Abstract: A first cylinder chamber of a hydraulic cylinder is connected to a pair of variable displacement pumps of which the first one is connected to a reservoir and second one is connected to the second cylinder chamber. This allows to bias the piston by a hydraulic force acting on either side of the piston corresponding to the direction of motion. This is obtained by adjusting the delivery volume of both the pumps such that the volume supplied is larger than the volume drained. Metering the difference of both the delivery volumes results in the desired biasing counter-pressure.

Abstract: A service valve circuit of a hydraulic excavator connected beforehand for use in controlling a special attachment in addition to a prescribed actuator control valve. The service valve circuit comprises a confluence valve 17 for performing electromagnetic proportional flow rate control, disposed in a confluence circuit 16 in communication with the section between inflow circuits 3F and 3R of two variable pumps 2F and 2R, an electrical switch 21 for switching the confluence valve 17 on or off according to a required flow rate and a volume 22 for adjusting the quantity of flow after passing through a confluence valve 17 in a range of flow for a maximum of one to two pumps. Since the requirement of confluence with respect to a required quantity of flow for a special attachment e and the quantity of confluence are set in advance, there will be no excess or shortage of the quantity of confluence.

Abstract: A hydraulic circuit apparatus for use in construction vehicles which is arranged to reduce pressure losses that occur when all the implement operating valves are kept at their neutral positions, to reduce the power consumption by all hydraulic pumps when the hydraulic circuit for implements require only a small amount of pressurized fluid, and to transmit a command signal to unload the surplus pressurized fluid when occasion demands. The circuit comprises a surplus pressurized fluid control circuit (50) to facilitate the regulation of changes in the fluid flow rate when changing over valves. The surplus pressurized fluid control circuit (50) has a pilot actuated type unloading valve (11) provided in a surplus pressurized fluid supply conduit (51) which is connected through a check valve 20 to a hydraulic pump (P.sub.1). The hydraulic pump (P.sub.1) is for the exclusive use of the implement. The conduit (51) is also connected to a drain conduit (Ct).

Abstract: A control system having a flow-dividing selector valve mechanism (52) for changing the channels for causing a pressure fluid to flow from two main pumps (40), (50) into two control valve groups (60), (70) therethrough, and confluent selector valve mechanisms (80), (90) for causing the pressure fluid flowing into each group to flow into a working device control valve of the other group. The confluent selector valve mechanism (80) of the group wherein the working device control valve (62) has a need to compensate for the flow of fluid thereinto cancels the confluence function. The system has a mechanism for restricting the stroke of the spool of a working device control valve (160) to be subjected to varying loads to cause the fluid discharged from the actuator connected thereto to flow into the actuator again when the load is small. A sequence valve (170) operates the spool stroke restricting mechanism (190) by a pilot primary pressure.

Abstract: A hydraulic control circuit adequate to control a main hydraulic actuator and auxiliary hydraulic actuators. The main actuator drives farm machinery mounted to an agricultural tractor or the like. The auxiliary actuators drive farm attachments independent of said farm machinery. At least two hydraulic pumps and at least two sets of control valves are connected in series. The exit of one hydraulic pump is connected with the other hydraulic pump via a check valve. Said one hydraulic pump is connected with a tank via an openable valve upstream of the check valve. The upstream set of control valves is used to control the auxiliary hydraulic actuators needing more flow rate than the downstream set of control valves. The openable valve has an offset valve at its one end to determine the direction of flow. The openable valve is either opened or closed by the pressure admitted from the downstream side of the upstream set of control valves.

Abstract: An actuator system for a control surface of an aircraft having a hydraulic system and a source of actuation system commands. The actuator system includes hydraulic circuits connected to the aircraft hydraulic system and an electrically-powered hydraulic circuit integrated with the actuator. The electrically-powered hydraulic circuit includes an electric motor connected to a hydraulic fluid pump. The pump can be controlled to adapt to the power requirements to actuate the control surface.

Abstract: The use of a pair of small variable displacement hydraulic pumps in a hydraulic system offers some advantages. The output of the two pumps of the known systems is normally not combined, but is selectively combined under a majority of the operating conditions. The subject load sensing hydraulic control system has first and second hydraulic circuits with each circuit having a plurality of pilot operated control valves operatively connected to a variable displacement pump. The output flow of both pumps is normally made available to both hydraulic circuits through a combiner valve so that the output capability of both pumps can be used to satisfy the demand for fluid by a single control valve or by one or more of the control valves from each circuit. A valve arrangement connects the highest load pressure of the control system to both pumps when the output flow thereof is being combined.

Abstract: A charge flow distribution valve routes all charge pump flow into a main pump until the main pump has sufficient inlet pressure. The valve opens to a first stage which routes excess charge flow to lubrication circuits. At a slightly higher main pump inlet pressure, it also routes oil to an inlet of the charge pump.

Abstract: A hydraulic actuator control circuit capable of increasing the flow rate of the working fluid supplied to hydraulic actuators when the load on the hydraulic actuators increases beyond predetermined values includes a first valve group having a plurality of pilot controlled selector valves connected, respectively, to hydraulic actuators, a second valve group having a plurality of pilot controlled selector valves connected, respectively, to lines connecting the hydraulic actuators to the pilot controlled selector valves of the first valve group, two hydraulic pumps connected, respectively, to the first and second valve groups, and a tank for containing working fluid.

Abstract: A pump and regulator valve assembly having multiple pump and multiple regulator valve means that establish pressures of two or more operating pressure levels in a control system wherein the valve means has multiple valves that selectively respond to varying flow demands of the different regions of the control system to connect one or more pumps to reduced pressure regions when the flow demands of higher pressure regions are satisfied.

Abstract: A self-regulating hydraulic control circuit for controlling the flow of fluid to and from the cylinder of a double-acting hydraulic motor employs two pumps, one of which supplies fluid at a relatively high pressure and low displacement while the second pump is a relatively high displacement pump which operates only against a relatively low pressure requirement. The system is especially adapted for applications where, during a working stroke, the piston of the hydraulic motor moves from a start position through a first portion of the stroke during which the piston encounters but a minimal resistance to movement and then suddenly encounters a high resistance to movement. One example of such an application would be a press in which, at some point during the stroke of the piston, a tool carried by the piston initially encountered a workpiece.

Abstract: A hydraulic fluid circuit system is provided for use in a vehicle and having a priority and a second fluid circuit therein. A variable displacement pump is the primary fluid source for the priority circuit, and a fixed displacement pump is the primary fluid source for the second fluid circuit. A demand valve responsive to differential fluid pressure between the priority circuit and the output of the variable displacement pump selectively switches increasing amounts of output from the fixed displacement pump into the priority circuit in proportion to the output of the variable displacement pump. The demand valve includes a three positioned spool valve. The priority circuit may include a hydraulic steering system, and the second fluid circuit may include an implement or accessory circuit.

Abstract: A control system for controlling input power to hydraulic pumps of a hydraulic system including a prime mover and a plurality of variable displacement hydraulic pumps driven by said prime mover. The control system comprises: a first computing unit for computing, for each of the hydraulic pumps, an input torque control value concerning a distribution of input torques of said hydraulic pumps from a representative pressure obtained on the basis of a discharge pressure of at least one other hydraulic pumps; a second computing unit for determining an input torque for each of the hydraulic pumps on the basis of a corresponding one of the input torque control values determined by the first computing unit; and a third computing unit for determining an object discharge rate of each of the hydraulic pumps from the input torque obtained by the second computing unit and an own discharge pressure of each of the hydraulic pumps.

Abstract: A vehicle is described having a front pair of ground contacting wheels, a rear pair of ground contacting wheels, an internal combustion engine, hydraulic motors for driving each said ground contacting wheel, and a plurality of variable flow hydraulic pumps for driving the hydraulic motors. In such a vehicle the internal combustion engine (7) is arranged to drive directly first and second variable displacement pumps (12, 13) for driving the motors (46, 47) of the front pair of wheels (2) and the motors (47, 48) of the back pair of wheels (3) respectively as well as first and second boost pumps (14, 15), while a control valve (22) is supplied with hydraulic fluid from one of the boost pumps (14) and is arranged to give an output hydraulic pressure which is dependent on the speed of the engine (7).

Abstract: A hydraulic pressure system comprising a hydraulic pump, a hydraulic motor, a pair of main hydraulic pressure lines connecting the pump and the motor so as to form a closed loop or circuit, a booster line for supplying a hydraulic pressure from a booster pump to the low pressure side of the closed circuit, a pilot line for taking out a pilot pressure from the high pressure side of the circuit to operate an actuator for controlling the hydraulic pump and the hydraulic motor, and a boost pressure regulator for causing the pressure in the booster line to rise only when the differential pressure between the two main hydraulic pressure lines of the closed circuit becomes lower than a predetermined level.

Abstract: A power steering system for motor vehicles includes a two chamber piston and cylinder actuator connected to an output member output member of the steering system and first and second sources of fluid pressure having different absolute pressures p1 and p2, respectively, wherein p2 is greater than p1. A regulating valve is connected between the sources and the actuator for controlling the pressure medium sources to each chamber of the actuator in response to torque applied to an input element of the steering system. An additional pump is connected between at least one of the sources and the actuator for increasing the pressure difference in the actuator when appropriate. The fluid utilized is air, and the system normally operates without the use of the additional pump using only the pressure jump p2-p1 between the first and second sources.

Abstract: A control for a power drive assembly having a primary energy source, a hydrostatic pump driven by the energy source and a consumer of energy has a multiway valve between the pump and consumer and a control pressure dependent valve receiving fluid from the pump controlling its position and connections between a source of pressure fluid and a spring biased operating cylinder connected to a control lever on the primary energy source controlling operation thereof.

Abstract: A hydraulic system for an aircraft to provide improved reserve capability for the thrust reverser power system. There is a fluid reservoir having a vent tube with an inlet location located above the bottom wall of the reservoir. In the event that fluid in the reservoir reaches a predetermined low level, supply and pressure isolation valves isolate at least one pump from the rest of the hydraulic system, and also start that pump operating, with a reserve supply of fluid being available for supplying power for the thrust reverser.

Abstract: A hydraulic system for an aircraft to provide improved reserve capability for the steering and reserve brake power system. There is a fluid reservoir having a vent tube with an inlet location located above the bottom wall of the reservoir. In the event that fluid in the reservoir reaches a predetermined low level, supply and pressure isolation valves isolate at least one pump from the rest of the hydraulic system, with a reserve supply of fluid being available for supplying power for the steering wheel and reserve brakes.

Abstract: A double-staged, rotary pump and a fluid flow control device is disclosed. An inner rotary member is fixed to a rotatable drive shaft. The inner rotary member has n circumferentially spaced radially projecting teeth. An intermediate rotary member having n+1 internal teeth encircles the inner rotary member and is mounted for rotation about an axis eccentrically disposed from the drive shaft axis. The intermediate member has n+1 circumferentially spaced radially projecting teeth. An outer rotary member having n+2 circumferentially spaced internal teeth encircles the intermediate member and is mounted for rotation about an axis coincident with the drive shaft axis. The inner rotary member drivingly engages the intermediate rotary member which in turn drivingly engages the outer rotary member, all members rotating in the same direction.

Abstract: A power assisted steering system of the type which includes a hydraulic reaction mechanism for controlling the hydraulic power assist in accordance with an increase or decrease of the vehicle speed. The system includes primary and secondary hydraulic pumps, the primary pump having the function of applying hydraulic pressure to the power cylinder and the secondary pump having the function of applying hydraulic pressure to the reaction mechanism in proportion to the vehicle speed. The secondary pump is unitedly assembled with the primary pump to be driven by the prime mover, and comprises a first control valve for controlling the quantity of fluid applied to the reaction mechanism for the secondary pump in a constant amount, and a second control valve for controlling the pressure of fluid controlled by the first control valve in accordance with the vehicle speed.

Abstract: A hydraulic apparatus for a vehicle having a propulsion engine comprises a control valve, a flow dividing valve, pumps driven by the engine for delivering fluid to the valves, and steering and implement circuit operatively connected to the control and flow dividing valves. The control valve includes plunger provided with orifices having variable degrees of openings and a spool connected to the plunger and the flow dividing valve includes a spool. With the hydraulic apparatus this constructed, fluid having an amount necessary for operating the steering circuit is always fed thereinto by operatively connecting the spools of the control and flow dividing valves and sharing the fluid into the steering and implement circuit by controlling the fluid dividing valve in accordance with pressure difference between the upstream and downstream portions of the orifices in the control valve.

Abstract: A hydraulic drive system including at least one hydraulic actuator, two variable displacement hydraulic pumps each connected to the hydraulic actuator to form a closed circuit therewith and connected in parallel with each other, two prime movers each driving one of the hydraulic pumps, and directional control valves each arranged between the hydraulic actuators and one of the hydraulic pumps. The directional control valves are each operative to shut, when one of the prime movers associated therewith is shut down, the hydraulic pump connected to the shutdown prime mover off the other hydraulic pump and the hydraulic actuator, to thereby prevent the hydraulic pump from being rotated by the pressure fluid delivered by the other hydraulic pump.

Abstract: In a hydrostatic auxiliary power steering apparatus, a short-circuit passage of a control valve establishes a restricted flow path from a pump pressure line to a reservoir return line in the neutral position of the control valve wherein all other flow paths are blocked. A fixed flow restrictor in the pump pressure line conducts a continuous flow from one of two pumps connected to the pressure line for regulation of the fluid power steering circuit by the pressure drop across the flow restrictor. If one of the pumps is of the variable volume type, the pressure downstream of the flow restrictor is utilized to regulate pump flow adjustment. If fluid under operating pressure is supplied to both the fluid power steering circuit and another fluid operating circuit, a flow dividing valve controlled by the pressure differential across the flow restrictor distributes pressurized fluid between the two fluid circuits.

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: 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 hydraulic system having two pumps, typically driven by two independent prime movers, a primary and secondary reservoir and associated valving to permit the system to run as one system or two independent systems, all for the purpose of redundancy and safety. The system senses fluid level in the primary reservoir and actuates the valves to establish two independent hydraulic systems, each with its own reservoir, when the fluid level drops below a predetermined level. The system is particularly advantageous in twin-engine aircraft where three hydraulic systems are employed, one off of each engine, and the third system uses two pumps, one driven by each engine.

Abstract: A hydrostatic transmission (10) includes a variable displacement pump (12) for driving a fluid motor (14) in first and second directions. First and second high pressure conduits (20,22) connects the pump (12) and motor (14) in a continuous fluid circuit. A control pump (40) supplies make-up fluid to the first and second high pressure conduits (20,22) and simultaneously provides pressurized control fluid to a system control (50) for controlling the operation of the hydrostatic transmission (10). First and second low pressure conduits (24,26) are respectively disposed about the first and second high pressure conduits (20,22) and defines first and second spaces (28,30) therebetween. A pressure control arrangement (32) is connected to the first and second spaces (28,30) to control the maximum pressure level in the spaces (28,30) upon the failure of one of the high pressure conduits (20,22).

Abstract: A working fluid supply system for a hydraulic power booster and a power steering system includes first and second fluid supply pumps, a hydraulic power boosting apparatus, a power steering unit, various fluid passages connecting thereto and a control apparatus. The first pump supplies pressurized working fluid to a first inlet port of the hydraulic power boosting apparatus. The second pump, controlled by the control apparatus, selectively supplies pressurized working fluid to a second inlet port of the power boosting apparatus to render the fluid supply flow rate applied to the power boosting apparatus substantially constant at a predetermined level when the fluid discharge rate of the first pump is less than the predetermined level. By this, a sufficient amount of pressurized working fluid is supplied to the hydraulic power boosting apparatus to fully operate it under all actual engine speeds.

Abstract: Implement and steering actuators are selectively actuated through steering and implement control valves respectively by fluid power output of respective steering and implement pumps. A pressure compensator is provided for at times diverting excess fluid from the steering pump to the implement control valve, and the implement pump applies fluid pressure to the implement valve through an unloading valve that gives the charging of an accumulator by the implement pump preference over operation of the implement actuator. The sensing of loss of fluid power in the steering pump activates an emergency control valve to connect the accumulator to the steering valve and to disconnect the pressure compensator from the implement control valve.

Abstract: A hydraulic fluid feeding device for a power steering device is proposed which has a plurality of pumps for feeding hydraulic fluid to the power steering device and a flow path change-over valve for switching the paths between the pumps and the power steering device, wherein the feeding rate of the hydraulic fluid to the power steering device is controlled by the action of the flow path change-over valve. The flow path change-over valve is operated according to the magnitude of the load exerted on the power steering device so that hydraulic fluid from all the pumps combined is fed to the power steering device when the load is great, and the hydraulic fluid from at least one of the pumps is fed to the power steering device when the load is small. With this device, the control of the feeding rate becomes efficient. It also becomes possible to bypass the hydraulic fluid from some of the pumps to a tank, independently of the delivery rates of the pumps, so that the power consumption may be reduced.

Abstract: The invention is an integrated hydraulic control circuit for actuating the thrust reversers and variable exhaust nozzle on high performance gas turbine engine powered aircraft. The hydraulic circuits for both systems are integrated into a single housing and are served by common elements. The circuit for the deployment and stowage of the thrust reverser buckets is hydraulically sequenced inhibiting the application of hydraulic power to the actuators prior to withdrawal of the locking pin. In a like manner, the thrust reversers must be fully retracted before the locking pin is deployed. The hydraulic circuit for the thrust reversers also includes a pressure compensating circuit which reduces the pressure applied to thrust reverser actuators with the thrust reversers in the stowed position.

Abstract: A load responsive system employing a fixed displacement pump and a variable displacement pump in a parallel circuit as a source of fluid in an open-center load sensing system. The load response control valve includes an unloading spool which is flow responsive in the operative positions of the control valve and maintains a constant .DELTA..rho. across the control valve by dumping the pump flow to reservoir; the control valve .DELTA..rho. being greater than the .DELTA..rho. of the pump compensator means so that the variable displacement pump will remain destroked until the system utilizes the full flow of the fixed displacement pump at which time the variable displacement pump strokes-out upon demand.

Abstract: Conditional exchanging of working fluid between plural fluid circuits (13A, 13B) having separate supply pumps (18A, 18B) is provided for without continuously bleeding fluid from the pump control pressure lines (21A, 21B). Each circuit (13A, 13B) has a pump control (19A, 19B) responsive to a control pressure, a plurality of fluid motors (14A, 15A, 16A, 14B, 15B, 16B), and a group of resolver valves (38A, 38B) which compare motor pressures and intercommunicate the pump control (19A, 19B) with the most highly pressurized motor (14A, 15A, 16A, 14B, 15B, 16B). At times when fluid from one circuit (13A, 13B) is being delivered to a motor (16A, 16B) of another circuit (13A, 13B), the pressure comparing function of the resolver group (38A, 38B) of the one circuit (13A, 13 B) is extended to include the motor (16A, 16B) of the other circuit (13A, 13B). Among other uses, the system (11) may be used on excavator vehicles having plural fluid motors performing a variety of different functions.

Abstract: A system is disclosed for controlling the flow of fluid from a pair of pumps (15,15') to a steering system (11) and a pair of auxiliary load circuits (13,13'). The steering system includes valving (43) defining a variable flow control orifice (45), and the steering system normally operates with a pressure differential X across the variable orifice, and provides load pressure signals (47,49,49',53,53') representative of demand for fluid by the steering system. Fluid flow from the pumps is controlled by a pair of priority flow control valves (21,21') including a pair of valve members (27,27') each of which is biased by a spring (29,29') toward a position permitting flow to the steering system. The spring (29) exerts a biasing force equivalent to the pressure differential X while the spring (29') exerts a biasing force equivalent to a pressure differential Y, which is less than X.

Abstract: The displacement controllers of a first variable displacement pump supplying fluid for hoe and travel functions of an excavator and a second pump supplying fluid for the excavator house swing function are connected to shuttle valves which operate to couple to the controllers the lesser of the power beyond fluid pressures emanating from travel function and swing function control valves. A bypass circuit is arranged to couple power beyond flow from the swing function control valve to join the flow being outputed from the first pump when the pressure of the last-named power beyond flow exceeds the lesser of that emanating from the travel control functions. Lead compensators are provided to make the controllers more responsive to circuit demands and a power limiting valve is provided for automatically connecting pressure for destroking the pumps to relieve engine load when the engine speed falls to a predetermined minimum.

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: 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 hydraulic system having a reservoir fed charge pump supplying pressurized fluid through a charge passage and a filter to the inlet of a supply pump for direction controlled fluid devices includes a reservoir connected unloading valve assembly connected to the charge passage and parallel with the filter. The fluid devices return fluid through a return passage connected to the unloading valve assembly which maintains back pressure on the devices at charge passage pressure. The unloading valve assembly includes an unloading valve movable in response to a predetermined fluid pressure at the inlet of the supply pump to unload the charge and return passage by connecting them to the reservoir. As the devices require more fluid from the supply pump causing the pressure at the inlet of the supply pump to drop, the unloading valve proportionately blocks the charge and return passages from the reservoir to circulate return fluid into the charge passage.

Abstract: A drive system useful for driving reciprocating equipment such as saw mill log carriages or the like is disclosed. The drive system includes a plurality of fixed displacement pumps driven by a prime mover. The pumps in turn drive one or more fixed displacement hydraulic motors which drive the carriage. The pumps are provided with pressure responsive unloading valves which unload at different pressures so that as pressure on the system builds up one or more pumps are sequentially unloaded. An accumulator is charged at low pressures and provides fluid for driving the motors when required at the higher pressures. The inertial forces in the heavy carriage, during the time when the carriage is slowing down, are used to drive the fixed displacement motors as pumps. During this portion of the cycle, the motors are interconnected with the accumulator so that the pumping action of the motors is used to recharge the accumulator.

Abstract: A fluid transmission circuit in which three or more pumps, adapted to be driven in unison by a prime mover operating at constant power output, draw fluid from a reservoir and deliver it to a reversible fluid motor via a control valve incorporating forward, neutral and reverse positions, the motor being driven, when the circuit is in use, against a fluctuating resistive force. The fluid outputs of two or more of said pumps are controlled by the output of a diverting valve whose input is connected by a separate pressure-sensing line to the fluid flow through the motor and which is initially biassed into a position in which each of said fluid outputs from said pumps is delivered to the motor.

Abstract: A pumping system for pumping liquid clay or slip into a filter press comprises a hydraulically-powered double-acting ram for pumping the slip and a hydraulic control circuit for the ram. The control circuit includes a pair of hydraulic pumps one of which provides a high pressure, low volume delivery and the other of which provides a low pressure high volume delivery, and valves controlling the supply of oil from these pumps to the ram according to the resistance encountered by the ram.

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: A valve device having a pressure operable valve piston, particularly for booster steering systems, to selectively control pressure flow to a consumer device such as a hydraulic servomotor in order to permit use of a reserve pump in event of failure of a main pump. The valve in a neutral position blocks the output of both pumps to a sump but is responsive to a first increase in flow rate beyond a predetermined limit to shunt flow from the reserve pump to a sump. Upon further increase in flow rate the valve piston moves to a position to also shunt part of the output from the main pump to a sump. Differential pressure acting on a valve piston effects shifting and means are provided to vary the differential pressure required to shift the valve piston so that a greater differential pressure is needed for the shifting of the valve piston for the partial shunting of the main pump output. Signal means is actuated by movement of the valve piston to apprise a vehicle driver that the valve device is operative.

Abstract: This invention discloses a brake system for use in automotive vehicles having Otto engines which includes a vacuum operated brake booster and a vacuum pump for generating the necessary vacuum for effective operation of the brake booster. A vacuum pump is positioned between and connected to the vacuum brake booster and the inlet manifold or carburetor induction pipe of an Otto engine. Means are provided for automatically switching the vacuum pump on if there is an insufficient amount of vacuum in the brake booster and also at the same time there is a predetermined amount of vacuum in the intake manifold.

Abstract: A control system for plural motor driven pumps is disclosed. The control system includes a control valve which provides for unloading one pump by diverting the flow of operating fluid from that pump back to reservoir whenever the flow through the valve or the load pressure exceeds a preselected level.

Abstract: A fluid system of work elements of a work vehicle has first and second 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 passing fluid between the first and second fluid circuits in response to control signals passing between said circuits.

Abstract: A dual hydraulic motor drive system is provided for powering a material loading elevator of a self-loading scraper vehicle. Such drive system includes a pair of hydraulic motors which are disposed in a fluid circuit having a blocker valve movable between a first position to direct fluid pressure to just one of the motors to provide high speed, low torque operation of the elevator and a second position to direct fluid to both of the motors to provide low speed, high torque operation of such elevator. Actuator means responsive to loading resistance affecting the elevator being effective to automatically position the blocker valve in its first position during normal loading conditions and to shift it to its second position when severe loading conditions are encountered so as to prevent stalling of the elevator.

Abstract: The disclosure relates to plural, motor driven hydraulic pump circuits, including circuits having the pumps in at least one circuit operated in pairs with all pumps being driven by a single prime mover. A speed responsive control device unloads one pump in one circuit when engine speed drops below a predetermined value without regard to the source of the condition causing the slowdown. Also included is a crossover means for sensing the pressure in aother circuit for preventing reloading of the unloaded pump when speed rises above the predetermined value unless and until the pressure including the pressure sensed in the other circuit is below a predetermined pressure.

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.