Steve Debénath, 11 Impasse du Caladon, 06480 La Colle sur Loup, France Tél : (+33) 0620614920 eMail : steve.debenath@cegetel.net

Mouthpiece Unit for Hybrid-Circuit Diving Apparatus

         The present invention relates to a mouthpiece unit for use in breathing apparatus for a diver or the like, the mouthpiece unit comprising a housing, said housing comprising an inlet channel, a demand valve, a breathing chamber, a mouthpiece channel, and a rebreather channel, wherein:

(a)      the inlet channel is arranged to admit a breathable gas to the demand valve from a supply of pressurized gas;

(b)    the demand valve is arranged to admit gas to the breathing chamber from the inlet channel in response to a low pressure condition in the breathing chamber;

(c)    the mouthpiece channel communicates with the breathing chamber and opens towards an exterior end adapted to carry a diver's mouth bit; and

(d)    the rebreather channel has at least a communicating state in which the rebreather channel is in communication with the breathing chamber.

A mouthpiece unit of this type has been known from US-A-5 368 018 (see Figures 1 and 2 therein) or US-A-5 577 498 (see Figures 1 and 6 therein), these documents describing examples of the prior breathing apparatus art compiled in the international patent classes B63C 11/22 and 11/24 pertaining to breathing equipment of divers. Such a mouthpiece unit is used in breathing apparatus for diving, in particular it can be utilized in closed or semi-closed circuit breathing apparatus, also termed rebreathers, which recirculate the diver's breathing gas in a unidirectional flow through a container including an absorbent (e.g. soda lime) to remove CO₂ from the diver's exhalation gas so that the cleansed gas can be inhaled again and again and the oxygen in the gas can be consumed substantially completely rather than having to be expelled into the water due to the CO₂ content.

Therefore, the gas supply (bottle) to be carried by a diver can be considerably reduced as only the oxygen actually used by the diver's metabolism needs to be supplemented to the breathable gas mixture circulating from his mouthpiece to the carbon dioxide absorbent and back to the mouthpiece. Further, an inert non-toxic gas (such as nitrogen and/or helium), which needs to be used as a diluent to keep the partial pressure of oxygen below its toxic threshold of 1.6 bars, is neither used by the diver nor expelled into the water so that the basic amount of inert gas to be carried by the diver only needs to be sufficient to fill the volume of the closed circuit and the diver's lungs at the envisaged maximum diving depth. This economic use of inert gas further decreases the volume of pressurized gas required to be carried along in a bottle, for example.

Circuit hoses from the mouthpiece to the carbon dioxide absorbent and from the carbon dioxide absorbent back to the mouthpiece may be connected to the mouthpiece unit in any one of two ways:

(i) The mouthpiece unit may comprise one rebreather channel, with both circuit hoses being connected to that rebreather channel. Each circuit hose comprises a checkvalve to make sure that the breathing gas circulates in one defined direction so that the diver exhales gas always to the same side (input side) of the absorbent container and inhales gas always from the same side (output side) of the absorbent container. If there is a common leg connecting both circuit hoses to the one rebreather channel (said leg and the two circuit hoses forming a "Y"), the common leg should be relatively short (e.g. shorter than the diver's windpipe) to avoid gas being shifted back and forth in said leg (= dead space) without passing by the absorbent; otherwise, too much accumulated CO₂ might be re-inhaled by the diver.

(ii) The mouthpiece unit may preferably comprise two rebreather channels, with each circuit hose being connected to a respective rebreather channel of the mouthpiece unit. Each rebreather channel of the mouthpiece unit or each circuit hose comprises a checkvalve to make sure that the breathing gas circulates in one defined direction so that the diver exhales gas always to the same side (input side) of the absorbent container and inhales gas always from the same side (output side) of the absorbent container. As both rebreather channels are connected directly to the mouthpiece unit, there is no dead space in which CO₂ might accumulate.

To reduce the breathing resistance in the (semi-)closed circuit mode, one or two breathing bags - also termed counterlungs - may be connected to the circuit upstream or/and downstream of the absorbent container. When the diver descends quickly under water, these bags may tend to collapse temporarily as the ambient pressure increases. This phenomenon, or a failure of the closed circuit (such as a wet absorbent), or a spontaneous effort of the diver may make him want to breathe more breathable gas than is being available from the closed circuit. To overcome the shortage, the demand valve responds to the low pressure situation (caused by the diver trying to inhale) and admits additional gas from the diver's gas supply (e.g. bottle) to the breathing chamber. In such an open-circuit breathing mode (not using the absorber circuit; not recirculating gas but exhausting it; also referred to as scuba diving), gas admission through a demand valve constitutes a standard way of supplying additional breathing gas to the diver. As the mouthpiece unit according to the preamble of claim 1 makes use of both closed-circuit and open-circuit gas supply techniques, it may be called a hybrid-circuit mouthpiece unit. Owing to the availability of a demand valve, the counterlungs of the absorber or rebreather circuit can be dimensioned small to render the breathing apparatus compact.

As mentioned above, the mass of oxygen used by the diver in a closed or semi-closed circuit breathing mode needs to be replenished in the circuit with oxygen from the diver's supply bottle. Particularly in a semi-closed circuit mode, a basic supplement of oxygen or gas including oxygen may be added to the circulating gas at a substantially continuous or constant flow rate. In conventional (semi-)closed circuit breathing apparatus, the oxygen flow is injected either into the inhalation branch of the absorber circuit or into the mouthpiece (US-A-5 960 793, Figure 7, supply line 84). The flow rate is conventionally controlled by a flow valve disposed in the proximity of the supply bottle and/or in a backpack to be carried by the diver (see e.g. US-A-5 960 793, Figure 7, flow rate adjustment orifice 84a).

The arrangement of the flow rate valve in conventional (semi-)closed circuit rebreathers has a drawback in the form of an additional supply line from the gas supply bottle to the absorber circuit or the mouthpiece unit, adding to the complexity and cost of rebreathers.

Regarding conventional hybrid-circuit breathers, US-A-5 368 018 or US-A-5 577 498 do not address any basic oxygen flow, the designers possibly relying on the fact that the diver can get additional breathing gas by actuating the demand valve whenever he feels the need to inhale more deeply.

However, if no permanent basic flow of oxygen is provided to the diver, there is a risk of early fatigue which may affect the diver's attention, health and security. On the other hand, if a continuous minimum flow of oxygen were to be provided using the design of conventional closed-circuit rebreathers (as disclosed in US-A-5 960 793, for example), the resulting pipe circuitry would introduce the complexity thereof.

Therefore, an object to be achieved by the present invention is to ensure a continuous oxygen injection in a hybrid-circuit breathing apparatus without adopting the complex injection structure of conventional (semi-)closed circuit rebreathers.

       This object is accomplished by a mouthpiece unit having the features defined in the preamble of claim 1 and further comprising a flow valve interposed between the inlet channel and the breathing chamber of the mouthpiece housing and arranged to admit gas to the breathing chamber from the inlet channel at a substantially continuous, preferably constant, minimum flow rate.

As the flow valve is advantageously arranged in the mouthpiece unit, there is no need for a flow valve to be provided near a gas bottle or for a dedicated supply line to be arranged from a backpack toward the absorber circuit or to the mouthpiece. Fresh gas is permanently injected into the hybrid mouthpiece unit at a predetermined rate from the inlet channel of the mouthpiece housing (which receives fresh pressurized gas for the demand valve from the supply bottle or the like). In other words, no special supply line is required to make the continuous oxygen flow pass to the breathing chamber in order to maintain the diver's energy and concentration level, and no flow rate control valve needs to be integrated into a backpack, bottle valve or absorber circuit. This produces a new degree of freedom for the design of hybrid-circuit breathing apparatus. The advantages of open-circuit and closed-circuit breathers are combined in a simple manner, in particular allowing a simple modular structure of the semi-closed circuit breather portion since no interfering pipe connection is required between the gas bottle and the absorber circuit. Thus, the absorber circuit can be designed freely, manufactured using inexpensive standard components, and assembled and operated easily by the diver. Hence, the appreciated closed-circuit technique - which allows divers to use smaller bottles and/or to stay under water for longer periods of time - becomes accessible to a broader market segment.

Owing to the permanent oxygen supplement by the open-circuit part of the hybrid-circuit mouthpiece unit, the closed-circuit part of the overall breathing apparatus - in particular the counterlungs and absorbent containers - can be dimensioned smaller, or only one counterlung may be used, so that the bulky constitution of conventional closed-circuit breathers can be made more compact and flexible to increase the diver's comfort. As the mouthpiece unit is the only intersection point between the open circuit and the closed circuit, each of the circuits can be designed and optimized substantially independently of the other. For example, the gas bottle of the open circuit may be carried on the diver's back while the CO₂ absorbent container and the counterlung(s) of the closed circuit may be carried on his belly or chest, or vice versa. In an alternative arrangement, the counterlung(s) may be carried on the diver's back or shoulders while the absorbent container may be kept on his belly or chest etc. This flexibility also permits various ways of balancing the diver's weights according to his preferences and needs. Handling the components of the two circuits is facilitated and easier to understand so that more divers can benefit from hybrid circuit breathers in standard sports diving situations under safe circumstances

In a preferred embodiment of the mouthpiece unit according to the subject invention, the flow valve of the mouthpiece comprises means for adjusting the flow rate to different diving/activity situations and/or different divers (e.g. men/women) that require a different oxygen flow rate. Preferably, the minimum flow rate can be adjusted by a diver or diving trainer in accordance with the envisaged usage. If necessary, the flow rate can be adjusted even during diving since the means for adjusting the throughput rate of the flow valve are preferably provided near the flow valve, i.e. on the mouthpiece unit which is within the diver's reach (as opposed to prior closed-circuit breathers where the flow valve is provided in the backpack, for example). This additional possibility enhances the diver's safety in specific emergency situations, or helps to avoid emergencies in the beginning. A pre-adjustment or calibration of the flow rate to a specific value for a specific use may also be performed by the manufacturer of the flow valve and/or mouthpiece unit.

In a particularly economic implementation, the flow valve may be embodied by the demand valve comprising means for keeping the demand valve in a minimum open state to admit the minimum flow rate from the inlet channel to the breathing chamber through the demand valve. The other function of the demand valve, i.e. to admit fresh gas on the diver's demand, continues to be fulfilled. Demand valves as such have been well-known in the art, they usually comprise a diaphragm that buckles toward a trigger lever when the pressure on the lever side of the diaphragm is lower than the pressure on the other side of the diaphragm, with the lever opening an inlet valve when displaced by the diaphragm. In the arrangement according to this embodiment, the demand valve may advantageously serve two functions, the second function being to ensure a permanent flow of oxygen into the breathing chamber of the mouthpiece unit at a given rate, which is preferably adjustable.

For the reasons mentioned above, the flow rate of the flow valve is preferably adjustable. When the flow valve is embodied by a demand valve comprising a usual purge button for manually opening the demand valve to expel water from the mouthpiece unit, the flow rate may be adjusted in an advantageously simple fashion by slightly depressing the purge button such as to bias the demand valve to a minimum open state, and keeping the purge button in that depressed position. To this end, the purge button itself or/and a structure supporting the purge button may be adjustable to bias the purge button against the trigger lever of the demand valve to maintain the latter in a minimum open state. Fine adjustment may be achieved by a screwing operation of the purge button or structure supporting it.

To avoid any interference between the demand and flow functions of the demand valve, the flow valve may be advantageously embodied by a second valve provided in addition to the demand valve, the second valve comprising a path for admitting the minimum flow rate from the inlet channel to the breathing chamber through the second valve. In this way, the flow rate of the flow valve can be used, and preferably adjusted, independently of the structure and function of the demand valve, and the demand valve does not need to be designed for fine adjustment of a continuous (e.g. constant) flow. As the dedicated second valve can be more precise than the demand valve in adjusting the oxygen flow, the diver's gas supply can be used more economically allowing him to extend his periods under water or to carry a smaller gas bottle, i.e. to make the breathing apparatus more compact.

Where the second valve comprises an external flow button for manually opening the second valve, the second valve preferably comprises adjusting means for biasing the flow button to a minimum open state of the second valve. A flow button accessible from the outside of the mouthpiece housing will be arranged in a watertight manner; therefore, biasing the flow button constitutes an advantageous way of acting on the flow valve without having to open the mouthpiece unit and without admitting water into the mouthpiece unit.

       The applicant therefore reserves the right to direct a future claim to a mouthpiece unit (8; 8"; 8"') according to original claim 6, wherein the second valve (33) comprises a flow button for manually opening the second valve (33), the second valve (33) comprising adjusting means for biasing the flow button to a minimum open state of the second valve.

In an advantageous specific design of the mouthpiece unit according to the preceding paragraph, the flow button may be a push button linearly displaceable in a button passage penetrating a wall of the mouthpiece housing, the passage being threaded at least at an outer end thereof, and a screw element engaging the threaded end of the passage such as to keep the push button in a depressed position biasing the second valve to a minimum open state.

In a particularly versatile embodiment, the mouthpiece unit may be arranged to be selectively switched to an open circuit mode or a semi-closed circuit mode. To this end, the mouthpiece unit may comprise a switching member operable to selectively assume a first state in which the rebreather channel is not in communication with the breathing chamber, or a second state in which the rebreather channel is in communication with the breathing chamber.

In the open-circuit mode of the mouthpiece unit, the diver's exhalation gas is exhausted into the ambient water rather than directed to the absorber circuit. To enable the diver to exhaust gas from his lungs into the water without releasing the mouthpiece, the mouthpiece unit is provided with an exhaust valve. On the other hand, in the closed-circuit mode of mouthpiece unit, the diver's exhalation gas has to be directed to the absorber circuit rather than exhausted into the ambient water. To this end, the exhaust valve is disabled in the closed-circuit mode such that gas from the diver's lungs is not exhausted into the water when the diver exhales at a normal exhalation pressure.

To meet these diverging requirements of the exhaust valve for the open and closed circuit modes, the exhaust valve may be arranged to be enabled or disabled, respectively, by the diver in accordance with the circuit mode that he has selected or is going to select.

In a preferred embodiment, however, the exhaust valve is arranged to allow a diver's exhalation gas to exit the breathing chamber toward the outside of the mouthpiece housing when the switching member is in its first state (= open circuit), and arranged to prevent a diver's exhalation gas from exiting the breathing chamber toward the outside of the mouthpiece housing when the switching member is in its second state (= closed circuit). According to this advantageous arrangement, the exhaust valve automatically assumes the function appropriate for each of the operating modes of the mouthpiece unit, i.e. the exhaust valve is open in the open-circuit mode and closed in the closed-circuit mode as soon as the mouthpiece unit is switched from one mode to the other. Therefore, the diver cannot forget to switch the function of the exhaust valve when he switches the circuit mode of the mouthpiece unit. This feature thus contributes to the diver's safety and comfort.

In a special embodiment, said exhaust valve that is automatically adapted to the circuit modes communicates with the breathing chamber in both the first and second states of the switching member. In other words, when the exhaust valve is to be disabled in order to be ready for the closed-circuit mode this is not effected by isolating the exhaust valve from the breathing chamber (in contrast to the prior art according to US-A-5 368 018) but by modifying the characteristics of the exhaust valve itself, i.e. by modifying its sensitivity to pressure differences between its input and output sides. Such a modification may be achieved by locking the diaphragm of the exhaust valve in the closed-circuit mode, or by applying variable (spring) forces to the diaphragm of the exhaust valve to bias it into its closed position.

The latter design option may be advantageously utilized to provide the exhaust valve with a safety function in the closed-circuit mode: When the switching member of the mouthpiece unit is in its second state (closed-circuit mode), the exhaust valve may be arranged to exhaust gas from the breathing chamber to the outside of the mouthpiece housing if a difference between the gas pressure inside the breathing chamber and an ambient pressure outside the mouthpiece housing exceeds a threshold value.

In other words, if the pressure in the breathing chamber becomes much higher than the pressure outside the mouthpiece housing, due to the diver ascending quickly or exhaling forcefully or due to a pressure regulation problem in the gas supply system, the exhaust valve turns active again and allows gas to leave from the breathing chamber into the ambient environment. Thus, the exhaust valve can be considered as a safety valve, or overpressure valve, because it protects the diver from excessive system pressures that otherwise might enter and damage his lungs. As the exhaust valve may serve as a safety valve, no other valve is required for that purpose in the closed circuit, i.e. a dedicated safety valve - as is usual in closed-circuit rebreathers - can be omitted from the closed circuit.

It is emphasized that this feature of the exhaust valve and its advantageous effects on safety and economy are independent of the presence of absence of a flow valve in the mouthpiece unit, i.e. the exhaust valve may advantageously have said dual functions - serving as a normal exhaust valve in the open-circuit mode and as a safety valve in the closed-circuit mode - in any mouthpiece unit that can be switched from an open-circuit mode to a closed-circuit mode, irrespective of any other features of the mouthpiece unit.

       The applicant therefore reserves the right to direct a claim to a mouthpiece unit (8; 8'; 8"; 8"') according to the preamble of claim 1 and comprising the characterising features of original claim 7, wherein in the second state of the switching member (30, 32; 30, 30b, 30c, 30d) the exhaust valve (28) is arranged to exhaust gas from the breathing chamber (21) to the outside of the mouthpiece housing if a difference between the gas pressure inside the breathing chamber (21) and an ambient pressure outside the mouthpiece housing exceeds a threshold value.

The applicant further reserves the right to direct a claim to breathing apparatus for a diver or the like, comprising:

-      a mouthpiece unit (8; 8'; 8"; 8"') arranged according to any of the original claims, including at least one rebreather channel (9a, 11a);

-      a bottle (1) for containing a pressurized breathable gas including oxygen;

-      a pressure reducing valve (4) provided at an outlet of the gas bottle (1);

-      a flexible pipe (6) for connecting the outlet of the pressure reducing valve (4) to an inlet channel (20) of the mouthpiece unit (8; 8'; 8"; 8"'); and

-      a pair of circuit hoses (9, 11) for connecting the at least one rebreather channel (9a, 11a) of the mouthpiece unit (8; 8'; 8"; 8"') to an input pipe (43a) and an output pipe (43b; 44a), respectively, of an absorbent container (10, 10a, 10b) accommodating material for absorbing CO₂ from gas, each of the hoses (9, 11) including a checkvalve (9b, 11b), said checkvalves (9b, 11b) allowing gas to flow only in one direction in the circuit from the mouthpiece unit (8; 8'; 8"; 8"') through the absorbent container (10, 10a, 10b) and back to the mouthpiece unit (8; 8'; 8"; 8"'), one or both of the hoses (9, 11) being preferably connected to a respective breathing bag (13, 12).

Such breathing apparatus is advantageous in that it comprises the advantageous mouthpiece unit of the invention allowing the components of the open and closed circuits of the breathing apparatus to be divided into separate modules so as to be designed substantially independently of each other, as mentioned above, the only intersection point of the circuits being in the mouthpiece unit. The mouthpiece unit can be separated easily and quickly from the open-circuit, i.e. from the gas supply bottle, if the supply conduit from the bottle valve (e.g. a usual first-stage pressure-reducing valve) is connectable to the inlet channel of the mouthpiece unit using an intermediate-pressure quick-connect plug provided at the end of the supply conduit, and a mating socket provided on the mouthpiece unit.

One particularly advantageous benefit of the additional degree of freedom for the designer resides in the possibility to break the closed circuit down into modules that may be simply assembled, and reassembled by the user, at the user's convenience and demand (e.g. relating to a specific diving project) as there is only a minimum structural interference between the open and closed circuits. Further, an advantageous modular structure may be applied to the absorbent container (also termed filter), i.e. the absorbent container may be provided in the form of a plurality of container modules connected to each other such that, in use, the gas flowing in the closed circuit flows through each said module.

       The applicant therefore reserves the right to direct a claim to breathing apparatus whose absorbent container (10) is provided in the form of a plurality of container modules (10a, 10b) connected to each other such that, in use, the gas flowing in said circuit flows through each said container module (10a, 10b).

An advantageous absorbent container lending itself to such a modular structure may be provided by arranging for the input side or/and output side of the absorbent container to be connectable to a second absorbent container of equal type to form a combined absorbent container having increased capacity for absorbing CO₂. To this end, in one exemplary implementation of the container, the input side of the container may comprise a male connector pipe while its output side may comprise a female connector pipe, or vice versa. In addition or alternatively, at least one end of the container may carry a threaded lid that can be removed to screw said end to a mating end of a second container of substantially equal type. An intermediate coupling sleeve or ring having a threaded inner or outer periphery may be used to interconnect neighbouring filter containers. By so doing, filter containers of practically any absorbent capacity can be assembled and tailored to a diver's variable needs. For short-term diving excursions, a small filter capacity will be sufficient. A small filter may allow a single counterlung to be used (instead of the usual two counterlungs) without creating excessive breathing resistance in the closed circuit. As a result, a smaller and less bulky closed circuit can be assembled. In addition to this advantageous minimization of the closed circuit, the modular components thereof can be worn by the diver on any part of his body, as mentioned above.

In another preferred embodiment, at least part of the wall of the absorbent container is transparent so that colour changes of the absorbent material (crystals) as it becomes contaminated with carbon dioxide can be noted by the diver, as is known as such in the art (e.g. from US-A-4 108 171, column 6, lines 45 to 47). In this way, the diver will know when the absorbent material is going to be used up, and he can extend his diving period accordingly without having to waste absorbent capacity or he can adapt the filter capacity more precisely to a given diving schedule (before diving) to minimize the required filter capacity and bulk without jeopardizing safety.

Finally, in a particularly preferred series arrangement of absorbent container modules, the last container module - as seen in the direction of gas flow in the circuit - comprises a transparent wall portion while the first container module may be opaque. The opaque container may be less expensive in terms of manufacturing cost/effort/time or provide any other desired technical function(s) while the last container module will still allow the diver to make maximum use of his filter capacity in terms of uncontaminated absorbent crystals as the colour of the absorbent material in the last container module will change last. Incidentally, this is a reason why a series arrangement of container modules is preferred over a parallel arrangement thereof even though a parallel arrangement of filter modules constitutes an alternative that is likewise contemplated in the modular circuit design approach of the subject invention.

As to the fields of application of the present invention, it is to be noted that the compact modular breathing or respiratory apparatus can be utilized not only for diving purposes but also for mountain climbing in high altitudes, for airline or combat pilots, for astronauts, for parachutists, for fire fighters, for mobile or stationary medical assistance (hospitals), or instead of gas masks for use in military or nuclear environments (laboratories, power plants, etc)