A hydraulic circuit for a construction machine is disclosed, which can prevent a loss of pressure during a combined work. The hydraulic circuit includes a variable displacement hydraulic pump, at least two hydraulic actuators driven by hydraulic fluid that is supplied from the hydraulic pump, control valves installed in a center bypass path of the hydraulic pump and shifted to control a start, a stop, and a direction change of the hydraulic actuators, parallel flow paths having inlets branched and connected to predetermined positions on an uppermost stream side of the center bypass path and outlets connected to inlet ports of the control valves, bleed-off paths formed on the control valves other than the lowermost downstream side control valve among the control valves to selectively communicate with the center bypass path, the bleed-off paths communicating with the center bypass path when the plurality of control valves are shifted for a combined work, and a switching valve installed on a lowermost downstream side of the center bypass path to intercept the center bypass path when pilot signal pressure is applied.

A servo actuator is provided which may comprise a controller configured to control a plurality of solenoid valves based upon an output signal. The plurality of solenoid valves may be used to control the position of the object. For example, a set of solenoid valves, of the plurality of solenoid valves, may be configured to conduct fluid from a tank into a first chamber of the cylinder, conduct fluid from the tank into a second chamber of the cylinder, conduct fluid from the second chamber of the cylinder into a first solenoid valve and/or conduct fluid from the first chamber of the cylinder into the first solenoid valve. The first solenoid valve, of the plurality of solenoid valves, may be configured to conduct fluid from the set of solenoid valves into a vent valve based upon a pulse width modulation (PWM) signal received from the controller.

Modular directional valve with two or more crossing elements (E1 . . . En) fed by a variable displacement (PA), negative control or load sensing pump.

A pressure regulator (5) is placed in the entry side and only on the bypass line and upstream of the first element (E1 . . . En).

In the single drive, it makes the flow rate to the utility independent of the load and allows setting a maximum flow rate at the end of the stroke; in multiple drives, it ensures that the sum of the required flow rates is independent of the loads.

A pneumatic device having a pneumatic cylinder and a piston movably mounted in the pneumatic cylinder to divide an interior of the pneumatic cylinder into two chambers. The chambers are connected to a line network having a valve assembly. The line network, in a plurality of operating states of the valve assembly serving for venting the respective chamber, connects the respective chamber to at least a respective selected one of a plurality of outflow openings, of the pneumatic device, and in a further operating state of the valve assembly, disconnects the respective chamber from the outflow opening. A control installation of the pneumatic device adjusts the operating state of the valve assembly. The line network is designed so that, in at least three of the operating states for venting the respective chamber, the connection between the respective chamber and the outflow opening is established by mutually dissimilar flow resistances.

An object to reduce a relief amount at the start of turning. A hydraulic drive system of a construction machine includes: a turning control valve disposed on a first circulation line extending from a first pump; a boom control valve disposed on a second circulation line extending from a second pump; first and second regulators, which change tilting angles of the first and second pumps; and a controller, which controls one or more solenoid proportional valves, which output a secondary pressure to the first and second regulators. While a turning operation is being performed, if a discharge pressure of the first pump is higher than a first setting value and a discharge pressure of the second pump is lower than a second setting value, the controller lowers first and second horsepower control lines that restrict discharge flow rates of the first and second pumps.

A pneumatic manifold with internal and external porting is machined in a specific sequence for pressurized and exhausting air control. Electro-pneumatic valves and or blocking plates are fastened and sealed to the positions of exterior porting. The electro-pneumatic valves complete the pneumatic circuit already machined in the manifold. Electro-pneumatic valves can be added or removed depending on the required functions. Other exterior ports on the manifold allow for but are not limited to connection of a pressure transducer, exterior pilot feeds, individual open/close speed controls, individual secondary slow down speed controls for open and close. The manifold allows the mounting of three electro-pneumatic valves wherein each valve controls a certain specific sequential function. When used with a compatible means of electronic control, the manifold can replace most pneumatic control devices driving a pneumatic actuator for the purpose of moving an access mechanism, such as a garage door.

This disclosure relates to a construction machine utilizing battery and hydraulic power and comprising an electronic power unit comprising a battery and an electric motor, a hydraulic pump driven by the electronic power unit and discharging hydraulic fluid, a hydraulic line through which the hydraulic fluid discharged from the hydraulic pump moves, a main control valve installed on the hydraulic line and controlling the supply of the hydraulic fluid to at least one of propulsion devices or various working devices requiring hydraulic power, a bypass cut valve installed downstream of the main control valve on the hydraulic line and configured to open and close the hydraulic line, and a controller initiating a warm-up mode to increase the output of the electronic power unit and open the bypass cut valve.

A working machine control system includes: a split-flow fluid pressure pump configured to discharge a working fluid from a first discharge port and a second discharge port; a communication switching valve configured to be switched by a switch signal when any one of a first operation valve and a second operation valve is switched so as to allow a first neutral passage and a second neutral passage to communicate with each other; a neutral cut valve configured to be switched by the switch signal so as to block communication between a tank and one of the first neutral passage and the second neutral passage for the first operation valve or the second operation valve that is not switched; and a discharge flow rate adjusting device configured to adjust the fluid pressure pump so as to reduce a discharge flow rate thereof when the switch signal is inputted from any one of the first operation valve and the second operation valve.

A hydraulic working machine is provided that uses a variable displacement pump and open center type flow rate control valve for a controlling a hydraulic actuator, and has a negative control throttle disposed in a center bypass oil passage to generate a negative control pressure. A hydraulic pump control system performs virtual bleed-off control for reducing the bleed-off flow rate of the center bypass oil passage, and can operate the hydraulic actuator with the same performance as an open center control. The control system includes a bypass cut valve disposed upstream from the negative control throttle to reduce flow through the center bypass oil passages, and a negative control pressure output valve that outputs a virtual negative control pressure. The control system is configured to reduce the bleed-off flow rate by operating the bypass cut valve when virtual bleed-off control is performed, and to reduce the pump flow rate by the bleed-off reduction flow rate.

A control arrangement for supplying a plurality of hydrostatic actuators includes a pump with an output connected to a circulating line that opens into a tank. The control arrangement has a metering port and an individual pressure compensator for each actuator. The individual pressure compensators are connected in series by the circulating line. Some of the pressure medium are configured to be branched off from the circulation channel for the respective actuator by the individual pressure compensators and fed to the metering port disposed downstream of the individual pressure compensator. The pressure medium that is not required is forwarded from each individual pressure compensator into the circulating line and is fed back from the last individual pressure compensator to the tank by the circulating line. The actuators are prioritized based on the order of their individual pressure compensators and move independently of the load pressure without expensive load sensing lines.