In a load sensing hydraulic control circuit, a pressure compensator elaborates both a load sensing pressure signal to control a pump unit and a pressure compensated power flow for actuators, the power flow being either split or alternatively directed to at least a first and a second actuator control valves so that a differential pressure across the first and second control valves is controlled by the pressure compensator. In one embodiment, the circuit is onboard a construction vehicle to power actuators such is travel left, travel right, swing, boom, arm, bucket and the like.

A servo valve is provided with a first elastic portion, a second elastic portion, and a connecting portion. The first elastic portion extends in an X direction inside a valve body and has a first elastic force exerted on a movable element toward an X2 direction. The second elastic portion extends in the X direction inside the valve body and has a second elastic force exerted on the movable element toward an X1 direction. The connecting portion is connected to the first elastic portion and the second elastic portion inside the valve body, and is in abutment against a step portion of the valve body and a spool of the movable element at a neutral position of the movable element.

A servo valve is provided with a first elastic portion, a second elastic portion, and a connecting portion. The first elastic portion extends in an X direction inside a valve body and has a first elastic force exerted on a movable element toward an X2 direction. The second elastic portion extends in the X direction inside the valve body and has a second elastic force exerted on the movable element toward an X1 direction. The connecting portion is connected to the first elastic portion and the second elastic portion inside the valve body, and is in abutment against a step portion of the valve body and a spool of the movable element at a neutral position of the movable element.

An apparatus for monitoring the pressurisation of a control valve for a hydraulic actuator and a control valve. The apparatus including a spool movable along an axis (X), wherein the spool is configured to control the flow of hydraulic fluid through the control valve based on its position along the axis (X), and wherein in an unpressurised state of the control valve the spool occupies a first axial position, and in a pressurised state of the control valve the spool occupies a second, different axial position. The apparatus also including a position sensor configured to monitor the position of the spool within the control valve and detect whether the spool occupies the first axial position or the second axial position, wherein the first axial position and the second axial position correspond to neutral positions of the spool.

A method for controlling a speed of a hydraulic cylinder (2) in a hydraulic system (1) is provided. The hydraulic system (1) may include a hydraulic cylinder (2) fluidly connected to a load-holding valve arrangement (3) including a first load-holding valve (4) connected to a first end (5) of the hydraulic cylinder (2) and a second load-holding valve (6) connected to a second end (7) of the hydraulic cylinder (2). The hydraulic system (1) may further include a flow-control valve arrangement (8) comprising a directional flow-control valve (9) and at least one hydraulic pump (10).

The invention provides a hydraulic circuit for feeding an actuator (1) comprising first and second chambers (5, 6), the circuit comprising a slide valve (10) with a slide (16) that is movable between first and second extreme positions (18, 19) on either side of a stable central position (17) so that: in the central position, it connects the chambers (5, 6) of the actuator to a return port; in the first extreme position (18), it connects the first chamber (5) to a feed port and the second chamber to the return port; and in the second extreme position (19), it connects at least the second chamber (6) to the feed port.

According to the invention, the hydraulic circuit includes pressure-maintaining means (20) for maintaining pressure in the first chamber of the actuator while the slide is passing through the central position on being moved from the first extreme position to the second extreme position.

A hydraulic actuator with no friction and zero leakage and its drive system are provided. The hydraulic actuator includes a thickened disc structure A and a thickened disc structure B. The second end face of the thickened disc structure A is connected with the first end face of the thickened disc structure B, and a control cavity is formed between the second end face of the thickened disc structure A and the first end face of the thickened disc structure B. The drive oil access hole is arranged on the thickened disc structure B, and the control cavity is connected with the drive oil access hole. The displacement output method based on elastic deformation is adopted, which completely avoids the nonlinear phenomena such as leakage and friction, and reduces the difficulty of high-precision control of the actuator.

A hydraulic actuator with no friction and zero leakage and its drive system are provided. The hydraulic actuator includes a thickened disc structure A and a thickened disc structure B. The second end face of the thickened disc structure A is connected with the first end face of the thickened disc structure B, and a control cavity is formed between the second end face of the thickened disc structure A and the first end face of the thickened disc structure B. The drive oil access hole is arranged on the thickened disc structure B, and the control cavity is connected with the drive oil access hole. The displacement output method based on elastic deformation is adopted, which completely avoids the nonlinear phenomena such as leakage and friction, and reduces the difficulty of high-precision control of the actuator.

An apparatus for monitoring the pressurisation of a control valve for a hydraulic actuator and a control valve. The apparatus including a spool movable along an axis (X), wherein the spool is configured to control the flow of hydraulic fluid through the control valve based on its position along the axis (X), and wherein in an unpressurised state of the control valve the spool occupies a first axial position, and in a pressurised state of the control valve the spool occupies a second, different axial position. The apparatus also including a position sensor configured to monitor the position of the spool within the control valve and detect whether the spool occupies the first axial position or the second axial position, wherein the first axial position and the second axial position correspond to neutral positions of the spool.

A directly-controlled hydraulic directional valve includes a housing, control piston, first and second springs, double-stroke solenoid, spring plate, adjustment device, and electronics. The piston is longitudinally displaceable in a bore in the housing, either directly or via a control sleeve. The springs are positioned in a region of an end of the piston remote from the solenoid. One end of each spring is supported on the spring plate, which is clamped between the springs and the piston. The other end of the first spring is fixed to the housing, and the other end of the second spring is fixed to the adjustment device. The first spring exerts a force on the piston in a first direction, and the second spring exerts a force on the piston in a second opposite direction, so as to bias the piston into a preferred position. The solenoid is mounted on a side of the housing, and is operable to move the piston out from the preferred position in opposite directions proportional to an electric current from the electronics, such that the piston moves to the preferred position in response to each of non-actuation of the solenoid and a fault in the electronics. The adjustment device is operable to alter a position of the other end of the second spring to adjust the preferred position of the piston.