Friedrichshafen, Germany/Kortrijk, Belgium. Lower fuel consumption, less noise pollution, greater comfort and performance, combined with a broad torque range put the ZF-EcoLife 6-speed automatic transmission into a class of its own. The stop/start function combined with the engine that can be switched off contributes to this by enabling major fuel savings in urban use. The Dutch manufacturer VDL Bus & Coach has been volume producing the automatic transmission with stop/start function since the end of 2016 and the savings potential produced by this operation has been proved
"We are delighted that the stop/start function in ZF-EcoLife can demonstrate its benefits in daily use. Together with the already established cost-effectiveness of the transmission, it offers the operator an additional increase in efficiency," says Andreas Moser, head of the Axle & Transmission Systems for Buses & Coaches Business Unit at ZF.
When subjected to the current IBC test for 2017, the VDL Citea with EcoLife with the start/stop function showed the best consumption data by a wide margin.
Made for one another
City buses are often stuck in stop-and-go traffic, waiting for red lights or roadworks, as well as stopping at the many designated stops en route. The stop/start function in the ZF-EcoLife automatic transmission is suited to the city bus. This new function automatically shuts off the engine when the bus comes to a standstill, reducing fuel consumption levels to zero. As the driver moves their foot from the brake pedal to the accelerator pedal, the engine and the transmission system are ready for an immediate start. From a transmission perspective, ZF has mastered, in addition to the basic fuel savings, the particular challenges regarding the high activation frequency and the very short transmission response times. This gives the vehicle manufacturer complete flexibility with regard to the vehicle-end implementation of the stop/start strategy. The stop/start function is available for the most frequent maximum engine torques, ranging from 1,000 to 1,600 Newton meters, which are required in city buses.
Fine-tuning with a big impact
The converter and the lock-up clutch are reinforced, improving the robustness of the transmission. The present hydraulics system has been adapted to meet the challenging response times. These design enhancements were integrated into the current volume production transmission. This underlines again the flexible and robust basic design of the ZF-EcoLife transmission.
For the stop/start function to operate effectively even after a longer engine standstill, it is essential that the transmission's shift elements are refilled with oil as soon as the accelerator pedal is engaged – only then is the vehicle ready to pull away. To ensure this, there was no need for ZF to develop and install an external oil accumulator for the ZF-EcoLife application, as the ZF primary retarder was easily integrated into the transmission.