Abstract: A hinge device comprising: a first cheek plate and a second cheek plate meshing with each other, and one of which is designed to be secured to the seat proper while the other is designed to be secured to the seat back, said first cheek plate being provided with a collar and with a non-slit ring fastened to the collar, the collar having an outside surface extending along a first axis, and said second cheek plate having a cylindrical inside surface extending along a second axis parallel to and distant from said first axis; an eccentric mechanism mounted to move in rotation about one axis from among the first axis and the second axis, and interconnecting the first cheek plate and the second cheek plate, said ring being interposed between the collar and the eccentric mechanism; and a control mechanism for turning the eccentric mechanism and for driving the first cheek plate relative to the second cheek plate.