A Major Shift
How automated transmissions keep changing trucking
By Paul Abelson
Perhaps it’s just a matter of ego, but one of the things that always separated truckers from passenger car drivers was the ability to shift multi-range transmissions. Today, an entire generation of motorists is clueless when faced with a standard transmission.
In the mid-1950s, when I learned to drive, we had only 3-speed column shift gearboxes. The Drivers Ed teacher believed that if you could drive with a clutch, you could drive anything. He was right. First gear was not synchronized in those “3 on the tree” days, before “4 on the floor” became popular. To get into first, you had to come to a stop or learn to double clutch and match vehicle and engine speeds. That skill demonstrated its value when I learned to drive trucks.
Truckers not only learned double clutching, many mastered the art of twin stick shifting, using a main and auxiliary transmission, each with its own control. Terms like 4X3, 5X2 and 6X4 defined the numbers of gears in the main and auxiliary boxes, yielding as many as 24 forward speeds. As a result, trucks were controllable, but at the end of a shift drivers had aching left legs and sore right shoulders. Safety was an issue as drivers took their eyes off the road to match tachometer and speedometer readings while trying to master three pedals with two feet.
Many drivers learned to “float the gears.” If you released torque by lifting the throttle, shifting into neutral and adjusting engine rpm for the next gear, you could shift by letting the gears float together without using the clutch. Even though all transmission makers frowned on clutchless shifting, the veterans rarely missed shifts or ground gears. But “rarely” doesn’t mean never. And missing shifts contributes to transmission wear. Damage was slight but progressive. Over time, it could become significant.
Range selector mechanisms, developed first by Fuller Manufacturing, integrated the two gearboxes using air to engage overdrive gears. But it wasn’t until the early 1990s that Eaton introduced the first step toward true automation: the Top 2. These transmissions, usually 10-speeds, used a computer to shift between the top two gears. Research showed that for long -haul drivers, more than 90 percent of total shifts were between those gears. From 1 into 9, it was still a manual box.
Automatic transmissions were available from Allison, but due to cost and complexity, they were generally confined to vocational applications.
Truckers needed a way to keep the benefits of a manual transmission and still have convenience of an automatic. That was the genesis of the automated manual transmission (AMT). In the late 1990s, Eaton computerized the method of floating gears used by skilled drivers. The then-new SAE J1939 data sharing protocol allowed the transmission’s computer control to share information and commands with the engine control unit (ECU).
Eaton’s AutoShift still required the driver to depress the clutch pedal when starting and stopping until the truck was in neutral or under way. Once rolling, the transmission controller told the ECU when to apply torque and when to ease off and to tell the shifter when to float the gears. With the computer control, every shift was perfect. If a shift couldn’t be completed because it would lug or overspeed the engine, the computer would not initiate the shift.
The first time I drove an AutoShift, I went over the Ozark Mountains across Missouri. There were long 6 percent grades where I would never try to shift gears for fear of getting stuck in neutral and losing all engine braking. With the AutoShift in manual mode, I stab-braked to cut speed and pushed the button to get to a lower gear. It worked, sometimes twice on the same hill, proving its worth as a safety feature.
The market grows
Soon others entered the AMT market. Automation actually started in Europe, and Meritor teamed up with Germany’s ZF to introduce the Freedom Line. Originally available in either 12- or 16-speed, the Freedom Line had a computer-actuated clutch, so no clutch pedal was needed. It was the first two-pedal (throttle and brake only) AMT in North America.
Throughout the first decade of the 21st century, Eaton and ZF-Meritor battled in the courts over patent issues while Eaton continued to develop its AMT line. Improvements in computers allowed Eaton to add a computer-controlled clutch. The resulting two-pedal transmission was called the UltraShift. Over time, variants tailored for specific applications were introduced.
Today, Eaton features six models under the UltraShift PLUS label. All share Hill Start Aid software and sensors that, when engaged, prevent rollbacks for the first few seconds after brakes are released. Start-up on hills is simpler and safer, especially for novices. Gear selection and shift decisions are based on grade-sensing, and weight computation as well as driver commands. Working with the engine controller, sensors look at throttle position and the rate of pedal movement to calculate the driver’s demands.
In the last few years, Europe-based truck makers have adapted their proprietary transmissions for American highway and load conditions. First was Volvo with its I-Shift, a two-pedal 12-speed designed to operate with Volvo’s own engines.
When an AMT is mated to a nonproprietary engine, commands and data are exchanged in general terms because the multi-dimensional calculations engine makers develop for performance and economy are not shared outside the company. A transmission and engine made by the same manufacturer can be programmed to work together more precisely and save an additional percent or two in mpg.
Volvo’s I-Shift adds measurement of torque demand, and air and rolling resistance to weight, throttle demand, vehicle speed and grade changes to select the optimal gear for the Volvo engine it’s mated with. Its Eco-Roll feature uses the truck’s kinetic energy to allow the engine to disengage when going down moderate hills, rolling out longer before returning to power and so saving as much as 2 percent fuel when used. I-Shift also has an optional kick-down feature with three programmable settings and an option to select between economy and performance modes. These are a few of the features available when engine and transmission share data without restriction.
Mack’s mDRIVE is part of the Volvo family and shares many of the I-Shift’s features just as Volvo and Mack share many engine features. Demand for automated transmissions has risen to the point that Mack and Volvo recently made them standard equipment on their trucks.
Last year, Detroit introduced the DT12, a 12-speed AMT designed to work with Detroit engines used by Freightliner and Western Star. It has many of the same features as its counterparts, including eCoast to maximize fuel efficiency by letting the engine idle while cruising down steep grades. Its variable speed cruise control allows the engine brake to control speed: +3 mph when in low for steep grades; +6 mph when in medium for rolling hills; off for flat terrain and areas with noise restrictions. The engine brake is disabled when in cruise control.
With most proprietary truck makers building their own engines and transmissions, Eaton has announced partnerships with Cummins and PACCAR to develop UltraShift PLUS gearboxes, taking advantage of the proprietary engine data from each manufacturer. They also announced a new series of transmissions, the Fuller Advantage Series, in both manual and AMT versions, to be available the first quarter of 2014.