| 摘要 |
PURPOSE:To immediately restore a steering faculty when the amount of return oil is decreased due to the damage in a main oil passage by operating an electromagnetic selector valve in response to a signal from a flow detector provided in a return oil passage to cut off a damaged oil passage portion of the main oil passage from an operating system. CONSTITUTION:When a main oil passage 23b is damaged and oil is discharged into the air, almost all the oil sucked by an auxiliary pump 3a is supplemented to a suction oil passage 20a. Accordingly, little oil is returned to an oil tank 9a through a return oil passages 31a and 32a. Therefore, a differential pressure between the front and the rear of the orifice 36a of a differential flow detector 33a is suddenly decreased. This differential pressure is detected and, when the value detected and the time elapsed reach preset values, an autoisolation valve 8a is changed over from a (b) to an (a) positions. Therefore the main oil passages 20a-23a of a main variable pump 2a are cut off from the damaged oil passage 23b and a steering faculty by hydraulic cylinders 12a and 12' is restored.
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