ZF begins volume production of plug-in hybrid transmission

ZF has begun volume production for its groundbreaking hybrid drive technology. The BMW X5 xDrive40e will be the first model worldwide to feature the new ZF plug-in hybrid in volume production.

The company has integrated a high-performance and compact electric motor into its latest 8-speed automatic transmission generation. Based on this, it created a hybridized drive system that has been specifically designed to meet plug-in requirements. Vehicles can now be driven purely electrically, i.e. with zero local emissions, over comparably long distances and significantly faster with up to 120kph. As a result, the standard cycle according to ECE 101 shows fuel reductions by up to 70 percent – depending on the capacity of the battery system. Furthermore, the ZF automatic transmission and the combustion engine act as well-matched driveline partners, which ensures the usual high level of efficiency and dynamic qualities.

"Electrifying the driveline is an essential means for ZF to further increase efficiency and significantly reduce emissions," emphasises Dr. Stefan Sommer, CEO of ZF Friedrichshafen AG. "As plug-in hybrid vehicles become more prolific, consumers are exposed to the performance capability of hybrid technology in general, for which we expect demand to increase for a long time, and our plug-in hybrid transmission in particular. It makes individual mobility more environmentally friendly, more dynamic, and also more sustainable, and is completely suitable for everyday use at the same time."

The most significant difference of the modularly designed ZF hybrid transmission compared to the volume-produced 8HP is its integrated electric motor, which is placed in the housing instead of the torque converter and fits into any available installation space.

Despite its compact dimensions, the electric motor proves to be very strong. For the BMW X5 model, it provides a maximum power of 83 kW (113 HP) and a torque of 250 Nm from a standstill. That means that the vehicle can be driven purely electrically at a speed of up to 120kph and within a range of 31 kilometres. When the vehicle decelerates, the electric motor is used as a generator to convert the braking energy into electric energy and to charge the battery.

Focus on purely electric driving
ZF says it is focusing on the plug-in functionality with the new generation of hybrid transmissions based on the 8-speed automatic transmission. Purely electric driving thus represented one key area of development. To this end, the drag torque of the separating clutch to the combustion engine must be as low as possible.

In addition, clearly improved torsional vibrational decoupling better supports the downsizing and downspeeding concept. The functionality of the starting element has been improved and the associated comfort has increased: Two dampers have been installed to reduce the torsional vibrations of the combustion engine; one is configured as a speed-adaptive damper. Thus all current combustion engines can be operated at high load from idling speed without annoying noise or vibrations.

The electric motor, which is designed as a permanent-field synchronous machine (PSM), is integrated fully into the transmission housing and is cooled by atomized oil.

The integrated starting element is able to transfer up to 550 Nm of starting torque. Comfort and robustness have been improved, compared to the previous generation, by introducing a host of measures in terms of mechanics, hydraulics, functionality, and manufacturing.

Modular hybrid kit
The hybrid construction kit from ZF presents diverse application possibilities: Based on hybrid-capable basic transmissions, individual tailor-made solutions are coming to life. The hybrid components used are part of ZF's product portfolio. One core component is the electric motor; it is available in various output versions depending on the hybrid class. For full hybrid applications, ZF also supplies a hybrid module with an integrated separating clutch – a technical precondition for purely electric driving. Another key factor is efficient hybrid management: Only then can perfect interaction between the hybrid hardware, control electronics, software, and power electronics be ensured. ZF customers benefit from the fact that the technology company develops all components itself.

This comprehensive system expertise facilitates the integration into a cost-efficient and versatile overall system: Mild, full, and plug-in hybrid applications can be realised with a high percentage of identical parts, thus creating major synergy effects.