JP2018131995A - 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 17 on the basis of an upstream NOx detection value detected by an upstream NOx sensor 15, and a downstream NOx detection value detected by a downstream NOx sensor 19; a diagnosis section 32 for diagnosing the reduction catalyst 17 on the basis of the NOx purification rate calculated by the purification rate calculating section 31; a diagnosis stop section 33 for stopping diagnosis of the reduction catalyst 17 when an ammonia detection value detected by an ammonia sensor 18 is larger than a prescribed threshold; and a threshold change section 34 for changing the threshold in accordance with the upstream NOx detection value.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 diagnose SCR degradation even when the ammonia concentration downstream of the SCR increases.

  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 for reducing and purifying NOx contained in the exhaust gas in the exhaust passage by a reduction purification reaction, and on the upstream side of 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. NOx of the reduction catalyst based on an ammonia sensor for detecting the ammonia concentration, an upstream NOx detection value detected by the upstream NOx sensor, and a downstream NOx detection value detected by the downstream NOx sensor A purification rate calculation unit for calculating a purification rate, and the return based on the NOx purification rate calculated by the purification rate calculation unit A diagnosis unit that diagnoses the catalyst, a diagnosis stop unit that stops diagnosis of the reduction catalyst when the ammonia detection value detected by the ammonia sensor is greater than a predetermined threshold value, and the threshold value according to the upstream NOx detection value And a threshold value changing unit for changing.

  Further, the threshold value changing unit increases the threshold value according to the upstream NOx detection value when the upstream NOx detection value becomes high.

  According to the technique of the present disclosure, even when the ammonia concentration downstream of the SCR increases, SCR deterioration diagnosis can be effectively performed.

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 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, and a selective reduction catalyst (hereinafter referred to as SCR) in order from the exhaust upstream side. ) 17, an ammonia sensor 18 and a downstream NOx sensor 19 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 ammonia sensor 18, the downstream NOx sensor 19, and the notification unit 20.

  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 gas is collected in the pores and surfaces of the partition walls.

  The upstream NOx sensor 15 and the downstream NOx sensor 19 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 17 as the upstream NOx concentration, and inputs the detected value to the ECU 30. The downstream NOx sensor 19 detects the NOx concentration and ammonia concentration in the exhaust downstream of the SCR 17 as the downstream NOx concentration, and inputs the detected values to the ECU 30.

  The urea water addition nozzle 16 adds the urea water pumped up from the urea water tank 21 by the urea water pump 22 into the exhaust pipe 12 upstream of the SCR 17. 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 17 on the downstream side as a reducing agent.

  The SCR 17 is formed, for example, by supporting zeolite or the like on a porous ceramic carrier. The SCR 17 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 18 detects the ammonia concentration in the exhaust gas downstream of the SCR 17 and inputs the detected value to the ECU 30. The notification unit 20 notifies the vehicle user that there is an abnormality in the exhaust system 1. The alerting | reporting part 20 is provided in the panel etc. (not shown) of the driver's seat of a vehicle so that the user of a vehicle can visually recognize, for example, and displays a warning.

  FIG. 2 is a schematic configuration diagram illustrating the diagnostic apparatus 100 according to the present embodiment. The diagnostic device 100 includes an upstream NOx sensor 15, an ammonia sensor 18, a downstream NOx sensor 19, a notification unit 20, and an ECU 30.

  The ECU 30 includes a NOx purification rate calculation unit 31, a diagnosis unit 32, a diagnosis stop unit 33, and a threshold value change unit 34 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, based on the downstream NOx concentration detection value _{S Nox2} inputted by the upstream NOx concentration detection value _{S NOx1} and downstream NOx sensor 19 that is input by the upstream NOx sensor 15, flows through the exhaust pipe 12 exhaust The NOx purification rate C of the SCR 17 is calculated, and the value of the NOx purification rate C is output to the diagnosis unit 32. Specifically, NOx purification rate calculating unit 31, for example, from the upstream NOx concentration detection value _{S NOx1} subtracting the downstream NOx concentration detection value _{S Nox2,} by dividing the value by the upstream NOx concentration detection value _{S NOx1,} the The NOx purification rate C is calculated.

  The diagnosis unit 32 diagnoses whether or not the SCR 17 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 32 diagnoses that the SCR 17 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 32 diagnoses that the SCR 17 is deteriorated and notifies the notification unit 20 to that effect. Accordingly, the notification unit 20 notifies the vehicle user that the SCR 17 is in a degraded state.

  Further, when a notification to stop the diagnosis of the SCR 17 is input from the diagnosis stop unit 33, the diagnosis unit 32 stops the diagnosis of the SCR 17 while the notification is input.

The diagnosis stop unit 33 determines whether or not the ammonia concentration detection value S _NH3 input by the ammonia sensor 18 is larger than the threshold value T input by the threshold value changing unit 34. The diagnosis unit 32 is notified that the diagnosis of the SCR 17 is stopped until the threshold T is reached. The threshold T is an ammonia concentration value for the diagnosis unit 32 to stop the diagnosis of the SCR 17. The reason why the diagnosis of the SCR 17 is stopped when the ammonia concentration detection value S _NH3 is larger than the threshold value T is that the downstream NOx concentration detection value S _NOx2 also increases and the NOx purification rate C decreases because the ammonia concentration downstream of the SCR ₁₇ increases. This is because the diagnosis unit 32 may erroneously diagnose that the SCR 17 has deteriorated.

The threshold changing unit 34 changes the threshold T according to the upstream NOx concentration detection value _SNOx1 input by the upstream NOx sensor 15 and outputs the value of the threshold T to the diagnosis stopping unit 33. Here, the threshold value changing unit 34 has, for example, a map (not shown) indicating a correspondence relationship between the upstream NOx concentration value and the ammonia threshold value as shown in Table 1. The map can be calculated in advance through experiments or the like.

Then, the threshold value changing unit 34 changes the threshold value T to the ammonia threshold value corresponding to the upstream NOx concentration detection value _SNOx1 with reference to the map. Here, the ammonia threshold value between the ammonia threshold values shown in the map can be calculated by linear interpolation based on the upstream NOx concentration value and the ammonia threshold value shown in the map. For example, when the upstream NOx concentration value is 75 ppm, the ammonia threshold value is calculated as 15 ppm, and when the upstream NOx concentration value is 150 ppm, the threshold value is calculated as 25 ppm.

Specifically, the threshold value changing unit 34 increases the threshold value T when the upstream NOx concentration detection value _SNOx1 becomes high. For example, when the upstream NOx concentration detection value _SNOx1 is 100 ppm, the threshold T is 20 ppm. At this time, when the upstream NOx concentration detection value _SNOx1 increases from 100 ppm to 150 ppm, the threshold value changing unit 34 calculates an ammonia threshold value 25 ppm corresponding to the upstream NOx concentration value 150 ppm and sets the threshold value T from 20 ppm to 25 ppm. Increase to. The diagnosis unit 32 lowers the threshold T when the upstream NOx concentration detection value _SNOx1 becomes low. For example, when the upstream NOx concentration detection value _SNOx1 decreases from 100 ppm to 75 ppm, the threshold value changing unit 34 calculates an ammonia threshold value 15 ppm corresponding to the upstream NOx concentration value 75 ppm, and decreases the threshold value T from 20 ppm to 15 ppm. .

  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 17 (step S11). Subsequently, the threshold value changing unit 34 changes the threshold value T to an ammonia threshold value corresponding to the upstream NOx concentration detection value _SNOx1 (step S12).

Subsequently, the diagnosis stopping unit 33 determines whether or not the ammonia concentration detection value _SNH3 is larger than the threshold T (step S13). And when larger than the threshold value T (step S13: YES), the diagnosis part 32 stops the diagnosis of SCR17 until it becomes below the threshold value T (step S14), and when it becomes below the threshold value T after that, processing is performed. Returns to step S11. On the other hand, if it is equal to or less than the predetermined threshold T (step S13: NO), the diagnosis unit 32 determines whether or not the SCR 17 has deteriorated (step S15).

  If the SCR 17 has not deteriorated (step S15: NO), the process returns to step S11. If the SCR 17 has deteriorated (step S15: YES), the diagnosis unit 32 causes the SCR 17 to deteriorate. To the notification unit 20, the notification unit 20 notifies the vehicle user that the SCR 17 has deteriorated (step S16), and then the diagnosis processing 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 19 detects the NOx concentration and ammonia concentration in the exhaust downstream of the SCR 17 as the downstream NOx concentration, and the diagnostic unit 32 detects the NOx. The SCR 17 is diagnosed based on the purification rate C, and the diagnosis of the SCR 17 is stopped when the ammonia concentration detection value S _NH3 is larger than the threshold T, and the threshold changing unit 34 determines the threshold T according to the upstream NOx concentration detection value S _NOx1. To change. Thus, when the ammonia concentration downstream of the SCR 17 increases, the downstream NOx concentration detection value _SNOx2 increases and the NOx purification rate C decreases, but when the upstream NOx concentration detection value _SNOx1 is high, the NOx purification rate C Therefore, the diagnosis of the SCR 17 can be continued without stopping. Therefore, even when the ammonia concentration downstream of the SCR 17 is increased, the deterioration diagnosis of the SCR 17 can be effectively performed.

For example, since when the ammonia concentration detection value _{S NH3} when the upstream NOx concentration detection value _{S NOx1} of 100ppm is 100ppm has a large influence on the NOx purification rate C of the ammonia concentration detected value _{S NH3,} diagnosis unit 32, The diagnosis of SCR17 is stopped. Meanwhile, since the upstream NOx concentration detection value _{S NOx1} is when the ammonia concentration detection value _{S NH3} at 1000ppm is 100ppm, the less influence on the NOx purification rate C of the ammonia concentration detected value _{S NH3,} diagnosis unit 32, Continue without stopping the diagnosis of SCR17.

The threshold changing unit 34, when the upstream NOx concentration detection value _{S NOx1} becomes high, increasing the threshold value T in accordance with the upstream NOx concentration detection value _{S NOx1.} Thereby, for example, since the threshold value T can be easily changed based on a map indicating the correspondence relationship between the upstream NOx concentration value and the threshold value, the deterioration diagnosis of the SCR 17 can be performed more effectively.

  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 the present embodiment, the oxidation catalyst 13, the filter 14, the upstream NOx sensor 15, the urea water addition nozzle 16, the SCR 17, the ammonia sensor 18, and the downstream NOx sensor 19 are provided in 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 19 may be upstream of the ammonia sensor 18, and may be configured in various other orders.

  In this embodiment, the diagnostic device 100 includes the upstream NOx sensor 15, the ammonia sensor 18, the downstream NOx sensor 19, the notification unit 20, and the ECU 30, but may include various other configurations of the exhaust system 1. Good.

Further, in the present embodiment, the diagnosis stop unit 33 notifies the diagnosis unit 32 that the diagnosis of the SCR 17 is stopped when the ammonia concentration detection value S _NH3 is larger than the threshold value T. Diagnosis should be stopped.

  Further, 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 detects the NOx concentration. What is necessary is just to detect.

  Furthermore, although SCR17 was used in this embodiment, it is not restricted to this, For example, another NOx catalyst may be sufficient and it may have an ammonia slip catalyst.

  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 20 performed warning display, for example, a character display, a symbol display, or lighting of a lamp | ramp may be sufficient, and you may alert | report by an audio | voice etc.

  Further, in the present embodiment, the ammonia threshold value between the ammonia threshold values shown in the map is calculated by linear interpolation based on the upstream NOx concentration value and the ammonia threshold value shown in the map. Regarding the ammonia threshold value between the ammonia threshold values shown, the ammonia threshold value may be changed stepwise as a constant ammonia threshold value, and the ammonia threshold value may be changed according to the upstream NOx concentration value.

1 exhaust system 10 engine 12 exhaust pipe 15 upstream NOx sensor 17 SCR
18 Ammonia sensor 19 Downstream NOx sensor 30 ECU
31 NOx purification rate calculation unit 32 Diagnosis unit 33 Diagnosis stop unit 34 Threshold change unit 100 Diagnosis device

Claims (2)

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 concentration;
A purification rate calculation unit that calculates a NOx purification rate of the reduction catalyst based on an upstream NOx detection value detected by the upstream NOx sensor and a downstream NOx detection value detected by the downstream NOx sensor;
A diagnostic unit that diagnoses the reduction catalyst based on the NOx purification rate calculated by the purification rate calculation unit;
A diagnosis stop unit for stopping the diagnosis of the reduction catalyst when the ammonia detection value detected by the ammonia sensor is larger than a predetermined threshold;
A threshold value changing unit for changing the threshold value according to the upstream NOx detection value;
A diagnostic apparatus comprising: The diagnostic device according to claim 1, wherein the threshold value changing unit increases the threshold value according to the upstream NOx detection value when the upstream NOx detection value becomes high.

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