Goodbye, hydraulics: Electric steering saves fuel

Goodbye, hydraulics: Electric steering saves fuel
08 February 2011


Detroit, Michigan -- Electric power steering, like other fuel-saving devices, is catching on quickly as automakers hustle to meet federal fuel-economy standards.

According to a forecast by Nexteer Automotive, a Michigan-based producer of steering systems, the global adoption rate will soar from 30 percent in 2009 to 50 percent in 2020.

TRW Automotive predicts that 75 percent of vehicles produced in North America will have electric power steering by 2015.

"The transition to electric is really rapid," says Charlie Cregeur, TRW's director of product planning for global steering. Corporate average fuel economy "is a catalyst. It's really being driven by the regulations."

In the 2016 model year, US new-vehicle fleet averages must reach 35.5 mpg. Automakers say electric power steering can improve fuel economy by roughly 4 percent over vehicles with hydraulic units.

Ford Motor Co. illustrates the trend. Last year, the company said electric power steering would be standard equipment on 90 percent of its models by 2012.

The 2011 Ford F-150 pickup features a Nexteer unit, while the Focus and Fiesta have electric power steering systems produced by TRW Automotive.

Parasitic losses

Traditional hydraulic steering draws power from a belt connected to the engine.

A belt-driven hydraulic pump activates a piston, which exerts force on the steering rack when the motorist turns the steering wheel. The rack, in turn, is connected to the front wheels via the tie rods.

Hydraulic steering is inefficient because it's always "on." Whether the car is turning or not, the belt provides power to the pump. That causes a parasitic loss of power, increasing fuel consumption.

An electric steering system replaces the hydraulic piston and pump with an electric motor. The motor draws electricity from the battery, but only when the vehicle is turning. The result: no parasitic power loss.

Electric power steering has another advantage: It is much easier to install on the assembly line because the system has no hoses, pumps or hydraulic fluid.

Electric power steering prices range from $150 to $450, depending on the features. For example, the control unit can be programmed to adjust the car's course to account for misaligned tyres, crosswinds and damaged road surfaces.

Major suppliers of electric power steering systems include ZF Friedrichshafen AG, TRW Automotive Holdings Corp., Nexteer Automotive, Mando Corp., NSK Ltd. and JTEKT Corp.

Small cars first

Electric power steering caught on first in small European cars, then gradually spread to light trucks. Because small cars suffer the biggest performance penalty from a hydraulic system's parasitic losses, that made sense.

It took a little longer to design an electric power steering unit that can handle big vehicles at slow speeds, say, during parking.

To deal with those peak power demands, Nexteer and TRW developed systems with the motor and control unit connected to the steering rack. For small cars, those components are mounted on the steering column inside the passenger compartment.

Some automakers have experimented with a pure steer-by-wire system, in which the steering wheel has no mechanical linkage to the steering gear. But Bob Remenar, CEO of Nexteer Automotive, expects only modest demand for such systems.

After all, a mechanical link - such as a standard rack and pinion unit - between the steering wheel and tyres retains a big advantage: If the power steering fails, motorists can still steer the vehicle, though with considerable effort.

Now that electric power steering has proven adequate for big pickups, most light vehicles are potential candidates for electric power steering, Remenar says.

As gasoline prices rise - and as CAFE deadlines loom - demand will increase for fuel-saving technologies. When automakers introduce new platforms, "they are moving very, very rapidly to electric power steering," Remenar says. "The world is converting fast."