A lightweight electrified drive axle by ZF
ZF has combined several lightweight design and construction solutions in one electric vehicle demonstrator called the Innovation Prototype, which features lightweight axle systems and electric front-wheel drive. The concept makes use of carbon fiber, glass fiber (using advanced production techniques) and aluminum.
The prototype is powered by a 120.7 hp (90 kW) electric drive module located centrally on the front axle. The electric axle module includes the inverter with a capacity of 120 kW, required to convert DC current from a battery to AC current to power an AC asynchronous brushless traction motor. With a two-stage transmission, the electric drive axle weighs 45 kg, setting a new benchmark and representing a 40 percent reduction compared to the use of conventional materials. The drive module can be used both as main powertrain as in this case, or as a rear axle in a dual-mode hybrid vehicle; it provides enough power to propel compact or sub-compact vehicles. A more powerful version has been developed, producing 161 hp (120 kW) and 2500 Nm (1843 lb ft) of axle torque suitable for the mid-sized luxury segment.
The front axle is equipped with a suspension strut and knuckle module made from fiber reinforced plastics (FRP), not only saving overall weight in the vehicle, but reducing unsprung mass for improved functioning of the suspension. A new composite process produces a smooth surface on the components without the need for further finishing. The mounting for the front axle is self-aligning and made from a hybrid combination of carbon fiber injection-molded polyamide and high-strength steel.
The rear axle is just as advanced in its design. An adjustable stabilizer concept means body roll characteristics can be tuned to individual customer requirements. The stabilizers are also manufactured from FRP or CRP, the latter giving a weight saving of 50 percent. The semi-independent rear suspension is also a hybrid material manufactured from steel and carbon fiber and incorporates ZF lightweight dampers. The dampers are manufactured from aluminum rather than steel, with plastic-coated damper mounts; they are 25 percent lighter than conventional dampers as a result.
ZF has also introduced the Electric Twist Beam (eTB) axle, which has progressed from concept to prototype form. The eTB is a semi-independent rear suspension, with electric wheel motors producing 40 kW each. The use of individual wheel motors also provides the opportunity for torque vectoring, useful for improving a vehicle’s agility or as part of a stability control system to improve safety. The axle has been designed with body connection points comparable to existing series production vehicles and is also compatible with existing production brake technology.