HYDRAULIC DRIVE DEVICE FOR WORKING MOTOR VEHICLE

摘要

An operation check valve (15a) is provided in a counter balance valve (15) attached to a hydraulic cylinder (7) for a boom, a solenoid switch valve (20), a power source (41), and a limit switch (42) are additionally provided, and an output port of the solenoid switch valve (20) and a pilot port of the operation check valve (15a) are connected through a pilot pipe line (33). A direction control valve (11) is constructed as a four-position valve with a float position (11d). The limit switch (42) is usually in the OFF position. The limit switch is put to the ON position when the direction control valve (11) is switched to the float position (11d), and this excites the solenoid switch valve (20) and switches it from a position (20a) to a position (20b). In this way, a float mechanism is realized in a working motor vehicle of which hydraulic cylinder for a boom has a valve device provided with a fall prevention function, such as a fall prevention valve or a counter balance valve.