Electronically Controlled Oxygen Regulators

Abstract

A regulator apparatus for breathable gas includes an oxygen supply valve and an expiratory/air inlet valve mounted in the wall of a mask or other breathing chamber. A differential pressure sensor and an oxygen partial pressure sensor are also mounted on the mask and generate electrical signals in accordance with conditions in the mask. The differential pressure signal, which varies with the breathing of the user, is passed, along with the variable partial pressure signal, into an electronic control circuit which controls the operation of the valves in accordance with the breathing cycle and the oxygen partial pressure so as to maintain proper breathable gas conditions in the mask. When less than 100 percent oxygen supply is needed, the expiratory/air inlet valve and the oxygen valve are opened for appropriate relative time intervals during an inspiration so as to pass oxygen and diluting air into the mask in appropriate ratios. Altitude responsive elements are incorporated to bias the control circuit appropriately in accordance with increasing altitude, this biasing, of course, resulting in modification of the operation of the valves.

Parent Case Text

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of our copending application Ser. No. 586,171, filed Oct. 12, 1966, now abandoned.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to regulator apparatus for breathable gas, and more particularly, although not exclusively, to oxygen demand regulators used by aviators.

Present-day pneumatic oxygen systems are limited in response by the rate at which the gas flows in pipe lines and the rate at which signals can be transmitted through these gas flows. Small delays which are practically inherent in such systems give rise to undesirable peaks in the cyclic flow patterns, resulting in relatively high total swings and aggravating instability. A further disadvantage arises from the fact that the expiratory valve usually is compensated for pressure by applying the regulator delivery pressure to the control chamber of the valve. This means that the expiratory valve has to be slightly overcompensated or spring-loaded, to ensure that there is no leakage overboard. An oxygen injector is normally used to provide air dilution in mechanically operated demand systems, although there are alternative systems. The injector type is normally regarded as the better, but it has limitations in control of oxygen richness, especially at low flow rates.

It is an object of this invention to avoid the aforesaid disadvantages, and to provide a regulator requiring a minimum of breathing effort by the user, to improve his comfort and reduce his awareness that breathing is being maintained under artificial conditions.

In general, according to the invention, an oxygen supply valve and an expiratory/air inlet valve are incorporated in a mask or other breathing chamber, whereby the oxygen valve can be controlled to supply oxygen to the mask or chamber, and the expiratory/air inlet valve can be controlled so as to function as an expiratory valve during an exhalation, and as an inlet valve for diluting air during the inhalation, during which inhalation all oxygen may be admitted, or oxygen and diluting air may be admitted, or all air may be admitted where there is no need for additional oxygen. These valves are electrically controlled by an electronic circuit so as to be varied from their normal conditions, wherein the expiratory/air inlet valve is normally open, and the oxygen valve is normally closed. Control signals for the electronic circuit are derived, firstly, from a differential pressure transducer mounted in the wall of the mask or chamber, this transducer being responsive to the breathing cycle of the user, and thus tending to control the electronic circuit, and hence the valves, in accordance with the breathing cycle of the user. Therefore, apart from any other controls, the differential pressure transducer normally would respond to an exhalation by controlling the circuit so as to tend to actuate the expiratory/air inlet valve to an open state, and so as to close the oxygen valve, corresponding to the normal states of these valves. The transducer would respond to an inhalation by tending to control the circuit so as to close the expiratory/air inlet valve, and open the oxygen valve. However, the circuit is also controlled by an oxygen partial pressure sensor which emits a varying signal in accordance with the oxygen partial pressure within the mask or chamber. This signal is combined in the circuit with the signal from the pressure transducer, and the resultant signal appropriately modifies the operation of the valves so as to maintain a desired condition within the mask or chamber. Thus, the oxygen valve can be controlled so as to maintain a 100 percent oxygen condition, or can be controlled in conjunction with the air inlet valve so as to supply oxygen and diluting air in appropriate ratios, or can be maintained in a closed condition when additional oxygen is not needed.

A system in accordance with the invention may also include altitude responsive elements which bias the control circuit in accordance with changing altitude by increasing the supply of oxygen when a predetermined altitude is reached, by initiating a small positive safety pressure in the mask at a predetermined altitude, and by initiating pressure breathing when required.

A substantial advantage of the invention lies in the fact that the electronic units, other than the units mentioned above as being mounted on the mask, can be situated in any convenient location, as opposed to mechanical systems in which the complete apparatus usually has to be situated near the user's mouth.

Other and further objects, features and advantages of the invention will become apparent to those skilled in the art from the ensuing description of an exemplary embodiment, taken in conjunction with the accompanying drawings illustrating a preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing one way in which the various units in the apparatus are interconnected in accordance with a preferred embodiment.

FIGS. 2, 3 and 4 are sectional elevations of three units of the apparatus shown in FIG. 1.

FIG. 5 is a more detailed circuit diagram of the block diagram circuit shown in FIG. 1.

FIG. 6 shows an alternative arrangement and interconnection of the altitude reference sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, FIG. 1 shows a breathable gas regulator apparatus for use by an aviator wearing a mask 1. Only an oxygen delivery valve 2, a partial pressure oxygen sensor 3, a pressure transducer 4, and a combined expiratory/air inlet or air mix valve 5, are mounted on the mask 1. The other units can be mounted elsewhere, either on the aviator's person, or in the aircraft. The valve 5 also serves as an air mix valve, which admits air into the mask to mix with the oxygen that enters through the valve 2.

The electronic control circuit components are connected as illustrated diagrammatically in FIG. 1, and include a free-running multivibrator 13, a conventional transistorized diode pump 14, preamplifier 16, safety pressure bias 19, a triangular wave oscillator 18, a variable gain pulse amplifier 20 with two amplifier circuits and two outputs, an altitude reference sensor 15, and power amplifiers 21 and 22.

The structure of the transducer 4 is shown in FIG. 2, and comprises a metalized diaphragm 6 clamped by nylon screws at its edge between member 7, 8, shaped to provide spaces on opposite faces of the diaphragm. One of these spaces is in communication with the interior of the mask 1 through a passage 9 passing through a projection having a peripheral groove 10, into which the edge of an aperture in the wall of the mask fits. The space on the opposite face of the diaphragm is in communication with the ambient atmosphere through an aperture 11. The diaphragm 6 and member 8 are insulated from one another, and comprise the conductive plates of a capacitor, and are respectively connected through terminals 12, 12a, to the multivibrator 13.

The partial pressure sensor 3 is conventional, and may be of the Beckman type.

Details of the combined expiratory/air-inlet valve are shown in FIG. 3. A cylindrical member 23 is secured to the mask, this member being formed with a peripheral groove 24, into which the edge of an aperture in the mask is sealed. The gases enter and leave the mask through an annular passageway between the member 23 and a coil 25. The flow is controlled by a valve plate 26, having a flange 27, arranged to move toward or away from the lower edge of the member 23. During the exhalatory phase, the valve is held fully open by a compression spring 28. During the inhalatory phase, the valve is appropriately actuated by the electric current supply to the coil 25 from the amplifier 22, the coil 25 being arranged to attract an armature 29 carrying the plate 26. To avoid parasitic back pressure, the pressures on opposite sides of the plate 26 are substantially equalized by mounting this plate on a diaphragm 30, which closes a cavity 31, the only communication from outside with this cavity being through an aperture 32 in the diaphragm and plate.

The oxygen valve is shown in detail in FIG. 4. This valve has a body 33 formed with a peripheral groove 34, into which the edge of an aperture in the mask 1 is sealed. The body 33 is formed with a cavity 35, arranged to be connected to a source of oxygen under pressure through an inlet 36. The flow into the mask is controlled by a valve poppet 37 carried by a piston 38 reciprocable in the tube 39 under the action of a compression spring 40. The area of the piston 38 is such as pneumatically to balance the valve poppet 37. Leakage past the piston is prevented by a sealing ring 41. The opposite end of the piston 38 is maintained at ambient pressure through an aperture 42. A coil 43 surrounding the tube 39 is supplied from the amplifier 21. Thus, the position of the valve poppet depends on the current received by the coil 43, and the rate of the spring 40.

The altitude reference sensor 15, as shown schematically in FIG. 5, comprises an absolute aneroid assembly designed to feed electrical signals to one part of the amplifier 20, as will be described in more detail subsequently. In the alternative arrangement of FIG. 6, the altitude reference sensor is connected directly to amplifier 21.

Safety pressure bias 19, as shown schematically in FIG. 5, also comprises an aneroid assembly designed to bias the circuit by feeding a constant electrical signal into the circuit at a predetermined altitude.

When the aviator dons the mask and makes a demand on the apparatus at ground level, the pressure transducer 4 senses a small negative pressure and thereby determines that gas is required. A signal is thus provided that initiates the delivery of gas into the mask. At the beginning of the expiratory phase, the transducer 4 senses a small positive pressure, and changes the output signal, and so tends to set the valves 2 and 5 for the discharge of exhaled gas from the mask, the oxygen valve 2 then being normally closed and the expiratory valve 5 normally fully open.

As the differential pressure on the diaphragm 6 of transducer 4 changes, as a result of the aviator breathing, the varying strain in the diaphragm brings about a variation in capacitance which, in turn, changes the frequency of the multivibrator. Over a reasonable range, this frequency is substantially proportional to the pressure on the diaphragm and, by using a conventional transistorized diode pump 14, an output voltage is achieved, which is proportional to the differential pressure on the diaphragm. Though pulsed, this output is of sufficiently high frequency to be considered as a straight D.C. voltage of varying amplitude. By choosing an arbitrary reference point within the ambit of this voltage variation, the valves 2 and 5 can be operated for one breathing phase when the voltage is negative with respect to this point, and for the other phase when the voltage is positive with respect to this point. The transducer, thus, tends to influence the circuit to control the valves in accordance with the breathing cycle of the user. However, the valves 2 and 5 are not under the direct control of this voltage, but are under the control of this voltage taken in conjunction with signals derived from the partial pressure oxygen sensor 3, as well as from the altitude reference sensor 15 at higher altitudes. The partial pressure sensor 3 is used to maintain the desired partial pressure in the mask at all times, and the altitude sensor 15 is used to modulate the proportion of air to oxygen in the mask, and to initiate the control of pressure breathing when the ambient pressure renders this necessary.

The output of the partial pressure sensor 3 is a small current, the magnitude of which depends on the partial pressure of the oxygen in the mask. This current is amplified in pre-amplifier 16, the output of which is added to the output of triangular wave oscillator 18 in variable gain pulse amplifier 20, so that within variable gain pulse amplifier 20 is derived a series of pulses of mark/space ratio proportional to partial pressure, the frequency being consistent with the optimum speed of the valves 2 and 5, and with the physiological requirements of the user. Output signals from variable gain pulse amplifier 20 are delivered by way of power amplifiers 21 and 22 to the oxygen valve 2 and the combined expiratory/air inlet valve 5. When the altitude increases, the partial pressure of oxygen decreases, and the resulting lower signal from the partial pressure sensor 3 is amplified, and subsequently fed to the oxygen delivery valve 2 and to the combined expiratory/air inlet valve 5 so that air and oxygen are admitted during the inspiratory phase, to a degree that maintains the correct partial pressure. The system automatically changes to 100 percent oxygen during the inspiration phase when the air mix system cannot maintain the correct oxygen partial pressure. Pulses of appropriate polarity received by the pulse amplifier 20 result in the oxygen valve 2 and expiratory valve 5 being opened alternately, to provide the correct mixture of air and oxygen, this mixture being proportional to the ratio of mark to space intervals in the pulses. For example, when 25 percent oxygen is required, this mark/space ratio would be 1:3, whereby the oxygen valve opens for the duration of each mark interval, and the valve 5 opens for the duration of each space interval.

Explaining this in a somewhat different manner, the free-running multivibrator operates at a high frequency, the frequency being proportional to the differential pressure across sensor 4. The output of diode pump 14 is thus a voltage proportional to the differential pressure. Assuming for the moment that safety pressure bias is zero, the output of 19 is also a voltage proportional to the differential pressure. This forms one input to 20, to which is added a second input, the output of 16 (being a voltage proportional to oxygen partial pressure), and a third input, the triangular wave output of 18. The first and second inputs thus will raise or lower the triangular waveform input relative to the switching level of amplifier 20, and thus determine the output of 20. For instance, the effect of a combination of the differential pressure and partial pressure signals may leave the triangular waveform below the switching level of 20, and hence effect a zero output of 20, which would leave the valves in their normal states. On the other hand, the combination of signals might place part of the triangular waveform above the switching level of 20, and hence effect a pulsed output of 20. Finally, the combination of signals might raise the entire triangular waveform above the switching level of 20, and hence effect a continuous full output of 20. It is evident that between continuous zero output of 20 and continuous full output of 20, the mark/space ratio of the pulse output of 20 is capable of full modulation to provide any appropriate proportion of oxygen to diluting air, since the mark/space ratio determines the oxygen/air proportions, and the triangular waveform, in passing from below to above the switching level of 20, effects first a zero output of 20, then a pulsed output of increasing mark/space ratio, and then a full continuous output of 20. It will be understood that each pulse or mark represents an oxygen valve open signal and an expiratory/air inlet valve closed signal, and vice versa for the spaces or zero output times.

When the operating altitude reaches that which requires a slight positive pressure to prevent any mask seal leakage, allowing air to enter and reduce the oxygen partial pressure, the safety pressure bias 19 provides a bias that increases the amount of oxygen. This bias is in the form of a constant additional signal, and the effect is that the output of the pressure transducer 4 now operates about a new datum pressure. The expiration phase is not affected.

The altitude reference sensor 15 comprises an absolute aneroid assembly designed to modulate the electrical signals to the amplifier 21 by biassing the respective pulse width modulation circuit in variable gain pulse amplifier 20. If the altitude increases above that which can be accommodated by the admission of 100 percent oxygen into the mask during the inhalation phase, the altitude reference sensor 15 is effective so as to increase the oxygen pressure in the mask by acting in conjunction with the pressure transducer 4 to prolong the opening of the valve 2 and thus initiate pressure breathing.

In a condition where g loading occurs, tending to open the expiratory/air-inlet valve 5, any reduction of pressure within the mask will be automatically countered by signals that will feed back to close expiratory valve 5 and open oxygen delivery inlet 2, similar to the action of inhaling by the user. Should the g loading be sufficient to cause the user to "black-out," even to the extent that his respiration becomes insufficient to operate the valves 2, 5, they will remain electronically balanced to maintain a supply of oxygen through the mask until his respiration takes command again. If cabin decompression occurs the change in differential pressure affecting the transducer 4 causes immediate response in the electronic circuit to further open the oxygen delivery valve 2 accordingly, and should the altitude be such that assisted or pressure breathing is required, the altitude sensor 15 would act together with the transducer 4 to immediately override the previously introduced bias and provide a new datum pressure to ensure that the correct pressure is maintained in the mask, and it may also be arranged to ensure that pressure is put into, for example, a pressure jerkin.

To meet emergencies, an electrical battery may be carried as well as a separate oxygen supply, and automatic initiation of these services may be provided for. Integration of the apparatus with a centralized warning system presents no difficulties, as signals of the type required are available.

As shown in FIG. 6, the output of altitude reference sensor 15 may be taken to power amplifier 21 instead of amplifier 20. In this alternative arrangement, the output pulses from 20 may be prolonged by a charge on capacitor C (FIG. 6) which is modulated by the variable resistor RV coupled to the altitude reference capsule. Fixed resistor R provides a leakage path across C. At high altitudes, the valve of RV would be low, so as to prolong the pulses, and provide a longer open time for the oxygen valve.

From the foregoing, it will be seen that the system, as required, supplies 100 percent air, or 100 percent oxygen, or variable mixtures of air and oxygen, and additionally introduces safety pressure (1 inch w.g. positive pressure in the mask) at perhaps 12,000 feet to 40,000 feet, whereafter a 40,000 feet pressure equivalent is maintained in the mask (and jerkin) above 40,000 feet. Additionally, the system has the advantage of being basically a fail safe system. Thus, assuming failure of the pressure transducer 4, between ground level and the introduction of safety pressure at 12,000 feet, the user will draw ambient air through the expiratory/air inlet valve, since its neutral state is open. Between 12,000 feet and 40,000 feet, the partial pressure sensor would sense reduced oxygen content, and tend to close the expiratory/air inlet valve and open the 0.sub.2 inlet which is biased open to give 1 inch w.g. safety pressure. As there is no exhalatory pressure signal to open the combined valve, any excess pressure can disperse through the normal relief valve (not shown) or around the edges of the mask. Above 40,000 feet, the system would operate in substantially the same manner, but with the addition of pressure breathing pressure in the mask.

Should the partial pressure sensor fail, between ground level and the introduction of safety pressure at 12,000 feet, the oxygen inlet valve and the combined valve would operate under direct inhalation and exhalation signals from the pressure transducer. Between 12,000 feet and 40,000 feet, the operation would be the same, with the addition of safety pressure biasing the oxygen inlet valve to give the 1 inch w.g. safety pressure. Above 40,000 feet, there would be the further addition of pressure breathing pressure in the mask.

Should the combined expiratory/air inlet valve fail between ground level and 12,000 feet, if the failure were due to a broken spring, during inhalation the valve plate of the combined valve would be sucked to a closed position and the oxygen inlet valve opened by signal from the pressure transducer. If the failure were due to a failed coil, normal low altitude breathing of air would occur, since the spring would hold the valve plate of the combined valve open. Between 12,000 feet and 40,000 feet, if failure should occur because of a broken spring the operation would be substantially the same as for below 12,000 feet, but with increasing altitude the safety pressure in the mask would make suckling closure of the valve plate more difficult, but the partial pressure sensor would sense reducing oxygen content and influence the solenoid of the valve toward closing, and thus give near normal conditions. If the failure were due to a failed coil, the spring would hold the valve plate open and therefore the partial pressure sensor would sense a low oxygen content, and so bias the oxygen inlet valve to open wider, with some waste of oxygen. Above 40,000 feet, if failure were due to a broken spring, the valve plate would want to remain open, but the partial pressure sensor would sense low oxygen content, and so influence the solenoid of the valve to close it, thereby overcoming the failure and giving near normal conditions. If the failure were due to a failed coil, the valve plate would remain open and the partial pressure would sense low oxygen content, so energizing the oxygen inlet valve to open further. This would give a large waste of oxygen as the inlet would have to at least match the flow through the open valve.

Assuming failure of the oxygen inlet valve, normal breathing through the combined valve would take place up to the introduction of safety pressure at 12,000 feet. At and above 12,000 feet, with increasing altitude the partial pressure sensor would sense a reducing oxygen content, until the emergency oxygen system came into play.

To further amplify the overall operation of the system, a general summary of the operation will be given hereafter, followed by a detailed description of the action of the control circuit in controlling the valves during a typical range of operations.

In general, the primary or initial control stems from the differential pressure transducer 4, which influences the control circuit to tend to open and close the oxygen and expiratory/air inlet valves 2, 5, according to the breathing of the user. For instance, the differential pressure transducer 4 influences the control circuit to tend to open the oxygen valve 2, and close the expiratory/air-inlet valve 5 during an inspiration, and vice versa during an expiration. However, the control circuit also is influenced by the partial pressure oxygen sensor 3, which influences the control circuit to vary the operation of the valves 2 and 5 to maintain a predetermined range of oxygen partial pressure. Toward achieving this end, the partial pressure oxygen sensor 3 functions primarily during the inspiration phase to control the opening of the oxygen valve 2 to admit oxygen, and the opening of the expiratory/air-inlet valve 5 to admit diluting air, in such proportions that the desired oxygen partial pressure is maintained in the mask 1.

As the altitude increases, and hence the partial pressure of oxygen decreases, the partial pressure sensor 3 tends to cause the introduction of more oxygen by prolonging the open periods of the oxygen valve 2 and shortening the open periods of the expiratory/air-inlet valve 5 during the inspiration phase, this process continuing with increasing altitude until the oxygen partial pressure sensor 3 constrains the system to 100 percent oxygen by terminating the opening of the expiratory/air inlet valve 5 during the inspiration phase. At ground level, where oxygen is not needed, pressure transducer 4 influences the oxygen and expiratory/air-inlet valves 2 and 5 to tend to open and close with the breathing of the user, but the influence of the pressure transducer 4 is overridden by the partial pressure sensor 3 to maintain the oxygen valve 2 in a fully closed position and the expiratory/air-inlet valve 5 in a fully open position, during both inspiration and expiration. In addition to the pressure transducer 4 and the partial pressure sensor 3, there is an altitude reference sensor 15 which influences the oxygen valve 2 to increase the oxygen supply at a predetermined altitude, and initiates pressure breathing when ambient pressure renders this necessary. At a lower predetermined altitude, safety pressure bias 19 influences the circuit to increase the oxygen supply to maintain a slight positive safety pressure in the mask 1.

During a typical range of operations, commencing at zero feet, ground level, with the oxygen and power supplies selected ON, the user, with oxygen mask correctly fitted, applies alternatively positive and negative pressures to the transducer, as exhalation and inhalation take place. These pressures acting on the transducer vary the capacity of the transducer capacitor, in parallel with one of the capacitors in the multivibrator 13, thus varying the output frequency of the multivibrator proportionally with the breathing cycle of the user. This output, fed to the transistorized diode pump 14, charges the capacitor, via the diode, on the positive pulse, the capacitor discharging across the resistor between pulses. The voltage at the wiper tapping on the resistor is, therefore, a pulsed D.C. voltage of amplitude proportional to the differential pressure in the mask. Assuming a voltage datum level somewhere between the maximum and minimum amplitudes of this voltage, voltages below this level will be considered negative with respect to the set datum, and voltages above will be considered positive. Though pulsed, this output is of sufficiently high frequency to be considered as a straight D.C. voltage of varying amplitude.

Ignoring for a moment the safety pressure bias 19 (which only becomes operative above 12,000 feet) and considering it as a straightforward amplifier, the positive output from the transistorized diode pump 14 is phase inverted to become a negative amplified input to the variable gain pulse amplifiers 20, and when summated with the triangular waveform output of 18 raises the operating level of said triangular waveform by an amount equal to the amplitude of the output from 19. Likewise, a negative output from the transistorized diode pump 14 would suppress, or lower, the operating level of the triangular waveform relative to the switching level of the pulse amplifiers 20.

If and when the positive output of the transistorized diode pump 14 reaches a voltage of sufficient amplitude to raise the triangular waveform above the built-in switching level of the pulse gain amplifiers a pulsed output of mark/space ratio dependent on the amplitude of the transistorized diode pump 14 output will be obtained from the pulse gain amplifiers 20. This output, after power amplification, energizes the coils of the two valves 2 and 5 for a period equal to the Mark, i.e., a time proportional to the amplitude of the output signal voltage from the transistorized diode pump.

The triangular wave oscillator 18, of course, produces a stable signal which is fed into the two parallel variable gain pulse amplifiers 20 and summated with the variable inputs of the transducer 4 and partial pressure sensor 3.

At ground level the summated signal inputs to the variable gain pulse amplifier 20 leave the triangular waveform below the switching level of the two amplifiers, thereby giving no output from 20 and leaving the valves 2 and 5 in a de-energized state.

While the oxygen content of the air breathed through the open valve 5 is sufficient, the valves remain de-energized. As the oxygen content decreases the deficiency is detected by the partial pressure sensor 3, thereby varying the summated signals to the variable gain pulse amplifiers 20, and closing the gap between the triangular waveform and the switching level of the amplifiers until the oxygen content drops below the required level and part of the triangular waveform is above the switching level of the amplifiers 20. Modulation continues so that, with less oxygen detected by the partial pressure transducer 3, more of the triangular waveform is above the switching level of the pulse gain amplifiers 20, thereby giving a pulsed output from the amplifiers 20 proportional to the oxygen content and breathing cycle of the user, the pulsed outputs energizing valves 2 and 5 via power amplifiers 21 and 22. Oxygen from valve 2 decreases the signal from the partial pressure sensor 3 via the pre-amp 16, thereby dropping the triangular waveform, relative to the switching level, changing the mark/space ratio and the quantity of oxygen supplied via valve 2. The oxygen content of the mask thereby is kept substantially constant at varying altitudes up to approximately 40,000 feet.

By summating both variable signal sources with the triangular waveform output of 18, the ratio of the mark/space output of the variable gain pulse amplifier 20 is proportional to the mask pressure and oxygen content of the mask.

At approximately 12,000 feet, the safety pressure bias 19 comes into operation, summating an additional signal to the output of the transistor diode pump 14 and effectively setting a new datum to the system by biasing the amplifier in 19, whereby the summated signals to the variable gain pulse amplifiers 20 have the effect of raising the triangular waveform toward the switching level of the amplifiers 20, sufficient to ensure that the valve 2 remains open long enough to maintain a pressure of approximately 1" water gauge in the mask.

At approximately 40,000 feet the altitude reference sensor 15 is operative, the output of which is summated with the signal inputs to one of the variable gain pulse amplifiers 20, the one feeding the power amplifier 21, thereby extending the open period of the oxygen valve 2 over and above that period determined by the signals received from the prior sources. As valves 2 and 5 are now open together for a period, determined by the altitude above, and relative to, 40,000 feet, oxygen under pressure flows through the mask, maintaining the mask oxygen content and pressure at that of 40,000 feet. The altitude reference sensor does not vary the operation of the expiratory/air-inlet valve.

Claims

We claim:

1. Regulator apparatus for providing breathable gas in a chamber, comprising a chamber adapted for communication with the breathing organs of a user, conduit means adapted to connect an oxygen source with said chamber, a first valve in said conduit means, a passageway connecting said chamber with the exterior thereof, a second valve in said passageway, electronic control means connected with and controlling said first and second valves, and including an oxygen partial pressure sensor and a differential pressure transducer connected with said chamber and said control means and responsive to gas conditions within said chamber for providing combined signals to influence said control means so as to tend to operate said valves to maintain predetermined gas conditions in said chamber, wherein said differential pressure transducer provides a signal which influences said control means to tend to open said first valve and close said second valve upon an inspiration by the user and vice versa upon an expiration by the user, and wherein said partial pressure sensor provides a signal which influences said control means to tend to open said first valve and close said second valve when the oxygen partial pressure falls below a predetermined level and vice versa when the oxygen partial pressure is above a predetermined level, and said electronic control means responds to the combined effect of said signals by passing appropriate control signals to said valves, and wherein said electronic control means comprises means for emitting a pulsed signal of mark/space ratio dependent upon the level of the combined signals received from said transducer and said sensor, and wherein said first and second valves are arranged to react oppositely in response to the same pulsed signal, whereby one valve is open during a mark and the other valve is closed, and vice versa during a space, such that gas conditions within said mask vary with said mark/space ratio.

2. Regulator apparatus as claimed in 1 wherein said control means includes a wave oscillator emitting a stable wave and a pulse amplifier connected to said oscillator for emitting said pulsed signal in accordance with the operating level of said wave relative to a predetermined switching level of the pulse amplifier, and wherein said signals from said transducer and said sensor are combined with said wave to vary the operational level thereof relative to the switching level of said pulse amplifier.

3. Regulator apparatus as claimed in claim 2 wherein said first valve comprises an electromagnetically operated oxygen inlet valve, and said second valve comprises an electromagnetically operated expiratory/air inlet valve for discharging exhaled gases and for selectively admitting ambient air during inhalation in accordance with the mark/space ratio of said pulsed signal.

4. Regulator apparatus as claimed in claim 3 wherein said oxygen inlet valve is a normally closed valve, and said expiratory/air inlet valve is a normally open valve.

5. Regulator apparatus as claimed in claim 3 further comprising a safety pressure bias connected to the electronic control means for biassing said wave so as to vary the operational level thereof in the sense to maintain a positive pressure in the chamber when a predetermined altitude is reached.

6. Regulator apparatus as claimed in claim 3 further comprising an altitude reference sensor for providing a further additional signal only to said oxygen inlet valve so as to increase the oxygen supply to the chamber at and above a predetermined altitude while said expiratory/air inlet valve remains under the control of said transducer and said sensor.

7. Regulator apparatus for providing breathable gas in a chamber comprising a chamber adapted for communication with breathing organs of a user, conduit means adapted to connect an oxygen source with said chamber, a passageway connecting said chamber with the exterior thereof, a first valve in said conduit means, a second valve in said passageway, electronic control means connected with and controlling said first and second valves, and including an oxygen partial pressure sensor and a differential pressure transducer responsive to gas conditions within said chamber for providing combined signals for operation of said control means, said oxygen partial pressure sensor sensing the proportion of oxygen within said gas, and said pressure transducer sensing the total pressure of said gas according to the breathing demand of said user, a waveform generator connected to the electronic control means, said partial pressure sensor and said pressure transducer emitting signals to said electronic control means for summation with a signal from said waveform generator to produce a control signal to said first and second valves to maintain said gas conditions correct in proportion of oxygen and rate of delivery to satisfy demands of the user.

8. Regulator apparatus as claimed in claim 7, further comprising a safety pressure bias connected to the electronic control means for, at a predetermined altitude below 20,000 feet, automatically introducing an electrical bias signal to said summation to modify said control signal to said first and second valves to maintain a positive pressure in said chamber while above said altitude.

9. Regulator apparatus as claimed in claim 8, further comprising an altitude reference sensor connected to the electronic control means for, at a predetermined altitude above 30,000 feet, adding a second electrical bias signal to said control signal to said first valve only to increase said rate of delivery of oxygen, said increased rate being proportional to altitude above that at which the second bias is initially introduced.