Hydraulic control system

A hydraulic control system comprising a hydraulic pump and a hydraulic actuator using the hydraulic pump as a hydraulic supply source,

• wherein the system is provided with a direction change-over valve having supply/discharge valve passages for the hydraulic actuator and changing over supply/discharge directions, a flow control valve arranged at an upstream side of the direction change-over valve for controlling a supply flow rate from the hydraulic pump to the direction change-over valve, and a control means for controlling an operation of the direction change-over valve and the flow control valve;
• a discharge flow rate for the hydraulic actuator is configured to be controlled based on an opening area of the discharge valve passage from of the direction change-over valve, and a supply flow rate from the hydraulic pump to the hydraulic actuator is configured to be controlled based on an opening area of the supply valve passage to of the direction change-over valve and an opening area of the flow control valve;
• wherein the control means comprises:
• a target supply flow rate setting means to set up a target supply flow rate from the hydraulic pump to the hydraulic actuator depending on an operating amount of a hydraulic actuator's manipulator;
• a direction change-over valve's opening area setting means to set up the opening area of the supply/discharge valve passages for the direction change-over valve depending on the operating amount of the hydraulic actuator's manipulator;
• a target differential pressure setting means to set up a target differential pressure between a hydraulic pump pressure and a load pressure of the hydraulic actuator;
• and a calculation means to calculate a target opening area of the flow control valve for supplying the target supply flow rate to the hydraulic actuator based on the target supply flow rate preset above, the opening area of the supply valve passage to of the direction change-over valve, and the target differential pressure;
• and wherein the control means controls an operation of the flow control valve so as to keep the target opening area calculated by the calculation means.