Method for controlling hydraulic system of construction machinery
View Patent ↗The method for controlling the hydraulic system of construction machinery according to the present disclosure includes an engine speed prediction step, in which a variable rated engine speed, which varies within a range larger than a fixed rated engine speed and smaller than a high idle engine speed for the fixed rated engine speed and a virtual engine speed, which is to be input later, are predicted to output a virtual engine speed value predicted before an actual engine speed is input. Accordingly, when an operation load is applied, pump torque may initially have a margin, and even though an engine speed is decreased due to the operation load, it is possible to prevent an engine speed decrease phenomenon in which the engine speed becomes remarkably smaller than the rated engine speed.
1. A method for controlling a hydraulic system of construction machinery, the method comprising:
a maximum value setting step, in which when a required torque value for a pump is generated, the required torque value is set to a maximum value;
a power conversion step, in which a power value matched to a current load mode and the maximum value is output;
an inclination limit step, in which a conversion speed of the power value per hour is limited;
an engine speed prediction step, in which a virtual engine speed value is predicted based on a previously input engine speed;
a PID control step, in which proportional integral derivative control is performed so that the actual engine speed converges toward the virtual engine speed; and
a final power output step, in which the pump is controlled with a final power value obtained by adding a first power value determined by the current load mode, a second power value determined by the required torque value for the pump, and a third power value deduced by the PID control.
2. The method of claim 1 , wherein a rated engine speed according to the current load mode is a variable rated engine speed varied within range larger than a fixed rated engine speed and smaller than a high idle engine speed for the fixed rated engine speed.
3. The method of claim 2 , wherein an initial value of the variable rated engine speed is controlled to be larger than the fixed rated engine speed by 70 rpm to 95 rpm.
4. The method of claim 1 , further comprising:
a saturation prevention step, in which a value of a control width of the actual engine speed during the process of converging the actual engine speed to the virtual engine speed in the PID control step is limited not to deviate from a predetermined upper limit and lower limit.
5. The method of claim 1 , wherein in the engine speed prediction step, the virtual engine speed to be input later is predicted by receiving the actual engine speed from the engine control device by using a digital lead filter.
6. The method of claim 1 , further comprising:
a load mode selection step, in which an operator selects any one mode among a plurality of load modes divided according to a size of a load; and
a load mode confirmation step, in which a load mode ratio, an inclination weighted value, and initial power are set according to the load mode selected in the load mode selection step.
7. The method of claim 1 , wherein in the maximum value setting step, the required torque value for the pump is generated according to an operation displacement of a joystick or a pedal.
8. The method of claim 1 , wherein in the power conversion step, a use ratio of full power transmitted from the engine is set according to a load map selected by the current load mode.
9. The method of claim 1 , wherein in the engine speed prediction step, the virtual engine speed value is predicted by using a digital lead filter.