Ceramic honeycomb filter with enhanced thermal shock resistance
Thermal shock resistance of a ceramic honeycomb structure is increased through modifications of the cell wall joints. Wall joints can be modified such that a longitudinally-extending opening is created, putting two or more cells that meet at the wall joint in fluid communication through such opening. In such a case, all walls that meet at such a modified joint must join at least one other wall at that joint. Alternatively, wall joints can be modified by providing stress concentrating notches which extend into the joint from two or more cells that share the joint.
1. A monolithic ceramic honeycomb filter comprising multiple longitudinally-extending cells defined by porous walls that meet to form wall joints that are common to at least three cells; wherein a portion of the wall joints are modified wall joints, which modified wall joints each contain a longitudinally extending opening such that at least two longitudinally-extending cells are in fluid communication through the longitudinally extending opening at each of such modified wall joints, provided that all walls meeting at a modified wall joint are longitudinally joined to at least one other wall at the modified wall joint and said longitudinally extending cells are comprised of inlet and outlet cells with the inlet and outlet cells are not in fluid communication through the modified wall joint.
2. The honeycomb filter of claim 1 wherein the longitudinally-extending cells include a first set of cells that perform a first function and at least one other set of cells that perform a second function, and all longitudinally-extending cells that are in fluid communication through a longitudinally-extending opening at a particular modified wall joint perform the same function.
3. The honeycomb filter of claim 2 , wherein no cell is in fluid communication with more than one other cell through a longitudinally-extending opening in a modified wall joint.
4. The honeycomb filter of claim 3 , wherein the concentration of modified joints varies within the honeycomb structure.
5. The honeycomb filter of claim 4 , wherein the honeycomb structure contains at least one region proximate to the central longitudinal axis of the structure and at least one more peripheral region that partially or entirely encircles the central region, and the concentration of modified joints in the central region is higher than in at least one peripheral region.
6. The honeycomb filter of claim 4 wherein the ceramic is acicular mullite, cordierite, cordierite-spinel, spodumeme, silicon carbide or an aluminum-titanate-based material.
7. The filter of claim 1 , which is a soot filter for an internal combustion engine.