Planetary Gear Bearing Geometry for Misalignment and Sliding Control
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Solution Overview
Problem
The asymmetrical stiffness of satellite carriers in planetary gear transmissions for hovering aircraft leads to misalignment and reduced service life due to deflection and sliding of rolling bodies, resulting in power loss and heat generation, especially under low lubrication conditions.
Innovation Solution
The design incorporates rolling bearings with concave inner raceways and spherical outer raceways, featuring hourglass-shaped rolling bodies that minimize sliding and maintain rolling motion, along with a lubrication system to prevent seizure, ensuring the rolling bodies remain parallel to the axis during torque transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional rolling bearings with cylindrical raceways are used in planetary gear satellite carriers, then the structure is simple and easy to manufacture, but the asymmetrical stiffness causes misalignment and sliding of rolling bodies under torque transmission
Solution Approach 1:
The patent applies spheroidality by replacing the conventional cylindrical inner raceway with a concave spherical inner raceway. This curved surface allows the rolling bodies (spheroids) to self-align and maintain optimal contact during torque transmission, eliminating the misalignment and sliding problems caused by asymmetrical stiffness in conventional cylindrical raceways.
2Device complexity
If conventional cylindrical roller bearings are used, then the bearing design is simple, but sliding motions occur causing power loss and heat generation under low lubrication
Solution Approach 1:
The patent changes the geometric parameters of the bearing components by using spheroidal rolling bodies instead of cylindrical rollers and providing them with rotational freedom about their own axes. This parameter change transforms the contact mechanics from sliding-dominated to rolling-dominated, significantly reducing power loss and heat generation even under low lubrication conditions.
Solution Approach 2:
The patent introduces dynamic capability by allowing the spheroidal rolling bodies to rotate freely about their own axes in addition to their orbital motion around the bearing center. This dynamic degree of freedom enables the rolling bodies to adapt to varying load conditions and maintain optimal rolling contact, preventing sliding and energy loss.
3Power
If the satellite carrier has asymmetrical stiffness to accommodate power transmission, then torque transmission is enabled, but deflection occurs causing misalignment of rotation axes
Solution Approach 1:
The patent applies asymmetry in a controlled manner by using spheroidal rolling bodies with different moment of inertia about different axes. The spheroids have higher moment of inertia about their radial axes than about their polar axis, creating an asymmetric mass distribution that naturally stabilizes the rolling motion and compensates for the asymmetrical stiffness of the satellite carrier, maintaining alignment of rotation axes during torque transmission.
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 sliding motions, enhances the service life of the planetary gear by maintaining efficient power transmission and reducing heat generation, even under reduced lubrication conditions, thereby improving the overall performance and reliability of the transmission system.
Implementation Method 1
rolling bearings with concave inner raceways and spherical outer raceways, featuring hourglass-shaped rolling bodies that minimize sliding and maintain rolling motion
Implementation Method 2
along with a lubrication system to prevent seizure
Data Source
Figure 1~2
Figure 3
Figure 4~7
AI summary
A planetary gear (21) is provided comprising a sun (15) rotatable around a first axis, a crown (17) angularly fixed with respect to the first axis; two satellites (19) that are meshing, rotatable around respective second axes; a satellite carrier (30) rotatable around the first axis and comprising at least two first pins (32) with respect to which the satellites (19) are rotatable around respective third axes; and a plurality of bearings (40) comprising: a first ring (41) defining a first raceway (42) that is at least partially spherical; a second ring (43) defining a second raceway (44); and a plurality of rolling bodies (45; 46) shaped as an hourglass rolling on the first spherical raceway and a second raceway; each rolling body being in contact with the raceways at a line with axial ends (61; 63, 62; 64) lying on respective straight lines tilted between them and converging in a point lying on a median plane of the rolling body and on the second axis; the straight lines define a first angle, whose bisector lies on the first median.