Downhole drilling tool

Abstract

A downhole drilling tool 136 comprises a drillstring 138, a drilling head 140, and a freewheel 144 for transferring drive from the drillstring to the drilling head. The freewheel 144 is positioned between the drillstring 138 and the drilling head 140.

1 . A downhole drilling tool comprising and a drilling head, wherein a freewheel for transferring drive from the drillstring to the drilling head is positioned between the drillstring and the drilling head, wherein the freewheel, comprises:
 a shaft mounted for rotation within a housing, a cylinder mounted about the shaft disposed between the shaft and the housing, the cylinder having radially disposed drive faces, a drive element provided on the shaft and a drive element provided on the housing, in use, the cylinder moving between a locked position in which the drive faces of the cylinder engage the drive elements of the shaft and housing respectively and a release position in which the cylinder rotates freely between the drive elements.   
   
   
       2 . A downhole drilling tool as claimed in  claim 1 , wherein the cylinder comprises:
 a resilient coil mounted about the shaft disposed between the shaft and the housing, in use, the resilient coil moving between a locked position in which first and second ends of the coil engage the drive elements of the shaft and housing respectively and a release position in which the coil rotates freely between the drive elements.   
   
   
       3 . A downhole drilling tool as claimed in  claim 2 , wherein the resilient coil comprises a helical coil. 
   
   
       4 . A downhole drilling tool as claimed in  claim 3 , wherein, in use, fluid flows through the helical coil. 
   
   
       5 . A downhole drilling tool as claimed in any one of  claims 2  to  4 , wherein the resilient coil is mounted on ball bearings, the ball bearings being received in tracks on the shaft and in tracks provided on the internal circumference of the resilient coil. 
   
   
       6 . A downhole drilling tool as claimed in  claim 1 , wherein a portion of the shaft is tapered. 
   
   
       7 . A downhole drilling tool as claimed in  claim 1 , wherein the housing corresponds to a part of the drillstring, and the shaft corresponds to a part of the drilling head. 
   
   
       8 . A downhole drilling tool comprising a drillstring and a drilling head, wherein a freewheel for transferring drive from the drillstring to the drilling head is positioned between the drillstring and the drilling head, the freewheel comprising:
 a first race;   a second race;   a locking ring interposed between the first race and the second race, and at least one locking element retained partly in a recess of the first race and partly in a recess of the locking ring, in use, the locking element moving between a locked position in which the locking ring is forced into engagement with the second race and a release position in which the locking ring is released from the second race.   
   
   
       9 . Downhole drilling tool as claimed in  claim 8 , wherein the first race and locking ring have a plurality of recesses, and the freewheel flier comprises a plurality of locking elements interposed between the first and second races. 
   
   
       10 . A downhole drilling tool as claimed in any one of  claims 8  to  9 , wherein the locking element is a ball bearing. 
   
   
       11 . A downhole drilling tool as claimed in any one of  claims 8  to  9 , wherein the locking element is a roller. 
   
   
       12 . A downhole drilling tool comprising a drillstring and a drilling head, wherein a freewheel for transferring drive from the drillstring to the drilling head is positioned between the drillstring and the drilling head, the freewheel, comprising:
 a first race;   a second race:   a guide ring interposed between the first race and the second race, and at least one locking element retained partly in a recess of the first race and partly in a recess of the guide ring, in use, the locking element moving between a locked position in which the locking element is forced into engagement with the second race and a release position in which the locking element is released from the second race.   
   
   
       13 . A downhole drilling tool as claimed in  claim 12 , wherein the first race and guide ring have a plurality of recesses, and the freewheel flintier comprises a plurality of locking elements interposed between the first and second races. 
   
   
       14 . A downhole drilling tool as claimed in any one of  claims 12  to  13 , wherein the locking element is a ball bearing. 
   
   
       15 . A downhole drilling tool as claimed in any one of  claims 12  to  13 , wherein the locking element is a roller. 
   
   
       16 . A downhole drilling tool comprising a drillstring and a drilling head, wherein a freewheel for transferring drive from the drillstring to the drilling head is positioned between the drillstring and the drilling head, wherein the freewheel comprises:
 a first race having a resilient latching member; and   a second race having at least one recess therein; the resilient latching member of the first race being adapted to engage the at least one recess of the second race for transferring drive from one of the races to the other.   
   
   
       17 . A downhole drilling tool as claimed in  claim 16 , wherein the resilient latching member is integral with the first race. 
   
   
       18 . A downhole drilling tool as claimed in  claim 17 , wherein the resilient latching member is formed by providing a slit which extends from an edge of the first race substantially circumferentially through the first race. 
   
   
       19 . A downhole drilling tool as claimed in  claim 16 , wherein a plurality of recesses are provided in the second race, 
   
   
       20 . A downhole drilling tool as claimed in  claim 19 , wherein the or each recess is asymmetric, and includes a substantially radial face for engaging the end of the resilient latching member. 
   
   
       21 . A downhole drilling tool as claimed in  claim 16 , wherein the first race is positioned within the second race and the resilient latching member is biased radially outwards towards the second race. 
   
   
       22 . A downhole drilling tool as claimed in  claim 16 , wherein the first race is positioned around the second race and the resilient latching member is biased radially inwards towards the second race.