Abstract: A work vehicle includes a fluid circuit to operate at least one implement for performing work, the fluid circuit having at least a first operating mode and a second operating mode. The first operating mode is configured to operate within a first predetermined flow rate range within a first predetermined fluid pressure level range. The second operating mode is configured to operate within a second predetermined flow rate range and within a second predetermined fluid pressure level range. In response to the fluid circuit operating within the second operating mode, a maximum pressure value of the second predetermined fluid pressure level range is greater than a maximum pressure value of the first predetermined fluid pressure level range, and a maximum value of the second predetermined flow level range is less than a maximum value of the first predetermined flow level range.

Abstract: A hydraulic control device includes: a hydraulic pump connected in parallel to steering and boom cylinders; a steering control valve that controls the direction of operating oil flowing through the steering cylinders; a boom control valve that connects the hydraulic pump to a tank when the valve is at a neutral position and controls the direction of the oil flowing through the boom cylinders when the valve is at an offset position; a meter-in pressure compensator that increases flow rate of the oil flowing through a variable restrictor of the steering control valve in accordance with pressure in front of and behind the restrictor; and a bleed-off pressure compensator that decreases flow rate of the oil flowing through the boom control valve in accordance with the increase in pressure of the oil flowing through the steering cylinders to maintain the predetermined pressure of the oil in the steering control circuit.

Abstract: A main relief valve 13 includes a biasing force altering unit 60, which constitutes, in combination with a gate lock valve 23 and a gate lock lever 24, relief pressure altering means for manually switching the relief pressure of the main relief valve 13 between a first pressure (a standard pressure of 25 MPa, for example) and a second lower pressure for engine start-up (e.g., 3.0 MPa). This allows the main relief valve 13 to return the hydraulic fluid discharged from a hydraulic pump 2 to a tank T in conjunction with an unloading valve 9 when multiple actuators 5a, 5b, . . . are not in operation under the ambient temperature below freezing point. As a result, it is possible to reduce the load on the hydraulic pump during cold engine start-up without compromising the anti-hunting characteristics of the unloading valve, thereby improving the engine start-up performance.

Abstract: A control pressure switching valve is disposed between a displacement regulator and a pressure control valve. The control pressure switching valve is switched between a control position (j), in which a load sensing control pressure (PLS) is permitted to be outputted from the pressure control valve to the displacement regulator, and a control release position (k), in which the load sensing control pressure (PLS) to be outputted to the displacement regulator is reduced to a prescribed low pressure value. When the regeneration of a filter is determined to be necessary, the controller switches the control pressure switching valve to the control release position (k). When the load sensing control pressure (PLS) is reduced to the low pressure value with the control pressure switching valve switched to the control release position (k), the displacement regulator increases a delivery displacement of a hydraulic pump, thereby increasing rotational load of an engine.

Abstract: A control device for a hybrid construction machine includes a discharge pressure introduction passage that leads a discharge pressure from a variable volume pump to a regulator, and a load pressure introduction passage that leads one of a maximum load pressure of respective actuators and a load pressure of a hydraulic motor to the regulator. A controller, having determined that the actuators are in an inoperative condition on the basis of a detection result from an operating condition detector, excites a solenoid of a solenoid pilot control valve such that a discharge oil from the variable volume pump is led to the hydraulic motor, and controls the regulator such that a differential pressure between the discharge pressure of the variable volume pump and the load pressure of the hydraulic motor is kept constant.

Abstract: A flow control system for a hydraulic pump of a construction machine that can variably control a discharge flow rate of the hydraulic pump in accordance with load pressure generated by a hydraulic actuator. According to the system, the discharge pressure of the hydraulic pump and the operation rate of the operation lever for the hydraulic actuators is detected, and standard load pressures of the respective hydraulic actuators are set. If the discharge pressure of the hydraulic pump is higher than preset load pressures of the hydraulic actuators, the discharge flow rate of the hydraulic pump is reduced in proportion to the operation rate in accordance with degrees of loads generated by the hydraulic actuators. If the discharge pressure of the hydraulic pump is lower than the standard load pressures of the hydraulic actuators, the discharge flow rate of the hydraulic pump is controlled in proportion to the operation rate.

Abstract: A regulator that performs control such that a tilt angle of a variable volume pump increases as a pilot pressure in a pilot flow passage decreases is provided, and when a controller determines that all of a plurality of operation valves for controlling a flow of a discharged oil that is led from the variable volume pump to respective actuators are in a neutral position, the controller supplies the discharged oil from the variable volume pump to a regenerative hydraulic motor by setting a solenoid valve in an open position and sets a pilot flow passage change-over solenoid valve in a blocking position such that the pilot pressure led to the regulator through the pilot flow passage is reduced by a pressure reducing valve.

Abstract: A hydraulic system for a machine is disclosed. The hydraulic system may have a first pump with variable displacement and being load-sense controlled, and a first hydraulic circuit associated with the first pump. The hydraulic system may also have a second pump with variable displacement and being electro-hydraulically controlled, and a second hydraulic circuit associated with the second pump. The hydraulic system may further have a flow-sharing valve arrangement configured to selectively share fluid flow between the first and second hydraulic circuits.

Abstract: Cut-in-cut-out valves for hydraulic circuits. The hydraulic circuits include a hydraulic pump outputting a variable pressure controlled by a slaving line, an accumulation circuit, a return line to the reservoir, a cut in-cut-out valve. The hydraulic circuits also include a cut-in-cut-out valve having four orifices, a first orifice connected to the supply line, a second orifice connected to the slaving line, a third orifice connected to the return line leading to the reservoir, and a fourth orifice connected to the accumulation circuit. The cut-in-cut-out valve alternates between two positions as a function of the pressure in the accumulation circuit, a cut-in position in which the first, second and fourth orifices are connected to each other, and a cut-out position in which the first and fourth orifices are closed.

Abstract: A hydraulic system, and associated method of control, includes an operator input device, a source of hydraulic fluid flow, and a plurality of actuators. At least one valve associated with each actuator for controlling a flow of fluid to and from the actuator. A controller is responsive to a signal from the operator input device to calculate a hydraulic pressure to be supplied to each of the actuators. The controller controls the source of hydraulic fluid flow and the valves for powering the actuators with the calculated hydraulic pressure. The controller also monitors a sensed parameter to determine whether the actuators can be powered with the calculated hydraulic pressure, and in response to a determination that the actuators cannot be powered with the calculated hydraulic pressure, calculates a discrepancy ratio and modifies actuation of the actuators with the discrepancy ratio.

Abstract: A hydraulic drive device for a construction machine includes an engine stopping unit and a discharge rate control unit. The engine stopping unit stops the engine when a predetermined state of the construction machine has continued for a predetermined period of time. The discharge rate control unit controls a discharge rate control pressure being input to the regulator, when an exhaust emission control device performs regeneration control, or performs warm-up control, and the gate lock lever is in the open position.

Abstract: Disclosed is a controller of a hybrid, construction machine wherein electric power is generated by utilizing the standby flow rate of first and second main pumps, and the standby flow rate is converted into energy. Pilot channels are connected to the upstream side of on/off valves which are closed when first and second main pumps ensure a standby flow rate, and a controller unit judges that the first and second main pumps are discharging at the standby low rate based on pressure signals from first and second pressure sensors, and brings first and second solenoid valves to an open position.

Abstract: A negative control type hydraulic system in which the use of a pilot pump and a load pressure generator between a hydraulic pump and a control valve is not required to prevent a power loss.

Abstract: A hydraulic pump controlling apparatus of a construction machine according to the present disclosure includes: a hydraulic pump in which a swash plate angle is controlled to control a discharge flow; an auxiliary pump; a control valve controlling a flowing direction of a fluid discharged from the hydraulic pump and selectively supplying the fluid to an actuator; an orifice and a relief valve connected between a center bypass line of the control valve and a tank T to be parallel to each other; signal pressure selecting units receiving a fluid passing through the center bypass line of the control valve and a fluid discharged from the auxiliary pump, and selecting the pressure of any one of the fluids as a signal pressure; and a regulator receiving the signal pressure selected from the signal pressure selecting units to control the swash plate angle of the hydraulic pump, and the signal pressure selecting unit selects the pressure of the fluid discharged from the auxiliary pump as the signal pressure and transfe

Abstract: A hydraulic system for an operator controlled machine, the system including at least one actuator for moving a machine component, a source of pressurized fluid for delivering pressurized fluid at a system pressure to a control valve which is operable under operator control, to control the flow of fluid from the source to the actuator at a load pressure, along a load pressure path, a flow control apparatus for controlling the flow of fluid from the source to the control valve, the flow control apparatus including an actuating part which is biased by a resilient device to a condition in which the flow control apparatus provides for a maximum flow of fluid to the control valve, actuating part movement by the resilient device being resisted by system pressure fluid and being supported by fluid at a control pressure, the control pressure being derived from the load pressure, and wherein the system includes a pressure control device to which the load pressure is communicated, the pressure control device being opera

Abstract: A hydraulic control system that includes a controller that controls the accumulator flow rate control valve and a discharge flow rate of the hydraulic pump, wherein the controller: determines a minimum value among an operation demand flow rate to be demanded by an operation amount of hydraulic actuator operating members, a pump flow rate to be determined by a discharge pressure of the hydraulic pump under a constant horsepower control and a maximum flow rate of the hydraulic pump such that the determined minimum value is an actuator supply flow rate to be supplied to the plurality of hydraulic actuators, and controls the discharge flow rate and the accumulator flow rate so as to supply the actuator supply flow rate corresponding to a total flow rate of the discharge flow rate and the accumulator flow rate.

Abstract: A method is provided for recuperating potential energy during a lowering operation of a load, wherein a hydraulic system is adapted to lift and lower the load. In the method, at least two energy recuperation modes are provided, one of the modes is selected in response to a current operating state, and the hydraulic system is controlled according to the selected mode.

Abstract: The present invention relates to a converter comprising a pump which is driven directly or indirectly by a natural force such as a water swell, it being possible for a hydraulic machine to be driven by the pump. The hydraulic machine is force-coupled to an electrical machine which may function as a generator or a motor. According to the present invention, the force acting on the pump is regulated via a control loop as a function of oscillation parameters of the natural force.

Abstract: A control system for a swashplate pump is disclosed. The control system may have a tiltable swashplate, at least one actuator movable to tilt the swashplate, a supply of pressurized fluid, and a drain. The control system may also have a first circuit connectable to the supply of pressurized fluid and to the drain and configured to control operation of the at least one actuator, and a second circuit connectable to the supply of pressurized fluid and to the drain and configured to control operation of the at least one actuator. The control system may further have a failsafe valve configured to connect the first circuit to at least one of the supply and the drain only during a normal operating condition, and to connect the second circuit to the supply and to the drain only during a failsafe condition.

Abstract: A method and apparatus for controlling a hydraulic power system is provided that includes a hydraulic motor and a hydraulic pump configured to supply hydraulic fluid to the hydraulic motor. A relief valve is provided that is configured to release hydraulic fluid from a location between the hydraulic pump and the hydraulic motor when a pressure of the hydraulic fluid exceeds a predetermined relief pressure. Above a predetermined threshold pressure for the system, the displacement of the pump is adjusted to at least a minimum displacement that is based on a total demanded flow for the system that includes a desired flow of hydraulic fluid across the relief valve and a first hydraulic fluid flow consumed by the motor.

Abstract: In an over-loading prevention device including a hydraulic pump, a control valve, and a control lever, a discharge-quantity control unit performs constant-torque control which decreases a discharge quantity in proportion to an increase in a discharge pressure in the pump to control an input torque of the pump uniformly. An operation-state detection unit detects an actuation state of the control lever. A control unit outputs a control signal that sets the pump input torque to a minimum torque according to the constant-torque control, to the discharge-quantity control unit when the control lever is operated over a predetermined speed, and subsequently changes a level of the control signal to a maximum torque according to the constant-torque control in accordance with a predetermined control pattern to raise the pump input torque.

Abstract: The present disclosure is directed toward a hydraulic control system. The system may have a pump and a tool actuator configured to move a tool with a flow of pressurized fluid provided by the pump. The system may further have a tool control valve configured to control the flow of pressurized fluid to the tool actuator. The system may also have a controller operably connected with the tool control valve and the pump. The controller may be configured to receive a tool movement request. The controller may further be configured to estimate a change in a flow demand across the tool control valve associated with the tool movement request. The controller may also be configured to command adjustment of a discharge flow rate of the pump based on the estimated change in flow demand to satisfy the tool movement request.

Abstract: A hydraulic system has a variable displacement pump that sends fluid from a tank into a supply conduit from which separate open-center control valves convey the fluid to each one of a plurality of hydraulic actuators. The control valves have open-center orifices connected in series between a bypass node and the tank, thereby forming a bypass passage. Pressure at the bypass node controls displacement of the pump. A valve arrangement is connected between an outlet of the pump and the bypass node and is responsive to an amount of fluid flow through the supply conduit to the plurality of hydraulic functions, wherein as the amount of fluid flow increases, the valve arrangement causes fluid flow to the bypass node to decrease. Thus the pressure at the bypass node varies as a function of the operation of the control valves.

Abstract: For both adjustable flow restrictors D1, D2 having variable cross-sections a common adjustment element 21 is provided mechanically coupling the restrictors in a hydraulic damping assembly D for regulating parameters of a regulating system S, in particular of a variable displacement pump P, the restrictors D1, D2 being provided in discharge paths 12, 13 such that the restrictor cross-sections can be varied within an adjustment stroke h. The common adjustment element 21 allows to simultaneously and oppositely vary the flow restriction cross-sections A of both flow restrictors having a variable cross-section. The restrictor cross-sections A of both flow restrictors D1, D2 having a variable cross-section of a hydraulic damping assembly S in a regulating system S of a variable displacement pump P can be varied simultaneously and oppositely according to an imminent specification of the system set by the manufacturer.

Abstract: A hydraulic control system for a machine is disclosed. The hydraulic control system may have a pump configured to pressurize fluid, a displacement control valve configured to affect displacement of the pump, and a tool control valve configured to receive pressurized fluid from the pump and to selectively direct to the pressurized fluid to a hydraulic actuator. The hydraulic control system may also have a controller in communication with the displacement control valve. The controller may be configured to determine a pressure gradient across the tool control valve substantially different than a desired pressure gradient, to determine a desired condition of the displacement control valve based the pressure gradient, and to determine a flow force applied to the displacement control valve based on the desired condition. The controller may be further configured to generate a load sense response signal directed to the displacement control valve based on the desired condition and the flow force.

Abstract: A fixed/variable hybrid system has modified constant flow open center hydraulic valves (“fixed/variable valves”), including an open center core, spools, a power core, and a tank galley. A small fixed displacement pump provides fluid at a constant rate to the open center core. A variable displacement piston pump provides fluid directly to the power core as needed. Activation of spools partially restricts the open center core causing an increase in fluid pressure that is communicated to the variable displacement piston pump's load sense signal port, causing the pump to increase fluid flow and pressure to the power core. Activated spools direct pressurized fluid from the power core to the applications through selected hydraulic ports. Activated spools also direct fluid flow from selected hydraulic ports via the tank galley to a hydraulic tank. Pumping the majority of fluid only on an as-needed basis results in significant efficiencies.

Abstract: A hydraulic system for a machine is disclosed. The hydraulic system has a source of pressurized fluid and a fluid actuator with a first chamber. The hydraulic system also has a first valve configured to selectively fluidly communicate the source with the first chamber. The first valve further includes a first element movable between a flow passing, at which fluid from the source flows to the first chamber, and a flow blocking position, at which fluid from the source is blocked from the first chamber and a second element configured to selectively drain a control passageway associated with the first element to cause the first element to move. The hydraulic system further has a proportional pressure compensating valve configured to control a pressure of a fluid directed between the source and the first valve dependent upon the pressure of the control passageway.

Abstract: In a hybrid working machine in which the maximum engine output is set at the average power and the maximum pump input is set to be larger than the maximum engine output in a normal state, in an abnormal state in which the level of charge of a battery decreases and assistance ability of a motor function of a power machine is lost, the minimum pump flow rate is reduced to a value equal to or smaller than a standby flow rate, the standby flow rate being the minimum pump flow rate used in normal state control, and a set value of the maximum pump input is changed such that the maximum pump input is smaller than the maximum engine output.

Abstract: A pump control assembly includes a fluid pump assembly having a fluid pump and a load sensing valve. The fluid pump includes a fluid inlet and a fluid outlet. The fluid pump includes a variable displacement mechanism. The load sensing valve is adapted to adjust the position of the variable displacement mechanism. The load sensing valve includes a first end and an oppositely disposed second end. An actuator is in fluid communication with the fluid pump assembly. A position sensor monitors the position of the actuator. A ramping valve provides selective fluid communication between the fluid outlet of the fluid pump and the first end of the load sensing valve. An electronic control unit is in electrical communication with the position sensor and the ramping valve. The electronic control unit transmits an output current to the ramping valve in response to the position of the actuator.

Abstract: A control system actuates at least two hydraulic consumers that may be supplied with pressure medium via a pump, in the case of which an electrically or electrohydraulically adjustable metering orifice (8) is situated in the pressure medium flow path to each of the consumers. The pressure medium flow to the consumer may be adjusted by the metering orifice. A device may adjust the pump pressure or the pumped quantity once a maximum load pressure in the supply line (22, 24) of a consumer has been reached, depending on the demand for pressure medium by one consumer or the other consumer.

Abstract: A pump torque control system is capable of preventing hunting due to interference between speed sensing control and control of an engine speed of a prime mover when the temperature of a hydraulic fluid is low. A maximum absorption torque is set in a regulator 31 that controls displacement volumes of hydraulic pumps 2 and 3 based on a deviation between target and actual engine speeds of a prime mover 1. A second modification factor calculating section 45 and a control gain modifying section 49, which are included in a controller 23 that performs speed sensing control to ensure that the maximum absorption torque of the hydraulic pumps 2 and 3 is reduced, change a control gain of the speed sensing control based on a value detected by the hydraulic temperature sensor 34 to ensure that the control gain is reduced as the temperature of the hydraulic fluid is reduced.

Abstract: A sequence valve for a hydraulic circuit provides a control signal through a control signal port to a pressure responsive flow source to maintain pressure in an accumulator between a low pressure setting and a high pressure setting. The valve includes accumulator, flow source and drain ports, in addition to the control signal port. A spool controls communication between the control signal port and the drain port. A piston is moved by pressure in the accumulator port against a control spring to close communication between the control signal port and the flow source port, and to move the valve spool to close communication between control signal port and the drain port. A differential between the net cross sectional area of the spool establishes the differential between the high and low pressure settings of the accumulator.

Abstract: A flow rate control device of a hydraulic pump in a power steering system, may include an upper cam ring having a cam profile, which is fixedly installed, a lower cam ring having a cam profile, which is engaged with the upper cam ring to be relatively rotatable about the upper cam ring, and a rotor including a plurality of vanes and engaged with the upper and lower cam rings to form an inner space therebetween to pressurize oil by protruding the vanes in the inner space by centrifugal force while rotating.

Abstract: A control for a variable displacement pump disposed in a hydraulic system obtains a requested signal from a manual control device and provides a command signal to a valve operating to adjust a displacement setting of the variable displacement pump. The control provides the command signal based on the requested signal, and scales the requested signal based on a sensed or calculated load of the system.

Abstract: A lubrication system is provided that includes a pump operatively connected to one or more supply lines for delivery of a lubricant, the system including a first pressure sensor associated with the supply line at a first position, and a second pressure sensor associated with the supply line at a second position downstream of the first position and pump, a controller configured to receive pressure signals and control operation of the pump based upon the pressure differential between the pressures at the first position and second position. The pressure differential may be employed to determine when a pressure at a third position downstream of the second position has been achieved. At least one of the pressure sensors may be positioned adjacent to the pump, the controller further being operable to deactivate the pump in the event that a maximum pump pressure has been met.

Abstract: A device having a hydraulic drive for civil engineering work has least one shaft that can be rotated by a hydraulic motor. The hydraulic motor is operated by fluid of a hydraulic circuit that is supplied by a hydraulic pump. The hydraulic motor has a changeable displacement, and means for changing the volume stream are provided. A sensor for measuring the fluid pressure is disposed in the hydraulic circuit, and is connected with a control and regulation unit, by way of which the displacement of the hydraulic motor is adjustable, and by way of which the means for a change in the volume stream can be turned on. The control and regulation unit is set up so that in the event of a pressure drop in the hydraulic circuit, a reduction in the displacement of the hydraulic motor as well as a reduction in the volume stream is brought about.

Abstract: Torque control for a construction machine three-pump system that can accurately control the total absorption torque of first, second, and third hydraulic pumps and effectively use the output torque of an engine. A pump base torque computation section 42 calculates a pump base torque Tr from a target rotation speed. A subtraction section 44 calculates a reference value Tf for the maximum absorption torque available to the first and second hydraulic pumps 2, 3 by subtracting a third pump reference absorption torque T3r from the pump base torque Tr. A correction torque computation section 45 calculates a correction torque value from the delivery pressure of the third hydraulic pump 4. An addition section 46 calculates a target absorption torque Tn by adding the correction torque value Tm to the reference value Tf. A first regulator 31 is controlled so as to obtain the target absorption torque Tn.

Abstract: A hydraulic system is presented with a hydraulic fluid, with a work element actuable by the fluid, with a fluid pump for the application of a fluid pressure to the fluid, with the fluid pump being operable to generate a reference depression in the system, and with a pressure sensor for the measurement of the fluid pressure which is in communication with a control unit which is designed to carry out a calibration of the pressure sensor with reference to the reference depression.

Abstract: An open center hydraulic system that includes a variable displacement pump having an inlet, an outlet and a sensing port, the pump configured to provide reduced fluid flow in response to a predetermined fluid pressure differential between the outlet and the sensing port. A first fluid circuit and a second fluid circuit each serve as signal lines with the pump sensing port. During operation of the second fluid circuit, reduced fluid flow from the pump outlet is achieved as a result of the sum of induced fluid pressure reductions of respective controlled pressure reduction devices approaching the predetermined pump fluid pressure differential.

Abstract: A method for overpressure control in a hydraulic system having multiple hydraulic pumps, with each hydraulic pump being connected by a respective hydraulic circuit for actuating a single respective hydraulic actuator, includes actuating a first variable displacement hydraulic pump, the first hydraulic pump being fluidly linked by a first hydraulic circuit to a first hydraulic actuator for powering the first hydraulic actuator. Upon detecting a pressure that exceeds a predetermined threshold pressure, the flow rate of the first hydraulic pump is electronically modified to a second flow rate lower than the first flow rate whereby the pressure in the first hydraulic circuit is reduced to a pressure that is below the predetermined threshold pressure.

Abstract: An electric actuator of the present invention includes a hydraulic fluid supply device and an actuator actuated in response to an input of hydraulic fluid from a variable-volume pump. The hydraulic fluid supply device includes an adjustable-speed motor, the variable-volume pump which is driven by the adjustable-speed motor and ejects hydraulic fluid, an electric motor control unit which controls the adjustable-speed motor so as to achieve an intended rotation speed, and a pump control unit which controls the variable-volume pump so that the ejection volume of the variable-volume pump decreases with an increase in the ejection pressure of the variable-volume pump.

Abstract: The described system and method allow a controller to calibrate a transmission variator of a continuously variable transmission for torque control by obtaining static and dynamic qualities and parameters of the variator through an automated calibration procedure. The system and method employ a pair of transmission mode configurations and operational configurations in combination to obtain system-specific information. In this way, the system is able to calibrate out the system variations to provide effective feed forward torque control of the continuously variable transmission. In an embodiment, a first calibration operation is performed while the transmission is neutralized and a second calibration operation is performed while the transmission is engaged in a mode providing a fixed variator output speed.

Abstract: A hydraulic drive system for an actuator uses a pair of pressure compensated hydraulic machines to control flow to and from the drive chambers of the actuator. The capacity of one of the machines is limited in a motoring mode to determine a maximum rate of efflux from one of the chambers. The pressure of fluid supplied to the other of said chambers is maintained at a predetermined level to provide motive force. The machines are mechanically coupled to permit energy recovery and charge an accumulator to store surplus energy.

Abstract: A hydraulic control assembly, in particular for controlling hydraulic consumers of a mobile machine, includes a load reporting line (26) that can be subjected to the highest load pressure of a plurality of hydraulic consumers, triggered simultaneously each via a respective main control valve (38, 57), and that is connectable by an end portion (26a) to a pump regulator (25). A pressure limiting valve (50) limits the control pressure in the end portion (26a) of the load reporting line (26). The pressure limiting valve (50) is adjustable as a function of the magnitude of a pilot control signal serving to trigger a main control valve (38, 57).

Abstract: A valve assembly has a flow summation node coupled to a displacement control port of the first pump. Each valve in the assembly has a variable metering orifice controlling flow from an inlet to a hydraulic actuator and has a variable source orifice conveying fluid from a supply conduit to a flow summation node. The source orifice enlarges as the metering orifice shrinks. Each valve includes a variable bypass orifice and the bypass orifices of all the control valves are connected in series forming a bypass passage between a bypass node and a tank. The bypass node is coupled to the flow summation node and receives fluid from a second pump. At each valve, a source check valve conveys fluid from the supply conduit to the inlet and a bypass supply check valve conveys fluid from the bypass passage to the inlet.

Abstract: An engine lag down control system for construction machinery has a machinery body controller having first, second and third torque control units and a solenoid valve. The first torque control unit controls a torque control valve to a minimum pump torque corresponding to a target number of engine revolutions when a non-operated state of a control device has continued beyond a monitoring time. The second torque control unit controls the torque control valve such that the above-described minimum pump torque is held for a predetermined holding time subsequent to the operation of the control device from the non-operated state. The third torque control unit controls the torque control valve such that from a time point of a lapse of the predetermined holding time, the pump torque is gradually increased on a basis of a predetermined torque increment rate.

Abstract: An electric power actuator and a method of controlling such an actuator are disclosed. The actuator (1) can include means (17, 26) for limiting the pressure difference in both chambers (9, 10) of a hydraulic jack (8) of the actuator (1) to a limit pressure which is lower than an opening pressure of a pressure relief valve (11) of the actuator (1).

Abstract: A hydrostatic pump (1) with a variable displacement volume can be operated in a closed circuit and is driven by a drive engine (2), in particular by an internal combustion engine. To control the displacement of the pump (1), a control device (4) is provided which can be actuated as a function of the speed-dependent control pressure which is a function of the speed of the drive engine (2). To improve the control characteristics of the pump, a switchover device (35) is provided, by which the pump (1) can be switched between a speed-dependent displacement control by the speed-dependent control pressure and a volume flow-dependent delivery control, in which the control device (4) of the pump (1) can be controlled as a function of the actuation of an actuator mechanism (28).

Abstract: A fixed/variable hybrid system has modified constant flow open center hydraulic valves (“fixed/variable valves”), including an open center core, spools, a power core, and a tank galley. A small fixed displacement pump provides fluid at a constant rate to the open center core. A variable displacement piston pump provides fluid directly to the power core as needed. Activation of spools partially restricts the open center core causing an increase in fluid pressure that is communicated to the variable displacement piston pump's load sense signal port, causing the pump to increase fluid flow and pressure to the power core. Activated spools direct pressurized fluid from the power core to the applications through selected hydraulic ports. Activated spools also direct fluid flow from selected hydraulic ports via the tank galley to a hydraulic tank. Pumping the majority of fluid only on an as-needed basis results in significant efficiencies.

Abstract: A hydraulic implement system for a machine is disclosed. The hydraulic implement system may have a boom member, a boom actuator, and a boom operator control device movable to indicate a related operator desired boom member velocity. The hydraulic implement system may also have an implement pivotally connected to the boom member, an implement actuator, and an implement operator control device movable to indicated a related operator desired implement velocity. The range of the implement operator control device may be divided into a first portion and a second portion. The hydraulic implement system may also have a controller configured to selectively limit a velocity of the implement during manipulation of the implement operator control device within the first portion such that a lift velocity of the boom member of at least 65% of the desired boom member velocity is always possible.