Drive assembly for a drug delivery device and drug delivery device

1. A drive assembly for a drug delivery device, comprising:

a guide nut, the guide nut being rotatable around an axis of the assembly,

a locking means, the locking means being radially movable with respect to the axis in order to engage with the guide nut and to inhibit a rotation of the guide nut,

a body in which the guide nut and the locking means are arranged,

a piston rod,

a cartridge holder that can be attached to and removed from the body, and

a fastener, the fastener being part of or fastened to the cartridge holder and being provided to move the locking means radially with respect to the axis thereby engaging the locking means with the guide nut when the cartridge holder is attached to the body, and to hold the locking means in a position in which the locking means is engaged with the guide nut for drug delivery,

wherein

a screw thread coupling the guide nut and the piston rod enables a helical movement of the piston rod with respect to the guide nut, the helical movement comprising a rotation around the axis and a simultaneous shift along the axis,

the locking means is a resilient element having a first end fastened to the body, the locking means extending in an azimuthal direction from the first end to a second, free end for engaging with the guide nut,

the fastener is a longitudinally protruding part of the cartridge holder, and

the fastener is moved on a circle that is concentric with the guide nut, and is thus made to slide over the locking means and engages the locking means with a structured outer surface of the guide nut by a rotation of the cartridge holder with respect to the body.

2. The drive assembly according to claim 1 , wherein the guide nut is a toothed wheel having notches or interspaces between teeth, and the locking means comprises an edge or a hook engaging the notches or the interspaces.

3. The drive assembly according to claim 1 , wherein the drive assembly is configured such that the locking means is not engaged with the guide nut during a reset operation when the cartridge holder is not attached to the body.

4. The drive assembly according to claim 1 , further comprising: a web of the body inhibiting a movement of the guide nut in a direction of the axis while permitting a rotation of the guide nut around the axis when the locking means is not engaged with the guide nut.

5. The drive assembly according to claim 4 , further comprising: a drive sleeve arranged within the body, the drive sleeve being coupled with the piston rod by means of a further screw thread.

6. The drive assembly according to claim 5 , wherein the screw thread and the further screw thread have opposite senses of rotation.

7. The drive assembly according to claim 5 , further comprising: a clutch, by which the drive sleeve can be rotationally locked with respect to the body in a releasable manner.

8. The drive assembly according to claim 7 , wherein a shift of the drive sleeve with respect to the body along the axis is converted into a helical movement of the piston rod with respect to the body when the drive sleeve is rotationally locked with respect to the body and the locking means is engaged with the guide nut.

9. A drug delivery device comprising the drive assembly according to claim 1 .

10. The drug delivery device according to claim 9 , having a shape of an injection pen.

11. The drug delivery device according to claim 9 , further comprising: a clutch, by which a drive sleeve can be rotationally locked with respect to the body in a releasable manner.

12. The drug delivery device according to claim 11 , wherein the drive assembly is configured such that a shift of the drive sleeve with respect to the body along the axis is converted into a helical movement of the piston rod with respect to the body when the drive sleeve is rotationally locked with respect to the body and the locking means is engaged with the guide nut.