Bottom Bracket Planetary Gearbox for Low-Drag E-Bike Shifting
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Solution Overview
Problem
Existing bicycle drive assemblies face challenges in efficiently transmitting torque while minimizing drag torque and allowing for no-load gear changes, especially when using electric motors.
Innovation Solution
The drive assembly incorporates a bottom bracket gearbox with a planetary assembly and brake shift elements, allowing for multiple gear ratios and decoupling of the electric motor to avoid drag torque, while enabling no-load gear changes and additional functions like hill holding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the electric motor is mechanically connected to the gearbox output shaft, then power transmission is enabled, but drag torque occurs when the motor is decoupled
Solution Approach 1:
The patent extracts the electric motor from the direct mechanical connection to the gearbox output shaft by introducing a planetary assembly as an intermediate stage. The motor connects to the planetary assembly input, which then transmits power to the gearbox, allowing the motor to be decoupled without creating drag torque on the output shaft.
Solution Approach 2:
The planetary assembly acts as an intermediary between the electric motor and the gearbox. It provides a mechanical advantage that allows the motor to be disconnected without transmitting drag torque to the gearbox output, while still enabling power transmission when engaged.
2Adaptability or versatility
If a multi-stage gearbox is used, then gear changes are possible, but the structure becomes more complex
Solution Approach 1:
The patent implements a nested planetary assembly within the bottom bracket gearbox structure. The planetary gear set is integrated into the existing multi-stage gearbox, with planetary gears nested within the gear train, providing additional gear ratios without significantly increasing external dimensions or structural complexity.
3Loss of energy
If the motor is always connected to the drive train, then continuous power transmission is possible, but energy is lost during coasting
Solution Approach 1:
The patent introduces dynamic engagement and disengagement capabilities through the planetary assembly and brake shift elements. The system can dynamically switch between connected and decoupled states, allowing the motor to be disconnected during coasting to reduce energy loss while reconnected when power transmission is needed.
Solution Approach 2:
The planetary assembly allows the motor to be extracted from the direct drive path, enabling selective engagement. When the motor is decoupled through the planetary mechanism, it does not create drag torque on the gearbox output, allowing efficient coasting while maintaining the option for continuous power transmission when needed.
Data Source
AI summary
The present invention relates to a drive assembly (100; 200; 300; 400; 500) for a bicycle. The drive assembly (100; 200; 300; 400; 500) has a bottom bracket gearbox (10), a prime mover (18) and a planetary assembly (110, 412). The planetary assembly (110, 412) includes a first planetary gear set (110) having a first rotary element, a second rotary element and a third rotary element. The drive assembly (100; 200; 300; 400; 500) has a stationary component (22) and a first brake shift element (B1). The first rotary element is mechanically operatively connected to the output (20) of the prime mover (18). The second rotary element is in the form of an output of the planetary assembly (110). The third rotary element is rotationally fixable on the stationary component (22) by the brake shift element (B1).