| 摘要 |
A power-assisted hydraulic steering system for use in connection with a vehicle having a steering linkage which couples a steering wheel to a vehicle steering actuator, an electrically actuated hydraulic pump, and a tank of hydraulic fluid. The steering system includes a boost cylinder connected to the steering actuator, a hydraulic spool valve fluidly coupling the pump and tank to the boost cylinder, and a switch coupled to the pump. A spool which is mechanically coupled to the steering actuator is mounted within the valve for reciprocal motion between neutral, extended and retracted positions, and is biased to the neutral position by a centering spring which establishes a power-assist threshold. The switch senses the position of the spool, and switches the pump on when the spool is in the extended and retracted positions. When steering forces applied to the steering actuator by rotation of the steering wheel are less than the power-assist threshold, the spool will remain in the neutral position with the pump switched off and the valve fluidly isolating the pump and tank from the boost cylinder. When steering forces applied to the steering actuator by rotation of the steering wheel are greater than the power-assist threshold, the linkage housing forces the spool to the retracted or extended position depending on the direction of the rotation, thereby switching the pump on and driving the boost cylinder and steering actuator through a power-assist retraction or extension stroke. |
