Abstract: A hydraulic circuit for a backhoe loader having two double-acting cylinders for the arm and bucket of the loader and respective directional valves for the cylinders. There are heavy demands on the oil pump of the system when the two cylinders are moved simultaneously from one extreme position to another which requires substantially two whole cylinder volumes of oil. The cylinders are arranged in parallel relative to the pump. A first source of pressure medium displaced from one cylinder is used to perform work in the other cylinder and the other cylinder is also supplied with a second source of pressure medium directly from a pump. The line section through which the first source of pressure medium is supplied is shunted to a tank by valving apparatus upon a predetermined pressure being reached to freely accommodate the simultaneous movements of the cylinders.

Abstract: A hydraulic circuit for running a crawler vehicle which comprises a running frame portion provided with motors for running the crawler vehicle and an upper swivel portion turnably disposed on the running frame portion via a swivel joint. Electro-magnetic proportional flow directional control valve (a directional control valves) (15) for controlling the running motors are disposed between the swivel joint (41) and the running motors (19). The number of the high pressure passages in the swivel joint (41) can be reduced, because of increase of pressure resistance, the size of the swivel joint can be small, and accordingly, the hydraulic circuit for running a crawler vehicle can be inexpensive, and possibility for leakage of pressure oil becomes low.

Abstract: A hydraulic drive system for construction machines comprising a valve group (52) including a plurality of directional control valves (9-13) of center bypass type, a center bypass line (2a) for connecting in series center bypasses of the plural directional control valves to a low-pressure circuit (29), a plurality of bleeding-off variable restrictor means (56) respectively disposed in the center bypasses of the plural directional control valves, a pressure compensating valve (20) provided in the center bypass line, and first and second differential pressure detecting lines (22, 24) connected to the center bypass line for transmitting a differential pressure to the pressure compensating valve.

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: A hydraulic control circuit for building machinery includes a hydraulic cylinder to operate a tool. To stabilize vibrations of the tool around the pitch axis, a hydraulic accumulator is provided to be connected to a pressure source via a fill line. A shut-off valve is disposed in the fill line, which valve is subjected to the pressure in the accumulator such that in operating the cylinder the accumulator is loaded to a pressure corresponding to the load pressure. The system is very simple in structure and fluid losses are eliminated.

Abstract: An improved hydraulic system for a vehicle includes a swash plate type variable capacity hydraulic pump that is operably coupled to an engine. A hydraulic motor for driving an air conditioning compressor and a power steering hydraulic mechanism having less fluid demand than that of the hydraulic motor are disposed in a first and a second fluid lines respectively. First, second and third nozzles are disposed within the fluid lines. The volume of fluid controlled by the first nozzle is larger than that of the second nozzle, which is larger than that of the third nozzle. The first fluid line is depressurized by the first nozzle when the hydraulic motor is used, while the second fluid line is depressurized by the second nozzle when the power steering mechanism is used. When neither the hydraulic motor nor the power steering mechanism is used, the pressure in the fluid line on the circulation side is reduced to nearly zero by the third nozzle.

Abstract: A proportional distributor embodying a controlled slide valve and a pressure compensator slide valve associated with additional positioning means whereby the pressure drop in the controlled slide valve depends upon the difference between the working and load sensing pressures according to a linear function with a strictly positive coefficient and a strictly negative constant. Each compensator slide valve operates according to the same linear function or at least one of its proportional distributors has a compensator slide valve operating according to a different linear function.

Abstract: A hydraulic drive system for construction machines includes a hydraulic pump (1), a plurality of hydraulic actuators (2, 3) driven by a hydraulic fluid supplied from the hydraulic pump, a plurality of flow control valves (4, 5) for controlling flow rates of the hydraulic fluid supplied to the actuators, respectively, and a plurality of distribution compensating valves (6, 7) for controlling differential pressures across the flow control valves, respectively, the plurality of actuators including a first actuator (2) which undergoes a relatively large load pressure and a second actuator (3) which undergoes a smaller load pressure than that of the first actuator.

Abstract: An apparatus controls a fluid system of a work vehicle. The work vehicle has an engine and at least one fluid circuit which has a pump driven by the engine. A plurality of control valves controllably pass fluid from the pump to a plurality of respective work elements. The control valves have movable valve stems. A work attachment which has a respective control valve is added to the fluid system. A plurality of operator control elements provide demand signals in response to selected settings. Each demand signal is indicative of a requested fluid flow to a respective work element or work attachment. A memory device stores select parameters of the fluid system. One of the select parameters is a predetermined priority value representing the precedence in which fluid is delivered from the pump to the control valve of the work attachment. A controller receives the predetermined priority value of the work attachment and the demand signals.

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 hydraulic drive system comprising a prime mover (21), a hydraulic pump (22) driven by the prime mover, a plurality of hydraulic actuators (23-28) driven by hydraulic fluid supplied from the hydraulic pump, a plurality of flow control valves (29-34) for controlling flow of the hydraulic fluid supplied to the actuators, and a plurality of pressure compensating valve (35-40) for controlling respective differential pressures across the respective flow control valves, in which each of the pressure compensating valves applies a control force (f-F.sub.c) in a valve opening direction for setting a target value of the differential pressure across the flow control valve. There are provided a first detector (60) for detecting the target rotational speed (N.sub.0) of the prime mover (21), and controllers (61, 62, 63) for controlling the control force on the basis of the target rotational speed detected by at least the first detector such that the control force (f-F.sub.

Abstract: A hydraulic drive system for construction machines includes a hydraulic pump (1), a plurality of hydraulic actuators (2, 3) driven by a hydraulic fluid supplied from the hydraulic pump, a plurality of flow control valves (4, 5) for controlling flow rates of the hydraulic fluid supplied to the actuators, respectively, and a plurality of distribution compensating valves (6, 7) for controlling differential pressures across the flow control valves, respectively, the plurality of actuators including a first actuator (2) which undergoes a relatively large load pressure and a second actuator (3) which undergoes a smaller load pressure than that of the first actuator.

Abstract: A hydraulic apparatus for an industrial vehicle adapted for enabling to carry out a pump capacity control whenever necessary, and including a variable capacity type hydraulic pump driven by an engine, a flow dividing valve disposed in an outlet pipe line of the pump and adapted for dividing a flow of a pressurized hydraulic oil into a flow required for a power steering hydraulic circuit and a balance flow for a cargo handling hydraulic circuit, a switching valve pilot-operated by a pressure of the cargo handling hydraulic circuit and adapted for selecting a supply pilot pressure between a pressure of the power steering hydraulic circuit downstream with respect to the flow dividing valve and a pressure of the outlet pipe line upstream with respect to the flow dividing valve, and a capacity control valve pilot-operated by a differential pressure between the supply pilot pressure and the pressure of the outlet pipe line and adapted for controlling a capacity varying mechanism of the pump.

Abstract: A convertible vehicle has a body with a passenger compartment, a pair of passenger access doors each having a window and a pair of rear quarter windows, all mounted on the body for movement between raised and lowered positions. A folding top is mounted on the body for movement between a raised position covering the passenger compartment and a lowered position opening the passenger compartment. A hydraulic system includes a hydraulic pump, two hydraulic top actuators for raising and lowering the top, and a pair of hydraulic window actuators operatively connected to the quarter windows for raising and lowering the windows with less pressure than required to raise and lower the top. A hydraulic circuit connects all of the cylinders in parallel which enables sequential operation of the windows and then the top. A three-position control switch enables the windows to be lowered and raised when the top is in raised or lowered position by moving the control to respective "down" and "up" positions.

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 system for the hydraulic operating circuit associated with a vehicle lifting device in which the circuit is provided with pressure fluid control valves and flow sensors which are operative on the vehicle lowering cycle to establish substantial evenness of the lowering mechanism and protection against malfunction of an operating component to arrest the travel of the vehicle lifting device in its lowering cycle.

Abstract: The present invention relates to a hydraulic motor capable of presenting two active cubic capacities of different values, as described in FR-A-2 481 755, and comprising in particular a shuttle valve presenting an inner conduit, wherein a bleeding conduit is arranged in the member for selecting the cubic capacity and communicates with the inner conduit of the shuttle valve, which it connects to an evacuation, while a calibrated restriction is disposed in the bleeding conduit. One application is the production of refrigeration of the hydaulic fluid for supplying this mechanism in closed circuit.

Abstract: A source of pressurized hydraulic fluid has a variable fluid output rate and a control system which varies the fluid output rate responsive to a load sense control signal, e.g., a variable displacement pump. The pressurized fluid is made available to a plurality of hydraulic actuators through a corresponding plurality of work control valves. A load sense line is utilized to sense the pressure of the fluid in each hydraulic actuator and to apply a total load sense signal to the control system. A conduit containing a pressure reducing valve provides fluid communication between the output of the source of fluid and the load sense line to pass fluid therethrough to the load sense line only when the pressure in the load sense line is less than a predetermined value. Maintaining at least this minimum pressure in the load sense line minimizes lag in the load sense signal which would otherwise occur as a result of the loss of fluid in the load sense line due to the bleeding of the load sense line.

Abstract: A fluid pressure control system comprising a first selector valve for controlling the action of a first actuator, a second selector valve for controlling the action of a second actuator, a first flow control valve for controlling a fluid to be supplied to the first actuator, and a second flow control valve for controlling a fluid to be supplied to the second actuator. A pressure reducing valve is provided for reducing the pressure of the fluid supplied to the second actuator. The pressure on the outlet side of the pressure reducing valve is controlled by the proportional pressure relief valve which is controlled by an external pilot pressure. This system is applicable, for example, to a hydraulic excavator.

Abstract: An electrohydraulic system includes a plurality of electrohydraulic devices individually controlled by microprocessor-based control electronics. The device controllers are connected in common by a bidirectional serial data bus to a master controller for coordinating operation of the various devices. Internal programming within the master controller establishes a repetitive time-sequence of windows for communications with the various device controllers for downloading control signals and parameters, and for uploading data indicative of system status and operation. The various device controllers include internal programming for operating the associated hydraulic devices as a function of control signals and parameters received from the master controller. Pseudo-devices are also connected to the bus for time-division multiplexed communication with the master controller and for performing overall system coordination and analysis.

Abstract: A power transfer unit coupling two otherwise separate hydraulic systems for bidirectional transfer of hydraulic power therebetween without transfer of fluid between the two systems. Control of the power transfer unit is effected using only hydraulic pressures, and static operation of the unit is maintained without power transfer until a determined pressure differential between the coupled systems is achieved to reduce wear and increase service life of the unit. Once dynamic power transferring operation of the unit is initiated, a pressure differential lower than the determined level is maintained between the two systems.

Abstract: An electrohydraulic system which includes a plurality of electrohydraulic devices individually controlled by microprocessor-based control electronics. A central controller for coordinating operation among the various devices includes a host controller for providing low speed serial and/or parallel output of control signals, and a master controller having a low speed serial and parallel I/O port for connection to the host controller, and a high speed serial I/O port connected by a full duplex bidirectional data bus in common to all of the device controllers.

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 hydraulic control system comprising a hydraulic actuator having opposed openings adapted to alternately function as inlets and outlets for moving the element of the actuator in opposite directions and a pump system with load sensing control for supplying fluid to said actuator. A meter-in valve is provided to which the fluid from the pump is supplied and a manual or electrohydraulic controller alternately supplies fluid at pilot pressure to the meter-in valve for controlling the flow therefrom to the actuator to control direction and displacement of movement of the meter-in valve and the direction and velocity of the actuator. A pair of lines extends from the meter-in valve to the respective openings of the actuator. A meter-out valve is associated with each line to the actuator for controlling flow out of the actuator. Each meter-out valve is operated by the pilot pressure from the controller.

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

Abstract: A material handling vehicle is provided which includes a lower truck chassis and an upper material handling structure pivotally supported by the lower chassis, all functions of which vehicle are driven by a single engine. The material handling vehicle is controllable from a main truck cab on the truck chassis or from an upper operator's cab mounted on the upper structure. The single engine provides highway travel power and power to all excavator functions, while the vehicle, including remote travel and implement manipulation capabilities, may be controlled from the upper operator cab. The main engine, when used for over the highway travel, powers the driven wheels through a power shift transmission in a conventional manner.

Abstract: A combine includes a variable displacement, reversible delivery pump which drives main drive wheels via a main hydraulic drive unit and which drives a pair of steerable wheels via auxiliary hydraulic drive units. A pair of pressure-limiting and relieving valves are connected between the auxiliary drive units and the pump so that auxiliary drive units with lower pressure ratings than that of the main drive units can be used. The valves relieve pressure from the auxiliary drive units during dynamic braking.

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

Abstract: A secondarily controlled hydrostatic machine with variable volume is connected to a line with impressed system pressure which is fed by a primary unit. By switching over the primary unit the secondary unit is subjected to a displacement amount which results in as large as possible a pivot angle of the secondary unit to obtain the highest possible efficiency. The switching over takes place in dependence upon an upper and lower switching point corresponding to the desired pivot angle range of the secondary unit.

Abstract: A hydraulic feed control system for log debarkers having three infeed and three outfeed rolls. Each roll is driven by its own hydraulic motor. Each infeed motor is connected in series with a corresponding outfeed motor whereby three pairs of motors are defined. The hydraulic fluid is pumped through a three way flow divider which divides the fluid equally to each of these pairs. Each of the motors has a special crossover relief with a directional flow control that will prevent the excessive pressure that may be created by one of the motors in the series from effecting the pressure to the other motors. The special relief is also provided with a direct line into the oil reservoir which if needed either of the motors in series may siphon oil from the reservoir through the directional flow control valve without affecting the other motor. The return line from the outfeed (down flow) motor joins a common return which is separate from the relief return to tank.

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

Abstract: An electro-pneumatic pressure regulator control system for precisely adjusting the pressure of fluids applied to a fluid-powered tool such as hydraulic cylinders, pneumatic wrenches and the like includes a current-to-pressure (I/P) transducer, and a fluid conduit coupled in fluid communication between the I/P transducer and the tool including a pressure-to-current (P/I) transducer. In addition, the control system includes an interface which converts an information signal generated in a microprocessor to a current signal of a discrete amplitude for driving the I/P transducer. The interface preferably includes digital, solid state circuitry providing accurate control of the signal being delivered to the I/P transducer. In a preferred form of the present invention, a plurality of sub-control electro-pneumatic regulator systems are selectively activated by a single computerized control.

Abstract: A control having a primary work system, a secondary work system, a first fluid flow generating system, and a second fluid flow generating system is provided. A control signal delivering device is provided to deliver a control signal having a magnitude responsive to a relative location of a control valve between a first and second position of a control valve. A control signal receiving device receives the control signal and separately controls the flow rate deliverable from the first and second flow generating system in response to the magnitude of the control signal received. The control signal receiving device has a set point value which is representative of a preselected magnitude of the received control signal. The second fluid flow generating system is controlled to deliver fluid only in response to the magnitude of the received control signal having a value greater than preselected deliverable flow rate.

Abstract: The invention relates to apparatus for supplying a pressurized fluid to a hydraulic system. The apparatus has a diverting path in parallel with the main supply line which is designed and is operable to minimize the inherent losses associated with such a diverting path. In the unit herein the diverting path has a pressure regulating valve and constant pressure drop valve in series. A control line branches from between the two valves and a load sensing is utlized to bias the pressure regulating valve in a closing direction.

Abstract: A hydrostatic drive is provided having an adjustable pump connected with a pump servo positioned by a control pressure from a line connected between the consumer and an adjustable measuring restrictor which in turn is connected to a switching means which includes a plurality of hollow ended main spools in boreholes in a housing, and secondary spools in said hollow ends acting with radial passages in the main spool to form parallel connected restrictors.

Abstract: A system for limiting the torque of a multiple hydraulic system power drive unit wherein plural hydraulic motors are connected to a common torque-summing output device. The system has at least two separate hydraulic circuits, with there being a pressure-limiting valve in each circuit which controls the porting of motor pressure to a low pressure return line and which sums the motor pressure existing in the fluid circuit in which the valve is positioned and the pressure in the other hydraulic circuit whereby the maximum pressure of the fluid delivered to the motor cannot exceed one-half the maximum pressure when both circuits are active to limit the torque applied to the torque-summing output device.

Abstract: Control arrangement for regulating the speed of movement of a hydrostatic energy consumer is provided in which the ratio between pressure supplied and power on the output side is constant, in particular, a piston capable of sliding in a cylinder connected to a pressure main line, characterized in that an initial hydrostatic displacement machine is connected between the pressure main line and the consumer and is coupled with a second hydrostatic displacement machine on the shaft side, the second hydrostatic displacement machine is adjustable with respect to its displacement volume per revolution and is connected on the one hand to the pressure main line and on the other hand to a chamber carrying a lower pressure, where the adjusting element of this second displacement machine is connected with an r.p.m.-regulating device.

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

Abstract: A 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: A hydraulic control system for regulating the distribution of fluid from a variable displacement pump to a plurality of fluid actuated devices is disclosed. The control system includes at least first and second control valves, each of which valves regulates the flow of fluid to a fluid actuated device. Each of the first and second control valves includes, respectively, a first means for developing a first pressure signal and a second means for developing a second pressure signal. A selector means senses the first and second pressure signals and transmits a control pressure signal which is the smaller of the two pressure signals to a fluid actuated displacement control means which regulates the displacement of the pump in response to the magnitude of the control pressure signal.

Abstract: To limit the power output of a hydraulic assembly consisting of plural driven hydraulic motors, hydraulic pumps driving said motors, a single pump driving motor and control means for controlling the hydraulic flow to said drive hydraulic motors, a controller is provided which is supplied with an input signal from a subtractor which in turn is supplied with signals from a reference value setting device and an actual value setting device, the actual value setting device sensing the speed of the driving motor. An output signal of the controller is applied to all of the control means and is multiplied in each control means by a signal proportional to the setting of said control means, in order to obtain the flow control signal.

Abstract: A hydraulic excavator is disclosed which includes two sets of manual control valves for selectively placing a pair of variable displacement pumps in and out of communication with hydraulically driven components such as propelling motors, arm cylinders and boom cylinders. In order to minimize the per-cycle displacement of the pumps when same are discommunicated from all the driven components, a sensing valve is provided which is pilot operated from the sets of manual control valves. When all the manual control valves are in neutral, the sensing valve directs pressurized fluid from a charging pump to a pump-displacement adjustment mechanism thereby causing same to reduce the per-cycle displacement of the pumps to a minimum.

Abstract: A pressure control mechanism for the hydraulic control system of a log skidder. Hydraulic circuits for the boom and the grapple of a log skidder are interconnected to provide a pressure control mechanism for the grapple of the skidder. Provided in the interconnecting hydraulic lines for the grapple cylinder and the boom cylinder, between the rod end of the boom cylinder and the base end of the grapple cylinder, is a two-way valve and a check valve. This mechanism provides flow from the boom cylinder to the grapple cylinder. The weight of the load pressurizes the boom cylinder and this pressure is transferred to the grapple cylinder.

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 drive system with an adjustable pump is provided with branch lines from a main delivery line to several consumers, an arbitrarily actuatable switch in each branch line, an adjustable parallel connecting restrictor in each branch line with an adjusting element loaded on one side by pressure from either the main delivery line or the branch line and on the other side by a spring and control pressure and a source of common control pressure furnishing the control pressure to the adjusting element through a check valve.

Abstract: One or more pressure regulators limit the operating pressure of fluid supplied to a fluid pressure operated device from a common pump and control the level of the operating pressure through pilot valves connected to the regulators. Each fluid operated device is connected by its regulator to a common fluid reservoir when flow is blocked in the pump pressure and suction lines to limit the operating pressure while minimizing pump drive energy loss.

Abstract: A vehicle propulsion system is provided with an auxiliary hydraulic drive having a variable displacement motor connected to ground engaging wheels by a clutch. A multiple position control has a first position which causes clutch engagement and positions a motor displacement member in a position which permits fluid drive of the motor. The control has a second position which causes clutch disengagement and positions the motor displacement member in a zero displacement condition which prevents fluid drive of the motor. Preferably the control is responsive to motor output speed and reduces motor displacement as speed increases.

Abstract: A control for a variable displacement motor which utilizes a motor speed sensitive signal for moving the displacement of the motor toward a zero displacement setting position including a device for generating a conditioned variable signal representative of motor speed, circuitry for receiving said signal and upon the signal reaching a predetermined intermediate value applying the signal to the control device for motor displacement for causing reduction in motor displacement and with various devices in the circuit for modifying the variable signal to provide a desired relation between motor speed and motor displacement. Utilization of such controls individually associated with plural variable displacement motors driving vehicle wheels and driven by one pump protects against spin-out of one of the wheels.

Abstract: A self propelled combine having forward main drive wheels and rear steerable wheels. A hydrostatic drive including a variable displacement motor is arranged to drive the main drive wheels. An electronic-hydraulic control system is automatically operable to drive the rear steerable wheels in response to sensing preselected pressure and combine attitude values while automatically varying the displacement of the hydrostatic drive motor to minimize combine speed changes and to provide torque as required under varying loads imposed by hilly terrain or increasing amounts of grain collected in the grain tank of the combine.