Direct drill bit drive

Claim 1

A direct-drive drill string comprising: an upper tubular drive section provided with a drive motor having a shaft and adapted to be traversed and driven by a flushing liquid; a gear section below said drive section and provided with gearing driven by said shaft and formed with an output member; a bearing section below said gear section, a plurality of radial bearings rotatably journaling said inner tube, all of said sections having a non-rotating outer tube, a rotating inner tube in at least said bearing section, and radial bearings disposed between said inner and said outer tubes, at least one of said radial bearings having inner and outer races of which one is axially elongated to accommodate axial movement of said inner tube relative to said outer tube; a drill bit connected to said inner tube below said bearing section and rotatably entrained by said inner tube; means defining an annular space between said inner and outer tubes intermediate said drive section and said gear section; means for introducing oil into said annular space whereby said annular space serves as an oil reservoir; at least one axial bearing in contact with oil from said reservoir for receiving axial force generated by said motor upon the operation thereof by said liquid; means for angularly coupling the inner tube connected to said bit with said output member of said gearing so as to permit axial displacement of the inner tube carrying said bit within said outer tube; spring means braced between said inner tube carrying said bit and said outer tube for yieldably resisting axial displacement of said inner tube carrying said bit; and further axial bearings cooperating with said spring means and the inner tube carrying said bit for enabling rotation of said inner tube carrying said bit while spring force is applied thereto, said flushing liquid passing through said inner tube to said bit.