Abstract: A vehicle is disclosed having a hydraulic system. The hydraulic system includes a pressure regulator that maintains the output pressure from a hydraulic pump above a predetermined minimum pressure.

Abstract: Disclosed is a hydraulic system for utility vehicles, in particular agricultural tractors, for supplying primary and/or auxiliary pressure medium consumers (6, 11, 12) with pressure medium, comprising a pump (1), whose pressure and flow are controlled as a function of the load pressure of the pressure medium consumers by a pressure and flow controller (13) to which whenever auxiliary pressure medium consumers (11, 12) are operating, a higher load pressure compared to the actual load pressure is reported through an amplifier device. In order to obtain rapid response of an actuated auxiliary pressure medium consumer it is proposed that the amplifier device (29) consists of a proportionally controllable pressure reducing valve (39).

Abstract: A hydraulic control system for a working machine according to the present invention comprises a hydraulic pump for supplying working oil to a hydraulic actuator through a control valve, a relief mechanism disposed on the discharge side of the pump, the relief mechanism assuming an open state when a pump discharge pressure which varies according to the pump flow rate exceeds a predetermined pressure and assuming a closed state when the pump discharge pressure becomes the predetermined one or lower, an ordinary control means for controlling the pump flow rate in accordance with working information, and a pressure feedback control means for controlling the pump flow rate in accordance with the pump discharge pressure. In this system, out of controls performed by both control means, control wherein the flow rate by one control becomes smaller than that of the other is selected, thereby opening/closing control of the relief mechanism is performed.

Abstract: A method is described for controlling a hydraulic system, particularly of mobile working machine, with at least one internal combustion engine driving at least one hydraulic pump with adjustable volumetric displacement and possibly additional fixed-displacement pumps.

Abstract: A hydraulic control apparatus is provided to prevent failure that can occur due to hunting, to elevate performance of a hydraulic control valve, and to improve operation efficiency by effectively conducting bleed off. The hydraulic control apparatus can include a first change over valve group that can include a change over valve connected with a first delivery line associated with the variable capacity pump, and arranged to have load sensing function. A second change over valve group can also be provided, and can include at least one change over valve connected with a second delivery line associated with the variable capacity pump. An open and close motion valve and a compensation valve can be configured to constitute a pressure compensation flow control means connected through the second delivery line and the second change over valve group.

Abstract: To keep one of three hydraulic pumps unaffected by variations in torque of the remaining hydraulic pumps when the three hydraulic pumps are used, displacements of the first and second hydraulic pumps are controlled based on their own delivery pressures P1,P2 and a pressure P3? obtained by reducing through a reducing valve 14 a delivery pressure P3 from the third hydraulic pump, while a displacement of the third hydraulic pump 3 is controlled only by its own delivery pressure P3. The pressure oil delivered from the third hydraulic pump 3, therefore, remains unaffected by variations in delivery flow rates from the first and second hydraulic pumps 1,2, in other words, by variations in their torque consumptions, so that the third hydraulic pump is assured to provide a stable flow rate.

Abstract: A protection system is provided for a work machine with a power source. At least one sensor is configured to monitor a fluid parameter of a work machine system external to the power source. The sensor is further configured to produce a signal indicative of a value of the fluid parameter. The component protection system has a control module in communication with the at least one sensor, the control module being configured to derate a power source output base upon the value of the fluid parameter.

Abstract: The present invention lowers energy loss while at the same time enhancing the responsiveness of a steering control system. When a steering controller is operated rapidly, the aperture area of a steering flow control valve 4 rapidly increases, and the differential pressure (Pp?-PL) across the steering flow control valve 4 rapidly decreases. When the differential pressure (Pp?-PL) across the steering flow control valve 4 rapidly decreases, a flow control valve 6 is biased by the spring force of a spring 6f and quickly moves to the side of a valve position 6b to increase the differential pressure (Pp?-PL) and make it correspond to a set pressure. Thus, the pressure oil of a surplus flow ?, which up to this point has been flowing to a discharge oil line 7, is quickly supplied from the flow control valve 6 to a steering hydraulic cylinder 5 via the steering flow control valve 4. Thus, an output Q? starts quickly relative to an input St.

Abstract: Laying apparatus and method for cables, lines, conductors or suchlike. The apparatus comprises at least a hydraulic circuit provided with a variable delivery feed pump and with a motor connected to the feed pump in order to drive laying members for the cables and suchlike. The hydraulic circuit comprises detectors able to detect the value of pressure of the oil inside the hydraulic circuit and to compare it with a pre-determined pressure value, and valves connected to the detectors and able to reduce the delivery of the feed pump in the event that the pressure measured exceeds the pre-determined pressure value.

Abstract: An apparatus is provided which has sensors that detect pressure on opposite sides of a control valve which controls the flow of hydraulic fluid from a source to a hydraulic actuator. The sensors produce electrical signals indicating those pressures. In response to the sensor signals, a controller produces an output signal the operates a proportional control valve to thereby regulate pressure at a node of the hydraulic circuit. Several mechanisms are described that react to the pressure at the node by varying the pressure of the fluid being supplied to the main valve so that a controlled pressure level is achieved.

Abstract: To keep one of three hydraulic pumps unaffected by variations in torque of the remaining hydraulic pumps when the three hydraulic pumps are used, displacements of the first and second hydraulic pumps are controlled based on their own delivery pressures P1, P2 and a pressure P3? obtained by reducing through a reducing valve 14 a delivery pressure P3 from the third hydraulic pump, while a displacement of the third hydraulic pump 3 is controlled only by its own delivery pressure P3. The pressure oil delivered from the third hydraulic pump 3, therefore, remains unaffected by variations in delivery flow rates from the first and second hydraulic pumps 1,2, in other words, by variations in their torque consumptions, so that the third hydraulic pump is assured to provide a stable flow rate.

Abstract: The invention relates to a method for controlling a pressure supply device in a hydraulic circuit, especially in a hydraulic circuit in an automatic gearbox which comprises an hydraulic pump, a pressure control valve and a consumer. The hydraulic pump is controlled if the system pressure falls below a specific lower threshold value and is switched off if a specific higher threshold value of the system pressure is reached or exceeded. In the data on the system pressure is not available, the current system pressure is calculated.

Abstract: A method and an apparatus for monitoring the operation of a percussion device, which percussion device comprises a percussion piston and a pressure channel for supplying pressure medium to the percussion device for moving the percussion piston. The method and the apparatus measure pressure pulsation of the pressure medium acting in the pressure channel, which pressure pulsation is depicted as a pressure curve. From pressure pulsation are determined parameters depicting the operating state of the percussion device and the operating state of the percussion device is determined on the basis of the parameters. In addition, an arrangement for controlling the operation of the percussion device on the basis of the operating state of the percussion device.

Abstract: A fuel injection control unit, including an electronic governor and a controller for an engine performs control in a governor region based on an isochronous characteristic. A working machine controller receives a delivery pressure signal P and controls a regulator such that, when the delivery pressure of a hydraulic pump exceeds a predetermined pressure P1, the displacement of the hydraulic pump does not exceed a value decided in accordance with a preset pump absorption torque curve. The working machine controller controls the regulator such that, when the delivery pressure of the hydraulic pump 2 is not higher than the predetermined pressure P1, the displacement of the hydraulic pump is increased as the delivery pressure of the hydraulic pump lowers from the predetermined pressure P1.

Abstract: An electrohydraulic actuation system in which the quantity of fluid being fed to hydraulic actuators under higher load pressure among those of a plurality of electrohydraulic actuators can be prevented from becoming deficient. In the electrohydraulic actuation system (100), a selection valve (141), a two-position valve (142), a spring (143) and a hydraulic cylinder (144) for altering delivery alter delivery of the working oil of a variable delivery hydraulic pump (111) based on the maximum pressure of the working oil being fed to hydraulic motors (122, 132) and the delivery pressure of working pump (111), and pressure gauges (145, 146, 147, 148, 149) and a computer (not shown) alter the rotatim speeds of motors (123, 133) at a substantially same rate for them.

Abstract: An integrated valve system (51) for use with a variable displacement hydrostatic pump (11), including a relief and check valve assembly (75) and a pressure override (POR) section, operable to communicate pressure above a predetermined POR setting from the high pressure side (15) of the HST closed loop to a stroking cylinder (29) to destroke the pump (11). A high pressure relief spring (83) determines the relief setting, and a POR compression spring (109) determines the POR setting, the relief spring and the POR spring being seated independently of each other, such that the POR setting may be adjusted without effecting the operation of the relief and check valve assembly (75).

Abstract: A hydraulic control system is presented that includes a hydraulic actuator, an operation command unit that provides a first control operation signal, a directional control valve unit with a directional control valve that supplies pressure oil to the hydraulic actuator based on the first control operation signal, a variable displacement hydraulic pump having a discharge rate that changes in response to the first control operation signal, a differential pressure generating unit that generates a differential pressure between pressure of the hydraulic pump and oil pressure and outputs a second control operation signal indicative of the differential pressure. The hydraulic control system further includes a control quantity correcting unit that corrects the first control operation signal based on the second control operation signal, and a discharge rate control unit that controls the discharge rate of the variable displacement hydraulic pump based on the corrected first control operation signal.

Abstract: A circuit for controlling a discharge amount of a hydraulic pump to an actuator irrespective of a load pressure of the actuator even when an engine operates at a low speed has a variable displacement hydraulic pump connected with the engine; an actuator connected with the hydraulic pump; a center-bypass directional switching valve in a flow path between the hydraulic pump and the actuator for controlling start, stop and directional switching of the actuator during a switching operation; a pilot signal generating means in a down stream side of the center bypass for controlling the discharge amount of the hydraulic pump; and a discharge amount adjusting valve in a supply path of the actuator of the directional switching valve for controlling a discharge amount of hydraulic fluid to the actuator.

Abstract: An open circuit system that uses a two-position three-way logic valve that automatically compensates for remote pressure in the system. The system has a pump that sends a pump supply through an orifice to the two-position three-way logic valve. Then depending on the load sense signal, the valve either allows the flow of the pump supply to the compensation relief valve or alternatively, the logic valve prevents the flow from the pump supply. The load sensing signal determines whether the valve will allow flow from the pump supply.

Abstract: A method and apparatus for controlling the motor output speed of a variable displacement hydraulic motor are disclosed. The method may include determining a value indicative of a motor output speed, determining a value indicative of a desired motor output speed, determining a desired position of a control valve using a nonlinear feedback control law, and, controlling the motor output speed as a function of the control valve position, wherein the nonlinear feedback control creates a first order system response.

Abstract: The present invention relates to a drive comprising a hydro machine whose injection volume is changeable, comprising an adjustment device for the changing of the injection volume of the hydro machine, comprising a first control valve which is in communication with the adjustment device and which is connected such that it effects a position of the adjustment device causing a low injection volume in a first position and effects a position of the adjustment device causing—compared with this—a large injection volume in a second position.

Abstract: To provide a control system, which can realize a saving in energy and an improvement in the efficiency of work, for a construction machine having an engine, hydraulic pumps, pump regulators, a fuel injection system, hydraulic actuators, control valves including plural flow control valves, and control devices, a controller is constructed including an engine speed control for correcting an inputted reference target engine speed NRO to obtain a corrected target engine speed NROO, a pump absorption torque control for determining a target maximum pump absorption torque value TRO, and a first correcting system for correcting the corrected target engine speed NROO and the target maximum pump absorption torque value TRO into a new target engine speed NRO1 and a new target maximum pump absorption torque TR1, respectively, in accordance with a coolant temperature signal TH1 detected by a coolant temperature detector.

Abstract: A hydraulic control circuit of a boom cylinder for a work machine, which, when controlling the supply and discharge of pressurized oil with respect to a boom cylinder, improves fuel efficiency, work efficiency in combined operations, and work efficiency and operationality in work of difficult boom operations, such as debris raking-up work and bumping work, etc. The hydraulic control circuit of a boom cylinder is provided with a first change valve for holding the boom control valve in the neutral position, a communication line for causing the head side oil chamber and the rod side oil chamber to communicate with each other, an opening and closing valve for opening and closing the communication line, and a pilot operation check valve that is changed to an unidirectional state where, although an oil flow from the head side oil chamber to the rod side oil chamber is permitted, a reverse flow is hindered, and a bi-directional state is permitted where the oil flows in both directions.

Abstract: There is provided an oil supply unit for a running power transmission of a vehicle. The oil supply unit includes a housing, a hydraulic pump of a variable displacement type, a detecting mechanism and a control mechanism. The detecting mechanism is constructed to monitor a driven state of an engine. The control mechanism is constructed to operate an output adjusting member of the hydraulic pump to thereby regulate the discharge quantity against the suction quantity of the hydraulic pump based on the driven state of the engine.

Abstract: A fluid controller (21) of the static load signal type which includes controller valving (25), a fluid inlet port (27), a control fluid port (33), a fluid return port (37), and a load signal port (39). The controller includes valving (25) which defines a neutral position (N) and an operating position (R), and further defines a variable load sense drain orifice, having a maximum flow area when the valving is in the neutral position and a decreasing flow area as the valving is displaced toward the operating position. The valving defines a variable load sense boost orifice (91) communicating from the inlet port (27) to the load signal port (39), the boost orifice having a maximum flow area when the valving is in neutral, and a decreasing flow area as the valving is displaced toward the operating position.

Abstract: In a fluid system, a source of pressurized fluid operably communicates with first and second actuators. First and second control valves control fluidly communicates with the first and second actuators. A first pressure compensating valve fluidly communicates with the first control valve and first actuator. A first signal conduit fluidly communicates with fluid flow being directed by the first control valve to the first pressure compensating valve and first actuator. A second pressure compensating valve fluidly communicates with the second control valve and second actuator. A second signal conduit fluid communicates with fluid flow being directed by the second control valve to the second pressure compensating valve and second actuator. A control signal pressure generated from a greater of a first signal pressure carried by the first signal conduit and a second signal pressure carried by the second signal conduit fluidly communicates with the first and second pressure compensating valves.

Abstract: A hydraulic system includes a pressurized fluid supply, a plurality of non-priority elements each including a signal port and a supply port, at least one priority implement including a signal port and a supply port and a priority valve arrangement. The priority valve arrangement is adapted to receive fluid from the pressurized fluid supply and selectively apportion fluid between the supply port of the priority implement and the supply ports of the plurality of non-priority elements. The valve arrangement includes a signal circuit operative to establish a flow priority between the priority implement and the plurality of non-priority implements and the signal circuit is in fluid communication with the priority supply. The signal circuit includes a pilot portion and a dynamic load portion and the signal port of the priority implement is in fluid communication with the priority valve arrangement through the dynamic load portion of the signal circuit.

Abstract: A fluid system for plural motor driven pumps is disclosed. The fluid system includes a hydraulic motor, a fluid reservoir, and a plurality of fixed displacement pumps. A control valve selectively directs flow of fluid to either a reservoir or the hydraulic motor. A control system responsive to an external condition and an internal condition generates a signal for each condition. The control valve is operated by the signals. The internal signal may be generated by an internal pressure monitoring device.

Abstract: A control system for operating a hydraulic system includes a user input device which generates an input signal indicating desired movement of a hydraulic actuator. A mapping routine converts the input signal into a velocity command indicating desired actuator velocity. A valve opening routine transforms the velocity command into a flow coefficient which characterizes fluid flow through the valve assembly and from the flow coefficient produces a set of control signals designating levels of electric current to apply to valves within the valve assembly. A pressure controller regulates pressure in the supply line in response to the velocity command. When the hydraulic system has a plurality of functions, the control system adjusts each velocity command to equitably apportion fluid to each function when the aggregate flow being demanded by the functions exceeds the total flow available from a source.

Abstract: A fluid controller (21) of the static load signal type which includes controller valving (25), a fluid inlet port (27), a control fluid port (33), a fluid return port (37), and a load signal port (39). The controller includes valving (25) which defines a neutral position (N) and an operating position (R), and further defines a variable load sense drain orifice, having a maximum flow area when the valving is in the neutral position and a decreasing flow area as the valving is displaced toward the operating position. The valving defines a variable load sense boost orifice (91) communicating from the inlet port (27) to the load signal port (39), the boost orifice having a maximum flow area when the valving is in neutral, and a decreasing flow area as the valving is displaced toward the operating position.

Abstract: The present invention intends to improve a hydraulic control unit and prevent the occurrence of hunting as well as to reduce the size of the hydraulic control unit.

Abstract: A method is provided for controlling displacement of a variable displacement pump coupled to a load. The method includes determining an electrical signal to be applied to a proportional solenoid for a desired pump displacement based on known pump characteristics. The electrical signal is provided to the proportional solenoid. The displacement of the variable displacement pump is controlled based on the electrical signal to the proportional solenoid.

Abstract: In the hydraulic tool, a main body section includes a cylinder and a piston. A head section is attached to the cylinder, includes a movable part. The piston is capable of rotating about the cylinder with the movable part. A control section is provided to the cylinder and includes oil paths and a switching valve. A piston valve reciprocally moves to control communication between a first and a second cylinder chambers. A concave is provided in a bottom face of the cylinder, escapes an end of the piston valve from a position at which the end of the piston valve contacts a bottom face, and shuts off the communication between the chambers. A projection is provided at a position different from the concave, makes the end of the piston valve contact the bottom face and allows the communication between the chambers.

Abstract: Disclosed herein is a hydraulic-pump controller that is capable of controlling absorbed pump torque in good balance against engine output at all times. In this hydraulic-pump controller, the discharge flow rates of the operating oil that are discharged from hydraulic pumps (9, 10) according to manipulation of manipulation units (12, 13) are predicted based on the discharge pressure of the hydraulic pumps (9, 10) that are driven by an engine (1), and based on the manipulation amount of the manipulation units (12, 13) that manipulate hydraulic actuators (27, 28), or a physical quantity correlating with the manipulation amount. Based on the predicted discharge flow rates and the discharge pressure, the absorbed torque of the hydraulic pumps is computed. Then, the predictive engine speed of the engine (11) is computed from the absorbed torque of the hydraulic pumps (9, 10) computed.

Abstract: A variable delivery pump is provided for use in a work system. The variable delivery pump includes a variable delivery control arrangement that uses reduced pressure from the variable delivery pump to control the delivery of fluid from the pump. The reduced pressure is directed to a first port of the variable delivery control arrangement and acts to bias the flow changing mechanism to a maximum position when the work system does not require fluid flow. When the work system needs pressurized fluid, the reduced pressure that is also being directed across a flow restrictor is progressively blocked thus causing a variable valve arrangement to controllably direct reduced pressurized fluid to a second fluid port of the flow changing mechanism in opposition to the pressurized fluid at the first fluid port. In the subject arrangement, small orifices requiring large flows is eliminated. Consequently, the subject control arrangement is not adversely subject to high viscosity oils.

Abstract: A fluid control system incorporates an orificing device between each of a plurality of pilot operated control valves in connection with a control device and a resolver. The pilot operated control valves are actuated by the control device to control different functions of a work machine. The actuation of the pilot operated control valves produces pressure flows that are sent to the respective resolver. The orificing devices include a plurality of steps that may be varied in size and shape to dampen the pressure flow to the respective resolver so that independent control for the pilot operated control valves is achieved. Additionally, a precision edge is defined within each of the orificing devices to control the flow of pressurized hydraulic fluid through the respective orificing device and maintain a consistent viscous drag therethrough independent of temperature and oil-viscosity variations.

Abstract: The present invention provides a hydraulic control system with preferred operating performance, response in operation and stability, and with system efficiency enhanced greatly.

Abstract: In a hydraulic drive system in which a target compensated differential pressure for each of pressure compensating valves 21a, 21b is set in accordance with a differential pressure between a pump delivery pressure and a maximum load pressure, and a target LS differential pressure is set as a variable value depending on a revolution speed of an engine 1, a fixed throttle 32 and a signal pressure variable relief valve 33 are disposed in a maximum load pressure line 35. A relief setting pressure PLMAXO of the signal pressure variable relief valve 33 is set so as to satisfy PLMAXO=PR−PGR+a (where a is a value smaller than PGR) with respect to a target LS differential pressure PGR and a setting pressure PR of the main relief valve 30.

Abstract: A speed control apparatus and method of a working vehicle which can reduce a working speed and a traveling speed of the vehicle to a desired speed range in correspondence to a change of working conditions at a time of a vehicle crane operation. A controller sets an optional hydraulic pump absorbing curve when an operator selects the crane operation mode. When the speed is adjusted by the operator, a pump tilt and rotation angle is automatically controlled to a pump absorbing torque in correspondence to the crane working speed along the optional pump absorbing torque curve.

Abstract: The present invention provides for a control system 20 of a hydraulic construction machine for enhancing a responsibility and stability of a work implement movement. The control system 20 comprises a variable displacement type hydraulic pump 2, a hydraulic actuator 7 driven by hydraulic fluid delivered from the pump 2, a flow control valve 5 for controlling the flow rate of the hydraulic fluid to the hydraulic actuator 7 in response to a travel amount of an operating lever 8, the variable bleed valve 14 disposed in the bleed-off hydraulic circuit 13 through which exhausts the hydraulic fluid supplied to the hydraulic actuator 7 and a controller 15 for controlling the flow rate through the variable bleed valve 14.

Abstract: The invention refers to control devices applied in a hydrostatic transmission, which includes a motor pump MP, a hydrostatic circuit HC 1 and HC 2 and an impelling pump IP, which is formed by a rotor 1, a stator 2 and a body 3; the fluid debit is infinitely variable and is obtained by the radial and variable decentralisation of the said stator 2, by means of the impulsion of the rods A and B. The devices are constituted by pistons 4 and 5, which impel the rods A and B, and are inserted in cylinders 6 and 7; by springs systems 9, 10 and 11, which regulate the position of the pistons and of the rods, and by a command formed by a valve 8, inserted in a vacuum circuit with ways V1 and V2, which communicate with the cylinder 7.

Abstract: A method and a control arrangement for driving at least one hydraulic consumer are disclosed. The control arrangement comprises a pump whose output is adjustable as a function of the load pressure of a consumer. The consumer is driven through a proportional directional valve forming a measuring orifice, a pressure compensator being associated with the directional valve, allowing the pressure drop across the measuring orifice to be maintained constant irrespective of the load pressure. According to the invention, a low load pressure is indicated to the pump when the pressure compensator is completely open, so that the pressure drop across the measuring orifice is reduced.

Abstract: A method and system for controlling the steady-state speed of a cylinder in an electrohydraulic system having multiple cylinders includes a plurality of levers for controlling each of the cylinders. A controller, in communication with the levers and the hydraulic cylinders, has a limited number of parameters defining at least one desired relationship between steady-state speed and lever position for each of the cylinders stored therein. The controller further determines a current desired relationship for each of the cylinders from the associated at least one desired relationships. Upon detecting movement of the lever, the controller determines a current position of the lever associated with one of the cylinders and then controls the steady-state speed of the associated cylinder based on the limited number of parameters defining the current desired relationship and the position of the lever.

Abstract: The present invention provides a hydraulic controller for a variable capacity hydraulic transmission. This hydraulic controller reduces the load of the engine to improve fuel efficiency while maintaining a hydraulic pressure which is necessary for the control of the skew angles of the swash plates of the variable capacity type hydraulic pump and hydraulic motor that are incorporated in the transmission. The hydraulic controller adjusts the hydraulic pressure supplied to the servo cylinders 92 and 96 which are to tilt the pump swash plate 32 and the motor swash plate 38, to a minimum necessary pressure on the basis of the pressure Ph of the oil passage which is at the higher pressure in the hydraulic closed circuit 26.

Abstract: A hydraulic circuit system having a load sensing system including a hydraulic pump, a plurality of hydraulic actuators driven by a hydraulic fluid delivered from the hydraulic pump, a plurality of control valves disposed between the hydraulic pump and the plurality of acutators, a signal detecting hydraulic line to which a signal pressure based on a maximum load pressure among the plurality of hydraulic actuators is introduced, and pump control means for controlling a delivery pressure of the hydraulic pump to be held higher than the signal pressure by a predetermined value.

Abstract: A hydrostatic vehicle drive has a control (5) for controlling an output torque of the drive and another control device (5) for controlling the output torque of a hydrostatic drive, the control device (5) having a controllable pressure-limiting valve (6) by means of which the working pressure can be adjusted and which is used for sensitive control of the output torque of a hydraulic motor (3). The pressure-limiting valve (6) can be controlled by a proportionally adjustable pressure-reducing valve (7).

Abstract: A fixed throttle 12 is provided in a delivery line 11a of a fixed pump 11 driven by an engine 9 for rotation together with a hydraulic pump 1, and a differential pressure detecting valve 31 is provided in association with the fixed throttle 12 to detect a differential pressure across the fixed throttle 12 and to output a pressure lower than the detected differential pressure by a predetermined value. The output of the differential pressure detecting valve 31 is introduced, as a signal pressure, to a pressure bearing section 5c of a load sensing valve 5, thereby setting a target differential pressure. With that arrangement, a pressure in link with an engine revolution speed can be directly employed as the set differential pressure of the load sensing valve, and the structure of the load sensing valve can be avoided from being complicated.

Abstract: In a hydraulic shovel which operates in a high-speed operation mode and a low-speed operation mode, an object of the present invention is to satisfy both low fuel consumption operation speed.

Abstract: A hydraulic line slit 20 formed in a valve body 50 of a flow distribution valve 5-1, a control chamber 70, and a hydraulic line 31-1 are connected to a signal transmitting hydraulic line 9. A lap portion 32 is formed in the hydraulic line slit 20, the lap portion 32 having a check valve function with a lap amount X when the valve body 50 is in a cutoff position. A 2-position, 3-way valve 11 is disposed in the hydraulic line 31-1. The valve 11 connects the control chamber 70 of the flow distribution valve 5-1 to only the signal transmitting hydraulic line 9 when an external signal F is not applied, and to both the signal transmitting hydraulic line 9 and a lower-pressure detecting hydraulic line 35, which is connected an outlet passage 5b of a flow distribution valve 5-2 on the side of a hydraulic actuator 3-2, when the external signal F is applied.

Abstract: An electrohydraulic control device (10) for a double-acting consumer (11) is proposed, in which a continuous volumetric flow control to and from the consumer (11) is possible with two proportional 4/2-way magnet valves (12, 13), each with one seat valve function (26), and by means of two blocking valves (29, 38) of the seat valve type; free floating is attainable as the fourth work position. The magnet valves (12, 13) are structurally identical and are each connected into the volumetric flow to the consumer and the volumetric flow leaving the consumer; each consumer connection (28, 36) is sealed off tightly by a seat valve function (26) of the magnet valves (12, 13) and a blocking valve (29, 38). The magnet valves (12, 13) have a main control member (57) and a pilot control member (58), which cooperate in the manner of a followup controller and make do without a separate control oil supply, so that high hydraulic capacities can be controlled continuously and with short response times.