JPH11179157A - Electric heating catalytic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the manufacturing cost of a catalytic apparatus comprising a preliminary catalyst support to be electrically heated and a main catalyst support which is not electrically heated by forming an oxide film on the surface of metal foil constituting the preliminary catalyst and arranging the preliminary catalyst and the main catalyst without keeping a space between the catalysts. SOLUTION: This electrically heating catalytic apparatus for treating an exhaust gas of an internal combustion engine comprises a preliminary catalyst support 2 to be electrically heated and which is formed into a cylindrical shape by mutually laying a metal corrugated foil 4 and a metal flat foil 5 surface-coated with insulating films and rolling the foils on a center electrode 6 while forming an electric current route along the rolled corrugated foil 4 and flat foil 5. The apparatus further comprises a main catalyst support 3 formed into a cylindrical shape by mutually laying those metal corrugated foil and metal flat foil and rolling the foils and joining the contact parts of the corrugated foil and flat foil. In this case, the catalyst supports 2, 3 are electrically insulated by the insulating films on the surfaces of the corrugated foil 4 and the flat foil 5. Oxide films are formed by heating the corrugated foil 4 and the flat foil 5 at high temperature in atmospheric air and the oxide films are used as the insulating films.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying exhaust gas of an internal combustion engine having a structure in which a metal carrier formed by laminating metal foils is used as a catalyst carrier to generate heat and to raise the catalyst activation temperature in a short time. The present invention relates to an electric heating catalyst device.

[0002]

2. Description of the Related Art In order to purify exhaust gas of an internal combustion engine, a catalyst device in which a catalyst is carried on a metal carrier formed by stacking metal foils to form a honeycomb body is disposed in an exhaust gas passage of the internal combustion engine.
It purifies HC, CO, NO _{2 and the} like in the exhaust gas. However, since the exhaust gas purifying catalyst has a significantly reduced exhaust gas purifying ability at a temperature lower than the activation temperature, when the temperature of the catalyst is low, such as when the internal combustion engine is started, the harmful substances in the exhaust gas, especially HC, There is a problem that the CO substance is not purified by the catalyst and is released to the atmosphere as it is.

[0003] In order to solve this problem, a honeycomb body in which metal foils are laminated is used as a preliminary catalyst carrier, and an electric current is passed through the preliminary catalyst carrier when the internal combustion engine is started.
There has been proposed an electrically heated catalyst device in which a metal catalyst carrier itself is heated to raise the temperature to a catalyst activation temperature (300 to 400 ° C.) in a short time.

As shown in FIG. 5, the electric heating type catalyst device comprises an electrically heated pre-catalyst carrier 2 and a main catalyst carrier 3 arranged in series in a casing connected to an exhaust gas passage. Exhaust gas exerts an exhaust gas purifying action in a short time by the catalyst heated in the electrically heated pre-catalyst carrier 2, and also promotes an exhaust gas purifying effect of the rear main catalyst carrier 3 by promoting the temperature rise of the catalyst. It is configured to be.

[0005] The electrically heated pre-catalyst carrier 2 used here
Is a cylinder obtained by using a metal corrugated foil 4 and a flat foil 5, forming an insulating film on at least one surface thereof, laminating the corrugated foil 4 and the flat foil 5, and winding around a center electrode 6. Metal honeycomb body, an outer cylinder 8 containing the honeycomb body, and an external electrode 9 mounted on the outer cylinder while being electrically insulated.
And a power supply (not shown) for supplying electricity between the external electrode 9 and the outer cylinder 8. The wiring from the center electrode 6 is connected to the external electrode 9. The corrugated foil 4 and the flat foil 5 are shown in FIG.
To form a honeycomb structure as shown in FIG.
Are electrically insulated because they have an insulating film on the surface. When a voltage is applied between the center electrode 6 and the outer cylinder 8 to start energizing the pre-catalyst carrier 2, a current flows independently through the corrugated foil 4 and the flat foil 5, thereby increasing the temperature of the pre-catalyst carrier. be able to. A method is also used in which a part of the contact portion between the corrugated foil 4 and the flat foil 5 is joined while breaking the insulating film by local brazing to break down the insulating film, and the junction is heated as a heating resistance of the preliminary catalyst carrier 2. It had been.

In order to quickly raise the temperature of the catalyst in the pre-catalyst carrier 2, it is advantageous that the heat capacity of the pre-catalyst carrier is small, and the length of the pre-catalyst carrier needs to be reduced. Further, the corrugated foil and the flat foil of the preliminary catalyst carrier are formed by the center electrode 6 and the outer cylinder 8.
Are not joined except for the vicinity. Since the length is short and only partially joined, the pre-catalyst carrier has a structure that is very weak against shearing force in the flow direction of the exhaust gas. Deformation called scope deformation is likely to occur.

Some of the metal foils constituting the pre-catalyst carrier 2 may not have an insulating film, and some of the contact portions between the flat foil and the corrugated foil may be joined by brazing. In addition, when the pre-catalyst carrier 2 and the main catalyst carrier 3 are disposed in close contact with each other, there is a problem that the pre-catalyst carrier and the main catalyst carrier are conducted to break electrical insulation. Therefore, conventionally, P
CT Publication No. 96/38657 (PCT / JP96 /
As disclosed in US Pat. No. 01474), when such a pre-catalyst carrier that is weak against shearing force is incorporated into the catalyst device, a retainer 10 is provided downstream of the pre-catalyst carrier, and the retainer 10 and the retainer support ring 11 Measures have been taken to support the preliminary catalyst carrier 2 (FIG. 5).

[0008]

In a conventional method for holding a pre-catalyst carrier using a retainer, a support mechanism for an outer cylinder for incorporating the retainer into the catalyst device, a support mechanism for the pre-catalyst carrier on the retainer, and the like are provided. This necessitates a reduction in the cost of the catalyst device.

An object of the present invention is to make it possible to arrange a preliminary catalyst carrier and a main catalyst carrier in close contact with each other and to solve these problems.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the gist thereof is as follows.

[0011] First, a current-carrying pre-catalyst carrier formed by laminating a metal foil having an oxide film on its surface, and a current-carrying heating formed by laminating a metal foil downstream of the pre-catalyst carrier on the exhaust gas side. In the electric heating catalyst device for purifying exhaust gas of an internal combustion engine having a main catalyst carrier that is not performed, the metal foil constituting the preliminary catalyst carrier has an oxide film on at least a surface in contact with the main catalyst carrier, An electric heating catalyst device wherein a preliminary catalyst carrier and the main catalyst carrier are arranged without providing a space.

Since the metal foil constituting the pre-catalyst carrier has an oxide film on at least the surface in contact with the main catalyst carrier, even if it is arranged without providing a space between the metal foil and the main catalyst carrier, the insulation is maintained. It is not destroyed, and the current flow path of the preliminary catalyst carrier is secured. A complicated support mechanism such as a retainer is not required, and the cost of the catalyst device can be reduced.

The second is an energization heating pre-catalyst carrier formed by laminating a metal foil having an oxide film on the surface, and an energization heating formed by laminating the metal foil downstream of the pre-catalyst carrier on the exhaust gas side. In the electric heating catalyst device for purifying exhaust gas of an internal combustion engine having a main catalyst carrier which is not performed, at least one of a downstream end surface of the preliminary catalyst carrier and an upstream end surface of the main catalyst carrier is coated with an insulating ceramic adhesive. An electric heating catalyst device, wherein the preliminary catalyst carrier, the ceramic adhesive layer and the main catalyst carrier are arranged in this order without providing a space.

The first invention can be used without any problem if the voltage applied to the pre-catalyst carrier is 20 V or less. However, if the applied voltage is higher than 20 V, the oxide film of the foil constituting the pre-catalyst carrier can be used. May be destroyed, resulting in poor insulation. According to the second invention, the insulating ceramic adhesive layer 1 provided between the preliminary catalyst carrier and the main catalyst carrier
Can provide sufficient insulation resistance, so that even when the applied voltage exceeds 20 V, the preliminary catalyst carrier and the main catalyst carrier can be closely arranged.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION A current-carrying pre-catalyst carrier 2 according to the present invention is obtained by laminating a metal corrugated foil 4 and a metal flat foil 5 each having an insulating film formed on the surface thereof in advance and winding them around a center electrode 6 so as to form a center side. It is formed in a cylindrical shape while forming current paths along the corrugated foil 4 and the flat foil 5 wound from the outer periphery to the outer periphery. The main catalyst carrier 3 is formed by laminating a metal corrugated foil and a metal flat foil, winding the same, and joining a contact portion between the corrugated foil and the flat foil to form a cylindrical shape. In the first invention, the electrical insulation between the preliminary catalyst carrier 2 and the main catalyst carrier 3 is as follows:
This is performed by the insulating film on the surface of the corrugated foil 4 and the flat foil 5 constituting the preliminary catalyst carrier 2. The insulating film forms an oxide film by heating the corrugated foil and the flat foil at a high temperature in the air, and this oxide film can be used as the insulating film. If the thickness of the oxide film is 0.5 μm or more, it is effective as the insulating film of the present invention. The oxide film formed on the surface of the metal foil can be partially removed, but at least the oxide film on the surface in contact with the main catalyst carrier is used for maintaining electrical insulation with the main catalyst carrier. It is necessary to secure.

In the second invention, means for applying an insulating ceramic adhesive to at least one of the downstream end face of the preliminary catalyst carrier 2 and the upstream end face of the main catalyst carrier 3 includes:
As shown in FIG. 3, a method in which the end surface of the catalyst carrier to be coated with the adhesive is shallowly immersed in the liquid surface of a container filled with the paste-like insulating ceramic adhesive 13 and the adhesive is applied, A method of applying the agent by brush or spray can be used. By adjusting the viscosity of the paste-like ceramic adhesive, the amount of the adhesive adhering to the end surface of the catalyst carrier can be adjusted.

The adhesive adhered to the end face of the catalyst carrier has a sectional shape shown in FIG.
The strong insulating ceramic adhesive layer 1 can be formed by evaporating water as a solvent by drying.

As the insulating ceramic adhesive, the coefficient of thermal expansion of the adhesive is the coefficient of thermal expansion of the metal foil (14 × 10 ⁻⁶ /
C.), which is difficult to peel off due to thermal stress, and a silica-based or silica-alumina-based adhesive can be used. As the silica-based adhesive, for example, there is a product name “Aron Ceramic C”, the main component (aggregate) is silica, the binder is an alkali metal silicate,
The temperature is 0 ° C., the coefficient of thermal expansion is 13 × 10 ⁻⁶ / ° C., and the coating thickness on the end face of the catalyst carrier is suitably from 10 to 200 μm. As the silica-alumina adhesive, for example, there is a trade name "Sumiceram S-208C", the main component is silica-alumina, the binder is a metal phosphate, the heat-resistant temperature is 1600 ° C, and the thermal expansion coefficient is 11 × 10 ^-6 / ° C.

[0019]

(Example 1) The preliminary catalyst carrier 2 has a thickness of 30 μm.
It was manufactured using aluminum-containing stainless steel flat foil having a width of 10 mm and a width of 10 mm, and corrugated corrugated foil. By passing the metal foil through an air atmosphere oxidation furnace, or by holding a loosely coiled metal foil at a high temperature in an air oxidation furnace, a 0.7 μm thick oxide film as an insulating film is formed on the surface. Formed. The atmosphere temperature of the atmospheric oxidation furnace was 1200 ° C., the holding time was 30 minutes, and the holding time was adjusted so that the actual oxide film thickness was 0.7 μm. The corrugated foil and the flat foil on which the oxide film formation is completed are
To form a preliminary catalyst carrier 2. The main catalyst carrier 3 is formed by winding an aluminum-containing stainless steel flat foil having a thickness of 30 μm and a width of 100 mm and a corrugated corrugated foil, and brazing the contact portion between the flat foil and the corrugated foil. Formed. By providing the preliminary catalyst carrier 2 and the main catalyst carrier 3 without providing any space between them, and providing the outer cylinder 8 outside thereof, the electric heating catalyst device shown in FIG. 1 was manufactured.

When the electric heating catalyst device is arranged in an exhaust gas system of an automobile and a battery voltage of 12 V is applied between the outer electrode 9 and the outer cylinder 8 of the pre-catalyst carrier 2 at the time of starting the engine, the pre-catalyst carrier 2 As a result, the temperature of the catalyst was quickly raised and the exhaust gas was purified. Displacement 2
Exhaust gas temperature 100 ~ 900 ℃ with 000cc engine
As a result of conducting a heat cycle test, no telescope-like displacement of the pre-catalyst carrier 2 and no decrease in the electric heating function were observed. Regarding the purification performance, the temperature rise of the spare catalyst carrier is slightly delayed due to the heat conduction to the main catalyst carrier, but the temperature rise of the main catalyst carrier due to heat transfer through the exhaust gas is faster than that of the conventional retainer system. In other words, the purification performance was improved compared to the conventional retainer system.

On the other hand, the external electrode 9 of the electric heating catalyst device
When a voltage of 24 V is applied between the external catalyst 8 and the outer cylinder 8, a local dielectric breakdown occurs between the auxiliary catalyst carrier and the main catalyst carrier when the energization is repeatedly turned on and off. It was found that applying a voltage of 24 V was not appropriate.

(Example 2) The pre-catalyst carrier 2 was prepared as described in Example 1.
Using the same aluminum-containing stainless steel foil as in Example 1, an oxide film having a thickness of 0.7 μm was formed as an insulating film on the surface as in Example 1, and the corrugated foil and flat foil were wound around the center electrode 6. Formed. A ceramic adhesive was applied to the downstream end face of the preliminary catalyst carrier 2. As the adhesive, Aron Ceramic C (trade name) was selected as a ceramic adhesive having a coefficient of thermal expansion close to the coefficient of thermal expansion (14 × 10 ⁻⁶ / ° C.) of the metal foil. A ceramic adhesive layer 1 having a thickness of 30 μm as shown in FIG. The same main catalyst carrier as in Example 1 was used. Preliminary catalyst carrier 2, ceramic adhesive layer 1
And the main catalyst carrier 3 are arranged in this order without providing a space,
By providing the outer cylinder 8 on the outside, the electric heating catalyst device shown in FIG. 2 was manufactured.

When the electric heating catalyst device is arranged in an exhaust gas system of an automobile, and a battery voltage of 24 V is applied between the external electrode 9 of the pre-catalyst carrier 2 and the outer cylinder 8 at the time of starting the engine, the pre-catalyst carrier 2 There was no problem in the electrical insulation between the catalyst carrier and the main catalyst carrier 3, and the heating of the preliminary catalyst carrier 2 enabled rapid temperature rise of the catalyst and purification of exhaust gas. As in Example 1, no decrease in the current heating function in the heat cycle test was observed. Regarding the purification performance, as a result of increasing the applied voltage to 24 V, a purification performance even better than that of Example 1 could be obtained.

[0024]

According to the present invention, a current-carrying pre-catalyst carrier formed by laminating a metal foil having an oxide film on the surface and a current-carrying pre-catalyst formed by laminating a metal foil downstream of the pre-catalyst carrier on the exhaust gas side are not used. In the electric heating catalyst device for purifying exhaust gas of an internal combustion engine having a catalyst carrier, an oxide film is formed on all surfaces of a metal foil constituting the preliminary catalyst carrier, and the preliminary catalyst carrier and the main catalyst carrier are separated by a space. By arranging the heating device without providing the same, the need for a retainer can be eliminated, and the production cost of the electrically heated catalyst device can be reduced, and the purification performance can be improved. Furthermore, by applying an insulating ceramic adhesive to at least one of the downstream end face of the preliminary catalyst carrier and the upstream end face of the main catalyst carrier, the electrical insulation between the preliminary catalyst carrier and the main catalyst carrier is further improved, The voltage applied to the preliminary catalyst carrier could be increased.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an electric heating catalyst device of the present invention.

FIG. 2 is a cross-sectional view showing an electric heating catalyst device of the present invention.

FIG. 3 is a schematic view showing a method for applying an insulating ceramic adhesive according to the present invention.

FIGS. 4A and 4B are cross-sectional views of a pre-catalyst carrier having a ceramic adhesive layer according to the present invention, wherein FIG. 4A is an overall view and FIG.

FIG. 5 is a view showing a conventional electric heating catalyst device;
(A) is a sectional view, and (b) is an exploded perspective view.

FIG. 6 is a partial cross-sectional view showing a laminated state of a corrugated foil and a flat foil of a preliminary catalyst carrier.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 ceramic adhesive layer 2 preliminary catalyst carrier 3 main catalyst carrier 4 corrugated foil 5 flat foil 6 center electrode 8 outer cylinder 9 external electrode 10 retainer 11 retainer support ring 13 ceramic adhesive

Claims (2)

[Claims] An electrically heated pre-catalyst carrier formed by laminating a metal foil having an oxide film on its surface, and a main body that is formed by laminating a metal foil downstream of the pre-catalyst carrier on the exhaust gas side and is not electrically heated. An electric heating catalyst device for purifying exhaust gas of an internal combustion engine having a catalyst carrier, wherein the metal foil constituting the preliminary catalyst carrier has an oxide film on at least a surface in contact with the main catalyst carrier, And the main catalyst carrier are arranged without providing a space. 2. A current-carrying pre-catalyst carrier formed by laminating a metal foil having an oxide film on the surface, and a current-carrying pre-catalyst formed by laminating a metal foil downstream of the pre-catalyst carrier on the exhaust gas side. An electric heating catalyst device for purifying exhaust gas of an internal combustion engine having a catalyst carrier, wherein at least one of a downstream end face of the preliminary catalyst carrier and an upstream end face of the main catalyst carrier is coated with an insulating ceramic adhesive, An electric heating catalyst device comprising a catalyst carrier, the ceramic adhesive layer and the main catalyst carrier arranged in this order without providing a space.