GB2101668A

GB2101668A - Double throw lock

Info

Publication number: GB2101668A
Application number: GB08202676A
Authority: GB
Inventors: Michael George Mander
Original assignee: WJ Goodwin and Son Ltd
Current assignee: WJ Goodwin and Son Ltd
Priority date: 1981-01-29
Filing date: 1982-01-29
Publication date: 1983-01-19
Also published as: GB2101668B

Abstract

A dead bolt 12 is movable relative to a casing 10 between a first position wherein it is retracted with respect to the casing, a second position (Fig. 6) wherein it is partially extended from the casing, and a third position (Fig. 7) wherein it is fully extended from the casing. The dead bolt 12 is composed of a main bolt member 27. A rotatable cam lobe 23 of a key-operated cylinder lock 22 engages in a recess 37 in the main bolt member 26 in order to move the dead bolt 12 between its retracted and partially extended positions. Movement of the dead bolt 12 from its retracted position to its partially extended position causes the auxiliary bolt member 27 to extend from the main bolt member 26 and thereby define a further recess 42 in which the cam lobe 23 can engage to move the dead bolt between its partially extended and fully extended positions. In the event that the auxiliary bolt member 27 does not extend from the main bolt member 26, a tall piece 48 thereon engages the cam of the lock unit 22 and obstructs the latter from extending the dead bolt 12 into its fully extended position. <IMAGE>

Description

SPECIFICATION Double throw lock This invention relates to locking devices of the so-called "double throw" type wherein a dead bolt is movable between positions in which it is respectively retracted with respect to a casing, partially extended from the casing, and fully extended from the casing.

In conventional locking devices of this type, the dead bolt is generally longer than that employed in a single-throw lock, since provision must be made for the bolt to be engaged by an operating member therefore during movement between its partially extended and fully extended positions as well as between its retracted and partially extended positions. Because the bolt is comparatively iong, it has not generally been possible to incorporate such a locking device within a closure whose frame is of relatively small ,depth: for example, an extruded aluminium door frame is typically only 2" deep, whereas a conventional double throw locking device may be 3" deep.

In order to overcome this problem, a locking device has been developed wherein the dead bolt is composed of a main bolt member and an auxiliary bolt member which telescope as the bolt is moved between its retracted and partially extended positions. The main bolt member has a recess therein which is engaged by the operating member in order to move the dead bolt between these two last-mentioned positions, while extension of the auxiliary bolt member from the main bolt member causes a further recess to be defined which the operating member can engage to move the dead bolt between its partially extended and fully extended positions. Because the main auxiliary bolt members are telescoped when the dead bolt is in its retracted position, the depth of the locking device is greatly reduced compared with conventional double-throw locks.

Examples of such constructions are disclosed in German OS 2 400 570 and German OS 2 461 888.

There is a problem with this type of construction however. After a period of use, the auxiliary bolt member can tend to stick to the main bolt member so that it does not extend therefrom as the dead bolt is extended. Such sticking may, for example, result from rusting of the components. In the event that the dead bolt is moved into its fully extended position while still in this condition, there will be no further recess for the operating member to engage in order to retract the dead bolt once again. Accordingly, once fully extended it will be impossible for the dead bolt to be retracted leaving the closure in a permanently locked condition.

It is an object of the present invention to overcome this problem.

According to the present invention, a locking device for a closure comprises a casing and a dead bolt movable relative to the casing between a first position wherein it is retracted with respect to the casing, a second position wherein it is partially extended from the casing, and a third position wherein it is fully extended from the casing, the dead bolt being composed of a main bolt member having a recess therein in which an operating member can engage to move the dead bolt between its first and second positions and an auxiliary bolt member which during movement of the dead bolt from its first position to its second position extends relative to the main bolt member to define a further recess in which the operating member can engage to move the dead bolt between its second and third positions, the auxiliary bolt member having a tail piece which is disposed so as to engage a fixed abutment in the event that the auxiliary bolt member does not extend from the main bolt member as aforesaid.

In this way, it will be impossible for the dead bolt to be moved to its fully extended position without the auxiliary bolt member extending, and accordingly it will always be possible for the closure to be unlocked even under such fault conditions.

Preferably, the fixed abutment is constituted by the operating member itself, which may be in the form of a key or, where a key-operated lock unit (such as a cylinder lock) is employed, it may be constituted by a rotatable cam of the lock unit.

The locking device may also comprise a latch bolt which is movable between extended and retracted positions relative to the casing, and operating means which causes the latch bolt to be retracted when the dead bolt is in its first position and the operating member is moved in the opposite direction to that for extending the dead bolt. The operating means can include an interlock plate having a configurated slot therein and the dead bolt can have a lateral projection thereon which engages in the configurated slot.

Desirably, the interlock plate is guided for movement transversely of the direction of extension and retraction of the dead bolt, and the slot is configurated such that during movement of the dead bolt from its second position to it first position the interlock plate is moved to bring an abutment thereon into the path of the operating member.

Advantageously, the locking device further comprises means applying a biassing force-to the dead bolt in a direction transverse to the direction of its extension and retraction, in order to prevent the dead bolt from overshooting its second position. Such means may be in the form of a torsion spring having one end thereof engaged with a fixed abutment (for example part of the casing) and the other end thereof bearing against the dead bolt. Alternatively, the means applying the biassing force may be in the form of a spring accommodated within a configurated slot (such as that provided in the above-mentioned interlock plate), and the dead bolt may have a lateral projection thereon which is received in the configurated slot.In the latter case, the spring preferably has a part which co-operates with an edge portion of the slot to define a resilient constriction therebetween, and the lateral projection is received in the constriction when the dead bolt is in its second position. The spring may also have a further part which co-operates with a further edge portion of the slot to define a further resilient constriction therebetween through which the lateral projection must pass as the dead bolt is moved into and out of its third position.

In a particular example of the invention the main bolt member comprises a first part defining a tongue of the dead bolt and having therein a channel which extends in the direction of extension and retraction of the dead bolt, and a second part which is secured in face-to-face relation with the first part so as to overlie the channel, and the auxiliary bolt member is slidably received in the channel. The channel may also house a spring to bias the auxiliary bolt member into its extended position relative to the main bolt member.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic side view of a locking device according to the present invention, showing a dead bolt thereof in a retracted position; Figure 2 is a similar view to Figure 1 but showing the dead bolt in a partially extended position; Figure 3 is also a similar view to Figure 1, but showing the dead bolt in a fully extended position and with parts of the locking device removed for the sake of clarity; Figure 4 is an exploded perspective view of the dead bolt; Figures 5, 6 and 7 are diagrams illustrating the dead bolt in its retracted, partially extended and fully extended positions, respectively; Figure 8 is a perspective view of a spring which forms part of the locking device;; Figure 9 is a side view of an interlock plate which forms part of a modified example of the locking device; and Figure 10 is a detail of part of the interlock plate shown in Figure 9.

Referring first to Figures 1 to 8, the locking device shown therein comprises a casing 10 which in use is set into an extruded aluminium frame of a closure, for example, such that a facing plate 11 thereof is flush with an edge of the closure. A dead bolt 12 is slidably mounted in the casing 10 for movement relative thereto between a first position (see Figure 1) wherein it is retracted into the casing, a second position (see Figure 2) wherein it is partially extended from the casing, and a third position (see Figure 3) wherein it is fully extended from the casing. The dead bolt 1 2 is guided in such sliding movement by a guide pin 1 3 thereon whose ends are received in respective guide grooves (not shown) formed in opposite side walls of the casing 10.

In each of its first, second and third positions, the dead bolt 12 is held against extension and retraction by means of a tumbler plate 14 housed within the casing 10. The tumbler plate 14 is slidable perpendicularly to the direction of extension and retraction of the dead bolt, and is guided in such sliding movement by lugs 1 5 (shown in broken lines in Figure 3) which engage in respective elongate slots 1 6 in the casing side wall. A torsion spring 16' (see Figure 3) acts on the tumbler plate 14 to bias the latter downwardly.The tumbler plate 14 is provided with a notched recess 1 7 which is adapted to engage either one of a pair of corresponding notched projections 1 8 on the dead bolt 12 according to whether the latter is in its retracted or partially extended position, and with a slot 1 9 having lateral cut-outs 20 which receives a lug 21 (shown in chain-dotted line in Figure 3) on a side of the dead bolt. When the dead bolt is being moved between its various extended and retracted positions, the lug 21 travels along the main part of the slot 19: however, when the dead bolt reaches one of the said positions, the lug 21 becomes engaged by an appropriate one of the cut-outs 20, for example as indicated in Figure 3.

Thus, in any one of its extended and retracted positions, the dead bolt is locked by a three-fold abutment with the tumbler plate 14, one such abutment being provided between the lug 21 and the appropriate cut-out 20, the other two abutments being provided by respective pairs of engaging surfaces in the notched recess 1 7 and on the appropriate one of the notched projections 18. Such three-fold abutment greatly enhances the security provided by the locking device.

The dead bolt 1 2 is extended and retracted relative to the casing 10 by means of a keyoperated cylinder lock unit 22: in the illustrated construction, the lock unit 22 is of the so-called dual profile kind, but it may equaliy well be of oval type. The lock unit 22 includes a rotatable cam having a lobe 23 which, when a key of the lock unit is turned, engages the dead bolt in a manner to be described later and also contacts a cam surface 24 on the bottom of the tumbler plate 14 to lift the latter and thereby release the dead bolt for extension or retraction movement. Reference numberal 25 denotes a bolt by means of which the lock unit 22 is secured within the casing 10.

Referring now more particularly to Figure 4, the dead bolt is composed of a main bolt member 26 and an auxiliary bolt member 27 which can telescope relative to one another. The main bolt member 26 comprises a main body part 28 which defines a tongue 29 of the dead bolt and which has a tail portion 30 extending rearwardly from the tongue 29, the aforementioned notched projections 1 8 being provided on the tail portion 30. A channel 31 is formed in the main body part 28 and extends parallel to the direction of extension and retraction of the dead bolt, the channel 31 having a groove 32 formed in its base wall.A pair of facing plates 33 and 34 are secured in face-to-face relationship with the main body part 28 and on opposite sides thereof, one of the facing plates 34 overlying the channel 31 and having a tail portion 35 which is generally congruent with the tail portion 30 but which is laterally spaced therefrom. Aligned abutments 36 depend from the tail portions 30 and 35 respectively so as to define aligned recesses 37 in the main body part 28 and the facing plate 34.

The tail portions 30 and 35 also have aligned holes 38 therein through which the aforementioned guide pin 13 is passed.

The auxiliary bolt member 27 is slidably received in the channel 31 and is interposed between the tail portions 30 and 35. The guide pin 1 3 extends through an elongate slot 39 in the auxiliary bolt member 27 to limit the amount by which the latter can telescope relative to the main bolt member 26. A pin 40 on the auxiliary bolt member is slidably engaged in the groove 32 in the main bolt member, and a compression spring (not illustrated) is disposed between the pin 40 and the fore end of the groove 32 to bias the auxiliary bolt member into an extended position with respect to the main bolt member. An abutment 41 depends from the tail end of the auxiliary bolt member and, when the latter is extended from the main bolt member, cooperates with the abutments 36 to define a further recess 42 (see Figures 6 and 7) which is similar to the recesses 37.When the auxiliary bolt member is retracted into the main bolt member, the abutment 41 lies between the abutments 36.

Although reference has been made above to there being two aligned abutments 36 and two aligned recesses 37, for the sake of convenience in the ensuing description reference will be made to these abutments and recesses in the singular.

The manner in which the dead bolt 12 is extended and retracted will now be explained in detail with reference to Figures 5 to 7. When the dead bolt is in its retracted position (Figure 5) the tail end of the auxiliary bolt member 27 abuts against a rear wall 43 of the casing 10 and is thereby held in a retracted position with respect to the main bolt member 26. In order to move the dead bolt into its partially extended position (Figure 6), the key of the lock unit 22 is turned so as to rotate the cam lobe 23 anticlockwise as viewed in the drawings.As the cam lobe 23 moves into the recess 37 in the main bolt member 26, it engages the cam surface 24 of the tumbler plate 14 and lifts the latter, inter alia to disengage the notched recess 1 7 from the foremost notched projection 1 8 on the dead bolt 1 2 and thereby free the dead bolt for extension movement. Upon further rotation, the cam lobe 23 contacts a forvvard edge 44 of the recess 37 and moves the main bolt member 26 to the left as viewed in the drawings. At this time, the spring bias acting on the auxiliary bolt member 27 causes the latter to remain with its tail end in contact with the casing rear wall 43, and thus the auxiliary bolt member extends from the main bolt member to define the aforementioned recess 42.

When the dead bolt 1 2 has reached its partially extended position, the cam lobe 23 disengages from the edge 44 and also lowers the tumbler plate 1 4 to lock the dead bolt in position.

In order to extend the dead bolt 12 to its fully extended position (Figure 7), the key is turned once more to rotate the cam lobe 1 3 through a - further revolution in an anticlockwise direction. As before, the cam lobe first lifts the tumbler plate 14 to free the dead bolt for extension movement.

The cam lobe then contacts a forward edge 45 of the recess 42 (defined by a trailing edge of the abutment 36) and moves the main bolt member 26 to the left. At this point, the guide pin 13 engages a forward end of the slot 39 in the auxiliary bolt member 27 and causes the latter to be carried forward with the main bolt member.

When the dead bolt reaches its fully extended position, the cam lobe 23 disengages from the edge 45 and lowers the tumbler plate 14 to lock the dead bolt in position.

To retract the dead bolt 12 from its fully extended to its partially extended position, the key is turned to rotate the cam lobe 23 in a clockwise direction. After lifting the tumbler plate 14 to free the dead bolt, the cam lobe engages a trailing edge 46 of recess 42 (formed by a forward edge of the abutment 41) and moves the auxiliary bolt member 27 to the right, the main bolt member 26 of course being carried with the auxiliary bolt member at this time due to the abutment between the guide pin 13 and the forward end of the slot 39. To retract the dead bolt further into its retracted position, the key is turned to rotate the cam lobe 23 through a further clockwise revolution. During this action, the cam lobe engages a trailing edge 47 of the recess 37 (formed by a forward edge of the abutment 36) and moves the main bolt member 26 to the right.

At this time, the rear casing wall 43 abuts against the tail end of the auxiliary bolt member 27 and thereby prevents the latter from moving, so that the auxiliary bolt member retracts into the main bolt member against the action of its bias.

By arranging for the auxiliary and main bolt members to telescope relative to one another as the dead bolt is moved between its retracted and partially extended positions, the effective length of the dead bolt when retracted is reduced, enabling the depth of the locking device to be reduced also.

This in turn enables the locking device to be installed in closures whose frames are comparatively shallow, such as extruded aluminium doorframes as mentioned previously.

After a period of use, the components of the locking device may start to corrode, particularly where the locking device is provided on an external door where it is exposed to the outside elements. Such corrosion in certain cases can cause the auxiliary bolt member 27 to stick to the main bolt member 26 as the dead bolt is moved from its retracted to its partially extended position. To prevent any malfunction of the locking device due to this effect, the auxiliary bolt member 27 is provided with a tail piece 48 which extends downwardly and rearwardly from the lower end of the abutment 41.In the event of the auxiliary bolt member sticking as aforesaid, the tail piece 48 comes into contact with the cam of the lock unit 22 as the dead bolt reaches its partially extended position and thereby obstructs the cam lobe 23 from rotating into contact with the edge 45 and moving the dead bolt into its fully extended position. The cam lobe can, however, still be rotated in the opposite direction into engagement with the edge 47 to return the dead bolt to its retracted position. Thus, even if the auxiliary bolt member does not extend from the main bolt member in the proper manner, the dead bolt can still be moved between its retracted and partially extended positions so that the locking device remains operative.Moreover, in the event of an attempt being made to move the dead bolt into its fully extended position when the auxiliary bolt member has not extended from the main bolt member, the action of the cam lobe 23 colliding with the tail piece 48 may suffice to release the auxiliary bolt member.

Referring back to Figures 1, 2 and 3, the locking device also comprises a latch bolt 49 which can be extended and retracted relative to the casing by means of an operating cam 50 connected to a manually operable handle (not shown). A spring 51 acts between a head 52 of the latch bolt 49 and a fixed abutment 53 on the casing 10 and serves to urge the latch bolt into its extended position, as shown, while a further spring 54 acts on the operating cam 50 to bias it into the illustrated position. The latch bolt 49 is preferably of the type disclosed in our co-pending UK Patent Application No. (our reference 1 02786J) of even date.

When the dead bolt 12 is moved to its retracted position to unlock the closure, before the closure can be opened the latch bolt 49 must be retracted also. It may be inconvenient for an operator of the lock to first withdraw the dead bolt 1 2 using a key and then retract the latch bolt 49 by means of the aforementioned handle, or to perform these two operations simultaneously using both hands. Accordingly, the locking device is provided with a mechanism which enables the latch bolt 49 to be retracted using the key which operates the dead bolt 12, so that both bolts may be retracted in a single operation and using only one hand.

More specifically, the mechanism includes an interlock plate 55 which is movable perpendicularly to the direction of extension and retraction of the dead bolt 12, the plate being guided in such movement inter alia by a projection 56 thereon which slides along an elongate slot (not shown) in the casing side wall.

The interlock plate 55 is provided with a configurated slot 57 in which the guide pin 13 on the dead bolt is received. The slot 57 includes a first portion 58 which extends parallel to the direction of extension and retraction of the dead bolt, a second portion 59 which is inclined to the portion 58, and a third portion 60 which is perpendicular to the direction of movement of the dead bolt 12 (i.e. parallel to the direction of movement of the interlock plate ). The guide pin 13 travels along the slot portion 58 when the dead bolt is moved between its partially extended and fully extended positions, and slides along the slot portion 59 when the dead bolt is moved between its partially extended and retracted positions.The interlock plate 55 is also provided with a downwardly extending arm 61 having an abutment 62 at its free end, and with an upwardly extending notched arm 63 which is engageable with a pin 64 on a cam plate 65, the cam plate being rotatable with the operating cam 50 and having an arm 66 which engages the latch bolt 49.

When the dead bolt 1 2 is in its fully extended or its partially extended position, the engagement between the guide pin 13 and the slot portion 58 holds the interlock plate 55 in a lowered position, shown in Figure 2, wherein the abutment 62 on the arm 61 is disposed out of the path of the cam lobe 23 and the notched arm 63 is disengaged from the pin 64. However, upon movement of the dead bolt to its retracted position, the engagement between the guide pin 1 3 and the inclined slot portion 59 serves to lift the interlock plate 55 into the position shown in Figure 1. In this position, the abutment 62 is disposed in the path of clockwise rotation of the cam lobe 23 and the notched arm 63 is engaged with the pin 64 on the cam plate 65.If the key operating the lock unit 22 is now turned so as to rotate the cam lobe 23 clockwise, the cam lobe will engage the abutment 62 from beneath and lift the interlock plate 55, thereby rotating the cam plate 65 and retracting the latch bolt 49. Such movement of the interlock plate 55 is permitted by engagement of the guide pin 1 3 with the slot portion 60, which also allows the interlock plate to be moved vertically when the latch bolt 49 is retracted by means of the aforementioned handle.

During operation of the dead bolt, there is a danger that the latter may overshoot its partially extended position when being extended or retracted. In order to overcome this problem, a torsion spring 66 (shown in detail in Figure 8) is provided which has one of its ends engaged with the casing 10, the other end thereof being flattened at 67 and bearing downwardly on an upper surface 68 of the dead bolt tongue 29. The spring 66 thus imparts a biassing force to the dead bolt which is transverse to the latter's direction of movement, and thereby imposes a small frictional resistance to movement of the dead bolt to prevent the latter from overshooting its partially extended position.As can be seen to advantage in Figure 7, when the dead bolt is fully extended the spring 66 is disengaged therefrom, and only comes into contact with the surface 68 when the dead bolt is moved towards its partially extended position.

As an alternative to employing the torsion spring 66, the interlock plate 55 may be modified in the manner illustrated in Figures 9 and 10 so that a spring 69 is accommodated within the configurated slot 57, whose portions 58 and 59 are now enlarged. The spring 69 is of generally Ushaped configuration and has an end of one of its limbs anchored in a part-circular recess 70 by means of a round slug of metal 71. The other limb of the spring 69 has a mid-portion 72 which is juxtaposed with a rounded projection 73 formed at the juncture of the slot portions 58 and 59, and a bent end portion 74 which is juxtaposed to an end of the slot portion 58. The portion 72 of the spring 69 co-operates with the projection 73 to define a resilient constriction 75 therebetween, while a similar resilient constriction 76 is defined between the spring 74 and an edge of the slot portion 58.

As the dead bolt 12 is moved into its partially extended position, either from its fully extended position or its retracted position, the guide pin 13 thereon initially comes into contact with an end of the projection 73, as indicated in broken lines at 1 3a or 1 3b in Figure 10. As the dead bolt moves into its actual partially extended position, the guide pin 13 lifts the interlock plate 55 slightly as it rides under the projection 73, and at the same time deflects the portion 72 of the spring 69 downwardly so that it can pass into the resilient constriction 75, as indicated in chain-dotted lines at 1 3c in Figure 10. The spring 69 thus applies a lateral biassing force to the guide pin 13 which is sufficient to prevent the dead bolt from overshooting its partially extended position.It will be manifest that when the guide pin has reached the position 1 3c the tumbler plate 14 will already have been lowered to lock the dead bolt in its partially extended position. Consequently the force of the spring 69 acting on the guide pin will not cause the latter to ride out of the constriction 75.

In order for the dead bolt 12 to be moved into its fully extended position, the guide pin 13 must pass through the other resilient constriction 76.

When the dead bolt is in this position, the guide pin is engaged by the end portion 74 of the spring 69 and is urged thereby into contact with the end of the slot portion 58. Such holding of the guide pin in position at the end of the slot portion 58 serves to compensate for any backlash which may be present between the dead bolt 12 and the rotatable cam of the lock unit 22, so that the dead bolt is automatically held in a proper position whereby the cam lobe 23 can engage in the recess 37 without its movement being obstructed by the edges of the recess.

Claims

1. A locking device for a closure, comprising a casing and a dead bolt movable relative to the casing between a first position wherein it is retracted with respect to the casing, a second position wherein it is partially extended from the casing, and a third position wherein it is fully extended from the casing, the dead bolt being composed of a main bolt member having a recess therein in which an operating member can engage to move the dead bolt between its first and second positions and an auxiliary bolt member which during movement of the dead bolt from its first position to its second position extends relative to the main bolt member to define a further recess in which the operating member can engage to move the dead bolt between its second and third positions, the auxiliary bolt member having a tail piece which is disposed so as to engage a fixed abutment in the event that the auxiliary bolt member does not extend from the main bolt member as aforesaid.

2. A locking device as claimed in Claim 1, wherein the fixed abutment is constituted by the operating member.

3. A locking device as claimed in Claim 1 or 2, wherein the operating member is in the form of a rotatable cam of a key-operated lock unit.

4. A locking device as claimed in Claim 1,2 or 3, further comprising a latch bolt which is movable between extended and retracted positions relative to the casing and operating means which causes the latch bolt to be retracted when the dead bolt is in its first position and the operating member is moved in the opposite direction to that for extending the dead bolt.

5. A locking device as claimed in Claim 4, wherein the operating means includes an interlock plate having a configurated slot therein, and the dead bolt has a lateral projection thereon which engages in the configurated slot.

6. A locking device as claimed in Claim 5, wherein the interlock plate is guided for movement transversely of the direction of extension and retraction of the dead bolt, and the slot is configurated such that during movement of the dead bolt from its second position to its first position the interlock plate is moved to bring an abutment thereon into the path of the operating member.

7. A locking device as claimed in any preceding Claim, further comprising means applying a biassing force to the dead bolt in a direction transverse to the direction of its extension and retraction.

8. A locking device as claimed in Claim 7, wherein said means applying a biassing force is in the form of a torsion spring having one end thereof engaged with a fixed abutment and the other end thereof bearing against the dead bolt.

9. A locking device as claimed in Claim 7, wherein said means applying a biassing force is in the form of a spring accommodated within a configurated slot, and the dead bolt has a lateral projection thereon which is received in the configurated slot.

10. A locking device as claimed in Claim 7 when appended to Claim 5-or 6, wherein said means applying a biassing force is in the form of a spring accommodated within the configurated slot in the interlock plate.

11. A locking device as claimed in Claim 9 or 10, wherein the spring has a part which cooperates with an edge portion of the slot to define a resilient constriction when the dead bolt is in its second position.

12. A locking device as claimed in Claim 11, wherein the spring has a further part which cooperates with a further edge portion of the slot to define a further resilient constriction therebetween through which the lateral projection must pass as the dead bolt is moved into and out of its third position.

13. A locking device as claimed in any preceding Claim, wherein the main bolt member comprises a first part defining a tongue of the dead bolt and having therein a channel which extends in the direction of extension and retraction of the dead bolt, and a second part which is secured in face-to-face relation with the first part so as to overlie the channel, and the auxiliary bolt member is slidably received in the channel.

14. A locking device as claimed in Claim 13, wherein a spring is housed in the channel to bias the auxiliary bolt member into its extended position relative to the main bolt member.

1 5. A locking device for a closure, substantially as hereinbefore described with reference to Figures 1 to 8, or Figures 1 to 8 as modified by Figures 9 and 10 of the accompanying drawings.