HYDRAULIC DRIVE DEVICE FOR VERTICAL PIVOTING MOVEMENT OF LOAD CARRYING PLATFORM

摘要

[PROBLEMS] To simplify switching control of a directional control valve and to simplify the structure of a directional control valve for controlling operation of a hoist cylinder. [MEANS FOR SOLVING PROBLEMS] In a hydraulic drive device for vertical pivoting movement of a load carrying platform, a first directional control valve (10) has only three switchover positions that are a neutral position (10A) relating to operation of stopping and holding a load carrying platform, a switching position (10B) relating to operation of lifting the load carrying platform, and a switchover position (10C) relating to operation of forced lowering of the load carrying platform. Further, in the device, also a second directional control valve (12) has only three switchover positions that are a neutral position (12A) relating to operation of stopping and holding a load carrying platform, a switching position (12B) relating to operation of lifting the load carrying platform, and a switchover position (12C) relating to operation of allowing the load carrying platform to fall by its own weight. The device has a first on-off valve (13), a second on-off valve (14), and a third on-off valve (15) that are proportional control solenoid valves for switching an appropriate one of the first directional control valve (10) and the second directional control valve (12).