GB2053032A

GB2053032A - Gas separator

Info

Publication number: GB2053032A
Application number: GB8021702A
Authority: GB
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1979-07-10
Filing date: 1980-07-02
Publication date: 1981-02-04
Also published as: DE2927800C2; GB2053032B; DE2927800B1

Abstract

A separator for pressure gases, e.g. produced by a solid-matter gas generator for a device having a working piston (11) which is actuated by the gas, is so arranged that the pressure gas is conducted, prior to entry into working chamber (10), through a tube (12) which extends into a long bore (14) in the working piston (11). The tube (12) is open at its lower end (13) and the pressure gas flows through the annular space between the piston (11) and the tube (12) before acting onto the piston working surface (15). The outside (16) of the tube (12) and the inside of the piston (11) have spiral protrusions (17), (Fig. 3), to impose centrifugal forces on the pressure gas to effect separation of impurities therefrom. The inside of the tube (12) may also be provided with spiral protrusions. <IMAGE>

Description

SPECIFICATION Gas filter This invention relates to a gas filter, and more particularly to a filter for pressure gases produced by solid-matter gas generators, more expecially for devices having working pistons which are actuated by the pressure gas.

For applications in which it is required to have available, in a very short time, a volume of pressure gas which is as great as possible, pyrotechnical charges along the lines of cartridges are being developed which supply pressure gas into a working chamber. Such applications are known from motor-vehicle safety technology, where automatically-inflatable cushions are intended to serve as impactabsorbing bags or air-bags to protect the occupants from injury in the event of a collision, see for example German Offenlegungsschrift No. 23 50 102 and German Offenlegungsschrift No. 23 64 140. Other applications are known from aircraft technology, where, for example, external loads are intended to be dumped in flight.For this purpose, a suspension hook is withdrawn and an impulse is imparted to the external load, in order to prevent from flying-along with the aircraft after its physical separation therefrom, and in order to be able to conform to definite dropping parameters such as time and place.

The impulse is produced by gas cartridges being detonated, whereupon the pressure gas acts on one or more ram-like pistons, which extend in a period of time in the millisecond range and push the load away, see for example British Patent Specifications Nos.

1,058,997 and 1,248,926.

In general machine construction, too, it is known to equip actuating mechanisms of all kinds with solid-matter gas generators. In addition to the advantage that large volumes of pressure gas are available in very short periods, it is further noteworthy that gas-generating cartridges are very small as compared with systems having gas compressed in a cylinder, and the expenditure involved in the pyrotechnical triggering thereof for example by electrical means, is extremely low. In addition, after usage, the cartridges can be exchanged by hand easily and without any problems.

In many instances of use, however, solid matter contained in the pressure gas in the form of particles has a deleterious effect.

Without filtering, piston/cylinder movement systems or the like can fail after being actuated once or twice, because the solid matter particles settle on the piston and cylinder surfaces or valves of the systems become sooted or clogged and this thus leads to faulty functioning. The filtering of the hot gases, which are at a temperature in the range of 1000 to 1 200#C., is, of course, fraught with problems. On the one hand, because of the high temperatures the choice of filter material is restricted; on the other hand amounts up to 2500 1 /sec and more have to pass through relatively small filter surfaces. Finally, the filtering must not cause any pressure losses because this would lead to unacceptable prolongation of the overall delivery time.In the past use has been made of filters in which the pressure gas is filtered through materials such as quartz wool or other porous elements made from silicon oxide or dioxide, aluminium oxide or iron oxide.

An object of the invention is to provide an inexpensive filter for the purpose indicated which does not involve unacceptable pressure losses nor involves new space requirements in the device, and in which the disadvantages above discussed are avoided.

With this object in view the present invention provides a filter for pressure gas produced by a solid-matter gas generator, and more especially for a device having a working piston which is actuated by the pressure gas, characterised in that, prior to entry into a working chamber, the pressure gas is conducted through a tube which extends into a long bore in the working piston, the tube being open at its lower end and the pressure gas flowing through the long bore to the piston's working surface, and in that the outside of the tube and the long bore have spiral grooves formed therein for generating centrifugal forces in the pressure gas.

Without appreciable pressure loss, the pressure gas passes onto the piston working surface and the cylinder walls after any chemical and metallic residues have been precipitated on the surfaces of tube and long bore. It is also crucial that the filtration is effected in the cool region, i.e. after any chemical compounds have already been condensed out.

The principle of providing greater paths, without reducing the free passage, has, in practical tests led to best results. It can readily, and advantageously be incorporated into the necessary pressure-gas pipelines instead of being integrated in working pistons.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional elevation showing the path of the pressure gas to a working piston, at the instant of first inflow, in a preferred embodiment of the invention; Figure 2 is a view similar to Fig. 1, but showing the piston having been extended; and Figure 3 shows the form of the walls of the tube and long bore of the arrangement of Figs. 1 and 2.

In the various figures, the same reference numerals have been used for similar parts.

Fig. 1 illustrates a gas-powered actuating device comprising a working piston 11 which is shown in the withdrawn position or the position of rest. High pressure gas from a solid-matter gas generator (not shown) flows via a pipeline 20, as indicated by the arrows, into a tube 12 (see Fig. 2). This tube 12 is screwed into a socket in a rigid inlet part 21, but it may be fastened in some other suitable fashion. The tube 12 extends into a long internal bore 14 within the working piston 11. Depending on the length of the working piston 11, the tube 12 does not have to extend as far as the base, or the vicinity thereof, of the working piston 11. As a rule, a tube length in the order of magnitude of 10-1m will be adequate.

The tube 12 is open at its lower end 13, so that the pressure gas flows, with simultaneous reversal of its direction of flow, through the long bore 14 and passes, at the upper end thereof, into working chamber or cylinder 10, or onto the working surfaces 15 of the piston 11.

The piston 11 is sealed relative to the wall of the cylinder 10 in traditional manner with a sealing ring 22.

Fig. 2 shows the working piston 11 in an extended condition. A spring 23 at the bottom of the long bore 14 is without significance for the invention; its function resides merely in cushioning or buffering the working piston 11 relative to the tube 12 upon upward withdrawing movement of the former.

Fig. 3 shows the form of spiral windings formed as protrusions and grooves provided in the long bore 14 and on the outside 16 of the tube 12. Because of the steady (or constant) expansion and compression of the pressure gas, the latter is conducted, without hindrance to its passage, over a considerably enlarged surface and is set into spiral rotation, so that residues in the gas are subject to a force which acts in the direction of the spiral walls where they settle. In the figures only the walls of the long bore 14 and the exterior of the tube 12 are provided with the spiral windings; of course, to produce a larger surface on which impurities can settle, the inside 18 of the tube 12 can be provided with such spiral windings.

As a result of the enlarged path provided for the propelling gas, increased cooling of the pressure gas is achieved so that chemical residues can condense out and can settle together with the other impurities on the way.

In this way, and as a result of turbulence, with a free passage between the spiral windings, the pressure gas passes only after adequate precleaning onto the fouling-sensitive sliding surfaces for the working piston 11.

Endurance tests in practice have shown that a multiplication of the life of such parts occurs, without any measurable reduction in function.

In the case of applications in which a working piston is not available, or is not available in the necessary way, such as for instance in the case of an air-cushion in motor-vehicle safety technology, the filter can be arranged in the pressure-gas pipeline itself. The pressure-gas pipeline is then designed, at this point, along the lines of a double-walled tube, in which pressure gas flows along the outside of the inner tube 12 and through the inside thereof. The outside of the tube and the inside of the pressure-gas pipeline have the spiral windings, so that the previously-described effect occurs. Moreover, additionally also the inside of the tube can be provided, for surface enlargement, with the spiral windings.

Finally, in accordance with a further modification provision is made for the fact that several tubes each in the fashion of the tube 12, are arranged inside one another, so that a maximum surface results.

Claims

1. A filter for pressure gas produced by a solid-matter gas generator, and more especially for a device having a working piston which is actuated by the pressure gas, characterised in that, prior to entry into a working chamber, the pressure gas is conducted through a tube which extends into a long bore in the working piston, the tube being open at its lower end and the pressure gas flowing through the long bore to the piston's working surface, and in that the outside of the tube and the long bore have spiral grooves formed therein for generating centrifugal forces in the pressure gas.

2. A filter as claimed in claim 1, characterised in that the inside of the tube has spiral grooves.

3. A filter as claimed in claim 1 or 2, characterised in that the tube is arranged in the pressure gas pipeline and the inside of the pressure gas pipeline is provided with spiral windings in the region of the tube (12).

4. A filter as claimed in claim 1, 2 or 3, characterised in that it comprises several said tubes arranged in one another.

5. A filter for a pressure gas substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.