US3479850A - Master key attachment - Google Patents

Description

NOV- 25, J. K F

MASTER KEY ATTACHMENT Filed June 10, 1968 nvmewroe Jun K. FR YE nited States Patent 11.8. Cl. 70-447 12 Claims ABSTRACT OF THE DISCLOSURE A master key attachment is provided for turning a door key in a door lock to permit the door to be locked and unlocked with a master key. The attachment is secured to the look by fastening means which may be released only by a special tool and contains a master lock which operatively engages the door key in such a way that rotation of a master key in the master lock rotates the door key and the door lock. A primary advantage of the attachment resides in the fact that the door key may be removed only by authorized persons having the special tool required to release the attachment from the lock.

BACKGROUND OF THE INVENTION Field of the invention This invention relates generally to locks and more particularly to a novel master key attachment for a door lock.

Prior art When a private residence or other property is offered for sale through a real estate broker, the listing broker commonly obtains a key to the premises so that he may have free access to the property in the owners absence for the purpose of showing the same to prospective purchasers. However, possession of a single key by the listing broker creates an inconvenience for the reason that free access to real estate property for sale must generally extend to a number of different persons including, perhaps, several agents of the listing broker and, in the case of a multiple listing, the agents of other brokers.

At the present time, this problem is resolved by the use of a master key box which is secured to a part of the premises to be sold, for containing a door key to the premises. The key box has a closure with a master lock for which the listing broker retains a number of master keys. The box is strongly constructed in such a way that access to the door key within the box may be had only by unlocking the closure with one of the master keys. When a property is listed for sale, the listing broker attaches the key box to a part of the premises and places the door key inside the box. The master keys to the box are then distributed or otherwise made available to the brokers agents and other agents who desire to show the premises.

While such a master key box resolves the problem of inconvenience resulting from the availability of only a single door key to a property to be sold, use of the box often creates another problem. This latter problem resides in the fact that a real estate agent, after showing a property to a prospective purchaser, may neglect to return the door key to the master key box, either through inadvertence or through deliberate action in order to prevent an anticipated sale of the property to an interested purchaser from being lost due to sale of the property by another agent. In this latter regard, it is significant to note that such unethical practice of retaining the key to a listed property to be sold in order to protect an anticipated sale of the property is quite widespread and has incurred the displeasure of the FHA and other state real estate regulatory agencies who are quite concerned about See the problem. These agencies are currently seeking ways to prevent the practice.

The present invention provides a master key attachment for a lock which is primarily designed to replace the master key box discussed above and which avoids the above-noted and other disadvantages of such key boxes. However, it will become readily evident as the description proceeds that the present master key attachment may be used for purposes other than as a replacement for a master key box and may be employed to advantage by persons other than real estate brokers.

In general terms, the present master key attachment comprises a housing and a master lock carried by the housing. The housing is equipped with fastening means for securing the housing to a door lock, or the like, in such a way that the housing may be removed only with the aid of a special tool or key. The master lock embodies a master key-operated means, such as a cylinder, which is rotatable by rotation of a master key in the master lock. When the attachment is installed on a door lock containing a door key, the master lock cylinder operatively engages the door key in such a way that rotation of the cylinder by the master key rotates the door key in the door lock to lock and unlock the door. According to an important feature of the invention, the attachment is so uniquely constructed and arranged that the door key may be removed from the door lock only by removal of the attachment from the lock which requires the special tool to release the fastening means on the attachment housing. Accordingly, the present invention provides a master key attachment for a door lock which permits the door to be locked and unlocked with a master key and which avoids the earlier discussed problem arising from inadvertent or deliberate retention of the door key.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a side elevation illustrating a present master key attachment installed on a door lock;

FIGURE 2 is a section taken on line 22 in FIG- URE 1;

FIGURE 3 is a view looking in the direction of the arrows on line 33 in FIGURE 1;

FIGURE 4 is an enlarged section taken on line 4-4 in FIGURE 2;

FIGURE 5 is a section taken on line 55 in FIGURE 4; and

FIGURE 6 is a section taken on line 66 in FIG- URE 4.

Referring now to these drawings, there is illustrated a master key attachment 10 according to the invention installed on the lock 12 of a door 14. In general terms, the attachment has a housing 16 with fastening means 18 for securing the housing to the lock 12 in such a way that the attachment may be removed by authorized persons only. To this end, the fastening means 18 is so constructed and arranged as to require a special tool or key for releasing the fastening means to permit removal of the attachment. This tool will be made availably only to persons who are authorized to remove the master key attachment. Mounted on the attachment housing 16 is a master lock 20. This master lock has a master key-operated means 22 which is operatively connected to the key 24 for the door lock 12 in such a way that the door key may be operated to lock and unlock the door by rotation of a master key 26 in the master lock 20. As noted earlier, the present master key attachment 10 is intended primarily for use by real estate brokers to provide free access to listed properties in the owners absence. In this case, the attachment is installed on the door lock of a listed property to be sold by the listing broker, and the broker retains a number of master keys for the attachment for use by his agents and the agents of other brokers who wish to show the property to a prospective purchaser. A major advantage of the attachment resides in the fact that the door 14 may be opened only by persons in possession of the appropriate master key 26, and in the further fact that the door key 24 may be removed only by an authorized person, i.e. the listing broker or one of his agents, having the proper tool or key to release the attachment fastening means 18.

Referring now in greater detail to the drawings, the door lock 12 shown is contained within the handle 28 of a door latch mechanism 30. The door lock and latch mechanism are conventional and thus need not be explained in detail. Suflice it to say that the latch mechanism is fixed within a mortised opening in the door 14 and includes a beveled latch plunger 32 operated by rotation of the door handle 28. Plunger 32 is yieldably urged by a spring (not shown) Within the latch mechanism to an extended latching position shown in FIG- URE 2, wherein the beveled end of the plunger projects beyond the edge of the door for latching engagement with an apertured strike plate (not shown) mounted on the door frame when the door is closed, thus to latch the door in closed position. Rotation of the door handle 28 retracts the plunger 32 against spring action to release the door for opening. Operation of the door lock 12 to its locked condition by means of the door key 24 secures the door handle against rotation from the outer side of the door so as to permit locking of the door in closed position.

Door handle 28 has outer and inner knobs 34 and 36 by which the handle may be rotated.

The door lock 12 is contained within the outer doorknob 34 and has a key slot 38 opening through the outer face of the knob to receive the door key 24. Operation of the door lock to its locked and unlocked condition is accomplished by inserting the door key into the key slot and rotating the key in the appropriate direction.

Turning now to the present master key attachment 10, the attachment housing 16 comprises a split resilient ring 40 which is internally shaped and dimensioned to fit closely about the outer doorknob 34 in interlocking engagement with the knob. In this regard, it will be observed that the inner surface 42 of the ring has a concave curvature in transverse cross-section which approximately complements like corresponding curvature of the outer doorknob 34, such that removal of the ring from the knob requires radial expansion of the ring. Extending laterally out from the adjacent split ends of the ring 40 are a pair of confronting flanges 44. As Will appear presently, the fastening means 18 joins these flanges in such a way that the attachment housing ring 40 may be firmly constricted about the doorknob 34 to prevent both removal of the attachment from and rotation of the attachment relative to the knob. Inwardly joined to diametrically opposite sides of and extending outwardly from the housing ring 40 are a pair of struts 46. The outer ends of these struts are inwardly joined to diametrically opposite sides of an outer, generally discshaped housing end wall 48. Struts 46 are relatively rigid, though sufliciently laterally flexible to permit expansion of the housing ring 40 during installation of the master key attachment on and removal of the attachment from the doorknob 34 in the manner explained below.

It will be immediately recognized by those versed in the art that the attachment housing 16 may be cast, machined, or fabricated in any other convenient manner.

As just noted, the fastening means 18 joins the housing ring flanges 44 in such a way that the housing ring may be firmly constricted about the outer doorknob 34 to secure the master key attachment 16 against removal from and rotation relative to the knob. It Will be further recalled that the fastening means may be released only with the aid of a special tool, such that the housing can be removed only by an authorized person in possession of the tool. Various fastening or locking means may be employed for this purpose. The particular fastening means 18 illustrated comprises, essentially, a cap screw having a head 50 contained within a closefitting socket 52 entering one of the housing flanges 44 and a threaded shank 54 threaded in the outer flange. Entering the outer end face of the cap screw head 52 are means 56 for receiving a special tool or wrench 58 for tightening and releasing the screw. In this case, the two receiving means 56 comprise a number of sockets which enter the cap screw head axially and are arranged in an unusual pattern for receiving mating pins or studs 60 on the wrench 58. It is evident, therefore, that the cap screw 18 can be turned only with the aid of the special wrench 58. Of significance is the fact that the cap screw head 50 is completely contained Within the ring flange socket 52 in a manner such that the cap screw cannot be turned with an ordinary pliers or wrench.

The master lock 20 is axially mounted within the housing end wall 48. Here again, it will become evident as the description proceeds that a variety of master lock devices may be used in the present master key attachment. The particular master lock illustrated has an outer barrel 62 rigidly fixed within the housing end wall 48 and an inner cylinder which forms the earlier referred to master keyoperated means 22 of the lock. Lock cylinder 22 contains a key slot for receiving the master key 26 and tumblers (not shown) which coact with tumblers in the master lock barrel 62 to normally lock the cylinder against rotation relative to the barrel and, thereby, against rotation relative to the attachment housing 16. Insertion of the master key 26 into the key slot 64 positions these tumblers to release the lock cylinder 22 for rotation by the master key relative to the barrel 62.

Rigidly secured, as by means of a screw 66, to the inner end of the master lock cylinder 22 is a yoke 68. This yoke has arms 70 which extend generally axially from the cylinder toward the attachment housing ring 40 and define therebetween an intervening door key-receiving slot 72.

In use, the master key attachment 10 is installed on the door 14 by first inserting the door key 24 into the door key slot 38. The fastening means 18 on the attachment housing 16 is then released, by use of the special tool or Wrench 58, sufliciently to enable radial expansion of the housing ring '40 to the extent necessary to place the ring axially over the doorknob 34 and into surrounding relation with the knob. This installation step is performed in such a way that the outer end of the door key 24 enters the slot 72 in the master lock yoke 68. The fastening means 18 is then re-tightened to constrict the housing ring 40 about the doorknob 34 and thereby firmly clamp the attachment housing 16 to the knob. When thus securing the master key attachment 10 to the doorknob 34, the attachment housing 16 is angularly oriented relative to the knob in such a way that the master lock cylinder 22 and the door key 24 simultaneously occupy corresponding positions, i.e. either their locked or unlocked positions.

It is now evident that after the master key attachment 10 has been properly installed on the door 14, the door key 24 may be rotated to lock and unlock the door by, and only by, inserting a master key 26 into the master lock 20 and rotating the master key to its locking or unlocking position, as the case may be. Thus, the door 14 may be locked and unlocked from the outside only by persons having the proper master key. After being unlocked by a master key, the door is opened by rotating the master key attachment 10 rotate the doorknob and thereby retract the door latch plunger 32 to its unlatching position. This may be accomplished by continued rotation of the master key 26 after unlocking of the door, in the event that rotation of the master lock cylinder 22 relative to the attachment housing 16 is limited in some Way, or by physically grasping the master key attachment directly and rotating the attachment by hand. Conceivably, in

some types of door locks, the door latch plunger 32 may be retracted directly by unlocking rotation of the door key 24 rather than by rotation of the door handle 28. In this case, the door may be opened simply by rotating the master key 26 in the proper direction to unlock the door.

A particularly unique and important feature of the invention resides in the fact that the master key attachment is so constructed and arranged that the door key 24 may be removed from the door lock 12 only by removal of the attachment from the doorknob 34. Since the attachment can be removed only by authorized persons having the appropriate tool or wrench 58 to release the attachment housing fastening means 18, it is evident that the door key can be removed only by such authorized persons. The problem, discussed earlier, of inadvertent or deliberate door key retention by real estate agents when a conventional master key box is used, is thereby avoided in the present invention. Preferably, the door key receiving slot 72 in the master lock yoke 68 is laterally dimensioned to receive the door key with a relatively loose fit such as to permit limited rotation of the master lock cylinder 22 relative to the door key and hence relative rotation of the door key relative to the master lock cylinder. This permits the door key 24 to be jiggled in the event that the door lock 24 sticks, thus facilitating unlocking of the door 14.

While the invention has been described in what is presently conceived to be one of its most practical embodiments, it will be evident to those versed in the art that various modifications of the invention are possible.

The inventor claims:

1. In combination:

a door including a door lock,

a door key positioned within said lock for operating said lock, and

a master key attachment for said lock including a housing, means for releasably securing said housing to said door lock in a manner such that said housing may be removed by authorized persons only, and a master lock carried by said housing including a master key-operated means releasably connected to said door key for operating said door key to lock and unlock said door lock.

2. The combination according to claim 1, wherein:

said door lock has a key slot, said door key i positioned in said key slot and is rotatable to lock and unlock said door lock, and

said master key-operated means has a key slot for receiving a master key and is rotatable by said master key to rotate said door key.

3. The combination according to claim 2, wherein:

slight clearance is provided between said door key and master key-operated means to permit limited relative rotation of said door key and key-operated means to facilitate operation of said door lock by said master key when said door lock sticks.

4. The combination according to claim 2, wherein:

said master key-operated means comprises a cylinder rotatable within said housing on a rotation axis coinciding approximately with the rotation axis of said door key, and a slot on said axes receiving said door key.

5. The combination according to claim 4, wherein:

said slot i dimensioned to receive said door key with a slight clearance fit to permit limited relative rotation of said master lock cylinder and door key for facilitating operation of said door lock by said master key when said door lock sticks.

6. The combination according to claim 1, wherein:

said door has a handle containing said door lock, and

said housing is secured to said handle.

7. The combination according to claim 6, wherein:

said door include a door latch mechanism having a latch plunger operable between latching and unlatching positions by rotation of said handle, and

said housing is firmly secured to said handle for rotation of said handle by said housing.

8. The combination according to claim 1, wherein:

said door has a handle containing said door lock,

said housing includes a split radially resilient ring disposed in surrounding relation to said handle, and

said releasable securing means comprises a fastening means joining the split ends of said ring for constricting said ring firmly about said handle and adapted to be released by a special tool only.

9. A master key attachment for a door lock having a key position in said lock, comprising:

a housing,

means for releasably securing said housing to said lock in a manner such that said housing may be removed by authorized persons only, and

a master lock carried by said housing including master key-operated means adapted for releasable connection to said door key for operation of said door key to lock and unlock said door lock by rotation of a master key in said master lock.

10. A master key attachment according to claim 9,

wherein:

said door lock is contained within a door handle,

said housing comprises a split radially resilient ring adapted to be placed in surrounding relation to said handle, and

said housing securing means comprise fastening means joining the split ends of said housing ring for firmly constricting said ring around said handle and adapted to be released only by a special tool.

11. A master key attachment according to claim 9,

wherein:

said housing has an inner end for attachment to said door lock and an outer end,

said master key-operated means comprises a master lock cylinder rotatable within said outer end of the housing and having a master key slot, and

means secured to the inner end of said lock cylinder and defining a door key receiving slot opening toward the inner end of said housing for receiving said door key.

12. A master key attachment according to claim 11,

wherein:

said door lock is contained within a door handle,

the inner end of said housing comprises a split radially resilient ring adapted to be placed in surrounding relation to said door handle, and

said housing securing means comprises a fastening means joining the split ends of said housing ring for firmly constricting said ring about said handle and releasable only by a special tool.

References Cited UNITED STATES PATENTS 2,813,620 11/1957 Hansen 206-1 2,995,025 8/1961 Toepfer 70-58 3,167,945 2/1965 Goodman 70-428 3,210,972 10/1965 Johnson 70-211 3,23 6,075 2/ 1966 Williams 70-63 3,343,387 9/1967 Gochran 70-424 MARVIN A. CHAMPION, Primary Examiner R. L. WOLFE, Assistant Examiner US. Cl. X.R.

Images