To provide a hydraulic drive system for a work machine capable of securing a favorable operability in the case where hydraulic fluid discharged from a hydraulic actuator is regenerated for driving other hydraulic actuator. The hydraulic drive system for a work machine includes: a regeneration line that connects a bottom-side hydraulic chamber of a hydraulic cylinder to a portion between a hydraulic pump and a second hydraulic actuator; a regeneration flow rate adjustment device that supplies at least part of the hydraulic fluid discharged from the bottom-side hydraulic chamber to a portion between the hydraulic pump and the second hydraulic actuator through the regeneration line; a differential pressure calculating section that reads a pressure in the bottom-side hydraulic chamber of the hydraulic cylinder detected by a first pressure sensor and a pressure between the hydraulic pump and the second hydraulic actuator detected by a second pressure sensor, and calculates a differential pressure, or a differential pressure sensor; and a control unit that controls the regeneration flow rate adjustment device such as to gradually increase the flow rate of the hydraulic fluid flowing through the regeneration line according to an increase in the differential pressure calculated by the differential pressure calculation section or in the differential pressure detected by the differential pressure sensor.

A cylinder has a piston part, a cylinder part, and a pipe section connected to the piston or cylinder parts. A portion of the pipe section encloses a pressure compartment which receives a fluid to apply a pressure on a pressure surface so the piston part is displaced in a first stroke direction. A first return pressure compartment receives a fluid to apply a pressure on a first return pressure surface so that the piston part is displaced in a second return stroke direction. The first return pressure compartment is positioned on the outside of the pipe section, and the area of the first return pressure surface is substantially equal to the area of the return pressure surface so that a volume-neutral operation of the cylinder is provided. Also described is a hydraulic system, an excavator comprising the cylinder and a procedure for operation of the cylinder.

The present disclosure relates to a boom driving system for a hybrid excavator and a control method therefor, and more particularly, to a boom driving system for a hybrid excavator, which drives a hydraulic pump motor so as to move a boom upward and downward, and collects regenerative power of the boom using an electric motor so as to improve fuel efficiency, and a control method for the boom driving system. Provided in exemplary embodiments of the present disclosure is a boom driving system for a hybrid excavator and a control method therefor, which may allow an electric motor generator to normally produce electricity by allowing retraction speed and force of the boom actuator to be controlled to a target speed when a boom is moved downward.

A flow control apparatus and a flow control method for a construction machine are disclosed, which can perform ground leveling work for smoothing the ground by the self weight of a boom without supplying hydraulic fluid from a hydraulic pump to a hydraulic cylinder. The flow control method for a construction machine including a hydraulic pump, a hydraulic actuator connected to the hydraulic pump, a control valve controlling a flow direction of hydraulic fluid supplied to the hydraulic actuator, a work mode switching valve installed in a flow path between the control valve and the hydraulic actuator to perform switching between a normal work mode and a floating mode, a detection means for detecting a boom-down operation amount of an operation lever operated by a user, an electronic proportional valve controlling a discharge flow rate of the hydraulic pump, and a controller, the flow control method including a first step of determining whether the present mode is switched to the floating mode; a second step of changing the discharge flow rate of the hydraulic pump corresponding to the boom-down operation amount detected by the detection means if the present mode is switched to the floating mode; and a third step of outputting an electrical control signal to the electronic proportional valve so that the hydraulic pump can discharge the hydraulic fluid at the changed flow rate corresponding to the boom-down operation amount.

An excavator includes a hydraulic oil holding circuit that is provided in an oil passage between a bottom-side oil chamber of a boom cylinder and a control valve and is closed when the boom is not lowered, and a controller. The controller releases a closed state of the hydraulic oil holding circuit when the excavator is in a predetermined unstable state, and controls a released state so that an acting velocity in a lowering direction of the boom becomes less than or equal to a predetermined reference.

A hydraulic excavator (1) is provided with a controller (40) including an actuator control section (81) which, when an operation device (45, 46) is operated, controls at least one of a plurality of hydraulic actuators (5, 6, 7) in accordance with the velocities of the plurality of hydraulic actuators (5, 6, 7) and a predetermined condition. The controller (40) determines, based on a sensed value from a posture sensor (50), the direction of a load exerted on an arm cylinder (6) due to the weight of an arm (9), outputs, upon determining that the direction of the load is opposite to a driving direction of the arm cylinder (6), a second velocity Vamt2 to the actuator control section (81), and outputs, upon determining that the direction of the load is the same as the driving direction of the arm cylinder (6), a third velocity Vamt3 to the actuator control section (81).

A distance obtaining unit obtains the distance between a work implement and a design terrain. A work aspect determining unit determines a work aspect by the work implement. A limit velocity deciding unit limits the velocity of the work implement when the distance between the work implement and the design terrain becomes smaller. When the work aspect is surface compaction work and the distance between the work implement and the design terrain is within a first range of at least a portion that is equal to or less than a predetermined first distance, the limit velocity deciding unit increases the limit velocity of the work implement in comparison to when the work aspect is an aspect of a work other than surface compaction, or cancels the limiting of the velocity of the work implement.

A hydraulic control system is disclosed for an excavation machine including a tool linkage system. The hydraulic control system may have a first actuator configured to move a first link of the tool linkage system in response to input from an operator of the excavation machine, and a pressure sensor configured to generate a signal indicative of a pressure of the first actuator. The hydraulic control system may also have a second actuator configured to move a second link of the tool linkage system in response to input from the operator. In addition, the hydraulic control system may have a controller in communication with the pressure sensor, the first actuator, and the second actuator. The controller may be configured to automatically affect operation of the first actuator based on the pressure signal at times when movement of the second actuator is being requested by the operator and movement of the first actuator is being requested by the operator at a level less than a threshold.

A cargo vehicle includes a hydraulic pump driven by an engine, a cargo handling apparatus operated by hydraulic oil from the hydraulic pump, a cargo operating unit for performing an instruction operation to operate the cargo handling apparatus, an electromagnetic proportional control valve disposed between the hydraulic pump and the cargo handling apparatus, a valve controller that controls the electromagnetic proportional control valve depending on an operation state of the cargo operating unit, and a revolution detector that detects a revolution of the engine, wherein the valve controller controls the electromagnetic proportional control valve such that an opening degree of the electromagnetic proportional control valve is limited for a certain time when the revolution of the engine detected by the revolution detector is lower than a predetermined value.

To make it possible to prevent a decrease in work speed due to a decrease in the speed of a given actuator when an operator unintentionally performs a fine operation of the control lever of the other actuator in a state in which the given actuator is driven by the hydraulic fluid delivered from a plurality of pumps, a controller (41) sets, as a composite dead zone line serving as a boundary of a composite dead zone, a composite dead zone line such that as an operation amount in one direction of a control lever (12L) or (13L) of a control lever device (12) or (13) is increased, the width of the composite dead zone corresponding to an operation amount in the other direction of the control lever is widened, and corrects the operation amount in the other direction such that the demanded flow rate of an actuator increases from zero, when the control lever is operated in the other direction in a state in which the operation amount in the one direction of the control lever remains within a range of the composite dead zone, and the operation amount in the other direction exceeds the composite dead zone line.