Differential Planetary Gearbox With Axial Load Sharing
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Solution Overview
Problem
Differential planetary gearboxes face challenges in achieving consistent load sharing between multiple planets, particularly when using smaller diameter planets, which limits torque transmission and increases the risk of detrimental load distribution, leading to reduced efficiency and torque capacity.
Innovation Solution
The use of multiple planets with different helical angles and torsionally flexible pinion surfaces, combined with materials having a yield strength-to-stiffness ratio greater than 0.10, allows for consistent load sharing and improved torque transmission by enabling axial movement and flexibility in the gear sets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If more than three planets are used in a differential planetary gearbox, then the gear ratio capability is improved, but the load distribution becomes uneven and torque transmission efficiency deteriorates
Solution Approach 1:
The patent applies local quality by giving each planet gear a unique helical angle rather than using identical gears. This differentiation allows each planet to engage with the sun and ring gears at different contact patterns, distributing load more evenly across all planets while maintaining high gear ratio capabilities
Solution Approach 2:
The patent implements dynamics by making the planet gears axially movable rather than fixed in position. This axial mobility allows the planets to self-adjust their positions dynamically during operation, enabling them to share load more uniformly and preventing any single planet from bearing excessive torque
2Area of stationary object
If smaller diameter planet gears are used, then the center through hole size is increased, but the torque transmission capacity of each planet is reduced
Solution Approach 1:
The patent applies parameter changes by varying the helical angle parameter across different planet gears. This parameter differentiation compensates for the reduced size of each planet, allowing smaller diameter gears to transmit torque effectively by optimizing their engagement characteristics with the sun and ring gears through unique helical angles
Solution Approach 2:
By giving each small planet gear a distinct helical angle, the patent ensures that even though individual planets are smaller, their localized engagement properties are optimized for their specific position, enabling effective torque transmission despite reduced diameter
3Device complexity
If three or four planets take the majority of the load, then the remaining planets contribute less than 25% to torque transmission, but using only three larger planets would provide better torque transmission
Solution Approach 1:
The patent resolves this by making each planet gear unique with a different helical angle, which optimizes the engagement characteristics of each planet. This ensures that all planets contribute meaningfully to torque transmission rather than having a few dominate, maximizing the utility of having multiple planets while maintaining high torque efficiency
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 approach enables efficient torque transfer and load sharing among multiple planets, enhancing torque transmission capabilities while minimizing weight and maintaining a compact envelope, suitable for high-torque applications with minimal weight constraints.
Implementation Method 1
each first planetary gear set is axially movable, for example against an elastic element such as a spring with respect to an axis defined by the one or more sun gears
Implementation Method 2
separated by a torsionally flexible portion of the pinion surface
Data Source
AI summary
A torque transfer device has plural planets arranged for planetary rotation about one or more sun gears and within one or more ring gears. Each planet includes at least one planetary gear set comprising plural planetary gears connected to rotate together, but having a different diameter to form a differential gear system. To improve load sharing, the plural planetary gears of each planetary gear set may have a different helical angle, the plural planetary gear sets being axially movable with respect to one another. Alternatively or in addition, the planetary gears may be made flexible with respect to radial forces.