Tie Shaft Threaded Engagement Preventing Unwinding
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Solution Overview
Problem
Gas turbine engines with tie shaft connections face issues of pre-load reduction or loss due to unwinding conditions, which can lead to reduced torque transmission and assembly instability.
Innovation Solution
The use of a threaded engagement system with specific thread angles and pitches between the upstream hub, mid lock nut, and turbine lock nut, which applies a pre-load to the compressor and turbine rotors, and includes a tie shaft with complementary threads to maintain friction and prevent unwinding during engine operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a single coupling applies axial pre-load through compressor and turbine rotors to hold them together, then torque transmission is improved through friction, but the assembly experiences unwinding conditions where pre-load is substantially reduced or lost altogether
Solution Approach 1:
The single coupling is segmented into multiple couplings: a first coupling between the compressor rotor and tie shaft, and a second coupling between the turbine rotor and tie shaft. This segmentation distributes the pre-load application points along the tie shaft, preventing unwinding conditions by creating multiple friction interfaces that collectively maintain torque transmission while preserving pre-load integrity.
2Strength
If traditional welding or bolting methods are used to join rotor stages, then assembly strength is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
Multiple rotor stages are merged into a single separable assembly using the tie shaft connection system. The first and second couplings combine to hold both compressor and turbine rotors together on the same tie shaft, creating an integrated assembly that maintains strength through distributed friction interfaces while allowing for easier assembly and disassembly compared to welded or bolted flange connections.
3Ease of manufacture
If a tie shaft connection with threaded engagement is used, then ease of assembly is improved, but the threaded joints may experience unwinding under operational forces
Solution Approach 1:
The solution adds an axial dimension to the threaded engagement system. Lock nuts are positioned at different axial locations along the tie shaft to engage with corresponding threads on the compressor rotor coupling and turbine rotor coupling. This axial distribution of locking points prevents unwinding by creating multiple resistance points against rotational forces that would otherwise cause the threaded joints to loosen.
Data Source
Figure 1
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AI summary
A gas turbine engine (10) has a plurality of compressor rotors (16), as well as a plurality of turbine rotors (20). A tie shaft (24) of the engine (10) is constrained to rotate with the compressor and turbine rotors (16,20) during normal operating conditions. Further, an upstream hub (22) is in threaded engagement with the tie shaft (24). The threads (32) of the upstream hub (22) are handed in a first manner when viewed from an upstream location. A downstream abutment member (30) is positioned downstream of the turbine rotors (20) and is also in threaded engagement with the tie shaft. (22) Threads (52) of the downstream abutment member (30) are handed in the first manner when viewed from a downstream location. Accordingly, the compressor and turbine sections (14,18) of the engine (10) are reliably held together, and the tie shaft (24) is substantially prevented from unwinding. And a corresponding assembling method for a gas turbine engine.