Bicycle Bottom Bracket Force Sensor via Magnetic Field
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Solution Overview
Problem
Conventional bicycle chain force measuring devices mounted on the rear wheel axle do not accurately represent the treading force exerted on the bicycle, as this force is transmitted through the chainwheel and crank arms, leading to inaccurate measurements.
Innovation Solution
A force measuring device is designed to be mounted in the bottom bracket assembly, comprising a sleeve shell, ring body, sensor holding unit, and hall sensing unit, which detects strain displacement caused by the treading force on the spindle, generating a signal indicative of the force magnitude through a magnetic field change.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a force measuring device is mounted on the rear wheel axle to measure chain tension, then the device structure is simple and easy to install, but the measurement accuracy is poor because the bending of the rear wheel axle is not truly representative of the treading force
Solution Approach 1:
The patent introduces a magnetic field as an intermediary between the strain displacement and the sensor. The magnetic member moves with the strain displacement of the strain region, and its movement is detected by the hall sensor through magnetic field changes. This intermediary approach allows for non-contact measurement while maintaining high precision in measuring the treading force at the bottom bracket assembly.
2Measurement precision
If a force measuring device is mounted in the bottom bracket assembly to accurately measure treading force, then the measurement accuracy is improved, but the device structure becomes more complex
Solution Approach 1:
The patent replaces a purely mechanical measurement system with a hybrid system that incorporates magnetic field detection. Instead of using complex mechanical linkages or direct contact sensors, the invention uses a magnetic member that moves with the strain displacement and a hall sensor to detect the magnetic field changes. This substitution reduces mechanical complexity while maintaining or improving measurement accuracy.
Solution Approach 2:
The force measuring device is nested within the bottom bracket assembly structure. The sleeve shell is inserted between the spindle and the bottom bracket shell, the ring body is disposed on the inner tubular wall, and the sensor holding unit is integrated into the assembly. This nesting approach allows the measuring device to be compact and integrated without adding excessive external complexity to the bicycle frame.
3Difficulty of detecting and measuring
If the magnetic member is disposed close to the sensor to enhance signal strength, then the sensitivity is improved, but the measurement reliability decreases due to potential contact and signal interference
Solution Approach 1:
The magnetic field serves as an intermediary that allows the sensor to detect the position of the magnetic member without physical contact. The hall sensor detects changes in the magnetic field generated by the magnetic member as it moves with the strain displacement. This non-contact measurement approach maintains high sensitivity while ensuring measurement reliability by eliminating contact-related interference and wear.
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 solution allows for accurate measurement of the treading force exerted on the crank axle, providing more representative data of the bicycle chain tension by directly measuring the force at the bottom bracket assembly.
Implementation Method 1
The outer ring surface has a strain region which is configured to make a strain displacement corresponding to a treading force exerted on the spindle
Implementation Method 2
a magnetic member that is disposed to be displaceable with the strain displacement of the strain region and that is spaced apart from the sensor by a predetermined distance such that a magnetic field generated thereby is changed when the magnetic member is displaced with the strain displacement
Data Source
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AI summary
A force measuring device (100) for a bicycle (4) includes a sleeve shell (2) having a first shell-half outer wall (21a) and an inner tubular wall (22) which are disposed between a bottom bracket shell (46) and a spindle (42), a ring body (32) disposed on the inner tubular wall (22) and having a strain region (323) which is configured to make a strain displacement corresponding to a treading force (F1) exerted on the spindle (42), a sensor holding unit (31) defining a sensor activating zone (313) and a hall sensing unit (33) including a sensor (331) which is disposed in the sensor activating zone (313), and a magnetic member (332) which is displaceable with the straining movement to change a magnetic field generated thereby so as to give off a signal indicative of the magnitude of the treading force (F1).