Disclosed is a hydraulic circuit for construction equipment for controlling to selectively supply a hydraulic oil from a hydraulic pump to a hydraulic cylinder for driving a boom. The hydraulic circuit for construction equipment, according to the present invention, comprises: a hydraulic cylinder driven by a hydraulic oil of a hydraulic pump; a direction control valve installed on the oil passage between the hydraulic pump and the hydraulic cylinder; an operating device installed on the oil passage between a pilot pump and the direction control valve; a center by-pass switching valve installed at the most downstream side of a center by-pass passage of the hydraulic pump; a pressure detection sensor that detects the pressure of a hydraulic oil at the large chamber side of the hydraulic cylinder; a jack-up switching valve installed on the oil passage between the operating device and the center by-pass switching valve; and a flow control valve installed in the spool of the direction control valve.

A working machine is disclosed. A boom supports an arm. An upper revolving body supports the boom. A lower traveling body mounts the upper revolving body in a rotatable state. A hydraulic actuator drives a hydraulic oil while relieving the hydraulic oil. A first pump supplies the hydraulic oil to the hydraulic actuator. A pump state detector detects load of the first pump. A controller reduces a flow rate of the hydraulic oil from the first pump to the hydraulic actuator when the pump state detector detects a predetermined state.

Each of left and right direction switching valves includes: a pump port connected to a pump; a first compensation port connected to an upstream side of a corresponding pressure compensation valve; a second compensation port connected to a downstream side of the corresponding pressure compensation valve; a pair of supply/discharge ports connected to a corresponding travel motor; and a communication port. The communication ports of the left and right direction switching valves are connected by a communication line. When a spool shifts from a neutral position by the travel operation device, the pump port communicates with the first compensation port and the second compensation port communicates with one of the supply/discharge ports and the communication port. Each direction switching valve is configured wherein a degree of communication between the second compensation port and communication port increases in a shifting amount of the spool from the neutral position.

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.

Provided is a hydraulic drive apparatus including a specific working actuator making a working arm perform a traveling assist motion upon the slip, first and second traveling motors, first and second hydraulic pumps, a traveling selector valve switchable to a neutral position and a straight traveling position, a communication throttle portion between a working fluid passage and a traveling fluid passage in the straight traveling position, and a switching control part switching the traveling selector valve to the neutral position when a single operation action is performed and to the straight traveling position when a specific combined operation action including a forward traveling operation and the specific working operation is performed. The switching control section adjusts the opening of the communication throttle section to decrease the flow rate therethrough with an increase in the difference between the first and second pump pressures.

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 hydraulic pump is driven by an engine. A hydraulic motor is driven by hydraulic fluid discharged from the hydraulic pump thereby causing a vehicle to travel. A controller controls a rotation speed of the engine and a displacement of the hydraulic pump. The controller acquires a tractive force of the vehicle. The controller changes the rotation speed of the engine to a low speed side in accordance with a reduction in the tractive force.

A load sensing valve maintains a differential pressure at a set pressure by controlling a regulator in accordance with a differential pressure between a discharge pressure of a hydraulic pump and a load pressure of hydraulic actuators. A set pressure control device controls the set pressure. A controller controls the set pressure control device to reduce the set pressure more than when the work implement is being operated, when a predetermined determination condition that includes the work implement not being operated is satisfied.

A counter balance valve (71L) is located between a directional control valve (23) and a hydraulic motor (32L) and provided on the way of a pair of supply/discharge lines (25A, 25B). The counter balance valve (71L) allows a spool (72L) to be displaced axially based on a pressure difference between the supply/discharge lines (25A, 25B). The counter balance valve (71L) includes a communicating passage (73L) for communicating the supply/discharge lines (25A, 25B) when the displacement of the spool (72L) exceeds a predetermined amount (X.sub.CM), based on a pressure difference between the supply/discharge lines (25A, 25B). The communicating passage (73L) is provided in the spool (72L) of the counter balance valve (71L).