JP2700590B2 - Accumulator and bladder for accumulator used therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an accumulator used for a hydraulic device of an automobile, an industrial vehicle and the like, and a bladder for the accumulator used for the accumulator.

[0002]

2. Description of the Related Art An accumulator has a pressure accumulating function, and generally includes a metal shell and an accumulator bladder held in the shell and dividing the shell into two chambers. Such an accumulator bladder is manufactured by forming a rubber material into a thin film having a predetermined shape. The bladder made of such a rubber thin film is disposed inside the shell of the accumulator, and divides the internal space of the shell into two chambers as described above. A gas such as nitrogen gas is sealed in one of the chambers (gas chamber) to serve as a pressure transmitting fluid, and the other chamber (oil chamber)
The liquid is supplied according to the pressure of the liquid supply source. In this case, the gas sealed in one of the chambers gradually passes through the bladder made of a rubber thin film as the service period elapses, so that the gas sealing pressure is reduced and the function of the gas cannot be achieved.

[0003] Attempts have been made to improve the gas permeation resistance by adding additives to the rubber material constituting the bladder. However, in this case, although the gas permeation resistance is improved, the flexibility of the accumulator bladder itself is poor, and there is a new problem that a crack or the like is liable to be formed in long-term use.

[0004]

In order to solve the above-mentioned new problems, a rubber-resin composite film in which an ethylene-vinyl alcohol resin film is provided between rubber thin films and an adhesive layer is interposed has been proposed. (JP-A-2-165948). When an accumulator bladder is constructed using such a composite membrane, the ethylene-vinyl alcohol resin membrane is excellent in gas permeability resistance, so that the gas sealing pressure must be maintained for a long time. Becomes possible. However, when the use period of the rubber-resin composite film is extended (the number of times of bending is increased), the ethylene-vinyl alcohol copolymer (hereinafter abbreviated as “EVOH”) film is cracked or peeled. Therefore, there is a problem that the life of an accumulator using such an accumulator bladder is shortened.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an accumulator having high durability and a long life and a bladder for the accumulator used therefor.

[0006]

In order to achieve the above object, an accumulator according to the present invention comprises a shell, a bladder for an accumulator in the form of an elastic thin film which divides an inner space of the shell into two chambers, and The accumulator bladder includes a composite layer comprising the following (A) and (B) as a film forming element. (A) An elastic center layer mainly composed of a polyamide resin. (B) A gas shielding layer composed of an ethylene-vinyl alcohol copolymer directly laminated and integrated on both upper and lower surfaces of the above (A).

The bladder for accumulators according to the present invention is characterized in that a composite layer comprising an elastic center layer mainly composed of a polyamide resin and a gas shielding layer made of an EVOH resin directly integrated on the upper and lower surfaces thereof is used as a film forming element. It is configured to be included.

[0008]

The present inventors have paid attention to the excellent gas permeation resistance (gas barrier properties) of the above EVOH, and have made a series of studies to solve the above problems. As a result, when the EVOH films are formed directly on the upper and lower surfaces of the elastic center layer mainly composed of polyamide resin, the elastic center layer mainly composed of polyamide resin has intermediate elasticity between the rubber thin film and the EVOH film. It has been found that the film (gas shielding layer) made of EVOH does not crack or peel even if the use period becomes long (the number of times of repeated bending is large) and the durability of the accumulator bladder is improved. In this case, the polyamide resin, which is the main component of the elastic center layer, can be integrated by co-extrusion because its melting point is close to that of EVOH.
Since H reacts and adheres at the joint interface between the two, an adhesive for bonding the two is not required, and a decrease in the elasticity of the composite layer due to the use of the adhesive does not occur.

Next, the present invention will be described in detail.

[0010] The accumulator of the present invention comprises a shell and a bladder for an accumulator which divides the inside of the shell into two chambers.

The shell is not particularly limited as long as it is made of metal, but is usually made of iron or an aluminum alloy. The shape of the shell is not particularly limited.
Various shapes such as a box shape are used. It is preferable that two divided shells having a substantially hemispherical shell shape are abutted and finished into a substantially spherical shell shape. By doing so, the peripheral edge of the accumulator bladder is positioned on the inner peripheral edge of the opening of one of the hemispherical shell-shaped split shells, a ring-shaped holding material is attached thereto, and the opening inner peripheral edge of the split shell and Then, the peripheral portion of the accumulator bladder is sandwiched and fixed with the outer periphery of the ring-shaped holding member, and then the opening of one of the divided shells is abutted against the opening of the other divided shell to weld and finish the accumulator. Therefore, the manufacture of the shell becomes easier as compared with the conventional method of forming a shell by forming one disk into a spherical shell shape. Also, before welding both split shells, it is possible to check the mounting state of the accumulator bladder attached to the opening of one hemispherical shell-shaped split shell, and to ensure that the peripheral edge of the accumulator bladder is not properly installed. You can avoid it. In addition, since the outer peripheral portion of the accumulator bladder is sandwiched and fixed between the outer periphery of the ring-shaped holding portion and the inner peripheral edge of the opening of the split shell, the peripheral edge portion of the accumulator bladder can be firmly attached, and gas, oil leakage, and the like occur. Can also be prevented.

The accumulator bladder is constituted by using a polyamide resin as a main component of an elastic center layer, an EVOH forming gas shielding layers on both upper and lower surfaces thereof, and a rubber or the like for forming a rubber layer in some cases. I have.

The EVOH is not particularly limited, but it is preferable to use an EVOH having an ethylene content of 20 to 65% by weight (hereinafter abbreviated as "%") and the remainder consisting of vinyl alcohol. Preferably, the ethylene content is 32%. That is, if the ethylene content is 2
If it is less than 0% (the content of vinyl alcohol exceeds 80%), the gas barrier properties are improved, but the EVOH itself becomes hard and the flexibility is reduced, and it tends to be unsuitable for applications having a bending motion. Conversely, the ethylene content is 65%
This is because when the value exceeds the above, the reverse phenomenon tends to occur.

The polyamide resin includes nylon 6, nylon 66, nylon 6-10, nylon 6-1.
2 and the like are used alone or in combination. If such a polyamide resin contains the above nylon 6 or nylon 66 in the base, the melting point of EVOH will be approximated. Therefore, it is necessary to use various mixtures of nylon 6 and other nylon resins. Is possible. In particular, it is preferable to use a blend of the polyamide resin and the polyolefin resin. In this case, since the polyolefin resin has poor water absorption, water absorption of EVOH is prevented. That is, when EVOH absorbs water, its gas barrier resistance decreases, and the polyolefin resin prevents this.

The rubber forming the rubber layer is not particularly limited, and a conventionally known rubber such as acrylonitrile-butadiene rubber (NBR) is used.

The elastic center layer mainly composed of the above-mentioned polyamide resin has a bending elastic modulus intermediate between that of the rubber forming the rubber layer and that of the EVOH forming the gas shielding layer. The following equation (1) expresses the equation in descending order of the rate.

EVOH> Polyamide resin> Rubber (1)

In the present invention, for example, a bladder for an accumulator is manufactured as follows, and an accumulator is manufactured using the bladder. That is, an EVOH and a polyamide resin are co-extruded using an extruder, and a gas shielding layer made of an EVOH and an elastic layer made of a polyamide resin are respectively formed on the upper and lower surfaces of the elastic center layer mainly composed of the polyamide resin. Are integrally formed in this order to form a composite layer. In this case, the bonding interface between the gas shielding layer made of EVOH and the elastic center layer (elastic layer) made of polyamide resin is bonded by the reaction between them, as described above, so that an adhesive is not required. Next, a conventionally known adhesive is applied to both upper and lower surfaces of the elastic layer in the composite layer. Next, a rubber layer formed in a layered form is superposed on the rubber layer and then vulcanized and adhered. Thus, the accumulator bladder 22 having a layer structure as shown in FIG. 1 is obtained. In the figure, 1 is an elastic center layer made of a polyamide resin, 1 'is an elastic layer made of a polyamide resin, 2 is a gas shielding layer made of EVOH, and 3 is a rubber layer. FIG. 2 shows an accumulator equipped with the accumulator bladder. In the figure, 2
0 is an accumulator, 21 is a shell, 22 is an accumulator bladder, and 23 is a poppet. More specifically, the accumulator bladder obtained as described above is, as shown in FIG. 2, a lower divided shell of two substantially hemispherical shells 20a and 20b constituting a shell 21. The peripheral edge is positioned on the inner peripheral edge of the opening of the opening 20b, and the peripheral edge is positioned between the outer peripheral portion of the ring-shaped holding member 21a and the inner peripheral portion of the opening of the lower split shell 20b. To the split shell 20b. Then, the opening of the upper split shell 20a is brought into contact with the opening of the lower split shell 20b, and the accumulator 20 is formed by electron beam welding or the like.

Next, examples and comparative examples will be described together.

First, a bladder for an accumulator was manufactured as in Examples 1 and 2.

[0021]

Examples 1 and 2 and Comparative Examples 1 and 2 A polyamide resin (manufactured by DuPont, Super Tough Nylon ST811HS) was prepared as a material for forming the elastic center layer and a material for forming the elastic layer. A content of 32%, F-101 manufactured by Kuraray Co., Ltd.) was prepared.
Further, NBR was prepared as a material for forming a rubber layer. Next, the polyamide resin and EVOH were co-extruded from an extruder to a thickness shown in Table 1 below, and gas shielding layers were positioned on the upper and lower surfaces of the elastic center layer, and the elastic layers were stacked on the upper and lower surfaces. A composite layer having a five-layer structure was prepared.

Next, a conventionally known adhesive was applied to each of the upper and lower surfaces of the composite layer, and NBR was press-molded into a layer having a thickness shown in Table 1 below, and then vulcanized and bonded. Thus, a bladder 22 for an elastic thin film accumulator having a seven-layer structure was obtained as shown in FIG. In FIG.
1 is an elastic center layer, 2 is a gas shielding layer, 1 'is an elastic layer, and 3 is a rubber layer.

In Comparative Examples 1 and 2, the central layer made of EVOH was extruded to a thickness shown in Table 1 below, and a conventionally known adhesive was applied to both upper and lower surfaces thereof, and then NBR was applied.
Was press-molded into a layer having a thickness shown in Table 1 below, and then vulcanized and bonded to produce a three-layered accumulator bladder 22. Comparative Examples 1 and 2 are EVs
It has a three-layer structure in which rubber layers are stacked on the upper and lower surfaces of a central layer made of OH.

[0024]

[Table 1]

Next, the flexibility of the accumulator bladder 22 obtained as described above is examined by bending it with a finger, and it is set on a bending tester to alternately change the state shown in FIGS. 3 (A) and 3 (B). The occurrence of cracks in the EVOH layer of the accumulator bladder 22 was measured. Further, the nitrogen gas permeability of the accumulator bladder 22 at the initial stage and after the durability test was measured. In this case, a sample having a small nitrogen gas permeation amount was evaluated as ○ and a sample having a large nitrogen gas permeation amount was evaluated as x. Table 1 shows the test results. Table 1 shows that in the example, no crack was generated in the EVOH layer.

Measurement conditions in the above bending test are as follows.
Changed in one million cycles. The filling gas is N
_{Using two} gases, the pressure of the oil was changed in the range of 2.5 to 3 times the gas filling pressure, and the states of FIGS. 3A and 3B were generated. The durability test was performed as follows.・ Enclosed gas pressure: P ₀・ Operating pressure: P ₁ Endurance test condition: 0.3H when P ₁ / P ₀ is between 2.5 and 3.
_Operate at 80 ° C x 1 million times in _Z.

FIG. 4 shows another embodiment (Embodiment 3) of the accumulator bladder used in the present invention. That is, in this embodiment, the composite layer has a nine-layer structure, and rubber layers are provided on the upper and lower surfaces of the composite layer with an adhesive layer interposed therebetween. As described above, when the multilayer structure is used, the gas permeability resistance (gas barrier property) is improved even when the entire thickness is the same, and the bending resistance is also improved.

Next, using the accumulator bladders of Examples 1 to 3, an accumulator was manufactured as follows.

[0029]

Fourth Embodiment As shown in FIG. 5, an upper shell 110 and a lower shell 112 are prepared as two substantially hemispherical shells, and the accumulator bladder obtained in the above embodiment is prepared. For No. 22, the peripheral portion was formed to be a thick portion. Then, as shown, the accumulator bladder 22 is disposed in the lower divided shell 112, and the peripheral edge thereof is fixed to the inner peripheral surface of the opening of the lower divided shell 112 by the ring-shaped holding member 103. In this case, as shown in FIG.
A groove 113 is formed in the circumferential direction, and a step 114 is formed below the groove 113. The ring-shaped holding member 103 has a stepped structure in which a ring-shaped upper side has a large diameter and a lower side has a small diameter, and the upper side has an opening inner peripheral surface of the lower divided shell 112 as shown in FIG. , The step portion is positioned on the end face of the thick portion of the accumulator bladder 22, and the lower portion is positioned on the thick portion of the accumulator bladder 22. Then, in this state, using a caulking device (not shown),
03 is swaged as shown in FIG. As a result, the peripheral thick portion of the accumulator bladder 22 is
03 and the inner peripheral surface of the opening of the lower split shell 112. As a result of this caulking, the central portion on the upper side of the ring-shaped holding member 103 is inserted into the groove 113 formed in the inner circumferential surface of the opening of the lower split shell 112 along the circumferential direction. Therefore, the ring-shaped holding material 1
03 and the ring-shaped holding material 10
The degree of sealing between the third shell 112 and the lower split shell 112 is improved.
Therefore, the lower split shell 112 and the ring-shaped holding material 10
3 prevents gas and hydraulic oil from permeating and leaking. Further, the ring-shaped holding member 1 is formed by a step 114 provided on the inner peripheral surface of the opening of the lower divided shell 112.
03 does not occur, and the ring-shaped holding material 10
3, the effect of improving the positioning accuracy can be obtained. Thus, the accumulator bladder 22 is attached to the lower divided shell 112, and then the lower divided shell 11
The opening of the upper split shell 110 is aligned with the opening 2 as shown in FIG. 5 to finish the shell into a substantially spherical shell as a whole.
In this case, before the upper split shell 110 is attached, the attachment state of the accumulator bladder 22 can be visually checked, thereby preventing the occurrence of an improper attachment of the accumulator bladder 2. The opening of the upper split shell 110 and the lower split shell 11
The joining of the two openings is performed by electron beam welding or the like at the joint between the two openings. Thereby, since the penetration width can be reduced, it is possible to reduce or avoid the thermal effect on the peripheral thick portion of the accumulator bladder 22. Thus, the accumulator 100 as shown in FIG. 5 is obtained. In FIG. 5, 10
1e is an electron beam weld, 121 is a poppet, 151 is a plug having an oil port 150, and 153 is a gas plug. In the accumulator 100, the inner space of the shell is formed by the accumulator bladder 22 in the gas chamber 101a.
And an oil chamber 101b. The alternate long and short dash line indicates a state in which the accumulator bladder 22 is elastically deformed.
The three types of accumulators thus obtained (the accumulator bladders 22 have different film structures).
Have high durability and long life.

Although the upper shell 110 and the lower shell 112 form a substantially spherical shell in FIG. 5, the shape of the shell is not limited to a spherical shell.
It can be changed to various shapes such as a cylindrical shape and a box shape. Also, in FIG. 5, the spherical shell is formed by using two hemispherical shell-shaped divided shells 110 and 112. However, as in the conventional case, the spherical shell is formed by using a single plate. There is no problem if a shell is formed and the accumulator bladder 22 is mounted thereon.

[0031]

As described above, the accumulator of the present invention contains, as a film component, a composite layer in which a gas shielding layer made of EVOH is directly formed integrally on the upper and lower surfaces of an elastic center layer mainly composed of a polyamide resin. It is configured using an accumulator bladder. Therefore, the difference in bending elasticity between the bladder's rubber layer and the like and the EVOH is reduced by the polyamide resin elastic layer having an intermediate bending elasticity between them. As a result, even if bending is repeated, cracks and the like do not occur in the gas shielding layer made of EVOH in the bladder, and as a result, the life of the accumulator is significantly prolonged.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of an embodiment of the present invention.

FIG. 2 is a partial sectional view of an accumulator incorporating one embodiment of the present invention.

FIGS. 3A and 3B are explanatory diagrams of a bending test of a bladder for an accumulator. FIG.

FIG. 4 is a sectional view showing the configuration of another embodiment of the present invention.

FIG. 5 is a cross-sectional view of one embodiment of the accumulator of the present invention.

FIG. 6 is a cross-sectional view of a main part in a state before a ring-shaped holding member is caulked to a lower split shell in FIG. 5;

FIG. 7 is a cross-sectional view of main parts in a state after the ring-shaped holding member is caulked to the lower split shell in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Elastic center layer 1 'Elastic layer 2 Gas shielding layer 3 Rubber layer 20, 100 Accumulator 22 Accumulator bladder 21a, 103 Ring-shaped holding material 20a, 110 Upper split shell 20b, 112 Lower split shell 101a Gas chamber 101b Oil chamber

Claims (5)

(57) [Claims] 1. A bladder for an accumulator in the form of an elastic thin film that divides an inner space of the shell into two chambers,
An accumulator, wherein the elastic thin film accumulator bladder includes a composite layer comprising the following (A) and (B) as a film forming element. (A) An elastic center layer mainly composed of a polyamide resin. (B) A gas shielding layer composed of an ethylene-vinyl alcohol copolymer directly laminated and integrated on both upper and lower surfaces of the above (A). 2. The accumulator bladder according to claim 2, wherein said shell is formed into a substantially spherical shell shape by combining two substantially hemispherical shell-shaped divided shells. It is attached by being positioned inside the opening of the shell and fixed by a ring-shaped holding material, and the opening of one substantially hemispherical shell-like shell in the attached state abuts the opening of the other substantially hemispherical shell-like divided shell. 2. The accumulator according to claim 1, wherein the accumulator is welded. 3. A film-forming element includes a composite layer comprising an elastic center layer mainly composed of a polyamide resin and a gas shielding layer made of an ethylene-vinyl alcohol copolymer resin directly integrated on the upper and lower surfaces thereof. A bladder for an accumulator. 4. An elastic center layer mainly composed of a polyamide resin is laminated and integrated on both upper and lower surfaces of the gas shielding layer, and a rubber layer is laminated and formed on both upper and lower surfaces of the elastic layer via an adhesive layer. The bladder for an accumulator according to claim 3. 5. On both upper and lower surfaces of a composite layer comprising the elastic center layer and the gas shielding layers integrated on both upper and lower surfaces thereof,
4. The accumulator bladder according to claim 3, wherein an arbitrary number of elastic layers mainly composed of polyamide resin and said gas shielding layer are laminated.