Exhaust gas purification device for internal combustion engine and vehicle

Abstract

Exhaust gas purification device (U) placed on an exhaust gas duct (30) of an internal combustion engine (10), the device (U) comprising: a selective catalytic reduction (SCR) catalyst (40) placed in the exhaust gas duct (30); an upstream NOx sensor (61) and a downstream NOx sensor (62) that detect an amount of NOx in an exhaust gas on an upstream side and a downstream side of the SCR catalyst (40), respectively; a urea-water injection device (50) that injects urea-water into the exhaust gas duct (30) on the upstream side of the SCR catalyst (40); and a control device (100) that estimates an ammonia storage quantity in the SCR catalyst (40) and controls a urea water injection quantity of the urea water injection device (50) based on an estimated value of the ammonia storage quantity,wherein the control device (100) monitors the transition of a detection value of each of the upstream NOx sensor (61) and the downstream NOx sensor (62), characterized in that the control device (100) generates an abnormality detection signal indicating that an overload state in the SCR catalyst (40) occurs in a case where the rate of change of the detection value of the upstream NOx sensor (61) per unit time is equal to or greater than a second threshold, and the rate of change of the detection value of the downstream NOx sensor (62) per unit time is equal to or less than a third threshold, when the NOx cleaning rate of the SCR catalyst (40) falls to a first threshold or less.

Description

Technical field

[0001] The present disclosure relates to an exhaust gas purification device for an internal combustion engine and also to a vehicle. State of the art

[0002] An SCR catalyst exhaust gas purification system is known as an exhaust gas purification device for an internal combustion engine, which features selective catalytic NOx reduction (referred to here as "SCR catalyst") that selectively reduces NOx in an exhaust gas using ammonia (NH3) as a reducing agent (see, for example, patent literature (referred to below as "PTL") 1).

[0003] In an exhaust gas purification system of this type, the effective functioning of the NOx reduction features of the SCR catalyst requires controlling the amount of ammonia accumulated in the SCR catalyst (hereinafter referred to as the "ammonia storage quantity") to a suitable level. A common control method involves a control unit sequentially predicting the amount of ammonia consumed in the SCR catalyst based on various sensor data and supplying the SCR catalyst with urea solution, which is a precursor to the required amount of ammonia. List of citations from patent literature

[0004] PTL 1 Japanese Patent Application Publication No. 2012-189007 Brief description of the invention: Technical problem

[0005] The NOx removal reaction in the SCR catalyst is complex, and it is difficult to accurately calculate the amount of ammonia consumed based on this reaction in the control unit. Furthermore, the predicted value of the ammonia consumption includes an error that may be due to, for example, an error in the injection quantity of a urea-water injection device and / or a detection error in the NOx sensor.

[0006] For this reason, it is not uncommon for an estimated value of the ammonia storage quantity, calculated by the control unit, to deviate from the actual value. This then leads to a state in which the ammonia storage quantity in the SCR catalyst (hereinafter referred to as an "overstorage state") is excessive in some cases due to the widening of the discrepancy.

[0007] When such an overabundance condition occurs, the excess ammonia is desorbed by the SCR catalyst, and the desorbed ammonia is converted to NOx by the oxidation catalyst in a subsequent stage, causing a decrease in the NOx removal performance of the exhaust aftertreatment system. Even if the desorbed ammonia is expelled as ammonia by the oxidation catalyst in a subsequent stage, a downstream NOx sensor of the SCR catalyst will detect ammonia as NOx, and the control unit will determine that the NOx removal performance has deteriorated.

[0008] In the event of an overload condition, additional urea water or ammonia may also be expelled.

[0009] The present disclosure was made in view of the problems mentioned above, and one objective of the present disclosure is therefore to provide an exhaust gas purification device for an internal combustion engine and a vehicle, each of which is capable of detecting the occurrence of an overload condition in an SCR catalyst at an early stage. Solution to the problem

[0010] The present disclosure, which mainly solves the problems mentioned above, provides an exhaust gas purification device that is placed on an exhaust duct of an internal combustion engine, the device comprising the following: a selective catalytic reduction catalyst (SCR) that is placed in the exhaust duct; an upstream NOx sensor and a downstream NOx sensor that detect the amount of NOx in an exhaust gas on an upstream side or a downstream side of the SCR catalyst; a urea-water injection device that injects urea-water into the exhaust gas channel on the upstream side of the SCR catalyst; and a control device that estimates an amount of ammonia stored in the SCR catalyst and controls an amount of urea water injection from the urea water injection device based on an estimate of the amount of ammonia stored, wherein the control device monitors the transition of a detection value from each of the upstream NOx sensor and the downstream NOx sensor, and The control device generates an abnormality detection signal indicating that an overload condition in the SCR catalyst occurs in a case where the change in the detection value of the upstream NOx sensor per unit time is equal to or greater than a second threshold, and the change in the detection value of the downstream NOx sensor per unit time is equal to or less than a third threshold, when the NOx cleaning rate of the SCR catalyst falls to a first threshold or less.

[0011] Furthermore, in another aspect, a vehicle is provided that includes the exhaust gas purification device described above. Advantageous effects of the invention

[0012] According to an exhaust gas purification device of the present disclosure, the occurrence of an overload state in an SCR catalyst can be detected at an early stage. List of characters Fig. Figure 1 is a diagram illustrating an exemplary configuration of an exhaust gas purification device according to a first embodiment; Fig. Figure 2 is a block diagram illustrating an exemplary configuration of an ECU according to the first embodiment; Fig. Figure 3A is a diagram that illustrates an example of the behavior of the amount of NOx that is downstream of an SCR catalyst in a superposition state, and Fig. 3B is a diagram illustrating an example of the behavior of the rate of change of NOx in the superposition state; Fig. Figure 4A is a diagram that illustrates an example of the behavior of the amount of NOx that is upstream of the SCR catalyst in a superposition state, and Fig. 4B is a diagram illustrating an example of the behavior of the rate of change of NOx in the superposition state; Fig. Figure 5 is a diagram describing a correction processing operation performed by an overstorage state detection section according to the first embodiment; Fig. Figure 6 is a diagram illustrating an example of a specific operational sequence performed by the overstorage state detection section according to the first embodiment; Fig. 7A, Fig. 7B and Fig. Figures 7C are time diagrams illustrating examples of the behavior of a urea water injection quantity, an ammonia storage quantity in the SCR catalyst, and a NOx cleaning rate in the SCR catalyst in the exhaust gas purification device according to the first embodiment; Fig. Figure 8A is a diagram illustrating an example of the behavior of an SCR catalyst at a given temperature, and Fig. 8B is a diagram illustrating an example of the behavior of the rate of change of temperature; and Fig. Figure 9 is a diagram illustrating an example of a specific operational sequence performed by the overstorage state detection section according to the second embodiment. Description of embodiments

[0013] A detailed description of preferred embodiments of the present disclosure is given below with reference to the accompanying drawings. In this specification and the drawings, components that have essentially the same functions are identified by the same reference numbers, and a repeated description of the same is omitted. (First embodiment) [Configuration of the exhaust gas purification device]

[0014] The following is a description of a configuration of an exhaust gas purification device according to a first embodiment with reference to Fig. 1 given.

[0015] Fig. Figure 1 is a diagram illustrating an exemplary configuration of the exhaust gas purification device U according to the present embodiment.

[0016] The exhaust gas purification device U according to the present embodiment is mounted on a vehicle, such as a truck, and cleans, for example, NOx in an exhaust gas of the engine 10.

[0017] The engine 10 is configured to include, for example, a combustion chamber, a fuel injection device for injecting fuel into the combustion chamber, and an engine ECU (not illustrated) for controlling the fuel injection device and / or the like. The engine 10 burns and expands a gas mixture of fuel and air in the combustion chamber to generate energy. In the engine 10, the intake port 20 and the exhaust port 30 are connected. The intake port (for example, the intake pipe) 20 draws air into the combustion chamber, and the exhaust port (for example, the exhaust pipe) 30 expels exhaust gas, which is expelled from the combustion chamber after combustion, to the outside of the vehicle.

[0018] It should be noted that, according to the present embodiment, the engine 10 is a four-cylinder engine and is configured such that the intake duct 20 branches through an intake manifold into four combustion chambers and merges into the exhaust duct 30 from the four combustion chambers through an exhaust manifold.

[0019] The exhaust gas purification system U includes an SCR catalyst 40, a urea water injection device 50, various sensors 61 to 64 and an electronic control unit (ECU) 100.

[0020] The SCR catalyst 40 adsorbs ammonia from hydrolyzed urea water supplied by the urea water injection device 50 and selectively subjects NOx in the exhaust gas to reduction purification by the adsorbed ammonia. A generally known SCR catalyst can be used as the SCR catalyst 40, for example, one in which a NOx reduction catalyst, such as iron zeolite, copper zeolite, or vanadium, is supported on the surface of a ceramic substrate. It should be noted that the SCR catalyst 40 can be of the type in which urea water is converted to ammonia on a catalyst.

[0021] The urea-water injection device 50 injects urea-water into the exhaust gas channel 30 on an upstream side of the SCR catalyst 40. The urea-water injection device 50 includes, for example, a urea-water addition valve 51, a urea-water tank 52, and a supply pump 53.

[0022] In the urea-water injection device 50, urea water, pumped from the urea water tank 52 by the supply pump 53, is injected into the exhaust gas channel 30 by the urea water addition valve 51. Due to the high temperature of the exhaust gas, the urea water injected into the exhaust gas channel 30 is hydrolyzed, converted into ammonia, and fed to the SCR catalyst 40. The ammonia is then adsorbed onto the SCR catalyst 40 and reacts with NOx under the action of the SCR catalyst 40 to reduce and purify NOx.

[0023] The amount of urea solution injected by the urea solution injection device 50 into the exhaust port 30 is adjusted by the opening degree of the urea solution addition valve 51. The opening degree of the urea solution addition valve 51 is controlled by a control signal output by the ECU 100 (urea solution injection control section 103).

[0024] Various sensors 61 to 64 are provided to detect the condition of the exhaust gas flowing through the exhaust gas channel 30, the condition of the SCR catalyst 40, and / or the like. In particular, the exhaust gas channel 30 is equipped, for example, with an upstream NOx sensor 61, a downstream NOx sensor 62, a temperature sensor 63, and a flow rate sensor 64.

[0025] The upstream NOx sensor 61 is located on an upstream side of the SCR catalyst 40 in the exhaust channel 30 and detects the amount of NOx (i.e., the NOx concentration) flowing into the SCR catalyst 40. The downstream NOx sensor 62 is located on a downstream side of the SCR catalyst 40 in the exhaust channel 30 and detects the amount of NOx (i.e., the NOx concentration) flowing out of the SCR catalyst 40. The temperature sensor 63 detects the temperature of the exhaust gas emitted by the engine 10. The flow sensor 64 detects the flow rate of the exhaust gas emitted by the engine 10. These various sensors 61 to 64 sequentially transmit the sensor information obtained from their detection to the ECU 100.

[0026] The ECU 100 (which corresponds to the "control device" of the present invention) controls the operation of the exhaust gas purification system U. The ECU 100 includes, for example, a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), an input port, an output port, and / or the like. Each function of the ECU 100 described below is implemented by the CPU with reference to a control program and various data stored in the ROM, RAM, and / or the like. However, the function is not limited to processing by software and can, of course, be implemented by a dedicated hardware circuit.

[0027] It should be noted that the ECU 100 communicates with the engine 10 and the urea-water injection device 50 and / or the like, thereby controlling them and / or determining the status information of these components. Furthermore, the ECU 100 acquires sensor information from various sensors 61 to 64 to determine the condition of the exhaust gas flowing through the exhaust channel 30, the condition of the SCR catalyst 40 and / or the like. [Detailed configuration of the ECU 100]

[0028] Next, an example of a detailed configuration of the ECU 100 will be given with reference to the Fig. 2 to Fig. 7 described.

[0029] Fig. Figure 2 is a block diagram illustrating an exemplary configuration of the ECU 100 according to the present embodiment.

[0030] The ECU 100 includes the NOx cleaning rate detection section 101, the ammonia storage quantity estimation section 102, the urea water injection control section 103, the correction coefficient setting section 104 and the storage state detection section 105. <In Bezug auf den NOx-Reinigungsraten-Erfassungsabschnitt 101>

[0031] The NOx cleaning rate detection section 101 detects the NOx cleaning rate in the SCR catalyst 40 and sends the NOx cleaning rate to the storage state detection section 105. The NOx cleaning rate detection section 101 detects the NOx cleaning rate in the SCR catalyst 40, for example, based on the sensor signal from the upstream NOx sensor 61 (i.e., the amount of NOx flowing into the SCR catalyst 40) and the sensor signal from the downstream NOx sensor 62 (i.e., the amount of NOx flowing out of the SCR catalyst 40). <In Bezug auf den Ammoniakspeichermengen-Schätzabschnitt 102>

[0032] The ammonia storage quantity estimator 102 estimates the amount of ammonia stored in the SCR catalyst 40. Typically, the ammonia storage quantity estimator 102 calculates the amount of ammonia newly adsorbed in the SCR catalyst 40 based on the amount of urea-water injected by the urea-water injection device 50, and it calculates the amount of ammonia consumed in the SCR catalyst 40 based on the amount of NOx arriving at the SCR catalyst 40. The ammonia storage quantity estimator 102 then estimates the amount of ammonia stored in the SCR catalyst 40 at that time by subtracting the amount of ammonia consumed in the SCR catalyst 40 from the amount of ammonia newly adsorbed on the SCR catalyst 40.In other words, the ammonia storage quantity estimation section 102 sequentially updates the ammonia storage quantity stored in a storage section (for example, RAM) at that time, based on the transition of the urea water injection quantity and the transition of the consumed ammonia quantity in the SCR catalyst 40.

[0033] It should be noted that the amount of ammonia consumed in the SCR catalyst 40 is calculated, for example, based on the amount of NOx arriving at the SCR catalyst 40 (for example, sensor information from the upstream NOx sensor 61), the exhaust gas temperature (for example, sensor information from the temperature sensor 63), the exhaust gas flow rate (for example, sensor information from the flow rate sensor 64) and the amount of ammonia stored in the SCR catalyst 40 at that time.

[0034] Upon receiving a correction command from the overstorage state detection section 105, the ammonia storage quantity estimation section 102 corrects the estimated value of the ammonia storage quantity in the SCR catalyst 40 at that time, which is stored in a memory section (for example, RAM), to the storage capacity of the SCR catalyst 40 at that time. Thus, if the estimated value of the ammonia storage quantity in the SCR catalyst 40 deviates from the actual value, the estimated value of the ammonia storage quantity in the SCR catalyst 40 is brought back close to the actual value (described below with reference to Fig. 5 described).

[0035] The storage capacity of the SCR catalyst 40 at this time is converted by the SCR catalyst 40 at this time (i.e. exhaust gas temperature) using, for example, a characteristic curve stored in advance in a memory section (for example, ROM). <In Bezug auf den Harnstoffwasser-Einspritzsteuerabschnitt 103>

[0036] The urea-water injection control section 103 controls the urea-water injection from the urea-water injection device 50 by outputting an opening degree command signal to the urea-water addition valve 51. At this point, for example, the urea-water injection control section 103 controls the urea-water injection quantity of the urea-water injection device 50 such that the estimated value of the ammonia storage quantity in the SCR catalyst 40 is maintained at a target value by the ammonia storage quantity estimator 102. Thus, the SCR catalyst 40 is kept in a state in which the NOx removal rate is high.

[0037] It should be noted that the target value of the ammonia storage quantity in the SCR catalyst 40 can be appropriately changed at this time depending on the exhaust gas temperature and / or the like.

[0038] The urea-water injection control section 103 calculates the urea-water injection quantity, for example, based on a characteristic curve that links the difference between the estimated and target value of the ammonia storage quantity in the SCR catalyst 40 at that time and the urea-water injection quantity. The urea-water injection control section 103 then determines a value obtained by multiplying the urea-water injection quantity calculated using the characteristic curve by a urea-water injection correction coefficient (for example, any value between 0.5 and 1.5) set in the correction coefficient setting section 104. This value is then communicated to the urea-water injection device 50 as a command. <In Bezug auf den Korrekturkoeffizienten-Einstellabschnitt 104>

[0039] The correction coefficient setting section 104 sets a urea water injection correction coefficient, which serves as a correction coefficient when the urea water injection quantity is determined by the urea water injection control section 103.

[0040] The urea-water injection correction coefficient is primarily set to correct a device error of the urea-water injection device 50 (for example, an error in the actual valve opening degree of the urea-water addition valve 51 relative to the indicated valve opening degree specified by the opening degree command signal). Therefore, in some cases, the amount of urea-water actually injected by the urea-water injection device 50 deviates from the command value of the urea-water injection control section 103 due to a device error of the urea-water injection device 50. The exhaust aftertreatment device U then corrects this device error based on the urea-water injection correction coefficient.

[0041] The urea-water injection correction coefficient is initially set to "1.0" and is gradually reduced to "0.9", "0.8", etc., in accordance with the correction command of the overstorage state detection section 105. The urea-water injection correction coefficient serves to align the urea-water injection quantity, as specified by the command from the urea-water injection control section 103, with the actual urea-water injection quantity injected by the urea-water injection device 50.

[0042] It should be noted that appropriate adjustment of the urea water injection correction coefficient leads to an improvement in the estimation accuracy in the ammonia storage quantity estimation section 102 and also facilitates the reduction of the frequency of occurrence of a condition in which the estimated value of the ammonia storage quantity differs from the actual value. <In Bezug auf den Überspeicherungszustand-Erfassungsabschnitt 105>

[0043] The overstorage state detection section 105 detects the occurrence of an overstorage state in the SCR catalyst 40. Then, when the occurrence of the overstorage state in the SCR catalyst 40 is detected, the overstorage state detection section 105 issues a correction command (corresponding to an “abnormality detection signal” of the present invention) to the ammonia storage quantity estimation section 102 and correction coefficient setting section 104.

[0044] The overstorage state detection section 105 detects the occurrence of the overstorage state in the SCR catalyst 40 using the properties such that, due to the continuous ammonia from the SCR catalyst 40 during an overstorage state in the SCR catalyst 40, a certain amount of NOx is continuously detected downstream of the SCR catalyst 40, and additionally a correlation between the downstream NOx amount of the SCR catalyst 40 and the upstream NOx amount of the SCR catalyst 40 becomes weak.

[0045] In particular, the overload state detection section 105 monitors the transitions of the respective detection values ​​of the upstream NOx sensor 61 and the downstream NOx sensor 62, and when the NOx cleaning rate of the SCR catalyst 40 decreases to a first threshold value or less, the overload state detection section 105 determines whether the amount of change of the detection value of the upstream NOx sensor 61 per unit of time (for example, one second) is equal to or greater than a second threshold value (hereinafter referred to as the “first condition”) and the amount of change of the detection value of the downstream NOx sensor 62 per unit of time (for example, one second) is equal to or less than a third threshold value (hereinafter referred to as the “second condition”).In a case where both the first condition and the second condition are met, the overstorage state detection section 105 determines that the overstorage state occurs in the SCR catalyst 40.

[0046] It should be noted that the first threshold value, which serves as a determining criterion for a decrease in the NOx cleaning rate of the SCR catalyst 40, is, for example, a specific NOx cleaning rate that is normally detected when an overload condition occurs (for example, set to about 70%).

[0047] Fig. Figure 3A is a diagram illustrating an example of the behavior of the NOx quantity captured downstream of the SCR catalyst 40 in a superposition state, and Fig. Figure 3B is a diagram illustrating an example of the behavior of the rate of change of NOx in the superposition state. Fig. Figure 4A is a diagram that illustrates an example of the behavior of the NOx quantity upstream of the SCR catalyst 40 in a superposition state, and Fig. Figure 4B is a diagram illustrating an example of the behavior of the rate of change of NOx in the superposition state.

[0048] The amount of NOx detected downstream of the SCR catalyst 40 in an overstorage state is mainly due to unreacted ammonia in the SCR catalyst 40 (see Fig. 3) Furthermore, the NOx cleaning rate itself in the SCR catalyst 40 is kept at a high level to a certain extent in the overstorage state, and therefore the downstream NOx quantity that is captured after the SCR catalyst 40 does not contain much NOx that is contained in the exhaust gas from the upstream area and has flowed out without having been cleaned by the SCR catalyst 40.

[0049] Therefore, the overstorage state detection section 105 determines whether the rate of change of the detection value of the downstream NOx sensor 62 per unit time is equal to or less than the third threshold (second condition), thus detecting the state in which ammonia slip from the SCR catalyst 40 occurs continuously. A reference value is set as the third threshold, which serves as the determining criterion for the overstorage state detection section 105, indicating that a deviation in the amount of NOx detected downstream of the SCR catalyst 40 is small (for example, set to ± 5 ppm / s).

[0050] Meanwhile, the amount of NOx that is subsequently detected in the SCR catalyst 40 is the amount of NOx contained in the exhaust gas emitted by the engine 10 and varies greatly according to the operating condition of the engine 10 (see Fig. 4A).

[0051] Therefore, the storage state detection section 105 determines whether the rate of change of the detection value of the upstream NOx sensor 61 per unit time is equal to or greater than the second threshold (first condition), thereby determining the state in which the upstream NOx quantity detected upstream of the SCR catalyst 40 changes dynamically to a certain extent. That is, determining the state in which the first condition is met in addition to the second condition makes it possible to confirm that the downstream NOx quantity of the SCR catalyst 40 is constant in the situation where the NOx quantity flowing into the SCR catalyst 40 changes dynamically to a certain extent.By determining whether the first condition and the second condition are both met or not, it can thus be determined whether the cause of a decrease in the NOx cleaning rate of the SCR catalyst 40 is an understorage state in the SCR catalyst 40 or an overstorage state in the SCR catalyst 40.

[0052] It should be noted that the second threshold value, which serves as a determining criterion for the overload state detection section 105, is a reference value that indicates that the amount of upstream detected NOx changes dynamically to a certain extent (for example, set to ±50 ppm / s).

[0053] It should be noted that it is advantageous for the overstorage state detection section 105 to determine the continuity of the state. Therefore, it is beneficial for the overstorage state detection section 105 to determine that the second condition is met, for example, in a case where the state in which the rate of change of the detection value of the downstream NOx sensor 62 per unit time is equal to or less than the third threshold (for example, ±5 ppm / s) persists within a predetermined determination time (for example, 60 seconds).Likewise, it is advantageous that the overload state detection section 105 determines that the first condition is met in a case in which the state in which the change rate of the detection value of the upstream NOx sensor 61 per unit of time is equal to or greater than the second threshold (for example ±50 ppm / s) is equal to or greater than a predetermined frequency within a predetermined determination time (for example 60 seconds).

[0054] Fig. Figure 5 is a diagram describing a correction process by the overflow state capture section 105. The diagram in Fig. 5 displays the following transitions.

[0055] Diagram with solid line: Transition of the estimated ammonia storage quantity in the SCR catalyst 40.

[0056] Diagram with dotted line: Transition of the actual value of the ammonia storage quantity in the SCR catalyst 40.

[0057] Diagram with dashed line: Transition of storage capacity in the SCR catalyst 40.

[0058] It should be noted that the arrow T1 in Fig. 5 indicates the time at which the correction processing is carried out.

[0059] When the occurrence of the overstorage state in the SCR catalyst 40 is detected, the overstorage state detection section 105 issues a correction command to instruct the ammonia storage quantity estimation section 102 to correct the estimated value of the ammonia storage quantity, and issues a correction command to instruct the correction coefficient setting section 104 to correct the urea water injection correction coefficient.

[0060] The overstorage state is a condition in which the ammonia in the SCR catalyst 40 has accumulated up to a limit of the SCR catalyst 40's storage capacity. Therefore, when the occurrence of the overstorage state is detected, it means that although the actual value of the ammonia storage quantity is essentially 100% of the storage capacity, the estimated value of the ammonia storage quantity is approximately 80% of the storage capacity (that is, the estimated value of the ammonia storage quantity differs from the actual value).

[0061] Therefore, when the overstorage state is detected, the overstorage state detection section 105 issues a correction command to correct the estimated ammonia storage quantity to the storage capacity of the SCR catalyst 40 at that time.

[0062] The storage capacity of the SCR catalyst 40 varies depending on its temperature and typically decreases as its temperature increases. Therefore, when a correction command is received from the overstorage state detection section 105, the ammonia storage quantity estimation section 102 calculates the storage capacity of the SCR catalyst 40 at that time based on the exhaust gas temperature at that time, for example, using a pre-stored characteristic curve, and corrects the estimated ammonia storage quantity at that time to the storage capacity.

[0063] It should be noted that in Fig. 5 at time T1, the ammonia storage quantity estimation section 102 shows an aspect where the estimated value of the ammonia storage quantity in the SCR catalyst 40 is corrected to the storage capacity of the SCR catalyst 40 at that time. Fig. 5 sets this correction processing to a state in which the estimated value of the ammonia storage quantity in the SCR catalyst 40 matches the actual value at and after T1.

[0064] When the overstorage state is detected, the overstorage state detection section 105 further performs a correction in the direction in which the urea-water injection correction coefficient decreases. As a result, the urea-water injection correction coefficient is adjusted more appropriately. In other words, this leads to an improvement in the estimation accuracy of the ammonia storage quantity estimation section 102 and also reduces the frequency of occurrence of a state in which the estimated ammonia storage quantity deviates from the actual value.

[0065] Fig. Figure 6 is a diagram illustrating an example of a specific operational sequence performed by the Overload State Acquisition Section 105. The diagram in Fig. The illustrated flowchart 6, for example, is executed by the ECU 100 in accordance with a computer program at predetermined intervals (for example, every 100 ms).

[0066] Fig. Figure 7A is a time diagram that gives an example of the behavior of the urea water injection quantity in the urea water injection device 50.

[0067] Fig. Figure 7B is a time diagram that gives an example of the behavior of the ammonia storage quantity in the SCR catalyst 40. Fig. Figure 7C is a time-lapse diagram that shows an example of the NOx removal rate behavior in the SCR catalyst 40. It should be noted that time T2 in the Fig. 7A, Fig. 7B and Fig. 7C represents a point in time at which the overflow state detection section 105 issues a correction command.

[0068] It should be noted that Fig. Figure 7B shows the behavior of the estimated value (solid line) and the actual value (dotted line) of the ammonia storage quantity in the SCR catalyst 40. Furthermore, the exhaust gas purification device U controls the urea water injection quantity in such a way that the estimated value of the ammonia storage quantity in the SCR catalyst 40 becomes 90% of the storage capacity of the SCR catalyst 40.

[0069] In step S1, the storage state detection section 105 determines whether the NOx cleaning rate in the SCR catalyst 40 decreases to the first threshold (for example, 70%) or less. If the NOx cleaning rate in the SCR catalyst 40 does not decrease to the first threshold or less (step S1: NO), the storage state detection section 105 terminates the processing of the flowchart at this point. Fig. 6, without performing any specific processing. However, if the NOx cleaning rate in the SCR catalyst 40 decreases to the first threshold value or less (step S1: YES), the overstorage state detection section 105 continues processing to step S2.

[0070] It should be noted that in step S1, the overstorage state detection section 105 can determine, based on an integral value of the NOx cleaning rate, whether the NOx cleaning rate in the SCR catalyst 40 is decreasing or not. This makes it possible to avoid performing an unnecessary test run due to noise during NOx cleaning rate detection.

[0071] In step S2, the overload state detection section 105 determines whether the rate of change of the detection value of the upstream NOx sensor 61 per unit of time is equal to or greater than the second threshold. If the rate of change of the detection value of the upstream NOx sensor 61 is less than the second threshold (step S2: NO), the overload state detection section 105 terminates the processing of the flowchart at this point. Fig. 6, without performing any specific processing. However, if the change in the detection value of the upstream NOx sensor 61 is equal to or greater than the second threshold (step S2: YES), the overload state detection section 105 continues the processing to step S3.

[0072] In step S3, the overload state detection section 105 determines whether the rate of change of the detection value of the downstream NOx sensor 62 per unit of time is equal to or less than the third threshold. If the rate of change of the detection value of the downstream NOx sensor 62 is greater than the third threshold (step S3: NO), the overload state detection section 105 terminates the processing of the flowchart at this point. Fig. 6, without performing any specific processing. However, if the change in the detection value of the downstream NOx sensor 62 is equal to or less than the third threshold (step S3: YES), the overstorage state detection section 105 continues processing to step S4.

[0073] In step S4, the overstorage state detection section 105 determines that an overstorage state is occurring and sends a correction command to the ammonia storage quantity estimation section 102 and the correction coefficient setting section 104.

[0074] As a result, the ammonia storage quantity estimation section 102 performs a correction such that the estimated value of the ammonia storage quantity of the SCR catalyst 40 at that time, which is stored in a memory section, for example, a RAM, increases. At that time, for example, the ammonia storage quantity estimation section 102 corrects the estimated value of the ammonia storage quantity of the SCR catalyst 40 at that time, which is stored in the memory section, for example, in the RAM, to the storage capacity of the SCR catalyst 40 at that time.

[0075] It should be noted that in step S4, the processing in which the ammonia storage quantity estimation section 102 increases the estimated value of the ammonia storage quantity can be any method. This processing could, for example, be a method of incrementally increasing an estimated value of the ammonia storage quantity (for example, by 5% each time). Even with such a method, it is possible to repeatedly execute the processing of the flowchart from Fig. 6. It is possible to bring the estimated value of the ammonia storage quantity close to the actual value.

[0076] Furthermore, the correction coefficient setting section 104, which has received the correction command from the over-memory state acquisition section 105, performs a correction such that the urea-water injection correction coefficient stored in the memory section (for example, RAM) at that time decreases. At that time, the correction coefficient setting section 104 corrects the urea-water injection correction coefficient stored in the memory section (for example, RAM) at that time such that it is in a decreasing direction for one step.

[0077] This step S4 causes the amount of urea water injected by the urea water injection device 50 to decrease compared to the amount before the detection of the supercharge state, and the NOx cleaning rate in the SCR catalyst 40 recovers over time (see Fig. 7C).

[0078] Furthermore, reducing the urea water injection correction coefficient by this step S4 causes the urea water injection quantity per unit of the difference between the estimated value and the target value of the ammonia storage quantity to decrease, so that excessive injection due to a device fault of the urea water injection device 50 can be prevented.

[0079] It should be noted that when executing step S4, it is desirable to execute the processing of the flowchart in Fig. 6. To prohibit this for a predetermined time (for example, 10 minutes). This makes it possible to prevent repeated execution of the processing to correct the estimated ammonia storage quantity of the SCR catalyst 40 and the urea water injection correction coefficient before the NOx cleaning rate in the SCR catalyst 40 recovers.

[0080] The processing described above eliminates any discrepancy between the estimated and actual value of the ammonia storage quantity of the SCR catalyst 40. Furthermore, since the urea-water injection correction coefficient is also set to a suitable value, the frequency of occurrence of the discrepancy between the estimated and actual value of the ammonia storage quantity of the SCR catalyst 40 is also suppressed in the long term. [Effects]

[0081] As described above, the exhaust gas purification device U of the present embodiment can detect the occurrence of an overload state in an SCR catalyst at an early stage. Furthermore, the exhaust gas purification device U of the present embodiment makes it possible to detect the occurrence of an overload state in the SCR catalyst with high accuracy. Thus, an estimated value of the ammonia concentration and a urea-water injection correction coefficient can be corrected accordingly. (Second embodiment)

[0082] Next, a configuration of the ECU 100 according to a second embodiment will be described with reference to the Fig. 8 and Fig. 9 described. The ECU 100 according to the present embodiment differs from that of the first embodiment with respect to the determination conditions in the overstorage acquisition section 105. It should be noted that the description of the configuration common to the first embodiment is omitted.

[0083] The overstorage state detection section 105 according to the present embodiment introduces a third condition and a fourth condition as conditions for determining whether an overstorage state occurs or not, in addition to the first condition and the second condition described above, from the point of view of preventing a false detection of the overstorage state.

[0084] Fig. Figure 8A is a diagram illustrating an example of the behavior of a temperature of the SCR catalyst 40, and Fig. Figure 8B is a diagram illustrating an example of the behavior of the quantity of change.

[0085] Fig. Figure 9 is a diagram illustrating an example of a specific operational sequence performed by the overstorage state detection section 105 according to the present embodiment.

[0086] The flowchart of Fig. 9 differs from the flowchart of the Fig. 6 by the fact that the determination processing of step Sa according to the third condition and the determination processing of step Sb according to the fourth condition after step S3 of the flowchart of Fig. 6 will be added.

[0087] First, the overstorage state detection section 105 determines, as a third condition, whether the temperature of the SCR catalyst 40 is less than or equal to a fourth threshold, and whether the rate of change in the temperature of the SCR catalyst 40 is equal to or less than a fifth threshold (step Sa). If the temperature of the SCR catalyst 40 is equal to or less than the fourth threshold and the rate of change in the temperature of the SCR catalyst 40 is equal to or less than the fifth threshold (step Sa: YES), the overstorage state detection section 105 determines that the overstorage state may have occurred in the SCR catalyst 40. However, if the third condition is not met (step Sa: NO), the overstorage state detection section 105 determines that this is not a suitable time for determination (step Sa) and terminates the processing of the flowchart. Fig. 9.

[0088] In general, the temperature of the SCR catalyst 40 varies over time depending on the operating state of the engine 10, because the temperature of the SCR catalyst 40 depends on the exhaust gas temperature (see Fig. 8A and Fig. 8B). Then, when the temperature of the SCR catalyst 40 is high, ammonia slip from the SCR catalyst 40 occurs regardless of whether an overstorage condition occurs in the SCR catalyst 40. In particular, if the temperature of the SCR catalyst 40 rises rapidly, the amount of ammonia slip from the SCR catalyst 40 also increases.

[0089] To avoid erroneously detecting that the overstorage state in the SCR catalyst 40 occurs due to ammonia slip during high temperatures, the overstorage state detection section 105 sets a third condition as an additional determination condition. It should be noted that, for example, 350 °C is set as the fourth threshold for the temperature of the SCR catalyst 40, which serves as a determination criterion for the overstorage state detection section 105, and, for example, 5 °C / s is set as the fifth threshold for the temperature change of the SCR catalyst 40.

[0090] As a fourth condition, the overstorage state detection section 105 further determines whether the difference between the storage capacity and the estimated amount of ammonia stored in the SCR catalyst 40 is equal to or less than a sixth threshold (step Sb). If the difference between the storage capacity and the estimated amount of ammonia stored in the SCR catalyst 40 is equal to or less than the sixth threshold (step Sb: YES), the overstorage state detection section 105 determines that the overstorage state may have occurred in the SCR catalyst 40. However, if the fourth condition is not met (step Sb: NO), the overstorage state detection section 105 determines that this is not a suitable time for determination and terminates the processing of the flowchart. Fig. 9.

[0091] In general, the storage capacity of the SCR catalyst 40 depends on the temperature of the SCR catalyst 40 and thus varies over time depending on the operating state of the engine 10 (see diagram with dashed line in Fig. 5) Then, when the storage capacity of the SCR catalyst 40 decreases, for example, when the temperature of the SCR catalyst 40 rises rapidly, ammonia slip from the SCR catalyst 40 occurs. That is, if the estimated amount of ammonia stored is close to the storage capacity of the SCR catalyst 40, the overstorage state detection section 105 may determine that the estimated amount of ammonia stored differs from the actual value, even though the estimated amount of ammonia stored does not differ from the actual value.

[0092] To avoid such an incorrect determination, the overstorage state detection section 105 sets the fourth condition as an additional determination condition. It should be noted that in this case, it can be said that the overstorage state in the SCR catalyst 40 occurs temporarily; however, since the estimated value of the ammonia storage quantity does not deviate from the actual value, the overstorage state detection section 105, according to the present embodiment, sets the fourth condition as an additional determination condition from the standpoint of avoiding the execution of the correction processing itself.

[0093] The sixth threshold for the difference between the storage capacity and the estimated amount of ammonia storage, which serves as the determining criterion for the overstorage state detection section 105, is set (for example, set to approximately 5%).

[0094] As described above, according to the ECU 100 of the present embodiment, it is possible to detect an overstorage state in the SCR catalyst 40 with higher accuracy, that is, a state in which an estimated value of the ammonia storage quantity deviates from the actual value. (Other embodiments)

[0095] The present invention is not limited to the above embodiments, and various modifications are possible.

[0096] In the embodiments described above, the description is given as an example of a configuration in which the functions of the NOx cleaning rate detection section 101, the ammonia storage quantity estimation section 102, the urea water injection control section 103, the correction coefficient setting section 104, and the overstorage state detection section 105 are implemented by a single computer, but these functions can, of course, also be implemented by a plurality of computers. For example, the function of the ammonia storage quantity estimation section 102 and the function of the urea water injection control section 103 can each be provided in separate ECUs.

[0097] Furthermore, in the embodiments described above, the description was given as an example of an aspect in which the exhaust gas purification device U is applied to a diesel engine. However, the exhaust gas purification device U according to the present embodiment can be applied to a gasoline engine, without being limited to a diesel engine.

[0098] In the embodiments described above, the vehicle is illustrated as an example of the intended application of the exhaust gas purification device U, but the intended application of the exhaust gas purification device U is not limited to this. For example, the exhaust gas purification device U can be applied to a power generator, a construction machine, a ship, and / or the like.

[0099] Although specific examples of the present invention have been described in detail up to this point, these examples are merely illustrative and do not limit the appended claims. The technology described in the appended claims includes various modifications and variations of the specific examples illustrated above.

[0100] This application is based on Japanese patent application No. 2019-009471, filed on January 23, 2019, the entire contents of which are incorporated herein by reference. Commercial applicability

[0101] According to an exhaust gas purification device of the present disclosure, the occurrence of an overload state in an SCR catalyst can be detected at an early stage. Reference symbol list Exhaust gas purification system 10 Motor 20 Intake channel 30 Exhaust duct 40 SCR catalyst (catalyst of the selective NOx reduction type) 50 Urea water injection device 51 Urea water addition valve 52 Urea water tank 53 Supply pump 61 Upstream NOx sensor 62 Downstream NOx sensor 63 Temperature sensor 64 Flow sensor 100 ECU (control unit) 101 NOx Cleaning Rate Recording Section 102 Ammonia storage quantity recording section 103 Urea water injection control section 104 Correction coefficient setting section 105 Overload status recording section QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2019009471

[0100]

Claims

[1] An exhaust gas purification device placed on an exhaust duct of an internal combustion engine, the device comprising: a selective catalytic reduction (SCR) catalyst placed in the exhaust passage; an upstream NOx sensor and a downstream NOx sensor that detect an amount of NOx in an exhaust gas on an upstream side and a downstream side of the SCR catalyst, respectively; a urea water injection device that injects urea water into the exhaust passage on the upstream side of the SCR catalyst; and a control device that estimates an ammonia storage amount in the SCR catalyst and controls a urea water injection amount of the urea water injection device based on an estimated value of the ammonia storage amount, wherein the control device monitors the transition of a detection value of each of the upstream NOx sensor and the downstream NOx sensor, and the control device generates an abnormality detection signal indicating that an over-storage state occurs in the SCR catalyst in a case where a change amount of the detection value of the upstream NOx sensor per unit time is equal to or greater than a second threshold, and a change amount of the detection value of the downstream NOx sensor per unit time is equal to or less than a third threshold when a NOx purification rate of the SCR catalyst decreases to a first threshold or less. [2] The exhaust gas purification device according to claim 1, wherein the control device generates the abnormality detection signal only in a case where a temperature of the SCR catalyst is equal to or less than a fourth threshold, and a change amount of the temperature of the SCR catalyst is equal to or less than a fifth threshold. [3] The exhaust gas purification device according to claim 1, wherein the control device generates the abnormality detection signal only in a case where a difference between an ammonia storage capacity in the SCR catalyst and the estimated value of the ammonia storage amount is equal to or greater than a sixth threshold value. [4] An exhaust gas purification device according to claim 1, wherein the control device, when generating the abnormality detection signal, corrects the estimated value of the ammonia storage amount to a storage capacity of the SCR catalyst at that time. [5] The exhaust gas purification device according to claim 1, wherein the control device, when generating the abnormality detection signal, corrects a correction coefficient for adjusting the urea water injection amount such that the urea water injection amount decreases per unit amount of a difference between the estimated value and a target value of the ammonia storage amount. [6] A vehicle comprising the exhaust gas purification device according to claim 1.