Variable-Profile Spline Coupling for Turbine Shafts
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Solution Overview
Problem
Existing gear coupling devices for turbine and compressor shafts in aeronautical engines face issues with stress concentration and reduced service life due to constant spline profiles, leading to increased stress and potential weakness under extreme loading conditions.
Innovation Solution
The implementation of a gear mechanism with splines having a constant profile along a median zone, a smaller thickness zone, and a coupling zone where the splines' thickness increases towards the centring zone, eliminating free edges and reducing stress accumulation, while enhancing the shaft's strength and service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If splines have a constant profile along the entire length, then the manufacturing is simple, but stress concentration occurs at the downstream end leading to reduced service life
Solution Approach 1:
The patent applies local quality by varying the spline profile along its length. The downstream end portion has a different profile (different modulus or number of teeth) compared to the upstream end portion, creating locally optimized stress distribution. This resolves the contradiction by maintaining simple manufacturing through standardized spline sections while improving reliability by reducing stress concentration at the critical downstream end.
2Weight of moving object
If a cavity is provided between the downstream end of the spline and the downstream centring zone to lighten the shaft, then the shaft weight is reduced, but the zone becomes weaker under extreme loading
Solution Approach 1:
The patent resolves this contradiction by applying local quality through differentiated spline profiles in different zones. The downstream end portion has optimized spline geometry that compensates for the reduced material cross-section in the cavity zone. This local reinforcement through profile variation maintains strength under extreme loading while preserving the weight benefits of the cavity design.
3Stress or pressure
If the spline thickness is reduced at the downstream end to improve contact pressure distribution, then stress during normal operation is reduced, but tensile stress accumulates at the free edges creating critical zones
Solution Approach 1:
The patent resolves this contradiction by implementing local quality through different spline profiles in different zones. The downstream end portion has a specifically designed profile (different modulus or tooth count) that optimizes contact pressure distribution during normal operation while maintaining sufficient material cross-section to resist tensile stress accumulation at free edges, eliminating the critical zones created by uniform thickness reduction.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances torque transmission, reduces stress concentration, and increases the service life of the shafts by eliminating critical zones of weakness, thereby improving the overall durability and performance of the coupling device under extreme loading conditions.
Implementation Method 1
The splines of one engaging with the splines of the other
Implementation Method 2
the transmission of motion being, in the case of a turbine-compressor coupling, performed from the downstream turbine towards the upstream compressor
Implementation Method 3
the complementary surfaces enable axial centring of the two shafts in respect to each other
Implementation Method 4
In operation, heating and the torque transmitted deform the splines, closing the initial gap
Implementation Method 5
heating and the torque transmitted deform the splines, closing the initial gap
Data Source
AI summary
A device for coupling two shafts by a gear mechanism includes a coupling part ending one of the two shafts. The coupling part is fitted concentrically into a complementary coupling part ending the other shaft. Splines of the coupling part have a constant profile along a median zone of the coupling part and which, in a first zone in continuation of the median zone, has a smaller thickness, between flanks of a spline, than a maximum thickness of the same spline in the median zone. Splines of the coupling part continue, beyond the first zone, as far as a centering zone on the same side as the first zone. The splines and the spline bottoms have, in the coupling zone between the centering zone and the first zone, a profile that continuously couples the splines and the spline bottoms to the surface of the centering zone.