Axial piston-type hydraulic rotary machine

An axial piston-type hydraulic rotary machine comprising:

• a tubular casing;
• a rotational shaft that is rotatably provided in the casing;
• a cylinder block that is provided in the casing so as to rotate together with the rotational shaft and has a plurality of cylinder holes that are separated from one another in a circumferential direction and extend in an axial direction;
• a plurality of pistons, each piston of the plurality of pistons is inserted and fitted into a respective cylinder hole of the plurality of cylinder holes in the cylinder block to be reciprocally movable;
• and
• a valve plate that is provided between the casing and the cylinder block and in which one pair of supply and exhaust ports that communicate with the respective cylinder holes are formed, wherein
• a nitriding layer on which nitride-based treatment is performed at least including an opening side end surface and a piston sliding surface of each cylinder hole of the plurality of cylinder holes, the nitriding layer including a diffusion layer that is formed on a front surface side of a base material of the cylinder block and a compound layer that covers a front surface side of the diffusion layer, the compound layer being harder than the diffusion layer,
• wherein
• a cylinder inlet side tapered surface is formed on each of the cylinder holes in the cylinder block by a chamfer from the opening side end surface towards the piston sliding surface and the nitriding layer;
• each of the cylinder holes has a compound layer-removed portion at which the compound layer is not present on a front surface side of the nitriding layer at the piston sliding surface of each of the cylinder holes and at which the diffusion layer is located on the front surface side,
• a compound layer-removed surface includes a part of each of the cylinder holes where the compound layer-removed portion and the cylinder inlet side tapered surface of each of the cylinder holes intersect at an oblique angle,
• the compound layer-removed surface is machined into a tapered state in such a manner that the part where the compound layer-removed portion and the cylinder inlet side tapered surface intersect at the oblique angle has an angle α, and when a taper angle of the cylinder inlet side tapered surface is β and a maximum inclination angle at which each piston obliquely inclines in the respective cylinder hole is γ, the angle α is larger than the maximum inclination angle γ and is not more than the taper angle β.