US Patent 9097086 Well tractor with active traction control

A downhole tool that includes a tractor for assisting movement of the tool through deviated portions of a wellbore. The tractor includes a working fluid that damps vibrations in the tractor by adjusting the viscosity in the fluid. In an example, the working fluid is a magnetorheological fluid that has a viscosity that changes in response to applied electrical energy. The working fluid, which may be used for powering actuators on the tractor, may contain a suspension of magnetic particles.