Abstract: A hydraulic system includes a hydraulic pump, a reservoir, a hydraulic function, such as a cylinder, and a power beyond valve for controlling communication between the pump, the reservoir and the cylinder. The pump provides pressurized fluid at a pump output as a function of the pressure in a load sensing port. For generating a pump controlling load sensing signal in case that the cylinder does not generate such a signal, it is proposed to provide a valve which blocks in a first position or opens in a second position communication between the feed line of the cylinder and the load sensing port of the pump. The valve functions in dependence of control pressures acting on each side of a valve member. A spring is provided biased to urge the valve member to its first closed position. Further, shift valve means are provided to supply selectively different pressures to both sides of the valve member.

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: This invention has for its aim to provide a hydraulic circuit system arranged such that, even at the time of commencement of drive of a hydraulic actuator with a large inertia, a slow rise in the drive pressure can be achieved, thereby preventing the occurrence of hunting phenomenon. The hydraulic circuit system according to the present invention comprises a plurality of operating valves (15) provided in a discharge conduit (10a) of a hydraulic pump (10), and pressure compensating valves (18) provided in connection conduits between these operating valves (15) and respective hydraulic actuators (16), wherein each of the pressure compensating valves (18) is set at a highest value of load pressures of each of the hydraulic actuators (16), and the displacement of the pump is controlled by a change-over valve (14) adapted to be actuated by the difference between the pump discharge pressure and the load pressure.

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: A hydraulic pressure supply apparatus includes a variable displacement pump which is controlled to change its discharge flow rate and pressure in accordance with a condition of a load side. The pump is communicated with the load side through a conduit to which an accumulator is communicated through a proportional pressure reducing valve controlled so that its regulating pressure is higher than the pressure required in the load side and is lower than a target discharge pressure of the pump. Furthermore, when the pressure in the conduit is lower than the regulating pressure of the valve, the valve is opened and regulates the pressure in the conduit by allowing higher pressure flow from the accumulator.

Abstract: The present invention is directed to a hydro-mechanical or electro-hydro-mechanical control system utilized for positioning a mechanical device. The control system incorporates a control valve for selectively controlling the flow of hydraulic fluid to input ports of a power output transducer in response to a mechanically applied input signal. The power output transducer is then utilized to position a mechanical device. The control system is a closed loop circuit adapted to supply hydraulic fluid at a desired supply pressure to the control valve. The supply pressure is varied in relation to the absolute value of the pressure differential or load pressure exerted across the input ports of the power output transducer. A pressure regulating apparatus is provided for selectively regulating the supply pressure to a value that is nominally equal to the absolute value of the load pressure summed with a preselected supplemental pressure value across the regulating apparatus.

Abstract: The present invention relates to a hydraulic secondary control system comprising a hydrostatic machine as a secondary unit which is connected to a pressure line in which an impressed pressure of approximately constant value is generated by a hydrostatic machine as a primary unit. The volume capacity of the secondary unit determines the torque delivered to a load and the torque needed by the load determines the speed of the secondary unit. When the desired speed and thus the volume capacity of the secondary unit is too high, the capacity exceeding the capacity of the primary unit supplying the pressure line, the pressure breaks down. To prevent this, the present invention provides to calculate a permissible capacity as defined by the rotary angle for the secondary unit in accordance with the nominal quantities of the primary and secondary unit.

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 drive system for construction machines with an improved pressure compensating valve assembly comprising a first directional control valve (3, 5, 7) of closed center type connected in series with a second directional control valve (12) of open center type.

Abstract: A traveling speed changeover device for a hydraulic excavator which can optimize the traveling speed in accordance with the road conditions and which enables a working machine of the excavator to be operated during traveling without impairing the simultaneous operation characteristic. To this end, the traveling speed changeover device has a spring set force adjusting device which includes: a traveling speed changeover switch (5); a controller (7) for computing a signal set by the traveling speed changeover switch; a solenoid actuated control pressure changeover valve (6) which operates in accordance with a command given by the controller; and a spring force adjusting cylinder (9) for adjusting the set force of a differential pressure setting spring (11a) of a load sensing valve (11) in accordance with the operation of the solenoid actuated control pressure changeover valve.

Abstract: A hydrostatic power steering system is provided of the type including a steering control unit (3) operated by an input such as a steering wheel (1) to control flow from a source (8) to a steering cylinder (7). The source is operated in response to an electrical signal from a controller (82), controlled by a sensed pressure at a pressure detection port (64). The pressure at the port (64) is communicated from the main fluid path of the steering control unit (3), downstream of the fluid meter (18) when the spool (21) and sleeve (22) are relatively displaced. In systems in which the system reservoir (R) is at an elevated ("regulated tank") pressure, the pressure detection circuit is drained through a variable orifice (70) to a drain port (66), which is in communication with a sump (S) maintained at substantially atmospheric pressure. As a result, the steering system responds at a lower steering pressure, and the initial steering is smoother.

Abstract: A power sensing regenerator includes a pair of displacers (24 and 26) connected in tandem for dividing a flow of fluid from a pump (12) into predetermined proportions for servicing one or more loads (42). Flow control valves (32 and 34) regulate respective flows from the displacers (24 and 26) to the one or more loads (42). A control system, which includes differential pressure regulators of the flow control valves (32 and 34), responds to a difference between discharge pressures of the displacers (24 and 26) for reducing discharge pressure of the pump (12).

Abstract: A closed center-load sensing system, capable of varying a pump discharge volume easily and with a high degree of accuracy, includes a power source having an indicator for indicating a rotational speed, a variable volume hydraulic pump driven by the power source, actuators driven by pressure oil discharged from the variable volume hydraulic pump, change-over valves for controlling the flow of the pressure oil, an indicator for setting the rotational speed of the power source in a load sensing system in which the pressure difference between the pump pressure and the actuator load pressure is maintained at a predetermined pressure and the rate of flow of a discharge from the variable capacity hydraulic pump is varied when the pressure difference between a pump pressure and an actuator load pressure varies, a controller for computing and outputting a command signal for the rotational speed of the power source in response to a command signal from the indicator, and an electronic proportional control governor for c

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: The displacement of a variable displacement hydraulic pump (1) which is driven by a diesel engine (27) is so controlled as to be set to a first target displacement to keep a pump pressure higher than a load pressure by a predetermined target value, or a second target displacement to limit an input torque on the basis of the pump pressure. Provided is a stand-by flow rate control portion (65) which outputs a third target displacement larger than the minimum value of said first target displacement. The displacement of the pump (1) is controlled so as to be set to the third target displacement when the third target displacement is output from the stand-by flow rate control portion (65).

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 pressure compensating hydraulic directional valve comprising: a body provided with a movable slide; a passage through the body for connecting a distribution chamber associated with the slide to working orifices, the distribution chamber being selectively connectable to an admission orifice by the slide when moved; a load sensing line channel combined with means for selecting the maximum pressure selected from the pressure in the channel and the pressure of the fluid in the valve; and pressure compensating means placed in the passage and responsive to the difference between the pressure in the passage and the pressure in the channel to generate a fixed pressure drop in the pressurized fluid flowing through the passage towards the working orifices, the pressure compensating means being combined with the maximum pressure selecting means in such a manner that if the pressure in the channel is greater than or equal to the pressure of the fluid from the slide, then no communication exists between the passage and

Abstract: The present invention relates to a flow rate control apparatus for a hydraulic pump which is employed suitably in a hydraulic excavator or a hydraulic crane and driven by a rotating force of a motor. The flow rate control apparatus controls the discharging flow rate of the hydraulic pump to utilize the output power of the motor without an overload applied to the motor, and optimally controls the output flow rate of the pump depending upon an operation signal to provide an excellent operating characteristic to an operator under a high load operating condition applied to a hydraulic machine having hydraulic actuators driven on the basis of the discharge flow of the hydraulic pump.

Abstract: In a hydraulic system several consumers (5'; 5"; 5'") are supplied by a common regulating pump (1). The regulating pump (1) is controlled as a function between the pump pressure (delta P) and the highest load pressure. This pressure difference (delta P.sub.max) is related to a minimum pressure difference (delta P.sub.min), and the comparison signal is input in a control unit (21) to influence the reference value signals (S1, S2, S3) by which the individual valves (6'; 6"; 6'") are controlled.

Abstract: A hydraulic drive system for a construction machine comprising a plurality of distribution compensating valves (7a, 7b) for controlling the respective differential pressures across the plurality of flow control valves (6a, 6b), the distribution compensating valves respectively having first pressure bearing chambers (52a, 52b) acting in a valve-closing direction, second pressure bearing chambers (53a, 53b) acting in a valve-opening direction, and third pressure bearing chambers (54a, 54b) acting in the valve-closing direction to reduce target values of differential pressures across a plurality of associated flow control valves (6a, 6b). The system further comprises a fourth pressure bearing chamber (55a, 55b) provided in at least one of the plurality of distribution compensating valves (7a, 7b) and subjected to a second control pressure (P.sub.CT) for acting in the valve-opening direction to set a target value (.DELTA.P.sub.T) of the differential pressure across the associated flow control valve (6a, 6b).

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: A pilot-actuated, pressure-compensated flow and directional control valve assembly (11) is provided in which a main valve spool (95) is positioned in response to a pressure differential between a pilot chamber (119) and a reaction chamber (117). Flow of fluid from an inlet port (29) is controlled by means of a pilot valve assembly (97), into the pilot chamber (119), while fluid flows out of the pilot chamber (119) through a fixed orifice (67) to a pump load sense port (61). The main valve spool (95) acts as an inlet compensator. If the pressure at a load L is above inlet pressure, the main valve spool (95) acts as an inlet check, preventing reverse flow. If there is a higher load pressure at another load circuit in the system, such as a steering valve S, there will be an increase in pressure in the reaction chamber (117), thus closing off the main spool (95), reducing the flow from the inlet port (29) to the work port (47), and giving more priority to the steering valve S.

Abstract: This invention aims at providing a hydraulic circuit apparatus for supplying pressurized fluid into cylinders for a work implement arranged such that during normal operation of the work implement the flow rate of fluid discharged by a pump is controlled such that the difference between the discharge pressure of the pump and the load pressure is always kept constant, whilst during inching operation of the work implement the flow rate of fluid discharged by the pump is reduced.

Abstract: A hydraulic drive system for construction machines comprising a valve group (52) including a plurality of directional control valves (9-13) of center bypass type, a center bypass line (2a) for connecting in series center bypasses of the plural directional control valves to a low-pressure circuit (29), a plurality of bleeding-off variable restrictor means (56) respectively disposed in the center bypasses of the plural directional control valves, a pressure compensating valve (20) provided in the center bypass line, and first and second differential pressure detecting lines (22, 24) connected to the center bypass line for transmitting a differential pressure to the pressure compensating valve.

Abstract: An operation valve having a pressure compensation valve of relatively simple non-complicated internal body structure. In the valve body, a load pressure introducing passage, a check valve and a restriction are formed inside the spool comprising the operation valve. An intermediate pressure between an inlet pressure and an outlet pressure of the compensation valve which is arranged in the valve body, may be supplied to a pressure receiving section of the pressure compensation valve through an oil hole of the spool. The operation valve with the pressure compensation valve is of simple construction and may be easily manufactured.

Abstract: An apparatus for limiting the power output of a hydraulic system is disclosed. The hydraulic system has a variable displacement pump. The variable displacement pump has a movable swashplate and is driven by a source of motive power. The apparatus includes a memory device for storing a set of power modes. Each power mode has a predetermined power level associated with the hydraulic system and is defined by a plurality of set points. Each set point corresponds to a predetermined flow rate and discharge pressure of the pump. A device senses the speed of the source of motive power and producing a signal representative of the actual speed in response to the sensed speed. A device senses the pressure of the variable displacement pump and produces a signal representative of the actual pressure in response to the sensed pressure. A device senses the swashplate angle of the variable displacement pump and delivers a signal representative of the actual swashplate angle in response to the sensed swashplate angle.

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: The invention relates to a valve system for supplying fluid from a pair of fluid pressure sources to a load. A feed valve is provided which feeds--when required--a partial flow of the second fluid pressure source into the feed line of the load which is connected to the first fluid pressure source through a directional control valve. The feed valve comprises a pressure-compensating valve to control the volume of the partial flow and a switching valve to automatically open the pressure-compensating valve when required.

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: An apparatus for controllably actuating at least two hydraulic actuator is provided. The apparatus controllably provides pressurized hydraulic fluid to the hydraulic actuators through closed center spool valves. The apparatus receives operating signals and a pump pressure signal and responsively controls the output of a variable flow pump. In a first mode, the output flow of the pump is a function of the operating signals and the pump pressure signal. In a second mode, the output flow of the pump is a function of the operating signals alone.

Abstract: A hydraulic system includes a hydraulic pump which provides pressurized fluid at an output port as a function of pressure in a load sensing port, a hydraulic reservoir, and a load pressure sensing line connected to the load sensing port. A solenoid operated implement control valve controls fluid communication to and from a hydraulic function such as a cylinder. A supply control valve has a first position wherein the reservoir is communicated with the load sensing port and a second position wherein the pump output port is communicated with the load sensing port. A spring urges the valve member to its first position, and a solenoid is energizable to move the valve member to its second position. The solenoid is energized when the implement control valve is activated so that the supply control valve communicates pump pressure to the load sensing port and the pump will operate at full capacity whenever the second hydraulic function is operated.

Abstract: A delivery rate of a main hydraulic pump is controlled so that a load sensing differential pressure is held at a preset target value. In order to maintain the delivery rate of the pump substantially constant even in the case of external loads, inertial loads, and compressibility or leakage problems with the hydraulic fluid, there is provided a dead zone for permitting a deviation between the load sensing differential pressure and the preset target value.

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 system for a vehicle that includes an implement such as a bucket that is operated by a hydraulic actuator and a directional valve which controls flow from a load sensing variable displacement pump. A hydraulic bucket shake circuit is provided which is selectively operable to force the pump to a maximum displacement condition thereby providing standby pressure and flow to the directional valve so that the directional valve can be operated rapidly in order to shake the bucket and dislodge mud, clay and debris from the bucket or to allow penetration into frozen ground.

Abstract: A displacement controlling circuit system for a variable displacement pump, which system permits, following high or low rates of revolution of an engine for driving the pump, the displacement of the pump to be larger or smaller than a displacement determined on the basis of a difference between the pump delivery pressure and a load pressure. The displacement controlling circuit system comprises a revolution sensor (12) for detecting rates of revolution of the engine (9), and means (10, 11) for switching a load sensing valve (5) in such a manner that: when the detected rate of revolution of the engine is high, a displacement control member (2) of the variable displacement pump (1) is actuated in a displacement increasing direction; and, when the detected rate of revolution of the engine is low, the displacement control member (2) is actuated in a displacement decreasing direction.

Abstract: The present invention is directed to a hydro-mechanical or electro-hydro-mechanical control system utilized for positioning a mechanical device. The control system incorporates a control valve for selectively controlling the flow of hydraulic fluid to input ports of a power output transducer. The power output transducer is then utilized to position a mechanical device. The control system is a closed loop circuit adapted to supply hydraulic fluid at a desired supply pressure to the control valve. The supply pressure is varied in relation to the absolute value of the pressure differential or load pressure exerted across the input ports of the power output transducer. A pressure regulating apparatus is provided for selectively regulating the supply pressure to a value that is nominally equal to the absolute value of the load pressure summed with a preselected supplemental pressure value across the regulating apparatus.

Abstract: The flow changing response of fluid systems having variable displacements pumps are greatly effected by the inertia of the displacement changing mechanisms, such as, the swashplate and at least half of the fluid pumping piston assemblies. In the present invention, a fluid system is provided which has a first flow changing mechanism operable to maintain a relatively constant pressure differential across a variable orifice device in a valve mechanism to change the flow of the fluid being delivered from the fluid pump to the fluid system. Simultaneously therewith, a second flow changing mechanism having a fast acting bypass mechanism acts in parallel with the first flow changing mechanism to more quickly bypass fluid being delivered from the fluid pump to the fluid system thus eliminating pressure spikes in the fluid system. The second flow changing mechanism is operable to establish a second larger differential pressure across the variable orifice device.

Abstract: Disclosed is a swash plate type variable displacement pump. The pump comprises a spring which biases a swash plate in a direction of decreasing the tilting angle thereof, a hydraulic cylinder which controls the swash plate at the tilt angle according to a load on the pump by the resisting force against the biasing force of the spring, a valve allows a pressurized fluid to flow into the hydraulic cylinder when opened, and prevents the pressurized fluid from coming out of the hydraulic cylinder when closed, and a fluid discharge passage which gradually releases the resisting force of the hydraulic cylinder against the spring to slowly shift the tilt angle of the swash plate to 0.degree..

Abstract: A valve apparatus has a flow control valve having a supply passage communicating with a hydraulic fluid supply source, a load passage communicating with an actuator, and a first meter-in variable restrictor disposed between the supply passage and the load passage and opened dependent on an operation amount there; a first signal passage located downstream of the first variable restrictor and having a passage section for detecting load pressure of the actuator; a tank passage communicating with a reservoir tank; a discharge passage for communicating the first signal passage with the tank passage; and a second variable restrictor provided in the discharge passage and having its opening variable dependent on the operation amount of the flow control valve to produce in the first signal passage a control pressure different from the load pressure, the control pressure in the first signal passage being led to the hydraulic fluid supply source though a second signal passage.

Abstract: An engine-driven pump supplies pressurized hydraulic fluid to vehicle brake and steering circuits. A ground driven variable displacement pump controlled by a control circuit is de-stroked when the engine-driven pump is operational. The variable displacement pump includes a movable piston which divides a bore into a pilot chamber and a pump chamber. An outlet line with a check valve communicates fluid one way from the pump chamber to the vehicle circuits. An inlet line with a check valve communicates fluid one way from a reservoir to the pump chamber. A ground-driven rotatable cam member reciprocates the piston. A spring urges the piston towards the cam member and towards a full stroke position. A pilot line which communicates fluid pressure from an outlet of the engine-driven pump to the pilot chamber. When the engine-driven pump is operational the pressure in the pilot line moves the piston away from the cam member, thus de-stroking the variable displacement pump.

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: The invention relates to a variable displacement pump supplying fluid to a number of consumers. The pump control for adjusting the delivery rate is actuated by a signal which is produced by the respective highest loaded consumer. The signal is provided by a valve, in particular a pressure compensating valve which is associated with the consumer, and which valve opens a spool land when the valve becomes positioned at its control end range. A pressure signal from any pressure fluid source is delivered through the land to the pump controller. The control, according to the invention, offers a broad variety of possibilities for arranging the pressure compensation valve at various locations, engaging the valve by a variety of pressure differences, and using a number of pressure fluid sources of provide for the signal pressure to actuate the pump controller.

Abstract: A pressure compensating type hydraulic valve wherein a pressure compensation can be made according to the movement of the movable portion of a hydraulic actuator, and the movable portion of the actuator can be stopped against load pressure when it is located at its neutral position. This pressure compensating type hydraulic valve is arranged such that a spool (24) is moved in a valve hole (16) so as to allow a first actuating port (21) and a second actuating port (22) connected with pressure receiving chambers (13.sub.1, 13.sub.2), respectively, defined on both sides of a movable portion (13.sub.

Abstract: The invention relates to a control and regulating device for a hydrostatic transmission which comprises a reversible hydraulic pump that can be driven by a driving motor, at least one hydraulic motor that is connected via two working lines to the hydraulic pump, and an adjusting device that can be acted on by an adjusting pressure for adjusting the volume and direction of displacement of the hydraulic pump, together with a displacement-direction control valve for controlling and regulating the action of the adjusting pressure on the adjusting device, can be actuated as desired both by a control signal that is proportional to the speed of rotation of the driving motor and predetermines the direction of displacement of the hydraulic pump and by a working pressure signal that is proportional to the working pressure in the working line then carrying the high pressure.

Abstract: A hydraulic drive traveling system has a pressure compensated low control valve connected between a hydraulic pump and a variable displacement type hydraulic motor for controlling a flow rate of the hydraulic fluid supplied to the motor. The flow rate is controlled in accordance with the delivery pressure of the pump and demanded traveling speed of the motor. When the delivery pressure of the pump is at a high level, the motor is shifted to a first capacity. When the delivery pressure of the pump is low, the motor is shifted to either the second capacity or the first capacity depending upon the demanded traveling speed.

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 control system for a hydraulic pump in a hydraulic drive circuit includes at least one hydraulic pump whose displacement volume is variable, at least one hydraulic actuator driven by a hydraulic fluid delivered from the hydraulic pump, and a flow control valve connected between the hydraulic pump and the actuator for controlling a flow rate of the hydraulic fluid supplied to the actuator. In the control system, the target value of the differential pressure between the delivery pressure of the hydraulic pump and the load pressure of the actuator is preset, and the displacement volume is varied dependent on the deviation between the differential pressure and its target value for controlling a pump delivery rate so that the differential pressure is held at the target value.

Abstract: A continuously active pressure accumulator power transfer system for a vehicle or a like comprises an engine, a pump driven by the engine, a main pressure accumulator maintained at a substantially constant fluid pressure and fluid volume by the pump during operation, a fluid motor for propelling the vehicle which is supplied with driving fluid pressure from the pressure accumulator and auxiliary units for operating the vehicle. The auxiliary units are also operated by fluid pressure from the pressure accumulator. The fluid motor(s) and the auxiliary units are operated directly by fluid pressure from the accumulator without any direct connection with the engine.

Abstract: A flow control valve has a first variable restrictor to control a flow rate of a hydraulic fluid supplied from a hydraulic fluid supply line to a hydraulic actuator and a second variable restrictor to control a flow rate of the hydraulic fluid discharged from the hydraulic actuator to a hydraulic fluid return line. A pressure compensating valve holds constant a differential pressure across the first variable restrictor, and a recovery circuit having a recovery line has a check valve that allows flow of the hydraulic fluid only toward the supply line. The recovery circuit receives at least part of the hydraulic fluid discharged from the hydraulic actuator and returns it to the supply line at a portion between the pressure compensating valve and the first variable restrictor through the recovery line upon controlling of the discharged flow rate by the second variable restrictor to thereby recover the discharged hydraulic fluid.