A hydraulic work system can include a continuously variable displacement hydraulic pump that is powered by an engine and is in communication with a hydraulic actuator. A run-time displacement of the hydraulic pump for movement of the hydraulic actuator can be controlled based on a speed of the engine.

In one aspect, a system for controlling the supply of hydraulic fluid to an implement of a work vehicle may generally include a pump, a control valve coupled to the pump and first and second fluid lines provided in flow communication with output ports of the control valve. The system may also include a pressure control valve provided in flow communication with the second fluid line that is configured to regulate a fluid pressure of the hydraulic fluid being supplied to a hydraulic cylinder of the implement. Additionally, the system may include a bypass fluid line configured to provide a flow path for hydraulic fluid between the pump and the second fluid line that is independent of the control valve and a load sensing line configured to provide an indication of the fluid pressure of the hydraulic fluid being supplied to the hydraulic cylinder.

A load-controlled hydraulic supply for an attachment attached to an agricultural tractor includes a hydraulic high-pressure source providing a volume flow in a supply line, a pressure-compensated control valve including an actuation device for adjusting the volume flow in the supply line, a return line leading to a hydraulic reservoir, and a load-indicating line. The volume flow is adjusted based on pressure feedback prevailing at the load-indicating line.

A hydraulic system for a construction machine having a pressure compensation valve is disclosed, which improves operability when a combined operation of a swing device and an attachment is performed. The hydraulic system includes a hydraulic pump, attachment and swing operation devices, an attachment actuator and a swing motor connected to the hydraulic pump, a first control valve controlling hydraulic fluid being supplied to the actuator, a second control valve controlling hydraulic fluid being supplied to the swing motor, a check valve installed on a flow path for detecting load pressures of the actuator to take a maximum pressure of the load pressures, a first pressure compensation valve having an opening amount that is controlled by a difference between the maximum load sensing pressure and the pressure of a discharge flow path of the first control valve, a second pressure compensation valve having an opening amount that is controlled by a difference between the maximum load sensing pressure and the pressure of the discharge flow path of the second control valve, a maximum load pressure sensor detecting the pressure of a maximum load sensing pressure line, and a control unit controlling a discharge flow rate of the hydraulic pump, wherein the system is configured so that the swing load pressure is not connected to the first pressure compensation valve on the attachment side when a combined operation of the swing device and the attachment is performed.

A control method for controlling retraction of a boom is applied to a hydraulic system which combines retraction of the boom by self-weight with retraction of the boom by pressure. The control method includes: when the boom is retracted, controlling the self-weight retraction proportional valve to be at a maximum opening; obtaining an actual speed at which the boom is retracted; controlling a rotation speed of the pressure retraction motor to rise or an opening degree of the pressure retraction proportional valve to increase when the actual speed is less than a preset speed; and controlling the rotation speed of the pressure retraction motor to reduce or the opening degree of the pressure retraction proportional valve to decrease when the actual speed is greater than the preset speed.

Open centre hydraulic distributor, comprising: a free circulation line connecting a supply line from a negative control pump to a discharge; a delivery line connecting the supply line to users; at least one directional valve that intercepts the free circulation line and the delivery line, so that it narrows a transit area of the free circulation line and opens a transit area of the delivery line, and vice versa; a slide valve arranged on the free circulation line downstream of the directional valve; a valve device that is activated when a threshold value of a pressure delta between upstream and downstream of the directional valve is reached, and maintains this pressure delta equal to the threshold value; a negative control line to pick up a pressure signal from the free circulation line downstream of the directional valve and upstream of the slide valve.

A pressure-compensation controlled hydraulic pump, comprising an electric proportional pressure compensator, a hydraulic pump, a hydraulic control reversing valve and a servo cylinder; the electric proportional pressure compensator can be electrically connected to a controller, a first hydraulic control port of the hydraulic control reversing valve is connected to an internal oil drain path, and is connected to an internal output oil path by means of a hydraulic control oil inlet path provided with a first throttle valve, a second hydraulic control port is connected to the internal output oil path, and the pressure difference between an opening pressure of the electric proportional pressure compensator and an oil outlet pressure of the hydraulic pump can drive the hydraulic control reversing valve to perform reversing, and selectively enable a piston chamber of the servo cylinder to be in communication with the internal output oil path or the internal oil drain path.

A floating control system for a fixed displacement pump system is disclosed, which relates to the technical field of floating mechanisms and includes: a fixed displacement pump, floating control valves, a floating mechanism, boom function valves, an actuator and a control device, where the fixed displacement pump, the floating control valves and the floating mechanism are connected in sequence, the fixed displacement pump, the boom function valves and the actuator are connected in sequence, the floating control valves include a pressure reducing valve and a floating switching valve, and the boom function valves include a fixed differential overflow valve and a proportional directional valve; and the fixed differential overflow valve and the proportional directional valve are connected in parallel between the fixed displacement pump and an oil return tank, the floating switching valve and the fixed differential overflow valve are connected through a feedback oil path.