Hydraulic control system in working machines

Abstract

Problem: In a hydraulic excavator equipped with a swivel parking brake, the number of components is reduced and the circuit is simplified while the swivel parking brake is released during the operation of the working actuator as well as during the swivel. Solution: A common electromagnetic proportional valve that outputs a pilot pressure to the straight travel valve is shared as a pilot pressure output electromagnetic valve that outputs a pilot pressure to the brake switch valve, and a pilot pressure (second set pressure) necessary for switching the brake switch valve is set to a lower pressure than the pilot pressure (first set pressure) necessary for switching the traveling straight-going valve.

1 . A hydraulic control system in a working machine, characterized in that, the working machine which includes a lower travel body having a left and right travel device, an upper swivel body freely supported by the lower travel body, and a working unit mounted on the upper swivel body, is provided with the hydraulic control system, wherein the hydraulic control system includes a left and a right travel motors that drive the left and right travel device of the lower travel body, a swivel motor for swiveling the upper swivel body, a plurality of hydraulic actuators including working hydraulic actuators for driving the front working unit, a first and second hydraulic pumps for hydraulic supply of these hydraulic actuators, a left and right travel manipulator, a swivel manipulator, and a working manipulator which are operated to drive the left and right travel motors, the swivel motor, and the working hydraulic actuators respectively, a pilot-actuated straight travel valve switching connections of supply oil passages between the first and second hydraulic pumps and various hydraulic actuators, a swivel parking brake for braking swivel of the upper swivel body, and a pilot-actuated brake switch valve for supplying pressure oil to the swivel parking brake and switching to a brake-release state from a brake state,
 wherein the straight travel valve is configured to, by supplying a pilot pressure greater than or equal to a first set pressure, switch from a neutral position at which the first and second hydraulic pumps supply discharge oil from one hydraulic pump to the left travel motor and supply discharge oil from the other hydraulic pump to the right travel motor, to an actuation position at which the discharge oil from the one hydraulic pump is supplied to the left and right travel motors, and the discharge oil from the other hydraulic pump is supplied to the swivel motor and the working hydraulic actuators;   wherein the brake switch valve is configured to switch from a neutral position at which the swivel parking brake is in a brake state to an actuation position at which the swivel parking brake is in a brake release state by supplying a pilot pressure of the second set pressure lower than the first set pressure; and   wherein the straight travel valve and the brake switch valve are configured to be supplied with a pilot pressure from a common electromagnetic proportional valve, and a controller is provided to control the common electromagnetic proportional valve,   wherein the controller controls the common electromagnetic proportional valve without operating either the left and right travel manipulators, the swivel manipulator or the working manipulator, and not to output the pilot pressure when the left and right travel manipulators are operated and neither the swivel manipulator nor the working manipulator is operated, and to output the pilot pressure greater than or equal to the first set pressure when the left and right travel manipulators are operated and at least one of the swivel manipulator and the working manipulator is operated, and to output the pilot pressure greater than or equal to the second set pressure but less than the first set pressure when the left and right travel manipulators are not operated and at least one of the swivel manipulator and the working manipulator is operated.