JP2010275947A - Deterioration diagnostic system of exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve diagnostic accuracy in a deterioration diagnostic system of an exhaust emission control device including a selective reduction type catalyst. <P>SOLUTION: The deterioration diagnostic system acquires a physical quantity correlating to an endothermic quantity when moisture adsorbed to the selective reduction type catalyst is desorbed under a condition that a reducing agent is not supplied to the selective reduction type catalyst from an adding device, and diagnoses a degree of deterioration of the selective reduction type catalyst based on the acquired physical quantity. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  2. Description of the Related Art Conventionally, there has been proposed an exhaust purification system that includes a selective reduction catalyst disposed in an exhaust passage of an internal combustion engine, and a urea water addition device for adding urea water to exhaust flowing upstream from the selective reduction catalyst. .

In the above system, ammonia slip (a phenomenon in which ammonia (NH ₃ ) passes through the selective catalytic reduction catalyst) becomes more prominent as the selective catalytic reduction catalyst progresses. It was necessary to correct the amount of addition.

  As a method for diagnosing the degradation of the selective catalytic reduction catalyst, the operating time in which the temperature of the exhaust gas flowing into the selective catalytic reduction catalyst becomes equal to or higher than a predetermined temperature is integrated, and the degradation degree of the selective catalytic reduction catalyst increases as the cumulative time increases. Has been proposed (see, for example, Patent Document 1).

JP 2006-242094 A JP 2003-83042 A

Incidentally, the above-mentioned conventional techniques are viable diagnostic methods without additional concentration of NO _x sensor and the ammonia concentration sensor, etc., it can not be performed an accurate diagnosis by operation conditions such as conditions of use and the internal combustion engine There is sex.

Further, the amount (concentration) of nitrogen oxide (NO _x ) and ammonia (NH ₃ ) flowing out from the selective reduction catalyst when a reducing agent such as urea is supplied to the selective reduction catalyst is detected. Although a method of performing diagnosis is proposed, whether the difference between the detected value and the normal value is due to the failure / degradation of the reducing agent addition device, the failure / degradation of the sensor, or the degradation of the selective catalytic reduction catalyst Needed to be identified.

  The present invention has been made in view of the above circumstances, and an object thereof is to improve diagnosis accuracy in a deterioration diagnosis system for an exhaust purification device including a selective catalytic reduction catalyst.

  In order to solve the above-described problems, the present invention diagnoses the degree of deterioration of the selective catalytic reduction catalyst based on the amount of moisture that can be adsorbed by the selective catalytic reduction catalyst.

From the experiments and verifications of the present inventor, it was found that the purification ability of the selective catalytic reduction catalyst correlates with the amount of moisture (H ₂ O) that can be adsorbed by the selective catalytic reduction catalyst (saturation amount). That is, the purification capacity of the selective reduction catalyst correlates with the amount (saturation amount) of ammonia (NH ₃ ) that can be adsorbed by the selective reduction catalyst, and the amount of ammonia that can be adsorbed by the selective reduction catalyst is the selective reduction type catalyst. It was found that the catalyst correlates with the amount of moisture that can be adsorbed. Hereinafter, the amount of water that can be adsorbed by the selective catalytic reduction catalyst is referred to as the maximum water content, and the amount of ammonia that can be adsorbed by the selective catalytic reduction catalyst is referred to as the maximum ammonia amount.

  For example, when the purification capacity of the selective catalytic reduction catalyst is deteriorated, the maximum water content is reduced from the normal time (new time). This tendency becomes prominent as the selective catalytic reduction catalyst progresses. In other words, the maximum water content decreases as the selective catalytic reduction catalyst progresses.

  Therefore, it is possible to diagnose the degree of deterioration of the selective catalytic reduction catalyst by directly or indirectly acquiring the maximum water content of the selective catalytic reduction catalyst.

  The moisture adsorbed on the selective catalytic reduction catalyst absorbs the heat of exhaust and / or the selective catalytic reduction catalyst when desorbed from the selective catalytic reduction catalyst. The endothermic amount at that time correlates with the maximum water content. Therefore, the maximum moisture amount can be specified by specifying the endothermic amount when moisture is desorbed from the selective catalytic reduction catalyst.

  As a method for specifying the above-mentioned endothermic amount, the temperature of exhaust gas flowing out from the selective catalytic reduction catalyst (hereinafter referred to as “outgas temperature”) from the time when the moisture adsorption amount of the selective catalytic reduction catalyst reaches the maximum moisture content is used. A period (hereinafter referred to as a “detection period”) until the time when the temperature of the exhaust gas flowing into the selective catalytic reduction catalyst (hereinafter referred to as “inlet gas temperature”) is substantially equal (for example, the difference between the two is a certain value or less). ) Can be exemplified by a method for specifying the amount of heat deprived from the selective catalytic reduction catalyst and / or the exhaust gas.

  Here, when the internal combustion engine is cold-started, the inlet gas temperature and the outlet gas temperature rise with time. However, the outlet gas temperature is lower than the inlet gas temperature by the amount of heat transferred from the exhaust to the selective catalytic reduction catalyst.

  Further, if the moisture adsorption amount of the selective catalytic reduction catalyst does not reach the maximum moisture content, the moisture in the exhaust is adsorbed on the selective catalytic reduction catalyst. Since heat (moisture adsorption reaction heat) is generated when the selective catalytic reduction catalyst adsorbs moisture, the outgassing temperature rises. When the moisture adsorption amount of the selective catalytic reduction catalyst reaches the maximum moisture amount, the heat of moisture adsorption reaction is not generated, and the outgas temperature is once lowered. That is, the outlet gas temperature reaches a peak when the moisture adsorption amount of the selective catalytic reduction catalyst reaches the maximum moisture amount.

  Thereafter, when the bed temperature of the selective reduction catalyst rises to the moisture desorption temperature range, moisture begins to desorb from the selective reduction catalyst. Since heat is absorbed when moisture desorbs from the selective catalytic reduction catalyst, the temperature of the selective catalytic reduction catalyst and exhaust gas decreases. That is, when moisture begins to desorb from the selective catalytic reduction catalyst, the increase in the outgas temperature is hindered. As a result, the outgas temperature hardly increases or decreases.

  When all the moisture is desorbed from the selective catalytic reduction catalyst, the outgas temperature starts to rise again. When the bed temperature of the selective catalytic reduction catalyst rises to a temperature equivalent to that of the exhaust gas, the outlet gas temperature becomes equivalent to the inlet gas temperature.

  In view of the above-mentioned tendency, the total amount of difference between the inlet gas temperature and the outlet gas temperature in the period from the time when the moisture adsorption amount reaches the maximum moisture amount until the outlet gas temperature becomes equal to the inlet gas temperature ( It can be said that the integrated value) correlates with the heat absorption amount and the heat capacity of the exhaust emission control device.

Since the heat capacity of the exhaust purification device is constant, it can be said that the total amount described above correlates with the heat absorption amount. Therefore, by integrating the difference between the inlet gas temperature and the outlet gas temperature in the detection period, a physical quantity correlated with the endothermic amount (in other words, a physical quantity correlated with the maximum moisture amount) can be acquired.

  Note that the timing at which the moisture adsorption amount of the selective catalytic reduction catalyst reaches the maximum moisture amount (hereinafter referred to as “adsorption end timing”) is the timing at which the outlet gas temperature reaches a peak (in other words, the outlet gas) A method for identifying the timing at which the temperature shifts from an increasing tendency to a decreasing tendency can be exemplified.

  When the deterioration diagnosis is performed with the endothermic amount obtained by such a method as the correlation value of the maximum moisture amount, the deterioration diagnosis is performed with the calorific value when the selective catalytic reduction catalyst adsorbs moisture as the correlation value of the maximum moisture amount. Diagnosis accuracy can be improved more than the case.

  The amount of heat generated when the selective catalytic reduction catalyst adsorbs moisture varies not only with the degree of deterioration of the selective catalytic reduction catalyst, but also with the amount of moisture already adsorbed by the selective catalytic reduction catalyst at the start. On the other hand, the amount of water desorbed from the selective catalytic reduction catalyst becomes substantially equal to the maximum water content regardless of the amount of water already adsorbed by the selective catalytic reduction catalyst at the start. Therefore, the correlation between the endothermic amount and the maximum moisture amount when moisture is desorbed from the selective reduction catalyst is stronger than the correlation between the heat generation amount and the maximum moisture amount when the selective reduction catalyst adsorbs moisture.

  Next, as a method for diagnosing the degree of degradation of the selective catalytic reduction catalyst, a method of diagnosing that the degree of degradation of the selective catalytic reduction catalyst is higher as the maximum water content decreases, or the maximum water content is greater than or equal to a predetermined lower limit value. There can be mentioned a method of diagnosing that the selective catalytic reduction catalyst is normal in some cases and diagnosing that the selective catalytic reduction catalyst is degraded when the maximum water content is less than the lower limit.

  By the way, the above-described deterioration diagnosis needs to be performed when the bed temperature of the selective catalytic reduction catalyst is lower than the moisture desorption temperature range and a relatively large amount of moisture is supplied to the selective catalytic reduction catalyst. Therefore, the above-described deterioration diagnosis is preferably performed when the internal combustion engine is cold started.

  In addition to the degree of deterioration of the selective catalytic reduction catalyst, the maximum water content of the selective catalytic reduction catalyst may vary depending on the amount of ammonia adsorbed on the selective catalytic reduction catalyst. On the other hand, the ammonia supply amount for the selective reduction catalyst may be specified, and the deterioration diagnosis may be performed in anticipation of a decrease in the endothermic amount due to the specified ammonia supply amount.

  According to such a method, deterioration diagnosis of the selective catalytic reduction catalyst can be performed even when ammonia is supplied to the selective catalytic reduction catalyst. However, when there is a variation in the amount of ammonia supplied, there is a possibility that the diagnostic error will increase. For this reason, it can be said that the deterioration diagnosis of the selective catalytic reduction catalyst is preferably performed in the period from the cold start of the internal combustion engine to the start of the supply of ammonia.

  The present invention includes various technical ideas described above. Preferred specific requirements for such an invention include a selective reduction catalyst disposed in an exhaust passage of an internal combustion engine, an addition device for adding a reducing agent to exhaust flowing upstream from the selective reduction catalyst, and the addition device Acquisition means for acquiring a physical quantity correlated with an endothermic amount when moisture adsorbed on the selective reduction catalyst under the condition that no reducing agent is supplied from the selective reduction catalyst to the selective reduction catalyst; And diagnostic means for diagnosing the degree of deterioration of the selective catalytic reduction catalyst based on the physical quantity acquired by the acquisition means. The reducing agent referred to here is a reducing agent that generates a polar molecule such as ammonia by being thermally decomposed or hydrolyzed, and examples thereof include urea.

In the invention specified by these requirements, deterioration diagnosis is performed based on the endothermic amount when moisture is desorbed from the selective catalytic reduction catalyst. The endothermic amount at that time correlates with the maximum water content of the selective catalytic reduction catalyst. Therefore, the deterioration degree of the selective catalytic reduction catalyst can be diagnosed with high accuracy.

  In the above-described invention, the deterioration diagnosis is performed when the adding device does not add the reducing agent. For this reason, it is possible to prevent deterioration in diagnostic accuracy due to deterioration / failure of the addition device, and it is possible to prevent deterioration of exhaust emission (for example, deterioration of exhaust emission due to slipping of the reducing agent (ammonia slip)).

  Furthermore, the above-described invention can perform deterioration diagnosis without using a sensor for detecting the concentration of ammonia or nitrogen oxide. For this reason, it is possible to prevent a decrease in diagnostic accuracy due to deterioration / failure of the sensor.

  By the way, the internal combustion engine may be stopped before the above-described deterioration diagnosis is completed (for example, before moisture is completely desorbed from the selective catalytic reduction catalyst). If such operation is repeated, the chances of performing deterioration diagnosis are reduced.

  Therefore, the degradation diagnosis system of the present invention is designed so that when the operation method in which the internal combustion engine is stopped before the desorption of moisture from the selective catalytic reduction catalyst continues for a certain number of times, the selective catalytic reduction catalyst is used after the next startup. An accelerating means for accelerating the temperature rise may be further provided.

  At that time, the promotion means supplies a reducing component (for example, hydrocarbon (HC) or the like) to the selective reduction catalyst, or promotes the temperature increase of the selective reduction catalyst by increasing the load of the internal combustion engine. Also good. When the temperature increase of the selective catalytic reduction catalyst is thus promoted, it becomes possible to desorb all the moisture from the selective catalytic reduction catalyst at an early stage after the start. As a result, it is possible to increase the probability that the deterioration diagnosis ends before the internal combustion engine is stopped.

  In addition, if the operation state in which the amount of moisture in the exhaust gas is reduced before the above-described deterioration diagnosis ends, the period until the selective catalytic reduction catalyst reaches the desorption temperature range becomes longer, and before the deterioration diagnosis ends. Therefore, the possibility that the internal combustion engine is stopped increases. Furthermore, since the change in the outgas temperature becomes gentle, there is a possibility that accurate deterioration diagnosis cannot be performed.

  Therefore, the deterioration diagnosis system of the present invention further includes a prohibiting means for prohibiting the execution of the deterioration diagnosis when the operation state in which the amount of moisture in the exhaust gas decreases for a certain period or more before the deterioration diagnosis ends. May be. In addition, a lean operation state can be illustrated as an operation state in which the amount of moisture in the exhaust gas is reduced.

  According to this configuration, it is possible to avoid a decrease in diagnostic accuracy. However, if the prohibition of the execution of the deterioration diagnosis by the prohibiting means is repeated, the opportunity for the deterioration diagnosis is reduced, and it becomes difficult to detect deterioration of the selective catalytic reduction catalyst at an early stage. For this reason, the deterioration diagnosis system according to the present invention may further include an increase means for increasing the amount of moisture in the exhaust after the next start when the deterioration diagnosis by the prohibit means continues for a certain number of times. Good.

  The amount of water in the exhaust gas may be increased. As a method of increasing the amount of moisture in the exhaust, a method of adding moisture to the exhaust flowing upstream from the selective catalytic reduction catalyst, or a reduction (rich) of the air-fuel ratio of the air-fuel mixture used for combustion in the internal combustion engine A method etc. can be illustrated.

  ADVANTAGE OF THE INVENTION According to this invention, in the deterioration diagnostic system of the exhaust gas purification apparatus containing a selective reduction type catalyst, it becomes possible to improve diagnostic accuracy.

1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. It is a figure which shows the measurement result of the water | moisture-content adsorption | suction amount of a new selective reduction catalyst, an inlet gas temperature, and an outlet gas temperature when an internal combustion engine is cold-started. It is a figure which shows the measurement result of the water | moisture-content adsorption amount of the selective reduction type catalyst of a deterioration state, an inlet gas temperature, and an outlet gas temperature when an internal combustion engine is cold-started. It is a flowchart which shows the deterioration diagnostic routine in a 1st Example. It is a flowchart which shows the deterioration diagnostic routine in a 2nd Example.

  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 exhaust system of an internal combustion engine to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a compression ignition internal combustion engine (diesel engine) using light oil as fuel.

An exhaust purification device 3 including a selective reduction catalyst is disposed in the exhaust passage 2 of the internal combustion engine 1. The selective reduction catalyst is a catalyst that selectively adsorbs polar molecules such as ammonia and reduces and purifies NO _x in the exhaust gas using the adsorbed ammonia as a reducing agent.

  A urea addition valve 4 for adding a urea aqueous solution to the exhaust gas flowing through the exhaust passage 2 is attached to the exhaust passage 2 upstream from the exhaust purification device 3. A tank 5 for storing a urea aqueous solution is connected to the urea addition valve 4. The urea addition valve 4 and the tank 5 are an example of an addition apparatus according to the present invention.

The urea addition valve 4 adds an aqueous urea solution stored in the tank 5 into the exhaust when the selective catalytic reduction catalyst is in an active state. The urea aqueous solution added to the exhaust is thermally decomposed and hydrolyzed in the exhaust or in the selective reduction catalyst to generate ammonia. The produced ammonia is adsorbed by the selective reduction catalyst and reduces NO _x in the exhaust.

A first temperature sensor 6 for detecting the temperature of the exhaust gas flowing into the exhaust purification device 3 (incoming gas temperature) is attached to the exhaust passage 2 upstream from the exhaust purification device 3. Wherein the exhaust purification device downstream of the exhaust passage 2 from 3, and the second temperature sensor 7 for detecting the temperature of the exhaust gas flowing out from the exhaust purification device 3 (outlet gas temperature), detecting the concentration of NO _x contained in the exhaust A NO _x sensor 8 is attached.

The exhaust purification system configured in this manner is provided with an ECU 9. The ECU 9 is an electronic control unit that includes a CPU, a ROM, a RAM, a backup RAM, and the like. The ECU 9 is supplied with output signals from various sensors such as the first temperature sensor 6, the second temperature sensor 7, and the NO _x sensor 8. Further, the urea addition valve 4 and the like are electrically connected to the ECU 9.

  The ECU 9 controls the operation state of the urea addition valve 4 and the internal combustion engine 1 based on the output signals of the various sensors described above. For example, the ECU 9 performs deterioration diagnosis of the selective catalytic reduction catalyst in addition to known controls such as fuel injection control and urea addition control.

Hereinafter, a method for diagnosing deterioration of the selective catalytic reduction catalyst will be described. The deterioration diagnosis method of the present embodiment is a method of diagnosing the degree of deterioration of the selective catalytic reduction catalyst using the endothermic amount when desorbing the moisture adsorbed by the selective catalytic reduction catalyst as a parameter.

  The selective catalytic reduction catalyst has the property of polarly adsorbing water (water) as well as ammonia. The moisture adsorption of the normal selective catalytic reduction catalyst spreads from the upstream site to the downstream site. When the moisture adsorption amount of the selective catalytic reduction catalyst reaches a saturation level, the bed temperature of the selective catalytic reduction catalyst rapidly increases due to the heat of adsorption reaction.

  Thereafter, when the selective reduction catalyst rises to the moisture desorption temperature range, the moisture adsorbed on the selective reduction catalyst is desorbed. When moisture is desorbed from the selective catalytic reduction catalyst, heat is absorbed from the selective catalytic reduction catalyst and exhaust gas, so that the bed temperature and the outgas temperature are lowered. The endothermic amount accompanying the desorption of water correlates with the maximum water amount of the selective catalytic reduction catalyst. The maximum water content of the selective reduction catalyst correlates with the degree of deterioration. Therefore, it is possible to specify the degree of deterioration of the selective catalytic reduction catalyst by specifying the endothermic amount accompanying the desorption of moisture.

  Here, FIG. 2 shows temporal changes in the inlet gas temperature, outlet gas temperature, and moisture adsorption amount after the internal combustion engine 1 is cold started. The data shown in FIG. 2 was measured using a normal (new) selective reduction catalyst. The solid line in FIG. 2 indicates the moisture adsorption amount, the alternate long and short dash line indicates the inlet gas temperature, and the dashed line indicates the outlet gas temperature.

  In FIG. 2, when the internal combustion engine 1 is started (t0 in FIG. 2), the inlet gas temperature starts to rise and the moisture adsorption amount of the selective catalytic reduction catalyst starts to increase. The outlet gas temperature begins to rise more gently than the inlet gas temperature. This is thought to be due to the heat of the exhaust being taken away by the selective reduction catalyst.

  Since the adsorption of moisture in the selective catalytic reduction catalyst gradually spreads from the upstream site to the downstream site, as the moisture adsorption amount of the selective catalytic reduction increases, the generation site of the moisture adsorption reaction heat is also downstream from the upstream side. Move to the side. As a result, the outgas temperature rises as the moisture adsorption amount of the selective catalytic reduction increases.

  When the moisture adsorption amount of the selective catalytic reduction catalyst reaches the maximum moisture amount ΣVam (t1 in FIG. 2), in other words, when the moisture is adsorbed at the downstream end of the selective catalytic reduction catalyst, the output gas temperature reaches the peak Tomax. To reach. After the moisture adsorption amount of the selective catalytic reduction catalyst reaches the maximum moisture amount, no moisture adsorption reaction heat is generated, so that the outgas temperature decreases.

  Subsequently, when the bed temperature of the selective catalytic reduction reaches the desorption temperature range (t2 in FIG. 2), the moisture adsorbed on the selective catalytic reduction begins to desorb. When moisture begins to desorb from the selective catalytic reduction catalyst, an increase in the output gas temperature is hindered by the endothermic effect, so that the output gas temperature hardly increases or further decreases.

  As the amount of moisture adsorbed on the selective catalytic reduction catalyst decreases, the endothermic amount decreases, and the output gas temperature begins to rise gradually. When all the moisture adsorbed on the selective catalytic reduction catalyst has been desorbed (t3 in FIG. 2), the amount of increase in the outgas temperature (the amount of increase per unit time) increases, which is substantially equal to the input gas temperature. The temperature rises to an equivalent temperature (t4 in FIG. 2).

  Here, if the amount of moisture adsorption of the selective catalytic reduction catalyst at the start of the internal combustion engine 1 is zero, the amount of heat generated by moisture adsorption reaction correlates with the maximum amount of moisture of the selective catalytic reduction catalyst. However, if moisture is already adsorbed to the selective catalytic reduction catalyst at the time of starting the internal combustion engine 1, the amount of heat generated by moisture adsorption reaction does not correlate with the maximum amount of moisture.

On the other hand, the endothermic amount due to the water desorption reaction is generated after the maximum amount of water is adsorbed on the selective catalytic reduction catalyst, and thus correlates with the maximum amount of water. Therefore, the deterioration diagnosis of the present embodiment can accurately determine the maximum water content of the selective catalytic reduction catalyst, in other words, the degree of degradation of the selective catalytic reduction catalyst, using the endothermic amount accompanying the water desorption reaction as a parameter. It becomes possible.

  Note that it is difficult to detect the timing at which moisture begins to desorb from the selective catalytic reduction catalyst (t2 in FIG. 2) and the timing at which all the moisture has been desorbed from the selective catalytic reduction catalyst (t3 in FIG. 2). . For this reason, in the deterioration diagnosis of this embodiment, the timing at which the outlet gas temperature becomes equal to the inlet gas temperature (t4 in FIG. 2) from the timing (t1 in FIG. 2) when the selective catalytic reduction catalyst has finished adsorbing moisture. The integrated value of the difference between the incoming gas temperature and the outgoing gas temperature in the period up to this time (detection period) (the area of the portion indicated by the hatching in FIG. 2) is used as the correlation value of the endothermic amount.

  FIG. 3 shows changes over time in the inlet gas temperature, outlet gas temperature, and moisture adsorption amount when the selective catalytic reduction catalyst deteriorates. The data shown in FIG. 3 is measured under the same conditions as in FIG. A two-dot broken line in FIG. 3 indicates an outgas temperature at the time of deterioration.

  When the selective catalytic reduction catalyst deteriorates, the maximum water content decreases, so that the peak Tomax1 reaches an earlier time than the normal time (t10 in FIG. 3), and the peak Tomax1 at that time is higher than the normal peak Tomax. Lower. Further, since the endothermic amount decreases with the decrease in the maximum water content, the amount of decrease in the outgas temperature after reaching the peak Tomax1 is also smaller than normal, and the timing at which the outgas temperature becomes equal to the input gas temperature ( T40) in FIG. 3 is also earlier than the normal timing t4. As a result, the integrated value of the difference between the inlet gas temperature and the outlet gas temperature in the detection period (period from t10 to t40 in FIG. 3) is smaller than when the selective catalytic reduction catalyst is normal.

  Thus, when the deterioration diagnosis of the selective catalytic reduction catalyst is performed using the integral value of the difference between the inlet gas temperature and the outlet gas temperature in the detection period as a parameter, it is already adsorbed by the selective catalytic reduction catalyst when the internal combustion engine 1 is started. It is possible to diagnose the degree of deterioration of the selective catalytic reduction catalyst regardless of the amount of water.

Further, the deterioration diagnosis method of this embodiment is a method that can be performed when the urea addition valve 4 does not add the aqueous urea solution. For this reason, a decrease in diagnostic accuracy due to variations in the amount of urea aqueous solution added and an increase in exhaust emissions due to ammonia slip can be suppressed. Furthermore, the deterioration diagnosis of this embodiment is a method that can be performed without using the output signal of the NO _x sensor 8. Therefore, decrease in diagnostic accuracy due to the output characteristic of the NO _x sensor 8 is also suppressed.

  Here, the execution procedure of the deterioration diagnosis in the present embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing a deterioration diagnosis routine. The deterioration diagnosis routine is a routine stored in advance in the ROM of the ECU 9 or the like, and is a routine that is executed by the ECU 9 with the start of the internal combustion engine 1 as a trigger.

  In the deterioration diagnosis routine, the ECU 9 first determines in S101 whether or not the internal combustion engine 1 is being started. Examples of the determination method include a method of determining whether or not the ignition switch is switched from OFF to ON, or whether or not the starter switch is switched from OFF to ON. In addition, when an affirmative determination is made by either of the above two determination methods, it is considered that the internal combustion engine 1 is at the time of starting.

  If a negative determination is made in S101, the ECU 9 ends the execution of this routine. If a positive determination is made in S101, the ECU 9 proceeds to S102.

In S102, the ECU 9 determines whether or not a deterioration diagnosis execution condition is satisfied. The condition for executing the deterioration diagnosis is the bed temperature (outgas temperature) of the selective catalytic reduction catalyst at the time of the previous shutdown.
Is the desorption temperature, the bed temperature of the selective catalytic reduction catalyst at the time of the current start-up (for example, the outgas temperature when the ignition switch is turned on or the starter switch is turned on) is the desorption temperature For example, it is possible to exemplify a condition such as being less than (or an elapsed time from the previous operation stop to the current start time being a certain time or more).

  If a negative determination is made in S102, the ECU 9 ends the execution of this routine. If an affirmative determination is made in S102, the ECU 9 proceeds to S103. In S103, the ECU 9 determines whether or not the moisture adsorption process of the selective catalytic reduction catalyst has been completed (whether or not the moisture adsorption amount has reached the maximum moisture adsorption amount). Specifically, the ECU 9 monitors the detection value (outgas temperature) of the second temperature sensor 7 and determines whether or not the outgas temperature has changed from an increasing tendency to a decreasing tendency.

  If a negative determination is made in S103, the ECU 9 executes the process of S103 again. On the other hand, if an affirmative determination is made in S103, the ECU 9 proceeds to S104.

  In S104, the ECU 9 integrates the difference ΔT (= Tin−Tout) between the detection value (inlet gas temperature) Tin of the first temperature sensor 6 and the detection value (outlet gas temperature) Tout of the second temperature sensor 7 ( ΣΔT) is started. This integration process is continued until an affirmative determination is made in S105 described later.

  In S105, the ECU 9 determines whether or not the detected value (input gas temperature) Tin of the first temperature sensor 6 and the detected value (output gas temperature) Tout of the second temperature sensor 7 are equal (or the input gas temperature Tin). It is determined whether or not the difference from the outgas temperature Tout has become a certain value or less.

If a negative determination is made in S105, the ECU 9 returns to S104 described above. On the other hand, if an affirmative determination is made in S105, the ECU 9 proceeds to S106. S1
In 06, the ECU 9 determines whether or not the integrated value ΣΔT calculated in S104 is greater than or equal to the determination reference value α. The determination reference value α corresponds to the integrated value ΣΔT when the selective catalytic reduction catalyst can exhibit the necessary minimum purification capacity, and is a value smaller than the integrated value when the new reduction state is in effect.

  If an affirmative determination is made in S106 (ΣΔT ≧ α), the ECU 9 proceeds to S107 and determines that the selective catalytic reduction catalyst is normal. On the other hand, when a negative determination is made in S106 (ΣΔT <α), the ECU 9 proceeds to S108 and determines that the selective catalytic reduction catalyst has deteriorated. In addition, when executing the process of S108, the ECU 9 sends information for prompting the driver of the vehicle to repair or replace the selective reduction catalyst from an output device (speaker, display, warning light, etc.) in the vehicle interior. You may make it output.

  As described above, when the ECU 9 executes the deterioration diagnosis routine of FIG. 4, the acquisition means and diagnosis means according to the present invention are realized. As a result, it is possible to accurately diagnose deterioration of the selective catalytic reduction catalyst.

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

  The operation of the internal combustion engine 1 may be stopped before the deterioration diagnosis is completed. If such a state continues, the chance of performing deterioration diagnosis decreases.

If the internal combustion engine 1 is leaned before the deterioration diagnosis is completed, the amount of moisture in the exhaust gas decreases and the input gas temperature decreases. For this reason, the change of the outgas temperature in the moisture adsorption process and the moisture desorption process tends to be slow. Further, if the internal combustion engine 1 is leaned before the deterioration diagnosis is completed, the bed temperature of the selective catalytic reduction catalyst reaches the desorption temperature range before the moisture adsorption amount of the selective catalytic reduction catalyst reaches the maximum moisture content. There is also the possibility of an increase.

  Therefore, when the internal combustion engine 1 is leaned before the deterioration diagnosis is completed, it is desirable to prevent the deterioration of the diagnosis accuracy by prohibiting the execution of the deterioration diagnosis. However, if the situation in which the deterioration diagnosis is prohibited continues, the opportunity for the deterioration diagnosis is reduced.

  As described above, if the opportunity for performing the deterioration diagnosis decreases, it may become impossible to detect the deterioration of the selective catalytic reduction catalyst at an early stage. Therefore, in the deterioration diagnosis system of the present embodiment, the amount of moisture in the exhaust gas when the operation of the internal combustion engine 1 is stopped before the deterioration diagnosis is completed or when the deterioration diagnosis is prohibited for a certain number of consecutive times. And / or a process for promoting the desorption of moisture from the selective catalytic reduction catalyst.

  Hereinafter, the execution procedure of the deterioration diagnosis in the present embodiment will be described with reference to FIG. FIG. 5 is a flowchart showing a deterioration diagnosis routine in the present embodiment. In FIG. 5, the same processes as those in the deterioration diagnosis routine (FIG. 4) of the first embodiment are denoted by the same reference numerals.

  In the deterioration diagnosis routine of FIG. 5, when an affirmative determination is made in S102, the ECU 9 proceeds to S201 and determines whether or not the internal combustion engine 1 is being operated lean. If an affirmative determination is made in S201, the ECU 9 proceeds to S202.

  In S202, the ECU 9 determines whether or not the count value C of the counter is equal to or greater than a predetermined value C0. The counter is a counter that counts the total number of times that the deterioration diagnosis is prohibited due to the lean operation of the internal combustion engine 1 and the number of times that the operation of the internal combustion engine 1 is stopped before the deterioration diagnosis is completed. The predetermined value C0 is the number of times that it can be determined that deterioration of the selective catalytic reduction catalyst cannot be detected at an early stage, and is the number of times that has been adapted in advance.

  When a negative determination is made in S202 (C <C0), the ECU 9 increments the count value of the counter by one in S204 and ends the execution of this routine. In this case, deterioration diagnosis of the selective catalytic reduction catalyst is not performed. That is, execution of deterioration diagnosis is prohibited.

  If an affirmative determination is made in S202 (C ≧ C0), the ECU 9 proceeds to S203 and executes a water increase process for increasing the amount of water in the exhaust. As a specific execution method of the moisture increase process, a method of reducing (rich) the air-fuel ratio of the air-fuel mixture used for combustion in the internal combustion engine 1 can be exemplified.

  Note that if the air-fuel ratio of the air-fuel mixture is reduced by increasing the fuel injection amount, the output of the internal combustion engine 1 may increase unnecessarily. For this reason, the injected fuel may be post-burned by injecting fuel from the fuel injection valve in the period from the latter half of the expansion stroke to the first half of the exhaust stroke.

  The ECU 9 proceeds to S103 when the execution of the process of S203 is completed and when a negative determination is made in S201. If an affirmative determination is made in S103, the ECU 9 proceeds to S205. In S205, the ECU 9 determines whether or not the count value of the counter is equal to or greater than a predetermined value C0.

If an affirmative determination is made in S205, the ECU 9 proceeds to S206. In S206, the ECU 9 executes an early desorption process for desorbing moisture adsorbed on the selective catalytic reduction catalyst at an early stage. As a method for desorbing moisture adsorbed on the selective catalytic reduction catalyst at an early stage, a method for raising the bed temperature of the selective catalytic reduction catalyst to the desorption temperature range at an early stage is effective.

  As a method for quickly raising the bed temperature of the selective catalytic reduction catalyst to the desorption temperature range, a method of increasing the exhaust temperature by increasing the load of the internal combustion engine 1 or a reducing component (for example, fuel) in the exhaust gas. Examples thereof include a method of generating oxidation reaction heat of the reducing agent in the selective reduction catalyst by the addition.

  When the ECU 9 finishes executing the process of S206, the ECU 9 proceeds to S104. If the determination in S205 is negative, the ECU 9 skips S206 and proceeds to S104.

  ECU9 performs the process of S105 following the process of S104. If a negative determination is made in S105, the ECU 9 proceeds to S207. In S207, the ECU 9 determines whether or not the operation of the internal combustion engine 1 has been stopped, in other words, whether or not the operation of the internal combustion engine 1 has been stopped before the deterioration diagnosis is completed. If a negative determination is made in S207, the ECU 9 returns to S104. On the other hand, if an affirmative determination is made in S207, the ECU 9 proceeds to S204.

  In addition, when the ECU 9 finishes executing the process of S107 or S108, the process proceeds to S208. In S208, the ECU 9 resets the count value C of the counter to zero.

  Thus, when the ECU 9 executes the deterioration diagnosis routine of FIG. 5, in addition to the acquisition means and the diagnosis means according to the present invention, the promotion means, the prohibition means, and the increase means are realized. Therefore, even if the situation where the operation of the internal combustion engine 1 is stopped before the deterioration diagnosis is completed or the situation where the deterioration diagnosis is prohibited continues, the deterioration diagnosis of the selective catalytic reduction catalyst can be performed. As a result, it becomes possible to detect deterioration of the selective catalytic reduction catalyst at an early stage.

1 internal combustion engine 2 exhaust passage 3 exhaust purification device 4 the urea addition valve 5 Tank 6 first temperature sensor 7 and the second temperature sensor 8 NO _x sensor 9 ECU

Claims (5)

A selective reduction catalyst disposed in an exhaust passage of the internal combustion engine;
An addition device for adding a reducing agent to the exhaust gas flowing upstream from the selective catalytic reduction catalyst;
Acquisition of a physical quantity that correlates with an endothermic amount when moisture adsorbed on the selective catalytic reduction catalyst is desorbed from the selective catalytic reduction catalyst under conditions where no reducing agent is supplied from the addition device to the selective catalytic reduction catalyst Means,
Diagnosing means for diagnosing the degree of deterioration of the selective catalytic reduction catalyst based on the physical quantity acquired by the acquiring means;
An exhaust purification device deterioration diagnosis system comprising:   2. The acquisition unit according to claim 1, wherein the temperature of the exhaust gas flowing out from the selective catalytic reduction catalyst from the time when the moisture adsorption amount of the selective catalytic reduction catalyst reaches the maximum water content is the temperature of the exhaust gas flowing into the selective catalytic reduction catalyst. A deterioration diagnosis system for an exhaust gas purification apparatus, wherein differences between the inflow exhaust gas temperature and the outflow exhaust gas temperature are integrated during a period up to the same time point, and the integrated value is acquired as a physical quantity correlated with the amount of heat absorption.   3. When the operation in which the internal combustion engine is stopped before the moisture adsorbed on the selective catalytic reduction catalyst has been desorbed for a certain number of times or more is continued in the first or second aspect, A deterioration diagnosis system for an exhaust gas purification apparatus, further comprising a promoting means for promoting temperature.   4. The prohibition of prohibiting diagnosis by the diagnostic means when the internal combustion engine is leaned for a predetermined period or more before the moisture adsorption amount of the selective catalytic reduction catalyst reaches a saturation amount according to any one of claims 1 to 3. A deterioration diagnosis system for an exhaust gas purification apparatus, further comprising means.   5. The exhaust emission control device according to claim 4, further comprising an increasing means for increasing the amount of water flowing into the selective catalytic reduction catalyst after the next start when the prohibition of diagnosis by the prohibiting means continues for a certain number of times. Deterioration diagnosis system.

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