Abstract:
According to the present invention a catalyst substrate is provided with a peripheral mantle extending thereabout and having opposite end walls between which the substrate is disposed. At least one of the end walls acts as a forward seal which is maintained in close proximity with a corresponding sealing surface toward an inlet end of the catalytic converter housing. A retaining member is provided which maintains the sealing surfaces In close proximity to define a labyrinth seal therebetween.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to catalytic converters for treating combustion gasses. More particularly this invention relates to the mounting of a catalyst substrate in a catalytic converter housing. 
     BACKGROUND OF THE INVENTION 
     A typical catalytic converter comprises a cylindrical catalyst substrate mounted within a cylindrical catalytic converter housing. The catalyst substrate may be a ceramic honeycomb or a corrugated metal foil sheet and a flat metal foil sheet wound together into a spiral defining a matrix of passages. 
     In either case the catalyst substrate defines a multiplicity of the flow passages extending therethrough generally parallel to an axis of the catalyst substrate and, when installed therein, the catalytic converter housing. 
     Catalytic converters may be broadly grouped into vehicle sized units and stationary engine or industrial sized units. Vehicle sized units are considerably smaller than industrial sized ones and accordingly are relatively easy to remove and to disassemble. Catalyst substrate diameters for vehicle sized units would typically measure less than a foot (approximately 0.3 m). In contrast, large industrial sized units may have catalyst substrate diameters that measure on the order of six feet (approximately 2 m). The associated ducting and sheer size of the components typically precludes removal and axial disassembly of an industrial sized unit for replacing the catalyst substrate. Instead, large industrial sized catalytic converter housings are provided with a lateral access port for removal of the catalyst substrate from a side of the housing without removal or axial separation of the housing from its associated ductwork. 
     In use the catalytic converter housing both during heat up and steady state operation will typically be about 100° C. cooler than the catalyst substrate. This is because the substrate typically runs at exhaust temperature and has nowhere to conduct or radiate heat away. The housing in contrast will receive heat from its inside but can radiate or conduct heat into the surrounding atmosphere. Upon shutdown or low engine loads, the rate of the temperature loss from the housing tends to be less than that of the catalyst substrate because the housing is of heavy gauge metal whereas the catalyst substrate is thin sheet metal with a huge surface area. The housing under low engine load conditions can be 100-150° C. hotter than the catalyst substrate. 
     Considering the overall size of an industrial sized unit, the temperature differential can result in significant dimensional differences between the housing and the substrate. These must be accommodated to avoid undue stress damaging either component while ensuring adequate sealing therebetween so as to avoid exhaust gasses escaping between the housing and the substrate. 
     Most large industrial catalytic converters are sealed about the periphery of the catalyst substrate with a ceramic fibre material. Unfortunately such material is prone to erosion by high velocity gasses and mechanical breakdown through compression and vibration. Furthermore such material is easily torn and difficult to maintain in place during installation, particularly with larger units. 
     It is an object of the present invention to provide a catalytic converter design which allows for differential thermal expansion between the catalytic converter housing and the catalyst substrate without the use of fibrous gasketing materials yet ensuring an effective seal to avoid excessive gas flow between the substrate and the housing. 
     SUMMARY OF THE INVENTION 
     In very general terms, according to the present invention a catalyst substrate is provided with a peripheral mantle extending thereabout and having opposite end walls between which the substrate is disposed. At least one of the end walls acts as a forward seal which is maintained in close proximity with a corresponding sealing surface toward an inlet end of the catalytic converter housing. A retaining member is provided which maintains the sealing surfaces in close proximity to define a labyrinth seal therebetween. In other words, the gap is small enough that the preferred gas flow route is through the substrate rather than past the seal. 
     More specifically, a catalytic converter is provided which has a housing with side walls defining a catalyst chamber, an inlet opening and an outlet opening communicating with an interior of the catalyst chamber to provide a fluid flow path through the housing from the inlet opening through the chamber and out of the outlet opening. A catalyst substrate is mounted in the chamber and has a flow direction aligned with the fluid flow path. The catalyst substrate has a peripheral mantle extending thereabout. The peripheral mantle has a peripheral outer wall and a pair of spaced-apart end walls extending inwardly therefrom. The catalyst substrate is disposed between the end walls with one of the end walls being a forward end wall upstream of the catalyst substrate and facing toward the inlet opening. The other of the end walls is a rearward end wall downstream of the catalyst substrate and facing toward the outlet opening. The housing has a sealing surface in the chamber transverse to the flow direction and facing a forward end wall of the peripheral mantle. Locating means are provided and secured to the housing for locating the catalyst substrate relative to the chamber. The locating means include engaging means for engaging the peripheral mantle to limit movement of the catalyst substrate away from the sealing surface to maintain the forward end wall in closely spaced arrangement with the sealing surface thereby defining a labyrinth seal therebetween. The labyrinth seal avoids fluid leakage between the housing and the catalyst substrate to promote fluid flow through the substrate. The chamber further has a lateral access port for removal or installation of the catalyst substrate therein without axial separation of the housing. 
     The locating means may be a bar having forward and rearward securing means respectively at forward and rearward ends thereof. The securing means secure the bar to the housing with the forward end upstream of the rearward end. The engaging means may be a tab extending from a side of the bar for abutting against the rearward end wall of the peripheral mantle. The tab may be dimensioned to bend at a force input below that required to damage the peripheral mantle. 
     The forward securing means may be configured to accommodate laterally outward movement of the peripheral mantle in response to thermal expansion. The rearward securing means may be configured to accommodate longitudinal expansion of the housing. 
     The forward securing means may be a transversely extending slot and the rearward securing means may be a longitudinally extending slot. 
     The catalyst chamber may accommodate first and second axially aligned catalyst substrates with the first substrate being upstream of the second substrate. In such a case, each of the first and second catalyst substrates may have a respective peripheral mantle extending thereabout with respective forward and rearward end walls. The locating means may include a first tab and a second tab adjacent the first tab. The first tab engages is the rearward wall of the first catalyst substrate to limit movement of the first catalyst substrate away from the sealing surface of the housing. The second tab may engage the forward wall of the second catalyst substrate to limit movement of the second catalyst substrate toward the first catalyst substrate. 
     The locating means may be marked to distinguish the forward end from the rearward end. 
     The marking may be the numeral “1” placed between the first tab and the forward end. 
     A method is provided for sealing a catalyst substrate in a catalytic converter housing wherein the housing has sidewalls defining a catalyst chamber, an inlet opening upstream of the catalyst chamber and an outlet opening downstream of the catalyst chamber. The inlet and outlet openings provide a fluid flow path through the housing which further has a lateral access port for installation and removal of a catalyst substrate in the catalyst chamber without axial separation of the catalyst chamber. 
     The method comprises the steps of:
         (i) providing a peripheral mantle about the substrate, the peripheral mantle having first and second spaced apart inwardly extending walls with the substrate disposed therebetween;   (ii) providing the housing with an inwardly facing sealing surface extending about the inlet opening;   (iii) providing at least the first wall with an outwardly facing sealing surface for registering with the inwardly facing sealing surface of the housing;   (iv) providing a lateral locating means securable to the housing and having positioning means extending therefrom for engaging the peripheral mantle to limit movement of the peripheral mantle and the outwardly facing sealing surface away from the inlet opening and the inwardly facing sealing face to maintain a pre-determined gap therebetween; the gap forms a labyrinth seal transverse to the fluid flow path for restricting fluid leakage between the catalyst and the housing;   (v) providing a deflecting means acting between the locating means and the mantle for limiting the amount of force which may be applied by the locating means to the peripheral mantle to an amount which is below the yield strength of the peripheral mantle and the yield strength of the housing.       

     The deflecting means may extend from and be unitary with the locating means. The amount of force may be limited by the cross-sectional area of the deflecting means transverse to the flow direction. 
     A radial clearance may be provided between an outer periphery of the peripheral mantle and an interior of the catalyst chamber to accommodate relative differential thermally induced movement therebetween. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       Preferred embodiments of the invention are described in detail below with reference to the accompanying drawings in which: 
         FIG. 1  is an exploded perspective view illustrating a housing for a catalytic converter according to the present invention; 
         FIG. 2  is an enlargement of the encircled area  2  of  FIG. 1 ; 
         FIG. 3  is an axial section through a catalytic converter according to the present invention; 
         FIG. 4  is an enlargement of the encircled area  4  of  FIG. 3 ; 
         FIG. 5  is an exploded perspective view of a catalytic converter according to the present invention; 
         FIG. 6  is a plan view of a retaining bar for use with a catalytic converter according to the present invention; 
         FIG. 7  is an exploded perspective view of a catalytic converter according to the present invention; and, 
         FIG. 8  is an enlargement of the encircled area  8  of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A catalytic converter according to the present invention is generally indicated by reference  20  in the accompanying illustrations. The catalytic converter  20  has a housing  22  with a generally cylindrical centre section  24  tapering at one end toward an inlet opening  26  and at an opposite end toward an outlet opening  28 . The housing  22  defines a catalyst chamber  30 . The inlet opening  26  and outlet opening  28  communicate with the catalyst chamber  30  to provide a flow path  32  for exhaust gasses from the inlet opening  26  through the chamber/housing  22  and out of the outlet opening  28 . 
     The centre section  24  of the chamber  30  has a lateral access port  40  through the housing  22  through which a catalyst substrate  50  may be inserted into or removed from the chamber  30 . A cover  42  is provided to close the access port and prevent exhaust gasses from escaping. The cover  42  may be secured with any suitable releasable fasteners such as nuts and bolts. 
     The catalyst substrate  50  is illustrated as a metal foil type and has a multiplicity of passages  52  extending therethrough generally aligned with the flow path  32 . The catalyst substrate  50  has a peripheral mantle  54  extending thereabout. The peripheral mantle has a peripheral outer wall  56  and a pair of spaced-apart end walls extending radially inwardly therefrom. The end walls include a forward end wall  58  upstream of the catalyst substrate (i.e. facing toward the inlet) and a rearward end wall  60  downstream of the catalyst substrate (i.e. on the outlet side). The catalyst substrate  50  is nested in a channel defined by the peripheral outer wall  56 , the forward end wall  58  and the rearward end wall  60 . The nesting should be snug to avoid gas escape between the peripheral mantle  54  and the catalyst substrate  50 . The housing has a lip  70  extending inwardly into the chamber upstream of the catalyst substrate  50 . The lip  70  has a sealing surface  72  which faces the forward end wall  58  of the peripheral mantle  54 . The sealing surface  72  and the forward end wall  58  are in close juxtaposition to define a labyrinth seal  80  therebetween. 
     A guide  76  such as the flat bar illustrated in  FIG. 2  may be provided to assist in installation of the catalyst substrate  50 . The guide would engage the peripheral mantle  54  to prevent damage to the relatively soft catalyst substrate  50 . 
     The expression “labyrinth seal” refers to a method of sealing wherein a narrow gap rather than a resilient filler material is used to effect sealing. In a structure such as a catalytic converter, while it may be important to avoid exhaust gas escape from the housing  22 , perfect sealing is not required within the chamber  30 . The labyrinth seal  80  relies on the tendency of a fluid to seek the path of least resistance. As resistance to flow increases exponentially with fluid velocity, a narrow gap will not pass a significant amount of fluid at high velocities. Hence, in the present case, the fluid flow will substantially be through the passages  52  through the catalyst substrate rather than through the labyrinth seal  80 . A typical gap might be on the order of 1 mm nominal with a tolerance of ±½ mm as the peripheral mantle will typically close the gap by approximately ½ mm at operating temperatures. 
     The reason for having a labyrinth seal  80  adjacent an end wall of the peripheral mantle  54  rather than between the housing  22  and the peripheral outer wall  56  is one of tolerance. The diameter of the peripheral outer wall  56  may be as much as six feet (about 2 metres). Its breadth would typically only be about three inches (about 7.5 cm). Accordingly it will be appreciated that the thermal expansion and contraction of the peripheral mantle  54  will be, in an axial direction, be only a small fraction of what it would be in a radial direction. Accordingly, maintaining a close tolerance between the peripheral mantle  54  and the housing  22  is simpler in the axial rather than the radial direction. 
     As will be described in more detail below, industrial type catalytic converters are often sized to receive two catalyst substrates  50 . In most applications only one is installed and leaving the option of installing a second should one not prove effective enough or should future amendment of relevant regulations impose more stringent standards. Accordingly it is common practise to install a single catalyst substrate  50  adjacent the inlet opening  26  to allow space for a further catalyst substrate  50  to be installed downstream thereof. On this basis, the labyrinth seal is illustrated and described as being upstream of the catalyst substrate  50  toward the inlet opening  26 . While this may be the presently preferred arrangement, it is possible to reverse the arrangement and locate the lip  70  and sealing surface  72  adjacent the outlet opening  28  thereby defining the labyrinth seal downstream of the catalyst substrate adjacent the outlet opening. While the latter may not be the preferred arrangement, it should not be dismissed as a possible variant and accordingly the expressions “inlet”, “outlet”, “forward” and “rearward” both here and in the claims should be considered as preferences rather than as absolutes. 
     As the catalyst chamber  30  is broader than the peripheral mantle  54 , retaining or locating means in the form of a retaining bar  90  is provided to maintain the forward end wall in close juxtaposition to the sealing surface  72 . The retaining bar  90  has a forward end  92  and a rearward end  94 . The bar has an engaging means in the form of a first tab  96  which abuts against the rearward end wall  60  of the peripheral mantle  54  to limit movement of the peripheral mantle  54  away from the sealing surface  72 . While this arrangement has the benefit of not requiring further engaging features on the peripheral mantle  54 , it will be appreciated that a tab or slot or other projection could be provided on the peripheral mantle  74  for engaging the first tab  96 . 
     In use catalytic converters are occasionally subject to extreme temperature excursions out of the design norm, such as may be associated with engine malfunction. Ideally such should not damage the catalyst substrate  50  or the housing  22  as repair and/or replacement of these is very expensive and is further associated with costly downtime. Accordingly, the retaining bar  90  should be configured so as not to transfer destructive stresses to the peripheral mantle  54  or the housing  22 . This can be achieved by making the first tab  96  of a small enough cross-section to bend in response to axial loading rather than to damage the peripheral mantle  54 . 
     The retaining bar  90  may also be provided with a rearward retaining means in the form of a longitudinal slot  98  of its rearward end  94  to allow for axial growth of the housing  22 . Forward retaining means in the form of a transversely extending slot  100  may be provided at the forward end  92  of the retaining bar  90 . The transversely extending slot  100  accommodates radial expansion of the peripheral mantle  54  while maintaining it close up against the sealing surface  72 . 
     In cases where a second catalyst substrate  50  is installed, a second tab  102  may be provided on the retaining bar  90  adjacent the first tabs  96 . The second tab  102  principally keeps the two catalyst substrates  50  separated rather than keeping the second substrate  50  in sealing engagement with the housing  22 . 
     To avoid crack initiation and propagation a circular hole  104  may be provided at the origin of a partition line  104  between the first tab  96  and second tab  102 . A mark such as the numeral “1” identified by reference  106  may be provided to indicate which end of the retaining bar  90  is the forward end. Other markings might include “F” for “forward” or “U” for “upstream”. 
     The above description is intended in an illustrative rather than a restrictive sense. Accordingly, the scope of the invention should not be restricted to the specific embodiments described as variants may be apparent to persons skilled in such structures without departing from the spirit and the scope of the invention as defined by the claims which are set out below. 
     PARTS LIST 
     
         
           20  catalytic converter 
           22  housing 
           24  centre section 
           26  inlet opening 
           28  outlet opening 
           30  catalyst chamber 
           32  flow path 
           40  lateral access port 
           50  catalyst substrate 
           52  passages (through substrate) 
           54  peripheral mantle 
           56  peripheral outer wall 
           58  forward end wall 
           60  rearward end wall 
           70  lip 
           72  sealing surface 
           76  guide 
           80  labyrinth seal 
           90  retaining bar 
           92  forward end (of bar) 
           94  rearward end (of bar) 
           96  first tab 
           98  longitudinal slot 
           100  transverse slot 
           102  second tab 
           104  circular hole 
           106  mark