Hydraulic system for working machine and hydraulic control method for working machine

A hydraulic control method for a working machine, to control a hydraulic system including:

• a first hydraulic pump to output an operation fluid, the first hydraulic pump being constituted of a constant displacement pump;
• a second hydraulic pump to output the operation fluid, the second hydraulic pump being constituted of a constant displacement pump;
• a hydraulic actuator;
• a first fluid tube coupling the first hydraulic pump to the hydraulic actuator;
• a first control valve including a spool having:
• a first supply position allowing the operation fluid to be supplied to the hydraulic actuator, the operation fluid being outputted from the first hydraulic pump to the first fluid tube;
• and
• a first stop position preventing the operation fluid from being supplied to the hydraulic actuator, the operation fluid being outputted to the first fluid tube, the spool being moved between the first supply position and the first stop position and thereby to change a flow rate of the operation fluid to be supplied to the first fluid tube;
• a second fluid tube coupling the second hydraulic pump to the first fluid tube;
• a second control valve having:
• a second supply position allowing the operation fluid to be supplied to the first fluid tube, the operation fluid being outputted from the second hydraulic pump to the second fluid tube;
• and
• a second stop position preventing the operation fluid from being supplied to the first fluid tube actuator, the operation fluid being outputted to the second fluid tube, the second control valve being switched between the second supply position and the second stop position;
• and
• a control device,
• the hydraulic control method comprising:
• judging whether the second control valve is in the second supply position;
• judging whether a request to move the spool from the first supply position to the first stop position has been issued;
• and
• reducing a first movement speed to be lower than a second movement speed when control device determines that the second control valve is in the second supply position and that the request has been issued, the first movement speed being a speed at which the spool moves from the first supply position to the first stop position under a state where the second control valve is in the second supply position, the second movement speed being a speed at which the spool moves from the first supply position to the first stop position under a state where the second control valve is in the second stop position.

The hydraulic system according to claim

• wherein the first control valve includes:
• an input port to which the operation fluid outputted from the first hydraulic pump is supplied, the input port being connected to the first fluid tube;
• and
• an output port to supply the operation fluid to the hydraulic actuator, the output port being connected to the first fluid tube;
• and
• a tank port to output the operation fluid,
• wherein the spool close or open at least one of the input port, the output port and the tank port when moving from the first supply position to the first stop position,
• and wherein when a state closing the input port and the tank port is defined as a PT closing, a state connecting the input port to the tank port is defined as a PT opening, a state connecting the output port to the tank port is defined as a CT opening, and a state closing the output port and the tank port is defined as a CT closing, the control device slows a first speed transition of the spool moving from a position for the PT opening and the CT opening to another position for the PT opening and the CT closing in comparison with a second speed transition of the spool moving from a position for the PT closing to another position for the PT opening and the CT opening.