Abstract:
An improved system for providing fuel uses a centrifugal pump arrangement that provides dual pressure. The dual pressure pump assembly includes a centrifugal pump for supplying pressurized fluid to an associated downstream use, and an auxiliary pump stage for selectively boosting pressure of delivered flow. The auxiliary pump stage in one preferred arrangement includes a start and turbo-pump stage where inlet fuel from an associated airframe is fed to a centrifugal pump portion of the turbo-pump that outlets to an inlet of the centrifugal pump. The auxiliary pump stage in another arrangement includes a recirculation passage communicating with the outlet of the high-speed centrifugal pump and the turbine, and the outlets from the start and turbo-pump stage feed an inlet of the high speed centrifugal pump, and a flow valve is disposed in the recirculation passage. In still another arrangement, the auxiliary pump stage includes an electric motor for start-up.

Description:
BACKGROUND 
       [0001]    This disclosure relates to a fuel system for a jet engine application, and more particularly to a jet engine fuel pump arrangement that supplies different pressure needs of the system. 
         [0002]    Jet engine applications require high take-off pressure output. When applying a high-speed centrifugal pump technology to these jet engine applications, the pump generally becomes excessively large for the balance of operating condition requirements (e.g., idle, cruise, climb, etc.). The excessively large pump, in turn, creates a series of system issues revolving around the thermal impacts on the system. 
         [0003]    Jet engines typically use hydraulic power generated by the engine fuel system to power many variable geometry actuators of the engine. Many current jet engine fuel systems incorporate a component such as a servo fuel heater or similar means to keep the fuel supplied to the actuators (servo supply) above fuel system icing temperatures, for example ideally above 40° F., to avoid potential issues associated with ice formation. The servo fuel heater is typically located downstream of a fuel filter and upstream of an actuation control module which supplies pressurized fluid for low and high pressure actuators. 
         [0004]    Consequently, a need exists for a system and method that better addresses these competing system demands. 
       SUMMARY 
       [0005]    An improved system for providing fuel to a jet engine application is provided using a centrifugal pump arrangement that provides dual pressure. 
         [0006]    The system includes a dual pressure pump assembly having a centrifugal pump for supplying pressurized fluid to an associated downstream use. An auxiliary pump stage is operatively associated with the centrifugal pump for selectively boosting pressure of delivered flow to the associated downstream end-use. 
         [0007]    The auxiliary pump stage in one preferred arrangement includes a start and turbo-pump stage where inlet fuel from an associated airframe is fed to a centrifugal pump portion of the turbo-pump that outlets to an inlet of the centrifugal pump. 
         [0008]    The auxiliary pump stage in one arrangement includes a recirculation passage communicating with the outlet of the high-speed centrifugal pump and the turbine, and the outlets from the start and turbo-pump stage feed an inlet of the high speed centrifugal pump, and a flow valve is disposed in the recirculation passage. 
         [0009]    The auxiliary pump stage in an another arrangement includes a recirculation passage communicating with the outlet of the high-speed centrifugal pump and the turbine (and a flow valve is disposed in the recirculation passage), the outlet from the high speed centrifugal pump feeds (i) an inlet of a centrifugal start pump and (ii) selectively feeds the turbine portion of the turbo-pump (depending on the flow valve), and an outlet of the start pump boosts the pressure of the fuel directed downstream to the associated end use, and the outlet from the turbine is directed to an inlet of the high speed centrifugal pump. 
         [0010]    The auxiliary pump stage in one arrangement preferably includes an electric motor for start-up. 
         [0011]    The auxiliary pump stage preferably includes a recirculation passage receiving a portion of flow from an outlet of the centrifugal pump and directing the flow portion to an inlet of the centrifugal pump. 
         [0012]    In another arrangement, the auxiliary pump stage further includes a valve in the recirculation passage for controlling flow therethrough. 
         [0013]    The auxiliary pump stage further includes an ejector pump in a preferred arrangement that is interposed between the valve and the centrifugal pump inlet for receiving the flow portion from the centrifugal pump outlet and raising a pressure of inlet flow directed to the centrifugal pump inlet. 
         [0014]    One benefit of the disclosure is the ability to provide different pressure outputs from the centrifugal pump arrangement. 
         [0015]    Another advantage of the disclosure relates to potentially reducing system cost, weight, and envelope requirements by eliminating the need for a servo fuel heater or additional heat exchanger. 
         [0016]    Still another benefit resides in the ease with which the centrifugal pump arrangement can be incorporated into existing system designs. 
         [0017]    Still other features and benefits of the present disclosure will become apparent upon reading and understanding the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  schematically illustrates a fuel system that includes a first preferred embodiment of a two-pressure level pump arrangement. 
           [0019]      FIG. 2  schematically illustrates a fuel system that includes a second preferred embodiment of a two-pressure level pump arrangement. 
           [0020]      FIG. 3  schematically illustrates a fuel system that includes a two-pressure level pump. 
           [0021]      FIG. 4  schematically illustrates a preferred dual pressure high-speed centrifugal pump arrangement in a high pressure output mode. 
           [0022]      FIG. 5  schematically illustrates a preferred dual pressure high speed centrifugal pump arrangement in a low pressure output mode. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Turning first to  FIG. 1 , there is shown at least a portion of a fuel system  100  that includes a pump assembly or pump arrangement  102 . The pump arrangement  102  receives inlet fuel from an airframe  104  and delivers the fuel at a higher pressure to at least one downstream end use or end uses  106 ,  108 . More specifically, the first end-use  106  is generally referred to as a fuel control so that fuel is delivered by the pump arrangement through a fuel/oil heat exchanger  110 , and subsequently to a fuel filter  112 , where it is then delivered to the fuel control. Typically, fuel passes through the fuel filter  112  as directed to the fuel control  106  where the fuel is combusted as represented at  114 . A portion of the pressurized fuel from the pump arrangement  102  is likewise fed through the fuel/oil heat exchanger  110  and fuel filter  112  for delivery to the second end use, also referred to as an actuation control module  108 . This provides the desired pressurized fluid for low-pressure actuation represented at  120 , or high-pressure actuation as indicated at  122 . A servo fuel heater or heat exchanger  124  is provided upstream of the actuation control module  108  in order to sufficiently heat the fuel above a fuel system icing temperature, for example on the order of 40° F. However, and for reasons to be described in greater detail below, the servo fuel heater  108  may be eliminated with a corresponding savings in cost, weight, and envelope size requirements (and thus is represented with a dashed lead line). 
         [0024]    The pump arrangement  102  incorporates a dual pressure level high-speed centrifugal pump that combines a high-speed centrifugal pump stage  130 , and a start and turbo-pump stage  140 , a control or flow valve  150  to selectively provide recirculation of a portion of the pressurized fluid from the high speed centrifugal pump) 30  to the turbine portion of the turbo-pump, and an electric motor  160  to assist the start and turbo-pump stage. Generally, the valve  150  is used to select the use or non-use of the turbo-pump  140  schematically located either at an inlet  132  of the high-speed centrifugal pump stage ( FIG. 1 ) or at a discharge/outlet  134 ′ of the high-speed centrifugal pump stage ( FIG. 2 ). When the control valve  150  is open, the valve permits the application of a motive flow from the high-speed centrifugal stage discharge  134  to the turbo-pump motive port  142  and thereby causes the turbo-pump stage to raise the pressure to the inlet  132  of the high-speed centrifugal pump. More particularly, a centrifugal pump portion outlet  146  of the turbo-pump  140  is pressurized to a first pressure level by the application of motive power from the electric motor  160  and/or from the turbine portion of the turbo-pump stage when the control valve  150  is open. An outlet  148  of the turbine portion of the turbo-pump stage  140  is also connected or communicated to the inlet  132  of the high-speed centrifugal pump stage. In turn, the high-speed centrifugal stage raises the pressure and results in a higher pump discharge pressure at outlet  34  that is fed to the downstream end uses  106 ,  108 . 
         [0025]    When the valve  150  is closed, the valve impairs the application of a motive flow from the high-speed centrifugal stage discharge  134  to the turbo-pump motor port  142  and thereby causes the turbo-pump stage  140  to act as a pass through for inlet or discharge flow to/from the high speed centrifugal stage without an increase to the inlet/discharge pressure to/from the high-speed centrifugal stage. In turn, the high-speed centrifugal stage  130  raises the pressure of the fluid (e.g. fuel) and results in a reduced pump discharge pressure compared to when there is motive flow applied. 
         [0026]    While operating in a high-pressure mode (i.e. with the valve  150  open), the high-speed centrifugal pump stage  130  generates considerable fuel heating. During fuel system operating conditions where fuel temperatures is nearing the fuel system icing point, the high-pressure mode of the pump arrangement  102  can be selectively employed to maintain fuel system temperature above the icing point without the use of supplemental servo supply heating via the servo fuel heater  124 . In this manner, the servo fuel heater  124  and the associated plumbing may be removed from the system with a cost, weight, and substantial envelope volume reduction. 
         [0027]    In addition, an electric motor  160  is used to start the engine and power the turbo-pump stage during low engine shaft  180  speed operation. When starting a jet engine, shaft speeds are insufficient to result in any significant buildup of pressure by the typical high-speed centrifugal pump stage  130 . By using the electric motor  160  to power the turbo-pump  140  during the low engine shaft speed regime, sufficient pressure can be established with the turbo-pump stage thereby getting the engine to start and advance to the idle power setting where engine shaft speed is sufficient to obtain the needed pressure and flow output from the high-speed centrifugal pump stage  130  alone. The system architectures of  FIGS. 1 and 2  show a simple arrangement that does not require the use of isolation valves to direct the start stage flow as would be required in other schemes. Further, the type of pump used for the start stage is a centrifugal style and therefore works well with the same fuel control system as is used for normal engine operation above start-up. As the high-speed centrifugal pump  130  is capable of creating some hydraulic power at low engines shaft speeds, albeit at low pressure, this hydraulic power source can be used in conjunction with the electric motor to obtain the engine start, thereby minimizing the size of electrical power required by the turbo-pump start feature. 
         [0028]    As is evident in  FIG. 2  (where primed suffixes (′) are used with like reference numerals to refer to like components), inlet fuel  104 ′ is provided to the centrifugal pump inlet  132 ′and directed from the high-speed centrifugal pump outlet  134 ′toward the turbo-pump stage  140 ′. A portion of that flow is inlet to the centrifugal pump portion of the turbo-pump stage where the pressure is further raised before being directed to downstream end uses  106 ′,  108 ′. Depending on the position of the flow valve  150 ′, a portion of the flow from the outlet of the high-speed centrifugal pump  130 ′ is fed to the turbine portion of the turbo-pump stage  140 ′ to selectively assist the electric motor operatively associated with the turbo-pump stage. The outlet flow from the turbo-pump stage is then recirculated toward the inlet of the high-speed centrifugal pump stage. 
         [0029]    It is also represented in the figures that the pump arrangement and specifically, for example, the valve  150  and the electric motor, are connected to an electronic control unit (ECU)  170 . This is not intended to indicate that other components of the fuel system are not connected to the ECU but is merely representative that operation of a flow valve can be a simple on-off operation, or may be a variable or modulated flow, that is controlled by the ECU  170 . Likewise, still other components have been removed for ease of illustration and description, although it will be appreciated that the dual pressure high-speed centrifugal pump arrangement provides for different pressure needs of the system in a manner that is reliable, convenient, and cost-effective. 
         [0030]    Turning to  FIGS. 3-5 , like reference numerals in the “ 200 ” series to refer to like components (e.g., pump arrangement  102  of  FIGS. 1 and 2  is referred to as pump arrangement  202 ) the pump arrangement  202  incorporates a dual pressure level high-speed centrifugal pump that combines a high-speed centrifugal pump stage  230 , and an ejector pump stage  240 , and a control valve  250  to select the function of the ejector stage. Generally, the control valve  250  selects the use or non-use of the ejector pump  240  that is schematically illustrated as being located at the inlet to the high-speed centrifugal pump  230 . When the control valve  250  is open as represented in  FIG. 4 , the valve permits the application of a motive flow from an outlet  232  of the high-speed centrifugal stage discharge to the ejector pump motive port  242 , and thereby causes the ejector pump  240  to raise the inlet pressure to an inlet  234  of the high speed centrifugal pump  230 . In turn, the high speed centrifugal pump driven by shaft  236  creates a pressure rise to the working fluid (i.e. fuel) which results in a higher pump discharge pressure at the outlet  232 . 
         [0031]    When the valve  250  is closed ( FIG. 5 ), the valve impairs the application of a motive fluid from the high speed centrifugal pump outlet  232  to the ejector pump motive port  242 , and thereby causes the ejector pump  240  to act as a pass through for inlet flow from fuel inlet  204  (which may be received from a separate electric start pump  260  that is separately driven by electric power) to the high-speed centrifugal pump  230  without an increase to the inlet pressure at inlet  234  to the high-speed centrifugal pump. In turn, the high-speed centrifugal pump  230  applies or increases the pressure to the fluid and results in a reduced pump discharge pressure compared to when there is motive flow applied (i.e., when the valve is open as in  FIG. 4 ). 
         [0032]    While operating in the high-pressure mode with the valve  250  open, the high-speed centrifugal pump  230  generates considerable fuel heating. During fuel system operating conditions where fuel temperature is nearing the fuel system icing point, the high-pressure mode of the pump can be selectively employed to maintain fuel system temperature above the icing point without the use of supplemental servo supply heating via the servo fuel heater  224  ( FIG. 3 ). In this manner, the servo fuel heater  224  and its associated plumbing may be removed from the system with cost, weight, and substantial envelope volume reduction. 
         [0033]    It is also represented in  FIG. 3  that the pump arrangement and specifically, for example, the ejector flow valve  250  operation is connected to an electronic control unit (ECU)  270 . This is not intended to indicate that other components of the fuel system are not connected to the electronic control unit but is merely representative that operation of a flow valve  250  can be simple on-off, or may be a variable or modulated flow that is controlled by the ECU  270 . Likewise, still other components have been removed for ease of illustration and description, although it will be appreciated that the dual pressure high-speed centrifugal pump arrangement provides for different pressure needs of the system in a manner that is reliable, convenient, and cost-effective. 
         [0034]    This written description uses examples to describe the disclosure, including the best mode, and also to enable any person skilled in the art to make and use the disclosure. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. It is also noted that each feature of each specific embodiment disclosed herein is not considered essential to that specific embodiment, and that features disclosed in one embodiment can be added or substituted with another embodiment.