OEMs Combine Technologies to Maximize Fuel Efficiency

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Heavy-duty truck manufacturers have improved the fuel efficiency of their tractors through a combination of new technologies, powertrain improvements, enhanced aerodynamics and efforts to reduce rolling resistance.

See related story: Fleets Enjoy Fuel Efficiency Gains in New Trucks, But Express Concerns on Maintenance Costs (TT subscription or 14-day pass required.)

All North American Class 8 truck makers currently are building trucks with selective catalytic reduction (SCR) technology except Navistar, which has developed its exhaust gas recirculation, or EGR, technology, which does not require the use of diesel exhaust fluid.

On July 6, however, Navistar announced plans to add SCR in future engines as part of a strategy to use several technologies to meet emissions goals.

Mike McHorse, marketing segment manager for Freightliner Trucks at Daimler Trucks North America, said his company’s adoption of SCR has provided up to a 5% improvement in fuel efficiency.

“Customers moving from the previous EGR-based solution for EPA 2007 were really rewarded for moving to that technology from a fuel-efficiency standpoint. But also, the engines run at cooler temperatures, so we didn’t need to have the big cooling packages and so forth for that engine platform,” he said.

At the same time, the company also added new aerodynamic enhancements to its primary on-highway tractor, the Cascadia, in 2011.

Freightliner added a roof deflector to the top of the truck to drive air flow better over the top of the trailer and closed off two sections of the bumper to make it more aerodynamic, McHorse said.

The company also added side skirts to the chassis side fairings that help keep the air flow out from under the truck in crosswinds, he said.

The importance of these fuel gains has risen along with fuel prices.

“When diesel crested somewhere in the neighborhood of $3.50 a gallon, for most of our customers that run 120,000 miles a year, diesel fuel became their most expensive operating cost, over drivers,” McHorse said.

Officials at Volvo Trucks said their company improved its trucks’ fuel economy with the introduction of SCR engines in late 2009 to meet EPA 2010 standards, along with enhanced aerodynamic components and Volvo’s “XE” fuel-efficiency package, which utilizes the company’s engines and I-Shift transmission.

Volvo launched the XE package in September. “The XE — exceptional efficiency — concept reduces engine speed by 200 rpm, yielding an additional 3% fuel-efficiency gain,” said Ed Saxman, Volvo’s product manager for powertrain.

“Those powertrain enhancements were further complemented by cab and chassis enhancements in August of 2011 that, in conjunction with the engine improvements, can add up to an additional 3% fuel efficiency,” said Frank Bio, Volvo Trucks product manager for trucks. “These improvements include aerodynamic mirror brackets, new hood mirrors and under-bumper enhancements.”

Steve Schrier, a spokesman for Navistar Inc., the maker of International brand trucks, said an industrywide focus on aerodynamics has contributed and will continue to contribute to fuel-efficiency gains.

“Low-rolling-resistance tires and reduced vehicle weight are also major contributors,” he added, “and the integration between powertrain and vehicle, and the integration between tractor and trailer will continue to be the focus, moving forward.”

Schrier said that Navistar, in addition to its advances in aerodynamics, also has focused on cutting the weight of its tractors.

He described the company’s ProStar+ as the lightest Class 8 tractor on the market.

“Reducing vehicle weight falls under the ‘rolling resistance’ category. On average, for every 1,000 pounds of weight reduced, you can achieve a 1% [boost] in fuel efficiency,” he said, “and that’s not to mention the improved payload for customers, which goes right to a customer’s bottom line.”

In some specifications and driving conditions, customers report seeing upward of 9 miles per gallon with the ProStar+ equipped with the MaxxForce 13 engine, Schrier said.

Landon Sproull, chief engineer for Peterbilt Motors Co., said his company also has focused on improving the aerodynamics of its trucks.

In January 2011, Peterbilt launched the Model 587, which replaced the Model 387.

“With improved aerodynamics and forward visibility with a new lower hood design, the Model 587 helps move the air over the cab and onto the trailer,” Sproull said. “There were hundreds of computer analyses [needed] to tune the bumper and hood.”

Peterbilt also added two lightweight packages, he said, one for the Model 384 day cab, which weighs 13,900 pounds, and the other for the Model 386 48-inch sleeper/cab, weighing 16,400 pounds.

The company also adjusted the engine calibration and, with the Paccar MX13, added speed-control management and gear-down protections “that help the driver stay within the desired fuel-consumption map,” Sproull said.

David McKenna, director of powertrain sales and marketing at Mack Trucks Inc., emphasized the value of integrated manufacturing.

“Anytime that an engine is designed specifically to work with a transmission coupled to drive axles — and all managed by the same vehicle [engine control unit] — the opportunity to maximize performance is very real,” he said. “Information, data management and control offer the best route in which to optimize customer duty cycle performance — period.”

McKenna said Mack’s customers running 2011 and 2012 trucks have seen fuel economy improvements in the range of 3% to 5%.

“At $4 per gallon, that saves about $2,900 [in] fuel expense per year or $242 per month per truck,” he said.

During the truck design phase at Mack, anything that demonstrably and repeatedly shows a reduction in fuel consumption “moves to the top of the list,” McKenna said.