Transense's SAW sensors measure torque in the steering column, which is a vital input to enable the EPAS control system to function correctly. Unlike existing EPAS torque sensors, the SAW approach does not require a low stiffness 'torsion bar', over which to measure the twist, coupled with mechanical over-torque protection. Instead, the SAW sensor is stiff and can be a simple modification of a section of the steering column. Compared with conventional hydraulic power assisted steering ('HPAS') systems, in which the engine driven power assisted steering pump is always consuming power, EPAS systems only take power when needed (at parking speeds primarily) from the vehicle battery. This results in improved fuel economy (2-3 percent savings) and therefore cost savings, reduced weight and easier installation.
SAW Torque Sensor Design - EPAS