Patent Publication Number: US-8979140-B2

Title: Latch with an automatic locking function for a double door

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a latch for a latch assembly and, more particularly, to a latch for a latch assembly for a double door, providing an automatic locking function while closing a follower door of the double door. 
     A double door generally includes a primary door and a follower door pivotably mounted to two vertical beams of a door frame. A lock is mounted to the primary door and includes a handle on a side of the primary door and a first latch on an end face of the primary door. The first latch can be retracted into the primary door upon pivotal movement of the handle. Upper and lower latch assemblies are mounted to upper and lower ends of the follower door. The upper latch assembly includes an actuation latch extending beyond an end face of the follower door and a second latch normally extending beyond an upper face of the follower door. The lower latch assembly includes an actuation latch extending beyond the end face of the follower door and a third latch normally extending beyond a bottom face of the follower door. When the follower door is moving from an open position to a closed position, each of the second and third latches is moved from an extended, latching position to a retracted, unlatching position. When the follower door is in the closed position, the second latch is engaged in a groove in the door frame, and the third latch is engaged in a groove in the ground, locking the follower door. Since the first latch of the lock on the primary door is engaged with a receptacle in the follower door, the primary door can not be opened, either. Thus, the double door can be reliably locked. However, if the primary door is closed while the follower door is not completely closed (namely, the second latch is not aligned with the groove in the door frame, and the third latch is not aligned with the groove in the ground), the second and third latches can not be moved to the exact latching positions, leading to damage to the upper and lower latch assemblies. Furthermore, the first, second, and third latches may be deformed by the heat during a fire and, thus, moved to the unlatching position, leading to the risks of opening of the double door and spread of the fire. 
     Thus, a need exists for a latch assembly providing an automatic locking function for a double door. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention solves this need and other problems in the field of reliable locking of a double door by providing, in a first aspect, a latch for a latch assembly including a body having a locking end and an engagement end spaced from the locking end along a first axis. The engagement end of the body is adapted to engage with a connecting rod of a latch assembly. The body further includes a transverse groove extending along a second axis perpendicular to the first axis. The body further includes a face extending between the locking end and the engagement end. An engagement hole extends from the face of the body to the transverse groove. The body further includes a longitudinal hole extending from the engagement end to the transverse groove. The latch is movable along the first axis between a latching position and an unlatching position. The locking end of the latch in the unlatching position is adapted to be received in a door. The locking end of the latch in the latching position is adapted to extend out of the door into a groove in a door frame or the ground. A stop is made of a material having a melting point lower than a melting point of the body of the latch. The stop is received in the engagement hole of the body. A first ear is pivotably received in the transverse groove of the body. The first ear includes first and second ends spaced from each other along the first axis. The first ear further includes an inner side extending between the first and second ends. The first ear is pivotable between a storage position in the transverse groove and a blocking position partially extending out of the transverse groove. A pressing pin is received in the longitudinal hole and slideable along the first axis between a pressing position and a non-pressing position. A spring is mounted in the longitudinal hole. The spring biases the pressing pin to press against the inner side of the first ear and biasing the pressing pin from the non-pressing position to the pressing position. 
     When the first ear is in the storage position and the pressing pin is in the non-pressing position, the latch is pivotable between the latching and unlatching positions. When the latch is in the latching position and the first ear is in the storage position, if the stop is melted by heat, the pressing pin is moved by the spring from the non-pressing position to the pressing position and presses against the inner side of the first ear to pivot the first ear from the storage position to the blocking position, retaining the latch in the latching position. 
     In an embodiment, a second ear is pivotably received in the transverse groove of the body. The second ear includes first and second ends spaced from each other along the first axis. The second ear further includes an inner side extending between the first and second ends of the second ear. The second ear is pivotable between a storage position in the transverse groove and a blocking position partially extending out of the transverse groove. Each of the first and second ears further includes a coupling groove in the inner side thereof. The coupling groove has a limiting face. The coupling groove of the first ear divides the inner side of the first ear into a stop portion and a push portion. The coupling groove of the second ear divides the inner side of the second ear into a stop portion and a push portion. 
     When the first and second ears are in the storage positions and the pressing pin is in the non-pressing position, an outer end of the pressing pin presses against the push portions of the first and second ears, and the stop is sandwiched between and pressed against by the stop portions of the first and second ears. 
     When the first and second ears are in the blocking positions, the stop portions of the first and second ears press against each other, and the outer end of the pressing pin is received in the coupling grooves of the first and second ears. The limiting faces of the first and second ears press against the outer end of the pressing pin, preventing the first and second ears from pivoting from the blocking positions to the storage positions. 
     In a second aspect, a latch assembly includes a base having two sidewalls and an intermediate wall extending between the sidewalls. Each sidewall includes a movement groove and first and second engagement holes. The movement groove is located between the first engagement hole and the second engagement hole along a first axis. The intermediate wall includes a slot. The intermediate wall of the base is adapted to be mounted to an end face of a follower door of a double door. The sidewalls are adapted to be received in an interior space of the follower door. The follower door is pivotable between a closed position and an open position. 
     A movable member is movably received between the sidewalls of the base. The movable member includes two lateral walls spaced from each other along a second axis perpendicular to the first axis. The movable member further includes a connecting portion extending between the lateral walls. Each lateral wall includes a first end and a second end spaced from the first end along the first axis. First and second sliding grooves are defined in each lateral wall. The first sliding groove is located between the second sliding groove and the connecting portion along a third axis perpendicular to the first and second axes. The movement grooves of the sidewalls of the base are aligned with the first sliding grooves of the lateral walls of the movable member. 
     A first pin extends through the movement grooves of the sidewalls of the base and the first sliding grooves of the lateral walls of the movable member. A second pin extends through the first engagement holes of the sidewalls of the base and the second sliding grooves of the lateral walls of the movable member. The movable member is movable between an engagement position and a disengagement position along the first axis. 
     A follower is pivotably connected to the movable member. The follower includes an arm having first and second ends. The first pin extends through the first end of the arm, allowing the follower to pivot about a pivot axis defined by the first pin. An actuation member is pivotably received in the base and has first and second ends and a pivotal portion between the first and second ends of the actuation member. The second end of the actuation member faces the intermediate wall of the base. 
     A locking block is mounted between the lateral walls of the movable member. The locking block and the movable member are jointly movable between the disengagement position and the engagement position. A first spring is mounted between the locking block and the first pin. The first spring biases the locking block and the first pin away from each other along the first axis. 
     A limiting frame is fixed between the sidewalls of the base. The limiting frame includes a first wall and a second wall spaced from the first wall along the first axis. The limiting frame further includes a connecting wall extending between the first and second walls. The first wall includes an inner face and an outer face spaced from the inner face along the first axis. A slot extends from the inner face through the outer face of the first wall. The first and second walls are fixed to the intermediate wall of the base. The second end of the actuation member extends through the slot and is received between the first and second walls. 
     An actuation latch is movably received in the slot of the base. The actuation latch includes a base portion having first and second ends spaced from each other along the third axis. A wedge is formed on the second end of the actuation latch and has two actuation faces. The actuation latch is movable along the third axis between a releasing position in which the wedge is located outside of the base and a pressing position in which the wedge is received in the base. The actuation latch is adapted to be actuated by an end face of a primary door of the double door. When the follower door is in the closed position and the end face of the primary door is aligned with the end face of the follower door, the end face of the primary door presses against the actuation latch, moving the actuation latch from the releasing position to the pressing position. 
     A connecting rod includes a first end engaged with the locking block and a second end. A latch includes a body having a locking end and an engagement end spaced from the locking end along the first axis. The engagement end of the latch is engaged with the second end of the connecting rod. The body further includes a transverse groove extending along the second axis perpendicular to the first axis. The body further includes a face extending between the locking end and the engagement end. An engagement hole extends from the face of the body to the transverse groove. The body further includes a longitudinal hole extending from the engagement end to the transverse groove. The latch is movable along the first axis between a latching position and an unlatching position. The locking end of the latch in the unlatching position is adapted to be received in the follower door. The locking end of the latch in the latching position is adapted to extend out of the follower door into a groove in a door frame or the ground. 
     The latch further includes a stop made of a material having a melting point lower than a melting point of the body of the latch. The stop is received in the engagement hole of the body. A first ear is pivotably received in the transverse groove of the body. The first ear includes first and second ends spaced from each other along the first axis. The first ear further includes an inner side extending between the first and second ends. The first ear is pivotable between a storage position in the transverse groove and a blocking position partially extending out of the transverse groove. A pressing pin is received in the longitudinal hole and slideable along the first axis between a pressing position and a non-pressing position. A second spring is mounted in the longitudinal hole. The second spring biases the pressing pin to press against the inner side of the first ear and biases the pressing pin from the non-pressing position to the pressing position. 
     When first ear is in the storage position and the pressing pin is in the non-pressing position, the latch is pivotable between the latching and unlatching positions. 
     When the latch is in the latching position and the first ear is in the storage position, if the stop is melted by heat, the pressing pin is moved by the second spring from the non-pressing position to the pressing position and presses against the inner side of the first ear to pivot the first ear from the storage position to the blocking position, retaining the latch in the latching position. 
     When the follower door is in the open position, the latch is not aligned with the groove in the door frame or ground. When the follower door is in the closed position, the latch is aligned with the groove in the door frame or ground. 
     When the actuation latch is in the releasing position, the movable member is in the disengagement position, and the latch is in the unlatching position. 
     When the follower door is in the closed position and the actuation latch moves from the releasing position to the pressing position, the first end of the actuation latch pushes the second end of the actuation member to move the second end of the follower, causing the first pin to push the locking block via the first spring, moving the movable member from the disengagement position to the engagement position while pulling the first spring, thereby moving the locking end of the latch to the latching position to engage with the groove in the door frame or ground. 
     When the actuation latch is moved from the releasing position to the pressing position while the follower door is not in the closed position, the actuation member actuates the follower via the push pin, moving the first pin in the movement grooves of the base along the first axis and compressing the first spring, retaining the movable member in the disengagement position and retaining the latch in the unlatching position to avoid damage to the latch assembly. 
     The present invention will become clearer in light of the following detailed description of an illustrative embodiment of this invention described in connection with the drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The illustrative embodiment may best be described by reference to the accompanying drawings where: 
         FIG. 1  shows a diagrammatic front view of a double door to which two latch assemblies according to the present invention is mounted. 
         FIG. 2  shows an exploded, perspective view of one of the latch assemblies of  FIG. 1 . 
         FIG. 3  shows an exploded, perspective view of a latch of the latch assembly of  FIG. 2 . 
         FIG. 4  shows a partial, perspective view of the double door of  FIG. 1 . 
         FIG. 5  shows a cross sectional view taken along section line  5 - 5  of  FIG. 4 . 
         FIG. 5A  shows a cross sectional view taken along section line  5 A- 5 A of  FIG. 5 . 
         FIG. 6  shows a cross sectional view taken along section line  6 - 6  of  FIG. 5 . 
         FIG. 7  shows a cross sectional view taken along section line  7 - 7  of  FIG. 7 . 
         FIG. 8  shows a view similar to  FIG. 5 , with a primary door closed, and with a latch engaged in a groove in a door frame for the double door. 
         FIG. 9  shows across-sectional view taken along section line  9 - 9  of  FIG. 8 . 
         FIG. 10  shows a view similar to  FIG. 9 , with two ears of the latch moved from storage positions to blocking positions during a fire. 
         FIG. 11  shows a view similar to  FIG. 5 , with the latch not aligned with the groove of the door frame, and with the primary door moved to a closed position. 
     
    
    
     All figures are drawn for ease of explanation of the basic teachings of the present invention only; the extensions of the Figures with respect to number, position, relationship, and dimensions of the parts to form the preferred embodiment will be explained or will be within the skill of the art after the following teachings of the present invention have been read and understood. Further, the exact dimensions and dimensional proportions to conform to specific force, weight, strength, and similar requirements will likewise be within the skill of the art after the following teachings of the present invention have been read and understood. 
     Where used in the various figures of the drawings, the same numerals designate the same or similar parts. Furthermore, when the terms “first”, “second”, “third”, “fourth”, “lower”, “upper”, “top”, “bottom”, “inner”, “outer”, “end”, “portion”, “section”, “vertical”, “length”, and similar terms are used herein, it should be understood that these terms have reference only to the structure shown in the drawings as it would appear to a person viewing the drawings and are utilized only to facilitate describing the invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a double door  257  mounted to a door frame  31  on a floor or ground  299 . Door frame  31  includes two spaced vertical beams  33  on ground  299  and a top beam  35  extending between upper ends of vertical beams  33 . Top beam  35  includes a bottom side having a groove  37 . A groove  300  is defined in ground  299  and aligned with groove  37  of top beam  35 . 
     In the form shown, double door  257  includes a primary door  259  pivotably mounted to one of vertical beams  33  and a follower door  275  pivotably mounted to the other vertical beam  33 . Follower door  275  includes an interior space  293 . Primary door  259  includes two sides  271  and an end face  273  extending between sides  271  and extending perpendicularly to ground  299 . Follower door  275  includes two sides  276 , a top face  277  extending between sides  276  and facing top beam  35 , and a bottom face  279  extending between sides  276  and facing ground  299 . Each of top face  277  and bottom face  279  includes a mounting hole  295  in communication with interior space  293 . Follower door  275  further includes an end face  291  extending between sides  276  and between top and bottom faces  277  and  279 . Two engagement holes  297  are defined in end face  291  of follower door  275  and spaced from each other along a first axis X perpendicular to ground  299 . A receptacle  294  is defined in end face  291  and located intermediate engagement holes  297 . 
     Follower door  275  is pivotable about an axis parallel to first axis X between an open position and a closed position. When follower door  275  is in the open position, mounting holes  295  are not aligned with grooves  37  and  300 . When follower door  275  is in the closed position, mounting hole  295  in top face  277  is aligned with groove  37 , and mounting hole  295  in bottom face  279  is aligned with groove  300  in ground  299 . 
     A door lock  319  is mounted to primary door  259 . Door lock  319  can be of any desired form as conventional including but not limited to of a commercially available type. In the form shown, door lock  319  includes a latch  333  and a handle  331  operatively connected to latch  333 . Handle  331  is located on one of sides  271  of primary door  259 . Pivotal movement of handle  331  causes movement of latch  333  from an extended position outside of end face  273  of primary door  259  to a retracted position inside of primary door  259 . When follower door  275  is in the closed position, end face  273  of primary door  259  is aligned with end face  291  of follower door  275 , with a gap existed between end faces  273  and  291 , and with latch  333  engaged in receptacle  294  of follower door  275 . 
     According to the form shown, upper and lower coupling members  237  are respectively mounted in mounting holes  295  of follower door  275  ( FIG. 4 ). Each of upper and lower coupling members  237  includes a first portion  239 , a second portion  251 , and a third portion  253 . Second portion  251  extends perpendicularly to an end of first portion  239  and an end of third portion  253 , with first and third portions  239  and  253  parallel to and spaced from each other along first axis X. A receiving hole  255  is defined in each of first and third portions  239  and  253 , with receiving hole  255  of first portion  239  aligned with receiving hole  255  of third portion  253 . First portion  239  of upper coupling member  237  is fixed to top face  277  of follower door  275 , with second and third portions  251  and  253  of upper coupling member  237  extending through mounting hole  295  into interior space  293  of follower door  275 . First portion  239  of lower coupling member  237  is fixed to bottom face  279  of follower door  275 , with second and third portions  251  and  253  of lower coupling member  237  extending through mounting hole  295  into interior space  293  of follower door  275 . 
     In the form shown, two latch assemblies  10  are mounted in locations respectively adjacent to top and bottom faces  277  and  279  of follower door  275  and arranged in a symmetric manner relative to a horizontal plane that is perpendicular to first axis X, with receptacle  294  and latch  333  located in the horizontal plane. Each latch assembly  10  includes a base  20  ( FIG. 2 ) having two sidewalls  22  spaced along a second axis Y perpendicular to first axis X and an intermediate wall  38  extending between sidewalls  22 . Each sidewall  22  includes a first end  24  and a second end  26  spaced from first end  24  along first axis X. Each sidewall  22  further includes a movement groove  32  located between first and second ends  24  and  26 , a first engagement hole  28  located between first end  24  and movement groove  32 , and a second engagement hole  30  located in second end  26 . A slot  36  is defined in intermediate wall  38  and adjacent to second end  26  of each sidewall  22 . Slot  36  includes two edges spaced along first axis X, with a first engagement groove  42  defined in each edge of first slot  36 . Each sidewall  22  further includes a second engagement groove  44  in second end  26 . A hooked portion  40  is formed on intermediate wall  38  and located between movement groove  32  and slot  36  along first axis X and located in a space defined by sidewalls  22  and intermediate wall  38 . 
     In the form shown, a faceplate  46  is mounted to intermediate wall  38  and includes an opening  48  aligned with slot  36 . Screws are extended through faceplate  46  and intermediate wall  38  into end face  291  of follower door  275 . Intermediate wall  38  of base  20  and faceplate  46  of each latch assembly  10  are engaged in one of engagement holes  297  of follower door  275  ( FIGS. 4 and 5 ), with sidewalls  22  received in interior space  293  of follower door  275 , with first end  24  of each sidewall  22  of an upper one of latch assemblies  10  facing top beam  35 , and with first end  24  of each sidewall  22  of a lower one of latch assemblies  10  facing ground  299  ( FIG. 1 ). 
     According to the form shown, each latch assembly  10  further includes a movable member  50  movably received between sidewalls  22  of base  20 . Movable member  50  includes two lateral walls  52  spaced from each other along second axis Y and a connecting portion  66  extending between lateral walls  52 . Each lateral wall  52  includes a first end  54  and a second end  56  spaced from first end  54  along first axis X. Each lateral wall  52  further includes a first sliding groove  58  adjacent to second end  56  and a second sliding groove  60  adjacent to first end  54 , with first sliding groove  58  located between second sliding groove  60  and connecting portion  66  along a third axis Z perpendicular to first and second axes X and Y. Each lateral wall  52  further includes a mounting hole  64  in first end  54  and an engagement notch  62  in second end  56 . Connecting portion  66  includes a lug  70  adjacent to first end  54  of each lateral wall  52  and an engagement slot  68 , with lug  70  located between second end  56  of lateral wall  52  and engagement slot  68 . Lateral walls  52  of movable member  50  are received between sidewalls  22  of base  20 , with first sliding grooves  58  of lateral walls  52  aligned with movement grooves  32  of sidewalls  22 , with first engagement holes  28  of sidewalls  22  aligned with second sliding grooves  60  of lateral walls  52 , with connecting portion  66  facing intermediate wall  38 , and with lug  70  spaced from hooked portion  40  along first axis X. 
     In the form shown, each latch assembly  10  further includes a first pin  88  extending through movement grooves  32  of sidewalls  22  of base  20  and first sliding grooves  58  of lateral walls  52  of movable member  50 . Each latch assembly  10  further includes a second pin  89  extends through first engagement holes  28  of sidewalls  22  of base  20  and second sliding grooves  60  of lateral walls  52  of movable member  50 . Thus, movable member  50  is movable along first axis X between a disengagement position ( FIG. 5 ) and an engagement position ( FIG. 8 ). A spacing between lug  70  of movable member  50  in the disengagement position and hooked portion  40  of base  20  is smaller than a spacing between lug  70  of movable member  50  in the engagement position and hooked portion  40  of base  20 . Second sliding grooves  60  provide room for movement of second pin  89  while movable member  50  is moving between the engagement position and disengagement position. 
     According to the form shown, each latch assembly  10  further includes a spring  72  including a first end  74  attached to lug  70  and a second end  76  attached to hooked portion  40 , biasing movable member  50  from the engagement position to the disengagement position. 
     According to the form shown, each latch assembly  10  further includes a follower  78  pivotably connected to movable member  50 . Follower  78  includes two arms  85  spaced from each other along second axis Y and a connecting section  86  extending between arms  85 . Each arm  85  has first and second ends  82  and  84 . First pin  88  extends through first ends  82  of arms  85  of follower  78 , allowing follower  78  to pivot about a pivot axis defined by first pin  88 . Furthermore, follower  78  is movable together with first pin  88  in a length of each of first sliding grooves  58  and movement grooves  32  along first axis X. 
     According to the form shown, each latch assembly  10  further includes an actuation member  90  mounted in base  20  and having first and second ends  92  and  94  and a pivotal portion  96  between first and second ends  92  and  94 . A third pin  91  extends through second engagement holes  30  of sidewalls  22  of base  20  and pivotal portion  96  of actuation member  90 , allowing actuation member  90  to pivot about a pivot axis defined by third pin  91 . First end  92  of actuation member  90  is located between arms  85  of follower  78 . A push pin  98  is extended through second ends  84  of arms  85  of follower  78  and first end  92  of actuation member  90 , allowing follower  78  and actuation member  90  to pivot about a pivot axis defined by push pin  98 . Pivotal movement of actuation member  90  causes movement of follower  78  along first axis X. 
     According to the form shown, each latch assembly  10  further includes a limiting frame  101  fixed between sidewalls  22  of base  20  and having substantially U-shaped cross sections. Limiting frame  101  includes a first wall  103  and a second wall  113  spaced from first wall  103  along first axis X. Limiting frame  101  further includes a connecting wall  119  extending between first and second walls  103  and  113 . First wall  103  includes an inner face  103 A and an outer face  103 B spaced from inner face  103 A along first axis X. A slot  111  extends from inner face  103 A through outer face  103 B. A first engagement protrusion  115  is formed on a distal edge of each of first and second walls  103  and  113 . Each of first and second walls  103  and  113  includes two lateral edges spaced along second axis Y. A second engagement protrusion  117  is formed on each lateral edge of second wall  113 . Two wings  105  respectively extend from the lateral edges of first wall  103 , with each wing  105  having a pivot hole  109 . 
     In the form shown, each first engagement protrusion  115  of limiting frame  101  is engaged with one of first engagement grooves  42  of base  20 . Each second engagement protrusion  117  of limiting frame  101  is engaged with one of second engagement grooves  44  of base  20 . Thus, first and second walls  103  and  113  of limiting frame  101  are flush with the edges of slot  36 . Pivot holes  109  of limiting frame  101  are aligned with second engagement holes  30  of base  20 . Third pin  91  extends through pivot holes  109 , second engagement holes  30 , and pivotal potion  96  of actuation member  90 , fixing limiting frame  101  between sidewalls  22  of base  20 , with pivotal portion  96  of actuation member  90  located between wings  105 , with second end  94  of actuation member  90  extending through slot  111  and received between first and second walls  103  and  113 , with first end  92  of actuation member  90  located between first wall  103  of limiting frame  101  and movement grooves  32  of base  20  along first axis X. 
     According to the form shown, each latch assembly  10  further includes an actuation latch  131  movably received in slot  36  of base  20 . Actuation latch  131  includes a base portion  132  having a first end  133  and a second end  137  spaced from first end  133  along third axis Z. Second end  137  of base portion  132  includes a first end portion  136  and a second end portion  136  spaced from first end portion  136  along second axis Y. A wedge  134  is formed on second end  137  and located between first and second end portions  136 . Wedge  134  includes substantially triangular cross sections and includes two actuating faces  135  meeting at an edge, with each actuating face  135  having an end intersecting with second end  137 , and with actuating faces  135  located between first and second end portions  136  along second axis Y. Actuation latch  131  is located between first and second walls  103  and  113  of limiting frame  101 , with base portion  132  located between sidewalls  22  of base  20 . A width between first and second end portions  136  along second axis Y is larger than a width of slot  36  of base  20  along second axis Y. Wedge  134  extends through slot  36  of base  20 . Actuation latch  131  is movable along third axis Z between a releasing position in which wedge  134  extends out of base  20  ( FIG. 5 ) and a pressing position in which wedge  134  is received in base  20  ( FIG. 8 ). When actuation latch  131  is in the releasing position, second end  137  abuts the inner face of intermediate wall  38  of base  20 . 
     According to the form shown, each latch assembly  10  further includes a locking block  139  mounted between lateral walls  52  of movable member  50 . Locking block  139  includes a body  151  having a first surface  152  and a second surface  154  spaced from first surface  152  along first axis X. Locking block  139  further includes third and fourth surfaces  156  and  158  extending between first and second surfaces  152  and  154 , with third and fourth surfaces  156  and  158  spaced from each other along third axis Z. A locking hole  153  in the form of a screw hole extends from first surface  152  through second surface  154 . However, instead of a through-hole in the form shown, locking hole  153  can be defined in first surface  152  but spaced from second surface  154 . A projection  155  is formed on third surface  156 , and an engagement portion  157  is formed on fourth surface  158 . Engagement portion  157  includes an engagement hole  159  extending along second axis Y. Locking hole  153  is located between projection  155  and engagement hole  159 . Projection  155  is engaged in engagement slot  68  of movable member  50 , with third surface  156  abutting an inner face of connecting portion  66 , with engagement hole  159  of locking block  139  aligned with mounting holes  64  of lateral walls  52  of movable member  50 . Locking block  139  is jointly movable with movable member  50  between the engagement position and the disengagement position along first axis X. 
     According to the form shown, latch assembly  10  further includes a restraining member  177  mounted in movable member  50 . Restraining member  177  includes two sides  193  spaced from each other along second axis Y. Restraining member  177  further includes a limiting face  195  that is arcuate and extends between sides  193 . Each side  193  includes a first end  179  and a second end  191  spaced from first end  179  along first axis X. Each side  193  further includes a slot  211  between first and second ends  179  and  191 . A mounting hole  199  is defined in first end  179  of each side  193 , with slot  211  located between second end  191  and mounting hole  199 . A space  197  is defined between first ends  179  of sides  193  of restraining member  177  and spaced from slot  211 . A protuberance  213  is formed on second end  191  of each side  193  of restraining member  177 . 
     First ends  179  of sides  193  of restraining member  177  are engaged with locking block  139 , with engagement portion  157  received in space  197 , with engagement hole  159  aligned with mounting holes  199 , with each protuberance  213  engaged in one of engagement notch  62  of movable member  50 . Second pin  89  extends through first engagement holes  28  of base  20 , second sliding grooves  60  of movable member  50  and slots  211  of restraining member  177 . Second pin  89  moves in slots  211  while restraining member  177  and movable member  50  jointly move between the engagement position and the disengagement position. 
     According to the form shown, each latch assembly  10  further includes an engagement pin  515  extending through mounting holes  64  of movable member  50 , mounting holes  199  of restraining member  177 , and engagement hole  159  of locking block  139 . Thus, movable member  50 , locking lock  139 , and restraining member  177  are connected together by engagement pin  515  and jointly movable along first axis X between the disengagement position ( FIG. 5 ) and the engagement position ( FIG. 8 ). 
     According to the form shown, each latch assembly  10  further includes a spring  171  mounted between locking block  139  and first pin  88  and received in a space defined between lateral walls  52  of movable member  50  and located between connecting portion  66  of movable member  50  and limiting face  195  of restraining member  177 . Spring  171  includes a first end  173  abutting against second surface  154  of locking block  139  and a second end  175  abutting against first pin  88 . Spring  171  biases locking block  139  and first pin  88  away from each other along first axis X. 
     According to the form shown, each latch assembly  10  further includes a connecting rod  215  engaged with locking block  139 . Specifically, connecting rod  215  includes a first end  217  having an outer thread engaged with locking hole  153  of locking block  139 , allowing joint movement of connecting rod  215  and locking block  139 . Connecting rod  215  further has a second end  219 . 
     According to the form shown, each latch assembly  10  further includes a latch  411  connected to second end  219  of connecting rod  215 . Latch  411  includes a body  413  having a locking end  415  and an engagement end  417  spaced from locking end  415  along first axis X. Body  413  further includes two first faces  419  spaced from each other along second axis Y. Body  413  further includes two second faces  431  spaced from each other along third axis Z. A transverse groove  433  extends from one of first faces  419  through the other first faces  419  and is located between locking end  415  and engagement end  417  along first axis X. Transverse groove  433  includes an outer end face  433 A and an inner end face  433 B spaced from outer end face  433 A along first axis X. Body  413  further includes an engagement hole  435  and two pivot holes  437 . Each of engagement hole  435  and pivot holes  437  extends from one of second faces  431  through the other second face  431  along third axis Z. Engagement hole  435  extends through outer end face  433 A of transverse groove  433  and is located between pivot holes  437  along second axis Y. Each pivot hole  437  is located between outer end face  433 A and inner end face  433 B of transverse groove  433  along first axis X. Body  413  further includes a longitudinal hole  439  extending from an end face of locking end  415  through inner end face  433 B of transverse groove  433  along first axis X. Longitudinal hole  439  includes a first portion  451  contiguous to inner end face  433 B of transverse groove  433  and a second portion  453  having an inner thread threadedly engaged with second end  219  of connecting rod  215 . Body  413  of latch  411  is jointly movable with connecting rod  215  along first axis X between a latching position and an unlatching position. 
     According to the form shown, latch  411  further includes a stop  495  fixed in engagement hole  435  of body  41 . Stop  495  is made of plastic or a metal (such as tin alloy) having a melting point lower than a melting point of body  413 . A pivot  493  is mounted in each pivot hole  437 . 
     According to the form shown, latch  411  further includes two ears  455  pivotably received in transverse groove  433  of body  413 . Each ear  455  includes first and second ends  457  and  459  and inner and outer sides  471  and  477  extending between first and second ends  457  and  459 . In the form shown, inner side  471  is convex and includes a coupling groove  479  having a limiting face  480 . Coupling groove  479  divides inner side  471  into a stop portion  473  and a push portion  475 , with coupling groove  479  located between stop portion  473  and push portion  475  along first axis X. A pivotal groove  491  is defined in outer side  477  of each ear  455  and located between first end  457  and coupling groove  479  along first axis X ( FIG. 5A ). 
     Ears  455  are received in transverse groove  433  of body  413 , with each pivot  493  pivotably received in pivotal groove  491  of one of ears  455 . Thus, each ear  455  is pivotable about a corresponding pivot  493  between a storage position ( FIGS. 5 ,  5 A, and  8 ) and a blocking position ( FIG. 10 ). When ears  455  are in the storage position, ears  455  are located in transverse groove  433 . Stop  495  is located between first ends  457  of ears  455  along second axis Y ( FIG. 5A ). Furthermore, stop portion  473  of each ear  455  presses against an outer periphery of stop  495 . In this case, ears  455  can not pivot towards the blocking position. On the other hand, when ears  455  are in the blocking position, second end  459  of each ear  455  extends out of transverse groove  433  and beyond a corresponding first face  419  (first faces  419  are located between second ends  459  of ears  455  along second axis Y). 
     According to the form shown, latch  411  further includes a pressing pin  497  slideably received in longitudinal hole  439  of body  413 . Pressing pin  497  includes outer and inner ends  499  and  511 . Pressing pin  497  is received in first portion  451  of longitudinal hole  439 , and outer end  499  of pressing pin  497  faces ears  455 . Pressing pin  497  is movable along first axis X between a non-pressing position ( FIGS. 5 ,  5 A,  8 , and  8 ) and a pressing position ( FIG. 10 ). Pressing pin  497  in the non-pressing position is located between second ends  459  of ears  455 . 
     According to the form shown, latch  411  further includes a spring  513  mounted in longitudinal hole  439  and between inner end  511  of pressing pin  497  and second end  219  of connecting rod  215 . Spring  513  biasing outer end  499  of pressing pin  497  to press against push portions  475  of ears  455 . When ears  455  are in the storage position ( FIG. 5A ), outer end  499  of pressing pin  497  is sandwiched between second ends  459  of ears  455  while stop  495  is sandwiched between first ends  457  of ears  455 . Thus, ears  455  are positioned in the storage position, and stop  495  prevents ears  455  from pivoting from the storage position to the blocking position. 
     Now that the basic construction of latch assemblies  10  has been explained, the operation and some of the advantages of latch assemblies  10  can be set forth and appreciated. In particular, for the sake of explanation, only the detailed operation of upper latch assembly  10  will be described, and it will be assumed that primary door  259  is in an open position and the follower door  275  is in the closed position ( FIG. 5 ). Receiving holes  255  of upper coupling member  237  are aligned with groove  37  of top beam  35  of door frame  31 . Note that receiving holes  255  of lower coupling member  237  are aligned with groove  300  in ground  299 . End face  273  of primary door  259  is not aligned with end face  291  of follower door  275 . Actuation latch  131  of each latch assembly  10  is not pressed and is in the releasing position ( FIG. 5 ). Movable member  50  is in the disengagement position. Latch  411  is in the unlatching position. In this case, second ends  459  of ears  455  are located below third portion  253  of upper coupling member  237  along first axis X. 
     When primary door  259  is moved to a closed position, end face  273  of primary door  259  is aligned with end face  291  of follower door  275 , latch  333  is received in receptacle  294  of follower door  275 , end face  273  of primary door  259  presses against one of actuating faces  135  of actuation latch  131 , causing actuation latch  131  to move along third axis Z from the releasing position to the pressing position. First end  133  of actuation latch  131  presses against second end  94  of actuation member  90 , causing pivotal movement of actuation member  90  about the pivot axis defined by third pin  91 . First end  92  of actuation member  90  pushes push pin  98  and, thus, pushes first ends  82  of arms  85  of follower  78 , causing pivotal movement of follower  78  about the pivot axis defined by push pin  98 . First pin  88  received in movement grooves  32  of base  20  is pushed by first ends  82  of arms  85  of follower  78  to move along first axis X in a direction away from hooked portion  40 . Thus, first pin  88  presses against second end  175  of spring  171 , causing first end  173  of spring  171  to press against locking block  139 , which, in turn, causes movement of movable member  50  via engagement pin  515 . Thus, movable member  50 , locking block  139 , spring  171 , engagement pin  515 , and restraining member  177  move jointly from the disengagement position ( FIG. 5 ) to the disengagement position ( FIG. 8 ). 
     While movable member  50  is moving from the disengagement position to the engagement position, first end  74  of spring  72  is pulled by lug  70  of movable member  50 . Locking block  139  causes movement of latch  411  from the unlatching position ( FIG. 5 ) to the latching position ( FIG. 8 ) via connecting rod  215 . Thus, locking end  415  of latch  411  is engaged in groove  37  in top beam  35 . Note that locking end  415  of latch  411  of lower latch assembly  10  is engaged in groove  300  in ground  299 . As a result, follower door  275  can not pivot from the closed position to the open position relative to door frame  31 . Furthermore, primary door  259  can not be opened, either, because latch  333  of door lock  319  on primary door  259  is engaged in receptacle  294  of follower door  275 . Furthermore, when latch  411  is in the latching position, ears  455  of latch  411  is located between first portion  239  and third portion  253  of coupling member  237  along first axis X. 
     If handle  331  is operated to retract latch  333  from receptacle  294 , primary door  259  can be opened to disengage end face  273  of primary door  259  from actuation latch  131 . Spring  72  pulls movable member  50  from the engagement position to the disengagement position, and actuating latch  131  moves from the pressing position to the releasing position. Latch  411  is moved from the latching position to the unlatching position, disengaging locking end  415  from groove  37  of top beam  35 . Note that latch  411  of lower latch assembly  10  is also moved from the latching position to the unlatching position, disengaging locking end  415  from groove  300  in ground  299 . Thus, follower door  275  can be moved to the open position. 
     In a case that a fire occurs while both of follower door  275  and primary door  259  are in their closed positions (latch  411  is in the latching position), stop  495  melts due to the heat of the fire. Pressing pin  497  is actuated by spring  513  to move from the non-pressing position to the pressing position and presses against the push portions  475  of ears  455 , casing pivotal movement of each ear  455  from the storage position to the blocking position. When pressing pin  497  reaches the pressing position, second end  459  of each ear  455  is located outside of a corresponding first face  419  of body  413  of latch  411  ( FIG. 10 ). Stop portions  473  of ears  455  presses against each other, avoiding further pivotal movement of ears  455  and retaining ears  455  in the blocking position. Furthermore, outer end  499  of pressing pin  497  is received in coupling grooves  479  of ears  455 , and limiting face  480  of each coupling groove  479  presses against the outer periphery of pressing pin  497 , preventing ears  455  from pivoting from the blocking position to the storage position. Thus, ears  455  are retained in the blocking position, with second end  459  of each ear  455  located between first portion  239  and third portion  253  of upper coupling member  237  and pressing against third portion  253 . 
     With reference to  FIG. 11 , in a case that follower door  275  is not exactly in the closed position (i.e., receiving holes  255  of upper coupling member  237  are not aligned with groove  37  in top beam  35 , and receiving holes  255  of lower coupling member  237  are not aligned with groove  300  in ground  299 ), if primary door  259  is moved to the closed position, actuation latch  131  is moved to the pressing position, movement of latch  411  from the unlatching position to the latching position is hindered by top beam  35  (and movement of latch  411  of lower latch assembly  10  from the unlatching position to the latching position is hindered by ground  299 ). Thus, movable member  50  is retained in the disengagement position, and locking block  139 , restraining member  177 , spring  171 , and engagement pin  515  are not moved. However, first pin  88  moves along first axis X in the direction away from hooked portion  40  and compresses spring  171 , causing actuation member  90  to pivot about the pivot axis defined by third pin  91  and causing follower  78  to pivot about the pivot axis defined by push pin  98  without driving latch  411  to the latching position. This avoids damage to latch assembly  10  resulting from improper operation. 
     By providing ears  455  in latch  411 , latch  411  can be retained in the latching position by ears  455  that are pivoted to the blocking position after stop  495  melts during a fire, avoiding spread of the fire by avoid opening of double door  257 . Latch  411  can be used on currently available latch assemblies having a structure similar to latch assemblies  10 . 
     Each latch assembly  10  can automatically move latch  411  to the latching position while primary door  259  is moved to the closed position. Furthermore, even if actuation latch  131  of each latch assembly  10  is actuated by primary door  259  while latches  411  are not aligned with grooves  37  and  300 , only actuation member  90  and follower  78  are pivoted to cause first pin  88  to compress spring  171 . Latch  411 , movable member  50 , locking block  139 , and restraining member  177  are not moved, effectively protecting latch assembly  10  from improper operation. Furthermore, since latch  411  is operatively connected to actuation latch  131 , if latch  411  is picked with an intention to move actuation latch  131 , movement of actuation latch  131  from the pressing position to the releasing position is hindered by primary door  259 , providing an anti-pick function. 
     Now that the basic teachings of the present invention have been explained, many extensions and variations will be obvious to one having ordinary skill in the art. For example, each ear  455  does not have to include coupling groove  479 . In this case, when ears  455  are in the blocking position, pressing pin  497  moves to a position between inner sides  471  of ears  455 , and the weights of ears  455  are insufficient to move pressing pin  497  towards the non-pressing position. Thus, ears  455  can be retained in the blocking position. Furthermore, latch  411  can include only one ear  45 . 
     Furthermore, engagement hole  435  can extend from the end face of locking end  415  through outer end face  433 A of transverse groove  433  along first axis X. In this case, stop  495  extends along first axis X into engagement hole  435 , with a distal end of stop  495  located between first ends  457  of ears  455 . 
     Furthermore, only one latch assembly  10  is sufficient to lock double door  257 . In a case that only upper latch assembly  10  is utilized, since the downward moving direction of latch  411  along first axis X from the latching position to the unlatching position is the same as the acting direction of the gravitational force, upper latch assembly  10  does not have to include spring  72 , and latch  411  is biased by the gravitational force from the latching position to the unlatching position. 
     Thus since the invention disclosed herein may be embodied in other specific forms without departing from the spirit or general characteristics thereof, some of which forms have been indicated, the embodiments described herein are to be considered in all respects illustrative and not restrictive. The scope of the invention is to be indicated by the appended claims, rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.