Vertical back adjust for chairs

Claim 1

A mechanism for vertical adjustability and securement of a backrest of a chair including a housing having a first member and a second member, pivotally attached to each other at one end, said housing defining a passage therethrough adapted to receive the upright support of a chair backrest; a first link assembly disposed within said housing; a second link assembly disposed within said housing and pivotally connected to said first link assembly; said first and second link assemblies movable between a locked position and an unlocked position, said second link assembly engageable with and adjustable by said second housing member; a sleeve member carried by said second link assembly and engageable against the upright support when said first and second link assemblies are in said locked position; a rod carried by said first link assembly and spaced from said sleeve member so as to define a gap therebetween through which the upright support passes; means adapted to connect said second housing member to the chair backrest; resilient biasing means connected between said first link assembly and said second link assembly to urge said first and second link assemblies to assume said locked position, whereby movement of the chair backrest causes said first and second link assemblies to move between said locked and unlocked positions such that when the first and second link assemblies assume a locked position the upright support is gripped between said sleeve member and said rod and when said link assemblies are moved to said unlocked position said second link assembly is pivoted with respect to said first link to increase the gap between said sleeve member and said rod so as to allow vertical repositioning of the housing with respect to the upright support thereby providing vertical adjustability and securement of the chair backrest.