PURPOSE: To obtain uniform running forces for left and right-handed trucks by a method in which when various kinds of actuators are operated during the running period, pressure oil from an oil-pressure pump is uniformly supplied to left and right running motors.
CONSTITUTION: When running direction-switching valves 23 and 27 are solely operated, discharge oil from an oil-pressure pump 20 is preferentially supplied to the right running-switching valve 23, and the discharge oil from an oil-pressure pump 24 is supplied through a check valve 41b from a center bypass circuit to the left running-switching valve 27. When the slewing direction-switching valve 26 is operated during the period when running is made by operating the running direction-switching valves 23 and 27, the discharge oil of the oil-pressure pump 24 is preferentially used in the slewing operation through the slewing direction- switching valve 26 because of the presence of a throttle 42 in the pipeline 40, and only a part of the pressure oil is supplied to the left running direction- switching valve 27. Also, when boom direction-switching valves 22 and 44 are operated during the running period when the running direction-switching valves 23 and 27 are operated, the pressure oil of the oil-pressure pump 20 is preferentially supplied to the boom direction-switching valve 44.
OKABE SHINYA
TSURUMI GENICHI
KANEKO ZENJI
