Electric power assisted steering (EPS/EPAS) or motor-driven power steering (MDPS) use electric motors to provide the assistance instead of hydraulic systems. As with hydraulic types, power to the actuator (motor, in this case) is controlled by the rest of the power-steering system.Power steering helps driver steer with lesser effort on the steering wheel.
Sensors detect the position and torque of the steering column and the controller applies the assistive torque via motor. As the motor is connected to the steering column, this assistive torque helps to move the steering easily and smoothly without any effort and yet controlled for driver safety.
As the power of the motor is essentially infinitely variable, the level of assist can with the appropriate electronics, be varied electronically either automatically or manually (or not at all depending on the specific system used).
An example of adjustable electronic steering assist was implemented on the Fiat Punto around the beginning of the century
Though the alternator and battery may need to be slightly more powerful and thus heavier the overall weight and convenience savings are significant and the engine can also be more compact as it doesn’t need to mount an hydraulic pump (or as big of a pump) anymore.
Electronic steering has been said by many to “lack feel” in comparison to hydraulic steering due in part to a reduced feedback in the steering-wheel as the motor holds the steering in a fixed position with metal gears unlike the hydraulic fluid which has a small degree of flexibility (compression) allowing subtle details of the road to be felt through the steering-wheel while driving. Manufacturers are constantly striving to improve the perceived lack of feel and some progress has been made in this area.