Patent Application
20130051985
This application relates to a gas turbine engine including compressor and turbine rotors assembled using a tie shaft connection.
Gas turbine engines are known, and typically include a compressor, which compresses air and delivers it downstream into a combustion section. The air is mixed with fuel in the combustion section and combusted. Products of this combustion pass downstream over turbine rotors, causing the turbine rotors to rotate.
Typically, the compressor section is provided with a plurality of rotor serial stages, or rotor sections. Traditionally, these stages were joined sequentially, one to another, into an inseparable assembly by welding, or into a separable assembly by bolting using bolt flanges, or other structure to receive the attachment bolts.
More recently, it has been proposed to eliminate the welded or bolted joints with a single coupling which applies an axial force, or pre-load, through the compressor and turbine rotors to hold them together and create the friction necessary to transmit torque. While not prior art, some of these assemblies have experienced an unwinding condition where that pre-load is substantially reduced or lost altogether.
A gas turbine engine has a plurality of compressor rotors, as well as a plurality of turbine rotors. A tie shaft of the engine is constrained to rotate with the compressor and turbine rotors during normal operating conditions. Further, an upstream hub is located upstream of the compressor rotors and is in threaded engagement with the tie shaft. The threads of the upstream hub are handed in a first manner when viewed from an upstream location. A downstream abutment member is positioned downstream of the turbine rotors and is also in threaded engagement with the tie shaft. The threads of the downstream abutment member are handed in the first manner when viewed from a downstream location. Further disclosed is a method of assembling the gas turbine engine.
These and other features of the present disclosure can be best understood from the following specification and drawings, the following of which is a brief description.
The drawings can be briefly described as follows:
A downstream hub 26 is positioned at a downstream side of the compressor stack, and contacts a downstream-most compressor rotor 16D. The stack of compressor rotors is thus sandwiched between the upstream and downstream hubs 22, 26, and is secured by a mid lock nut, or mid abutment member, 28. Downstream hub 26 abuts the turbine stack, which is held against a turbine lock nut, or abutment member, 30. A low pressure turbine may be arranged to the right (or downstream) of the turbine lock nut 30. The mid and turbine lock nuts 28, 30 and the upstream hub 22 are in threaded engagement with the tie shaft 24, as discussed with reference to
Referring to
Notably, and in the example shown, the threads 32, 36 are right-handed threads. That is, viewing the upstream hub 22 from an upstream location (e.g., from left to right in
Similar to the threads 42, 46, the threads 52, 56 may be coarser than the threads 32, 36. As shown, the pitch of the threads 52, 56 is 10 TPI (roughly 3.9 threads-per-cm). Again, this TPI is exemplary. As will be appreciated from the exemplary assembly method shown in
Further, the clearance flanks 46C, 48C and 54C, 58C may be inclined at an angle of approximately 45° relative to a direction perpendicular to the engine axis A. The load flanks 46L, 48L, 54L, 58L may be arranged closer to the perpendicular direction, such as being inclined at approximately 7° thereto. Again, these angles are examples.
As shown in
While not shown, an additional nut may be driven to hold a bearing and seal package against the turbine rotors 20 and augment the final stack preload to ensure the necessary friction to transmit torque. Alternatively, the turbines can be held together by the lock nut 30 alone.
In an attempted tie shaft unwinding condition (e.g., during a sudden deceleration, or “snap” deceleration, of the turbine engine 10), the tie shaft may rotate clockwise CW relative to the counter-clockwise CCW rotation of the turbine engine 10, upstream hub 22 and the lock nuts 28, 30. Given the right-handed orientation of the threads 32, 36 of the upstream hub 22, this relative rotation will urge the tie shaft 24 in a direction D1 generally away from the upstream hub 22. However, due to the arrangement of the lock nuts 28, 30 relative to the tie shaft 24 (including the handedness and the pitch of the threads 42, 46, 52, 56), the relative clockwise CW rotation of the tie shaft 24 actually tightens the lock nuts 28, 30 relative to the tie shaft 24 and prevents the tie shaft from unwinding from the upstream hub 22. That is, the coarser threads 42, 46, 52, 56 urge the tie shaft 24 further in direction D2 than the finer threads 32, 36 urge the tie shaft 24 in the direction D1. Stated another way, the finer threads 32, 36 attempt to move the tie shaft 24 more slowly than the coarser threads 42, 46, 52, 56 would otherwise allow.
While the tie shaft 24 may axially move a distance D3 between the clearance flanks 44C, 48C, 54C, 58C, this axial movement is relatively minor, and will not result in any substantial loss in pre-load. In fact, the relative positions of the upstream hub 22 and the lock nuts 28, 30 remain substantially unchanged, even after the initial unwinding of the tie shaft 24, and therefore the pre-load is substantially maintained. Instead of unwinding altogether, the disclosed arrangement limits axial movement of the tie shaft 24 to the distance D3. Once the tie shaft 24 moves this relatively small distance, the lock nuts 28, 30 urge the tie shaft 24 in a direction D2 by way of engagement of the clearance flanks 44C, 48C, 54C, 58C, as represented in the row labeled “After Initial Tie Shaft Unwinding.”
While the threads 32, 36 have been shown and described as right-handed threads (when viewed from an upstream location) and the threads 42, 46, 52, 56 have been shown and described as being right-handed threads (when viewed from a downstream location) it is possible that the handedness of the threads could be reversed. That is, in a contemplated embodiment the threads 32, 36 could be left-handed when viewed from upstream, and the threads 42, 46, 52, 56 could be left-handed when viewed from downstream. In either case, the lock nuts 28, 30 would substantially prevent unwinding of the tie shaft 24 relative to the upstream hub 22.
Further, while it has been mentioned that the threads 32, 36 may have a pitch of 12 TPI and the threads 42, 46, 52, 56 may have a coarser pitch of 10 TPI, other pitch combinations are contemplated herein, including other combinations whether the threads 32, 36 have a finer pitch that the threads 42, 46, 52, 56.
The disclosed arrangement ensures that the compressor and turbine sections 14, 18 are reliably held together, and will be capable to resist the forces to be encountered during use, while still transmitting the necessary engine torque. In particular, the tie shaft is substantially prevented from unwinding, thus retaining the pre-load in the overall engine assembly, even in an attempted tie shaft unwinding condition. All these functions are accomplished within a minimal axial envelope and with the lowest locking hardware count.
One of ordinary skill in this art would understand that the above-described embodiments are exemplary and non-limiting. That is, modifications of this disclosure would come within the scope of the claims. Accordingly, the following claims should be studied to determine their true scope and content.
