In a method of driving a hydraulic system, a contracting force is applied to a hydraulic actuator, thereby causing hydraulic fluid from the hydraulic actuator to flow through a first hydraulic pump motor into a first accumulator, thereby causing the first hydraulic pump motor to apply rotational energy to a shaft. The rotational energy from the shaft is applied to a second hydraulic pump motor, thereby causing hydraulic fluid to be pumped from a second accumulator to a third accumulator so as to store energy in the third accumulator. Once energy is stored in the third accumulator, the second hydraulic pump motor is driven with hydraulic fluid stored in the third accumulator so as to apply rotational energy to the shaft, thereby driving the first hydraulic pump motor to pump hydraulic fluid from the first accumulator to the hydraulic actuator, thereby applying an expanding force to the hydraulic actuator.

An inexpensive engine assist device capable of performing stable energy regeneration from an accumulator and a working machine on which the engine assist device is mounted are provided. A variable capacity type main pump and a variable capacity type assist pump are directly connected to an engine. A return pressure oil flowing out from a fluid pressure actuator is temporarily accumulated by a sub-accumulator and is supplied to an inlet of the assist pump, and the assist pump pressurizes the return fluid pressure oil and supplies the return fluid pressure oil to a main accumulator. A controller calculates and controls an assist pump swash plate angle, and assist starting torque or charge starting torque, and introduces a pressure-accumulated fluid discharged from the main accumulator to the inlet of the assist pump or introduces a pressurized fluid discharged from an outlet of the assist pump into the main accumulator.

In a hydraulic driving system for construction machines, when track motors 3f and 3g are operated and the delivery pressure of a main pump 2 increases to a second value PS2 of the set pressure of a main relief valve 14, the set pressure of a signal pressure relief valve 16 increases from a third value PA1 to a fourth value PA2, which is smaller than the second value PS2 of the set pressure of the main relief valve 14, the difference between the second value PS2 and the fourth value PA2 being smaller than the target LS differential pressure. With such a structure, even if one of actuators reaches the stroke end and the delivery pressure of the hydraulic pump rises to the set pressure of the main relief valve, the other actuators do not stop, and further when the main relief valve is configured to increase the set pressure during operation of a specific actuator, the load pressure of the specific actuator does not increase to the increased set pressure of the main relief valve.

The present invention is related to a construction machine, the construction machine including: a main pump; a swing motor operated by the main pump; a swing valve configured to control flow of the hydraulic oil by the main pump to supply the hydraulic oil to the swing motor and to control the flow of the hydraulic oil having been discharged from the swing motor; a hydraulic oil control valve unit configured to control the flow of the hydraulic oil according to a pressure of the hydraulic oil at opposite ends; a first accumulator configured to store the hydraulic oil when the swing motor is decelerated; a regeneration control valve provided between the hydraulic oil control valve unit and the first accumulator; and a controller configured to control the hydraulic oil control valve unit and the regeneration control valve by determining acceleration or deceleration of the swing motor.

An object is to provide a cylinder device which can be used over a long period of time. The cylinder device includes a damper, a pump, a motor and an external tank. The damper has a cylinder, a first bracket, a piston, a piston rod and a second bracket. The piston is slidably inserted into an interior of the cylinder. The piston rod is inserted into the cylinder and connects the piston to an end located in the cylinder. The pump is disposed at one of right and left sides with respect to a central axis of the cylinder. The motor is disposed at the one side which is the same side as the pump with respect to the central axis of the cylinder. The external tank is disposed at the other side with respect to the central axis of the cylinder.

Swing kinetic and boom potential energy may be recovered in a machine having a movable work tool, a swing motor for rotating the work tool, a hydraulic cylinder for raising and lowering the work tool, a pump selectively connected to the swing motor and the hydraulic cylinder, and a power source outputting power to drive the pump. The machine may further include a first accumulator, a swing charge valve having a charge set pressure, and a boom charge valve. The swing charge valve selectively fluidly connect the swing motor to the first accumulator, and open to fluidly connect the swing motor to the first accumulator when a swing motor fluid pressure is greater than a charge set pressure of the swing charge valve. The boom charge valve may selectively fluidly connect a head-end chamber of the hydraulic cylinder to the first accumulator when the work tool is lowered.

A hydraulic control system may include a closed loop hydraulic circuit with at least one hydraulic motor. A plurality of variable displacement pumps may be fluidly connected in parallel in the closed loop hydraulic circuit. A plurality of hydraulic actuators may be configured to adjust the displacement of the variable displacement pumps. A pilot valve assembly may be configured to supply the hydraulic actuators with hydraulic fluid having a pilot pressure corresponding to a desired displacement of the variable displacement pumps. A pressure regulating device may be configured to limit the pilot pressure of the hydraulic fluid supplied to the hydraulic actuators when a working pressure in the closed loop hydraulic circuit reaches a maximum allowable working pressure.

A gangway comprises a fixed platform and a support structure connected to the fixed platform in a manner that allows the support structure to rotate with respect to the fixed platform between a raised stowed position and a lowered deployed position. A raising assembly is operative to rotate the support structure from the deployed position to the stowed position. The raising assembly includes at least one fluid actuated cylinder connected between the fixed platform and a distal end of the support structure. A raising actuator is usable by an operator to cause operation of the cylinder in a manner that rotates the support structure toward the stowed position.