Planet Carrier Stiffness Layout for Lower Gear Misalignment
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Solution Overview
Problem
Designing a compact and reliable epicyclic gearbox for aeronautic applications that minimizes planet gear misalignment during torque extraction, while avoiding the need to oversize components, which is challenging due to high load sharing factors and space constraints within the gas turbine engine flow path.
Innovation Solution
A planet-carrier design featuring a side plate, central ring, and support pylons with a stiffness-reducing feature, where the side-plate stiffness is significantly greater than the pillar stiffness, and the pillar stiffness is greater than the feature stiffness, arranged at an angle between 20° and 90°, to ensure equal load sharing and minimize misalignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the size of epicyclic gearbox components is increased to counteract planet pin misalignment during torque extraction, then reliability and robustness improve, but the gearbox becomes too large to fit within the gas turbine engine flow path
Solution Approach 1:
The invention applies local quality by creating a non-uniform stiffness distribution in the planet carrier structure. Specifically, the support pylons connecting the central ring to the side plate have varying stiffness characteristics - with the first support pylon having different stiffness than the second support pylon. This localized stiffness variation allows the structure to compensate for misalignment forces at specific locations without requiring a uniform increase in overall component size, thus maintaining compact gearbox dimensions while improving reliability
Solution Approach 2:
The invention employs parameter changes by modifying the stiffness parameters of the support pylons. The first support pylon is designed with a first stiffness value and the second support pylon with a second stiffness value, where these stiffness parameters are specifically tuned to counteract the misalignment effects during torque extraction. By changing these structural parameters rather than simply increasing overall size, the invention achieves improved reliability within constrained volume
2Reliability
If the number of planet gears is increased to five to nine pairs, then load sharing optimization is achieved, but space for planet-carrier reinforcement is significantly limited
Solution Approach 1:
The invention applies local quality by providing different reinforcement characteristics at different locations in the planet carrier. The first support pylon receives a first reinforcement feature while the second support pylon receives a second reinforcement feature, creating localized strength variations that correspond to the specific load distribution patterns created by having five to nine planet gears. This allows adequate reinforcement without increasing overall carrier volume
Solution Approach 2:
The invention employs segmentation by dividing the planet carrier into distinct structural elements - the central ring, side plate, and multiple support pylons - each with specific reinforcement features. This segmented approach allows targeted reinforcement at critical locations where the high number of planet gears create concentrated loads, rather than requiring uniform reinforcement throughout the entire carrier structure
3Manufacturing precision
If the planet-carrier structure is reinforced to reduce misalignment, then manufacturing precision of planet gear alignment improves, but device complexity increases
Solution Approach 1:
The invention employs parameter changes by modifying the stiffness parameters of the support pylons rather than adding complex geometric features. The first support pylon has a first stiffness value and the second has a second stiffness value, achieved through variations in cross-sectional area or material properties. This parameter-based approach to improving alignment precision is simpler to manufacture and analyze than complex geometric reinforcements
Data Source
AI summary
An apparatus and method for reducing planet gear misalignment of planet gears mounted on a planet-carrier in an epicyclic gearing. The apparatus and method of the present disclosure specifically provide for a stiffness-reducing feature, a pillar, and a side-plate, each with a respective stiffness. In several embodiments, the feature stiffness is less than the pillar stiffness which is at least 10% less than the side-plate stiffness. The stiffness-reducing feature and the pillar may make up a pylon which has an axis. The pylon axis may form an angle with the side plate which is less than 90° and greater than 20°.