This is connected with a driving mechanism which is suitable for an injection device, particularly a device for Administration of Drugs and pen device with this type of Drug Administration.The driving mechanism comprises a driving rotating Member (120) driven by Spring, a driven rotating Member (40), a Clutch (41121) for coupling the rotationally driven Member (40) and the impeller (120) in a Member State and allow rotation relative to the coupling between the right-wing and left-wing member driven (40) and the driving Member (120) in a State of decoupling, and a Spring (130) predisposing One Clutch (41121) to the coupling State and allows the relative axial Movement between the driving Member and the driven Member (120) (40) Toward the State decoupling Clutch () against the bias of the Spring (130).The Clutch includes a First Ring Tooth Crown (121) in the driving Member (120) and a Second Ring of corresponding Teeth of Crown (41) on the driven Member (40), each Tooth Crown (41, 121) has left and right angles of tooth in Ramp, such Allowing the Teeth (41,121) avoided each other in the State of disengaging the clutch with a different resistance to right or left. The material of the driving Member (120) can be polybutylene terephthalate (PBT) and polyoxymethylene (POM) and the material of the driven rotating Member (40) may be PBT, POM, polycarbonate (PC).In addition, The friction coefficient between teeth (m) (41, 121) can be between 0.13 and 0.07 and teeth (41, 121) may have a surface Roughness (RA) between 0.5 and 1.2.La presente está relacionada con un mecanismo impulsor que es adecuado para un dispositivo de inyección, especialmente un dispositivo de administración de fármacos de tipo bolígrafo y con tal dispositivo de administración de fármacos. El mecanismo impulsor comprende un miembro impulsor rotatorio (120) impulsado por resorte, un miembro impulsado rotatorio (40), un embrague (41, 121) para acoplar rotacionalmente el miembro impulsado (40) y el miembro im
