Lever lock

Abstract: A high security lever lock includes a device which is operable, in response to the turning in the lock of an incorrect key or the like implement 36 in the bolt retracting direction such as to lift the levers 5 to incorrect positions, to prevent return movement of the implement to the insertion position. The implement thereby becomes trapped in the lock and prevents access for further attempts at manipulation. False notches 9B are provided in some of the levers 5 to permit limited retraction of the bolt 2 with its stump 6 when set in certain incorrect combinations, the limited bolt retraction causing a pin 19A on the bolt to become trapped in the pocket 28 of a spring-loaded plate 27. Return extension of the bolt 5, and consequent release of the implement 36, is thereby prevented.

Description: The present invention relates to locks and more particularly to lever locks. By the term "lever locks" we mean locks of the well-known kind in which the key-recognition mechanism comprises a plurality of pivoted or slidable tumblers or detainers (the "levers"), each adapted in the normal locking condition of the lock to prevent retraction of the lock bolt by blocking a stump carried by the bolt, but each comprising a gate at a selected location to pass the stump. Each lever also has a surface, usually of arcuate form, (termed the "belly") adapted to be swept by a respective step of a correct key when the latter is turned in the lock, whereby to shift the levers to selected relative positions in which their respective gates in the levers become aligned with the bolt stump so as collectively to permit retraction of the bolt by passage of the stump through the aligned lever gates. It is recognised that, particularly when used in high security applications e.g. for securing the door of a safe or strongroom, such locks may come under attack from lock pickers with a view to manipulating the levers to their unlocking positions by the use of false keys or other implements inserted through the keyhole. One well-known means for increasing the security of the lock against such attacks is the so-called detector lever, as described for example in "An Encyclopaedia of Locks and Builders Hardware", by Josiah Parkes & Sons Ltd., England, 2nd Reprint July 1979, page 47. The feature of that mechanism is that if any one of the levers is lifted far enough beyond the level to which it would be set by the correct key during trials with a false key or other picking implement it causes the detector lever to lift into a position in which it becomes held up to block subsequent retraction of the bolt. This mechanism does not, however, prevent the offending implement from being turned back and removed from the lock so that an attempt might then be made to reset the detector lever with another implement inserted through the keyhole. From DE-C-147264 there is known a lever lock equipped with a special tumbler which, if overlifted with a false key turns into a position in which it partially obstructs the keyhole, in which position it is held by a ratchet device, to prevent removal of the false key, although the key is not prevented from turning by this tumbler. From DE-C-539444, which forms the basis for the preamble in claim 1, there is known a lever lock equipped with a special tumbler which is operable in response to a limited retraction of the bolt to block return extension of the bolt so that if a false key is turned in the lock it can become trapped therein. This special tumbler does not function as a normal lever in that it does not serve to block retraction of the bolt in the normal locking condition of the lock. On the other hand, in the key-trapping condition it is the special tumbler which serves to block the bolt against retraction as well as extension, with the normal levers apparently playing no part. In accordance with the present invention, there is provided a lock comprising a bolt carrying a stump; a plurality of pivoted or slidable levers each adapted in the normal locking condition of the lock to prevent retraction of the bolt by blocking said stump but each comprising a gate at a selected location to pass said stump; each lever having a surface adapted to be swept by a respective step of a correct key when the latter is turned in the lock, whereby to shift the levers to selected relative positions in which their respective gates become aligned with said stump so as collectively to permit retraction of the bolt by passage of the stump through the aligned gates; the lock further comprising a trap member separate from the levers which is operable in response to a limited retraction of the bolt to block return extension of the bolt whereby if an incorrect key or like implement is turned in the lock it can become trapped therein; characterised in that one or more of the said levers are configured adjacent to their respective gates with respective formations complementary to the formation of said stump so that if shifted by a said implement to respective positions in which said formations but not the gates of those levers are aligned with the stump said limited retraction of the bolt is possible but further retraction of the bolt is prevented by the engagement of the stump with those levers, and those levers are blocked from movement away from the positions to which they are shifted by said implement by virtue of their engagement with the stump. The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a view of the mechanism of one embodiment of a lever lock made in accordance with the invention, with its cap removed, in the normal locking condition; Figure 2 is a side view of the bolt of the lock of Figure 1; Figure 3 is a view similar to Figure 1 showing the lock mechanism in the course of unlocking with the correct key; Figure 4 is a view similar to Figure 1 showing the lock mechanism in the unlocking condition; Figures 5 and 6 are respectively side and end elevation views of the additional trap plate embodied in the lock; Figure 7 is a section through the trap plate on the line VII-VII of Figure 5; Figure 8 is a view similar to Figure 1 showing the lock mechanism when an attempt is made to withdraw the bolt with an incorrect key; and Figures 9 and 10 are respective views of the trap plate in the course of normal movement of the lock mechanism to the locking condition. The illustrated lock is intended for high security applications, e.g. for locking the door of a safe or strongroom. With reference to Figure 1, it has a casing 1 from which is extended and retracted the head 2 of a bolt 3. The plate-like tail 4 of the bolt has the usual talons or drive surfaces 4A,4B (Figure 2) for engagement with the bolt step of the key bit when the latter is turned in the appropriate sense to extend or retract the bolt. In the illustrated locking condition of the bolt, it is blocked from retraction by a pack of, say, ten levers 5 (of which only the nearest one is seen in Figure 1) lying in the path of the bolt stump 6. The levers are pivoted on a pin 7 and biased in the anticlockwise sense (as viewed) to their locking positions by leaf springs 8. Each lever has a gate 9 in its leading edge, however, which can pass the stump 6 to permit retraction of the bolt when the levers are set to their unlocking positions by turning the correct key. In this respect it will be understood that the gates 9 in different levers will be located at different heights and the levers will all be lifted through the correct distances to align their gates with the stump 6 when the respective steps on the correct key bit sweep their bellies 10. The lock also includes a barrel-and-curtain member 11 borne for rotation transversely to the line of movement of the bolt and defining the turning axis for the key. The barrel part 12 has a longitudinal slot 13 of a width sufficient only to accommodate the bit of the key and in the normal locking condition of the lock is aligned as shown in Figure 1, to register with the leg portion of the corresponding keyhole in the cap (not shown) which closes the proximal side of the casing 1. The curtain part 14 is in the form of a disc at the proximal end of the barrel 12, immediately behind the keyhole, and has a slot 15 to pass the key bit when in register with the keyhole. This curtain will block passage of the key or any similar bitted instrument in either direction through the leg portion of the keyhole, however, whenever it is turned away from the illustrated position. As thus far described, the lock is of generally conventional form. In addition, it comprises an arrester member 16 in the form of a profiled plate located to one side of the pack of levers 5, in the same plane as the curtain 14, and which is borne for limited sliding movement parallel to the bolt 3 by means of two slots 17,18 engaging respectively over the pin 7 and over a pin 19 mounted to the bolt. In the locking condition of the mechanism shown in Figure 1 the arrester 16 is held at the leftward extremity of its permissible movement (in the sense as viewed) with the bolt pin 19 at the leftward end of slot 18 and the trailing end of the arrester lying against the curtain 14. It is also held yieldably in this position by a detent spring 20. The purpose of the arrester 16 is fully explained in our copending United Kingdom patent application no. 2238343, to which reference is directed, but briefly it is to block turning of the barrel-and-curtain member 11 by any implement, while the mechanism is in its locking position, to a position in which the trailing ends of the lever bellies 10 could be surreptitiously inspected through the barrel slot 13. Turning of the element 11 in either sense is restricted in this regard by abutment of shoulders 21 and 22 of the curtain 14 with shoulders 23 and 24 of the arrester respectively. The normal unlocking movements of this mechanism to retract the bolt 3 from the Figure 1 condition will first be described. The correct key is inserted and given a complete turn in the clockwise sense. This firstly results in the key bit engaging the lever bellies 10 and lifting the levers to align their gates 9 with the bolt stump 6. Immediately thereafter the bolt step on the key bit engages the appropriate talon 4B to begin the retracting movement of the bolt. This all occurs in the arc of movement of the key prior to the point at which the curtain shoulder 21 meets the shoulder 23 of the arrester, the latter condition being shown in Figure 3. The coupling of the pin 19 in the slot 18 provides sufficient lost motion between the bolt 3 and arrester 16 to allow the arrester now to be shifted to the right by the shoulder 21 as the key 25 completes its revolution. The mechanism finishes in the condition shown in Figure 4, with the bolt 3 withdrawn and the levers 5 returned to their locking positions to trap the stump 6 in their pockets 9A, the barrel-and-curtain member 11 back to its starting position and the arrester 16 also withdrawn so that an abutment 26 on the arrester now lies against the curtain shoulder 21. The linear distance through which the bolt is retracted exceeds that through which the arrester is moved and hence in the unlocking condition the pin 19 on the bolt now lies at the right hand end (as viewed) of the arrester slot 18. As will be seen in the Figures, the illustrated lever 5 is provided with a set of so-called false notches 9B adjacent to its gate 9 and the facing edge of the bolt stump 6 is notched complementarily to enable the bolt to retract very slightly by interengagement of these notches when the lever 5 is lifted to two discrete levels apart from that which aligns its gate 9 with the stump 6. These formations serve to confuse attempts to feel the gate position by the use of picking tools, in known manner. They also come into play to fulfil an additional purpose in accordance with the present invention, however, together with the arrester 16 and an additional element 27 which shall be called herein a trap plate. The form of the trap plate 27 is more fully shown in Figures 5 to 7. It is a generally planar element with a profiled pocket 28 adjacent to which there is a tongue 29 bent up at an acute angle. There is also a bent up tag 30 and a bent down foot 31. This plate is pivoted on a pin 32 mounted to the arrester 16 and is biased in the clockwise sense (as viewed in Figure 1) by a spring 33 held around the pin 32 and between the tag 30 and a similar tag 34 on the arrester. In the locking condition of Figure 1 the trap plate 27 adopts the illustrated position by abutment of its foot 31 with a shoulder 35 of the lock case 1 under the pressure of the spring 33. In this condition a peripheral edge 28A of the pocket 28 in the trap plate overlies a reduced-diameter end portion 19A of the bolt pin 19 which extends laterally from the plane of the arrester 16 and slightly displaces the forward end of the trap plate laterally away from the arrester. This slight tilting of the plate 27 out of true parallelism with the arrester 16 is accommodated in its pivoted connection, while the action of the spring 33 is to press the trap plate laterally against the pin end 19A in addition to its pivotal bias. Let it be assumed that is the pack of levers 5 one half have false notches as exemplified at 9B ("notched-levers") while the remainder have an unbroken external profile adjacent to their respective gates 9 ("plain levers"). Let it also be supposed that an attempt is made by a potential safe-cracker to manipulate the lock from its locking condition illustrated in Figure 1 by simple trial and error using a large number of false keys or by some more sophisticated method using an implement of the same overall profile as a correct key inserted through the barrel-and-curtain 11 to try different combinations of lifts of the levers to see if they will pass the bolt stump 6. For any such combination of lifts which fails to align all the plain lever gates and all the notched lever gates or notch formations with the bolt stump it will be understood that the misaligned lever(s) will block any significant retracting movement of the bolt. If enough attempts are made, however, a combination may eventually be set up in which all the plain lever gates are aligned with the bolt stump and all the notched levers are also in one of their alignments with the bolt stump which will permit slight retraction of the bolt but only to the depth of the false notches (e.g. 9B). In view of the large number of combinations of false notch alignments which are possible with, say, five notched levers, it is highly probable that such a combination would be achieved before the unique combination in which all of the gates of all of the plain and notched levers are aligned with the bolt stump. Such a state of affairs is illustrated in Figure 8, in which a false key or other implement 36 in the barrel-and-curtain 11 has lifted the illustrated lever 5 to align its false notches 9B with the bolt stump 6 and will have also lifted all of the other, non-illustrated, levers to permit retraction of the bolt 3 to the depth of the notches 9B. This degree of retraction of the bolt is accomplished prior to any retraction of the arrester 16 by virtue of the lost-motion coupling between those elements as previously described, the detent spring 20 ensuring that the arrester is not displaced by friction with the bolt or through any other effect at this stage. Accordingly the bolt pin 19 is moved rearwardly in relation to the trap plate 27 pinned to the arrester, so that its end portion 19A moves past the peripheral edge 28A of the pocket 28 and the plate 27 is allowed to snap against the side of the arrester, thereby trapping the pin end 19A in its pocket 28. In this condition, the bolt 3 is blocked against return movement in the locking direction (leftward as viewed) since the pin end 19A abuts against the edge 28A of the trap plate pocket and the trailing end of the arrester 16, to which the trap plate 27 is connected, abuts against the curtain 14. The bolt is of course blocked against any further movement in the unlocking direction by the lever 5, which is itself prevented from falling by its interengagement with the bolt stump. Furthermore, since the bit of the false key or other implement 36 now lies between the bolt talons 4A and 4B it is prevented from turning in either direction by the blocked bolt and, since it is of course now misaligned with the keyhole (indicated at 1A in Figure 8) , the implement cannot be removed. In other words the lock mechanism is now completely jammed against movement in any direction and the offending implement is trapped in the lock, thus preventing any further attempt to manipulate the lock. Furthermore, access through the leg portion of the keyhole 1A for the insertion of any other implement in an attempt to free the mechanism is blocked by the curtain 14 which cannot be turned separately from the key. It will be appreciated that while the ability of the mechanism to adopt the above-described "lock out" condition of Figure 8 is of great advantage in defeating serious attempts to manipulate the lock it would equally be of great inconvenience if that condition was attained whenever an incorrect key was turned in the lock, e.g. through innocent mistake of an unauthorised key holder, or if it was easy for a malicious person to lock out unauthorised users by such means. That is why it is arranged in the preferred embodiment described herein that the "lock out" cannot occur at least until all of the plain levers have been correctly lifted to align their gates with the bolt stump - i.e. until a potential cracksman has gone some way to setting up the correct combination of lifts. In particular, it can readily be arranged in a bank or other such organisation where several such locks are employed to secure different items of equipment that none of the respective correct keys will cause a "lock out" condition if indavertently turned in the wrong lock. Returning to Figure 3, it will be appreciated that the initial retracting movement of the bolt 3 which leads to its pin end 19A becoming trapped in the pocket 28 will also occur during normal unlocking of the mechanism with the correct key, as shown in that Figure. Accordingly, the trap plate 27 must be arranged so as to be reset to its Figure 1 position after any normal unlocking-locking operation. This action will now be described. As the bolt 3 continues to be retracted from the Figure 3 position by clockwise turning of the correct key 25 retraction of the arrester 16 also commences, so that the foot 31 of the trap plate 27 is released from the lock case shoulder 35. As previously mentioned, the linear distance through which the bolt 3 is moved to the unlocking condition exceeds that through which the arrester 16 is moved so that in the fully retracted condition of Figure 4 the end of the pin 19 has moved to the right (in the sense as viewed) in the trap plate pocket 28, in so doing engaging the inclined edge 28B of the pocket 28 to pivot the plate 27 about the pin 32 so that its tongue 29 is now aligned with the pin 19. As the key is then turned anticlockwise to throw out the bolt 3 its linear movement again leads that of the arrester 16 so that the pin end 19A moves towards the tongue 29, the latter presenting a ramp surface under which the pin end 19A can slide as shown in Figure 9 to tilt the forward end of the trap plate 27 away from the arrester once more. When the bolt pin 19 reaches the end of the arrester slot 18 the arrester also commences its movement to the left and this continues until the foot 31 of the trap plate abuts the lock case shoulder 35 once more as shown in Figure 10, to pivot the plate 27 against the bias of the spring 33 with the pin end 19A now free of the pocket 28. The final movement of the bolt and arrester return the mechanism to the condition of Figure 1 in which the trap plate 27 is pivoted down to align the edge 28A of its pocket with the pin end 19A.

Claims: A lock comprising a bolt (3) carrying a stump (6); a plurality of pivoted or slidable levers (5) each adapted in the normal locking condition of the lock to prevent retraction of the bolt (3) by blocking said stump (6) but each comprising a gate (9) at a selected location to pass said stump (6); each said lever (5) having a surface (10) adapted to be swept by a respective step of a correct key when the latter is turned in the lock, whereby to shift the levers (5) to selected relative positions in which their respective gates (9) become aligned with said stump (6) so as collectively to permit retraction of the bolt (3) by passage of the stump (6) through the aligned gates (9); the lock further comprising a trap member (27) separate from the levers (5) which is operable in response to a limited retraction of the bolt (3) to block return extension of the bolt (3) whereby if an incorrect key or like implement (36) is turned in the lock it can become trapped therein; characterised in that one or more of the said levers (5) are configured adjacent to their respective gates (9) with respective formations (9B) complementary to the formation of said stump (6) so that if shifted by a said implement (36) to respective positions in which said formations (9B) but not the gates (9) of those levers are aligned with the stump (6) said limited retraction of the bolt (3) is possible but further retraction of the bolt (3) is prevented by the engagement of the stump (6) with those levers (5), and those levers (5) are blocked from movement away from the positions to which they are shifted by said implement (36) by virtue of their engagement with the stump (6). A lock according to claim 1 wherein a first plurality of levers (5) are configured with respective said formations (9B) and a second plurality of levers are configured without said formations, whereby said second plurality of levers must be shifted to the respective positions in which their gates (9) are aligned with said stump (6) before said limited retraction of the bolt (3) can take place. A lock according to claim 1 or claim 2 wherein said trap member (27) is biased towards a position to block the bolt (3) against return extension as aforesaid; in the normal locking position of the bolt (3) the trap member (27) being held away from its blocking position by abutment means (19A) carried by the bolt (3) but the trap member (27) being released by said abutment means (19A) to move to its blocking position when the bolt (3) is retracted through said limited distance. A lock according to claim 3 comprising means (29,35) setting said trap member (27) to its said held away position in response to the extension of the bolt (3) from its unlocking to its locking position by a correct key. A lock according to any preceding claim comprising a barrel member (11) to turn with the correct key and an arrester member (16) which in the locking position of the bolt (3) limits the extent to which the barrel member (11) is capable of being turned, the arrester member (16) being linked to the bolt (3) such as to prevent displacement of the arrester member (16) in the locking position of the bolt (3) but the arrester member (16) being displaceable by movement of the correct key when the latter is turned to retract the bolt (3) to its unlocking position, initial retraction of the bolt (3) leading displacement of the arrester member (16). A lock according to claim 5 wherein said trap member (27) is carried by said arrester member (16).

Inventors: JOHNS-HUNT JOHN, JOHNS-HUNT, JOHN
Applicants: CHUBB RESEARCH, CHUBB RESEARCH LIMITED
Application year: 1993
Main classification: E05B11
IPC codes: E05B11