Magnetostrictive Torque Sensor with Single Film Anisotropy
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Solution Overview
Problem
Magnetostrictive torque sensors for electric power steering systems face challenges with size and output characteristic variations due to thickness irregularities and complex manufacturing processes, leading to increased size and complexity.
Innovation Solution
A magnetostrictive torque sensor with a single magnetostrictive film having multiple magnetic anisotropies, where coils are positioned to confront regions of uniform thickness, reducing the need for large axial lengths and eliminating gaps, allowing for accurate torsional torque detection while minimizing size and manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple magnetostrictive films with opposite magnetic anisotropy are used, then torque detection capability is improved, but device size and manufacturing complexity increase
Solution Approach 1:
The single magnetostrictive film is segmented into different magnetic anisotropy regions through selective high-frequency heating while torque is applied. This creates functionally distinct regions (first and second magnetic anisotropy regions) within one continuous film structure, enabling differential torque detection without requiring multiple separate films or complex assembly processes
Solution Approach 2:
Multiple magnetostrictive films with opposite magnetic anisotropy are merged into a single continuous magnetostrictive film with different magnetic anisotropy regions. This integration maintains the torque detection functionality of multiple films while eliminating the complexity of manufacturing and aligning multiple separate films with coils
2Reliability
If magnetostrictive film thickness is increased to reduce output variations, then measurement stability is improved, but device size increases
Solution Approach 1:
Different regions of the magnetostrictive film are given different magnetic anisotropy properties through selective high-frequency heating. The first and second magnetic anisotropy regions have opposite magnetic anisotropy directions, which compensates for thickness variations and reduces output characteristic variations without requiring increased film thickness or axial length
Solution Approach 2:
The magnetic anisotropy parameter is changed in different regions of the magnetostrictive film through controlled high-frequency heating while torque is applied. By adjusting the heating conditions and torque application, the magnetic anisotropy direction is reversed in specific regions, creating compensation effects that stabilize output characteristics without increasing physical dimensions
3Manufacturing precision
If complex masking processes are used to form multiple magnetostrictive films, then magnetic anisotropy control is improved, but manufacturing time and cost increase
Solution Approach 1:
Torque is applied to the magnetostrictive film before high-frequency heating to establish the desired magnetic anisotropy orientation. This preliminary mechanical pre-conditioning ensures that when heating occurs, the magnetic anisotropy develops in the correct direction relative to the applied torque, enabling precise control without complex masking processes
Solution Approach 2:
The mechanical masking process is replaced with a field-based approach combining mechanical torque application and electromagnetic high-frequency heating. Instead of using physical masks to control film formation, the magnetic anisotropy is controlled through the interaction of applied torque and high-frequency electromagnetic fields, simplifying the manufacturing process while maintaining precision
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
The solution enables a compact, efficient magnetostrictive torque sensor that accurately detects torsional torque with reduced output variations, contributing to a smaller electric power steering apparatus and simplified manufacturing.
Implementation Method 1
a magnetostrictive torque sensor for detecting torque based on a change in a magnetic property due to magnetostriction
Implementation Method 2
a plurality of coils for detecting a change in a magnetic property of the magnetostrictive film
Data Source
AI summary
A magnetostrictive torque sensor includes a single magnetostrictive film disposed on a steering shaft, and first and second coils for detecting changes in a magnetic property of the magnetostrictive film. The single magnetostrictive film includes a first anisotropic region and a second anisotropic region, having respective magnetic anisotropies inverse to each other. The first coil is disposed in confronting relation to the first anisotropic region, whereas the second coil is disposed in confronting relation to the second anisotropic region.