A vehicle control surface, such as an aircraft horizontal stabilizer, is hydraulically controlled using solenoid operated valves (SOVs) controlling directional control valves and/or rate control valves with small numbers of ports, e.g. a four port three position directional control value and/or a four port two position rate control valve.

A vehicle control surface, such as an aircraft horizontal stabilizer, is hydraulically controlled using solenoid operated valves (SOVs) controlling directional control valves and/or rate control valves with small numbers of ports, e.g. a four port three position directional control value and/or a four port two position rate control valve.

A change-over valve comprises a spool housed in a spool housing, and a pilot chamber facing at least an end of the spool. An axial passage is formed in the spool along the axial direction. While being connected to a pilot chamber, the axial passage communicates with a tank passage via a small hole having an opening on an outer periphery of the spool in accordance with displacement of the spool, to discharge the air in the pilot chamber to the tank passage. Since the axial passage is formed at a location offset from a center axis of the spool, a length of the small hole is shortened and the small hole is easily processed.

A change-over valve comprises a spool housed in a spool housing, and a pilot chamber facing at least an end of the spool. An axial passage is formed in the spool along the axial direction. While being connected to a pilot chamber, the axial passage communicates with a tank passage via a small hole having an opening on an outer periphery of the spool in accordance with displacement of the spool, to discharge the air in the pilot chamber to the tank passage. Since the axial passage is formed at a location offset from a center axis of the spool, a length of the small hole is shortened and the small hole is easily processed.

A method is provided for compensating for the flow rate of a variable capacity-type hydraulic pump such that, when a manipulation lever is manipulated, a discontinuous section, which has no change in the discharge flow rate of the hydraulic pump, is eliminated.

A method is provided for compensating for the flow rate of a variable capacity-type hydraulic pump such that, when a manipulation lever is manipulated, a discontinuous section, which has no change in the discharge flow rate of the hydraulic pump, is eliminated.

The present invention relates to a hydraulic control system for construction machinery capable of variably adjusting a set pressure of a relief valve, which controls a set pressure of a hydraulic system, according to a value inputted by means of pressure in the hydraulic system or the manipulation of a joystick. The hydraulic control system comprises: a flow control valve installed in a passage between a hydraulic pump and a hydraulic actuator, for controlling the driving of the hydraulic actuator by being switched by a control signal according to the manipulation of the joystick; a main relief valve installed in a passage between an upstream-side discharge passage of the hydraulic pump and a hydraulic tank, for returning a working fluid to the hydraulic tank when a high load exceeding a set pressure occurs in the system; a pressure controlling means for controlling, either continuously or in stages, a set pressure of the main relief valve; a pressure sensing means for sensing a pressure at a discharge side of the hydraulic pump; and a controller for determining the value inputted by the manipulation of the joystick, and a required set pressure for the relief valve according to the system pressure sensed by the pressure sensing means, and then outputting a control signal to the pressure controlling means to enable a set pressure of the relief valve to be variably adjusted to a determined set pressure.

A speed controller capable of controlling an action speed of an external cylinder in one stroke in a step-wise manner. The speed controller includes a first flow path and a second flow path that allow a first port and a second port to be in communication with each other. The first flow path is provided with a first check valve for allowing flow from the first port to the second port. The second flow path is provided with a first needle valve, and an opening hole of the first check valve is constituted as a part of a flow path. The first needle valve adjusts the flow rate by changing an opening area of the opening hole with a tip portion fixed on a piston in the cylinder chamber. The speed controller further includes a third flow path allowing the first port and the cylinder chamber to be in communication with each other. The third flow path is provided with a second check valve for allowing flow from the first port to the cylinder chamber.

An axial differential pressure control valve (DPCV) having an annular body, a tubular body, a coaxial closing member for closing an outlet aperture for exit of the fluid from the tubular body, sealing separation means arranged between first and second chambers containing the return fluid and the delivery fluid, respectively, said separation means being movable axially upon activation of a thrust due to a pressure differential ΔP=P1−P2 and to the spring, wherein the closing member is fixed, and further comprising pins axially arranged between the ring nut and the abutment flange of the spring, wherein the pins pass through the pipefitting so as to come into contact with the said abutment flange and are designed to be displaced axially upon operation of the ring nut independently of the fixed closing member, so as to vary the compression of the spring.

A piston for a hydraulic valve of a rotation phaser, wherein the piston is configured hollow cylindrical, wherein the piston is axially movable in a central opening extending along a first longitudinal axis of a housing of the hydraulic valve, wherein operating connections of the housing are opened and closed according to a position of the piston, wherein the piston includes check valves which prevent an unintentional outflow of a hydraulic fluid flowing through the piston from an inner cavity of the piston in flow through openings of the piston associated with the operating connections, wherein the piston is configured with check valves in its inner cavity that open towards its interior cavity, wherein the check valves are fixated by a spacer element that is arranged between the two check valves. The invention also relates to a hydraulic valve for a rotation phaser of a cam shaft.