Abstract:
A lock consists of an elongated track which is attached to the panel of a door. A slider runs in the track from a retracted position in which the slider is spaced apart from the knob which operates the deadbolt to an engaged position in which the slider is in contact with the knob and prevents it from turning. The slider can be locked in that position by means of a locking pin. The pin may also be used to immobilizes the slider in the retracted position.

Description:
This Application claims priority pursuant to 35 USC 119 of Canadian application no. 2,793,264 filed on Oct. 19, 2012 the entire contents of which are hereby incorporated into the following application by reference. 
     FIELD OF THE INVENTION 
     This invention relates to a lock for a deadbolt and more particularly to a lock which, when engaged, prevents an unauthorized entry through a door and which can only be engaged or disengaged from within the door but not from outside the door. 
     BACKGROUND OF THE INVENTION 
     Deadbolts are engaged by turning a key or knob on the inside of a door and are usually used in conjunction with a lock that engages by the action of a spring. The deadbolt is intended to give an additional measure of protection to occupants of a house or apartment or to their belongings. However, the locks of both a deadbolt and a spring activated lock are subject to being picked. A deadbolt lock, in particular, is usually located in an enclosure on the outside wall of a door or insert into the door and are accessible to be picked by a potential intruder outside the door. 
     It is known to provide a locking device which prevents the key or knob of a deadbolt from being turned. The devices are positioned on the inside wall of a door and are accessible only to persons inside the door. U.S. Pat. No. 6,301,941 to Nicholsfigueiredo for example describes a bar which slides in a track attached to an inside wall of a door. The bar is in the shape of a yoke which engages the knob of a deadbolt and immobilizes it. The bar only does so however if the track is horizontal. If the bar extends downwardly from the knob, the yoke may slide downward and out of engagement with the knob. If the track extends upwardly from the knob, the yoke may accidently slide downward into engagement with the knob thereby making it impossible to open the door except from inside. If there is no one inside, the door may have to be broken to open it since the door cannot be opened from outside. Even if the track is horizontal the knob must fit into the yoke for the locking device to function properly and if the track shifts over time, the knob may not continue to fit into the yoke. 
     I have invented a lock for a deadbolt which overcomes many of the shortcomings of the lock described above. The track in which the bar travels may be oriented at any angle on a door so long as the bar when slid forward, contacts the knob. The track can accordingly be positioned so that it avoids decorative moulding or other projections on a door. Furthermore the bar can be immobilized in the track when it is not contacting the knob to prevent the bar from accidently sliding into contact with the knob. 
     The only way that my lock can be engaged or disengaged is by a person within the premises of a house or apartment. When properly used, the subject lock cannot engage accidently without human intervention and it cannot be engaged or disengaged by someone from outside the premises. As a result, a person cannot accidently lock himself out of a house or apartment since the subject lock can only be engaged and disengaged by him when he is inside the premises. 
     SUMMARY OF THE INVENTION 
     Briefly, the lock of my invention includes an elongated track adapted to be attached to the inner panel of a door. A slider is disposed in the track and travels in a direction from an inoperative position in which the slider is spaced apart from the knob which activates a deadbolt to an operative position in which the slider is in contact with the knob mid prevents the knob from rotating. The lock includes immobilizing means for selectively immobilizing the slider in the track when the slider is in the operative and inoperative positions. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The lock of the invention is described in detail with reference to the accompanying drawings in which: 
         FIG. 1  is an elevation of the side edge of a door in conjunction with a conventional deadbolt; 
         FIGS. 2 a  and 2 b    are perspective views of the lock of my invention arranged above and below, respectively, a knob for operating a deadbolt; 
         FIG. 3  is an enlarged perspective view of a slider and track of my lock; 
         FIGS. 4 and 5  are perspective views of the slider in a withdrawn and an extended position, respectively within the track; 
         FIG. 6  is an elevation of my lock in which the knob of a deadlock is free to turn; and 
         FIG. 7  is an elevation of my lock in which the knob of a deadlock is prevented from turning 
     
    
    
     Like reference characters refer to like parts throughout the description of the drawings 
     DESCRIPTION OF PREFERRED EMBODIMENT 
     With reference to  FIG. 1 , a conventional deadbolt-lock generally  10  is illustrated. The lock is composed of a deadbolt  12  which extends and retracts from the side edge  14  of a door  16 . Knob  18  on the inner panel  16   a  of the door controls the movement of the deadbolt. A mechanism for causing the deadbolt to function is within an enclosure  24  on the outer panel  16   b  of the door and is operated by key  26 . 
     With reference to  FIGS. 2 a  and 2 b   , the lock of this invention, generally  30 , is composed of a track  32  having a web  34  and U-shaped flanges  36  on opposite sides of the web. The flanges function to confine a slider  40  within the flanges but permit the slider to slide longitudinally in the direction of arrow  42  in the track but not to slide laterally. 
     The lock is positioned on the inner panel  38  of a door which separates an interior space such as the interior of a house from an exterior space such as the outdoors. 
     The slider is in the form of a flat bar having a forward or leading edge  40   a  which is relatively straight or flat and is generally perpendicular to the direction of travel  42  of the slider in the track. The track is positioned such that the forward edge of the slider slides toward and away from the knob  44  which controls the movement of a conventional deadbolt  46 . The forward edge need not make contact along its entire length with the knob as long as what contact there is, is sufficient to prevent the knob from rotating. 
     The track may be positioned on the inner panel of the door anywhere around the knob  44 : such as above it, as illustrated in  FIG. 2 a   , beneath it as illustrated in  FIG. 2 b    or horizontally beside it. As long as the position of the track is such that the slider slides toward and away from the knob and the forward edge  44   a  of the slider, in its forward-most position, contacts the knob and immobilizes it, the track is properly positioned. 
     With reference to  FIG. 3 , the track is attached to a door by a pair of screws  50  which extend through apertures in the web of the track and into the inner panel of the door. The slider is provided with two spaced apart openings, a forward opening  52   a  closer to the forward edge  40   a  of the slider and a rear opening  52   b  closer to the rear edge of the slider. The openings are of equal diameter. An opening,  54  also of equal diameter, is formed in the web of the track. 
     When the forward edge of the slider is in contract with the knob of the deadbolt as illustrated in  FIG. 2 b   , the rear opening  52   b  in the slider lines up with opening  54  in the track. When the forward edge of the slider is spaced apart from the knob of the deadbolt, as illustrated in  FIG. 2 a   , the forward opening  52   a  in the slider lines up with the opening  54  in the track 
     Immobilizing means in the form of a locking pin  56  serves to immobilize the slider in the track when it is extends through aligned openings in the slider and the track. In  FIG. 2 b   , the locking pin immobilizes the slider when it is in contact with the knob of the deadbolt and functions to immobilize the deadlock in an extended position to prevent the door from being opened. The slider is then in an operative position. When the locking pin is removed, the slider may be slid out of contact with the knob. The knob may then be turned to retract the deadbolt into the interior of the door. The slider is then in an inoperative position. 
     Locking of the knob of the deadbolt is therefore simply a matter of advancing the slider into contact with the knob of the deadbolt and immobilizing the slider hi an operative position by means of the locking pin. Unlocking the knob from an engaged position involves removing the locking pin and withdrawing the slider from the knob until the forward opening in the slider is in alignment with opening  54  in the track. The slider is then in an inoperative or withdrawn position and is im-mobilized in the track in this position by means of the locking pin. The knob may then be turned to retract or advance the deadbolt. 
     The locking pin may be a simple cylinder or it may be a conventional ball-locking pin having a spring activated ball  56   a  at its lower end as illustrated in  FIG. 3 . A ball-locking pin is preferred because once inserted into aligned openings in the slider and track, the pin will remain in place unless a force opposed to the bias of the spring is applied to the pin by physically pulling the pin out of the openings. The pin will accordingly not accidentally fall out of the openings. 
     In  FIG. 4  the slider is in an inoperative or withdrawn position and in  FIG. 5 , the slider is in an operative or extended position. 
     As previously indicated, the only way that the subject lock can be engaged or disengaged is by a person within the premises of a house or apartment. The subject lock cannot engage without human intervention except in one situation. If the lock is above the knob of a deadbolt and the slider is not immobilized by a locking pin, the slider may slide downward into engagement with the knob. In that case, the knob can still be turned by means of a key from outside the door. That is because if there is no locking pin to prevent the slider from moving, the knob will cause the slider to move upward so that it dues nut hinder its rotation. 
     Except in the above situation, the deadbolt cannot be engaged or disengaged by someone from outside the premises. As a result, a person cannot accidently lock himself out of a house or apartment since the subject lock can only be engaged and disengaged by him when he is inside the premises. 
     With reference to  FIGS. 3, 6 and 7 , the spacing between the track and the door can be adjusted by means of one or more washers  60  surrounding screws  50  which attach the track to a door. The screws allow the position of the slider to be adjusted to contact the knob of the deadbolt whether the knob is adjacent to the door or spaced apart from it. The washers also make it possible to position the track sufficiently far apart from the door to ensure that them is sufficient clearance for the spring loaded ball  56   a  of the locking pin to function. 
     It will be understood, of course, that modifications can be made in the lock of the invention without departing from the scope of the invention defined in the appended claims.