Positive displacement motor stators with diameter reliefs compensating for rotor tilt

A positive displacement motor (PDM) power section, comprising:

• a rotor and a stator, the rotor configured to be received within the stator, the rotor having a rotor length such that a first portion of the rotor length has a substantially uniform transverse cross-sectional profile;
• the stator having a longitudinal centerline;
• the stator further including an internal elastomer liner such that the elastomer liner provides the stator with a stator internal surface, wherein the stator internal surface has lobes formed therein, wherein the lobes define helical pathways in the stator internal surface, wherein the helical pathways define a contour length between a contour inlet end and a contour outlet end, wherein the contour length includes an outlet region starting at the contour outlet end and extending up to 25% of the contour length towards the contour inlet end;
• wherein transverse cross-sections of the elastomer liner taken orthogonal to the longitudinal centerline provide alternating lobes and valleys around a circumference of the stator such that 2× a distance between the longitudinal centerline and a zenith point of the lobes defines a minor diameter and 2× a distance between the longitudinal centerline and a nadir point of the valleys defines a major diameter;
• wherein the outlet region further includes a first relief length disposed thereon, wherein the first relief length extends between a first relief length inlet towards the contour inlet end and a first relief length outlet towards the contour outlet end;
• wherein the first relief length inlet has a first relief length inlet minor diameter and the first relief length outlet has a first relief length outlet minor diameter;
• wherein the first relief length outlet minor diameter is larger than the first relief length inlet minor diameter by more than 0.0002 inches per inch of first relief length;
• and
• wherein all of the first relief length opposes the first portion of the rotor length when the rotor is received within the stator.