Abstract:
In a cylinder lock, one or more tumblers of the rotatable cylinder are subjected to a magnetically operative biassing member.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to cylinder locks, of the type comprising: 
     a fixed lock body or stator, having a cylindrical cavity, 
     a cylinder or rotor, rotatably mounted within the cylindrical cavity of the fixed body and having an axial passage for receiving a key, 
     a plurality of locking tumblers slidably mounted within radial holes of the rotatable cylinder, opening on said axial passage, said tumblers being adapted to be engaged at one end thereof by a key having a predetermined profile in order to arrange themselves in a position in which they enable a free rotation of the rotatable cylinder within the fixed body, 
     a plurality of counter-tumblers, slidably mounted within holes which are formed in the fixed body of the lock and open on the cylindrical cavity of said fixed body, said holes for the counter-tumblers being adapted to become aligned with the holes for the tumblers in the rotatable cylinder at a given angular position of the latter, and 
     means for biassing the tumblers radially towards the axis of the rotatable cylinder when the latter is at said given angular position. 
     In the conventional locks of the above indicated type, the above mentioned biassing means are constituted by coil springs arranged within the holes of the fixed body wherein the counter-tumblers are movable, so as to push the counter-tumblers against the respective tumblers, towards the axis of the rotatable cylinder. These locks enable a burgler to determine the profile of the key which can open the lock, by inserting a tool within the key hole and pushing the tips of the lock tumblers by this tool, against the action of the above mentioned coil springs. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is that of proposing a new type of lock which has a higher degree of safety with respect to the conventional locks of the above indicated type. 
     In view of achieving this object, the invention provides a lock having all the above mentioned features and further characterized in that in the case of at least one of said tumblers the means for biassing this tumbler radially towards the axis of the rotatable cylinder are magnetically operative biassing means, which comprise a first permanent magnet arranged within the hole in the fixed body where the respective counter-tumbler is movable and a second permanent magnet associated with said key and adapted to draw the first permanent magnet towards the axis of the rotatable cylinder when the key is received within the rotatable cylinder, so that the first permanent magnet biasses the respective tumbler against the key. 
     Naturally, it is possible to provide one or more tumblers of the lock and, if desired, even all the tumblers of the lock, with magnetically operative biassing means. 
     According to a first solution, the above mentioned first permanent magnet is arranged within the respective hole of the fixed body between the respective counter-tumbler and an end wall of the hole. Alternatively, the first permanent magnet may be arranged within the respective hole of the fixed body between the respective counter-tumbler and the respective tumbler. 
     In order to improve the magnetic efficiency, preferably the tumbler and/or the respective counter-tumbler are made of ferromagnetic material. 
     The second permanent magnet is fixed within a seat formed in the key on a surface opposite to that which is for cooperating with the tumblers of the rotatable cylinder. 
     In case at least one of the tumblers of the rotatable cylinder has biassing means of the conventional type constituted by a coil spring arranged within the hole of the respective counter-tumbler, according to the invention the counter-tumblers associated with magnetically operative biassing means have a greater length than the counter-tumbler associated with coil spring biassing means. In this manner, a lock of conventional type can be transformed into a lock according to the invention with no modification to the geometry of the fixed body. 
     In case said key has a flattened active portion and accordingly the above mentioned axial passage for the key has a similar shape, having a general plane perpendicular to a plane containing the axes of the radial holes of the rotatable cylinder, the above mentioned active portion of the key has a first face having cavities adapted to cooperate with the tips of the lock tumblers and an opposite face in which the seat for each second permanent magnet is formed. 
     Due to the above mentioned features, when the key is not introduced into the lock, the first permanent magnet is not biassed towards the axis of the rotatable cylinder. Therefore it is impossible for a non-authorized person to introduce a tool into the key axial passage and press this tool against the tip of the above mentioned tumbler in order to determine the profile of the key which can open the lock. Thus, the lock according to the invention has a higher degree of safety with respect to the known locks. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is a perspective diagrammatic view of the lock according to the invention, with the associated key, 
     FIG. 2 is a cross-sectional view taken along line II—II of FIG. 1, 
     FIG. 3 shows the cross-section of FIG. 2 in a different operative condition, and 
     FIG. 4 shows a variant of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, reference numeral  1  designates a cylinder lock associated with a door frame  2  and adapted to cooperate with a key  3 . 
     As shown in FIG. 2, the lock  1  is a cylinder lock, comprising a lock fixed body  4  having a cylindrical cavity  5  where a cylinder  6  is rotatably mounted. 
     In the case of the illustrated example, the fixed body  4  of the lock is of the type including two body sections (only one of which is visible in the drawings) arranged symmetrically with respect to a plane  7 . The body section which is not shown in the drawings is identical and symmetrical to that shown. However, it is clearly apparent that the invention can be applied to any configuration of the fixed body. Also, in the case of the illustrated example, the two body sections are connected to each other by a bridge-like portion  8  in which a threaded hole  9  is formed for engagement of a screw (not shown) for securing the body  4  to the lock supporting structure  2 . The details of construction are not shown herein since they can be made in any known way and since they do not fall within the scope of the present invention. The same applies to the rotatable pawl mounted onto cylinder  6 , which occupies the gap  10  between the two body sections defined by the bridge-like portion  8 . 
     According to the conventional art, the rotatable cylinder  6  is provided with a plurality of locking tumblers  11  which are slidably mounted within radial holes  12  formed in the cylinder  6  and opening on an axial passage  13  formed in the rotatable cylinder  6  and adapted to receive the active portion  14  of the key. As shown in FIG. 1, in the case of the example described herein, the active portion  14  of the key  3  has a substantially flattened shape with a rectangular cross-section, and the passage  13  has a similar shape, with a general plane perpendicular to the plane containing the axes of the tumblers  11 . 
     Reference numeral  15  designates a plurality of counter-tumblers which are slidably mounted, according to the conventional art, within holes  16  which are formed in the fixed body and open on the cylindrical cavity  5  of the lock. The holes  16  are adapted to become aligned with the radial holes  12  of the rotatable cylinder  6  at a given angular position of the latter. 
     The tips of the tumblers  11  facing towards passage  13  which is for receiving the key are for cooperation with cavities  17  formed on a first face  14   a  of the active portion  14  of the key  3 , so that when this active portion  14  is fully received within passage  13 , the tumblers  11  are each brought to an axial position which does not prevent the free rotation of the rotatable cylinder  6  within cavity  5  of the fixed body  4 . 
     Also in the case of the illustrated example, all the tumblers  11  of the lock, except for one of them, are radially biassed towards the axis of the rotatable cylinder  6  by coil springs  18  which are interposed within the respective holes  16  between the respective counter-tumblers  15  and a closing element  19  which defines an end wall of the hole. However, according to the invention, one of the tumblers  11  is not subjected to the action of a coil spring. In this case, between the respective counter-tumbler  15  (which has a greater length than the other counter-tumblers  15 ) and the closure element  19  there is interposed a permanent magnet  20 , in form of a circular disk, and a second magnet  21  is fixed within a seat  22  formed on the face  14   b  of the active portion  14  of key  3 , opposite to face  14   a  having cavities  17 , so that when the key  3  is received within passage  13 , magnet  21  draws magnet  20 , so that the counter-tumbler  15  and the tumbler  11  associated with magnet  20  are biassed against the key. In order to improve the magnetic efficiency, the tumbler  11  and the counter-tumbler  15  which are associated with magnet  20  are preferably constituted of ferro-magnetic material. 
     FIG. 3 of the annexed drawings shows the condition of the lock when the key is introduced, with magnet  20  which, being drawn by magnet  21 , keeps tumbler  11  associated therewith against the key. When the key is withdrawn, the tumbler  11  associated with magnet  20  is no longer biassed towards passage  13 , so that it is free to fall within the respective hole  16 . Therefore, if a burgler introduces a tool into passage  13 , he is not able to press this tool against the above mentioned tumbler, since the latter is not biassed by any spring. For this reason, therefore, the lock according to the invention has a higher safety degree than the known locks. 
     FIG. 4 shows a variant in which magnet  20  is interposed between the respective tumbler  11  and the respective counter-tumbler  15 . 
     Naturally, it is possible to replace the biassing spring  18  with the magnet  20  and to provide a cooperating magnet  21  on the key for more than one tumbler of the lock and, if desired, for all lock tumblers. 
     Furthermore, 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. 
     For example, rather than providing a magnet  21  on the key, this magnet could be provided within hole  16  adjacent to magnet  20 , with polarities such as to obtain a repulsion force between the two magnets  20 ,  21  which would give rise to a force applied to tumbler  11 . This solution could be applied both in the case of FIG. 3, and in the case of FIG.  4 .