Magnetostrictive Torque Sensor Radial Coil Arrangement
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Solution Overview
Problem
Existing magnetostrictive torque sensors face challenges with size and accuracy due to long axial lengths of magnetostrictive films, leading to increased errors from bending moments and temperature gradients, which affect torque detection and mounting performance in electric power steering systems.
Innovation Solution
The design includes two magnetostrictive films with different magnetic anisotropies and detection coils wound around coil bobbins in parallel, reducing axial lengths and maintaining consistent axial positions, thereby minimizing bending moment-induced errors and temperature gradient effects, while also downsizing the sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the axial length of magnetostrictive films is increased to allow for variations in relative position between the magnetostrictive film and detection coil, then the detection accuracy is improved, but the total length of the rotary shaft becomes too long, making the sensor size rather large and deteriorating mounting performance
Solution Approach 1:
The patent transitions from a one-dimensional axial arrangement where detection coils are positioned at different axial locations to a two-dimensional radial arrangement where multiple detection coils are positioned at the same axial location but different radial positions. This dimensional change allows the magnetostrictive film to maintain a compact axial length while still providing sufficient detection coverage, resolving the contradiction between detection accuracy and sensor size.
Solution Approach 2:
The patent combines multiple detection coils (first and second detection coils) at the same axial position, allowing them to simultaneously detect magnetic flux changes from the magnetostrictive film. This merging approach enables accurate torque detection without requiring the coils to be spaced axially, thereby reducing the axial length of the magnetostrictive film and overall sensor size.
2Ease of manufacture
If the axial distance between detection coils is increased to accommodate manufacturing variations, then the ease of manufacture is improved, but the bending moment differences between coils increase, leading to larger detection errors
Solution Approach 1:
The patent positions detection coils in the radial direction rather than the axial direction, so that multiple coils operate at the same axial position. This eliminates the problem of bending moment differences that arise from axial spacing, as all coils experience identical bending moments while still allowing for manufacturing tolerances in radial positioning.
Solution Approach 2:
The patent assigns different functional roles to different coils: the first detection coil detects magnetic flux changes primarily from the magnetostrictive film, while the second detection coil detects both magnetostrictive film changes and yoke magnetic flux changes. This local differentiation allows the system to compensate for manufacturing variations while maintaining detection accuracy.
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 enhances torque detection accuracy, reduces size, and improves reliability by minimizing errors from bending moments and temperature gradients, facilitating easier mounting and improved steering sensation in electric power steering systems.
Implementation Method 1
a magnetostrictive torque sensor, which detects a torque on the basis of a change in magnetic characteristics resulting from a magnetostriction
Implementation Method 2
The magnetic anisotropies of the magnetostrictive films 91, 92 are different from each other. The magnetostrictive torque sensor 90 further includes a pair of detection coils 93, 94 arranged to face the magnetostrictive film 91 and to be separate from each other in an axial direction of the rotary shaft 99
Data Source
AI summary
A magnetostrictive torque sensor having a first magnetostrictive film and a second magnetostrictive film, which are both provided on a shaft and have different magnetic anisotropies. A first detection coil and a second detection coil are arranged to face the first magnetostrictive film, and a third detection coil and a fourth detection coil are arranged to face the second magnetostrictive film. The first and second detection coils are wound around the same coil bobbin, while the third and fourth detection coils are wound around another common coil bobbin.