E-bike Torque Measurement Using TMR Sensors and Magnetostriction
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Solution Overview
Problem
Conventional torque measurement systems for e-bike drives face challenges in differentiating between external magnetic interference fields and the internal torque-induced magnetic field, leading to inaccurate measurements and increased installation space requirements.
Innovation Solution
A system utilizing at least one rotatable shaft magnetized in an axial section with a TMR sensor designed for two- or three-dimensional magnetic field measurement, which evaluates changes in the magnetic field due to the magnetostrictive effect to determine torque, and an evaluation unit to differentiate interference and useful fields, reducing installation space and temporal offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional coil-based magnetic field sensors are used for torque measurement, then the system can detect magnetic flux changes, but external magnetic interference fields cannot be differentiated from the internal torque-induced magnetic field
Solution Approach 1:
The shaft is divided into multiple axial partial sections, each magnetized in different circumferential directions. This segmentation allows the measurement system to distinguish between torque-induced magnetic field changes and external interference fields by comparing the magnetic field patterns from different magnetized sections.
Solution Approach 2:
Different axial partial sections of the shaft are magnetized with different local qualities (different circumferential magnetization directions). This creates distinct magnetic field signatures for each section, enabling the sensor system to differentiate between useful torque signals and external magnetic interference based on the spatial distribution pattern.
2Measurement precision
If additional coils are introduced to compensate for magnetic field gradients, then interference fields may be differentiated from useful fields, but more installation space is required
Solution Approach 1:
The TMR sensor serves multiple functions simultaneously: it measures the magnetic field in three dimensions, detects torque-induced changes, and compensates for external interference fields. This multi-functionality eliminates the need for additional separate coil systems that would be required for gradient compensation, reducing installation space while maintaining measurement precision.
Solution Approach 2:
The patent replaces the conventional coil-based magnetic field sensing system with a TMR (tunnel magnetoresistance) sensor system. This substitution enables three-dimensional magnetic field measurement with a single sensor type, eliminating the need for multiple coil assemblies and reducing the overall installation space required for the torque measurement system.
3Measurement precision
If sensors are arranged to measure magnetic field changes, then torque can be detected, but temporal offsets between useful field and interference field measurements cause inaccurate torque determination
Solution Approach 1:
The TMR sensor continuously measures the magnetic field in three dimensions as the shaft rotates, providing continuous torque data without temporal gaps. The system processes magnetic field changes in real-time, eliminating the intermittent measurement approach that causes temporal offsets between useful field and interference field measurements.
Solution Approach 2:
The patent transitions from one-dimensional magnetic field measurement to three-dimensional measurement using TMR sensors. By measuring magnetic field changes in three dimensions simultaneously, the system can differentiate between torque-induced field changes and external interference in real-time, eliminating temporal offsets that occur in sequential one-dimensional measurement systems.
4Reliability
If a magnetoelastic torque sensor with multiple magnetized sections is used, then measurement reliability is increased, but the device complexity increases
Solution Approach 1:
The shaft itself serves as the magnetic field source through its magnetized axial partial sections, eliminating the need for separate external magnets or complex magnetization systems. The shaft's own magnetic properties are utilized to generate the measurement signal, simplifying the overall device structure while maintaining high measurement reliability.
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 approach reliably differentiates interference and useful fields, enhances measurement accuracy, and reduces installation space, providing continuous and robust torque measurement with reduced sensitivity to external fields.
Implementation Method 1
the at least one TMR sensor measures a change of the magnetic field due to the magnetostrictive effect in the magnetized partial section when the torque acts on the shaft
Data Source
AI summary
The invention relates to a system for torque measurement, in particular at a drive of an e-bike, including at least one shaft which is rotatable about an axis, is magnetized in at least one axial partial section, and onto which a torque to be measured can be applied, at least one TMR sensor, which is situated outside the shaft and is designed for at least two-dimensionally, in particular three-dimensionally, measuring a magnetic field and which is arranged in relation to the at least one partial section in such a way that, when the shaft rotates about the axis, the at least one sensor measures a change of the magnetic field due to the magnetostrictive effect in the magnetized partial section when the torque acts on the shaft, and an evaluation unit, which is connected to the at least one TMR sensor and is designed for determining a torque acting on the shaft based on the measured values of the magnetic field.