A flow control valve includes a valve body having an inner circumferential surface defining a longitudinal bore to which first and second fluid passages are connected. A spool is slidably inserted into the bore to allow a flow of fluid from the first to second fluid passage. A valve regulates a flow rate of fluid flowing through the first fluid passage. A first seat surface is defined between an area in which the first fluid passage is connected to the bore and an area in which the second fluid passage is connected to the bore. When the flow of fluid from the first to second fluid passage is initiated, an area of a gap between the first seat surface and the spool on a plane taken in a transverse direction is 5%˜50%, preferably 10%˜20% of an area of an opening defined by the first seat surface.

An electro-hydraulic control apparatus for construction machinery includes a control valve installed in a hydraulic line between a hydraulic pump and an actuator to control operations of the actuator according to a displacement amount of a spool therein, a spool displacement adjusting valve configured to output a secondary pressure in proportion to an inputted pressure command signal to the spool of the control valve to control the displacement amount of the spool of the control valve, a pressure sensor to detect the secondary pressure outputted from the spool displacement adjusting valve, and a controller configured to output the pressure command signal to the spool displacement adjusting valve according to a manipulation signal of the construction machinery, and to correct the pressure command signal when a pressure difference between the detected secondary pressure and a design pressure predetermined by the pressure command signal is out of a preset allowable range.

There is provided a work machine that is capable of realizing operability and energy saving ability that are equivalent to those of work machines that have a joint line to be used during swinging/boom raising operation, without incorporating a joint line for supplying a pressurized fluid from a second pump to a bottom-side chamber of a boom cylinder. The controller is configured to compute a hypothetical flow rate representing a flow rate in a hypothetical joint line, compute a first pump provisional target flow rate on the basis of an operation amount of a boom operation device, compute a second pump provisional target flow rate on the basis of an operation amount of a swing operation device, compute a first pump final target flow rate by adding the hypothetical flow rate to the first pump provisional target flow rate, and compute a second pump final target flow rate by subtracting the hypothetical flow rate from the second pump provisional target flow rate.

An example valve assembly is configured: generate a valve load-sense pressure signal indicative of a pressure level at a workport of an actuator; generate a pilot fluid signal to be communicated to a worksection of a valve assembly to enable shifting a spool in the worksection; compare a first pressure level of the valve load-sense pressure signal to a second pressure level of the pilot fluid signal; and communicate the pilot fluid signal to a load-sense port fluidly coupled to a load-sensing source of pressurized fluid when the second pressure level of the pilot fluid signal exceeds the first pressure level of the valve load-sense pressure signal.

Provided is a work machine with which responsiveness of a hydraulic actuator can be improved when driving the hydraulic actuator through an electric lever-type operation device. A controller 100 further includes: an operation direction determining section 116 configured to determine operation directions of operation devices 2a and 2b; and a standby pressure switching command section 117 configured to output a standby pressure switching command to a first target pilot pressure correction section 112 or a second target pilot pressure correction section 113 which corresponds to a solenoid proportional valve that does not correspond to the operation direction from among first solenoid proportional valves 41a, 42a, 42b, 43a, 43b, and 44a and second solenoid proportional valves 41b, 42c, 42d, 43c, 43d, and 44b. The first target pilot pressure correction section and the second target pilot pressure correction section are configured to switch a first standby pressure α to a second standby pressure β set lower than the first standby pressure in a case in which the standby pressure switching command has been inputted.

A hydraulic drive apparatus capable of automatic control with high accuracy regardless of regeneration operation includes a boom flow rate control valve, an arm flow rate control valve, a regeneration control valve, a pump control device for performing horsepower control, a posture detection device, a boom flow rate control device switchable between a normal control mode and an automatic control mode, and a regeneration control device. The boom flow rate control device adjusts the boom flow rate in the automatic control mode so that a work attachment moves along a target locus. The regeneration control device sets the regeneration control valve to a regeneration position in a low load situation and to a regeneration cut position in a high load situation, and lowers the regeneration rate in the low load situation when the boom flow rate control device is switched to the automatic control mode.

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).

The failure detection device is a failure detection device of a pilot circuit, the pilot circuit including: a pilot pressure source; a pilot pressure supply unit that supplies pilot pressure to a control valve; a pilot oil path that connects the pilot pressure source and a pilot pressure supply unit; and a pressure control unit that controls a pressure of the pilot oil path, the failure detection device including: a pressure sensor that measures the pressure on a downstream side in a pilot pressure supply direction of the pressure control unit; and a controller that controls the pressure control unit to sequentially switch the pressure of the pilot oil path and performs a failure diagnosis based on a measurement result of the pressure sensor at this time, as an operation lever which receives an operation for operating the actuator returns to a neutral state.

Lever neutrality is determined by whether or not operation levers are at a neutral position based on operation signals from operation levers. Pilot pressures are computed based on the operation signals from the operation levers; and pilot pressure signals are converted to current signals. A current interruption controller controls interruption and communication of the current signals to the solenoid proportional valves; and an operating condition is determined by determining whether a construction machine is in a manual operation state or a semiautomatic operation state. At least one hydraulic actuator is controlled to assist the operation of the operator, and when it is determined that the construction machine is in the semiautomatic operation state, the current interruption controller interrupts the current signals to all of the solenoid proportional valves only when it is determined that all the operation levers are at the neutral position.

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.