GB2492829A

GB2492829A - Double lock cylinder with key cylinder, thumbturn, and mis-alignment clutch

Info

Publication number: GB2492829A
Application number: GB201112108A
Authority: GB
Inventors: Steve Wilkes
Original assignee: Grouphomesafe Ltd
Current assignee: Era Home Security Ltd
Priority date: 2011-07-14
Filing date: 2011-07-14
Publication date: 2013-01-16
Anticipated expiration: 2031-07-14
Also published as: IE86904B1; IE20110344A1; CN102877695A; CN102877695B; GB2492829B; CN202299634U; GB201112108D0

Abstract

A double lock cylinder comprising: thumb-turn 114 permanently coupled with rotary cam 106 via slots 141 and lugs 139; a key cylinder on a second side selectively coupled to the cam via clutch 109 wherein protruding lug 132 of a key actuated drive dog 120 selectively engages in cam slot 142 and key cylinder slot 146. Drive dog 120 of the clutch is biased toward the key cylinder wherein it is disengaged from the cam by a first biasing means 122 and further comprises a movable plunger 121 biased toward the key cylinder by means 123. If the thumb-turn and cam are mis-aligned with the key cylinder upon insertion of a key, the key moves the plunger 121 away from the cylinder 104 wherein cylinder 104 and drive dog 120 rotate until protrusion 132 is aligned with cam slot 142; the drive dog then slides into engagement with the cam due bias 123 of plunger 121 preferably being a stiffer spring 123 than drive dog spring 122; plunger 121 and spring preferably acting within a bore of the drive dog.

Description

LOCK CYLINDER

The present invention relates to a lock cylinder comprising a cam for actuating the bolt of a lock. In particular, it relates to a lock cylinder having a barrel disposed on a first side of the cam, the barrel being coupled to a thumb-turn at one end thereof and to the cam at the other end so as to enable rotation of the cam by means of the thumb-turn, and a key operable cylinder disposed on a second, opposite side of the cam.

Removable lock cylinders are known in the art and are popular for residential doors worldwide. Examples of such cylinders are the Euro-cylinder' and the Oval-cylinder', which are recognisable by the profile of the lock cylinder when viewed end-on, the Euro-cylinder having a profile shaped like an enlarged keyhole and the Oval-cylinder having an oval shape.

Various configurations of these removable lock cylinders are available. A single lock cylinder comprises one key cylinder and, therefore, enables a door to be locked and unlocked from one side only. More commonly, lock cylinders are double ended with two key cylinders, which allows a key to be inserted from either side. Alternatively, one end of a double-ended lock cylinder may be provided with a thumb-turn knob for safety and convenience.

Double-ended lock cylinders typically have a shuttling drive dog device between the two key cylinders, which is selectively pushed into place by insertion of a key at one end or the other. Insertion of a key engages the drive dog device between the respective key cylinders with a central cam which, in turn, operates the mechanism of the lock into which the lock cylinder is fitted. Two keys cannot be inserted simultaneously, and the removal of a particular key may only be done when the associated key cylinder, and also the cam, is in a predetermined park' position. This contrasts with the double-ended lock cylinder having a thumb-turn at one end, in which the thumb-turn and cam may be left in any orientation by a user, as explained in more detail below.

Figure 1 is a perspective view of a known thumb-turn lock cylinder. Referring to Figure 1, a known thumb-turn lock cylinder 1 comprises a body 2, a key cylinder 4, a cam 6 and a thumb-turn 8.

Figure 2 is an exploded perspective view of the thumb-turn lock cylinder shown in Figure 1. Referring to Figure 2, the body 2 has first and second cylinders 10, 12 arranged coaxially for receiving the key cylinder 4 and a barrel 14 of the thumb-turn 8 respectively therein. The cam 6 comprises a cylindrical portion or hub 16 and an engagement portion 18 which projects radially from the hub 16 for engaging with a lock mechanism to which the lock cylinder 1 is fitted.

The lock cylinder 1 also comprises a drive dog 20, a drive dog spring 22 and a pair of circlips 23. The barrel 14 of the thumb-turn 8 is hollow, allowing the drive dog spring 22 to be seated therein. The drive dog 20 is a generally cylindrical member having a pair of diametrically opposed radial projections 24 disposed at a first end thereof. The projections 24 are arranged to engage with a corresponding pair of diametrically opposed slots 26 formed in the open end of the barrel 14 when the drive dog 20 is inserted therein, and act to couple rotational movement of the drive dog 20 to the thumb-turn 8, whilst allowing relative axial movement there between. A second end of the drive dog 20 is provided with an angled slot 28, which is shaped so as to receive the tip of a key, in use.

When installed in the body 2, the hub 16 of the cam 6 fits between the first and second cylinders 10, 12. Respective inward facing ends of the key cylinder 4 and the barrel 14 project into the hub 16. The pair of circlips 23 attach to the respective inward facing ends of the key cylinder 4 and the barrel 14 so as to retain them within the body 2.

Figures 3A and 3B are part cross-sectional side views showing the insertion of a key into the thumb-turn key cylinder of Figure 1, when the thumb-turn 8 is aligned with the key cylinder 4. Referring to Figure 3A, when the lock cylinder 1 is assembled, the drive dog is biased by the drive dog spring 22 such that is projects through the hub 16 of the cam 6 and abuts the inward facing end of the key cylinder 4. The cam 6 is always connected rotationally to the thumb-turn 8, by means of a pair of diametrically opposed lugs (not shown) provided on the radial inner surface of the hub 16 which engage with the slots 26 in the barrel 14 of the thumb-turn. Accordingly, the thumb-turn 8 and the cam 6, can be parked in any position within a possible 360 degrees of rotation. Rotation of the thumb-turn 8 and cam 6 also causes the drive dog 20 to rotate due to the engagement of the projections 24 on the drive dog 20 with the slots 26 on the barrel 14.

The key cylinder 4, which may be of a conventional pin tumbler configuration, can only be parked in one orientation when the key 30 is not inserted. Furthermore, the key cylinder 4 is not rotationally engaged with any of the thumb-turn 8, the cam 6 or the drive dog 20.

As shown in Figure 3A, when the thumb-turn 8 is aligned with the key cylinder 4, the angled slot 28 of the drive dog 20 is aligned with a key slot of the key cylinder 4.

Accordingly, as shown in Figure 3B, when the key 30 is inserted into the key cylinder 4, the tip of the key 30 is received within the angled slot 28 of the drive dog 20.

Figure 4 is a part cross-sectional side view showing operation of the thumb-turn lock cylinder of Figure 1 using a key. Referring to Figure 4, when the key 30 is turned by a user, the key cylinder 4 and the drive dog 20 are rotated together. Rotation of the drive dog 20 therefore causes simultaneous rotation of the thumb-turn 8 and cam 6, enabling a lock mechanism to which the lock cylinder 1 is attached to be locked/unlocked accordingly.

Figures SA and 5B are part cross-sectional side views showing the insertion of a key 30 into the thumb-turn key cylinder of Figure 1, when the thumb-turn 8 is not aligned with the key cylinder 4. Referring to Figure 5A, it will often be the case that the thumb-turn 8 and cam 6 are not left in a position where they are aligned with the key cylinder 4. As shown, in Figure 5A, the angled slot 28 of the drive dog 20 is misaligned by 180 degrees from the key cylinder 4. Accordingly, as shown in Figure 5B, when the key 30 is inserted into the key cylinder 4, the tip of the key 30 presses against the drive dog 20 and causes it to move into the barrel 14 of the thumb-turn 8, thereby compressing the drive dog spring 22. When a user subsequently turns the key 30, only the key cylinder 4 will be rotated until it aligns with the radial slot 28 of the drive dog 20. When this happens, the drive dog spring 22 biases the drive dog 20 toward the key cylinder 4 such that the tip of the key 30 is received within the angled slot 28. Thereafter, rotation of the key 30 also causes rotation of the drive dog 20, thumb-turn 8 and cam 6 as shown in Figure 4.

There is a problem with the thumb-turn lock cylinder having the above described configuration in that it is susceptible to being bypassed' or picked' using a lock-pick.

Figure 6 is a part cross-sectional side view of the thumb-turn lock cylinder of Figure 1 and a lock pick 32. Referring to Figure 6, the lock-pick 32 comprises a specially shaped piano wire 34 mounted in a pin-chuck 36, or similar.

Figure 7 is a front view of the thumb-turn lock cylinder of Figure 1 showing the lock pick 32 of Figure 6 when inserted therein. Referring to Figure 7, the wire 34 has a ioop or other cranked formation on its end which is shaped so as to pass through the key-way of the key cylinder 4. The main stem of the wire 34 must be close to the centre of the key cylinder 4.

Figure 8 is a part cross-sectional side view of the thumb-turn lock cylinder 1 of Figure 1 showing the lock pick 32 of Figure 6 inserted therein. Referring to Figure 8, when the wire 32 is full inserted in the key cylinder 4, it may depress the drive dog 20 against the drive dog spring 22. Accordingly, the wire 34 passes completely through the key cylinder 4 without rotationally engaging therewith.

Figure 9 is a part cross-sectional side view showing operation of the thumb-turn lock cylinder of Figure 1 using the lock pick 32 of Figure 6. Referring to Figure 9, when the lock pick 32 is rotated, it turns independently of the key cylinder 4. Thus, the lock pick 32 can be used to rotate the drive dog 20 and, therefore, the thumb-turn 8 and cam 6 in turn in order to unlock the door or window to which the lock cylinder 1 is attached, without rotating the key cylinder 4, i.e. the key cylinder 4 is bypassed'. The lock pick 32 may also be retracted after unlocking to leave little or no damage to the lock cylinder 1 or the door/window.

United Kingdom Patent Application No. 0304932.7 (publication No. GB-A-2386154) in the name of Banham Patent Locks Ltd published on 10 September 2003 describes a lock comprising a bolt-operating cam and having a thumb-turn on one side and a key operable plug on the other side. The lock includes clutch means for interconnecting the plug and the cam. A spring biased plunger is arranged within the barrel of the thumb-turn. The plunger includes a peg at one end which projects through an opening in the cam and abuts the clutch means. In turn, the clutch means is biased out of a recess in the end of the plug toward the cam by a pair of springs. In one state, the plunger peg acts to disengage the clutch means from the cam when no key is inserted in the plug.

Upon insertion of a key, the plunger peg is displaced so as to permit the clutch means to engage with the cam under the force of the pair of springs, in the case that the clutch means and plug are rotated such that a lug on the clutch means engages with a corresponding slot on the cam. However, there are a number of drawbacks to this arrangement. In particular, the lock has a complicated construction which is time consuming to assemble in view of the plunger being spring biased toward the cam from one side and the clutch means being spring biased toward the cam from the opposite side. Furthermore, the space required to incorporate the separate clutch means and plunger peg of the lock described above would adversely affect the application of such an arrangement to shorter lock cylinders, where there is a particular limit to the axial length of lock cylinder.

German Patent Application DE-A1-10317448 in the name of Aug. Winkhaus GmbH & Co. describes a double cylinder lock having a key cylinder and a thumb-turn disposed on opposite sides of a cam. The key cylinder 2 is provided with an actuator pin 10 which is operable to move a clutch element 9 into and out of engagement with the cam 4. In more detail, without a key 5 inserted in the key cylinder 2, a first spring 14 acts to bias the actuator pin 10 away from the cam 4 which, in turn, disengages the clutch element 9 from the cam 4. Upon insertion of the keyS, the actuator pin 10 is pressed in against the first spring 14, which allows the clutch element 9 to be moved into engagement with the cam 4 by a second spring 13, providing the clutch element 9 is aligned with the cam 4. If the clutch element 9 is not aligned with the cam 4, then it rotates together with the key cylinder 2 until it reaches the correct position which allows it to moved into engagement with the cam 4. Again, this arrangement is complicated to manufacture and assemble, in particular because the actuator pin 10 together with the first and second springs 14, 13 must be fitted with the key cylinder 2. Also, the use of above described arrangement in shorter lock cylinders would be limited due to the space required to accommodate the clutch element and actuator pin.

United Kingdom Patent Application GB-A-2201452 in the name of Chubb Lips Nederland by published on 1 September 1988 describes a double lock cylinder operable by a key from one side and by a motor or a thumb-turn from the other in which the key can be inserted even if the cam has been left in a misaligned position. However, again this arrangement is complicated in that it requires a separate coupling member 15 disposed in the key cylinder to be biased by insertion of the key into engagement the plunger 16 mounted in the bush 18. Furthermore, a disadvantage of this arrangement is the fact that coupling the drive from the key cylinder barrel 14 to the cam 4 is performed indirectly via three separate components, i.e. the coupling member 15, the plunger 16 and the cross pin 9.

It is an aim of the present invention to provide a thumb-turn lock cylinder which substantially overcomes or mitigates at least some of the above-mentioned problems.

According to the present invention, there is provided a lock cylinder comprising: a cam for actuating the bolt of a lock; a barrel disposed on a first side of the cam, the barrel being coupled to a thumb-turn at one end thereof and to the cam at the other end so as to enable rotation of the cam by means of the thumb-turn; a key operable cylinder disposed on a second, opposite side of the cam; and clutch means movable between a first state, in which the clutch means is rotationally coupled to the key cylinder and not coupled to the cam, and a second state, in which the clutch means is rotationally coupled to the key cylinder and is rotationally coupled to the cam by means of a projection on the clutch means being received within a slot in the cam; wherein the clutch means is biased toward the key cylinder into the first state by first biasing means and comprises a movable member which is movable relative to the clutch means and biased toward the key cylinder by second biasing means; and wherein the clutch means is arranged such that: i) in the case that the projection is aligned with the slot, the clutch means is movable into the second state directly in response to a correct key being fully into the key cylinder; and ii) in the case that the projection is not aligned with the slot, the movable member is arranged so as to move away from the key cylinder in order to accommodate a correct key fully inserted into the key cylinder and to allow rotation of the key cylinder and clutch means to effect alignment of the projection with the slot, the clutch means being movable into the second state in response to the biasing force exerted on the movable member when, in use, such alignment of the projection and the slot is effected.

Thus, the present invention provides a lock cylinder in which the key cylinder cannot be bypassed by means of the lock pick, because the clutch means are engaged with the key cylinder in both the first and second states such that rotation of the clutch means is not possible without a corresponding rotation of the key cylinder. This is achieved by means of an advantageous construction in which the clutch means comprises the movable member, where the clutch means and movable are each biased toward the key cylinder by first and second biasing means, respectively.

Conveniently, the clutch means is rotationally coupled to the key cylinder by means of the projection on the clutch means engaging with a corresponding slot on the key cylinder. Thus, a single projection provided on the clutch means enables the clutch means to be rotationally coupled to the key cylinder and/or the cam.

In a preferred embodiment, the first biasing means is a spring. This provides an advantageously simplified construction in which only a single spring is required to bias the clutch means into the first state. Preferably, the second biasing means is a spring which is stronger than the spring of the first biasing means. Thus, the spring forces of the first and second biasing means are conveniently selected such that in the case U) above, movement of the clutch means into the second state is in response to the biasing force of the spring of the second biasing means which overcomes the biasing force of the spring of the first biasing means.

Conveniently, the clutch means comprises a drive dog having a substantially cylindrical form, wherein the projection extends from the radial outer surface of the drive dog at a first end thereof. Preferably, in the first state, the first end of the drive dog abuts the key cylinder.

The drive dog may comprise an axial bore and the movable member is a plunger arranged so as to be received within the axial bore for axial movement therein. This arrangement is advantageous in that the space required to accommodate the drive dog and movable member in the axial direction is minimised. Conveniently, the axial bore of the drive dog comprises a step and the plunger comprises a collar which cooperates with the step of the axial bore to limit the movement of the plunger toward the key cylinder.

The plunger may be biased toward the key cylinder by means of a plunger spring disposed within the axial bore of the drive dog between the plunger and a second end of the drive dog. This arrangement is advantageous in that no additional space is required within the lock cylinder in order to accommodate the plunger spring.

In a preferred embodiment, the axial bore of the drive dog is a through bore and the clutch means comprises threaded fastening means arranged so as to engage with the through bore at the second of the drive dog so as to retain the plunger spring within the through bore. Accordingly, the plunger and plunger spring can be retained within the drive dog prior to the drive dog being installed, which facilitates assembly of the lock cylinder.

The first end of the drive dog may comprise a bevel portion diametrically opposed to the projection which advantageously defines a void which facilitates the accommodation of a key when fully inserted within the key cylinder.

Advantageously, the barrel is hollow and the drive dog is at least partially received within the barrel for axial movement into and out of the barrel. With this construction, the overall length in the axial direction required by the clutch means can be minimised.

Conveniently! the drive dog is biased out of the barrel toward the key cylinder by a drive dog spring disposed within the barrel.

The thumb-turn may be formed integrally with the barrel, which advantageously allows for a simplified construction and facilitates assembly of the lock cylinder.

Preferably, the cam comprises a hollow cylindrical hub portion having an annular rib formed on the radial inner surface thereof, wherein the slot in the cam is formed in the angular rib.

The lock cylinder may comprise a body having first and second cylinders for receiving the key cylinder and the barrel respectively therein. This construction ensures that the axes of rotation of the key cylinder and barrel can be precisely aligned with one another.

In a preferred embodiment, respective inward facing ends of the key cylinder and the barrel are received within respective opposite ends of the hub portion of the cam. With this arrangement, the cam is conveniently rotatable about and co-axial with the respective inward facing ends of the key cylinder and barrel. Furthermore, the annular rib conveniently serves to space the key cylinder from the barrel in the axial direction.

An embodiment of the present invention will now be described, by way of example only, with reference to Figures 10 to 14B of the accompanying drawings, in which: Figure 1 is a perspective view of a known thumb-turn lock cylinder; Figure 2 is an exploded perspective view of the thumb-turn lock cylinder shown in Figure 1; Figures 3A and 3B are part cross-sectional side views showing the insertion of a key into the thumb-turn lock cylinder of Figure 1, when the thumb-turn is aligned with the key cylinder; Figure 4 is a part cross-sectional side view showing operation of the thumb-turn lock cylinder of Figure 1 using a key; Figures 5A and SB are part cross-sectional side views showing the insertion of a key into the thumb-turn lock cylinder of Figure 1, when the thumb-turn is not aligned with the key cylinder; Figure 6 is a part cross-sectional side view of the thumb-turn lock cylinder of Figure 1 and a lock pick; Figure 7 is a front view of the thumb-turn lock cylinder of Figure 1 showing the lock pick of Figure 6 when inserted therein; Figure 8 is a part cross-sectional side view of the thumb-turn lock cylinder of Figure 1 showing the lock pick of Figure 6 inserted therein; Figure 9 is a part cross-sectional side view showing operation of the thumb-turn lock cylinder of Figure 1 using the lock pick of Figure 6; Figure 10 is a perspective view of an embodiment of a thumb-turn lock cylinder according to the present invention; Figures hA and 11B are exploded perspective views of the thumb-turn lock cylinder shown in Figure 10; Figures 12A and 12B are part cross-sectional side views showing the insertion of a key into the thumb-turn lock cylinder of Figure 10, when the thumb-turn is aligned with the key cylinder; Figure 13 is a part cross-sectional side view showing operation of the thumb-turn lock cylinder of Figure 10 using a key; and Figures 14A and 14B are part cross-sectional side views showing the insertion of a key into the thumb-turn lock cylinder of Figure 10, when the thumb-turn is not aligned with the key cylinder.

Referring to Figures 10, hA and 11B, the thumb-turn lock cylinder 100 generally comprises a body 102, a key cylinder 104, a cam 106, a thumb-turn 108 and clutch means 109. The body 102 comprises first and second cylinders 110, 112, which are arranged coaxially and which are adapted to receive the key cylinder 104 and a barrel 114 of the thumb-turn 108 respectively therein. The cam 106 comprises a cylindrical portion or hub 116 and an engagement portion 118 which projects radially from the hub 116 for engaging with a lock mechanism to which the lock cylinder 100 is fitted. The clutch means 109 comprises a drive dog 120, a plunger 121, a drive dog spring 122, a plunger spring 123 and a grub screw 125. The lock cylinder 100 also comprises a pair of circlips 126.

The drive dog 120 is a generally cylindrical member having first and second ends 127, 128 and an axial bore 130 formed there through. The first end 127 of the drive dog 120 is provided with a projection 132 which extends radially outward from its external surface.

The projection 132 is elongated in a direction parallel to the axis of the axial bore 130.

The first end 127 of the drive dog 120 also comprises bevel 134 of about 45 degrees which is diametrically opposed to the projection 132.

Referring now to Figure 12A, the axial bore 130 includes a step 136 disposed toward the first end 127 of the drive dog 120, such that the diameter of the axial bore 130 between the first end 127 of the drive dog 120 and the step 136 is smaller than the diameter between the step 136 and the second end 128 of the drive dog 120.

The plunger 121 is a cylindrical member having a collar 138 of increased diameter disposed at its trailing end. Accordingly, the plunger 121 can be seated within the drive dog 120 by inserting it into the axial bore 130 from the second end 128 until the collar 138 abuts the step 136. In this position, a leading end of the plunger 121 is partially exposed by virtue of the bevel 134 at the first end 127 of the drive dog 120. The plunger spring 123 is then inserted into the axial bore 130 of the drive dog 120 so that is abuts the trailing end of the plunger 121. Next, the grub screw 125 is screwed into the axial bore 130 at the second end 128 of the drive dog 120 so as to partially compress the plunger spring 123, thereby biasing the plunger 121 toward the first end 127 of the drive dog 120.

The barrel 114 of the thumb turn 108 is hollow, allowing the drive dog spring 122 to be seated therein. Accordingly, the drive dog 120, with the plunger 121 inside it, can be inserted into the barrel 114 such that the grub screw 125 rests against the drive dog spring 122.

The hub 116 of the cam 106 comprises an annular rib 140 disposed on its radial inner surface. The annular rib 140 is positioned mid-way along the axial length of the hub 116 and includes a slot 142 or notch therein. When installed in the body 102, the hub 116 of the cam 106 fits between the first and second cylinders 110, 112. Respective inward facing ends of the key cylinder 104 and the barrel 114 project into the hub 116 on opposite sides of the annular rib 140. The pair of circlips 126 attach to the respective inward facing ends of the key cylinder 104 and the barrel 114 so asto retain them within the body 102. A pair of diametrically opposed lugs 139 are provided on the radial inner surface of the hub 116 adjacent to the annular rib 140. The barrel 114 of the thumb-turn 108 has a corresponding pair of diametrically opposed slots 141 which engage with the lugs 139 so as to rotationally couple the thumb-turn 108 to the cam 106.

The inward facing end of the key cylinder 104 comprises a circular recess 143 which is coaxial with the key cylinder 104 and defined by an annular wall 144 which projects from the periphery of the inward facing end key cylinder 104 in a direction parallel to its major axis. The annular wall 144 comprises a pair of diametrically opposed slots 146, which are aligned with a key slot of the key cylinder 104 such that the slots 146 are in respective 12 o'clock and 6 o'clock positions when the pins of the key cylinder 104 are aligned with those in the body 102. As with the known thumb-turn cylinder described previously, the key cylinder 104, which may be of a conventional pin tumbler configuration, can only be parked in one orientation when a key 150 is not inserted.

Referring to Figure 12A, when the lock cylinder 100 is assembled, the drive dog 120 is biased by the drive dog spring 122 such that is projects through the hub 116 of the cam 106 and abuts the inward facing end of the key cylinder 104. In particular, the first end 127 of the drive dog 120 is received within the circular recess 143 of the key cylinder 104 such that the projection 132 is received within one of the slots 146. i.e. the slot 146 in the 6 o'clock position. By virtue of the projection 132 on the dog drive 120 engaging with the slot 146 of the key cylinder 104, the dog drive 120 and key cylinder 104 are coupled together such that rotation of the key cylinder 104 when a user turns a key 150 inserted therein causes a corresponding rotation of the drive dog 120 as will be described in more detail later.

Furthermore, as shown in Figure 12A, without a key 150 inserted in the key cylinder 104, there is a clearance between the projection 132 on the dog drive 120 and the annular rib of the cam 106. Accordingly, in this state, the drive dog 120 is not rotationally coupled to the cam 106. By contrast, the cam 106 is always rotationally coupled to the thumb-turn 108 by means of the lugs 139 on the hub 116 and the slots 141 in the barrel 114 described previously. Accordingly, the thumb-turn 108 and the cam 106 can be parked in any position within a possible 360 degrees of rotation. However, any rotation of the thumb-turn 108 and cam 106 when the drive dog 120 is in the position shown in Figure 12A merely results in the barrel 114 of the thumb-turn 108 rotating about the drive dog 120 which is kept in the same position by its engagement with the key cylinder 104 as described above.

In Figures 12A and 12B, the cam 106 is aligned with the drive dog 120 such that the slot 142 in the annular rib 140 is adjacent to the projection 132 on the first end 127 of the drive dog 120. Accordingly, as shown in Figure 12B, when a key 150 is inserted into the key cylinder 104, the tip of the key 150 pushes against the leading end of the plunger 121. The plunger spring 123 and the drive dog spring 122 are selected such that the force of the key 150 pressing against the end of the plunger 121 causes the drive dog spring 122 to compress before the plunger spring 123. As explained above, in Figure 12B, the projection 132 on the drive dog 120 is aligned with the slot 142 of the annular rib 140. Accordingly, as the drive dog 120 is compressed against the drive dog spring 122 as it is pushed into the barrel 114 of the thumb-turn 108, the projection 132 is received within the slot 142 of the annular rib 140. In this position, pad of the projection 132 is still received within the slot 146 in the inward facing end of the key cylinder 104.

Thus, by means of the projection 132, the drive dog 120 is rotationally coupled to both the key cylinder 104 and the cam 106, the cam 106 in turn being coupled to the thumb-turn 108 as explained previously.

Referring to Figure 13, when the key 150 is subsequently turned by a user, the key cylinder 104 is caused to rotate within the first cylinder 110 of the body 102. This causes the drive dog 120 to rotate, together with the cam 106, and thumb-turn 108. Thus, rotation of the cam 106 causes a lock mechanism to which the lock cylinder 100 is installed to be locked/unlocked accordingly. The key 150 can only be removed from the key cylinder 104 when in the orientation shown in Figure 12B. When the key 150 is removed, the drive dog spring 122 acts to bias the drive dog 120 toward the key cylinder 104 such that the projection 132 moves out of the slot 142 in the annular rib 140 of, thereby disengaging the drive dog 120 from the cam 106. Thus, once again the thumb-turn 108 and cam 106 can be freely rotated by a user and parked in any position.

Referring to Figure 14A, in view of the fact that the thumb-turn 108 and cam 106 can be parked in any position, it will often be the case that the slot 142 in the annular rib 140 of the cam 106 is not aligned with the projection 132 on the drive dog 120. Referring to Figure 14B, when the key 150 is inserted into the key cylinder 104, the tip of the key 150 presses against the leading end of the plunger 121. However, because the projection 132 on the drive dog 120 is not aligned with the slot 142 in the annular rib 140, movement of the drive dog 120 into the barrel 114 of the thumb-turn 108 is blocked.

Specifically, the projection 132 on the drive dog 120 abuts the annular rib 140 preventing further movement of the drive dog 120 in the axial direction toward the thumb-turn 108.

Accordingly, in order to accommodate the key 150 when fully inserted, the plunger 121 is compressed against the plunger spring 123 causing the collar 138 to lift away from the step 136 in the bore 130. When the key 150 is subsequently turned by a user, the key cylinder 104 rotates within the first cylinder 110 of the body 102. This causes the drive dog 120 to rotate as well, since the projection 132 at the first end 127 of the drive dog is engaged with the slot 146 in the inward facing end of the key cylinder 104.

However, the cam 106 and thumb-turn 108 are not rotationally engaged with or coupled to the drive dog 120, and thus remain stationary.

As the user continues to turn the key 150, the projection 132 on the drive dog 120 will eventually become aligned with the slot 142 in the annular rib 140. The plunger spring 123 is selected such that when the plunger 121 is displaced by the insertion of the key into the key cylinder 104, the biasing force exerted by the plunger spring 123 between the plunger 121 and the grub screw 125 is greater than the biasing force exerted by the drive dog spring 122 between the grub screw 125 and the thumb-turn 108. Accordingly, with the projection 132 and slot 142 in alignment, the plunger spring 121 extends, moving the grub screw 125 away from the trailing end of the plunger 121 and, therefore, causing the drive dog 120 to move relative to the plunger 121 in the axial direction into the barrel 114 of the thumb-turn 108. Axial movement of the drive dog 120 causes the projection 132 to engage with the slot 142 in the annular rib 140 of the cam 106 and this movement continues until the collar 138 on the plunger 121 abuts the step 136 in the bore 130 once again. Thereafter, further rotation of the key 150 and key cylinder 104 causes rotation of the drive dog 120, cam 106 and thumb-turn 108 as described above with reference to Figure 13. Accordingly, the lock mechanism to which the lock cylinder 100 is attached can be locked or unlocked accordingly.

A lock cylinder having the above-described configuration has the advantage that it is not possible for the key cylinder 104 to be bypassed using a lock pick. In particular, the drive dog 120 is always coupled to the key cylinder 104 by means of the projection 132 being engaged with the slot 146. Accordingly, rotation of the drive dog 120 is not possible unless the correct key 150 for the key cylinder 104 is inserted therein. Furthermore, this is achieved by means of a simplified construction which is easy to assemble. In particular, with the lock cylinder 100 described above, the plunger 121 and plunger spring 123 can be installed inside the bore 130 of the drive dog 120 using the grub screw 125, prior to the drive dog 120 being installed within the body 102. Thus, there is only one element of the clutch means 109, i.e. the drive dog 120, which needs to be aligned with the cam 106, thumb-turn 108 and key cylinder 104 during assembly of the lock cylinder 100.

Moreover, a lock cylinder having the above-described configuration has the advantage that it provides an anti-bypass function with a clutch means which is relatively compact.

Accordingly, the clutch means can be used in applications where the overall length of the lock cylinder restricted without the need to use a shorter key cylinder with a reduced number of pin tumblers, which would adversely affect the security provided by the lock cylinder.

It will be appreciated by the person skilled in the art that the thumb-turn may be formed as a single element comprising both the barrel and a portion to be grasped by a user's hand. Alternatively, these may be formed as separate elements which are coupled together in a suitable manner. Furthermore, whilst the term thumb-turn' has been used hereinbefore to refer to a manually operable element by which rotation of the cam can be effected by a user, it will be appreciated that such an element may have any suitable shape so as to enable the user to effect rotation thereof and need not necessarily be shaped so as to be grasped between a user's thumb and forefinger.

Claims

<claim-text>Claims: 1. A lock cylinder comprising: a cam for actuating the bolt of a lock; a barrel disposed on a first side of the cam, the barrel being coupled to a thumb-turn at one end thereof and to the cam at the other end so as to enable rotation of the cam by means of the thumb-turn; a key operable cylinder disposed on a second, opposite side of the cam; and clutch means movable between a first state, in which the clutch means is rotationally coupled to the key cylinder and not coupled to the cam, and a second state, in which the clutch means is rotationally coupled to the key cylinder and is rotationally coupled to the cam by means of a projection on the clutch means being received within a slot in the cam; wherein the clutch means is biased toward the key cylinder into the first state by first biasing means and comprises a movable member which is movable relative to the clutch means and biased toward the key cylinder by second biasing means; and wherein the clutch means is arranged such that: i) in the case that the projection is aligned with the slot, the clutch means is movable into the second state directly in response to a correct key being fully into the key cylinder; and ii) in the case that the projection is not aligned with the slot, the movable member is arranged so as to move away from the key cylinder in order to accommodate a correct key fully inserted into the key cylinder and to allow rotation of the key cylinder and clutch means to effect alignment of the projection with the slot, the clutch means being movable into the second state in response to the biasing force exerted on the movable member when, in use, such alignment of the projection and the slot is effected.</claim-text> <claim-text>2. A lock cylinder according to claim 1, wherein the clutch means is rotationally coupled to the key cylinder by means of the projection on the clutch means engaging with a corresponding slot on the key cylinder.</claim-text> <claim-text>3. A lock cylinder according to claim 1 or claim 2, wherein the first biasing means is a spring.</claim-text> <claim-text>4. A lock cylinder according to claim 3, wherein the second biasing means is a spring which is stronger than the spring of the first biasing means.</claim-text> <claim-text>5. A lock cylinder according to any preceding claim, wherein the clutch means comprises a drive dog having a substantially cylindrical form, wherein the projection extends from the radial outer surface of the drive dog at a first end thereof.</claim-text> <claim-text>6. A lock cylinder according to claim 5, wherein, in the first state, the first end of the drive dog abuts the key cylinder.</claim-text> <claim-text>7. A lock cylinder according to claim 5 or claim 6, wherein the drive dog comprises an axial bore and the movable member is a plunger arranged so as to be received within the axial bore for axial movement therein.</claim-text> <claim-text>8. A lock cylinder according to claim 7, wherein the axial bore of the drive dog comprises a step and the plunger comprises a collar which cooperates with the step of the axial bore to limit the movement of the plunger toward the key cylinder.</claim-text> <claim-text>9. A lock cylinder according to claim 7 or claim 8, wherein the plunger is biased toward the key cylinder by means of a plunger spring disposed within the axial bore of the drive dog between the plunger and a second end of the drive dog.</claim-text> <claim-text>10. A lock cylinder according to claim 9, wherein the axial bore of the drive dog is a through bore and the clutch means comprises threaded fastening means arranged so as to engage with the through bore at the second of the drive dog so as to retain the plunger spring within the through bore.</claim-text> <claim-text>11. A lock cylinder according to any one of claims 5 to 10, wherein the first end of the drive dog comprises a bevel portion diametrically opposed to the projection.</claim-text> <claim-text>12. A lock cylinder according to any one of claims 5 to 11, wherein the barrel is hollow and the drive dog is at least partially received within the barrel for axial movement into and out of the barrel.</claim-text> <claim-text>13. A lock cylinder according to claim 12, wherein the drive dog is biased out of the barrel toward the key cylinder by a drive dog spring disposed within the barrel.</claim-text> <claim-text>14. A lock cylinder according to any preceding claim, wherein the thumb-turn is formed integrally with the barrel.</claim-text> <claim-text>15. A lock cylinder according to claim any preceding wherein the cam comprises a hollow cylindrical hub portion having an annular rib formed on the radial inner surface thereof, wherein the slot in the cam is formed in the angular rib.</claim-text> <claim-text>16. A lock cylinder according to claim 15, wherein the lock cylinder comprises a body having first and second cylinders for receiving the key cylinder and the barrel respectively therein.</claim-text> <claim-text>17. A lock cylinder according to claim 16, wherein respective inward facing ends of the key cylinder and the barrel are received within respective opposite ends of the hub portion of the cam.</claim-text> <claim-text>18. A thumb-turn lock cylinder substantially as hereinbefore described with reference to Figures 10 to 14B of the accompanying drawings.</claim-text>