Hydraulic control system for construction machinery

Abstract

A hydraulic control system for a construction machine is disclosed, which can operate an arm cylinder and a bucket cylinder by supplying hydraulic fluid from respective hydraulic pumps to the arm cylinder and the bucket cylinder during a combined operation, such as an excavating work, in which an arm joystick and a bucket joystick are simultaneously operated. The hydraulic control system includes a first arm control valve installed in a flow path between the first hydraulic pump and the arm cylinder and shifted to control a start, stop, and direction change of the arm cylinder in response to an operation of the arm joystick, a second arm control valve installed in a flow path between the second hydraulic pump and the arm cylinder and shifted to make discharged hydraulic fluid of the second hydraulic pump join hydraulic fluid of the arm cylinder to be supplied if a control signal according to the operation of the arm joystick exceeds a set value, a bucket control valve installed in a path between the second hydraulic pump and the bucket cylinder and shifted to control a start, stop, and direction change of the bucket cylinder in response to the operation of the bucket joystick, and a confluence cutoff proportional valve installed in a path between the second hydraulic pump and the second arm control valve.

1 . A hydraulic control system for a construction machine, comprising:
 first and second variable displacement hydraulic pumps;   an arm cylinder connected to the first hydraulic pump;   a bucket cylinder connected to the second hydraulic pump;   an arm joystick and a bucket joystick configured to output control signals according to operation amounts thereof;   a first arm control valve installed in a flow path between the first hydraulic pump and the arm cylinder and shifted to control a start, stop, and direction change of the arm cylinder in response to an operation of the arm joystick;   a second arm control valve installed in a flow path between the second hydraulic pump and the arm cylinder and shifted to make discharged hydraulic fluid of the second hydraulic pump join hydraulic fluid of the arm cylinder to be supplied if the control signal according to the operation of the arm joystick exceeds a set value;   a bucket control valve installed in a path between the second hydraulic pump and the bucket cylinder and shifted to control a start, stop, and direction change of the bucket cylinder in response to the operation of the bucket joystick; and   a confluence cutoff proportional valve installed in a path between the second hydraulic pump and the second arm control valve and shifted to cut off confluence of the hydraulic fluid discharged from the second hydraulic pump with the discharged hydraulic fluid of the first hydraulic pump if discharge pressures of the first and second hydraulic pumps exceed a set value.   
     
     
         2 . A hydraulic control system including first and second variable displacement hydraulic pumps, an arm cylinder connected to the first hydraulic pump, a bucket cylinder connected to the second hydraulic pump, an arm joystick and a bucket joystick outputting control signals according to operation amounts thereof, a first arm control valve controlling hydraulic fluid supplied to the arm cylinder according to an operation of the arm joystick, a second arm control valve controlling the hydraulic fluid that is supplied from the second hydraulic pump to the arm cylinder if a control signal according to the operation of the arm joystick exceeds a set value, a bucket control valve controlling driving of the bucket cylinder according to an operation of the bucket joystick, and a confluence cutoff proportional valve making the hydraulic fluid of the second hydraulic pump join the hydraulic fluid of the first hydraulic pump if the arm cylinder is singly operated and cutting off a confluence function if the arm cylinder and the bucket cylinder are simultaneously operated, the hydraulic control system comprising:
 a first step of reading an arm-in control signal according to an operation amount of the arm joystick, a bucket-in control signal according to an operation amount of the bucket joystick, and discharge pressures of the first and second hydraulic pumps;   a second step of determining whether the arm-in control signal exceeds one set value and whether the bucket-in control signal exceeds the one set value;   a third step of determining whether the discharge pressure of the first hydraulic pump exceeds another set value and whether the discharge pressure of the second hydraulic pump exceeds the other set value; and   a fourth step of releasing the confluence function by applying control signals that are in proportion to the arm-in control signal and the bucket-in control signal to the confluence cutoff proportional valve if the arm-in control signal and the bucket-in control signal exceed the one set value and the discharge pressures of the first and second hydraulic pumps exceed the other set value.   
     
     
         3 . The hydraulic control system according to  claim 1 , wherein the confluence cutoff proportional valve operates in a first state of cutting off a flow path when the arm joystick and the bucket joystick are simultaneously operated, and in a second state of connecting the flow path when the arm joystick is singly operated. 
     
     
         4 . The hydraulic control system according to  claim 2 , wherein the confluence cutoff proportional valve operates in a first section where movement amounts are controlled to be gradually increased in proportion to the operation amounts of the arm joystick and the bucket joystick to release the confluence function, in a second section where the confluence cutoff state is maintained according to the increase of the operation amounts of the arm joystick and the bucket joystick, and in a third section where movement amounts are controlled to be gradually decreased in reverse proportion to the operation amounts of the arm joystick and the bucket joystick to be shifted to the confluence function. 
     
     
         5 . The hydraulic control system according to  claim 1 , wherein the confluence cutoff proportional valve comprises a solenoid valve that is shifted to open/close the flow path in response to an input of an electric signal. 
     
     
         6 . The hydraulic control system according to  claim 1 , wherein the confluence cutoff proportional valve comprises an electro proportional control valve that is shifted to open/close the flow path according to an input of an electric signal.