With a focus on improving both fuel economy and drivability, ZF will introduce a new family of 8-speed automatic transmissions—capable of handling up to 900 Nm of torque—in the 2010 model year. The newly developed 8-speeds will provide a 6% fuel economy benefit over existing 6-speed transmission systems, the company claims. Development of the transmission system took root in 2004 when engineers scrapped plans to modify ZF’s existing 6-speed architecture to accommodate two extra speeds: “At the end of the day we realized this type of solution was not a big leap forward. Our plans would have had too many open clutches, which would have produced too much drag force,” says Harald Naunheimer director of car driveline technology at ZF. Engineers decided to take a “completely new approach” with a new architecture that adds only two shift elements that has only two clutches open during operation for better response with a more direct shift feel: “We go from one speed to another just by closing one clutch and opening another,” Naunheimer explains.
The transmission also was designed to accommodate various hybrid applications, from start/stop to full-hybridization. “The complete system is modular on the input side and we can replace the torque converter with a hydraulic clutch and introduce an electric motor,” Naunheimer says. For mild-hybrid applications, ZF engineered a hydraulic storage system at the rear of the transmission that is spring loaded for instantaneous delivery of fluid to the transmission when the engine restarts. ZF has a production contract for the full-hybrid solution, which is expected to improve fuel economy by up to 20%, for introduction after 2010.—KMK