Pick-proof lock

Abstract

A pick-proof lock of the cylinder type primarily intended for use in doors, which includes a locking collar or sleeve slidably mounted around a portion of the cylinder plug and which contains a notch to receive a spring pressed pin which is contained in the cylindrical shell of the lock. The collar or sleeve is slidably and rotatively received in the shell and spring pressed for engagement of its notch with the pin, whereby rotation of the plug within the shell can only be accomplished to effect unlocking of the lock when the spring urged locking collar has been displaced rearwardly of the lock from a projected locking position to a retracted unlocking position. Since the locking collar and the pin which locks said collar to the shell do not communicate with the keyway of the plug, tools and other instruments normally used for picking locks are ineffective in picking the lock.

I claim as my invention: 
     
       1. A key operated lock cylinder including a shell having a longitudinally extending bore, a cylinder plug rotatively mounted in said bore, said shell having longitudinally spaced parallel sockets opening into said bore, spring pressed pin tumblers slidably mounted in said sockets, said plug having a keyway and being provided with radial bores opening into said keyway and outwardly of the plug periphery for alignment with said sockets in one position of rotation of the plug, pin tumblers slidably mounted in said plug bores and extending into the keyway and abutting the pin tumblers of the shell; said shell bore being enlarged beyond an innermost one of said sockets, a rotation limiting pin mounted radially in said shell and extending into said enlarged bore portion in close proximity to a part of the periphery of the plug, a collar slidably mounted on said plug within said enlarged bore portion and having a notch opening outwardly of the forward end thereof in which said rotation limiting pin is received, a compression spring carried by the plug within said enlarged bore portion and bearing against and urging the collar in a forward direction, said collar having a finger projecting into the keyway for non-rotatably connecting the collar to the plug, and a key having a blade notched to cause the pin tumblers to assume unlocked positions and having a forward end for engaging said finger to move said collar rearwardly and out of engagement with the pin to permit the key to rotate the plug within the shell to effect unlocking of the lock. 
     
     
       2. A key operated lock cylinder as in claim 1, a cam secured to the rear end of the plug and disposed against the rear end of the shell, said cam providing an abutment for the rear end of said compression spring. 
     
     
       3. A key operated lock cylinder as in claim 1, said notch having a circumferentially enlarged inner portion and a restricted outer portion opening through the front edge of the collar. 
     
     
       4. A key operated lock cylinder as in claim 1, said forward end of the key being blunt to engage the forward end of the finger. 
     
     
       5. A key operated lock cylinder as in claim 1, the forward end of said finger being disposed substantially in alignment with the innermost pin tumbler. .Iadd. 
     
     
       6.  A key operated lock cylinder comprising: a shell having a longitudinally extending bore;   a plug rotatively mounted in said bore having a keyway including an opening for insertion of a key, said plug having a locked position and an unlocked position;   locking means for restraining said plug in said locked position, said locking means being released when a key corresponding to said locking means is fully inserted into said keyway;   a rotation-limiting pin;   restraining notch means in a labyrinth means operatively associated with said rotation limiting pin to prevent rotation of said plug to said unlocked position;   resilient means for biasing engagement of said pin and labyrinth means to normally hold said rotation limiting pin in said restraining notch means;   said corresponding key displacing the relative positions of said pin and restraining notch means longitudinally of said bore, when said key is fully inserted, so that said pin is out of said restraining notch means and said labyrinth means to allow said plug to rotate to said unlocked position;   said labyrinth means having an enlarged portion constituting said restraining notch means, a restricted end portion, and an opening, said restricted end portion being located near the opening of said labyrinth means, said enlarged portion allowing a limited rotation of said plug when said locking means is released, said restricted end portion preventing the movement of said pin out of said labyrinth means unless said plug is positioned in said locked position. .Iaddend. .Iadd.   
     
     
       7.  The lock cylinder of claim 6, wherein said rotation limiting pin is radially mounted in said shell; and a collar is slidably mounted in said shell and operatively coupled to rotate with said plug, said labyrinth means being formed in said collar. .Iaddend. .Iadd.8. The lock cylinder of claim 7, wherein said labyrinth means is positioned on the edge of said collar nearest the opening of said keyway. .Iaddend. .Iadd.9. The lock cylinder of claim 7, wherein said collar further includes a trigger means positioned such that the end of said corresponding key will strike said trigger means to slide said collar, thereby disengaging said labyrinth means from said pin. .Iaddend. .Iadd.10. The lock cylinder of claim 9, wherein said trigger means is a finger projecting into said keyway from the edge of said collar nearest the opening of said keyway. .Iaddend. .Iadd.11. The lock cylinder of claim 6, further comprising:   a trigger assembly disposed inside said plug and operatively connected to said collar, said trigger assembly having a trigger formed on the end portion of said trigger assembly nearest the opening of said keyway;   said trigger being positioned such that the end of the corresponding key will strike said trigger to slide said trigger assembly and said collar longitudinally of said bore, thereby disengaging said restraining notch means from said pin. .Iaddend.