The 8-speed auto transmission promises six per cent savings over the second-generation six speed auto transmission

ZF has developed a new automatic transmission generation for passenger cars that is ready for market. Expectations are already high that with the automatic 8-speed transmission, ZF design engineers have succeeded in merging seemingly conflicting goals. The ZF automatic 8-speed transmission will add approximately six percent in fuel savings to the fuel savings already achieved with the improved automatic 6-speed speed from the second generation. This is primarily achieved by a fully new transmission concept. At the same time, compared to the previous model, the automatic 8-speed transmission will transfer more power, however, it successfully works with the same installation space and does not require any additional components. "Our main goal in developing this innovation was to find a transmission concept that again considerably reduces fuel consumption, thereby offering our customers solid added value without having to sacrifice performance," explains Dr. Michael Paul, executive vice president, Technology, and group executive of the Car Driveline Technology division. "The number of gears was not a priority in this process."

Fuel savings was a development goal

The more efficient new ZF automatic transmission offers fuel savings of an additional six percent. This considerably improves the already excellent fuel savings figures in the ZF second generation automatic 6-speed transmission, which went into production in 2006. To clarify: Compared to a automatic 5-speed transmission that is broadly used nowadays, overall fuel savings total about 14 per cent.

Two new innovations are mainly responsible for this spectacular fuel saving percentage. Compared to the automatic 6-speed transmission, the basis of the new ZF automatic transmission generation is a completely new gear set concept with four planetary gear sets and five shift elements. Since there are only two shift elements open per gear, the inner drag losses in the transmission are considerably reduced. In addition to the improved efficiency, this transmission concept also has higher overall gear spread. Moreover, the modern torsional damper systems in the torque converter mean better fuel economy and less CO2 emissions. These torsional dampers were also included in the automatic 6-speed transmission launched in 2006 and ensure rapid locking up of the converter clutch. Also, ZF has installed a smaller, axially parallel mounted vane cell pump in this new development.

Versatile combination

A further developmental focus was improving performance. The power-to-weight ratio of the newly developed automatic transmission has been improved; it transfers, with the same weight, a higher input torque than its predecessor. The automatic 8-speed transmission was designed with the same installation space as the previous version from ZF. With regard to shift comfort, response and shifting speeds, the newly developed automatic 8-speed transmission also operates at the already very high level of the second generation of automatic 6-speed transmissions.

The equipment options that the new automatic 8-speed transmission for car driveline technology offers are future-oriented: The new transmission is modularly designed such that it can be used for further start-up and all-wheel concepts without making changes to the basic transmission concept. Thus, the torque converter could be replaced by new clutches or completely omitted with the aid of an integrated starter clutch. The design engineers of the automatic 8-speed transmission saw to it that current and future ZF all-wheel concepts are compatible in terms of combination.

For the hybridization of the driveline as parallel hybrid, the automatic 8-speed transmission offers the option of implementing both a micro hybrid, with a crankshaft starter generator, as well as a full hybrid. All known hybrid functionalities can therefore be depicted in conjunction with the new automatic 8-speed transmission.