Patent Publication Number: US-7905522-B1

Title: Exit pushbar with blocking mechanism

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to exit devices that secure a door in the closed position. More specifically, the present invention relates to exit devices that keep a door closed when subjected to a high-energy impact as may occur when debris is hurled by a tornado against the door. 
     2. Description of Related Art 
     An “exit device” is a lock mechanism operated from the inside of an exit door through the use of a crossbar, pushbar, pushrail or panic bar actuator. The term “pushbar” will be used herein to refer to the above types of exit device actuators and other types of actuators including paddles and various other mechanisms that move towards the exit door to actuate the latch. The exit device is designed to open the exit door, allowing exit without prior knowledge of how the lock operates, whenever a horizontal force is applied to the pushbar actuator. Exit devices are typically required by fire or building codes and are used in public buildings where many people may be gathered, to provide rapid, safe and easy egress in case of emergency. 
     Exit devices of this general type may be seen in U.S. Pat. Nos. 4,384,738; 5,531,492 and U.S. Design Pat. No. 279,647 all of which are assigned to Sargent Manufacturing Company, the assignee of the present patent application. 
     Conventional exit devices typically include a mounting rail that is mounted on the interior surface of the exit door and a pushbar actuator that is mounted so that it can move towards the mounting rail to operate the exit device. The pushbar actuator is spring biased away from the exit door. When horizontal pressure is applied to the pushbar, it moves horizontally in towards the mounting rail, compresses the bias springs and retracts a latchbolt to open the exit door. 
     In a tornado rated exit device, the exit device must keep the exit door closed when subjected to a high-energy impact on the exterior surface of the door. The test to provide a tornado rating involves loading a cannon with a long 2″×4″ board of the type used in construction and firing it at a speed of one hundred miles per hour (160 kilometers per hour) into the exterior side of the exit door. The exit device must keep the exit door closed, and remain operable after the impact. 
     Conventional exit devices are unable to pass this test because the high-energy impact on the exterior side of the door pushes the mounting rail and the exit door towards the pushbar. The impact energy is so high that the door and mounting rail rapidly move towards the pushbar actuator, while the pushbar remains stationary due to inertia. As the door and mounting rail move towards the pushbar, the biasing springs that hold the pushbar away from the exit door are compressed and the door opens. 
     The exit device may also fail this test if the pushbar rebounds towards the exit door during dissipation of the impact energy. In both cases, the pushbar and the mounting rail move towards each other as a result of the high-energy impact. This relative motion compresses the bias springs and retracts the latchbolt exactly as if the pushbar had been pushed towards the mounting rail to operate the exit device in the normal manner. 
     The prior art has addressed this problem by increasing the strength of the bias springs that hold the pushbar away from the support rail. The increased spring strength prevents the pushbar from moving towards the mounting rail during the impact. While this is effective, it means that every time the door is operated the user must apply sufficient force to compress the stronger bias springs. This higher level of required force for normal operation is an undesirable characteristic for an exit device and makes it difficult to operate for the elderly and other users. 
     Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an exit device that operates with a normal level of force and which automatically blocks operation during a high energy impact, but which thereafter releases the blocking so that the exit device operates normally. 
     Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification. 
     SUMMARY OF THE INVENTION 
     The above and other objects, which will be apparent to those skilled in the art, are achieved in the present invention which is directed to an exit device including a latch, a mounting rail and a pushbar mounted for motion relative to the mounting rail between an inward position towards the mounting rail and an outward position away from the mounting rail. The pushbar operates the latch when moved to the inward position. At least one biasing spring acts to bias the pushbar towards the outward position. 
     The exit device further includes a blocking arm connected to the mounting rail and movable between a blocking position and a non-blocking position. The blocking arm is biased towards the non-blocking position and into contact with the mounting rail where it can receive transferred impact energy. The blocking arm moves outwards and away from the mounting rail into the blocking position to prevent motion of the pushbar towards the mounting rail during a high-energy impact against the door. 
     In one aspect of the invention the exit device further includes a pivot and a blocking arm spring, the pivot connecting the blocking arm to the mounting rail and the blocking arm spring acting to bias the blocking arm towards the non-blocking position into contact with the mounting rail where it may receive the transferred impact energy through the door and the mounting rail. 
     The blocking arm spring provides a biasing force that is sufficiently strong to hold the blocking arm in contact with the mounting rail in the non-blocking position before the high-energy impact, and sufficiently weak to allow the blocking arm to move to the blocking position away from the mounting rail during the high-energy impact against the door. 
     In another aspect of the invention, the exit device further includes a pair of connecting arms forming a parallelogram linkage with the pushbar and the mounting rail, and the blocking arm contacts at least one of the connecting arms to prevent inward motion of the pushbar when the blocking arm is in the blocking position. 
     The blocking arm pivot is preferably substantially vertical and the blocking arm preferably moves substantially horizontally between the non-blocking and the blocking positions. The high-energy impact against the door defines an impact direction and the blocking arm in the most highly preferred embodiment moves in the same direction as the impact direction when moving from the non-blocking position to the blocking position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view showing an exit device incorporating the present invention, the exit device including a latch mechanism, a mounting rail and a pushbar. The exit device is shown installed on an exit door and uses a vertical rod latch mechanism, the vertical rods being hidden inside the exit door and drawn in phantom. 
         FIG. 2  is a partial view of the mounting rail and pushbar portions of the exit device seen in  FIG. 1  looking upward from the bottom of  FIG. 1  with portions of the mounting rail and pushbar being cut away to show the blocking mechanism of the present invention. The blocking mechanism is shown in the non-blocking position, which allows the exit device to operate conventionally. 
         FIG. 3  is a partial view of the invention as illustrated in  FIG. 2  except that the blocking mechanism is shown in the blocking position. In this position, which is reached shortly after a high energy impact against the exterior of the exit door, the pushbar cannot move towards the mounting rail due to the action of the blocking mechanism. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     In describing the preferred embodiment of the present invention, reference will be made herein to  FIGS. 1-3  of the drawings in which like numerals refer to like features of the invention. 
       FIG. 1  shows an exit device  10  suitable for use in tornado-prone areas. The exit device  10  includes a latch mechanism  12 , a pushbar  14  and a mounting rail  16  mounted on an exit door  18 . The latch mechanism  12  that is illustrated is a vertical rod latch mechanism incorporating hidden vertical rods  20 ,  22  located inside the exit door  18 . Other latch mechanisms are also suitable, including designs that have a conventional latchbolt that extends out of the latch mechanism  12  and into a strike on the adjacent doorframe. 
     The exit device  10  is conventionally operated to open the door by applying pressure to the pushbar  14 . The pushbar  14  is spring biased away from the exit door  18  and the mounting rail  16 . When pressure is applied horizontally (approximately perpendicular to the face of the door) to the pushbar  14 , the pushbar moves inwards towards the exit door  18  and the mounting rail  16  to operate the latch  12  and retract the vertical rods  20 ,  22 . The exit door  18  can then swing open on hinges  24 . 
       FIG. 2  shows the exit device  10  looking upward from the bottom of  FIG. 1  towards the mounting rail  16  and pushbar  14 . Parts of the mounting rail and pushbar have been cut away to show the internal mechanism more clearly. The latch, which may be any type of conventional latch mechanism is not shown, but it will be understood that the inward motion of the pushbar operates the latch  12 . 
     The pushbar  14  moves inwards by means of a parallelogram linkage formed by connecting arms  26  and  28 , the mounting rail  16  and the pushbar  14 . Connecting arm  26  is pivotally connected to the mounting rail  16  via pivot  30  and to the pushbar by pivot  32 . Connecting arm  28  is pivotally connected to the mounting rail  16  with pivot  34  and to the pushbar by pivot  36 . Torsion springs  38  and  40  provide the spring force that biases the parallelogram linkage to hold the pushbar  14  away from the exit door  18  and the mounting rail  16 . 
     In normal operation, when sufficient force is applied to the pushbar  14 , the pushbar will pivot inwards towards the mounting rail  16  as the connecting arms  26  and  28  rotate about their respective pivots. The pushbar will remain parallel to the mounting rail and the torsion springs  38  and  40  will be compressed. The inward motion of the pushbar will actuate the latch mechanism  12  to open the door  18 . When the horizontal force is released, torsion springs  38  and  40  will rotate the connecting arms  26 ,  28  to move the pivots  32 ,  36  away from the mounting rail back to the position seen in  FIG. 2 . 
       FIG. 1  shows the interior side of exit door  18  where the exit device  10  is mounted. As previously described, during a high energy impact to the exterior side of door  18 , such as the impact delivered when tornado debris hits the exterior of the door, the door  18  and the mounting rail  16  can move towards the pushbar  14 , which remains stationary due to inertia. Alternatively, the pushbar may rebound towards the mounting rail during the impact event. In either case, however, the initial force against the exterior of the door is applied in the direction indicated by arrow  42  in  FIG. 2  and the relative motion of the mounting rail  16  and the pushbar  14  is to compress the torsion springs  38 ,  40 . 
     In prior art designs addressing the tornado impact problem, the strength of the springs corresponding to torsion springs  38  and  40  is increased to prevent this relative motion during the impact event. This solution, however, has the major disadvantage that the exit device becomes difficult to operate as the excessively strong springs must be compressed every time the exit device is used. In the present design, the torsion springs are of a conventional strength—strong enough to ensure that the pushbar will reliably return to the position seen in  FIG. 2  when no force is applied to the pushbar. The torsion springs do not need to be so strong that they prevent motion of the pushbar towards the mounting rail during the impact event. 
     The present invention addresses this problem by providing a blocking mechanism including a blocking arm  44 , a pivot  46  and a blocking arm spring  48 . The blocking arm is pivotally attached to the mounting rail  16  by the pivot  46  and lightly held against the mounting rail  16  by the blocking arm spring  48 , which is preferably a torsion spring. The pivot  46  allows the blocking arm  44  to move between the non-blocking retracted position seen in  FIG. 2 , where the head  50  of the blocking arm is held against the mounting rail  16  by torsion spring  48 , and the blocking extended position seen in  FIG. 3  where the head  50  of the blocking arm  44  has moved into interfering and blocking contact with stop  52  on the connecting arm  26 . 
     As can be seen in  FIG. 2 , in order for the door to open, the parallelogram linkage of the exit device requires that the connecting arm  26  pivot to move the stop  52  on the connecting arm  26  in the direction shown by arrow  54 . Stop  52  moves in an arc around pivot  30 . When tornado or other high energy debris impacts the door from the direction indicated by arrow  42 , energy is transferred from the impacting debris to the door  18  and from there to the mounting rail  16 . 
     This transfer of energy continues and transfers energy to the blocking arm  44 . The torsion spring  48  is initially holding the head  50  of the blocking arm  44  against the mounting rail  16  as in  FIG. 2 . Because the opposite end of the blocking arm  44  is connected to the mounting rail  16  by pivot  46 , the impact energy transferred to the blocking arm  44  causes the blocking arm to swing outward away from the mounting rail  16  to the blocking position seen in  FIG. 3 . 
     This outward swing of the blocking arm  44  occurs extremely rapidly—before the pushbar  14  and the mounting rail can move significantly towards each other to open the door. The torsion spring  48  is just strong enough to hold the blocking arm  44  against the mounting rail  16 , but not so strong that it prevents the outward swing of the blocking arm to the position in  FIG. 3 . It should be noted that pivot  46  is vertical and the weight of the blocking arm  44  is not be supported by the torsion spring  48 . 
     As the blocking arm  44  swings away from the door  18  and the mounting rail  16 , head  50  on the blocking arm moves directly into the blocking position of  FIG. 3  to prevent stop  52  from moving in the direction of arrow  54 . This blocks the opening motion of the pushbar during the initial impact and during any rebounding motion during the remainder of the impact event. The blocking arm acts to prevent the pushbar from operating the latch mechanism  12  by preventing motion of the pushbar towards the mounting rail. 
     The motion of the blocking arm is sufficiently rapid that it reaches the blocking position before the distance between the pushbar and the mounting rail can decrease significantly. It remains in this blocking position during any rebounding motion of the pushbar or door. 
     Once the impact event is over, the torsion spring  48  returns the blocking arm  44  to the position seen in  FIG. 2 . The exit device then functions normally and the door  18  may be opened. This design, which functions through energy transfer from the door to the blocking mechanism, provides a temporary lock for the exit device only during the brief period of the impact event. It has no negative impact on normal day-to-day operation of the exit device as will occur when the strength of the main biasing springs is increased as in the prior art. 
     While the present invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.