Sleeve Drive Shaft Torque Measurement in E-Bike Motor
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Solution Overview
Problem
Crank drive motor assemblies for electric bicycles face challenges in compactness and manufacturing costs, with existing designs often requiring complex and costly components to meet performance standards, particularly in ensuring optimal interaxial distance and integrating electronic functions for torque and pedaling speed detection.
Innovation Solution
The motor assembly features a sleeve drive shaft with a torsiometer function, utilizing strain gauges for temperature compensation, a single-piece sleeve design allowing for machining without heat treatments, and the use of low-cost sensors like TMR sensors, along with a compact encoder wheel position, to achieve a cost-effective and compact configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If crank drive motor assembly uses complex detection devices for torque and pedaling speed, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent combines the torque measurement function directly into the drive shaft structure itself, making the drive shaft act as both the mechanical transmission component and the torque sensor. This integration eliminates the need for separate complex detection devices while maintaining measurement precision through strain gauge instrumentation of the drive shaft.
Solution Approach 2:
The drive shaft is designed to perform multiple functions simultaneously: mechanical power transmission and torque measurement. By incorporating strain gauges into the drive shaft, it becomes a multi-functional component that serves both structural and sensing purposes, reducing overall device complexity.
2Measurement precision
If crank drive motor assembly uses traditional detection devices, then measurement precision is maintained, but manufacturing cost increases
Solution Approach 1:
The patent employs low-cost TMR (Tunnel Magnetoresistance) sensors instead of expensive traditional encoders for pedaling speed detection. These inexpensive magnetic sensors provide sufficient measurement precision while dramatically reducing manufacturing costs.
Solution Approach 2:
The patent replaces complex mechanical encoder systems with magnetic TMR sensors that use magnetic fields rather than mechanical contact. This substitution eliminates mechanical wear, reduces component complexity, and lowers manufacturing costs while maintaining detection precision.
3Volume of moving object
If crank drive motor assembly reduces dimensions for compactness, then volume is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent positions the encoder wheel in axial alignment with the receiving electronic board, utilizing the axial dimension rather than radial space. This dimensional arrangement allows for compact radial dimensions while maintaining accurate interaxial distances, effectively trading one dimension for another to achieve compactness without sacrificing precision.
4Adaptability or versatility
If crank drive motor assembly integrates electronic functions, then device functionality is improved, but device complexity increases
Solution Approach 1:
The patent integrates the encoder wheel and TMR sensors directly into the drive shaft assembly, combining mechanical and electronic functions in a single integrated unit. This merging reduces the number of separate components and simplifies the overall assembly while maintaining full electronic control functionality.
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
This configuration results in a more compact and cost-efficient crank drive motor assembly with improved performance, enabling better torque measurement and pedaling detection, while reducing production costs and enhancing compatibility with other bicycle components.
Implementation Method 1
said drive shaft (4) having the function of a torsiometer, two strain gauges (40) being applied to a second portion (47) of said drive shaft (4)
Implementation Method 2
the use of low-cost sensors like TMR sensors
Data Source
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AI summary
Motor assembly (1) for an electric bicycle, comprising: a containment case (6); a pedal shaft (3), rotatable with respect to the case (6) and arranged to bear at the two opposed ends as many bicycle pedal cranks (101); a drive shaft (4), rotatable with respect to the case (6) and arranged to integrally bear at least a bicycle front sprocket (102); a main electric motor (2) comprising a stator integral with the case (6) and a rotor coupled through a transmission (5) to said drive shaft (4); said drive shaft (4) being shaped as a sleeve coaxial and overlapped to said pedal shaft (3); said pedal shaft (3) being kinematically connected in rotation to said drive shaft (4) by means of an interposed freewheel (7) which makes the pedal shaft (3) integral with the drive shaft (4) in a rotation direction corresponding to the bicycle forward motion; said drive shaft (4) comprising: a first portion (46), arranged to support the front sprocket (102) and at which a most downstream member of said transmission (5) is fixed; a third portion (48), at which the freewheel (7) is positioned; and a second portion (47) acting as a torsiometer which connects the first portion (46) and the third portion (48); at least one strain gauge being placed on said second portion (47).