Navistar shows new fuel-saving powertrain

Navistar International has introduced a new fuel-saving powertrain with a 12.7-liter diesel whose exhaust is cleansed by an aftertreatment system using two-stage selective catalytic reduction, and a 14-speed automated manual transmission.

Called the S13 Integrated Powertrain, it will deliver up to 15% better fuel economy than did the current A26 diesel when it was introduced five years ago, executives said during an Aug. 16 program at the Las Vegas Motor Speedway in Nevada.

The powertrain takes its name from the S13 diesel, an inline six-cylinder design with numerous advanced “clean-burn” features that allow a simplified exhaust-gas recirculation system with no cooler. It has double overhead cams, a 23:1 compression ratio, relatively low-pressure oil pump, and a fixed geometry turbocharger – all to make the engine efficient and simple and easy to service and repair.

Rugged and quiet

Ruggedness will make the engine last for 1 million miles, said Michael Grahe, executive vice president for operations. It is both quiet and smooth, he said.

Quietness and smoothness will please drivers, and a quick two laps around the infield track of the speedway seemed to verify that. This reporter drove daycab and sleeper-cab versions of the LT highway tractor. With the self-shifting T14, operation was effortless.

The T14 transmission has two creeper gears, and close ratios up to a direct-drive 13th gear and overdrive 14th gear. With a truck loaded, it will run mostly in 13th-direct, which is where the greatest fuel economy gains will be. The 14th-overdrive gear will engage when loads are light or the truck is drifting downhill. The engine will come with a compression engine brake that will make up to 469 retarding horsepower.

The aftertreatment system will use two-stage dosing of exhaust fluid, first just downstream of the turbo and the second in the system’s box-like container that will also house a diesel particulate filter. Clean burning of the fuel in the engine will help reduce particulate matter – soot – and the diesel particulate filter will be passively cleaned by constant heat. No fuel-induced active regenerations should be needed, though they can be actuated if necessary.

Navistar’s last internal combustion powertrain

The powertrain was collaboratively developed over five years by Navistar engineers and their counterparts at Scania in Sweden and Brazil, who had begun two years earlier. It is the second product to come from the Navistar’s strategic alliance, then merger, with Traton of Europe between 2017 and ’21. The A26 diesel, based on a design from MAN of Germany, was the first. Navistar, Scania, MAN, Rio and Volkswagen Truck and Bus comprise Traton.

The coming electric revolution means “this is the last internal combustion powertrain we will develop from the ground up,” Grahe said.

Based on past experience, Navistar anticipates the engine will be used, with further refinement, for about 15 years, or well into the 2030s. Navistar’s aim is that half of all trucks sold in 2030 will be zero-emission, meaning electric propulsion, and all will be zero emission by 2050.

The S13 diesel has undergone 4 million miles of field testing in extreme climates from Arizona to Alaska, and 400,000 hours of dynamometer testing – the most Navistar has ever done with a product.

The engine is in production in Europe, where it’s called the Super 13, so it will have been in customer hands for two years before becoming available in North America in October of next year. In the meantime, the powertrain will be placed with North American customers for further testing and evaluation. A modular design allows the engine to meet the exhaust emissions limits of different countries relatively easily, as well as many trucking applications, Grahe said.

A range of ratings

The S13 diesel will come in seven ratings, from 370 hp and 1,250 lb-ft of torque to 515 hp and 1,850 lb-ft. Those include a 400-hp, 1,850 lb-ft version that will get the best-case 15% fuel economy improvement. Of that 15%, 12% will come from the new engine and 3% from aerodynamic improvements to the LT highway tractor, which will enter production next summer.

The powertrain will be standard in the LT, and will also go into the RH regional tractor, which will get similar aerodynamic smoothing. No manual transmissions will be offered in the highway tractors because there’s a strong industry wide trend toward automated gearboxes. Later, vocational trucks will get the S13.

“It will be the lightest 13-liter class powertrain in North America,” said David Hillman, director of integrated powertrain marketing.

An S13 diesel alone weighs 2,284 pounds without fluids. Engine and transmission together weigh about 30 pounds less than the current A26 diesel with an Eaton Endurant automated manual transmission, and 650 pounds less than a 14.9-liter Cummins X15 with an Endurant HD autoshifter, which International will continue to offer.

Navistar plans to produce the S13 diesel and T14 transmission at its expanded factory in Huntsville, Ala. LL

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