US2397248A - Accumulator bladder - Google Patents

Description

March 26, 1946. N. DE KISS 2,397,248

$ AGCUMULATOR BLADDER Filed Aug. 25, 1943 3a 4? l6 24 /a 20 l4 V "if m :26

1 L 27 4 T I I I I L ELL; 5

- INVENTOR. NICHOLAS DE KISS A TTOHNEY Patented Mar. 2 6, 1946 Nicholas dc Kiss, North Hollywood, Calif assignor, by mesne assignments, to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application August 25, 1943, Serial No. 499,967

.6 Claims. (Cl. 138-30) This invention relates to hydraulic-pneumatic accumulators of the bladder type for use in hydraulic systems, for example in the hydraulic systems of airplanes, and is a continuation in part of de Kiss, Serial Number 470,359, filed December 28, 1942.

Accumulators are used for storing hydraulic fluid under pressure. In general, they comprise a shell having an air. connection and a hydraulic connection, with a flexible partition between the air and hydraulic fluid so that the hydraulic fluid may act against the air without possibility of contamination by the air. The hydraulic fluid acts against the compressed air so that pressure will be maintained in the stored hydraulic fluid. It has been found that accumulators of the bladder type can be made lighter than accumulators of the diaphragm type, and it i with bladder type accumulators that this invention is concerned.

One of the tests to which all accumulators must be subjected is the application of a hydraulic test pressure which is usually double or triple the systempressure, when all air is removed from the accumulator. In such tests the bladder completely collapes, folding back upon itself and being pressed against the air inlet. To prevent the bladder from being extruded into the air inlet, and-thereby damaged, metal discs are inserted in the bladder to bridge or cover the air inlet hole. Therefore, means must be provided to center the metal discs upon collapse of the bladder so that they will fit over thealr inlet. Another very important reason for centering the lower half of the bladder. within the upper half relates to the problem of stretch. At low temperatures most or the synthetic rubbers suitable for use in hydraulic systems are quite brittle and stretch should be avoided. For this reason the lower half must fit evenly into the upper half and not be cocked at an angle where one wall might grab the other and form a'chord which would be stretched.

A further reason for promoting even collapse of the bladder relates to the trapping of fluid. For greatest volumetric efficiency the upper half of a bladder must stick closely to the accumulator shell so that no oil pockets will be formed. Therefore. the upper half of the bladder must be held closely to the shell, particularly at the midsection where th fold" takes place upon the collapse of the bladder. I

Also. means should be provided to cause a radius oi bend in the bladder at the point where tremely brittle at very low test temperatures and may crack ii a sharp bend is imposed upon it.

The present invention satisfies these require ments, and in general comprises a bladder which has a reinforcement along the lin of folding. The reinforcement causes the stationary part of the bladder to maintain its shape, preventing the trapping of oil, and centering the discs. It is often desirable to make the stationary portion of the bladder thicker than the flexible part, to aid in maintaining the shap of th stationary portion. In such cases the thick wall may terminate abruptly at the section of folding, and when the thinner flexible part folds, there is an appreciable radius oi bend which prevents cracking of the bladder material at low temperatures. In such a bladder the reinforcement is preferably imbedded in the stationary part of the bladder near the abrupt termination of the thick portion. In other constructions, an internal head is provided to give an appreciable radius of bond. in which case the reinforcement may be placed in the bead.

It is therefore an object of the invention to provide an accumulator bladder having its stationary portions reinforced to aid in maintaining its shape.

It is an. object of the invention to provide an accumulator with a bladder which will center metal discs over the air inlet of the accumulator.

Another object is to provide a bladder with an internal head which has stiffening means to hold the beaded portion of the bladder against the accumulator shell.

Still another object is to provid an accumulator-bladder which will simultaneously provide a radius of bend for the bladder material and also center metal discs with respect to an air inlet.

In the drawing forming a part of this specification:

Figure 1 is an elevation view, in full section, of

an accumulator oi the type embodying the present invention; and

Figure 2 isa fragmentary view of an accumulator shell and bladder showing a modification of the invention: and

Figure 3 is a sectional view of a mold for the bladder of Figure 2, showing one step in the forming-process.

Referring to Figur l, a shell in has welded to the bottom thereof a threaded hydraulic outlet fitting i2 through which hydraulic fluid enters and leaves the accumulator. Welded to the upper threaded at 18 and provided with a shoulder l8 and an inwardly projecting lip 20. Fitted within shell Us a bladder 22 having a preformed shape substantially like the interior of shell I. Formed on the upper end of bladder 22 is an outwardly projecting lip 24 which hooks over the inwardly projecting lip 20-of collar I4. The bladder 22 is preferably formed of an upper molded part 26 and a lower molded part 23 vulcanized together along the tapered surface 25. It will be noted that the upper half 26 of the bladder 22 is thicker than' the lower half 23. The lower half 23 may be tapered in section from the bottom of the thicker half to the bottom where it may be thinner. The thick upper half 26 terminates abruptly in a curved end 29. .Molded within curved end 29 is a continuous solid spring 21 which stilfens the end 29 and, being circular, acts as a compression member to hold the upper portion of the bladder against the shell l0. Secured to the bottom of bladder 22 is a lower disc 28 and an upper disc 30 held together by a screw 32. Lower disc 28 fits over hydraulic outlet l2 when the bladder is fully extended as shown in full lines, and upper disc 30 fits over the. air inlet as shown in dotted lines.

Placed wlthin collar :4 is a plug member 34 which rests on shoulder l8 and which fits snugly against the upper end of bladder 22 and holds bladder lip 24 in contact with collar lip 29. An annular nut 36 is threaded into collar l4 to hold plug 34 in place. A cotter pin 38 passes through collar I4 and fits in a slot 49 in nut 36 to lock nut 36 in position. Plug 34 has a central hole 42 2,se7,24e- H fluid under full pressure is then pumped in therethrough into which is threaded an air valve element 44.

In inserting the bladder 22 into the accumulator shell for assembly, opposite sides of the bladder and spring are pressed together and the bladder rolled about this elongated shape. The elongated mass is thrust into the opening of collar l4 and then allowed to uncoil, at the same time being manually straightened. The spring 21 is highly desirable because of practically no yielding under compression. This insures that the bladder 22 will at all times fit closely the shell l9, preventing the trapping' of liquid. The spring 21 may also be inserted in the bladder after it is molded by molding an annular cavity therein and fitting the spring into the inside of the end 29.

In operation, air is inserted into the accumulator through valve element 44 and the bladder assumes the general shape as shown in full lines. There it will be noted that lower disc 28 bridges the opening of hydraulic outlet !2, so that the air pressure will not force the bladder into the outlet I2 and damage the bladder by extrusion. Outlet I2 is then connected to a hydraulic system including a pump, and hydraulic fluid under pressure enters the accumulator forcing the bladder 22 upwardly until the air is compressed to a pressure equal to the hydraulic pressure. The thinner. more flexible part of the lower half yields first, collapsing regularly into the upper half so that a rolling motion is promoted which prevents trapping of fluid in the lower-half. There'- after, hydraulic fiuid'will be added to or subtracted from the accumulator according to the demands of the hydraulic system and-the pres-- sure available from the pump of the hydraulic system. At all times spring 21 aids in holding the upper bladder portion 26 against shell I0, preventing the trapping of liquid in that region.

When it is desired to test the accumulator, the air valve 44 is opened allowing all air to escape from the inside of the bladder 22. Hydraulic through fitting l2 andthe bladder gradually collapses, the thin lower half of the bladder projecting upwardly into the thicker upper half of the bladder, which maintains its position against the shell Ill because of its thicker section. The end 29 guides the lower half evenly into the upper half of the bladder because it is a thickened and reinforced portion, which will resist deformation to a relatively greater extent than the thinner wall of the lower half. The final state is that shown in broken lines in Figure 1, wherein the lower half of the bladder is pressed tightly against the upper half, and the disc 30 is centered over hole 42. It will be noted from an examination of these broken lines that there is an appreciable radius to the bend about end 29.. This radius is very important in preserving the blad der because at a low temperature such as 65 R, which may be encountered in actual use, the bladder material becomes somewhat brittle and often cracks if folded fiat upon itself without a radius being provided for the bend.

The bladder of Figure 2 differs from that of Figure 1 in that a bead replaces the curved end 29, and the spring, which is inserted in the bead, is of the coiled type instead of solid metal. A bladder 4| fits the shell l0 closely and has a thick upper portion 43 and a thin lower portion 45 with an inwardly projecting bead 46 formed at the juncture of the two portions. Imbedded in bead 46 is a continuous coiled spring 48. The bead 46 gives an appreciable radius of bend to the bladder when the lower half is folded inside the upper half as shown in broken lines.

. The mold for making the bladder 49 of Figure 2 is shown in Figure 3. The mold is composed of an outer member 50 and an inner member 52 having an annular recess 54 for forming the bead. A piece of uncured bladder material 46A is placed on the inside of recess 54 and the continuous spring .48 is placed over it. Thereafter the bladder material is poured into the mold and cured, part 46A being formed integrally there-. with. The mold part 52 is preferably made in several parts which may be removed through the. mouth of the cured bladder. This prevents stretching the opening of the bladder around the inner mold to remove it. The bladder may be of any relatively flexible material, such as plastic or other rubber-like substances. The coiled spring construction permits the manufacture of a one-piece bladder.

The invention has been described in detail with references to particular embodiments thereof. It is not limited to these embodiments, nor otherwise limited, except by the terms of the following claims.

I claim:

1. A bladder type accumulator comprising a shell having a liquid opening, abladder secured in said shell, means to apply a compressible fluid on one side of said bladder, the other side being exposed to the liquid admitted through the liquid opening, one part of said bladder being thick and adapted to remain substantially stationary in said shell, the other part of said bladder being thinand relatively flexible so that it will telescope into said thick portion, said thick portion forming a curved end at the juncture with the thin portion so that a pad of material is formed about which thethin portion may fold with an appreciable radius of bend to prevent cracking at low temperatures, and a reinforcement in said curved endand having a generally round transverse. cross section, and a reinforcement at the end opposite the end afllxed, said bladder also having an internal annular bead to centralize said reinforcement on said opening about which the bladder is fitted and to provide a radius of bend when said bladder is folded upon itself, and spring means reinforcing said annular bead to prevent collapse of the same. i

3. A bladder type accumulator comprising a shell having a hydraulic opening, a flexible bladder secured in said shell, means to apply a gas to one side of said bladder, the other side being adapted to contact liquid admitted by the hydraulic opening, said bladder having a stationary portion and a flexible portion which is adapted to telescope into said stationary portion, an 'internal bead on said bladder substantially at the line of juncture of the two portions, so that an appreciable radius of bend will be present when the portions are telescoped, and reinforcing means at said bead to cause the bladder to maintain its shape so that folding will occur at the juncture of the portions.

4. An accumulator having, in combination, a rigid container having openings at opposite ends, a bladder of molded flexible material disposed within said container and having one end secured to the container and communicating with one of said openings, an inturned annular rib of rounded cross-section molded around said bladder intermediate the ends thereof, and a flexible wire reinforcing member, embedded in said rib.

5. An accumulator comprising a shell having an air opening and a hydraulic opening, a flexible bladder secured therein and separating said air opening from said hydraulic opening, said bladder having a thickened portion normally conforming to the shell and a thinner portion adapted to telescope into said thickened portion, said thickened 4 portion terminating abruptly forming a termination line which allows the thinner portion to fold with an'appreciable radius of bend when the portions are teiescoped, and spring means of material substantially stifler than the bladder material reinforcing said thickened portion adjacent said termination line to resist collapse of same. I

6. A bladder type accumulator comprising a shell having a liquid opening, a bladder secured in said shell having a stationary portion which flts the shell closely and having a flexible portion adapted to telescope into the said stationary portion, and spring means of material substantially stifl'er than the bladder material reinforcing said bladder at the line of juncture of the portions, so that the random collapse of the stationary por,

tion is avoided.

NICHOLAS m: KISS.

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