US2743741A - Hydraulic accumulator - Google Patents

Description

Jan

U it d St e ten HYDRAULIC ACCUMULATOR Lewis R. rd, St. Lambert, Quebec, Canada, assignor to Techron Limited, a company of Canada Application September 29, 1952, Serial No. 312,049

4 Claims. (Cl. 138-31) The present invention relates to hydraulic accumulators. Without intending to restrict its field of usefulness, this invention is especially suited for use in aeroplane hydraulic systems.

- In order to provide a reserve of stored-up hydraulic energy in a hydraulic system whereby system pressure may be maintained approximately constant for a short period of time, against sudden or emergency demands which may be beyond the capacity of the pump or hydraulic generator supplying the device employed, until the demand slackens or the pump can catch up to demand, it is common practice to embody an accumulator in the hydraulic system.

Such accumulators may be of a variety of types. Some may consist of weights suspended about and/or acting upon a ram or piston acting upon the hydraulic system. Others may constitute a generally cylindrical or bulbous type of container or chamber wherein there is contained both hydraulic fluid and a gas under pressure.

In some of these prior art devices, the forces of gravity permit an arrangement whereby the heavier hydraulic fluid may occupy the lower or bottom portion of the enclosing chamber with the gas occupying the upper portion of the chamber.

Since sudden demands may exhaust the fluid available in the fluid-containing portion of the accumulator and permit the gas under pressure (which provides the reserve pressure stored energy) to escape, and since it maybe desirable for a variety of reasons to prevent the mixing of the gas under pressure and the hydraulic fluid, it is generally found desirable to separate the gas under pressure from the hydraulic fluid or oil. In some accumulator constructions this achieved by means of a resilient or elastic type-ofdiaphragm, sometimes of rubbei'or plastic, or a similar sack,-bag or envelope, fixed about its edges to the, enclosing container.

In other constructions, this separation is achieved by means of a suitably glanded piston which is free to move within the accumulator but separates theoil or hydraulic fluid which is in contact with'its" one face from the gas under pressure which'is in contact with its opposite face. Accumulators of this type are generally of a cylindrical over-all fon'n having a circular crossse'ction with parallel inner walls wherein the piston slidably fits so as to separate the hydraulic fluid under pressure from the gas under pressure.

There are certain disadvantages to such an arrangement in that the gas may escape past the glands of the floating piston and become mixed with the hydraulic fluid in addition, the pressure of the gas, for example, air, may vary considerably with temperature variations as may be encountered say, for example, in an aeroplane or other airborne device utilizing a hydraulic system.

In aeroplane service, in addition to the preceding objections, an accumulator which depends upon the compression of a gas, in a system operating at the relatively high pressures such as are commonly employed in such service, would be of large bulk and weight in order to achieve the requisite compression of the gas.

This in turn would increase the problems mentioned above, and would produce others, for instance, such an accumulator might be objectionable unless the accumulator can remain in an upright attitude, which can not be assured in such service.

The present invention aims to provide an accumulator of somewhat similar type to that outlined above, but in which the usual gas supply under pressure is replaced by a liquid in resilient compression, thereby reducing greatly the accumulators weight and bulk, and in which the pressure responsive element, be it a piston, a diaphragm or any equivalent element need not alone constirate the separator between the resilient liquid and'the systems pressure fluid.

The invention in its broadest aspect contemplates the use of what has been termed a liquid spring," that is to say, a body of liquid wholly filling a closed chamber and compressible resiliently by means of the movement into that chamber of a plunger. Thus in practical eflect the pressure responsive element which is acted upon by the hydraulic system fluid in the accumulator will be provided with an elongated extension or plunger of relatively much smaller diameter and effective area which will pass through and be sealed tightly within a hole opening through a suitable partition into a second chamber wholly filled with a liquid. Thereby a given system pressure, which may be taken as the normal pressure, will effect movement of the plunger into the liquid-filled chain ber to a position of equilibrium, thereby compressing the liquid therein. This does not require nor effect compression of the systems hydraulic liquid, because the systems unit pressure on the pressure responsive element is too low, yet the total pressure thereon is so magnified by the large difference in effective area as between the same and the plunger that the plunger will compress the liquid within the liquid-filled chamber. A given increase in system pressure moves the plunger farther into the liquid-filled chamber, further compressing the liquid therein, and conversely, upon a given decrease in system pressure the stored energy of the compressed liquid within the liquid-filled chamber is transmitted from the plunger to the pressure-responsive element and so to the system hydraulic liquid, tending to maintain the normal pressure on the latter.

Having thus generally described the nature of the inventiomparticular reference will be made to the accompanying drawing wherein accumulator constructions embodying the invention are illustrated largely diagrammati,

cally, and in which:

Figure 1 is a longitudinal axial sectional view of an accumulator construction which illustrates the principles of the invention applied in one form.

Figure 2 is a similarlongitudinai sectional view illustrating the accumulator construction in a somewhat moditied form. 5

"Withparticulaflreference to Figure 1' of the drawing an accumulator construction embodying the invention is shown as comprising a cylinder it) which preferably has a circular cross section and which is open one end. An outwardly extending flange 12 may surround the open end, to enable a cylinder head 14 to be suitably secured to close the cylinder, as by means of bolts with a packing if sealing 11 placed between the flange i2 and the head The cylinder end cap 14 is bored and may be tapped as indicated at 16 to provide an entry port adapted to receive a fluid pressure line 18 from the hydraulic system. The interior of the cylinder 10 is shaped to provide a first chamber 20 and a second chamber 22. The two chambers are separated by a partition 24, to receive which Patented May 1, a

the chamber 20 may be tapped and the complementall threaded cylinder head or block 24 is engaged therein to form the liquid-sealed partition between the chambers 26) and 22. The partition 24- is axially apertured, and may be tapped to receive a suitable packing gland 25, which includes an axial opening adapted to receive a piston extension or plunger 26. The plunger 26, in the form shown, is integral with and extends from a piston 23 which is slidably mounted in chamber 22 of the cylinder 19. in effect the plunger extends through and is tightly sealed in the partition 24, as it projects into chamber 20. Suitable rin s or glandslitl are provided on the piston 28 so as to seal the latter as it slides within the cylinder chamber 22.

. With this arrangement, when pressure fluid from the hydraulic system enters chamber 22, it causes movement of the piston 28, which in turn causes pioneer 26 to move into chamber 213 until parts reach a posi -n of equilibrium. By so doing, the volume of the fluid in chamber 23% is decreased, thereby resiliently compressing the liquid in chamber 20. Upon decrease in system pressure the sostored energy acts on plunger 26, tending to force the plunger and piston 23 outwards toward end cap 14, and maintaining system pressure approximately constant for a brief time.

The construction in Figure 2 is similar to that previous-- ly described, with the exception that the plunger 126 carries an axial end piece or extension 129 which passes through a glanded opening iii. in the end of chamber 129. This not only serves to keep the piston rod in axial alignment but also permits the use of a larger diameter plunger 126. The eiiective area of the plunger, subject to pressure within the chamber 12 is the difierence between the cross-sectional areas of the plunger proper, at 126, and of the extension 129, which, as can be seen, is still a small fraction of the eiiective area of the piston within its chamber 122.

While movement of the piston 28 towards the right may cause some compression of air within the space between the piston and the partition 24, this is minor in etiect as compared to the compression of the liquid within chamber 26'. Since the liquid from chamber 2t} must leak first into this space, and thence past the piston 23, before it can mix with the system liquid within the chamber 22, and vice versa, such admixture even if objectionable is extremely unlikely, given a good seal at 25.

I claim:

1. A hydraulic accumulator for use in hydraulic systems, comprising housing means defining a first closed chamber wherein all available space is filled with a liquid, a plunger penetrating and glanded in the wall of said chamber, and movable thereinto towards a position of equilibrium, to compress the contained liquid, said housing means defining also a second closed chamber having a port for connection to the hydraulic system and for admission of pressure fluid therefrom, a pressure-responsive member within said second chamber, exposed on one face to system pressure and of an effective area many times the effective area of the plunger within its chamber, to be moved by such pressure towards a position of equilibrium, and an operative connection between said pressure- I to move them into and to maintain them mutually in their positions of equilibrium, and to transmit movement of the pressure-responsive member under the influence of increase in system pressure to the plunger to further compress the liquid which fills the first chamber, and vice versa, to transmit stored pressure in the first chamber to the pressure-responsive member upon decrease of system pressure, to maintain pressure in the second chamber, and in the connected system, elevated.

2. A hydraulic accumulator for hydraulic systems, comprising a housing and a partition therein defining a first chamber wholly filled with liquid, and a second chamher, a port adapted for connection to the system and located to admit system pressure into said second chamber, a pressure-responsive member within said second chamber, exposed at one face to and capable of movement in a direction lengthwise of the chamber under the influence of pressure fluid admitted by way of said port, a plunger and means operatively connecting said plunger to and for movement conjointly with said pressure-responsive iember, said plunger penetrating and being glanded in said partition and closing said first chamber, for movement into said liquid filled first chamber, and being of an effective area which is a small fraction of the effective area of the pressure-responsive member in its chamber, said plunger through said operative connection serving to maintain said pressure-responsive member, under normal operating conditions, in a predetermined position Within the second chamber, the parts being so arranged that upon the occurrence of any-tendency for system pressure to drop, the energy stored by compression of liquid in t e liquid-filled chamber due to movement of the plunger thereinto is transmitted, through the operative connection, from the plunger to the pressure responsive member, tending to maintain system pressure within the second chamher.

3. A hydraulic accumulator as in claim 2, wherein.

References Cited in the file of this patent UNITED STATES PATENTS 117,043 Burr July 18, 1871 594,787 Gallagher Nov. 30, 1897 611,823 Steier Oct. 4, 1898 991,977 Guyton May 9, 1911 1,035,386 Prescott et al. Aug. 13, 1912 2,333,095 Dowty Nov. 2, 1943 2,346,667 Dowty Apr. 18, 1944

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