Construction machine

A construction machine including a hydraulic control system having a prime mover, a variable displacement hydraulic pump driven by the prime mover, a plurality of hydraulic actuators driven by discharge fluid of the hydraulic pump, a plurality of center bypass directional flow control valves arranged in a center bypass line having an upstream end connected to the hydraulic pump and a downstream end connected to a hydraulic fluid tank, and controlling flows of hydraulic fluid supplied from the hydraulic pump to the plurality of hydraulic actuators, and a plurality of operation devices provided correspondingly to the plurality of hydraulic actuators and operating the respective directional flow control valves, the construction machine comprising:

• an operation amount sensor detecting operation amounts of the plurality of directional flow control valves;
• a rotational speed sensor detecting a rotational speed of the prime mover;
• a center bypass control valve arranged downstream of the plurality of directional flow control valves in the center bypass line;
• and
• a controller that is configured to:
• control, if the rotational speed of the prime mover detected by the rotational speed sensor is equal to a rated rotational speed, which is an engine rotational speed used at a time of a normal work, the center bypass control valve such that an opening area of the center bypass control valve becomes a maximum value irrespective of the operation amounts of the plurality of operation devices detected by the operation amount sensor, and
• calculate, if the rotational speed of the prime mover detected by the rotational speed sensor is lower than the rated rotational speed, a combined opening area obtained by combining opening areas of the plurality of directional flow control valves in the center bypass line based on the operation amounts of the plurality of operation devices detected by the operation amount sensor, and to control the center bypass control valve such that the opening area of the center bypass control valve becomes smaller than the combined opening area.