Electrically Controlled Fixed-Displacement Pump, Variable-Displacement Motor Hydrostatic Transmission

Fixed-displacement pump, variable-displacement motor configurations are rarely utilized for hydrostatic transmission designs, but they can achieve several advantages over more traditional systems. Developing a hydraulic drivetrain to accomplish high efficiency at high torque is often difficult because variable-displacement pumps are less efficient at low displacements. However, a system that utilizes modern electro-hydraulic valves and an electrically controlled variable-displacement hydraulic motor is easy to modulate and achieves its peak efficiency at low speeds. During the 2005 ASABE (American Society of Agricultural and Biological Engineers) ¼ Scale Tractor Student Design Competition, one such system was compared to conventional hydrostats and belt driven continuously variable transmissions. The fixed pump, variable motor system proved to be easy to operate. An electronic controller was used to modulate motor displacement to maintain constant engine speed. From data gathered during the performance event, it was observed that the system utilized engine power more effectively than traditional hydrostatic transmission configurations.