Steering Parity

Electrically assisted power steering arrived first on small cars in Europe in the mid-1990s and rapidly ramped up on high-volume, low-priced models.

Despite the growth, a decade later some 80% of new cars worldwide still employ conventional hydraulic steering.

That soon will change. By 2010, about half of new cars will come with electrically assisted steering, an executive with No.2 steering supplier TRW Automotive tells Ward's at a media event in Mortefontaine, France.

Aly Badawy, TRW vice president-engineering, steering, linkage and suspension, says the early iterations of electric power steering were crude and offered assistance only at very low speeds, for instance, in parking lots. There was no variability in the amount of assistance offered.

The systems were inexpensive, and driving enthusiasts roundly panned the technology for responding slowly to steering inputs and lacking the appropriate “feel.”

Today's systems, Badawy says, are far more intelligent and offer varying amounts of assistance depending on driving conditions. The level is highest during low-speed maneuvering and is lowest at highway speeds.

The new systems are responsive and afford a much better on-center feel, which means every steering input is countered with a natural tendency to keep the vehicle going in a straight line.

At the media event at the CERAM test track, TRW demonstrated several vehicles with electrically assisted steering, including two that integrated electronic stability control for greater safety in emergency situations.

BMW AG was among the first auto makers to link steering and stability control in the '04 5-Series, however the steering system was powered by conventional hydraulics.

Integrating the two technologies can result in a 6% improvement in stopping distance, particularly on surfaces with varying levels of friction.

“When you brake in those situations, the car has a natural tendency to slide sideways,” Badawy says. “We can prevent that.”

By measuring vehicle speed, steering angle and the yaw motion of the vehicle, Badawy says ESC, when combined with electrically assisted steering, is certain to keep the vehicle going in the intended direction. TRW refers to this integration as Steering Torque Control.

“We can change the amount of steering assist to make it harder to go left if you should go right,” he says.

Badawy is so sure of TRW's Steering Torque Control that he encourages drivers to do the unthinkable in panic situations. “The safest thing to do is to take your hands off the wheel,” he says. “This system is smarter than you are.”

Within two years, TRW will begin producing active steering systems that integrate ESC with electrically assisted steering for a customer in Europe.

In addition, TRW has two other customers for the technology. For one, TRW will supply the ESC module, and for the other TRW will provide the electrically assisted steering, Badawy says.

Although near-term growth for electric power steering appears strong, certain customers, such as BMW, may remain wedded to conventional hydraulic systems, as some driving purists prefer them.

TRW says its active steering system, integrated with ESC, also can be added to pure hydraulic or electrically powered hydraulic steering configurations.

TRW's current customers for EPS include Renault SA and Nissan Motor Co. Ltd. Its customer base for electrically powered hydraulic steering (EPHS) include the Volkswagen Group (including Audi) and Adam Opel GmbH. Fiat Auto SpA uses both systems.

The difference between the two is that EPHS decouples the steering pump from the engine, reducing parasitic losses, and is driven by a small motor. With EPS, the pump is eliminated entirely, as are the hoses and fluid. Instead, a computer-controlled electric motor provides the steering rack with all the power necessary, on demand.

Badawy says TRW currently produces more than 1 million EPS systems annually, and that the number will balloon to 2.5 million units by 2008. Likewise, EPHS production is expected to grow from 1.8 million units this year to 3 million in 2007. Most of the growth will come in Asia and Europe.

The market for EPS in North America currently is very small. The Saturn Vue and Chevy Malibu are among the few vehicles offering it (supplied by Delphi Corp.)

Badawy says TRW has contracts to supply EPS to more than one customer for North American small-car programs in coming years. The volume from the programs is expected to reach 1 million steering systems by 2010, he says.

Improved fuel economy is the key driver behind the growth in EPS. Badawy quantifies the fuel-economy gain for a small or midsize car at more than 1 mpg, or about 3.5%.

Hydraulic power steering hampers fuel economy because the engine, whenever running, is constantly driving the pump, which is providing hydraulic fluid under pressure for steering assistance even when no turning is required.

Badawy says equipping a small car with EPS is equivalent to eliminating 110 lbs. (50 kg) of mass from the vehicle.

Because of cost and packaging, EPS has been used most often in small cars. TRW's latest iteration, however, opens the door to applications in much heavier vehicles, where fuel economy is critical.

Since the market emerged about a decade ago, the EPS module has been mounted on the steering column and is driven by a pinion.

TRW's latest version, a belt-driven unit mounted directly to the steering rack, uses pulleys to drive a ball screw, which translates rotational motion to axial motion, thereby turning the front wheels.

Badawy says this new approach is more efficient and is robust enough, unlike the column-mounted units, to drive heavier axles, such as those found in fullsize pickups and SUVs.

“We are working with customers in all platforms, in all markets,” Badawy says of EPS potential.

At the recent media event, TRW offered test drives in a 5-door Ford Focus and 3-door Peugeot 307, both equipped with the latest belt-driven EPS. Steering in the Focus was crisp and nicely balanced, without being noisy or feeling over-assisted.

TRW currently produces EPS in Pamplona, Spain, and manufactures EPHS in Shanghai and in Gelsenkirchen, Germany.

For a North American program, TRW's plant in Queretaro, Mexico, will produce a belt-driven EPS system beginning in 2008, Badawy says.