Suspension device for vehicle seat

A suspension device for a vehicle seat, which includes an upper frame, on which is mounted said seat, a lower frame fixed on a floor of the vehicle, a pair of X-shaped links interposed between said upper and lower frames, each of said pair of X-shaped links being essentially composed of a first link member and a second link member which are pivotally connected together, cross-wise, at their respective central pivot points, and a vertically active elastic means for resiliently acting on said X-shaped links to produce a vertical elasticity to said pair of X-shaped links, wherein in said first and second link members, either one pair of ends of both first link members or one pair of ends of both second link members are pivotally fixed at one of said upper and lower frames, while all other ends of said first and second link members are movably fitted in the corresponding upper and lower frames, wherein at least one of said upper and lower frames includes a pair of lateral frame sections each having a channel cross-section, wherein a slide frame is interposed and movably fitted in said lateral frame sections, such that both lateral frame sections of said slide frame are fitted within the respective lateral frame sections, and provided with at least one pair of rollers which are free to roll in said respective lateral frame sections of said at least one of said upper and lower frames, thereby allowing said slide frame to be movable along a longitudinal direction of one of said upper and lower frames, wherein one pair of said all another ends of said first and second link members are pivotally connected to said slide frame, and wherein said lateral frame section of said one of said upper and lower frames is formed with a cut-away portion, wherein said slide frame has, provided at said lateral frame section thereof, a support plate whose one end extends through said cut-away portion to project above said one of said upper and lower frames, wherein there is provided a fore-and-aft active elastic means for resiliently acting on said slide frame to give the same an elasticity forwardly and backwardly in said longitudinal direction of said one of said upper and lower frames, said fore-and-aft active elastic means comprising a pair of first and second spring means and a rod fixed on said lateral frame section associated with said one of said upper and lower frames, wherein one end of said support plate is slidably connected to said rod, with such an arrangement that said first and second spring means are so attached around said rod that they are disposed symmetrically relative to said one end of said support plate, whereby said first spring means acts to give an elasticity to a forward movement of said slide frame, while said second spring means acts to give an elasticity to a backward movement of said slide frame, thereby urging said slide frame in the forward and backward directions.