Abstract:
The head harness includes at least one expandable strap whose ends are connected to the mask for constituting a loop. The strap includes an element which is inflatable by pressurized gas for lengthening the strap up to a size sufficient for the user to locate the harness over his head. Pressurized gas is supplied to the element for increasing its size upon actuating of a manually controlled valve. Upon release of the valve, the strap contacts the head and maintains the mask. A selection valve authorizes venting of the inflatable element when in an &#34;emergency&#34; position and maintains a residual pressure in the inflatable element when in a &#34;comfort&#34; position. The harness or a storage box for the mask are designed for preventing storing of the mask in &#34;comfort&#34; position.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This is a Continuation in Part of application Ser. No. 07/523,832 filed May 16, 1990, now U.S. Pat. No. 5,690,102, which is a Continuation of Ser. No. 07/184,479, filed Apr. 21, 1988, abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to head harnesses for fast attachment of a respiratory mask to the head of a user and it is particularly suitable for use by crew members of high altitude aircraft. 
     As the cruising altitude of passenger and business airplanes increases, it becomes more and more difficult to protect the crew members against a sudden depressurization. However, it is necessary to prevent loss of consciousness of at least one pilot upon depressurization, for him to control the aircraft for return to a safe altitude. 
     Respiratory mask harnesses are known (French 1,506,342 or U.S. Pat. No. 3,599,636; U.S. Pat. No. 4,437,462) which have at least one expandable strap whose ends are connected to the mask and which includes an element which is inflatable by pressurized gas for diametrically enlarging the strap to a predetermined size, sufficient for the user to place the strap around the head. Such harnesses are used on airline planes and include manually controlled means which delivers pressurized gas to the inflatable element for expanding it diametrically upon a positive action and which vents the element upon relase for causing the strap to contract, to contact the head and to maintain the mask. 
     In a typical embodiment, the inflating gas consists of respiratory gas which is delivered to a demand regulator carried by the mask. 
     Such a head harness may be stored in a box in close proximity to the seat and may be grasped by the user with one hand and donned in a time as short as some seconds. However, if depressurization occurs at a very high altitude, lack of oxygen due to exposure to vacuum during some seconds may be sufficient for causing a delayed temporary loss of consciousness after which it will be too late for the pilot to resume aircraft control. 
     Such a risk is avoided if the pilot, or one of the pilots, continuously dons his respiratory mask as long as the aircraft is at a high altitude, for instance beyond 10,000 meters. On the other hand permanently donning the mask applied against the face causes fatigue and strain and is detrimental to comfort. If the mask is continuously fed with oxygen, the volume of the oxygen bottle stored on-board should be higher than presently required. 
     SUMMARY OF THE INVENTION 
     It is a general object of the invention to provide an improved inflatable head harness of the above-defined type. It is a more specific object to provide a fast donning head harness for respiratory mask which lowers the time period following pressurization failure before respiratory oxygen is available to the user while reducing the inconvenience and loss of comfort ancillary to long time use of the mask held on the face. It is a further object to prevent the respiratory mask and harness from being stored in inadequate conditions. 
     For that purpose, there is provided a head harness in which the manually controlled means additionally include selection valve for optionally venting the inflatable element or maintaining a predetermined residual gas pressure, lower than the full inflation pressure, in the inflatable element. 
     The selection valve may comprise a pressure holding valve having a control handle with at least two positions. In one of the positions, the valve is subjected to a closure force determining the residual pressure which may be predetermined, adjusted once for all or adjustable. In the last situation, the mask user may adapt the residual pressure to his or her morphology and this is of particular advantage if the same mask is continuously stored in the cockpit for use by individuals of quite variable size. 
     The pressure holding valve typically has a valve member slidably received on a rod and the control handle has an excentric cam for moving the rod toward a valve seat and resilient means bias the closure member of the valve toward the seat up to a predetermined position with respect to the rod. 
     In a typical embodiment, the manually controlled means for inflating the strap cooperate with the selection valve in such a way that, when the selection valve is in a situation where it maintains the gas pressure at said residual value, a slow increase may be caused by actuating the manually controlled means; that makes it possible for the user to re-establish the residual pressure by temporarily acting on the manually controlled means if the force applying the mask over the face increases due to leakage of the inflatable element. 
     The invention will be better understood from the following description of particular embodiments of the invention, given by way of examples. The description refers to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view illustrating the external aspect of a respiratory mask provided with a harness according to an embodiment of the invention; 
     FIG. 1A is a front view of a storing box; 
     FIGS. 2A and 2B are sketchy representations of a selection valve of simple structure, respectively in &#34;comfort&#34; and &#34;emergency&#34; positions; 
     FIGS. 3 and 4, similar to FIG. 2A, illustrate two modified embodiments; 
     FIGS. 4A, similar to a part of FIG. 4, indicates how an altitude responsive valve may be included in the harness; and 
     FIG. 5 is an illustration of a possible actual construction of a selection valve according to the sketchy representation of FIG. 3. 
     FIGS. 6 and 7 are schematic representations of a modified embodiment, respectively in &#34;normal&#34; and &#34;comfort&#34; condition. 
     FIG. 8 is a schematic representation of another embodiment. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, an emergency respiratory apparatus is illustrated in its position of use, when over the head of a user. The apparatus may be considered as having an oro-nasal face cover 10 (which may be provided with goggles for protection against smoke) secured to a rigid connecting block 14, straps 20 for maintaining the face cover 10 applied against the face and attached to the connecting block 14, and a housing 16. The housing contains a demand regulator and possibly a microphone. The assembly consisting of the straps 20, the connecting block 14 and the elements contained in the block may be considered as a harness 12 carrying the demand regulator and the face cover 10. 
     The connecting block is provided with an inlet for connection of a flexible hose 17 communicating with a source of pressurized respiratory gas. The connecting block communicates the regulator with the hose and has manually controlled means for inflating the harness, comprising a control valve for actuation by squeezing two ears 18 carried by the connecting block 14 between the thumb and index finger of the user. One of the ears 18 is rotatable for actuating the valve, as will be shown later. 
     When the control valve is at rest, it vents an internal volume of the connecting block to atmosphere for permitting retraction of the harness. When the valve is manually actuated, it delivers pressurized gas from the supply hose to the internal volume for harness inflation. 
     As illustrated in FIG. 1, the harness has two straps 20 each having an inner tube of resilient material contained in a substantially non-stretchable sheath which limits extension of the inner tubes. The length of the inner tubes at rest is such that they are able to apply the face over 10 onto the face with a pressure sufficient to provide the necessary airtightness. The invention would however be equally applicable to a harness having one or a plurality of non-stretchable bands, or even a ring, formed to contact the rear of the head and one or more pneumatic jacks for moving the band or ring away from the mask by a sufficient amount for easy donning. Such an arrangement including a band or a ring should be considered as constituting a strap. 
     According to the invention, the harness has selection valve means which, depending upon its condition, either provides an unrestricted communication between the straps and the internal volume of the connecting block or maintains a predetermined over-pressure with respect to the volume when the pressure in the volume decreases to a value lower than the pressure in the straps, typically to the ambient temperature. 
     Referring to FIGS. 2A and 2B, which illustrate a particularly simple embodiment of the invention, the manually controlled valve means comprises a body 21 defining a chamber 22 which continuously communicates with the internal volume 26 of the selection valve 28. The chamber 22 opens through an opening surrounded by a first valve seat into a space which receives pressurized gas from hose 17. It opens to atmosphere by a passage surrounded by a second seat. 
     The two seats respectively cooperate with an air inlet valve member 27 for admission of pressurized gas to chamber 22 and with a valve member 29 for venting to atmosphere, carried by a same stem driven by the rotatable ear 18. Gas pressure (and possibly the force of a return spring, not shown) biases the movable unit consisting of members 27-29 and stem 33 to the position illustrated in FIG. 2A. Then chamber 22 is vented to atmosphere. When the user grasps the harness and squeezes the rotatable ear 18, the movable unit moves (to the left on FIG. 2A), separates chamber 22 from atmosphere and connects it with the pressurized gas supply hose 17. 
     As illustrated in FIG. 2A, the selection valve 28 is formed with a passage 30 communicating the internal volume 26 with the straps 20, surrounded by a seat for receiving a closure member in the form of a poppet 32. The poppet 32 is slidably received on a rod 34 located coaxially to the seat. A control handle 36 movable by the harness user is drivably connected to the rod and makes it possible to move it between a position closest to the seat (as shown in FIG. 2A) and a position remote from the seat (as shown in FIG. 2B). In the embodiment of FIGS. 2A and 2B, the handle 36 consists of a rotatable lever pivotally received on the housing for rotation about an axis 37 and an excentric cam 38 having an abutting connection with rod 34. A spring 39 exerting a very slight force retains rod 34 in sliding contact with the excentric cam. A progressivity spring 40 is located between a flange of rod 34 and poppet 32 and retains the poppet in contact with a stop member 41 on the rod when the rod is in the remote or withdrawn position illustrated in FIG. 2B. The force exerted by spring 40 is in direct relation with the residual pressure in the straps when the rod is in the forward or closest position illustrated in FIG. 2A. 
     The amount of travel of rod 34 by the excentric cam 38 is so selected that the poppet 32 is clear of the seat and leaves a free communication between the straps 20 and the volume 26 when the handle is in the &#34;emergency&#34; position illustrated in FIG. 2B for use of the mask upon pressurization failure. On the other hand, the pressure in the straps cannot decrease beyond a value determined by the metering spring 40 and selected for use during extended time periods when the handle is in the &#34;comfort&#34; position illustrated in FIG. 2A before the user releases rotatable ear 18. 
     The modified embodiment of the harness illustrated in FIG. 3 has a residual pressure adjustment cam 42 located between the excentric cam 38 and the rod 34. The adjustment cam 42 determines the spacing between the rod and the excentric cam and consequently determines the compression force of spring 40 when the handle is in the &#34;comfort&#34; position illustrated in FIG. 3. 
     In the modified embodiment of FIG. 4, a non-return check valve 44 having a closure spring of low compression force is arranged for authorizing a gas flow from volume 26 toward the straps if the pressure in volume 26 exceeds the residual pressure in the straps. The non-return check valve 44 may be provided whether or not the selection valve has a residual pressure adjustment cam 42. Due to the provision of non-return check valve 44, the straps can be re-inflated to a predetermined pressure, even with handle 36 in the &#34;comfort&#34; position, if there is a leakage from the straps which progressively decreases the pressure in the latter. For re-inflation, the user gently squeezes the ears 18 until a sufficient pressure is obtained. The non-return check valve 44 preferably has a low cross-sectional flow area for re-inflation to occur slowly. As a result, the straps remain in contact with the head during reinflation and there is no risk of mis-location of the mask. A check valve 44 having a cross-sectional flow area of about 0.05-0.1 mm 2  generally gives satisfactory results for a supply pressure of 5 bars. 
     For avoiding the need for manual actuation upon failure of pressurization when the handle is in the &#34;comfort&#34; position, the device of FIG. 4 may additionally include an altitude responsive valve 52 having a valve closure member driven by altitude responsive bellows for automatically communicating the internal volume 26 with the straps, as shown in FIG. 4A. 
     The actual arrangement of the components of the harness may be as shown in FIGS. 1 and 5. The manually controlled handle 36 is carried by a U-shaped straddle 48 for rotation between a lower position (illustrated in full lines on FIG. 1) and a higher position (in dash-dot lines) about axis 37. A stem is carried by handle 36, parallel to axis 37, and at a distance therefrom to constitute the excentric 38. The residual pressure adjustment cam 42 is carried by stem 38 and has flats for abutting contact with rod 34. The flat sides prevent cam 42 from rotating untimely from the position into which it was manually moved. For easier angular adjustment of the cam 42 by the user, the cam is non-rotatably connected to a knurled wheel 50. The cam is freely rotatable on the excentrically mounted stem 38 for keeping the same angular position when the stem 38 is rotated about axis 37. 
     When the mask is not donned, it should be stored with handle 36 in &#34;emergency&#34; condition. If not, it would not be possible to inflate the harness in the embodiments of FIGS. 2A, 2B and 3 and inflation would be slow in the embodiment of FIG. 4. For fulfilling that purpose, the storing box 51 (FIG. 1A) for the emergency respiratory mask may be constructed for mask insertion to be possible only when the control handle 36 is in the &#34;emergency&#34; position. A simpler approach consists of covering that face of the handle which is apparent when in &#34;comfort&#34; position with a contrasting color. Then the reception box should be such that the handle can readily be checked when in stored condition. Still another approach consists in designing the manually controlled means so that it returns to &#34;normal&#34; position when the harness is inflated for undonning the mask 
     The mask may be used as follows. 
     When the mask is stored for being grasped if emergency conditions occur, the handle 36 is in &#34;emergency&#34; position and operation is identical to that of the prior art harnesses referred to above. 
     When the mask should be worn for a long time period in stand-by condition, the user removes it from the box. He grasps the ears 18 for inflating the harness and then rotates the handle 36 to &#34;comfort&#34;. If the selection valve is of the type illustrated in FIG. 5, the user moves the knurled wheel 50 to the position of maximum residual pressure. He positions the mask on the face and releases the ears. The harness de-inflates until the maximum residual pressure is reached. Then the user adjusts the residual pressure by acting on knurled wheel 50. 
     If there is a leakage of gas, the tension of the harness progressively increases. If it becomes excessive, the user slightly re-inflates the harness by squeezing the ears until he obtains the appropriate adjustment again. 
     Then, if there is an incident resulting for instance into depressurization or smoke in the cockpit, while the user is donning the mask in &#34;comfort&#34; position, he just swings handle 36 to &#34;emergency&#34; for causing complete venting of the harness and airtight application of the face cover on the face. Even before airtight contact is achieved, respiratory oxygen is available to the user. 
     Last, when the user wishes to remove the mask, he first moves the handle to &#34;emergency&#34; (which is the normal condition at rest) and then inflates the harness by squeezing the ears. 
     Referring to FIGS. 6 and 7, where the elements corresponding to those of FIGS. 1-4 are designated by the same reference numbers, a modified embodiment is shown, in which the elements are returned to &#34;normal&#34; condition when the harness is inflated by the wearer for undonning. 
     Referring to FIG. 6, a selection valve 28 has a seat for receiving a closure member 32. That closure member has a poppet fast with a stem 60 slidably received in a blind bore of rod 34. A cover 62 is loosely fastened to the poppet and arranged for airtight abutment against a seat surrounding passage 30. The poppet is formed with a hole 66 for slow inflation of the harness, as will be seen later. In emergency condition of the selection valve 28 (FIG. 6), the rod 34 in its rearmost position. An O-ring seal 68 located in a circular groove of a passage for the rod 34 provides an airtight barrier between the outside and volume 26. In the embodiment of FIGS. 6 and 7, the control handle 36 consists of a lever having a terminal hook gripping an end flange 70 of rod 34. 
     When the control handle 36 is manually moved to the &#34;comfort&#34; position illustrated in FIG. 7, it forces the rod 34 forwardly until the O-ring seal 68 snaps into a circular groove of the rod. Then the cover 62 is forced onto its seat by the poppet 32, with a force which depends on the degree of compression of the progressivity spring 40. The hole 66 is closed by the cover. 
     A valve for communicating the volume 26 and the harness straps 20 comprises a valve member 74 biased by a spring to a closure position. The valve member is arranged to be forced open by the rod 34 when the latter is moved to the sight beyond the position where the O-ring seal 68 engages the groove on rod 34. 
     Assuming that the selection valve 28 is initially in the comfort condition illustrated in FIG. 7, full inflation of the harness by actuation of manually controlled valve means for undonning causes a pressure to build up against the right hand flange of rod 34. The cross-section of the rod is such that the pressure force is sufficient for overcoming the retaining action of the O-ring 68 and to move back the rod and control handle to the position shown in FIG. 6. The mask may then be stored in such a condition that manual actuation of the manually controlled valve means under emergency conditions will cause immediate inflation of the straps and deinflation when the rotatable ear 18 is released. 
     Then, if the wearer wishes to obtain comfort conditions, he has only to move the control handle clockwise until the position illustrated in FIG. 7 is reached. A slight and temporary action on control handle 36 will temporarily open valve 74, partially depressurizing the harness. 
     It is important to note that existing masks having a fast donning harness (for instance as described in French patent 1,506,342 already mentioned) may easily be retrofitted, simply by adding means as illustrated in FIGS. 2 to 5. As a consequence, masks according to the invention and masks for use at lower altitudes may be manufactured with components most of which are common. And existing masks may be adapted to high altitude flight. 
     Still another embodiment causing the harness to revert to &#34;normal&#34; (i.e. emergency) condition when undonned prior to storage is illustrates in FIG. 8. The elements of FIG. 8 corresponding to those in FIG. 1 are designated by the same reference numbers. Again, the selection valve 28 has a rod 34 projecting through the housing of the valve and actuated by a control handle 36 through an angularly adjustable cam 38. A resilient latch 70 opposes return of the handle from the &#34;comfort&#34; position E (in full line) to the &#34;normal&#34; position N (in broken line). Altitude responsive bellows 72 provided with a push rod 74 for forcibly moving the rod 34 to the left fulfill the same function as the altitude responsive valve 52 of FIG. 4A. 
     Inflation of the harness straps may be obtained by pressing the handle 36 beyond the &#34;normal&#34; position, to the position indicated as F on FIG. 8. Then the handle forces a valve plunger 76 from the position shown in FIG. 8 to a position where it communicates the pressurized gas supply with the harness straps. 
     A restriction 78 may be provided to maintain a throttled flow toward the harness straps to compensate leaks due for instance to porosity of the straps. When the selection valve 28 is in normal position, that flow is evacuated through the poppet valve 32. In comfort position, the flow is only evacuated to atmosphere via the poppet valve when the pressure build-up in the harness straps overcomes the force of spring 40. 
     Full inflation for donning the mask is obtained by maintaining an action on the ears 18; upon release, there is deflation. 
     Change from normal to comfort condition is obtained by pressing the handle 36 beyond position C for a short time. 
     Full deflation when in comfort condition is obtained by exerting a short action on ear 18 to generate a pressure sufficient to unlock handle 36 and revert to normal. 
     Full inflation for undonning the mask is obtained by maintaining a force on ear 18 until the harness is fully expanded. Again the handle is brought back to position N if initially in comfort position.