Degradation diagnosis device for exhaust gas purification system

Abstract

Degradation diagnosis device (100) for an exhaust gas purification system (1) for purifying exhaust gas discharged from an internal combustion engine (10) into an exhaust pipe (2, 2a), the degradation diagnosis device (100) comprising: a degradation degree estimation section (101) that estimates a degradation degree due to corrosion of a constituent component in the exhaust gas purification system (1) based on a temperature of the exhaust gas and an injection amount of a reducing agent injected into the exhaust pipe (2, 2a); a determination section (102) that determines whether the degradation degree estimated by the degradation degree estimation section (101) exceeds a predetermined threshold; and an output section (103) that outputs a determination result produced by the determination section (102).

Description

Technical area

[0001] The present disclosure relates to a degradation diagnosis device for an exhaust gas purification system. State of the art

[0002] The exhaust gas emitted by an internal combustion engine contains nitrogen oxides (NOx). For NOx purification, an exhaust gas purification system is known. It includes an injector for injecting urea water as a reducing agent into an exhaust pipe and a reduction catalyst provided downstream of the injector in the exhaust pipe. This catalyst purifies NOx in the exhaust gas by reacting it with ammonia produced by hydrolysis of urea water.

[0003] In some exhaust gas purification systems, a mixer is arranged downstream of the injection nozzle in the exhaust pipe and upstream of the reduction catalyst to promote the mixing of urea water injected into the exhaust pipe and the exhaust gas flowing into the exhaust pipe.

[0004] During the hydrolysis of the urea water injected into the exhaust pipe, ammonium carbamate, a highly corrosive substance, is produced. For example, if the highly corrosive substance continues to adhere to the inner wall of the exhaust pipe, the support part that supports the mixer on the exhaust pipe, or similar components, the inner wall of the exhaust pipe, the support part of the mixer, or similar components may be corroded and worn.

[0005] DE 699 25 172 T2 relates to a catalyst in an exhaust passage of an internal combustion engine to absorb NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, and to release and reduce the absorbed NOx when the air-fuel ratio of the exhaust gas is rich.

[0006] EP 2 784279 A1 relates to an exhaust gas purification device for an internal combustion engine in which a gaseous reducing agent is supplied to an exhaust gas passage from a reducing agent passage, in which a pressure detecting device for detecting a pressure of the reducing agent, a temperature detecting device for detecting a temperature of the reducing agent and a determining device for determining whether the reducing agent is leaking are provided according to a difference between a saturation vapor pressure corresponding to the temperature of the reducing agent detected by the temperature detecting device and the pressure of the reducing agent detected by the pressure detecting device.

[0007] JP 2018-021514 A relates to a mixer unit comprising: a tube; a mixer inserted into the tube, which mixer contains a corrosion inhibitor and is configured to mix a reducing agent supplied from an injection nozzle to guide the exhaust gas generated during internal combustion; a concave part formed on one of the inner peripheral surface of the tube and the outer peripheral surface of the mixer; and a convex part integrally formed on the other of the inner peripheral surface of the tube and the outer peripheral surface of the mixer and fitted into the concave part when the mixer is inserted into the tube.

[0008] JP 2009-220033 A relates to a catalyst device coated with a catalyst component for the selective reduction of ammonia, which selectively reduces nitrogen oxide in an exhaust gas by using ammonia as a reducing agent on a carrier formed by containing an oxidizing catalyst. Summary of the inventionTechnical problem

[0009] It is difficult to accurately diagnose the degree of degradation due to corrosion of a component of the exhaust gas purification system, such as the corrosion condition of the inner wall of the exhaust pipe and the support part of the mixer, by visual inspection or the like.

[0010] As a result, it is difficult to detect deterioration of the exhaust gas purification system component at an early stage.

[0011] The object of this disclosure is to provide a degradation diagnosis device for an exhaust gas purification system which is capable of detecting the deterioration of a component in the exhaust gas purification system at an early stage. Solution to the problem

[0012] The degradation diagnosis apparatus for an exhaust gas purification system according to an embodiment of the present disclosure comprises: a degradation degree estimation section that estimates a degree of degradation due to corrosion of a component in the exhaust gas purification system based on a temperature of the exhaust gas and an amount of a reducing agent injected into the exhaust pipe; a determination section that determines whether the degradation degree estimated by the degradation degree estimation section exceeds a predetermined threshold; and an output section that outputs an investigation result created by the investigation section. Advantageous effects of the invention

[0013] According to the present disclosure, it is possible to detect deterioration of the constituent component in the exhaust gas purification system at an early stage. Brief description of the drawings Fig. 1 is a block diagram showing an example of a configuration of the exhaust gas purification system according to an embodiment of the present disclosure; Fig. 2 is a three-dimensional diagram showing an example of the interrelationship between the temperature of the exhaust gas, the injection amount of urea water and the corrosion amount of the connecting pipe; Fig. 3 is a graph showing an example of the mutual relationship between the exhaust gas temperature varying with time, the injection amount of urea water, and the corrosion amount of the connecting pipe. Description of embodiments

[0014] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. This embodiment will be described in a case where the present disclosure is applied to a diesel engine (an internal combustion engine) mounted on a motor vehicle. Hereinafter, the diesel engine is sometimes simply referred to as an engine.

[0015] An example of a schematic structure of the exhaust gas purification system 1 for purifying the exhaust gas which is led from the engine 10 into the exhaust pipe 2 is described with reference to Fig. 1 described.

[0016] As in Fig. 1, engine 10 is provided with an exhaust pipe 2 for discharging the exhaust gas from engine 10. The exhaust pipe 2 is provided with an exhaust gas purification system 1 for purifying the exhaust gas.

[0017] The exhaust gas purification system 1 includes a DPF 3 (diesel particulate filter), a urea selective catalytic reduction (SCR) catalyst 4, a urea-water injection device 5, a mixer 6, and a control device 7. The DPF 3 removes particulate matter (PM) contained in the exhaust gas. The SCR 4 is a selective reduction catalyst for reducing nitrogen oxides contained in the exhaust gas.

[0018] The DPF 3, for example, is a continuously regenerating DPF. The DPF 3 includes a filter body for collecting PM and an oxidation catalyst disposed on the upstream side of the exhaust flow with respect to the filter body. The filter body and the oxidation catalyst are contained in a housing. The exhaust pipe 2 is provided with the SCR 4 on the downstream side of the exhaust flow with respect to the DPF 3 (hereinafter referred to simply as the downstream side).

[0019] The SCR 4 uses ammonia as a reducing agent to reduce nitrogen oxides. The SCR 4 is implemented by supporting a catalyst component (e.g., a zeolite or similar) on a support (e.g., a honeycomb support or similar).

[0020] The DPF 3 and the SCR 4 are arranged in series along the flow of the exhaust gas to the exhaust pipe 2. The DPF 3 is located upstream of the SCR 4 (on the engine 10 side). The exhaust pipe 2 connects the downstream port of the DPF 3 and the upstream port of the SCR 4, in particular, sometimes referred to as the connecting pipe 2a.

[0021] The urea water injection device 5 includes a urea water tank 5a for storing urea water, a urea water pump 5b for pumping urea water from the urea water tank 5a, and a urea water injection nozzle 5c for injecting urea water into the connecting pipe 2a. The urea water injected into the connecting pipe 2a by the urea water injector 5c is hydrolyzed by exhaust heat. As a result, ammonia (NH3) is generated and supplied to the downstream side of the SCR 4.

[0022] The mixer 6 is arranged in the connecting pipe 2a downstream of the urea water injection device 5 and upstream of the SCR 4, the mixer 6 regulating the mixing of the exhaust gas with the reducing agent.

[0023] The control device 7 completely controls the operation of the exhaust gas purification system 1. The control device 7 includes a CPU for executing various control processes and a computer having a ROM, a RAM, a hard disk, or the like as a storage unit for storing various information and programs required for the operation of the CPU. The control device 7 controls the injection amount and injection duration of the urea water in the urea water injector 5c.

[0024] As described above, upon hydrolysis of the urea water injected into the connecting pipe 2a, a highly corrosive substance is generated, and if the highly corrosive substance continues to adhere to the inner wall of the connecting pipe 2a, the connecting pipe 2a may corrode and deteriorate. If the highly corrosive substance continues to adhere to the inner wall of the connecting pipe 2a, the connecting pipe 2a may corrode and deteriorate. In addition, due to the adhesion of the highly corrosive substance to the mixer 6, the support portion for supporting the mixer 6 on the connecting pipe 2a may corrode and deteriorate. As described above, the urea water injected into the connecting pipe 2a causes deterioration of the component of the exhaust gas purification system 1. However, it is difficult to accurately diagnose the degree of deterioration due to corrosion of the component of the exhaust gas purification system 1 by visual inspection or the like.Furthermore, since it is necessary to disassemble the exhaust system in a state where the vehicle is stopped to perform visual confirmation, it is difficult to perform visual confirmation at all. Therefore, in the present embodiment, the degradation diagnosis device 100 is provided for diagnosing the degradation of the exhaust gas purification system 1.

[0025] Next, the corrosion amount of the connecting pipe 2a will be described as an example of the degree of degradation due to corrosion of the constituent component in the exhaust gas purification system 1. The degradation diagnosis device 100 includes the corrosion amount estimation section 101 (corresponding to the deterioration degree estimation section in this disclosure), the determination section 102, and the output section 103.

[0026] The temperature sensor 8 detects the temperature of the exhaust gas (the temperature in the connecting pipe 2a).

[0027] The corrosion amount estimation section 101 estimates the total corrosion amount of the exhaust pipe 2 based on the exhaust gas temperature detected by the temperature sensor 8 and the injection amount per unit time of the urea water injected into the connecting pipe 2a (hereinafter referred to simply as the "injection amount"). Note that in the following description, the corrosion amount per unit time is simply referred to as the "corrosion amount."

[0028] The determination section 102 determines whether the estimated total corrosion amount exceeds a predetermined threshold and outputs the determination result.

[0029] Fig. Figure 2 is a three-dimensional figure showing an example of the mutual relationship between the temperature T [degC] of the exhaust gas, the injection amounts Q [mg / s] of urea water and the corrosion amounts A [mm / s]. Fig. shows the exhaust gas temperature Ti, the urea water injection amount Qi, and the corrosion amount Ai. Such a three-dimensional map is determined in advance, for example, through experiments. The map is stored in a storage unit (not shown) of the control device 7.

[0030] In the present embodiment, the corrosion amount estimation section 101 estimates the corrosion amount Ai with reference to the Fig. 2 based on the exhaust gas temperature Ti and the urea water injection amount Qi. In a case where a relational expression of the exhaust gas temperature Ti and the urea water injection amount Qi is provided in advance, the corrosion amount Ai can be obtained by substituting the exhaust gas temperature Ti and the urea water injection amount Qi into the relational expression.

[0031] A method for calculating the total corrosion amount ΣA using the above-mentioned corrosion amount A is described below.

[0032] Fig. Figure 3 is a graph showing the temperature T [degC] of the exhaust gas, the injection quantities Q [mg / s] of urea water, and the corrosion quantities A [mm / s], which change in time series. Fig. 3 represents the time t, and the vertical axis represents the respective numerical values of the temperature T of the exhaust gas, the injection amount Q of urea water, and the corrosion amount A. For example, the respective numerical values at the injection time tk are the temperature Tk of the exhaust gas, the injection amount Qk of urea water, and the corrosion amount Ak.

[0033] Section 101, Corrosion Amount Estimation, calculates the total corrosion amount ΣA [mm] by integrating the corrosion amount A [mm / s] with time. For example, Section 101, Corrosion Amount Estimation, calculates the total corrosion amount ΣA mn according to the progress from tm to tn by integrating the corrosion amount A from tm to tn.

[0034] As described above, the determination section 102 determines whether the total corrosion amount ΣA exceeds a predetermined threshold. The output section 103 outputs the determination result from the determination section 102. There are various ways to notify the driver or the like of the determination result. For example, the determination result may be displayed as a message on the vehicle monitor or output as an alarm sound via a buzzer. In addition, a vehicle-mounted communication unit (not shown) may notify the monitoring center (remote location) via a communication network.

[0035] The degradation diagnosis device 100 in the exhaust gas purification system 1 according to the above-described embodiment estimates the total corrosion amount of the connecting pipe 2a based on the temperature of the exhaust gas discharged from the engine 10 and the amount of urea water injected into the connecting pipe 2a, determines whether the estimated total corrosion amount exceeds a predetermined threshold, and outputs the determination result. In this way, it is possible to increase the accuracy of diagnosing the total corrosion amount of the connecting pipe 2a. Consequently, the corrosion of the connecting pipe 2a can be detected at an early stage. Furthermore, even when the vehicle is running, even when the exhaust pipe 2 is in a high-temperature state, it is possible to diagnose the degree of degradation due to corrosion without disassembling the exhaust system.

[0036] Furthermore, by informing the driver or the like of the determination result of whether the total corrosion amount exceeds a predetermined threshold, it is possible to prompt the early replacement and maintenance of the connecting pipe 2a. Furthermore, if the quality of the exhaust pipe and the like is determined under the assumption that the exhaust pipe and the like are used under the expected worst condition, the quality of the exhaust pipe and the like will be exaggerated. If the use of the exhaust pipe and the like is not assumed, there is a fear that the function of the exhaust pipe and the like may fail.However, since the degradation diagnosis device 100 of the present embodiment can detect corrosion of the exhaust pipe and the like early, it is possible to determine the quality of the component under the assumption of replacement. In a case where replacement of the component is assumed, an inexpensive material with good formability can be used in the manufacture of the component, thus preventing excessive quality. Furthermore, it is possible to ensure durability through, for example, component replacement and maintenance.

[0037] In the above embodiment, the estimation of the total corrosion amount of the connecting pipe 2a is performed by the corrosion amount estimation section 101 based on the injection amount of the urea water (reducing agent), but the present disclosure is not limited to this, and the estimation may be performed based on the injection time of the urea water, for example.

[0038] Furthermore, in the above embodiment, the degree of degradation due to corrosion of the component in the exhaust gas purification system 1 is the corrosion amount of the connecting pipe 2a, but the present disclosure is not limited to the connecting pipe 2a, and any component, such as the mixer 6 or the like, which deteriorates due to urea water injected into the exhaust pipe 2 may be used. In this case, a map of the degree of degradation due to corrosion of the component is created, to which the temperature of the exhaust gas and the injection amount of urea water are related. The corrosion amount estimation section 101 estimates the corrosion amount of the component with reference to the map.

[0039] Furthermore, in the above embodiment, the temperature of the exhaust gas is detected by the temperature sensor 8, but the present disclosure is not limited to this. The temperature of the exhaust gas can be estimated based on the temperature of the wall surface of the connecting pipe 2a.

[0040] Furthermore, in the above embodiment, the corrosion amount of the connecting pipe 2a is estimated based on the exhaust gas temperature and the reducing agent injection amount, but the estimated corrosion amount may be corrected based on the flow rate of the exhaust gas flowing through the connecting pipe 2a. The estimated corrosion amount may be corrected based on the reducing agent temperature.

[0041] This application is based on Japanese Patent Application No. 2018-056008 filed on March 23, 2018, the contents of which are incorporated herein by reference. Industrial applicability

[0042] The degradation diagnosis apparatus in the exhaust gas purification system 1 of the present disclosure is useful for a vehicle with an internal combustion engine in which degradation of the component of the exhaust gas purification system 1 is to be detected at an early stage. List of reference symbols 1 exhaust gas purification system 2 exhaust pipe 2a Connecting pipe 3 DPF 4 Urea SCR catalyst (SCR) 5 Device for injecting urea water 5a Urea water tank 5b Urea water pump 5c Urea water injector 6 mixers 7 Control device 8 temperature sensors 10 Engine 100 Degradation Diagnosis Device 101 Section on estimating the amount of corrosion 102 Investigation Section 103 Output section

Claims

[1] A degradation diagnosis device (100) for an exhaust gas purification system (1) for purifying exhaust gas discharged from an internal combustion engine (10) into an exhaust pipe (2, 2a), the degradation diagnosis device (100) comprising: a degradation degree estimation section (101) that estimates a degradation degree due to corrosion of a constituent component in the exhaust gas purification system (1) based on a temperature of the exhaust gas and an injection amount of a reducing agent injected into the exhaust pipe (2, 2a); a determination section (102) that determines whether the degradation degree estimated by the degradation degree estimation section (101) exceeds a predetermined threshold value; and an output section (103) that outputs a determination result prepared by the determination section (102). [2] The degradation diagnosis device (100) for the exhaust gas purification system (1) according to claim 1, wherein the degradation degree estimation section (101) estimates the degradation degree per unit time based on the temperature of the exhaust gas and the injection amount of the reducing agent per unit time. [3] The degradation diagnosis device (100) for the exhaust gas purification system (1) according to claim 2, wherein the degradation degree estimation section (101) estimates the degradation degree per unit time by referring to a map indicating the degradation degree per unit time to which the temperature of the exhaust gas and the injection amount per unit time of the reducing agent are related. [4] The degradation diagnosis device (100) for the exhaust gas purification system (1) according to any one of claims 1 to 3, wherein the degradation degree estimating section (101) estimates the temperature of the exhaust gas based on a wall surface temperature of the exhaust pipe (2, 2a). [5] The degradation diagnosis device (100) for the exhaust gas purification system (1) according to any one of claims 2 to 4, wherein the degradation degree estimation section (101) corrects the degradation degree based on a flow rate of the exhaust gas flowing in the exhaust pipe (2, 2a). [6] The degradation diagnosis device (100) for the exhaust gas purification system (1) according to any one of claims 2 to 5, wherein the degradation degree estimation section (101) corrects the degradation degree based on a temperature of the reducing agent. [7] The degradation diagnosis device (100) for the exhaust gas purification system (1) according to any one of claims 1 to 6, wherein the output section (103) outputs the determination result to a notification section that notifies the driver of a vehicle equipped with the exhaust gas purification system (1). [8] The degradation diagnosis device (100) for the exhaust gas purification system (1) according to any one of claims 1 to 7, wherein the output section (103) outputs the determination result to a communication section which reports to a monitoring center installed at a remote location via a communication network. [9] The degradation diagnosis device (100) for the exhaust gas purification system (1) according to any one of claims 1 to 8, wherein the degree of degradation due to corrosion of a component is a corrosion amount of the exhaust pipe (2, 2a). [10] A degradation diagnosis device (100) for the exhaust gas purification system (1) according to any one of claims 1 to 9, wherein the degree of degradation due to corrosion of a component is a corrosion amount of a support member for supporting a mixer (6) on the exhaust pipe (2, 2a), the mixer (6) serving to promote mixing of urea water injected into the exhaust pipe (2, 2a) and the exhaust gas flowing into the exhaust pipe (2, 2a).

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