| 摘要 |
<p>A machine has two fixed displacement pumps 54, 55 driven by an engine to supply fluid to control valves 24, 25, 26 that operate hydraulic actuators 21, 22, 23. The control valves 24, 25, 26 have open centres connected in series forming a path from the pumps 54, 55 to a tank 18. Flow through that path passes through an orifice 60, creating a pressure differential. The output of each pump 54, 55 is connected to a separate unloader valve 64, 72 that is operated by the pressure differential. The unloader valves 64, 72 open at different thresholds of the pressure differential to convey the output flow from the associated pump 54, 55 to the tank 18. Thus, all the flow from one pump 54, 55 is dumped into the tank 18 when fluid required to operate the machine is less than a first level, and all the flow from the other pump 54, 55 is dumped into the tank 18 when no fluid is required. This operation reduces the power demands the pumps place on the engine.</p> |
