By Paul Abelson, senior technical editor
At this year’s Mid-America Trucking Show, Volvo Trucks North America made what seems like an industry-changing announcement. Both its operating companies, Volvo and Mack, will soon offer automated manual transmissions (AMTs) as standard equipment. Manual transmissions will still be available, but only as special order. And that means that dealer inventory will most likely be predominantly AMTs.
While much of the company’s technology was developed in Europe, Volvo and Mack do a fair share of customer development here. And marketing decisions – especially with the far-reaching implications of this one – are also made here for North American market conditions.
So how did we get to a point in time when an OEM is offering AMTs as standard equipment?
A look back
In the 1980s when I entered the trucking industry, Eaton and Dana were the leading transmission makers, with Rockwell (now Meritor) holding a smaller but significant market share. Eaton and Dana later exchanged manufacturing facilities and associated technologies, giving Eaton all the clutch and transmission business and Dana the axle and drive shaft business. Roadranger became the marketing and service arm for the products of both companies. Mack held a share of the market, but only in its own trucks.
Eaton’s market research found that, for over-the-road trucking, more than 90 percent of all shifts were made between the top two gears. With overdrive transmissions, drivers could even preselect the upshift or downshift and, by increasing or decreasing throttle pressure, they could complete the shifts. To do that, an overdrive gearbox was needed. The technique wouldn’t work with a nine-speed transmission, the common fleet-spec of the day.
Concurrently, Society of Automotive Engineers members were working on industry standards for communicating computer information and commands through the truck.
If the transmission could tell the engine when to increase or decrease torque, the transmission could automate the vast majority of over-the-road shifts. Eaton introduced that as the “Top 2,” the first step to automation.
The next step was to automate the entire shifting process. Experienced drivers usually shifted without using the clutch. Over time, they developed a sense of the relationship between gears, vehicle speed and engine rpm. They know when to back off the throttle to shift into neutral, and how much to increase rpm to allow the gears to float together in a downshift, or to let engine speed decrease for an up-shift. While transmission manufacturers discourage this floating of gears, many drivers use the practice today.
The computer decision making was simple, and with the engine and transmission communicating, they were able to duplicate the process, with much greater precision. While the best drivers rarely missed a shift, the computers never did. The AMT that resulted was the Eaton AutoShift.
It had a clutch, as the automation process had not yet worked that into the calculations. It was needed only when starting and stopping.
To keep the driver in control, two features were incorporated: hold and low. Hold, now referred to as “manual,” allowed the driver to select hold to keep the transmission in a particular gear. Up or down buttons allowed shifting by the driver to the next desired gear. Low, useful when descending steep grades, allowed the transmission to shift down but not up, providing engine braking but preventing over speeding on less-steep stretches.
The first AMT was based on European transmission architecture. Introduced by a joint venture between ZF of Germany and Meritor, the Freedom Line had no clutch pedal. The computer actuated the clutch. Unlike American transmissions, European boxes had synchromesh transmissions and either 12 or 16 forward gears. Today, those with European heritage are all 12-speed.
Eaton decided to compete with Meritor in the courts rather than in the market place. The case was ultimately won by Meritor, but the delays it cost led to Meritor leaving the market. Meanwhile, Eaton developed a two-pedal (throttle and brake only) improvement on the AutoShift called the UltraShift. It was still based on traditional American transmission architecture, available in 10, 13 and 18 speeds.
Progress also continued on the computer side. Features like low-speed creep, holding on hills without roll-back and better fuel economy became possible through high speed computer-to-computer communication. But to make it all work, secrets like fuel-mapping, the complex and proprietary formulas that determine when and how fuel will be injected, must be shared. And engine makers are reluctant to share their secrets with outsiders. The answer was to control all facets of the system.
Mack and Volvo introduced the mDRIVE and I-Shift to work with their proprietary engines. Detroit, part of Daimler Trucks North America, introduced the DT12 transmission to work with Detroit engines. And Eaton, with no proprietary engine, is working with the two engine builders that have no transmissions of their own: Cummins and Navistar.
Computers are said to double in speed and capacity about every two and a half years. In the roughly 15 years since AMTs were introduced, the power of computers has grown 64 times. That has enabled engine computers to more precisely measure torque demand, grade sensing, vehicle weight and even drivers’ intentions by measuring not only throttle position, but also its rate of change. Soon, these integrated systems will become predictive by adding GPS to determine the grades ahead of the truck and the optimal way to negotiate them. All this will contribute to significantly better fuel economy and less wear and tear on equipment. LL