JP5375462B2 - NO oxidation catalyst deterioration detection apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for detecting deterioration in an NO oxidation catalyst, which easily detects deterioration in the NO oxidation catalyst. <P>SOLUTION: This device 1 for detecting deterioration in the NO oxidation catalyst 5 detects deterioration in the NO oxidation catalyst 5, and includes an execution determination means determining that deterioration determination of the NO oxidation catalyst 5 can be executed when adsorption quantity of NO<SB>2</SB>adsorbed by the NO oxidation catalyst 5 is less than saturation adsorption quantity, a flow-in side NOx concentration detection means detecting NOx concentration of exhaust gas flowing into the NO oxidation catalyst 5, a flow-out side NOx concentration detection means detecting NOx concentration of exhaust gas flowing out the NO oxidation catalyst 5, and a deterioration determination means determining that the NO oxidation catalyst 5 is deteriorated if difference resulting from subtracting a detection value of the flow out side NOx concentration detection means from a detection value of the flow in side NOx concentration detection means is not greater than a prescribed NOx concentration threshold when the execution determination means determines that deterioration determination of the NO oxidation catalyst 5 can be executed. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

The present invention relates to a deterioration detection device and method for a NO oxidation catalyst that detects deterioration of a NO oxidation catalyst that is disposed upstream of a NOx catalyst that purifies NOx in exhaust gas and that oxidizes NO in exhaust gas to NO ₂ .

NOx storage catalysts and urea SCR catalysts have been put to practical use in order to treat NOx in an oxygen-excess atmosphere such as diesel exhaust gas. In addition, a method has been proposed in which a NO oxidation catalyst is disposed upstream of these NOx catalysts, and NO ₂ is generated by increasing NOx purification performance of the NOx storage catalyst and urea SCR catalyst.

When the NO oxidation catalyst deteriorates due to heat, poisoning, or the like, the NO ₂ generation performance decreases, and the NOx purification capacity of the downstream NOx catalyst decreases.

  In the future, OBD (On-Board Diagnostics) regulations that require automatic diagnosis of deterioration and failures of exhaust gas purification apparatuses are going to be strengthened, and it is required to detect catalyst deterioration.

  Conventionally, as a means for detecting deterioration of an oxidation catalyst, regarding reduction in the oxidation activity of CO and HC, by adding fuel upstream of the oxidation catalyst (hereinafter referred to as CO, HC oxidation catalyst), the HC concentration and CO concentration in the exhaust gas are set. A method for determining deterioration of CO and HC oxidation catalyst by detecting an increase in exhaust gas temperature due to reaction heat of CO and HC oxidation reaction at elevated CO and HC oxidation catalyst has been proposed (for example, (See Patent Document 1).

JP 2008-121428 A

  However, although the above-mentioned method can detect CO and HC oxidation performance deterioration of the HC oxidation catalyst, in the case of the NO oxidation catalyst, it is necessary to supply NO to the NO oxidation catalyst. It is not suitable for determining the deterioration of the NO oxidation performance, and the NO oxidation performance deterioration cannot be detected.

  Accordingly, an object of the present invention is to provide an apparatus and a method for detecting deterioration of a NO oxidation catalyst that can solve the above-described problems and can easily detect deterioration of the NO oxidation catalyst.

In order to achieve the above object, according to the present invention, a NOx catalyst for purifying NOx in exhaust gas is provided in an exhaust pipe of an engine, and NOx in exhaust gas flowing into the NOx catalyst is provided in an exhaust pipe upstream of the NOx catalyst. A NO oxidation catalyst for previously oxidizing the NO oxidation catalyst to NO ₂ is provided, and the NO oxidation catalyst deterioration detection device detects the deterioration of the NO oxidation catalyst, wherein the adsorption amount of NO ₂ adsorbed on the NO oxidation catalyst is An NOx concentration in the exhaust gas flowing into the NO oxidation catalyst, and an execution determining means for determining whether or not the NO oxidation catalyst deterioration can be determined when the amount is less than the saturated adsorption amount, The inflow side NOx concentration detecting means for detecting the NOx concentration, the outflow side NOx concentration detecting means for detecting the NOx concentration of the exhaust gas flowing out from the NO oxidation catalyst, and the NO determination by the execution determining means. When it is determined that the deterioration of the catalyst can be determined, a difference obtained by subtracting the detection value of the outflow side NOx concentration detection means from the detection value of the inflow side NOx concentration detection means is obtained, and the difference is determined as a predetermined NOx. Deterioration determination means for determining that the NO oxidation catalyst has deteriorated when the concentration is equal to or lower than a concentration threshold value.

  Preferably, the NOx concentration threshold is zero.

  The deterioration determination means converts a difference obtained by subtracting the detection value of the outflow side NOx concentration detection means from the detection value of the inflow side NOx concentration detection means into a NO conversion rate, and the converted NO conversion rate is a predetermined NO conversion rate. It may be determined that the NO oxidation catalyst has deteriorated when the ratio is equal to or less than the rate threshold.

Preferably, a catalyst temperature detecting means for detecting the temperature of the NO oxidation catalyst is provided, and the NO oxidation catalyst has a lower NO ₂ saturation adsorption amount as the temperature is higher. After the detected value of the temperature detecting means is equal to or higher than a predetermined first temperature and the NO ₂ adsorption amount of the NO oxidation catalyst is equal to or lower than the NO ₂ saturated adsorption amount in the detected value of the catalyst temperature detecting means, the catalyst temperature detecting means When the detected value decreases to a predetermined second temperature lower than the predetermined first temperature, it is determined that the deterioration determination of the NO oxidation catalyst can be performed.

In order to achieve the above object, according to the present invention, a NOx catalyst for purifying NOx in exhaust gas is provided in an exhaust pipe of an engine, and NOx in exhaust gas flowing into the NOx catalyst is provided in an exhaust pipe upstream of the NOx catalyst. pre NO ₂ NO oxidation catalyst for oxidizing is provided, in its method of detecting degradation NO oxidation catalyst for detecting the deterioration of the NO oxidation catalyst, the NO adsorption amounts of NO ₂ adsorbed in the oxidation catalyst saturation adsorbs When the amount is less than the amount, the NOx concentration in the exhaust gas flowing into the NO oxidation catalyst is detected, the NOx concentration in the exhaust gas flowing out from the NO oxidation catalyst is detected, and the NOx concentration on the outflow side is subtracted from the NOx concentration on the inflow side. When the difference is equal to or less than a predetermined NOx concentration threshold, it is determined that the NO oxidation catalyst has deteriorated.

  According to the present invention, an excellent effect is achieved that the deterioration of the NO oxidation catalyst can be easily detected.

FIG. 1 is a schematic configuration diagram of a NO oxidation catalyst deterioration detection apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of the NO oxidation catalyst and the NOx sensor. FIG. 3 is a diagram for explaining the relationship between the temperature of the NO oxidation catalyst and the NO ₂ saturated adsorption amount. FIG. 4 is a diagram for explaining the relationship between the temperature of the NO oxidation catalyst and the NO ₂ production rate. FIG. 5 is an example of a control flow of the deterioration detection method according to the present embodiment. FIG. 6 is an example of a control flow of the deterioration detection method according to the present embodiment. FIG. 7 is a diagram for explaining the relationship between the temperature of the NO oxidation catalyst and the NO ₂ production rate. FIG. 8 is an example of a control flow of a deterioration detection method according to a modification of the present embodiment.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  A NO oxidation catalyst deterioration detection device (hereinafter referred to as a deterioration detection device) according to the present embodiment detects deterioration of a NO oxidation catalyst for automobile exhaust gas. For example, a diesel engine mounted on a vehicle (hereinafter referred to as an engine). ) Etc.

  A schematic structure of the engine and the deterioration detection device of the present embodiment will be described based on FIG.

  As shown in FIGS. 1 and 2, the engine 2 includes an engine body 11 in which a combustion chamber is formed, an exhaust pipe 3 for exhausting exhaust gas from the engine body 11, and exhaust gas provided in the exhaust pipe 3. And an electronic control unit 6 for controlling the exhaust gas purification system 12, the engine body 11, and the like.

  The engine body 11 is provided with an injector 15 for injecting and supplying fuel to the combustion chamber, an engine speed sensor 16 for detecting the engine speed, and the like. The fuel injection amount and injection timing of the injector 15 are controlled by the electronic control unit 6, and the detection value (engine speed) of the engine speed sensor 16 is input to the electronic control unit 6.

The exhaust gas purification system 12 purifies NOx (nitrogen oxide) 4 contained in the exhaust gas from the engine body 11 and NO (nitrogen monoxide) contained in the exhaust gas flowing into the NOx catalyst 4 in advance with NO ₂ ( NO oxidation catalyst 5 for oxidizing to (nitrogen dioxide) and a deterioration detecting device 1 for detecting deterioration of the NO oxidation catalyst 5 are provided.

  The NOx catalyst 4 of the present embodiment is a urea SCR catalyst (selective reduction type NOx catalyst) that reduces NOx in exhaust gas using ammonia as a reducing agent. The NOx catalyst 4 is formed by supporting a catalyst component (such as vanadium oxide or zeolite) on a carrier made of, for example, a ceramic honeycomb.

  The exhaust pipe 3 upstream of the NOx catalyst 4 is provided with a urea addition section 21 (urea water injection valve) for injecting and supplying urea water (urea aqueous solution) into the exhaust pipe 3. The urea addition unit 21 is connected to a urea water tank 22 mounted on the vehicle via a supply line 23. Further, the injection amount and the injection timing of the urea water in the urea addition unit 21 are controlled by the electronic control unit 6. The urea water injected from the urea addition unit 21 is decomposed into ammonia in the exhaust pipe 3 and supplied to the NOx catalyst 4.

  The NO oxidation catalyst 5 is provided in the exhaust pipe 3 upstream of the urea addition section 21 (and the NOx catalyst 4). The NO oxidation catalyst 5 is formed by, for example, supporting a catalyst component (such as palladium) on a carrier made of a ceramic honeycomb or the like.

  The deterioration detection device 1 determines whether or not the deterioration of the NO oxidation catalyst 5 can be determined based on the catalyst temperature detection means for detecting the temperature of the NO oxidation catalyst 5 and the detected value of the catalyst temperature detection means. And an upstream NOx sensor 7 serving as an inflow side NOx concentration detecting means for detecting the NOx concentration of the exhaust gas flowing into the NO oxidation catalyst 5, and an outflow detecting the NOx concentration of the exhaust gas flowing out from the NO oxidation catalyst 5. The detection values of the upstream and downstream NOx sensors 7 and 8 when it is determined that the deterioration determination of the NO oxidation catalyst 5 can be performed by the downstream NOx sensor 8 constituting the NOx concentration detection means and the execution determination means. Deterioration determining means for determining whether or not the NO oxidation catalyst 5 has deteriorated. In the present embodiment, the execution determination unit and the deterioration determination unit are configured by the electronic control unit 6, and the catalyst temperature detection unit is configured by a temperature sensor 9 and the electronic control unit 6 described later.

  The upstream NOx sensor 7 is disposed in the exhaust pipe 3 upstream of the NO oxidation catalyst 5, and is disposed in the exhaust pipe 3 between the engine 2 and the NO oxidation catalyst 5 in the illustrated example. The downstream NOx sensor 8 is disposed in the exhaust pipe 3 downstream of the NO oxidation catalyst 5, and is disposed in the exhaust pipe 3 between the NO oxidation catalyst 5 and the urea addition unit 21 in the illustrated example. The upstream NOx sensor 7 and the downstream NOx sensor 8 may be, for example, one that measures the amount of oxygen ions due to NOx in the exhaust gas and calculates the NOx concentration from the measured value. The detection values (NOx concentration) of the upstream NOx sensor 7 and the downstream NOx sensor 8 are respectively input to the electronic control unit 6.

  The catalyst temperature detecting means includes a temperature sensor 9 that detects the temperature of the exhaust gas flowing into the NO oxidation catalyst 5, and the electronic control unit 6 that obtains the temperature of the NO oxidation catalyst 5 based on the exhaust gas temperature detected by the temperature sensor 9. Consists of. The temperature sensor 9 is disposed in the exhaust pipe 3 upstream of the NO oxidation catalyst 5, and is disposed at the same position (same position in the exhaust gas flow direction) as the upstream NOx sensor 7 in the illustrated example. The detected value of the temperature sensor 9 is input to the electronic control unit 6, and the electronic control unit 6 estimates the temperature of the NO oxidation catalyst 5 from the detected value. The estimated temperature becomes the detection value of the catalyst temperature detection means.

  The exhaust pipe 3 is connected to the engine body 11 at the upstream end, and in order from the engine body 11 side (upstream side), the upstream side NOx sensor 7 and the temperature sensor 9, the NO oxidation catalyst 5, the downstream side NOx sensor 8, and urea addition The part 21 and the NOx catalyst 4 are arranged.

  Sensors such as the upstream NOx sensor 7, temperature sensor 9, downstream NOx sensor 8, engine speed sensor 16, and actuators such as the injector 15 and the urea addition unit 21 communicate with the electronic control unit 6. Connected as possible.

  The electronic control unit 6 (degradation determination means) obtains a difference obtained by subtracting the detection value of the downstream NOx sensor 8 from the detection value of the upstream NOx sensor 7, and when the difference is equal to or less than a predetermined NOx concentration threshold, It is determined that the oxidation catalyst 5 has deteriorated.

  In the present embodiment, the NOx concentration threshold is 0, and the electronic control unit 6 (degradation determination means) performs NO oxidation when the detected values of the upstream NOx sensor 7 and the downstream NOx sensor 8 are substantially the same. It is determined that the catalyst 5 has deteriorated. Note that “substantially the same” means that the detected values of the NOx sensors 7 and 8 are the same within the measurement error range of the upstream NOx sensor 7 and the downstream NOx sensor 8.

The electronic control unit 6 (implementation determining means) determines whether or not the adsorption amount of NO ₂ adsorbed on the NO oxidation catalyst 5 is less than the saturated adsorption amount, and when the NO oxidation catalyst 5 is less than the saturated adsorption amount, It is determined that the deterioration determination can be performed.

More specifically, the electronic control unit 6 (execution determination means) determines that the temperature of the NO oxidation catalyst 5 estimated from the detection value of the temperature sensor 9 is equal to or higher than a predetermined first temperature (hereinafter referred to as an execution determination temperature), and NO. After the NO ₂ adsorption amount of the oxidation catalyst 5 becomes equal to or less than the NO ₂ saturated adsorption amount at the estimated temperature of the NO oxidation catalyst 5, a predetermined second temperature (hereinafter, the temperature of the NO oxidation catalyst 5 is lower than the execution determination temperature). , It is determined that the deterioration determination of the NO oxidation catalyst 5 can be performed.

  The deterioration detection device 1 configured as described above forms part of an OBD device (on-vehicle failure diagnosis device) mounted on a vehicle. That is, an abnormality (for example, deterioration of the NO oxidation catalyst 5) of the exhaust gas purification system 12 is detected and monitored on the vehicle, and when the abnormality occurs, an alarm is displayed by the failure display lamp 31 to notify the driver and the details of the failure are stored. An OBD device to be held is provided, and the OBD device includes the deterioration detection device 1 of the present embodiment, the failure display lamp 31 and the like.

  The failure display lamp 31 is provided, for example, in a cab or the like, and its ON / OFF is controlled by the electronic control unit 6. The electronic control unit 6 includes a memory 32 for storing a failure content, and a diagnostic tool connector 34 to which a failure diagnosis tool 33 that reads the failure content stored in the memory 32 from the outside of the vehicle can be connected.

  Next, a method for detecting the deterioration of the NO oxidation catalyst according to the present embodiment (hereinafter referred to as a deterioration detecting method) will be described.

  The deterioration detection method of the present embodiment is a method for determining the deterioration of the NO oxidation catalyst 5. A means (electronic control unit 6) that can estimate the temperature of the NO oxidation catalyst 5 with the temperature sensor 9 or the like is provided. NOx concentration before and after (upstream and downstream) is detected (measured or estimated) by the NOx sensors 7 and 8 and the NO oxidation catalyst 5 is judged to be deteriorated based on the NOx concentration before and after the NO oxidation catalyst 5. .

NO ₂ generated in the NO oxidation catalyst 5 is high adsorptivity, if NO ₂ adsorption NO oxidation catalyst 5 has not reached saturation, NO ₂ is adsorbed in the NO oxidation catalyst 5. When the NOx concentration downstream from the NOx concentration upstream of the NO oxidation catalyst 5 estimated (detected) from the NOx sensors 7 and 8 before and after the NO oxidation catalyst 5 becomes smaller, NO ₂ is generated in the NO oxidation catalyst 5 and NO _2. Adsorption is happening. Degradation is determined based on the temperature of the NO oxidation catalyst 5 at this time and the degree of NO ₂ adsorption.

The deterioration detection method includes a NOx catalyst 4 such as a NOx storage catalyst or a urea SCR catalyst for purifying NOx in an oxygen-excess atmosphere such as diesel exhaust gas, and a NO oxidation catalyst disposed upstream of the NOx catalyst 4 In the exhaust gas purification system 12 that improves the NOx purification performance by generating NO ₂ at 5, the deterioration of the NO oxidation catalyst 5 is detected.

  In the degradation detection method, the temperature of the NO oxidation catalyst 5 is estimated by arranging a temperature sensor 9 upstream of the NO oxidation catalyst 5, and the NOx sensors 7 and 8 are arranged before and after the NO oxidation catalyst 5. The NOx concentration before and after the oxidation catalyst 5 can be estimated (detected).

If NO ₂ adsorption amount of the NO oxidation catalyst 5 is equal to or less than the predetermined NO ₂ adsorption amount threshold, performing the deterioration determination when the temperature of the NO oxidation catalyst 5 becomes deterioration judgment temperature T2.

  The NOx concentration estimated (detected) from the upstream NOx sensor 7 disposed upstream of the NO oxidation catalyst 5 at the time of the deterioration determination, and estimated (detected) from the downstream NOx sensor 8 disposed downstream of the NO oxidation catalyst 5. ) The degree of deterioration of the NO oxidation catalyst 5 is determined from the difference from the NOx concentration, and the deterioration is detected.

  Hereinafter, it demonstrates in detail based on FIGS. 3-6.

Figure 3 shows the relationship between the common NO saturation adsorption amount of the temperature and NO ₂ in the oxidation catalyst 5 (NO ₂ saturation adsorption amount). The horizontal axis in FIG. 3 is the temperature (catalyst temperature), and the vertical axis is the NO ₂ saturated adsorption amount.

As shown in FIG. 3, the NO ₂ saturation adsorption amount of the NO oxidation catalyst 5 decreases as the temperature rises.

For example, the temperature of the NO oxidation catalyst 5 is NO ₂ of a (NO ₂ saturation adsorption amount at a temperature A) in the NO oxidation catalyst 5 in A is to be adsorbed. When the temperature of the NO oxidation catalyst 5 is raised from A to T1, NO ₂ saturation adsorption amount b for reducing the (NO ₂ saturation adsorption amount at the temperature T1), the difference between the NO ₂ saturation adsorption amount a-b of NO ₂ Is desorbed from the NO oxidation catalyst 5.

When the NO ₂ adsorption amount of the NO oxidation catalyst 5 exceeds the NO ₂ saturation adsorption amount, the relationship between the NOx concentration CNOx1 upstream of the NO oxidation catalyst 5 and the NOx concentration CNOx2 downstream of the NO oxidation catalyst 5 is CNOx1 <CNOx2. It becomes. If the NO ₂ adsorption amount is equal to or less than the NO ₂ saturation adsorption amount, CNOx1 = CNOx2 or CNOx1> CNOx2, and the NO oxidation catalyst 5 determines whether the NO ₂ adsorption amount is equal to or less than the NO ₂ saturation adsorption amount. This can be determined from the NOx concentration before and after the catalyst 5.

If the NO ₂ adsorption amount is saturated when the temperature of the NO oxidation catalyst 5 is T1, when the temperature of the NO oxidation catalyst 5 falls from T1 to T2, NO ₂ can be adsorbed by c−b. That is, as the temperature of the NO oxidation catalyst 5 decreases from T1 to T2, the NO ₂ saturated adsorption amount of the NO oxidation catalyst 5 changes from the NO ₂ saturated adsorption amount b of T1 to the NO ₂ saturated adsorption amount c of T2. This increases, and NO ₂ can be adsorbed to the NO oxidation catalyst 5 by the difference c−b of the NO ₂ saturated adsorption amount.

At this time, if NO ₂ is generated by NO oxidation at the NO oxidation catalyst 5 at T2, the NO ₂ is adsorbed to the NO oxidation catalyst 5 and CNOx1> CNOx2, and it can be determined whether or not the NO oxidation reaction is occurring. That is, the NOx concentration at the outlet of the NO oxidation catalyst 5 is higher than the NOx concentration at the inlet, even though the temperature of the NO oxidation catalyst 5 is decreased from T1 to T2 and NO ₂ can be adsorbed to the NO oxidation catalyst 5. Is not low (when CNOx1 = CNOx2 or CNOx1 <CNOx2), it can be determined that NO is not normally oxidized by the NO oxidation catalyst 5, and thus the NO oxidation performance of the NO oxidation catalyst 5 is improved. It can be determined that it has deteriorated.

As described above, as can be seen from the graph of FIG. 3, the NO ₂ saturation adsorption amount increases when the temperature of the NO oxidation catalyst 5 is low and decreases as the temperature of the NO oxidation catalyst 5 increases.

When the NO ₂ adsorption amount of the NO oxidation catalyst 5 exceeds the NO ₂ saturated adsorption amount at the temperature of the NO oxidation catalyst 5, NO ₂ is desorbed from the NO oxidation catalyst 5. At this time, the NOx concentration downstream of the NO oxidation catalyst 5 becomes higher than the upstream NOx concentration.

When the NO ₂ adsorption amount is the same as the NO ₂ saturated adsorption amount, neither adsorption nor desorption occurs, so the NOx concentration downstream of the NO oxidation catalyst 5 does not change (is the same) as the upstream NOx concentration.

When the NO ₂ adsorption amount is smaller than the NO ₂ saturation adsorption amount, if NO ₂ is generated by the NO oxidation catalyst 5, the generated NO ₂ is adsorbed to the NO oxidation catalyst 5, and the NOx concentration downstream of the NO oxidation catalyst 5 is upstream. of it is lower than the NOx concentration, since the nO oxidation catalyst 5 nO ₂ is unless adsorption of nO ₂ does not occur is produced, unchanged the NOx concentration downstream of the NOx concentration upstream of the nO oxidation catalyst 5 (the same become).

Therefore, when the NO oxidation catalyst 5 deteriorates and NO ₂ is no longer generated, even if the NO ₂ adsorption amount is less than the NO ₂ saturated adsorption amount, the NOx concentration upstream and the downstream NOx concentration of the NO oxidation catalyst 5 Are the same.

Therefore, in the present embodiment, when the NO ₂ adsorption amount adsorbed on the NO oxidation catalyst 5 is less than the saturated adsorption amount, the NOx concentration of the exhaust gas flowing into the NO oxidation catalyst 5 is detected, and the NO oxidation catalyst 5 The NOx concentration of the exhaust gas that has flowed out is detected, a difference obtained by subtracting the NOx concentration on the outflow side from the NOx concentration on the inflow side is determined, and when the difference is substantially 0, it is determined that the NO oxidation catalyst 5 has deteriorated.

Here, in order to perform the above-described deterioration determination, it is a condition that the adsorption amount of NO ₂ adsorbed on the NO oxidation catalyst 5 is less than the saturated adsorption amount.

The conditions for performing the deterioration determination include two execution conditions. The first implementation condition is that the catalyst temperature of the NO oxidation catalyst 5 is the execution determination temperature T1, and the NO ₂ adsorption amount is equal to or less than the NO ₂ saturated adsorption amount b at the execution determination temperature T1. The second implementation condition is that the temperature of the NO oxidation catalyst 5 becomes the deterioration determination temperature T2 after the first implementation condition is satisfied (for example, immediately after).

  Based on FIG. 5, the control flow for determining whether or not the deterioration determination can be performed will be described. FIG. 5 shows an example of the control flow. The control flow in FIG. 5 is repeatedly executed in a predetermined control cycle by the electronic control unit 6 during operation of the engine 2.

  According to the control flow of FIG. 5, the electronic control unit 6 determines whether or not the NO oxidation catalyst 5 is in a state where the deterioration determination can be performed.

As shown in FIG. 5, the electronic control unit 6, when the temperature Tcat of the NO oxidation catalyst 5 becomes the same as T1 (Tcat = T1), the determination NO ₂ adsorption amount of whether following the NO ₂ adsorbed amount threshold Start. In the illustrated example, the NO ₂ adsorption amount threshold is set to the NO ₂ saturated adsorption amount b at the execution determination temperature T1. The execution determination temperature T1 is set to a temperature at which the NO ₂ saturated adsorption amount of the NO oxidation catalyst 5 is sufficiently reduced (below a certain amount). Execution determination temperature T1, it is desirable to 300 ° C. or higher, NO in the NO ₂ saturation adsorption amount c at a temperature of the NO oxidation catalyst 5 when performing the deterioration determination (deterioration determination temperature T2), execution determination temperature T1 ₂ The difference c−b obtained by subtracting the saturated adsorption amount b only needs to be equal to or higher than the temperature at which the NO ₂ saturated adsorption amount can be determined.

  More specifically, in step S1, the electronic control unit 6 determines whether or not the temperature Tcat of the NO oxidation catalyst 5 estimated from the detection value of the temperature sensor 9 is equal to or higher than the execution determination temperature T1.

When the temperature of the NO oxidation catalyst 5 is equal to or higher than a certain temperature, more specifically, when the temperature Tcat of the NO oxidation catalyst 5 obtained in step S1 is equal to or higher than the execution determination temperature T1, the electronic control unit 6 performs steps S2 and S2. In S3, it is determined whether or not NO ₂ of the NO oxidation catalyst 5 is equal to or less than the saturated adsorption amount.

  The electronic control unit 6 acquires the detected values (CNOx1, CNOx2) of the upstream NOx sensor 7 and the downstream NOx sensor 8 in step S2, and in step S3, the acquired upstream NOx concentration CNOx1, downstream NOx concentration CNOx2, and Compare

In step S3, when the downstream NOx concentration CNOx2 is less than the upstream NOx concentration CNOx1, the electronic control unit 6 determines that the NO ₂ adsorption amount is equal to or less than the NO ₂ saturation adsorption amount b (step S4), and first It is determined that the implementation condition (also referred to as deterioration determination start condition 1 in the figure) is satisfied (step A).

That is, the NOx concentration CNOx1 measured by the upstream NOx sensor 7 disposed upstream of the NO oxidation catalyst 5 is equal to or higher than the NOx concentration CNOx2 measured by the downstream NOx sensor 8 disposed downstream of the NO oxidation catalyst 5 (CNOx1> = CNOx2), it can be determined that the NO ₂ adsorption amount of the NO oxidation catalyst 5 is equal to or less than the NO ₂ saturated adsorption amount b at the temperature T1.

On the other hand, when the downstream NOx concentration CNOx1 is higher than the upstream NOx concentration CNOx1 of the NO oxidation catalyst 5 (NO in step S3), NO ₂ equal to or greater than the NO ₂ saturated adsorption amount b is adsorbed to the NO oxidation catalyst 5. This indicates that NO ₂ has been desorbed from the NO oxidation catalyst 5, so that deterioration cannot be determined.

  Next, after the first execution condition is satisfied in step A, when the temperature of the NO oxidation catalyst 5 reaches the deterioration determination temperature T2 (when the second execution condition is satisfied), the electronic control unit 6 determines the deterioration. Start.

At the start, the temperature of the NO oxidation catalyst 5 decreases from T1 to T2, and the NO ₂ saturation adsorption amount of the NO oxidation catalyst 5 increases, so that the NO oxidation catalyst 5 can sufficiently adsorb NO _2. It has become.

  Next, deterioration determination will be described.

Since the NO ₂ adsorption amount of the NO oxidation catalyst 5 is below a certain amount (NO ₂ saturated adsorption amount b at T1) and the NO ₂ adsorption amount is not saturated, NO ₂ is generated by the NO oxidation catalyst 5. In other words, it is in a state of being adsorbed by the NO oxidation catalyst 5.

When NO ₂ is generated and adsorbed, the NOx concentration (CNOx2) downstream of the NO oxidation catalyst 5 is lower than the upstream NOx concentration (CNOx1) by the amount of NO ₂ adsorbed by the NO oxidation catalyst 5. Whether or not the NO oxidation reaction in the NO oxidation catalyst 5 is occurring can be detected from the difference in NOx concentration detected (measured or estimated) by the NOx sensors before and after the NO oxidation catalyst 5. The determination of deterioration is performed by determining that deterioration has occurred when the NO oxidation activity is no longer exhibited at the deterioration determination temperature T2 (CNOx1 = CNOx2).

Here, since the NO oxidation activity is affected by the O ₂ concentration in the exhaust gas, the exhaust gas flow rate, and the like, it is desirable to change the deterioration determination temperature T2 in consideration of the exhaust gas conditions estimated from the engine operating conditions. For example, it is conceivable to correct the deterioration determination temperature T2 based on the engine load obtained from the fuel injection amount of the injector 15 and the detected value of the engine speed sensor 16.

FIG. 4 shows a NO ₂ production curve which is a relationship between the temperature of the NO oxidation catalyst 5 and the NO ₂ production rate (also referred to as NO conversion rate). The horizontal axis in FIG. 4 is the temperature (catalyst temperature), and the vertical axis is the NO ₂ production rate. Line L0 is the initial NO ₂ generation curve (NO ₂ generation curve before the NO oxidation catalyst 5 is deteriorated), the line L1 is a NO ₂ generation curve after degradation. Incidentally, NO ₂ generation rate, when the NOx concentration in exhaust gas flowing out of the NOx concentration of exhaust gas flowing into the NO oxidation catalyst 5 from CNOx1, NO oxidation catalyst 5 and CNOx2, NO ₂ generation rate = (CNOx1-CNOx2) / CNOx1 × 100.

As shown in line L1 in FIG. 4, when the NO oxidation catalyst 5 deteriorates, the NO ₂ generation rate in the low temperature region decreases, and the NO ₂ generation rate becomes 0 at the deterioration determination temperature T2. As described above, when the NO oxidation catalyst 5 is brought into a state in which NO oxidation is not exhibited at the deterioration determination temperature T2, it is determined that the NO oxidation catalyst 5 has deteriorated.

  Based on FIG. 6, the control flow for deterioration determination will be described. FIG. 6 shows an example of the control flow. The control flow in FIG. 6 is continuously executed by the electronic control unit 6 from Step A in the control flow in FIG. Further, the control flow of FIG. 6 includes steps S6 to S12. Steps S6 and S7 are for determining whether the second execution condition is satisfied, and Steps S8 to S12 are for actually determining deterioration. It is.

  In step S6, the electronic control unit 6 estimates the temperature Tcat of the NO oxidation catalyst 5 from the detection value (exhaust gas temperature) of the temperature sensor 9, and in step S7, whether the estimated temperature Tcat is the same as the deterioration determination temperature T2. Judge whether or not.

  In step 7, when the temperature Tcat of the NO oxidation catalyst 5 is the same as the deterioration determination temperature T2, the electronic control unit 6 determines that the second execution condition is satisfied, and the deterioration of the NO oxidation catalyst 5 from step S8. Start judgment.

  In step S9, the electronic control unit 6 acquires the detected values of the upstream NOx sensor 7 and the downstream NOx sensor 8, and in step S10, the upstream NOx concentration and the downstream NOx concentration of the acquired NO oxidation catalyst 5 are obtained. Are substantially the same.

  In step S10, when the NOx concentration upstream of the NO oxidation catalyst 5 is the same as the downstream NOx concentration, the NO oxidation catalyst 5 has no NO oxidation activity at the deterioration determination temperature T2. 5 is determined to be deteriorated (step S11). After determining that the NO oxidation catalyst 5 has deteriorated, the electronic control unit 6 performs a predetermined abnormality process. As the abnormality process, for example, it is conceivable that the failure display lamp 31 is turned on and the failure content that the NO oxidation catalyst 5 has deteriorated is stored in the memory 32.

  Thus, according to the present embodiment, it is possible to easily detect the deterioration of the NO oxidation catalyst 5 based on the NOx concentration difference before and after the NO oxidation catalyst 5.

Further, it is possible to erroneously detect the deterioration of the NO oxidation catalyst 5 by determining whether the deterioration determination of the NO oxidation catalyst 5 is feasible from the relationship between the temperature of the NO oxidation catalyst 5 and the NO ₂ saturated adsorption amount. (False diagnosis) can be prevented.

  In addition, this invention is not limited to the above-mentioned embodiment, Various modifications and application examples can be considered.

  For example, in the above-described embodiment, the NOx concentration threshold is set to 0, but the present invention is not limited to this.

  In the above-described embodiment, the electronic control unit 6 compares the NOx concentrations upstream and downstream of the NO oxidation catalyst 5 with each other. However, the present invention is not limited to this, and the NOx concentration CNOx1 upstream of the NO oxidation catalyst 5 and the downstream From the NOx concentration CNOx2, the approximate degree of NO oxidation can also be estimated (NO conversion rate = (CNOx1-CNOx2) / CNOx1 × 100). For example, as shown in FIG. 7, NO conversion at the degradation determination temperature T2 When the rate becomes equal to or lower than a predetermined NO conversion rate threshold value X1, the NO oxidation catalyst 5 may be determined to be deteriorated.

This modification will be described with reference to FIG. The control flow in FIG. 8 differs from the control flow in FIG. 6 in steps S91 and S101 for converting the NOx concentration into a NO conversion rate (NO ₂ generation rate), and the other steps are the same. Therefore, only step S91 and step S101 will be described, and description of other steps will be omitted.

  As shown in FIG. 8, after step S9, the electronic control unit 6 (degradation determination means) converts the difference obtained by subtracting the downstream NOx concentration CNOx2 from the upstream NOx concentration CNOx1 of the NO oxidation catalyst 5 into NO conversion in step S91. In step S101, it is determined whether or not the converted NO conversion rate is equal to or less than a predetermined NO conversion rate threshold value. When the NO conversion rate is equal to or less than the predetermined NO conversion rate threshold value, the NO oxidation catalyst 5 Is determined to have deteriorated. Even in this modification, the same effects as those of the above-described embodiment can be obtained.

1 Deterioration detection device (NO oxidation catalyst deterioration detection device)
2 Engine 3 Exhaust pipe 4 NOx catalyst 5 NO oxidation catalyst 6 Electronic control unit (execution judging means, deterioration judging means)
7 upstream NOx sensor (inflow side NOx concentration detection means)
8 Downstream NOx sensor (outflow NOx concentration detection means)

Claims (5)

A NOx catalyst for purifying NOx in the exhaust gas is provided in the exhaust pipe of the engine, and NO oxidation for previously oxidizing NO in the exhaust gas flowing into the NOx catalyst into NO ₂ in the exhaust pipe upstream of the NOx catalyst A deterioration detection device for a NO oxidation catalyst that is provided with a catalyst and detects the deterioration of the NO oxidation catalyst,
Implementation determination that determines whether or not the adsorption amount of NO ₂ adsorbed on the NO oxidation catalyst is less than the saturated adsorption amount, and determines that the deterioration determination of the NO oxidation catalyst is feasible when the adsorption amount is less than the saturated adsorption amount Means,
Inflow side NOx concentration detecting means for detecting the NOx concentration of the exhaust gas flowing into the NO oxidation catalyst;
Outflow side NOx concentration detecting means for detecting the NOx concentration of the exhaust gas flowing out of the NO oxidation catalyst;
A difference obtained by subtracting the detection value of the outflow side NOx concentration detection means from the detection value of the inflow side NOx concentration detection means when the execution determination means determines that the deterioration determination of the NO oxidation catalyst can be performed. A deterioration detecting device for NO oxidation catalyst, comprising: a deterioration determining means for determining that the NO oxidation catalyst has deteriorated when the difference is equal to or less than a predetermined NOx concentration threshold.   The deterioration detection apparatus for a NO oxidation catalyst according to claim 1, wherein the NOx concentration threshold is zero.   The deterioration determination means converts a difference obtained by subtracting the detection value of the outflow side NOx concentration detection means from the detection value of the inflow side NOx concentration detection means into a NO conversion rate, and the converted NO conversion rate is a predetermined NO conversion rate. The deterioration detection device for a NO oxidation catalyst according to claim 1, wherein it is determined that the NO oxidation catalyst has deteriorated when the ratio is equal to or less than a rate threshold value. Comprising catalyst temperature detecting means for detecting the temperature of the NO oxidation catalyst;
The NO oxidation catalyst has a lower NO ₂ saturation adsorption amount as the temperature is higher,
The execution determination means has a detection value of the catalyst temperature detection means equal to or higher than a predetermined first temperature, and a NO ₂ adsorption amount of the NO oxidation catalyst is equal to or less than a NO ₂ saturated adsorption amount in the detection value of the catalyst temperature detection means. After that, when the detected value of the catalyst temperature detecting means is lowered to a predetermined second temperature lower than the predetermined first temperature, it is determined that the deterioration determination of the NO oxidation catalyst can be performed. 3. The deterioration detection device for a NO oxidation catalyst according to any one of 3 above. A NOx catalyst for purifying NOx in the exhaust gas is provided in the exhaust pipe of the engine, and NO oxidation for previously oxidizing NO in the exhaust gas flowing into the NOx catalyst into NO ₂ in the exhaust pipe upstream of the NOx catalyst In a method for detecting deterioration of a NO oxidation catalyst, in which a catalyst is provided and detecting deterioration of the NO oxidation catalyst,
When the adsorption amount of NO ₂ adsorbed on the NO oxidation catalyst is less than the saturated adsorption amount, the NOx concentration of the exhaust gas flowing into the NO oxidation catalyst is detected, and the NOx concentration of the exhaust gas flowing out from the NO oxidation catalyst is determined. And detecting a difference obtained by subtracting the NOx concentration on the outflow side from the NOx concentration on the inflow side, and determining that the NO oxidation catalyst has deteriorated when the difference is equal to or less than a predetermined NOx concentration threshold. A method for detecting deterioration of an oxidation catalyst.

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