GB2308862A - Plate tumbler locks - Google Patents

Abstract

A lock has tumbler plates 15 which are raised by the bits of key 12 against spring bias to enable the free passage of a bolt projection 23 through aligned slots 22 in the plates. To frustrate unauthorised attempts to determine the correct lift of the plates 15, at least one of the plates 15a has a formation 25 which, when such an attempt is made on that plate, engages a formation 28 on the bolt projection 23 to lock the plate to the projection. Preferably, as shown, the projection 23 is slidably mounted on the bolt for limited vertical movement.

Description

"Safety lock" The present invention relates to safety locks for doors of dwellings, gates and the like, of the doublebit type, comprising a casing, which is to be fixed to the door, a bolt movable within the casing between an opened position, in which it is retracted within the casing and a closed position projecting outside of the casing, in which said bolt is to be received within a seat in the door frame, a lock mechanism for actuating the bolt, including a plurality of safety plates superimposed upon each other and having mating windows with a toothed profile, said plates being movable against the action of spring means as a result of the engagement of a double-bit key having a predetermined profile, so that said windows define a free passage for a safety stud supported by the bolt.

In recent times apparatus have become available which enable a housebreaker to reconstruct the profile of the key which opens the lock. These apparatus are used by introducing a test instrument inside the lock and bringing this instrument in contact with the various safety plates of the lock in sequence in order to detect the position which each plate must assume in order to leave the passage for the safety stud which is supported by the bolt free.

The object of the present invention is that of providing a safety lock of the type indicated at the beginning, by which an operation such as that mentioned above, for detecting the profile of the key which opens the lock, is rendered difficult or even impossible.

In order to achieve this object, the invention provides a lock of the type indicated at the beginning, characterized in that said safety stud and a tooth of the window of at least one of said safety plates have parts with mating profiles adapted to become engaged with each other.

Due to said feature, if, in the closed condition of the lock, a housebreaker tries to move this safety plate to the position in which the safety stud is unlocked, said parts with mating profiles of the safety stud and the tooth of said safety plate engage with each other, so that the safety plate becomes rigidly connected to the bolt and prevents the operation of the lock.

In a preferred embodiment, said safety stud is slidably supported by the bolt in a direction parallel to the direction of movement of the safety plates and is biassed by spring means towards an end position. Due to this further feature, if, after that the safety stud has been locked on said plate as a result of the engagement of said parts with mating profiles, the housebreaker tries to disengage the plate from the stud, this operation is rendered impossible, since the plate is followed by the stud in all its movements.

Yet according to a further preferred feature, said bolt is further provided with an auxiliary engagement element biassed by spring means towards a position projecting from the bolt, in which this engagement element is able to snap engage a cooperating hole of said safety plate when the latter is brought to a position in which said parts with mating profiles become engaged with each other. Thus, the anchoring of the safety plate to the bolt, which takes place as a result of a try to detect the profile of the key which opens the lock, by means of a test instrument, is rendered further stable and not disengageable.

Preferably, said parts with mating profiles of the safety stud of the bolt and said safety plate are a slot formed along one side of the safety stud and a projection on one side of a tooth of the safety plate which is adapted to become engaged within said slot.

Due to said features, the possibility to detect the profile of the key which opens the lock by introducing a test instrument inside the lock is prevented with relatively simple and inexpensive means.

Further features and advantages of the invention will become apparent from the description which follows with reference to the annexed drawings, given purely by way of non limiting example, in which: figure 1 is a perspective exploded view of a lock according to the invention, figure 2 is a perspective view of the bolt forming part of the lock of figure 1, figures 3-6 are cross-sectional views at an enlarged scale taken along lines III-III, IV-IV, V-V and VI-VI of figure 2, and figure 7 is a view at an enlarged scale of a detail of the lock of figure 1.

In the drawings, reference numeral 1 generally designates a safety lock comprising a casing 2 of sheet metal having a bottom wall 2a, an upper wall 2b, a lower wall 2c, a first side wall 2d and a second side wall 2e. These walls define a cavity which is covered by a covering plate 3 fixed by screws 4 to a plurality of internally threaded bushes 5 welded to the bottom wall 2a and projecting inside the cavity of casing 2.

According to the conventional art, inside the casing 2 there is slidably mounted a bolt 6 comprising a steel plate 7 with a side 7a bent at 90" to which there are welded four cylindrical steel fingers 8 which are slidably mounted within circular holes 9 formed in the side wall 2d of casing 2. The sliding of bolt 6 within casing 2 is further driven by the engagement of a bush 5 within a slot 7b of plate 7. In this manner, plate 7 is slidably guided within casing 2 (which is fixed to the door) between a closed position of the lock (shown in figure 1) in which the fingers 8 project outside of wall 2d so as to be received within cooperating seats formed in the fixed frame of the door (not shown), and an opened position of the lock, in which the fingers 8 are retracted inside the casing 2.

Also according to the conventional art, plate 7 has a window 7c on one edge of which a rack 10 is formed.

Rack 10 is to be engaged by the active part 11 of a key 12 which is inserted inside casing 2 through a keyhole 13 formed in the covering plate 3. The key 12 is of the so called double-bit type, with the active part 11 having two flag-like portions 14 having toothed edges 14a on opposite sides, with a predetermined profile. The rotation of key 12 inside casing 2 causes subsequent engagement of the two flag-like portions 14 on the teeth of rack 10, so as to cause the bolt 6 to move between the closed position and the opened position of the lock.

Yet according to the conventional art, in order to enable only a key 12 having a predetermined profile 14a to open the door, inside casing 2 there are mounted a plurality of safety plates 15A and 15 which are superimposed upon each other. Plates 15A, 15 are slidably mounted inside casing 2 in a direction parallel to the bottom wall 2a and orthogonal to the direction of movement of bolt 6. Plates 15A, 15 are guided in this movement by the engagement of bushes 5 within longitudinal slots 16 formed in the safety plates 15A, 15. Each safety plate is further provided with a pin spring 18 projecting from the upper edge thereof and having a free end 18a abutting against a fixed surface 19 inside casing 2 so as to bias each safety plate to a lowered end position.Yet according to the conventional art, the safety plates 15A, 15 have mating apertures 20 which allow for the passage of the active part 11 of key 12 and each have an upper edge 20a which is to be engaged by a respective portion of the profile of the flag-like portions 14 of the key.

Furthermore, yet according to the conventional art, the safety plates 15A, 15 have mating windows 21 having a substantially elongated rectangular shape, with their major edges having a toothed profile, including a plurality of teeth 22.

Yet according to the conventional art, a safety stud 23 of prismatic shape supported by the plate 7 of bolt 6 engages through windows 21 of the safety plates 15A, 15.

Figure 1 of the annexed drawings also shows the conventional latch 24 which is slidably mounted in a cooperating circular hole 25 of wall 2d and a bush 26 with an inner square hole for engagement of a shaft associated to a handle or knob controlling the latch 24. However, the mechanism connecting these members is not described herein, since it can be made in any known way and it does not fall, taken alone, within the scope of the present invention. For the same reason, figure 1 does not show two further plates which are to be slidably mounted within two slots 27, 28 formed in the walls 2b, 2c of the casing. These plates are to be connected, according to the conventional art, to two locking bars adapted to engage cooperating seats formed above and below the door to provide a further degree in the safety of the locked condition of the door.These plates are also to be connected by a mechanical transmission to the bolt 6 so as to be driven by the movement of the bolt itself. As already indicated, these details are not illustrated in the drawings since they are known per se and since their deletion from the drawings renders the latter easier to be understood.

According to the invention, the safety stud 23 has an axial slot 28. Furthermore, at least one of the safety plates 15, in the illustrated example the safety plate indicated by 15A which is in the closest position relative to plate 7, has its window 21 with the upper edge having an end tooth 24 (see also figure 7) whose side has a tooth 25 with a profile mating that of the cross section of slot 28 of the safety stud 23.

The lock according to the invention operates in the conventional way when it is actuated by its key 12.

When the key is inserted inside the casing 2 and rotated around its axis, the toothed profiles 14a engage in sequence the edges 29a of the apertures 20 of the safety plates 15 so as to cause an upward movement of plates 15, against the action of springs 18. If the profile 14a is the predetermined one for which the lock is constructed, the safety plates are thus moved to determined positions in which the mating windows 21 of the safety plates define a free aisle for passage of safety stud 23. Therefore, the bolt 6 is free to move, as a result of the engagement of the active part of the key on rack 10, between its closed and opened positions. As already discussed, this manner of operation is the conventional one which is typical of safety locks of the so-called double-bit type.

In recent times, the housebreakers have made use of devices able to reconstruct the profile 14a of the key which opens the lock by inserting inside casing 2 a test instrument which is brought in contact with the edges of windows 21 of safety plates 15. In this manner, the housebreaker causes a movement of each safety plate to detect for each plate the position in which this plate leaves the passage for safety stud 23 free. By a suitable device, the housebreaker can then reconstruct the profile of the key which opens the lock and can then manufacture the key.

In the case of the lock according to the invention, if, in the closed condition of the lock which is shown in figure 1, the housebreaker acts on safety plate 15A moving vertically upwardly this plate against the action of the spring 18 which is associated therewith in order to locate the position in which this plate leaves the passage for safety stud 23 free, tooth 25 fits within slot 28 of safety stud 23, so that any further movement of safety plate 15A relative to safety stud 23 becomes impossible. Therefore, the housebreaker cannot perform the above described operations which are necessary to reconstruct the profile of the key which opens the lock. The safety stud 23 can be rigidly connected to plate 7, according to the conventional art.However, the preferred embodiment which is shown in the drawings has stud 23 slidably supported by plate 7 in a direction parallel to the direction of movement of safety plates 15.

More in detail, with reference to figures 2-4, the safety stud 23 is slidably mounted within a slot 30 of plate 7 and is rigidly connected to a supporting plate 31 which is slidably mounted between plate 7 and a counter-plate 32 fixed to plate 7. A helical spring 33 is arranged in the gap defined between plate 7 and counter-plate 32 and biasses the safety stud 23 towards a lowered end position.

Due to this arrangement, once the safety stud 23 has been locked on tooth 24 of safety plate 15A, as a result of the unauthorized operation which has been described above, the stud follows safety plate 15A in all its movements, so that the housebreaker is not able in any way to disengage the safety stud 23 from safety plate 15A by moving the latter. In the case of this preferred embodiment, once the tooth 24 of safety plate 15A has been locked on safety stud 23, the lock becomes inoperative. Therefore, the lawful user will realize that the unauthorized operation has been performed and will have to call for the assistance of a skilful technician to re-establish normal operation of the lock, this disturbance being obviously absolutely acceptable compared with the risk that a housebreaker may reconstruct a key which opens the lock.

Naturally, while the embodiment of the invention which has been shown has a slot 28 on safety stud 23 and a tooth 25 on safety plate 15A, any other different configuration of the parts which are to become mutually engaged, including the provision of a cavity in tooth 24 and a projection on safety stud 23, is possible.

Similarly, this measure may be provided on any one of the safety plates.

Yet a further feature of the preferred embodiment provides that plate 7 of bolt 6 has a further engagement element 34 in form of a cylindrical pin (see also figures 2 and 5, 6) slidably mounted within a circular hole 35 of plate 7. Pin 34 has an enlarged head 36 which is biassed by a spring leaf 37 having one end fixed to plate 7 by a rivet 38, towards a position of abutment against plate 7, in which pin 34 projects from this plate so as to be engaged within a hole 39 of safety plate 15A when the latter reaches the position of mutual engagement of safety stud 23 and tooth 24. In this manner, if the lock is brought in said condition as a result of the above described unauthorized operation, the bolt 6 becomes further locked to safety plate 15A.

As it is clearly apparent from the foregoing description, the lock according to the invention is able to prevent any try of detecting the profile of the key which opens the lock.

Naturally, while the principle of the invention remains the same, the details of construction and the embodiments may widely vary with respect to what has been described and illustrated purely by way of example, without departing from the scope of the present invention.

Claims (5)

1. Safety lock for doors of dwellings, gates and the like, comprising a casing (2), which is to be fixed to the door, a bolt (6) movable within the casing (2) between an opened position in which it is retracted within the casing (2) and a closed position projecting outside of the casing (2), in which it is to be received within a seat in the door frame, a lock mechanism for actuating the bolt (6), including a plurality of safety plates (15, 15A), superimposed upon each other, and having mating windows (21), with toothed profile, and movable against the action of spring means (18), as a result of the engagement of a double-bit key (12) having a predetermined profile, to a position in which said windows (21) define a free passage for a safety stud (23) supported by the bolt (6), characterized in that said safety stud (23) and a tooth (24) of the window (21) of at least one of said safety plates (15A) have parts (28, 25) with mating profiles adapted to become engaged with each other.

2. Lock according to claim 1, characterized in that the safety stud (23) is slidably supported by the bolt (6) in a direction parallel to the direction of movement of the safety plates (15, 15A) and is biassed by spring means (33) towards an end position.

3. Lock according to claim 1, characterized in that the bolt (6) is further provided with an auxiliary engagement element (34) biassed by spring means (37) towards a position projecting from the bolt (6), in which it is able to snap engage a cooperating hole (39) of said safety plate (15A) when said safety plate (15A) reaches its position in which said parts with mating profiles are engaged with each other.

4. Lock according to claim 1, characterized in that said parts with mating profiles include a longitudinal slot (28) formed on one side of said safety stud (23) and a projection (25) on one side of said tooth (24) of the window (21) of said safety plate (15A).

5. Lock according to claim 1, characterized in that said safety stud (23) is rigidly connected to the bolt (6).