Segmented Bicycle Drive Train for High Torque and Low Unsprung Mass
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Solution Overview
Problem
Existing bicycle transmissions, such as rear hub gears and bottom bracket transmissions, suffer from high unsprung mass, limited torque capacity, and point-like load engagement issues, making them unsuitable for modern bicycles with high torque demands and suspension systems.
Innovation Solution
A drive train with two separate sub-gears: a bottom bracket shifter with n gears and a secondary gear in the rear wheel hub, allowing for a total of 2n or 3n gears without changing the gear step, with power transmission via shift cables or electrical switching, and asymmetric tooth design for improved load-bearing capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If rear hub gears are used to provide multiple gears, then gear range is improved, but mass increases to approximately two kg and exceeds torque capacity of 130 Nm
Solution Approach 1:
The transmission system is divided into two separate sub-gears: a bottom bracket shifter with n basic gears and a secondary gear in the rear wheel hub with two or three gears. This segmentation allows the system to achieve a total of 2n or 3n gears while distributing the mass and functional requirements across separate components, with the bottom bracket shifter handling high torque and the rear hub gear providing gear multiplication.
2Force
If conventional bottom bracket transmissions are designed to handle high peak torques, then torque capacity is improved, but the transmission must handle very high peak torques largely undamped with no reserves for shock peaks
Solution Approach 1:
The transmission is segmented into a bottom bracket shifter designed for high torque capacity (e.g., 400 Nm) and a secondary rear hub gear. This segmentation allows the bottom bracket shifter to handle peak torques and shock loads while the secondary gear provides additional gear ratios, creating torque reserves for shock peaks caused by pedal impacts, tandem drive, or motor coupling.
Solution Approach 2:
The system design incorporates torque reserves in the bottom bracket shifter (capable of 400 Nm) that cushion against peak torques and shock loads before they can damage the transmission. This prior cushioning capacity handles shock peaks from pedal impacts, tandem drive, and motor coupling without compromising reliability.
3Adaptability or versatility
If a large number of gears are provided with only one pawl per gear, then gear variety is improved, but point-like load occurs on teeth and pawls can be switched unfavorably under load
Solution Approach 1:
The transmission is divided into two sub-gears, each with multiple gears and multiple pawls. The bottom bracket shifter contains n basic gears with multiple pawls for reliable engagement, while the secondary rear hub gear provides two or three additional gears. This segmentation ensures that each sub-gear has sufficient pawls to distribute loads and avoid point-like loading, maintaining strength while providing a total of 2n or 3n gears.
4Device complexity
If all gears are accommodated in the rear wheel hub, then gear integration is improved, but unsprung mass increases and torque capacity is limited to 130 Nm
Solution Approach 1:
The transmission system is segmented with the bottom bracket shifter (containing n basic gears) positioned at the bottom bracket where it can handle high torques, and a secondary gear (with two or three gears) positioned in the rear wheel hub. This segmentation allows the rear hub to have reduced unsprung mass while maintaining torque capacity, as the primary torque handling function is performed by the bottom bracket shifter.
5Force
If all gears are accommodated in the bottom bracket transmission, then torque handling is improved, but axial space requirements increase and coupling of additional drives becomes difficult
Solution Approach 1:
The transmission is segmented into a bottom bracket shifter with n basic gears that handles high torque, and a secondary rear hub gear with two or three gears that provides additional ratios. This segmentation reduces the axial space requirements in the bottom bracket area while maintaining torque handling capacity, and creates space for coupling additional drives such as electric motors or tandem drives into the bottom bracket shifter.
Data Source
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Figure 2A
AI summary
The invention relates to a drive train for muscle-operated single or multi-track vehicles, comprising a crank-driven bottom bracket mechanism which is connected on the output side to a chain drive or belt drive, from which a chain or belt can be fed directly or shiftably to a pinion of a rear wheel hub, wherein in the drive train except in the bottom bracket mechanism, which is designed as a primary shift transmission (G01) with n gears or with variable transmission ratio, a secondary mechanism (G02) is arranged as a shiftable rear wheel hub mechanism with m = two or m = three gears, wherein n and m are natural numbers. According to the invention, in the drive train except in the bottom bracket mechanism which is designed as a primary shift transmission (G01) with n gears, a secondary mechanism (G02) is arranged as a shiftable rear wheel hub transmission with m = two or m = three gears.