Single-Shaft Motor Drive Unit Torque Detection Without One-Way Clutch
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Solution Overview
Problem
Conventional single-shaft motor drive units for electric assist bicycles suffer from noise during torque detection due to vibrations from one-way clutches, limited material choices for torque sensors, and incompatibility with coaster brakes, which affect torque detection capability and braking functionality.
Innovation Solution
A single-shaft motor drive unit configuration without a one-way clutch on the driving force transmission path, using a cylindrical human power transmission member with a magneto-striction torque sensor and a rotation detector to accurately detect pedal rotation, allowing for coaster brake activation and improved torque detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a one-way clutch is provided on the driving force transmission path to allow coaster brake operation, then coaster brake functionality is improved, but vibrations from the one-way clutch cause noise during torque detection
Solution Approach 1:
The patent divides the driving force transmission path into two separate paths: one path for forward driving force transmission that excludes the one-way clutch to avoid vibrations, and another path for coaster brake operation that includes the one-way clutch. This segmentation allows torque detection to occur on the vibration-free path while maintaining coaster brake functionality through the separate braking path.
Solution Approach 2:
The patent introduces a separate coaster brake mechanism as an intermediary system that handles reverse rotation braking independently from the main driving force transmission path. This mediator allows the primary transmission path to remain free of one-way clutches for accurate torque detection, while the intermediary coaster brake system provides the necessary reverse braking capability.
2Ease of operation
If a one-way clutch is provided on the driving force transmission path, then reverse rotation control is improved, but the choice of materials for torque sensor components is limited
Solution Approach 1:
The patent segments the transmission system so that the main driving path excludes one-way clutches, allowing use of materials optimized for torque sensor compatibility (such as non-magnetic or low-magnetic-interference materials). The reverse rotation control function is separated into the coaster brake system, which can use different materials appropriate for its specific function.
3Ease of operation
If a one-way clutch is provided on the driving force transmission path, then reverse rotation management is improved, but vibrations are transmitted to the torque sensor
Solution Approach 1:
The patent creates separate transmission paths: a forward driving path without one-way clutches that eliminates vibration transmission to the torque sensor, and a separate coaster brake path that handles reverse rotation management. This segmentation isolates the torque sensor from harmful vibrations while maintaining reverse rotation control capability.
Solution Approach 2:
The coaster brake mechanism serves as an intermediary system that manages reverse rotation independently, preventing vibrations from being transmitted to the main driving force transmission path and torque sensor. The intermediary braking system absorbs the reverse rotation energy without affecting the primary transmission path.
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
Enhances torque detection reliability, supports coaster brake functionality, and allows for the use of materials with high wear resistance, reducing noise and improving the overall performance of the electric assist bicycle.
Implementation Method 1
a magneto-striction generation portion and a coil that detects a change of magnetism on the magneto-striction generation portion
Data Source
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AI summary
An electric assist bicycle is provided with a so-called single-shaft motor drive unit that can satisfactorily keep torque detection capability. 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 and a combined-force member 29 that combines a human driving force and an auxiliary driving force from a motor 21. A one-way clutch is not provided on a driving force transmission path including the crank shaft 7a, the human power transmission member 28, and the combined-force member 28. The human power transmission member 28 and the combined-force member 29 are always rotated in response to a rotation of the crank shaft 7a. Moreover, a rotation detector 10 is provided to detect a rotation of the combined-force member 29.