Proposal of Pre-load-type Magnetostrictive Torque Sensor for EPS

Abstract

In this paper, sensitivity improvement method of magnetostrictive-type torque sensor for EPS was examined. Ni-Fe film which had stronger reverse magnetostrictive effect was selected. However, impedance of the Ni-Fe film decreased in both rotatory direction when detecting impedance gradient with a solenoid coil, therefore the rotation's direction couldn’t be decided. Hence a new method was devised for doing high frequency heating while twisting a steering shaft after Ni-Fe plating processing to it to move a peak point by finding a stress-relaxation phenomenon of Ni-Fe film by the heat-treatment. It could improve not only sensitivity but also hysteresis characteristics of it.