A range-extender (REx or REEV) is a simple and efficient system: it is an electric vehicle with a smaller battery that is charged by a gasoline engine when power runs low. Traditionally, REx is considered a series hybrid, meaning only the electric motor drives the wheels, while the internal combustion engine acts solely as a generator to power the battery. Modern REx engines are compact, lightweight, and tuned for high efficiency, operating at constant speeds. This is reported by Autocar.co.uk .
The similarity between REx and PHEV (plug-in hybrid) is that both types of vehicles can be plugged into the grid to charge and driven in pure electric mode. However, the main difference is that in a PHEV system, both the engine and the electric motor are used to drive the wheels. Traditional hybrids like the Toyota Prius and PHEV models are called "parallel hybrids" because both power sources can transmit torque to the wheels simultaneously.
Like other hybrids, REx has a more complex structure than pure electric vehicles because it includes both combustion and electric powertrains. Another aspect is that the engine in an REx system can remain idle for a long time, but modern systems automatically start the engine periodically for maintenance cycles. This technology is especially useful in regions where charging infrastructure is not well-developed.
Currently, REx technology is very popular among Chinese manufacturers because its high-voltage battery is much smaller and cheaper than that of a pure electric vehicle. This reduces the total cost of the car. Suppliers like Horse Powertrain are already offering modular REx units. Horse, a joint venture between Renault and Geely, is producing compact C15 blocks that can be installed on any electric vehicle platform.
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