ZF Friedrichshafen AG, Friedrichshafen, Germany, has introduced a new generation 8-speed automatic transmission for hybrid drives. Typically, hybrid transmissions are built by taking an efficient automatic transmission and replacing the torque converter with an electric motor with a higher power density, but ZF’s transmission is designed specifically for hybridisation from the start.
The new transmission’s modular construction system reportedly enables mild, full, and plug-in hybrid drives to achieve top performances between 24–160 kW. The power electronics are no longer designed as a separate unit, but instead 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.
ZF stated that it estimates that at least 70% of all new vehicles in 2030 will still have an internal combustion engine (ICE). 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.
The company believes that it 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 kW and a continuous output of 80 kW. The maximum torque, which can be attained without actuating the internal combustion engine, is 450 N m, 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.
In addition to plug-in hybrids with high voltages of around 300 V, mild hybrids are also expected to play a key role in the coming decade. They have a voltage level of 48 V and allow for considerable CO2 savings by generating power through regenerative braking recovery that can later be used as drive power.
Furthermore, mild hybrids are said to lower pollutant emissions by providing additional power during launch and acceleration processes – driving conditions in which conventional internal combustion engines emit a relatively high amount of pollutants in a short amount of time. 48 V drives can be installed on several locations in the driveline. Installation on the crankshaft at the engine output (Position 1) and on the input shaft (Position 2) are particularly efficient.
The new generation from ZF is suitable for both installation types. The electric motor can reach a maximum power of up to 25 kW and thus optimally support the internal combustion engine in virtually all operating parameters.
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.