SPLINE JOINT

Abstract

A spline joint comprising: a sidewall extending along and around an axis defining an axial direction of the joint, wherein the sidewall defines a passage extending from a first end to a second end; wherein the passage is arranged to receive an end of a shaft at the first end; and wherein an engagement portion of an inner surface of the sidewall adjacent the first end is arranged to engage a shaft received in the passage, to transmit torque to the shaft; a base wall extending across the passage and axially spaced from the first end of the passage; an opening formed through the base wall; and an inner wall extending around the opening and in the axial direction from the base wall, such that an annular trough arranged to retain lubricant for the spline joint is defined between the sidewall and the inner wall.

Claims

1. A spline joint comprising: a sidewall extending along and around an axis defining an axial direction of the joint, wherein the sidewall defines a passage extending from a first end to a second end; wherein the passage is arranged to receive an end of a shaft at the first end; and wherein an engagement portion of an inner surface of the sidewall adjacent the first end is arranged to engage a shaft received in the passage, to transmit torque to the shaft; a base wall extending across the passage and axially spaced from the first end of the passage; an opening formed through the base wall; and an inner wall extending around the opening and in the axial direction from the base wall, such that an annular trough arranged to retain lubricant for the spline joint is defined between the sidewall and the inner wall.

2. The spline joint of claim 1, wherein the spline joint is axisymmetric.

3. The spline joint of claim 1, wherein the inner wall extends from a first end, to a second end; and wherein the first end of the inner wall is between the first end of the passage and the base wall, and the second end of the inner wall is at the base wall.

4. The spline joint of claim 3, wherein the engagement portion extends a portion of the axial length of the sidewall from the first end; and wherein the first end of the inner wall is axially spaced from the engagement portion.

5. The spline joint of claim 1, wherein the trough is arranged to provide lubricant to the engagement portion through centrifugal force.

6. The spline joint of claim 5, wherein the axial direction is at least 45 degrees to horizontal.

7. The spline joint of claim 6, wherein the axial direction is perpendicular to horizontal.

8. The spline joint of claim 1, wherein the spline joint is an articulating spline.

9. The spline joint of claim 1, including: a second engagement portion arranged to engage another shaft extending in the axial direction, wherein the second engagement portion is radially outside the engagement portion on the inner surface the passage, and wherein the second engagement portion is arranged to be received within the other shaft, such that the spline joint comprises an adapter arranged to join a first shaft received in the passage and a second shaft receiving the spline joint.

10. The spline joint of claim 9, wherein the second engagement portion is arranged to form a rigid joint to the second shaft.

11. The spline joint of claim 1, wherein the spline joint is formed in an end of a shaft, such that the spline joint joins a shaft incorporating the passage and a shaft received in the passage.

12. A gas turbine engine for an aircraft comprising: an engine core including a turbine, a compressor, and a core shaft driven by the turbine; an accessory unit for driving hydraulic, pneumatic and electrical systems of the turbine engine; a fan located upstream of the engine core, the fan comprising a plurality of fan blades and being driven by the engine core; and an accessory drive train for providing a portion of the power of the core shaft to the accessory unit, wherein the accessory drive train extends radially from the core shaft; and wherein the accessory drive train includes a spline joint, wherein the spline joint comprising: a sidewall extending along and around an axis defining an axial direction of the joint, wherein the sidewall defines a passage extending from a first end to a second end; wherein the passage is arranged to receive an end of a shaft at the first end; and wherein an engagement portion of an inner surface of the sidewall adjacent the first end is arranged to engage a shaft received in the passage, to transmit torque to the shaft; a base wall extending across the passage and axially spaced from the first end of the passage; an opening formed through the base wall; and an inner wall extending around the opening and in the axial direction from the base wall, such that an annular trough arranged to retain lubricant for the spline joint is defined between the sidewall and the inner wall.

13. The gas turbine engine of claim 12, including: a lubrication system arranged to deliver lubricant to the spline joint, during engine operation, wherein the lubrication system is driven by the accessory unit; and wherein the trough of the spline joint delivers lubricant, when the lubrication system is not primed.

14. The gas turbine engine of claim 13, wherein a radial width of the trough between the sidewall and inner wall, and an axial length of the inner wall is arranged such that the volume of lubricant in the trough on engine shutdown is equal or substantially equal to the volume of lubricant held in the joint during use; and wherein excess lubricant flows through the opening.

15. The gas turbine engine of claim 12, wherein the core shaft has a principal axis, the accessory drive train includes a first shaft, operatively coupled to the spline joint, and wherein the first shaft extends at an angle of 45 degrees or more from the principal axis defined by the core shaft.

16. The gas turbine engine of claim 12, including a power gearbox that receives an input from the core and outputs drive to the fan, wherein the power gearbox is a step down gearbox.

17. The gas turbine engine of claim 12, wherein: the turbine is a first turbine, the compressor is a first compressor, and the core shaft is a first core shaft; the engine core further comprises a second turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor.

18. The gas turbine engine of claim 17, wherein the second core shaft is arranged to rotate at a lower rotational speed than the first core shaft; and the input to the power gearbox is provided by the second core shaft.

Description

[0047] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0048] FIG. 1 is a sectional side view of a gas turbine engine;

[0049] FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

[0050] FIG. 3 is a partially cut-away view of a power gearbox for a gas turbine engine;

[0051] FIG. 4 is a schematic sectional side view of an accessory unit and accessory drive train of a gas turbine engine;

[0052] FIG. 5A schematic sectional side view of a spline joint adapter for use in the drive train of FIG. 4;

[0053] FIG. 5B perspective view of a spline joint adapter of FIG. 5A;

[0054] FIG. 5C sectional perspective view of a spline joint adapter of FIG. 5A;

[0055] FIG. 6A is a perspective section view of a spline joint between two shafts, using the adapter of FIG. 5A, at engine shut-down;

[0056] FIG. 6B is a perspective section view of a spline joint between two shafts, using the adapter of FIG. 5A, at engine start-up;

[0057] FIG. 6C is a perspective section view of a spline joint between two shafts, using the adapter of FIG. 5A, during engine operation;

[0058] FIG. 7A is a perspective section view of a first alternative spline joint between two shafts; and

[0059] FIG. 7B is a perspective section view of a second alternative spline joint between two shafts.

[0060] FIG. 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

[0061] In use, the core airflow A is accelerated and compressed by the low pressure compressor 14 and directed into 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 is combusted. The resultant hot combustion products then expand through, and thereby drive, the high pressure and low pressure turbines 17, 19 before being exhausted through the nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 by a suitable interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

[0062] An exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 2. The low pressure turbine 19 (see FIG. 1) drives the shaft 26, which is coupled to a sun wheel, or sun gear, 28 of the epicyclic gear arrangement 30. Radially outwardly of the sun gear 28 and intermeshing therewith is a plurality of planet gears 32 that are coupled together by a planet carrier 34. The planet carrier 34 constrains the planet gears 32 to process around the sun gear 28 in synchronicity whilst enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled via linkages 36 to the fan 23 in order to drive its rotation about the engine axis 9. Radially outwardly of the planet gears 32 and intermeshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

[0063] Note that the terms low pressure turbine and low pressure compressor as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 23) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft 26 with the lowest rotational speed in the engine (i.e. not including the gearbox output shaft that drives the fan 23). In some literature, the low pressure turbine and low pressure compressor referred to herein may alternatively be known as the intermediate pressure turbine and intermediate pressure compressor. Where such alternative nomenclature is used, the fan 23 may be referred to as a first, or lowest pressure, compression stage.

[0064] The epicyclic gearbox 30 is shown by way of example in greater detail in FIG. 3. Each of the sun gear 28, planet gears 32 and ring gear 38 comprise teeth about their periphery to intermesh with the other gears. However, for clarity only exemplary portions of the teeth are illustrated in FIG. 3. There are four planet gears 32 illustrated, although it will be apparent to the skilled reader that more or fewer planet gears 32 may be provided within the scope of the claimed invention. Practical applications of a planetary epicyclic gearbox 30 generally comprise at least three planet gears 32.

[0065] The epicyclic gearbox 30 illustrated by way of example in FIGS. 2 and 3 is of the planetary type, in that the planet carrier 34 is coupled to an output shaft via linkages 36, with the ring gear 38 fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held fixed, with the ring (or annulus) gear 38 allowed to rotate. In such an arrangement the fan 23 is driven by the ring gear 38. By way of further alternative example, the gearbox 30 may be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

[0066] It will be appreciated that the arrangement shown in FIGS. 2 and 3 is by way of example only, and various alternatives are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used for locating the gearbox 30 in the engine 10 and/or for connecting the gearbox 30 to the engine 10. By way of further example, the connections (such as the linkages 36, 40 in the FIG. 2 example) between the gearbox 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft and the fixed structure 24) may have any desired degree of stiffness or flexibility. By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 2. For example, where the gearbox 30 has a star arrangement (described above), the skilled person would readily understand that the arrangement of output and support linkages and bearing locations would typically be different to that shown by way of example in FIG. 2.

[0067] Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

[0068] Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

[0069] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 20, 22 meaning that the flow through the bypass duct 22 has its own nozzle that is separate to and radially outside the core engine nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine 10 may not comprise a gearbox 30.

[0070] The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

[0071] Gas turbine engines 10 such as the one discussed above include an accessory unit 25 that can provide power to the hydraulic, pneumatic and electrical systems 41 of an aircraft on which the engine 10 is mounted. The accessory unit 25 can also power ancillary systems of the gas turbine engine 10, such as a lubrication system 42.

[0072] The accessory unit 25 is located radially outside the core engine 11. The drive for the accessory unit 25 is taken from the core shaft 27 interconnecting the high pressure turbine 17 and the high pressure compressor 15. The drive is provided by a drive train 50 extending from the core shaft 27 to the accessory unit. In the example shown, the drive train 50 is formed of a first shaft 52, and a second shaft 54.

[0073] The radial drive train 50 is coupled to the core shaft 27 at an internal gearbox 29, which transmits torque from the core shaft 27 to the first shaft 52. The torque is transmitted to the second shaft 54 through a spline joint 60, and into an external gearbox (not shown) within the accessory unit. The external gearbox provides a mount for the various accessory systems, and transmits appropriate geared drive to each system.

[0074] The drive train 50 has an axis 56 extending down the centre of the first radial shaft 52. As shown in FIG. 4, the drive train 50 extends in an axial direction, as well as a radial direction. Therefore, the drive train axis 56 is inclined with respect to the principle axis 9 of the engine 10. The incline may be defined by a first angle 58 between the principle axis 9 and the drive train axis 56 or a second angle 58 between the radial direction (radial to the principal axis 9) and the drive train axis 56. The sum of the first and second angle 58, 58 is always 90 degrees.

[0075] The principal axis 9, and drive train axis 56 are parallel when the first angle 58 is 0 degrees and the second angle is 90 degrees (i.e. the drive train axis 56 extends fully axially), and the axes 9, 56 are perpendicular when the first angle 58 is 90 degrees and the second angle 58 is 0 (i.e. the drive train axis 56 extends fully radially). The principle axis 9 of the engine defines the horizontal direction.

[0076] The spline joint 60 is formed by an adapter 62, which forms a rigid spline connection to the first shaft 52, and an articulating spline connection to the second shaft 54. The rigid spline connection to the first shaft 52, means that the adapter 62 is fully constrained with respect to the first shaft 52, with no freedom of movement. Therefore, an axis 64 extending centrally through the adapter 62 will always be coincident with the axis 56 of the drive train 50 and first shaft 52.

[0077] The articulating spline connection formed with the second shaft 54, on the other hand, allows the second shaft 54 to move relative to the adapter 62 and the first shaft 52, whilst still transferring torque from the adapter 62 to the second shaft 54. Generally, the movement can be seen as a pivoting of the second shaft 54 relative to the drive train axis 56, so that the second shaft does not extend along the drive train axis 56. The pivot point for the second shaft 54 may be at the adapter 62 or the accessory unit 25.

[0078] In use, there may be some relative movement of the different regions of the gas turbine engine 10. The use of an articulating spline accommodates any relative movement of the core 11, and the region in which the accessory unit 25 is mounted, without damage being caused.

[0079] The adapter 62 will now be described in more detail, with reference to FIGS. 5A to 5C. The adapter 62 is formed of a cylindrical sidewall 66 formed around and along the joint axis 64. The sidewall 66 defines a passage 68 extending through the adapter 60.

[0080] At a first end 70, the passage 68 is open. A plurality of axially extending (with respect to the joint axis 64) ridges 74 are formed on an inner surface 76 of the sidewall 66. The plurality of ridges 74 extend around the circumference of the passage 68, and along a portion of the length of the passage 68, to form an engagement portion of the passage 80. The engagement portion 80 extends to a first axial length along the passage 68, towards the second end 72.

[0081] At the second end 72 of the passage 68, opposite the first end 70, the passage 68 is closed by a circular end wall 82, extending perpendicular to the joint axis 64. An opening 84 is formed in the centre of the end wall 82, such that the joint axis 64 extends through the opening 84. A cylindrical inner wall 86 extends from the edge of the opening 84, into the passage 68.

[0082] An annular trough 88 is formed between the inner wall 86 and the sidewall 66. The base of the trough 88 is formed by the end wall 82. The trough 88 has a radial width 90 between the sidewall 66 and the inner wall 86, and a depth defined by the axial length 92 that the inner wall extends into the passage 68, from the end wall 82.

[0083] The inner wall 86 has a first end 94 received in the passage 68, and a second end 96 at the end wall 88. The first end 94 of the inner wall 86 is at a second axial position along the passage 68. The second axial position is provided between the first axial position (the extent of the engagement portion 80) and the end wall 82, such that an axial spacing is provided between the engagement portion 80 and the trough 88.

[0084] An annular flange 98 is formed on the outer surface 78 of the sidewall 66, between the first end 70 and the second end 72. The flange 98 extends around the circumference the sidewall 66, and extends radially outward, with a first face 100 facing towards the first end 70 of the passage 68, and an opposing second axial face 102, facing the opposite direction. The first face 100 includes a step 106 in the axial direction.

[0085] An annular outer wall 104 extends axially from the second axial face 102 of the flange 98, towards the second end 72 of the passage 68. The outer wall 104 extends along a portion of the length of the sidewall 66 towards the second end 72, and is radially spaced from the sidewall 68, such that the outer wall 104 aligns with the step 106 in the first axial face 100 of the flange 98. An annular outer portion 108 of the second axial face 102 of the flange 98 is formed radially outward of the outer wall 104.

[0086] Axially extending (with respect to the joint axis 64) ridges 110 are formed on an outer surface 111 of the outer wall 104, extending around the circumference of the outer wall 104, and along the length of the outer wall 104, to form a second engagement portion 112.

[0087] The sidewall 66, inner 86, outer wall 104, flange 98, opening 84 and trough 88 are axisymmetric around the axis of the joint 64.

[0088] FIGS. 6A to 6C schematically illustrate the adapter 62 of FIGS. 5A to 5C coupled to a first shaft 52 and a second shaft 54, to form a spline joint 60, in various different usage scenarios. The first and second shafts 52, 54 are both cylindrical shafts having respective passages 114, 116 extending through them, which are open at both ends.

[0089] The first shaft 52, which is the radially inner shaft, with reference to FIG. 4, has a plurality of axially extending (with respect to the joint axis 64) ridges 118 on an inner surface 120 of the passage 114 adjacent the end 122 of the shaft 52 which engages the adapter 62. The ridges 118 extend around the circumference of the passage 114, and along a portion of the length of the passage 114, to form an engagement portion of the passage 120. The engagement portion 124 extends to a first axial length along the passage 114, away from the end 122.

[0090] In the assembled joint 60, the first shaft extends over the second end 72 of the adapter 62, around the outer wall 104. The ridges 110 of the second engagement portion 112 of the adapter 62 engage the ridges 118 of the engagement portion 124 of the first shaft 52, so that torque is transmitted from the first shaft 52 to the adapter 62.

[0091] The end 112 of the first shaft includes a annular flange 126 that has a face 128 facing towards and mating with the annular outer portion 108 of the adapter 62. A plurality of nuts and bolts (not shown) passing through the flange 126 in the shaft 52 and the annular outer portion 108 of the flange 98 of the adapter 62, to secure the first shaft 52 to the adapter 62. As such, the joint of the first shaft 52 to the adapter 62 is a rigid joint.

[0092] The second shaft 54 extends into the open end 70 of the passage 68. Axially extending (with respect to the joint axis 64) ridges 130 are formed on an outer surface 132 of the outer wall second shaft 54, at an end 136 received in the passage 68. The ridges 130 extend around the circumference of the shaft 54, along at least a portion of the length of the shaft 54, to form an engagement portion 134 on the second shaft

[0093] The ridges 74 of the first engagement portion 80 of the adapter 62 engage the ridges 130 of the engagement portion 134 of the second shaft 54, so that torque is transmitted from the adapter 62 to the second shaft 54. The second shaft 54 is not secured to the adapter 54. Furthermore, there is some radial clearance between the outer surface 132 of the second shaft 54, and the inner surface 76 of the passage. Whilst the ridges 74, 130 may still engage to transfer torque, this clearance is sufficient to allow some relative movement of the adapter 62 and second shaft 54. Therefore, the joint between the second shaft 54 and the adapter 62 is an articulating spline.

[0094] The second shaft 54 only extends partway into the passage 68. The second shaft 54 extends a sufficient length into the passage that the engagement portions 80, 134 can transfer torque over the range of movement of the articulating spline, but an axial spacing is still provided between the end 136 of the second shaft 54 and the first end 94 of the inner wall 86. Radial projections (not shown) may extend into the passage, and/or be formed in the outer surface of the second shaft 132 to limit the extent the second shaft 54 extends into the passage 68, or the axial position of the second shaft may be limited in other suitable ways.

[0095] FIG. 6A illustrates the spline joint 60 during and after engine shutdown. Oil, or other lubricant 138, that is used to lubricate the engagement portions 80, 134 during engine operation, is collected in the trough 88 formed at the closed end 72 of the passage 68.

[0096] FIG. 6B illustrates the spline joint 60 during engine start-up, when the accessory drive train 50 starts to rotate. Centrifugal force acting on the lubricant 138 causes the lubricant to migrate to the sidewall 66, and up the sidewall 66 to the engagement portions 80, 134. This provides lubricant 138 to the joint 60. The arrows in FIG. 6B illustrate the direction in which the lubricant 138 migrates.

[0097] FIG. 6C illustrates the spline joint 60 during normal operation of the engine 10. Lubricant 138 is provided to the joint through the passage 116 formed in the second shaft 54. The lubricant 138 is provided by the lubrication system 42. In use, the lubricant 138 may escape out of the open end 70 of the adapter 62. Escaped lubricant 138 may be collected and recycled as part of the turbine engine lubrication system 42.

[0098] After the engine has shut down, lubricant remaining at the engagement portions 80, 134 is collected in the trough for use on the next start-up.

[0099] The lubrication system 42, which provides lubricant 138 during normal engine operation, is driven by the accessory unit 25, which in turn is driven by the core shaft 27. This means that at engine start-up, before there is sufficient rotation to drive the lubrication system 42, the lubrication system 42 is not primed and cannot provide lubricant to the joint 60. However, as discussed above, the centrifugal force acting on the lubricant 138 in the trough ensures lubricant is provided form engine turn-on.

[0100] The axial height 92 of the inner wall 86 and the radial width 90 of the trough 88 are selected, taking into account the angle 58 of the drive train axis 56, such that the trough 88 can collect sufficient lubricant 138 to lubricate the engagement portions 80, 134 until the lubrication system 42 can provide lubricant. Therefore, the trough 88 holds the same amount of lubricant 138 as would be held in the articulated spline at any given point during normal use.

[0101] The axial height 92 of the inner wall 86 is limited to ensure that excess lubricant 138 is not collected. Instead, excess lubricant flows through the passage formed by the inner wall 86 and the opening 84 in the end wall 82. Where the drive train axis 56 (and joint axis 64) are not completely radial, the lubricant 138 in the trough 88 is not axisymmetric, with respect to the joint axis 64. This can lead to unbalanced loads, which are undesirable. Limiting the volume of lubricant 138 limits the amount of unbalanced loads. Ensuring that the joint 60 is axisymmetric also helps this.

[0102] In use, a pressure different may build up between the core engine 11, and the region in which the accessory unit 25 is mounted. The inner wall 86 and opening 84 form a chimney 140 that allows air or fluid to pass through the opening 84, from the first shaft 52 to the second shaft 54, such that the pressure different does not force axial movement of the second shaft 54 relative to the first shaft 52.

[0103] In the example discussed above, the drive train axis 56 is inclined relative to the principal axis 9 of the engine 10. It will be appreciated that the spline joint 60 incorporating a chimney 140 arranged to form a trough 88 may be used in any drivetrain with appropriate incline. For example, the absolute value of the first angle 58 between principal axis 9 and drive train axis 56 may be between 45 degrees and 90 degrees. This ensures that sufficient lubricant 138 is retained in the trough 88, and the load of the lubricant 138 is sufficiently axisymmetric around the drive train axis 56. The drive train may also include a step aside gearbox, or the like, within the drive train, to enable variations or sideways steps in the drive train axis 56.

[0104] In the examples discussed above, the rigid joint between the adapter 62 and the first shaft 52 is formed on an outer wall 104, spaced from the sidewall 66. In other examples, the engagement portion 112 may be formed on the outer surface 78 of the sidewall 66. In further examples, the rigid joint may be formed by receiving the first shaft 52 within the passage 68.

[0105] Furthermore, in the above examples, the wall 82 forming the base of the trough 88 is provided at the end 72 of the passage 68. However, it will be appreciated that the base of the trough 88 may be formed by a wall extending across the passage 68 at any position along the passage. Furthermore, in some examples, the base of the trough 88 may not extend perpendicular to the wall 68. Instead, the base may be at an inclined or shaped. For example, the end wall 82 may be perpendicular to the axis of the second shaft 54, or may be inclined towards the inner wall 86, to enable collection of lubricant and/or to promote feeding of lubricant 138 to the joint at engine start up.

[0106] In the above examples, the joint 60 between the shafts 52, 54 is formed by an adapter 62. It will be appreciated that this is by way of example only. In alternative examples, the shafts 52, 54 may connect directly to each other.

[0107] In one example embodiment, shown in FIG. 7A, the second shaft 54 may be received within the open end 122 of the first shaft 52. The end 122 of the first shaft 52 may be provided with an engagement portion 142 in a similar manner to the first end 70 of the adapter 62, so that the joint is an articulating joint. A wall 144 is provided extending perpendicular across the passage 114 formed by the first shaft 52, spaced form the end 122, so that a trough 146 is formed in the end of the first shaft 52. A chimney 148 is formed in the trough 146, in a similar manner to the adapter 62 discussed above. The trough 146 collects lubricant 138 in a similar manner to that discussed in relation to FIG. 6A, and lubricates the articulating spline in a similar manner to the trough 88 formed in the adapter 62, as discussed in relation to FIG. 6B. In use, lubricant is provided by a separate system 42 driven by the accessory unit 25, as shown in FIG. 6C.

[0108] In another example embodiment, shown in FIG. 7B, the first shaft 52 is received in the end 136 of the second shaft. In this embodiment, the first shaft engagement portion 150 is formed on the outside of the first shaft 52, near the end 122 of the first shaft 52, and the second shaft engagement portion 152 is formed on the inner of the second shaft 54, near the end 136 of the second shaft 54. In this way, the first shaft 52 is connected by an articulating joint, rather than the second shaft 54.

[0109] In this example embodiment, a trough 154, with a chimney 156, is formed in the end 122 of the first shaft 52, in a similar manner to that shown in FIG. 7A. Furthermore, a weir or step 158 is formed in the inner surface of the second shaft 54, axially above the engagement portion 152.

[0110] In this embodiment, lubricant 138 is collected in the trough 154, in a similar manner to that discussed in relation to FIG. 6A. On engine start up, the lubricant 138 is drawn up the side of the trough 154, in a similar manner to that discussed in relation to FIG. 6B. The lubricant is further drawn up the side of the second shaft 54, until it reaches the weir 158, which prevents the lubricant being drawn any further. Instead, lubricant builds up behind the weir 158, to lubricate the engagement portions 150, 152. The radial width of the weir 158 control the amount of lubricant retained. Once the layer of lubricant is thicker than the weir, 158, lubricant continues to be drawn up the second shaft 54. As such, the weir 158 should be sized to retain lubricant in the joint. In normal use, lubricant is provided by a separate system 42 driven by the accessory unit 25, as shown in FIG. 6C.

[0111] It will also be appreciated that the joints shown in FIGS. 7A and 7B may be formed by an adapter. In this example, the trough 146, 154 is again formed in the end 122 of the first shaft 52, and the adapter is either received in the end of the first shaft 52 (in a similar manner to that shown in FIG. 7A), or receives the first shaft 52 (in a similar manner to that shown in FIG. 7B).

[0112] In one example of a joint formed by an adapter with an articulating joint to the first (lower) shaft 52, the second shaft 54 is connected to the adapter by a rigid joint. The second shaft 52 may be received in an end of the adapter to form a rigid joint, or may receive an end of the adapter, to form a rigid joint. The rigid joint may include a further connection between the adapter and second shaft 54, for example through nuts and bolts. In yet further examples, both shafts 52, 54 may be connected to the adapter by articulating joints. In one example, both joints are lubricated at engine start up by troughs 88, 146, 154a first 88 formed in the adapter, and a second 146, 154 formed in the end 122 of the first shaft 52. In other examples, one of the joints may be lubricated by a trough, and the other by other suitable lubrication means.

[0113] In the examples discussed above, the chimney 140, 148, 156 is formed by a single opening 84 in a wall 82, 144 forming a base of the trough 88, 146, 154, surrounded by an inner wall 86 at the edge of the opening 84. In other examples, the inner wall 86 may have a larger diameter than the opening 84, so that the inner wall 86 is spaced from the edge of the opening 84. In other examples, the inner wall 86 may surround a plurality of openings, rather than a single one.

[0114] In the examples discussed above, the spline joint 60 has been discussed in relation to an inclined drive train 50 for an accessory unit 25, mounted away from the engine core 11. However, it will be appreciated that the spline joint 60 may be used at any situation having a vertical or inclined drive shaft. The joint 60 may be used at any position within a gas turbine engine 10, or any other situation where lubrication of articulated spline joints is required. In addition, the joint does not necessarily have to be used when connecting two shafts. The joint may be used where a shaft connects into a gearbox, or the accessory unit 25, as required.

[0115] In the examples discussed above, the shafts 52, 54 and adapter are cylindrical. However, it will be appreciated that any suitable shape shaft may be used. Furthermore, the trough 88, 146, 154 may be used to collect lubricant, and lubricate an articulating joint during engine transients, when power to the lubrication system 42 is interrupted, as well as at shut down and start up.

[0116] 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.