JP2011220142A - Catalyst deterioration determination device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance accuracy of deterioration determination of a catalyst when a temperature of the catalyst varies.SOLUTION: A catalyst deterioration determination device for internal combustion engine includes: a purification rate calculator for calculating a purification rate of NOx on the basis of NOx concentration on upstream and downstream sides of a NOx catalyst; a purification rate corrector for correcting the purification rate to a value in a predetermined normal state, assuming that a proportion of an amount of ammonia which the NOx catalyst adsorbs to an amount of ammonia which the NOx catalyst can adsorb at a maximum is a determined value; and a determiner for determining the deterioration determination of a selective reduction NOx catalyst on the basis of the purification rate after corrected by the purification rate corrector during reduction of the temperature of the NOx catalyst.

Description

  The present invention relates to a catalyst deterioration determination device for an internal combustion engine.

When the difference between the measured value and the estimated value of the ammonia concentration in the exhaust downstream of the selective reduction type NOx catalyst (hereinafter referred to as NOx catalyst) that supplies urea as a reducing agent is larger than a predetermined value, the NOx catalyst A technique for determining that a deterioration has occurred is known (for example, see Patent Document 1).
At this time, the ammonia concentration according to the operating state of the internal combustion engine is estimated with reference to a map in which the ammonia concentration corresponding to the engine speed, the load, and the temperature of the NOx catalyst is set.

By the way, when estimating the ammonia concentration or NOx concentration in the exhaust gas downstream of the NOx catalyst, the NOx purification rate in the NOx catalyst (hereinafter, “NOx purification rate” is simply referred to as “purification rate”) is considered. Is done. In addition to the deterioration of the NOx catalyst, this purification rate is, for example, the ratio of NO ₂ in NOx flowing into the NOx catalyst (hereinafter, this ratio is referred to as the NO ₂ ratio) or N
It depends on the temperature of the Ox catalyst. Therefore, if the deterioration determination is performed using the purification rate obtained at that time as it is, it is determined that the purification rate is deteriorated although the purification rate is reduced due to a cause other than the deterioration. For this reason, the purification rate actually obtained may be corrected to a value in a predetermined reference state, and the ammonia concentration or NOx concentration may be estimated based on the corrected purification rate. That is, the value of the purification rate is calculated when the temperature of the NOx catalyst, the ratio of NO ₂ , etc. are the reference values. Further, the deterioration of the NOx catalyst can be determined based on the corrected purification rate.

Here, the purification rate also varies depending on the adsorption ratio of ammonia in the NOx catalyst. The adsorption ratio is the ammonia amount adsorbed by the NOx catalyst (hereinafter referred to as ammonia adsorption amount) relative to the ammonia amount that can be adsorbed to the maximum by the NOx catalyst (hereinafter referred to as maximum ammonia adsorption amount). Here, since it is difficult to measure the ammonia adsorption amount, a preset fixed value is used as this value. In other words, an assumed value is used for the adsorption rate instead of an actual value, and the purification rate is corrected based on the assumed value of the adsorption rate.

However, since the maximum ammonia adsorption amount changes when the temperature of the NOx catalyst changes, the adsorption ratio also actually changes due to the temperature change of the NOx catalyst. For this reason, it is difficult to accurately obtain the purification rate during a transient operation in which the temperature of the NOx catalyst changes.

JP 2006-125323 A JP 2002-250220 A JP 2009-293444 A

  The present invention has been made in view of the above-described problems, and an object thereof is to further improve the accuracy of determination of catalyst deterioration when the temperature of the catalyst changes.

In order to achieve the above object, an internal combustion engine catalyst deterioration determination apparatus according to the present invention provides:
Selective reduction type NOx which is provided in an exhaust passage of an internal combustion engine and selectively reduces NOx by a reducing agent
A catalyst,
Reducing agent supply means for supplying a reducing agent into the exhaust gas upstream of the selective reduction type NOx catalyst;
Upstream detection means for detecting the NOx concentration in the exhaust upstream from the selective reduction type NOx catalyst;
Downstream detection means for detecting the NOx concentration in the exhaust downstream of the selective reduction type NOx catalyst;
Temperature detecting means for detecting the temperature of the selective reduction type NOx catalyst;
In the internal combustion engine catalyst deterioration determination device provided with
A purification rate calculation means for calculating a NOx purification rate in the selective reduction type NOx catalyst based on the NOx concentration detected by the upstream detection means and the downstream detection means;
Assuming that the ratio of the ammonia amount adsorbed by the selective reduction NOx catalyst to the ammonia amount that can be adsorbed to the maximum by the selective reduction NOx catalyst is a predetermined value, the purification rate is set to a value in a predetermined reference state. Purification rate correction means for correcting,
Deterioration determination of the selective reduction type NOx catalyst is performed based on a post-correction purification rate that is a purification rate after being corrected by the purification rate correction unit when the temperature detected by the temperature detection unit is decreasing. A determination means;
Is provided.

Here, when the temperature of the NOx catalyst decreases, the maximum ammonia adsorption amount (ammonia amount that can be adsorbed to the maximum by the selective reduction type NOx catalyst) increases. However, even if the maximum ammonia adsorption amount is increased, ammonia is not immediately adsorbed to the NOx catalyst. Therefore, at the time when the temperature of the NOx catalyst is lowered or immediately after that, the adsorption ratio (selective reduction type) Ratio of the amount of ammonia adsorbed by the selective reduction type NOx catalyst to the amount of ammonia that can be adsorbed to the maximum by the NOx catalyst)
Becomes lower. Here, since the NOx purification rate is affected by the adsorption rate, the purification rate correction means corrects the purification rate according to at least the adsorption rate. This correction is performed to convert the purification rate obtained by the purification rate calculation means into a value in a predetermined reference state. This reference state is a state in which, for example, the NO ₂ ratio, the temperature of the NOx catalyst, and the adsorption ratio are the respective reference values. In other words, the purification rate correction means can correct the purification rate also by, for example, the NO ₂ ratio and the temperature of the NOx catalyst.

By the way, the adsorption ratio before correction is set to a predetermined value because it is difficult to obtain an accurate value. The predetermined value here is a value that the adsorption ratio can take or an ideal value, and can be set to 100%, for example. However, since the actual adsorption rate decreases during the transition, the difference between the purification rate after correction using the accurate adsorption rate and the corrected purification rate obtained by the purification rate correction means becomes large. . Note that the purification rate after correction using an accurate adsorption ratio is the purification rate when corrected correctly, and can be the corrected purification rate obtained during steady operation. The purification rate after correction using this accurate adsorption rate is substantially the same as during steady operation before the NOx catalyst temperature drops because the effects of NO ₂ ratio, NOx catalyst temperature, adsorption rate, etc. have been removed. Value. On the other hand, the purification rate correction means corrects the purification rate with the adsorption ratio as a predetermined value. Therefore, when the temperature of the NOx catalyst decreases, the corrected purification rate decreases even if the NOx catalyst does not deteriorate.

On the other hand, the maximum ammonia adsorption amount decreases as the degree of deterioration of the NOx catalyst increases. Further, as the degree of deterioration of the NOx catalyst increases, the increase amount of the maximum ammonia adsorption amount with respect to the temperature decrease amount decreases. For this reason, the actual adsorption ratio at the time of transition in which the temperature of the NOx catalyst is lowered becomes higher as the degree of deterioration increases. That is, NOx
The actual amount of decrease in the adsorption ratio when the temperature of the catalyst decreases is smaller as the degree of deterioration of the NOx catalyst is larger. Then, the greater the degree of deterioration of the NOx catalyst, the smaller the amount of reduction in the post-correction purification rate obtained by the purification rate correction means.

As described above, the amount of reduction in the post-correction purification rate when the temperature of the NOx catalyst is lowered varies depending on the degree of deterioration of the NOx catalyst. Therefore, it is possible to determine the deterioration of the NOx catalyst according to the corrected purification rate.

In the present invention, the determination means, when the amount of decrease in the corrected purification rate is equal to or less than a determination value for determining whether the selective reduction NOx catalyst is normal or deteriorated, It can be determined that the selective reduction type NOx catalyst has deteriorated.

  That is, as the degree of deterioration of the selective reduction type NOx catalyst is larger, the amount of reduction in the corrected purification rate when the temperature of the NOx catalyst is decreased becomes smaller. It can be determined that the catalyst has deteriorated.

  In addition to the reduction amount of the corrected purification rate, the reduction rate of the corrected purification rate (the reduction amount per unit time), the difference between the target value of the corrected purification rate and the value obtained by the purification rate correction means, etc. Thus, it is possible to determine the deterioration of the NOx catalyst.

  According to the present invention, it is possible to further improve the accuracy of the catalyst deterioration determination when the temperature of the catalyst changes.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its exhaust system. It is a graph showing the relationship between the temperature and NO ₂ ratio and purification rate of the NOx catalyst. It is a graph showing the relationship between the temperature and NO ₂ ratio and purification rate of the NOx catalyst when the adsorption rate is not 100%. It is the figure which showed the relationship between the temperature of a NOx catalyst, and the maximum ammonia adsorption amount. 4 is a time chart showing changes in temperature, ammonia adsorption amount, adsorption ratio, and corrected purification rate in a normal NOx catalyst. 3 is a time chart showing changes in temperature, ammonia adsorption amount, adsorption rate, and corrected purification rate in a deteriorated NOx catalyst. 3 is a time chart showing the transition of the temperature, the ammonia adsorption amount, the adsorption ratio, and the purification rate of the NOx catalyst. It is the flowchart which showed the flow of deterioration determination of the NOx catalyst which concerns on an Example.

  Hereinafter, a specific embodiment of a catalyst deterioration determination device for an internal combustion engine according to the present invention will be described based on the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its exhaust system according to the present embodiment. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders. In this embodiment, a urea SCR system is employed.

  An exhaust passage 2 is connected to the internal combustion engine 1. In the middle of the exhaust passage 2, a selective reduction type NOx catalyst 4 (hereinafter referred to as NOx catalyst 4) is provided.

An injection valve 5 that injects a reducing agent into the exhaust gas in the exhaust passage 2 upstream of the NOx catalyst 4.
Is attached. As the reducing agent, urea water is used. The injection valve 5 is opened by a signal from the ECU 10 described later and injects urea water into the exhaust gas. In this embodiment, the injection valve 5 corresponds to the reducing agent supply means in the present invention.

The urea water injected from the injection valve 5 is hydrolyzed by the heat of the exhaust gas to become ammonia (NH ₃ ) and supplied to the NOx catalyst 4. This NH ₃ reduces NOx. The injection amount and injection timing of urea water from the injection valve 5 can be feedback controlled based on, for example, the NOx purification rate in the NOx catalyst 4.

A first NOx sensor 7 for measuring the NOx concentration in the exhaust is attached to the exhaust passage 2 upstream of the injection valve 5. Further, in the exhaust passage 2 downstream of the NOx catalyst 4, N in the exhaust gas is exhausted.
A second NOx sensor 8 for measuring the Ox concentration and a temperature sensor 9 for measuring the temperature of the exhaust are attached. In the present embodiment, the first NOx sensor 7 corresponds to the upstream side detection means in the present invention. In the present embodiment, the second NOx sensor 8 corresponds to the downstream side detection means in the present invention. Further, in the present embodiment, the temperature sensor 9 corresponds to the temperature detecting means in the present invention. Instead of measuring the NOx concentration by the first NOx sensor 7, the NOx concentration may be estimated based on the operating state of the internal combustion engine 1. For example, the relationship between the engine speed and the engine load and the NOx concentration may be obtained in advance through experiments or the like and stored.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 controls the operation state of the internal combustion engine 1 according to the operation conditions of the internal combustion engine 1 and the request of the driver.

  In addition to the above sensors, the ECU 10 outputs an electric signal corresponding to the amount of depression of the accelerator pedal 11 by the driver to detect the engine load, and an accelerator position sensor 12 for detecting the engine speed. 13 are connected via electric wiring, and the output signals of these various sensors are input to the ECU 10.

  On the other hand, the injection valve 5 is connected to the ECU 10 via electric wiring, and the ECU 10 controls the opening and closing timing of the injection valve 5.

Then, the ECU 10 calculates the NOx purification rate in the NOx catalyst 4 (hereinafter, “NOx purification rate” is simply referred to as “purification rate”). The purification rate is the amount of NOx purified by the NOx catalyst 4 with respect to the amount of NOx flowing into the NOx catalyst 4. The amount of NOx purified by the NOx catalyst 4 can be obtained as the difference between the amount of NOx flowing into the NOx catalyst 4 and the amount of NOx flowing out of the NOx catalyst 4. The purification rate can be obtained by replacing the NOx amount with the NOx concentration.

Here, the purification rate includes the temperature of the NOx catalyst 4, the NOx, in addition to the degree of deterioration of the NOx catalyst 4.
NO ₂ ratio (hereinafter, “NO ₂ ratio in NOx” is simply referred to as “NO ₂ ratio”)
The adsorption ratio (that is, the amount of ammonia adsorbed on the NOx catalyst 4 with respect to the amount of ammonia that can be adsorbed to the maximum by the NOx catalyst 4) also varies. For example, as the temperature of the NOx catalyst 4 they are high, also closer to NO ₂ ratio is 50%, further increases the purification rate closer to 100% adsorption percentage. Therefore, it is necessary to distinguish between the case where the purification rate is low due to these factors and the case where the purification rate is low due to deterioration of the NOx catalyst 4.
For this reason, in this embodiment, the purification rate is corrected based on these physical quantities that affect the purification rate. That is, the purification rate actually obtained is corrected to the purification rate in the reference state. The reference state is a state where the temperature of the NOx catalyst 4 and the NO ₂ ratio are the respective reference values. The value obtained in this way is used as the corrected purification rate. Note that the relationship between the temperature and NO ₂ ratio of the NOx catalyst 4 and the correction value of the purification rate is obtained in advance through experiments and mapped. Further, it is assumed that the adsorption ratio before correction is, for example, 100% because it is difficult to obtain accurately.

Here, FIG. 2 is a graph showing the relationship between the temperature and NO ₂ ratio of the NOx catalyst 4 and the purification rate. A and B in FIG. 2 are the purification rates actually obtained, and C is the corrected purification rate. In FIG. 2, the reference value of the temperature of the NOx catalyst 4 is, for example, 240 ° C., the reference value of the NO ₂ ratio is, for example, 50%, and the reference value of the adsorption ratio is, for example, 100%. The purification rate indicated by A is the purification rate when the NO ₂ ratio is lower than the reference value and the temperature of the NOx catalyst 4 is lower than the reference value, and assuming that these physical quantities are the reference values, The corrected purification rate indicated by C is obtained. Further, since the purification rate indicated by B is the purification rate when the NO ₂ ratio is higher than the reference value and the temperature of the NOx catalyst 4 is lower than the reference value, it is assumed that these physical quantities are reference values. Is a post-correction purification rate indicated by C. The reference values for the temperature of the NOx catalyst 4, the NO ₂ ratio, and the adsorption ratio may be other values.

By the way, if the adsorption ratio is actually 100%, the corrected purification rate can be obtained accurately, but if it is not actually 100%, the corrected purification rate is obtained accurately. Can not be. For example, during a transient operation in which the temperature of the NOx catalyst 4 changes, the maximum ammonia adsorption amount increases as the temperature decreases, and the maximum ammonia adsorption amount decreases as the temperature increases. In particular, when the temperature of the NOx catalyst 4 is lowered, ammonia is not immediately adsorbed to the NOx catalyst 4, so that the adsorption rate is also lowered.

As a result, even if the corrected purification rate is calculated assuming that the reference value of the adsorption rate is 100%, the actual adsorption rate is not 100%, and thus the corrected purification rate does not indicate an accurate value. . Here, FIG. 3 shows the temperature and NOx of the NOx catalyst 4 when the adsorption ratio is not 100%.
It is the figure which showed the relationship between ₂ ratio and a purification rate. In FIG. 3, A and B are the purification rates actually obtained, C is the corrected purification rate when the adsorption ratio is accurately determined, and D and E are the adsorption ratio accurately determined. This is the post-correction purification rate when not.

  That is, in FIG. 3, the difference between C and D and the difference between C and E occur in the corrected purification rate. As described above, the post-correction purification rate cannot be accurately obtained. Therefore, if the deterioration determination of the NOx catalyst 4 is performed based on the post-correction purification rate, an erroneous determination may be made.

Here, FIG. 4 is a graph showing the relationship between the temperature of the NOx catalyst 4 and the maximum ammonia adsorption amount. A solid line is a value at the time of a new article, and a broken line is a value at the time of deterioration. The lower the temperature of the NOx catalyst 4, the greater the maximum ammonia adsorption amount. In addition, the maximum ammonia adsorption amount is smaller when it is deteriorated than when it is new. The change amount of the maximum ammonia adsorption amount with respect to the change amount of the temperature of the NOx catalyst 4 is smaller at the time of deterioration than when it is new. That is, the amount of change in the adsorption rate when the temperature of the NOx catalyst 4 changes is smaller when the NOx catalyst 4 is deteriorated than when it is new.

Then, a difference appears between the amount of change in the post-correction purification rate when the temperature of the NOx catalyst 4 is lowered and when it is new. Therefore, the deterioration determination of the NOx catalyst 4 can be performed based on the amount of change in the post-correction purification rate when the temperature of the NOx catalyst 4 decreases.

FIG. 5 is a time chart showing changes in temperature, ammonia adsorption amount, adsorption ratio, and corrected purification rate in the normal NOx catalyst 4. Note that the period from F to G is a period during which the temperature of the NOx catalyst 4 decreases due to deceleration. The solid line in the amount of adsorbed ammonia shows the NOx catalyst 4
The amount of ammonia adsorbed on the one-dot chain line is the maximum ammonia adsorption amount. Further, the solid line in the adsorption ratio indicates an actual value, and the alternate long and short dash line indicates a reference value, that is, 100%. The solid line in the post-correction purification rate is a value when the pre-correction adsorption rate is assumed to be 100%. The one-dot chain line in the post-correction purification rate is a value when the purification rate is accurately corrected to the reference state, and may be a value calculated with an accurate adsorption rate. Normal NOx
The post-correction purification rate of the catalyst 4 may be a value that converges during steady operation. The corrected purification rate when the purification rate is accurately corrected to the reference state is set as the target value of the corrected purification rate.

As shown in FIG. 5, when the temperature of the NOx catalyst 4 decreases, the maximum ammonia adsorption amount increases accordingly, but the degree of increase in the amount of ammonia adsorbed on the NOx catalyst 4 is lower than that. . For this reason, the adsorption ratio is gradually increased and then gradually increased to approach the reference value. Here, the corrected purification rate is calculated on the assumption that the adsorption rate is 100%. Therefore, when the actual adsorption rate is reduced, the corrected purification rate is calculated without removing the effect of the decrease. The If the purification rate is corrected based on the actual adsorption rate, correction is performed so as to increase the reduced adsorption rate to the reference value, and thus correction is performed in the direction of increasing the corrected purification rate. However, if the adsorption rate is assumed to be 100%, this correction (correction in the direction of increasing the post-correction purification rate) is not performed, so the post-correction purification rate is lowered due to the effect of the decrease in the adsorption rate. . Therefore, due to the change in the adsorption ratio, the post-correction purification rate is also gradually reduced from the target value and then gradually increases to approach the target value. Thus, the amount of change in the post-correction purification rate when the temperature of the NOx catalyst 4 decreases is relatively large.

On the other hand, FIG. 6 is a time chart showing changes in temperature, ammonia adsorption amount, adsorption ratio, and corrected purification rate in the deteriorated NOx catalyst 4. Note that the period from F to G is the same as the period shown in FIG. Further, the one-dot chain line in the post-correction purification rate indicates the target value of the normal NOx catalyst 4 that is the same as the one-dot chain line shown in FIG. 5, and the two-dot chain line is the target value of the deteriorated NOx catalyst 4. The target value of the deteriorated NOx catalyst 4 is a value when the purification rate of the deteriorated NOx catalyst 4 is accurately corrected to the reference state, and may be a value calculated with an accurate adsorption ratio. Alternatively, the post-correction purification rate of the deteriorated NOx catalyst 4 may be a value that converges during steady operation.

As shown in FIG. 6, when the temperature of the NOx catalyst 4 decreases, the maximum ammonia adsorption amount increases accordingly, but the degree of increase in the ammonia amount adsorbed on the NOx catalyst 4 is lower than that. . However, the degree of increase (inclination) and the amount of increase in the maximum ammonia adsorption amount at this time are small compared to the normal NOx catalyst 4. For this reason, the amount of decrease in the adsorption rate is
It becomes smaller compared to the normal catalyst 4. Then, the amount of decrease in the corrected purification rate is also smaller than that of the normal catalyst 4. This becomes more remarkable as the degree of deterioration of the NOx catalyst 4 increases. Thus, the amount of change in the post-correction purification rate when the temperature of the NOx catalyst 4 decreases is relatively small. That is, it can be determined that the degree of deterioration of the NOx catalyst 4 is larger as the amount of change in the post-correction purification rate when the temperature of the NOx catalyst 4 is lower is smaller.

In this embodiment, if the amount of decrease in the post-correction purification rate when the temperature of the NOx catalyst 4 decreases is equal to or less than the determination value, it is determined that the NOx catalyst 4 has deteriorated. Here, the determination value is the upper limit value of the reduction amount of the post-correction purification rate in the deteriorated NOx catalyst 4. This determination value is obtained in advance by experiments or the like. In this way, it is possible to determine the deterioration of the NOx catalyst 4 based on the corrected purification rate obtained during transient operation.

Note that the difference between the maximum value of the purification rate after correction before the temperature of the NOx catalyst 4 is lowered (or the target value) and the minimum value of the purification rate after correction when the temperature is lowered is the NOx catalyst. 4 can be the amount of decrease in the post-correction purification rate when the temperature decreases. In addition, the amount of decrease in the post-correction purification rate during the specified period can be the amount of decrease in the post-correction purification rate when the temperature of the NOx catalyst 4 decreases.

Further, if the rate of decrease in the post-correction purification rate when the temperature of the NOx catalyst 4 is reduced is equal to or less than the determination value, it can be determined that the NOx catalyst 4 has deteriorated. Here, in the deteriorated NOx catalyst 4, the increase in the maximum ammonia adsorption amount at the time of the temperature decrease is moderate, so the decrease in the post-correction purification rate is also moderate. That is, the reduction rate of the post-correction purification rate becomes small. Note that the determination value in this case is the upper limit value of the reduction rate of the post-correction purification rate in the deteriorated NOx catalyst 4.
This determination value is obtained in advance by experiments or the like. Further, the reduction rate may be a reduction amount per unit time or may be a reduction amount in a specified period. Even in this case, it is possible to determine the deterioration of the NOx catalyst 4 based on the corrected purification rate obtained during the transient operation.

  In this embodiment, after the degree of deterioration of the NOx catalyst 4 is calculated, the reducing agent addition amount from the injection valve 5 may be corrected according to the degree of deterioration of the NOx catalyst 4. Here, it is also conceivable to perform feedback control of the reducing agent addition amount based on the corrected purification rate. However, when the post-correction purification rate does not show an accurate value, the reducing agent addition amount is not appropriate. In feedback control, it takes time until the adsorption ratio converges.

  On the other hand, when the temperature of the NOx catalyst 4 is lowered, the maximum ammonia adsorption amount increases. Therefore, if the reducing agent is added to the NOx catalyst 4 and the adsorption amount is rapidly increased, the purification rate can be quickly increased.

  Therefore, in this embodiment, after determining the deterioration of the NOx catalyst 4, a physical quantity that affects the increase / decrease in the adsorption ratio, such as the temperature of the NOx catalyst 4, the amount of reducing agent added, the purification rate, the amount of change in the adsorption ratio, Learn the relationship between changing periods. Then, when the adsorption ratio changes, the amount of change in the adsorption ratio is predicted according to the learned relationship, and the reducing agent addition amount is adjusted. That is, feedforward control of the reducing agent addition amount is performed. Thereby, an adsorption | suction ratio can be raised rapidly and it can be made to converge. The amount of change in the adsorption ratio and the period of change are correlated with the amount of change in the corrected purification rate and the period of change. Can be used. For example, as the predicted value of the change amount of the adsorption ratio is larger, the reducing agent addition amount is increased.

In this way, when the adsorption ratio changes, the amount of change in the adsorption ratio can be predicted, and the reducing agent addition amount can be adjusted in advance based on this predicted value, so feedback based on the purification rate Compared with the control, the adsorption rate can be quickly increased and the amount of ammonia passing without reacting with the NOx catalyst 4 can be reduced.

FIG. 7 is a time chart showing the transition of the temperature, the ammonia adsorption amount, the adsorption ratio, and the purification rate of the NOx catalyst 4. The solid line in the ammonia adsorption amount is the ammonia adsorption amount when the reducing agent addition amount is feedforward-controlled according to this embodiment, and the broken line is the ammonia adsorption amount when the reducing agent addition amount is feedback-controlled based on the purification rate. The alternate long and short dash line is the maximum ammonia adsorption amount. In addition, the alternate long and short dash line in the adsorption ratio indicates the reference value, that is, 100%, the solid line is the adsorption ratio when the feed amount of the reducing agent added according to the present embodiment is controlled, and the broken line indicates the purification rate. This is the adsorption ratio when the amount of reducing agent added is feedback controlled. The alternate long and short dash line in the purification rate indicates the target value, the solid line is the purification rate when the feed amount of the reducing agent is controlled according to this embodiment, and the broken line is the reducing agent based on the purification rate. This is the purification rate when the addition amount is feedback controlled.

As shown in FIG. 7, when the temperature of the NOx catalyst 4 decreases, the maximum adsorption amount increases accordingly, but compared with that, the degree of increase in the ammonia adsorption amount when the reducing agent addition amount is feedback-controlled. Is low. On the other hand, the increase degree of the ammonia adsorption amount when the reducing agent addition amount is feedforward-controlled is higher than the increase degree of the ammonia adsorption amount when the reducing agent addition amount is feedback controlled. That is, when the reducing agent addition amount is fed forward, the ammonia adsorption amount is rapidly increased by increasing the reducing agent addition amount as the temperature of the NOx catalyst 4 decreases. As a result, the adsorption ratio also increases more quickly when the feedforward control is performed than when the feedback control is performed. For this reason, the purification rate also increases more quickly when the feedforward control is performed than when the feedback control is performed.

  In this way, by adjusting the amount of reducing agent added by feedforward control, the purification rate can be increased more quickly than feedback control by the purification rate, and ammonia can be prevented from passing through the catalyst 4.

FIG. 8 is a flowchart showing a flow for determining deterioration of the NOx catalyst 4 according to this embodiment. This routine is repeatedly executed by the ECU 10 every predetermined time.

In step S101, it is determined whether a condition for determining deterioration of the NOx catalyst 4 is satisfied. This condition is a condition necessary for accurately determining the deterioration of the NOx catalyst 4. For example, it is determined whether the operating state (for example, engine speed and engine load) of the internal combustion engine 1 is within a predetermined range and the temperature of the NOx catalyst 4 is within a predetermined range. Step S10
When an affirmative determination is made at 1, the process proceeds to step S102, and when a negative determination is made, the process proceeds to step S110.

In step S102, the corrected purification rate is calculated. First, the purification rate is calculated based on the NOx concentration obtained by the first NOx sensor 7 and the second NOx sensor 8. If the NOx concentration obtained by the first NOx sensor 7 is the upstream NOx concentration and the NOx concentration obtained by the second NOx sensor 8 is the downstream NOx concentration, the purification rate can be calculated by the following equation.
Purification rate = (Upstream NOx concentration−Downstream NOx concentration) / (Upstream NOx concentration)
Note that the NOx amount passing through each sensor per unit time may be calculated from the NOx concentration obtained by each sensor, and the purification rate may be calculated using the NOx amount.

This purification rate is corrected based on the temperature obtained by the temperature sensor 9 and the NO ₂ ratio, and the corrected purification rate is calculated. The NO ₂ ratio can be estimated based on the engine speed, the amount of fuel (which may be an engine load), the combustion temperature, and the like. Since a well-known technique can be used for this estimation, description is abbreviate | omitted.

The relationship between the temperature and NO ₂ ratio obtained by the temperature sensor 9 and the correction value of the purification rate is obtained in advance through experiments or the like, mapped, and stored in the ECU 10. In this embodiment, the ECU 10 that calculates the purification rate in step S102 corresponds to the purification rate calculation means in the present invention, and the ECU 10 that calculates the corrected purification rate in step S102 is the purification rate correction means in the present invention. It corresponds to.

In step S103, it is determined whether or not the adsorption ratio has changed by a specified value or more within a specified period. In this step, it is determined whether or not it is a transient time when the temperature of the NOx catalyst 4 decreases,
It is determined whether or not the temperature of the NOx catalyst 4 has decreased so that the deterioration determination of the NOx catalyst 4 can be performed. For the specified period and specified value in this step, optimum values are obtained in advance through experiments or the like. If an affirmative determination is made in step S103, the process proceeds to step S104, and if a negative determination is made, the process proceeds to step S107.

In step S104, it is determined whether the amount of change in the corrected purification rate is greater than a determination value. This amount of change may be, for example, the difference between the maximum value and the minimum value of the post-correction purification rate. This maximum value may be the target value of the purification rate. The determination value is the upper limit value of the amount of change in the post-correction purification rate in the deteriorated NOx catalyst 4. This determination value is obtained in advance by experiments or the like. In this embodiment, the ECU 10 that processes step S104 corresponds to the determination means in the present invention.

If an affirmative determination is made in step S104, the process proceeds to step S105, where NOx
It is determined that the catalyst 4 is normal. On the other hand, if a negative determination is made in step S104, the process proceeds to step S106, where it is determined that the NOx catalyst 4 has deteriorated. Here, normal means that the degree of deterioration does not exceed an allowable limit. Deteriorating means that the degree of deterioration exceeds an allowable limit.

In step S107, it is determined whether the corrected purification rate is higher than a threshold value. Since this step is executed when the adsorption ratio does not change much, it can be said that the corrected purification rate shows an accurate value. Therefore, the deterioration determination of the NOx catalyst 4 is performed using the corrected purification rate value as it is. In this case, the greater the degree of deterioration of the NOx catalyst 4, the lower the corrected purification rate. The threshold value is an upper limit value of the post-correction purification rate when the NOx catalyst 4 is deteriorated.

If an affirmative determination is made in step S107, the process proceeds to step S108 and NOx
It is determined that the catalyst 4 is normal. On the other hand, if a negative determination is made in step S107, the process proceeds to step S109, where it is determined that the NOx catalyst 4 has deteriorated.

In step S110, storage (learning) of the relationship between the physical quantity that affects the increase / decrease in the adsorption ratio such as the temperature of the NOx catalyst 4, the reducing agent addition amount, the purification rate, the amount of change in the adsorption ratio and the changing period. It is determined whether or not is completed. If an affirmative determination is made in step S110, the process proceeds to step S111. If a negative determination is made, this routine is terminated.

  In step S111, it is determined whether the adsorption ratio has changed. That is, it is determined whether or not the feedforward control of the reducing agent addition amount according to the present embodiment can be performed. If an affirmative determination is made in step S111, the process proceeds to step S112, and if a negative determination is made, this routine is terminated.

  In step S112, the reducing agent addition amount is increased or decreased based on the learning result in step S110.

As described above, according to this embodiment, it is possible to determine the deterioration of the NOx catalyst 4 based on the amount of change in the post-correction purification rate when the temperature of the NOx catalyst 4 decreases. This makes it possible to determine the deterioration of the NOx catalyst 4 even during transient operation.

In addition, since the amount of addition of the reducing agent can be feedforward controlled in accordance with the degree of deterioration of the NOx catalyst 4, it is possible to increase the purification rate and suppress the reducing agent from passing through the NOx catalyst 4.

1 Internal combustion engine 2 Exhaust passage 4 Selective reduction type NOx catalyst 5 Injection valve 7 First NOx sensor 8 Second NOx sensor 9 Temperature sensor 10 ECU
11 Accelerator pedal 12 Accelerator opening sensor 13 Crank position sensor

Claims (2)

A selective reduction type NOx catalyst that is provided in an exhaust passage of the internal combustion engine and selectively reduces NOx by a reducing agent;
Reducing agent supply means for supplying a reducing agent into the exhaust gas upstream of the selective reduction type NOx catalyst;
Upstream detection means for detecting the NOx concentration in the exhaust upstream from the selective reduction type NOx catalyst;
Downstream detection means for detecting the NOx concentration in the exhaust downstream of the selective reduction type NOx catalyst;
Temperature detecting means for detecting the temperature of the selective reduction type NOx catalyst;
In the internal combustion engine catalyst deterioration determination device provided with
A purification rate calculation means for calculating a NOx purification rate in the selective reduction type NOx catalyst based on the NOx concentration detected by the upstream detection means and the downstream detection means;
Assuming that the ratio of the ammonia amount adsorbed by the selective reduction NOx catalyst to the ammonia amount that can be adsorbed to the maximum by the selective reduction NOx catalyst is a predetermined value, the purification rate is set to a value in a predetermined reference state. Purification rate correction means for correcting,
Deterioration determination of the selective reduction type NOx catalyst is performed based on a post-correction purification rate that is a purification rate after being corrected by the purification rate correction unit when the temperature detected by the temperature detection unit is decreasing. A determination means;
An apparatus for determining catalyst deterioration of an internal combustion engine, comprising: The determination means, when the amount of decrease in the corrected purification rate is equal to or less than a determination value for determining whether the selective reduction NOx catalyst is normal or deteriorated, the selective reduction NOx
2. The catalyst deterioration determination apparatus for an internal combustion engine according to claim 1, wherein it is determined that the catalyst has deteriorated.

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