Magnetostrictive Torque Sensor Plated Layer Compressive Stress
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Solution Overview
Problem
Existing magnetostrictive torque sensors face challenges in maintaining detection accuracy when excessive torque is applied, as they rely on increasing the hardness of the rotary shaft, which may lead to plastic deformation and film peeling.
Innovation Solution
A magnetostrictive torque sensor with a plated layer on a rotary shaft's outer surface, where compressive stress is induced through polishing, and a plating current density of 50 to 60 A/dm² is used to form a magnetostrictive film with a small crystallite diameter, reducing hysteresis and allowing for increased plastic deformation tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the hardness of the rotary shaft is increased to suppress plastic deformation and film peeling, then the reliability of the magnetostrictive film is improved, but the plastic deformation tolerance of the rotary shaft deteriorates
Solution Approach 1:
The invention applies different properties to different parts of the rotary shaft: the outer circumferential surface is hardened through carburizing treatment to prevent film peeling, while the inner portion maintains higher ductility to tolerate plastic deformation. This local differentiation resolves the contradiction between film reliability and deformation tolerance.
Solution Approach 2:
The rotary shaft employs a composite structure with a hardened outer layer (carburized layer) and a softer inner core. This composite material approach allows the surface to provide protection against film peeling while the core provides plastic deformation tolerance, simultaneously satisfying both requirements.
2Reliability
If the hardness of the rotary shaft is increased to maintain detection accuracy under excessive torque, then the magnetostrictive film stability is improved, but the detection accuracy deteriorates due to stress concentration
Solution Approach 1:
By hardening only the outer circumferential surface rather than the entire shaft, the invention prevents film peeling at the critical surface location while allowing the inner portion to deform plastically, thereby maintaining detection accuracy by avoiding stress concentration in the magnetostrictive film.
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 maintains high detection accuracy without increasing the rotary shaft's hardness, reducing stress on the magnetostrictive film and minimizing hysteresis, even under excessive torque conditions.
Implementation Method 1
a magnetostrictive film that is arranged on a rotary shaft having a substantially columnar shape so as to surround the rotary shaft around its axis, for detecting a rotational torque about the axis acting on the rotary shaft based on a change in a magnetic property of the magnetostrictive film
Implementation Method 2
Compressive stress remains on an outer circumferential surface of a region of the rotary shaft around which the magnetostrictive film is arranged
Implementation Method 3
a step of using a plating current density set in a range of 50 to 60 A/dm{circumflex over ( )}2 to form a plated layer of the magnetostrictive film
Data Source
AI summary
A magnetostrictive torque sensor is provided that is capable of maintaining high detection accuracy, even when an excessive torque acts on a rotary shaft. The magnetostrictive torque sensor includes a magnetostrictive film 71 that is arranged on a second steering shaft 23, or a rotary shaft, having a substantially columnar shape so as to surround the second steering shaft 23 around its axis, and detects a rotational torque about the axis acting on the second steering shaft 23 based on a change in a magnetic property of the magnetostrictive film 71. Compressive stress remains on an outer circumferential surface of a sensor region 77 of the second steering shaft 23 around which the magnetostrictive film 71 is arranged. A plated layer of the magnetostrictive film 71 is arranged on the outer circumferential surface of the sensor region 77 in which compressive stress remains.