Backrest articulation with a sequenced variation of the angular position.

The device comprises a ring gear (21) having a stepped segment with two convex faces, each defining an angular sequence. A ratchet (32) has a tooth (35) that follows the convex faces until being supported against the stop surface. A plate (40) pivots the ratchet at an angle so that the tooth disengages from an angular stop to allow passage of a seat from one sequence to another sequence.