The present invention relates to an anti-snap cylinder lock, for use particularly, but not exclusively, to lock external doors.

Cylinder locks are well known, and are commonly used to control lock cases mounted inside doors, so they can be locked in their surrounding doorframe. They comprise a cylindrical lock mechanism which extends through the thickness of the door, with an internal side which is accessible from an inside of the doorframe, and an external side which is accessible from an outside of the doorframe. On the internal side is an internal lock actuation assembly, for example a key operated pin and tumbler mechanism, and on the external side is an external equivalent. In the middle is a rotatable lock engaging element, usually in the form of a rotatable cam body. When either the internal or external lock actuation assembly is operated, for example by inserting the key and rotating it, the lock actuation assembly in question connects with the lock engaging element so the rotation applied by the user is transferred thereto, which activates the lock case to change its status between locked and unlocked conditions.

A clutch mechanism is commonly provided to allow for either the internal or external lock actuation assembly to selectively engage with the cam body, so the lock can be operated from either side of the door without the other lock actuation assembly being affected.

Usually the clutch mechanism is activated to connect the lock actuation assembly in question to the cam body by being driven axially into engagement therewith by the end of the key as it is inserted into the lock from that side. In some configurations an internal spring is provided to bias the clutch mechanism into engagement in one direction. This is useful if one of the lock actuation assemblies is a thumb bolt or the like, so the user need only turn the tumb bolt to open the lock.

A problem with locks of this kind is that they can be broken and the lock engaging element actuated with relative ease. By using common hand tools such as screwdrivers, mole grips and the like it is possible to snap off one of the lock actuation assemblies from the cylinder lock, which exposes the lock engaging element for manual rotation, or if that is removed the internals of the lock case itself.

One way to prevent this from occurring is to provide the external lock actuation assembly with an anti-snap mechanism which acts to secure the cylinder lock in a locked state if the external lock actuation assembly is removed or damaged. The external lock actuation assembly is provided with a weak point which suffers failure when subjected to a pre-determined force which would be experienced during an attack. When this failure occurs some kind of spring loaded safety mechanism then activates to place the cylinder lock in a locked condition. As such, a defensive configuration is adopted before the attacker can gain full access to the internal components of the cylinder lock or the lock case.

However, a major problem with systems of this kind is that once this deliberate failure has occurred, the cylinder lock is then entirely inoperable from either side thereof. This means the door cannot be opened from the inside after an attack, which can itself be a security or safety risk, or a significant inconvenience.

Furthermore, known spring loaded safety mechanisms which act to place the cylinder lock in a locked condition can be weak and ineffective if subjected to further force. For instance, a small pin which may lock the rotatable lock engaging element to an adjacent part to prevent its rotation can break if subjected to impact forces applied axially to the cylinder lock, or such a pin can be dislodged from its lock position. A safety mechanism arrangement which can cope with greater impact forces is needed.

The present invention is intended to overcome some of the above described problems.

Therefore, according to the present invention a cylinder lock comprises a rotatable lock engaging element, a first lock actuation assembly comprising a first clutch for engaging said lock engaging element for rotation, and a second lock actuation assembly comprising a second clutch for engaging said lock engaging element for rotation, in which said second lock actuation assembly comprises a weak point which suffers failure when subjected to a pre-determined force, which failure allows removal of at least part of said second lock actuation assembly, in which a first spring biases said first clutch into an advanced position when said removal occurs, and in which said cylinder lock comprises a spring loaded locking pin which engages a slot on said first clutch in said advanced position to connect said first clutch to said lock engaging element.

Thus, the present invention provides a mechanism whereby if the cylinder lock is attacked it will snap at the weak point, and when part of the second lock actuation assembly is removed the lock engaging element will then lock itself to the first clutch. This achieves two relevant things. Firstly the first lock actuation assembly will control the rotational position of the lock engaging element, and in particular it will prevent it from being rotatable from the now dismantled second lock actuation assembly, thereby defaulting the cylinder lock to a locked state in the event of an attack. Secondly though, by locking itself to the first lock actuation assembly the lock engaging element will be controllable thereby. As such, after an attack the cylinder lock can still be operated from the first side.

It is the intended that a cylinder lock of the present invention will be built to comply with BSEN 1303:2005, TS007 three-star rating and SS312 diamond standards, which govern the ability of a lock to withstand external attacks such as snapping, drilling, hammer punching, plug extraction and other kinds of manipulation.

The cylinder lock of the invention can be arranged either way around in a door, but it will be appreciated that the first side should be the internal side, and the second side the external side, as that is the side most likely to be attacked. However, for ease of explanation the invention will be described by reference to the first and second sides of the cylinder lock.

Preferably the first lock actuation assembly and the second lock actuation assembly can be arranged opposite to one another on an axis, and the lock engaging element can be arranged on the axis between them. The first clutch can comprise a first body which can be movable along the axis between a first disengaged position in which it is axially displaced from the lock engaging element and a first engaged position in which it is co-axial with the lock engaging element and engages it for rotation. Likewise, the second clutch can comprise a second body which can be movable along the axis between a second disengaged position in which it is axially displaced from the lock engaging element and a second engaged position in which it is co-axial with the lock engaging element and engages it for rotation. This configuration is an efficient and expedient arrangement of parts in a cylinder lock.

The pin can be disposed in a radially extending housing formed in the lock engaging element. Thus, when the slot comes into axial alignment with the housing in the advanced position of the first clutch, the pin will move radially inwardly so a part of it is disposed in the slot.

Preferably the first clutch moves along the axis when it moves into the advanced position as referred to above, and the slot can be greater in axial extent than the pin. As such the first clutch is then moveable along the axis relative to the lock engaging element when it is connected to the lock engaging element by the pin. The distance the first clutch is movable along the axis relative to the lock engaging element depends on the difference in axial extent between the pin and the slot. This difference can be relatively small, for example 1 or 2mm, however this is enough to achieve an important technical advantage. In particular, if the first clutch is subjected to further attack by a potential intruder after it has moved to the advanced position, the loose connection between the first clutch and the pin means less impact force applied to the first clutch may be transferred to the pin. In the advanced position the first spring is biasing the first clutch forward, which means the 1 or 2mm space between the first clutch and the pin is on the second lock actuation assembly side of the slot, and the first clutch floats on the first spring. Therefore some of any impact force applied to the first clutch may be absorbed by the first spring, and/or by movement of the slot over the pin. These factors may be relatively minor, but they may improve the resistance of the cylinder lock to attack.

In an alternative arrangement to that described above the housing can be greater in axial extent than the pin. This achieve all the same results as above, except that the spacing is provided between the pin and the housing, rather than between the pin and the slot.

However, preferably both the housing and the slot are greater in axial extent than the pin. What this means is that when the pin engages the slot in the advanced position of the first clutch, it is angularly displaceable from a plane normal to the axis in a first direction by a biasing force of the first spring, and in an opposite second direction by a force opposite to the biasing force.

With this configuration the pin delimits the relative movement in each direction of the first clutch in relation to the lock engaging element by binding at its ends in the slot and the housing and/or at the junction of the slot and the housing. This makes breaking the pin even harder, because a direct radial impact force cannot be applied, as would be the case if the pin were engaged along its axial length against the sides of the slot and the housing. Once again, the improvements provided here may be relatively small, but they do serve to improve the resistance of the cylinder lock to attack.

The lock engaging element can be any mechanical device which is capable of engaging a component of any known lock case. However, preferably it can comprise a radially extending cam body for rotational engagement with components of a lock case with which the cylinder lock is used. Such a shape of cam body is standard with known cylinder locks. If so, the housing can be formed the cam body. What this means is that the housing can be axially long in length, and in particular axially longer than would be the case if it were located elsewhere on the lock rotating element, which in turn means the pin can be axially long in length. This improves the functionality of the pin, and of the interface between the first clutch and the lock engaging element in the advanced position of the first clutch, as described above.

The lock engaging element can comprise an axially extending aperture through which the first clutch and the second clutch can be axially movable. The first clutch can comprise a first end face and the second clutch can comprise a second end face, which can be forced into engagement with one another by the first spring. As such, movement of the first clutch into the first engaged position can axially displace the second clutch into the second disengaged position, and movement of the second clutch into the second engaged position can axially displace the first clutch into the first disengaged position. Once again, this is a simplex arrangement with movement of one clutch into place simultaneously displacing the other.

In a preferred embodiment the first clutch can be disposed in a first chamber, and the first spring can comprise a coil spring mounted under compression between a first wall of the first chamber and the first clutch, and which biases the first clutch into the first engaged position and the second clutch into the second disengaged position. The first spring ensures that the first and second clutches remain in contact with one another, and it also means that the cylinder lock defaults to the first engaged position. As explained above, it also biases the first clutch into the advanced position in the event of removal of part of the second lock actuation assembly.

The second clutch can be disposed in a second chamber, which can itself comprise a second wall, and a second end face of the second clutch can abut against the second end wall when the second clutch is in the second disengaged position.

Therefore, the above described failure can allow for removal of the second end wall, such that said first clutch is axially movable from the first engaged position to the advanced position by the first spring.

In one embodiment of the invention a first clutch pad can be disposed between the first wall and the first spring, which first clutch pad can be axially movable inside the first chamber between a standby position next to the first wall, and a forward position in which it is displaced from the first wall. The first lock actuation assembly can then comprise a first key slot with an opening in the first wall; the cylinder lock can comprise a key, and when the key is fully inserted into the first lock actuation assembly a first end thereof can protrude through the opening and move the first clutch pad to the forward position. This serves to better engage the first clutch with the lock engaging element, because the first spring is compressed further, increasing the axial biasing of the first clutch into the first engaged positon.

A similar second clutch pad can be dispsed between the second wall and the second clutch, which is axially movable inside the second chamber between a standby position next to the second wall, and a forward position in which it is displaced form the first wall. The second lock actuation assembly can then comprise a second key slot with an opening in the second wall, and when the key is fully inserted into the second lock actuation assembly the first end thereof can protrude through the opening and move the second clutch pad to the forward position. This arrangement ensures a smooth interaction between the key and the cylinder lock in use.

It will be appreciated that the rotational engagement between the first clutch and the lock engaging element in the first engaged position, and between the second clutch and the lock engaging element in the second engaged position can be any mechanical interface which is capable of transmitting a rotational force either radially or axially. However, in a preferred construction the aperture in the lock engaging element can comprise an inner surface, which can itself comprise at least one axially extending slot. The first clutch can then comprise a first clutch outer surface, which can comprise at least one first axially extending rib for rotational engagement with the at least one axially extending slot. Likewise, the second clutch can comprise a second clutch outer surface, which can comprise at least one second axially extending rib for rotational engagement with the at least one axially extending slot.

Further, it will also be appreciated that the rotational engagement between the first lock actuation assembly and the first clutch, and between the second lock actuation assembly and the second clutch can be any mechanical interface which is capable of transmitting a rotational force either radially or axially. However, preferably the first lock actuation assembly can comprise a first barrel with a first chamber at a first end thereof; the first clutch can be disposed in the first chamber, the first chamber can comprise a first side wall with at least one first axially extending trough for rotational engagement with the at least one first axially extending rib. Likewise, the second lock actuation assembly can comprise a second barrel with a second chamber at a second end thereof; the second clutch can be disposed in the second chamber, the second chamber can comprise a second side wall with at least one second axially extending trough for rotational engagement with the at least one second axially extending rib. Therefore, the at least one first axially extending rib and the at least one second axially extending rib can facilitate the simultaneous rotational engagement between the first lock actuation assembly, the first clutch and the lock engaging element in the first engaged position, and between the second lock actuation assembly, the second clutch and the lock engaging element in the second engaged position.

Preferrably the inner surface can comprise two diametrically opposed axially extending slots, the first side wall can comprise two diametrically opposed first axially extending troughs, the second side wall can comprise two diametrically opposed second axially extending troughs, the first clutch can comprise two diametrically opposed first axially extending ribs, and the second clutch can comprise two diametrically opposed second axially extending ribs.

Preferably the lock engaging element can comprise a radially extending disc portion disposed between the first lock actuation assembly and the second lock actuation assembly, and a second flange portion extending normally in a second direction from an outer end of the disc portion. The second lock actuation assembly can then comprise a second outer surface portion, with the second flange portion arranged radially outside it. A second race bearing can then be disposed between the second outer surface portion and the second flange portion.

This arrangement is advantageous because an efficient bearing is provided between the lock engaging element and the second lock actuation assembly. Such a bearing is required for the smooth operation of the cylinder lock when the lock engaging element rotates in relation to the second lock actuation assembly, such as is the case when the cylinder lock is operated in the first engaged positon. A radial race bearing is much smoother than other types of bearing used in known cylinder locks, and it will have a better life cycle.

Another advantage of this particular arrangement is that the second race bearing is located inside the cylinder lock, underneath the second flange portion. This makes it much harder to tamper with than known arrangements, in which a bearing is located axially between the lock engaging element and the second lock actuation assembly. It also reduces the width of any gap between the lock engaging element and the second lock actuation assembly. In known examples this gap can be relatively large to accommodate the bearing structure. In the present invention the gap between a second end of the second flange portion and the second lock actuation assembly can be very small. Therefore, the internal race bearing arrangement of the present invention results in a more robust cylinder lock.

Following on from the above, the lock engaging element can comprise a first flange portion extending normally in a first direction from the outer end of the disc portion. The first lock actuation assembly can then comprise a first outer surface portion, with the flange portion arranged radially outside it. A first race bearing can be disposed between the first outer surface portion and the first flange portion. This is the same arrangement as is provided between the lock engaging element and the second lock actuation assembly, and it operates in the same way and provides the same advantages.

Both the first race bearing and the second race bearing can use 27 1.5mm diameter steel ball bearings.

In one version of the invention the cylinder lock can comprise a first cylinder block housing the first lock actuation assembly, a central cylinder block housing the lock engaging element, and a second cylinder block housing the second lock actuation assembly. The central cylinder block can comprise a substantially U-shaped body with a base portion, a first arm and a parallel second arm which define a space therebetween. The lock engaging element can be disposed in the space.

This construction provides a very strong security housing for the lock engaging element. Preferably the central cylinder block is made of high strength carbon steel, which is produced using known quenching and tempering processing techniques. The Rockwell Hardness of the central cylinder block is between 27-31.

In order to provide for the above described configuration of first race bearing and second race bearing, the first arm can comprise a first mounting slot at an outer end thereof, and the first lock actuation assembly can then comprise a first barrel mounted in the first cylinder block and the first mounting slot, with a first end thereof proud of the first mounting slot. The first end of the first lock actuation assembly can comprise said first outer surface portion, such that the first race bearing is supported between the first end of the first lock actuation assembly and the first flange radially outside it.

Likewise, the second arm can comprise a second mounting slot at an outer end thereof, and the second lock actuation assembly can comprise a second barrel mounted in the second cylinder block and the second mounting slot with a second end thereof proud of the second mounting slot. The second end of the second lock actuation assembly can comprise said second outer surface portion, such that the second race bearing is supported between the second end of the second lock actuation assembly and the second flange radially outside it. The second mounting slot can comprise an inner side facing the space, and an outer side facing the second cylinder block. The weak point can then comprise a waisted section of the second barrel located in the second mounting slot adjacent to the outer side. Therefore, if the second lock actuation assembly is attacked and the second barrel snaps at the weak point, the second cylinder block, and the parts of the second lock actuation assembly housed therein, will separate from the rest of the cylinder lock. As described above, this will involve the removal of the second wall of the second chamber, allowing the first spring to advance the first clutch into the advanced position.

The first lock actuation assembly and the second lock actuation assembly can be any known kind of manually or key operated lock actuation assembly. However, in a preferred construction the first lock actuation assembly can comprise a first key activated pin tumbler lock assembly, and the second lock actuation assembly can comprise a second key activated pin tumbler lock assembly. Preferably the first key activated pin tumbler assembly and second key activated pin tumbler assembly can be the track rail key type, which uses a key with flat edges and a track formed on one side comprising dimples to activate the pins of the assemblies. Such system are known, and are advantageous because the pin assemblies are smaller, and also because they have significantly increased anti-drill, anti-pick and anti-bump characteristics over traditional systems.

The invention can be performed I various ways, but one embodiment will now be described by way of example, and with reference to the accompanying drawings, in which:

Figure 1 is a cross-sectional side view of a cylinder lock according to the present invention;

Figure 2 is the same cross-sectional side view of the cylinder lock as shown in Figure 1 ;

Figure 3 is an exploded perspective view of cylinder block components of the cylinder lock as shown in Figure 1 ;

Figure 4 is a perspective of the cylinder lock as shown in Figure 1 , with a portion of the lock engaging element part threof removed for illustrative purposes;

Figure 5 is an end view of first clurch and lock engaging element parts of the cylinder lock as shown in Figure 1 ; Figure 6 is an end view of first clutch and first chamber parts of the cylinder lock as shown in Figure 1 ;

Figure 7 is a cross-sectional view of the cylinder lock as shown in Figure 1 , with the cross-section through a cam body part of the cylinder lock;

Figure 8 is a cross-sectional side view of the cylinder lock as shown in Figure 1 ; and

Figure 9 is a cross-sectional view of part of the cylinder lock as shown in Figure 1 , with the cross-section through a cam body part of the cylinder lock.

As shown in Figure 1 a cylinder lock 1 comprises a rotatable lock engaging element 2, a first lock actuation assembly 3 comprising a first clutch 4 for engaging the lock engaging element 2 for rotation, and a second lock actuation assembly 5 comprising a second clutch 6 for engaging the lock engaging element 2 for rotation. The second lock actuation assembly 5 comprises a weak point 7 which suffers failure when subjected to a pre-determined force, which failure allows removal of at least part of the second lock actuation assembly 5, as shown in Figure 9. A first spring 8 biases the first clutch 4 into an advanced position when the removal occurs. The cylinder lock 1 also comprises a spring loaded locking pin 9, visible in Figure 7, which engages a slot 10 on the first clutch 4 in the advanced position to connect the first clutch 4 to the lock engaging element 2.

The cylinder lock 1 is sized and shaped as a Euro cylinder lock, so it fits inside known lock cases. It engages such lock cases in the known way with a radially extending cam body 11 , visible in Figure 4, which is rotated in the cylinder lock 1 in use to interact with the internal mechanisms of such lock cases.

Referring to Figure 3, the cylinder lock 1 is made from three axially aligned frame pieces, namely a first cylinder block 12, a U-shaped central cylinder block 13 and a second cylinder block 14. The first cylinder block 12 comprises a first boss 15, with a first pair of holes 16 and 17. The central cylinder block 13 comprises a first opening 18, and a first pair of apertures 19 and 20 which dissect the first opening 18 and are normal thereto. It also comprises a second opening 21 , visible in Figure 1 , and a second pair of apertures 22 and 23 which dissect the second opening 21 and are normal thereto. The second cylinder block 14 comprises a second boss 24, with a second pair of holes 25 and 26. To secure the first cylinder block 12 to the central cylinder block 13 the first boss 15 is disposed in the first opening 18, with the first pair of holes 16 and 17 aligned with the first pair of apertures 19 and 20. Two rivets 27 and 28 are arranged in the first pair of apertures 19 and 20 and the first pair of holes 16 and 17 respectively to secure the first cylinder block 12 to the central cylinder block 13. To secure the second cylinder block 14 to the central cylinder block 13 the second boss 24 is disposed in the second opening 21 , with the second pair of holes 25 and 26 aligned with the second pair of apertures 22 and 23. Two rivets 29 and 30 are arranged in the second pair of apertures 22 and 23 and the second pair of holes 25 and 26 respectively to secure the second cylinder block 14 to the central cylinder block 13.

The central cylinder block 13 is made of high strength carbon steel, which is produced using known quenching and tempering processing techniques. The Rockwell Hardness of the central cylinder block 13 is between 27-31.

The first cylinder block 12 comprises a first upper annular portion 31 and a first lower radial portion 32. The central cylinder block 13 comprises a base portion 33, a first arm 34 and a parallel second arm 35 which define a space 36 therebetween. A first annular mounting slot 37 is provided at an outer end 38 of the first arm 34, and a second annular mounting slot 39 is provided at an outer end 40 of the second arm 35. The second cylinder block 14 comprises a second upper annular portion 41 and a second lower radial portion 42.

Referring back to Figure 1 , a first barrel 43 of the first lock actuation assembly 3 is rotationally mounted in the first annular portion 31 and the first annular mounting slot 37, with a first end 44 thereof proud of the first annular mounting slot 37. Five spring mounted driver pins 45 of the first lock actuation assembly 3 are disposed in the first lower radial portion 32, such that they are aligned for co-operation with the first barrel 43. In particular, in the locked state shown in Figure 1 the five spring mounted driver pins 45 extend into the first barrel 43, thereby preventing axial rotation thereof. Upon insertion of a key 46 of the correct shape into first key slot 47, five key pins 48 are depressed such that the five driver pins 44 are displaced from the first barrel 43, allowing it to be manually rotated in the first annular portion 31 and the first annular mounting slot 37.

Likewise, a second barrel 49 of the second lock actuation assembly 5 is rotationally mounted in the second annular portion 41 and the second annular mounting slot 39, with a second end 50 thereof proud of the second annular mounting slot 39. Five spring mounted driver pins 51 of the second lock actuation assembly 5 are disposed in the second lower radial portion 42, such that they are aligned for co-operation with the second barrel 49. In particular, in the locked state shown in Figure 1 the five spring mounted driver pins 51 extend into the second barrel 49, thereby preventing axial rotation thereof. Upon insertion of a key 46 of the correct shape into second key slot 52, as shown in Figure 8, five key pins 53 are depressed such that the five driver pins 51 are displaced from the second barrel 49, allowing it to be manually rotated in the second annular portion 41 and the second annular mounting slot 39.

Referring to Figurea 1 and 2, the first barrel 43 comprises a first chamber 54 at the first end 44, in which is housed the first clutch 4 for reciprocal axial movement therein between a first engaged position, as shown in Figures 1 and 2 and a first disengaged position as shown in Figure 8. The first spring 8 is a coil spring mounted under compression between a first end wall 55 of the first chamber 54 and the first clutch 4, which biases the first clutch 4 into the first engaged position as shown in Figures 1 and 2, and also into the advanced position as shown in Figure 9, as explained further below. Disposed axially between the first end wall 55 and the first spring 8 is a first clutch pad 56, which is axially movable inside the first chamber 54 between a standby position next to the first end wall 55, as shown in Figures 1 and 2, and a forward position in which it is displaced from the first end wall 55, as shown in Figure 7. The first key slot 47 comprises an opening 57 in the first end wall 55, and when the key 46 is fully inserted into the first lock actuation assembly 3 as shown in Figure 7, a first end 58 thereof protrudes through the opening 57 and moves the first clutch pad 56 to the forward position. This serves to better engage the first clutch 4 with the lock engaging element 2, as described further below, because the first spring 8 is compressed further, increasing the axial biasing of the first clutch 4 into the first engaged positon.

The second barrel 49 comprises a second chamber 59 at the second end 50, in which is housed the second clutch 6 for reciprocal axial movement therein between a second

disengaged position as shown in Figures 1 and 2, and a second engaged position as shown in Figure 8. Disposed axially between the second clutch 6 and a second end wall 60 of the second chamber 59 is a second clutch pad 61 , which is axially movable inside the second chamber 59 between a standby position next to the second end wall 60, as shown in Figures 1 and 2, and a forward position in which it is displaced from the second end wall 60, as shown in Figure 8. The second key slot 52 comprises an opening 62 in the second end wall 60, and when the key 46 is fully inserted into the second lock actuation assembly 5 as shown in Figure 8, the first end 58 thereof protrudes through the opening 62 and moves the second clutch pad 61 to the forward position, and the second clutch 6 to the second engaged position, against the force of the first spring 8. When the key 46 is not disposed in the second lock actuation assembly 5, the first spring 8 bases the second clutch 6 into the second disengaged position as shown in Figures 1 and 2, in which a second end face 63 thereof abuts against the second clutch pad 61 , which itself abuts against the second end wall 60 of the second chamber 59.

As is clear from Figures 1 and 2, the first lock actuation assembly 3 and the second lock actuation assembly 5 are arranged opposite to one another on axis A-A, with the lock engaging element 2 arranged on the axis A-A between them. The first clutch 4 comprises a first annular body 4 which is movable along the axis A-A between the first disengaged position, as shown in Figure 8, in which it is axially displaced from the lock engaging element 2, and a first engaged position, as shown in Figures 1 and 2 in which it is co-axial with the lock engaging element 2 and engages it for rotation. Likewise, the second clutch 6 comprises a second annular body 6 which is movable along the axis A-A between a second disengaged position, as shown in Figures 1 and 2, in which it is axially displaced from the lock engaging element 2, and a second engaged position, as shown in Figure 8, in which it is co-axial with the lock engaging element 2 and engages it for rotation.

The lock engaging element 2 comprises a radially extending disc portion 64 disposed between the first barrel 43 and the second barrel 49, a first flange portion 65 extending normally in a first direction from an outer end 66 of the disc portion 64, and a second flange portion 67 extending normally in a second direction from the outer end 66 of the disc portion 64. The disc portion 64 has an axially extending aperture 68 through which the first clutch 4 and the second clutch 6 are axially movable. The first clutch 4 comprises a first end face 69 and the second clutch comprises 6 a second end face 70, which are forced into engagement with one another by the first spring 8. As such, movement of the first clutch 4 through the aperture 68 into the first engaged position axially displaces the second clutch 6 into the second disengaged position, and movement of the second clutch 6 through the aperture 68 into the second engaged position axially displaces the first clutch 4 into the first disengaged position.

The first clutch 4 comprises a first clutch boss 69' on the first end face 69, which is located in a second clutch slot 70' on the second end face 70. This interconnection between the first clutch 4 and the second clutch 6 ensures that they stay properly aligned with one another on the axis A-A.

Referring to Figure 5, which is an end view of just the first cluch 4 and the lock engaging element 2, the aperture 68 comprises an inner surface 71 , which features a pair of diametrically opposed axially extending slots 72 and 73. The first clutch 4 comprises a first clutch outer surface 74, which comprises a first pair of diametrically opposed axially extending ribs 75 and 76 for rotational engagement with the axially extending slots 72 and 73. The second clutch 6 comprises a similar pair of diametrically opposed axially extending ribs (not visible) which are also for rotational engagement with the axially extending slots 72 and 73. Therefore, when the first clutch 4 is in the first engaged position, as shown in Figures 1 and 2, and is co-axial with the lock engaging element 2, rotation thereof rotates the lock engaging element 2. Likewise, when the second clutch 6 is in the second engaged position, as shown in Figure 8, and is coaxial with the lock engaging element 2, rotation thereof rotates the lock engaging element 2.

Referring to Figure 6, which is an end view of just the first clutch 4 and the first baeel 43, the first chamber 54 comprises a first side wall 77 with a pair of diametrically opposed axially extending troughs 78 and 79 for rotational engagement with the first pair of axially extending ribs 75 and 76. The second chamber 59 comprises a similar pair of axially diametricall opposed axially extending troughs (not visible), for rotational engagement with the second pair of ribs (not visible), in the same way. As at least some part of the first clutch 4 is always located in the first chamber 54, rotation of the first barrel 43 rotates the first clutch 4. Likewise, as at least some part of the second clutch 6 is always located in the second chamber 59, rotation of the second barrel 49 rotates the second clutch 6.

Therefore, the first pair of axially extending ribs 75 and 76, and the second pair of axially extending ribs (not visible) facilitate the simultaneous rotational engagement between the first lock actuation assembly 3, the first clutch 4 and the lock engaging element 2 in the first engaged position as shown in Figures 1 and 2, and between the second lock actuation assembly 5, the second clutch 6 and the lock engaging element 2 in the second engaged position, as shown in Figure 8.

Referring to Figures 1 and 2, the first barrel 43 comprises a first outer surface portion 80, which is co-axial with the part of the first barrel 43 which protrudes from the first annular mounting slot 37. The first flange portion 65 is arranged radially outside the first outer surface portion 80. A first race bearing is disposed between the first outer surface portion 80 and the first flange portion 65, which comprises annular grooves 81 and 82 cut into the first outer surface portion 80 and the first flange portion 65 respectively, and 27 1.5mm diameter steel ball bearings 83.

Likewise, the second barrel 49 comprises a second outer surface portion 84, which is co-axial with the part of the second barrel 49 which protrudes from the second annular mounting slot 39. The second flange portion 67 is arranged radially outside the second outer surface portion 84. A second race bearing is disposed between the second outer surface portion 84 and the second flange portion 67, which comprises annular grooves 85 and 86 cut into the first outer surface portion 84 and the first flange portion 67 respectively, and 27 1.5mm diameter steel ball bearings 87.

Referring to Figure 7, this shows a cross-sectional view of the cylinder lock 1 with the plane of the cross-section passing through the middle of the cam body 1 1 , so as to illustrate the pin 9, and its location in a radially extending housing 88 formed in the cam body 11. A second coil spring 89 is arranged between the pin 9 and the housing 88, which biases the pin 9 towards the axis A-A. This housing 88 is overlaid by the first clutch 4 in the first engaged position shown in Figures 1 , 2 and 7. It is then overlaid by the second clutch 6 in the first disengaged position shown in Figure 8. Therefore, the pin 9 is contained in the housing 88 in these positions, and has no function to play in the normal operation of the cylinder lock 1. However, when the first clutch 4 moves to the advanced position as shown in Figure 9, the slot 10 aligns with the housing 88 and the second spring 89 biases the pin 9 radially inwardly into the slot 10. As shown in Figure 9, in this positon the pin 9 is located in both the housing 88 and the slot 10, and connects the lock engaging element 2 to the first clutch 4.

Referring to Figure 9, this also shows a cross-sectional view of the cylinder lock 1 with the plane of the cross-section passing through the middle of the cam body 1 1 , so as to illustrate the pin 9, and its position in the advanced position of the first clutch 4. The slot 10 has a greater axial extent than the pin 9. As such the first clutch 4 is moveable along the axis A-A relative to the lock engaging element 2 when it is connected to the lock engaging element 2 by the pin 9. The housing 88 also has a greater axial extend than the pin 9. As such, when the pin 9 engages the slot 10 in the advanced position of the first clutch 4, it is angularly displaceable from a plane normal to the axis A-A in a first direction by the biasing force of the first spring 8, and in an opposite second direction by a force opposite to the biasing force. The pin 9 delimits the relative movement in each direction of the first clutch 4 in relation to the lock engaging element 2 by binding at its ends 90 and 91 in the slot 10 and the housing 88 and/or at the junction 92 of the slot 10 and the housing 88.

Referring to Figure 8, the second mounting slot 39 comprises an inner side 93 facing the space 36, and an outer side 94 facing the second cylinder block 14. The weak point 7 comprises a waisted section 7 of the second barrel 49 located in the second mounting slot 39 adjacent to the outer side 94. The waisted section 7 is formed by machining a groove into the second barrel 49. The first lock actuation assembly 3 and the second lock actuation assembly 5 are key activated pin tumbler lock assemblies which are actuatable by key 46. They are the track rail key type, and as such the key 46 has flat edges, one of which 95 is visible in Figure 7. Referring to Figure 8, the key 46 has a track 96 formed on one side 97 comprising dimples 98 to activate the key pins 48 and 53 of the first lock actuation assembly 3 and the second lock actuation assembly 5.

The cylinder lock 1 operates as follows. It is mounted in a door to be locked (not shown) with the first lock actuation assembly 3 on the internal side of the door, and the second lock actuation assembly 5 on the external side of the door. The terms "internal" and "external" are relative, with the internal side being that which is to be protected from forced entry. This will normally be at the entrance to a building but it will be appreciated that it could be inside a building.

The lock cylinder 1 will function with any known lock case, and it can be actuated to place such a lock case in a locked condition and in an unlocked condition in the known ways, via rotation of the lock engaging element 2.

The cylinder lock 1 defaults to the configuration shown in Figures 1 and 2 in which both the first lock actuation assembly 3 and the second lock actuation assembly 5 are locked, in the sense that they cannot be manually rotated without the key 46. The driver pins 45 of the first lock actuation assembly 3 extend into the first barrel 43, thereby preventing rotation axial thereof. As such, the first barrel 43 cannot be rotated, and neither can the first clutch 4 or the lock engaging element 2 because of the rotational connection between the first barrel 43, the first clutch 4 and the lock engaging element 2 as a result of the location of the first pair of axially extending ribs 75 and 75 in the troughs 78 and 79 and the slots 72 and 73 under the biasing of the first spring 8. In other words, the locked condition of the first barrel 43 places the lock engaging element 2 in a locked condition.

At the same time, the second clutch 6 is displaced into the second disengaged position by the first spring 8, which means that the lock engaging element 2 is functionally disengaged from the second lock actuation assembly 5. The second barrel 49 is also prevented from rotation anyhow because the driver pins 51 extend into the second barrel 49, thereby preventing axial rotation thereof. In order to actuate the cylinder lock 1 from the first side, to either lock or unlock the associated door, the key 46 is fully inserted into the first key slot 47 until its first end 58 protrudes through the opening 57 and pushes the first clutch pad 56 to its forward position, as shown in Figure 7. This compresses the first spring 8 and ensures engagement between the first clutch 4 and the lock engaging element 2. The dimples 98 of the track 96 depress the key pins 48 such that the driver pins 45 are displaced from the first barrel 43, allowing it to be axially rotated in the first annular portion 31 and the first annular mounting slot 37. Due to the rotational connection between the first barrel 43, the first clutch 4 and the lock engaging element 2 as a result of the location of the first pair of axially extending ribs 75 and 75 in the troughs 78 and 79 and the slots 72 and 73, manual rotation of the first barrel 43 by turning the key 46, rotates the lock engaging element 2 to engage the lock case to lock or unlock the associated door.

This rotational movement is supported by the second race bearing 85-87. In particular, the second flange portion 67 rotates relative to the second outer surface portion 84, which remains stationary because the second lock actuation assembly 5 remains in a locked condition. As such the groove 86 rotates about the groove 85, supported by the ball bearings 87. This ensures smooth rotational movement of the first barrel 43 and the lock engaging element 2.

When the key 46 is removed from the first lock actuation assembly 3, the cylinder lock 1 reverts to the default locked condition shown in Figures 1 and 2.

In order to open the door from the second side the key 46 is fully inserted into the second key slot 52 until its first end 58 protrudes through the opening 62 and pushes the second clutch pad 61 to its forward position, as shown in Figure 8. This moves the second clutch 6 into the second engaged position, and simultaneously displaces the first clutch 4, against the force of the first spring 8, into the first disengaged position. The dimples 98 of the track 96 depress the key pins 53 such that the driver pins 51 are displaced from the second barrel 49, allowing it to be axially rotated in the second annular portion 41 and the second annular mounting slot 39. Due to the rotational connection between the second barrel 49, the second clutch 6 and the lock engaging element 2 as a result of the location of the second pair of axially extending ribs (not visible) in the troughs (not visible) and the slots 72 and 73, manual rotation of the second barrel 49 by turning the key 46, rotates the lock engaging element 2 to engage the lock case to lock or unlock the associated door.

This rotational movement is supported by the first race bearing 81-83. In particular, the first flange portion 65 rotates relative to the first outer surface portion 80, which remains stationary because the first lock actuation assembly 3 remains in a locked condition. As such the groove 82 rotates about the groove 81 , supported by the ball bearings 83. This ensures smooth rotational movement of the second barrel 49 and the lock engaging element 2.

When the key 46 is removed from the second lock actuation assembly 5 the cylinder lock 1 reverts to the default locked condition shown in Figures 1 and 2, because the first spring 8 biases the first clutch 4 back into the first engaged position and the second clutch 6 back into the second disengaged position. This is a safety feature because forced rotation of any part of the second lock actuation assembly 5 during an attack will not rotate the lock engaging element 2 to unlock the associated door.

In the event of an attack on the second lock actuation assembly 5, the second barrel 49 is designed to break at the weak point 7. This occurs if the second lock actuation assembly 5 is forcibly rotated, or if it is subjected to axial impact forces. This failure occurs before any such attack forces can be transmitted to the lock engaging element 2.

This failure will lead to the portion of the second barrel 49 outside the weak point 7 being removable. This could involve it being axially withdrawn from the second annular portion 41 of the second cylinder block 14, or it could occur if the entire second cylinder block 14 is snapped off. This is the state of the cylinder lock 1 in Figure 9.

In either case, the second end wall 60 is removed from the cylinder lock 1 , which results in the first spring 8 moving the first clutch 4 to the advanced position, as shown in Figure 9. As soon as the slot 10 is radially aligned with the housing 88, the second spring 89 forces the pin 9 into the slot 10. This connects the first clutch 4 to the lock engaging element 2.

This connection means that the rotational position of the lock engaging element 2 is determined by the condition of the first lock actuation assembly 3. As the first lock actuation assembly 3 is in a locked condition, in the sense that the first barrel 43 cannot be rotated without the key 46 being inserted into the first key slot 47, the lock engaging element 2 is rotationally locked in position. This means that the attacker cannot manually rotate the lock engaging element 2 to unlock the associated door. As such, the cylinder lock 1 has an anti-snap mechanism which acts to maintain the cylinder lockl in a locked state if attacked such that the second lock actuation assembly 5 is removed. However, because the lock engaging element 2 is rotationally connected to the first clutch 4, actuation of the first lock actuation assembly 3 will serve to unlock the door, in the manner described above. The first clutch 4 is in the advanced position, but it is still located in both the first chamber 54 and the aperture 68, so rotation of the first barrel 43 will rotate the lock engaging element 2. This is advantageous because after an attack the cylinder lock 1 can still be operated to open the door from the inside.

When the first clutch 4 is connected to the lock engaging element 2 in this way, it is still movable back and forth on the axis A-A. This is because the slot 10 and the housing 88 both have a greater axial extent than the pin 9. The slot 10 has the greatest axial extent, so the first clutch 4 is moveable along the axis A-A relative to the lock engaging element 2 by virtue of the slot 10 moving around the pin 9 when it is normal to the axis A-A. However, in addition to the pin 9 is angularly displaceable from a plane normal to the axis A-A in a first direction by the biasing force of the first spring 8, and in an opposite second direction by a force opposite to the biasing force. This second force can be applied by the intruder when trying to break the cylinder lock 1. The pin 9 delimits the relative movement in each direction of the first clutch 4 in relation to the lock engaging element 2 by binding at its ends 90 and 91 in the slot 10 and the housing 88 and/or at the junction 92 of the slot 10 and the housing 88.

This arrangement improves the resistance of the cylinder lock 1 to attack. In particular, the floating condition of the first clutch 4 on the first spring 8 in the advanced position means an element of any impact force applied to the first clutch 4 is absorbed by the first spring 8, and/or by movement of the slot 10 over the pin 9. Further, the floating condition will also make it harder for an attacker to engage the first clutch 4 to damage it, as it will move about.

In addition to this, when the pin 9 is angularly displaced from a plane normal to the axis A-A, and its ends 90 and 91 bind in the slot 10 and the housing 88, it is difficult to break because a direct radial impact force cannot be applied, as would be the case if the pin 10 were engaged along its axial length against the sides of the slot 10 and the housing 88.

Another advantage of cylinder lock 1 over known examples is that the second race bearing 85-87 is located inside the cylinder lock 1 , underneath the second flange portion 67. This makes it much harder to tamper with than known arrangements, in which a bearing or connection clip is located axially between the lock engaging element and the second lock actuation assembly. This arrangement also reduces the width of any gap between the lock engaging element 2 and the second lock actuation assembly 5. Furthermore, the robust shape of the central cylinder block 13, and the strong material it is made from, mean it is also highly resistant to attack.

The present invention can be altered without departing from the scope of claim 1. For example, in one alternative embodiment a cylinder lock is provided which is similar to cylinder lock 1 , except that the first lock actuation assembly is a thumb blot arrangement instead of a key actuated pin tumbler arrangement.

Therefore, the present invention provides a mechanism whereby if the cylinder lock is attacked it will snap at the weak point, and when part of the second lock actuation assembly is removed the lock engaging element will then lock itself to the first clutch. As such the first lock actuation assembly will control the rotational position of the lock engaging element, and in particular it will prevent it from being rotatable from the now dismantled second lock actuation assembly, thereby defaulting the cylinder to a locked state in the event of an attack. Secondly, by locking itself to the first lock actuation assembly the lock engaging element will be controllable thereby. As such, after an attack the cylinder lock can still be operated from the first side. In addition, the present invention also provides a cylinder lock in which the first clutch is axially movable when it is in the advanced position, in order to provide greater resistance to attack. Furthermore, the present invention also provides a cylinder lock with an improved and much more secure bearing arrangement between the parts, which is housed in a much stronger construction of central cylinder block.