A Range-Extended Electric Vehicle (REEV) powertrain primarily uses an electric motor to drive the wheels and includes a smaller combustion engine solely to generate electricity, extending the vehicle's range.
In more detail, the REEV powertrain works like this:
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Electric Motor Propulsion: The vehicle is driven exclusively by a powerful electric motor, providing immediate torque and smooth acceleration.
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Battery as Primary Energy Source: The electric motor draws power from a battery pack, typically rechargeable from an external source (plug-in).
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Range-Extending Combustion Engine: A smaller internal combustion engine (ICE) is present, but it does not directly drive the wheels. Instead, it turns a generator to produce electricity.
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Generator for Electricity Production: The generator supplies power to either recharge the battery pack or directly power the electric motor, thus extending the driving range beyond the battery's capacity. Think of it as an on-board charging system.
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Operation Strategy: REEVs are typically designed to operate in electric-only mode until the battery reaches a certain low state of charge. At that point, the range extender (engine and generator) kicks in to maintain the battery level.
Key Characteristics of a REEV Powertrain:
- Electric Drive: All driving power comes from an electric motor.
- Range Extension: A combustion engine extends the driving range beyond the battery's limit.
- Series Hybrid: REEVs are a type of series hybrid, where the engine only generates electricity and does not directly contribute to propulsion.
- Potential for High Efficiency: Optimized engine operation at a constant speed can lead to improved fuel efficiency compared to traditional hybrids.
- Reduced Emissions: While not zero-emission, REEVs can significantly reduce emissions, especially if the majority of driving is done in electric-only mode.
Example:
The BMW i3 with the range extender option is a well-known example of a REEV. The electric motor drives the wheels, and a small gasoline engine acts as a generator to recharge the battery when it gets low.
In summary, a REEV powertrain combines the benefits of electric driving with the security of extended range provided by a combustion engine. It's a series hybrid configuration where the engine's sole purpose is to generate electricity for the electric motor.
