Patent attributes
An axial spring balancing pin tumbler lock includes a cylindrical shell, a plug rotationally disposed within the shell and rotatable by a tubular key. The shell contains a plurality of first pin bores annularly and evenly defined to the axis of the shell for receiving first pins and first springs. The plug has a through aperture for engaging with a elongated spindle, a key bore coaxially defined on front end for receiving the tubular key, a plurality of third pin bores annularly and evenly defined on front end with same depth of the key bore for receiving third pins, and a plurality of second pin bores defined on rear end of the plug for receiving second pins and second springs. Each second pin may contacts the tubular key and one of third pins simultaneously. The extension force of the second spring at its preloaded length is stronger than that of the first spring at its fully loaded length so both second pin and third pin are urged by compound extension force to their most extended position while the first pin is at its most retracted position. The extended third pins bridge the shear plane of the lock, the plug is then blocked from rotating. Since the third pins are isolated from the opening keyway and are not driven by key notches or external force directly, the conventional lock picking or bumping methods must fail.
