Fuel transfer pumps for inflight aircraft refueling applications are generally known in the art, and typically comprise a plurality of submersible pump units mounted directly within the reservoir fuel tank of a tanker aircraft. The pump units each include an impeller driven by an hydraulic motor to deliver fuel at a relatively high flow rate through an off-loading fuel line and appropriate releasible coupling to refuel another aircraft. Significant research effort in such pump units has been directed to the development of a design which is substantially explosion proof, particularly with respect to explosion hazard created by overheating of impeller bearings when the tank is substantially drained of fuel. See, for example, U.S. Patent 5,215,430.

In some instances, it is necessary or desirable for the primary fuel tanks of a tanker aircraft to be refueled while in flight. During such refueling procedure, fuel is off-loaded from a second tanker aircraft by appropriate operation of fuel transfer pumps located on the second aircraft, for flow through an appropriate releasible coupling and an on-loading fuel line and/or manifold to refill the primary fuel tanks. However, when this tanker refueling procedure is completed, it is necessary to evacuate residual fuel trapped in the fuel line or manifold of the refueled transfer aircraft, wherein these fuel flow passages are typically located to pass through or in close proximity to aircraft cabin spaces.

In the past, residual fuel trapped in the fuel line or manifold has been evacuated to the main reservoir fuel tanks by connecting the fuel line to the suction side of a vapor removal pump provided to improve high altitude performance when the main fuel transfer pumps are operated. However, in an improved explosion proof fuel transfer pump of the type described in U.S. Patent 5,215,430, such vapor removal pump is not necessary and is thus not provided.

There exists, therefore, a need for an effective and improved means for evacuating residual fuel from the fuel line or manifold of a tanker aircraft, particularly in conjunction with an explosion proof fuel transfer pump of the type described in U.S. Patent 5,215,430. The present invention fulfills this need and provides further related advantages.

SUMMARY OF THE INVENTION In accordance with the invention, an improved fuel transfer pump is provided for use in aircraft inflight refueling systems, wherein the improved fuel transfer pump includes an auxiliary jet-type scavenge pump for use in evacuating residual fuel trapped within a fuel line or manifold within the aircraft at the conclusion of a refueling procedure.

The fuel transfer pump comprises a submersible pump adapted for mounting directly within the reservoir fuel tank of a tanker aircraft, and includes an hydraulic motor for rotatably driving an impeller which delivers the fuel through a high pressure outlet for flow to another aircraft being refueled. The fuel transfer pump of this type is typically provided as one of several pumps in a system, all of which are mounted within the fuel tanks and adapted for concurrent operation for high flow delivery of fuel to the receiver aircraft. In the preferred system, the auxiliary jet-type scavenge pump is provided on one of the multiple fuel transfer pumps.

The scavenge pump comprises a venturi element connected along a recirculation conduit having an upstream end tapped into the high pressure discharge side of the fuel transfer pump, and a downstream end in open flow communication with the fuel tank. The venturi element has a suction throat coupled by a suction line to the fuel line or manifold to be evacuated. When fuel line evacuation is desired, the fuel transfer pump equipped with the scavenge pump is operated to provide pressurized fuel at the discharge side thereof. A portion of this pressurized fuel is recirculated through the scavenge pump, resulting in the application of a vacuum to the suction line which effectively evacuates residual fuel from the fuel line or manifold to the fuel tank.

In accordance of one aspect of the invention, a flow baffle is mounted along the recirculation conduit at a location downstream from the venturi element. This flow baffle is designed to ensure flooding of the venturi element with fuel, sufficient to prime the scavenge pump so that the desired vacuum will be generated to draw fuel through the suction line to the fuel tank.

Other features and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawings illustrate the invention. In such drawings: FIGURE 1 is a schematic diagram illustrating an inflight refueling system for aircraft, including a fuel transfer pump equipped with an auxiliary fuel line scavenge pump in accordance with the invention; FIGURE 2 is a fragmented perspective view illustrating the fuel transfer pump with auxiliary scavenge pump; and FIGURE 3 is an enlarged fragmented sectional view taken generally on the line 3-3 of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the exemplary drawings, an improved fuel transfer pump referred to generally by the reference numeral 10 is provided for use in an inflight aircraft refueling system. The fuel transfer pump 10 is equipped with an auxiliary fuel line scavenge pump 12 for evacuating residual fuel from a fuel line 14 or associated manifold 15 of an aircraft.

A refueling system for a tanker aircraft is shown generally by the reference numeral 16 in schematic form in FIGURE 1. The refueling system 16 is designed primarily to deliver fuel 18 from a main reservoir fuel tank or tanks 20 on the tanker aircraft, through an off-loading fuel line 21 and a coupling assembly 22 to a receiver aircraft 24. The coupling assembly 22 is designed, as is known in the art, to incorporate a pair of coupling members adapted for releasible inflight interconnection so that the refueling procedure can take place while the tanker aircraft and receiver aircraft are inflight generally in tandem to each other. The refueling system 16 generally includes one or more of the fuel transfer pumps 10 mounted directly within the main reservoir fuel tank 20. Each fuel transfer pump 10 is of a submersible pump design, preferably in accordance with the explosion proof pump shown and described in U.S.

Patent 5,215,430 which is incorporated by reference herein. The fuel transfer pump 10 includes an hydraulic motor 26 for rotatably driving an impeller 28 to draw in fuel through an intake 30, and to discharge that fuel under pressure through a pump outlet 32 and the off-loading fuel line 21 to the coupling assembly 22 and the receiver aircraft. As shown, a control valve 36 is typically provided along the off-loading fuel line 21.

It may be periodically necessary to replenish the fuel supply contained within the main or primary wing tanks 23 of the tanker aircraft, by way of an inflight refueling procedure during which fuel is delivered from a second, resupply tanker aircraft 38 equipped with a similar refueling system. In this regard, the two tanker aircraft include engaging releasible components of a second coupling assembly 40 through which fuel can be off-loaded from the resupply aircraft 38, through the fuel line 14 and manifold 15 to refill the main wing tanks 23. As shown, a control valve 42 is normally provided along the fuel line 14, at a location near the fuel tank 23. The intake fuel line 14 and the manifold 15 are typically located or otherwise pass through or in close proximity to one or more cabin areas of the tanker aircraft. The present invention is directed to evacuation of residual fuel in the fuel line 14 and/or the manifold 15, subsequent to inflight refueling of the tanker aircraft.

Fuel line evacuation occurs by operation of the scavenge pump 12, which is provided with one of the fuel transfer pumps 10 mounted within the fuel tank 20. In general, the scavenge pump 12 comprises a small venturi-type jet pump through which a small fuel flow is recirculated to the fuel tank 20, each time the fuel transfer pump 10 is operated. This venturi- type jet pump provides a simple yet effective structure, having no moving parts, for inducing a small vacuum that can be used to evacuate residual fuel from the fuel line 14.

More specifically, as shown best in FIGS. 2 and 3, the scavenge pump 12 comprises a relatively short recirculation conduit 48 mounted by a bracket 50 or the like onto the exterior of the high pressure discharge housing 52 of the fuel transfer pump 10.

One end of the recirculation conduit 48 is in flow communication with the interior of the discharge housing 52, via a small bleed port 54. When the fuel transfer pump 10 is operated, a portion of the fuel within the discharge housing 52 is diverted through the bleed port 54 for passage through a narrow injector or jet orifice 56 mounted within the recirculation conduit 48 near the bleed port.

A suction line 58 is connected to the recirculation conduit 48, at a location generally at the outlet side of the injector nozzle 56, which defines a venturi throat at which a vacuum is induced by jet flow through the nozzle 56. This vacuum is coupled via the suction line 58 through an appropriate control valve 60 to the fuel line 14 and/or the fuel manifold 15 associated therewith. When the control valve 60 is open, the vacuum in the suction line 58 is effective to draw fuel from the fuel line 14 and manifold 15 for passage through the suction line 58 to the recirculation conduit 48 of the scavenge pump 12.

This vacuum-drawn fuel is merged with the jet flow through the recirculation conduit 12 for return directly into the fuel tank 20.

After the main tanker aircraft has been refueled, evacuation of the fuel line 14 and manifold 15 may be accomplished quickly and easily by operating the fuel transfer pump 12 for a brief time interval with the off-loading control valve 36 in a closed position. The pump 10 thus exhibits a significant fuel pressure in the discharge housing 52, to cause a relatively high pressure fuel flow through the injector nozzle 56. This fuel flow is effective to induce a vacuum for evacuating the fuel line 14, with the on-loading control valve 42 appropriately closed and the suction line valve 60 open during the evacuation step.

In accordance with one aspect of the invention, the scavenge pump 12 is equipped with a flow baffle 62 to insure rapid and proper priming of the scavenge pump 12 when fuel line evacuation is desired. Such priming is particularly important in the event that the discharge end of the recirculation conduit 48 is not submersed in fuel, such as when the main fuel tank is empty or nearly emptied.

The flow baffle 62 comprises an open-sided cup element mounted at the downstream end of the recirculation conduit 48, in a position defining an open downstream end 64. Fuel injected through the nozzle 56 within the recirculation conduit 48 splatters and floods against the flow baffle 62 to thus insure partial filling of the recirculation conduit 48 sufficient to submerge the nozzle 56, before fuel can spill over the upper edge of the baffle 62, for draining directly into the fuel tank 20. Thus, when the fuel transfer pump is operated to evacuate the fuel line 14 and manifold 15, the baffle 62 ensures rapid filling of the recirculation conduit 48, sufficient to ensure the desired venturi suction flow action along the suction line 58.

A variety of modifications and improvements to the invention will be apparent to those skilled in the art. For example, it will be understood that the scavenge pump 12 can be coupled through appropriate valve elements to evacuate residual fuel from the off- loading fuel line 21, if necessary or desirable.

Accordingly, no limitation on the invention in intended by way of the foregoing description and accompanying drawings, except as set forth in the appended claims.