Patent ID: 8197450

Claim:
An injection device comprising: a. a housing for a dose setting and injecting mechanism, the housing having a proximal end and a distal end, b. a rotatable dose setting member, c. an axially displaceable piston rod having a first thread and an additional longitudinally extending helical track, d. a central opening in the housing for engaging the additional longitudinally extending track of the piston rod, thus guiding the angular movement of the piston rod during axial translation of the piston rod, e. a threaded nut engaging the first thread of the piston rod, the nut being rotatably locked to the dose setting member during dose setting, f. a rotational coupling mechanism having a coupling member which is axially displaceable from a first position to a second position, the rotational coupling mechanism allowing angular movement of the nut relative to the coupling member during dose setting while preventing angular movement between the nut and the coupling member during injection, wherein the coupling member is angularly coupled to the housing so as to be forced to move angularly as a function of axial displacement of the coupling member relative to the housing during at least a part of the axial displacement from said first to said second position.