JP2008190364A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine, provided with water absorption material and NOx absorption material on an exhaust passage in this order from the upstream side, in which prohibition to NOx absorption ability due to water is favorably avoided, so that NOx absorption ability of the NOx absorption material is sufficiently secured. <P>SOLUTION: A main exhaust passage 14 is provided to which exhaust gas emitted from the internal combustion engine 10 flows in. A bypass passage 20 is provided to bypass the main exhaust passage 14. The water absorption material 24 and the NOx absorption material 28 are provided on the bypass passage 20 in this order from the closer side to an upstream side connection part 20a. At the time when it is determined that dissociation of water from the water absorption material 24 is started, a changing valve 22 is controlled to prevent exhaust gas from flowing into the NOx absorption material 28. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus provided with an adsorbent for adsorbing unpurified components that could not be purified by a catalyst downstream of a catalyst in an exhaust passage.

  Conventionally, for example, Patent Document 1 discloses a technique for purifying a ventilation gas by dry-treating ventilation gas emitted from a road tunnel with a zeolite-based adsorbent and adsorbing and removing NOx. In this conventional technique, a silica gel-based dehumidifying agent (moisture adsorbing material) for adsorbing moisture contained in the ventilation gas is arranged upstream of the flow of the ventilation gas with respect to the adsorbing material for adsorbing NOx. I have to.

Japanese Patent Laid-Open No. 1-155934 JP 2002-138820 A

  A catalyst for purifying exhaust gas is provided in the exhaust passage of the internal combustion engine. However, at the time of cold start when the temperature of the catalyst is decreasing, exhaust gas containing NOx may be discharged outside until the catalyst is warmed up and activated. Further, the exhaust gas contains a large amount of moisture generated by the combustion of fuel. Therefore, on the exhaust passage of the internal combustion engine, a moisture adsorbing material for adsorbing moisture that inhibits the NOx adsorbing capacity of the NOx adsorbing material is arranged on the upstream side of the flow of the exhaust gas, as in the above-described conventional technology. It is possible to arrange a NOx adsorbent downstream of the moisture adsorbent.

  In the configuration including the moisture adsorbent and the NOx adsorbent in the exhaust passage as described above, the amount of moisture adsorbed on the moisture adsorbent reaches a saturated state, or the amount of moisture exceeding the moisture adsorption capacity of the moisture adsorbent If it flows into the moisture adsorbent, the moisture that could not be adsorbed by the moisture adsorbent flows into the downstream NOx adsorbent. When moisture flows into the NOx adsorbent, the NOx adsorption capacity of the NOx adsorbent is greatly hindered, and the NOx adsorbed on the NOx adsorbent is likely to be desorbed.

  The present invention has been made to solve the above-described problems, and in an internal combustion engine having a moisture adsorbent and a NOx adsorbent on the exhaust passage from the upstream side, the NOx adsorption ability is hindered by moisture. It is an object of the present invention to provide an exhaust gas purification apparatus for an internal combustion engine that can suitably avoid the above-described problem and sufficiently ensure the NOx adsorption capacity of the NOx adsorbent.

A first invention is a main exhaust passage through which exhaust gas discharged from an internal combustion engine flows;
A bypass passage that branches 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;
A flow path switching means capable of switching an inflow destination of exhaust gas between the main exhaust passage and the bypass passage;
A moisture adsorbent disposed in the bypass passage and having a function of adsorbing moisture;
A NOx adsorbent having a function of adsorbing NOx, disposed in the bypass passage on the downstream side of the flow of exhaust gas from the moisture adsorbent when adsorbing moisture to the moisture adsorbent;
Moisture desorption judgment means for judging whether or not desorption of moisture has started from the moisture adsorbent;
A flow path control means for controlling the flow path switching means so that exhaust gas does not flow into the NOx adsorbent when it is determined that desorption of moisture has started;
It is characterized by providing.

  The second invention is characterized in that, in the first invention, the moisture desorption determining means determines whether or not moisture desorption is started based on the temperature of the moisture adsorbing material. .

  According to the first aspect of the present invention, the NOx adsorption operation on the NOx adsorbent is terminated when it is determined that the desorption of moisture from the moisture adsorbent has started, so that NOx desorption due to moisture is suppressed. be able to.

  According to the second aspect of the present invention, by estimating the inflow of moisture into the NOx adsorbent based on the temperature of the moisture adsorbent disposed upstream rather than on the temperature of the NOx adsorbent, the flow path switching means The switching determination can be made more quickly, and the adsorption can be reliably terminated before NOx is desorbed from the NOx adsorbent.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a configuration of an internal combustion engine system including an exhaust purification device according to Embodiment 1 of the present invention. An internal combustion engine 10 shown in FIG. 1 includes an intake passage 12 for taking air into the cylinder and an exhaust passage through which exhaust gas discharged from the cylinder flows.

  The exhaust passage of the present embodiment includes a main exhaust passage 14 for discharging exhaust gas from the cylinder, and a bypass passage 20 described later. A front catalyst (SC) 16 and a rear catalyst (UF) 18 capable of purifying exhaust gas are arranged in series in the main exhaust passage 14 from the upstream side.

  The system of this embodiment includes a bypass passage 20 as a passage that bypasses the main exhaust passage 14. The bypass passage 20 branches from the main exhaust passage 14 at the upstream connection portion 20a located downstream of the rear catalyst 18, and again enters the main exhaust passage 14 at the downstream connection portion 20b located downstream of the upstream connection portion 20a. It is configured to merge. A switching valve 22 for switching the inflow destination of the exhaust gas between the main exhaust passage 14 and the bypass passage 20 is disposed in the upstream connection portion 20a. The switching valve 22 is controlled 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). During normal operation of the internal combustion engine 10, the switching valve 22 is controlled so that the bypass passage 20 is closed, so that the exhaust gas passes through the main exhaust passage 14 as it is to the atmosphere without passing through the bypass passage 20. Released.

  Two adsorbents are arranged in the middle of the bypass passage. Specifically, a moisture adsorbing material 24 having a function of adsorbing moisture contained in the exhaust gas is disposed on the upstream side of the main exhaust passage 14, that is, on the side close to the upstream side connection portion 20a. As such a water | moisture-content adsorption material 24, a zeolite-type raw material can be used, for example. A temperature sensor 26 for detecting the temperature of the moisture adsorbent 24 is incorporated in the moisture adsorbent 24.

  The bypass passage 20 has a function of adsorbing NOx, which is an unpurified component contained in the exhaust gas, on the downstream side of the moisture adsorbent 24, that is, on the side far from the upstream connection portion 20a. 28 is arranged. As such a NOx adsorbent 28, for example, a material in which iron Fe is supported on zeolite can be used.

  Further, a return passage 30 communicates with the bypass passage 20 at a portion between the upstream connection portion 20 a and the moisture 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. Note that the connection destination of the return passage 30 may not be the intake passage 12 as long as it is an upstream passage of the rear catalyst 18, and may be, for example, an upstream portion of the front catalyst 16 in the main exhaust passage 14.

  The system of this embodiment includes an ECU (Electronic Control Unit) 40. A water temperature sensor 42 for detecting the engine coolant temperature is connected to the ECU 40 together with various sensors for controlling the internal combustion engine 10 and the temperature sensor 26. The ECU 40 is connected to various actuators such as the switching valve 22 and the purge control valve 32 described above.

[Operation of Embodiment 1]
FIG. 2 is a diagram for explaining the system operation according to the first embodiment of the present invention.
(Operation during adsorption)
First, with reference to FIG. 2 (A), the operation performed for adsorbing NOx and moisture in the exhaust gas discharged from the cylinder when the internal combustion engine 10 is cold started to the adsorbents 24 and 28 will be described. To do.

  As shown in FIG. 2A, the adsorption operation starts when the switching valve 22 closes the main exhaust passage 14 when the internal combustion engine 10 is cold-started. Further, during this adsorption operation, the purge control valve 32 is also controlled to be closed.

  In the state as described above, all of the exhaust gas discharged from the internal combustion engine 10 is introduced from the main exhaust passage 14 into the bypass passage 20. The exhaust gas introduced into the bypass passage 20 sequentially passes through the moisture adsorbing material 24 and the NOx adsorbing material 28 and then returned to the main exhaust passage 14 and then released into the atmosphere.

  If the exhaust gas is introduced into the NOx adsorbent 28 beyond the adsorption capacity of the NOx adsorbent 28, the NOx once adsorbed on the NOx adsorbent 28 is desorbed, leading to deterioration of exhaust emission. Therefore, it is necessary to end the NOx adsorption operation at an appropriate timing before the desorption of NOx from the NOx adsorbent 28 starts. The setting of the timing for ending the NOx adsorption operation is a characteristic part of the present embodiment, and will be described later with reference to FIG. In addition, when it is time to end such an adsorption operation, the switching valve 22 is controlled so as to close the bypass passage 20.

  According to the above-described adsorption operation, moisture contained in the exhaust gas is removed by being adsorbed by the moisture adsorbent 24. The NOx contained in the exhaust gas is removed by being adsorbed by the NOx adsorbent 28. Thereby, it is possible to prevent NOx from being released into the atmosphere at the time of cold start when the pre-stage catalyst 16 is not yet activated.

(Purge operation)
FIG. 2B is a diagram for explaining the purge operation of the present embodiment. As shown in FIG. 2B, in the present embodiment, a purge operation is performed in which NOx adsorbed on the NOx adsorbent 28 is returned to the intake passage via the return passage 30.

  The purge operation is shown in FIG. 2B when a predetermined purge start timing has arrived, such as when the pre-stage catalyst 16 is activated in a state where the switching valve 22 is controlled so as to close the bypass passage 20. Thus, the purge control valve 32 is opened. According to such a purging operation, a part of the exhaust gas discharged from the cylinder uses the negative pressure generated in the intake passage 12 of the internal combustion engine 10 to use the downstream connection portion 20b from the main exhaust passage 14. And is introduced into the bypass passage 20.

  As a result, the exhaust gas that has been relatively warm after startup is supplied to the adsorbent 28 and the like, so that NOx is desorbed from the NOx adsorbent 28 and purged to the intake passage 12 via the return passage 30. The NOx returned to the intake passage 12 is purified by the catalyst 16 and the like in an active state after being subjected to combustion again.

[Characteristics of Embodiment 1]
As shown in FIG. 1, in the present embodiment, the moisture adsorbing material 24 is arranged on the upstream side of the NOx adsorbing material 28 during the adsorption operation. For this reason, since moisture is previously removed by the moisture adsorbent 24 upstream of the NOx adsorbent 28, dry exhaust gas can be introduced into the NOx adsorbent 28, and the NOx adsorption performance by the NOx adsorbent 28 is enhanced. Can be maintained.

  However, during the adsorption operation, the amount of moisture adsorbed on the moisture adsorbent 24 may reach a saturated state, or an amount of moisture exceeding the moisture adsorption capacity of the moisture adsorbent 24 may flow into the moisture adsorbent 24. Water that has not been adsorbed by the moisture adsorbent 24 will flow into the downstream NOx adsorbent 28. When moisture flows into the NOx adsorbent 28, the NOx adsorbing capacity of the NOx adsorbent 28 is greatly hindered, and the NOx adsorbed on the NOx adsorbent 28 is likely to be desorbed.

  Therefore, in the present embodiment, when it is determined that the desorption of moisture from the moisture adsorbent 24 arranged upstream of the NOx adsorbent 28 is started, the switching valve 22 is controlled to open the inlet of the bypass passage 20. The NOx adsorbing operation was terminated by closing. More specifically, in the present embodiment, the moisture adsorbent 24 is determined by determining whether or not the temperature of the moisture adsorbent 24 detected by the temperature sensor 26 has become a predetermined value or higher when the adsorption operation is performed. The start point of desorption of water from was determined.

  FIG. 3 is a time chart showing the state of control when the NOx adsorption operation is terminated in the first embodiment of the present invention. As shown in FIG. 3, when exhaust gas containing moisture is introduced and moisture is adsorbed to the moisture adsorbent 24, the temperature of the moisture adsorbent 24 rises due to moisture adsorption heat. However, when a certain amount or more of moisture is adsorbed on the moisture adsorbent 24, more moisture cannot be adsorbed and the moisture flows into the NOx adsorbent 28.

  The predetermined value T1 of the moisture adsorbent 24 shown in FIG. 3 is a value for determining when a certain amount of moisture is adsorbed on the moisture adsorbent 24 to the extent that the desorption of moisture from the moisture adsorbent 24 is started. It is. In the present embodiment, when the temperature of the moisture adsorbing material 24 reaches the predetermined value T1, the bypass passage 20 is closed from the state where the bypass passage 20 is opened (the state of “with adsorption” shown in FIG. 3). The position of the switching valve 22 is switched so as to be in the “no adsorption” state shown in FIG.

  FIG. 4 is a flowchart of a routine executed by the ECU 40 in order to realize the adsorption operation and the purge operation in the present embodiment. 4 is started immediately after the internal combustion engine 10 is started.

  In the routine shown in FIG. 4, it is first determined whether or not the engine coolant temperature is equal to or lower than a set temperature (step 100). As a result, when it is determined that the engine coolant temperature is higher than the set temperature, that is, when the warm-up is completed, the current processing cycle is promptly terminated.

  If it is determined in step 100 that the engine coolant temperature is equal to or lower than the set temperature, that is, if it is determined that the engine is cold starting, the switching valve 22 is opened and the purge control valve is opened. 32 is closed (step 102). The switching valve 22 normally closes the inlet of the bypass passage 20, but if it is recognized at the time of cold start in step 102, the main exhaust passage 14 and the bypass passage 20 are in communication with each other. It is switched to become. Thereby, the adsorption operation is started.

  Next, it is determined whether or not the temperature of the moisture adsorbing material 24 has reached a predetermined value T1 (step 104). Here, the temperature of the moisture adsorbing material 24 is directly measured by the temperature sensor 26, but instead of this, the temperature of the moisture adsorbing material 24 is based on the exhaust gas temperatures before and after the moisture adsorbing material 24. It is also possible to use a method for estimating.

  When it is determined in step 104 above that the temperature of the moisture adsorbing material 24 has reached the predetermined value T1, that is, when it is determined that the desorption of moisture from the moisture adsorbing material 24 is started. The switching valve 22 is closed to close the bypass passage 20 (step 106). Thus, the NOx adsorption operation is completed.

  Next, it is determined whether or not the purge operation start timing has come (step 108). More specifically, in this step 108, whether or not the catalyst 16 or the like is in an active state, and whether or not the temperature of the exhaust gas introduced into the bypass passage 20 is within a temperature range suitable for performing the purge operation. Further, a determination based on whether or not the internal combustion engine 10 is in a stable operation state that does not cause a problem even if the purge operation is performed is executed.

  If it is determined in step 108 that the purge operation start timing has come, the purge control valve 32 is opened (step 110). Next, the purge amount determination is executed (step 112). Specifically, it is determined whether or not the current purge amount has reached a predetermined set amount. The current purge amount can be estimated based on the relationship between the elapsed time after opening the purge control valve 32 in step 110 and the purge gas temperature.

  If it is determined in step 112 that the purge amount has reached the set amount, the purge control valve 32 is closed (step 114). Thereby, the purge operation is terminated.

  According to the routine shown in FIG. 4 described above, when the temperature of the moisture adsorbing material 24 reaches the predetermined value T1, the switching valve 22 is switched to start the desorption of moisture from the moisture adsorbing material 24. , NOx adsorption operation can be terminated. In other words, the adsorption capacity of the NOx adsorbent 28 can be estimated from the temperature of the moisture adsorbent 24. According to such control, the NOx adsorption operation is terminated immediately before the moisture flows into the NOx adsorbent 28, that is, before the NOx adsorbed on the NOx adsorbent 28 is desorbed by the moisture. it can. For this reason, it becomes possible to utilize the NOx adsorption capability of the NOx adsorbent 28 to the maximum extent.

  Further, according to the above routine, the switching valve is estimated by estimating the inflow of moisture into the NOx adsorbent 28 based on the temperature of the moisture adsorbent 24 disposed upstream rather than the temperature of the NOx adsorbent 28. 22 can be determined more quickly, and the adsorption can be reliably terminated before NOx is desorbed from the NOx adsorbent 28.

  In the first embodiment described above, the switching valve 22, the return passage 30, and the purge control valve 32 correspond to the “flow path switching means” in the first invention. When the ECU 40 executes the process of step 104, the “moisture desorption determination means” in the first aspect of the invention executes the process of step 106, thereby “flow path control in the first aspect of the invention”. Each means is realized.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. 5 and FIG.
The system of the present embodiment can be realized by causing the ECU 40 to execute a routine shown in FIG. 6 described later instead of the routine shown in FIG. 4 using the hardware configuration shown in FIG.

[Characteristics of Embodiment 2]
FIG. 5 is a time chart showing the state of control when the NOx adsorption operation is terminated in the second embodiment of the present invention.
In Embodiment 1 described above, it is determined whether or not the temperature of the moisture adsorbing material 24 during the adsorption operation has reached a predetermined value T1, thereby determining the desorption start time of moisture from the moisture adsorbing material 24. I am doing so. On the other hand, in this embodiment, it is determined whether or not the temperature increase degree of the moisture adsorbent 24 during the adsorption operation is less than the predetermined value X1, thereby determining the start point of desorption of moisture from the moisture adsorbent 24. Like to do.

  As described above, when moisture is adsorbed on the moisture adsorbent 24, the temperature of the moisture adsorbent 24 rises due to moisture adsorption heat. On the other hand, when the adsorbed moisture is desorbed from the moisture adsorbent 24, the temperature of the moisture adsorbent decreases due to the heat of desorption. Therefore, if the amount of desorption becomes greater than the amount of adsorption due to an increase in the amount of moisture flowing into the moisture adsorbent 24, the temperature rise of the moisture adsorbent 24 decreases.

  The predetermined value X1 of the temperature rise degree of the moisture adsorbing material 24 shown in FIG. 5 is determined when a certain amount of moisture is adsorbed by the moisture adsorbing material 24 so that the desorption of moisture from the moisture adsorbing material 24 is started. It is a value to do. In the present embodiment, when the temperature rise of the moisture adsorbing material 24 falls below the predetermined value X1, the bypass passage 20 is closed from the state where the bypass passage 20 is opened (the state of “with adsorption” shown in FIG. 5). The position of the switching valve 22 is switched so as to be in a state (“no adsorption” state shown in FIG. 5).

  FIG. 6 is a flowchart of a routine executed by the ECU 40 in order to realize the adsorption operation and the purge operation in the present embodiment. It is assumed that the routine shown in FIG. 6 is started immediately after the internal combustion engine 10 is started. In FIG. 6, the same steps as those shown in FIG. 4 in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 6, the switching valve 22 is opened after the internal combustion engine 10 is cold-started (step 102), and after the adsorption operation is started, the temperature rise degree of the moisture adsorbent 24 is then set to a predetermined value. It is determined whether or not the value is below X1 (step 200).

As a result, when it is determined that the temperature increase degree of the moisture adsorbing material 24 is lower than the predetermined value X1, that is, when it is determined that the desorption of moisture from the moisture adsorbing material 24 is started, In order to close the bypass passage 20, the switching valve 22 is closed (step 106). Thus, the NOx adsorption operation is completed.
In the routine shown in FIG. 6, a series of processes in steps 108 to 114 are subsequently executed. Since these processes are the same as those in the routine shown in FIG. 4, detailed description thereof will be given here. Shall be omitted.

  According to the routine shown in FIG. 6 described above, the desorption of moisture from the moisture adsorbing material 24 is started by switching the switching valve 22 when the temperature rise of the moisture adsorbing material 24 falls below the predetermined value X1. At this point, the NOx adsorption operation can be terminated. According to such control, the NOx adsorption operation is terminated immediately before the moisture flows into the NOx adsorbent 28, that is, before the NOx adsorbed on the NOx adsorbent 28 is desorbed by the moisture. it can. For this reason, it becomes possible to utilize the NOx adsorption capability of the NOx adsorbent 28 to the maximum extent.

It is a figure for demonstrating the structure of an internal combustion engine system provided with the exhaust gas purification apparatus in Embodiment 1 of this invention. It is a figure for demonstrating the system operation | movement of Embodiment 1 of this invention. 3 is a time chart showing the state of control when the NOx adsorption operation is terminated in Embodiment 1 of the present invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a time chart showing the mode of control at the time of ending NOx adsorption operation in Embodiment 2 of the present invention. It is a flowchart of the routine performed in Embodiment 2 of this invention.

Explanation of symbols

10 internal combustion engine 12 intake passage 14 main exhaust passage 16 front catalyst 18 rear catalyst 20 bypass passage 20a upstream connection portion 20b downstream connection portion 22 switching valve 24 moisture adsorbent 28 NOx adsorbent 30 return passage 32 purge control valve 40 ECU ( Electronic Control Unit)

Claims (2)

A main exhaust passage through which exhaust gas discharged from the internal combustion engine flows;
A bypass passage that branches 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;
A flow path switching means capable of switching an inflow destination of exhaust gas between the main exhaust passage and the bypass passage;
A moisture adsorbent disposed in the bypass passage and having a function of adsorbing moisture;
A NOx adsorbent having a function of adsorbing NOx, disposed in the bypass passage on the downstream side of the flow of exhaust gas from the moisture adsorbent when adsorbing moisture to the moisture adsorbent;
Moisture desorption judgment means for judging whether or not desorption of moisture has started from the moisture adsorbent;
A flow path control means for controlling the flow path switching means so that exhaust gas does not flow into the NOx adsorbent when it is determined that desorption of moisture has started;
An exhaust emission control device for an internal combustion engine, comprising:   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the moisture desorption determination unit determines whether or not moisture desorption has started based on the temperature of the moisture adsorbent.

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