Device for locking and unlocking two mechanical members by means of a bistable elastic element

A unit comprising two mechanical members (2, 3) and a device for locking and unlocking the two mechanical members (2, 3) wherein the two mechanical members are coupled for rotation to form the unit (1) by means of a splined coupling (30, 33), said device comprising elastic means (36) secured to a first member (2) of said two members (2, 3) and adapted for co-operation with a second member (3) of said two members (2, 3), characterised in that said elastic means (36) comprise a bistable elastic element (36) having first (50) and second (52) alternative steady positions, said bistable elastic element being provided with hooking means (46, 48) adapted for co-operating in said first position (50) with said second member (3) to keep said members axially coupled, and for disengaging in said second position (52) from said second member (3) to allow separation of members (2, 3) forming said coupled unit (1) said bistable elastic element (36) consists of a metallic diaphragm of substantially cup-like circular disc shape (36) adapted to elastically deform for alternatively reaching two steady positions (50, 52) upon being subjected to axial forces of alternative, opposite directions wherein said hooking means (46) consist of a number of hooks (48) axially folded and projecting from a surface of said cup-like circular disc shape (36), said hooks being angularly equally spaced on a circumference concentric and adjacent to an outer edge (38) of said disc (36), said hooks being so shaped as to engage a circular rim (47) disposed within an end (24) of said second mechanical member (3) when said disc is in said first steady position (50).