Planet Gear Pin Clearance for Aircraft Powerbox Load Management
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Solution Overview
Problem
Aircraft engines generate significant torsional loads that exert unevenly distributed loads on journal bearings in power gearboxes, leading to pinching and increased contact stresses, which reduces the reliability of the journal bearings and power gearboxes.
Innovation Solution
The planet gear is designed with a non-zero clearance between the pin and the gear rim, allowing for deflection and deformation under torsional forces, thereby maintaining a positive clearance that enhances load capacity, reduces heat generation, and increases reliability, while also reducing material and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the clearance between the pin and gear rim is reduced to increase load capacity, then the contact stress increases and reliability decreases
Solution Approach 1:
The invention changes the clearance parameter from a fixed small value to a variable that maintains a minimum threshold. By establishing that clearance must remain greater than zero under radial forces, the design dynamically adjusts the operational parameters to prevent pinching while maintaining load capacity.
2Reliability
If the clearance between the pin and gear rim is increased to reduce contact stress, then the load capacity decreases
Solution Approach 1:
The invention uses a computational model that copies and simulates the complex nonlinear behavior of the gear-pin interaction. By creating a detailed mathematical representation of the system including geometry, material properties, and contact mechanics, the model predicts clearance variations and contact stresses without requiring physical prototypes or excessive safety margins.
3Strength
If more material is used in the planet gear to increase strength, then the weight of the aircraft increases
Solution Approach 1:
The invention optimizes the planet gear geometry parameters (inner radius, outer radius, thickness) to achieve the minimum material required for strength. By using the computational model to predict exact stress distributions and clearance variations, the design removes unnecessary material while maintaining required strength, directly reducing aircraft weight.
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 design improves the load capacity and reliability of the planet gear and power gearbox by maintaining a positive clearance, reducing stress and strain, and decreasing the aircraft's weight by minimizing material usage.
Implementation Method 1
The journal bearing includes a pin surrounded by a fluid film. The fluid film allows the gear rim to rotate around the stationary pin.
Implementation Method 2
The fluid film allows the gear rim to rotate around the stationary pin
Implementation Method 3
The planet gear rim may deflect and deform. The clearance is greater than 0 when a radial force is applied to the planet gear.
Implementation Method 4
determining the bending stress neutral axis radius, the thickness, the Young's modulus of elasticity, and the width based on the radial force
Data Source
AI summary
A planet gear includes a pin and an annular planet gear rim. The pin has a pin radius. The pin includes a pin outer surface. The annular planet gear rim has an inner radius and an outer radius. The annular planet gear rim includes an inner surface and an outer surface. The inner surface and the pin outer surface define a clearance therebetween. The clearance is greater than 0 when a radial force is applied to the planet gear.