Honeycomb filter

A honeycomb filter comprising:

• a honeycomb substrate having porous partition walls defining a plurality of cells which extend from an inflow end face as an end face on an exhaust gas inflow side to an outflow end face as an end face on an exhaust gas outflow side and which become through channels for a fluid;
• and
• plugging portions disposed in end portions of the plurality of cells on one of an inflow end face side and an outflow end face side,
• wherein the cells of part of the plurality of cells are inlet plugged cells whose end portions are closed by the plugging portions on the inflow end face side of the honeycomb substrate, and the residual cells among the plurality of cells are outlet plugged cells whose end portions are closed by the plugging portions on the outflow end face side of the honeycomb substrate,
• wherein the plurality of cells are arranged so that a periphery of one of the inlet plugged cells is surrounded with eight of the outlet plugged cells in a cross section perpendicular to a central axis direction of the honeycomb substrate,
• a shape of an open end of each of the inlet plugged cells in the cross section is a square in which a length of one side is L1,
• the outlet plugged cells include square outlet plugged cells and rectangular outlet plugged cells,
• a shape of an open end of each of the square outlet plugged cells in the cross section is a square in which a length of one side is L2, and L2 is smaller than L1,
• a shape of an open end of each of the rectangular outlet plugged cells in the cross section is a rectangle in which a length of a long side is L1 and a length of a short side is L2,
• in each diagonal direction of the square in which the length of the one side is L1 in the cross section, four of the square outlet plugged cells are arranged adjacent to the inlet plugged cell,
• in a linear direction perpendicular to each side of the square in which the length of the one side is L1 in the cross section, four of the rectangular outlet plugged cells are arranged so that the cells are adjacent to the inlet plugged cell and so that the long side of the rectangle in the cross section is parallel to one side of the square in which the length of the one side is L1 in the cross section,
• a partition wall thickness of the partition walls is defined as t,
• a distance from an intermediate point of the thickness of the partition wall defining one side of the open end of the square in which the length of the one side is L1 in the cross section to an intermediate point of the thickness of the partition wall defining a side facing the one side is defined as a partition wall center distance a,
• a distance from an intermediate point of the thickness of the partition wall defining a long side of the open end of the rectangle in the cross section to an intermediate point of the thickness of the partition wall defining a side facing the long side is defined as a partition wall center distance b, and
• the partition wall center distance a, the partition wall center distance b and the partition wall thickness t satisfy the following equation (1),
• 0.95<b/at<1.90 (1).