CONTROL SYSTEM FOR PILOT OPERATED VALVE

摘要

Earthmoving vehicles commonly employ hydraulic systems (12) to control raising and lowering the operating implements. Hydraulic systems (12) of this type normally include a pilot control valve (34) having a spool (64) shiftable in response to a shifting force resulting from selectively directing pilot pressure thereto. Problems are encountered when hydraulic systems (12) are used to perform additional functions by shifting the spool (64) to positions requiring additional spool (64) travel. This additional spool (64) travel requires a considerable increase in shifting force, which results in a considerable reduction in the pilot pressure range available for raise and lower modulation. To eliminate this problem, a control system (14) for a pilot operated valve (34) is provided which includes an apparatus (50) for shifting the control valve spool (64) the additional travel distance by changing the magnitude of the shifting force acting thereon without changing the magnitude of the pilot pressure normally reserved for implement raise and lower modulation.