HYDRAULIC PUMP

PROBLEM TO BE SOLVED: To provide a hydraulic pump capable of maintaining a satisfactory lubrication state between a piston and a swash plate, inhibiting abrasion and seizure and prolonging an operation life. SOLUTION: The hydraulic pump comprises a drive shaft 1 and the swash plate 6 wherein the drive shaft 1 rotates, and the piston 4 in slide contact with the swash plate 6 reciprocates in an axial direction. Numerous dimples of minute concave shapes are randomly formed in at least one of a contact portion 48 on the swash plate side of the piston 4 and a contact portion 47 on the piston side of the swash plate 6 for receiving the piston contact portion. A surface roughness parameter Ryni of a surface in which the dimples are formed is within a range of 0.4μm ≤ Ryni ≤ 1.0μm. A Sk value is equal to or smaller than -1.6. Either the contact portion 48 on the swash plate side of the piston 4 or the contact portion 47 on the piston side of the swash plate 6 thereby attains the high ability of forming an oil film and can have a long life time even in a state that the thickness of the oil film is extremely thin at low viscosity and thin lubrication. COPYRIGHT: (C)2008,JPO&INPIT