Abstract: A feedback apparatus according to the present invention elastically interconnects the swashplate of a variable displacement hydraulic unit with the valve spool of a hydraulic unit displacement control, and is constructed such that a predetermined spring preload force is developed. A feedback spring extends along the valve spool and is surrounded by an elongated housing coupled with the swashplate. Axially movable spring guides are interposed between opposite ends of the spring and a flange formed at each end of the housing. A suitable spacer is positioned between the spring and at least one of the spring guides to compress the spring to a length representative of the desired preload.

Abstract: The invention refers to a hydraulic system comprising at least a variable displacement pump and at least a consumer. Means are provided to generate electrical limit signals when at least one of the consumers, preferrably a load leading consumer indicates the need for an increased delivery rate or when the variable displacement pump indicates a hydraulic under-supply. In response to the limit signals generated by the consumer need or the pump are varied in a control circuit to adjust the control signals delivered to the servo devices of the hydraulic systems such that the pump control is optimized and that the flow rates to the consumers are decreased in the mode of under-supply. In addition very simple electrical circuits are disclosed to substantially reduce the expenditure of the system.

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: 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: In an apparatus for controlling the operation of hydraulic motors having infinitely adjustable eccentricity, wherein a flow-control valve between a pump and a hydraulic motor supplied with pressure medium and a control valve for adjusting the eccentricity of the hydraulic motor as a function of the operating pressure required by the hydraulic motor are provided, in connection with pressure optimization for keeping constant the torque of the hydraulic motor, the hydraulic motor is provided with a regulating device (7,10) which is mechanically connected to the eccentric (3) and transmits an eccentric adjustment outward, wherein this mechanical regulating device (7,10) acts on the flow-control valve (17) in such a way that, as a function of the change in the eccentricity, the flow-control valve (17) controls the pressure-medium quantity supplied to the hydraulic motor in such a way that the speed of the hydraulic motor is kept constant.

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: An operating speed change-over device is equipped with an automatic speed change-over valve which opens and closes a pilot fluid line that connects a pilot port of a capacity change-over valve of a capacity-variable hydraulic motor to a pilot pump. The automatic speed change-over valve has one pilot port that is connected to a pressurized fluid feed line leading to the hydraulic motor and has another pilot port connected to the return fluid line of the hydraulic motor. The automatic speed change-over valve is changed over by an effective differential pressure between the two fluid lines.

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 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: 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: 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 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: A hydrostatic drive assembly with an adjustable pump driven by a primary power source, which acts on several consumers of hydrostatic energy, is disclosed which has a control and regulating device with nominal speed value pickups and adjustable restrictors for each consumer. In order to obtain a control and regulating device at a low production cost, one that operates with a low power loss, it is proposed that the nominal speed value pickup send an electric signal to an electronic control device, that each consumer be provided with an actual speed value pickup, which the control device, and the restrictors assigned to each of the consumers in their connection lines are designed as electromagnetic throttle valves controlled by the electronic control device.

Abstract: A control device for a hydrostatic drive for at least two actuators, having a variable displacement pump whose adjusting device is acted on in accordance with the displacement and/or the flow pressure, wherein each actuator has associated with it, in its hydraulic supply line, a control valve and a preceding displacement controller in the form of a pressure compensator, is simplified while ensuring accurate control. This is achieved by associating with the control device an electronic regulating device which, depending on a measuring element that detects the opening position of the pressure compensator, controls, by means of an adjusting member associated with the adjusting device, the displacement setting of the pump, increasing it as the opening of the pressure compensator(s) becomes larger and decreasing as the opening becomes smaller.

Abstract: A control device for a hydrostatic drive for at least two actuators having a variable displacement pump whose adjusting device can be acted on as a function of the displacement and/or of the delivery pressure, wherein a control valve is associated with each actuator in its hydraulic supply line and the delivery flow for each actuator is determined by means of a pressure compensator as a function of the valve preset at the control valve, is simplified while ensuring accurate control. This is achieved by having the adjusting device always set the pump at a displacement which is slightly less than the sum of the actual instantaneous volume flows required by the actuators.

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 hydraulic control system for simultaneously driving two hydraulic loads of a production machine by means of a variable delivery pump feeding drive fluid to the two loads through separate load lines, in accordance with independently controllable programs of flow rate and pressure, the two load lines being controlled by two proportional P/Q valves, the pump being continuously adjusted for a constant pressure gradient in the load line which carries the higher pressure, the other load line having a pressure imbalance compensating device in the form of either a flow rate measuring device, a pressure balancing valve, or a displacement-to-voltage converter connected to the associated load.

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 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: A variable displacement motor control responsive to the pressure differential across the motor, with provisions for reverse motor operation and for aiding load conditions.

Abstract: An arrangement for operating a diesel-hydraulic drive on a construction machine in limit-load control with a microprocessor controller in which the installed hydraulic power is greater than the rated output of the diesel engine. Upon thermal and/or diesel-engine overload the hydraulic power which can be taken off is reducible; in the case of non-output loading, after a selectably predetermined time the diesel engine can be switched to idling speed of rotation and hydraulic displacement pumps can be operated with minimum delivery oil quantity; and the adjustable hydraulic displacement pumps can be adjusted in accordance with selectably predeterminable output curves.

Abstract: A pump supplies via in each case a directional valve with associated pressure balance fluid or pressure medium to a plurality of loads. When the pump power is not sufficient a proportional quantity reduction is achieved at all loads in that the control voltages of the control members for electrical actuation of the directional valves 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 displacement, whereupon when the limit value is exceeded a control signal is generated with which the stroke of the driven directional valves is reduced.

Abstract: A power-transmitting system provides conservation of (speed) X(torque) product between an input shaft and an output shaft. It represents the equivalent of the power being transmitted through the system. This power is transformed into the form of incompressible fluid flow at high pressure by a volumetric pump coupled to the input shaft. This fluid flow is forced at that pressure into a volumetric motor. The fluid then pushes on pistons which are constrained by a fixed enclined track. The pistons are laterally guided in a rotor and radially arranged therein. The enclined track forms a closed curved surface which surrounds these pistons and the resultant of the reactions of the track surface on the pistons results in a torque being exerted on the rotor. The structure supporting the track surface is slidable in a manner such that the piston strokes are adjustable between zero and a set maximum.

Abstract: A displacement control for a variable displacement hydraulic motor wherein the control is a summing pressure compensator control which is responsive to the pressures of a plurality of loads so that the average, weighted average, or total pressures of the loads can be sensed to generate a control signal for increasing the displacement of at least one motor when the plurality of pressures have a sum or average above a predetermined level. The summing pressure compensator control can also include an overpressure sensing device which is responsive to the pressure of one load, or the highest pressure of more than one load, to also provide a control signal to increase motor displacement. The increase in motor displacement limits the pressure of the motor system.

Abstract: A hydraulic control system comprising a hydraulic actuator having opposed openings adapted to alternately function as inlets and outlets for moving the element of the actuator in opposite directions and a pump system with load sensing control for supplying fluid to said actuator. A meter-in valve is provided to which the fluid from the pump is supplied and a manual or electrohydraulic controller alternately supplies fluid at pilot pressure to the meter-in valve for controlling the flow therefrom to the actuator to control direction and displacement of movement of the meter-in valve and the direction and velocity of the actuator. A pair of lines extends from the meter-in valve to the respective openings of the actuator. A meter-out valve is associated with each line to the actuator for controlling flow out of the actuator. Each meter-out valve is operated by the pilot pressure from the controller.

Abstract: The invention relates to a speed regulating device for a hydrostatic drive unit comprising a pump of variable feed volume and a motor in a hydraulic circuit, wherein the pump is driven by a drive motor of variable speed, and there is provided a regulating valve which controls the loading of a hydraulic adjustment device on the pump in dependence on the pressure differential in front of and behind an adjustable throttle arranged in the hydraulic circuit, in such a way that the feed volume is changed in inverse proportion to a speed change in the drive motor. It is the aim of the invention to produce a simple construction for the speed regulating device which can also be easily controlled in reverse operation and can be easily operated.

Abstract: A servo-mechanism includes a piston and cylinder unit controlled by a valve coupled in known manner by a linkage means to a movable control element to provide closed loop servo operation to position the piston and cylinder unit piston rod according to the position of the movable element. The movable element is fast with an annular gear segment of an epicyclic gear mechanism of which the sun gear forms a main control input and the planet pinion carrier forms an override input. The mechanism is of utility in an hydraulic transmission of the variable stroke pump/fixed stroke motor type, the overrride input being actuable by a pump port pressure limit sensor.

Abstract: A hydraulic or the like drive system which can include a variable-speed pump with at least one control element. The control element can be connected to a pump control piston arranged in a pump control cylinder, the position of which is determined by a control pressure. The drive system can further include a conveying conduit connected to the pump and a return conduit which leads to the respective reservoir, and can furthermore include control elements, with the conduit emanating from the pump are connected--by intervention of a respective branch line--several demand points which respectively can be connected to the conveying conduit by means of an in the respective branch line arranged, randomly movable valve. The valve has two auxiliary pistons arranged in the main piston of the valve and each auxiliary piston houses a reversing piston.

Abstract: A control apparatus for a hydraulic motor for use in a construction vehicle driven by hydraulic power has a hydraulic motor, a hydraulic pump serving as a pressurized fluid supply source, a manually operable directional control valve connected across supply and discharge conduits for the hydraulic motor, a brake valve section including a counterbalancing valve and a pair of relief valves all of which are connected across the conduits extending between the directional control valve and the hydraulic motor, and a selector valve for controlling the supply of control pressurized fluid introduced through a shuttle valve connected across the conduits into a displacement control cylinder contained in the hydraulic motor. The selector valve is of a pilot operated type remotely controlled by pilot pressurized fluid supplied from an external pressurized fluid supply source.

Abstract: An automatic transmission, for a vehicle with an engine, includes a hydraulic fluid pump which supplies pressurized hydraulic fluid. The engine load is detected, and the pump output is controlled so as to increase with increase of the load on the engine. If the pump is one whose output per one revolution of its input member is variable, then its output may be thus controlled by increasing its output per one revolution along with increase in engine load. And, if the pump is a variable capacity type vane type hydraulic fluid pump the output of which per one revolution of its input member is controlled by varying the eccentric position of a controlling member thereof, then its output per one revolution may be thus controlled by detecting the eccentric position of the controlling member using a sensor, and by varying this eccentric position in a feedback manner to achieve a target eccentric position which is determined to give a pump output per one revolution varying as an increasing function of engine load.

Abstract: For a drive system comprising a hydrostatic adjustable machine an electrical control is provided with which the actuator of the machine is driven so that for acceleration, retardation and braking, i.e. when the machine moves from motor mode to pump mode, a predetermined operating behavior of the machine necessarily results. The particular input desired value for the speed is transformed so that suddenly occurring abrupt acceleration, retardation and braking operations are avoided and in particular on abrupt entry of desired values increased safety against operating errors is achieved.

Abstract: Hydraulic control arrangement for a driven working device particularly mounted on an agricultural vehicle, comprises a hydromotor for driving a working device, a blocking unit having a blocking valve and a pushing piston, a control valve including a control slider which controls the blocking unit and has three control edges, and a control chamber, two working chambers, and two return chambers, a throttle valve having a throttle slider and a spring arranged in a chamber and loading the throttle slider, a working conduit leading from an inlet via the throttle slider, the first control edge of the control slider and the blocking valve to the hydromotor and allowing a load pressure-independent control, a control conduit branching from the working conduit and extending via the third control edge of the control slider, the control chamber and the second return chamber to a tank, and supplied with a control pressure medium in a lowering position of the control slider via the throttle slider, and two throttle points

Abstract: In a vehicle speed control system, a vehicle speed command set corresponding to the position of a vehicle speed setting lever is fed into a dead area setting circuit in which the value of the vehicle speed command is changed to be not smaller than a preset minimum speed of the vehicle when it falls out of the dead area. Then the command is supplied into different delay compensating circuit depending on whether it is an acceleration command or a deceleration command. Further, the command outputted from the delay compensating circuit is subtracted by a brake signal generated by the operation of a brake pedal. The command thus subtracted causes a mechanical brake signal to generate when the speed of the vehicle is zero or minus.

Abstract: A hydraulic lifting and lowering system for battery-powered lift trucks includes an electronic control system which reduces or limits operator selected lifting commands in accordance with the current being drawn by an electric motor connected to drive a variable-displacement pump, and in accordance with the state-of-charge of the vehicle battery, to control a proportional valve which meters fluid flow to a lift cylinder.

Abstract: Disclosed is a control arrangement for a hydrostatic drive of the type having a power-driven adjustable pump, a pressure responsive setting cylinder coupled to the pump, a hydraulic motor connected via pressure conduits to the pump and a measuring motor coupled to the hydraulic motor to rotate with a proportional rotary speed. A supply pump is connected in a control circuit including the measuring motor and a nominal or desired value generator in the form of an adjustable throttle by means of which the desired rotary speed of the hydraulic motor is adjusted. Deviations between the actual and desired speeds produce a differential control flow which is fed to the setting cylinder which adjusts the position of an adjusting member of the pump for so long as until the deviation equals zero.

Abstract: An improved hydraulic auxiliary drive system for driving the normally non-driven wheels of a vehicle is disclosed. A variable displacement motor having a tiltable swash plate operable between zero and full displacement positions drives the normally non-driven wheels and a variable displacement pump supplies pressure fluid to the motor. A spring biases the swash plate toward its zero displacement position and a servo mechanism is connected with the swash plate for tilting the same. A first supply delivers pressure fluid to the servo mechanism to tilt the swash plate toward its full displacement position and a second supply delivers pressure fluid to the servo mechanism to tilt the swash plate toward its zero displacement position. The first supply includes a pressure control valve to control the pressure thereof.

Abstract: An apparatus for regulating the speed of internal combustion engine of a hydrostatic system. A fuel control means acts to control the quantity of fuel delivered to the engine responsive to the immediate hydraulic flow demanded by operation of the hydrostatic system. The speed of the engine is set to one of a plurality of discrete levels in response to the required flow being within one of a corresponding plurality of preselected ranges.

Abstract: An apparatus for controlling both pump displacement of a variable displacement hydraulic pump and the quantity of fuel delivered to an internal combustion engine for the purpose of delivering a requested hydraulic flow at a highly efficient operating point. The apparatus includes an underspeed control means for reducing pump displacement in response to the operating speed of the engine lugging below a desired operating speed. Additionally, a fuel control means operates to reduce the quantity of fuel delivered to the engine in response to the operating speed of the engine rising above the desired operating speed.

Abstract: Normally feathered propeller blades of a wind power generating system unfeather in response to the actuation of a power cylinder that responds to actuating signals. Once operational, the propellers generate power over a large range of wind velocities. A maximum power generation design point signals a feather response of the propellers so that once the design point is reached no increase in power results, but the system still generates power. At wind speeds below this maximum point, propeller speed and power output optimize to preset values. The propellers drive a positive displacement pump that in turn drives a positive displacement motor of the swash plate type. The displacement of the motor varies depending on the load on the system, with increasing displacement resulting in increasing propeller speeds, and the converse.

Abstract: The hydrostatic control system for an articulate loader provides an improved method for controlling the output of a hydrostatic drive unit for a front end loader, with cooperative connecting means disposed between a pair of axially aligned drive pumps to provide selective output of one or both pumps as dictated by operation of the control mechanism.

Abstract: A hydraulic driven electric generator and air conditioning system for simultaneously generating controlled quality electrical power and producing air conditioning in a desired area has a variable displacement hydraulic pump for pumping a hydraulic fluid is driven by a prime engine means. The pump is hydraulically connected to a fixed displacement hydraulic motor which is powered by the fluid flow. The first motor drives an electrical generator means for generating electricity having a rotating blower fan mounted within a generator housing. A second hydraulic motor is hydraulically connected to the output of the first motor and is used to provide power to an air conditioning means. Means monitoring the passage of blower teeth of the rotating blower fan produces an electric output responsive to changes detected in the rotation of the blower fan.

Abstract: A fan drive system (10) controls the start-up of a fluid driven fan motor (16) in response to an engine being started. Since the fan motor (16) is many times located remote from the engine, it is important to start the fan motor (16) turning simultaneously when the engine is started. A control mechanism (32) changes the displacement of a pump (12) to operate at an operative position for a predetermined time period from initial start-up to ensure that the motor (16) starts to turn the fan (22). The control mechanism (32) automatically reduces the pump displacement to a standby position at the expiration of the predetermined time period to conserve energy.

Abstract: A control system for a hydraulically driven vehicle having a variable displacement hydraulic motor connected with a variable displacement hydraulic pump in a closed loop and driven thereby.A spring-applied and fluid-released brake is mounted on an output shaft of the motor. A regulator is operatively connected to the motor for controlling the displacement thereof in response to a fluid pressure at both ports thereof. When fluid pressure at either one of the ports of the motor exceeds a predetermined level, the variable displacement motor is changed over to a high displacement position thereby generating a large braking force when the vehicle is to be stopped.

Abstract: A fluid control system (10) for controlling the torque of a fluid motor (22) and varying the flow to the fluid motor (22) has a mechanism (56) to control the torque and flow in proportion to the operator's input to a pilot operated control valve (16) that controls the fluid motor (22). The mechanism (56) controls the torque and flow of the fluid motor (22) during both acceleration and deceleration of the fluid motor (22). The fluid control system eliminates the need for special, complicated control valves.

Abstract: A hydraulic control system for regulating the distribution of fluid from a variable displacement pump to a plurality of fluid actuated devices is disclosed. The control system includes at least first and second control valves, each of which valves regulates the flow of fluid to a fluid actuated device. Each of the first and second control valves includes, respectively, a first means for developing a first pressure signal and a second means for developing a second pressure signal. A selector means senses the first and second pressure signals and transmits a control pressure signal which is the smaller of the two pressure signals to a fluid actuated displacement control means which regulates the displacement of the pump in response to the magnitude of the control pressure signal.

Abstract: A torque control for a drive system having a hydraulic transmission connectable to a prime mover (30) and having a pair of hydraulically-connected displacement devices V and F, with one device having variable displacement, a torque sensor (35) generates a torque signal representative of prime mover output torque in either driving or braking mode, torque demand generators (47,47') generate a torque demand signal selectively in either driving or braking modes, a governor valve (63) compares the torque signals and generates a control signal and a control servo 17, responsive to the control signal, controls the displacement of the variable displacement device V to eliminate any difference in torque signals.

Abstract: A fluid pressure system has a reservoir and a variable delivery pump having an inlet connected to the reservoir and an outlet. A control valve connected to a control motor and feedback line with the feedback line adapted to control the fluid flow to and from the control motor to vary the pump displacement, to maintain the pressure at the pump outlet at a difference above the pressure in the feedback line. A control valve is adapted to control the fluid flow between the outlet, the load motor and the reservoir. The control valve is adapted to control the fluid flow between the load motor, the reservoir and a control line and is operable in a neutral position to block off the pump outlet from the load motor and to connect said control line to the reservoir. The control valve is operable to another position which connects said load motor to the control line before the pump outlet is connected to the load motor.

Abstract: A control is provided for the drive of a motor vehicle with differential-speed steering and with a hydrostatic power transmission unit on each side of the vehicle, where the adjusting element of each of the two power transmission units is provided with a spring-loaded adjusting piston that can be acted upon by control pressure, in which case two pairs of control pressure pick-offs are provided, of which two are assigned to forward and backward movement and the other two are assigned to cornering, where a pressure-dependent switchable pilot valve is installed in the connecting line between a control pressure pick-off assigned to a cornering direction and the adjusting element of the assigned power transmission unit, the pilot valve connects this control pressure pick-off assigned to the cornering direction with a specific pressure chamber of the adjusting element of the power transmission unit on the side of the vehicle on the inside of the curve, so that through actuation of the control pressure pick-off dete

Abstract: A system for varying the speed and displacement of a variable-displacement hydraulic motor and for providing a feedback signal which prevents the motor from stalling when an operator tries to reduce the motor displacement below the stall level. The system is especially useful for operating a hydraulic winch system on a wire rope crane. A variable displacement hydraulic pump provides pressurized fluid to operate a variable displacement hydraulic motor for lifting loads supported by the wire rope. The motor speed is controlled by varying the displacement of the pump and/or the motor, with the motor speed generally increasing as motor displacement decreases. The motor could stall if the crane operator decreases motor displacement below a critical value. A feedback signal coupled to the motor controls the motor displacement to prevent motor stalls.

Abstract: A hydraulic control system which is of an open center parallel circuit arrangement for aerial boom devices with two return lines, said system having control valves for upper and lower boom arms, wherein the lower boom control valve overrides the upper boom control valve. The system includes a valve connected to a pump actuating engine and responsive to hydraulic pressure to increase the speed of the fluid pump when the flow or pressure in one return line is reduced due to diversion of fluid within the system into the second return line. The system also includes a normally open relief valve carried by the boom supporting turntable adjacent its pivotal connection to the lower boom and operable to control a winch actuator and to deactivate said winch actuator when the boom is in an unstable position.