Abstract: A hydrostatic vehicle drive has a control (5) for controlling an output torque of the drive and another control device (5) for controlling the output torque of a hydrostatic drive, the control device (5) having a controllable pressure-limiting valve (6) by means of which the working pressure can be adjusted and which is used for sensitive control of the output torque of a hydraulic motor (3). The pressure-limiting valve (6) can be controlled by a proportionally adjustable pressure-reducing valve (7).

Abstract: A hydraulic circuit includes a pump controlled by a two-stage non-feedback proportional control assembly. The first stage of the control assembly includes a single non-feedback proportional control valve that generates a displacement magnitude hydraulic signal that is proportional to an input signal. The second stage of the control assembly includes a directional control valve located downstream of the proportional control valve for conditioning and routing the displacement magnitude signal to the pump with an appropriate directional indicator.

Abstract: A control arrangement is provided to control the output of a hydrostatic transmission in response to a selectable input from an operator. This is accomplished by having a adjustable relief valve connected to the pilot control arrangement that controls the displacement of the variable displacement pump of the hydrostatic transmission. The adjustable relief valve vents a portion of the pilot control pressure being directed to the variable displacement pump in response to the pressure between the variable displacement pump and the fluid motor of the hydrostatic transmission and the setting of the adjustable relief valve by the operator.

Abstract: The neutral override circuit of this invention includes a variable displacement pump controlled by a servo fluidly connected to a displacement control that is biased to a neutral position. A charge pump is connected to the pump and the displacement control. A solenoid-operated neutral override brake control valve is connected to the charge circuit upstream of the displacement control valve and is normally biased to an open position. However, the solenoid urges the valve to a closed position in a response to a signal indicating that the brake has been released. In the open position, the valve dumps charge flow to the pump case until the supply pressure to the displacement control is inadequate to overcome the centering bias of the displacement control. The characteristics of the brake control valve can be set so that some minimum charge pressure and lubricating flow are still provided to the rotating elements of the pump.

Abstract: An axle driving apparatus comprising a common housing in which a hydraulic pump and a hydraulic motor fluidly connected with each other and an axle driven by the hydraulic motor are disposed, At least one of the hydraulic pump and the hydraulic motor is variable in displacement and has a capacity changing device for changing its capacity. A hydraulic actuator is provided in the housing for controlling the capacity changing device. A control valve for hydraulically controlling the hydraulic actuator is provided in the housing. A center section for fluidly connecting the hydraulic pump and the hydraulic motor with each other is fixedly disposed in the housing and a driving part of the hydraulic actuator and the control valve are incorporated in the center section. A rotary member operatively connected to a human-operated traveling control member provided on a vehicle is rotatably supported by the housing.

Abstract: A control circuit, in particular for a slewing gear of a digger, has a hydraulic fluid tank (21), connected to two adjusting pressure chambers (10, 11). Each of the connections contains a separate brake valve (19, 20). The first of the valves (19) is operated by the differential between the working pressure in the first working conduit (2), and the control pressure in the control conduit (33, 34) charged with the higher pressure. The second valve (20) is operated by the differential between the working pressure in the second working circuit (3) and the control pressure in the control circuit charged with the higher pressure. Slow braking by the brake valves is interrupted when the slewing gear swings out against a resistance such as a heap of debris.

Abstract: The invention provides a hydraulic circuit for construction machines, capable of obtaining a satisfactory suspending capability during load suspending work, and having an improved operation efficiency with a decrease in the working speed of a load suspending operation minimized, the hydraulic circuit including a suspension mode switch for setting a working mode to a suspension mode, a lift detecting sensor for detecting a predetermined actuator which has been operated to a load lifting side, a relief valve control unit capable of freely setting an object pressure of the relief valve 14 to a normal set level and a high set level higher than the normal set level, a cutoff valve control unit capable of freely switching the cutoff valve to a cutoff operation executing mode and a cutoff operation disengaging mode, and a controller adapted to increase a set pressure of the relief valve by outputting an instruction to the relief valve control unit when the controller receives a suspension mode signal and a lift dete

Abstract: A load sensing hydraulic control system for use in a work machine and adaptable for controlling the displacement of a variable displacement hydraulic pump. The control system includes a signal duplicating valve connected in fluid communication with both the pump controller and a fluid pressure source, and a sensor positioned and located for sensing the fluid pressure to the pump controller and outputting a signal to the controller indicative thereof. In response to signals received from the at least one sensor, the controller outputs a representative signal to the signal duplicating valve indicative of the highest pressure sensed by the at least one sensor, the signal duplicating valve being thereafter operable to allow fluid flow to pass therethrough to the pump controller.

Abstract: A hydraulic drive system includes a variable displacement pump unit having a rotor rotatably supported within a housing on a main rotor axis, and an input shaft coupled to the rotor by mating bevel reduction gears. A main pump includes a plurality of main hydraulic cylinders fixedly supported relative to the housing; a ring member supported by a journal at variable eccentricity; a plurality of pistons sealingly slidable in corresponding ones of the cylinders that are coupled by respective followers to the shaft input by the ring member for reciprocating movement; and inlet and exhaust one-way check valves fluid coupled to each of the cylinders. A hydraulic actuator of the pump unit moves the journal in response to fluid pressure.

Abstract: The invention relates to a hydraulic controller, in particular for the control of the rotating mechanism of an excavator. In a hydraulic drive circuit a drive hydraulic pump (2) and a drive hydraulic motor are provided, which are connected via working lines (3, 4). The hydraulic controller includes an adjustment arrangement (9) for adjusting a setting piston (12) arranged between two setting pressure chambers (10, 11) and acting upon the displacement volume of the drive hydraulic pump (2). Further, a pre-control arrangement (8) is provided which acts upon one of the setting pressure chambers (10, 11) with a setting pressure, in dependence upon the pressure difference between two control lines (6, 7).

Abstract: A displacement control device for a hydraulic unit includes: an actuator for applying operator input force to a movable member for varying displacement of the unit; a control valve having a spool and a sleeve displaceable with respect to each other, one of these being coupled with the movable member and the other being coupled with the actuator, the control valve being capable of generating a control signal based upon the relative displacement of the spool and sleeve; a servo which is operatively connected to the movable member and receives the control signal so as to move the movable member and change the fluid displacement of the unit in response to the control signal; and a bias coupling connecting the spool and the sleeve of the control valve. Thus, a preload force is interposed between and the spool and the sleeve such that relative displacement between the spool and the sleeve takes place when the feedback force exceeds the preload force.

Abstract: The invention relates to a hydraulic controller (1), in particular for the control of the rotating mechanism of an excavator. A hydraulic motor (5) is driven by means of a hydraulic pump (2) in a hydraulic drive circuit, the hydraulic pump (2) and the hydraulic motor (5) being connected by a first and a second working line (3, 4). The hydraulic controller (1) includes an adjustment arrangement (26) for adjusting a setting piston (28a), acting on the displacement volume of the hydraulic pump (2), arranged between two setting pressure chambers (26, 27), in dependence upon the pressure difference between two control lines (20, 21). In accordance with the invention, a respective separate brake valve (24; 25) is provided in each connection between each of the two setting pressure chambers (26; 27) with the pressure fluid tank (10).

Abstract: A variable displacement pump assembly (11) of the type including a tiltable swashplate (29) to vary the pump displacement. The assembly includes a main control valve (43) having a housing (44). The assembly includes an input section (65) disposed between the valve housing (44) and the pump housing (61). The input section (65) defines a cylinder bore (77, 79) in which a piston member (81) is disposed and is connected by a mechanical input (59) to a valve spool (51) of the main control valve. The piston defines first (87) and second (89) piston chambers and a solenoid valve (105) is responsive to a remote electrical input signal (111, 113) to control the fluid pressure in the piston chambers, and therefore, the position of the valve spool (51).

Abstract: A rotary control valve includes a directional control valve having a rotatable valve element for controlling the direction of fluid flow from an input passage to a pair of control ports and from the control ports to a drain passage. A pressure regulating valve is connected to a source of pilot pressure and has a valve spool for controlling the regulated pressure level of pilot fluid in the input passage. A cam is connected to the valve element for unitary rotation therewith. A spring and a plunger are disposed between the valve spool and the cam so that the valve spool is mechanically moved in a rectilinear direction by the cam in either direction from a neutral position to increase the level of the regulated pressure in the input passage proportional to the degree of rotation of the rotatable valve element.

Abstract: A hydraulic control system according to the present invention for a construction machine is provided with a directional control valve switchable by a pilot control valve, a hydraulic cylinder, a pilot pump, a selector valve for selecting one of a maximum value out of pilot pressures of the pilot control valve, a flow control unit for controlling the flow rate of a variable displacement hydraulic pump, a pressure-reducing valve for converting a delivery pressure of the pilot pump to a pump control signal, which controls driving of the flow control unit, in accordance with a pilot pressure guided to a first signal line connected to the selector valve, a branch line connecting the pilot pump and the pressure-reducing valve with each other, and a second signal line for guiding the pump control signal, which has been converted at the pressure-reducing valve, to the flow control unit.

Abstract: A hydrostatic transmission has a pair of overcenter variable displacement pumps, each having a flow control element controlled by a double acting actuator to control direction and flow rate of the pump. Fluid pressure in first and second chambers of each actuator are equal at a neutral position of the transmission. A forward control valve controllably communicates the first chambers of both actuators to a tank through a first orifice to reduce the pressure in the first chambers to simultaneously move the flow control elements in a first direction for forward travel. A reverse control valve controllably communicates the second chambers of both actuators to the tank through a second orifice to reduce the pressure in the second chambers to simultaneously move the flow control elements in a second direction for reverse travel.

Abstract: A continuously variable hydrostatic transmission includes an input shaft connected to drive a hydraulic pump unit, a grounded hydraulic motor unit, and an output shaft. A wedge-shaped swashplate is pivotally mounted to the output shaft in driving connection to receive output torque resulting from the exchange of pressurized hydraulic fluid between the pump and motor units through ports in the swashplate. A hydraulically actuated ratio controller is pivotally linked to the swashplate to selectively adjust the swashplate angle relative to the output shaft axis and thereby change transmission ratio.

Abstract: A hydraulic circuit for supplying a plurality of series-operated consumers of a hydraulically controlled installation, in particular of an injection molding machine, having a pump with feed-flow pressure control, is described. To be able to slow down greater moving masses with very little expenditure in regard to circuitry and devices, only a portion of the consumers, such as the extruder, the injection unit and possibly the ejector are operated in open circulation, while at least one selected further consumer, such as the clamping unit of the injection molding machine, where a greater mass must be moved in alternating directions, is moved in semi-closed or closed circulation.

Abstract: An electrohydraulic steering system has a three position pilot operated directional valve disposed between a variable displacement pump and a pair of steer cylinders. The directional valve controls the direction of fluid flow from the pump to the steer cylinders while the displacement of the variable displacement pump is controlled to vary the rate of fluid flow to the steer cylinders. The directional valve is moved to an on position in response to a pilot signal delivered thereto from a pilot valve device while the displacement setting of the variable displacement pump is varied by an electrical signal delivered to a displacement controller from a position sensor mechanism.

Abstract: A control (27)is disclosed which may be used as an automotive drive control for a variable displacement hydrostatic pump (11). The pump displacement is controlled by servos (37, 39) by control pressure from a charge pump (21). As a pedal (P) of a vehicle engine (E) is depressed, an increasing pressure differential across a fixed orifice (79) moves a control spool (73) to port control fluid to a first servo port (A). If engine speed becomes excessive, or in response to an external pressure signal (121) representing another vehicle condition, the control spool (73) is moved to a position (FIG. 5 )in which control pressure is ported to a second servo port (B), thus positively reducing the displacement of the pump (11).

Abstract: A hydraulic drive system comprises a controller (12) and several condition sensors. A boom-up target flow rate setting section determines a boom-up target flow rate based on signals from a pressure sensor (11) and a rotational speed meter (16), a pump delivery rate detecting section determines a pump delivery rate based on signals from a tilt angle sensor (15) and the rotational speed meter (16), a differential pressure detecting section and a center bypass flow rate calculating section determine a center bypass flow rate based on signals from pressure sensors (9, 10), a boom cylinder calculating section determines a boom cylinder flow rate from the pump delivery rate and the center bypass flow rate, and a first pump target displacement volume calculating section calculates a first pump target tilt angle .theta..sub.1 in accordance with the difference between the boom-up target flow rate and the boom cylinder flow rate. In this case, .theta..sub.1 is larger than a second pump target tilt angle .theta..sub.

Abstract: A fluid pressure driving system for a vehicle includes a reservoir tank in which an amount of fluid is stored, a variable capacity oil pump sucking the fluid from the reservoir tank and discharging the resultant fluid, a control device for adjusting a quantity of the fluid discharged from the variable oil pump, and a distributor valve having an inlet port for receiving the fluid from the variable capacity oil pump. The distributor valve discharges a fixed amount of the fluid and the remaining amount of the fluid from a first outlet port thereof and a second outlet port thereof, respectively. A first passage connects the first outlet port of the distributor valve and the reservoir tank. A second passage connects the second outlet port of the distributor valve and the reservoir tank. A power steering device is associated with a steering wheel and disposed in the first passage. A hydraulic motor is disposed in the second passage, and a cooling fan is mounted rotatably on the hydraulic motor.

Abstract: A device for controlling the variable capacity motor incorporated in a hydraulic drive vehicle, wherein a control valve for reducing the oil pressure for controlling the motor is provided to pilot hydraulic piping extending from a control pump or controlling the capacity of the motor, and changeover valves are provided for performing changeover between operation and non-operation of the pressure reduction valve. The above structure serves to control the minimum capacity of the variable capacity hydraulic motor while reducing the pressure of pilot oil introduced from the control pump and, when a pressure in the main circuit exceeds a preset value, the changeover valves operate even when the pressure reduction valve is in operation so as to cancel such operation for continuously controlling the vehicle.

Abstract: A hydraulic control system has first and second actuators that can be selectively moved to a second operating position dependant upon the pressure of hydraulic fluid being simultaneously transmitted thereto through a common conduit. The force of the springs of the first and second actuators is selected so that when the pressure of the hydraulic fluid is at a preselected low pressure, only one of the actuators is moved to its second position and both of the actuators is moved to their second positions when the fluid is at a preselected high pressure. The use of a common conduit for carrying fluid to the actuators eliminates the expense and complexity of providing another flow path between rotatable parts of a vehicle.

Abstract: Reversible hydraulic motors driven by fluid from variable displacement pumps are useful in driving various mechanisms of earthmoving machines. The subject pilot control circuit includes a pilot operated valve in each of a pair of signal passages which communicate a pilot signal from a control valve to a pump displacement control. The pilot operated valve in one of the signal passages is shifted to a position blocking fluid flow therethrough by the pilot signal in the other signal passage. An accumulator means stores a portion of the pilot signal from the other signal passage and causes the pilot operated valve in the one signal passage to remain in the blocking position for a predetermined time after the pilot signal is vented from the other signal passage.

Abstract: The invention refers to a hydraulic circuit for limiting the torque of a hydrostatic hydraulic motor connected in closed circuit to a hydraulic pump, which in braking mode operates as a hydraulic pump, in which pressure control valves are connected before and after the hydraulic motor. For the solution of this problem to develop such a hydraulic circuit which limits the maximum torque at the shaft of the hydraulic motor to approximately identical values independent of the fact whether the hydraulic motor is operated in the motor mode or in the pump mode, the pressure control valves consist of pilot-operated pressure control valves (6,7; 8,9). There is provided at least one on-off valve (5) which, when the hydraulic motor (2) is in the motor mode, switches the pilot-operated pressure control valve of the pressure side to a higher maximum pressure, and in pump mode it switches the pilot-operated pressure control valve of the other pressure side to a lower maximum pressure.

Abstract: A process for controlling a hydrostatic adjustment gear (HG) of a hydrostatic-mechanical, continuous, split-output torque shift transmission, where a displacement volume (V.sub.new) is controlled following the engagement of a clutch (K2, K3) of a new gear, taking into consideration a leakage volume (DV.sub.old) in respect to a theoretical displacement volume (V.sub.th), after which the clutch (K2, K3) of the respective previously operating gear, which is still turning, is disengaged, where each new displacement volume (V.sub.new) is determined from the prior leakage volume (DV.sub.old) in accordance with different hydraulic pressure conditions in the adjustment gear (HG) prior to and following the shifting operation, where the setting of the new displacement volume (V.sub.new), which is determined in accordance with the hydraulic pressure conditions from the prior leakage volume (DV.sub.old), takes place in respect to the theoretical displacement volume (V.sub.th) in accordance with a new leakage volume (DV.

Abstract: A displacement control valve has a valve body with a fluid metering valve spool axially movable between pilot pressure chambers formed at opposite ends of an interior bore in the valve body. An internal spring feedback apparatus is mounted on the valve spool in one of the pilot pressure chambers and elastically interconnects the swashplate of a variable displacement hydraulic unit with the valve spool. An elongated housing surrounds the spring and spring guides and is mechanically coupled with the swashplate. The housing and spring guides form a fluid seal between the valve spool and the valve body to seal the pilot pressure chamber in which the feedback apparatus is mounted.

Abstract: The invention relates to a variable displacement pump supplying fluid to a number of consumers. The pump control for adjusting the delivery rate is actuated by a signal which is produced by the respective highest loaded consumer. The signal is provided by a valve, in particular a pressure compensating valve which is associated with the consumer, and which valve opens a spool land when the valve becomes positioned at its control end range. A pressure signal from any pressure fluid source is delivered through the land to the pump controller. The control, according to the invention, offers a broad variety of possibilities for arranging the pressure compensation valve at various locations, engaging the valve by a variety of pressure differences, and using a number of pressure fluid sources of provide for the signal pressure to actuate the pump controller.

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 variable displacement hydrostatic unit (11) includes a swashplate (23), the position of which is controlled by a servo piston (73). A multiple mode control (33) is disclosed, including a main valve member (63) and a secondary valve member (65), both of which are attached to a linkage member (61) by which movement of a manual control handle (47) actuates the main and secondary valve members. The flow of control pressure from a charge pump (21) ot the servo piston (73) is controlled by a pair of solenoid valves (83,85) having two control conditions. In one, control pressure flows through the main valve member (63) to give a normal operating mode (FIG. 6), while in the other control condition, control pressure flows through the secondary valve member (65) to provide a secondary operating mode (FIG. 7).

Abstract: A hydraulic circuit for a hydraulic shovel includes a variable displacement hydraulic pump; selector valves communicated with the variable displacement hydraulic pump; actuators communicated with the selector valves; variable relief valves provided in a discharge oil passage of the variable displacement hydraulic pump and also provided in input oil passages of some of the actuators; a pilot hydraulic pump communicated with the variable relief valves through pilot oil passages; a solenoid valve provided in the pilot oil passage for changing set pressures of the variable relief valves; a regulator for controlling a discharge quantity of the variable displacement hydraulic pump; and a pilot oil passage for communicating the solenoid valve with the regulator.

Abstract: A hydraulic system for a construction machine comprising plural hydraulic actuators (23-28) driven by fluid supplied from a pump (22), first and second flow control valves (29-34) for controlling flows of fluid supplied to the first and second actuators, and first and second distribution compensating valves (35-40) for controlling first differential pressure (.DELTA.P v1-.DELTA.P v6) produced between inlets and outlets of the first and second flow control valves. The first and second distribution compensating valves have respective drives (45-50, 35c-40c) for applying control forces (Fc1-Fc2) in accordance with the second differential pressure to the associated distribution compensating valves, to thereby set target values of the first differential pressures. The hydraulic system includes first means (59) for detecting the second differential pressure (.DELTA.

Abstract: Described herein is a hydraulic pump control circuit for travelling construction machine, the circuit being of the type including various hydraulic actuators divided into two groups to be driven by first and second pumps, respectively, left and right vehicle drive motors provided in the respective groups, and a change-over valve located on the discharge side of the first and second pumps and switchable to a position for supplying the oil pressure from the second pump in parallel to the left and right vehicle drive motors. According to the invention, the control circuit is provided with a pilot proportioning valve located between a discharge flow rate control regulator for the second pump and a pilot pressure source, and means for applying the pilot pressures acting on left and right vehicle drive valves to pilot ports of the pilot proportioning valve, the proportioning valve being operated by the sum of the pilot pressures applied to the pilot ports to produce a control pressure for the second pump regulator.

Abstract: A variable displacement hydraulic pump and a hydraulic motor are connected in a closed circuit. A pressure oil supply means includes the variable displacement hydraulic pump and a tilting controlling means for controlling a tilt angle of the hydraulic pump and supplies an amount of pressure oil corresponding to the tilt angle of the hydraulic pump to the hydraulic motor. When rotation of a prime mover is detected by a rotation detecting means, an opening and closing valve is changed over to a first position in which the pressure oil supply means is permitted to supply pressure oil. When stopping of the prime mover is detected by the rotation detecting means, the opening and closing valve is changed to a second position in which the pressure oil supply means is inhibited from supplying pressure oil.

Abstract: Overheating of hydraulic fluid in a hydraulic motor system subject to aiding loads can be avoided without paying a weight or volume penalty by providing a return port (64) adapted to be connected to the system return (22) in fluid communication with a cavity (46) within an hydraulic motor housing (32) that houses the swash plate (34). A pressure relief valve (62) is connected to the supply port (38) of the hydraulic motor (30) as well as to the return port (64) and is operative to open when the pressure at the supply port (38) increases as a result of an aiding load so as to allow recirculation of hydraulic fluid through the motor (30). By placing the swash plate cavity (46) in the recirculation line, increased heat sink capacity is added to the system without increasing weight or volume.

Abstract: A coaxial hydraulic actuator system utilizes a vane pump close coupled to a vane actuator. The vane pump includes a rotatable housing which is perpendicularly movable by a control piston to direct fluid flow through first and second fluid conduits in a pintle port transfer shaft. The transfer shaft conduits are in communication with first and second variable volume compartments in the vane actuator. Thus, controlled movement of the vane pump housing results in corresponding resulting angular movement between the actuator vane and the actuator housing. This relative angular positioning can be used to control the relative positioning between first and second loads, such as the rotors of a dual permanent magnet generator.

Abstract: A hydraulic drive system is equipped with an engine, a plurality of hydraulic pumps adapted to be driven by the engine and including a variable displacement hydraulic pump provided with a displacement varying mechanism, a hydraulic motor connected to the variable displacement pump, a hydraulic actuator for actuating the displacement varying mechanism of the variable displacement hydraulic pump, a working fluid feeding means for feeding the hydraulic actuator with a hydraulic fluid of a pressure according to the degree of control of an accelerator lever which is adapted to instruct a target revolution number of the engine, and a low-pressure circuit for allowing the hydraulic fluid to be discharged therethrough from the hydraulic actuator.

Abstract: A speed control system for a working vehicle comprises a hydrostatic transmission for propelling the vehicle, a hydraulic cylinder and a control valve. The hydraulic cylinder includes a cylinder case operatively connected to a control shaft for varying a swash plate angle of the hydrostatic transmission, and a piston rod fixed to a case containing the hydrostatic transmission. The control valve is fixed to the cylinder case and includes a spool extending parallel to the hydraulic cylinder and operatively connected to a foot pedal for manually controlling the hydrostatic transmission. The cylinder case is shiftable following a shift of the valve spool.

Abstract: A vehicular steering mechanism of overly complex construction is known which displaces a left turn control valve or a right turn control valve through separated cams in response to the rotation of a steering wheel. The subject steering mechanism is simpler, more economical and more compact by including an input shaft and a single actuating cam which are conjointly rotatable away from a neutral position in either direction. The actuating cam defines a profiled guide slot of a substantially spiral shape, and a cam follower assembly is cooperatively associated therewith including a cam following roller wheel that is received in the profiled guide slot. The cam follower assembly includes a bellcrank supporting the roller wheel and indirectly connected to a left turn control valve and a right turn control valve. The vehicle is steered by the controlled rotation of the bellcrank and the subsequent displacement of the control valves and. The steering mechanism also includes an effective centering and stop assembly.

Abstract: A closed-loop hydrostatic transmission is disclosed of the type with a fluid pump (10) and a fluid motor (12), both of which are variable displacement. A pair of stroking cylinders (36,38) varies the displacement of the motor between minimum displacement and maximum displacement, under the control of a motor stroking valve (70) which includes a stroking valve member (90) movable in response to changes in fluid pressure in a pressure chamber (110). The displacement of the pump is controlled by a main controller (50) in response to movement of an input handle (60). Whenever the handle (60) is moved to the neutral position, a neutral switch (122) is closed, thus generating a neutral signal which is transmitted to an electromagnetic valve member (114), which controls the pressure in the fluid pressure chamber (110) to command the motor to maximum displacement.

Abstract: An improved closed-loop hydrostatic transmission system is provided of the type including a pump (11), a motor (13), and a pair of conduits (15 and 17). The system includes a main control valve (43) and a charge pump (23) which is the sole source of make-up fluid to the closed-loop system and the sole source of control fluid for varying the pump. The system includes a power limiting means comprising first and second pressure relief valve means (75 and 77) operable to provide fluid communication from whichever side of the closed-loop is at high pressure to the system reservoir whenever system pressure exceeds the predetermined maximum pressure. The motor is adapted to transmit drive torque to a reversible load (37) of the type having a known inertia and a predeterminable time of deceleration from maximum speed operation in one direction to a standstill condition.

Abstract: The torque of a hydraulic machine is dependent of the fluid pressure delivered to the machine and is further dependent of the adjustment of its volume of through-put. In response to a load coupled to the machine, a speed results which is controlled by a speed control system acting on the adjusting system of the hydraulic machine. According to the invention, an electro hydraulic speed control comprises a pair of control circuits which are connected to, but operate independent of each other. Thus the electrical control circuit produces a control signal y.sub.e1 from the difference of the actual value and the desired value of the speed for adjusting a hydraulic restricting means which produces a hydraulic pressure signal p.sub.st in the hydraulic control circuit which pressure signal is compared with a hydraulic reference signal p.sub.o to produce a differential pressure signal p.sub.o -p.sub.st which is applied to the adjusting cylinder of the hydraulic machine.

Abstract: Reversible hydraulic motors drdiven by fluid from variable displacement pumps are useful in driving various mechanisms of earthmoving machines. It is desirable to control both the speed and direction of the motor with a single lever. The subject hydraulic control system includes a selector valve which has a fluid control section for directing pilot fluid to a reversing valve to reverse the direction of the motor. A signal control valve is mechanically actuated by movement of the selector valve to the operating position so that a regulated pressure control signal is directed to a displacement control of variable displacement pump to regulate the volumetric output of the pump and thus the operating speed of the motor.

Abstract: A hydraulic drive circuit system is equipped with an accelerator pedal and an accelerator lever for respectively instructing target revolution numbers for an engine, a link plate for selecting greater one of the instruction values, and a linkage and a switch for controlling valves respectively so as to close the flow passage of a line interposed between a charge pump and a low pressure line irrespective of the instruction value of the accelerator pedal when the accelerator lever has not been controlled but for controlling the valves so as to restrict the flow passage of the line in accordance with the instruction value of the accelerator pedal when the accelerator lever has been controlled.

Abstract: A steer-by-driving control for controlling a hydrostatic steering unit to permit consistent operator input during forward and reverse travel has a valve assembly including a distribution valve and a pair of sleeve valves. The sleeve valves are rotatably mounted on the distribution valve and are interconnected by a gear arrangement. One sleeve valve is rotated by the operator in response to a steer request while the other sleeve member, due to the gearing, rotates oppositely. The distribution valve member controls fluid flow through forward and reverse steer passages formed in the sleeve valves to a signal valve for distribution to a control member of a hydrostatic unit. The distribution valve member is subjected to rotary input from the hydrostatic steering unit to stop fluid flow when the proper steer position has been reached. The signal valve is positioned according to the direction of the vehicle operation to selectively send the steer signals to the proper portions of the hydrostatic control.

Abstract: A hydraulic drive system to actuate the piston of a cylinder unit comprises a first hydrostatic machine having variable displacement, a second hydrostatic machine mechanically coupled to said first machine and operating as a signal generator either in a pump mode or a motor mode, and a third hydrostatic machine of fixed displacement mechanically coupled to said first machine, which third machine is hydraulically connected to said cylinder unit. In response to zero speed or rotation of the drive system the piston of the cylinder unit may be stopped in any position, or, respectively, raised or lowered. The variable displacement machine may operate as a pump and as a generator in which latter case energy is recovered in lowering a load.

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: The invention relates to a hydraulic control system for changing the speed and direction of a hydraulically operated tracked vehicle (1). The hydraulic control system is equipped with a feed pump (34) for the control fluid and with hydraulic undercarriage pumps (12) and (13). The undercarriage pumps (12) and (13) comprise regulating cylinders (18) and (19) subjected to the control fluid and intended for adjusting the pump pivoting angle. The regulating cylinders (18) and (19) are each equipped with two regulating-cylinder chambers (26, 28) and 25, 27) separated from one another by a regulating piston (22) and (23).

Abstract: A hydraulic circuit for a large crane furnished with a counterweight carriage detachably connectable to the swivel unit of the crane.