Electric systems
Main article: Electric Power Steering
Electric Power Steering systems, such as those found on the Honda NSX, Chevrolet Cobalt, Honda S2000, Saturn VUE V6, 2009 Toyota Corolla, Toyota RAV 4, Toyota Prius, Suzuki Swift and on most FIAT Lancia and Peugeot as also the Peugeot 307 model, use electric components with no hydraulic systems at all. Sensors detect the motion and torque of the steering column and a computer module applies assistive power via an electric motor coupled directly to either the steering gear or steering column. This allows varying amounts of assistance to be applied depending on driving conditions. Most notably on FIAT group cars the amount of assistance can be regulated using a button named "CITY" that switches between two different assist curves (boost curve), while on Volkswagen/Audi group cars, the amount of assistance is automatically regulated depending on vehicle speed.
In the event of component failure, a mechanical linkage such as a rack and pinion serves as a back-up in a manner similar to that of hydraulic systems. The software in the computer module enables the flexibility of "tuning" the characteristics of the electric power steering system to suit the preference of the vehicle designers. The "feel" is often set a bit on the light side so a criticism commonly expressed is a lack of steering "feel".
Electric power steering is limited to smaller vehicles. This is because the 12 volt electrical system is limited to 80 amps of current which, in turn, limits the size of the motor to less than 1 kilowatt. (12.5 volts times 80 amps equals 1000 watts.) Vehicles such as trucks and SUVs require a more powerful motor. An upcoming new 42 volt electrical system standard may enable use of electric power steering on larger vehicles.
Electric systems have a slight advantage in fuel efficiency (almost 1 MPG) because there is no hydraulic pump constantly running, whether assistance is required or not, and this is the main reason for their introduction. Their other big advantage is the elimination of a belt-driven engine accessory, and several high-pressure hydraulic hoses between the hydraulic pump, mounted on the engine, and the steering gear, mounted on the chassis. This greatly simplifies manufacturing.
