Hydraulic control system

A hydraulic control system comprising a hydraulic driving system including a variable displacement hydraulic pump, a hydraulic actuator driven by a hydraulic fluid delivered from said hydraulic pump, a flow control valve for controlling a flow of the hydraulic fluid supplied from said hydraulic pump to said hydraulic actuator, and manipulation means for operating said flow control valve;

• first signal pressure generating means for generating, as a first hydraulic signal, a pressure depending on a status variable of said hydraulic driving system;
• and a pump controller including pressure detecting means for detecting the first hydraulic signal generated by said first signal pressure generating means and converting the detected first hydraulic signal into a first electric signal, a control unit for receiving the first electric signal from said pressure detecting means, executing certain arithmetic operation and outputting a second electric signal, and a pump regulator driven in accordance with the second electric signal from said control unit for controlling the displacement of said hydraulic pump;
• wherein said pump controller further includes second signal pressure generating means for generating a second hydraulic signal depending on the second electric signal from said control unit and driving said pump regulator hydraulic signals;
• wherein said pump regulator comprises an actuator for operating a displacement varying mechanism of said hydraulic pump and a control switching valve for controlling the operation of said actuator, and said control switching valve comprises a control spool, a pressure receiving sector provided at one end of said control spool for receiving said second hydraulic signal, and biasing means provided at the other end of said control spool opposite to said pressure receiving sector, a characteristic of said biasing means being set such that said control switching valve can be operated by the first hydraulic signal generated by said first signal pressure generating means and said pump regulator can operate said displacement varying mechanism of said hydraulic pump in the working range of said first hydraulic signal whereby a characteristic of said pump regulator is set such that said pump regulator can be operated by the first hydraulic signal generated by said first signal pressure generating means;
• and
• wherein said control unit calculates, based on the first electric signal from said pressure detecting means, a value adapted for making the working range of the second hydraulic signal generated by said second signal pressure generating means substantially at the same level as the working range of the first hydraulic signal generated by said first signal pressure generating means, and determines said second electric signal with said value being as a target value of the second hydraulic signal generated by said second signal pressure generating means, followed by outputting to said second signal pressure generating means whereby characteristics of said control unit and said second signal pressure generating means are set such that the working range of the second hydraulic signal generated by said second signal pressure generating means is substantially at the same level as the working range of the first hydraulic signal generated by said first signal pressure generating means.