GB2265662A - A locking mechanism with master key and subordinate key - Google Patents

Abstract

The present invention relates to a locking mechanism operable by key means and consisting of a cylinder 2 rotatable within a lock body 1 with tumbler pins 4, 5 located in aligned bores 8a, 9 and further pins 5, 6 in angularly spaced further bores 8b in the body 1. A master key is insertable at position A-A to operate the lock, but can also be removed at position B- B to allow the tumbler 5 to enter cylinder bore 9 and so provide another break point between tumblers 5 and 6 for the use of a subordinate key inserted at B-B. <IMAGE>

Description

A LOCKING MECHANISM WITH MASTER KEY AND SUBORDINATE KEY TECHNICAL FIELD OF INVENTION The present invention relates to locking mechanism operable by key means and in particular relates to a locking mechanism system having two separate and distinct releasing means, one of which is a master key and the other is a subordinate key.

BACKGROUND OF INVENTION In the conventional locking mechanism, there is one key to operate the tumblers and spring means included in the working mechanism in a barrel.

The same key is used to bring the lock into an operative and in-operative position. Further description of the background is provided by reference to Figure 1 and Figure 2. In the prior art locking mechanism there is provided a cylindrical key plug (2) which is detained in a outer lock cylinder (1) by means of a circlip (10). A plurality of radially disposed bores (8) extending from the external circumferential surface of the outer lock cylinder (1) into the body of the cylindrical key plug (2) are provided for. A set of key and tumblers (3), a push down tumblers (pins) (4) and compression springs (7) are also received through the bores openings (8) in the outer lock cylinder and retained in the bores. A cover plate (11) blocks all the bore openings (8) of the outer lock cylinder. The key end tumblers (3) are of varying lengths.A key is provided with serrated edges whrein the serrated edges are of varying heights such that when the key is inserted fully into the key plug (2) all the key end tumblers (3) are contained within the bores (9) in the key plug and all the push down tumbers (4) are contained within bores (8) in the outer lock cylinder (1) without any key end tumbler (3) or push down tumbler (4) extending into the outer lock cylinder and key plug respctively. Thus in the prior art lockirit mechanisms, the kcey end tumblers (3) and the serrated edges of the key are dimensioned in a manner such that with the key inserted into an operative position, the key plug (2) can be rotated to a second position.

One of the disadvantages of the prior art locking system as described above is that the locking mechanism can be opened through the use of an unauthorised duplicate key of the same configuration as the authorised key.

Thus when the authorised operator of the lock hands over the authorised key to a third person, that third person can through the use of a idanticafly duplicated key open the lock without the knowledge and consent of the authorised user. This causes serious problems where the authorised user is by necessity required to hand over the authorised key to a third person, for example a vehicle owner hands over the vehicle to a garage mechanic to attend to the vehicle, or to a car jockey to park the vehicle.

The third person can produce an unauthorised duplicate key of the original key and later use the key to gain access to the vehicle or the premises in which the lock is fitted.

Thus it is an object of the present invention to provide a locking mechanism wherein the lock cannot be operated using a key identical to the authorised key when a sub-ordinate key is handed over to a third person.

Fig. 1 is an assembly sequence drawing of an embodiment of the invention.

Fig. 2 is a cut-out perspective view of the locking mechanism in an open position and the master key placed in position.

Fig. 3 is a cross sectional view of the locking mechanism minus the key, in locked position.

Fig. 4 is a vertical sectional side view of the locking mechanism taken on the line "AA" in Figure 3 showing the state in which the master key is inserted into the lock and the lock is in an operative position.

Fig. 5 is a vertical sectional side view taken on the line "B-B" in Figure 3 showing the state in which the subordinate key is inserted into the lock and it is operative.

Fig. 6 is also a vertical sectional side view taken on the line "A-A" of Figure 3 showing the state in which the subardinate key is inserted into the lock and it is inoperative.

Fig. 7 is a blown out perspective view of another embodiment of the invention Referring to Figs 1 to 6, there is shown the structure and operation of a two-key cylinder lock according to this invention where the lock is mounted for use as a keyed ignition switch of an automobile.

The locking mechanism includes a solid tubular lock cylinder (1). The lock cylinder includes at least two longitudinal series of radially disposed tumbler holes (8a), (8b). The longitudinal series of holes are approximately 300 part The said tumbler holes (8a, 8b) extend from the external surface of the outer lock cylinder to the internal surface of the outer lock cylinder (1).

The key plug (2) is accommodated snugly into the central void (20) of the outer lock cylinder such that the key plug (2) is rotatable within the said central void (20). The key plug includes one longitudinal series of radially disposed guide holes (9) extending from the external surface towards the central longitudinal axis of the key plug. The key plug also includes a longitudinal key way passage (22) whose cross-section is congruent to the cross-section of the key. Each of the guide holes (9) in the key plug (2) are in radial alignment with each of the corresponding holes in the lock cylinder (see Fig.3).The key plug (2) is rotatable along its longitudiXal axis such that the holes (8a, 8b) in the lock cylinder can be aligned to the holes (9) in key plug, thus enabling a key to be inserted into the keyway passage (22) at two positions, namely position A-A, and B-B, in E5g. 3 That is when the key plug is at the AA position without the introduction of an authorised key into the key hole, the key and tumblers (3) and part of push down tumblers (4) will be retained within the guide holes (9) in the key plug. This would correspond to the locking mechanisms being in a locked position. When the appropriate authorised key is inserted into the key hole (22), the push down tumblers (4) are pushed back into the retained holes (8a). The interface between the lower end of the push down tumbler (4) and the upper end of the key end tumblers is flush with the interface between the internal surface of the outer lock cylinder and the external surface of the key-plug, enabling the key plug to be rotated about its longitudinal axis, and thus "opening" the lock.

In the present embodiment the push down tumblers (4) are of equal length.

The key end tumblers (3) are of varying length and the length of each key nd tumbler is such that an open position with the appropriate key inserted in the key way (22) and the lock mechanism in an open position, the interface between the end of the push down tumbler and the key end tumbler is flush with the interface between the internal surface of the outer lock cylinder and the external surface of the key-plug. Thus the key plug can be rotated to open the lock. (see Fig. 2).

If a wrong key is inserted into the key way (22), then the said interface between the two sets of push down tumblers and the key end tumblers will not be flush with interface of the outer lock cylinder and the key plug, thus making it impossible to rotate the lock to switch on the ignition switch.

In the present invention, an additional set of holes (8b) are provided in the lock cylinder (1). Each hole is configured to receive an intermediate pin (5), push down tumbler pin (6) and a biasing means, preferably a spring (?1).

When the key plug is rotated from a AA position to a BB position (see Fig.3) using an authorised master key, the key end tumblers (3) which are initially inside the key plug hole (9) and in alignment with the first tumbler holes (8a) are now in alignment with second tumbler holes (8b), The intermediate pins (5) are of varying lengths such that in each corresponding tumbler bore hole and key plug hole (9) when the authorised subordinate key is in position in the key passageway at position BB, the interface between the intermediate pins (5) and the tumbler pins (6) are flush with interface between the inner surface of the lock cylinder and the outer surface of the key plug (see Fig.

5). If a sub-ordinate key is introduced into the key hole, as before, the interfaces between the intermediate pins (5) and the such down tumbler pins (8) would not be flush with the interface between the internal surface of the lock cylinder and upper surface of the key plug at position AA.

The subordinate key (12B) has a totally different serration cutting from the master key (12A). Usually the positions of the serrations in the subordinate key correspond to the serration in the master key, but the serrations in the subordinate key are slightly deeper than the serrations in the master key.

The operation of the locking system and the method of use of the master key and the subordinate key will now be described. The master key is withdrawn when the key hole is at BB position rather than at the AA position as in conventional use. When the master key (12A) is so withdrawn frorn the key hole at the BB position, it will be seen that key end tumbler pins (3) will still be retained within the guide holes (9) and the pins would be in alignment with the second retainer holes (8B). When the appropriate subordinate key (12B) is introduced into the key hole ( which is at the BB position), the key end tumbler pins (3) and the intermediate pins (5) are within the guide holes (9).At this position, the interface between push down tumbler pins (6) and the intermediate pins (5) is flush with the interface between the internal surface of the lock cylinder (1) and the outer surface of the key plug (2). This allows the key to further rotate the key plug (2) about its longitudinal axis.

If the master key (12A) is rotated from the key hole at the B-3 position to the A-A posifosl, the intermediate pins (5) would be retained in the second retainer holes (sub) and the key end tumblers (3) would be moved from the B-B position to the A-A position but would still be retained in the guide holes (9).

Thus when the subordinate key (12B) is introduced into the key hole at the A-A position, the key end tumbler pins (3) and part of the push down tumbler pins (4) would be within the guide holes (9) in the key plug (2).

At this position it would not be possible to rotate the key plug (2) and thereby operate the locking mechanism. At this position only the master key (12A) can be used to push back the push down tumbler pins (4) into the retainer holes (8A), thus facilitating the interface between the push down tumbler pins (4) and the key end tumblers (3) to be flush with the interface between the lock cylinder and the key plug.

It will be appreciated that when the subordinate key (12BJ is moved from the B-fl position to the A-A position, the guide holes (9) would contain the intermediate pins (5) and the key end tumbler pins (3). At this position the push down tumbler pins (4) would be contained within the first retainer holes (spa).

Thus in operating the locking system, the vehicle owner can operate the locking mechanism, with the master key (12A) without the need for the subordinate key (12B). The key plug (2) can be rotated from position A-A to B-B and further with the use of the master key (12A). Before handling the vehicle to a third person (say a car jockey or a mechanic) the owner will remove the master key (12A) from the locking mechanism at the B-B position instead of from the A-A position as in the conventional manner. The owner will hand over the subordinate key (12B) to the third person. The third person will be able to operate the locking mechanism as explained hereinbefore. When the owner takes possession of the vehicle, he will get back the subordinate key (12B) from the said third person also.Thereafter the owner will remove the key from the key hole from the B-B position and he shall thereafter drive the vehicle using the master key. Under the method of operating the lock system, the owner must always withdraw and insert the subordinate key at the BB position only. If third person intends to remove the vehicle without authority he may produce a duplicate key of the subordinate key (12B). Such third person may attempt to remove the car without the owner' knowledge with the use of the duplicate subordinate key.

As explained earlier, if the owner had removed the master key (12A) from the A-A position, it would not now be possible for the third person to operate the locking mechanism with the use of the duplicate subordinate key.

It must be emphasised that although the locking mechanism and the manner of operating the mechanism by the use of a master key and a subordinate key, was described with reference to a car ignition locking mechanism and the relationship between the owner of the vehicle and the mechanic, the locking mechanism and the manner of operating the system can be advantageously used in a variety of situations, for example in situations where persons at different managerial or operational hierachy levels need to have varying degree of access to locked systems, e.g. computers, rooms, equipment etc.

The invention has been described with reference to a specific embodiment where a serrated key is used to operate the locking mechanism. The novel principles of this invention can be adopted for use in locking systems where the key includes a plurality of dimples of varying diameters and depths (see Fig.7).

For the ease of explanation and for purpose of clarity only two sets of pins in the first retainer holes (8a) and another two sets of pins in the second retainer holes (8b) are included. But the invention need not be limited to two sets of pins in each of the retaIner holes. Additional sets of pins can be included to provide a more complex locking mechanism, but incorporating the inventive principles encompassed in the embodiment described herein.

Claims (7)

1. A locking mechanism operable by key means consisting of a lock cylinder body (I) with an annular bore (20) and at least one bore (8a) extending through from the external surface to the internal surface a key plug body (2) consisting of a key hole (22) along the central longitudinal axis, and at least one guide hole (9) extending radially from the external surface into the key hole (22), said guide hole (9) positioned along the longitudinal axis in such a manner that when the key plug (2) is secured to the lock cylinder body (1), the bore (spa) In the lock cylinder body (I) is in L straight line alignment with the bore (9) in the key plug body, and the key plug body (2) is rotatable within the annular bore (20) of the lock cylinder body at least one key end tumbler pin (3), a push down tumbler pin (4) and a biasing means (7) all introduceable into the bore (8a) in the lock cylinder body and into the bore in the key plug body (2), a sealing means to seal off the external opening of the bore (8a) of the lock-cylinder body (1) after the introduction of the key-end tumbler pin (3) and push down tumbler pin (4) and the biasing means into the bore in the lock-cylinder body characterised in that lock cylinder body (1) (8a) includes at least one other second bore (8b) extending through from the external surface to the internal surface, and the locking mechanism includes at least a set two pins, and biasing means to be introduceable into each of the second bore (8b), and a subordinate key means (12B) wherein the key plug body (2) is rotatable by the use of the subordinate key when the master key is withdrawn from the key hole (22) at a second position (BB) and is not rotatable by the use of the subordinate key (12B) when the master key (12A) is withdrawn from the key hole at a first position (AA) (hereinafter described as "locking mechanism as hereinbefore described',).

2. A locking mechanism according to claim 1 wherein the locking mechanism includes a plurality of sets each sets consisting of at least two sets of pins (S,6) and biasing means (71), all introduceable into a corresponding second set of bores (8b) in the lock cylinder body (1), the said bores extending through from the external surface to the internal surface of the said lock cylinder body.

3. A locking mechanism according to claims 1 and 2 wherein the sets of pins (5,6) are of equal lengths or of variable lengths.

4. A locking mechanism according to claim 3 wherein one set of pins (5) proximate to the key plug body (2) is of varying lengths.

5. A locking mechanism according to claim 1 wherein the master key (12A) and the subordinate key (12B) includes at least one groove and ridge.

6. A locking mechanism according to claim 1 wherein the master key (12A) and the subordinate key (12B) includes at least one dimple of pre-determined diameter and depths.

7. A locking mechanism substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.