Hybrid PDM Stator Tapering to Compensate Rotor Tilt

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Solution Overview

Problem

Existing positive displacement motors (PDMs) suffer from rotor tilt, which causes stress concentrations, stator damage, and potential failure due to imbalanced fluid pressures and interference fits, particularly at the outlet end, leading to torque loss and uncontrolled rotor motion.

Innovation Solution

Implementing a tapered stator design with aggressive tapers, especially near the outlet, to separate the rotor from the stator and reduce stress concentrations, maintaining rotor stability and reducing frictional contact.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If high modulus elastomers are deployed in the stator to assist in high power delivery, then power output is improved, but stress concentrations in the stator rubber are magnified due to leaky interference fits

Engineering Contradiction:

Improvepower outputVSAvoidstator rubber stress concentration

Core Design Contradiction:

PowerVSStrength

Solution Approach 1:

The stator lobes are designed with different interference fit characteristics at different locations. Specifically, the stator lobes at the outlet end have a reduced interference fit (or clearance fit) compared to the inlet end, creating local quality variations that prevent stress concentrations at critical locations while maintaining high power delivery through the overall stator design

Inventive Principle:

Principle #3Local quality

2Power

If the PDM is designed to be inefficient or leaky to enable high pressure drop and high torque generation, then torque output is improved, but rotor tilt occurs due to imbalanced forces

Engineering Contradiction:

Improvetorque generationVSAvoidrotor tilt

Core Design Contradiction:

PowerVSStability of the object's composition

Solution Approach 1:

The stator lobes are designed with asymmetric interference fit characteristics along the length of the PDM. The outlet end stator lobes have a different (reduced) interference fit compared to the inlet end, creating an asymmetric pressure distribution that compensates for rotor tilt by balancing the imbalanced forces that would otherwise cause rotor displacement

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The reduced interference fit at the outlet end is designed in advance to counteract the rotor tilt effect before it can cause damage. This preliminary design feature creates a compensating force distribution that prevents the rotor from tilting excessively, thereby preventing stress concentrations and stator damage before they occur

Inventive Principle:

Principle #9Preliminary anti-action

3Strength

If aggressive tapers are implemented near the outlet to separate rotor from stator and reduce stress concentrations, then stator damage is reduced, but frictional contact is minimized

Engineering Contradiction:

Improvestator damage resistanceVSAvoidfrictional contact

Core Design Contradiction:

StrengthVSForce

Solution Approach 1:

The taper is applied locally only to the outlet end stator lobes, while the inlet end maintains full interference fit. This localized modification reduces frictional contact only where it is most critical (at the outlet end where rotor tilt occurs), while maintaining effective power transmission through the rest of the stator

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS20260071545A1Compensation for rotor tilt in hybrid PDM stators

Publication Date: 2026.03.12 ABACO DRILLING TECHNOLOGIES LLC

AI summary

Minor diameter enlargements are engineered into a stator in a positive displacement motor (PDM) power section to relieve stator stress concentrations at the lower (downhole) end of the power section in the presence of rotor tilt. The stator may be a hybrid construction of heterogenous materials.