Patent Description:
During cruise portions of flight, most commercial passenger aircraft operate at altitudes exceeding fourteen thousand feet. At these altitudes, insufficient oxygen may be present in the ambient air to sustain human consciousness or life. Accordingly, cabins of the aircraft are pressurized, often to altitudes equating approximately eight thousand feet. At such "cabin altitudes," sufficient oxygen normally will be present in ambient air to avoid hypoxia and thereby sustain human consciousness and life.

Loss of cabin pressurization when an aircraft is flying above, e.g., fourteen thousand feet, therefore, creates risk of passengers (and crew) experiencing hypoxia. Aircraft hence typically are fitted with emergency oxygen systems configured to supply supplemental oxygen to passengers temporarily while an aircraft operator reduces the flight altitude of the aircraft. The systems include cup-shaped face masks connected to sources of oxygen via flexible tubing and stored pre-use in, for example, drop out boxes (DOBs).

These systems additionally require both electrical power and signals from the aircraft to function, thus creating significant power-management issues for operation of the aircraft. Existing systems, for example, use pyrotechnic-activated devices to break seals on oxygen bottles, typically requiring approximately 126W of aircraft power to activate the pyrotechnies. Additional electrical power is required to operate the control boards of the systems and, in some cases, to actuate latches in the DOBs.

Commonly-owned <CIT>, whose contents are incorporated herein in their entirety by this reference, discusses this need for electrical energy to commence oxygen flow and control oxygen supply during emergencies. One such solution disclosed in the Rittner patent to reduce the amount of Peak power needed from the aircraft is to employ an energy storage unit (e.g. a rechargeable battery). The storage unit cooperates with an energy harvesting element (e.g. a Peltier or photovoltaic element) to recharge. The preamble part of claim <NUM> is disclosed in <CIT>.

Documents <CIT>, <CIT>, <CIT> and <CIT> disclose other emergency oxygen systems.

A general problem associated with modern aircraft is the desire to provide an overall lightweight construction of the aircraft to reduce fuel consumption of the aircraft. It is to be understood that such lightweight construction may comprise a reduction of weight of structural components like wings of the aircraft but may also comprise a reduction of the weight of cabin interior elements, including passenger service units (PSU) and the like. It is an object of the invention to provide an oxygen breathing device allowing such lightweight construction of modern aircraft.

A still further object in design of modern aircraft is to allow efficient manufacturing and maintenance of the aircraft to reduce manufacturing and maintenance costs. It is an object of the invention to provide an emergency oxygen system allowing such reduced manufacturing and maintenance costs.

A still further object is to retrofit existing aircrafts without inducing substantial modifications and incurring high costs.

According to a first aspect, the invention provides an emergency oxygen system for aircraft comprising:.

So, the device of the present invention may be configured to be electrically inert (dormant) - thus not needing any stand-by power - until it is switched on for being used. Therefore, the electricity consumed is reduced which at least therefore reduce the fuel consumption, if the device is powered by the aircraft and may also reduce the weight of the aircraft and the maintenance cost (in order to check, charge and eventually change the battery) if the device is powered by a battery.

The emergency oxygen systems for aircraft rarely are needed during commercial flight, so any electricity used to power them in stand-by mode is effectively wasted. On the other hand, the devices need to operate as reliably as possible during certain emergencies, even if inadequate power might be available from the aircraft engines. Thus, for example, utilizing the invention together with storage batteries or capacitors as a power source could both allow the systems to be electrically autonomous (i. no power directly from the aircraft is required) while avoiding undue drain on the batteries when the oxygen supply system is idle.

The electronics board and the flow control valve may in particular adjust either the value of the flow of breathing gas supplied to the aircraft passenger or the time during which the breathing gas flows towards the passenger mask per breath. The electronics board and the flow control valve may also adjust the flow of breathing gas, so that the passenger has a determined quantity of breathing gas available.

According to another feature in accordance with the invention, preferably the power source is a stored power source, in particular a battery.

Therefore, extensive wiring, manufacturing efforts and increased weight are avoided, and retrofitting and modifications of the aircraft configuration are eased.

According to another feature in accordance with the invention, preferably the switching device comprises an input point and an output point, the power source is connected to the input point, the electronics board is connected to the output point, and the switching device has an impedance higher than <NUM><NUM> ohm, preferably higher than <NUM><NUM> ohm, in the second state between the input point and the output point.

Therefore, the power consumption of the switching device is very low when the switch is in the second state.

According to a supplementary feature in accordance with the invention, preferably the impedance between the input point and the output point is lower than <NUM> ohm, in the first state.

Therefore, power consumption of the switching device is very low when the switch is in the first state.

According to the invention, the switch is of electrical or electronic type, the switching device further comprises an activation line, the switching device is configured to actuate the switch to switch from the second state to the first state when a (low power) activation signal is present in the activation line.

Therefore, the device may be energized (switched on) by a low power signal from an emergency system of the aircraft.

According to a supplementary feature in accordance with the invention, preferably the switching device is configured to uphold the switch in the first state, even if the activation signal in the activation line disappears.

Therefore, power consumption is reduced and control of the state of the switching device is eased.

According to a supplementary feature in accordance with the invention, preferably the switching device comprises an input point, an output point and an ON point, the power source is connected to the input point, the electronics board is connected to the output point, the switching device is configured to send the activation signal from the ON point to an ON line through the activation line, and the switching device is configured to send an output signal from the output point to the ON line through an upholding line.

Therefore, the activation signal has not to keep on being present to uphold the switching device in the first state which reduces power consumption.

According to another feature in accordance with the invention, preferably the emergency oxygen system comprises a test switch interposed between the power source and the activation line.

Therefore, the emergency oxygen system can be easily energized (switched on) for being tested.

According to another feature in accordance with the invention, preferably the emergency oxygen system comprises a receiver configured to receive an emergency signal and send the activation signal in the activation line.

Therefore, the device can be energized (switched on), in particular from the emergency system of the aircraft, without having to provide a wire for connecting the emergency system of the aircraft to the emergency oxygen system.

According to another feature in accordance with the invention, preferably the emergency oxygen system further comprises a container, at least one mask and a latch, the container includes a door movable between a closed position and an open position, the latch has a locking state and a releasing state, in the locking state, the latch is configured to secure the door in the closed position in order to maintain the mask within the container, in the releasing state, the latch is configured to release the door, the activation line is connected to the latch, and the latch is configured to be driven in the unlocking state when the activation signal is present in the activation line.

Therefore, the same signal is used for opening the door of the container containing the mask and energizing (switching on) the device.

According to an alternative feature in accordance with the invention, preferably the emergency oxygen system further comprises a container, at least one mask and a latch, the container includes a door movable between a closed position and an open position, the latch has a locking state and a releasing state, in the locking state, the latch is configured to secure the door in the closed position in order to maintain the mask within the container, in the releasing state, the latch is configured to release the door, and the electronics board is configured to control the unlocking state of the latch.

Therefore, no separate signal is required for opening the door of the container containing the mask as the emergency oxygen system can control the latch once energized (switched on).

According to the invention, the switching device comprises a deactivation line configured to switch the switch from the first state to the second state in case a (low power) deactivation signal is present in the deactivation line, and the electronics board is configured to send the deactivation signal in the deactivation line.

Therefore, the device of the present invention further may return to an inert state when activity no longer is needed. Thus, power can be saved, in particular when the emergency oxygen system was energized (switched on) only for testing.

According to a supplementary feature in accordance with the invention, preferably the electronics board comprises an ambient pressure sensor configured to sense ambient pressure, and the electronics board is configured to determine whether ambient pressure sensed by the pressure sensor is higher than a depressurization threshold and send the deactivation signal in the deactivation line in case the ambient pressure is higher than the depressurization threshold.

Therefore, the emergency oxygen system can determine that it was energized (switched on) only for testing and it may switch off itself when the test procedure is completed.

According to a supplementary feature in accordance with the invention, preferably the electronics board comprises a controller configured to control the flow control valve based on the ambient pressure sensed by the ambient pressure sensor.

Therefore, the ambient pressure sensor enables to determine if emergency oxygen system is energized (switched on) for testing, and if not the ambient pressure sensor enables to adjust the flow of breathing gas supplied to the passenger(s), so that the passenger(s) are not supplied with more breathing gas than the required flow which depends on the ambient pressure.

According to another feature in accordance with the invention, preferably the emergency oxygen system comprises an actuator of aneroid type, and the actuator is configured to have a dimension below an ambient pressure threshold, so that the switch is in the first state.

Therefore, the emergency oxygen system can be automatically energized (switched on) when the ambient pressure is too low to enable passenger to normally breath ambient air without requiring supplemental wiring throughout the aircraft.

According to another feature in accordance with the invention, preferably the emergency oxygen system comprises an initiator with a Shape Memory Alloy element to cause a seal of the source of breathing gas to be punctured and the initiator is connected to the controller, preferably by an electrical wire, so that the initiator is controlled by the controller.

According to another feature in accordance with the invention, preferably the switch is a transistor.

A low-power signal may trigger the transistor to an "on" state so as to connect a power source to a to-be-powered product. An exemplary signal may be on the order of one milliwatt (<NUM> mW) in some versions of the present invention which employ a metal-oxide-semiconductor field-effect transistor (MOSFET) as a low-power switch, although persons skilled in the art will recognize that lower or higher power signals conceivably may be utilized in connection with other types of switching components.

According to an alternative feature in accordance with the invention, preferably the switch is a relay.

According to another feature in accordance with the invention, preferably the emergency oxygen system further comprises the source of breathing gas.

According to another aspect, the invention provides a method of operating an emergency oxygen system including:.

Therefore, the electrically-powered emergency oxygen system needs not utilize power from the aircraft when idle or in stand-by mode the emergency oxygen system as it may be electrically inert unless needed to supply oxygen. The power consumption is reduced (null) when the passenger needs no breathing gas and the flow of breathing gas is reduced to the minimum required by the passenger(s) when the ambient air does not provide enough oxygen to the passenger(s).

According to another feature in accordance with the invention, preferably the operation (ii) includes receiving an activation signal to cause the switching device to electrically connect the power source to the electronics board.

According to a supplementary feature in accordance with the invention, preferably the operation (iii) includes upholding (maintaining) the power source connected to the electronics board regardless of the activation signal.

According to an alternative supplementary feature in accordance with the invention, preferably the operation (ii) includes receiving the activation signal to cause the switching device to electrically connect the power source to the electronics board and to cause at least one mask released from a container.

According to another feature in accordance with the invention, preferably the operation (iii) includes transmitting a deactivation signal from the electronics board so as to cause the switching device to electrically disconnect the electronics board from the power source.

According to a supplementary feature in accordance with the invention, preferably the method comprises detecting a test procedure and during an operation (iv) achieving a test procedure and then transmitting the deactivation signal from the electronics board so as to cause the switching device to electrically disconnect the electronics board from the power source.

According to a supplementary feature in accordance with the invention, preferably the test procedure includes receiving an activation signal and determining that ambient pressure is higher than a depressurization threshold.

According to another feature in accordance with the invention, preferably the operation (iii) includes adjusting the flow of breathing gas based on ambient pressure.

Other objects, features, and advantages of the present invention will be apparent to persons skilled in the art with reference to the remaining text and drawings of this application.

Depicted in <FIG> is an emergency oxygen system <NUM> constituting an exemplary implementation of the present invention.

The emergency oxygen system <NUM> is intended to deliver complementary breathing gas (oxygen) to passengers on-board an aircraft. The emergency oxygen system <NUM> is implemented in an aircraft, more accurately in the cabin of an aircraft. The cabin of the aircraft is pressurised so that cabin ambient air <NUM> is pressurised and includes a standard rate of oxygen (about <NUM> %). The emergency oxygen system <NUM> is intended to deliver complementary breathing gas (oxygen) to passengers on-board an aircraft in case of depressurisation due to the failure of pressurisation device or an uncontrolled leak between the cabin and outside, and/or when toxic gases, in particular fumes, are present in the cabin ambient air <NUM>. In a variant, the emergency oxygen system <NUM> could be intended to deliver complementary oxygen to crewmembers.

As shown in <FIG>, the emergency oxygen system <NUM> mainly comprises a breathing gas supply circuit <NUM>, an electronics board <NUM>, a power source <NUM> and a switching device <NUM>. The emergency oxygen system <NUM> also comprises an activation device <NUM>.

In the embodiment shown in <FIG>, the power source <NUM> is a stored power source, preferably a battery. The battery is preferably a non-rechargeable battery, preferably of alkaline type. But, the battery can also be a rechargeable battery, preferably of cadmium type, but it can also be of lithium type or other convenient type. In a variant of power source of stored type, the power source can comprise a capacitor and/or a coil. In another variant, any desired source may be utilized, in particular stabilized power supply. Possible alternate or additional implementations may include electro-magnetic induction (power and/or data), light modulation, etc..

The breathing gas supply circuit <NUM> comprises a source of breathing gas <NUM>, a regulator <NUM>, a delivery valve <NUM>, a plurality (three are illustrated) of masks <NUM> for passengers (users), first tubing <NUM> and second tubing <NUM>. In a variant, the breathing gas supply circuit <NUM> may comprise a plurality of delivery valves <NUM>, one per mask <NUM>. In a variant, the breathing gas supply circuit <NUM> could comprise only one mask.

The delivery valve <NUM> is disposed between the source of breathing gas <NUM> and the mask <NUM> The delivery valve <NUM> is connected to the source of breathing gas <NUM> by the first tubing <NUM>, preferably rigid tubing, which supplies the delivery valve <NUM> with breathing gas.

The illustrated masks <NUM> are face masks having a cup-shape internally defining a cavity and may be provided with a reservoir (not illustrated). The masks <NUM> are connected to the delivery valve <NUM> by the second tubing <NUM>, preferably flexible tubing. The masks <NUM> preferably comprise at least one inlet valve through which breathing gas flows into the cavity, an ambient valve which enables each passenger to breath cabin ambient air <NUM> diluting the breathing gas and an exhalation valve to enable gas within the cavity to exhaust the masks <NUM> when the passenger exhales.

The electronics board <NUM> comprises a controller <NUM> and a pressure cabin altitude sensor <NUM>. The cabin altitude sensor <NUM> senses the pressure within the cabin <NUM> (also referred to as cabin altitude). The controller <NUM> is configured to control the delivery valve <NUM> to provide a flow of breathing gas to the masks <NUM> through second tubing <NUM>, in order to supply aircraft passengers with breathing gas when the cabin altitude (pressure in the cabin) is sufficiently high as to induce hypoxia. In a continuous supply mode, the flow of breathing gas is adjusted based on the number of masks <NUM> used by a passenger and on cabin pressure sensed by the pressure sensor <NUM>. Preferably, the flow is adjusted to a plurality of non-null values. In an alternative supply mode, the flow may be interrupted to adjust a volume of breathing gas (preferably to a plurality of non-null values) per breath based on the ambient pressure.

Lines <NUM> schematically represents the connection between the controller <NUM> and the delivery valve <NUM> which may be wires or any appropriate known connection, such as radio, Bluetooth and wifi for instance.

The breathing gas supply circuit <NUM> additionally may include a manifold <NUM> in gaseous communication with the source of breathing gas <NUM>. The manifold <NUM> may, if appropriate, have a relief valve <NUM> or other means of venting gas if the pressure thereof exceeds a particular threshold. Downstream of the manifold <NUM> may be a HP reducer and/or a regulator <NUM>, which functions to decrease or otherwise regulate the pressure of the oxygen from the manifold <NUM> before the oxygen flows to passengers of the aircraft. The HP reducer and/or the regulator <NUM> preferably reduces the absolute pressure between <NUM> bar and <NUM> bar.

The regulator <NUM> may be controlled by the controller <NUM> to adjust the absolute pressure downstream the regulator <NUM>, based on the ambient pressure. In such a case, the delivery valve <NUM> is optional. The regulator <NUM> may be electrically controlled by wire <NUM> or any appropriate known connection, such as radio, Bluetooth and wifi for instance. A more detailed description of such a real-time controlled regulator may be found in document <CIT>.

Also, included as part of the breathing gas supply circuit <NUM> may be an initiator <NUM>. The source of breathing gas <NUM> is initially sealed. The initiator <NUM> may comprise any suitable mechanism for establishing gas flow from the source of breathing gas <NUM> to the manifold <NUM>. One possible version of initiator <NUM> may utilize at least one SMA (Shape Memory Alloy) whose change in shape upon heating may cause a seal of the source of breathing gas <NUM> to be punctured. The initiator <NUM> is connected to the controller <NUM> by an electrical wire <NUM> or any appropriate known connection, so that the initiator <NUM> is controlled by the controller <NUM>.

The breathing gas supply circuit <NUM> may further comprise an aircraft altitude sensor, an exhalation gas sensor and a blood oxygen saturation sensor connected to the controller <NUM>, in order to adjust the flow of breathing gas.

The emergency oxygen system further comprises a container <NUM>. The container <NUM> comprises a housing <NUM> having an opening and a door <NUM>. The door <NUM> is movable with respect to the housing <NUM> between a closed position (shown in <FIG>) and an open position. In the closed position, the door <NUM> obstructs the opening of the housing <NUM>. In the open position, the door <NUM> is away from the opening. In the illustrated embodiment, the door <NUM> is rotatably mounted on the housing <NUM> between the closed position and the open position.

In the embodiment shown in <FIG>, before use (emergency situation) the breathing gas supply circuit <NUM>, the power source <NUM>, the electronics board <NUM>, the switching device <NUM> and the activation device <NUM> are within the housing <NUM> and the door <NUM> is in the closed position which thus define a passenger service unit (PSU). When the door <NUM> is in the open position, the masks <NUM> can drop outside of the housing <NUM> to be caught by the passengers seated on the seats which are below the container <NUM>.

The emergency oxygen system <NUM> further comprises a latching assembly <NUM> to secure the door <NUM> in the closed position. The latching assembly <NUM> comprises a lever <NUM>, an actuator <NUM> and a shape memory based wire <NUM>. The lever <NUM> forms a latch and is movable with respect to the housing <NUM> between a protruding position and a retracted position. In the embodiment shown in <FIG>, the lever <NUM> is rotatably mounted on the housing <NUM>. As shown in <FIG>, in the protruding position the lever engages the door <NUM>, in order to secure the door <NUM> in the closed position. In the retracted position, the lever <NUM> disengages the door <NUM>, so that the door <NUM> is released and may move towards the open position by gravity.

The lever <NUM> is urged, for instance by a spring (not illustrated), towards the protruding position. The shape memory material based wire <NUM> is connected at an end to the lever <NUM> and at an opposite end it is connected to the housing <NUM>. The actuator <NUM> may actuate the shape memory material based wire <NUM>, by heating the shape memory material based wire <NUM>, in order to produce a contraction of the length of the shape memory material based wire <NUM>, so that the lever <NUM> moves from the protruding position to the retracted position. A release hole (not illustrated) may be provided in the door to manually move the lever <NUM> into the retracted position.

The emergency oxygen system <NUM> comprises an aircraft emergency system <NUM>. Preferably, the aircraft is equipped with a plurality of containers <NUM> each container <NUM> enclosing one breathing gas supply circuit <NUM>, one power source <NUM>, one electronics board <NUM>, one switching device <NUM> and one activation device <NUM> and being dedicated to a row of (<NUM> to <NUM>) seats whereas the aircraft is equipped with only one aircraft emergency system <NUM>. In the embodiment illustrated, the aircraft emergency system <NUM> comprises an aircraft emergency controller <NUM> and a transmitter <NUM>. In case of emergency situation, such as depressurisation or presence of fumes, the aircraft emergency controller <NUM> sends a door opening signal <NUM> to the actuator <NUM> in order to actuate the shape memory material based wire <NUM> and open the door <NUM> and/or control the transmitter <NUM> in order to send an emergency signal <NUM>. In the embodiment shown in <FIG>, the door opening signal <NUM> is transmitted by a wire to each container <NUM> and the emergency signal <NUM> is transmitted without wire, for instance by radio, Bluetooth, wifi or the like.

Instead of being controlled by the aircraft emergency system <NUM> the latching assembly <NUM> can be controlled by the controller <NUM>. In such a case, when the controller <NUM> supplied in power from the power source <NUM>, the controller <NUM> controls the actuator <NUM> in order to move the lever in the retracted position in order to open the door <NUM>. Line <NUM> schematically represents the connection between the controller <NUM> and the actuator <NUM>.

In the embodiment shown in <FIG>, the power source <NUM> is a battery having a positive terminal (or phase pole) and a negative terminal (or neutral pole).

The switching device <NUM> is interposed between the power source <NUM> and the electronics board <NUM>, in order to connect/disconnect the power supply of the electronics board <NUM>. The switching device <NUM> comprises a main switch T1 configured to have a first state (ON state) in which the power from the power source <NUM> is supplied to the electronics board <NUM> (the electronics board <NUM> is connected to the power source <NUM>) and a second state (OFF state) in which the electronics board <NUM> is not supplied with power from the power source <NUM> (the electronics board <NUM> is disconnected from the power source <NUM>).

In the embodiment shown in <FIG> and <FIG>, the switching device <NUM> cuts only the connection of the electronics board <NUM> to the positive terminal of the power source <NUM>, the connection of the electronics board <NUM> to the negative terminal (ground GR) of the power source <NUM> remaining. In a variant, the switching device <NUM> could simultaneously cut both the connection of the electronics board <NUM> to the positive terminal and to the negative terminal of the power source <NUM>.

The switching device <NUM> comprises an input point (terminal) <NUM>, an output point (terminal) <NUM>, an ON point (terminal) <NUM> and an OFF point (terminal) <NUM>. The power source <NUM> is connected to the input point. The electronics board <NUM> is connected to the output point <NUM> to enable the electronics board <NUM> to be powered. The activation device <NUM> is connected to the ON point <NUM> in order to control the main switch T1 to switch from the second state to the first state (ON state). The controller <NUM> is connected to the OFF point <NUM> in order to control the main switch T1 to switch from the first state to the second state (OFF state).

It should be noticed that the input point <NUM>, the output point <NUM>, the ON point <NUM> and the OFF point <NUM> are specified for the understanding of the emergency oxygen system <NUM>, but may be distinguishable as particular points. Moreover, the switching device <NUM>, the activation device <NUM> and the electronics board <NUM> may be supported by the same support element (printed circuit board).

The activation device <NUM> is connected to the aircraft emergency controller <NUM> and/or the actuator <NUM>, so that a first activation signal <NUM> is transmitted to the ON point <NUM> of the switching device <NUM> consecutively to the door opening signal <NUM> sent by the aircraft emergency controller <NUM>. The first activation signal <NUM> may be identical to the door opening signal <NUM>, the door opening signal <NUM> being transmitted to the ON point <NUM> of the switching device <NUM>, but in variant (not illustrated) it may indirectly derives from the door opening signal <NUM>, for instance as being sent by a sensor detecting the open position (or not closed position) of the door <NUM>.

The activation device <NUM> comprises a receiver <NUM> configured to receive the emergency signal <NUM> sent by the transmitter <NUM> of the aircraft emergency system <NUM> and send a second activation signal <NUM> to the switching device <NUM> through the ON point <NUM>.

The activation device <NUM> comprises a depressurisation switch <NUM> and an aneroid type actuator <NUM>. In the embodiment illustrated in <FIG>, the depressurisation switch <NUM> is interposed between the power source <NUM> and the ON point <NUM> of switching device <NUM>. The depressurisation switch <NUM> is urged to an open state (OFF state) when the cabin of the aircraft is normally pressurised. In case of depressurisation, the aneroid type actuator <NUM> expends and moves the depressurisation switch <NUM> in a closed state (ON state) in which the depressurisation switch <NUM> makes electrical circuit between the power source <NUM> and the ON point <NUM>, so that a third activation signal <NUM> is sent to the switching device <NUM> through the ON point <NUM>.

The activation device <NUM> further comprises a test switch <NUM>. In the embodiment illustrated in <FIG>, the test switch <NUM> is interposed between the power source <NUM> and the ON point <NUM> of switching device <NUM>. The test switch <NUM> is urged to the open state (OFF state). In order to initiate a testing procedure, the test switch <NUM> is depressed and moves in a closed state (ON state) in which the depressurisation switch <NUM> makes electrical circuit between the power source <NUM> and the ON point <NUM>, so that a fourth activation signal <NUM> is sent to the switching device <NUM> through the ON point <NUM>.

The controller <NUM> may send a deactivation signal <NUM> to the switching device <NUM> through the deactivation point <NUM>. In particular, when ambient pressure sensed by the pressure sensor <NUM> is higher than a depressurization threshold, the controller <NUM> controls a test procedure and then sends the deactivation signal <NUM> in the deactivation line.

As shown in <FIG>, the switching device <NUM> comprises the main switch T1, an ON switch T2 and an OFF switch T3. The OFF switch T3 controls the state of the ON switch T2, which in turn controls the state of the main switch T1.

In the embodiment shown in <FIG>, the main switch T1, the ON switch T2 and the OFF switch T2 are transistors. The main switch T1 is a P-type MOSFET. The ON switch T2 and the OFF switch T3 are N-type MOSFETs. Transistor.

In a variant (not illustrated) the main switch T1, the ON switch T2 and the OFF switch T3 could each be a relay, preferably the main switch T1 and the ON switch T2 being of normally open type, and the OFF switch T3 being of normally closed type. The substitution of relays for transistor as above mentioned would not substantially modify the operation of the switching device <NUM>, but energy efficiency of the emergency oxygen system <NUM> would be reduced.

The main switch T1 is interposed electrically between (the input point <NUM> connected to) the power source <NUM> and (the output point <NUM> connected to) the electronics board <NUM>. The main switch T1 functions as a low-power switch, either electrically connecting the electronics board <NUM> to the power source <NUM> or electrically disconnecting the electronics board <NUM> from the power source <NUM>, depending on its operational state. When the main switch T1 is in the ON state, an output signal <NUM> from the power source <NUM> (through the input point <NUM>) is sent to the electronics board <NUM> (through the output point <NUM>). When the main switch T1 is in the OFF state, no output signal <NUM> is sent to the electronics board (through the output point <NUM>).

The ON switch T2 may be driven in the ON state by the first activation signal <NUM>, the second activation signal <NUM>, the third activation signal <NUM> or the fourth activation signal <NUM> through an activation line <NUM> and an ON line <NUM>.

The ON switch T2 may also be driven by the output signal <NUM>, uphold in the ON state, through an upholding line <NUM> and the activation line <NUM>.

Diodes D1 (in the upholding line <NUM>) and D2 (in the activation line <NUM>) isolate the output signal <NUM> through the upholding line <NUM> from the first activation signal <NUM>, the second activation signal <NUM>, the third activation signal <NUM> or the fourth activation signal <NUM> through the activation line <NUM> other (i.e. performing a logical "or" function to supply only one of the activation signals <NUM>, <NUM>, <NUM>, <NUM> and output signal <NUM> to ON switch T2 at any given time).

Resistor R1 serves as a pull-down resistor for the first activation signal <NUM>, the second activation signal <NUM>, the third activation signal <NUM> or the fourth activation signal <NUM> in the activation line <NUM>. Resistor R2 serves as a pull-down resistor for the deactivation signal <NUM> in a deactivation line <NUM> connected to the deactivation point <NUM>. Resistor R3 in the activation line <NUM> functions to allow OFF switch T3 to control ON switch T2 without shorting the Output signal <NUM> to ground GR. Resistor R4 prevents shorting the power source <NUM> to ground GR when the ON switch T2 is driven in the ON state.

The OFF switch T3 may be driven by the deactivation signal <NUM> in the ON state sent in the deactivation line <NUM> from the electronics board <NUM>. Consequently, the ON line <NUM> is connected to ground GR, so that the ON switch T2 is driven in the OFF state and the main switch is then driven in the OFF state.

Claim 1:
An emergency oxygen system (<NUM>) for aircraft comprising:
a breathing gas supply circuit (<NUM>) to be connected upstream to a source of breathing gas (<NUM>) and downstream to at least one mask (<NUM>), the breathing gas supply circuit (<NUM>) comprising a flow control valve (<NUM>, <NUM>) configured to adjust the flow of breathing gas supplied to the mask (<NUM>),
an electronics board (<NUM>) configured to control the flow control valve (<NUM>, <NUM>),
a power source (<NUM>),
wherein
the emergency oxygen system (<NUM>) further comprises a switching device (<NUM>) interposed between the power source (<NUM>) and the electronics board (<NUM>), the switching device comprising a switch (T1) configured to have a first state in which power from the power source (<NUM>) is supplied to the electronics board (<NUM>) and a second state in which the electronics board (<NUM>) is not supplied with power from the power source (<NUM>),
the switch (T1) is of electrical or electronic type,
the switching device (<NUM>) further comprises an activation line (<NUM>),
the switching device (<NUM>) is configured to actuate the switch (T1) to switch from the second state to the first state when an activation signal (<NUM>, <NUM>, <NUM>, <NUM>) is present in the activation line (<NUM>),
characterised in that
the switching device (<NUM>) comprises a deactivation line (<NUM>) configured to switch the switch (T1) from the first state to the second state in case a deactivation signal (<NUM>) is present in the deactivation line (<NUM>), and
the electronics board (<NUM>) is configured to send the deactivation signal (<NUM>) in the deactivation line (<NUM>).