Digital Displacement Motoring Characteristics of Dynamic Energy Recovery and Hydraulic Transformation

Abstract The Digital Displacement® Pump (DDP) is a highly innovative hydraulic 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. The Digital Displacement® Pump/Motor (DDPM) technology is expected to improve component and system efficiency as well as enable recovery of useful energy which would otherwise be lost. The machine’s unique capabilities include direct hydraulic transformation, allowing for pressure amplification or reduction on the machine pump service, with the pumping cylinders purely driven by the motoring ones. This paper presents the efficiency results of a newly developed Digital Displacement machine, which comprises 30 radially arranged DD modules with a total displacement of 300cc/rev. Test demonstrator data shows overall pumping and motoring efficiency above 94.5% for most of the datapoints (at 100% displacement fraction) within the main working operation envelope for excavators, i.e. 150–250 bar and 1400–1800 rpm. The machine also allows for dynamic energy recovery, with a peak efficiency of 93.5% achieved from the hydraulic input power to the DDP150D to the mechanical shaft power of the prime mover. The paper concludes that the machine’s capabilities make it a promising solution for hydraulic transformation, with a peak efficiency of above 90% as a hydraulic transformer achieved for both pressure amplification and reduction at the pump service.