EP0413555A1

EP0413555A1 - Positive pressure breathing apparatus

Info

Publication number: EP0413555A1
Application number: EP90308926A
Authority: EP
Inventors: Keith Simpson; Simon Kugler; James Alexander Hammerton-Fraser; Beverley Aleck Hinchliffe; Andrew Richard Thomas Tatarek-Gintowt
Original assignee: Sabre Safety Ltd
Current assignee: Sabre Safety Ltd
Priority date: 1989-08-18
Filing date: 1990-08-14
Publication date: 1991-02-20
Also published as: GB2235136A; GB8918901D0

Abstract

In positive pressure breathing apparatus comprising a face mask 1 having a fan 2 driven by a motor 3 powered by an electric battery 4 to maintain a pressure above atmospheric pressure within the face mask 1, a pressure sensitive electronic module 8, which comprises a pressure transducer and a control circuit including a pulse generator, senses the pressure within the interior of the face mask 1 and provides D.C. pulses from the electric battery 4 to the fan motor 3. The width of the pulses provided by the pressure sensitive electronic module 8 varies in accordance with the instantaneous pressure sensed within the face mask 1 so as to cause the fan 2 to supply air to the interior of face mask 1 at a rate to meet the requirements of the wearer while maintaining a substantially constant positive pressure within the interior of the face mask 1.

Description

This invention relates to positive pressure breathing apparatus.
In positive pressure breathing apparatus a positive pressure greater than the ambient pressure is maintained within a protective device such as a face mask or a hood surrounding the respiratory passages of a wearer so that, if there is any leakage, the leakage will all be outward from the protective device thus providing a high degree of protection against the ingress of noxious fumes into the gas which the wearer of the apparatus is breathing.
In such breathing apparatus the positive pressure is conventionally provided by means of an air mover such as a blower or a fan which delivers air through a filter to the interior of a face mask, helmet or hood. The air mover, which may be a battery-driven electrical device, removes from the wearer the need to overcome the resistance of the filter and so reduces the breathing effort required.
If the air mover delivers air at a constant speed in such breathing apparatus there is a considerable waste of energy because a high flow of air of the order of 160 litres per minute is required only during the inhale part of the breathing cycle. In order to conserve the energy of the electric battery driving the air mover and to extend the life of the filter, proposals have previously been made to reduce the flow of air during the exhale part of the breathing cycle. Such previous proposals respond to a higher pressure generated during exhalation and utilize either mechanical electrical switching or a fluidic control of the breathing air supply during exhalation to conserve battery energy and improve filter life. These prior devices are not thoroughly reliable because of constructional imperfections in the apparatus and the general incompatability of interphasing these components with a substrate such as a flexible face mask. A mechanical electrical switch mounted on a flexible face mask does not give consistent operation.
In accordance with the present invention it is proposed to utilize pulse width modulation to provide an improved control of the air mover so that the air flow into the protective device is matched more closely to the demands of the wearer than in prior art devices and the supply of excess filtered air is substantially avoided thereby conserving battery energy and extending filter life.
According to the present invention there is provided positive pressure breathing apparatus comprising protective means for surrounding the respiratory passages of a wearer thereof to exclude noxious atmospheric gases from the space within the protective means and adjacent to the said respiratory passages, air moving means for supplying breathable gas to the protective means, and an electric power source for driving the air moving means, characterised in that electronic control means is provided for effecting pulse width modulation of the power source in dependence on the gas pressure within the protective means whereby the rate of supply of breathable gas by the air moving means to the protective means is varied in accordance with the demands of the wearer.
By utilizing pulse width modulation of the power from an electric power source such as an electric battery, the voltage applied to the air moving means is reduced without dissipating power from the electric battery.
More specifically in accordance with the present invention there is provided a positive pressure breathing apparatus comprising protective means for surrounding the respiratory passages of a wearer thereof to exclude noxious atmospheric gases from the space within the protective means and adjacent to the said respiratory passages, air moving means comprising a fan and a motor for driving the fan to supply breathable gas to the protective means at a rate faster than the rate of leakage of gas from the protective means, and an electric battery for supplying power to the fan motor to drive the fan, characterised in that a pressure sensitive electronic module is provided for causing the power applied from the electric battery to the fan motor to be supplied as D.C. pulses, the width of the pulses being modulated in dependence on the pressure sensed within the protective means whereby the speed of the fan motor is regulated according to the demand of the wearer.
Breathing apparatus in accordance with the present invention may employ entirely electronic means for reducing the air flow into the protective means during the exhalation part and the rest part of the breathing cycle.
Conveniently the pressure sensitive electronic module comprises a pressure transducer which produces an electrical output signal proportional to the instantaneous gas pressure within the protective means and a pulse generator for generating pulses, the width of the pulses being varied in inverse relation to the electrical output signal from the pressure transducer.
In the embodiment which will be described, the electrical output signal is an analogue signal which is utilized in the pulse width modulation of the pulses generated by the pulse generator. However it is within the scope of the present invention for the electrical output signal from the pressure transducer to be in digital form and for the digital signal to be processed before being applied to control the power fed from the electric battery to the fan motor by pulse width modulation.
Conveniently the pressure sensitive electronic module additionally includes means for giving a visible warning of an unusually low gas pressure within the protective means, said visible warning means being energised under control of the pressure sensitive electronic module.
The protective means is preferably a full face mask but it may also be either a hood or an orinasal mask.
The present invention will be further understood from the following detailed description of a preferred embodiment thereof which is made, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a diagrammatic representation of positive pressure breathing apparatus according to the present invention, and
Figure 2 is a flow diagram setting out the process steps performed in a pressure sensitive electronic module utilized in the apparatus of Figure 1.

Referring to Figure 1 of the accompanying drawings there is indicated diagrammatically a full face mask 1, the interior of which, when used normally, is slightly over-pressurised with clean filtered air for breathing purposes. The clean filtered air is delivered into the interior of the face mask 1 by a fan 2 which is driven by an electric motor 3 which consumes a low voltage D.C. current from an electric battery 4.
Breathing air is drawn from the interior of the face mask 1 by the wearer's lung depicted diagrammatically at 5.
The face mask 1 additionally includes an inhale valve 6 and a exhale valve 7. The itihale valve 6 closes down the output from the fan 2 when the pressure within the face mask 1 rises to a level in excess of the pressure of gas delivered from the fan 2. The inhale valve 6 also ensures that no discharge from the interior of the face mask 1 occurs as a contra-flow through the fan 2 and the filter (not shown).
The exhale valve 7 is biased to the closed position in order to promote the build-up of a positive pressure above the ambient atmospheric pressure within the interior of the face mask 1. The exhale valve 7 will open at a predetermined positive pressure within the face mask 1 and allows the essential discharge of exhaled gases and extraneous air delivered by the fan from the interior of the face mask 1 to the surrounding atmosphere.
Positioned within the interior of the face mask 1 is a pressure sensitive electronic module 8 which may be a specially designed electronic chip. Module 8 performs the essential function in accordance with the present invention of sensing the pressure within the interior of the face mask 1 and providing D.C. pulses from the electric battery 4 to the fan motor 3, the width of the pulses being chosen as a result of the sensing of the pressure within the face mask 1 to cause the fan 2 to supply air to the interior of the face mask 1 at a rate to meet the demand of the wearer while maintaining a positive pressure within the interior of the face mask 1. The operation of the pressure sensitive electronic module 8 will be further described in relation to Figure 2 of the accompanying drawings.
A light emitting diode 9 is secured to a rigid part of the face mask 1, for example a part of the visor assembly, in order to provide a visible warning to the wearer of the face mask 1 that the gas pressure within the face mask 1 is falling to an unusually low level, indicating an unsatisfactory performance and the need for the wearer to take prompt action to withdraw from the noxious atmosphere. The unsatisfactory performance may be due to the electric battery nearing the end of its useful life or to the filter becoming blocked or to part of the face mask 1 no longer providing a proper seal.
The light emitting diode 9 is energised to give the visible warning to the wearer by a threshold circuit within the pressure sensitive electronic module 8.
Referring now to Figure 2 there are shown the process steps performed by the pressure sensitive electronic module 8. The module 8 effectively comprises a pressure transducer which produces an electrical voltage output signal proportional to the instantaneous gas pressure in the interior of the face mask 1 and a control circuit including a pulse generator.
The pressure transducer may be a piece of silicon having a Wheatstone bridge thereon and, as the gas pressure within the face mask 1 changes the silicon flexes with the result that the resistance in the arms of the Wheatstone bridge change and a variable voltage output is given.
The pressure transducer thus performs steps 11 and 12 of Figure 2. The control chip mounted with the pressure transducer in or on the face mask 1 in a position where the pressure within the face mask 1 can be monitored, then carries out the following functions:
Step 13. - The signal from the transducer is inverted.
Step 14. - An offset is added to the inverted signal in order to control the minimum power input from the electric battery 4 to the fan motor 3.
Step 15. - The modified signal is converted into pulses of width proportional to the voltage at a frequency high enough for the flux not to die down in the motor windings between pulses. Advantageously a pulse frequency of the order of 16 kilohertz or higher is used.
Step 16. - The signal from the pulse generator of Step is used to drive a power transistor which switches the power to the fan motor 3 at instants and for periods determined by the widths of the pulses.
In operation the motor speed will be changed speedily in response to a change in pressure within the face mask 1 sensed by the pressure transducer. The change in motor speed leads to another change in pressure which in turn is picked up by the pressure transducer and fed back by the electronic module 8 thereby providing continuous adjustment of the speed of the fan 2 to changes of pressure within the face mask 1 and matching the flow of air into the face mask 1 to the requirements of the wearer whilst maintaining a substantially constant pressure in the face mask.
By the use of the present invention as hereinbefore described with reference to the accompanying drawings, there is an automatic reduction in fan speed and energy consumption for almost two thirds of the respiratory cycle, that is the periods of the cycle within which there is no inhalation. In consequence extended periods of operational use of the positive pressure powered breathing apparatus, are achieved as compared with known apparatus.
Furthermore, in breathing apparatus according to the present invention, the fan speed during inhalation will be set according to the work rate of the wearer, faster, deeper breathing at a high work rate leading to a higher fan speed than slow breathing by a wearer who has just donned the breathing apparatus and has not started energetic physical movement.
Also in breathing apparatus according to the present invention the fan speed is responsive solely to the gas pressure within the face mask or other protective means, and is not affected, as happens in some prior proposals, by unpredictable conditions within the face mask, such as air flow patterns around a diaphragm or a flap valve. The pressure sensitive electronic module may be arranged in any position, within or outside the face mask or other protective means, from which the pressure within the face mask can be sensed.
The operation of the apparatus according to the present invention is not adversely affected by a failure of the wearer correctly to don the protective means. Also the pressure sensitive electronic means is resistant to impact shock and to vibration.
The pressure sensitive electronic module of positive pressure breathing apparatus according to the present invention has no moving parts or mechanical switching of electrical contacts and hence has improved reliability of performance.
Furthermore the electronic circuitry of the control chip of the pressure sensitive electronic module may readily accommodate threshold settings adaptable to provide indications of potential failures.

Claims

1. Positive pressure breathing apparatus comprising protective means (1) for surrounding the respiratory passages of a wearer thereof to exclude noxious atmospheric gases from the space within the protective means (1) and adjacent to the said respiratory passages, air moving means (2,3) for supplying breathable gas to the protective means (1), and an electric power source (4) for driving the air moving means (2,3), characterised in that electronic control means (8) is provided for effecting pulse width modulation of the power applied to the air moving means (2,3) from the electric power source (4) in dependence on the gas pressure within the protective means (1) whereby the rate of supply of breathable gas by the air moving means (2,3) to the protective means (1) is varied in accordance with the demands of the wearer.

2. Positive pressure breathing apparatus comprising protective means (1) for surrounding the respiratory passages of a wearer thereof to exclude noxious atmospheric gases from the space within the protective means (1) and adjacent to the said respiratory passages, air moving means (2,3) comprising a fan (2) and a motor (3) for driving the fan (2) to supply breathable gas to the protective means (1) at a rate faster than the rate of leakage of gas from the protective means (1) and an electric battery (4) for supplying power to the fan motor (3) to drive the fan (2), characterised in that a pressure sensitive electronic module (8) is provided for causing the power applied from the electric battery (4) to the fan motor (3) to be supplied as D.C. pulses, the width of the pulses being modulated in dependence on the pressure sensed within the protective means (1) whereby the speed of the fan motor (3) is regulated according to the demand of the wearer.

3. Positive pressure breathing apparatus according to Claim 2 characterised in that the pressure sensitive (8) electronic module comprises a pressure transducer which produces an electrical output signal proportional to the instantaneous gas pressure within the protective means (1) and a pulse generator for generating pulses, the width of the pulses being varied in inverse relation to the electrical output signal from the pressure transducer.

4. Positive pressure breathing apparatus according to Claim 2 or Claim 3 characterised by additionally including visible warning means (9) energable under control of the pressure sensitive electronic module (8) for giving a visible warning of an unusually low gas pressure within the protective means (1).

5. Positive pressure breathing apparatus according to any one of the preceding claims characterised in that the protective means (1) is a full face mask.

6. Positive pressure breathing apparatus according to any one of the preceding claims characterised in that the protective means (1) is a hood.

7. Positive pressure breathing apparatus according to any one of the preceding claims characterised in that the protective means (1) is an orinasal mask.