GREENSBORO, N.C. – Volvo Trucks has introduced a new concept called ‘downspeeding,’ which takes the industry-wide shift towards lower engine speeds to a new, well, low. Introduced as the XE13 (exceptional energy) powertrain package, Volvo’s latest fuel-saving tactic allows the engine to cruise at just 1,150 rpm at 65 mph – about 200 rpm lower than the average truck sold today.

Ed Saxman, Volvo’s powertrain product manager, said that translates to a 3% fuel savings compared to typical overdrive transmissions in a similar operation.

“For every 100 rpm you reduce engine speed while travelling at 65 mph, you are saving 1.5% fuel,” Saxman explained. “So lowering it 200 rpm means this is 3% better than an equal overdrive transmission and 1.5% better than a direct drive. These are numbers we stand behind.”

That means a truck averaging 7 mpg can achieve 7.2 mpg with the XE13 package.

“It’s an easy two-tenths of a mile per gallon and that’s $2,000 per year per truck” in fuel savings, Saxman said.

The XE13 powertrain package requires a very specific set of specifications, including: a Volvo D13 engine with 425 hp and 1,750 lb.-ft. of torque; a Volvo I-Shift overdrive transmission with a 0.78:1 ratio; axle ratios of 2.64 to 2.69; and of course the proprietary software that makes it all work. One of the great enablers is the I-Shift’s 28% step, which falls precisely between the 38% step of 10-speeds and the 18% step characteristic of splitter transmissions. The real key, of course, is the high level of integration that exists between engine and transmission, which Volvo officials say makes their latest feat of engineering something that’s very difficult for competitors to replicate.

“The 28% step is one of the needs, the high horsepower engine brake, 1,750 lb.-ft. torque is one of the needs and we’re alone there in the 13-litre market,” Saxman said.

The XE13 is aimed towards linehaul fleets and approved for gross weights of up to 88,000 lbs. (Volvo’s marketing materials will tell you it’s limited to 80,000 lbs, but 40 tonnes is fine, Saxman told Truck News).

“This is for mainstream trucks,” he added. The effects of the XE13 package will go unnoticed during stop-and-go city driving, but the software was programmed with US interstate driving in mind, as well as Canadian highways, Saxman hastened to add. It’s expected the new package will be particularly attractive to bulk haulers and other truckers who are frequently lightly loaded or empty, since the benefits are enhanced at lower weights.

Another piece of the puzzle is Volvo’s impressive engine brake, which achieves strong performance because of an extra bump on the camshaft that allows air to flow back into the engine, producing more mass in the chamber and providing for better retardation.

I recently had the chance to drive a Volvo VN670 with the XE13 package between Hagerstown, Md. and Greensboro, N.C.; a route that alternated between flat terrain, rolling hills and some decent-sized grades. Volvo felt the route was indicative of the variety of terrain that its North American customers will encounter on a daily basis. Virginia is a 70-mph state, and even at 70 the D13 engine cruised along at 1,240 rpm. The same engine in a similarly spec’d VN with a 10-speed manual would be spinning at 1,512 rpm, according to officials. At 65 mph, the XE package ran at about 1,150 rpm while a comparable 10-speed would run at 1,404.

Engine speed remained low even while pulling some steep hills, and downshifts were rarely required. When they were, it was no big deal as the I-Shift took care of everything. The VN670 with XE13 package basically runs in its sweet spot at any given speed.

Driving a truck with the XE13 package was precisely as Volvo reps said it would be. The rpms remained low under all operating conditions. A nice byproduct of the lower engine speed was a quieter cab interior. Like, car quiet. It is easy to see how the new development will benefit customers.

It’s such a simple premise: lower engine speeds result in less fuel consumption. The term downspeeding, coined by a Volvo employee, simply means the package produces less engine rpm for the same road speed. It’s verifiable from behind the wheel, although the fuel savings would need to be proven over time. There is little reason to doubt them, however, when it is just plain common sense that a slower running engine will consume less fuel. Volvo’s Saxman admitted the entire industry is chasing lower engine speeds but in Volvo’s case, it is using its advanced I-Shift automated transmission to essentially drive the engine.

“You used to drive it up to 2,100 rpm in every gear, because that’s just how you drove,” he said. “We’re seeing a paradigm shift.”

Because the I-Shift is an essential ingredient to the XE13 package, even drivers who are resistant to a fuel-efficient driving style will have no choice but to run the engine slow and improve their mpg.

Interestingly, Volvo is already succeeding in convincing its customers to spec’ a highly integrated vehicle. Eighty per cent of Volvo trucks sold today have Volvo power under the hood and about 40% of those have the I-Shift transmission.

Customers will be pleased to learn the new package is available for next to nothing; the upcharge will be no more than a couple hundred bucks, Saxman said.

“It will be very quickly recouped,” he added.

Volvo’s engineers and designers have been busy. The XE13 package marks the latest in a string of fuel-saving developments from the company. Its adoption of selective catalytic reduction (SCR) to comply with EPA2010 emissions requirements was not unique, yet it provided a 5% fuel economy improvement over EPA07 models.

A new aerodynamic package introduced earlier this year provided a further 3% improvement in fuel mileage, the company noted. The truck I drove was outfitted with the latest aero package, including a shift to rectangular, hood-mounted mirrors that provide greater visibility than the previous round design while also improving airflow. The package also included full chassis fairings, cab side fairing extensions and an aerodynamic bumper with full airflow deflector. The XE package provides up to a 3% further improvement above and beyond all that. The VN670 I drove was also decked out in one of Volvo’s new interiors, also introduced earlier this year. The new interior design features a softer colour pallet and a greater selection of materials. The earthy tones take a cue from today’s contemporary interior design trends.

All in all, the new Volvo VN670 with aerodynamic package and homey interior is among the slickest looking trucks on the road. It’s also clearly one of the most efficient to operate, when spec’d with the new XE13 powertrain package.