EPS System Description - Torque Sensor
The torque sensor is mounted on the rack and pinion gearbox, and uses non-contact inductance to detect steering wheel torque forces. The pinion shaft assembly consists of an input shaft, a torsion bar, a planetary pinion gear and the torque sensor sleeve.
The sensor cover incorporates an interface circuit (torque detection circuit) and a coil assembly. (coil 1/coil 2).
Detection Principle of Torque Sensor
Detection circuit consists of a main signal circuit to output sensor value to system and a sub signal circuit for fail-safe control. A torque sensor detects change of magnetic flux in the coil 1 and coil 2 as wave shape and amplifies them in torque sensor circuit to generate main signal and sub signal. Voltage of the main signal increases and that of the sub circuit decreases when driver turns the steering wheel to right to generate steering torque. Steering to left exerts the opposite of the above. Also, no steering torque exerts 2.5 V on both main and sub signal. The level change of these voltage is output to a control unit as steering signal. While the system makes judgment of steering direction and steering torque based on the main signal, it monitor the main signal by comparing it with the sub signal in full time. The EPS control unit runs fail-safe control when it detects any difference between these output signals (absolute value of voltage).