| 摘要 |
PROBLEM TO BE SOLVED: To prevent a body from being lowered when the body is locked in an erected attitude by a safety pin. SOLUTION: The safety pin 8 is inserted into the vehicle body 1 and the body 3 of a dump truck to lock the body 3 in an erected attitude. A solenoid proportional pressure control valve 30 and a solenoid selector valve 40 are controlled by a controller 48 based on the operation position signal of an electric lever 50 to switch a hoist valve 13 to a hold position, a lift position, a float position, or a descent position. A pressure switch 60 detecting that the lowering pressure of a hoist cylinder 5 extender or shrunk by the output pressure oil of the hoist valve 13 is a first set pressure and a potentiometer 9 detecting the position of the body 3 are provided. When the body 3 is not lowered by the set decent quantity after the pressure switch 60 is turned on, the controller 48 outputs a signal to set the hoist valve 13 to the float position so that the body 3 is not lowered while the safety pin 8 is inserted.
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