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: A vehicle includes a pump configured to output fluid at a commanded pressure when driven by a motor. A first hydraulic device is operably connected to the pump and configured to operate in response to receiving fluid at a first pressure. A second hydraulic device is operably connected to the pump and configured to execute a shift command in response to receiving fluid at a second pressure. A control processor is configured to control the commanded pressure in accordance with a priority scheme. That is, the control processor is configured to direct at least a portion of the commanded pressure from the first hydraulic device to the second hydraulic device for a duration of a shift command based on the priority scheme and redirect at least a portion of the commanded pressure to the first hydraulic device upon completion of the shift action.

Abstract: Hydraulically driven arrangement for the linear movement of a mass body consisting of two double acting cylinders coupled in parallel, whereby one operating cylinder is a control cylinder for controlling the movement of the mass body, which is split into an acceleration phase, a movement phase and a brake phase. The other operating cylinder is connected as a drive cylinder to the hydraulic power pack as an energy storage, in a manner that the power pack during the acceleration phase of the mass body generates the drive energy for the drive cylinder, and the drive cylinder in the brake phase of the mass body, which serves as a pump for charging the hydraulic power pack. The control cylinder and drive cylinder each have a piston with a one-sided piston rod coupled to the mass body. The control cylinder and the drive cylinder are controlled by hydraulically separated, independent control circuits.

Abstract: A shock absorption device and a control method thereof for a small swing radius (SSR) excavator are provided, which can relieve shock generated on a boom cylinder by controlling only the discharge flow rate of hydraulic pumps, being supplied to the boom cylinder, even without controlling a main control valve when a boom of the excavator ascends at its maximum height through manipulation of a control level.

Abstract: A hydraulic system for actuating a clutch and/or a variable speed drive unit of a belt-driven conical-pulley transmission of a vehicle, such as a commercial vehicle, and having a variable transmission ratio and a torque sensor. The hydraulic system includes at least one hydraulic energy source. A selector and check valve is provided for supplying additional components besides the torque sensor and is connected between the hydraulic energy source, the additional components, and the torque sensor in such a way that the torque sensor includes priority in being supplied with hydraulic medium.

Abstract: A method of controlling a pump and motor system having at least one of a variable displacement pump and a variable displacement motor. The method may comprise providing an engine drivingly coupled to a primary load and a secondary load, the secondary load being driven by the pump and motor system. The method may also comprise sensing a change in engine speed in response to a change in the primary load. The method may further comprise changing the engine speed to compensate for the primary load change. The method may further comprise changing a displacement of the at least one variable displacement pump and the variable displacement motor to maintain a constant secondary load.

Abstract: The invention relates to a sequence valve for use in a hydraulic plant, which sequence valve has a pressure-controlled slide valve (5) with a spring return and in a starting position defines a first cavity (10), which cavity is connected with a tank and the hydraulic plant, and in a second, pressurized position closes off the connection with the tank. The cavity is connected to a second cavity (18) via a channel (15, 16, 17) in the slide valve, and the second cavity is adapted to be connected with a pump via a throttle (20) and is positioned on the same side of the slide valve as the spring (7). The sequence valve has a third cavity (19), which is adapted to be connected with the pump and is positioned on the opposite side of the slide valve from the spring, and the second and the third cavity are connected with each other via a fixed throttle with a short flow channel. The invention also relates to downhole tractor with the sequence valve.

Abstract: A method for controlling an engine in a work machine includes determining a base engine operating limit; determining a hydraulic system load on the engine; calculating a modification value for the base engine operating limit; generating a modified engine operating limit based on the modification value and the base engine operating limit; generating an engine control signal based on the modified engine operating limit; and transmitting the engine control signal to operate the engine at the modified engine operating limit to thereby supply additional power from the engine to the drive train to at least partially compensate for the hydraulic system load.

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 pneumatic drive system (1) in which the movement of an output drive unit (7) of a pneumatic drive (2) is controlled by control valve means (25 and 26) which are connected with the working chambers (12 and 13) of the pneumatic drive (2). The control valve means (25 and 26) comprise at least one air economy setting (30) setting a choke cross section and a high power setting (29) defining a flow cross section larger than it. Actuating means (12 and 13) serve to ensure that the control valve means (25) are switched over, in a fashion dependent on the air pressure obtaining in the at least one working chamber (12 and 13) from the normally assumed air economy setting (30) into the high power setting (29), when the output drive unit (7) meets with an increased resistance to motion.

Abstract: The present disclosure provides a machine configured so that its ground speed is at least in part dependent on the measured force that is applied to an attachment attached thereto. The present disclosure also provides an attachment for a machine that is configured to provide feedback to the machine it is configured to be attached to, wherein the feedback is representative of the force applied to the attachment. The present disclosure also provides a method of automatically controlling the ground speed of a machine based on feedback measured in an attachment attached to the machine.

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: The invention relates to a hydraulic control arrangement for a mobile machine tool, particularly for a forklift, comprising at least two hydraulic loads (10, 12), one of them having a lifting function. According to the invention, the two loads are each controlled via a LUDV valve with inflow measuring diaphragm (36, 44) and LUDV pressure regulator (46) connected downstream.

Abstract: [Problem] To provide a hydraulic drive system for a hydraulic excavator, which makes it possible to efficiently perform grading work by using residual energy of pressure oil in a hydraulic circuit although no attention has been paid to the residual energy in conventional technologies. [Solution] A hydraulic drive system for a hydraulic excavator is provided with a boom cylinder 1 and arm cylinder 2, a main hydraulic pump 4 for feeding pressure oil to both the cylinders 1,2, a directional control valve 7 for a boom and directional control valve 8 for an arm to control flows of pressure oil to be fed to the boom cylinder 1 and arm cylinder 2, respectively, and a reservoir line 8c connecting the directional control valve 8 for the arm with a working oil reservoir 6.

Abstract: A hydraulic system for a mobile machine having an implement is disclosed. The hydraulic system may have a hydraulic actuator configured to move the implement, a storage device configured to store pressurized fluid, and a valve operable to fluidly communicate the storage device with the hydraulic actuator. The hydraulic system may also have a sensor associated with the mobile machine to generate a signal indicative of a speed of the mobile machine, and a controller in communication with the valve and the sensor. The controller may be configured to compare the speed of the mobile machine to a setpoint and to determine an amount of time elapsed while the speed of the mobile machine exceeds the setpoint. The controller may further be configured to selectively operate the valve to fluidly communicate the storage device with the actuator based on the elapsed amount of time and the speed to cushion movement of the implement.

Abstract: There are provided: a travel circuit HC1 that is formed through a closed circuit connection of a variable displacement hydraulic pump 2 driven by an engine 1 and a variable displacement hydraulic motor 3; a work circuit HC2 that includes a work hydraulic pump 4 that is driven by the engine 1 and a work hydraulic actuator 114, 115 that operates by pressure oil from the work hydraulic pump 4; a relief valve 14 that relieves high pressure oil of the travel circuit HC1; a rotation speed control unit 10, 18 that controls the engine rotation speed in correspondence to an operation amount of an accelerator pedal 9; a state detection unit 21, 22 that detects a vehicle state of high load travel and high load work; and a speed limitation unit 10 that reduces an upper limit of engine rotation speed when the vehicle state of high load travel and high load work is detected by the state detection unit 21, 22.

Abstract: The invention relates to a valve arrangement having an adjustable control valve (10), comprising a control slide (12) for actuating at least one consumer connection (A,B), and having an LS control line, wherein the differential pressure of two actuating pressures (Xa, Xb) serves for the actuation of the control slide (12). Due to the fact that the actuating pressures (Xa, Xb) also actuate a logic valve, which in turn influences an additional valve, and/or actuates a pressure scale that is connected upstream to the control valve (10) having the control slide (12), the difference of the two actuating pressures (Xa, Xb) initially displaces the control slide of the control valve, wherein the higher or the lower of the two actuating pressures (Xa, Xb) either actuate the further valve in the form of the additional valve, and/or influences the pressure scale.

Abstract: A hydraulic system for limited wheel slip of a traction drive system includes first and second pilot directional valves between a hydraulic pump and first and second hydraulic wheel motors. If a wheel slips, the first or second pilot directional valves moves to a first position directing some hydraulic fluid through a restricted passage to the slipping motor and the remainder through an unrestricted passage to the opposite motor. Absent wheel slip, the pilot directional valve is in a second position directing all of the hydraulic fluid through an unrestricted passage to the corresponding motor. The first and second pilot directional valves detect wheel slippage and move between the first and second positions based on a first pilot signal corresponding to the pressure sensed entering the respective pilot directional valve, which is balanced against a biased spring and a second pilot signal from the opposite motor.

Abstract: To provide a hydraulic drive device for a work machine that is capable of ensuring reduction in fuel consumption even in actual work where an operating condition changes every moment. Operating condition identifying unit (41) for identifying the operating condition and hydraulic pump control system (40b) for controlling absorption torque of hydraulic pump (18) are provided. When the operating condition identified by operating condition identifying unit (41) is a specific operating condition, hydraulic pump control system (40b) controls the absorption torque of hydraulic pump (18) to achieve hydraulic pump absorption torque characteristic line (PLb) matching the absorption torque of hydraulic pump (18) with output torque of engine (17) at engine output torque point Mb at which a fuel consumption rate is substantially minimum.

Abstract: A power pack unit includes a first hydraulic pump including a first pump enclosure accommodating a first pump cartridge. A second hydraulic pump includes a second pump enclosure accommodating a second pump cartridge. A hydraulic fluid reservoir is positioned between the first and second hydraulic pumps. A first end of the reservoir is secured to the first pump enclosure and a second end of the reservoir is secured to the second pump enclosure. The first and second hydraulic pumps and the reservoir can extend along a common axis. First and second motors can be connected to the first and second pumps. The entire structure can extend along a common axis.

Abstract: An array of valve sections in a hydraulic system are connected to a supply line, a tank return line, and a load sense line. One valve sections includes a control valve with a metering orifice through which fluid flows from the supply line to a valve outlet. A load sense node is coupled by a load sense orifice to the load sense line. A load sense pressure limiter prevents pressure at the load sense node from exceeding a threshold level. A pressure compensator is connected in a fluid path between the valve outlet and one of the hydraulic actuators. The pressure compensator opens and closes the fluid path in response to pressure at the valve outlet and pressure at the load sense node, thereby governing the maximum amount of pressure that the respective valve section can apply to the hydraulic actuator.

Abstract: A method for controlling an engine in a work machine includes determining a base engine operating limit; determining a hydraulic system load on the engine; calculating a modification value for the base engine operating limit; generating a modified engine operating limit based on the modification value and the base engine operating limit; generating an engine control signal based on the modified engine operating limit; and transmitting the engine control signal to operate the engine at the modified engine operating limit to thereby supply additional power from the engine to the drive train to at least partially compensate for the hydraulic system load.

Abstract: A wheel loader automatically adjusts the bucket angle with respect to the ground. The wheel loader includes a hydraulic pump, a tilt cylinder and a tilt valve, a detector which detects that the tilt cylinder is at a control origin, a target setting device which sets a target value for the length of the tilt cylinder, and a control device. The control device calculates a required oil amount for the tilt cylinder to arrive from the control origin to the target length, calculates an oil amount distributed to the tilt cylinder after it has arrived at the control origin, and stops the operation of the tilt cylinder when the distributed oil amount reaches the required amount.

Abstract: A hydraulic control system for a swiveling construction machine includes at least one hydraulic travel motor, a first hydraulic actuation device, a second hydraulic actuation device and a hydraulic diverter valve assembly. The at least one hydraulic travel motor is configured to move the swiveling construction machine in a first travel speed and a second travel speed based on a variable pilot pressure signal. The first hydraulic actuation device is configured to actuate a first function of an implement. The second hydraulic actuation device is configured to actuate a second function of an implement. The hydraulic diverter valve assembly is configured to divert hydraulic power between the first hydraulic actuation device and the second hydraulic actuation device while maintaining operation of the at least one hydraulic travel motor in one of the first and the second speeds.

Abstract: A system and process for controlling propulsion and steering of a track trencher excavation machine powered by an engine includes a multiple mode propulsion and steering control system that performs a plurality of functions depending on a selection of one of a plurality of operational modes. A controller generates a vehicle propulsion hydrostatic drive signal using an engine speed to determine a load multiplier. The load multiplier being defined as a function of the engine speed and an operator adjustable load control setting.

Abstract: A system and process for controlling and actuating an excavation implement during excavation between an above-ground position and an operator specified below-ground position and for maintaining the specified below-ground position once achieved. The actuation of the excavation implement is regulated by use of an operator modifiable relationship between an engine operating speed and an actuator speed. The actuation of the excavation implement is further regulated by use of an operator modifiable relationship between an attachment drive speed and the actuator speed. A computer network controls the actuation of the excavation implement in response to inputs from the operator and feedback from the engine speed, the attachment drive speed, and an actuator position sensor as the excavation implement progresses through the earth.

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: A pressure-compensating directional control valve, for actuating hydraulic actuators, comprising at least one modular valve body, with one through receptacle for a slidable shuttle, a driving fluid delivery port connected to a pump, a discharge fluid port, a first output opening and a second output opening, connected to the first and second chamber, of a hydraulic actuator, at least one bridge for selective communication, by way of the shuttle, of the delivery port with the first or second chambers of the actuator, for actuation thereof, a unidirectional hydrostat connected to the bridge to draw selectively a pressure signal of the load of the actuator, the signal for adjusting selectively the delivery pressure of the pump so as to keep substantially constant the pressure drop between the delivery port and the actuator in any load condition.

Abstract: The invention relates to a device (1) and a method for the controlled braking of a vehicle using a hydrostatic drive (3). The hydrostatic drive (3) comprises at least 2 pivotable hydraulic engines (6) that are each connected to an axle of the drive (3) and are driven by a hydraulic pump (5). The braking torque is carried out primarily by means of the actuating element (16) of the braking system. The excessive braking or blocking of individual wheels is prevented by an antiblocking function. To this end, the actual rotational speed of each individual hydraulic engine (6) is compared with a nominal value and the resulting regulating deviation (F) is converted by means of a regulator into a regulating variable (R) which superimposes the primarily defined control variable (S). The dynamic axle load displacement is taken into account as a result of the deceleration of the vehicle.

Abstract: A computing section computes a reference revolution-speed decrease modification amount DNLR; and multiplies an engine revolution speed modification gain KNL by a reference revolution-speed decrease modification amount DNL and then DNLR, to thereby compute an engine revolution-speed decrease modification amount DND based on input change of an operation pilot pressure, which is modified in accordance with DNLR. At the time when a lever operation input from an operation command unit is changed from full stroke to half stroke, if a pump delivery pressure is in a pressure range of a pump absorption torque control region Y where the pump delivery pressure is lower than that in a region X, the reference revolution-speed decrease modification amount computing section 700v computes the modification amount DNLR to be 0, and therefore lowering of a target engine revolution speed with auto-acceleration control is not caused.

Abstract: A circuit arrangement includes a load sensing system (LS) with individual loads (10,14) arranged in series forming a series section, and in parallel forming a parallel section. A hydraulic supply circuit (12) includes a supply pump (P) and a runback (16) for fluid. The load sensing system (LS) determines the highest load pressure in the series section and the parallel section. The loads of the parallel section can be actuated independently from the pressure level of the loads of the series section due to the highest load pressure being transferred as a control pressure to a valve unit (18) such that, as long as the load pressure of the parallel section is higher than the load pressure of the series section, the valve unit restricts the runback (16) so that the pressure of the supply pump (P) matches or exceeds the pressure required in the parallel section. Sufficient fluid pressure for the load in the parallel section is ensured independently of the number of loads in the series section.

Abstract: The invention relates to a method for regulating a hydrostatic drive system which has at least one pump which is driven by an internal combustion engine and at least one hydraulic motor which is driven by the pump, and comprises the method steps: determining the volume flow rate flowing through the hydraulic motor; determining a first adjustment nominal value for the hydraulic motor as a function of the previously determined volume flow rate rate; determining a second adjustment nominal value by modifying the first adjustment nominal value by a correction value which is determined as a function of the nominal/actual value deviation of the internal combustion engine rotational speed by means of a vehicle-specific characteristic curve which incorporates the different power profiles for traction and overrun operation, respectively, of the internal combustion engine, with the hydraulic motor being adjusted in such a way that a substantially constant pressure level is generated at the maximum power level of the in

Abstract: A hydraulic system is provided. The hydraulic system includes a source of pressurized fluid, a first control valve, a first actuator, a second control valve, a second actuator, and a relief. The first control valve is coupled to the source of pressurized fluid. The first actuator is coupled to the first control valve and has a first end and a second end. The second control valve is coupled to the source of pressurized fluid. The second actuator is coupled to the second control valve and has a first end and a second end. The relief has an input and an output, with the input coupled to the first end of the second actuator and the output coupled to the second end of the second actuator and the second end of the first actuator.

Abstract: There is disclosed a flow valve and a flow distributor for the pressure fluid supply of several consumers. Each flow valve includes a metering orifice and a pressure regulator. A pressure regulator piston of the pressure regulator is provided with two control edges one of which is active during “accumulating” of pressure fluid flows and the other is active during “dividing” of a pressure fluid flow. The flow valve moreover comprises at least one LS control edge by which a LS cross-section via which a pressure corresponding to the load pressure is indicated into a load-indicating line can be controlled to be opened when the pressure regulator is opened.

Abstract: A control for a working apparatus having a boom arm. The apparatus includes a controller operable to receive signals from at least one pressure sensor. The at least one pressure sensor detects pressure of hydraulic fluid in at least one chamber of a control valve. The controller compares the signals from the at least one pressure sensor to parameters generated by testing the working apparatus. The controller predicts boom arm oscillations based on the comparison of the signals with the parameters, and generates a control signal in response to predicting the boom arm oscillations.

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 system for a work machine having a linkage system is disclosed. The hydraulic system has a tank configured to hold a supply of fluid and at least one hydraulic actuator associated with the linkage system to affect movement of the linkage system. The at least one hydraulic actuator has a first pressure chamber and a second pressure chamber. The hydraulic system also has an independent metering valve associated with the first pressure chamber. The independent metering valve has a valve element movable between a first position at which fluid communication between the first pressure chamber and the tank is blocked, and a second position at which fluid is allowed to drain from the first pressure chamber to the tank. The hydraulic system further has at least one sensor configured to sense a parameter indicative of a pressure in the second pressure chamber, and a controller in communication with the independent metering valve and the sensor.

Abstract: A pressure regulator includes a housing, a metering spool, a first pressure chamber at a reference pressure to which one end of the metering spool is exposed, a spring within the first pressure chamber acting against the one end of the metering spool, a second pressure chamber containing hydraulic fluid at the regulated pressure acting against the opposite end of the metering spool, wherein the position of the metering spool relative to the housing is a position of equilibrium that changes to maintain a predetermined pressure difference between the reference pressure and the regulated pressure. An abutment against which the opposite end of the spring reacts is provided and a third pressure chamber at a control pressure acts on the abutment, such that the control pressure can be changed to adjust the position of the abutment to change the pre-load of the spring to adjust the value the predetermined pressure difference.

Abstract: The invention relates to a regulating device for hydrostatic piston machines consisting of an actuating piston (2) which can be removed between two end positions which can be impinged upon by actuating pressure exerted thereon in an opposite direction. An actuating pressure regulating valve (5) is used to regulate the actuating pressure. The actuating regulating valve (5), which is used to regulate the actuating pressure, comprises a regulating piston which can be shifted from a neutral position and which can be impinged upon with a regulating force which is dependent on the position of the actuating piston (2). The regulating force is directed counter to a control force acting upon the regulating piston (6) and the regulating force is zero when the regulating device (1) is in a rest position. When the regulating device (1) is in a rest position, the regulating piston (6) is in a neutral position and the actuating piston (2) is a specific end position.

Abstract: A hybrid actuation system comprises first and second actuator arrangements (10, 12) arranged to apply first and second output loads respectively to a common element (14). A control method for controlling the operation of the hybrid actuation system includes the steps of supplying first and second demand signals to the first and second actuator arrangements (10, 12) respectively to cause movement of the common element (14) into a demanded position, monitoring the first and second output loads applied by the first and second actuator arrangements (10, 12) and generating an output signal indicative of the difference between the first and second output loads. The first and second demand signals are corrected in response to the output signal to compensate for any difference between the first and second output loads, thereby to ensure the first and second output loads applied to the common element (14) are substantially identical and synchronized.

Abstract: A drive mechanism is disclosed which includes a hydraulic pump whereby at least two hydraulic motors may be supplied with pressure medium. The drive mechanism in accordance with the invention has on the meter-in side or on the meter-out side of each hydraulic motor a variable hydraulic resistor that is biased into a basic position of minimum open cross-section and may be subjected to a control pressure in a direction of increased open cross-section. This control pressure is dependent on the pressure on the meter-in side or on the meter-out side of the hydraulic motor.

Abstract: The invention relates to a hydraulic actuator for actuating a gas exchange valve (1) of an internal combustion engine, which valve is especially closed by the effect of a spring. The actuator is configured by a feed pump (6) with intermittent and thus variable delivery. The feed pump (6) has a high frequency and can be equipped for this purpose with piezoelectric, magnetorestrictive and/or electrochemical actuators as the feed elements. Optionally, the feed pump (6) can be operated with a stop valve (7) that is disposed downstream of the gas exchange valve (1) and that is controlled or regulated depending on the feed pump.

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: A hydraulic circuit comprises first and second cylinders, and a piston disposed in each of the cylinders. A pump communicates with one side of one of the pistons, and a pressure relief valve has a position wherein the pump communicates with another side of the one piston and with the other piston.

Abstract: A travel motor hydraulic control system for a construction machine having a plurality of hydraulic pumps which supply individually pressurized fluid for a plurality of hydraulic travel motors and a plurality of flow control valves which control the flow rate of the pressurized fluid to be supplied to the motor during an ordinary work. A controller receives a control signal representative of a travel control lever stroke sensed by a position sensor and a control signal detected by a pressure sensor, determines if the vehicle is traveling up a slope, and transmits a command signal to a solenoid operated valve to move a pilot operated shut off valve toward a valve-closing position, thereby the travel hydraulic motors are individually supplied the pressurized fluid from the hydraulic pumps.

Abstract: A first object of the present invention is to make do with a simple hydraulic circuit, which does not utilize a pressure compensation valve, and to enable the use of an inexpensive, low-precision pressure detector, to enable the maintenance of continuous control at all times using simple controls, and to get by without shocking the operator or the mechanical parts, and to cancel the load dependency of a hydraulic actuator flow during combined operation without limiting the control system of the hydraulic pump. In a device according to the present invention, a correction factor for correcting a control input of a operating member corresponding to a pertinent operating valve is calculated for each operating member on the basis of a ratio between a detected differential pressure across an operating valve, and a minimum differential pressure selected from among detected differential pressures across a plurality of operating valves.

Abstract: The composite operation efficiency can be improved in a work machine with a plurality of hydraulic actuators. In the control section the flows to be shared to the respective hydraulic actuators are calculated on the basis of the permissible flow in compliance with an operating quantity of an operating tool, and control commands are outputted to an electromagnetic pressure valve so that the corresponding shared flows are supplied to the respective hydraulic actuators.

Abstract: A hydraulic pilot circuit having a pilot pump which discharges pilot oil, and a plurality of pilot valves which control a plurality of hydraulic directional control valves by supplying the pilot oil with control, wherein heating of hydraulic oil due to retaining pilot pressure oil is reduced, and controllability is not damaged even if the plurality of pilot valves are operated at the same time, because sufficient pilot oil is supplied to the pilot valves. A variable displacement pump is adopted as the pilot pump. An operation detecting means detects operating condition of the hydraulic pilot valves, a controller computes the necessary discharge of the pilot pump for operating the hydraulic directional control valves from the operating condition, and the pilot pump discharges only the necessary oil flow.

Abstract: A hydraulic circuit (10) is disclosed for use in controlling a horizontal boring machine which requires hydraulic fluid under pressure for rotating a drill bit or backreamer through a rotation circuit and hydraulic fluid under pressure for thrusting the drill bit or backreamer within the bore hole through a thrust circuit. Pressures from both the thrust circuit and control circuit are combined through restrictors in a mixing zone or area (26). The control port of a diversion valve (32) is connected to mixing zone (26). When the combined pressure in the mixing zone exceeds the adjustable spring bias on the diversion valve, the diversion valve will open, diverting fluid from the thrust circuit to a low pressure zone. This will cause a reduction in the pressure in the rotation circuit as well. The reduction of both pressures will reduce the combined pressure in the mixing zone (26), causing the diversion valve to close and the pressures to increase.