Patent Publication Number: US-2017356347-A1

Title: Accessory gearbox assembly and a gas turbine engine comprising an accessory gearbox assembly

Description:
The present disclosure relates to an accessory gearbox assembly and in particular to an accessory gearbox assembly for a gas turbine engine. 
     An accessory gearbox assembly generally comprises an accessory gearbox and a plurality of accessories. The accessory gearbox comprises a gear train of spur gears, each of which is arranged to drive a respective one of the accessories. The accessories are either mounted on the front of the accessory gearbox, the back of the accessory gearbox or the front and the back of the accessory gearbox. The accessories include a low pressure fuel pump, a high pressure fuel pump, a fuel flow governor, an oil pump, a hydraulic pump, a starter motor, an electrical generator, a tachometer, a permanent magnet alternator, e.g. a permanent electrical generator. Thus, the accessory gearbox carries and drives the accessories. The accessory gearbox is driven by a drive shaft which extends generally radially with respect to the axis of the gas turbine engine from an internal gearbox driven by one or more shafts of the gas turbine engine. 
     The accessory gearbox is mounted on the fan casing of a turbofan gas turbine engine, for example at the bottom of the fan casing, or is mounted on the core engine casing of a turbofan gas turbine engine. 
     The accessory gearbox also comprises an accessory gearbox casing which encloses the gears of the gear train. In a conventional accessory gearbox the weight, inertia etc. of the accessories is carried by the gearbox casing. In a conventional accessory gearbox each accessory is secured, e.g. bolted, at one end to the accessory gearbox casing and thus each accessory is cantilevered off the accessory gearbox casing and thus each accessory acts as a parasitic mass hung off the accessory gearbox casing. Large accessories, e.g. electrical generators, transmit large loads into the accessory gearbox and accessory gearbox casing in response to movements of the gas turbine engine and/or accessory gearbox, especially following the unlikely event of a release of a fan blade from the fan of a turbofan gas turbine engine. 
     The accessory gearbox comprises for each accessory a gear and associated gear shaft mounted on the accessory gearbox casing by two bearings, e.g. two roller bearings, splines on the end of each gear shaft to drive the accessory, a seal where the gear shaft passes through the accessory gearbox casing, a shaft of the accessory supported on the accessory casing by two bearings, e.g. two roller bearings, splines on the shaft of the accessory which is arranged to mesh with the splines on the corresponding gear shaft and a seal where the shaft of the accessory passes through the casing of the accessory. Thus, there are a large number of component parts which adds weight and cost to the accessory gearbox assembly and increases the number of component parts which may fail. 
     The present disclosure seeks to provide an accessory gearbox assembly which reduces or overcomes the above mentioned problem(s). 
     According to a first aspect of the present disclosure there is provided an accessory gearbox assembly comprising an accessory gearbox and a plurality of accessories arranged to be driven by the accessory gearbox, the accessory gearbox comprising a gear train and an accessory gearbox casing enclosing the gears of the gear train, each accessory is driven by a drive shaft, each accessory has a first end and a second opposite end, each accessory is secured at the first end to the accessory gearbox casing and the second opposite end of at least two of the plurality of accessories are secured to a structural cross member. 
     A first plurality of accessories may be secured to a first side of the accessory gearbox casing, the drive shafts of the first plurality of accessories are parallel and the second opposite end of at least two of the first plurality of accessories are secured to a first structural cross member. 
     The at least two of the plurality of accessories may be the largest and/or the heaviest accessories secured to the first side of the accessory gearbox. 
     The largest and/or the heaviest accessories may be electrical generators. 
     The second opposite end of more than two of the plurality of accessories may be secured to the structural cross member. 
     The second opposite end of all the plurality of accessories may be secured to the structural cross member. 
     A second plurality of accessories may be secured to a second opposite side of the accessory gearbox casing, the drive shafts of the second plurality of accessories are parallel and the second opposite end of at least two of the second plurality of accessories are secured to a second structural cross member. 
     The second opposite end of more than two of the second plurality of accessories may be secured to the second structural cross member. 
     The second opposite end of all the second plurality of accessories may be secured to the second structural cross member. 
     The drive shaft of each accessory may be supported on an associated accessory casing by two bearings, the drive shaft of each accessory has at least one gear, the gear on the drive shaft of each accessory is arranged to mesh with one or more gears on the corresponding drive shaft of other accessories or the gear on the drive shaft of each accessory is arranged to mesh with one or more idler gears which mesh with the gears on the corresponding drive shaft of other accessories, the gear train comprises the gears on the drive shafts of the accessories, and the gears on the drive shafts of the accessories are all enclosed by the accessory gearbox casing of the accessory gearbox. 
     The accessory gearbox may comprise a gear and an associated drive shaft for each accessory, each drive shaft is supported on an associated accessory casing by two bearings, the gear on the drive shaft of each accessory is arranged to mesh with one or more gears on the corresponding drive shaft of other accessories, and the gears on the drive shafts of the accessories are all enclosed by the accessory gearbox casing of the accessory gearbox. 
     The accessory gearbox may comprise a gear and an associated gear shaft for each accessory, each gear shaft is mounted on the accessory gearbox casing by two bearings, each gear shaft has splines on an end of each gear shaft to drive the accessory, each accessory has a drive shaft supported on an associated accessory casing by two bearings, the drive shaft of each accessory has splines arranged to mesh with the splines on the corresponding gear shaft, the gear train comprises the gears for the associated accessories, and the gears, gear shafts and bearings for the gear shafts are all enclosed by the accessory gearbox casing of the accessory gearbox. 
     According to a second aspect of the present disclosure there is provided a gas turbine engine comprising an accessory gearbox assembly comprising an accessory gearbox and a plurality of accessories arranged to be driven by the accessory gearbox, the accessory gearbox comprising a gear train and an accessory gearbox casing enclosing the gears of the gear train, each accessory is driven by a drive shaft, each accessory has a first end and a second opposite end, each accessory is secured at the first end to the accessory gearbox casing and the second opposite end of at least two of the plurality of accessories are secured to a structural cross member. 
     A first plurality of accessories may be secured to a first side of the accessory gearbox casing, the drive shafts of the first plurality of accessories are parallel and the second opposite end of at least two of the first plurality of accessories are secured to a first structural cross member. 
     The at least two of the plurality of accessories may be the largest and/or the heaviest accessories secured to the first side of the accessory gearbox. 
     The largest and/or heaviest accessories may be electrical generators. 
     The second opposite end of more than two of the plurality of accessories may be secured to the structural cross member. 
     The second opposite end of all the plurality of accessories may be secured to the structural cross member. 
     A second plurality of accessories may be secured to a second opposite side of the accessory gearbox casing, the drive shafts of the second plurality of accessories are parallel and the second opposite end of at least two of the second plurality of accessories are secured to a second structural cross member. 
     The second opposite end of more than two of the second plurality of accessories may be secured to the second structural cross member. 
     The second opposite end of all the second plurality of accessories may be secured to the second structural cross member. 
     The drive shaft of each accessory may be supported on an associated accessory casing by two bearings, the drive shaft of each accessory has at least one gear, the gear on the drive shaft of each accessory is arranged to mesh with one or more gears on the corresponding drive shaft of other accessories or the gear on the drive shaft of each accessory is arranged to mesh with one or more idler gears which mesh with the gears on the corresponding drive shaft of other accessories, the gear train comprises the gears on the drive shafts of the accessories, and the gears on the drive shafts of the accessories are all enclosed by the accessory gearbox casing of the accessory gearbox. 
     The accessory gearbox may comprise a gear and an associated drive shaft for each accessory, each drive shaft is supported on an associated accessory casing by two bearings, the gear on the drive shaft of each accessory is arranged to mesh with one or more gears on the corresponding drive shaft of other accessories and the gears on the drive shafts of the accessories are all enclosed by the accessory gearbox casing of the accessory gearbox. 
     The accessory gearbox may comprise a gear and an associated gear shaft for each accessory, each gear shaft is mounted on the accessory gearbox casing by two bearings, each gear shaft has splines on an end of each gear shaft to drive the accessory, each accessory has a drive shaft supported on an associated accessory casing by two bearings, the drive shaft of each accessory has splines arranged to mesh with the splines on the corresponding gear shaft, the gear train comprises the gears for the associated accessories, and the gears, gear shafts and bearings for the gear shafts are all enclosed by the accessory gearbox casing of the accessory gearbox. 
     The gas turbine engine may be an aero gas turbine engine, a marine gas turbine engine, an industrial gas turbine engine or an automotive gas turbine engine. 
     The aero gas turbine engine may be a turbojet gas turbine engine, a turbo-propeller gas turbine engine, a turbo-shaft gas turbine engine or a turbofan gas turbine engine. 
     The accessory gearbox may be mounted on a fan casing of the turbofan gas turbine engine or the accessory gearbox may be mounted on a core engine casing of the turbofan gas turbine engine. 
     According to a third aspect of the present disclosure there is provided an accessory gearbox assembly comprising an accessory gearbox and a plurality of accessories arranged to be driven by the accessory gearbox, the accessory gearbox comprising a gear train and an accessory gearbox casing enclosing the gears of the gear train, each accessory has a drive shaft supported on an associated accessory casing by two bearings, the drive shaft of each accessory has at least one gear, the gear on the drive shaft of each accessory is arranged to mesh with one or more gears on the corresponding drive shaft of other accessories or the gear on the drive shaft of each accessory is arranged to mesh with one or more idler gears which mesh with the gears on the corresponding drive shaft of other accessories, the gear train comprises the gears on the drive shafts of the accessories, and the gears on the drive shafts of the accessories are all enclosed by the accessory gearbox casing of the accessory gearbox. 
     According to a fourth aspect of the present disclosure there is provided a gas turbine engine comprising an accessory gearbox assembly comprising an accessory gearbox and a plurality of accessories arranged to be driven by the accessory gearbox, the accessory gearbox comprising a gear train and an accessory gearbox casing enclosing the gears of the gear train, each accessory has a drive shaft supported on an associated accessory casing by two bearings, the drive shaft of each accessory has at least one gear, the gear on the drive shaft of each accessory is arranged to mesh with one or more gears on the corresponding drive shaft of other accessories or the gear on the drive shaft of each accessory is arranged to mesh with one or more idler gears which mesh with the gears on the corresponding drive shaft of other accessories, the gear train comprises the gears on the drive shafts of the accessories, and the gears on the drive shafts of the accessories are all enclosed by the accessory gearbox casing of the accessory gearbox. 
     The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects of the invention may be applied mutatis mutandis to any other aspect of the invention. 
     Embodiments of the invention will now be described by way of example only, with reference to the Figures, in which: 
    
    
     
         FIG. 1  is a sectional side view of a gas turbine engine having an accessory gearbox assembly according to the present disclosure. 
         FIG. 2  is an enlarged view in the direction of arrow A in  FIG. 1 . 
         FIG. 3  is a schematic plan view of an accessory gearbox assembly according to the present disclosure. 
         FIG. 4  is a schematic plan view of a further accessory gearbox assembly according to the present disclosure. 
         FIG. 5  is an enlarged schematic cross-sectional view along line B-B of  FIG. 3 . 
         FIG. 6  is an alternative enlarged schematic cross-sectional view along line B-B of  FIG. 3 . 
     
    
    
     With reference to  FIG. 1 , a gas turbine engine is generally indicated at  10 , having a principal and rotational axis  11 . The engine  10  comprises, in axial flow series, an air intake  12 , a propulsive fan  13 , an intermediate pressure compressor  14 , a high-pressure compressor  15 , combustion equipment  16 , a high-pressure turbine  17 , and intermediate pressure turbine  18 , a low-pressure turbine  19  and an exhaust nozzle  20 . A nacelle  21  generally surrounds the engine  10  and defines both the intake  12  and the exhaust nozzle  20 . 
     The gas turbine engine  10  works in the conventional manner so that air entering the intake  12  is accelerated by the fan  13  to produce two air flows: a first air flow into the intermediate pressure compressor  14  and a second air flow which passes through a bypass duct  22  to provide propulsive thrust. The intermediate pressure compressor  14  compresses the air flow directed into it before delivering that air to the high pressure compressor  15  where further compression takes place. 
     The compressed air exhausted from the high-pressure compressor  15  is directed into the combustion equipment  16  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines  17 ,  18 ,  19  before being exhausted through the nozzle  20  to provide additional propulsive thrust. The high  17 , intermediate  18  and low  19  pressure turbines drive respectively the high pressure compressor  15 , intermediate pressure compressor  14  and fan  13 , each by suitable interconnecting shafts  23 ,  24  and  25  respectively. 
     The gas turbine engine  10  further comprises an accessory gearbox assembly  28 . The accessory gearbox assembly  28  is drivingly connected to the shaft  23  connecting the high pressure compressor  15  and the high pressure turbine  17  via drive means  30 . However, in other embodiments the accessory gearbox assembly  28  may be driven by the shaft  24  connecting the intermediate pressure compressor  14  and the intermediate pressure turbine  18  or by the shaft  25  connecting the fan  13  and the low pressure turbine  19 . In this arrangement the drive means  30  comprises an internal gearbox  32  provided at the upstream end of the shaft  23 . The internal gearbox  32  comprises a bevel gear  34  at the upstream end of the shaft  23  and a bevel gear  36  arranged on the radially inner end of a radial drive shaft  38 . The bevel gear  36  on the radial drive shaft  38  is arranged to mesh with the bevel gear  34  on the shaft  23 . The radial drive shaft  38  extends through a strut extending across the flow path from the intermediate pressure compressor  14  to the high pressure compressor  15 . 
     An intermediate gearbox, alternatively known as a step aside gearbox,  40  is provided at the radially outer end of the radial drive shaft  38 . The intermediate gearbox  40  comprises a bevel gear  42  on the radially outer end of the radial drive shaft  38  and a bevel gear  44  arranged on an inner end of a further drive shaft  46 . In this example the further drive shaft  46  is an angled drive shaft. The bevel gear  42  on the radial drive shaft  38  is arranged to mesh with the bevel gear  44  on the further drive shaft  46 . The further drive shaft  46  extends through a strut extending across the bypass duct  22 . The casing of the intermediate gearbox  40  is mounted on the core engine casing  66 . The core engine casing  66  is secured to a fan casing  41  which surrounds the fan  13  by a plurality of radially extending circumferentially spaced fan outlet guide vanes  68 . The fan casing  41  is integrated into the structure of the nacelle  21 . 
     A bevel gear  48  is provided on the radially outer end of the further drive shaft  46  and the bevel gear  50  is arranged to mesh with a bevel gear  50  on a final drive shaft  52 . The final drive shaft  52  is arranged to provide drive for the accessory gearbox assembly  28 . The accessory gearbox assembly  28  comprises an accessory gearbox  54  and a plurality of accessories  56  arranged to be driven by the accessory gearbox  54 . The accessory gearbox  54  is mounted on the fan casing  41  and within the nacelle  21 . 
     The accessory gearbox  54  is generally arcuate to correspond with the curvature of the fan casing  41 , as shown in  FIG. 2 , and the opposite circumferential ends, with respect to the axis of the gas turbine engine  10 , of the accessory gearbox  54  are secured by struts  60  extending from the accessory gearbox casing  58  to the fan casing  41 . The accessory gearbox  54  may be secured to the fan casing  41  by other struts extending from the accessory gearbox casing  58  to the fan casing  41  between the ends of the accessory gearbox  54 . 
     An arrangement of the accessory gearbox assembly  28  is shown more clearly in  FIG. 3 . The accessory gearbox assembly  28  comprises a gear train (not shown) and an accessory gearbox casing  58  enclosing the gears of the gear train. Each accessory  56  is driven by a drive shaft  57 . Each accessory  56  has a first end and a second opposite end and each accessory  56  is secured at the first end to the accessory gearbox casing  58 . In this arrangement the accessories  56  are secured to the accessory gearbox casing  58  by fasteners, e.g. bolts  59  and nuts, but other suitable fasteners, e.g. bolts and threaded inserts or screws, may be used. A plurality of accessories  56  are secured to a first side  58 A of the accessory gearbox casing  58  and the second opposite end of at least two of the plurality of accessories  56  are secured to a structural cross member  62 . The drive shafts  57  of the accessories  56  secured to the first side  58 A of the accessory gearbox casing  58  are parallel. In this arrangement the accessories  56  are secured to the structural cross member  62  by fasteners, e.g. bolts  64  and threaded inserts, but other suitable fasteners, e.g. screws or bolts and nuts, may be used. The structural cross member  62  is spaced from the first side  58 A of the accessory gearbox  54  and in this particular example is parallel to the first side  58 A of the accessory gearbox  54 . 
     The at least two of the plurality of accessories  56  are the largest and/or the heaviest accessories secured to the first side  58 A of the accessory gearbox  54 . The largest and/or heaviest accessories  56  may be electrical generators. In some arrangements the second opposite end of more than two of the plurality of accessories  56  are secured to the structural cross member  62  and in other arrangements the second opposite end of all the plurality of accessories  56  may be secured to the structural cross member  62 . 
     A second plurality of accessories  56  are secured to a second opposite side  58 B of the accessory gearbox casing  58  and the second opposite end of the second plurality of accessories  56  are unsupported. The drive shafts  57  of the second plurality of accessories  56  secured to the second opposite side  58 B of the accessory gearbox casing  58  are parallel. In this arrangement the accessories  56  are secured to the accessory gearbox casing  58  by fasteners, e.g. bolts  59  and nuts, but other suitable fasteners, e.g. bolts and threaded inserts or screws, may be used. 
     The accessories  56  include a starter motor  56 A, an oil pump  56 B, a hydraulic pump  56 C, a low pressure fuel pump  56 D, an aircraft electrical generator  56 E, a high pressure fuel pump  56 F, an engine electrical generator  56 G, a fuel flow governor  56 G. Other accessories, for example a tachometer, a permanent magnet electrical generator, a permanent magnet alternator, to provide power to the engine electronic control unit (EEC) are also mounted on and driven by the accessory gearbox  54 . 
     A further arrangement of the accessory gearbox assembly  28 A is shown more clearly in  FIG. 4 . The accessory gearbox assembly  28  comprises a gear train (not shown) and an accessory gearbox casing  58  enclosing the gears of the gear train. Each accessory  56  is driven by a drive shaft  57 . Each accessory  56  has a first end and a second opposite end and each accessory  56  is secured at the first end to the accessory gearbox casing  58 . In this arrangement the accessories  56  are secured to the accessory gearbox casing  58  by fasteners, e.g. bolts  59  and nuts, but other suitable fasteners, e.g. bolts and threaded inserts or screws, may be used. A plurality of accessories  56  are secured to a first side  58 A of the accessory gearbox casing  58  and the second opposite end of at least two of the plurality of accessories  56  are secured to a structural cross member  62 . The drive shafts  57  of the accessories  56  secured to the first side  58 A of the accessory gearbox casing  58  are parallel. In this arrangement the accessories  56  are secured to the structural cross member  62  by fasteners, e.g. bolts  64  and threaded inserts, but other suitable fasteners, e.g. screws or bolts and nuts, may be used. The structural cross member  62  is spaced from the first side  58 A of the accessory gearbox  54  and in this particular example is parallel to the first side  58 A of the accessory gearbox  54 . 
     The at least two of the plurality of accessories  56  are the largest and/or the heaviest accessories secured to the first side  58 A of the accessory gearbox  54 . The largest and/or heaviest accessories  56  may be electrical generators. In some arrangements the second opposite end of more than two of the plurality of accessories  56  are secured to the structural cross member  62  and in other arrangements the second opposite end of all the plurality of accessories  56  may be secured to the structural cross member  62 . 
     A second plurality of accessories  56  are secured to a second opposite side  58 B of the accessory gearbox casing  58  and the second opposite end of at least two of the second plurality of accessories are secured to a second structural cross member  62 A. The drive shafts  57  of the second plurality of accessories  56  secured to the second opposite side  58 B of the accessory gearbox casing  58  are parallel. In this arrangement the accessories  56  are secured to the accessory gearbox casing  58  by fasteners, e.g. bolts  59  and nuts, but other suitable fasteners, e.g. bolts and threaded inserts or screws, may be used. In this arrangement the accessories  56  are secured to the structural cross member  62 A by fasteners, e.g. bolts  64  and threaded inserts, but other suitable fasteners, e.g. screws or bolts and nuts, may be used. In some arrangements the second opposite end of more than two of the second plurality of accessories  56  may be secured to the second structural cross member  62 A. In some arrangements the second opposite end of all the second plurality of accessories  56  may be secured to the second structural cross member  62 A. The second structural cross member  62 A is spaced from the second side  58 B of the accessory gearbox  54  and in this particular example is parallel to the second side  58 B of the accessory gearbox  54 . 
     The accessories  56  include a starter motor  56 A, an oil pump  56 B, a hydraulic pump  56 C, a low pressure fuel pump  56 D, an aircraft electrical generator  56 E, a high pressure fuel pump  56 F, an engine electrical generator  56 G, a fuel flow governor  56 G. Other accessories, for example a tachometer, a permanent magnet electrical generator, a permanent magnet alternator, to provide power to the engine electronic control unit (EEC) are also mounted on and driven by the accessory gearbox  54 . 
     The advantage of the present disclosure is that it uses the accessories themselves to increase the stiffness of the accessory gearbox assembly by connecting/linking the free ends of two or more of the accessories by a structural cross member. This ensures that the accessories contribute to the stiffness and strength of the accessory gearbox assembly. The free ends of the accessories are constrained and this reduces the displacements of the accessories and hence reduces the stresses the accessories induce within the accessory gearbox especially during extreme events, such as a fan blade off. This allows the accessory gearbox casing to be reduced in thickness, reducing weight and cost. 
     The accessory gearbox assembly  28  in one example, as shown in  FIG. 5 , comprises for each accessory  56  a gear  70  and associated gear shaft  72  mounted on the accessory gearbox casing  58  by two bearings, e.g. two roller bearings,  74  and  76  splines  78  on the end of each gear shaft  72  to drive the accessory  56  and a seal  80  where the gear shaft  72  extends through the accessory gearbox casing  58 . A shaft  82  of the accessory  56  is supported on the accessory casing  84  by two bearings, e.g. two roller bearings, only one of which  86  is shown, splines  88  on the shaft  82  of the accessory  56  which are arranged to mesh with the splines  78  on the corresponding gear shaft  72  and a seal  90  where the shaft  82  of the accessory  56  passes through the casing  84  of the accessory  56 . The gears  70 , which are arranged to drive the accessories  56 , are arranged to mesh to form a gear train. The gears  70 , gear shafts  72  and bearings  74 ,  76  for the gear shafts  72  are all enclosed by the accessory gearbox casing  58  of the accessory gearbox  54 . There may be idler gears supported on the accessory casing by two bearings, e.g. two roller bearings, between and meshing with the gears  70  which are arranged to drive the accessories  56 . The gears  70 , gear shafts  72  and bearings  74 ,  76  for the gear shafts  72 , the idler gears and bearings are all enclosed by the accessory gearbox casing  58  of the accessory gearbox  54 . In this arrangement the splines  78  extend radially outwardly from the gear shaft  72  and the splines  88  extend radially inwardly from the shaft  82 , but the splines  78  may extend radially inwardly from the gear shaft  72  and the splines  88  may extend radially outwardly from the shaft  82 . 
     The accessory gearbox assembly  28 C in another example, as shown in  FIG. 6 , comprises a shaft  92  of the accessory  56  supported on the accessory casing  94  by two bearings, e.g. two roller bearings, only one of which  96  is shown, at least one gear  98  on the shaft  92  of the accessory  56  and a seal  98  where the shaft  92  of the accessory  56  extends through the casing  94  of the accessory  56 . There may be a seal where the shaft  92  of the accessory  56  passes through the accessory gearbox casing  58 A of the accessory gearbox  54 A and the gear  98  on the shaft  92  of each accessory  56  is arranged to mesh with one or more gears  98  on the corresponding shaft  92  of other accessories  56  or mesh with one or more idler gears which mesh with the gears  98  on the corresponding shaft  92  of other accessories  56 . Thus, the gears  98  mounted on the shafts  92  of the accessories  56  build up the gear train within the accessory gearbox casing  58 A as the accessories  56  are mounted onto the accessory gearbox casing  58 A. The apertures in the accessory gearbox casing  58 A each have a diameter large enough to enable the gear  98  on the shaft  92  of the corresponding accessory  56  to pass there-through. The accessories are designed to support the gear train and to react the gear loads. This arrangement removes the requirement for gear shafts mounted on the accessory gearbox casing and bearings to mount the gear shafts on the accessory gearbox casing and within the gearbox itself. Mounting the drive gears on the accessories effectively reduces the accessory gearbox to a slim and light weight accessory gearbox casing to contain lubricant, oil, and provide the gear train lubrication system and this would enable a significant cost and weight reduction. 
     Although the present disclosure has referred to the drive shafts of the accessories being arranged parallel at the first and second sides of the accessory gearbox it may be possible to provide one or more accessories which have a drive shaft arranged at another angle, for example an accessory may be provided at an end of the accessory gearbox, or at an arcuate side of the accessory gearbox, and driven for example by a bevel gear and the second end of such an accessory may also be secured to a structural cross member. 
     Although the present disclosure has been described with the use of removable fasteners to secure the accessories to the structural cross member and the second structural cross member it may be equally possible to the weld, braze or bond one or more of the accessories to the structural member and/or to the second structural member. The structural member and/or the second structural member may comprise a suitable material for example a metal, e.g. steel, titanium, aluminium etc., or a composite material, a fibre reinforced material, e.g. a metal matrix composite. 
     Although the present disclosure has been described with reference to the accessories in particular positions with respect to the accessory gearbox it is equally possible to provide each of them at any other suitable position. 
     Although the present disclosure has been described with reference to mounting the accessory gearbox on the fan casing it may be equally possible to mount the accessory gearbox on the core engine casing. 
     Although the present invention has been described with reference to a turbofan gas turbine engine, it is equally applicable to a turbojet gas turbine engine, a turbo-shaft gas turbine engine and a turbo-propeller gas turbine engine. Although the present invention has been described with reference to an aero gas turbine engine it is equally applicable to a marine gas turbine engine, an industrial gas turbine engine and an automotive gas turbine engine or other type of turbomachine. 
     It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.