Composite Planet Gear Mass Reduction for Gas Turbine Load
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Solution Overview
Problem
Large, high-speed epicyclic or planetary gearboxes in geared gas turbine engines face challenges with high centrifugal loads on planet gear bearings, making it difficult to use rolling element bearings and susceptible to damage with journal bearings, while ring bending introduces stress and affects load distribution and fatigue.
Innovation Solution
The use of a gear comprising a steel annular structure with radially extending teeth and a metal matrix composite annular structure, where the metal matrix includes steel, aluminium, or titanium alloys, and reinforcing materials like ceramics, to reduce mass and maintain stiffness, and the gear is manufactured using additive layer manufacturing or sintering processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the diameter of planet gear bearings is increased to carry centrifugal load, then bearing capacity is improved, but the diameter and mass of planet gears increase
Solution Approach 1:
The planet gear is constructed as a composite structure with a steel first annular structure providing strength and a metal matrix composite second annular structure reducing mass. The MMC contains reinforcing materials (ceramics, fibres, or particles) embedded in a metal matrix (aluminium, steel, or titanium alloy), creating a material that maintains stiffness and strength while significantly reducing density compared to solid steel construction.
2Reliability
If journal bearings are used instead of rolling element bearings, then bearing suitability for centrifugal load is improved, but susceptibility to damage from lubricant supply interruption worsens
Solution Approach 1:
The invention changes the fundamental parameters of the bearing system by reducing planet gear mass through MMC construction. This mass reduction decreases centrifugal loads on bearings, allowing the use of rolling element bearings with improved reliability and reduced susceptibility to damage, while the reduced loads make the system more tolerant of lubrication variations.
3Strength
If ring bending is reduced through mass reduction, then load distribution and fatigue resistance are improved, but manufacturing complexity increases
Solution Approach 1:
The planet gear employs local quality differentiation through its composite construction: the steel first annular structure provides localized strength where needed for tooth engagement, while the metal matrix composite second annular structure provides localized mass reduction for stiffness improvement. This spatial differentiation of material properties optimizes both mechanical performance and manufacturing efficiency.
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 solution reduces the mass of the planet gear while maintaining or increasing stiffness, minimizing ring bending and improving load distribution, thus enhancing the durability and performance of the gearbox under high centrifugal loads.
Implementation Method 1
a metal matrix composite, the metal matrix composite comprising a metal matrix and reinforcing material
Implementation Method 2
the gear is manufactured using additive layer manufacturing or sintering processes
Implementation Method 3
the gear is manufactured using additive layer manufacturing or sintering processes
Data Source
AI summary
A gas turbine engine comprises a gearbox comprising a sun gear, an annulus gear, a plurality of planet gears and a carrier. The sun gear meshes with the planet gears and the planet gears mesh with the annulus gear. A planet gear comprises a first annular structure, a plurality of teeth extending radially from the first annular structure and a second annular structure abutting and secured to a cylindrical surface of the first annular structure. The first annular structure and the teeth consist of steel, the second annular structure comprises a metal matrix composite, the metal matrix comprising aluminium, aluminium alloy, steel, titanium or titanium alloy, the reinforcing material comprising titanium diboride, titanium carbide or titanium nitride. The second annular structure reduces the mass but maintains, or increases, the stiffness of the planet gear to carry centrifugal loads and to maintain roundness of the planet gears.