Abstract: Disclosed is a hydraulic system for a machine having a pump, a steering circuit and first and second hydraulic implements, e.g., a hydraulic loader and a backhoe, powered by first and second valve sections, respectively. In the improvement, the system includes a priority valve receiving fluid from the pump and configured for movement between a first position and a second position. In the first position, the priority valve flows fluid to the steering circuit and to the second valve section and in the second position, the priority valve flows fluid to the both valve sections which are connected in series.

Abstract: A flow control system is arranged in a hydraulic circuit provided with a variable displacement hydraulic pump, plural actuators and a pump controller. The pump controller controls the displacement of the pump so that a delivery pressure becomes higher by a predetermined value than a maximum load pressure of the plural actuators, whereby the flow rate of pressure oil to the actuators is controlled. The system includes plural valve units connected between the pump and the actuators. Each valve unit has an operating and correcting variable restrictors. The system also includes pressure compensation valves, which are each arranged on an upstream side of a restrictor group consisting of the operating and correcting variable restrictors.

Abstract: A vehicle mounted hydraulic system is provided with a flow control system that allows and maintains sufficient fluid flow through the pump, regardless of pump speed or fluid usage requirements by the hydraulically operated devices, to prevent cavitation or undue pump wear.

Abstract: A hydraulic recovery device in a hydraulic system having a pump (1) driving a plurality of actuators through a plurality of control valves (2, 3), the hydraulic recovery device comprising a variable resistance valve (6, 60) in a first line being controlled by a control signal (Px), a third line, a check valve (7) disposed in the third line for allowing the hydraulic fluid to flow only in a direction from the first line toward the second line.

Abstract: The invention relates to a method for, in a hydrostatic transmission having a preferably variable displacement hydraulic pump (P) feeding a number of hydraulic motors (M1, M2, M3, M4) provided in association with respective drive wheels, drive tracks or corresponding drive apparatus, mutually balancing the flow of hydraulic fluid through the different hydraulic motors (M1-M4) by individually controlling of the flow from and/or to the same, whereby the individual flows of hydraulic fluid through the respective hydraulic motors (M1-M4) are detected and compared across respective restrictions (14, 15) being variable dependent on the total flow but being of mutually equal size and whereby, for optimum control or balancing, the detected differences in flow through the different hydraulic motors are in themselves used directly for the balancing.

Abstract: A fluid operated device has a high pressure fluid cylinder, a low pressure fluid cylinder and a plurality of valves which operate to fluidically connect the two cylinders to provide a compound fluidic device. The device utilizes the exhaust of the high pressure cylinder as input to the low pressure cylinder thereby increasing the amount of work obtained from the pressurized fluid. In the preferred embodiment, the fluid operated device is connected to a compressing cylinder which, through operation of the fluid operated device, increases the fluid pressure of a working fluid. The plurality of valves includes a pair of two-way valves and two quick exhaust valves to increase the cycle speed of the fluid operated device.

Abstract: A hydraulic control valve apparatus including a flow control valve having a pair of variable throttles, a feeder passage, a pair of load passages, directional control valve devices comprise a seat valve having a seat valve body movably disposed in a housing to form an auxiliary variable throttle in the feeder passage, and a control variable throttle (33) formed in the seat valve body for changing an opening area in accordance with an amount of movement of the seat valve body; (b) a pilot line (24, 29-31, 35-37) for communicating a portion (7C) of the feeder passage upstream of the auxiliary variable throttle with a downstream portion (7A, 7B) of the feeder passage through the control variable throttle to determine the amount of movement of the seat valve body in accordance with a flow rate of the hydraulic fluid passing through the pilot line; and (c) pilot flow control (400; 401; 403; 405; 406; 407; 408) having a pilot variable throttle (45) disposed in the pilot line and input (800; 52-59; 159, 54-59; 231A,

Abstract: In a pneumatic control circuit, five three-port, two-position, directional control valves, three of which have manual controls, and two shuttle valves are arranged for controlling a first pneumatic device and a second pneumatic device in an operating mode wherein the second pneumatic device cannot be readily enabled before the first pneumatic device is enabled. A first control valve having a manual control is arranged to control the first pneumatic device. A second control valve having a pilot valve is arranged to control the second pneumatic device. A pilot control valve having a manual control is arranged to connect the first control valve to the pilot valve of the second control valve via a shuttle valve. A holding control valve has a cam control, which is operated by the second pneumatic device, and has an outlet connected to the pilot valve of the second control valve.

Abstract: A hydraulic drive system for hydraulic working machines has a variable displacement hydraulic pump, at least one actuator driven by the hydraulic fluid, a directional control valve of center bypass type for controlling the flow of the hydraulic fluid, a center bypass line for connecting the center bypass passage of the control valve to a reservoir and a fixed restrictor disposed in the center bypass line. A first control signal that determines a first target displacement of the hydraulic pump is determined by using the pressure generated by the fixed restrictor. A second control signal is generated for determining a second target displacement of a hydraulic pump. A third control signal, which is the larger one of the first and second control signals, provides a target displacement that is applied to a pump regulator that controls the displacement of the hydraulic pump.

Abstract: A fluid pressure driving system for a vehicle includes a reservoir tank in which an amount of fluid is stored, a variable capacity oil pump sucking the fluid from the reservoir tank and discharging the resultant fluid, a control device for adjusting a quantity of the fluid discharged from the variable oil pump, and a distributor valve having an inlet port for receiving the fluid from the variable capacity oil pump. The distributor valve discharges a fixed amount of the fluid and the remaining amount of the fluid from a first outlet port thereof and a second outlet port thereof, respectively. A first passage connects the first outlet port of the distributor valve and the reservoir tank. A second passage connects the second outlet port of the distributor valve and the reservoir tank. A power steering device is associated with a steering wheel and disposed in the first passage. A hydraulic motor is disposed in the second passage, and a cooling fan is mounted rotatably on the hydraulic motor.

Abstract: An unloading valve is connected to a hydraulic pump, the unloading valve being opened when a differential pressure between a delivery pressure of the hydraulic pump and a maximum load pressure exceeds a predetermined value, for discharging a part of a flow rate of a hydraulic fluid delivered from the hydraulic pump to a reservoir. A fixed restriction for generating a control pressure corresponding to the flow rate of the hydraulic fluid discharged through the unloading valve is connected downstream of the unloading valve. A control device for the hydraulic pump is constructed to reduce the delivery rate of the hydraulic pump as the control pressure generated by the fixed restriction is raised, and increase the pump delivery rate as the control pressure is lowered.

Abstract: The present invention provides an apparatus for controllably actuating a work implement. The work implement includes at least a first linkage and a second linkage. The apparatus produces a control signal, senses the position and velocity of the first and second linkages and responsively produces position and velocity signals. The apparatus responsively produces a command signal as a function of the control signal and the position and velocity signals. The command signal controls actuation of the first linkage such that dynamic coupling between the first and second linkages is minimized.

Abstract: A fluid operated device has a high pressure fluid cylinder, a low pressure fluid cylinder and a plurality of control valves which operate to fluidically connect the two cylinders to provide a compound fluidic device. The device utilizes the exhaust of the high pressure cylinder as input to the low pressure cylinder thereby increasing the amount of work obtained from the pressurized fluid. In the preferred embodiment, the fluid operated device is connected to a compressing cylinder which, through operation of the fluid operated device, increases the fluid pressure of a working fluid.

Abstract: In a driving mechanism of a circuit breaker having first and second hydraulic operation apparatuses respectively driving a main contact and a resistor contact, a sequential control valve is provided between the first and second hydraulic operation apparatuses. The sequential control valve detects the operation of a differential piston for opening the main contact and switching the differential piston for sequentially opening the resistor contact after the opening of the main contact.

Abstract: A device for controlling multiple hydraulic actuators to protect a system from an overpressure caused by increasing the load on an individual actuator. By controlling the supply of hydraulic fluid to a pair of cylinders each associated with a pilot valve so that each cylinder always has enough fluid pressure to operate, the device of the present invention prevents the shutdown of the device caused by too much fluid going to the actuator operating at the maximum pressure. Thus all actuators continue to operate even if one is overpressured.

Abstract: An improvement in a multiple intensifier system having two intensifier units with reciprocating piston assemblies to supply very high pressure water. When one of the piston assemblies travels faster than the other, so that these reached an end stroke position at the same time, there can be an abrupt pressure drop. To alleviate this, a first embodiment isolates the compensator control lines of the pumps of the two intensifier units so as to maximize volumetric flow rates during such pressure drops to give the slower moving piston assembly a boost at the beginning of its subsequent stroke. Another embodiment provides an accumulator in the fluid control line for the compensators, and a further embodiment provides a pressure reference supply pump to alleviate pressure variations in the fluid control line.

Abstract: A hydraulic circuit for controlling the speed of multiple hydraulic fluid power devices when the flow demand of the devices exceeds the flow capacity of a pressure source supplying hydraulic fluid under pressure to the devices has multiple pressure controlled proportional flow supply valves for controlling the supply of hydraulic fluid to the power devices. Load sense pressures which indicate the pressure delivered by the valves to the corresponding devices are compared to determine the highest load sense pressure, which is compared to the supply pressure by a proportional speed sensing valve to regulate the pilot pressure. In the preferred embodiment, the pilot pressure is regulated by the proportional speed sensing valve to be equal to the differential between the supply pressure and the highest load sense pressure, and a limit control is provided in one form of the proportional speed sensing valve.

Abstract: The flow rate of oil under pressure for operating an attachment for a hydraulic excavator or the like according to the type of attachment is controlled by a simple hydraulic circuit, capable of easily switching the flow rate and also capable of finely adjusting the flow rate. The circuit has directional control valves (2-4, 6-8), pressure compensating valves (17, 18) disposed at outlet ports of each of the directional control valves, load sensing valves (23, 24) for controlling discharges from the variable capacity type main hydraulic pumps (1, 5), and circuits (21, 22) for feeding back the maximum valve of load pressure between each actuator and the associated direction control valve to the pressure compensating valves and the load sensing valves via a shuttle valve (20). A directional control valve (4), which controls the attachment, has a restricting element for restricting an opening area of a spool of the directional control valve.

Abstract: A plurality of directional control valves (5, 6) respectively disposed between a hydraulic pump (50) and a plurality of actuators (3, 4) each comprises a pump port (9), a pressure chamber (10), a feeder passage (11), actuator ports (12a, 12b), a reservoir port (13), first meter-in variable restrictors (15a, 15b) disposed between the pump port and the pressure chamber, and a pressure compensating valve (16) disposed between the pressure chamber and the feeder passage and having a pair of opposite ends, one of which is subjected to a pressure in the pressure chamber and the other of which is subjected to a maximum load pressure among the plurality of actuators. The hydraulic pump (1) includes a pump flow control device (2) for controlling a delivery rate of the hydraulic pump so that a delivery pressure of the hydraulic pump is held higher by a predetermined value than the maximum pressure obtained, as a load sensing pressure, from load pressures of the plurality of actuators.

Abstract: The present invention relates to a valve assembly for the supply of users in hydraulic control systems with pressurized fluid for the load pressure (LS) independent control of several simultaneously actuated hydraulic users wherein the ratio of the partial flows once set is maintained at undersupply of the system with the pressurized fluid. When the demand of the users exceeds the maximum output flow of the variable displacement pump, the (high) priority users receive the demanded quantity whereas the low priority users receive a reduced quantity by switching the control pressure for the low (i.e. no) priority users via a directional control valve and a pressure relief valve to a lower pressure level. Only when undersupply of the entire system occurs, i.e. when the maximum output flow of the variable displacement pump is no more sufficient despite the limitation of the control pressure for the low priority users, then the presently flowing partial flows of all users are reduced proportionally.

Abstract: The invention is an improvement in a control system having first, second and third sources of fluid at differing pressures. The improvement comprises a tripath pressure selector network connected to the first and second sources. A pressure-sensing device connects the network and the third source when the third source is at a predetermined minimum pressure. The invention has particular utility in mobile construction machinery having, e.g., steering, implement and brake hydraulic circuits, at differing pressures. In one embodiment, the third source is a brake hydraulic circuit. The improvement helps assure that adequate pilot pressure is available for a "downstream" pilot control valve.

Abstract: A control device for hydraulic operating cylinders of a tailgate of a vehicle to determine maximum pressures arising in the operation and, particularly, overloading of the tailgate, resulting in excessive pressures. A power-driven hydraulic pump (1) is connected to a reservoir (4) and, via branch lines (8', 8"), with associated gate control valves (10, 13) which include a closing cylinder (14) for the tailgate. A pressure intensifier piston-cylinder unit (15) is connected parallel to the branch pipes. An electric pressure-sensitive switch (16), which is also connected to a counter (17) and to an interrupter switch (18) for the electric pump motor, switches off the pump motor (2) when the predetermined pressure is exceeded. This switch is connected to the closing cylinder (14) for the tailgate.

Abstract: A hydraulic circuit for a swivel working machine, in which the operation of the working unit is speeded up when the swiveling body and the working unit are simultaneously operated, includes, for this purpose, first and second operating valves (15.sub.1 and 15.sub.2) connecting the delivery conduit of a hydraulic pump (10) to a swiveling hydraulic motor (16.sub.1) and to a working unit cylinder (16.sub.2), and pressure compensating valves (18) provided between the first operating valve (15.sub.1) and the swiveling hydraulic motor (16.sub.1) and between the second operating valve (15.sub.2) and the working unit cylinder (16.sub.2), the load pressure of the swiveling hydraulic motor (16.sub.1) and the load pressure of the working unit cylinder (16.sub.

Abstract: A load sensing control system for a hydraulic machine sets a variable target differential pressure between a delivery pump pressure and a load pressure of an actuator. A control factor is determined that becomes larger as the deviation between the target differential pressure and the actual differential pressure is increased, and that becomes smaller as the differential pressure deviation is decreased. The control factor also becomes larger as the target differential pressure becomes smaller. The target displacement volume for the hydraulic pump is based on the differential pressure deviation, which is calculated from the target differential pressure and the control factor.

Abstract: In the hydraulic apparatus (1) according to a first aspect of the present invention, mid-pressures between the inlet side and outlet side pressures of a first and a second pressure compensating valves (4, 4') are permitted to act on the flow rate decreasing side pressure receiving surfaces (4b, 4b') thereof through first and second mid-pressure supplying means (13, 13'), thereby restraining operational error and malfunction of the pressure compensating valves (4, 4'). In the hydraulic apparatus (20) according to a second aspect of the present invention. when actuating valves are made to assume neutral position, holding pressures of hydraulic actuators (5, 5') are permitted to act on flow rate decreasing side pressure receiving surfaces (4b, 4b') of pressure compensating valves (4), (4') so that spools of the pressure compensating valves are held at compensating position, thereby improving the response of the hydraulic actuators (5, 5') to lever actuation.

Abstract: In a controller (229) of a hydraulic control system for construction machines, a valve control signal calculating function (301) works such that when an operation pattern signal (A-I) for actuators (201, 202 . . . ) is outputted, it selects corresponding one of plural output patterns for an auxiliary valve control pressure stored, as a function of a differential pressure signal between a pump delivery pressure and a maximum load pressure, in relation to the operation pattern signals, followed by calculating an auxiliary valve control pressure (Pc) dependent upon the differential pressure signal based on the selected output pattern, and also selects corresponding one of plural sets of rates of change (K . . . , K . . . ) for the auxiliary valve control pressure stored in relation to the operation pattern signals, followed by combining the calculated auxiliary valve control amount with the selected set of speed changes to calculate each of valve control signals (S21-S26).

Abstract: This invention provides a hydraulic circuit system capable of reducing the flow rate distribution error in supplying pressurized fluid from a single hydraulic pump into a plurality of hydraulic actuators, and also supplying pressurized fluid quickly. The circuit is simplified to reduce manufacturing costs.

Abstract: A control device for hydraulic operating cylinders of a combined lifting platform and closing wall of a vehicle, having a hydraulic fluid pump (1), driven by a motor (2), which pump can be made to communicate with a fluid supply (4) and, via pump branch lines (8', 8") beginning at a pump line (8), with a chamber of at least one lifting cylinder (11) and of at least one closing cylinder (14) of the lifting platform and closing wall, respectively, via associated control valves (9, 10; 12, 13), wherein a pressure transformer and piston cylinder unit (15) is connected parallel to the pump branch lines (8', 8").

Abstract: In a pressure-control device for affecting the closing behavior of powershift clutches (K.sub.1 -K.sub.X) in a powershift transmission, a regulating valve (1) cooperates with a damping device (2) as pressure-control valve. Chokes (4, 40, 400) for a more or less smooth connection are arranged in combination with pressure lines (P.sub.S, P.sub.R) over the pressure cycle when the clutch concerned (K.sub.1 -K.sub.X) is engaged. The travel of the damper piston (21) in a direction toward the regulating valve (1) is shortened by a pressurizing piston device (3) cooperating with the piston (21) of the damping device (2). Thus the time for the slipping phase in the engaged clutch concerned is shortened and, together with a higher initial pressure after the clutch is filled, the friction is limited.The limitation of the friction can also be obtained by adding a second choke in parallel in the control pressure line (Pr) by which the choked cross section is increased.

Abstract: A valve apparatus (30) of a hydraulic valve system has a plurality of directional control valves (78, 79) that control the flow of the hydraulic fluid to a plurality of actuators (34, 35). Check valves (59, 60) are provided for taking out, as a first control pressure, a maximum load pressure among load pressures of the plurality of actuators, first pressure generating devices (89, 91) for generating second control pressures different from the first control pressure, and second pressure generating devices (90, 92) for generating third control pressures different from said first and second control pressures.

Abstract: A drive system for a work vehicle is provided which includes first and second hydrostatic transmissions which are responsive to respective control signals for driving first and second ground engaging devices at a rate responsive thereto. A sensor is provided sensing the position of a manually operable control element and responsively producing a desired speed signal. A memory device is adapted to store data relates the desired speed signal to the first and second control signals in a preselected manner. A processor is provided for receiving the desired speed signal, responsively retrieving at least a portion of the data from the memory device, and producing the first and second control signals in response to the retrieved data and the desired speed signal. An adjusting device is provided for receiving at least one of the control signals, permitting controllable adjustment of the control signal so as to vary the speed of a respective ground engaging device.

Abstract: A hydraulic control circuit for building machinery includes a hydraulic cylinder to operate a tool. To stabilize vibrations of the tool around the pitch axis, a hydraulic accumulator is provided to be connected to a pressure source via a fill line. A shut-off valve is disposed in the fill line, which valve is subjected to the pressure in the accumulator such that in operating the cylinder the accumulator is loaded to a pressure corresponding to the load pressure. The system is very simple in structure and fluid losses are eliminated.

Abstract: When a hydraulic circuit for driving actuators of a construction machine or the like includes a single hydraulic pump and a plurality of direction changeover valves connected to the hydraulic pump for controlling the respective actuators, operation of one of the direction changeover valves may result in undesirable change in the output oil pressure of the other direction changeover valves. The inventive hydraulic circuit includes means for driving a regulator of the hydraulic pump in response to any oil puressure change at the inlets of the direction changeover valves corresponding to the output oil pressure change, thereby compensating for the pressure change.

Abstract: An improved hydraulic system for a vehicle includes a swash plate type variable capacity hydraulic pump that is operably coupled to an engine. A hydraulic motor for driving an air conditioning compressor and a power steering hydraulic mechanism having less fluid demand than that of the hydraulic motor are disposed in a first and a second fluid lines respectively. First, second and third nozzles are disposed within the fluid lines. The volume of fluid controlled by the first nozzle is larger than that of the second nozzle, which is larger than that of the third nozzle. The first fluid line is depressurized by the first nozzle when the hydraulic motor is used, while the second fluid line is depressurized by the second nozzle when the power steering mechanism is used. When neither the hydraulic motor nor the power steering mechanism is used, the pressure in the fluid line on the circulation side is reduced to nearly zero by the third nozzle.

Abstract: A hydraulic circuit arranged to prevent the load pressure in one of the hydraulic actuators at the time of starting from becoming abnormally high thereby preventing fluid under pressure from being relieved by the safety valve when a plurality of hydraulic actuators are operated at the same time, wherein the function of one of the pressure compensating valves is temporarily enhanced by introducing the load pressure in the hydraulic actuator so as to supply a large quantity of fluid under pressure to the hydraulic actuator connected to the pressure compensating valve so that the operating speed of the hydraulic actuator can be increased.

Abstract: A first hydraulic circuit comprises a variable displacement hydraulic pump driven by a prime mover, a variable displacement hydraulic motor connected in a closed circuit to the variable displacement hydraulic pump, and a displacement control means for controlling a displacement of the variable displacement hydraulic motor. A second hydraulic circuit comprises a hydraulic pump driven by the prime mover, and drives a loader attachment. A displacement limitation means limits the maximum value of the displacement of the variable displacement hydraulic motor in accordance with a load pressure of the second hydraulic circuit. For example, the displacement limitation means reduces the maximum value of the displacement of the variable displacement hydraulic motor in proportion to the pressure in the second hydraulic circuit. The motor torque is controlled by directly adjusting the displacement of the motor, and a load of the hydraulic motor can thus be stably controlled.

Abstract: Disclosed is a hydraulic system for driving both an air conditioning compressor and a power steering mechanism. Pressured fluid discharged from a variable capacity pump is supplied to a hydraulic motor for driving the air conditioning compressor and to the power steering mechanism. A controller controls the discharging capacity of the variable capacity pump in accordance with loads on the hydraulic motor and the power steering mechanism.

Abstract: A system for automatically controlling the actuators of a construction vehicle. The system comprises electronic controller, an automatic selecting switch for selecting automatic control for actuators, as requested, control levers for being manipulated by an operator in order to instruct the controller of desired operations of the actuators, and positional sensors for sensing respective positions of the actuators and outputtng signals corresponding to the positions of the actuators to the controller. In the system, the actuators during performing repeated operations are such automatically controlled that they are controlled during a first operation by the operator's manipulations for the control levers, thereafter, during each sequential operation, they are automatically controlled by the controller on the basis of electric control currents having been automatically calculated by virtue of a displacement ratio between the actuators during a just previous operation.

Abstract: A hydraulic circuit for controlling the speed of multiple hydraulic fluid power devices when the flow demand of the devices exceeds the flow capacity of a pressure source supplying hydraulic fluid under pressure to the devices has multiple pressure controlled proportional flow supply valves for controlling the supply of hydraulic fluid to the power devices. Load sense pressures which indicate the pressure delivered by the valves to the corresponding devices are compared to determined the highest load sense pressure, which is compared to the supply pressure by a proportional speed sensing valve to regulate the pilot pressure. In the preferred embodiment, the pilot pressure is regulated by the proportional speed sensing valve to be equal to the differential between the supply pressure and the highest load sense pressure, and a limit control is provided in one form of the proportional speed sensing valve.

Abstract: A track-laying vehicle has two tracks, each with a hydrostatic drive unit, where at least one drive motor 1, 2 adjustable in working volume is provided in each drive unit and to which at least one pressure medium supply line 3, 4, 5, 6 connected to a hydrostatic pump leads and which has a working volume adjusting device 9, 11, 10, 12 that can be influenced by a signal dependent on the operating pressure. To avoid unintentional changes in direction of the track-laying vehicle in the case of different resistances to the tracks, it is proposed to connect the pressure medium supply lines 3, 4, 5, 6 of all the drive motors 1, 2 to a shuttle valve circuit 32, 33, 34 which determines the highest of the operating pressures of the hydrostatic drive unit and empties in a signal line 19 that is connected to the control elements of the working volume adjusting devices 9, 11, 10, 12 of all the drive motors 1, 2.

Abstract: A valve system is provided for the load-independent control of a plurality of simultaneously operated hydraulic consumers, i.e. regardless of variations in load pressure. Fluid flow in a consumer line to each consumer passes across a compensating flow control valve, i.e. a compensator. The valve piston thereof being displaceable to the open position by a pressure downstream of a flowmeter against the opposing resistance offered by a spring and by the respective maximum load pressure of the consumers at a time. The actual highest load pressure is also available at a regulator for the common variable displacement supply pump feeding the consumers.

Abstract: A construction machine has a flow control device (2, 8, 10 ) for controlling a flow rate of the hydraulic fluid supplied to an actuator, and a pump control device (2, 40, 42) for controlling a delivery rate of the hydraulic pump such that the pump delivery rate is reduced as a load of the actuator increases, and is increased as the load of the actuator decreases. A magnitude of the load exerted on the actuator is detected (6), and an abrupt reduction in the load of the actuator based on the detected load is monitored. The hydraulic fluid supplied to the actuator is limited when it is determined that the actuator has reached a predetermined condition related to an abrupt reduction in the load, for the purpose of preventing an abrupt increase in the actuator speed incidental to an abrupt drop of the load not occurring during ordinary work.

Abstract: A hydraulic drive system comprising a prime mover (21), a hydraulic pump (22) driven by the prime mover, a plurality of hydraulic actuators (23-28) driven by hydraulic fluid supplied from the hydraulic pump, a plurality of flow control valves (29-34) for controlling flow of the hydraulic fluid supplied to the actuators, and a plurality of pressure compensating valve (35-40) for controlling respective differential pressures across the respective flow control valves, in which each of the pressure compensating valves applies a control force (f-F.sub.c) in a valve opening direction for setting a target value of the differential pressure across the flow control valve. There are provided a first detector (60) for detecting the target rotational speed (N.sub.0) of the prime mover (21), and controllers (61, 62, 63) for controlling the control force on the basis of the target rotational speed detected by at least the first detector such that the control force (f-F.sub.

Abstract: A hydraulic actuator is driven by hydraulic fluid discharged from a hydraulic pump, for controlling driving of the actuator. A valve has a meter-in circuit for introducing the hydraulic fluid discharged from the hydraulic pump into the actuator. The valve also has a meter-out circuit for returning fluid from the actuator, into a tank. The meter-out circuit is provided with a main valve for controlling the return fluid from the actuator, and a pilot circuit including a variable restrictor. When the main valve is closed, the pilot circuit is closed, and when the main valve is open, its degree of opening varies depending upon an amount of restriction of the variable restrictor. A controller varies the amount of restriction of the variable restrictor valve in accordance with the driving pressure of the actuator.

Abstract: For a load independent control of a plurality of simultaneously actuable hydraulic users, a throttle valve (pressure compensator) is assigned to the control valve of each user at a location downstream with respect to the metering orifice formed by said control valves; said throttle valve is subjected in opening direction to the pump pressure and in closing direction, via a shuttle valve, either to a load pressure of the respective user or to a pressure which is determined by the highest load pressure occurring for one of said users. Said highest load pressure which is reported by a shuttle valve chain is supplied as control pressure to a pressure reducing valve, the input side thereof being connected with the pressure line of the pump and the output side thereof being connected to control lines leading to the throttle valves assigned to the individual control valves and to the control line for the pump control.

Abstract: Hydraulic control of reversible hydraulic motors typically requires several different valves to provide for the various operating parameters. The subject hydraulic control circuit has only a pair of electrohydraulic control valves to provide all the typical operating parameters. Operation of the control valves is controlled by a microprocessor in response to receiving command signals from a manually controlled command signal outputting device which establishes a desired fluid flow rate and direction of flow through the control valves.

Abstract: A hydraulic drive system for a crawler mounted vehicle has a hydraulic pump, a plurality of actuators including a pair of left and right travel motors and at least one other actuator that are driven by hydraulic fluid delivered from the hydraulic pump. The system further contains a plurality of flow control valves for controlling flows of the hydraulic fluid supplied to the respective actuators, and a plurality of distribution compensating valves for controlling differential pressures across the respective flow control valves, the plurality of distribution compensating valves each having drive parts to set a target value of the differential pressure across the associated flow control valve. The hydraulic drive system also has a speed selector for outputting a select signal to change operation speeds of the pair of travel motors, and a controller and a control pressure generator for controlling the drive parts of the distribution compensating valves associated with the pair of travel motors.

Abstract: A single hydraulic pump (6) is employed in a vehicle for supplementing fluid to a hydrostatic transmission (1) and for supplying fluid to a fluid-operated clutch (2) and to high pressure-actuated hydraulic actuators (3, 4, 5). Fluid discharge path (7) of the pump is connected to the hydrostatic transmission through a pressure-reducing valve (8). Fluid drain path (9) of the reducing valve is fashioned to a fluid supply path for the clutch. A second fluid supply path (11) is connected to the discharge path for supplying fluid to the hydraulic actuators and include a relief valve (12) or orifice (12A) for maintaining fluid pressure in the discharge path higher than the output pressure of the reducing valve. A high pressure relief valve (10) for establishing fluid pressure to be applied to the actuators is connected to the discharge path for minimizing a discharge pressure required to the pump.

Abstract: A hydraulic circuit for a piece of construction equipment such as a hydraulic shovel. The operation of the hydraulic shovel is controlled by a number of hydraulic actuators which are provided with a high pressure oil through selector valves. A main relief valve prevents an excessive pressure from developing in the vicinity of a main pump, and port relief valves associated with the individual actuators prevent excessive pressures from reaching each actuator. Pilot lines carry a biasing oil pressure from a pilot pump to the main relief valve and to at least one of the port relief valves to boost the relief pressures in the circuit in response to a signal from an operator controlled switch. Simultaneously with effecting a boosting of relief pressure in the relief valves, the operator controlled switch renders one of the actuators inoperative using a shut-off valve so that it may not be operated while the relief pressures are boosted.

Abstract: A hydraulic system for a construction machine comprising plural hydraulic actuators (23-28) driven by fluid supplied from a pump (22), first and second flow control valves (29-34) for controlling flows of fluid supplied to the first and second actuators, and first and second distribution compensating valves (35-40) for controlling first differential pressure (.DELTA.P v1-.DELTA.P v6) produced between inlets and outlets of the first and second flow control valves. The first and second distribution compensating valves have respective drives (45-50, 35c-40c) for applying control forces (Fc1-Fc2) in accordance with the second differential pressure to the associated distribution compensating valves, to thereby set target values of the first differential pressures. The hydraulic system includes first means (59) for detecting the second differential pressure (.DELTA.