US Patent 8171645 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 pair of torsion springs held axially on the blade axis pin and within a pair of bushings are stationary relative to the knife handle. One leg of each spring is fixed to a bushing. The opposite leg of the spring rides in a pocket formed in the surface on the blade axially around the opening through which the blade axis pin is inserted. As the blade rotates from the closed position toward the open position, the legs of the springs rotate through and cooperate with structures formed on the bushings to transfer the spring pressure instantly to the blade to drive the blade open.