Lower fuel consumption and lower CO2₂ emissions are central themes that drive development at ZF. The company is focusing on efficient solutions for conventional drives, hybrid and all-electric drive systems, as well as intelligent lightweight design. The ZF portfolio already includes all components for the electrified driveline including control units and power electronics. Beginning in 2016, ZF will bundle its e-mobility activities in a new E-Mobility Division.
“Electrifying the driveline is an essential means for ZF to further increase efficiency and significantly reduce emissions,” stresses Dr. Stefan Sommer, Chief Executive Officer of ZF Friedrichshafen AG. “By combining all activities associated with the electrification of cars and commercial vehicles under one roof, we are acknowledging the enormous importance of these advanced technologies, which are already shaping the future.” Just how seriously ZF is taking the gradual transformation of conventional driveline technology to electromobility, says Sommer, is now also reflected in the company structure with the E-Mobility Division.
Electric axle drive system
A key product in this respect is the electric drive axle system with a very high power-to-weight ratio. The electric motor, single-speed transmission complete with differential, housing, and cooling unit, as well as the power electronics complete with control software form an integrated, extremely compact unit, which is located in the center of the axle. The complete drive module only weighs 113 kilograms. The high-revving concept – up to 13,000 revolutions per minute are possible – enables up to 150 kW of power to be generated from the electric motor, which is configured as an asynchronous traction motor. The axle torque of the electric motor totaling 3,500 Nm already delivers a maximum motor torque of 380 Nm from a standing start.
ZF managed to address the resulting challenges placed on the noise characteristics associated with the high-revving concept by utilizing a single-speed transmission solution already proven in volume production. Together with the effective integration of the electric motor, this virtually eliminates all occurring vibrations. The technology company is now further developing this electric drive system into a modular kit for various vehicle and performance classes ready for volume production.
Uncompromising interim step: plug-in hybrid transmission
ZF has achieved the aim of all-electric, locally zero-emission motoring without limiting the overall range for volume production vehicles – thanks to its plug-in hybrid transmission. The technology company 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 at up to 120 km/h. As a result, the standard cycle according to ECE 101 (Economic Commission for Europe) shows fuel reductions of up to 70 percent – depending on the capacity of the battery system. Furthermore, the automatic transmission and the combustion engine act as well-matched driveline partners. This ensures the usual high level of efficiency and dynamic qualities. The BMW X5 xDrive40e was the first model worldwide to feature the new ZF plug-in hybrid transmission in volume production.
Reversing the weight spiral: ZF lightweight design for cars
With each decade, car chassis have continuously become safer and more efficient. However, higher payloads, increased driving stability, and better dynamic driving properties also often mean more complex axles with increased weight. ZF has been working to reverse this trend for a number of years. The newest version of a wheel-guiding transverse spring made of glass-fiber reinforced plastics (GRP), which ZF has integrated into a lightweight rear axle for passenger cars, is impressive testimony to these efforts. The ZF design delivers a comparable performance, yet weighs about 13 percent less than a multilink rear suspension.
What makes this possible above all is the holistic lightweight design approach that ZF also systematically applies in other product areas. For example, the developers have designed a significantly lighter axle drive for the driveline. ZF has already been reducing the weight of the chassis on volume production cars through dampers, control arms, and braking systems using lightweight design for many years. In the passenger compartment too, ZF is shedding the pounds through innovative airbag housings and weight-optimized pedals.