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Steering, Parking and Saving Fuel

How electric steering improves not only a driver's capability, but saves fuel. And why steer-by-wire may work for lift trucks, but won't make it to your driveway anytime soon.

How electric steering improves not only a driver's capability, but saves fuel. And why steer-by-wire may work for lift trucks, but won't make it to your driveway anytime soon.
#Mercury #Lincoln #engineer


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According to a recent online study by Harris Interactive, 31% of drivers actively avoid parallel parking whenever possible. Think about it: Nearly a third of drivers pass by that slot along the curb in order to find a more capacious space of one sort or another. What's more, the study found that one in five men rate their parallel parking skills as either "fair" or "poor." Now how many men do you know who think that their driving skills are anything other than just this side of Michael Schumacher? Probably a whole lot fewer than one in five. Yet there it is, a full 20% admitting that their parallel parking capability isn't what it could be. (Two in five women made the same admission, and we're submitting that they're undoubtedly a bit more objective about their driving skills than men.)

The Harris poll was taken on behalf of Ford Motor. Ford has developed a technology, Active Park Assist, that is clearly aimed at upping the capability (and confidence) of drivers. What's more, it will keep drivers from driving around, looking for a parking space, when a perfectly good slot is right there.

Martin Frey, Electric Power Steering Manager at Ford, explains that the Active Park Assist system is made possible through the deployment of what they call "EPAS" at Ford—Electric Power Assist Steering. Briefly, the Active Power Assist system has the driver cruising along for a parking place push a button on the console when she sees a likely spot. Ultrasonic sensors measure the space and determine whether it is viable for parking. Then the system has the driver confirm that she wants to park. The driver's role is that of shifting the transmission and working the accelerator and brake pedals. But as for steering, it is completely hands-off, and the steering wheel spins as though controlled by a ghost. But it is actually being operated by EPAS.

Active Park Assist, which is available on a range of Ford, Mercury and Lincoln models, is just one of the functions that EPAS facilitates. For example, another is Pull-Drift Compensation. Frey explains this by noting that sometimes drivers are on an open road and there is a cross-wind pushing against the car, requiring the driver to compensate with the steering wheel, or there is a crown in the road that requires adjustment. Although it may not seem to be a big deal, the minor adjustments that drivers make to handle these conditions contribute to fatigue on long drives. With the Pull-Drift Compensation, the EPAS system determines that (1) the car is headed straight and (2) the driver has her hands on the wheel. When the system detects a pulling or driving condition caused by wind or a crowned road surface, it provides torque to adjust the steering, making it easier for the driver. It is done in an imperceptible manner.

Yet even though the EPAS system is doing the job behind the scenes, even though the driver probably doesn't know that the additional torque is being provided by the electric motor (the same one that spins the wheel for the Active Park Assist), it turns out that drivers really like it: the 2008 Ford Escape, one of the first vehicles with the Pull-Drift Compensation feature in the company's lineup, received 50% fewer complaints about its steering than non-equipped vehicles.

Frey says that not only is the company pursuing electric power steering systems in a big way because of improvements for the customer, but because of their goal to become best-in-class when it comes to fuel economy. In fact, by 2012, Ford plans to have more than 85% of its fleet fitted with electric power steering systems—"Including trucks," he emphasizes.

What does the electric power steering system have to do with fuel economy? More than you might think. First of all, it should be noted that the systems come with a cost that is greater than that of conventional hydraulic systems. But vis-á-vis achieving the kind of fuel economy that Ford is working to achieve, it is, in Frey's words "a good buy."

The fundamental situation is this. You are driving 70 mph along the highway. Straight. Yet despite that, with a hydraulic system you have a fixed displacement pump under the hood that is turning at whatever speed the front-end accessory drive is spinning it at, Frey says. "It's moving a lot of fluid when it doesn't need to be. It's a big parasitic loss." Which means that fuel is being consumed that doesn't need to be. With an electric system, the motor isn't working unless it needs to be.

So here's the issue regarding how the electric system improves fuel economy. "For a small car, where the pump parasitic loss is a bigger percentage of the total output, it could be a full mile-per-gallon. For a bigger vehicle, with a big engine, the pump is a smaller fraction, so it might be a 0.3 or 0.5 mile-per-gallon improvement."


Steer-by-Wire? (Nope.)
So do you think that you're going to be having a steer-by-wire system anytime soon? After all, just think of the advantages as regards design and packaging. For example, as Ted Seeger, Chief Engineer, Electronic Steering Systems, Delphi Steering, points out, "There would be great flexibility in designing the car. You could put actuators at the corners"—as in actuators that would be used to move each of the wheels in the desired direction—"and thereby free-up space in the middle of the car." As in there would be no steering column, no steering gear, no linkage. There would be the possibility of having greater consistency across vehicle platforms, because although the size of the actuators might be adjusted to handle the size of the wheels to be steered, the other elements would probably be the same.

But there is some tentativeness as regards steer-by-wire for the simple reason that, Seeger notes, "I don't know of an active program that is moving toward implementation. The focus is on electric power steering."

So if you're waiting, don't hold your breath.

However, this is not because there needs to be the development of something that doesn't exist. "If someone wanted a system, the building blocks are available to put it together." However, there are is a non-trivial factor related to that: expense. This is not simply because there is no volume production at the moment, which, of course, is a factor, but because there are issues related to developing a system that has redundancy and fault tolerance. After all, when you don't have things like a column and a steering gear, there needs to be a way to minimize the possibility of system failure as well as a way to have a fail-safe mode.

As Ford's Martin Frey points out, the fail safe system would necessitate some means by which the steering wheel would be connected to the wheels to be steered in the case of a steer-by-wire system failure, so essentially what you might be saving in the way of eliminating mechanicals from a conceptual point of view would be eliminated by the necessity of having mechanisms for safety concerns.

There are a couple more factors. For example, consider the power draw that would be added to a vehicle with a steer-by-wire system. While the discussions of 42-volt systems have gone by the wayside during the past few years, in order to have a robust steer-by-wire system along with all of the other things that are putting draws on the power system of luxury vehicles—and let's face it: this is the type of vehicle where deployment would undoubtedly occur first—the current systems are insufficient.

And for another thing, consider that what a steer-by-wire system means is that while the driver may be turning the steering wheel, this is all about sending digital information to controllers. "We would need a faster communications protocol," Seeger says, and suggests that something like FlexRay would be required. (FlexRay is a communications protocol that provides such things as a deterministic cycle-based message transport, synchronization service so there is a common time-base to all nodes, and means to have a redundant communication path.)

So while it isn't likely to be steer-by-wire anytime soon (so stop holding your breath), Seeger says that there is an on-going transformation of the fleet from hydraulic systems to electric power steering driven by three things:
1. Higher gas prices
2. A global push toward more "green" vehicles.
3. CO2 reduction requirements
And the increasing number of hybrid systems is making a difference, too, from the standpoint that when the internal combustion engine is shut down, the hydraulic pump isn't operating as is ordinarily the case, so an electric system that's independent of the engine is essential.


Industrial-Grade Steer-by-Wire

Although steer-by-wire is undoubtedly years away for the auto industry, it is actually becoming something of a standard in industrial vehicles. That’s right: if you spot, say, a new forklift in a factory, odds are that it may be fitted with a steer-by-wire system. Says Geoff Rondeau, product manager, Thomson (thomsonlinear.com), “It’s fairly standard in the lift-truck market, and the marine market is also headed down that path.” What’s more, he says, the off-highway and heavy-equipment manufacturers are also making the transition to steer-by-wire.

He explains that many of these applications are based on the desire for variable steering ratios. That is, steering response is predicated on vehicle speed. So if you’re driving a lift truck at a slow speed, then you’ll have a higher steering ratio, which you don’t want if you’re briskly moving down the aisle. “It’s about ergonomics and efficiency,” he says.

Thomson produces a torque feedback device that allows there to be a haptic interface so that the driver can have a feeling that the wheels are being turned, which is something that is taken for granted in electro-hydraulic but is not inherent in steer-by-wire systems.



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