Abstract: A hydraulic system for a work machine is disclosed. The hydraulic system has a reservoir configured to hold a supply of fluid and a source configured to pressurize the fluid. The hydraulic system also has a fluid actuator, a first valve, and a second valve. The first valve is configured to selectively fluidly communicate the source with the fluid actuator to facilitate movement of the fluid actuator in a first direction. The second valve is configured to selectively fluidly communicate the fluid actuator with the reservoir to facilitate movement of the fluid actuator in the first direction. The hydraulic system further has a proportional pressure compensating valve configured to control a pressure of a fluid directed between the fluid actuator and the reservoir.

Abstract: The invention is a fan revolution control method for controlling a pump-motor system, by controlling the fan revolution speed of a cooling fan adapted to be rotated by a fan motor to cool cooling target fluids. The pump-motor system drives the fan motor by a hydraulic fluid fed from a fan pump driven by an engine. The pump-motor system is controlled so the fan revolution speed starts from the minimum fan revolution speed when the engine is started up; the minimum fan revolution speed is maintained for at least several seconds; after the elapse of several seconds, the fan revolution speed is gradually increased from the minimum fan revolution speed. The fan revolution speed reaches a target fan revolution speed over a period of at least several seconds. The method prevents generation of peak pressure or pressure hunting.

Abstract: A hydraulic control device includes first and second pumps, a swing control spool, a boom first-speed control spool, a boom second-speed control spool, a swing motor, a boom cylinder, a pilot control valve, and a confluence line for merging the hydraulic flow from the boom second-speed control spool with that from the boom first-speed control spool. Provided on the confluence line is a swing priority valve having an orifice for variably reducing the hydraulic flow supplied to the boom cylinder through the confluence line. A swing priority control line is provided to interconnect a pressure receiving part of the swing priority valve and a swing control pilot pressure signal line of the pilot control valve in such a manner that an aperture area of the variable orifice of the swing priority valve is reduced in proportion to the magnitude of a swing control pilot pressure of the pilot control valve.

Abstract: A hydraulic control system for a work machine is disclosed. The hydraulic control system has a fluid actuator, a supply of pressurized fluid, and a control valve movable to selectively pass pressurized fluid to the fluid actuator. The hydraulic control system also has a sensor configured to sense the pressure of the pressurized fluid passed to the fluid actuator and a controller in communication with the control valve and the sensor. The controller is configured to receive an input indicative of a desired velocity of the fluid actuator and to determine a fluid flow rate corresponding to the desired velocity. The controller is also configured to determine a ratio of the sensed pressure to a stall pressure of the supply and to scale down the determined flow rate an amount based on the determined ratio. The controller is further configured to move the control valve an amount corresponding to the scaled down flow rate.

Abstract: A hydraulic circuit arrangement with a fixed displacement pump driven by an electric motor, a lifting cylinder, a load-holding valve arranged in the line between pump and lifting cylinder, a priority valve, which is acted upon by the pump, being arranged between pump and load-holding valve and distributing the volumetric flow flowing from the pump to the lifting cylinder, on the one hand, and to at least one further consumer of a load-sensing system, on the other hand. In the first of its two extreme positions, the priority valve connects both the lifting cylinder and the at least one further consumer in each case to the pump and, in the second of its two extreme positions, only connects the at least one further consumer to the pump while the lifting cylinder is completely cut off.

Abstract: A multistage mast assembly for use on a lift truck and method of operation for staging first and second mast sections of the multistage mast assembly. Each mast section has a retracted position and an extended position. The apparatus includes a mast staging hydraulic circuit which diverts hydraulic fluid from the second mast section actuator to the first mast section actuator using a multi-position valve having an open position and a restricted flow position. In the restricted flow position, hydraulic pressure in a hydraulic line supplying the second mast section increases to divert hydraulic fluid to the first mast section actuator before the second mast section reaches its extended position.

Abstract: A hydraulic system has at least one primary hydraulic functions and a plurality of secondary hydraulic functions all of which are connected in parallel to a supply conduit and a return conduit. A first pressure relief valve prevents pressure in the supply conduit from exceeding a first limit and second pressure relief valve prevents the pressure at the secondary hydraulic functions from exceeding the lower second pressure limit. Novel pressure relief circuits are provided which enable only two pressure relief valves to provide one of two pressure limits at more than two hydraulic functions.

Abstract: A hydraulic control device for controlling a boom-arm combined operation in an excavator includes a boom low-speed control spool and an arm high-speed control spool provided on parallel lines for receiving hydraulic flow from a second hydraulic pump via the parallel lines. A boom priority valve is provided on the parallel line interconnecting the second hydraulic pump and the arm high-speed control spool for throttling the parallel line to cause the hydraulic flow of the pump to be supplied to the boom low-speed control spool prior to the arm high-speed control spool. The boom priority valve has a pressure receiving part remaining in fluid communication with a boom pilot valve through a boom priority control signal line and a variable orifice section for reducing an opening area of the parallel line in proportion to the magnitude of a boom priority control signal pressure delivered to the pressure receiving part.

Abstract: A hydraulic system for a work machine is disclosed. The hydraulic system has a source of pressurized fluid and a fluid actuator with a first chamber and a second chamber. The hydraulic system also has a first valve configured to selectively fluidly communicate the source with the first chamber and a second valve configured to selectively fluidly communicate the source with the second chamber. 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 and second valves.

Abstract: A hydraulic control system has a pilot pressure supply circuit that applies a pressure differential dependent on engine speed to opposite sides of an anti-stall valve to turn off the pilot flow when the pressure differential falls below a certain value, resulting in holding the positions of the hydraulic devices being controlled until engine speed recovers.

Abstract: A hydraulic system has a source, a plurality of fluid actuators, and a controller. The controller is configured to receive an input indicative of which of the plurality of fluid actuators are a first and a second type of fluid actuator, to receive an input indicative of a desired flow rate for the plurality of fluid actuators, and to determine a current flow rate of the source. The controller is further configured to demand the desired flow rate for the first type of fluid actuator and to demand a scaled down desired flow rate for the second type of fluid actuator when a total desired flow rate exceeds the current flow rate of the source, and to demand a scaled down desired flow rate for all of the plurality of fluid actuators when the desired flow rate for the first type of fluid actuator exceeds the current flow rate of the source.

Abstract: The invention relates to a method for controlling at least two hydraulic actuators, to a monitoring valve and a rock drilling apparatus. The monitoring valve (10) is connected to the input channel of a first actuator through a sensing channel (9) and controls a load-sense circuit (6?) of a second actuator. The pressure of the load-sense circuit (6?) is set by a force of a spring element (12) and biased by a control element (42) of the monitoring valve with differential pressure sensing.

Abstract: A concrete transfer system for a concrete pump car has a pair of concrete input tubes mounted in a hopper, first and second drive cylinders operating with the concrete input tubes for inputting and outputting the concrete by pressure pistons each having a driving rod, an oil pressure pump for supplying oil to the first and second drive cylinders, and a movement sensor for each of the driving rods. A control unit receives a sensing signal from each sensor and there are a plurality of logic valves operated by the control unit that are selectively opened and closed to supply oil to opposite sides of the driving rod of each of the cylinders. A high-low pressure selection valve operates to perform the concrete transfer at either high or low oil pressure.

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: A hydraulic circuit for use with a backhoe includes first, second and third pumps; left and right traveling unit valve sections-receiving pressure oil from the first and second pumps independently of each other; a front implement valve section receiving combined pressure oil including oil from respective center oil passages of the left and right traveling unit valve sections; and a swiveling valve section receiving pressure oil from the third pump. A parallel oil passage having a restrictor extends parallel to a center oil passage of the swiveling valve section. The front implement valve section also receives pressure oil from the center oil passage of the swiveling valve section and the parallel oil passage. A load sensing system controls flow amounts of the first and second pumps according to a hydraulic load generated in a front implement operation.

Abstract: In a hydraulic controller for construction machine according to the present invention, wherein there are provided regulators for each of a first and a second capacity variable hydraulic pump, each of the regulators being controlled, detecting the discharge pressure of each pump, in such a manner that one of the pumps absorbs a part of torque while the other thereof absorbs the remaining torque, and wherein a boom raising operation causes pressure oil from the pumps to be joined together and then supplied to a boom cylinder, while also a rotating operation causes pressure oil from the second pump to be supplied to a rotating motor, is provided a flow rate distribution controller adapted to control the regulators in such a manner that a difference in flow rate is provided between the pumps so that the first pump shows a higher flow rate at the start of a combined operation of raising and rotating, and that, on a steady rotating state which results in an increase in the discharge pressure difference between the

Abstract: A hydraulic control apparatus which is used in order to prevent the blade from falling over on the pitch back side during a dual tilting operation, and to operate the left and right tilting cylinders in a uniform manner even in case where there is a large difference in the load pressure between the left and right tilting cylinders. In cases where it is desired to perform a dual tilting operation, the operator moves the operating lever either leftward or rightward while pressing the dual tilting switch of the operating lever. As a result of the switch being pressed, an electrical control signal that places the flow-combining/flow-dividing switching valve or flow-combining/flow-dividing valve in the flow-dividing position is generated by the controller, and the electrical control signal is output to the flow-combining/flow-dividing switching valve so that the flow-combining/flow-dividing switching valve or flow-combining/flow-dividing valve is switched to the flow-dividing position.

Abstract: Hydraulic flow to tractor attachments such as a sweeper, snow thrower, breaker, auger or cold planer may be increased by diverting pressurized hydraulic fluid from the auxiliary pump. A diverter valve between the auxiliary pump and the auxiliary circuit of the loader hydraulic system may direct flow to either the backhoe hydraulic system, the rockshaft hydraulic system, or the auxiliary circuit of the loader hydraulic system. The additional flow from the auxiliary pump is provided at a mid-inlet position and is not available to the loader boom or bucket circuits, to preserve tractive horsepower needed during loader work.

Abstract: A hydraulic apparatus realizes the same function as that of a variable discharge pump by regulating a hydraulic device such as a control valve in a state always operated at a substantially constant number of revolutions with a high efficiency regardless of the type of a hydraulic pump driven by a driving source such as a heat engine or electric motor. This hydraulic apparatus drives a hydraulic pump with a driving source internally or additionally provided with a predetermined amount of inertia, so as to construct a fixed pressure hydraulic source, and further provides peripheral devices corresponding to a required load, so as to open/close a control valve according to a state of a load including an energy accumulating device, a hydraulic motor, or the like such that the load can be supplied with an operating fluid ranging from a low flow rate at a high pressure to a high flow rate at a low pressure.

Abstract: A hydrostatic drive system (1) has at least one user. A control valve device (3; 4; 5; 6) to control the user is actuated by an actuation signal. A delivery flow regulation device (11) is triggered by a load pressure signal of the user. The drive system has a safety device (20) with a function position (21b) in which the actuation signal is routed to the control valve device (3; 4; 5; 6) and the load pressure signal is routed to the delivery flow regulation device (11), and a safety position (21a) in which the control valve device (3; 4; 5; 6) is discharged by the actuation signal and the delivery flow regulation device (11) by the load pressure signal. The safety device (20) also has a discharge position (21c) in which the connection of the control valve device (3; 4; 5; 6) with the user is discharged.

Abstract: In series between pump and tank are two throttle devices, one of which includes a controllable throttle valve having a piston, of which one side supports a valve head, which forms the boundary of an annular gap between an inflow duct and an outflow duct. A hydraulic control path extends from the inflow duct through the throttle opening to the tank, running through a precontrol bore in the piston. To prevent an unwanted leakage fluid stream, one end of the precontrol bore at the annular gap in the region of the inflow duct is positioned so that it remains opened for a closed annular gap, and the other end of the precontrol bore on the other side of the piston is arranged where the piston, in response to the controllable throttle valve being completely opened, pushes against a stop face and, in so doing, automatically closes this other end.

Abstract: A fluid pressure control circuit includes a fluid pressure device which is operated by a fluid pressure; a control valve which is connected to the fluid pressure device via a connecting passage, and which changes a flow rate of predetermined fluid that is to be supplied to the fluid pressure device or that is to be discharged from the fluid pressure device according to a position of a valve element; and a pressure difference reflecting device which moves the valve element based on a difference in the fluid pressure between predetermined two different portions in the connecting passage and which changes the flow rate of the fluid that is to be supplied or to be discharged through the control valve according to the fluid pressure difference. With this fluid pressure control circuit, it is possible to obtain excellent responsiveness during supply/discharge of the fluid, change in the fluid pressure or the like, without increasing the amount of the fluid to be consumed.

Abstract: One preferred embodiment of the present invention, provides an auxiliary hydraulic drive system having a total hydraulic flow. The system includes a primary hydraulic pump operable to provide hydraulic flow for an implement, and a flow control valve in communication with the hydraulic flow. The flow control valve operates to allow an optimum flow rate and diverts the excess flow amount when the total hydraulic flow exceeds the optimum flow rate. A secondary hydraulic pump is selectively operable to provide additional hydraulic flow. A control system is operable to engage the secondary pump when the total hydraulic flow drops below a minimum flow level; and the control system operates to disengage the secondary pump when the total hydraulic flow exceeds a maximum flow level. In a further embodiment, the invention provides a control unit for a hydraulic system. The control unit includes a sensor to measure total hydraulic fluid flow in a system; and a controller coupled to the sensor.

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 plurality of hydraulic actuators are connected by valve assemblies to fluid supply and return conduits. Desired operating velocities are specified for the hydraulic actuators and used to define the amounts of fluid flow required by each actuator to move at the respective velocity. Provide the requisite flow amounts, fluid at related pressures must be provided at the different hydraulic actuators. In order for those pressures to occur, a pump has to furnish fluid at a greater pressure to allow for supply conduit losses. A process is provided for determining the pressure that the pump must provide to satisfy the greatest pressure that is necessary for the desired operation of all the hydraulic actuators.

Abstract: A priority circuit is provided that is in communication with an open circuit pump and priority and auxiliary systems. The circuit comprises a first valve with an inlet in communication with the pump, an outlet in communication the priority system, and a load sensing inlet in communication with the priority system, wherein the first valve modulates to maintain a predetermined pressure differential between pressure at the load sensing inlet and pressure at the outlet. The circuit further comprises a second valve with an inlet in communication with the pump, an outlet in communication with the auxiliary system, and a load sensing inlet in communication with the priority system, wherein the second valve is normally closed and opens when pressure at the load sensing inlet of the second valve is less than pressure at the inlet of the second valve minus the predetermined pressure differential of the first valve.

Abstract: An articulated wheel loader provides a cushioned deceleration at the limits of its turning to the left and to the right by reducing fluid flow through a hydraulic steering cylinder as the articulated frames approach abutment. The throttled fluid flow causes a variable displacement pump to de-stroke, which further cushions the deceleration.

Abstract: An apparatus and method for controlling hydraulic output to a plurality of actuatable devices are disclosed. The apparatus includes a plurality of main valves coupled, respectively, to the actuatable devices and to respective secondary valves, and also an adjustment valve that is coupled between a pressure source and one or more of the secondary valves. The adjustment valve receives a first indication of a pressure at the one or more secondary valves, and a second indication related to a highest load pressure. The adjustment valve allows pressure to be provided from the pressure source to the one or more secondary valves when the second indication exceeds the first indication, such that an equal amount of fluid flow occurs with respect to each of those secondary valves that is reduced in comparison with the fluid flow to any other secondary valves that are not connected to the adjustment valve.

Abstract: The flow of fluid to a hydraulic actuator is controlled by a valve assembly which operates in different metering modes at various points in time. The metering mode to use in selected in response to the hydraulic load that acts on the valve associated with the hydraulic actuator. Specifically the load is determined and then compared to threshold levels associated with the different metering modes to choose the metering mode for use a given point in time.

Abstract: A hydraulic valve system (1) has a supply connection arrangement having a high-pressure connection (P) and a low-pressure connection (T), a working connection arrangement, having two working connections (A, B) connectable with a motor (2), with a directional valve (4), which is arranged between the supply connection arrangement (P, T) and the working connection arrangement (A, B), and with a compensation valve (8), which is acted upon in a first operation direction by a spring (22) and a pressure in a pressure chamber (23), which is connected with a load-sensing line (LS), and in a second operation direction, which is opposite to the first operation direction, by a pressure at the directional valve (4).

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. The hydraulic control unit is used in a several-directional-control-valves-assembled-type hydraulic control system 1 having a load sensing function. The hydraulic control unit has a PLS port. The PLS port is supplied with a maximum load pressure in the hydraulic control system. The compensator of the hydraulic control unit includes a metering orifice imparted with a function equivalent to a check valve. The compensator is imparted with the function of a shuttle valve (directional control valve), and by allowing the shuttle valve to operate independently of the compensator the pressure PLS is adjusted constantly.

Abstract: In the present invention, it is possible to supply hydraulic fluid by the amount needed in an option tool even when a combined work is performed by engaging an option tool having a different operation pressure to a work apparatus. The hydraulic circuit for an option tool of heavy equipment comprises a poppet valve which is openably and closably installed in a flow path of a supply side of the option tool spool, a first spool which is installed in a flow path between the poppet valve and the option tool spool and has an opening portion adapted to maintain a constant pressure difference when the first spool is switched by pilot pressure discharged from the pilot pump, and a second spool which is installed in a down stream side of the poppet valve and is switched when an over load occurs due to an over pressure exceeding the degree set in the option tool for thereby closing the poppet valve.

Abstract: Hydraulic oil supplied from pumps (12),(13) to an attachment actuator (60) is controlled by attachment control valves (27),(28). Hydraulic oil supplied from pumps (12),(13) to other actuators (52),(54),(56),(58) is controlled by other control valves (21) through (26). Control conditions for operating the attachment actuator (60) alone and control conditions for operating the attachment actuator (60) simultaneously with any of the other actuators (52),(54),(56),(58) are discriminated by the pilot pressure sensors (32),(34),(36),(38). Control characteristics of the attachment control valves (27),(28) are controlled by a controller (43) based on the discriminated control conditions.

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 plurality of hydraulic actuators are connected between a supply line and a tank return line. A separate desired velocity is requested for each hydraulic actuator. In response to a respective metering mode and the desired velocity for each hydraulic actuator, the flow requirements that each hydraulic actuator has from the supply and return lines are derived. A determination is made as to what fractions of the required flows can be provided by the flow levels that are available from the supply and return lines. Those fractions are used to convert the desired velocity for the given hydraulic actuator into a velocity command which indicates the velocity of the given hydraulic actuator that can be achieved with the available fluid flows. The respective velocity command is used to control the flow of fluid to each hydraulic actuator.

Abstract: An actuator is part of a hydraulic circuit branch that has a first electrohydraulic proportional valve connecting the actuator to a supply line containing pressurized fluid and a second electrohydraulic proportional valve connecting the actuator to a tank return line. A method for operating the valves includes requesting a desired velocity for the hydraulic actuator and sensing a parameter which varies with changes of a force on the actuator. The desired velocity and the parameter are used to derive an equivalent flow coefficient which characterizes fluid flow in the hydraulic circuit. From the equivalent flow coefficient, first and second valve flow coefficient are derived and then employed to activate each of the first and second electrohydraulic proportional valves. The coefficients may characterize either conductance or restriction in the respective part of the hydraulic system.

Abstract: An oil hydraulic circuit having a pilot operated control valve, for performing control of pressure oil supply to a hydraulic actuator and a pilot valve gear for outputting a pilot pressure to the control valve, that improves operationality when a fine operation is performed. The pilot valve gear has a first pressure controller that outputs a pilot pressure corresponding to the degree of operation of an operating lever and a second pressure controller that reduces the pilot pressure outputted from the first pressure controller based on a signal from an operating speed changeover switch and outputs the reduced pilot pressure to the control valve.

Abstract: A fan drive system includes a pump, at least one implement arrangement in fluid communication with the pump and a fan drive unit driveably connected to the pump. The fan drive unit is in fluid communication with the pump through a modulation valve. A signal operator is structured and arranged to receive at least one implement signal and a fan drive signal and generate a load signal output, wherein the pump is adapted to modify an output flow of the pump in response to the load signal. A control valve is urged to respond under the influence of a sensed condition and is in fluid communication with the modulation valve and the signal operator through a signal conduit.

Abstract: A plurality of hydraulic actuators are connected between a supply line and a tank return line. A separate desired velocity is requested for each hydraulic actuator. In response to a respective metering mode and the desired velocity for each hydraulic actuator, the flow requirements that each hydraulic actuator has from the supply and return lines are derived. A determination is made as to what fractions of the required flows can be provided by the flow levels that are available from the supply and return lines. Those fractions are used to convert the desired velocity for the given hydraulic actuator into a velocity command which indicates the velocity of the given hydraulic actuator that can be achieved with the available fluid flows. The respective velocity command is used to control the flow of fluid to each hydraulic actuator.

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 a 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: The present invention discloses a traveling control device, including a crawler type right and left traveling body; a right and a left hydraulic motor for operating the right and left traveling body said right and left hydraulic motors each having a pump as a hydraulic source; an operator means for outputting an operation command to the right and the left hydraulic motor; and a pump pressure controller means for controlling pump pressure to be supplied to the right and the left hydraulic motor according to a control input of the operator means, wherein the pump pressure controller means controls the pump pressure based on different pump pressure properties for single traveling in which only one of hydraulic motors is operated, and for double traveling in which both of hydraulic motors are simultaneously operated.

Abstract: A fluid system having a common source of pressurized fluid is provided to selectively control the speed and/or pressure of a first hydraulic circuit while also providing flow/pressure priority to a second hydraulic circuit. The first hydraulic circuit includes a first electrically controlled proportional relief valve connected between the source of pressurized fluid and a first fluid actuator and a second electrically controlled proportional relief valve connected between the reservoir and a point downstream of the first electrically controlled proportional relief valve. The second hydraulic circuit is connected to the source of pressurized fluid in parallel with the first hydraulic circuit.

Abstract: A small self-propelled loader has hydraulic drive motors and at least one work cylinder, and has a hydraulic system that efficiently utilizes the available horse power from an internal combustion engine on the loader. The engine drives a tandem pump and the flows from two sections of the tandem pump pass through a first diverter valve that permits using the flow from each of the pump sections to drive a respective one of the drive motors. The return or drain flow from valves controlling the drive motors is connected to a second diverter valve to selectively direct the drain flow from the drive motors for operating remote work cylinders. Alternately, the first diverter valve directs the output from one pump section to the work cylinders, so that when the loader is standing still or moving very slowly, the work cylinder has adequate flow, and flow from the other pump section is split to power the drive motors.

Abstract: A control arrangement to supply-pressure medium to at least two hydraulic consumers having a variable-displacement pump controlled according to required flow and the setting of which can be changed by a, pump controller as a function of highest load pressure of the actuated hydraulic consumers; two adjustable meter-in variable restrictors, a first of which is arranged between a feed line, which leads from the variable-displacement pump, and a first hydraulic consumer, and the second of which is arranged between the feed line and a second hydraulic consumer; and two pressure compensators, a first of which is connected downstream of the first meter-in variable restrictor and the second of which is connected downstream of the second meter-in variable restrictor, and the control piston of which can be acted on in opening direction by the pressure downstream of the associated meter-in variable restrictor.

Abstract: A fluid system having a common source of pressurized fluid is provided to selectively control the speed and/or pressure of a first hydraulic circuit while also providing flow/pressure priority to a second hydraulic circuit. The first hydraulic circuit includes a first electrically controlled proportional relief valve connected between the source of pressurized fluid and a first fluid actuator and a second electrically controlled proportional relief valve connected between the reservoir and a point downstream of the first electrically controlled proportional relief valve. The second hydraulic circuit is connected to the source of pressurized fluid in parallel with the first hydraulic circuit.

Abstract: A hydraulic oil flow controller for a construction machine comprises an operating valve 6 for supplying hydraulic oil discharged from hydraulic pimps 1 and 2 to an attachment, an attachment operating unit 11 for transmitting a pilot signal corresponding to the manipulated variable of the operating valve 6 and a solenoid control valve 12 for changing the flow characteristics of the pilot signal in accordance with a command from a controller 19. An increase and/or decrease signal is sent to the solenoid control valve 12 through the controller 19 from a monitor device 18 so that the flow of the hydraulic oil supplied to the actuator of the attachment is increased and/or decreased. Accordingly, a coefficient of fluctuation of the flow relative to a coefficient of fluctuation of the manipulated variable can be decreased in the work of the attachment of a hydraulic shovel and the operation efficiency upon operation of the attachment can be improved.

Abstract: A hydraulic system for excavators or other working machines, comprising a branching device for feeding special consumers with particularly high power consumption. The special consumer is supplied with priority until a maximum supply level is reached, which is lower than the maximum output of the hydraulic source. The remaining output difference is made available without restriction to the other consumers in the hydraulic system, wherein the distribution of the remaining flow of hydraulic fluid is not influenced. Thus, the operating ability of the machine equipped with the hydraulic system is maintained completely and in the standard manner. Any possible slow-down of the adjustment movement of a consumer is reflected proportionally in the movements of all other consumers, so that the ratios of the operating speeds or reaction speeds of the individual consumers among themselves remain the same.

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: 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 seat valve body mounted in a hydraulic line between a pump line and feeder lines to control hydraulic fluid supplied to variable throttles and to auxiliarily control hydraulic fluid flowing in a load line comprises a first seat valve having a variable control throttle displaced by a difference between a load pressure of the load line and a discharge pressure of the hydraulic pump and varying an opening area from the pump line to the feeder lines based on a displacement amount thereof, a second seat valve having a pilot variable control throttle displacing with respect to the first seat valve, determining a displacement amount of the first seat valve, and varying an opening area based on a displacement amount thereof; and a pilot spool having a pilot variable throttle determining a displacement amount of the pilot variable control throttle of the second seat valve upon switching.