The present disclosure relates to a zeroing device comprising a piston movable along an axis, at least one biasing member for biasing the piston along the axis, and an axially displaceable zeroing member limiting axial movement of the at least one biasing member. The present disclosure further relates to a variable displacement hydraulic unit including said zeroing device.

A lift apparatus and method for driving a downhole reciprocating pump is disclosed and includes a hydraulic cylinder having a piston and a hydraulic fluid port, the piston being coupled to a rod for driving the reciprocating pump, the piston being moveable between first and second ends of the cylinder in response to a flow of hydraulic fluid through the hydraulic fluid port. A variable displacement hydraulic pump is responsive to a displacement control signal to draw hydraulic fluid from a reservoir and to produce a controlled flow of hydraulic fluid at the outlet. The apparatus also includes a valve connected between the hydraulic fluid port and the reservoir, the valve being responsive to a valve control signal for controlling discharge of hydraulic fluid from the hydraulic fluid port of the cylinder back to the reservoir to facilitate movement of the piston through a downstroke away from the second end toward the first end of the cylinder. The apparatus further includes a first sensor located proximate the first end of the cylinder and operable to produce a first signal indicating a proximity of the piston to the first sensor, a second sensor located proximate the second end of the cylinder and operable to produce a second signal indicating a proximity of the piston to the second sensor, and a controller operably configured to generate the displacement control signal and the valve control signal in response to receiving the first signal and the second signal.

Control device for hydraulic variable displacement pumps operated in an open hydraulic circuit and adjustable in their displacement volume by means of a servo control device. The control device comprises a control piston with two control edges to which pressure can be applied by means of pressurized pressure fluid from a variable displacement pump, the control piston being mounted in a housing so that it shifts longitudinally. The housing of the control piston comprises an inlet for the connection of a high pressure line of a variable displacement pump, an outlet which can be connected to a tank and a servo connection which can be linked to a servo cylinder, whereby a link between the inlet and the servo connection can be made via a first control edge. It is possible to create a link between the servo connection and the outlet via a second control edge.

A hydraulic actuator includes a variable-delivery positive-displacement pump, a member able to continuously vary the delivery of the pump, the member being actuated by a ram supplied by a first directional-control valve commanded on the basis of an actuator movement instruction. The actuator comprises a second directional-control valve commanded on the basis of an output pressure of the pump, the second directional-control valve comprising two positions, one of them, known as the rest position, obtained as long as the output pressure of the pump is below a predetermined pressure and transmitting the output from the first directional-control valve to the double-acting ram and the other, referred to as the active position, transmitting the output pressure of the pump to the ram so as to reduce the output pressure of the pump without passing via the first directional-control valve.

A hydraulic actuator includes a variable-delivery positive-displacement pump, a member able to continuously vary the delivery of the pump, the member being actuated by a ram supplied by a first directional-control valve commanded on the basis of an actuator movement instruction. The actuator comprises a second directional-control valve commanded on the basis of an output pressure of the pump, the second directional-control valve comprising two positions, one of them, known as the rest position, obtained as long as the output pressure of the pump is below a predetermined pressure and transmitting the output from the first directional-control valve to the double-acting ram and the other, referred to as the active position, transmitting the output pressure of the pump to the ram so as to reduce the output pressure of the pump without passing via the first directional-control valve.

The present disclosure relates to an adjusting device for adjusting the swash plate of an axial piston machine comprising an adjusting piston, which is connected to the swash plate of the axial piston machine via an adjusting lever, and a regulator for adjusting the adjusting pressure acting on the adjusting piston in dependence on a control force acting on a control piston of the regulator, wherein the adjusting piston is connected to the control piston via a feedback spring. In accordance with the present disclosure the feedback spring is at least partly received in a pot-shaped recess of the control piston.

A pump system includes a pressure compensator and a speed compensator for controlling the displacement of a variable displacement pump having an inlet and an outlet. The variable displacement pump is driven by a drive shaft powered by an electric motor. The pressure compensator adjusts the displacement of the variable displacement pump based on a pump pressure at the pump outlet. The speed compensator adjusts a maximum magnitude of the displacement of the variable displacement pump based on a speed of the electric motor.

The invention relates to a method and a device for determining of at least one end position of a displacement element of an adjustable hydraulic machine, in particular of the axial piston type, shiftable or displaceable between two ends position a by means of a displacement unit between a first end position and a second end position. According to the invention the determination of having reached an end position of displacement takes place by means of a measurement circuit, whose electrical characteristics are changed jumpily when an end position is reached. This is done by connecting a partial branch of the measuring circuit with earth, when a moveable element comes into electric contact with a limit stop assigned to the corresponding end position.

The invention relates to a method and a device for determining of at least one end position of a displacement element of an adjustable hydraulic machine, in particular of the axial piston type, shiftable or displaceable between two ends position a by means of a displacement unit between a first end position and a second end position. According to the invention the determination of having reached an end position of displacement takes place by means of a measurement circuit, whose electrical characteristics are changed jumpily when an end position is reached. This is done by connecting a partial branch of the measuring circuit with earth, when a moveable element comes into electric contact with a limit stop assigned to the corresponding end position.

A variable displacement axial piston pump including a cylinder block defining a plurality of cylinder bores, each receiving a piston. A swash plate having a piston-supporting surface is pivotally supported relative to the cylinder block. A port block defines first and second pumping ports arranged in fluid communication with the plurality of cylinder bores such that, during operation of the pump, one of the first and second pumping ports is configured to supply fluid to the cylinder bores for pumping, and the other of the first and second pumping ports is configured to receive fluid pumped from the plurality of cylinder bores. The swash plate partially defines at least one variable volume control chamber, and the swash plate is operable to tilt with respect to the port block in response to a fluid pressure change in the at least one control chamber.