A single-structured torque sensor using a magnetostrictive ring attached to the steering shaft of the steering-by-wire system of an automobile was developed. An (Fe0.80Ga0.15Al0.05)99Zr0.5C0.5 alloy, which exhibited the large magnetostriction of 134ppm and the strong tensile stress of over 800MPa, was used for the magnetostrictive torque ring. However, the sensitivity of the torque ring sensor was 0.12 © 10 ¹4 TN ¹1 m ¹1 , which is smaller than the 0.8 © 10 ¹4 TN ¹1 m ¹1 needed for a steering-by-wire system. The ring was therefore heattreated at 743K under a compressed stress of 100MPa via the spark plasma sintering method to increase the sensitivity of torque. As a result, the sensitivity of the torque ring sensor increased to 0.72 © 10 ¹4 TN ¹1 m ¹1 although depending on the residual magnetic flux density.

Effect of Heat Treatment under Stress on Torque Sensing Using Magnetostrictive (Fe–Ga–Al)–Zr–C Alloy Ring

Galfenol (FeGaAlZrC) alloy ring was used for torque-sensing by detecting a leakage flux from the ring surface based on the inverse magnetostriction effect. This leakage flux changes depending on the magnetic parameter such as magnetostrictive strain(λ), residual magnetization (Mr), applied or residual stresses(σ) of the ring. Beside, the hoop stress (σh)which is one of the residual stress factor in the ring also has strong effect on torque-sensing because this affects those magnetic parameters. The fitting gap between ring and shaft was four kinds of 6, 10, 20 and 30 μm and hoop stress (σh) in each case can be estimated from the elastic formula of material-mechanics. As a result, torque sensitivity showed the maximum value in the case of 10 micrometers gap and it decreased toward the gaps of 10 and 20 μm and drastically decreased in the case of minimum gap of 6 μm. This change of torque sensitivity depending fitting gap is discussed based on the magnetic domain mobility and inelastic material effect at the interface of Galfenol ring and rotating shaft.

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FeGaAlZrC(Galfenol)磁歪合金リング式トルクセンサへのたが応力の影響

Ferromagnetic Co-Ni alloys of less than 35 at%Ni exhibit a phase transformation from γ-phase (FCC) to e phase (HCP): both phases are stable at higher and lower temperatures, respectively. Since both phases of these alloys exhibit high magnetization and thermoelastic martensitic transformation, it is expected as new ferromagnetic shape memory alloy. In this study, We prepared a rapid-solidified Co-32 at%Ni foil and analyzed thermoelastic and stress-induced martensite phase in temperature range of 77 to 673 K from observation of the texture, structure, magnetic property and Barkhausen noise. From these results, it is found that 1) the thermoelastic martensitic transformation is not reversible and 2) a stress-induced martensite phase is transformed to a austenite phase by heating. The result is caused by the mechanism of the transformation from a γ phase (HCP) to a e-phase (FCC).

https://www.jstage.jst.go.jp/article/jinstmet/69/8/69_8_643/_pdf

岡崎禎子

Papers

FeGaAlZrC(Galfenol)磁歪合金リング式トルクセンサへのたが応力の影響

急冷凝固Co-Ni薄帯の応力誘起FCC-HCPマルテンサイト相変態

岡崎 禎子

Papers

FeGaAlZrC(Galfenol)磁歪合金リング式トルクセンサへのたが応力の影響

急冷凝固Co-Ni薄帯の応力誘起FCC-HCPマルテンサイト相変態

岡崎禎子