perfect components for electric cars
ZF Friedrichshafen AG uses its expertise in driveline electrification: The technology company has developed an electric drive for small and mid-sized passenger cars. The drive is tailored to future requirements in urban traffic – the drive module, which is located in a central position on the axle, develops 90 kW of mechanical power and high torque right from low speeds. This allows it to display the full acceleration potential of powerful combustion engines.
ZFs electric motors are already used in current volume-production hybrid vehicles where they help reduce CO2 emissions and keep the air clean in big cities. Now, ZF is using this experience in driveline electrification for the electric axle drive. It serves as a complete driveline solution for electric passenger cars up to the compact class: "With this concept, we are proving our expertise also for purely electric vehicles," 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. "Ultimately in Germany, for instance, approx. 90 percent of daily journeys are under 60 kilometers – a distance that can already be easily covered with purely electric cars."
Practical system efficiency
The ZF system consists first and foremost of an electric motor which, as an asynchronous motor, does not require any rare earth elements such as neodymium or dysprosium. Added to which are a compact one-speed ratio unit, the power electronics, and the control software. Thanks to the two-stage transmission and the innovative high-speed design – the electric motor with energy conversion efficiency that has been optimized for everyday usage reaches 21 000 revolutions per minute –, it is possible to achieve superb performance while using less material. Already when starting, the compact drive creates a torque of 1.700 Nm on the vehicle axle. So the car accelerates from 0 to 100 km/h in nine seconds. A maximum of 90 kW is available on the axle.
By offering the electric axle drive, ZF has also solved a problem of many purely electrically powered vehicles. After all, the interaction between electric motor and inverter can lead to losses in certain driving cycles. ZF is capable of minimizing these losses by optimizing the electric system as a whole, thus increasing the range by up to six percent. Currently, the electric
axle drive weighing 45 kilograms, which sets the benchmark in terms of power density, is a development project which ZF intends to fine-tune until it is ready for standard production.
Even more powerful in the future
Further extended versions of the electric axle drive are already in the pipeline: Output power is planned to increase to more than 120 kilowatts and at least 2 000 Nm of axle torque. At the same time, ZF is working on a modular system with various power classes to optimally meet the requirements of various customers and models. In the uprated variants, the ZF system is no longerthe preserve of subcompact and compact cars: In the form of an axle hybrid module the electric drive innovation is also suited to front-wheel drive vehicles through to the mid-size luxury segment.
ZF innovation prototype: electromobility and lightweight construction
ZF demonstrates the potential that lies particularly in the combination of electromobility and lightweight construction strategies by rolling out its innovation prototype based on a subcompact car. Here, lightweight suspension components augment the electric drive axle including inverter, thus increasing both the range and the driving dynamics of the electric vehicle.
In the ZF innovation prototype, the lightweight construction measures in the suspension were tailored optimally to the specific requirements of electromobility: The weight saving helps directly increase the range or the payload of the electrically driven passenger cars. Weight savings and the reduction in unsprung masses however also offer advantages for convention
al vehicles by lowering fuel consumption and increasing driving dynamics.
At the front axle, a lightweight suspension strut and knuckle module made out of fiber-reinforced plastics (FRP) provides damping and wheel guidance. Innovative FRP design ensures a smooth surface. The weight saving is enormous: Up to 50 percent lower than the standard version made out of steel. A self-aligning support with hybrid design also replaces the conventional component made out of steel at the front axle of the innovation prototype. ZF helps save up to 16 percent weight here through the combined usage of carbon fiber, injection-molded polyamide, and high-strength steel.
With an innovative semi-independent rear suspension, the ZF engineers not only reduce weight in the innovation prototype; they also increase the variability. Thanks to a flexible stabilizer concept, the roll behavior can be tailored specifically to customer requirements. This interface enables FRP stabilizers to be mounted, thus saving additional weight – up to 50 percent for instance in the case of the CRP stabilizer which ZF fits to the innovation prototype.
The ZF semi-independent rear suspension is made out of steel and carbon fiber reinforced plastic. It is ideally combined with ZF lightweight dampers which are 25 percent lighter than conventional dampers, thanks to the usage of aluminum in combination with plastic-coated damper mounts and an optimized design.
17 June 2013
ZF expert in driveline electrification