Koyo Seiko Company, Ltd.

Hiroshi Ooishi

Manabu Takaoka

Kazumasa Tabata

A hydraulic power steering apparatus having a hydraulic cylinder as a source for generating a force assisting a steering force, and comprising a directional control valve which switches the feeding direction of pressured oil to the hydraulic cylinder, and a constraining device which constrains its switching operation responsive to the vehicle speed, characterized in that an oil pressure control valve for controlling oil pressure fed to the directional control valve and constraining device is controlled by pressure of a vehicle speed sensor pump which develops oil pressure corresponding to the vehicle speed, and in that a sudden change of a constraining force caused by external disturbance signals such as electromagnetic waves is prevented and the constraining force corresponding to the vehicle speed can be obtained, by introducing oil pressure, which becomes higher or lower responsive to changes of the vehicle speed, into the constraining device to generate the constraining force responsive to the oil pressure.

Hydraulic power steering apparatus

A hydraulic pressure control valve of the present invention applied in hydraulic power steering includes a cylindrical casing whose plural first grooves disposed on its circumferential surface at stated intervals are brought in communication with different destinations of pressure oil, and a valve body which is inserted rotatably into the casing and whose second grooves of the same number as the first grooves, disposed on its peripheral surface at stated intervals are brought in communication alternately with a high pressure source and a low pressure source, and a portion thereof is disconnected with the low pressure source. At corners on the casing opposing each other across the communicating portions on both sides of the disconnected portion of the valve body, notches are formed in such a shape that, until the relative angular displacement between the valve body and casing reaches the predetermined magnitude, variations of communicating areas produced between the first and second grooves by the relative angular displacement is substantially not produced. In the hydraulic pressure control valve, the first groove of the valve body interposed between the notches is not in communication with the low pressure source, and the pressurized oil which flows in through one communicating portion of this portion is introduced into the groove of the adjacent casing through the other communicating portion without flowing back to the low pressure source, so that flowing noises of pressured oil produced when the relative displacement is produced between the valve body and casing can be reduced sharply.

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Osaka, Japan

Hiroshi Ooishi