Dose delivery mechanism

Abstract

A dose delivery mechanism includes a piston rod and a nut. The piston rod forms an outer thread meshing with an inner thread of the nut, and during dose setting, the nut is rotated relative to the piston rod to advance the nut with respect to the piston rod by a first distance into a distal direction, an actuation member that is movable by a user to effect delivery of a set dose, and a housing. A second threaded connection is configured to cause the actuation member to travel a second distance into the distal direction during dose setting. The actuation member is coupled via the nut to the piston rod during dose delivery to advance the piston rod by the first distance into a proximal direction upon proximal movement of the actuation member by the second distance, and the second distance is less than 1.5 times the first distance.

Dependencies are inferred from the claim text.