GB2241983A - Locks - Google Patents

Abstract

A lock includes a pack of levers 5 (i.e. pivoted/slidable tumblers/detainers) and an acid-responsive relocker comprising a bar 15 pivoted in the upper part of the casing 1 and normally supported by a spring-metal strip 17. The strip 17 is of e.g. phosphor bronze and has a bend 20 seated in a drain hole 21 in the bottom of the casing 1. In the event of acid being poured or sprayed into the keyhole in an attempt to dissolve the levers 5 the acid will flow over the strip 17 in the region of the bend 20 and disintegrate the same before the levers are significantly weakened, thus allowing the relocker bar 15 to fall and apply an additional blockage to retraction of the bolt 3. The bar 15, being located in the upper part of the casing, is itself unlikely to be contacted by the acid and can maintain the lock in a secure condition notwithstanding eventual destruction of the levers. <IMAGE>

Description

Locks The present invention relates to lever locks.

By the term "lever locks" we mean key locks of the wellknown kind in which the key-recognition mechanism comprises a plurality of pivoted or slidable tumblers or detainers (termed "levers"), which in the locking condition collectively block retraction of the bolt or other such locking member, and each of which has a surface, usually of arcuate form, which is swept by a respective step of the correct bitted key when the latter is turned in the lock, whereby to shift the levers to selected relative positions in which they collectively permit retraction of the locking member.

One way in which thieves may attack such a lock, on a safe for example, is to pour or spray acid through the keyhole with the intention of dissolving sufficient portions of the levers or bolt stump (or other such abutment portion of the locking member or of an intermediate member which cooperates with the levers) as to permit the bolt to be retracted without use of the correct key. One way in which to reduce the likelihood of success with this form of attack is to make such components of the lock from an acid-resistant material such as chromised iron or certain grades of stainless steel, instead of the traditional brass. Such materials are expensive and difficult to work, however, and in any event may still be susceptible to attack by certain reagents which might be obtained.

In this regard, use of the term "acid" within this specification is intended, where the context so permits, to embrace all forms of reagent having substantial solvent or corrosive power in relation to the material(s) from which the levers and/or a cooperating abutment are made, whether or not chemically acidic.

Another approach aimed at defeating acid attack on a lever lock, known from West German Offenlegungsschrift no.

3226444, is to employ an acid-responsive relocker. By the term "relocker" we mean an additional mechanical element, separate from the levers, which can be actuated to move into a position in which it will block forced retraction of the bolt, automatically upon the dissolution of triggering means. In the said Offenlegungsschrift the relocker is in the form of a spring-biased blocking pin carried by the bolt, at its lower margin, and normally retained by an element of material susceptible to dissolution by acid. In the event of acid being poured in through the keyhole, therefore, it will flow down onto the relocker, destroy its retainer, and thereby permit the pin to be shot into a detention in the bottom of the lockcase to resist forced retraction of the bolt irrespective of the possible destruction of vital parts of the levers.The positioning of the relocker, however, means that the blocking pin must itself be made of a highgrade material resistant to the reagents which attack the levers and its retainer, otherwise it too will be rendered ineffective. Even so, if a second reagent is then employed to which the material of the blocking pin is susceptible, its location in the bottom of the lockcase means that it is in an optimal position to be attacked and may thereby be more readily overcome.

In one aspect the present invention seeks to obviate this weakness of the prior art acid-responsive relocker and accordingly resides in a lever lock including a relocker positioned above at least those portions of the levers which normally serve to block forced retraction of the bolt or other such locking member, and triggering means at least a portion of which is susceptible to dissolution by acid (as hereinbefore defined) and is positioned below the aforesaid portions of the levers, the relocker being linked to said triggering means whereby dissolution of said portion thereof is effective to actuate the relocker.

By thus positioning the relocker above the portions of the levers which normally serve to block forced retraction of the bolt, and preferably within the uppermost portion of the lockcase, it is itself less likely to be contacted by acid intended to destroy the levers and correspondingly more likely to remain effective in blocking the bolt or the like notwithstanding dissolution of vital portions of the levers and irrespective of the material from which it is made.

In a preferred embodiment, the triggering means is in the form of a strip or leaf of spring metal which is normally held between the relocker and a lower portion of the lockcase. This element will be work hardened in producing its spring qualities, which will act to accelarate its dissolution by acid (stress corrosion).

In a particularly preferred arrangement, this element has a bend seated in a drain aperture in a lower surface of the lockcase to promote rapid dissolution in the event or an acid attack and ensure that the relocker will be actuated before there is any risk of the levers being rendered ineffective.

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; and Figure 2 is partial section on the line II-II of Figure 1 showing the trigger element for the acid-responsive relocker incorporated in the lock.

With reference to Figure 1, the illustrated lock, which may for example be fitted in a safe door for locking its main boltwork, has a casing 1 from which is extended and retracted the head 2 of a brass bolt 3. The plate-like tail 4 of the bolt will have the usual talons or drive surfaces (not shown) 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 brass levers 5 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 usual barrel-and-curtain member which turns with the key is seen at 11, (its key aperture 12 aligning with the keyhole in the cap of the casing), and is normally indexed in the illustrated keyinsertion position by a spring-biased detent lever 13.

As thus far described, the lock is of essentially conventional construction. In accordance with the present invention, however, an additional acid-responsive relocker is incorporated as follows.

Pivoted on a pin 14 in the uppermost portion of the casing 1 is a brass relocker bar 15, being biased by a spring 16 to turn in the anti-clockwise sense (as viewed).

Normally, however, this bar is held in the illustrated inoperative position by a trigger element 17, the form of which is more clearly seen in Figure 2. The trigger element 17 comprises a spring metal strip bent into the illustrated shape and lightly compressed between the bar 15 and the lower surface of the casing 1. More particularly, it has an upper 90" bend 18 upon which the relocker bar 15 is seated, an intermediate 450 bend 19 and a lower 900 bend 20 which seats in a drain hole 21 in the bottom of the casing. It is made e.g. from phosphor bronze, thus to be susceptible to dissolution by any acid which is likely to be successfully employed in an attack upon the levers 5.

In the event that acid is poured or sprayed into the casing 1 through the keyhole in an attempt to dissolve away the leading edges of the levers 5 or the bolt stump 6, the reagent will flow down through the drain hole 21 and over the lower bend 20 of the trigger element 17. If a concerted attack is to be mounted the acid supply through the keyhole must be continually replenished so that the bend 20, which is a highly stressed and work hardened region of the element 17, will be continually subject to the fresh, chemically active reagent and the trigger element will rapidly weaken and disintegrate in this region. When this occurs it can no longer support the relocker bar 15 which accordingly pivots down to engage its nose in a cut-out 22 in the bolt tail to resist any subsequent attempt at forced retraction of the bolt.

The rapid dissolution of the trigger element will ensure that the relocker is actuated in this way before there is any danger of substantial weakening of the levers by the acid. The relocker bar 15 itself, being located in the upper portion of the casing 1, will normally be out of reach of the acid and may therefore be constructed without especial regard to its own acid-resisting properties.

Claims (6)

1. A lever lock including a relocker positioned above at least those portions of the levers which normally serve to block forced retraction of the bolt or other such locking member, and triggering means at least a portion of which is susceptible to dissolution by acid (as hereinbefore defined) and is positioned below the aforesaid portions of the levers, the relocker being linked to said triggering means whereby dissolution of said portion thereof is effective to actuate the relocker.

2. A lock according to claim 1 wherein the triggering means is in the form of a strip or leaf of spring metal which is normally held between the relocker and a lower portion of the case of the lock.

3. A lock according to claim 2 wherein said strip or leaf has a bend seated in a drain aperture in a lower surface of the case of the lock.

4. A lock according to any preceding claim wherein the relocker is normally positioned entirely above both the levers and the locking member.

5. A lock according to any preceding claim wherein the relocker comprises a bar pivoted in an upper portion of the case of the lock which is adapted to fall when actuated to engage an upper portion of the locking member.

6. A lock substantially as hereinbefore described with reference to the accompanying drawings.