Planetary Gear Journal Bearing Geometry for Lubricating Film Stability
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Solution Overview
Problem
Planetary gearings in gear fan engines face high centrifugal forces and torques, leading to deformation of planet slide bearing pins and planet gears, which compromises the lubricating film and increases the risk of metal-on-metal contact due to uneven lubricating film pressure.
Innovation Solution
The design incorporates a recess at the axial face sides of the planet gear and a crowning of the planet slide bearing pin, reducing stiffness and mass while maintaining optimal lubricating film thickness, thereby preventing excessive pressure and metal-on-metal contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the planet slide bearing pin is affixed at its ends in support plates, then the planet gear can transmit high torques, but the planet slide bearing pin is subject to bending which increases lubricating film thickness in the center and reduces it at the ends, leading to excessive lubricating film pressure and metal-on-metal contact
Solution Approach 1:
The planet gear is designed with varying local properties: the axially forward and rearward face sides have different stiffness characteristics due to the recesses. This allows the ends of the planet gear to be more flexible locally, accommodating the bending of the planet slide bearing pin without compromising overall torque transmission, while maintaining adequate lubricating film thickness at the ends
Solution Approach 2:
The stiffness parameter of the planet gear is modified by introducing recesses at the face sides. This changes the mechanical properties of the planet gear from uniform to non-uniform stiffness distribution, allowing the gear to deform in a controlled manner that maintains lubricating film integrity under high centrifugal forces and torques
2Strength
If the planet gear is made with sufficient mass to withstand high centrifugal forces and torques, then the gear can handle the loads, but the excessive mass increases the bearing load and reduces operational efficiency
Solution Approach 1:
Instead of uniformly reducing the planet gear mass, recesses are introduced only at the axially forward and rearward face sides where material can be removed without compromising the overall structural integrity and load-bearing capacity. This localized material removal reduces mass while maintaining strength in the critical load-bearing regions
Solution Approach 2:
The planet gear is segmented into regions of different mass distribution through the recesses. The central region maintains sufficient mass for strength, while the face side regions have reduced mass through recesses, creating a non-uniform mass distribution that optimizes both strength and 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 configuration reduces the risk of metal-on-metal contact, improves load-bearing behavior, and allows for weight reduction of the planet gear and neighboring components, enhancing the overall operational stability and efficiency of the gear fan engine.
Implementation Method 1
The planet slide bearing pin and the planet gear form a lubricated journal bearing, wherein the adjoining contact surfaces of the slide bearing are separated from each other by a slide bearing gap
Implementation Method 2
the planet slide bearing pin that is affixed at its ends in support plates is subject to bending as a result of the occurring forces
Implementation Method 3
In gear fan engines, planetary gearings are exposed to very high centrifugal forces and torques that deform the planet slide bearing pin and the planet gear
Data Source
AI summary
A planetary gearing includes a sun gear rotating about a rotation axis and driven by a sun shaft; planet gears driven by the sun gear, each planet gear having an axially forward face side and an axially rearward face side; a ring gear engaging the planet gears; and planet slide bearing pins, wherein respectively one planet slide bearing pin is arranged inside a planet gear forming a lubricated journal bearing. At an axially forward face side and/or axially rearward face side, each planet gear forms a recess that extends inside the planet gear starting from the face side, and the planet slide bearing pins respectively form one crowning at their abutment surface such that their outer diameter decreases from a maximum outer diameter to at least an axial end of the abutment surface and has a minimum at the axial end.