Patent attributes
In a seat back structure, an auxiliary frame having a pressure receiving portion and a headrest mounted thereon is movably provided in seat back frame via guide element and link element. The guide and link elements are respectively disposed in upper and lower portions respectively of the auxiliary and seat back frames. Biasing element is provided to the link element, such that a line of force of the former is positioned on one side of a pivotal point of the link element, thereby retaining the headrest at initial position, and that, when excessive backward load is applied to the pressure receiving portion, the link element is rotated to displace the line of force toward another side of the first pivotal point, whereby the auxiliary frame is displaced forwardly and upwardly of the seat back frame, thereby causing the headrest to move to a position for supporting a head of seat occupant.
