BACKGROUND TO THE INVENTION A lock cylinder is a device which may be fitted to a latch mechanism (such as a door latch mechanism) or the like so as to make the latch mechanism key-controlled. Thus, the latch mechanism will typically have an opening formed therein of a particular size and shape so as to receive a standardised lock cylinder. The lock cylinder may therefore be manufactured by other than the manufacturer of the latch mechanism.

DESCRIPTION OF THE PRIOR ART Lock cylinders typically include a rotatable plug located within the body of the lock cylinder. The body of the lock cylinder carries a number of lock pins which are biassed by springs towards the plug. The plug has apertures which carry respective plug pins. When the correct key is inserted into the key-way the plug pins are pushed outwardly a predetermined distance by the key, each plug pin engaging a respective lock pin so that the lock pins are also pushed outwardly, against the force of the springs. It is arranged that the length of the respective plug pins, together with the formation of the correct key, result in the junction between each plug pin and its respective lock pin being aligned along the periphery of the plug, so that the plug can be rotated within the body. However, when the key is removed, or the incorrect key is inserted, the junctions are

not aligned, and parts of one or more of the lock pins project into the plug, effectively preventing rotation of the plug.

The lock cylinder also incorporates an actuator which can be driven by the plug and which can engage with components of the latch mechanism to which the lock cylinder is fitted; accordingly, rotation of the plug can cause the actuator to drive the latch mechanism components into or out of a locked condition.

The lock cylinder may be"single-ended"comprising a single plug and an actuator, or it may be"double-ended"comprising two opposed plugs with an actuator therebetween. Single- ended lock cylinders are used with latch mechanisms requiring key-control from one direction only (for example from one side of a panel to which the latch mechanism is fitted), whilst double-ended lock cylinders are used with latch mechanisms requiring key-control from two opposed directions (for example from both sides of a panel to which the latch mechanism is fitted).

The plug will typically have a key-way of a particular profile, which profile may be unique to the plug manufacturer. The correct key will need to match the profile if it is to be fitted into the key-way.

The plug is often manufactured from a solid bar of a suitable material (such as brass), and the pin apertures and the key-way are formed within the plug by machining operations. Since the key-way is machined into the plug it is necessary that the key-way extend to the peripheral edge of the plug.

When the lock cylinder is fitted to the latch mechanism, and the latch mechanism is assembled to the panel or other member which it is to secure, one end of the lock cylinder, herein referred to as the"front end"is accessible to a

user, and in particular permits the introduction of a key into the plug.

During assembly, the plug is inserted into the lock cylinder body from the front end and is retained there by a locking ring or other component so as to prevent the inadvertent removal of the plug from the body. It is however known for an intending intruder to seek to disable a lock cylinder by forcibly removing the plug from the front end of the lock cylinder, and the locking ring cannot always prevent this.

Once the plug is removed and the lock cylinder disabled, the latching device can often be by-passed.

International patent application W097/07309 discloses a lock cylinder constructed in separable sections which enables the plug to be fitted into the body of the lock cylinder from the"rear end", i. e. the end opposed to the front end of the cylinder.

US patents 3,702,553 and 4,472,953 disclose lock cylinders, and in particular plugs for a lock cylinder, which can be made in two separate elements. Since the two elements of the plug can be made separately, they may be made as die- castings rather than being machined from solid. In US patent 3,702,553 the two elements of the plug are held together by a sleeve prior to insertion into the body of the lock cylinder.

It is also known to fit a rotatable"anti-drill"disc adjacent the front end of a lock cylinder, which disc can rotate substantially freely so that attempts to drill out the plug can be made more difficult or even impossible, the disc spinning with the drill and so preventing the drill from removing a significant amount of metal from the disc or plug.

SUMMARY OF THE INVENTION It is an object of the present invention to seek to provide an improved lock cylinder, and a plug therefor, which has advantages over the known lock cylinders.

According to the invention there is provided a lock cylinder having a body containing a rotatable plug, the body having a front end which in use can receive a key, the plug having a key-way formed therein and at least one aperture adapted to receive a lock pin, the plug being manufactured from at least two separate elements, each element having a portion of the key-way formed therein, the plug being assembled into the lock cylinder body from the end opposed to the front end.

Since the plug is manufactured in at least two separate elements, the key-way does not need to extend to the periphery of the plug, but can be more centrally-located therein. In addition, the plug elements can be die-cast rather than being machined from a solid bar. Furthermore, it is not necessary that the elements of the plug are all made from the same material, i. e. it may be desirable for the element having the pin aperture or apertures to be of a relatively hard material such as brass with the aperture (s) machined thereinto, with the remaining element or elements die-cast of an aluminium and/or zinc-based material.

The assembly of the lock cylinder with the plug being fitted from the end opposed to the front end enables provision to be made to reduce the likelihood of the plug being forcibly removed from the front end of the lock cylinder, i. e. the ability to fit the lock cylinder from the rear is a particular advantage in that the forced removal of the plug from the lock cylinder by an intending intruder can be made much more difficult.

Preferably, the lock cylinder body includes lip means adjacent its front end, the lip means having a smaller dimension than the diameter of the plug. Accordingly, the lip means can reduce the likelihood of the forced removal of the plug from the front end of the lock cylinder. Since the lip means is preferably of the same material as the remainder of the body, and is ideally integral therewith, it is far more resistant to forced removal than a locking ring or the like, which is itself fitted from the front end and so which is liable to unauthorised removal from the front end.

Desirably, the lock cylinder includes a rotatable disc, in the form of an"anti-drill"disc; usefully the disc is located between the lip means and the plug, the disc having a larger diameter than the dimension of the lip means.

Accordingly, the assembly of the plug from the rear end has the additional advantage that an anti-drill disc can be inserted adjacent the front end, which anti-drill disc is substantally permanently retained by the lip means. The rotatable disc will have an opening therethrough so as to permit the key to be inserted through the disc and into the key-way of the plug.

In a preferred embodiment the profile of the opening of the disc does not exactly match the profile of the key-way of the plug. With such embodiments, an intending intruder who seeks to make a duplicate key, or perhaps to seek to use a "master"key, will not be able to learn the profile of the key-way of the plug by observation of the opening of the rotatable disc, and it may be arranged that the key-way of the plug includes at least one additional rail or other formation not present in the opening of the rotatable disc, so that an incorrect key can be passed through the disc and yet cannot be inserted into the key-way.

Usefully, the profile of the key-way is not uniform along its complete length. Thus, one or more features of the key-

way can be arranged to terminate part-way along the key-way, so that only specific keys with a correspondingly non- uniform profile can be fitted thereinto. In this way, even if an intending intruder learns the profile of the key-way present at the front end of the plug, it may not be possible to manufacture a duplicate key which can be fitted into the plug. With prior art designs in which the key-way is machined into a solid plug the profile of the key-way is uniform along the length of the key-way, but the inventor has appreciated that this is not necessary with a plug formed of more than one separate element, so increasing the level of security available.

There is also disclosed a plug for fitment into a lock cylinder as defined herein, the plug being formed from separate elements.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is an end view of a prior art lock cylinder, of "Euro-profile" ; Fig. 2 is an enlarged view of the profile of a key adapted to fit the key-way of the lock cylinder of Fig. l ; Fig. 3 is a side view of part of the lock cylinder of Fig. l ; Fig. 4 is a side view of a part of a lock cylinder made up of separable sections; Fig. 5 is a side view, partly in section, of part of a lock cylinder according to the invention;

Fig. 6 is an end view of the plug for use in the lock cylinder of Fig. 5; Fig. 7 is an end view of the rotatable anti-drill disc of the lock cylinder of Fig. 5; Fig. 8 is a side view of one of the separate elements of the plug of Fig. 6; Fig. 9 is a side view of part of the key suited to fit into the key-way of the plug of Fig. 6; Fig. 10 is an end view of an alternative design of plug; and Fig. 11 is an end view of a further alternative design of plug.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS The prior art lock cylinder 10 of Fig. l is of"Euro- profile". The lock cylinder of the invention (Fig. 5) is also of"Euro-profile". However, it will be appreciated that the profile of the lock cylinder is determined by the latch mechanism into which the lock cylinder is to be fitted, so that the invention could be utilised with alternative profiles as desired.

Fig. 1 is an end view of a lock cylinder 10, viewed towards the"front end"12. Thus, the front end 12 has the entrance to the key-way 14, and is the end which is visible to the user in use, and into which the user inserts the key 16 (Fig. 2).

The lock cylinder includes a rotatable plug 20 into which the key-way 14 is machined in known fashion. The form of

the key-way is usually chosen by the particular plug manufacturer, and may be unique to that manufacturer. It will be understood that the key 16 must have a profile corresponding to the keyway 14. The key-way 14 shown is schematic only, and it will be understood that the design of a particular profile, i. e. the number and positioning of any rails 22 and recesses 24, as well as the overall dimensions of the key-way, is almost unlimited.

The plug 20 has an enlarged end 26, which serves to limit the distance by which the plug may be inserted into the body 30 of the lock cylinder 10. The key-way 14 extends through the enlarged end 26. The enlarged end 26 has a substantially circular depression 32 formed therein to facilitate insertion of the key.

As will be understood by those skilled in the art, the plug 20 also carries a number of pins (not seen) which engage with spring-biassed lock pins (also not shown) carried by the lock cylinder, specifically by the portion 34 of the "Euro-profile"lock cylinder 10. It is arranged that upon insertion of the correct key 16 into the key-way 14, the plug 20 can be rotated within the lock cylinder body 30, enabling rotation of the lug 36 carried by the plug to drive the actuator 40, which can in turn interact with the latch mechanism (not shown) in known fashion. When the key is removed, or the incorrect key is inserted, rotation of the plug is prevented.

In known fashion, the plug 20 is fitted into the body 30 from the front end. Though not shown in the drawings, means must be provided to seek to prevent the forced removal of the fitted plug from the front end, which means may comprise a locking ring, face plate or escutcheon subsequently secured to the lock cylinder (or to the latch mechanism) and which covers a part of the enlarged end 26.

The lock cylinder 10 is double-ended, and comprises two opposed plugs 20 fitted into two opposed parts of the body 30 of the lock cylinder, one plug and body part being to either side of the actuator 40.

Fig. 4 shows a"sectional"double-ended lock cylinder made up of two opposed lock cylinder parts 42 (which may be identical), between which is located a connecting part or bridge 44. This lock cylinder is somewhat similar to that disclosed in international patent application W097/07309.

It will be understood that such an arrangement, comprising an assembly of separable sections, allows access to the rear end 28 of the body 30, and so permits the plug 20 to be inserted from the rear end (access to the rear end is available when the parts 42 and 44 are separated, whereas in the"one-piece"embodiment of Figs. 1 and 3 it is not physically possible to insert the plug from the end adjacent the actuator 40). However, in the design shown in Fig. 4 the plug 20 is identical to the plug 20 of Fig. 3, and so is designed to be fitted from the front end.

The present invention requires the lock cylinder to be assembled from separable sections, since it is a feature that the plug be inserted from the rear end opposed to the front end. In the embodiment of Fig. 5 therefore, the lock cylinder section 46 is adapted to be secured to a connecting part or bridge (not shown in Fig. 5, but see the bridge 44 of Fig. 4); the lock cylinder part 46 may be secured to the connecting part or bridge by any suitable method such as any of those disclosed in the stated prior document. The connecting part or bridge may subsequently be secured to another lock cylinder section 46 to form a double-ended lock cylinder, if desired.

The lock cylinder section 46 includes a through bore 50 which is narrowed adjacent the front end 52; specifically the narrowing provides a lip 54 which is of smaller

dimension than the diameter of the plug 56. Ideally, the lip 54 is circular, so that the diameter of the lip is smaller than the diameter of the plug 56. In this embodiment the lip 54 is continuous, but in other embodiments the lip is discontinuous, comprising one or more inwardly projecting"fingers".

It will be recognised that the provision of a lip which is of smaller dimension than the diameter of the plug is only practical with designs in which the key-way is centrally located within the plug; i. e. in designs in which the key- way is machined into the plug and necessarily extends to the periphery of the plug, the lip would obscure a part of the key-way and prevent insertion of the key. With the present invention, however, the manufacture of the plug from two or more separate elements enables the key-way to be spaced from the periphery of the plug so that the lip 54 does not obscure any of the key-way.

Located between the lip 54 and the plug 56 is a rotatable disc 60. The disc 60 has an opening 62 formed therein (see also Fig. 7), to permit a key of a particular profile to be passed therethrough and into the aligned key-way 64 (Fig. 6) in the plug 54. Specifically, however, the key-way 62 in the disc 60 is sufficiently narrow to prevent a drill bit from engaging the plug 56, so that if an intending intruder seeks to drill out the plug, the drill bit will only engage the disc 60, and will cause this disc to rotate, effectively preventing the drill from removing more than an insignificant amount of material.

It will be noted that the lip 54 is integral with the body of the lock cylinder part 46; whilst anti-drill discs are known in themselves, it has not previously been possible to fit such a disc so securely to a lock cylinder, i. e. without requiring a separate covering plate or escutcheon, which could itself be removed from the front end by a determined intending intruder.

Whilst the bore 50 of the lock cylinder part 46 is shown continuous except for the lip 54 adjacent the front end 52, in alternative embodiments there can be an additional step in the bore adjacent the lip 54, and which additional step serves to locate the anti-drill disc, and specifically which step prevents the plug 56 from being moved into clamping engagement with the disc, which clamping engagement might reduce the effectiveness of the disc.

The end of the bore 50 adjacent the end opposed to the free end 52 is threaded, and can receive an externally threaded collar 60, which serves to secure the plug 56 within the bore 50. The plug 56 carries an arm 58 which can pass through the collar 60 and engage the actuator (not shown) of the lock cylinder.

The plug 56 is shown slightly smaller than the bore 50 in the drawing of Fig. 5, though it will be understood that in practice the plug is a tight but sliding fit within the bore 50, i. e. so that it is able to rotate when the correct key has been inserted, but is prevented from substantial free play.

Whilst in certain embodiments it might be desirable for the opening in the disc 60 to be a simple rectangle through which the key could be passed, it is a valuable additional security feature of the invention that the disc 60 can have a differently profiled opening than that of the key-way 64, and this feature is shown in Figs. 6 and 7. Thus, the key- way 64 includes two recesses 66a, 66b (which will accommodate respective rails on the correct key 68 (Fig. 9)), and two rails or projections 70a, 70b (which will locate into corresponding recesses in the key 68). The opening 62 in the disc 60 has corresponding recesses and projections.

However, the opening 62 has an additional recess 72, which is not present in the key-way 64. Accordingly, an intending intruder who seeks to by-pass the lock cylinder by inserting

a"master"key for example, and who obtains a key with a profile matching that of the opening 62, will be unable to insert that key into the key-way 64.

Clearly, the opening 62 can have any feature (or features) in addition to those present in the key-way 64, enabling a key having the correct form of the key-way 64 to pass through the opening, but preventing certain keys which can pass through the opening 62 from entering the key-way 64.

In an alternative, though less desirable, embodiment, the key-way in the plug can be of plain design, perhaps of rectangular cross-section without any rails or recesses.

The anti-drill disc could, however, have rails and recesses and serve to make the lock cylinder specific to the key profile of a particular manufacturer, for example. Such an embodiment would avoid the additional security benefit outlined above, but would result in a very simple and perhaps universal design of plug.

Fig. 6 also shows the plug 56 formed as two separate elements 74 and 76, which in this embodiment are substantially "halves"of the plug 56. The elements 74 and 76 are preferably die-cast, and each includes a part of the pin aperture (s) (not shown), which apertures will carry the plug pin (s) in the assembled plug, and which can receive a part of a respective lock pin when the correct key is not present in the key-way.

Another beneficial feature of the invention is shown in Figs. 8 and 9. Thus, since a part of the key-way is formed in each element 74,76 of the plug, it is not necessary that the profile of the key-way be uniform along its length. In the embodiment shown, the recess 22b terminates before the end 78 of the key-way 64. It is therefore necessary that the corresponding rail 80 of the correct key 68 also terminates before the end of the key so that the key 68 can be fully inserted into the key-way. Once again, it is not

possible for an intending intruder observing the key-way at the front end of the plug to know whether or not any of the recesses in the key-way 64 terminate short of the end of the key-way, and he may find that a key which matches the profile of the key-way at the front end of the plug cannot be fully inserted into the key-way unless one or more features of the key profile change along its length.

This feature enables a lock cylinder manufacturer more securely to control the copying of keys, in that key cutting machines are typically only able to machine the edge 82 of the key 68 (Fig. 9), but are unable to machine the rail 80 for example. Accordingly, the lock cylinder manufacturer may be better able to control the supply of key blanks having the desired rail formations, and could for example supply lock cylinders with a particular formation to one part of a territory, and lock cylinders with a different formation to another part of the territory, key blanks for the respective parts of the territory being non- interchangeable.

It is of course possible to alter the profile in more than one place along the length of the key-way, but in order to avoid the insertion of an incorrect key it is necessary that the alternation in profile involve additional material towards the end of the key-way, since removal of material would not prevent the insertion of an incorrect key.

Another suitable location for the addition of material would be adjacent the lower terminal end of the key-way 64, such as in the area shown in dotted outline 84 in Fig. 8.

In the embodiment of Fig. 10, the plug 86 is made of three separate elements, and in this embodiment the elements are not all of the same material. Thus, the two elements 88 and 90, which are the more complex elements since they together form the majority of the key-way, are die cast, for example from an aluminium or zinc-based material. The element 94 has a portion of the key-way but importantly is the element

into which the pin apertures are formed; to better ensure reliable operation of the pins it may be preferred that the pin apertures are drilled into a hard material such as brass, and in this embodiment the element 94 is made of brass for this purpose. It will be noted that the element 94 also includes a part of the key-way, but in other embodiments the relationship between the elements can be altered so that the element into which the pin apertures are formed does not carry any of the key-way.

Fig. 11 shows an alternative plug 96 made up of four elements, each element containing a part of the key-way.

Clearly, other embodiments having more than four elements can be provided, as can yet other embodiments having different constructions with two, three or four elements, as desired. Also, it is not necessary that the key-way be of generally rectangular configuration, and it could instead be generally of"L"form,"T"form,"U"form, circular or polygonal form, for example, with rails and/or recesses provided to give the key-way its desired (manufacturer- specific) profile; the number and arrangement of the elements could be chosen for the particular form desired.

Whatever the specific design of the plug, and the number of elements making up the plug, the plug may initially be assembled into a sleeve (not shown) which will retain the elements together prior to assembly into the body. The sleeve may alternatively be sized to fit within the bore of the body, so that the sleeve is a permanent feature of the assembled lock cylinder, the sleeve having pin apertures aligned with the respective pin apertures of the plug and being secured to rotate with the plug.

In embodiments in which the sleeve is a permanent feature of the assembled lock cylinder, the internal profile of the sleeve and the corresponding periphery of the plug can alternatively be acircular, so that the sleeve and plug are

maintained in a particular angular relationship without possibility of the plug rotating within the sleeve. The internal profile of the sleeve may be hexagonal, square or triangular for example, with the periphery of the plug being similarly configured. In certain embodiments, the periphery of the plug may be polygonal, with the number of sides of the polygon matching the number of elements making up the plug.

Alternatively, the external profile of the plug and the internal profile of the sleeve may be generally circular, but with the sleeve carrying an internally projecting lug or the like which can locate within a corresponding recess in one element of the plug, so that the one element of the plug can be retained in position relative to the sleeve by the lug, with the remaining element (s) being retained in position by their engagement with the one element.