Bottom Bracket Gear Layout for Compact Mid-Drive E-Bikes
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Solution Overview
Problem
Existing electric bicycles face challenges with weight distribution and maintenance issues due to the use of derailleur or hub gears, and there is a need for a compact, lightweight bottom bracket gear system that can accommodate an auxiliary drive without increasing overall weight.
Innovation Solution
A bottom bracket gear system with an input-side and output-side hollow shafts arranged next to each other on the bottom bracket shaft, featuring a freewheel between the input stage and the bottom bracket shaft, and a reduction gear to reduce torque, allowing for a compact and lightweight design that integrates an auxiliary drive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a bottom bracket gear shifter is used to achieve favorable weight distribution, then the weight distribution is improved, but the device size increases and leaves no space for an electric motor
Solution Approach 1:
The patent places the auxiliary drive (electric motor) inside the hollow shaft of the bottom bracket gear shifter. The motor is nested within the existing structure, utilizing the internal space of the hollow shaft rather than adding external volume. This allows the system to maintain favorable weight distribution at the bottom bracket while accommodating the electric motor without significantly increasing overall device size.
2Stability of the object's composition
If a bottom bracket gear shifter is used to achieve favorable weight distribution, then the weight distribution is improved, but the device weight increases making the e-bike too heavy
Solution Approach 1:
The patent combines the bottom bracket gear shifter and the auxiliary drive into a single integrated unit. The motor, transmission components, and gear shifter mechanisms are merged into one compact assembly that fits within the bottom bracket area. This integration eliminates the need for separate components and reduces overall weight while maintaining favorable weight distribution.
Solution Approach 2:
The auxiliary drive components are nested within the hollow shaft of the bottom bracket gear shifter. By placing the motor and transmission elements inside the existing hollow structure, the patent avoids adding external weight while still achieving the desired weight distribution. The nested arrangement allows the system to utilize the space efficiently without increasing overall mass.
3Area of stationary object
If derailleur gears are used due to insufficient space at the bottom bracket, then the space constraint is resolved, but the gear system becomes unprotected and maintenance-intensive
Solution Approach 1:
The patent merges the advantages of both bottom bracket gear shifters and hub gears by creating an integrated bottom bracket system with enclosed protection. The gear components are housed within a protected structure at the bottom bracket, combining the space efficiency of bottom bracket placement with the maintenance-free benefits of enclosed hub gear design. The chain and sprockets are shielded from external contaminants while maintaining compact dimensions.
4Reliability
If hub gears are used to achieve maintenance-free operation, then the reliability is improved, but the weight at the rear wheel increases leading to unfavorable weight distribution
Solution Approach 1:
The patent extracts the gear transmission functionality from the rear wheel hub and relocates it to the bottom bracket area. By taking out the gear mechanism from the hub and placing it at the bottom bracket with an integrated auxiliary drive, the system achieves maintenance-free operation through enclosed protection while maintaining favorable weight distribution. The heavy gear components are positioned at the bottom bracket rather than at the rear wheel, improving weight balance.
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 system achieves a favorable weight distribution by reducing the weight of the gearbox components while enabling the integration of an auxiliary drive, maintaining a compact size, and preventing the motor from powering the cyclist's legs during sudden stops.
Implementation Method 1
a freewheel is arranged between the input stage and the bottom bracket shaft
Implementation Method 2
The input stage, designed as a reduction gear, decreases the torque that the gearbox transmits
Data Source
Figure 1
Figure 2~4
Figure 5
AI summary
The invention relates to a bottom bracket gear system (1) of an electric bicycle (64) with an auxiliary drive (22), in particular in the form of a mid-drive motor. The bottom bracket gear system (1) has a gearbox (4). In order to make the gearbox as small and light as possible, an input stage (14) is arranged at the gearbox input (10) of the gearbox (4). The input stage (14) is designed to be arranged between a bottom bracket axle (6) and/or the auxiliary drive (22) and is configured as a speed-up gear.