Abstract: A work machine includes: a main circuit that supplies a working fluid from a pump to an actuator; a pilot circuit that introduces part of the working fluid from the pump, to a pilot pressure receiving section of a control valve; a bleed-off passage that connects the pump and a tank. The pilot circuit is provided with: a first pressure reducing valve that generates a pilot primary pressure; and second and third pressure reducing valves that generate a pilot secondary pressure to be applied to the control valve and a bleed-off valve. A moving area of a spool of the bleed-off valve has a first moving area where an opening area of a restrictor changes stepwise, and a second moving area where the opening area of the restrictor changes continuously. A controller controls the third pressure reducing valve such that the spool is positioned in the first moving area at the time of non-operation of the actuator, and the spool is positioned in the second moving area at the time of operation of the actuator.

Abstract: A work machine includes: a first pump and a second pump that are driven by an engine; a hydraulic actuator driven by a hydraulic working fluid supplied from the first pump; a control valve that controls a flow of the hydraulic working fluid supplied to the hydraulic actuator; a solenoid valve that reduces a pressure of the second pump to generate a pilot pressure for operating the control valve; a controller that controls the solenoid valve; an engine operating section that enables operation for activating the engine; and a rotation speed sensor that senses a rotation speed of the engine.

Abstract: 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.

Abstract: There is provided a construction machine that draws attention from the surroundings of the machine body when the prime mover is started and that can have the operator reliably confirm the surroundings of the machine body before the prime mover is started. An engine start control section 23 of a main controller 22 inhibits an engine 18 from starting when a key switch 12 is operated while a horn switch 21 is not operated, inhibits the engine 18 from starting when the key switch 12 is operated for the duration until a first set time T1 elapses after the operation of the horn switch 21 has been finished, permits the engine 18 to start in a case the key switch 12 is operated for the duration until a second set time T2 elapses after the first set time T1 has elapsed, and inhibits the engine 18 again from starting when the key switch 12 is operated if the engine 18 is not started for the duration until the second set time T2 elapses.

Abstract: To provide a work machine that makes it possible to drive actuators faster and more accurately by supplying flows to the actuators accurately at target rates without depending on load variations in a case where the machine body is controlled automatically by command inputs of a controller, while high operability is ensured for manual operation by an operator. In a case where a machine control function is cancelled via a machine control switch, a controller cancels limitation of the flow rate of a hydraulic fluid supplied to a plurality of directional control valves, the limitation being performed by the auxiliary flow rate control devices, and in a case where the machine control function is selected via the machine control switch, the controller causes the auxiliary flow rate control devices to limit the flow rate of the hydraulic fluid supplied to the plurality of directional control valves.

Abstract: There is provided a work machine which can improve accuracy of control of an actuator when a pressure difference between a hydraulic pump and the actuator is large and the demanded flow rate of the actuator is small. An auxiliary flow rate controller is configured such that an opening area of a main valve changes between a maximum opening area and zero according to the opening area of a pilot variable restrictor when the opening area of the pilot variable restrictor is equal to or more than a predetermined opening area and that the opening area of the main valve is zero irrespective of the opening area of the pilot variable restrictor when the opening area of the pilot variable restrictor is less than the predetermined opening area.

Abstract: In a specific state where the raising operation of a boom 25 and the swing operation of an upperstructure 21 are performed at the same time to supply a hydraulic oil from a first pump 2 to a cylinder 7a through a first valve 6a, and to supply the same from a second pump 3 to a motor 7b through a second valve 6b, a controller 10 outputs the command current for opening a valve 13, and supplies a part of the hydraulic oil supplied to the motor 7b from the second pump 3 to the cylinder 7a through the third valve 6c when the motor 7b does not reach a steady swing state, and outputs a command current for closing the valve 13 when the motor 7b is in the steady swing state.

Abstract: A hydraulic drive system includes a swing directional control valve 81 and a third boom directional control valve 82 that are connected to a third hydraulic pump 33. Furthermore, the hydraulic drive system includes: a second auxiliary directional control valve 84 that is connected to the third hydraulic pump 33, and is connectable with a second special hydraulic actuator 64 for driving special attachments; and a first selector valve 96 that is connected to the third hydraulic pump 33 upstream of the second auxiliary directional control valve 84, and is connectable with an additional hydraulic pump 97. The first selector valve 96 switches the hydraulic fluid source of the second special hydraulic actuator 64 connected to the second auxiliary directional control valve 84 at least between the third hydraulic pump 33 and the additional hydraulic pump 97.

Abstract: There is provided a construction machine that draws attention from the surroundings of the machine body when the prime mover is started and that can have the operator reliably confirm the surroundings of the machine body before the prime mover is started. An engine start control section 23 of a main controller 22 inhibits an engine 18 from starting when a key switch 12 is operated while a horn switch 21 is not operated, inhibits the engine 18 from starting when the key switch 12 is operated for the duration until a first set time T1 elapses after the operation of the horn switch 21 has been finished, permits the engine 18 to start in a case the key switch 12 is operated for the duration until a second set time T2 elapses after the first set time T1 has elapsed, and inhibits the engine 18 again from starting when the key switch 12 is operated if the engine 18 is not started for the duration until the second set time T2 elapses.

Abstract: 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.

Abstract: A work machine capable of driving each actuator more speedily and more accurately by ensuring high operability in a case of operator's manual operation, while accurately supplying a hydraulic fluid at a target flow rate to the actuator without depending on a load fluctuation in a case of automatic control over a machine body in response to a command input from a controller is provided. The controller controls a plurality of auxiliary flow controllers in such a manner that supply flow rates to a plurality of directional control valves from hydraulic pumps either fluctuate in response to load fluctuations of a plurality of hydraulic actuators when an area limiting control function invalidation instruction is issued, or do not fluctuate in response to the load fluctuations of the plurality of hydraulic actuators when an area limiting control function validation instruction is issued.

Abstract: In a specific state where the raising operation of a boom 25 and the swing operation of an upperstructure 21 are performed at the same time to supply a hydraulic oil from a first pump 2 to a cylinder 7a through a first valve 6a, and to supply the same from a second pump 3 to a motor 7b through a second valve 6b, a controller 10 outputs the command current for opening a valve 13, and supplies a part of the hydraulic oil supplied to the motor 7b from the second pump 3 to the cylinder 7a through the third valve 6c when the motor 7b does not reach a steady swing state, and outputs a command current for closing the valve 13 when the motor 7b is in the steady swing state.

Abstract: A construction machine is provided. If the rotational speed of a prime mover is set lower than a rated rotational speed and the delivery rate of a hydraulic pump is lowered, the construction machine can prevent deterioration of the operability in slow speed operation works by keeping wide a lever operation range in which the rate of flow supplied to a hydraulic actuator is variable.

Abstract: A work machine capable of driving each actuator more speedily and more accurately by ensuring high operability in a case of operator's manual operation, while accurately supplying a hydraulic fluid at a target flow rate to the actuator without depending on a load fluctuation in a case of automatic control over a machine body in response to a command input from a controller is provided.

Abstract: To provide a work machine that can stop unexpected operation of actuators faster than it actually occurs even if unintended operation occurs at the time of gate lock lever switching that leads to such unexpected operation. In the work machine, a controller switches a lock valve from a lock position to a release position in a case where a lock operation device is operated from a permission position to a prohibition position; decides, on the basis of a result of detection by a pressure sensor, whether or not a pilot hydraulic fluid has been output from a pilot valve until first time elapses after the lock valve is switched to the release position; keeps the lock valve at the lock position if it is decided that the pilot hydraulic fluid has been output until the first time elapses; and switches the lock valve from the lock position to the release position if it is decided that the pilot hydraulic fluid has not been output until the first time elapses, and second time elapses.

Abstract: To provide a work machine that can stop unexpected operation of actuators faster than it actually occurs even if unintended operation occurs at the time of gate lock lever switching that leads to such unexpected operation. In the work machine, a controller switches a lock valve from a lock position to a release position in a case where a lock operation device is operated from a permission position to a prohibition position; decides, on the basis of a result of detection by a pressure sensor, whether or not a pilot hydraulic fluid has been output from a pilot valve until first time elapses after the lock valve is switched to the release position; keeps the lock valve at the lock position if it is decided that the pilot hydraulic fluid has been output until the first time elapses; and switches the lock valve from the lock position to the release position if it is decided that the pilot hydraulic fluid has not been output until the first time elapses, and second time elapses.

Abstract: A hydraulic drive system includes a swing directional control valve 81 and a third boom directional control valve 82 that are connected to a third hydraulic pump 33. Furthermore, the hydraulic drive system includes: a second auxiliary directional control valve 84 that is connected to the third hydraulic pump 33, and is connectable with a second special hydraulic actuator 64 for driving special attachments; and a first selector valve 96 that is connected to the third hydraulic pump 33 upstream of the second auxiliary directional control valve 84, and is connectable with an additional hydraulic pump 97. The first selector valve 96 switches the hydraulic fluid source of the second special hydraulic actuator 64 connected to the second auxiliary directional control valve 84 at least between the third hydraulic pump 33 and the additional hydraulic pump 97.

Abstract: To provide a work machine that makes it possible to drive actuators faster and more accurately by supplying flows to the actuators accurately at target rates without depending on load variations in a case where the machine body is controlled automatically by command inputs of a controller, while high operability is ensured for manual operation by an operator. In a case where a machine control function is cancelled via a machine control switch, a controller cancels limitation of the flow rate of a hydraulic fluid supplied to a plurality of directional control valves, the limitation being performed by the auxiliary flow rate control devices, and in a case where the machine control function is selected via the machine control switch, the controller causes the auxiliary flow rate control devices to limit the flow rate of the hydraulic fluid supplied to the plurality of directional control valves.

Abstract: In a construction machine with a hydraulic pilot type hydraulic control device, occurrence of jerking is prevented. A hydraulic excavator 1 having hydraulic pumps 51L and 51R, travel motors 22L and 22R, traveling operating levers 34L and 34R, a pilot pump 54, hydraulic pilot valves 55La, 55Lb, 55Ra, and 55Rb, and directional control valves 53L and 53R includes: changeover switches 35L and 35R which change the operating mode of the traveling operating levers 34L and 34R; pilot pressure adjusting devices 5L and 5R which adjust the pilot pressure applied to the directional control valves 53L and 53R; and pilot pressure sensors 56La, 56Lb, 56Ra, and 56Rb. The pilot pressure adjusting devices apply the pilot pressure at the time when the operating mode of the traveling operating levers 34L and 34R is changed to a control mode, to the directional control valves 53L and 53R.

Abstract: To prevent increase/decrease in pump flow rate due to load variation with change in the posture of a work attachment and improve the operability in arm pushing operation.