Curvic Coupling Protrusion to Prevent Turbine Overspeed
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Solution Overview
Problem
In aircraft gas turbine engines, the disengagement of splined teeth in curvic couplings due to tie rod breakage can lead to overspeeding of the high pressure turbine, which is difficult to control and poses serious safety risks.
Innovation Solution
Incorporating a protrusion on one of the splined teeth of the coupling halves, positioned away from the axis, to prevent complete disengagement and induce tilting, promoting friction with stator parts to create a braking effect during uncoupling, thereby controlling the consequences of tie rod failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a fixed curvic coupling with inter-engaged splined teeth is used to transmit torque between rotating elements, then torque transmission and centering precision are improved, but the risk of complete disengagement and overspeeding increases in the event of tie rod breakage
Solution Approach 1:
A protrusion is added to one of the splined teeth that engages with a corresponding groove on the opposing coupling half before normal operation. This preliminary engagement feature ensures that even if the tie rod breaks and axial compression is lost, the protrusion-groove interface prevents complete disengagement of the coupling halves, maintaining reliability while preserving full torque transmission capability during normal operation.
2Device complexity
If the coupling halves are designed with only inter-engaged splined teeth without additional safety features, then device complexity is reduced, but the consequence of tie rod breakage becomes uncontrolled overspeeding
Solution Approach 1:
Instead of redesigning the entire coupling mechanism, a localized protrusion feature is added to one or more splined teeth. This local modification creates a safety function with minimal additional complexity. The protrusion engages with a corresponding groove to provide a mechanical stop that prevents complete disengagement, thereby controlling the harmful overspeeding effect while maintaining simplicity of the overall coupling structure.
3Object-affected harmful factors
If the protrusion is positioned away from the axis on the splined tooth, then tilting effect and friction braking are improved during uncoupling, but manufacturing precision requirements increase
Solution Approach 1:
The protrusion is deliberately positioned asymmetrically away from the rotational axis on the splined tooth, creating an offset that generates a tilting moment when the coupling halves separate. This asymmetric positioning causes the coupling half to tilt and engage frictionally with stator parts, providing passive braking. The asymmetric design is simple to manufacture and does not require high precision, as the offset distance can be relatively large to ensure effective tilting action.
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
The protrusion ensures that the splined teeth remain engaged, preventing overspeeding by creating a tilting effect that generates friction with the labyrinth seal, effectively controlling the rotor's speed and maintaining engagement until the turbine is blocked.
Implementation Method 1
the protrusion on the distal end will create a tilting zone of one of the coupling halves, therefore of one of the rotating elements, relative to the other, thus with a misalignment of this element. This should promote friction against stator parts of the turbomachine, inducing heating under the effect of contact, which will lead to braking of the rotor.
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
In order to master the consequences of a decoupling event on an axial toothed coupling mechanism (47) of an assembly of rotary elements (33, 35) of a gas turbine, and in a situation of initiation of axial decoupling, an excrescence (51) positioned on one of the fluted teeth of the assembly, away from the coupling axis (X), will cause the two coupling halves to pivot relative to one another about said excrescence.