Resilient Annulus Gear Mounting for Geared Gas Turbine Engines
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Solution Overview
Problem
The existing design of annulus gears in geared gas turbine engines faces a conflict between needing to be stiff to handle radial tooth loads and flexible to minimize overloads due to pitch errors and misalignment, leading to axial divergence and oil leakage issues.
Innovation Solution
The annulus gear is resiliently mounted at both its forward and rearward ends to a static supporting structure, with a damping volume of hydraulic fluid and conduits to reduce vibrations, and a damping linkage connecting the annulus gear to the static support structure to manage movement and maintain a consistent oil film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the annulus gear is made as a stiff ring to accept radial tooth loads, then the gear can handle radial loads without failing in fatigue, but the annulus gear becomes rigid and cannot minimize overloads due to pitch errors or misalignment
Solution Approach 1:
The annulus gear is made dynamically adaptable through resilient mounting at both ends, allowing it to change its effective stiffness based on operating conditions. The gear can flex locally to accommodate pitch errors and misalignment while maintaining overall structural integrity for radial load bearing.
Solution Approach 2:
The mounting parameters are changed from fixed rigid support to resilient elastic support, allowing the annulus gear to adjust its position and orientation dynamically. This enables the gear to optimize between stiffness for load bearing and flexibility for error accommodation.
2Adaptability or versatility
If the annulus gear is made flexible to minimize overloads due to pitch errors, then the gear can accommodate manufacturing inaccuracies, but the annulus gear cannot accept radial tooth loads effectively
Solution Approach 1:
The resilient mounting creates a dynamic system where the annulus gear can flex locally to accommodate pitch errors while the overall structure maintains sufficient stiffness for radial load bearing. The system adapts its effective stiffness based on the specific loading and error conditions.
Solution Approach 2:
Different parts of the annulus gear system have different stiffness characteristics. The gear teeth and body maintain high stiffness for load bearing, while the resilient mounting provides localized flexibility to accommodate pitch errors and misalignment.
3Device complexity
If the backing ring is mounted in a cantilevered single-sided configuration, then the structure is simpler, but axial divergence occurs between the annulus gear and backing plate
Solution Approach 1:
The mounting structure is segmented into multiple support points along the axial length of the annulus gear. This distributes the support function across multiple locations, preventing axial divergence while avoiding the complexity of a fully rigid multi-point mounting system.
Solution Approach 2:
The resilient mounting creates a dynamically stable system where the annulus gear can accommodate minor movements through elastic deformation while maintaining overall axial alignment. The system self-adjusts to maintain stability without requiring complex rigid constraints.
4Adaptability or versatility
If the gap between the annulus gear and stiff outer annulus widens axially, then the annulus gear can accommodate movements, but oil leakage increases and pressure balance is disrupted
Solution Approach 1:
The resilient mounting creates a dynamic seal system where the annulus gear maintains optimal spacing from the outer annulus through elastic support. This dynamic positioning accommodates thermal expansion and operational movements while maintaining consistent oil film thickness and preventing leakage.
Solution Approach 2:
The resilient mounting provides continuous feedback through elastic deformation, automatically adjusting the annulus gear position to maintain optimal spacing. This self-regulating mechanism prevents excessive gap formation that would lead to oil leakage while allowing necessary movements.
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 configuration reduces axial divergence, minimizes oil leakage, and enhances vibration damping, allowing for a more stable and efficient operation of the gearbox while maintaining a lightweight design.
Implementation Method 1
The damping volume of hydraulic fluid may reduce vibrations in the system
Implementation Method 2
the annulus gear should be flexible. When the annulus gear flexes locally the clearance between the annulus gear and the stiff outer annulus changes
Implementation Method 3
the oil is caused to be pushed into or out of the reservoir in the space between the rings and the resistance of the oil to this movement causes a force which opposes the flexing of the annulus gear
Data Source
AI summary
A gas turbine engine comprising a gearbox, the gearbox comprising a sun gear, an annulus gear, a plurality of planet gears and a carrier, each planet gear being rotatably mounted in the carrier by at least one bearing, the sun gear meshing with the planet gears and the planet gears meshing with the annulus gear, the sun gear, the planet gears and the annulus gear comprising gear teeth, the annulus gear having a length in the axial direction and an axially forward end and an axially rearward end and wherein the annulus gear is resiliently mounted to a supporting structure at both its axially forward and axially rearward ends.