With nearly every info-packed story in the print pages of Fleet Equipment, there are nuggets of information left on the editing room floor, usually due to limited space on the printed page. Thanks to the supercomputers that enable the hive-mind that is the Internet, we can bring you all the info we amass in a fun bullet point list. Check out the additional powertrain integration info that we weren’t able to squeeze into the magazine:

Engines

• In terms of application, there is no one correct application for engine downspeeding, according to Kevin Baney, Kenworth chief engineer. Any application that spends time at cruise speeds can benefit from the fuel economy improvements. It is vitally important to understand the vehicle’s operating conditions to get the correct balance of performance and fuel economy.

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• Our panel of powertrain experts agree that downspeeding is most likely best suited for linehaul and regional haul applications. However, particular attention needs to be paid to the operating speed for each vehicle when finalizing the spec. Aaron Peterson, Navistar chief performance engineer, on-highway tractor, explains: “Downsped drivetrains are limited to approximately 7 MPH of operating range in top gear due to the lower target engine speeds. If not spec’d correctly, the vehicle will experience increased shifts and more time operating gear down thereby hurting fuel economy. We definitely recommend working with the vehicle OEM to select the correct rear axle ratio factoring in all aspects of the customers operation.”
• “Downsped engines are most efficient in applications that involve high percentages of time in top gear and in cruise at speeds greater than 62 mph – the conditions in which most over-the-road trucks operate,” added John Moore, Volvo Trucks product marketing manager-powertrain. “If a fleet manager has trucks that usually operate in mountainous terrain, conventional drivelines are a better choice as they would not require as much shifting of gears.”

Transmissions

• Kenworth introduced new software calibrations between the engine and transmission to optimize RPMs during acceleration and deceleration, and when pulling up and coasting down hills. In addition, targeting low-engine RPMs allows transmissions and axles — both with optimized gear ratios — to minimize parasitic losses throughout the powertrain, thus improving fuel economy. On the drivability side, calibrations between the engine and transmission improve vehicle control at slow speeds and when pulling hills. The end result is a more fuel-efficient and integrated truck that provides an improved driving experience. This helps customers increase their profitability and attract drivers.

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