Abstract: A piston is cylindrical and includes: a concave spherical portion formed at one of end portions of the piston and having a partially spherical shape; a cylindrical hollow portion formed at the other end portion of the piston; and an oil passage formed between the concave spherical portion and the hollow portion, the concave spherical portion and the hollow portion communicating with each other through the oil passage. The concave spherical portion includes a concave spherical surface formed by forging and having a partially spherical shape. A convex spherical portion of a shoe is supported by the concave spherical surface so as to be slidable and rotatable. An area of contact between the concave spherical surface and a predetermined master ball corresponding to the convex spherical portion is 40% or more of an entire area of the concave spherical surface.

Abstract: A piston in a liquid-pressure rotating device in which pistons are arranged at a cylinder block rotatable together with a rotating shaft, includes: a cylindrical peripheral wall main body portion including a hollow portion, an opening portion formed at one end of the body portion and communicating with the hollow portion; a lid portion welded to an inner peripheral surface of the opening portion sealing the hollow portion and including an outer surface formed as a pressure receiving surface which receives liquid pressure; and a stress reducing portion provided on an inner peripheral surface of the body portion, the inner peripheral surface in contact with or close to an end portion of a welded portion formed between the opening portion and the lid portion, the end portion located at the hollow portion side, the stress reducing portion configured to reduce stress acting on the end portion of the welded portion.

Abstract: A piston is cylindrical and includes: a concave spherical portion formed at one of end portions of the piston and having a partially spherical shape; a cylindrical hollow portion formed at the other end portion of the piston; and an oil passage formed between the concave spherical portion and the hollow portion, the concave spherical portion and the hollow portion communicating with each other through the oil passage. The concave spherical portion includes a concave spherical surface formed by forging and having a partially spherical shape. A convex spherical portion of a shoe is supported by the concave spherical surface so as to be slidable and rotatable. An area of contact between the concave spherical surface and a predetermined master ball corresponding to the convex spherical portion is 40% or more of an entire area of the concave spherical surface.

Abstract: A sliding end part of a shoe has an annular seal part located to surround one opening of a lubricant supply hole and sliding on a slide-receiving surface. The sliding end part has a first pad part that has a height from a reference surface lower than the seal part, that is located on the same circumference to partially surround the opening, and that faces the seal part in a radial direction via an annular groove present on an inner side in the radial direction of the seal part. The sliding end part has a second pad part that has a height from the reference surface lower than the seal part, that is located on the same circumference to partially surround the opening, and that faces the seal part in the radial direction via an annular groove present on an outer side in the radial direction of the seal part.

Abstract: The piston includes a body having a hollow chamber defined therein, and a member inserted in the hollowed chamber to define an oil passage between an inner peripheral surface of the hollow chamber and an opposing outer peripheral surface of the member. This reduces the dead volume and, as a result, improves the compressibility. In addition, the increased cooling performance prevents the fusing of the piston to the cylinder.

Abstract: A piston in a liquid-pressure rotating device in which pistons are arranged at a cylinder block rotatable together with a rotating shaft, includes: a cylindrical peripheral wall main body portion including a hollow portion, an opening portion formed at one end of the body portion and communicating with the hollow portion; a lid portion welded to an inner peripheral surface of the opening portion sealing the hollow portion and including an outer surface formed as a pressure receiving surface which receives liquid pressure; and a stress reducing portion provided on an inner peripheral surface of the body portion, the inner peripheral surface in contact with or close to an end portion of a welded portion formed between the opening portion and the lid portion, the end portion located at the hollow portion side, the stress reducing portion configured to reduce stress acting on the end portion of the welded portion.

Abstract: A gap between an outer peripheral surface of a cylinder block and an inner periphery surface of a housing serves to reduce an agitation resistance of an operating oil with a simple arrangement. So this reduces an agitation loss and improves or increases a conversion efficiency between a hydraulic energy and a rotational energy.

Abstract: To improve productivity and increase seizing resistance and abrasion resistance of a sliding surface of a tilt adjustment cylinder, a plurality of pistons are arranged cirumferentially in a cylinder block configured to rotate with a rotating shaft. Tip end portions of the pistons slide along the swash plate, and the pistons reciprocate. The swash plate is supported to tilt with respect to the rotating shaft. Further, a tilt adjustment driving portion is included. The tilt adjustment driving portion includes tilt adjustment large- and small-diameter cylinder chambers and tilt adjustment large- and small-diameter pistons configured to slide in the cylinder chambers to change the tilt angle of the swash plate. A sliding surface of the inner peripheral surface of each of the cylinder chambers includes a quenched portion formed by quenching using laser light, the sliding surface being a surface on which the tilt adjustment piston slides.

Abstract: A plurality of pistons arranged in a circumferential direction in a cylinder block are configured to rotate with a rotating shaft. Tip end portions of the pistons slide along a swash plate. The swash plate supported by a swash plate supporting portion tilts with respect to the rotating shaft, and includes a tilt adjustment driving portion configured to change a tilt angle. The tilt adjustment driving portion includes a tilt adjustment large-diameter cylinder chamber, a tilt adjustment small-diameter cylinder chamber, a tilt adjustment large-diameter piston configured to slide in the cylinder chamber to change the tilt angle, and a tilt adjustment small-diameter piston configured to slide in the cylinder chamber to change the tilt angle. A sliding surface of each of the inner peripheral surfaces of the cylinder chambers includes a quenched portion formed by laser light, the sliding surface being a surface on which the tilt adjustment piston slides.

Abstract: A solid fats and oils is impregnated in an air space of a stone matrix, as lubrication particles, of a grinding stone. The fats and oils is melted out of the air space to a peripheral surface of the grinding stone to lubricate friction between the grinding stone and a workpiece and to create a space again in the air space of the stone matrix. The created space can perform to receive a cutting tip and to discharge it. The melted lubrication particles lubricate friction between the grinding stone and the workpiece to restrain a generation of heat in order to reduce a grinding resistance. As a result, it restrains a loss of grinding particles on the peripheral surface of the grinding stone to keep a high quality of the grinding characteristics of the workpiece and to extend a truing interval and a life of the grinding stone.

Abstract: A cooling apparatus includes a lubricating fluid tank, a lubricating fluid nozzle, a lubricating fluid regulating device, a cooling fluid tank, a cooling fluid nozzle and a cooling fluid regulating device. The cooling fluid nozzle supplies cooling fluid to the workpiece to enhance cooling effect of the cooling fluid. The lubricating fluid nozzle feeds lubricating fluid to the machining zone to prevent frictional heat generated in the machining zone from raising temperature of the workpiece. Since an appropriate amount of the lubricating fluid within the range helps the cooling effect of the cooling fluid, a quantity of the cooling fluid is reduced within the minimum range of the cooling fluid. A consumption of the lubricating fluid is much smaller than that of the cooling fluid. Therefore, a total amount of the fluids is extremely reduced. The range of flow rates of the lubricating fluid has an upper limit that is preferably approximately 100.0 cm3/h or smaller in 1.