Locks – Operating mechanism – Key
Reexamination Certificate
1999-09-14
2001-10-23
Barrett, Suzanne Dino (Department: 3627)
Locks
Operating mechanism
Key
C070S395000, C070S398000
Reexamination Certificate
active
06305200
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to tumbler locks, more particularly, to a device for preventing a key from being inserted into a tumbler lock.
2. The Prior Art
Tumbler locks have a variety of uses, the most prevalent being as building door locks and as automotive ignition and door locks. There are occasions when it is desired to prevent a tumbler lock from being opened, even by the correct key. For example, a worker is given a key to a room that is only to be used during normal business hours. Or a person is loaned a car, but is told not to open the trunk. Or a person renting a locker is behind in his/her rental payments. In all cases, the key will be able to open the lock at any time, but for some reason, the person in possession of the key is to be prevented from doing so. A number of devices have been developed over the years to prevent the correct key from opening a lock, for example, U.S. Pat. No. 1,696,326 issued to Roethlisberger, U.S. Pat. No. 1,728,310 issued to Sundel, U.S. Pat. No. 2,068,936 issued to Unterberg, and U.S. Pat. No. 3,408,842 issued to Barnes et al. The common element of these disclosures is a plug that is inserted into the keyway that prevents any key from being completely inserted.
The plug of Roethlisberger fits into the keyway so that the outer tumblers return to rest on the lower arm of the plug, in front of the upper extension, blocking the plug from being removed. The major shortcoming of this design is that the plug must be long enough so that all of the tumblers drop onto the lower arm. If the arm is too short, the outermost tumblers will drop below the arm, to their normal locked position. If this should happen, the plug cannot be removed, even by the mating extractor, because the extractor cannot be inserted past the outermost tumbler. Another related shortcoming is that the inner end of the keyway must be at least partially closed so that the plug cannot be pushed too far and preventing the outermost tumbler from dropping as describe above.
The plug of Sundel solves the problems of Roethlisberger with an external plate that prevents the plug from being inserted too far into the keyway. However, unlike Roethlisberger, when the plug of Sundel is installed, it is very visible because to the external nature of the plate. Also, the external plate gives a person attempting to remove the plug a point of leverage, which may result in destruction of the lock.
The plug of Unterberg also attempts to solve the problem of being pushed to far into the keyway by using a notch in the upper surface of the plug that the innermost tumbler can fall into. However, because the notch must pass all of the other tumblers, it must be sloped on both sides. So it is still possible for the plug to be pushed too far into the keyway. Unterberg also uses a small external hook that prevents the plug from being inserted too far. However, the hook, like the external plate of Sundel, makes the plug more visible and gives a person leverage in an attempt to remove the plug, which would be relatively easy to do, since there is nothing holding the plug firmly in the keyway.
Unterberg and the plug of Barnes also have the problem that they, like Roethlisberger, must be long enough to extend over all of the tumblers. If the outermost tumbler should drop in front of the plug, the plug could not be removed. The flat end of the upper arm of the plug would be caught against the tumbler and the flat end of the extractor could not be inserted past the tumbler.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a keyway plug for preventing the correct key from opening a tumbler lock.
Another object is to provide a keyway plug that is hidden from casual inspection behind the outermost tumbler in the keyway.
The keyway plug of the present invention provides a means for preventing the correct key from opening a tumbler lock, while overcoming the deficiencies of the prior art. It includes a plug and an extractor. The plug fits into the keyway to block entrance of a key. Its tip is similar to the tip of an ordinary key. An arm extends from the tip along the keyway. Unlike the plugs of the prior art, the arm of the first embodiment of the plug does not have to extend across all of the tumblers. The arm is short enough that the outermost tumbler drops behind the plug, and the height of the arm is less then the height of the tumbler, hiding the plug from casual inspection.
An extractor is used to remove the plug from the keyway. The extractor includes a narrow finger, the upper edge of which includes a hook that mates with a matching hook in the lower edge of the plug arm.
To overcome the problem of the prior art plugs where the outermost tumbler prevents the plug from being removed with the extractor, the innermost part of the lower edge of the arm forms a shaped cutout that slopes downwardly toward the plug tip. The inner end of the extractor finger has a level upper edge. As the extractor is being inserted into the keyway, the end of the extractor forces the plug tip upwardly against the innermost tumblers. The plug will move upwardly because of the play between the keyway and plug. As the plug tip moves upwardly, the central tumblers push down on the plug arm, causing the outer end of the arm to tip downwardly below the level of the outermost tumbler. The outer end of the arm has a chamfer to push the outermost tumbler up out of the way as the plug is being extracted. When the extractor and plug hooks become aligned, the tumblers push the plug back down against the extractor, and when the extractor is pulled from the keyway, the hooks mate to pull the plug from the keyway.
Other objects of the present invention will become apparent in light of the following drawings and detailed description of the invention.
REFERENCES:
patent: 1696326 (1928-12-01), Roethlisberger
patent: 1728310 (1929-09-01), Sundel
patent: 1807540 (1931-05-01), Makranczy
patent: 2068936 (1937-01-01), Unterberg
patent: 2591652 (1952-04-01), Ziegliss
patent: 2662390 (1953-12-01), Michnoff et al.
patent: 3276233 (1966-10-01), Russel et al.
patent: 3408842 (1968-11-01), Barnes et al.
patent: 4120184 (1978-10-01), Gerlach
patent: 5950466 (1999-09-01), Moen
patent: 289878 (1966-09-01), None
patent: 52-15799 (1977-05-01), None
Barrett Suzanne Dino
Morse, Altman & Martin
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