This example shows a hydraulic transmission system built of a variable-displacement pump and a fixed-displacement motor. The pipes between the pump and the motor are connected by two replenishing valves (check valves) and a charge pump on the pump side and two pressure relief valves on the motor side. The motor dirves a mechanical load consisting of an inertia, viscous friction, and time-varying torque. The system is tested with both positive and negative pump flow rate by varying the pump displacement.
This plot shows the mass flow rates through the pump, motor, and valves in the transmission system. Flow from the charge pump through the check valves compensate for external leakage through the pump and motor casing.
This plot shows the torque generated by the motor as well as the torque driving the pump and the mechanical load. It also shows the pressures in the two transmission pipes switch between high and low pressures as the pump is reversed.