Conventional variable displacement hydraulic pumps and motors suffer from poor efficiency at low displacements, primarily due to the friction and leakage associated with hydrodynamic bearings, which do not scale with output power. A variable displacement adjustable linkage pump has been developed which can achieve zero displacement and has a constant top dead center position of the pistons, regardless of displacement. This architecture employs roller element bearings in its pin joints, significantly reducing the mechanical losses at low displacements as compared to the hydrodynamic bearings of variable axial piston and bent axis machines. Previous work has described the experimentally validated efficiency model for a low-power single-cylinder pump. In this paper, the optimization and machine design of an 8.5 kW, high pressure, variable displacement, triplex prototype are presented and the potential applications are discussed. It will be shown that this architecture can achieve greater than 90% efficiency across the majority of the operating region. The pump can be applied to a wide range of applications with little compromise, compared with present variable displacement pumps.
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