Gas Turbine Gearbox Planet Pin Clearance Design
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Solution Overview
Problem
Existing gas turbine engine gearboxes face challenges in managing loads and preventing metal-to-metal contact between planet gears and pins, leading to potential failure and inefficiency.
Innovation Solution
The design incorporates a planetary gearbox assembly with planet gears that maintain a non-zero clearance between the pin and the planet gear rim, along with specific ratios for the bending stress neutral axis radius to rim thickness and average rim radius to rim thickness, which helps distribute forces evenly and prevent contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If planet gears are designed with zero clearance between pin and planet gear rim, then load capacity is maximized, but metal-to-metal contact occurs leading to failure
Solution Approach 1:
The patent applies parameter changes by optimizing the clearance parameter between the pin and planet gear rim. Instead of using zero clearance for maximum load capacity, the invention introduces a specific non-zero clearance value that prevents metal-to-metal contact while maintaining adequate load capacity. This parameter optimization resolves the contradiction between strength and reliability.
2Power
If planet gears operate with metal-to-metal contact, then load transfer is efficient, but heat generation increases causing inefficiency
Solution Approach 1:
The patent introduces an intermediary clearance between the pin and planet gear rim that acts as a buffer zone. This clearance prevents direct metal-to-metal contact while still allowing effective load transfer through controlled engagement. The intermediary space reduces friction and heat generation, resolving the contradiction between power transmission efficiency and energy loss.
3Reliability
If clearance between pin and planet gear rim is increased, then metal-to-metal contact is prevented, but load capacity decreases
Solution Approach 1:
The patent applies parameter changes by determining an optimal clearance value that balances reliability and load capacity. Through mathematical relationships involving the bending stress neutral axis radius and rim thickness, the invention identifies a specific clearance parameter that prevents metal-to-metal contact while maintaining sufficient load capacity, thus resolving the contradiction between these two parameters.
Data Source
AI summary
An epicyclic power gear box for a gas turbine engine delivers torque from a low speed shaft to the primary fan. The gear box includes a planet gear, a bearing pin for the planet gear, sun gear and ring gear. The planet gear and bearing pin are arranged so that a clearance between the two is maintained during a takeoff condition for the gas turbine engine. The planet gear can be characterized by a pin clearance parameter, a ratio of bending stress neutral axis radius to rim thickness, a gear pinch ratio, and/or a ratio of average rim radius to rim thickness.