Lubricant Effects in Hydraulic Motor Starting Efficiency

This paper presents an investigation of the fluid properties that affect starting efficiency in hydraulic motors. Starting efficiency is important because it often determines the minimum displacement of motors in mobile hydraulic systems. The boundary friction, thermophysical and pressure-viscosity coefficients of prototype fluids have been characterized. These hydraulic fluids have been evaluated in geroler, axial piston, and radial piston motors under constant torque starting conditions in accordance with the ISO 4392-2 standard test method. Correlations between starting efficiency and fluid boundary friction, thermophysical and pressure-viscosity coefficients have been identified. The relative impact of these fluid properties varied with motor design.