Abstract: A system and method of controlling torque of plural variable displacement hydraulic pumps in construction equipment are provided, which can control torque of the variable displacement hydraulic pumps so that the total amount of torque of the hydraulic pumps does not exceed the preset amount of torque by presetting the torque so that the engine does not stop even at maximum load of the hydraulic pumps or by presetting the speed of the engine or the used torque of the hydraulic pumps in consideration of the fuel economy or working speed.

Abstract: A dual pump hydraulic system is provided for a vehicle driven by an internal combustion engine. The system includes a first circuit with a first high pressure pump supplying hydraulic fluid to the first subsystem at a higher pressure. The system also includes a second circuit with a second lower pressure pump supplying hydraulic fluid to the second subsystem at a second pressure. A first valve controls communication between the first pump and the second circuit. A second valve is operable to communicate the second pump with the first circuit when pressure in the first circuit is less than a second threshold pressure or when commanded by a control unit. A check valve prevents fluid flow from the first circuit back into to the second valve.

Abstract: According to the present disclosure, a hydraulic control apparatus for construction machinery comprises: hydraulic pumps; first and second control valve units which control the flow directions of working oil discharged from the hydraulic pumps to supply the working oil to first and second work machines, respectively, and which control the degree of opening of flow channels which interconnect the first and second work machines and the hydraulic pumps, respectively; and a control unit which controls the first and second control valve units in accordance with operating signals inputted from first and second operating units.

Abstract: In a work vehicle, a cutoff-pressure-setting part sets cutoff pressure at a predetermined first pressure value when vehicle speed is greater than a predetermined first speed threshold, and at a second pressure value greater than the first pressure value when vehicle speed is equal to or less than a second speed threshold less than the first speed threshold. When the vehicle is moving forward and the forward/backward switch lever is in forward motion position, or when the vehicle is moving backward and the forward/backward switch lever is in backward motion position, the second speed threshold is set to a predetermined first value. When the vehicle is moving forward and the forward/backward switch lever is in backward motion position or when the vehicle is moving backward and the forward/backward switch lever is in forward motion position, the second speed threshold is set to a second value lower than the first value.

Abstract: A hydraulic device has a first pump, a second pump, an operating state detector configured and arranged to detect an operating state, a connection switching unit configured and arranged to selectively connect the second pump to either a first hydraulic oil line or a second hydraulic oil line, and a switching controller configured to control, based on the operating state detected by the operating state detector, a switching operation of the connection switching unit. The switching controller is further configured to inhibit the switching operation of the connection of the second pump when the detected operating state is such that at least one of clutches of a multi-stage transmission and a steering device is in a state transition or at least one brake of the steering device is being operated.

Abstract: In a vehicular hydraulic control circuit equipped with a mechanically-operated oil pump and an electrically-operated oil pump, a hydraulic control device is provided for reducing a high load imposed on the electrically-operated oil pump, when the electrically-operated oil pump is started during stoppage of the mechanically-operated oil pump. When the electrically-operated oil pump (72) is started from a state in which both the mechanically-operated oil pump (70) and the electrically-operated oil pump (72) are stopped, the mechanically-operated oil pump (70) is pre-started, and then the electrically-operated oil pump (72) is started. Therefore, oil pressure pre-generated by the mechanically-operated oil pump (70) can reduce a load imposed on the electrically-operated oil pump (72). As a result, excessive current that may occur in a control circuit for the electrically-operated oil pump (72) can be prevented.

Abstract: Hydraulic systems and methods for using such systems in a variety of machinery, including but not limited to machines having multiple functions performed by one or more hydraulic circuits. The systems enable valves and actuators within the systems to reconfigure themselves so that flow from assistive loads on one or more actuators can be used to move one or more other actuators subjected to a resistive load.

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 system for providing hydraulic power in a machine transmission includes a first hydraulic variator and a second hydraulic variator, each variator having a mechanical input to a hydraulic pump, and a hydraulic motor linked to the hydraulic pump via a hydraulic circuit, and a mechanical output from the hydraulic motor. In an embodiment, the first hydraulic circuit side of one variator is hydraulically connected to the first hydraulic side of the other variator, and the second hydraulic circuit sides are likewise linked together. A common input is geared to the inputs of the variators and a common output is geared to the outputs of the variators, tying the pump and motor of each variator to rotate at the same speed as the counterpart components of the other variator.

Abstract: A hydraulic system for a machine is disclosed. The hydraulic system may have a tank configured to hold a supply of fluid, a pump configured to draw fluid from the tank and pressurize the fluid, a first cylinder operatively connected between a first side of a work tool and an undercarriage of the machine, and a second cylinder operatively connected between a second side of the work tool and the undercarriage of the machine. The hydraulic system may also have a first electro-hydraulic valve associated with the first cylinder and configured to selectively regulate a flow of pressurized fluid to the first cylinder independently of the second cylinder, and a second electro-hydraulic valve associated with the second cylinder and configured to selectively regulate a flow of pressurized fluid to the second cylinder independently of the first cylinder.

Abstract: A hydraulic drive system for an actuator uses a pair of pressure compensated hydraulic machines to control flow to and from the drive chambers of the actuator by varying the controlled pressure of one of the machines. The machines are mechanically coupled to permit energy recovery and charge an accumulator to store supplies energy. The drive system may be combined with other services including a transmission for incorporation in a vehicle. The transmission uses a pressure compensated supply and torque control of the wheels.

Abstract: When controlling each operational process in a molding cycle by variably controlling the number of revolutions of a drive motor 3 in a hydraulic pump 2, a hydraulic pump 2 where at least multiple fixed discharge flow rate Qo and Qs can be set is used as the hydraulic pump 2. At the same time, the fixed discharge flow rates Qo . . . are set corresponding to operational processes based upon predetermined conditions in advance, respectively, and the hydraulic pump 2 is switched to the fixed discharge flow rates Qo . . . by corresponding to each operational process at the time of molding. At the same time, each operational process is controlled by variably controlling the number of revolutions of the drive motor 3.

Abstract: A method and system for configuring a hydromechanical transmission having a hydraulic pump and a hydraulic motor driven by the hydraulic pump and a pressure-driven actuator employs a particular torque-pressure curve configuration to maximize torque resolution with respect to actuator pressure changes while ensuring that the curve is substantially monotonic in each dimension and at any available motor speed within a predetermined motor speed limit and any available actuator pressure within predetermined actuator pressure limits. The resultant four-dimensional association between actuator pressure, motor speed, primary power source speed and motor torque allows selection of an actuator pressure to provide a desired torque.

Abstract: In a work machine, a control unit controls a pilot control valve for controlling the opening area of a first direction switch valve in executing the combined operation to be less than or equal to that in executing a single operation. The combined operation represents an operation of simultaneously operating first and second actuators. The single operation represents an operation of operating only the first actuator. Further, the control unit determines the opening area of the first direction switch valve in the combined operation based on a hydraulic pressure detected by a hydraulic pressure detector unit.

Abstract: A traveling device for crawler type heavy equipment is provided, which can improve manipulability by preventing an abrupt decrease/increase of a traveling speed of the equipment when a combined operation, in which a left/right traveling device and a working device are simultaneously driven, is performed. The traveling device for crawler type heavy equipment includes a variable orifice shifted to intercept the supply of the hydraulic fluid toward the traveling device in response to the signal pressure in the combined working mode if a load pressure of the working device is relatively higher than that of the traveling device.

Abstract: There is provided a hydraulic system, including an oil tank storing operating oil, a hydraulic actuator, and a hydraulic pump which draws the operating oil from the oil tank and supplies the operating oil to the hydraulic actuator. The hydraulic system is provided with an operating oil separating unit which is located at a midway point of a main tube sending the operating oil from the hydraulic pump to the hydraulic actuator and which separates a part of the operating oil supplied, from the hydraulic pump to return the part of the operating oil to the oil tank. A universal testing machine including the hydraulic system is also provided.

Abstract: A vehicle control device including an input member drive-connected to a power source; a mechanical pump; an electric pump assisting the mechanical pump; a drive mechanism transmitting the rotational driving force of the input member to an output member; a fluid coupling between the input member and the drive transmission mechanism and including a lock-up engagement element which receives hydraulic oil discharged from the mechanical pump and the electric pump to operate; a state detection unit that detects the state of the one or more factors that the discharge of the electric pump; and a control unit which executes a first or second control mode, wherein the first control mode permits engagement of the lock-up engagement element if a first condition is satisfied based on the one or more factors, and wherein a second control mode inhibits engagement of the lock-up engagement element if the first condition is not satisfied.

Abstract: A hydraulic system for use in a work vehicle with a powered implement is disclosed. In one embodiment, the hydraulic system may include a first hydraulic circuit including a first hydraulic pump with a low pressure and low flow output, switch and valve; a second hydraulic circuit including a second hydraulic pump with a high flow and high pressure output, switch and valve; and a third hydraulic circuit including a third hydraulic pump with a high flow and high pressure output, switch and valve. The first, second, and third circuits each include an output selectively combinable with each other by an operator control which controls the switch and valve configurations. The hydraulic system has several configurations.

Abstract: A torque converter coupled to a transmission has a torque converter operating mode and a lockup operating mode. A first pump may be configured to supply transmission fluid to a plurality of electro-hydraulic transmission components. A second pump may be configured to supply transmission fluid to a lubrication system of the transmission. A valve may be configured to route transmission fluid supplied by the second pump through the torque converter during the torque converter operating mode. Means may also be provided for selectively routing at least some of the transmission fluid supplied by the first pump through the torque converter. Illustratively, transmission fluid supplied by the first pump may, but need not, be routed to the torque converter only during the torque converter operating mode or only during the torque converter operating mode if the temperature of transmission fluid exiting the torque converter exceeds a threshold temperature.

Abstract: The present invention is to provide an electro hydrostatic actuator excellent in a snubbing characteristic including a cylinder type actuator main body 1, a piston 2 having a piston rod, the piston slidingly moving in a cylinder of the actuator main body, a motor 18, a pump 19 for supplying fluid according to the rotation of the motor, a mechanism for adjusting a running amount of the fluid into and from the cylinder according to the motion of the piston, and a reservoir 8 for adjusting the supply of the fluid corresponding to a volume difference generated according to the motion of the piston, and a controller 17 which controls the number of revolutions of the motor according to the calculated load torque, and a snubbing control method used for this. An electro hydrostatic actuator of realizing a snubbing mechanism capable of increasing energy efficiency, when used for a landing gear retraction/extension device of an airplane, can be provided.

Abstract: In a method of controlling an injection molding machine M which controls specified operational processes in a molding cycle by variably controlling the rotation speed of a driving motor 3 in a hydraulic pump 2 and driving a specified hydraulic actuators 4a, 4b, . . . , in lowering the pressure Pd of the operational process to a specified pressure Pn, the pressure Pd is forcibly lowered by controlling the driving motor 3 in reverse rotation.

Abstract: In one aspect, the disclosure herein provides an apparatus that in one configuration includes a first hydraulic power unit for supplying a first fluid under pressure to a first chamber for controlling motion of a first movable member and a second hydraulic power unit for supplying a second fluid under pressure to a second chamber for controlling motion of a second movable member, an input device configured to provide an input signal for controlling the motions of the first and second movable members and a processor configured to: receive the input signal from the input device; and independently set, in response to the input signal from the input device, a first electrical actuator to control an amount and flow rate of the first fluid to the first hydraulic power unit and a second electrical actuator to control an amount and flow rate of the second fluid to the second hydraulic power unit for controlling the motion of the first and second movable members.

Abstract: Heavy equipment includes first and second hydraulic pumps, and first and second hydraulic actuators, where the first hydraulic actuator facilitates a first work function of the heavy equipment and the second hydraulic actuator facilitates a second work function of the heavy equipment. The heavy equipment further includes valving and a computerized controller. The valving is configured to allow the first hydraulic pump to be coupled to the first hydraulic actuator and the second hydraulic actuator, and to allow the second hydraulic pump to be coupled to the first hydraulic actuator and the second hydraulic actuator. The computerized controller is coupled to the valving, and has a logic module.

Abstract: A hydraulic system includes a plurality of pumps that provide pressurized fluid to a plurality of hydraulic actuators some of which work more that others. That system is controlled by producing a usage value for each of the plurality of pumps which indicates an amount that the respective pump has worked. One of the pumps is assigned to each hydraulic actuator in response to the usage values. The pumps with lower usage values are assigned to hydraulic actuators which work more, so as to equalize the use of each pump. The assignment of pumps to hydraulic actuators changes with changes in the usage values for the plurality of pumps. When a given one of the plurality of hydraulic actuators is to operate, hydraulic fluid is routed from the assigned pump to that given one of the plurality of hydraulic actuators.

Abstract: When constructing an injection molding machine M that is equipped with hydraulic pumps 2, which control discharge flow rates by variably controlling the number of revolutions of a drive motor 3, and that drives hydraulic actuators 4a . . . by these hydraulic pumps 2; the injection molding machine M is equipped with a hydraulic drive member 6 having multiple hydraulic pumps 2p and 2q, and a hydraulic oil supply circuit 5 jointly or individually supplying hydraulic oil to be discharged from multiple hydraulic pumps 2p and 2q to a hydraulic actuator 4a, 4b, 4c, 4d or 4e selected from the multiple hydraulic actuators 4a . . . .

Abstract: A flow management system capable of providing adjustable hydraulic fluid flow or pressure at a common line to supply bidirectional pumps in electro-hydrostatic actuation systems and conditioning re-circulated hydraulic fluid. The system enables flow sharing between multiple actuation systems and minimization of energy consumption by a power-on-demand approach and/or electrical energy regeneration while eliminating the need for an accumulator. The system has particular application to electro-hydrostatic actuation systems that typically include bi-directional electric motor driven pumps and unbalanced hydraulic actuators connected within closed circuits to provide work output against external loads and reversely recover energy from externally applied loads.

Abstract: A hydraulic system for actuating a motor vehicle transmission by a control hydraulic power source that includes a control hydraulic pump for providing a high hydraulic pressure, a control pressure accumulator, and a low-pressure hydraulic pump for providing low-pressure volumetric flow of hydraulic fluid for operating a low-pressure hydraulic component. The low-pressure pump is operatively drivingly connected with the control hydraulic pump that is connected in a charged manner with the control pressure accumulator and with a transmission actuator.

Abstract: A hydraulic drive system for an actuator uses a pair of pressure compensated hydraulic machines to control flow to and from the drive chambers of the actuator by varying the controlled pressure of one of the machines. The machines are mechanically coupled to permit energy recovery and charge an accumulator to store supplies energy. The drive system may be combined with other services including a transmission for incorporation in a vehicle. The transmission uses a pressure compensated supply and torque control of the wheels.

Abstract: A hydrostatic differential transmission comprising a cylinder housing containing an input pump and an output pump. The two hydraulic pumps are mounted with the output pump inside the input pump. The input pump has an adjustable swash plate. The output pump has a fixed swash plate. The pistons of the input and output pumps share inter-connected piston bore housings. An adjustable control selectively pivots the adjustable swash plate between a neutral position, where the swash plate is at a 90 degree angle to the input shaft and maximum tilt of the swash plate for a one-to-one ratio of the input shaft and output shaft.

Abstract: A two-stage system for delivering fuel to a gas turbine including a first stage variable pump for serving as a primary source of fuel, a second stage fixed pump for selectively supplementing the variable pump, a bypass valve connected to the fixed pump for loading and unloading the fixed pump and a regulator valve assembly connected to the variable pump and the bypass valve for controlling operation of the variable pump and the bypass valve. Preferably, the two-stage system also includes a control valve connected to the regulator valve assembly for setting a pressure differential across the regulator valve assembly and, thereby, loading and unloading the fixed pump.

Abstract: The operating system for a construction machine gives advice on efficient operation to an operator. A specified state value relating to the operational condition of the construction machine, for example, the hydraulic oil pressure or engine speed, is detected (S101), and the frequency distribution of the state value in prescribed time intervals is calculated (S102). The variable range of the state value is classified into plural regions beforehand, and different target values are pre-set for each these regions. For each region, the frequency distribution is compared with the target value (S104, 106, 108, 110, 112), and as a result of the comparison, a applicable message is selected from the prescribed messages and output (S105, 107, 109, 111, 113). The output message may also be selected according to the combination of the comparison results for the plural state values such as the hydraulic oil pressure and engine speed.

Abstract: A system and method for operating a two-stage, high-pressure pumping system includes a low-pressure pump having an output configured to deliver a hydraulic fluid under a low-pressure at a high-volume to drive a tool associated with the two-stage, high-pressure, pumping system under low load conditions. The system also includes a high-pressure pump having an output configured to deliver the hydraulic fluid under a high-pressure at a low-volume to drive the tool under high load conditions. A pilot-operated device is included that is configured to selectively drive the tool with pressure from at least one of the output of the low-pressure pump and the output of the high-pressure pump. The pilot-operated device receives pilot pressure from the output of the low-pressure pump to control selectively driving the tool with the output of the two stage pump.

Abstract: A configurable hydraulic system facilitates a variety of oilfield cementing and other oilfield or related applications. The system employs a plurality of prime movers to drive a plurality of loads. The plurality of prime movers and loads are coupled with a configurable hydraulic system that maintains a separate, sealed hydraulic system associated with each prime mover. The configurable hydraulic system also enables the load configuration driven by each prime mover to be changed without losing the benefit of a separate, sealed hydraulic system associated with each specific prime mover.

Abstract: A hydraulic device has a first pump, a second pump, an operating state detector configured and arranged to detect an operating state, a connection switching unit configured and arranged to selectively connect the second pump to either a first hydraulic oil line or a second hydraulic oil line, and a switching controller configured to control, based on the operating state detected by the operating state detector, a switching operation of the connection switching unit The switching controller is further configured to inhibit the switching operation of the connection of the second pump when the detected operating state is such that at least one of clutches of a multi-stage transmission and a steering device is in a state transition or at least one brake of the steering device is being operated.

Abstract: A hydraulic control system in a working machine includes hydraulic cylinders that make a working part ascend and descend; a first main pump that suctions oil from an oil tank and discharges the oil; an accumulator that accumulates oil discharged from weight holding side oil chambers of the hydraulic cylinders when the working part descends; and a hybrid pump that suctions accumulated oil pressure in the accumulator and discharges the oil pressure. When the working part ascends, discharged oil from the hybrid pump is supplied to the weight holding side oil chambers of the hydraulic cylinders. When an insufficient supply flow from the hybrid pump to the hydraulic cylinders exists, a complementary flow corresponding to the insufficient supply flow is supplied from the first main pump to the weight holding side oil chambers of the hydraulic cylinders.

Abstract: A system and method of controlling torque of plural variable displacement hydraulic pumps in construction equipment are provided, which can control torque of the variable displacement hydraulic pumps so that the total amount of torque of the hydraulic pumps does not exceed the preset amount of torque by presetting the torque so that the engine does not stop even at maximum load of the hydraulic pumps or by presetting the speed of the engine or the used torque of the hydraulic pumps in consideration of the fuel economy or working speed.

Abstract: Actuator control system and method comprising an electric motor driving a hydraulic pump in fluid delivery communication with a source of hydraulic fluid; a variable speed controller operatively coupled to the motor for driving the pump at variable speeds; an external hydraulic actuator in fluid delivery communication with the pump for receiving pressurized fluid flow from the pump; and a feedback loop operatively coupled from the motor to the controller for providing feedback signals correlative to a pressure of the pressurized fluid flow through the driven pump for driving the external hydraulic actuator in response to the feedback signals for providing electronic velocity and force control of actuation of the external hydraulic actuator. The actuator control system and method can operate on one or many high-pressure hydraulic linear and/or rotary actuators on different pieces of hydraulically driven equipment and with different velocity requirements actuating in different directions.

Abstract: A straight traveling hydraulic circuit is provided. In case of performing a combined operation in which a fine operation of a working device and a fine traveling of a traveling device are simultaneously required, the straight traveling hydraulic circuit can allow the working device and the traveling device to operate independently, and thus prevent a declination or sudden traveling of the equipment. In case of performing the combined operation by simultaneously operating the traveling device and the working device, first and second center bypass shifting valves installed on the lowermost stream side of first and second center bypass passages are shifted by a pilot signal pressure that shifts a straight traveling valve installed on an upper stream side of the second center bypass passage, so that the degree of opening of the first and second center bypass passages is reduced to operate the working device and the traveling device independently.

Abstract: In a hydraulic unit (A) including a hydraulic pump configured to be driven by a motor (2) and a hydraulic cylinder (3) for actuating a chuck, a fixed displacement hydraulic pump is combined with an adjustable speed motor (2) for driving the pump. In order to concurrently provide rapid movement of the cylinder (3) and reduction in the surge pressure, upon the cylinder (3) actuating the chuck, after a teaching movement is imparted to the cylinder (3) to determine an operating stroke of the cylinder (3) based on the number of rotations of the motor (2), the motor (2) is rotated at a high rotational speed for movement until a preset deceleration start point short of the end of movement of the cylinder (3) within the determined operating stroke and then rotated at a low rotational speed for deceleration from the deceleration start point to the end of movement of the cylinder (3), thereby allowing the chuck to chuck a work with a soft touch.

Abstract: A torque converter coupled to a transmission has a torque converter operating mode and a lockup operating mode. A first pump may be configured to supply transmission fluid to a plurality of electro-hydraulic transmission components. A second pump may be configured to supply transmission fluid to a lubrication system of the transmission. A valve may be configured to route transmission fluid supplied by the second pump through the torque converter during the torque converter operating mode. Means may also be provided for selectively routing at least some of the transmission fluid supplied by the first pump through the torque converter. Illustratively, transmission fluid supplied by the first pump may, but need not, be routed to the torque converter only during the torque converter operating mode or only during the torque converter operating mode if the temperature of transmission fluid exiting the torque converter exceeds a threshold temperature.

Abstract: A fluid system includes a controllable first pump unit for supplying fluid pressure to at least one implement; a prime mover arranged to supply a driving torque to the first pump The first pump unit is arranged to supply fluid pressure to the implement. The fluid system further includes a controllable second pump unit connected to a fluid accumulator. The prime mover is arranged to supply a driving torque to the second pump unit in order to accumulate fluid pressure in the accumulator during periods of low demand. Fluid pressure from the accumulator is arranged to drive the second pump unit to assist the prime mover during periods of high demand in order to supply an additional driving torque in excess of the available driving torque from the prime mover.

Abstract: A control method for controlling a hydraulic actuator to impart oscillatory excitation to a load, the actuator comprising at least one hydraulic chamber and a movable member capable of moving in said chamber between two extreme positions under the action of a liquid under pressure, wherein the method comprises the steps consisting in: determining an operating point for said actuator, which operating point corresponds to a rest position of said movable member; applying a hydraulic command to bring said movable member into correspondence with said rest position; and applying a hydraulic command to cause said movable member to perform reciprocating movement about said rest position, said reciprocating movement being adapted to apply a desired excitation to said load; the rest position of said movable member being selected to be significantly off-center relative to said extreme positions.

Abstract: A hydraulic system for a work vehicle including a manifold assembly configured to prioritize hydraulic fluid flow to priority functions over a wide range of engine speeds.

Abstract: The invention relates to a hydraulic system for actuating a belt-driven conical-pulley transmission with a variably adjustable transmission ratio, of a vehicle, having at least one hydraulic energy source and having a moment sensor that is supplied with working medium by a pump flow of the hydraulic energy source. The invention is distinguished in that a disconnecting valve device is connected between the hydraulic energy source and the moment sensor, which makes it possible to connect or disconnect an additional pump flow of the hydraulic energy source, depending on need.

Abstract: A hydraulic circuit for a hydraulic working machine is composed of a main pump 21, a boom cylinder 11 arranged for extension or contraction by pressure oil from the main pump 21, a directional control valve 22 for controlling flows of pressure oil to be fed from the main pump 21 to a bottom chamber 11a and rod chamber 12b of the boom cylinder 11, a control unit 23 for performing a change-over control of the directional control valve 22, a pilot pump 24, a jack-up selector valve 25 for controlling a flow of pressure oil delivered from the pilot pump 24, a flow control valve 26 connected on an upstream side of the directional control valve 22 to a meter-in port of the directional control valve 22 such that the flow control valve 26 can be changed over by the jack-up selector valve 25, and a center bypass selector valve 27 connected on a downstream side of the directional control valve 22 to a center bypass port of the directional control valve 22 such that the center bypass selector valve 27 can be changed over

Abstract: A hydraulic system for an agricultural vehicle is proposed. The hydraulic system comprises a main hydraulic circuit, which is fed with hydraulic fluid by a main hydraulic pump, a variable displacement charge pump which supplies charge pressure to the main hydraulic pump, and a lubricating hydraulic circuits. In order to keep efficiency losses on the vehicle to a minimum, particularly at high engine speeds, part of the hydraulic fluid delivered by the charge pump can be diverted to the lubricating hydraulic circuit.

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 drive system for an actuator uses a pair of pressure compensated hydraulic machines to control flow to and from the drive chambers of the actuator by varying the controlled pressure of one of the machines. The machines are mechanically coupled to permit energy recovery and charge an accumulator to store supplies energy. The drive system may be combined with other services including a transmission for incorporation in a vehicle. The transmission uses a pressure compensated supply and torque control of the wheels.

Abstract: A method of reducing the load of at least one engine arranged in an hydraulic excavator during a speed overload situation of a respective engine, includes reducing a delivery quantity of at least one hydraulic secondary consumer until the respective engine has been returned to a desired operational speed range.

Abstract: A boom control circuit for controlling hydraulic fluid fed to a boom cylinder is provided separately and independently from a travel/stick/bucket control circuit, which serves to control hydraulic fluid fed to travel motors, a stick cylinder, and a bucket cylinder. The boom control circuit includes a boom pump, an energy recovery motor disposed in a return passage through which return fluid from the boom cylinder 8bmc passes, and a boom motor generator connected to the energy recovery motor. The aforementioned boom pump is connected through a clutch to the boom motor generator. The invention is capable of providing a work machine of which a boom control circuit is adapted to function independently so that the flow rate required by the boom control circuit can be easily ensured.