Abstract: A control system that uses an algorithm to control the fan speed in a cooling system for an engine is disclosed. The algorithm is adapted to maintain a cooling medium at a set temperature instead of an operating temperature range of the cooling medium. The algorithm is also adapted to maintain a cooling medium at a set temperature and to build a cooling safety margin in response to an engine output torque percentage that is below an output torque percentage setpoint.

Abstract: A control system that uses an algorithm to control the fan speed in a cooling system for an engine is disclosed. The algorithm is adapted to maintain a cooling medium at a set temperature instead of an operating temperature range of the cooling medium. The algorithm is also adapted to maintain a cooling medium at a set temperature and to build a cooling safety margin in response to an engine output torque percentage that is below an output torque percentage setpoint.

Abstract: An example valve assembly is configured: generate a valve load-sense pressure signal indicative of a pressure level at a workport of an actuator; generate a pilot fluid signal to be communicated to a worksection of a valve assembly to enable shifting a spool in the worksection; compare a first pressure level of the valve load-sense pressure signal to a second pressure level of the pilot fluid signal; and communicate the pilot fluid signal to a load-sense port fluidly coupled to a load-sensing source of pressurized fluid when the second pressure level of the pilot fluid signal exceeds the first pressure level of the valve load-sense pressure signal.

Abstract: The invention relates to a device for supplying ports to a machine section (26) of a hydraulic machine arrangement (40), the device (10) comprising a low-pressure inlet port (12), a leakage inlet (16), a low-pressure chamber (18) having a low-pressure opening (22) for establishing fluid communication with the machine section (26), a high-pressure outlet port (14), and a high-pressure chamber (20) that is in fluid communication with the high-pressure outlet port (14), the high-pressure chamber (20) having a high-pressure opening (24) for establishing fluid communication with the machine section (26), wherein the low-pressure inlet port (12) is in fluid communication with the low-pressure chamber (18), wherein a leakage path (36) extends from the high-pressure chamber (20) through the machine section (26) to the leakage inlet (16), characterized in that the device (10) further comprises a control valve member (28) connecting the leakage inlet (16) to the low-pressure chamber (18), wherein the control valve memb

Abstract: A hydraulic system includes: a regulator that adjusts a tilting angle of a pump; and a controller that controls the regulator such that a discharge flow rate of the pump is a lower one of an operation-requiring flow rate and a horsepower control flow rate. The controller stores a first horsepower control line and a second horsepower control line lower than the first control line. When an operating point exceeds the first horsepower control line, the controller decreases the tilting angle of the pump; when the operating point falls below the second horsepower control line, the controller increases the tilting angle of the pump. When the operating point exceeds the first control line or falls below the second control line, it is shifted and positioned between the first control line and the second horsepower control line, keeping the tilting angle of the pump as it is.

Abstract: The present disclosure relates to a method for controlling a swing motor in a hydraulic system and a hydraulic system. The method for controlling the swing motor in the hydraulic system and the hydraulic system according to the exemplary embodiment of the present disclosure may ensure the sufficient amount of hydraulic oil in a make-up line in a situation in which the hydraulic oil needs to be supplementarily supplied to the swing motor in the hydraulic system. Therefore, it is possible to prevent the occurrence of cavitation in the swing motor by stably supplying the amount of hydraulic oil at the point in time where the hydraulic oil needs to be supplementarily supplied to the swing motor. In addition, it is possible to prevent the occurrence of abnormal noise which is harsh to the ear when the cavitation occurs.

Abstract: Abnormality detection device for a hydraulic circuit with oil pump capable of increasing pressure of oil sucked through a suction port and discharging the oil through discharge ports; a switching unit switching between fully and partially discharged states; a pressure regulation unit regulating oil pressure; and a hydraulic pressure detection unit that detects the oil pressure includes: a storage unit that stores a maximum discharge pressure in the partially discharged state; a switching control unit that switches to either one of the discharged states; a pressure regulation control unit that sets a target pressure higher than the maximum discharge pressure in the partially discharged state, and performs pressure regulation control to achieve the target pressure; and a determination unit that determines whether the switching unit has a fixation abnormality in one of the discharged states by comparing hydraulic pressure with maximum discharge pressure in the partially discharged state.

Abstract: In accordance with an example embodiment, a system for managing a unique hydraulic system warmup method is described. A warmup system controller is central to the system and provides an interfacing point for communication to hardware components and a machine operator. The warmup system issues commands based on sensor inputs in light of defined rules and/or known physical properties of hydraulic fluids. Hydraulic system warmup is managed by the warmup system controller, which is configured to issue commands to affect hydraulic pumps and valves. By way of a controller managed process, the system functions to maximize hydraulic system pressure and limiting release of pressures in the lines, such that the pumps are able to maintain maximum pressure for a sufficient period of time.

Abstract: Provided is a work machine including: a variable-displacement pump 2; an actuator 5 driven by a hydraulic fluid delivered from the pump 2; a flow control valve 4 of an open-center type that controls a flow rate of the hydraulic fluid supplied to the actuator 5; a bleed-off line 8a connecting the actuator flow control valve 4 to a tank 6; a bleed-off flow control valve 8 disposed in the bleed-off line 8a; an operating device 3 that specifies operation of the actuator 5; a bleed-off control device 14 that controls a degree of opening of the bleed-off flow control valve 8 in accordance with an amount of manipulation of the operating device 3; and a pump control device 15 that controls, in accordance with the degree of opening of the bleed-off flow control valve 8, a pump flow rate by correcting a reference pump flow rate that is based on the amount of manipulation of the operating device 3.

Abstract: A system and a method for operating a hydraulic driven work machine including a hydraulic travel motor having a variable displacement is provided, wherein a flow of hydraulic fluid generated by a hydraulic pump is provided to the travel motor and wherein a control valve is provided for controlling the flow of hydraulic fluid from the hydraulic pump to the travel motor. The hydraulic pump is provided with a hydraulic control depending on a load signal generated by the travel control valve and the travel motor is provided with an electric control according to a desired driving behavior.

Abstract: A hydraulic control system includes a first oil passage, a first oil pump, a second oil passage, a second oil pump and a check valve. The first oil pump is disposed in the first oil passage. The second oil passage bypasses the first oil pump, includes an intake oil passage and a discharge oil passage, the intake oil passage and the first oil passage are connected to each other at a connection point, and the discharge oil passage includes an air vent hole. The second oil pump is disposed in the second oil passage, configured to take in oil from the intake passage, and configured to discharge the oil into the discharge oil passage. The check valve is provided between the connection point and the air vent hole, configured to restrict flow of the oil from the air vent hole toward the connection point via the second oil pump.

Abstract: Provided is a hybrid construction machine (driving the upper swing structure using a hydraulic motor and an electric motor together) capable of regenerating the energy of the upper swing structure in deceleration or stopping into electric power and using the regenerated electric power for assisting the driving of the upper swing structure, while also being capable of securing satisfactory operational feeling and operation capability even when the electric motor does not operate. When the electric motor is not driven, a controller controls a hydraulic circuit system (specifically, a swing direction/flow rate control valve, a center bypass cut valve and a regulator) so as to increase output torque of the hydraulic motor by an amount corresponding to torque to be compensated for the non-driving of the electric motor compared to cases where the electric motor is driven.

Abstract: A hydrostatic variable displacement pump (2) has a displacement volume set by an electro-hydraulic control device (10) provided with a safety function. In a fault scenario, the variable displacement pump (2) is set to a neutral position. The electro-hydraulic control device (10) has a single electro-hydraulic setpoint encoder (30) to specify the setpoint of the displacement volume of the variable displacement pump (2) and an electrically actuatable valve device (35) connected in series downstream of the setpoint encoder (30), by which the direction of displacement of the variable displacement pump (2) is controlled and which is provided with the safety function.

Abstract: A control device for a hybrid construction machine includes a discharge pressure introduction passage that leads a discharge pressure from a variable volume pump to a regulator, and a load pressure introduction passage that leads one of a maximum load pressure of respective actuators and a load pressure of a hydraulic motor to the regulator. A controller, having determined that the actuators are in an inoperative condition on the basis of a detection result from an operating condition detector, excites a solenoid of a solenoid pilot control valve such that a discharge oil from the variable volume pump is led to the hydraulic motor, and controls the regulator such that a differential pressure between the discharge pressure of the variable volume pump and the load pressure of the hydraulic motor is kept constant.

Abstract: A fluid controller comprising a housing separating an interior of the housing from an inflatable bladder is disclosed, the fluid controller including a plurality of valves fluidly coupling the interior of the housing to the inflatable bladder through a respective opening in the housing, a pump located at least partly within an interior of the housing, wherein the plurality of valves and respective orifices are configured to provide a fluid path between the interior of the housing and the inflatable bladder during inflation of the inflatable bladder, and wherein a valve and respective orifice is biased open to provide a fluid path between the interior of the housing and the inflatable bladder for fluid release.

Abstract: Cut-in-cut-out valves for hydraulic circuits. The hydraulic circuits include a hydraulic pump outputting a variable pressure controlled by a slaving line, an accumulation circuit, a return line to the reservoir, a cut in-cut-out valve. The hydraulic circuits also include a cut-in-cut-out valve having four orifices, a first orifice connected to the supply line, a second orifice connected to the slaving line, a third orifice connected to the return line leading to the reservoir, and a fourth orifice connected to the accumulation circuit. The cut-in-cut-out valve alternates between two positions as a function of the pressure in the accumulation circuit, a cut-in position in which the first, second and fourth orifices are connected to each other, and a cut-out position in which the first and fourth orifices are closed.

Abstract: A controller includes a storage unit that stores a map in which an operation amount and an upper limit value of suction torque of a hydraulic pump are associated with each other, for each operation content identified by a cylinder that is an operation object out of the cylinders, and by a direction of operation performed on this cylinder; an operation torque determination unit that determines the upper limit value of suction torque for each cylinder by using the map stored in the storage unit when an actuation command relating to at least one cylinder is input by an operation lever; a high-level selection unit that selects the maximum upper limit value of suction torque out of the upper limit values of suction torque determined by the operation torque determination unit; and a regulator that regulates a displacement of the hydraulic pump so as to obtain torque equal to or lower than the suction torque selected by the high-level selection unit.

Abstract: A hydraulic drive device for a construction machine includes an engine stopping unit and a discharge rate control unit. The engine stopping unit stops the engine when a predetermined state of the construction machine has continued for a predetermined period of time. The discharge rate control unit controls a discharge rate control pressure being input to the regulator, when an exhaust emission control device performs regeneration control, or performs warm-up control, and the gate lock lever is in the open position.

Abstract: Disclosed is a controller of a hybrid, construction machine wherein electric power is generated by utilizing the standby flow rate of first and second main pumps, and the standby flow rate is converted into energy. Pilot channels are connected to the upstream side of on/off valves which are closed when first and second main pumps ensure a standby flow rate, and a controller unit judges that the first and second main pumps are discharging at the standby low rate based on pressure signals from first and second pressure sensors, and brings first and second solenoid valves to an open position.

Abstract: A travel control device for a work vehicle includes: a hydraulic pump; a plurality of hydraulic motors connected to the hydraulic pump in parallel through a closed-circuit connection, that drive different wheels with pressure oil delivered from the hydraulic pump; a slip detection device that detects a slip occurring at each of the wheels; and a flow control device that reduces, upon detection of a slip occurring at any of the wheels by the slip detection device, a quantity of pressure oil supplied to a hydraulic motor for driving the wheel at which the slip has been detected, among the plurality of hydraulic motors.

Abstract: A hydraulic system has a variable displacement pump that sends fluid from a tank into a supply conduit from which separate open-center control valves convey the fluid to each one of a plurality of hydraulic actuators. The control valves have open-center orifices connected in series between a bypass node and the tank, thereby forming a bypass passage. Pressure at the bypass node controls displacement of the pump. A valve arrangement is connected between an outlet of the pump and the bypass node and is responsive to an amount of fluid flow through the supply conduit to the plurality of hydraulic functions, wherein as the amount of fluid flow increases, the valve arrangement causes fluid flow to the bypass node to decrease. Thus the pressure at the bypass node varies as a function of the operation of the control valves.

Abstract: A lubrication system is provided that includes a pump operatively connected to one or more supply lines for delivery of a lubricant, the system including a first pressure sensor associated with the supply line at a first position, and a second pressure sensor associated with the supply line at a second position downstream of the first position and pump, a controller configured to receive pressure signals and control operation of the pump based upon the pressure differential between the pressures at the first position and second position. The pressure differential may be employed to determine when a pressure at a third position downstream of the second position has been achieved. At least one of the pressure sensors may be positioned adjacent to the pump, the controller further being operable to deactivate the pump in the event that a maximum pump pressure has been met.

Abstract: A hydraulic driving device for a working machine surely prevents behavior of a single rod double acting cylinder not intended by an operator when discharge pressure of a main pump is raised to raise exhaust gas temperature to temperature required for burning particulate matter. A selector valve 160 interposed between a spool valve 61 and a rod chamber of a single rod double acting cylinder 51 and a section (a filter regeneration time actuation valve 122, a vehicle body controller 150) controlling the selector valve, are provided. A switch control section prevents a flow of oil directed from the rod chamber of the cylinder toward the spool valve by actuating the selector valve by a poppet of the selector valve when a by-pass cut valve 110 is controlled to increase a load of an engine 21 to a degree exhaust gas temperature reaches temperature required for burning particulate matter.

Abstract: A hydraulic drive system for a hydraulic working machine sets a delivery pressure at a preset value upon raising a temperature of exhaust gas to a temperature needed for combustion of particulate matter by increasing a load to be applied to an engine. In a non-operation state, a variable restrictor is controlled by a controller and a delivery pressure control valve to increase a delivery pressure of a variable displacement hydraulic pump, so that the load is increased to raise the temperature of exhaust gas to the temperature needed for the particulate matter combustion. At this time, the controller controls the delivery pressure control valve such that a delivery pressure to be detected by a delivery pressure sensor will conform with a preset reference delivery pressure. The reference delivery pressure is set to a minimum pressure that can provide the exhaust gas with combustion heat.

Abstract: The invention relates to a drive system for an infeed conveyor (22) of a harvester (10), having an adjustable hydraulic pump (66), the flow rate and flow direction of which can be adjusted by means of a first actuator (76), said hydraulic pump being connected to a hydraulic motor (68) which drives the infeed conveyor (22). A controller (70) is connected to a foreign-body detection device (108) and to a first valve (90) for controlling the actuator (76) that controls the hydraulic pump (66). The controller (70) controls the first valve (90) at least for a short time by reversing the flow direction is a foreign body appears. In addition, it is suggested that the hydraulic motor (68) has an adjustable displacement volume, and that the controller (70) increases the hydraulic motor displacement volume (68) is a foreign body appears.

Abstract: A load sense valve assembly includes a first valve in flow communication with a pump discharge line, a second valve in flow communication with the first valve, and a third valve in flow communication with the first valve. The first valve can be a solenoid actuated directional control valve. The second and third valves can be hydraulic pilot actuated directional control valves.

Abstract: Laying apparatus and method for cables, lines, conductors or suchlike. The apparatus comprises at least a hydraulic circuit provided with a variable delivery feed pump and with a motor connected to the feed pump in order to drive laying members for the cables and suchlike. The hydraulic circuit comprises detectors able to detect the value of pressure of the oil inside the hydraulic circuit and to compare it with a pre-determined pressure value, and valves connected to the detectors and able to reduce the delivery of the feed pump in the event that the pressure measured exceeds the pre-determined pressure value.

Abstract: A valve is provided for a hydraulic system having a source of pressurized fluid, a fluid actuator, and a proportional pressure compensating valve. The valve has a bore in fluid communication with the source and the fluid actuator. The valve also has a valve element disposed in the bore and movable between a flow blocking position and a flow passing position to selectively fluidly communicate the source with the fluid actuator. The valve also has a valve signal passageway disposed within the valve element and configured to be in fluid communication with a pressurized fluid having a signal pressure indicative of pressure supplied to the fluid actuator. The valve further has first and second orifices disposed within the valve element in fluid communication with the valve signal passageway and the bore. The valve signal passageway is configured to communicate the signal pressure with the first and second orifices.

Abstract: A device for generating rotational energy for hydraulic fluids, which includes at least one hydraulic cylinder, the at least one hydraulic cylinder comprising at least two chambers, wherein each of the at least two chambers are in fluid communication with the other. The hydraulic fluid is displaced from the hydraulic cylinder to an accumulator and a valve, which controls the release of the hydraulic fluid to a hydraulic motor. The hydraulic motor receives the hydraulic fluid from the accumulator and valve creating torque to drive a wheel or other device.

Abstract: The present invention lowers energy loss while at the same time enhancing the responsiveness of a steering control system. When a steering controller is operated rapidly, the aperture area of a steering flow control valve 4 rapidly increases, and the differential pressure (Pp?-PL) across the steering flow control valve 4 rapidly decreases. When the differential pressure (Pp?-PL) across the steering flow control valve 4 rapidly decreases, a flow control valve 6 is biased by the spring force of a spring 6f and quickly moves to the side of a valve position 6b to increase the differential pressure (Pp?-PL) and make it correspond to a set pressure. Thus, the pressure oil of a surplus flow ?, which up to this point has been flowing to a discharge oil line 7, is quickly supplied from the flow control valve 6 to a steering hydraulic cylinder 5 via the steering flow control valve 4. Thus, an output Q? starts quickly relative to an input St.

Abstract: Laying apparatus and method for cables, lines, conductors or suchlike. The apparatus comprises at least a hydraulic circuit provided with a variable delivery feed pump and with a motor connected to the feed pump in order to drive laying members for the cables and suchlike. The hydraulic circuit comprises detectors able to detect the value of pressure of the oil inside the hydraulic circuit and to compare it with a pre-determined pressure value, and valves connected to the detectors and able to reduce the delivery of the feed pump in the event that the pressure measured exceeds the pre-determined pressure value.

Abstract: A hydrostatic vehicle driving system structured from an engine to a drive axle in a working vehicle. A hydraulic pump driven by the engine and a variable displacement hydraulic motor for driving the drive axle are fluidly connected with each other through a hydraulic circuit. A motor capacity control system controls capacity of the hydraulic motor in correspondence to the condition of load on the engine. The motor capacity control system comprises load-detection means detecting hydraulic pressure in the hydraulic circuit replacing the load on the engine, a hydraulic actuator for changing the capacity of the hydraulic motor, and actuator-control means controlling the hydraulic actuator according to the detection of hydraulic pressure by the load-detection means.

Abstract: A fluid pressure control circuit includes a fluid pressure device which is operated by a fluid pressure; a control valve which is connected to the fluid pressure device via a connecting passage, and which changes a flow rate of predetermined fluid that is to be supplied to the fluid pressure device or that is to be discharged from the fluid pressure device according to a position of a valve element; and a pressure difference reflecting device which moves the valve element based on a difference in the fluid pressure between predetermined two different portions in the connecting passage and which changes the flow rate of the fluid that is to be supplied or to be discharged through the control valve according to the fluid pressure difference. With this fluid pressure control circuit, it is possible to obtain excellent responsiveness during supply/discharge of the fluid, change in the fluid pressure or the like, without increasing the amount of the fluid to be consumed.

Abstract: A circuit for controlling a discharge amount of a hydraulic pump to an actuator irrespective of a load pressure of the actuator even when an engine operates at a low speed has a variable displacement hydraulic pump connected with the engine; an actuator connected with the hydraulic pump; a center-bypass directional switching valve in a flow path between the hydraulic pump and the actuator for controlling start, stop and directional switching of the actuator during a switching operation; a pilot signal generating means in a down stream side of the center bypass for controlling the discharge amount of the hydraulic pump; and a discharge amount adjusting valve in a supply path of the actuator of the directional switching valve for controlling a discharge amount of hydraulic fluid to the actuator.

Abstract: A method is provided for controlling displacement of a variable displacement pump coupled to a load. The method includes determining an electrical signal to be applied to a proportional solenoid for a desired pump displacement based on known pump characteristics. The electrical signal is provided to the proportional solenoid. The displacement of the variable displacement pump is controlled based on the electrical signal to the proportional solenoid.

Abstract: A hydrostatic vehicle driving system structured from an engine to a drive axle in a working vehicle. A hydraulic pump driven by the engine and a variable displacement hydraulic motor for driving the drive axle are fluidly connected with each other through a hydraulic circuit. A motor capacity control system controls capacity of the hydraulic motor in correspondence to the condition of load on the engine. The motor capacity control system comprises load-detection means detecting hydraulic pressure in the hydraulic circuit replacing the load on the engine, a hydraulic actuator for changing the capacity of the hydraulic motor, and actuator-control means controlling the hydraulic actuator according to the detection of hydraulic pressure by the load-detection means.

Abstract: A target fan rotational speed (R.P.M.) corresponding to a temperature detected by a temperature detector is determined according to a set correlation and the capacity of a variable-capacity hydraulic pump is varied so that the rotational speed of a cooling fan becomes that determined target fan rotational speed. It thereby becomes possible to precisely control the blowing air volume (R.P.M.) of the cooling fan, and, when the cooling fan is driven with a hydraulic source, to construct a hydraulic circuit with fewer parts. Moreover, in cases where the torque absorbed by the fan-drive hydraulic motor fluctuates, control is effected to suppress fluctuations in the cooling fan rotational speed and stabilize the rotation. Furthermore, in cases where the load on the fan-drive hydraulic motor fluctuates, control is effected to suppress fluctuations in the cooling fan rotational speed and stabilize the rotation.

Abstract: Workability and operability of hydraulically-operated equipment is enhanced by optimally changing in accordance with the work content a responsiveness of an output signal relative to an input signal of each hydraulic control device, which constitutes a hydraulic system, at times heightening quick reaction capabilities, and at other times heightening steadiness. As a quantity of state of a load pressure signal of a hydraulic actuator, for example, is inputted to a response suppressing portion, and in accordance with a high-pass filter, a higher frequency fluctuation component in a pressure signal is extracted.

Abstract: A hydrostatic drive system with an adjustable pump in the delivery flow has at least one consuming device connected to the pump. Associated with each consuming device are actuation devices that specify the direction of movement and the speed of movement. A control valve device controls the direction of movement and the speed of movement. The delivery flow of the pump can be adjusted to the hydraulic flow required by the actuated consuming devices. The hydrostatic drive system makes possible the operation of the consuming devices independently of the load and the operation of the consuming devices independently of the direction of the load, in a simple manner and with lower energy losses. Associated with each consuming device is a delivery flow sensor that measures the hydraulic flow discharged from the consuming device to a reservoir, and/or a delivery flow sensor that measures the hydraulic flow from a delivery line of the pump to the consuming device.

Abstract: The invention provides a pump controller for a construction machine that allows an operator to set the maximum speed of a specific actuator arbitrarily without altering the negative control and acquire a smooth operation. The pump controller comprises a plurality of control valves to supply actuators with a controlled pressure oil, a variable displacement hydraulic pump to supply the plural control valves with the pressure oil in parallel, a center bypass connected in parallel to the control valves, and a restrictor to generate a control pressure for negatively controlling the variable displacement hydraulic pump installed at a terminal end of the center bypass.

Abstract: In an apparatus and a method for controlling the displacement of a steering pump for a work vehicle, the pressure loss can be decreased and the discharge of the steering pump can effectively be utilized even in a simultaneous operation with a work machine. The apparatus includes a steering gear preference flow-dividing valve (20) for supplying an oil quantity from the discharge of the steering pump (2) to a steering operation valve, so that the differential pressure between the input pressure and output pressure of the meter-in opening of the steering operation valve (10) is kept constant. The residual oil quantity is supplied to a work-machine operation valve (17, 18).

Abstract: A hydrostatic drive system is provided for a vehicle, in particular an industrial truck, with a hydrostatic traction drive system (16), a hydraulic work system (13) and a hydraulic steering system (9). The invention provides a drive system that is compact and exhibits improved operating behavior during the change from traction operation to coasting operation.

Abstract: The present invention is a control device for a variable displacement hydraulic pump by which the absorption horsepower of the hydraulic pump increases with excellent responsiveness and ON/OFF operations of a cut-off control of the maximum pressure can be selected. To this end, a hydraulic pump (2), a slow return valve (25) and a switching valve (24) placed parallel to each other in a flow path connecting a servo piston (4) and a servo valve (5); a solenoid valve (26), for controlling the pilot pressure of the switching valve (24); and an ON/OFF operation selectable selector (30), connected to a control device (10), are included; and the controlling device (10) outputs a command signal to the solenoid valve (26) when the selector (30) is switched ON to lower the operation speed of the swash plate angle of the hydraulic pump (2).

Abstract: Supply water temperature in a cooling tower is detected by a temperature detector, and based on the temperature detected by the temperature detector, a flow control valve in a hydraulic pressure supply line is controlled. As a result, operation of a hydraulic motor connected to a cooling fan can be controlled to efficiently cool down the water temperature to reach a preset temperature. Further, by a pressure-compensated variable displacement regulator of a variable displacement pump, the flow control valve is controlled to have irreducibly minimum pressure difference such that pressure on upstream side is slightly higher than the pressure on downstream side. Therefore, discharge pressure of the variable displacement pump can be suppressed to the irreducibly minimum value, and capacity of the variable displacement pump can be controlled to match the opening degree of the flow control valve.

Abstract: An improved pressure-compensated hydraulic system for feeding hydraulic fluid to one or more hydraulic actuators. A remotely located, variable displacement pump provides an output pressure equal to a control input pressure plus a constant margin. A pressure compensation system requires that a load-dependent pressure be provided to the pump input through a load sense circuit. An isolator transmits the load-dependent pressure to the pump control input, while preventing fluid from leaving the load sense circuit and flowing to the remotely located pump. A valve section, which controls the fluid flow between the pump and actuator, has a pressure compensating valve with a piston and spool controlling a pressure differential across a main control valve orifice by moving within a bore in response to a pressure differential between a pump supply pressure and the load sense pressure.

Abstract: A hydraulic control system is intended to easily hydraulically back up a trouble caused in an electric system, while employing a control unit (13) to utilize the advantage of electric control, when the displacement of a hydraulic pump (1) is controlled in accordance with a status variable of a hydraulic driving system. To this end, a pump regulator (16) is constructed so as to increase the tilting amount .theta. of a swash plate (1a) with a reduction in pressure of a second hydraulic signal Pc. A characteristic of the pump regulator is set such that a negative control pressure Pco can be employed to operate the pump regulator in place of the second hydraulic signal, and characteristics of a fixed throttle (10) and a spring (18d) in the pump regulator are set such that the pump regulator can be operated in the working range of the negative control pressure.

Abstract: Methods and apparatus for improving control of pressurized fluid flow through bootstrap power steering systems are disclosed. In particular, the methods include differentially measuring control pressure across internal flow control orifices as directly as possible. Differential control pressure measurements are made between Kelvin supply, or return, pressure values and a control pressure port of a control valve. In addition, methods and apparatus for improved speed sensitive control of steering assist and/or driver selectable steering effort are also disclosed. One of the methods comprises an extension of the method of differentially measuring control pressure across the internal flow control orifices wherein a range of control pressures are enabled. In addition, a method of improving low speed tactile steering feel wherein an electronically variable orifice is activated in order to provide additional fluid flow thereby increasing "on-center" hydraulic pressure gain is disclosed.

Abstract: A control valve is provided in a line between a variable displacement hydraulic pump and a hydraulic cylinder. The control valve controls flow rate of working fluid supplied to the hydraulic cylinder according to a manipulated variable of a lever. The control increases a discharge of the hydraulic pump in association with the increase in the manipulated variable and also controls to suppress the discharge as the discharge pressure of the hydraulic pump increases. A proper response corresponding to the operator's feeling can be realized in consideration of an actual pressure loaded on an actuator on the basis of a positive control system.

Abstract: A system for controlling a discharge flow rate of a variable displacement pump within an oil hydraulic circuit is disclosed. A bypass with a flow restricting valve couples the pressure control chamber of the discharge flow rate controller to the tank line to thereby allow a part of the oil in the pressure control chamber to escape through the bypass to the tank line. This escape occurs when a highly pressured oil is rapidly injected into the pressure control chamber of the discharge flow rate controller as a result of switching operations of both the pressure compensated valve and the load sensing valve.

Abstract: Methods and devices for enabling simplified bootstrap hydraulic systems for use in bootstrap hydromechanical and electrohydraulic vehicular power steering systems are disclosed. A simplified bootstrap control valve is provided wherein the control valve's load circuit is not interdicted in any way. The simplified bootstrap control valve comprises a four-way control valve having input slots formed in an open-center manner, intermediate slots formed in an open-center manner, return slots formed in a closed-center manner, and a passage for picking off the pressure value present in the intermediate slots. The pressure value present in the intermediate slots is utilized for regulating pumping apparatus providing fluid to the simplified bootstrap control valve such that pressure value present in the intermediate slots is substantially maintained at a preselected value. A simplified servo motor-positive displacement pump assembly of integrated construction is also provided.