Patent ID: 7021712

Claim:
A chair, comprising: a) a hollow tubular seat frame, having at least two spaced apart open ends; b) a hollow tubular backrest frame, having a pair of spaced apart open ends aligned with and pivotally connected to the open ends of the seat frame at fixed pivot points; c) a stop bar, having a back side disposed within one of the seat frame and the backrest frame; d) a limit stop, disposed internally within at least one of the seat frame and backrest frame, having a stop surface, configured to abut the back side of the stop bar, to prevent rotation of the backrest frame relative to the seat frame beyond a maximum backwardly rotated position; e) a substantially solid elongate spring element, extending from within each open end of the backrest frame into the corresponding open end of the seat frame, configured to bias the backrest frame in the upright position, and to resiliently resist backward rotation of the backrest frame; f) a spring retainer, having a receiving slot, disposed within each open end of the hollow tubular seat frame, a forward end of he spring element being disposed within the receiving slot; and g) a cam surface, disposed below the spring element, configured to provide a rearwardly-moving fulcrum point for the spring element, so as to increase the effective flexural resistance of the spring element as the backrest is rotated backwardly.