Abstract: A hydraulic circuit for supplying a plurality of series-operated consumers of a hydraulically controlled installation, in particular of an injection molding machine, having a pump with feed-flow pressure control, is described. To be able to slow down greater moving masses with very little expenditure in regard to circuitry and devices, only a portion of the consumers, such as the extruder, the injection unit and possibly the ejector are operated in open circulation, while at least one selected further consumer, such as the clamping unit of the injection molding machine, where a greater mass must be moved in alternating directions, is moved in semi-closed or closed circulation.

Abstract: A hydraulic system incorporating a double acting piston and cylinder and a bi-directional pump/motor derives energy from a drive system when operating in the pump mode and delivers energy to the drive system when in the pump mode and includes a circulation valve for supplementing fluid flow to and from and fluid supply in accordance with the unequal demands of the chambers driving the hydraulic actuator in one direction or the other by circulating fluid between the chambers.

Abstract: A first cylinder chamber of a hydraulic cylinder is connected to a pair of variable displacement pumps of which the first one is connected to a reservoir and second one is connected to the second cylinder chamber. This allows to bias the piston by a hydraulic force acting on either side of the piston corresponding to the direction of motion. This is obtained by adjusting the delivery volume of both the pumps such that the volume supplied is larger than the volume drained. Metering the difference of both the delivery volumes results in the desired biasing counter-pressure.

Abstract: A hub clutch for locking or unlocking a wheel drive shaft to or form a hub clutch housing, comprises: a drive gear fixed to the wheel drive shaft; a slide gear slidably engaged or disengaged with or from the drive gear to lock or unlock the wheel drive shaft to or form the hub clutch housing; an elastic member for urging the slide gear into engagement or disengagement with or from the slide gear; a pressure source for supplying pressure into a pressure chamber formed between the wheel drive shaft and the hub clutch housing to shift the slide gear against an elastic force of the elastic member; and in particular a pressure supplementing switch for supplementing pressure supplied from the pressure source into the pressure chamber, whenever pressure within the pressure chamber drops below a predetermined value.

Abstract: An electro-hydraulic actuator having an electric motor disposed in a hydraulic fluid reservoir and connected to drive a hydraulic fluid pump. The actuator includes a piston rod which extends or retracts as a piston is hydraulically driven in a cylinder. An actuator housing forms the reservoir and cylinder and contains hydraulic passages connecting the pump, reservoir and cylinder. The actuator includes a one-way filter for filtering the hydraulic fluid. The hydraulic pump is preferably a rotating piston type and includes a port plate which allows the pump to drive the piston while the retract and extend chambers of the pump have different or unbalanced fluid drive ratios. A load limiting valve protects the system from excessive hydraulic pressure and a position sensor detects the position of the piston rod.

Abstract: A single hydraulic pump (6) is employed in a vehicle for supplementing fluid to a hydrostatic transmission (1) and for supplying fluid to a fluid-operated clutch (2) and to high pressure-actuated hydraulic actuators (3, 4, 5). Fluid discharge path (7) of the pump is connected to the hydrostatic transmission through a pressure-reducing valve (8). Fluid drain path (9) of the reducing valve is fashioned to a fluid supply path for the clutch. A second fluid supply path (11) is connected to the discharge path for supplying fluid to the hydraulic actuators and include a relief valve (12) or orifice (12A) for maintaining fluid pressure in the discharge path higher than the output pressure of the reducing valve. A high pressure relief valve (10) for establishing fluid pressure to be applied to the actuators is connected to the discharge path for minimizing a discharge pressure required to the pump.

Abstract: The position of a controlled system is regulated with a hydraulic actuator, which is directly linked to a hydraulic pump. The pump is driven in either direction by an electric motor, which is controlled by the output of rotatory direction and driving power generated from a controller based on a desired position and the feedback input of the actual position of the controlled system and the rotatory speed of the electric motor. The controller further includes a gain-variable amplifier for amplifying a deviation of the controlled value from a desired value with a gain characteristic curve of a shape appropriate to the controlled system, attaining a stable and well follow-up control of position.

Abstract: A hydraulic lifting arrangement for a lift assembly on a materials-handling vehicle includes a working piston-cylinder device (17) for raising and lowering the lift assembly, a reversible pump assembly (40) for operating the piston-cylinder device, and an electric motor for driving the pump assembly. The piston-cylinder device (17) is a double-acting device and has two working chambers (28,29), which are connected to the pump assembly by connecting pipes (46,47). The pump assembly comprises a first and a second hydraulic pump (41,42) having fixed displacements. The pumps are so arranged in the system that together they supply hydraulic medium to and receive hydraulic medium from solely the first chamber (28) whereas only the pump motor (41) supplies and receives hydraulic medium to and from the second chamber (29).

Abstract: A closed loop hydraulic system for use in a rotary drilling apparatus includes an extendible-retractable feed cylinder and a valve for biasing the feed cylinder. A variable, reversible displacement pump is provided for pumping fluid from either of the first and second pump ports, including pumping fluid to the feed cylinder. A reservoir retains a supply of fluid for the system. A check valve is provided for supplying additional fluid to the pump in response to the feed cylinder being extended. An overcenter valve is connected to each of the first and second ports for controlling flow from the system in response to pressures received from the first and second ports when the feed cylinder is extended and retracted.

Abstract: A compact electric adjusting drive for locking systems, fan flaps or the like in motor vehicles includes a fluidic force transmission system between the electric motor and the adjusting element movable to and fro between two end positions.

Abstract: Conventional piston-cylinder hydraulic actuators require external pressure sources. The hydraulic actuator disclosed utilizes the centrifugal head developed in its chambers. The piston (36) is attached to shaft extension (24) which is splined to the actuator cylinder (20). The cylinder (20) rotates with the shaft (16) to develop a centrifugal fluid head which is selectively directed from the outlet port (40a, 40b) of a contracting chamber through a servo valve (46) to the return passageway (46b, 46a) of an expanding chamber to axially displace piston (36) and shaft (16). An accumulator in the fluid circuit retains fluid displaced from the cylinder (20).

Abstract: This invention relates to integrated electro-hydraulic actuators for use aboard aircraft or elsewhere. A balanced, double-acting hydraulic ram or motor (12) is connected between a support (16) and a member to be moved relative to the support. The ram includes first and second changeable volume hydraulic chambers (30, 32). A reversible hydraulic pump (38) is connected by a pair of conduits (44, 46) to the ram chambers (30, 32). The pump (38) displaces hydraulic fluid from one chamber to another for the purpose of causing a pressure differential between them. A hydraulic accumulator (60) provides leakage makeup fluid to the actuator, and further provides a quiescent pressure to the actuator when it is in a substantially nonoperative condition. A conduit (62) may connect the accumulator (60) to the ram (12). A laminar leakage flow path within the actuator permits hydraulic connection of the accumulator (60) to the ram (12) without use of valves.

Abstract: This disclosure pertains to a completely digital, electrically powered servo wherein the servo actuator is minutely incremented at a frequency proportional to the magnitude of an error binary number. The binary error is derived from the difference of a binary reference representing the commanded position of the actuator and a binary feedback representing the position of the actuator. The direction of each increment has the polarity which reduces the difference between the reference and feedback binary numbers. The power unit of the servo is electrohydraulic; however, the servo is entirely electrically controlled and powered. Hydraulic fluid is confined to the power unit where it serves as a link between two solenoid driven piston pumps, a common mode volume adjuster and a hydraulic actuator. The direction the actuator is incremented is dependent on which of the two solenoids the error polarity directs pulsed electrical power.

Abstract: The invention relates to a reaction hydraulic control unit for use in steering systems of the type having a differential type servomotor. In steering systems of this type having a differential piston type servomotor there exists a condition during the piston centering operation when the unit is in neutral wherein the servomotor piston has a slower centering speed when the transfer of medium is from the nonrod side to the rod side of the servomotor. The unequal centering times causes annoyance to drivers because that condition is transmitted to the steering wheel. This problem is addressed by providing steering controlled valving for exhausting fluid from the nonrod chamber of the servomotor to the system tank after the control unit has returned to its neutral position and during the centering operation of the servomotor piston.

Abstract: A hydraulic drive system including a main line, a variable displacement hydraulic pump and another main line connected to a single rod cylinder in a closed hydraulic circuit, and a flushing valve having a first switching position in which one main line is communicated with a low pressure line and a second switching position in which the other main line is communicated with the low pressure line. The flushing valve is operative to maintain at least one of the two main lines in communication with the low pressure line at all times while moving from one switching position to the other switching position, to keep a lock-up phenomenon from taking place in the closed hydraulic circuit. The system further includes a pressure generating device for generating between the two main lines a pressure differential necessary for effecting switching of the flushing valve.

Abstract: Means are disclosed for dissipating supercharge pressure in a hydraulic system including a reversible pump (18) directly connected to a hydraulic cylinder (22). Supercharge pressure results from unequal areas on either side of a piston (24) of a single-ended hydraulic cylinder (22). When the piston moves towards the blind end of the cylinder (22), more fluid is displaced from the cylinder than is admitted to the cylinder on the opposite side of the piston. Means responsive to a pressure at a first port (82) of the pump (18) opens a passage between the second port (76) of the pump (18) and a fluid reservoir (16), allowing fluid in excess of the pump's intake requirements to pass to the reservoir (16). In a first embodiment of the invention, a rocker mechanism (60) is actuated by a piston (66) responsive to pressure at the first port (82) pressing against a first end (20) of the rocker mechanism (60), the second end (74) of the rocker mechanism (60) displacing a check ball (38) of a keep-full valve.

Abstract: A counterbalancing hydraulic system for exerting a torque on a member such as a spud pile by means of at least two substantially identical hydraulic cylinders, piston rods of which engage the pile at a distance from one another, the pistons being subjected to pressure in opposite senses, while the portion of each cylinder remote from the piston rod communicates through a main displacer pump motor each with the portion of the other cylinder located on the side of the piston rod and the portion of each cylinder remote from the piston rod communicates through an auxiliary displacer pump motor with a medium reservoir.

Abstract: The invention relates to improved jack-pump devices comprising a pump with a sliding piston forming first and second pump chambers, one on each side, a jack with a sliding piston forming first and second jack-chambers, one on each side, a first valve between the pump chambers, acting unidirectionally from the second to the first pump chambers, a second valve between the first chambers of the pump and the jack, and a communication device between the second chambers of the pump and the jack, the pump and jack pistons being slidably mounted and axially aligned in the same body filled with fluid, a fixed transverse partition disposed in the cylinder body between the two pistons, and a plunger for compensating variations of volume, slidably mounted in one of the two second chambers, close to the corresponding extremity of the body.The main application is as a lifting device for regulating the height of members or parts of moving machines, of seats for chairs, vehicles, building stays, etc.