Patent Publication Number: US-6342004-B1

Title: Automatic fire shutter mechanism for rack mounted chassis systems

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to rack mounted chassis systems employed in central offices. More particularly, this invention relates to mechanisms for preventing the propagation of fire through such rack mounted chassis systems. 
     2. Description of the Background Art 
     Often fire safety requirements prohibit the easy propagation of fire in central offices and other facilities where rack mounted chassis systems are often deployed. Specifically, the rack mounted chassis systems typically include a plurality of chassis that are mounted in aligned racks. Each chassis typically includes aligned vents to provide for the natural convection cooling upwardly through each of the chassis. Unfortunately, this path for natural convection cooling also creates a path or chimney for the propagation of fire. 
     Therefore, it is an object of this invention to provide an improvement which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the advancement of the rack mounted chassis art. 
     Another object of this invention is to provide a shutter mechanism for blocking the propagation of fire through rack mounted chassis systems. 
     Another object of this invention is to provide a shutter mechanism comprising at least a pair of apertured shutters which are placed in an overlapping contiguous manner and moveable between (1) an aligned position (i.e., open) wherein the holes in the apertured shutters are aligned and (2) a blocking position (i.e., closed) wherein the holes in the apertured shutters are not aligned such that the shutter mechanism may be employed within rack-mounted chassis systems to allow the free-flow of air therethrough and upon sensing a fire condition, to block the propagation of fire therethrough. 
     Another object of this invention is to provide a shutter mechanism including alignable shutters of material having alignable holes therethrough, wherein such shutters are spring-loaded to be urged toward a non-aligned position, but held in such an aligned position by means of a fusible link which fuses upon exceeding a predetermined temperature whereupon the shutters are then urged to the non-aligned or closed position so as to stop the propagation of fire therethrough. 
     The foregoing has outlined some of the pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings. 
     SUMMARY OF THE INVENTION 
     For the purpose of summarizing this invention, this invention comprises a shutter mechanism for minimizing the opportunity for fire to spread by shutting off the vents often used in a natural convection cooled chassis. It accomplishes this by reacting automatically to the intense heat build-up of a present flame. 
     More particularly, the automatic fire shutter mechanism of the invention is intended to be employed within rack-mounted chassis systems. The shutter mechanism comprises a pair of apertured shutters, each of which include a plurality of holes therethrough. The holes within the respective shutters are patterned so as to be capable of being aligned with each other to allow the free flow of air therethrough and such that when the holes are non-aligned, the air flow is blocked and there is no path for the free passage of fire therethrough. 
     In the preferred embodiment, the shutters are spring-loaded to constantly urge the shutters into a non-aligned or closed position, but are normally retained in an aligned or open position by means of a fusible link. The fusible link preferably comprises a heat-sensitive material which fuses (i.e., breaks or melts) when the temperature exceeds a predetermined amount, whereupon the spring mechanism then urges the shutters to a non-aligned position to block the passage of fire therethrough. Accordingly, the chimney effect that would normally occur in prior art chassis systems is blocked upon closing of the shutters to their non-aligned position. 
     The foregoing has outlined rather broadly the more pertinent and important features of the present invention in order that the detailed description of the invention that follows may be better understood so that the present contribution to the art can be more fully appreciated. Additional features of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which: 
     FIG. 1 is a perspective view, partially exploded, of a typical chassis showing the intended placement of the shutter mechanism of this invention; 
     FIG. 2 is a perspective view of the shutter mechanism of the invention; and 
     FIG. 3 is an exploded perspective view of the shutter mechanism of the invention. 
    
    
     Similar reference characters refer to similar parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The shutter mechanism  10  of the invention comprises two thin apertured shutters  20 A &amp;  20 B, each having a pattern of a plurality of holes  30 . Preferably, the thin apertured shutters  20 A and  20 B are planar in configuration and are composed of an inflammable material such as metal. The shutters  20 A and  20 B are secured in an overlapping and contiguous position parallel and adjacent to each other and within opposing side guides  22 A and  22 B that are generally U-shaped or L-shaped in cross-section. Preferably, at least one of the guides (e.g.,  22 A) is fixedly secured to the opposing side of one of the shutters (e.g.,  20 A) allowing the other shutter (e.g.  20 B) to slide longitudinally along the surface thereof. The opposing side guides  22 A and  22 B provide longitudinal rigidity to the shutter mechanism  10  and may also serve to align the shutters  20 A &amp;  20 B in longitudinal alignment with each other; however, in early prototypes, too of close tolerances, have been found to cause binding. 
     As illustrated in FIGS. 2 and 3, the pattern of the plurality of holes  30  essentially comprise the same pattern for the respective shutters  20 A and  20 B. Thus, when the pattern of holes  30  of one shutter  20 A is aligned with the pattern of holes  30  of the other shutter  20 B a free flow of air may pass therethrough. However, upon sliding of one of the shutters  20 B longitudinally relative to the other shutter  20 A such that the holes  30  are in a non-aligned position, there is no passageway for the flow of air from one side of the shutter mechanism  10  to the other. In this regard, it is noted that the pattern and configuration of the respective holes  30  of the respective shutters  20 A and  20 B need not necessarily be the same provided the holes  30  are configured in a pattern which is alignable to allow passage of the air therethrough and provided the shutters  20 A and  20 B may be non-aligned to prevent the passage of air therethrough in the event of a fire. For example, the patterns may the same with the hole configurations being different and, conversely, the hole configurations may the same with the patterns being different, provided the shutters  20 A and  20 B may be moved to a non-aligned position to prevent the passage of air therethrough in the event of a fire. 
     The shutters  20 A &amp;  20 B are movable from an “open” position with the hole  30  being in the aligned position to a “closed” position with the holes  30  being in the non-aligned position when the temperature exceeds a predetermined amount, thereby closing off the airflow through the shutter mechanism  10 . 
     The movement of the shutters  20 A &amp;  20 B may be accomplished by an active mechanism such as a dual-acting solenoid or a single-acting solenoid with a return spring, controlled by a temperature sensor (thermistor), such that the shutters  20 A &amp;  20 B are urged to the “closed” position when the temperature exceeds a predetermined amount as sensed by the sensor. 
     However, in a preferred embodiment, movement of the shutters  20 A &amp;  20 B may be accomplished by a passive mechanism that urges the shutters  20 A &amp;  20 B to the “closed” position by means of spring mechanism  35  but holds the shutters  20 A &amp;  20 B in the “open” by means of a heat-fusible link  40 . The preferred structure of the spring mechanism  35  comprises springs  35 A and  35 B whose one ends are connected to protruding tabs  37 A and  37 B punched outwardly in a protruding manner from the movable shutter  20 B and whose other ends are connected to corresponding tabs  39 A and  39 B punched outwardly in a protruding manner from the non-moveable shutter  20 A. Alternatively, but less preferably, one of the ends of the springs  35 A and  35 B may be connected to the chassis  50  in which the shutter mechanism is installed instead of to the non-moveable shutter  20 A. Also alternatively, by less preferably, in lieu of the springs  35 A and  35 B, a leaf or compression spring mounted within the chassis  50  in alignment with the movable shutter  20 B such when the shutter mechanism  10  is installed in the chassis  50 , the spring engages the movable shutter  20 B to urge it toward the “closed” position. 
     It should be appreciated that the moveable shutter  20 B is urged into a non-aligned position as shown in FIG.  2 . The non-alignment of the holes  30  is assured by positioning tabs  39 A and  39 B that function as stops to U-shaped slots  41 A and  41 B formed in the shutter  20 B such that non-alignment of the respective holes  30  is assured once the link  40  fuses. 
     The fusible link  40  is composed of a material that is heat sensitive such that it breaks into two or melts once the link  40  is subjected to a predetermined temperature. The fusible link  40  is secured to the respective shutters  20 A and  20 B by means of a fastener  40 A that is secured through a hole in the moveable sheet  20 B, the head of which is essentially flush with the undersurface of the moveable sheet  20 B so as to not obstruct the sliding of the shutters  20 A and  20 B. The other end of the fusible link  40  is connected by a fastener  40 B to a stand-off  43  fixedly mounted (such as by swaging) to the non-moveable sheet  20 A and that passes through a slot  42  formed in the movable shutter  20 B. It should be appreciated that upon fusing of the link  40 , springs  35 A and  35 B urge the movable shutter  20 A to slide along the mating surface of the other shutter  20 A to a position wherein the holes  30  are in a “closed” or “non-aligned” position, thereby blocking the flow of air (or fire) therethrough. 
     Further improvements to the shutter mechanism  10  of the invention may include one or more fasteners and springs positioned between washers  44  similarly connected to stand-offs  43  fixedly mounted (such as by swaging) to the non-moveable sheet  20 A and that passes through corresponding slots  46  formed in the movable shutter  20 B to prevent jamming, buckling or other separation of the shutters  20 A and  20 B that otherwise might occur upon exposure to excessive temperatures. Furthermore, it has been determined that the non-alignment of the holes  30  can additionally, or in lieu of the positioning tabs  39 A and  39 B, be assured by the slots  42  and  46  in which the stand-offs  43  slide functioning as stops such that non-alignment of the respective holes  30  is assured once the link  40  fuses. 
     The shutter mechanism  10  is intended to be positioned above a typical chassis  50  mounted in a rack; however, the shutter mechanism  10  may be positioned below a typical chassis  50  or above and below the chassis  50 . 
     During operation with the shutter being in its “open” position by link  40 , the natural convection cooling of the chassis  50  occurs as normal. In the event of a fire, the link fuses (i.e., melts) whereupon spring  35  forces the shutters  20 A &amp;  20 B to slide to a position with the respective holes  30  being non-aligned, thereby “closing” the shutter mechanism  10 . 
     The shutter time may be controlled by varying the force of the spring  35  and/or the fusibility of the link  40 . 
     The shutter mechanism  10  of the invention enables an instrument to pass the fire propagation test requirements imposed commonly on rack mounted chassis used in the telecommunications industry (i.e., NEBS SR-3580) by containing flames from burning components inside the chassis. It accomplishes this while maintaining the form factor of the typical chassis design and without any significant degradation of cooling capacity. It is simple, reliable and inexpensive. 
     The present disclosure includes that contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention. 
     Now that the invention has been described,