Abstract:
A pressure retention valve with integrated valve is disclosed. The pressure retention valve with integrated valve includes a housing; an outer piston positioned in the housing; a main seal between the outer piston and the housing; an inner piston positioned in the outer piston, the inner piston having a bore containing a valve; a spring between the housing and a top of the outer piston; an ambient bore in the housing above the main seal; an outlet in the housing below the main seal; and a vessel connection in the housing adjacent to the bore of the inner piston. Methods of supplying fuel to a gas consuming system using the pressure retention valve are also described.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to a high pressure tank system, and more particularly to a high pressure tank system with a pressure retention valve with an integrated valve. 
     The tank vessel is a key component in a high pressure storage system. High pressure storage systems are used in a wide variety of applications including vehicle applications, such as vehicles run by hydrogen, or compressed natural gas (CNG). It is desirable to use fiber composite vessels (known as “type 4” vessels) for the tank because they have a good storage to weight ratio. Type 4 vessels have two layers: an outer layer, made of a carbon fiber matrix for example, designed to bear the mechanical load; and an inner layer, or liner, made of a bubble of plastic or aluminum, designed to prevent leaking. 
     To ensure that the liner is firmly supported by the outer layer, a minimum pressure should be maintained in the tank at all times. If pressurizing is started from an initial pressure below the minimum pressure, the liner might rupture, and the contents would flow through the outer layer into the environment. 
     Conventional gas tank systems use an electrical pressure sensor signal to maintain the minimum pressure. The signal is evaluated in a vehicle controller. If the minimum pressure is reached, the tank valve(s) are closed. This system is an active system, requiring a controller, pressure sensor, algorithm, and electrical power to control the minimum pressure. The residual non-usable gas amount depends on the accuracy of the pressure sensor. However, the pressure sensors have a tolerance limitation which has to be considered, and they do not have good accuracy at low pressure. In addition, drift of the sensor signal can occur over time. Due to the high deviation in the low pressure range, a significant pressure safety margin has to be added to the nominal minimum operation pressure. This leads to a reduction in the amount of usable hydrogen/gas mass, and thus to a lower range for the vehicle. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention is a pressure retention valve with integrated valve. In one embodiment, the pressure retention valve with integrated valve includes a housing; an outer piston positioned in the housing; a main seal between the outer piston and the housing; an inner piston positioned in the outer piston, the inner piston having a bore containing a valve; a spring between the housing and a top of the outer piston; an ambient bore in the housing above the main seal; an outlet in the housing below the main seal; and a vessel connection in the housing adjacent to the bore of the inner piston. 
     Another aspect of the invention is a method of supplying fuel to a gas consuming system. In one embodiment, the method includes providing a tank vessel, the gas consuming system connected to the tank vessel by a pipe, a refueling line connected to the pipe between the tank vessel and the gas consuming system, and a pressure retention valve with integrated valve connected to the pipe between the tank vessel and the refueling line connection, the pressure retention valve comprising: a housing; an outer piston positioned in the housing; a main seal between the outer piston and the housing; an inner piston positioned in the outer piston, the inner piston having a bore containing a valve; a spring between the housing and a top of the outer piston; an ambient bore in the housing above the main seal; an outlet in the housing below the main seal; and a vessel connection in the housing adjacent to the bore of the inner piston; selecting a minimum operating pressure for the tank vessel; when a tank vessel pressure is greater than the minimum pressure, the tank vessel pressure lifting the inner piston from a bottom of the housing and opening a path from the vessel connection to the outlet, a top of the inner piston remaining in contact with the outer piston and lifting the outer piston, and supplying fuel to the gas consuming system; and when the tank vessel pressure is less than the minimum pressure, the tank vessel pressure being insufficient to lift the inner piston from the bottom of the housing or being insufficient to maintain the inner piston in the lifted position, closing the path from the vessel connection to the outlet, the top of the inner piston remaining in contact with the outer piston, and ending the supply of fuel to the gas consuming system. 
    
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
         FIG. 1  is an illustration of one embodiment of a tank system with the pressure retention valve with an integrated check valve. 
         FIG. 2  is an illustration of one embodiment of a pressure retention valve with an integrated check valve and its operation when the minimum pressure is reached. 
         FIG. 3  is an illustration of the normal operation of the pressure retention valve with the integrated check valve shown in  FIG. 2 . 
         FIG. 4  is an illustration of the operation of the pressure retention valve with an integrated check valve shown in  FIG. 2  during fueling. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention optimizes the operating range of a high pressure gas tank with a minimum operation pressure. The gas tank system includes a pressure retention valve with an integrated valve. The valve operates as a self-contained tank vessel shut-off valve when the minimum pressure is reached, and it provides valve functionality to permit fueling of the tank. 
     This allows the minimum vessel pressure to be controlled mechanically. It reduces the minimum pressure tolerance compared to a conventional electrical pressure measurement and shut-off system. This results in a lower pressure safety margin to minimum allowed vessel pressure, and consequently either a higher range or a smaller tank system with equal range. 
     The pressure retention valve with the integrated valve reduces the complexity of controlling the minimum pressure in the vessel because pressure sensors and related connectors, wiring, controller, and software are not needed. There are no solenoids or other electrical components near the vessel or the fueling line. The minimum vessel pressure can be maintained even when the electrical system is inoperable or disconnected. There are no electromagnetic compatibility problems. It reduces costs and requires less service because there is no need to compensate for pressure sensor drift. It is more reliable and safer than the prior art control. 
     The combination of the pressure retention valve and the valve in one housing reduces the number of parts and the number of piping connections and sealings to ambient. The advanced sealing construction, which involves sealings without relative movement, results in a highly reliable valve with reduced service operation, and very low friction. 
       FIG. 1  shows a feed system  10  for gas consuming system  15 , such as a fuel cell. The feed system includes one or more tank vessels  20 . Each tank vessel has a shutoff valve  25 . The tank vessel(s)  20  are connected to the fuel cell  15  by a pipe  30 . During normal operation the feed flow is from the tank vessel(s)  20  to the fuel cell  15 . There is a check valve  35  connected to the pipe  30  to allow refueling of the tank vessel(s)  20 . During fueling, the flow is from the check valve  35  to the tank vessel(s)  20 . There is also a pressure retention valve with an integrated valve  40  between the tank vessel(s)  20  and the fuel cell  15 . 
     The pressure retention valve  40  is shown in more detail in  FIGS. 2-4 . The pressure retention valve  40  includes a housing  45 . The housing  45  has a narrower upper portion  50  and a wider lower portion  55  with a shoulder  60  between the upper portion  50  and the lower portion  55 , and a bottom  65 . 
     There is an outer piston  70  with a top  75 , sides  80 , and a flange  85  extending outward from the sides  80 . Between the shoulder  60  of the housing  45  and the flange  85  of the outer piston  70 , there is a main seal  90 . The main seal  90  can be an o-ring, for example. 
     There is an inner piston  95  with a top  100 , sides  105 , and a flange  110  extending outward from the sides  105 . The inner piston  95  has a upper bore  115  and a wider lower bore  120 . The lower bore  120  contains a check valve spring  125  and check valve ball  130 . 
     There is a seal  155  between the top  100  of the inner piston  95  and the underside of the top  75  of the outer piston  70 . There is a seal  160  between the flange  110  of the inner piston  95  and the bottom  65  of the housing  45 . 
     There is a vessel connection  165  in the bottom  65  of the housing  45  which connects the tank vessel(s)  20  to the pressure retention valve  40 . The vessel connection  165  aligns with the lower bore  120  of the inner piston  95 . 
     There is an outlet  170  in the side of the lower portion  55  of the housing  45 . The pipe  30  connects the outlet  170  with the fuel cell  15  and the check valve  35  which allows refueling of the tank vessel(s). 
     There is an ambient bore  175  in the side of the upper portion  50  of the housing  45 . 
     The main spring  180  in the upper portion  50  of the housing  45  exerts pressure on the upper side of the top  75  of the outer piston  70 . The adjusting screw  185  is used to adjust the main spring  180 . 
       FIG. 2  illustrates the operation of the pressure retention valve  40  when the minimum pressure condition is reached (p tank &lt;p min ). The tank pressure exerts pressure on the effective area  195 . However, the resulting force is too low to lift the inner piston  95 . The opposing closing force is the sum of the main spring  180 , and ambient pressure pressing on the upper area  200 . The main seal  90 , and seals  155 ,  160  have enough pre-load to guarantee leak tightness. The adjusting screw  185  is used to change the pre-load of the main spring  180 , which sets the desired closing pressure, p min , of the outer piston  70 . At normal operation, the force balance between the outer  70  and the inner piston  95 , based on pressure and spring force, results in a direct contact between the two pistons. Therefore, there is no disconnection between the inner piston  95  and the outer piston  70 , and the refueling path is closed by seal  155 . 
       FIG. 3  illustrates the operation of the pressure retention valve  40  in normal operation, i.e., when the tank vessel pressure is greater than the minimum operating pressure (p tank &gt;p min ). In normal operation, the tank delivers hydrogen to the fuel cell. The tank pressure exerts pressure on the effective area  195 , resulting in a force lifting the inner piston  95 . The top  100  of inner piston  95  is in contact with the underside of the top  75  of the outer piston  70 . The opposing closing force is the sum of the main spring  180 , ambient pressure (the pressure through ambient bore  175 ) pressing on the upper area  200  of the outer piston  70  and the squeezing of main seal  90 . When the tank pressure is high enough, the inner piston  95  lifts along with the outer piston  70 , and hydrogen flows from the vessel connection  165  to the outlet  170 . 
       FIG. 4  illustrates the operation of the pressure retention valve  40  during refueling (p anode &gt;p tank ). The fueling pressure at the outlet (or anode) is higher than the tank pressure, and it is applied to effective area  205 . Thus, the outer piston  70  moves upward and disconnects from the inner piston  95 . Seal  155  does not provide a seal because of the space between the outer piston  70  and the inner piston  95 , and the pressure difference over the check valve spring  125  and check valve ball  130  opens the refueling path. The refueling path remains open as long as the refuel pressure force on the effective area  205  is greater than the sum of the ambient pressure applying upper area  200 , main spring  180 , and main seal  90 . 
     It is noted that terms like “preferably,” “commonly,” and “typically” are not utilized herein to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present invention. 
     For the purposes of describing and defining the present invention it is noted that the term “device” is utilized herein to represent a combination of components and individual components, regardless of whether the components are combined with other components. For example, a “device” according to the present invention may comprise an electrochemical conversion assembly or fuel cell, a vehicle incorporating an electrochemical conversion assembly according to the present invention, etc. 
     For the purposes of describing and defining the present invention it is noted that the term “substantially” is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term “substantially” is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.