A hydraulic system for a working machine, the system comprising: an electric machine connected to a first hydraulic machine and to a second hydraulic machine via a common axle, an output side of the second hydraulic machine being connected to an input side of the first hydraulic machine, wherein the first hydraulic machine is a variable displacement hydraulic machine with unidirectional flow; at least one hydraulic consumer hydraulically coupled to an output side of the first hydraulic machine via a supply line and configured to be powered by the first hydraulic machine; a first return line hydraulically coupling the hydraulic consumer to the input side of the first hydraulic machine.

Provided is a hydraulic circuit, for a construction machine, which drives an actuator by merging pressure oil from a fixed-volume pump into a center bypass oil path from a variable-volume pump to an oil tank, wherein the flow rate of flow from the fixed-volume pump to the center bypass oil path can be controlled in accordance with a requested flow rate of the actuator. A distribution direction-switching valve, which has a first oil path from a fixed-volume pump to an oil tank and a second oil path from the fixed-volume pump to a first center bypass oil path, has a first signal reception unit which causes a spool to slide in a direction in which the first oil path is formed, and a second signal reception unit which causes a spool to slide in a direction in which the second oil path is formed, and determines a distribution ratio of pressure oil flowing to the first oil path and the second oil path in accordance with the difference in size of the signals received by the first signal reception unit and the second signal reception unit, the first signal reception unit receiving a signal based on a negative control signal.

A drive control method of a hydraulic actuator of a construction machine includes: determining whether a rotation operation lever and a working device operation lever are operated; calculating the required pressure of a hydraulic cylinder fix a working device according to the operation amount of the rotation operation lever; calculating the required flow rates of a swing motor and the hydraulic cylinder for the working device, the required flow rates corresponding to the operation amounts of the working device operation lever and the rotation operation lever; calculating the opening areas of the first and second proportional solenoid valves of an inlet side and an outlet side by using the calculated required pressure and required flow rates of the hydraulic cylinder for the working device and the swing motor; and calculating current values to be inputted into the first and second proportional solenoid valves of the inlet side and the outlet side according to preset data values or a table in comparison with the calculated opening areas of the first and second proportional solenoid valves of the inlet side and the outlet side.

A hydraulic control system includes a flow rate control valve; a variable displacement hydraulic pump which is connected to the flow rate control valve and discharges hydraulic pressure to the flow rate control valve; a pump discharge pressure detector which is installed in a section where the flow rate control valve and the variable displacement hydraulic pump are connected, and detects the discharge pressure of the hydraulic pressure discharged from the variable displacement hydraulic pump to the flow rate control valve; and a hydraulic controller including a detection unit which is connected to the pump discharge pressure detector, detects the discharge pressure of the variable displacement hydraulic pump and converts the discharge pressure to a pump discharge pressure value, a comparison unit which receives the pump discharge pressure value from the detection unit, compares the pump discharge pressure value with a pre-stored lowest recognition pressure value, and determines whether the pump discharge pressure value is greater or less than the lowest recognition pressure value, and a calculation unit which, by interworking with the comparison unit, if the pump discharge pressure value is less than the lowest recognition pressure value, calculates a control pressure by recognizing the control

The electro-hydrostatic actuator system for raising and lowering aircraft landing gear (1) is provided with at least one hydraulic actuator (21, 22) that is constituted so as to perform retraction and deployment of landing gear (11), a hydraulic circuit (33), a hydraulic pump (32), an electric motor (31), a controller (4) constituted so as to control the operation of the electric motor upon receiving an instruction relating to retraction of the landing gear or an instruction relating to deployment of the landing gear, and a sensor (34) that detects the discharge pressure of the hydraulic pump. The controller feeds back the discharge pressure that the sensor has detected, and controls the operation of the electric motor so that the discharge pressure of the hydraulic pump becomes a target discharge pressure.

The present disclosure generally relates to a railroad track ballast tamping vehicle and associated methods of use, wherein the vehicle comprises: a rigid frame; a variable-displacement servo-pump operatively coupled to the vehicle; at least one linear hydraulic actuator operatively coupled to the frame at a proximal end of the at least one linear hydraulic actuator and comprising: at least one internal cavity for receiving hydraulic fluid from the variable-displacement servo-pump via a hydraulic hose; and an actuator rod passing through a first internal cavity and a second internal cavity of the at least one linear hydraulic actuator; and a tamping tool operatively coupled to a distal end of the at least one linear hydraulic actuator. A tamping pad associated with the tamping tool may be lowered into ballast underlying railroad tracks and between railroad track ties for performing ballast tamping operations.

This hydraulic drive system includes: a hydraulic pump that supplies a working fluid to a hydraulic actuator; a meter-in control valve that controls a flow rate of the working fluid flowing from the hydraulic pump to the hydraulic actuator; a meter-out control valve that controls a flow rate of the working fluid being drained from the hydraulic actuator into a tank; and a regeneration valve that supplies, to the hydraulic actuator, the working fluid drained from the hydraulic actuator. The meter-out control valve is connected to the hydraulic actuator in parallel with the regeneration valve.

Provided is a hydraulic machine including an actuator, a first pump and a second pump configured to supply pressurized fluid to the actuator, a driving motor configured to drive the first and second pumps, a first operator input device through which an operator's desire to operate the actuator is input, and a controller. The controller determines displacements of the first and second pumps corresponding to the operator's desire and a speed of rotation of the driving motor and controls the first pump, the second pump, and the driving motor to operate according to the displacements of the first and second pumps and the speed of rotation of the driving motor finally determined in the determination of the displacements of the first and second pumps.

A header is supported by a pair of hydraulic float cylinders, where a float pressure to the cylinders is directly controlled by an electronic control supplying a variable control signal to a PPRR valve arrangement to maintain the float pressure at a predetermined value. At the set pressure a predetermined lifting force is provided to the header. A position sensor is used to generate an indication of movement and/or acceleration and/or velocity. The electronic control is arranged, in response to changes in the sensor signal, to temporarily change the control signal to vary the lifting force and thus change the dynamic response of the hydraulic float cylinder. A lift force greater than that required to lift the header can be provided by a lift cylinder and can be opposed in a controlled manner to apply a controlled downforce by the back of the same cylinder or by a separate component.

A hydraulic apparatus comprises first and second manifolds each of which is connected to a plurality of actuators via corresponding actuator valves connected in parallel and operated responsive to inputs to regulate the flow of fluid to the actuators. A plurality of working chambers are connectable to either the first or second manifold and have a net flow which is controlled responsive to a negative feedback signal. The negative feedback signal is determined in response to a calculated pressure or flow rate in virtual fluid flow paths extending from the first and second manifolds.