Hybrid Propulsion
Drive concepts which involve at least two different energy sources are called hybrid propulsions or hybrid drives. The objective of such drives is to combine the conceptual advantages of one energy source with another in order to avoid the conceptual disadvantages of individual drives (e.g. environmental influence on the combustion engine, insufficient operating range of electric drives).
From the multitude of realized or theoretically conceivable concepts, only two will be presented more in detail here.

a) Parallel hybrid
The figure shows the design of a parallel hybrid consisting of a combustion engine with fuel tank, electric motor with battery, and transmission.
The characteristic feature of this concept involves a coupling of the torques of both machines ahead of the transmission so that the transmission ratios can be used for both engines.
The concept offers three operating conditions. Apart from pure battery operation, the vehicle can also be exclusively driven by the combustion engine.
The third operating condition involves the hybrid drive in which one of the two engines or both as the case may be, are activated by the drive management depending on power requirements and speed. Generally the thing to do would be to cover small power requirements exclusively by the electric motor, while higher speeds and larger power requirements would warrant the need for the combustion engine. When driving at full speed, both engines are activated such that the individual power outputs add up. Minor decelerations serve for regenerative braking. In this case the electric motor operates as a generator. The resulting energy is supplied back to the batteries.