Jidosha Kiki Co., Ltd.

Yukimitsu Minamibata

Yasuyoshi Emori

Ikuo Nomura

Tetsuya Koike

Takao Kojima

A vehicle speed responsive power steering apparatus enables a pressure which acts upon a power cylinder to be variably controlled in accordance with a vehicle speed or the like, thus allowing an assisting force to be controlled in a variable manner. A control valve CV selectively connects a pump P and a tank T to left and right chambers CL, CR of a power cylinder. The control valve comprises a first and a second fluid pressure bridge circuit 10, 20. The first fluid pressure bridge circuit includes a left and a right path 12, 13, in which a first and a second pair of variable throttles 1R, 1L and 2L, 2R are disposed which are opened or closed in response to a steering operation. The left and the right chamber of the cylinder are connected to the respective paths at the junctions between the variable throttles. A pair of paths 21, 22 branch from a supply path 11 extending from the pump, and a second fluid pressure bridge circuit is defined between the paths 21, 22, in parallel relationship with the first fluid pressure bridge circuit. The second fluid pressure bridge circuit includes variable throttles 3L, 3R, 4R, 4L which are opened and closed in response to a steering operation, and a vehicle speed responsive variable throttle valve 6 which is controlled to be opened or closed in accordance with a vehicle speed.

Power steering apparatus

The durability of a rack bushing which supports of a rack shaft of a rack and pinion steering system is improved. A bushing holder 18 is fixedly mounted in one end of a steering body 6, and a rack bushing 2 is held within the bushing holder in order to support a rack shaft 4 in a slidable manner. An end of the rack bushing is formed with a locking flange 2b, which fits in an annular groove 18a formed in the bushing holder. Adjacent to the end where the flange is formed, the inner peripheral surface of the rack bushing is formed with a portion of an increased diameter 2c which avoids its contact with the rack shaft. The portion of an increased diameter extends inward beyond the region of the annular groove and a chamfer 18c formed on sidewall of such groove of the bushing holder.

Rack bushing for rack and pinion steering system

In each of both ends of a land portion provided between channels which are formed in a slidable contact surface of a rotor assembled in a sleeve so as to be rotationally displaceable relative to the sleeve and thus control connection and disconnection of fluid paths, a chamfer is formed from an edge to a throttling action end portion of the land portion of the rotor so as to have at least one flat acting surface and a curved acting surface continuously connected to the flat acting surface. The curved acting surface of the chamfer is formed to have a smooth, continuously curved surface with a radius of curvature which decreases gradually from a connection portion with respect to the flat acting surface to a point at which it is connected to an outer diameter portion of the rotor. When a throttling action is performed by rotationally displacing the rotor with respect to the sleeve, an angle defined between the flat and curved acting surfaces at a connection point between them and an angle defined between the curved acting surface and a tangent at a point at which the curved acting surface is connected to the outer diameter portion of the rotor are maintained small, which reduces fluid noise caused by cavitation.

Fluid control valve device

A subpump has its discharge flow rate increased in response to an increase in a vehicle speed. A variable throttle is disposed in a discharge passage from the subpump, and an oil pressure taken from the upstream side of the variable throttle is introduced into a hydraulic reaction chamber to produce a steering action. A main pump has its flow rate increased or decreased in accordance with a number of revolutions thereof, and feeds a pressure oil to a power steering control valve through a passage in which a fixed restriction is disposed. An oil pressure which prevails upstream of the fixed restriction acts upon the variable throttle to change its area of opening, thereby controlling the steering force.

Steering force control system for power steering

A reaction pressure control mechanism of power steering apparatus includes a power cylinder, to which a pressure oil discharged from an oil pump is supplied through a control valve, and oil discharged from the oil pump is branched to be introduced into a hydraulic reaction chamber, which produces steering reaction. A pair of variable restrictions are formed in a supply and discharge passage to and from the hydraulic reaction chamber, and a single spool which is operated by a solenoid is effective to increase the opening of one of the variable restrictions while reducing the opening of the other restriction. A plunger is disposed in opposing relationship with a rod associated with the solenoid and on which the spool is fixedly mounted so that when the oil pressure in the reaction chamber exceeds a given value, such oil pressure is introduced to the backside of the plunger to cause the spool to be driven back, thus reducing the opening of the variable restriction associated with the supply passage.

Reaction pressure control mechanism of power steering apparatus

A hydraulic reaction device of a power steering apparatus includes a vehicle-speed responsive pump, a reaction plunger, a hydraulic reaction chamber, a path, and a variable control unit. The vehicle-speed responsive pump has a pressure oil discharge flow rate which changes in accordance with a vehicle speed. The reaction plunger selectively constraining relative pivotal displacement between input and output shafts constituting a rotary flow path switching valve of the power steering apparatus. The hydraulic reaction chamber receives the pressure oil from the pump to apply a reaction oil pressure to the reaction plunger. The path is arranged to connect the hydraulic reaction chamber to a tank. The variable control unit (a variable throttle portion 37 of a reaction oil pressure control valve 11) for variably controlling a flow rate of the pressure oil flowing through the path. The variable control unit is variably controlled in accordance with a magnitude of an oil pressure in a main oil pressure path extending from a main pump to the left and right chambers of the power cylinder.

Hydraulic reaction device for power steering apparatus

A valve sleeve is fitted around valve rotor to define a rotary valve. The valve sleeve is characterized by the configuration of axially extending grooves which are formed in its internal surface. Specifically, the axial groove has a bottom surface which includes a lengthwise portion having a constant depth. The bottom surface of the groove is connected to the wall surfaces which are located at the opposite lengthwise ends as well as with the opposite lateral side walls by arcuate surfaces. At least one of the wall surfaces which are located at the lengthwise ends has an angle of inclination which exceeds 60.degree..

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Saitama, Japan

Yukimitsu Minamibata