Abstract: A boom cylinder circuit is provided with a boom control valve for controlling supply and discharge of hydraulic oil to and from a boom cylinder, and a merge switching valve operable to be switched between a supply position at which hydraulic oil is suppliable from a first hydraulic pump to the boom control valve, and a blocking position at which a flow of hydraulic oil is blocked. A controller switches the merge switching valve to the blocking position when a combined operation of a boom lowering operation and an arm pushing operation is detected by pilot pressure sensors, and switches the merge switching valve to the supply position when only one of the boom lowering operation and the arm pushing operation is detected.

Abstract: A hydraulic control device that reduces the loss of the power of a pump in combined operation of boom lowering and arm pushing. A controller performs single control of increasing capacity of a first pump in accordance with increase in an operation amount of a boom operation member, in a single operation of the boom lowering. On the other hand, the controller restricts the capacity of the first pump compared to capacity in the single control, during a restriction control period when the combined operation of boom lowering and arm pushing is detected, and the operation amount of the boom operation member is a prescribed operation amount or more.

Abstract: Provided is an apparatus for driving a boom of a construction machine, allowing required power to be reduced. The apparatus includes a boom cylinder, a variable-displacement hydraulic pump , a control valve guiding hydraulic oil discharged by the hydraulic pump to the boom cylinder, a boom-raising-operation detector boom-cylinder pressure detectors, a supply selector valve switchable between a permitting position for permitting the hydraulic oil to be supplied from the hydraulic pump a head-side chamber of the boom cylinder and a blocking position for blocking the supply, a supply oil passage permitting hydraulic oil to be supplied to the head-side chamber during the blocking, and a controller which brings the supply selector valve into the blocking position and reduces volume of the hydraulic pump upon judging that excavation reaction force extends the boom cylinder even with no supply of hydraulic oil from the hydraulic pump to the head-side chamber.

Abstract: Provided is a slewing type construction machine including an upper slewing body and a slewing speed sensor that detects a slewing speed of the upper slewing body, enabling accurate control to be achieved regardless of an error in output from the slewing speed sensor. The construction machine includes an upper slewing body, a slewing motor, a hydraulic pump, a control valve, a slewing operation device, a slewing brake, a slewing speed sensor, a slewing operation detector that detects an operation applied to the slewing operation device, and a controller. The controller stores, during a slewing operation, a slewing speed detected by the slewing speed sensor at set time intervals, actuates the slewing brake based on a neutral return operation of the slewing operation device, and resets a stored value of the slewing speed that is stored during actuation of the slewing brake, to zero.

Abstract: A boom cylinder circuit is provided with a boom control valve for controlling supply and discharge of hydraulic oil to and from a boom cylinder, and a merge switching valve operable to be switched between a supply position at which hydraulic oil is suppliable from a first hydraulic pump to the boom control valve, and a blocking position at which a flow of hydraulic oil is blocked. A controller switches the merge switching valve to the blocking position when a combined operation of a boom lowering operation and an arm pushing operation is detected by pilot pressure sensors, and switches the merge switching valve to the supply position when only one of the boom lowering operation and the arm pushing operation is detected.

Abstract: Provided is an apparatus for driving a boom of a construction machine, allowing required power to be reduced.

Abstract: A hydraulic control device that reduces the loss of the power of a pump in combined operation of boom lowering and arm pushing. A controller performs single control of increasing capacity of a first pump in accordance with increase in an operation amount of a boom operation member, in a single operation of the boom lowering. On the other hand, the controller restricts the capacity of the first pump compared to capacity in the single control, during a restriction control period when the combined operation of boom lowering and arm pushing is detected, and the operation amount of the boom operation member is a prescribed operation amount or more.

Abstract: Provided is a slewing type construction machine including an upper slewing body and a slewing speed sensor that detects a slewing speed of the upper slewing body, enabling accurate control to be achieved regardless of an error in output from the slewing speed sensor. The construction machine includes an upper slewing body, a slewing motor, a hydraulic pump, a control valve, a slewing operation device, a slewing brake, a slewing speed sensor, a slewing operation detector that detects an operation applied to the slewing operation device, and a controller. The controller stores, during a slewing operation, a slewing speed detected by the slewing speed sensor at set time intervals, actuates the slewing brake based on a neutral return operation of the slewing operation device, and resets a stored value of the slewing speed that is stored during actuation of the slewing brake, to zero.

Abstract: A hydraulic motor is rotationally driven as pressure oil from a hydraulic pump is supplied by way of a control valve. A remote control valve is adapted to switch the control valve. A bypath line is connected to both hydraulic lines of the hydraulic motor. A communicating valve has a position for closing the bypath line and a position for opening the bypath line. A throttle valve controls the communicating valve, wherein the throttle valve is adapted to set the communicating valve to a closed position at the time when the remote control valve is operated for rotating, and to set the communicating valve to an open position at the time when the remote control valve is returned to a neutral position, as well as to allow the pressure oil of deceleration side to be released by a predetermined time, whereby the flapping of the machine which may be caused, such as at the time when the rotation is stopped in the hydraulic excavator, can be avoided.

Abstract: The present invention comprises: a hydraulic motor rotationally driven as pressure oil from a hydraulic pump is supplied by way of a control valve; a remote control valve adapted to switch the control valve; a bypath line connected to both hydraulic lines of the hydraulic motor; a communicating valve having a position for closing the bypath line and a position for opening the bypath line; and a throttle valve for controlling the communicating valve, wherein the throttle valve is adapted to set the communicating valve to a closed position at the time when said remote control valve is operated for rotating, and to set the communicating valve to an open position at the time when said remote control valve is returned to a neutral position, as well as to allow the pressure oil of deceleration side to be released by a predetermined time, whereby the flapping of the machine which may be caused such as at the time when the rotation is stopped in the hydraulic excavator can be avoided.

Abstract: A hydraulic control apparatus for a working machine in which a flow rate and a direction of pressure oil discharged from a hydraulic pump are controlled by a control valve to supply it to a swing motor, comprising: a bleed-off oil path for bleeding off a part of the pressure oil supplied to the swing motor, a cut valve provided on the bleed-off oil path to adjust a bleed-off amount, a controller for controlling the cut valve through a solenoid proportional valve, and pressure sensors for detecting an operating amount of a remote control valve for swing, characterized in that the controller sets the bleed-off amount according to the operating amount detected by the pressure sensors, controls an opening area of the cut valve on the basis of the bleed-off amount set, and suppresses the shock when sudden swinging operation takes place.

Abstract: A hydraulic control system in a construction machine is provided with a hydraulic pump delivering hydraulic oil, a directional control valve controlling flow of the hydraulic oil, an actuator driven by the hydraulic oil outputted from the directional control valve, and a tank into which the hydraulic oil delivered from the hydraulic pump is bleeded. A cut-off valve controlling flow of the bleeded hydraulic oil is arranged between the directional control valve and the tank. Transient characteristics are added to a signal controlling the cut-off valve so that variation of the signal is suppressed to be small. Transient characteristics are added also to a signal controlling the hydraulic pump so that variation of the signal is suppressed to be small. Thereby the construction machine can travel smoothly.