Dose limiting mechanism

Abstract

An injection device comprises a dose selector, rotatable by a user to set a dose to be ejected from the injection device and a drive assembly including a drive shaft () and a plunger element (), the drive assembly being capable of providing an axial force for ejecting a dose of medicament from a medicament container. A dose limit nut () is provided which is rotationally coupled to but not axially coupled to said drive shaft. The plunger element is threaded so that the dose limit nut is engaged with said plunger element via said thread, in order to guide relative axial movement between the dose limit nut and the plunger element. The dose limit nut is provided with dose limiting endstops which are capable of limiting axial travel of said dose limit nut with respect to said plunger element, so as to limit maximum and minimum doses of medicament which can be set by the user. In addition, the dose limit nut comprises a last dose rotary endstop feature which prevents further rotation of said dose limit nut with respect to said drive shaft so as to prevent the user setting a dose that is greater than an injectable volume of medicament remaining in said medicament container.