Abstract: A combined hydraulic circuit to be used with a hydraulically powered implement of a motorized equipment and its engine-driven host vehicle. The combined hydraulic circuit allows the implement to be operated with a vehicle, such as a tractor, which does not have the adequate capacity to power the implement without the usual requirement of using an hydraulic fluid reservoir and a filter in the independent hydraulic circuit of the implement. Instead, the implement uses the tractor hydraulic circuit to clean, cool and pressurize in part the hydraulic fluid in its hydraulic circuit which has a hydraulic motor or a hydraulic cylinder driven by a hydraulic pump. This hydraulic pump can be a generated orbital rotor pump since the supplied fluid entering the pump is already pressurized unlike a circuit that uses a hydraulic fluid reservoir. The implements may be rotary brooms, mowers, portable saw mills, hoeing machines, loaders or snowblowers.

Abstract: A low breakout power transfer unit for transferring power between first and second hydraulic systems includes first and second pump/motor units to allow fluid flow between the first and second pump/motor units and the first and second hydraulic systems, respectively. The transfer unit includes a detection device for sensing fluid flow demand in the hydraulic systems and values for automatically isolating the pump/motor units from the hydraulic systems when the detection means senses substantially no fluid flow demands in a hydraulic system. The transfer unit includes a bypass device for each pump/motor unit for recirculating pumped fluid in excess of fluid flow demand.

Abstract: The invention is an improvement in a control system having first, second and third sources of fluid at differing pressures. The improvement comprises a tripath pressure selector network connected to the first and second sources. A pressure-sensing device connects the network and the third source when the third source is at a predetermined minimum pressure. The invention has particular utility in mobile construction machinery having, e.g., steering, implement and brake hydraulic circuits, at differing pressures. In one embodiment, the third source is a brake hydraulic circuit. The improvement helps assure that adequate pilot pressure is available for a "downstream" pilot control valve.

Abstract: An oil pump which delivers an operating oil to a power steering mechanism of vehicle is designed to reduce the power which is wasted during a high speed operation. A subpump of a reduced capacity having a number of revolutions which varies with a vehicle speed is provided, in addition to a vane pump which delivers an operating oil to the power steering mechanism. A discharged oil from the subpump is delivered to act upon the rear surface of the vanes to enable a pumping action of the vane pump when operating at low speeds while the delivery of the discharged oil to the rear surface of the vanes is interrupted to cease the pumping action of the vane pump, and is delivered to the power steering mechanism when operating at higher speeds.

Abstract: A control system for automatically controlling the operation of a hydraulic system for heavy construction equipment. The system of this invention provides a controller optimally connected to sensors and to control devices on the hydraulic system so that it automatically and optimally preheats the engine coolant and the hydraulic fluid of the heavy construction equipment before a normal starting operation in order to reach to an optimal operating temperature in a relatively short time. The control system automatically checks the operating temperature of the engine coolant and the hydraulic fluid by temperature sensors, and alarms the operator to any overheat condition by an alarm device. The control system also automatically controls the operational mode in order to remove the overheat condition thus preventing the temperature of the engine coolant and the hydraulic fluid from rising above a predetermined temperature.

Abstract: An apparatus for controlling hydraulic pumps for a construction machine wherein the construction machine includes first and second hydraulic pumps adapted to be driven by an engine and hydraulic actuators hydraulically connected to the first and second hydraulic pumps via first and second actuating valves is disclosed. A controlling section calculates extra horse powers .DELTA.HP.sub.1 and .DELTA.HP.sub.2 based on reference allowable absorptive horse powers set relative to the first and second hydraulic pumps and actual absorptive horse powers (HP.sub.01) and (HP.sub.02) derived from the first and second hydraulic pumps. In addition, the controlling section calculates allowable discharge capacities (V.sub.1P) and (V.sub.2P) based on the number (N) of revolutions of the engines, pressures (P.sub.1) and (P.sub.2) of hydraulic oils discharged from the first and second hydraulic pumps, the extra horse powers .DELTA.HP.sub.1 and .DELTA.HP.sub.2 and allowable discharge capacities (V.sub.1P) and (V.sub.2P).

Abstract: In accordance with the present invention, a fuel flow circuit comprises a source of fluid, a first means for pressurizing the combustible fluid and pumping the pressurized fluid along a first path leading to a combustion apparatus for an internal combustion engine. The first means for pressurizing further pumping the combustible fluid along a second path to a first fluid-driven actuator adaptable to control some aspect of the engine. The first means for pressurizing further pumping the combustible fluid along a third path to a second means for pressurizing the combustible fluid. The second means for pressurizing pumping the combustible fluid along a fourth path, including a first diverting means, to a second fluid-driven actuator adapted to control some aspect of the engine or exhaust nozzle.

Abstract: A hydrostatic transmission for a vehicle, such as a commercial walk-behind mower, comprises a fixed displacement pump, first and second reversible hydraulic motors for driving first and second ground engageable wheels, respectively, of the vehicle, and first and second spool valves for controlling hydraulic fluid flow from the fixed displacement hydraulic pump to the first and second hydraulic motors, respectively. The transmission may have a further fixed displacement hydraulic pump arranged in tandem with the first mentioned pump, a fluid pressure operated device and a third spool valve movable between a first position in which hydraulic fluid from the further pump is supplied to the pressure operated device and a second position in which hydraulic fluid from the further pump is supplied to the first and second spool valves to supplement hydraulic fluid from the first mentioned hydraulic pump.

Abstract: A prioritizing method and arrangement for a hydraulic system including two independent hydraulic fluid supply units (4, 5) adapted to jointly and severally supply hydraulic fluid to at least two hydraulic components (2, 3). A cross-communication between the at lest two hydraulic components (2, 3) is controlled, with a flow of hydraulic fluid from one of the two hydraulic fluid supply units (5) being diverted to one of the at least two hydraulic components (3) to a substantial exclusion of the other of the at least two hydraulic components (2) in dependence upon an operating condition of the other of the two hydraulic fluid supplying units (5). A biasing force (F) acts upon the prioritizing arrangement so as to define an operating stage at which the respective hydraulic fluid supplying units (4, 5) exclusively supply hydraulic fluid to the respective ones of the at least two hydraulic units (2, 3).

Abstract: A hydraulic control valve which is equipped with two direction change-over valve groups individually having traveling change-over valves, and first and second hydraulic pumps corresponding to those direction change-over valve groups. The traveling section valve of one of the change-over groups is equipped with a communication valve. Each section valve has its valve body formed therethrough with signal conduits individually extending perpendicular to spool bores. The two traveling section valves are formed with annular grooves in spool bores positioned to correspond to said signal conduits. The individual working machine section valves other than the traveling section valves are formed with annular grooves in the spool portions corresponding to the signal conduits to provide the communications between the upstreams and downstreams of the signal conduits only when the spools are in their neutral states.

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: An apparatus for controlling a power shovel or like construction machine which assures that various control modes for performing certain operations can reliably be selected by merely activating a switch corresponding to the operation to be performed. When a certain operation is selected, a CPU and an operation panel inputs a signal indicative of the selected operation into a pump controller. The pump controller outputs a signal indicative of the magnitude of the target engine revolution number and a magnitude of composite suction torque of the pumps adapted to the selected operation to an electric governor controller and a TVC valve. In response to this signal, the governor controller controls a governor and swash plates of the pumps such that the target engine revolution number is reached and the output torque from the engine matches the composite suction torque of the pumps.

Abstract: A controller for a hydraulic fluid flow control apparatus determines a quantity necessary for loading/unloading operations according to a signal from a lever operating degree detector, and controls a variable displacement type hydraulic pump to obtain the quantity. Accordingly, unnecessary hydraulic fluid flow in the hydraulic apparatus is reduced. The controller determines when a vehicle is stopped according to a signal from a clutch ON-OFF detector or a neutral sensor, and can raise the rpm of an engine. Therefore, when the loading/unloading operations are being executed while the vehicle is stopped, there is no need to operate the accelerator pedal.

Abstract: A hydraulic drive controlling apparatus for a construction machine has at least one variable displacement type hydraulic pump, a plurality of actuators driven with a hydraulic fluid from the hydraulic pump, directional control valves driven in accordance with amounts of manipulation of operation means for controlling the plurality of actuators, means for detecting a delivery pressure of the hydraulic pump, means for selecting maximum one of load pressures of the plurality of actuators, and first control means for controlling displacement of the hydraulic pump to bring a differential pressure between the delivery pressure and the maximum load pressure to a specified value.

Abstract: A control circuit for a hydraulic actuator which allows the hydraulic actuator to be operated readily without much skill and at a suitable speed in accordance with a load applied thereto. The control circuit includes a change-over valve provided intermediately of a pilot pipe line communicating with a pilot oil chamber of a hydraulic change-over valve which belongs to one of a pair of hydraulic change-over valve sets of a hydraulic operating circuit for the hydraulic actuator. The change-over valve is normally urged to a position wherein the pilot oil chamber of the hydraulic change-over valve is communicated with a tank, but is changed over, when a hydraulic pressure higher than a predetermined value acts upon a pilot oil chamber of the change-over valve, to another position in which the pilot oil chamber of the hydraulic change-over valve is communicated with the pilot pipe line.

Abstract: For the production and exact control and regulation of very high pressures, in particular for actuating a press, two pressure intensifiers are provided which each have a differential piston. The second pressure intensifier is connected via a shutoff valve to the first pressure intensifier and to the load or consumer. Both pressure intensifiers have a small volume compared with the volume required by the consumer. By activating the second pressure intensifier fluid can be exchanged between the consumer and the first pressure intensifier to replenish the first pressure intensifer in a pressure buildup phase and to empty the first pressure intensifier in a pressure relief phase.

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 control system for a hydraulic tandem pump assembly including a primary pump for supplying fluid under pressure to a power-assisted steering device and a secondary pump for supplying fluid under pressure to a hydraulic motor of an engine cooling fan, which pumps are mounted on a common drive shaft for rotation therewith.

Abstract: A common relief valve circuit for controlling or monitoring two or more pumps. The circuit includes two fixed displacement pumps with the pumps being connected to at least two valve bodies or sections that supply fluid to hydraulic cylinders for operating earth-working buckets or the like. A main relief valve is connected to the inlet of a first valve section, and a check valve is connected in a parallel cavity line in the first valve section. The check valve remains closed under conditions where a valve spool in the first valve section is shifted but a valve spool in the second valve section is not shifted or when a valve spool in the second valve section is shifted and a valve spool in the first valve section is not shifted.

Abstract: A universal control system for hydraulic cylinders to enable controlled increments of movement for varying uses including shaping members and lifting and lowering of loads. The lift control system is utilized to synchronize the raising or lowering of a load by, for example, four simultaneously-acting pump-operated hydraulic rams which have plural increments of movement. A sensor associated with the load adjacent each ram measures incremental movement of the load. A master controller controls the operation of the rams in accordance with the sensed increments and operates each pump simultaneously and independently until each pump achieves a preselected increment of movement of a ram, to maintain the load substantially level, followed by movement of all the rams through another increment of movement until the total lifting or lowering movement is achieved.

Abstract: A hydraulic drive system for a construction machine in which a hydraulic circuit has at least one hydraulic pump, at least first and second hydraulic actuators driven by a hydraulic fluid discharged from the pump, and at least first and second directional control valves connected to the pump in parallel with each other for controlling flows of hydraulic fluid supplied from the pump to the first and second actuators, respectively, and a control unit is responsive to first and second operation signals for driving the first and second actuators, respectively, to produce first and second control signals for actuating the first and second valves and deliver such control signals thereto, respectively, each of the first and second valves having a degree of opening changed in accordance with a level of the corresponding one of the first and second control signals for controlling a flow rate of hydraulic fluid supplied to the corresponding one of the first and second actuators.

Abstract: A drive system having two hydrostatic gears (1, 2) driven by a common driving motor or by a plurality of driving motors having a fixed speed ratio, each having a pump (5, 6) and a hydraulic motor (7, 8) and in which the delivery or intake volume setting of the pumps (5, 6) and/or the hydraulic motors (7, 8) is performed by hydraulic servomechanisms (13, 14) of which the control pressures in the control pressure lines (23, 24) can be varied as desired either independently or together by means of pressure indicating valves (26) connected to each of the gears (1, 2) and supplied by an auxiliary source of pressure (9, 10) is arranged so that, at least on starting, the outputs of the gears (1, 2) are as nearly as possible equal.

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

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

Abstract: 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 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: Engine BMEP being a major contributor to the gap between conventional automobile road fuel mileage and the theoretically possible, indicates the desirability of a continuously variable road wheel/engine speed ratio. There is described a double swash plate, regenerative, hydrostatic system, with a mechanical bypass. The two swash plates facilitate optimization of hydraulic parameters as well as engine BMEP and the rear one which is the primary controller permits modulation of regenerated energy in both directions, with optimum efficiency and facility.

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 hydraulic circuit arrangement for controlling a plurality of actuators connected to a high pressure line of a main pump parallel to each other has a sequence valve interposed in a line bypassing from the high pressure line to a reservoir. In the bypass line a throttle is interposed between the sequence valve and the reservoir. A regulator for controlling the displacement of the main pump is connected to the bypass line between the sequence valve and the throttle at a pilot chamber thereof. An auxilially pump is connected to the high pressure line parallel with the sequence valve. A delivery line of the auxilially pump has a bypass line interposed with a relief valve. The main pump may be switched to unloaded condition for the stand-by condition of the actuators and to loaded condition for the operation condition of the actuators.

Abstract: A control system for a hydraulic circuit including at least first and second variable displacement volume type hydraulic pumps, at least first and second hydraulic actuators driven by the pumps, and valves for controlling hydraulic connections between the pumps and the actuators. The control system includes a device for deciding the order of priority of hydraulic connections between the first actuator and the first and second hydraulic pumps and the order of priority of hydraulic connections between the second pump and the first and second actuators. A first sensor is provided for sensing maximization of the displacement volume of the first pump, sensing that the displacement volume of the second pump has become substantially zero. A device decides target displacement volumes of the first and second pumps based on information supplied at least by the priority order deciding device and first and second sensor.

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 hydrostatic drive in which the ratio of pressure to force is constant is provided having a consumer of hydraulic energy connected to a high pressure system line, a first displacement means interposed between the consumer and the pressure system line, speed regulating means acting on the first displacement means to regulate the speed thereof, a second displacement means connected to the first displacement means by a drive shaft and receiving fluid from the pressure system line, volume output adjusting means acting on one of said first and second displacement means to adjust the volume output per revolution and coupling means connecting the adjustable displacement means with the consumer of hydraulic energy.

Abstract: A motor vehicle having a pair of front drive wheels and a rear steerable drive wheel mounted on a main frame. A sub-frame secured to the main frame intermediate the front and rear drive wheels carries an internal combustion engine and a pump assembly. The pump assembly has a first pump operable to deliver fluid under pressure to fluid operated motors operably connected to the front drive wheels and a second pump operable to deliver fluid under pressure to a fluid operated motor operably connected to the rear drive wheel. The internal combustion engine and pump assembly are located below a seat and floor with both the engine and pump assembly positioned transversely of the main frame of the vehicle. The rear wheel is mounted on the frame for angular movement about a generally upright axis. A fluid operated double acting piston and cylinder assembly operates to angularly move the rear wheel about the upright axis to steer the vehicle.

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

Abstract: In a control for a hydrostatic drive system with a primary energy source and with an adjustable pump and at least one adjustable consumer of hydrostatic energy and with a pump adjusting piston connected with the adjusting element of the pump and capable of sliding in a pump adjustment cylinder, where the load on the pump adjustment cylinder is regulated by means of a servo control valve, also with a constant pump connected to the drive shaft of the pump, the delivery line of which leads to a restrictor and to which a signal-pressure line is connected in front of the restrictor, where the pressure-signal present in it regulates a relief valve jet, which in turn is located in a control-signal line, the improvement characterized in that an additional restrictor is located in the control-signal line and means are provided for switching the pressure gradient in it to the servo control valve.

Abstract: A jacking mechanism for jacking a well casing or other well pipe vertically, and including a hydraulic control system in which a reversible variable displacement pump acts in one condition to deliver pressure fluid in parallel with another pump to the lower end of a jacking cylinder to actuate the piston thereof upwardly, with fluid discharging from the upper end of the cylinder to the variable displacement pump and being metered therethrough to regulate the rate of upward movement of the piston. In a second condition of the apparatus, flow through the variable displacement pump is reversed to lower the piston, and a variable restriction valve regulates discharge of fluid from the lower end of the cylinder to act with the variable displacement pump in regulating downward movement of the piston and supported pipe.

Abstract: The control mechanism is for pneumatic apparatus of the kind comprising a piston-and-cylinder motor coupled between two relatively-movable parts (such as door-leaves) for driving them, when energized, to a predetermined relative position. A pilot valve is actuated when required to switch the apparatus to an emergency mode by isolating the motor from its power source and discharging it into an emergency reservoir having a volume large compared with the maximum volume of gas in the motor. While the pilot valve is actuated, the relatively-movable parts are urged towards their predetermined relative positions by a force small compared with the normal operating force. The pilot valve may be arranged to operate operation of an emergency release bolt, on obstruction detected by a detector valve (in which case a timing reservoir provides time delay before full power is restored), on power failure, or as required.

Abstract: A lift truck hydraulic control system designed to conserve energy includes a pair of separately controlled pumps (21, 22). One pump (21) supplies pressure fluid to a valve (12) for a steering cylinder (11) by way of a high priority port (34) of a priority valve (32) with the low priority flow passing to parallel connected lift and tilt valves (19, 18) which control operation of the lift cylinder (15) and tilt cylinders (16, 17), respectively. The capacity of pump (21) is sufficient to provide proper, effective operation of the steering and tilt functions but is not adequate to provide hydraulic fluid flow for high speed expansion of the lift cylinder (15). The other pump (22) is operated to supply additional pressure fluid flow for high speed lift only when the lift valve (19) is shifted to a raise position. In one embodiment, a low speed lift is obtained by using the output of the pump (21) and a high speed lift is obtained by selectively adding the output of the second pump 22.

Abstract: A rotary vacuum pump is proposed, having a rotor with vanes which rotates eccentrically within a housing bore. Each vane is coupled with a body which is ineffective at relatively low pump rpm; however, at higher rpm, the body engages the vane in such a manner that it removes the vane from its track within the housing bore.In this manner, an rpm-dependent shutoff device is created for the pump. In cooperation with the furnishing of underpressure as an auxiliary pressure in motor vehicles, the pump is used to supplement the underpressure which prevails when the internal combustion engine is at low, idling rpm; this prevailing underpressure is at a very low pressure level, and so when it is thus supplemented there is sufficient auxiliary vacuum force available over the entire rpm range.

Abstract: In a preferred embodiment, for a turbine driven by hydraulic fluid, the combustion cylinder's piston is lubricated by the hydraulic fluid and drives the hydraulic fluid, and during the driven movement of the piston, movement of that piston causes the return reciprocal movement of another piston of another hydraulic combustion cylinder, and a starter motor is connected to drive both the turbine and the reciprocatable pistons.

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 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: 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: In a load responsive fluid power and control system employing plurality of control valves with positive and negative load compensation, a closed loop pressurized exhaust system supplied with a make-up and fluid exchange pump equipped with an unloading device responsive to positive and negative load system pressures.

Abstract: PCT No. PCT/US79/00415 Sec. 371 Date June 13, 1979, Sec. 102(e) Date June 13, 1979 PCT Filed June 13, 1979 PCT Pub. No. WO80/02824 PCT Pub. Date Dec. 24, 1980The drives (34,34') of a vehicle are each driven by a pump (18) and motor (22) of a hydrostatic transmission (23). A servo-system (20) associated with each pump (18) is adapted to be controlled by a steering arrangement (35,36) for selectively rotating the drives (34,34') relative to each other. An interlock valve (43,44) is associated with each steering arrangement to stop the drives (34,34') of the vehicle when steering pedals (37,38) thereof are both depressed into certain positions (N,R) of operation. Thus, the operator of the vehicle is prevented from placing the vehicle in an unwanted mode of operation, such as in reverse, when the operator desires another mode of operation, such as braking of the vehicle.

Abstract: In a load responsive fluid power and control system employing plurality of control valves with positive and negative load compensation, a closed loop pressurized exhaust system supplied with a make-up and fluid exchange pump equipped with an unloading device responsive to positive and negative load system pressures.

Abstract: A fluid transmission which includes a hydraulic pump combination and a hydraulic motor. The hydraulic pump combination includes a first pump which is a variable volume, variable direction pump and a second pump which is a constant volume, constant direction pump. The combined outputs of the first and second pumps are directed to a hydraulic motor at variable rates and in reversible directions.