Turning green

DN Staff

October 2, 2000

11 Min Read
Turning green

If the notion of a fuel-efficient sports utility vehicle or pickup truck seems laughable, it may be time to stop chuckling. After years of putting power and size first, two automakers in July announced concrete plans to produce light trucks that also go easy on the gas. Ford Motor Company (Dearborn, MI) vowed to improve the fuel efficiency of its entire SUV fleet 25% by 2005, while General Motors (Pontiac, MI) pledged to increase the fuel economy of its most popular full-size pickup truck models by 15%.

The promised changes come at a time when SUVs and large pickup trucks have emerged as the popular villains of our roadways. Consumers adore them for their utility and muscular image, and that adoration shows up in sales figures that have exploded more than tenfold over the past two decades. Environmentally minded critics, meanwhile, condemn these massive vehicles for their gas guzzling, polluting ways. Jason Mark, a mechanical engineer and transportation co-director at the non-profit think tank Union of Concerned Scientists (Berkeley, CA), notes that today's SUVs and other light trucks frequently fall short of federal fuel economy rules-even though the standard for light trucks, at 20.7 mpg, is far lower than the 27.5 mpg for cars. "Automakers are struggling to meet fuel economy standards at a time when they've increased light-truck power by as much as 50%," he says, adding that light trucks often fail to meet car emissions guidelines as well.

There's little doubt that Ford and GM will encounter plenty of engineering potholes on the new road to fuel economy. Both companies will attempt to improve fuel usage without sacrificing the power and size that draw consumers to these vehicles in the first place. It's a tough strategy, one that Jim Clarke, Ford's chief engineer for advanced powertrain development, describes as "optimize, not compromise." But it's a strategy that may keep everyone happy. Consumers will get to keep their brawny vehicles and will likely see a significant windfall at the gas pump. Ford, for example, estimates that its 25% translates on average to a savings of 1,700 gallons of gasoline over the lifetime of the vehicle-or roughly a $2,400 savings for the consumer. Environmentalists could win too. After all, many of measures that increase fuel economy tend to decrease emissions.

So how will these automakers reconcile fuel economy and performance? Ford's self-improvement plan rests on advances in conventional automotive technologies, while GM will mostly rely on a new hybrid-electric powertrain to meet its target. Over time, these two strategies may converge. Ford does have a hybrid-electric version of its Escape scheduled to hit the road in 2003. And GM is working variable-displacement engines and other enhancements of conventional technology. For now, though, these two companies have taken two different routes to fuel economy. Here's a look at them:

Today's technology to boost tomorrow's fuel economy

It's been more than two years since Ford announced that all its SUVs would be "low emission vehicles" under federal guidelines. But for the engineers that design Ford's SUVs, the clock began to tick loudly in July when CEO Jac Nasser made a public commitment to improve SUV fuel economy 25% by 2005. That timetable, as well as cost and volume considerations, mean that Ford engineers will initially tackle emissions with tools they have at hand, including many technologies now in production for cars. Perhaps the most remarkable thing about Ford's plans is just how unremarkable its technical choices are. "The technology we're developing is technology that we already understand and that we know how to do at high volume," says Clarke. "It's all relatively conventional by today's state of the art."

Diesel engines, hybrid powertrains, and alternative material will play a role in the long run, Clarke acknowledges, "but this initiative does not depend on them." What the 25% reduction will depend on is improved engine and powertrain efficiency. According to Clarke, these two areas will make the biggest contribution to fuel economy, though he can't yet estimate the magnitude of the efficiency improvements and resulting savings.

Clarke outlines Ford's SUV engine strategy as one of raising the specific power output-that is, employing smaller, more efficient engines. And he cites a collection of "variable" technologies that can help: Variable cam phasing and variable valve lift will address pumping inefficiencies. Variable displacement engines will match power requirements to cylinder utilization. The company also has plans to develop variable compression ratio technology-an undertaking that Clarke terms a "major step," since there aren't any such engines in production today. Clarke adds that these technologies will see use separately and in conjunction with one another. "Their potential for fuel economy is substantial," he says.

As for transmissions, Clarke predicts that Ford's next-generation SUVs will have more speeds than the usual four. "You'll see a lot with six speed transmissions," he says. Ford engineers will also work to fine-tune transmission in other ways, looking at details such as torque converter design, pump pressures, friction, and gear ratios.

Other opportunities for fuel economy could come from adjustments to how SUVs idle. Reducing idle speed and automatically switching into neutral can save fuel. So can idle-off systems, which shut down and restart the engine rather than idling at all. Clarke reports interest in all these idling alternatives but cautions that they would call for "major changes" in transmission design-and in the case of idle-off, to the vehicle's electrical system.

Overall SUV streamlining, though perhaps not as important as engine and transmission improvements, will also cut fuel usage. Clarke believes there's room to make incremental improvements to coefficients of drag and rolling efficiencies. There's also a chance to cut vehicle weights through parts consolidation and the use of alternative materials. "We'll look at every nut, bolt, and washer to reduce weight, " he says.

Ford will also consider alternative materials with Clarke pointing to the weight-reducing triumvirate of magnesium, aluminum, and plastics. "There won't be any surprises," he says. "Each works well in some places." Magnesium, both die cast and thixomolded, will find its way into seat backs and instrument panels. Long before there is ever an all-aluminum SUV, this light-weight, high-strength metal can lighten doors, hoods, and other selected components. And Clarke forecasts the use of more plastics. "Plastic intake manifolds are a good deal, better than aluminum for the cost and weight," he notes.

All the fine-tuning that Ford SUVs will soon undergo may raise some concerns about cost and performance. But on both scores, Clarke insists that the concerns are misplaced. "There are some synergies between fuel economy and cost," he says. For example, smaller engines tend to cost less than bigger ones, offsetting at least some of the cost of the engine advancements. The parts consolidation that cuts weight can also cut costs. Even performance doesn't have to suffer. "A nice spin-off of higher specific output is that you end up with a light engine that has more power," Clarke says.

Another approach

Ford isn't the only one looking to use today's technology to improve tomorrow's emissions. Jason Mark, a mechanical engineer who serves as transportation co-director for the Union of Concerned Scientists (Berkeley, CA), last year created a "technical blueprint" for improving the fuel economy of the most popular SUV, the 1999 Ford Explorer. Mark created two virtual SUVs and fed their energy and emissions behavior into a computer model developed by University of California researchers.

The first of these virtual, called the Exemplar, incorporates a host of automotive technologies that are currently in production, including an engine with variable valve control, overhead camshaft, and lower idle speed. "The engine accounts for a substantial jump in fuel economy," says Mark. He also assumed a modest weight reduction of 15% as well as some basic streamlining-a coefficient-of-drag reduction of 10% and a rolling drag reduction of 23%. A second vehicle, the Exemplar Plus, took fuel economy a step further by adding some technologies not currently in mass production-most notable "idle off" and a continuously variable transmission. The bottom line: both vehicles significantly improved on the Explorer's baseline mileage. The Exemplar also did so while improving important performance benchmarks.

"There aren't any technical barriers to improving fuel economy," Mark says. For the complete report and explanation of the energy-and-emissions calculations he used in his analysis, check out www.ucsusa.com.

An SUV blueprint

Miles Per Gallon(CAFEtests)



Streamlining features

Performance0-60, sec% grade at 55mph

Emission standard

CostsVehicle priceLifetime fuel cost

A hybrid transmission that handles the big loads

General Motor's latest plan to boost fuel economy centers on its biggest pickup trucks, the Chevrolet Silverado and GMC Sierra, which will receive a new hybrid-electric powertrain designed to boost fuel efficiency by 15%. "To make the most impact on society, we wanted to go after the vehicles that have the biggest fuel economy issues," says Gary Ostby, total vehicle integration engineer at GM's truck division.

Fifteen percent may seem like paltry progress compared to the 50% gains promised by hybrid electric cars. But these trucks intentionally represent a middle ground between fuel economy and performance, according to Stephen Poulos, GM Powertrain's chief engineer for parallel hybrid propulsion. "We would rather err on the side of the performance," he says.

To that end, GM's hybrid truck differs from hybrid-electric cars, whose electric motors typically go hand in hand with engine downsizing. GM's hybrid, by contrast, marries an electric motor and rechargeable energy storage system with the same 5.3 liter, V8 engine used by the hybrid's gasoline-only forbears. Poulos explains that this full-size engine preserves all the performance measures customers care about-such as acceleration, payload, and towing capacity. "The performance under all conditions remains unchanged," he says.

The hybrid's electric motor powers only a limited number of functions. "We use the electric machine judiciously to improve inefficient operations," Poulos says. It does, for example, replace the starter and alternator and enables the engine to run in a fuel-saving "idle-off" mode, according to Ostby. As for which other functions will be handled by the electrical system, Poulos will only say that the motor "improves efficiency at certain critical times" and, more mysteriously, that this hybrid "does things that have never been done before."

Because the hybrids "electric machine" had to be integrated within an existing truck powertrain, GM's engineering team faced packaging challenges. "Electric motors typically have a rectangular shape in cross section, making it difficult to package them with conical transmission components," Poulos says. To get the motor to fit without changing the powertrain envelope GM engineers "played with variables" such as the motor's size and shape, Poulos reports.

The engineering team also had to find a home for system's "energy storage box"-which consists of battery and control components. "The real challenge was trying to find space the customer didn't regularly use," says Ostby. Taking up usable bed space just wasn't an option, but fortunately, the extended cab trucks offered some real estate under the rear seat. On the downside, trucks without an extended cab-which have been eclipsed by models with more spacious extended cabs-can't accommodate the box in its current configuration.

Beyond packaging, the integration also required plenty of controls development. "Getting an electric motor and gasoline engine to work together transparently to the customer is a major controls issue," says Ostby.

Far from just a technology demonstration, GM had already built at least one of its new hybrid trucks by last summer, even though the trucks won't be available in production volumes until 2004. The company will launch a demo fleet within a few months, giving some of its customers an early chance to kick the tires on these new hybrids.

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