JP2700594B2 - 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 problem, for example, a composite film in which a polyolefin-based resin layer such as polyethylene or polypropylene is laminated on both surfaces of an ethylene-vinyl alcohol copolymer as a barrier layer via an adhesive layer. Has been proposed. And the ethylene-vinyl alcohol copolymer usually has an ethylene content of 26-4.
7% by weight is used. When a bladder for an accumulator is configured using such a composite membrane, the ethylene-vinyl alcohol copolymer has excellent gas permeability resistance, and thus can maintain the gas sealing pressure for a long period of time. Becomes However, the composite membrane is
Extended use period (increased number of bending cycles)
Then, the ethylene-vinyl alcohol copolymer (hereinafter abbreviated as "EVOH") film cracks and peels off. Therefore, there is a problem that the life of an accumulator using such an accumulator bladder is shortened.

On the other hand, in order to improve the flexibility (low-temperature characteristics), a plasticizer is added to the barrier layer forming material. For example, a material obtained by adding a plasticizer to a soft vinyl chloride resin (PVC) for medical use at about 10 to 40% by weight or a material obtained by adding glycerin to polyvinyl alcohol is used. However, when a plasticizer is contained, the gas barrier property is reduced because this aids gas permeability. For this reason, in order to improve the gas barrier properties, the overall thickness must be increased, and if the thickness is increased as described above, there is a problem that the bending resistance is reduced. Further, there is a problem that the added plasticizer is scattered and the flexibility is reduced.

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

[0007]

According to the present invention, there is provided a bladder for an accumulator in the form of an elastic thin film which divides an inner space of the shell into two chambers.
The elastic thin film accumulator bladder is made of ethylene having a flexural modulus of 18,000 to 33000 kgf / cm ² .
As a film-forming element, a composite layer comprising a barrier layer composed of a vinyl alcohol copolymer and an elastic layer composed of a material having a flexural modulus of 1,000 to 10,000 kgf / cm ² and formed in contact with the barrier layer is included. Accumulator as the first gist, flexural modulus 18000 ~
A barrier layer made of an ethylene-vinyl alcohol copolymer of 33000 kgf / cm ² and a flexural modulus of 1000
A ^second aspect of the present invention provides a bladder for an accumulator including, as a film forming element, a composite layer made of a forming material of 1 to 10,000 kgf / cm ² and formed of an elastic layer in contact with the barrier layer.

[0008]

In other words, the present inventors have paid attention to the excellent gas permeability resistance (gas barrier property) of the EVOH, and have made a series of studies to solve the above problems. As a result, E
When forming a laminate having a layer structure in which an elastic layer is formed in contact with a barrier layer made of VOH, a material having a specific flexural modulus is used as a material for forming the barrier layer and the elastic layer. When formed using
Even if the period of use is long (the number of repeated bending is large), E
The inventors have found that cracks and peeling do not occur in the barrier layer made of VOH, and that the durability of the accumulator bladder is improved. Also, in contact with the barrier layer,
The present inventors have found that since the elastic layer is directly formed, the step of forming the adhesive layer can be omitted as in the related art, and the step of forming the layer can be simplified.

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 at the inner peripheral edge of the opening of one of the hemispherical shell-shaped split shells, and a ring-shaped holding material is attached thereto, and the inner peripheral edge of the opening of the split shell is opened. Then, the peripheral portion of the accumulator bladder is sandwiched and fixed between 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. Further, 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 portion of the accumulator bladder can be firmly attached, and gas, oil leakage and the like occur. Can be prevented.

[0012] The accumulator bladder comprises an EVOH forming a barrier layer having a specific flexural modulus, an elastic layer forming material having a specific flexural modulus, and a forming material for forming a rubber layer in some cases. It is configured using.

It is preferable to use the EVOH having an ethylene content of 32% by weight (hereinafter abbreviated as "%") and the remainder being vinyl alcohol. That is, the ethylene content is less than 32% (the vinyl alcohol content is 6%).
If it exceeds 8%), the gas barrier property is improved, but the ethylene-vinyl alcohol copolymer itself becomes hard and the flexibility is reduced, and the ethylene-vinyl alcohol copolymer tends to be unsuitable for applications having a bending motion.

It is necessary to use an EVOH having a flexural modulus in the range of 18,000 to 33000 kgf / cm ² . That is, the flexural modulus is 1800
If it is less than 0 kgf / cm ² , the gas barrier properties will be poor, and if it exceeds 33000 kgf / cm ² , the flexibility will be poor.

As the material for forming the elastic layer, it is necessary to use a material having a flexural modulus in the range of 1,000 to 10,000 kgf / cm ² . Particularly preferably 3000 to 5000
kgf / cm ² . That is, the flexural modulus is 100
If it is less than 0 kgf / cm ² , the difference in flexural modulus from the above-mentioned EVOH becomes large, and the load on the barrier layer made of EVOH when bending becomes large. On the contrary, 10,000 kgf /
If it exceeds cm ² , the flexibility tends to be poor. As the material for forming the elastic layer, a polyamide resin is suitably used, and among them, super tough nylon having a property more flexible than conventionally known nylon is particularly preferably used.

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, when manufacturing a bladder for an accumulator, EVOH and an elastic layer forming material are charged into each material input section of an extruder for forming a composite layer, and coextruded into a so-called sandwich structure having a three-layer structure, for example.
Using VOH as a barrier layer, elastic layers are integrally formed on both upper and lower surfaces to form a composite layer. At this time, the barrier layer made of EVOH and the elastic layers formed on both surfaces thereof are melted and fused by heat at the time of extrusion molding, so that an adhesive is not required. Thus, the accumulator bladder 22 having a three-layer structure as shown in FIG. 1 is obtained. In the figure, 1 is EVO
The barrier layer 2 made of H is an elastic layer integrally formed on the upper and lower surfaces thereof. As shown in FIG. 2, the accumulator bladder 22 obtained as described above has an accumulator bladder 22 on the inner peripheral edge of the opening of the lower divided shell 21 of the two substantially hemispherical shells. Is fixed to the lower divided shell 21 by pinching and fixing the peripheral portion between the outer periphery of the ring-shaped holding member 21a and the inner peripheral edge of the opening of the lower divided shell 21. Then, the opening of the upper split shell 20a is brought into contact with the opening of the lower split shell 21, and the accumulator 20 is manufactured by electron beam welding or the like. In the figure, 23 is a poppet.

In the accumulator bladder 22 thus obtained, the thickness of the barrier layer 1 made of EVOH is appropriately set in accordance with the required gas permeability, but is preferably set in the range of 200 μm or less. preferable. That is, if the thickness of the barrier layer 1 exceeds 200 μm, the bending resistance tends to decrease. Further, the thickness of the elastic layer 2 is preferably set to 300 μm or less. Further, it is preferable that the elastic layers 2 formed on the upper and lower surfaces of the barrier layer 1 have the same thickness. That is, by making the thickness of each elastic layer 2 the same, the barrier layer 1 becomes the center during the bending motion, and the generated stress is reduced. In the accumulator bladder 22 having the three-layer structure, the ratio of the thickness (α) of the upper and lower elastic layers 2 to the thickness (β) of the barrier layer 1 is α / β ≧ 1.
Is preferable from the viewpoint of the effect.

As shown in FIG. 3, a rubber layer 3 is further formed on the upper and lower surfaces of the accumulator bladder 22 having the three-layer structure with an adhesive layer 4 interposed therebetween to produce an accumulator bladder 23 having a multilayer structure. May be. As a method of forming the accumulator bladder 23 having the multilayer structure, an adhesive layer 4 is formed on both upper and lower surfaces of the composite layer having the three-layer structure, and a rubber layer forming material is press-formed with a press machine, and the elastic layer is formed. There is a method of vulcanization bonding on two surfaces. As the material for forming the rubber layer 3, for example, a bending elastic modulus of 100
acrylonitrile-butadiene rubber (NBR) having a weight of not more than kgf / cm ² .

The accumulator bladder of the present invention is not limited to the one in which the elastic layers 2 are formed on the upper and lower surfaces of the barrier layer 1 as shown in FIG. The barrier layer 1 may be formed on both upper and lower surfaces of the elastic layer 2.

Further, the accumulator bladder of the present invention is not limited to the multilayer structure shown in FIGS. 1 and 3, and may have a multilayer structure in which further layers are formed.

Next, examples will be described together with comparative examples.

First, a bladder for an accumulator was manufactured as follows.

[0023]

Examples 1 to 6 and Comparative Examples 1 to 6 EVOH (ethylene content 32%, Kuraray F-
101) and a special nylon super-tough nylon (Dupont, S
T811HS). Then, this material was co-extruded from an extruder to a thickness shown in Tables 1 to 3 described below, thereby producing a three-layered accumulator bladder 22 (2 mm thick) shown in FIG. In the figure, 1 is a barrier layer and 2 is an elastic layer. Further, the composite layer was vulcanized and bonded to both sides of the composite layer via an adhesive layer using NBR, thereby obtaining a multi-layered accumulator bladder 23 as shown in FIG. The thickness, flexural strength and flexural modulus of the NBR are shown in Tables 1 to 3 below together with those of the barrier layer and the elastic layer.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

The accumulator bladders 30 having the three-layer structure and the multi-layer structure thus obtained are subjected to a bending test machine, and alternately changed to the states shown in FIGS. Of the EVOH layer was measured. Further, the nitrogen gas permeability after the bending test was measured by using the accumulator bladder. Then, those with a small amount of nitrogen gas permeated were marked with ○,
Those that were large were evaluated as x. The results are shown in Tables 1 to 3 above. The measurement conditions in the bending test were changed at 80 ° C. in 1 million cycles. The filling gas used was N ₂ gas, and the gas filling pressure was 2.5 to
The state of FIGS. 4 (A) and (B) was generated by changing the oil pressure within a range of three times. The durability test was performed as follows.

Enclosed gas pressure: P ₀ Working pressure: P ₁ Durability test condition: Operate 80 ° C. × 1 million times at 0.3 Hz between P ₀ /2.5-3.

From the results shown in Tables 1 and 2, cracks occurred in all of the comparative examples. On the other hand, the product of the example had good gas barrier properties and did not crack.

Next, an accumulator was manufactured using the accumulator bladder of the above embodiment as follows.

[0031]

[Embodiments 7 to 12] That is, as shown in FIG. 5, the upper divided shell 110 is divided into two substantially hemispherical shells.
And the lower split shell 112 were prepared, and the peripheral part of the accumulator bladder 22 having the three-layer structure obtained in the above embodiment was formed to be a thick part. Then, as shown, the accumulator bladder 22 is disposed in the lower divided shell 112, and the peripheral portion thereof is placed in the lower divided shell 112.
Is fixed to the inner peripheral surface of the opening with a ring-shaped holding member 103. In this case, as shown in FIG. 6, a groove 113 is previously formed in the circumferential direction on the inner peripheral surface of the opening of the lower split shell 112, 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, the ring-shaped holding member 103 is swaged as shown in FIG. 7 by using a swaging device (not shown). As a result, the peripheral thick portion of the accumulator bladder 22 is sandwiched and fixed between the lower outer peripheral portion of the ring-shaped holding member 103 and the inner peripheral surface of the opening of the lower split shell 112. Due to this caulking, the upper central portion of the ring-shaped holding material 103
A groove 113 formed in the inner circumferential surface of the opening of the lower split shell 112 along the circumferential direction is hardly inserted. Therefore, the degree of fixation of the ring-shaped holding member 103 is improved, and the degree of sealing between the ring-shaped holding member 103 and the lower divided shell 112 is improved. Therefore, the lower split shell 11
Gas and hydraulic oil are prevented from permeating and leaking from between the ring 2 and the ring-shaped holding member 103. Further, the step 114 provided on the inner peripheral surface of the opening of the lower split shell 112 prevents the ring-shaped holding member 103 from being displaced and the like, and an effect of improving the positioning accuracy of the ring-shaped holding member 103 can be obtained. In this way, the lower split shell 1
12, an accumulator bladder 22 is attached. Then, the upper split shell 1 is inserted into the opening of the lower split shell 112.
The openings 10 are aligned as shown in FIG. 5 to finish the shell into a substantially hemispherical shell as a whole. In this case, the upper split shell 1
Before the mounting of the accumulator 10, the mounting state of the accumulator bladder 22 can be checked with the naked eye, thereby making it possible to prevent the mounting failure of the accumulator bladder 2 from occurring. And the upper split shell 11
The joint of the opening of the lower split shell 112 and the opening of the 0 is made by electron beam welding or the like at the joint of 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, 101e is an electron beam welded part,
121 is a poppet, 151 is a plug having an oil port 150, and 153 is a gas plug. This accumulator 1
At 00, the internal space of the shell is divided by the accumulator bladder 22 into a 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. 6 obtained in this way
Each type of accumulator has 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 sphere, but may be cylindrical or box-like. And various other shapes. Further, 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. The accumulator bladder 22 may be attached to the accumulator.

[0033]

As described above, the accumulator of the present invention is formed in a state of being in contact with the barrier layer made of an EVOH having a specific flexural modulus and a forming material having a specific flexural modulus. It is configured using a bladder for an accumulator including a composite layer composed of an elastic layer as a film forming element. For this reason, even if bending is repeated, cracks and the like do not occur in the barrier layer made of EVOH in the bladder, and the life of the accumulator is greatly extended.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the configuration of an embodiment of an accumulator bladder according to the present invention.

FIG. 2 is a partial sectional view of an accumulator bladder incorporating the accumulator bladder of FIG. 1;

FIG. 3 is a sectional view showing the configuration of another embodiment of the accumulator bladder of the present invention.

FIGS. 4A and 4B are explanatory diagrams of a bending test of a bladder for an accumulator.

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 crimped to a lower split shell in FIG. 5;

FIG. 7 is a cross-sectional view of a main part of FIG. 5 after the ring-shaped holding member has been caulked to the lower split shell.

[Explanation of symbols]

 Reference Signs List 1 barrier layer 2 elastic layer 3 rubber layer 20, 100 accumulator 22 accumulator bladder 21a, 103 ring-shaped holding material 20a, 110 upper divided shell 21, 112 lower divided 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,
The elastic thin film accumulator bladder is made of ethylene having a flexural modulus of 18,000 to 33000 kgf / cm ² .
As a film-forming element, a composite layer comprising a barrier layer composed of a vinyl alcohol copolymer and an elastic layer composed of a material having a flexural modulus of 1,000 to 10,000 kgf / cm ² and formed in contact with the barrier layer is included. An accumulator. 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 flexural modulus of elasticity of 18,000 to 33000 kg.
ethylene f / cm ² - a barrier layer comprising a vinyl alcohol copolymer, flexural modulus 1000~10000k
A bladder for an accumulator, characterized in that the bladder for an accumulator comprises a composite layer made of a material of gf / cm ² and an elastic layer formed in contact with the barrier layer as a film-forming element. 4. The accumulator bladder according to claim 3, wherein said elastic layer is formed of a polyamide resin. 5. The accumulator bladder according to claim 3, wherein a rubber layer is formed on an outermost layer, and an elastic layer is formed on the rubber layer via an adhesive layer.