Hydraulic control system for excavators - has adjusters for low rpm valve reacting to rpm deviations

摘要

The hydraulic system for an excavator controls the HP output of a number of variable displacement pumps driven by a single main drive. The system has a pilot pressure source with a fixed displacement pump, driven by the main drive, to control the pump displacements relative to the RPM output of the main drive. There are also low RPM control valves with adjusting units controlling the connection of the pilot control pressure and the pump displacement units under RPM deviation of the main drive, and allowing a change of pump displacement proportional to the connected load. Each adjusting unit contains a proportioning flow-controlled aperture parallel to the valves.