GB2565379B

GB2565379B - A lock cylinder for a locking mechanism

Info

Publication number: GB2565379B
Application number: GB1717621.5A
Authority: GB
Inventors: Jennings David; Mcloughlin John
Original assignee: UAP Ltd
Current assignee: UAP Ltd
Priority date: 2017-07-11
Filing date: 2017-10-26
Publication date: 2019-10-16
Anticipated expiration: 2037-10-26
Also published as: GB2565379A; GB201711110D0; GB201717621D0

Description

A LOCK CYLINDER FORA LOCKING MECHANISM

The present invention relates to a lock cylinder for a lockingmechanism for doors and other similar closures. Such lock cylinders arecommonly called euro-lock cylinders or euro-cylinders. A euro-lock cylinder is designed to operate a rotatable cam with aprojecting cam lever that bears against a dead bolt or similar portion of alocking mechanism to move it to an open (retracted) or to a closed (extended)position when the cam is rotated. Rotation of the cam is usually accomplishedeither via a pin tumbler lock mechanism that requires a key to operate or viaa thumb-turn mechanism. Locking mechanisms that comprise such a lockcylinder may incorporate a lock cylinder with two pin tumbler lockmechanisms on opposite sides of the cam so that keys are required to open adoor from both sides. Alternatively, the lock cylinder may incorporate atumbler lock mechanism on one side of the cam and a thumb-turn mechanismon the opposite side of the cam, the former typically being used on an exteriorside of a door and the latter on an interior side. In both cases, the cam isusually selectively connected to one or other of these mechanisms by a biasedclutch arrangement that is axially slidable between two positions wherein it isengaged by one of these arrangements to rotate the cam as the key or thumb-turn is rotated but is not engaged by the other of the arrangements in orderthat it can rotate freely relative thereto. A problem with known locking mechanisms of this type is that they canbe broken into with relative ease to gain access to the dead bolt of the lockingmechanism. The application of force via a tool from the exterior side of thelock mechanism can break off part of the lock cylinder on one side of the cam,exposing the cam and allowing the cam to be rotated or removed to leave thelocking mechanism exposed for further tampering.

The object of the present invention is to provide an improved lockcylinder that obstructs access to the locking mechanism and therefore any dead bolt operating arrangement forming a part of it if the lock cylinder isattacked and broken into.

Hereafter and in the claims the word “normal’ describes a standardcondition of the lock cylinder as it would leave the factory and underconditions of ordinary use after fitment, in other words when it has not beentampered with or broken into. The term “snapped condition” describes thecondition of that part of a lock cylinder that remains in position in a lockingmechanism after it has been broken into and part of it removed.

According to the present invention there is provided a lock cylinder fora locking mechanism, the lock cylinder comprising a casing defining a longitudinal axis; a rotatably mounted cam comprising a radially projecting lever that isadapted to actuate the locking mechanism on rotation of the cam; first and second cores rotatably mounted within the casing on eitherside of the cam respectively; a clutch arrangement and a biasing means for placing either the first orthe second core into engagement with the cam; and a locking mechanism adapted to operate if the casing is broken and thefirst core removed; wherein the cam or a first part thereof is movable along the longitudinal axisrelative to the casing but is retained in a normal operating position against theforce of the biasing means while the casing remains unbroken but when thecasing is broken and the first core removed, the cam or said first part thereofis moved axially by the biasing means and frees the locking mechanism foroperation, which operation locks the cam or said first part thereof to thesecond core and against further axial movement and removal from theremaining casing.

Preferably, after operation of the locking mechanism the second core isable to engage the cam or a part thereof to rotate the lever.

In one embodiment of the invention the cam may comprise said firstpart that is movable along the longitudinal axis relative to a second part thatcomprises the lever, said first part being retained in a normal operatingposition relative to said second part against the force of the biasing meanswhile the casing remains unbroken but when the casing is broken and the firstcore removed, said first part of the cam is moved axially relative to said secondpart of the cam by the biasing mean and frees the locking mechanism foroperation.

Other preferred but non-essential features of the present invention aredescribed in the dependent claims appended hereto.

The present invention will now be described by way of example withreference to the accompanying drawings, in which:-

Fig. 1 is a side view of a first embodiment of lock cylinder in accordancewith the present invention when in a normal condition;

Fig. 2 is a perspective view of the lock cylinder shown in Fig, 1;

Fig. 3 is an exploded view of the cylinder shown in Fig. 2;

Figs. 4 and 5 are sectional views of the central part of the lock cylinderalong the lines IV-IV and V-V respectively in Fig. 1;

Fig. 6 is a side view of a remaining part of the lock cylinder when in asnapped condition;

Fig. 7 is a view along the line VII-VII in Fig 6;

Fig. 8 is a view along the line VIII-VIII in Fig. 6 but to an enlarged scale;

Fig. 9 is a perspective, exploded view of a cam of the lock cylinder to anenlarged scale as compared to the other drawings;

Fig. 10 is a perspective view of the cam when the lock cylinder is in anormal condition as is the case in Figs. 1 to 5;

Fig. 11 is a perspective view of the cam when the lock cylinder is in asnapped condition as is the case in Figs. 6 to 8;

Figs. 12 and 13 are views from below of the cam shown in Figs. 10 and11 respectively;

Fig. 14 is a view similar to Fig. 6 but of a modified arrangement;

Fig. 15 is a view along the line XV-XV in Fig. 14;

Fig. 16 is a perspective view of a cam of the modified arrangementshown in Figs. 14 and 15 when the lock cylinder is in a normal condition;

Fig. 17 is an exploded view of a second embodiment of lock cylinder inaccordance with the present invention;

Fig. 18 is a side view, similar to Fig. 6, of a remaining part of the secondembodiment of lock cylinder when in a snapped condition;

Fig. 19 is a view along the line XIX in Fig 18; and

Fig. 20 is a view along the line XX-XX in Fig. 18.

In the drawings and following description, details of lock mechanismsand other elements forming part of the described embodiments of lockcylinder that are not relevant to the present invention have been omitted forclarity. A first embodiment of lock cylinder in accordance with the invention isshown in Figs. 1 to 13 and comprises a casing 1 with first and second cylindricalportions 2 and 3 between which is a gap in which a cam 4 is located centrallyof the casing 1. The cylindrical portions 2 and 3 define a longitudinal axisalong which are respectively located first and second lock cores 5, 6 onopposite sides of the cam 4. The cores 5, 6 are retained in position by circlips7 that locate in annular grooves 8 provided in the cores 5, 6 and that can bearagainst the inner surfaces of the cylindrical portions 2 and 3 on either side ofthe cam 4. The cores 5 and 6 may comprise conventional pin tumbler lockmechanisms comprising a keyway 9 and bores 10 (see Fig. 7) housing key pins(not shown) movable when a key is inserted into the keyway 7 to act on biaseddriver pins (not shown) that are located within corresponding bores (notshown) formed in a radially projecting part 11 of the casing 1 that spans itslength. In other embodiments other lock mechanisms may be employed, forexample wafer lock mechanisms.

Whilst the illustrated first embodiment of lock cylinder shows first andsecond cores 5, 6 on opposite sides of the cam 4 that comprise pin tumblerlock mechanisms, other embodiments of lock cylinder in accordance with theinvention may comprise a core 5 of a first pin tumbler lock mechanism on oneside of the cam 4 and a core 6 of a thumb-turn mechanism on the other sideof the cam 4. Such an arrangement will be familiar to those skilled in the art.In use, the core 5 of the lock cylinder is intended to be located on an exteriorside of the door or closure and the core 6 is located on an interior side. It istherefore the core 5 on the exterior side of the cylinder that will be attackedwith a view to its removal should a break-in be attempted and the core 6 thatwill remain in a snapped condition of the lock cylinder. The same applies tothe second embodiment of lock cylinder that is described below with referenceto Figs. 17 to 20.

It will be appreciated that in all the embodiments of the presentinvention the pin tumbler lock and thumb-turn mechanisms operate in a conventional way but the manner in which they interact with the cam and aclutch arrangement provided to be selectively connected to one or other ofthese mechanism is the subject of the present invention and this will now bedescribed.

In the first embodiment of the invention and as is described in moredetail below with particular reference to Figs. 9 to 13, the cam 4 comprises afirst part 12 in the form of a substantially hollow, cylindrical body and a secondpart that comprises a radially projecting lever 13. In the normal condition ofthe lock cylinder, the first part 12 is rotatably mounted between the first andsecond cylindrical portions 2, 3 of the casing 1. Rotation of the first part 12moves the lever 13 so that in use it can bear against a spring-loaded portion ofan adjacent locking mechanism with which the lock cylinder is operationallylinked. Rotation of the first part 12 is effected by means of a clutcharrangement that comprises first and second actuators 14 and 15 and a biasingmeans, preferably in the form of a pair of compression springs 16. The firstand second actuators 14,15 respectively contact the inner ends of the first andsecond cores 5, 6 and are retained in contact with one another by the springs 16. The first actuator 14 takes the form of a short bar that is located within anadjacent part of the first part 12 of the cam 4 and comprises two wings 17 thatproject radially outwards on opposite sides of the bar. The second actuator 15is saddle-shaped and straddles the inner end of the second core 6. Legs 18 ofthis actuator 15 respectively locate in the ends of a pair of channels 19 definedby the second core 6. The springs 16 are also respectively located in thechannels 19 and act against the legs 18 of the actuator 15 to bias the clutcharrangement such that the second actuator 15 is normally engaged with thefirst part 12 of the cam 4. In this position the legs 18 engage between internalprojections 20 within the first part 12 of the cam 4 so that rotation of the core6 and thereby the actuator 15 also rotates the cam 4. However, when thisoccurs the first actuator 14 is out of engagement with the first part 12 of thecam 4 so that the actuator 14 and first core 5 remain motionless as the cam 4rotates. Conversely, axial movement of the first actuator 14 inwardly againstthe force of the springs 16 moves the actuator 14 into engagement with the first part 12 of the cam 4 and the second actuator 15 out of engagement withthe first part 12 of the cam 4. This axial movement occurs when a key isinserted into the keyway 9 of the first core 5. The tip of the blade of the keypushes the first actuator 14 further into the first part 12 of the cam 4 so thatits wings 17 engage with the projections 20, at the same time pushing thesecond actuator 15 out of the engagement with the projections 20. Hence,turning of the first core 5 by the key rotates the cam 4 but leaves the secondactuator 16 and second core 6 unmoved.

It will be appreciated that in this embodiment the springs 16 bias theclutch arrangement such that the second actuator 15 is normally engaged withthe first part 12 of the cam 4 and the first actuator 14 is out of engagement withthe first part 12 of the cam 4. This is because the second actuator 15 is linkedto the core 5 on the interior side of the lock cylinder to provide a fail-safearrangement if the lock cylinder is tampered with, as is described below, sothat the lock cylinder can always be actuated from the interior side.

In order to thwart an attempt to gain access to a dead bolt operatingarrangement actuated by the cam 4 if the lock cylinder is attacked and brokeninto, the lock cylinder also incorporates a locking mechanism that is adaptedto operate if the casing 1 is broken and the first, exterior core 5 removed.

The locking mechanism comprises at least one and preferably a pair ofbiased locking elements 21 which are normally retained in respective cavities22 defined by the second core 6. While the elements 21 and cavities 22 couldtake many forms, preferably the elements 21 are in the form of spring-loadedlocking pins that are normally located in bores 22. Preferably, the bores 22 aretransversely aligned on opposite sides of the inner end of the second core 6and are straddled by the legs 18 of the second actuator 15. The pins 21 aretherefore located within the hollow body of the cam 4 and, in the normalcondition of the lock cylinder, the spring loading 23 biases the pins 21 intoengagement with an adjacent inner surface of the first part 12 of the cam 4, asshown in Fig, 4. However, this surface of the first part 12 of the cam 4 defines at least one and preferably a respective pair of apertures or depressions 24(apertures in the illustrated embodiment) that are moved into alignment withthe locking pins 21 when the lock cylinder is in its snapped condition. Thiscauses the pins 21 to enter the apertures or depressions 24 and thereby lockthe second, inner core 6 to the first part 12 of the cam 4, as shown in Fig. 7.This prevents removal of the cam 4 from the lock cylinder, thereby protectingaccess to the casing of an adjacent locking mechanism, and also preventsrotation of the cam 4 from the exterior of the lock cylinder as the cam 4 isrestrained by the locking mechanism of the second core 6.

Alignment of the pins 21 with the apertures or depressions 24 takesplace because the first part 12 of the cam 4 is movable along the longitudinalaxis of the lock cylinder relative to the second part 13. It will be appreciatedthat normally, the first part 12 is retained in a normal operating positionrelative to the second part 13 by the first core 5 against the force of the springs16. However, when the casing 1 is broken and the first core 5 is removed, thefirst actuator 14 also falls away and the first part 12 of the cam 4 is free to bemoved axially by the springs 16.

The structure of a first embodiment of cam 4 will now be described inmore detail with particular reference to Figs. 9 to 13.

As described above, the first part 12 of the cam 4 comprises a hollow,substantially cylindrical body. This body defines a pair of longitudinallyaligned parallel grooves 25 between which is located a radially projecting peg26. The second part 13 of the cam 4 comprises the radially projecting leverwhich slides along the grooves 25 and fits over the peg 26, which has anenlarged end to retain the second part 13 in a radial direction. The second part13 can therefore move axially along the grooves 25 relative to the first part 12while still being retained by the peg 26. In addition, the second part 13 isretained in a position covering the peg 26 by a blocking strip 27 that is forcefitted into a channel 28 that straddles the parallel grooves 25. Preferably, thefit of the second part 13 over the peg 26 should be a slight friction fit to prevent it “wandering” axially during normal rotational operation of the cam 4.Persons skilled in the art will appreciate that other mechanisms to preventsuch wandering are also possible. The blocking strip 27 also restrains thesecond part 13 of the cam 4 from significant movement towards the first core5 during normal operation of the locking cylinder. Additional swaging maybeused to prevent the blocking strip 26 from becoming detached both duringnormal operation of the lock cylinder use and after lock snapping.

In normal operation of the lock cylinder, the clutch arrangement 14,15selectively places either the first core 5 or the second core 6 into engagementwith the cam 4 against the force of the biasing means 16 as described above.However, when the lock cylinder 1 is snapped and the first core 5 is removed,the biasing means 16 acts to move the cam 4 that is no longer restrained bythe first core 5 and actuator 14, which falls away. Initially, the first and secondparts 12 and 13 of the cam 4 move together away from the second core 6.However, the second part 13 of the cam 4, which is usually in a partially rotatedposition out of the vertical, as shown in Fig. 6, will hit a face 29 of the casingin a cut-out portion 30 of the radially projecting part 11 of the casing 1 thataccommodates the second part 13. This occurs after a short distance of travelthat will be typically less than 1 mm. This impact stops axial motion of thesecond part 13 but the biasing means 16 provides sufficient force to overcomethe friction between the second part 13 and the peg 26. The first part 12 of thecam 4 is therefore moved relative to the second part 13, which travels alongthe grooves 25 in a direction away from the blocking strip 27 until the spring-loaded locking pins 21 align with the apertures 24 in the first part 12 of thecam 4. When this occurs, the locking pins 21 enter the apertures 24 andrestrain further axial movement of the first part 12 of the cam 4. The cam 4 isnow locked in position, being secured to the second core 6, as described above.

In order to ensure that the casing 1 of the lock cylinder snaps in apredetermined way in the unfortunate event that a break-in is attempted, thecasing 1 is provided with one or more weakened areas in order that it breaksat a predetermined position conducive to the aforementioned operation of the locking mechanism. In the illustrated embodiment the casing 1 is providedwith a weakened area in the form of a sacrificial cut 31, as shown in Figs. 1 to 3, that is located close to the face 29 of the cut-out portion 30 on the exteriorside of the casing 1. This ensures that most or the whole of the exteriorcylindrical portion 2 can be broken away so that the first core 5 and the firstactuator 14 also fall away from the remaining components of the lock cylinder. A modified arrangement of cam 4 will now be described with referenceto Figs. 14 to 16, which also show consequential changes to the casing 1. Inthis modification, a first part 12A of the cam 4 still comprises a hollow,substantially cylindrical body with apertures 24 but instead of carrying a peg26, it comprises a cut-away portion into which slides a the second part 13A,which comprises a part-cylindrical portion 13B that is integrally formed withthe radially projecting lever 13C. Preferably, the side edges of the part-cylindrical part i3Afit into grooves or undercut regions at the edges of the cut-away portion of the first part 12A, which holds the second part 13A in positionwhile still enabling the first and second parts 13A to move axially relative toeach other when required. However, in order to prevent the second part 13Afrom wandering axially during normal operation of the lock cylinder, it isretained in position by a static pin 32 that projects from a bore 32 in the casing1 adjacent the cut-out portion 30 on the interior side of the casing 1. Theprojecting end of the pin 32 runs freely in a groove 34 that encircles the cam 4, having a first section that that runs around the first part 12A and a secondsection that runs across the second part 13A. These two groove sections matchup during normal operation of the lock cylinder. The pin 32 prevents axialwandering of the radially projecting lever during normal use of the lockcylinder and has no negative effect upon the ability to open the lock cylinderfrom its interior side after the lock cylinder has been snapped. It will beappreciated, however, that the pin 32 does not prevent axial movement of thefirst part 12A of the cam 4 relative to the second part 13A in the snappedcondition of the lock cylinder when the first part 12A is moved away from theinterior side by the springs 16. In fact, the pin 32 retains the second part 13Ain position while allowing the first part 12A to move.

In normal operation of the lock cylinder with the modified cam 4, theclutch arrangement 14,15 operates as described above. When the lock cylinder1 is snapped and the first core 5 is removed, the biasing means 16 acts to movethe first part 12A of the cam 4 that is no longer restrained by the first core 5and actuator 14, which falls away. However, the second part 13A of the cam 4is retained in position by the static pin 32. In a similar way to that describedabove with regard to the first embodiment, the first part 12A moves axiallyuntil the spring-loaded locking pins 21 align with the apertures 24. When thisoccurs, the locking pins 21 enter the apertures 24 and restrain further axialmovement of the first part 12A of the cam 4. The cam 4 is now locked inposition, being secured to the second core 6, as described above.

It will be appreciated that other embodiments of two-part cam arepossible in addition to those described herein that fall within the scope of thepresent invention.

The second embodiment of lock cylinder will now be described withreference to Figs 17 to 20. Identical parts or parts with an identical functionto those described above in the first embodiment of the invention are giventhe same reference numerals.

In the second embodiment, as in the first embodiment, the lockcylinder comprises a casing 1 with first and second cylindrical portions 2 and3 between which is a gap in which a cam 4 is located centrally of the casing 1.However, in this embodiment, the cam 4 is in one piece and comprises anintegral lever 13. It does not, therefore, comprise relatively movable first andsecond parts; rather, the whole of the cam 4 is movable relative to the casing1 for a short distance along the longitudinal axis after lock snapping. Thislongitudinal movement is only up to around 1 mm but is sufficient to causeoperation of a locking mechanism, as is described below.

The cylindrical portions 2 and 3 define a longitudinal axis along whichare respectively located first and second lock cores 5, 6 on opposite sides ofthe cam 4. As before, the cores 5, 6 are retained in position by circlips 7 thatlocate in annular grooves 8 provided in the cores 5, 6 and that can bear againstthe inner surfaces of the cylindrical portions 2 and 3 on either side of the cam 4. The cores 5 and 6 may comprise conventional pin tumbler lock mechanismscomprising a keyway 9 and bores 10 housing key pins (not shown) movablewhen a key is inserted into the keyway 7, other lock mechanisms or a thumb-turn as described above. A clutch arrangement is provided along with a biasingmeans, preferably in the form of a spring 16, for placing either the first or thesecond core 5 or 6 into engagement with the cam 4. The clutch arrangementcomprises first and second actuators 14 and 15 and these together with thebiasing means 16 are similar but not identical to the same parts as describedabove with respect to the first embodiment. However, they operate in the sameway. The first actuator 14 takes the form of a two adjacent short bars a firstbar 35 and a second bar 36 that respectively engage within adjacent parts ofthe first core 5 and the cam 4. The first bar 35 is cylindrical but the second bar36 comprises longitudinal projections 36a on one side that straddle the firstbar 35 and can engage within channels 37 defined by the first core 5. The otherside of the second bar 36 is similar to the actuator 14 of the first embodimentand comprises a projecting nose 38 that can engage between internalprojections 39 within the cam 4 so that rotation of the core 5 and thereby thesecond bar 36 also rotates the cam 4. The second actuator 15 is not saddle-shaped but also comprises a short bar with a nose 40, radially projecting wings41 and a central cavity 42 in which the spring 16 is located, the free end of thespring 16 bearing against an internal end face 43 of the core 6 between twochannels 19 defined by the core 6 that are similar to those of the firstembodiment. The wings 41 can also locate within the channels 19 so that theclutch arrangement operates in a similar way to the clutch arrangement of thefirst embodiment and can selectively place either the first core 5 or the secondcore 6 into engagement with the cam 4. Again, in this embodiment the spring16 biases the clutch arrangement such that the second actuator 15, which is onan interior side of the locking mechanism, is normally engaged with the cam 4 and the first actuator 14, which is on an exterior side of the lockingmechanism, is out of engagement with the first part 12 of the cam 4.

The locking mechanism is also similar but not identical to that in thefirst embodiment as it comprises a single locking element that is normallyretained in a cavity defined by the second core 6. However, as before, thelocking element is in the form of a spring-loaded locking pin that is normallylocated in a cavity in the form of a bore 22. Here, the bore 22 is transverselyaligned along a vertical axis when the lock has been installed. The bore 22passes all the way through the second core 6 and the locking pin 21 and itsspring-loading 23 are retained within the second core 6 by a force-fit ball 44that bears against an adjacent interior surface of the cam 4. However, othermeans of retaining the locking pin 21 and spring-loading 23 can be used, forexample swaging or the use of a small grub screw. The locking pin 21 istherefore located within the hollow body of the cam 4 and, in the normalcondition of the lock cylinder; the spring-loading 23 biases it into engagementwith an adjacent inner surface of the cam 4. However, this surface alsodefines an aperture or depression 24 that is moved into alignment with thelocking pin 21 when the lock cylinder is in its snapped condition, as shown inFig. 20. This causes the pin 21 to enter the apertures or depressions 24 andthereby lock the second, inner core 6 to the cam 4, Removal of the cam 4 fromthe lock casing 1 is thereby prevented and the presence of the cam 4 preventsaccess to the casing of an adjacent locking mechanism, and also rotation of thecam 4 from the exterior of the lock cylinder as the cam 4 is restrained by thelocking mechanism of the second core 6.

In normal operation of the lock cylinder, the actuators 14 and 15 of theclutch arrangement selectively place either the first core 5 or the second core6 into engagement with the cam 4 against the force of the biasing means 16,as described above. However, when the lock cylinder 1 is snapped and the firstcore 5 is removed, the biasing means 16 acts to move the cam 4 that is nolonger restrained by the first core 5 and actuator 14, which falls away, awayfrom the second core 6 and towards the face 29 of the casing in the cut-outportion 30. After a very short distance of travel, as indicated above, the spring- loaded locking pin 21 aligns with the aperture 24 in the cam 4. When thisoccurs, the locking pin 21 enters the apertures 24 and restrains further axialmovement of the cam 4. The cam 4 is now locked in position, and secured tothe second core 6, as described above.

Also as before, in order to ensure that the casing 1 of the lock cylindersnaps in a predetermined way, the casing 1 is provided with a weakened areain the form of a sacrificial cut 31 that is located close to the face 29 of the cut-out portion 30 on the exterior side of the casing 1. A further feature of the invention that applies to both embodimentsdescribed above is that after the lock cylinder 1 has been snapped, theremaining actuator 15 is still capable of movement along the longitudinal axisof the casing 1 against the force biasing means, namely the spring or springs16, in the same way as when the lock cylinder 1 was complete. The end face ofnose 40 of the actuator 15 usually protrudes through the exposed end of thecam 4. However, as it can move back into the cam 4 it tends to thwart attemptsto grip it by a tool such as a pair of pliers and may be rounded or otherwiseshaped to prevent it from being gripped firmly. It may also be strengthenedby the use of a hardened insert or similar to thwart attacks by a drill.

Even after it has been snapped, the lock cylinder of the invention is stillcapable of operating to allow at least one opening of the door or closure fromits interior side. This is usually now a legal requirement of such lock cylindersfor reasons of safety. When in a snapped condition, it will be appreciated thata key 9 can still be inserted into the keyway of the second core 6 or a thumbturn used to rotate the core 6 along with the first and second portions of thecam 4 to operate an adjacent dead bolt or similar portion of a lockingmechanism with which the lock cylinder is associated.

Claims

1. A lock cylinder for a locking mechanism, the lock cylinder comprising a casing defining a longitudinal axis; a rotatably mounted cam comprising a radially projecting leverthat is adapted to actuate the locking mechanism on rotation of thecam; first and second cores rotatably mounted within the casing oneither side of the cam respectively; a clutch arrangement and a biasing means for placing either thefirst or the second core into engagement with the cam; and a locking mechanism adapted to operate if the casing is brokenand the first core removed; wherein the cam or a first part thereof is movable along the longitudinalaxis relative to the casing but is retained in a normal operating positionagainst the force of the biasing means while the casing remainsunbroken but when the casing is broken and the first core removed, thecam or said first part is moved axially by the biasing means and freesthe locking mechanism for operation, which operation locks the cam orsaid first part to the second core and against further axial movementand removal from the remaining casing.

2. A lock cylinder as claimed in Claim 1, wherein after operation of thelocking mechanism the second core is able to engage the cam or a partthereof to rotate the lever.

3. A lock cylinder as claimed in Claim 1 or Claim 2, wherein the camcomprises said first part that is movable along the longitudinal axisrelative to a second part that comprises the lever, said first part beingretained in a normal operating position relative to said second partagainst the force of the biasing means while the casing remainsunbroken but when the casing is broken and the first core removed,said first part of the cam is moved axially relative to said second part of the cam by the biasing mean and frees the locking mechanism foroperation.

4. A lock cylinder as claimed in Claim 3, wherein the first part of the camcomprises a substantially cylindrical body and defines a pair oflongitudinally aligned grooves in which the second part of the camlocates and along which it can move relative to the first part of the cam.

5. A lock cylinder as claimed in Claim 4, wherein a blocking strip is locatedin a channel that straddles the parallel grooves to restrain the secondpart of the cam from significant movement towards the first core duringnormal operation of the locking cylinder.

6. A lock cylinder as claimed in Claim 4 or Claim 5, wherein the first partof the cam comprises a projecting peg located between the parallelgrooves over which the second part of the cam is fitted.

7. A lock cylinder as claimed in any of Claims 3 to 6, wherein the secondpart of the cam is restrained from significant movement by abutmentagainst a surface of the casing when the first part of the cam is movedaxially by the biasing means after the casing has been broken and thefirst core removed.

8. A lock cylinder as claimed in any of Claims 3 to 6, wherein the secondpart of the cam is restrained from significant movement by a static pinthat projects from a portion of the casing into a groove defined by thesecond part of the cam.

9. A lock cylinder as claimed in Claim 8, wherein the groove comprises afirst section that that runs around the first part of the cam and a secondsection that runs across the second part of the cam, the two sectionsmatching up during normal operation of lock cylinder.

10. A lock cylinder as claimed in any of Claims 1 to 9, wherein the lockingmechanism comprises a biased locking element that is normallyretained within a cavity in the second core by engagement with asurface of the cam.

11. A lock cylinder as claimed in Claim 10, wherein said surface of the camdefines an aperture or depression that is moved into alignment with thelocking element when the cam or said first part thereof is moved axiallythereby permitting the locking element to be moved into the apertureor depression to secure the cam or said first part thereof to the secondcore.

12. A lock cylinder as claimed in any of Claims 1 to 11, wherein the lockingmechanism comprises a biased locking element that is located in atransversely aligned cavity defined by the second core and that locatesin an aperture or depression defined by the cam or said first partthereof.

13. A lock mechanism as claimed in any of Claims 1 to 11, wherein thelocking mechanism comprises a pair of biased locking elements that arerespectively located in transversely aligned cavities on opposite sides ofthe second core and locate in a pair of apertures or depressions onopposite sides of the first part of the cam.

14. A lock cylinder as claimed in Claim 12 or Claim 13, wherein the or eachbiased locking element comprises a spring-loaded locking pin that islocated in said transversely aligned cavity, which is in the form of abore in the second core.

15. A lock cylinder as claimed in any of Claims 1 to 14, wherein the clutcharrangement comprises first and second actuators that respectivelycontact inner ends of the first and second cores and that are retained incontact with one another by the biasing means, axial movement of the first core against the force of the biasing means moving the firstactuator into engagement with the cam and the second actuator out ofengagement with the cam.

16. A lock cylinder as claimed in Claim 15, wherein the biasing meansbiases the clutch arrangement such that the second actuator isnormally engaged with the cam and the first actuator is out ofengagement with the cam.

17. A lock cylinder as claimed in Claim 15 or Claim 16, wherein the secondactuator is saddle-shaped and straddles the inner end of the secondcore.

18. A lock cylinder as claimed in Claim 17, wherein legs of the saddle-shaped second actuator respectively locate in a pair of channels definedby the second core.

19. A lock cylinder as claimed in Claim 18, wherein the biasing meanscomprises a pair of springs that are respectively located in the pair ofchannels defined by the second core and that act against the legs of thesaddle-shaped second actuator.

20. A lock cylinder as claimed in any of Claims 17 to 18 when dependent onClaim 13, wherein the transversely aligned cavities in the second coreare straddled by and arranged at right angles to the legs of the saddle-shaped second actuator.

21. A lock cylinder as claimed in any of Claims 1 to 20, wherein the casingcomprises an area of weakness that causes snapping of the casingtransversely with respect to said longitudinal axis between the cam andsaid first core should an attempt be made to break the lock cylinder.