Increased fuel economy and decreased exhaust emissions are the two most major demands for automobile manufacturers. Passenger vehicles consume a huge amount of fuel all over the world. This significant usage of it for passenger vehicles is the motivation for developing a vehicle that improves the fuel economy. The high power density of hydraulic pumps/motors and accumulators making hydraulic technology look promising for passenger vehicles especially the new developed units. In this paper, real-time simulation model of VW Passat mechanical gear-shift powertrain as a baseline for this study will first be presented to assure the common circumstances and conditions used in all the other introduced transmissions. After that, three different concepts of hydrostatic drivetrains will be simulated to indicate their potentials to apply in passenger vehicles. First, the well-known continuously variable hydrostatic transmission (CV-HST) integrated with a controlled engine to operate in minimum fuel consumption points will be discussed. An algorithm based on engine specific fuel consumption has been developed to set an Ideal Operating Line (IOL) of the engine. This allows the engine being connected to the input shaft of the transmission to operate mostly in efficient operating points. Next, a pressure coupling secondary control hydrostatic transmission (SC-HST) will also be simulated. Finally, a new series hydraulic hybrid drivetrain, known as the Hydrid, configured with recently developed components by Innas B.V was introduced. Some control algorithms are suggested and evaluated by simulations.
The study indicates that the series hydraulic hybrid drivetrain using Innas Hydraulic Transformer (IHT) and the floating cup constant displacement units will lead the benchmark as the most efficient solution for the whole drivetrain.