Cars are easy to drive because of power steering, which reduces the effort needed for the driver to turn the front wheels. Traditionally, this has been done with a fluid-filled hydraulic pump, but today, many automakers are turning to electric power-assisted steering (EPAS), which uses an electric motor instead.
Ford uses the system on its 2011 F-150 pickup truck. It’s variable-assist, meaning that the steering feels lighter at low speeds so it’s easy to steer when parking, and gets tighter at high speeds to give the driver confidence.
“It saves up to four per cent fuel economy, versus a hydraulic system where the pump runs all the time whether you’re steering or not,” says Garry Smith, EPAS supervisor for Ford.
The system combines information from a variety of sensors, including those that measure vehicle speed and steering wheel position, and determines how much assist to provide. More commonly found in cars, Smith says this is the first time EPAS has been used in a volume-production truck.
“The challenge was to steer a heavy vehicle with only 12 volts available,” Smith says. “That was the key hurdle to putting it in a truck. There’s only so much electrical power available with a typical 12-volt battery system in a truck, and this pulls a lot of current.
“We use an intelligent energy management system that always puts power to things like the steering or the headlights, and draws it from others to even out the energy load. If you’re using the power steering a lot, when you’re making several turns, it will turn things like the heated seats and rear defroster off and then back on.”