Patent ID: 9651061
Date: 2017-05-16
CPC Classifications: E02F,F15B,Y10T

Claim:
1. 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 electronic controller, the electronic controller being 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 a first 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 a second state that the fluid path to the hydraulic actuator is closed; calculate a virtual bleed opening area from a given virtual bleed opening area characteristic related to the directional control valve, based on an operation amount of an operation member for changing a position of the directional control valve, under the situation where the directional control valve is in the first state, calculate, based on the calculated virtual bleed opening area and a discharge pressure of the hydraulic pump, a virtual negative control pressure when a negative control system is assumed, and calculate a first control command value for the hydraulic pump based on the virtual negative control pressure; calculate a second control command value for the hydraulic pump when the directional control valve is in the second state, the second control command value being calculated using a dummy value so that a discharge flow rate of the hydraulic pump becomes a predetermined flow rate; and control the hydraulic pump based on the first control command value when the directional control valve is in the first state, and control the hydraulic pump based on the second control command value when the directional control valve is in the second state.