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August 24, 2012

Detroit's New Automatic is a Fuel Saver

The automated 12-speed transmission from the Detroit brand of Daimler Trucks N.A. was rolled out in August. It's the latest automated transmission introduction to the N.A. truck market, with calibrations and programming new for the North American operating environment. However, the mechanicals within the transmission have been well proven in millions of miles and over a hundred thousand Mercedes-Benz cabovers in Europe and other world markets, often at far higher gross combination weights than our 80,000 pounds. The transmission will be available in the Freightliner Cascadia Evolution starting in May 2013.

The Detroit DT 12 is a three-speed main transmission with a range-change and hi-lo splitter to give 12 forward speeds and an available four speeds in reverse. The single countershaft and aluminum casing give it a weight advantage of 100 pounds compared to Freightliner's existing offering – the Eaton Ultrashift Plus – which will continue as a second automated transmission option. The first Detroit DT 12 transmission is the DA1750 direct rated 1,750 pound-feet and the OA2050 overdrive at 2,050 pound-feet. It will be the larger of a pair of transmissions: later in 2013, the lighter B transmission DB1550 and OB1650 with input torques reflected in the model designations will be available with weight savings of 680 pounds compared to the Eaton.

According to the company, the DT 12 has a number of features and some significant benefits compared to competitive transmissions, with the shifter the most apparent. This is a steering column-mounted shift stalk, though somewhat more robust than the usual column stalk. It’s a convenient alternative to the visually unappealing dash-mounted shift pad. Like the pad, though, it doesn’t impede a driver's passage through the cab or into the sleeper.

In use, the DT 12 can be operated in automatic or manual. In either case, pulling the shifter up towards the wheel initiates upshift; pressing away, downshift. In the end of the lever is a switch to allow users to select Auto or Manual mode, or a quick touch selects Economy or Performance shift schedule. This same column shifter is also the selector for the engine retarder, with off, two, four and six-cylinder brake application as the lever is pulled down through four detents. Forward, reverse and neutral are selected with a rotary switch embedded in the shifter. A neat feature is a neutral reminder and selector if the driver forgets to take the transmission out of a drive position while setting the brakes and keying off.

With the MT 12, there are new features for the cruise control. One is a dash-mounted switch that allows for selection of different levels of "float" in the cruise setting. In low, it will allow speed to gain 3 mph before cruise control applies the engine brake. On medium, it allows twice this margin before application. In the highest position, it removes all interaction with the truck speed, allowing the truck to roll and take maximum flat or mildly rolling terrain.

Another feature designed to improve fuel economy is eCoast. This senses when the truck is rolling on any kind of a downgrade and drops engine torque to zero. The transmission then goes to neutral and the engine speed drops to idle. While this may be considered a little-used feature, in the recent coast-to-coast economy demonstration Freightliner, the demonstration truck was in e-Coast mode for 25% of the mileage covered, accounting for significant fuel savings.

At the other end of the performance spectrum, there is a throttle kickdown switch where a detent is provided in the throttle movement. Punching through this causes a downshift and a change to the fueling schedule so acceleration is akin to the transmission being in performance mode.

In the different shift modes, the transmission will upshift at 1400-1450 to drop back onto peak torque at 1000 rpm; in performance mode, shift points are higher to get the engine into the higher horsepower, shifting at 1700 rpm or more, depending on conditions the transmission recognizes, such as grade, throttle demand, gross vehicle weight and so on.

Upshifting, there is interaction between the transmission and the engine brake. With the proprietary interface, the electronics do a lot more than just speed the shift. Initially, the retarder aggressively reduces engine speed but then as engine speed approaches synchronous between gear and road speed, two cylinders start to fuel even if the other four are still in retarder mode. This keeps the turbocharger spooled up and when the upshift completes, the engine is sooner on power in the next gear. The advantage of this sequence is to punch the shift through as quickly as possible and also to minimize the torque break during the shift. Thus the truck slows less during the shift. Since there is less roll-off of speed, the feature saves more fuel.

Another feature of the advanced communications is driveline protection – the transmission senses engine torque applied and will dial it down to prevent wind-up in the driveline. This protects the drivetrain and provides a more comfortable driving experience, according to Detroit.

The new transmission also has Daimler’s Virtual Technician, the on-board diagnostics and prognostics feature that detects fault codes and transmits them behind the scenes to the Customer Support Center. Service decisions are then based on the nature of the fault code, the mission of the truck and the availability of dealer support.

With implementation of the new automated transmission, there's a new dash display for Cascadia in 2013 that is currently referred to as IDB4. It includes information about the gears selected as well as up and down arrows for shift advice when in manual mode. It also indicates whether the transmission is in Performance or Economy mode. There is also a dash warning light that illuminates with a fault code and activation of Virtual Technician.


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