JP2009174445A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for both suppressing clogging of a nozzle hole of an addition valve and improving exhaust emission, in an exhaust emission control device for an internal combustion engine having: the addition valve for adding a reducing agent from the nozzle hole facing the inside of an exhaust passage to exhaust gas; and a storage reduction type NOx catalyst. <P>SOLUTION: In the exhaust emission control device for the internal combustion engine, when recovery control for recovering purification capacity of the storage reduction type NOx catalyst is performed, at least combustion rich is performed by a combustion rich means, and an air fuel ratio of exhaust gas flowing in to the storage reduction type NOx catalyst is reduced to a target air fuel ratio. The exhaust emission control device is further provided with a forced addition means performing forced addition control for forcedly adding the reducing agent to the addition valve at predetermined target timing when the recovery control is performed. The target timing is determined so that the reducing agent for the forced addition control is made to flow into the storage reduction type NOx catalyst while NOx or SOx is separated from the storage reduction type NOx catalyst. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  In recent years, internal combustion engines mounted on automobiles and the like, particularly diesel engines and lean burn gasoline engines capable of combusting an air-fuel mixture in an oxygen-excess state, have a NOx catalyst for purifying NOx in the exhaust gas in the exhaust system of the internal combustion engine. Techniques for placement have been proposed. As an example of this NOx catalyst, nitrogen oxide (NOx) in the exhaust gas is occluded when the air-fuel ratio of the inflowing exhaust gas is high, and occluded when the air-fuel ratio of the inflowing exhaust gas is reduced and a reducing agent is present. An NOx storage reduction catalyst that reduces NOx while removing NOx is known.

  In this specification, the term “occlusion” is used to include both “absorption” and “adsorption”. In addition, the term “detachment” from the NOx storage agent is used to include the meaning of “desorption” corresponding to “adsorption” in addition to “release” corresponding to “absorption”.

  Here, the NOx storage reduction catalyst stores SOx in addition to NOx in the exhaust. As the NOx or SOx storage amount in the NOx catalyst increases, the purification capacity of the catalyst decreases, so the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is reduced and the reducing agent is supplied to reduce the purification capacity of the catalyst. Recovery control (for example, NOx reduction processing, SOx poisoning recovery processing, etc.) for recovering the gas is performed.

  Examples of a method for reducing the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst include a method for reducing the air-fuel ratio of the exhaust gas discharged from the internal combustion engine (hereinafter also referred to as “combustion rich”). Combustion richness is achieved by reducing the air-fuel ratio of the exhaust discharged from the internal combustion engine by reducing the intake air amount by the intake throttle valve, increasing the EGR gas amount, sub-injection performed after the main injection into the cylinder, etc. Can be made.

  Further, a reducing agent (for example, fuel) is injected from an addition valve in which an injection hole is formed so as to face the exhaust passage of the internal combustion engine, and the reducing agent is added to the exhaust gas flowing into the NOx storage reduction catalyst. A method for reducing the fuel ratio can be exemplified.

  By the way, since the exhaust gas discharged from the internal combustion engine contains smoke and SOF, if smoke or SOF enters the nozzle hole of the addition valve, it may become a deposit and clog the nozzle hole. Therefore, if the combustion rich is executed when the recovery control for the NOx storage reduction catalyst is performed, the combustion state deteriorates and the amount of smoke and SOF emissions increases, and the possibility that the injection valve nozzle hole becomes clogged increases.

In this regard, Patent Document 1 discloses that an exhaust gas purification apparatus for an internal combustion engine that adds a reducing agent to exhaust gas through an addition valve formed with an injection hole so as to face the exhaust passage has a large amount of smoke in the exhaust gas. A technique for suppressing clogging of the injection hole by forcibly carrying out the addition of the reducing agent by the addition valve when it is predicted that the situation will occur (hereinafter referred to as clogging of the injection hole of the addition valve) is disclosed. The addition for suppressing the above is also referred to as “forced addition”). In addition, as a situation where a large amount of smoke is generated, a time when the internal combustion engine is accelerated, a time when the combustion mode is switched between the normal combustion mode and the low temperature combustion mode is disclosed.
Japanese Patent Laid-Open No. 2005-83196

  However, when the combustion rich is performed as described above, the oxygen concentration of the exhaust discharged from the internal combustion engine becomes low. If forced addition is performed on the addition valve in conjunction with the rich combustion, the reducing agent in the NOx storage reduction catalyst may not be sufficiently oxidized. As a result, the reducing agent for forced addition or the hydrocarbons (HC), carbon monoxide (CO), etc. originally contained in the exhaust discharged from the internal combustion engine pass through the NOx storage reduction catalyst, and the exhaust emission deteriorates. There was a case.

  The present invention has been made in view of the above prior art, and an object of the present invention is to provide an addition valve for adding a reducing agent to exhaust gas from an injection hole facing the exhaust passage and an occlusion reduction type NOx catalyst. It is an object of the present invention to provide a technology capable of achieving both suppression of injection hole clogging in an addition valve and improvement of exhaust emission in an exhaust gas purification apparatus for an internal combustion engine.

In order to achieve the above object, an exhaust emission control device for an internal combustion engine according to the present invention employs the following means.
That is, the NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine,
Combustion rich means for performing combustion rich to lower the air-fuel ratio of the exhaust discharged from the internal combustion engine;
An addition valve for adding a reducing agent to the exhaust from the injection hole facing the exhaust passage upstream of the NOx storage reduction catalyst;
With
When performing recovery control to recover the purification capacity of the NOx storage reduction catalyst, at least the combustion rich means executes combustion rich to lower the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst to the target air-fuel ratio In an exhaust gas purification device for an internal combustion engine,
When performing the recovery control, further comprising a forced addition means for performing a forced addition control for forcibly adding a reducing agent to the addition valve at a predetermined target timing,
The target timing is determined such that a reducing agent for the forced addition control flows into the NOx storage reduction catalyst while NOx or SOx is released from the NOx storage reduction catalyst. To do.

  Here, the purification of the NOx storage reduction catalyst is performed as in the case of performing the NOx reduction process for reducing the NOx stored in the NOx storage reduction catalyst or the SOx poisoning recovery process for recovering the sulfur poisoning. When carrying out recovery control for restoring the capacity, the reducing agent is supplied while lowering the air-fuel ratio of the exhaust gas flowing into the catalyst. In the recovery control in the present invention, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is lowered to the target air-fuel ratio by executing the combustion rich by the combustion rich means at least.

  In the present specification, the above “at least” means that the exhaust air-fuel ratio is reduced by adding the reducing agent from the addition valve, and the exhaust air-fuel ratio is reduced and the combustion rich is executed together. It means that the air-fuel ratio may be lowered. The target air-fuel ratio is desirably determined so that NOx occluded in the form of nitrate or the like can be reliably separated from the NOx storage reduction catalyst. For example, the target air-fuel ratio is set as a substantially stoichiometric air-fuel ratio or rich air-fuel ratio. In addition, as a reducing agent from an addition valve, fuel (light oil) etc. can be illustrated, for example.

  When combustion rich is executed during recovery control, the exhaust from the internal combustion engine contains a large amount of smoke and SOF, and the smoke and SOF that enter the nozzle hole of the addition valve become deposits and the nozzle hole is easily clogged. End up. Therefore, in the present invention, the forced addition control is performed when the recovery control is performed to suppress the clogging of the injection hole in the addition valve.

  When combustion rich is executed in the recovery control, NOx and SOx are released from the NOx storage reduction catalyst. Therefore, in the present invention, the target timing for forcibly adding the reducing agent in the forced addition control is set such that the reducing agent for the forced addition control while the NOx or SOx is released from the NOx storage reduction catalyst is the storage reduction type. Decide to flow into the NOx catalyst. According to this, a redox reaction occurs between the reducing agent for the forced addition control flowing into the NOx storage reduction catalyst and NOx or SOx. That is, the reducing agent for forced addition control can be oxidized using the NOx or SOx as an oxidizing agent. Here, NOx or SOx functioning as an oxidant is originally included in NOx or SOx that is stored in the NOx storage reduction catalyst and then desorbed from the catalyst due to execution of combustion rich, as well as in the exhaust gas flowing into the catalyst. Also included are NOx and SOx.

  According to the present invention, since the reducing agent for forced addition control can be reliably oxidized, the release of the reducing agent into the atmosphere is suppressed. Accordingly, it is possible to suitably achieve both suppression of nozzle hole clogging in the addition valve and improvement of exhaust emission.

  By the way, in one recovery control, the amount of NOx released when NOx is released from the NOx storage reduction catalyst or the amount of SOx released when SOx is released changes over time. Here, the NOx desorption amount may be defined as the mass of NOx per unit time desorbing from the NOx storage reduction catalyst. Similarly, the SOx desorption amount may be defined as the mass of SOx per unit time desorbing from the NOx storage reduction catalyst.

  When recovery control is executed, the NOx separation amount or SOx separation amount gradually increases as the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst decreases, and eventually reaches the peak value (maximum value). To do. Then, after reaching the peak value, the NOx separation amount and the SOx separation amount gradually decrease.

  Therefore, when NOx occluded in the NOx storage reduction catalyst is reduced by performing recovery control, the NOx desorption amount desorbing from the NOx storage reduction catalyst is compulsory within a range in which the NOx removal amount is maintained above the first reference value. The target timing may be determined so that the reducing agent for addition control flows into the NOx storage reduction catalyst.

  The first reference value is a lower limit value of the NOx removal amount necessary and sufficient to cause the reducing agent for forced addition control to react with NOx released from the catalyst in the NOx storage reduction catalyst and oxidize it. You can ask for it.

  Further, when SOx stored in the NOx storage reduction catalyst is reduced by the recovery control, the SOx release amount released from the NOx storage reduction catalyst is compulsory within a range in which the SOx release amount is maintained at the second reference value or more. The target timing may be determined so that the reducing agent for addition control flows into the NOx storage reduction catalyst. The second reference value is a lower limit value of the amount of SOx released that is necessary and sufficient to cause the reducing agent for forced addition control to react with SOx released from the catalyst in the NOx storage reduction catalyst and oxidize. You can ask for it.

  By determining the target timing as described above, the reducing agent for forced addition control can be more reliably oxidized by NOx or SOx released from the NOx storage reduction catalyst. In the present invention, the period during which the reducing agent for forced addition control flows into the NOx storage reduction catalyst is a part of the period during which the NOx removal amount is maintained at the first reference value or more, or the SOx removal amount is the second. It may be a part of the period maintained above the reference value.

Further, when the forced addition control is performed, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is made rich in a spike (with a short time) in a relatively short cycle, the NOx storage reduction type
It is preferable to perform forced addition control in synchronization with NOx or SOx periodically leaving the x catalyst.

In order to achieve the above object, an exhaust emission control device for an internal combustion engine according to the present invention includes:
An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
Combustion rich means for performing combustion rich to lower the air-fuel ratio of the exhaust discharged from the internal combustion engine;
A rear catalyst provided in an exhaust passage downstream of the NOx storage reduction catalyst;
An addition valve for adding a reducing agent to the exhaust from the injection hole facing the exhaust passage between the NOx storage reduction catalyst and the rear catalyst;
With
When performing recovery control to recover the purification capacity of the NOx storage reduction catalyst, at least the combustion rich means executes combustion rich to lower the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst to the target air-fuel ratio In an exhaust gas purification device for an internal combustion engine,
When performing the recovery control, further comprising a forced addition means for performing a forced addition control for forcibly adding a reducing agent to the addition valve at a predetermined target timing,
The target timing is determined so that the reducing agent for the forced addition control flows into the rear catalyst while NOx or SOx flowing out from the NOx storage reduction catalyst flows into the rear catalyst. It may be characterized.

  In the above configuration, the reducing agent is added to the exhaust gas from the addition valve in order to purify harmful substances in the exhaust gas in the post-stage catalyst, or to increase the temperature of the post-stage catalyst. For example, the post-stage catalyst may be a selective reduction type NOx catalyst. In that case, the reducing agent supplied to the selective reduction type NOx catalyst may be a reducing agent derived from ammonia. The ammonia-derived reducing agent includes ammonia and an ammonia generator that generates ammonia. For example, ammonia water, urea water, etc. can be illustrated as a reducing agent derived from ammonia.

  For example, when urea water is employed as the reducing agent, the urea water added to the exhaust gas is hydrolyzed to generate ammonia. The ammonia is supplied to the selective reduction type NOx catalyst, whereby NOx is reduced. On the other hand, for the NOx storage reduction catalyst, recovery control is performed by causing at least the combustion rich means to execute combustion rich and reducing the air-fuel ratio of the exhaust gas flowing into the catalyst to the target air-fuel ratio as described above. .

  In the above configuration, when recovery control to the NOx storage reduction catalyst is performed, the nozzle hole of the addition valve disposed on the downstream side of the NOx storage reduction catalyst is likely to be clogged with smoke or SOF. In the present invention, clogging of the addition valve is suppressed by executing the forced addition control when the recovery control is performed. That is, when combustion rich is executed in the recovery control, NOx and SOx flow out from the NOx storage reduction catalyst and flow into the downstream downstream catalyst. Therefore, the target timing when the reducing agent is forcibly added from the addition valve in the present invention is determined so that the reducing agent for forced addition control flows into the rear catalyst while the NOx or SOx flows into the rear catalyst. Is done.

  According to this, it is possible to oxidize the NOx or SOx flowing into the rear catalyst by using the reducing agent for forced addition control as an oxidizing agent. Here, NOx or SOx is NOx or SOx that is originally contained in the exhaust discharged from the internal combustion engine, in addition to NOx or SOx released from the NOx storage reduction catalyst by execution of rich combustion. NOx or SOx that has passed through without being occluded is also included. According to the present invention, since the reducing agent for forced addition control can be reliably oxidized, the reducing agent can be prevented from passing through the rear catalyst and being released into the atmosphere. Therefore, it is possible to suitably achieve both suppression of nozzle hole clogging in the addition valve and improvement of exhaust emission.

  Further, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is made rich in a spike in a relatively short period in the recovery control, the reducing agent for the forced addition control is intermittently or You may supply a reducing agent continuously. In that case, it is preferable to synchronize the timing when the reducing agent for forced addition control flows into the rear catalyst and the timing when NOx or SOx flows into the rear catalyst.

In order to achieve the above object, an exhaust emission control device for an internal combustion engine according to the present invention includes:
An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
Combustion rich means for performing combustion rich to lower the air-fuel ratio of the exhaust discharged from the internal combustion engine;
An addition valve for adding a reducing agent to the exhaust from the injection hole facing the exhaust passage upstream of the NOx storage reduction catalyst;
With
When performing recovery control to recover the purification capacity of the NOx storage reduction catalyst, at least the combustion rich means executes combustion rich to lower the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst to the target air-fuel ratio In an exhaust gas purification device for an internal combustion engine,
When performing the recovery control, further comprising a forced addition means for performing a forced addition control for forcibly adding a reducing agent to the addition valve at a predetermined target timing,
The target timing is that the reducing agent for the forcible addition control after the oxygen storage amount of the NOx storage reduction catalyst recovers to a third reference value or more upon completion of the combustion rich by the combustion rich means. It may be characterized in that it is determined to flow into the catalyst.

  Here, the NOx storage reduction catalyst has an oxygen storage capacity. When the air-fuel ratio of the exhaust gas flowing into the catalyst is high, oxygen in the exhaust gas is stored, and when the air-fuel ratio of the exhaust gas decreases, the stored oxygen is released. Can be made. In the present invention, when the recovery control is performed, the air-fuel ratio of the exhaust gas is remarkably lowered, so that most of the oxygen stored in the catalyst is released. When the forced addition control is executed in a state where the oxygen storage amount is small as described above, the reducing agent for the forced addition control cannot be sufficiently oxidized by the NOx storage reduction catalyst, and the reducing agent moves to the downstream side of the catalyst. There is a possibility of slipping through.

  Therefore, the target timing in the present invention is that the reducing agent for the forced addition control flows into the NOx storage reduction catalyst after the oxygen storage amount of the NOx storage reduction catalyst recovers to the third reference value or more by the end of the combustion rich. To be determined. The third reference value is a lower limit value of the oxygen storage amount that can be determined to be sufficient to oxidize the reducing agent for forced addition control with the oxygen stored in the NOx storage reduction catalyst, and is previously determined experimentally. be able to.

  According to this, when the reducing agent for forced addition control flows into the NOx storage reduction catalyst, the oxygen storage amount once reduced by the execution of the recovery control is restored to the third reference value or more. The reducing agent can be reliably oxidized. Therefore, it is possible to suitably achieve both suppression of nozzle hole clogging in the addition valve and improvement of exhaust emission.

In order to achieve the above object, an exhaust emission control device for an internal combustion engine according to the present invention includes:
An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
Combustion rich means for performing combustion rich to lower the air-fuel ratio of the exhaust discharged from the internal combustion engine;
An addition valve for adding fuel as a reducing agent to the exhaust from the injection hole facing the exhaust passage upstream of the NOx storage reduction catalyst;
An HC adsorption oxidation catalyst provided in an exhaust passage downstream of the NOx storage reduction catalyst and capable of adsorbing and oxidizing hydrocarbons contained in exhaust gas;
With
When performing recovery control to recover the purification capacity of the NOx storage reduction catalyst, at least the combustion rich means executes combustion rich to lower the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst to the target air-fuel ratio In an exhaust gas purification device for an internal combustion engine,
When carrying out the recovery control, further comprising a forced addition means for executing a forced addition control for forcibly adding fuel to the addition valve at a predetermined target timing,
The target timing is determined so that the fuel for the forced addition control after the adsorption amount of the hydrocarbon adsorbed on the HC adsorption oxidation catalyst decreases to a fourth reference value or less due to the end of the combustion rich by the combustion rich means. It may be characterized in that it is determined to flow into the HC adsorption oxidation catalyst.

  According to the above configuration, the hydrocarbons in the exhaust gas that has passed through the NOx storage reduction catalyst are adsorbed by the HC adsorption oxidation catalyst, and the exhaust gas having excess oxygen flows into the HC adsorption oxidation catalyst, and is adsorbed by the catalyst. The hydrocarbons are oxidized. Here, when the recovery control is performed, the exhaust gas contains more hydrocarbons than usual due to the rich combustion. As a result, the amount of adsorption of hydrocarbons in the HC adsorption oxidation catalyst increases.

  If the forced addition control is executed at this time, the fuel for the forced addition control, that is, the hydrocarbon, cannot be absorbed by the HC adsorption oxidation catalyst, and there is a high possibility that this fuel will slip through downstream. Therefore, in the present invention, after the combustion rich is completed, the air-fuel ratio of the exhaust gas flowing into the HC adsorption oxidation catalyst is changed to the lean side, and then the adsorbed hydrocarbons are oxidized to some extent and become relatively small. During this period, execution of forced addition control is awaited.

  In other words, in the present invention, the target timing is that the fuel applied to the forced addition control after the adsorption amount of hydrocarbons adsorbed on the HC adsorption oxidation catalyst decreases to the fourth reference value or less due to the end of combustion rich It is determined to flow into the catalyst. The fourth reference value is the upper limit of the amount of adsorption of hydrocarbons in the HC adsorption oxidation catalyst that can be judged to be surely adsorbed by the HC adsorption oxidation catalyst even if the fuel for forced addition control is added to the exhaust gas. Value.

  According to this, the fuel for the forced addition control is reliably adsorbed by the HC adsorption oxidation catalyst and can be reliably oxidized on the catalyst. Further, since the forced addition control is executed after the combustion rich is completed, oxygen for oxidizing the fuel can be sufficiently supplied. Therefore, according to the present invention, it is possible to suitably achieve both suppression of the injection hole clogging in the addition valve and improvement of exhaust emission.

  The means for solving the problems in the present invention can be used in combination as much as possible.

  According to the present invention, in the exhaust gas purification apparatus for an internal combustion engine provided with the addition valve for adding the reducing agent to the exhaust gas from the nozzle hole facing the exhaust passage of the internal combustion engine and the NOx storage reduction catalyst, the injection at the addition valve It is possible to achieve both suppression of clogging of holes and improvement of exhaust emission.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are intended to limit the technical scope of the invention only to those unless otherwise specified. is not.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which an exhaust gas purification apparatus for an internal combustion engine according to the present embodiment is applied and an intake / exhaust system thereof. The internal combustion engine 1 shown in FIG. 1 is a four-cycle diesel engine.

  An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1. A throttle 4 is provided in the middle of the intake passage 2. The throttle 4 is opened and closed by an electric actuator. An air flow meter 5 that outputs a signal corresponding to the flow rate of the intake air flowing through the intake passage 2 is provided in the intake passage 2 upstream of the throttle 4. The air flow meter 5 measures the amount of fresh intake air in the internal combustion engine 1.

On the other hand, an NOx storage reduction catalyst (hereinafter simply referred to as “NOx catalyst”) 6 is provided in the middle of the exhaust passage 3, and the exhaust passage 3 is connected to a muffler (not shown) downstream of the NOx catalyst 6. ing. For example, the NOx catalyst 6 uses alumina as a carrier, and on the carrier, an alkali metal such as potassium (K), sodium (Na), lithium (Li), or cesium (Cs), barium (Ba) or calcium ( It is configured to support at least one selected from alkaline earths such as Ca), rare earths such as lanthanum (La) or yttrium (Y), and a noble metal such as platinum (Pt). In this embodiment, a NOx catalyst constituted by supporting barium (Ba) and platinum (Pt) on a support made of alumina and further adding ceria (Ce ₂ O ₃ ) having oxygen storage capacity. It was adopted.

  The NOx catalyst 6 configured in this way occludes (absorbs and adsorbs) NOx in the exhaust when the oxygen concentration of the exhaust flowing into the NOx catalyst 6 is high. On the other hand, when the oxygen concentration of the exhaust gas flowing into the NOx catalyst 6 decreases, NOx is released (released) from the NOx catalyst 6. The NOx released from the NOx catalyst 6 reacts with reducing components (hydrocarbon (HC), carbon monoxide (CO), etc.) contained in the exhaust gas, and is reduced and purified.

  In this embodiment, the exhaust passage 3 upstream of the NOx catalyst 6 is provided with a fuel addition valve 7 for adding fuel as a reducing agent into the exhaust from the nozzle hole. That is, the injection hole for injecting fuel in the fuel addition valve 7 is formed so as to face the exhaust passage 3. The fuel addition valve 7 is opened by a signal from the ECU 20 described later to inject fuel. In this embodiment, the fuel addition valve 7 corresponds to the addition valve in the present invention.

  The internal combustion engine 1 configured as described above is provided with an ECU 20 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 20 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  The ECU 20 has an accelerator opening sensor 13 that can detect an engine load by outputting an electric signal corresponding to the amount of depression of the accelerator pedal 12 by the driver, and a crank position sensor 14 that detects the engine speed via electric wiring. The output signals of these various sensors are input to the ECU 20. On the other hand, the fuel injection valve 11 and the fuel addition valve 7 are connected to the ECU 20 via electrical wiring, and the ECU 20 controls the opening and closing timing of the fuel injection valve 11 and the fuel addition valve 7.

  For example, the ECU 20 performs control related to fuel injection of the fuel injection valve 11 based on the operating state of the internal combustion engine 1 that is grasped from the output signals of various sensors. The fuel injection amount and injection timing are basically determined based on a depression amount of the accelerator pedal 12 detected by the accelerator opening sensor 13 and an engine speed detected by the crank position sensor 14 (shown in the figure). It is determined with reference to (omitted).

  Here, since the NOx occlusion capacity of the NOx catalyst 6 is limited, the NOx occlusion capacity of the NOx catalyst 6 is saturated when the internal combustion engine 1 is operated for lean combustion over a long period of time. Therefore, in this embodiment, before the NOx occlusion capacity of the NOx catalyst 6 is saturated, NOx reduction processing for reducing and purifying NOx occluded in the NOx catalyst 6 is performed.

  Specifically, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 6 (hereinafter referred to as “inflow exhaust air-fuel ratio”) is made rich in a spike (short time) in a relatively short cycle toward the target air-fuel ratio. In other words, so-called rich spike control is executed. The target air-fuel ratio in this embodiment is set as a rich air-fuel ratio. As a result, NOx occluded in the NOx catalyst 6 is released from the NOx catalyst 6 and is reduced by reacting with HC, CO, etc. in the exhaust. The NOx reduction process in the present embodiment is an example of the recovery control in the present invention.

  In the rich spike control, the inflow exhaust air-fuel ratio is reduced to the target air-fuel ratio by reducing the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 or by injecting fuel from the fuel addition valve 7. be able to. That is, by supplying a reducing agent to the NOx catalyst 6 by these means, NOx occluded in the NOx catalyst 6 can be reduced.

  Here, when lowering the air-fuel ratio of the exhaust discharged from the internal combustion engine 1, the ECU 20 reduces the intake air amount by changing the throttle 4 to the closed side or during the expansion stroke after performing the main injection. Alternatively, the fuel injection valve 11 is caused to perform sub-injection (post injection) for injecting fuel again during the exhaust stroke. Further, the internal combustion engine 1 in this embodiment may include an EGR device that recirculates a part of the exhaust gas flowing through the exhaust passage 3 to the intake passage 2. In this case, even if the amount of exhaust gas (EGR gas) recirculated from the exhaust passage 3 to the intake passage 2 is increased, the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 can be reduced. good.

  Here, the reduction of the exhaust air-fuel ratio discharged from the internal combustion engine 1 is hereinafter referred to as “combustion rich”. In this embodiment, the ECU 20 that controls the throttle 4 and the fuel injection valve 11 to execute the combustion rich corresponds to the combustion rich means in the present invention. The reduction in the exhaust air-fuel ratio caused by injecting fuel from the fuel addition valve 7 is hereinafter referred to as “exhaust addition rich”.

  In the present embodiment, when rich spike control is executed, at least combustion rich is executed, and the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 is lowered compared to the base air-fuel ratio. The base air-fuel ratio is the air-fuel ratio of the internal combustion engine 1 when the rich spike control is not executed, and is set by the load of the internal combustion engine 1 or the like. According to this, the air-fuel ratio of the air-fuel mixture can be greatly reduced in the combustion chamber of the internal combustion engine 1, and CO with high NOx reduction efficiency is generated in the combustion chamber, so that the NOx reduction efficiency can be increased. .

  However, depending on the operating state of the internal combustion engine 1, it may be difficult to reduce the inflow exhaust air-fuel ratio to the target air-fuel ratio only by executing the combustion rich. For example, when the amount of fuel injection from the combustion injection valve 11 is large, such as during high-load operation of the internal combustion engine 1, the combustion state of the air-fuel mixture in the combustion chamber may become unstable. In that case, the inflow exhaust air-fuel ratio can be reliably lowered to the target air-fuel ratio by executing the exhaust addition rich together.

Specifically, in this embodiment, the ECU 20 determines whether or not the execution condition of the rich spike control is satisfied. The execution condition of the rich spike control is satisfied when it is determined that the NOx reduction process or the SOx poisoning recovery process should be executed in this embodiment. For example, the NOx occlusion amount and the SOx occlusion amount in the NOx catalyst 6 are estimated based on the operation history of the internal combustion engine 1 and the rich spike control is performed when these estimated values reach a predetermined value or more set for each of them. The execution condition is met.

  Then, the ECU 20 detects the operating state of the internal combustion engine 1. Specifically, the current output value of the accelerator opening sensor 13, the output value of the crank position sensor 14, the output value of the air flow meter 5, etc. are read by the ECU 20. Then, the ECU 20 sets the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 that is a target when performing the combustion rich based on the current base air-fuel ratio and the target air-fuel ratio, and the throttle 4 And the post-injection amount by the fuel injection valve 11 are controlled, and combustion rich is executed. If the inflow exhaust air-fuel ratio cannot be reduced to the target air-fuel ratio only by executing the combustion rich, the ECU 20 determines the fuel addition amount and the addition timing for the exhaust addition rich by the fuel addition valve 7, and the exhaust Additive rich is performed.

  By the way, when the combustion rich is executed in the rich spike control as described above, the amount of smoke and SOF discharged from the internal combustion engine 1 is increased as compared with the normal operation. When this smoke or SOF component enters the nozzle hole of the fuel addition valve 7, it becomes a deposit and the nozzle hole is easily clogged.

  Therefore, the ECU 20 forcibly adds fuel into the exhaust from the fuel addition valve 7 in order to suppress clogging of the nozzle hole of the fuel addition valve 7 that is likely to occur due to rich combustion (hereinafter referred to as “forced addition”). Control). As a result, the smoke or SOF deposited in the nozzle hole of the fuel addition valve 7 can be washed away by the fuel.

  Next, the timing (hereinafter referred to as “forced addition timing”) Tm for adding fuel for forced addition control in this embodiment will be described. In this embodiment, the forced addition timing Tm corresponds to the predetermined target timing in the present invention. FIG. 2 is a time chart illustrating the rich combustion ON / OFF, the inflow exhaust air-fuel ratio A / F, and the NOx release amount Qdn in the NOx catalyst 6 when the rich spike control is executed.

  The time chart shown in the uppermost row shows ON / OFF of rich combustion. Here, rich combustion is executed when ON, and is not executed when OFF. That is, in FIG. 2, combustion rich is performed from time t1 to time t2.

  The time chart shown in the middle stage shows the inflow exhaust air-fuel ratio A / F, and the time chart shown in the bottom stage shows the NOx release amount Qdn. The NOx release amount Qdn is the release amount per unit time of NOx released from the NOx catalyst 6 as the inflow exhaust air-fuel ratio A / F decreases. In this embodiment, the NOx release amount Qdn corresponds to the NOx release amount in the present invention.

  When combustion rich is turned on at time t1, that is, when execution of combustion rich is started, the inflowing exhaust air-fuel ratio A / F decreases toward the target air-fuel ratio. As a result, since NOx stored in the NOx catalyst 6 is released, the NOx release amount Qdn increases. Here, the NOx release amount Qdn is not constant when the combustion rich is performed, and increases as time passes after the start of NOx release as shown in the figure, but eventually reaches the peak value (maximum value) Qdnpeak. This is because the NOx occlusion amount gradually decreases due to the release of NOx. The NOx release amount Qdn gradually decreases after reaching the peak value Qdnpeak. Then, when the execution of the combustion rich is completed at time t2, the NOx release amount Qdn rapidly decreases and finally the NOx release amount Qdn becomes zero.

In the forced addition control of this embodiment, the fuel for forced addition control is added to the fuel addition valve 7 so that an oxidation-reduction reaction occurs with NOx. By doing so, the fuel concerning forced addition control can be reliably oxidized using NOx as an oxidant. The NOx includes NOx originally included in the exhaust gas discharged from the internal combustion engine 1 and flowing into the NOx catalyst 6 in addition to NOx released from the NOx catalyst 6 by execution of the rich combustion.

  Here, the symbol Qdnb shown in the figure indicates the reference NOx release amount. The reference NOx release amount Qdnb is a lower limit value of the NOx release amount sufficient to oxidize the fuel for forced addition control with the NOx released from the NOx catalyst 6, and is obtained experimentally in advance. In this embodiment, the reference NOx release amount corresponds to the first reference value in the present invention.

  Here, the beginning of the period in which the NOx release amount Qdn is maintained at the reference NOx release amount Qdnb or more is shown in the drawing at time t3 and the end at time t4. The forcible addition timing Tm in the present embodiment is within the range from time t3 to time t4, that is, within the period during which the NOx release amount Qdn is maintained at or above the reference NOx release amount Qdnb. It is determined to flow into the catalyst 6. Here, after the fuel for the forced addition control is added from the fuel addition valve 7, there may be a slight time lag until the fuel actually flows into the NOx catalyst 6. In this respect, the forced addition timing Tm in the present embodiment is determined in consideration of this time lag.

  As described above, according to this control, the smoke and SOF deposited in the nozzle hole of the fuel addition valve 7 can be caused to flow by the fuel, and the fuel can be reliably oxidized in the NOx catalyst 6. Accordingly, it is possible to suitably achieve both suppression of nozzle hole clogging and improvement of exhaust emission in the fuel addition valve 7.

  In FIG. 2, the inflow exhaust air-fuel ratio A / F and the NOx release amount Qdn change linearly with time, but this is merely a simulation and may be, for example, curved. Of course it is good. Of course, the period during which the fuel for the forced addition control flows into the NOx catalyst 6 may be a partial period in the range from the time t3 to the time t4. In order to oxidize the fuel with NOx more reliably, the forced addition timing Tm is determined so that the fuel from the fuel addition valve 7 flows into the NOx catalyst 6 at a timing when the NOx release amount Qdn becomes near the peak value Qdnpeak. Also good.

  Regarding the relationship between the time t1 at which the execution of the rich combustion related to the rich spike control is started, the time t3 that determines the period during which the NOx release amount Qdn is maintained above the reference NOx release amount Qdnb, the time t4, and the forced addition timing Tm It may be obtained experimentally in advance and stored in the ECU 20 as a map. Further, the forcible addition timing Tm may be determined by detecting the NOx release amount Qdn from the NOx catalyst 6 with a NOx sensor.

  Next, an application example of forced addition control in the present embodiment will be described. In the application example described below, the fuel for the forced addition control is oxidized by the SOx released from the NOx catalyst 6 when performing the SOx poisoning recovery process for recovering the SOx poisoning of the NOx catalyst 6.

  When SOx contained in the exhaust gas flows into the NOx catalyst 6, it is occluded by a mechanism substantially similar to that of NOx. When the SOx occlusion amount increases, SOx poisoning that reduces the NOx occlusion capacity of the NOx catalyst 6 occurs, so the SOx poisoning recovery process is performed.

  Specifically, the ambient temperature of the NOx catalyst 6 is raised to a high temperature range of approximately 600 to 650 ° C. and rich spike control is performed to bring the inflow exhaust air-fuel ratio A / F to the target air-fuel ratio that is the rich air-fuel ratio. Reduce. Then, the SOx stored in the NOx catalyst 6 is released from the NOx catalyst 6 and is reduced by reacting with HC and CO.

  Here, the forcible addition timing Tm in this application example is determined so that the fuel for the forcible addition control flows into the NOx catalyst 6 while SOx is released from the NOx catalyst 6. The release amount per unit time of SOx released from the NOx catalyst 6 in the SOx poisoning recovery process is referred to as SOx release amount Qds. The forcible addition timing Tm is determined so that the fuel related to the forcible addition control flows into the NOx catalyst 6 within a range in which the SOx release amount Qds is maintained at the reference SOx release amount Qdsb or more.

  The reference SOx release amount Qdsb is a lower limit value of the SOx release amount sufficient to oxidize the fuel for forced addition control to SOx released from the NOx catalyst 6, and is obtained experimentally in advance. In this embodiment, the SOx release amount Qds corresponds to the SOx release amount in the present invention, and the reference SOx release amount Qdsb corresponds to the second reference value. According to this, the fuel concerning forced addition control can be reliably oxidized using SOx as an oxidizing agent. The SOx includes SOx that is discharged from the internal combustion engine 1 and that is originally contained in the exhaust gas that flows into the NOx catalyst 6 in addition to SOx that is released from the NOx catalyst 6 by the execution of the rich combustion.

  Next, a second example will be described as an embodiment for carrying out the present invention. FIG. 3 is a diagram showing a schematic configuration of the internal combustion engine 1 to which the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment is applied and its intake and exhaust system. In FIG. 3, the same components as those shown in FIG.

  In the present embodiment, the exhaust passage 3 downstream of the NOx catalyst 6 is provided with a selective reduction type NOx catalyst (hereinafter referred to as “SCR catalyst”) 21 that reduces and purifies NOx in the exhaust by supplying ammonia. Further, the exhaust passage 3 between the NOx catalyst 6 and the SCR catalyst 21 is provided with a urea addition valve 22 for adding urea water as a reducing agent into the exhaust from the nozzle hole. The nozzle hole for injecting urea water in the urea addition valve 22 is formed so as to face the exhaust passage 3 in the same manner as the nozzle hole of the fuel addition valve 7. The urea addition valve 22 is electrically connected to the ECU 20 and is opened by a signal from the ECU 20 to add urea water into the exhaust gas.

  The urea water added to the exhaust gas from the urea addition valve 22 is hydrolyzed in the exhaust gas to generate ammonia. The ammonia flows into the SCR catalyst 21 together with the exhaust gas, whereby ammonia that acts as a NOx reducing agent is supplied to the SCR catalyst 21. In this embodiment, the urea addition valve 22 corresponds to the addition valve in the present invention. In this embodiment, the SCR catalyst 21 corresponds to the latter stage catalyst in the present invention.

  On the other hand, the NOx reduction process and the SOx poisoning recovery process for the NOx catalyst 6 are the same as in the first embodiment. That is, the ECU 20 performs rich spike control by combustion rich or a combination of combustion rich and exhaust addition rich. During the rich spike, smoke and SOF components in the exhaust gas increase, so that forced addition control for forcibly adding fuel and urea water from the fuel addition valve 7 and the urea addition valve 22 is executed.

  Since the forced addition control for the fuel addition valve 7 has already been described, a description thereof will be omitted, and the forced addition control for the urea addition valve 22 will be described. Part of the NOx released from the NOx catalyst 6 in the NOx reduction process for the NOx catalyst 6 flows out from the NOx catalyst 6 and flows into the SCR catalyst 21. Further, a part of the SOx released from the NOx catalyst 6 in the SOx poisoning recovery process flows out from the NOx catalyst 6 and flows into the SCR catalyst 21.

In this embodiment, the urea water for forced addition control is oxidized by NOx or SOx flowing into the SCR catalyst 21 as described above. That is, the forcible addition timing Tm is determined so that the urea water for the forcible addition control is oxidized by NOx or SOx flowing into the SCR catalyst 21. The NOx or SOx referred to here is NOx or SOx originally contained in the exhaust gas exhausted from the internal combustion engine 1 in addition to NOx or SOx separated from the NOx catalyst 6 by the execution of rich combustion. NOx or SOx that has passed through the catalyst 6 is also included. As a result, the urea water for forced addition control is reliably oxidized using NOx or SOx as an oxidant, so that it is possible to suitably achieve both suppression of nozzle hole clogging in the urea addition valve 22 and improvement of exhaust emission. .

  Further, in this embodiment, the SCR catalyst 21 is provided on the downstream side of the NOx catalyst 6, but instead of this, another type of exhaust purification catalyst may be disposed, and the oxidation catalyst, the oxidation ability and the NOx storage ability may be provided. Any filter such as a particulate filter having

  Next, a third example will be described as an embodiment for carrying out the present invention. The configuration of the internal combustion engine 1 and its intake / exhaust system in this embodiment is the same as the configuration shown in FIG.

  Here, the NOx catalyst 6 has an oxygen storage capacity, stores oxygen when the air-fuel ratio of the exhaust gas flowing into the catalyst is high, and releases the stored oxygen when the air-fuel ratio of the exhaust gas decreases. In the forced addition control according to this embodiment, the fuel is oxidized using oxygen stored in the NOx catalyst 6 as an oxidant.

  The forced addition control which suppresses clogging of the nozzle hole of the fuel addition valve 7 in the present embodiment will be described with reference to FIG. FIG. 4 is a time chart illustrating the ON / OFF of rich combustion in the rich spike control, the inflow exhaust air-fuel ratio A / F, and the oxygen storage amount Qo in the NOx catalyst 6. Here, the oxygen storage amount Qo means the amount of oxygen stored by the oxygen storage capability of the NOx catalyst 6.

  In FIG. 4, rich combustion ON / OFF is shown at the top, the inflow exhaust air-fuel ratio A / F is shown at the middle, and the oxygen storage amount Qo is shown at the bottom. Since rich combustion ON / OFF and inflow exhaust air-fuel ratio A / F have already been described, description thereof will be omitted. As shown in the figure, when the combustion rich is turned on at time t1, that is, when the combustion rich is started and the inflow exhaust air-fuel ratio A / F is lowered, the stored oxygen is released from the NOx catalyst 6, so the oxygen storage amount Qo is reduced. Decrease.

  On the other hand, when the combustion rich is turned off at time t2, that is, when the combustion rich ends, the lean air-fuel ratio exhaust gas flows into the NOx catalyst 6, so the oxygen storage amount Qo increases. Here, the symbol Qob shown in the figure indicates the reference oxygen storage amount Qob. The reference oxygen storage amount Qob is a lower limit value of the oxygen storage amount that can be determined to be sufficient to oxidize the fuel for forced addition control with the oxygen stored in the NOx catalyst 6, and is obtained experimentally in advance. In this embodiment, the reference oxygen storage amount Qob corresponds to the third reference value in the present invention.

  Here, a time point at which the oxygen storage amount Qo recovers until the oxygen storage amount Qo becomes equal to or greater than the reference oxygen storage amount Qob is illustrated in the drawing as time t5. The forced addition timing Tm of this embodiment is determined so that the fuel related to the forced addition control flows into the NOx catalyst 6 after time t5. That is, the forcible addition timing Tm is determined so that the fuel for the forcible addition control flows into the NOx catalyst 6 after the oxygen storage amount Qo recovers to the reference oxygen storage amount Qob or more by the end of the combustion rich. In other words, the flow of fuel for forced addition control into the NOx catalyst 6 is waited until the oxygen storage amount Qo becomes equal to or greater than the reference oxygen storage amount Qob.

In addition, said time t5 can be calculated | required based on the map in which the relationship between the elapsed time from the time t2 when combustion rich is turned off, and the oxygen storage amount Qo was stored. The forced addition timing Tm can be determined based on the time required for the fuel added from the fuel addition valve 7 to flow into the NOx catalyst 6 and the time t5. In this embodiment, an air-fuel ratio sensor or an O2 sensor for detecting the inflow exhaust air-fuel ratio A / F is arranged in the exhaust passage 3 upstream of the NOx catalyst 6, and the forced addition timing Tm is determined based on these detected values. You may do it. In FIG. 4, the inflowing exhaust air-fuel ratio A / F and the oxygen storage amount Qo change linearly with time, but this is merely a simulation, and for example, even if it changes in a curved line. Of course it is good.

  As described above, according to this control, the fuel for the forced addition control can be reliably oxidized by the oxygen stored in the NOx catalyst 6. Therefore, it is possible to suitably achieve both suppression of the injection hole clogging and improvement of exhaust emission in the fuel addition valve 7.

  Next, a fourth example will be described as an embodiment for carrying out the present invention. FIG. 5 is a diagram illustrating a schematic configuration of an internal combustion engine 1 to which the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment is applied and an intake / exhaust system thereof. In FIG. 5, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. As shown in the drawing, in this embodiment, a sweeper 23 capable of adsorbing and oxidizing HC contained in the exhaust is disposed in the exhaust passage 3 downstream of the NOx catalyst 6. The sweeper 23 can oxidize the adsorbed HC when the oxygen-excess exhaust flows. In this embodiment, the sweeper 23 corresponds to the HC adsorption oxidation catalyst in the present invention.

  Next, forced addition control for suppressing clogging of the injection hole of the fuel addition valve 7 in this embodiment will be described with reference to FIG. FIG. 6 is a time chart illustrating the rich combustion ON / OFF in the rich spike control, the inflow exhaust air / fuel ratio A / F, and the HC adsorption amount Qhc in the sweeper 23. In the same figure, rich combustion ON-OFF is shown in the uppermost stage, inflow exhaust air-fuel ratio A / F is shown in the middle stage, and HC adsorption amount Qhc is shown in the lowermost stage. Since rich combustion ON / OFF and inflow exhaust air-fuel ratio A / F have already been described, description thereof will be omitted. In this embodiment, the HC adsorption amount Qhc corresponds to the hydrocarbon adsorption amount in the present invention.

  As shown in the figure, the inflow exhaust air-fuel ratio A / F is substantially equal to the base air-fuel ratio until the combustion rich is turned on at time t1, that is, until the combustion rich is started, and the oxygen-excess exhaust flows into the NOx catalyst 6. Accordingly, the HC in the exhaust gas flowing into the sweeper 23 is adsorbed and oxidized by the sweeper 23, so that the HC adsorption amount Qhc is kept small.

  On the other hand, when the combustion rich is executed at time t1, the inflowing exhaust air-fuel ratio A / F decreases to the target air-fuel ratio that is the rich air-fuel ratio, so that the HC oxidation reaction in the sweeper 23 is not performed. Then, the amount of HC that flows into the sweeper 23 and is adsorbed increases due to an increase in the reducing component in the exhaust gas, so the HC adsorption amount Qhc increases rapidly. When the combustion rich ends at time t2, the inflow exhaust air-fuel ratio A / F is changed to the lean side. As a result, the oxidation reaction of HC adsorbed by the sweeper 23 during the rich combustion is promoted, and the HC adsorption amount Qhc decreases.

The symbol Qhcb shown in the figure indicates the reference HC adsorption amount Qhcb. The reference HC adsorption amount Qhcb is an HC adsorption amount Qhc that can be determined that even if fuel for forced addition control is added from the fuel addition valve 7, the fuel is reliably adsorbed by the sweeper 23 and there is no risk of slipping through the sweeper 23. This is the upper limit value and is experimentally obtained in advance. In this embodiment, the reference HC adsorption amount Qhcb corresponds to the fourth reference value in the present invention. As a result of the HC adsorption amount Qhc increased from the reference HC adsorption amount Qhcb, the oxidation of oxygen is promoted by the end of combustion rich,
The time point when the amount decreases to the reference HC adsorption amount Qhcb is shown in the figure as time t6.

  The forced addition timing Tm of the present embodiment is determined so that the fuel related to the forced addition control flows into the NOx catalyst 6 after time t6. That is, the forcible addition timing Tm is determined so that the fuel for the forcible addition control flows into the sweeper 23 after the HC adsorption amount Qhc decreases below the reference HC adsorption amount Qhcb due to the end of combustion rich.

  In other words, until the HC adsorption amount Qhc decreases below the reference HC adsorption amount Qhcb, the flow of fuel for forced addition control into the sweeper 23 is on standby. As a result, the fuel for forced addition control is reliably adsorbed by the sweeper 23 and oxidized by reacting with oxygen in the exhaust. Therefore, it is possible to suitably achieve both suppression of the injection hole clogging and improvement of exhaust emission in the fuel addition valve 7.

  In FIG. 6, the inflowing exhaust air-fuel ratio A / F and the HC adsorption amount Qhc change linearly with time, but this is merely a simulation and may be, for example, curved. Of course it is good.

1 is a diagram illustrating a schematic configuration of an internal combustion engine to which an exhaust gas purification apparatus for an internal combustion engine according to a first embodiment is applied and an intake / exhaust system thereof. 6 is a time chart illustrating an example of rich combustion ON / OFF, inflow exhaust air-fuel ratio A / F, and NOx release amount Qdn in the NOx catalyst when executing rich spike control. It is a figure which shows schematic structure of the internal combustion engine which applies the exhaust gas purification apparatus of the internal combustion engine which concerns on Example 2, and its intake / exhaust system. 5 is a time chart illustrating an example of rich combustion ON / OFF in rich spike control, inflow exhaust air-fuel ratio A / F, and oxygen storage amount Qo in a NOx catalyst. FIG. 6 is a diagram illustrating a schematic configuration of an internal combustion engine to which an exhaust gas purification apparatus for an internal combustion engine according to a fourth embodiment is applied and an intake / exhaust system thereof. 5 is a time chart illustrating an example of rich combustion ON / OFF in rich spike control, inflow exhaust air-fuel ratio A / F, and HC adsorption amount Qhc in a sweeper.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake passage 3 ... Exhaust passage 4 ... Throttle 6 ... Occlusion reduction type NOx catalyst 7 ... Fuel addition valve 11 ... Fuel injection valve 20 ... ECU
21..Selective reduction type NOx catalyst 22..Urea addition valve 23..Sweeper

Claims (6)

An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
Combustion rich means for performing combustion rich to lower the air-fuel ratio of the exhaust discharged from the internal combustion engine;
An addition valve for adding a reducing agent to the exhaust from the injection hole facing the exhaust passage upstream of the NOx storage reduction catalyst;
With
When performing recovery control to recover the purification capacity of the NOx storage reduction catalyst, at least the combustion rich means executes combustion rich to lower the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst to the target air-fuel ratio In an exhaust gas purification device for an internal combustion engine,
When performing the recovery control, further comprising a forced addition means for performing a forced addition control for forcibly adding a reducing agent to the addition valve at a predetermined target timing,
The target timing is determined such that a reducing agent for the forced addition control flows into the NOx storage reduction catalyst while NOx or SOx is released from the NOx storage reduction catalyst. An exhaust purification device for an internal combustion engine. In the case of reducing NOx stored in the NOx storage reduction catalyst by performing the recovery control,
The target is set so that the reducing agent for the forcible addition control flows into the NOx storage reduction catalyst within a period in which the NOx release amount that is released from the NOx storage reduction catalyst is maintained at a first reference value or more. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein timing is determined. In the case where SOx stored in the NOx storage reduction catalyst is reduced by performing the recovery control,
The target is set so that the reducing agent for the forced addition control flows into the NOx storage reduction catalyst within a range in which the amount of SOx release from the NOx storage reduction catalyst is maintained at a second reference value or more. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein timing is determined. An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
Combustion rich means for performing combustion rich to lower the air-fuel ratio of the exhaust discharged from the internal combustion engine;
A rear catalyst provided in an exhaust passage downstream of the NOx storage reduction catalyst;
An addition valve for adding a reducing agent to the exhaust from the injection hole facing the exhaust passage between the NOx storage reduction catalyst and the rear catalyst;
With
When performing recovery control to recover the purification capacity of the NOx storage reduction catalyst, at least the combustion rich means executes combustion rich to lower the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst to the target air-fuel ratio In an exhaust gas purification device for an internal combustion engine,
When performing the recovery control, further comprising a forced addition means for performing a forced addition control for forcibly adding a reducing agent to the addition valve at a predetermined target timing,
The target timing is determined so that the reducing agent for the forced addition control flows into the rear catalyst while NOx or SOx flowing out from the NOx storage reduction catalyst flows into the rear catalyst. An exhaust gas purification apparatus for an internal combustion engine characterized by the above. An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
Combustion rich means for performing combustion rich to lower the air-fuel ratio of the exhaust discharged from the internal combustion engine;
An addition valve for adding a reducing agent to the exhaust from the injection hole facing the exhaust passage upstream of the NOx storage reduction catalyst;
With
When performing recovery control to recover the purification capacity of the NOx storage reduction catalyst, at least the combustion rich means executes combustion rich to lower the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst to the target air-fuel ratio In an exhaust gas purification device for an internal combustion engine,
When performing the recovery control, further comprising a forced addition means for performing a forced addition control for forcibly adding a reducing agent to the addition valve at a predetermined target timing,
The target timing is that the reducing agent for the forcible addition control after the oxygen storage amount of the NOx storage reduction catalyst recovers to a third reference value or more upon completion of the combustion rich by the combustion rich means. An exhaust emission control device for an internal combustion engine, wherein the exhaust gas purification device is determined to flow into a catalyst. An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
Combustion rich means for performing combustion rich to lower the air-fuel ratio of the exhaust discharged from the internal combustion engine;
An addition valve for adding fuel as a reducing agent to the exhaust from the injection hole facing the exhaust passage upstream of the NOx storage reduction catalyst;
An HC adsorption oxidation catalyst provided in an exhaust passage downstream of the NOx storage reduction catalyst and capable of adsorbing and oxidizing hydrocarbons contained in exhaust gas;
With
When performing recovery control to recover the purification capacity of the NOx storage reduction catalyst, at least the combustion rich means executes combustion rich to lower the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst to the target air-fuel ratio In an exhaust gas purification device for an internal combustion engine,
When carrying out the recovery control, further comprising a forced addition means for executing a forced addition control for forcibly adding fuel to the addition valve at a predetermined target timing,
The target timing is determined so that the fuel for the forced addition control after the adsorption amount of the hydrocarbon adsorbed on the HC adsorption oxidation catalyst decreases to a fourth reference value or less due to the end of the combustion rich by the combustion rich means. An exhaust gas purification apparatus for an internal combustion engine, wherein the exhaust gas purification apparatus is determined to flow into an HC adsorption oxidation catalyst.

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