| 摘要 |
<p>PROBLEM TO BE SOLVED: To change upper-limit torque of a torque limiter only by changing a connection between a relief valve and a vent port.SOLUTION: There is provided a power transmission device 2 that transmits force for letting a tubing device 3 rotate a casing tube 4 to a kelly-bar 9 when an internal excavation device comprising the kelly-bar 9 and an excavation bucket excavates the inside of the casing tube 4 rotated and pushed in by the tubing device 3 to be inserted. Further, the power transmission device has a torque limiter main body part 20 which cuts off the power transmission between the casing tube 4 and kelly-bar 9 when a transmitted torque exceeds a preset upper-limit torque. Further, the torque limiter main body part 20 has a hydraulic motor 10, and the upper-limit torque is set by connecting an outlet port of the hydraulic motor 10 to an inlet port through a relief valve 121.</p> |
