In a honeycomb structure, porous partition walls are arranged to surround cells extending from an inflow end face of the honeycomb structure body to an outflow end face thereof, intersection points at which the partition walls arranged in a latticed manner in the inflow end face intersect include a first intersection point that is one intersection point, and second intersection points one of which is the other intersection point in the partition wall including the first intersection point, and which are adjacent to the first intersection point, and the inflow end face has concave/convex portions each including the first intersection point as a bottom portion and the peripheral second intersection points of the first intersection point as top portions, or each including the first intersection point as a top portion and the peripheral second intersection points of the first intersection point as bottom portions.

A honeycomb formed body containing a ceramics raw material, the honeycomb formed body including: a pillar shaped honeycomb structure portion having a plurality of rectangular cells, the cells being defined by partition walls and extending from a first end face to a second end face to form flow paths; an outer peripheral portion having outer peripheral portions X where the partition walls are covered with an outer peripheral wall; and outer peripheral portions Y where the partition walls are exposed. Each of the outer peripheral portions X includes a tapered portion having a gradually deceasing thickness of the outer peripheral wall toward a boundary portion with an adjacent outer peripheral portion Y. The tapered portion requires a length equal to or more than one time of an average cell pitch in the outer peripheral direction until thickness of the outer peripheral wall is halved.

The honeycomb filter includes a honeycomb substrate having porous partition walls defining a plurality of cells and plugging portions. In a cross section, the cells are arranged so that a periphery of an inlet plugged cell including an open end whose shape is a square in which a length of one side is L1 is surrounded with four rectangular outlet plugged cells each including an open end whose shape is a rectangle in which a length of one side is L1 and a length of the other side is L2 (L1>L2) and four square outlet plugged cells each including an open end whose shape is a square in which a length of one side is L2. A partition wall center distance a, a partition wall center distance b and a partition wall thickness t satisfy the following equation (1):
0.95<b/at<1.90   (1).

An exhaust gas purification filter is configured to he disposed in an exhaust passage in a gasoline engine. The exhaust gas purification filter includes partition walls including a plurality of pores, a plurality of cells partitioned by the partition walls, and sealing portions alternately sealing ends of a plurality of the cells in the exhaust gas purification filter. The partition walls each have an average pore diameter of more than 16 μm and less than 21 μm, and have a ratio of an average surface opening diameter of the pores in a partition wall surface to the average pore diameter of the partition wall of 0.66 or more and 0.94 or less.

A honeycomb filter includes a pillar-shaped honeycomb substrate including a porous partition wall that defines a plurality of cells extending from an inflow end face to an outflow end face, an inflow side plugging portion disposed at the inflow end face of the honeycomb substrate to plug open ends of outflow cells and an outflow side plugging portion disposed at the outflow end face of the honeycomb substrate to plug open ends of inflow cells other than the outflow cells. The honeycomb substrate includes the partition wall that defines two of the inflow cells by division. An average of the plugging length L.sub.IN of the inflow side plugging portions disposed in the outflow cells of the honeycomb substrate is larger than an average of the plugging length L.sub.OUT of the outflow side plugging portions disposed in the inflow cells of the honeycomb substrate.

A honeycomb filter includes a pillar-shaped honeycomb substrate including a porous partition wall that defines a plurality of cells extending from an inflow end face to an outflow end face, an inflow side plugging portion disposed at the inflow end face of the honeycomb substrate to plug open ends of outflow cells; and an outflow side plugging portion disposed at the outflow end face of the honeycomb substrate to plug open ends of inflow cells other than the outflow cells. The honeycomb substrate includes the partition wall that defines two of the inflow cells by division. An average of the plugging length L.sub.OUT of the outflow side plugging portions disposed in the inflow cells of the honeycomb substrate is larger than an average of the plugging length L.sub.IN of the inflow side plugging portions disposed in the outflow cells of the honeycomb substrate.

A plugged honeycomb structure includes a honeycomb structure body, and a plurality of plugging portions, the honeycomb structure body further includes pass-through hole portions each of which is formed in at least a part of a partition wall intersection portion in which the partition walls intersect in one end face and each of which interconnects a pair of cells facing each other at a position corresponding to the partition wall intersection portion to enable pass-through of a fluid, and a value obtained by dividing a diameter of a first virtual inscribed circle inscribed at a position of a minimum hole width of the pass-through hole portion by a diameter of a second virtual inscribed circle inscribed at a position of a minimum plugging width between the plugging portions facing each other is in a range of 0.05 to 0.74.

A plugged honeycomb segment includes a honeycomb segment having a quadrangular prism shape which includes porous partition walls arranged to surround a plurality of cells and an outermost circumferential wall, and a plugging portion, wherein a porosity of the partition walls is 30 to 70%, in a cross section orthogonal to the cell extending direction, an inflow cell surrounded by the partition walls is a hexagon, and an outflow cell is a square, one outflow cell is surrounded by four inflow cells, the cell located at the outermost circumference includes a complete cell and an incomplete cell, and a thickness of the outermost circumferential wall in contact with the incomplete cell (T1), a thickness of the outermost circumferential wall in contact with the complete cell (T2), and a thickness of the partition walls (WT), satisfy 0.200 mm<T1<T2−(½×WT) and T2≤0.700 mm.

A honeycomb filter includes a honeycomb structure body having a porous partition wall disposed to surround a plurality of cells and a plugging portion disposed at one end of the cells, wherein the plurality of cells are arranged in a square grid pattern along a first direction and a second direction in a section orthogonal to an extending direction of the cells, the shape in the section is a deformed square having a specific corner, the specific corner includes a first curved portion, a second curved portion, and a connecting portion, a radius of curvature R1 of the first curved portion and a radius of curvature R2 of the second curved portion are 40 to 80 μm, respectively, and a center distance between a center of curvature O1 of the first curved portion and a center of curvature O2 of the second curved portion is 80 to 200 μm.

An object of the present invention is to provide a honeycomb filter capable of achieving a combination of high collection efficiency and low pressure loss. The honeycomb filter comprises a ceramic honeycomb substrate in which a multitude of cells through which a fluid flows are disposed in parallel in a longitudinal direction and are separated by cell walls, each cell being sealed at an end section at either the fluid inlet side or the fluid outlet side, and a filter layer which, among the surfaces of the cell walls, is formed on the surface of the cell walls of those cells in which the end section at the fluid inlet side is open and the end section at the fluid outlet side is sealed by a sealing material, wherein the thickness of the filter layer increases gradually from the fluid inlet side toward the fluid outlet side.