Tilt control mechanism, particularly for knee-tilt chair

Claim 1

In a pedestal-type chair having a base assembly provided with a vertically upwardly projecting pedestal thereon, a seat structure disposed adjacent the upper end of the pedestal, and a knee-type tilt mechanism operatively connecting the seat structure to the pedestal for permitting tilting of the seat structure relative to the pedestal about a substantially horizontally extending tilt axis which extends sidewardly of the seat structure and is disposed in close proximity to the front edge thereof, said tilt axis being positioned forwardly from and in nonintersecting relationship to a vertical axis defined by the pedestal, the knee-tilt mechanism including a housing structure which is mounted on the pedestal and pivotally supports thereon a support structure for relative tilt therebetween about the tilt axis, the support structure being fixedly secured to the seat structure, and spring means coacting between said housing and support structures for imposing a restoring torque on the seat structure which normally maintains the seat structure when unoccupied in a substantially zero-tilt position, said seat structure being tiltable rearwardly about the tilt axis relative to the pedestal through a predetermined maximum tilt angle, comprising the improvement wherein said knee-tilt mechanism includes means responsive to the tilt of said seat structure for causing the restoring torque to increase according to a first predetermined pattern as the seat structure moves from the zero-tilt position to an intermediate position and for thereafter causing the restoring torque to change according to a second predetermined pattern as the seat structure tilts from said intermediate position to said maximum tilt angle so that the restoring torque generated according to said second predetermined pattern is less than the restoring torque which would be generated if the first predetermined pattern was extended from said intermediate position to said maximum tilt angle, said responsive means including cam-and-follower means coacting between said housing and seat structure, said cam-and-follower means including a cam nonrotatably mounted on one of said structures and a follower nonrotatably mounted on the other of said structures, said follower being supported on said other structure for movement relative thereto along a direction which is generally parallel with said tilt axis, said spring means normally urging said follower into engagement with a cam surface which is defined on said cam, said spring means and said cam-and-follower means cooperating to cause said restoring torque to increase at a first rate per degree of tilt as the seat tilts from said zero-tilt position to said intermediate position, and said spring means and said cam-and-follower means cooperating to cause said restoring torque to increase at a second rate per degree of tilt as the seat structure moves from said intermediate position to said maximum tilt position, said second rate being substantially smaller than said first rate.