Magnetostrictive Torque Sensor Cutoff Circuit
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Solution Overview
Problem
Existing magnetostrictive torque sensors in electric power steering systems face instability and potential damage due to the application of DC excitation voltage when the ignition switch is turned on, leading to uncomfortable steering and risk of detection coil disconnection or damage from excessive current.
Innovation Solution
A magnetostrictive torque sensor design that includes a cutoff circuit to prevent the application of excitation voltage to the detection coil for a predetermined interval after power-on, using a relay or switching elements to ensure an AC current is maintained, thereby preventing saturation and excessive current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If excitation voltage is applied to the detection coil immediately after power-on, then torque detection can begin without delay, but excessive current flows causing instability and potential damage to the detection coil
Solution Approach 1:
The cutoff circuit is configured to automatically prevent excitation voltage application during a predetermined interval immediately after power-on. This preliminary protective action occurs before normal operation begins, preventing excessive current flow and magnetization saturation that would otherwise damage the detection coil or cause unstable torque detection signals.
Solution Approach 2:
The excitation voltage application is controlled in a periodic manner: blocked during the predetermined startup interval, then enabled for normal operation. This time-based periodic control ensures the detection coil is protected during vulnerable startup conditions while allowing full functionality during stable operation.
2Loss of time
If DC excitation voltage is applied to the detection coil at startup, then the system can initialize quickly, but the magnetostrictive film becomes magnetized causing unstable detection signals and uncomfortable steering
Solution Approach 1:
The cutoff circuit applies a preliminary counter-action by blocking the excitation voltage during the predetermined interval after power-on. This prevents the harmful magnetization of the magnetostrictive film that would occur with immediate DC voltage application, thereby preventing signal instability and steering discomfort before they can occur.
3Measurement precision
If the excitation voltage is continuously applied to the detection coil, then accurate torque measurement is maintained, but the detection coil is at risk of disconnection or damage from excessive current during startup
Solution Approach 1:
The cutoff circuit performs a preliminary protective function by preventing excitation voltage application during the vulnerable startup period. This preliminary action eliminates the harmful excessive current that would otherwise flow through the detection coil, protecting it from disconnection or damage while allowing accurate torque measurement to begin after the protective interval expires.
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 design stabilizes the detection signal and prevents excessive current flow, ensuring accurate torque measurement and extending the lifespan of the detection coil by maintaining an AC current and avoiding DC voltage application during startup.
Implementation Method 1
a magnetostrictive film having magnetic anisotropy is attached on a surface of the shaft. When a torque is applied to the shaft from the outside, a magnetic permeability change in the magnetostrictive film corresponding to twisting force is detected
Implementation Method 2
a detection coil for detecting a change in a magnetic property of the magnetostrictive film to detect a torque applied to the shaft
Data Source
AI summary
A magnetostrictive torque sensor includes a shaft having a magnetostrictive film; a detection coil for detecting a change in a magnetic property of the magnetostrictive film; and a cutoff circuit for supplying an excitation signal for detecting the change in the magnetic property and inhibiting the excitation signal from being supplied to the detection coil for a predetermined interval from power on. The cutoff circuit cuts off the excitation signal I and its inverted signal to the bridge circuit.