Linkage Torque Transmission for Non-Coaxial E-Bike Crank Drives
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Solution Overview
Problem
Electric power-assisted bicycles face challenges with increased Q factor due to large motor units, leading to dynamic imbalance, reduced pedaling cadence, safety issues in bends, and increased friction and noise from manufacturing tolerances and deformation, which affect efficiency and user experience.
Innovation Solution
A torque transmission device with an input disc, output disc, and intermediate disc connected by pairs of links that allow torque transmission between non-coaxial spindles, reducing axial width and friction, and incorporating a reducer and free wheel to manage motor assistance and decoupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If a small, light electric motor with small diameter is used, then weight and size are reduced, but torque is limited requiring a reducer and free wheel that increase axial width
Solution Approach 1:
The torque transmission device is nested within the bottom bracket shell, integrating the motor, reducer, free wheel, and torque transmission mechanism into a compact coaxial arrangement. This nesting allows all components to share the same axial space, minimizing the overall axial width while maintaining the necessary functional elements.
Solution Approach 2:
The invention transitions from radial expansion to axial compactness by arranging all transmission elements (motor, reducer, free wheel, torque transmission device) in a coaxial configuration. This dimensional reorganization allows the system to fit within the constrained axial space of the bottom bracket shell while maintaining adequate torque transmission capability.
2Loss of energy
If manufacturing tolerances are reduced to improve coaxiality, then friction and noise are reduced, but manufacturing cost increases significantly
Solution Approach 1:
The torque transmission device automatically compensates for coaxiality deviations through its mechanical design. The linkage mechanism between the input and output shafts inherently adjusts to misalignment, eliminating the need for extremely tight manufacturing tolerances while maintaining low friction and noise levels.
Solution Approach 2:
The invention changes the operational parameters of the torque transmission system to accommodate normal manufacturing tolerances. By designing the linkage geometry and clearance parameters appropriately, the system maintains efficient torque transmission and low friction without requiring ultra-precise coaxiality, thus reducing manufacturing costs.
3Reliability
If the crank axle is strengthened to resist deformation under pedaling force, then reliability improves, but weight and complexity increase
Solution Approach 1:
The torque transmission device acts as an intermediary between the motor output and the crank axle. It transmits torque while accommodating crank axle deformation through its mechanical linkage design, protecting the crank axle from excessive stress without requiring the axle itself to be overly strengthened.
Solution Approach 2:
The torque transmission device incorporates mechanical elements that cushion and absorb deformation forces before they reach the crank axle. This prior cushioning protects the crank axle from peak loads and deformation, maintaining reliability without requiring excessive strengthening of the axle.
4Ease of operation
If pedal spacing (Q factor) is reduced to improve dynamic balance and safety, then pedaling efficiency and safety improve, but the space required for motor unit components increases
Solution Approach 1:
All motor unit components (motor, reducer, free wheel, torque transmission device) are nested in a compact coaxial arrangement within the bottom bracket shell. This nesting minimizes the radial footprint and pedal spacing while maintaining all necessary functional elements, allowing standard Q factor geometry.
Solution Approach 2:
The invention reorganizes the motor unit components from a radial layout to a coaxial axial layout. This dimensional change concentrates all components within a small radial envelope, reducing pedal spacing to standard values while maintaining adequate space for all transmission elements along the axial direction.
Data Source
AI summary
A torque transmission device includes an input disc, an output disc, an intermediate disc positioned between the input disc and the output disc, a first pair of links coupled by a first side to the input disc and by a second side, opposite to the first side, to the intermediate disc, the links of the first pair being positioned diametrically opposite each other relative to the intermediate central axis, a second pair of links coupled by a first side to the intermediate disc and by a second side, opposite to the first side, to the output disc, the links of the second pair being positioned diametrically opposite each other relative to the intermediate central axis of the intermediate disc, the two pairs of links being aligned in two respective directions perpendicular to each other.