US Patent 8375590 Knife blade opening mechanism

A folding knife incorporates an opening assist mechanism that functions to drive the blade from the closed to the open position. A torsion spring is retained axially on the blade axis pin and within a bushing that is stationary relative to the knife handle. One leg of the spring is fixed relative to the handle. The opposite leg of the spring extends through and rides in a partial annular groove in the bushing and acts on the blade as it is moved between the open and closed positions.