Patent ID: 7458211

Claim:
A hydraulic control system for heavy construction equipment comprising: a main variable displacement hydraulic pump with a hydraulic pressure supply passage extended from one side thereof; a pilot pump for generating a pilot pressure signal; a plurality of actuators driven by a hydraulic fluid discharged from the main variable displacement hydraulic pump; a switching valve interposed between the main variable displacement hydraulic pump and the actuators and connected to the hydraulic pressure supply passage; a first flow control device interposed between the main variable displacement hydraulic pump and the actuators; a load pressure signal passage for guiding a part of the hydraulic fluid, which is supplied by a switching motion of the switching valve, to a tank via the first flow control device; a bypass passage branched from the hydraulic pressure supply passage; a second flow control device installed on one side of the bypass passage and operated in an open direction or a closed direction according to the pressure difference between the pressure in the load pressure signal passage, pressure of a spring, and pressure in the bypass passage to adjust the flow rate of the hydraulic fluid passing through the bypass passage; a pressure generator installed at the most downstream side of the bypass passage; and a flow control device for the main variable displacement hydraulic pump installed on one side of the main variable displacement hydraulic pump to control the flow rate of the hydraulic fluid being discharged from the main variable displacement hydraulic pump by adjusting the inclination angle of a swash plate in the main variable displacement hydraulic pump; wherein when the switching valve is in a neutral mode, the flow rate of the hydraulic fluid being discharged from the main variable displacement hydraulic pump is minimized by using the pilot pressure signal constantly produced by the pilot pump, and, when the switching valve is operated, an additional input signal is applied to the pressure generator, so that the flow rate of the hydraulic fluid being discharged from the variable displacement hydraulic pump is controlled by the pressure produced from the pressure generator.