Anomaly detection device

Abstract

Anomaly detection device for an exhaust gas purification system (10), comprising an admixture valve (50) provided in an exhaust gas duct (31a) of an internal combustion engine (30) for admixing a reducing agent in a liquid state to a NOx purification catalyst (33) that purifies an exhaust gas of NOx, a tank (40) for storing the reducing agent and a pump (44) for discharging the reducing agent stored in the tank (40) by a forward rotation and for drawing the reducing agent back into the tank by a reverse rotation, with: a switching part (70: S72, S76) for switching the mixing valve (50) to an open state and a closed state a plurality of times in a state of reverse rotation of the pump (44); a recovery section (70: S78) for obtaining a variation quantity of a rotational speed of the pump (44) or a correlated value of the variation quantity caused by a switching of the mixing valve (50), as a rotational variation parameter (ΔDU); and a test part (70: S24 to S56) for checking whether the mixing valve (50) is anomalous, based on at least two rotation variation parameters, wherein The test part (70: S24, S26) tests the mixing valve (50) by comparing the rotation change parameter obtained at a preceding switching time and the rotation change parameter obtained at a subsequent switching time, each with different threshold values ​​(K1, K2).

Description

[0001] The present invention relates to an anomaly detection device applied to an exhaust gas purification system which adds a liquid reducing agent to an exhaust gas channel of an internal combustion engine.

[0002] In recent years, a urea-SCR (selective catalytic reduction) system has been developed and mass-produced as an exhaust gas purification system for cleaning NOx (nitrogen oxides) from exhaust gas with a high cleaning rate in a machine (especially a diesel engine) of a vehicle and the like.

[0003] The urea SCR system comprises a pump and an injection valve, which acts as a blending valve. The pump supplies a pressurized urea solution (a urea water solution) to a reducing agent channel stored in a tank. The injection valve mixes the urea solution (the urea water solution) into the exhaust duct of the engine.

[0004] In the urea SCR system, the exhaust gas is cleaned by a NOx reduction reaction at a NOx removal catalyst (hereinafter referred to as an SCR catalyst) in the exhaust manifold. During NOx reduction, ammonia (NH3) is first produced by hydrolyzing urea solution injected into the exhaust manifold by the injection valve, using heat from the exhaust gas. This ammonia is then adsorbed by the SCR catalyst. The NOx is reduced and removed from the exhaust gas by a reduction reaction with ammonia at the SCR catalyst.

[0005] In such a urea SCR system, if the operation of the injection valve is hindered by urea crystallization or if a foreign substance enters the injection valve from the exhaust side through an injection orifice, the injected quantity of urea solution can become abnormal. To counteract this potential abnormality, the following patent specification proposes a device for checking whether the injection valve is abnormal, that is, whether an abnormality exists in the injection valve, by using a pump duty cycle (hereinafter referred to as a pump duty cycle) to control a current supplying the pump. More precisely, it discloses a device for checking whether or not an abnormality exists in the injection valve based on the pump duty cycle in a non-injection state of urea solution during injection control.

[0006] Patent specification: JP 2013-249 801 A

[0007] In the urea SCR system disclosed in the patent document, the injection valve is checked for anomalies based on the pump duty cycle in the middle section of the injection control system. However, in a state where injection control is not active, for example, when the SCR catalyst is inactive due to low temperature, the pump duty cycle used for anomaly detection does not vary. Therefore, it is not possible to accurately determine whether the injection valve has an anomaly. The aim is to develop a technology suitable for determining the presence or absence of an anomaly in the injection valve in a state where blending control, such as injection control, is not active.Such a problem is not limited to cases where urea water is used, but is a common problem even in other cases where a liquid other than the reducing agent is used.

[0008] Further state of the art is disclosed in the following documents.

[0009] DE 10 2014 226 502 A1 discloses a method for monitoring a conveying system for a liquid medium. In this method, the conveying system comprises at least one pump for pumping the liquid medium from a tank, at least one metering valve, and at least one return line to the tank. A check valve is provided in the return line. To monitor the check valve, the pump is operated in a back-suction mode with the metering valve closed. The resulting negative pressure is used as a good test criterion for the check valve based on at least one operating characteristic of the conveying system.

[0010] DE 10 2009 029 408 A1 discloses a method for monitoring the function of an SCR catalyst system. The SCR catalyst system is disclosed as an exhaust aftertreatment system for an internal combustion engine, comprising at least one feed pump, at least one multi-way valve, at least one metering valve, and at least one pressure sensor. It is characterized in that, during a backflow mode of the SCR catalyst system, the build-up of a vacuum in the SCR catalyst system is monitored based on at least one measured value from the pressure sensor, and if the at least one measured value deviates from an expected reference value, a malfunction of the SCR catalyst system is inferred.

[0011] The present invention addresses the problem described above, and one object of the invention is to provide an anomaly detection device suitable for checking, in a state where no mixing control is performed, whether a mixing valve is anomalous, i.e., whether an anomaly exists in the mixing valve.

[0012] According to the present invention, an anomaly detection device for an exhaust gas purification system is provided, comprising an admixture valve, which is provided in an exhaust gas channel of an internal combustion engine for admixing a reducing agent to a NOx cleaning catalyst that cleans NOx in an exhaust gas, a tank for storing the reducing agent and a pump for unloading the reducing agent stored in the tank by a forward rotation and for drawing the reducing agent back into the tank by a reverse rotation.The anomaly detection device comprises a switching section for switching the mixing valve to an open state and a closed state a plurality of times in a state of reverse rotation of the pump, a recovery section for obtaining a variation quantity of a rotational speed of the pump or a correlated value of the variation quantity caused by a switching of the mixing valve as a rotation change parameter, and a test section for checking whether the mixing valve is anomalous, based on at least two rotation variation parameters. Fig. Figure 1 is a schematic view showing the basic features of an exhaust gas purification system of a machine; Fig. 2 is a flowchart showing an anomaly detection process according to a first embodiment; Fig. 3 is a flowchart showing a variation set extraction process; Fig. 4 is a time diagram showing a change in the rotational speed of a pump in an injection valve control system; Fig. Figure 5 is a schematic view showing changes in urea water during anomaly detection processing; Fig. Figure 6 is a time graph showing a variation of a pump duty cycle during anomaly detection processing; Fig. Figure 7 is a time graph showing a variation in the pump duty cycle during anomaly detection processing; Fig. Figure 8 is a time graph showing a variation in the pump duty cycle during anomaly detection processing; Fig. Figure 9 is a flowchart showing an anomaly check processing procedure according to a second embodiment; and Fig. Figure 10 is a time graph showing a change in the pump duty cycle during anomaly detection processing. (First embodiment)

[0013] An exhaust gas purification system 10, to which a pump control unit 70, which relates to an anomaly detection device according to a first embodiment, is applied, will be described below with reference to the drawings. The exhaust gas purification system 10 cleans exhaust gas of NOx by using a selective catalytic reduction (SCR) catalyst and is configured as a urea SCR system. The exhaust gas purification system 10 is applied to various vehicles to which a diesel engine (hereinafter referred to as an engine) 30, which is an internal combustion engine, is attached. The exhaust gas purification system 10 can also be applied to construction equipment, such as cranes, agricultural equipment, such as tractors, and the like.

[0014] As in Fig. As shown in Figure 1, in the exhaust gas purification system 10, an exhaust pipe 31, forming an exhaust channel 31a, is connected to the machine 30 in a machine exhaust system. A diesel particulate filter (DPF) 32 and an selective catalytic reduction (SCR) catalyst 33 are arranged successively in the exhaust pipe 31, starting from the upstream side of the exhaust gas flow. Between the DPF 32 and the SCR catalyst 33, a urea-water injection valve 50 (hereinafter referred to as an injection valve) is also provided in the exhaust pipe 31. This valve injects urea water (an aqueous urea solution) as a liquid reducing agent into the exhaust channel 31a and supplies it with this solution. The injector 50 is mounted in such a way that only one front end is located inside the exhaust pipe 31 in order to avoid as much as possible the influence of heat applied by the high temperature exhaust gas (e.g. 600°C).In the present embodiment, the SCR catalyst 33 is a NOx cleaning catalyst, and the injection valve 50 is a blending valve.

[0015] The DPF 32 is a PM removal filter for capturing PM (particulate matter) in the exhaust gas. The DPF 32 incorporates a platinum-based oxidation catalyst and removes HC and CO along with a soluble organic fraction (SOF), which is one of the PM components. The PM trapped in the DPF 32 are burned and removed by post-injection or a similar process after the main fuel injection in the engine 30, allowing the DPF 32 to be used continuously.

[0016] The SCR catalyst 33 cleans the exhaust gas of NOx by promoting the following reduction reaction (exhaust gas purification reaction) of NOx, as illustrated below. In these reactions, the injection valve 50, which is provided on the upstream side of the SCR catalyst 33, is supplied with urea water by injection to generate ammonia (NH3), which is the reducing agent for NOx. 4NO + 4NH3 + O2 → 4N2 + 6H2O (Equation 1) 6NO2 + 8NH3 → 7N2 + 12H2O (Equation 2) NO + NO2 + 2NH3 → 2N2 + 3H2O (Equation 3)

[0017] In the exhaust pipe 31, an oxidation catalyst can be provided on the downstream side of the SCR catalyst 33 as an ammonia removal device. This oxidation catalyst removes ammonia (NH3) discharged from the SCR catalyst 33, i.e., excess ammonia.

[0018] Each configuration of the urea-water injection system 20, which injects urea-water by means of an injection valve 50 at the exhaust aftertreatment system 10, will be described next. For convenience, in the following description, assuming that the injection valve 50 is supplied with urea-water from a urea-water tank 40 (hereinafter referred to as a tank), one side of the tank 40 will be referred to as an upstream side, and one side of the injection valve 50 will be referred to as a downstream side.

[0019] In Fig. In the present embodiment, tank 40 is a sealed container with a liquid supply lid, and urea solution of a predetermined, specified concentration is stored within the tank 40. The urea concentration is 32.5%, at which the freezing temperature (freezing point) is lowest. At a urea concentration of 32.5%, the urea solution freezes at -11°C or lower.

[0020] Tank 40 and injection valve 50 are connected by a supply pipe 42. The upstream side end section of the supply pipe 42 is substantially connected to the center of a bottom surface of tank 40 to allow the urea solution stored in tank 40 to flow into the supply pipe 42. In the present embodiment, the supply pipe 42 is designed as the channel for the reducing agent.

[0021] A urea water pump (hereinafter referred to as a pump) 44 is provided in the middle section of the supply pipe 42. The pump 44 is an electric pump, driven by a current supplied by a pump control unit 70, and pressurizes the urea water from the tank 40 and supplies the injection valve 50 with the urea water via the supply pipe 42.

[0022] The pump 44 has an impeller 45 and supplies the urea solution according to the rotational speed of the impeller 45. The pump 44 is also capable of rotating the impeller 45 in both forward and reverse directions. The urea solution in the tank 40 is discharged by the forward rotation (normal rotation) of the pump 44, and the urea solution is drawn back into the tank 40 by the reverse rotation of the pump 44.

[0023] The pump 44 is equipped with a rotation detection sensor 46. The rotation detection sensor 46 detects a rotational speed N, which is the number of rotations per unit of time of the pump 44, and detects, for example, a discharge (pressure feed) speed of the urea water from the pump 44.

[0024] The supply pipe 42 is equipped with a pressure sensing sensor 48 on the downstream side of the pump 44. The pressure sensing sensor 48 detects the pressure P in the supply pipe 42 (which is referred to below as pipe pressure) and detects, for example, the discharge pressure of the urea solution through the pump 44.

[0025] The injection valve 50 is connected to a downstream section of the supply pipe 42. The injection valve 50 has essentially the same configuration as an existing fuel injection valve (an injector), and therefore its configuration will be briefly described here. The injection valve 50 is configured as an electromagnetic on / off valve, comprising a drive part made of an electromagnetic solenoid or the like, and a valve body part having a needle 52 for opening and closing a front-end injection port. It is driven to open and close in response to a drive signal supplied by a pump control unit 70.That is, when the electromagnetic solenoid is excited in response to the drive signal, the needle 52 moves in the opening direction according to the excitation, and the front-end injection port is opened by the movement of the needle 52, so that the urea water is injected.

[0026] A branch pipe 54, which is a return pipe, is connected to the supply pipe 42. The branch pipe 54 connects a branch section B on the downstream side of the pump 44 in the supply pipe 42 and the tank 40. The pressure sensing sensor 48 is provided in a section of the supply pipe 42 at a location between the pump 44 and the branch section B.

[0027] One end of the branch pipe 54 is connected to the bottom surface of the tank 40. A check valve 60 is provided at one end of the branch pipe 54. The check valve 60 closes when the pressure in the branch pipe 54 is lower than a predetermined pressure, thus preventing urea solution stored in the tank 40 from flowing into the branch pipe 54. The check valve 60 is open when the pressure in the branch pipe 54 is higher than the predetermined pressure, allowing the urea solution to flow from the supply pipe 42 into the branch pipe 54 to return to the tank 40.

[0028] A heating element 62 is provided in tank 40. The heating element 62 is, for example, an electric heater and thaws the urea solution frozen in tank 40 by means of an excitation based on a command signal from the pump control unit 70. It is sufficient for the heating element 62 to be located in a position suitable for thawing the frozen urea solution, and it can be located near a suction opening of the supply pipe 42.

[0029] A heating element 64 is provided on an outer periphery of the supply pipe 42. The heating element 64 is, for example, an electric heater and thaws the urea water that is frozen in the tank 40 by means of excitation by the pump control unit 70.

[0030] A temperature sensor 66 is provided in tank 40. The temperature sensor 66 is, for example, a temperature-sensitive diode or a thermistor and measures the temperature of the urea solution in tank 40. An ambient air temperature sensor 68 is provided outside of tank 40. The ambient air temperature sensor 68 is, for example, a temperature-sensitive diode or a thermistor, which is spaced away from tank 40 and measures the temperature of the ambient air around the vehicle to which the machine 30 is attached.

[0031] The pump control unit 70 is an ECU (electronic control unit) that performs control functions related to exhaust gas purification and is configured as a microcomputer comprising a CPU, ROM, RAM, an input / output interface, and the like. The pump control unit 70 obtains the rotational speed N from the rotation sensor 46, the pipe pressure P from the pressure sensor 48, the temperature of the urea solution in the tank 40 from the temperature sensor 66, and the ambient air temperature from the ambient air temperature sensor 68. Based on these acquired values, the pump control unit 70 controls each component of the urea solution injection system 20. In the present embodiment, the pump control unit 70 is an anomaly detection device.

[0032] At the time of pressurization of the urea solution to the side of the injection valve 50, more precisely, the pump 44 is energized to rotate in the forward direction. As a result, the urea solution in the tank 40 is discharged and flows downstream. The urea solution is pumped out of the pump 44 and supplied to the injection valve 50. The excess urea solution flows back into the tank 40 through the check valve 60.

[0033] Furthermore, when the urea solution is drawn back into tank 40, pump 44 is driven in reverse. As a result, the urea solution in supply pipe 42 is drawn back into tank 40. This prevents the urea solution from remaining in supply pipe 42 while the vehicle is stationary after machine 30 has stopped, thus preventing damage to supply pipe 42 due to freezing and expansion of the urea solution.

[0034] The urea solution is supplied by injection into the exhaust pipe 31 via the injection valve 50, when the urea solution is pressurized to the side of the injection valve 50. The SCR catalyst 33 is then supplied with the urea solution along with the exhaust gas in the exhaust pipe 31, and the exhaust gas is purified by the reducing reaction of NOx in the SCR catalyst 33. During NOx reduction, for example, the urea solution is hydrolyzed at a high temperature of the exhaust gas heat by the following reaction. (NH2) 2CO + H2O → 2NH3 + CO2 (Equation 4)

[0035] Ammonia (NH3) is produced as a byproduct. The ammonia is adsorbed onto the SCR catalyst 33, and NOx in the exhaust gas is selectively reduced and eliminated by the ammonia in the SCR catalyst 33. That is, through the reduction reaction with ammonia (the preceding reaction equations Equation 1 to Equation 3) on the SCR catalyst 33, NOx is reduced and purified.

[0036] In the operation described above, the pump control unit 70 controls the duty cycle (pump duty cycle) DU of the current supplying the pump 44 during the pressure feed of the urea solution to the side of the injection valve 50, thus controlling the amount of urea solution supplied to the injection valve 50, i.e., the injection quantity Q of urea solution. Therefore, if an anomaly in the injection quantity Q occurs due to urea crystallization and / or the ingress of a foreign substance into the injection valve 50 from the side of the exhaust pipe 31 through the injection orifice of the injection valve 50, it is possible to check, based on the pump duty cycle DU, whether the injection valve 50 is anomalous, i.e., whether an anomaly exists in the injection valve 50.

[0037] However, in a state where the urea water pressure feeding to the injection valve 50 is not carried out, for example in a state where the SCR catalyst 33 is inactive at a low temperature, there is a small difference in the pump duty cycle DU used when checking the anomaly of the injection valve 50, and it is therefore difficult to determine the anomaly at the injection valve 50 accurately.

[0038] The pump control unit 70 according to the present embodiment performs an anomaly check to solve the aforementioned problem. During the anomaly check, while the pump 44 is rotating in reverse, the injection valve 50 is switched between the open state (hereinafter referred to as the open state) and the closed state. The variation ΔDU of the pump duty cycle caused by the state switching of the injection valve 50 is then obtained, and the injection valve 50 is checked based on this variation ΔDU to determine whether it is normal or anomalous, thus determining the presence or absence of an anomaly in the injection valve 50. It is therefore possible to accurately determine the anomaly of the injection valve 50 in a state where the urea solution is not pressurized to the side of the injection valve 50.

[0039] Fig. Figure 2 shows a flowchart of an anomaly check process performed in the present embodiment. The anomaly check process is performed repeatedly at predetermined time intervals while the machine 30 is in operation.

[0040] When the anomaly check processing is started, the first step, S10, checks whether machine 30 is operational. More precisely, it checks whether the ignition switch of the vehicle to which machine 30 is attached is in the "on" position.

[0041] If a negative determination (NO) is made at step S10, the anomaly check processing is terminated. Conversely, if a positive determination (YES) is made at step S10, step S12 checks whether it is possible to execute the anomaly check processing. Using temperature sensor 66 and ambient air temperature sensor 68, it is checked, more precisely, whether the urea solution in tank 40 has thawed (not frozen). Using rotation sensor 46, it is further checked whether the urea solution is being pressurized and fed to injection valve 50.

[0042] If the temperature measured by at least either the temperature sensor 66 or the ambient air temperature sensor 68 is -11°C or lower, and the urea solution is frozen, or if the pump 44 is rotating in the forward direction and the urea solution is pressurized to the side of the injection valve 50, a negative determination indicating that execution of the anomaly check processing is not possible is made at step S12, and the anomaly check processing is terminated. In this case, necessary processing, such as thawing the urea solution, can be carried out.If, on the other hand, the urea water is thawed and the urea water is not pressurized to the side of the injection valve 50, i.e., one is in the position before the urea water is pressurized to the injection valve 50, a positive determination indicating that an execution of the anomaly check processing is possible is made at step S12, and a step S14 is executed.

[0043] In step S14, the injection valve 50 is closed. In a subsequent step S16, which keeps the injection valve 50 closed, the urea solution is filled into the pump 44 and the supply pipe 42 by the forward and reverse rotation of the pump 44. More precisely, the forward and reverse rotations of the pump 44 are repeated alternately a specified number of times. The prescribed number of times is, for example, 50. As a result, the air remaining in the pump 44 and the supply pipe 42 is discharged to the tank 40 via the check valve 60, and the supply pipe 42 is filled with the urea solution.

[0044] In the present embodiment, reference is made to a state in which the urea water is filled into the supply pipe 42 within an area comprising the pump 44, as a result of the urea water being filled into the pump 44 and the supply pipe 42, as a state in which the supply pipe 42 is filled with the urea water.

[0045] Step S17 checks whether the urea water filling process is complete. More precisely, it checks whether the forward and reverse rotations of pump 44 have been repeated alternately the specified number of times. If step S17 fails, step S16 is executed again. Conversely, if step S17 is successful, pump 44 is reversed in step S18. Pump 44 continues to reverse until the anomaly check is complete.

[0046] In the following steps S20 and S22, the variation sets ΔDU of the pump duty cycle DU are obtained. The variation set ΔDU obtained in step S20 is referred to below as the first variation set ΔDU1, and the variation set ΔDU obtained in step S22 is referred to as the second variation set ΔDU2.

[0047] The first variation set ΔDU1 and the second variation set ΔDU2 are generated by a variation set extraction process that is described in Fig. The winner is the one who shows 3. Fig. Figure 3 shows a flowchart illustrating a variation quantity recovery process. In this process, step S70 first recovers a closing duty cycle DUc, which indicates the pump duty cycle when injector 50 is in the closed state. Next, step S72 switches injector 50 from the closed to the open state.

[0048] In step S74, after a predetermined time from the switching of injector 50 to the closed state, an open duty cycle DUo, which indicates the pump duty cycle when injector 50 is in the open state, is obtained. In step S76, injector 50 is then switched from the open state to the closed state. Finally, in step S78, the variation set ΔDU, which is an absolute value of the difference between the closed duty cycle DUc obtained in step S70 and the open duty cycle DUo obtained in step S74, is obtained, thus concluding the variation set acquisition process.

[0049] In the variation quantity recovery process, the injection valve 50 is switched between the open and closed states in steps S72 and S76, during which the pump 44 rotates backwards. In step S78, the variation quantity ΔDU of the pump duty cycle DU, caused by the switching of the injection valve 50, is recovered. In the present embodiment, the processing in steps S72 and S76 is a switching section, the processing in step S78 is a recovery section, and the variation quantity is a correlation value and a rotation variation parameter.

[0050] During step S20, specifically when the urea solution is filled into the supply pipe 42, the injection valve 50 is switched from the closed to the open state, while the pump 44 rotates in reverse. The first variation ΔDU1 is obtained when the injection valve 50 switches from the closed to the open state. By executing step S20 and step S22 sequentially, the injection valve 50 is switched from the closed to the open state multiple times while the pump 44 rotates in reverse, and the first variation ΔDU1 and the second variation ΔDU2 are obtained.

[0051] Once the first variation set ΔDU1 and the second variation set ΔDU2 are obtained, steps S24 to S54 are performed to check, based on these two sets, whether the anomaly is present in the injection valve 50. In the present embodiment, the processing in steps S24 to S54 is a test step.

[0052] In step S24, more precisely, it is first checked whether the first variation quantity ΔDU1 is greater than a predetermined first threshold value K1. The predetermined first threshold value K1 is a threshold for checking the anomaly of the injection valve 50 based on the variation quantity ΔDU, which is calculated in a state where the supply pipe 42 is filled with the urea solution.

[0053] If a positive determination is made in step S24, a further check is performed in step S26 to see if the second quantity of variation ΔDU2 is greater than a predetermined second threshold K2. The predetermined second threshold K2 is a threshold for checking the anomaly of the injection valve 50 based on the quantity of variation ΔDU, calculated in a state where the supply pipe 42 is not filled with the urea solution.

[0054] Assuming the injection valve 50 is operating normally, during step S20 (S72) it switches from the closed to the open state, drawing the urea solution into the pump 44 and the supply line 42 to return to the tank 40. Therefore, between the first switching of the injection valve 50 (S20) and the second switching of the injection valve 50 (S22), the amount of urea solution filled into the supply line 42 (in other words, the amount of air flowing from the valve 50) differs. In the present embodiment, to account for this difference, the second threshold K2 is set to be different from the first threshold K1. More precisely, the second threshold K2 is set to a value that is lower than the first threshold K1.

[0055] If a positive determination is made in step S26, step S28 determines that injector 50 is normal, meaning there is no anomaly in injector 50, thus ending the anomaly check processing. Conversely, if a negative determination is made in step S26, step S30 recovers the variation set ΔDU of the pump duty cycle DU. The variation set ΔDU recovered in step S30 is subsequently referred to as a third variation set ΔDU3. This third variation set ΔDU3 is obtained through the variation set recovery process described in Fig. The winner is the one who shows 3.

[0056] Step S32 checks whether the third variation set ΔDU3 is greater than the second threshold K2. If step S32 confirms this, step S28 is executed, and the anomaly check is terminated.

[0057] If a negative determination is made at step S32, a difference ΔGA of the variation set ΔDU is obtained. Here, the difference ΔGA is smaller than the absolute value of the difference between the first variation set ΔDU1, obtained at step S20, and the second variation set ΔDU2, obtained at step S22, and smaller than the absolute value of the difference between the first variation set ΔDU1, obtained at step S20, and the third variation set ΔDU3, obtained at step S30.

[0058] In step S36, it is checked whether the difference ΔGA is greater than a predetermined third threshold K3. The predetermined third threshold K3 is a threshold for checking whether the anomaly is present at the injection valve 50, based on the difference ΔGA between the variation quantity ΔDU in the state where the urea solution is filled into the supply pipe 42 and the variation quantity ΔDU in the state where the urea solution is not contained in the supply pipe 42. The third threshold K3 is set to be less than the first threshold K1 and greater than the second threshold K2. In the present embodiment, the state where the urea solution is not present in the supply pipe 42 in a region encompassing the pump 44 is referred to as "not containing the urea solution in the supply pipe 42".

[0059] If a positive determination is made in step S36, step S28 is executed, thereby terminating the anomaly check processing. Conversely, if a negative determination is made in step S36, step S38 determines that injector 50 is anomalous, thereby terminating the anomaly check processing.

[0060] If a negative determination is made in step S24, step S40 further checks whether the second variation set ΔDU2 is greater than the second threshold K2. If a positive determination is made in step S40, step S42 calculates the difference ΔGA of the variation set ΔDU. The difference ΔGA in step S42 is the absolute value of the difference between the first variation set ΔDU1, obtained in step S20, and the second variation set ΔDU2, obtained in step S22.

[0061] In a subsequent step S44, it is checked whether the difference ΔGA is greater than the predetermined third threshold K3. If step S44 yields a positive result, step S28 is executed, thus terminating the anomaly check. Conversely, if step S44 yields a negative result, step S46 determines that injector 50 is anomalous, thereby terminating the anomaly check.

[0062] If, on the other hand, a negative result is obtained in step S40, the third variation set ΔDU3 is obtained in step S48. In a subsequent step S50, it is checked whether the third variation set ΔDU3 is greater than the predetermined second threshold K2. If a negative result is obtained in step S50, step S46 is executed, thereby terminating the anomaly check processing.

[0063] If a positive determination is made at step S50, the difference ΔGA of the variation set ΔDU is obtained at step S52. The difference ΔGA at step S52 is the absolute value of the difference between the first variation set ΔDU1, obtained at step S20, and the third variation set ΔDU3, obtained at step S48.

[0064] In the subsequent step S54, it is checked whether the difference ΔGA is greater than the predetermined third threshold K3. If step S54 yields a positive result, step S28 is executed, thus terminating the anomaly check processing. If step S54 yields a negative result, step S46 is executed, thus terminating the anomaly check processing.

[0065] An example of the control unit for injector 50, which features anomaly detection processing, is shown in Fig. 4 shown. Fig. Figure 4 is a time diagram showing a variation of the rotational speed N in the control for the injection valve 50. Fig. 4(a) shows a variation of the pipe pressure P, Fig. 4(b) shows a variation of the rotational speed N, and Fig. Figure 4(c) shows a variation of the open and closed states of the injector 50. Fig. 4. A pulsation caused by a disturbance other than the injection of the injector 50 is eliminated from the pipe pressure P and the rotational speed N. The pulsation is also not in Fig. 6 and Fig. 7 shown.

[0066] It is assumed that, as in Fig. As shown in Figure 4, the vehicle's ignition switch is turned on and the machine 30 is started at time t1. In the present embodiment, it is further assumed that the urea solution in the tank 40 is frozen at time t1 of the machine 30 being started. A thawing process to defrost the urea solution in the tank 40 is therefore carried out by using the heating element 62.

[0067] If the urea solution in tank 40 has thawed at time t2 and the thawing process is complete, the anomaly check process is executed for a duration from time t2 to time t3. The anomaly check process will be described later. After completion of the anomaly check process, the filling process is started at time t3. During the filling process, the supply pipe 42 is filled with the urea solution by rotating the pump 44 in the forward direction.

[0068] At time t3, more precisely, the system is filled with urea solution by means of a rotational speed feedback control in a state where the injection valve 50 is closed. When the pipe pressure P reaches a reference pressure Po at time t4, filling with urea solution then occurs via a pressure feedback control in a state where the injection valve 50 is closed.

[0069] If the pipe pressure P reaches a target pressure Ptg at time t5, the filling process is terminated, and the injection process is carried out for a duration from time t5 to time t6. During the injection process, the pipe pressure P is maintained at the target pressure Ptg, and the injection valve 50 is opened and closed based on the machine operating conditions to inject the urea solution.

[0070] When the vehicle's ignition switch is turned off and machine 30 stops at time t6, the injection process is terminated and the suction process is initiated. During the suction process, the urea solution in pump 44 and supply line 42 is drawn back to tank 40 by reversing the pump 44. If the suction process then ends at time t7, the control for the injection valve 50 is terminated.

[0071] The anomaly detection process will be described next. As in Fig. As shown in Figure 4, if the anomaly check processing was started at time t2, the supply pipe 42 is filled with the urea solution by rotating the pump 44 forwards and backwards at time t11. When the filling of the urea solution is completed at time t12, the pump 44 is then reversed at time t13 in a state where the supply pipe 42 is filled with the urea solution.

[0072] An example of anomaly detection processing after urea water filling is in Fig. 5 to Fig. 8 shown. Fig. Figure 5 shows, more precisely, changes in the urea water fill state in the supply pipe 42 when the injection valve 50 is switched between the closed state and the open state in a state in which the pump 44 is turned backwards. Fig. Figure 5(a) shows the urea water filling state when the injection valve 50 is in the closed state. Fig. Figure 5(b) shows the urea water filling state when the injection valve 50 is switched to the open state. Fig. Figure 5(c) shows the urea-water filling condition in which the amount of urea-water filled into the supply tube 42 is less than a predetermined target amount in the state in which the injection valve 50 is in the closed position. Fig. Figure 5 shows the urea water injection system 20 in a simplified manner, and the description of the pump control unit 70 etc. is omitted.

[0073] Fig. 6 to Fig. Figure 8 shows variations in the pump duty cycles DU during anomaly detection processing. Fig. 6 to Fig. Figure 8 shows (a) a variation of the pump duty cycle DU, (b) a variation of the variation set ΔDU, and (c) a variation of the open and closed states of the injection valve 50.

[0074] In Fig. 6. After time t13, pump 44 is rotated backwards, and in this state the closed and open states of the injection valve 50 are switched. Fig. 6. During a duration from time t13 to time t14, the pump 44 is rotated backwards while the injection valve 50 is closed. In this state, as described in Fig. Figure 5(a) shows the supply pipe 42 filled with the urea water in an area containing the pump 44. At this time, the pump duty cycle DU is a first closing duty cycle DUc1.

[0075] During a period from time t14 to time t15, air flows from the injection hole of injector 50, as long as injector 50 is open. As in Fig. As shown in Figure 5(b), the supply pipe 42 is filled with air in the section containing the pump 44. As a result, the pump duty cycle DU decreases to an open duty cycle DUo, since the load on the pump 44 decreases, and the first set of variations ΔDU1 (ΔDU1 = DUc1 - DUo) is won.

[0076] Conversely, during a period from time t15 to time t16, the injection valve 50 is closed. However, due to the reverse rotation of the pump 44, the state in which the urea solution is not present in the supply pipe 42 is maintained. Although the pump duty cycle DU increases to a second closing duty cycle DUc2, as a result, the second closing duty cycle DUc2 becomes smaller than the first closing duty cycle DUc1.

[0077] During a period from time t16 to time t17, the pump duty cycle DU decreases again to the open duty cycle DUo, as soon as the injection valve 50 is reopened. The second set of variations ΔDU2 (ΔDU2 = DUc2 - DUo) is obtained as a result.

[0078] When the first variation ΔDU1 and the second variation ΔDU2 are obtained, the first variation ΔDU1 and the second variation ΔDU2 are checked by comparison with the thresholds K1 and K2, respectively. In this case, the first variation ΔDU1, obtained at the preceding switchover time, and the second variation ΔDU2, obtained at the subsequent switchover time, are compared and checked using the thresholds K1 and K2, which differ from each other. More precisely, since the amount of urea water loaded into supply pipe 42 before the switchover time is large, the first variation ΔDU1, obtained at the preceding switchover time, is used to establish the first comparison threshold K1, which is comparatively large.The second variation ΔDU2 is obtained at the subsequent switching time, at which time the amount of urea water filled into the supply pipe 42 before the switchover is small (no urea water is present in the supply pipe 42). The second variation ΔDU2 is therefore compared and verified by using the second threshold K2, which is smaller than the first threshold K1.

[0079] As in Fig. As shown in Figure 6(b), if the first variation set ΔDU1 is greater than the first threshold K1 and the second variation set ΔDU2 is greater than the second threshold K2, the injector 50 is determined to be normal. At time t17, in the state where the pump 44 is reverse-rotated, the injector 50 is switched from the open state to the closed state.

[0080] The reverse rotation of the pump is then stopped at time t20, and the anomaly check processing is terminated.

[0081] If, on the other hand, a closing anomaly occurs in injector 50 and injector 50 is maintained in the closed state, the pump duty cycle DU is maintained at the closing duty cycle DUc regardless of the switching of injector 50. For this reason, both the first variation set ΔDU1 and the second variation set ΔDU2 become zero and are less than the first threshold K1 and the second threshold K2, respectively. It is determined as a result that injector 50 is anomalous.

[0082] Furthermore, if an open anomaly occurs at injector 50 and injector 50 is not closed, the pump duty cycle DU does not decrease to the closed duty cycle DUc, regardless of the switching of injector 50. Since the first variation set ΔDU1 is therefore smaller than the first threshold K1 and the second variation set ΔDU2 is smaller than the second threshold K2, it is determined that injector 50 is anomalous.

[0083] Even if there is no anomaly in the injection valve 50, if air bubbles are mixed into the urea solution filled into the supply pipe 42, for example, the amount of urea solution filled into the supply pipe 42 will be less than the target amount, as specified in Fig. Figure 5(c) shows this. In this case, the pump duty cycle DU during the period from time t14 to time t15 is the third closing duty cycle DUc3, which is smaller than the first closing duty cycle DUc1, and the first variation ΔDU1 (ΔDU1 = DUc3 - DUo) becomes smaller than the first threshold K1. Since, on the other hand, the injector 50 is normal, the second variation ΔDU2 (ΔDU2 = DUc2 - DUo) becomes larger than the second threshold K2.

[0084] In the present embodiment, if the first variation quantity ΔDU1 is less than the first threshold K1 and the second variation quantity ΔDU2 is greater than the second threshold K2, the difference ΔGA between the first variation quantity ΔDU1 and the second variation quantity ΔDU2 is obtained. The quantities of urea water charged into the supply pipe 42 before the switchover differ between the first variation quantity ΔDU1, obtained at the preceding switchover time, and the second variation quantity ΔDU2, obtained at the subsequent switchover time. The difference ΔGA is therefore caused by the difference in the quantities of urea water charged into the supply pipe 42 before the switchover time. It is thus possible to check whether the injection valve 50 is anomalous based on the difference ΔGA.The difference ΔGA is, more precisely, compared and verified using the third threshold value K3. If the difference ΔGA is greater than the third threshold value K3, it is determined that injector 50 is normal. Conversely, if the difference ΔGA is less than the third threshold value K3, it is determined that injector 50 is abnormal.

[0085] Furthermore, even if no anomaly occurs at the injection valve 50, for example, in a state where the urea solution is not contained in the supply pipe 42, the variation ΔDU of the pump duty cycle DU is small due to the switching. As in Fig. As shown in Figure 8(a), if a disturbance other than noise is larger than the injection of injector 50, it is not possible to obtain the second set of variations ΔDU2 exactly. In this case, as shown in Figure 8(a), Fig. As shown in 8(b), the second set of variations ΔDU2, obtained during a duration from time t16 to time t17, may in some cases be smaller than the second threshold K2.

[0086] In the present embodiment, if the second variation quantity ΔDU2 is less than the second threshold value K2, the third variation quantity ΔDU3, which is the variation quantity ΔDU in a state where the urea solution is not contained in the supply pipe 42, is recovered. From time t17 to time t18, the injection duty cycle DU increases to the second closing duty cycle DUc2 due to the closing of the injection valve 50. From time t18 to time t19, the pump duty cycle DU decreases to the open duty cycle DUo due to the opening of the injection valve 50. The third variation quantity ΔDU3 (ΔDU3 = DUc2 - DUo) is recovered as a result.

[0087] When the third variation set ΔDU3 is obtained, the first variation set ΔDU1 and the third variation set ΔDU3 are compared and checked by using the thresholds K1 and K2, respectively. As in Fig. As shown in Figure 8(b), more precisely, if the first obtained variation set ΔDU3 is greater than the first threshold K1 and the third obtained variation set ΔDU3 is greater than the second threshold K2, then the injector 50 is determined to be normal. At time t19, the injector 50 is then switched from the open to the closed state while the pump 44 is rotating backwards. The reverse rotation of the pump 44 is then stopped at time t20, and the anomaly check processing is terminated.

[0088] According to the embodiment described above, the following effects are achieved.

[0089] In the present embodiment, the anomaly detection process is performed before the injection process. It is therefore possible to detect an anomaly of the injection valve 50 at an earlier stage than with the conventional method, in which the anomaly detection process is performed in the middle of the injection process.

[0090] In the present embodiment, the injection valve 50 is switched between the open and closed states (S72, S76) when the pump 44 is rotated in the reverse direction (S18) during the anomaly test. If the injection valve 50 is functioning normally, switching between its open and closed states changes the load on the pump 44, and therefore the variation ΔDU of the pump duty cycle DU becomes large. Conversely, if the injection valve 50 is anomalous, the variation ΔDU of the pump duty cycle DU becomes small. That is, there is a correlation between the variation ΔDU of the pump duty cycle DU and the presence or absence of an anomaly in the injection valve 50.It is therefore possible to check for the presence or absence of an anomaly in injector 50 based on the variation set ΔDU in a state where injection control is not performed.

[0091] In the present embodiment, when the urea solution is filled into the supply pipe 42 (S16), the injection valve 50 switches from the closed to the open state. If the injection valve 50 is functioning normally, the variation ΔDU of the pump duty cycle DU in a state where the supply pipe 42 is filled with the urea solution is greater than the variation ΔDU of the pump duty cycle DU in a state where the urea solution is not present in the supply pipe 42. Therefore, it is possible to accurately determine the presence or absence of an anomaly in the injection valve 50 based on the variation ΔDU of the pump duty cycle DU in a state where the supply pipe 42 is filled with the urea solution.

[0092] In the present embodiment, the switching of the injection valve 50 from the closed state to the open state is performed multiple times (S20, S22) while the supply pipe 42 is filled with the urea solution. It is therefore possible that the amount of urea solution loaded into the supply pipe 42 before the switching varies, causing a difference between the first variation ΔDU1, obtained at the preceding switching time, and the second variation ΔDU2, obtained at the subsequent switching time.

[0093] In the present embodiment, the first variation quantity ΔDU1, obtained at the preceding switching time, and the second variation quantity ΔDU2, obtained at the subsequent switching time, are checked by comparison with different threshold values ​​K1 and K2, respectively (S24, S26). As a result, it is possible to adequately check whether the injection valve 50 is anomalous by considering the difference in the amount of urea solution filled into the supply pipe 42.

[0094] In the present embodiment, it is further tested whether the injection valve 50 is anomalous based on the difference ΔGA between the first variation quantity ΔDU1, obtained at the preceding switching time, and the second variation quantity ΔDU2, obtained at the subsequent switching time (S36, S44, S54). As a result, it is possible to test whether the injection valve 50 is normal or anomalous based on the difference in the amount of urea solution filled into the supply pipe 42. (Second embodiment)

[0095] The pump control unit 70 according to a second embodiment will next be described with reference to Fig. 9 and Fig. 10. The pump control unit 70 according to the second embodiment differs from the pump control unit 70 according to the first embodiment with regard to its anomaly detection processing. The anomaly detection processing in the second embodiment will be described below.

[0096] The anomaly testing procedure in the second embodiment differs from the anomaly testing procedure in the first embodiment in that the supply pipe 42 is not supplied with the urea solution. With regard to Fig. 9 will be processed in the same way as the same processing that is carried out with reference to Fig. 2 was described, but not described for brevity.

[0097] As in Fig. As shown in Figure 9, during anomaly detection processing, after the injection valve 50 switches to the closed state at step S14, a recovery count value M (M: natural number), which indicates the number of times the variation set ΔDU is recovered, is set to "1" at step S80. At a subsequent step S82, the variation set ΔDU is recovered. The variation set ΔDU is, as described in Figure 9, Fig. The variation quantity recovery process described in Figure 3 is obtained. That is, during the processing of step S82, the variation quantity ΔDU is obtained when the injection valve 50 is switched from the closed state to the open state in a state in which the pump 44 is rotating backwards, with the urea water not contained in the supply pipe 42.

[0098] In step S84, it is checked whether the recovery count has reached a target count value Mtg (Mtg: a natural number equal to or greater than "2"). If a negative result is determined in step S84, the recovery count value M is incremented by "1" in step S86, and step S82 is executed. The processing of step S82 is thus repeated multiple times.

[0099] If, on the other hand, a positive determination is made in step S84, a total variation set ΔDUM, which is the sum of the Mtg units of the variation sets ΔDU obtained in step S82, is obtained in step S88. In a subsequent step S90, it is checked whether the injector 50 is normal or anomalous based on the total variation set ΔDUM. That is, in the processing of step S90, based on a plurality of variation sets ΔDU obtained at each switching time, the injector 50 is checked to see if an anomaly is present.

[0100] More precisely, the system checks whether the total variation quantity ΔDUM is greater than a predetermined threshold value KM. The threshold value KM is set to detect an anomaly in the injector based on the variation quantity ΔDU caused in the state where supply pipe 42 does not contain the urea solution. The threshold value KM is greater than the second threshold value K2. If a positive determination is made at step S90, step S92 determines that the injector 50 is normal, thus ending the anomaly check. Conversely, if a negative determination is made at step S90, step S94 determines that the injector 50 is anomalous, thus ending the anomaly check.

[0101] An example of anomaly detection processing is in Fig. Figure 10 shows the target count value Mtg illustrated as "4". That is, Fig. Figure 10 shows a case in which the injection valve 50, in the state where no urea water is contained in the supply pipe 42, while the pump 44 rotates backwards, switches from the closed state to the open state four times.

[0102] Fig. Figure 10(a) shows a variation of the pump duty cycle, Fig. 10(b) shows a variation of the total variation set ΔDUM, and Fig. Figure 10(c) shows a variation of the state of the injector 50. Note that the variation set ΔDU is determined to be normal if the variation set ΔDU is greater than the second threshold K2, and that the variation set ΔDU is determined to be anomalous if the variation set ΔDU is less than the second threshold K2.

[0103] In Fig. 10. It is assumed that the pump 44 rotates backwards after time t21, and in this state the injection valve 50 switches between the closed and open states. In Fig. 10 During each duration from t21 to t22, from t23 to t24, from t25 to t26, and from t27 to t28, the pump 44 is reversed in the state where the urea solution is not contained in the supply pipe 42, and the injection valve 50 is kept in the closed state. The pump duty cycle DU at this time is the closing duty cycle DUc.

[0104] During each duration from t22 to t23, from t24 to t25, from t26 to t27, and from t28 to t29, the injection valve 50 is opened, and the load on the pump 44 decreases. The pump duty cycle DU decreases to the open duty cycle DUo. The variation set ΔDU (ΔDU = DUc - DUo) is thus obtained, and the total variation set ΔDUM, which is the sum of the variation sets ΔDU, is obtained.

[0105] If the set of variations ΔDU is obtained four times, and the total set of variations ΔDUM, which is the sum of such four sets of variations ΔDU, is obtained, the total set of variations ΔDUM is checked by comparison with the threshold KM. If the total set of variations ΔDUM is larger than the threshold KM, as is the case in Fig.As shown in Figure 10(b), it is determined that the injector 50 is normal. In the state in which the pump 44 is rotating backwards at time t29, the injector 50 is then switched from the open state to the closed state. The reverse rotation of the pump 44 is stopped at a subsequent time t30, thereby terminating the anomaly check processing.

[0106] As described above, in the present embodiment, when the urea solution is not contained in the supply pipe 42, the injection valve 50 switches between the open and closed states a multiple times (S82). Since the variation ΔDU of the pump duty cycle DU caused by the switching in the state where the supply pipe 42 does not contain the urea solution is small, it is difficult to verify with high accuracy whether the injection valve 50 is normal or abnormal based on only a single variation ΔDU.

[0107] In the present embodiment, it is checked whether the injector 50 is normal or anomalous based on a plurality of variation sets ΔDU. More precisely, the injector 50 is checked for anomalies based on the total variation set ΔDUM, which is calculated by summing the multiple variation sets ΔDU. As a result, it is possible to check the presence or absence of an anomaly in the injector 50 with high accuracy.

[0108] In the present embodiment, the urea solution is not filled into the supply pipe 42. Therefore, it is not necessary to fill the urea solution during the anomaly test procedure, resulting in a reduction of the time required to perform the anomaly test. Furthermore, it is possible to suppress external disturbances that occur during the filling of the supply pipe with the urea solution, such as a disturbance that the charge of the urea solution is less than the target amount, or a disturbance that causes air to mix into the urea solution during filling due to rocking or tilting of the vehicle. As a result, it is possible to check for the presence or absence of an anomaly in the injection valve 50 with high accuracy.

[0109] The present invention is not limited to the embodiments described above, but can be implemented differently, as illustrated below.

[0110] The liquid reducing agent is not limited to urea water, but can, for example, be an ammonia-based compound for injection.

[0111] Although the urea water is injected into the exhaust duct 31a as an example, the exhaust duct 31a can alternatively be supplied with the urea water by mixing it in the form of droplets.

[0112] Although the variation set ΔDU of the pump duty cycle DU is used as the rotation variation parameter, alternatively a variation set of the rotational speed of pump 44 can be used as the rotation variation parameter, provided that a variation set of a current supplying pump 44 is acceptable. A variation set of the supply pipe pressure P can also be used as an alternative.

[0113] In the first embodiment, the anomaly detection process is illustrated by loading the urea solution into the supply pipe 42 only once. However, without being limited to this example, the urea solution can be loaded into the supply pipe 42 multiple times. Based on the difference ΔGA in the pump duty cycle obtained after each loading, it is possible to check for the presence or absence of an anomaly at the injection valve 50 by differentiating the charge quantity of the urea solution loaded into the supply pipe 42 each time.

[0114] In the second embodiment, the variation set ΔDU is obtained, for example, by switching the injection valve 50 from the closed state to the open state. However, without being limited to this example, the variation set ΔDU can also be obtained by switching the injection valve 50 from the open state to the closed state. Furthermore, the variation set ΔDU can be obtained in both cases: switching the injection valve from the closed state to the open state and switching the injection valve 50 from the open state to the closed state.

[0115] In the second embodiment, the injector 50 is tested as an exemplary method for testing the injector 50 based on the multiple variation sets ΔDU based on the total variation set ΔDUM. However, without being limited to this example, the injector 50 can, for instance, be tested based on a mean value of a maximum value of the plurality of variation sets ΔDU, insofar as it is permissible to test the injector 50 based on a maximum value of the plurality of variation sets.

Claims

[1] Anomaly detection device for an exhaust gas purification system (10) comprising an admixture valve (50) provided in an exhaust gas duct (31a) of an internal combustion engine (30) for admixing a reducing agent in a liquid state to a NOx purification catalyst (33) that purifies an exhaust gas of NOx, a tank (40) for storing the reducing agent and a pump (44) for discharging the reducing agent stored in the tank (40) by a forward rotation and for drawing the reducing agent back into the tank by a reverse rotation, comprising: a switching part (70: S72, S76) for switching the mixing valve (50) to an open state and a closed state a plurality of times in a state of reverse rotation of the pump (44); a recovery section (70: S78) for obtaining a variation quantity of a rotational speed of the pump (44) or a correlated value of the variation quantity caused by a switching of the mixing valve (50), as a rotational variation parameter (ΔDU); and a test part (70: S24 to S56) for checking whether the mixing valve (50) is anomalous, based on at least two rotation variation parameters, wherein The test part (70: S24, S26) tests the mixing valve (50) by comparing the rotation change parameter obtained at a preceding switching time and the rotation change parameter obtained at a subsequent switching time, each with different threshold values ​​(K1, K2). [2] Anomaly detection device for an exhaust gas purification system (10) comprising an admixture valve (50) provided in an exhaust gas duct (31a) of an internal combustion engine (30) for admixing a reducing agent in a liquid state to a NOx purification catalyst (33) that purifies an exhaust gas of NOx, a tank (40) for storing the reducing agent and a pump (44) for discharging the reducing agent stored in the tank (40) by a forward rotation and for drawing the reducing agent back into the tank by a reverse rotation, comprising: a switching part (70: S72, S76) for switching the mixing valve (50) to an open state and a closed state a plurality of times in a state of reverse rotation of the pump (44); a recovery section (70: S78) for obtaining a variation of a rotational speed of the pump (44) or a correlated value of the variation caused by a switching of the mixing valve (50), as a rotational change parameter (ΔDU); and a test part (70: S24 to S56) for checking whether the mixing valve (50) is anomalous, based on at least two rotation variation parameters, wherein The test part (70: S36, S44, S54) tests the mixing valve (50) based on a difference (ΔGA) between the rotation change parameter obtained at a preceding switching time and the rotation change parameter obtained at a subsequent switching time. [3] Anomaly detection device according to claim 1 or 2, wherein the switching part (70: S72, S76) in a state in which the reducing agent is filled into a channel (42) of the reducing agent connecting the pump (44) and the mixing valve (50) switches the mixing valve (50) from the closed state to the open state during reverse rotation of the pump (44); and the test part (70: S24 to S56) checks whether the mixing valve (50) is anomalous based on the rotation change parameter obtained when the mixing valve (50) is switched from the closed state to the open state by the switching part (70: S72, S76). [4] Anomaly detection device for an exhaust gas purification system (10) comprising an admixture valve (50) provided in an exhaust gas duct (31a) of an internal combustion engine (30) for admixing a reducing agent in a liquid state to a NOx purification catalyst (33) that purifies an exhaust gas of NOx, a tank (40) for storing the reducing agent and a pump (44) for discharging the reducing agent stored in the tank (40) by a forward rotation and for drawing the reducing agent back into the tank by a reverse rotation, comprising: a switching part (70: S72, S76) for switching the mixing valve (50) to an open state and a closed state a plurality of times in a state of reverse rotation of the pump (44); a recovery section (70: S78) for obtaining a variation of a rotational speed of the pump (44) or a correlated value of the variation caused by a switching of the mixing valve (50), as a rotational change parameter (ΔDU); and a test section (70: S24 to S56) for checking whether the mixing valve (50) is anomalous, based on at least two rotation variation parameters, wherein the switching section (70: S72, S76) in a state in which no reducing agent is included in a channel (42) of the reducing agent connecting the pump (44) and the mixing valve (50) switches the mixing valve (50) between the open state and the closed state a plurality of times during reverse rotation of the pump (44); and The test section (70: S36, S44, S54) based on a plurality of rotation change parameters (ΔDUM) obtained by the acquisition section (79: S78) at each switching time, checks whether the mixing valve is anomalous.

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