Hydraulic system for leveling apparatus in excavator and forestry equipment

A hydraulic system for a leveling apparatus in excavator and forestry equipment, including an engine, a hydraulic tank, a main hydraulic pump and a pilot pump respectively connected to the engine, a main control valve installed between the main hydraulic pump and the hydraulic pump to control a start, a stop, and a direction change of a working device in accordance with fluid pressure being supplied through a main flow path during a spool shifting, and a tilt plate tiltably installed between an upper frame and a lower frame and provided with a first tilt shaft and a second tilt shaft apart from each other at a specified angle, the hydraulic system comprising:

• a pair of first and second actuators, installed between the upper frame and the lower frame, for rocking a lower part of the upper frame in a direction of the first tilt shaft during their extension and contraction, and another pair of third and fourth actuators for rocking the lower part of the upper frame in a direction of the second tilt shaft;
• first leveling control valves, installed between the main hydraulic pump and the first and second actuators, for simultaneously controlling extension and contraction of the first and second actuators in accordance with fluid pressure being supplied through a leveler flow path branching from the main flow path during the spool shifting;
• second leveling control valves, installed between the main hydraulic pump and the third and fourth actuators, for simultaneously controlling extension and contraction of the third and fourth actuators in accordance with the fluid pressure being supplied through the leveler flow path branching from the main flow path during the spool shifting;
• a reducing valve, installed between the leveler flow path and the hydraulic tank, for receiving the fluid pressure from the leveler flow path and discharging a reducing pilot signal pressure;
• flow control valves, connected between the reducing valve and the first and second leveling control valves, for discharging the pilot signal pressure for the spool shifting of the first leveling control valve and the second leveling control valve when a control signal is applied from a preset leveling controller;
• shuttle valves, connected to secondary pilot pressure ports of the flow control valves, for discharging the pilot signal pressure to a selector pilot flow path during the spool shifting of either of the first leveling control valve and the second leveling control valve;
• a shutoff valve, installed at a lowermost downstream of a center bypass flow path connected to the main hydraulic pump, for shutting off the fluid pressure returning to the hydraulic tank through the center bypass flow path in accordance with the pilot signal pressure;
• and
• a selector valve, installed between the shutoff valve and the pilot pump, for opening the pilot flow path connected from the pilot pump to the shutoff valve in accordance with the pilot signal pressure being supplied from the shuttle valves.