JP2012036857A - Device for diagnosing catalyst degradation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for diagnosing catalyst degradation, in which a cost increase is suppressed and which can determine to what extent a catalyst has degraded.SOLUTION: The device for diagnosing the catalyst degradation includes: a selective reduction type catalyst 25 which is provided in an exhaust passage 19 of an engine 10 and which reduces and purifies NOx contained in exhaust gas circulating through the exhaust passage 19; an NOratio obtaining means 33 for obtaining an NOratio as a ratio of NOto NOx contained in the exhaust gas circulating through the selective reduction type catalyst 25; a NOx purification ratio obtaining means 34 for obtaining a NOx purification ratio as a ratio of NOx reduced and purified by the selective reduction type catalyst 25, on the basis of the amount of NOx on the upstream and downstream sides of the selective reduction type catalyst 25; and a degradation determining means 35 for determining the degree of the degradation of the selective reduction type catalyst 25 on the basis of the NOratio obtained by the NOratio obtaining means 33, the NOx purification ratio obtained by the NOx purification ratio obtaining means 34, and a temperature of the selective reduction type catalyst 25.

Description

  The present invention relates to a catalyst deterioration diagnosis apparatus that determines a deterioration degree of a catalyst used in an exhaust gas purification apparatus for an internal combustion engine.

  An exhaust gas from an internal combustion engine (hereinafter also referred to as an engine), particularly a diesel engine, contains nitrogen oxides (hereinafter referred to as NOx) that are air pollutants. Accordingly, a selective catalytic reduction (hereinafter abbreviated as SCR) for purifying NOx is installed in the exhaust passage of the engine, and urea water as a reducing agent is added to the exhaust flowing into the SCR. Thus, a technique is known in which the exhaust gas is purified by reducing NOx in the exhaust gas in the SCR.

  The SCR is configured, for example, by supporting a catalyst on a honeycomb structure carrier in which a plurality of minute holes parallel to each other in the axial direction communicate with each other. In the exhaust gas purification apparatus using the SCR, a nozzle as a urea water addition apparatus for adding urea water to the exhaust gas is provided on the upstream side of the SCR. The urea water added from the nozzle is decomposed into ammonia by exhaust heat in the exhaust pipe and on the SCR, and acts as a reducing agent for NOx. Ammonia in the vicinity of the SCR is once adsorbed by the SCR, and NOx is reduced to nitrogen by promoting the denitration reaction between the ammonia and NOx in the exhaust gas by the SCR.

By the way, as the SCR continues to be used, it gradually deteriorates due to the influence of heat and the like. As such deterioration with time progresses, the ability to reduce NOx and purify exhaust, that is, the NOx purification rate decreases. If the exhaust gas cannot be purified by properly reducing NOx, NOx is released into the atmosphere, which may adversely affect the environment.
In order to solve such a problem, the following Patent Document 1 describes whether or not the NOx purification rate has decreased due to the deterioration of the NOx selective reduction catalyst from the temperature of the NOx selective reduction catalyst (SCR) and the NOx emission amount. An abnormality detection device for an internal combustion engine has been proposed. In this abnormality detection device, the decrease in the NOx purification rate is caused by the deterioration of the NOx selective reduction catalyst or the supply amount or quality of urea water is abnormal due to the change pattern of the NOx purification rate with respect to the catalyst temperature. This is to determine whether this is the cause.

JP 2009-138626 A

However, the abnormality detection device described in Patent Document 1 determines whether or not the NOx selective reduction catalyst has deteriorated depending on whether or not a predetermined specified value has been exceeded. In other words, it is impossible to determine how much the NOx selective reduction catalyst has deteriorated, and it is not possible to obtain information such as how much can be used and when replacement is necessary.
The present invention has been devised in view of such problems, and an object of the present invention is to provide a catalyst deterioration diagnosis apparatus that can determine how much a catalyst has deteriorated.

  It is another object of the present invention to provide a catalyst deterioration diagnosis device that suppresses an increase in cost by making a determination using a NOx sensor.

In order to solve the above problems, a catalyst deterioration diagnosis device of the present invention is provided in an exhaust passage of an engine, and a selective reduction type catalyst that reduces and purifies NOx contained in exhaust flowing through the exhaust passage, and the selection A first NOx sensor that is provided downstream of the reduction catalyst and detects a first NOx value that is the amount of NOx contained in the exhaust gas that has passed through the selective reduction catalyst, and exhaust gas after being discharged from the engine Engine out NOx value acquisition means for acquiring an engine out NOx value that is the amount of NOx contained therein, and a NO ₂ ratio that is a ratio of NO ₂ to NOx contained in the exhaust gas that circulates through the selective catalytic reduction catalyst and NO ₂ ratio acquisition means for, based on the amount of NOx in the upstream side and downstream side of the selective reduction catalyst is in a ratio of NOx to be purified are reduced by the selective reduction catalyst And NOx purification rate obtaining means for obtaining Ox purification rate, the temperature of the NO ₂ the NOx purification rate and the selective reduction catalyst obtained by the acquired the NO ₂ ratio the NOx purification rate acquisition means by the ratio acquiring means Deterioration determining means for determining the degree of deterioration of the selective catalytic reduction catalyst based on this.

The NO ₂ ratio obtaining means obtains the NO ₂ ratio on the basis of said engine-out NOx value acquired by the first NOx value detected by the first NOx sensor and the engine-out NOx value acquiring means It is preferable.
Alternatively, in the exhaust passage of the engine, an oxidation catalyst provided on the upstream side of the selective reduction catalyst on the downstream side of the engine and on the upstream side of the selective reduction catalyst on the downstream side of the oxidation catalyst. And a second NOx sensor that detects a second NOx value that is an amount of NOx contained in the exhaust gas flowing into the selective catalytic reduction catalyst, wherein the NO ₂ ratio acquisition means includes the second NOx Preferably, the NO ₂ ratio is acquired based on the second NOx value detected by the sensor and the engine out NOx value acquired by the engine out NOx value acquisition means.

Preferably, the engine-out NOx value acquisition means acquires the engine-out NOx value based on a map indicating a correspondence relationship between the engine speed, the engine load, and the engine-out NOx value set in advance. .
The engine-out NOx sensor may further include an engine-out NOx sensor that is provided upstream of the oxidation catalyst and detects the engine-out NOx value contained in the exhaust after being discharged from the engine. Preferably, the engine out NOx value is acquired by the engine out NOx sensor.

  Moreover, it is preferable to further provide a notifying means for notifying the result of determination by the deterioration determining means.

  According to the catalyst deterioration diagnosis apparatus of the present invention, the degree of deterioration of the selective catalytic reduction catalyst can be determined by the first NOx sensor provided on the downstream side of the selective catalytic reduction catalyst. It is possible to determine whether or not the exhaust gas has deteriorated. In addition to suppressing the deterioration of exhaust gas due to catalyst deterioration in advance, control according to the state of deterioration of the catalyst can be performed, and clean exhaust gas can always be maintained.

Further, when the NO ₂ ratio is acquired by the first NOx sensor provided on the downstream side of the selective catalytic reduction catalyst, an increase in cost can be suppressed and deterioration determination can be performed with a simple configuration.
Further, when the NO ₂ ratio is acquired by the second NOx sensor provided on the downstream side of the oxidation catalyst and on the upstream side of the selective reduction catalyst, it is not necessary to consider the influence of NOx purified by the selective reduction catalyst, The NO ₂ ratio can be easily obtained.

Moreover, when acquiring an engine out NOx value from a map, a cost increase can be suppressed and deterioration determination can be implemented with a simple configuration.
Further, when the engine-out NOx value is detected by a sensor, the NOx purification rate and the NO ₂ ratio can be acquired more accurately, and the determination accuracy can be improved.
Further, when providing a means for notifying the driver of the degradation level of the selective catalytic reduction catalyst, for example, the driver can be urged to perform maintenance or replace the selective catalytic reduction catalyst.

It is a typical whole block diagram which shows the exhaust gas purification apparatus with which the catalyst deterioration diagnostic apparatus concerning 1st and 2nd embodiment of this invention was applied. 6 is a map (engine-out NOx map) showing the relationship between the operating state of the internal combustion engine used in the catalyst deterioration diagnosis apparatus according to the first and second embodiments of the present invention and the amount of NOx contained in exhaust gas. It is a map (NOx sensor characteristic map) which shows the characteristic of the NOx sensor used with the catalyst deterioration diagnostic apparatus concerning 1st and 2nd embodiment of this invention. FIG. 4A is a map (deterioration determination map) showing the relationship among the NO ₂ ratio, catalyst temperature, and NOx purification rate used in the catalyst deterioration diagnosis apparatus according to the first and second embodiments of the present invention, and FIG. FIG. 4B shows a case where the degree of deterioration is almost intermediate, and FIG. 4C shows a case where the degree of deterioration is large. It is a control flow which shows the diagnostic method by the catalyst deterioration diagnostic apparatus concerning 1st embodiment of this invention. It is a control flow which shows the diagnostic method by the catalyst degradation diagnostic apparatus concerning 2nd embodiment of this invention.

  Hereinafter, the disclosed catalyst deterioration diagnosis apparatus will be described with reference to the drawings. Note that the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described in the following embodiment.

[1. First embodiment]
[1-1. overall structure]
A catalyst deterioration diagnosis apparatus according to this embodiment will be described with reference to FIGS. The catalyst deterioration diagnosis device according to the present embodiment can be applied not only to a vehicle but also to a vehicle equipped with an engine, such as a ship, but here, it is applied to a vehicle such as a general passenger car, a truck, or a bus. An example will be described.

  As shown in FIG. 1, the engine 10 is here configured as a diesel engine of an in-line 6-cylinder engine. Each cylinder of the engine 10 is provided with a fuel injection valve 11. Each fuel injection valve 11 is supplied with pressurized fuel from a common rail 12, and injects fuel into the cylinder of the corresponding cylinder when the valve is opened. The engine 10 may be a gasoline engine, and the number of cylinders is not limited to this. In FIG. 1, the engine 10 is mounted on the front side (front) of the vehicle so that exhaust flows toward the rear side (rear) of the vehicle. However, the arrangement on the vehicle is not limited to this.

  An intake manifold 13 is mounted on the intake side of the engine 10, and an intake passage 14 connected to the intake manifold 13 is provided with an air cleaner 15, a compressor 16 a of a turbocharger 16, and an intercooler 17 from the upstream side. An exhaust manifold 18 is mounted on the exhaust side of the engine 10, and a turbine 16 b of a turbocharger 16 connected coaxially with the compressor 16 a is connected to the exhaust manifold 18. An exhaust passage 19 is connected to the turbine 16b, and the exhaust passage 19 extends toward the rear of the vehicle. An exhaust purification device 20 is provided in the middle of the exhaust passage 19.

[1-2. Configuration of exhaust purification device]
The exhaust purification device 20 includes an upstream exhaust purification device 21 provided on the exhaust upstream side, a downstream exhaust purification device 22 provided on the exhaust downstream side of the upstream exhaust purification device 21, an upstream exhaust purification device 21 and A urea water addition nozzle 28 provided between the downstream side exhaust purification devices 22 is provided. Each of the upstream side exhaust purification device 21 and the downstream side exhaust purification device 22 is configured such that a catalyst or the like is disposed in the axial direction in a cylindrical casing so that the exhaust gas flows, and the upstream side exhaust purification device 21. And the downstream side exhaust purification apparatus 22 is installed so that exhaust_gas | exhaustion flows linearly.

The upstream side exhaust purification device 21 includes a pre-stage oxidation catalyst (Diesel Oxidation Catalyst, hereinafter referred to as DOC) 23 disposed on the upstream side, and a particulate filter (hereinafter referred to as DPF) disposed on the downstream side. (Abbreviated) 24. Hereinafter, the upstream side exhaust purification device 21 is referred to as a DPF device 21.
The DPF device 21 has a function of collecting particulate matter (hereinafter abbreviated as PM) contained in exhaust gas and a function of continuously oxidizing and removing the collected PM. In addition, PM is a particulate material in which fuel, lubricant components, sulfur compounds, and the like that remain unburned around carbon black smoke (soot) are attached.

The DOC 23 is an oxidation catalyst having an oxidizing ability with respect to components in the exhaust, and a catalyst material is supported on a honeycomb-shaped carrier made of metal, ceramics, or the like. Components in the exhaust gas oxidized by the DOC 23 include NO, hydrocarbons in unburned fuel, and carbon monoxide. For example, NO ₂ is produced when NO is oxidized by DOC23.
The DPF 24 is a porous filter (for example, a ceramic filter) that collects PM. The inside of the DPF 24 is divided into a plurality of parts along the flow direction of the exhaust by a porous wall. A large number of pores having a size commensurate with the particulates of PM are formed in the wall. When the exhaust gas passes near or inside the wall body, PM is collected on the wall body and the wall body surface, and the exhaust gas is filtered. Such regeneration control of the DPF 24 is controlled by the controller 30 described later. PM collected by the DPF 24 by the regeneration control is removed, and the DPF 24 is regenerated and purified.

The downstream side exhaust purification device 22 includes a selective reduction catalyst (Selective Catalytic Reduction, hereinafter abbreviated as SCR) 25 disposed on the upstream side, and a post-stage oxidation catalyst (Clean Up Catalyst, hereinafter, disposed on the downstream side). 26 (abbreviated as CUC). Hereinafter, the downstream side exhaust purification device 22 is referred to as an SCR device 22.
The SCR 25 is a urea-added nitrogen oxide selective reduction type catalyst, which has a function of hydrolyzing urea water supplied from the upstream side to ammonia and adsorbing ammonia, and is further exhausted using the adsorbed ammonia as a reducing agent. NOx is reduced to N ₂ . Note that the function of adsorbing ammonia is not an essential function for the SCR 25, and the type of catalyst is arbitrary. For example, it is conceivable to use a catalyst such as zeolite or vanadium.

CUC26 is an oxidation catalyst for removing excess ammonia in the reduction reaction at SCR25.
The urea water addition nozzle 28 provided between the DPF device 21 and the SCR device 22 injects urea water as a reducing agent stored in the urea water tank 29 into the exhaust gas toward the SCR 25 by the addition device 27. And add. The amount of urea water added and the timing of addition are controlled by urea water addition control means 31 described later.

[1-3. controller]
A controller (ECU, Engine (electronic) Control Unit) 30 is a CPU that executes various arithmetic processes related to engine control and exhaust purification control, a ROM that stores programs and data necessary for the control, arithmetic results of the CPU, etc. Are temporarily stored, and an input / output port for inputting / outputting signals to / from the outside.

An engine speed sensor (not shown) for detecting the engine speed is provided in the vicinity of a crankshaft (not shown) of the engine 10, and an accelerator pedal operation amount (accelerator opening) by a driver is provided at an arbitrary position of the vehicle. An accelerator opening sensor (not shown) for detecting the degree) is provided.
The SCR device 22 is provided with a temperature sensor 42 that detects the exhaust temperature upstream of the SCR 25, and detects the temperature of the exhaust gas flowing into the SCR 25. The exhaust temperature is used as the catalyst temperature of the SCR 25. Further, a NOx sensor (first NOx sensor) 41 is provided in the exhaust passage 19 on the downstream side of the SCR device 22, and the amount of NOx contained in the exhaust gas after passing through the DPF device 21 and the SCR device 22. The first NOx value corresponding to (for example, NOx concentration, mass, molar concentration, etc.) is always detected.

  The detection by the NOx sensor 41 is continuously performed at a constant cycle, for example, 10 times per second, and the detection results are accumulated for a certain period (for example, 20 to 30 seconds), and the accumulated NOx value is first determined. NOx value. This is for suppressing the influence of the variation in the detection result by the NOx sensor 41 and improving the determination accuracy. However, the above detection method is merely an example, and the period and the period can be set as appropriate.

  The controller 30 is connected to sensors such as a NOx sensor 41, a temperature sensor 42, an engine speed sensor, and an accelerator opening sensor, and devices such as the fuel injection valve 11 and the addition device 27 of each cylinder of the engine 10. . The detection results obtained by the various sensors are transmitted to the controller 30, and the devices such as the fuel injection valve 11 and the addition device 27 are driven and controlled based on these detection results.

The controller 30 includes a functional element as urea water addition control means 31 for controlling the amount of urea water added as a reducing agent in the exhaust gas toward the SCR 25, and the amount of NOx contained in the exhaust gas after being discharged from the engine 10. The function element as the engine-out NOx value acquisition means 32 for acquiring the engine-out NOx value and the ratio of NO _{2 to} the amount of NOx contained in the exhaust gas after passing through the DPF device 21 and the SCR device 22 are acquired. Functional elements as NO ₂ ratio acquisition means 33, functional elements as NOx purification rate acquisition means 34 for acquiring a NOx purification rate indicating how much NOx contained in exhaust gas has been reduced and purified in SCR 25, And a functional element as a deterioration determination means 35 for determining the deterioration degree.

  The urea water addition control means 31 controls the amount of urea water as a reducing agent to be added to the exhaust toward the SCR 25 by the urea water addition nozzle 28 and the timing of addition. During normal driving, urea water is appropriately added to reduce NOx and purify exhaust gas in the SCR 25. In this catalyst deterioration diagnosis device, in particular, in order to determine deterioration of the SCR 25, the urea water is temporarily added. To stop or to start addition again.

The engine-out NOx value acquisition means 32 acquires an engine-out NOx value corresponding to the amount of NOx contained in the exhaust gas after being discharged from the engine 10 and before flowing into the DPF device 21. The dimension of the engine-out NOx value acquired here is assumed to be the same dimension as the first NOx value described above.
In this embodiment, as shown in FIG. 2, the engine speed detected by the engine speed sensor, the engine load (torque) determined from the accelerator position detected by the accelerator position sensor, and the engine-out NOx value Is stored in the controller 30 in advance, and the engine-out NOx value is estimated according to the operating state of the engine 10. For example, when the engine speed is high and the torque is large, the engine-out NOx value becomes a large value, and a large amount of NOx is exhausted from the engine 10.

  The estimation of the engine-out NOx value by the engine-out NOx value acquisition means 32 is continuously estimated from the engine-out NOx map at the same period as the detection by the NOx sensor 41, for example, 10 times per second, 41 and during the same period (for example, 20 to 30 seconds), and the accumulated NOx value is set as the engine-out NOx value. This is for the same purpose as suppressing the influence of variation in the detection result by the NOx sensor 41 and increasing the determination accuracy. However, the detection method described above is merely an example, and the period and the period are appropriately set. Is possible. Further, the engine-out NOx value is not limited to a method of estimating from a predetermined map, and may be calculated by, for example, a predetermined mathematical formula.

The NO ₂ ratio acquisition means 33 is used for the amount of NOx (first NOx value) contained in the exhaust gas after passing through the DPF device 21 and the SCR device 22 by the NOx sensor 41 provided on the downstream side of the SCR device 22. A ratio of the amount of NO ₂ (hereinafter referred to as NO ₂ ratio) is acquired. For obtaining the NO ₂ ratio, a map showing the characteristics of the NOx sensor shown in FIG. 3 (hereinafter referred to as NOx sensor characteristic map) is used, and the NOx sensor 41 with respect to the engine out NOx value obtained by the engine out NOx map is used. A NO ₂ ratio is acquired from the ratio of the acquired first NOx value. The NOx sensor characteristic map is a map obtained as a result of investigating the influence of NO ₂ in the exhaust on the output of the NOx sensor, and the output value of the NOx sensor decreases as the NO ₂ ratio increases.

Here, in this embodiment, since the NOx sensor 41 is provided on the downstream side of the SCR device 22, the following conditions are required to use this NOx sensor characteristic map.
[Condition A] The urea water addition by the urea water addition nozzle 28 is stopped.
[Condition B] Ammonia is not adsorbed on SCR25.
The above [Condition A] and [Condition B] are required because if either [Condition A] or [Condition B] is not satisfied, NOx is reduced in the SCR device 22 and the engine out NOx value This is because the NO ₂ ratio cannot be obtained from the characteristics of the NOx sensor because the value of the NOx and the first NOx value are different.

  The NOx purification rate acquisition means 34 acquires the NOx purification rate, which is the ratio of NOx that is reduced and purified by the SCR 25, from the engine-out NOx value and the first NOx value according to the following equation (1).

ここで、ＮＯｘ_ＥはエンジンアウトＮＯｘ値を、ＮＯｘ１は第一ＮＯｘ値を表す。

Here, NOx _E represents the engine-out NOx value, and NOx1 represents the first NOx value.

Deterioration determining means 35, and NO ₂ ratio obtained by NO ₂ ratio acquisition means 33, and the NOx purification rate obtained by the NOx purification rate acquisition means 34, based on the temperature of SCR25 detected by the temperature sensor 42, the SCR25 Determine the degree of deterioration.
4 (a) to 4 (c) are maps (hereinafter referred to as a deterioration determination map) showing a correspondence relationship between the NO ₂ ratio, the NOx purification rate, and the catalyst temperature, and FIG. 4 (a) shows the degree of deterioration. FIG. 4C shows a small and almost new state (hereinafter referred to as a low degree of deterioration), FIG. 4C is a usable state, but a high degree of deterioration (hereinafter referred to as a high degree of deterioration), and FIG. FIGS. 4A and 4C show states that are approximately in the middle of the deterioration levels (hereinafter referred to as medium deterioration levels). Here, three maps of small, medium, and large degrees of deterioration are shown, but the deterioration determination map is not limited to this, and a map in which the degree of deterioration is further subdivided is stored in advance in the ROM in the controller 30. Alternatively, for example, linear interpolation may be performed between the subdivided degradation determination maps.

Here, the SCR 25 is new means that a desired NOx purification rate can be obtained under conditions where the catalyst temperature, the NO ₂ ratio and the urea water concentration are present. The standard. The degree of deterioration is made small, medium, and large according to the decrease in the NOx purification rate with respect to the amount of NOx that can be purified in the new state as a reference.
In this catalyst deterioration diagnosis device, assuming that urea water as a reducing agent is added at an appropriate concentration, as shown in FIGS. 4 (a) to 4 (c), the deterioration degree of the SCR 25 is the NO ₂ ratio. It can be determined by the three parameters of catalyst temperature and NOx purification rate.

Deterioration determining means 35, for example at a catalyst temperature of SCR25 is Z [℃], NO ₂ at a ratio acquisition means 33 NO ₂ ratio obtained by the X, obtained NOx purification rate by the NOx purification rate acquisition means 34 Y If it is, it determines with the deterioration degree of SCR25 being in the deterioration degree of FIG.4 (b).
Further, as shown in FIG. 1, the vehicle is provided with a display panel (notification means) 43 and an alarm (notification means) 44 for notifying the driver of the degree of deterioration of the SCR 25. When the deterioration determination unit 35 determines the deterioration degree of the SCR 25, the deterioration degree of the SCR 25 is displayed on the display panel 43. If the deterioration degree of the SCR 25 is determined to be large and needs to be replaced, the display panel 43 or the alarm 44 This prompts the driver to replace the SCR 25 and informs the driver of the determination result.

[1-4. Action, effect]
Since the catalyst deterioration diagnosis apparatus according to the present embodiment is configured as described above, the determination of the degree of deterioration of the SCR 25 can be performed according to the flowchart of FIG. Each of the following steps is performed by each function (means) assigned to the hardware of the computer being operated by software (computer program). Note that the NOx sensor 41 always detects the NOx value.

  As shown in FIG. 5, first, in step S10, it is determined whether or not the flag F = 0. Since the flag F = 0 at the start, the YES route is initially selected and the process proceeds to step S20. If flag F = 1, the process proceeds to step S100. In step S20, the urea water addition control means 31 determines whether or not the urea water addition is stopped. If the addition is stopped, the process proceeds to step S30, and if the urea water is still added, the process returns. .

  Next, it is determined whether or not the ammonia adsorbed on the SCR 25 has been consumed (step S30). In this determination, for example, when the first NOx value detected by the NOx sensor 41 rises to a predetermined value, it may be determined that the consumption is completed, and when a predetermined time elapses after the addition of urea water is stopped, You may make it determine with completion. In any case, if the addition of urea water is stopped, the NOx purification is continued by the ammonia adsorbed on the SCR 25, but after a predetermined time, all the adsorbed ammonia is used for the reduction of NOx. Therefore, all adsorbed ammonia is consumed. Steps S20 and S30 determine whether or not the above [Condition A] and [Condition B] are satisfied.

If it is determined in step S30 that the adsorbed ammonia has been consumed, the process proceeds to step S40, and the first NOx value is detected by the NOx sensor 41 (step S40). On the other hand, if the adsorbed ammonia has not yet been consumed in step S30, the process returns. The first NOx value is a value integrated as described above.
Next, in order to acquire the engine-out NOx value, the engine speed and the engine load are detected, and based on these, the engine-out NOx value is acquired from the engine-out NOx map of FIG. 2 (step S50). Then, based on the first NOx value and the engine-out NOx value, the NO ₂ ratio is acquired using the NOx sensor characteristic map of FIG. 3 (step S60).

After acquiring the NO ₂ ratio, in order to acquire the NOx purification rate, urea water as a reducing agent is added again to the SCR 25 by the urea water addition control means 31 (step S70), and a timer is started ( Step S80). Then, the flag F is set to 1 (step S90), the time is counted by a timer, and integration is performed as in the following equation (2) (step S100).
t _n ← t _n-1 + t (2)

Here, the subscript n indicates the current control cycle, and n-1 indicates the previous control cycle. In step S110, the integrated time t _n is determined whether exceeds a predetermined time t _0, and return if not exceed the predetermined time t _0, the process proceeds from step S10 to step S100, and repeats. This predetermined time t ₀ is a time until NOx is purified by adding urea water to the exhaust gas toward the SCR 25 and the NOx value detected by the NOx sensor 41 is stabilized, and can be acquired in advance by an experiment or the like. It is. The condition for redetecting the first NOx value after re-adding the urea water is not limited to the method of determining based on time as shown in FIG. 5, for example, the first NOx detected by the NOx sensor 41. The first NOx value may be re-detected when the value decreases and stabilizes at a constant value.

In step S110, the integrated time t _n is when it is judged to have exceeded a predetermined time t _0, detects the first NOx value at that time again (step S120). Then, the timer is reset to 0 and stopped (step S130), the flag F is reset to 0 (step S140), and the engine out NOx value is acquired again from the engine operating state (step S150).

Next, the NOx purification rate is calculated and acquired from the first NOx value acquired in step S120 and the engine-out NOx value acquired in step S150 (step S160). Further, the temperature of the SCR 25 is detected from the temperature sensor 42 (step S170), and the deterioration degree of the SCR 25 is determined from the NO ₂ ratio, the NOx purification rate, and the catalyst temperature (step S180). The determination result is displayed on the display panel 43, or when the degree of deterioration is high and needs to be replaced, the alarm 44 is sounded in addition to the display panel 43 to notify the driver (step S190).

Therefore, according to the catalyst deterioration diagnosis device, the NO ₂ ratio is calculated based on the first NOx value and the engine out NOx value obtained from the NOx sensor 41 and the engine out NOx map provided on the downstream side of the SCR device 22, respectively. The NOx purification rate is acquired, and the degree of deterioration of the SCR 25 can be determined based on the acquired NO ₂ ratio, the NOx purification rate, and the catalyst temperature. Therefore, it is possible to determine how much the catalyst has deteriorated with a simple configuration. As a result, not only exhaust deterioration due to catalyst deterioration can be suppressed in advance, but also control according to the state of catalyst deterioration can be performed, and clean exhaust can always be maintained.

Further, since the NO ₂ ratio and the NOx purification rate are acquired by the NOx sensor 41 provided on the downstream side of the SCR device 22, an increase in cost can be suppressed and the deterioration determination can be performed with a simple configuration. In addition, the display panel 43 and the alarm 44 notify the passenger of the degree of deterioration of the SCR 25, thereby prompting maintenance or replacement of the SCR 25.
[1-5. Modified example]
In the above embodiment, the engine-out NOx value acquisition means 32 has acquired the engine-out NOx value from the engine-out NOx map shown in FIG. 2, but the method for acquiring the engine-out NOx value is not limited to this, for example, in FIG. 2, a NOx sensor (hereinafter referred to as an engine-out NOx sensor) 61 that detects an engine-out NOx value may be provided in the exhaust passage 19 of the engine 10 and upstream of the DPF device 21. .
In this case, since the NOx purification rate and the NO ₂ ratio can be acquired more accurately, the determination accuracy of the deterioration degree of the SCR 25 can be improved.

[2. Second embodiment]
[2-1. Constitution]
Next, a catalyst deterioration diagnosis apparatus according to a second embodiment of the present invention will be described with reference to FIG. The catalyst deterioration diagnosis device of the present embodiment is configured in the same manner as that of the first embodiment except for the portions related to the urea water addition control means 31 and the NO ₂ ratio acquisition means 33. Elements corresponding to those are denoted by the same reference numerals as those in the first embodiment, and redundant descriptions are omitted.

  As shown by a one-dot chain line in FIG. 1, this catalyst deterioration diagnosis device is provided with a NOx sensor (hereinafter referred to as a second NOx sensor) 51 downstream of the DPF 24 and upstream of the SCR 25 and flows into the SCR 25. A second NOx value that is the amount of NOx contained in the exhaust gas is detected. That is, in the present embodiment, the NOx values on both the upstream side and the downstream side of the SCR 25 can be detected. It is assumed that the dimension of the second NOx value detected here is the same dimension as the first NOx value described above.

The NO ₂ ratio acquisition means 33 in the present catalyst deterioration diagnosis device uses the second NOx sensor 51 provided on the upstream side of the SCR 25 to correspond to the amount of NOx (second NOx value) contained in the exhaust gas before flowing into the SCR 25. to get the ratio of the amount of NO _2. NO The _second rate of acquisition, similar to the first embodiment is used the NOx sensor characteristic map shown in FIG. 3, the engine-out NO ₂ from the ratio of the second NOx value for the engine-out NOx values obtained by the NOx map Get the ratio. That is, in this embodiment, since the NO ₂ ratio can be acquired without being affected by the SCR 25, the urea water addition control means 31 does not need to perform any particular control, and the above-mentioned [Condition A] and It is not necessary to satisfy [Condition B].

Similar to the first embodiment, the NOx purification rate acquisition means 34 calculates and acquires the above-mentioned equation (1) from the engine-out NOx value and the first NOx value, and the temperature of the SCR 25 is also the first embodiment. Similarly to the above, it is detected by the temperature sensor 42. That is, among the three parameters used for determining the deterioration of the SCR 25, the present embodiment differs from the first embodiment only in obtaining the NO ₂ ratio.

[2-2. Action, effect]
Since the catalyst deterioration diagnosis apparatus according to the present embodiment is configured as described above, the determination of the deterioration degree of the SCR 25 can be performed according to the flowchart of FIG.
As shown in FIG. 6, the first NOx value is detected by the NOx sensor 41 at step T10, the second NOx value is detected by the second NOx sensor 51 at step T20, and from the engine out NOx map at step T30. An engine out NOx value is acquired. Further, the temperature sensor 42 detects the temperature of the SCR 25 (step T40).

Next, the NO ₂ ratio is acquired from the acquired second NOx value and engine out NOx value using the NOx sensor characteristic map shown in FIG. 3 (step T50). Further, the NOx purification rate is acquired from the acquired first NOx value and engine-out NOx value using the above-described equation (1) (step T60). Then, from the acquired NO ₂ ratio, NOx purification rate, and catalyst temperature, the deterioration determination map shown in FIG. 4 is used to determine the deterioration degree of the SCR 25 (step T70), and the determination result is displayed on the display panel 43. In the case where the degree of deterioration is high and replacement is required, in addition to the display panel 43, an alarm 44 is sounded to notify the driver (step T80).

Therefore, according to the present catalyst deterioration diagnosis device, the NOx purification rate and the NO ₂ ratio are acquired from the two NOx sensors 41 and 51 provided on the upstream side and the downstream side of the SCR 25 and the engine-out NOx map. Since the deterioration degree of the SCR 25 can be determined based on the NO ₂ ratio and the NOx purification rate and the catalyst temperature detected by the temperature sensor 42, it is possible to accurately determine how much the catalyst has deteriorated. As a result, not only exhaust deterioration due to catalyst deterioration can be suppressed in advance, but also control according to the state of catalyst deterioration can be performed, and clean exhaust can always be maintained.

In addition, since the NO ₂ ratio is acquired by the second NOx sensor 51 on the upstream side of the SCR 25, ammonia may be adsorbed on the SCR 25, and deterioration determination is performed even if urea water is added to the exhaust gas toward the SCR 25. be able to. That is, since it is not necessary to consider the influence of the SCR 25, it is not necessary to satisfy the above [Condition A] and [Condition B], it is not necessary to perform addition control of urea water, and the deterioration determination control is simplified. And the judgment conditions are relaxed.
In addition, the display panel 43 and the alarm 44 notify the passenger of the degree of deterioration of the SCR 25, thereby prompting maintenance or replacement of the SCR 25.

[2-3. Modified example]
In the second embodiment, the engine-out NOx value acquisition unit 32 acquires the engine-out NOx value from the engine-out NOx map shown in FIG. 2, but the method for acquiring the engine-out NOx value is not limited to this. 1, a NOx sensor (hereinafter referred to as an engine-out NOx sensor) 61 for detecting an engine-out NOx value is provided in the exhaust passage 19 of the engine 10 and upstream of the DPF device 21 as indicated by a two-dot chain line. Also good.
In this case, since the NOx purification rate and the NO ₂ ratio can be acquired more accurately, the determination accuracy of the deterioration degree of the SCR 25 can be further improved.

[3. Others]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In the above embodiment, the engine-out NOx value acquisition means 32 acquires the engine-out NOx value by either one of the engine-out NOx map and the engine-out NOx sensor 61, but the engine out NOx value is obtained using both the map and the sensor. You may make it acquire a NOx value. For example, either one may be configured to check the other acquisition result, and each detection result may be averaged. By using both the map and the sensor, it is possible to obtain a more accurate engine-out NOx value.

The catalyst deterioration diagnosis device can also be applied to a vehicle that does not include the DPF device 21.
In the above embodiment, NO ₂ ratio, a first NOx value or the second NOx value, based on the engine-out NOx values, has been described means for obtaining the NOx sensor characteristic map of Fig. 3, NO ₂ The method for acquiring the ratio is not limited to this. For example, the NO ₂ ratio may be estimated and calculated using a NO sensor that detects the amount of NO alone and a NOx sensor that detects both the amounts of NO and NO ₂ . Or it may be configured to grasp the NO ₂ ratio with NO ₂ analyzer. By grasping the NO ₂ ratio in the exhaust, it is possible to obtain the same effect as the above-described embodiment.

10 Engine 19 Exhaust passage 20 Exhaust purification device 21 DPF device (upstream exhaust purification device)
22 SCR device (downstream exhaust purification device)
23 Pre-stage oxidation catalyst (DOC)
24 Diesel particulate filter (DPF, particulate filter)
25 Selective reduction catalyst (SCR)
26 Back-stage oxidation catalyst (CUC)
27 Adding Device 28 Urea Water Adding Nozzle 29 Urea Water Tank 30 Controller (ECU)
31 Urea water addition control means 32 Engine out NOx value acquisition means 33 NO ₂ ratio acquisition means 34 NOx purification rate acquisition means 35 Deterioration determination means 41 NOx sensor (first NOx sensor)
42 Temperature sensor 43 Display panel (notification means)
44 Alarm (notification means)
51 NOx sensor (second NOx sensor)
61 Engine-out NOx sensor

Claims (6)

A selective reduction catalyst provided in an exhaust passage of the engine for reducing and purifying NOx contained in the exhaust gas flowing through the exhaust passage;
A first NOx sensor that is provided downstream of the selective catalytic reduction catalyst and detects a first NOx value that is the amount of NOx contained in the exhaust gas that has passed through the selective catalytic reduction catalyst;
Engine-out NOx value obtaining means for obtaining an engine-out NOx value that is the amount of NOx contained in the exhaust gas after being discharged from the engine;
And NO ₂ ratio acquisition means for acquiring a NO ₂ ratio is the ratio of NO ₂ with respect to NOx contained in the exhaust flowing through the selective reduction catalyst,
NOx purification rate acquisition means for acquiring a NOx purification rate that is a ratio of NOx that is reduced and purified by the selective reduction catalyst based on the amounts of upstream and downstream NOx of the selective reduction catalyst;
Determining the degree of deterioration of the selective reduction catalyst based on the temperature of the NO ₂ ratio acquiring means by acquired the NOx purification rate and the selective reduction catalyst obtained by the NO ₂ ratio and the NOx purification rate acquisition means has A catalyst deterioration diagnosis apparatus comprising: a deterioration determination unit. The NO ₂ ratio obtaining means obtains the NO ₂ ratio on the basis of said engine-out NOx value acquired by the first NOx value detected by the first NOx sensor and the engine-out NOx value acquiring means The catalyst deterioration diagnosis apparatus according to claim 1, wherein: An oxidation catalyst provided in the exhaust passage of the engine on the upstream side of the selective catalytic reduction catalyst on the downstream side of the engine;
A second NOx sensor that is provided on the downstream side of the oxidation catalyst and upstream of the selective reduction catalyst, and detects a second NOx value that is the amount of NOx contained in the exhaust gas flowing into the selective reduction catalyst; Further comprising
The NO ₂ ratio obtaining means obtains the NO ₂ ratio on the basis of said engine-out NOx value acquired by the second NOx value detected by the second NOx sensor and the engine-out NOx value acquiring means The catalyst deterioration diagnosis apparatus according to claim 1, wherein: The engine-out NOx value obtaining means obtains the engine-out NOx value based on a map indicating a correspondence relationship between the engine speed, the engine load, and the engine-out NOx value set in advance. The catalyst deterioration diagnostic apparatus according to any one of claims 1 to 3. An engine-out NOx sensor that is provided upstream of the oxidation catalyst and detects the engine-out NOx value contained in the exhaust after being discharged from the engine;
The catalyst deterioration diagnosis apparatus according to any one of claims 1 to 4, wherein the engine-out NOx value acquisition unit acquires the engine-out NOx value by the engine-out NOx sensor. The catalyst deterioration diagnosis apparatus according to claim 1, further comprising a notification unit that notifies a result of determination by the deterioration determination unit.

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