US Patent 6938911 Folding wheelchair

A folding wheelchair includes two side frame units arranged in parallel at two sides, each side frame unit formed of two four-bar linkages arranged at different elevations, a plurality of folding bars transversely coupled between the side frame units, two sets of guide rods respectively coupled to the side frame units and adapted to guide folding of the wheelchair between the extended position and the collapsed position, and two swivel hooks for hooking on the pivot between each set of guide rods to lock the wheelchair in the extended position.