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: A hydraulic system for an automatic transmission operatively connected to an internal combustion engine that is operable in a start-stop mode. The hydraulic system includes a hydraulic energy source to supply the hydraulic system with hydraulic energy, the hydraulic energy source including at least one electrically driven hydraulic pump to supply the hydraulic system with hydraulic energy during a stopping phase of the internal combustion engine. To achieve a reduction in fuel consumption and CO2 emissions, provision is included to enable the electrically driven hydraulic pump to be switched on in addition to a mechanically driven hydraulic pump, as needed during an operating phase of the internal combustion engine.

Abstract: A tree felling machine has a main pump for operating functions of the machine such as the drive wheels or tracks, the steering, the brakes, and the lifting and extension of the boom, and a separate saw pump for driving the cutting element, for example, a circular disc saw driven by a hydraulic motor. Both pumps are driven by the same prime mover, i.e. the same internal combustion engine, and the power division between the two pumps is determined by the operator and by the hydraulic control system. In particular, a control provided in the cab is controllable by the human operator to limit the maximum power that the saw pump can draw from the prime mover. In addition, the power that the saw pump can draw from the prime mover is limited by a combination of the displacement setting of the main pump, the output pressure of the saw pump, and the pressure exerted on the load by the main pump.

Abstract: A hydraulic pressurizer system comprises a drive source, which drives a hybrid vehicle, a mechanical oil pump, which is driven by the drive source, an electrical motor, which is activated by a 12V battery, an electrical oil pump, which is driven by the electrical motor, and a control unit, which activates the electrical motor. The pressurizer further comprises a ratio-change mechanism, which is activated by hydraulic oil supplied by the mechanical oil pump and by the electrical oil pump to establish a speed change ratio, at which the rotational driving force of the drive source is transmitted to wheels with a rotational speed change. The control unit memorizes a characteristic value, which is specified from the temperature of the hydraulic oil and from the rotational speed of the electrical motor, and a threshold value for the rotational speed of the electrical motor, which threshold value corresponds to the characteristic value.

Abstract: A load control structure for a work vehicle comprises: a device for detecting operating position of a manually operated speed change operating element; an engine load detection device for detecting load on an engine of the work vehicle; a swash plate position detecting device for detecting an operating position of a swash plate of a variable displacement pump of a hydrostatic continuously variable speed change device; a pump operating device for steplessly operating the swash plate of the variable displacement pump; a motor operating device for operating a swash plate of a variable displacement motor of the hydrostatic continuously variable speed change device between at least two speed change positions including a higher speed position and a lower speed position; a control device for controlling the operations of the pump operating device and the motor operating device.

Abstract: A swing control circuit is provided separately from a hydraulic actuator control circuit. The swing control circuit includes a swing pump motor connected to closed circuits of a swing motor through a solenoid valve that serves as a directional control valve. A swing motor generator is connected to the swing pump motor. The swing motor generator is connected to an electric power storage device of a hybrid type drive system. An exterior-connecting passage for feeding hydraulic fluid to hydraulic actuators of a lower structure and a work equipment is drawn from a pipeline between the swing pump motor and the solenoid valve. A connecting passage solenoid valve is disposed in the exterior-connecting passage. The invention enables hydraulic energy generated in the swing system to be directly fed to the outside of the swing system.

Abstract: A hydraulic system includes a first pump that delivers hydraulic fluid to a first load outlet point and to a second load outlet point, a second pump that delivers hydraulic fluid to the second load outlet point, but not to the first load outlet point, a pressure detector for detecting the load pressure at the first load outlet point and a pressure detector for detecting the load pressure at the second load outlet point. The system includes a controller for controlling the first pump on the basis of the detected load pressure at the first load outlet point and the detected load pressure at the second load outlet point, and a controller for controlling the second pump on the basis of the detected load pressure at the second load outlet point but not on the basis of the detected load pressure at the first load outlet point.

Abstract: A hydraulic drive system for storing and releasing hydraulic fluid includes a high pressure storage device, a low pressure storage device, and a pump-motor operating at a range of pump-motor speeds for converting between hydraulic energy and mechanical energy. The pump-motor is disposed between the high pressure device and the low pressure device. In normal operation, the hydraulic drive system enters a motoring mode where hydraulic energy is released from the high pressure storage device and converted to mechanical energy using the pump-motor. It also enters a pumping mode where mechanical energy is converted into hydraulic energy. A neutral state exists where hydraulic energy is neither stored nor released from the high pressure storage device. An approach for compensating for temperature changes using varying pressure limits helps to maintain the hydraulic drive system in normal operation, thereby promoting efficiency within the hydraulic drive system.

Abstract: A hydraulic circuit for a construction machine is disclosed, which can prevent an energy loss of a hydraulic system by automatically reducing revolution of an engine when a working device such as a boom is not driven. The hydraulic circuit includes first to third hydraulic pumps, first to third switching valves for controlling hydraulic fluid fed to working devices, a fourth switching valve for controlling hydraulic fluid fed to left and right traveling devices, a confluence switching valve for selectively supply the hydraulic fluid from the third hydraulic pump to either the working devices on the first hydraulic pump side or the working devices on the second hydraulic pump side, a signal line for traveling devices, signal lines for working devices, and a shuttle valve for selecting any one of the signal pressure formed in the signal line for the traveling devices and the signal pressure formed in the signal lines for the working devices.

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: The present invention relates to a trim actuator actuating system having two separate hydraulic power supply systems, through which it is possible for the first time to use a hydraulic linear actuator as a trimmable horizontal stabilizer actuator in an aircraft. The at least one hydraulic linear actuator is coupled to the first power supply system in such a way that it applies hydraulic power to the linear actuator during normal operation. In order to ensure the application of pressure to the hydraulic linear actuator in case of breakdown, in such a case, the pressure application to the hydraulic linear actuator is maintained with the aid of the second hydraulic power supply system.

Abstract: A hydraulic control system for a work machine is disclosed. The hydraulic control system has a first pump, a second pump, an operator control device, and a controller. The first and second pumps are configured to pressurize a fluid. The operator control device is movable through a range of motion from a neutral position to a maximum position to generate a corresponding control signal. The controller is in communication with the first pump, the second pump, and the operator control device. The controller is configured to receive the control signal, affect operation of the first pump in response to the control signal as the operator control device is moved throughout the range of motion, and affect operation of the second pump in response to the control signal only as the operator control device is moved through a portion of the range of motion.

Abstract: Temperature of each cooling target fluid is detected. When the flow rate of a cooling target fluid passing through a cooling system is high, the fan revolution speed of a cooling fan of the cooling system is controlled to achieve a target fan revolution speed so that the detected temperature of the cooling target fluid reaches a preset target temperature. In cases where the engine is in a low idling state, the flow rate of each cooling target fluid passing through the cooling system is reduced. The fan revolution speed of the cooling fan is controlled to achieve a new target fan revolution speed that is lower than the target fan revolution speed.

Abstract: To keep one of three hydraulic pumps unaffected by variations in torque of the remaining hydraulic pumps when the three hydraulic pumps are used, displacements of the first and second hydraulic pumps are controlled based on their own delivery pressures P1,P2 and a pressure P3? obtained by reducing through a reducing valve 14 a delivery pressure P3 from the third hydraulic pump, while a displacement of the third hydraulic pump 3 is controlled only by its own delivery pressure P3. The pressure oil delivered from the third hydraulic pump 3, therefore, remains unaffected by variations in delivery flow rates from the first and second hydraulic pumps 1,2, in other words, by variations in their torque consumptions, so that the third hydraulic pump is assured to provide a stable flow rate.

Abstract: A control system for a work machine (101) including an electric machine (202), a hydraulic machine (204) and at least one hydraulic cylinder (108). The electric machine (202) is connected in a driving manner to the hydraulic machine (204). The hydraulic machine (204) is connected to a piston side (208) of the hydraulic cylinder (108) via a first line (210) and a piston-rod side (212) of the hydraulic cylinder (108) via a second line (214). The hydraulic machine (204) is adapted to be driven by the electric machine (202) and supply the hydraulic cylinder (108) with pressurized hydraulic fluid from a tank (216) in a first operating state and to be driven by a hydraulic fluid flow from the hydraulic cylinder (108) and drive the electric machine in a second operating state.

Abstract: A joining directional control valve 13 is disposed to supply, to an arm cylinder 4, not only a hydraulic fluid delivered from a first hydraulic pump 1, but also a hydraulic fluid delivered from a second hydraulic pump 2 when an arm directional control valve 14 is driven. Respective delivery pressures of the hydraulic pumps 1, 2 are detected by pressure sensors 101, 102, and the opening area of a recovery control valve 6 is controlled depending on a lower one of the detected pressures from the pressure sensors 101, 102 such that, even in the combined operation of the arm cylinder 4 and another actuator 3, 4, the hydraulic fluid can be recovered for return to the arm cylinder 4 when the load pressure of the arm cylinder 4 is low. Thus, by supplying the hydraulic fluids from the two hydraulic pumps to the particular actuator for which the hydraulic fluid is to be recovered, a recovery flow rate is ensured when the load of the particular actuator is low in the combined operation.

Abstract: For connection to a hydraulic power supply of a tractor, wherein the tractor comprises a plurality of hydraulic supply circuits, and wherein each hydraulic supply circuit comprises a pair of quick couplers for connecting the hydraulic supply circuit to a hydraulic device, a hydraulic motor apparatus comprises a first pair of hydraulic lines adapted for connection to the quick couplers of a first hydraulic supply circuit; a second pair of hydraulic lines adapted for connection to the quick couplers of a second hydraulic supply circuit; and a hydraulic motor connected to both the first and second pairs of hydraulic lines such that fluid can flow from both the first and second hydraulic supply circuits through the hydraulic motor to drive the hydraulic motor.

Abstract: One preferred embodiment of the present invention, provides an auxiliary hydraulic drive system having a total hydraulic flow. The system includes a primary hydraulic pump operable to provide hydraulic flow for an implement, and a flow control valve in communication with the hydraulic flow. The flow control valve operates to allow an optimum flow rate and diverts the excess flow amount when the total hydraulic flow exceeds the optimum flow rate. A secondary hydraulic pump is selectively operable to provide additional hydraulic flow. A control system is operable to engage the secondary pump when the total hydraulic flow drops below a minimum flow level; and the control system operates to disengage the secondary pump when the total hydraulic flow exceeds a maximum flow level. In a further embodiment, the invention provides a control unit for a hydraulic system. The control unit includes a sensor to measure total hydraulic fluid flow in a system; and a controller coupled to the sensor.

Abstract: A rotary flow combiner allows flow from multiple pressure compensated hydraulic pumps; with or without load sensing to be combined into a single outlet. The flows are combined in such a way that each input to the rotary flow combiner has equal flow. The flow from each pump is optimized in such a way that the output from the rotary flow combiner can achieve the maximum range of flow and pressure and so that all the pumps in the multiple pump system are supplying fluid flow at all times. A check valve can allow the rotary flow combiner to pull hydraulic fluid direct from a reservoir in parallel to a lower flow pump such that the volume of flow from the lower pump combined with the fluid drawn directly from the reservoir will match the flow from the higher flow pump.

Abstract: The present invention is directed to controlling an operation oil supplied to an option apparatus without changing a design of a control valve assembly which controls an operation oil supplied to a traveling motor, etc. when additionally engaging an option apparatus to a small size excavator.

Abstract: A hydraulic valve is used to judiciously shunt oil from lowering ends of the hoist and stick cylinders that have been plumbed to achieve near horizontal movement. This allows the use of cylinders that have unequal rod/bore ratios or to compensate for certain transient effects that may require the exchange of oil to the reservoir. The action of the hydraulic valve acts without obtrusive operator intervention and is essentially automatic. This allows for greater flexibility in the design of the boom system, allows the boom system to perform various tasks, while not requiring obtrusive intervention from the operator.

Abstract: A device arrangement structure for hybrid construction equipment capable of reducing devices of a charging system in size is provided. For this purpose, in the device arrangement structure: a hydraulic pump (47) is connected to an engine (41) via a first power take-off (46); and a regenerative motor (59), which is regenerated by return oil from hydraulic actuators (10a, 10b), and a generator motor (55), which assists an engine as an electric motor to drive hydraulic pump and generates power with surplus torque of the regenerative motor, are provided in parallel with the hydraulic pump via the first power take-off.

Abstract: A control system for operating a hydraulic system includes a user input device which generates an input signal indicating desired movement of a hydraulic actuator. A mapping routine converts the input signal into a velocity command indicating desired actuator velocity. A valve opening routine transforms the velocity command into a flow coefficient which characterizes fluid flow through the valve assembly and from the flow coefficient produces a set of control signals designating levels of electric current to apply to valves within the valve assembly. A pressure controller regulates pressure in the supply line in response to the velocity command. When the hydraulic system has a plurality of functions, the control system adjusts each velocity command to equitably apportion fluid to each function when the aggregate flow being demanded by the functions exceeds the total flow available from a source.

Abstract: According to the invention, traveling bypass cut-off valves are disposed in center bypass passages respectively which are located between traveling direction control valves and working direction control valves disposed downstream of the valves, wherein, when at least a traveling motor and any of working actuators are operated simultaneously, the traveling bypass cut-off valves are switched from neutral position to another position. Thereby, when travel and work by working actuators are performed simultaneously, interference between pressure oil fed to traveling motors and pressure oil fed to the working actuators is to be prevented.

Abstract: The two boom members and hydraulic cylinders of a knuckle boom tree harvesting machine are so arranged and proportioned that with a single control movement during reaching and retracting actions the working tool head is made to travel in an approximately horizontal path. The cylinders and control valve are so connected that during horizontal reaching action load-supporting pressurized oil from a collapsing cylinder is not required to be dumped to the reservoir in the conventional heat generating manner, but is rather shunted directly to an extending cylinder where it continues to do useful load support work. Energy waste to hydraulic oil heat and fuel consumption is significantly reduced. Although these advances have been particularly developed for disc saw felling and stroke delimbing of trees they can also be applied to other knuckle boom applications where horizontal reaching is a major function.

Abstract: A first given pressure is provided to a first side of an air pressure cylinder that in turn drives a cutting member under the influence of the first given pressure. A second given pressure is provided to a second side of the air pressure cylinder that is greater than the first given pressure during a non-cutting state of the air cylinder. The cutting member remains stationary as long as the second given pressure is greater than the first given pressure. To transition to a cutting state, the second given pressure is rapidly reduced to a value below the first given pressure value during a cutting state of the air pressure cylinder for moving the cutting member to cut a web.

Abstract: An hydraulic power assembly 10 is provided, including at least one primary hydraulic power unit 20 supplying hydraulic fluid 30 to a hydraulic system 34, and a contingency hydraulic power unit 50 utilizing the orbiter's helium storage tank 52 to power a contingency hydraulic drive 56 to supply hydraulic fluid 30 from a contingency hydraulic fluid reserve 58 to the hydraulic system 34 during peak loading conditions.

Abstract: In a work vehicle that has several hydraulic actuators a system and method for controlling and scaling flow between the actuators includes an electronic controller that is connected to several hand controls that provide a proportional signal indicating how far the operator has moved the hand controls. The controller reads the hand controls and proportionally scales the total available flow to make sure the operator does not demand too much fluid from the hydraulic pump.

Abstract: A method for operating a hydraulic drive apparatus in which flows of oil discharged from a plurality of hydraulic drive sources each using a hydraulic pump are merged in order to drive an actuator. At least in a pressure control mode, one of the hydraulic drive sources (main hydraulic drive source) is operated in a regular manner, and the other hydraulic drive source (auxiliary hydraulic drive source) is operated such that at A merge point where the oil flows merge, the pressure of oil from the auxiliary hydraulic drive source becomes lower than the pressure of oil from the main hydraulic drive by a predetermined amount. Thus, an ordinary pressure control signal is applied to the main hydraulic drive to perform an ordinary pressure control.

Abstract: The two boom members and hydraulic cylinders of a knuckle boom tree harvesting machine are so arranged and proportioned that with a single control movement during reaching and retracting actions the working tool head is made to travel in an approximately horizontal path. The cylinders and control valve are so connected that during horizontal reaching action load-supporting pressurized oil from a collapsing cylinder is not required to be dumped to the reservoir in the conventional heat generating manner, but is rather shunted directly to an extending cylinder where it continues to do useful load support work. Energy waste to hydraulic oil heat and fuel consumption is significantly reduced. Although these advances have been particularly developed for disc saw felling and stroke delimbing of trees they can also be applied to other knuckle boom applications where horizontal reaching is a major function.

Abstract: A tandem fixed displacement pump circuit with torque control includes first and second pumps that draw fluid from a reservoir to supply respective load circuits, pressure relief valves for each of the load circuits, and a pilot operated sequence valve that monitors the pressure for each of the circuits and reduces the pressure of one of the circuits as the pressure in the other circuit rises. The sequence valve modulates to control the pressure in the secondary priority circuit so that a predetermined input torque value is not exceeded.

Abstract: A control apparatus for an industrial vehicle is disclosed. The vehicle has a rear axle that is swingable during straight travel of the vehicle and can be fixed during turning of the vehicle. A damper looks or unlocks the rear axle. A controller has a memory that stores a first value and a second value of an angular velocity rate that represents an angular velocity per unit time. The controller activates or deactivates the damper. The controller activates the damper to lock the rear axle when the angular velocity rate is greater than the first value. The controller deactivates the damper to unlock the rear axle when the angular velocity rate is kept smaller than the second value for a predetermined time period after the angular velocity rate has become smaller than the second value.

Abstract: A boom and drive train hydraulic system is described having a pressure source, preferably a pump operated by a motor, said pressure source providing hydraulic fluid at a high pressure to a first set of valves used to operate the drive train of the system. The first set of valves is equipped with a power beyond for allowing the hydraulic fluid to flow from the first set of valves to a second set of valves. At the second set of valves a pressure control is provided to reduce the pressure to a desired lower pressure. The second set of valves provides the hydraulic fluid at this reduced pressure to the boom portion of the system. The differential of the pressures is approximately 5,000 psi for the track system and approximately 2,500 psi for the boom system.

Abstract: A total power regulation device for a plurality of variable displacement pumps (1, 2), each having a regulation valve (18) which regulates its displacement volume, which is acted upon--against a counter-pressure--by a control pressure corresponding to the working pressure of the variable displacement pump. When the control pressure exceeds the counter-pressure, the regulation valve regulates the variable displacement pump along a characteristic line (KL) of constant torque. To adjust the desired values of the individual drive torques simply, and to prevent torques from exceeding a desired value, an electronic control unit (16)--connected to measuring detectors (25) for detecting the displacement volumes of the variable displacement pumps--stores the desired value totals of the counter-pressures and the torque characteristic lines (KL) of the variable displacement pumps, and has a desired value setting device (27) for dividing the desired value total.

Abstract: A hydraulic drive assembly includes a variable displacement pump fluidly connected in a closed loop circuit with a motor for driving an ancillary device, such as a fan. An auxiliary pump can be operatively connected to the pump, the motor and a reservoir for replenishing fluid losses in the closed loop circuit. An auxiliary circuit connected to the pump has a recirculating passage fluidly connected to the closed loop circuit downstream of the motor to reduce the necessary reservoir volume. A method for smoothly and continuously adjusting the output of the pump to drive the ancillary device is also disclosed.

Abstract: Hydraulic control circuit for working components, in particular in earth-moving machines, said machines comprising a front group provided with actuators controlled by first hydraulic distributors (1,2) and a rear excavator group provided with actuators controlled by second hydraulic distributors (3-8), in said rear excavator group there being present a main arm actuated by a main actuator (13) controlled by a main distributor (3) located upstream of the remaining second distributors (4-8). The main actuator (13) supplies in series the remaining second distributors (4-8) when the pressure downstream thereof is less than a predetermined value and instead discharges the fluid under pressure when said pressure downstream thereof reaches or exceeds said predetermined value. In the front group there is also provided an additional distributor (A-B) which sends the fluid under pressure immediately downstream of the main distributor (3) of the rear excavator group via a bypass line (23).

Abstract: Apparatus and method for controlling equipment of driving a ram of a hydraulic press. Four proportional sheet valves PA, PB, TA and TB are connected with a hydraulic circuit, in which a hydraulic cylinder 2 for driving a ram 1, a hydraulic pump 3 and so on are set up, a so as to form a full-bridge hydraulic circuit. A compression proportional sheet valve PAp and a hydraulic pump 40 are connected as a hydraulic power source with high pressure and small flow rate parallel with the sheet valve PA being in the oil supply position side in the hydraulic circuit. An NC controller controls timing of turn-on of the proportional sheet valves PA, PB, TA and TB as well as change of the valves PA and Pap by PWM signal to pilot valves of the sheet valves PA, PB, TA and TB. The valves PA and TB are turned on in the down stroke of the ram 1, the valves PB and TA are turned on in the up stroke of the ram 1, and the valve Pap is turned on in the compression stroke.

Abstract: For enabling a boom to be smoothly raised during the triple combined operation of boom-up, arm-crowd and bucket-crowd in a hydraulic circuit system for a hydraulic excavator, in a first valve group of a hydraulic valve apparatus (12), a variable throttle valve (70) is installed in a feeder passage (32) of a bucket directional control valve (21) downstream of a load check valve (32a), and a secondary pressure C as a boom-up operation command is introduced through a line (71) to a pilot control sector (70a) of the variable throttle valve (70) which sector operates in the throttling direction, so that when the secondary pressure C is 0 or small, the variable throttle valve (70) is fully opened and, as the secondary pressure C increases, an opening area of the variable throttle valve (70) is reduced to restrict the flow rate of a hydraulic fluid supplied through the bucket directional control valve (21).

Abstract: An auxiliary drive apparatus which comprises an engine, a first hydraulic pump driven by the engine, a second hydraulic pump driven by the engine and integrally connected to the first hydraulic pump, a third hydraulic pump driven by the engine and integrally connected to the second hydraulic pump, a first pressure limiting valve connected in parallel to the first hydraulic pump, a first vacuum breaking valve connected in parallel to the first hydraulic pump, a first hydraulic motor connected in series to the first hydraulic pump, a second pressure limiting valve connected in parallel to the second hydraulic pump, a second vacuum breaking valve connected in parallel to the second hydraulic pump, a second hydraulic motor connected in series to the second hydraulic pump, a third pressure limiting valve connected in parallel to the third hydraulic pump, a third vacuum breaking valve connected in parallel to the third hydraulic pump, and a third hydraulic motor connected in series to the third hydraulic pump.

Abstract: A conveying system (43) is disclosed including a vertical auger (27) which receives material from a horizontal auger (25). The vertical auger is driven by a hydraulic motor (37) and the horizontal auger is driven by a hydraulic motor (35). A pressure response valve (89) responds to a pressure signal (93), representative of the load on the motor (37) driving the vertical auger to unload or bypass the motor (35) driving a horizontal auger. As the load on the vertical auger decreases, the valve (89) gradually communicates more flow to the motor (35) driving the horizontal auger, thus feeding more material (grain) to the vertical auger.

Abstract: A hydraulic control circuit for uniform controlled movement of stripping and guiding arms in a tree delimbing apparatus. The piston rods of said cylinders are mechanically coupled to rotate tubular sleeve members with affixed stripping and guide arms between outward and inward positions. The stripping levers and guide arms open and close about a felled tree in a uniform manner for delimbing operations. A valve is provided for actuation to permit the guiding arms to be held in an open position, while the stripping arms are closed about a tree to accommodate a bent trunk.

Abstract: A single rod three chamber fluid cylinder is driven in an initial rapid advance forward stroke by a main pump, pumping fluid through a proportional directional control valve to act against a first equal area at the head end of the piston. Fluid expelled from a second equal area at the rod side of the piston is returned to the reservoir through a proportional directional control valve which is in a first position while a two position valve is in its first position allowing an accumulator to fill a third chamber exposed to a third area of the head side. When shifting to the feed stroke, the two position valve switches to its second position disconnecting the accumulator to the third area and connecting the main pump to the third area while also connected to the first equal area. Upon the return stroke of the piston, the fluid from the first equal area is returned to the sump and the fluid from the third area is routed to the accumulator.

Abstract: A hydraulic drive system for actuating a reciprocating member such as a polished rod in a pump jack device, and for acting as a counterbalance and/or for energy conservation. The system has two hydraulic circuits and a prime mover. A first circuit includes a cylinder for driving an output member which may be connected to the polished rod, a first pump of the variable displacement, reversible flow type, together with a pair of fluid lines forming with the cylinder a closed-loop circuit. A controller is programmed to control the setting of the first pump so as to establish the velocity profile of the output member. A second hydraulic circuit is also in the form of a closed-loop containing first and second pumps, at least one of which is of the variable displacement type and is also controlled by the controller.

Abstract: Simultaneous operation efficiency in a case where a plurality of actuators are operated by one or a plurality of hydraulic pumps is improved. A delivery pressure passage (1a) of one hydraulic pump (1) and that (1a) of the other hydraulic pump (1) communicate with each other through a first short-circuit passage (39) via a pair of check valves (38, 38), and an unload valve (40) is provided in this first short-circuit passage (39). The load pressure introduction passages (6, 6) on the left and right hydraulic pumps (1, 1) communicate with each other through a second short-circuit passage (36) via a pair of check valves (35, 35), and a relief valve (37) is provided in this short-circuit passage (36).

Abstract: An exhaust manifold (25) of a fluid power and control system, the pressure of which is varied when the fluid motor (10) is subjected to a bidirectional positive or negative type load (W). This exhaust manifold (25) is also supplied from a source of exhaust manifold pressurizing oil (29) other than the system pump (18). This source of exhaust manifold pressurizing oil (29) may include a flow amplifying device (57) which is activated when the fluid motor (10), in the form of a cylinder, moves a load in the direction of its piston rod end (11) and when the piston rod end (11) of cylinder (10) is subjected to a negative load pressure and when the pressure in the exhaust manifold (25) drops below a certain minimum preselected level.

Abstract: A device for recovering energy, in particular potential energy in working machines, has a hydraulically actuatable working cylinder linked to a hydropneumatic storage. At least another working cylinder is provided. The two working cylinders are mutually linked by their rod end chambers to transfer fluid and are linked to a hydraulic circuit having at least one pump. The other working cylinder is also linked at its piston end chamber to a hydraulic circuit having a pump. The energy generated by the movements of the working machine can be effectively stored in a failure-proof manner and called back at defined moments in time.

Abstract: An improvement in a multiple intensifier system having two intensifier units with reciprocating piston assemblies to supply very high pressure water. When one of the piston assemblies travels faster than the other, so that these reached an end stroke position at the same time, there can be an abrupt pressure drop. To alleviate this, a first embodiment isolates the compensator control lines of the pumps of the two intensifier units so as to maximize volumetric flow rates during such pressure drops to give the slower moving piston assembly a boost at the beginning of its subsequent stroke. Another embodiment provides an accumulator in the fluid control line for the compensators, and a further embodiment provides a pressure reference supply pump to alleviate pressure variations in the fluid control line.

Abstract: A hydraulic system for a vehicle adapted for operating a plurality of reel mower cutting units and for driving at least one vehicle component such as drive wheels or power steering. The vehicle carries an engine near the front of the vehicle which generates heat. The system includes a fluid reservoir located remote from the engine and near the rear of the vehicle. An input line is coupled with the reservoir, and a first pump is operatively coupled with the input line. A first motor receives fluid from the first pump for driving a reel mower, and a branched line having first and second branches receives fluid from the first motor. The first branch is a first return line extending to the reservoir. A second pump having a lower capacity than the first pump is operatively coupled with the second branch, and a second motor receives fluid from the second pump for driving the vehicle component.

Abstract: A hydraulic actuating apparatus for opening and closing a movable cover (convertible top) of a vehicle includes a piston/cylinder device, a reversible, motor driven pump for supplying hydraulic fluid to the piston/cylinder device to cause it to open or close the vehicle cover, and an auxiliary manual pump for supplying hydraulic fluid to the piston/cylinder device in the event of failure of the reversible pump.

Abstract: The invention relates to a power control device for two variable displacement pumps, each with an adjusting device which can be acted upon by adjusting pressure, a power control valve associated therewith, which is acted upon by a first control pressure corresponding with the operating pressure of the variable displacement pump to be adjusted against a pressure difference in the direction of the control position, in which the adjusting pressure loading is controlled in the direction of reduced displacement of the variable displacement pumps along a hyperbolic control curve, whereby the pressure difference results from a spring-arrangement backpressure counteracting the first control pressure and a second control pressure corresponding with the operating pressure of the other variable displacement pump and with increase of the same drops from a maximum value to a minimum value.