Patent ID: 7578360

Claim:
A dynamic damper installed in a drill string above a drill bit, the damper comprising: an inner cylindrical string section having an upper end connected to an upper portion of the drill string; an outer cylindrical string section supported concentrically on the inner string section and having a lower end connected to a lower portion of the drill string; wherein the inner and outer string sections are engaged via a spiral trapezoidal threaded section oriented so that relative rotation between the string sections will cause relative axial movement between the string sections; a spring disposed between the inner and outer string sections, the spring being pre-tensioned so that axial movement between the outer and inner string sections occurs only when combined axial force and torque on the string sections exceed a predetermined value; a cylindrical jacket arranged externally on the outer string section and connected to the inner string section such that the jacket protects the inner and outer string sections and constitutes a limitation for axial movement between the inner and outer string sections; two oil-filled volumes located between the inner and outer string sections and being connected such that relative axial movement of the inner and outer sections forces displacement of oil from one of the volumes to the other volume, thus dampening movement between the string sections; wherein torque caused by locking of the drill bit attached to the lower portion of the drill string effects relative rotation between the inner and outer string sections when said torque exceeds a selected spring tension; wherein said relative motion between the inner and outer string sections is an axial movement that lifts and loosens the drill bit from its locked position; wherein said lifting and loosening of the drill bit reduces said torque such that the spring tension pushes the drill bit in a direction away from the damper.