Turbine Rotor Locking Assembly for Small-Shaft Locknut Torque
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Solution Overview
Problem
Turbine rotor assemblies with small diameter shafts face high torque requirements for locknut tightening and loosening, which exceed the strength of conventional axial tabs, making it difficult to achieve proper shaft preload and stability during assembly and disassembly.
Innovation Solution
A power turbine rotor locking assembly with a plurality of torque resistance features on the aft rotor stage and a tooling fixture with corresponding slots, which engage to resist circumferential movement and distribute torque effectively, allowing for secure assembly and disassembly even on small diameter shafts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional axial tabs are used to support the rotor shaft during locknut tightening and loosening, then the assembly is simple and easy to manufacture, but the tabs cannot withstand the high torque required for small diameter shafts
Solution Approach 1:
The torque resistance function is segmented from the simple axial tabs to a dedicated tooling fixture with multiple slots. This fixture can be selectively engaged with the rotor shaft during assembly and disassembly operations, providing the necessary torque resistance without permanently increasing the complexity of the rotor shaft itself.
Solution Approach 2:
A tooling fixture acts as an intermediary between the locknut and the rotor shaft during tightening and loosening operations. This fixture transfers the high torque loads from the locknut to the rotor shaft through multiple engagement points, allowing the use of smaller diameter shafts that would otherwise be insufficient for direct torque application.
2Weight of moving object
If the diameter of the turbine shaft is reduced, then the overall engine size and weight are reduced, but the torque required to tighten the locknut exceeds the strength of the shaft and supporting tabs
Solution Approach 1:
The tooling fixture serves as a mechanical intermediary that amplifies the torque capacity of the reduced-diameter shaft. By distributing the torque load across multiple slots and engagement points, the fixture enables small diameter shafts to withstand locknut tightening torques that would otherwise exceed their strength limits.
Solution Approach 2:
Instead of increasing shaft diameter to handle torque, the solution moves to another dimension by adding a tooling fixture with multiple slots arranged circumferentially. This transforms the torque resistance from a single-dimension shaft property to a multi-point structural system, enabling small diameter shafts to achieve high torque capacity through geometric arrangement rather than material volume.
3Reliability
If high torque is applied to the locknut to achieve proper axial preload, then the rotor assembly remains tight during operation, but the tabs experience excessive shear and bearing stresses
Solution Approach 1:
The stress resistance function is segmented from the tabs to a dedicated tooling fixture with multiple slots. This fixture distributes the shear and bearing stresses across multiple engagement points during locknut tightening, preventing any single tab from experiencing excessive localized stresses that would compromise assembly stability.
Solution Approach 2:
The stress distribution is improved by moving from a simple tab arrangement to a multi-dimensional tooling fixture with slots arranged in specific patterns. This geometric arrangement in multiple dimensions allows the fixture to distribute loads more effectively across the rotor shaft, reducing peak stresses while maintaining the high axial preload needed for operational reliability.
Data Source
AI summary
A power turbine rotor locking assembly including a rotor shaft. The assembly also includes an aft rotor stage surrounding the rotor shaft. The assembly further includes a locknut torqued to the rotor shaft. The assembly yet further includes a plurality of torque resistance features located on an aft side of the aft rotor stage. The assembly also includes a tooling fixture having a plurality of corresponding torque resistance features, the corresponding torque resistance features selectively engageable with the torque resistance features of the aft rotor stage to resist circumferential movement during assembly and disassembly of the locknut with the rotor shaft.