ZF Develops Automatic 8-Speed Transmission for Passenger Cars
"Our main development target was to find a transmission concept which allows for significant additional fuel consumption reduction and thus offers tangible added value to our customers and drivers without making any compromises in terms of performance", explains Dr. Michael Paul, ZF Executive Vice President, Technology and Group Executive of the Car Driveline Technology division. "The number of gears was not given top priority."
Fuel consumption savings as development target
The new, more powerful ZF multi-ratio automatic transmission allows for consumption savings of six percent. This means that the excellent consumption values of the second-generation automatic ZF 6-speed transmission which entered volume production only in 2006 have been further improved considerably. To make it clear: Compared to an automatic 5-speed transmission which is still widely used today the consumption reduction amounts to approx. 14 %.
Two innovations are mainly responsible for these spectacular consumption values. Compared to the automatic 6-speed transmission, the basis of the new ZF automatic transmission generation is an entirely new transmission concept featuring four planetary gear sets and five shift elements. Only two shift elements are opened in each gear which leads to considerably lower drag losses. Besides the improved efficiency, this transmission concept features a higher total ratio. Modern torsional vibration damping systems in the torque converter also have a positive impact on consumption and CO2 emissions. These systems also allow for a quick lock-up of the converter clutch in the second generation automatic 6-speed transmission presented in 2006. Furthermore, ZF now uses a small vane cell pump mounted parallel to the axle.
Another development focus was the increase in performance. The power-to-weight ratio of the new automatic transmission is higher and can transmit a higher input torque at the same weight, in comparison to the previous model. The automatic 8-speed transmission gets by with the same installation space as the previous versions made by ZF. In terms of shift comfort, response and shifting speed, also the new automatic 8-speed transmission operates at the already very high level of the second generation of the automatic 6-speed transmission.
The equipment options offered with the new automatic 8-speed transmission for passenger car driveline technology are trend-setting. The new transmission has been designed in such a way that it can serve as a modular system for further starting and all-wheel concepts without changing the basic transmission concept. This way, a torque converter could be replaced by new clutches or could be omitted completely when an integrated starting clutch is used. The design engineers of the automatic 8-speed transmission have also paid attention to the compatibility with today's and future ZF all-wheel concepts.
For the hybridization of the driveline, the automatic 8-speed transmission offers the possibility of implementing both a micro hybrid with a crankshaft starter generator and a full hybrid in the form of a parallel hybrid. All known hybrid functions can thus be implemented in combination with the new automatic 8-speed transmission.