Continuously-variable planetary transmission with elongated rolling elements
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Solution Overview
Problem
Conventional continuously-variable planetary transmissions for bicycles suffer from limited efficiency and transmission range, high manufacturing costs, and complex structures due to high axial forces and Hertzian contact stresses, especially when shifting under load.
Innovation Solution
A continuously-variable planetary transmission design featuring elongated, rotationally symmetric planetary rolling elements with convexly curved lateral surfaces and a fixed support element, allowing for a wider transmission range and increased efficiency by minimizing spin/roll ratios and axial forces, thus enabling easy shifting even under load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional friction-gear transmissions with spherical or double-conical rolling elements are used, then the transmission can be compact, but the efficiency is limited and transmission range is restricted due to high spin/roll ratios and axial forces
Solution Approach 1:
The patent changes the geometric parameters of the rolling elements from spherical or double-conical shapes to elongated cylindrical shapes with specific length-to-diameter ratios. This parameter change reduces the spin/roll ratio and minimizes axial forces, thereby improving transmission efficiency while enabling a wider transmission range through optimized effective radius variation.
Solution Approach 2:
The patent modifies the curvature characteristics of the rolling elements by using elongated cylindrical shapes with convexly curved lateral surfaces instead of spherical or double-conical geometries. This curvature modification reduces contact stresses and minimizes spin motion, leading to higher efficiency and extended transmission range.
2Ease of operation
If conventional continuously-variable planetary transmissions are used, then shifting is easy and quiet, but the manufacturing costs are high and the structure is complex due to high axial forces and Hertzian contact stresses
Solution Approach 1:
The patent extracts and eliminates the need for complex axial force management systems by using elongated rolling elements that naturally minimize axial forces through their geometry. This simplifies the transmission structure by removing the need for heavy-duty axial bearings and complex support mechanisms, thereby reducing device complexity while maintaining ease of operation.
Solution Approach 2:
By changing the geometric parameters of the rolling elements to elongated cylindrical shapes, the patent reduces Hertzian contact stresses and axial forces, which simplifies the overall transmission structure and reduces manufacturing complexity while preserving the quiet and easy shifting characteristics.
3Device complexity
If conventional friction-gear transmissions are used, then the construction is simple and hub transmissions are hermetically sealed, but the overall range of ratios is limited and maximum efficiency is much lower than fixed-ratio transmissions
Solution Approach 1:
The patent changes the geometric parameters of the rolling elements to elongated cylindrical shapes with optimized dimensions, which reduces spin/roll ratios and minimizes energy losses. This parameter optimization enables the simple friction-gear construction to achieve efficiency levels comparable to or exceeding fixed-ratio transmissions while maintaining construction simplicity.
Solution Approach 2:
The patent enhances the dynamic performance of the simple friction-gear construction by using elongated rolling elements that enable continuous and smooth variation of the effective radius. This dynamic optimization allows the transmission to achieve high efficiency across a wide range of ratios while maintaining the simplicity and hermetic sealing of hub transmissions.
4Volume of moving object
If spherical or double-conical rolling elements are used, then the transmission structure is compact, but wear is increased and manufacturing costs are high due to high axial forces and Hertzian contact stresses
Solution Approach 1:
The patent modifies the curvature and shape of the rolling elements from spherical or double-conical to elongated cylindrical forms with convexly curved lateral surfaces. This shape modification distributes contact stresses more favorably, reduces Hertzian contact stresses, and minimizes wear while maintaining a compact transmission structure.
Solution Approach 2:
By changing the geometric parameters of the rolling elements to elongated cylindrical shapes with specific length-to-diameter ratios, the patent reduces axial forces and contact stresses, thereby improving wear resistance and reliability while keeping the transmission structure compact and manufacturing costs low.
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
The design achieves an efficiency of over 90% with a transmission range exceeding 600%, reducing wear and manufacturing costs while maintaining a compact and simple structure.
Implementation Method 1
frictional rolling contact with a planetary rolling element, by which the planetary rolling element is held movably around the transmission axis
Data Source
AI summary
A continuously-variable planetary transmission including: (a) first and second spaced rotatable transmission elements spaced around a transmission axis and having first and second contact points, respectively; (b) at least one support element in fixed radial position with respect to the transmission axis and each having a third contact point; and (c) at least one elongate, rotationally-symmetric, rotatable planetary rolling element, each rolling element (1) contacting the transmission elements at the first and second contact points and each support element at its third contact point, the contact points each in frictional rolling connection to the at least one rolling element and (2) being supported by the first and second transmission elements and the at least one support element with freedom to move around the transmission axis; and (d) an adjusting device for displacing the center of each planetary rolling element to change the ratio of the transmission.