DE3100939A1 - Catalytic emission control unit for exhaust gases from internal combustion engines and method for its manufacture - Google Patents

Description

Catalytic ^ cleaning unit for exhaust gases from internal combustion engines and methods of making them

The invention relates to catalytic cleaning units or Converters for exhaust gases of internal combustion engines of motor vehicles and particularly to such units, in which the catalyst is supported by a monolithic body, extend through the thin walled StrömungsJkanäle. Such units are known; however, problems arise.

Such units almost always include a metal housing having an inlet and an outlet within of the exhaust system of an internal combustion engine can be arranged, and one or more monolithic ceramic or metallic catalyst carriers, which are arranged within the housing and a Having a plurality of parallel thin-walled flow channels extending therethrough and substantially communicate directly with the housing inlet and outlet. The ceramic monolithic supports

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however, they are quite brittle and, like the metallic supports, can be destroyed by crushing. Since such carriers are normally subjected to considerable stresses in use due to mechanical vibrations , shocks and pulsating gases, they must not only be isolated from contact with the hard metal of the housing, but also from excessive movement relative to it, both laterally and laterally are also supported axially to the gas flow channels without any destructive pressure or squeezing forces occurring. This problem is further complicated by the fact that the thermal expansion coefficients of the carrier and the housing differ, resulting in a different expansion and contraction over the usual temperature range occurring during use, ie from room temperature to about 950 ° and possibly even up to 125O ° C, occurrence. The carrier is directly subjected to such high temperatures because of the heat that occurs during the catalytic cleaning process. It is therefore very desirable to thermally isolate the carrier from the housing.

The problem is further complicated by the need to provide a way to avoid thermal shocks to withstand, i.e. the rapid rise and fall in temperature that is detected during use, that the service life must be such that the current US federal regulation of 75,000 km is met and the structure is designed to ensure the most economical production possible will.

These problems are the subject of numerous publications and attempts to solve them without a noticeable progress has been made. Examples of such documents and publications of attempts to solve these problems are

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"Development Of Canistering System For Monolithic Catalysts ¹ * - Abthoff, Oblander and Santiago SAE paper held at the Automobile Engineers Meeting, Dearborn, Michigan, October 1976.

"Expandable Inorganics Mount / Protect Catalytic Converter Element" - Hogan Article in Design-News, Oct. 20, 1975 and US-PSen

39 38 232 39 59 865

39 78 567

40 20 539 40 70 158 40 93 423 and

¹⁵ DE-AS 25 15 732.

From the foregoing it can be seen that different types of housings and devices for supporting a monolithic ceramic catalyst carrier therein have been proposed. With such a The carrier is supported in the housing by a grid made of a metal wire between the Carrier and the housing is arranged. Examples of such constructions are in US Pat. No. 3,978,567 and 40 20 539. However, such a type is not satisfactory because the wire mesh, even if it is made of corrosion-resistant steel to soften, corrode or scale the tends to occur high operating temperatures. This problem is exacerbated by the fact that at the operating temperature the housing expands more than the carrier and the mesh does not expand sufficiently, to transfer adequate support forces to the wearer. It therefore loses its ability to imitate the wearer Support the housing accordingly. Such a defective arrangement leads to a destructive contact of the carrier with the housing or to a destructive

Relative movement in between.

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In another type, the inorganic material is foamed and hardens in the space between the Carrier and the housing. An example of this type is described in US Pat. No. 3,959,865. the Difficulty in turn is to create an appropriate support for the wearer without destructive pressure forces are exerted on this. However, such support is very difficult at any acceptable level of consistency in the foamable materials.

A comparable arrangement is described in US-PS 39 38 232. One of the two-shell housing is here Type that has two longitudinally split clips loosely around a support with a space in between Outer circumference arranged in between. A pourable, somewhat resilient refractory material is in this gap provided, solidified and fired. The housing parts are then attached to one another to create a Compressive bias in the support supporting the wearer to produce refractory material. With this arrangement, however, it is rather difficult to obtain a constant, predetermined Generate compressive bias.

Another type is elastic, resistant to high temperatures and compressible Mat made of ceramic fibers with a certain degree of tension between the carrier and the housing. In one arrangement described in US Pat. No. 4,093,423, the mat is around the carrier wound with such a total cross-section, which is larger than the inner cross-section of the housing. These The assembly is pushed into the housing from one end through a reducing funnel. That’s not the only thing this end-to-end arrangement is somewhat difficult, but there can also be a predetermined degree of compressive stress in the arranged mat cannot be maintained throughout. As a result, either will be inadequate

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Support for the carrier or destructive compressive stresses obtain. Another arrangement using an elastic, against high temperatures Resistant and compressible mat made of ceramic fibers as a support for a wearer is described in U.S. Patents 4,093,423 and 4,070,158. With this arrangement, the assembled mat and the carrier are in a pre-rolled sheet metal shell overlapping ends are wound together that are pulled together around the mat around a certain ridge to squeeze. However, it is also difficult to maintain a predetermined level of compressive stress consistently get in the mat.

It has also been suggested to use an expanding or swelling material to support a Inserting the carrier in a housing, the material originally being arranged with a compressive preload, to effectively support the wearer. When heated, the material swells more than necessary during use, in order to compensate for the space created around the carrier, which can be traced back to the heated housing. This increases the compressive stress for a corresponding support of the carrier, without this destructive stresses occur. The two US patents cited above and the one also cited above DE-AS suggest the use of an intumescent material. However, this only describes the use proposed a housing integral on the circumference, into which a carrier is inserted from one end, the has previously been wrapped with a mat made of a swelling material. In US-PS 40 93 423 is a such end-to-end assembly is not only difficult to perform without either the mat or the carrier will be damaged but it can too

not continuously a predetermined ridge of a pressure r

prestress can be obtained in the support material. Inso- | distant can occur during the subsequent heating- |

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the compressive stresses on the carrier are either insufficient or lead to damage.

The invention is therefore based on the object of an improved catalytic cleaning unit for exhaust gases of internal combustion engines, which has a monolithic catalyst carrier, which is in the metal housing is included.

Another object of the invention is to provide such a unit that has a long service life has, the carrier both before installation and during use in a motor vehicle without damage adequately supported, creating effective thermal insulation between the carrier and its housing, is simple in construction and inexpensive to manufacture and assemble.

This object is achieved by the invention. 20th

The invention relates to a catalytic cleaning unit for exhaust gases from internal combustion engines according to Claim 1.

According to the invention is a two-shell housing and a Mat made of an intumescent material is provided, which is wrapped around a catalyst carrier, wherein the overall diameter of the wrapped carrier is larger is than the inside diameter of the housing. The two halves of the case are wrapped around the carrier laid and then assembled, attaching the two halves together and the material squeeze. The thickness of the mat is between the diameter of the gap on the circumference the carrier and the housing in relation, with an assembled mat density within of a certain area is obtained. In this area compressive forces are generated, which the wearer

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effectively prevent damaging movement relative to the housing. These forces increase with expansion of the material on heating, but not to such an extent that the support is damaged.

Further advantages, features and details of the invention are described below on the basis of two embodiments with reference to the drawing.

Show it

Pig. 1 shows a longitudinal section through a catalytic

Cleaning unit which is the first embodiment of the invention;

Figure 2 is an end view of the unit shown in Figure 1;

3 shows a longitudinal section through a catalytic cleaning unit, which the second embodiment of the invention represents and

Figure 4 is a sectional view of the assembly shown in Figure 3 taken along line 4-4.

In Figs. 1 and 2 there is a catalytic purification unit 10 for exhaust gases from internal combustion engines, which is the first embodiment of the invention. The unit 10 includes a metal housing 12 from the clamshell Type with an enlarged cylindrical main section 14, end sections 16 that are asymmetrical taper to circular inlets and outlets 18 which are flanged 20 around the unit 10 to be installed in an exhaust system (not shown) of an internal combustion engine. Although the main section 14 in The figure is shown cylindrical, it can of course have other conventional cross-sectional shapes, for example oval, elliptical, rectangular, square, etc. Although the tapered end

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Sections 16 are shown asymmetrically, they can of course be symmetrical to the main section 14, for example frustoconical.

As mentioned above, the housing 12 is in two parts, which may have a similar shape, provided that the housing is divided along a plane of symmetry. The meeting edges of the parts are with outwardly bent connecting flanges 22 Mistake. After these parts have been assembled, as will be described below, the flanges 22 are welded or otherwise appropriately joined together attached to prevent gas leakage, a unitary housing 12 being made.

In the main section 14 of the housing 12 are one or more conventional monolithic ceramic catalyst supports or body 24 included. Each body 24 is cylindrical and has a honeycomb-like structure, i.e., a plurality of parallel, thin-walled and narrow gas flow channels 26 extending therethrough extend one end to the other. The walls of the channels 26 are catalyzed in a conventional manner coated or impregnated to remove the undesirable and dangerous exhaust gas components of an internal combustion engine to convert them into harmless or less dangerous substances. As is to be expected, such carriers are 24 quite sensitive to mechanical stresses, especially compressive stress, although they are resistant to high temperatures and the corrosive effects of the exhaust gases.

As shown, the unit 10 includes two such supports 24, the end faces spaced within of the housing 12 are arranged with an inner and circumferentially extending rib 28 between the two carriers is provided. The diameter of the carrier 24 is smaller than the corresponding inner

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measurements of the main portion 14 of the housing 12, creating a circumferential gap or space between the Supports and the housing is created. In the gap is an elastic, swellable material 30 that is radially compressed, provided on the arrangement of the housing parts to the material sufficient to put under bias to the carrier 24 against a frontal, radial or diagonal damaging Movement with respect to the housing 12 to be returned. The swellable material has a coefficient of expansion which is larger than that of the housing.

When the unit 10 is heated during operation, the expansion of the material 30 increases the compressive stress therein, which hinders the movement of the carriers 24 relative to the housing 12 even more, without the compressive stresses increasing to the point of crushing forces or otherwise transferring damaging forces to the carrier. Preferably, the swellable material 30 used is a material called Interam, manufactured by the 3M Company. The product called Interam is a ceramic fiber matrix in which small pieces of a swellable material such as mica are mixed together. It is prepared in the form of a sheet or mat, the thickness of which increases at temperatures above about 400 ⁰ C. Interam has a high coefficient of thermal expansion, is heat-resistant up to around 1100 ° C, has good thermal insulation properties and is elastic even at high temperatures. Although the above publication "Expandable Inorganics Mount / Protect Catalytic Converter Element" suggests the use of Interam to support monolithic ceramic carriers of a catalytic cleaning unit, it only suggests that the carrier be wrapped with Interam and then the carrier is wrapped in an end face the front open housing is pushed. As explained above, each

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but with such a unit considerable difficulties.

Intensive research has now shown that the assembled density of Interam and prior to heating must be within a certain range to achieve the desired results. If the value is too low, the wearer will not be restrained from damaging movement that occurs relative to the housing 12 both before and during the occurrence of normal high temperatures to which Interam is exposed in use. If the value is too high, the expanding interam will exert damaging compressive stresses on the carrier when the unit is heated to operating temperatures. It has now been found that the desired density range for monolithic ceramic substrates of 31 or 46.5 cells / cm ² (200 or 300 cells / square inch) with a 0.3 mm (0.012 ") thick web of about 0.64 g / cm2. cm ³ (40 lbs / ft ³⁾ to about 1.53 g / cm ³ (95 lbs / ft ³⁾ extends.

Carriers 24 of the aforesaid type are manufactured by manufacturers within acceptable dimensional tolerances. For example, any carrier with an outside diameter of 10.16 cm (4 ⁿ ) with a typical diameter tolerance of 1-1.5 mm (0.04-0.06 ") can be used in a unit of normal size. Because of this wide range of possibilities In diameter, it is important that the unit 10 have a minimal circumferential gap between the support 24 and the housing 12 for a given interam mat of a given thickness and density, and with this in mind, the unit 10 must also be designed to accommodate it has a maximum circumferential gap between the carrier 24 and the housing 12 for the same particular interam mat of appropriate thickness and density.

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For example, if the unit 10 is to have a maximum gap of 4 mm (0.158 "), a mat 30 of Interam with a thickness of 4.2 mm (0.165") and a basis weight of 0.256 g / cm would if it were is compressed within such a 4 mm gap during installation, have an installation density of about 0.64 g / cm. A smaller gap would of course lead to a greater installation density for the same mat. Therefore, the unit must be designed to have a minimal void that does not create an installation density greater than about 1.53 g / cm ³ (95 lbs / ft ³ ). The investigation has also shown that there is a relationship between the minimum and maximum gap.

After such a corresponding interpretation of the gap, the thickness of the mat is then calculated in such a way that that the mat density at the time of installation is within the above range. If on the other hand the mat is used with a certain thickness and a certain basis weight, the Unit 10 designed with regard to the maximum and minimum gaps so that the densities of Interam can be generated in the desired area during installation. When assembling the parts will be the mats 30 wrapped with the appropriate thickness around the carrier 24, this exactly in one of the Housing parts are arranged. The other part is then clipped onto the first part to make the Compress mats 30 on and within the desired density range. The flanges 22 are then welded or appropriately fastened to one another in some other way around gas-tight seams and to produce a unitary housing 12. The mats 30 are now under a sufficient one Compressive stress to the carrier 24 in the housing against damaging movement thereto both laterally as well as in the longitudinal direction or axially correspondingly

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to cut. When used in a motor vehicle, the unit 10 is heated to a certain temperature which will expand the mats 30 enough to increase the forces holding the supports 24 in place, but not to the extent that damaging forces are developed.

The mats 30 made of a swelling material not only effectively support the carrier 24, but also cushions or dampen any mechanical vibration or impact transmitted through the mats to the supports, because of the elasticity inherent in the mats.

3 and 4, there is also shown a unit 40 which is the second embodiment of the invention represents. This unit 40 is a somewhat modified type of clamshell housing 42. The housing 42 is similar to that shown in Figs. It has a cylindrical main section 40 with only a single monolithic ceramic catalyst carrier 46 and tapered end portions 48, which are each provided with connecting flanges 50. The end sections 48 are, however, symmetrical about the main section 44. The housing 42 is in the longitudinal axis in FIG divided into two parts. However, instead of having outwardly bent flanges on each part only a single part is provided with flanges 52 along both longitudinal edges, which form the rim-shaped longitudinal edge regions of the other part overlap.

The unit 40 has corresponding dimensions which are the same as those of the unit 10 and is shown in FIG Assembled in the same way as the unit with the exception that the flanges 52, which form the rim-shaped Overlap edge areas of the other housing part, have the advantage that the damage the mat 54 by flowing out between the meeting edges of the housing parts during installation to a minimum

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1 can be restricted.

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Claims (8)

Claims 1 J Catalytic cleaning unit for exhaust gases from internal combustion engines of motor vehicles with a monolithic catalyst carrier which has generally parallel flow channels, a circumferential surface which surrounds the flow channels and a catalyst on the walls of these channels, a metal housing which surrounds the circumferential surface of the catalyst carrier and this is adapted, wherein generally uniformly a gap between the metal housing and the catalyst carrier is uniformly present and the housing has two halves which are connected to one another substantially in a plane which is generally parallel to the flow channels, and a swellable material which the Space between the housing and the circumferential surface fills and between the case and the peripheral surface are compressed to such a density within a range is what leads to compressive forces that are effective in terms of the wearer against damaging movement 1 30048/0566 RO o37ö OBERURSEL · · IDENSTRASSE 10 ix! \ * oM ^ n-.iI d OFFICE a050 FREISING ' SCHNEGGSTRASSF. 3-5 ΓΙ-Ι Mlnl'O & WI IKIl-A 52t> M / p.iw.1 .1 BRANCH OFFICE 33Λ) PASSAU LUnWIGSTRASSE 2 TII iWM »0» l » Support the housing, allowing for expansion when the unit is heated to normal operating temperatures this material increases these forces, but not enough to damage the carrier. 2. Unit according to claim 1, characterized in that the carrier is ceramic » 3. Unit according to claim 1 or 2, characterized in that the swellable material consists of a mat Comprises ceramic fibers and the width of the gap between the carrier and the housing is related to the mat thickness, whereby the corresponding density range is obtained.
15th 4. Unit according to one of claims 1 to 3, characterized characterized in that the swellable material has a ceramic fiber matrix mixed therein small particles of mica. 5. The unit of any one of claims 1 to 4, characterized in that the density ranges from about 0.64 g / cm ³ (40 lbs / ft ³ ) to about 1.53 g / cm ³ (95 lbs / ft ³ ) lies. 6. Method of manufacturing the catalytic purification unit according to claim 1, characterized in that one a monolithic catalyst carrier with a multiple of generally parallel flow channels extending therethrough from one end to the other, a circumferential surface that the channels surrounds, and with a catalyst on the walls of these channels a mat made of ceramic fibers that form a swellable Have material, of greater thickness than that of a gap between the support and a metal housing, which generally includes the circumferential 130048/0566 ] surface of the carrier surrounds and is adapted to this, with a gap between the carrier and the metal housing is provided and the housing consists of two halves that are substantially connected to each other are connectable in a plane which runs generally parallel to the flow channels, wrapped around, arranges the two halves of the housing around the wrapped mat and clamps the parts together, wherein Compressive forces are generated in the mat, which prevent the wearer from moving relative to the housing effectively prevent the two halves of the housing being clamped together in this way and the thickness of the mat correlates with the width of the gap, whereby a density of the compressed mat is obtained within a range conducive to compressive forces leads that effectively support the carrier against damaging movement with respect to the housing, the expansion taking place when the unit is heated to normal operating temperatures of the swellable material leads to an increase in the forces, but not so far that the wearer damaged. 7. The method according to claim 6, characterized in that the mat is a ceramic fiber matrix in the small particles of mica are mixed together. 8. The method according to claim 6 or 7, characterized in that the carrier is ceramic. 130048/056 6