Seat structure

A seat structure comprising:

• a seat back section provided with an elastic supporting mechanism for a seat back which supports a cushioning member arrangement frame for a seat back provided for arranging a cushioning member for a seat back such that the cushioning member arrangement frame for a seat back can be displaced according to load fluctuation to the cushioning member for a seat back;
• and
• a seat cushion section provided with an elastic supporting mechanism for a seat cushion which supports a cushioning member arrangement frame for a seat cushion provided for arranging a cushioning member for a seat cushion such that the cushioning member arrangement frame for a seat cushion can be displaced according to load fluctuation to the cushioning member for a seat cushion, wherein
• the seat cushion section is provided with a platform frame and a parallel linkage having a front link portion and a rear link portion which are disposed in the vicinity of a front portion of the platform frame and in the vicinity of a rear portion thereof, respectively,
• the cushioning member arrangement frame for a seat cushion is provided with a front portion supporting frame disposed between a pair of front link portions of the parallel linkage and a rear portion supporting frame disposed between a pair of rear link portions of the parallel linkage,
• the elastic supporting mechanism for a seat cushion is provided with a torsion bar coupled to at least one of a rotation center of the front link portion and a rotation center of the rear link portion,
• the front link portion and the rear link portion of the parallel linkage are attached such that positions of the front portion supporting frame and the rear portion supporting frame supported by the front link portion and the rear link portion are displaced obliquely forward and downward at a load applying time while being displaced obliquely backward and upward at a load removing time,
• a cushion pan with flexibility for supporting the cushioning member for a seat cushion which is supported by the front portion supporting frame and the rear portion supporting frame is disposed at a lower portion of the cushioning member for a seat cushion,
• the cushion pan includes a hole portion formed at a site including a position corresponding to at least an ischial tuberosity of a person,
• the cushion pan is provided with a front portion engagement portion engaged with the front portion supporting frame and a rear portion engagement portion engaged with the rear portion supporting frame, and the cushion pan is provided such that, when load pressing a front edge portion of the cushion pan at a leg stretching time of a person acts on the cushion pan, the cushion pan is rotated about the front portion supporting frame such that a portion of the cushion pan positioned on the side of a hip of a person rises upwardly,
• the front portion engagement portion comprises a pair of plate springs projecting from the cushion pan downwardly such that the plate springs can clamp the front portion supporting frame, and
• the rear portion engagement portion is formed of a plate spring having a bent portion obtained by bending a base plate portion joined to a lower face of the cushion pan downward and then bending the same backward, where the bent portion is inserted below the rear portion supporting frame so that the rear portion supporting frame is clamped between the bent portion and the lower face of the cushion pan.