A lock comprising an inner handle assembly, a latch assembly having a latch bolt, and an outer handle assembly, the outer handle assembly comprising:
- an outer handle;
- an outer rose including an axial hole for pivotally receiving an end of the outer handle, the outer rose further including at least one post for connection with the inner handle assembly;
- a lock core set mounted in the outer handle and including a lock core that is actuatable by a key to turn, the lock core having a tailpiece;
- an outer spindle including a first end connected to the outer handle to turn therewith and a second end including at least one positioning slot;
- an actuating sleeve rotatably mounted in the outer spindle, the actuating sleeve including a hole on an end thereof, the tailpiece extending through the hole of the actuating sleeve, the hole being so configured that the actuating sleeve is turned when the lock core and the tailpiece are turned, the actuating sleeve and the outer spindle being so configured that longitudinal movement of the actuating sleeve relative to the outer spindle is not allowed, the actuating sleeve further including at least one guide slot each having an inclined section and a horizontal section;
- a locking plate mounted in the actuating sleeve and including at least one wing, the wing being extended through the guide slot into the positioning slot of the outer spindle, the wing being retainable by the horizontal section of the guide slot, the wing being driven by the inclined section of the guide slot to allow longitudinal movement;
- an unlatching member including a first end releasably engaged with the locking plate to allow or prevent joint rotation of the unlatching member and the locking plate, the unlatching member further including a second end operably connected to an inner handle of the inner handle assembly, the unlatching member being operably connected to the latch bolt such that rotation of the unlatching member causes retraction of the latch bolt;
- a cap fixed to the second end of the outer spindle and including a hole through which the unlatching member extends, the hole of the cap allowing free rotation of the unlatching member;
- wherein when the lock is in an unlocked state, the first end of the unlatching member is engaged with the locking plate to allow joint rotation;
- and
- wherein when the lock is switched from the unlocked state to a locked state, said wing of the locking plate is guided by the inclined section of the guide slot, and then retained in the horizontal section the guide slot, the locking plate being moved away a predetermined longitudinal distance and thus disengaged from the first end of the unlatching member to prevent joint rotation such that the unlatching member is can not be turned to avoid destruction caused by an exerted force when the outer handle is separately turned and idled while the lock is in the locked state.