A single-rod hydrostatic actuator or pump-controlled actuator, comprises a hydrostatic pump connected in a closed circuit to a single-rod hydraulic cylinder where the cylinder velocity is directly controlled by the pump flow, without the need of intermediary valves. Due to the absence of throttling losses, the efficiency of hydrostatic actuators is considerably superior to the efficiency of conventional valve-controlled circuits. However, because of the differential areas at the cap and rod sides of the cylinder, the flows coming into and out of the cylinder do not match. Several attempts have been made to this date to produce a stable, robust and reliable circuit that can be used in everyday applications but no circuit has ever been conceived to reach the high standards of reliability and robustness required by industry. The current invention solves the problem of the differential flows with a design that is reliable, oscillation-free and robust. The present conception is based on the correction of a misstated theory concerning the modus operandi of hydrostatic actuators. The resulting design can be translated into different embodiments using electronic or hydraulic technologies and uses only logical combinations of the pressure readings at the cap and rod-sides of the circuit.

An actuator control arrangement includes a hydraulic actuator having a housing and a piston rod axially moveable within the housing, a stop disposed within the housing to limit the extent of movement of the piston rod into the housing, and a solenoid valve arranged between a pressure source and the actuator. The solenoid valve is switchable between a first mode and a second mode in response to an electric control signal, wherein, in the first mode, the solenoid valve creates a fluid flow path from the pressure source to the actuator so as to locate the stop in its neutral position and in the second mode, the solenoid valve creates a fluid flow path to release pressure from the actuator to permit the stop to move to its retracted position. In the event of electrical failure, the stop will set the actuator to its neutral position.

A hydraulic drive device for an industrial vehicle includes a tank, a hydraulic pump, a capacity control valve, a plurality of hydraulic cylinders, a plurality of direction switching valves, a first hydraulic oil passage, a second hydraulic oil passages, a pilot line, a relief valve, a relief pressure setting portion, a plurality of operation detecting portions, and a control unit. The control valve controls the hydraulic pumps so that a differential pressure between a discharge pressure of the hydraulic pump and a pilot pressure of the pilot line is to be a predetermined pressure. The control unit controls the relief pressure setting portion.

Provided are an apparatus and a method for controlling spool displacement of a construction machine, which are capable of improving regeneration efficiency of the construction machine, and improving a fuel efficiency characteristic of the construction machine by reducing pressure loss in the operating mode by adjusting the quantity of spool displacement in a regeneration mode when a current pressure of a main pump is less than a predetermined operating pressure, and determining whether the construction machine is in an operating mode or the regeneration mode in real time according to an operating angle of a joystick and the current pressure of the main pump when the current pressure of the main pump is greater than or equal to the predetermined operating pressure to variably change the quantity of spool displacement in the operating mode.

Modular directional valve with two or more crossing elements (E1 . . . En) able, acting only on the entry side, to manage a variable displacement pump (PA) of the load sensing type. In particular, this management allows in a single drive, unlike the conventional crossing distributors, to make the flow rate to the utility independent of the load and allows setting a maximum flow rate at the end of the stroke; in multiple drives, it ensures that the sum of the required flow rates is independent of the loads. A compensated flow rate regulator is placed in the entry side so as to act only on the bypass line LC upstream of the first element (E1 . . . En) while a proportional choke is placed on the load line consisting of a 2-way 2-position tray.

A counter pressure valve arrangement for controlling a pressure level of a hydraulic fluid in a return line from a hydraulic actuator arrangement. The counter pressure valve arrangement comprises a counter pressure valve having: a moveable valve member; a counter pressure regulating port configured for being connected to the hydraulic actuator arrangement via the return line; a tank port configured for being connected to a tank or low pressure reservoir for storing low pressure hydraulic fluid; and a pump port configured for being connected to a source of pressurised hydraulic fluid. A first position of the valve member effects fluid communication between the pump port and the counter pressure regulating port for supplying pressurised hydraulic fluid to the return line (4), and a second position of the valve member effects fluid communication between the counter pressure regulating port and the tank port for discharging hydraulic fluid from the return line to the tank.

A counter pressure valve arrangement for controlling a pressure level of a hydraulic fluid in a return line from a hydraulic actuator arrangement. The counter pressure valve arrangement comprises a counter pressure valve having: a moveable valve member; a counter pressure regulating port configured for being connected to the hydraulic actuator arrangement via the return line; a tank port configured for being connected to a tank or low pressure reservoir for storing low pressure hydraulic fluid; and a pump port configured for being connected to a source of pressurised hydraulic fluid. A first position of the valve member effects fluid communication between the pump port and the counter pressure regulating port for supplying pressurised hydraulic fluid to the return line, and a second position of the valve member effects fluid communication between the counter pressure regulating port and the tank port for discharging hydraulic fluid from the return line to the tank.

A system and method for providing redundancy in hydraulic circuits in multi-cycle hydraulic tools is described. The problems of dysfunctional hydraulic tool due to the failure of electromechanical actuators are addressed by providing redundant actuators and associated circuitry design.

A work machine including: a hydraulic cylinder 20 configured to drive a work implement 3; a control valve 22 configured to connect a delivery line of a hydraulic pump 21 switchingly to a bottom fluid chamber and a rod fluid chamber of the hydraulic cylinder 20 and a tank; a pilot pump 23 configured to output a pilot pressure to drive the control valve 22; an engine 24 configured to drive the hydraulic pump 21 and the pilot pump 23; and an accumulator 26 configured to accumulate a return hydraulic fluid from the hydraulic cylinder 20 is provided with: a bypass line 41 configured to connect the bottom fluid chamber of the hydraulic cylinder 20 and a delivery line 21a of the hydraulic pump 21 by bypassing the control valve 22 and be provided with the accumulator 26 thereon; a pressure-accumulation control valve 27 provided between the bottom fluid chamber of the hydraulic cylinder 20 and the accumulator 26; a release control valve 28 provided between the accumulator 26 and the delivery line 21a; and a hydraulic system controller 30 configured to open the release control valve 28 if an engine revolution speed N becomes lower than a set value Ns.

Modular directional valve with two or more crossing elements (E1 . . . En) able, acting only on the entry side, to manage a variable displacement pump (PA) of the load sensing type.

In particular, this management allows in a single drive, unlike the conventional crossing distributors, to make the flow rate to the utility independent of the load and allows setting a maximum flow rate at the end of the stroke; in multiple drives, it ensures that the sum of the required flow rates is independent of the loads.

A compensated flow rate regulator is placed in the entry side so as to act only on the bypass line LC upstream of the first element (E1 . . . En) while a proportional choke is placed on the load line consisting of a 2-way 2-position tray.