Catalytic Converter For Exhuast Gases

Abstract

A catalytic converter adapted for use in the exhuast systems of internal combustion engines comprises a housing including as a part thereof a tubular shell having a differentially hardened fibrous lining to resiliently support, insulate, and secure a monolithic type catalyst element. The ends of the tubular shell and the fibrous lining are angularly deformed inwardly to protect the corners of the catalyst, to minimize gas impingement on the fibrous material, and to mechanically retain the catalyst in position.

Description

RELATED APPLICATION

U.S. application Ser. No. 207,794, entitled "Catalytic Reactor with Monolithic Element," filed of even date herewith of Hubert H. Nowak and assigned to the assignee hereof concerns features relating to the fibrous mounting layer and impregnation thereof.

BRIEF SUMMARY OF THE INVENTION

It is the basic purpose of this invention to provide an improved type mounting for a monolithic type or honeycomb catalyst element which is suitable for mass manufacture and for use in exhaust systems of automotive internal combustion engines.

The invention accomplishes this purpose by use of an impregnated fibrous sleeve to mount the monolithic catalyst element on a tube or ring which forms a part of the converter housing. Preferably, prior to assembly of the housing, at least the downstream end of the sleeve and preferably the ring are angularly deformed inwardly to provide a combination seal, retainer, and protector for the catalyst element.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross section through a catalytic converter embodying the invention;

FIG. 2 is a cross section along the line 2--2 of FIG. 1, and;

FIG. 3 is an enlarged partial subassembly view (prior to crimping) of the catalyst element, the fibrous sleeve, and the housing ring.

DESCRIPTION OF THE INVENTION

The catalytic converter 1 has a three piece housing comprising an inlet header cone 3, an outlet header cone 5, and an intermediate round tubular ring 7 which fits inside of and is welded to annular end sections 9 on the cones as seen at 11. The inlet and outlet cones have suitable collars 13 at their outer ends whereby they may be secured to conduits in the exhaust system of an internal combustion engine. The converter 1 contains a monolithic type honeycomb catalyst element 15 which has a large number of cellular passages 17 through which gas can flow from the inlet chamber 19 in cone 3 to the outlet chamber 21 in cone 5. The element 15 is constructed of a suitable refractory or ceramic material and appropriate catalytic material is deposited on the walls of the passages 17 whereby the refractory material serves as a support for the catalytic material, a more extensive description of one form of element 15 being found in U.S. Pat. No. 3,441,381. Catalytic elements of this type are very fragile and in the course of manufacture, particularly on a large scale, it is very easy for them to become damaged, particularly at the corners. They are also subject to wearing, abrasion, chipping, and fracture in use due to shock loads, differential expansion rates as compared with the metal of the container, and relative abrasive movement between it and the harder metal part.

In accordance with this invention, there is a resilient wall or interface 23 between the element 15 and the metal ring 7. The wall is preferably formed of ceramic fiber material such as blown alumina silica felted fibers sold under the tradenames "Fiberfrax," "Cera Fiber," or "Kaowool." Other high temperature resistant fibers, such as (but not limited to) asbestos, may also be used to form the layer 23 in certain applications. In a typical assembly where the element is 4 - 5 inches in diameter a felted layer or sleeve of ceramic fibers about one-fourth inch thick is wrapped around the element 15. This combination of fiber 23 and element 15 is then inserted into ring or shell 7, the diameter of which is such that the wall 23 is radially compressed to a nominal three-sixteenths inch thickness. In the presently preferred arrangement, the fiber wrap 23 extends longitudinally beyond the ends of the element 15, as seen at 25 and 27 for, preferably, about one-eighth inch; and the metal shell 7 extends beyond the ends of element 15 for, preferably, about one-fourth inch as seen at 29 and 31. The ends 29 and 31 of the ring 7 are curled or deformed inwardly on angles of preferably about 30.degree. and this causes the ends 25 and 27 of the fiber sleeve to curl over the corners of the element so that they can protect them without closing off any flow channels 17 of the element.

After assembly and end crimping of the ring 7, the element 15, and the layer 23, a suitable rigidizer, binder, and adhesive liquid containing a high temperature withstanding material, such as an aqueous colloidal solution of silica containing from 15 to 40% Si O.sub.2 by weight or other suitable organic binder is applied to the layer 23. This solution may be applied before assembly to the shell and/or element or may be injected by needle or other suitable means into the layer 23. The amount of solution used is controlled so that it is insufficient to penetrate and coat the walls of channels 17 but large enough to provide the necessary amount of dry silica (or binder) needed to harden the ends of the layer. After injection the assembly 33 is put through a drying process, for example, placed in an oven at a temperature of about 250.degree. F or higher, so that the water or other liquid in the colloidal solution is removed. In drying, the silica solids migrate with the liquid vehicle to the points where vaporization occurs and are deposited at those points to a substantially greater degree than elsewhere. This means that the silica solids tend to concentrate at the exposed ends 25 and 27 of the sleeve 23 and to a lesser extent at the interfaces of the sleeve and the ring 7 and the element 15. Selective heating, instead of oven drying, can be used, if desired, to control the areas of deposition of silica.

After complete drying, the silica serves to bond the fibers of sleeve 23 together and to the adjacent surfaces of ring 7 and element 15. The hardened silica provides an effective positive seal against gas leakage from the usual broken cell walls around the outside of the honeycomb element 15. Further, the hardened silica rigidizes and seals the ends 25 and 27 of the fiber to form a positive gas barrier making the sleeve gas impervious. It also provides a positive, nonmetallic mechanical lock between the element 15 and the metal ring 7 so that the element is well supported but is not in contact with metal. Despite the effects just mentioned, the bulk of the fiber wrap 23 between the hardened surface layers has very little hardened silica, if any, and is, after drying, practically as resilient as the original fiber layer before hardening. Thus, the layer 23 functions as an absorbent barrier to insulate and protect the element 15 from mechanical shocks. It also functions as a thermal insulation barrier between the metal shell 7 and the element 15. It is apparent that the density and hardness of layer 23 can be controlled by control of the nature and amount of the rigidizer and adhesive liquid.

The ring 7 and sleeve 23 serve as a carrier and protector for the frangible element 15 and minimize the possibility of damage to the element during assembly of the unit 33 with the headers 3 and 5. As indicated, this assembly is completed to form converter 1 by welding, or other suitable fastening, as shown at 11.

In use of the converter 1, exhaust gas enters the inlet header 3 and flows directly through the catalyst treated passages 17 of the honeycomb 15 into the outlet chamber 21 and then out of the converter. The radially extending or angular flange portions 35 and 37 at the inlet and outlet sides of the assembly 33, in addition to the functions mentioned above, serve also to deflect gas away from the sleeve 23 and into the element 15 to minimize impingement upon and erosion of the sleeve.

It will be seen that the described mounting of the element 15 on metal shell 7 has many desirable features. It enables nearly 100 percent of the volume of element 15 to be used since none of the passages 17 are blocked off. It provides effective positive sealing against leakage around the outside of the element, despite the usual rough and broken outer surface of the element, and eliminates the need for a special seal coating on the outside of the element. It eliminates abrasion of the element by eliminating all metal contact with the element. It provides positive mechanical locking as well as adhesive bonding of the element to the shell 7 and converter housing. It provides a resilient interface between the element 15 and the shell 7 which gives a high degree of mechanical shock resistance and which eliminates stringent dimensional tolerances. Since the ceramic fibers are stable up to the usual maximum catalyst operating temperatures (about 2,300.degree. F), the converter is operative and safe at all temperatures encountered in normal usage of the element. The simple structure of the converter 1 enables the thickness of the layer 23 to be readily varied in accordance with the degree of thermal and shock insulation desired. The arrangement provides for substantially stress-free relative movement between the element and ring 7 such as occasioned by different rates of thermal expansion and contraction. The thermal insulating properties of layer 23 also minimize the temperature of the metal housing to protect the surrounding environment, provide for faster warm-up and better heat retention in the catalyst and minimum cross sectional thermal gradients due to conductive heat loss into the metal shell, and enable a better selection of metals for use in the shell because of metal isolation from very high temperatures, for example, low grade, low expansion ferritic stainless steel might be used.

While a presently preferred embodiment of the invention has been illustrated and described, it will be apparent that modifications thereof are within the spirit and scope of the invention. For example, in some assemblies it may be desirable to provide the flange means at one end only (preferably at the outlet end 37 to secure mechanical holding force) and eliminate the other flange means. Other means of holding the fiber portion 25 and/or 27 in bent position may be used, for example, a fold or indentation in shell 7 spaced from an end of the shell or the angle of the cone 3 or 5. Broadly, a structural assembly advantage is still achieved if the bent corners are entirely eliminated as the sleeve 7 fits inside of the inner ends of cones 3 and 5 and facilitates formation of the housing. Also, the subassembly 33 may be connected to inlet and outlet flow conduits of varying types and structures.

Claims

I claim:

1. A catalytic converter for purifying the exhaust gas of an internal combustion engine comprising a tubular metal shell, a gas pervious refractory catalyst element inside said shell and arranged so that flow through the element is substantially axial with respect to the axis of the shell, means resiliently mounting said element inside said shell so that the outer surface of the element is spaced from the inner surface of the shell, an inlet conduit having a flange fitting around the outside of and welded to one end of the shell, an outlet conduit having a flange fitting around the outside of and welded to the other end of the shell, said element having inlet and outlet end faces, said resilient mounting means comprising a nonmetallic resilient fibrous insulating layer in the space between said surfaces and having an end portion axially overlapping one end face of the element and bent over the adjacent end corner of the element.

2. A converter as set forth in claim 1 wherein said layer end portion overlaps the outlet end face of the element and extends inwardly at an angle over the outlet end corner of the element and the outlet end of the shell has a flange extending inwardly over said end portion of the fibrous layer to hold said layer in place over said outlet end corner.

3. A converter as set forth in claim 1 wherein the adjacent end of the shell has a shoulder adjacent the bent end portion of the fibrous layer to hold said bent layer portion in place over said corner.

4. A converter as set forth in claim 3 wherein said fibrous layer contains a differentially dispersed solid material deposited on the fibers in heavy concentrations adjacent the exposed surfaces of the layer and adjacent the outer layer surfaces in juxtaposition to said element and shell surfaces and in materially less concentration in the center portion of the layer whereby said center portion is resilient, said deposited material serving to harden and seal said exposed and outer layer surfaces and to bond the outer layer surfaces to said element and shell.

5. A converter as set forth in claim 4 wherein said fibrous layer is in contact with and bonded to said shell surface and said element surface and in compression between them and serves to seal the outside of the element.

6. A subassembly for use in a catalytic converter for purifying the exhaust gases of an internal combustion engine comprising a tubular metal shell having a longitudinal axis and opposite longitudinal end portions, a cylindrical fluid pervious frangible catalyst element having a longitudinal axis and longitudinally separated inlet and outlet end faces each with an outer circumferential corner, said element having an outer surface and said shell having an inner surface larger in cross section than said element outer surface, said element being positioned inside of said shell so that said axes are substantially coaxial and to provide a substantially uniform width annular space between said surfaces forming a substantially annular chamber with an axis substantially coaxial with said axes, an annular resilient nonmetallic fibrous insulating member in said annular chamber and serving to resiliently mount said element in said shell, fluid flow through said shell being substantially parallel to said axes, said shell end portions extending longitudinally beyond said inlet and outlet end faces of said element to protect said corners during handling of the subassembly, and flange means mechanically holding the shell, element, and member in substantially permanent longitudinal positions with respect to each other including radially extending portions of said fibrous member extending across and engaging said circumferential corners.

7. A combination as set forth in claim 6 wherein said flange means includes radially extending portions of said shell engaging and holding said fibrous member portions against said circumferential corners.

8. A catalytic converter for purifying the exhaust gases of internal combustion engines comprising a housing including a tubular shell, a frangible gas pervious refractory catalyst element inside said shell having inlet and outlet end faces with outer circumferential end corners and arranged so that flow through the element and faces is substantially axial with respect to the axis of the shell, means resiliently mounting said element inside said shell so that the outer surface of the element is spaced from the inner surface of the shell, an inlet means at one end of the shell, an outlet means at the other end of the shell, said resilient mounting means comprising a nonmetallic resilient fibrous insulating layer in the space between said surfaces having an axially and circumferentially extending portion axially overlapping an end face of the element and radially extending over the adjacent circumferential end corner of the element, said housing including means holding said layer portion over said corner.

9. A converter as set forth in claim 8 wherein said axially and circumferentially extending portion overlaps the inlet end face of the element and extends over the inlet end corner.

10. A converter as set forth in claim 8 wherein said axially and circumferentially extending portion overlaps the outlet end face of the element and extends over the outlet end corner.

11. A converter as set forth in claim 10 including a second axially and circumferentially extending portion axially overlapping the inlet end face of the element and radially extending over the inlet end corner, said housing including second means holding said second layer portion over said inlet corner.

12. A catalytic converter for purifying the exhaust gases of an internal combustion engine comprising a tubular metal shell having an outer cylindrical surface of substantially round uniform diameter cross section along most of the length of the shell, a gas pervious refractory catalyst element inside said shell and arranged so that flow through the element is substantially axial with respect to the axis of the shell, means resiliently mounting said element inside said shell so that the outer surface of the element is spaced from the inner surface of the shell, an inlet conduit having a flange fitting around the outside of and welded to said round outer cylindrical surface at one end of the shell, an outlet conduit having a flange fitting around the outside of and welded to said round outer cylindrical surface at the other end of the shell.

13. A converter as set forth in claim 12 including flange means engaging the outer circumferential corner at the outlet end of the element and providing a mechanical holding means against substantial axial displacement of the element in a downstream direction, said flange means comprising a fibrous layer in contact with said corner and a radial flange on the shell in contact with the fibrous layer.

14. A converter as set forth in claim 12 wherein said resilient mounting means includes a fibrous sleeve in the space between the element and shell, and flange means engaging the outer portion of the outlet end of the element and providing a mechanical holding means against substantial axial displacement of the element in a downstream direction, said flange means comprising a radially inwardly extending flange formed on the end of the shell, said flange means further comprising a radially inwardly extending flange formed on the fibrous sleeve and sandwiched between the shell flange and the element.

15. A converter as set forth in claim 12 including retainer means supported by said shell engaging the outer circumferential corner of the element at the outlet end thereof to resist substantial downstream displacement of the element.

16. A catalytic converter for purifying the exhaust gases of an internal combustion engine comprising a tubular metal shell, a gas pervious refractory catalyst element inside said shell and arranged so that flow through the element is substantially axial with respect to the axis of the shell, said element having a downstream end, means resiliently mounting said element inside said shell so that the outer surface of the element is spaced from the inner surface of the shell, an inlet conduit at one end of the shell, an outlet conduit at the other end of the shell, and flange means reacting against the downstream end of the element and providing a mechanical holding force against downstream axial displacement of the element in one direction and comprising a fibrous layer extending radially inwardly from the outer surface of the element and in contact with the downstream end of the element and a radial flange formed integrally on the shell in contact with the fibrous layer.

17. A subassembly for use in a catalytic converter for purifying the exhaust gases of an internal combustion engine comprising a tubular metal shell having a longitudinal axis and opposite longitudinal end portions, a cylindrical fluid pervious frangible catalyst element having a longitudinal axis and longitudinally separated inlet and outlet end faces each with an outer circumferential corner, said element having an outer surface and said shell having an inner surface larger in cross section than said element outer surface, said element being positioned inside of said shell so that said axes are substantially coaxial and to provide a substantially uniform width annular space between said surfaces forming a substantially annular chamber with an axis substantially coaxial with said axes, a fibrous member in said annular chamber and serving to resiliently mount said element in said shell, fluid flow through said shell being substantially parallel to said axes, said shell end portions extending longitudinally beyond said inlet and outlet end faces of said element to protect said corners during handling of the subassembly, and flange means mechanically holding the element against movement in a downstream direction in the shell including a radially extending portion of said fibrous member extending across and engaging said outlet circumferential corner and a radially extending portion of said shell engaging said radially extending fibrous member portion.