The subject matter of this specification can be embodied in, among other things, an electrohydraulic positioning control system that includes a shuttle valve configured to direct fluid flow between a selectable one of a first fluid port and a second fluid port, and a fluid outlet configured to be fluidically connected to a fluid actuator, a first servo valve controllable to selectably permit and block flow between the first fluid port, a fluid source, and a fluid drain, a second servo valve controllable to selectably permit and block flow between the second fluid port, the fluid source, and the fluid drain, a first servo controller configured to provide a first health signal and control the first servo valve based on a second health signal, and a second servo controller configured to provide the second health signal and control the second servo valve based on the first health signal.

The system is an improved valve/actuator architecture using a 4-way blocked-port architecture and area asymmetry providing numerous advantages over the conventional practice. The system uses fewer control circuits and provides for reduced component parts—it reduces hose, tubing and fitting requirements (lower cost, improved packaging, less installation labor and less leakage due to fewer connections). It also eliminates the need for a spring for static load support and other suspension control components (such as a sway bar). The system simplifies the mechanical design thereby reducing cost, aids in packaging, eliminates hysteresis losses of the spring and reduces moving mass thereby lowering response time. The system further allows regeneration of hydraulic power thereby increasing overall efficiency. The system further eliminates one half of throttling loss in a servo-valve.

A spool valve device includes: a housing with channels; a spool moving to change channel connection statuses; an electric actuator including an electric motor and linear-motion conversion mechanism, the motor rotating an output shaft by torque corresponding to a drive current supplied to the motor, the mechanism converting rotational output shaft movement into straight movement and applying thrust corresponding to the torque to the spool to change position; a biasing member applying biasing force to the spool against the actuator thrust; an angle detector detecting an motor output shaft angular position; a driving portion driving the motor by controlling drive current flow supplied to the motor based on a position command input and the angular position detected by the angle detector; and an abnormality determining portion calculating the spool position based on the detected angular position and determine presence or absence of operation spool abnormality.

The subject matter of this specification can be embodied in, among other things, a fluid valve assembly that includes a first fluid port, a second fluid port, a third fluid port, a valve spool configured to be positioned at a first position, a second position away from the first position, a third position away from the first position opposite the second valve position, the valve spool defining a first fluid duct configured to fluidly connect the first fluid port to the second fluid port in the first valve position, a second fluid duct configured to fluidly connect the first fluid port to the third fluid port in the second valve position, and a third fluid duct configured to fluidly connect the first fluid port to the second fluid port in the third valve position.

A four-position switching valve includes first and second pistons for driving a spool in a valve body, and a spool moving mechanism part that moves the spool to first and second intermediate switching positions between one-end side and the other-end-side switching positions. The spool moving mechanism part includes a compression spring that moves the spool back in the opposite direction by moving to the switching position on one end side and the other end side of the spool. The compression spring moves the spool to the first intermediate switching position when the spool moves to one-end-side switching position and the pressure on the second piston is released, and moves the spool to the second intermediate switching position when the spool moves to the other-end-side switching position and the pressure on the first piston is released.

A four-position switching valve includes first and second pistons for driving a spool in a valve body, and a spool moving mechanism part that moves the spool to first and second intermediate switching positions between one-end side and the other-end-side switching positions. The spool moving mechanism part includes a compression spring that moves the spool back in the opposite direction by moving to the switching position on one end side and the other end side of the spool. The compression spring moves the spool to the first intermediate switching position when the spool moves to one-end-side switching position and the pressure on the second piston is released, and moves the spool to the second intermediate switching position when the spool moves to the other-end-side switching position and the pressure on the first piston is released.

A valve group includes an inlet module and at least one service module connected to the inlet module, the inlet module having a housing, a pressure port, a pressure gallery, a tank port, a tank gallery, a spool movable in the housing to interrupt in a first position a connection between the pressure port and the pressure gallery and to connect in a second position the pressure port and the pressure gallery. A first pressure transducer is provided to detect a first pressure in the pressure gallery and a second pressure transducer is provided to detect a second pressure in the tank gallery, the pressure transducers being connected to a controller determining the position of the spool based on the pressures read from the pressure transducers.

A control device, for a hydraulic consumer (22) and susceptible to vibrations, includes a valve (24) having a control spool (40) controllable by an actuating device (46). The valve (24) has a pressure supply port (P), to which a pressure compensator valve can be connected, which can be supplied with pressure fluid from a pressure supply device. The actuating device (46) has a motor (74). A load-pressure-dependent force on the control spool (40) can be generated by a control device (66). That force at the control spool (40) acts on an electronic motor controller (208) of the DC motor (74), which detects a change of the force and acts as a damping of the vibrations of the consumer (22) against this change of force.

To provide a drift-prevention valve device, a blade device, and a working machine capable of operating an actuated unit and preventing the machine body from drifting with a simple configuration. The drift-prevention valve device is provided with a non-return valve 41 that allows the flow of hydraulic oil from a control valve 28 to a head chamber 34h of a blade cylinder 34 and blocks the flow of the hydraulic oil in the reverse direction; and a piston accommodation part 42 separately disposed from an accommodation part 70 of the non-return valve 41, configured to movably accommodate a power piston 43. The power piston 43 defines a first piston chamber 42p1 communicating with a rod chamber of 34r of the blade cylinder 34 and a second piston chamber 42p2 for drain positioned on a poppet 71 side of the non-return valve 41 and communicating with a tank 52. The power piston 43 is connected to the poppet 71 of the non-return valve 41, so that the power piston 43 can be operated by the difference between the urging force of the poppet 71 by a spring 72 of the non-return valve 41 and a rod chamber pressure of the blade cylinder 34.

A hydraulic control valve unit includes an input port hydraulically coupled to a pump, a working port hydraulically coupled to the working load, and a return port connected to a hydraulic tank. The unit includes a control slide movable into different working positions in an axial direction for controlling a hydraulic flow between the hydraulic ports and a slide housing surrounding the control slide. The control slide includes a control segment which is delimited in the axial direction by a control edge, and cooperates with an axial housing segment of the slide housing for controlling a flow cross section for hydraulic flow at the control segment. The control slide is rotationally driven about an axis of rotation in a rotational direction. The control edge of the control segment or the housing segment cooperating with the control segment is designed such that the flow cross section has a different size depending on a rotational position of the control slide.