JP2007154717A - Exhaust emission control device and exhaust emission control method for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device and an exhaust emission control method for an internal combustion engine capable of converting NO<SB>X</SB>in exhaust gas without thermally damaging NO<SB>X</SB>catalyst in a downstream even during regeneration of a particulate filter. <P>SOLUTION: In the exhaust emission control device including a downstream side NO<SB>X</SB>catalyst and an upstream side particulate filter arranged in the exhaust gas passage of the internal combustion engine, and purifying exhaust gas discharged from the internal combustion engine, a heat exchanger for dropping temperature of exhaust gas flowing into the NO<SB>X</SB>catalyst is provided between the particulate filter and the NO<SB>X</SB>catalyst. The heat exchanger can be arranged in the exhaust gas passage or can be arranged in a bypass part with providing the bypass part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an exhaust gas purification device and an exhaust gas purification method for exhaust gas discharged from an internal combustion engine, and more particularly to an exhaust gas purification device and an exhaust gas purification method for an internal combustion engine that can efficiently reduce NO _x in the exhaust gas. .

Conventionally, in exhaust gas discharged from an internal combustion engine such as a diesel engine black smoke particles (hereinafter, referred to as PM) and nitrogen oxides (hereinafter, referred to as NO _X), etc. are included. For this reason, a countermeasure is taken to purify the exhaust gas by providing a particulate filter (hereinafter sometimes referred to as PM filter or simply a filter), an NO _x catalyst, or the like as an exhaust gas aftertreatment device.
For example, when a PM filter is provided as a post-processing device, PM in exhaust gas is collected by the PM filter, and periodically burned by a burner or by high-temperature exhaust gas that has passed an oxidation catalyst. PM is removed by burning (oxidizing) or the like. Further, when the NO _x catalyst is provided as the aftertreatment device, NO and NO ₂ in the exhaust gas are absorbed by the NO _x catalyst, and a reducing agent such as urea and raw gas (HC) is supplied to reduce the reaction. Disassembled and discharged.

Further, in order to both eliminate the PM and NO _X, the exhaust gas purifying apparatus is disclosed which has both with these PM filter and NO _X catalyst. More specifically, as shown in FIG. 8, a particulate filter 412 in which an oxidation catalyst is integrally supported is provided in the middle of the exhaust pipe 409 through which the exhaust gas 408 from the diesel engine 401 flows, and the particulate filter the middle exhaust pipe 409 downstream of the 412, _the NO _X storage reduction catalyst 411 is provided, the particulate filter 412 and _the NO _X storage exhaust pipe 409 to the bypass line 417 is branched from the middle _the NO _X storage between the reduction catalyst 411 The exhaust pipe 409 is connected to the middle of the exhaust pipe 409 on the downstream side of the reduction catalyst 411 and can be switched to guide the exhaust gas 408 to either the NO _x storage reduction catalyst 411 side or the bypass line 417 side at the branch portion of the bypass line 417. An exhaust purification device provided with a switching valve 418 (see, for example, Patent Document 1).
Japanese Patent Laying-Open No. 2005-214159 (Claims Fig. 1)

However, the exhaust gas purification device disclosed in Patent Document 1 is configured to discharge the exhaust gas by bypassing the NO _X storage reduction catalyst during regeneration of the particulate filter, and during that time, NO _X in the exhaust gas is removed. It was something that could not be done.
On the other hand, when the regeneration of the particulate filter, when passing directly NO _X catalyst in high-temperature exhaust gas, the problem remains that generates heat deterioration and thermal damage of the NO _X catalyst.

Accordingly, the inventors of the present invention have made diligent efforts, and in the exhaust gas purification apparatus provided with the upstream PM filter and the downstream NO _x catalyst, when regenerating the PM filter, the temperature of the exhaust gas that has passed through the PM filter is converted into a heat exchanger. The present invention has been completed by finding that such a problem can be solved by passing the NO _x catalyst through the NOx catalyst.
That is, an object of the present invention is to provide an exhaust purification device and an exhaust purification method capable of purifying NO _{x in} exhaust gas while preventing thermal deterioration and thermal damage of the NO _x catalyst even during regeneration of the PM filter. Is to provide.

According to the present invention, there is provided an exhaust purification device for purifying exhaust gas exhausted from an internal combustion engine, including an upstream particulate filter and a downstream NO _x catalyst disposed in an exhaust passage of the internal combustion engine. Te, between the particulate filter and the NO _X catalyst, exhaust gas purification apparatus for an internal combustion engine having a heat exchanger for reducing the temperature of the exhaust gas flowing into the NO _X catalyst is provided, solving the problems described above can do.

  In configuring the exhaust gas purification apparatus for an internal combustion engine of the present invention, it is preferable to provide a heat exchanger in the exhaust passage.

Further, in configuring the exhaust purification system of an internal combustion engine of the present invention, between the particulate filter and the NO _X catalyst, branches from the exhaust passage provided with a bypass section that joins again the exhaust passage, and the bypass portion It is preferable to provide flow path control means for controlling the amount of exhaust gas flowing into the exhaust passage, and to arrange the heat exchanger in the bypass section.

In configuring the exhaust gas purification apparatus for an internal combustion engine of the present invention, it is preferable to provide a temperature sensor in the vicinity of the inlet of the NO _x catalyst.

Another aspect of the present invention is to purify exhaust gas exhausted from an internal combustion engine using an upstream particulate filter and a downstream NO _x catalyst disposed in the exhaust passage of the internal combustion engine. In this exhaust purification method, when the particulate filter is regenerated, the exhaust gas that has passed through the particulate filter is subjected to heat exchange using a heat exchanger to lower the temperature and pass through the NO _x catalyst. An exhaust purification method for an internal combustion engine.

In carrying out the exhaust gas purification method for an internal combustion engine of the present invention, at least a part of the exhaust gas is subjected to heat exchange in accordance with the temperature of the exhaust gas measured by a temperature sensor arranged near the inlet of the NO _x catalyst. It is preferable to make it.

  In carrying out the exhaust gas purification method for an internal combustion engine of the present invention, the heat exchanger is a heat exchanger provided in the exhaust passage, and controls the on / off of the heat exchanger or the degree of heat exchange. Thus, it is preferable to exchange heat at least part of the exhaust gas.

In carrying out the exhaust gas purification method for an internal combustion engine according to the present invention, the heat exchanger is arranged in a bypass portion that branches from the exhaust passage between the particulate filter and the NO _x catalyst and joins the exhaust passage again. It is preferable that at least a part of the exhaust gas is heat-exchanged by controlling a flow path control means for controlling the flow rate of the exhaust gas flowing into the exhaust passage and the bypass portion.

According to the exhaust purification system of an internal combustion engine of the present invention, between the upstream side of the PM filter and a downstream side of the NO _X catalyst, by providing a predetermined heat exchanger, the reproduction or the like of the PM filter, NO _X Since the temperature of the exhaust gas flowing into the catalyst can be controlled, thermal deterioration and thermal damage of the NO _x catalyst can be prevented.
Further, since the temperature of the exhaust gas flowing into the NO _x catalyst can be controlled, the exhaust gas can pass through the NO _x catalyst even during regeneration of the PM filter, so that NO _x is released into the atmosphere. This can be prevented.

Further, according to the exhaust gas purification method for an internal combustion engine of the present invention, even when the temperature of the exhaust gas that has passed through the PM filter becomes high, such as during regeneration of the PM filter, the upstream PM filter and the downstream PM filter the predetermined heat exchanger provided between the NO _X catalyst, by controlling the temperature of the exhaust gas flowing into the NO _X catalyst, it is possible to prevent thermal deterioration and thermal damage of the NO _X catalyst.
Also, by controlling the temperature of the exhaust gas flowing into the NO _x catalyst, the exhaust gas can be passed through the NO _x catalyst even during regeneration of the PM filter, so that NO _x is released into the atmosphere. Can be prevented

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments relating to an internal combustion engine exhaust purification apparatus and an internal combustion engine exhaust purification method according to the present invention will be specifically described below with reference to the drawings as appropriate. However, this embodiment shows one aspect of the present invention and does not limit the present invention, and can be arbitrarily changed within the scope of the present invention.

[First Embodiment]
The first embodiment of the present invention forms contain NO _X catalyst of the particulate filter and the downstream side of the upstream side disposed in the exhaust passage of an internal combustion engine, for purifying exhaust gas discharged from an internal combustion engine In the exhaust purification apparatus and the exhaust purification method, a heat exchanger is provided in the exhaust passage between the particulate filter and the NO _x catalyst for reducing the temperature of the exhaust gas flowing into the NO _x catalyst. An exhaust purification device for an internal combustion engine and an exhaust purification method using such an exhaust purification device.

1. Exhaust Purification Device (1) Basic Configuration An exhaust purification device 10 for an internal combustion engine of the present embodiment includes an upstream PM filter 13 disposed in an exhaust passage 11 of the internal combustion engine 5 as shown in FIG. a NO _X catalyst 15 on the downstream side, with including, between the PM filter and NO _X catalyst, and a predetermined heat exchanger 20.
The exhaust gas purification apparatus 10 for an internal combustion engine collects PM in exhaust gas discharged from the internal combustion engine 5 by a PM filter, and similarly reduces NO _x (NO or NO ₂ ) in the exhaust gas by a NO _x catalyst. can do. Therefore, it is possible to release the pollutant after removing it from the exhaust gas.
Hereinafter, it divides into each site | part and demonstrates in detail.

(2) Internal combustion engine As the internal combustion engine 5 that discharges exhaust gas, a diesel engine or a gasoline engine is typical. In particular, it is suitable to target a diesel engine in which an exhaust purification device must be attached.
Further, the operating state detection means 17 of the internal combustion engine shown in FIG. 1 is a means for detecting the rotational speed, the fuel injection amount, the fuel injection timing, etc. of the internal combustion engine 5, and also takes the detection results into consideration. It is preferable that the PM filter regeneration timing can be controlled.

(3) an exhaust passage The exhaust passage 11 is connected to an exhaust port of an internal combustion engine, in the way, PM filter 13 and NO _X catalyst 15 and the like are disposed. The cross-sectional shape of the exhaust passage 11 is not particularly limited, such as a circle, an ellipse, or a prism.

(4) PM filter Moreover, the PM filter 13 can use a well-known thing suitably, For example, it can be set as the filter of the honeycomb structure comprised from the ceramic material.
This PM filter purifies exhaust gas by collecting PM and other fine particles in the exhaust gas. However, the collected amount of PM increases as the collection of PM, etc. continues, and the exhaust pressure of the internal combustion engine rises, adversely affecting the engine performance. Need to be regenerated.

For example, a combustion burner that emits a flame is disposed upstream of the filter 13, and the PM collected by the filter is burned (oxidized) by the emitted flame or by the exhaust gas that is forcibly heated. Can do.
In addition, an oxidation catalyst is disposed upstream of the filter, and a burner capable of emitting incomplete combustion gas containing a large amount of CO and an injection device capable of injecting fuel gas (HC) are disposed further upstream of the oxidation catalyst. By providing, the exhaust gas is heated using the oxidation heat when CO or HC is oxidized by the oxidation catalyst, and the PM collected by the filter is burned (oxidized) by the high-temperature exhaust gas. Can do. In addition, when an oxidation catalyst is arranged upstream of the PM filter, the exhaust gas is heated by the oxidation heat by oxidizing CO and HC with the oxidation catalyst by post-injection with the internal combustion engine when the filter is regenerated. The PM collected by the filter can be burned by the gas. The oxidation catalyst is not particularly limited, and a known catalyst such as a catalyst in which platinum is supported on alumina and a rare earth element such as cerium added to the catalyst can be used.

In addition, regarding the regeneration time of the PM filter, for example, the pressure sensors are arranged on the upstream side and the downstream side of the PM filter, and by checking the pressure difference measured by them, the degree of clogging of the filter is estimated, Timing can be measured.
In order to burn the PM collected by the filter with the high temperature exhaust gas, the exhaust gas needs to be in a high temperature state, for example, about 600 ° C. or more.

(5) NO _X catalyst As for the NO _X catalyst 15, it is possible to suitably use a known, for example, on the surface or inside of such alumina fiber, platinum (Pt), potassium (K), sodium (Na ), Cesium (Cs), barium (Ba), calcium (Ca), lanthanum (La), yttrium (Y), rhodium (Rb), and the like.
This NO _x catalyst purifies exhaust gas by reducing NO _x in the exhaust gas. For example, together with the exhaust gas is occluded NO _X in the lean state and which in the exhaust gas to a rich state by reducing the NO _X emission, which selectively reduced to purify the NO _X using urea as a reducing agent There is.

As for the supply timing of the reducing agent such as HC and urea, for example, by arranging lambda sensors upstream and downstream of the NO _x catalyst, and verifying the difference in air-fuel ratio measured by them, NO _The timing can be measured by estimating the amount of _X absorbed or using a map created in advance based on the operating state of the internal combustion engine.

In addition, this NO _x catalyst is generally activated in the range of 200 to 500 ° C., and the reduction reaction of NO _x becomes efficient, while being excessively hot (for example, a value exceeding about 700 ° C.). If it becomes, it has the characteristic of becoming easy to deteriorate or damage by heat.

Moreover, it is preferable to arrange an oxidation catalyst downstream of the NO _x catalyst. As a result, when a reducing agent more than the amount necessary for the NO _x reduction reaction is supplied, HC and urea can be oxidized and released, thereby preventing air pollution. That is, in order to prevent being released as HC or ammonia, it can be decomposed and released into carbon dioxide, nitrogen oxides, water and the like.

Further, when urea is used as the reducing agent, it is preferable to dispose an oxidation catalyst upstream of the urea addition section on the upstream side of the NO _x catalyst. As a result, the NO / NO ₂ ratio can be made close to 1: 1 in order to oxidize NO contained in the exhaust gas to NO ₂ to make the reduction reaction rate using urea most efficient. . Also for this oxidation catalyst, a known one can be used as appropriate as in the above-described oxidation catalyst.

(6) heat exchanger The exhaust gas purifying apparatus of the present embodiment, between the PM filter 13 and the NO _X catalyst 15, passes through the PM filter 13, controls the temperature of the exhaust gas flowing into the NO _X catalyst 15 The heat exchanger 20 for performing is provided. Even when the temperature of the exhaust gas that has passed through the PM filter 13 is remarkably high, such as when the PM filter 13 is regenerated by the heat exchanger 20, the temperature of the exhaust gas flowing into the NO _x catalyst 15 can be efficiently reduced. Thus, thermal degradation and thermal damage of the NO _x catalyst 15 can be prevented.

As an aspect of this heat exchanger, as shown in FIG. 2A, a heat exchanger 20A that cools the exhaust gas by circulating the cooling water W around the exhaust passage 11, or FIG. As shown in FIG. 4, various configurations such as a heat exchanger 20B for cooling the exhaust gas by blowing the cooling air A using the fan 14 to the exhaust passage 11 are conceivable.
By adopting a configuration using such cooling water W or cooling air A, the degree of cooling of the exhaust gas can be controlled by controlling the operating state of the cooling means. Therefore, it is possible to prevent the exhaust gas from being cooled at a time other than the regeneration timing of the PM filter, the temperature of the NO _x catalyst being lowered, and the purification efficiency from being lowered. Also in the reproduction or the like of the PM filter, corresponding to the temperature of the exhaust gas flowing into the NO _X catalyst, by controlling precisely the degree of cooling of the exhaust gas, the purification efficiency in the NO _X catalyst in a suitable state Can keep.
Among them, the cooling efficiency can be remarkably improved by using the heat exchanger 20A using the cooling water shown in FIG.

  Further, as shown in FIG. 2 (c), in combination with the heat exchanger of FIG. 2 (a) and FIG. 2 (b), a plurality of fin members 12 are provided in the exhaust passage 11 to dissipate the heat quantity of the exhaust gas. It can also be set as the heat exchanger 20C comprised easily. With such a configuration in which the fin member 12 is provided, when it is desired to reduce the temperature of the exhaust gas, since the cross-sectional area of the exhaust passage is increased, heat can be exchanged efficiently. When the temperature of the gas is relatively low and it is not desired to lower the temperature further, the supply of cooling water or cooling air can be stopped to provide a heat insulating effect.

(7) Temperature sensor When the heat exchanger 20 that can switch the operating state using cooling water, cooling air, or the like is provided, as shown in FIG. 3, the NO _x catalyst 15 in the exhaust passage 11 is provided. Preferably, a temperature sensor 21 for measuring the temperature of the exhaust gas is provided on the upstream side. Based on the temperature of the exhaust gas measured by the temperature sensor 21, by controlling the operation state of the heat exchanger 20 using cooling water or cooling air, the temperature of the exhaust gas flowing into the NO _X catalyst 15 By controlling, the NO _x purification efficiency can be maintained in a suitable state.
Location of such a temperature sensor 21 is not particularly limited as long as between the heat exchanger 20 and the NO _X catalyst 15, to be able to measure the temperature of the exhaust gas flowing into the more accurate NO _X catalyst 15 Therefore, it is preferable that the NO _x catalyst 15 is disposed in the vicinity of the inlet.

(8) Control means In the case where the heat exchanger 20 capable of switching the operation state using cooling water, cooling air, or the like is provided, the temperature is measured by the temperature sensor 21 as shown in FIG. Control means 22 for controlling the operating state of the heat exchanger 20 can be provided based on the temperature and the like. That is, the control means 22 controls the introduction amount of cooling water, cooling air, etc. in order to maintain the NO _x catalyst 15 at the activation temperature and keep the NO _x purification efficiency in a suitable state.
For example, when the exhaust gas that has passed through the filter and has been heated is cooled by a heat exchanger during regeneration of the PM filter, but the temperature of the exhaust gas has dropped below the activation temperature, the heat exchanger switch is The exhaust gas temperature is slightly increased by turning it off or weakening the operating state. In this way, by switching the operating state of the heat exchanger and controlling the temperature of the exhaust gas flowing into the NO _X catalyst to be within a predetermined range, the NO _X purification efficiency in the NO _X catalyst is in a suitable state. Can be kept in.

  Further, the control means preliminarily determines the exhaust gas based on the operating state such as the rotational speed of the internal combustion engine, the fuel injection amount, the injection timing, the PM accumulation amount in the PM filter, the air-fuel ratio upstream of the PM filter, and the like. It can also be configured to send a signal to the heat exchanger after predicting the temperature.

2. Exhaust gas purifying method Next, using the exhaust gas purifying apparatus 10 of the present embodiment described above will be described in detail exhaust gas purifying method for purifying PM and NO _X in the exhaust gas.
In such an exhaust gas purification method for an internal combustion engine, when the PM filter is regenerated, the exhaust gas that has passed through the PM filter is subjected to heat exchange using a heat exchanger to lower the temperature and pass through the NO _x catalyst. It is characterized by that.
In the following description, an example will be described in which a heat exchanger having a configuration in which the temperature of exhaust gas is lowered using cooling water is used as the heat exchanger.

First, during the operation of the internal combustion engine, the exhaust gas discharged, after passing through the PM filter, by passing the NO _X catalyst, perform the reduction of the collecting or NO _X in PM.
At this time, for example, when the pressure loss on the upstream side and downstream side of the filter is measured and exceeds a predetermined value, it is determined that the amount of PM collected in the filter exceeds the predetermined amount, and is collected by the filter. The filter is regenerated by forcibly burning (oxidizing) PM. In the NO _X catalyst, at a predetermined time, the NO _X is reduction by supplying a reducing agent such as CO or HC and urea release is converted into nitrogen, and the like.

At this time, at the time of regeneration of the PM filter, it is used for burning (oxidizing) PM, and the temperature of the exhaust gas that has passed through the filter is in a high temperature state (about 600 to 800 ° C.). If the NO _x catalyst is allowed to flow, the NO _x catalyst may be thermally deteriorated or thermally damaged.
Therefore, in the exhaust gas purification method of the present embodiment, an exhaust gas purification device having a predetermined heat exchanger is used between the PM filter and the NO _x catalyst, and the exhaust gas that has passed through the filter is regenerated when the PM filter is regenerated. The heat is exchanged using a heat exchanger to lower the temperature and pass through the NO _x catalyst to prevent such thermal damage.

For example, in an operation state in which the PM filter is not regenerated, as shown in FIG. 4A, the switch of the heat exchanger 20 using cooling water is turned off so as not to operate. In this state, PM in the exhaust gas is collected by the filter 13. Further, the NO _x in the exhaust gas is reduced and released by the downstream NO _x catalyst 15. In such a normal operation state, the temperature of the exhaust gas is generally in the range of 100 to 400 ° C., and the NO _x catalyst is not thermally deteriorated or damaged.

Next, at the time of regeneration of the PM filter, the PM collected by the filter is forcibly burned using a combustion burner or the like. At this time, the exhaust gas that passes through the filter and flows into the NO _x catalyst is in a considerably high temperature state. For example, the temperature near the inlet of the NO _x catalyst may be 600 ° C. or higher. Therefore, as shown in FIG. 4B, the switch of the heat exchanger 20 using the cooling water is turned on to supply the cooling water W to the periphery of the exhaust passage 11. As a result, the collected PM can be burned, and the temperature of the exhaust gas that has passed through the filter 13 can be lowered to flow into the NO _x catalyst 15. Therefore, thermal deterioration and thermal damage of the NO _x catalyst can be prevented. Even in such a case, since the exhaust gas passes through both the PM filter and the NO _x catalyst, it is not released into the atmosphere as it is.
Note that by measuring the temperature of the exhaust gas with a temperature sensor arranged in the vicinity of the inlet of the NO _x catalyst, it is possible to accurately determine the timing for turning on the switch of the heat exchanger.

Also, during reproduction of the PM filter, in a state in which to operate the heat exchanger, subsequently, the temperature sensor disposed near the entrance of the NO _X catalyst, for measuring the temperature of the exhaust gas flowing into the NO _X catalyst. If the temperature of the exhaust gas flowing into the NO _x catalyst is too low, the heat exchanger 20 is switched off again or cooled as shown in FIG. 4 (c). By controlling the flow rate and temperature of the water W, the temperature of the exhaust gas flowing into the NO _x catalyst 15 is controlled to increase. Thus, while lowering the temperature of the exhaust gas in order to prevent thermal damage or the like of the NO _X, even purification efficiency of the NO _X can be maintained so as not to decrease.
The on / off operation of the switch and the control of the flow rate and temperature of the cooling water can be repeatedly performed in accordance with the temperature of the exhaust gas flowing into the NO _x catalyst.

  Next, when the regeneration of the PM filter is completed, the temperature of the exhaust gas that has passed through the filter also returns to about 100 to 400 ° C., so there is no need to lower the temperature using a heat exchanger, so heat exchange The device is turned off to the state shown in FIG.

As described above, according to the exhaust gas purifying method of the present embodiment, the reproduction or the like of the PM filter, when the temperature of the exhaust gas flowing into the NO _X catalyst exceeds a predetermined temperature, the exhaust gas passing through the PM filter, by flowing the NO _X catalyst by lowering the temperature by using a heat exchanger, it is possible to prevent thermal deterioration and thermal damage of the NO _X catalyst.
Further, to measure the temperature of the exhaust gas flowing into the NO _X catalyst, corresponding to the temperature, on-off and the switch of the heat exchanger, by controlling the flow rate such as cooling water or cooling air, of the NO _X catalyst A reduction in the purification rate can be suppressed.

[Second Embodiment]
The second embodiment of the present invention forms contain NO _X catalyst of the particulate filter and the downstream side of the upstream side disposed in the exhaust passage of an internal combustion engine, for purifying exhaust gas discharged from an internal combustion engine in the exhaust purification apparatus and an exhaust purifying method, between the particulate filter and the NO _X catalyst, branches from the exhaust passage, flows again provided with a bypass section that joins the exhaust passage, the bypass portion and the exhaust passage exhaust An exhaust gas purification apparatus for an internal combustion engine, characterized by comprising a flow path control means for controlling the amount of gas, and a heat exchanger disposed in the bypass section, and an exhaust gas purification method using such an exhaust gas purification apparatus It is.
Hereinafter, the exhaust gas purification apparatus and the exhaust gas purification method of the internal combustion engine of the present embodiment will not be described with respect to the points common to the first embodiment, and will be described focusing on the different points.

1. Exhaust Purification Device (1) Basic Configuration An exhaust purification device 110 for an internal combustion engine in the exhaust purification device of the present embodiment is an upstream PM disposed in an exhaust passage 111 of the internal combustion engine 105 as shown in FIG. a filter 113, a NO _X catalyst 115 downstream, with including, between the PM filter 113 and NO _X catalyst 115 provided with a predetermined bypass portion 123, flows into the bypass portion 123 and the exhaust passage 111 A flow rate ratio control means 119 for controlling the amount of exhaust gas is provided, and the heat exchanger 120 is arranged in the bypass portion 123.
Exhaust gas purifying apparatus 110 of such internal combustion engine, similarly to the exhaust gas purifying apparatus of the first embodiment, after removing the contaminants such as PM and NO _X from the exhaust gas can be released.
In the exhaust gas purifying apparatus of the present embodiment, and the internal combustion engine 105, exhaust passage 111, PM filter 113, NO _X catalyst 115, the type of the heat exchanger 120, the temperature sensor 121, an exhaust purifying apparatus of the first embodiment Since it can be set as the structure similar to what was provided in, description here is abbreviate | omitted.

(2) Bypass portion The exhaust passage 111 in the exhaust gas purification device 110 for the internal combustion engine of the present embodiment branches from the exhaust passage 111 between the PM filter 113 and the NO _x catalyst 115 and joins the exhaust passage 111 again. A bypass part 123 is provided. Further, the exhaust gas purification device 110 includes a flow rate ratio control means 119 for controlling the flow rate ratio of the exhaust gas that passes through the exhaust passage 111 and the bypass portion 123. By providing such a bypass portion 123, a part or all of the exhaust gas discharged from the internal combustion engine 105 and passing through the exhaust passage 111 can be caused to flow into the heat exchanger 120. Further, by providing the flow rate ratio control means 119, the exhaust gas can be allowed to flow into the exhaust passage 111 and the bypass portion 123 with the ratio being controlled. Therefore, it is possible to finely control the temperature of the exhaust gas flowing into the NO _x catalyst 115 by controlling the amount of exhaust gas to be heat exchanged using the heat exchanger 120.

For example, if the temperature of the exhaust gas that has passed through the filter is in a considerably high temperature state and you want to reduce the temperature of the exhaust gas to a considerable extent, all the exhaust gas that has passed through the filter must pass through the bypass side. Thus, the temperature of the exhaust gas can be efficiently reduced.
Conversely, if the temperature of the exhaust gas passing through the filter exhaust gas temperature is below the normal operating conditions, not only it is not necessary to lower the temperature of the exhaust gas, by reducing a decrease in the purification efficiency of the NO _X Therefore, all the exhaust gas that has passed through the filter is allowed to pass through the exhaust passage side. That is, there is no need to exchange heat between the exhaust gases.
On the other hand, when the temperature of the exhaust gas that has passed through the filter changes in the vicinity of the heat resistance temperature of the NO _x catalyst, the exhaust gas passage side and the bypass part side are passed at an appropriate ratio by the flow rate control means. The temperature of the exhaust gas in a state where the exhaust gases that have passed through the respective sides merge is controlled so that the NO _x purification efficiency in the NO _x catalyst can be maintained in a suitable state.

  The diameter, length, shape, etc. of the bypass are not particularly limited. Further, since the heat exchanger arranged in the middle of the bypass section can be configured to use cooling water or cooling air, as described in the first embodiment, it is combined with the control of the flow rate ratio control means. Thus, the temperature of the exhaust gas can be controlled more finely by controlling the flow rates of the cooling water and the cooling air.

(3) Flow rate ratio control means Further, in the exhaust purification device 10 of the present embodiment, the exhaust passage 111 side and the bypass are bypassed based on the temperature measured by the temperature sensor 121 arranged in the vicinity of the inlet of the NO _x catalyst 115. The flow rate ratio control means 119 for setting the flow rate ratio of the exhaust gas flowing through the section 123 side is provided. The flow rate control unit 119, for example, as shown in FIG. 5, and the exhaust passage 111 and both or valve portion 128 provided in one of the bypass portion 123, the temperature of the exhaust gas flowing into the NO _X catalyst 115 Correspondingly, control means 129 for controlling the opening degree of each valve portion 128 can be configured so as to maintain the temperature so as not to cause thermal deterioration and thermal damage of the NO _x catalyst.

As the valve portion 128 in the example of the flow rate ratio control means shown in FIG. 5, rotatable valve bodies 128A and 128B as shown in FIG. 6 (a) or (b), or a shutter as shown in FIG. 6 (c). The member 128C or the like can be used.
Further, as shown in FIG. 5, the control means for adjusting the opening degree of the valve unit directly measures and reflects the temperature of the exhaust gas by the temperature sensor 121 arranged in the vicinity of the inlet of the NO _x catalyst 15. Thus, a signal can be sent to the valve unit 128. Alternatively, the exhaust gas temperature is predicted in advance based on data such as the operating state such as the rotational speed of the internal combustion engine, the fuel injection amount, the injection timing, the PM accumulation amount in the PM filter, and the air-fuel ratio upstream of the PM filter. Above, it can also comprise so that a signal may be sent with respect to a valve part.

2. Exhaust gas purifying method Next, using the exhaust gas purifying device 110 of the present embodiment described above will be described in detail exhaust gas purifying method for purifying PM and NO _X in the exhaust gas.
The exhaust gas purification method for an internal combustion engine according to the present embodiment differs from the exhaust gas purification method according to the first embodiment in that a part or all of the exhaust gas that has passed through the PM filter is bypassed when the PM filter is regenerated. By passing through the side, the temperature is lowered by heat exchange using a heat exchanger arranged in the middle of the bypass section, and the NO _x catalyst is passed through.

First, during the operation of the internal combustion engine, the exhaust gas discharged, after passing through the PM filter, by passing the NO _X catalyst, perform the reduction of the collecting or NO _X in PM.
At this time, for example, when the pressure loss on the upstream side and downstream side of the filter is measured and exceeds a predetermined value, it is determined that the amount of PM collected in the filter exceeds the predetermined amount, and is collected by the filter. The filter is regenerated by forcibly burning (oxidizing) PM. In the NO _X catalyst, the predetermined time, the the NO _X by reduction by supplying a reducing agent such as CO or HC and urea release is converted into nitrogen, and the like.

At this time, at the time of regeneration of the PM filter, it is used for burning (oxidizing) PM, and the temperature of the exhaust gas that has passed through the filter is in a high temperature state (about 600 to 800 ° C.). If the NO _x catalyst is allowed to flow, the NO _x catalyst may be thermally deteriorated or thermally damaged.
Therefore, in the exhaust purification method of the present embodiment, part or all of the exhaust gas that has passed through the PM filter is allowed to pass through the bypass portion and heat exchange is performed using a heat exchanger disposed in the middle of the bypass portion. As a result, the temperature of the exhaust gas is lowered and the NO _x catalyst is allowed to pass through, thereby preventing such thermal damage.

For example, in the operation state where the PM filter is not regenerated, as shown in FIG. 7A, the flow rate ratio control means 119 is controlled so that the exhaust gas does not flow into the bypass part 123 where the heat exchanger 120 is arranged. . In this state, PM in the exhaust gas is collected by the filter. Further, the NO _x in the exhaust gas is reduced and released by the downstream NO _x catalyst. In such a normal operation state, the temperature of the exhaust gas is generally in the range of 100 to 400 ° C., and the NO _x catalyst is not thermally deteriorated or damaged.

Next, at the time of regeneration of the PM filter, the PM collected by the filter is forcibly burned using a combustion burner or the like. At this time, the exhaust gas that passes through the filter and flows into the NO _x catalyst is in a considerably high temperature state. For example, the temperature near the inlet of the NO _x catalyst may be 600 ° C. or higher. Therefore, as shown in FIG. 7 (b), the flow rate control means 119, all of the exhaust gas is passed through the bypass 123 side, after lowering the temperature by the heat exchanger 120, the NO _X catalyst 115 Let it flow. As a result, the collected PM can be burned, and the temperature of the exhaust gas that has passed through the filter can be lowered to flow into the NO _x catalyst. Therefore, thermal deterioration and thermal damage of the NO _x catalyst can be prevented. Even in such a case, since the exhaust gas passes through both the PM filter and the NO _x catalyst, it is not released into the atmosphere as it is.
In addition, by measuring the temperature of the exhaust gas with a temperature sensor disposed in the vicinity of the inlet of the NO _x catalyst, it is possible to accurately determine the timing of flowing the exhaust gas to the bypass side.

Also, during reproduction of the PM filter, in a state in which the exhaust gas is passed through the bypass portion, subsequently, the temperature sensor disposed near the entrance of the NO _X catalyst, measuring the temperature of the exhaust gas flowing into the NO _X catalyst To do. Then, when the temperature of the exhaust gas flowing into the NO _x catalyst is too low, as shown in FIG. 7C, a part of the exhaust gas again passes through the exhaust passage 111 side. The flow rate ratio control means 119 is controlled. As a result, the temperature of the exhaust gas can be lowered to prevent thermal damage or the like of the NO _x catalyst 115, and the NO _x purification efficiency can be maintained without being lowered.
The adjustment of the flow rate ratio between the exhaust passage side and the bypass portion by the flow rate control means can be repeatedly performed in accordance with the temperature of the exhaust gas measured in the vicinity of the inlet of the NO _x catalyst.

  Next, when regeneration of the PM filter is completed, the temperature of the exhaust gas that has passed through the filter also returns to about 100 to 400 ° C. Therefore, it is not necessary to lower the temperature using a heat exchanger, and all the exhaust gas The flow rate ratio control means is controlled so as to pass through the exhaust passage side.

As described above, according to the exhaust purification method of the present embodiment, when the temperature of the exhaust gas flowing into the NO _x catalyst exceeds a predetermined temperature, such as during regeneration of the PM filter, one of the exhaust gases that have passed through the PM filter. the part or the whole, is passed through the bypass portion, by flowing into the NO _X catalyst after having allowed to cool with a heat exchanger, it is possible to prevent thermal deterioration and thermal damage of the NO _X catalyst.
Further, the temperature of the exhaust gas flowing into the NO _x catalyst is measured, and the flow rate ratio of the exhaust gas passing through the exhaust passage side and the bypass portion side is controlled in accordance with the temperature, thereby purifying the NO _x catalyst. The efficiency can be prevented from decreasing.

It is a figure which shows the structure of the exhaust gas purification apparatus of 1st Embodiment. It is a figure which shows the structural example of a heat exchanger. It is a figure which shows the structure provided with the temperature sensor and control means for controlling the operating state of a heat exchanger. It is a figure provided in order to demonstrate the exhaust gas purification method of 1st Embodiment. It is a figure which shows the structure of the exhaust gas purification apparatus of 2nd Embodiment. It is a figure which shows the structural example of a flow rate ratio control means. It is a figure provided in order to demonstrate the exhaust gas purification method of 2nd Embodiment. It is a figure provided in order to demonstrate the structure of the conventional exhaust gas purification apparatus.

Explanation of symbols

5: engine, 10: exhaust gas purification device, 11: exhaust passage, 13: PM filter, 15: NO _X catalyst 17: operating condition detecting means, 19: control means, 20: heat exchanger, 21: temperature sensor, 105: engine, 110: exhaust gas purification device, 111: exhaust passage, 113: PM filter, 115: NO _X catalyst, 117: operating condition detecting means, 119: flow rate control means, 120: heat exchanger, 121: temperature Sensor: 123: Bypass part: 128: Valve part, 129: Control means

Claims (8)

In an exhaust emission control device for purifying exhaust gas exhausted from the internal combustion engine, comprising an upstream particulate filter and a downstream NO _x catalyst disposed in an exhaust passage of the internal combustion engine,
Wherein between the particulate filter and the NO _X catalyst, an exhaust purification system of an internal combustion engine, characterized in that it comprises a heat exchanger for reducing the temperature of the exhaust gas flowing into the NO _X catalyst.   The exhaust purification device for an internal combustion engine according to claim 1, wherein the heat exchanger is provided in the exhaust passage. Between the particulate filter and the NO _X catalyst, and branched from the exhaust passage, with again comprises a bypass section which merges into the exhaust passage, the amount of exhaust gas flowing into the exhaust passage and the bypass section The exhaust gas purification apparatus for an internal combustion engine according to claim 1, further comprising a flow path control means for controlling, wherein the heat exchanger is disposed in the bypass section. An exhaust purification system of an internal combustion engine according to claim 1, characterized in that it comprises a temperature sensor near the inlet of the NO _X catalyst. With NO _X catalyst upstream particulate filter and the downstream side of which is disposed in an exhaust passage of an internal combustion engine, in the exhaust purification method for purifying exhaust gas discharged from the internal combustion engine,
When regenerating the particulate filter, the exhaust gas that has passed through the particulate filter is subjected to heat exchange using a heat exchanger to lower the temperature and pass through the NO _x catalyst. An exhaust purification method for an internal combustion engine. Internal combustion engine according to claim 5, wherein the NO _X in correspondence to the temperature of the exhaust gas measured by the temperature sensor disposed near the inlet of the catalyst, characterized in that to heat exchange at least part of the exhaust gas Exhaust purification method.   The heat exchanger is a heat exchanger provided in the exhaust passage, and heat-exchanges the at least a part of the exhaust gas by controlling on / off or heat exchange degree of a switch of the heat exchanger. The exhaust gas purification method for an internal combustion engine according to claim 5 or 6, The heat exchanger is disposed in a bypass section that branches from the exhaust passage between the particulate filter and the NO _x catalyst and joins the exhaust passage again. 8. The heat exchange of at least a part of the exhaust gas is performed by controlling flow path control means for controlling a flow rate of the exhaust gas flowing in. 8. Exhaust gas purification method for internal combustion engine.

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