Abstract: A steady operation method for a hydraulic machine such as a generator operating at a variable revolution speed is performed in accordance with the following steps. A head or load of the hydraulic machine is first detected and a basic signal is obtained on the basis of the thus detected value so as to control the revolution speed of the hydraulic machine. On the other hand, a vibration or hydraulic pressure variation is detected and the thus detected value is converted into an auxiliary signal through an auxiliary signal converter. The revolution speed of the hydraulic machine operating at a variable speed is controlled in such a manner as that the revolution speed is controlled by the basic signal when the auxiliary signal is below a predetermined upper limit thereof regarding the vibration or hydraulic pressure variation, and otherwise, the revolution speed is controlled by a signal other than the basic signal when the auxiliary signal is beyond the upper limit thereof.

Abstract: A pressure-compensated flow-control valve with an adjustable limiting device controls the maximum speed of a fluid motor and eliminates an additional valving element found in prior art device. The flow control valve includes a flow limiting throttle opening integral with the flow control spool. The spool can be selectively rotated to adjust the effective size of the throttle opening thereby limiting flow through the valve. The spool establishes a constant rate of flow determined by the throttle opening or a directional control valve. By incorporation of the flow limiting function within the flow control spool, the overall cost and complexity of the pressure compensated flow control valve is reduced.

Abstract: A hydraulic system having an axial piston pump as a control pump which is regulated by a regulating device as a function of the demands with respect to volumetric flow and pressure of a load circuit supplied by it. On the suction side, the control pump is optionally provided with a partial amount of its maximum delivery volume by a feed pump, while the remaining part of the corresponding delivery quantity is drawn in directly from a storage container, bypassing the feed pump. Possibly impermissibly high vacuums on the suction side of the control pump are detected by a suction safety device which acts on the control pump via its regulating device so that the control pump delivers smaller quantities of hydraulic fluid unitl permissible operating conditions are reached.

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: Backhoes are useful for digging trenches, ditches, etc. However, a performance deficiency caused by the formation of voids in the hydraulic control motor occurs sometimes if the swinging mass of the backhoe is abruptly stopped by quickly moving the directional control valve to the neutral position. The present invention provides a control circuit having a charging valve for communicating pressurized fluid from the supply conduit connected to the pump to charge the makeup valves with pump discharge fluid to minimize or avoid the formation of voids when the directional control valve is moved to the neutral position to stop the swinging movement of the backhoe mechanism.

Abstract: A control circuit for a reversible hydrostatic transmission including a reversible pump having first and second working lines, and a control member having forward and reverse positions to normally direct a working fluid through the first and second working lines respectively. A servo-motor has forward and reverse positions to hold the pump control member in either its forward or reverse positions, and a first subcircuit is provided to conduct a control fluid to the servo motor to hold that motor in either its first or second positions. This first subcircuit includes a pair of piston and cylinder units, with each of these units having a control pressure chamber and a working pressure chamber.

Abstract: The invention concerns a hydraulic system for supplying a hydrostatic steering system. A central variable capacity hydraulic fluid pump supplies the steering system and a secondary consuming device via separate respective compensated pressure maintaining valves. The steering system and secondary consuming device are controlled by respective load report lines which are brought together at a changeover valve which is operative to permit the higher reported pressure to be delivered to a volume governor for the pump. Upon the secondary consuming device entering a neutral condition or a fluid loss condition, the changeover valve moves to block the load report line to the secondary consuming device; and a control circuit, including a branch line from the feed line to the steering system, maintains a higher pressure in the load report line of the steering hydraulic circuit than in the line of the secondary consuming device.

Abstract: A multiway valve is provided having a load feedback wherein a pressure-reducing element that reduces the pressure conveyed to a connection through the valve with a control pressure signal line is controlled as a function of the displacement of a valve piston in the multiway valve.

Abstract: A hydrostatic drive with an adjustable pump and several consumers is provided in which one or several consumers simultaneously can be selectively connected with the pump, in which case the connection to a consumer can be effected by an arbitrarily actuable control valve having a throttling effect in the intermediate positions, where the loading of the adjusting element of the pump is controlled by a pump adjusting valve, which in turn is regulated by the pressure differential arising at the regulated control valve so that it is regulated to a constant pressure differential, where the highest prevailing pressure in a line between the regulated control valve and the regulated consumer is conveyed through a control pressure line to the control pressure chamber on the spring side of the pump adjusting valve and where a pressure limiting valve is connected to the pump delivery line and provided on the spring side with a control pressure chamber connected with the control pressure line (load-sensing signal line).

Abstract: Hydraulic control circuit for working members of earth-moving machines including linear and rotary hydraulic actuators associated with respective hydraulic distributors for the operation of respective working members. The rotary hydraulic actuators with their distributors are grouped in a circuit separate from the linear hydraulic actuators and are provided with braking valve means constituted by a single counterbalance valve connected in a common discharge line, the opening of which is controlled by a pilot pressure signal corresponding to the lowest supply pressure for the rotary actuators.

Abstract: A progressive hydraulic distributor with a slide for controlling a hydraulic actuator. The distributor has an internal load sensing passage that detects the operating pressure in the hydraulic fluid inlet or outlet passage and superimposes this pressure on the action of the spring of a feed valve. Thus, the difference between the up-flow and the down-flow of progressivity in the slide of the distributor is constant.

Abstract: An adjustable hydrostatic machine is connected to a pressure line with impressed system pressure. The pressure difference applied at the machine is set at a control valve so that the stroke volume of the machine in idling operation is set to an adjustment belonging to a predetermined load torque. In idling operation the machine is thus operated at large stroke volume with small pressure difference. If it is then necessary to furnish the load torque a switching valve is opened so that at the machine the full pressure difference is immediately applied, the machine can furnish the desired torque and the time loss necessary for setting the machine is eliminated.

Abstract: A dual pressure source, or selectively alternative high pressure source, control system for a variable displacement hydraulic unit servo mechanism wherein normal control of the unit is provided by the low pressure source, such as a transmission charge pump, and wherein a high pressure source of control fluid with a restrictive orifice is provided to initiate servo movement, especially under conditions generating high internal friction. The flow restrictive orifice generates a pressure drop in a high pressure control line once the servo mechanism starts to move, inducing flow through such line. Thus, the control system provides a momentary source of high pressure fluid but permits control rate changes which are substantially independent of the hydraulic unit working pressure. Preferably, the high pressure source is a shuttle selected highest pressure of a transmission main loop incorporating the hydraulic unit.

Abstract: A variable displacement, pressure compensated, axial piston pump has an electrohydraulic servo valve connected to the pressure compensator mechanism to enable the pressure setting of the mechanism to be changed from a remote location.

Abstract: An apparatus for controlling the fluid flow delivered to work elements of a work vehicle. In the operation of hydraulic work vehicles, when quick or multiple implement movement is required, the fluid pumps often are requested to surpass their capability in providing fluid flow to the work elements. A flow-limiting situation then occurs wherein some of the work elements are not receiving the requested flow and therefore cannot perform their requested functions. To solve this problem, the total available flow and the total requested flow from the pumps are monitored. If the total requested flow is not great enough to cause a flow-limiting situation, the operators demands are communicated to control valves which control fluid flow to the respective work elements. However, if the total requested flow is greater than the total available flow, the operators demand signals are "scaled down" in order to prevent a flow-limiting situation.

Abstract: An anti-plug control for a drive to prevent jamming of a driven working element in response to an overload wherein said drive includes a hydrostatic transmission having a variable displacement unit and a fixed displacement unit connected in closed circuit. A servo control cylinder is connected to a swash plate of the variable displacement unit for causing positioning thereof. A normally closed pressure-responsive valve monitors the pressure in the high pressure side of the closed circuit and is openable when the pressure reaches a predetermined value to deliver fluid from the closed circuit to the servo control cylinder and modify the displacement of the variable displacement unit to increase the speed of the working element to attempt clearing the overloaded condition of the working element.

Abstract: A variable displacement pump system including a pressure compensator for operating a pump adjusting mechanism to vary the displacement by applying hydraulic fluid to the pump adjusting mechanism and a spring biased piston applying a yielding force to the pump adjusting mechanism opposing the pressure compensator. A load sensing valve senses the pressure of the load to which fluid is supplied from the pump through a system valve and applies this load pressure to work in unison with the spring biased piston for purposes of urging the pump towards its maximum displacement.

Abstract: A pressure compensated hydraulic valve (2) is provided with a housing (4) having a reciprocal spool (6) for communicating hydraulic fluid to work ports (8,10). Pressure compensating means (58) is provided in the same housing with the valve and senses work port pressure by hydraulic fluid flow through the spool from the work port and creates a substantially fixed differential pressure across the spool by controlling the pressure after the flow has passed through the spool.

Abstract: A vibration roller comprises a power limiting device (20) engaging the travelling lever (3), the vibration roller having a prime mover (1), a hydrostatic pump for the travelling drive, which hydrostatic pump is driven by the prime mover and arranged to be controlled by a travelling lever (3), and a vibration drive driven by the prime mover. The power limiting device comprises a stepped piston (27) slidingly movable in a stepped bore (24). The fluid pressure in the travelling drive and in the vibration drive engage the steps thereof. The stepped piston (27) is movable into the setting range of the travelling lever (3), by the sum of the fluid pressures, such that the maximum deflection of the travelling lever is limited to values, at which the total power consumption of the vibration roller does not exceed the limiting power of the prime mover.

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: A hydrostatic drive with a pump is provided having a delivery line coming from the latter, to which at least one consumer is connected through a branch line, and an adjustable restrictor in the branch line, where the adjusting element of the restrictor is loaded on one side by an arbitrarily regulatable pressure, the improvement comprising means whereby the adjusting element of the restrictor is loaded on the other side by the pressure in the branch line between the restrictor and the consumer.

Abstract: A hydraulic system comprises an accummulator for supplying hydraulic fluid to a load, a variable displacement pump for charging the accummulator and a valve means for adjusting the pump to deliver a high pressure for charging the accummulator and then to a low pressure when the load is supplied with fluid from the accummulator. By this operation, in which the pump is switched between the zero stroke positions of high and low pressure, the losses of the pump are decreased and the lifetime is increased.

Abstract: An improved power steering system for vehicles is utilized in association with a variable discharge pump for supplying pressure fluid to one of both cylinder chambers divided by a piston of a power cylinder, selectively. The power steering system includes a variable throttle provided in a fluid supplying passage between the pump and the cylinder chamber. Upon rotation of a steering shaft, an adjusting member adjusts a cross sectional area of the variable throttle in accordance with the variable steering torque. The power steering system also includes a discharge quantity controller for controlling a discharge quantity of the pressure fluid of the pump so that a pressure differential between up and downstreams of the variable throttle is constant. The discharge quantity of the pressure fluid of the pump is changed to be suitable to the any variable steering torque.

Abstract: A composite hydraulic system for a work vehicle which has two separate hydraulic circuits. Included in the composite system are three pumps, two of which supply the two circuits on the vehicle. A third pump transfers hydraulic fluid between the two hydraulic circuits. An engine operates all three pumps simultaneously and means are provided whereby the third pump under certain conditions operates as a motor to provide regeneration.

Abstract: The invention relates to a hydraulic system of the type in which a pump unit supplies pressurized fluid to a plurality of bidirectional servomotors. The system includes at least two modules each of which includes a bidirectional servomotor, a control valve and a compensating valve on the upstream side of the control valve. The pump unit includes a feedback loop having a throttle and a pump pressure regulator in series. Each of the modules has a sensing conduit connected to a common header which is operable to sense load pressure at the upstream side of the control valve for controlling the compensating valve in accordance with the load pressure. A pressure divider comparator valve is connected to the header and a point in the feedback loop between the throttle and the pump pressure regulator. The comparator valve is operable to compare the pressure at such point with the pressure in the header and to bleed pressurized fluid from that point to the tank to equalize the pressures.

Abstract: A fluid operated pump displacement control system is provided wherein a self pressure is defined as a first control signal, and characterized in that an arbitrary switchable second control signal different from the first control signal is added to the first control signal, and a displacement is adapted to be switched to a displacement corresponding to a value of the second control signal as added to the first control signal. Further, a fluid operated pump displacement control system is provided comprising a control circuit connected to respective displacement control devices of variable displacement pumps and adapted to be operated by discharge pressure fluid from a discrete control pump.

Abstract: An output control apparatus for a hydrostatic drive in open circuit is described which has a device for regulating the delivery of the hydraulic pump. In addition to conventional output control by way of an output valve, the arrangement of an additional control piston which acts on the spool of the output valve provides the possiblity of adjusting the delivery as a function of the restoring pressure of a load during its working movement in a return direction, with reduced power consumption.

Abstract: A pressure-compensating hydraulic system is disclosed for preventing unauthorized use of an associated material handling implement. The system includes a variable displacement hydraulic fluid pump, and a load-sensing pressure-compensator for varying the output of the pump responsively to the pressurized fluid demands of the system. In order to prevent unauthorized use of the associated implement, the invention contemplates the provision of an override mechanism for negating the demand-responsive characteristics of the system. In this manner, a movable member of the implement, such as one of its stabilizers or its loader bucket, is positioned so as to immobilize the implement, with the member thus maintained in this position since the system will not respond to the demand for pressurized fluid to move the member from this immobilizing condition.

Abstract: A multi-function valve usable in a hydrostatic transmission and having valve components mounted in a single valve body to provide pressure limiter and high pressure relief functions and with the structure also providing a bypass function and for supply of makeup fluid to the hydrostatic transmission. The multi-function valve has a charge check valve member and a relief valve member in associated relation and movable upon the occurrence of a predetermined pressure differential thereacross to perform control functions. One pressure differential results from a flow through an orifice and with the flow being controlled by a poppet valve member normally held closed by a heavy spring which establishes a system pressure at which the pressure limiter function will occur. With this structure, the pressure limiter function occurs in advance of the high pressure relief function and under the control of a single heavy spring.

Abstract: A control system for a variable displacement pump or pumps driven by a vehicular engine for supplying pressurized fluid to implement actuators via implement control valves. Included is a servomechanism comprising a servoactuator section coupled to each variable displacement pump for varying the per cycle displacement thereof, a servovalve section for operating the servoactuator section by fluid pressure from a fixed displacement pump, and a control section for actuating the servovalve section. The servomechanism control section has a control piston displaced by variable fluid pressures from the variable displacement pumps against the effect of at least two springs. The springs are so arranged that their spring constant changes as the control piston travels to a predetermined position intermediate the opposite extreme positions thereof, in order to make possible the constant torque control of each variable displacement pump for the effective use of the engine output horsepower.

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, a pump for supplying fluid to said actuator, a pilot operated meter-in valve to which the fluid form the pump is supplied for controlling the direction of movement of the actuator, and pilot operated meter-out valves associated with each opening of the actuator for controlling the flow out of said actuator. The pressure of fluid being supplied to the actuator by the meter-in valve is sensed and caused to produce a force opposing the movement of the meter-out valve controlling flow from the actuator.

Abstract: A control system for a variable displacement pump or pumps driven by a vehicular engine for supplying pressurized fluid to implement actuators via implement control valves. The engine has several output conditions each with a different output torque characteristic. The control system includes a servomechanism comprising a servoactuator section coupled to the pump for varying the per cycle displacement thereof, a servovalve section for operating the servoactuator section by fluid pressure from a fixed displacement pump, and a control section for actuating the servovalve section. The servomechanism control section is fluid operated from a torque control valve, which delivers a controlled degree of fluid pressure from the fixed displacement pump to the control section in order to correspondingly vary the torque requirement of the variable displacement pump.

Abstract: The invention relates to a supply circuit supplying two pressure-using members in parallel, by means of a power-regulated variable displacement pump. Manipulators, associated to the distributors controlling said pressure-using members are fed with a fluid whose pressure can vary as a function of the speed driving the pump and are of a potentiometric type. The invention finds an application in the supply circuit of a hydraulic shovel.

Abstract: An apparatus for use in controlling a variable displacement pump in a hydrostatic transmission comprises servo-positioning means for varying the displacement of the variable displacement pump, signal producing means for producing a first signal dependent on the rotational speed of the input shaft of the variable displacement pump and means communicating the first signal dependent on the rotational speed of the input shaft to the servo-positioning means to increase or decrease the displacement of the variable displacement pump as the rotational speed of the input shaft increases or decreases. A second signal dependent on the output pressure of the variable displacement pump is communicated to the servo-positioning means to act in opposition to the first signal to tend to reduce or increase the displacement of the variable displacement pump.

Abstract: A pump control assembly (16) controls the displacement of a pump (11) and provides a standby pressure (87) that is greater than the difference (96) between the load pressure and the pump discharge pressure. A valve mechanism (38) provides a predetermined pressure signal to a valve member (23) for adding a force to the valve member to provide a control signal to an actuating member (17) which adjusts the pump's flow and pressure to a standby condition. The pump control assembly provides a more precise control of the standby position while eliminating large, bulky springs.

Abstract: A hydraulic drive system and a bicycle having such system as its drive train, the system including a pump, preferably a vane pump, operably connected to the bicycle pedal crank, the pump delivering pressurized fluid to a hydraulic motor operably connected to the wheel or mechanism to be driven, e.g., the bicycle drive wheel. The pump has an impeller eccentrically disposed in a housing, and a piston-cylinder mechanism is provided to change the eccentricity of the pump impeller with respect to the pump housing as a function of hydraulic system pressure, to thereby maintain a constant input force, e.g., pedal pressure, and rotation rate, for a wide range of speeds. The motor also has an impeller eccentrically disposed in a housing, and a spacer bar connected between the pump and motor housings automatically adjusts the motor impeller eccentricity with changes in the pump impeller eccentricity, thereby further maintaining constant pedal pressure and rotation rate for a wide range of speeds.

Abstract: Control for a continuously adjustable drive, equipped with a signal transmitter arbitrarily actuatable by a manipulation element, in which the conversion setting imposed on the drive is influenced by the position of the manipulation element, in which case an additional r.p.m.-dependent signal is superimposed on the signal emitted by the signal transmitter, at least at excessively small drive r.p.m.'s, where the arbitrarily adjustable signal transmitter preferably is a pressure-regulating valve to which the pressure impounded in front of a restrictor in the delivery line of a constant pump is fed.

Abstract: An electrohydraulic control system which includes first and second electrically controlled fully variable hydraulic pumps adapted to be driven by the vehicle engine. In the specific embodiment of the invention herein disclosed, the first pump is coupled to the steering and braking control valves, and the second pump is coupled to the bucket and hoist control valves. An electrically controlled poppet valve selectively interconnects the respective pump outputs. Operator-responsive controllers, namely a bucket/hoist joy-stick controller, a vehicle propulsion controller and a steering controller, provide associated electrical signals as respective functions of operator demand. Electrically operated valves control application of hydraulic fluid to the bucket and hoist drive mechanisms, and pressure and position sensors are connected to such valves and actuating mechanisms.

Abstract: The present invention provides an improved control system for a driven cable reel mounted on a vehicle wherein the reel is adapted to pay-in and pay-out electrical cable to supply power to the vehicle, such as a mine car. The control system modifies the torque supplied by the reel drive so as to maintain a relatively constant tension on the cable. The improved control system has a first or basic output which provides higher torque when the reel is paying in cable and provides lower torque when the reel is paying out cable, the difference in drive torque being necessary to compensate for the reversal of frictional characteristics during paying in and paying out of the cable. The control system further provides a transient condition output signal to modulate the drive of the cable reel in a manner which compensates for acceleration and deceleration of the cable reel to reduce cable slack and prevent a sudden increase in cable tension which could cause cable breakage.

Abstract: A control system for a hydrostatic power transmission having a variable displacement hydraulic pump (2) and a hydraulic actuator (3) connected in a closed or semi-closed circuit, wherein the displacement of the pump or the delivery thereby is adjustable in accordance with a manipulated variable of an operating lever (13). A control unit of the system (16) is operative to calculate a hydraulic pump displacement command (X) on the basis of a manipulated variable signal (X.sub.

Abstract: A control device for a hydrostatic transmission including apparatus for sensing a speed of a prime mover which powers a variable displacement pump of the hydrostatic transmission and for regulating the displacement of the variable displacement pump in accordance with the speed of the prime mover, is disclosed. The control device also includes apparatus for transmitting a mechanical feedback signal representative of the displacement of the variable displacement pump to the control device to maintain the variable displacement pump at a displacement proportional to the speed of the prime mover.

Abstract: A fluid flow control system has a capability of operating selectively in a power matching mode, in which power consumption is low, and a maximum flow mode in which high responsivity and high speed features can be appreciated. For this purpose, a mode selector valve is used to switch the system between these two modes.

Abstract: A variable displacement rotary piston pump has a rotor splined to a driven shaft, a plurality of radially directed cylinders, each having a slidable piston fitted therein, a pumping ring surrounding the rotor and mounted eccentrically of the axis of the rotor with which the pistons maintain contact and are caused to move within the cylinders, a piston return ring engageable with notches formed on the pistons and an eccentric mounted for rotation to which the pumping ring is secured having an actuator pin whose movement determines the position of the pumping ring with respect to the rotor, thereby regulating the flow rate of the pump. The pump destrokes above the idle speed of the engine from which it is driven and limits the flow rate of the pump. A venturi orifice establishes a differential pressure which is applied across a flow control valve, which directs hydraulic fluid at discharge pressure to one or the other of two control pistons thereby adjusting the eccentric position.

Abstract: A variable displacement pump has a swashplate controlled by a pair of pistons. A shuttle valve communicates the highest pressure pump workport to an operator-controlled displacement control valve. A pressure-responsive override valve is connected in series between the displacement control valve and the pistons. When an override pressure is achieved, the override valve blocks communication of the control valve with the pair of pistons and communicates the pump workports directly to the pistons for rapid destroking.

Abstract: A power regulation device for a hydraulic pump includes a slidable piston having a first end face with a first diameter and a second, opposite end face with a smaller diameter, the second end face being biased by operating fluid pressure from the hydraulic pump and the first end face being biased by an adjustable fluid pressure for controlling the operation of the hydraulic pump; a compression spring which biases the piston in a direction against that of the adjustable fluid pressure; a measuring spring, one end of which biases the piston in the same direction as the compression spring; a power valve having a control slider member which is biased in one direction by the other end of the measuring spring and by the operating fluid pressure from the pump and in the opposite direction by a compression spring, the control slider member including a transverse channel for supplying the adjustable fluid pressure to the first end face of the piston during idling and normal operations and for connecting the adjustable

Abstract: A control system has two fixed-displacement pumps for supplying pressurized fluid to a pair of steering cylinders via a steering valve and to a pair of implement cylinders via an implement valve. Connected next to the pumps is a demand valve which is pilot operated to deliver to the steering cylinder pair the pressurized fluid from only one pump upon slight displacement of the steering valve and the pressurized fluid from both pumps upon greater displacement of the steering valve. The demand valve is further pilot operated to deliver to the implement cylinder pair the pressurized fluid from only one pump when the implement valve is actuated in a direction to lower the implement assembly, and the pressurized fluid from both pumps when the implement valve is actuated in a direction to raise the implement assembly.

Abstract: A variable displacement pump has a swashplate controlled by a pair of pistons. A shuttle valve communicates the highest pressure pump workport to an operator-controlled displacement control valve. A pressure-responsive override valve is connected in series between the displacement control valve and the pistons. When an override pressure is achieved, the override valve blocks communication of the control valve with the pair of pistons and communicates the pump workports directly to the pistons for rapid destroking. A neutral bypass valve is formed out of a sleeve of the displacement control valve to bypass control pressure to sump when the displacement control valve is in neutral. A pressure-reducing valve limits the pressure acting on the stroke control valve to limit response rates and reduce erosion. The override valve includes orifices which, in intermediate positions, provide flow rate control of the fluid flow to the swashplate control pistons.

Abstract: A valve assembly (16) for use in a fluid system (10) includes a flow control valve (82) which controls fluid flow between a fluid inlet port (34) and a fluid supply passage (36) in response to the load requirements. A main control spool (96) is selectively movable between a neutral position and first and second actuated positions. A load sensing passage (78) communicates a load signal from an actuator (26) to the spring chamber (50) of the flow control valve (82). A drain passage (80) communicates the load sensing passage (78) with the reservoir (14) when the main control spool (96) is in the neutral position. A blocking mechanism (138) blocks the load sensing passage (78) when the main control spool (96) is in the neutral position and opens one of the inlet port (34) and the supply passage (36) to the spring chamber (50) so that the flow control spool (82) is held in an open position.

Abstract: A pressure limiter for a variable displacement pump of a hydrostatic transmission and which is remotely variable and operable to reduce pump stroke when a system pressure limit is exceeded to limit torque applied to an output shaft of the transmission. The pressure limiter has a valve with a valve member which senses system pressure and when system pressure exceeds a certain value the valve member operates to direct system pressure to a servo cylinder for the variable displacement pump to move the swashplate of the pump in a destroking direction. The pressure limiter valve has a spring acting on the valve member in a direction opposite to the force of system pressure and a piston is associated with the spring. A remotely set variable control pressure can be applied to the piston to vary the effective force of the spring and value of system pressure at which the pressure limiter valve will open to destroke the pump.

Abstract: A circuit pressure control system for a hydrostatic power transmission having a variable-displacement hydraulic pump driven by a prime mover, a hydraulic actuator for actuating a load and a displacement adjusting mechanism for the hydraulic pump. The hydraulic pump and actuator are connected together in closed or semi-closed circuit, and the displacement adjusting mechanism is actuated by a signal indicative of the operating lever manipulated variable and a signal indicative of the actual displacement of the hydraulic pump to control the speed of the hydraulic actuator.