Performance Map and Film Thickness Characterization of Hydraulic Fluids

A new approach is presented for the evaluation of hydraulic fluids for pump wear performance. The approach uses performance maps developed in terms of rolling and sliding velocities to establish lubrication and failure regimes for test fluids. Testing pathways within the performance map can determine the fluid attributes for wear, scuffing and traction (friction). The measurement of oil film thickness with optical interferometry is used as part of a comprehensive approach for fluid evaluation. These measurements allow the lubricated contact itself to provide the viscous film forming properties of the fluid. An “effective” pressure-viscosity coefficient is determined for a range of fluid types. Performance mapping, together with film thickness measurements, provide an insight into the fundamental chemical and physical attributes of the fluid. The new approach provides an alternative to the limited reliability of bench tests and the time consuming and expensive hydraulic pump tests.