| 摘要 |
A compressor piston divides a first compartment into two compression chambers, while a hammer piston divides a second compartment into two drive chambers, each of the compression chambers being connected to a respective one of the drive chambers to form a closed fluid system wherein reciprocation of the compressor piston causes cyclic compression and expansion of the fluid in the compression chambers and thus in the drive chambers, to effect a cyclic impacting of the hammer piston with a bit adapter connected to the drill bit. A mud motor rotates a shaft to drive an oscillator which reciprocates the compressor piston. The oscillator can comprise roller elements in the compressor piston in engagement with canted grooves in the shaft. While drilling mud drives the motor and then passes downwardly to flush the drill bit and the borehole, the drilling mud is isolated from the closed fluid system. The bit adapter slides axially, so that when the drill bit is not in contact with a borehole bottom, the bit adapter and the hammer piston move downwardly to a position where the two drive chambers are in direct communication such that the reciprocation of the compressor piston does not actuate the hammer piston. Each of the pistons is an annular piston having a bleed passageway between its chambers, permitting the chambers to equalize when the pistons are stationary. The superatmospheric pressure is such that the hammer piston reciprocates at a frequency within +/-20% of natural resonant frequency. |
