Shaft system and method for assembling a shaft system

Abstract

A shaft system and method for assembly, the shaft system comprising a first shaft part 1 and a second shaft part 2, the second shaft part 2 at least in part being concentrically positioned within the first shaft part (see fig. 1). One of the two shaft parts 1, 2 comprises an axial stop device 4 for the other shaft part 2, 1 and at least one scalloped spigot 11, 12 with scallops 19 at the circumference. The other one of the two shaft parts 2, 1 comprises at least one assembly scallop 21 and at least one spigot 22 without scallops. The at least one spigot 22 without a scallop and / or the at least one scalloped spigot 11, 12 is associated, e.g. coupled, with at least one mechanical functional element 40, for example a bearing or seal of a gas turbine engine. There is an axial cavity (18; fig. 2) between the two shaft parts facilitating an axial fluid flow (F; figs. 2, 6-8) between the two shaft parts.

Description

Field This disclosure relates to a shaft system, for example for a gas turbine engine. Background Shaft systems, i.e., systems in which two or more shafts are located concentrically to another, are generally known, in particular in gas turbine engines for aircraft. In a two-shaft gas turbine engine, a first shaft part connects e.g. the low pressure units (compressor, turbine) of the engine and a second shaft part connects the high pressure units (compressor, turbine) of the engine. It is also known that a fluid, such as, e.g., air, can flow between the two shaft parts. Such systems are disclosed in United States patent application US 2021 / 0164350 A1 and Russian patent RU 2 379524C1. Efficient designs for such multi-shaft systems are required, in particular systems which can be efficiently assembled, in particular for small gas turbines. Summary In a first aspect there is provided a shaft system comprises a first shaft part and a second shaft part, the second shaft part at least in part being concentrically positioned within the first shaft part in an assembled state. One of the two shaft parts comprises an axial stop device for the other shaft part and at least one scalloped spigot comprising scallops at the circumference. This means that the axial stop device and the at least one scalloped spigot can be positioned on the first shaft part (external or female shaft part) or the second shaft part (internal or male shaft part). The respective other one of the two shaft parts comprises at least one assembly scallop and at least one spigot without scallops. Again this means that the second shaft part (external or female shaft part) or the first shaft (internal or male shaft part) can comprise the features mentioned. And the at least one spigot without a scallop and / or the at least one scalloped spigot is associated, in particular coupled, with at least one mechanical functional element. That mechanical functional element is, e.g., a bearing device or a sealing, coupled to a shaft part. The bearing device can be, e.g. a ball bearing device, a roller bearing device or a journal bearing device. The sealing device can be, e.g. a labyrinth sealing device. The mechanical functional element could also be another engine components in an aircraft engine, e.g. a turbine stage, a compressor stage, or a turbine overspeed protection system. The radially support of the functional mechanical element can reduce radial misalignment to the functional mechanical element from the engine axis and can reduce mechanical stresses which may exist in the element at extreme I catastrophic engine events e.g. a core blade / fan blade off event. Furthermore, there is an axial cavity between the two shaft parts facilitating an axial fluid flow between and / or through the two shaft parts. The use of an assembly scallop on one shaft part in connection with scalloped spigots on the other shaft part allows an efficient assembly, as the shaft parts can effectively aligned circumferentially. Therefore, the two shaft parts are complementary. For example, the surface of an exterior shaft part facing the interior shaft part comprises the radial protrusions of the scalloped spigots. These scalloped spigots are circumferentially aligned with the assembly scallop during assembly. This means that scallops of the assembly scallop of one shaft part can be associated with radial notches on the other shaft part to facilitate assembly of the two shaft parts. To facilitate a particular efficient assembly, the diameters of the at least two scalloped spigots decrease in an assembly direction of the shaft system. In some embodiments the assembly scallop comprises at least one fillet on the axial and / or radial surface. This reduces the mechanical stress in the region where the assembly scallop abuts the stop device. Furthermore, it is possible that during assembly, gaps are formed between the assembly scallop and the at least two scalloped spigots even under worst case conditions. In some embodiments the fluid flow within the shaft system comprises an oil flow or an air flow at least in part in axial direction of the shaft system or in part in a radial direction. This way, the fluid can e.g. be channeled to areas in a gas turbine engine where it is needed. In some embodiments the distal end of one shaft part - as seen in assembly direction -comprises a stop device, in particular, a full ring stop device for the other shaft part. This means that e.g. a part such as the assembly scallop of the interior shaft part can abut the stop device when the interior shaft part is inserted into the exterior shaft part. But it is also possible, that the assembly scallop is positioned on the exterior shaft part, so that it can abut a stop device on the interior shaft part. To lower the flow resistance for the fluid, the first shaft part comprises axial openings for the fluid flow at the end of the second shaft part facing the entry of the fluid flow. These opening can serve as a kind of funnel for the fluid flow. The shaft system can be used in a gas turbine engine. In a second aspect there is provided a gas turbine engine that includes at least one shaft system of the first aspect In a third aspect there is provided a method for assembling a shaft system of the first aspect. At the beginning of the assembly, the assembly scallop on one shaft part and notches of the at least two of the scalloped spigots of the other shaft part are circumferentially aligned. And subsequently the interior shaft part is forced axially into the exterior shaft part in the assembly direction overcoming the fits of the spigot ring and the fit of at least one scalloped spigot. Brief description of the drawings Embodiments will now be described by way of example only, with reference to the Figures, in which: FIG. 1A shows a sectional view of a shaft system at a first stage of an assembly process of an interior shaft part into an exterior shaft part; FIG. 1B shows a sectional view of the shaft system shown in FIG. 1A in a subsequent stage of assembly; FIG. 1C shows a sectional view of the shaft system shown in FIG. 1A in an assembly stage subsequent to the one shown in FIG. 1B; FIG. 1D shows a sectional view of the shaft system shown in FIG. 1A in the final stage of assembly; FIG. 2 shows a sectional and partial view of the embodiment of the shaft system shown in FIGS. 1Ato 1D; FIG. 2A shows a sectional view of a scalloped spigot of the embodiment shown in FIG. 2 in the planes A-A and B-B in the assembled condition; FIG. 2B shows a sectional view of the assembly scallop of the embodiment shown in FIG. 2 in the plane C-C during assembly; FIG. 2C shows a detail of the abutment of the assembly scallop of the embodiment shown in Fig 2 with a stop device; FIG. 3A shows a perspective and sectional view of an exterior shaft part of the embodiment of the shaft system according to FIGS. 1A to 1D; FIG. 3B shows a perspective and sectional view of an internal shaft part of the embodiment of the shaft system according to FIGS. 1A to 1D; FIG. 3C shows a perspective and sectional view of the shaft system in an assembled state with the parts shown in FIGS. 3A and 3B: FIG. 4 shows a sectional and partial view of an alternative to the embodiment of the shaft system shown in FIGS. 1A to 1D; FIG. 4A shows a detail in FIG. 4; FIG. 5 shows a perspective and sectional view of the internal shaft part of the embodiment of the shaft system according to FIGS. 1A to 1D; FIG. 6 shows a schematic sectional view of a further embodiment of the shaft system with a stop device on an exterior shaft part; FIG. 7 shows a schematic sectional view of an embodiment with a stop device on the exterior shaft part; FIG. 8 shows a schematic sectional view of an embodiment with an airflow from the front of an aircraft engine to the rear. The following table lists the reference numerals used in the drawings with the features to which they refer: Ref no. Feature Figure 1 First (exterior) shaft part 1A 1B 1C 1D 2 2A 2B 3A 3C 4 4A 6 7 8 2 Second (interior) shaft part 1A 1B 1C 1D 2A 2B 3B 3C 4 4A 5 6 7 8 3 Distal end of exterior shaft part 1A 1B 1C 1D 2 3A 4 6 7 4 Stop device 1A 1B 10 1D 2 2C 3A 30 4 4A 6 7 8 5 Opening in exterior shaft part for fluid flow 1A1B1C1D23A 3C678 11 First scalloped spigot on one shaft part 1A1B1C23A3C478 12 Second scalloped spigot one shaft part 1A1B1C1D23A 3C4678 13 Axial opening for the entering fluid flow 3A 14 Surface 2C 15 Curved section 2C 17 Chamfer at stop device 2C 18 Axial cavity / gap within shaft system 2 2A 3A 19 Scallop on scalloped spigot 1A3A 21 Assembly scallop 1A 1B 1C 1D 2C 3A 3B 3C 4 4A 5 6 7 8 22 Spigot 1A1C1D3B68 23 Scallop on the assembly scallop 2B 3A 3B 5 24 Notch in a scalloped spigot 1A2B3A5 25 Chamfer on assembly scallop 5 26 First fillet (axial direction) 5 27 Second fillet (circumferential direction) 5 31 First gap 2B 32 Second gap 2B 33 Third gap 2B 40 Mechanical functional element 1A3A 3C 100 Shaft system 1A1B1C1D2B 3C68 A Assembly direction 1A 1B 1C 1D 2 3A 3C 4 5 6 7 8 A-A Plane 2A B-B Plane 2A C-C Plane 2 Di 1 Diameter of first spigot 1A D12 Diameter of second spigot 1A F Fluid flow 2 4A 6 7 8 R Rotational axis 1A1B1C1D67 Detailed description Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those 5 skilled in the art. FIGS. 1A to 1D show sectional views in a plane through a rotational axis R of an embodiment of a shaft system 100. The shaft system 100 which can e.g. be used in a gas turbine of an aircraft, is not shown in full for reasons of simplicity. The shaft system 100 comprises an interior shaft part 2 (also termed as male part) and an 10 exterior shaft part 1 (also termed as female part), the interior shaft part 2 being located within the exterior shaft part 2 (see e.g. FIG. 1D or 3C). The second shaft part 2 is concentrically surrounded by the first shaft part 1. Such a two-part shaft system 100 can, e.g., be used in a gas turbine engine to connect the low pressure units (compressor, turbine) and the high pressure units (compressor, turbine) within the gas turbine engine in a generally known way. The shaft system 100 can also be used in other configurations and device other than gas turbine engines. In the embodiment shown, the assembly direction A of the second shaft part 2 (i.e. the male part) into the first shaft part 1 (i.e. the female part) of the two-shaft system 100 is from right to left, as indicated by an arrow. It should be noted that not all features of the embodiment are shown in each of the FIGS. 1A to 1D. In the embodiment shown in FIGS. 1A to 1D, the external first shaft part 1 comprises two spigots 11, 12 with scallops at the inner surface (see e.g. FIG. 3A). A spigot 11,12 can be understood as a relatively short projection on a shaft part 1, 2 designed to allow the fit with another shaft part 2,1. It should be noted that the scalloped spigots 11,12 are here located on the inner circumference of the first shaft part 1, i.e. the female part. In an alternative embodiment the scalloped spigots 11, 12 are located on the outer surface of the second shaft part 2, i.e. the male part. In the embodiment of FIGS. 1A to 1D the other shaft part 2, i.e. the male part, comprises one assembly scallop 21 and at least one spigot 22 without scallops (see e.g. FIG. 3B). The two scalloped spigots 11,12 inside the first shaft part 1 each have different radial dimensions, i.e., different diameters Du, D12. The two scalloped spigots 11,12 are located axially along the shaft system 100. The first scalloped spigot 11 is located towards the right end (i.e. the entry) of the shaft system 100. The second scalloped spigot 12 is located axially further to the left. The diameters Dn, D12 decrease in the direction A of assembly, i.e., the diameter Dn of the first scalloped spigot 11 is the smallest, the diameter D12 of the second scalloped spigot 12 is the largest. In the system shaft system 100 herein, two scalloped spigots 11, 12 are used. In alternative embodiments three or more than two scalloped spigots 11,12 can be used in different arrangements. The scalloped spigots 11,12 comprise scallops 19 and notches 24 (see e.g. FIG. 3A) which are circumferentially positioned around the spigots 11, 12. Another feature of the embodiment shown in FIGS. 1B and 1C is a coupling between the first scalloped spigot 11 with a mechanical functional element 40. In the case shown in FIG. 1A to 1D, the first scalloped spigot 11 is associated or coupled with a sealing 40, here a labyrinth sealing. The labyrinth sealing 40 is located radially outwards from the first scalloped spigot 11. In an alternative embodiment, the mechanical functional element 40 is, e.g., a bearing device (ball bearing, roller bearing, journal bearing). Towards the distal end 3 of the first shaft part 1, i.e., the left end in FIG. 1A, the first shaft part 1 comprises a stop device 4, here in the form of a full ring stop device 4. In a fully assembled stage, which will be described below, the assembly scallop 21 abuts that stop device 4, i.e., in the case the interior shaft part 1 is positioned fully within the exterior shaft part 2. In FIG. 2C (Detail CU), the abutment of the assembly scallop against the stop device 4 is shown. Now the assembly of the shaft system 100 with the two shaft parts 1, 2 will be described in the context of FIGS. 1A to 1D. In FIG. 1A the second shaft part 2 is just inserted in the assembly direction A into the hollow first shaft part 1. The second shaft part 2 is a solid shaft which can e.g. be used in an aircraft engine. The assembly in the case shown here is from the rear part of an aircraft engine. In FIG. 1B a subsequent stage of the assembly is shown, in which the second shaft 2 is inserted to a large extent into the first shaft part 1, but no physical contact between the shaft parts 1,2 exists yet. The assembly scallop 21 passed through the first scalloped spigot 11. The scallops of the assembly scallop 21 fit through respective notches 24 in the first scalloped spigot 11 which provides some radial alignment during assembly (see also FIGS. 3A and 3B). In FIG. 10 a further stage of the assembly is shown, in which the second shaft part 2 is further inserted into the first shaft part 1. Now the assembly scallop 21 passes through the second scalloped spigot 12. Again, the assembly scallop 21 fits through the respective notches 24 in the second scalloped spigot 12, providing some radial alignment (see also FIGS. 3A and 3B). After a first circumferentially alignment (see FIG. 1), to reach the situation shown in FIG. 1D, some axial force has to be applied to the second shaft part 1 in the assembly direction A to overcome the spigot seats. The assembly scallop 21 then meets the abutment face of the stop device 4. For the assembly, the scallops of the scalloped spigots 11, 12 and notches 24 are first circumferentially aligned and then the interior shaft part 2 is forced into the exterior shaft 1 part to overcome the fits of the scalloped spigots 11, 12. FIG. 2 shows a sectional, axial view of the embodiment shown in FIGS. 1A to 1D to describe a fluid flow F through an assembled shaft system 100 (as shown in FIG. 1D). The fluid flow F first flows in axial direction through the space between the two shaft parts 1, 2, in particular through the notches 24 (see FIG. 3A) in the scalloped spigots 11, 12 and gaps 18 (see FIG. 2A) and then through the openings 5 in the first shaft part 1 radially outward. FIG. 2A shows the sectional views along the planes A-A and B-B indicated in FIG. 2. The fluid flow F goes through the axial cavity 18 between the interior shaft part 2 and the exterior shaft part 1. In the shown example, an airflow F axially flows through shaft system 100. Between the second scalloped spigot 12 and the stop device 4, the first shaft part 1 comprises openings 5 (see e.g. FIG. 3A) for the fluid flow F, so that the air can leave the shaft system 100 in a radial direction, e.g., for cooling purposes. In other embodiments, the fluid flow F might comprise an oil flow. FIG. 2B shows a sectional view of the assembly scallop 21 in the plane C-C indicated in FIG. 2 during assembly. The scallops 23 of the assembly scallop 21 align with notches 24 of the scalloped spigots 11, 12, here the second scalloped spigot 12 is depicted. The association of the scallops 23 on the assembly scallop 21 with the notches 24 means that they generally fit each other, but there are gaps 31, 32, 33 formed between the scallops and the notches 24. As seen in FIG. 2B, the first gap 31 is located radially between the second shaft part 2 and the first shaft part 1, circumferentially between two scallops 23. The second gap 32 is located between the sidewalls of the scallop 23 and the associated notch 24. The third gap 33 is located between the radial top part of a scallop 23 and the deepest part of the notch 24. These gaps 31,32, 33 can be derived from the applied design tolerances, so that the two shaft parts 1,2 can be assembled with a significantly low risk of damage to one another i.e. scratched. In a variation to the embodiment shown here, chamfers could be located onto the comers of the notches 24 such that even if a build line misaligns the two shaft parts 1,2, scratches would not go into the high stress fillets (see FIGS. 2C and 5). The assembly scallop 21 and the notches 24 on the scalloped spigots 11, 12 are so designed that in worst case conditions (WCC), those gaps 31, 32, 33 are always present. In FIG. 2C (Detail CU in FIG. 2), the abutment of the assembly scallop 21 against the stop device 4 is shown. Fillets 26, 27 are best seen in FIG. 3B or 5. The stop device 4 has a chamfer 17. In FIGS. 3A, 3B and 3C, a further view of the embodiment of a shaft system 100 described above is shown. FIG. 3A shows a perspective sectional view of the first shaft part 1. The assembly direction A of the first shaft part 1 is indicated by an arrow. Here, two scalloped spigots 11,12 are used. At the distal end - as seen from the assembly direction A - the full ring is a stop device 4 for the second shaft part 2. The circumferential scallops 19 and the notches 24 of the scalloped spigots 11, 12 can be seen. FIG. 3A also shows an optional feature in the first scalloped spigot 11. The notches 24 between scallops 23 are widened into axial openings 13 at the entry side of the first shaft part 1. The fluid flow F, described above, would enter into those axial openings 13, so that the fluid flow resistance is lowered. FIG. 3B shows the respective internal second shaft part 2 which is to be inserted into the first shaft part 1. In particular the assembly scallop 21 with scallops 23 can be seen. The full (i.e., the assembled) shaft system 100 is shown in FIG. 3C. In FIG. 4 and 4A a variation of the shaft system shown in FIGS. 1A to 1D is depicted. The above description generally applies for this embodiment as well. The difference is in the region of the stop device 4. The assembly scallop 21 is a spigot scallop here which has dual function of restraining the second shaft part 2 axially and radially. The arrangement can save axial space in the aeroengine 100. FIG. 5 shows a different view on the assembly scallop 21 on the second shaft part 2, which is e.g. shown in FIG. 3B. The scallops 23 comprise fillets 26, 27 (or grooves) in axial and radial directions at the seat of the scallops 23. Those fillets 26, 27 cooperate with corners 17 on the stop device 4 which can be seen e.g. in FIG. 2B. The areas of the fillets 26, 27 are the ones with a high stress load. In FIGS. 6 to 8 further embodiments are described, which are variations of the embodiments described above. Therefore, the above description is also applicable in general to those variations. The mechanical functional element 40 is not shown here for the sake of simplicity. In FIG. 6 a shaft system 100 is shown in an assembled state for which the assembly direction A is reversed. In the embodiment of FIGS. 1 to 5 the second shaft part 2, i.e. the internal shaft part was assembled from the rear of an engine, i.e. from right to the left in the figures. In the embodiment of FIG. 6 the second shaft part 2 is assembled A from the front of the engine, that is from the left to the right as indicated by an arrow. In this embodiment of the shaft system 100 the second shaft part 2 is concentrically positioned within the in the first shaft part 1. The second shaft part 2 comprises an axial stop device 4 for first shaft part 1. The stop device 4 in this embodiment is at the end of the second shaft part 2 which is close to the entry opening, once the shaft system 100 is assembled. There is one scalloped spigot 11 on the second shaft part 2 comprising scallops 19 at the circumference. The first shaft part 1 comprises an assembly scallop 21 and one spigot 22 without scallops. Essentially, this is a reverse arrangement to the embodiment of FIGS. 1A to 1D. The embodiment also comprises axial openings 13 facilitating the axial fluid flow F between the two shaft parts 1, 2. The axial fluid flow F is directed from the rear of the engine, i.e. from right to left in FIG. 6. The embodiment shown in FIG. 7 is a variation of the embodiment shown in FIG. 6. Here the first shaft part 1, i.e. the exterior shaft part comprises spigots and the second shaft part comprises two scalloped spigots 11, 12. The embodiment of FIG. 8 is also a variation of the embodiment of FIG. 6, with the assembly direction A reversed, i.e. here from the right to the left. The stop device 4 is positioned on second shaft part 2, the internal shaft part. The assembly scallop 21 is positioned on the first shaft part 1, the external shaft part. In FIG. 8 the assembled state is shown in which the assembly scallop 21 abuts the stop device 4. Here the air flow F is from the front of the engine, i.e. from left to right. 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.

Claims

1. A shaft system (100) comprising a first shaft part (1) and a second shaft part (2), the second shaft part at least in part being concentrically positioned within the first shaft part;one of the two shaft parts (1, 2) comprises an axial stop device (4) for the other shaft part (2, 1) and at least one scalloped spigot (11, 12) comprising scallops (19) at the circumference;the other one of the two shaft parts (2, 1) comprises at least one assembly scallop (21) and at least one spigot (22) without scallops;the at least one spigot (22) without a scallop and / or the at least one scalloped spigot (11, 12) is associated, in particular coupled, with at least one mechanical functional element (40); andthere is an axial cavity (18) between the two shaft parts (1, 2) facilitating an axial fluid flow (F) between the two shaft parts (1, 2).

2. The shaft system of claim 1, wherein the scallops (23) of the assembly scallop (21) of one shaft part (1, 2) are associated with notches (24) on the other shaft part (2, 1) to facilitate assembly of the two shaft parts (1,2).

3. The shaft system of claim 1 or 2, wherein the at least one mechanical function element (40) is a bearing device or a sealing device.

4. The shaft system of claim 3, wherein the bearing device (40) is a ball bearing, a roller bearing device or a journal bearing device.

5. The shaft system of claim 3, wherein the sealing device (40) is a labyrinth sealing device.

6. The shaft system of any preceding claim, wherein the mechanical functional element (40) is an engine component of an aircraft engine, in particular a turbine stage, a compressor stage or a turbine overspeed protection system.

7. The shaft system of any preceding claim, wherein the diameters of the at least one scalloped spigot (11, 12) decrease in an assembly direction (A).

8. The shaft system of any preceding claim, wherein the assembly scallop (21) comprises at least one fillet (26, 27) on the axial and I or radial surface.

9. The shaft system of any preceding claim, wherein during assembly gaps (31, 32, 33) are formed between the assembly scallop (21) and the at least two scalloped spigots (11, 12) even under worst case conditions.

10. The shaft system of any preceding claim, wherein the fluid flow (F) comprises an oil flow or an air flow at least in part in axial direction of the shaft system (100) or in part in a radial direction.

11. The shaft system of any preceding claim, wherein the distal end (3) of one shaft part (1, 2) as seen in assembly direction (A) comprises a stop device (4), in particular, a full ring stop device (4) for the other shaft part (2, 1).

12. The shaft system of any preceding claim, wherein the first shaft part (1) comprises axial openings (13) for the fluid flow (F) at the end for the second shaft part (1) facing the incoming fluid flow (F).

13. A gas turbine engine including at least one shaft system of any preceding claim.

14. A method for assembling a shaft system (100) of any preceding claim, wherein themethod comprises:a) circumferentially aligning the assembly scallop (21) on one shaft part (1,2) and notches (24) of the at least two of the scalloped spigot (11, 12) of the other shaft part (2, 1), and subsequentlyb) forcing the interior shaft part (2) axially into the exterior shaft part (1) in the assembly direction (A) to overcome the fits of the spigot ring and at least one scalloped spigot (11, 12).

Images