Abstract: A displacement control valve includes a valve element having a first operative position communicating a displacement controller of a variable displacement hydraulic pump with a tank for increasing the pump displacement and a second operative position communicating a discharge passage of the pump with the control port for decreasing pump displacement. The discharge passage communicates with a first end of the valve element to generate a force biasing the valve element toward the second position. An opposing biasing force is exerted on the valve element in opposition to the pressure generated force acting on the first end of the valve element so that a predetermined pressure level is established in the discharge passage when the forces acting on the valve element are equalized.

Abstract: A hydraulic control system is intended to easily hydraulically back up a trouble caused in an electric system, while employing a control unit (13) to utilize the advantage of electric control, when the displacement of a hydraulic pump (1) is controlled in accordance with a status variable of a hydraulic driving system. To this end, a pump regulator (16) is constructed so as to increase the tilting amount .theta. of a swash plate (1a) with a reduction in pressure of a second hydraulic signal Pc. A characteristic of the pump regulator is set such that a negative control pressure Pco can be employed to operate the pump regulator in place of the second hydraulic signal, and characteristics of a fixed throttle (10) and a spring (18d) in the pump regulator are set such that the pump regulator can be operated in the working range of the negative control pressure.

Abstract: The present invention proceeds from a control arrangement for at least two hydraulic consumers which has a positive displacement pump the setting of which is variable by a load-sensing regulator which can be acted on via a load-signaling line by the highest load pressure, on which a maximum-pressure and an output regulation are superimposed, two displaceable metering diaphragms a first one of which is connected between the positive displacement pump and a first hydraulic consumer and the second between the positive displacement pump and a second hydraulic consumer, and two pressure compensators a first one of which is arranged behind the first metering diaphragm and the second behind the second metering diaphragm and the regulating pistons of which can be acted on, in opening direction on a front side, by the pressure behind the corresponding metering diaphragm and in closing direction on the rear side by the pressure in the load-signaling line.

Abstract: A control valve is provided in a line between a variable displacement hydraulic pump and a hydraulic cylinder. The control valve controls flow rate of working fluid supplied to the hydraulic cylinder according to a manipulated variable of a lever. The control increases a discharge of the hydraulic pump in association with the increase in the manipulated variable and also controls to suppress the discharge as the discharge pressure of the hydraulic pump increases. A proper response corresponding to the operator's feeling can be realized in consideration of an actual pressure loaded on an actuator on the basis of a positive control system.

Abstract: A pressure compensation valve has a check valve portion with a check valve bore with an inlet port and an outlet port in a valve body, a valve in the check valve bore for establishing and blocking communication between the inlet port and the outlet port, a pressure reduction valve portion constructed by forming a pressure reducing valve bore having a first port, a second port and a third port and being coaxial with the check valve bore in the valve body, a spring-biased spool in the pressure reduction valve bore to define a first pressure chamber communicating with the first port and a second pressure chamber communicating with the third port at both sides, making the second port communicate with the third port by a pressure of the first pressure chamber, and blocking communication between the second port and the third port by the pressure in the second pressure chamber.

Abstract: A pressure compensation valve comprises a check valve portion having an inlet port that is connected to a discharge path of a hydraulic pump, an outlet port that is connected to an inlet side of a directional control valve, and a valve for controlling an area of opening between both ports. A pressure reduction valve portion has a spool that defines at its both sides a first pressure chamber and a second pressure chamber, respectively, and is adapted to be slidable to allow the valve to be thrusted in a first direction in which the area of opening is increased under a self-load pressure applied to the first pressure chamber and to be slidable to allow the valve to be thrusted in a second direction in which the area of opening is decreased under a pressure within the second pressure chamber.

Abstract: A control system for a variable-displacement hydraulic pump having an adjustment device and being electrical current-adjustable as required for supplying pressure to a first hydraulic apparatus (13), and pressure-adjustable for supplying pressure to a second hydraulic apparatus (14), in which case the pressure rating and the setting of the pilot valve controlled by the second hydraulic apparatus (14) may be programmed by a control signal. The control system includes a first control valve (18) that can be actuated by the weight of the load of the first apparatus (13) and by a spring (23) when switching to a higher displacement, or by the pump pressure when switching to a lower displacement. The system further includes a second control valve (19) which can be exposed to a force corresponding to the control signal (25) when switching to a higher displacement, or to the pump pressure when switching to a lower displacement.

Abstract: An improved pressure-compensated hydraulic system for feeding hydraulic fluid to one or more hydraulic actuators. A remotely located, variable displacement pump provides an output pressure equal to input pressure plus a constant margin. A pressure compensation systems requires that a load-dependent pressure be provided to the pump input through a load sense circuit. A reciprocally spooled, multi-ported isolator transmits the load-dependent pressure to the pump input but prevents fluid in the load sense circuit from leaving the load sense circuit and flowing through a relatively long conduit leading to the remotely located pump. In a multi-valve array, at least one valve section has a backflow-preventing shuttle valve which prevents backflow through the pressure compensation system if a main relief valve is operative.

Abstract: A pressure-responsive hydraulic control system (10) has a load-sensing flow-compensated pump (S) connected to a plurality of work sections; with a direction control valve (26, 26') and a pressure compensator valve in each work section; and with a flow-regulated logic check system (45); a flow-metered logic check system (40); an isolation circuit (60, 160, 260); and an induced load check system (70). Each pressure compensator valve is supplied flow-metered fluid from the respective direction control valve and supplies flow-regulated fluid to a hydraulic motor. The flow-regulated logic check system (45) provides a flow-regulated maximum output signal, and the flow-metered logic check system (40) provides a flow-metered maximum output signal.

Abstract: There is provided a displacement control system for a variable displacement hydraulic pump which has a displacement control piston assembly (6) having a large diameter chamber (7) for operating a displacement control member (5) of the variable displacement hydraulic pump selectively in a direction of smaller displacement and in a direction of larger displacement, first control valve (8) and second control valve (9) for selectively communicating the large diameter chamber of the displacement control piston assembly with a pump discharge line and a tank, the first control valve being placed at a supply position by the pump discharge pressure, and at a drain position by a spring associated with the displacement control piston assembly via a feedback lever, and the second control valve being placed at a first position by the pump discharge pressure for communicating the pump port and the large diameter chamber and at a second position by a load pressure for communicating the pump port and the large diameter chamb

Abstract: A hydraulic drive system for a construction machine includes a pump for delivering fluid under pressure from a fluid reservoir, at least one hydraulic actuator selectively driven by the pressurized fluid, and at least one closed-center directional control valve connected in parallel to the pump. The control valve has an "off" position which blocks fluid flow therethrough and at least one "on" position for controlling the flow of fluid to the hydraulic actuator. A control device generates a signal for actuation of the hydraulic actuator. A control unit receives the control device signal for operating the control valve associated with the hydraulic actuator. A bypass line leads from the pump back to the reservoir. A variable position bypass valve is interposed in the bypass line and controls flow through the bypass line. The control unit modulates the bypass valve for optimum operation. A hybrid control senses pressure in the actuator and modifies the control signal in response to the load pressure.

Abstract: In a displacement control system for a variable displacement type hydraulic pump for supplying a discharge pressurized fluid of the variable displacement type hydraulic pump to an actuator via a direction control valve and then controlling a displacement of said variable displacement type hydraulic pump for maintaining a pressure difference between a discharge pressure of said variable displacement type hydraulic pump 1 and a load pressure at a portion between a direction control valve and an actuator, wherein an inlet side pressure of said direction control valve is detected as said discharge pressure.

Abstract: An operating valve assembly incorporates a pressure compensation valve and is capable of contributing down-sizing of a hydraulic circuit. The valve assembly includes an operating valve, compensation valves and a load pressure detecting portion. A valve body of the operating valve defines a spool bore extending laterally through the valve body at a vertically intermediate portion of the valve body, a load pressure detecting port at a laterally intermediate portion of the spool bore, and a respective pump port, actuator port and tank port at each side of the load pressure detecting port. The operating valve also includes a spool within the spool bore. The pressure compensation valves are arranged at left and right sides of an upper portion of the valve body and the load pressure detecting portion, for supplying load pressure to the load pressure detecting port, is formed in the spool.

Abstract: Apparatus and method for controlling at least one hydraulic cylinder by the hydraulic fluid discharged by a hydraulic pump through a control valve. The hydraulic control system includes sensors to sense the conditions of the system and produce responsive signals. In the first stage, a controller determines an initial pump displacement output value and an initial spool displacement output value as a function of the system condition signals according to a plurality of feedback linearization control laws. In the second stage, a second controller produces an output signal for the hydraulic pump and an output signal for the control valve as a function of the initial pump displacement output value, the initial spool displacement value and an input command signal according to linear control laws.

Abstract: A tool with a battery, an electrical motor, and a control system. The control system has a trigger control that connects the battery to a timer and a voltage monitor. The trigger control has a user actuated switch and a timer actuated switch. At the end of a tool operational cycle, when the user is not actuating the user actuated switch, the timer actuated switch can supply electricity to the control system. After a predetermined period of time, the timer actuated switch can then automatically electrically disconnect the control system from the battery to conserve battery power.

Abstract: The invention relates to a hydrostatic propulsion drive having a drive motor, of variable speed, for a hydraulic machine of a hydraulic transmission, a setting device for the displacement volume of the hydraulic machine, a device for generating a setting pressure proportional to the speed of the drive motor in a setting pressure line, a pilot valve in the setting pressure line which is coupled with the setting device and--dependent upon its though-flow position within a through-flow adjustment range of effective follow-up into the closed position--controls the volume of a pressure medium supplied to the setting device, and in a through-flow end position beyond the effective follow-up acts upon the setting device with the speed-proportional setting pressure.

Abstract: A fluid pressure control system for hydraulic excavators includes a load sensing valve in communication with first and second pressure compensator valves via a load sensing line and responsive to a load sensing pressure developed in the load sensing line for regulating the discharge volume of a working fluid and a swing torque regulator lying midway of the load sensing line between the load sensing valve and the first pressure compensator valve to selectively allow and inhibit a fluid communication between the first pressure compensator valve and the load sensing valve depending on the pressure of a pilot fluid.

Abstract: A one-piece terminal block (73) is provided as a hydraulic linking element as well as a mechanical carrier for control valves (68 to 72) of a boom control unit, for an operating mode selector valve (74), and for switching elements of a pressure supply device (77). A pressure line (119), return line (132), control line (166), and a further return line (167,168) are designed as bores extending in an axial direction of the terminal block, from which connection channels originate which terminate within terminal arrays (163, 163.sup.I to 163.sup.IV) in a bore layout for the valves. Sections (102') of a load feedback line (102), which are serially connectable to each other by comparative valves (114) are formed by individual longitudinal bores (188,188.sup.I to 188.sup.

Abstract: The current operational condition is discriminated as being the vehicle propulsion condition or the performing work condition. When the vehicle propulsion operational condition is discriminated, the maximum engine revolution speed is limited to a first revolution speed and the maximum displacement is limited to a first displacement value. When the performing work condition is discriminated, the maximum engine revolution speed is limited to a second revolution speed equal to or lower than the first revolution speed and the maximum displacement is limited to a second displacement value higher than the first displacement value.

Abstract: This invention aims to improve the operability in a hydraulic drive machine. According to a load Pp on work machine actuators 3 and 4, a differential pressure of a discharge pressure Pp of a hydraulic pump and a load pressure PLS is varied. Further, the differential pressure is varied so that the differential pressure between the discharge pressure Pp of the hydraulic pump 2 and the load pressure PLS decreases as the load Pp on the work machine actuators 3 and 4 increases and a rotational speed .epsilon.E of an engine decreases. Furthermore, the rotational speed .epsilon.E of the engine 1, discharge pressure Pp of the hydraulic pump 2, the operation amounts S1 and S2 of the various operation levers are detected, respectively, the absorbing torque of the hydraulic pump 2 is set based on the detected rotational speed .epsilon.E and a target rotational speed .epsilon.

Abstract: A circuit arrangement for controlling the output torque of a hydrostatic machine connected to a hydraulic system having an impressed operating pressure. The circuit arrangement has a control element for changing the output torque of the machine based upon operating parameters corresponding to pressure, speed, temperature and the like. Control means are supplied with a desired torque value for generating a control signal for actuating the control element. Pick-up means are connected to the control means and to the control element for picking up a pivotal angle .alpha. or an eccentricity E, respectively, representing an actual displacement volume of the hydrostatic machine. The pivotal angle .alpha. and the eccentricity E are measured in either an analog or a digital manner. When measured in an analog manner, the desired value of the pivotal angle is .alpha.=M/P and the desired value of the eccentricity is E=M/P, where M is the torque and P is the pressure.

Abstract: A method for putting into operation a vehicle with an electronically controlled automotive hydrostatic transmission, wherein an output current of an electronic control by means of at least one proportional pressure-reducing valve is used for generating a control pressure acting upon the servo system of the variable displacement pump. The method is performed by the following steps: a) determining a limit value of a driving regime of the vehicle; b) detecting, digitizing and reading-in at least one current operational parameter of the transmission into the electronic control; c) determining and detecting at least one characteristic value of the output current of the electronic control corresponding to the value of the driving regime of the transmission to the one proportional pressure-reducing valve, and d) calculating a current characteristic on the basis of the value of the output current for achieving reproducible driving properties.

Abstract: A delivery control device for hydraulic pumps suitable for controlling the pump delivery such that the pump's delivery characteristics are not influenced by load acting on actuators is disclosed. The device also reduces the pump delivery in cases where no actuator is being operated but instantly increases the pump delivery in the event either actuator is operated. The device has a branch line branched from a pilot line and adapted for draining the swash plate's regulating pilot oil from the pilot line to a return tank, and a relief valve provided in the branch line, selectively opened in response to a preset pressure applied thereto. The preset pressure for opening the relief valve is the delivery pressure of the hydraulic pump.

Abstract: A pressure governor for a pump (11) employed as a variable displacement pump for supplying pressurized fluid to a hydraulic power consumer (54) is disclosed. The governor includes a differential pressure regulator (13) connected to the pump for establishing the output flow of the pump. The state of the regulator is controlled by a pressure-regulated valve (21). Valve (21) is, in its initial state, set so as to allow a high volumetric flow out of the pump. A portion of the flow out of the pump returned to the pressure regulated valve to force the valve into a second state. The movement of the valve into the second state resets the valve so that a portion of the output of the pump is applied to the pressure regulator. This flow, in turn, causes the regulator to reduce the output flow from the pump. Thus, the initial output flow of the pump is reduced so as to minimize the possibility that large sustained output flows will damage the components of the hydraulic power consumer to which the flow is applied.

Abstract: An improved pressure-compensated hydraulic system for feeding hydraulic fluid to one or more hydraulic actuators. A remotely located, variable displacement pump provides an output pressure equal to input pressure plus a constant margin. A pressure compensation systems requires that a load-dependent pressure be provided to the pump input through a load sense circuit. A reciprocally spooled, multiported isolator transmits the load-dependent pressure to the pump input but prevents fluid in the load sense circuit from leaving the load sense circuit and flowing through a relatively long conduit leading to the remotely located pump. In a multi-valve array, at least one valve section has a backflow-preventing shuttle valve which prevents backflow through the pressure compensation system if a main relief valve is operative.

Abstract: A controller 24 includes function generators 151, 152. The function generator 151 is set to have such a characteristic that as the detected value P.sub.N of a negative control pressure from a pressure sensor 21 is reduced, a first target tilting amount .theta..sub.N increases from a minimum value to a maximum value, and the function generator 152 is set to have such a characteristic that as the detected value P.sub.B of a control input (pilot pressure) for driving a boom cylinder 6 is increased, a second target tilting amount .theta..sub.B increases from a predetermined minimum value to the same maximum value as the above maximum value. Minimum one of the two target tilting amounts from both the function generators is selected, and a proportional solenoid valve 25 is driven based on the selected minimum tilting amount.

Abstract: A hydraulic device for construction machinery includes a hydraulic pump; a hydraulic actuator having two fluid chambers; actuator fluid lines leading from each of the fluid chambers; pump fluid line leading from the pump; fluid tank fluid line leading to the fluid tank; operating lever to be operated by an operator; a direction switching unit connected to the actuator lines, the fluid tank fluid line, and the pump fluid line, and which is controlled in accordance with the direction of operation of the operating lever; inflow variable restriction located between the pump and the actuator fluid lines and whose restriction area is controlled in accordance with the degree of operation of the operating lever; outflow variable restriction located in between the fluid tank and the actuator fluid lines; and a pressure difference controller for controlling the difference in pressure between the inlet and exit ports of the inflow variable restriction.

Abstract: A hydromechanical transmission shifting control system and method includes a hydromechanical transmission and a number of clutches connected to the transmission. A microcontroller receives various signals generated by the operator, engine, transmission, and the load. The microcontroller controls the ratio of the input to output speed of the transmission as well as the engagement or disengagement of the number of clutches based upon the various input signals.

Abstract: A control device provides a reliable way of pressure controlling a hydraulic distributor and an associated first hydraulic circuit when pressurized hydraulic fluid is simultaneously supplied to at least one other hydraulic circuit. Pilot pressure oil enters and exits the distributor through inlet and outlet passages in the pilot line. An apparatus for regulating pilot oil flow rate is interposed between the pilot line inlet passage and the hydraulic fluid line. The device includes a pressure head detection apparatus having inlet ends connected to the pilot line inlet passage and to the hydraulic circuit and an outlet end connected to the hydraulic fluid source for controlling the flow rate of the hydraulic fluid based on the highest pressure requirement.

Abstract: Hydraulically actuated grapple tongs mounted to a log skidder are useful, for example, in gripping a bunch of logs that are being dragged from one site to another. Maintaining a grip on the logs during the dragging operation with known hydraulic systems generates heat within the hydraulic systems. The subject hydraulic system includes first and second variable displacement load sensing pumps commonly connected to a control valve which controls fluid flow to an actuator. A load pressure signal is directed through a first signal line to a displacement controller of the first pump and to a pressure responsive valve normally resiliently biased to a position at which the first signal line is communicated to a displacement controller of the second pump. When the load pressure signal in the first signal line exceeds a predetermined value, the valve is moved to a position blocking communication of the load signal to the displacement controller of the second pump.

Abstract: An operating valve assembly incorporates a pressure compensation valve and is capable of contributing down-sizing of a hydraulic circuit. The valve assembly includes an operating valve, compensation valves and a load pressure detecting portion. A valve body of the operating valve defines a spool bore extending laterally through the valve body at a vertically intermediate portion of the valve body, a load pressure detecting port at a laterally intermediate portion of the spool bore, and a respective pump port, actuator port and tank port at each side of the load pressure detecting port. The operating valve also includes a spool within the spool bore. The pressure compensation valves are arranged at left and right sides of an upper portion of the valve body and the load pressure detecting portion for supplying load pressure to the load pressure detecting port is formed in the spool.

Abstract: A pressurized fluid supply system, in which a plurality of pressure compensation valves are connected to a pump discharge line of a hydraulic pump in parallel, and direction control valves are provided at the outlet side of each pressure compensation valve to supply a discharged pressurized fluid from the hydraulic pump to a plurality of actuators. The pressure compensation valves include a check valve portion establishing and blocking communication between the pump discharge line and the inlet port of the direction control valve, and a pressure reduction valve portion for supplying a reduced pressure from the pump discharge line. The check valve portion shifts in a valve opening direction in response to an inlet pressure and shifts in a valve closing direction in response to an outlet pressure. The pressure reduction valve portion has a first and a second pressure chamber.

Abstract: The present invention provides for a control apparatus for independently operating at least two users. The users can be the tilt cylinders and the lift cylinders of a loader. The control apparatus provides for the adjustment of the control valves and for the adjustment of the pressure control apparatus of the variable displacement pump means in dependency of each other. In accordance with the invention, the control position of the control spool of the control valve controlling the user with the largest load provides for a measure (or for the adjustment) of the pressure control device of the variable displacement pump. In this manner an extremely effective and economic operation of the hydraulic system comprising the control apparatus and the users is obtained.

Abstract: An apparatus for and a method of controlling the engine and pumps of hydraulic construction equipment capable of achieving automation of the hydraulic construction equipment by controlling the oil quantity fed to solenoid controlled proportional valves such that it is proportional to the manipulation amount of a manipulation command unit through a computation performed by a controller on the basis of engine RPM data from an engine RPM detection unit and pump delivery pressure variation data from a pump delivery pressure detection units so that the suction horse power of each of the pumps corresponds to the maximum output horse power of the engine and by controlling the oil quantity fed to the hydraulic cylinders 105a and 105b by oil quantity control valves such that it corresponds to the manipulation amount and manipulation ratio from the manipulation command unit.

Abstract: An accumulator charging valve has a first valve spool determining a cut-in pressure level at which fluid from a pump is directed to an accumulator and a second valve spool determining the cut-out pressure level at which fluid is no longer directed to the accumulator. When the pressure at the accumulator reaches a predetermined high level, the second valve spool moves to a position communicating an inlet port with an intermediate passage. The first spool is normally at a position blocking the intermediate passage from an outlet port so that a flow path is established through a pair of orifices reducing the pressure in the intermediate passage and the inlet port. The reduced pressure is transmitted to an actuating chamber to hold the second valve spool in the above noted position and to a pump displacement controller to destroke the pump to a low standby pressure displacement.

Abstract: In a hydraulic system with a pump (1) and a load (4, 104), a pressure relief valve (16) is connected to the pump pressure side (3) and open when a difference between pump pressure and maximum load pressure exceeds a predetermined pressure. Pump pressure is controlled by a pump controller (22), such that the pressure difference set by the pressure relief valve is greater than a pressure difference set by the pump controller. A controller (20) presets the pump delivery rate, depending on changes in input signals (s1, s2) and regulates the pump delivery rate in dependence on a pressure difference signal (U). The pressure relief valve includes a position sensor, which generates the pressure difference signal.

Abstract: The present invention provides a method for pressure control of an adjustable pump for a hydraulic system including at least a load. Depending on the size of the system, i.e. the servo cylinder, hydrostatic machine and the line tubing, the fluid volume contained in the system between the adjustable pump and the low pressure side of the load is largely different. In controlling the load pressure in such a system, for example a press or a molding machine for plastic material, a pressure controller adaptively and automatically adjusts the damping factor of the controller and thus the controlling quality independent of the fluid volume of the system to a constant value. It is a benefit of the invention that all adjusting operations of the pressure controller are eliminated which have been necessary heretofore to obtain an appropriate control of the fluid system.

Abstract: A hydraulic drive system comprises a check valve cb1 for detecting a pressure on the outlet side of a pressure compensating device VB1, a maximum load pressure detecting line SL1 for selecting higher one of the pressure detected by the check valve cb1 and a load pressure of an actuator associated with a hydraulic pump P1 and supplying it as a signal pressure, a check valve cb2 for detecting a pressure on the outlet side of a pressure compensating device VB2, a maximum load pressure detecting line SL2 for selecting higher one of the pressure detected by the check valve cb2 and a load pressure of an actuator associated with a hydraulic pump P2 and supplying it as a signal pressure independently of the maximum load pressure detecting line SL1, and a passage 300 for joining hydraulic fluids supplied from the hydraulic pumps P1, P2 and passing through variable restrictors RB1, RB2 with each other and supplying it to an actuator B. Mutual independence between the two hydraulic pumps P1, P2 can be thereby ensured.

Abstract: A hydraulic oil volume change-over control apparatus for a hydraulic excavator subjects a hydraulic pump to load sensing control so as to set an optimum volume of hydraulic oil while an engine for driving the hydraulic pump is operated at a rotational speed at which the fuel consumption of the engine is minimum, by setting a low power mode during breaker work or the like which is performed with a smaller volume of hydraulic oil than that needed during normal excavating work.

Abstract: A hydraulic drive system for actuating a reciprocating member such as a polished rod in a pump jack device, and for acting as a counterbalance and/or for energy conservation. The system has two hydraulic circuits and a prime mover. A first circuit includes a cylinder for driving an output member which may be connected to the polished rod, a first pump of the variable displacement, reversible flow type, together with a pair of fluid lines forming with the cylinder a closed-loop circuit. A controller is programmed to control the setting of the first pump so as to establish the velocity profile of the output member. A second hydraulic circuit is also in the form of a closed-loop containing first and second pumps, at least one of which is of the variable displacement type and is also controlled by the controller.

Abstract: A hydraulic drive system for a battery operated portable compression tool. The tool has an electric motor. The drive system has a self-regulating variable displacement pump with a rotatable conduit frame having radial conduits, pistons reciprocally located in the conduits, and a ring bearing surrounding the conduit frame in an eccentric adjustable location. Ends of the pistons are located against the inside of the ring bearing. A valve plate located against a front end of the rotatable conduit frame to control entry and exit of fluid into and out of the conduit frame as it is rotated.

Abstract: A hydraulic control system is designed to permit the use of a plurality of small substantially identical existing valve assemblies in place of a lesser number of larger valve assemblies. In one embodiment, a first pair of variable displacement load sensing hydraulic pumps communicate with a manifold connected to a first valve assembly and another pair of variable displacement load sensing hydraulic pump communicate with a second manifold connected to second and third valve assemblies. A crossover conduit interconnects the manifolds so that fluid from all four pumps can be used by any one of the valve assemblies or shared by two or all three of the valve assemblies. In another embodiment, a third pair of variable displacement load sensing hydraulic pumps communicate with the first manifold 12 which also has another valve assembly connected thereto.

Abstract: A device for controlling a hydraulic motor (10) comprises a directional valve (15) connected to a pressure fluid pump (11; 50) via a feed passage (17) and a pilot valve (19) activated safety shut-off valve (18) incorporated in the pressure fluid feed passage (17) between the pump (11; 50) and the directional valve (15) and shiftable from a normally open position to a closed position to, thereby, block the fluid communication between the pump (11; 50) and the directional valve (15) in emergency situations. A shunt valve (16) for short circuiting at least a part of the pump flow to a tank or, alternatively a displacement adjusting means (51) of a variable displacement pump (50) are activated by a load sensing pressure derived from a load sensing port (15e) on the directional valve (15), which load sensing pressure is discharged to tank (12) via the shut-off valve (18) as the latter is shifted to its closed position.

Abstract: A hydrostatic drive system having consumers (6, 8) connected to a demand regulated pump (1) and actuated by a directional control valve (5, 7) is disclosed. The consumers can be connected downstream of the control valves via return valves to a load-sensing line (12). To provide for load-independent allocation of the delivered flow when the consumers are simultaneously actuated, each directional control valve (5, 7) is assigned a pressure balance (9, 10) which can be controlled directly or indirectly by a signal difference formed from a load pressure signal and a delivered pressure signal.

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: An improvement in and method of operating a load sensing system in which a variable displacement, pressure compensated pump delivering hydraulic fluid to a fluid operating device through a directional control valve is controlled by a load-sensing system pressure limiter which is set so that the system operates at the maximum continuous system operating pressure. By also setting pump destroke pressure slightly higher than the necessary operating pressure for the load, optimum performance of the pump is realized. The load-sensing system pressure limiter is configured as a poppet which is placed inside of the body of the directional control valve and is biased by an adjustable spring force to the closed position. Preferably, the poppet connects the load sensing core of the directional control valve to an exhaust passage therein so as to require minimal modification of the directional control valve.

Abstract: A hydraulic drive system comprises a controller (12) and several condition sensors. A boom-up target flow rate setting section determines a boom-up target flow rate based on signals from a pressure sensor (11) and a rotational speed meter (16), a pump delivery rate detecting section determines a pump delivery rate based on signals from a tilt angle sensor (15) and the rotational speed meter (16), a differential pressure detecting section and a center bypass flow rate calculating section determine a center bypass flow rate based on signals from pressure sensors (9, 10), a boom cylinder calculating section determines a boom cylinder flow rate from the pump delivery rate and the center bypass flow rate, and a first pump target displacement volume calculating section calculates a first pump target tilt angle .theta..sub.1 in accordance with the difference between the boom-up target flow rate and the boom cylinder flow rate. In this case, .theta..sub.1 is larger than a second pump target tilt angle .theta..sub.

Abstract: A method for controlling a hydraulic motor with a hydraulic valve comprising an inlet section which includes a pump and tank connection and a maneuvering section having a slide (B1) and a load signal system (L1, L2, L3). The hydraulic valve also includes two regulating constrictions (S3, S4) which can be connected to and from a motor (C), such as a hydraulic piston-cylinder device. The maneuvering slide (B1) also includes a load level detecting constriction (S2) and a load signal drain (S5), and the pump generates an idling pressure. When maneuvering the maneuver slide (B1), the load signal Ps of the load signal system is increased by a further constriction (S1) located between the pump connection and that side of the load detecting constriction (S2) that has the higher pressure during the maneuvering process.

Abstract: A control device for an actuator adapted to control a discharge pressure of a variable discharge pump by means of a regulator and capable of ensuring sufficient flow control range of change-over valves with respect to a spool stroke even when the number of rotations of an engine for driving the variable discharge pump is reduced to decrease a discharge rate of fluid from the variable discharge pump. Elastic force of a spring of a valve constituting the regulator is adjusted by means of a cylinder associated with a throttle lever for controlling the engine. Also, a control valve is arranged so as to be associated with the throttle lever, so that a pressure on a downstream side of the variable discharge pump is increased to change over the 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.