How many speeds does an automatic transmission need? According to ZF, the answer is 8. Their aim was to minimize fuel consumption while maximizing performance and according to ZF, this new 8 speed delivers a 6 percent fuel saving over their 6 speed and 14 percent over a 5 speed. It requires no more installation space than a 6 speed and the modular design can be adapted for use with AWD and hybrid drivetrains.
ZF Press release follows:
ZF has designed a new 8-speed automatic transmission generation for passenger cars. The new 8-speed transmission allows for additional fuel savings of approximately six percent compared with the optimized second generation of 6-speed automatic transmission, with increased torque capacity, while utilizing the same installation space without requiring more components. This is achieved through a completely new transmission concept.
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 consumption savings 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.
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, leading to considerably lower drag losses. In addition to the improved efficiency, this transmission concept features a higher total ratio spread.
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. Furthermore, ZF now uses a small vane cell pump mounted parallel to the main axis.
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, while utilizing the same installation space as a 6-speed. In terms of shift comfort, response and shifting speed, the new 8-speed transmission operates at the already very high level of the second generation of the ZF 6-speed automatic.
The equipment options offered with the new automatic 8-speed transmission are trend-setting. The new transmission has been designed in such a way that it can serve as a modular system 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. Design engineers have also paid attention to the compatibility with current 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 8-speed automatic transmission.