A lock assembly includes a mounting fire plate configured for attachment to the door. A first lockset includes a lockset fire plate and a first operator assembly having a first operator handle. The first operator assembly is mounted to the lockset fire plate. At least one fusible link is configured to releasably couple the lockset fire plate of the first lockset to the mounting fire plate. The at least one fusible link is configured to melt during a fire condition to release the lockset fire plate from the mounting fire plate to facilitate a separation of the first lockset including the lockset fire plate from the mounting fire plate and the door by force of gravity.

CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a non-provisional application based upon U.S. provisional patent application Ser. No. 61/738,980, entitled “LOCK ASSEMBLY HAVING QUICK RELEASE DOUBLE FIRE PLATE”, filed Dec. 18, 2012, from which priority is claimed, and which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to door locks, and, more particularly, to a lock assembly having a quick release double fire plate. 
         [0004]    2. Description of the Related Art 
         [0005]    Some doors and associated lock assemblies, such as those used in commercial buildings, are designed to aid in protecting against the spread of fire by preventing the passage of fire from one room to another. In order to do so, a lock assembly may be designed to ensure that the associated door is maintained in a closed and latched state in the event of fire. In some such lock assemblies, pivot joints in the lock actuation linkage may be designed with internal fusible links which may be melted at fire temperatures to render the lock actuation linkage nonfunctional, and thus the door remains latched. However, in such a design it may be difficult to determine by direct observation whether the lock assembly has been rendered nonfunctional. 
         [0006]    What is needed in the art is a lock assembly configured to aid in preventing the spread of fire by providing a lock assembly having a quick release double fire plate. The present invention provides such a solution. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a lock assembly configured to aid in preventing the spread of fire by providing a lock assembly having a quick release double fire plate. 
         [0008]    The invention, in one form thereof, is directed to a lock assembly for use with a door. The lock assembly includes a mounting fire plate configured for attachment to the door. A first lockset includes a lockset fire plate and a first operator assembly having a first operator handle. The first operator assembly is mounted to the lockset fire plate. At least one fusible link is configured to releasably couple the lockset fire plate of the first lockset to the mounting fire plate. The at least one fusible link is configured to melt during a fire condition to release the lockset fire plate from the mounting fire plate to facilitate the separation of the first lockset including the lockset fire plate from the mounting fire plate and the door by force of gravity. 
         [0009]    The invention, in another form thereof, is directed to a lock assembly for use with a door. The lock assembly includes a latch assembly having a retractable bolt, and a spindle that drives the latch assembly. An exterior lockset is coupled to the door. The external lockset has an exterior operator assembly, a credential reader, and an exterior operator handle. The exterior lockset is configured such that the exterior operator handle is selectively coupled to the latch assembly. A mounting fire plate is attached to an interior of the door. An interior lockset has an interior operator assembly, a control electronics module, an interior operator handle, and a lockset fire plate to which is mounted the interior operator assembly and the control electronics module. The interior operator assembly is operatively coupled to the latch assembly via the spindle. The control electronics module is electrically connected to the credential reader. The control electronics module is configured to operatively couple the exterior operator handle to the latch assembly when a valid credential is read by the credential reader. At least one fusible link is configured to releasably couple the lockset fire plate of the interior lockset to the mounting fire plate. The at least one fusible link is configured to melt during a fire condition to release the lockset fire plate of the interior lockset from the mounting fire plate, and the mounting fire plate and the lockset fire plate are configured such that the interior lockset will fall in a direction away from the door by the force of gravity to decouple the interior lockset from the spindle that drives the latch assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0011]      FIG. 1  is a door edge view of a lock assembly in accordance with an embodiment of the present invention, installed on a door. 
           [0012]      FIG. 2  is a perspective view of the exterior lockset of the lock assembly of  FIG. 1 , as viewed from the exterior of the door. 
           [0013]      FIG. 3  is a perspective view of the interior lockset of the lock assembly of  FIG. 1 , as viewed from the interior of the door. 
           [0014]      FIG. 4  is a perspective view of the interior lockset of  FIG. 3 , with the escutcheon and battery cover removed. 
           [0015]      FIG. 5  is an exploded view of the interior lockset of  FIG. 4 , and showing the interior mounting fire plate and lockset fire plate, with the mounting fire plate attached to the door. 
           [0016]      FIG. 6  is an enlarged perspective view of a fusible link stud used in mounting the lockset fire plate of the interior lockset to the mounting fire plate that is attached to the door. 
           [0017]      FIG. 7  is a perspective view that shows the mounting fire plate remaining attached to the door after the interior lockset has fallen away following destruction of the fusible link studs. 
       
    
    
       [0018]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate an embodiment of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Referring now to the drawings and particularly to  FIGS. 1-3 , there is shown a lock assembly  10  in accordance with the present invention for mounting on a door  12 , and which includes an exterior lockset  14 , an interior lockset  16 , a latch assembly  18 , and a strike  20 . 
         [0020]    Exterior lockset  14  includes an exterior operator assembly  22 , a credential reader  24 , and an exterior escutcheon  26 . Exterior operator assembly  22  includes an exterior operator handle  28 . 
         [0021]    Interior lockset  16  includes an interior operator assembly  30 , a control electronics module  32 , an interior escutcheon  34 , and a battery cover  36 . Interior operator assembly  30  includes an interior operator handle  38 . Control electronics module  32  is electrically connected to credential reader  24  of exterior lockset  14 . 
         [0022]    As is customary in the art, latch assembly  18  is configured with a bolt actuator mechanism (not shown) and a retractable bolt  40 . 
         [0023]    Exterior lockset  14  is configured such that exterior operator handle  28  is selectively coupled to latch assembly  18 . In a locked condition, exterior operator handle  28  is decoupled from latch assembly  18 , and thus a rotation of exterior operator handle  28  does not result in a retraction of bolt  40 . In an unlocked condition, exterior operator handle  28  is coupled to latch assembly  18 , and thus a rotation of exterior operator handle  28  will result in a retraction of bolt  40 . 
         [0024]    The unlocked condition may be achieved by providing a valid credential, e.g., an RFID card, to be read by credential reader  24 , which in turn sends a signal to control electronics module  32 . Control electronics module  32  then compares the read credential to a database of stored authorized credentials, and if a match is found, responds by operatively coupling the exterior operator handle  28  to latch assembly  18  via a coupling mechanism (not shown). Additionally, exterior lockset  14  is provided with a mechanical override in the form of a key operated interchangeable keyed lock core  42 . 
         [0025]    Interior lockset  16  is configured such that during normal operation interior operator handle  38  is always operatively coupled to latch assembly  18 , such that a rotation of interior operator handle  38  always will result in a retraction of bolt  40 . However, in accordance with the present invention, interior lockset  16  is configured such that when a sufficient temperature is reached during a fire condition, then interior lockset  16  will release and fall in a direction away from door  12 , and thus will be decoupled from latch assembly  18 . 
         [0026]    Referring also to  FIG. 4 , with reference to  FIG. 3 , interior escutcheon  34  has been removed to expose the internal components and connections. Referring also to  FIG. 5 , an interior mounting fire plate  44  is mounted to the interior side of door  12  using permanent fasteners, such as steel screws. Interior lockset  16  includes an interior lockset fire plate  46  to which is mounted the interior operator assembly  30  and control electronics module  32  via fasteners  47 . 
         [0027]    In turn, lockset fire plate  46  is mounted by a temperature sensitive releasable coupling  48  to mounting fire plate  44 , wherein in the present embodiment the temperature sensitive releasable coupling  48  is a plurality, e.g., four as shown, of fusible links in the form of fusible studs collectively referenced by element number  48 , and individually identified as fusible stud  48 - 1 , fusible stud  48 - 2 , fusible stud  48 - 3 , and fusible stud  48 - 4 . The combination of the mounting fire plate  44 , lockset fire plate  46 , and fusible studs  48  fauns a quick release double fire plate arrangement. Each fusible stud  48  is made of durable non-steel material, such as zinc, aluminum, polymer, or other non-ferrous suitable alloy, having a melting point (temperature) lower than that of mounting fire plate  44  and lockset fire plate  46 . Mounting fire plate  44  and lockset fire plate  46  are made from a material, e.g., steel or similar alloy, having a higher melting point (temperature) than that of the fusible studs. Each fusible stud  48  is respectively held in position on lockset fire plate  46  with a corresponding retaining ring  50 , individually identified as retaining ring  50 - 1 , retaining ring  50 - 2 , retaining ring  50 - 3 , and retaining ring  50 - 4 . 
         [0028]    Referring to  FIG. 6 , there is shown an exemplary fusible stud  48 . Each fusible stud  48  includes a head portion  52 , a shaft portion  54 , and a retaining ring slot  56 . A diameter D1 of head portion  52  is larger than a diameter D2 of shaft portion  54 . Shaft portion  54  extends distally way from head portion  52  to define an annular shoulder  58 . The retaining ring slot  56  is formed as an annular groove around shaft portion  54 , with retaining ring slot  56  being axially spaced from head portion  52  to define an axial extent of shoulder  58 . Retraining ring slot  56  is configured to receive a corresponding retaining ring  50  in a clip-fastener relationship. 
         [0029]    Referring again to  FIGS. 4 and 5 , mounting fire plate  44  is formed as an elongate U-shaped channel that includes a base portion  60  and two side rails  62 ,  64  that project outwardly from base portion  60 . Side rail  62  is laterally spaced from side rail  64  across the lateral extent of base portion  60 . A longitudinal extent of mounting fire plate  44  is arranged to be vertical when mounting fire plate  44  is mounted on door  12 . Side rail  62  includes an angled edge  62 - 1  positioned at an upper portion of side rail  62 , which diverges outwardly and downwardly from base portion  60 . Side rail  64  includes an angled edge  64 - 1  positioned at an upper portion of side rail  64 , which diverges outwardly and downwardly from base portion  60 . 
         [0030]    Mounting fire plate  44  further includes four holes  66  configured to annularly receive the head portion  52  of respective fusible studs  48 . In particular, side rail  62  includes two longitudinally spaced holes  66 - 1 ,  66 - 2  and side rail  64  includes two longitudinally spaced holes  66 - 3 ,  66 - 4 . Holes  66 - 1 ,  66 - 2  are respectively sized to receive the head portion  52  of respective fusible studs  48 - 1 ,  48 - 2 . Holes  66 - 3 ,  66 - 4  are respectively sized to receive the head portion  52  of respective fusible studs  48 - 3 ,  48 - 4 . 
         [0031]    Lockset fire plate  46  is formed as an elongate U-shaped channel that includes a base portion  70  and four side tabs  72 ,  74 ,  76  and  78  that project outwardly from base portion  70 . Side tabs  72 ,  74  are laterally spaced from side tabs  76 ,  78  across the lateral extent of base portion  70 . Side tab  72  is longitudinally spaced from side tab  74 , and side tab  76  is longitudinally spaced from side tab  78 . Lockset fire plate  46 , including base portion  70  and side tabs  72 ,  74 ,  76  and  78 , is dimensioned to be received between side rail  62  and side rail  64  of mounting fire plate  44 . 
         [0032]    Side tab  72  has an outwardly projecting elongate member  72 - 1 , such as a screw, configured to engage in sliding contact the angled edge  62 - 1  of side rail  62  of mounting fire plate  44 . Also, side tab  76  has an outwardly projecting elongate member  76 - 1 , such as a screw, configured to engage in sliding contact the angled edge  64 - 1  of side rail  64  of mounting fire plate  44 . 
         [0033]    Lockset fire plate  46  further includes four holes  80  configured to receive the shoulder  58  of the shaft portion  54  of respective fusible studs  48 . In particular, side tab  72  includes a hole  80 - 1  and side tab  74  includes a hole  80 - 2  that respectively correspond to the longitudinally spaced holes  66 - 1 ,  66 - 2  of side rail  62 . Also, side tab  76  includes a hole  80 - 3  and side tab  78  includes a hole  80 - 4  that respectively correspond to the longitudinally spaced holes  66 - 3 ,  66 - 4  of side rail  64 . 
         [0034]    Each of holes  80 - 1 ,  80 - 2  is sized to receive the shoulder  58  of fusible stud  48 - 1  and fusible stud  48 - 2 , respectively, with the remainder of the shaft portion  54  of fusible studs  48 - 1 ,  48 - 2  passing through the respective side tabs  72 ,  74  to expose the retaining ring slots  56  for receiving respective retaining rings  50 - 1 ,  50 - 2 . Each of holes  80 - 3 ,  80 - 4  is sized to receive the shoulder  58  of fusible stud  48 - 3  and fusible stud  48 - 4 , respectively, with the remainder of the shaft portion  54  of fusible studs  48 - 3 ,  48 - 4  passing through respective side tabs  76 ,  78  to expose the retaining ring slots  56  for receiving respective retaining rings  50 - 3 ,  50 - 4 . 
         [0035]    Stated differently, when assembled, side tab  72  of lockset fire plate  46  is interposed between head portion  52  of fusible stud  48 - 1  and retaining ring  50 - 1 , with head portion  52  of fusible stud  48 - 1  projecting outwardly from lockset fire plate  46  to engage hole  66 - 1  of mounting fire plate  44 . Likewise, side tab  74  of lockset fire plate  46  is interposed between head portion  52  of fusible stud  48 - 2  and retaining ring  50 - 2 , with head portion  52  of fusible stud  48 - 2  projecting outwardly from lockset fire plate  46  to engage hole  66 - 2  of mounting fire plate  44 . Side tab  76  of lockset fire plate  46  is interposed between head portion  52  of fusible stud  48 - 3  and retaining ring  50 - 3 , with head portion  52  of fusible stud  48 - 3  projecting outwardly from lockset fire plate  46  to engage hole  66 - 3  of mounting fire plate  44 . Side tab  78  of lockset fire plate  46  is interposed between head portion  52  of fusible stud  48 - 4  and retaining ring  50 - 4 , with head portion  52  of fusible stud  48 - 4  projecting outwardly from lockset fire plate  46  to engage hole  66 - 4  of mounting fire plate  44 . 
         [0036]    In accordance with the present invention, the mounting fire plate  44 /lockset fire plate  46  configuration described above provides a quick release double fire plate design that allows interior lockset  16  on the non-keyed side of door  12  to release and fall away quickly in the case of a fire. For example, each of mounting fire plate  44  and lockset fire plate  46  may be made of steel material, and are held together only with the non-steel fusible studs  48 . In case of a fire, lockset fire plate  46  will be released from and will separate from mounting fire plate  44  because the non-steel fusible studs  48  melt away. 
         [0037]    As the lockset fire plate  46  begins to fall by the force of gravity, outwardly projecting elongate members  72 - 1 ,  76 - 1  of lockset fire plate  46  engage and slide along angled edges  62 - 1 ,  64 - 1  of mounting fire plate  44  that diverge, i.e., angle downwardly, away from door  12 , so as to force the upper portion of lockset fire plate  46  to move away from the door, thus separating lockset fire plate  46  with interior lockset  16  from mounting fire plate  44  and door  12 . As such, referring to  FIGS. 5 and 7 , a spindle driver  82  of interior operator assembly  30  will decouple from the spindle  84  that drives latch assembly  18 , as interior lockset  16  falls by the effects of gravity to the floor. 
         [0038]    In addition, since control electronics module  32  of interior lockset  16  enables the operation of exterior lockset  14 , once interior lockset  16  falls off of door  12 , latch assembly  18  cannot be operated by either of exterior operator handle  28  or interior operator handle  38 . Thus, the door  12  remains latched and closed, which helps to prevent the spread of a fire. 
         [0039]    As shown in  FIG. 7 , once interior operator assembly  30  falls away, mounting fire plate  44  remains mounted to door  12 , thus reducing the size of any through hole through door  12  at spindle  84 . Thus, mounting fire plate  44  serves as a secondary fire plate which further helps to prevent the spread of a fire. 
         [0040]    Thus, the present invention advantageously allows the entire lockset  16  to fall away from the door  12  quickly in the case of a fire, thus disabling the actuation of the latch assembly  18 , while also allowing lockset  16  to be secure and strong during normal usage, and making it possible to determine by direct observation whether lock assembly  10  has been rendered nonfunctional. 
         [0041]    While this invention has been described with respect to embodiments of the invention, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.