A hydraulic system of a construction machine includes: control valves interposed between a main pump and hydraulic actuators; and first solenoid proportional valves connected to pilot ports of the control valves. The hydraulic system further includes: an unloading valve including a pilot port; and a second solenoid proportional valve connected to the pilot port of the unloading valve by a secondary pressure line and connected to an auxiliary pump by a primary pressure line. A switching valve including a pilot port connected to the secondary pressure line by a pilot line is interposed between the auxiliary pump and the first solenoid proportional valves.

A power control system for a forestry machine may include an engine control module and a pump control module. The engine control module may be configured to control an engine speed of an engine of the forestry machine. The engine speed may be limited in accordance with a maximum engine speed. The pump control module may determine whether a first function of the forestry machine is activated, determine whether a sensed pressure of a pump associated with the first function is greater than or equal to a high pressure setpoint, and output a control signal indicating a request for a power increase in response to determining that the first function is activated and the sensed pressure is greater than or equal to the high pressure setpoint. The engine control module may increase the maximum engine speed in response to the request for the power increase from the pump control module.

A hydraulic system according to one aspect of the present disclosure includes: control valves interposed between a main pump and hydraulic actuators; and solenoid proportional valves connected to pilot ports of the control valves. Among the solenoid proportional valves, a first solenoid proportional valve and a second solenoid proportional valve are connected to a pair of pilot ports of a particular control valve, respectively. The first solenoid proportional valve and the second solenoid proportional valve are directly connected to an auxiliary pump. The solenoid proportional valves except the first solenoid proportional valve and the second solenoid proportional valve are connected to the auxiliary pump via a switching valve. The switching valve includes a pilot port that is connected, by a switching pilot line, to a first pilot line between the first solenoid proportional valve and the particular control valve.

A hydraulic system of a construction machine includes: control valves interposed between a main pump and hydraulic actuators; and first solenoid proportional valves connected to pilot ports of the control valves. The hydraulic system further includes: an unloading valve including a pilot port; and a second solenoid proportional valve connected to the pilot port of the unloading valve by a secondary pressure line and connected to an auxiliary pump by a primary pressure line. A switching valve including a pilot port connected to the secondary pressure line by a pilot line is interposed between the auxiliary pump and the first solenoid proportional valves.

An operation control device for a working vehicle comprises a hydraulic actuator to drive the hydraulic working device, operating oil supply source for driving the hydraulic actuator, an operating oil supply control device that performs control to supply operating oil to the hydraulic actuator, an operating device to be operated to make the hydraulic actuator work and a working gain setting device that sets a gain of working speed of the hydraulic actuator corresponding to the operation of the operating device. The operating oil supply control device controls operating oil supply from the operating oil supply source to the hydraulic actuator based on the operation output signal from the operating device and the working speed gain set by the working gain setting device.

The present invention provides a controller for a hydraulic apparatus. The controller is configured to determine (410) that a mode change criteria has been met for the hydraulic apparatus. In response to the determination, the controller is configured to control (420) a valve arrangement to change a first actuator chamber of a hydraulic actuator between being fluidly connected to a hydraulic machine and fluidly isolated from a second chamber of the hydraulic actuator, and being fluidly connected to both the second actuator chamber and the hydraulic machine. Further in response to the determination, the controller is configured to control (430) the hydraulic machine to change a flow rate of hydraulic fluid flowing through the hydraulic machine to regulate a movement of the hydraulic actuator during the control of the valve arrangement.

Provided is a hydraulic machine. A pump pressurizes fluid using power provided by a power source. An actuator works using the pressurized fluid from the pump. A recovery part recovers energy from fluid discharged from the actuator. A first operator input device receives a desired input from an operator to select an eco-mode or a boost mode. The recovery part includes an accumulator storing hydraulic energy by receiving the fluid discharged from the actuator and an assist unit assisting the power source using the hydraulic energy stored in the accumulator. The controller controls the pump such that output power of the pump does not exceed Plmax when the eco-mode is selected or the assist unit does not assist the power source and that the output power does not exceed P2max when the boost mode is selected and the assist unit assists the power source, where Plmax < P2max.

To perform a work with the same operability under a dead weight of a front work equipment in any of a float work and a normal work, when a bucket descends in the air, and after contacting the ground, to perform a work with the operability being maintained as it is when performing the float work, and to perform a work while pressurized hydraulic fluid is supplied from a hydraulic pump when performing the normal work. A lower-ing control during a float working mode is performed in a valve passage state in a first region at which the lowering control is performed under the dead weight of the from work equip-ment without being supplied with hydraulic fluid from the hydraulic pump, regardless of whether or not the bucket is in contact with the ground, and the lowering control during a normal working mode is performed in a valve passage state at the first region in a non-ground-contacting state and at a second region in which the hydraulic fluid can be supplied from the hydraulic pump n a ground-contacting state.

A work machine includes: a hydraulic actuator that is driven by a hydraulic fluid from a hydraulic pump; an open-center directional control valve that is arranged on a center bypass line, and controls a flow of the hydraulic fluid to be supplied to the hydraulic actuator; a CB cut valve arranged between a directional control valve and a hydraulic working fluid tank on the center bypass line; and a machine controller that controls an opening of the CB cut valve. The machine controller restricts the opening of the CB cut valve when operation on the hydraulic actuator is in a fine operation state in which the operation on the hydraulic actuator is within a predetermined range representing a region of fine operation, and the fine operation state is continued longer than a predetermined period, and fully opens the CB cut valve otherwise.

A method for preventing prime mover stall for a work machine including a hydraulic system having a plurality of control valves served by a hydraulic pump. The method can include determining an actual required flow rate value for the plurality control valves and a total maximum flow rate to the plurality of control valves that will enable the prime mover to operate without stalling. The method can also include operating the plurality of control valves such that the combined total flow of the plurality control valves is at or below the total maximum flow rate such that the pump operates at a condition below which prime mover stall will occur. The method can also include setting a flow sharing allocated specific criteria in which the flow reduction takes place during a flow saturation condition for each of the plurality of control valves such that the total sum of the flow rates (calculated based on the criteria) is equal to or less than the total maximum flow rate.