Torque Sensor with Ferromagnetic Rings for Bicycle Drive Units
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Solution Overview
Problem
Existing torque sensors for detecting torque on a shaft are prone to disruptive influences from mechanical interference voltages and external far fields, which can lead to measurement errors and require sensitive and costly magnetic field sensors.
Innovation Solution
The torque sensor employs ferromagnetic ring bodies arranged around a magnetized drive shaft to amplify and concentrate magnetic flux, with magnetic field sensors positioned between these rings to average and compensate for fluctuations, allowing for precise torque detection using less sensitive sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic field sensors are used to detect torque on a shaft, then torque detection is enabled, but mechanical interference voltages and external far fields cause measurement errors and require highly sensitive (costly) sensors
Solution Approach 1:
Ferromagnetic ring bodies are introduced as intermediary elements between the magnetized drive shaft and the magnetic field sensors. These ring bodies serve as magnetic flux conductors that guide and concentrate the magnetic flux from the shaft to the sensors, while simultaneously providing mechanical stability and electrical isolation. This intermediary structure enables the use of less sensitive, more cost-effective sensors while maintaining measurement accuracy.
Solution Approach 2:
Multiple ferromagnetic ring bodies are combined in a stacked arrangement around the drive shaft, with each ring body contributing to the overall magnetic flux concentration. The ring bodies are positioned at different axial locations and combined to create a cumulative effect that amplifies the magnetic signal while averaging out mechanical interference voltages across the entire structure.
2Measurement precision
If highly sensitive magnetic field sensors are used to compensate for interference, then measurement accuracy improves, but device cost and complexity increase
Solution Approach 1:
The ferromagnetic ring bodies act as magnetic flux amplifiers that concentrate and guide the magnetic field lines from the magnetized drive shaft to the sensors. This flux concentration effect increases the magnetic signal strength at the sensor location, enabling the use of standard, less sensitive magnetic field sensors while maintaining high measurement accuracy.
Solution Approach 2:
The ferromagnetic ring bodies extend in the axial dimension, creating a three-dimensional magnetic flux path that concentrates field lines from the radial dimension onto the sensor surface. This dimensional transformation amplifies the magnetic flux density at the sensor location, reducing the sensor sensitivity requirements.
3Measurement precision
If ferromagnetic ring bodies are arranged around the drive shaft, then magnetic flux is amplified and concentrated, but device structure becomes more complex
Solution Approach 1:
The ferromagnetic structure is divided into multiple discrete ring bodies that are stacked around the drive shaft. Each ring body is a simple, identical component that can be manufactured and positioned independently. This segmentation simplifies manufacturing and assembly while the collective arrangement of multiple rings provides the desired magnetic flux amplification and mechanical stability.
Solution Approach 2:
The ferromagnetic ring bodies serve multiple functions simultaneously: they concentrate and guide magnetic flux to the sensors, provide mechanical support and positioning for the sensor assembly, and offer electrical isolation between the magnetized shaft and the non-magnetized sensor components. This multi-functionality reduces the need for additional separate components.
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 effectively reduces mechanical interference and external interference, enabling precise torque detection while minimizing the need for sensitive magnetic field sensors, thus reducing costs and improving measurement accuracy.
Implementation Method 1
magnetic fields that occur between the ferromagnetic ring bodies in the drive shaft are amplified by the ferromagnetic ring bodies
Implementation Method 2
magnetic field sensors, which detect changes in the magnetic properties of the magnetized drive shaft by detecting a magnetic flux or a magnetic flux density
Implementation Method 3
These effects are based on the fact that magnetic, particularly ferromagnetic, materials are deformed as a result of an externally applied magnetic field
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
The present invention relates to a torque sensor (1) for detecting a torque applied to a magnetized drive shaft (4), wherein the torque sensor (1) comprises at least two ferromagnetic ring bodies (2) spaced apart from one another and configured to enclose the magnetized drive shaft (4), and at least one magnetic field sensor (3) arranged between the ferromagnetic ring bodies (2) and configured to detect a magnetic flux density between the ferromagnetic ring bodies (2). The present invention also relates to a drive unit (10) comprising a drive shaft (4) and the torque sensor (1).