| 摘要 |
A power steering apparatus comprises a fluid source for supplying pressurized fluid, a power cylinder having a pair of fluid chambers, a control valve, and a drain control mechanism. The control valve is composed of first and second control portions. The first control portion has four paths connecting the fluid source and the reservoir, and each of the four paths is formed with a variable orifice of center-open type. The second control portion has two supply paths communicating the fluid source with the fluid chambers of the power cylinder, each of the supply paths being formed with a variable orifice of center-open type, and two drain paths communicating the fluid chambers with the reservoir, each of the drain paths being formed with a variable orifice of center-closed type. The drain control mechanism is responsive to differential pressure between the fluid chambers of the power cylinder to control the communication of one fluid chamber under high pressure with the reservoir, and is responsive to a vehicle speed to control the communication of both fluid chambers with the reservoir.
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