Patent ID: 8087903

Claim:
In a hydraulic rotary machine having within a casing a rotational shaft, a cylinder block rotationally interlocked with said rotational shaft and formed with a plural number of cylinder bores, and pistons slidably received in said cylinder bores and adapted to slide back and forth within said cylinder bores while said rotational shaft and said cylinder block are put in rotation in synchronism with each other: a multitude of minute pits formed at least either on sliding surfaces on the side of said cylinder bores on said cylinder block or on sliding surfaces on the side of said pistons, each one of said minute pits being in an elliptical shape defining a moderately sloped surface in one side and an acutely sloped surface in the other side; said moderately sloped surfaces of said minute pits being oriented to face a direction in which said pistons are put in sliding movement in said cylinder bores under a greater load than in the other direction.