Patent ID: 6438952
Filing Date: 2002-08-27
Classification: E02F,F15B

Abstract:
A hydraulic circuit system comprising a hydraulic pump , a plurality of hydraulic actuators driven by a hydraulic fluid delivered from said hydraulic pump, a plurality of control valves disposed between said hydraulic pump and said plurality of actuators, a signal detecting hydraulic line to which a signal pressure based on a maximum load pressure among said plurality of hydraulic actuators is introduced, and pump control means for controlling a delivery pressure of said hydraulic pump to be held higher than said signal pressure by a predetermined value,said plurality of control valves comprising respectively main valves including meter-in variable throttles for controlling flow rates of the hydraulic fluid supplied to said hydraulic actuators , and flow distribution valves disposed between said meter-in variable throttles and said actuators, each of said flow distribution valves including a valve body which has one end positioned in an inlet passage connected to said meter-in variable throttle and the other end positioned in a control chamber, said valve body being moved through a stroke depending on balance between a pressure in said control chamber and a pressure in said inlet passage to control the pressure in said inlet passage, thereby controlling a differential pressure across said meter-in variable throttle, wherein said hydraulic circuit system further comprises a first hydraulic line provided in each of said plurality of control valves for, when a load pressure of the associated hydraulic actuator is the maximum load pressure, detecting that load pressure and introducing the detected load pressure to said control chamber; a second hydraulic line provided in each of said plurality of control valves for connecting said control chamber to said signal detecting hydraulic line and introducing the signal pressure in said signal detecting hydraulic line to said control chamber when the load pressure of the associated hydraulic actuator is not the maximum load pressure; a third hydraulic line for connecting said signal detecting hydraulic line to a reservoir; a first throttle disposed in said third hydraulic line; and a second throttle disposed in said second hydraulic line of at least one of said plurality of control valves for, when the load pressure of the associated hydraulic actuator is the maximum load pressure, cooperating with said first throttle to modulate that load pressure and introducing the modulated load pressure, as the signal pressure, to said signal detecting hydraulic line.