US2480558A - Accumulator - Google Patents

Description

N. DE KISS ACCUMULATOR Aug. 30, 1949.

Filed March 9, 1944 A 5.1 .eorqr/A/G ran/r52:

IN V EN TOR.

ATTORNEY Patented Aug. 30, 1949 2,480,558 Al .GUMULA'roR Nicholas de Kiss, North Hollywood, Calif., assignor, by mesne assignments, to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application March 9, 1944, Serial Ne. 525,705

3 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.

Fhis application is a --con'tinuation-'in-part of my application Serial No. 495,711, filed July 22, 1-943, now Patent No.' 2,'3-78,467, June 19, 1945, and entitled Accumulator bladder.

The usual airplane hydraulic :system has a power driven :pump which is continuously operated. There :are many devices operated by the fluid :under :pressure from :the pump, but since they are operated intermittently the required liquid may ;be "less .or .greater than .the output of the pump. When the .liquid demandis ,less than :the pump -;outp,ut, liquid is stored under pressure-in an accumulator, .and when the accumulator is filled, the jp lpzoutput is .bypassed to the reservoir. When the-liquid demand-exceeds thecapacity of the ,pump, the accumulator supplies thenecessary liquid under pressure. Thus one purpose-of an accumulator is to permit the use-of a small pump for a hydraulicsystem with momentary demands in excess of the capacity of .the .pump. a

.In generaL-accumulators comprise a shell having an air chamber and a hydraulic chamber with a flexible partition between the air. and the hydraulic fluid so that the hydraulic ffluidwill notibe contaminated by having theair dissolve into 'it. The hydraulic Jfluid is under pressure from a pump and acts against compressed air which hasbeen placed in 'the air chamber. "The compressedair exerts a constant pressure on the liquid'but is compressible-so-that varying quantities of liquidmaybe stored in the accumulator. Since accumulatorshave ahigh internal" pressure, a spherical shape offers-the greatest strength for the least amount ofmetal and for this reason most accumulators are spherical. The fiexlble partition separating the oil and air maybe a diaphragm or abladder, 'bothof whichareusually formed of synthetic rubber. 'Ithas been found thatzaccumulatorsof the bladder type are much lighter in :weight 5 than accumul ato'rs of the diaphragm-type. .Thezpresent invention relatesito bladder type accumulators.

-A bladder accumulator of the typezto whichthe invention applies hasa bag shaped bladder for-med of a flexiblemoveable, half andna stationaryhalf. If the volume ,of hydraulic fluidincreases .the flexible section telescopes into the. rigid section, compressing "the airwhich is maintained on.the inside ofthe'bladder. Since it'islimportant that the volumetric 'efliciency .is maintained .7 at all timeathe bladder must fit the inside of the spherical shell very {closely when the bladder is fully extended so that there will be complete eliminatiOnbf-thefluid whenfluidis withdrawn from-the hydraulic chamber. When the fluid is added to the accumulator the flexible part of the bladder should telescope in an orderly fashion into the. more rigid ,portion so that cavities will not be formed which will create pocketsof the trapped liquid when the bladder thereafter expands .or extends due to the subtraction of liquid. The present invention relates to a bladder formed in such a .Way that it will collapse in an orderly fashion, and expand in an orderly fashion to prevent trapping .Of fluid. Various attempts have been made to promote anorderly collapseanjdexpansion of the flexible portion .of the bladder to prevent trapping of fluid. For example, the walls of the ,fiexibleportionlhave'beenmade much thinner than the .walls of'the rigid portion. The rigid and flexible portions have been ,made er differing materials or composition. Also, the stationary portion of the bladder hasbeen reinforced with steel springs or other devices to render itinflexible. ,Another attempt consistsof the tapering of the walls ofthe flexible ,portionso that the cross section of the wall will be the thinnest in the part where it is desired to promote the collapse first. The present invention consists in .making the center of the flexible portionof'thebladder flat instead of curved. A spherical object will not collapse readily when subjected to uniform fluid pressure, even though it be made of a flexible material. The flatting of the otherwise spherical shape of the bladder reduces or eliminates the structural arch strengthof the flexible portion, causing theflatted portion to telescope first before the otherflexible portions collapse. "The flatted portion must stretch an appreciable amount to touchthe inside of-the spherical shell, andby placing it directly over the hydraulic outlet all fluid will. be excluded from the accumulator before the hydraulic outlet-is covered.

-It1is thereforean object of the invention to control the collapse of a generally spherical bladder-bycontrolling'theshape of the bladder.

Itis anotherv objectof the invention to control the collapse of a generally spherical bladder'by flatting-that part'of the spherical shape which is to-be telescoped or collapsed-first.

Another object of-the invention is to provide an accumulatorbladder having a flatted portion and of suflicient size to weaken the structural arch of a generally spherical'bladder.

Still another object of the invention is to provide an accumulator so shaped that during elastic stretching of the bladder it progressively contacts the shell walls and excludes all liquid.

Other objects and advantages of the invention will be apparent in the following description and claims:

The drawing forming a part of this specification is an elevation view in full section of an accumulator having a bladder made according Referring to the drawing, a generally spherical shell 19 has fine holes l2 drilled in the bottom and a threaded fitting I4 is welded to the shell around the holes. A collar 16 is welded to the upper part of shell and has an internal shoulder i8 and a protruding internal flange 20. Seated on shoulder 18 is a cover plate 22 held in position by a nut 24 engaging internal threads on collar l5. Cover 22 is axially drilled and retains an air valve 26 and a porous metal plug 28.

Placed within shell 10 is a bladder 30 which is preferably formed of an oil resistant, rubber-like material such as Buna-S. The bladder has a stationary half 3| and a flexible half 33 having a flatted lower portion 32. Formed on the inside of bladder 30 at the midpoint is a bead 34 which forms a pad of material about which the bladder can fold when it completely collapses. This feature is important since most bladder materials are extremely brittle at low temperatures, such as at -60 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 of collar l6. Plate 22 snugly fits the top and inside of flange 36, securely looking it, and the bladder as a whole, to the shell I0. In operation on a 1,000 p. s. i. hydraulic system, air under a pressure of about 300 p. s. i. is forced into the interior of bladder through valve 26. This flattens bladder 30 tightly against the shell ill. The accumulator then is connected to the pressure passes into shell Hi, The liquid forces the bladder 30 upwardly until the air is com pressed 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 It. This condition results only when the lower part of the bladder is partially telescoped within the upper part, as shown by the upper broken lines in the figure. Thereafter, the air is compressed and expanded according to the liquid demands of the hydraulic system. The air exerts a continuous pressure on the liquid by means of the bladder which pressure never falls below the charging pressure of 300 p. s. i. Varying air charges are used depending on the hydraulic system, the higher air 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 to accommodate varying volumes of liquid.

If the flexible portion 33 of the bladder does not collapse regularly, the stationary portion 3| may be forced from its close contact with the shell 10. When this occurs, there is always the danger that oil may be trapped in pockets when the bladder is later extended. Also, the flexible portion 33 may dimple asymmetrically and create a pocket when it later starts to extend. The present invention tends to promot the regular collapse of telescoping of the bladder because of the flatted portion 32. This flatted portion decreases the structural strength of the otherwise spherical shape of the bladder and gives a point of least resistance when the flexible portion of the bladder is subjected to a uniform fluid pressure, Thus, the center por-' tion 32 will always give in or collapse first, and since the telescoping action is initiated at a central point it is more likely to continue thereafter in a regular fashion. Also, on extension.

The extent of the flatted portion 32 may vary considerably depending upon specific bladder designs. The dimensions shown in the figure represent the limits of practicable designs for the flatted portion. In the figure it will be noted that the flatted portion has a diameter approximately equal to the spherical radius or one half of the diameter of the bladder, and this represents the outer limit of flatted area. The inner limit which has been found practicable, is one fourth of the diameter of the bladder or one half of the spherical radius. This range of flatted portions on a bladder from one fourth to one half of the bladder diameter represents practical limits and not necessarily operational limits. For this reason these limits should best be defined as approximate for purposes of the claims appended hereto.

It will be noted from the drawing that the flexible portion 33 of the bladder does not contact the shell in its lower regions when in a normal, or free, position. In order for the bladder to be fully extended as shown in dotted lines when all liquid is eliminated from the accumulator, the bladder must stretch slightly, which approximates about 5%. The stretching of the rubber is likely to take place uniformly in the bladder material of the flexible portion because of the generally spherical shape. Since the portions adjacent to the bead 34 have only a slight amount of stretching until they contact the wall of shell In this region will make the first contact. The contact of the bladder with th shell therefore will be progressive from the bead to the hydraulic outlet 14. Thus, the divergence of the flexible part of the bladder from the wall of shell ii] causes the stretching to take place progressively if the normal divergence increases from the bead 3 1 to th hydraulic outlet Hi. This diverging construction of the bladder is particularly well suited for bladders having a flatted portion. The flatted portion is the portion of maximum stretch and is therefore the last portion to contact the hydraulic outlet M. The flat portion therefore is placed directly over the hydraulic outlet where liquid will be squeezed out of the accumulator by the bladder before this flatted portion contacts the holes i2 and stops further hydraulic flow from the accumulator.

The diverging wall must nevertheless approximate a spherical form. Shown in the drawing is one desirable dimension for this divergence. A rotating center of one fifth of the spherical radius defines a circle which is a rotating center for a secondary radius. This secondary radius is about four fifths of the spherical radius and has radial centers on the rotating center. Thus the lower half 33 of the bladder contacts the shell I0 near bead 3 3, but thereafter diverges an increasing amount. The flatted portion 32 aids in the diverging structure as explained above.

Although the invention has been described with reference to particular embodiments thereof, it is not limited to these embodiments nor otherwise except by the terms of the following claims.

I claim:

1. An accumulator bladder for use in a generally spherical accumulator shell, said bladder having an opening and being adapted to be secured to said shell adjacent said opening; a first zonal portion of said bladder adjacent said opening being of generally spherical curvature and so dimensioned with respect to said shell as to fit against the wall of the shell and the remaining portion of the bladder being flexible and adapted to telescope into said first zonal portion; said flexible portion comprising a second zonal portion of generally spherical curvature joined at one edge to said first zonal portion; the end of said flexible portion opposite said opening being flat and at least as thin as said second zonal portion to form a. structurally weak portion to control the telescopic action of said flexible portion into said zonal portion in response to pressure against Said flexible portion.

2. An accumulator bladder as described in claim 1 in which the diameter of said flat end is at least one fourth and not substantially in excess of one half the bladder diameter.

3. An accumulator bladder according to claim 1 in which said second zonal portion is of progressively smaller radius from the edge joined to said first zonal portion to the end joined to said flat end.

NICHOLAS DE KISS.

REFERENCES CITED Ihe following references are of record in the file of this patent:

UNITED STATES PATENTS

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