Abstract:
Disclosed herein is a fuel metering pump for delivering fuel to rocket or jet engine having a motor driven face cam and a pair of reciprocating rolling diaphragm pump mechanisms movable through opposite suction and pump strokes. The face cam has a ramping cam surface that extends radially more than 180 degrees. This permits both pump mechanisms to be simultaneously in the pump stroke for a portion of the pump stroke so that they alternately reciprocate through the suction and pump strokes at essentially a constant velocity, thereby providing an essentially non-pulsating flow of fuel to the engine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit to provisional application Ser. No. 60/133,594, filed May 11, 1999. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to fuel delivery systems for stationary and propulsion gas turbine engines, and in particular, to rocket and jet engine fuel delivery systems having fuel metering pumps. 
     The high burn rates of rocket and jet engines requires the fuel delivery system to be capable of precisely metering fuel. Traditionally, fuel delivery systems for rocket and jet engines, particularly those used for propulsion, have included a fuel pump, a pressure accumulator and a fuel metering device, all of which being separate components mounted on or near the engine at distinct locations and coupled to the engine and fuel source by suitable fuel lines. The accumulator operates to dampen pulsation or ripple in the fuel caused by the pump so that the metering device can accurately dispense the appropriate amount of fuel to the engine fuel atomizer. The use of multiple components is expensive and occupies space, which is limited for propulsion systems. 
     It is desirable to reduce the number of components in the fuel delivery by combining the fuel pump and metering device into one unit. However, if one component is to serve as both the pump and the metering device, it must meet the requires of the rocket and jet engine industry for both the pump and the metering device. Some of the attributes of a jet engine fuel pump include the ability to pump particle contaminated fuel for an extended time period. It must have good dry lift capacity and be able to operate with vapor-to-liquid ratios at the pump inlet of 0.45 or greater. Moreover, if no accumulator or fluid muffler is to be used, the pump must also be able to provide generally non-pulsating fuel flow. The requirements of a jet engine metering device include low power consumption and low hysteresis, i.e., the ability to operate with high efficiency and low friction. The device must also be able to provide a wide range of flow rates accurately, i.e., have a high turn-down ratio. Additionally, the device must be compact and have minimal internal leakage. 
     Typically in the rocket and jet industry, the fuel delivery systems employ gear pumps which create a pressure differential by moving the fuel through a series of intermeshing teeth running at a high frequency. Gear pumps consume a lot of power and leak internally and are therefore less than ideal for rocket and jet engine use. Moreover, due to reliability concerns, gear pumps used for propulsion applications typically are powered by an engine driven gear box (rather than an electric motor) and therefore must be coupled to a separate metering valve via suitable fuel lines, which increases expense and occupies additional space. 
     SUMMARY OF THE INVENTION 
     The inventor of the present invention has recognized that a compact and reliable fuel delivery system meeting the stringent requirements of rocket and jet engine applications could be achieved using a specially designed constant pressure, cam operated metering pump with rolling diaphragms that prevent degradation of the pump from fuel and contaminants. 
     Specifically, the present invention provides a system for supplying combustible fuel to a fuel consuming device. The deliver system includes a fuel metering pump pumping combustible fuel from a fuel source through a fuel line to the fuel consuming device. The fuel metering pump has a housing defining an outlet port and an inlet port. The inlet port is in communication with the fuel source and a pair of pump chambers. Each pump chamber is sealed by a diaphragm to which is connected a pumping member biased at one end to abut a motor driven face cam. The face cam is operated by the motor to alternately reciprocate the pumping members through pump and suction strokes within the pump chambers. The fuel metering pump meters substantially constant pressure fuel through the fuel line to the fuel consuming device without the need for an accumulator or separate metering valve. 
     In a preferred form, the fuel consuming device is a gas turbine, rocket or jet engine. The gas turbine engine may be for a stationary or land-based vehicular applications or for propulsion of air and space vehicles. The fuel delivery system, however, is also particularly suited for use with fuel cells. 
     In another preferred form, the fuel source includes a fuel tank and the pump housing is mounted to the fuel tank over an opening therein. In this way, no input fuel lines are required and the vapor-to-liquid ration of the pump is maximized. 
     In yet another preferred form, the fuel delivery system of the present invention further include an electronic controller for controlling the speed of an electric motor driving the face cam. A speed sensor is electrically coupled to the controller and positioned near the circumference of the face cam. The face cam has teeth at its circumference that are detected by the sensor and used by the controller to operate the motor. 
     One aspect of the invention is that the face cam includes an increasingly ramped cam surface extending through more than 180 degrees, which abuts cam followers to move the pumping members through the pump and suction strokes. Preferably, the raised ramped surface extends to 200 degrees providing a 20 degree overlap wherein both pumping members are in the pump stroke. This provides a smooth transition from the pumping stroke to the suction stroke of each pumping member. In this way, the face cam imparts a constant velocity motion to the pumping members so as to minimize pressure ripple associated with swash plates of traditional piston pumps. This non-pulsating fuel flow makes the pump particularly well suited for use in high precision applications such rockets and jet engines. 
     Another aspect of the invention is that the ambient side of the pump chambers is sealed from the fuel by the diaphragms, which prevent fuel, contaminants and debris from entering the cam chamber and the electric motor. This also obviates the need for expensive close fitting surfaces in the pump chambers with highly polished surfaces. As such, little or no internal friction occurs, which maximizes efficiency and resistence to contaminated fuel. The seal of the diaphragms ambient air in the pump chambers to vent to the cam chamber of the housing. The pumping action then causes equal cross-transfer of displaced air volume, thereby eliminating pressure build up in the pump chambers. Moreover, the seal of the diaphragm eliminates the need for an external motor shaft seal. 
     The present invention also provides a fuel metering pump suitable for delivering fuel to rockets and jet engines. Specifically, the pump includes a drive mechanism comprising a drive motor having an axial shaft and a disk-shaped face cam mounted to the motor shaft having a ramped cam surface at an outer face. The ramped cam surface of the face cam extends radially more than 180 degrees so that both pump mechanisms are simultaneously in the pump stroke for a portion of the pump stroke and so that the pumping members alternately reciprocate through the suction and pump strokes at essentially a constant velocity. The pump also includes a pair of pumping members movable through opposite suction and pump strokes and disposed in separate pump chambers defined by a housing mounted over an orifice of a fuel tank. The housing has an inlet controlled by a reed valve to be in communication with the fuel. Each pumping member includes a cam roller biased against the face cam by a spring so as to be contacted by the ramped cam surface. A connector rod is connected to the cam roller at one end and a head plate is connected at the opposite end of the connector rod. A fuel resistant diaphragm is attached to the head plate so as to roll back as the pumping members are moved through the suction and pump strokes. 
     These and still other advantages of the present invention will be apparent from the description of the preferred embodiments which follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of the fuel delivery system of the present invention; 
     FIG. 2 is a top plan view of the fuel metering pump of the fuel delivery system cut away to show the fuel outlet connection; 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  of FIG. 2 showing pump and drive mechanisms within a pump housing; 
     FIG. 4 is a break out view of a speed sensor positioned adjacent an edge of a face cam; 
     FIG. 5 shows displacement and torque curves of the fuel metering pump of the present invention; and 
     FIGS. 6A-6C illustrate the pump and drive mechanisms at three positions of the cam profile. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The jet engine fuel delivery system of the present invention is shown schematically in FIG.  1  and is referred to generally by reference numeral  10 . The fuel delivery system  10  employs a fuel metering pump  12  (“pump”) mounted over an opening in an onboard fuel tank  14  to pump combustible fuel contained therein through a suitable fuel line  16  to a fuel atomizer (not shown) of a gas turbine engine  18 . The gas turbine engine  18  is preferably any suitable rocket or jet engine used for stationary (or land-based vehicular) and propulsion applications. The pump  12  will be described in detail below, however, in general it is a specially designed dual chamber rolling diaphragm pump capable of precisely metering non-pulsating fuel to the jet engine  18 . The pump  12  draws fuel in past inlet check valves  20  and  21  during a suction stroke and pumps out the fuel through outlet check valves  22  and  23  in fluid communication with the fuel line  16 . The pump  12  is controlled by control circuitry of an onboard electronic controller  24  coupled by a control/feedback line  26 . 
     Referring to FIGS. 2-3, the fuel metering pump  12  will now be described in detail. The pump  12  is confined in a housing  30  having a mounting flange  32  at its suction end for bolting the pump  12  to the fuel tank  14  over a suitably sized opening  33  (see FIG.  3 ). Fuel coupler  34  and electrical junction  36  are attached at openings in the housing  30  for connection of the fuel line  16  and the control/feedback line  26 , respectively. Referring to FIG. 3, the housing  30  includes a rim  38  extending below the mounting flange  32  into the fuel tank  14  and to which is mounted a pump chamber cover  40 . The rim  38  includes a circumferential groove  41  for containing a resilient seal (not shown) for sealing against the inner diameter fuel tank opening  33 . Since the pump  12  is mounted to the fuel tank  14  no fuel intake lines are needed providing for a compact package and maximizing the vapor-to-liquid ratio of the pump  12 . At the opposite end of the housing  30  is an opening for receiving and mounting an electric motor  42 . 
     Referring still to FIG. 3, a circular face cam  44  is suitably mounted to a rotatable shaft  46  of the motor  42 . Roller bearings  48  are disposed between the back of the face cam  44  and the face of the motor  42  to reduce axial loading on the motor  42 . The face cam  44  has a ramped cam surface  50  at its front face against which ride rollers  52  and  53  of respective movable pumping members  54  and  55  aligned in parallel 180 degrees apart. The rollers  52  and  53  are biased against the cam surface  50  by springs  56  and  57  and are rotatably mounted at one end of connector rods  58  and  59 , respectively. The connector rods  58  and  59  fit through respective cylindrically walled openings  60  and  61  (around which the springs are disposed) in a partition  62  of the housing  30  into respective cylindrical pump chambers  66  and  67 . At the pump chamber end of the pumping members  54  and  55  are mounted pump heads  68  and  69  comprised of inner  72  and  73  and outer  74  and  75  head plates sandwiching diaphragms  76  and  77 , respectively. The pump heads  68  and  70  are mounted by threaded fasteners  80  and  81  threaded into respective connector rods  58  and  59 . 
     The pump chamber cover  40  includes cylindrical recesses that cooperate with the housing  30  to form the pump chambers  66  and  67 . The diaphragms  76  and  77  are captured along their circumference between the housing  30  and the pump chamber cover  40  and are sized roll back upon itself as the pumping members  54  and  55  are reciprocated. The diaphragms  76  and  77  exhibit zero leakage so as to seal the inside of the housing  30  and prevent fuel, contaminants and debris from entering the cam chamber  82  and the electric motor  42 . Thus, the pump  12  does not require close fitting surfaces in the pump chambers  66  and  67  with highly polished surfaces. As such, little or no internal friction is produced, which maximizes efficiency and resistence to contaminated fuel. Moreover, there is no need for an external motor shaft seal. 
     The seal of the diaphragms  76  and  77  also allows the partition  62  to have a plurality of openings  84  in communication with the pump chambers  66  and  67 . The openings  84  allow air to vent from within the ambient side of the pump chambers  66  and  67  to the cam chamber  82  of the housing  30 . The pumping action then causes equal cross-transfer of displaced air volume, thereby eliminating pressure build up in the pump chambers  66  and  67 . 
     The pump chamber cover  40  includes the inlet ports  86  and  87  and outlet ports  88  and  89 . The inlet port  86  and outlet port  88  are in fluid communication with pump chamber  66  and are controlled by inlet check valve  20  and outlet check valve  22 . Similarly, the inlet port  87  and outlet port  89  are in fluid communication with pump chamber  67  and are controlled by inlet check valve  21  and outlet check valve  23 . The inlet ports  86  and  87  are also covered by mesh screens  90  and  91  to further ensure that debris and contaminants do not enter the pump chambers  66  and  67 . 
     Referring to FIGS. 4 and 5A the housing  30  also has an opening leading to the cam chamber  82  for a speed sensor  92  connected to electrical junction  36  through an opening in the housing  30  which in turn is connected to the controller  24  via line  26  (see FIGS. 1 and 2) forming a motor control/feedback loop. The speed sensor  92  is preferably a suitable proximity sensor positioned adjacent the edge of the face cam  44  which includes radial teeth  94  (one shown) having gaps therebetween. The speed sensor  92  detects each tooth  94  and emits a pulse the frequency of which is determined by the number of teeth on the outer diameter of the face cam  44  and its rotational velocity. The pulse signal can be used directly or after digital-to-analogue conversion, depending upon the capabilities of the controller  24 . The controller  24  then uses this information to adjust the electric motor  42  as needed to compensate for differences between actual and expected motor speeds and corresponding fuel flow rates. Specifically, a computer model of pump speed is generated by the controller  24  (or an external processor) to analyze stability and gross transients. Speed loop gains are determined, preferably using a proportional-integral-derivative loop, and a close loop response is determined. 
     In one preferred embodiment, the pump  12  is approximately 2.7 inches in diameter, 4.75 inches in length and weighs 2.25 lbs. The motor  42  is a brush D.C. motor with a rated current of 2.0 amps and a stall current of 6.0 amps. The housing  30 , pump chamber cover  40 , connector rods  58  and  59 , face cam  44 , and head plates  72 - 75  are anodized aluminum providing for the low weight of the pump  12 . The diaphragms  76  and  77  are preferably a fluorosilicone coated fabric material having a minimum shelf life in excess of ten years. The rollers  52  and  53  are a thin dense chrome and the roller bearings  48  are standard steel bearings and the springs  56  and  57  are suitable compression springs. The inlet check valves  20  and  21  are a deflecting reed type valve for low inertia and pressure drop across the inlet ports  86  and  87 , preferably less then 1.0 psid at 400 pph. The outlet check valves  22  and  23  are preferably spring loaded flat poppet type valves. The poppet springs  96  and  97  bias the respective outlet check valves  22  and  23  to close the outlet ports  88  and  89  in the event of positive tank pressure. The inlet screens  90  and  91  preferably filter particles larger than 100 microns. 
     This construction provides a pump  12  that is rated at 300 pph with a maximum of 400 pph and a controllable flow range of 20-400 pph correlating to a 20/1 turndown ratio. The pump has a rated pressure rise of 30 psid and the speed ranges from 0 to 4,200 rpm. The pressure at motor stall is 190 psid minimum at −40 degrees F. 
     Referring now to FIGS. 5 and 6, operation of the electric motor  42  rotates the face cam  44  which in turn reciprocates the pumping members  54  and  55  via the cam surface  50  contacting the rollers  52  and  53 . The cam surface  50  is specially designed to define a cam profile in which the ramped portion extends through more than 180 degrees. Preferably, the ramped cam surface  50  extends through 200 degrees such that there is 20 degrees of overlap in which both pumping members  54  and  55  are moving in a pump stroke for 10 degrees of rotation. 
     Referring in particular to FIG. 6, the cam surface  50  includes 180 degree upward linear ramp with a flattened ramp for 20 degrees. The flattened ramp is roughly one-half the slope of that from 0 to 180 degrees. The cam surface  50  ramps down linearly from 200 to 315 degrees and is flat to 360 degrees. Referring to FIG. 5, the pump displacement of pumping member  54  is shown by line A and for pumping member  55  by line B and the pump torque is illustrated by line C based upon a 30 psid rise to the fuel atomizer of the jet engine. As shown, pumping member  54  (line A) is in the pump stroke from 0 to 200 degrees of the face cam  44  and in the suction stroke from 201 to 359 degrees. The pumping member  55  (line B) is in the pump stroke from 180 to 20 degrees and in the suction stroke from 21 to 179 degrees of the face cam  44 . 
     Thus, as shown diagrammatically in FIG. 6A, the pumping member  54  pumps out fuel and pumping member  55  draws in fuel when the face cam  44  is rotated through 0-180 degrees. As it rotates continues to rotate through 200 degrees, the pump  12  is as shown in FIG. 6B with both pumping members  54  and  55  in the pump stroke, however, with pumping member  54  nearing the end and pumping member  55  just beginning. As illustrated by line C of FIG. 5, the pump  12  provides a peak torque of approximately 15.5 oz.-in. during this overlap portion of the cam surface  50  wherein both pumping members  54  and  55  are in the pump stroke. As the face cam  44  finishes its rotation, the pump is as shown in FIG. 6C, with the pumping member  54  in the suction stroke and the pumping member  55  in the pump stroke. 
     The cam surface  50 , in particular the overlapping portion, provides a smooth transition from the pumping stroke to the suction stroke of each pumping member  54  and  55 . In this way, the face cam  44  imparts a constant velocity motion to the pumping members  54  and  55 , at any motor speed, so as to minimize pressure ripple associated with swash plates of traditional piston pumps. This non-pulsating fuel flow makes the pump  12  particularly well suited for use in high precision applications such rockets and jet engines. 
     The present invention may include other aspects not specifically delineated in the aforementioned preferred embodiments. For example, the size and speed of the electric motor can be varied. Also, the above described a tank mounted embodiment, however, it is possible for the fuel metering pump to be connected to the fuel source inline with suitable fuel lines. Moreover, the fuel metering pump could be used in a fuel delivery system having a fuel cell as the fuel consuming device. Thus, the above in no way is intended to limit the scope of the invention. Accordingly, in order to apprise the public of the full scope of the present invention, reference must be made to the following claims.