Autoinjector with an inner plunger which disengages the outer plunger to retract the syringe carrier

1. An autoinjector comprising:

a case;

a chassis slidably arranged in the case, the chassis configured to rotate relative to the case;

a syringe carrier operably coupled to the chassis;

an outer plunger selectively engaged to the chassis;

an inner plunger selectively engaged to the outer plunger; and

a drive spring applying a biasing force to the outer plunger, the biasing force being applied to the inner plunger when the inner plunger is engaged to the outer plunger,

wherein the rotation of the chassis relative to the case causes the inner plunger to rotate relative to the outer plunger and disengage the outer plunger to remove the biasing force from the drive spring on the inner plunger, and

wherein, when the inner plunger disengages the outer plunger, the biasing force of the drive spring pushes the chassis to retract the syringe carrier relative to the case.

2. The autoinjector according to claim 1 , further comprising:

a needle shroud slidably arranged in the case, wherein axial movement of the needle shroud relative to the case causes rotation of the chassis relative to the needle shroud.

3. The autoinjector according to claim 1 , further comprising:

a firing nut rotatably disposed on the chassis, the firing nut engaging the outer plunger when in a first angular position and disengaging the outer plunger when in a second angular position.

4. The autoinjector according to claim 3 , wherein the case includes a stem adapted to rotate the firing nut from the first angular position to the second angular position.

5. The autoinjector according to claim 4 , wherein, when the firing nut is in the second angular position, the biasing force of the drive spring pushes the outer plunger in a distal direction relative to the case.

6. The autoinjector according to claim 2 , wherein the needle shroud includes a guide track adapted to engage a pin on the chassis.

7. The autoinjector according to claim 6 , wherein the pin moves from an angled portion to an axial portion of the guide track causing rotation of the chassis relative to the needle shroud when the needle shroud translates relative to the case.

8. The autoinjector according to claim 1 , further comprising:

a coupling carrier coupled to the syringe carrier and selectively engaged to the inner plunger.

9. The autoinjector according to claim 8 , wherein the coupling carrier includes resilient arms adapted to releasably engage the inner plunger, and wherein the biasing force of the drive spring causes the inner plunger to deflect the resilient arms when a front stop on the syringe carrier abuts a shroud shoulder on the needle shroud.

10. The autoinjector according to claim 9 , wherein, when the resilient arms disengage the inner plunger, the inner plunger is adapted to push a stopper in a syringe.

11. The autoinjector according to 8 , wherein the chassis includes a resilient clip adapted to engage a stop on the coupling carrier.

12. The autoinjector according to claim 11 , wherein, when the biasing force of the drive spring pushes the chassis, the clip engages the stop and retracts the coupling carrier and the syringe carrier relative to the case.

13. The autoinjector according to claim 2 , further comprising:

a control spring axially biasing the needle shroud relative to the case.

14. The autoinjector according to claim 4 , wherein rotation of the chassis relative to the needle shroud causes rotation of the firing nut to a third angular position in which the firing nut is adapted to advance over the stem.

15. The autoinjector according to claim 2 , wherein the needle shroud includes a resilient non-return clip adapted to engage the case and prevent translation of the needle shroud relative to the case.