Mud Motor Radial Bearing
A mud motor bearing assembly, comprising: a stationary housing having an inner wall surface defining an interior bore; a rotatable drive shaft extending through the interior bore of the stationary housing, the rotatable drive shaft having a tubular drive shaft with a uniform outer diameter terminating at an outlet section with an enlarged outer diameter, the rotatable drive shaft including an inner bore for passage of a drilling fluid; a bearing section bearing a radial load and an axial load, the bearing section including at least a pair of stationary bearing rings and at least a pair of rotating bearing rings in stacked arrangement, each of the stationary bearing rings having an inner periphery and an outer periphery, the outer periphery of each of the stationary bearing rings operatively engaged to the inner wall of the stationary housing, the inner periphery of each of the stationary bearing rings including a projection, each of the rotating bearing rings having an inner periphery and an outer periphery, the inner periphery of each of the rotating bearing rings operatively engaged to the tubular drive shaft, the outer periphery of each of the rotating bearing rings including a projection, the projections of the pair of stationary bearing rings forming a recess that accommodates the projection of one of the pair of rotating bearing rings in sliding engagement; wherein the stacked arrangement alternates between at least partially overlapping stationary bearing rings and rotating bearing rings.
Mud motor bearings
Mud motor bearings, or ball bearings have conventionally been used to react thrust, or axial, loads in down hole mud motors. When low rpm power sections are used in the application such bearings provide sufficient life and reliability. However, bearing component fatigue causes life to decrease linearly as speed increases. This fatigue makes ball bearings unsuitable for high rpm motors. Standard engineering practice dictates that ball bearings are specified according to L10 life, or the number of revolutions a group of identical bearings is expected to sustain before 10% fail. As revolutions are related to speed, bearings operating in a higher speed motor will fail before those operating in a low speed motor, e.g. one could roughly expect a 90% reduction in bearing life if speed was increased from 100 to 1000 rpm. In addition to life, friction and horsepower losses are often of interest in drilling. Ball bearings are referred to as frictionless bearings due to the rolling nature of the elements, however in practice frictional losses exist due to rolling resistance and sliding. An order of magnitude approximation of the coefficient of friction (cof) for an angular contact bearing operating in ideal non-abrasive lubricant conditions is 0.0032.1 In drilling mud, the cof can be assumed to be significantly higher.