Patent Application
20090095366
This invention relates to hydraulic accumulators of the bladder type.
The inventor's prior U.S. Pat. No. 7,121,304, which is incorporated herein by reference, discloses a low permeation bladder accumulator utilizing a metal foil bladder coated with protective polymer. For application of such accumulators as energy storage devices in hydraulic hybrid motor vehicles, it is desired that the accumulators be able to last millions of charging and discharging cycles without need for repair. It is therefore desirable to provide structural improvements to obtain good durability and reliability of such accumulators. It is also desirable to provide for easy assembly of such devices.
U.S. Pat. No. 5,054,373 to Brault discloses a pressure vessel utilizing a diaphragm type flexible separator comprising an impermeable metal film sandwiched between two protective films that is purportedly durable through repetitive cycles of deformation. Brault further discloses a manufacturing method comprising separate fabrication of each flat layer, successively nesting the preformed layers inside each other in a vacuum to prevent air pockets forming between the layers, and then adhesively bonding the layers together in a press to form the diaphragm type separator. The Brault method's use of a press to bond the metal film layer to the protective layers is not viewed as a method for manufacturing or assembling that would be simple or practical when applied to a more three-dimensional or “bag-shaped” accumulator bladder which comprises a metal foil layer and a protective layer.
As used herein, a bladder refers to a balloon-shaped, cylindrical-shaped or bag-shaped separator that fills or compresses with pressure changes between the inside and outside of the bladder, and is generally anchored to a vessel wall at a neck/port at one end of the bladder. In contrast, a diaphragm separator is generally circular or dome-shaped, and anchored at its periphery to the vessel, and flexes somewhat up into one chamber or down into another chamber depending on differences in pressure.
One object of the present invention is to provide an accumulator bladder with extremely low permeation of gas at high pressures.
Another object of the present invention is to provide an easy method for manufacturing and assembly of such low permeation accumulator bladders.
Another object of the invention is to provide a bladder position sensor to help avoid an undesired accumulator shut-off in such accumulators.
With reference to
The preferred structure, and materials for bladder 21 will now be described. Bladder wall 30 of bladder 21 is preferably made with more than one layer as represented in
The foil surface 33 that is closest to the gas and foam within the bladder 21 may be either non-coated and exposed to gas in the accumulator or may be covered or coated with a protective laminate layer 34 that is breathable (i.e. readily permeable to gas) to avoid welting and tearing of the foil 32. In other words, if a low permeation coating or laminate were placed on the interior of the foil instead of a breathable layer, some gas that inevitably passed anyway through layer 34 to the surface 33 of metal foil layer 32 would be trapped between layers 32 and 34, and as the gas is cycled between high and low pressures (e.g. 5000 psi to 2000 psi) the gas compresses and expands accordingly. This would result in the permeated gas creating a bubble in that space that can grow and tear the foil 32 and thus cause gas permeation through the layers 32 and 31 of the bladder wall 30 as well (i.e., thereby resulting in a loss of gas-impermeability of bladder 21).
A method for assembling the accumulator 20 of the first embodiment of the present invention will now be set forth. In a first step, a metal foil or foil laminate bag utilizing at least metal foil layer 32 is pre-fabricated. The foil bag is preferably slightly oversized with relation to the interior volume of accumulator 20 such that the bag does not need to stretch to fill the interior volume of the accumulator. The foil bag is then inserted through fixture 22 into bladder 21, which may be comprised of only layer 31. An adhesive may be applied to the interior of bladder layer 31 to reduce relative motion and wear between the two bags.
An alternative and preferred method of assembling the accumulator 20 involves fabricating the bladder wall layer 31 in two or more parts to allow open access to the interior of the bladder. An adhesive is applied to the interior of bladder layer 31. Foil layer 32, optionally pre-bonded with a layer 34, is then applied to the interior of bladder layer 31 in the form of sheets dr strips. To cover the inside of the spherical/dome ends of bladder wall layer 31, overlapping triangular strips are preferably used. The bladder parts (e.g. the sleeve and two end domes) are then spliced together. At connection points (e.g., where an end dome and cylindrical portion join), the foil may be overlapped and then bonded (e.g. by means of a resistively heated band applied around the connections for a determined period of time).
For the adhesive in either of the two methods of assembly described above, paint-on or spray-on contact adhesives may be used. Preferably, a non-aerosol adhesive is applied (e.g., using a paint brush) to decrease the possibility of aeration/bubbles. As one example, a preferred commercially available paint-on adhesive Scotch-Grip #847L Nitrile-Rubber-based Rubber & Gasket Adhesive provides good adhesion between PET/foil and nitrile rubber. As a second example, commercially available Scotch-Weld #10 Neoprene-based contact adhesive provides adequate adhesion between D-Con foil and nitrile rubber. Applicant has found that other methods of applying foil (e.g., plating or vapor deposition) besides gluing have not been practical or effective in forming a durable gas-impermeable bladder.
Finally, as shown in the accumulator embodiment of
In a further alternative embodiment, the position sensor arrangement involving contact element 53 could be used in an accumulator using a bellows instead of a bladder, with for example a metal (or another material such as nylon) bellows such as that shown in
While particularly useful for high pressure accumulators in hydraulic hybrid motor vehicles 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.
From the foregoing it will also be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.
