JP2004176592A - Apparatus and method for purifying exhaust gas of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for holding an electric heater which can stably and rationally hold the electric heater disposed in an exhaust passage in an apparatus for purifying the exhaust gas of an engine having the electric heater for raising catalytic bed temperature. <P>SOLUTION: The apparatus for purifying the exhaust gas of an engine purifies the exhaust gas exhausted from the engine. The catalyst 13 for purifying the exhaust gas is disposed in a catalyst containing case 11. The catalyst 13 for purifying the exhaust gas is supported by a catalyst supporting mat 15 interposed between the surface of the inner wall in the case and the outer peripheral surface of the filter of the catalyst 13 for purifying the exhaust gas. The electric heater 17 is built in this catalyst supporting mat 15 so as to raise the catalytic bed temperature, thereby stably holding the electric heater 17. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying technique for purifying exhaust gas discharged from an engine with an exhaust gas purifying catalyst, and more particularly to a technique for holding an electric heater provided to maintain a catalyst bed temperature at an active temperature.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an engine, particularly a diesel engine, an exhaust purification device mainly including an exhaust purification catalyst such as an oxidation catalyst or a three-way catalyst is installed in an exhaust passage, and harmful components in exhaust gas exhausted from the engine are removed. Purification processing has been performed. The exhaust gas purifying catalyst has an active temperature, and when the exhaust gas temperature is lower than the active temperature, the exhaust gas purifying action is not effectively realized. In consideration of this point, an exhaust heating device is arranged around the exhaust gas purifying catalyst, and controls the electric heater according to the operating state of the engine to maintain the catalyst bed temperature at the active temperature. Has been proposed (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-6-33747 (paragraph number (0023), see FIG. 1)
[0004]
[Problems to be solved by the invention]
According to the conventional purification device described above, the catalyst bed temperature is raised to the activation temperature by the heating action of the electric heater, and the exhaust purification catalyst is activated regardless of the operating state of the engine to improve the purification action. it can. However, no suitable proposal has been made for a structure for holding the electric heater in the exhaust passage.
[0005]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide an exhaust gas purifying apparatus for an engine having an electric heater for raising the temperature of a catalyst bed. An object of the present invention is to provide an electric heater holding technique capable of stably and rationally holding an electric heater to be arranged.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, an exhaust gas purification device for an engine according to the present invention is configured as described in claims 1 to 4 of the claims. It should be noted that the invention according to each of these claims is characterized in that the exhaust purification catalyst is disposed in the exhaust passage, and the exhaust purification catalyst is disposed between the inner wall surface of the exhaust passage and the outer peripheral surface of the exhaust purification catalyst. In an exhaust gas purifying apparatus for an engine including a catalyst supporting mat that performs heating and an electric heater that raises a catalyst bed temperature of an exhaust gas purifying catalyst, it is possible to stably and rationally maintain an electric heater disposed in an exhaust passage. It is a technology that we can do.
[0007]
Generally, the exhaust gas purifying catalyst is disposed in a catalyst housing case that forms a part of an exhaust passage. And it is supported by a catalyst support mat interposed between the inner wall surface of the catalyst housing case and the outer peripheral surface of the exhaust gas purifying catalyst. The catalyst support mat preferably has properties such as heat resistance, thermal expansion properties, and flexibility, and closes the gap between the inner wall surface of the case and the outer peripheral surface of the catalyst to prevent exhaust gas from flowing out through the gap. I have. The exhaust gas purifying catalyst is configured by, for example, carrying a noble metal having a function of purifying exhaust gas in a honeycomb filter.
In the exhaust gas purifying apparatus for an engine according to the first aspect, focusing on the fact that the catalyst support mat surrounds and supports the outer periphery of the filter which is a component of the exhaust gas purification catalyst, the electric heater is incorporated in the catalyst support mat. Thus, the electric heater is held.
Therefore, according to the first aspect of the present invention, the exhaust gas purifying catalyst can be heated or kept warm by the electric heater incorporated in the catalyst supporting mat, so that the operation is performed at a low temperature immediately after the start or the exhaust gas temperature does not rise to the activation temperature. Even in this state, the catalyst bed temperature can be raised or maintained at the activation temperature. Since the electric heater is configured to be incorporated in the catalyst support mat, it can be maintained in a stable state. Compared with a configuration in which the electric heater is disposed between the exhaust purification catalyst and the catalyst support mat, for example, In addition, the space in the exhaust passage is not narrowed, and the presence of the electric heater does not cause a problem that the assemblability of the exhaust purification catalyst and the catalyst supporting mat is impaired.
[0008]
In addition, as for the incorporation of the electric heater into the catalyst supporting mat, for example, as described in claim 2, the catalyst supporting mat has a laminated structure in which at least two mat members are overlapped, and the electric heater is sandwiched between the mat members. It is preferable to adopt a configuration in which the holding is performed. By employing such a configuration, the workability of assembling the electric heater to the catalyst supporting mat can be improved.
[0009]
According to a third aspect of the present invention, there is provided an exhaust gas purifying apparatus for an engine, comprising: temperature detecting means for detecting the temperature in the exhaust passage; and control means for controlling energization of the electric heater and interruption of energization based on the temperature detected by the temperature detecting means. ing. The control unit is configured to perform control such as energizing the electric heater when the temperature detected by the temperature detecting unit is equal to or lower than the activation temperature, and stopping energizing the electric heater when the detected temperature is equal to or higher than the activation temperature. You. As a result, the energization and suspension of the electric heater are repeated, so that the catalyst bed temperature of the exhaust gas purifying catalyst is raised or maintained at the activation temperature. As a result, the exhaust purification catalyst is activated, and the exhaust gas can be effectively purified.
[0010]
The exhaust gas purifying catalyst preferably has a structure in which a noble metal having a catalytic action is supported on a ceramic filter (corresponding to claim 4). Further, the electric heater is preferably a PTC heater (corresponding to claim 5).
Here, the PTC heater self-generates heat by energization, and the heat increases the resistance value to further increase the calorific value. However, the rate of increase in the resistance value decreases due to the temperature rise, and eventually the predetermined upper limit temperature (heat value) ) Is a resistance element having a constant resistance value. Therefore, by setting the activation temperature at which the catalyst is activated as the upper limit temperature, a low-cost heating means with a simple configuration can be provided.
[0011]
In the case of an industrial vehicle such as a forklift, it is rarely used that the engine is continuously operated at a high speed because of the working form, and the exhaust gas temperature does not often rise to the activation temperature of the exhaust purification catalyst. Therefore, when applied to an engine of an industrial vehicle as described in claim 6, even if the exhaust bus is used in an operation state in which the exhaust bus temperature does not rise to the activation temperature, the exhaust gas purification processing is performed. Can be performed effectively.
[0012]
According to the seventh aspect of the present invention, an electric heater is incorporated in the catalyst support mat and energization of the electric heater and stop of energization are controlled based on the temperature of the exhaust gas in the exhaust passage. It is possible to provide an exhaust gas purification method for an engine that can raise or maintain the catalyst bed temperature to the activation temperature and rationally purify the exhaust gas.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present embodiment is applied to an engine mounted on an industrial vehicle such as a forklift, in particular, to an exhaust purification device of a diesel engine. FIG. 1 shows an exhaust gas purifying apparatus for an engine according to the present embodiment.
The exhaust gas purification apparatus 10 according to the present embodiment is provided in a form that is incorporated in a downstream side of an exhaust passage connected to an exhaust manifold of a diesel engine, for example, in a muffler. The exhaust gas purification device 10 includes a catalyst housing case (container) 11, an exhaust gas purification catalyst 13, a catalyst support mat 15, and an electric heater 17.
[0014]
The catalyst accommodating case 11 forms a part of an exhaust passage, is formed in a hollow shape having an inlet and an outlet for exhaust gas, and has an exhaust purification catalyst 13 disposed therein. In the figure, the flow direction of the exhaust gas is indicated by arrows. The exhaust purification catalyst 13 has a configuration in which a noble metal such as platinum or palladium having a catalytic action is supported on a ceramic filter formed in a honeycomb shape, for example, and is supported on the catalyst housing case 11 via a catalyst support mat 15. Have been.
The catalyst support mat 15 has properties such as heat resistance, thermal expansion properties, and flexibility, and is disposed so as to be wound around almost the entire outer peripheral surface of the filter of the exhaust purification catalyst 13 to support the exhaust purification catalyst 13. . In other words, the catalyst support mat 15 supports the exhaust purification catalyst 13 by being interposed so as to fill the space between the inner wall surface of the catalyst housing case 11 and the outer peripheral surface of the exhaust purification catalyst 13. Therefore, the catalyst supporting mat 15 has a sealing function for preventing exhaust gas from flowing downstream between the inner wall surface of the catalyst accommodating case 11 and the outer peripheral surface of the exhaust gas purifying catalyst 13, and a filter and a catalyst accommodating member. It has a catalyst protection function for preventing direct contact with the case 11 to prevent cracking of the ceramic filter.
[0015]
The electric heater 17 as a catalyst heating means is incorporated over the entire inside of the catalyst support mat 15. Therefore, as shown in the drawing, when the catalyst supporting mat 15 is interposed over substantially the entire length of the exhaust gas purifying catalyst 13 in the flow direction of the exhaust gas, the heating wire (Nichrome wire) constituting the electric heater 17 becomes the exhaust gas. It is integrated in a direction along the flow direction, for example, in a meandering shape. That is, the electric heater 17 is arranged so as to uniformly heat the exhaust purification catalyst 13 over the entire gas flow direction. One end of the heating wire is connected to the heater electrode 17a on the plus side, and the other end of the heating wire is connected to the heater electrode 17b on the minus side. The heater electrode 17a on the plus side is connected to the battery 21 via the relay switch 19, and the heater electrode 17b on the minus side is body-grounded.
In addition, as shown in FIG. 2, for example, the electric heater 17 is incorporated into the inside of the catalyst support mat 15 by laminating two sheet-like mat members 15a and 15b to form the catalyst support mat 15 having a laminated structure. When the mat members 15a and 15b are overlapped, the heating wire is sandwiched between the mating surfaces so that the catalyst supporting mat 15 with a heater having a stable holding structure can be provided.
[0016]
Further, the exhaust gas purification device 10 includes an ignition switch 23, a temperature sensor 25 for detecting exhaust gas temperature, and an electronic control device 27 (hereinafter referred to as an electronic control device 27) for controlling energization to the electric heater 17 based on the outputs of the ignition switch 23 and the temperature sensor 25. , ECU). The temperature sensor 25 is attached to the catalyst housing case 11 and detects the temperature of the exhaust gas immediately after passing through the exhaust purification catalyst 13. If the temperature of the exhaust gas detected by the temperature sensor 25 is equal to or lower than the activation temperature of the exhaust purification catalyst 13 (for example, 300 ° C.), the ECU 27 turns on the relay switch 19, energizes the electric heater 17, and detects the detected temperature. If the temperature is equal to or higher than the activation temperature (for example, 300 ° C.), the relay switch 19 is turned off to stop energizing the electric heater 17. The above-mentioned temperature sensor 25 corresponds to the temperature detecting means according to the present invention, and the ECU 27 corresponds to the control means according to the present invention.
[0017]
The engine exhaust purification device 10 according to the present embodiment is configured as described above. Therefore, when the ignition switch 23 is turned on and the engine is started, the ECU 27 keeps the relay switch 19 on until the exhaust gas temperature detected by the temperature sensor 25 reaches the activation temperature of the catalyst. For this reason, the electric heater 17 is energized to heat the exhaust purification catalyst 13, and the catalyst bed temperature is raised. On the other hand, when the exhaust gas temperature detected by the temperature sensor 25 reaches the activation temperature of the catalyst, the relay switch 19 is turned off, and the power supply to the electric heater 17 is stopped. That is, according to the present embodiment, the activation and de-energization of the electric heater 17 are repeated based on the fluctuation of the exhaust gas temperature with the activation temperature of the catalyst as the reference value, whereby the catalyst bed temperature of the exhaust purification catalyst 13 is reduced. Heat or keep the temperature at the activation temperature. As a result, the exhaust purification catalyst 13 is activated, and the action of purifying the exhaust gas can be improved.
[0018]
By the way, among special vehicles such as industrial vehicles such as forklifts, it is often difficult to secure a space for installing an exhaust gas purification device near an engine due to the structure of the vehicle. It is indispensable to mount the catalyst in a position, for example, by mounting the catalyst in a muffler. For this reason, there is a tendency that the exhaust gas is cooled before flowing into the exhaust gas purification device, and the heat cannot be sufficiently utilized. Further, in the case of a forklift, it is often operated in a manner of being left idle for a long time, repeatedly starting and stopping, because of the work form. In such a case, the exhaust gas temperature may not rise to the activation temperature of the catalyst. According to the present embodiment, by providing the electric heater 17, the exhaust purification catalyst 13 is heated or kept warm to secure the catalyst bed temperature at the activation temperature, and a stable catalyst is obtained regardless of the operating state of the engine. Purifying action can be obtained.
[0019]
Further, in the present embodiment, since the electric heater 17 is incorporated in the catalyst support mat 15, the electric heater 17 is directly attached to the outer peripheral surface of the filter of the exhaust purification catalyst 13, for example. Can be easily secured. In addition, by incorporating the electric heater 17 in the catalyst support mat 15, the electric heater 17 is placed in the catalyst support mat 15 before the exhaust purification catalyst 13 and the catalyst support mat 15 are attached to the catalyst housing case 11. You can put it together. Thus, there is no problem that the presence of the electric heater 17 impairs the assemblability of the exhaust purification catalyst 13 and the catalyst support mat 15 into the catalyst housing case 11.
As shown in FIG. 2, when the two mat members 15a and 15b are overlapped to form the catalyst supporting mat 15 having a laminated structure, the electric heater 17 is sandwiched between the two mat members 15a and 15b. The attached catalyst support mat 15 can be easily obtained.
[0020]
Note that the present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist of the present invention.
For example, in the above-described embodiment, a heating wire (Nichrome wire) is used as the heating heater 17, but a PTC heater may be used instead. The PTC heater self-generates heat when energized, and the heat increases the resistance value to further increase the calorific value. However, the rate of increase in the resistance value decreases due to the temperature rise, and eventually the PTC heater at a predetermined upper limit temperature (calorific value). The resistance element has a constant resistance value and has a so-called self-temperature control function. Therefore, by setting the activation temperature at which the catalyst is activated as the upper limit temperature of the PTC heater, the exhaust purification catalyst 13 can be heated or kept warm using the self-temperature control function. Thus, the ECU 27, the temperature sensor 25, and the relay switch 19 described in the embodiment can be eliminated, so that a low-cost catalyst heating means with a simple configuration can be provided.
Further, in the above-described embodiment, the case where the invention is applied to a diesel engine mounted on a forklift is described, but the type of vehicle and the type of engine are not limited.
Further, the assembling of the electric heater 17 to the catalyst supporting mat 15 is not limited to the sandwiching structure between the two mat members 15a and 15b. If the catalyst support mat 15 is molded using a mold, for example, the electric heater 17 can be assembled to the catalyst support mat 15 by insert molding. In this case, as shown in FIG. 3, the heating wire forming the heating heater 17 is formed so that the outer surface thereof is partially exposed from the mat surface, and the heating wire is assembled at the time of assembling into the catalyst housing case 11. The exposed portion may be configured to directly contact the outer surface of the filter of the exhaust purification catalyst 13.
In the exhaust purification catalyst 13, the filter is made of ceramic, but may be a metal filter.
[0021]
【The invention's effect】
As described in detail above, according to the present invention, in an exhaust gas purifying apparatus for an engine having an electric heater for raising the catalyst bed temperature, the electric heater arranged in the exhaust passage is stably and rationally held. It is possible to provide a heater holding technique capable of performing the following.
[Brief description of the drawings]
FIG. 1 is a drawing showing an engine exhaust purification device according to an embodiment.
FIG. 2 is a diagram illustrating a structure for assembling an electric heater to a catalyst support mat.
FIG. 3 is a view showing a modified example of an assembling structure of an electric heater to a catalyst supporting mat.
[Explanation of symbols]
10 Exhaust gas purification device 11 Catalyst storage case (exhaust passage)
13 Exhaust gas purification catalyst 15 Catalyst support mat 17 Electric heater 25 Temperature sensor (temperature detecting means)
27 Electronic control unit (control means)

Claims (7)

An exhaust purification catalyst disposed in an exhaust passage; a catalyst support mat disposed between an inner wall surface of the exhaust passage and an outer peripheral surface of the exhaust purification catalyst to support the exhaust purification catalyst; An exhaust gas purification device for an engine, comprising: an electric heater for raising a catalyst bed temperature of a catalyst for use in an engine.
An exhaust gas purification device for an engine, wherein the electric heater is incorporated in the catalyst support mat. 2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the catalyst support mat has a laminated structure in which at least two mat members are overlapped, and the electric heater is held and held between the mat members. 3. An exhaust gas purification device for an engine. 3. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the temperature detecting unit detects the temperature in the exhaust passage, and energizing and discontinuing energizing the electric heater based on the temperature detected by the temperature detecting unit. 4. An exhaust gas purification device for an engine, comprising: control means for controlling the exhaust gas. The exhaust gas purifying apparatus according to any one of claims 1 to 3, wherein the exhaust gas purifying catalyst has a structure in which a noble metal having a catalytic action is supported on a ceramic filter. Exhaust gas purification device. The exhaust gas purification device for an engine according to any one of claims 1 to 4, wherein the electric heater is a PTC heater. The exhaust gas purification device for an engine according to any one of claims 1 to 5, wherein the engine is an engine of an industrial vehicle. An exhaust purification catalyst disposed in an exhaust passage; a catalyst support mat disposed between an inner wall surface of the exhaust passage and an outer peripheral surface of the exhaust purification catalyst to support the exhaust purification catalyst; An electric heater for raising the catalyst bed temperature of the catalyst for exhaust gas, comprising:
Incorporating the electric heater in the catalyst support mat, energizing the electric heater when the temperature detected by the temperature detecting means arranged in the exhaust passage is equal to or lower than a predetermined value, and when the detected temperature is equal to or higher than the predetermined value. Repeating the step of stopping the energization of the electric heater to maintain the catalyst bed temperature of the exhaust purification catalyst at an active temperature to purify the exhaust gas.

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