There are a number of approaches to implementing power generation and transmission in a gas/electric hybrid vehicle concept. Those involved in hybrid research have identified two core pathways: the Series Configuration and the Parallel Configuration. Background materials from the DOE describe the differences.

The internal combustion engine is used strictly to turn a generator that produces electricity for the vehicle’s battery pack and electric motor. There is no mechanical connection between the engine and the wheels.

Benefits:

• The engine never idles, which reduces vehicle emissions.
  • The engine drives the generator to run at optimal performance.
    • The design allows for a variety of options when mounting the engine and vehicle components.
      • Some Series hybrids do not need a transmission.
      The downside of this design is that it requires larger, and, therefor, heavier, battery packs than parallel vehicles. In addition, the engine works hard to maintain battery charge because the system is not operating in parallel.

      There is a direct mechanical connection between the internal combustion engine and the wheels, as in a conventional vehicle, but it also has an electric motor that provides additional drive power to the wheels. This allows the use of a smaller internal combustion engine. For example, the engine can be used for highway driving, but rely on a power boost from the electric motor for accelerating.

      Benefits:

      • The vehicle has more power because both the engine and the electric motor can supply power simultaneously.
        • Most parallel vehicles do not need a separate generator because the motor can regenerate the batteries.
          • Because the power is directly coupled to the road, it can be more efficient.

          One additional concept being considered for parallel hybrids is a combination alternator/starter/ flywheel device. This electrical machine would electronically balance the engine, start the engine, and take power from the engine and turn it directly into electricity. The device could also provide extra power to the drive train when needed for hill climbing or quick acceleration.