Patent ID: 8020934

Claim:
A chair backrest elevating device comprising: a slide base formed with a slide way, said slide way provided with a recessed hole and a positioning rod with an opening, said slide base having two opposite sides respectively bored with a plurality of insert holes; an adjusting unit combined with said positioning rod of said slide base, said adjusting unit composed of a sustaining member, a movable block, a spring, a positioning block and an elastic retainer, said sustaining member disposed with two slot ways and a groove formed between said two slot ways, said movable block and said positioning block orderly received in one of said two slot ways, said spring positioned between said movable block and said positioning block to push and prop them up, said positioning block bored with an insert hole, said elastic retainer positioned in said groove between said two slot ways, said elastic retainer having one end forced in said insert hole of said positioning block and another end resisting against an inner wall of another said slot way; a fixing plate unit combined with said slide way of said slide base, said fixing plate unit composed of a fitting block and a fixing plate, said fitting block bored with an adjusting opening having one side formed with a plurality of engage grooves vertically, said adjusting opening further having an upper end formed with a stop wall and a lower end provided with a beveling surface, said fitting block having two opposite edges respectively fixed with lots of bent bars respectively formed with a projecting edge, said fixing plate having an upright portion provided with a fitting opening and a flat portion bored with plural insert holes; and a slide cover covering both said adjusting unit and said fixing plate unit and assembled with said insert holes of said slide base, said slide cover provided with plural projections respectively fitted thereon with a soft ring, said slide cover bored with a positioning hole in the center, said slide cover further disposed with plural insert holes at two opposite sides and a threaded hole between every two said insert holes.