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.
The hardest working, most abused part of a truck is the clutch, and a replacement costs plenty. No. 2 is the driveshaft, a chronic problem in some operations.
Clutches and driveshafts work together and, in traditional trucks, their lives depend upon the driver’s operating skills and habits. “The Eaton UltraShift LHP is ideal for owner-operators coming out of a 13-speed manual,” Steurer says. “It saves wear on the clutch and drivetrain.”
Effective manual transmission driving comes down to control of the application of torque as well as clutch engagement time. The driver needs to start in a low enough gear and avoid applying throttle so the engine rpm will stay low. The clutch pedal also needs to be modulated carefully to avoid abrupt torque application.
What many drivers do, especially when tired or frustrated, is grab the third or fourth gear position from the bottom and then apply throttle, holding the engine rpm above 1,000, to get the truck moving. The result is twice as much torque and six to eight times as much wear on the clutch as a start in a low enough gear at 600 rpm. In any situation with repeated starts, this causes the clutch to overheat, which then accelerates wear. This is why a poor driver can destroy in less than 100,000 miles a clutch that could last 600,000 or more.
These same conditions abuse the drivetrain. Ceramic clutches grab too fast when they heat up because of careless use. The torque applied to the driveshafts increases in combination with this harshness. If a careless or uncoordinated driver releases the pedal abruptly, the driveshafts wind up violently just before the vehicle lurches forward. This kind of driving often results in broken driveshaft parts or failed bearings. The extreme rubbing within the clutch parts greatly accelerates wear there, too.
An automated transmission eliminates these problems, Allen says. The Freedomline uses an organic clutch facing, which is softer and more sensitive to operating technique, but engages more smoothly. With 12 ratios to pick from, the tireless electronic module in the Freedomline always shifts to the right starting gear instead of taking short cuts. The automated compares engine torque and vehicle speed, and if the truck is loaded or on a hill, the transmission processor will quickly decide to grab a lower gear. The processor enables the unit to monitor engine torque and clutch position as it is released. The result is a smooth release at constant torque, eliminating excessive driveline stress.
Similar functions occur in the Eaton Fuller UltraShift LHP, which uses a conventional twin-plate ceramic clutch. This transmission is an electronic version of the 13-speed, but achieves 14 ratios by using the splitter at one point in low range where it’s normally locked out.
This gives an extra starting gear – the “1st” position on the digital indicator – between the Low and 1st positions on a 13-speed. Not only does the unit often start in a lower gear, but the driver also can signal the transmission to engage Low when he is on a hill. This significantly reduces clutch wear.
In addition, the very narrow splits among Low, 1st and 2nd should mean greatly enhanced performance starting and accelerating on very steep grades.
Both of these transmissions will beat even the fastest driver in uphill acceleration by shifting very quickly – the Freedomline via de-clutching and use of a small but effective internal brake, the UltraShift through use of a more powerful inertia brake alone.
If your truck frequently starts and accelerates uphill, this performance increase not only will make you and the drivers behind you smile; the time savings also will increase the number of legal miles you can drive, helping to earn back the investment in the automated unit.
The Freedomline’s use of an organic clutch lining, which grabs more smoothly, guarantees comfortable starts with little drivetrain stress, Allen says. Driver comfort is enhanced by its use of quieter helical gears with curved teeth throughout. These gears are also more finely machined than traditional gears, further reducing noise, Allen says.
Taking some of the driver fatigue out of shifting is an attractive prospect for many, since learning to shift a constant mesh gearbox can be the hardest part of learning to drive.
“The LHP is great for owner-operators who might want to share some driving with their spouses,” says William Batten of Eaton. Thanks to savings on fuel and repairs, moreover, the extra comfort can end up costing practically nothing, or even saving money over the long run.
SLOW BUT AUTOMATIC PAYBACK
Automateds cost at least $3,000 more than their simpler mechanical brothers. Even so, long before a truck hits 1 million miles, you can get a return on that investment in two ways:
6.1 mpg = 18,033 gallons
x $2.16 per gallon
$38,951 annual fuel cost
$38,951 annual fuel cost
x .03 improved fuel efficiency
$1,169 annual fuel savings
Philadelphia Freightliner’s service department estimates the cost saved by not replacing driveshafts on a twin-screw tractor: $4,500
Eaton’s Scott Steurer notes that the UltraShift LHP will save wear on the driveline. Its use could spare all but the best drivers the necessity of replacing the clutch at 300,000 miles. Extending the clutch life to 600,000 miles earns back: $1,800
HOW FULLY AUTOMATICS WORK
As long as you need a clutch, the transmission isn’t truly automatic. The better term for a clutch-dependent system is automated, not automatic.
Fully automatic transmissions are a special case on heavy-duty trucks, with option prices of $10,000 to $15,000 and up. Fully automatics really shine in applications where frequent, difficult starts make clutch and driveshaft wear a constant problem.
Fully automatics are ideal in applications that spend a lot of time accelerating from 0-20 mph. Among owner-operator segments, dump trucks, mixers and oil-field trucks are ideal applications, says Larry Riekert, Caterpillar on-highway manager.
At the heart of the fully automatic is the torque converter, a hydraulic drive element that is bolted to the flywheel and replaces the clutch. The torque converter eliminates all standard clutch wear and will last nearly forever if the transmission is driven and maintained properly. The hydraulics and electronics that handle shifts between gears eliminate all unnecessary shock loads, greatly extending the life of driveshafts and other drivetrain parts.
In a dump truck that spends a lot of time in a quarry, for example, an automatic can significantly increase the number of loads handled per day, which often means higher earnings. It also saves a lot of money in downtime and maintenance.
And the elimination of shifting in such an extremely demanding vocation is a relief – even to drivers raised on gear-jamming.
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