The present invention relates to an emergency oxygen supply system. Emergency oxygen supply systems are provided in aircraft, to enable passengers and crew to breath without loss of consciousness in event of loss of cabin pressure at elevated altitude.

In the words of Wikipedia, there are two systems that are typically found on aircraft:

- A gaseous manifold system, which connects all oxygen masks to a central oxygen supply, usually in the cargo hold area. Pulling down on one oxygen mask starts the oxygen supply for that mask only. The entire system can usually be reset in the cockpit or in some other location in the aircraft.

- A chemical oxygen generator system connected to all masks in the compartment. Pulling down on one oxygen mask removes the firing pin of the generator igniting a mixture of sodium chlorate and iron powder, opening the oxygen supply for all the masks in the compartment. Oxygen production cannot be shut off once a mask is pulled, and oxygen production typically lasts at least 15 minutes. During the production of oxygen, the generator becomes extremely hot and should not be touched. A burning smell may be noted and cause alarm among passengers, but this smell is a normal part of the chemical ^' reaction. This system can be found on the McDonnell Douglas MD-80 aircrafts, whose system is also unique in the fact that the face masks are clipped to the inside of the compartment door and do not drop out and hang, by the oxygen tube, in front of the passengers.

In view of weight and heat generation, there is interest in replacing chemical oxygen generation systems with gaseous oxygen systems, albeit without the complexity of a central oxygen supply.

Self-Contained Breathing Apparatus is known, particularly in the form used under-water by divers as Self-Contained Underwater Breathing Apparatus - hence the acronym SCUBA. Such apparatus releases air via a demand valve on breathing in by the user and provides all the air required for the user to breath, as is of course necessary underwater, but not in an aircraft at elevated altitude where the air is simply too thin.

It is known to release oxygen on breathing of ambient air for patients whose breathing is inadequate to draw in sufficient air. Reduction of pressure in a delivery tube, due to breathing in, causes a regulator to release a pulse of oxygen per inhalation from an intermediate reservoir into the delivery tube. Such a pulse regulator can be electromechanical or purely mechanical.

An electromechanically regulated, aircraft, pulse, emergency oxygen supply system has been proposed.

The object of the present invention is to provide a more economic, purely mechanical, pulse, emergency oxygen supply system for aircraft.

According to the invention there is provided an emergency oxygen supply system comprising: a source of compressed oxygen, means for releasing oxygen from the source in response to (in case of) a drop in air pressure, at least one oxygen mask, a respective mechanical breath-actuated valves for releasing a pulse of oxygen into the or each mask and a pressure reducer for releasing oxygen from the source into an intermediate reservoir upstream of the breath-actuated, pulse valves.

Normally the components of the system will be for aircraft use and housed in a dedicated compartment in the base of luggage bins above passenger seating, with means for releasing the or each mask to a user in response to a drop in air pressure. Whilst we can envisage providing the breath-actuated pulse valve(s) in the compartment, with a pressure reducer and a respective intermediate reservoir upstream of each mask's pulse valve, with a tube to the mask downstream of the pulse valve; in the preferred embodiment, the or each pulse valve is arranged at the mask. In this arrangement, the intermediate reservoir or at least part of it is provided as the internal volume of the respective tube to the or each mask.

The pressure reducer can be a single pressure regulator for supplying multiple tubes for multiple masks, or indeed a respective regulator for each tube. The or each regulator will normally be throttled to ensure that the amount of oxygen released as each pulse is not significantly augmented, during release of the oxygen in the tube as a pulse, by flow through the regulator prior to closure of the pulse valve for accumulation of the next pulse in the tube. Alternatively the pressure reducer can be a simple throttle supplying multiple tubes, or indeed a respective throttle for each tube, the throttle being sized to increase the pressure in the tube(s) to at least that appropriate to refill the tube during a normal breathing period.

Whilst the source of oxygen will normally be a bottle or cylinder housed in a compartment also housing the mask(s) ready for release, it can include a pipe to the compartment from a remote bottle or cylinder(s). This arrangement is preferred only in parts of the aircraft potentially vulnerable to an engine fan blade damage.

The source of compressed oxygen may contain compressed pure gaseous oxygen or an oxygen rich mixture of gases.

In accordance with a particular preferred feature of the invention, a first pulse augmenter may be provided. In a possible embodiment, this comprises a reservoir arranged to be filled with oxygen for the first pulse and isolated thereafter by a shut off valve actuated by differential pressure resulting from release of the first pulse.

For instance, each first pulse augmenter comprises a throttle in a passage from the pressure regulator to the respective pulse valve, downstream of the throttle a branch passage leading to the augmenter reservoir arranged to fill prior to a first pulse being released by the pulse valve, a further passage leading from upstream of the throttle to one side of a augmenter diaphragm, the other side of the augmenter diaphragm being open to the branch passage, the diaphragm carrying an obturator arranged to engage with and close an orifice across the branch passage between intermediate the passage and the reservoir, the obturator being initially held out of the orifice by a spring so that, prior to a first breath taken by a user of the respective mask, the augmenter reservoir and the tube are filled with oxygen via the branch passage and, when the user takes the first breath, the pulse valve allows oxygen in the tube and the reservoir into the mask as an augmented first pulse, the throttle generating a build up of pressure on the further passage side of the diaphragm before the pressure rises in the branch passage causing a differential pressure across the diaphragm causing it to move with seating of the obturator in the orifice, the reservoir being then not filled and not available to augment subsequent oxygen pulses, the mechanism comprising a mechanical latch locking the obturator in the position closing the orifice during the followings pulses.

As an optional feature of the invention, a barometric pulse compensation valve may be provided. In a possible embodiment the oxygen reservoir has an adjustable volume and/or pressure depending upon the barometric pressure thus providing a variable volume pulse to the mask. This means that an altimetric sensing device may adjust the pressure and/or flow from pressure regulator 15 into tube 5.

This could be embodied by a reservoir that has its volume controlled by the movement of a diaphragm which has one side connected to the barometric pressure and the other side linked to the oxygen reservoir and control by the reservoir pressure and or a spring. A further refinement could link the barometric pressure to the pressure regulator to adjust the pressure of the oxygen supplied to the oxygen reservoir.

To help understanding of the invention, a specific and non limiting embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic perspective view of an emergency oxygen supply system of the invention;

Figure 2 is a side view of an oxygen cylinder and deployed mask of the system of Figure 1;

Figure 3 is cross-sectional view of the oxygen cylinder of Figure 1 and

Figure 4 is a view similar to Figure 3 of a first pulse augmenter.

Referring to the drawings, an emergency oxygen system compartment 1 has an oxygen cylinder 2 with a oxygen flow pressure reducer release valve 3. Housed in the compartment are a plurality of masks 4 having respective oxygen supply tubes 5.

A closure flap 6 is retained by a barometric latch 7 which can be a solenoid released latch, wired to a central barometric switch 8 applying power to and the aircraft's solenoids in the event of cabin pressure reduction. Release of the closure flap 6 releases the masks 4 for passengers to grasp and use.

Each mask 4 has a pair of conventional non-retum valves 11, 12 to the ambient atmosphere.

Inhalation valve 11 allows the user to draw in ambient air, for inhalation with oxygen as described below, whilst exhalation valve 12 allows exhalation to ambient. In accordance with the invention, the mask 4 also carries a pulse valve 14 connected to its tube 5 and opening into the mask. The pulse valve 14 is of the type that opens on pressure reduction in the mask, induced by inhalation causing a pressure differential across the inhalation valve.

The mechanical breath-actuated valve may include has a housing including a gas intake portion, an intermediate portion, and a gas outlet portion; a movable valve stem between the intake and intermediate portions, a spring biasing the stem towards the closed position; with the outlet portion having an exterior surface with a gas outlet opening located therein. That is to say, the mechanical breath-actuated valve allow passage of oxygen into the mask when relative negative pressure is sensed into the mask at the downstream outlet of said mechanical breath-actuated valve during inhalation. Oxygen contained in a reservoir portion of said mechanical breath-actuated valve is then allowed to flow through the downstream outlet of the valve. Thus a discrete volume of oxygen in a form of a pulse is provided by the mechanical breath-actuated valve into the mask very rapidly and before inhalation. The flow of oxygen in the mask terminates when the reservoir portion of said mechanical breath-actuated valve is depleted. When this occurs the mechanical breath-actuated valve closes and the reservoir portion of said mechanical breath-actuated valve begins to refill. The negative pressure occurring when the user takes a breath at which the mechanical breath-actuated valve 14 is activated produces a flow of oxygen that operates before the inhalation valve opens. Upon exhalation, positive pressure in the mask occurs and flow from mechanical breath- actuated valve 14 has already ceased as exhalation valve 12 opens.

For example, the mechanical breath-actuated (pulse) valve may be the type of the one disclosed in documents US20150040906A1.

Opening of this valve 14 allows the oxygen stored in the tube 5 to be released as a pulse into the mask 4. On release of the pulse, the pulse valve 14 closes again for accumulation of a fresh pulse's worth of oxygen in the tube 5. In this way, the tube 5 acts as a reservoir determining how much oxygen is to be released as each successive pulse.

At the compartment end of each tube 5, a pressure reducer 15 is connected. This can be a pressure regulator or a simple throttle. It allows oxygen to flow into the tube 5 to a pressure such that, taking account of the volume of the tube 5, it acts as a reservoir for each pulse released by the pulse valve 14. The pressure downstream the pressure reducer 15 can be set between 2 bar and 10 bar with a preferred pressure between 4 bar and 7 bar.

In case the tube 5 is connected to one mask 14, the tube 5 volume may have a volume between 10 ml and 80 ml, with a preferred volume between 15 ml and 50 ml, for supplying gas to one mask 14.

The tube(s) 5 may be flexible and made of PVC.

Upstream of the pressure regulators 15 is the oxygen release valve 3. This may have a body 21 clamping a diaphragm 22 to a seat 23 in a mouth of the cylinder 2. The body carries for example a spring loaded pin 24 held from piercing the diaphragm 22 by a withdrawable yoke 25. This is connected by a cord 26 to each of the masks 4 of a length to hold up the released masks 4 just short of the passengers needing to use it, whereby grasping of a mask 4 pulls the yoke 25 clear of the pin 24, releasing it to release oxygen. The body has a passageway 27 from the region of the pin's piercing end to a union 28 to a pipe 29 leading oxygen to the pressure regulator 15.

The body also carries a spring loaded plunger 31, which bears on the middle of the diaphragm 22. The outer end of the plunger 31 is connected to a flag 32. Should the pressure of the oxygen in the cylinder 2 drop through leakage, the plunger 3 deflects the diaphragm 22 and this is witnessed by the flag 32.

The invention is not intended to be restricted to the details of the above described embodiment. For instance, the system could have only a single mask 4 for use in a lavatory.

Further as shown in Figure 2, optional first pulse augmenters 41 can be provided downstream from the pressure regulator 15. Each oxygen supply tube 5 may have a first pulse augmenter 41. These can be provided in the compartment 1 at the feed into the tube 5. Alternatively, they can be provided at the respective masks 4.

As shown in Figure 4, each first pulse augmenter 41 may have a throttle 42 in a passage 43 from the pressure regulator 15 to the respective pulse valve 14. Downstream of the throttle 42 a branch passage 44 leads to an augmenter reservoir 45 arranged to fill prior to a first pulse being released by the pulse valve 14. A further passage 46 leads from upstream of the throttle 42 to one side of a diaphragm 47. The other side of the diaphragm 47 is open to the branch passage 44.

The diaphragm 47 carries a cone 48 arranged to engage with and close an orifice

49 across the branch passage 44 between intermediate the passage 43 and the reservoir 45. Initially the cone 48 is help out of the orifice 49 by a spring latch 50.

In this state, prior to a first breath taken by a user of the respective mask 4, the reservoir 45 and the tube 5 are filled with oxygen via the passage 44. When the user takes the first breath, the pulse valve 14 allows oxygen in the tube 5 and the reservoir 45 into the mask 4 as an augmented first pulse. The result, due to the throttle 42 is a build up of pressure on the further passage 43 side of the diaphragm 47 before the pressure rises in the branch passage 44. This causes a differential pressure across the diaphragm 47, causing it to move with seating of the cone 48 in the orifice 49. The reservoir 45 is then not filled and is not available to augment subsequent oxygen pulses. The spring latch 50 comprises a U shaped, spring clip 51 which engages as a detent in a groove 52 in backing member of the cone 48, with the diaphragm 47 captive between the cone 48 and the backing member. The free end 53 of the backing member is conical. When the differential pressure displaces the diaphragm 47, the clip 51 is held by an abutment 54 and passed in an over- centre manner over the ridge 55 between the groove and conical end 53. As soon as it has passed over-centre, the spring clip 51 acts on the conical end to keep the shut off valve comprised by the cone 48 and the orifice 49 closed. Thereafter as the supply tube 5 fills for each successive pulse, it is the volume of the tube which determines the amount of oxygen in each pulse.