Abstract:
Hydrogen gas flow from high pressure storage to a lower pressure hydrogen-using device is managed using one or more axial flow pressure regulators comprising a cup-shaped housing with an inlet for high pressure hydrogen gas at one end of the flow axis and a closure with a low pressure hydrogen outlet at the other end of the flow axis. A piston head with a piston stem are aligned on the flow axis and a hydrogen flow passage is formed up the stem and through the piston head to the hydrogen flow outlet. One or more combinations of a corrugated tubular bellows (or like expansive sealing vessel) with static seals attaching one bellows end to the piston stem or head and the other bellows end to the housing or closure are used to accommodate axial movement of the piston while isolating and containing hydrogen gas flow from a high pressure chamber at a flow entrance to the piston stem to a low hydrogen pressure chamber at the piston head and closure outlet.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 61/040,804, filed on Mar. 31, 2008. The disclosure of that application is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention pertains to the delivery of hydrogen gas from a high pressure storage container to a hydrogen-consuming fuel cell, or other hydrogen-consuming or using device, at a lower pressure. More specifically, this invention pertains to a pressure regulator with a body and a piston defining a high pressure hydrogen chamber and a reduced pressure chamber and using a combination of bellows and seals to deliver hydrogen without leaks and with minimal friction. 
       BACKGROUND OF THE INVENTION 
       [0003]    Hydrogen is a clean fuel that may be used to produce electricity in a fuel cell. The automotive vehicle industry and others are interested in adapting hydrogen fuel cells for power generation. 
         [0004]    A hydrogen fuel cell is an electrochemical device that comprises an anode and cathode separated by and connected to a proton-conducting electrolyte. The anode receives a flow of hydrogen gas and the cathode receives a flow of oxygen or air. Many individual cells may be stacked in series flow arrangement to deliver an electrical current at a specified power level. The fuel cell may be operated to generate an electrical current to drive an electric motor or other power-consuming device. 
         [0005]    A fuel cell stack is operated by drawing hydrogen gas from a nearby storage vessel in which hydrogen is typically stored under relatively high pressure. One or more flow control pressure regulators may be employed to provide a pressure reduction of a hydrogen stream flowing from its high pressure storage to anode chambers of the fuel cell stack. The flow control pressure regulator(s) may be required to reduce hydrogen pressure from 30-700 bar tank pressure to 4-9 bar line pressure. Then, at an input manifold to the anode side of the fuel cell stack, the pressure may be further reduced from 4-9 bar line pressure to 1-2 bar anode chamber pressure. In each of these flow regulators the hydrogen flow rate may vary widely, e.g., between 0.02 and 2.0 g/s. 
         [0006]    The operating temperatures of the pressure regulators are subject to conflicting influences. The temperature in on-board hydrogen storage vessels may vary in a range from about −80° C. to 85° C., depending on driving cycle and filling status. After refueling, hydrogen temperature may be as high as 85° C. which is an upper limit for the materials of the vessels. Driving reduces the temperature in storage vessels as the gas expands and pressure decreases. If the weather is cold and hydrogen flow from storage high (for example, under full engine load), the remaining hydrogen cools significantly. Depending on the design of the storage system and environmental influences, the gas flow temperature may reach −80° C. when, for example, the ambient temperature is −25° C. and after thirty minutes of full power fuel cell operation. 
         [0007]    This substantial range in pressures and temperatures makes it difficult to control hydrogen gas flow. Moreover, pressurized hydrogen may react with some metal container materials and is capable of leaking through small openings. It has been difficult to design flow control pressure regulators that are effective and efficient in managing the flow rate of hydrogen from a storage vessel to the anode chambers of a fuel cell stack when the regulators may be subjected to such temperature and pressure cycling. 
       SUMMARY OF THE INVENTION 
       [0008]    A pressure regulator is adapted and provided for control of hydrogen gas flow from high pressure storage to a lower pressure hydrogen-using device. 
         [0009]    In an illustrative embodiment of the invention, the regulator has a body for accommodating a piston module (comprising a piston head and stem) and one or more combinations of a flexible corrugated tubular bellows with static seals fixing the tubular ends of the bellows in the regulator body as are described. One or more bellows of hydrogen impermeable material (e.g., thin sheets of stainless steel or polyethylene) are used to separate pressure chambers within the regulator. Other types of metallic or plastic, flexible and expansible vessels can be used to provide the function of a bellows. Preferably, the regulator body is round. 
         [0010]    The regulator body has a central longitudinal axis for hydrogen flow from one end of the flow axis to the other. The regulator body is adapted to accommodate reciprocal movement of the piston head and attached stem along the axis. One end of the pressure regulator body has an end surface with an opening and inlet passage for receiving higher pressure hydrogen gas. The inlet passage may terminate with a sealing surface within the body for engagement with the unattached end of the piston stem. The opposite end of the regulator body (with respect to the central flow axis) is open for assembly of the piston module and bellows and sealing elements in the body. When the regulator has been assembled, the regulator body is closed with a bonnet, lid, or other suitable closure member. The piston head lies adjacent the closure member. The closure member has an opening for the flow of lower pressure hydrogen from the regulator to another regulator or hydrogen-consuming device. 
         [0011]    The unattached end of the piston stem has an opening (such as a diametrical bore) and a central duct or bore for flow of hydrogen up the piston stem and through a central opening in the piston head toward the hydrogen gas outlet in the closure. The regulator body is shaped to form an internal chamber of higher pressure hydrogen around the piston stem to force hydrogen gas into the flow duct in the stem. The regulator body, piston head, and closure member also form an internal chamber of lower pressure hydrogen gas at the gas flow outlet from the regulator. 
         [0012]    In many embodiments of the invention, the regulator body will also be shaped to accommodate a coil spring (or other expanding device) to exert a predetermined force on the stem side of the piston head. The portion of the regulator body containing the spring is typically vented to the atmosphere so that this chamber of the body does not see hydrogen flow and is maintained at atmospheric pressure. But high pressure hydrogen acts on the piston stem and enters the axial flow passage through the stem and piston head. And lower pressure hydrogen acts on the piston head against the spring force. It is the response of the piston to spring force acting on one side of the piston head and hydrogen gas pressure acting on the other side of the piston head that prompts movement of the piston head and stem toward and away form the sealing seat of the hydrogen gas inlet. The regulator structure so far described accounts for the regulating function of the device. But means must be provided for preventing leakage of hydrogen within and from the regulator and for permitting low friction movement of the piston along the axis of the regulator. 
         [0013]    In accordance with some embodiments of the invention, a first tubular bellows of corrugated shape is used to confine higher pressure hydrogen gas around the piston stem and the opening into the stem passage. The first bellows may also prevent hydrogen from entering the spring-containing chamber of the regulator which is at nominal atmospheric pressure. One tubular end of the first bellows is attached to the regulator body using a static seal or its equivalent. The other end of the bellows is attached to the piston (head or stem or both) using a second static seal device or the equivalent. The parallel ridges and valleys of the flexible corrugated bellows tube permit it to readily lengthen and shorten in accommodation of axial movement of the piston module in response to hydrogen pressure differentials on opposite faces of the piston head. 
         [0014]    The bellows and seals may be formed of materials that are impervious to hydrogen gas and operable in the temperature and pressure environment of the regulator. For example, the corrugated tubular bellows may be formed of a stainless steel tube or a polyethylene (preferably ultrahigh molecular weight polyethylene) tube. Sometimes the bellows may comprise a metal layer and a polymer layer. The seals are typically in the shape of rings bonding the tubular ends of the bellows to adjacent body or piston surfaces. Such seals may be made of a suitable resilient polymeric material and may contain internal metal springs that energize or bias the bellows end against contacting surfaces to prevent leakage of hydrogen. In some embodiments a seal is formed by a seam weld between a bellows end and an adjacent regulator element. 
         [0015]    In other embodiments of the invention, a second combination of a tubular corrugated bellows and static end seals is used to confine hydrogen gas in the low pressure chamber between the piston head and gas outlet. One end of this second bellows is sealed to the perimeter of the piston head and the other end of the second bellows is sealed to the regulator body or closure member or both. The second bellows and seals may be formed of materials selected from the groups of materials that are found useful for the first bellows and its seals. 
         [0016]    In some embodiments of the invention, supporting rings on the outer or inner circumference of the high pressure chamber bellows may provide support for it. And in some embodiments of the invention the inside surface or outside surface (or both surfaces) of the bellows may be coated with a dry lubricant like boron nitride or diamond-like carbon for lubrication. 
         [0017]    Other objects and advantages of the invention will be apparent from detailed descriptions of preferred embodiments. In these descriptions, reference will be made to drawing figures which are briefly described in the following section of this specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a cross-sectional view of a high-pressure regulator having a bellows in each of the high pressure and low pressure chambers in combination with separate spring-biased static ring seals. 
           [0019]      FIG. 2  is a cross-sectional view of a high-pressure regulator having a bellows in each of the high pressure and low pressure chambers in combination with separate conventional static ring seals. 
           [0020]      FIG. 3  is a cross-sectional view of a high-pressure regulator having a bellows in each of the high pressure and low pressure chambers in combination with static seals formed as an integral part of each bellows. 
           [0021]      FIG. 4  is a cross-sectional view of a high-pressure regulator having a bellows in each of the high pressure and low pressure chambers in combination with spring-biased static seals that are formed as integral parts of the bellows. 
           [0022]      FIG. 5  is a cross-sectional view of a high-pressure regulator having bellows in each of the high pressure and low pressure chambers with spring-energized static seals that are part of the bellows. The low-pressure chamber bellows is welded to the piston. 
           [0023]      FIG. 6  is a cross-sectional view of a high-pressure regulator having bellows in each of the high pressure and low pressure chambers with the bellows in the high pressure chamber also acting as the piston spring. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0024]    In accordance with an embodiment of the invention, a pressure regulator described herein provides a regulator body that contains an interior piston assembly to control fluid flow through the regulator, especially hydrogen gas flow. The outlet pressure of the pressure regulator may remain substantially unaffected by variations in the relatively high inlet pressure by relying upon direct outlet pressure feedback to control the fluid pressure. A high pressure chamber is formed on one side of a piston head and a low pressure chamber on the other side. A combination of bellows and seals are used to define the chambers, thus minimizing leakage of hydrogen and facilitating low friction movement of a piston module. The pressure regulator uses a compressive force balance across the piston assembly to maintain the regulator outlet pressure at a predetermined pressure or set point. Examples of some preferred high-pressure regulators are described in the following specification. 
         [0025]    Referring now to  FIG. 1 , a cross-sectional view of a first embodiment of a pressure regulator  10  for a high-pressure gas dispensing system for a hydrogen fuel cell is shown. In general, and in this embodiment, high-pressure regulator  10  comprises a piston assembly or module  12  disposed within a substantially single or unitary round cylindrical body  14 . A round, generally flat, closure disk  16  (lid or bonnet) is bolted to body  14 . The round pressure regulator body  14  has a central round inlet passage  18  which extends along central axis  20  of regulator body  14 . Inlet passage  18  terminates in a valve seat  22 . The inlet face  24  or inlet passage  18  (or both) of regulator body  14  is adapted by means, not illustrated, to receive a tube or other conduit of high pressure hydrogen gas in a leak-free connection. 
         [0026]    Round closure member  16  has a central outlet passage  26  (on regulator body axis  20 ) for the flow of relatively low pressure hydrogen gas to anode surfaces of a fuel cell. Outlet passage  26  is also adapted by means, not shown, for a gas-tight connection with a hydrogen flow conduit. 
         [0027]    Piston assembly  12  comprises a relatively flat round piston head  28  centered on regulator body axis  20 . Piston head  28  is attached to one end of a round hollow piston stem  30  (or shaft) which is also centered on regulator body axis  20 . Attached (bolted in this example) to the upstream end (with respect to hydrogen flow) of piston stem  30  is a seal  32  of truncated cone shape adapted to engage inlet valve seat  22 . Piston stem  30  fits into a round cylindrical chamber  34  of regulator body  14 . A circumferential flange  35  on piston stem  30  loosely centers the piston stem from the adjacent cylinder body wall. Chamber  34  receives relatively high pressure hydrogen gas through pressure regulator inlet  18  and valve seat  22 . As illustrated in  FIG. 1 , the piston module  12 , including piston stem  30  is shown in an open position for receiving high pressure hydrogen gas in pressure regulator  10 . 
         [0028]    Piston stem  30  has a longitudinal axial bore-passage  36  with two right-angle diametrical bores  38  for admission of high pressure hydrogen gas from regulator body chamber  34 . Hydrogen gas flows through passage  36  into a relatively low pressure chamber  40  between the outer (downstream) surface  42  of piston head  28  and the inner surface  44  of closure member  16 . Low pressure hydrogen gas exits low pressure chamber  40  through pressure regulator outlet passage  26 . 
         [0029]    Pressure regulator body  14  has a radially outer chamber  46  shaped to receive a suitable spring  48  or other device for applying a force against reaction plate  50  bolted to the inside surface  52  of piston head  28 . The force of spring  48  tends to move the piston stem  30  away from valve seat  22  to admit high pressure hydrogen into the regulator  10 . Chamber  46  is shaped to receive, enclose, and seat one end of spring  48 . Chamber  46  is vented through vent passage  54  to the atmosphere. Thus, chamber  46  is maintained at substantially atmospheric pressure during operation of pressure regulator  10 . 
         [0030]    Spring  48  acts with a predetermined force on inside surface  52  of piston head  28  while hydrogen pressure in low pressure chamber  40  acts on the outside surface  42  of piston head  28 . Piston module  12  moves in reaction to any imbalances in these respective forces in operation of pressure regulator  10 . In accordance with embodiments of this invention, the low friction movement of piston module  12  and retention of flowing hydrogen in the pressure regulator  10  are managed by the use of suitable seals and one or more chamber defining bellows. 
         [0031]    A first bellows  56  separates high hydrogen pressure chamber  34  from ambient pressure chamber  46 . Bellows  56  is shaped like a corrugated round tube with radially extending flat ends  58 ,  60 . Bellows  56  may be suitably formed of a sheet material of, for example, stainless steel or ultrahigh molecular weight polyethylene that is impervious to hydrogen at the operating temperatures and pressures of the pressure regulator  10  and retains flexibility for its function that will be described further. 
         [0032]    Bellows end  58  extends radially outwardly from a radial groove of bellows  56  and is rigidly fixed to a corresponding internal shoulder  62  on regulator body  14  against an intervening C-shaped ring seal body  64 . Bellows annular end  58  is clamped against a side of a radially inwardly facing, C-shaped ring seal body  64  with a bolted clamp ring  66 . Ring seal body  64  comprises an internal spring  68  that prevents leakage of hydrogen through the attachment of bellows end  58  to shoulder  62  of regulator body  14 . 
         [0033]    Bellows end  60  is clamped between shoulder  70  of round piston stem  30  and piston head  28  with intervening C-shaped ring seal  72 . In this embodiment, C-shaped ring seal  72  has a smaller diameter than seal  64  but seal  72  is spring energized using a seal construction like that of seal  64 . The C-shaped body portions of seals  64  and  72  may be formed of a suitably flexible synthetic polymer material that is generally impervious to hydrogen. The internal spring members of these seals may be suitably formed of metal coils or bent sheet metal strips that are shaped in a known manner to bias the polymeric seal bodies against the bellows and adjacent regulator surfaces to be sealed. 
         [0034]    Thus, the parallel alternating ridges and grooves of corrugated bellows  56  permit bellows  56  to freely lengthen and shorten as piston module  12  reacts to hydrogen pressures in chambers  34  and  40  and to spring  48 . But seals  64  and  72  do not move; they function as static seals. Dynamic seal designs are not required in the pressure regulator of this invention because of the use of bellows. 
         [0035]    A second bellows  74  separates high pressure chamber  40  from ambient pressure chamber  46 . In this embodiment, bellows  74  is of larger diameter than bellows  56  but is of similar shape and function. Bellows  74  is shaped like a corrugated round tube with flat radially-extending ends  76 ,  78 . Radially inwardly extending bellows end  76  is fixed between reaction plate  50  and piston head  28  by spring energized, static, C-shaped ring seal  80 . Bellows end  78  is clamped between pressure regulator body  14  and closure member  16  using spring energized, static, C-shaped ring seal  82 . Seals  80  and  82  may be formed polymeric bodies and energizing springs like the constructions of seals  64  and  72 . 
         [0036]    Low pressure chamber bellows  74  (like high pressure chamber bellows  56 ) may be made of stainless steel or UHMW-PE sheet material or other suitably flexible and hydrogen impervious material. And again, the parallel alternating ridges and grooves of corrugated bellows  74  (like the corrugations of bellows  56 ) readily permits bellows  74  to lengthen and shorten as piston module  12  reacts to hydrogen pressures in chambers  34  and  40  and to spring  48 . 
         [0037]    The above described combinations of bellows with static seals for defining and sealing the high pressure chamber and the low pressure chamber of pressure regulator  10  confines hydrogen within the regulator and allows for free and responsive movement of the piston module. Direct sealing contact is not required between the piston head or stem and surrounding surfaces of the regulator body. The respective bellows move with the piston and confine the flowing hydrogen gas. Static seals may be employed that do not have to slide against a contacting surface as they function to retain the flow of hydrogen within regulator  10 . 
         [0038]    Other embodiments for fixing and sealing bellows members to pressure regulator components will be described with reference to drawing  FIGS. 2-6 . For simplicity of illustration the shape of the piston module and enclosing body members are not significantly changed and parts or components that are not changed are identified with the same numerals as are employed in description of pressure regulator body  10  of  FIG. 1 . However, different ways of sealing or fixing the ends of the respective bellows will be described. Where a feature of a bellows, a seal or other regulator component has been changed it is identified with a three digit number including, as the first digit, the number of the figure and, as the following two digits, the numbers generally associated with the part. For example, seals  264  and  272  described in  FIG. 2  serve a similar function, but are somewhat changed in shape or function from seals  64  and  72  described with reference to  FIG. 1 . 
         [0039]    In  FIG. 2 , high pressure chamber bellows  56  and low pressure chamber bellows  74  are of the same structure and materials as described in the embodiment of  FIG. 1 . The only difference in the  FIG. 2  embodiment is that pressure regulator  210  comprises static seals  264  and  272  used with high pressure chamber bellows  56  are not spring energized. Solid ring seals  264  and  272  may, for example, be made of aluminum or polytetrafluoroethylene. Likewise, solid ring seals  280  and  282  used with low pressure chamber bellows  74  are not spring energized. Solid ring seals may also be made of aluminum or polytetrafluoroethylene. 
         [0040]    In the embodiment of the pressure regulator  310  construction of  FIG. 3 , high pressure chamber corrugated tubular bellows  356  and associated static ring seals  364  and  372  are formed as an integral bellows/seal structure. The bellows/seal seal structure may be molded of a suitable polymer such as ultrahigh molecular weight polyethylene. Ring seal bodies  364 ,  372  are molded to the annular ends of bellows  356 . Likewise, low pressure chamber corrugated tubular bellows  374  is formed with integral ring seal bodies  380 ,  382  formed at the ends of bellows  374 . 
         [0041]    In the embodiment of the pressure regulator  410  construction of  FIG. 4 , high pressure chamber corrugated tubular bellows  456  is molded, or otherwise formed with integral ring seal bodies  464  and  472  at the annular ends of the bellows. Again, the bellows  456  and ring seal bodies  464  and  472  may be molded of polyethylene or other suitable material. In this embodiment, however, each of ring seal bodies contains a spring (as illustrated as spring  468  in seal body  464 ). Spring body  472  contains a like molded-in or implanted metal spring, such as those described in connection with the  FIG. 1  illustration of this invention. Similarly, low pressure chamber bellows  474  has integral ring seal bodies  480  and  482  at the ends of the bellows  474 . And ring seal bodies  480 ,  482  contain internal springs for urging seal bodies against adjacent surfaces of the pressure regulator  10 . 
         [0042]    In the embodiment of  FIG. 5 , piston module  512  of pressure regulator  510  does not include a reaction plate (like plate  50  in  FIG. 1 ) bolted to the upstream side of piston head  528 . Spring  548  bears directly against the upstream face of piston head  528 . 
         [0043]    One annular end of low pressure chamber bellows  574  is attached to the downstream face of piston head  528  with a linear (circular) seam weld  580 . Seam weld  580  replaces a static seal, like spring-energized ring seal  80  in  FIG. 1 . The other annular end of low pressure chamber bellows  574  is clamped between pressure regulator body  14  and closure member  16  with spring-energized static ring seal  582 . 
         [0044]    In this example, high pressure chamber bellows  556  is secured to regulator body  14  with spring-energized static ring seal  568  and to the upstream side of piston head  528  with spring-energized static ring seal  572 . 
         [0045]    In the embodiment of  FIG. 6  regulator body  614  of pressure regulator  610  has been modified to eliminate the use of a spring such as is illustrated at  48  in the  FIG. 1  embodiment and in  FIGS. 2-5 . In this example, high pressure chamber bellows  656  is adapted to apply a spring force in the upstream side of piston head  628 . For example, bellows  656  may be made with stainless steel such that the corrugated shape of the tubular bellows applies a suitable spring force for regulator function. 
         [0046]    In this embodiment, low pressure chamber bellows  674  is fixed at one end by seam weld  680  to the down stream face of piston head  628  and at the other end it is clamped between pressure regulator body  614  and closure member  16  with spring-energized static ring seal  682 . 
         [0047]    The pressure regulators of this invention are adapted for pressure reduction and flow control of a gas like hydrogen which tends to react with some materials and leak through small openings. The pressure regulators use a selected combination of bellows and static seals to enhance the performance of a pressure regulator to be used in managing the flow of hydrogen gas from a high pressure storage site to a low pressure application such as in anode chambers of a fuel cell. In some embodiments it is preferred to use a bellows in defining both a high pressure chamber and a low pressure chamber of the regulator. In other embodiments it may be preferred to use a bellows for one pressure chamber and a different means, such as dynamic seals, for the other chamber. Various combinations of bellows and static sealing means have been illustrated in this specification. But obviously other combinations of bellows and static seals may be used within the scope of this invention.