Lock cylinder

Abstract

The lock cylinder comprises a cylinder housing, an internal lock barrel and an external lock barrel located within the cylinder housing, a rotatable cam, and a clutch. The clutch comprises a clutch sleeve which rotationally couples the clutch to the cam. The clutch sleeve has a first position with respect to the cam which allows selective engagement of the internal or external lock barrels with the cam when a suitable key is inserted into the respective lock barrel, such that rotation of the key within the lock barrel rotates the cam and a second position with respect to the cam in which the clutch sleeve has moved laterally with respect to the first position. In the second position the clutch sleeve is permanently rotationally coupled to the internal lock barrel, such that the cam is only rotatable by rotation of the internal lock barrel.

Description

[0001] Lock cylinder

[0002] Field of the Invention

[0003] The present invention concerns a lock cylinder. More particularly, but not exclusively, this invention concerns a lock cylinder resistant to snap attacks.

[0004] Background of the Invention

[0005] Lock cylinders may be subject to various types of attack. For example, lock cylinders may be damaged in an attempt to gain access to the internal workings of a lock, which may allow an attacker to unlock the lock and gain unauthorised entry through the door or window the lock was securing.

[0006] Some lock attacks include snapping the external part of the lock cylinder away from the internal part of the lock cylinder, and manipulating a clutch in the lock cylinder in such a way as to unlock the lock, or alternatively looking to directly manipulate the mechanism of a lock once exposed by a snapping attack. In order to prevent this, some lock cylinders are provided with sacrificial sections to control the snapping of the external part of the lock cylinder, and spring-loaded clutches which move into a secure position once the external part of the lock cylinder has been removed. However, spring-loaded clutches may jam or otherwise be prevented from moving the clutch into a secure position, potentially leaving the clutch open to external interference. For example, some attacks may comprise the attacker squirting liquid into the lock or lock cylinder, and then freezing the liquid with a compressed air-spray. The frozen liquid may hold a spring-loaded clutch in a vulnerable position following a snapping attack.

[0007] The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved lock cylinder.

[0008] Summary of the Invention

[0009] The present invention provides, according to a first aspect, a lock cylinder comprising a cylinder housing, an internal lock barrel and an external lock barrel located within the cylinder housing, a rotatable cam, and a clutch, the clutch comprising a clutch sleeve which rotationally couples the clutch to the cam, the clutch sleeve having a first position with respect to the cam which allows selective engagement of the internal lock barrel or external lock barrel with the cam when a suitable key is inserted into the respective lock barrel such that rotation of the key within the lock barrel rotates the cam, and a second position with respect to the cam in which the clutch sleeve has moved laterally with respect to the first position, and in the second position the clutch sleeve is permanently rotationally coupled to the internal lock barrel, such that the cam is only rotatable by rotation of the internal lock barrel.

[0010] As would be understood by the skilled person, a lock cylinder conventionally has an internal side and an external side. The internal side is accessible on the secure side of the door or window the lock cylinder is attached to, and the external side is accessible on the unsecure side of the door or window the lock cylinder is attached to. The skilled person will also appreciate that a lock cylinder has a longitudinal axis extending from the internal side to the external side of the lock cylinder, and movement of components along this longitudinal axis is movement in a lateral direction. The skilled person will also be familiar with the conventional lock barrel pin tumbler arrangement where a series of spring-loaded pins require alignment via a suitably shaped key in order to allow rotation of the lock barrel. If no key is present, or an unsuitable key is inserted into the lock barrel, the spring-loaded pins prevent the rotation of the lock barrel. This provides the conventional locking and unlocking process of inserting a suitable key, rotating the key such that the lock barrel also rotates within the cylinder housing, which consequently also causes the cam of the lock cylinder to rotate. The cam may move into a position in which it engages with an aperture in a door frame, for example, or may drive an additional locking element to extend from a door or window into a corresponding aperture in a door or window frame. The permanent coupling of the clutch sleeve to the internal lock barrel means that the clutch sleeve is no longer moveable between engagement with the external lock barrel and internal lock barrel, unlike in the first position.

[0011] Preferably, the clutch sleeve is moved into the second position when the lock cylinder experiences a snapping attack, wherein the cylinder housing is snapped and the external lock barrel and surrounding cylinder housing is moved away from the remainder of the lock cylinder. Advantageously, the action of snapping the cylinder housing and removing it from the remainder of the lock cylinder physically moves the clutch sleeve into the second position.

[0012] The clutch may comprise an internal clutch plate associated with the internal lock barrel. The clutch may comprise an external clutch plate associated with the external lock barrel. A spindle may join the internal clutch plate with the external clutch plate. The internal clutch plate may be engaged with the clutch sleeve when a suitable key is inserted into the internal lock barrel. When the internal clutch plate is engaged with the clutch sleeve, rotation of the internal clutch plate may result in rotational movement of the clutch sleeve. Movement of the internal clutch plate into engagement with the clutch sleeve may move the external clutch plate out of engagement with the clutch sleeve. The external clutch plate may be engaged with the clutch sleeve when a suitable key is inserted into the external lock barrel. When the external clutch plate is engaged with the clutch sleeve, rotation of the external clutch plate may result in rotational movement of the clutch sleeve. Movement of the external clutch plate into engagement with the clutch sleeve may move the internal clutch plate out of engagement with clutch sleeve. The movement of the internal clutch plate is translated to movement of the external clutch plate, and vice versa, via the spindle. The internal clutch plate and external clutch plate may comprise one or more engagement elements which correspond to engagement elements on the clutch sleeve. For example, the internal clutch plate may comprise one or more pins which engage with corresponding apertures in the clutch sleeve when the internal clutch plate is engaged with the clutch sleeve. The pin or pins may be arranged to transfer rotational motion of the internal clutch plate into rotational movement of the clutch sleeve. Alternatively, the pin or pins may be provided on the clutch sleeve and the corresponding aperture or apertures provided on the internal clutch plate. A similar arrangement may be provided between the external clutch plate and the clutch sleeve. The external clutch plate may be engaged with the clutch sleeve via a Reuleaux polygon being received within a correspondingly shaped aperture. For example, the external clutch plate may comprise a protrusion with a Reuleaux polygon crosssection, and a correspondingly shaped aperture being provided in the clutch sleeve. For example, the protrusion may have a Reuleaux triangle cross-section, and the clutch sleeve may comprise an aperture with a corresponding Reuleaux triangle cross- section. Provision of a Reuleaux polygon cross-section may make it more difficult for an attacker to attempt to manipulate the clutch sleeve in the event of a snapping attack. For example, the smooth edges of the Reuleaux polygon may cause a tool being used in an attack, for example a wire or screwdriver, to slip when attempting to apply torque to the clutch sleeve.

[0013] The internal clutch plate may comprise one or more formations, for example a pair of wings, which engage with corresponding formations in the internal lock barrel, for example a pair of grooves. The respective formations may rotationally couple the internal clutch plate to the internal lock barrel whilst allowing lateral movement of the internal clutch plate relative to the internal lock barrel. The external clutch plate may comprise one or more formations, for example a pair of wings, which engage with corresponding formations in the external lock barrel, for example a pair of grooves. The respective formations may rotationally couple the external clutch plate to the external lock barrel whilst allowing lateral movement of the external clutch plate relative to the external lock barrel.

[0014] The clutch sleeve may be located at least partially within the cam. The clutch sleeve may be located within the cam such that the clutch sleeve is laterally moveable with respect to the cam, but rotationally coupled to the cam. The rotational coupling of the clutch sleeve to the cam means that when the clutch sleeve is rotated, the cam is also rotated. The clutch sleeve may comprise a cam engagement formation, such as a groove or protrusion, and the cam may comprise a corresponding clutch sleeve engagement formation, such as a protrusion or groove. The engagement formations may be configured to restrict relative rotational movement between the clutch sleeve and the cam. Therefore, the engagement formations rotationally couple the clutch sleeve and the cam, so that rotational movement of the clutch sleeve results in rotational movement of the cam. The engagement formations may be configured to allow relative lateral movement between the clutch sleeve and the cam. Therefore, the engagement formations allow lateral movement of the clutch sleeve from the first position with respect to the cam to the second position with respect to the cam.

[0015] The clutch sleeve may be located partially within the internal lock barrel. The clutch sleeve may be located partially within the cam and partially within the internal lock barrel. The part of the clutch sleeve located within the cam may have a greater diameter than the part of the clutch sleeve located within the internal lock barrel. There may be a shoulder between the two different diameter parts of the clutch sleeve.

[0016] The clutch sleeve may house a pin. The pin may be biased, for example, being a spring-loaded pin. When the clutch sleeve is in the first position, the pin may be fully enclosed within the clutch sleeve, such that the pin does not prevent relative rotational movement of the clutch sleeve and the internal lock barrel. When the clutch sleeve is in the first position, the pin may be held within the clutch sleeve by abutting an internal wall of the internal lock barrel. In the first position, when the external clutch plate is engaged with the cam sleeve, the cam sleeve is free to move rotationally relative to the internal lock cylinder, with the pin sliding around the internal wall of the internal lock barrel. The internal lock barrel may comprise an aperture, the aperture configured to receive at least part of the pin. When the clutch sleeve is in the second position, the clutch sleeve has laterally moved to a position where the pin and the aperture align. The biasing of the pin pushes the pin into the aperture, thereby rotationally coupling the clutch sleeve to the internal lock barrel.

[0017] The clutch sleeve may be pulled into the second position when the lock cylinder experiences a lock attack, for example a snapping lock attack. The lock cylinder may comprise a break line, the break line being a weakened portion of the cylinder housing designed to break away under a snapping attack. The break line may be located between the cam and the external lock barrel. The external lock barrel may be configured such that in the event of a snapping attack, the cylinder housing snaps at the break line and pulling the external lock barrel away from the remainder of the lock cylinder results in the clutch sleeve being moved laterally from the first position to the second position. The lock cylinder may comprise a circlip located between the outer lock barrel and the external clutch plate. When the cylinder housing is snapped and the snapped portion including the outer lock barrel is moved away from the remainder of the lock cylinder, the circlip may be configured to engage with the outer clutch plate, such that the outer clutch plate is moved laterally away from the lock cylinder. The movement of the outer clutch plate may result in corresponding movement of the inner clutch plate, which abuts the clutch sleeve and also moves the clutch sleeve in the same lateral direction. The lateral movement of the clutch sleeve may bring the pin into alignment with the aperture in the internal lock barrel, such that the pin extends into the aperture and the clutch sleeve is consequently in the second position. The pin has been described as being housed in the clutch sleeve and the aperture in the internal lock barrel. When the cam is in the locked position, the clutch sleeve may be oriented such that the aperture in the internal lock barrel is vertically underneath the pin. Such an arrangement may be advantageous in the event that the biasing of the pin is reduced, for example due to a rusty spring, or any other spring related issues. In such an arrangement, even if a spring fails, when the clutch sleeve is moved laterally by a snapping attack, the pin may fall into the aperture under gravity.

[0018] In an alternative embodiment, the opposite arrangement may be provided, with the pin located within the locking cylinder and the aperture in the clutch sleeve. However, because of the restraints on space in the respective components, it is more likely to be the first described arrangement.

[0019] The lock cylinder may comprise one or more seals, for example rubber firings, located between distinct components of the lock cylinder. The one or more seals may be located between moveable components of the lock cylinder and the cylinder housing. For example, there may be an O-ring seal located between the clutch sleeve and the cam, or between the clutch sleeve and the cylinder housing. The one or more seals may reduce or prevent water ingress into the lock, for example during adverse weather conditions and / or as a result of an attack on the lock. Preventing water ingress during a lock attack may nullify the lock attack, or reduce the effect of the lock attack. In particular, the one or more seals may prevent damage to the internal mechanism of the lock cylinder that could be exploited by an attacker.

[0020] It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

[0021] Description of the Drawings

[0022] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0023] Figure 1 shows a side view of a lock cylinder according to a first embodiment of the invention; Figure 2 shows a perspective view of the lock cylinder;

[0024] Figure 3 shows a cross-sectional view of the lock cylinder;

[0025] Figure 4 shows a cross-sectional view of the lock cylinder with a key inserted into the internal lock barrel;

[0026] Figure 5 shows a cross-sectional view of the lock cylinder with a key inserted into the external lock barrel;

[0027] Figure 6 shows a cross-sectional view of a section of the lock cylinder;

[0028] Figure 7 shows a cross-sectional view of the lock cylinder following a snapping attack;

[0029] Figure 8 shows an exploded view of the lock cylinder;

[0030] Figure 9 shows an front cross-sectional view of the cam and clutch sleeve of the lock cylinder; and

[0031] Figures 10 and 11 show an exploded view of part of a lock cylinder according to an alternative embodiment of the invention.

[0032] Detailed Description

[0033] Figure 1 shows a lock cylinder 10 with an internal lock barrel 12 and an external lock barrel 14 located within a cylinder housing 11. The cylinder housing 11 is a solid metal component in which the various moving components of the lock cylinder 10 are housed. The skilled person will appreciate that the terms internal and external do not necessarily mean lock is located with the external side outdoors and the internal side indoors, but that the internal side is the secure side, and the external side is the unsecured side. So, the external side may be exposed to the outdoors, or may be, for example, an internal corridor or a building, and the internal side may be the inside of a room, or perhaps also exposed to the outdoors, but on the secure side of an external compound. In figure 1, the external side is to the left hand side of the lock cylinder 10 and the internal side is to the right hand side of the lock cylinder 10.

[0034] The lock cylinder 10 is configured to be inserted through a door leaf (not shown) with a suitably sized and shaped lock aperture, and the lock cylinder 10 is conventionally secured within the lock aperture via a bolt being screwed into the cylinder housing 11. The lock cylinder 10 has a longitudinal axis X-X, and where movement is described as being lateral, the movement is parallel to the longitudinal axis X-X. Where movement is described as being rotational, it is rotational around the longitudinal axis X-X. The lock cylinder 10 includes a cam 16 which may be selectively engaged with the internal lock barrel 12 or external lock barrel 14 when a suitable key has been inserted into the respective lock barrel. The cam 16 may be rotated between a position in which the cam 16 is housed within the external boundaries of the cylinder housing 11, and a position in which the cam 16 extends away from the external boundaries of the cylinder housing 11. This may allow the cam to extend into an appropriate aperture within the frame of the door leaf or may drive a lock mechanism associated with the lock cylinder 10 to engage with a corresponding aperture.

[0035] As can be seen in the cross-sectional view shown in Figure 3, the lock cylinder 10 is of the type commonly referred to in the art as a pin tumbler lock. The internal lock barrel 12 and external lock barrel 14 include a series of pins which may be engaged by a suitably shaped key in order to allow rotation of the internal lock barrel 12 or external lock barrel 14 within the cylinder housing 11. The internal pin arrangements of the internal lock barrel 12 and external lock barrel 14 are conventional and well understood by a skilled person, so no further description will be provided.

[0036] The lock cylinder 10 further includes a clutch mechanism 18 which enables the selective engagement of the cam 16 with the internal lock barrel 12 or the external lock barrel 14. The clutch mechanism 18 comprises an internal clutch plate 20 associated with the internal lock barrel 12 and an external clutch plate 22 associated with the external lock barrel 14. The internal clutch plate 20 and external clutch plate 22 are mechanically fastened to each other via a spindle 24, via any suitable fixing mechanism intended to be permanent, such as riveting or welding. Each of the internal clutch plate 20 and external clutch plate 22 includes a pair of pins which extend away from the clutch plate and are configured to be received within corresponding apertures in a clutch sleeve 26. The pins 201 of the internal clutch plate 20 can be seen in Figure 8, as can the apertures 261 in the clutch sleeve 26 which are configured to receive the pins of the external clutch plate 22. One of the pins 221 of the internal clutch plate 22 can be seen in Figure 6.

[0037] The internal clutch plate 20 and external clutch plate 22 are laterally moveable relative to the clutch sleeve 26. When the appropriate key is inserted into the internal lock barrel 12 the tip of the key pushes the internal clutch plate 20 towards the clutch sleeve 26 such that the pins 201 extending from the internal clutch plate 20 engage with the internal apertures of the clutch sleeve 26 and the pins 221 extending from the external clutch plate 22 do not engage with the external apertures 261 of the clutch sleeve 26. This is best shown in figure 4. The internal clutch plate 20 is now rotationally fixed to the clutch sleeve 26 such that rotation of the key within the internal lock barrel 12 causes the internal clutch plate 20 to rotate, also causing the clutch sleeve 26 to rotate. A similar process occurs when the appropriate key is inserted into the external lock barrel 14. The tip of the key pushes the external clutch into engagement with the clutch sleeve 26 such that the pins extending from the external clutch plate 22 engage with the clutch sleeve 26 and the pins extending from the internal clutch plate 20 do not engage with the clutch sleeve 26. This is best shown in figure 5. The external clutch plate 22 is now rotationally fixed to the clutch sleeve 26 such that rotation of the key within the external lock barrel 14 causes the external clutch plate 22 to rotate, also causing the clutch sleeve 26 to rotate. The clutch sleeve 26 is rotationally fixed to the cam 16, with the consequence that the cam 16 is rotated by the rotation of the key within the external lock barrel 14, thereby moving the cam 16 as required. This describes the working of the lock cylinder 10 in normal operation, when an appropriate key is inserted into one of the internal lock barrel 12 or the external lock barrel 14.

[0038] The clutch sleeve 26 is partially surrounded by the cam 16 in such a way as to be rotationally fixed to the cam 16, with the consequence that the cam 16 is rotated by the rotation of the key within the internal lock barrel 12, thereby moving the cam 16 between the locked and unlocked position as required and as described above. As can be seen in figure 9, the clutch sleeve 26 includes a groove 262 into which extends a corresponding protrusion 161 in the cam 16. The groove 262 extends in the lateral direction, thereby allowing relative motion in the lateral direction between the clutch sleeve 26 and the cam 16, but preventing relative rotational movement. The clutch sleeve 26 also partially extends into the internal lock barrel 12, which will be further described with reference to the operation of the lock when a snapping attack occurs.

[0039] A seal 32 is positioned towards the outer end of the clutch sleeve 26, between the external circumference of the clutch sleeve 26 and the cylinder housing 11. The seal 32 may prevent or reduce water or other liquid ingress into the internal side of the locking cylinder 10, for example due to an attacker squirting water into the locking mechanism in an attempt to damage or obstruct the working of the locking cylinder. In other embodiments, a seal is not provided, and the clutch sleeve 26 is of a sufficiently close fit that water or other liquid ingress is reduced or prevented.

[0040] The lock cylinder 10 may be attacked, and the operation of the lock cylinder 10 when under snapping attack will now be described. As can be seen, there is a break line 28 formed in the cylinder housing 11 between the external lock barrel 14 and the rest of the lock cylinder 10. The break line 28 weakens the connection of the external lock barrel 14 to the remainder of the lock cylinder 10, such that if a snapping attack takes place, the cylinder housing 11 breaks at the break line 28. The break line 28 therefore controls the point at which the cylinder housing 11 snaps under a snapping attack. As can be seen in figure 6, there is a circlip 30 secured to the external lock barrel 14 and engaged with appropriately shaped wings 222 on the external clutch plate 22. If the cylinder housing 11 is snapped and pulled away from the remainder of the cylinder lock 10, the external lock barrel 14 engages the circlip 30, which will be removed in the same direction as the external lock barrel is being pulled, thereby pulling the external clutch plate 22 laterally outwards with respect to the lock cylinder 10. As the external clutch plate 22 is mechanically attached to the internal clutch plate 20 via the spindle 24, the internal clutch plate 20 is also pulled across with the external clutch plate 22. As can be seen in Figure 7, the internal clutch plate 20 is pulled across further than when a key is inserted into the internal lock barrel 12. The internal clutch plate 20 abuts the clutch sleeve 26 and also pulls that across, towards the external side of the lock. Within the clutch sleeve 26 there is a spring-loaded pin 34. In the normal operation of the lock, the pin 34 is contained within the clutch sleeve 26, and does not affect the operation of the lock cylinder 10. When the lock cylinder 10 is attacked by snapping, the clutch sleeve 26 is pulled across to a position where there is a suitably shaped aperture 36 in the internal lock barrel 12, into which the pin 34 extends due to the bias provided by the springloading. The pin 34 thereby permanently engages the internal lock barrel 12 to the cam 16, via the clutch sleeve 26. The cam 26 may still be rotated by a suitable key inserted into the internal lock cylinder 12, allowing use of the cylinder lock 10 from the internal side of the lock cylinder 10 even after a snapping attack. However, the attacker is unable to manipulate movement of the cam 16 from the external side of the locking cylinder 10. If the attacker attempts to push the external clutch plate 22 back into engagement with the cam sleeve 26, even if they are able to do so, no rotational movement of the external clutch plate 22 is allowed because the cam sleeve 26 is connected to the internal lock barrel 12 via the pin 36. Rotational movement is only permitted when a suitable key is inserted into the internal lock barrel 12. Therefore, a robust and secure lock cylinder 10 is provided.

[0041] As can be seen best in figure 8, a circlip 38 is also provided between the internal lock barrel 12 and the internal clutch plate 20 in order to fix the lateral position of the internal lock barrel and retain the internal lock barrel within the lock housing.

[0042] Figures 10 and 11 show an exploded view of part of a lock cylinder according to a second embodiment of the invention. The majority of the lock cylinder components are the same as in the first embodiment, and the general operation of the lock cylinder is also the same. In order to avoid unnecessary duplication, the similar components will not be described again. The difference in the second embodiment is that the external clutch plate 22 includes a protrusion 280 with a cross-section in the shape of a Reuleaux triangle. The clutch sleeve 26 comprises a corresponding sized and shaped aperture 282, which receives the protrusion 280 when the external clutch plate 22 is engaged with the clutch sleeve 26, and rotationally couples the external clutch plate 22 and clutch sleeve 26 together. In the event of a snapping attack, if the clutch sleeve 26 becomes exposed, the aperture 282 has curved sides and corners, which will make it difficult to apply torque to the clutch sleeve 26 via an attacker using a wire or screwdriver.

[0043] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0044] The embodiment shown in the figures includes a seal to prevent or reduce liquid ingress into the inner workings of the lock cylinder. In an alternative embodiment, a seal may be omitted. In such an arrangement, liquid ingress may be reduced by having a close fit between the various internal components of the lock cylinder 10 and the cylinder housing 11. Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

Claims1. A lock cylinder comprising: a cylinder housing, an internal lock barrel and an external lock barrel located within the cylinder housing, a rotatable cam, and a clutch, the clutch comprising a clutch sleeve which rotationally couples the clutch to the cam, the clutch sleeve having a first position with respect to the cam which allows selective engagement of the internal lock barrel or external lock barrel with the cam when a suitable key is inserted into the respective lock barrel such that rotation of the key within the lock barrel rotates the cam, and a second position with respect to the cam in which the clutch sleeve has moved laterally with respect to the first position, and in the second position the clutch sleeve is permanently rotationally coupled to the internal lock barrel, such that the cam is only rotatable by rotation of the internal lock barrel.

2. A lock cylinder as claimed in claim 1, the clutch comprising an internal clutch plate associated with the internal lock barrel, an external clutch plate associated with the external lock barrel, and a spindle joining the internal clutch plate with the external clutch plate.

3. A lock cylinder as claimed in claim 2, wherein the internal clutch plate is engaged with the clutch sleeve when a suitable key is inserted into the internal lock barrel.

4. A lock cylinder as claimed in claim 2 or claim 3, wherein the external clutch plate is engaged with the clutch sleeve when a suitable key is inserted into the external lock barrel.

5. A lock cylinder as claimed in any of claims 2 to 4, wherein the external clutch plate is engaged with the clutch sleeve via a Reuleaux polygon being received within a correspondingly shaped aperture.

6. A lock cylinder as claimed in any of claims 2 to 5, wherein the internal clutch plate comprises one or more formations which engage with corresponding formations in the internal lock barrel, and the respective formations rotationally couple the internal clutch plate to the internal lock barrel whilst allowing lateral movement of the internal clutch plate relative to the internal lock barrel.

7. A lock cylinder as claimed in any of claims 2 to 6, wherein the external clutch plate comprises one or more formations which engage with corresponding formations in the external lock barrel and the respective formations rotationally couple the external clutch plate to the external lock barrel whilst allowing lateral movement of the external clutch plate relative to the external lock barrel.

8. A lock cylinder as claimed in any preceding claim wherein the clutch sleeve is located at least partially within the cam, such that the clutch sleeve is laterally moveable with respect to the cam, but rotationally coupled to the cam.

9. A lock cylinder as claimed in any preceding claim, wherein the clutch sleeve comprises a cam engagement formation and the cam comprises a corresponding clutch sleeve engagement formation, the engagement formations configured to restrict relative rotational movement between the clutch sleeve and the cam and allow relative lateral movement between the clutch sleeve and the cam, thereby allowing lateral movement of the clutch sleeve from the first position with respect to the cam to the second position with respect to the cam.

10. A lock cylinder as claimed in any preceding claim, wherein the clutch sleeve is located partially within the internal lock barrel.

11. A lock cylinder as claimed in any preceding claim, wherein the clutch sleeve is located partially within the cam and partially within the internal lock barrel.

12. A lock cylinder as claimed in any preceding claim, wherein the clutch sleeve houses a pin.

13. A lock cylinder as claimed in claim 12, wherein the pin is a biased pin.

14. A lock cylinder as claimed in claim 12 or claim 13, wherein when the clutch sleeve is in the first position, the pin is fully enclosed within the clutch sleeve, such that the pin does not prevent relative rotational movement of the clutch sleeve and the internal lock barrel.

15. A lock cylinder as claimed in any of claims 12 to 14, wherein the internal lock barrel comprises an aperture, the aperture configured to receive at least part of the pin.

16. A lock cylinder as claimed in claim 15, wherein when the clutch sleeve is in the second position, the clutch sleeve has laterally moved to a position where the pin and the aperture align and the pin is at least partially received in the aperture, thereby rotationally coupling the clutch sleeve to the internal lock barrel.

17. A lock cylinder as claimed in any preceding claim, wherein the clutch sleeve is pulled into the second position when the lock cylinder experiences a snapping attack.

18. A lock cylinder as claimed in any of claims 2 to 17, comprising a circlip located between the external lock barrel and the external clutch plate, wherein when the cylinder housing is snapped and the external lock barrel moved away from the remainder of the lock cylinder, the circlip is configured to engage with the outer clutch plate, such that the outer clutch plate is moved laterally away from the lock cylinder, resulting in corresponding movement of the inner clutch plate, which abuts the clutch sleeve and also moves the clutch sleeve in the same lateral direction, from the first position to the second position.

19. A lock cylinder as claimed in any preceding claim, comprising one or more seals located between distinct components of the lock cylinder.

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