Abstract: A shovel includes a lower traveling body, an upper turning body turnably mounted on the lower traveling body, a hydraulic pump mounted on the upper turning body, a hydraulic actuator configured to be driven with hydraulic oil discharged by the hydraulic pump, a bleed valve configured to control the flow rate of a portion of the hydraulic oil discharged by the hydraulic pump, the portion flowing to a hydraulic oil tank without going through the hydraulic actuator, and a control device configured to control the opening area of the bleed valve in accordance with the magnitude of pulsation in the pressure of hydraulic oil supplied from the hydraulic pump to the hydraulic actuator.

Abstract: A hydraulic system includes: an operation device that outputs an operation signal corresponding to an operating amount of an operating unit; a pump that supplies hydraulic oil to a hydraulic actuator via a control valve; a bleed valve that defines a bleed flow rate, at which the hydraulic oil is released to a tank; and a controller that controls the bleed valve, so an opening area of the valve decreases in accordance with increase in the operation signal. The controller: when a rapid acceleration operation is not performed on the device, changes the opening area of the valve between a maximum value and zero along a normal opening line; and when the rapid acceleration operation is performed, changes the opening area of the valve between the maximum value and minimum value greater than zero along a special opening line from when the operation is started until a predetermined time elapses.

Abstract: Methods of controlling an actuator during operation using a hydraulic circuit, and related apparatus, are described. The circuit has a first path section along which fluid is supplied to a first chamber of the actuator using a first valve and a second path section along which fluid is extracted from a second chamber of the actuator using a second valve. Pressure data associated with a pressure of the fluid supplied to the first side of the actuator are obtained, a pilot pressure pPilot is produced based on the data and the first and second valves are configured based on the pilot pressure pPilot.

Abstract: A balanced panel punch drive system. The system includes a main hydraulic drive including an outer casing forming an internal housing and a main piston slidably disposed within the internal housing. A main fluid chamber, a first output chamber and a second output chamber are formed within the internal housing. A pump is fluidly connected to the main fluid chamber by an input line. A first die hydraulic cylinder and a second die hydraulic cylinder each have an outer casing forming an internal housing and a die piston slidably disposed within the internal housing. An opening is formed through an end of the outer casing sized to receive a distal end of the die piston therethrough. A first output line fluidly connects the first output chamber to the first die hydraulic cylinder and a second output line fluidly connects the second output chamber to the second die hydraulic cylinder.

Abstract: A work machine has a controller which has an area limiting control section correcting the pilot pressures of pilot lines, a regeneration control section adjusting the flow rate of the hydraulic fluid caused to flow from a tank side line of an arm cylinder into a pump side line thereof between zero and a predetermined upper limit value, and a regeneration control switching section that issues an order to the regeneration control section to set the predetermined upper limit value to a first set value when the function of the area limiting control section is invalid and that issues an order to the regeneration control section to set the predetermined upper limit value to a second set value that is smaller than the first set value when the function of the area limiting control section is effective.

Abstract: A control system for construction machinery includes a main control valve installed in a hydraulic line between a hydraulic pump and actuators, and including a first group of electro proportional pressure reducing valves outputting a secondary pressure in proportion to an external pressure command signal to a first spool for controlling a first group of actuators of the actuators, and a second group of electro proportional pressure reducing valves outputting a secondary pressure in proportion to an external pressure command signal to a second spool for controlling a second group of actuators of the actuators, a first pressure sensor configured to detect the secondary pressure outputted from the first group of electro proportional pressure reducing valves and a second pressure sensor configured to detect the secondary pressure outputted from the second group of electro proportional pressure reducing valves, and a controller configured to output pressure command signals to the electro proportional pressure redu

Abstract: Apparatuses, systems and methods are provided for controlling one or more fluid actuated devices; e.g., actuators such as hydraulic cylinders. A method is provided, for example, involving actuation fluid, a first actuator and a second actuator. During this method, a quantity of the actuation fluid within the second actuator is pressurized using a quantity of the actuation fluid within the first actuator.

Abstract: A work machine pump control system includes: a pump horsepower control valve (22) which causes a first urging force determining a limited horsepower (F) of a hydraulic pump and a second urging force due to a delivery pressure of the hydraulic pump to act on a spool in opposition to each other and which controls the pump flow rate such that it does not exceed the limited horsepower (F); a target pump flow rate computation section (42) computing a target pump flow rate based on an operation pressure (px) and a load pressure (py); a target horsepower computation section (41) which computes a required horsepower (Freq) corresponding to an operation pressure (px) from a relationship related to the operation pressure (px) and which computes a target horsepower (Ftar) based on the required horsepower (Freq); and a pump horsepower control section (35) which controls the pump horsepower control valve (22) such that the target pump flow rate (Qtar) is delivered with the limited horsepower (F) determined by the pump hor

Abstract: A method for controlling a valve spool that includes providing a control valve having a first end and a second end with a spool disposed therebetween, a hydraulic component, a controller, a first control circuit and a second control circuit, selectively controlling the pressure in the first end and the second end with the controller, identifying an active state, with the controller, and applying an active pressure to both the first end and the second end with the corresponding first control circuit and second control circuit during the active state, and identifying a first command, with the controller, and providing a command pressure to the first end through the first control circuit and a release pressure to the second end through the second control circuit during the first command. Wherein, the spool is moved within the control valve and the hydraulic component is engaged during the first command.

Abstract: A work vehicle detects pressure of hydraulic oil supplied to an arm cylinder. The work vehicle determines operation details for an arm. The work vehicle includes a relief valve capable of setting a relief pressure of hydraulic oil in a hydraulic circuit at one of a first set pressure and a second set pressure that is greater than the first set pressure. The work vehicle sets the relief pressure of the relief valve at the first set pressure, on the conditions that the detected pressure is equal to or greater than a predetermined value, and that it is determined that the operation details indicate an excavation operation. The work vehicle sets the relief pressure of the relief valve at the second set pressure when the conditions are not satisfied.

Abstract: A straight traveling apparatus for a construction machine and a control method thereof are provided which can allow a curved travel when the working device is operated during the curved travel.

Abstract: In a hydraulic driving system for construction machines, when track motors 3f and 3g are operated and the delivery pressure of a main pump 2 increases to a second value PS2 of the set pressure of a main relief valve 14, the set pressure of a signal pressure relief valve 16 increases from a third value PA1 to a fourth value PA2, which is smaller than the second value PS2 of the set pressure of the main relief valve 14, the difference between the second value PS2 and the fourth value PA2 being smaller than the target LS differential pressure. With such a structure, even if one of actuators reaches the stroke end and the delivery pressure of the hydraulic pump rises to the set pressure of the main relief valve, the other actuators do not stop, and further when the main relief valve is configured to increase the set pressure during operation of a specific actuator, the load pressure of the specific actuator does not increase to the increased set pressure of the main relief valve.

Abstract: The hydraulic fluid energy recovery apparatus includes a fluid communication line for holding a bottom-side hydraulic fluid chamber and a rod-side hydraulic fluid chamber of a hydraulic cylinder in fluid communication with each other, a fluid communication valve connected to the fluid communication line for adjusting the pressure and/or flow rate of a hydraulic fluid passing through the fluid communication line in a manner that allows for adjustment of a degree of opening of the fluid communication valve, first pressure detecting means for detecting a signal indicative of pressure at the bottom-side hydraulic fluid chamber of the hydraulic cylinder, an amount-of-operation detecting means for detecting an amount of operation of the operating means, and a control device for capturing the signal of pressure at the bottom-side hydraulic fluid chamber of the hydraulic cylinder detected by the first pressure detecting means.

Abstract: A hydraulic apparatus based on a confluence control mode includes a load sensing unit provided with first and second reversing valves, and a throttle governing unit provided with a fourth reversing valve. A confluence valve and a one-way valve, which communicate with the load sensing unit and the throttle governing unit, are arranged on a parallel oil path arranged in parallel with the fourth reversing valve. The confluence valve includes a confluence channel that controls opening and closing of the parallel oil path to shunt fluid of the throttle governing unit to the load sensing unit. A first pilot pressure acting on the first reversing valve and a second pilot pressure acting on the second reversing valve act on the confluence valve independently or simultaneously to change a position of the confluence channel, thus implementing reversing of the confluence valve.

Abstract: Systems and methods for use with a variable pressure actuator control system for a gas turbine engine are provided. A variable pressure actuator control system for a gas turbine engine may comprise a controller, a pressure regulating electro-hydraulic servo valve assembly (P-EHSV), including a variable restriction flow path, in electronic communication with the controller, a position regulating electro-hydraulic servo valve assembly (X-EHSV), including a network of flow paths, in electronic communication with the controller, a bypass regulator (BPR) in fluid communication with at least one of a pump, the P-EHSV, or the X-EHSV, the BPR configured to be controlled by the P-EHSV via a bypass pressure to vary an available pressure, and an actuator comprising an actuator piston. The variable pressure actuator control system may minimize pressure when possible to increase mission capability for a gas turbine engine.

Abstract: A hydraulic control device that reduces the loss of the power of a pump in combined operation of boom lowering and arm pushing. A controller performs single control of increasing capacity of a first pump in accordance with increase in an operation amount of a boom operation member, in a single operation of the boom lowering. On the other hand, the controller restricts the capacity of the first pump compared to capacity in the single control, during a restriction control period when the combined operation of boom lowering and arm pushing is detected, and the operation amount of the boom operation member is a prescribed operation amount or more.

Abstract: An electrical pressure control load sense system having a pump connected inline to an operator control spool valve and a compensation circuit. The system also has a plurality of sensors, at least one pressure transducer, a micro-processor, a fixed orifice, a proportional pressure relief valve, and a swashplate angle sensor.

Abstract: A hydraulic circuit for a construction machine including a center bypass passage including a group of directional control valves arranged in tandem; and a bleed-off valve arranged in the center bypass passage on a downstream side of the group, wherein each directional control valve includes a first internal passage causing the pressurized oil supplied to the directional control valve to flow out to the center bypass passage and a second internal passage supplying the pressurized oil to a cylinder port, wherein a parallel passage is formed by the center bypass passage and the first internal passage by causing the pressurized oil discharged from the hydraulic pump to flow to the center bypass passage on the downstream of the directional control valve, wherein the second internal passage supplies the pressurized oil from the center bypass passage through an opening of a spool and/or the bypass passage to the cylinder port.

Abstract: A pressure control valve for a construction machine is disclosed, which prevents self-weight descent of a working device due to leakage of hydraulic fluid in a neutral position of the working device.

Abstract: The present disclosure relates to a hydraulic pressure control device for a swing motor for construction machinery, and more particularly, to a hydraulic pressure control device for a swing motor for construction machinery, which supplements working fluid in the swing motor when a turning operation of an upper body of construction machinery is performed and then stopped. The hydraulic pressure control device for the swing motor for construction machinery according to the present disclosure including the aforementioned configuration may rapidly secure the amount of makeup fluid required by the swing motor when the swing motor is stopped by directly receiving the working fluid discharged from the hydraulic pump P, thereby improving durability of equipment and preventing a cavitation phenomenon.

Abstract: A work machine includes a swing hydraulic motor and a swing electric motor for driving an upper swing structure. A capacitor supplies electricity to the swing electric motor and an operating device outputs through one operation, an operating signal for concurrently operating the swing hydraulic motor and the swing electric motor. A main controller switches between a hydraulic-alone drive mode and an electric-alone drive mode, the hydraulic-alone drive mode being a mode to drive only the swing hydraulic motor selected from the swing hydraulic motor and the swing electric motor when the operating device is operated, the electric-alone drive mode being a mode to drive only the swing electric motor selected from the swing hydraulic motor and the swing electric motor when the operating is operated. Therefore, the actuator that malfunctions can easily be specified among the plurality of mounted actuators.

Abstract: To provide a work machine that can suppress a steep fluctuation in engine power.

Abstract: The present invention controls a proportional control valve controlling the maximum flow of the flow pump to perform controlling the maximum flow of the hydraulic oil pump after checking whether the pump joint control is normal, receiving a flow value of the flow pump controlled by the proportional control valve, checking an error when the flow value received during a control of the maximum flow has an error, and assigning a weight value to the checked error to compensate for the flow value. Therefore, the present invention may decrease a number of an engine revolution speed and lower a driving fuel consumption and reduce a driving noise.

Abstract: The invention relates to a hydraulic apparatus comprising a hydraulic pump (30) which is connectable to a hydraulic fluid tank, an electric motor (2) as a drive means for the hydraulic pump (30), which electric motor comprises a motor shaft and a motor housing cover (4), and a control valve assembly (12) connected to the pump (30) to control at least one hydraulic consumer which is connectable to the pump (30) and is to be supplied by the pump (30) with hydraulic fluid from the hydraulic fluid tank, wherein the pump (30) is fixed on the motor housing cover (4) and the motor housing cover (4) comprises a holding adapter (10) on which the control valve assembly (12) is fixed.

Abstract: A hydraulic actuation system includes a differential unit having a hydraulically-actuated differential, a power steering unit, a hydraulic pump, a reservoir, a controller, an electronically-controlled flow control manifold, and a proportional pressure control solenoid valve. A flow control manifold may control fluid flow to the power steering unit and the differential. The manifold may include a manifold inlet connected to a pump; first manifold outlet connected to a differential; second manifold outlet connected to a reservoir; third manifold outlet connected to a power steering unit; two-way solenoid valve connected to a manifold inlet and controlled by a controller; flow control valve connected to a two-way solenoid valve and a first manifold outlet; and a pressure differential sensing valve connected to a two-way solenoid valve, the manifold inlet, and the third manifold outlet. A proportional pressure control solenoid valve may connect the first manifold outlet and the differential.

Abstract: Electronic control systems and related control methods for controlling electric drive motors for propelling a vehicle and electric auxiliary motors for performing work. The apparatus is shown in use with a vehicle that includes a mowing deck. Features of the control systems allow for safe and efficient use of the vehicle. These features include a power take-off timeout, automatic fail-safe brake (parking), and customized drive characteristics.

Abstract: A control system for hybrid construction machine includes an engine, a main pump to be driven by the engine, a rotary shaft linking an assist pump, a regenerative hydraulic motor and a motor generator, and a clutch for linking the engine and the rotary shaft.

Abstract: A hydraulic system for an access arrangement having a platform configured for movement between a deployed position and a stowed position, the hydraulic system including: at least one hydraulic power unit configured to urge hydraulic fluid through a hydraulic circuit; at least one hydraulic cylinder directly or indirectly connected to a portion of the platform and configured to urge the platform towards at least one of the stowed position and the deployed position, wherein the at least one hydraulic cylinder is in fluid communication with the hydraulic power unit; and a pressure regulating valve in a path between the at least one hydraulic power unit and the at least one hydraulic cylinder, wherein the pressure regulating valve is operable to prevent the at least one hydraulic cylinder from urging the platform to the stowed position if a load on the platform exceeds a specified threshold.

Abstract: In the working machine, first and second pilot flow paths are directly or indirectly connected to a tank flow path (52). A first restrictor is disposed between the first pilot flow path and the tank flow path. A second restrictor is disposed between the second pilot flow path and the tank flow path. An actuator control unit is configured to control an actuator based on a hydraulic pressure detected by a first hydraulic pressure detector unit and that detected by a second hydraulic pressure detector unit sensor.

Abstract: There is provided a driving device for a work machine, having a closed hydraulic circuit system for driving cylinders with hydraulic pumps, the driving device making the speed of operation substantially the same in both directions of piston rod extension and contraction.

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: The device to actively control the vibrations of an articulated arm consisting of a plurality of segments each comprising at least its own actuator associated with a hydraulic drive circuit including a block valve. At least one of said actuators is associated with an hydraulic control circuit of the vibrations, comprising at least a sensor able to detect the vibrations and/or the position of one or more segments, a processing unit to process the signals of the sensor/sensors and a pump commanded by the electronic command board and cooperating with said block valve. The hydraulic control circuit is associated with the hydraulic drive circuit.

Abstract: The operability when performing a combined arm-crowd and bucket operation can be improved. A hydraulic drive device for a hydraulic excavator includes: a bucket directional control valve and a second arm directional control valve, which are connected in parallel tandem with a first hydraulic pump; a first arm directional control valve that is connected to a second hydraulic pump; and a flow rate restriction device that restricts the flow rate of pressure oil supplied to the second arm directional control valve, during crowd operation of a bucket. This flow rate restriction device includes a variable throttle whose opening is controlled so as to become smaller as a bucket operating device is operated to the crowd side, the variable throttle being provided in a bypass path connecting to the supply port of the second arm directional control valve.

Abstract: The invention relates to a hydraulic control arrangement for a mobile machine tool, particularly for a forklift, comprising at least two hydraulic loads (10, 12), one of them having a lifting function. According to the invention, the two loads are each controlled via a LUDV valve with inflow measuring diaphragm (36, 44) and LUDV pressure regulator (46) connected downstream.

Abstract: Disclosed is a hydraulic system for controlling the degree of openness of an arm regeneration valve by driving an electronic proportional control valve during a combined operation of simultaneously operating an arm and a swing device.

Abstract: A method for controlling a working machine including a hydraulic system for controlling a plurality of work functions, including lift and tilt of an implement, includes the steps of determining a maximum pressure of a hydraulic fluid for performing a certain task with the implement individually for at least one of the work functions, and delivering the hydraulic fluid, pressurized at most to the determined maximum pressure, to the work function.

Abstract: A method for controlling an automated clutch, which comprises a hydraulic clutch actuating system having a hydrostatic actuator, the pressure of which is detected. The method includes using the pressure of the hydrostatic actuator to adapt the characteristic curve of the clutch.

Abstract: A valve arrangement has an adjustable control valve (10) including a control slide (12) for actuating at least one consumer connection (A, B) and an LS control line. The differential pressure of two actuating pressures (xa, xb) serves for the actuation of the control slide (12). Since the actuating pressures (xa, xb) also actuate a logic valve, which in turn influences an additional valve, and/or actuates a pressure compensator connected upstream to the control valve (10), the difference of the two actuating pressures (xa, xb) initially displaces the control slide of the control valve. The higher or the lower of the two actuating pressures (xa, xb) either actuate the further valve in the form of the additional valve, and/or influences the pressure compensator.

Abstract: A valve assembly has a flow summation node coupled to a displacement control port of the first pump. Each valve in the assembly has a variable metering orifice controlling flow from an inlet to a hydraulic actuator and has a variable source orifice conveying fluid from a supply conduit to a flow summation node. The source orifice enlarges as the metering orifice shrinks. Each valve includes a variable bypass orifice and the bypass orifices of all the control valves are connected in series forming a bypass passage between a bypass node and a tank. The bypass node is coupled to the flow summation node and receives fluid from a second pump. At each valve, a source check valve conveys fluid from the supply conduit to the inlet and a bypass supply check valve conveys fluid from the bypass passage to the inlet.

Abstract: A vehicle includes a pump configured to output fluid at a commanded pressure when driven by a motor. A first hydraulic device is operably connected to the pump and configured to operate in response to receiving fluid at a first pressure. A second hydraulic device is operably connected to the pump and configured to execute a shift command in response to receiving fluid at a second pressure. A control processor is configured to control the commanded pressure in accordance with a priority scheme. That is, the control processor is configured to direct at least a portion of the commanded pressure from the first hydraulic device to the second hydraulic device for a duration of a shift command based on the priority scheme and redirect at least a portion of the commanded pressure to the first hydraulic device upon completion of the shift action.

Abstract: Hydraulically driven arrangement for the linear movement of a mass body consisting of two double acting cylinders coupled in parallel, whereby one operating cylinder is a control cylinder for controlling the movement of the mass body, which is split into an acceleration phase, a movement phase and a brake phase. The other operating cylinder is connected as a drive cylinder to the hydraulic power pack as an energy storage, in a manner that the power pack during the acceleration phase of the mass body generates the drive energy for the drive cylinder, and the drive cylinder in the brake phase of the mass body, which serves as a pump for charging the hydraulic power pack. The control cylinder and drive cylinder each have a piston with a one-sided piston rod coupled to the mass body. The control cylinder and the drive cylinder are controlled by hydraulically separated, independent control circuits.

Abstract: A shock absorption device and a control method thereof for a small swing radius (SSR) excavator are provided, which can relieve shock generated on a boom cylinder by controlling only the discharge flow rate of hydraulic pumps, being supplied to the boom cylinder, even without controlling a main control valve when a boom of the excavator ascends at its maximum height through manipulation of a control level.

Abstract: A hydraulic system for actuating a clutch and/or a variable speed drive unit of a belt-driven conical-pulley transmission of a vehicle, such as a commercial vehicle, and having a variable transmission ratio and a torque sensor. The hydraulic system includes at least one hydraulic energy source. A selector and check valve is provided for supplying additional components besides the torque sensor and is connected between the hydraulic energy source, the additional components, and the torque sensor in such a way that the torque sensor includes priority in being supplied with hydraulic medium.

Abstract: A method of controlling a pump and motor system having at least one of a variable displacement pump and a variable displacement motor. The method may comprise providing an engine drivingly coupled to a primary load and a secondary load, the secondary load being driven by the pump and motor system. The method may also comprise sensing a change in engine speed in response to a change in the primary load. The method may further comprise changing the engine speed to compensate for the primary load change. The method may further comprise changing a displacement of the at least one variable displacement pump and the variable displacement motor to maintain a constant secondary load.

Abstract: The invention relates to a sequence valve for use in a hydraulic plant, which sequence valve has a pressure-controlled slide valve (5) with a spring return and in a starting position defines a first cavity (10), which cavity is connected with a tank and the hydraulic plant, and in a second, pressurized position closes off the connection with the tank. The cavity is connected to a second cavity (18) via a channel (15, 16, 17) in the slide valve, and the second cavity is adapted to be connected with a pump via a throttle (20) and is positioned on the same side of the slide valve as the spring (7). The sequence valve has a third cavity (19), which is adapted to be connected with the pump and is positioned on the opposite side of the slide valve from the spring, and the second and the third cavity are connected with each other via a fixed throttle with a short flow channel. The invention also relates to downhole tractor with the sequence valve.

Abstract: A method for controlling an engine in a work machine includes determining a base engine operating limit; determining a hydraulic system load on the engine; calculating a modification value for the base engine operating limit; generating a modified engine operating limit based on the modification value and the base engine operating limit; generating an engine control signal based on the modified engine operating limit; and transmitting the engine control signal to operate the engine at the modified engine operating limit to thereby supply additional power from the engine to the drive train to at least partially compensate for the hydraulic system load.

Abstract: An open center hydraulic system that includes a variable displacement pump having an inlet, an outlet and a sensing port, the pump configured to provide reduced fluid flow in response to a predetermined fluid pressure differential between the outlet and the sensing port. A first fluid circuit and a second fluid circuit each serve as signal lines with the pump sensing port. During operation of the second fluid circuit, reduced fluid flow from the pump outlet is achieved as a result of the sum of induced fluid pressure reductions of respective controlled pressure reduction devices approaching the predetermined pump fluid pressure differential.

Abstract: A pneumatic drive system (1) in which the movement of an output drive unit (7) of a pneumatic drive (2) is controlled by control valve means (25 and 26) which are connected with the working chambers (12 and 13) of the pneumatic drive (2). The control valve means (25 and 26) comprise at least one air economy setting (30) setting a choke cross section and a high power setting (29) defining a flow cross section larger than it. Actuating means (12 and 13) serve to ensure that the control valve means (25) are switched over, in a fashion dependent on the air pressure obtaining in the at least one working chamber (12 and 13) from the normally assumed air economy setting (30) into the high power setting (29), when the output drive unit (7) meets with an increased resistance to motion.

Abstract: The present disclosure provides a machine configured so that its ground speed is at least in part dependent on the measured force that is applied to an attachment attached thereto. The present disclosure also provides an attachment for a machine that is configured to provide feedback to the machine it is configured to be attached to, wherein the feedback is representative of the force applied to the attachment. The present disclosure also provides a method of automatically controlling the ground speed of a machine based on feedback measured in an attachment attached to the machine.

Abstract: Torque control for a construction machine three-pump system that can accurately control the total absorption torque of first, second, and third hydraulic pumps and effectively use the output torque of an engine. A pump base torque computation section 42 calculates a pump base torque Tr from a target rotation speed. A subtraction section 44 calculates a reference value Tf for the maximum absorption torque available to the first and second hydraulic pumps 2, 3 by subtracting a third pump reference absorption torque T3r from the pump base torque Tr. A correction torque computation section 45 calculates a correction torque value from the delivery pressure of the third hydraulic pump 4. An addition section 46 calculates a target absorption torque Tn by adding the correction torque value Tm to the reference value Tf. A first regulator 31 is controlled so as to obtain the target absorption torque Tn.