Planetary Gear Shaft Prestress for Load-Induced Alignment
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Solution Overview
Problem
In planetary gears, twisting deformation of the planet carrier causes geometric axes of rotation to become skewed, impairing meshing between planet wheels and other components, leading to reduced torque transfer capacity and shorter lifespan, necessitating costly material upgrades for flexible shafts.
Innovation Solution
Planet wheel shafts are prestressed in an unloaded state to be skewed relative to the axial direction, with this skewness being reduced by twisting deformation in the planet carrier under load, minimizing material tension and maintaining alignment closer to the axial direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If planet wheel shafts are made more flexible to compensate for twisting deformation, then the skewedness of geometric axes of rotation is reduced and meshing is improved, but material tensions in the planet wheel shafts increase
Solution Approach 1:
The planet wheel shafts are designed with non-uniform flexibility distribution along their length. Specifically, the shafts have different flexibilities at different locations, with the portion near the planet carrier being more flexible than the portion near the planet wheel. This local differentiation allows the shaft to accommodate twisting deformation where needed while maintaining sufficient stiffness for torque transfer in other regions, thus resolving the contradiction between meshing quality and torque transfer capacity.
2Strength
If planet wheel shafts are made more rigid to improve torque transfer capacity, then material tensions decrease, but the skewedness of geometric axes of rotation increases and meshing is impaired
Solution Approach 1:
The shaft design implements local quality by creating a flexibility gradient along the shaft length. The region closer to the planet carrier is designed with higher flexibility to accommodate twisting and maintain proper geometric axis alignment, while the region closer to the planet wheel maintains higher rigidity for effective torque transfer. This spatial differentiation of mechanical properties resolves the contradiction between rigidity and flexibility requirements.
3Ease of manufacture
If uniform flexibility is provided in planet wheel shafts, then manufacturing is simplified, but load sharing between planet wheels is not equalized
Solution Approach 1:
The invention applies local quality by designing planet wheel shafts with position-dependent flexibility characteristics. The shafts have different flexibilities at different locations along their length, specifically tailored to equalize load distribution among planet wheels. This non-uniform flexibility profile compensates for the twisting deformation that occurs in the planet carrier, ensuring that all planet wheels share the load equally even though the manufacturing process is more complex than uniform shafts.
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 extends the life of bearings, reduces the need for skewedness compensation in planet wheel design, and decreases material tension in shafts, thereby enhancing torque transfer capacity without requiring expensive materials.
Implementation Method 1
Each of the planet wheel shafts is prestressed in the unloaded situation where the planet carrier is free from the twisting deformation caused by torque directed to the planet carrier, and, in the loaded situation, prestress of each of the planet wheel shafts is reduced in a response to the twisting deformation of the planet carrier
Implementation Method 2
the above-mentioned first and second end-sections of the planet carrier are twisted with respect to each other. The twisting deformation of the planet carrier leads to a situation where geometric axes of rotation of the planet wheels are skewed with respect to the axial direction of the planetary gear
Data Source
Figure 1
Figure 2a~2c
Figure 3a~3b
AI summary
A planetary gear comprises a planet carrier (104), a sun wheel, a gear ring (103), and planet wheels (105-107) meshing with the sun wheel and with the gear ring. Each planet wheel shaft (109) of the planetary gear is arranged to rotatably support a respective planet wheel so that, in an unloaded situation, a geometric axis of rotation (113) of the planet wheel is skewed (α) with respect to the axial direction (z) of the planetary gear. In a loaded situation, torque directed to the planet carrier causes twisting deformation in the planet carrier and thereby the skewedness of the geometric axis of rotation is at least partly eliminated by the twisting deformation. Thus, in the loaded situation, the direction of the geometric axis of rotation can be closer to the axial direction than in a planetary gear where there is no skewedness in an unloaded situation.