Abstract:
A fire extinguishing apparatus includes a structure defining a first chamber containing an electrically operable explosive device. The apparatus also has a piezoelectric cell capable of producing an electrical output in response to the impact upon the piezoelectric cell. The apparatus also has a container of nonflammable pressurized fluid in contact with the structure, and a mechanical detection mechanism with a thermal sensor for producing a mechanical force at an established temperature. The mechanical force produced by the mechanical detection mechanism is applied to the piezoelectric cell to produce the electrical output that actuates the electrically operable explosive device.

Description:
BACKGROUND 
       [0001]    This invention relates to fire detection and suppression, and more particularly to pyrotechnically actuated fire extinguishers which may be installed within vehicles. 
         [0002]    There are a wide variety of fire detection and extinguishing technologies and fire extinguisher constructions. These include propellant-actuated extinguishers and extinguishers charged with compressed and/or liquified gas. 
         [0003]    Early propellant-actuated extinguisher disclose a fire extinguisher wherein a liquid extinguishing medium, such as methyl bromide, is expelled from its container by gas evolved from the burning of a pyrotechnic charge. The charge is originally stored in a container which includes electric squibs. The charge container is mounted in an upper end of the vessel within a container cup. Opposite the container cup, an outlet from the vessel is formed by an elbow fitting sealed by a rupturable diaphragm. Ignition of the pyrotechnic charge ruptures a wall of the charge container and vents combustion gases into the vessel. The combustion gases serve as a gas piston acting on the surface of the liquid rupturing the diaphragm which sealed the outlet and propelling the liquid out of the extinguisher. 
         [0004]    The application of a propellant-actuated extinguisher to use in modern vehicles discloses an extinguisher in many ways similar, but the exemplary fire suppressant utilized is Halon 1301. The lower end of the extinguisher vessel is sealed by a rupturable diaphragm. A gas generating device is mounted atop the neck of the vessel. The exemplary gas generating composition is 62% sodium oxide and 38% copper oxide. In either exemplary example, the propellant-actuated extinguisher again contains a pyrotechnic charge to create a gaseous pressure in a bottle. The pyrotechnic charge is wired to the vehicle fire and overheat detection system, which will send an electric current to activate the charge upon detection of an overheat or fire condition. 
         [0005]    In extinguishers charged with compressed or liquefied gas, a valve is opened to actuate the extinguisher. In these extinguishers, a pyrotechnical actuator is supplied with an electric current that ignites an internal pyrotechnical charge. The lit charge is turned into mechanical energy, such as by moving a firing pin. The firing pin pushes against a lever that turns a spindle. The spindle releases a beam that allows a plug to open in the valve, which allows for the compressed contents of the extinguisher to be released. 
         [0006]    In many integrated detection and suppression systems electrical power is supplied from a detection system to a pyrotechnical actuator to initiate fire suppression. This leaves the system vulnerable to failure of the power supply, detection system or the interconnecting cables between the detection system and the fire suppression actuation mechanism. While a fully powered detection system may offer the best performance it is clearly unacceptable for the extinguishing system to fail during a fire event. 
       SUMMARY 
       [0007]    In a first embodiment, a fire extinguishing apparatus includes a structure defining a first chamber containing an electrically operable explosive device. The apparatus also has a piezoelectric cell capable of producing an electrical output in response to the impact upon the piezoelectric cell. The apparatus also has a container of nonflammable pressurized fluid in contact with the structure, and a mechanical detection mechanism with a thermal sensor for producing a mechanical force at an established temperature. The mechanical force produced by the mechanical detection mechanism is applied to the piezoelectric cell to produce the electrical output that actuates the electrically operable explosive device. 
         [0008]    In another embodiment, a fire suppression apparatus includes a pressure container with a material contained therein and a cartridge in communication with the pressure container. The cartridge has a container cup with a pyrotechnic actuator with electrical leads. A piezoelectric electric element is connected to the electrical leads, and a mechanical detection mechanism based upon a temperature sensitive element capable of generating a mechanical force above a threshold temperature of the temperature sensitive element. 
         [0009]    In yet another embodiment, a fire detection and suppression system includes at least one fire detection apparatus, a power supply, a control unit, at least one electrical lead wire from the control unit to a piezoelectric generator, a pressure container with a material contained therein, a pyrotechnic actuator with electrical leads to the piezoelectric generator; and a mechanical detection mechanism based upon a temperature sensitive element capable of generating a mechanical force above a threshold temperature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention will be further explained with reference to the drawing figures listed below, wherein like structures are referred to by like numerals throughout the several views. 
           [0011]      FIG. 1  is a combined schematic and elevation view showing an integrated detection and suppression system. 
           [0012]      FIG. 2  is an elevation view of a suppression system. 
           [0013]      FIG. 3  is a cross-section of a temperature sensitive mechanism for a suppression system. 
           [0014]      FIG. 4  is a cross-section of another embodiment of a temperature sensitive mechanism for a suppression system. 
           [0015]      FIG. 5  is a cross-section of still another embodiment of a temperature sensitive mechanism for a suppression system. 
       
    
    
       [0016]    While the above-identified drawing figures set forth individual embodiments of the invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art which fall within the spirit and scope of the principles of this invention. 
       DETAILED DESCRIPTION 
       [0017]    A mechanical detection mechanism based upon a temperature sensitive element can be employed to generate a mechanical force above a threshold temperature. The generated mechanical force can then be applied to a piezoelectric element to produce an electrical pulse to fire a pyrotechnical actuator. The piezoelectric element could be either a piezoelectric generator which applies power to fire an existing pyrotechnical actuator or a piezoelectric element to directly ignite a pyrotechnical composition within a pyrotechnical actuator. The aim of the device is to provide a single actuation element that is suitable for use with either an electrically operated detection system or an unpowered mechanically operated detection system. Such a device would be compatible with existing system designs allowing the use of the same pyrotechnical actuator for both powered and unpowered modes of operation. 
         [0018]    The mechanical detection mechanism based upon the temperature sensitive element is illustrated in the exemplary embodiments in  FIGS. 1-5 . Referring to  FIG. 1 , a fire detection and suppression system  10  is shown. The system includes fire extinguisher  12 , control unit  14 , power supply  16 , primary fire detector  18 , and wiring leads  20 . Primary fire detector  18  may include one or more smoke detectors, overheat detectors, optical flame detectors or similar devices known within the art. Similarly, wiring leads  20  are electrical wires or cables also known in the art. Control unit  14  will receive signals from fire detectors  18  and send a signal to provide current to activate actuating mechanism  28 . The current comes from power supply  16 , which may be a generator, battery, or similar power source known within the art. 
         [0019]    As illustrated in  FIGS. 1 and 2 , Fire extinguisher  12  includes container  22 , distribution system  24 , valve assembly  26 , actuating mechanism  28 , and temperature activated force mechanism  30 . In the embodiment of  FIG. 1 , temperature activated force mechanism  30  is located remotely from container  22 , distribution system  24 , valve assembly  26 , and actuating mechanism  28 . In the embodiment of  FIG. 2 , temperature activated force mechanism  30  is adjacent valve assembly  26 , and in one embodiment may be in direct contact with valve assembly  26 , actuating mechanism  28 , and/or container  22 . 
         [0020]    Container  22  is a pressure vessel, often referred to as a bottle. Container  22  is constructed from a metal alloy or similar high strength rigid material that can withstand high pressure. Container  22  houses a fire extinguishing material, such as a fire retardant or fire suppressant, which may be either a fluid or particulate matter. A source of gas pressurizes the fire extinguishing material at least when the bottle is in a discharging condition and the fire extinguishing material is discharged through an outlet when fire extinguisher  12  is in the discharging condition. Valve assembly  26  connects container  22  with distribution system  24 . Distribution system  24  as illustrated is a pipe or tube that will lead to one or more nozzles for spreading the fire extinguishing material over a selected area to be protected, although other systems are known to those of skill in the art. 
         [0021]    Valve assembly  26  is connected to actuating mechanism  28 . In one embodiment, fire extinguisher  12  is charged with compressed or liquefied gas, and valve assembly  26  is opened to actuate the extinguisher. In these extinguishers, a pyrotechnical actuator is supplied with an electric current that ignites an internal pyrotechnical charge. The lit charge is turned into mechanical energy, such as by linearly moving a firing pin. The firing pin pushes against a lever that turns a spindle. The spindle releases a beam that allows a plug to open in the valve, which allows for the compressed contents of the extinguisher to be released. 
         [0022]    In another embodiment, valve assembly  26  has a valve element having a closed position sealing an outlet to the distribution system  24 , and an open position permitting discharge of the suppressant through the outlet. In one embodiment, valve assembly contains a valve element that is shiftable from the closed position to the open position responsive to a pressure within the bottle exceeding a discharge threshold pressure, whereupon fire extinguisher  12  enters the discharging condition and discharges the fire extinguishing material through the outlet. 
         [0023]    In various implementations, the valve element of valve assembly  26  may comprise a poppet having a head and a stem connected to the head. The head may have a fore surface facing the interior of container  22  and an opposite aft face from which the stem extends along a poppet axis. Valve assembly  26  may have a locking element which in the pre-discharge condition has a first portion engaged to the poppet and a second portion held relative to container  22 . In the pre-discharge condition the locking element transmits force to the poppet which retains the poppet in the closed position and, responsive to the pressure within container  22  exceeding the discharge threshold pressure the locking element ruptures, whereupon the pressure within container  22  drives the poppet to the open position and fire extinguisher  12  enters the discharging condition. A valve return spring may bias the poppet toward the closed position. The return spring is effective to return the poppet from the open position to the closed position when the fire extinguishing material has been substantially discharged from fire extinguisher  12 . In another embodiment, the pyrotechnical actuator applies force to release a locking element at which point the pressure within container  22  drives the poppet to the open position and fire extinguisher  12  enters the discharging condition. 
         [0024]    The valve element may comprise a head having a fore face facing the interior of container  22  and an opposite aft face and a collapsible shaft between the head and a valve body. In the pre-discharge condition, when the pressure within container  22  is lower than the discharge pressure, axial compression of the shaft may be effective to resist rearward movement of the head and retain the head in the closed position. Responsive to the pressure within the bottle exceeding the discharge threshold pressure the shaft may collapse via buckling, whereupon the pressure within container  22  drives the head to the open position and fire extinguisher  12  enters the discharging condition. The source of gas to create pressure within container  22  may comprise a chemical propellant charge. The chemical propellant charge may have a combustion temperature of less than about 825° C. The chemical propellant charge may have gaseous combustion products consisting essentially of nitrogen, carbon dioxide, water vapor and mixtures thereof. The chemical propellant charge may consist essentially of a mixture of 5-aminotetrazole, strontium nitrate, and magnesium carbonate. 
         [0025]    The source of gas may comprise a replaceable cartridge containing a chemical propellant charge. A cartridge holder assembly known within the art may hold the cartridge and may have a first end mounted within an aperture at an upper end of container  22  and a second end immersed within the suppressant when fire extinguisher  12  is in the pre-discharge condition. A closure may close the first end, and replaceable squib may be mounted within the closure. The discharge threshold pressure may be between about 2 MPa and about 10 MPa. The fire extinguishing material may be selected from the group consisting of PFC&#39;s, HFC&#39;s, water, and aqueous solutions. In this embodiment, actuating mechanism  28  includes a pin that is driven by a pyrotechnic charge. The pin will pierce the cartridge with the propellant to start the discharge of fire extinguishing material from container  22 . 
         [0026]    In one embodiment, fire extinguishing material is contained by container  22  when fire extinguisher  12  is in a pre-discharge condition. A replaceable cartridge contains a chemical propellant charge that is activated by actuating mechanism  28 . Actuating mechanism  28  is a pyrotechnic charge for a gas generator in the cartridge. When activated, the gas generator releases a poppet that is spring biased toward a first position in which it blocks a path between the cartridge and the suppressant. Upon combustion of the propellant in the gas generator, the poppet shifts under pressure applied by combustion gasses to a second position wherein such path is unblocked and the combustion gasses may communicate with and pressurize fire extinguishing material in container  22 . 
         [0027]    In another embodiment, fire extinguishing material is contained by container  22  when the extinguisher is in a pre-discharge condition. A cartridge in valve assembly  26  contains a chemical propellant charge. Actuating mechanism  28  is mounted adjacent valve assembly  26  and ignites the propellant. Actuating mechanism  28  is a pyrotechnic device that has a body, a replaceable percussion cap primer having a primer charge, a firing pin, a spring, and a solenoid. The solenoid has a fixed coil and a plunger, coupled to the firing pin by a sear and shiftable, by energizing of the coil, from a first position at least to a second position. Such a shift draws the firing pin away from the primer until the plunger reaches the second position, whereupon release of the sear allows the firing pin to be driven by the spring to impact the primer and cause ignition of the primer charge which in turn causes ignition of the chemical propellant charge so as to pressurize the suppressant and discharge fire extinguishing material from fire extinguisher  12 . The solenoid is driven by electrical current from wiring leads  20 . In the absence of enough current to drive the solenoid, the primer charge is ignited, creating a small explosion that will drive the firing pin. 
         [0028]    Aside from being connected to power supply  16  via wiring leads  20 , actuation mechanism  28  is also connected to temperature activated force mechanism  30 . Temperature activated force mechanism  30  includes a temperature sensing apparatus  34 , piezoelectric generator  32 , and wiring leads  36 . Again, wiring leads  36  are electrical wires or cables also known in the art. In an alternate embodiment, the system may not necessarily require control unit  14 , separate power supply  16 , and wiring  20  if the detection mechanism is a secondary mechanical detection system described further herein, and not primary fire detector  18 . 
         [0029]    Piezoelectric generator  32  is a piezoelectric device known within the art. For example, typical piezoelectric stack generators are manufactured by Piezo systems Inc. A technical concern with the use of piezoelectric generators is the susceptibility of piezoelectric devices to fail at temperatures close to the Curie temperature of the piezoelectric material. PZT has a typical Curie temperature of 350° C. and should be able to function up to a temperature of at least 250° C. Higher temperature materials are also available, such as modified bismuth titanate, which is able to withstand temperatures in excess of 700° C. 
         [0030]    As previously stated, actuating mechanism  28  may be a pyrotechnic actuator. Typical pyrotechnical actuators used in fire suppression systems, for example Metron™ actuators, require a firing pulse between 6-16 mJ. The Metron™ actuators contain a charge that is lit to create a small explosion that forces out a firing pin. The firing pin actuates a lever, gear, or similar mechanical element that is used to operably move a valve from a closed position to an open position. Commercially available piezoelectric generators, built up from stacks of thin piezoelectric layers, can be designed to produce a high current, low voltage output and are capable of delivering 10-20 mJ for an applied force of 1-2 kN. These devices are therefore more than capable of supplying sufficient energy to directly fire a Metron™. 
         [0031]    Typically piezoelectric stack generators are of the order of 20×5×5 mm and are compatible with application of a force from a simple temperature sensitive spring loaded or fluid pressure driven detection mechanism. In order to generate a pulse of sufficient magnitude it will be necessary to apply the force from the detection element over a short period of time in the form of a short sharp impact. 
         [0032]    Several embodiments of temperature activated force mechanism  30  including temperature sensing apparatus  34  and piezoelectric generators  32  are illustrated in  FIGS. 3-5 . Temperature sensing apparatus in some embodiments may have an activation temperature between 80° C. and 250° C. or higher, or any subset thereof, including an exemplary range of between 100° C. and 125° C., and all components are designed as required by the specific application of the embodiment. 
         [0033]    In  FIG. 3 , temperature sensing apparatus  34  includes housing  40 , sensing element  42 , actuation pin  44 , and spring  46 . Housing  40  includes base portion  47  and side walls  48  and  49 , which are constructed from a metal alloy or similarly rigid and fire resistant material. The material should also allow for heat transfer through the walls  48  and  49  of housing  40 . Actuation pin  44  is formed from a similar material as housing  40 . The base of actuation pin is in contact with spring  46 , while the center shaft is surrounded by sensing element  42 . Spring  46  is illustrated as a metal coil spring in compression between base portion  47  of housing  40  and the base of actuation pin  44 . In other embodiments, spring is any elastic or resilient structure capable of providing a force on the end of actuation pin  44 . 
         [0034]    Sensing element  42  is a temperature dependent material, such as eutectic solder or solidified salt solution. In the solid state, the temperature dependent material holds actuation pin in place, creating a compressive force on spring  46 . Upon reaching a set threshold temperature, the solder or solidified eutectic salt solution will melt and become fluid. This will allow the stored compressive force on spring  46  to release and drive pin  44  towards piezoelectric generator  32 . The force on the piezoelectric generator will create a current that is sent via wiring leads  36  to actuation mechanism  28  to spark the pyrotechnic charge therein, thus discharging the fire extinguishing material from fire extinguisher  12  either through the opening of a valve, or through the creation of pressure from the pyrotechnic charge acting as a gas generator as previously described. To fabricate the temperature sensing apparatus  34 , actuation pin  44  is placed between the walls  48  and  49  of housing  40  at a preset distance from the base end. Liquid sensing element  42  is poured into housing  40  and allowed to set. Spring  46  is placed at the base of actuation pin  44  and base portion  47  is then placed into position, creating the compressive force on spring  46 . 
         [0035]      FIG. 4  illustrates a second embodiment of temperature sensing apparatus  34 , which includes housing  50 , sensing element  52 , actuation pin  54 , and diaphragm  56 . Sensing element  52  is an intumescent material. The force to drive actuation pin  54  is supplied by the intumescent material. Housing  50  is constructed from a metal alloy, and acts to contain sensing element  52  on all sides, while allowing for linear motion in the direction of shaft  58  of pin  54 . The intumescent material pushes against base  57  of actuation pin  54  which is held in place against the action of the intumescent material by diaphragm  56 . When the intumescent material is heated above a threshold temperature, actuation pin  54  ruptures diaphragm  56  and shaft  58  of actuation pin  54  applies force to the piezoelectric generator  32 , which creates a current sent to actuation mechanism  28  via wiring leads  36 . An example of a suitable intumescent material is a thermostatic wax. 
         [0036]      FIG. 5  illustrates a third embodiment of temperature sensing apparatus  34 , which includes housing  60 , sensing element  62 , diaphragm  64 , and pin  66 . The unpowered linear heat detector of temperature sensing apparatus  34  generates force by the increase in pressure of a fluid contained within a thin sensing tube. In the particular example shown, sensing element  62  is the fluid pressure and applies force to base  67  of pin  66  which is held in place against the action of the fluid pressure by diaphragm  64 . When the pressure of the fluid exceeds a threshold value due to an increase in temperature, shaft  68  of pin  66  ruptures diaphragm  64  and is forced out to apply force to the piezoelectric generator  32 . 
         [0037]    Piezoelectric stacks are relatively high cost elements (for example, around $100 in small volumes), and as such it would be preferable to use a lower cost (for example, &lt;$5) single crystal such as those commonly used in piezoelectric igniters. The use of a piezoelectric stack to fire an existing pyrotechnical actuator is the direct use of the spark generated by a piezoelectric igniter to initiate combustion of the pyrotechnical charge in actuation mechanism  28 . In one embodiment, this requires the use of a pyrotechnical actuator capable of being fired by a single electrical spark. 
         [0038]    The spark generated by a piezoelectric igniter is more suited to the ignition of a flammable gas rather than a solid pyrotechnical charge; however, in a compact actuator a solid charge is required to generate sufficient force to drive the actuator. In one embodiment, a pyrotechnical actuator a piezoelectric igniter is used to ignite a flammable gas which in turns ignites a pyrotechnical charge. In another embodiment, the device in which the spark electrodes are housed in a free space are separated by a thin gauze from the pyrotechnical charge. The free space would be filled with a flammable gas which could be ignited by a piezoelectric igniter to fire the pyrotechnical charge. 
         [0039]    The benefits of the disclosed embodiments for the fire detection and suppression system are that the system provides a means for incorporating a secondary emergency release mechanism in an electrically operated system which operates in the event of system failure without the need to alter the design of the existing fire extinguisher design. Further, a means for using an unpowered, self contained detection mechanism with existing electrically operated extinguishers is now provided. Thus, with the embodiments disclosed, the system allows for a single pyrotechnical actuation element for use with either an electrically operated detection system or an unpowered mechanically operated detection system enabling commonality of parts between different installations. With the disclosed embodiments, there is no need to worry about power failures, electrical detection errors from the control unit and detection devices, or wire failures during a fire incident as the mechanical temperature sensing apparatus  34  will act as a backup and redundant system. 
         [0040]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.