A work machine pump control system includes: a pump horsepower control valve (22) which causes a first urging force determining a limited horsepower (F) of a hydraulic pump and a second urging force due to a delivery pressure of the hydraulic pump to act on a spool in opposition to each other and which controls the pump flow rate such that it does not exceed the limited horsepower (F); a target pump flow rate computation section (42) computing a target pump flow rate based on an operation pressure (px) and a load pressure (py); a target horsepower computation section (41) which computes a required horsepower (Freq) corresponding to an operation pressure (px) from a relationship related to the operation pressure (px) and which computes a target horsepower (Ftar) based on the required horsepower (Freq); and a pump horsepower control section (35) which controls the pump horsepower control valve (22) such that the target pump flow rate (Qtar) is delivered with the limited horsepower (F) determined by the pump horsepower control valve (22).

A hydraulic excavator includes: a hydraulic pump driven by power generated by an engine; a work device that operates by a plurality of hydraulic cylinders driven by power generated by the hydraulic pump; an actuator control section that controls the boom cylinder in such a manner that a tip end of a bucket is located on or above a target surface; a control point position calculation section that calculates a bucket claw tip position on the basis of angle sensors; and a power generator control section that imposes more limitations on output power ranges of the engine and the hydraulic pump when a distance between the claw tip position and the target surface is equal to or smaller than a threshold D than those when the distance between the claw tip position and the target surface is larger than the threshold D.

Provided is a hydraulic drive system for a work machine configured with a single solenoid proportional valve for a regeneration circuit, wherein substantially the same actuator speed can be secured irrespective of whether or not hydraulic fluid discharged from a hydraulic actuator is regenerated for driving of another hydraulic actuator. The hydraulic drive system includes: a regeneration line that connects a bottom-side hydraulic chamber of a hydraulic cylinder 4 to a portion between a hydraulic pump device 50 and a second hydraulic actuator 8, and a regeneration flow rate adjustment device that supplies, at an adjusted flow rate, at least part of the discharged hydraulic fluid to a portion between the hydraulic pump device 50 and the second hydraulic actuator; a discharge flow rate adjustment device that discharges, at an adjusted flow rate, the discharged hydraulic fluid to a tank; one electric drive device 22 that simultaneously controls the regeneration flow rate adjustment device and the discharge flow rate adjustment device; and a control unit 27 that outputs a control command to the electric drive device in such a manner that falling speed of a first driven body does not vary significantly, irrespective of the magnitude of the regeneration flow rate caused by the regeneration flow rate adjustment device.

A pump device includes a variable capacity first pump, a tilt actuator that controls a tilt angle of a swash plate of the first pump in accordance with the control pressure, a regulator that regulates the control pressure in accordance with a front-rear differential pressure of a control valve, a fixed capacity second pump driven by the same drive source as the first pump, the control actuator that operates in accordance with the front-rear differential pressure a resistor so as to drive the regulator to reduce the control pressure in response to an increase in the front-rear differential pressure of the resistor, an auxiliary passage that leads an auxiliary pressure to the control actuator, the auxiliary pressure acting on the control actuator against a upstream pressure of the resistor, and a switch valve that switches between connecting and shutoff the auxiliary passage.

A controller unit is included in a liquid-pressure driving system for use in a working machine configured to supply an operating liquid to an actuator to move a structural body by the actuator. The controller unit includes: a gyro sensor configured to output a signal corresponding to an operation velocity of the structural body; and a controller configured to control a flow rate of the operating liquid supplied to the actuator, based on the signal output from the gyro sensor and corresponding to the operation velocity of the structural body, wherein: the controller is attached to the structural body; and the gyro sensor is incorporated in the controller.

A drive system for a construction machine capable of appropriately controlling a distribution flow rate to each hydraulic actuator and improving operability by an operator is provided. A flow rate distribution section that computes a distribution flow rate of a hydraulic fluid supplied to each of a plurality of hydraulic actuators on the basis of a demanded flow rate, sets, within a distributable region set for computing a range of a distributable flow rate that is a flow rate of the hydraulic fluid suppliable to each of at least two hydraulic actuators driven by a combined operation among the plurality of hydraulic actuators from a plurality of hydraulic pump devices for the at least two hydraulic actuators, a distribution region for computing a range of the distribution flow rate of the hydraulic fluid actually supplied to each of the at least two hydraulic actuators, and computes the distribution flow rate in such a manner that the distribution flow rate falls within the distribution region and a ratio among the distribution flow rates of the plurality of hydraulic actuators is equal to a ratio among the demanded flow rates of the plurality of hydraulic actuators.

A hydraulic drive apparatus includes: an accumulator for receiving hydraulic fluid discharged from a hydraulic actuator during a lowering drive; an accumulator flow regulator capable of changing a flow rate of hydraulic fluid to be introduced to the accumulator from a closed circuit; a regeneration actuator for converting energy of the hydraulic fluid accumulated in the accumulator into motive force; a regeneration selector valve interposed between the accumulator and the regeneration actuator; a pump control section for limiting a pump discharge flow rate during the lowering drive; and a speed control section for operating the accumulator-flow-rate regulator so as to bring an actuating speed of the hydraulic actuator close to a target speed during the lowering drive.

A hydraulic system for a working machine is a load sensing (LS) system and includes a first hydraulic actuator and a first control valve for controlling the flow of hydraulic fluid from a pump to the first hydraulic actuator and for draining hydraulic fluid from the first hydraulic actuator, respectively, and a second hydraulic actuator and a second control valve for controlling the flow of hydraulic fluid from the pump to the second hydraulic actuator and for draining hydraulic fluid from the second hydraulic actuator, respectively. The hydraulic system further includes a first hydraulic circuit for providing an LS pressure for the first actuator and a second hydraulic circuit for providing an LS pressure for the second actuator. At least one of the first and second hydraulic circuits includes an offset valve for changing the LS pressure before providing the LS pressure to the pump.

The hydraulic drive system includes a hydraulic pump, a plurality of variable displacement actuators, and a control unit. The hydraulic pump discharges a hydraulic fluid. The variable displacement actuators each receive a pressure of the hydraulic fluid discharged from the hydraulic pump to operate corresponding one of a plurality of drive parts. The control unit controls displacement varying parts of the variable displacement actuators. The control unit controls the displacement varying parts of the variable displacement actuators, based on sensed pressures in fluid inflow parts of the variable displacement actuators in operation, such that the pressures in the fluid inflow parts of the variable displacement actuators in operation approach a common target pressure.

A shovel includes a first pump 14L; a second pump 14R; a hydraulic swing motor 21; a pump/motor 14A configured to generate an engine-assist torque in response to hydraulic oil from the hydraulic swing motor 21 during swing deceleration; an accumulator 80 configured to accumulate the hydraulic oil flowing out of the hydraulic swing motor 21 during swing deceleration; a regeneration valve 22G configured to switch open/close of transfer from a discharge port 21L to the pump/motor 14A and the accumulator 80; and a controller configured to control the regeneration valve 22G. During swing deceleration, the controller adjusts an open area of the regeneration valve 22G in such a way that a swing flowing-out pressure becomes a swing braking target pressure, and causes the hydraulic oil flowing out of the hydraulic swing motor 21 to flow into the pump/motor 14A and the accumulator 80 at the same pressure.