Study on Development of Torque and Angle Sensor for EPS

In this paper, we will present a torque and angle sensor for use in electrical power steering (EPS) systems. The developed sensor has torsion angle sensing capabilities between the input and output shafts linked by a torsion bar as well as multi-turn angle sensing of the steering wheel. The sensor is technically based on inductive position sensing for torque measurement and magnetic position sensing for additional multi-turn angle measurement. Digital output single edge nibble transmission (SENT) and pulse width modulation (PWM) are applied to strengthen noise performance in an automotive environment and enhance diagnostic capabilities. The torque channel consists of two electrically isolated sensors that can function independently. The angle channel also has five redundancies using angle information from inductive and magnetic channels during operation, even though there is only one reference signal for initialization. These redundancies allow an electronic control unit (ECU) to crosscheck the sensor signals to detect faults inside the sensor or during data transmission. The sensor itself also has self-diagnostic functions that can check internal faults such as an open/short circuit on the printed circuit board or application-specific integrated circuit (ASIC) problems. Finally, sensor performances are evaluated using a dedicated function tester. The measured performances are sufficiently acceptable for stable control of EPS systems and good feeling for drivers.