DE4128924A1 - ELECTRICALLY HEATED CATALYST CONVERTER - Google Patents

Description

The present invention relates to an electrically heated th catalyst converter for use in cleaning the Exhaust gases from an internal combustion engine.

Some automotive exhaust systems contain a catalytic converter wall ler and other exhaust emission control systems to the Rei to help the exhaust gases passing through most. A catalyst converter is a device in which a kata lysator is distributed on the surface of a support structure, through which the exhaust gases flow. If the exhaust gases through the Catalyst converters pass through, unburned react Hydrocarbons, carbon monoxide and nitrogen oxides in the Exhaust with the catalyst to form carbon di oxide, water vapor or nitrogen. So these reactions occur, the exhaust gas with the correct chemical composition be kept and the catalyst must be off have a sufficiently high temperature. While warming up after a cold start, pollutants essentially flow without reaction through the converter until the catalyst turns off heated to an onset temperature (light-off temperature), where the reactions reach significant proportions. The The effectiveness of the catalyst then increases further until the Converter is fully warmed up and its operating temperature has reached.

To the amount of while warming up from the tail pipe To reduce pollutants emitted have been various Procedures suggested by which the converter temperature should be made to rise faster. To heard: move the converter closer to the machine, that Exhaust system between machine and converter with thermal insulation tion to provide the thermal mass of the exhaust system between lower the machine and converter and the converter to be heated electrically.  

In US-A 37 70 389 an electrically heated transducer be wrote that from a ribbed corrugated metal foil (plate-fin corrugated metal foil) is built, which with Alumina coated and spirally wound. The Coating results in insulation between adjacent fo layered layers and carries the precious metals used as a catalyst tall. The film is heated by the fact that its length extension a voltage is applied.

A problem with the converter according to US-A 37 70 389 form electrical shorts between the layers of film may occur. In addition, tests have shown that gewic kelt converter of the type according to this US-A 37 70 389 by Auf winding and ejection of the film layers can fail, so there are problems with durability. Procedure to to prevent winding, such as brazing or mechani fixing the film, cannot be used, since they are metal to metal contact between the foils evoke layers. In addition, wound converters are only possible with either circular or oval cross sections and fourth, the plate corrugation results in the neighboring th foil layers have line contact with each other, increased Risk of short circuit, and it will also the thermal mass of the Device increased, d. H. it takes longer for the onset temperature maturity is reached.

Another problem with the devices mentioned after State of the art is that the devices a very high current of approx. 500 to 600 A from the 12 V vehicle battery draw. Such current values are undesirable in Hin look at the battery life. In addition, there are Systems with low voltage and high current also from us Degree of efficiency is undesirable since a considerable proportion of the System resistance and power consumption in the Zulei tings occurs.

The present invention is directed to ver improved catalyst support for use in a catalyze to create sator converters.

This goal is achieved with a catalyst carrier Claim 1.

The metal foil strip is preferably a corrugated one Fe-Cr-Al alloy strip. The preferred world lung consists of alternating angular strips, d. H. one Herringbone pattern, causing the film strip to be repeated can be folded back to create a mono to form lith cuboids without the problem of being adjacent interlocking layers. In addition, there is an advantage a herringbone pattern curl to see that the Risk of occurrence of an electrical short between neighboring film layers is reduced because the Kon clock between the layers is limited to point contacts instead of the line contact when using the usual plates corrugation. With a certain entrance area size Herringbone curl usually requires less film as a plate corrugation with the same throughput, and on in this way the thermal mass can be reduced.

The electrical resistance of the foil monolith is before preferably designed to match the lei power supply achievable voltage and power adapted is, whereby a maximum heating efficiency is achieved. Such a resistance adjustment becomes a function of specific resistance and the dimensions of the film, where, when herringbone curl is used, the geometry this herringbone curl must be taken into account. When out setting the resistance value of the monolith to a certain A high voltage system can then be used as the power source  and low current can be used. The use of a such power supply can be different when inserted the 12 V power supply of the motor vehicle battery eliminate emerging problems.

The film strip is with an insulating layer covers to adjacent film layers when folded against each other the isolate. The metal foil strip has an oxide layer, preferably an aluminum oxide layer, which we covering the entire surface of the strip. Although different oxide layer morphologies are satisfactory can have a lendable effect (e.g. knots, rosettes or leaves), becomes a layer with whiskers with a high cross-sectional ratio nis preferred. A heat resistant, electrically insulating The layer can then be applied over this aluminum oxide layer be.

The insulating layer can be an aluminum oxide gel layer followed by an alumina wash layer.

The whiskers are made of aluminum in the practical version minium oxide layer a capillary action, which helps that the alumina gel coating solution, which is preferred before the wash layer is applied, the Fo lien area covered and connects closely to it. The gel Coating can be an excellent foundation for on bring in the wash layer since the dried gel partly when touching the wet wash layer again goes into solution and thereby an excellent bond between forms the coatings.

Electrical leads are connected to both ends of the Fo line strip attached, and the film monolith is in front preferably in a non-conductive material (e.g. a ceramic matte) struck the monolith against the outside man  isolate tel. To heat the monolith, one Tension applied in its longitudinal direction.

The invention can create a heated metal monolith fen with a very durable design that is not based on the oval or round shapes from previous spiral-wound ones Foil converter is limited. In addition, an interpretation with high resistance, d. H. with one by certain dimensions Resistance design criteria determined resistance of an electrical supply with high voltage and ge wrestle allow current values.

To this end, the invention provides a catalyst converter according to An saying 10.

The invention is described below with reference to the drawing exemplified in more detail; in this shows:

Fig. 1 is a perspective, partially cut representation of an embodiment of a catalyst converter;

Fig. 2 is a schematic representation of the electrically heated metal foil monolith of the catalyst converter from Fig. 1;

Fig. 3 is a partial sectional view of some layers of the electrically heated metal foil monolith from Fig. 2;

Fig. 4 is a partially cutaway plan view of some layers of the electrically heated metal foil monolith from Fig. 2; and

Fig. 5 is a partial end view of the electrically beheiz th metal foil monolith in FIG. 2.

Fig. 1 shows a catalytic converter arrangement 10 which is used for cleaning the light emitted by an internal combustion engine exhaust gases. The arrangement 10 has an electrically heatable catalyst carrier unit 12 in a container 14 which has upper and lower mutually adapted jackets. The container 14 is designed so that it allows the inclusion of the Ka converter assembly 10 in a (not shown) engine exhaust system and is generally made of stainless steel or another in the exhaust gas environment under the vehicle body according to durable material.

When installed in this manner, exhaust gases exiting the engine enter container 14 at inlet 16 , pass through catalyst carrier unit 12 , converting harmful exhaust gas components into less harmful substances, and then exit the container at outlet 18 .

The catalyst converter assembly 10 is here so Darge that it contains a single electrically heated catalyst carrier unit 12 , but it is also possible to provide similar units with several catalyst carriers, both heated and unheated. In such a case, the electrically heated catalyst carrier unit 12 is arranged upstream of the unheated catalyst carriers, or in other words in the inlet area of the catalyst converter, so that heating of the unit 12 also the onset of the converter (ie the start of effective chemical reactions) ) the unheated support supports.

In addition, various methods of mounting such a catalyst carrier assembly within a container such as container 14 are well known, and therefore will not be discussed further in this description.

The electrically heated catalyst carrier unit 12 has a metal foil monolith 20 which is constructed from a metal foil strip 22 , and this is repeatedly folded back over itself across the front or inlet region of the monolith 20 , as best seen in FIG. 2. The metal foil strip 22 preferably comprises an alloy of iron-chromium-aluminum (Fe-Cr-Al). The strip 22 may also contain other elements as needed to design its metallurgical and electrical properties for predetermined applications.

By changing the length of the respective film layers, the monolith 20 can be designed such that it can take up practically any cross section.

The film strip 22 is provided with corrugations formed therein, which in this case are designed as an alternating angle strip pattern according to FIGS . 3 and 4. The use of such a pattern prevents adjacent layers from nesting when folding the layers and additionally results in a contact of the layers in point relationship, so that the contact area between adjacent strips and the risk of electrical short circuits between them is kept low. Other corrugation patterns can be used with similar success.

An electrical lead 23 , 24 is attached to each end of the film monolith 20 . In operation of the converter 10 , a voltage source (not shown) can be applied via the lines 23 , 24 of the monolith 20 in order to heat the catalyst carrier and thereby reduce the time required to reach the onset temperature.

In order to effectively use the power supplied, the dimensions of the film strip 22 of the monolith 20 are selected such that its electrical resistance is trimmed to a predetermined value based on the following equation:

R = ρL / δw,

in which:

ρ = the specific resistance of the film,
L = the (total) film length,
w = the film width,
δ = the film thickness,

and where:

L ≈ [(4 / b² + 1 / a²) ^1/2 ] A,

in which:

a = amplitude,
b = wavelength of the corrugation pattern and
A = front surface size.

The use of the given equations in the determination The dimensions of the monolith allow the selection one best suited for the particular application Service design. In the present case, a is preferred Monolith resistance of about 2.5 Ω applied, which the use of relatively low current in the range of 25 to 32 A. and a relatively high voltage in the range of 62 to 80 V er calls for what a power consumption of the converter in Range from 1500 to 2500 W results. That is from the standpoint safety and durability.  

The specified interpretation clearly differs in to a high degree from one with current values of 500 A and more for an electric heated converter with one Monoliths with an electrical resistance in the mΩ range are required, directly through the 12 V network of the force vehicle is heated.

In order for the film strip 22 to have a high resistance path in its longitudinal direction when folded in the manner shown, electrical insulation must be provided between the adjacent layers. The insulation shown in Fig. 5 must be effective without interfering with the flow of exhaust gases through the monolith 20 , and must provide a very large resistance to damage in which adjacent layers of film form an electrical contact with each other, so that no electrical short circuit can occur.

The device applied to the film strip 22 Isolierbeschich device is formed by various individual layers. The (not shown) first or base layer is aluminum oxide, which essentially covers the entire film strip 22 be. The aluminum oxide layer is oxidized onto the surface of the film strip 22 using a method similar to that described in US Pat. No. 4,588,499 and in US Pat. No. 4,318,828, to which reference is expressly made here. The oxide can be in various forms, but a layer with high cross-sectional ratio whiskers is preferred. The whiskers act in a capillary manner to absorb and hold the subsequent layers and thus contribute to an overall electrically insulating layer which is highly resistant to peeling and loss.

The second layer applied to the film strip 22 is an aluminum oxide gel coating 26 ( FIG. 5). The gel is similar to that described in US Pat. No. 4,318,828 and is typically prepared so that 5% by weight aluminum oxide monohydrate is mixed with water and 5% by weight nitric acid. Various layers of gel coating 26 can be applied to the folded, whisker-coated strip in its uncompressed state (as described later) to ensure adequate coverage of all of the film layers.

The third layer applied to the film strip 22 is an aluminum oxide contact layer (alumina washcoat) 28 . The washing or contact layer 28 can also be another commercially available contact layer, as long as it has properties that allow a corresponding connection to the aluminum oxide gel layer 26 .

There are various options for applying the insulated layers to be written on the strip 22nd However, it is preferred to apply the alumina gel layer 26 to the folded uncompressed film monolith 20 . In other words, the gel coating 26 is applied after the film strip 22 has been folded into the shape of the monolith 20 , but before the further steps described in detail below are carried out. The application of the gel layer 26 on the film strip 22 , if this is not yet compressed, ensures that the gel layer 26 covers the film strip 22 evenly and thereby creates good insulation between adjacent layers of the strip 22 . If necessary, several layers of 26 aluminum gel can be applied.

After the application of the aluminum oxide gel layer 26 , the film monolith 20 is compressed to the size required for fitting into the catalyst carrier jacket 30 . The jacket 30 of FIG. 1 generally includes a two-piece clamp jacket assembly which is secured around the monolith 20 and rigidly holds the monolith 20 in the container 14 .

Other container designs, e.g. B. with one-piece pipe jackets individual end cones can also be used.

In order to prevent the formation of electrical short circuits between the metal foil monolith 20 and the jacket 30 , an insulating material such as a ceramic mat 32 is wrapped around the outer circumference of the compressed film monolith 20 before it is inserted into the jacket 30 .

The assembled monolith 20 can receive an additional aluminum oxide gel coating 26 , which then penetrates into the insulating material and gives it additional strength and rigidity, and at the same time reduces its willingness to absorb the subsequently applied precious metals.

The aluminum oxide gel coating 26 creates a good basis for the subsequent application of the cover or glaze layer (washcoat) 28 , since the dried gel partly comes back into solution when it comes into contact with the wet cover layer. This creates a very tough connection between the two coatings.

The previous description has been directed to a monolith composed of a single film strip, however, in order to achieve greater flexibility in selecting the most suitable resistance value for the monolith 20 , it is also proposed to use more than one film strip 22 in a single monolith 20 , as shown in Fig. 2. The monoliths are electrically connected in parallel to reduce the overall resistance of the catalyst converter 10 . Alternatively, the monoliths can also be connected in series (in a manner not shown) in order to increase the resistance of the catalyst converter.

Claims (10)

1. catalyst support for use in a catalyst converter, with a metal foil monolith ( 20 ) from a corrugated foil strip ( 22 ) which is repeatedly folded back onto itself over an inlet area of the monolith; characterized in that it contains: an oxide layer covering substantially the entire surface of the film strip; a heat-resistant electrically insulating layer ( 26 , 28 ) which covers the oxide layer in order to electrically isolate adjacent layers of the film strip from one another and thus to obtain an electrical path of high resistance in the longitudinal direction of the film strip and to obtain electrical lines ( 23 , 24 ) , which are each connected to the respective ends of the foil strip, whereby a voltage for heating the catalyst carrier can be applied via the electrical lines. 2. Catalyst carrier according to claim 1, characterized net that the oxide layer alumina whisker with high Cross-sectional ratio includes. 3. Catalyst carrier according to claim 1 or 2, characterized in that the electrically insulating layer ( 26 , 28 ) comprises an oxide layer covering the aluminum oxide gel coating ( 26 ) and an aluminum oxide cover layer (washcoat) (28) which the aluminum gel -Coating covered. 4. Catalyst carrier according to one of claims 1, 2 or 3, characterized in that a ceramic mat ( 32 ) is placed around the outside of the metal foil monolith ( 20 ) and that a holding jacket ( 30 ) is provided around the metal foil monolith and the ceramic mat; the ceramic mat is designed to then electrically isolate the metal foil monol from the holding jacket. 5. Catalyst carrier according to one of the preceding claims che, characterized in that the metal foil mono lith is designed to have an electrical resistance value to have based on the equation: R = ρL / δw, the individual expressions in the description are defined. 6. Catalyst carrier according to one of the preceding claims che, characterized in that the electrical contr value of the metal foil monolith is designed so that it is for use with a voltage source a voltage higher than 12 V is suitable. 7. Catalyst carrier according to one of the preceding claims che, characterized in that the film strip too an alternating angular stripe pattern (herringbone ster) is curled. 8. A catalyst carrier according to one of the preceding and workman surface, characterized in that two or more metal foil strips connected in parallel with one another ( 22 ) are provided. 9. A catalyst carrier according to one of claims 1 to 7, characterized in that two or more metal foil strips ( 22 ) electrically connected in series with one another are provided. 10. Catalyst converter, which includes
a catalyst carrier according to one of the preceding claims and
a voltage source that is designed to generate a voltage of more than 12 V.