Hybrid and dual clutch transmission modules are now offered to the heavy truck sector as options with ZF’s TraXon modular platform. In addition to the conventional torque converter and dry clutch modules, this basic, compact transmission can be specified with TraXon Hybrid, integrating a 120 kW, 1000 Nm electric motor, and the TraXon Dual module, promised to deliver barely-perceptible gearshifts plus enhanced fuel economy and driver comfort.
The basic TraXon transmission can transmit torque of over 3000Nm, and can be ordered with 12 or 16 forward gears and two or four reverse gears; overdrive is an additional option. TraXon is said to emit 6 dB less noise than ZF’s previous AS Tronic system, thanks to its new design, improved housing and anti-rattling damper. ZF claims efficiency of 99.7%.
TraXon Dual requires little modification over the basic unit, says ZF, but its parallel partial clutches give particular benefit in the upper gears and allow for “long” rear axle ratios, aiding fuel economy on long-distance trips. Shifting between the upper gears—enabling the driver to optimize the transmission ratios both for performance and economy—is a more comfortable, less disruptive process. This is due to the quick shifts and, with most gear changes, lack of interruption to the tractive force. This benefit also applies to starting off in the lower gears.
Fuel efficiency is further enhanced by the TraXon Hybrid module, mounted in the clutch bell housing. This enables functions including all-electric driving at low speeds and for short distances, boosting of the combustion engine, start-stop to cut the engine when idling, and energy recuperation, which can direct otherwise wasted energy for auxiliary power supply to items such as cooler units and to electrical features in the driver’s cab. It has the potential to facilitate additional functions, such as “coasting”—the switch-off of the diesel engine when rolling, giving potential fuel savings of around 3%—as well as the fitment of quiet, efficient electric PTOs (Power Take-Offs) rather than noisier mechanical units, such as those currently used in municipal waste trucks or ambulances operating in residential areas.
The projected fuel saving of around 5% for the hybridization of heavy commercial vehicles is less than the 20% ZF suggests is possible in the lighter-weight delivery vehicle sector. However, “…with the considerably higher mileage and fuel consumption of heavy trucks, hybrid technology is nevertheless an economical solution that goes easy on resources and pays off within a reasonable time period,” says Winfried Gründler, Head of Truck and Van Driveline Technology, ZF. “Studies have shown that the use of hybrid drives in heavy trucks bears considerable savings potential.”
Arguably the cleverest innovation in the TraXon platform is in its control system, which uses sensors to constantly monitor speed, pitch and direction of rotation, and allows the integration of predictive technologies. The satellite navigation-based PreVision GPS directly feeds location and map data into the transmission to select the optimal gearshift for the upcoming terrain or road topography, or to prevent an unsuitable gearshift which might compromise fuel efficiency. It anticipates factors such as steep hills, ongoing sections of mountainous roads, or sharp bends and sudden curves.
PreVision GPS can also work with the “coasting” function to simply decouple the driveline when the truck is rolling (down a gentle slope, for example) and to predict when the transmission should be put back into gear, or to apply brakes as necessary. These anticipatory gearshift strategies have the potential to reduce trip times, as well as fuel consumption and tailpipe emissions, smoothing out progress and maintaining optimum speeds.
The TraXon Hybrid and PreVision GPS technologies are both showcased in the ZF Innovation Truck, presented at the September 2014 IAA Commercial Vehicles Show in Hannover. The Innovation Truck—a 25.25 m-long tractor-trailer combination—can be remotely maneuvered at low speeds (and with zero emissions) by using a tablet app, is compatible with autonomous steering systems and features advanced Bluetooth-enabled telematics.