| 摘要 |
A power steering system for a vehicle. The system includes a hydraulic power cylinder, first and second hydraulic lines, a bypass passage through which the first and second hydraulic lines are connected with each other, and a flow passage change-over device adapted to close the bypass passage during steering assisting. A supply passage and a return passage are disposed in parallel with each other to form part of each of the first and second hydraulic lines. The flow passage change-over device is disposed in each of the first and second hydraulic lines. A differential pressure regulating valve is disposed in each of the return passages and adapted to allow hydraulic fluid to flow toward the hydraulic pressure source in a condition where pressure on side of the hydraulic power cylinder becomes higher than a set pressure or higher than pressure on side of the hydraulic pressure source.
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