Safety lock for pivoted seat backs

Claim 1

IN A SEAT ASSEMBLY INCLUDING A SEAT, A SEAT BACK, AND SPACED PAIRS OF PIVOT BRACKETS ON THE SEAT AND SEAT BACK, ONE BRACKET OF EACH PAIR BEING MOUNTED ON THE SEAT AND THE OTHER BRACKET OF EACH PAIR BEING MOUNTED ON THE SEAT BACK, AND EACH PAIR OF PIVOT BRACKETS HAVING ALIGNED PIVOT OPENINGS THEREIN ADAPTED TO RECEIVE A PIVOT SHAFT FORMING THE AXIS OF PIVOTAL MOVEMENT OF THE SEAT BACK RELATIVE TO THE SEAT: THE COMBINATION THEREWITH A SAFETY LOCK FOR THE SEAT BACK, COMPRISING A PIVOT SHAFT EXTENDING SLIDABLY THROUGH THE PIVOT OPENINGS OF AT LEAST ONE OF SAID PAIRS OF PIVOT BRACKETS FOR LONGITUDINAL ADJUSTMENT BETWEEN LOCKING AND UNLOCKING POSITIONS, LOCKING MEANS ON THE PIVOT SHAFT AND ASSOCIATED PIVOT BRACKETS ARRANGED FOR MUTUAL ENGAGEMENT IN THE LOCKING POSITION OF THE PIVOT SHAFT TO SECURE THE SEAT BACK AGAINST PIVOTAL MOVEMENT RELATIVE TO THE SEAT AND FOR MUTUAL DISENGAGEMENT IN THE UNLOCKING POSITION OF THE PIVOT SHAFT TO RELEASE THE SEAT BACK FOR PIVOTAL MOVEMENT RELATIVE TO THE SEAT, AND OPERATOR MEANS ON THE SHAFT FOR MOVING THE LATTER.