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: The invention relates to a pump assembly having a pump with reversible and adjustable controls, the pump controls having a neutral nonflow position and varying positions in opposite directions for effecting corresponding varying rates of flow in the opposite directions. The pump controls include a control valve for the adjusting function which is cooperable with resetting apparatus.

Abstract: The present invention is directed to a power control for an automatic transmission which consists of two valves, the first of which is a characteristic valve providing a pressure differential linearly proportional to an input speed signal provided by a prime mover driven fixed displacement pump, and a second valve which is modulated by the pressure differential generated by the first valve and by a pressure feedback proportional to the torque transmitted by the transmission. The power control provides a series of linear control curves proportional to input speed and is useful as either an automotive type control or an anti-stall control, or a combination of both.

Abstract: An electric motor driven inline hydraulic apparatus comprises a common housing, a stationary shaft mounted in said housing and spaced pump cylinder block subassemblies that rotate around and are mounted on said shaft. Each subassembly includes a cylinder block and a plurality of circumferentially spaced pistons. The cylinder block subassemblies are positioned such that the pistons of one subassembly extend toward the other subassembly. A common yoke plate is mounted between the two cylinder blocks and bears the two groups of piston shoes, one on each of its two bearing surfaces. Each cylinder block is driven independent of and in direction opposite to the other by an electric motor integrally mounted such that its hollow rotor houses the block and drives it. All components described above are contained in one housing and operate submerged in hydraulic fluid.

Abstract: A control apparatus for a variable displacement pump includes a variable displacement pump having an inlet port and a discharge port driven by an external engine. A piston assembly is provided for varying the amount of displacement of the pump. The control apparatus further includes a switching valve for switching operational fluid which is to be applied to and operates the piston assembly, an additional pump a control pressure a magnitude of which is proportional to the rotational speed of the external engine, a balance piston for transducing the control pressure from the additional pump into a force and for applying the force to one end of the switching valve. A discharge line is provided connecting the discharge port of the variable displacement pump with an external load, and a pilot line is branched off from the discharge line into the switching valve for applying a pressure in the discharge line to the other end of the switching valve.

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: A power control device for an adjustable hydrostatic pump with a lever controlling a control valve piston and a pressure measuring piston loaded with feed pressure acting on said lever to control the pressure feed to a servo piston is provided wherein the pressure measuring piston loaded with feed pressure is mounted in a structural member slidable with the servo piston and slides lengthwise of the lever and the control valve piston is biased by resilient member toward the pressure measuring piston.

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: In a free piston type oscillating compressor, closed spaces separate from gas springs are provided, and pressures of the closed spaces are regulated, whereby the amplitude, and central position of the stroke, of a free piston can be precisely controlled.

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 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: Disclosed herein is a device for controlling displacement of a variable displacement hydraulic pump comprising a displacement control system for receiving a discharge pressure of the variable displacement hydraulic pump and a discharge pressure of a fixed displacement hydraulic pump to control the displacement of the variable displacement hydraulic 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: A control system for a hydraulic circuit having at least first and second hydraulic pumps of the variable displacement type, a first hydraulic actuator arranged for hydraulic connection with the first pump through first valve to be driven thereby, and a second hydraulic actuator arranged for selective hydraulic connection with said first and second pumps through second and third valve respectively to be driven thereby.

Abstract: A multiple displacement motor driven power drive unit having two separate hydraulic systems each with a variable displacement hydraulic motor having its output connected to a torque summing gear train. A control provides for operation of one or the other of the motors at full displacement while the other motor is at zero displacement and free-wheels. There is a manual mechanical control operation with both motors simultaneously set at one-half of full displacement and driving the torque summing gear train. The change in motor displacements to one-half full displacement accomplishes velocity summing within the hydraulics. The multiple displacement motor driven power drive unit accomplishes the power efficiency of a multiple motor driven power drive unit utilizing a speed summing gear train with fixed displacement motors, but without the complexities associated with the use of a speed summing gear train and brakes.

Abstract: There is disclosed a hydraulic circuit system for use in a swivel type excavator. The circuit system having a plurality of variable displacement pumps for supplying pressurized fluid for manipulations of work implements and swivel means of the excavator, and control means operative to automatically adjust pump displacement to the output hosepower of a prime mover driving the pumps. The control means includes hydraulic pressure detector means, servo-control means respectively provided in the pumps, negative control valves for respectively controlling the servo-control means by the action of the pressure detector means, cut off valves respectively connected in series with the negative control valves, and summing valves respectively connected in series with some of the cut off valves so as to control pressurized fluid to be supplied into the servo-control means by the action of the fluid pressure delivered from the pumps.

Abstract: A control and regulating arrangement for an adjustable hydrostatic unit is provided in which the regulating device has an auxiliary control constant pump in the feed line of which there is a restrictor, in which case the pressure retained in front of the latter acts on a pressure chamber in which a regulating piston capable of sliding against the force of a spring and which influences the position of a regulating piston connected with the final control element of the hydrostatic unit and capable of sliding in a regulating cylinder is capable of sliding, characterized in that the unit is a hydrostatic motor and the auxiliary control pump is connected to its output shaft.

Abstract: A power regulating device for a hydrostatic pump with at least one pressure-loaded piston which adjusts a stroke-varying member and is controlled by a valve with two springs acting upon one side of the valve and a gauge piston loaded by the delivery pressure and a lever through which a force proportional to the delivery pressure acts upon the other side of the valve, is provided with an additional spring which acts upon the gauge piston via an intermediate member in the same direction in which the delivery pressure acts, and with a second pressure medium source arranged to act with a variable control pressure upon the intermediate member against the additional spring.

Abstract: A civil machine having a flow-rate controller which applies a preset signal instead of a normal flow-rate signal to a variable type hydraulic pump when delivery pressure of the hydraulic pump exceeds a preset pressure value. The normal flow-rate signal corresponds to the position of an operating lever. The preset signal has a value of minimum flow rate to hold a working tool in a certain posture. With this control system, pressure loss and temperature rise in hydraulic operating oil as well as fuel consumption of the machine can be reduced and cycle time of the work can be improved.

Abstract: The present invention relates to a reciprocating pump in which a plunger is reciprocated by means of a crankshaft, a connecting rod and a crosshead. The reciprocating pump further includes cushioning means which is disposed between the crosshead and the plunger and capable of adjusting its cushioning force and absorbing the plunger stroke, whereby the delivery pressure is adjustable through adjustment of the cushioning force of the cushioning means and the delivery volume or rate is also adjustable through absorption of the plunger stroke by the cushioning means.

Abstract: A pump displacement control valve alternately connects charge pressure and pump output high pressure to the displacement control chamber of a variable displacement pump and includes a check valve which prevents high pressure fluid from entering the charging circuit.

Abstract: A control system for variable displacement hydraulic pumps for use in a hydraulically operated construction vehicle having a fixed displacement hydraulic pump, a plurality of reducing valves operatively interlocked with work implement control valve units of the vehicle disposed on the delivery sides of the variable displacement pumps, control sections for controlling respective flow rate of the variable displacement pumps and equipment for exerting delivery pressures of both the fixed and variable displacement pumps and output pressure of the reducing valve on the control units. The control system exhibits three control functions, i.e., flow control for varying the angle of the swash plate of the variable displacement pump in proportion to the manipulating position of the respective work implement controlling valve, constant torque control in proportion to the delivery pressures of the variable displacement pumps, and cut-off control for reducing relief losses.

Abstract: A hydrostatic drive system includes a hydraulic motor driven by a variable displacement axial piston pump with alternative intake and output ports. A charge pump generates a charge pressure which is communicated only to the pump intake port via a charge valve unit. The pump displacement is controlled by a swashplate which is moved by servo pistons which receive fluid from a displacement control valve. A three check valve unit communicates the higher of pump intake, outlet and charge fluid pressures to an inlet of the displacement control valve.

Abstract: A pressure compensated pump which supplies fluid to a common header has an automatic pressure compensator adjustment mechanism which adjusts the pressure setting of the pressure compensator in response to changes in the displacement of the pump, such that the compensator pressure setting of the pump is reduced when the displacement of the pump increases to increase pump flow and the pressure setting is increased when the displacement of the pump decreases to reduce pump flow.

Abstract: The invention concerns a system for successively producing fluid flows at staggered values. This system includes for example an epicycloidal differential of which a shaft is coupled to an engine, and the other two shafts to two pumps respectively producing the maximum necessary flow and producing the minimum flow; to each pump is connected a brake; when the circuit, for example a jack, fed by this system becomes saturated, the pressure of the fluid sent by the high flow pump increases and reaches a threshold detected by a pressure detector-switch, the latter applies the brake which stops the pump and releases the brake of the other pump. The invention is applicable for example to feeding hydraulic jacks, in particular for turboshaft engines.

Abstract: A regulating device is provided for an aggregate of several pumps driven by a primary source at least one of which is adjustable and with a constant volume auxiliary control pressure pump driven by the same primary source in the delivery line of which a restrictor is located with the pressure gradient in front of and following the restrictor acting on the control pressures of an hydraulically regulated discharge valve in a drain line connected to the delivery line of the auxiliary pump, the drain line being connected in front of the restrictor, adjusting means connected to each adjustable pump and a control pressure line to which all adjusting means are connected, branching off from the drain line ahead of the discharge valve.

Abstract: A control means for a variable displacement pump (12) driven by an engine (10) and having a servo-cylinder (78) determining the displacement of the variable pump (12). A charge pump (14) is driven by the engine (10) and supplies charge pressure to the variable pump (12) through an orifice (40). Pilot conduits (42,44) on each side of the orifice (40) sense the pressure drop due to flow and relay the resulting signals to each end of a metering spool (52) in a speed control valve (46), which is arranged to control the pressure in the servo-cylinder (78). A spring (90) biases the servo-cylinder (78) toward an extreme position for the variable pump (12) and opposes the pressure directed to the servo-cylinder (78) by the speed valve (46) in order to provide a smooth transition between the extreme positions for pump displacement.

Abstract: A variable speed engine (10) drives a tractive effort drive train (12) and fixed and variable displacement pumps, (14 and 16) arranged to supply fluid pressure to a hydraulic work system (24). The displacement of the variable pump (16) is determined by a control ram (42) and a conduit (44, 53, 74) interconnects the variable pump output and the control ram (42). An engine speed control valve (60) and a system pressure compensator valve (46) interposed in series in said conduit (44, 53, 74). The two valves (60 and 46) maintain the variable pump (16) at full output except when low engine speed and high system pressure exists simultaneously.

Abstract: Flow-pressure compensated valves are employed in servo-systems for variable displacement pumps to maintain discharge pressure above a minimum pressure level and above the load pressure in a fluid actuator, during the working range of the pumps. In addition, such systems may also include a horsepower limiting valve for ensuring that the rating or predetermined range of horsepower consumption of the pumps is not exceeded. Prior art systems normally continually bleed-off pump discharge or load pressure signals when such horsepower requirements are exceeded to, thus, effect an undesirable horsepower loss in the system. In addition, control systems of this type normally cannot be packaged in modular form and are not adapted for use with pumps of various capacities and sizes. The improved fluid circuit (10) of this invention includes a horsepower limiting arrangement (39) for blocking communication of an actuator pressure signal (P.sub.

Abstract: A hydraulic system comprising a full flow supercharged variable displacement pump and a fixed displacement charge pump adapted to be driven by the same prime mover as the variable displacement pump for supplying fluid to the variable displacement pump. An orifice is provided in the supply line to the variable displacement pump, a circuit is provided from a point downstream of the orifice to tank pressure, and a feedback valve is provided in series with the circuit. The feedback valve comprises a pair of mutually and oppositely adjustable flow restrictions in series with said circuit. The restrictions are connected to the displacement varying means to vary them equally and oppositely in proportion to the movements of the displacement varying means.

Abstract: A hydraulic system for a vehicle having an engine (10) governed to run within a predetermined speed range; the engine (10) arranged to drive a motive power train (11), a charge pump (14), a variable displacement pump (12) and a fixed displacement pump (15). The variable and fixed pumps (12 and 15) are arranged to supply hydraulic fluid pressure to a work circuit (26). A flow signal is created by passing the output from the charge pump (14) through an orifice (40), which signal is routed to a speed valve (46) which directs fluid to a control ram (78) to reduce the displacement of the pump (15) during a predetermined intermediate portion of said speed range.

Abstract: An improved fuel supply apparatus includes a booster pump assembly which is disposed in a fuel tank of an aircraft and is operable to supply fuel to an engine. The rate at which fuel is supplied by the booster pump assembly varies with variations in the demand for fuel by the engine. The booster pump assembly includes a pump having a small volumetric discharge capacity and a second pump having a large volumetric discharge capacity. An electric motor is provided to continuously drive the small pump. A fluid coupling is engaged to connect the large pump with the motor when the discharge pressure from the small pump decreases in response to an increase in demand for fuel by the engine. To engage the fluid coupling, a control assembly directs a flow of fuel to a space between input and output elements of the coupling. When the output pressure from the small pump increases due to a decrease in demand for fuel by the engine, the fluid coupling is drained to disconnect the large pump from the motor.

Abstract: A multi-stage fluid compressor has an input and an output line and variable volume cylinders. A plurality of actuators change the volumes of the cylinders in accordance with control signal. Sensors sense the pressure of fluid entering each stage and provide signals representative of the sensed pressures. Another sensor senses the pressure of the discharge fluid and provides a corresponding signal. A circuit connected to the actuators and to the sensors provides the control signals to the actuators in accordance with the pressure signals from the pressure sensors.

Abstract: According to the invention, there is provided a power control system designed to effectively utilize the output power of an engine with the aid of a simple tilt control device, even if any of the pumps are operated under a no load condition. The control system comprises a pressure selector valve with the output pressures of two variable volume pumps of the same capacity being fed thereto, the lower output pressure being selected by the selector valve and introduced to a pilot portion of a tilt control of at least one of the other variable volume pumps, the output pressure of which is fed either directly or through another pressure selector valve to a pilot portion of at least one of the variable volume pumps of the same capacity, thereby controlling the power of the multiple pumps.

Abstract: A hydraulic control system for a variable displacement pump, comprising a prime mover for driving the variable displacement pump, a fixed displacement pilot pump driven by the common prime mover, a pressure compensating valve connected to the pilot pump and the variable displacement pump, a cut-off control valve connected to the pressure compensating valve and the variable displacement pump, and a servo booster connected to the cut-off control valve and the pilot pump for controlling the displacement of the variable displacement pump.

Abstract: A hydraulic control system for variable displacement pumps, comprising at least two variable displacement pumps, a prime mover for driving the variable displacement pumps, a fixed displacement pilot pump driven by the common prime mover, a pressure compensating valve comprising a two-stage proportional pressure reducing valve and a negative proportional pressure reducing valve, the pressure compensating valve being connected to the variable displacement pumps and the fixed displacement pilot pump, and at least two servo boosters each being mechanically connected to the respective variable displacement pumps for controlling the displacement therefrom, the servo boosters being connected to the fixed displacement pilot pump and the pressure compensating valve and controlled thereby.

Abstract: Variable displacement pumps are each provided with internal biasing means which adjusts displacement in response to spring forces, discharge pressures and net swivel torque forces in order to limit output pressure and to avoid overtaxing the power output capabilities of the motor which drives the pumps. In a system where a plurality of such pumps each supply a separate fluid-operated device but are driven by a single motor, the internal displacement control means of each pump may be arranged to be responsive in part to the discharge pressure of each other pump. The pumps may operate at different power output levels and if one experiences a relatively heavy load, the displacements of the others also reduce if necessary to avoid exceeding the power limitations of the drive motor from a total system overload.

Abstract: A feeder for apparatus for ejecting a mixture of liquids, e.g. urethane foam, comprises a pair of swash plate proportioning pumps one individual to each of the liquids, e.g. resin and isocyanate, each proportioning pump being fed by a gear pump from a supply of the respective liquid. Seepage along the drive shafts of the isocyanate pumps is continuously removed by bathing them in a recirculating stream of flushing agent. The swash plate and gear pumps and flushing agent pump are all driven by a single motor from a common chain drive. The liquids are heated during passage through separate hoses to a common dispensing head or gun, by immersed coil electric resistance heaters extending lengthwise freely within the hoses. A novel control system is provided for the hose heater circuit, the adequacy of the liquid supply and other operating conditions.

Abstract: Two variable displacement pumps each having a horsepower (or torque) control valve, a pressure limiting valve, and a displacement feedback valve are interconnected to provide fluid flow paths from the high pressure zone of one pump to the low pressure zone of the other pump via the horsepower control valve and the displacement feedback valve of the respective pumps and vice versa. When one pump is utilizing less than one-half of the available engine torque as at deadhead operation or low displacement operation wherein its pressure limiting valve determines the maximum delivery pressure or wherein the pump is in standby operation, its displacement feedback valve will correspondingly increase the back pressure of the horsepower control valve of the other pump so that the latter may utilize the torque deficiency of the former to bring the total torque utilization of both pumps to the engine torque limit.

Abstract: An arrangement for pumping fluids includes at least one variable-output pump and a drive therefor. An auxiliary pump is also driven by the drive and discharges control fluid at a discharge rate which corresponds to the speed of rotation of the drive. A throttle valve is located in a discharge conduit of the auxiliary pump, and the pressure of the control fluid upstream of the throttle valve controls the displacement of a slide valve between two positions thereof in one of which the control slide controls the variable-output pump toward increasing the output thereof, while in the other of such positions the pump is controlled toward a reduced output thereof. In addition to the pressurized fluid, which acts on the control slide with a first force, a spring is provided which acts on the control slide with a second force opposing the first force.

Abstract: A hydraulic pumping arrangement for pumping a liquid to a hydraulic system, which comprises pumping means for pumping the liquid, swash means including a variable swash member which enables the liquid output of the pumping means to be infinitely varied between minimum and maximum, a first piston-and-cylinder arrangement for increasing the position of the swash member to increase the liquid output of the pumping means, a second piston-and-cylinder arrangement for decreasing the position of the swash member to decrease the liquid output of the pumping means, control means for controlling the flow of liquid for the second piston-and-cylinder arrangement, switching means operative to pass liquid from the system to the control means at a first condition in the system and operative to stop liquid from the system passing to the control means at a second condition in the system, and valve means for isolating the pumping arrangement from the system and from a main pump normally supplying liquid to the system, the cont

Abstract: A hydraulic system having at least two pumps including a variable-displacement pump and a constant-displacement pump, both driven from a common prime mover, includes a control-pressure pump operated by the shaft of the prime mover and operating with its input a valve which controls the pressure of a control piston acting upon a spring which bears upon the control member in a direction opposite to its setting piston. A cylinder of the setting piston is connected to the output of the adjustable-displacement pump.

Abstract: A combined summing and underspeed valve including a valve body having a bore, a spool within the bore, an outlet from the bore in the body intermediate the ends of the bore, a pair of spaced inlets in the bore for receiving fluid under pressure to apply force to opposite ends of the spool, at least two additional inlets in the body for receiving fluid under pressure to apply force to one of the ends of the spool, and pistons for isolating fluid from the inlet of the pair applying force to the spool one end from fluid from the additional inlets while applying force to the spool.

Abstract: A hydraulic system for controlling the displacement of a plurality of variable displacement pumps driven by a single prime mover including a source of pilot fluid under pressure including a fixed displacement pump adapted to be driven by the prime mover proportional to the speed thereof, a double-piloted, underspeed valve having an inlet and an outlet, the outlet being adapted to be connected to the variable displacement pumps for controlling displacement thereof, a conduit connecting one of the pilots to the source, an additional conduit, including a flow restricting device, connecting the other of the pilots to the source, and a summing valve having ports adapted to be connected to respective ones of the pumps, a port connected to the second conduit and a port connected to the inlet of the underspeed valve.

Abstract: A hydrostatic transmission is disclosed which includes a pump assembly in which a main pump, a charge pump, and an auxiliary pump are commonly housed and are drivingly connected to a single shaft assembly. An external fluid connection is provided through which fluid is directed from the auxiliary pump to a power take off, and valving is provided to short circuit the auxiliary pump when power is not demanded. Means of controlling the rate of operation of the valve are also provided to prevent excessive pressure rise rates at the outlet of the auxiliary pump upon actuation of the valving.

Abstract: A hydraulic control device for protecting a drive from excess loading conditions includes at least one pump having adjustable members for controlling the quantity of fluid transported by the pump. A pressure-responsive control slide is mounted for movement relative to a housing and is moved towards respective positions, each of which corresponds to a normally loaded condition of the drive by a control pump which generates a pressure force which is indicative of the rpm of the drive at normally loaded conditions. The device further includes an arrangement for securing the control slide when the drive is subjected to loads in excess of the respective normally loaded conditions so that a valve member is permitted to move in response to excess loads relative to the control slide after the latter has been secured in said respective positions by the securing arrangement between switching positions in which the adjustable members are operative to adjust the quantity of fluid being transported by the pump.

Abstract: In a hydraulic system having a plurality of variable displacement pumps driven by a prime mover, each pump has a variable ratio input device connected to a load sensing means. Each variable ratio input device automatically reduces the displacement of its respective pump by the same proportion when the prime mover is overloaded irrespective of the displacement setting of the pump and automatically increases the displacement of its pump by the same proportion up to the set displacement when the prime mover is not overloaded.

Abstract: A hydraulic power system having a plurality of variable displacement pumps for supplying pressurized fluid for manipulation of an implement includes a control system operative to automatically adjust pump displacement to the output horsepower of a prime mover driving the pumps of the system. The control system includes underspeed valve means responsive to a deviation in the speed of the prime mover from a predetermined normal speed and a selectable second speed to transmit a fluid pressure signal to a servocontrol means for adjusting the displacement of the pumps. The control system includes a valve for selectively conditioning the control system to cause the underspeed valve to respond to a deviation of the selected engine speed and an indicator for indicating the conditioning of the control system.

Abstract: In combination with a pump having a variable rate of flow, a device for varying such rate of flow is governed by the pressure generated by the pumps through a variable transmission mechanism the ratio of which depends on the said rate of flow, whereby the power output of the pump can be maintained at a predeterminate value. The device can be used with two pumps for limiting the total power output of both pumps, as being governed by the average of the two pressures.

Abstract: A torque limiting control for a pair of variable displacement hydraulic pumps having displacement varying means and servo means including springs urging each of the displacement varying means to a position for maximum pump displacement and fluid operated means acting in opposition to the springs to shift said displacement varying means for reduction in pump displacement, said control including means for summing the fluid pressures generated by both pumps and controlling the servo means for the two pumps to progressively move the displacement varying means for reduction of pump displacement as the sum of the fluid pressures rises above a predetermined value at a certain pump displacement and thereby limit the sum of the torques required by said pumps.