Vehicle seat structure incorporating a seat belt

Vehicle seat structure incorporating a seat belt in which a diagonal strap of the seat belt coming from a winder passes through a strap guide ring fixed to an upright of a backrest armature, while a lap strap and a locking tongue are fixed to a seat part armature, in which structure the backrest armature is composed of two uprights which, joined together by at least one crosspiece are joined to the seat part armature by a fixed or articulated connection, wherein at least the upright of the backrest armature secured to the strap guide ring consists of a section piece extruded in lightweight metal alloy, composed of a tubular body reinforced by structural members that create latero-posterior longitudinal box sections, this tubular body receiving, in its region for fixing to a crosspiece, and by inter-fitting, an insert with a transverse bore which coincides with transverse bores formed in this upright, whereas each of the ends of the crosspiece passing through one or other of the uprights and the corresponding insert is connected to this upright in terms of translation by its end being folded back against the outer face of the upright and by a circular ridge formed on it being pressed against the inner face of this upright, and is connected in terms of rotation by radial deformations forming notches and penetrating the corresponding insert.