Hydraulic control apparatus and method

A hydraulic control apparatus that controls a hydraulic pump in a construction machine in which a hydraulic actuator is connected to the hydraulic pump via a directional control valve of a closed center type, and in which an unloading valve, which is connected to a tank, is provided between the directional control valve and the hydraulic pump, the hydraulic control apparatus comprising:

• an unloading valve controlling part configured to control the unloading valve such that fluid communication between the hydraulic pump and the tank is blocked in a situation where the directional control valve is in such a state that a fluid path to the hydraulic actuator is opened, and such that the fluid communication between the hydraulic pump and the tank is established in a situation where the directional control valve is in such a state that a fluid path to the hydraulic actuator is closed;
• an command value calculating part configured to operate under the situation where the directional control valve is in such a state that the fluid path to the hydraulic actuator is opened, wherein the command value calculating part calculates, based on an operation amount of an operation member for changing a position of the directional control valve and a discharge pressure of the hydraulic pump, a virtual negative control pressure when a negative control system is assumed, and calculates a control command value for the hydraulic pump based on the virtual negative control pressure;
• and
• a correcting part configured to operate under the situation where the directional control valve is in such a state that the fluid path to the hydraulic actuator is closed, wherein the correcting part corrects the control command value or a parameter, which is used in calculating the control command value, such that a discharge flow rate of the hydraulic pump is a predetermined flow rate.