Optical Rotation Detection for Magnetostriction Torque Sensors
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Solution Overview
Problem
Existing electric assist bicycles with magneto-striction torque sensors face interference from rotation sensors, leading to reduced torque detection capability due to external noise and bending stress, and lack effective mechanisms to prevent auxiliary driving force transmission when the rider stops pedaling.
Innovation Solution
The design incorporates a cylindrical human power transmission member with a magneto-striction generation portion for torque detection, an optical rotation detector, and a one-way clutch to prevent auxiliary driving force transmission, ensuring high torque detection capability and compact motor drive unit configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magneto-striction torque sensor is used for detecting human driving force, then torque detection capability is improved, but rotation sensors (permanent magnets) cause external disturbance and noise that reduces detection capability
Solution Approach 1:
The patent replaces the magnetic field-based rotation sensor with an optical sensor system. A light source emits light that reflects off a reflective surface attached to the rotating member, and a light receiver detects the reflected light. This optical detection method eliminates the permanent magnet and its associated magnetic field interference, thereby removing the noise source that disturbed the magneto-striction torque sensor while maintaining rotation detection capability.
2Strength
If the crank shaft is made resistant to large bending stress, then structural strength is improved, but material selection is limited and torque detection capability may be reduced
Solution Approach 1:
The patent divides the crank shaft into two separate functional members: a rotating member that handles bending stress and rotation, and a torque transmitting member that transmits torque to the torque sensor. The rotating member is designed to withstand bending stress, while the torque transmitting member is optimized for torque detection. This segmentation allows each component to be independently optimized for its specific function without compromising the other.
3Stability of the object's composition
If motor drive unit is disposed at intermediate position between front and rear wheels, then traveling stability is improved, but device complexity increases
Solution Approach 1:
The patent merges the rotating member and torque transmitting member into a single integrated crank shaft structure. The crank shaft simultaneously performs rotation to withstand bending stress and transmits torque to the torque sensor through its splined portion. This integration reduces the number of separate components and simplifies the overall drive unit configuration while maintaining the stability benefits of the intermediate motor position.
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 enhances torque detection accuracy, reduces noise interference, and prevents unnecessary motor operation when pedaling stops, improving riding efficiency and stability.
Implementation Method 1
a magneto-striction generation portion 105a for a torque sensor is formed on the outer periphery of the human power transmission member 104
Implementation Method 2
a rotation detector that detects a rotation of one of the intermediate cylinder and the human power transmission member, the rotation detector being an optical sensor
Data Source
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AI summary
An electric assist bicycle is provided so as to detect a torque by means of a magneto-striction torque sensor and keep high torque detection capability while detecting a rotation of a crank shaft or the like. The outer periphery of a crank shaft 7a has a cylindrical human power transmission member 28 having a torque sensor 31 for detecting a human driving force, an intermediate cylinder 23 that receives a human driving force transmitted from the human power transmission member 28, and an interlocking member 29 that receives the human driving force transmitted from the intermediate cylinder 23. A one-way clutch 30 is disposed between the intermediate cylinder 23 and the interlocking member 29. A rotation detector 10 is provided to detect a rotation of a rotating body 11 attached to the intermediate cylinder 23. The rotation detector 10 is an optical sensor.