JP2018131994A - Diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively diagnose deterioration of a reduction catalyst.SOLUTION: A diagnostic device includes: a purification rate calculating section 31 for calculating NOx purification rate of a reduction catalyst 18 on the basis of an upstream NOx detection value detected by an upstream NOx sensor 15, a downstream NOx detection value detected by a downstream NOx sensor 20, and an ammonia detection value detected by an ammonia sensor 19; and a diagnosis section 33 for diagnosing the reduction catalyst 18 on the basis of the NOx purification rate calculated by the purification rate calculating section 31. The purification rate calculating section 31 subtracts the value resulting from subtracting the ammonia detection value from the downstream NOx detection value from the upstream side NOx detection value, and then, divides the value by the upstream NOx detection value, and thus, calculates the NOx purification rate.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a diagnostic apparatus, and more particularly to a diagnostic apparatus in an engine exhaust system.

Conventionally, a selective reduction catalyst (hereinafter referred to as SCR) that selectively reduces and purifies NOx in exhaust gas using ammonia (NH ₃ ) produced by hydrolysis and thermal decomposition of urea water by exhaust heat as a reducing agent. Exhaust systems comprising are known.

  As an exhaust system of this type, for example, an exhaust purification system disclosed in Patent Document 1 includes a NOx inflow amount read from an upstream NOx sensor provided upstream of the SCR and a NOx outflow read from a downstream NOx sensor provided downstream of the SCR. The SCR NOx purification rate is calculated using the amount as a parameter (see, for example, Patent Document 1).

JP 2013-227950 A

  By the way, in a general NOx sensor, it is difficult to detect the ammonia concentration and the NOx concentration separately, and since the ammonia concentration is also detected by the NOx sensor as the NOx concentration, the NOx purification rate cannot be accurately calculated. There are challenges. In particular, in a situation where ammonia slip is often caused, the ammonia concentration downstream of the SCR increases, so that the detection value of the downstream NOx sensor also increases and the NOx purification rate decreases. As a result, in an exhaust system that performs SCR degradation diagnosis based on the NOx purification rate, there is a risk of misdiagnosing that the SCR is degraded.

  An object of the technology of the present disclosure is to provide a diagnostic device that can effectively perform SCR degradation diagnosis by calculating the NOx purification rate more accurately.

  The technology of the present disclosure is provided in the exhaust passage of the engine, and is provided on the upstream side of the reduction catalyst that reduces and purifies NOx contained in the exhaust gas in the exhaust passage by a reduction purification reaction, and the reduction catalyst. An upstream NOx sensor that detects the NOx; a downstream NOx sensor that detects the NOx and detects ammonia contained in the exhaust gas as NOx; and a downstream of the reduction catalyst. An ammonia sensor that detects ammonia, an upstream NOx detection value detected by the upstream NOx sensor, a downstream NOx detection value detected by the downstream NOx sensor, and a detection by the ammonia sensor A purification rate calculation unit that calculates a NOx purification rate of the reduction catalyst based on the detected ammonia value, and the purification rate A diagnosis unit for diagnosing the reduction catalyst based on the NOx purification rate calculated by the outlet, and the purification rate calculation unit from the downstream NOx detection value to the upstream NOx detection value The NOx purification rate is calculated by subtracting a value obtained by subtracting the ammonia detection value and dividing the value by the upstream NOx detection value.

  Further, the technology of the present disclosure further includes a temperature sensor that detects the temperature of the reduction catalyst, and the diagnosis unit has a temperature detected by the temperature sensor in a temperature range where the reduction purification reaction is stable. In addition, the reduction catalyst is diagnosed.

  Further, according to the technology of the present disclosure, a filter that is provided on the upstream side of the upstream NOx sensor, collects particulate matter contained in the exhaust, and a filter that burns and removes the particulate matter deposited on the filter. A filter regeneration control unit that controls regeneration, and the diagnosis unit stops diagnosis of the reduction catalyst while the filter regeneration control unit is performing the filter regeneration.

  According to the technique of the present disclosure, SCR degradation diagnosis can be effectively performed by calculating the NOx purification rate more accurately.

It is a schematic block diagram which shows the exhaust system of the diesel engine provided with the diagnostic apparatus which concerns on this embodiment. It is a functional block diagram which shows the diagnostic apparatus which concerns on this embodiment. It is a flowchart figure explaining the diagnostic process which concerns on this embodiment.

  Hereinafter, based on an accompanying drawing, a diagnostic device concerning an embodiment of the present invention is explained. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  FIG. 1 is a schematic configuration diagram illustrating an exhaust system 1 of a diesel engine (hereinafter simply referred to as an engine) 10 including a diagnostic device according to the present embodiment. The exhaust manifold 11 of the engine 10 is connected to an exhaust pipe 12 that guides the exhaust discharged from the engine 10 to the atmosphere. The exhaust pipe 12 includes, in order from the exhaust upstream side, an oxidation catalyst 13, a particulate filter (hereinafter simply referred to as a filter) 14, an upstream NOx sensor 15, a urea water addition nozzle 16, a temperature sensor 17, and a selective reduction catalyst ( (Hereinafter referred to as SCR) 18, an ammonia sensor 19, and a downstream NOx sensor 20 are provided.

  The exhaust system 1 is provided with an electronic control unit (hereinafter, ECU) 30. The ECU 30 performs various controls of the exhaust system 1 and includes a known CPU, ROM, RAM, input port, output port, and the like. The ECU 30 is electrically connected to the upstream NOx sensor 15, the urea water addition nozzle 16, the temperature sensor 17, the ammonia sensor 19, the downstream NOx sensor 20, and the notification unit 21.

  The oxidation catalyst 13 is formed by, for example, supporting an oxidation catalyst component on the surface of a ceramic carrier such as a honeycomb structure, and when unburned fuel is supplied by post injection of an exhaust injector or an in-cylinder injector (not shown), This is oxidized to raise the exhaust temperature. The filter 14 is formed, for example, by arranging a large number of cells partitioned by porous partition walls along the flow direction of the exhaust gas and alternately plugging the upstream side and the downstream side of these cells. The particulate matter in the exhaust (hereinafter referred to as PM) is collected in the pores and the surface of the partition walls.

  The upstream NOx sensor 15 and the downstream NOx sensor 20 are sensors that detect the NOx concentration in the exhaust gas and also detect the ammonia concentration as the NOx concentration. The upstream NOx sensor 15 detects the NOx concentration and ammonia concentration in the exhaust upstream of the SCR 18 as the upstream NOx concentration, and inputs the detected values to the ECU 30. The downstream NOx sensor 20 detects the NOx concentration and ammonia concentration in the exhaust gas downstream of the SCR 18 as the downstream NOx concentration, and inputs the detected value to the ECU 30.

  The urea water addition nozzle 16 adds urea water pumped up from the urea water tank 22 by the urea water pump 23 into the exhaust pipe 12 upstream of the SCR 18. The urea water injected into the exhaust pipe 12 from the urea water addition nozzle 16 is hydrolyzed and thermally decomposed by exhaust heat to generate ammonia, and is supplied to the SCR 18 on the downstream side as a reducing agent.

  The temperature sensor 17 detects the temperature of the inlet of the SCR 18 in the exhaust pipe 12 and inputs the detected value to the ECU 30. The SCR 18 is formed, for example, by supporting zeolite or the like on a porous ceramic carrier. The SCR 18 adsorbs ammonia supplied as a reducing agent and selectively reduces and purifies NOx from the exhaust gas passing through the adsorbed ammonia.

  The ammonia sensor 19 detects the ammonia concentration in the exhaust gas downstream of the SCR 18 and inputs the detected value to the ECU 30. The notification unit 21 notifies the vehicle user that there is an abnormality in the exhaust system 1. For example, the notification unit 21 is provided on a panel or the like (not shown) of a driver's seat of the vehicle so that a user of the vehicle can visually recognize the information, and displays a warning.

  FIG. 2 is a functional block diagram showing the diagnostic device 100 according to the present embodiment. The diagnostic device 100 includes an upstream NOx sensor 15, a temperature sensor 17, an ammonia sensor 19, a downstream NOx sensor 20, a notification unit 21, and an ECU 30.

  The ECU 30 includes a NOx purification rate calculation unit 31, a filter regeneration control unit 32, and a diagnosis unit 33 as some functional elements. Each of these functional elements will be described as being included in the ECU 30 which is an integral hardware, but any one of these functional elements can be provided in separate hardware and read out from a ROM (recording medium). It can also be realized by software mainly composed of programs executed by the CPU.

NOx purification ratio calculating unit 31, the upstream NOx concentration detection value _{S NOx1} inputted by the upstream NOx sensor 15, the downstream NOx concentration detection input by the ammonia concentration detection value _{S NH3} and the downstream NOx sensor 20 that is input by the ammonia sensor 19 Based on the value _SNOx2 , the NOx purification rate C of the SCR 18 in the exhaust flowing through the exhaust pipe 12 is calculated, and the value of the NOx purification rate C is output to the diagnosis unit 33.

Specifically, NOx purification rate calculating unit 31, the upstream NOx concentration detection value _{S NOx1,} subtracts a value obtained by subtracting the ammonia concentration detection value _{S NH3} from the downstream NOx concentration detection value _{S Nox2,} upstream NOx the value The NOx purification rate C is calculated by the following equation (1) divided by the concentration detection value _SNOx1 .
_{C = (S NOx1 - (S} NOx2 -S NH3)) / S NOx1 ··· (1)
The filter regeneration control unit 32 performs control related to filter regeneration that raises the exhaust gas temperature to the combustion temperature of PM and burns and removes PM accumulated on the filter 14. Specifically, the filter regeneration control unit 32 estimates the PM accumulation amount of the filter 14 from the traveling distance of the vehicle or the differential pressure before and after the filter 14 detected by a differential pressure sensor (not shown). When the predetermined upper limit threshold is exceeded, filter regeneration is started, and the filter 33 is notified to that effect while performing filter regeneration.

  When the filter regeneration is started, the filter regeneration control unit 32 transmits an instruction signal for causing an exhaust injector (not shown) to perform exhaust pipe injection, or transmits an instruction signal for causing each in-cylinder injector (not shown) to perform post injection. Then, the exhaust temperature is raised to the PM combustion temperature (for example, about 550 ° C.) by executing the exhaust pipe injection or the post injection. Then, the filter regeneration control unit 32 terminates the filter regeneration when the PM accumulation estimated amount has decreased to a predetermined lower threshold value indicating combustion removal, and terminates the notification to the diagnosis unit 33 that the filter regeneration is being performed. .

  The diagnosis unit 33 diagnoses whether or not the SCR 18 has deteriorated based on the value of the NOx purification rate C input by the NOx purification rate calculation unit 31. Specifically, the diagnosis unit 33 diagnoses that the SCR 18 is not deteriorated, for example, when the NOx purification rate C is larger than a predetermined NOx purification rate (for example, 50%). On the other hand, when the NOx purification rate C is equal to or lower than the predetermined NOx purification rate, the diagnosis unit 33 diagnoses that the SCR 18 is deteriorated and notifies the notification unit 21 to that effect. Thus, the notification unit 21 notifies the vehicle user that the SCR 18 is in a degraded state.

At this time, the diagnosis unit 33 determines whether the temperature of the inlet of the SCR 18 is in a temperature range where the reduction and purification reaction of the SCR 18 is stable based on the temperature detection value S _temp input by the temperature sensor 17. When the reductive purification reaction is in a stable temperature range, it is diagnosed whether the SCR 18 is deteriorated. Here, the temperature range in which the reduction and purification reaction of the SCR 18 is stable may be, for example, a temperature range in which the temperature of the normal SCR 18 can exhibit a NOx purification rate equal to or higher than a predetermined threshold. The temperature range calculated by experiment etc. may be sufficient, and the temperature within an active temperature range may be sufficient, for example, it is a 250-320 degreeC temperature range.

  Further, the diagnosis unit 33 stops diagnosis of the SCR 18 when notified by the filter regeneration control unit 32 that filter regeneration is being performed, and resumes diagnosis of the SCR 18 when notification of filter regeneration is completed. . Specifically, the diagnosis unit 33 stops the diagnosis of the SCR 18 because the exhaust gas temperature is raised to the PM combustion temperature and the reduction and purification reaction of the SCR 18 becomes unstable while the filter is being regenerated.

  FIG. 3 is a flowchart for explaining the diagnosis process according to the present embodiment. The diagnosis processing according to the present embodiment is started, for example, when the vehicle power is turned on (ignition switch key switch ON).

  First, the NOx purification rate calculation unit 31 calculates the NOx purification rate C of the SCR 18 in the exhaust flowing through the exhaust pipe 12 (step S11). Subsequently, the filter regeneration control unit 32 determines whether or not filter regeneration is being performed (step S12). If the filter regeneration is being performed (step S12: YES), the diagnosis unit 33 stops the diagnosis until the filter regeneration is completed (step S13). Thereafter, when the filter regeneration is terminated, the process proceeds to step S11. Return to. On the other hand, when filter regeneration is not performed (step S12: NO), the diagnosis unit 33 determines whether or not the reduction purification reaction of the SCR 18 is in a stable temperature range (step S14).

  If the reduction purification reaction is not in a stable temperature range (step S14: NO), the process returns to step S11, and if the reduction purification reaction is in a stable temperature range (step S14: YES). The diagnosis unit 33 determines whether or not the SCR 18 has deteriorated (step S15).

  If the SCR 18 has not deteriorated (step S15: NO), the process returns to step S11. If the SCR 18 has deteriorated (step S15: YES), the diagnostic unit 33 causes the SCR 18 to deteriorate. The notification unit 21 notifies the vehicle user that the SCR 18 has deteriorated (step S16), and then the diagnosis process according to the present embodiment is terminated.

As described above in detail, according to the diagnostic apparatus 100 of the present embodiment, the downstream NOx sensor 20 detects the NOx concentration and ammonia concentration in the exhaust downstream of the SCR 18 as the downstream NOx concentration, and the NOx purification rate calculation unit 31. but the upstream NOx concentration detection value _{S NOx1,} subtracts a value obtained by subtracting the ammonia concentration detection value _{S NH3} from the downstream NOx concentration detection value _{S Nox2,} by dividing the value by the upstream NOx concentration detection value _{S NOx1} Then, the NOx purification rate C is calculated. As a result, when the ammonia concentration downstream of the SCR 18 increases, the downstream NOx concentration detection value S _NOx2 increases, but the NOx purification rate C can be calculated without the influence of the ammonia concentration. Therefore, even when the ammonia concentration downstream of the SCR 18 increases, the deterioration diagnosis of the SCR 18 can be effectively performed by calculating the NOx purification rate C more accurately.

Further, the diagnosis unit 33 diagnoses the SCR 18 when the temperature detection value S _temp is in a temperature range where the reduction purification reaction is stable. Thereby, the deterioration diagnosis of the SCR 18 can be performed more effectively by diagnosing the SCR 18 in a state where the NOx purification rate C is stable. Further, the diagnosis unit 33 stops the diagnosis of the SCR 18 while the filter regeneration is being performed. Thereby, when the exhaust temperature is raised to the PM combustion temperature and the reduction and purification reaction of the SCR 18 becomes unstable, the diagnosis of the SCR 18 can be diagnosed more effectively by stopping the diagnosis of the SCR 18.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

  For example, in this embodiment, the oxidation catalyst 13, the filter 14, the upstream NOx sensor 15, the urea water addition nozzle 16, the temperature sensor 17, the SCR 18, the ammonia sensor 19, and the downstream NOx sensor 20 are provided in this order from the exhaust upstream side. For example, the upstream NOx sensor 15 may be upstream of the oxidation catalyst 13, and the downstream NOx sensor 20 may be upstream of the ammonia sensor 19, and may be configured in various other orders. .

  In the present embodiment, the diagnostic apparatus 100 includes the upstream NOx sensor 15, the temperature sensor 17, the ammonia sensor 19, the downstream NOx sensor 20, the notification unit 21, and the ECU 30, but is not limited thereto, and other exhaust systems. One various configurations may be provided.

  In the present embodiment, the upstream NOx sensor 15 detects the NOx concentration in the exhaust gas and also detects the ammonia concentration as the NOx concentration. However, the present invention is not limited to this. For example, the upstream NOx sensor 15 has only the NOx concentration. May be detected.

  Furthermore, in this embodiment, after calculating the NOx purification rate C of the SCR 18, it is determined whether or not the filter regeneration is performed, and it is determined whether or not the reduction purification reaction is in a stable temperature range. For example, it is possible to calculate the NOx purification rate C of the SCR 18 after determining whether or not the filter regeneration is being performed and determining whether or not the reduction purification reaction is in a stable temperature range. Well, control can be performed in various other orders.

  Furthermore, in this embodiment, when filter regeneration is being performed, diagnosis is stopped until filter regeneration is completed. However, the present invention is not limited to this. For example, the diagnosis unit 33 determines that filter regeneration is not performed. The SCR 18 may be diagnosed, and various other controls can be performed.

  Furthermore, in the present embodiment, the SCR 18 is used. However, the present invention is not limited to this. For example, another NOx catalyst may be used, and an ammonia slip catalyst may be further provided on the downstream side of the SCR 18.

  Further, in the present embodiment, the temperature sensor 17 detects the temperature of the inlet of the SCR 18, but not limited to this, for example, the temperature of the outlet of the SCR 18 may be detected as long as the temperature of the SCR 18 can be detected or estimated.

  Furthermore, in this embodiment, although the engine 10 used the diesel engine, it can apply widely also to other internal combustion engines, such as a gasoline engine.

  Furthermore, in this embodiment, although the alerting | reporting part 21 performed the warning display, for example, a character display, a symbol display, or lighting of a lamp may be sufficient, and you may alert | report by an audio | voice etc.

DESCRIPTION OF SYMBOLS 1 Exhaust system 10 Engine 12 Exhaust pipe 14 Particulate filter 15 Upstream NOx sensor 17 Temperature sensor 18 SCR
19 Ammonia sensor 20 Downstream NOx sensor 30 ECU
31 NOx purification rate calculation unit 32 Filter regeneration control unit 33 Diagnosis unit 100 Diagnosis device

Claims (3)

A reduction catalyst that is provided in the exhaust passage of the engine and that reduces and purifies NOx contained in the exhaust in the exhaust passage by a reduction and purification reaction;
An upstream NOx sensor that is provided upstream of the reduction catalyst and detects the NOx;
A downstream NOx sensor that is provided downstream of the reduction catalyst, detects the NOx, and detects ammonia contained in the exhaust gas as NOx;
An ammonia sensor that is provided downstream of the reduction catalyst and detects the ammonia;
The NOx purification rate of the reduction catalyst is calculated based on the upstream NOx detection value detected by the upstream NOx sensor, the downstream NOx detection value detected by the downstream NOx sensor, and the ammonia detection value detected by the ammonia sensor. A purification rate calculation unit to perform,
A diagnosis unit that diagnoses the reduction catalyst based on the NOx purification rate calculated by the purification rate calculation unit;
With
The purification rate calculation unit subtracts a value obtained by subtracting the ammonia detection value from the downstream NOx detection value with respect to the upstream NOx detection value, and divides the value by the upstream NOx detection value to thereby calculate the NOx. A diagnostic device characterized by calculating a purification rate. A temperature sensor for detecting the temperature of the reduction catalyst;
The diagnostic device according to claim 1, wherein the diagnostic unit diagnoses the reduction catalyst when the temperature detected by the temperature sensor is in a temperature range where the reduction purification reaction is stable. A filter that is provided on the upstream side of the upstream NOx sensor and collects particulate matter contained in the exhaust;
A filter regeneration control unit for controlling filter regeneration for burning and removing the particulate matter deposited on the filter;
Further comprising
The diagnosis device according to claim 1, wherein the diagnosis unit stops diagnosis of the reduction catalyst while the filter regeneration control unit is performing the filter regeneration.

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