JPH05318662A - Accumulator and bladder therefor - Google Patents

Abstract

PURPOSE:To provide an accumulator having high durability and a long life. CONSTITUTION:An elastic membrane like bladder 22 for an accumulator dividing the inner space of the shell of the accumulator into two chambers contains a composite layer consisting of an elastic center layer 1 based on a polyamide resin and the gas barrier layers 2 composed of an ethylene/vinyl alcohol copolymer directly integrally laminated on both surfaces of the center layer 1 as film forming elements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an accumulator used in a hydraulic system for automobiles, industrial vehicles and the like, and an accumulator bladder used in the accumulator.

[0002]

2. Description of the Related Art An accumulator has a function of accumulating pressure and is generally composed of 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 arranged inside the shell of the accumulator, and divides the internal space of the shell into two chambers as described above. Then, gas such as nitrogen gas is enclosed in one of the chambers (gas chamber) to become a pressure transmitting fluid, and the other chamber (oil chamber)
Then, 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 rubber thin film bladder with the lapse of the use period, so that the gas sealing pressure is lowered and the function thereof is not fulfilled.

Therefore, attempts have been made to improve the gas permeation resistance by adding an additive to the rubber material forming the bladder. However, in this way, although the gas permeation resistance is improved, the flexibility of the accumulator bladder itself becomes poor, and there is a new problem that cracks or the like are likely to occur during 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 with an adhesive layer interposed is proposed. (Japanese Patent Laid-Open No. 2-165948). When constructing an accumulator bladder using such a composite film, since the ethylene-vinyl alcohol resin film is excellent in gas permeation resistance, it is necessary to maintain the gas filling pressure for a long period of time. Is possible. However, when the rubber resin composite film is used for a long period of time (the number of times of repeated bending increases), the ethylene-vinyl alcohol copolymer (hereinafter abbreviated as “EVOH”) film cracks and peels. 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 thereof is to provide an accumulator having high durability and a long life, and an accumulator bladder used for the accumulator.

[0006]

In order to achieve the above object, the accumulator of the present invention comprises a shell and an elastic thin film accumulator bladder that divides the internal space of the shell into two chambers. The accumulator bladder of (1) includes a composite layer (A) and (B) described below as a film forming element. (A) An elastic center layer mainly composed of a polyamide resin. (B) A gas shielding layer made of an ethylene-vinyl alcohol copolymer directly laminated on both upper and lower surfaces of (A).

In the accumulator bladder of the present invention, a composite layer composed of an elastic center layer mainly composed of polyamide resin and a gas shielding layer made of EVOH resin directly integrated on both upper and lower surfaces thereof serves as a film forming element. It is configured to be included.

[0008]

The present inventor paid attention to the excellent gas permeation resistance (gas barrier property) of EVOH and carried out a series of studies in order to solve the above problems. As a result, when the EVOH films are directly formed 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 an elasticity intermediate between the rubber thin film and the EVOH film. It has been found that the film becomes a buffer layer and the EVOH film (gas shielding layer) is not cracked or peeled off even when the period of use is 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 it has a melting point close to that of EVOH, and during this extrusion, the polyamide resin and EVO are integrated.
Since H and H are reactively bonded at the bonding interface between them, an adhesive for bonding them is unnecessary, and the elasticity of the composite layer does not decrease due to the use of the adhesive.

Next, the present invention will be described in detail.

The accumulator of the present invention comprises a shell and an accumulator bladder that divides the interior of the shell into two chambers.

The shell is not particularly limited as long as it is made of a metal, but normally, a shell made of iron or aluminum alloy is used. The shape of the shell is also not particularly limited, and it is a substantially spherical shell, a tubular shape,
Various shapes such as a box shape are used. It is preferable that two split shells having a substantially hemispherical shell shape are butted to each other and finished into a substantially spherical shell shape. By doing so, the peripheral edge of the accumulator bladder is positioned at the inner peripheral edge of the opening of one of the hemispherical shell-shaped split shells, and the ring-shaped holding member is attached thereto, and the inner peripheral edge of the split shell is opened. The peripheral portion of the accumulator bladder is clamped and fixed to the outer periphery of the ring-shaped holding material, and then the opening of the one split shell is butted against the opening of the other split shell to finish the accumulator. Therefore, the shell can be manufactured more easily than the conventional method in which one disk is formed into a spherical shell shape to form the shell. Also, before welding the two split shells, it is possible to check the mounting state of the accumulator bladder attached to the opening of one of the hemispherical shell-shaped split shells, making sure that the peripheral edge of the accumulator bladder is properly attached. You can avoid it. Further, since the peripheral portion of the accumulator bladder is clamped 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 portion of the accumulator bladder can be firmly attached, and gas, oil leakage, etc. occur. Can also be prevented.

The accumulator bladder is formed by using a polyamide resin which is a main body of the elastic center layer, EVOH which forms gas shielding layers on both upper and lower surfaces thereof, and rubber for forming a rubber layer in some cases. There is.

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

As the above polyamide resin, nylon 6, nylon 66, nylon 6-10 and nylon 6-1 are used.
2 and the like can be used alone or in combination. Such a polyamide resin has a melting point similar to that of EVOH if the above-mentioned nylon 6 or nylon 66 is contained in the base. Therefore, various mixtures of nylon 6 and other nylon resins should be used. Is possible. In particular, it is preferable to use the polyamide resin and the polyolefin resin as a blend. By doing so, the polyolefin resin is poor in water absorption, so that water absorption for EVOH is prevented. That is, when EVOH absorbs water, the gas barrier resistance is lowered, and the polyolefin resin prevents this.

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

The elastic center layer mainly composed of the polyamide resin described above has a bending elastic modulus intermediate between that of the rubber forming the rubber layer and EVOH forming the gas shielding layer. If expressed in order from the highest ratio, the following expression (1) is obtained.

EVOH> polyamide resin> rubber ... (1)

In the present invention, for example, an accumulator bladder is manufactured in the following manner, and the accumulator is manufactured using the bladder. That is, an EVOH and a polyamide resin are coextruded by using an extrusion molding machine, and a gas shielding layer made of EVOH and an elastic layer made of a polyamide resin are provided on both upper and lower sides 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, since 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 of both as described above, the adhesive is unnecessary. 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 layers is superposed on the rubber layer, and then vulcanized and bonded. In this way, the accumulator bladder 22 having the layer structure as shown in FIG. 1 is obtained. In the figure, 1 is an elastic center layer made of polyamide resin, 1'is an elastic layer made of polyamide resin, 2 is a gas shielding layer made of EVOH, and 3 is a rubber layer. An accumulator equipped with this accumulator bladder is shown in FIG. In the figure, 2
0 is an accumulator, 21 is a shell, 22 is an accumulator bladder, and 23 is a poppet. More specifically, as shown in FIG. 2, the accumulator bladder obtained as described above has a lower split shell of two split hemispherical shell-shaped split shells 20a, 20b forming the shell 21. The inner peripheral edge of the opening of 20b is positioned at the peripheral edge, and the peripheral edge is clamped and fixed 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. Of the split shell 20b. Then, the accumulator 20 is configured by abutting the opening of the upper split shell 20a with the opening of the lower split shell 20b and performing electron beam welding or the like.

Next, examples and comparative examples will be described together.

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

[0021]

Examples 1 and 2 A polyamide resin (Super Tough Nylon ST811HS manufactured by DuPont) was prepared as an elastic center layer forming material and an elastic layer forming material, and EVOH (ethylene content 32) was prepared as a gas shielding layer forming material.
%, F-101 manufactured by Kuraray Co., Ltd. was prepared. In addition, NBR was prepared as a material for forming a rubber layer. Next, the above polyamide resin and EVOH were fed from an extruder to the following Table 1.
By coextrusion to the thickness shown in Fig. 5, a gas-shielding layer was positioned on both upper and lower surfaces of the elastic center layer, and a composite layer having a five-layer structure was prepared in which elastic layers were stacked on the upper and lower surfaces thereof.

Next, a conventionally known adhesive was applied to each of the upper and lower surfaces of the composite layer, and NBR was press-formed into a layer having a thickness shown in Table 1 below, and then vulcanized and adhered. In this way, as shown in FIG. 1, an elastic thin film accumulator bladder 22 having a seven-layer structure was obtained. 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 the comparative example, the central layer made of EVOH was extrusion-molded to the thickness shown in Table 1 below, and a conventionally known adhesive was applied to both upper and lower surfaces thereof, and then a rubber layer made of NBR was formed. The layer was press-molded to a thickness shown in Table 1 below, and then vulcanized and adhered to manufacture an accumulator bladder 22. Comparative Examples 1 to 3 have a five-layer structure in which elastic layers made of polyamide resin are stacked on the upper and lower surfaces of a central layer made of EVOH, and a rubber layer is stacked on each elastic layer. Nos. 4 and 5 have a three-layer structure in which rubber layers are stacked on the upper and lower surfaces of a central layer made of EVOH.

[0024]

[Table 1]

Next, the flexibility of the accumulator bladder 22 obtained as described above is examined by bending it with fingers, and it is subjected to a bending tester to alternate the states shown in FIGS. 3 (A) and 3 (B). And the occurrence of cracks in the EVOH layer of the accumulator bladder 22 was measured. In addition, the nitrogen gas permeability of the accumulator bladder 22 was measured at the initial stage and after the durability test. 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. The results of these tests are shown in Table 1. From Table 1, it can be seen that in the examples, the EVOH layer is not cracked at all.

The measurement conditions in the above bending test are 80 ° C. and 1
It was changed in the cycle of, 000,000 times. The enclosed gas is N
_Two gases were used, and the pressure of oil was changed in the range of 2.5 times to 3 times the gas filling pressure to generate the states of FIGS. 3 (A) and 3 (B). The durability test was performed as follows.・ Enclosed gas pressure: P ₀・ Working pressure: P ₁ Durability test condition: 0.3 H when P ₁ / P ₀ is between 2.5 and 3.
_Operate at 80 ℃ x 1 million times with _Z.

FIG. 4 shows another embodiment (third embodiment) 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 both 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 permeation resistance (gas barrier property) is improved and the flex resistance is improved even if the entire thickness is the same.

Next, using the accumulator bladders of Examples 1 to 3 above, accumulators were produced as follows.

[0029]

Fourth Embodiment As shown in FIG. 5, an upper split shell 110 and a lower split shell 112 are prepared as two substantially hemispherical shell-shaped split shells, and the bladder for accumulator obtained in the above embodiment is prepared. For No. 22, the peripheral portion was formed as a thick portion. Then, as shown in the drawing, the bladder 22 for accumulator is arranged in the lower split shell 112, and the peripheral portion thereof is fixed to the inner peripheral surface of the opening of the lower split shell 112 by the ring-shaped holding material 103. In this case, as shown in FIG. 6, the inner peripheral surface of the opening of the lower split shell 112 is previously
A groove 113 is formed in the circumferential direction, and a step portion 114 is formed below the groove 113. The ring-shaped holding member 103 has a stepped structure in which the upper side of the ring has a large diameter and the lower side has a small diameter. The step portion is positioned on the end surface 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 that state, a ring-shaped holding material 1 is used by using a caulking device (not shown).
03 is caulked as shown in FIG. As a result, the thick-walled peripheral portion of the accumulator bladder 22 becomes
The outer peripheral portion of 03 and the inner peripheral surface of the opening of the lower split shell 112 are sandwiched and fixed. By this caulking, the central portion on the upper side of the ring-shaped holding material 103 is in a state in which it is difficult to fit in the groove 113 formed along the circumferential direction on the inner peripheral surface of the opening of the lower split shell 112. Therefore, the ring-shaped holding material 1
The degree of fixation of No. 03 is improved and the ring-shaped holding material 10
The degree of sealing between 3 and the lower split shell 112 is improved.
Therefore, the lower split shell 112 and the ring-shaped holding material 10
The permeation and leakage of gas and hydraulic oil from between 3 and 3 are prevented. Further, the ring-shaped holding material 1 is provided by the step portion 114 provided on the inner peripheral surface of the opening of the lower split shell 112.
No misalignment of 03, etc., and the ring-shaped holding material 10
Thus, the effect of improving the positioning accuracy of No. 3 can be obtained. In this way, the accumulator bladder 22 is attached to the lower split shell 112, and then the lower split shell 11 is attached.
The opening of the upper split shell 110 is aligned with the opening of No. 2 as shown in FIG. 5, and the shell is finished to have a substantially spherical shell shape as a whole.
In this case, the mounting state of the accumulator bladder 22 can be visually confirmed before the upper split shell 110 is mounted, and thus it is possible to prevent the defective mounting of the accumulator bladder 2 from occurring. Then, the opening of the upper split shell 110 and the lower split shell 11
The two openings are joined by electron beam welding or the like at the joints of both openings. As a result, the penetration width can be narrowed, so that it is possible to reduce or avoid the thermal influence on the peripheral thick portion of the accumulator bladder 22. In this way, the accumulator 100 as shown in FIG. 5 is obtained. In FIG. 5, 10
Reference numeral 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 this accumulator 100, the internal space of the shell is set to the gas chamber 101a by the accumulator bladder 22.
And the oil chamber 101b. The alternate long and short dash line shows the state in which the accumulator bladder 22 is elastically deformed.
Three types of accumulators obtained in this way (the accumulator bladder 22 has a different film structure)
Have high durability and long life.

In FIG. 5, the upper split shell 110 and the lower split shell 112 form a substantially spherical shell shape, but the shell shape is not limited to the spherical shell shape.
It can be changed into various shapes such as a cylinder and a box. Further, in FIG. 5, the spherical shell-shaped shell is configured by using the two hemispherical shell-shaped split shells 110 and 112, but as in the conventional case, a single plate is used to form a spherical shell-shaped shell or the like. There is no problem even if a shell is made and the bladder 22 for accumulator is attached thereto.

[0031]

As described above, the accumulator of the present invention includes, as a film constituent, a composite layer in which a gas shielding layer made of EVOH is directly formed on both upper and lower surfaces of an elastic center layer mainly composed of polyamide resin. It is configured using a bladder for accumulator. Therefore, the difference in flexural elasticity between the rubber layer or the like of the bladder and the EVOH is alleviated by the polyamide resin elastic layer having the intermediate flexural elasticity. As a result, even if the 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 extended.

[Brief description of drawings]

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

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

FIG. 3A and FIG. 3B are explanatory views of a bending test of an accumulator bladder.

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

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

FIG. 6 is a cross-sectional view of essential parts in a state before caulking the ring-shaped holding material to the lower split shell in FIG.

FIG. 7 is a cross-sectional view of essential parts in a state after the ring-shaped holding material in FIG. 5 is caulked to the lower split shell.

[Explanation 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

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[Procedure amendment]

[Submission date] April 5, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

[0021]

Examples 1 and 2, Comparative Examples 1 and 2 A polyamide resin (Super Tough Nylon ST811HS manufactured by DuPont) was prepared as an elastic center layer forming material and an elastic layer forming material, and EVOH (ethylene was used as a gas shielding layer forming material. A Kuraray F-101) having a content of 32% was prepared.
In addition, NBR was prepared as a material for forming a rubber layer. Next, the polyamide resin and EVOH were co-extruded from an extrusion molding machine 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 further stacked on the upper and lower surfaces thereof. A composite layer having a five-layer structure was prepared.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

In Comparative Examples 1 and 2, the center layer made of EVOH was extrusion-molded to have the thickness shown in Table 1 below, and the conventionally known adhesive was applied to the upper and lower surfaces of the center layer.
The rubber layer made of (1) was press-formed into a layer having a thickness shown in Table 1 below, and then vulcanized and adhered to manufacture a bladder 22 for accumulator having a three-layer structure. EV of Comparative Examples 1 and 2
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.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction content]

[0024]

[Table 1]

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

[Figure 6]

[Figure 3]

[Figure 4]

[Figure 5]

[Figure 7]

Claims (5)

[Claims] 1. A shell and an elastic thin film accumulator bladder that divides the internal space of the shell into two chambers,
An accumulator characterized in that 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 made of an ethylene-vinyl alcohol copolymer directly laminated on both upper and lower surfaces of (A). 2. The shell is finished into a substantially spherical shell shape by combining two substantially hemispherical shell-shaped split shells, and the accumulator bladder has a peripheral portion at one of the substantially hemispherical shell split shells. It is attached by positioning it inside the opening part of and fixing it with a ring-shaped holding material, and the opening of one of the substantially hemispherical shell-shaped divided shells of this attached state is butted The accumulator according to claim 1, which is welded. 3. A film forming element includes a composite layer comprising an elastic center layer mainly composed of polyamide resin and a gas shielding layer made of ethylene-vinyl alcohol copolymer resin directly integrated on both upper and lower surfaces thereof. The bladder for accumulator which is characterized by. 4. An elastic center layer mainly made of polyamide resin is integrally laminated on the upper and lower surfaces of the gas shielding layer, and a rubber layer is laminated on the upper and lower surfaces of the elastic layer via an adhesive layer. The bladder for accumulator according to claim 3. 5. The upper and lower surfaces of a composite layer comprising the elastic center layer and the gas shielding layers integrated on the upper and lower surfaces thereof,
The accumulator bladder according to claim 3, further comprising an elastic layer mainly made of a polyamide resin and an arbitrary number of the gas shielding layers.