IMPROVEMENTS IN AND RELATING TO DRIVE MECHANISMS SUITABLE FOR USE IN DRUG DELIVERY DEVICES

摘要

The invention relates to a drive mechanism for use in a drug delivery device comprising: a housing (2) having an internal and an external thread; a piston rod (32) having a non-circular cross section, and which is threadedly engaged with the internal thread of the housing (2); a unidirectional coupling located between the housing (2) and the piston rod (32); a dose dial sleeve (50), which is threadedly engaged with the external thread of the housing (2) and being rotatable with respect to the housing (2); a drive sleeve (60), located between the housing (2) and the piston rod (32), which is axially displaceable but not rotatable with respect to the piston rod (32); and a clutch means located between the drive sleeve (60) and the dose dial sleeve (50). When the dose dial sleeve (50) and the drive sleeve (60) are de-coupled by the said clutch means, rotation of said dose dial sleeve (50) with respect to the said drive sleeve (60) is allowed. When the dose dial sleeve (50) and drive sleeve (60) are coupled by the said clutch means, rotation of the dose dial sleeve (50) with respect to the said drive sleeve (60) is prevented.