Abstract
Digital Displacement® hydraulic pumps are a type of radial-piston machine with solenoid operated on/off valves used to individually control the pressurization of each cylinder on a stroke-by-stroke basis, thus adjusting the pump’s overall displacement. Previously developed cylinder enabling strategies based on using full strokes can lead to low frequency vibration, whereas partial stroke strategies pose challenges in audible noise and component lifetime. A new enabling algorithm is proposed, Quantized Part Stroke (QPS), which seeks to minimize the low frequency content in the pump output, as well as limiting noise due to actuating the valve near mid-stroke. The operating displacement fraction is quantized such that only integer fractions of displacement are permitted, the fraction’s denominator relating directly to a minimum allowable frequency in the pump output. This quantization is applied such that the chosen displacement fraction is higher than the demand and then part strokes are used to exactly achieve the desired flow. Simulation results are presented comparing this algorithm with well-known alternatives, as well as test data from a 12-cylinder pump showing a clear decrease in low frequency pulsation in the hydraulic system pressure, without a significant change in audible noise from the pump.
