An example spool includes a shaft varying in diameter along a length of the shaft, and a plurality of annular lands formed on the shaft and spaced-apart by respective reduced diameter annular neck portions. The plurality of annular lands comprise at least one annular metering land, and wherein the at least one annular metering land comprises: one or more sine notches formed as a portion of a sine wave, and one or more additional notches having a different shape from the one or more sine notches.

A control system (50) for an electro-hydraulic servo-actuator (26) envisages: a controller (55), to generate a control current (I.sub.c), designed to control actuation of the electro-hydraulic servo-actuator (26), implementing a position control loop based on a position error (e.sub.p), the position error (e.sub.p) being a difference between a reference position (Pos.sub.ref) and a measured position (Pos.sub.meas) of the electro-hydraulic servo-actuator (26); and a limitation stage (58), coupled to the controller (55) to provide a limitation of the actuator speed of the electro-hydraulic servo-actuator (26); the limitation stage (58) limits a rate of change of a driving current (I.sub.d) to be supplied to the electro-hydraulic servo-actuator (26), in order to limit the actuator speed.

Systems and methods for control of multi-function hydraulic commands of a multi-function electrohydraulic system are provided. In one aspect, a system for hydraulic control includes a first function in fluid communication with a first electrohydraulic control valve and a second function in fluid communication with a second electrohydraulic control valve. The system includes a controller in communication with the first electrohydraulic control valve and the second electrohydraulic control valve. The controller can be configured to receive an input target command, determine an achievable function rate based on the input target command, where the achievable function rate maintains a proportional relationship between the input target command and the achievable function rate. The controller can also map the achievable function rate to an output command based on a predetermined relationship between the achievable function rates and the output commands and supply the output command to the first and second electrohydraulic valves.

A control system (50) for an electro-hydraulic servo-actuator (26) envisages: a controller (55), to generate a control current (I.sub.c), designed to control actuation of the electro-hydraulic servo-actuator (26), implementing a position control loop based on a position error (e.sub.p), the position error (e.sub.p) being a difference between a reference position (Pos.sub.ref) and a measured position (Pos.sub.meas) of the electro-hydraulic servo-actuator (26); and a limitation stage (58), coupled to the controller (55) to provide a limitation of the actuator speed of the electro-hydraulic servo-actuator (26); the limitation stage (58) limits a rate of change of a driving current (I.sub.d) to be supplied to the electro-hydraulic servo-actuator (26), in order to limit the actuator speed.

The present disclosure relates to a hydraulic valve arrangement comprising a first pilot operated proportional directional control valve having a first valve member that is displaceable in a first and a second axial direction for controlling direction of supply and discharge of hydraulic fluid to and from a hydraulic actuator, a first proportional electro-hydraulic control valve for controlling displacement of the first valve member in the first axial direction, a second proportional electro-hydraulic control valve for controlling displacement of the first valve member in the second axial direction, and a second pilot operated proportional control valve having a second valve member configured to be controlled by the first and second proportional electro-hydraulic control valves via a shuttle valve arrangement. Individual meter-in and meter-out control of the hydraulic actuator is providable by having the second pilot operated proportional control valve configured to operate as a meter-in valve of the hydraulic actuator and the first pilot operated proportional directional control valve configured to operate as a meter-out valve of the hydraulic actuator, or by having the first pilot operated proportional directional control valve configured to operate as a meter-in valve of the hydraulic actuator and the second pilot operated proportional control valve configured to operate as a meter-out valve of the hydraulic actuator. The present disclosure also relates to a vehicle comprising a hydraulic actuator and a hydraulic valve arrangement for controlling the motion of the hydraulic actuator.

A construction machine that precisely enables derivation of the operation characteristics of hydraulic actuators in a high-velocity area with less calibration operation is provided. A controller (10) has a calibration mode in which the controller (10) derives operation characteristics (α(xs)) representing a relation among a spool position (xs) of a meter-in valve (8a1), an operation velocity (Va) of a hydraulic actuator (4a), and a differential pressure (ΔP) across the meter-in valve (8a1), and is configured to, in a case where the spool position (xs) of the meter-in valve (8a1) has changed in a direction to increase the opening area of the meter-in valve (8a1) in the calibration mode, output a command signal to increase the opening area of a bleed-off valve (8b1) to a bleed-off solenoid proportional pressure-reducing valve (8b2) as a command signal to reduce the differential pressure (ΔP).

Systems and methods for control of multi-function hydraulic commands of a multi -function electrohydraulic system are provided. In one aspect, a system for hydraulic control includes a first function in fluid communication with a first electrohydraulic control valve and a second function in fluid communication with a second electrohydraulic control valve. The system includes a controller in communication with the first electrohydraulic control valve and the second electrohydraulic control valve. The controller can be configured to receive an input target command, determine an achievable function rate based on the input target command, where the achievable function rate maintains a proportional relationship between the input target command and the achievable function rate. The controller can also map the achievable function rate to an output command based on a predetermined relationship between the achievable function rates and the output commands and supply the output command to the first and second electrohydraulic valves.

This hydraulic drive system includes: a hydraulic pump capable of changing a discharge flow rate of a working fluid; a meter-in control valve that controls a meter-in flow rate of the working fluid flowing from the hydraulic pump to a hydraulic actuator; a meter-out control valve that is provided separately from the meter-in control valve and controls a meter-out flow rate of the working fluid being drained from the hydraulic actuator into a tank; an operation device that outputs an operation command; a first pressure sensor that detects a drainage pressure of the hydraulic actuator; and a control device that sets a target meter-out flow rate according to the operation command from the operation device and controls an opening degree of the meter-out control valve on the basis of the drainage pressure detected by the first pressure sensor and the target meter-out flow rate.

Even where the differential pressure across a directional control valve associated with each actuator is very small, flow dividing control of the plurality of directional control valves can be performed stable, and even where a demanded flow rate suddenly changes at the time of transition from composite action to single action or the like, a sudden change of the flow rate of hydraulic fluid to be supplied to each actuator is prevented to implement superior combined operability. Further, the meter-in loss of the directional control valves can be reduced to implement a high energy efficiency. To this end, a plurality of pressure compensating valves 7a, 7b and 7c for controlling such that the pressure in the downstream side of the meter-in opening of a plurality of directional control valves 6a, 6b and 6c becomes equal to the highest load pressure are individually arranged in the downstream side of meter-in openings of the plurality of directional control valves 6a, 6b and 6c, and demanded flow rates for the directional control valves 6a, 6b and 6c are calculated from input amounts of operation levers. Besides, the meter-in pressure loss of a predetermined directional control valve is calculated from the demanded flow rates for and meter-in opening areas of the directional control valves 6a, 6b and 6c, and the set pressure of the unloading valve 15 is controlled using the value of the meter-in pressure loss.

This hydraulic drive system includes: first and second circuit systems; first and second hydraulic pumps; a merge valve that opens and closes a merge passage connecting the hydraulic pumps; an operation device that outputs an operation command corresponding to an amount of operation specifying an amount of actuation of first and second hydraulic actuators; and a control device that controls the merge valve according to the operation command from the operation device. The first circuit system includes: a first meter-in control valve that controls a meter-in flow rate of the working fluid that flows to the first hydraulic actuator; and a first meter-out control valve that controls a meter-out flow rate of the working fluid that is drained from the first hydraulic actuator into a tank. The control device controls an opening degree of the first meter-in control valve and an opening degree of the first meter-out control valve.