Description of the Prior Art Conventionally, as illustrated in Fig. 3, a fuel-metering unit 20, such as a cartridge fuel pump, is driven off a splined shaft 32 that is housed within an accessory gearbox 30. The accessory gearbox 30 has an enclosed casing 34 which houses a reduction gear set 36. The reduction gear set 36 is driven by a drive gear 40, which is mounted to a starter shaft 42 rotatably secured by a bearing mount 44. The reduction gear set 36 is affixed to the shaft 32 whose internal splines 33 are in meshing engagement with the external splines of a complementarily shaped stub shaft 22 protruding from a casing 24 of the fuel-metering unit 20. To facilitate mounting of the fuel-metering unit 20 to the accessory gearbox 30, the fuel-metering unit 20 has a flanged pad 26 which abuts a corresponding flanged pad 46 on the accessory gearbox 30.

Although the prior-art configuration described above permits removable mounting of an accessory to the accessory gearbox 30, this configuration suffers from certain shortcomings, namely, undesirably high weight and high overhung moment, not to mention the high number of parts involved. Because of these characteristics, the prior-art configuration is suboptimal for light-weight applications.

SUMMARY OF THE INVENTION It is therefore an aim of the present invention to provide an improved configuration for connecting a fuel-metering unit or other such accessory to an accessory gearbox.

Therefore, in accordance with a general aspect of the present invention, there is provided a gas turbine engine accessory in combination with a gearbox of a gas turbine engine, the accessory being removably mounted to the gearbox and having an integral drive shaft extending into the gearbox, and a driven gear mounted on the drive shaft, the driven gear being adapted to directly engage a drive gear of said gearbox.

In accordance with a further general aspect of the present invention, there is provided a gas turbine engine driving arrangement comprising a gas turbine engine accessory integrated to an accessory gearbox, the accessory comprising an open-ended accessory casing, the open-ended accessory casing being adapted to be removably mounted to an accessory gearbox casing having a complementary opening, the accessory casing and gearbox casing mating to form a fully enclosed unit.

In accordance with a still further general aspect of the present invention, there is provided a gas turbine engine comprising at least a compressor, a combustor adapted to receive compressed air from the compressor, a turbine for extracting power from the combustion gases leaving the combustor, an accessory gearbox having at least one drive gear driven by the turbine; and at least one gas turbine engine accessory removably mounted to the accessory gearbox, the accessory having at least one drive shaft with at least one driven gear mounted to the drive shaft, the driven gear meshing with the drive gear of the accessory gearbox.

BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made to the accompanying drawings, showing by way of illustration the preferred embodiment thereof, in which :

Fig. 1 is a schematic cross-sectional view of a gas turbine engine to which an embodiment of the present invention is applied; Fig. 2 is a cross-sectional view of a compact configuration of a fuel- metering unit and accessory gearbox in accordance with an embodiment of the present invention; and Fig. 3 is a cross-sectional view of a prior-art configuration of a fuel- metering unit and accessory gearbox.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 illustrates a gas turbine engine 10 of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan 12 through which ambient air is propelled, a multistage compressor 14 for pressurizing the air, a combustor 16 in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section 18 for extracting energy from the combustion gases.

The turbine section 18 drives various accessories, such as a fuel pump, oil pump, hydraulic pump, air pump, or electric generator, via an accessory gearbox 30' (Fig. 2).

Fig. 2 illustrates an embodiment of the present invention in which a fuel-metering unit 20', in this application called a'cartridge fuel pump', is partially embedded in the accessory gearbox 30'. The fuel-metering unit 20'and the accessory gearbox 30'are partially encased within an accessory casing 24'and a gearbox casing 34', respectively. The accessory casing 24'and the gearbox casing 34 have complementary openings so that a portion of the fuel-metering unit 20 can be inserted, or"embedded", in the accessory gearbox 30' (which acts like a receptacle or socket). A spigot or peripheral portion 60 of the unit 20'is adapted to matingly engage at least one of the casings 24'and 34, and an appropriate seal member 62 is provided to seal the connection (an'o-ring'type seal 62 is shown, although other suitable seal types, such as face seals or other seals, may be employed). Once embedded, the fuel-metering unit 20'and the accessory gearbox 30'together form a

fully encased unit. The unit 20'is, itself, not fully encased, since its embedded assembly position allows it to become encased as part of an assembly with the gearbox-thus permitting a less-than complete (i. e. non-contiguous) casing for the unit 20'alone, representing a portion of the weight savings achieved, as discussed further below.

As shown in Fig. 2, an embedded portion 50 represents about one half of the length of the cartridge fuel pump, although it should be appreciated that the degree to which the accessory is embedded in the accessory gearbox 30'will vary according to design exigencies, such as the depth inside the accessory gearbox of a drive gear that is to mesh with a driven gear of the accessory. Preferably, a sufficient amount of the accessory is embedded in the gearbox to permit a portion of the accessory casing to be absent, so that the accessory is open casing to be closed by assembly with the gearbox.

The fuel-metering unit 20' (the cartridge fuel pump in this example) is powered by a drive shaft 35. Affixed to the drive shaft 35 is a reduction gear set 36'.

As shown, the reduction gear set 36'has a driven gear 36a'and a spacer gear 36b'.

The driven gear 36a'meshes with, and is driven by, a drive gear 40'mounted to a starter shaft 42'which is, in turn, rotatably secured by a bearing mount 44'. The spacer gear 36b'is in meshing engagement with a stationary gear 37 provided in the gearbox casing 34'for ensuring proper alignment of the drive shaft 35 so that torque imparted to the driven gear 36a'by the drive gear 40'does not cause the drive shaft 35 to deflect or wobble unduly. As will be appreciated by persons skilled in the art, the drive gear 40'may be connected to any accessory drive shaft that receives torque from the turbine shaft. The drive shaft 35 is preferably not a splined set, but rather a single or integral shaft extending into the unit 20'and to which the gear 36a'is affixed, such that gear set 36 drives the unit 20'directly. This aspect contributes to the weight savings in the concept, as will be discussed further below.

The partial embedding of the fuel-metering unit 20'in the accessory gearbox 30'results in a compact and lightweight configuration. Not only are weight and overhung moment reduced, but so is the number of parts. By embedding the

fuel-metering unit 20'in the accessory gearbox 30', the drive shaft 35 of the unit 20' is directly connected to the reduction gear set 36. The splined shaft 32 (shown in Fig. 3) is thus eliminated, as are the flanged pads 26,46. Further, since the fuel- metering unit 20'and the accessory gearbox 30'are not individually fully encased, the amount of casing material required is also reduced. As will be appreciated by persons skilled in the art, this compact configuration can be advantageously used on gas turbine engines of all sizes and all types to reduce weight, overhung moment and complexity.

In order to ensure that the driven gear 36a'of the reduction gear set 36' meshes correctly with the drive gear 40'of the accessory gearbox 30'when the unit is assembled, the fuel-metering unit 20'may further be provided with a mounting face (in this case, above the spigot) to abut the casing 34'of the gearbox 30'. Suitable fasteners (not shown) secure the device to the gearbox. The drive shaft 35 and reduction gear set 36'extend below the mounting face by a predetermined distance calculated to ensure that the driven gear 36a'mounted to the drive shaft 35 meshes with the drive gear 40'of the accessory gearbox 30'.

Furthermore, to facilitate connection of the fuel-metering unit 20'to the accessory gearbox 30', the fuel-metering unit 20'may also include a spigot 60 having a circular lip integrally formed with the mounting face for centering the fuel- metering unit 20'with respect to the accessory gearbox 30'. hi operation, when the gas turbine engine 10 is running, the rotation of the turbine shaft drives the accessory gearbox 30'which, in turn, powers the embedded cartridge fuel pump (or other fuel-metering unit) 20. The cartridge fuel pump, or other fuel-metering unit, pumps fuel to a plurality of fuel injectors which inject the fuel into the combustor 16 where the fuel and compressed air from the compressor 14 are combusted to generate hot gases. These hot gases impinge on a plurality of turbine blades which drive the turbine shaft. The rotation of the turbine shaft, as noted earlier, powers the cartridge fuel pump 20'via the accessory gearbox 30'.

Although Fig. 2 illustrates a fuel-metering unit in a compact, "embedded"configuration with an accessory gearbox 30', it should be understood that other accessories may also be embedded in the gearbox 30'in the same compact configuration. Instead of a fuel-metering unit, the embedded accessory could be an oil pump, a hydraulic pump, an air pump, or an electric generator (this is not intended to be an exhaustive list). In each case, the drive shaft of the accessory is provided with a reduction gear set or a driven gear for meshing with a drive gear of the accessory gearbox. Persons skilled in the art will appreciate that other accessories may also be embedded within an accessory gearbox in the manner described.

The embodiments of the invention described above are intended to be exemplary. Those skilled in the art will therefore appreciate that the forgoing description is illustrative only, and that various alternatives and modifications can be devised without departing from the spirit of the present invention. Accordingly, the present is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.