Gearbox

Auto-injector for administering a dose of a liquid medicament (M), the auto-injector having a distal end (P) and a proximal end (D) with an orifice to be applied against an injection site and comprising:

• an elongate housing arranged to contain a syringe with a hollow needle and a stopper for sealing the syringe and displacing the medicament (M), wherein the syringe is slidably arranged with respect to the housing;
• a drive spring capable of, upon activation:
• pushing the needle from a retracted position into an advanced position through the orifice and past the proximal end (P), and
• operating the syringe to supply the dose of medicament (M), wherein a shroud is arranged at least partially inside the housing, the shroud slidable in longitudinal direction between at least a retracted position, in which the needle is exposable and an advanced position, in which the needle is covered by the shroud, wherein the shroud is arranged to be locked in the retracted position prior to manual operation of the drive collar and wherein the shroud is arranged to be pushed towards the advanced position by a syringe spring when the drive spring has been released, wherein the shroud is slidable from the retracted position in distal direction (D) into an unlocking position by a small distance against the bias of at least one flexural element, wherein a plurality of protrusions are arranged to allow the drive collar to be operated only, when the shroud is in the unlocking position, wherein the a plurality of protrusions are arranged to prevent the drive collar from being operated otherwise
• a drive collar arranged to lock the drive spring in a compressed state prior to manual operation and capable of, upon manual operation, releasing the drive spring for injection, and
• a gearbox arranged between the drive spring and the syringe or the stopper.