be determined that the concentration of the urea aqueous solution is in an abnormal state, it is possible to limit the measures to relatively loose measures such as warning.

Here, the first condition in which bubbles can be generated in the urea aqueous solution may be the start of the reducing agent supply device 30. As shown in FIG. 3, when the driving of the pump 41 of the reducing agent supply device 30 is started and the urea aqueous solution starts to be filled in the reducing agent supply device 30, the air filling the device is returned together with the urea aqueous solution 59. It is mixed into the storage tank 50 via the above, and bubbles are generated in the urea aqueous solution in the storage tank 50. Further, the first condition may be the start of traveling of the vehicle. Even before the reducing agent supply device 30 is started, when the vehicle starts running, bubbles may be generated in the urea aqueous solution due to disturbances such as shaking during acceleration and vibration of the internal combustion engine 5. In addition, the first condition may include an appropriate condition in which bubbles may be generated in the urea aqueous solution. Then, the first determination unit 115 ends the execution of the first determination when any one of these first conditions is satisfied.

<4. Flowchart>
Next, with reference to FIG. 6, an example of a method for diagnosing the concentration of the urea aqueous solution executed by the control device (diagnosis device) 100 will be described.

First, when the control device 100 is activated (step S11), the first determination unit 115 and the second determination unit 116 of the processing unit 110 determine whether or not the thawing control of the urea aqueous solution is completed (step S13). .. The thawing control unit 118 of the processing unit 110 executes thawing control when the urea aqueous solution is frozen, ends the thawing control when it is determined that the frozen urea aqueous solution has been thawed, and stores the completion of the thawing control. Store in unit 140. The defrost control unit 118 stores the completion of the defrost control in the storage unit 140 even when the defrost control is not required.

When the thawing control of the urea aqueous solution is not completed (S13 / No), the first determination unit 115 and the second determination unit 116 repeat the determination in step S13 until the thawing control of the urea aqueous solution is completed. When the thawing control of the urea aqueous solution is completed (S13 / Yes), the first determination unit 115 and the second determination unit 116 start the first determination and the second determination, respectively (step S15).

Next, the first determination unit 115 determines whether or not the deviation (| C_u-C0 |) between the detected concentration C_u and the reference concentration C0 is equal to or less than the first threshold value thre_A (step S17). When the deviation between the detected concentration C_u and the reference concentration C0 (| C_u-C0 |) exceeds the first threshold value thre_A (S17 / No), the first determination unit 115 indicates that the concentration of the urea aqueous solution is abnormal. Determine (step S33). On the other hand, when the deviation between the detected concentration C_u and the reference concentration C0 (| C_u-C0 |) is equal to or less than the first threshold value thre_A (S17 / Yes), the first determination unit 115 indicates that there is no abnormality in the concentration of the urea aqueous solution. Determine (step S19).

Next, the first determination unit 115 determines whether or not the condition for increasing bubbles (first condition) in the urea aqueous solution in the storage tank 50 is satisfied (step S21). For example, the first determination unit 115 determines whether or not any of the preset conditions such as the reduction agent supply device 30 has been started and the vehicle has started running is satisfied. To determine. When the first condition is not satisfied (S21 / No), the first determination unit 115 returns to step S17 and repeats the first determination. On the other hand, when the first condition is satisfied (S21 / Yes), the first determination unit 115 ends the execution of the first determination (step S23).

Next, the second determination unit 116 determines whether or not the deviation (| C_u-C0 |) between the detected concentration C_u and the reference concentration C0 is equal to or less than the second threshold value thre_B (step S25). When the deviation between the detected concentration C_u and the reference concentration C0 (| C_u-C0 |) exceeds the second threshold value thre_B (S25 / No), the second determination unit 116 indicates that the concentration of the urea aqueous solution is abnormal. Determine (step S33). On the other hand, when the deviation between the detected concentration C_u and the reference concentration C0 (| C_u-C0 |) is equal to or less than the second threshold value thre_B (S25 / Yes), the second determination unit 116 indicates that there is no abnormality in the concentration of the urea aqueous solution. Judgment (step S27).

Next, the second determination unit 116 determines whether or not the elapsed time T from the start of the second determination has reached the preset threshold value T1 (step S29). This threshold value T1 sets the end time of the second determination, and is set to, for example, 30 minutes. The elapsed time T may be the elapsed time after the diagnostic device 100 is started, or the elapsed time after the reducing agent supply device 30 is started.

When the elapsed time T has not reached the threshold value T1 (S29 / No), the second determination unit 116 returns to step S25 and repeats the second determination. On the other hand, when the elapsed time T has reached the threshold value T1 (S29 / Yes), the second determination unit 116 ends the execution of the second determination (step S31).

When it is determined in step S33 that there is an abnormality in the concentration of the urea aqueous solution, the control device 100 executes an appropriate process according to the abnormality due to the first determination or the abnormality due to the second determination. For example, when the first determination result shows an abnormality (S17 / No), it is difficult to supply an appropriate amount of urea aqueous solution corresponding to _{NO X in the exhaust gas, so that the control device 100 has a control device 100.} The output of the internal combustion engine may be limited or the start of the internal combustion engine may be stopped so that _{the NO X} concentration in the exhaust gas is reduced. On the other hand, when the second determination result shows an abnormality (S25 / No), the control device 100 may execute a warning process for notifying a passenger such as a driver of the abnormality in the concentration of the urea aqueous solution. good. For example, the control device 100 may execute at least one process of generating a warning sound, lighting a warning lamp, or displaying a warning.

In the method for diagnosing the concentration of the aqueous urea solution described based on the flowchart of FIG. 6, the execution of the first determination is terminated when the first condition is satisfied after the control device 100 is started. However, the first determination unit 115 restarts the first determination even after the execution of the first determination is once completed in a state where there are few bubbles in the urea aqueous solution in the storage tank 50. It is also good. FIG. 7 is a flowchart showing an example in which the first determination is restarted after the execution of the first determination is completed.

After the execution of the first determination is completed, the first determination unit 115 determines whether or not the second condition presumed to be a state in which there are few bubbles in the urea aqueous solution in the storage tank 50 is satisfied. (Step S41). The second condition is, for example, that a predetermined time or more has passed since the start of driving the pump 41 of the reducing agent supply device 30, the rotation speed Ne of the internal combustion engine 5 is equal to or less than a predetermined threshold value, and the vehicle speed V is high. It can be less than or equal to a predetermined threshold.

After starting the driving of the pump 41, with the passage of time, the air filled in the device while the vehicle is stopped is discharged to the outside of the device, and the air bubbles generated in the storage tank 50 disappear. Therefore, one of the second conditions is that a predetermined time or more has passed since the operation of the pump 41 was started. Further, when the rotation speed Ne of the internal combustion engine 5 is low and the vehicle speed V is low, the fluctuation of the urea aqueous solution in the storage tank 50 is small, and bubbles are unlikely to be generated in the urea aqueous solution. Therefore, the second condition includes that the rotation speed Ne of the internal combustion engine 5 is equal to or less than a predetermined threshold value and the vehicle speed V is equal to or less than a predetermined threshold value. In addition, the second condition may be set as appropriate.

When the second condition is not satisfied (S41 / No), the first determination unit 115 repeats the determination in step S41 until the second condition is satisfied. On the other hand, when the second condition is satisfied (S41 / Yes), the first determination unit 115 resumes the execution of the first determination (step S43).

Next, the first determination unit 115 determines whether or not the deviation (| C_u-C0 |) between the detected concentration C_u and the reference concentration C0 is equal to or less than the first threshold value thre_A (step S45). When the deviation between the detected concentration C_u and the reference concentration C0 (| C_u-C0 |) exceeds the first threshold value thre_A (S45 / No), the first determination unit 115 indicates that the concentration of the urea aqueous solution is abnormal. Determine (step S49). On the other hand, when the deviation between the detected concentration C_u and the reference concentration C0 (| C_u-C0 |) is equal to or less than the first threshold value thre_A (S45 / Yes), the first determination unit 115 indicates that there is no abnormality in the concentration of the urea aqueous solution. Judgment (step S47). If no abnormality is found in the concentration of the urea aqueous solution, the first determination unit 115 returns to step S41 and repeats the first determination while the second condition is satisfied.

As shown in FIG. 7, the second condition that the number of bubbles in the urea aqueous solution in the storage tank 50 is reduced even after the first determination unit 115 once finishes the execution of the first determination. By executing the first determination while the above is satisfied, the concentration of the urea aqueous solution can be diagnosed more accurately.

As described above, the control device (diagnosis device) 100 of the reducing agent supply device 30 according to the present embodiment has a detection concentration C_u of the concentration sensor 51 in a state where there are few bubbles in the urea aqueous solution in the storage tank 50. The first determination is performed using the relatively small first threshold value thre_A as the threshold value of the deviation (| C_u-C0 |) from the reference concentration C0. Further, in the control device 100 according to the present embodiment, in a state where bubbles in the urea aqueous solution in the storage tank 50 can increase, the deviation between the detection concentration C_u of the concentration sensor 51 and the reference concentration C0 (| C_u-C0 | ) Is used as the second threshold value thre_B, which is relatively large, to execute the second determination.

Therefore, when the detection concentration C_u of the concentration sensor 51 is highly reliable, a diagnosis with relatively high accuracy can be performed by the first determination. On the other hand, when the reliability of the detection concentration C_u of the concentration sensor 51 is low in a state where bubbles can be contained in the urea aqueous solution, the actual concentration of the urea aqueous solution may be approximated to the reference concentration C0 by the second determination. Regardless, it is possible to prevent erroneous determination as an abnormality.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

5 ... Internal combustion engine, 10 ... Urea SCR system, 11 ... Exhaust pipe, 13 ... Selective reducing catalyst, 30 ... Reducing agent supply device, 31 ... Injection valve, 41 ... Pump, 51 ... concentration sensor, 100 ... control device (diagnostic device), 110 ... processing unit, 114 ... concentration detection unit, 115 ... first determination unit, 116 ... second Judgment unit, 120 ... Injection valve control unit, 122 ... Pump control unit

Claims (7)

In a diagnostic device that diagnoses the concentration of a liquid reducing agent used for purifying the exhaust gas of an internal combustion engine mounted on a vehicle by using a concentration sensor installed in a tank that stores the liquid reducing agent.
A first determination unit that executes a first determination for determining whether or not the deviation between the detection value of the concentration sensor and the reference concentration of the liquid reducing agent is equal to or less than the first threshold value.
A second determination for determining whether or not the deviation between the detected value of the concentration sensor and the reference concentration of the liquid reducing agent is equal to or less than a second threshold value larger than the first threshold value is executed. Equipped with a judgment unit
The first determination unit starts executing the first determination after the diagnostic apparatus is activated, and when the first condition for increasing the number of bubbles in the liquid reducing agent in the tank is satisfied, the first determination unit is established. Finish the execution of the judgment of
The second determination unit is a diagnostic device that executes the second determination after at least the first condition is satisfied. The diagnostic device according to claim 1, wherein the first condition is the start of a reducing agent supply device that supplies the liquid reducing agent to the exhaust passage of the internal combustion engine. The diagnostic device according to claim 1, wherein the first condition is the start of traveling of the vehicle. The diagnosis according to claim 1, wherein the second determination unit starts executing the second determination after the diagnostic apparatus is activated, and continues the second determination even after the first condition is satisfied. Device. The first determination unit starts executing the first determination after the diagnostic apparatus is activated and after the liquid reducing agent in the tank is thawed.
The diagnostic device according to claim 4, wherein the second determination unit starts executing the second determination after the start of the diagnostic device and after the thawing of the liquid reducing agent in the tank. After the first condition is satisfied and the execution of the first determination is completed, the first determination unit satisfies the second condition that the vibration of the liquid reducing agent in the tank is reduced. The diagnostic device according to any one of claims 1 to 5, which executes the first determination when the device is present. In a diagnostic method for diagnosing the concentration of a liquid reducing agent used for purifying the exhaust gas of an internal combustion engine mounted on a vehicle by using a concentration sensor installed in a tank for storing the liquid reducing agent.
During the period from the start of the diagnostic device until the first condition for increasing the number of bubbles in the liquid reducing agent in the tank is satisfied, the deviation between the detection value of the concentration sensor and the reference concentration of the liquid reducing agent is different. While executing the first determination to determine whether or not it is equal to or less than the first threshold value,
After the start of the diagnostic apparatus and at least after the first condition is satisfied, the deviation between the detection value of the concentration sensor and the reference concentration of the liquid reducing agent is equal to or less than the second threshold value larger than the first threshold value. A diagnostic method that performs a second determination to determine the presence or absence.

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