| 摘要 |
A hydraulic system includes a hydraulic pump, a reservoir, a hydraulic function, such as a cylinder, and a power beyond valve for controlling communication between the pump, the reservoir and the cylinder. The pump provides pressurized fluid at a pump output as a function of the pressure in a load sensing port. For generating a pump controlling load sensing signal in case that the cylinder does not generate such a signal, it is proposed to provide a valve which blocks in a first position or opens in a second position communication between the feed line of the cylinder and the load sensing port of the pump. The valve functions in dependence of control pressures acting on each side of a valve member. A spring is provided biased to urge the valve member to its first closed position. Further, shift valve means are provided to supply selectively different pressures to both sides of the valve member. In an open-center hydraulic system, the valve means the shift valve means connects the first side of the valve member to the reservoir and the second side of the valve member to the feed line. In a closed-center system, the shift valve means will be changed over to connect the first side of the valve member to the feed line and the second side of the valve member to the pump outlet.
|
