A hydraulic system is disclosed for assisting starting of a machine having an engine. The hydraulic system may include a work tool, a pump driven by the engine to pressurize fluid, and an actuator configured to receive pressurized fluid from the pump and move the work tool. The hydraulic system may also include an accumulator configured to selectively receive pressurized fluid from the pump and from the actuator, an electric starter configured to start the engine, and a motor selectively supplied with fluid from the accumulator to assist the electric starter in starting the engine.

According to the present invention, a hydraulic system of construction equipment is implemented as a close center system, which converts an input signal of an electric or hydraulic joystick into a speed signal of a work apparatus, and controls a speed of the work apparatus regardless of an external load condition, thereby minimizing fatigue of a worker to improve work efficiency, improving a work apparatus operation ability of an unskilled person, and patterning standardized work to implement automation of construction equipment.

A working machine is provided, which includes a prime mover, a first traveling pump driven by power of the prime mover to supply operation fluid through a connector fluid tube, a traveling motor including first and second ports connected to the connector fluid tube, the traveling motor configured to be switched in a first speed and a second speed higher than the first speed, a first pressure detector to detect first traveling-pump pressure near the first port, a second pressure detector to detect second traveling-pump pressure near the second port, and a controller configured, with the traveling motor switched in the second speed, to automatically shift down the traveling motor from the second speed to the first speed, when a differential pressure between the first traveling-pump pressure and the second traveling-pump is equal to or more than a deceleration threshold.

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 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).

A working machine includes a first traveling fluid line through which operation fluid applied to a first pressure receiving portion when a traveling operation member is operated, a second traveling fluid line through which operation fluid applied to a second pressure receiving portion when the traveling operation member is operated, a third traveling fluid line through which operation fluid applied to a third pressure receiving portion when the traveling operation member is operated, a fourth traveling fluid line through which operation fluid applied to a fourth pressure receiving portion when the traveling operation member is operated, and a controller configured or programed to judge, first, second, third and fourth pilot pressures, whether the traveling operation member is operated in a direction corresponding to any of spin-turn, pivotal-turn and straight-traveling.

A working machine includes a first pressure detector configured to detect a first pilot pressure that is a pressure of operation fluid passed through a first traveling fluid line, a second pressure detector configured to detect a second pilot pressure that is a pressure of operation fluid passed through a second traveling fluid line, a third pressure detector configured to detect a third pilot pressure that is a pressure of operation fluid passed through a third traveling fluid line, a fourth pressure detector configured to detect a fourth pilot pressure that is a pressure of operation fluid passed through a fourth traveling fluid line, and a controller configured or programed to judge in which of the left-front, right-front, left-rear and right-rear operation areas an operational position of the traveling operation member exists.

A working machine includes a controller to perform automatic deceleration to automatically reduce a first rotation speed of a left traveling motor to output a power to a left traveling device on a left portion of a machine body and a second rotation speed of a right traveling motor to output a power to a right traveling device on a right portion of the machine body by shifting a speed stage of each of the left and right traveling motors from a second speed to a first speed that is lower than the second speed. The controller is configured or programmed to determine, based on the second rotation speed, a left threshold for judging whether to perform the automatic deceleration in left pivot turn of the machine body, and to determine, based on the first rotation speed, a right threshold for judging whether to perform the automatic deceleration in right pivot turn of the machine body.

A hydraulic driving system includes a hydraulic cylinder with a cylinder tube and a cylinder rod, a main pump, a hydraulic-fluid path, a charge pump, a stroke position detecting unit, and a pump control unit. The hydraulic-fluid path forms a closed circuit between a main pump and the hydraulic cylinder. The cylinder rod expands or contracts depending on how hydraulic fluid is supplied and exhausted to and from first and second chambers. The charge pump replenishes hydraulic-fluid in the hydraulic-fluid path. The pump control unit performs flow-rate reduction control in which the pump control unit reduces a suction flow rate so that a suction flow rate of the main pump is equal to or less than a maximum discharge flow rate of the charge pump when the stroke position becomes closer to a stroke end of the cylinder rod than a prescribed reference position during the flow rate reduction control.