FR2640018A1 - Composite flexible separator for a pressure tank, its method of production, and pressure tank including such a flexible separator - Google Patents

Abstract

This is a pressure tank the flexible separator 12 of which includes three layers, namely an outer layer 21A, an inner layer 21B, and an intermediate gas-permeable layer 23. According to the invention, the intermediate layer 23 includes a metal leaf 24. Application, in particular, to pressure tanks intended to equip braking circuits.

Description

"Flexible composite separator for pressure tank,
its production process, and pressure tank
having such a flexible separator "
The present invention relates generally to pressure tanks, of the type used for example as pressure accumulators or transmitters.

 It relates more particularly to the case where such a pressure reservoir comprises, in a rigid body, a flexible separator in the form of a membrane, which, for a partition between two different fluids, separates the internal volume of this body into two separate chambers, flexible separator being engaged, by its outlet, with a support member, which, integral with said body, holds said outlet pressed against the internal surface thereof.

 In the case of, for example, a pressure accumulator to be installed in diversion on any hydraulic circuit, one of the two chambers is a gas chamber, that is to say a chamber sealingly confining a load determined gas under pressure while the other is a chamber to liquidate this other chamber being intended to be placed in communication with the hydraulic circuit concerned.

 One of the problems to be solved in the production of pressure reservoirs of this type is that its flexible separator must respond to a certain number of characteristics which, without other, are hardly compatible.

 I1 must indeed, at the same time, present a certain capacity of elastic deformation, and, therefore, to do this, be made of deformable material, be able to withstand the temperature, be able to resist the aggressiveness of fluids to contact of which there is, and, more particularly, of the liquid present in the liquid chamber, in particular when it is a brake fluid, as may be the case in braking circuits of the type commonly known as RABS ", and jointly oppose any appreciable diffusion in this liquid of the gas present under load in the associated gas chamber.

 Otherwise, such diffusion of gas in this liquid could lead to a dangerous disturbance of the hydraulic circuit served.

 However, the deformable materials having satisfactory gas impermeability performance are generally incompatible with certain fluids, such as brake fluids, and / or are not suitable for certain conditions of use, such as those in which the temperature occurs.

 For example, to make a Butyl-type elastomer more gas-tight, a filler must be added to it, which together makes it sensitive to brake fluids.

 To overcome difficulties of this type, it has long been proposed to make a flexible separator in a composite manner, for a dissociation of the functions which it has to assume.

 This is the case, in particular, in French patent No 1,272,420, in which the flexible separator is in practice constituted by two separate partitions, the outermost partition, made of elastic material, being intended to ensure the compatibility of the together with the liquid to be taken into consideration, while the innermost partition, made of non-elastic material, is chosen to be impermeable to gases.

 This is also the case in the French patent which, filed on December 7, 1979 under No. 79 30152, was published under No. 2,443,622.

 According to a similar arrangement, it is also known to produce the flexible separator in three adjacent layers of deformable material, namely, two elastic layers, one external, the other internal, and an intermediate layer with low permeability. gas, which has the disadvantage that a certain amount of gas can nevertheless migrate into the liquid after an extended period of use.

 A provision of this type is mentioned in the French patent application which, filed on August 21, 1987 under No 87 11815, was published under No 2.603.075.

 In this French patent application No. 87 11815, the decision is made, however, to use an intermediate layer permeable to gases, this intermediate layer then constituting a sort of drain, which, capturing the gas diffusing through the internal layer, then evacuates this gas outside the rigid body concerned.

 Due to the systematic loss of gas of which it is the object, a pressure tank of this type necessarily only has a limited lifespan.

 It is therefore specific to certain applications, and in particular to the equipment of braking circuits of the "ABS" type here more particularly targeted, these having to have, without prior revision, a service life equal to that of the vehicles concerned. .

 When the decision is made to use an intermediate layer which is genuinely impermeable to gases, the difficulty lies in the production of this intermediate layer, both with regard to its constituent material and with regard to its geometry.

 In French patent No 1,272,420, this gas-impermeable layer, which then forms a separate partition, is made of polyurethane, and it is in the form of a sort of bellows which deploys more or less depending on the load. gas.

 But, apart from the fact that such a partition is relatively awkward to produce, polyurethane is not entirely satisfactory when the impermeability to gases sought is particularly high, and, in the case of rapid and numerous repetitive work cycles, as is the case. in the case of "ABS" type braking circuits, the mechanical resistance of an intermediate layer thus produced may prove to be insufficient.

 The present invention generally relates to a provision providing, on the contrary, a particularly satisfactory and safe solution to the problem of producing a flexible separator which is both compatible with an aggressive liquid and which, despite everything, is highly impermeable to gases. , superior to that of the art known to date.

 More specifically, it firstly relates to a flexible composite separator for a pressure tank of the kind comprising three adjacent layers of deformable material, namely an outer layer, an inner layer, and an intermediate layer impermeable to gases, this flexible separator being generally characterized in that the intermediate layer comprises a metal sheet; it also relates to a pressure tank comprising such a flexible separator.

 The gas impermeability of metal sheets is well known; it is due to the molecular structure of their metallic constituent.

 However, extending exclusively in two directions, a metal sheet, whether taken in isolation or sandwiched between two protective sheets by adhering to them, does not normally lend itself to any conformation in flexible separator membrane, and one should normally expect a low mechanical resistance to repetitive deformation cycles of the type of which such a flexible separator is subject to in a pressure tank.

 The implementation of a metal sheet for the constitution of such a flexible separator is therefore normally completely foreign to those skilled in the art.

 The present invention is based on the discovery, a priori surprising, that it is on the contrary possible to conform a flexible separator membrane to a metal sheet, and that, with certain precautions, it retains its entire integrity even when it is subjected to repetitive strain cycles.

 On the first point, -the discovery relates to the fact that, as experience confirms, it is perfectly possible to conform a flexible separator membrane, by the hydro-forming technique known per se, initially flat, even when it is a blank comprising a metal sheet or formed from such a metal sheet.

 From this point of view, the present invention also relates to a process for the production of a flexible separator of the kind concerned, this process being generally characterized in that it consists in making each of the layers which constitute this flexible separator, and to fit them successively into each other, and in that, as regards the manufacture of the intermediate layer, an initially flat blank is formed by hydro-forming.

 On the second point, the discovery related to the fact that, in order to preserve the integrity of the metallic sheet of the intermediate layer thus produced, and the fatigue tests confirm it, it is necessary that the internal layer, forming at this Regarding the protective layer, be able to maintain this intermediate layer in the area of the neutral fiber of the assembly.

 The internal layer of the flexible separator according to the invention is established accordingly.

The characteristics and advantages of the invention will become apparent from the description which follows, by way of example, with reference to the appended schematic drawings in which
Figure 1 is an axial sectional view of a flexible separator according to the invention
Figures 2, 3 show, each respectively, on a larger scale, the details of Figure 1 identified by inserts IIr III thereon
Figure 4 is an exploded axial sectional view, which, similar to that of Figure 1, individually represents each of the constituent layers of the flexible separator according to the invention
Figure 5 shows, on a larger scale, the detail of Figure 4 identified by an insert V in this Figure 4
Figure 6 is a view similar to that of Figure 5, for an alternative embodiment of the layer concerned
Figure 7 is, on the scale of Figure 1, an axial sectional view of a pressure tank equipped with a flexible separator according to the invention.

 As illustrated in these figures, and, more particularly, in FIG. 7, it is a question of equipping a pressure tank 10 comprising a rigid body 11, and, in this rigid body 11, a flexible separator 12, in the form of a membrane, and, more specifically, in the form of a pocket or bladder, which separates the internal volume of this rigid body 11 into two separate chambers 13A, 13B, said flexible separator 12 being engaged by its outlet 14 , with a support member 15, which, integral with the rigid body 11, maintains said outlet 14 pressed against the internal surface thereof.

 In the embodiment shown, the rigid body 11 consists of two shells 16A, 16B, duly butted together and suitably secured to each other, in practice by welding, namely, a shell lower, 16A, forming the bottom, and an upper shell 16B, forming a cover.

 Jointly, in this embodiment, the support member 15 is an annular member comprising, on the one hand, a cylindrical part 17, by which it is applied to the internal surface of the lower shell 16A of the rigid body 11, in being suitably secured, in practice by welding, to the latter, and, on the other hand, a part 18, which is shaped as a hook, and by which it grips, at its outlet 14, the flexible separator 12, by pressing this outlet 14 against said internal surface of this lower shell 16A.

 The shells 16A, 16B, and the support member 15, can for example be metallic.

 As shown diagrammatically in broken lines in FIG. 7, the assembly is completed, on the one hand, on the side of the chamber 13B, which is in practice a gas chamber, by a valve 18B suitable for loading this gas chamber 13B, and, on the other hand, on the side of the chamber 13A, which is in practice a liquid chamber, and which, in FIG. 7, is reduced to nothing, by a conduit 18A suitable for the connection of this liquid chamber 13A to the hydraulic circuit to serve this conduit 18A defining, for this purpose, under the control of a valve, constituted, in this case, by a button 20 carried at its base by the flexible separator 12, an orifice liquid passage not detailed in this figure 7.

 These provisions being well known in themselves, and not being the subject of the present invention, they will not be described in more detail here.

 In a manner also known per se, the flexible separator is a composite separator comprising three adjacent layers, namely a layer of external deformable material 21A r an internal layer 21B, and an intermediate layer 23 impermeable to gases.

 According to the invention, the intermediate layer 23 comprises a metal sheet 24.

 For example, in FIG. 5, it is reduced to such a metal sheet 24.

 As a variant, in FIG. 6, it is formed of a metal sheet 24 sandwiched between two protective sheets of synthetic material 21A, 21B, one external the other internal, and adhering to these, in the manner, for example, composite sheets sold under the commercial designation "VALERON".

 Anyway, the metal sheet 24 used is for example an aluminum sheet.

 Its thickness is extremely small, of the order of, for example, 0.01 to 0.1 mm.

 For example, when the metal sheet 24 is used in isolation, its thickness can be of the order of 0.075 mm.

 When it is implemented sandwiched between two protective sheets 21A, 21B, its thickness can be of the order of 0.02 mm, the two protective sheets 21A, 21B then themselves having a thickness of l '' order of 0.03 mm.

 Of course, the numerical values indicated above are given only by way of example and should in no way be considered as limiting the invention.

 The outer layer 21A and the inner layer 21B, for their part, are preferably made of elastically deformable material.

 In practice, they are made of elastomer, and, for example, of elastomer of the Butyl type.

 For the constitution, jointly, of a bead 25 capable of cooperating in stowage with the hook-shaped part 18 of the support member 15, they both include, at their outlet, a bead, respectively 26A, 26B, which projects radially outward for the outer layer 21A, and which projects radially inward for the inner layer 21B.

 The thickness of the external layers 21A and internal 21B is for example of the order of 1.2 to 1.6 mm, and, for example, of the order of 1.4 mm.

 But, as before, these numerical values are given only for information, without being in any way limiting of the invention.

 In practice, the external layer 21A being intended to be in contact with the fluid present in the liquid chamber 13A, it is established so as to be inert with respect to this fluid.

 Therefore, the elastomer which constitutes it is, in practice, a pure elastomer, that is to say an elastomer devoid of any specific charge for gas impermeability.

 For simplicity, and to facilitate the manufacture of the assembly, it is the same for the inner layer 21B.

 Jointly, this internal layer 21B is chosen so as to be able to maintain the intermediate layer 23 in the region of the neutral fiber of the assembly.

 In other words, it has mechanical characteristics and thickness suitable for enabling it to thus maintain this intermediate layer 23 in the region of this neutral fiber.

 It then advantageously controls the radius of curvature of this intermediate layer 23.

 For example, and notwithstanding the above, the material constituting this internal layer 21B is less flexible than that constituting the external layer 21A, and the latter is thicker than the internal layer 21B.

 As a variant, the material constituting the internal layer 21B is more flexible than that constituting the external layer 21A, and the latter is thinner than the internal layer 2tub.

 But r according to an embodiment with which very good results have been obtained, the materials constituting the inner 21B and outer 21A layers have the same degree of flexibility, and this inner layer 21B and this outer layer 21A have substantially the same thickness.

 Preferably, and as shown, the various layers 21A, 23, 21B thus constituting the flexible separator 12 according to the invention are adjacent to each other.

 Preferably, also, they are devoid of any connection between them, in order to be able to play in service with each other, which is favorable to a limitation of the constraints within them.

 However, if desired, they can be joined, for example by gluing.

 Preferably also, and as shown, the button 20 carried by the flexible separator 12 according to the invention is engaged only with the single outer layer 21A, said button 20 comprising, projecting, a lug 27 by which it is snapped onto said outer layer 21A, by means of an axial bore 28 thereof.

 Together, the intermediate layer 23 and the internal layer 21B each have, in correspondence, a local deformation in the form of a dome, respectively 30r 31B, by which they bypass this lug 27.

 For the production of the flexible separator 12 according to the invention, the various layers 2IA, 23, 21B which constitute it are produced in isolation, and, as shown diagrammatically in FIG. 4, they are then successively fitted one into the other, for example vacuum, to prevent the formation of any air pocket between them.

 As regards the external layers 21A and internal 21B, it is carried out, in the usual manner, by molding.

 As for the intermediate layer 23, and as shown diagrammatically by a broken line in FIG. 4, it is carried out by hydro-forming, starting from a blank 23 ′ initially flat.

 Since the hydro-forming technique is well known in itself, the corresponding arrangements will not be described here.

 Whatever the case may be, the various layers 21A, 23 and 21B are produced so as to present, at rest, a configuration complementary to that of the lower shell 16A of the rigid body 11.

 In the embodiment shown, this configuration corresponds to that of a hemisphere surmounted by a cylindrical crown.

 Once these layers 21A, 23 and 21B have been produced and fitted, the flexible separator 12 which they jointly constitute is disposed inside the lower shell 16A of the rigid body 11, in engagement with the corresponding support member 15.

 The latter is then welded to this lower shell 16A, and the assembly is closed by the upper shell 16B.

 The corresponding provisions being well known in themselves, they will not be described here.

 At rest, the flexible separator 12 bears under tension against the internal surface of the lower shell 16A of the rigid body 11.

 In service, it deforms more or less, releasing, between itself and the internal surface of the lower shell 16A of the rigid body 11 r a liquid chamber 13A more or less large.

 In Figure 7, has been shown in broken lines its maximum deformation.

 Of course, the present invention is not limited to the embodiment described and shown, but encompasses any variant.

Claims (15)

 1. Flexible composite separator for a pressure tank, of the type comprising three adjacent layers of deformable material, namely an external layer (21A), an internal layer (21B), and an intermediate layer (23) impermeable to gases, characterized in that that the intermediate layer (23) comprises a metal sheet (24).  2. Flexible separator according to claim 1, characterized in that the intermediate layer (23) is reduced to a metal sheet (24).  3. Flexible separator according to claim 1, characterized in that the intermediate layer (23) is formed of a metal sheet (24) sandwiched between two protective sheets of synthetic material (21 A, 21B) and adhering to those -this.  4. Flexible separator according to any one of claims 1 to 3, characterized in that the metal sheet (24) is an aluminum sheet.  5. Flexible separator according to any one of claims 1 to 4, characterized in that one and the other of the outer (21A) and inner (21B) layers are made of elastically deformable material, for example elastomer.  6. Flexible separator according to claim 5, characterized in that, intended to be in contact with any given fluid, the outer layer (21B), at least, is inert with respect to such a fluid.  7. Flexible separator according to any one of claims 1 to 6, characterized in that the internal layer (2il) has mechanical characteristics and thickness suitable for enabling it to maintain the intermediate layer (23) in the region of the neutral fiber of the set.  8. Flexible separator according to claim 7, characterized in that the material constituting the internal layer (2 lu) is less flexible than that constituting the external layer (21A), and the latter is thicker than the  9. Flexible separator according to claim 7, characterized in that the material constituting the internal layer (21B) is more flexible than that constituting the external layer (21A), and the latter is thinner than the internal layer (21B).  10. Flexible separator according to claim 7, characterized in that the materials constituting the internal (21B) and external (21A) layers have the same degree of flexibility, and this internal layer (21B) and this external layer (2 lA) have substantially the same thickness.  he. Flexible separator according to any one of Claims 1 to 10, characterized in that the various layers (21A, 23, 21B) which constitute it are devoid of joining together.  12. Flexible separator according to any one of claims 1 to 11, characterized in that, carrying a button (20), said button (20) is engaged only with its only outer layer (21A), said button (20) comprising a lug (27) by which it is snapped onto said outer layer (21A) by means of a bore (28) thereof, and the intermediate layer (23) and the inner layer (21B) each comprising in correspondence a local deformation in the form of a dome (30, 31B) by which they bypass said lug (27).  13. A method for producing a flexible separator according to any one of claims 1 to 12, characterized in that it consists in making each of the layers (21A, 23, 21B) which constitute it, in isolation, and in nest successively in each other.  14. Method according to claim 13, characterized in that, for the manufacture of the intermediate layer (23), one starts from an initially flat blank (23 '), and it is shaped by hydro-forming.  15. Pressure tank of the kind comprising a rigid body (11), and, in this rigid body (11), a flexible separator (12) in the form of a membrane which separates the internal volume into two separate chambers (13A, 13B) , said flexible separator (12) being engaged, by its outlet (14), with a support member (15), which, integral with said rigid body (11), holds said outlet (14) pressed against the internal surface of the latter, characterized in that said flexible separator (12) conforms to any one of claims 1 to 12.  16. Pressure tank according to claim 15, characterized in that, at rest, the flexible separator carries under tension against the internal surface of the rigid body (11).