Asymmetrical Planetary Gear Train for Helicopter Power Transmission
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Solution Overview
Problem
Current planetary gear trains in helicopters face challenges in increasing the power-to-weight ratio and achieving quiet operation while maintaining efficient torque and rotational speed transmission to the rotor shaft, as they are limited by the number of teeth meshing and pressure angles.
Innovation Solution
The design introduces a planetary gear train with asymmetrical teeth, where at least two teeth of each planetary gear simultaneously mesh with the sun gear and crown wheel, featuring different pressure angles on each side, allowing for a higher number of teeth meshing and a contact ratio greater than 2.5, which reduces stress and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the number of teeth of planetary gears is set to the semidifference between crown wheel and sun gear teeth, then the pressure angles coincide with working pressure angles, but the number of simultaneously meshing teeth is limited to substantially one
Solution Approach 1:
The patent applies asymmetry by providing planetary gears with different numbers of teeth on different sides (first side has Za teeth, second side has Zb teeth). This asymmetric tooth configuration allows the gear to simultaneously mesh with both the sun gear and crown wheel with multiple teeth engaged, breaking the conventional symmetry that limited meshing to one tooth. The asymmetric design enables increased load distribution while maintaining proper pressure angle alignment.
Solution Approach 2:
The patent changes the tooth count parameters by specifying that the number of teeth Za on the first side and Zb on the second side satisfy specific relationships with the sun gear teeth Zs and crown wheel teeth Zc. These parameter changes (Za > Zb, and specific modular relationships) enable multiple simultaneous meshing points while maintaining manufacturing precision for pressure angles.
2Strength
If more teeth are made to mesh between planetary gears and sun gear or crown wheel, then load distribution improves, but the teeth cannot simultaneously mesh on different sides with both sun gear and crown wheel
Solution Approach 1:
The asymmetric tooth configuration (different tooth counts Za and Zb on opposite sides of each planetary gear) resolves the meshing conflict by allowing each planetary gear to engage multiple teeth with the sun gear on one side while simultaneously engaging multiple teeth with the crown wheel on the other side. This asymmetric design distributes loads across multiple tooth contacts without creating complex interference in the meshing paths.
Solution Approach 2:
The patent effectively uses the dimensional aspect of the planetary gear's rotation about its own axis combined with its revolution around the sun gear. By varying tooth counts in different angular positions (dimensions), the invention enables multiple simultaneous meshing contacts that would be impossible with uniform tooth distribution, thereby improving load distribution without excessive complexity.
3Power
If conventional planetary gear trains are used, then torque and rotational speed transmission is achieved, but the power-to-weight ratio and noise reduction are limited
Solution Approach 1:
The asymmetric planetary gear design enables more efficient load distribution across multiple teeth, allowing for reduced gear sizes while maintaining the same power transmission capability. This reduces the overall weight of the gear train. The different tooth counts Za and Zb optimize the meshing configuration to minimize material requirements while preserving torque transmission efficiency.
Solution Approach 2:
By changing the tooth count parameters (Za, Zb, Zs, Zc relationships) and pressure angle parameters differently on each side of the planetary gears, the invention optimizes the gear train for higher power density. This allows the same power transmission with fewer or smaller gears, reducing weight while maintaining or improving power-to-weight ratio.
Data Source
AI summary
Described herein is a planetary gear train, comprising: a sun gear that can turn about an axis and comprises a plurality of first teeth; a fixed crown wheel comprising a plurality of second teeth; and two planetary gears, each comprising a plurality of third teeth, the planetary gears each meshing with the crown wheel and the sun gear and able to turn about second axes, which are in turn able to turn about the first axis; at least two third teeth simultaneously mesh with second teeth and further two third teeth simultaneously mesh with first teeth; the third teeth comprise a first and a second side, which have, respectively, a first and a second pressure angle different from one another; and the number of the third teeth is different from the absolute value of the semidifference between the number of the first teeth and of the second teeth.