Abstract: In accordance with the present invention, a fuel flow circuit comprises a source of fluid, a first means for pressurizing the combustible fluid and pumping the pressurized fluid along a first path leading to a combustion apparatus for an internal combustion engine. The first means for pressurizing further pumping the combustible fluid along a second path to a first fluid-driven actuator adaptable to control some aspect of the engine. The first means for pressurizing further pumping the combustible fluid along a third path to a second means for pressurizing the combustible fluid. The second means for pressurizing pumping the combustible fluid along a fourth path, including a first diverting means, to a second fluid-driven actuator adapted to control some aspect of the engine or exhaust nozzle.

Abstract: A hydraulic drive system for a construction machine comprising a prime mover (1), a hydraulic pump (2) of variable displacement type driven by the prime mover, at least one hydraulic actuator (6) driven by a hydraulic fluid delivered from the hydraulic pump, control valves connected between the hydraulic pump and the actuator for controlling a flow rate of the hydraulic fluid supplied to the actuator dependent on the operation amount of control apparatus, pump control apparatus for controlling a displacement volume of the hydraulic pump dependent on the operation amount of the control apparatus such that the delivery rate of the hydraulic pump is increased with an increase in the operation amount, and prime mover control apparatus (29) for controlling a revolution speed of the prime mover.

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 drive system has a hydraulic pump (1), an actuator (2), a flow control valve (5) disposed between the hydraulic pump and the actuator, a pressure compensating valve (8; 8A; 8B) having a valve spool (23; 23A; 23B) that controls the differential pressure (Pz-PLS) across the flow control valve, and a pump delivery rate control device (9) for controlling a flow rate of the hydraulic fluid delivered from the hydraulic pump dependent on a differential pressure (Pd-PLS) between a pump pressure and a load pressure of the actuator.

Abstract: A valve apparatus (10; 10A) has at least one directional control valve (31; 31A) having a pair of variable restricting sections (43, 44) disposed between a supply passage (35) communicating with a hydraulic fluid supply source (11) and a pair of load passages (36, 37) communicating with an actuator (12). A pressure controller (32) or a pressure compensating valve (32A) is provided for holding a differential pressure across the variable restricting sections at a predetermined value. A detection line (57; 57A) is branched from a first passage (32; 86, 87) located between the pair of variable restricting sections and the pair of load passages for receiving a load pressure produced upon operation of the actuator. A check valve (59) or shuttle valve (90, 91) is provided for selecting a maximum load pressure and a control line (61, 62) introduces the selected maximum load pressure, as a control pressure, to the pressure controller or pressure compensating valve.

Abstract: A loading/unloading control apparatus for a industrial vehicle control the discharge capacity of a variable displacement type hydraulic pump in accordance with the detected result of the amount of load applied to a loading/unloading hydraulic actuator or with a manual setting by an operator, thereby to obtain the most suitable working speed of the actuator for loading/unloading operations.

Abstract: An improved RAM air turbine (30) for the generation of emergency power on an airplane is disclosed. The RAM air turbine has an operational range in which reduced power is produced by a power controller (40) at speeds at which stalling of the RAM air turbine would occur under the control of a governor (16) which adjusts the pitch of the blades (12) of the turbine in combination with a pressure regulator (150) controlling the output of pressurized hydraulic fluid from a variable displacement hydraulic pump (19).

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 construction machines includes a hydraulic pump (1), a plurality of hydraulic actuators (2, 3) driven by a hydraulic fluid supplied from the hydraulic pump, a plurality of flow control valves (4, 5) for controlling flow rates of the hydraulic fluid supplied to the actuators, respectively, and a plurality of distribution compensating valves (6, 7) for controlling differential pressures across the flow control valves, respectively, the plurality of actuators including a first actuator (2) which undergoes a relatively large load pressure and a second actuator (3) which undergoes a smaller load pressure than that of the first actuator.

Abstract: A load sensing hydraulic drive circuit comprises a variable displacement pump delivering fluid to a flow control valve for controlling flow to an actuator. A pump controller controls a delivery rate of the pump such that a differential pressure between a delivery pressure of the pump and a load pressure of the actuator is equal to a first predetermined value. An unloading valve is connected between the pump and the flow control valve for holding the differential pressure between the delivery pressure of the pump and the load pressure of the actuator less than a second predetermined value. A demanded flow rate of the flow control valve is detected and the unloader valve is controlled based on the demanded flow rate such that when the demanded flow rate is small, the second predetermined value is smaller than the first predetermined value, and when the demanded flow rate increases, the second predetermined value becomes larger than the first predetermined value.

Abstract: A hydraulic drive system for a civil-engineering and construction machine, includes an unloading valve connected to a discharge line of a hydraulic pump for relieving a hydraulic fluid from the hydraulic pump to a tank when a differential pressure between a delivery pressure of the hydraulic pump and a load pressure of an actuator exceeds a first predetermined value, for controlling the differential pressure. The unloading valve has a spool, a first receiving chamber arranged adjacent to one end of the spool, and a second pressure receiving chamber arranged adjacent to the other end of the spool, the delivery pressure of the hydraulic pump being introduced into the first pressure receiving chamber and the load pressure of the hydraulic actuator being introduced into the second pressure receiving chamber.

Abstract: A hydraulic apparatus for an industrial vehicle adapted for enabling to carry out a pump capacity control whenever necessary, and including a variable capacity type hydraulic pump driven by an engine, a flow dividing valve disposed in an outlet pipe line of the pump and adapted for dividing a flow of a pressurized hydraulic oil into a flow required for a power steering hydraulic circuit and a balance flow for a cargo handling hydraulic circuit, a switching valve pilot-operated by a pressure of the cargo handling hydraulic circuit and adapted for selecting a supply pilot pressure between a pressure of the power steering hydraulic circuit downstream with respect to the flow dividing valve and a pressure of the outlet pipe line upstream with respect to the flow dividing valve, and a capacity control valve pilot-operated by a differential pressure between the supply pilot pressure and the pressure of the outlet pipe line and adapted for controlling a capacity varying mechanism of the pump.

Abstract: A hydrostatic transmission with a pair of pump/motor connected in a closed loop state by a pair of hydrostatic circuit. The hydrostatic transmission comprises a differential pressure detecting means which detects the differential pressure between the circuits and a displacement correcting means which, in case an operation to establish a neutral status has been carried out, controls the displacement volume of the pump/motor on the side where the pumping action is carried out toward a direction in which the magnitude of this differential pressure is held within a set range.In case the set range is set to a value with which a vehicle cannot run, the phenomenon of creep running will not occur.

Abstract: An energy regenerative circuit in a hydraulic apparatus wherein when a direction control valve is at the actuator unloaded-side chamber acting position, the discharge fluid line of a variable displacement pump is connected to a fluid tank via the direction control valve, by-pass fluid line change-over valve and by-pass fluid line that has a signal orifice. The by-pass fluid line is connected to a capacity control mechanism of the variable displacement pump via a signal fluid line on the upstream side of the signal orifice. The loaded-side chamber of the actuator is so connected that the pressurized fluid thereof is partly added through the direction control valve to the fluid line through which the pressurized fluid discharged from the variable displacement pump is fed to the loaded-side chamber.

Abstract: A hydrostatic transmission in a closed circuit which includes a hydraulic engine having a stroke-volume control device and a hydraulic pump connected to said hydraulic engine by two pressure lines. The stroke volume of the pump and/or the engine is regulated by the stroke-volume control device. The closed circuit includes a reversing valve which is connected to both pressure lines and is controlled by the prevailing pressures in the pressure lines. The reversing valve connects the pressure line carrying the lower pressure to a delivery valve and connects the pressure line carrying the higher pressure to a pressure-reducing valve so that the level of the control pressure in the stroke-volume control device is determined. A pressure-reducing valve is located in each pressure line and the pressure-reducing valves and the reversing valve are combined as a single combination valve.

Abstract: Described is a control circuit for a hydraulic power lift driven by a displacement pump which has a check valve releasable at least for lowering movements of the power lift, a actuation means switching the check valve off and on to control the flow from a pump line into an operating line leading to the power lift and vice-versa, and a load-sensing line carrying the load pressure and connected to the operating line, by which the variable-displacement pump is capable of being activated. The actuating means has an actuating unit switching the check valve off and on and a servo valve, activated simultaneously and controlling the flow to and from the power lift, with at least three switch positions. In the starting position of the actuating means, the latter connects the load-sensing line and the operating line, by way of the servo valve, with the tank and, after passage through a central position, the operating line with the pump line.

Abstract: A hydraulic drive system has a variable displacement type pump, at least one hydraulic actuator driven by hydraulic fluid and a directional control valve for controlling a flow of the hydraulic fluid supplied to the actuator. The flow rate of the hydraulic fluid discharged from the hydraulic pump is controlled by a drive device that drives a displacement volume varying device of the hydraulic pump. A load-sensing control device controls the operation of the drive device and is responsive to a differential pressure between a discharge pressure of the hydraulic pump and a load pressure of the actuator to thereby hold the differential pressure at a setting value. The drive system further has an instruction device that instructs a change in the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the actuator. The instruction is received by a differential pressure setter capable of changing the setting value of the differential pressure.

Abstract: A hydraulic driving apparatus has at least one hydraulic pump, a plurality of hydraulic actuators driven by hydraulic fluid discharged from the hydraulic pump, a tank to which return fluid from the plurality of hydraulic actuators is discharged, and a flow control valve associated with each of the plurality of hydraulic actuators. The flow control valve has a first main variable restrictor for controlling flow rate of the hydraulic fluid supplied from the hydraulic pump to the hydraulic actuator, and a second main variable restrictor for controlling flow rate of the return fluid discharged from the hydraulic actuator to the tank. A pump control operative in response to the difference between the discharge pressure of the hydraulic pump and the maximum load pressure of the hydraulic actuators normally controls the discharge rate of the hydraulic pump so that the pump discharge pressure is raised more than the maximum load pressure by a predetermined value.

Abstract: Disclosed is a hydraulic control system mounted in a hydraulic circuit of a hydraulic excavator and adapted to increase the relief hydraulic pressure and the flow rate. In accordance with one aspect of the invention, a hydraulic control system for a hydraulic excavator having power constant control and cut-off control comprises: a variable relief valve (60) for increasing the pressure upon receipt of a pilot signal (Pc7), a solenoid valve (80) for connecting or disconnecting the pilot signal (Pc7), a variable cut-off control valve 10A which, upon receipt of a pilot signal (Pc6), cancels the cut-off control, a solenoid valve (70) for connecting or disconnecting the pilot signal (Pc6) and an electric circuit (X01) in which a switch (90) for opening or closing the solenoid valves (70, 80) is provided. In accordance with a second aspect of the invention, a timer is provided in the electric circuit (X02) used in the first aspect of the invention.

Abstract: Disclosed is a preferably electrohydraulic control for a load-dependently operating variable displacement pump, which is equipped with a differential pressure control device for ensuring a predetermined pressure drop at the control edge of a directional valve integrated into the consumer supply line. The differential pressure control device has a servo valve, the valve spool of which can be brought out of a first position, increasing the output volume of the variable displacement pump, against the compressive force of a spring and of a control pressure led off from the supply pressure upstream of the directional valve, by the pump pressure into a second position, reducing the output volume.

Abstract: A hydrostatic auxiliary power steering mechanism with load-dependent performance for controlling a variable displacement pump includes an orifice for generating a pressure difference. A control valve in a valve borehole contains a movable valve piston. Orifice is formed between the discharge opening cross-section of a pressure line into the valve borehole and a central spool land provided on valve piston and reveals a cross-section that can be altered as a function of the position of the control valve. The cross-section of orifice has its smallest value when the control valve is in the neutral middle position and can be made larger by adjusting the control valve in both directions.

Abstract: A hydrostatic drive system consists respectively of an adjustable primary and secondary unit which are connected together via a conduit train with impressed pressure. The volume flow of the primary unit is regulated in dependence upon the impressed pressure and the volume flow of the secondary unit as a function of the speed. To avoid pronounced dropping of the impressed pressure the power of the secondary unit is limited. For this purpose a circuit is provided in which the volume flows of the primary and secondary units are compared. The power limitation intervenes when the volume flow of the secondary unit exceeds the volume flow of the primary unit.

Abstract: Pressure compensating valves located downstream of the directional control valves are useful in providing load independent, proportional flow control hydraulic systems and normally serve as load checks. The subject load check and pressure compensating valve is designed for use in a hydraulic system in which the pressure of a common pressure signal directed to all the pressure compensating valves of the system is limited to a predetermined maximum level. The pressure compensating valve includes a valve element disposed downstream of a metering orifice, a separate load piston disposed in end-to-end relationship with the valve element in a common bore and a pressure compensating spring disposed in a chamber behind the load piston and biasing the load piston and valve element to the load check position.

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.

Abstract: A hydraulic drive controlling apparatus for a construction machine has at least one variable displacement type hydraulic pump, a plurality of actuators driven with a hydraulic fluid from the hydraulic pump, directional control valves driven in accordance with amounts of manipulation of operation means for controlling the plurality of actuators, means for detecting a delivery pressure of the hydraulic pump, means for selecting maximum one of load pressures of the plurality of actuators, and first control means for controlling displacement of the hydraulic pump to bring a differential pressure between the delivery pressure and the maximum load pressure to a specified value.

Abstract: An energy regenerative circuit in a hydraulic apparatus wherein when a direction control valve is at the actuator unloaded-side chamber acting position, the discharge fluid line of a variable displacement pump is connected to a fluid tank via the direction control valve, by-pass fluid line change-over valve and by-pass fluid line that has a signal orifice. The by-pass fluid line is connected to a capacity control mechanism of the variable displacement pump via a signal fluid line on the upstream side of the signal orifice. The loaded-side chamber of the actuator is so connected that the pressurized fluid thereof is partly added through the direction control valve to the fluid line through which the pressurized fluid discharged from the variable displacement pump is fed to the loaded-side chamber.

Abstract: A control device for a variable displacement hydrostatic machine having a stroke-volume regulator which is responsive to an actuating pressure. The control device includes a booster pump. The delivery pressure of the machine is the actuating pressure unless the delivery pressure of the machine is insufficient in which case the actuating pressure is a feed pressure produced by the booster pump. The control device includes a plurality of delivery-pressure lines and a proportioning pressure regulator having an outlet pressure which is proportionally reduced relative to the intake pressure connected between each delivery-pressure line and the stroke-volume regulator.

Abstract: A hydrostatic driving gear is described comprising a primary unit rotationally driven by a driving engine and a secondary unit rotationally driving an actuator. Each unit comprises a variable displacement hydraulic engine, in particular an axial piston engine. They cooperate in an open circuit. The primary unit and secondary unit each have a displacement adjusting device and can be continuously adjusted in respect of their direction of displacement through a zero displacement center position in two directions of displacement. The displacement adjusting device of the primary unit has associated with it a pressure flow controller which holds the working pressure at a constant presettable value. The displacement adjusting device of the secondary unit has associated with it a speed of rotation detecting device, having a position sensor to detect the flow setting.

Abstract: A hydraulic lift is raised by hydraulic fluid which passes through a servo valve and is lowered when the servo valve exhausts the hydraulic lift to a reservoir. The hydraulic fluid travels to and from the lift through a service line in which a blocking valve is disposed. A control unit opens the blocking valve against a spring bias in response to the application of a control pressure to a control element disposed on one side of the control unit. The control pressure is supplied via a control line which also actuates the servo valve. A branch control line branches from the control line and applies pressure to another control element which acts counter to the first-mentioned control element. The branch control line includes tow throttles between which a discharge line is connected and communicates with the reservoir.

Abstract: A hydraulic control system that comprises a hydraulic pressure line, a hydraulic fluid control mechanism and a lag network coupling the pressure line to the control mechanism for restricting flow of hydraulic flow therethrough, and thereby delaying and damping response of the control mechanism to fluid pressure fluctuations at the hydraulic line. The lag network comprises check valve that includes a flow passages interconnecting the hydraulic line and the control mechanism, a valve element, and a spring resiliently urging the valve element to close the passage, such that resistance to fluid flow increases as fluid flow decreases between the hydraulic pressure line and the control mechanism. Preferably, a pair of such check valves are connected in parallel between the hydraulic pressure line and the control mechanism for controllably restricting fluid flow in both directions.

Abstract: A hydraulic switching system has an adjustable delivery volume pump connected to a pump regulating unit that is controlled by a load-sensing regulator. The load-sensing regulator is connected to a control pressure line that carries the maximum hydraulic energy consumer pressure required by at least one hydraulic energy consumer. The hydraulic energy consumer connected to the pump is controlled by a multiway valve having a given adjustment path. In order to increase the fine-controllability of the hydraulic energy consumer when desired, a pressure-compensated flow control valve which is located in the control pressure line is switched in and out of the system.

Abstract: Control system for a load-sensing hydraulic drive circuit comprising; at least one hydraulic pump; hydraulic actuators driven by the hydraulic pump; and a pressure compensated flow control valve between the pump and each of the actuators, for controlling a flow rate of fluid to each actuator in response to a control signal. The control system has first detection means for detecting a differential pressure between the pump delivery pressure and the maximum load pressure; second detection means for detecting the pump delivery pressure; first means for calculating a differential pressure target pump delivery amount Q.DELTA.p to hold the differential pressure constant; second means for calculating an input limiting target pump delivery amount QT based on at least a pressure signal from the second detection means and an input limiting pump function; third means for selecting one of the differential pressure target delivery amount Q.DELTA.

Abstract: A load-independent control device for hydraulic users has an initial position in which a control line transmitting a load pressure is connected with a tank. The control device has a control valve for the user and a switching valve, which can be controlled independently of the control valve, and has a cutoff position as well as a through position, in which it connects with the control line transmitting the load pressure to the tank.

Abstract: The apparatus for the feed and control of the speed and torque of a hydraulic motor having variable swept volume according to this invention comprises a hydraulic feed device for the motor, adapted for supplying the required flow rate of hydraulic fluid under all conditions at the working pressure, a constant pressure hydraulic control circuit associated with the hydraulic device or devices for varying the swept volume fo the motor, adapted for modifying the swept volume itself in relation to the pressure of the hydraulic fluid supplied to the motor, and a flow regulator valve with proportional control, piloted by an electronic regulator generating a control signal for the valve and receiving the signal of a sensor of the rotational speed of the motor and a reference signal.

Abstract: A fluid pressure control system comprising a first selector valve for controlling the action of a first actuator, a second selector valve for controlling the action of a second actuator, a first flow control valve for controlling a fluid to be supplied to the first actuator, and a second flow control valve for controlling a fluid to be supplied to the second actuator. A pressure reducing valve is provided for reducing the pressure of the fluid supplied to the second actuator. The pressure on the outlet side of the pressure reducing valve is controlled by the proportional pressure relief valve which is controlled by an external pilot pressure. This system is applicable, for example, to a hydraulic excavator.

Abstract: An electrohydraulic system for control of a variable output pump includes a microprocessor-based controller receiving inputs from condition sensors coupled to the pump and command inputs from a remote master controller. The controller supplies outputs to an electrohydraulic valve for metering hydraulic fluid to a pump control port and thereby controlling pump operation in any one of a number of preselected and prestored pump control modes. A hydromechanical valve is connected in parallel with the electrohydraulic valve for controlling pump operation in the event of electrical malfunction or failure. Circuitry connected between the pump condition sensors and the control computer prevents aliasing errors due to mismatch between the computer sampling frequency and pump speed.

Abstract: A control load such as a cylinder or the like is driven at a constant speed by controlling the flow rate of a variable delivery pump. The control mode is switched to the pressure control to keep the stop pressure constant on the basis of an increase in pressure when the control load stops. A remaining delivery amount which will be necessary to raise the delivery pressure to an object stop pressure when the load stops and an excess delivery volume due to the operation time lag when it is assumed that the delivery by the pump is stopped at the present time are predicted. When they coincide, the delivery amount of the pump is set to zero and the control mode is switched to the pressure control. On the other hand, the product of a load volume and a fluid compressibility is calculated from the increase in pressure when the load stops. The feedback gain of the pressure control is controlled on the basis of the calculated value of this product.

Abstract: A bidirectional hydraulic servomotor system includes a variable-displacement motor which may impel or brake movement of a load member that either resists or assits movement by the servomotor, respectively. The direction of load movement is under control of a directional control valve with motor displacement and function (impelling or braking) being effected automatically to achieve controlled load movemement with minimal consumption of hydraulic fluid.

Abstract: A control for a variable displacement pump in which a displacement control element is made responsive to a load sensing valve and a pilot pressure relief valve. A control fluid is supplied to the pressure relief valve and the load sensing valve and the control pressure fluid controls the working pressure fluid which operates the stroking piston for the pump.

Abstract: A control valve for construction equipment adapted to operate a control mechanism in which a central by-pass passage is provided with a pilot pressure generating mechanism such as an orifice or the like and which is adapted to generate a pilot pressure due to pressure loss of fluid passed through the pilot pressure generating mechanism when a valve connected to the central by-pass passage is set at an open position, resulting the pilot pressure acting to control a discharge rate of a variable discharge pump. The control valve includes a valve body, in which a first spool and a second spool are arranged in series in such a manner that inner ends of the first and second spools are opposite to each other. An outer end of the second spool faces a second pilot chamber. A centering spring is arranged so as to act on an outer end of the first spool, so that the inner ends of both spools may be abutted against each other and received in a first pilot chamber when the spools are at their normal position.

Abstract: According to the parent patent on inadequate power of the delivery pump the flow rate set at the directional control valves for the consumers is reduced in equal proportions in that electrical signals proportional to the flow rates are supplied to a summation stage and the sum voltage is compared in a comparison stage with a limit value corresponding to the maximum pump delivery flow. When the limit value is exceeded a control signal is generated with which the stroke of all the driven directional control valves can be jointly reduced. According to the application of addition the signal voltage supplied to the summation stages and corresponding to the respective flow rate can be obtained in a displacement pickup associated with each directional control valve or in a pressure pickup measuring the pilot pressure if the directional control valves are not controlled electrically but hydraulically.

Abstract: A pump supplies a plurality of consumers each via a directional control valve with pressure balance. When the pump delivery is not adequate, manifesting itself in a dropping of the pump pressure, the pressure balance of the consumer with the highest load pressure is displaced out of the end position of its regulating position into a further control position in which a control pressure line is connected via a throttle point to a discharge so that by means of the throttle point a control pressure is generated which is used for equiproportional reduction of the supply flow to the consumers. This is done either by reducing the stroke of the directional control valves or by acting on the pressure balances in the closure direction.

Abstract: An excavator has a number of different hydraulically powered functions that are controlled by a closed center hydraulic system that features a pair of variable displacement, engine driving hydraulic pumps, the displacement of which is responsive to the demands of the system. The flow to the various hydraulic motors is controlled by pilot operated load sensing control valves that direct fluid pressure to a load sensing line when one of the hydraulic motors in the system is being operated. The load sensing line is connected to the control system of the pumps to place the pumps in stroke when a flow of pressurized fluid is required. The flow of the load sensing pressure to the controls for one of the pumps can be optionally disconnected to place said pump in a standby condition and thereby reduce the flow capacity of the hydraulic system at the option of the operator.

Abstract: The hydraulic control is constructed for time-sharing of the pump which normally controls the turning mechanism, to operate other hydraulic equipment in conjunction with other pumps.

Abstract: An electrohydraulic system for control of a variable output pump includes a microprocessor-based controller receiving inputs from condition sensors coupled to the pump and command inputs from a remote master controller. The controller supplies outputs to an electrohydraulic valve for metering hydraulic fluid to a pump control port and thereby controlling pump operation in any one of a number of preselected and prestored pump control modes. A hydromechanical valve is connected in parallel with the electrohydraulic valve for controlling pump operation in the event of electrical malfunction or failure. Circuitry connected between the pump condition sensors and the control computer prevents aliasing errors due to mismatch between the computer sampling frequency and pump speed. A pump torque sensor measures pump input shaft torque.

Abstract: A control circuit and specific embodiments thereof are provided using a four-port infinitely variable pilot operated pressure-compensator spool valve and a three-port infinitely variable pilot operated load sense spool valve in series to regulate the output pressure of a variable displacement radial piston pump. The valves are so constructed that both must be correctly positioned to put the pump into full stroke, while either valve can de-stroke the pump. The three-port valve is pilot controlled between the load sense pressure and the outlet pressure, while the four-port valve is controlled between the pump inlet and outlet pressures. A check valve and orifice are positioned between the two control valves and the crankcase control line of the pump to assist in stabilizing the pump output. A relief valve is provided on the crankcase line to minimize output spikes. In an alternative embodiment, a single three-port valve is controlled between the inlet and outlet pressures of the pump.

Abstract: A variable pressure control for controlling displacement of a variable displacement over-center pump utilizes a pair of remotely variable pressure limiter three-way valves which are associated one with each of a pair of servo cylinders operably connected to a swash plate of the pump and acting in opposition for positioning of the swash plate. The pressure limiter valves each control the communication of a servo cylinder with either system pressure or drain and are remotely operable to set a displacement of the pump and limit the pressure of the fluid delivered by the pump. This structure enables setting of pump displacement without the use of a displacement control valve associated with the servo cylinders.

Abstract: A gain reduction circuit is provided for use with a pressure flow compensated variable displacement pump in a power-on-demand hydraulic system. An orifice and a check valve are connected in parallel between a pressure-flow compensating valve and the control for the variable displacement pump. A second orifice is connected between the pump control and sump. A relief valve is connected in parallel with both orifices. The circuit operates to allow a quick increase in pump output, while damping variations in the pump control to prevent or minimize oscillation of the pump outlet pressure around the desired value. In alternative embodiments, the check valve may be omitted if larger orifices are used, or the check valve may be provided and the second orifice omitted.

Abstract: There is disclosed an hydrostatic transmission having a control and regulating device for adjusting the driving torque with superimposed output power limit regulation, the transmission comprising a drive unit comprising an hydraulic pump having a variable output, and an hydraulic motor arranged to be operated by the hydraulic pump; a servo-adjusting device arranged to control the output of the hydraulic pump in order to adjust the working pressure in the transmission, said device comprising a servo piston arranged for two-way adjustment of the hydraulic pump in two directions, and a control valve arranged to subject the servo-piston to an adjusting pressure so that the piston can adjust the operation of the hydraulic pump; a servo-valve spool provided in said control valve and arranged, in dependence upon the desired direction of adjustment of the hydraulic pump, to be subjected on the one hand to a control pressure and on the other hand to the working pressure prevailing in the transmission or a regulating p