Abstract:
A method for determining a characteristic such as partial pressure or percentage of a gaseous constituent in a first gas mixture flow in a flow chamber in which there is alternating flow in opposite directions between the first gas mixture flow and a second gas mixture flow. The steps may include a) introducing the first gas mixture flow into a sensing chamber when the first gas mixture flow flows in the flow chamber, b) preventing introduction of gas from the flow chamber into the sensing chamber at least when the second gas mixture flow flows in the flow chamber, c) sensing the characteristic of the first gas mixture flow in the sensing chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the United States national phase of International Application No. PCT/IB2011/000781 filed on Feb. 28, 2011 and published in English on Sep. 1, 2011 as International Publication No. WO2011/104635, which application claims priority to U.S. Provisional Application No. 61/308,476 filed on Feb. 26, 2010, the contents of both of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method for determining a characteristic such as partial pressure or percentage of a gaseous constituent and a regulator of breathing mask for aircraft occupant. The gaseous constituent is in particular oxygen or carbon dioxide. 
     BACKGROUND OF THE INVENTION 
     The partial pressure or percentage of oxygen (and carbon dioxide) are particularly useful in order to satisfy the needs of the user while reducing the consumption in pure oxygen (provided by an oxygen cylinder, a chemical generator or a liquid oxygen converter) or gas highly enriched in oxygen provided in particular by an on-board oxygen generator system (OBOGS). 
     But, when two gases having different mixtures successively flow in opposite directions in a chamber, the measurement of a characteristic of a gaseous constituent in the first gas mixture flow is disturbed by the second gas mixture. The invention aims at reducing this problem. 
     SUMMARY OF THE INVENTION 
     For this purpose the invention provides a method for determining a characteristic such as partial pressure or percentage of a gaseous constituent in a first gas mixture flow in a flow chamber where flows alternatively said first gas mixture flow and a second gas mixture flow in opposite directions comprising the following steps: 
     a) introducing the first gas mixture flow into a sensing chamber when the first gas mixture flow flows in the flow chamber, 
     b) preventing introduction of gas from the flow chamber into the sensing chamber at least when the second gas mixture flow flows in the flow chamber, 
     c) sensing said characteristic of the first gas mixture flow in the sensing chamber. 
     According to another feature in accordance with the invention, preferably the method further has the following steps:
         providing a user with a breathing mask for aircraft occupant including a demand regulator,   generating a respiratory gas flow by breathing in of the user into the flow chamber, and   generating an exhalation gas flow by breathing out of the user into the flow chamber, one amongst the respiratory gas flow and the exhalation gas flow being the first gas mixture flow and the other being the second gas mixture flow.       

     According to a supplementary feature in accordance with the invention, preferably the method further has the following steps:
         splitting the flow chamber in a respiratory chamber and sensing chamber,   inserting an isolation valve between the sensing chamber and the respiratory chamber, in order to prevent introduction of the second gas mixture flow into the sensing chamber,   generating the first gas mixture flow into the respiratory chamber, by breathing of the user into the respiratory chamber.       

     According to a supplementary feature in accordance with the invention, preferably the method further comprising feeding the respiratory chamber with the first gas mixture flow through the sensing chamber and the isolation valve. 
     According to an alternative feature in accordance with the invention, preferably the method comprising feeding sensing chamber with the first gas mixture flow through the respiratory chamber and the isolation valve. 
     According to another feature in accordance with the invention, preferably the method further comprises introducing the first gas mixture flow into the sensing chamber from the flow chamber during step a). 
     According to a supplementary feature in accordance with the invention, preferably the method further comprises: 
     d) detecting the occurrence of the first gas mixture flow in the flow chamber,
         during step a), putting the sensing chamber in flow communication with the flow chamber when the occurrence of the first gas mixture flow in the flow chamber is detected.       

     According to another supplementary feature in accordance with the invention, preferably the method further comprises preventing communication between the flow chamber and the sensing chamber when the occurrence of the first gas mixture flow in the flow chamber is not detected. 
     According to another feature in accordance with the invention, preferably the method further comprises:
         placing a solid ionic conductor of a pump electrochemical cell interposed between the flow chamber and the sensing chamber, and   during step a), pumping said gas constituent from the flow chamber into the sensing chamber through the solid ionic conductor.       

     Otherwise, the invention provides a method for protecting aircraft occupant comprising the steps of: 
     a) providing a user with a breathing mask for aircraft occupant, 
     b) providing a respiratory gas including a mixture of breathable gas and dilution gas to the user, 
     c) sensing partial pressure or percentage of oxygen or carbon dioxide in exhalation gas flow generated by the user, 
     d) adjusting the rate of oxygen or breathable gas in the respiratory flow in accordance with the partial pressure or percentage of oxygen or carbon dioxide. 
     It appears that the partial pressure or percentage of oxygen or carbon dioxide in exhalation gas flow is an efficient indication concerning the oxygen need of user. Therefore, the consumption in oxygen can be accurately adjusted. 
     The invention also provides a breathing mask for aircraft occupant including a demand regulator, said regulator comprising:
         a breathable gas supply line to be connected to a source of breathable gas and supplying a flow chamber with breathable gas,   a dilution gas supply line to be connected to a source of dilution gas and supplying the flow chamber with dilution gas,   a dilution adjusting device adjusting the rate of dilution gas in the respiratory gas supplied to the flow chamber, the dilution adjusting device comprising a dilution valve and a control device controlling the dilution valve in accordance with a dilution signal generated by the gas sensor in function of the partial pressure or percentage of oxygen or carbon dioxide in exhalation gas.       

     In advantageous embodiments, the breathing assembly preferably further has one or more of the following features: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present invention will appear in the following detailed description, with reference to the appended drawings in which: 
         FIG. 1  shows a breathing mask comprising a flow chamber, 
         FIG. 2  schematically represents a first flow and a second flow in the flow chamber of the breathing mask, according to a sensing device not within the scope of the invention, 
         FIG. 3  represents variations of the first flow in the flow chamber during the time, 
         FIG. 4  represents variations of the second flow in the flow chamber during the time, 
         FIG. 5  represents measurements provided by gas sensors placed in the flow chamber, 
         FIG. 6  represents a first embodiment of a sensing device in accordance with the invention, 
         FIG. 7  represents a second embodiment of a sensing device in accordance with the invention, 
         FIG. 8  represents a third embodiment of a sensing device in accordance with the invention, 
         FIG. 9  represents a fourth embodiment of a sensing device in accordance with the invention, 
         FIG. 10  represents a step of a method according to the invention using the sensing device of the fourth embodiment, 
         FIG. 11  is a flowchart representing different steps according to the invention, 
         FIG. 12  represents a method according to the invention, 
         FIG. 13  represents a variation of the method represented in  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  discloses main functions of a breathing mask  4  for occupant of an aircraft, in particular for pilot disposed in a cabin  10  of an aircraft. 
     The breathing mask  4  comprises a demand regulator  1  and an oronasal face piece  3  fixed to a tubular connecting portion  5  of the regulator  1 . When a user  7  dons the breathing mask  4 , the oronasal face piece  3  is put to the skin of the user face  7  and delimits a respiratory chamber  9 . 
     The demand regulator  1  has a casing  2  including a breathable gas supply line  12 , a dilution gas supply line  14  and a respiratory gas supply line  16 . The respiratory gas supply line  16  has a downstream end in fluid communication with the respiratory chamber  9 . 
     The breathable gas supply line  12  is supplied at its upstream end with pressurized oxygen by a source of breathable gas  8  through a feeding duct  6 . In the embodiment shown, the pressurized source of breathable gas  8  is a cylinder containing pressurized oxygen. The breathable gas supply line  12  supplies the respiratory chamber  9  with breathable gas through the respiratory gas supply line  16 , the downstream end of the breathable gas supply line  12  being directly in fluid communication with the upstream end of the respiratory gas supply line  16 . 
     The dilution gas supply line  14  is in communication by its upstream end with a source of dilution gas. In the illustrated embodiment, the dilution gas is air and the source of dilution gas is the cabin  10  of the aircraft. The dilution gas supply line  14  supplies the respiratory chamber  9  with dilution gas through the respiratory gas supply line  16 , the downstream end of the dilution gas supply line  14  being directly in fluid communication with the upstream end of the respiratory gas supply line  16 . So, in the embodiment illustrated, the breathable gas and the dilution gas are mixed in the respiratory gas supply line  16  of the casing  2 , i.e. before supplying the respiratory chamber  9  through the tubular connecting portion  5 . Therefore a flow  62  of respiratory gas flows in the respiratory gas supply line  16  and the respiratory chamber  9 , the respiratory gas including breathable gas and dilution gas mixed. 
     The regulator  1  further comprises an exhaust line  18  and an exhaust valve  20 . The exhaust valve  20  is disposed between the downstream end of the exhaust line  18  and the cabin  10  (ambient air). The upstream end of the exhaust line  18  is in communication with the respiratory chamber  9  of the oronasal face piece  3  through the tubular connecting portion  5  and receives a flow  64  of gas exhaled by the user. Concerning the exhaust of the exhalation gas flow  64 , the exhaust valve  20  functions as a check valve which opens under the pressure of the exhalation gas flow  64  and closes for preventing air of the cabin  10  from entering into the flow chamber  30 . 
     The user  7  breathes in and breathes out in the respiratory chamber  9 . The exhalation line  18  is in communication directly or through the respiratory chamber  9  with the respiratory gas supply line  16 . Therefore, the gas supply line  16 , the respiratory chamber  9  and the exhalation line  18  define a flow chamber  30  without separation. 
     The demand regulator  1  further has a pressure adjusting device  22  and a dilution adjusting device  24 . 
     The pressure adjusting device  22  adjusts the pressure in the flow chamber  30  and in particular in the respiratory chamber  9 . In the embodiment illustrated, the pressure adjusting device  22  comprises in particular a main valve disposed between the feeding duct  6  and the respiratory gas supply line  16 . 
     The dilution adjusting device  24  adjusts the rate of oxygen in the respiratory gas flow  62 . In the embodiment illustrated, the dilution adjusting device comprises in particular a dilution valve  23  and a control device. The dilution valve  23  is disposed between the dilution gas supply line  14  and the respiratory gas supply line  16 . The control device controls the dilution valve  23 . 
     Demand regulator starts supplying first gas mixture (respiratory gas) in response to the user of the breathing mask breathing in and stops supplying respiratory gas when the user stops breathing in. 
     One can refers to prior art, such as for example to document U.S. Pat. No. 6,789,539 for a more detailed description of a demand regulator. The present invention is also applicable to other types of dilution adjusting device  24 , such as the dilution adjusting device disclosed in patent application PCT/FR2011/050359 or U.S. Pat. No. 6,789,539 included by reference. 
       FIG. 2  schematically represents the flow chamber  30  in which alternatively flows a first gas mixture flow  32  and a second gas mixture flow  34 . In order to adjust the rate of oxygen to deliver to the user  7 , a characteristic (in particular the partial pressure or percentage of a gaseous) of a gaseous constituent (in particular oxygen or carbon dioxide) of the first gas mixture flow  32  is to be detected by a gas sensor. 
     The first gas mixture flow  32  may be either the respiratory gas flow  62  or the exhalation gas flow  64 , which means that the characteristic of the gaseous constituent to sense may be either in the respiratory gas or in the exhalation gas. So, the first gas mixture flow  32  flows from the tubular connecting portion  5  to (the mouth or nose of) the user  7  or from the user  7  to the tubular connecting portion  5 . Conversely, the second gas mixture flow  34  may be either the exhalation gas flow  64  or the respiratory gas flow  62 . 
     As represented schematically in  FIG. 3 , between the time 0 and the time T 1 , the gas content in the flow chamber  30  reaches the gas content of the first gas mixture flow  32  and then between the time T 1  and the time T 1 +T 2 , the first gas mixture flow  32  becomes absent from the flow chamber  30 . 
     As represented schematically in  FIG. 4 , between the time 0 and the time T 1 , the second gas mixture flow  34  becomes absent from the flow chamber  30  and then, between the time T 1  and the time T 1 +T 2 , the gas content in the flow chamber  30  reaches the gas content of the second gas mixture flow  34 . 
     It should be noticed that in  FIGS. 3 and 4  the time for filing the flow chamber  30  is neglected. 
     So, it may be considered by simplification that successively during a T 1  period the first gas mixture flow  32  flows in the flow chamber  30  in a first direction, then during a T 2  period the second gas mixture flow  34  flows into the flow chamber  30  in a second direction opposite to the first direction, then the first gas mixture flow  32  flows again in the flow chamber  30  during another T 1  period, and so on. The T 1  period may be considered as equal to the T 2  period, and called T. 
     The gaseous content of the first gas mixture flow  32  being different from the second gas mixture flow  34 , the second gas mixture flow  34  disturbs the measurement of the characteristic of the gaseous content of the first gas mixture flow  32 . It should be understood that the first gas mixture and the second gas mixture may content the same constituents (at least some identical constituents), and only differ in the percentage of some of the constituents (in particular percentage of oxygen, carbon dioxide and steam). 
       FIG. 5  presents three measurements  42   a ,  42   b ,  42   c  provided by gas sensors having different response times Tr for the above described example. The measurements  42   a ,  42   b ,  42   c  correspond to gas sensors having a response time respectively equal to T/10, T/2 and 2T. 
     It appears that the gas sensor providing measurements  42   a ,  42   b  are suitable for the present example, whereas the gas sensor providing measurement  42   c  is not appropriate. 
     So, the shorter the response time of the gas sensor is, the more accurate the measurement is. But, a sensor with a short time response is generally more expensive than a sensor with a longer time response, and sometimes a sensor with a time response satisfying for a particular application does not exist. 
       FIG. 6  represents a first embodiment of a device  100  in accordance with the invention. The device  100  is a portion of the breathing mask  4  represented in  FIG. 1 . 
     The device  100  comprises a flow direction sensor, a shutter, a driving device  51  and a gas sensor placed in a sensing chamber  40  in fluid communication with the flow chamber  30  through a passage  66 . 
     The flow direction sensor and the gas sensor are connected to the control device. The flow direction sensor detects if the flow direction in the flow chamber  30  corresponds to the direction of the first flow mixture  32 . In variant, the flow direction sensor may detect if the flow direction in the flow chamber  30  corresponds to the direction of the second flow mixture  34 . 
     The shutter movable between an active position in which it closes the passage  66  and an inactive position in which it is away from the passage  66 . 
     The control device  60 -controls the driving device  51  in order to place the shutter open position when the flow direction sensor detects the first gas flow  32 , so that the first gas mixture flow  32  (partially) enters in the sensing chamber  40 . Moreover, the control device controls the driving device  51  in order to place the shutter in closed position when the flow direction sensor does not detect the first gas flow  32 , so that the second the second gas mixture flow  34  is prevented from entering in the sensing chamber  40 . 
     Therefore, the sensing chamber  40  contains only gas mixture of the first gas mixture flow  32  at any time. So, the gas sensor transmits a dilution signal which accuracy is not influenced by the second gas mixture flow  34 . The control device controls the dilution valve  24  in accordance with the dilution signal generated by the gas sensor. 
     The gas sensor is adapted to determine in particular partial pressure (or percentage) in oxygen (or carbon dioxide) of the gas contained in the sensing chamber  40 . 
     The flow direction sensor includes in particular a pressure sensor, a pressure gauge sensor, a pressure differential sensor, thermistances, a sensor of the state of a check valve or a piezo sensor device comprising a flexible sheet and detecting the direction of the curvature of the flexible sheet. 
       FIG. 7  represents a second embodiment of a device  100  in accordance with the invention. 
     In this second embodiment, the characteristic of the gaseous constituent to sense is in the respiratory gas, so that the first gas mixture flow  32  is the respiratory gas flow  62  and the second gas mixture flow  34  is the exhalation gas flow  64 . 
     An isolation valve  36  is inserted between the respiratory gas supply line  16  and the respiratory chamber  9 . The gas sensor, in connection with the control device, is placed in the respiratory chamber  16  which forms the sensing chamber  40 . The isolation valve  36  prevents gas from entering into the sensing chamber  16 ,  40  from the respiratory chamber  9 . 
     In the embodiment illustrated, the isolation valve  36  is a check valve. In variant, it may be an inspiration valve similar to the exhaust valve  20 . 
       FIG. 8  represents a third embodiment of a device  100  in accordance with the invention. 
     In this third embodiment, the characteristic of the gaseous constituent to sense is in the exhalation gas, so that the first gas mixture flow  32  is the exhalation gas flow  64  and the second gas mixture flow  34  is the respiratory gas flow  62 . 
     The isolation valve  36  is inserted between the respiratory chamber  9  and the exhalation line  18 . The gas sensor, in connection with the control device, is placed in the exhalation line  18  which forms the sensing chamber  40 . The isolation valve  36  prevents gas from entering into the respiratory chamber  9  from the exhalation line  18 . 
       FIG. 9  represents a fourth embodiment of a device  100  in accordance with the invention. 
     The gas detector comprises a pumping plate  44 , a first disk of solid ionic conductor  45 , a common plate  46 , a second disk of solid ionic conductor  47  and a sensing plate  48 . 
     The pumping plate  44 , the common plate  46  and the sensing plate  48  are electrodes preferably made of platinum films. 
     The pumping plate  44 , the common plate  46  and the sensing plate  48  are of substantially annular form. Therefore, the sensing chamber  40  is delimited by the common plate  46 , the first ionic conductor  45  and the second ionic conductor  47 . 
     A current source  39  is inserted between the pumping plate  44  and the common plate  46 . The common plate  46  and the sensing plate  48  are connected to the control device, as well as the flow direction sensor. 
     The pumping plate  44 , the first solid ionic conductor  45  and the common plate  46  define a pumping electrochemical cell  56 . The common plate  46 , the second solid ionic conductor  47  and the sensing plate  48  define a sensing electrochemical cell  58 . 
     The ionic conductors  45 ,  47  define solid electrolyte. They are preferably made in zirconium dioxide suitably adapted for the conduction of ions of oxygen O 2 . 
     The gas sensor further comprises an optional filter  49  surrounding the pumping electrochemical cell  56  and the sensing electrochemical cell  58 . The filter  49  prevents particles from entering into the sensor. Therefore, the gas sensor includes a buffer chamber  41  extending between the flow chamber  30  and the pumping electrochemical cell  56  (and the sensing electrochemical cell  58 ). 
     The gas sensor may be placed either in the respiratory chamber  9 , in the respiratory gas supply line  16  or in the exhalation line  18 , and of any of the first to third embodiment described above. 
     As illustrated in  FIG. 10 , when the electrical power supply  39  outputs a pumping current  i  at the value Ip, oxygen ions are transported through the ionic conductors  45  from the sensing chamber  40  to the buffer chamber  41 . Therefore, an evacuation phase  28  corresponds to a phase of pumping current i equal to Ip. So, the partial pressure in Oxygen PO 2  in the sensing chamber  40  decreases. The voltage Vs between the sensing plate  48  and the common plate, called Nerst voltage, increases. 
     When the electrical power supply  39  outputs a pumping current  i  at the value −Ip, oxygen ions are transported through the ionic conductor  45  from the buffer chamber  41  to the sensing chamber  40 . Therefore, a pressurisation phase  26  corresponds to a phase of pumping current i equal to −Ip. So, the partial pressure in Oxygen PO 2  in the sensing chamber  40  increases and the Nerst voltage Vs between the sensing plate  48  and the common plate  46  decreases. 
     In operation, the control device causes a repetitive sequence where the oxygen pumping current I is successively reversed to maintain the Nerst voltage Vs between to predetermined values V 1 , V 2 . 
     Therefore, the partial pressure of Oxygen in the sensing chamber  40  varies between two values PO 2 low and PO 2 high. 
     The period of oscillation Tp is proportional to the oxygen partial pressure in the buffer chamber  41 . Therefore, period of the pumping cycle is used to determine the ambient oxygen partial pressure. 
     The transportation of the oxygen through the ionic conductor  45  during the pressurisation phase  26  creates a pressure drop in the buffer chamber  41 . The low porosity of the external filter  49  limits the entry of the ambient gas into the sensor and is responsible of the main delay (high response time) in the oxygen partial pressure measurement. 
     The response time of the gas sensor generates an error in the measurement of the oxygen partial pressure in the first gas mixture flow  32 , due to the second gas mixture flow  34 . 
     As shown in  FIG. 11 , in order to limit the error in the measurement of the oxygen partial pressure in the first gas mixture flow  32 , the direction of the flow in the flow chamber  30  is sensed by the direction gas sensor. During step S 38 , based on the signal provided by the flow direction sensor, the control device determines if the flow in the flow chamber  30  is in the direction of the first gas mixture flow  32 . If Yes, during a measurement period, the pressurization phase  26  and the evacuation phase  28  repetitively and alternatively follows one another. If No, as shown in  FIG. 12 , during a period without measurement, the pressurisation of the sensing chamber  40  is stopped, no pressurisation phase  26  occurring during the period without measurement. Consequently, diffusion of the second gas mixture flow  34  into the gas sensor buffer  41  is reduced and the sensing accuracy of the gas sensor  42  is improved. For example, the gas sensor measurement process is active during inspiration of the user and stopped during exhalation of the user if the characteristic of the gaseous component to be sensed is in the respiratory gas. 
     In a variant shown in  FIG. 13 , during the period without measurement, preferably at the beginning, an evacuation phase  28  is achieved. During the evacuation phase  28  of the period without measurement, as shown in  FIG. 13 , the pumping current i is preferably lower than during the evacuation phase  28  of the measurement period, i.e. lower than Ip. Therefore, the evacuation phase  28  of the period without measurement lasts during all the period without measurement or at least more than half of the period without measurement.