Patent Abstract:
A breathing apparatus for an aircraft crew member has a breathing mask provided with a demand regulator and connected to a source of breathing gas, such as a pressurized oxygen cylinder or preferably an OBOGS. The apparatus includes an individual buffer plenum specific to the mask on a line for feeding the regulator of the mask from the source. The volume of the plenum is sufficient to provide for at least two typical breaths of the mask wearer in succession. A non-return check valve is located between the plenum and the source.

Full Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to breathing apparatus for protecting crew members, in particular the technical flight crew, of an airplane against the risks associated with depressurization at high altitude and/or the occurence of smoke in the cockpit. 
   A major, although non-exclusive application lies in passenger airliners that can reach high altitudes, and above all so-called “jumbo” or “super-jumbo” aircraft of very large capacity. 
   At present, each airliner pilot has breathing apparatus comprising a mask fitted with a demand regulator connected to a source of breathing gas. Aviation regulations require that the mask can be put into place and supply oxygen to its wearer in less than 5 seconds. At present, this result is generally achieved by using a mask with a pneumatic harness that can be inflated and deflated, such as one of those described in documents FR-A-1 506 342 (or GB 1175080), FR-A-2 784 900, and U.S. Pat. No. 5,623,923, the content of which is incorporated herein by way of reference. The source of gas under pressure must be capable of instantly delivering oxygen or air greatly enriched in oxygen at a pressure which is sufficient for inflating the harness and feeding the regulator of the mask. In general, the source is a cylinder of oxygen under pressure. 
   On airliners, another installation is provided to supply passengers with breathing gas in the event of depressurization and to ensure survival until the airplane has come down to an altitude where normal breathing is possible at ambient atmospheric pressure. 
   On passenger “jumbos”, the necessary supply of oxygen requires a very large weight. 
   In order to reduce this mass, the oxygen supply can be replaced by an on board oxygen generator, such as a battery of on-board oxygen generator systems (OBOGS) fed with air derived from the compressor of one or more of the engines. However, such generators supply air that is highly enriched in oxygen only after a delay has elapsed from the command to supply oxygen. In addition, the output pressure of an OBOGS depends on the rotational speed of the engine and the air supplied is enriched in oxygen to a degree that is variable. The pressure initially available can be too low to inflate the fast-donning harness. The initial degree of enrichment can also be insufficient. A common buffer tank for acting as a supply of very enriched air is placed at the outlet of the OBOGS, but that solution is far from perfect, particularly since the available pressure can be insufficient for inflating a harness and since the presence of an oxygen transfer pipe causes a further delay. Other types of on-board generator and even common oxygen supplies present similar drawbacks. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an improved breathing apparatus of the type having an oxygen supply and a mask with an inflatable pneumatic harness apparatuses. It is a more specific object to provide apparatus adapted to large capacity airliners having a common supply for the crew and passegers. It is a more particular object to provide apparatus which guarantees that breathing gas at a pressure which is sufficient to make rapid donning possible and guarantees that the oxygen content of the gas breathed in is sufficient from the very first breaths of the user, before the airplane reaches an altitude at which oxygen availability becomes essential, possibly even prior to takeoff. 
   To this end, there is provided a breathing apparatus having a line for feeding the regulator of a mask, said line including an individual plenum specific to the mask (or to a small number of masks) and of sufficient volume to provide for at least two typical breaths in succession, the plenum being being provided with an inlet check valve for connection to a generator of oxygen or more frequently oxygen-enriched air. The pressure inside said plenum is thus the maximum pressure supplied by the generator during a preceding period. 
   When using an OBOGS, which deliversgas whose oxygen content varies, in particular depending on the instant in its oxygen-delivery cycle, it is preferable to provide the feed line with a control valve that enables the plenum to be filled initially only when oxygen content is greater than a predetermined threshold, e.g. 94%. The valve can also be kept closed whenever the admission pressure is too low. 
   Once the first breaths have been breathed and the generator is operating under steady conditions, or in the event of the plenum being emptied while the generator is still not fully satisfying the conditions specified above, means are typically provided to enable gas from the generator to flow freely to the regulator of the mask. 
   In practice, a plenum for storing 3 to 5 liters of expanded gas suffices. Present mask harnesses generally require a pressure of about 2 bars and a volume of about 1 liter for inflation purposes. As a general rule, an OBOGS delivers pressure that can vary over a ratio of 1 to 6 depending on engine speed. For an OBOGS delivering pressure that varies over the range 0.5 bars to 3 bars, the maximum pressure reached when the engines are at full power for climbing greatly exceeds the pressure required in the plenum. 
   The invention makes it possible to use a common on-board generator both for the crew and for passengers, and to avoid carrying oxygen cylinders which are heavy and require frequent verification, except cylinders that might be required for possible therapeutic reasons. 
   The plenum can often be incorporated in a mask storage box which causes oxygen to flow to the regulator on being opened. The plenum is then directly connected to a hose feeding both the regulator and the harness of the mask. This configuration only requires a small increase in the size of a box such as that described in document U.S. Pat. No. 6,039,045, for example. 
   The above features and others, will be better understood on reading the following description of particular embodiments, given as non-limiting examples. The description refers to the accompanying drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified view of apparatus constituting a particular embodiment of the invention, having a full face mask, and shown with the mask out of the storage box; and 
       FIG. 2  shows a modified embodiment. 
   

   DETAILED DESCRIPTION 
   The apparatus shown in  FIG. 1  comprises a breathing mask  10  with a regulator  12  enabling dilution with ambient air and with a pneumatic harness  14  which can be constituted, in particular, by any one of the various types described in the above-mentioned patent applications. When not in use, the mask and the harness are stored in a box  16  provided with a two-flap door  18 ,  20 . A valve  22  carried by the case of the box is interposed between a flexible hose  26  connected to the regulator of the mask and a feed pipe  24 . The valve  22  is so placed and arranged to communicate the hose with the pipe  24  when the user of the mask  10  pulls the mask out from the box and the flap  18  opens. Sometimes, the box also carries a switch for selecting between operation of the regulator with dilution (providing protection against hypoxia only) and without dilution (for providing protection against smoke or at very high altitude). 
   In steady conditions of operation, the pipe  24  receives air highly enriched in oxygen from a generator  30 , generally constituted by an OBOGS battery with alternate absorption and delivery cycles. Two OBOGS are shown in  FIG. 1. A  same single generator feeds a large number of masks. By way of example each OBOGS includes a molecular sieve. Such OBOGS are commercially available, e.g. making use of the dispositions described in U.S. Pat. No. 4,561,865, and the prior art cited therein. 
   In the embodiment of the invention shown in  FIG. 1 , a feed line provides a connection between the storage box and an outlet manifold  32  of the generator  30 . There is found in succession, from the downstream end to the upstream end of the line: a plenum  34 , a non-return check valve  36  and a control valve (typically a solenoid valve)  38 . The check valve guarantees that a volume of air that is highly enriched in oxygen under a pressure sufficient to inflate the harness is maintained in the plenum even during periods when the generator  30  is delivering air at a pressure that is lower than the pressure required inside the plenum  34 . As illustrated, a three-port control valve  38  is associated with a control module  40  which ensures that, so long as the mask is stored, the plenum is fed with gas coming from the generator  30  only when that gas has an oxygen content in excess of a threshold, e.g.  94  ±2%. For this purpose, a gas analyzer  42  is connected to the feed line to the plenum  34  and supplies a signal to the module  40 . The module  40  can also have a pressure takeoff  44  and be arranged or programmed to cut off communication of the manifold  32  with the plenum  34  unless the pressure supplied by the generator exceeds a predetermined value, higher than the value needed to ensure that the harness  14  can be fully inflated. 
   In a simplified embodiment, the solenoid valve  38  is controlled to put the manifold  32  into communication with the check valve  36  as long as the oxygen content of the breathing gas exceeds the threshold. 
   In another variant, suitable for use when the source of oxygen-enriched gas initially and immediately provides an oxygen content that is sufficiently high, the valve  38  can be omitted. 
   In another variant, the module  40  is designed to control the solenoid valve so as to put the manifold  32  into communication with the check valve  36  on receiving a signal indicating that the flap  18  of the box has been opened. This ensures that the mask is fed continuously while it is being worn. 
   In the modified embodiment shown in  FIG. 2 , the mask  10  is designed to be stored other than in a mask box. It is connected by the flexible hose  26  to a separate plenum. The connection between the plenum  34  and a solenoid valve  38  includes a non-return check valve  36 . In the example shown, the solenoid valve  38  is connected to a control module  40  which puts the manifold  32  into communication with the check valve  36 :
         when the oxygen content as measured by a gas analyzer  42  exceeds a determined value; and   when the pressure in the plenum  34  as measured by a sensor  44  is below a determined value, so as to provide breathing gas directly from the source.       

   Other embodiments are also possible, optionally using solenoid valves, in particular depending on the nature of generator  30 . 
   The bank of OBOGS is typically for supplying boxes containing emergency passenger masks, as well as the masks of the crew members, with oxygen enriched air. 
   When using OBOGS generators, an exemplary method of operating the complete installation is as follows. 
   During initial climbing of the airplane after takeoff, at least one of the generators  30  is put into operation to extract oxygen selectively. Since the jet engines are then operating at full power the air which passes through the molecular sieve of the generator is at high pressure. 
   Once the molecular sieve becomes saturated, atmospheric air feed is transferred to another OBOGS. A set of valves provided on the first OBOGS is controlled so as to communicate the outlet of the OBOGS with the manifold  32  and the OBOGS is heated to deliver oxygen. Since the pressure is high, and since the gas has a high oxygen content, the individual buffer plenums  34  are filled to a pressure that is sufficient for inflating harnesses. Means can be provided to deplete the buffer plenum of the air it might have been contained prior to being filled with oxygen enriched air under pressure. One or more common storage tanks  46  can also be filled at this stage in addition to the individual plenums. 
   Once these operations have been performed and the second OBOGS has also become saturated in oxygen, the first OBOGS can be refilled so as to ensure that a maximum supply of oxygen enriched air is available. 
   In a variant, at least one of the generators is controlled to implement an absorption/delivery cycle prior to take-off so that the pilots have oxygen-rich gas under pressure available and suitable for enabling them to don their masks, e.g. in the event of smoke. 
   Under all circumstances, the pilots are able to don the breathing mask in a few seconds whatever the altitude and very highly enriched breathing gas is immediately avalable for breathing. 
   One or more common tanks give the passengers access to oxygen as well, but with a delay that can be somewhat longer. Since the generators are initially saturated in oxygen and under pressure, they enable the feed to be maintained under high pressure during the time needed to descend to an end-of-cruising altitude, in the range 5000 meters to 8000 meters, where a lower pressure suffices for breathing requirements, and where pressure is indeed lower because the engines are operating at reduced speed. 
   Numerous possible modifications will immediately appear to those familiar with the relevant art. For instance a same plenum of increased capacity can be shared between two pilots.

Technology Classification (CPC): 0