Cycloidal Reduction Gear Layout for Compact E-Bike Torque Drive
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Solution Overview
Problem
Existing electrically assisted bicycles face issues with mechanical reduction gears that are bulky, heavy, and inefficient, particularly when pedaling in reverse or during sudden stops, leading to discomfort, potential damage, and aesthetic concerns due to their large size and weight.
Innovation Solution
A mechanical reduction gear system featuring a rotor, planet carrier, and satellites with eccentric cams, which minimizes radial size and weight while maintaining a high reduction ratio, incorporating a cycloidal gearbox design with an Oldham joint for smooth operation and reduced friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If traditional reduction gears are used in electrically assisted bicycles, then the motor can provide assistance torque, but the system becomes bulky, heavy, and aesthetically unappealing
Solution Approach 1:
The patent integrates the reduction gear system within the bottom bracket housing, nesting the planet carrier, satellites, and cams inside the existing bicycle frame structure. This eliminates the need for external bulky gear housings while maintaining the high reduction ratio (1/40 to 1/60) necessary for motor assistance torque multiplication.
Solution Approach 2:
The patent uses a cycloidal reduction mechanism with planet carriers and satellites that achieve high reduction ratios through rotational eccentricity rather than multiple sequential gear stages. This dimensional approach (using orbital motion and eccentric cams) reduces the radial and axial space requirements compared to traditional multi-stage planetary or spur gear systems.
2Power
If traditional reduction gears are used, then motor assistance is provided, but the system generates additional friction and noise during pedaling
Solution Approach 1:
The patent employs a freewheel mechanism that dynamically engages or disengages the reduction gear system based on torque direction. During backward pedaling or coasting, the freewheel disengages the motor drive from the chainring, eliminating friction losses. During forward pedaling with motor assistance, the system engages only when needed, minimizing continuous friction exposure.
Solution Approach 2:
The patent extracts the friction-generating elements from the main pedaling path by placing the reduction gear in a separate motor-driven transmission path. The cyclist's direct pedaling torque bypasses the reduction gear, while motor torque is multiplied through the gear system. This separation ensures that gear friction does not add to the cyclist's pedaling effort.
3Power
If high reduction ratio is used to increase torque, then motor assistance is effective, but the radial size of the reduction gear increases
Solution Approach 1:
The patent achieves high reduction ratios by nesting multiple functional elements within the bottom bracket housing: the motor, planet carrier, satellites, cams, and freewheel all occupy overlapping spatial volumes rather than requiring sequential radial arrangement. This nested configuration maintains compact radial dimensions while achieving 1/40 to 1/60 reduction ratios.
4Weight of moving object
If simple freewheel mechanism is used for motor disconnection, then the system is lightweight, but it becomes noisy and generates high friction torque
Solution Approach 1:
The patent introduces an Oldham joint as an intermediary mechanism between the motor drive and the chainring. This joint provides smooth torque transmission with minimal friction and noise, replacing traditional direct-drive or simple freewheel mechanisms. The Oldham joint's cross-shaped geometry allows for controlled angular movement while maintaining continuous positive engagement without the impact loading and noise characteristic of simple pawl-and-ratchet freewheels.
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 solution provides a compact, lightweight, and efficient mechanical reduction gear system that enhances the pedaling experience by reducing friction and noise, improving comfort, and preventing damage during reverse pedaling and sudden stops, while maintaining the bike's aesthetic appeal.
Implementation Method 1
a mechanical reducer (5) comprising a rotor (32), an outer ring (55) of pitch diameter D55
Implementation Method 2
at least one satellite (51, 52, 53) of pitch diameter D50 intended to rotate inside the ring with an eccentricity of value "e" equal to half the difference between the diameter D55 and the diameter D50
Data Source
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AI summary
Disclosed is a mechanical reduction gear (5) comprising a rotor (32), an outer ring gear (55) of pitch diameter D55, a planet carrier (57), which comprises at least one planet gear (51, 52, 53, 51', 52') of pitch diameter D50 designed to rotate inside the ring gear with an eccentricity of value "e" equal to half the difference between the diameter D55 and the diameter D50; e = ½(D55 - D50); the at least one planet gear being mounted so as to be able to rotate on the rotor (32) by means of an eccentric (315, 316, 317) comprising at least one cam (3101, 3102, 3171, 3172); the cam comprising an inner surface (31012, 31022, 31712, 31722) that is cylindrical of diameter D31 and an outer surface (31013, 31023, 31713, 31723) that is cylindrical of diameter D504, the diameter D504 being equal to the sum of the diameter D30 and double the eccentricity "e"; D504 = D31 + 2e.