Catalytic Converter for Exhaust Gases

U.S. application Ser. No. 207,794, entitled "Catalytic Reactor with Monolithic Element," filed on Dec. 14, 1971 and now U.S. Pat. No. 3,771,967, issued Nov. 13, 1973, of Hubert H. Nowak and assigned to the assignee hereof concerns features relating to the fibrous mounting layer and impregnation thereof.

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.

FIG. 1 is a longitudinal cross section through a catalyst 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.

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 1/4 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 3/16 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 1/8 inch; and the metal shell 7 extends beyond the ends of element 15 for, preferably, about 1/4 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 2300.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.