Patent ID: 6269637
Filing Date: 2001-08-07
Classification: E02F

Abstract:
A hydraulic control circuit for a working machine comprising a hydraulic actuator operated to move a working implement, and a pilot-operated directional control valve for controlling supply of pressurized oil to said hydraulic actuator, said hydraulic control circuit including:a pressure control valve for controlling supply of pilot pressurized oil to said directional control valve in accordance with a command from a control unit;a pilot valve for delivering the pilot pressurized oil to said pressure control valve in accordance with manipulation of a control member;a pilot pump oil line capable of supplying the pilot pressurized oil to said pressure control valve from a pilot oil pressure source without passing said pilot valve; anda selector valve for supplying the pilot pressurized oil delivered from said pilot valve to said pressure control valve when said control member is manipulated, and supplying the pilot pressurized oil from said pilot pump oil line to said pressure control valve when said control member is not manipulated, said control unit including:determining means for determining whether said working implement has entered a preset interference prevention area based on input signals from attitude detecting means for detecting an attitude of said working implement; andinterference prevention control means for outputting a control command to said pressure control valve, causing the pilot pressurized oil to be supplied to said pilot-operated directional control valve in the direction to move said working implement away from the interference prevention area, when said determining means determines that said working implement has entered the preset interference prevention area.