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Hybrid vehicles, i.e., those containing two or more sources of power, have the potential of increased fuel economy under certain types of driving conditions. Systems currently being investigated include combinations of heat engines, electric drives, fly-wheels, and accumulators. In order to obtain fuel economy improvements over conventional vehicles, efficient components are required as well as a good system design. Hybrid powerplants appear more promising for heavier vehicles.

Four alternative fluid power systems were analyzed to determine their efficiencies and standby power consumption while providing hydraulic power for power steering and a hitch for an agricultural tractor operating over a typical duty cycle. The investigation shows that a significant reduction in losses can be achieved with systems incorporating both split flow and variable delivery capabilities. These characteristics reduce losses by providing the required flow and pressure to each function without a large pressure drop for the function operating at the lower pressure. These systems can be used to improve efficiencies whenever there are multiple, simultaneous hydraulic power demands which require significantly different pressures.