GB2565379A

GB2565379A - A lock cylinder for a locking mechanism

Info

Publication number: GB2565379A
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: 2019-02-13
Anticipated expiration: 2037-10-26
Also published as: GB2565379B; GB201717621D0; GB201711110D0

Abstract

A cylinder lock with a clutch 15, 16 biased, e.g. by spring 16, for placing either of two rotatable cores 5, 6, in engagement with cam 4. When the exterior side casing is removed along with the exterior core 5 the cam or a first part of the cam moves axially by the bias 16 until it is retained in place by a locking mechanism 21 preventing further axial movement and removal of the cam or the first part thereof. The cam locking mechanism may include two spring biased pins 21 held in apertures 22 of the interior core 6 normally laterally offset from pin receiving apertures 24 in cam 4. The locking mechanism may lock the cam to the internal core 6 and allow rotation of the cam with the internal core. The cam may be a single part (figure 17) or may comprise a first cam part 4 and a second cam part 13, with relative movement limited by a blocking piece 27 (fig. 9).

Description

A LOCK CYLINDER FORA LOCKING MECHANISM

The present invention relates to a lock cylinder for a locking mechanism for doors and other similar closures. Such lock cylinders are commonly called euro-lock cylinders or euro-cylinders. A euro-lock cylinder is designed to operate a rotatable cam with a projecting cam lever that bears against a dead bolt or similar portion of a locking 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 accomplished either via a pin tumbler lock mechanism that requires a key to operate or via a thumb-turn mechanism. Locking mechanisms that comprise such a lock cylinder may incorporate a lock cylinder with two pin tumbler lock mechanisms on opposite sides of the cam so that keys are required to open a door from both sides. Alternatively, the lock cylinder may incorporate a tumbler lock mechanism on one side of the cam and a thumb-turn mechanism on the opposite side of the cam, the former typically being used on an exterior side of a door and the latter on an interior side. In both cases, the cam is usually selectively connected to one or other of these mechanisms by a biased clutch arrangement that is axially slidable between two positions wherein it is engaged 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 order that it can rotate freely relative thereto. A problem with known locking mechanisms of this type is that they can be broken into with relative ease to gain access to the dead bolt of the locking mechanism. The application of force via a tool from the exterior side of the lock 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 the locking mechanism exposed for further tampering.

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

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

According to the present invention there is provided 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 lever that is adapted to actuate the locking mechanism on rotation of the cam; first and second cores rotatably mounted within the casing on either side of the cam respectively; a clutch arrangement and a biasing means for placing either the first or the second core into engagement with the cam; and a locking mechanism adapted to operate if the casing is broken and the first core removed; wherein the cam or a first part thereof is movable along the longitudinal axis relative to the casing but is retained in a normal operating position against the force of the biasing means while the casing remains unbroken but when the casing is broken and the first core removed, the cam or said first part thereof is moved axially by the biasing means and frees the locking mechanism for operation, which operation locks the cam or said first part thereof against further axial movement and removal from the remaining casing.

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

In one embodiment of the invention the cam may comprise said first part that is movable along the longitudinal axis relative to a second part that comprises the lever, said first part being retained in a normal operating position relative to said second part against the force of the biasing means while the casing remains unbroken 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 for operation.

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

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

Fig. l is a side view of a first embodiment of lock cylinder in accordance with the present invention when in a normal condition;

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

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 cylinder along 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 a snapped 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 an enlarged scale as compared to the other drawings;

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

Fig. 11 is a perspective view of the cam when the lock cylinder is in a snapped 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 and 11 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 arrangement shown 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 in accordance with the present invention;

Fig. 18 is a side view, similar to Fig. 6, of a remaining part of the second embodiment 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 mechanisms and other elements forming part of the described embodiments of lock cylinder that are not relevant to the present invention have been omitted for clarity. A first embodiment of lock cylinder in accordance with the invention is shown in Figs, l to 13 and comprises a casing 1 with first and second cylindrical portions 2 and 3 between which is a gap in which a cam 4 is located centrally of the casing 1. The cylindrical portions 2 and 3 define a longitudinal axis along which are respectively located first and second lock cores 5, 6 on opposite sides of the cam 4. The cores 5, 6 are retained in position by circlips 7 that locate in annular grooves 8 provided in the cores 5, 6 and that can bear against the 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 mechanisms 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 biased driver pins (not shown) that are located within corresponding bores (not shown) formed in a radially projecting part 11 of the casing 1 that spans its length. In other embodiments other lock mechanisms maybe employed, for example wafer lock mechanisms.

Whilst the illustrated first embodiment of lock cylinder shows first and second cores 5, 6 on opposite sides of the cam 4 that comprise pin tumbler lock mechanisms, other embodiments of lock cylinder in accordance with the invention may comprise a core 5 of a first pin tumbler lock mechanism on one side of the cam 4 and a core 6 of a thumb-turn mechanism on the other side of 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 exterior side of the door or closure and the core 6 is located on an interior side. It is therefore the core 5 on the exterior side of the cylinder that will be attacked with a view to its removal should a break-in be attempted and the core 6 that will remain in a snapped condition of the lock cylinder. The same applies to the second embodiment of lock cylinder that is described below with reference to Figs. 17 to 20.

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

In the first embodiment of the invention and as is described in more detail below with particular reference to Figs. 9 to 13, the cam 4 comprises a first part 12 in the form of a substantially hollow, cylindrical body and a second part that comprises a radially projecting lever 13. In the normal condition of the lock cylinder, the first part 12 is rotatably mounted between the first and second cylindrical portions 2, 3 of the casing 1. Rotation of the first part 12 moves the lever 13 so that in use it can bear against a springloaded portion of an adjacent locking mechanism with which the lock cylinder is operationally linked. Rotation of the first part 12 is effected by means of a clutch arrangement that comprises first and second actuators 14 and 15 and a biasing means, preferably in the form of a pair of compression springs 16. The first and second actuators 14, 15 respectively contact the inner ends of the first and second 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 an adjacent part of the first part 12 of the cam 4 and comprises two wings 17 that project radially outwards on opposite sides of the bar. The second actuator 15 is saddle-shaped and straddles the inner end of the second core 6. Legs 18 of this actuator 15 respectively locate in the ends of a pair of channels 19 defined by the second core 6. The springs 16 are also respectively located in the channels 19 and act against the legs 18 of the actuator 15 to bias the clutch arrangement such that the second actuator 15 is normally engaged with the first part 12 of the cam 4. In this position the legs 18 engage between internal projections 20 within the first part 12 of the cam 4 so that rotation of the core 6 and thereby the actuator 15 also rotates the cam 4. However, when this occurs the first actuator 14 is out of engagement with the first part 12 of the cam 4 so that the actuator 14 and first core 5 remain motionless as the cam 4 rotates. Conversely, axial movement of the first actuator 14 inwardly against the 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 with the first part 12 of the cam 4. This axial movement occurs when a key is inserted into the keyway 9 of the first core 5. The tip of the blade of the key pushes the first actuator 14 further into the first part 12 of the cam 4 so that its wings 17 engage with the projections 20, at the same time pushing the second 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 second actuator 16 and second core 6 unmoved.

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

In order to thwart an attempt to gain access to a dead bolt operating arrangement actuated by the cam 4 if the lock cylinder is attacked and broken into, the lock cylinder also incorporates a locking mechanism that is adapted to 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 of biased locking elements 21 which are normally retained in respective cavities 22 defined by the second core 6. While the elements 21 and cavities 22 could take many forms, preferably the elements 21 are in the form of spring-loaded locking pins that are normally located in bores 22. Preferably, the bores 22 are transversely aligned on opposite sides of the inner end of the second core 6 and are straddled by the legs 18 of the second actuator 15. The pins 21 are therefore located within the hollow body of the cam 4 and, in the normal condition of the lock cylinder, the spring loading 23 biases the pins 21 into engagement with an adjacent inner surface of the first part 12 of the cam 4, as shown 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 with the locking pins 21 when the lock cylinder is in its snapped condition. This causes the pins 21 to enter the apertures or depressions 24 and thereby lock the 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 protecting access to the casing of an adjacent locking mechanism, and also prevents rotation of the cam 4 from the exterior of the lock cylinder as the cam 4 is restrained by the locking mechanism of the second core 6.

Alignment of the pins 21 with the apertures or depressions 24 takes place because the first part 12 of the cam 4 is movable along the longitudinal axis of the lock cylinder relative to the second part 13. It will be appreciated that normally, the first part 12 is retained in a normal operating position relative to the second part 13 by the first core 5 against the force of the springs 16. However, when the casing 1 is broken and the first core 5 is removed, the first actuator 14 also falls away and the first part 12 of the cam 4 is free to be moved axially by the springs 16.

The structure of a first embodiment of cam 4 will now be described in more 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 longitudinally aligned parallel grooves 25 between which is located a radially projecting peg 26. The second part 13 of the cam 4 comprises the radially projecting lever which slides along the grooves 25 and fits over the peg 26, which has an enlarged end to retain the second part 13 in a radial direction. The second part 13 can therefore move axially along the grooves 25 relative to the first part 12 while still being retained by the peg 26. In addition, the second part 13 is retained in a position covering the peg 26 by a blocking strip 27 that is force fitted into a channel 28 that straddles the parallel grooves 25. Preferably, the fit 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 prevent such wandering are also possible. The blocking strip 27 also restrains the second part 13 of the cam 4 from significant movement towards the first core 5 during normal operation of the locking cylinder. Additional swaging may be used to prevent the blocking strip 26 from becoming detached both during normal operation of the lock cylinder use and after lock snapping.

In normal operation of the lock cylinder, the clutch arrangement 14, 15 selectively places either the first core 5 or the second core 6 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 first core 5 is removed, the biasing means 16 acts to move the cam 4 that is no longer restrained by the first core 5 and actuator 14, which falls away. Initially, the first and second parts 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 rotated position out of the vertical, as shown in Fig. 6, will hit a face 29 of the casing in a cut-out portion 30 of the radially projecting part 11 of the casing 1 that accommodates the second part 13. This occurs after a short distance of travel that will be typically less than 1 mm. This impact stops axial motion of the second part 13 but the biasing means 16 provides sufficient force to overcome the friction between the second part 13 and the peg 26. The first part 12 of the cam 4 is therefore moved relative to the second part 13, which travels along the 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 the cam 4. When this occurs, the locking pins 21 enter the apertures 24 and restrain further axial movement of the first part 12 of the cam 4. The cam 4 is now 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 a predetermined way in the unfortunate event that a break-in is attempted, the casing 1 is provided with one or more weakened areas in order that it breaks at a predetermined position conducive to the aforementioned operation of the locking mechanism. In the illustrated embodiment the casing 1 is provided with 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 exterior side of the casing 1. This ensures that most or the whole of the exterior cylindrical portion 2 can be broken away so that the first core 5 and the first actuator 14 also fall away from the remaining components of the lock cylinder. A modified arrangement of cam 4 will now be described with reference to Figs. 14 to 16, which also show consequential changes to the casing 1. In this modification, a first part 12A of the cam 4 still comprises a hollow, substantially cylindrical body with apertures 24 but instead of carrying a peg 26, 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 with the radially projecting lever 13C. Preferably, the side edges of the part-cylindrical part 13A fit 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 position while still enabling the first and second parts 13A to move axially relative to each other when required. However, in order to prevent the second part 13A from wandering axially during normal operation of the lock cylinder, it is retained in position by a static pin 32 that projects from a bore 32 in the casing 1 adjacent the cut-out portion 30 on the interior side of the casing 1. The projecting 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 second section that runs across the second part 13A. These two groove sections match up during normal operation of the lock cylinder. The pin 32 prevents axial wandering of the radially projecting lever during normal use of the lock cylinder and has no negative effect upon the ability to open the lock cylinder from its interior side after the lock cylinder has been snapped. It will be appreciated, however, that the pin 32 does not prevent axial movement of the first part 12A of the cam 4 relative to the second part 13A in the snapped condition of the lock cylinder when the first part 12A is moved away from the interior side by the springs 16. In fact, the pin 32 retains the second part 13A in position while allowing the first part 12A to move.

In normal operation of the lock cylinder with the modified cam 4, the clutch arrangement 14, 15 operates as described above. When the lock cylinder 1 is snapped and the first core 5 is removed, the biasing means 16 acts to move the first part 12A of the cam 4 that is no longer restrained by the first core 5 and actuator 14, which falls away. However, the second part 13A of the cam 4 is retained in position by the static pin 32. In a similar way to that described above with regard to the first embodiment, the first part 12A moves axially until the spring-loaded locking pins 21 align with the apertures 24. When this occurs, the locking pins 21 enter the apertures 24 and restrain further axial movement of the first part 12A of the cam 4. The cam 4 is now locked in position, being secured to the second core 6, as described above.

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

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

In the second embodiment, as in the first embodiment, the lock cylinder comprises a casing 1 with first and second cylindrical portions 2 and 3 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 an integral lever 13. It does not, therefore, comprise relatively movable first and second parts; rather, the whole of the cam 4 is movable relative to the casing 1 for a short distance along the longitudinal axis after lock snapping. This longitudinal movement is only up to around 1 mm but is sufficient to cause operation of a locking mechanism, as is described below.

The cylindrical portions 2 and 3 define a longitudinal axis along which are respectively located first and second lock cores 5, 6 on opposite sides of the cam 4. As before, the cores 5, 6 are retained in position by circlips 7 that locate in annular grooves 8 provided in the cores 5, 6 and that can bear against the 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 mechanisms comprising a keyway 9 and bores 10 housing key pins (not shown) movable when 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 biasing means, preferably in the form of a spring 16, for placing either the first or the second core 5 or 6 into engagement with the cam 4. The clutch arrangement comprises first and second actuators 14 and 15 and these together with the biasing means 16 are similar but not identical to the same parts as described above with respect to the first embodiment. However, they operate in the same way. The first actuator 14 takes the form of a two adjacent short bars 35 and 36 that respectively engage within adjacent parts of the first core 5 and the cam 4. The bar 35 is cylindrical but the 36 comprises longitudinal projections 36 on one side that straddle the bar 35 and can engage within channels 37 defined by the first core 5. The other side of the bar 36 is similar to the actuator 14 of the first embodiment and comprises a projecting nose 38 that can engage between internal projections 39 within the cam 4 so that rotation of the core 5 and thereby the 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 wings 41 and a central cavity 42 in which the spring 16 is located, the free end of the spring 16 bearing against an internal end face 43 of the core 6 between two channels 19 defined by the core 6 that are similar to those of the first embodiment. The wings 41 can also locate within the channels 19 so that the clutch arrangement operates in a similar way to the clutch arrangement of the first embodiment and can selectively place either the first core 5 or the second core 6 into engagement with the cam 4. Again, in this embodiment the spring 16 biases the clutch arrangement such that the second actuator 15, which is on an 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 locking mechanism, 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 the first embodiment as it comprises a single locking element that is normally retained in a cavity defined by the second core 6. However, as before, the locking element is in the form of a spring-loaded locking pin that is normally located in a cavity in the form of a bore 22. Here, the bore 22 is transversely aligned along a vertical axis when the lock has been installed. The bore 22 passes all the way through the second core 6 and the locking pin 21 and its spring-loading 23 are retained within the second core 6 by a force-fit ball 44 that bears against an adjacent interior surface of the cam 4. However, other means of retaining the locking pin 21 and spring-loading 23 can be used, for example swaging or the use of a small grub screw. The locking pin 21 is therefore located within the hollow body of the cam 4 and, in the normal condition of the lock cylinder; the spring-loading 23 biases it into engagement with an adjacent inner surface of the cam 4. However, this surface also defines an aperture or depression 24 that is moved into alignment with the locking pin 21 when the lock cylinder is in its snapped condition, as shown in Fig. 20. This causes the pin 21 to enter the apertures or depressions 24 and thereby lock the second, inner core 6 to the cam 4, Removal of the cam 4 from the lock casing 1 is thereby prevented and the presence of the cam 4 prevents access to the casing of an adjacent locking mechanism, and also rotation of the cam 4 from the exterior of the lock cylinder as the cam 4 is restrained by the locking mechanism of the second core 6.

In normal operation of the lock cylinder, the actuators 14 and 15 of the clutch arrangement selectively place either the first core 5 or the second core 6 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 first core 5 is removed, the biasing means 16 acts to move the cam 4 that is no longer restrained by the first core 5 and actuator 14, which falls away, away from the second core 6 and towards the face 29 of the casing in the cutout portion 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 this occurs, the locking pin 21 enters the apertures 24 and restrains further axial movement of the cam 4. The cam 4 is now locked in position, and secured to the second core 6, as described above.

Also as before, in order to ensure that the casing 1 of the lock cylinder snaps in a predetermined way, the casing 1 is provided with a weakened area in the form of a sacrificial cut 31 that is located close to the face 29 of the cutout portion 30 on the exterior side of the casing 1. A further feature of the invention that applies to both embodiments described above is that after the lock cylinder 1 has been snapped, the remaining actuator 15 is still capable of movement along the longitudinal axis of the casing 1 against the force biasing means, namely the spring or springs 16, in the same way as when the lock cylinder 1 was complete. The end face of nose 40 of the actuator 15 usually protrudes through the exposed end of the cam 4. However, as it can move back into the cam 4 it tends to thwart attempts to grip it by a tool such as a pair of pliers and may be rounded or otherwise shaped to prevent it from being gripped firmly. It may also be strengthened by 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 still capable of operating to allow at least one opening of the door or closure from its interior side. This is usually now a legal requirement of such lock cylinders for reasons of safety. When in a snapped condition, it will be appreciated that a key 9 can still be inserted into the keyway of the second core 6 or a thumb turn used to rotate the core 6 along with the first and second portions of the cam 4 to operate an adjacent dead bolt or similar portion of a locking mechanism 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 lever that is adapted to actuate the locking mechanism on rotation of the cam; first and second cores rotatably mounted within the casing on either side of the cam respectively; a clutch arrangement and a biasing means for placing either the first or the second core into engagement with the cam; and a locking mechanism adapted to operate if the casing is broken and the first core removed; wherein the cam or a first part thereof is movable along the longitudinal axis relative to the casing but is retained in a normal operating position against the force of the biasing means while the casing remains unbroken but when the casing is broken and the first core removed, the cam or said first part is moved axially by the biasing means and frees the locking mechanism for operation, which operation locks the cam or said first part against further axial movement and removal from the remaining casing.

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

3. A lock cylinder as claimed in Claim 1 or Claim 2, wherein the cam comprises said first part that is movable along the longitudinal axis relative to a second part that comprises the lever, said first part being retained in a normal operating position relative to said second part against the force of the biasing means while the casing remains unbroken 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 for operation.

4. A lock cylinder as claimed in Claim 3, wherein the first part of the cam comprises a substantially cylindrical body and defines a pair of longitudinally aligned grooves in which the second part of the cam locates 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 located in a channel that straddles the parallel grooves to restrain the second part of the cam from significant movement towards the first core during normal operation of the locking cylinder.

6. A lock cylinder as claimed in Claim 4 or Claim 5, wherein the first part of the cam comprises a projecting peg located between the parallel grooves 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 second part of the cam is restrained from significant movement by abutment against a surface of the casing when the first part of the cam is moved axially by the biasing means after the casing has been broken and the first core removed.

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

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

10. A lock cylinder as claimed in any of Claims l to 9, wherein on operation the locking mechanism locks the cam or said first part thereof to the second core.

11. A lock cylinder as claimed in Claim 10, wherein the locking mechanism comprises a biased locking element that is normally retained within a cavity in the second core by engagement with a surface of the cam.

12. A lock cylinder as claimed in Claim 11, wherein said surface of the cam defines an aperture or depression that is moved into alignment with the locking element when the cam or said first part thereof is moved axially thereby permitting the locking element to be moved into the aperture or depression to secure the cam or said first part thereof to the second core.

13. A lock cylinder as claimed in any of Claims 10 to 12, wherein the locking mechanism comprises a biased locking element that is located in a transversely aligned cavity defined by the second core and that locates in an aperture or depression defined by the cam or said first part thereof.

14. A lock mechanism as claimed in any of Claims 10 to 12, wherein the locking mechanism comprises a pair of biased locking elements that are respectively located in transversely aligned cavities on opposite sides of the second core and locate in a pair of apertures or depressions on opposite sides of the first part of the cam.

15. A lock cylinder as claimed in Claim 13 or Claim 14, wherein the or each biased locking element comprises a spring-loaded locking pin that is located in said transversely aligned cavity, which is in the form of a bore in the second core.

16. A lock cylinder as claimed in any of Claims l to 15 wherein the clutch arrangement comprises first and second actuators that respectively contact inner ends of the first and second cores and that are retained in contact with one another by the biasing means, axial movement of the first core against the force of the biasing means moving the first actuator into engagement with the cam and the second actuator out of engagement with the cam.

17. A lock cylinder as claimed in Claim 16, wherein the biasing means biases the clutch arrangement such that the second actuator is normally engaged with the cam and the first actuator is out of engagement with the cam.

18. A lock cylinder as claimed in Claim 16 or Claim 17, wherein the second actuator is saddle-shaped and straddles the inner end of the second core.

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

20. A lock cylinder as claimed in Claim 19, wherein the biasing means comprises a pair of springs that are respectively located in the pair of channels defined by the second core and that act against the legs of the saddle-shaped second actuator.

21. A lock cylinder as claimed in any of Claims 18 to 20 when dependent on Claim 14, wherein the transversely aligned cavities in the second core are straddled by and arranged at right angles to the legs of the saddle-shaped second actuator.

22. A lock cylinder as claimed in any of Claims l to 21, wherein the casing comprises an area of weakness that causes snapping of the casing transversely with respect to said longitudinal axis between the cam and said first core should an attempt be made to break the lock cylinder.