JP2005248760A - Reducing agent adding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reducing agent adding device, for suitably maintaining reduction processing by adding reducing agent even when clogging occurs. <P>SOLUTION: The reducing agent of an amount depending on a target adding amount Fa which is set based on an operational status of an internal combustion engine is added from an adding valve disposed upstream in exhaust to the exhaust catalyst. It is determined whether the exhaust catalyst is clogged or not, and increase correction of the target adding amount Fa is performed (S110) if the clogging is determined (YES in S108). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a reducing agent addition apparatus for adding a reducing agent to an exhaust purification catalyst of an internal combustion engine that performs combustion at a lean air-fuel ratio, such as a diesel engine or a gasoline engine that performs lean combustion.

  In this type of reducing agent addition device, nitrogen gas temporarily stored in the exhaust purification catalyst is supplied by supplying the reducing agent to the exhaust purification catalyst from an addition valve provided upstream of the exhaust purification catalyst. Oxides (NOx) and sulfur oxides (SOx) that poison the exhaust purification catalyst are desorbed and reduced.

Here, since the added reducing agent is difficult to atomize when the exhaust temperature is low, the reducing agent tends to adhere to the wall surface of the exhaust passage. When the reducing agent adheres to the wall surface of the exhaust passage in this way, the amount of the reducing agent that reaches the exhaust purification catalyst is insufficient, and the reduction treatment with the reducing agent does not function sufficiently. Therefore, conventionally, the amount of the reducing agent adhering to the wall surface is estimated based on the exhaust temperature, and the amount of reducing agent added is corrected by increasing the amount corresponding to the amount adhering to the wall surface, thereby suppressing the shortage of the reducing agent. Has been proposed (see, for example, Patent Document 1).
JP-A-6-129238

  According to the conventional apparatus, when a reducing agent adheres to the wall surface of the exhaust passage, adverse effects caused by the reducing agent can be suppressed. However, in the exhaust purification catalyst, the following inconveniences may occur in addition to the adverse effects caused by the wall surface adhesion.

  That is, in such an exhaust purification catalyst, so-called clogging may occur in which a hole through which exhaust passes is partially blocked by adhesion of fuel or soot in the exhaust. When such clogging occurs, a part of the added reducing agent comes to adhere to the catalyst end face of the clogged portion, and the amount of reducing agent adhering to the catalyst end face decreases to reach a saturated state. During the period, the reducing agent used for the reaction at the exhaust purification catalyst will be insufficient. This is not preferable because it prevents the NOx and SOx from being promptly released / reduced in the exhaust purification catalyst and causes a decrease in the purification performance of the exhaust purification catalyst.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a reducing agent addition device that can suitably maintain a reduction treatment by addition of a reducing agent even when clogging occurs. There is to do.

Hereinafter, means for achieving the above-described object and its operation and effects will be described.
In the first aspect of the present invention, an exhaust gas is supplied with an amount of reducing agent corresponding to a target addition amount set based on an operating state of an internal combustion engine from an addition valve provided upstream of an exhaust purification catalyst. In the reducing agent addition apparatus for adding to the catalyst, a determination means for determining whether or not the exhaust purification catalyst is clogged, and the target addition amount is corrected to be increased when it is determined that the exhaust purification catalyst is clogged. The gist of the present invention is to provide correction means.

  According to the above configuration, even when the exhaust purification catalyst is clogged and a part of the reducing agent adheres to the end surface of the catalyst, the target addition amount is corrected by increasing the target addition amount. The shortage of the reducing agent can be compensated, and the reduction treatment of the exhaust purification catalyst can be suitably executed.

  The invention according to claim 2 is the reducing agent addition apparatus according to claim 1, wherein the correction means increases the correction amount in the first half of the addition period of the reducing agent when the target addition amount is corrected to increase. The gist is to set it.

  When the reducing agent adheres to the end face of the catalyst due to clogging, the amount of adhesion is large immediately after the start of addition of the reducing agent, and then gradually decreases and becomes saturated. According to the said structure, the shortage of the reducing agent mentioned above can be eliminated at an early stage by promptly shifting to such a saturated state.

  Further, in the invention according to claim 3, in the reducing agent addition apparatus according to claim 1 or 2, the correction means sets the target addition amount so that the target addition amount is maximized immediately after the addition of the reducing agent. The gist is to do.

According to this configuration, it is possible to make the transition to the saturated state more quickly, and it is possible to resolve this shortage of the shortage of the reducing agent earlier.
Further, the invention according to claim 4 is the reducing agent addition apparatus according to any one of claims 1 to 3, wherein the correction means is configured such that the target addition amount increases with time from the start of addition of the reducing agent. The gist is to set this so that it gradually decreases.

  As described above, the amount of the reducing agent adhering to the catalyst end face gradually decreases after the addition is started. Therefore, the necessity for increasing the target addition amount gradually decreases. In this regard, according to the above configuration, it is possible to suppress the target addition amount from being unnecessarily increased.

  In addition, the invention according to claim 5 is the reducing agent addition apparatus according to any one of claims 1 to 4, wherein the addition of the reducing agent from the addition valve is intermittently performed in a plurality of times. Control means for driving and controlling the addition valve as described above, and the correction means sets the correction amount so as to maximize the correction amount for the first addition of the plurality of reducing agent additions. The gist.

  In the apparatus in which the addition of the reducing agent from the addition valve is intermittently performed in a plurality of times, the first addition among the plurality of times the reducing agent is added, as in the invention according to claim 5. It is desirable to adopt a configuration in which this is set so that the correction amount is maximized.

  Further, in the same configuration, the target addition amount is increased and corrected only for the first addition of the plurality of reducing agent additions, that is, the increase correction amount is substantially set to “0” for subsequent additions. It is possible to adopt a configuration in which no operation is performed. Alternatively, the increase correction amount required for the first addition among the plurality of reducing agent additions is maximized, and the subsequent increase correction amount is reduced, and each time addition is further performed in the same configuration, A configuration in which the increase correction amount is gradually reduced can also be adopted.

  Further, the invention according to claim 6 is the reducing agent addition apparatus according to any one of claims 1 to 5, wherein the exhaust purification catalyst has an upstream catalyst and a downstream catalyst, and the determination means. Detecting a bed temperature of the upstream catalyst and a bed temperature of the downstream catalyst by adding a reducing agent, and determining whether the upstream catalyst is clogged based on a comparison result of each bed temperature. Is the gist.

  When the exhaust purification catalyst has an upstream catalyst and a downstream catalyst, when the upstream catalyst is clogged, the amount of the reducing agent that reacts with the upstream catalyst is reduced by that amount. Is difficult to rise. Accordingly, the temperature relationship between these bed temperatures is different from that in the case where the upstream catalyst is not clogged. According to the above configuration, it is possible to determine whether or not the upstream catalyst is clogged based on the difference in temperature relationship.

  Further, the invention according to claim 7 is the reducing agent addition apparatus according to claim 6, wherein the correction means is based on a comparison result between the bed temperature of the upstream catalyst and the bed temperature of the downstream catalyst. The gist is to calculate the correction amount for the increase correction.

  As described above, when clogging occurs in the upstream catalyst, the bed temperature of each catalyst is different from that in the case where clogging does not occur in the upstream catalyst. Furthermore, such a difference becomes more prominent as the degree of clogging occurring in the upstream catalyst is larger. According to the above configuration, the target addition amount can be increased and corrected in accordance with the degree of occurrence of clogging in the upstream catalyst, and the shortage of the reducing agent can be suitably suppressed.

  The invention according to claim 8 is the reducing agent addition apparatus according to any one of claims 1 to 7, wherein the determination means adds a reducing agent and exhausts downstream of the exhaust purification catalyst. The gist is to detect a change in properties and determine the presence or absence of clogging based on the detection result.

  When clogging occurs in the exhaust purification catalyst, even if a reducing agent is added, the amount of reducing agent used for the reaction in the exhaust purification catalyst and the amount of exhaust purification catalyst are reduced by the amount that part of the reducing agent adheres to the catalyst end face. The amount of reducing agent that passes is reduced. Therefore, the properties of the exhaust gas after passing through the exhaust purification catalyst are different from those in the case where clogging does not occur. According to the above configuration, the presence or absence of clogging of the upstream catalyst can be determined based on the difference in the exhaust properties.

  The above-described attachment of the reducing agent to the catalyst end face becomes most noticeable when the exhaust temperature is low, that is, when the reducing agent added from the addition valve is difficult to atomize. For this reason, in the inventions described in the above claims, for example, a configuration in which the target addition amount is corrected to be increased on condition that the exhaust gas temperature is low may be employed. According to this configuration, it is possible to avoid unnecessary increase correction of the target addition amount.

Hereinafter, an embodiment in which the reducing agent supply apparatus according to the present invention is embodied will be described.
FIG. 1 is a block diagram showing a schematic configuration of a vehicle internal combustion engine and its peripheral devices to which the present embodiment is applied.

  As shown in FIG. 1, the internal combustion engine 10 is provided with a fuel injection valve 18 that directly injects fuel into the combustion chamber 16, and the fuel injection valve 18 is a pressure accumulation pipe to which fuel is supplied from a fuel pump 20. 22 is connected.

The intake passage 12 of the internal combustion engine 10 is provided with an intake air amount sensor 52 for detecting the amount of air taken into the combustion chamber 16 (intake air amount GA).
A catalyst device 30 is provided in the exhaust passage 14 of the internal combustion engine 10. The catalyst device 30 includes a plurality of catalysts each containing an exhaust purification catalyst.

  A NOx storage reduction catalyst is accommodated in the upstream upstream catalyst 32. With this NOx occlusion reduction catalyst, NOx is occluded in the NOx occlusion reduction catalyst when the exhaust gas is in an oxidizing atmosphere (lean) during engine operation. In a reducing atmosphere (stoichiometric or rich), NOx stored in the NOx storage reduction catalyst is released as nitrogen oxide (NO) and is reduced by hydrocarbon (HC) or carbon monoxide (CO). In this way, NOx is purified.

  A filter having a wall portion formed in a monolith structure is accommodated in the downstream catalyst 34 disposed downstream of the upstream catalyst 32, and exhaust gas passes through the minute holes in the wall portion. ing. The filter surface is coated with a NOx storage reduction catalyst. For this reason, NOx purification is performed as described above. Moreover, since particulate matter (PM) in the exhaust is trapped on the filter surface, the oxidation of PM is started by active oxygen generated during NOx occlusion in an oxidizing atmosphere, and the entire PM is oxidized by excess oxygen in the surroundings. . In a reducing atmosphere (stoichiometric or rich), oxidation of PM is promoted by a large amount of active oxygen generated from the NOx storage reduction catalyst. As a result, PM purification as well as NOx purification is performed.

Further, an oxidation catalyst 36 is disposed further downstream than the downstream catalyst 34, and HC and CO are oxidized and purified here.
The exhaust passage 14 of the internal combustion engine 10 is provided with a reducing agent addition device for adding fuel as a reducing agent into the exhaust. This reducing agent addition device is constituted by the fuel pump 20, the addition valve 44, a supply pipe 46 that connects the fuel pump 20 and the addition valve 44, and the like. The addition valve 44 is attached to the upstream side of the catalyst device 30 in the exhaust passage 14 (specifically, the exhaust manifold). Then, for example, when the reducing agent is added from the addition valve 44, the exhaust gas temporarily becomes a reducing atmosphere, whereby the NOx stored in the upstream catalyst 32 and the downstream catalyst 34 is reduced and purified, and further the downstream catalyst. In 34, the purification of PM is also executed.

  A first exhaust temperature sensor 54 for detecting an exhaust temperature (Tup) is disposed between the upstream catalyst 32 and the downstream catalyst 34 in the exhaust passage 14. Further, between the downstream catalyst 34 and the oxidation catalyst 36, a second exhaust temperature sensor 56 for detecting the exhaust temperature (Tlo) and an air-fuel ratio sensor 58 for detecting the air-fuel ratio of the exhaust, respectively. Has been placed.

  In the present embodiment, the PM regeneration control mode, the sulfur poisoning (hereinafter referred to as S poisoning) recovery control mode, the NOx reduction control mode, and the normal control mode are used as catalyst control modes for executing control processing for each catalyst. There are four types of modes. When a mode other than the normal control mode is selected, the reducing agent is added from the addition valve 44.

  In particular, the PM regeneration control mode is a mode in which PM accumulated in the downstream catalyst 34 is combusted and discharged as carbon dioxide (CO2) and water (H2O). The S poisoning recovery control mode is a mode in which sulfur is released when the NOx storage reduction catalyst in the upstream catalyst 32 and the downstream catalyst 34 is poisoned with S and the NOx storage capacity is reduced. In these modes, the catalyst bed temperature is increased (for example, 600 to 700 ° C.) by continuously repeating the addition of the reducing agent from the addition valve 44.

  The NOx reduction control mode is a mode in which NOx occluded by the NOx occlusion reduction catalyst in the upstream side catalyst 32 and the downstream side catalyst 34 is reduced to nitrogen (N2), CO2 and H2O and released. In this mode, the catalyst bed temperature is controlled to a relatively low temperature (for example, 250 to 500 ° C.) by intermittently adding the reducing agent from the addition valve 44 with a relatively long time.

  The electronic control unit 50 is mainly composed of a digital computer including a CPU, a ROM, a RAM and the like and a drive circuit for driving each device. The electronic control unit 50 reads output signals from various sensors such as the intake air amount sensor 52, the first exhaust temperature sensor 54, the second exhaust temperature sensor 56, and the air-fuel ratio sensor 58 described above. Then, the electronic control unit 50 executes the opening / closing control of the fuel injection valve 18 and the opening / closing control of the addition valve 44 based on the engine operation state obtained from these signals, the state of each catalyst, and the like. In the present embodiment, the electronic control unit 50 functions as a control unit that drives and controls the addition valve so that the addition of the reducing agent from the addition valve is intermittently executed.

Here, the S poison recovery mode will be described in detail.
The S poisoning recovery mode is selected on the condition that the S poisoning amount estimated based on the fuel injection amount, the reducing agent addition amount, and the like has become a predetermined value or more.

  When this mode is selected, temperature increase control is first started. Specifically, in addition to the normal fuel injection from the fuel injection valve 18, after injection for injecting fuel from the fuel injection valve 18 is performed in the expansion stroke, the exhaust stroke, and the like. As a result, the exhaust temperature is increased and the amount of HC in the exhaust gas is increased, and the bed temperatures of the upstream side catalyst 32 and the downstream side catalyst 34 reach the temperature at which the reducing agent can be added by the addition valve 44 (300 ° C. or higher). Rise. Thereafter, the addition of the reducing agent from the addition valve 44 is started, whereby the bed temperatures of the upstream catalyst 32 and the downstream catalyst 34 are increased to a temperature at which SOx can be released (600 ° C. or higher).

  Thereafter, the catalyst control shifts to S release control. As shown in FIG. 2 (a) as an example of the drive mode of the addition valve 44, in the S release control, the reducing agent is added from the addition valve 44 over a predetermined time T1 (several seconds) and the predetermined time T2 (several seconds to several tens of seconds). The addition is stopped repeatedly. When the reducing agent is added, the exhaust air-fuel ratio is slightly richer than the stoichiometric air-fuel ratio as shown in FIG. 2B, as an example of the change in the air-fuel ratio of the exhaust gas passing through the downstream catalyst 34. The amount of the reducing agent added is adjusted so as to be reduced to a low ratio. Further, as shown in FIG. 3 as an example of the drive mode of the addition valve 44 at the time of addition of the reducing agent, the addition of the reducing agent at the predetermined time T1 is intermittently performed by opening and closing the addition valve 44 several times every very short period. This process is repeated, and the amount of addition is adjusted by adjusting the valve opening time in each opening / closing drive.

  Then, by repeating the addition of the reducing agent and the stop of the addition, the bed temperatures of the upstream catalyst 32 and the downstream catalyst 34 are maintained at 600 ° C. or more, and the exhaust air-fuel ratio becomes a predetermined ratio α, so that the upstream catalyst The release and reduction of SOx and SOx from the 32 and the downstream side catalyst 34 are achieved.

  By the way, in the present embodiment, even when the above-described clogging occurs in the upstream catalyst 32, the downstream catalyst 34 can collect and remove PM and occlude and reduce NOx. The execution of the catalyst control is continued. However, in this case, when the S release control is executed, the reducing agent that reaches the downstream catalyst 34 becomes insufficient due to the adhesion of the reducing agent to the catalyst end face described above. For this reason, the exhaust air-fuel ratio becomes unnecessarily lean, which is one factor that hinders recovery of the downstream catalyst 34 from S poisoning. In the temperature increase control executed prior to the S release control, a certain amount of reducing agent adheres to the catalyst end face. However, in the S release control, a larger amount of reducing agent is added than in the temperature increase control. In addition, when the execution of S release control is started, it is inevitable that the reducing agent adheres to the end face of the catalyst, and therefore the exhaust air / fuel ratio is unnecessarily lean.

  Therefore, in the present embodiment, the presence or absence of clogging in the upstream catalyst 32 is determined, and when it is determined that clogging has occurred, the reducing agent addition amount in the S release control is increased and corrected, and the downstream catalyst is corrected. The air-fuel ratio of the exhaust gas passing through 34 is rapidly reduced to a predetermined ratio α.

Hereinafter, a specific processing procedure of processing related to S release control including such increase correction processing will be described.
FIG. 4 is a flowchart showing a specific processing procedure of processing related to S release control, and a series of processing shown in this flowchart is executed by the electronic control unit 50 as processing at predetermined intervals.

  As shown in FIG. 4, in this process, first, reduction that can reduce the air-fuel ratio of the exhaust gas that passes through the catalysts 32 and 34 to the predetermined ratio α based on the intake air amount GA and the fuel injection amount. An agent addition amount (target addition amount Fa) is calculated (step S100).

  After the target addition amount Fa is calculated, it is determined whether or not it is the first reducing agent addition (opening drive of the addition valve 44) after the start of the execution of the S release control, and when it is the first reducing agent addition. (Step S102: YES), the above-described increase correction of the reducing agent addition amount is executed.

  Here, when the reducing agent adheres to the end face of the catalyst due to clogging, the amount of adhesion is large immediately after the start of the execution of the S release control, and then gradually decreases and becomes saturated. Then, the exhaust air-fuel ratio is unnecessarily leaned during the period until the amount of adhesion becomes saturated. Based on this point, in this process, immediately after the start of the S release control, that is, by correcting the addition amount for the first reducing agent addition, the adhesion amount is quickly shifted to the saturated state, and the reduction described above is performed. The shortage of drugs is resolved early.

When the reducing agent is added for the first time, first, an increase correction for compensating the amount of the reducing agent attached to the inner wall of the exhaust passage 14 (specifically, the exhaust manifold) is executed. This increase correction is executed regardless of the occurrence of clogging. Specifically, first, it is determined whether or not the wall surface temperature Tex of the exhaust manifold estimated based on the engine rotation speed and the fuel injection amount is lower than a predetermined temperature (step S104). If the temperature is lower than the predetermined temperature (step S104: YES), the reducing agent adhesion amount (manifold adhesion amount Kex) to the exhaust manifold inner wall is calculated based on the wall surface temperature Tex, and based on the manifold adhesion amount Kex. Thus, the target addition amount Fa is corrected to increase from the following equation (1) (step S106).

Fa ← Fa + Kex (1)

Note that, as the wall surface temperature Tex is lower, the amount of reducing agent attached to the inner wall of the exhaust manifold increases, so that a larger amount is calculated as the manifold attached amount Kex.

  On the other hand, when the wall surface temperature Tex is equal to or higher than the predetermined temperature (step S104: NO), the target addition amount Fa is not increased because the reducing agent hardly adheres to the inner wall of the exhaust manifold (step S106 is jumped). ).

After such processing, an increase correction according to the above-described clogging occurrence state is executed.
First, it is determined whether or not clogging has occurred in the upstream side catalyst 32 from the determination result of the determination process previously performed in conjunction with the temperature raising process (step S108).

Hereinafter, this determination process will be described.
When clogging occurs in the upstream catalyst 32, the amount of the reducing agent that reacts in the upstream catalyst 32 is reduced accordingly, so that the bed temperature is difficult to rise. Therefore, the relationship between the bed temperature of the upstream catalyst 32 and the bed temperature of the downstream catalyst 34 is different from that in the case where the upstream catalyst is not clogged.

Specifically, the difference in temperature relationship appears as follows.
FIG. 5 shows an example of an increase in the bed temperature of the upstream catalyst 32 and the downstream catalyst 34 when the temperature increase control is executed. As shown in the figure, when the clogging does not occur, the bed temperature (solid line) of the upstream catalyst 32 rises to substantially the same temperature as the bed temperature of the downstream catalyst 34, whereas clogging occurs. Is generated, the bed temperature (one-dot chain line) of the upstream side catalyst 32 becomes lower than the bed temperature of the downstream side catalyst 34 where clogging does not occur.

  In the above determination process, the bed temperature of the upstream catalyst 32 and the bed temperature of the downstream catalyst 34 at the time of executing such temperature increase control are compared. When the difference between the catalyst bed temperatures is larger than a predetermined value, it is determined that clogging has occurred because the difference is increased due to clogging.

  In the present embodiment, the exhaust temperature Tup having a high correlation with the bed temperature of the upstream catalyst 32 is the index value of the same bed temperature, and the exhaust temperature Tlo having a high correlation with the bed temperature of the downstream catalyst 34 is the index value of the same bed temperature. Are detected and used for the determination process. Further, the difference “Tlo-Tup” between the exhaust temperatures is used as the catalyst bed temperature difference in the determination process. Since the bed temperature of the downstream side catalyst 34 changes slightly behind the bed temperature of the upstream side catalyst 32, in order to improve the determination accuracy for the presence or absence of clogging, such a delay is considered in the determination process. It is desirable that In the present embodiment, this determination process functions as a determination unit that determines whether the exhaust purification catalyst is clogged.

If it is determined that clogging has occurred in such determination processing (step S108 in FIG. 4: YES), the amount of reducing agent adhering to the catalyst end surface based on the catalyst bed temperature difference (end surface adhesion) Amount Ked) is calculated, and the target addition amount Fa is corrected to be increased from the following equation (2) based on the end face adhesion amount Ked (step S110).

Fa ← Fa + Ked (2)

In the present embodiment, the process in step S110 functions as a correction unit that corrects the target addition amount by an increase when it is determined that clogging has occurred.

  Here, when the upstream side catalyst 32 is clogged, the larger the degree is, the lower the bed temperature of the upstream side catalyst 32 becomes, and the difference between the catalyst bed temperatures increases. Further, as the degree of such clogging increases, the amount of reducing agent attached to the end face of the catalyst also increases. In order to compensate for this, it is necessary to increase the amount of reducing agent added. Based on these points, in the present embodiment, the larger the difference between the catalyst bed temperatures, the larger the end face adhesion amount Ked is calculated. Thereby, the reducing agent addition amount is corrected to increase in a manner corresponding to the degree of occurrence of clogging in the upstream catalyst 32.

  On the other hand, if the clogging has not occurred (step S108: NO), the reducing agent is hardly adhered to the catalyst end face, and the target addition amount Fa is not increased (step S110 is jumped). ).

  Thus, after the increase correction of the target addition amount Fa according to the occurrence state of clogging is appropriately performed, the reducing agent addition based on the target addition amount Fa is executed (step S112). Specifically, the addition valve 44 is driven and controlled while the valve opening time in each opening and closing drive of the addition valve 44 is adjusted according to the target addition amount Fa.

  In the second and subsequent additions of the reducing agent (step S102: NO), the increase correction according to the above-described exhaust manifold wall surface temperature Tex and the increase correction according to the occurrence of clogging are not performed. The reducing agent addition according to the target addition amount Fa calculated based on the operating state is executed.

FIG. 6 shows an example of the drive mode of the addition valve 44 immediately after the start of the execution of the S release control according to the present embodiment.
As shown in FIG. 6, in the S release control, when it is determined that the clogging has occurred, the target addition amount calculated based on the engine operating state in the first reducing agent addition after the start of the execution. Fa is corrected to increase. As a result, the amount of the reducing agent attached to the catalyst end face is quickly saturated, and the shortage of the reducing agent due to the attachment can be quickly resolved. Therefore, unnecessary leaning of the air-fuel ratio of the exhaust gas passing through the downstream side catalyst 34 is quickly eliminated, and the reduction process is suitably executed.

As described above, according to the present embodiment, the effects described below can be obtained.
(1) When clogging occurs, the target addition amount Fa calculated based on the engine operating state is corrected to increase. For this reason, even when a part of the reducing agent adheres to the catalyst end face due to the occurrence of clogging, the shortage of the reducing agent due to the adhesion can be compensated, and the reduction treatment of the downstream catalyst 34 is preferable. Will be able to run.

  (2) The target addition amount Fa is corrected to increase only for the first reducing agent addition after the start of the execution of S release control. As a result, the amount of reducing agent adhering to the catalyst end face can be quickly saturated, and the above-mentioned shortage of reducing agent can be resolved quickly.

  (3) The bed temperature of the upstream catalyst 32 and the bed temperature of the downstream catalyst 34 at the time of executing the temperature increase control is detected, and clogging occurs because the difference between the bed temperatures is larger than a predetermined value. Judgment was made. Thereby, the presence or absence of clogging can be determined based on the difference between the catalyst bed temperatures that increases when clogging occurs.

  (4) Since the end face adhesion amount Ked is calculated based on the difference between the catalyst bed temperatures, the amount of reducing agent added can be increased and corrected in accordance with the degree of occurrence of clogging. It becomes possible to compensate for the shortage.

The embodiment described above may be modified as follows.
In the above embodiment, the bed temperature of the upstream catalyst 32 and the bed temperature of the downstream catalyst 34 may be directly detected and used for the determination process.

  In the above embodiment, for example, it is determined that clogging has occurred when a value obtained by dividing the bed temperature of the downstream catalyst 34 by the bed temperature of the upstream catalyst 32 is equal to or greater than a predetermined value. The presence or absence of clogging may be determined based on the ratio.

  -It is also possible to determine the presence or absence of clogging based on the difference in the rising speed of each catalyst bed temperature or the ratio of the same speed. As shown by the solid line in FIG. 5, when the temperature raising control is started when no clogging occurs, the added reducing agent reacts in the upstream catalyst 32 immediately after that, so that the bed temperature is increased. It rises faster than the bed temperature of the downstream catalyst 34. On the other hand, as shown by the one-dot chain line in FIG. 5, when clogging occurs, the rate of increase in the bed temperature of the upstream catalyst 32 becomes low. According to the above configuration, it is possible to determine the presence or absence of clogging based on the relationship between the rising speeds of the catalyst bed temperature.

  In the above embodiment, as the upstream catalyst 32 and the downstream catalyst 34, those whose bed temperature rises to substantially the same temperature by executing the temperature rise control when clogging has not occurred are used. Instead, it is also possible to use a catalyst whose bed temperature becomes different after the temperature rise. In such a configuration, based on the temperature relationship such as the difference or ratio of the catalyst bed temperatures or the difference or ratio of the rising speed, specifically, the actual temperature relationship and the temperature when no clogging has occurred. The presence or absence of clogging may be determined based on the difference from the relationship.

  Prior to the execution of the S release control, the reducing agent is added at an appropriate timing that does not cause instability of the catalyst control, and the exhaust air-fuel ratio on the downstream side of the upstream side catalyst 32 accompanying the addition is reduced. It is also possible to determine whether clogging has occurred based on the change. When clogging occurs, even if a reducing agent is added, the amount of reducing agent used in the reaction at the exhaust purification catalyst, or the reducing agent that passes through the exhaust purification catalyst, as much as a part of it adheres to the catalyst end face. The amount of. Therefore, the air-fuel ratio of the exhaust gas after passing through the exhaust purification catalyst becomes lean compared to the case where no clogging occurs. According to the above configuration, it is possible to determine whether the upstream catalyst is clogged based on the difference in the exhaust air-fuel ratio.

  If it is difficult to saturate the amount of reducing agent attached to the catalyst end face by increasing correction at the first reducing agent addition after the start of the S release control execution, multiple reductions after the start of the S release control execution The addition amount of the reducing agent may be corrected to increase over the addition of the agent. In addition, after the start of the S release control, when the intermittent reducing agent addition from the addition valve 44 is executed for the first time over the predetermined time T1 (see FIG. 2A), the addition is executed. It is also possible to correct the amount added to increase.

  In addition, in the configuration in which the increase correction is performed over a plurality of times of addition of the reducing agent, the above-described reduction is performed by performing the increase correction so that the correction amount for the first addition after the start of the S release control is maximized. It is possible to quickly resolve the shortage of agents. As such a configuration, it is possible to employ a configuration in which the amount of increase correction required for the first addition is maximized and the amount of increase correction thereafter is reduced.

  In addition, it is also possible to adopt a configuration in which the increase correction amount is gradually reduced every time addition is performed in the same configuration. Here, as described above, the amount of the reducing agent adhering to the end face of the catalyst gradually decreases after the addition is started. Therefore, the necessity for increasing the target addition amount Fa gradually decreases. In this regard, according to the above configuration, the target addition amount Fa can be suppressed from being increased unnecessarily.

  Not limited to the increase correction so that the correction amount for the first addition after the start of the S release control is maximized, but when the reducing agent is added from the addition valve 44 over the predetermined time T1, the predetermined time T1 Even when the increase correction is performed so that the correction amount becomes the largest in the first half, the above-described shortage of the reducing agent can be quickly resolved.

  The present invention can also be applied to a reducing agent supply device that continuously adds a reducing agent from an addition valve and adjusts the amount of addition of the reducing agent through variable control of the lift amount of the addition valve. In the same configuration, it is also possible to adopt a configuration in which the increase correction amount for the target addition amount is set to gradually decrease with the passage of time from the start of the S release control.

  The increase correction of the target addition amount based on the occurrence of clogging can be executed when the NOx reduction mode is selected. Even in the NOx reduction control mode, the process of reducing the air-fuel ratio of the exhaust gas to the predetermined ratio α is performed by adding the reducing agent from the addition valve. For this reason, when clogging occurs, the reducing agent adheres to the end face of the catalyst at the start of the addition of the reducing agent in the NOx reduction control mode, resulting in unnecessary leaning of the exhaust air-fuel ratio. According to the above configuration, it is possible to suitably suppress unnecessary leaning of the exhaust air-fuel ratio when the NOx reduction mode is selected.

  In the above embodiment, the target addition amount may be corrected to be increased on condition that the exhaust gas temperature is low. According to this configuration, the reducing agent addition amount can be increased only when the reducing agent is not easily atomized and the reducing agent easily adheres to the end face of the catalyst, and unnecessary increase correction of the target addition amount can be performed. It can be avoided.

  -It is also possible to increase the increase correction amount as the exhaust temperature is lower. As a result, since the reducing agent is not easily atomized, the amount of increase correction can be set larger as the amount of reducing agent attached to the catalyst end surface increases, and unnecessary increase correction of the target addition amount is preferably avoided. Will be able to.

  In the above embodiment, the present invention is applied to a reducing agent addition apparatus that adds fuel as a reducing agent. However, the present invention is also applied to a reducing agent supply apparatus that supplies other substances as a reducing agent such as urea. Is applicable.

  -The present invention can be applied not only to a reducing agent addition device that adds a reducing agent to an exhaust purification catalyst having a plurality of catalysts, but also to a reducing agent addition device that adds a reducing agent to an exhaust purification catalyst having only one catalyst. It is.

1 is a block diagram showing a schematic configuration of an internal combustion engine to which an embodiment of the present invention is applied and its peripheral devices. (A), (b) The timing chart which shows an example of the control aspect of the exhaust air fuel ratio in S discharge | release control. The timing chart which shows an example of the drive mode of the addition valve at the time of reducing agent addition of S release control. The flowchart which shows the specific process sequence of the process concerning S discharge | release control. The graph which shows transition of the catalyst bed temperature at the time of execution of temperature rising control. The timing chart which shows an example of the drive mode of an addition valve immediately after the execution start of S discharge | release control.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 12 ... Intake passage, 14 ... Exhaust passage, 16 ... Combustion chamber, 18 ... Fuel injection valve, 20 ... Fuel pump, 22 ... Accumulation piping, 30 ... Catalyst device, 32 ... Upstream catalyst, 34 ... Downstream Side catalyst, 44 ... addition valve, 46 ... supply pipe, 50 ... electronic control unit, 52 ... intake air amount sensor, 54 ... first exhaust temperature sensor, 56 ... second exhaust temperature sensor, 58 ... air-fuel ratio sensor.

Claims (8)

In a reducing agent addition device for adding a reducing agent in an amount corresponding to a target addition amount set based on an operating state of an internal combustion engine from an addition valve provided on the exhaust upstream side of the exhaust purification catalyst,
Determination means for determining whether or not the exhaust purification catalyst is clogged;
A reducing agent addition apparatus comprising: a correction unit that corrects the target addition amount to be increased when it is determined that clogging has occurred in the exhaust purification catalyst. The reducing agent addition apparatus according to claim 1, wherein the correction unit sets the correction amount to be large in the first half of the reducing agent addition period when the target addition amount is corrected to be increased. The reducing agent addition apparatus according to claim 1, wherein the correction unit sets the target addition amount so that the target addition amount is maximized immediately after the addition of the reducing agent. The reducing agent addition apparatus according to any one of claims 1 to 3, wherein the correction unit sets the target addition amount so that the target addition amount gradually decreases with time from the start of addition of the reducing agent. In the reducing agent addition apparatus as described in any one of Claims 1-4,
The controller further comprises a control means for driving and controlling the addition valve so that the addition of the reducing agent from the addition valve is intermittently performed in a plurality of times, and the correction means includes the reducing agent addition in the plurality of times. A reducing agent addition device characterized in that the correction amount for the first addition of is maximized. The exhaust purification catalyst has an upstream catalyst and a downstream catalyst, and the determination means detects a bed temperature of the upstream catalyst and a bed temperature of the downstream catalyst by adding a reducing agent, The reducing agent addition apparatus according to any one of claims 1 to 5, wherein the upstream catalyst is determined based on a temperature comparison result to determine whether or not the upstream catalyst is clogged. The reducing agent addition apparatus according to claim 6, wherein the correction unit calculates a correction amount for the increase correction based on a comparison result between the bed temperature of the upstream catalyst and the bed temperature of the downstream catalyst. The determination unit adds a reducing agent, detects an exhaust property change on the downstream side of the exhaust purification catalyst, and determines the presence or absence of the clogging based on the detection result. The reducing agent addition apparatus described in 1.

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