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 a free wheel which in an engaged position transmits drive from a drillstring to a drilling head and in a disengaged position does not transmit drive, the freewheel comprising first and second races, a space being defined between the first and second races, the space acting as a conduit for transferring drilling fluid from the drillstring to the drilling head in both the engaged and disengaged positions. 
   
   
       2 . A downhole drilling tool as claimed in  claim 1 , wherein the freewheel comprises: a locking element interposed between said first and second races;
 one of said races having a wedge-shaped portion upon which the locking element moves between the disengaged position in which the first race is disengaged from the second race and the engaged position in which the locking element locks the first and second races together, and the other of said races having a depression formed in a surface thereof, the depression being shaped to receive at least a portion of the locking element when the locking element is in the engaged position.   
   
   
       3 . A downhole drilling tool as claimed in  claim 2 , wherein said other of said races has a plurality of depressions formed in the surface thereof. 
   
   
       4 . A downhole drilling tool as claimed in  claim 3 , wherein said one of said races has a plurality of wedge-shaped portions, and the freewheel further comprises a plurality of locking elements interposed between the first and second races. 
   
   
       5 . A downhole drilling tool as claimed in  claim 2 , wherein the locking element is a ball bearing. 
   
   
       6 . A downhole drilling tool as claimed in  claim 2 , wherein the wedge-shaped portion or portions are formed in an end face of the first race, and the depression or depressions are formed in an end face of the second race. 
   
   
       7 . A downhole drilling tool as claimed in  claim 6 , wherein the one or more depressions are grooves that extend in a generally circumferential direction relative to the axis of rotation of the driven member. 
   
   
       8 . A downhole drilling tool as claimed in  claim 6 , wherein the one or more wedge-shaped portions are curved in a generally circumferential direction relative to the axis of rotation of the driving member. 
   
   
       9 . A downhole drilling tool as claimed in  claim 2 , wherein the locking element is a roller. 
   
   
       10 . A downhole drilling tool as claimed in  claim 2 , wherein the depression is a hole. 
   
   
       11 . A downhole drilling tool as claimed in  claim 2 , wherein the depression is a recess. 
   
   
       12 . A downhole drilling tool as claimed in  claim 2 , wherein the depression is a groove that extends in a direction parallel to the axis of rotation of the driving and driven members. 
   
   
       13 . A downhole drilling tool as claimed in  claim 2 , wherein the wedge-shaped portion is formed on the first race, and the depression is formed in the surface of the second race. 
   
   
       14 . A downhole drilling tool as claimed in  claim 4 , wherein the number of depressions is greater than the number of locking elements. 
   
   
       15 . A downhole drilling tool as claimed in  claim 2 , wherein the driven member is able to rotate freely when the locking element is in the disengaged position, and the driving and driven members are engaged when the locking element is in the engaged position in which the locking element is jammed into the depression by the wedge-shaped portion. 
   
   
       16 . A downhole drilling tool as claimed in  claim 1 , 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 1 , wherein the freewheel, comprises:
 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.   
   
   
       18 . A downhole drilling tool as claimed in  claim 1 , wherein the freewheel, comprises
 a first race;   a second race;   a guide ring interposed between the first race and the second race, and at 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.   
   
   
       19 . A downhole drilling tool as claimed in  claim 1 , wherein the freewheel comprises
 a shaft mounted for rotation within a housing, a resilient coil mounted about the shaft disposed between the shaft and the housing, a drive element provided on the shaft and a drive element provided on 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.   
   
   
       20 . A downhole drilling tool as claimed in  claim 1 , wherein the freewheel, comprises
 a shaft mounted for rotation within a housing, a cylinder mounted about the ;Fr 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 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.