Adjustable stairway having retractable wheel carriage

Claim 1

A portable, adjustable stairway, comprising: a frame; a stair assembly including first and second opposed pairs of tread support bars pivotally coupled to said frame, and a plurality of step treads extending between and pivotally coupled to said first and second pairs of tread support bars; height adjustment means operably, pivotally coupled to said frame and to said stair assembly for shifting said stair assembly from a lowered position to a plurality of raised positions; biasing means for urging said stair assembly away from said lowered position and into said raised positions; and a retractable wheel carriage assembly operably coupled to said frame, said retractable wheel carriage assembly including-- a first carriage member operably, pivotally coupled to said frame along a first pivot axis said first carriage member including a first carriage member lever arm; a second carriage member operably, pivotally coupled to said frame along a second pivot axis, said second carriage member including a second carriage member lever arm; a first wheel assembly operably carried by said first carriage member spaced from said first pivot axis, and a second wheel assembly operably carried by said second carriage member spaced from said second pivot axis, whereby the weight of said stairway urges said first and second wheel assemblies from lowered, ground engaging positions below said frame to raised, ground clearing positions, and locking means for selectively locking said wheel assemblies in said lowered positions; and means operably coupling said first and second lever arms for simultaneous shifting of said first and second wheel assemblies between said lowered and raised positions, said first and second pivot axes being fixed in relative position to each other and said frame, said means operably coupling said first and second lever arms presenting a third pivot axis shiftable relative to said first and second pivot axis.