Effect of Hoop-Stress on Torque Sensing Using Inverse Magnetostriction of FeGaAlZrC Alloy Ring

Abstract

Fig. 1 Elements of the torque transducer and the magnetic parameters concerning with ring type torque sensor by using inverse magnetostriction. (H T ＝Magnetization strength, M r ＝Residual magnetization, s＝Applied stress) 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 (l), residual magnetization (M r ), applied or residual stresses(s) of the ring. Beside, the hoop stress (s h )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 mm and hoop stress (s h ) 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 mm and drastically decreased in the case of minimum gap of 6 mm. 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.

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

“…After the ring and shaft were connected with the most suitable hoop-stress, 11) the ring was magnetized in the circumferential direction. The processes of magnetizing the ring and fitting between the ring and shaft were carried out at the Technical Research Institute, Nissan Motor Co., Ltd. and Namiki Precision Jewel Co., Ltd. Figure 3 shows a torque sensing system using a magnetostrictive ring.…”