JP5321255B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently adsorb NOx in exhaust gas using active oxygen and purify desorbed NOx and remaining active oxygen, using a simple structure. <P>SOLUTION: An exhaust passage 14 of an internal combustion engine 10 is provided with an NOx adsorbent 32, an ozone generator 36, and a return-flow passage 40. When the temperature is low, the ozone generator 36 supplies ozone to the NOx adsorbent 32, and the NOx adsorbent 32 adsorbs NOx in the exhaust gas. At a temperature of a desorption temperature of NOx or above, the return-flow passage 40 returns the flow of NOx desorbed from the NOx adsorbent 32 to an intake system, and the NOx is reduced by a combustion inside a cylinder. Thereby, the reduction treatment of NOx can be realized, with a simple structure. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an exhaust emission control device suitably used for an internal combustion engine, and more particularly to an exhaust emission purification device for an internal combustion engine configured to use active oxygen.

  As a conventional technique, for example, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2007-12097), an exhaust gas purification apparatus for an internal combustion engine configured to supply ozone to an exhaust system is known. A conventional exhaust emission control device includes an EGR passage that recirculates exhaust gas to an intake system, and an ozone supply device that supplies ozone to the EGR passage.

  In the prior art, when the internal combustion engine is stopped, ozone is supplied to the EGR passage, and the deposits adhered to the EGR cooler and the EGR valve due to particulate matter (PM) in the exhaust gas are oxidized by ozone. The configuration is to be removed. As another prior art, there is also known an exhaust purification device in which a NOx adsorbing material is provided in an exhaust passage of an internal combustion engine and a NOx component in exhaust gas is adsorbed by the NOx adsorbing material.

JP 2007-120297 A

  By the way, in the above-mentioned prior art, the purpose is to oxidize and remove deposits adhering to the EGR cooler and the EGR valve with ozone, and there is no description regarding NOx purification. In another conventional technique, the NOx component in the exhaust gas is adsorbed on the NOx adsorbent. However, in order to maintain the performance of the adsorbent, it is necessary to periodically desorb the adsorbed NOx. For this reason, the prior art requires a mechanism for purifying the desorbed NOx in addition to the NOx adsorbent, and there is a problem that the structure of the system becomes complicated.

  The present invention has been made in order to solve the above-described problems, and the object of the present invention is to effectively adsorb NOx in exhaust gas using active oxygen and to leave desorbed NOx. An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can reliably purify active oxygen with a simple structure.

1st invention is provided in the exhaust passage of an internal combustion engine, NOx adsorption means which can adsorb NOx in exhaust gas at least in the presence of active oxygen,
Active oxygen supply means for supplying active oxygen to the NOx adsorption means;
A recirculation passage connected to the exhaust passage on the downstream side of the NOx adsorption means and recirculating NOx desorbed from the NOx adsorption means to the intake system;
A bypass passage that is connected to the exhaust passage at a position that bypasses the NOx adsorption means, and that is provided with a catalyst that purifies at least NOx in the exhaust gas;
A flow path switching means capable of switching a flow path of the exhaust gas between the NOx adsorption means and the bypass passage;
Auxiliary power means for generating auxiliary power for assisting the internal combustion engine;
The active oxygen supply means when the temperature of the exhaust gas is equal to or lower than the upper limit adsorption temperature as compared with the upper limit adsorption temperature that is the upper limit of the temperature at which the NOx adsorption means can adsorb NOx in the presence of active oxygen. Adsorption control means for operating
The temperature of the exhaust gas is equal to or higher than the desorption temperature as compared with the desorption temperature set to a temperature at which NOx adsorbed on the NOx adsorption means starts to desorb and higher than the upper limit adsorption temperature. When the stoichiometric combustion control for controlling the air-fuel ratio of the internal combustion engine to be the stoichiometric air-fuel ratio is executable, the NOx desorbed from the NOx adsorbing means is recirculated while performing the stoichiometric combustion control. One desorption combustion control means for recirculation to the intake system through the passage;
When the exhaust gas temperature is equal to or higher than the desorption temperature and the execution of the stoichiometric combustion control is difficult, the NOx adsorption is performed while the stoichiometric combustion control is executed with the auxiliary power means operated. Other desorption combustion control means for recirculating NOx desorbed from the means to the intake system via the recirculation passage;
When the exhaust gas temperature is equal to or higher than the desorption temperature and it is difficult to execute the stoichiometric combustion control, the exhaust gas is circulated to the bypass passage by the flow path switching means while performing the lean combustion control. An exhaust flow path control means,
It is characterized by providing.

The second invention is provided in the exhaust passage downstream of the connection position of the recirculation passage, and an exhaust flow rate variable means for variably setting the flow rate of the exhaust gas flowing through the exhaust passage;
An exhaust flow rate control means for suppressing the flow rate of the exhaust gas by the exhaust flow rate variable means during the NOx desorption operation;
It is set as the structure provided with.

According to a third aspect of the present invention, a NOx purifying catalyst is provided in the exhaust passage on the downstream side of the NOx adsorbing means and can purify at least NOx in the exhaust gas.

  According to the first invention, the NOx adsorption means can efficiently adsorb NOx in the exhaust gas in a state where the active oxygen is supplied by the active oxygen supply means. Further, when the adsorbed NOx is desorbed, the NOx can be recirculated to the intake system through the recirculation passage, and the desorbed NOx can be reliably reduced by combustion in the cylinder. On the other hand, even when active oxygen remains during NOx adsorption, this active oxygen can be recirculated to the intake system through the recirculation passage and decomposed by combustion in the cylinder.

  Therefore, desorption NOx and residual active oxygen can be purified by utilizing normal combustion performed in the cylinder. As a result, for example, a NOx catalyst or the like does not have to be arranged on the downstream side of the NOx adsorption means, so that the system structure can be simplified. Moreover, since it is not necessary to forcibly enrich the air-fuel ratio by rich spike control or the like in order to perform NOx reduction processing, the enrichment is insufficient and NOx is discharged to the outside, or the air-fuel ratio is disturbed to the rich side. Can be prevented, and exhaust emission can be improved. Furthermore, depositing deposits in the intake system or in the cylinder can be suppressed by recirculating surplus active oxygen to the intake system, and anti-knocking performance can be improved.

Further , the NOx adsorbing means can adsorb a large amount of NOx as compared with when no active oxygen is supplied by supplying active oxygen in a low temperature region below the upper limit adsorption temperature. In addition, since the NOx desorption temperature increases in the presence of active oxygen, the adsorption amount of NOx can be increased even at the same temperature. Therefore, the adsorption control means can significantly improve NOx adsorption performance using these characteristics, and can adsorb a large amount of NOx efficiently.

The desorption combustion control means can perform stoichiometric combustion control by maintaining the air-fuel ratio of the internal combustion engine at the stoichiometric air-fuel ratio when NOx is desorbed from the NOx adsorption means. Thereby, NOx recirculated to the intake system can be efficiently reduced, and generation of NOx due to combustion in the cylinder can be suppressed.

In consideration of the operation performance of the internal combustion engine and the like, the operation region in which combustion control (stoichiometric combustion control) suitable for NOx reduction processing can be performed may be limited. However, by using the auxiliary power means in combination, the driving performance can be ensured even during the stoichiometric combustion control. Thus, in the internal combustion engine, the stoichiometric combustion control can be performed at a desired timing without being affected by the operation state and the like, and the reduction process of NOx desorbed in a wide operation region can be performed.

Further , depending on the operation state of the internal combustion engine, it may be difficult to execute combustion control (stoichiometric combustion control) suitable for NOx reduction treatment even in a temperature region where NOx desorption operation occurs. In this case, the exhaust passage control means can cause the exhaust gas to flow through the bypass passage by switching the passage switching means, and can purify NOx in the exhaust gas by the catalyst in the bypass passage. Thereby, it is possible to stand by without desorbing the desorbed NOx to the intake system until the stoichiometric combustion control becomes possible. Therefore, it is possible to avoid that the execution condition of the combustion control is limited according to the NOx desorption temperature or the like, or that the desorption temperature of the NOx adsorption means is limited according to the execution condition of the combustion control or the like. Therefore, the degree of freedom in control design and the degree of freedom in selecting NOx adsorption means can be expanded.

According to the second aspect of the invention, the exhaust gas flow rate control means can appropriately suppress (squeeze) the flow rate of the exhaust gas on the downstream side of the reflux passage during the NOx desorption operation. As a result, the exhaust pressure can be increased at the inflow position of the recirculation passage, and the gas containing the desorbed NOx can be smoothly introduced from the exhaust passage into the recirculation passage.

According to the third aspect of the invention, a NOx purification catalyst such as a three-way catalyst can be provided on the downstream side of the NOx adsorption means. Thereby, the NOx desorbed from the NOx adsorption means can be purified not only by combustion in the cylinder but also by the NOx purification catalyst. Therefore, even if a part of the NOx passes through the combustion chamber, the NOx purification catalyst can reliably prevent the NOx from being released into the atmosphere.

It is a whole block diagram for demonstrating the system configuration | structure of Embodiment 1 of this invention. In Embodiment 1 of this invention, it is a block diagram which shows typically the characteristic part of an exhaust system. It is explanatory drawing for demonstrating control of ECU. It is explanatory drawing which shows the state from which the adsorption | suction performance of a NOx adsorbent changes according to the presence or absence of ozone. In Embodiment 1 of this invention, it is a flowchart which shows the control performed by ECU. It is a whole block diagram for demonstrating the system configuration | structure of Embodiment 2 of this invention. In Embodiment 2 of this invention, it is a flowchart which shows the control performed by ECU. It is a whole block diagram for demonstrating the system configuration | structure of Embodiment 3 of this invention. It is a whole block diagram for demonstrating the system configuration | structure of Embodiment 4 of this invention.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
The first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an overall configuration diagram for explaining a system configuration according to the first embodiment of the present invention. The system of the present embodiment includes an internal combustion engine 10 made of, for example, a diesel engine. The internal combustion engine 10 has an intake passage 12 that sucks intake air into the cylinder of each cylinder, and exhaust gas discharged from each cylinder. And a flowing exhaust passage 14. The intake passage 12 is provided with a throttle valve 16 that increases or decreases the intake air amount in accordance with the accelerator opening or the like.

  The internal combustion engine 10 also includes a fuel injection valve 18 that injects fuel into each cylinder, and a fuel addition valve 20 that adds fuel to the exhaust gas. The fuel addition valve 20 is used, for example, when reducing NOx adsorbed on the NOx catalyst, or when oxidizing PM collected in the DPF. Further, between the intake passage 12 and the exhaust passage 14, a supercharger 22 that supercharges intake air using exhaust pressure, and an EGR passage 24 that recirculates a part of the exhaust gas as EGR gas to the intake system. And are provided. The EGR passage 24 is provided with an EGR valve 26 that adjusts the flow rate of the EGR gas and an EGR cooler 28 that cools the EGR gas.

  The exhaust passage 14 is provided with an oxidation catalyst 30, a NOx adsorbent 32, and a DPF 34 sequentially from the upstream side to the downstream side, and these devices are arranged on the downstream side of the EGR passage 24. The oxidation catalyst 30 purifies HC, CO, etc. in the exhaust gas by oxidation. A DPF (diesel particulate filter) 34 collects PM in the exhaust gas and purifies it by oxidation.

  The NOx adsorbing material 32 is the NOx adsorbing means of the present embodiment, and is made of a material that can adsorb NOx in the exhaust gas at least in the presence of ozone. More specifically, the NOx adsorbent 32 is composed of a ceramic material such as alumina or zeolite, or a catalyst having a metal supported thereon. The material of the NOx adsorbent 32 will be described in detail with reference to FIG. 4 described later. In the present invention, the NOx adsorbing means is not limited to the ceramic material, and may be constituted by, for example, a NOx storage reduction (NSR) catalyst. Further, in this specification, the term “adsorption” includes all concepts similar to “occlusion”, “absorption”, “retention”, “collection”, and the like.

  The exhaust passage 14 is provided with an ozone generator 36 as active oxygen supply means for supplying ozone to the NOx adsorbent 32. As the ozone generator 36, for example, a form in which ozone is generated while flowing dry air or oxygen as a raw material in a discharge tube to which a high voltage can be applied, or any other type can be used. The ozone generator 36 includes an ozone supply port 38 for supplying ozone into the exhaust passage 14 at a position downstream of the oxidation catalyst 30 and upstream of the NOx adsorbent 32.

  Furthermore, the system of the present embodiment includes a recirculation passage 40 that connects the intake passage 12 and the exhaust passage 14. The reflux passage 40 is configured to recirculate NOx desorbed from the NOx adsorbent 32 to the intake system as a reflux gas. More specifically, one end side of the recirculation passage 40 (recirculation gas inflow side) is connected to the exhaust passage 14 on the downstream side of the NOx adsorbent 32 and the DPF 34. In addition, the other end side (the outflow side of the reflux gas) of the reflux passage 40 is connected to the intake passage 12 on the upstream side of the supercharger 22.

  The reflux passage 40 is provided with an electromagnetically driven reflux control valve 42 that controls the flow rate of the reflux gas, and a cooler 44 that cools the reflux gas. The recirculation passage 40 is mainly used for NOx desorption recirculation control, which will be described later. Like the EGR passage 24, the recirculation passage 40 is also used for normal EGR control for recirculating a part of the exhaust gas to the intake system. is there.

  On the other hand, the exhaust passage 14 is provided with an exhaust valve 46 that variably sets the exhaust gas flow rate downstream of the connection position of the reflux passage 40. The exhaust valve 46 is an exhaust flow rate variable means of the present embodiment, and is constituted by an electromagnetically driven flow control valve or the like. During the NOx desorption recirculation control, the flow rate of the exhaust gas is moderately suppressed by the exhaust valve 46, and the pressure (exhaust pressure) on the inflow side of the recirculation passage 40 is kept slightly higher than in normal operation. Thereby, the NOx desorbed from the NOx adsorbent 32 is introduced into the recirculation passage 40 together with the exhaust gas.

  FIG. 2 is a configuration diagram schematically showing a characteristic part of the exhaust system in the first embodiment of the present invention. The system according to the present embodiment includes a sensor system including various sensors necessary for controlling the vehicle and the internal combustion engine, and an ECU (Electronic Control Unit) 60 for controlling the operating state of the internal combustion engine 10. Yes. The sensor system includes a temperature sensor 48 and a NOx sensor 50 shown in FIG.

  Here, the temperature sensor 48 detects the temperature of the exhaust gas at or near the NOx adsorbent 32 as the temperature of the exhaust system. The NOx sensor 50 detects NOx in the exhaust gas on the downstream side of the NOx adsorbent 32. Furthermore, the sensor system includes, for example, an air flow meter that detects the intake air amount, a rotation sensor that detects the engine speed, a water temperature sensor that detects the cooling water temperature of the internal combustion engine, an air-fuel ratio sensor that detects the exhaust air-fuel ratio, and the like. These sensors are connected to the input side of the ECU 60 together with the sensors 48 and 50 described above. On the other hand, various actuators are connected to the output side of the ECU 60. This actuator includes a fuel addition valve 20, an EGR valve 26, an ozone generator 36, a reflux control valve 42, and an exhaust valve 46 in addition to the fuel injection valve 18, spark plug, and the like provided in each cylinder. .

  The ECU 60 drives each actuator while detecting the operating state of the internal combustion engine using a sensor system. Specifically, based on the output of the sensor system, the fuel injection amount, injection timing, ignition timing, etc. for each cylinder are set, and the actuator is driven in accordance with these settings. Further, the ECU 60 performs combustion control so that the exhaust air-fuel ratio is maintained in an appropriate range by adjusting the fuel injection amount according to the exhaust air-fuel ratio detected by the air-fuel ratio sensor. In this case, since the internal combustion engine 10 is a diesel engine, the exhaust air-fuel ratio is maintained in a lean state in normal combustion control.

The ECU 60 is configured to execute NOx adsorption control and NOx desorption recirculation control in accordance with the temperature state of the exhaust system. Hereinafter, these controls will be described with reference to FIG. FIG. 3 is an explanatory diagram for explaining the control of the ECU.
(NOx adsorption control)
In the NOx adsorption control, during the above-described normal combustion control (lean combustion control), when the temperature of the exhaust system is equal to or lower than a predetermined adsorption upper limit temperature (for example, about 200 ° C.), the ozone generator 36 is operated, Ozone is supplied to the upstream side of the NOx adsorbent 32. Here, the NOx adsorbent 32 can adsorb NOx efficiently even in a low temperature region where the adsorption performance is not so high in the presence of ozone.

FIG. 4 is an explanatory diagram showing a state in which the adsorption performance of the NOx adsorbent changes depending on the presence or absence of ozone. The data shown in this figure was obtained by the experiment of the present inventor. The maximum NOx amount (saturated adsorption amount) that can be adsorbed by a certain amount of adsorbent for each of the presence and absence of ozone is shown. Show. As shown in FIG. 4, the inventor of the present application extremely improves the adsorption performance as long as ozone is supplied in a low temperature region below the upper limit adsorption temperature in any of the adsorbents shown in (1) to (3) below. I was able to confirm that.
(1) A material formed only of ceramics such as alumina and zeolite (2) A catalyst in which a metal such as Pt and Fe is supported on the ceramic material (3) An alkali element and an alkaline earth element are supported on the ceramic material catalyst

  More specifically, as the NOx adsorbent 32, it is preferable to use a material that does not contain an alkali element and an alkaline earth element, that is, the material (1) or (2). This is because materials containing alkali elements and alkaline earth elements can increase the amount of NOx adsorbed by forming NOx and nitrate by these elements, but are easily poisoned by the sulfur content in the exhaust gas. There are characteristics. Accordingly, if ozone is supplied to the materials (1) and (2), a NOx adsorbent having high NOx adsorption performance and strong against sulfur poisoning can be easily realized. In particular, with the material (1), a ceramic material that does not contain a catalyst component can be used as a high-performance NOx adsorbent.

  Furthermore, according to the present inventors confirmed by experiment, in ceramic materials such as cordierite and zeolite, the desorption temperature of NOx can be increased by supplying ozone. That is, when ozone is supplied, NOx desorption can be suppressed even at the same temperature as when non-supplying, and the amount of NOx adsorbed at that temperature can be increased. According to the present embodiment, the NOx adsorbent 32 having higher adsorption performance can be realized by utilizing this characteristic.

  On the other hand, in FIG. 3, when the temperature of the exhaust system becomes higher than the upper limit temperature of adsorption, the effect of ozone on the NOx adsorption rate decreases, and the loss of ozone due to thermal decomposition gradually increases. become. Therefore, in this case, the supply of ozone to the NOx adsorbent 32 is stopped, and the NOx adsorption control is terminated.

  Further, during the NOx adsorption control, as shown in FIG. 3, normal EGR control is executed as necessary. In normal EGR control, exhaust gas is recirculated to the intake system via the EGR passage 24 and the recirculation passage 40. At this time, the ECU 60 adjusts the opening degrees of the EGR valve 26 and the reflux control valve 42 according to the operating state (engine speed, load factor, water temperature, etc.) of the internal combustion engine, and thereby the EGR gas that is recirculated to the intake system To control the flow rate.

(NOx desorption reflux control)
When the temperature of the exhaust system becomes equal to or higher than the predetermined desorption temperature, NOx adsorbed on the NOx adsorbent 32 starts to be desorbed, so NOx desorption recirculation control is executed. Here, the NOx desorption temperature has a substantially constant value according to the material of the NOx adsorbent 32, the amount of NOx adsorbed, and the like, and can be easily determined by experiments or the like. In the present invention, the determination as to whether or not the NOx desorption operation has started may be based on, for example, a detection signal from the NOx sensor 50 instead of the exhaust system temperature. That is, when the amount of NOx detected by the NOx sensor 50 exceeds a predetermined reference value, it may be determined that the NOx desorption operation has started and the NOx desorption reflux control is started.

  In the NOx desorption / reflux control, first, the exhaust pressure including the NOx desorbed from the NOx adsorbent 32 is increased by appropriately reducing the opening degree of the exhaust valve 46 to increase the exhaust pressure at the inflow position of the reflux passage 40. Into the reflux passage 40. This exhaust gas flows into the intake passage 12 via the recirculation passage 40 and is sucked into each cylinder. At this time, the ECU 60 executes stoichiometric combustion control instead of the above-described normal combustion control (lean combustion control). In the stoichiometric combustion control, the fuel injection amount and the like are controlled so that the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio. Further, during the NOx desorption reflux control, the supply of ozone is held in a stopped state.

  According to the stoichiometric combustion control described above, it is possible to realize a state (so-called low temperature combustion) in which the air-fuel mixture close to the stoichiometric air-fuel ratio is combusted at a relatively low temperature. By this low temperature combustion, NOx recirculated to the intake system can be efficiently reduced, and generation of new NOx by combustion in the cylinder can be suppressed.

  Further, when most of the NOx is desorbed from the NOx adsorbent 32 and the NOx desorption operation is completed, the desorption NOx is hardly detected by the NOx sensor 50, so it is determined that the desorption operation has been completed. it can. In this case, the ECU 60 returns the exhaust valve 46 to the normal opening (fully opened) and switches the stoichiometric combustion control to the normal lean combustion control, thereby ending the NOx desorption reflux control.

[Specific Processing for Realizing Embodiment 1]
FIG. 5 is a flowchart showing the control executed by the ECU in the first embodiment of the present invention. The routine shown in this figure is repeatedly executed during operation of the internal combustion engine. In the routine shown in FIG. 5, first, it is determined whether or not the temperature (or exhaust temperature) of the NOx adsorbent 32 is equal to or lower than the upper limit adsorption temperature (step 100). When this determination is satisfied, the above-described NOx adsorption control is started. To do. That is, ozone is supplied to the NOx adsorbent 32 by the ozone generator 36 to adsorb NOx in the exhaust gas (step 102).

  Subsequently, the ECU 60 determines whether or not the NOx adsorption amount has reached a predetermined saturated adsorption amount (step 104). The amount of NOx adsorbed is calculated based on, for example, the concentration of NOx in the exhaust gas calculated based on the operating state of the internal combustion engine, the elapsed time since the start of ozone supply, and the temperature of the exhaust system. By comparing this calculated value with the saturated adsorption amount stored in advance, the determination process in step 104 can be performed. When the determination in step 104 is established, the supply of ozone is stopped and the NOx adsorption control is terminated (step 106).

  Next, the ECU 60 determines whether or not the temperature of the exhaust system is equal to or higher than a predetermined desorption temperature (step 108). When this determination is established, the above-described NOx desorption recirculation control is started (step 110). Subsequently, it is determined whether or not the NOx desorption operation is completed based on the detection signal of the NOx sensor 50, and the NOx desorption reflux control is continued until the desorption operation is completed (step 112). Then, when the determination in step 112 is established, the NOx desorption reflux control is terminated (step 114).

  As described above in detail, according to the present embodiment, the NOx once adsorbed by the NOx adsorbent 32 can be recirculated to the intake system by the recirculation passage 40, and the NOx desorbed from the adsorbent 32 is in-cylinder. It can be reliably reduced by combustion. On the other hand, even when ozone remains during NOx adsorption, the ozone can be recirculated to the intake system through the recirculation passage 40 and decomposed by combustion in the cylinder.

  Therefore, desorption NOx and residual ozone can be purified by utilizing normal combustion performed in the cylinder. Thereby, for example, a NOx catalyst or the like does not need to be arranged on the downstream side of the adsorbent 32, so that the structure of the system can be simplified. Moreover, since it is not necessary to forcibly enrich the air-fuel ratio by rich spike control or the like in order to perform NOx reduction processing, the enrichment is insufficient and NOx is discharged to the outside, or the air-fuel ratio is disturbed to the rich side. Can be prevented, and exhaust emission can be improved. Furthermore, by depositing excess ozone into the intake system, deposit accumulation in the intake system and in the cylinder can be suppressed, and anti-knock performance can be improved.

  In the present embodiment, an exhaust valve 46 is provided on the downstream side of the reflux passage 40. Thus, during the NOx desorption operation, the exhaust valve 46 can appropriately suppress (squeeze) the flow rate of the exhaust gas on the downstream side of the reflux passage 40. As a result, the exhaust pressure can be increased at the inflow position of the recirculation passage 40, and the gas containing the desorbed NOx can be smoothly introduced from the exhaust passage 14 into the recirculation passage 40.

  In the present embodiment, as shown in FIG. 1, the case where the inlet of the reflux passage 40 is connected to the exhaust passage 14 on the downstream side of the DPF 34 is illustrated, so the exhaust valve 46 is provided on the downstream side of the reflux passage 40. It was set as the structure provided. However, in the present invention, for example, when some structure that serves as exhaust resistance is disposed on the downstream side of the reflux passage 40 and the exhaust pressure is sufficiently high at the inlet of the reflux passage 40, the exhaust valve 46 (exhaust gas) is not necessarily used. There is no need to provide flow rate variable means. Specifically, for example, when the inlet of the reflux passage 40 is connected between the NOx adsorbent 32 and the DPF 34 (upstream of the DPF 34), the DPF 34 becomes exhaust resistance, so that the flow of the reflux passage 40 is increased. Exhaust pressure is secured at the inlet. Accordingly, in this case, the exhaust valve 46 may be eliminated.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. The present embodiment includes a bypass catalyst arranged in parallel with the NOx adsorbent, and the configuration is different from that of the first embodiment including this point. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 2]
FIG. 6 is an overall configuration diagram for explaining a system configuration according to the second embodiment of the present invention. The system of the present embodiment includes a bypass passage 70, a bypass catalyst 72, and switching valves 74 and 76 in addition to the configuration of the first embodiment. The bypass passage 70 is connected to the exhaust passage 14 at a position where the NOx adsorbent 32 is bypassed. The bypass catalyst 72 is a catalyst capable of purifying at least NOx in the exhaust gas, for example, in an intermediate temperature range equal to or higher than the above-described desorption temperature, and is provided in the bypass passage 70.

  The switching valves 74 and 76 are composed of electromagnetically driven on-off valves or the like, and constitute flow path switching means for switching the exhaust gas flow path between the NOx adsorbent 32 and the bypass passage 70. That is, when one switching valve 74 is opened and the other switching valve 76 is closed, the exhaust gas passes through the NOx adsorbent 32. Further, when one switching valve 74 is closed and the other switching valve 76 is opened, the exhaust gas flows through the bypass passage 70. In addition, as a flow-path switching means of this invention, it is good also as a structure which replaces with the switching valves 74 and 76, and provides a single three-way valve etc. in the connection position of the exhaust passage 14 and the bypass passage 70.

(NOx purification control in intermediate temperature range)
Depending on the operation state of the internal combustion engine, it may be difficult to execute the stoichiometric combustion control in an intermediate temperature region where the NOx desorption operation occurs. In this case, the stoichiometric combustion control is not forcibly executed and the lean combustion control or the like is executed, but it becomes difficult to burn the desorbed NOx well. For this reason, in this embodiment, when the stoichiometric combustion control is not executed in the intermediate temperature range, the exhaust gas is circulated through the bypass passage 70 and the NOx in the exhaust gas is purified by the bypass catalyst 72. Then, until the stoichiometric combustion control becomes possible, the desorbed NOx is waited without being returned to the intake system.

[Specific Processing for Realizing Embodiment 2]
FIG. 7 is a flowchart showing the control executed by the ECU in the second embodiment of the present invention. The routine shown in this figure is repeatedly executed during operation of the internal combustion engine. In the routine shown in FIG. 7, first, in steps 200 to 208, NOx adsorption control is executed by the same procedure as in the first embodiment, and it is determined whether or not the temperature of the exhaust system is equal to or higher than the desorption temperature.

  When the determination in step 208 is satisfied, it is determined whether or not the operation state is suitable for NOx desorption / reflux control, that is, whether or not the operation state is capable of executing stoichiometric combustion control (step 210). When this determination is established, the switching valves 74 and 76 are switched to the NOx adsorbent 32 side to cause the exhaust gas to flow through the NOx adsorbent 32 (step 212). In steps 214 to 218, NOx desorption reflux control is executed by the same procedure as in the first embodiment.

  On the other hand, when the determination in step 210 is not established, the switching valves 74 and 76 are switched to the bypass passage 70 side to cause the exhaust gas to flow through the bypass catalyst 72 and execute the NOx purification control (step 220).

  In the present embodiment configured as described above, it is possible to obtain substantially the same operational effects as in the first embodiment. In particular, in the present embodiment, since the bypass passage 70 and the bypass catalyst 72 are provided, the execution condition of the combustion control is limited according to the NOx desorption temperature or the like, or the execution condition of the combustion control is adjusted. Thus, it can be avoided that the desorption temperature of the NOx adsorption means is limited. Therefore, when designing a system, the degree of freedom in design of control and the degree of freedom of selection of NOx adsorption means can be expanded.

Embodiment 3 FIG.
Next, a third embodiment of the present invention will be described with reference to FIG. The present embodiment includes a NOx purification catalyst and is characterized by this point. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 3]
FIG. 8 is an overall configuration diagram for explaining a system configuration according to the third embodiment of the present invention. In addition to the configuration of the first embodiment, the system of the present embodiment includes a three-way catalyst 80 as a NOx purification catalyst provided in the exhaust passage 14 on the downstream side of the NOx adsorbent 32. As is generally known, the three-way catalyst 80 purifies NOx, HC, CO, etc. in the exhaust gas when the exhaust air-fuel ratio is within a predetermined range (purification window) including the stoichiometric air-fuel ratio. be able to.

  In the present embodiment configured as described above, it is possible to obtain substantially the same operational effects as in the first embodiment. In particular, in the present embodiment, NOx desorbed from the NOx adsorbent 32 can be purified not only by combustion in the cylinder but also by the three-way catalyst 80. Therefore, even if part of NOx passes through the combustion chamber, the three-way catalyst 80 can reliably prevent this NOx from being released into the atmosphere.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to FIG. The present embodiment includes auxiliary power means, and this is a feature. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 4]
FIG. 9 is an overall configuration diagram for explaining a system configuration according to the third embodiment of the present invention. The system of the present embodiment is mounted on a vehicle such as a hybrid vehicle, and includes an electric motor 90 as auxiliary power means in addition to the configuration of the third embodiment. The electric motor 90 generates auxiliary power by being supplied with power from the battery 92, and the power generated by at least one power source of the internal combustion engine 10 and the electric motor 90 is the power split mechanism 94 and the speed reducer 96. And transmitted to the wheel 98 via A power generator 100 is connected to the power split mechanism 94, and the power generated by the power generator 100 is charged to the battery 92 via the inverter 102.

The ECU 60 is configured to operate any one (or both in some cases) of the internal combustion engine 10 and the electric motor 90 and to switch the power source according to the driving state of the vehicle. Further, in the present embodiment, when performing NOx desorption reflux control, both the internal combustion engine 10 and the electric motor 90 are driven by the ECU 60. That is, the ECU 60 is configured to execute stoichiometric combustion control in the internal combustion engine 10 while assisting the internal combustion engine with the power of the motor.

In the present embodiment configured as described above, it is possible to obtain substantially the same operational effects as in the first and third embodiments. In particular, in the present embodiment, the electric motor 90 can expand the operating range in which the stoichiometric combustion control can be performed. That is, since the internal combustion engine 10 is a diesel engine that performs lean combustion at normal times, an operation region in which stoichiometric combustion control can be performed may be limited in consideration of operation performance and the like. However, in the present embodiment, by using the electric motor 90 in combination, the operation performance can be ensured even during the stoichiometric combustion control. As a result, the internal combustion engine 10 can perform the stoichiometric combustion control at a desired timing without being affected by the driving situation of the vehicle. Therefore, by applying it to a hybrid vehicle, the effect of NOx desorption reflux control can be sufficiently exhibited in a wide driving range.

  In the above embodiment, steps 100, 102, 200, and 202 in FIGS. 5 and 7 show specific examples of the adsorption control means, and steps 110 and 214 show specific examples of the desorption combustion control means. Yes. Steps 210, 212, and 220 show specific examples of the exhaust flow path control means, and steps 110 and 214 show specific examples of the exhaust flow rate control means.

  In the second embodiment, the bypass passage 70 and the bypass catalyst 72 are provided in the configuration of the first embodiment. However, the present invention is not limited to this, and the bypass passage 70 and the bypass catalyst 72 may be provided for the third and fourth embodiments. That is, the bypass passage 70, the bypass catalyst 72, and the three-way catalyst 80 may be provided in one system, or these may be applied to a hybrid vehicle.

In the embodiment, ozone has been described as an example of the active oxygen added to the exhaust gas. However, the present invention is not limited to this, and instead of ozone, other types of active oxygen (for example, oxygen negative ions represented by O ⁻ , O ²⁻ , O ₂ ⁻ , O ₃ ⁻ , O _n ^−, etc.) are used. ) May be added to the exhaust gas.

  Furthermore, in the embodiment, the case where the present invention is applied to the internal combustion engine 10 including a diesel engine has been described as an example. However, the present invention is not limited to this, and is widely applied to various internal combustion engines including, for example, a gasoline engine. To get.

10 Internal combustion engine 12 Intake passage 14 Exhaust passage 16 Throttle valve 18 Fuel injection valve 20 Fuel addition valve 22 Supercharger 24 EGR passage 26 EGR valve 28 EGR cooler 30 Oxidation catalyst 32 NOx adsorbent (NOx adsorbing means)
34 DPF
36 Ozone generator (active oxygen supply means)
38 Ozone supply port 40 Recirculation passage 42 Recirculation control valve 44 Cooler 46 Exhaust valve (exhaust flow rate variable means)
48 Temperature sensor 50 NOx sensor 60 ECU
70 Bypass passage 72 Bypass catalyst (catalyst)
74, 76 switching valve (flow path switching means)
80 Three-way catalyst (NOx purification catalyst)
90 Electric motor (auxiliary power means)

Claims (3)

NOx adsorption means provided in the exhaust passage of the internal combustion engine and capable of adsorbing NOx in the exhaust gas at least in the presence of active oxygen;
Active oxygen supply means for supplying active oxygen to the NOx adsorption means;
A recirculation passage connected to the exhaust passage on the downstream side of the NOx adsorption means and recirculating NOx desorbed from the NOx adsorption means to the intake system;
A bypass passage that is connected to the exhaust passage at a position that bypasses the NOx adsorbing means, and is provided with a catalyst that purifies at least NOx in the exhaust gas;
A flow path switching means capable of switching a flow path of the exhaust gas between the NOx adsorption means and the bypass passage;
Auxiliary power means for generating auxiliary power for assisting the internal combustion engine;
The active oxygen supply means when the temperature of the exhaust gas is equal to or lower than the upper limit adsorption temperature as compared with the upper limit adsorption temperature that is the upper limit of the temperature at which the NOx adsorption means can adsorb NOx in the presence of active oxygen Adsorption control means for operating
The temperature of the exhaust gas is equal to or higher than the desorption temperature as compared with the desorption temperature set to a temperature at which NOx adsorbed on the NOx adsorption means starts to desorb and higher than the upper limit adsorption temperature. When the stoichiometric combustion control for controlling the air-fuel ratio of the internal combustion engine to be the stoichiometric air-fuel ratio is executable, the NOx desorbed from the NOx adsorbing means is recirculated while performing the stoichiometric combustion control. One desorption combustion control means for recirculation to the intake system through the passage;
When the exhaust gas temperature is equal to or higher than the desorption temperature and the execution of the stoichiometric combustion control is difficult, the NOx adsorption is performed while the stoichiometric combustion control is executed with the auxiliary power means operated. Other desorption combustion control means for recirculating NOx desorbed from the means to the intake system via the recirculation passage;
When the exhaust gas temperature is equal to or higher than the desorption temperature and it is difficult to execute the stoichiometric combustion control, the exhaust gas is circulated to the bypass passage by the flow path switching means while performing the lean combustion control. An exhaust flow path control means,
An exhaust emission control device for an internal combustion engine, comprising: Exhaust flow rate varying means provided in the exhaust passage downstream from the connection position of the reflux passage and variably setting the flow rate of exhaust gas flowing through the exhaust passage;
An exhaust flow rate control means for suppressing the flow rate of the exhaust gas by the exhaust flow rate variable means during the NOx desorption operation;
The exhaust emission control device for an internal combustion engine according to claim 1 , comprising: The exhaust purification device for an internal combustion engine according to claim 1 or 2 , further comprising a NOx purification catalyst provided in the exhaust passage on the downstream side of the NOx adsorption means and capable of purifying at least NOx in the exhaust gas.

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