Abstract:
A storage unit door locking system is shown for securing and locking a storage unit door and preventing forced entry wherein the door is attached to a doorjamb. The locking system has a door plate which is mounted to the door with an extension plate that extends beyond the edge of the door and abuts the front face of the doorjamb when the door is closed. A sliding bolt slidably mounted to, but spaced apart from, the door plate slides behind the doorjamb trapping the doorjambs between the extension plate and the sliding bolt. A recessed lock is inserted through matching aligned holes in the extension plate, doorjamb, and sliding bolt and locked. This physically locks the doorjamb to the extension plate and sliding bolt which prevents forced entry with the use of crowbars or other prying devices normally used to separate the doorjamb from the door and locks contained thereon.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a locking system and more particularly to a locking system for storage unit doors. 
     2. Background Information 
     The use of walk-in storage units for storing household, office, and other items has increased dramatically in recent years. Unfortunately, there has also been a dramatic increase in theft of items from storage units which results in a need for more effective locking systems for the storage units. 
     Exterior walls of a typical storage unit are made of corrugated sheet metal. The storage unit doors are typically either horizontally swinging or roll-up type doors also made of corrugated sheet metal. Framing the door entrance is a sheet metal doorjamb. 
     Traditionally, the storage unit door is closed with a sliding bolt mechanism which can include a lock. The locking mechanism is secured to the door and has a member extending beyond the vertical edge of the door which abuts the doorjamb when the door is closed. The bolt mechanism slides behind the doorjamb to trap the doorjamb between the bolt and the extending member to prevent the door from swinging open. Traditionally, these sliding bolts were locked and held in place by means of a padlock. However, thieves easily overcome these locks by simply cutting the padlocks with bolt cutters when no one is around. 
     In an attempt to solve this problem, the sliding bolt mechanisms were designed with a recessed lock as shown in FIGS. 1 and 2. The recessed lock inserts through a hole in the door plate and a matching, aligned hole in the bolt when the bolt is slid into a locking position. When the recessed lock is inserted through the holes and turned with a key, it is locked in position and holds the bolt in the locking position. Once again, thieves are able to overcome this locking mechanism by prying the doorjamb with a crowbar or other prying device thereby allowing the bolt and door to swing free. It is desirable to have a slide-bolt locking mechanism with a key activated recess lock for a storage unit door which cannot be overcome by prying the doorjamb with a prying device to free the bolt and open the door. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide an improved storage unit door locking system to prevent forced entry. 
     It is a further object of this invention to provide a locking system for a storage unit door which utilizes a recessed locking device. 
     It is a further object of this invention to provide a locking system for a storage unit door which utilizes a sliding bolt for ease of operation. 
     It is a further object of this invention to provide a locking system for a storage unit door which prevents forced entry by the use of a prying device to pry the doorjamb to free the locking bolt. 
     It is a further object of this invention to provide a locking system for a storage unit door which secures the locking bolt to the doorjamb. 
     In order to achieve these objectives, this invention provides for a locking mechanism which is comprised of a door plate which is affixed to the storage unit door. The door plate is equipped with an extension plate which extends beyond the vertical edge of the storage unit door such that when the door is closed, the extension plate abuts the doorjamb and is flush against the doorjamb. The door plate is further equipped with a sliding bolt behind the door plate which slides behind the doorjamb and traps the doorjamb between the extension plate and sliding bolt. 
     A recessed lock is used to lock and hold the sliding bolt into place. The recessed lock slides into matching, aligned holes in the extension plate, doorjamb and the sliding bolt. When the recessed lock is inserted into the holes and the key is turned and removed, the recessed lock is locked in place and further locks the sliding bolt and extension plate in place. Since the doorjamb is physically locked to the steel extension plate and steel sliding bolt, it cannot be pried open with the use of a crowbar. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view depicting the prior art mechanism with a recessed lock. 
     FIG. 2 is an exploded perspective view depicting the same prior art mechanism shown in FIG.  1 . 
     FIG. 3 is a perspective view of a locking mechanism mounted to the storage unit door and set in the locked position. 
     FIG. 4 is an exploded perspective view of the locking mechanism shown in FIG.  3 . 
     FIG. 5A is a cross sectional view taken along line  5 — 5  of FIG. 3 while the mechanism is in a locked position. 
     FIG. 5B is a cross sectional view taken along line  5 — 5  of FIG. 3 while the mechanism is in an unlocked position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the prior art shown in FIGS. 1 and 2, a door  1  locks into a doorjamb  2  by a sliding bolt  3  that extends into an opening (not shown) in the doorjamb  2 . The sliding bolt  3  is slidably attached to the door  1  by a door plate  4  which is secured to the door  1  by back plate  5  and held together by bolts  6   a ,  6   b ,  7   a  and  7   b  threadably connecting into spacers  8   a  and  8   b , respectively. The spacers  8   a  and  8   b  provide the separation space needed for movement of the sliding bolt  3 . Back plate  5  is inside the door  1  and door plate  4  is outside the door  1 . A recessed lock  9  by extending through aligned holes locks the sliding bolt  3  in the extended position. However, when the door  1  is locked and the sliding bolt  3  locked into its extended position in the doorjamb  2 , the door  1  and doorjamb  2  may be easily pried apart by a crowbar or similar prying device. 
     Referring to FIGS. 3 and 4, a storage unit door  10  made of corrugated metal is shown in a closed position such that the right vertical edge of the storage unit door  10  is adjacent a doorjamb  12 . A locking mechanism  14  is mounted to the storage unit door  10 . The locking mechanism  14  is equipped with a door plate  16 , an extension plate  18 , a bolt  20 , a bolt handle  22 , a protecting flange  23 , an outer spacer  26 , an inner spacer  32 , and a mounting plate  44 . In the preferred embodiment, each of the component parts of the locking mechanism is made of steel. 
     The outer spacer  26  and inner spacer  32  are interiorly threaded through their depth and mounted to the back surface of the door plate  16  by means of a stove pipe screws  28   a  and  28   b  passing through square holes  30   a  and  30   b  centered vertically in the door plate  16 . In the preferred embodiment, the outer spacer  26  is circular and the inner spacer  32  is oval with a horizontal major diameter. The depth of the outer spacer  26  and inner spacer  32  are equal and sufficient to allow the door plate  16  to mount between corrugations in the storage unit door  10  with the outer spacer  26  and inner spacer  32  filling the gap between the storage unit door  10  and the door plate  16  at its vertical center. Horizontal flat surfaces  39  are cut into opposite sides of a rear portion  38  of the inner spacer  32  creating shoulder  40  (See FIG.  4 ). 
     The locking mechanism  14  is mounted to the storage unit door  10  with a mounting plate  44  which mounts to the back surface of the storage unit door  10  by means of two screws  46   a  and  46   b  passing through aligned holes  45   a  and  45   b  in the mounting plate  44  and the storage unit door  10  and screwing into the backs of the outer spacer  26  and the inner spacer  32 . In the preferred embodiment of the invention, the mounting plate  44  is a horizontally elongated rectangular plate and serves a dual purpose. First, it is used to brace and secure the locking mechanism  14  to the storage unit door  10 . Second, it prevents would-be thieves from prying the screws  46   a  and  46   b  through the storage unit door  10  and dismantling the locking mechanism  14 . 
     The bolt  20  is positioned to slide between the storage unit door and the door plate  16 . The bolt  20  has a horizontal elongated opening  42 . The vertical width of this opening  42  is sufficient to allow the bolt  20  to fit over the rear portion  38  of the inner spacer  32  with minimal clearance and slide on the flat surfaces  39  of the inner spacer  32 . The horizontal length of the opening  42  is sufficient to allow the bolt  20  to slide on the rear portion  38  of the inner spacer  32  from a locked position, as shown in FIGS. 3 and 4, to an unlocked position as shown in FIG. 5 b.    
     The bolt  20  is equipped with a bolt handle  22  which extends perpendicularly from the end of the bolt  20  opposite the doorjamb  12 . The bolt handle  22  extends through and slides within a rectangular opening  24  in the door plate  16 . The rectangular opening  24  is positioned on the door plate  16  and has a horizontal length sufficient to allow the bolt  20  to move from the unlocked position into the locked position. 
     The locking mechanism  14  is positioned on the storage unit door  10  so that when the storage unit door  10  is closed, the back surface of the extension plate  18  abuts and rests flush against the doorjamb  12  (see FIG.  3 ). While the locking mechanism  14  is in this position, the bolt  20  can be slid horizontally on the flat surfaces  39  of the rear portion  38  of the inner spacer  32  until the bolt  20  extends into the locking position behind the doorjamb  12 . The shoulder  40  acts as a stop and prevents the bolt  20  from moving towards the door plate  16  while the bolt  20  is being slid horizontally and insures that the bolt  20  will slide behind the doorjamb  12  (see FIGS. 5A and 5B. 
     When the bolt  20  is slid into the locked position behind the doorjamb  12  to lock the storage unit door  10  in place, a recessed lock  48  is inserted and extends through an opening  50  in the extension plate  18 , an opening  52  in the doorjamb  12 , and an opening  54  in the bolt  20  (see FIGS. 4,  5 A and  5 B). The recessed lock  48  is cylindrical with vertical flat surfaces  56  cut into opposite sides of a rear portion  58  of the recessed lock  18  creating a shoulder  60  toward the front end  62  of the recessed lock  48  (see FIG.  4 ). The shoulder  60  acts as a stop and abuts the front surface of the extension plate  18  when the recessed lock  48  is fully inserted. To frustrate tampering, the peripheral of the front end  62  of the recessed lock  48  is frustroconical in shape and terminates near the shoulder  60 . In one preferred embodiment of this invention, the recessed lock  48  is manufactured by L.A.I., model number KM4540. However, it is anticipated that other conventional recessed locks could perform adequately in this invention. 
     An exteriorly threaded shaft  64  extends perpendicularly from the rear vertical surface  65  of the recessed locked  48 . The shaft  64  rotates as the activating key (not shown) is inserted in the front face  66  of the recessed lock  48  and turned. The rotating shaft  64  extends through a circular opening (not shown) in a rotating plate  68  which is secured to the rotating shaft  64  with a nut  70  (see FIGS.  4  and  5 A). The front face of the rotating plate  68  abuts a shoulder (not shown) on the rotating shaft  64  which extends from the rear face  65  of the recessed lock  48  a sufficient distance to allow the rotating plate  68  to rotate with minimal clearance. The rotating plate  68  can be rotated 90 degrees from a unlocked position to a locked position. The size and shape of the rotating plate  68  is such that when it is in the unlocked position, its outer edges do not extend beyond the outer edges of the rear face  65  of the recessed lock  48 , and when the rotating plate  68  is rotated 90 degrees to the locked position, the outer edges of the rotating plate  68  extend horizontally beyond the outer edges rear face  65  of the recessed lock  48 . 
     The shapes of the opening  50  in the extension plate  18  and the opening  54  in the bolt  20  are the same, circular with flat vertical sides. The major and minor diameters of the opening  50  and the opening  54  are sufficient to allow the rear portion  58  of the recessed lock  48  to pass through with minimal clearance. The flat sides of the opening  52  and the opening  54  engage the flat surfaces  56  of the rear portion  58  of the recessed lock  48  and prevent rotation of the recessed lock  48  with respect to the extension plate  18  and bolt  20 . 
     When the recessed lock  48  is fully inserted such that the shoulder  60  abuts the front face of the extension plate  18 , the depth of the rear portion  58  of the recessed lock  48  is sufficient to allow the rear portion  58  of the recessed lock  48  to pass through the openings  50 ,  52 , and  54  such that the outer edge of the rear face  65  of the recessed lock  48  extends beyond the rear face of the bolt  20  with minimal clearance. If the activation key (not shown) is then inserted into the face  66  of the recessed lock  48  and turned 90 degrees, it will cause the rotating shaft  64  to turn, rotating the rotating plate  68  approximately 90 degrees. In this rotated position, the outer edges of the rotating plate  68  extend horizontally beyond the outer edges of the rear face  65  of the recessed lock  48  a sufficient distance to provide an interference with the back surface of the bolt  20  and thereby preventing removal of the recessed lock  48  (see FIG.  5 A). In this manner, the extension plate  18 , doorjamb  12 , and bolt  20  are physically locked together. This prevents a prying device, such as a crowbar, from separating the doorjamb  12  from the locking mechanism  14  as was possible in the prior art. 
     A protecting flange  23  extends perpendicularly toward the storage unit door  12  from the end of the door plate  16  opposite the extension plate  18 . The protecting flange  23  is centered vertically on the door plate  16  and has a height and width sufficient to cover the gap created between the door plate  16  and the corrugations in the door  10  and prevent the insertion of prying devices or other tools of forced entry between the door plate  16  and the storage unit door  10 . 
     Although the invention has been described with specific embodiments, this description is not meant to be construed in a limited sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the inventions will become apparent to persons skilled in the art upon the reference to the description of the invention. It is, therefore, contemplated that the appended claims will cover such modifications that fall within the scope of the invention.