Inner locking cylinder with captive key

Abstract

A dead bolt lock set is designed to be key actuated on the inside as well as on the outside of the door. For the inside there is an inside tailpiece in engagement with a drive slot in the dead bolt hub. A lost motion circumferential recess on the inside tailpiece provides stops at positions such that when the key is inserted on the inside and turned to lock the dead bolt by action of a micro drive pin, the key cannot be returned in reverse direction to key release position without unlocking the dead bolt. Consequently, the key must remain captive in the inside keyway to keep the dead bolt locked because of being held in the cylinder by the pin tumblers. When the lock has been locked from the outside, the drive slot in the head of the tailpiece is rotated out of line with the inside key slot. Under this condition when unlocking from the inner trim, the tailpiece and washer are forced inward by the key tip compressing the conical spring and allowing full key insertion. Bolt retraction (unlocking) may be accomplished by rotation of the key in the bolt extended direction until the key tip aligns with the tailpiece drive slot, then rotating the key back to the vertical (withdrawn) position, or, in the alternative, rotating the key in the retract direction, whereby the micro pin contacts the lost motion stop on the tailpiece head thereby driving the mechanism to the retracted position. The captive key mechanism is fail safe in that in the event the conical spring fails to return the tailpiece to a position abutting the end of cylinder plug for captive kay operation, the mechanism will still function as a standard cylinder allowing normal locking and unlocking.