Abstract: A nitriding layer (13) is formed on the front surface side of a base material of a cylinder block (7) including an opening side end surface (7B) and each cylinder hole (12). Then, a piston sliding surface (12A) of each cylinder hole (12) is formed as a compound layer-removed hole (17) by removing a compound layer (16) that is located on the front surface side of the nitriding layer (13) by using polishing means such as, for example, honing and so forth. Further, a compound layer-removed surface (18) is formed on a part (A) where a compound layer-removed hole (17) and a cylinder inlet side tapered surface (12B) of each cylinder hole (12) intersect by using the polishing means such as, for example, the honing and so forth. This compound layer-removed surface (18) is formed as a tapered-state inclined surface of an angle ?.

Abstract: A nitriding layer (13) is formed on the front surface side of a base material of a cylinder block (7) including an opening side end surface (7B) and each cylinder hole (12). Then, a piston sliding surface (12A) of each cylinder hole (12) is formed as a compound layer-removed hole (17) by removing a compound layer (16) that is located on the front surface side of the nitriding layer (13) by using polishing means such as, for example, honing and so forth. Further, a compound layer-removed surface (18) is formed on a part (A) where a compound layer-removed hole (17) and a cylinder inlet side tapered surface (12B) of each cylinder hole (12) intersect by using the polishing means such as, for example, the honing and so forth. This compound layer-removed surface (18) is formed as a tapered-state inclined surface of an angle ?.

Abstract: A plurality of rotating side brake disks and a plurality of non-rotating side brake disks are arranged outside in the radial direction from a motor shaft in a brake case while alternately overlapping with each other. A frictional material is provided on the non-rotating side brake disk, and an oil groove is provided in a frictional engaging surface of this frictional material. It is configured such that, when a braking force is applied by a brake piston to the motor shaft, lubricant oil flowing into the brake case from a lubricant oil inlet port flows from the outer diameter side to the inner diameter side between the rotating side brake disk and the non-rotating side brake disk only through the oil groove. As a result, the lubricant oil having flowed into the brake case efficiently cools the frictional engaging surface.

Abstract: A plurality of rotating side brake disks and a plurality of non-rotating side brake disks are arranged outside in the radial direction from a motor shaft in a brake case while alternately overlapping with each other. A frictional material is provided on the non-rotating side brake disk, and an oil groove is provided in a frictional engaging surface of this frictional material. It is configured such that, when a braking force is applied by a brake piston to the motor shaft, lubricant oil flowing into the brake case from a lubricant oil inlet port flows from the outer diameter side to the inner diameter side between the rotating side brake disk and the non-rotating side brake disk only through the oil groove. As a result, the lubricant oil having flowed into the brake case efficiently cools the frictional engaging surface.

Abstract: A spline connection structure is provided with a shaft spline and a bore spline. The shaft spline is comprised of plural involute teeth formed on a shaft, while the bore spline is comprised of plural involute teeth formed on a hub and maintained in engagement with the teeth of the shaft spline. The hub is provided with at least one cylindrical hole and a thin wall portion facing a lower end portion of the cylindrical hole. The thin wall portion is pressed by a pressing member inserted in the cylindrical hole to widen an interval between at least two of the teeth of the bore spline, said at least two teeth being located in a vicinity of the thin wall portion, such that at least one of the at least two teeth is pressed against at least one associated tooth of the teeth of the shaft spline and is restrained to restrict movement of the hub relative to the shaft.