North America is following Europe down the road to “shiftless-ness,” as automatic and automated manual transmissions continue to gain popularity in heavy trucks. More than eight out of 10 Class 8 trucks in Europe are now sold with self-shifters, and it appears that three out of 10 get them in the U.S. And that figure’s growing. The reasons include better fuel economy and easier driver recruiting and productivity than with manuals, along with greater safety.
Most automated manual transmissions go into highway tractors, but Eaton offers three vocational versions of the UltraShift Plus for on/off-road trucks such as dumps and mixers.
In 2013, about 30% of all heavy truck gearboxes sold in North America were self-shifters. That’s not a definitive figure, says Ryan Trzybinski, Eaton’s development and product planning manager for commercial vehicle transmissions. But it’s clearly a trend, and “our mix from manual to automated transmissions has moved 2% to 4% in the last two years.” The company continues to offer variations of its UltraShift Plus automated manual transmission as well as the Smart Advantage powertrain product offered jointly with Cummins.
Eaton’s experience with AMTs goes back to a completely mechanical (and unsuccessful) gearbox called Cemat in the late 1980s, and to the AutoShift with a manual clutch in the ‘90s. The company now offers a 6-speed midrange UltraShift and 10-, 11-, 13- and 18-speed heavy UltraShift Pluses.
What’s jumbling the numbers in Eaton’s current reports is that several truck original equipment manufacturers are now selling proprietary AMTs, and Eaton can’t count them like it does its own products. Those proprietary products are catching on quickly:
Volvo: Almost 70% of Volvo trucks with Volvo engines – which in turn is 87% of production – have the I-Shift, reports Chris Stadler, product marketing manager, powertrain components. Volvo also sells Eaton UltraShift Pluses in trucks with Cummins diesels, and Allison automatics with some Cummins Westport natural gas engines.
Introduced in 2007, the 12-speed I-Shift is now standard in most Volvo models. Customers can still take a manual transmission in exchange for a credit of about $2,000.
“We’ve gone up 15 points in one year” with the I-Shift, Stadler says. “It’s taken off a lot quicker in the last few years, faster than anyone imagined. Integration of engine with transmission created the fuel economy advantage.”
Mack: Mack’s mShift, based on the I-Shift and electronically altered to match the power and torque characteristics of Mack diesels, went into 40% of Pinnacle models last year, “and we expect it to continue growing in the future,” says Roy Horton, powertrain product marketing manager. Mack also sells Allisons in its MR refuse trucks, its MHD (medium heavy duty) models, and with some Cummins Westport gas engines.
“Manual transmissions represent about half of our overall truck sales,” he adds.
Daimler Trucks North America: Detroit’s DT12 AMT is gaining quick acceptance in Freightliner trucks, accounting for almost 10% of Cascadia sales last year, says Brad Williamson, manager, engine and component marketing for DTNA.
This Mack Pinnacle tractor’s mDrive transmission has a keypad selector on the dash. A lever type is optional.
“Many who ordered some of the earliest production units are now coming back for additional units, and some have even changed all of their 2014 orders to the DT12. We are anticipating that number will grow in 2014 and beyond.”
For now, the DT12 is an on-highway transmission, but Detroit will sooner or later offer it with power take-off mounts for vocational trucks. Daimler continues to offer Eaton automated and Allison automatic transmissions.
Allison: Allison has long been an important vendor to OEMs, and its latest product is the TC10. “TC” means twin countershaft (as in mechanical gearbox) and torque converter, and the transmission has both. It also uses planetary gearsets and wet clutches to deliver continuous power, which makes it automatic rather than automated.
It went into production in last year’s fourth quarter and “has been very well received by end-users,” says Lou Gilbert, director of North American marketing and global brand development.
Allison’s 4000 series full automatics remain standard equipment in most heavy trash-collection trucks, and are being promoted in heavy construction trucks in a Paydirt program that ends this month. The 1000, 2000 and 3000 series automatics continue to take a large share of Class 6 and 7 medium-duty truck sales and are offered by all domestic OEMs.
Midrange: Class 2-5 commercial trucks are almost completely given to automatic transissions. General Motors uses the Allison 1000 in its Class 2 and 3 Chevrolet and GMC trucks with Duramax diesels, and its own Hydra-Matics with gasoline engines. Aisin automatics go into Ram domestic and Isuzu imported diesel trucks, and Ram uses a Chrysler automatic with gasoline engines. GM’s Hydra-Matic is used with a GM gasoline engine in Isuzu’s Class 3 NPR Gas truck. Ford uses its own TorqShift automatic up to F-650, and later will employ it in the new F-650 and F-750 series due out next year.
Mitsubishi Fuso alone uses an automated mechanical transmission, called Duonic, in its Class 3 and 4 trucks.
This concrete truck’s vocational-type Eaton UltraShift Plus transmission has a keypad selector mounted to the driver’s right. The colorful paddle device has controls for the mixer drum.
Putting it together
In a recent development in heavy-duty road tractors, automated manual transmissions are increasingly paired with proprietary diesels specially tuned to cruise at 1,150 rpm to 1,175 rpm. This is right in the engine’s torque peak and 150 rpm to 200 rpm slower than before (which in turn was 200 rpm less than was common 10 years ago).
Volvo calls this “downspeeding” and sells it in its XE (exceptional efficiency) package. Mack’s version is called Super Econodyne. Detroit doesn’t have a specific name, but its DD13 and DD15 engines likewise loaf when mated to a DT12 AMT. So does a Cummins ISX15 with an Eaton UltraShift Plus 10-speed in the Smart Advantage package, and the companies just announced a version using the Cummins Westport ISX12 G natural gas engine.
Low engine speed cuts internal friction and uses torque to keep a rig moving. This reduces fuel use by 3% to 5% over faster revving engines. The AMTs quickly and smoothly downshift to maintain performance on upgrades or while passing, then upshift again to slow their engines and resume maximum economical cruising. They float shift (without the clutch) and when needed, they engage and disengage their automated clutches more delicately than most drivers can.
A skilled driver with a multi-speed manual transmission can try to duplicate that computer-aided precision, but can seldom do it all day, every day like an AMT can.
Precise and consistent operation of all AMTs, even with higher-speed diesels, save 2% to 6% in fuel, the manufacturers say. This can rather quickly pay off the upcharge. AMTs also reduce wear and tear on clutches and drivelines, and greatly ease the work of drivers. Because they’re so much easier to operate than manuals, AMTs expand the pool of potential drivers for any fleet.
A manager can hire the best people he can find and teach them to drive – easy with an AMT compared to a non-synchronized manual – instead of being limited to the best drivers available.
Downspeeding makes proper gearing even more vital than it’s always been, the manufacturers note. The ratios of a transmission’s top gear and the truck’s drive axle must be carefully calibrated with wheel and tire size to keep the engine revving where desired. Most AMTs use overdrive ratios in their highest gears, so axle ratios needn’t be as fast – numerically low – as they otherwise would. But with an engine spinning at 1,150 rpm, the axle will be faster than if the engine cruised at 1,350 or higher. Sharp sales people using good spec’ing programs can quickly set up these details.
Trucks equipped with automated manual transmissions, like this Volvo VHD, have a lever or push-button shift selector but no clutch pedal, because the clutch is automated, like the transmission.
Manuals still lead
If 30% of all Class 8 trucks had automated or automatic transmissions last year, then 70% still had manuals, so they still constitute a large majority.
Builders say manuals typically are bought by large fleets whose executives want to save purchasing dollars, and by individual operators who as a matter of pride and satisfaction would rather shift for themselves. Other buyers need to cut weight, or want to keep things simple, which is increasingly difficult in this age of engine and chassis complexity.
Ten-speed transmissions remain the most common manual type for heavy highway trucks, though 13- and 18-speed boxes are popular among owner-operators and are usually used with high-horsepower engines. Trucks employed in construction and other vocations tend to have 11-speed “low-low” transmissions with three ratio ranges instead of the two in highway transmissions. Maxitorque products are especially popular in Mack’s own vocational trucks, and Mack builds its own manuals for highway tractors while also offering Eaton manuals.
Eaton makes by far the most manual gearboxes for Class 8 trucks. A recent innovation from Eaton is the Fuller Advantage transmission that runs without a lube-oil cooler. This does away with the cooler and its 10 feet of external hoses, while the amount of oil is cut by 7 pints, from 24 to 17. With less oil to churn, parasitic loss is reduced and fuel economy is 1.7% better, Eaton’s Trzybinski says.
The cooler-less design is also used in the Smart Advantage AMT. Both have overdrive top gears because they are the most popular type of 10-speed. Overdrives benefit more from reduction of oil churn because the OD gear set continues to cause its own churn – something advocates of direct-drive transmissions have wagged their fingers at for years (even though a fuel economy benefit is hard to measure). But the Advantage design could be applied to direct-drive 10-speeds, and possibly to multi-speed transmissions.
Meanwhile, more direct-drive top-gear models are being sold as some trucking operations change from longhaul with high gross weights to regional haul with lighter loads, Trzybinski reports. A more lightly loaded rig needs less overall ratio coverage (a relationship between transmission and axle gearing). The lighter rig might need 15.4 overall ratio coverage instead of the heavier rig’s 17.3, so the overdrive top gear can be eliminated.
One final note: While automated transmissions now dominate the heavy truck market in Europe, manuals are still favored in lighter trucks and cars. While driving them, Europeans simply prefer to shift for themselves.
Over here, it’s the opposite. Ram’s heavy-duty pickup in base trim is the only light truck still available with a manual transmission, a Mercedes 6-speed (a holdover from the days of Daimler ownership of Chrysler). It costs less to buy, but the manual’s rarity commands a premium when it sits on a used-vehicle lot because there are still gear-jammin’ enthusiasts among Americans.