Patent ID: 8919115

Claim:
A hydraulic drive device for a hydraulic excavator, which is provided in the hydraulic excavator including a front attachment, the front attachment being connected to a swing body in a vertically rotatable manner and including an arm, a bucket, an arm cylinder, and a bucket cylinder, comprising: an engine; a first hydraulic pump, a second hydraulic pump, and a pilot pump that are driven by the engine; a bucket directional control valve and a second arm directional control valve that are each connected in parallel tandem with the first hydraulic pump, the bucket directional control valve controlling a flow of pressurized oil supplied to the bucket cylinder, the second arm directional control valve controlling a flow of pressurized oil supplied to the arm cylinder; a swing directional control valve and a first arm directional control valve that are each connected in parallel tandem with the second hydraulic pump, the swing directional control valve controlling a flow of pressurized oil supplied to a swing motor for rotating the swing body, and the first arm directional control valve controlling a flow of pressurized oil supplied to the arm cylinder; a flow rate restriction device that restricts a flow rate of pressurized oil supplied to the second arm directional control valve; and a disable control device that performs a control to disable the restriction of the flow rate by the flow rate restriction device when a pressure of pressurized oil discharged from the first hydraulic pump becomes a high pressure equal to or higher than a predetermined pressure regardless of each operation status of the crowd operation of the bucket and the crowd operation of the arm and swing operation of the swing body, wherein the flow rate restriction device, when not disabled, restricts the flow rate of pressurized oil supplied to the second arm directional control valve is during crowd operation of the bucket so that a combined operation of arm-crowd and bucket-crowd is achieved.