Dose delivery device with gearing

A dose delivery device comprising:

• a housing;
• a piston rod configured to move axially without rotation relative to the housing, the piston rod comprising a piston rod thread;
• a nut engaging the piston rod thread;
• a dose selector rotationally locked to the nut;
• a connector configured to move axially without rotation relative to the housing;
• a first gear configured to rotate without axial movement relative to the housing, the first gear being coupled to the connector by a first engagement, the first engagement being a first helical thread;
• and
• a second gear coupled to the nut so as to permit relative rotation but not relative axial movement between the second gear and the nut, the second gear being coupled to the connector by a second engagement and to the first gear by a third engagement,
• wherein the third engagement is a straight track, which permits relative axial movement but prevents relative rotation between the first and second gears.

A method of operating a dose delivery device, which comprises a housing and a piston rod configured to move axially without rotation relative to the housing;

• the method comprising:
• in a dose setting mode, rotating a dose selector relative to the housing, the dose selector being rotationally locked to a nut, which thereby moves in a backward direction along a thread of the piston rod through a first axial distance;
• and
• transmitting the axial movement of the nut through a gearing mechanism to a connector that is configured to move axially without rotation relative to the housing, such that the connector moves in the backward direction from an initial position through a second axial distance greater than the first axial distance;
• wherein the gearing mechanism comprises:
• a first gear that rotates without axial movement relative to the housing, the first gear being coupled to the connector by a first engagement, the first engagement being a first helical thread;
• and
• a second gear coupled to the nut so as to permit relative rotation but not relative axial movement between the second gear and the nut, the second gear being coupled to the connector by a second engagement and to the first gear by a third engagement.