US2378467A - Accumulator bladder - Google Patents

Description

June'19, 1'945. 4 N. 155 KISS ACCUMULATOR BLADDER Fi-led'iluly 22; 1943 uvmvrox. NICHOLAS DE KISS F/GZ rizdq ATTORNEY Patented June 19, 1945 UNITED ACCUMULATOR BLADDER.

Nicholas de Kiss, North Hollywood, Calif., assignor, by mesne assignments, to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application July 22, 1943, Serial No. 495,711

(Cl. 1ss so) Claims.

This invention relates to hydraulic pneumatic accumulators of the bladder type for use in hydraulic power systems, and relates more particularly to the construction of thebladder.

Accumulators are devices for storing liquid underoperating pressures. They are necessary becausethe liquid demand of a hydraulic-system may be greater at any one instant than the capacity of the pump which supplies the liquid under pressure. When such a condition exists, the accumulator supplies the deficiency and is in turn recharged with liquid when the demands of the system are less than the capacity of the pump. Such an arrangement permits the use of a small pump for a relatively large hydraulic system.

Accumulators in general are chambers wherein incompressible liquid may act upon a compressible medium which maintains the liquid under pressure. Air is preferred to springs as the compressible medium since it is lighter. when air is used, it must be carefully isolated from the liquid since it would dissolve into the liquidunder pressure and come out of solution when the pressure is relieved, creating troublesdme air pockets and bubbles. For this reason a fiexible partition is provided between air and liquid. This partition may be in the form of a diaphragm or a bladder. The present invention relates to bladder type accumulators.

A bladder type accumulator changes its liquid capacity'by the collapse and expansion of the bladder undervarying volumes of liquid. Ob-

viously, if liquid is permanently trapped in pockets and therefore has a high volumetric efliciency;

This bladder is of the type wherein one half is flexible and the other half is comparatively rigid and secured in place, the flexible half collapsing into the rigid half. The present invention comprises the making of the bladder in such a manner that the movable part is made of flezfible material and the stationary part. is made of relatively rigid material.

It therefore an object of the invention to provide an accumulator wherein bladder flexibility is regulated by the use of difierent compounds of rubber-like material.

Another object is to provide an accumulator bladder having diflerent portions made out of varying compounds to vary the flexibility of the various portions.

In the drawing forming a part of this specificafion:

Figure l is an elevational view in full section of an accumulator having a bladder made according to the invention;

Figure 2 is an elevation view in full section, but on a reduced scale, of the bladder of Figure l, with an indication of the zones of different compounds; and

Figure 3 is a view in full section of a portion of a bladder in the region of the bead, made according to a modification of the invention.

Referring to Figure 1, a generally spherical shell ID has fine holes l2 drilled in the bottom, and a threaded fitting H3 is welded to theshell around the holes. A collar I6 is welded to the upper part of shell l0 and has an internal shoulder l8 and a protruding internal flange 20. Seated on shoulder i8 is a cover plate 22 held in position by a nut 24 engaging internal threads on collar I5. Cover 22 is axially drilled and retains an air valve 26 and a porous metal plug 28.

Placed within shell ill is a bladder 30 having a fabric reinforcement 32 secured thereto in the region of holes It. This reinforcement prevents the extrusion of the bladder material through holes I2 when the bladder is subjected to air pressure. Formed on the inside of bladder 30 at the mid point is a head 34 which forms a pad of material about which the bladder can fold when its collapses. This feature is important since most bladder materials are extremely brittle at low temperatures, such as at F., and tend to crack if sharply folded or bent. Formed on the top of bladder 30 is an external flange 36 which hooks over the inwardly projecting flange 20 of collar l6. Plate 22 snugly fits the top and inside of flange 3B, securely locking it, and the bladder as a whole, to the shell III.

In operation on a 1,000 p. s. i. hydraulic system,

air under a pressure of about 3q0 p. s. i. is forced into the interior of bladder 30 through valve 26. This flattens bladder 30 tightly against the interior of shell [0. The accumulator is then connected to the hydraulic system at fitting l4, and liquid under pressure passes into shell It. The liquid forces the bladder 30 upwardly until the air, is compressed to a pressure which equals that of the liquid. At rated pressure, the compressed air occupies slightly less than a third of the total volume in shell ID. This condition results only when the lower part of the bladder is collapsed within the upper part, as shown by the broken lines in Figure 1. Thereafter, the air is compressed and expanded according'to the liquid demands of the hydraulic system. The bladder and air exert a continuous pressure on the liquid which never falls below the charging pressure of 300 p. s. i. Varying air charges are used depending on the hydraulic system, the higher pressures giving more power but less liquid capacity.

From the foregoing, it is evident that there is considerable flexing of the lower half of the bladder while the upper half should remain stationary. When bladders are used that are all made of the same composition of synthetic rubber, the upper half is likely to fold and move under the influence of hydraulic pressure. If this occurs, trapping of fluid between the shell and the upper part of the bladder occurs. This represents a "dead" volume in the accumulator cutting down its volumetric efllciency. To prevent this, the present invention provides a bladder wherein the upper half is made of a stiffer material than the lower half. a

Shown in Figure 2 is an illustration of the zones of difierent compoundings of bladder material. Synthetic rubber of the Buna S type is the most suitable for bladder purposes, since it is more flexible at low temperatures than most oil resistant, rubber-like substances. The material is molded to the desired shape. The lower half 40 is madeof the most flexible type of Buna S material. The upper part 42 of bladder 30 is made of a very stiff compound of Buna S, so that it will always hold its molded shape, and be close to the inside of shell Ill, preventing the-trapping of oil. The

rim part, 44 of bladder 30 is molded of a hard and stiff compound of Buna S so that it cannot stretch out of the position in which it is locked by cover plate 22. The molding of the bladder is performed so that all the compounds form a continuous i bladder which is .free of joints or weak spots at the juncture of the various materials. The matter of compounding for different hardness and 'flexibilities is well known to the rubber art and will not be described here.

Shown in Figure 3 is a modification of the invention, comprising in general separate moldings of a stiff upper portion and a flexible lower portion which are vulcanized together. The advan-- tage of this construction is that the extent of the varying materials is accurately controlled. An upper portion 80 having an integral bead I2 is molded of a stiff compounding of any suitable rubber-like 'material. The thin lower section 84 is molded of very flexible material and has a tapered edge 86. These two sections are then vulcanized together to form a complete bladder. I

It will be noted that there is practically no elastic stretching of the bladder. The different compounds do not, therefore, control stretching but control the flexibility or rigidity of the various parts of the bladder. Nor is the bladder subject to tensional or torsional stresses since the air may be edually satisfactory. Nor is the invention limited in any other manner, except by the terms of the following claims.

I claim":

1. An accumulator bladder adapted to be positioned within and-secured at one end to an accumulator shell and comprising a molded bag having two portions each made from a material of different compound from the other, one of the portions being formed and being made of a relatively stiff compound in order to follow the contour of said shell and the other portion being .made of a relatively flexible compound in order to telescope into said stiif portion.

2. An accumulator bladder comprising a bag adapted to be secured within an accumulator shell, said bag having an opening and an outwardly projecting flange at said opening adapted to secure the bag in said shell, one part of the bag opposite the opening being made of a compound that is relatively flexible, that portion of the bag between the opening and said one part being made of a compound that is different from the compound of said one part and that is relatively less flexible, and said flange portion of the bag being made of a compound that is different from and stifier than the compounds from which the said other portions are made.

3. An. accumulator bag comprising a molding of Buna S material in which one portion is made of a Buna S compound that is relatively flexible and the other portion is'made of a Buna S compound that is relatively stiff and adapted to provide a circumferential bending area over which said one portion is collapsed without losing its shape.

4. An accumulator bladder for use within an accumulator shell and comprising a relatively inflexible part adapted to remain stationary'in contact wltha portion of the shell and a relatively pressure and liquid pressure are equal during operation.

The invention is not limited to the specific type of accumulator shown. Nor is it limited to the use of Buna S compounds, as other compounds flexible part adapted to be moved into and out of the stationary part in response to volume changes within said shell on the inside and outside of said bladder respectively, in which the relative flexibilities of said stationary and flexible parts is substantially controlled by forming said parts of different compositions of different stiffness.

5. An accumulator bag comprisin a molding of rubber-like material in which one part is stationary and the other part is adapted to telescope into and out of the stationary part, the stationary part being thickened at its juncture with the telescoping part to provide a shoulder about which the telescoping part folds with a substantial radius of curvature when fully *telescoped, in which at least said thickened portion of said bag is formed of a compound that is relatively stiff as compared to the compound of which the telescop-

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