FR2685740A1 - FLEXIBLE SEPARATION ELEMENT FOR A HYDRAULIC ACCUMULATOR COMPRISING A VINYL ETHYLENE ALCOHOL COPOLYMER GAS CUTTING LAYER AND AN ELASTIC POLYAMIDE RESIN LAYER - Google Patents

Abstract

A flexible separating element for a hydraulic accumulator, which divides an inner space of a battery envelope into two parts which define a gas chamber and a liquid chamber, respectively. The flexible separating element (22) comprises a solid layer composite part (4) which consists of at least one gas barrier layer (1) and at least one elastic layer (2), each layer for stopping the gas consisting of a copolymer of ethylene and vinyl alcohol, and each elastic layer containing as main component a polyamide resin selected from a group consisting of PA 6, PA 6-6, PA 6-10 and from PA 6-12. The composite layered portion includes two adjacent layers which are a gas barrier and an elastic layer.

Description

The present invention relates to a hydraulic accumulator used in

hydraulic systems for

  automobiles and other vehicles and equipment

  industrial, and a flexible separating element in the form of a membrane or pocket or bladder,

  used in such a hydraulic accumulator.

  A hydraulic accumulator has the function of storing a pressurized hydraulic fluid and generally comprises a metal casing and a flexible separating element, such as a rubber membrane or a rubber bag or bladder, which

  divides the inside of the envelope into a chamber containing

  a gas and a chamber containing a liquid The membrane or bladder (generically referred to in this

  following "flexible separating element") is in one

  appropriate rubbery texture, of desired shape and

  relatively small thickness The separating element

  flexible is attached to the inside of the envelope and it coo-

  father with the wall of the envelope to define the rooms

  The gas chamber is filled with a suitable gas, such as nitrogen, while an oil or pressurized liquid is stored in the chamber.

  liquid chamber The oil is introduced into the chamber

  of liquid from a source of hydraulic pressure

  that, and the compressed gas acts as a cushion or a res-

  During use of the accumulator, the gas trapped in the gas chamber can gradually

  through the thin flexible separating element and

  come unable to perform its function, because of the decrease in the gas pressure resulting from the passage

  slow gas through the separating element.

  One solution to the problem above is

  to add one or more appropriate additives to the

  rubber position of the flexible separating element, to try to improve the resistance of the separating element to the penetration of the gas Although the additives can improve the resistance to gas penetration (gas tightness or impermeability) of the element

  separation, the flexibility of the separating element

  This tends to decrease as a result and the separating element may crack after a period of use.

  relatively long inside the envelope of the

  cumulative, which also creates a problem.

  In order to solve the problem above, one

  proposed to interpose a layer of copoly-

  mother of ethylene-vinyl alcohol between thin adjacent rubber layers in a flexible separating element, in such a way that the resin layer is

  bound to the rubber layers by adhesive layers

  An example of a multi-layered structure of

  rubber-resin is described in JP-A-2 165 948

  that this rubber-resin structure is used for a membrane or a flexible bladder in an accumulator

  hydraulics, the layer (s) of ethylene resin

  vinyl alcohol, which have a high degree of impermeability

  gas, help maintain the pressure of the

  charge of gas in the battery envelope

  However, the ethylene-vinyl alcohol copolymer resin layers have the disadvantage of cracking and peeling off the rubber layers after a long period of time. use during which the membrane or bladder undergoes a large number of bending deformations or displacements As a result, the life expectancy of the accumulator using a

  such membrane or bladder is reduced.

  An impermeable elastic membrane is described

  in US Patent No. 05,036,110.

  takes two first layers, each consisting of a first material, and a second layer interposed between

  the first layers and consisting of a second ma-

  The first subject is chosen from the group

  comprising thermoplastic polyurethanes, polyurethanes

  amide ethers sequences, flexible polyesters and

  mixtures of these materials, while the second

  re is selected from the group consisting of copolymers

  ethylene and vinyl alcohol, polyamides, chlo-

  polyvinylidene chloride and mixtures thereof.

  Although the second layer is waterproof

  to a gas, some of the first materials listed below

  have an insufficient resistance to heat and tend to deteriorate during the use of an accumulator in which the temperature of a fluid stored under pressure is relatively high.

  other raw materials may be softened by ex-

  position to a hydraulic fluid, such as a brake fluid, and they tend to have a useful life

relatively short.

  The present invention therefore has for first ob-

  to provide a flexible separating element for a hydraulic accumulator, this element having a long service life to ensure a long service life

of the accumulator.

  A second object of the invention is to

  a long-lasting hydraulic accumulator

of useful life.

  The first object can be reached according to a first aspect of the present invention which

  provides a flexible separating element

  hydraulic unit, which divides the interior of an enve-

  lump of the accumulator in two parts which constitute

  a gas chamber and a liquid chamber, respectively

  the flexible separating element including a composite layered part which comprises at least one

  gas barrier layer and at least one elastic layer.

  The integral or integral layered composite part comprises two adjacent layers which are one of said at least one gas barrier layer and one of said at least one elastic layer. Each of said at least one gas barrier layer consists of a copolymer of ethylene and vinyl alcohol, and each of said at least one elastic layer contains as main component a polyamide resin, commonly referred to as PA, selected from a group consisting of PA 6,

PA 6-6, PA 6-10 and PA 6-12 -

  Usually, two layers of rubber are bonded by a bonding agent to the opposite surfaces of the composite layer component of the element

flexible separation.

  In one embodiment of the flexible separating element, the integrated layer composite part comprises a central gas stop layer and two elastic layers which are formed on the respective opposite surfaces of the central gas stopping layer. another embodiment of the flexible separating element, the integrated layer composite part comprises an elastic central layer and two gas barrier layers which are formed on the surfaces

  respective opposites of the elastic core layer.

  The present flexible separator has been developed as a result of extensive research and investigation by the Applicant, who has investigated an excellent property of a copolymer of ethylene and vinyl alcohol (EVOH copolymer), as a gas barrier, namely a high degree of gas impermeability (resistance to gas infiltration) of the EVOH Plus copolymer, the central gas barrier layer interposed between the adjacent elastic layers, or EVOH copolymer gas barrier layers formed on opposite surfaces of the resilient core layer effectively function to prevent a gas contained in the gas chamber from

  the accumulator to slowly cross the section to

  embedded in the flexible separating element while at the same time the elastic core layer or the elastic layers on opposite surfaces of the central gas barrier layer act as a layer or

  buffers to protect the layer or layers

  stopping of the EVOH copolymer gas against

  suration or separation from adjacent layers

  The function of the elastic layer or layers

  It seems to depend on the elasticity or flexibility value which is intermediate between that of the EVOH gas gas barrier layer (s) and that of rubber layers which are usually formed on the opposite surfaces of the layered composite part. As a result, the durability of the flexible separating element is greatly increased, even under operating conditions of the accumulator in which the separating element is subjected to repeated bending deformation. provided for the accumulator is increased

correspondingly.

  In addition, since the polyamide resin used as the main component of the layer or layers

  Elastics have a melting point close to that of the copo-

  the two materials for the elastic and gas barrier layers can be coextruded so as to simultaneously form the elastic and quenching layers of the

  adjacent or alternating gases At this moment, the two substances

  res react chemically with each other, so that the elastic and gas-stopping layers are mutually bonded to their interfaces, without the use of a bonding agent or adhesive which would lower the elasticity of

the flexible separating element.

  The ethylene-vinyl alcohol copolymer (copo-

  EVOH) may preferably comprise from 20 to 65%

  by weight of ethylene, the balance being vinous alcohol

  In particular, the EVOH copolymer whose ethylene content (by weight) is 32% is preferred. When the ethylene content is less than 20% by weight (the vinyl alcohol content being greater than 80%), the stopping the gas layer or layers

  gas stoppage is greatly increased but the flexi-

  is excessively reduced, so that the gas barrier layer or layers is / are unable to

  undergo bending deformation or repositioning

  When the ethylene content exceeds 65%, the gas barrier layer (s) can not

  a property of stopping the gas to a sufficiently high degree

  Vee. The polyamide resin for the elastic layer (s) may preferably be selected from the group consisting of PA 6, PA 6-6, PA 6-10 and

  PA 6-12, which can be used alone or in combination

  The polyamide resin comprising PA 6 or

  PA 6-6 has a melting point close to that of a copoly-

  In this respect, the polyamide resin may be a

  mixture of PA 6 and other polyamides of the same type.

  In addition, the elastic layer can contain at most

  % and preferably 30 to 40% by weight of a poly-

  olefin such as EPM and EPDM In this case, the polyolefin material acts to prevent the EVOH copolymer of the gas barrier layer from absorbing an aqueous component. If the EVOH copolymer absorbs a component

  the gas barrier arresting property of the

stopping of the gas is degraded.

  The modulus of elasticity in flexion of the layer

  which contains at least 50% by weight of a

  Polyamide is intermediate between those of the rubber layers and the EVOH copolymer gas barrier layers. When the two elastic layers are formed on opposite surfaces of a central gas barrier layer, it is desirable that the the Mv wafer of the EVOH copolymer gas barrier layer

  and the flexural strength M of the elastic layers

  should be determined in such a way as to satisfy the

  the following Mv / M <3 Mv = 16 Ev Lv 3

M = 16 EL 3

  in which Ev: Modulus of elasticity in bending of the central gas stopping layer Mv: Thickness of the central gas stopping layer E: Flexural elasticity modulus of the elastic layers L: Thickness of the elastic layers

  The rubber layers that are usually

  formed on opposite surfaces of the integral or integrated composite

  flexible separation can be made of any material

  usually used for a membrane, a

  pocket or bladder flexible hydraulic accumulator.

  For example, the rubbery layers may be

  acrylonitrile butadiene rubber (NBR).

  The second object mentioned above can be achieved in accordance with another aspect of the present invention which provides a hydraulic accumulator comprising an envelope and a flexible separating member which is disposed in the envelope and which divides the interior of the housing. the two-part shell constituting a gas chamber and a liquid chamber, respectively, the flexible separating member including an integrated layer composite portion which includes at least one gas barrier layer and at least one elastic layer, each of said at least one gas barrier layer consisting of a copolymer of ethylene and vinyl alcohol, and each of said at least one elastic layer containing

  as a main component a polyamide resin.

  integrated layer composite fabric consists of two

  adjacent ones which consist of one of said at least one gas barrier layer and one of said at least one

less an elastic layer.

  The present hydraulic accumulator has a plus

  long service life, because of the best dura-

  flexibility of the flexible separating element as described

upper.

  The battery envelope is usually

  made of a suitable metallic material,

  such as iron, steel and metal alloys, for example

  an aluminum alloy The envelope can have any

  desired shape, for example a substantially spherical shape

  that a cylindrical or parallelepiped form

than.

  The envelope may include a larger part

  substantially hemispheric and a lower part

  hemispherical material which are welded end to end to each other at their open ends,

  in order to generate a substantially spherical configuration

  that this construction of the envelope in two parts

  allows easy assembly of the accumulator,

  relatively to a usual envelope in one piece.

  In addition, the present arrangement facilitates mounting or

  fixing of the flexible separating element to the

  especially because of the fact that the

  separation at the bottom of the envelope.

  pe before soldering the two parts of it one

to the other.

  The accumulator may comprise a ring of

  intended for fixing the peripheral part of the

  flexible separation to a region of the circumferential surface

  interior conferencing of the lower part of the

  Veloppe near the open end The lower part of the envelope may have a groove formed

  in the aforementioned region of the inner surface,

  say that the retaining ring has a part that is

  crimped or pressed against the surface defining the

  above, and a part which presses the

  of the separating element against the inner circumferential surface of the lower part of the envelope.

  In addition to the foregoing, the invention

  tion still contains other provisions which

  will be described in the following description.

  The invention will be better understood by means of

  supplementary description below, which refers to

  attached drawings in which: Figure 1 is an elevational view in partial section of a hydraulic accumulator according to an embodiment of the present invention; Figure 2 is a partial sectional view of a flexible separating element in the form of a flexible membrane fixed in the accumulator of Figure 1;

  FIG. 3 is a sectional view of a component part

  integrated layer site of the membrane of Figure 1, which consists of a central gas stop layer and two elastic layers;

  Figure 4 is a partial section of the

  flexible separation member according to another embodiment of the invention; Figure 5 is a partial sectional view of the flexible separating element according to another embodiment of the invention; FIGS. 6A and 6B are views illustrating the bending deformation of the membrane of FIG. 4, when an oil pressure applied to the membrane is

  modified during a test of the accumulator of the

  Figure 2; FIG. 7 is an elevation view and

  section of an embodiment of an accumulator con-

  form to the present invention; FIG. 8 is a fragmentary sectional view on a larger scale of the accumulator of FIG. 7, before a retaining ring for fixing the membrane is crimped against a lower hemisphere of the envelope of the accumulator; Figure 9 is a partial view on a larger scale after crimping the retaining ring of Figure 8 against the lower hemisphere;

  Figure 10 is a partial section of the

  in yet another embodiment of the present invention; Fig. 11 is an elevational view partially in section of an accumulator which utilizes the separating element of Fig. 10; and

  Figure 12 is a partial section of the

  separation according to yet another method of

embodiment of the invention.

  It should be understood, however, that these drawings and the corresponding descriptive parts are given solely by way of illustration of the subject of the invention, of which they do not in any way constitute

a limitation.

  We now describe the preferred modes of

implementation of the invention.

  Reference is made first to Figures 1 and 2 to describe a hydraulic accumulator built

  in a first embodiment of the invention.

  The hydraulic accumulator, which is generally indicated by the reference numeral 20 in FIG.

  body or envelope 21 made of metallic material.

  loppe 21 consists of two parts which are

  shifted, namely an upper hemisphere 21a and a lower hemisphere 21b which are placed end to end and welded to each other at their open ends,

  to define an inner closed capacity.

  cited is divided by a flexible membrane 22 into a chamber

  20a containing a gas and a chamber 20b containing

  an oil or a liquid, on the upper and the lower side

  bottom of the membrane 22 The lower hemisphere 21 b is

equipped with a valve 23.

  Before welding the two hemispheres 21 a and 21 b

  to each other by a beam-welding process

  electrons, the flexible membrane 22 is fixed at its periphery to the open end of the lower hemisphere 21b so that the peripheral portion of the membrane 22 is

  held and clamped between a retaining ring 24 and an over-

  inner circumferential face of the open end portion of the lower hemisphere 21 b After attaching the flexible membrane 22 to the lower hemisphere 21b,

  two hemispheres 21a, 21b per beam of elec-

  trons, to produce the substantially spherical envelope

21 of the accumulator.

  The flexible membrane 22 consists of a central gas stop layer 1, two elastic layers 2 formed on the opposite surfaces of the gas barrier layer 1, and two rubber layers 3 formed on

  the outer surfaces of the elastic layers

  2 The central gas barrier layer 1 is manufactured

  a copolymer of ethylene and vinyl alcohol (hereinafter referred to as "EVOH copolymer", where appropriate), while the elastic layers 2 are made of a polyamide resin. gas 1

  and the two elastic layers 2 cooperate to

  staging a composite layer with solid or

  In order to produce this integrated layer composite part 4, the selected ethylene-vinyl alcohol copolymer and polyamide resin are coextruded to simultaneously form the central gas barrier layer 1

  of EVOH copolymer and the two elastic layers

  sine polyamide 2, so that the two elastic layers

  2 are related to the opposite surfaces of the diaper

  stopping the gas because of a chemical reaction of the

  EVOH polymer and polyamide resin at the contact interfaces Thus, an adhesive agent is not necessary

  to form the layered composite part 4.

  Then a binding substance is applied

  known in the art to the opposite surfaces of the

  The two layers of rubber 3 are formed by pressing a suitable rubbery material. The rubber layers 3 are bonded to the opposite surfaces of the composite part.

  with integral layers 4 during the subsequent vulcanization

  the rubbery material is thus obtained.

  flexible membrane 22 shown in Figure 2.

  In order to better illustrate the principle of

  In this invention, examples of the flexible membrane according to the invention, as well as

comparative examples.

EXAMPLE 1

  The composite part is first prepared

  4, as shown in Figure 3.

  ethylene-vinyl alcohol copolymer (EVOH) F-1 O 1 furnace

  nor by KURARAY CO Ltd (Japan), which contains 32% by weight of ethylene, is used for the central layer for stopping the gas 1, while a polyamide resin of NYLON SUPERDUR ST 811 HS type supplied by Du Pont is used for the elastic layers 2 The EVOH copolymer and the polyamide resin are coextruded to form the three-layer composite part 4, the gas barrier layer 1 having a thickness of 50 Wn and each of the two elastic layers

  2 having a thickness of 80 Wm, as indicated in

  Then, the three layer composite part 4 thus prepared is coated on its opposite surfaces with a known adhesive agent and the layers of

  NBR rubber 3 by pressing and vulcanizing

  that rubber layer 3 has a thickness of 1790 gm,

  as also shown in Table 1.

  In this case, the five-ply flexible membrane 22 is obtained.

  2 preferably, the thickness τ of each elastic layer 2 and the thickness (b) of the central gas barrier layer 1 are determined from FIG.

  to satisfy the formula o / (> 1.

EXAMPLE 2

  A seven-layer composite part is prepared

* integral 6 as shown in Figure 4, by coextru-

  the same materials that were used in the e-

  xample 1 Composite part 6 consists of the composite part

  three-layer site 4 of Figure 3, two outer layers

  gas stoppages formed on the elastic layers

  2 (inner elastic layers), and two layers

  outer elastic members 2 'formed on the outer layers

  As shown in Table 1, all the gas barrier layers 1, 1 'have the same thickness of 50 gm, and the inner elastic layers 2 have the same thickness of 50 pm. while the outer elastic layers 2 'have the same thickness of 80 gm. Preferably, the thickness i of each outer elastic layer 2', the thickness> of each gas barrier layer 1,1 'and the thickness y of each layer

  inner elastic band 2 are determined so as to

  satisfy the formula d A / (>, 1, and the formula 0,1

<3.5.

EXAMPLE 3

  An eleven-layer composite part is prepared

  8 as shown in FIG.

  trusion of the same materials which were used in Examples 1 and 2 Composite part 9 comprises the

  Three-layer composite 4 of Figure 3, two sections

  intermediate gas stoppers 1 'formed on the composite part 4, two intermediate elastic layers 2 formed on the intermediate gas stop layers 1', two outer layers of gas stop 1 i formed on the intermediate elastic layers 2, two outer layers of gas stop 1 'formed on the intermediate elastic layers 2, and two elastic layers

  2 'formed on the intermediate layers ex-

  Afterwards, the

  of NBR 3 rubber on the elastic layers ex-

  2 ', so that a flexible membrane is obtained

  at thirteen layers 28 as shown in FIG.

  The layers 1,1 ', 2 and 2' have the values of

  the thickness indicated in Table 1.

  thickness 4 of the outer elastic layers 2 ', the

  thickness (of each gas barrier layer 1,1 'and the

  thickness Y of each inner elastic layer or

  are determined in such a way as to satisfy the

  inequalities od / (>> 1, and 0.1 <P / (A 3.5, as in the e-

xample 2.

TABLE 1

  EXAMPLES Comparative Examples i 2 3 i 2 LAYER Thickness t 1 50 50 50 100 50

CENTRAL * 2

  IMPERMEABLE Flexural strength Mv 0.04 0.04 0.04 0.32 0.04

GAS (1)

  Modulus of elasticity * 3 20000 20000 20000 20000 20000 OTHER Thickness * 1 50 50

LAYERS

  WATERPROOF Resistance to bending Mv * 2 0.04 0, 04

GAS (1 ')

  Modulus of elasticity * 3 20000 20000 LAYERS Thickness'1 80 80 80

BANDS

  EXTERIOR Flexural strength M 2 0.03 0.03 0.03

(2 ')

  Modulus of elasticity * 3 4000 4000 4000 F "Lrn K, (n" Il 01 I

TABLE 1 (CONTINUED)

  EXAMPLES Comparative Examples 1 2 3 i 2 OTHER Thickness 50 50 30

LAYERS

  ELASTIC Bending resistance 2 0.008 0.008 0.002 (2) Modulus of elasticity * 3 4000 4000 4000 * 1 LAYERS in Thickness 1 1790 1590 1390 1470 1900 1950

RUBBER IN

  RUBBER Modulus of elasticity * 3 100 100 100 100 100 (3) Mv / M 1.33 1.33 1.33 1.33 6 / t 1.6 1.6 1.6 1.6 t / i P 1 0.6 * 1: pm * 2 2: da N cm * 3: da N / cm 2 1 H- M- 61 x oe On "It

COMPARATIVE EXAMPLES 1 AND 2

  Two comparative samples are prepared. Each sample consists of a central layer for stopping the gas, formed by

  extrusion of the same EVOH copolymer which was used in Examples 1 to 3, and in two layers

  of NBR rubber which are formed by pressing and bonding

  sound by means of an adhesive agent to the opposite surfaces of

  the gas barrier layer The thickness of the gas layer

  gas and that of the rubber layers of the two

  Samples are shown in Table 1.

  The flexible membranes 22, 26 and 28 of Examples 1, 2 and 3 and the samples of Comparative Examples 1 and 2 are evaluated with regard to flexibility.

  crack resistance and gas permeability.

  Flexibility is determined by manual bending of the samples in accordance with the invention and samples

  To test the samples for

  In view of the resistance to cracking of the EVOH copolymer gas barrier layers, the samples are placed in a device as shown in FIGS. 6A and 6B. During the endurance test, one of the chambers on one side of the The sample membrane is filled with nitrogen gas while the pressure is cyclically varied.

  applied to the other chamber, in order to provoke

  Repeated bending of the membrane as shown in Figures 6A and 6B The amount of nitrogen gas passing through the membrane samples

  measured during an initial period of the endu-

  After completion of the test The results of the flexibility and endurance tests are indicated in

Table 2 below.

  In the endurance test using the device

  shown in FIGS. 6A and 6B, the hydraulic pressure

  applied to each membrane sample is modified

  2.5 times the pressure of the nitrogen gas and 3 to 18 times the pressure of the nitrogen gas, alternatively, to cause bending deformation or displacement of the samples This cycle of pressure variation is repeated a million times at a frequency of 0.3 Hz, 5 to 800 C.

TABLE 2

EXAMPLES Comparative Examples

1 2 3 1 2

  Flexibility good good good good good Number of cracks in gas barrier layers; zero zero zero | Gas permeability N 2 I initial period zero none zero none zero after endurance test zero none none yes yes Table 2 shows that the flexible membranes 22, 26 and 28 according to the present invention give

  results far better than those of the comparative examples

rations.

  Referring now to FIGS. 7 to 9 to describe an accumulator 100 that uses the membrane

  Figure 2 The accumulator 100, which is of

  truction similar to that of the accumulator 20 of the

  1, comprises a metal body or envelope

  spherically constituted of an upper hemisphere and a lower hemisphere 110,112, as shown on

  FIG. 7 The accumulator 100 is assembled from the

next.

  Initially, the flexible membrane 22, the peripheral portion 22a is relatively thicker, as shown in Figure 8, is positioned in

  the lower hemisphere 112 so that the peri-

  22a is fixed by a retaining ring 103 to the inner circumferential surface of the hemisphere 112, near the open end to which the hemisphere 112 will then be welded to the upper hemisphere 110 For this, the lower hemisphere 112 has a throat

  circumference 113 formed in the interior surface

  re, near the open end face, and an over-

  Circumferential groove 114 formed below the throat

  circumferential 113 as shown in FIG.

  The retaining ring 103 has a shoulder structure having a large diameter portion 103a, a portion of

  small diameter 103 b and a shoulder portion 103 c.

  To fix the membrane 22, we first position the mem-

  brane 22 and the retaining ring 103 so that the

  22a peripheral portion of the membrane 22 is in con-

  tact with a region of the circumferential surface

  lower hemisphere 112 which is at a distance from the circumferential groove 113, and

  so that the large-diameter part 103 has of the

  103 is in contact with a region of the

  inner face in which the groove 113 is formed, while the small diameter and shoulder portions 103b and 103c are in contact with the thicker peripheral portion 22a of the diaphragm 22 In this situation, the retaining ring 103 is pushed back or crimped, in its part situated in front of the groove 113, so that this part is pressed against the surface of the groove 113,

  as shown in FIG. 9 Thus, the peripheral portion

  22 a of the membrane 22 is clamped by and between the outer surface of the small diameter parts and

  shoulder 103 b, 103 c of the ring 103 and the inner surface

  The presence of the circumferential groove 113 and the crimping of the ring 103 provide a solid attachment of the diaphragm 22 and improve the fluid tightness between the diaphragm 22 and the lower hemisphere 112. prevents the passage and leakage of gas and hydraulic fluid through

  the interface between the membrane 22 and the lower hemisphere

  The excess thickness 114 provided below the groove 113 ensures precise positioning of the ring of

  103 and the membrane 22 with respect to the hemisphere

lower sphere 112.

  After fixation of the flexible membrane 22 to the lower hemisphere 112, the upper and lower hemispheres 110 and 112 are placed in abutment against each other.

  the other at their open end faces, as

  7, so as to define a substantially spherical envelope of the accumulator 100. At this moment, it is possible to check the quality of the fixation of the membrane.

  22 at the bottom hemisphere 112, before closing the

  lower mispter 112 by the upper hemisphere 110.

  The two hemispheres 110,112 are welded to each other at their end faces by an electron beam welding technique as shown in FIG. 7 since the welding region 101 is at a substantial distance from the peripheral portion 22a of the diaphragm 22, the peripheral portion 22a is protected against a harmful influence of the heat generated during the welding. The accumulator 100 is thus obtained which comprises a gas chamber 101a. , defined by the membrane

  22 and the upper hemisphere 110, and a chamber of

  quide in the form of an oil chamber 101 b defined

  by the membrane 22 and the lower hemisphere 112

  accumulator 100 is provided with a valve 121 associated with the

  this bottom of the membrane 22, an oil pipe 151 having an oil passage 150 in communication with

  the oil chamber 101b, and a gas manifold 153 as

  in the gas chamber 101 a The position of the

  brane 22 when elastically moved is

  shown in phantom in Figure 7.

  Referring to Figs. 10 and 11, a modified embodiment of the present invention in which an accumulator 30 utilizes a flexible membrane is described.

  32 of which the composite part with solidarity layers 14 differs

  In this embodiment, the membrane 32 cooperates with the envelope 21 to define a gas chamber 30a and a chamber of liquid or

of oil 30 b.

  The composite layered part 14, described more particularly with reference to FIG. 11, consists of five layers, namely a central elastic layer 11, the main component of which is a polyamide resin, and two layers 12 for stopping the gas in one. EVOH copolymer formed on the opposite surfaces of

  the central elastic layer 11, and two elastic layers

  outer ticks 11 'formed on the barrier layers

  respective gas 12 The composite five-part

  Solids 14 is formed by coextrusion using

  the chosen polyamide resin and the EVOH copolymer so as to simultaneously form the elastic layer

  11, and the gas barrier layer 12 and the

  outer elastic members 11 'on each side of the central elastic layer 11 No adhesive agent is used to form the five-layer composite portion

  integral 14 of the membrane 32 Two layers of rubber

  rubber 13 are bonded to the outer surfaces of the outer elastic layers 1, then the prepared membrane 32 is fixed in the casing 21 of the accumulator 30,

  as shown in Figure 11.

  EXAMPLES 4 and 5 The five-layer composite part 14 is first prepared by coextrusion of the same materials, for the gas barrier layers 12 and the elastic layers 11, 11 ', which have been used in Examples 1 to 3 , so that the EVOH copolymer gas stop layers 12 are formed on opposite surfaces of the diaper

  central elastic 11 of polyamide resin and that the

  11 'outer resilient polyamide resin

  formed on the respective gas barrier layers 12.

  The layers 11, 11 'and 12 of Examples 4 and 5 have the

  thickness values given in Table 3 below.

  after. Then the five-layer composite part

  14 thus prepared is coated on its opposite surfaces

  with a known adhesive agent, and the layers of

  NBR 13 are formed by pressing and vulcanizing

  The rubber layers 13 have the thickness values shown in Table 3. In this way,

  the flexible membrane with seven layers 32 is obtained

shown in Figure 10.

COMPARATIVE EXAMPLES 3 TO 7

  Five comparative samples are prepared

  sample of Comparative Examples 3 to 5 is

  layer of five layers, namely a central layer of ar-

  firing of the EVOH copolymer gas formed by extrusion,

  two elastic layers made of polyamide resin

  by extrusion on the central barrier layer of the

  two layers of NBR rubber formed by pres-

  wise and bonded by an adhesive agent to the surfaces opposite

  of the central blocking layer of the copolymer gas

  EVOH The samples of Examples 6 and 7 are

  three layers, namely a central layer of ar-

  of the EVOH copolymer gas and two layers of rubber

  The copolymer EVOH, the polyamide resin and the NBR rubber used are the same as those used in Examples 4 and 5. The thickness values of the constituent layers of the samples.

  comparisons are shown in Table 3.

  The flexible membranes 32 of the

  Examples 4 and 5 and the samples of the comparative examples

  3 to 7, with regard to flexibility, crack resistance and gas permeability, in the same way as described above with regard to Examples 1 to 3 and Comparative Examples 1 and 2. flexibility and endurance tests are

  also shown in Table 3.

  Table 3 shows that the membranes 32 of Examples 4 and 5 do not exhibit cracking of the

gas barrier layers 12.

  Referring to Figure 12 which shows a flexible membrane 34 which is a modification of the membrane 32 of Figure 10 The membrane 34 comprises a composite nine-layer integral part 16, which is composed of the composite five-layer part 14 of

  the membrane 32 of FIG. 10, of two outer layers

  stopping the gas 12 in EVOH copolymer formed

  on the elastic intermediate layers of resin

  lyamide 11 'of the five-layer composite part 14,

  and two outer elastic layers of resin

  11 The two layers of NBR rubber 13 are formed on the outer elastic layers 11 'Thus, the membrane 34 comprises two inner layers of gas stop 12 , two outer layers of gas stop

  12, a central elastic layer 11, two elastic layers

  intermediate ticks 11 'and two elastic layers

outside 11 '.

TABLE 3

EXAMPLE Comparative Examples

4 5 3 4 5 6 7

  LAYER Thickness elastic layer 100 150 CENTRAL Thickness layer EVOH 200 100 100 100 70 Flexural strength 2 0, 064 0.216 2.56 0.32 0.32 0.32 0.11 LAYERS Thickness 1 100 100 _

STOP OF * 2

  GAS EVOH Flexural strength 0.32 0.32 ELASTIC LAYER Thickness 1 150 150 300 120 240

(LAYER NO

  CENTRAL) Flexural Strength 0.216 0.216 1, 728 0.11 0.88 RUBBER LAYER Thickness 1 1900 1850 1700 2160 1920 2400 2400 FLEXIBILITY Good Good Poor Good Good Good PERMEABILITY IN Initial Period None None None Slightly Detected GAS N 2 After Test None None None None None Yes Yes NUMBER OF CRACKS DS GAS STOP LAYERS None None None None None 4 5 * 1: Pm * 2:: dan "JI) 0 n

  In the illustrated examples, each of the members

  branes 22, 26, 28, 32 and 34 comprises two layers of

  rubber 3.13 on opposite sides of the composite layer composite part 4,6,8,14,16 However, the rubber layers may be removed.

  Although the battery envelope

  20,30,100 of Figures 1,7 and It is sensible-

  spherical, the envelope may have any other

  figuration, for example cylindrical or parallelepiped-

  In addition, although the envelope of the illustrated accumulator consists of two parts in the form of the upper and lower hemispheres 21a, 21b, 110, 112, the envelope may be a one-piece structure having an opening through which one can install

  the membrane or bladder inside the envelope.

  As is apparent from the above, the invention is not limited to those of its modes

  implementation and application that have just been

  written more explicitly; she embraces it at

  all variants which may come to the mind of the technician without departing from the

  neither of the scope of the present invention.

Claims (18)

  1. Flexible separating element for accumula-   hydraulic unit, which divides an inner space of an envelope (21, 110, 112) of the accumulator into two parts which constitute a gas chamber (20 a, 101 a) and a chamber of liquid (20 b, 101 b). ), respectively, characterized in that: said flexible separating member (22,26,28,32,34) comprises a composite layered composite (4,6,8,14,16) which consists of at least a diaper   stopping gas (1,1 ', 12) and at least one elastic layer   (2 ', 11, 11'), said solid-layer composite part comprising two adjacent layers which are one of said at least one gas barrier layer and one of said at least one elastic layer, each of said at least one gas barrier layer consisting of   a copolymer of ethylene and vinyl alcohol, and each   one of said at least one elastic layer containing as main component a polyamide resin selected from a group consisting of PA 6, PA 6-6, PA 6-10 and PA 6-12.   2. flexible separating element according to claim 1, characterized in that said   least one gas barrier layer comprises a central layer   gas stop (1), and said at least one elastic layer comprises two elastic layers (2), said   central gas stopping layer (1) being interposed between   to be said two elastic layers (2) and in contact with these.   Flexible separating element according to Claim 1, characterized in that the at least one gas barrier layer comprises a central gas-stopping layer (1), and two outer layers for stopping the gas (1 '). and said at least one elastic layer comprises two inner elastic layers (2) and two outer elastic layers (2 '), said central gas stopping layer (1) being interposed between and   in contact with said two elastic layers   (2), and said two outer gas barrier layers (1 ') being formed on said two inner elastic layers (2), respectively, while   two outer elastic layers (2 ') are   on said two outer layers of stop of the gas (1 '), respectively.   Flexible separating element according to Claim 1, characterized in that the said at least one gas barrier layer comprises a central gas-stop layer (1), two intermediate gas-stop layers (1 ') and two outer layers of gas stop (1 '), and said at least one elastic layer comprises two inner elastic layers (2), two intermediate elastic layers (2) and two outer elastic layers (2'), said central layer of stopping the gas (1) being interposed between and in contact with said two inner elastic layers (2), said two intermediate gas stopping layers (1 ') being formed on said two inner elastic layers (2),   respectively, said two elastic layers   mediates (2) being formed on said two layers   gas stopping means (1 '), respectively, said two outer layers of stopping gas (1') being   formed on said two intermediate elastic layers   res (2), respectively, and said two elastic layers   outer ones (2 ') being formed on said two   outer layers of gas stop (1 '), respectively.   5. flexible separating element according to claim 1, characterized in that said at least   an elastic layer comprises a central elastic layer   trale (11) and two outer elastic layers (11 '), and said at least one gas barrier layer comprises two gas barrier layers (12), said central elastic layer (11) being interposed between and in contact with said two gas barrier layers (12), respectively, and said two outer elastic layers (11 ') being formed on said two elastic layers (12), respectively. Flexible separating element according to claim 1, characterized in that said at least one   an elastic layer comprises a central elastic layer   trale (11), two intermediate elastic layers (11 ') and two outer elastic layers (11'), and said   at least one gas barrier layer comprises two   internal gas stop (12) and two layers   external gas stop (12), said elastic layer   with the central unit (11) interposed between and in contact with said two inner gas stop layers (12), said two intermediate elastic layers   (11 ') being formed on said two inner layers   stopping the gas (12), respectively, said two outer gas stopping layers (12) being formed on said two intermediate elastic layers (11 '), and said outer elastic layers (11')   being formed on said two outermost layers of turn off gas (12).   Flexible separating element according to claim 2, characterized in that each of said   two elastic layers (2,2 ') and said central layer   gas stop (1) have thicknesses a and (,   respectively, which satisfy i (/ p '>, 1.   Flexible separating element according to Claim 3 or 4, characterized in that each of the   said outer elastic layers (2 ') and said cou-   central gas stop (1) have thicknesses c "and   (b, respectively, which satisfy e / (> 1.   Flexible separating element according to claim 8, characterized in that each of said   at least one elastic layer (2,2 ') with the exception of said outer elastic layers (2') has a thickness g which satisfies 0,1 <y / (b <3,5.   10 Flexible separating element next   any one of claims 1 to 9, characterized   in that it further comprises two layers of rubber (3, 13) bonded by an adhesive agent to the opposite surfaces of said composite layered composite part (4,6,8, 14,16).   11. Flexible separating element next   any one of claims 1 to 10, characterized   in that said copolymer of ethylene and vinyl alcohol   that comprises from 20 to 65% by weight of ethylene, the rest being vinyl alcohol.   12. Flexible separating element next   any one of claims 1 to 11, characterized   in that each of said at least one elastic layer   that (2, 2 ', 11, 11') consists essentially of   less than 50% by weight of said polyamide resin and at most 50% by weight of a polyolefin material.   13. Hydraulic accumulator comprising a   envelope (21,110,112) and a separating element   pl (22,26,28,32,34) which is disposed in said enve-   loppe and which divides an interior space of said enve-   two-piece loppe defining a gas chamber   (20 a, 101 a) and a liquid chamber (20 b, 101 b),   respectively, characterized in that said flexible separating element (22,26,28,   32,34) comprises a solid layer composite part   res (4,6,8,14,16) which consists of at least one   gas stopper (1,1 ', 12) and at least one elastic layer (2,2', 11,11 '), said integral layer composite part comprising two adjacent layers   which consist of one of the at least one layer of ar-   of the gas and one of the at least one elastic layer   that each said at least one layer of gas stop being   consisting of a copolymer of ethylene and vinyl alcohol   that, and each said at least one elastic layer contains   as the main component a polyamide resin selected from a group consisting of PA 6, PA 6-6, PA 6-10 and PA 6-12.   14. Hydraulic accumulator following the   claim 13, characterized in that said-enve-   loppe (21,110,112) comprises a sensitive upper part   hemispherical (21a, 110) and a substantially hemispherical lower portion (21b, 112) which are welded to each other end to end at their open ends, said hydraulic accumulator further comprising a   retaining ring (24, 103) for securing a peripheral portion   (22a) of said flexible separating element (22,26,28,   32,34) to a region of a circumferential surface   lower part of said lower part (21b, 112) near said open end.   15 Hydraulic accumulator following the   claim 14, characterized in that said part   substantially hemispherical bottom (112) has a groove (113) in said region of said surface   inner circumferential circumference, and said retaining ring   bar (103) has a portion (103a) crimped against a surface defining said groove, and a portion (103b, 103c) which presses said peripheral portion (22a) of said flexible divider (22) against said circumferential surface interior of said lower portion (112).   16. Hydraulic accumulator according to one   any of claims 13 to 15, characterized in   said flexible separating element (22,26,28,32,34) consists of a flexible membrane which cooperates with the   said envelope (21, 110, 112) to define said chambers   gas and liquid (20 a, 20 b, 101 a, 101 b) on the opposite sides of said membrane.   17. Hydraulic accumulator according to one   any of claims 13 to 16, characterized in that   said at least one gas barrier layer comprises a central gas stopping layer (1), and said   least one elastic layer comprises two elastic layers   (2), said central gas stopping layer (1) being interposed between and in contact with said two elastic layers (2).   18. Hydraulic accumulator according to one   any of claims 13 to 16, characterized in that   said at least one elastic layer comprises a central elastic layer (11), and said at least one gas barrier layer comprises two gas barrier layers, said central elastic layer being interposed between and in contact with said two layers stop some gas.