NACFE report: Downspeeding can generate 2% to 3% fuel savings

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Fleet Owner / October 28, 2015

Group says downspeeding is now a “primary” powertrain-focused strategy among OEMs to improve fuel economy for both long-haul and regional trucks that operate at highway speeds much of the time.

A new confidence report issued by the North American Council for Freight Efficiency (NACFE) this week indicates [claims] that downspeeding – the practice of using fast gear ratios that lower the speed of the engine – can cut commercial truck fuel consumption by 2% to 3% because it allows the engine to operate at the most fuel-efficient RPM when generating only the minimal horsepower required under cruise conditions.

NACFE added that downspeeding is now a “primary” powertrain-focused strategy among OEMs to improve fuel economy for both long-haul regional-haul day cab tractors that operate at highway speeds much of the time – largely because complementary technologies make it “more attractive” in heavy-duty truck applications.

The group said it researched nine different downspeeding applications using both proprietary and supplied engine and transmission combinations configured in one of two formats:

A direct drive transmission and a fast axle ratio. The fast axle ratio direct drive transmission specification is optimal in terms of friction and fuel consumption reduction, but given the potential for driveline failure some manufacturers only approve it for true line haul applications where the highest torque conditions occur infrequently.

An overdrive transmission and slightly slower rear axle ratios. The somewhat slower axle ratio of an overdrive transmission spec subjects the transmission output, driveshafts, and axles to far less torque. This makes it appropriate for both line haul and regional and city delivery applications.

NACFE suggested that an automatic or automated mechanical transmission (AMT) should be spec’d on any downsped engine. But if a manual transmission is selected, the engine’s torque response during clutch engagement must be specifically tailored to the drivetrain to gain the expected fuel savings.

The group stressed, however, that downsped-configured powertrains can come with higher cost and higher risk of damage

“Downsped axles, being less flexible, are much more sensitive to sudden shocks,” NACFE noted in its report. “The need to spec an automatic or AMT with a higher output torque capability, a certain clutch with a higher capacity damper, and higher torque driveshafts and rear axles leads to greater upfront costs.”

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Carbon War Room Says "Yes!" to Downspeeding

Todays Trucking / October 28, 2015

Although it has been around for decades, downspeeding—the practice of using fast gear ratios that lower the speed of the engine—has become more widespread because of recent complementary technologies that have made it more attractive.

Downspeeding is now one of the primary powertrain-focused strategies for improving the fuel economy of both over-the-road long-haul tractor-trailers and regional-haul daycab trucks that operate at highway speeds much of the time.

The latest Confidence Report released today by the North American Council for Freight Efficiency (NACFE) and Carbon War Room explores the benefits and challenges of downspeeding for Class 8 tractors. When optimally applied, downspeeding improves fuel efficiency and lowers the operating RPMs of the engine under cruise conditions, while helping in other areas such as noise reduction and improved drivability.

The study team found that as a result of these changes to the powertrain, fleets can reduce fuel consumption by 2–3% because downspeeding allows the engine to operate at the most-fuel-efficient RPM when generating only the minimal horsepower required under cruise conditions.

The report also contains a confidence matrix that expresses the study team’s confidence in downspeeding, and offers recommendations for fleets interested in using this technology to improve fuel economy.

The North American Council for Freight Efficiency is a non-profit organization dedicated to doubling the freight efficiency of North American goods movement. NACFE operates as a nonprofit in order to provide an independent, unbiased research organization for the transformation of the transportation industry.

Carbon War Room was founded in 2009 as a global nonprofit by Sir Richard Branson and a group of likeminded entrepreneurs. It intervenes in markets to accelerate the adoption of business solutions that reduce carbon emissions at gigaton scale and advance the low-carbon economy. CWR merged with Rocky Mountain Institute (RMI) in 2014 and now operates as an RMI business unit.

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NACFE Class 8 downspeeding study confirms 2 to 3 percent fuel economy boost

Commercial Carrier Journal (CCJ) / October 28, 2015

The North American Council for Freight Efficiency released a new confidence report highlighting the benefits and disadvantages of diesel engine downspeeding technology in Class 8 applications this week.

Mike Roeth, executive director of NACFE, noted that the report drew on unbiased experts from across the trucking industry, including OEMs, component suppliers, engine and drivetrain manufacturers and large and small fleets to paint as comprehensive a picture as possible on how downspeeding is being used in trucking today.

Downspeeding, Roeth noted, uses high-speed rear axles combined with high-torque, lower-RPM diesel engines. With this powertrain combination, a diesel engine revs less at any given highway speed and therefore receives corresponding fuel economy boost. NACFE found the typical downspeeded truck gained between a 2- and 3-percent increase in fuel economy, compared to tractor-trailers running conventional powertrains.

Roeth said the study determined that there are two basic downspeeding configurations commonly found in trucking today. The first, and most common spec, relies on a direct-drive transmission, which delivers higher fuel economy numbers. Some fleets are opting for the second choice, which uses an overdrive transmission with a slightly slower rear axle.

“The key enabler in all cases are the new generation of electronically-controlled automated manual transmissions,” Roeth noted. “These transmissions make downspeeding more attractive and practical for fleets today, particularly when they are mated with finely-tuned engine parameters to optimize fuel economy and mitigate torque management problems.”

Significantly increased low-end engine torque is one drawback to downspeeding. Roeth says drivetrain component suppliers manage this problem by using larger, more robust axle gearing and driveline components, in addition to enhanced electronic engine programming.

The study determined that spec’ing more robust axle and driveline components generally adds between $500 and $1,000 to the vehicle acquisition cost. But, it also noted that fuel savings offset these numbers. Based on a five-year average diesel prices, NACFE calculates fuel savings of approximately $1,500 per year. Plugging in current low fuel prices yields a annual saving of approximately $1,000 per year per downspeeded truck.

Roeth said the study found mixed responses on downspeeding technology from drivers. On the positive side of the ledger, drivers with downspeeding experience complimented the “significantly” quieter ride at highway speeds combined with “snappy” acceleration and low-end power.

On the other hand, the study found that many fleets were reluctant to order downspeeded trucks, fearing that uninitiated drivers would reject them and either leave or decline to hire onto a fleet equipped with them.

Resell values remain a worry for other fleets as well, since NACFE found that downspeeding is a spec that works best in long haul, steady-state driving applications.

As a result, current estimates show only about 25 percent of new, long-haul tractors are currently being spec’d with downspeeded powertrains. But, based on the report’s findings, NACFE strongly recommends long-haul fleets consider the spec as a way to incur significant annual fuel savings. “The key for fleets interested in adopting this spec is to work closely with both OEMs and component suppliers to insure the vehicles are spec’d correctly,” Roeth added. “If that’s the case, our study found they perform very well in their designated application while delivering significant fuel savings to fleets.”

Access the complete NACFE study on engine downspeeding here.

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Downspeeding can contribute 2-3% in fuel savings: NACFE report

Truck News / October 28, 2015

A new confidence report released today by the North American Council for Freight Efficiency (NACFE) and Carbon War Room claims that downspeeding can slash truck fuel consumption by 2-3% when optimally applied.

Downspeeding is the practice of speeding up the rear axle on trucks to lower the speed of the engine, allowing the truck to run at the most fuel-efficient RPM under cruise conditions, thus saving fuel and money. Downspeeding can also help in other areas like noise reduction and improved driveability, NACFE said.

According to the report, downspeeding is now a primary focus for OEMs to help improve fuel economy for regional and long-haul applications that operate at highways speed, mainly because of the technologies that complement it to make downspeeding more attractive.

“We see (downspeeding) in two configurations,” said Mike Roeth operation lead, trucking efficiency with NACFE. “The first is downspeeding with a direct drive transmission. And that’s being done by fleets (that) are most aggressive on fuel economy.

The other is downspeeding with an overdrive transmission with a slower rear axle ratio. That offers different advantages but loses that direct drive opportunity.”

NACFE said one of its main conclusions from the report is that, after the finding it can improve fuel economy by 2-3%, downspeeding should be adopted by long-haul operations.

“We strongly consider that in long-haul fleets, they be considering downspeeding,” Roeth said.

One of the only concerns with downspeeding NACFE found in its research is that it poses a risk of potential driveline failures. However, NACFE said by talking to the right people, you can avoid this is you think downspeeding is the right move for your business.

“One of the concerns we uncovered is the consequences of potential driveline failure due to higher torque,” Roeth said. “The good news is the component manufactures and truck manufactures, have solutions for that. And that particularly happens in day cab, pick-up and delivery type of operation where there’s the opportunity to deal with that higher torque. But, there are solutions there, and we recommend that anyone considering downspeeding speak about this with your transmission supplier, rear axle supplier, engine suppler…to make sure that the spec’ will work for you and your duty cycle and your business practices as a fleet.”

For more information visit www.TruckingEfficiency.org.