ZF continues to promote driveline electrification, pursuing a well-founded and target-oriented development strategy to accommodate all the requirements of the automotive future. The technology company focuses on a modular approach which meets the requirements for functionality on the one hand and the commercial demands of the customers on the other. Thus, ZF's portfolio includes all components of an economically electrified driveline—now and in the future: from the electric motor, hybrid modules, control units and power electronics, right up to complete, plug-in-capable hybrid transmissions.
"Electrification of the vehicle driveline is not a single goal for ZF," says Michael Hankel, member of the Board of Management at ZF Friedrichshafen AG and responsible for the Car Powertrain Technology and Car Chassis Technology divisions. "The essential aim is to reduce the direct and indirect consumption of fossil fuels and, consequently, also CO₂ emissions. Our development strategy for electric drives focuses on this aim."
New transmission generation for plug-in hybrids
ZF is focusing on plug-in functionality with the new generation of hybrid transmissions based on the 8-speed automatic transmission (8HP). Purely electric motoring thus represents 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, the downsizing and downspeeding concept is taken into account by means of much better torsional vibrational decoupling. 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 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 peak output of the electric drive is 90 kW; the constant power is 45 kW.
The integrated starting element is able to transfer 550 Nm of starting torque. Thanks to a host of measures relating to the areas of mechanics, hydraulics, functionality and manufacture, comfort and ruggedness have been improved compared with the previous generation.
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 hybrid modules 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 is developing all components itself.
This comprehensive systems expertise facilitates the integration into a cost-efficient and versatile overall system: Mild, full and plug-in hybrid applications can be realized with a high percentage of identical parts creating synergies. The hybrid transmissions and hybrid components from ZF show their advantages in numerous current volume production vehicles – among other things, the hybrid version of the 8HP is available in the BMW Active Hybrid 7 and the Audi Q5 hybrid quattro. The ZF hybrid module is installed in the Volkswagen Jetta Hybrid.
Power electronics – everything from a single source
The hybrid system is completed with ZF power electronics. These play an important role in converting energy in the hybrid system. On the one hand, they convert the battery power from DC voltage to three-phase AC voltage for the motor. On the other hand, the energy generated by the motor during energy recuperation, for instance during braking, is converted back into DC voltage to charge the battery.
The power electronics also act as a control unit for the electric drive. Their task is to control the electric motor and ensure that the electric acceleration on the driveline required by the driver is provided with no interruption in tractive power and without any fluctuations.
The power electronics are also a central hub in the network of driveline control units.
Ultimately the DC/DC on-board transformer is another important component integrated into the power electronics. The DC/DC on-board transformer converts the energy from the high-voltage battery for the vehicle's 12V power supply.
The ZF systems approach offers customers maximum performance in the hybrid system since the individual components are perfectly matched.