Provided is a work machine hydraulic control system capable of detecting abnormality in a pump output power switching device independently of the abnormality state of the pump output power switching device.

A hydraulic control system of a hydraulic excavator is equipped with an accumulator 21 connected to a hydraulic line 25A between a pilot pump 17 and a pilot valve 20, an unloading valve 27 that is a pump output power switching device, a pressure sensor 29 detecting the pressure of the hydraulic fluid supplied to the pilot valve 20, and a controller 30 having a pump output power control section 31 switching the unloading valve 27 in accordance with the pressure detected by the pressure sensor 29. The controller 30 further has an abnormality determination section 32 that computes a command continuation time in a state in which a command output to the unloading valve 27 is not changed. In the case where this command continuation time is not less than a predetermined value, it determines that the unloading valve 27 is abnormal, and outputs the determination result.

A work machine has a controller which has an area limiting control section correcting the pilot pressures of pilot lines, a regeneration control section adjusting the flow rate of the hydraulic fluid caused to flow from a tank side line of an arm cylinder into a pump side line thereof between zero and a predetermined upper limit value, and a regeneration control switching section that issues an order to the regeneration control section to set the predetermined upper limit value to a first set value when the function of the area limiting control section is invalid and that issues an order to the regeneration control section to set the predetermined upper limit value to a second set value that is smaller than the first set value when the function of the area limiting control section is effective.

A work machine including a front control section configured to calculate a limit command value for restricting an operation of a front work implement includes: for example, a bypass line that bypasses, for example, the proportional solenoid valve in, for example, the pilot line; for example, a bypass valve disposed in, for example, the bypass line; a switch configured to output a signal to turn on or off control by the front control section; an on/off determining part configured to determine whether the signal from the switch is an on signal that brings front control into an on state or an off signal that brings the front control into an off state; an open/close command part configured to generate an open/close command signal to open the bypass valve when the signal is determined to be the off/off signal.

A work machine includes: a boom; a dipper stick attached to a distal end of the boom; a bucket attached to a distal end of the dipper stick; and a loading determination unit configured to determine that an operation of the work machine is a loading operation for loading an excavated matter into a loading target under a condition that the bucket moves across a reference level.

A hydraulic circuit (11) of a hydraulic excavator (1) is provided with a main hydraulic circuit (11A) including a boom cylinder (5D), a pilot hydraulic circuit (11B) for operating the boom cylinder (5D) and a recovery hydraulic circuit (11C) including an accumulator (29). In this case, the recovery hydraulic circuit (11C) is provided with a recovery control valve (31) that recovers pressurized oil discharged from the boom cylinder (5D) to the accumulator (29), a main supply control valve (34) for supplying pressurized oil accumulated in the accumulator (29) to the main hydraulic circuit (11A) and a pilot supply control valve (37) for supplying pressurized oil accumulated in the accumulator (29) to the pilot hydraulic circuit (11B).

A working machine includes a prime mover, a rotation-speed operation actuator, a rotation detector, a hydraulic pump, a hydraulic unit, an operation valve capable of changing a pilot pressure of a pilot fluid supplied from the hydraulic pump to the hydraulic unit in accordance with an operation of an operation member, an actuation valve operating in accordance with a control signal and capable of changing a primary pressure as the pilot pressure of the pilot fluid supplied from the hydraulic pump to the operation valve, and a controller that outputs the control signal based on a difference between target and actual rotation speeds to the actuation valve to control an opening thereof. The controller has a mode including calculating the control signal based on the difference, correcting the calculated control signal, and increasing or decreasing a target primary pressure value set in accordance with the control signal.

A hydraulic system for a working machine includes a hydraulic pump to output a hydraulic fluid, an operation device operable to supply a pilot fluid in accordance with an amount by which the operation device is operated, a hydraulic actuator to be operated by the hydraulic fluid, a pilot fluid passage connected to the operation device, a first control valve connected to the pilot fluid passage and to be operated by the pilot fluid to control a flow of the hydraulic fluid, a second control valve to be operated by the pilot fluid to control a flow of the hydraulic fluid, a proportional valve to change a pressure of the pilot fluid to operate the second control valve, a pressure detector provided in the pilot fluid passage to detect a pressure in the pilot fluid passage, and a controller to control the proportional valve based on the pressure.

A hydraulic excavator is provided which can suppress the fuel consumption amount and improve the work efficiency by reducing the hydraulic pressure loss generated when a plurality of hydraulic actuators different in load are operated simultaneously. The hydraulic excavator includes a center bypass flow control valve that is arranged at the most downstream of a center bypass line and limits the flow rate of hydraulic fluid passing through the center bypass line in response to the operation amount of the second operation device in a case where a second operation device is operated, and a spool stroke limitation device that, in a case where a first operation device and the second operation device are operated simultaneously, limits the spool stroke amount of a second directional control valve in response to the operation amount of the first operation device in a state in which the spool stroke amount of a third directional control valve is controlled in response to the operation amount of the second operation device.

A construction machine incorporates a hydraulic closed circuit system capable of suppressing, even where a selector valve is stuck in an open state by a failure of the selector valve or a control system therefor, unintended operation of a hydraulic actuator and continuing operation of a machine body. The construction machine includes first sensors that detect open-closed states of a plurality of switching valves, first compulsory valve closing devices that change over the plurality of switching valves to a closed position irrespective of open-close control by a machine body controller, and a valve device controller that controls, when it is detected based on the open-closed states of the plurality of selector values detected by the first sensors that one of the plurality of selector values is stuck in an open state, the first compulsory valve closing device such that other selector valve connected to one of the plurality of closed circuit pumps to which the one selector valve is connected is closed.

In a working machine, a controller is configured or programmed to control actuation of a blocking switching valve and a solenoid valve, to cause the blocking switching valve to unblock a first pilot fluid passage to perform switching to a first operation pattern in which an operation device operates a first device via a first control valve and a first hydraulic actuator, and cause the blocking switching valve to block a second pilot fluid passage and control the solenoid valve based on pilot pressure detected by a pressure detector to perform switching to a second operation pattern in which the operation device operates a second device via a second control valve and a second hydraulic actuator.