Reprinted with permission from the February 2020 issue of TLT, the official monthly magazine of the Society of Tribologists and Lubrication Engineers, an international not-for-profit professional society headquartered in Park Ridge, Ill., www.stle.org.
Smart fleet operators are cutting costs, improving cash flow and reducing greenhouse gases.
- Cash flow remains a critical business concern for fleet operators.
- The average truck contributes 33.3 times more carbon dioxide than a car annually.
- New lube techniques for transmissions, axles and components are generating huge fuel savings.
In the 1977 classic comedy Smokey and the Bandit, the Bandit and his partner Snowman drive their Kenworth rig from Atlanta to Texarkana and back in under 28 hours to pick up a few hundred cases of beer. And, well, $80,000. Making $80,000 (in 1977 dollars) for a 1,400 mile run is a great profit margin. But real truck drivers don’t have such fantastical cash flows, so ways to keep the truck running in tip-top shape and improve fuel efficiency (other than not outracing Smokey) also will improve their bottom line. And concerns about fuel efficiency these days go beyond income. With the transportation sector contributing about 20% of global emissions (1), a trucker being able to cut down yearly emissions by almost as much as a car just by using best practices will save money and help with carbon pollution. Heavy duty vehicles and fleets consume a high rate of fuels and give off large amounts of greenhouse gases. Average driving distances in the U.S. for a heavy-duty truck, says STLE-member Philip Ma, global technical marketing manager at BASF, run about 100,000 miles per year, corresponding to about 153 million metric tons (Mt) of carbon dioxide puffed into the atmosphere. Compare that to the average passenger car driving about 11,500 miles per year and emitting about 4.6 Mt of carbon dioxide. “The best practice to gain additional energy efficiency is to use fuel-efficient synthetic lubricant in drive trains components such as transmission and axles,” says Ma. “The gain in energy efficiency is in addition to the benefits of longer oil drain interval—and its reduced maintenance cost—and longer component life.” But owners can’t use just any synthetic lubricant, according to BASF technical service manager and STLE-member Donna Mosher. Lubricants need to follow specifications released by the original equipment manufacturers. “When talking about best practices, ‘do what the OEMs say’ is the overall theme,” says Mosher. Why not just continue to use the classics? If it was good enough for Snowman, why isn’t it still? Just as car chases in movies have gotten more complicated since a convoy helped Snowman elude Smokey, so have heavy duty drivetrains. “Many truck owners say, ‘Well, I’ve always used an SAE 50 or SAE 80W-90, and it’s always worked for me.’ What they don’t understand is how things have changed over time,” says Mosher. Just in the last 10 years, for example, a magnitude of transformations have taken place, let alone since the 1970s. Those transformations have saved the U.S. 2.9 billion gallons of diesel, 218,000 tons of particulate matter and 29 million tons of CO2 (2). The first thing an owner needs to know is the equipment within the truck, which can then be used to determine the OEM specifications. Transmissions and axles have different manufacturers. In addition to specs, OEMs specify drain interval for fluids (or how often the fluids need to be replaced), which in most cases exceeds 500,000 miles. Another factor that needs to be taken into account to determine best practices for particular trucks are duty cycles, or how the truck is being used. Understanding the differences in OEM specifications, combined with regular maintenance, will help truck drivers and owners stay on top of their own best practices. Know your truck: equipment At the front end of the truck drivetrain is the transmission. There are four major heavy-duty truck transmission manufacturers: Eaton (3), Daimler (4), Volvo (5) and Allison (6). Each OEM has different design goals for their equipment, so their components are different. Because each OEM wants to get the best out of their entire system, they tailor their fluid to the components. The lubricants are part of the system. Using a non-specified lubricant that doesn’t address each transmission’s unique characteristics can damage the transmission—cutting fuel efficiency, ruining seals, making it harder to shift or perhaps even shortening the life of the drivetrain. “Transmissions are an incredibly expensive part of the truck,” says STLE-member Michael Costello, director of strategic research and development director at Lubrizol in Wickliffe, Ohio. “They can run $10,000-$20,000, so owners want to take care of them. The best practice is to pick a fluid that’s appropriate for the transmission you’re using. OEMs have a specification for each one.” At the other end of the drivetrain is the axle. Although fluid specifications are highly customized to individual transmissions, heavy duty axle fluid is a bit behind, so best practices have more latitude. “Axles contain gears that turn 90 degrees because wheels are oriented perpendicular to the engine. Formulators can create a fluid that improves the energy efficiency of that gearbox by reducing drag, internal friction and surface friction,” says Costello. New designs are the next step in making axles more energy efficient. In conventional axles, a gear will drag itself through the oil and then fling the oil upward to lubricate all the other gears and bearings in the axle. New technology—called lubrication management or dry sumps—lifts the gear above the oil and sprays it rather than allowing the gear to splash. The gear moves easier, so it’s more efficient with less drag loss. Know your truck: components Within each brand of transmission are different types of technologies. Some are manual transmissions, some are automated mechanical transmissions, and some are automatic transmissions. Each type of transmission has its own designs—they might have different types of gears, different loads on the gears and different gear ratios. “One of the key things in a heavy-duty transmission is that they usually use a synchronizer instead of a clutch plate,” says Costello. “It’s the same idea as a clutch plate, but it’s a slightly different way of doing it. It’s conical instead of flat. The synchronizer material varies from manufacturer to manufacturer. So different synchronizer materials require different fluids.” Manual transmissions (MT) (such as Eaton) and automatic transmissions (AT) (such as Allison) require distinct fluids. Automatic transmissions have torque converters, which means they generate a lot of heat, so the fluid has to handle higher heat. In addition, the automatics have a lot of friction modifiers for smooth shifting. And then there are automated mechanical or automated manual transmissions (AMT) (such as Daimler, Eaton and Volvo). “In an automated mechanical transmission, the guts are pretty much the same as a manual, but they add electronics and a shifter system to make it shift automatically,” says Mosher. “There are only two pedals for the driver. They just press D for drive. So it’s a lot easier for the driver. It’s not an automatic transmission, but it reduces what you lose in efficiency by not using a torque converter.” Most automated manual transmissions have electronic components, some of which are located inside the transmission. This arrangement requires a transmission fluid to have copper corrosion protection to make sure the electrical system is protected. Know your truck: service requirements In the best of worlds, transmissions and axles are closed systems, meaning fluid won’t be outright lost. (Of course, leaks change that equation.) Even so, the mechanisms within the systems dirty up the fluids. And heat eventually breaks fluid down. So the fluid in transmissions and axles must be changed out at the proper intervals. Understanding the recommendations for each component is essential for regular maintenance and also to protect the warranty. Eaton’s newest transmission has the largest transmission fluid drain interval to date — 750,000 miles. But how hard a truck works will affect its own particular interval. A long drain interval means the fluid has to be able to last that long and not change over time. A damaged transmission due to the wrong fluid means a custom, curtailed maintenance schedule. “You’ll have to drain your transmission oil a lot sooner,” says Mosher. “Probably at 60,000 miles instead of 750,000 miles.” Know your application Are you the one road-running beer from Atlanta to Texarkana, or are you in the Arctic Circle running in the diamond mines? Fuel efficiency benefits aren’t the same across the board. They depend on the duty cycle of the truck. Long hauls across the country get better fuel efficiency—typically, though not always, because the result also depends on what loads they’re running. “Each truck application is unique,” Mosher says. It’s hard to talk duty cycle without also talking about drain intervals for transmission and axle fluids. Long drain intervals will only make it that far with certain types of work. “Drain intervals are tied to duty cycles,” says Costello. “If you’re running a truck on the highway, doing long haul cross country, a 500,0000 mile drain interval is fine. But working a mining operation, driving a truck off-road through mud and dirt, going really slow with heavy loads—those trucks won’t get to half a million miles. They may only do 50,000 miles before they need to change the fluid.” Costello explains that because the trucks are going so slow, the oil gets much hotter, which means it degrades and has to be changed more often. The fluid in a truck traveling down the highway, on the other hand, is cooled by the air coming underneath the body of the truck going across transmission and axle. “Going slow is worse for the lubricant,” Costello says. Sometimes the duty cycle is part of the truck build. Compared to manuals, automated mechanical transmissions have physically higher duty cycles. “They’re typically shifting more often than a manual transmission. So the fluid needs to work a little more and last longer,” says Mosher. The duty cycle is important enough that OEMs consider the application when recommending transmission types, such as whether it will be used in agriculture, as a bulk hauler or some other job (7). Get the best performance Premium synthetic oils can provide benefits when they have the right OEM specifications. OEMs are talking less about the viscosity grade of transmission fluids and more about the specification number these days. And some lubricants are specifically designed to improve energy efficiency such as BASF’s EMGARD XFE 75W-85 extra fuel-efficient axle lubricant (8) and Eaton’s PS-386 transmission fluid (9). “We say an energy-efficient lubricant typically will increase fuel mileage 1%-2%,” says Mosher. “To put it into perspective, a 1% improvement is about 500 dollars a year per truck.” Not many axle fluids on the market are specifically designed for better fuel efficiency (10)—again, about 1%-2% improvement can be achieved by selecting one. Drivers and owners should look to their OEMs for specifications particular to their products. “On the axle side of things, they’re just learning about how lubricants impact fuel efficiency,” says Mosher. “Now axle manufacturers are running a lot of new experimental oils and learning it actually makes a difference. We don’t really tailor fluids to each axle manufacturer yet. But we likely will in the future.” At the moment, axles are pinned to their viscosities. The two most common viscosity grades currently in use are SAE 75W 90 and the higher viscosity SAE 80W 140. Mosher expects in the future those viscosity grades will decrease, and axle manufacturers will probably recommend 75W-85 and maybe 75W-110. “Lower viscosities will improve the efficiency of the axle,” Mosher says. “The churning losses go down when the viscosity decreases.” Lower viscosities also enable the new technologically advanced dry sumps that require the oil flows at cold temperatures. If the lubricant is not flowing at the temperatures at which the vehicle starts, it’s not going to get to the gears and bearings to protect them. This could possibly happen at truck start-up. Dry sumps typically use a lower volume of oil, thus they also require a new kind of lubricant that can remove the heat properly. “New lubricant is enabling the dry sump technology,” Costello says. “The lubricant isn’t itself more fuel efficient but it is enabling OEMs to create a system that is more fuel efficient.” The franchise reboot Today, Snowman would be driving a Kenworth W990, an 18-speed automated mechanical transmission, 605 hp with 1,850 lb.-fts. of torque and a gross combination weight of 80,000 pounds. His truck’s gas mileage would have doubled from four miles per gallon to eight. His carbon footprint—which was not even mentioned in Smokey and the Bandit or its sequels—would have dropped from about 255 metric tons of CO2 to 128. And his truck’s life expectancy, assuming he didn’t crash it (or get impounded) while bootlegging beer, would go from 100,000 miles to a million. To stay ahead of Smokey, he’s going to want his fuel-efficient drivetrain synthetic lubricants and the OEM specifications to play a starring role.
REFERENCES 1. Ritchie, H. and Roser, M. (2019), “CO2 and Greenhouse Gas Emissions,” published online at OurWorldInData.org. Available here. 2. “2017 Fact Book,” Heavy Duty Trucking, August 2019, pg. 56. Available here. 3. Available here. 4. Available here. 5. Available here. 6. Available here. 7. Available at here. 8. EMGARD, BASF. Available here. 9. Available here. 10. Available here.
Written by: Mary Beckman, is a freelance science writer based in Richland, Wash. You can contact her at firstname.lastname@example.org.