Internal accumulator for hydraulic systems

Accumulators normally are teed into existing conduits and require large amounts of space or are placed in spool type bores having a spring biased piston slidably disposed therein. Most times these accumulators require a bladder that is vented to the atmosphere or a fluid chamber connected to a reservoir. In the subject invention, an accumulator 24 is provided that has a fluid filled member 36 which can be disposed in a closed chamber 32 of a housing 30 and connected to a source of pressurized fluid. The fluid filled member 36 has a fixed maximum surface to volume ratio and is capable of being compressed when subjected to a pressure higher than the pressure within. The accumulator may be integral with other components in the hydraulic system 10 and can be made with varying volumetric capacities and varying precharged pressures in order to match the requirements of the hydraulic system.

TECHNICAL FIELD 
This invention relates generally to accumulators and more specifically to 
accumulators located within hydraulic systems that are an integral part of 
the system. 
BACKGROUND ART 
Accumulators for use in hydraulic systems are well known. These 
accumulators normally use a chamber having one end filled with a gaseous 
fluid and the other end connected to the hydraulic fluid with an 
elastomeric member separating the gas from the hydraulic fluid. In most 
applications, these types of accumulators are large in size and require 
extra space in order to place them in systems that are many times limited 
in space. Other types of accumulators have been used in order to conserve 
space. These types use a special spool type bore having a piston and a 
spring disposed therein to bias the piston in one direction. These types 
are also very expensive to incorporate in a hydraulic since they require 
special controlled size bores and expensive machining. In the above types 
of accumulators, it is normally necessary to provide a vent to the 
atmosphere/reservoir or at least provide a pre-charge gas pressure. 
The present invention is directed to overcoming one or more of the problems 
as set forth above. 
DISCLOSURE OF THE INVENTION 
In one aspect of the present invention, an accumulator is provided and 
adapted for use in a hydraulic system having a source of pressurized 
fluid. The accumulator includes a housing defining a closed chamber 
therein connected to the source of pressurized fluid by a conduit and a 
hollow, fluid filled member having a relatively fixed maximum surface to 
volume ratio and cable of being compressed.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to the drawings, and more particularly to FIG. 1, a hydraulic 
system 10 is illustrated and includes a source of pressurized fluid 12, 
such as a hydraulic pump, a directional valve 14 connected to the source 
of pressurized fluid by a conduit 16, a fluid actuator 18 connected to the 
directional valve 14 by respective conduits 20,22, and respective 
accumulators 24 of a plurality of accumulators connected to the respective 
conduits 16,20,22. Each of the accumulators 24 has a conduit 26 that 
connects the respective accumulator 24 to the appropriate conduits 
16,20,22. Even though a plurality of accumulators 24 are illustrated, it 
is recognized that in some systems it may not be necessary to have all of 
the illustrated accumulators 24 and likewise some systems may require more 
accumulators depending on system needs. Even though the respective 
accumulators 24 are illustrated as being connected externally to the 
respective conduits 16,20,22, it is recognized that the respective 
accumulators 24 could be an integral part of the directional valve 16, the 
actuator 18, or other system components, such as hydraulic manifold 
blocks, without departing from the essence of the subject invention. 
Additionally, it is recognized that in order to make the accumulators 24 
an integral part of the system, it is necessary only to provide a drilled 
or cored opening with a passage or conduit 26 connecting the drilled or 
cored opening with the source of pressurized fluid 12. 
In the subject hydraulic system, the pressure in any conduit 16,20,22 may 
be considered as being a source of pressurized fluid 12. Consequently, any 
of the accumulators 24 may be disposed in any portion of the hydraulic 
system 10. As noted above the accumulators 24 may be integral with any 
system components. When the accumulators 24 are integral with the system 
components, the closed chamber 32 is formed in the component by a drilled 
passage or the like and the hollow, fluid filled member 36 is placed in 
the drilled passage. In some systems, such as integrated hydraulic 
systems, several different hydraulic components are disposed in one 
manifold block. Therefore it could be beneficial to provide a drilled 
passage therein that receives the member 36 and the needed passage 34 or 
conduit 26 is also an integral part of the manifold block. 
Since each accumulator 24 of the plurality of accumulators are the same, 
only one will be described in detail hereafter. The accumulator 24 
illustrated in FIG. 2 includes a housing 30, a closed chamber 32 defined 
therein, and a passage 34 connecting the closed chamber 32 with the 
conduit 26, and a hollow, fluid filled member 36 disposed in the closed 
chamber 32. In the subject embodiments, the fluid filled member 36 is a 
gas filled member. However it is recognized that the fluid filled member 
could be filled or partially filled with a liquid. The gas filled member 
36 has a non-extensible cover 38 that maintains a fixed maximum surface to 
volume ratio at a predetermined pressure level of the pressurized gas 
contained therein. The gas filled member 36 is capable of being compressed 
when subjected to an external pressure that is greater than the pressure 
within. 
The housing 30 is generally cylindrical in cross-section and defines a 
longitudinal axis 40. The gas filled member 36 has a shape generally the 
same as 5 the shape of the housing 30 and has a total volume less than the 
volume of the closed chamber 32. 
Referring to FIG. 3, another embodiment of the subject accumulator 24 is 
illustrated. Common elements have like element numbers. In the arrangement 
of FIG. 3, a plurality of hollow, gas filled members 36 are disposed in 
the closed chamber 32. Each member 36 of the plurality of gas filled 
members is a generally spherically shaped member 36. Each member 36 could 
be the same size as illustrated or each could be different in size or a 
mix of equal and varied sizes. 
Referring to FIGS. 4 and 5, another embodiment of the accumulator 24 is 
illustrated. Common elements have like element numbers. The hollow, gas 
filled member 36 disposed in the closed chamber 32 is a multi-sided member 
having a plurality of apexes 42 that extend parallel with the longitudinal 
axis 40 of the housing 30. The gas filled member 36 illustrated is shaped 
generally like a five pointed star, but it is recognized that various 
other multi-sided members could be utilized without departing from the 
essence of the subject invention. In order to ensure that the multi-sided 
member is generally an inextensible member, respective chords 43 are 
embedded at the inner apexes along the longitudinal length and secured one 
to one another generally at and along the longitudinal axis 40. 
Referring to FIGS. 6 and 7, another embodiment of the accumulator 24 is 
illustrated. Common elements have like element numbers. The housing 30 and 
the gas filled member 36 of FIGS. 6 and 7 are elliptically shaped along 
the longitudinal axis 40. A rigid member 44 is disposed within the gas 
filled member 36 and has opposed sides 46,48 and a plurality of openings 
50 defined therein. The opposed sides 46,48 are in intimate contact with 
opposed portions of the inner surface of the gas filled member 36. The 
intimate contact lies general parallel along the longitudinal axis 40. 
It is recognized that various forms of the subject invention could be 
utilized without departing from the essence of the subject invention. For 
example, the hollow, gas filled member 36 could be an elastomeric member 
having a non-extensible "skin" to maintain the desired fixed maximum 
surface to volume ratio. Likewise, even though the accumulators 24 are 
illustrated diagrammatically as being large in size, it is recognized that 
the accumulators 24 are generally very small in size and are normally 
integral with other components within the hydraulic system 10. 
Additionally, the gas filled member 36 of the various embodiments could be 
filled or partially filled with a fluid having a volume and/or viscosity 
change when in the presence of an electrical field. Substituting such a 
fluid for the gas in the above embodiments would create an electrically 
selectable and dynamically variable device whose damping and 
compressibility characteristics could be modified continuously to suit 
specific control system needs. The diagrammatic representations are for 
illustrative purposes only. 
INDUSTRIAL APPLICABILITY 
During operation of the hydraulic system 10, pressurized fluid is directed 
from the source of pressurized fluid 12 through the directional valve 14 
to the desired end of the actuator 18. The pressurized fluid in the 
respective conduits 16,20,22 is directed to the associated ones of the 
accumulators 24 through the respective conduit 26. 
In the event of a failure in the source of pressurized fluid 12, the 
accumulator 24 connected to the conduit 16 provides a volume of 
pressurized fluid to the directional valve 14 until the pressure in the 
conduit 16 decreases to a level below the precharge of the accumulator 24. 
In systems where the source of pressurized fluid 12 is at a remote 
distance from the directional valve 14, the accumulator 24 can be 
positioned close to the directional valve 14. Consequently, when the 
directional valve 14 is moved to a position directing pressurized fluid to 
the actuator 18, any sudden rush of fluid to the actuator 18 can be 
supplemented by the accumulator 24 without permitting a decrease in the 
pressure of the fluid in the conduit 16 that might otherwise occur due to 
the frictional losses of the flow of fluid between the source of 
pressurized fluid 12 and the remotely located directional valve 14. 
The accumulators 24 connected to the respective conduits 20,22 act to 
provide a volume of fluid to the actuator 18 to offset leakage in the 
actuator 18, to provide a damping or cushion to overcome pressure spikes 
developed in the respective conduits 20,22 during operation, or to provide 
a damping function to absorb the high loads attributed to the actuator 18 
reaching the end of its travel. 
In the subject embodiments, the accumulators are normally small in size and 
integral with other components of the system 10. Each of the accumulators 
24 have a volumetric capacity in the range of 320-1250 cubit millimeters 
(approximately 0.5-2 cubic inches). It is recognized that the volumetric 
capacity could be larger than that noted above depending on system 
requirements and permissible space. 
Referring to the embodiment of FIG. 2, since the conduit 26 and the passage 
34 are connected, the pressurized fluid in the respective conduits 
16,20,22 is in communication with the closed chamber 32 and in effective 
contact with the hollow, gas filled member 36. Once the pressure acting on 
the outer surface of the gas filled member 36 exceeds the pressure of the 
precharged gas, the gas filled member 36 compresses. The compression of 
the gas filled member 36 increases the usable volume of the closed chamber 
32 and likewise increases the pressure of the gas within the gas filled 
member 36. 
In the embodiment of FIG. 3, the pressurized fluid acts on the outer 
surface of each of the plurality of generally spherically shaped elements 
36. By controlling the size and number of the generally spherically shaped 
elements 36, the hydraulic system can be closely "tuned" or controlled, as 
needed, in order to offset pressure spikes or cavitation. 
In the embodiment of FIGS. 4 and 5, the pressurized fluid acts on the outer 
surface of the multi-sided gas filled member 36. By using a multi-sided 
gas filled member 36, a greater surface area may be exposed to the 
pressurized fluid in the hydraulic system 10. Consequently, the size of 
the closed chamber 32 may be smaller while still maintaining the desired 
characteristics of the accumulator 24 for the hydraulic system 10. Since, 
it is more difficult to cause a spherical or cylindrical surface to 
collapse, the multi-sided gas filled member 36 has many external surfaces 
for the pressurized fluid to act on. 
In the embodiment of FIGS. 6 and 7, The pressurized fluid acts on the outer 
surface of the elliptical surface. By using an elliptical surface, the 
pressurized fluid acting on the external surface thereof causes the gas 
filled member 36 to more easily compress. The rigid member 44 disposed in 
the gas chamber functions to force the otherwise cylindrical member into 
an elliptical shape. The plurality of openings 50 permits unrestricted 
communication between opposite side of the rigid member 44. The gas filled 
member 36 is made generally by first placing the rigid member 44 inside 
the gas filled member 36, then sealing the ends at the same time that the 
inside of the chamber is filled and pre-pressurized with gas. In the 
subject embodiment, the gas filled member 36 could be, for example, a 
re-enforced elastomeric hose. 
In each of the above noted embodiments, the gas filled member 36 is sized 
and pre-pressurized to meet the requirements of a particular hydraulic 
system. The precharge of the gas is controlled to a predetermined level. 
In order to ensure that the fixed maximum surface to volume ratio is 
maintain, the gas filled members 36 can be maintained in a pressurized 
vessel until installed in a housing or system. 
The gas filled members 36 can be filled with gas in a controlled high 
pressure environment and when they are removed from the high pressure 
environment, the gas therein would be a pressurized gas at a predetermined 
pressure. In order to make the gas filled member 36 more dense, the gas 
chamber could be filled with a foam or other porous material. 
In order to provide a quick way of determining which gas filled members of 
a certain size to use in specific applications, each gas filled member 
having a different precharge could be identified by different colors or 
have other identifying marks thereon. 
In view of the foregoing, it is readily apparent that the accumulators 24 
described herein are easily made integral with other components of the 
hydraulic system 10 and the volumetric capacities and precharged pressure 
can be controlled to satisfy the requirements of the particular hydraulic 
system. Likewise, it is apparent that the respective accumulators 24 may 
be placed in various locations within the hydraulic system 10 either 
integral with other components or connected to existing conduits. 
Other aspects, objects and advantages of the invention can be obtained from 
a study of the drawings, the disclosure and the appended claims.