Position damping device for a window blind

A position damping device for a window blind, being applied to a window blind with slat being expanded and collected horizontally, resulting in damping to a pull cord effectively to define a height position of the slat when the slat is lowered down at any height, comprising

• a machine part which is formed by two base plates combined up and down, with two ends of the machine part being provided with an opening to connect the interior;
• a spring scroll wheel, an axis of which is vertically pivoted on the base plate in the abovementioned machine part, with the spring scroll wheel including a reed to link a power wheel and a feedback wheel, and with the power wheel and the feedback wheel being gnawed outward with two release idlers to release and collect a pull cord;
• and
• a longitudinal surface, which is protruded with a straight-bar shaped damping shear pillar having a shear ridge, with a longitudinal line of the damping shear pillar being parallel to the axis of the release idler, with the damping shear pillar being disposed vertically on a base plate between an opening and an outer circumference of the release idler in an outlet direction of a slot, and a planar angle of the provided shear ridge facing toward the overrun passage of the pull cord in work.