Fluid changes are just as important to automated transmissions as to manuals.
Automated transmissions are increasingly popular. Arvin Meritor, maker of the Freedomline model, says self-shifters are 40 percent of its sales in Class 8s.
Eaton’s Fuller division, which offers a wider variety of manuals, says 12 percent to 15 percent of its sales are automated hardware nearly identical to its manual gearboxes.
Automateds cost at least $3,000 more than their simpler mechanical brothers, but in exchange they offer improved fuel economy, better acceleration on hills, and substantial savings in repair and maintenance costs, especially in the toughest applications.
America may be “the land of automatics,” in the words of Charlie Allen, ArvinMeritor national service director, but to some truckers, these almost robotic devices are strictly for novices or softies, and not the serious owner-operator. Whether that is true depends, to some extent, on the driver himself, and just how good he is.
Even the best drivers can’t be expected to get the fuel economy of an automated transmission, Allen says. “Drivers don’t make optimal decisions,” he says.
At a given cruise speed, a really good driver can do only one thing to improve fuel economy: Shift up. These days, lugging a diesel engine down too low is almost impossible. Going up a gear, or even just a split, can make a whopping difference in fuel use. Caterpillar recommends cruise rpm near 1,300 for normal 80,000-pound loads when running its C15 engine at a cruising speed of 65 mph. Other engine makers don’t advise going quite that low, but chugging along at 1,500 rpm or less is the name of the game.
Upshifting saves fuel by reducing engine friction and increasing turbo boost, compression and air utilization. Good drivers know instinctively to shift up or split up, especially when running at lower speeds where drag is minimal. One problem is that even the best driver won’t bother to shift up if he knows a grade or a slowdown is just ahead.
An automated unit, in contrast, cares only about vehicle speed and load, so it shifts up as soon as you back out of the throttle. “This system doesn’t get tired of shifting,” Allen says.
An unsophisticated driver will try to find a single gear he can stay in, especially when running in traffic or rolling terrain. But what about the savvy professional who has been out there for years? Even with a multi-speed transmission, the owner-operator will gear and specify his truck to climb gentle grades without a shift. To many, shifting constantly is a sign you’re driving a turkey and creates too much fatigue.
Automateds eliminate shifting-related fatigue as a factor, which “means you can gear more aggressively, and take advantage of the automated shifting,” Allen says. Some customers running Freedomlines have turned in their 3.55:1 rears for 3.21 ratios or even 3.07s. This means much of their cruising occurs at lower rpm, and that saves fuel.
The Freedomline has 12 evenly spaced ratios with steps of 28 percent to 30 percent between each gear, much closer than those of the typical 10-speed. The soon-to-be-released Eaton Fuller UltraShift LHP is based on 13-speed hardware, which means steps of 20 percent or less from about 30 mph. More gears, electronically shifted, mean consistently lower cruise rpms for both transmissions.
Those close steps past 30 mph are especially useful with engines such as Caterpillar’s ACERT designs, as they “want to operate in tight rpm bands,” says Scott Steurer, Eaton product line manager.