Design, Dynamic Modelling and Experiment Validation of A Novel Alternating Flow Variable Displacement Hydraulic Pump

High power density, good controllability, and low cost are the most appealing characteristics that make hydraulic systems the best choice for many applications. Current state-of-the-art hydraulic variable displacement pumps show high efficiency at high displacement while they have poor efficiencies at low displacement. This paper proposes a novel alternating flow (AF) variable displacement hydraulic pump to: 1) eliminate metering losses by acting as a high-bandwidth pump for displacement control; 2) achieve high efficiency across a wide range of operating conditions and displacements; and 3) allow multiple units to be easily common-shaft mounted for a compact multi-actuator displacement control system from a single prime mover. A dynamic model using first principles describes the cylinder pressure, flows between pairs of cylinders, and net inlet and outlet flows as a function of the pumps phase-shift angle. The model captures hydraulic check valve dynamics, the effective bulk modulus, leakage flows, and viscous friction. Piston kinematics and dynamics are discussed and energy loss models are presented. A first prototype of the AF pump was constructed from two inline triplex pumps that were modified so that three piston pairs were created. Experiment tests were conducted and used to validate the model. After model validation, simulation results from the model can offer an initial evaluation of this novel pump concept and potential applications and can be used to guide the design for future prototype of the AF hydraulic pump.