Mechanical chair-height control mechanism

Claim 1

In a chair having a seat means, a base assembly having an upwardly projecting pedestal defining a central opening which projects vertically downwardly thereof, a vertically elongated spindle which is at least partially externally threaded and has the upper end portion thereof nonrotatably connected to said seat means, the lower portion of said spindle being rotatably supported within the central opening of said pedestal, and a load-released height-adjusting mechanism coacting between said spindle and said pedestal for permitting the seat means and spindle to be vertically displaced a preselected distance between a raised position when the seat means is unoccupied and a lowered position when the seat means is occupied, said height-adjusting mechanism permitting free rotation of the seat means when the latter is occupied and is in said lowered position, said height-adjusting mechanism permitting the height of said seat means to be vertically adjusted relative to the pedestal when the seat means is in said raised position and the unoccupied seat means is rotated relative to the pedestal, said height-adjusting mechanism including a nut threadably engaged with said spindle and sprinig-urged upwardly toward said raised position, said height-adjusting mechanism also including a clutch means for nonrotatably connecting the nut to the pedestal when in said raised position, the nut being disengaged from the clutch means when in said lowered position, the improvement wherein said clutch means comprises a one-piece clutch member having an annular clutch plate positioned above said nut in surrounding relationship to said spindle, said clutch means also including a sleevelike part which is concentrically fixed to said clutch plate and projects axially downwardly therefrom in surrounding relationship to said spindle, said sleevelike part concentrically surrounding said nut and projecting axially downwardly therefrom in concentric surrounding relationship to the upper end of said pedestal, and coupling means coacting between said sleevelike part and said pedestal for defining a bayonet-type connection therebetween for stationarily coupling said clutch member to said pedestal, said bayonet-type coupling means including a first plurality of locking flanges which are fixed to and project radially outwardly from said pedestal in circumferentially spaced relationship therearound so as to define recesses between circumferentially adjacent locking flanges, said coupling means also including a plurality of circumferentially spaced, radially inwardly projecting locking tabs formed on said sleevelike part adjacent the lower free end thereof, said locking tabs being angularly spaced apart by intermediate spaces, said sleevelike part also having annular shoulder means formed internally thereof and directed axially downwardly, said shoulder means being spaced directly axially above said locking tabs for defining a narrow groove therebetween in which to accommodate said locking flanges.