Planetary Bearing Pin Crowning for Uniform Lubrication Under Load
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Planetary gears in geared turbofan engines face significant centrifugal forces and torques, leading to deformation and increased lubricating film pressure at the ends of the planetary journal bearing pin, risking metal-to-metal contact and wear, while increasing the wall thickness to enhance rigidity results in weight penalties detrimental to aerospace applications.
Innovation Solution
The planetary plain bearing pin features a varying inner diameter with a maximum at one axial end and a minimum at the other, combined with a crowned outer surface that decreases in diameter towards the ends, creating a uniform lubricating film thickness and reducing stress without increasing weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the wall thickness of the planetary plain bearing pin is increased to improve rigidity, then the bearing load capacity and wear resistance are improved, but the weight of the component increases significantly
Solution Approach 1:
The patent applies local quality by varying the wall thickness of the planetary plain bearing pin along its axial length. The pin has maximum wall thickness at the axial ends where bending moments are highest due to centrifugal forces, and reduced wall thickness in the middle section where stresses are lower. This non-uniform thickness distribution optimizes rigidity where needed while minimizing weight overall, resolving the contradiction between strength and weight.
2Ease of manufacture
If the planetary plain bearing pin maintains a cylindrical shape with uniform wall thickness, then the manufacturing is simple, but the lubricating film thickness becomes non-uniform under centrifugal forces causing metal-to-metal contact at the ends
Solution Approach 1:
The patent changes the geometric parameters of the bearing pin by introducing axial crowning (varying the outer diameter along the axial direction) and non-uniform wall thickness. The outer diameter is maximum at the axial ends and minimum in the middle, which compensates for the deformation under centrifugal forces and maintains a more uniform lubricating film thickness distribution, preventing metal-to-metal contact while remaining manufacturable.
3Weight of moving object
If the axial bore of the planetary plain bearing pin is enlarged at both axial ends, then the weight is reduced and rigidity is improved, but the structural strength at the ends may be compromised
Solution Approach 1:
The patent applies local quality by creating an axial bore with varying diameter - maximum at the axial ends and minimum in the middle section. This configuration removes material from high-stress regions (the ends) to reduce weight, while the maximum wall thickness at the ends (due to the bore geometry) maintains structural strength where bending moments are highest. The non-uniform bore design optimizes the strength-to-weight ratio.
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 enhances the rigidity and reduces wear of the planetary plain bearing pin, maintaining a sufficient lubricating film thickness to prevent metal contact, while minimizing weight and optimizing the bearing load, thus addressing the challenges of deformation and wear under centrifugal forces.
Implementation Method 1
The inner diameter of the axial bore of the planetary plain bearing pin varies between the axially front end and the axially rear end of the inner surface and has a maximum at at least one axial end
Implementation Method 2
The planetary plain bearing pin and the planetary wheel forming a lubricated plain bearing in which the adjacent contact surfaces of the plain bearing are separated from one another by a plain bearing gap
Implementation Method 3
the planetary plain bearing pins on their contact surface in each case form a crown in the sense that their outer diameter decreases from a maximum outer diameter to at least one axial end of the contact surface
Implementation Method 4
The sun gear rotates around an axis of rotation of the planetary gear and is driven by a sun shaft. The planetary gears are driven by the sun gear and mesh with the ring gear.
Implementation Method 5
The planetary gears are driven by the sun gear and mesh with the ring gear. A planetary plain bearing pin is arranged in a planet wheel
Implementation Method 6
In geared turbofan engines, planetary gears are subjected to very large centrifugal forces and torques that can deform the planetary journal bearing pin and planetary gear
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to a planetary gear (100) comprising: a sun gear (3); a plurality of planet gears (4); a ring gear (5); and a plurality of planet bearing pins (6), wherein each planet bearing pin (6) is arranged in a planet gear (4) and the planet bearing pin (6) and the planet gear (4) form a lubricated sliding bearing. The planet bearing pin (6) is provided with an axial bore (690) and has an inner surface (69) comprising an axially forward end (691) and an axially rear end (692).It is provided that the inner diameter (m) of the axial bore (690) of the planetary bearing pin (6) varies between the axially front end (691) and the axially rear end (692) of the inner surface (69) and has a maximum at at least one axial end (691, 692), and that the planetary bearing pins (6) each form a crown on their contact surface (60) such that their outer diameter (e) decreases from a maximum outer diameter (D) towards at least one axial end (65, 66) of the contact surface (60) and has a minimum at the axial end (65, 66).