Abstract: A hydraulic pump unloading system having an engine driving two hydraulic pumps which are connected in parallel to a load-supporting member. An unloading valve is connected in the hydraulic line with one of the two pumps and is shiftable between positions for directing flow to the load and for directing flow to a reservoir, depending upon the pressure and or flow in the hydraulic line. Also, a pressure-compensated flow-control valve is connected in the line with the other pump and, under certain conditions, directs fluid pressure to the unloading valve for setting the unloading valve in either the operative or the unloading position, all depending upon the hydraulic condition at the load-supporting member. Further, either an additional valve or a spring can be effective on the unloading valve for controlling the operative and the unloading position of the unloading valve.

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: A first control valve of a fluid circuit connecting a first pump to a fluid motor has a signal port in communication with an inlet port when the first control valve is at a selected position at which substantially the total output of the first pump is directed to the motor. A valve device connects a second pump to the fluid circuit in response to a valve spool of the first control valve being moved to said selected position. The valve device has a valve member movable between a first position at which the second pump is in communication with a tank and a second position at which the output of the second pump is combined with the output of the first pump in the fluid circuit. A device moves the valve member to the second position in response to the valve spool of the first control valve being moved to said selected position. The device includes first and second actuation devices associated with the first and second ends of the valve member.

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 hydraulic drive circuit for tracked vehicles is provided in the form of two hydrostatic transmissions, one for each track with a control system for one track acting as a master control and the other transmission control following as a slave unit, except as modified by the signal from a manual steering control.

Abstract: A hydrostatic drive system for connecting a prime mover and a hydraulically operable load such as a hydraulic motor connected to the vehicular wheel has a constant-displacement pump and a variable-displacement pump both connected to the prime mover. The variable-displacement pump is completely reversible and is of maximum displacement substantially greater than the constant displacement pump. This variable-displacement pump is permanently connected across the hydraulic motor of the load. A clutch connects the constant-displacement pump to the same shaft as the variable-displacement pump. The outputs of the constant-displacement pump may be connected by a valve either in parallel to the outputs of the variable-displacement pump, or may simply connect them together for operation of the load only by the variable-displacement pump.

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 control system has override for fluid operated work elements served by at least two variable displacement pumps each serving a separate circuit. At least two work elements are served by the first circuit and at least one work element is served by the second circuit. The discharge rate of the first pump is controlled by a signal delivered from a summing valve in response to the pressures of the first and second circuits during operation of a preselected one of the work elements of the first circuit and controlled by a modified pilot pressure signal in response to operation of only the other work element of the first circuit.

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 load sensitive hydraulic circuit for material handling equipment is energized by a prime mover. The hydraulic circuit includes variable displacement pumps coupled to the prime mover and having pressure and flow compensating control means for varying the volumetric output. Each pump is connected to a valve bank which controls various hydraulic actuators of the material handling equipment. Load pressure feedback is provided to the pump compensators for establishing pump flows to operate the actuators at a fixed pressure differential in excess of load pressure. The valve banks contain pressure compensated valves for providing desired fluid flow rates and speeds in the hydraulic actuators. Means are provided to sense reductions in the prime mover speed resulting from excessive hydraulic loads.

Abstract: A hydraulic power system having a plurality of variable displacement pumps for supplying pressurized fluid for manipulation of one or more implements includes control means operative to automatically adjust pump displacement to the output horsepower of a prime mover driving the pumps of a system. The control means includes an underspeed valve responsive to a deviation in the speed of the prime mover from any one of a wide range of selected speeds to transmit a fluid pressure signal to servo control means for adjusting the displacement of the pumps in proportion to engine output. The control means includes an infinitely variable orifice adjustable with throttle movement for adjusting the underspeed valve to respond to a deviation from a wide range of selected engine speeds.

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 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 one or more implements includes control means operative to automatically adjust pump displacement to the output horsepower of a prime mover driving the pumps of the system. The control system includes an underspeed valve responsive to a deviation in the speed of the prime mover from any of a wide range of selected speeds to transmit a fluid pressure signal to servocontrol means for adjusting the displacement of the pumps. The underspeed control means includes an infinitely variable orifice connected by way of lost motion linkage to the engine throttle control for adjusting the underspeed valves to respond to a deviation of an infinite range of engine speeds.

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 pump assembly having at least two variable displacement pumps each having a separate pump control assembly are interconnected for control in response one to the other. Each pump control assembly has first and second biasing means acting on a respective swash plate. The first and second biasing means have interconnecting fluid pathways formed through a pump control housing. Means are provided within the housings for modifying the discharge pressures of the separate pumps to provide a resultant pressure signal for controlling the second biasing means.

Abstract: A fluid system of work elements of a work vehicle has first, second, and third fluid circuits each having a pump connected to a work element through a control valve assembly that is operated by a pilot pump. A fluid control means is provided for controllably combining fluid from each of the circuits with another one of the circuits.

Abstract: Apparatus of a fluid system of a work vehicle for controlling the fluid delivered to work elements of the vehicle in response to the load exerted on the fluid system by the work elements.

Abstract: Two adjustable-stroke pumps are driven off a common drive shaft and supply fluid to respective consumers via respective control valves settable by the user of the system. Each pump is provided with its own pressure regulator operative for regulating the output pressure of the respective pump by automatically adjusting the setting of the stroke-adjustment member of the pump. Transducers generate first signals indicative of the settings of the stroke adjustment members and second signals indicative of the settings of the control valves. A control arrangement maintains the settings of the volume-adjustment members in correspondence with the settings of the control valves by automatically altering the operation of the pressure regulators in response to discrepancies between the settings indicated by the first and second signals.

Abstract: A hydraulic pump arrangement and control circuit for supplying fluid at high volume and a high pressure to a work circuit. The system utilizes a fixed displacement pump, a variable displacement pump, a dual pressure compensator, and an unloading valve working together to provide high pressure fluid delivery while reducing the horsepower requirements of the fixed displacement pump and the variable displacement pump. High flow is provided through the utilization of the combined pumps and high pressure is attained through the unloading of the fixed displacement pump through the unloading valve and destroking of the variable displacement pump in response to signals provided by the dual pressure compensator.

Abstract: A first pump and a second pump have respective mechanical inputs and are operative when the mechanical inputs are driven at constant speed for pumping fluid at an adjustable volumetric flow rate and at a constant non-adjustable volumetric flow rate, respectively, the maximum volumetric flow rate of the first pump being at least as great as that of the second pump. Connecting conduits connect the first pump in hydraulic circuit with an hydraulic consumer. An adjusting mechanism is provided for adjusting the volumetric flow rate of the first pump. A control arrangement is provided for bringing the second pump into and out of hydraulic circuit with the consumer in dependence upon the operation of the adjusting mechanism.

Abstract: A fluid feed device comprising a constant cylinder capacity pump and at least one variable cylinder capacity pump driven from a single prime mover, the variable cylinder capacity pump being provided with a regulator for reducing its cylinder capacity as the feed pressure increases. The regulator is such as to reduce the power absorbed by the variable cylinder capacity pumps as the pressure increases by an amount equal to the increase in the power absorbed by the constant cylinder capacity pump such that the total power absorbed by the pumps remains constant and equal to the power of the prime mover.

Abstract: A hydraulic power system having a plurality of variable displacement pumps for supplying pressurized fluid for manipulation of an implement includes control means operative to automatically adjust pump displacement to the output horsepower of a prime mover driving the pumps of a system. The control system includes underspeed valve means responsive to a deviation in the speed of the prime mover from a predetermined normal speed to transmit a fluid pressure signal to a servo control means for adjusting the displacement of the pumps. The underspeed valve means includes adjusting means for adjusting the underspeed valve to respond to a deviation from other engine speeds different from the normal operating speed.

Abstract: A hydraulic pump arrangement and control circuit for supplying fluid at high volume and high pressure to a work circuit. The system utilizes a fixed displacement pump, a variable displacement pump with a compensator, and a relief valve at a pressure setting higher than the variable displacement pump's compensator setting.

Abstract: A hydraulic backhoe utilizes two pairs of hydraulic pumps to power independent crawler track drives in any forward or reverse direction, and high or low speed ranges; allowing, for example, a wide arc turn either left or right, forward or backward. Through a novel hydraulic circuit, these pumps also power other functions such as boom, bucket and stick drives in high speed or low speed modes. This flexibility is accomplished by the use of a manually controlled track speed selector valve, an unloading valve and check valve between a track function valve and another function valve in each of the two hydraulic circuits. Full hydraulic pressure is available to all functions at all times except when a track drive is in high speed range. Conventional high-low or unloading operation of the other functions is had when the related track drive is not operating.

Abstract: Apparatus for controlling the stroke of the movable member in a high pressure hydraulic machine, such as a hydraulic press, to permit the member to be positioned to an accuracy of 0.0005 inch and held at such position for a preselected time. The movable member is coupled to a piston movable within a cylinder which receives pressurized fluid. An adjustable threaded rod and nut arrangement is movable by movement of the piston within the cylinder, and an extension of the rod carries an actuating device for sequentially operating a first and then second valve. Operation of the first valve greatly reduces the speed of the movable member and operation of the second valve stops the movable member at its exact predetermined position. An adjustable time delay is coupled with the output from the second valve to maintain the movable member at such position for a preselected time thus maintaining the pressure on the article being formed in the machine.

Abstract: A pair of hydraulic motors are operatively drivingly connected to a common rotatable member and are employed for transmitting power thereto from a pair of prime movers. A first hydraulic circuit communicates with one of the hydraulic motors and includes a pump driven by one of the prime movers while a second hydraulic circuit communicates with the other of the hydraulic motors and includes a fixed displacement pump and a variable displacement pump driven by the other prime mover. A device associated with the variable displacement pump is responsive to fluid pressures in the first and second hydraulic circuits for automatically varying the output displacement of the variable displacement pump so that a predetermined relationship is maintained between the fluid pressures in the first and second hydraulic circuit.

Abstract: A hydrostatic transmission control for a hydrostatic transmission having a variable displacement pump and a variable displacement motor including pressure-responsive displacement control means for the pump and motor with a displacement control valve for each of the pump and motor and positionable by a control pressure to set the displacement of the pump or motor with which it is associated. In dual path control of two hydrostatic transmissions, a master circuit has a first valve for setting a control pressure to determine the speed of operation of the transmissions and a second valve for determining the direction of operation of the transmissions, with operation of both valves by a single control handle. The master circuit connects into two branch circuits, each leading to the displacement controls for one of the hydrostatic transmissions and with each branch circuit having its own steering control valve.

Abstract: This gas pressure control system is intended primarily for testing gauges by providing an accurate static gas pressure over a wide range, preferably from zero to 10,000 pounds per square inch. The system is equipped with a pressure intensifier that operates automatically to raise the delivery pressure above the supply pressure when necessary. The supply may be a bottle of nitrogen under pressure of two thousand two hundred pounds per square inch, and the pressure intensifier is preferably a cylinder-and-piston motor-pump combination with a displacement ratio such as 70 to 1.

Abstract: An apparatus and method for operating an auxiliary hydraulic load at low noise levels. A pump having a capacity which is sufficiently large to supply the load with the necessary volume of hydraulic fluid at relatively low pump speeds is driven by an engine operating at a speed near its idling speed. Throttle control means control the fuel supply to the engine at a level sufficient to drive the pump while maintaining the engine speed near its idling speed. When the engine speed is increased to a predetermined level in excess of its idling speed, means are provided to maintain the output from the pump at or below a predetermined flow rate to not overload the pump means or the auxiliary load. The pump may include a variable displacement pump or a plurality of fixed displacement pumps with means to vary the pump output in response to the pressure demand from the auxiliary load to maintain the torque input requirements for the pump below a predetermined level.

Abstract: An apparatus and method for operating an auxiliary hydraulic load at low noise levels. A pump having a capacity which is sufficiently large to supply the load with the necessary volume of hydraulic fluid at relatively low pump speeds is driven by an engine operating at a speed near its idling speed. Throttle control means control the fuel supply to the engine at a level sufficient to drive the pump while maintaining the engine speed near its idling speed. When the engine speed is increased to a predetermined level in excess of its idling speed, means are provided to maintain the output from the pump at or below a predetermined flow rate to not overload the pump means or the auxiliary load. The pump may include a variable displacement pump or a plurality of fixed displacement pumps with means to vary the pump output in response to the pressure demand from the auxiliary load to maintain the torque input requirements for the pump below a predetermined level.

Abstract: A booster for a fluid pressure operated system in which relatively low pressure is used in the system and the booster is designed to be positioned immediately adjacent the fluid operated mechanism so as to eliminate the need for high pressure fittings and components. The booster has a spool which is shiftable in response to pressure build up in the mechanism. The spool acts as a sliding valve to direct fluid flow through a pressure converter such as a turbine or volumetric motor-pump located inside the spool.