Oil Lubricated Main Drive Shaft for Fuel Pump

This invention relates to fuel pump drive shafts.

Fuel pump main drive shafts typically incorporate a spline at each end. The spline at the outboard end is connected to the engine gearbox while the spline at the inboard end is connected to a rotating pump component. While the spline attached to the engine gearbox is lubricated by oil, the spline at the other end is lubricated by less lubricous fuel, thereby resulting in unequal spline wear. The basic problem is that observation of spline wear at the readily accessible outboard end of the shaft provides no indication of spline wear at the inaccessible inboard end, whereby actual inspection is necessary to ascertain the extent of wear at the inboard end.

In accordance with the invention, equal lubrication is furnished at both ends of a fuel pump main shaft without requiring the imposition of weight and space penalties.

Succinctly stated, a main drive shaft in a fuel pump incorporates conduits and passages which transport lubricating oil from the engine gearbox to the inboard spline, and thence, back to the gearbox. The drive shaft embodies seal means to separate the oil adjacent to the inboard spline from the fuel.

Accordingly, it is a primary object of the invention to provide a fuel pump having a main drive shaft with both ends lubricated by oil.

This and other objects and advantages of the invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:

The drawing shows a sectional side elevational view of a fuel pump incorporating the invention.

Referring to the drawing, there is shown a gear pump, generally designated 2, incorporating the invention. The pump 2 is adapted to supply fuel to a gas turbine engine (not shown) having a gearbox, generally indicated at 4. The pump 2 has a housing 6 which defines a pumping cavity 8 in which a pair of meshing gears 10 and 12 are contained. The gears 10 and 12 are respectively carried by integral shafts 14 and 16 which are, in turn, supported for rotation by bearings 18, 20 and 22, 24, respectively. Gear 10 is the driving gear and gear 12 is the driven gear. A main drive shaft, generally indicated at 26, forms a driving interconnection between the engine gearbox 4 and the shaft 14 which carries the driving gear 10.

The gearbox 4 has a flange 28 which is connected to a flange 30 on the pump housing 6 by a series of bolts. A drive shaft 32 is rotatably mounted within the engine gearbox 4 by bearings, such as shown at 34. The drive shaft 32 incorporates an integral flange 36 which is in wiping engagement with a carbon faced seal 38 adapted to isolate any fuel which may be present between the pump housing 6 and the gearbox from the bearings 34. The gearbox drive shaft 32 is provided with a plurality of internal splines 40 which are in driving engagement with a plurality of external splines 42 on the outboard end of the pump main drive shaft 26. The inboard end of the main drive shaft 26 has similar external splines 44 which are in driving engagement with a plurality of internal splines 46 formed within an elongated cavity 48 in the shaft 14.

Within the pump housing 6, a carbon faced seal 50 is mounted in engagement with a flange 52 on the main drive shaft 26 for preventing fuel in the pumping cavity 8 from entering the volume defined 53 between the pump housing 6 and the gearbox 4. This volume 53, which is usually empty, communicates with an overboard drain 54. Should fuel leak into this volume it will be evacuated to the atmosphere via the overboard drain 54. An O-ring seal 56 disposed in an annular recess in the main drive shaft 26 contacts the inner surface of the gearbox drive shaft 32, whereby oil in the gearbox is sealed from the volume which communicates with the overboard drain. It will be appreciated that the pump 2 and gearbox 4 are generally conventional insofar as these elements have been described.

The main drive shaft 26 embodies a hollow interior essentially constituted by three bores 58, 60 and 62 of progressively increasing diameters. A lubrication tube 64 having a lubricant supply passage 65 is disposed within the hollow interior of the shaft 26 with its outer periphery in close fitting engagement with the bore 58 and a bushing 66 at the inboard end of the main drive shaft 26. Surrounding the tube 64 is defined an annular lubricant return passage 68. Lubricating oil is supplied to the tube 64 at its inlet or outboard end via an oil jet 70 (at a slightly higher pressure than the surrounding area) in the engine gearbox 4 which has its axis aligned with that of the tube 64. The inboard or outlet end of the tube 64, which bears against a transverse wall 72 at the base of cavity 48 in the shaft 14, has a plurality of circumferentially distributed slots 74 through which oil is radially directed into a space 76 between the inboard end of the shaft 26 and the adjacent walls of the cavity 48. Oil from the space 76 enters the area of engagement between splines 44 and 46, providing lubrication which has heretofore been accomplished by fuel. In order to facilitate the flow of oil through the tube 64, the interior passage thereof preferrably has a progressively increasing diameter, thereby defining a truncated conical shape. Such a configuration provides something akin to centrifugal pumping action.

A return path for the oil in the area of spline engagement is provided by a plurality of radially extending passages 78 in the shaft 26 which communicate with the outer end of this area and the annular passage 68. Another series of radially extending passages 80 fluidly interconnect the annular passage 68 and a volume adjacent to the outer periphery of the shaft 26 located between the seal 56 and the splines 40 and 42. Oil from this latter mentioned area proceeds back into the gearbox 4 through the splines 40 and 42.

In order to prevent the fuel which envelops the intermediate portion of the shaft 26 inboard of the flange 52 from contaminating the oil in the area of engagement between splines 44 and 46, a seal must be provided. To this end, O-ring seals 82 and 84 are mounted in annular recesses on the shaft 26 in sealing contact with the wall of the cavity 48. A drain passage 86, which connects the outer periphery of the shaft 26 lying between the seals 82 and 84 and the volume 53 insures that fuel leaking past the seal 82 will not contaminate the oil but will instead proceed into volume 53. In like manner, any oil leaking past the seal 84 will not mix with fuel but will proceed to the volume 53 through the drain passage 86.

In operation, oil proceeds from the jet 70 into the inlet of the tube 64. Oil passing through the tube emerges through the slots 74 into the space 76 from where it enters the area of engagement between the splines 44 and 46. Oil from the splines 44 and 46 travels back to the gearbox 4 through passages 78, 68 and 80. Should either fuel or oil leak past the respective 0-ring seals 82 and 84, it will be transferred to the volume 53 via the drain passage 86.

Obviously, many variations and modifications are possible in light of the above teachings without departing from the scope or spirit of the invention as defined in the appended claims.