Comparison of Airborne Sound Quality Between Digital Displacement® & Traditional Axial Piston Pumps

Abstract

Abstract Digital Displacement® Pump (DDP) is a variable displacement radial piston pump, driven by a central crankshaft, wherein each cylinder can be independently controlled. With each crank rotation a given cylinder may idle, operate a full pumping stroke or operate a partial stroke. Variable displacement is achieved by utilising one of, or a combination of, these control options. The fundamental design differences between DDP and traditional axial piston pump determine different mechanical and fluid forcing is generated, producing a distinctly different Noise, Vibration and Harshness (NVH) characteristic. DDP is the first major disruptor in the field of hydraulic pumps and as such the difference in human perception should be addressed and understood. This paper presents a comparison of the airborne noise radiated from DDP096 and two axial piston pumps, in a semi-anechoic chamber and on two identical 20-tonne excavators. The test chamber data shows that across a wide range of speeds and pressures, DDP is on average 3.5 dB quieter than a comparable axial piston pump. Coupled with a significant reduction in Prominence Ratio, DDP has on average a 12% better Articulation Index, whilst the transient nature of a radial piston pump shows detriment in other psychoacoustic metrics. The observed trends are also apparent when pumps are compared on working excavators.