Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
  • F15B1/00—Installations or systems with accumulators; Supply reservoir or sump assemblies
  • F15B1/02—Installations or systems with accumulators
  • F15B1/024—Installations or systems with accumulators used as a supplementary power source, e.g. to store energy in idle periods to balance pump load
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
  • B60K6/00—Arrangement or mounting of plural diverse prime-movers for mutual or common propulsion, e.g. hybrid propulsion systems comprising electric motors and internal combustion engines
  • B60K6/08—Prime-movers comprising combustion engines and mechanical or fluid energy storing means
  • B60K6/12—Prime-movers comprising combustion engines and mechanical or fluid energy storing means by means of a chargeable fluidic accumulator
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
  • F15B1/00—Installations or systems with accumulators; Supply reservoir or sump assemblies
  • F15B1/02—Installations or systems with accumulators
  • F15B1/04—Accumulators
  • F15B1/08—Accumulators using a gas cushion; Gas charging devices; Indicators or floats therefor
  • F15B1/24—Accumulators using a gas cushion; Gas charging devices; Indicators or floats therefor with rigid separating means, e.g. pistons
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
  • F15B2201/00—Accumulators
  • F15B2201/20—Accumulator cushioning means
  • F15B2201/205—Accumulator cushioning means using gas
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
  • F15B2201/00—Accumulators
  • F15B2201/30—Accumulator separating means
  • F15B2201/31—Accumulator separating means having rigid separating means, e.g. pistons
  • F15B2201/312—Sealings therefor, e.g. piston rings
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
  • F15B2201/00—Accumulators
  • F15B2201/40—Constructional details of accumulators not otherwise provided for
  • F15B2201/405—Housings
  • F15B2201/4053—Housings characterised by the material
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/60—Other road transportation technologies with climate change mitigation effect
  • Y02T10/62—Hybrid vehicles

Definitions

• This invention relates generally to accumulators for high pressure applications, and more particularly to high pressure accumulators of the piston-in-sleeye (or "piston
• Hybrid refers to the pombination of one or more conventional interna! combustion engines with a secondary power system.
• the secondary power system typically serves the functions of receiving and storing excess energy produced by the engine and energy recovered from braking events, and redelivering this energy to supplement the engine when necessary. This frees the internal combustion engine to operate more efficiently, while the secondary power system acts in concert with it to make sure that enough power is available to meet road load demands ' and any excess power is stored for later use.
• a hydraulic power system takes the form of one or more hydraulic accumulators for energy storage and one or more hydraulic pumps, motors, or pump/motors for power transmission.
• Hydraulic accumulators operate on the principle that, energy may be stored by compressing a gas.
• An accumulator's pressure vessel contains a captive charge of gas, typically nitrogen, which becomes compressed as a hydraulic pump pumps liquid into the vessel. The liquid thereby becomes pressurized and when released may be used to drive a hydraulic motor.
• a hydraulic accumulator thus utilizes two distinct working media, one a compressible gas
• gas shall refer to the gaseous medium and the term “fluid” shall refer to the liquid working medium, as is customary in the art.
• the gas travels with it, generally into a low pressure accumulator (or reservoir) where the fluid is stored until needed again.
• a significant quantity of gas may thus over time become trapped in the low pressure accumulator.
• the loss of this gas would nevertheless also represent a gradual depletion of the gas pre-charge of the high pressure accumulator and thus would lead to the need for occasional gas recharging (which would not be a desirable result for consumers, particularly for use in a motor vehicle application).
• such gas in the ' low pressure accumulator may also become entrained as bubbles or gas pockets in fluid that is later pumped back out, causing the pump to experience potentially damaging effects such as cavitation or torque fluctuations. Further, the accumulating volume of . gas reduces the effective fluid capacity
• Some elastic bladder materials have properties that
• poly-vinyl alcohol can be used on the gas side of the bladder, but even with such coatings
• Standard piston accumulators are also well represented in the art.
• the hydraulic fluid is separated from the compressed gas by means of a piston which seals against the inner walls of a cylindrical pressure vessel and is free to move longitudinally as fluid enters and leaves and the gas compresses and expands.
• the piston does not need to be flexible, it may be made of a gas impermeable material such as steel.
• the interface between the piston and the inner wall of the cylinder must be controlled tightly to ensure a good seal, and the degree of dimensional tolerance necessary to ensure a good seal increases the cost of manufacturing. It also
• Standard piston accumulator vessels tend to be made of thick, high strength steel and are very heavy.
• Standard piston accumulators have a much higher weight to energy storage ratio than either steel or composite bladder accumulators, which makes them undesirable for mobile vehicular applications (as such increased weight would, for example, reduce fuel economy for the vehicle).
• piston accumulators for the same capacity (i.e., size) and pressure rating are many times heavier (e.g., by up to 10 times) than an accumulator with a lightweight composite pressure vessel design, as would be preferred in such applications where accumulator weight is an issue. Therefore, despite their potentially superior gas impermeability, piston accumulators are largely impractical for vehicular applications. 4.
• Piston-in-Sleeve Accumulator Designs One piston accumulator concept, considered, for example, for military aircraft applications, utilizes a piston and sleeve assembly, in which the piston resides within and seals against a cylindrical sleeve that is separate from the inner wall of the pressure vessel.
• This piston-in-sleeve approach provides at least two benefits over the prior art for high pressure accumulators, namely (i) separating the pressure containment function of the vessel wall from its piston sealing function, allowing an effective seal to be pursued with a sleeve independently of issues relating to pressure vessel construction, and (ii) providing an intervening (aka "interstitial") volume between the sleeve and vessel wall which may be filled with the charge gas to provide a safety factor against explosion in the event of puncture of the pressure vessel (e.g., by a bullet in military combat).
• U.S. Patent 2,417,873 Huber 1947
• U.S. Patent 2,703,108 McQuistion. 1955
• Patent Re24,223 (Ford 1956), and later U.S. Patent 4,714,094 (Tovagliaro 1987) each teach the use of a piston and sleeve assembly on a high pressure accumulator.
• Such designs comprise a generally thickwalled strong cylindrical pressure vessel constructed of a steel alloy, and a metal sleeve which is thin relative to the vessel walls. The sleeve is permanently attached to the inner surface of one end of the pressure vessel near its circumference, creating (with the piston) a closed or "inside" chamber for the working fluid.
• the other end of the sleeve extends toward the other end of the vessel and is generally left open to create an "outside" chamber that consists of the open volume of the sleeve, the remaining volume of the pressure vessel, and the intervening/interstitial space between the outer wall of the sleeve and the inner wall of the pressure vessel, each filled with the gaseous medium of the accumulator.
• the sleeve In operation of these prior art piston-in-sleeve accumulator designs, the sleeve must be tightly retained and centered within the vessel to prevent radial movement, for example, due to vibrations in use with mobile (e.g. aircraft) applications. Sleeve movement would fatigue the rigid fixed end of the sleeve possibly leading to leakage due to cracking, distortion, or wear of the sealing gasket if one is present.
• the outer walls of the vessel must be thicker than would be necessary for pressure containment alone because the walls must be prevented from expanding and thus loosening the sleeve or distorting it from the true circular form necessary for piston sealing.
• Prior art piston-in-sleeve designs also uniformly contain the fluid within the closed (inside) chamber, with the charge gas residing on the other side of the piston and in the interstitial space between the sleeve and vessel wall.
• This fluid-inside, gas-outside arrangement is used in the prior art for at least two reasons.
• this arrangement is naturally preferable because it maximizes the fluid capacity and hence energy capacity of the device.
• the working medium that resides inside the sleeve may be discharged completely, while some portion of the medium outside the sleeve will always remain trapped in the interstitial space; because working capacity is determined by how much fluid may be discharged, it is a natural choice to have the fluid reside on the inside of the sleeve and gas on the outside.
• the Tovagliaro device still requires an internal metallic core to the vessel wall (in addition to the composite envelope, likely at least in part to resist permeation of the gas under pressure out through the composite vessel wall) and a thickened metal area at one (flat) end of the accumulator (to enable providing a removable end cap and to tightly retain and center the sleeve, as discussed above).
• the Tovagliaro device would still remain undesirably heavy for a hydraulic hybrid motor vehicle application, and would also entail significantly greater manufacturing cost than desired (e.g., because of complexity of the design and entailing vessel construction with both a composite envelope and metallic core and end).
• the internal metallic core (or liner) used in conjunction with composite materials would be unacceptable for use in hydraulic hybrid vehicles.
• the object of the present invention is to provide a high pressure piston and sleeve accumulator design that is lightweight, adaptable to service in mobile vehicles, and can be mass produced at low cost, while maintaining or exceeding the superior low gas permeability properties of state of the art prior art piston accumulators.
• the present invention utilizes a piston and sleeve design, but through various means enables use of a thoroughly lightweight and easy to manufacture composite pressure vessel therewith, thereby providing a lightweight low permeation high pressure accumulator and satisfying a long felt need for such an accumulator in the art.
• applicant meets these needs through one or more of various modifications from the piston accumulator prior art, including placing working fluid instead of charge gas between the sleeve and vessel wall, assembling and using the piston-in-sleeve device with domed vessel ends and without the aid of removable end caps, using fatigue-resistant plastic internal liner material, and/or providing means to withstand harmful effects of radial flexing of the composite vessel wall at high pressures.
• Figure 1 shows a sectional view of a preferred embodiment of the invention.
• Figure 2 depicts an alternate embodiment of the invention, in which the piston has an oil- or grease-filled double seal that is pressure balanced by means of a pressure balancing channel filled with grease.
• FIG. 3 depicts another embodiment of the invention, in which the double seal is
• Figure 4 shows an alternative piston embodiment for the present invention, with both bearings on the same (oil) side of the piston seal.
• Figure 5 presents an alternative embodiment for the piston sleeve of the present invention, utilizing S-shaped transitions through areas of stress on the piston sleeve.
• a lightweight composite cylindricaji outer pressure vessel 10 with rounded ends is presented.
• Suitable materials for vessel 10 comprise carbon fiber wrap, E-glass, or one of many other strong and lightweight materials, such as may be found for high pressure bladder accumulators of the prior art.
• Suitable materials for vessel 10 may include materials that are gas-permeable at high pressures (e.g., 5000 psi).
• Vessel 10 is preferably lined with a thin liner 12 made of fatigue-resistant plastic, but may also be made of
• Metal end bosses 12a and 12b reside at the ends of the vessel 10 to provide access to the interior of the vessel and are preferably embedded within liner 12, if liner 12 is provided.
• Non-permeable sleeve unit 13 resides within vessel 10 (and liner 12 if provided), and is thin relative to the wall of pressure vessel 10.
• Sleeve unit 13 is preferably welded to metal end boss 12a by means of a weld joint such as that depicted in the position of weld 15, or at a similar location such as at other points on the interior of metal end boss 12a.
• Other joining means for example, a threaded connection with an appropriate sealing means may alternatively be employed.
• Charge gas port 23 communicates with inner working medium chamber 24.
• Hydf ⁇ sailic fluid port 26 ⁇ $ ⁇ &t ⁇ nicates with outer working medium chamber 25, which includes interstitial volume 16 between sleeve 13 and liner 12 (or if no liner, between sleeves 13 and cylinder wall 10).
• Shutoff valve 27 resides in port 26 and acts to close port 26 as the fluid volume approaches zero.
• Piston 14 is slidably contained within sleeve 13.
• the aineir wo ⁇ Mng medium chamber 24 formed by piston 14 and sleeve 13 is filled with charge gas at a pressure typical of the art.
• Chamber 24 may also contain foam 40 to avoid heat hncrease m chamber 24 as the charge gas is compressed, as will be understood in the art. T&e addition of foam 40 in chamber 24 may also be utilized to provide structural support for sleeve 13 if desired.
• Outer chamber 25 is filled with hydraulic fluid.
• piston 14 will unove longitudinally within sleeve 13 in reaction to forces resulting from the balancing of pressure between the gasjn chamber 24 and the fluid in chamber 25. Charge gas is prevented from contacting the fluid by means of piston seal 19.
• Slider bearings 31 and 32 preferably encircle piston 14 and act to facilitate its longitudinal movement within sleeve 13.
• Sleeve 13 of the present invention additionally preferably contains a finite element analysis (FEA) engineered fatigue resistant, flexhsg end-dome section between the cylindrical portion of sleeve 13 and its attachment to Metal end boss 12a, to assure fatigue resistance associated with sleeve radial movement in response to vibrations (e.g., in vehicle travel).
• FEA finite element analysis
• the preferred example of such an end-dome uses classic "S shape" transitions 35 through areas of high stress for the sleeve, as shown in Figure 5 and as will be known and understood in the art.
• a preferred method to prepare the accumulator for operation begins by introducing fluid working medium into chamber 25 through fluid port 26 so as to cause interstitial space 16 and chamber 25 (which may be larger or smaller than depicted depending on the position of piston 14) to fill entirely with fluid to the exclusion of any residual gases that may be present from manufacturing and assembly.
• a charge gas such as nitrogen is then introduced through gas charge port 23 at a designated pre-charge pressure, perhaps for example 1000 psi.
• the pressure of the initial gas charge will cause piston 14 to move longitudinally toward the opposite end of the vessel, expelling fluid from chamber 25 as the piston sweeps through it.
• Valve bumper 29 will eventually exert pressure on shutoff valve stem 27 causing fluid port 26 to close and fluid to cease exiting.
• Fluid will continue to be present in interstitial space 16 and represents a volume of non- working fluid that will always be present in this space.
• charge port 23 is sealed by conventional gas valve means as is known in the art. In this manner the accumulator is brought to its proper pre-charge pressure.
• fluid is pumped into chamber 25 through valve port 26 by a hydraulic pump/motor or other means as is known in the art. Also as known in the art, this causes charge gas in chamber 24 to become compressed as fluid causes piston 14 to move into it.
• pressure vessel 10 will exhibit a natural tendency to expand slightly in diameter, particularly near its center.
• Utilizing oil instead of gas in the interstitial space 16 outside of the sleeve 13 in the present invention avoids gas loss problems that would otherwise occur from an attempted use of composite pressure vessel 10 in a high pressure accumulator of this type, as the gas is thus contained solely within 24 surrounded by non-permeable sleeve 13 and piston 14. Fluid (unlike gas) will not permeate from interstitial space 16 through composite pressure vessel 10 at high pressures, thus also eliminating the necessity for a non-gas-permeable metallic barrier between space 16 and composite vessel 10. Maintaining gas on the inside of sleeve 13 away from vessel wall 10 also reduces heat transfer from the compressed gas to outside of the vessel, therefore providing some reduction in overall energy loss for the system.
• piston 14 may take on the additional role of shaping the cross sectional area of sleeve 13 so as to cause it to conform to the shape of piston 14, thus ensuring a good seal regardless of any local deformations in the
• FIG. 2 depicts an alternative embodiment of the piston used with the invention, employing a dual seal design for the piston.
• Piston 14 is encircled by seals 19 and 20, which are separated by an oil- or grease-filled space 21 that also encircles the piston.
• the dual seals provide additional anti-permeation sealing above that of the single seal of the previous embodiment.
• pressure balancing passage 22 is provided to allow pressure communication between space 21 and fluid chamber 25.
• a non-flowing but pressure transmitting viscous medium such as (for example) a highly viscous grease is interposed in passage 22 in order that space 21 and chamber 25 do not physically communicate, but only reach a pressure balance via the interposed column of viscous medium.
• FIG. 3 depicts yet another embodiment that employs a similar pressure balancing dual seal.
• pressure balancing piston 30 is interposed in passage 22 instead of the viscous medium means employed in the previous embodiment, and similarly acts to prevent physical contact between media in space 21 and chamber 25 while providing for pressure balancing between the two.
• Figure 4 depicts a third embodiment of the piston for use with the present invention.
• bearings 31 and 32 are both located on the same side of the piston seal 19, preferably toward the fluid (oil) chamber's side of piston seal 19.
• both bearings will stay fully lubricated by the fluid (oil) from chamber 25 in operation, and therefore may reduce wear and debris formation that can otherwise result over time with use of a dry bearing.
• the sleeve 13 may be formed integrally with its own chamber end dome section and also integrally with the gas port 23 that supplies the chamber 24. This enables the sleeve 13 to be fixed within the vessel by inserting the sleeve unit within the socket for gas port 23, and reduces manufacturing effort and cost. Because the integral sleeve unit 13 does not need to be physically joined with an inner end surface of the vessel, it also helps enable use of vessels with a thoroughly composite construction. The effect of unit vibration on the fixed end of the sleeve 13 may also be reduced by allowing the thinner necked end portion of the sleeve unit to flex somewhat, thereby accommodating these forces without causing fatigue to a rigid joint.
• the aforementioned reduced stresses on the sleeve also obviate the need to involve the pressure vessel walls 10 in the function of centering or reinforcing the sleeve 13.
• the use of composite materials for the pressure vessel construction now becomes more practical, because effective sleeve centering and retention is no longer dependent on resisting pressure-related changes in the vessel diameter.
• the inner sleeve 13 may be very thin, because it need not support any substantial differential pressure, and thus may be inexpensively manufactured.
• the sleeve 13 may also be constructed of deformable material that is locally retained in a circular shape for sealing by a circular piston 14 as it moves longitudinally within the sleeve.
• the inner sleeve 13 may be fit relatively tightly into the outer pressure vessel 10 to maximize the potential storage space for the compressed gas and working volume for the accumulator size.
• Use of a thin sleeve fitting tightly within the pressure vessel (i.e., with minimum slip clearance between the sleeve and the pressure vessel's inside wall) at atmospheric assembly pressure is not done in the prior art.
• the invention is adaptable to service in mobile vehicles, is lightweight, and can be mass produced at low cost, while maintaining the low gas permeability properties of prior art piston accumulators: While particularly useful for high pressure accumulators for the reasons as discussed above, it will also be understood that the device of the present invention may be used for other purposes as well, including, for example, as a lower pressure accumulator for a wide variety of applications.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Transportation (AREA)
• Supply Devices, Intensifiers, Converters, And Telemotors (AREA)

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Citations (8)

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• 2005
  • 2005-03-07 US US11/074,147 patent/US7108016B2/en not_active Expired - Fee Related
• 2006
  • 2006-03-06 EP EP06748297A patent/EP1856437A2/en not_active Withdrawn
  • 2006-03-06 AU AU2006220676A patent/AU2006220676A1/en not_active Abandoned
  • 2006-03-06 CA CA002600321A patent/CA2600321A1/en not_active Abandoned
  • 2006-03-06 WO PCT/US2006/007877 patent/WO2006096620A2/en not_active Ceased
  • 2006-03-06 CN CN2006800074278A patent/CN101142434B/zh not_active Expired - Fee Related
  • 2006-03-06 JP JP2008500793A patent/JP4938757B2/ja not_active Expired - Fee Related

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