Downhole percussion drilling apparatus

Abstract

A downhole percussion drilling apparatus includes a housing and a piston rotatably supported within an interior bore of the housing. A first engagement surface serves as a cam surface. A second engagement surface serves as a follower surface. The cam surface has a plurality of inclined planes each of which terminates in a drop off. With each rotation of the piston, the follower surface rises up each of the inclined planes and then falls down each of the drop offs of the cam surface thereby imparting a series of percussive hammering impacts to the piston.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
     
         1 . A downhole percussion drilling apparatus, comprising: 
 an elongate tubular housing adapted for insertion down a borehole, the housing having an outer surface and an inner surface which defines an interior bore;    a piston rotatably supported within the interior bore of the housing, the piston having an exterior surface, a first end and a second end, the first end being adapted for connection to a downhole motor assembly that imparts a rotary motion to the piston and the second end being adapted for connection to a drill bit assembly;    a first engagement surface non-rotatably coupled to and projecting from the inner surface of the housing into the interior bore;    a second engagement surface non-rotatably coupled to and projecting from the exterior surface of the piston into the interior bore;    one of the first engagement surface and the second engagement surface serving as a cam surface and the other of the first engagement surface and the second engagement surface serving as a follower surface, the cam surface having a plurality of inclined planes each terminating in a drop off such that with each rotation of the piston the follower surface rises up each of the inclined planes and then falls down each of the drop offs of the cam surface thereby imparting a series of percussive hammering impacts to the piston; and    springs within the interior bore between the inner surface of the housing and the outer surface of the piston to maintain the first engagement surface and the second engagement surface engaged during rotation of the piston and allow limited axial travel of the piston relative to the housing during the percussive hammering impacts.    
     
     
         2 . The downhole percussion drilling apparatus as defined in  claim 1 , wherein the biasing force exerted by the springs to maintain the first engagement surface and the second engagement surface engaged, decreases as bit weight increases, thereby allowing the force behind the percussive hammering impacts to be adjusted by altering the bit weight.  
     
     
         3 . The downhole percussion drilling apparatus as defined in  claim 2 , wherein the first engagement surface and the second engagement surface become disengaged the bit weight exceeds the biasing force exerted by the springs to maintain the first engagement surface and the second engagement surface in engagement.  
     
     
         4 . The downhole percussion drilling apparatus as defined in  claim 1 , wherein a first sleeve is positioned in the interior bore which is non-rotatably coupled to the inner surface of the housing, the first engagement surface being carried by the first sleeve; and 
 a second sleeve is positioned in the interior bore which is non-rotatably coupled to the exterior surface of the piston, the second engagement surface being carried by the second sleeve.    
     
     
         5 . The downhole percussion drilling apparatus as defined in  claim 1 , wherein an off bottom bearing is provided and an hydraulic damper is provided to shield the off bottom bearing from the percussive hammering impacts.