Abstract:
An automatic locking mechanism engages a deadbolt lock after a prescribed time interval following entry. The mechanism employs a spring-operated mechanical timer, which may be actuated when a key or thumbturn is turned to unlock the door, and avoids the need for a key to set the deadbolt. The mechanism includes a gear system for retracting and inserting the deadbolt and a mechanical restraint to withhold the deadbolt until the timer has expired. In a suggested embodiment, a cam attached to one of the timer gears removes the restraint when the timer runs down. This deploys the deadbolt, automatically locking the door. In another embodiment, automatic locking may optionally be disabled by inhibiting coupling between the gear system and the timer spring.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is related to the field of lock mechanisms and, more particularly, to automatic lock mechanisms. 
     2. Description of the Related Art 
     Security is an increasingly important concern for both home and business. Despite the existence of numerous types of alarms and electronic security systems, the primary barrier to unauthorized entry in most cases is a locked door, and an important factor contributing to an overall level of security is the impregnability of the lock. 
     Furthermore, in situations calling for frequent entry and egress, such as a home, convenience is also an important consideration. No matter what advantages a lock may offer, if it is overly complicated or requires a great deal of effort to operate, people will tend to avoid using it. Users often deliberately circumvent elaborate, but inconvenient, security systems. 
     It is well known that deadbolt lock mechanisms provide greater security and are more resistant to unauthorized entry than conventional doorknob key locks. Unfortunately, standard deadbolt mechanisms lack the convenience of key locks, and therefore, are less frequently used than they might otherwise be. While the majority of doorknob key locks can be set to automatically lock the door when it is closed, a deadbolt lock typically must be locked from the outside with a key. Upon leaving a building, an additional step is therefore required to secure it with a deadbolt lock, compared with the automatic locking feature of the doorknob key lock. This may be sufficient encouragement for people to forego the greater security of the deadbolt. An automatic mechanism that engages a deadbolt without the need for a key would add greatly to the convenience of the deadbolt lock. This, in turn, would conduce to wider use of the deadbolt lock, and enhanced security. 
     Previous approaches to automatic locking mechanisms suffer from a variety of drawbacks. Many of these designs employ electronic timers or actuators. For example, U.S. Pat. No. 3,677,043 to Cox describes an electrically-actuated remote control door lock. Electronic timers are capable of great precision and longevity, and they can be readily integrated with other intrinsic circuitry, e.g., as in an electronic combination lock. However, in the event of power loss such mechanisms may become ineffective. In the worst case, this could mean leaving a door unsecured, or on the other hand, locking out individuals with rightful access. Other approaches to automatic locking make use of pneumatic timing devices. For example, U.S. Pat. No. 4,643,106 to Aragona describes a method for automatically relocking a lock after a prescribed time delay, in which the time delay depends on the compression of air by a piston and cylinder. There are problems with such designs, however. The seals in dashpots and similar devices are prone to wear and subject to temperature changes, which may result in substantial variation in the timing characteristics. 
     SUMMARY OF THE INVENTION 
     The problems outlined above are in large part solved by an automatic deadbolt locking mechanism as described herein. The mechanism comprises a deadbolt lock with means for automatically engaging the lock, along with a mechanical timer. The mechanical timer may comprise a system of gears and a coil spring. When the key, or a thumbturn, is turned to unlock the door, the primary gear within the system of gears may be made to rotate, winding the spring and simultaneously compelling the other gears to rotate at a rate determined by their relative gear ratios. The speed at which the primary gear rotates may be determined, for example, by a small propeller or centrifugal weights, as are commonly employed in mechanical clocks. The time required for the spring to completely unwind and restore the gears to their initial orientations constitutes the timer interval. 
     The deadbolt lock further comprises a deadbolt, which may be pushed into the locked position by a compression spring. Gear teeth on the deadbolt may mesh with teeth on a drive gear, such that when the key or thumbturn is turned the deadbolt is retracted from its locked position. A catch prevents the deadbolt from returning to the locked position until the timer runs down. The catch may be disengaged by a cam on one of the timer gears that, when rotated into position, lifts the retaining catch and releases the deadbolt. Once this happens, the compression spring immediately thrusts the deadbolt into the locked position. 
     Thus, unlocking the door may activate the deadbolt locking mechanism. Upon this unlocking of the door, after a prescribed interval the timer may automatically reengage the deadbolt lock. Additionally, in one embodiment, a pushbutton may be included in the mechanism that enables or disables the timing mechanism. This function may be useful if it is desired to allow the door to remain unlocked for some period of time. 
     A method is also contemplated herein for automatically relocking a deadbolt, after a prescribed time interval subsequent to unlocking the door. This method may further comprise means for optionally disabling automatic operation, allowing the mechanism to function as a conventional deadbolt lock. 
     The method and mechanism described herein are believed to be advantageous by providing increased convenience when using a deadbolt lock. Deadbolt locks are known to offer greater security against unauthorized entry than doorknob locks. Automatic activation of a deadbolt is believed to increase the likelihood that the deadbolt lock will be used. A mechanical design as described herein is believed to have inherently greater reliability than other designs, such as power-dependent electronic systems, pneumatic or hydraulic systems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which: 
     FIG. 1 is a side view of an embodiment of the automatic deadbolt locking mechanism, shown in the locked configuration; 
     FIG. 2 is a front view of the automatic deadbolt locking mechanism embodiment of FIG. 1; and 
     FIG. 3 is a side view of the embodiment of the automatic deadbolt locking mechanism shown in FIG. 1, where the mechanism is shown in the unlocked configuration. 
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to FIG. 1, a side view of one embodiment of an automatic deadbolt locking mechanism is shown. Other embodiments are possible and contemplated. The components of the lock are shown in FIG. 1 as they appear when the door is locked. For the discussion which follows, we take this to be the “initial state” of the mechanism. In this view the door is closed, with the doorjamb  10  to the left and the door  12  to the right. A recess in the doorjamb  16  is dimensioned to receive the deadbolt  14  when the door is locked, and a compression spring  18  may apply force to thrust the deadbolt  14  into the recess  16 . However, the spring  18  can be prevented from thrusting deadbolt  14  into recess  16  by a pair of catches,  20  and  22 . In the embodiment of FIG. 1, lower catch  20  is attached to the deadbolt  14 , while upper catch  22  is attached to a fixed point  24  within the door and pivots about point  24 ; when the tip of lower catch  20  engages the tip of upper catch  22  the deadbolt is held in place. 
     The mechanism may also comprise a system of gears  28 ,  30 , and  32 , which are mutually coupled and designed to turn at different rates. The primary gear  28  is coupled to a reduction gear  30  which is, in turn, coupled to secondary gear  32 . The ratio of gear  28  to gear  30  is such that gear  30  rotates at a much higher rate than gear  28 . Gear  32 , on the other hand, rotates at a rate comparable to that of gear  28 . A cam  36  attached to gear  32  may be used to lift the upper catch  22 , disengaging it from the lower catch  20 , as the gear rotates counterclockwise. The speed of rotation of gear  30  may be limited by means of a governor  34 , consisting of one of a number of devices commonly employed for this purpose in mechanical clocks. In one embodiment, a small propeller attached to the shaft of gear  30  creates a drag force that acts against the rotation of the gear, limiting its rate of rotation. Since they are coupled to gear  30 , gears  28  and  32  experience this drag force as well. Primary gear  28  turns freely on a main shaft  38  that is turned by the door key or thumbturn. A slot  40  may be formed within the primary gear  28  through which a pin  42  extends. The pin is attached to the main shaft  38  and serves to transfer rotation of the shaft to the primary gear. 
     A front view of the mechanism of FIG. 1 is shown in FIG.  2 . The deadbolt  14  and the lower catch  20  are shown at the top. Turning freely on main shaft  38 , and mounted directly behind primary gear  28 , is drive gear  50 . In this embodiment, gear teeth  52  on the lower catch  20  mesh with teeth on the drive gear  50 . Therefore, when the drive gear  50  turns clockwise (viewed as in FIG. 1) the deadbolt slides out of the recess  16 . The pin  42  attached to main shaft  38  is also visible in the view of FIG. 2, penetrating the slot in primary gear  28 . Fixed to shaft  38  may be a clutch disk  54 , which is designed to interface with the drive gear  50 . Their opposing surfaces comprise a ratcheting mechanism; when clutch disk  54  rotates counterclockwise it turns independently of drive gear  50 , but when rotated clockwise it is coupled to the drive gear, forcing the gear to turn with it. 
     Turning freely on main shaft  38  and just in front of the primary gear  28  shown in FIG. 1 may be a coupling disk  44 . On the front surface of this disk may be mounted a coil spring  46 , one end of which is attached to the coupling disk at point  48  and the other end of which is attached to a fixed point  56  within the door. Thus, when coupling disk  44  rotates, it winds or unwinds the coil spring. Coupling disk  44  may be thrust forward or retracted, bringing it into or out of contact with primary gear  28 . This may be accomplished for example, by a pushbutton. In a preferred embodiment of the locking mechanism, the coupling disk is normally not in contact with the primary gear unless the button is pushed. The opposing surfaces of the primary gear  28  and coupling disk  44  are designed to interlock with one another when they are brought into contact with one another, such that the coupling disk and the primary gear are made to rotate together. As explained in greater detail below, automatic relocking of the deadbolt is enabled when the coupling disk  44  is in its forward position, engaging the primary gear  28 . When the coupling disk is retracted, the locking mechanism functions as a conventional deadbolt lock. Note that items  16 ,  18 - 22 ,  28 - 34 ,  38 , and  42 - 56  are preferably made of metal, but other suitable materials could conceivably be used. Furthermore, the shapes and spatial arrangement of the components described herein and indicated in the accompanying drawings are intended to suggest a particular embodiment which illustrates the principles underlying the automatic deadbolt locking mechanism. Other embodiments employing these principles are contemplated and should be considered within the scope of the present invention. 
     Operation of the automatic deadbolt embodiment of FIGS. 1-3 may now be described. To open the door a key or thumbturn is turned in the lock, causing main shaft  38  to rotate clockwise (viewed as in FIG.  1 ). Because of the ratcheting action described above, as shaft  38  rotates clockwise it causes clutch disk  54  to engage drive gear  50  and force it to rotate in the same direction. As the drive gear rotates clockwise it draws the deadbolt  14  out of recess  16 , unlocking the door. At the same time, pin  42  attached to shaft  38  forces primary gear  28  to rotate clockwise. Coupled secondary gear  32  rotates clockwise as well, moving cam  36  out from under the upper catch  22  and enabling the upper catch to engage the tip of lower catch  20 . At this time, if coupling disk  44  is in its forward position it rotates along with primary gear  28 , winding coil spring  46 . 
     When the door has been unlocked, shaft  38  is returned to its original orientation and the key, if used, is withdrawn. At this time, the components appear as shown in FIG.  3 . Note that pin  42  has returned to its original position, while slot  40  has rotated clockwise. Also note that upper catch  22  has captured lower catch  20  and prevents the compression spring from thrusting the deadbolt  14  into recess  16 . At this point, the operation of the locking mechanism will depend on whether or not automatic locking is enabled. 
     If the coupling disk  44  was in contact with the primary gear when the door was unlocked, it will have rotated with the primary gear and wound coil spring  46 . Now, as the coil spring  46  unwinds, coupling disk  44  and primary gear  28  turn counterclockwise. However, observe that while the lower and upper catches  20  and  22  are engaged, the deadbolt is prevented from entering the recess and the door remains unlocked. 
     As coil spring  46  continues to unwind, primary gear  28  and secondary gear  32  eventually return to their orientations as shown in FIG.  1 . It is believed that their rate of rotation is a consistent and predictable function of the respective gear ratios, the characteristics of coil spring  46  and the drag force associated with governor  34 . When secondary gear  32  has rotated sufficiently to lift upper catch  22  with cam  36 , the tip of lower catch  20  is released. This allows compression spring  18  to thrust deadbolt  14  into recess  16 , automatically locking the door. 
     On the other hand, if coupling disk  44  was retracted, it will not have rotated along with primary gear  28  when the door was unlocked, and coil spring  46  will not be wound. In this case, primary and secondary gears  28  and  34  will not rotate back to their original orientation when the key is withdrawn. Therefore, cam  36  will not be brought into position to disengage lower and upper catches  20  and  22 , so deadbolt  14  will not be released. The door must then be relocked manually by turning the key or thumbturn counterclockwise. When this is done, counterclockwise rotation of main shaft  38  and the action of pin  42  in slot  40  will cause primary gear  28  to also rotate counterclockwise. This rotation is coupled to secondary gear  34  by reduction gear  30 . As the secondary gear rotates it brings into position cam  36 , lifting upper catch  22  and allowing compression spring  18  to thrust the deadbolt back into recess  16 , which locks the door. Note that this mode of operation is essentially that of a conventional deadbolt lock. 
     It will be appreciated by those skilled in the art having the benefit of this disclosure that this invention is believed to present a system and method for implementing an automatic deadbolt locking mechanism. Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Such details as the number of gears and the types of springs used in the mechanical timer described herein are exemplary of a particular embodiment. It is intended that the following claims be interpreted to embrace all such modifications and changes and, accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.