WORKING MACHINE, AND QUICK LOAD-DROPPING METHOD

摘要

A tank (16) and a main hydraulic pump (17) are connected through conduits (21, 22) to a head-side working chamber (13) and a rod-side working chamber (14) of a hydraulic actuator (12), respectively. A direction control valve (18) and a quick drop valve (36) are connected to the conduits (21, 22). A hydraulic circuit is provided with an electromagnetic change-over valve (42) for switching the quick drop valve (36) from a non-quick drop position (37) to a quick drop position (38). In case the operation rate of an operation lever (33) exceeds a decision reference rate when the direction control valve (18) is switched from a neutral position (23) to a downward action position (25), an excitation signal is outputted from a control device (32) to the electromagnetic change-over valve (42) so as to perform a quick drop of a blade (11), so that the quick drop valve (36) is switched from the non-quick drop position (37) to the quick drop position (38).