Patent Publication Number: US-6667013-B1

Title: Catalytic converter and method for mounting of converter

Description:
BACKGROUND 
     It is generally accepted that one way to ensure that catalytic converters for internal combustion engines fulfil the requirements for rapidly becoming active after starting the engine, is to provide a first converter close to the engine manifold, where the exhaust gas from the beginning has a high enough temperature to effect a light-off of the converter, and a second converter further down along the exhaust pipe where temperature and vibration are less demanding. Such divided converter systems are described in patents U.S. Pat. No. 5,444,978, EP 629 771, EP 761 939, and DE 44 42456. The extreme oscillations of pressure and temperature, as well as the high peak temperature make it difficult to get sufficient lifetime of the first manifold converter, and many suggested designs include means for easy replacement, or for bypassing it as soon as the second, main converter is operative, as shown in DE 44 42456. 
     The present invention is a new type of manifold converter and a way to mount it close to the engine, where the converter is less vulnerable to heat fluctuation and vibration, and where a rapid light-off is assured. 
     DESCRIPTION 
     The converter and its mounting is described with reference to the figures, where FIG. 1 shows the configuration of the engine system, FIG. 2 a section through part of the engine and manifold with the manifold converter. 
     Catalytic converters usually comprise a monolith body with numerous parallel channels, the inner surfaces of which are coated with active catalyst layers. The monolith is commonly either an extruded ceramic body or a multiple of smooth and corrugated metal foils joined by brazing or welding. Ceramic bodies are brittle, however, and have to be elaborately mounted with resilient padding. Brazed or welded metallic monoliths develop large thermal stresses, and at their elevated temperatures there is a great risk of failure of welds or brazes. 
    
    
     The invention will now be described more in detail by reference to the enclosed drawing which illustrates a preferred embodiment of the invention. 
     FIG. 1 is a side view of a device according to the invention. 
     FIG. 2 is a cross section of the device shown in FIG.  1 . 
    
    
     According to the invention, catalytic converters with a metal monolith ( 13 ) are mounted between the engine exhaust ports ( 11 ) in the engine block ( 10 ) and the manifold ( 12 ), one converter per cylinder. Compared to designs with one converter per manifold, this leads to a lower average temperature and less risk of creep failure of the metal, but a wider temperature range. The monolith ( 13 ) and its mantle ( 14 ) can then be made of thinner metal than would otherwise be possible. 
     To reduce the thermal stresses in radial and tangential directions, the monolith ( 13 ) is made without brazes or welds, and the layers held together mechanically by tangential inward ridges ( 15 ) of smooth metal foils interlocking with notches in the corrugations of the corrugated metal foils, as described in patent SE 461 018. Variations in thermal expansion will then be accepted as radial play or as slight rotation of the inner parts relative to the outer parts. The ridges ( 15 ) of this design also have the added advantage of equalizing the turbulence in the axial direction, to make the whole length of the converter equally active, reduce the longitudinal thermal stresses and allow a comparatively short converter. 
     The converter is located at the exhaust port ( 11 ) of the engine, where the variations in exhaust gas velocity are greatest, which also ensures sufficient turbulence and lets the ignition point for the catalytic reaction fluctuate somewhat to avoid overheated spots. 
     One major advantage with the mechanical interlocking, as compared with brazing or welding, is that the mantle ( 14 ) around the monolith layers can be made much thinner than with other designs and interlock with the layers through the same type of tangential inward ridges ( 16 ). In previous designs, the mantle is so heavy and the monolith so long, that it has to be suspended at both ends, but according to the invention, it is sufficient to provide the thin mantle with a flange ( 17 ) behind or in front of the monolith ( 13 ). The thickness of the mantle is preferably in the range from 0.1 to 0.5 mm, and the length of the monolith from 25 to 50 mm. The mantle and the flange are preferably made from one integral piece of material by deep drawing or swaging. 
     The flange is clamped between the engine block ( 10 ) and the manifold ( 12 ). No bolt holes are needed in the flange ( 17 ). The mantle should not touch the inside of the manifold, but have a distance of a few millimeters, which should be open, without any insulating mat. To keep the converter centered in the manifold, a shallow recess ( 18 ) can be made in either the manifold or the engine block, or the neck ( 20 ) of the mantle between the flange and the monolith be made with locally raised areas. It can also be advantageous to extend the mantle past the monolith as a very narrow flange ( 19 ) which does not normally carry any load, but serves to guide the converter during the mounting operation to avoid scratching the mantle ( 14 ). 
     In the figures and the description, the converters have been described as extending into the manifold ( 12 ), which is a prefered embodiment with best mechanical stability, but for engine blocks of certain types or especially tightly bent manifolds, it is also possible to turn it with the monolith extending into exhaust port ( 11 ) of the engine block. 
     Catalytic converters made and mounted according to the invention can also be fitted to existing engines with little extra effort, compared to prior types which require redesigned or duplicated manifolds.