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ZF designs new generation 8-speed automatic transmission for hybrid drives

ZF designs new generation 8-speed automatic transmission for hybrid drives
Photo courtesy of ZF

ZF estimates that at least 70% of all new vehicles in 2030 will still have an internal combustion engine. Nevertheless, a plug-in hybrid drive could considerably lower the engine‘s CO2 emissions. This is contingent on electric range and electric power, both of which must allow for driving in everyday traffic with battery power only.

ZF has laid the foundation for this with the plug-in model of the new generation 8- speed automatic transmission. The electric motor has a maximum power of 160 kilowatts and a continuous output of 80 kilowatts. The maximum torque, which can be attained without actuating the internal combustion engine, is 450 newton meters, thus allowing for swift passing, even in e-mode. This does not require a significant increase of the packaging size since ZF relies on a new generation of internally developed electric motors and uses welded copper rods instead of coiled copper wire. This technology, known as the “hairpin technique,“ allows the copper fill level to be significantly increased, which has a decisive impact on the power density.

Traditionally, hybrid transmissions are built by taking an efficient automatic transmission and replacing the torque converter with an electric motor with a higher power density. ZF has now turned the tables by intelligently designing its new generation 8-speed automatic transmission for hybridization from the start. The modular construction system enables mild, full, and plug-in hybrid drives to achieve top performances between 24 and 160 kilowatts. The power electronics are no longer designed as a separate unit, but instead are fully integrated into the transmission housing without increasing the outer dimensions of the transmission. With a new, significantly smaller hydraulic control unit, ZF has created the required installation space for the electric and electronic components.

Each additional component of the new 8-speed construction kit was also intelligently designed for hybrid operation. This is clearly evident when it comes to the oil circuit. Previously, two oil pumps were used: a very efficient vane cell pump driven directly by the internal combustion engine and a second electric pump and/or pulse memory for electric operation. In the future, a single power-split pump will be used. When the internal combustion engine is shut down, it is driven by a small, directly attached electric motor. The mechanics of the new transmission system also contribute to efficient hybrid operation. Although the body remains the same with four planetary gear sets and five shift elements, efficiency was further increased by fine-tuning the friction power. Thanks to this, CO2 emissions were lowered by one gram per kilometer during operation with the internal combustion engine. During electric operation, the range has increased accordingly.

ZF will begin manufacturing the new generation 8-speed automatic transmission in Saarbrücken, Germany, in 2022. The market launch in China and the United States will follow shortly thereafter.