Seat and its application particularly to a vehicle

A multi-position seat, having at least one normal position and one relaxation position, for a vehicle and comprising a seat part (10) with a framework (11) for a cushion (13), a backrest (20) with a framework (21) for a cushion (23), an underframe (30) adapted to rest the seat on a floor, an articulation (40) making it possible to change the relative positions of these seat part and backrest cushions (13, 23) and of linkage rod means (50) for automatically controlling the relative displacements of these seat part and backrest cushions (13, 23) during the change in their relative positions, wherein said articulation (40) connects said backrest framework (21 ) and said underframe (30) wherein these linkage rod means (50) comprise a connecting rod assembly (51 ) made, on the one hand, of a top connecting rod (511) having a first extremity (5111), which is retained and mounted pivotably relative to said framework (21) of the backrest, and having a free second extremity (5112), and, on the other hand, of a bottom connecting rod (512) having a posterior extremity (5122), which is connected and mounted pivotably relative to said free second extremity (5112) of said top connecting rod (511), and having an anterior extremity (5121), said bottom connecting rod (512) carrying said framework (11) of the seat part, a scissor-type stay (52) made, on the one hand, from an upper branch (521) with one end (5211) which is retained close in the vicinity of said anterior extremity (5121) of said bottom connecting rod (512) and with one free end (5212) and, on the other hand, of a lower branch (522) with one free end (5222) which is connected and mounted pivotably relative to said free end (5212) of said upper branch (521) and with one end (5221) which is retained and mounted pivotably relative to said underframe (30), a cam (56) which has a specific profile, and also a cam follower (57) which interacts with said cam (56), wherein one of said cam (56) and cam follower (57) is associated with said underframe (30), and wherein the other of said cam (56) and cam follower (57) is associated with said top connecting rod (511).