Textured surfaces for improved lubrication at high pressure and low sliding speed of roller/piston in hydraulic motors

The present study investigates the potential of surface textures to improve the friction situation of the piston/roller contact in hydraulic motors at low speed and high pressure. A self-adjusting flat on flat rig, with conditions representative of an actual hydraulic motor, is used in a reciprocating sliding motion. The samples are made out of the same materials and the surface finishing operations are the same as used in the motor.The piston surfaces are textured using newly developed embossing tools comprising micromechanically formed all-diamond surfaces. The textured surfaces involve parallel grooves and crossed grooves, each of four different spacings. Also polished surfaces were tested. Un-textured—as tumbled—surfaces are used as reference.Generally, it was found that the friction level was only marginally influenced by the textures. However, the friction fluctuations were reduced. SEM investigations disclosed rather severe modifications of the surfaces during use, primarily caused by plastic deformation of the surface layer. The results and their practical implications are discussed.