JP2007051605A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine providing high NOx conversion performance. <P>SOLUTION: This device is provided with a NOx storage reduction catalyst provided in an exhaust gas passage of the internal combustion engine performing lean combustion and a fuel addition valve provided in an upstream side of the NOx storage reduction catalyst in the exhaust gas passage. The NOx storage reduction catalyst stores NOx in exhaust gas when air fuel ratio of exhaust gas flowing into the same is lean and reduces stored NOx by making air fuel ratio of exhaust gas rich. Fuel is added to exhaust gas by fuel injection from the fuel addition valve to make exhaust gas air fuel ratio tentatively rich, and NOx storage capacity of the NOx storage reduction catalyst is recovered. Fuel addition by the fuel addition valve is performed (S106) when an engine operation condition shifts from an operation condition where fuel cut control is performed to an operation condition where the fuel cut operation is stopped (YES in S100). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine in which a NOx storage reduction catalyst is provided in an exhaust passage.

  In an internal combustion engine that performs lean combustion, such as a diesel engine, a NOx occlusion reduction catalyst for purifying NOx (nitrogen oxide) in exhaust gas is provided in the exhaust passage. This NOx occlusion reduction catalyst occludes NOx in the exhaust when the exhaust air-fuel ratio is lean, that is, when the surrounding atmosphere is in a high oxygen concentration state. On the other hand, when the exhaust air-fuel ratio is made rich, in detail, the surrounding atmosphere is brought into a low oxygen concentration state, and unburned fuel components such as hydrocarbon (HC) and carbon monoxide (CO) are contained in the exhaust. When it is made to include, the NOx occlusion reduction catalyst releases and reduces the occluded NOx. Specifically, NOx occluded in the NOx occlusion reduction catalyst is released due to the decrease in oxygen concentration, and the released NOx is reduced and purified through reaction with unburned fuel components contained in the exhaust.

  Here, the NOx occlusion amount of the NOx occlusion reduction catalyst is limited. Therefore, in the internal combustion engine, if the lean combustion with the exhaust air-fuel ratio leaning is continued for a long period of time, the NOx occlusion amount of the NOx occlusion reduction catalyst reaches the limit capacity, and no more NOx can be occluded.

  Therefore, conventionally, for example, as in the exhaust gas purification apparatus described in Patent Document 1, a fuel addition valve is provided upstream of the NOx storage reduction catalyst in the engine exhaust passage, and the same condition is obtained when the NOx storage amount reaches a predetermined amount. The fuel is injected from the fuel addition valve, and the fuel is added to the exhaust gas. As a result, the air-fuel ratio of the exhaust gas passing through the NOx occlusion reduction catalyst becomes richer, NOx occluded in the NOx occlusion reduction catalyst is released and reduced, and the NOx reduction ability is restored.

In addition, as a prior art document concerning this invention, the following patent documents 2 other than the said patent document 1 is mentioned.
JP 2002-213232 A JP 2001-90593 A

  Here, the amount of NOx contained in the exhaust gas varies depending on the engine operating state. Further, when the NOx occlusion amount increases, the ratio of the NOx occlusion rate (M2) stored in the NOx occlusion reduction catalyst to the NOx amount (M1) in the exhaust gas flowing into the NOx occlusion reduction catalyst (NOx occlusion rate (= M2)) / M1)) is lowered.

  For this reason, when the NOx occlusion rate is high, it does not depend on the NOx amount in the exhaust gas, and even when the NOx occlusion rate is low, when the engine operating state is low in the exhaust gas, it is discharged to the outside of the exhaust passage without being purified. It can be said that the amount of NOx produced is small. On the other hand, when the engine is in an operation state in which the NOx occlusion rate is low and the amount of NOx in the exhaust gas is large, a large amount of NOx is discharged to the outside of the exhaust passage without being purified.

  Therefore, in order to suppress the amount of NOx released to the outside without purification, when the engine is in an operation state where the amount of NOx in the exhaust gas is large, the NOx storage reduction catalyst has a high NOx storage rate, that is, NOx. It is desirable that the amount of occlusion is small.

  Since the apparatus described in Patent Document 1 performs fuel addition under the condition that the NOx occlusion amount reaches a predetermined amount, it cannot be said that fuel addition is performed to meet such a tendency. This leaves room for improvement.

  Note that the present invention is not limited to a device that adds fuel to exhaust through fuel injection from the fuel addition valve described above, but may be a device that adds fuel to exhaust through fuel injection into a combustion chamber in an expansion stroke or an exhaust stroke of an internal combustion engine. These facts are generally common.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust purification device for an internal combustion engine in which high NOx purification performance can be obtained.

Hereinafter, means for achieving the above-described object and its operation and effects will be described.
The invention according to claim 1 is provided in an exhaust passage of an internal combustion engine that performs lean combustion, and stores NOx in the exhaust when the exhaust air-fuel ratio is lean and makes the exhaust air-fuel ratio rich. A NOx occlusion / reduction catalyst for reducing NOx occluded in the fuel, and a fuel addition means for adding fuel into the exhaust upstream of the NOx occlusion reduction catalyst, and the exhaust air / fuel ratio through fuel addition by the fuel addition means In the exhaust purification device for an internal combustion engine that temporarily restores the NOx occlusion ability of the NOx occlusion reduction catalyst when the engine operation state shifts from the deceleration state to another operation state, the fuel addition means The main point is to perform fuel addition.

  When the engine operating state is the acceleration state, the ratio of the intake air amount to the fuel injection amount (combustion air-fuel ratio) becomes a rich ratio and the combustion temperature increases, so the amount of NOx contained in the exhaust increases. . Therefore, if the NOx occlusion reduction catalyst is in a state where the NOx occlusion amount is small when the acceleration state is reached, it can be said that the amount of NOx discharged without purification is suitably reduced.

  In the above configuration, when the engine operation state shifts from the deceleration state to another operation state, in other words, when there is a high possibility that the engine operation state will subsequently become the acceleration state, fuel addition for reducing the NOx occlusion amount is executed. . Therefore, according to the above configuration, the NOx occlusion reduction catalyst can be kept in a state where the NOx occlusion amount is small prior to the acceleration state where the amount of NOx contained in the exhaust gas is large, so that high NOx purification performance can be obtained. become.

The other operating states are a constant speed state and an acceleration state.
According to a second aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, the shift is that the fuel injection amount is less than the first predetermined amount and is greater than or equal to the first predetermined amount. The gist is that the determination is made when the state is equal to or greater than the second predetermined amount, which is the amount.

  Normally, when the engine speed is greatly reduced, the fuel injection amount is set to a very small amount, for example, fuel cut control is executed. Therefore, it can be determined that the vehicle is in a deceleration state when the fuel injection amount is small, and it can be determined that the operation state is other than the deceleration state when the fuel injection amount is large. According to the above configuration, it is possible to determine that the engine operating state has shifted from the deceleration state to another operating state based on the fuel injection amount.

The addition of fuel into the exhaust can be performed by a fuel addition valve provided upstream of the NOx storage reduction catalyst in the exhaust passage, as in claim 3.
According to a fourth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the third aspect, the wall surface temperature of the exhaust passage becomes equal to or higher than a predetermined temperature after the start of execution of fuel addition by the fuel addition valve. The gist of this is to delay the period until.

  When the vehicle is in a deceleration state with a small amount of fuel injection, the exhaust temperature is low and the temperature of the exhaust passage wall surface is low. Therefore, when the engine operating state shifts from the deceleration state to another operating state where the fuel injection amount is relatively large and the exhaust temperature increases, the temperature of the exhaust passage wall surface gradually increases to a temperature commensurate with the exhaust temperature. Here, when fuel is added from the fuel addition valve, a part of the added fuel may adhere to the exhaust passage wall surface. Such adhesion of the added fuel is likely to occur when the temperature of the exhaust passage wall surface is low. Therefore, if fuel addition is performed when the temperature of the exhaust passage wall surface is low immediately after the engine operating state is shifted, there is a possibility that the added fuel adheres and the fuel cannot be properly added to the exhaust.

  In this regard, according to the above configuration, it is possible to wait for the temperature of the exhaust passage wall surface to rise after the engine operating state has shifted, and to start the fuel addition from the fuel addition valve. Can be added properly.

  The wall surface temperature of the exhaust passage is preferably the wall surface to which the fuel injected from the fuel addition valve adheres, or the wall surface temperature changing with a very high correlation with the wall surface. In addition to directly detecting the wall surface temperature by a sensor provided in the exhaust passage, the wall surface temperature can also be estimated based on operating conditions such as a fuel injection amount, an engine rotational speed, an air-fuel ratio, and the like.

  The gist of the invention according to claim 5 is that in the exhaust gas purification apparatus for an internal combustion engine according to claim 3, the start of fuel addition by the fuel addition valve is delayed for a predetermined period after the transition.

  According to the above configuration, it is possible to wait for the temperature of the exhaust passage wall surface to rise after the engine operating state shifts, and to start the fuel addition from the fuel addition valve so that the fuel is appropriately supplied to the exhaust gas. Can be added.

  According to a sixth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the fifth aspect, the predetermined period is a period until the integrated value of the fuel injection amount after the transition becomes a predetermined value or more. Is the gist.

  According to the above configuration, it is determined that the wall surface temperature of the exhaust passage rising due to a part of the generated heat is increased when the total amount of heat generated by the fuel combustion after the engine operating state is shifted is increased. Then, fuel addition from the fuel addition valve can be executed.

  According to a seventh aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the fifth or sixth aspect, the predetermined period is set longer as the duration of the deceleration state immediately before the transition is longer. This is the gist.

  Here, the wall temperature of the exhaust passage decreases and decreases as the duration of the deceleration state increases. Regardless of such a temperature trend, in order to start fuel addition after the wall surface temperature has become sufficiently high, the predetermined period may be set to a sufficiently long period. However, if the predetermined period is lengthened, the engine operation state is more likely to be accelerated before the start of fuel addition. Therefore, it is desirable that the predetermined period is set to a short period.

  In the above configuration, the longer the duration of the deceleration state immediately before the engine operating state transitions, in other words, the longer the period required for the wall temperature of the exhaust passage to rise to an appropriate temperature, the longer the predetermined period. Is set to a long period. Therefore, according to the above configuration, fuel addition can be started after the wall surface temperature of the exhaust passage becomes moderately high while setting the predetermined period as short as possible.

In addition, when the said structure is applied to Claim 6, the said predetermined period can be set to a long period by setting the said predetermined value to a larger value, so that the said continuation time is long.
The invention according to claim 8 is provided in the exhaust passage of the internal combustion engine that performs lean combustion, and stores NOx in the exhaust when the exhaust air-fuel ratio is lean and makes the exhaust air-fuel ratio rich. A NOx occlusion / reduction catalyst for reducing NOx occluded in the fuel, and a fuel addition means for adding fuel into the exhaust upstream of the NOx occlusion reduction catalyst, and the exhaust air / fuel ratio through fuel addition by the fuel addition means In the exhaust gas purification device for an internal combustion engine that temporarily restores the NOx storage capacity of the NOx storage reduction catalyst when the engine operation state shifts from an operation state other than the acceleration state to the acceleration state, the fuel The gist of the present invention is to add the fuel by the adding means.

  When the engine operating state is the acceleration state, the combustion air-fuel ratio becomes a rich ratio and the combustion temperature increases, so the amount of NOx contained in the exhaust gas increases. Therefore, if the NOx occlusion reduction catalyst is in a state where the NOx occlusion amount is small when the acceleration state is reached, it can be said that the amount of NOx discharged without purification is suitably reduced.

  In the above configuration, when the engine operation state shifts from the operation state other than the acceleration state to the acceleration state, in other words, immediately after the NOx amount in the exhaust gas increases or the NOx amount starts to increase, Fuel addition for reducing the NOx occlusion amount is executed. Therefore, according to the above configuration, when the engine operating state is the acceleration state, the NOx storage reduction catalyst can be brought into a state where the NOx storage amount is small, and high NOx purification performance can be obtained.

The driving state other than the acceleration state is a deceleration state or a constant speed state.
The fact that the engine operating state has shifted from the operating state other than the accelerated state to the accelerated state is determined when the operating speed toward the acceleration side of the accelerator operating member is equal to or higher than a predetermined speed, as in claim 9. Alternatively, as in claim 10, it is possible to make a judgment when the increasing speed of the fuel injection amount becomes equal to or higher than a predetermined speed.

  Further, the addition of fuel into the exhaust gas can be performed by a fuel addition valve provided upstream of the NOx storage reduction catalyst in the exhaust passage, as in claim 11.

(First embodiment)
Hereinafter, a first embodiment in which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is embodied will be described.

FIG. 1 shows a schematic configuration of an internal combustion engine to which an exhaust emission control device according to the present embodiment is applied.
As shown in FIG. 1, the internal combustion engine 10 includes a fuel injection valve 14 that directly injects fuel into the combustion chamber 12. The fuel injection valve 14 communicates with a pressure accumulation pipe 16, and fuel is supplied from the fuel tank 20 through the fuel pump 18 into the pressure accumulation pipe 16. The internal combustion engine 10 is a diesel engine mounted on a vehicle. When the internal combustion engine 10 is operated, so-called lean combustion is performed.

  A NOx occlusion reduction catalyst 30 is provided in the middle of the exhaust passage 22 of the internal combustion engine 10. The NOx storage reduction catalyst 30 stores NOx when the exhaust air-fuel ratio is lean, and releases and reduces NOx stored by making the exhaust air-fuel ratio rich, for example, so as to release and reduce NOx in the exhaust. Purify.

  Further, a fuel addition valve 26 as a fuel addition means is provided in the exhaust passage 22 upstream of the NOx occlusion reduction catalyst 30, more specifically, in the exhaust manifold 24. The fuel pump 18 communicates with the fuel addition valve 26, and fuel is supplied from the fuel tank 20 through the fuel pump 18. When the fuel addition valve 26 is driven to open, fuel is added to the exhaust gas.

  The vehicle is provided with various sensors for detecting the driving state and the operation state. Specifically, for example, the intake air amount sensor 42 for detecting the amount of air sucked into the combustion chamber 12 of the internal combustion engine 10 (intake air amount GA) and the rotational speed of the output shaft 28 of the internal combustion engine 10 ( A rotational speed sensor 44 for detecting the engine rotational speed NE) is provided. In addition, an accelerator sensor 46 for detecting the depression amount of the accelerator pedal 32 (accelerator depression amount ACC), a temperature sensor 48 for detecting the temperature of the exhaust gas flowing out from the NOx storage reduction catalyst 30, and the like are also provided.

  The electronic control unit 40 includes a drive circuit for driving various actuators such as the fuel injection valve 14 and the fuel addition valve 26 in addition to the CPU, ROM, and RAM. The electronic control unit 40 takes in the output signals of the various sensors and performs various calculations. Based on the calculation results, the drive control of the fuel injection valve 14 (fuel injection control) and the drive control of the fuel addition valve 26 (fuel addition) Control).

  In the fuel injection control of the present embodiment, the amount of fuel injected into the combustion chamber 12 (fuel injection amount Q) is adjusted in accordance with the engine operating state. Specifically, a control target value (target fuel injection amount TQ) for the fuel injection amount Q is calculated based on the accelerator depression amount ACC and the engine speed NE, and the target fuel injection amount TQ and the actual fuel injection amount Q The fuel injection valve 14 is driven to open so that the two coincide. In the fuel injection control, fuel cut control for stopping fuel injection when the vehicle is decelerated is executed. Specifically, this fuel cut control is executed when, for example, a condition such as the vehicle traveling speed is equal to or higher than a predetermined speed and the accelerator pedal 32 is not depressed is satisfied.

  Further, in the fuel addition control of the present embodiment, when the NOx occlusion capacity of the NOx occlusion reduction catalyst 30 decreases, the fuel addition valve 26 is driven to open and fuel is added to the exhaust, and the NOx occlusion capacity is recovered. Figured.

  In this valve opening drive, in detail, the ratio of the exhaust gas flowing into the NOx storage reduction catalyst 30 becomes a rich side at a ratio suitable for the release of NOx from the NOx storage reduction catalyst 30 and the reduction of the released NOx. Therefore, the amount of fuel added per unit time is adjusted so that the NOx occlusion amount can be efficiently reduced by adding as little fuel as possible. Through such valve opening drive of the fuel addition valve 26, the exhaust air-fuel ratio temporarily becomes rich, NOx occluded in the NOx occlusion reduction catalyst 30 is released and reduced, the NOx occlusion amount decreases, and the NOx occlusion decreases. The NOx storage capacity of the reduction catalyst 30 is recovered.

  Incidentally, as shown in FIG. 2, when fuel is added to the exhaust, the valve opening drive of the fuel addition valve 26 is executed over a predetermined period Tc such that the valve opening drive over a predetermined time Ta is executed every predetermined time Tb. . The fuel addition amount per unit time is adjusted by changing the predetermined time Ta or the predetermined time Tb.

  Here, in the fuel injection control according to the present embodiment, when the accelerator pedal 32 is largely depressed and the vehicle and the internal combustion engine 10 are in an accelerated state, the fuel injection amount Q is set to a very large amount. Therefore, at this time, the ratio between the intake air amount GA and the fuel injection amount Q (combustion air-fuel ratio) becomes a rich ratio, the combustion temperature increases, and the amount of NOx contained in the exhaust increases. If the NOx occlusion reduction catalyst 30 is in a state where the NOx occlusion reduction amount is small at the time of such acceleration, the amount of NOx that is not occluded by the NOx occlusion reduction catalyst 30 and is exhausted to the outside of the exhaust passage 22 is reduced. It is preferably reduced.

  Incidentally, the fuel cut control is executed when the vehicle is greatly decelerated, for example, when the vehicle is temporarily stopped at an intersection or decelerated before a curve. When the vehicle speed is reduced to a certain extent during vehicle deceleration, the fuel cut control is stopped and fuel injection is resumed. Then, immediately after the fuel injection is restarted in this way, there is a high possibility that the vehicle and the internal combustion engine 10 will be in an accelerated state, such as when the vehicle restarts or accelerates after passing a curve.

  Based on this situation, in the fuel addition control of the present embodiment, when the engine operating state changes from the operating state in which the fuel cut control is executed to the operating state in which the execution is stopped, in other words, thereafter, the engine is brought into the acceleration state. When the possibility is high, the fuel addition valve 26 is driven to open, and the NOx occlusion amount of the NOx occlusion reduction catalyst 30 is reduced to increase the NOx occlusion rate.

Hereinafter, the processing related to such fuel addition control will be described in detail with reference to the flowchart shown in FIG.
The series of processing shown in this flowchart conceptually shows a specific processing procedure of the fuel addition control processing, and the actual processing is performed as an electronic control unit as processing executed every predetermined cycle. 40.

  As shown in FIG. 3, in this process, it is first determined whether or not the engine operating state has shifted from an operating state in which fuel cut control is executed to an operating state in which the execution is stopped (step S100). Specifically, the fuel injection from the fuel injection valve 14 is stopped (fuel injection amount Q = 0) at the previous execution of this process, and the fuel injection is resumed at the current execution of this process. It is determined that the engine operating state has shifted to the state (Q> 0).

If the engine operating state shifts in this way (step S100: YES), then whether or not the following conditions are satisfied on the condition that the execution of the fuel cut control has not been resumed (step S102: NO). Is determined (step S104).
-The temperature of the exhaust manifold 24 is equal to or higher than a predetermined temperature.
-The bed temperature of the NOx storage reduction catalyst 30 is equal to or higher than the activation temperature. Specifically, the temperature of the exhaust gas flowing out from the NOx storage reduction catalyst 30 is equal to or higher than a predetermined temperature.

  Note that the predetermined temperature is set by obtaining, through experimental results, a temperature at which fuel adhesion to the wall surface of the exhaust passage 22 to be described later can be appropriately avoided. In the present embodiment, the temperature of the exhaust manifold 24 (to be exact, an estimated value) at that time is calculated based on the engine operating state such as the intake air amount GA and the fuel injection amount Q. Used in step S104.

  When both of the above conditions are satisfied (step S104: YES), the fuel addition valve 26 is driven to open in the above-described manner (step S106), and then this process is temporarily terminated (step S100). Return to processing.)

  If the fuel cut control is started before both of the above conditions are satisfied (step S104: NO and step S102: YES), the fuel addition valve 26 is not opened and the operation of step S100 is not executed. Return to processing.

Hereinafter, the effect | action by the fuel addition control process concerning this Embodiment is demonstrated, referring FIG.
FIG. 4 is a timing chart showing an example of the processing mode of the fuel addition control process.

  Prior to time t10 in FIG. 4, fuel cut control is executed, and fuel injection from the fuel injection valve 14 is stopped (FIG. 4A). At this time, since the low-temperature air sucked into the combustion chamber 12 is discharged from the combustion chamber 12 to the exhaust passage 22, the temperature of the exhaust manifold 24 (b) in FIG. )) And the bed temperature of the NOx storage reduction catalyst 30 ((c) in the figure) are both lowered.

  When execution of the fuel cut control is stopped at time t10, high-temperature exhaust gas flows through the exhaust passage 22 thereafter, so that the temperature of the exhaust manifold 24 and the bed temperature of the NOx storage reduction catalyst 30 become the temperature of such exhaust gas. Gradually rises to the appropriate temperature.

  Here, when fuel is added from the fuel addition valve 26, part of the added fuel may adhere to the wall surface of the exhaust passage 22 such as the wall surface of the exhaust manifold 24. Such adhering fuel tends to occur when the wall surface temperature of the exhaust passage 22 is low. Therefore, if fuel addition is performed when the wall temperature of the exhaust passage 22 immediately after the execution of the fuel cut control is low, the added fuel will adhere and the fuel cannot be added to the exhaust properly. There is a fear.

  When the bed temperature of the NOx storage reduction catalyst 30 is lower than the activation temperature, the stored NOx cannot be properly reduced when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 30 is set to the rich side. .

  In this respect, in the present embodiment, after the execution of the fuel cut control is stopped, the period until the temperature of the exhaust manifold 24 becomes equal to or higher than the predetermined temperature and the bed temperature of the NOx storage reduction catalyst 30 becomes equal to or higher than the activation temperature. The execution start of the valve opening drive of the fuel addition valve 26 is delayed. That is, after the wall surface temperature of the exhaust passage 22 and the bed temperature of the NOx storage reduction catalyst 30 rise, the fuel addition from the fuel addition valve 26 is started, and the fuel is appropriately added to the exhaust gas. It becomes like this.

  Specifically, when the temperature of the exhaust manifold 24 becomes equal to or higher than a predetermined temperature and the bed temperature of the NOx storage reduction catalyst 30 becomes equal to or higher than the activation temperature at time t11, the fuel addition valve is used for a predetermined period (time t11 to t12). The valve 26 is driven to open, and fuel is added to the exhaust gas ((d) in the figure). As a result, the NOx stored in the NOx storage reduction catalyst 30 is released and reduced, and the NOx storage reduction catalyst 30 is in a state where the NOx storage amount ((e) in the figure) is small.

  Therefore, at the time t13 immediately after that, when the engine operation state becomes an acceleration state and the amount of NOx in the exhaust gas becomes extremely large, a large amount of NOx is stored in the NOx storage reduction catalyst 30, and remains unpurified. The amount of NOx discharged to the outside of the exhaust passage 22 is suitably reduced.

  As described above, according to the present embodiment, prior to the acceleration state in which the amount of NOx contained in the exhaust gas is extremely high, the NOx storage reduction catalyst 30 is brought into a state in which the NOx storage amount is small, that is, the NOx storage rate is high. I can keep it. Accordingly, a large amount of NOx in the exhaust gas is stored in the NOx storage reduction catalyst 30 when the acceleration state is reached, and high NOx purification performance can be obtained.

As described above, according to the present embodiment, the effects described below can be obtained.
(1) Since the engine operation state shifts from the operation state in which the fuel cut control is executed to the operation state in which the execution of the control is stopped, the valve opening drive of the fuel addition valve 26 is executed. Prior to the acceleration state, the NOx occlusion reduction catalyst 30 can be kept in a state where the NOx occlusion amount is small, and high NOx purification performance can be obtained.

  (2) Since the start of the opening operation of the fuel addition valve 26 is delayed for a period until the temperature of the exhaust manifold 24 becomes equal to or higher than the predetermined temperature after the execution of the fuel cut control is stopped, The fuel addition from the fuel addition valve 26 can be started after waiting for the rise, and the fuel can be appropriately added to the exhaust gas.

(Second Embodiment)
Hereinafter, a second embodiment that embodies an exhaust emission control device for an internal combustion engine according to the present invention will be described focusing on differences from the first embodiment.

This embodiment differs from the first embodiment in the following points.
In the fuel addition control (see FIG. 3) according to the first embodiment, one of the conditions for starting the valve opening drive of the fuel addition valve 26 is “the temperature of the exhaust manifold 24 is equal to or higher than a predetermined temperature”. The condition is set.

  In contrast, in the fuel addition control according to the present embodiment, instead of the above condition, “the integrated value ΣQ of the fuel injection amount Q after the execution of the fuel cut control is stopped is equal to or greater than the predetermined value Qa. Is set. As a result, it is determined that the wall surface temperature of the exhaust passage 22 rising due to a part of the generated heat has increased due to the increase in the total amount of heat generated by the fuel combustion after the fuel injection has been resumed. Fuel addition from the addition valve 26 is started.

Hereinafter, the fuel addition control according to the present embodiment will be described with reference to the flowchart of FIG.
The series of processing shown in this flowchart conceptually shows a specific processing procedure of the fuel addition control processing, and the actual processing is performed as an electronic control unit as processing executed every predetermined cycle. 40.

  As shown in FIG. 5, when it is determined in this process that the engine operating state has shifted from an operating state in which fuel cut control is executed to an operating state in which execution of the control is stopped (step S100: YES), the engine The predetermined value Qa is calculated based on the execution duration time of the fuel cut control immediately before the operating state shifts (step S200). Specifically, as the predetermined value Qa, as shown in FIG. 6, a larger value is calculated as the execution duration time is longer. The reason why the predetermined value Qa is calculated in this way will be described in detail later.

Thereafter, on the condition that the execution of the fuel cut control has not been resumed (step S102: NO), it is determined whether or not both of the following conditions are satisfied (step S202).
The integrated value ΣQ is not less than a predetermined value Qa.
-The bed temperature of the NOx storage reduction catalyst 30 is equal to or higher than the activation temperature.

  When both of the above conditions are satisfied (step S202: YES), the fuel addition valve 26 is driven to open in the above-described manner (step S106), and then this process is temporarily terminated (step S100). Return to processing.) If the fuel cut control is started before both of the above conditions are satisfied (step S202: NO and step S102: YES), the fuel addition valve 26 is not opened and the operation of step S100 is not executed. Return to processing.

Hereinafter, the effect | action by the fuel addition control concerning this Embodiment is demonstrated, referring FIG.
FIG. 7 is a timing chart showing an example of the processing mode of the fuel addition control process.

  Before time t20 in FIG. 7, fuel cut control is executed, and fuel injection from the fuel injection valve 14 is stopped (FIG. 7A). Therefore, both the temperature of the exhaust manifold 24 and the bed temperature of the NOx occlusion reduction catalyst 30 ((c) in the figure) are lower than when fuel cut control is not performed.

  When the execution of the fuel cut control is stopped at time t20, the integrated value ΣQ of the fuel injection amount Q thereafter ((b) in the figure) becomes equal to or greater than the predetermined value Qa, and the bed temperature of the NOx storage reduction catalyst 30 is activated. During the period until the temperature rises (time t20 to t21), the start of the opening operation of the fuel addition valve 26 is delayed. Thereafter, the fuel addition valve 26 is driven to open for a predetermined period (time t21 to t22), and fuel addition to the exhaust is executed ((d) in the figure). As a result, the NOx stored in the NOx storage reduction catalyst 30 is released and reduced, and the NOx storage reduction catalyst 30 is in a state where the NOx storage amount ((e) in the figure) is small.

  As described above, according to the present embodiment, the NOx occlusion reduction catalyst 30 is in a state where the NOx occlusion amount is small, that is, the NOx occlusion rate, before the acceleration state where the amount of NOx contained in the exhaust gas is extremely large at the time t23 immediately after that. Can be kept high. Accordingly, a large amount of NOx in the exhaust gas is stored in the NOx storage reduction catalyst 30 when the acceleration state is reached, and high NOx purification performance can be obtained.

  Here, as the execution duration time of the fuel cut control becomes longer, the wall surface temperature of the exhaust passage 22 decreases and becomes lower. Regardless of such a temperature trend, in order to start fuel addition after the wall surface temperature becomes sufficiently high, the start of the fuel addition can be greatly delayed by setting the predetermined value Qa to a sufficiently large value. That's fine. However, if the delay period is lengthened, there is a high possibility that the engine operating state will be in an accelerated state before the start of fuel addition, so it is desirable that the delay period be set to a short period.

  In the present embodiment, the longer the fuel cut control execution duration immediately before the engine operating state transitions, in other words, the longer the period required for the wall temperature of the exhaust passage 22 to rise to an appropriate temperature. A large value is calculated as the predetermined value Qa (see FIG. 6), and the delay period is set to a long period. Therefore, fuel addition can be started after the wall surface temperature of the exhaust passage 22 has become moderately high while setting the delay period as short as possible.

  In the present embodiment, the relationship between the predetermined value Qa at which fuel adherence to the wall surface of the exhaust passage 22 is appropriately avoided and the execution duration time is obtained through experimental results and stored in the electronic control unit 40. In the fuel addition control process, a predetermined value Qa is calculated based on the relationship (step S200 in FIG. 5).

As described above, according to the present embodiment, in addition to the effect described in (1) described above, the effects described in (3) and (4) below can be obtained.
(3) Start of fuel addition by the fuel addition valve 26 from when the fuel cut control is stopped until the integrated value ΣQ of the fuel injection amount Q after the stop of the control becomes equal to or greater than the predetermined value Qa The period was delayed. Therefore, it is determined that the wall surface temperature of the exhaust passage 22 rising due to a part of the generated heat increases as the total amount of heat generated by the fuel combustion after the fuel injection is resumed increases. Fuel can be added from the fuel addition valve 26, and fuel can be appropriately added to the exhaust gas.

  (4) A larger value is calculated as the predetermined value Qa as the execution duration time of the control immediately before the fuel cut control is stopped is longer. Therefore, the fuel addition can be started after the wall surface temperature of the exhaust passage 22 is appropriately increased while setting the period for delaying the start of execution of the fuel addition to be as short as possible.

(Third embodiment)
Hereinafter, a third embodiment that embodies an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described focusing on differences from the first and second embodiments.

This embodiment is different from the first and second embodiments only in the processing contents of the processing relating to fuel injection control.
Hereinafter, the fuel addition control according to the present embodiment will be described with reference to the flowchart of FIG.

  The series of processes shown in this flowchart conceptually shows a specific processing procedure of the process related to the fuel addition control, and the actual process is performed as a process executed every predetermined cycle. It is executed by the control unit 40.

  As shown in FIG. 8, in this process, it is first determined whether or not the engine operating state has shifted from the operating state other than the accelerated state to the accelerated state (step S300). Here, it is determined that the engine operating state has shifted to the acceleration state when the operating speed of the accelerator pedal 32 (specifically, the increasing speed of the accelerator depression amount ACC) has become equal to or higher than a predetermined speed.

  When it is determined that the engine operating state has shifted to the acceleration state (step S300: YES), the condition is that the bed temperature of the NOx storage reduction catalyst 30 is equal to or higher than the activation temperature (step S302: YES). After the fuel addition valve 26 is driven to open in this manner (step S304), the present process is temporarily terminated (returns to the process of step S300).

  When it is not determined that the engine operating state has shifted to the acceleration state, or when the bed temperature of the NOx storage reduction catalyst 30 is lower than the activation temperature (step S300: NO or step S302: NO), the fuel addition valve The process returns to the process of step S300 without executing the valve opening drive of 26.

Hereinafter, the effect | action by the fuel addition control concerning this Embodiment is demonstrated, referring FIG.
FIG. 9 is a timing chart showing an example of a processing mode of the fuel addition control process when the bed temperature of the NOx storage reduction catalyst 30 is equal to or higher than the activation temperature.

  Before time t30 in FIG. 9, the accelerator depression amount ACC (FIG. 9A) is kept substantially constant, and fuel addition from the fuel addition valve 26 (FIG. 9B) is not executed.

  When the accelerator pedal 32 is depressed at time t30, it is assumed that the engine operating state is in an accelerated state, and the fuel addition valve 26 is driven to open for a predetermined period thereafter (time t30 to t31), and fuel addition to the exhaust is executed. Is done. Thereby, the NOx stored in the NOx storage reduction catalyst 30 is released and reduced, and the NOx storage amount of the NOx storage reduction catalyst 30 ((c) in the figure) is reduced.

  As described above, according to the present embodiment, when the engine operating state shifts to the acceleration state, in other words, immediately after the NOx amount in the exhaust gas increases or the NOx amount starts to increase, the NOx occlusion occurs. The amount can be decreased once. Thereby, when the engine operating state is the acceleration state, the NOx occlusion reduction catalyst 30 can be brought into a state in which the NOx occlusion amount is small, that is, a state in which the NOx occlusion rate is high. A large amount of oil is occluded, and high NOx purification performance can be obtained.

(Other embodiments)
Each of the above embodiments may be modified as follows.
In the first embodiment, the temperature of the exhaust manifold 24 may be directly detected by providing a temperature sensor in addition to calculating based on the operating state engine operating state.

  Further, the temperature of a portion other than the exhaust manifold 24 in the exhaust passage 22 may be estimated or detected, and this may be used for the determination in the process of step S104 (FIG. 3). Specifically, it is possible to use the temperature of the turbocharger when the exhaust-drive turbocharger is provided, the temperature of the exhaust pipe, or the like. As the temperature used for the above judgment, it is desirable to use the temperature of the wall surface to which the fuel injected from the fuel addition valve 26 adheres or the temperature of the wall surface having a very high correlation with the wall surface. Incidentally, since the bed temperature of the NOx storage reduction catalyst 30 changes due to the reaction heat, the correlation between the exhaust temperature on the upstream side and the exhaust temperature on the downstream side of the NOx storage reduction catalyst 30 is low, and the temperature of the wall surface to which the fuel adheres. And the wall surface temperature of the exhaust passage 22 on the downstream side of the NOx storage reduction catalyst 30 is also low in correlation. Therefore, it is desirable to use the temperature of the upstream portion of the NOx storage reduction catalyst 30 for the above determination.

  In the second embodiment, in the fuel addition control process, a condition such as “the integrated value ΣQ of the fuel injection amount Q after the execution of the fuel cut control has stopped is equal to or greater than a predetermined value Qa” (FIG. 5). Step S202) was set. Instead of the conditions for the fuel injection amount integrated value, as shown in FIG. 10 as an example of change of the fuel addition control process, “the elapsed time after the execution of the fuel cut control is stopped is equal to or longer than the predetermined time Td. May be set (step S402). Further, the predetermined time Td may be calculated based on the execution duration time of the control immediately before the execution of the fuel cut control is stopped (step S400). In this configuration, as shown in FIG. 11, the longer the execution duration time, the longer the predetermined time Td may be set.

  In addition, a condition such as “the integrated value ΣGA of the intake air amount GA after the execution of the fuel cut control is equal to or greater than a predetermined value GAa”, or “the engine rotation after the execution of the fuel cut control is stopped”. It is also possible to set a condition such as “the integrated value ΣNE of the speed NE has become equal to or greater than the predetermined value NEa”. In these configurations, the predetermined value GAa or the predetermined value NEa may be set to a larger value as the execution continuation interval is longer.

  In short, it is only necessary that the start of fuel addition by the fuel addition valve 26 can be delayed for a predetermined period after the execution of the fuel cut control is stopped. Thereby, the effect according to the effect as described in (3) mentioned above is acquired. In addition, in this case, by setting the predetermined period to a longer time as the execution duration is longer, an effect similar to the effect described in (4) above can be obtained.

Note that a configuration in which the predetermined period is set to a longer time as the execution duration time is longer can be omitted.
In the first and second embodiments, the condition for determining that the engine operating state has shifted is arbitrary as long as it can be determined that the engine operating state has shifted from the deceleration state to another operating state. Can be changed. For example, when it is determined that the operating state in which the fuel cut control is performed has shifted to the operating state in which the fuel cut control is stopped, the fuel injection amount Q is reduced from the first predetermined amount Qb to the second predetermined amount. What is necessary is just to judge that the engine operation state has shifted when the state becomes equal to or higher than Qc (Qb ≦ Qc). Usually, when the engine speed NE is decelerated, the fuel injection amount Q is set to a very small amount. Therefore, it can be determined that the vehicle is in the deceleration state when the fuel injection amount Q is small, and it can be determined that the operation state is other than the deceleration state when the fuel injection amount Q is large. According to the above configuration, it is possible to determine that the engine operating state has shifted from the deceleration state to another operating state based on the fuel injection amount Q.

  Further, the determination is not limited to the determination based on the fuel injection amount Q, and the determination may be made based on the operation state and operation state of the vehicle and the internal combustion engine 10. Examples of such driving states and operating states include the accelerator depression amount ACC, the engine speed NE, the intake air amount GA, the traveling speed of the vehicle, the operation amount of the brake operation member, and the like.

In addition, after the engine operating state shifts, the start of fuel addition from the fuel addition valve 26 may be started immediately without delay.
In the third embodiment, the condition for determining that the engine operating state has shifted from the operating state other than the accelerated state to the accelerated state can be changed as appropriate. The engine operating state has shifted to the acceleration state when, for example, the increasing speed of the fuel injection amount Q, the increasing speed of the engine rotational speed NE, the increasing speed of the intake air amount GA, or the increasing speed of the vehicle traveling speed is equal to or higher than a predetermined speed. It is possible to judge with certain things.

The present invention can also be applied to an internal combustion engine provided with another accelerator operation member such as an accelerator lever instead of the accelerator pedal.
The present invention is also applicable to an exhaust purification device in which fuel is added to exhaust gas by injecting fuel from a fuel injection valve into a combustion chamber in an expansion stroke or an exhaust stroke separately from fuel injection for generating torque. Can do.

  The present invention can be applied to a gasoline engine in which lean combustion is performed in addition to a diesel engine.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows the schematic structure about 1st Embodiment which actualized the exhaust gas purification device of the internal combustion engine concerning this invention. The timing chart which shows an example of the drive mode about the fuel addition valve of 1st Embodiment. The flowchart which shows the specific process sequence about the fuel addition control process concerning 1st Embodiment. (A)-(e) The timing chart which shows an example of the process aspect about the fuel addition control process. The flowchart which shows the specific process sequence about the fuel addition control process concerning the 2nd Embodiment of this invention. The schematic diagram which shows the relationship between the predetermined value and execution continuation time in 2nd Embodiment. (A)-(e) The timing chart which shows an example of the process aspect about the fuel addition control process concerning 2nd Embodiment. The flowchart which shows the specific process sequence about the fuel addition control process concerning the 3rd Embodiment of this invention. (A)-(c) The timing chart which shows an example of the process aspect about the fuel addition control process. The flowchart which shows the specific process sequence about the example of a change of the fuel addition control process concerning 2nd Embodiment. The schematic diagram which shows the relationship between the predetermined time in the example of a change, and execution duration.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 12 ... Combustion chamber, 14 ... Fuel injection valve, 16 ... Accumulation piping, 18 ... Fuel pump, 20 ... Fuel tank, 22 ... Exhaust passage, 24 ... Exhaust manifold, 26 ... Fuel addition valve, 28 ... Output Axis 30 ... NOx occlusion reduction catalyst 32 ... accelerator pedal 40 ... electronic control unit 42 ... intake amount sensor 44 ... rotation speed sensor 46 ... accelerator sensor

Claims (11)

It is provided in the exhaust passage of an internal combustion engine that performs lean combustion, and stores NOx in the exhaust when the exhaust air-fuel ratio is lean, and reduces the stored NOx by making the exhaust air-fuel ratio rich. A NOx occlusion reduction catalyst; and a fuel addition means for adding fuel into the exhaust upstream of the NOx occlusion reduction catalyst, and the exhaust air-fuel ratio is temporarily made rich through the fuel addition by the fuel addition means. In an exhaust gas purification apparatus for an internal combustion engine that recovers the NOx storage capacity of a NOx storage reduction catalyst,
An exhaust gas purification apparatus for an internal combustion engine, wherein fuel addition by the fuel addition means is executed when the engine operation state shifts from a deceleration state to another operation state. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
The transition is determined when the fuel injection amount is less than the first predetermined amount and when the fuel injection amount is changed to a state equal to or greater than a second predetermined amount that is equal to or greater than the first predetermined amount. An exhaust purification device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2,
The exhaust gas purification apparatus for an internal combustion engine, wherein the fuel addition means is a fuel addition valve provided upstream of the NOx storage reduction catalyst in the exhaust passage. The exhaust gas purification apparatus for an internal combustion engine according to claim 3,
The start of fuel addition by the fuel addition valve is delayed for a period after the transition until the wall surface temperature of the exhaust passage becomes equal to or higher than a predetermined temperature. The exhaust gas purification apparatus for an internal combustion engine according to claim 3,
The start of fuel addition by the fuel addition valve is delayed for a predetermined period after the shift. The exhaust gas purification apparatus for an internal combustion engine according to claim 5,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the predetermined period is a period until the fuel injection amount integrated value after the transition becomes equal to or greater than a predetermined value. The exhaust gas purification apparatus for an internal combustion engine according to claim 5 or 6,
The exhaust gas purification apparatus for an internal combustion engine, wherein the predetermined period is set to a longer period as the duration time of the deceleration state immediately before the transition is longer. It is provided in the exhaust passage of an internal combustion engine that performs lean combustion, and stores NOx in the exhaust when the exhaust air-fuel ratio is lean, and reduces the stored NOx by making the exhaust air-fuel ratio rich. A NOx occlusion reduction catalyst; and a fuel addition means for adding fuel into the exhaust upstream of the NOx occlusion reduction catalyst, and the exhaust air-fuel ratio is temporarily made rich through the fuel addition by the fuel addition means. In an exhaust gas purification apparatus for an internal combustion engine that recovers the NOx storage capacity of a NOx storage reduction catalyst,
An exhaust emission control device for an internal combustion engine, wherein fuel addition by the fuel addition means is executed when the engine operating state shifts from an operating state other than the accelerated state to the accelerated state. The exhaust emission control device for an internal combustion engine according to claim 8,
The shift is determined when the operating speed of the accelerator operating member toward the acceleration side becomes equal to or higher than a predetermined speed. The exhaust gas purification apparatus for an internal combustion engine according to claim 8 or 9,
The shift is determined when the increasing speed of the fuel injection amount becomes equal to or higher than a predetermined speed. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 8 to 10,
The exhaust gas purification apparatus for an internal combustion engine, wherein the fuel addition means is a fuel addition valve provided upstream of the NOx storage reduction catalyst in the exhaust passage.

Images