JP2014098359A - Deterioration diagnosis device for scr system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of curbing wrong diagnosis in a deterioration diagnosis device for a SCR system which comprises: a selective reduction type catalyst; an oxidation catalyst arranged downstream of the selective reduction type catalyst; a NOsensor arranged downstream of the oxidation catalyst; and means to diagnose deterioration of the selective reduction type catalyst from a measurement of the NOsensor.SOLUTION: A deterioration diagnosis device for a SCR system comprises: a selective reduction type catalyst; a reducing agent supplying device which supplies the selective reduction type catalyst with a reducing agent; an oxidation catalyst arranged downstream of the selective reduction type catalyst; a NOsensor arranged downstream of the oxidation catalyst; and means to perform deterioration diagnosis of the selective reduction type catalyst with a measurement of the NOsensor as a parameter. The deterioration diagnosis of the selective reduction type catalyst is performed when a NOpurification rate of the oxidation catalyst is low.

Description

The present invention relates to a technique for diagnosing deterioration of an exhaust purification device disposed in an internal combustion engine, and more particularly to a technique for diagnosing deterioration of a selective catalytic reduction (SCR).

Conventionally, as a system for purifying nitrogen oxide (NO _x ) contained in exhaust gas of an internal combustion engine, a selective reduction catalyst disposed in an exhaust passage of the internal combustion engine, and ammonia (NH ₃ ) or NH to the selective reduction catalyst An exhaust purification system (so-called SCR system) including a reducing agent supply device that supplies a reducing agent that is a precursor of No. ₃ is known.

Further, in the SCR system, a configuration in which an oxidation catalyst is arranged in an exhaust passage downstream of the selective reduction catalyst has been proposed for the purpose of purifying NH ₃ flowing out from the selective reduction catalyst (for example, Patent Documents). 1).

JP 2010-185372 A JP 2011-096310 A JP 2009-191756 A

By the way, when an abnormality occurs in the selective reduction catalyst of the SCR system, it is necessary to quickly detect the abnormality of the selective reduction catalyst and notify the vehicle driver or the like. In response to such a demand, a technique has been proposed in which a NO _X sensor is disposed downstream of the selective reduction catalyst, and deterioration or abnormality of the selective reduction catalyst is diagnosed using a measured value of the NO _X sensor as a parameter.

However, as described in Patent Document 1, in the configuration in which the oxidation catalyst is arranged downstream of the selective reduction catalyst and the NO _X sensor is arranged downstream of the oxidation catalyst, the measured value and selection of the NO _X sensor are selected. In some cases, the correlation with the degree of deterioration of the reduced catalyst becomes low. In such a case, if the deterioration diagnosis of the selective catalytic reduction catalyst is performed based on the measured value of the NO _X sensor, the degradation of the selective catalytic reduction catalyst may not be accurately diagnosed.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a selective reduction catalyst disposed in an exhaust passage of an internal combustion engine and an exhaust passage downstream of the selective reduction catalyst. In a deterioration diagnosis apparatus for an SCR system, comprising an oxidation catalyst, a NO _X sensor arranged downstream of the oxidation catalyst, and a means for diagnosing the deterioration of the selective catalytic reduction catalyst from the measured value of the NO _X sensor. It is in providing the technique which can be suppressed.

In order to solve the above-described problems, the present invention provides a selective reduction catalyst disposed in an exhaust passage of an internal combustion engine, and a reducing agent supply device that supplies ammonia or a reducing agent that is a precursor of ammonia to the selective reduction catalyst. When an oxidation catalyst disposed in the exhaust passage downstream of the selective reduction catalyst, and the NO _X sensor arranged downstream of the exhaust passage of the oxidation catalyst, a selective reduction catalyst deterioration of the measured value of the NO _X sensor as a parameter In the deterioration diagnosis apparatus for an SCR system, comprising: a diagnostic means for performing a diagnosis; a NO _x purification rate of the oxidation catalyst (the amount of NO _x reduced in the oxidation catalyst relative to the amount of NO _x flowing into the oxidation catalyst) When the ratio is low, the deterioration of the selective catalytic reduction catalyst is diagnosed.

Specifically, the degradation diagnosis device for the SCR system of the present invention is:
A selective reduction catalyst disposed in an exhaust passage of the internal combustion engine;
A reducing agent supply device that supplies ammonia or a reducing agent that is a precursor of ammonia to the selective catalytic reduction catalyst;
An oxidation catalyst disposed in an exhaust passage downstream of the selective catalytic reduction catalyst;
And NO _X sensor disposed in the exhaust passage downstream of the oxidation catalyst,
Wherein when a lower first 1NO _X purification rate is NO _X purification rate of the oxidation catalyst, the measured value of the NO _X sensor as a parameter, and so and a diagnostic means for diagnosing the deterioration of the selective reduction catalyst .

In the configuration in which the oxidation catalyst is disposed in the exhaust passage downstream of the selective reduction catalyst, NH ₃ and NO _X in the exhaust gas may cause a redox reaction in the oxidation catalyst. In such a case, the measured value of the NO _X sensor becomes smaller than when the oxidation catalyst does not cause a redox reaction between NH ₃ and NO _X.

Therefore, the degradation diagnosis of the selective reduction catalyst when the 1NO _X purification rate is high is performed, in spite of the selective reduction catalyst is degraded, is erroneous diagnosis selective reduction catalyst has not deteriorated There is a possibility.

On the other hand, according to the deterioration diagnosis device for the SCR system of the present invention, the deterioration diagnosis of the selective catalytic reduction catalyst is performed during the period when the first NO _X purification rate is low (preferably, the period during which NO _X is not reduced by the oxidation catalyst). Done. As a result, although the selective catalytic reduction catalyst has deteriorated, a situation in which a misdiagnosis that the selective catalytic reduction catalyst has not deteriorated hardly occurs. Therefore, according to the deterioration diagnosis device for the SCR system of the present invention, the deterioration diagnosis of the selective catalytic reduction catalyst can be performed more accurately.

The period of the 1NO _X purification rate is increased, subject to changing the diagnostic criteria, it may be implemented deterioration diagnosis of the selective reduction catalyst. For example, the selective reduction measurements of the NO _X sensor calculates a first 2NO _X purification rate is NO _X purification rate of the selective reduction catalyst as a parameter, the first 2NO _X purification rate calculated is smaller than the threshold value as a condition in the case of diagnosis of type catalyst has deteriorated, the period during which the 1NO _X purification rate is higher compared to the period to be lower, may change the threshold value to a larger value.

NO _X purification rate calculated measurements of the NO _X sensor as a parameter includes a first 1NO _X purification rate and the 2NO _X purification rate. However, when the first 1NO _X purification rate is low (preferably, when the NO _X can not be reduced in the oxidation catalyst) is NO _X purification rate calculated from the measured value of the NO _X sensor is approximately equal to the first 2NO _X purification rate become. On the other hand, when the first 1NO _X purification rate is high, NO _X purification rate calculated from the measured value of the NO _X sensor is larger than the 2NO _X purification rate. Therefore, even when the selective reduction catalyst is degraded, the higher the first 1NO _X purification rate, there is a possibility that the NO _X purification rate is calculated from the measured value of the NO _X sensor becomes equal to or higher than the threshold. As a result, although the selective catalytic reduction catalyst is deteriorated, there is a possibility that the selective catalytic reduction catalyst is erroneously diagnosed as not being deteriorated.

In contrast, according to the degradation diagnosis device of the SCR system of the present invention, compared with the case when the 1NO _X purification rate is high low, threshold used in the deterioration diagnosis of the selective reduction catalyst is to a large value. Therefore, there when the selective reduction catalyst has deteriorated when the 1NO _X purification rate is high, even if carried out degradation diagnosis of the selective reduction catalyst, is calculated from the measured value of the NO _X sensor N
O _X purification rate hardly exceeds the threshold.

As a result, even if the deterioration diagnosis of the selective reduction catalyst is performed when the 1NO _X purification rate is high, despite the selective reduction catalyst is deteriorated, when the selective reduction catalyst has not deteriorated Misdiagnosed situations are less likely to occur. Therefore, according to the deterioration diagnosis device for the SCR system of the present invention, the deterioration diagnosis of the selective catalytic reduction catalyst can be performed more accurately.

Note that when the 1NO _X purification rate is high, sets the threshold value of the maximum value larger than that can take the NO _X purification rate calculated from the measured value of the NO _X sensor, substantial degradation diagnosis of the selective reduction catalyst It may not be performed.

Here, the 1NO _X purification rate, the flow rate and the exhaust gas passing through the oxidation catalyst, correlated to the temperature of the oxidation catalyst (bed temperature). For example, when the amount of exhaust passing through the oxidation catalyst is less than a predetermined amount, NO _X and NH ₃ in the exhaust easily react with each other in the oxidation catalyst. Therefore, when the amount of exhaust gas passing through the oxidation catalyst is less than the predetermined amount it can be considered as first 1NO _X purification rate is high. Therefore, when the amount of exhaust gas passing through the oxidation catalyst is less than the predetermined amount, the deterioration diagnosis of the selective catalytic reduction catalyst is not performed, or the threshold value used for the diagnostic diagnosis of the selective catalytic reduction catalyst is changed to a large value. Good. Note that the amount of exhaust gas that passes through the oxidation catalyst correlates with the intake air amount of the internal combustion engine unless secondary air or the like is added in the exhaust passage upstream of the oxidation catalyst. Therefore, when the intake air amount of the internal combustion engine is less than the predetermined amount, the deterioration diagnosis of the selective catalytic reduction catalyst is not performed, or the threshold value used for the diagnostic diagnosis of the selective catalytic reduction catalyst is changed to a large value. Also good.

Further, when the temperature of the oxidation catalyst belongs to a predetermined temperature range, NO _X and NH ₃ in the exhaust gas easily react with each other in the oxidation catalyst. Therefore, when the temperature of the oxidation catalyst belongs to a predetermined temperature range, the deterioration diagnosis of the selective catalytic reduction catalyst is not performed, or the threshold used for the diagnostic diagnosis of the selective catalytic reduction catalyst may be changed to a large value. Here, the “predetermined temperature range” varies depending on the specification of the oxidation catalyst, but can be experimentally obtained in advance.

When NO _X is purified (reduced) in the oxidation catalyst, the first NO _X purification rate tends to increase. Therefore, when the first NO _X purification rate tends to increase (when NO _X is purified in the oxidation catalyst), the deterioration diagnosis of the selective catalytic reduction catalyst is not performed or is used for the diagnostic diagnosis of the selective catalytic reduction catalyst. The threshold value may be changed to a large value.

Incidentally, the 1NO _X purification rate can be calculated from measurement of the amount and NO _X sensor of the NO _X flowing into the oxidation catalyst. The amount of the NO _X flowing into the oxidation catalyst can be calculated from the NO _X purification rate of the selective reduction catalyst to the amount of the NO _X flowing into the selective reduction catalyst. However, since whether the selective reduction catalyst has degraded is unknown, it is difficult to accurately determine the NO _X purification rate of the selective reduction catalyst.

In contrast, if the first 1NO _X purification rate is determined only whether increasing, it was assumed that the selective reduction catalyst is degraded assumption, or a selective reduction catalyst has not deteriorated The amount of NO _X flowing out from the selective catalytic reduction catalyst (the amount of NO _X flowing into the oxidation catalyst) may be obtained by using the second NO _X purification rate in the case.

However, if the magnitude of the threshold is changed between the period when the first NO _X purification rate is high and the period when the first NO _X purification rate is low, the amount of change in the threshold size may be determined according to the increase in the first NO _X purification rate. preferable. Here, increasing the amount of the 1NO _X purification rate when the oxidation catalyst shifts from a low state of NO _X purification rate to a higher state, it is better when being degraded than when selective reduction catalyst has not deteriorated growing. Therefore, when the first 2NO _X purification rate is used on the assumption that the selective reduction catalyst has not deteriorated, in spite of the selective reduction catalyst has deteriorated when the selective reduction catalyst has not deteriorated There is a possibility of misdiagnosis. Therefore, the 2NO _X purification rate when it is assumed that the selective reduction catalyst is degraded (hereinafter, referred to as "provisional first 2NO _X purification") is used, it is preferable to obtain the first 1NO _X purification rate.

According to the present invention, the selective reduction catalyst disposed in the exhaust passage of the internal combustion engine, the oxidation catalyst disposed in the exhaust passage downstream of the selective reduction catalyst, and the NO _X sensor disposed downstream of the oxidation catalyst, In the degradation diagnosis device for an SCR system, comprising a means for diagnosing degradation of the selective catalytic reduction catalyst from the measured value of the NO _X sensor, erroneous diagnosis can be suppressed.

It is a figure which shows schematic structure of the internal combustion engine to which this invention is applied, and its exhaust system. It is a diagram showing the relationship between the exhaust flow rate and the 1NO _X purification rate Enoxasc through the bed temperature and the ammonia oxidation converters ammonia oxidation converters. When the SCR converter has deteriorated, a diagram showing a bed temperature of the ammonia oxidation converters, exhaust flow through the ammonia oxidation converters, the time course of total NO _X purification rate ENOX. It is a flowchart which shows the process routine which ECU performs when the deterioration diagnosis process of an SCR converter is performed in a 1st Example. It is a flowchart which shows the other example of the processing routine which ECU performs when the deterioration diagnosis process of an SCR converter is performed in a 1st Example. It is a flowchart which shows the process routine which ECU performs when the deterioration diagnosis process of an SCR converter is performed in a 2nd Example. Is a diagram showing the relationship between the bed temperature and the exhaust flow rate and the temporary second 2NO _X purification rate Enoxscr0 when SCR converter is in the deterioration state.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example 1>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied and its exhaust system. An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) or a spark ignition type internal combustion engine (gasoline engine) capable of lean combustion (lean burn operation).

  An exhaust passage 2 is connected to the internal combustion engine 1. The exhaust passage 2 is a passage for circulating burned gas (exhaust gas) discharged from the cylinder of the internal combustion engine 1. In the middle of the exhaust passage 2, a first catalyst casing 3 and a second catalyst casing 4 are arranged in series from the upstream side.

  The first catalyst casing 3 includes, for example, an oxidation catalyst and a particulate filter inside a cylindrical casing. In that case, the oxidation catalyst may be carried on a catalyst carrier disposed upstream of the particulate filter, or may be carried on the particulate filter.

The second catalyst casing 4 includes a catalyst carrier 40 (hereinafter referred to as “SCR converter 40”) carrying a selective reduction catalyst and a catalyst carrier 41 (hereinafter referred to as “SCR converter 40”) carrying an oxidation catalyst in a cylindrical casing. The catalyst carrier of the SCR converter 40 has, for example, a honeycomb-shaped cross section formed of cordierite, Fe—Cr—Al heat-resistant steel, or the like. A monolith type substrate having an alumina-based or zeolite-based active component (support) coated thereon, and an ammonia oxidation converter 41 is supplied to the SCR converter 40 from a reducing agent addition valve 5 described later. Among the agents, it is a catalyst that oxidizes the reducing agent that has passed through the SCR converter 40.

Addition of a reducing agent for adding (injecting) ammonia (NH ₃ ) or a reducing agent that is a precursor of NH ₃ into the exhaust passage 2 between the first catalyst casing 3 and the second catalyst casing 4. A valve 5 is attached. The reducing agent addition valve 5 is a valve device having an injection hole that is opened and closed by the movement of a needle. The reducing agent addition valve 5 is connected to a reducing agent tank 51 via a pump 50. The pump 50 sucks the reducing agent stored in the reducing agent tank 51 and pumps the sucked reducing agent to the reducing agent addition valve 5. The reducing agent addition valve 5 injects the reducing agent fed from the pump 50 into the exhaust passage 2. The opening / closing timing of the reducing agent addition valve 5 and the discharge pressure of the pump 50 are electrically controlled by an electronic control unit (ECU) 9.

Here, the reducing agent stored in the reducing agent tank 51 is NH ₃ gas or an aqueous solution such as urea or ammonium carbamate. In this embodiment, an aqueous urea solution is used as the reducing agent.

When the urea aqueous solution is injected from the reducing agent addition valve 5, the urea aqueous solution flows into the second catalyst casing 4 together with the exhaust gas. At that time, the urea aqueous solution receives heat from the exhaust and the SCR converter 40 and is thermally decomposed or hydrolyzed. When the urea aqueous solution is thermally decomposed or hydrolyzed, NH ₃ is generated. The NH ₃ generated in this way is adsorbed or occluded by the SCR converter 40. NH ₃ adsorbed or occluded in the SCR converter 40 reacts with nitrogen oxides (NO _x ) contained in the exhaust gas to generate nitrogen (N ₂ ) and water (H ₂ O). That is, NH ₃ functions as a NO _X reducing agent.

The internal combustion engine 1 configured as described above is provided with an ECU 9. The ECU 9 is an electronic control unit that includes a CPU, ROM, RAM, backup RAM, and the like. Various sensors such as a first NO _X sensor 6, a second NO _X sensor 7, an exhaust temperature sensor 8, a crank position sensor 10, an accelerator position sensor 11, and an air flow meter 12 are electrically connected to the ECU 9.

The first NO _X sensor 6 is disposed in the exhaust passage 2 between the first catalyst casing 3 and the second catalyst casing 4, and the amount of NO _X contained in the exhaust gas flowing into the second catalyst casing 4 (hereinafter referred to as “NO NO”). _The electric signal correlated with the “ _X inflow amount” is output. Second NO _X sensor 7 is arranged from the second catalyst casing 4 in the exhaust passage 2 downstream, the amount of the NO _X flowing out from the second catalyst casing 4 (hereinafter, referred to as "NO _X outflow") correlates with Outputs electrical signals. The exhaust temperature sensor 8 is disposed in the exhaust passage 2 downstream from the second catalyst casing 4 and outputs an electrical signal correlated with the temperature of the exhaust gas flowing out from the second catalyst casing 4. The crank position sensor 10 outputs an electrical signal correlated with the rotational position of the output shaft (crankshaft) of the internal combustion engine 1. The accelerator position sensor 11 outputs an electrical signal that correlates with the operation amount of the accelerator pedal (accelerator opening). The air flow meter 12 outputs an electrical signal correlated with the amount (mass) of air taken into the internal combustion engine 1.

The ECU 9 is electrically connected to various devices (for example, a fuel injection valve) attached to the internal combustion engine 1, the reducing agent addition valve 5, the pump 50, and the like. The ECU 9 electrically controls various devices of the internal combustion engine 1, the reducing agent addition valve 5, the pump 50, and the like based on the output signals of the various sensors described above. For example, the ECU 9 performs the SCR converter 40 in addition to known controls such as fuel injection control of the internal combustion engine 1 and addition control for intermittently injecting the reducing agent from the reducing agent addition valve 5.
A process (deterioration diagnosis process) for diagnosing the deterioration of is executed.

In the deterioration diagnosis process, the ECU 9 first determines the NO _X amount (NO _X inflow amount) flowing into the second catalyst casing 4 based on the output signals of the first NO _X sensor 6 and the second NO _X sensor 7. A ratio of the amount of NO _X purified by the second catalyst casing 4 (hereinafter referred to as “NO _X purification rate Enox”) is calculated. Specifically, ECU 9 according to the following equation (1), calculates the NO _X purification rate ENOX.
Enox = 1− (Anoxout / Anoxin) (1)
In the equation (1), Anoxout is an output signal (NO _X inflow amount) of the second NO _X sensor 7, and Anoxout is an output signal (NO _X outflow amount) of the first NO _X sensor 6.

Subsequently, the ECU 9 determines whether or not the NO _X purification rate Enox calculated according to the equation (1) is less than a threshold value. If the NO _X purification rate Enox is less than the threshold value, the SCR converter 40 deteriorates. Diagnose that. When the first NO _X sensor 6 is not provided in the exhaust passage 2 of the internal combustion engine 1, the NO _X inflow amount Anoxin is calculated using the operation state (intake air amount, fuel injection amount, etc.) of the internal combustion engine 1 as a parameter. It may be calculated.

By the way, when the SCR converter 40 is deteriorated, the amount of NH ₃ adsorbed on the SCR converter 40 is reduced and the amount of NO _X reduced by the SCR converter 40 is reduced as compared with the case where the SCR converter 40 is not deteriorated. . In such a case, NH ₃ and NO _X flowing out from the SCR converter 40 flow into the ammonia oxidation converter 41. Here, when the flow rate of the exhaust gas passing through the ammonia oxidation converter 41 is small, or when the temperature of the ammonia oxidation converter 41 belongs to a predetermined temperature range, the ammonia oxidation converter 41 causes an oxidation-reduction reaction between NH ₃ and NO _X. May be triggered. That is, when the flow rate of the exhaust gas passing through the ammonia oxidation converter 41 is small, and or when the temperature of the ammonia oxidation converter 41 belongs to a predetermined temperature range, a possibility that NO _X in the ammonia oxidation converter 41 is purified (reduced) There is.

FIG. 2 shows the temperature (bed temperature) of the ammonia oxidation converter 41, the exhaust flow rate, and the NO _x purification rate of the ammonia oxidation converter 41 (NO _x purified by the ammonia oxidation converter 41 with respect to the amount of NO _x flowing into the ammonia oxidation converter 41). The ratio of _X amount (hereinafter referred to as “first NO _X purification rate”) is a diagram showing the relationship with Enoxasc.

In FIG. 2, the first NO _X purification rate Enoxasc tends to be high in a specific temperature range. Further, the 1NO _X purification rate Enoxasc, it tends to increase towards the time less than when the flow rate of exhaust gas that passes through the ammonia oxidation converter 41 is large. Then, the temperature of the ammonia oxidation converter 41 belongs to a predetermined temperature range from T1 to T2, and when the flow rate of the exhaust gas passing through the ammonia oxidation converter 41 is smaller than the predetermined amount, the 1NO _X purification rate Enoxasc is greater than zero . In other words, consider the temperature of the ammonia oxidation converter 41 belongs to a predetermined temperature range, and when the flow rate of the exhaust gas passing through the ammonia oxidation converter 41 is smaller than the predetermined amount, NO _X in the exhaust gas is purified by the ammonia oxidation converters 41 be able to.

Therefore, when the temperature of the ammonia oxidation converter 41 belongs to a predetermined temperature range and the flow rate of the exhaust gas passing through the ammonia oxidation converter 41 is less than a predetermined amount, the NO _X purification rate Enox calculated by the equation (1) is , NO _X purification rate of the SCR converter 40 (hereinafter, referred to as "the 2NO _X purification rate Enoxscr") and will include a first 1NO _X purification rate Enoxasc. Hereinafter, the NO _X purification rate Enox calculated by the equation (1) is referred to as “total NO _X purification rate Enox”.

As a result, even when the SCR converter 40 is deteriorated, the temperature of the ammonia oxidation converter 41 belongs to a predetermined temperature range and the flow rate of the exhaust gas passing through the ammonia oxidation converter 41 is less than a predetermined amount. When the deterioration diagnosis of the converter 40 is performed, decrement of the 2NO _X purification rate Enoxscr is compensated by a 1NO _X purification rate Enoxasc, there is a possibility that the total NO _X purification rate Enox becomes equal to or higher than the threshold.

3, when the SCR converter 40 has deteriorated, the temperature of the ammonia oxidation converters 41 (bed temperature), the exhaust gas passing through the ammonia oxidation converter 41 flow rate (exhaust flow rate), the total NO _X purification rate Enox It is a figure which shows a time-dependent change.

In FIG. 3, during the period S in which the bed temperature of the ammonia oxidation converter 41 belongs to a predetermined temperature range from T1 to T2 and the exhaust flow rate is less than the predetermined amount Flwex, the bed temperature of the ammonia oxidation converter 41 is from T1 to T2. period not belonging to a predetermined temperature range, and the exhaust flow rate compared to the period in which a predetermined amount or more Flwex, total nO _X purification rate Enox indicates a large value. Further, shown in the period S, the bed temperature of the ammonia oxidation converter 41 is relatively low, and when the exhaust flow rate is relatively small, the total NO _X purification rate Enox is a value greater than or equal to the threshold Enoxth.

  On the other hand, the deterioration diagnosis device for the SCR system of the present embodiment is such that the bed temperature of the ammonia oxidation converter 41 belongs to a predetermined temperature range from T1 to T2 and the exhaust flow rate is less than the predetermined amount Flwex. 40 deterioration diagnosis was not performed. In other words, when the bed temperature of the ammonia oxidation converter 41 does not belong to the predetermined temperature range from T1 to T2 or when the exhaust gas flow rate becomes equal to or greater than the predetermined amount Flwex, The deterioration diagnosis of the converter 40 is performed. When the deterioration diagnosis of the SCR converter 40 is performed under such conditions, it is difficult to cause a situation in which the SCR converter 40 is not deteriorated even though the SCR converter 40 is deteriorated. As a result, the deterioration diagnosis of the SCR converter 40 can be performed more accurately.

  Hereinafter, the execution procedure of the deterioration diagnosis process in the present embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing a processing routine executed by the ECU 9 when the deterioration diagnosis process is performed. The processing routine shown in FIG. 4 is stored in advance in the ROM of the ECU 9 and is periodically executed by the ECU 9.

In the processing routine of FIG. 4, the ECU 9 first determines whether or not an execution condition for the deterioration diagnosis processing is satisfied in the processing of S101. Specifically, the ECU 9 satisfies the execution condition of the deterioration diagnosis process on the condition that the internal combustion engine 1 is in the warm-up completion state and the first NO _X sensor 6 and the second NO _X sensor 7 are in the active state. It is determined that If a negative determination is made in S101, the ECU 9 once ends the execution of this processing routine. On the other hand, if a positive determination is made in S101, the ECU 9 proceeds to the process of S102.

  In the process of S102, the ECU 9 determines whether or not the bed temperature Tempasc of the ammonia oxidation converter 41 belongs to a predetermined temperature range (a temperature range of T1 or more and T2 or less). At this time, the ECU 9 uses the measured value of the exhaust temperature sensor 8 as the bed temperature Tempasc of the ammonia oxidation converter 41. When the exhaust temperature sensor 8 is disposed in the exhaust passage 2 between the first catalyst casing 3 and the second catalyst casing 4, the bed temperature of the ammonia oxidation converter 41 is measured using the measured value of the exhaust temperature sensor 8 as a parameter. Tempasc may be calculated (estimated). If an affirmative determination is made in S102, the ECU 9 proceeds to the process of S103.

In the process of S103, the ECU 9 determines whether or not the flow rate Flw of the exhaust gas passing through the ammonia oxidation converter 41 is less than a predetermined amount Flwex. At that time, the ECU 9 uses the measured value of the air flow meter 12 as the flow rate Flw of the exhaust gas passing through the ammonia oxidation converter 41. If an affirmative determination is made in S103, there is a possibility that the first 1NO _X purification rate Enoxasc increases. Therefore, the ECU 9 proceeds to S104, and ends the present processing routine without performing the deterioration diagnosis process of the SCR converter 40. That is, in S104, the deterioration diagnosis process of the SCR converter 40 is prohibited. As a result, despite the deterioration of the SCR converter 40, it is difficult to cause a situation in which a false diagnosis is made that the SCR converter 40 is not deteriorated.

Also, if a negative determination is made in step S102 or the step S103, the first 1NO _X purification rate Enoxasc lower. Therefore, the ECU 9 proceeds to the process of S105 and executes the deterioration diagnosis process of the SCR converter 40. Specifically, the ECU 9 calculates the total NO _X purification rate Enox from the measured values of the first NO _X sensor 6 and the second NO _X sensor 7 and the above formula (1), and the total NO _X purification rate Enox is a threshold value. It is determined whether it is smaller than Enoxth. When the total NO _X purification rate Enox threshold Enoxth smaller than, ECU 9 diagnoses the SCR converter 40 has deteriorated, it informs the fact to the driver of the vehicle. As a notification method at that time, a method of lighting a warning light provided in the vehicle interior, a method of displaying a message on a display device provided in the vehicle interior, or a warning sound or sound from a sound output device provided in the vehicle interior A method of outputting a voice message can be used.

According to the embodiment described above, based on the measured value of the second NO _X sensor 7 disposed downstream of the ammonia oxidation converter 41, the deterioration diagnosis processing of the SCR converter 40 disposed upstream of the ammonia oxidation converters 41 In the deterioration diagnosis device to be performed, it is difficult for erroneous diagnosis to occur, so that deterioration diagnosis of the SCR converter 40 can be performed more accurately.

In addition, after it is diagnosed that the SCR converter 40 is deteriorated in the deterioration diagnosis process, the bed temperature of the ammonia oxidation converter 41 belongs to a predetermined temperature range and / or the flow rate Flw of the exhaust gas passing through the ammonia oxidation converter 41 is given. You may make it restrict | limit the driving | running state of the internal combustion engine 1 so that it may become less than fixed amount Flwex. In that case, it is possible to reduce as much as possible the amount of the NO _X discharged to the atmosphere after the SCR converter 40 has deteriorated.

Further, when the bed temperature of the ammonia oxidation converter 41 belongs to the predetermined temperature range and the flow rate Flw of the exhaust gas passing through the ammonia oxidation converter 41 is less than the predetermined amount Flwex, the deterioration diagnosis is performed by changing the value of the threshold Enoxth. You may be made to be. Specifically, when the bed temperature of the ammonia oxidation converter 41 belongs to a predetermined temperature range and the flow rate Flw of the exhaust gas passing through the ammonia oxidation converter 41 is less than the predetermined amount Flwex, the bed temperature of the ammonia oxidation converter 41 is predetermined. The threshold value Enoxth may be changed to a larger value than when it does not belong to the temperature range or when the flow rate Flw of the exhaust gas passing through the ammonia oxidation converter 41 is equal to or greater than the predetermined amount Flwex. Change amount at that time may be a variable value that is changed according to the 1NO _X purification rate Enoxasc, or may be a fixed value that is determined according to the maximum value of the 1NO _X purification rate Enoxasc .

  When the deterioration diagnosis of the SCR converter 40 is performed according to the above-described procedure, the ECU 9 may perform the deterioration diagnosis process according to a processing routine as shown in FIG. The difference between the processing routine shown in FIG. 5 and the processing routine shown in FIG. 4 described above is that, when an affirmative determination is made in S103, the processing in S201, that is, the threshold Enoxth value is changed instead of executing the processing in S104. The process is executed, and then the process of S105 (process for executing the deterioration diagnosis process) is performed. When the deterioration diagnosis process is executed according to the processing routine shown in FIG. 5, it is possible to increase the execution frequency of the deterioration diagnosis process while suppressing the occurrence of misdiagnosis.

  In the present embodiment, the deterioration diagnosis process is not performed when the bed temperature of the ammonia oxidation converter 41 belongs to a predetermined temperature range and the flow rate Flw of the exhaust gas passing through the ammonia oxidation converter 41 is less than the predetermined amount Flwex. However, when the flow rate Flw of the exhaust gas passing through the ammonia oxidation converter 41 is less than the predetermined amount Flwex, the deterioration diagnosis process may not be performed regardless of the floor temperature Tempasc of the ammonia oxidation converter 41, or When the bed temperature Tempasc of the ammonia oxidation converter 41 belongs to a predetermined temperature range, the deterioration diagnosis process may not be performed regardless of the flow rate Flw of the exhaust gas passing through the ammonia oxidation converter 41. In that case, the deterioration diagnosis process may be performed less frequently, but the deterioration diagnosis logic can be simplified. Further, when only the flow rate Flw of the exhaust gas passing through the ammonia oxidation converter 41 is used as a parameter, a misdiagnosis can be made difficult to occur even in a configuration in which the exhaust gas temperature sensor 8 is not provided.

<Example 2>
Next, a second embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

Differences between this embodiment and the first embodiment described above lies in the method of determining the period of first 1NO _X purification rate Enoxasc increases. That is, in the first embodiment described above, while using a flow rate Flw of the exhaust gas passing through the bed temperature Tempasc and ammonia oxidation converter 41 of the ammonia oxidation converter 41 as a parameter, in this embodiment, first 1NO _X purification rate Enoxasc Is used as a parameter.

When the ammonia oxidation converter 41 NO _X is purified is first 1NO _X purification rate Enoxasc exhibits an upward trend. Therefore, in this embodiment, when the first 1NO _X purification rate Enoxasc shows an upward trend, and is not performed deterioration diagnosis of the SCR converter 40.

  Hereinafter, the execution procedure of the deterioration diagnosis process in the present embodiment will be described with reference to FIG. FIG. 6 is a flowchart showing a processing routine executed by the ECU 9 when the deterioration diagnosis process of the SCR converter 40 is performed. In FIG. 6, the same processes as those in the process routine of the first embodiment described above (see FIG. 4) are denoted by the same reference numerals.

In the processing routine of FIG. 6, when an affirmative determination is made in the processing of S101, the ECU 9 proceeds to the processing of S301 and calculates the amount of NO _X flowing into the ammonia oxidation converter 41. Specifically, ECU 9 includes a first 2NO _X purification rate when it is assumed that the SCR converter 40 has deteriorated (hereinafter referred to as "provisional first 2NO _X purification rate Enoxscr0") and the measured value of the first NO _X sensor 6 From this, the amount of NO _X flowing out from the SCR converter 40 (the amount of NO _X flowing into the ammonia oxidation converter 41) is calculated. Provisional first 2NO _X purification rate Enoxscr0 is calculated from the correlation shown in FIG. Figure 7 is a diagram showing the correlation between the flow rate and the temporary second 2NO _X purification rate Enoxscr0 of the exhaust gas passing through the bed temperature and the SCR converter 40 of the SCR converter 40 in a deteriorated state. Provisional first 2NO _X purification rate Enoxscr0 is decreased as the bed temperature increases the exhaust flow rate when less than the predetermined temperature, the bed temperature becomes substantially constant regardless of the exhaust gas flow rate when the predetermined temperature or higher. Incidentally, the deterioration state referred to herein is, under conditions in ammonia oxidation converter 41 NO _X is hardly purified, the total NO _X purification rate Enox is a degraded slightly about smaller than the threshold value Enoxth, in other words, the total NO _X purification The deterioration state is such that the rate Enox becomes maximum in a range where the ratio Enox is smaller than the threshold value Enoxth. As the exhaust flow rate and bed temperature to be used for calculating the provisional first 2NO _X purification rate Enoxscr0, it is assumed that the measurement values of the exhaust temperature sensor 8 of the air flow meter 12 is used.

Here, returning to the processing routine of FIG. 6, the ECU 9 executes the process of S302 after executing the process of S301. That, ECU 9 calculates a first 1NO _X purification rate Enoxasc from _the amount of NO _X calculated in the processing of S301 and _(the amount of NO _X flowing into the ammonia oxidation converter 41) and the measured value of the second NO _X sensor 7.

Subsequently, ECU 9 proceeds to step S303, and a second 1NO _X purification rate Enoxascold calculated in the 1NO _X purification rate Enoxasc and S302 in the previous execution of this routine calculated by the S302, the per predetermined period increase the amount of the 1NO _X purification rate Enoxasc ΔEnoxasc a (= Enoxasc-Enoxascold) calculated, the amount of rise DerutaEnoxasc it is determined whether a predetermined amount α or more. The certain amount α is a value larger than zero, and is a value determined in advance by an adaptation process using an experiment or the like. If an affirmative determination is made in S303, the ECU 9 executes the process of S104. On the other hand, if a negative determination is made in S303, the ECU 9 executes the process of S105.

According to the embodiment described above, the same effects as those of the first embodiment described above can be obtained. In this embodiment, (when the NO _X is purified in ammonia oxidation converter 41) when the first 1NO _X purification rate Enoxasc tends to increase but has dealt with the case of not performing the deterioration diagnosis processing of the SCR converter 40, The deterioration diagnosis process may be performed by changing the value of the threshold Enoxth. The change amount of the threshold Enoxth at that time may be determined according to the magnitude of the above-described increase amount ΔEnoxasc. For example, the change amount (increase amount) of the threshold Enoxth may be increased when the increase amount ΔEnoxasc is larger than when it is small.

Also, the first and second embodiments described above can be combined. That, ECU 9, the temperature of the ammonia oxidation converter 41 belongs to a predetermined temperature range and flow rate of the exhaust gas passing through the ammonia oxidation converter 41 is equal to or greater than a predetermined amount, and, second 1NO _X purification rate Enoxasc is trending On the condition, the deterioration diagnosis process of the SCR converter 40 may be prohibited or the threshold value Enoxth of the deterioration diagnosis process may be changed. In that case, the accuracy of the deterioration diagnosis process can be further improved.

1 Internal combustion engine 2 Exhaust passage 3 First catalyst casing 4 Second catalyst casing 5 Reductant addition valve 6 First NO _X sensor 7 Second NO _X sensor 8 Exhaust temperature sensor 9 ECU
50 Pump 51 Reductant tank

Claims (5)

A selective reduction catalyst disposed in an exhaust passage of the internal combustion engine;
A reducing agent supply device that supplies ammonia or a reducing agent that is a precursor of ammonia to the selective catalytic reduction catalyst;
An oxidation catalyst disposed in an exhaust passage downstream of the selective catalytic reduction catalyst;
And NO _X sensor disposed in the exhaust passage downstream of the oxidation catalyst,
Diagnostic means when the lower first 1NO _X purification rate is NO _X purification rate, to diagnose the selection deterioration of reduction catalyst the measured value of the NO _X sensor as a parameter in the oxidation catalyst,
An SCR system deterioration diagnosis device comprising: According to claim 1, wherein the means for diagnosing the NO _X sensor of the 2NO _X purification rate is NO _X purification rate of the selective reduction catalyst calculates the measured value as a parameter, first 2NO _X purification rate calculated is Diagnosing that the selective catalytic reduction catalyst is degraded when it is smaller than the threshold,
When the deterioration diagnosis of the selective reduction catalyst is performed when the first NO _X purification rate is high, the deterioration diagnosis of the selective reduction catalyst is performed when the first NO _X purification rate is low, compared to the case where the deterioration diagnosis of the selective reduction catalyst is performed. A deterioration diagnosis apparatus for an SCR system in which a threshold value is changed to a large value. According to claim 1 or 2, wherein when the amount of exhaust gas passing through the oxidation catalyst is less than a predetermined amount, the deterioration diagnosis device for SCR systems to be determined to be high the first 1NO _X purification rate. In any one of claims 1 to 3, wherein when the temperature of the oxidation catalyst belongs to a predetermined temperature range, the deterioration diagnosis device for the SCR system first 1NO _X purification rate is determined to be high. 5. The amount of nitrogen oxides flowing out from the selective catalytic reduction catalyst and the measured value of the NO _X sensor when the selective catalytic reduction catalyst is assumed to be deteriorated in any one of claims 1 to 4. when NO _X purification rate is calculated as a parameter tends to increase, deterioration diagnosis device of the SCR system first 1NO _X purification rate is determined to be high.

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