Sensor for Modern Steering Assist Systems

A torque sensor is presented in this paper that is designed for application on electric power steering systems. The sensor is based on a novel magnetic principle where the magnetic flux path is modified by a torsion bar which is placed in the steering shaft. A multipole magnetic ring is placed on one side of the torsion bar (e.g. input shaft) and two soft magnetic stators on the other side (e.g. output shaft). The magnetic field strength between these two stators is a direct measure of the steering torque angle and is detected by a standard Hall effect magnetic field sensor. This magnetic field signal is nearly constant along the circumference and therefore the magnetic filed sensor can be mounted stationary with respect to the rotating steering shaft. Two linear Hall sensors are used to detect the magnetic field strength for the purpose of redundancy. This novel non-contact technology allows a simple and robust design. The functional principle and the design will be presented as well as 3D magnetic field simulations enabling an optimization of the magnetic circuit.