A hydraulic drive apparatus for an industrial vehicle includes a cargo-handling device, a hydraulic control device, a cargo-handling-device operating member, and a switching member. When a first operation of the cargo-handling-device operating member is performed, an open-close valve is opened to hydraulic oil flowing in a first direction to cause the hydraulic oil to bypass a throttle. When a second operation of the cargo-handling-device operating member is performed while the switching member is in a first state, the open-close valve is closed against hydraulic oil flowing in a second direction to cause the hydraulic oil to flow through the throttle. The throttle provided in a flow route of the hydraulic oil between a main control valve and the cargo-handling device reduces a flow rate of the hydraulic oil to restrict cargo handling.

A pressure control device is provided and includes a body which has a groove-shaped flow path including a groove part and a widened part connected to the groove part and having a width larger than a width of the groove part, and a filter unit which captures foreign matters mixed in a fluid which passes through the groove-shaped flow path. The filter unit includes a frame body being in a cylindrical shape and including a through hole part which penetrates in a direction along a central axis, and at least one filter member being in a planar plate shape disposed to intercept the through hole part and supported inside the frame body, in which the filter unit is accommodated in the widened part so that a direction orthogonal to the central axis of the frame body is along a depth direction of the widened part.

A propeller hydraulic actuation system, includes a double-acting dual chamber hydraulic pitch change actuator. The pitch change actuator includes a first pressure circuit having first fluid supply lines and a first hydraulic chamber and a second pressure circuit having second fluid supply lines and a second hydraulic chamber. A piston separates the first and second chambers. At least one pressure sensor is provided for obtaining pressure measurements from which a load differential (F) applied to the piston by the circuits can be calculated. A closed loop controller is arranged to control the fluid supplied to the first and second pressure circuits, wherein the closed loop controller includes an actuator position loop arranged to utilise feedback on the actuator position to control the actuator position.

Electrically controllable hydraulic system for a vehicle transmission and method for controlling the same An electrically controllable hydraulic system (1) for a vehicle transmission comprises a pressure pump system (4a, 4b) and a subsystem (1A) comprising a transmission element (2) and an electrically controlled hydraulic pressure controlling module (1B) including a hydraulic valve element (15) for controlling a hydraulic pressure for actuating the transmission element (2) and an electromagnetically controllable operating element (21) for operating the hydraulic valve element (15). The subsystem (1A) and the pressure controlling module (1B) have a first and a second cut-off frequency (f1, f2) with f2>f1. The hydraulic system includes a driver circuit (32) for driving the pressure controlling module (1B) that comprises a full bridge circuit and a control circuit (42) for simultaneously controlling both switching elements of the driver circuit with a duty cycle according to an input value of the input signal (Iset) dithered with a frequency (f.sub.dith) in the range (f1, f2).

According to an embodiment, a variable pressure device includes a channel constituting unit and a switch valve mechanism. The channel constituting unit constitutes a channel including a first regulator and second regulators that are arranged in series to the first regulator and are in parallel to one another. The switch valve mechanism selectively connects the second regulators to the first regulator. Opening areas of the second regulators are different from one another.

An automatic oil return structure has a main body assembly mounted between an oil storage bag and a piston, and having a pressure regulating blocking unit, a pressure regulating elastic unit, an engaging unit, and an engaging elastic unit. The pressure regulating elastic unit pushes the pressure regulating blocking unit to block a first pressure regulating channel. An engaging groove is formed radially inward on the pressure regulating blocking unit. The engaging elastic unit pushes the engaging unit toward the pressure regulating blocking unit. When a pressure in the first pressure regulating channel is higher than a set value and the pressure regulating blocking unit is pushed away to a set distance, the engaging unit is pushed to engage with the engaging groove of the pressure regulating blocking unit such that the pressure regulating blocking unit is unmovable to avoid blocking the first pressure regulating channel.

An automatic oil return structure has a main body assembly mounted between an oil storage container and a housing, and having a pressure regulating blocking unit, a pressure regulating elastic unit, an engaging unit, and an engaging elastic unit. The pressure regulating elastic unit pushes the pressure regulating blocking unit to block a first pressure regulating channel. An engaging groove is formed radially inward on the pressure regulating blocking unit. The engaging elastic unit pushes the engaging unit toward the pressure regulating blocking unit. When a pressure in the first pressure regulating channel is higher than a set value and the pressure regulating blocking unit is pushed away to a set distance, the engaging unit is pushed to engage with the engaging groove of the pressure regulating blocking unit such that the pressure regulating blocking unit is unmovable to avoid blocking the first pressure regulating channel.

An in-port sequencing valve configured to be utilized with a clamping device of a workpiece clamping system having a fixture plate, a number of fixture datums, and a number of clamping devices. The in-port sequencing valve includes a housing, a pre-load adjuster, a valve spring, and a valve piston. The pre-load adjuster is configured to be set to a selected valve activation setting. The valve spring is compressed an amount corresponding to the valve activation setting. The valve piston is configured to be shifted from a closed position to an open position when a force due to hydraulic fluid pressure overcomes a threshold spring force of the valve spring corresponding to the valve activation setting. The in-port sequencing valve can be set to a selected valve activation setting so that the clamping devices clamp the workpiece in a selected order according to the valve activation setting.

A system for controlling a felling saw in a forestry machine, the felling saw being driven by a hydraulic pump and saw motor circuit. The system includes an instrument for measuring a rotational speed of the felling saw and generating a signal indicative of the rotational speed, a calculator for calculating a power consumption of the hydraulic pump and saw motor circuit adjusted as a function of the signal indicative of said rotational speed, and a controller for adjusting hydraulic settings of the hydraulic pump or/and saw motor circuit based on the calculated power consumption. A method for controlling the felling saw is also disclosed.

A gas-powered drive system has a drive which includes a first chamber and a second chamber which are separated from one another by a piston. One of the chambers is connected to a gas source to drive the work element and the other chamber is connected via an exhaust air throttle to a gas sink by means of a reversing valve to movement of the piston. A control valve is assigned to the driving chamber through which the driving chamber can be filled with gas from the gas source. The opening cross-section of the control valve is set as a function of a control pressure.