Range Extender: More Than Just Extra Range
ZF has significantly advanced the technical concept of the range extender. As a result, the range extender primarily caters to the needs of Chinese electric car manufacturers, but it also has the potential to boost the electric mobility markets in Europe and North America.
Sometimes it takes a bit longer for great ideas to catch on. An example of this is the range extender. As the name suggests, it extends the range of an electric vehicle. A range extender system essentially consists of an additional electric motor that acts as a generator, an inverter for voltage conversion and a small combustion engine. The latter powers the generator, which charges the high-voltage battery on the go whenever needed. This means there is no longer a mandatory stop for charging an electric vehicle with a low battery level. The system transforms battery electric vehicles (BEVs) into range extended electric vehicles (REEVs).
One of the pioneers in using range extenders was General Motors with the compact car "Chevrolet Volt." It started rolling off the production lines in the U.S. in 2011, and later on, it was also available in Canada, Europe and South Korea under the brand name of Opel. But volumes remained low. Electric vehicles with increasingly powerful drive batteries and the rise of plug-in hybrids (PHEVs) have caused the REEV concept to fall into a deep slumber. "We recognized the advantages of range extenders early on and equipped the first electric taxis in London with them back in 2018. Now, we are offering a modular solution that significantly reduces the carbon footprint compared to PHEVs," says Kay Schmidt, responsible product line manager for range extender systems at ZF.
ZF’s "electric range extender (eRE)": an innovative, modular e-drive system.
Strong Demand in China
Chinese electric vehicle manufacturers have been increasingly adopting range extender drives for some time now, driven by a significant surge in domestic demand for REEVs. The prospect of driving electrically without having to compromise much on range is just too tempting. ZF has adapted to this development and is working on a modular range extender drive. Its name is "electric Range Extender (eRE)." Indeed, it could potentially revitalize the somewhat sluggish electric vehicle market with BEVs in Europe and the USA. Major manufacturers like Hyundai, Ford and Stellantis are showing interest in the range extender technology and are planning to launch vehicles equipped with it within the next two years.
The Difference Between REEVs and PHEVs and What They Have in Common
Electric vehicles with range extenders have specific advantages. Like plug-in hybrids, REEVs also have a socket for charging, but they additionally feature on-board power generation. It recharges the drive battery while on the move, which means the battery can be smaller. This reduces vehicle weight and the purchase price. The range extender compensates for the reduced battery capacity and the associated shorter range. In addition, the drive technology in an electric vehicle with range extender is simpler than that in a plug-in hybrid. This speeds up development times.
In its traditional form, a REEV is a series hybrid where propulsion is purely electric; neither the small internal combustion engine nor the associated electric motor drives the wheels. Only the PHEV offers the choice between electric and internal combustion engine driving. Both drive concepts share the fact that they are a preliminary stage on the path to pure electric mobility. They drastically reduce CO2 emissions. Another similarity between REEVs and PHEVs is that their potential range makes them equally suitable for regions with less developed charging infrastructure.
Developed in China for the World
In November 2023, ZF began developing its modular range extender system "eRE" –- which includes an electric motor, inverter with software and planetary gearset – at its tech center in Shanghai. The engineers ensured that it is suitable for both 400-volt and 800-volt architectures. It also does not matter whether a customer uses traditional silicon semiconductors (Si) or silicon carbide (SiC) ones. Since a permanently excited electric motor (PSM) with scalable power outputs of 70kW to 110kW serves as a generator in the "eRE," the range extender is highly efficient. "One advantage for our customers is that we can rely on robust and proven components from our electric and hybrid vehicle portfolio for the range extender. This also makes us competitive in terms of price," says Dr. Otmar Scharrer, Head of Research & Development for Electrified Powertrain Technology at ZF.
ZF's Range Extender With Unique Additional Benefit
However, the ZF developers did not want to stop at the traditional range extender functionality. In an enhanced version of the "eRE," they added an intelligent clutch and a differential, transforming it into the "eRE+." This makes it possible for the range extender's electric motor to either operate as a generator or, if desired, to power the front wheels, creating a four-wheel drive. Scharrer, Head of E Research & Development, said: "With our "eRE+," which even reaches a power output of up to 150kW, we have practically further developed the concept of the range extender and created a world first."
Other advantages of ZF's range extender are its compact dimensions and easy installation on the internal combustion engine. The compact design is further enhanced by integrating the inverter into the housing of the electric motor. After ZF started its range extender project early, volume production is scheduled to begin in the course of 2026.
