Downhole drilling tool with freewheel device

摘要

A downhole tool comprises a drillstring and a drilling head. A freewheel is positioned between the drillstring and drilling head and used to transfer drive from the drillstring to the drilling head. The freewheel comprises a shaft 108 mounted for rotation within a housing 110. A cylinder 112 is mounted about the shaft between the shaft and the housing. The cylinder has a pair of drive faces located on radial planes of the cylinder and drive elements 116, 120 are located on the shaft and housing. In use, the cylinder moves between a locked position in which the drive faces engage the drive elements of the shaft and the housing and a release position in which the cylinder rotates freely between the drive elements. The cylinder may comprised a resilient, helical coil or spring, the ends of the coil engaging the drive elements of the shaft and housing. The coil may be mounted on ball bearings.