Shifting to Automated Transmissions
Automatics are the choice in more than half of all new medium-duty trucks, but self-shifting transmissions in various forms are built into only a small number of heavy-duty units. Yet that number is growing, simply because automated shifting makes it physically easier to drive big trucks. And that is important to companies trying to recruit and train new drivers.
Technology is helping to set a trend that could have a major impact on over-the-road trucking, mainly by reducing driver workload. The key is faster communication between the engine and the transmission. Truck drivers may not know much about the J1939 high-speed data link, but it lets them keep their attention on the road rather than on the gear shift.
Developed by the German company Bosch and adopted in North America by the Society of Automotive Engineers, the J1939 runs as much as 10 times faster than previous data links. It allows automatic transmissions in trucks to operate more efficiently and cheaply.
The J1939 link is “quicker, smarter and bigger” than previous data links, said Al Lesesky, president of Vehicle Enhancement Systems in Rock Hill, S.C., and a consultant on electronics for heavy trucks.
The electronic stream of the advanced link runs at 250 kilobaud — 250,000 bits of data per second. This capacity makes room for antilock braking, with its automatic traction control, to send messages to the engine between the data spurts from the transmission.
J1939’s baud rate also means the reaction of electronic controls is more agile. The engine tells the transmission how fast it’s spinning and, through the speedometer sensor, how fast the vehicle is traveling. The transmission reacts to that information and to power demands from the driver, through the electronic accelerator pedal, to pick the right gear for the situation.
If a shift is needed, the transmission tells the engine to speed up or slow down to synchronize gear speed. This is what the driver does on a double-clutch or float-shift (without the clutch) on a manual transmission, which on a heavy truck has no mechanical synchronizers. With automation, the transmission and engine synchronize to make gear changes, leaving the driver free to keep the truck under control.
The engine-transmission interface also can be made with mechanical links. Vacuum and pneumatic lines controlled shifting of automatic transmissions in the “old days,” but they are more complex and less precise. Now, electronic data links greatly improve the function, leading to a number of new products from manufacturers.
Electronic controls and data links were adopted by General Motors’ Allison Transmission Division for its latest fully automatic products and some earlier models. Allisons have a big following in urban and suburban service. They go into almost six of 10 new mid-range trucks, as well as in most school and transit buses. Demand is so high that Allison can’t build enough.
Such demand creates opportunities for automated mechanical transmissions — AMTs — from other builders. Eaton, Meritor Wabco and Transmission Technology Corp., which makes Spicer-brand products, now offer transmissions with varying degrees of automation. The more work the electronic controls do, the higher the price. But most AMTs cost one- to two-thirds less than Allison’s full automatics.
Lower price means AMTs eventually will take some market share in mid-range trucks from Allison, their makers believe. Transmission Technology thinks manual products will keep a third of the market, with Allison and other manufacturers splitting the remainder evenly.
Large-scale conversions to “shiftlessness” began last year for highway fleets. U.S. Xpress and H.O. Wolding are among carriers that began purchasing tractors with Eaton’s AutoShift, which retains a manual clutch and clutch pedal for starting and stopping but does most of the shifting work.
Previously, fleets bought lesser forms of automation that shifted only the top two gears. But this constitutes more than 90% of the shifting work once a highway tractor is under way. Various Fuller and Spicer transmissions have this feature.
For the full story, see the March 29 print edition of Transport Topics. Subscribe today.
