JP2009002255A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of restraining lowering of adsorption efficiency in an adsorbing material in the internal combustion engine furnished with the adsorbing material of an unpurified component in an exhaust passage. <P>SOLUTION: This exhaust emission control device of the internal combustion engine is furnished with a by-pass passage 20 provided in a manner branched from the exhaust passage 14 , a change-over valve 22 to change an inflow destination of exhaust gas between the exhaust passage 14 and the by-pass passage 20, and the NOx adsorbing material 24 arranged in the by-pass passage 20 to adsorb NOx included in the exhaust gas. Execution of purge-treatment is prohibited when fuel cut is executed in a state where the temperature of the NOx adsorbing material 24 is raised higher than a prescribed value in the purge-treatment of adsorbed NOx adsorbed to the NOx adsorbing material 24 in cold starting. Alternatively, the execution of the fuel cut is prohibited when the purge-treatment is executed in the state where the temperature of the NOx adsorbing material 24 is raised higher than the prescribed value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device for an internal combustion engine provided with an adsorbent capable of adsorbing unpurified components in exhaust gas when the internal combustion engine is cold started.

  Conventionally, for example, as disclosed in JP-A-5-171929, an internal combustion engine in which an adsorbent capable of adsorbing unburned gas is disposed in a branch passage branched from the downstream of an exhaust purification catalyst in an exhaust passage. Engine exhaust purification devices have been proposed. The catalyst has low activity at low temperatures and cannot sufficiently purify unburned gas during cold start. Thus, by providing an adsorbent capable of adsorbing unburned gas even at low temperatures, the unburned gas is prevented from being discharged into the atmosphere.

JP-A-5-171929

  By the way, when the adsorbent that adsorbs unpurified components such as unburned gas is disposed on the exhaust passage as in the conventional exhaust purification device, the adsorption capacity of the unpurified component that is the adsorption target component in the adsorbent ( Adsorption efficiency) is reduced by adsorbing moisture contained in the exhaust gas. Therefore, it is conceivable that exhaust gas having a low water content during fuel cut of the internal combustion engine is introduced into the adsorbent and the adsorption component is desorbed, but the exhaust gas during fuel cut contains a lot of oxygen. Therefore, when the adsorbent is heated to a high temperature, a large amount of oxygen is adsorbed and the adsorbing ability may be reduced. For this reason, in the said conventional exhaust purification apparatus which does not consider the influence of the oxidation reaction in this adsorbent, the room for improvement is still left from a viewpoint of maintaining the adsorption performance in an adsorbent high.

  The present invention has been made to solve the above-described problems, and is an internal combustion engine that can suppress a decrease in adsorption efficiency in an adsorbent in an internal combustion engine provided with an unpurified adsorbent in an exhaust passage. An object of the present invention is to provide an exhaust purification device.

In order to achieve the above object, a first invention is an exhaust purification device for an internal combustion engine,
A main exhaust passage through which exhaust gas discharged from the internal combustion engine flows;
A bypass passage that branches off from the main exhaust passage at an upstream connection portion with the main exhaust passage, and merges with the main exhaust passage again at a downstream connection portion downstream from the upstream connection portion;
Switching means for switching an inflow destination of the exhaust gas between the main exhaust passage and the bypass passage;
An adsorbent disposed in the bypass passage and having a function of adsorbing unpurified components contained in the exhaust gas of the internal combustion engine;
Purge introduction means for purging the unpurified components adsorbed on the adsorbent by introducing exhaust gas into the adsorbent;
A purge execution permission / rejection determination unit that determines whether or not the purge execution unit is permitted to execute during a period in which the fuel cut of the internal combustion engine is performed;
It is characterized by providing.

According to a second invention, in the first invention,
A temperature acquisition means for acquiring the temperature of the adsorbent;
The purge execution permission / refusal determination means prohibits execution of the purge execution means when the temperature of the adsorbent is higher than a predetermined value.

According to a third invention, in the first invention,
A determination means for determining the progress of the oxidation reaction in the adsorbent;
The purge execution permission / refusal determination means permits the execution of the purge execution means when the determination means determines that the oxidation reaction in the adsorbent is in progress.

In order to achieve the above object, a fourth invention is an exhaust gas purification apparatus for an internal combustion engine,
A main exhaust passage through which exhaust gas discharged from the internal combustion engine flows;
A bypass passage that branches off from the main exhaust passage at an upstream connection portion with the main exhaust passage, and merges with the main exhaust passage again at a downstream connection portion downstream from the upstream connection portion;
Switching means for switching an inflow destination of the exhaust gas between the main exhaust passage and the bypass passage;
An adsorbent disposed in the bypass passage and having a function of adsorbing unpurified components contained in the exhaust gas of the internal combustion engine;
Purge introduction means for purging the unpurified components adsorbed on the adsorbent by introducing exhaust gas into the adsorbent;
Fuel cut execution permission / refusal control means for determining whether or not the internal combustion engine performs fuel cut during a period in which the purge execution means is being executed;
It is characterized by providing.

A fifth invention is the fourth invention,
A temperature acquisition means for acquiring the temperature of the adsorbent;
The fuel cut execution permission / refusal control means prohibits execution of the fuel cut when the temperature of the adsorbent is higher than a predetermined value.

According to a sixth invention, in the fourth invention,
A determination means for determining the progress of the oxidation reaction in the adsorbent;
The fuel cut execution permission / refusal control means permits the execution of the fuel cut when the determination means determines that an oxidation reaction in the adsorbent is in progress.

  According to the first aspect of the invention, it is determined whether or not the purge process is permitted during the period in which the fuel cut of the internal combustion engine is being performed. Since the exhaust gas during fuel cut has a small water content compared with that during normal operation, when the purge process is executed with such exhaust gas, the moisture adsorbed on the adsorbent is effectively purged. Adsorption capacity is improved. On the other hand, since the exhaust gas during fuel cut contains a large amount of oxygen, there is a risk of promoting the oxidation of the adsorbent depending on the surrounding environment of the adsorbent. According to the present invention, whether or not the purge process can be performed can be appropriately determined, so that the adsorption capacity of the adsorbent can be maximized.

  According to the second aspect of the present invention, when performing the purge process of the adsorbed unpurified component, if the temperature of the adsorbent is raised to a temperature higher than a predetermined value, Purging with exhaust gas is prohibited. When the temperature of the adsorbent is raised to a high temperature, the oxidation reaction in the adsorbent is promoted. According to the present invention, since the purge process during fuel cut is prohibited, it is possible to effectively suppress a situation where the adsorption capacity is reduced due to oxidation of the adsorbent. Further, when the temperature of the adsorbent is lower than a predetermined value, the purge process during the fuel cut is permitted, so that the adsorbed water is effectively purged using the exhaust gas having a low water content. be able to.

  According to the third aspect of the present invention, when the purge process of the adsorbed unpurified component is executed, if it is determined that the oxidation reaction in the adsorbent is in progress, the exhaust gas during the fuel cut of the internal combustion engine The purge operation by is permitted. When the adsorbent has already been oxidized, even if a large amount of oxygen is introduced into the adsorbent, no further oxidation reaction takes place. Therefore, according to the present invention, by permitting the purge process during the fuel cut, the purge process of the moisture adsorbed on the adsorbent can be preferentially executed, and the adsorbent is in an oxidized state. The adsorption capacity can be maximized.

  According to the fourth aspect of the present invention, it is determined whether or not the fuel cut of the internal combustion engine is permitted during the period in which the adsorbent purge process is performed. Since the exhaust gas during fuel cut has a small water content compared with that during normal operation, when the purge process is executed with such exhaust gas, the moisture adsorbed on the adsorbent is effectively purged. Adsorption capacity is improved. On the other hand, since the exhaust gas during fuel cut contains a large amount of oxygen, there is a risk of promoting the oxidation of the adsorbent depending on the surrounding environment of the adsorbent. According to the present invention, it is possible to appropriately determine whether or not to execute fuel cut, so that the adsorption capacity of the adsorbent can be maximized.

  According to the fifth aspect of the present invention, when the temperature of the adsorbent is raised to a temperature higher than the predetermined value, the execution of the fuel cut of the internal combustion engine during the purge process is prohibited. When the temperature of the adsorbent is raised to a high temperature, the oxidation reaction in the adsorbent is promoted. According to the present invention, since the fuel cut during the purging process is prohibited, it is possible to effectively suppress the situation where the adsorption capacity is reduced by introducing a large amount of oxygen into the adsorbent and promoting the oxidation reaction. it can.

  According to the sixth aspect, when it is determined that the oxidation reaction in the adsorbent is in progress, the fuel cut of the internal combustion engine during the purge process is permitted. When the adsorbent has already been oxidized, even if a large amount of oxygen is introduced into the adsorbent, no further oxidation reaction takes place. For this reason, according to the present invention, by permitting fuel cut during the purge process, the moisture purge process of the adsorbent can be performed using the exhaust gas having a low moisture content, and the adsorbent is oxidized. The adsorption capacity in the state can be maximized.

  Several embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining a schematic configuration of an internal combustion engine system including an exhaust purification device as Embodiment 1 of the present invention. As shown in FIG. 1, the exhaust purification system of the present embodiment includes an internal combustion engine (hereinafter also referred to as “engine”) 10. The engine 10 is connected to an intake passage 12 for taking air into the cylinder and an exhaust passage 14 through which exhaust gas discharged from the cylinder flows. A front-stage catalyst (SC) 16 and a rear-stage catalyst (UF) 18 are disposed in series in the exhaust passage 14 in order from the upstream side as a catalyst for purifying exhaust gas.

  The system of the present embodiment also includes a bypass passage 20 that bypasses a part of the exhaust passage 14. The bypass passage 20 branches from the exhaust passage 14 at the upstream connection portion 20a located downstream of the upstream catalyst 16, and joins the exhaust passage 14 again at the downstream connection portion 20b located downstream of the upstream connection portion 20a. It is configured as follows. A switching valve 22 for switching the inflow destination of the exhaust gas between the exhaust passage 14 and the bypass passage 20 is disposed in the upstream connection portion 20a. The switching valve 22 is driven to open and close when the engine intake negative pressure acting on the negative pressure diaphragm 22a is controlled by an electromagnetic valve (not shown).

  A NOx adsorbent 24 having a function of adsorbing NOx contained in the exhaust gas is disposed in the bypass passage 20. As such NOx adsorbent 24, for example, metal ion exchange zeolite such as Fe ion exchange zeolite can be used. Further, the NOx adsorbent 24 is incorporated with a temperature sensor 52 for detecting the temperature of the NOx adsorbent 24.

  The system according to the present embodiment includes an ECU (Electronic Control Unit) 50 as shown in FIG. In addition to the temperature sensor 52 described above, various sensors such as an air-fuel ratio sensor and a water temperature sensor for controlling the engine 10 are connected to the input unit of the ECU 50. In addition to the switching valve 22 described above, various actuators for controlling the engine 10 are connected to the output portion of the ECU 50. The ECU 50 drives each device in accordance with a predetermined program based on various types of input information.

[Operation of Embodiment 1]
Next, the operation of the system controlled by the ECU 50 will be described. Here, of the various operations realized by the system, the operation related to the NOx adsorbent 24 will be described.

(Operation at cold start)
When the engine 10 is cold started, an operation for adsorbing NOx in the exhaust gas discharged from the cylinder to the NOx adsorbent 24 is performed. Specifically, the switching valve 22 switches the inflow destination of the exhaust gas to the bypass passage 20 side.

  In such a state, all of the exhaust gas discharged from the engine 10 is introduced from the exhaust passage 14 into the bypass passage 20. The exhaust gas introduced into the bypass passage 20 passes through the NOx adsorbent 24 and then returns to the exhaust passage 14 to be released into the atmosphere. At the time of cold start, since the activity in the front catalyst 16 and the rear catalyst 18 is not expressed, NOx contained in the exhaust gas cannot be purified by the front catalyst 16 and the rear catalyst 18. However, by introducing all of the exhaust gas into the bypass passage 20, NOx contained in the exhaust gas is adsorbed by the NOx adsorbent 24 and removed. Thereby, the situation where NOx that cannot be purified by the front catalyst 16 and the rear catalyst 18 is released into the atmosphere can be effectively suppressed.

(Operation after catalyst warm-up)
After the engine 10 is started, the temperature of the exhaust gas flowing into the front catalyst 16 rises, so that the temperature of the front catalyst 16 eventually rises to the activation temperature. When the front catalyst 16 is activated, NOx contained in the exhaust gas can be purified by the front catalyst 16 together with other unpurified components. Accordingly, when it is detected that the temperature of the front catalyst 16 has risen to the activation temperature, the switching valve 22 is operated to switch the inflow destination of the exhaust gas from the bypass passage 20 to the exhaust passage 14. As a result, the exhaust gas purified by the front catalyst 16 passes through the exhaust passage 14 and is discharged into the atmosphere without passing through the NOx adsorbent 24.

(Adsorption NOx purge process)
Next, the purge processing operation of NOx adsorbed by the NOx adsorbent 24 (hereinafter referred to as “adsorption NOx”) when the engine 10 is cold started will be described. As described above, during the period from the start of the cold start of the engine 10 until the activity of the front catalyst 16 is manifested, exhaust gas is introduced into the bypass passage 20 and NOx that could not be purified by the front catalyst 16 is adsorbed by NOx. Adsorbed on the material 24. These adsorbed NOx are purged from the NOx adsorbent 24 when the purge execution condition is satisfied, and purified by the rear catalyst 18.

  That is, as the warm-up operation of the engine 10 progresses, the temperature of the rear catalyst 18 disposed at a relatively distant location from the engine 10 eventually rises to the activation temperature so that NOx can be purified in the rear catalyst 18. Become. Therefore, when it is detected that the temperature of the rear catalyst 18 has risen to the activation temperature, the switching valve 22 is operated to switch the inflow destination of the exhaust gas from the exhaust passage 14 to the bypass passage 20. As a result, the exhaust gas discharged from the cylinder is introduced into the bypass passage 20. As a result, the exhaust gas that has become relatively warm after startup is introduced into the NOx adsorbent 24, so that the adsorbed NOx is desorbed from the NOx adsorbent 24 and purified by the post-stage catalyst 18 disposed downstream of the exhaust passage 14. Is done.

  Here, in the engine 10, a fuel cut may be performed according to various control requests. The exhaust gas during fuel cut has a lower moisture content than the exhaust gas during normal operation. For this reason, when the fuel cut is executed in the period when the purge execution condition is satisfied and the purge process is performed, the moisture purge in the NOx adsorbent 24 can be executed effectively. More specifically, as described above, the NOx adsorption efficiency in the NOx adsorbent 24 is reduced by adsorbing moisture contained in the exhaust gas. For this reason, exhaust gas with a low water content is introduced into the NOx adsorbent 24 by executing the moisture purge using the exhaust gas at the time of fuel cut, so the moisture purge amount is effectively increased. And the adsorption capacity of the adsorbent can be effectively recovered.

  However, on the other hand, the exhaust gas during fuel cut contains a larger amount of oxygen than the exhaust gas during normal operation. For this reason, if the fuel cut is performed during the purge operation, exhaust gas containing a large amount of oxygen is introduced into the NOx adsorbent 24, and the NOx adsorbent 24 is oxidized to increase the adsorption efficiency. May decrease.

  FIG. 2 is a diagram schematically showing the relationship between the purge temperature in the NOx adsorbent 24 and the subsequent adsorption capacity. As shown in this figure, the higher the purge temperature in the NOx adsorbent 24, the more actively the oxidation reaction occurs, and the subsequent adsorption capacity (adsorbable amount) in the NOx adsorbent 24 decreases. That is, the oxidation reaction in the NOx adsorbent 24 does not cause a problem when the temperature of the NOx adsorbent 24 is low, but in particular, when the temperature of the NOx adsorbent 24 is raised to a high temperature, the NOx adsorbent 24 There is a possibility that the oxidation reaction in the material 24 is actively performed and the adsorption efficiency is greatly reduced.

  Therefore, in the system of the present embodiment, when the fuel cut is performed during the period when the purge execution condition is satisfied and the purge operation is performed, only when the NOx adsorbent 24 is heated to a high temperature, The purge operation is prohibited. More specifically, when the adsorption NOx purge process is being executed, that is, during a period when the switching valve 22 is operated and the inflow destination of the exhaust gas is switched from the exhaust passage 14 to the bypass passage 20, When the fuel cut is performed, the purge operation is prohibited only when the temperature of the NOx adsorbent 24 is raised to a temperature higher than a predetermined value. Thereby, the situation where the oxidation reaction in the NOx adsorbent 24 is actively performed can be avoided, and the situation where the adsorption efficiency in the NOx adsorbent 24 is reduced can be effectively suppressed.

[Specific Processing in Embodiment 1]
Next, with reference to FIG. 3, the specific content of the process performed in this Embodiment is demonstrated. FIG. 3 is a flowchart of a routine in which the ECU 50 executes the purge process prohibition determination during the adsorption NOx purge process period. Note that the routine shown in FIG. 3 is repeatedly executed during a period in which the execution of the purge process is determined by another routine.

  In the routine shown in FIG. 3, it is first determined whether or not the fuel cut of the engine 10 is being executed (step 100). Specifically, the determination is made by detecting a control signal of an actuator (for example, an injector) in the engine 10. As a result, when it is determined that the fuel cut of the engine 10 has not been executed, it is determined that it is not particularly necessary to prohibit the purge process, the process proceeds to the next step, and the purge process is permitted (step 102). ). Here, specifically, the switching valve 22 is operated to connect the bypass passage 20 and the inflow destination of the exhaust gas is switched to the bypass passage 20 side. Thus, the adsorption NOx purge process is executed. Further, since the exhaust gas having a low water content is introduced into the NOx adsorbent 24, desorption of the adsorbed water (water purge) is promoted.

  On the other hand, when it is determined in step 100 that the fuel cut of the engine 10 is being performed, the process proceeds to the next step, and the temperature of the NOx adsorbent 24 reaches a temperature at which the oxidation reaction is actively performed. It is determined whether or not (step 104). Specifically, first, the temperature Ta of the NOx adsorbent 24 is detected based on the output signal of the temperature sensor 52. Next, the temperature Ta is compared with the predetermined value T1. As the predetermined value T1, a value defined as a temperature at which the oxidation reaction in the NOx adsorbent 24 is actively performed is used. As a result, if the establishment of Ta> T1 is not recognized, it is determined that the oxidation reaction in the NOx adsorbent 24 is within the allowable range even when the exhaust gas during the fuel cut is introduced, and the routine proceeds to step 102 above. , Purge processing is allowed.

  On the other hand, if the establishment of Ta> T1 is recognized in step 104, it is determined that the oxidation reaction in the NOx adsorbent 24 exceeds the allowable range, and the process proceeds to the next step, and the purge operation is prohibited. Step 106). Here, specifically, the switching valve 22 is operated to close the bypass passage 20, and the inflow destination of the exhaust gas is switched to the exhaust passage 14 side.

  As described above, according to the exhaust purification system of the present embodiment, when the fuel cut is performed during the period in which the adsorption NOx purge process is being performed, the temperature of the NOx adsorbent 24 becomes higher than a predetermined value. The purge operation is prohibited only when the temperature is raised. Thereby, the situation where the oxidation reaction in the NOx adsorbent 24 is actively performed can be avoided, and the situation where the adsorption efficiency in the NOx adsorbent 24 is reduced can be effectively suppressed. Further, in the case where the temperature of the NOx adsorbent 24 is lower than a predetermined value, that is, in a range where the oxidation reaction in the NOx adsorbent 24 is not actively performed, the purge operation is permitted, whereby the moisture of the NOx adsorbent 24 is allowed. Purge can be performed effectively, and the adsorption ability reduced by moisture adsorption can be recovered.

  By the way, in Embodiment 1 mentioned above, NOx as an unpurified component discharged at the time of cold start of engine 10 is effectively used using NOx adsorbent 24 for adsorbing NOx contained in exhaust gas. Although it is supposed to adsorb, the adsorbent used to adsorb unpurified components is not limited to this. That is, an HC adsorbent for adsorbing hydrocarbon (HC) as an unpurified component contained in the exhaust gas may be used.

  In Embodiment 1 described above, in the purge operation of the adsorption NOx, the desorption NOx is purged in the post-stage catalyst 18 disposed downstream of the NOx adsorbent 24. However, the purge operation is executed. The configuration for this is not limited to this. That is, as described below, the desorbed NOx may be recirculated to the intake passage 12.

  FIG. 4 is a diagram for illustrating a schematic configuration of an internal combustion engine system including an exhaust purification device as a modification of the first embodiment of the present invention. In the system shown in FIG. 4, elements common to the system shown in FIG. 1 are denoted by the same reference numerals, and descriptions thereof are omitted or simplified.

  As shown in FIG. 4, in the middle of the bypass passage 20, a return passage 30 communicates with a portion between the upstream connection portion 20 a and the NOx adsorbent 24. The return passage 30 includes a purge control valve 32 in the middle thereof and communicates with the intake passage 12 at the end thereof.

  According to such a configuration, the purge control valve 32 is opened when a predetermined purge start condition is satisfied. Thereby, a part of the exhaust gas discharged from the cylinder passes through the downstream connecting portion 20b from the exhaust passage 14 to the bypass passage 20 using the negative pressure generated in the intake passage 12 of the engine 10. be introduced. Desorbed NOx and desorbed moisture are introduced into the intake passage 12 via the return passage 30. The desorbed NOx returned to the intake passage 12 is purified by the pre-stage catalyst 16 which is in an active state after being subjected to combustion again. The desorbed moisture is released as it is through the exhaust passage 14 into the atmosphere. Thereby, desorption NOx and desorption moisture can be processed effectively.

  In the first embodiment described above, the exhaust passage 14 is the “main exhaust passage” in the first invention, the switching valve 22 is the “switching means” in the first invention, and the NOx adsorbent 24 is the above-described first embodiment. It corresponds to the “adsorbent” in the first invention. Further, when the ECU 50 executes the process of step 102, the “purge execution means” in the first invention executes the process of step 100 or 104, so that the “purge execution means” in the first invention is executed. "Execution permission determination means" is realized respectively.

  In the first embodiment described above, the temperature sensor 52 corresponds to the “temperature acquisition means” in the second aspect of the present invention.

Embodiment 2. FIG.
[Features of Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIG. The system of the present embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG. 5 to be described later using the hardware configuration shown in FIG.

  The second embodiment is characterized in that fuel cut prohibition is executed instead of the purge operation prohibition in the first embodiment described above. That is, in the above-described first embodiment, when the temperature of the NOx adsorbent 24 is raised to a temperature higher than a predetermined value, the purge operation during the fuel cut of the adsorbed NOx is prohibited. The progress of the oxidation reaction in the NOx adsorbent 24 is suppressed. On the other hand, in the second embodiment, the progress of the oxidation reaction in the NOx adsorbent 24 is suppressed by prohibiting the execution of the fuel cut during the execution of the adsorption NOx purge process. Thereby, the oxidation reaction in the NOx adsorbent 24 can be effectively suppressed while continuing the purge process.

[Specific Processing in Second Embodiment]
Next, with reference to FIG. 5, the specific content of the process performed in this Embodiment is demonstrated. FIG. 5 is a flowchart of a routine in which the ECU 50 executes the fuel cut prohibition determination during the adsorption NOx purge process period. Note that the routine shown in FIG. 5 is repeatedly executed during a period in which the execution of the purge process is determined by another routine.

  In the routine shown in FIG. 5, it is first determined whether or not a fuel cut execution request has been issued in the engine 10 (step 200). As a result, if it is determined that a fuel cut execution request has not been issued, this routine is immediately terminated. On the other hand, if it is determined in step 200 that a fuel cut execution request has been issued, the process proceeds to the next step, in which purge processing is being performed, that is, exhaust gas is introduced into the NOx adsorbent 24. It is determined whether or not (step 202). Specifically, it is determined whether or not the bypass passage 20 side of the switching valve 22 is opened. As a result, if it is determined that the exhaust gas is not introduced into the NOx adsorbent 24, the purge process in the NOx adsorbent 24 has not been executed, and therefore the fuel cut is permitted (step 204).

  On the other hand, if it is determined in step 202 that exhaust gas is introduced into the NOx adsorbent 24, the process proceeds to the next step, and the temperature of the NOx adsorbent 24 is set to a temperature at which the oxidation reaction is actively performed. It is determined whether or not it has been reached (step 206). Here, specifically, the same processing as step 104 shown in FIG. 4 is executed. As a result, if the establishment of Ta> T1 is not recognized, it is determined that the oxidation reaction in the NOx adsorbent 24 is within the allowable range even when the exhaust gas during the fuel cut is introduced, and the routine proceeds to step 204 above. Execution of fuel cut is permitted.

  On the other hand, if it is determined in step 206 that Ta> T1 is established, it is determined that the oxidation reaction in the NOx adsorbent 24 exceeds the allowable range, the process proceeds to the next step, and fuel cut execution is prohibited. (Step 208).

  As described above, according to the exhaust purification system of the present embodiment, the temperature of the NOx adsorbent 24 exceeds the predetermined value when a fuel cut request is issued during the period in which the adsorption NOx purge process is executed. However, when the temperature is raised to a high temperature, execution of fuel cut is prohibited. Thereby, it is possible to effectively avoid a situation in which the oxidation reaction in the NOx adsorbent 24 is actively performed while continuing the purge operation in the NOx adsorbent 24.

  By the way, in Embodiment 2 mentioned above, NOx as an unpurified component discharged at the time of cold start of engine 10 is effectively used using NOx adsorbent 24 for adsorbing NOx contained in exhaust gas. Although it is supposed to adsorb, the adsorbent used to adsorb unpurified components is not limited to this. That is, an HC adsorbent for adsorbing hydrocarbon (HC) as an unpurified component contained in the exhaust gas may be used.

  In the second embodiment described above, in the purge operation of adsorption NOx, the desorption NOx is purged in the post-stage catalyst 18 disposed downstream of the NOx adsorbent 24. However, the purge operation is executed. The configuration for this is not limited to this. That is, the hardware configuration shown in FIG. 4 may be used to recirculate the desorbed NOx to the intake passage 12.

  In the second embodiment described above, the exhaust passage 14 is the “main exhaust passage” in the fourth invention, the switching valve 22 is the “switching means” in the fourth invention, and the NOx adsorbent 24 is the above-mentioned It corresponds to the “adsorbent” in the fourth invention. Further, the “fuel cut execution permission determination means” according to the fourth aspect of the present invention is realized by the ECU 50 executing the processing of step 202 or 206 described above.

  In the second embodiment described above, the temperature sensor 52 corresponds to the “temperature acquisition means” in the fifth aspect of the present invention.

Embodiment 3 FIG.
[Features of Embodiment 3]
Next, a third embodiment of the present invention will be described with reference to FIG. The system of the present embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG. 6 to be described later using the hardware configuration shown in FIG.

  In the third embodiment, when most of the region in the NOx adsorbent 24 has already been oxidized, the moisture purge in the NOx adsorbent 24 is executed with priority over the purge of adsorbed NOx. There are features. That is, when the NOx adsorbent 24 has already been oxidized mostly, even if the NOx adsorbent 24 is exposed to an oxidizing atmosphere, it is not further oxidized. For this reason, in such a case, even if the temperature of the NOx adsorbent 24 is raised to a high temperature, the exhaust gas having a low moisture content is not prohibited to the NOx adsorbent 24 without prohibiting the time of fuel cut. By introducing the moisture purge in the NOx adsorbent 24 can be executed effectively. Thereby, the NOx adsorption capacity in a state where the NOx adsorbent 24 has been oxidized can be maximized.

[Specific Processing in Embodiment 3]
Next, with reference to FIG. 6, the specific content of the process performed in this Embodiment is demonstrated. FIG. 6 is a flowchart of a routine in which the ECU 50 executes the purge process prohibition determination during the adsorption NOx purge process period. Note that the routine shown in FIG. 6 is repeatedly executed during a period in which the execution of the purge process is determined by another routine.

  In the routine shown in FIG. 6, it is first determined whether or not the fuel cut of the engine 10 is being executed (step 300). Here, specifically, the same processing as step 100 shown in FIG. 3 is executed. As a result, when it is determined that the fuel cut of the engine 10 has not been executed, it is determined that it is not particularly necessary to prohibit the purge process, the process proceeds to the next step, and the purge process is permitted (step 302). ). Here, specifically, the same processing as step 102 shown in FIG. 3 is executed. Thereby, the adsorption NOx and adsorbed moisture purging process is executed.

  On the other hand, when it is determined in step 300 that the fuel cut of the engine 10 is being executed, the process proceeds to the next step, and the temperature of the NOx adsorbent 24 reaches a temperature at which the oxidation reaction is actively performed. It is determined whether or not (step 304). Here, specifically, the same processing as step 104 shown in FIG. 3 is executed. As a result, if the establishment of Ta> T1 is not recognized, it is determined that the oxidation reaction in the NOx adsorbent 24 is within the allowable range even if the exhaust gas during fuel cut is introduced, and the routine proceeds to step 302 above. The purge process is permitted, and the adsorption NOx and adsorbed moisture purge process is executed.

  On the other hand, if the establishment of Ta> T1 is recognized in step 304 above, it is determined that the oxidation reaction in the NOx adsorbent 24 exceeds the allowable range, the process proceeds to the next step, and the NOx adsorbent 24 is already oxidized. It is determined whether or not it has been performed (step 306). Here, specifically, the oxidation state is determined based on a temperature sensor provided on the NOx adsorbent 24 or a detection signal of the NOx sensor. As a result, if it is determined that most of the NOx adsorbent 24 has already been oxidized, the oxidation reaction may proceed further even if the purge process is performed with the exhaust gas at the time of fuel cut. Therefore, the process proceeds to step 302, and the purge operation is permitted.

  On the other hand, if it is determined in step 306 that the NOx adsorbent 24 has not been oxidized in the majority of the NOx adsorbent 24, the oxidation reaction proceeds when the purge process is executed with the exhaust gas at the time of fuel cut. In step 308, the process proceeds to the next step and the purge operation is prohibited. Here, specifically, the same processing as step 106 shown in FIG. 3 is executed.

  As described above, according to the exhaust purification system of the present embodiment, the NOx adsorbent 24 is already oxidized even when the fuel cut is performed during the period during which the adsorption NOx purge process is being performed. If it is, the purge operation is permitted. Thereby, the moisture purge in the NOx adsorbent 24 can be effectively executed, and the NOx adsorption capability in a state where the NOx adsorbent 24 is oxidized can be maximized.

  By the way, in Embodiment 3 mentioned above, NOx as an unpurified component discharged at the time of cold start of engine 10 is effectively used using NOx adsorbent 24 for adsorbing NOx contained in exhaust gas. Although it is supposed to adsorb, the adsorbent used to adsorb unpurified components is not limited to this. That is, an HC adsorbent for adsorbing hydrocarbon (HC) as an unpurified component contained in the exhaust gas may be used.

  In Embodiment 3 described above, in the purge operation of the adsorption NOx, the desorption NOx is purged in the post-stage catalyst 18 disposed downstream of the NOx adsorbent 24. However, the purge operation is executed. The configuration for this is not limited to this. That is, the hardware configuration shown in FIG. 4 may be used to recirculate the desorbed NOx to the intake passage 12.

  Further, in the above-described third embodiment, even if the purge processing is prohibited in the purge prohibition control shown in the first embodiment, the purge processing is performed when the NOx adsorbent 24 is already oxidized. However, the control to execute the present invention is not limited to the purge prohibition control, although the adsorption capability of the NOx adsorbent 24 is improved by moisture purge. In other words, even when the fuel cut is prohibited in the fuel cut prohibition control shown in the second embodiment, if the NOx adsorbent 24 has already been oxidized, the fuel cut is permitted and the moisture purge is effectively performed. It is good also as performing to.

  In the third embodiment described above, the “determining means” in the third or sixth aspect of the present invention is realized by the ECU 50 executing the process of step 306.

It is a figure for demonstrating schematic structure of an internal combustion engine system provided with the exhaust gas purification apparatus as Embodiment 1 of this invention. It is a figure for demonstrating the relationship between adsorption material purge temperature and adsorption | suction capability. 3 is a flowchart of a routine executed in Embodiment 1 of the present invention. It is a figure for demonstrating schematic structure of an internal combustion engine system provided with the exhaust gas purification device as a modification of Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 2 of this invention. It is a flowchart of the routine performed in Embodiment 3 of the present invention.

Explanation of symbols

10 Internal combustion engine
12 Intake passage 14 Exhaust passage 16 Pre-stage catalyst (SC)
18 Rear catalyst (UF)
20 Bypass passage 22 Switching valve 24 NOx adsorbent 30 Return passage 32 Purge control valve 50 ECU (Electronic Control Unit)
52 Temperature sensor

Claims (6)

A main exhaust passage through which exhaust gas discharged from the internal combustion engine flows;
A bypass passage that branches off from the main exhaust passage at an upstream connection portion with the main exhaust passage, and merges with the main exhaust passage again at a downstream connection portion downstream from the upstream connection portion;
Switching means for switching an inflow destination of the exhaust gas between the main exhaust passage and the bypass passage;
An adsorbent disposed in the bypass passage and having a function of adsorbing unpurified components contained in the exhaust gas of the internal combustion engine;
Purge introduction means for purging the unpurified components adsorbed on the adsorbent by introducing exhaust gas into the adsorbent;
A purge execution permission / rejection determination unit that determines whether or not the purge execution unit is permitted to execute during a period in which the fuel cut of the internal combustion engine is performed;
An exhaust emission control device for an internal combustion engine, comprising: A temperature acquisition means for acquiring the temperature of the adsorbent;
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the purge execution permission determination unit prohibits execution of the purge execution unit when a temperature of the adsorbent is higher than a predetermined value. A determination means for determining the progress of the oxidation reaction in the adsorbent;
2. The internal combustion engine according to claim 1, wherein the purge execution permission determination unit permits execution of the purge execution unit when the determination unit determines that the oxidation reaction in the adsorbent is in progress. Engine exhaust purification system. A main exhaust passage through which exhaust gas discharged from the internal combustion engine flows;
A bypass passage that branches off from the main exhaust passage at an upstream connection portion with the main exhaust passage, and merges with the main exhaust passage again at a downstream connection portion downstream from the upstream connection portion;
Switching means for switching an inflow destination of the exhaust gas between the main exhaust passage and the bypass passage;
An adsorbent disposed in the bypass passage and having a function of adsorbing unpurified components contained in the exhaust gas of the internal combustion engine;
Purge introduction means for purging the unpurified components adsorbed on the adsorbent by introducing exhaust gas into the adsorbent;
Fuel cut execution permission / refusal control means for determining whether or not the internal combustion engine performs fuel cut during a period in which the purge execution means is being executed;
An exhaust emission control device for an internal combustion engine, comprising: A temperature acquisition means for acquiring the temperature of the adsorbent;
5. The exhaust emission control device for an internal combustion engine according to claim 4, wherein the fuel cut execution permission / refusal control means prohibits execution of the fuel cut when the temperature of the adsorbent is higher than a predetermined value. A determination means for determining the progress of the oxidation reaction in the adsorbent;
5. The internal combustion engine according to claim 4, wherein the fuel cut execution permission / refusal control means permits the fuel cut to be executed when the determination means determines that an oxidation reaction in the adsorbent is in progress. Engine exhaust purification system.

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