E-Bike Drivetrain Layout Using Split Torque Transmission
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Solution Overview
Problem
Existing electric assisted bicycles have limited flexibility in the layout of motor units and other components, which affects the operability and moment of inertia, making it difficult to change posture on rough terrain.
Innovation Solution
The motor unit is separated from the bottom bracket, with torque transmission via annular transmission members on either side of the bottom bracket, allowing for increased flexibility in positioning and reducing the moment of inertia by positioning the motor unit closer to the crankshaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the motor unit is directly connected to the bottom bracket, then the torque transmission is simple, but the flexibility in positioning the motor unit is limited
Solution Approach 1:
The torque transmission system is segmented into multiple independent transmission paths: a first transmission path from the motor unit to the crankshaft, and a second transmission path from the crankshaft to the rear wheel. This segmentation allows the motor unit to be positioned independently without being constrained by direct connection requirements, thereby improving positioning flexibility while maintaining manageable system complexity through modular design.
Solution Approach 2:
The crankshaft serves as an intermediary component that receives torque from the motor unit through the first transmission path and then transmits it to the rear wheel through the second transmission path. This intermediary role of the crankshaft decouples the motor unit positioning from the rear wheel drive system, enabling greater flexibility in motor unit placement without increasing overall system complexity.
2Ease of operation
If the motor unit is positioned far from the crankshaft, then there is more space for other components, but the moment of inertia increases reducing operability
Solution Approach 1:
The motor unit is positioned in a different spatial dimension relative to the crankshaft, specifically above or beside it rather than directly connected along the traditional chain line. This dimensional repositioning reduces the moment of inertia around the crankshaft for improved operability, while the annular transmission members extend outward to provide sufficient space for other components like the battery in different spatial zones.
3Adaptability or versatility
If the motor unit is separated from the bottom bracket, then the flexibility in layout is improved, but the torque transmission path becomes more complex
Solution Approach 1:
The annular transmission members serve multiple functions: they transmit torque from the motor unit to the crankshaft, accommodate the separated positioning of the motor unit, and provide structural support for the transmission system. This multi-functionality reduces the need for additional specialized components, thereby limiting the increase in device complexity despite the improved layout flexibility enabled by motor unit separation.
Data Source
AI summary
A first sprocket 54L is disposed on a left side of a bottom bracket 51 and configured to rotate integrally with a crankshaft 52. A second sprocket 54R is disposed on a right side of the bottom bracket 51 and configured to rotate integrally with the crankshaft 52. A first chain 56L is wound around an outer periphery of a third sprocket 23a provided to a motor output shaft 23 and an outer periphery of a first sprocket 54L and transmits torque from the third sprocket 23a to the first sprocket 54L. A second chain 56R is wound around an outer periphery of a fourth sprocket 55a provided to an axle 12a of a rear wheel 12 and an outer periphery of a second sprocket 54R and transmits torque from the second sprocket 54R to the fourth sprocket 55a.