Geared Gas Turbine Engine Annulus Gear Mounting
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Solution Overview
Problem
The existing geared gas turbine engines with helical or double helical gear arrangements face mesh misalignment issues due to the axial force component, leading to increased noise, vibration, stress, and wear, particularly at operating conditions different from the optimized micro-geometry correction for one specific condition.
Innovation Solution
The gearbox design secures the annulus gear to a surrounding structure using a radially extending member, with a specific axial spacing and positioning that balances the moments created by axial and separation forces, reducing misalignment between the annulus gear and planet gears, thereby minimizing noise, vibration, and stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the annulus gear is secured by a flange at its middle, then the gear structure is simplified and easy to manufacture, but mesh misalignment occurs between the annulus gear and planet gears due to axial mesh force component
Solution Approach 1:
The patent applies asymmetry by positioning the radially extending member (flange) at an asymmetric location relative to the annulus gear. Instead of being at the middle, the flange is positioned such that its face nearest the middle is axially spaced from the middle by a first distance, and the reference diameter is radially spaced from the securing point by a second distance, with the ratio of first distance to second distance between 0.5 and 1.2. This asymmetric positioning creates a moment that counteracts the axial mesh force component, thereby eliminating mesh misalignment between the annulus gear and planet gears while maintaining structural simplicity.
2Manufacturing precision
If micro-geometry correction is applied to minimize misalignment, then mesh alignment is improved at one operating condition, but transmission error increases at other operating conditions leading to noise, vibration, and wear
Solution Approach 1:
The patent applies preliminary action by pre-positioning the radially extending member at a specifically calculated location before the gearbox operates. The flange position is determined in advance based on the ratio of first distance to second distance being between 0.5 and 1.2, which pre-compensates for axial mesh forces across all operating conditions. This preliminary structural configuration eliminates the need for micro-geometry correction and prevents transmission errors, noise, vibration, and wear throughout the entire operating range, rather than optimizing for only one condition.
3Length of stationary object
If the flange is located in the middle of the annulus gear, then the radial spacing is minimized, but axial mesh force causes mesh misalignment
Solution Approach 1:
The patent applies parameter changes by modifying the axial position parameter of the radially extending member relative to the annulus gear. Instead of placing the flange face at the middle (zero axial spacing), the patent positions it such that the face nearest the middle is axially spaced from the middle by a first distance, with the ratio of first distance to second distance between 0.5 and 1.2. This parameter adjustment creates a balancing moment that counteracts axial mesh forces, achieving both minimal radial spacing and precise mesh alignment simultaneously.
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. Each planet gear is rotatably mounted in the carrier by a bearing. The sun gear meshes with the planet gears and the planet gears mesh with the annulus gear. The sun gear, the planet gears and the annulus gear comprise helical gear teeth. The annulus gear is secured to a surrounding structure by a radially extending member. A face of the flange nearest the middle of the annulus gear is axially spaced from the middle of the annulus gear by a first distance. The reference diameter of the annulus gear is radially spaced from a point at which the radially extending member is secured to the surrounding structure by a second distance. The ratio of first distance to second distance is between and including 0.5 and 1.2 such that misalignment between the annulus gear and the planet gears is reduced to minimise vibrations, noise, stress and wear of the gearbox.