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Automatic 8-Speed Transmission for Better Fuel Economy
ZF has designed a new automatic transmission generation for passenger cars: With the automatic 8-speed transmission the chassis and driveline specialist succeeds once more in combining seemingly contradictory goals. The automatic ZF 8-speed transmission allows for additional fuel savings of approximately six percent compared with the already optimized automatic 6-speed transmission of the second generation. This is achieved above all by a completely new transmission concept. At the same time, the automatic 8-speed transmission transmits more power in comparison to the previous model, but still gets by with the same installation space and does not require more components. Last week, the new 8-speed transmission was presented for the first time at the 28th International Vienna Motor Symposium.
“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 economy as development target
The new, more powerful ZF stepped-ratio automatic transmission allows for fuel economy savings of around six percent, improving further upon the excellent consumption values of the second-generation ZF 6-speed automatic transmission which entered volume production in 2006. When compared to an automatic 5-speed transmission which is still widely used today, fuel consumption is reduced by about 14 percent.
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 fuel economy and CO2 emissions. These systems also allow for a quick lock-up of the converter clutch in the second generation 6-speed automatic transmission. 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.
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