Abstract: A working vehicle includes: a vehicle body provided with a traveling device; a hydraulic pump including a swashplate configured to change an output of the hydraulic pump according to a swashplate angle; a traveling motor including an output shaft having a rotation speed variable according to the output of the hydraulic pump and capable of transmitting power of the output shaft to the traveling device; an angle detector configured to detect the swashplate angle that is an angle of the swashplate; and a swashplate control unit configured to control the swashplate angle on the basis of control information relating to control of the swashplate angle and an actual swashplate angle that is the swashplate angle detected by the angle detector.

Abstract: A construction machine is provided that can cause each hydraulic actuator to accurately operate according to operation by an operator in combined operation in which a hydraulic fluid of a hydraulic pump is subjected to flow dividing and is supplied to plural hydraulic actuators. A controller 10, in a case of determining that combined operation is being carried out, controls a regulator 7a in such a manner that the delivery flow rate of a hydraulic pump 7 becomes larger than the total target flow rate of plural hydraulic actuators 4a, 5a, and 6a, and controls the respective opening amounts of plural directional control valves 8a1, 8a3, and 8a5 in such a manner that the difference between the respective target flow rates of the plural hydraulic actuators and the respective inflow flow rates of the plural hydraulic actuators sensed by velocity sensors 12 to 14 becomes small.

Abstract: A hydraulic work system can include a continuously variable displacement hydraulic pump that is powered by an engine and is in communication with a hydraulic actuator. A run-time displacement of the hydraulic pump for movement of the hydraulic actuator can be controlled based on a speed of the engine.

Abstract: Systems and methods for control of multi-function hydraulic commands of a multi-function electrohydraulic system are provided. In one aspect, a system for hydraulic control includes a first function in fluid communication with a first electrohydraulic control valve and a second function in fluid communication with a second electrohydraulic control valve. The system includes a controller in communication with the first electrohydraulic control valve and the second electrohydraulic control valve. The controller can be configured to receive an input target command, determine an achievable function rate based on the input target command, where the achievable function rate maintains a proportional relationship between the input target command and the achievable function rate.

Abstract: A method controls the movement of a boom, wherein the boom is moved by a plurality of hydraulic drives. Each hydraulic drive is fed with a hydraulic medium, the pressure and/or volume flow of which is adjustable. The method predefines a desired direction of movement and a desired speed of a boom tip; predictively calculates a pressure and/or a volume flow required for each of the hydraulic drives that are required for the desired direction of movement and desired speed; subsequently generates a supply pressure depending on the predictively calculated pressures and/or subsequently generating a supply volume flow as a function of the predictively calculated volume flows; and subsequently feeds the hydraulic drives required for the desired direction of movement and desired speed with the hydraulic medium having a respective feed pressure and/or a respective feed volume flow such that the boom tip moves in the desired direction of movement at the desired speed.

Abstract: An electric motor pump system includes a variable displacement pump, an electric motor connected to drive the variable displacement pump, a first control piston configured to limit an output pressure characteristic of the pump, and a second control piston controlled via a servo valve according to an output speed of the electric motor. In embodiments, the second piston is configured to maintain a substantially constant output flow of the pump as the output speed of the electric motor changes. With embodiments, the first and second control pistons may be configured to act on a yoke of the variable displacement pump.

Abstract: A hydraulic system for controlling an implement on a work machine may include a hydraulic reservoir, a hydraulic pump in fluid communication with the reservoir, a central valve in fluid communication with the pump and configured for controlling the implement, a load sense pressure relief system, and a controller. The controller may be configured for controlling the central valve and the load sense pressure relief system and selecting between operating the hydraulic system at a first pressure and a second pressure based on a factor relating to implement position.

Abstract: An engine (12) drives a variable capacity-type hydraulic pump (16), discharged hydraulic oil is selectively supplied to a cooling fan (19) and a hoist cylinder (11) in accordance with switching of a selection valve (17), thereby controlling the same on the basis of each target value. A pump discharge pressure (Pp) of the hydraulic oil discharged from the hydraulic pump (16) and a motor supply pressure (Pm) of the hydraulic oil supplied to a hydraulic motor (18) via the selection valve (17) are detected by sensors (27, 28) and are compared with pressure determination values stored in advance as a pump discharge pressure (Pp) and an actuator supply pressure (Pm) generated when the target value is achieved. Presence/absence of abnormality in the hydraulic actuator control device (15) is determined on the basis of a result of the comparison, and when abnormality is determined to have occurred, control is performed to minimize the capacity of the hydraulic pump (16).

Abstract: A method is provided for detecting inadmissible operating states of a work hydraulics of an agricultural tractor. The method includes providing at least one electrically actuated control valve, a branch allocated to the at least one control valve, and an operating unit for the manual actuation of the work hydraulics of a front linkage. The method also includes connecting the at least one electrically actuated control valve to a hydraulic consumer via a hydraulic coupling, supplying hydraulic fluid to a hydraulic lifting device of the front linkage, detecting a state variable indicative of a connection state of the hydraulic coupling by a sensor unit and communicated to a control unit, and deactivating the operating unit if the control unit identifies by way of the evaluation of the state variable that a hydraulic consumer is connected to the hydraulic coupling.

Abstract: Provided is a working vehicle capable of increasing lifting operation speed of a working device without increasing cost, even when provided with a circuit configuration that prioritizes a steering operation over a working device operation. A wheel loader 1 comprises a priority valve 451 configured to allow hydraulic oil discharged from a hydraulic pump 41 to flow into a steering drive circuit 43 preferentially over a working device drive circuit 44, and further comprises: an electric steering lever 30; a pair of solenoid control valves 34A, 34B configured to control a steering directional control valve 33; and a controller 5. The controller 5 is configured to control the pair of solenoid control valves 34A, 34B so as to limit operation speed of a steering 3 when determining that an engine 40 is in a low idle state and a lift arm 21 is performing a lifting operation.

Abstract: A hydraulic work system can include a continuously variable displacement hydraulic pump that is powered by an engine and is in communication with a hydraulic actuator. A run-time displacement of the hydraulic pump for movement of the hydraulic actuator can be controlled based on a speed of the engine.

Abstract: To achieve reduction of fuel consumption and enhancement of operability, in a hydraulic control circuit provided with a bypass oil passage formed by being branched from a discharge line of a hydraulic pump and extending to an oil tank, and a bypass valve having variable opening area for controlling a flow rate of the bypass oil passage, and to accurately perform pump pressure control through opening area control of the bypass valve without being affected by a condition of each time.

Abstract: A turn-drive apparatus capable of securing high acceleration at the time of turning start with a reduced relief loss includes a hydraulic pump of a variable capacity type, a turning motor, a turning control device, a relief valve, and a flow rate control device that controls a pump flow rate. The flow rate control device calculates a relief-cut-control target pump flow rate on the basis of the sum of a minimum relief flow rate and a turning-speed flow rate, and inputs a pump capacity command to the variable capacity-type hydraulic pump based thereon. The flow rate control device makes the relief-cut-control target pump flow rate larger than the sum of the minimum relief flow rate and the turning-speed flow rate at the time of turning start.

Abstract: A hydraulic system for a work vehicle includes a first pump with a first swashplate providing a first flow in a first circuit and a second pump with a second swashplate providing a second flow in a second circuit. A supplemental pump with a supplemental swashplate provides a supplemental flow to a supplemental circuit. A first valve selectively enables flow from the supplemental circuit to the first circuit. A second valve selectively enables flow from the supplemental circuit to the second circuit. A controller determines to operate the supplemental pump in one of a standby condition and a use condition based in part on a first angle of the first swashplate and a second angle of the second swashplate.

Abstract: A working machine includes a first traveling fluid line through which operation fluid applied to a first pressure receiving portion when a traveling operation member is operated, a second traveling fluid line through which operation fluid applied to a second pressure receiving portion when the traveling operation member is operated, a third traveling fluid line through which operation fluid applied to a third pressure receiving portion when the traveling operation member is operated, a fourth traveling fluid line through which operation fluid applied to a fourth pressure receiving portion when the traveling operation member is operated, and a controller configured or programed to judge, first, second, third and fourth pilot pressures, whether the traveling operation member is operated in a direction corresponding to any of spin-turn, pivotal-turn and straight-traveling.

Abstract: A dual pressure margin priority circuit and method for controlling flow from a pump to steering valve and low priority inlets. A steering pressure valve controls flow from pump to steering valve inlets, and provides a steering valve load sense pressure. A priority valve controls flow from pump to low priority inlets. A load sense cutoff valve has a first inlet receiving the steering valve load sense pressure. The load sense cutoff valve controls flow through the priority valve based on steering valve load sense pressure at the first cutoff valve inlet. The cutoff valve can include a second inlet coupled to tank, and a load sense input coupled to the steering valve load sense pressure. The cutoff valve can be a pressure limiter valve. The priority and steering pressure valves can be 2-way proportional flow spool valves with bias springs, and contributing and opposing load sense inputs.

Abstract: A system for controlling hydraulic fluid flow within a work vehicle includes a pilot conduit fluidly configured to receive a pilot flow of the hydraulic fluid from a fluid supply conduit such that an operation of a compensator valve is controlled based on a pressure of the pilot flow. Furthermore, the system includes a pilot conduit valve configured to adjust the pressure of the pilot flow within the pilot conduit. A computing system is configured to determine the pressure of the hydraulic fluid within the fluid supply conduit downstream of the flow control valve based on the data captured by a pressure sensor. Furthermore, the computing system is configured to control an operation of the pilot conduit valve to selectively adjust the pressure of the pilot flow within the pilot conduit based on the determined pressure.

Abstract: Even where the differential pressure across a directional control valve associated with each actuator is very small, flow dividing control of the plurality of directional control valves can be performed stable, and even where a demanded flow rate suddenly changes at the time of transition from composite action to single action or the like, a sudden change of the flow rate of hydraulic fluid to be supplied to each actuator is prevented to implement superior combined operability. Further, the meter-in loss of the directional control valves can be reduced to implement a high energy efficiency.

Abstract: A work vehicle includes a bypass passage formed in an operational valve of a dump cylinder and configured to feed pressure oil from a hydraulic pump to a power steering device when the operational valve is under a neutral state and an oil feeding passage equipped with an orifice, the orifice-equipped oil feeding passage being configured to feed the pressure oil from the hydraulic pump to a rod side oil chamber of the dump cylinder when the operational valve is under the neutral state.

Abstract: Provided is a hydraulic drive apparatus of a work machine capable of reducing a surge pressure. The hydraulic drive apparatus includes a control valve interposed between the hydraulic pump and a hydraulic actuator, an operation device moving the control valve in response to an actuator operation, an unload valve, an unload operation valve changing a pilot pressure of the unload valve in response to an input of an unload operation command, a target pressure calculation part, and an unload operation command part. The target pressure calculation part calculates a target pressure that increases with an increase in the holding pressure of the hydraulic actuator. The unload operation command part inputs an unload operation command to the unload operation valve to make the pump pressure of the hydraulic pump follow the target pressure.

Abstract: A control device for a hydraulic machine such as a revolving excavator work machine in which a load-sensing pump control system is adopted The control device prevents variation in pump control characteristics among a plurality of hydraulic machines and also prevents variation in the operating speed of individual drive units in the hydraulic machines The control device; and it is configured to perform, by using a storage unit and a calculation unit outside the hydraulic machine, a process of causing an engine rotation state and a hydraulic actuator operation state to be specific states and calculating a correction rate for a control output value of an electromagnetic proportional valve for generating a control pressure, based on detection of an error in the flow rate of a hydraulic pump or its substitute numerical value such as the rotational speed and the like of a traveling motor which is easily detectable from outside.

Abstract: A boom lift system includes a primary conduit, a pump-motor arrangement having a motor operable to drive a pump to move a fluid through the primary conduit, first and second actuators in fluid communication with the primary conduit and actuatable in response to first and second user input to perform hydraulic function via the fluid, a valve arrangement configured to control flow of the fluid from the primary conduit to the first and second actuators, and a controller programmed to selectively actuate the valve arrangement in response to the first and second user inputs. When the controller receives both of the inputs, the valve arrangement is actuated by the controller to vary the flow rate of fluid to each of the first and second actuators. When the controller receives only one of the first input or the second input, the controller varies a flow rate output of the pump.

Abstract: A hydraulic drive device for an industrial vehicle includes a tank, a hydraulic pump, a capacity control valve, a plurality of hydraulic cylinders, a plurality of direction switching valves, a first hydraulic oil passage, a second hydraulic oil passages, a pilot line, a relief valve, a relief pressure setting portion, a plurality of operation detecting portions, and a control unit. The control valve controls the hydraulic pumps so that a differential pressure between a discharge pressure of the hydraulic pump and a pilot pressure of the pilot line is to be a predetermined pressure. The control unit controls the relief pressure setting portion.

Abstract: A controller determines a target rotation speed of an engine from an operation amount of an accelerator operating member. The controller determines whether a vehicle is in coasting deceleration. The controller decreases a differential pressure between a first circuit and a second circuit of a hydraulic circuit according to a deviation between an actual rotation speed of the engine and the target rotation speed, or the operation amount of the accelerator operating member when the vehicle is in the coasting deceleration.

Abstract: The hydraulic pressure generating device includes a regulator (spool valve) formed by a cylinder body, a spool which slidably moves within the cylinder body, a pilot chamber in which a pilot pressure which is a hydraulic pressure moving the spool along in an axial direction is inputted and an output chamber out of which an output pressure which is a hydraulic pressure corresponding to the pilot pressure is outputted, wherein the hydraulic pressure generating device further includes a spool position obtaining portion which obtains a relative position of the spool relative to the cylinder body and a pilot pressure controlling portion which controls the pilot pressure based on the relative position obtained by the spool position obtaining portion.

Abstract: Provided is a work machine hydraulic control system capable of detecting abnormality in a pump output power switching device independently of the abnormality state of the pump output power switching device. A hydraulic control system of a hydraulic excavator is equipped with an accumulator 21 connected to a hydraulic line 25A between a pilot pump 17 and a pilot valve 20, an unloading valve 27 that is a pump output power switching device, a pressure sensor 29 detecting the pressure of the hydraulic fluid supplied to the pilot valve 20, and a controller 30 having a pump output power control section 31 switching the unloading valve 27 in accordance with the pressure detected by the pressure sensor 29. The controller 30 further has an abnormality determination section 32 that computes a command continuation time in a state in which a command output to the unloading valve 27 is not changed.

Abstract: A valve block arrangement configured as a closed center system includes at least one main spool for controlling a hydraulic consumer. The main spool is configured to open and close at least one pressure medium connection between a hydraulic pump and the consumer in controlled, continuous fashion and, in at least one embodiment, is electrically activated. A bypass flow path with a cut valve branches off between the adjustable, hydraulic pump and the main spool. The cut valve is configured to open and close a pressure medium connection between the hydraulic pump and a tank in controlled, continuous fashion. The cut valve is electrically activatable.

Abstract: To reduce the cost by reducing the number of parts and simplify the control of regeneration in the hydraulic actuator even though the meter-in control and the meter-out control can be performed separately while the supply and the discharge of hydraulic fluid is controlled. A meter-in valve that controls supply flow from a hydraulic pump into a hydraulic cylinder is provided, and meter-out switching valve that switches the direction of supply and discharge of the hydraulic oil into the hydraulic cylinder and controls the discharge flow from the hydraulic cylinder to the oil tank is installed on the down stream side of the meter-in valve, and further, a regeneration control valve is installed on the down stream side of the meter-out switching valve.

Abstract: Provided is a hydraulic control system for a construction machine, including: a control valve (31) for controlling supply and discharge of hydraulic fluid to and from an arm cylinder (4); an operation lever (6) for controlling the position of a spool of the control valve (31); a meter-out flow passage (34) for passing therethrough hydraulic fluid discharged from the arm cylinder; a variable restrictor (23a) provided in the meter-out flow passage; pressure sensors (41, 42) for detecting a magnitude of a negative load applied by an external force to the arm cylinder in a same direction as an actuation direction of the arm cylinder; and a controller (45) for reducing an opening area of the variable restrictor (23a) according to an increase in the magnitude of the negative load calculated with a detection value from the pressure sensors (41, 42).

Abstract: A dual pressure margin priority circuit and method for controlling flow from a pump to steering valve and low priority inlets. A steering pressure valve controls flow from pump to steering valve inlets, and provides a steering valve load sense pressure. A priority valve controls flow from pump to low priority inlets. A load sense cutoff valve has a first inlet receiving the steering valve load sense pressure. The load sense cutoff valve controls flow through the priority valve based on steering valve load sense pressure at the first cutoff valve inlet. The cutoff valve can include a second inlet coupled to tank, and a load sense input coupled to the steering valve load sense pressure. The cutoff valve can be a pressure limiter valve. The priority and steering pressure valves can be 2-way proportional flow spool valves with bias springs, and contributing and opposing load sense inputs.

Abstract: A hydraulic system is disclosed for use with a machine. The hydraulic system may have a pump configured to pressurize fluid, a first actuator configured to receive pressurized fluid from the pump, and an accumulator configured to receive fluid from the first actuator. The hydraulic system may also have a second actuator configured to receive pressurized fluid from the pump and the accumulator, and a pilot circuit configured to receive pressurized fluid from the pump and the accumulator. The hydraulic system may further have at least one valve movable to provide priority of fluid flow from the accumulator to the pilot circuit over the second actuator when a pressure of the accumulator is less than a low-pressure threshold.

Abstract: In a control device for construction machinery, a system operating point calculation unit calculates a plurality of combinations of engine rotational speed and engine torque with which demanded power of an engine can be generated; and calculates system efficiency in each of the combinations according to discharge pressure of a hydraulic. A rotational speed calculation unit calculates target rotational speed of the engine as the engine rotational speed in one of the combinations of the engine rotational speed, the engine torque and the system efficiency calculated by the system operating point calculation unit that includes desired system efficiency. A displacement calculation unit calculates target displacement of the hydraulic pump based on the target rotational speed calculated by the rotational speed calculation unit and demanded flow rate of the hydraulic pump. With this control device, the engine and the hydraulic pump can be controlled at an efficient operating point.

Abstract: A hydraulic drive system includes a pump, a steering actuator, a loading/unloading apparatus actuator, a drive device, a relief valve, and an input unit. The drive device: flows hydraulic oil from the pump to the loading/unloading apparatus actuator when an operating tool is operated; flows the hydraulic oil from the pump to the steering actuator when a steering has become an operated state from a non-operated state regardless of an operation of the operating tool; and causes the hydraulic oil from the pump to be discharged to a tank via the relief valve to increase the torque of an engine when an increase instruction is inputted to the input unit and the steering is in a non-operated state.

Abstract: A system for determining an estimated output from a variable displacement hydraulic pump includes a prime mover, a torque sensor, a pressure sensor, and a displacement sensor. A controller is configured to determine the output torque from the prime mover, determine an input torque to the variable displacement hydraulic pump based upon the output torque, determine an output from one of the pressure sensor and the displacement sensor based upon the signals. The controller is further configured to determine a failure of another of the pressure sensor and the displacement sensor and determine an estimated output from the another of the pressure sensor and the displacement sensor based upon the input torque to the variable displacement hydraulic pump and the output from the one of the pressure sensor and the displacement sensor.

Abstract: A fluid control system including a variable displacement pump having a load system control and configured to operate in an open center mode. A pump control is operable between a first arrangement and a second arrangement. The pump control receives pressurized fluid from a first load sensor pressure in fluid communication with the pump and an actuator return pressure in fluid communication with an actuator configured to operate using pressurized fluid from the system, the pump control providing a selective pump control pressure to the pump load system control. When the system is operating in a standby mode, the pump operates in a first minimized displacement condition. When the system is in a stall mode, the pump operates in a second minimized displacement condition.

Abstract: A method for controlling a hydrostatic drive unit of a work vehicle is disclosed. The method may generally include determining a reference swashplate position for a hydraulic pump of the hydrostatic drive unit, wherein the reference swashplate position is associated with an uncompensated current command, and monitoring an actual swashplate position of the hydraulic pump, wherein the actual swashplate position differs from the reference swashplate position due to a loading condition of the work vehicle. In addition, the method may include determining a current compensation based at least in part on the actual and reference swashplate positions and generating a compensated current command by adjusting the uncompensated current command based on the current compensation, wherein the compensated current command is associated with a compensated swashplate position for the hydraulic that differs from the reference swashplate position.

Abstract: A void protection system for a mining shovel having an operator input device includes an independent metering valve assembly including one or more fluid source-cylinder valves for fluidly connecting the fluid source to the hydraulic cylinder. The system also includes a sensor assembly for monitoring the fluid pressure within the rod end and the head end of the hydraulic cylinder, and a control module. The control module is configured to monitor movement of the operator input device, monitor pressure within the hydraulic cylinder, increase the opening of the corresponding fluid source-cylinder valve and increase fluid flow from the fluid source to fill corresponding end of the hydraulic cylinder until pressure in the corresponding end of the hydraulic cylinder is above a first threshold pressure.

Abstract: A hydraulic control system for a machine is disclosed. The hydraulic control system may have a pump configured to pressurize fluid, and a motor driven by a flow of pressurized fluid from the pump. The hydraulic control system may also have a first accumulator configured to receive pressurized fluid discharged from the motor and to selectively supply pressurized fluid to the motor, and a second accumulator configured to receive pressurized fluid discharged from the motor and selectively supply pressurized fluid to the motor.

Abstract: A method is provided for controlling a hydraulic system of a working machine, which hydraulic system includes a first hydraulic machine for providing hydraulic fluid to a first actuator of the working machine, and a second hydraulic machine for providing hydraulic fluid to a second actuator of the working machine and for providing hydraulic fluid to the first actuator. The method includes using a first control mode, and in the first control mode allowing a flow of hydraulic fluid from the second hydraulic machine to the second actuator, wherein the pump pressure of the second hydraulic machine is selected based on the load pressure of the second actuator independently of the load pressure of the first actuator.

Abstract: Disclosed is a swing control apparatus of construction machinery, including: a hydraulic pump discharging working oil for driving a swing motor and controlling a discharge flux according to an input pump command value Vpump; a pressure sensor sensing pressure of the working oil discharged from the hydraulic pump; and a control unit calculating the pump command value Vpump based on a swing operation quantity Vsw input from the swing operation unit to output the calculated pump command value to the hydraulic pump, wherein when the input swing operation quantity Vsw is larger than a preset reference swing operation quantity Vswo and the discharge pressure Ppump of the hydraulic pump detected by the pressure sensor is lower than a first reference pressure Pswr1, the control unit calculates a converted swing operation quantity Vsw? gradually increasing from the reference swing operation quantity Vswo to the input swing operation quantity Vsw and calculates the pump command value Vpump of the hydraulic pump corresp

Abstract: A controller carries out horsepower control to determine a flow rate of a hydraulic pump based on first characteristics and second characteristics, which each define a maximum input setting of the hydraulic pump by a discharge pressure of the hydraulic pump and a flow rate of the hydraulic pump, and based on the discharge pressure. When the discharge pressure is less than a set pressure and when a state where the discharge pressure is equal to or greater than the set pressure has not continued for a set time period, then the controller determines the flow rate based on the first characteristics, and when the state where the discharge pressure is equal to or greater than the set pressure has continued for the set time period, then the controller determines the flow rate based on the second characteristics.

Abstract: A hydraulic brake mechanism for use in hydraulic systems to provide braking of a hydraulic motor is disclosed. The brake mechanism provides proper braking under a range of operating conditions, including (1) the start of flow from the pump to the brake and motor and braking is not desired; (2) operating conditions in which constant flow is provided from the pump to the brake and motor and braking is not desired; (3) operating conditions in which abrupt decreases of flow from the pump to the brake and the motor occur, for example where flow is reduced due to being drawn by another work element or hydraulic load, but under which a reduced supply flow is still present and braking is not desired; and (4) operating conditions in which the hydraulic flow from the pump to the brake mechanism and the motor is shut off completely and braking is desired.

Abstract: A device for varying the stroke of first and second hydraulic machines. At least one piston is functionally connected to axes of the hydraulic machines. Depending on power demanded by a driver, the piston can be acted upon, via position and high pressure control valve units of a valve system, with pressures that correspond to a pressure present in the hydraulic machines and that act in a first adjustment direction of the hydraulic machines axes. Pressure in the hydraulic machines is controlled by the position control valve unit and is limited by the high pressure control valve unit. The piston can be acted upon by the valve system with pressures that correspond to the pressure present in the hydraulic machines and that act in a second adjustment direction of the axes of the hydraulic machines, and action of the position control valve unit can be reversed.

Abstract: The present invention relates to a device for controlling a hydraulic pump of construction machinery.

Abstract: A valve arrangement includes at least two valves and a housing which is configured as an installation cartridge. One of the valves is configured as a pressure regulator and the other of the valves is configured as a delivery flow regulator. The valve arrangement is configured to be inserted or screwed into a variable-displacement pump, thereby minimizing the spatial requirement of the valve arrangement.

Abstract: Methods, apparatuses, and computer program products for controlling the torque load of multiple variable displacement hydraulic pumps are described herein. A pump displacement limit for each variable displacement hydraulic pump is determined using a nonlinear control law to limit the total pump torque load of the variable displacement hydraulic pumps on the engine. The value of the actual pump displacement of each variable displacement hydraulic pump is controlled based upon the respective determined pump displacement limit.

Abstract: A pump control device for a construction machine includes a pump regulator, a pump pressure detector, a travelling operation detector, a working operation detector, and a controller instructing the pump flow rate depending on the pump pressure to the pump regulator. The controller stores first and second P-Q characteristics as a horsepower characteristic and instructs the pump flow rate to the pump regulator, based on the first P-Q characteristic when a travelling operation is detected, and based on the second P-Q characteristic when a working operation is detected. The second P-Q characteristic is equal to the first P-Q characteristic in a low-pressure region while is one giving a low characteristic relatively to the first P-Q characteristic so as to increase a horsepower difference as the pump pressure increases, in intermediate-pressure and high-pressure regions.

Abstract: A hydraulic pump driven by an engine, a hydraulic actuator, and a negative control circuit are provided on an open center hydraulic circuit, for guiding the hydraulic pressure in the center bypass to the hydraulic pump, as a negative control pressure. A negative control pressure control device controls the negative control pressure to an arbitrary value is also provided. The pump characteristic of the hydraulic pump is set such that the discharge flow rate is minimized when the negative control pressure in the negative control circuit is equal to or greater than a first predetermined pressure. Furthermore, an idling detection device that detects whether the hydraulic actuator is in a non-operated state or not is provided. The negative control pressure is forcefully controlled to the first predetermined pressure or higher when the non-operating state is detected.

Abstract: A method for overpressure control in a hydraulic system having multiple hydraulic pumps, with each hydraulic pump being connected by a respective hydraulic circuit for actuating a single respective hydraulic actuator, includes actuating a first variable displacement hydraulic pump, the first hydraulic pump being fluidly linked by a first hydraulic circuit to a first hydraulic actuator for powering the first hydraulic actuator. Upon detecting a pressure that exceeds a predetermined threshold pressure, the flow rate of the first hydraulic pump is electronically modified to a second flow rate lower than the first flow rate whereby the pressure in the first hydraulic circuit is reduced to a pressure that is below the predetermined threshold pressure.

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.