Seathinge

Claim 1

A seat-hinge for connecting the back to the sitting portion of a seat and comprising a first member to be fixed relative to the sitting portion and carrying a first toothed sector centered on an axis A, said axis A extending, in operation, horizontally and transversely of the sitting portion, a second member to be fixed relative to the back and carrying a second toothed sector centered on an axis B parallel to axis A, the sectors being engageable and disengageable with one another in response to movement of the two axes A and B towards and away from coincidence and the second member being provided with an opening which is centered on axis B and houses a hub; a rotary cam fixed to said hub, a control handle accessible, in use, to a person sitting on the seat and linked to the cam so that the operation of this handle causes rotation of the cam about axis B, a surface defined by the first member for coacting with an active area of the rotary cam, and a spring means for angularly urging the cam and the handle in the direction which corresponds to the mutual engagement of the two toothed sectors, the active area of the rotary cam being formed by an outward projection from the remainder of the rim of the cam and the radially outermost surface of the projection having the form of an arc of a spiral about axis B and having ends of greater and smaller radius which are joined to the said remainder of the rim by a narrower neck portion such that at least the said end of the greater radius overhangs the adjacent portion of the said remainder of the rim of the cam, the surface defined the first member for coacting with the active surface of the cam forming part of the edge of an aperture in the first member and having a first section in the form of an arc of a spiral about axis A upon which, in operation, the spiral arc surface of the cam projection slides and against which said surface of said cam projection then jams, responsive to rotation of the cam in a first direction, so as to lock the hinge, and an adjacent cut-out section providing a bearing zone against which the said end of greatest radius of the spiral arc surface of the cam projection bears, responsive to reverse rotation of the cam, to unlock the hinge such that, in operation, the cam rocks about this bearing zone to cause axes A and B to move apart and disengage the toothed sectors.