As is well known, the purification of exhaust gases from internal combustion engines, particularly in mobile vehicles, is generally achieved by a catalytic converter in which a ceramic or metallic element having a honeycomb cell structure, which is disposed in a gas-tight sheet metal shell, acts as a catalyst carrier. More precisely, this honeycomb cell structure or catalyst substrate is covered with a catalyst that contains a precious metal which functions, in the presence of a stoichiometric mixture of exhaust gases, to convert noxious or otherwise environmentally unfriendly components of the exhaust gas, such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx), to carbon dioxide (CO2), water (H2O) and nitrogen (N).
A single sheet of rectangular shaped mat support material having a groove on one end and complimentary tongue on the other, or other combination of complimentary attachment features, is disposed between the catalyst substrate and shell. The sheet of mat support material is wrapped around the lateral (outer) peripheral surface of the ceramic or metallic element such that the tongue and groove engage. The wrapped catalyst substrate is then disposed within the gas-tight shell.
Currently, a uniformly compressed piece of the mat support material is used between the catalyst substrate's outer surface and the shell to prevent axial movement of the catalyst substrate. Axial movement is resisted by the product of the mat support material force, the coefficient of friction between the catalyst substrate and the mat support material, and/or the coefficient of friction between the mat support material and shell. However, when using catalyst substrates that have frangible walls, for fast warm-up and low flow restriction, the catalyst substrate tends to be too weak to resist the mat support material forces necessary to prevent axial movement.
Consequently, there exists a need to reduce the axial movement of a catalyst substrate during operation of a catalytic converter.