GB2036198A - Sealing gaiters - Google Patents

Abstract

A gaiter cover comprises a plastics or rubber shrouded spring 10 or a spring inter threaded with a shroud 12, 14 such that the cover naturally retains itself between relatively movable walls in a pressure responsive pneumatic brake actuator to preclude entry of foreign matter to a region surrounding the gaiter cover. <IMAGE>

Description

SPECIFICATION Improvements in or relating to gaiter covers in fluid pressure responsive devices This invention relates to gaiter covers, especially in fluid pressure responsive devices.

An example of a practical application of a prior art gaiter cover will first be described by way of example, with reference to Fig. 1 of the accompanying drawings which illustrate a known form of combined air-operated spring brake and service brake for heavy road vehicles, known as the brake actuator Type 9 to Type 12, sold by the Applicants, and fully described in the Applicants' Technical Pamphlet 7/006.

Referring to Fig. 1, this illustrates the internal structural details of the actuator with the parts in the relative positions occupied when the spring brake is held-off by air pressure in a chamber F, and the service (diaphragm X) brake is not applied. The complete actuator is screwed in use into a wedge brake expander body (not shown) by the threaded mounting tube A and is secured by a locking ring nut B.

A service brake diaphragm X, a push-rod assembly C and a front portion of the service brake chamber D are secured by the bolted clamp ring E to the cast aluminium spring brake chamber F.

A spring brake piston G and a powerful brake compression spring H are retained by a spring ring J and a cast aluminium head K. A spring release bolt L is environmentally protected by a detachable breather cap M. An air filter N prevents air-borne direct from being drawn into the actuator.

Unscrewing of the release bolt L in the end of a long piston boss P allows a spring brake piston rod 0 to retract into the piston G, thus relieving the pressure of the spring H on the push-rod C. Air pressure seals R are fitted to the piston G and the piston rod Q. A gaiter cover in the form of a flexible rubber boot S prevents dirt from entering the actuator mechanism through the tube A.

Full details of the operation of the brake actuator shown in Fig. 1 are not necessary for the purposes of the present invention, and it suffices to say that the boot or gaiter cover S is required to compress and expand longitudinally in the manner of a bellows while maintaining a reliable seal at either end thereof during operation of the actuator shown in Fig.

1.

It will be seen in Fig. 1, that the left end of the boot or gaiter cover S is tightly fitted round an inward extension of the tube A. The right end of the cover S is similarly a tight fit round the inner end of the push-rod C. It will be readily obvious that because of the constructional details of the brake actuator, the fitting of the boot or gaiter cover S in its proper end positions prior to application of the clamp ring E will present some difficulty.

It is therefore an object of the invention to provide an improved gaiter cover which, within limits, is self-sealing at its ends and does not require complex manoeuvring for assembly into its intended operational position.

According to the present invention, there is provided a fluid pressure responsive device having a pressurable chamber separated from a further chamber by a pressure responsivemember, a wall of the further chamber facing the pressure-responsive member having an aperture providing access for mechanical linkage between an outer region and the pressure-responsive member and a gaiter cover retained between the pressure-responsive member and the aperture to provide a flexible partition between the further chamber and the outer region, said gaiter cover incorporating a coiled resilient spring or the envelope of said gaiter and a coiled reilient spring being mutually inter-threaded.

According to a first subsidiary aspect of the invention, there is provided a method of manufacturing a gaiter cover, comprising the steps of internally and/or externally applying a layer of flexible membrane or fabric or fabric-like material to a coiled compression spring such as to shroud the inside of outside of the spring, and then applying a coating of a flexible material to the membrane or fabric or material-shrouded spring whereby to form a flexible shrouded spring in the form of a compressible gaiter cover.

Thus the spring supports the membrane or the fabric or fabric-like material which, in turn, act as a shape-defining former for the flexible coating.

The coating may be applied by dipping the shrouded spring in a vessel containing the coating in liquid form, the coating being such as to subsequently dry or cure to a dry skin.

Alternatively, the coating may be internally and/or externally painted or sprayed onto the shrouded spring, or shrunk onto the shrouded spring.

Preferably, the membrane or fabric or fabric-like material is, before being coated, shaped to have tucks, folds, or convolutions such that the completed cover may more readily accommodate torsional twisting of the spring as the cover is alternately compressed and released.

According to a second subsidiary aspect of the invention, there is provided a gaiter cover comprising a coiled compression spring having an internal and/or external shroud of a membrane or layer of flexible fabric or fabriclike material, said membrane or fabric or material being internally and/or externally provided with a coating of a flexible material.

In said first and second aspects of the invention, the spring may be a cylindrical spring or a conical spring or a biconical spring.

In said first and second aspects of the invention, said membrane may be substantially impermeable sheet of plastics material, and said fabric may be a sheet-woven, or knitted from synthetic fibre, for example nylon. Alternatively, the fabric-like material may be flexible fine-gauge metal wire mesh or gauze.

In said first and second aspects of the invention, the flexible coating may be a natural or synthetic latex or rubber, or a plastics material such as a thermoplastic polymer.

Preferably said coating is impermeable to liquids.

In order that the invention may be more clearly understood and readily put into effect, preferred embodiments of the same will now be described, by way of examples only, with reference to Figs. 2-4 of the accompanying drawings wherein: Figure 1 illustrates a prior art brake actuator already discussed; Figure 2 is a half-section in a radial plane of a first embodiment of the invention; Figure 3 is a half-section and half-view of a second embodiment of the invention; Figure 4 is a view to an enlarged scale of the section IV of Fig. 3; and Figures 5 and 6 illustrate further embodiments of brake actuators employing the invention.

Referring first to Fig. 2, (which, being symmetrical, has only its upper half above the central axis "CL-CL" actually shown) a helical steel compression spring 10 is fitted with a matching conical inner membrane 12, for example, of sheet plastics material, and the assembly of the spring 10 and the membrane 12 is given an external coating 14 of paintedon or sprayed-on rubber material to form a gaiter cover.

Alternatively, the coating 14 may be a thermally shrunk-on sleeve of plastics material. As an optional extra, the cover may be provided with end guide plates such as the steel plate 16, which serve to widen the areas of support of the ends of the cover.

Not shown in Fig. 2 are tucks, folds, or convolutions in the membrane 12, such that the finished cover has areas which are relatively slack in the uncompressed state of the cover, but which stretch to accomodate the twisting of the spring 10 as it is compressed.

The membrane 1 2 provides a ready foundation for the application of the coating 14 and so enables the easy fabrication of a cover without special moulds or other facilities being required.

The coating 14 is preferably of such a material and such a minimum thickness as to be waterproof and oilproof.

The cover of Fig. 2 may readily be substituted for the boot S of Fig. 1, with the small (left) end of the cover fitting over the inner end of the tube A, and the larger (right) end of the cover being self-seating (assuming the spring 10 to be slightly compressed) on the diaphragm plate Y. (In view of the continuous surface presented by the diaphragm plate Y, the guide plate 1 6 is not strictly necessary in this case).

Referring now to Fig. 3, this illustrates (with the upper half in section and the lower half in external view) a second embodiment of the invention. This second embodiment comprises a conical steel compression spring 20 which is fitted with a nylon fabric stocking 22 enveloping and shrouding the sides of the spring 20. With the stocking 22 shrouding the spring 20, this assembly is dipped into a vessel containing liquid material or synthetic latex or rubber to coat the assembly. The coated assembly is then withdrawn from the vessel, and the remanent layer or coating 24 dries or cures naturally or with the application of heat and/or radiation to form a rubbery flexible impermeable coating, thereby to form a gaiter cover.Fig. 4 shows the detail IV in Fig. 3 to an enlarged scale, and illustrates how the spring 20 and the stocking 22 are covered, both internally and externally, and also "glued" together by the coating 24.

The gaiter cover of Fig. 3 may be used as a substitute for the boot S in Fig. 1, as described in respect of the first embodiment of Fig. 2.

The gaiter covers of Figs. 2 and 3 may be used in many applications other than as boot substitutes in Fig. 1, i.e., in any situation where a gap between two relatively movable parts has to be covered or sealed. For example, one or more of the covers of the invention may be used between fixed and moving members in linear actuators other than brake actuators, e.g. vehicle steering racks, and also to seal gear-change operating members where they enter the gearbox. An advantage of the present invention is that the gaiter cover need only be compressively restrained whereas prior art covers (such as in Fig. 1) need compressive and tensile restraint at both ends.

The cover of the invention may be constructed with a membrane or fabric covering the exterior of the spring or moulded to the interior of the spring, or be applied both internally and externally. Similarly, the coating may be internal only or external only, with the coating on the same side (inside or outside) or the other side of the spring than the membrane or fabric, or the coating may be both internal or external.

In an alternative arrangement, the coiled spring may not be moulded or otherwise formed integrally with the gaiter cover and in Fig. 5, a form of air pressure operable brake actuator is shown wherein a bellows 1 3 and the coiled spring 10 are mutually interthreaded.

Referring to Fig. 5, this shows a diaphragm type of fluid pressure brake actuator comprising a pressure plate 1 between which and a non-pressure plate 2 there is clamped a diaphragm 3 by a clamping ring 4, the ends of which are drawn together by a suitable tensioning bolt, not shown. The pressure plate 1 is provided with an input port 5 and the nonpressure plate 2 is provided with a vent 6 to the exterior. The diaphragm 3 is engaged by a push plate 7 connected via a rod 8 providing mechanical communication between the push plate 7 and an outer region 9.

The push plate 7 is urged ieftwards to normally withdraw the rod 8 to its furthest extent, by a return spring located generally centrally having regard to the aperture 11 via which the rod 8 communicates with the outer region 9 by being retained between the heads of three or more captive mounting studs such as 12.

The outer region 9 in the present example is assumed to contain an hydraulic portion of an air over hydraulic actuator arrangement and, in such a case, it is important to prevent the passage of any contaminating material between the non-pressure chamber to the right of the diaphragm 3 and the outer region 9. In accordance with the present invention, therefore, a moulded flexible bellows 1 3 provided which establishes a flexible partition between the non-pressure chamber of the pneumatic actuator and the said outer region.

The moulded bellows is sufficiently resilient to retain itself between the push plate 7 and the facing end wall containing the aperture 11.

Furthermore, by arranging the configuration of the moulding to be hellical, it can be located within the coils of the spring as shown in the drawing.

In operation, a desired pneumatic pressure is applied to the input port 5 which effects a deflection of the diaphragm 3 and push plate 7 to exert a force via the rod 8 to the outer region and to the piston of an hydraulic actuator from whence hydraulic fluid is applied to slave cylinders at appropriate locations of the vehicle or other machine in which the apparatus is installed. The slight reduction of volume in the non-pressure chamber is relieved of any pressure increase by virtue of the vent 6 to the exterior and by virtue of the flexible partition provided by the bellows 13, there is virtually no possibility of contamination passing between the non-pressure chamber and the outer region 9.

Referring to Fig. 6, this shows a piston-type of actuator in generally schematic form wherein the gaiter is mutually inter-threaded within the coiled spring. Again, the actuator comprises a pressurable region and a nonpressurable region separated by a pressure responsive member in the form of a piston 24 with a sliding annular seal 25. The piston is urged leftwards in a direction to withdraw a piston rod 26 which provides mechanical connection between the piston 24 and means, not shown, in the outer region 29. Again, this means, not shown, may be an hydraulic piston. The region 29 is contained within a part 30 which has a spigot portion 31 conveniently providing a stop against which the piston may abut in the fully deflected position. In addition to the spring 32 extending between the wall of the non-pressure chamber of the actuator and the piston, there is provided a flexible moulded bellows 33, the shape of which is again arranged to interleave with the coils of the spring. Again, the flexible bellows provides a flexible partition between the further chamber 22 and the outer region 29 to prevent the passage of any contaminating material from the pneumatic actuator to the said outer region.

An extra heavy gaiter cover, for use in any of the above embodiments, or more especially in cases where there is to be little relative movement ofthe cover ends or walls, may be made by applying to a suitable fabric-like material in the form of a fine metal mesh or gauze, a coating of a quality and quantity suitable for the cover's intended duty.

Claims (11)

1. A fluid pressure responsive device having a pressurable chamber separated from a further chamber by a pressure responsive member, a wall of the further chamber facing the pressure-responsive member having an aperture providing access for mechanical linkage between an outer region and the pressure-responsive member and a gaiter cover retained between the pressure-responsive member and the aperture to provide a flexible partition between the further chamber and the outer region, said gaiter cover incorporating a coiled resilient spring or the envelope of said gaiter and a coiled resilient spring being mutually inter-threaded.

2. A method of manufacturing a gaiter cover, comprising the steps of internally and/ or externally applying a layer of flexible membrane or fabric or fabric-like material to a coiled compression spring such as to shroud the inside or outside of the spring, and then applying a coating of a flexible material to the membrane or fabric or material-shrouded spring whereby to form a flexible shrouded spring in the form of a compressible gaiter cover.

3. A method as claimed in Claim 2 wherein the coating is applied by dipping the shrouded spring in a vessel containing the coating in liquid form, the coating being such as to subsequently dry or cure to a dry skin.

4. A method as claimed in Claim 2 wherein the coating is internally and/or externally painted or sprayed onto the shrouded spring, or shrunk onto the shrouded spring.

5. A method as claimed in claim 2 wherein the membrane or fabric or fabric-like material is, before being coated, shaped to have tucks, folds, or convolutions such that the completed cover may more readily accommodate torsional twisting of the spring as the cover is alternately compressed and released.

6. A gaiter cover comprising a coiled compression spring having an internal and/or external shroud of a membrane or layer of flexible fabric or fabric-like material, said membrane or fabric or material being internally and/or externally provided with a coating of a flexible material.

7. A method or gaiter as claimed in Claim 2, 3, 4, 5 or 6, wherein the spring may be a cylindrical spring or a conical spring of a biconical spring.

8. A method or gaiter as claimed in Claim 2, 3, 4, 5, 6 or 7 wherein said membrane is a substantially impermeable sheet of plastics material, and said fabric may be a sheetwoven, or knitted from synthetic fibre.

9. A method or gaiter as claimed in Claim 2, 3, 4, 5, 6 or 7 wherein said membrane is a flexible fine-gauge metal wire mesh or gauze.

10. A method or gaiter as claimed in Claim 2, 3, 4, 5, 6, 7, 8 or 9 wherein the flexible coating is natural or synthetic latex or rubber.

11. A method of manufacture of a gaiter cover substantially as described herewith with reference to Fig. 2 or Figs. 3 and 4 of the accompanying drawings.

1 2. A fluid pressure responsive device substantially as described herein with reference to Fig. 1, or Fig. 6 employing a gaiter cover manufacture as claimed in any of Claims 2 to 11.