Abstract:
An electronically-operable door strike employing a guard clip for deterring picking of the locking mechanism therein, a springless solenoid designed to avoid the undesirable build-up of residual magnetism and which incorporates air gaps for dissipating heat, thus prolonging the useful life of the solenoid, and a face plate for mounting the strike into a door jamb.

Description:
This is a continuation-in-part of application Ser. No. 10/039,472, filed Jan. 4, 2002, now U.S. Pat. No. 6,634,685. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is directed to door locking devices and, more particularly, to electromagnetically controlled door locks that are actuatable from remote locations throughout a building. Such locks, known generally as “electric strikes”; are commonly used to prevent the opening of an associated access obstructing member, such as a door, in hotels, offices, apartment buildings, storage cabinets and appliances. In a preferred embodiment the electric strike of the present invention employs a guard clip for deterring picking of the locking mechanism, a springless solenoid designed to prevent the build-up of residual magnetism which otherwise impairs a solenoid&#39;s ability upon activation to release the locking mechanism, and a one piece face plate for mounting in a doorjamb which serves to house the electric strike and guide the latch bolt associated with an access obstructing member into engagement with the latch bolt keeper of the electric strike. The present invention is also directed to a method of mounting the one piece face plate and its associated electric strike onto an aluminum doorframe in a manner which requires significantly less cutting of the doorframe by the installation technician than by other methods known in the art. 
   2. Description of the Related Art 
   Electronically-operable door strikes installed in a doorjamb to secure a door against opening are known in the art. Electric strikes typically provide a latch bolt keeper mounted on a pivot. The ability of the keeper to rotate on the pivot is electronically controlled. When the keeper is free to rotate to a latch bolt releasing position, the latch bolt associated with the access obstructing member is not retained in the door jamb and the access obstructing member can be opened. When the keeper is not free to rotate, that is, it is in its latch bolt securing position, the latch bolt is retained by the latch bolt keeper, thus securing the door. 
   Fundamentally, the function of an electric door strike is based on the fact that a retractable stop lever engages the latch bolt keeper and holds it in its latch bolt securing position. That is, the stop lever prevents the latch bolt keeper from rotating. The stop lever is sometimes held in its engaging position with the latch bolt keeper by a lock lever spring-urged into interlocking relationship with the stop lever. To permit the latch bolt keeper to rotate to its latch bolt releasing position, a solenoid is often employed. The solenoid is electronically energized, normally by means of a circuit completing switch remote from the door strike, and the lock lever is moved out of its locking engagement with the stop lever by the action of the solenoid plunger either pulling or pushing the lock lever. The stop lever, no longer being engaged by and being held in position by the lock lever, is incapable of resisting pivoting of the latch bolt keeper when force is applied to the keeper. The keeper is therefore able to be rotated and the door thus able to be opened. 
   One drawback of some of the electric strikes heretofore available is the ease with which they can be picked open and defeated by the insertion of a tool for unauthorized movement of the latch bolt keeper to a latch bolt releasing position. U.S. Pat. No. 3,638,984 to Davidson and U.S. Pat. No. 3,861,727 to Froerup et al. disclose a latch bolt keeper provided with a lateral edge projection arranged to occupy an overlapping position with respect to an edge of the strike plate and thus close the space between this edge and the adjacent face of the latch bolt keeper so as to provide against the insertion of a picking tool. U.S. Pat. No. 4,026,589 to Hanchett, Jr. also discloses a latch guard which precludes insertion of a tool. Finally, U.S. Pat. No. 4,056,277 to Gamus et al. discloses a plurality of pin-like protrusions positioned to form a barrier to prevent access by a tool to the ball and socket arrangement which serves to hold the latch keeper of that invention in place. Unlike the prior art electric strikes heretofore disclosed, the present invention utilizes a unique guard clip designed to prevent a tool from gaining access to the lock lever and further, by means of its fish hook-like configuration, to redirect any tool which is inserted into the electric strike away from the lock lever and the stop lever. 
   Another disadvantage of the electric strikes heretofore available is the undesirable build-up of residual magnetism within the solenoid or on the solenoid plunger. It is essential for proper operation of a solenoid that it lose its magnetic force once input electrical power to the solenoid is removed, thus allowing the solenoid plunger to return to its original position. Any magnetic field which remains when electrical power is removed is termed residual magnetism. The residual magnetism present in prior art electric strikes is occasioned by the frequent contact between two ferrous metal surfaces such as a ferrous metal solenoid plunger striking a ferrous metal lock lever during repeated energization and de-energization of the solenoid. Build-up of residual magnetism during repeated cycling of the solenoid results in the eventual failure of the solenoid&#39;s ability to remotely disengage the lock lever and the stop lever so as to permit the latch bolt keeper to be rotated and the access obstructing member opened. In some electric strikes termed “fail-safe” or “power to lock” by those of skill in the art, the plunger is pulled into the solenoid body when energized. This action of the plunger pulls the spring-resistive lock lever into engagement with the stop lever, thus preventing the latch bolt keeper from pivoting from its latch bolt securing position to its lockset latch bolt releasing position. When the solenoid is de-energized, the spring-urged lock lever returns to its original position where it is disengaged from the stop lever, thus allowing the latch bolt keeper to be pivoted to its lockset latch bolt releasing position. Upon the build-up of residual magnetism along the plunger or solenoid body, however, the plunger can remain in contact with the lock lever or not fully exit the body of the solenoid, thus compromising the ability of the lock lever to disengage from the stop lever. In the operation of other electric strikes, termed “fail-secure” by those of skill in the art, the plunger is pulled from its starting position into the body of the solenoid upon energization and this action releases the stop lever, thus permitting the latch bolt keeper to rotate. Upon de-energization the plunger exits the solenoid body by means of a spring and is returned to its starting position. Again, however, upon the build-up of residual magnetism along the plunger, the plunger may not be able to be completely returned to its starting position by the spring mechanism, thus compromising the solenoid&#39;s ability to return the stop lever or lock lever to a position where the latch bolt keeper is prevented from rotating. 
   Yet an additional drawback of prior art electric strikes is the large amount of cutting into a steel door jamb which is necessary to install the strike and its associated face plate. The American National Standards Institute (“ANSI”) standard face plate measures 4⅞ inches in length by 1¼ inches in width. Typically, electric strike face plates also utilize an auxiliary ramp which measures 3⅜ inches in length, thus necessitating that a corresponding length of the door jamb be removed at a depth of about one-half inch or more to properly seat the face plate and auxiliary ramp into the jamb. This large amount of cutting requires more time and money to install than otherwise would be necessary with an electric strike and face plate arrangement that reduces the amount of door jamb cutting required for installation. 
   This problem exists not only in the steel door industry but also in the aluminum/glass door industry which does not follow the ANSI standards. The aluminum/glass door industry manufactures what is commonly known in the trade as “storefronts”. A storefront is a door consisting of a glass panel surrounded and supported by an aluminum frame which is hung from a hollow aluminum doorjamb by means of hinges. A storefront-type entryway is common in many retail establishments such as those found in a strip mall. Architects, designers, and owners of these retail establishments commonly determine the specifications for the storefront including the door jamb. The door jambs are typically pre-fabricated and include a “cut-out” portion to accommodate the dimensions of the doorframe hardware specified by the architect/designer or owner, usually that of the largest selling U.S. manufacturer of such hardware for aluminum/glass doors. The dimensions of the cut-out are therefore commonly either 4⅝ inches in height by 1 9/16 inches in width or 2⅝ inches in height by 1 9/16 inches in width. When the decision is later made by the owner of the retail establishment to install or retrofit a prior art electric strike and associated faceplate into the cut-out portion of the aluminum door jamb, a significant amount of cutting of the door jamb is required, thereby requiring an extended amount of time for the installer and a corresponding high cost. 
   A still further drawback of prior art electric strike face plates occurs in those installations where the electric strike is required to be installed in door jambs which measure 4 inches or wider and the door is to be center hung. In those instances the auxiliary ramp and face plate comprise two or more pieces, thus again requiring more time for installation than if a one-piece face plate and auxiliary ramp were provided. 
   SUMMARY OF THE INVENTION 
   For the foregoing reasons, there is a need for an electric strike which overcomes the hereto before described problem of residual magnetism associated with a frequently cycled or continuous duty solenoid plunger. There is a further need for an electric strike in which a tool cannot be used to pry away the lock lever from the stop lever permitting the latch bolt keeper to be rotated and the access obstructing member opened by a tampering intruder. There is yet a still further need for an electric strike and face plate which reduces the amount of door jamb cutting necessary for its installation. 
   It is thus an object of the present invention to provide an electronically-operable door strike which utilizes a solenoid which avoids the build-up of residual magnetism along the solenoid body or plunger which otherwise would render the electric strike inoperable. 
   It is a further object of the present invention to provide an electronically-operable door strike which embodies an improved guard to the insertion of a picking tool and which redirects a picking tool away from contacting the lock lever or the stop lever. 
   It is a still further object of the present invention to provide an electronically-operable door strike and one piece face plate with fill lip and auxiliary ramp arrangement which reduces the amount of door jamb material which must be removed for installation of the face plate. 
   It is yet a still further object of the present invention to provide an electronically-operable door strike and associated one piece face plate that can be uniquely retrofitted into an existing aluminum door jamb cut-out of the dimensions previously noted thereby reducing the amount of cutting of the door jamb required to install the electric strike and its face plate, thus realizing a cost savings for the installation. 
   In accordance with the foregoing objects, an electronically-operable door strike which employs a guard clip for deterring picking of the locking mechanism, a springless solenoid designed to avoid the build-up of residual magnetism and a face plate which reduces the amount of door jamb cutting required for installation of the electric strike and face plate arrangement is disclosed. Briefly stated, the invention is practiced by utilizing a guard clip which protects the lock lever and the stop lever from tampering by a tool inserted into the door strike along an edge of the latch bolt keeper and which by virtue of its “fish hook” configuration redirects the tool away from the lock lever. In addition, to avoid the build-up of residual magnetism, a solenoid comprising a ferrous metal shell and front cap, a rear cap of non-ferrous material such as non-ferrous metal, and a ferrous metal plunger with a non-ferrous metal protuberance is provided. An air gap is maintained between the front cap and the plunger body during movement of the plunger to avoid the build-up of residual magnetism between the front cap and the plunger body. An additional air gap is provided between the plunger and a spool within which the plunger moves and around which a wire coil is wrapped inside of the solenoid shell. This additional air gap aids in the dissipation of heat generated when the wire coil of the solenoid is electronically-activated and the plunger is repeatedly cycled. Finally, the face plate associated with the electric strike is designed with a fill lip and flange tongue arrangement which reduces the amount of the door jamb which must be removed for the installation of the electric strike and face plate in comparison with heretofore known electric strike and face plate arrangements. 
   Further objects, features, aspects and advantages will be readily apparent to those skilled in the art and a better understanding of the present invention may be had by reference to the following detailed description taken in connection with the following drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front plan view of the electric strike of the present invention with the cover removed and showing the lock lever in its position engaged with and immobilizing the stop lever such that the latch bolt keeper is maintained in its latch bolt securing position; 
       FIG. 2  is an exploded perspective view of the electric strike of the present invention; 
       FIG. 3  is a front plan view similar to  FIG. 1  showing the solenoid plunger striking the lock lever and the lock lever moved to its position allowing the stop lever to be pivoted and the latch bolt keeper rotated to its latch bolt releasing position; 
       FIG. 4  is a front plan view similar to  FIG. 3  showing the latch bolt keeper rotated to its latch bolt releasing position; 
       FIG. 5  is a side view of the electric strike of the present invention with the cover removed and showing the solenoid in its non-activated position and the lock lever in its engaged position with the stop lever; 
       FIG. 6  is a side view similar to  FIG. 5  but showing the solenoid in its activated position and the lock lever in its disengaged position with the stop lever; 
       FIG. 7  is a cross-sectional view along line  7 — 7  of  FIG. 1 ; 
       FIG. 8  is a cross-sectional view along line  8 — 8  of  FIG. 4  showing the relationship between the stop lever and the rotated latch keeper; 
       FIG. 9  is a perspective view of the guard clip; 
       FIG. 10  is a cross-sectional view of the solenoid along line  10 — 10  of  FIG. 5  when the latch bolt keeper is in its latch bolt securing position; 
       FIG. 11  is a cross-sectional view of the solenoid along line  11 — 11  of  FIG. 6  when the solenoid is energized and the latch bolt keeper is in its latch bolt releasing position; and 
       FIG. 12  is an exploded perspective view of the solenoid. 
       FIG. 13  is a front plan view of the face plate and electric strike of the present invention installed within a door jamb. 
       FIG. 14  is a cross-sectional view along line  14 — 14  of FIG.  13 . 
       FIG. 15  is a side view of the face plate of the present invention installed within a door jamb. 
       FIG. 16  is a front plan view of a further embodiment of the face plate with the electric strike installed within a door jamb. 
       FIG. 17  is an exploded rear perspective view of the face plate of the present invention with a dust shield and electric strike. 
       FIG. 18  is an exploded perspective view of a common prior art face plate and an aluminum door jamb depicting an existing cut-out portion in the prefabricated door jamb. 
       FIG. 19  is an exploded perspective view of a common prior art face plate and its associated electric strike depicting the amount of an aluminum door jamb which must be removed to retrofit the strike and face plate into an existing cut-out portion in the prefabricated door jamb. 
       FIG. 20  is an exploded perspective view of the electric strike and its associated face plate of the present invention depicting the amount of an aluminum door jamb which must be removed to retrofit the strike and its face plate into an existing cut-out portion in the prefabricated door jamb. 
       FIG. 21  is an exploded perspective view of another common prior art face plate and an aluminum door jamb depicting an existing cut-out portion in the prefabricated door jamb. 
       FIG. 22  is an exploded perspective view of a common prior art face plate and its associated electric strike depicting the amount of an aluminum door jamb which must be removed to retrofit the strike and face plate into an existing cut-out portion of the prefabricated door jamb. 
       FIG. 23  is an exploded perspective view of the electric strike of the present invention and another embodiment of its associated face plate depicting the amount of an aluminum door jamb which must be removed to retrofit the strike and its face plate into an existing cut-out portion in the prefabricated door jamb. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings there is shown in  FIG. 1  an electrically-operable door strike as generally indicated by the numeral  10 . The electric strike is comprised of a base  12  having a front edge  12   a  and a rear edge  12   b . To base  12  are fixedly secured a pair of spaced-apart support blocks  14   a  and  14   b  each provided with threaded openings  11  (see  FIG. 2 ) for receiving screws to fixedly hold a pair of end panels  13   a  and  13   b  and a cover  13   c . Support blocks  14   a  and  14   b  also carry a shaft pin  16  (see  FIG. 2 ) for rotatably supporting a latch bolt keeper  18 . The cross-sectional configuration of the latch bolt keeper may best be observed in FIG.  7 . Mounted circumferentially around shaft pin  16  is a cylindrical turning spring  15  which urges the latch bolt keeper  18  into its latch bolt securing position wherein the front edge portion  17  of latch bolt keeper  18  protrudes beyond front edge  12   a  of base  12  (as best seen in FIG.  1 ), through face plate  31  ( FIG. 2 ) and engages the latch bolt of an adjacent door (not shown). 
   Referring to  FIG. 1 , the stop lever  20 , which extends substantially along the entire length of base  12 , is pivotally secured at one end by means of a pivot pin  21  extending normal to base  12 . The free end of stop lever  20  contains shoulder  34  (see  FIG. 3 ) from which tooth  27  protrudes for engagement with angled notch  29  located on the free end of lock lever  22 . The shape of tooth  27  can be angular, curved or have a hook-like appearance. The shape of the angled notch  29  similarly can be angular, curved, or have a hook-like appearance. Lock lever  22  is itself pivotally secured at its opposite end by means of pivot pin  24  extending normal to base  12 . The stop lever  20  is urged into its locking position whereby it prevents latch bolt keeper  18  from pivoting around shaft pin  16  by means of a torsion spring  26  (see  FIG. 5 ) which, with one leg, engages the wall of support block  14   a  (see  FIG. 1 ) and with its other leg fits into depression  28  of stop lever  20 . The lock lever  22  is urged into its interlocking position with the stop lever by means of a torsion spring  30  (see  FIG. 2 ) which engages either both lock lever  22  and pivot pin  24  or both lock lever  22  and support block  14   b . In this interlocking position, tooth  27  of shoulder  34  of stop lever  20  hooks into angled notch  29  on the free end of the lock lever  22 . When lock lever  22  is moved from its locking position shown in  FIG. 1  into its releasing position shown in  FIG. 3  against torsion spring  30  by action of plunger  44  (see  FIG. 12 ) in a manner to be described, it permits retraction of the stop lever  20 . Stop lever  20 , however, is initially maintained in its position in which it contacts latch bolt keeper  18  by torsion spring  26 . Due to the pivotal motion of the latch bolt keeper  18  by the latch bolt during the opening of the door, the rear edge portion  19  of the latch bolt keeper  18  pushes the stop lever  20  which then pivots and retracts into its open, latch bolt releasing position shown in FIG.  4 . After the latch bolt has been released by the latch bolt keeper  18  and the door has been opened, the cylindrical turning spring  15  returns the latch bolt keeper  18  into the latch bolt securing position shown in FIG.  1 . In this position, under the action of torsion spring  26 , the stop lever  20  snaps with its shoulder  34  behind the free end of the lock lever  22  which is returned to its locking position by spring  30 , thus maintaining the latch bolt keeper  18  in its latch bolt securing position. 
   When tooth  27  and notch  29  are engaged in an interlocking relationship, pressure exerted on latch bolt keeper  18  in an attempt to rotate latch bolt keeper  18  about shaft pin  16  to its latch bolt releasing position serves to more firmly engage tooth  27  and notch  29  and hence stop lever  20  and lock lever  22 , thus increasing the locking force or holding integrity of those two levers as they hold the latch bolt keeper  18  in its latch bolt securing position. If both tooth  27  and notch  29  are angled at 90 degrees so that they perpendicularly intersect each other, vibrations applied to the electric strike  10  through the door or door jamb can cause stop lever  20  to vibrate and walk out of its contact with lock lever  22 , thus allowing latch bolt keeper  18  to be rotated to its latch bolt releasing position. Therefore, both tooth  27  and notch  29  are preferably angled at less than 90 degrees. With the arrangement of tooth  27  and notch  29  heretofore described, it is observed that a load or force applied to latch bolt keeper  18  in an attempt to rotate latch bolt keeper  18  into its latch bolt releasing position will not disengage stop lever  20  from lock lever  22 ; however, the slightest amount of force applied directly to lock lever  22  pivots lock lever  22  on pivot pin  24  resulting in the disengagement of the stop lever  20  from the lock lever  22 . 
   Rear edge portion  19  of latch bolt keeper  18  is beveled at an angle of approximately 35 degrees as best illustrated in FIG.  7 . Front edge portion  23  of stop lever  20  is also beveled at an angle of about 35 degrees. Thus when latch bolt keeper  18  is pivoted about shaft pin  16  (as shown on FIG.  8 ), rear edge portion  19  of the keeper contacts the front edge portion  23  of stop lever  20  and rotates stop lever  20  on pivot pin  22 . Rear edge portion  19  of keeper  18  is permitted to slid behind stop lever  20  by virtue of beveled front edge portion  23  of stop lever  20  and beveled rear edge portion  19  of latch bolt keeper  18 . The pivoting motion of latch bolt keeper  18  to its latch bolt releasing position is stopped by shell  42  (see  FIG. 5 ) of solenoid  35 . In this manner neither the rear edge portion  25  of stop lever  20  (see  FIG. 4 ) nor the beveled rear edge portion  19  of latch bolt keeper  18  extends beyond rear edge  12   b  of base  12  when latch bolt keeper  18  is pivoted to its latch bolt releasing position. The effect is that the electric strike of the present invention is compact and small in dimension and can be used particularly in those applications where space in the door jamb is limited. The electric strike of the present invention has a height (H) of about 1 11/16 inches or of about 1 13/16 inches and a width (W) of about 1 1/32 inches (see FIG.  5 ). Further with respect to size, electric strike  10  has a back set (the depth an electric strike requires to fit into a doorframe) of only about one (1) inch. This feature is important as it allows electric strike  10  to fit into more applications such as doorframes, storage cabinets and appliances with less restrictions due to size. 
   As best illustrated in  FIGS. 1 and 9 , guard clip  54  is a separate element, not an integral part of base  12 , which is disposed between support block  14   b  and latch bolt keeper  18  to minimize the ability of a potential intruder to insert a tool into electric strike  10  along latch bolt keeper  18  for purposes of contacting lock lever  22  and disengaging it from stop lever  20 . In those instances where a tool is successfully inserted into electric strike  10 , guard clip  54  is also intended to preclude access by the tool to lock lever  22  which, otherwise, could be contacted by the tool and disengaged from stop lever  20 . Arm  56  of guard clip  54  is comprised of three portions. First portion  56   a  is of sufficient length to extend perpendicularly from front edge  12   a  of base  12  to at least pivot pin  24  of lock lever  22 . Second portion or tab  56   b  of arm  56  is angled away from latch bolt keeper  18  toward lock lever  22  until third portion or flange  56   c  of arm  56  is again angled toward shoulder  34  of stop lever  20 . Because of the shape and dimensions of arm  56  of guard clip  54 , arm  56  prevents access to lock lever  22  by a tool inserted into electric strike  10  between guard clip  54  and latch bolt keeper  18 . Furthermore, any tool, such as an unfurled paperclip or wire, which is inserted into electric strike  10  in this manner will be directed away from lock lever  22  by means of the “fish hook” configuration of arm  56 . A guard clip which is not angled in the manner heretofore described will not redirect an inserted tool away from lock lever  22 . 
   For moving the lock lever  22  against the force of torsion spring  30  there serves a springless solenoid  35  having an axis that extends in the longitudinal direction of base  12 . The solenoid  35 , which takes up a substantial portion of the length of the base  12 , comprises wire coil  37  wound on a spool  36  made of a thermoplastic polyester resin, such as polyethylene terephthalate polyester resin, high temperature plastic, or other synthetic material. With the solenoid  35  there is associated a front cap  38 , a rear cap  40 , a cylindrical shell  42  and a plunger  44  which is movable within the spool  36 . Plunger  44  is comprised of a plunger body  46  and a protuberance or plunger tip  48  as best seen in  FIGS. 10-12 . Plunger body  46  is cylindrical in shape and constructed of 1018 soft steel or other ferrous metal. Plunger tip  48  is also cylindrical in shape having a smaller diameter than that of plunger body  46 . Plunger tip  48  is constructed of stainless steel or other non-ferrous metal. This choice of materials for plunger tip  48  aids in avoiding the build-up of residual magnetism between front cap  38  and the plunger tip  48  through repeated travel of the plunger tip through the front cap  38 , as will be described, in response to repeated cycling of energizing and de-energizing the solenoid  35 . Front cap  38  has a hole  39  centrally disposed therein through which plunger tip  48  is movable when solenoid  35  is energized. Front cap  38  is constructed of 1018 soft steel or other ferrous metal which acts as a magnet to pull plunger  44  toward it when solenoid  35  is energized. To direct plunger  44  toward front cap  38  when solenoid  35  is energized, rear cap  40  also has a hole  41  centrally disposed therein through which plunger body  46  is moveable when solenoid  35  is energized. Rear cap  40  is constructed of aluminum, stainless steel, other non-ferrous metal, or other non-ferrous material which will not become magnetized when solenoid  35  is energized. Shell  42  is constructed of steel or other ferrous metal. The shell  42  functions not only as an enclosure for wire coil  37 , spool  36  and plunger  44  but also as a stop for latch bolt keeper  18  when it is pivoted about shaft pin  16  into its latch bolt releasing position. Plunger body  46  and plunger tip  48  are supported during the travel of plunger  44  by holes  39  and  41  in front cap  38  and rear cap  40 , respectively. Plunger body  46  and plunger tip  48  do not contact spool  36 . Thus, a first air gap  47  (see  FIGS. 10 and 11 ) is created between the outer surface of plunger  44  and the inner surface of spool  36 . First air gap  47  helps to avoid the build-up of residual magnetism along plunger  44  and further aids in dissipating the build-up of heat in solenoid  35  when the solenoid is energized. This has several advantages. First, air gap  47  helps to avoid expansion of spool  36 , and a resulting shrinkage of the inside diameter of spool  36 , which otherwise would cause friction or binding between plunger  44  and spool  36  during travel of the plunger towards front cap  38  when solenoid  35  is energized. Second, solenoid  35  is able to be operated at a lower voltage than if no air gap were present because heat does not build-up inside of solenoid  35 . Heat build-up would otherwise increase the resistance of wire coil  37  thus requiring more voltage to operate solenoid  35 . 
   When solenoid  35  is energized, plunger body  46  is, by the resulting magnetic attracting forces, moved toward front cap  38  (see FIG.  11 ). During its motion caused by magnetic attraction, the plunger tip  48  exits the front cap  38  through hole  39  and strikes an aluminum or other non-ferrous metal actuator pin  50  which extends laterally from the underside of the lock lever  22  and which is disposed in the path of travel of the plunger tip  48 . As a result of the collision between the plunger tip  48  and the actuator pin  50 , the lock lever  22  is pivotally moved about pivot pin  24  into its releasing position against the force of spring  30 . The pivotal motion of lock lever  22  and its underlying actuator pin  50  is stopped by end panel  13   b . As a result, a second air gap  52  is maintained between plunger body  46  and front cap  38 , as best illustrated in FIG.  11 . This second air gap  52  further resists the build-up of residual magnetism between plunger  44  and front cap  38  which might otherwise result from the repeated striking of plunger  44  against front cap  38  during repeated energization/de-energization cycling of the solenoid. The pivotal motion of lock lever  22  into its releasing position in turn releases stop lever  20  from its engagement with lock lever  22 , thereby permitting stop lever  20  to pivot away from latch bolt keeper  18  thus allowing latch bolt keeper  18  to pivot to its latch bolt releasing position upon shaft pin  16 . Once the door or other access obstructing member has been opened and latch bolt keeper  18  returned to its latch bolt securing position by the urging of turning spring  15 , stop lever  20  is again urged to its closed position by torsion spring  26 , spring  30  also urges lock lever  22  into its closed position engaging stop lever  20 . When the lock lever  22  returns to its closed position, the actuator pin  50  underlying lock lever  22  strikes plunger tip  48  and returns a portion of the plunger tip  48  and the associated plunger  44  to the confines of the solenoid shell  42 , with end panel  13   a  serving as a stop for the travel of the plunger  44  through hole  41  of rear cap  40 . In the manner heretofore described, plunger  44  moves from a starting position within non-energized solenoid  35  to a stop lever striking position when solenoid  35  is energized, and returns to the starting position when the solenoid is de-energized, all without the urging of any springs within solenoid  35 . 
   Also provided for housing and mounting the electric strike  10  of the present invention within a doorjamb is face plate  60  (see FIGS.  13 - 16 ). Face plate  60  is constructed of flat stock steel and is of one piece construction. Face plate  60  comprises lip  62  which is convex and overlaps edge  64  of door jamb  66  when face plate  60  is secured to door jamb  66  by screws or other attaching means inserted through holes  68  within face plate  60 . Face plate  60  further comprises flange tongue  70  which is displaced a distance apart from the outer edge  72  of face plate  60  (see  FIG. 14 ) and the inner edges  74  of face plate  60  (see  FIG. 13 ) thereby forming a channel  76  (see  FIG. 15 ) which serves as a guide for the latch bolt associated with an access obstructing member to engage with the latch bolt keeper  18  and place the latch bolt keeper into its latch bolt securing position. 
   The arrangement of the face plate  60  and electric strike  10  within a standard width (e.g., 1⅜ inches or 1¾ inches) door jamb is depicted in  FIGS. 13 and 14 . In those instances where the door jamb is wider (such as 4 inches or greater) and the access obstructing member is center hung, thus necessitating the location of the electric strike on or about the centerline  72  of door jamb  66 , the embodiment of face plate  60  depicted in  FIG. 16  would be utilized. Therein, face plate  60  is of one piece construction and the width of lip  62  and flange tongue  70  are extended from the electric strike  10  to edge  64  of door jamb  66 . 
   Installation of face plate  60  within door jamb  66  requires less cutting and removal of door jamb material (typically metal such as steel or aluminum) than installation of prior art electric strike face plates. Prior art electric strike face plates utilize an auxiliary ramp which requires that a length (l) of door jamb measuring 3⅜ inches at a minimum depth (d) of ½ inch be removed to seat the face plate and ramp into the door jamb. In the present invention much less door jamb material is required to be removed to install the face plate because lip  62  wraps around door jamb  66  (see  FIG. 14 ) thereby requiring only nominal cutting of the edge  64  of door jamb  66  to accommodate the width of narrow notch  76  (about 1⅛ inches) and the depth  80  (about 7/16 inch) of narrow notch  76  below the about ⅛ inch cut-out  82  which is precut into standard prefabricated steel door jambs. Prior art face plates associated with electric strikes typically require a wider (3⅜ inches) notch  76  and/or a greater depth cut  80  (about ½ inch or more) within the door jamb to effect proper installation. A further advantage of face plate  60  is that lip  62  acts as a trim skirt to cover and hide from view that portion of the edge  64  of door jamb  66  which must be cut to accommodate installation of face plate  60 . This is of particular advantage in those instances where installation of face plate  60  is performed by a technician in a door jamb which has already been installed in a doorway and hence precise cutting of the door jamb, such as is possible in a factory, is unlikely to occur. 
   The installation advantages of face plate  60  and electric strike  10  of the present invention are further illustrated in  FIGS. 18  to  20  which depict the retrofitting of face plate  60  and electric strike  10  into a door jamb  66  constructed of aluminum. 
   Referring to  FIG. 18 , there is depicted an aluminum door jamb  66  and existing door jamb cut-out portion  102  sized to receive prior art face plate  100 . The dimensions of cut-out portion  102  are sized by the aluminum door jamb manufacturer to accommodate the dimensions of the doorframe hardware specified by the architect/designer or the owner of, for example, a retail establishment. The dimensions of the cut-out portion  102  are most commonly either 4⅝ inches in height (h) by 1 9/16 inches in width (w) (as shown in  FIG. 18 ) or 2⅝ inches in height (h) by 1 9/16 inches in width (w) (as shown in  FIG. 21 ) because these are the dimensions of the doorframe hardware of the largest selling U.S. manufacturer of such hardware for aluminum/glass doors. In either instance the cut-out depth (d) is generally 3/32-inches into sidewall  106  of door jamb  66 . 
   Oftentimes there is a need to increase the security of an access obstructing member, such as a door in a building. In such an instance, it becomes desirable to retrofit an electric strike and its associated face plate into the existing cut-out portion  102  of an aluminum door jamb. Although there are many different sizes which are available, two common sizes of face plates manufactured by the electric strike industry for use in aluminum frames are: (a) a face plate measuring 6⅞ inches in height (Y) by 1⅝ inches in width (X) which is designed for use in conjunction with an electric strike having a height (H) of 4⅝ inches; and (b) a face plate measuring 4⅞ inches in height (Y) by 1¼ inches in width (X) which is designed for use in conjunction with an electric strike having a height (H) of 2⅝ inches. Therefore, using these two common sizes as examples, to retrofit a 4⅝ inch electric strike required also retrofitting an electric strike face plate  104  having a height (Y) of 6⅞ inches (see  FIG. 19 ) into an existing aluminum door jamb cut-out portion  102  having a height (h) of 4⅝ inches. This required significant cutting of the door jamb  66  and associated door jamb sidewall  106  by the installation technician. As a consequence, the time and cost for the installation increased. Further, as can be observed in  FIGS. 18 and 19 , retrofitting an aluminum door jamb to accommodate a prior art face plate  104  having a height (Y) of 6⅞ inches and a width (X) of 1⅝ inches, along with its associated 4⅝ inch (H) electric strike requires that the height (h) of the prefabricated cut-out portion  102  be expanded from 4⅝ inches to 6⅞ inches. Additionally, the width (w) of the cut-out portion  102  needs to be expanded from 1 9/16 inches to 1⅝ inches and the depth (d) of the cut-out portion  102  needs to be increased from 3/32-inches to ⅞-inches along a length (l) of 3⅜ inches. In addition, either one or both of mounting tabs  108  for face plate  104  must be replaced and relocated and one or both of holes  110  for securing mounting tabs  108  to door jamb  66  must be redrilled. 
   By employing the electric strike  10  and face plate  60  of the present invention (see FIG.  20 ), the amount of cutting of door jamb  66  and door jamb sidewall  106  during retrofitting is significantly less. This is in part because face plate  60  of the present invention having a height (Y) of 4⅝ inches is designed to be installed into an aluminum door jamb with an electric strike  10  of the present invention having a height (H) of about 1 11/16 inches or of about 1 13/16 inches. Furthermore, face plate  260  of the present invention having a height (Y) of 2⅝ inches (see  FIG. 23 ) is designed to be installed into an aluminum door jamb with electric strike  10  of the present invention having a height (H) of about 1 11/16 inches or of about 1 13/16 inches. 
   Referring to  FIG. 20 , there is shown electric strike  10  and face plate  60  of the present invention. Face plate  60  has a height (Y) of 4⅝ inches. Retrofitting face plate  60  into an existing aluminum door jamb cut-out portion  102  having a height (h) of 4⅝ inches requires only nominal cutting of door jamb  66 . Neither the height (h) of the cut-out portion nor the width (w) of the cut-out portion needs to be expanded. Only the depth (d) of the cut-out portion needs to increased from 3/32-inches to ½-inch along a length (l) of 2 1/16 inches along sidewall  106 . Therefore, when utilizing the electric strike  10  and face plate  60  of the present invention, a savings of time and money for a retrofitting installation is realized when compared to the prior art. 
   The installation advantages of a further embodiment of face plate  260 , and electric strike  10 , of the present invention are additionally illustrated in  FIGS. 21  to  23  which depict the retrofitting of a further embodiment of face plate  260  and electric strike  10  into a door jamb  66  constructed of aluminum. 
   Referring to  FIG. 21 , there is depicted an aluminum door jamb  66  and existing door jamb cut-out portion  202  sized to receive prior art face plate  200 . The dimensions of cut-out portion  202  are sized by the aluminum door jamb manufacturer to accommodate the dimension of the doorframe hardware specified by the architect/designer. The dimensions of the cut-out portion  202  are about 2⅝ inches in height (h) by about 1 9/16 inches in width (w). The cut-out depth (d) is about 3/32 inches into sidewall  106  of door jamb  66 . 
   As can be observed in  FIGS. 21 and 22 , retrofitting an aluminum door jamb to accommodate a prior art face plate  204  having a height (Y) of 4⅞ inches and a width (X) of 1¼ inches, along with its asociated 2⅝ inch (H) electric strike requires that the height (h) of the prefabricated cut-out portion  202  be expanded from 2⅝ inches to 4⅞ inches. Additionally, the depth (d) of the cut-out portion  202 , needs to be increased from 3/32-inches to ⅞ inches along a length (l) of 3⅜ inches. In addition, either one or both of mounting tabs  108  for face plate  204  must be replaced and relocated and one or both holes  10  for securing mounting tabs  108  to doorjamb  66  must be redrilled. 
   By employing the electric strike  10  and face plate  260  of the present invention (see FIG.  23 ), the amount of cutting of door jamb  66  and door jamb sidewall  106  during retrofitting is significantly less. This is in part because face plate  260  of the present invention having a height (Y) of 2⅝ inches is designed to be installed into an aluminum door jamb with an electric strike  10  of the present invention having a height (H) of about 1 11/16 inches or of about 1 13/16 inches. 
   Referring to  FIG. 23 , there is shown electric strike  10  and face plate  260  of the present invention. Face plate  260  has a height (Y) of 2⅝ inches. Retrofitting face plate  260  into an aluminum door jamb cut-out portion  202  having a height (h) of 2⅝ inches requires only nominal cutting of door jamb  66 . Neither the height (h) of the cut-out portion nor the width (w) of the cut-out portion needs to be expanded. Only the depth (d) of the cut-out portion needs to be increased from 3/32-inches to ⅝-inches along a length (l) of 2⅝ inches along sidewall  106 . Therefore, when utilizing the electric strike  10  and face plate  260  of the present invention, a savings of time and money for retrofitting installation is realized when compared to the prior art. 
   Referring to  FIG. 17 , the face plate may optionally include dust shield  84 . The dust shield serves to prevent door jamb filler (typically cement, concrete, wood chips and the like) from entering the face plate channel  76  after installation of the face plate and electric strike into a door jamb and subsequently obstructing the travel of the latch bolt of an adjacent door (not shown) to the latch bolt keeper  18 . Dust shield  84  is constructed of aluminum, steel, or other metal and is connected to face plate  60  and the electric strike by screws or other connecting means. 
   An electronically-operable door strike and face plate is provided which readily avoids the problems and shortcomings associated with the prior art. The preferred embodiment has been illustrated and described. Further modifications and improvements may be made thereto as may occur to those skilled in the art and all such changes as fall within the true spirit and scope of this invention are to be included within the scope of the claims to follow.