Abstract: In an oil pump employing a cam ring, and inner and outer rotors in meshed-engagement, two housings are provided at opposite ends of the cam ring. A plurality of volume chambers are defined between inner and outer teeth of the rotors. Two axial holes are formed in the cam ring. A first one of the axial holes is positioned corresponding to a mesh portion having a minimum volume, whereas the second axial hole is positioned corresponding to a trap portion having a maximum volume. A suction port and a discharge port are formed at least in one of the housings and are open to the volume chambers between the mesh and trap portions. All are positioned at a line symmetry of an axis line between the mesh and trap portions. At least one of the two axial holes is formed as a slot extending along the axis lines.

Abstract: A power steering system includes first and second drain passages connected to the first and second passages, respectively, and first and second passage switching valves arranged at connections of the first and second drain passages and the first and second passages, respectively. When a hydraulic pump operates to discharge the hydraulic pressure to the first passage, the first passage switching valve provides fluid communication between pump-side and cylinder-side portions of the first passage and closes off the first drain passage. And when the hydraulic pump stops, the first switching valve provides fluid communication between the cylinder-side portion of the first passage and the first drain passage.

Abstract: An inscribed gear pump that provides a housing, an outer rotor formed with a plurality of inner teeth continuously at an internal circumference thereof which is rotatably provided to an inside of the housing, an inner rotor formed with a plurality of outer teeth continuously at an external circumference thereof which is rotatably provided to an inside of the outer rotor, drive shaft rotatably drives the inner rotor. Volume chambers which are formed between the inner teeth and the outer teeth. A suction port is open at an area of the volume chamber increase in a volume gradually. A discharge port is open at an area of the volume chamber that decreases in a volume gradually. An area between a start portion of the suction port and an end portion of the discharge port have contact portions of the inner teeth and outer teeth, where the number is an integer more than 2 at a portion of a volume chamber having a maximum volume of a side of a trap portion.

Abstract: A power steering system and a method of charging the power steering system with hydraulic fluid are provided. Hydraulic fluid is selectively supplied to hydraulic chambers of a power cylinder via oil passages from a reversible pump, according to a steering torque. In addition, a bypass passage is provided between oil passages. A normally open switching valve is provided in the bypass passage. When the system is assembled, the hydraulic fluid is supplied from an oil reservoir via the switching valve or the reversible pump, and circulated in the hydraulic circuit. The air in the hydraulic circuit is discharged via the switching valve.

Abstract: An oil pump comprises a cam ring, an outer rotor having inner teeth, which is rotatably provided inside of the cam ring, an inner rotor having outer teeth, which is engageable with the inner teeth of the outer rotor, a drive shaft which ratatably drive the inner rotor. A first housing and second housing are provided at opposite ends of the cam ring. A plurality of volume chambers are formed between the inner teeth of the outer rotor and the outer teeth of the inner rotor. A first axial hole is formed in the cam ring and is positioned corresponding to a mesh portion having a minimum volume of the volume chambers. A second axial hole is formed in the cam ring and is positioned corresponding to a trap portion having a maximum volume of the volume chambers. A suction port and a discharge port are formed at least in one of said housings and are open to the volume chambers between the mesh portion and the trap potion.

Abstract: A trochoid pump for supplying hydraulic fluid to a power cylinder in a power steering system. The trochoid pump includes a housing formed therein with an annular operating chamber. Outer rotor having internal teeth and inner rotor having external teeth are rotatably accommodated in the operating chamber in such a manner that the internal and external teeth are engageable with each other. A driving shaft is provided for rotationally driving the inner rotor. A low pressure passage is opened to a clearance between an outer peripheral surface of the outer rotor and an inner peripheral surface of the operating chamber within a discharge region at side of an engaging section at which the volume of the pump chamber is the minimum so as to release a high pressure applied to the outer peripheral surface of the outer rotor, to a low pressure side.

Abstract: A power steering system and a method of charging the power steering system with hydraulic fluid are provided. Hydraulic fluid is selectively supplied to hydraulic chambers of a power cylinder via oil passages from a reversible pump, according to a steering torque. In addition, a bypass passage is provided between oil passages. A normally open switching valve is provided in the bypass passage. When the system is assembled, the hydraulic fluid is supplied from an oil reservoir via the switching valve or the reversible pump, and circulated in the hydraulic circuit. The air in the hydraulic circuit is discharged via the switching valve.

Abstract: A power steering system includes first and second drain passages connected to the first and second passages, respectively, and first and second passage switching valves arranged at connections of the first and second drain passages and the first and second passages, respectively. When a hydraulic pump operates to discharge the hydraulic pressure to the first passage, the first passage switching valve provides fluid communication between pump-side and cylinder-side portions of the first passage and closes off the first drain passage. And when the hydraulic pump stops, the first switching valve provides fluid communication between the cylinder-side portion of the first passage and the first drain passage.

Abstract: A traction distributing apparatus includes a first block engaged with a motor casing wit its rotation being restricted and having an end face which comes in plane contact with an end face of a cylinder block so as to allow fluid communication between their passages, and a second block engaged with the housing or the motor casing with its rotation being restricted and having an end face which comes in plane contact with an end face of the motor casing or the housing so as to allow fluid communication between their passages. A first biasing mechanism is arranged with the first block to hydraulically bias the first block to the end face of the inner rotor, and a second biasing mechanism is arranged with the second block to hydraulically bias the second block to the end face of the motor casing or the housing.

Abstract: A fluid pump unit has a flow control valve which returns a portion of a working fluid discharged from a pump assembly when rotation speed of a rotor increases to become greater than a predetermined value. The flow control valve includes an essentially cylindrical spool chamber defined in a pump case, and a valve spool movably housed within the spool chamber. The spool chamber has a pair of through openings on the side wall thereof which through openings are selectively open and closed by movement of the spool valve. The pump case is formed with a pair of drain passages which are respectively communicated with the through openings of the spool chamber independently of each other. When rotation speed of a rotor of the pump assembly becomes greater than a predetermined value, the spool valve opens the through openings to return a part of the discharged working fluid to an inlet passage through which working fluid is introduced from a fluid source into the pump assembly.

Abstract: A plunger pump including a plurality of plunger chambers, each slidably accommodating a plunger associated with a rotatable cam shaft having an eccentric cam for pressurizing fluid within said plunger chamber, comprises an essentially cylindrical casing with the plunger chamber and a partition wall dividing an internal space defined within the casing into a low-pressure chamber communicaitng through a fluid passage formed in type plunger with the plunger chamber and a high-pressure for receiving the pressurized fluid from the plunger chamber. The casing and the partition wall are integrally formed. The casing has a circular opening through which the shaft is inserted into the low-pressure chamber and another circular opening which is sealingly closed by a lid having high-rigidity. The casing also has an inlet port through which fluid is introduced into the low-pressure chamber and an outlet port through which the pressurized fluid is discharged from the high-pressure chamber.