ZF Develops 8-Speed Automatic Transmission for Passenger Cars; 6% Additional Fuel Savings, and Support for Hybridization
2 May 2007
|The basis of the new ZF automatic transmission generation is a new transmission concept featuring four planetary gear sets and five shift elements.|
ZF has designed a new 8-speed automatic transmission for passenger cars based on a new transmission concept featuring four planetary gearsets and five shift elements. The automatic ZF 8-speed transmission enables additional fuel savings of approximately six percent compared to the current generation of 6-speed transmissions. Compared to a 5-speed, the new 8-speed reduces fuel consumption by about 14%.
At the same time, the automatic 8-speed transmission transmits more power in comparison to the previous model, but uses the same installation space and does not require more components.
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. The number of gears was not given top priority.—Dr. Michael Paul, ZF Executive Vice President, Technology and Group Executive of the Car Driveline Technology division
|Better transmission spreading and a significantly better internal efficiency allow for consumption savings of up to six percent in the new ZF automatic 8-speed transmission compared to the direct predecessor model with six speeds. Click to enlarge.|
In the new design based on the four planetary gearsets and five shift elements, only two shift elements are opened in each gear which leads to considerably lower drag losses.
Besides the improved internal 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. 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 new transmission has been designed in such a way that it can serve as a modular system for hybrid and all-wheel applications without changing the basic transmission concept.
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.
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