Magnetostrictive Torque Sensor Hydrogen Removal
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Solution Overview
Problem
Magnetostrictive torque sensors used in electric power steering systems experience a shift in detected steering torque signals at high ambient temperatures, causing uneven auxiliary steering forces when turning the steering wheel rightward or leftward, leading to discomfort for the driver.
Innovation Solution
A magnetostrictive torque sensor with a 40 μm thick Ni—Fe alloy film is treated to reduce hydrogen content through thermal desorption gas analysis, ensuring that the hydrogen desorbed by 150°C, 300°C, and 400°C is within specific ppm limits, maintaining consistent steering torque signal magnitude regardless of steering direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the magnetostrictive film is used at high ambient temperatures, then the sensor operates in realistic vehicle conditions, but the detected steering torque signal shifts and becomes uneven between rightward and leftward turning
Solution Approach 1:
The patent applies preliminary heat treatment at 300-400°C before the magnetostrictive film is subjected to service conditions. This pre-treatment removes hydrogen and stabilizes the film's magnetic properties in advance, preventing signal shifts when the sensor is later exposed to high ambient temperatures during vehicle operation
Solution Approach 2:
The patent changes the thermal and compositional parameters of the magnetostrictive film by controlling hydrogen content through heat treatment. By adjusting the temperature and duration of heat treatment, the film's magnetic characteristics are optimized to maintain signal consistency across a wide temperature range from -30°C to 80°C
2Ease of manufacture
If hydrogen content in the magnetostrictive film is high, then the film is easier to manufacture, but the magnetic characteristics become unstable at elevated temperatures
Solution Approach 1:
The patent incorporates preliminary heat treatment as a standard manufacturing step immediately after film deposition. This pre-treatment removes excess hydrogen while the film is still in its as-deposited state, stabilizing the magnetic characteristics before the film is assembled into the sensor and subjected to service conditions
Solution Approach 2:
The patent converts the harmful effect of hydrogen (which causes magnetic property degradation) into a beneficial process feature. By deliberately applying heat treatment to remove hydrogen, the manufacturing process transforms the potential defect into an opportunity to enhance film stability and ensure consistent performance across temperature variations
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 reduced hydrogen content stabilizes the magnetostrictive film's magnetic characteristics, eliminating signal shifts at high temperatures and ensuring consistent steering effort, enhancing driver comfort by maintaining equal auxiliary steering forces during rightward and leftward turns.
Implementation Method 1
thermal desorption gas analysis is performed thereon in which the magnetostrictive film is heated at a temperature rise rate of 5° C. per minute
Implementation Method 2
the alternating-current resistance and the like of coils provided around the magnetostrictive films vary according to an inverse magnetostriction characteristic due to magnetic anisotropy
Data Source
AI summary
A method for producing a magnetostrictive torque sensor which detects steering torque applied to a steering shaft. A magnetostrictive film is formed on the steering shaft and then subjected to heat treatment, which decreases a weight ratio of hydrogen included in the magnetostrictive film. Thermal desorption gas analysis is performed on at least a portion of the magnetostrictive film undergoing the heat treatment step. A portion of the magnetostrictive film having a thickness of 40 μm or less is heated at a temperature rise rate of 5° C. per minute. A weight ratio of a total amount of hydrogen desorbed from the portion of the magnetostrictive film due to the heat treatment to a weight before the heat treatment is no more than 3 ppm up to 150° C., wherein the weight ratio is no more than 10 ppm up to 300° C., and no more than 15 ppm up to 400° C.