This paper deals with the determination of set values for the real-time control of a power-split Hybrid Electric Vehicle (HEV). Different programming problems are formulated for the operating modes 'hybrid propulsion', 'electrical propulsion' and 'regenerative braking'. Numerically robust solution procedures are developed and applied to these problems. The resulting set values for the power plants are stored in look up tables and embedded into the vehicle controller. It is shown that the model of the drivetrain losses inherent in the programming problems influences the fuel consumption a great deal. Numerical computations reveal which of the losses influence the fuel consumption most. Furthermore, a way of circumventing a detailed description of the mechanical gearbox losses is derived from a physical understanding of the energy flow through the transmission. The considerations are not restricted to a specific drivetrain, but are to a great extent generally applicable to hybrid electric vehicles of the power-split type.
Keywords: hybrid electric vehicles, power-split HEV, energy flow, continuously variable transmission, CVT, circulating power, stop–start operation, regenerative braking, operating strategy, fuel consumption, set values, real-time control, alternative propulsion