Hybrid Transmission Coupling Geometry for Debris-Ejecting Spline Teeth

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Solution Overview

Problem

Conventional hybrid transmission components in gas turbine engines face unpredictable interface pressures due to manufacturing variations, leading to excessive wear and mechanical behavior variations, primarily caused by debris trapped within the interface of metallic couplings and composite bodies.

Innovation Solution

The hybrid transmission component features a metallic coupling with optimized spline teeth geometry, including a curved and planar surface at the leading end, which shears and lifts debris out of the interface, minimizing pressure variations and enhancing load carrying capability and fatigue properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If conventional spline tooth geometry is used, then manufacturing is simpler, but debris is trapped in the interface causing excessive wear and pressure variation

Engineering Contradiction:

Improvespline tooth manufacturing simplicityVSAvoidinterface pressure stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The leading end of each spline tooth is designed with a curved surface instead of a flat surface. This curvature allows debris to be lifted and ejected from the interface between the metallic coupling and composite body, preventing debris accumulation that causes pressure variation and wear.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The geometry parameters of the spline tooth leading end are optimized by introducing specific curvature radius and rake angle parameters. These parameter changes transform the cutting action to efficiently eject debris while maintaining manufacturing feasibility.

Inventive Principle:

Principle #35Parameter changes

2Strength

If larger diameter and longer interfaces with more spline teeth are used to handle higher load intensity, then load carrying capability is improved, but manufacturing variation is magnified causing unacceptably high variation in mechanical behaviour

Engineering Contradiction:

Improveload carrying capabilityVSAvoidinterface pressure consistency

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The curved surface at the leading end of spline teeth ensures consistent debris ejection across the entire interface, even in large-scale components with many spline teeth. This geometric feature compensates for manufacturing variations by providing a self-cleaning action that maintains uniform interface pressure distribution.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The spline tooth geometry is designed to automatically eject debris during the normal assembly process without requiring additional cleaning steps. The curved leading end acts as a self-cleaning mechanism that maintains interface quality throughout the component's service life.

Inventive Principle:

Principle #25Self-service

3Shape

If the leading end of spline teeth is designed to centralize the composite body, then alignment is improved, but cutting efficiency is reduced due to debris being pushed to the interface

Engineering Contradiction:

Improvecentralization capabilityVSAvoidcutting efficiency

Core Design Contradiction:

ShapeVSProductivity

Solution Approach 1:

The curved surface combines both centralization and debris ejection functions. The curvature geometry is designed to guide the composite body into proper alignment while simultaneously lifting debris away from the cutting interface, achieving both functions without compromise.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The leading end geometry features asymmetric curvature with a specific rake angle that creates different functions at different portions of the surface. The asymmetry enables the leading end to perform both centralization and debris ejection simultaneously during the assembly process.

Inventive Principle:

Principle #4Asymmetry

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 optimized geometry ensures efficient debris ejection, reducing wear and deformation, thereby stabilizing mechanical behavior and improving the load-carrying capacity of the joint.

Implementation Method 1

an angle of the cutting face (i.e., leading end) directs the cutting force away from the surface of the composite body, thereby acting to shear and lift out the debris from the cut

Methodology Applied

Scientific EffectShear stress: Shear Stress

Data Source

PatentEP4575181A1Hybrid transmission component for a gas turbine engine

Publication Date: 2025.06.25 ROLLS ROYCE PLC

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Figure 2B

AI summary

A hybrid transmission component (100, 200, 300, 350, 400, 500, 600) for a gas turbine engine (10) has a composite body (102, 402, 502, 602), and a metallic coupling (104, 304, 354, 404, 504, 604) joined with the composite body (102, 402, 502, 602) and defining a longitudinal axis (106) along its length. The metallic coupling (104, 304, 354, 404, 504, 604) includes a plurality of spline teeth (120) extending from a circumferential surface (114) and angularly separated from each other about the longitudinal axis (106). Each spline tooth (120) from the plurality of spline teeth (120) extends radially from a root (122) to a tip (124) with respect to the longitudinal axis (106) and extends axially from the leading end (126) along the longitudinal axis (106). The leading end (126) of each spline tooth (120) includes a curved surface (128) extending from the root (122) and a planar surface (130) extending from the curved surface (128) to the tip (124). The planar surface (130) is inclined obliquely to the longitudinal axis (106) by a rake angle (α).