Knuckle-Style PDM Transmission for Misaligned Torque Transfer
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Solution Overview
Problem
Existing rotary power transmission assemblies in bottom hole assemblies (BHAs) face challenges in transferring torque efficiently due to misalignment of rotating power shafts, leading to instability, high stress concentrations, and wear on components, particularly in high-power subterranean positive displacement motors (PDMs).
Innovation Solution
A knuckle-style ball-CV transmission design with torque transfer elements (TTEs) and balls that allow for floating movement and tilting during misaligned rotation, maintaining continuous torque transfer contact and reducing stress concentrations by encapsulating the ball within the TTE and shaft wing recesses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Woodruff key designs are used to transfer torque, then large TTEs are provided, but the TTEs become unstable during misaligned rotation and experience high stress concentrations
Solution Approach 1:
The patent employs spherical balls instead of traditional Woodruff key TTEs. These spherical elements can accommodate misaligned rotation between the drive shaft and housing while maintaining stable contact. The spherical geometry allows the balls to roll and adjust to angular deviations, preventing the instability and stress concentrations that plague linear TTE designs during deviated wellbore operations.
Solution Approach 2:
The patent introduces dynamic adjustment capability through the spherical ball mechanism. The balls can dynamically reposition themselves during rotation to maintain optimal contact surfaces, adapting to changing alignment conditions. This dynamic behavior contrasts with static TTE designs that cannot adjust to misalignment, thereby maintaining stability throughout the rotation cycle.
2Stability of the object's composition
If bridge designs are used to improve TTE stability, then the aspect ratio is shortened in the circumferential direction, but torque transfer capability is limited
Solution Approach 1:
The spherical ball geometry inherently provides stability without requiring a shortened aspect ratio. The sphere maintains uniform contact properties in all directions, allowing it to stabilize during misaligned rotation while preserving full torque transfer capability through its diameter. This eliminates the compromise between stability and torque capacity that bridge designs must make.
Solution Approach 2:
The patent transitions from planar TTE contact surfaces to three-dimensional spherical contact. This dimensional change allows contact to occur at multiple points around the sphere, distributing loads more effectively and maintaining torque transfer capability while providing stability during angular deviations. The spherical geometry adds rotational freedom without sacrificing load-bearing capacity.
3Adaptability or versatility
If ball/CV designs with sliding TTE constrained by radial groove are used, then freedom to tilt is provided, but balls physically disengage from TTE during misaligned rotation
Solution Approach 1:
The spherical ball design with recessed mating surfaces ensures continuous engagement by allowing the balls to nestle into their receptacles during tilt. The curved geometry of the recesses in both the drive shaft and housing maintains contact throughout the range of motion, preventing the disengagement that occurs with linear groove constraints.
Solution Approach 2:
The patent implements a nested configuration where spherical balls are received within recesses formed in both the drive shaft and housing. This nesting arrangement allows the balls to remain captured within the assembly during misaligned rotation, maintaining continuous engagement while providing the necessary freedom to tilt and accommodate angular deviations.
4Power
If Foote ball design with sliding TTE constrained by radial groove is used, then torque transfer is enabled, but torque transfer angle is suboptimal and mechanical advantage is limited
Solution Approach 1:
The spherical ball interface with recessed contact surfaces optimizes the torque transfer angle by allowing contact at the most advantageous points on the sphere. This geometry enables the balls to self-align to optimal contact positions, maximizing mechanical advantage and torque transfer efficiency compared to constrained linear TTE designs.
Solution Approach 2:
The dynamic capability of the spherical balls to rotate and tilt within their recesses allows continuous optimization of the torque transfer angle during misaligned rotation. This dynamic adjustment maintains optimal mechanical advantage throughout the rotation cycle, whereas fixed-angle designs lose efficiency as misalignment increases.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design enables efficient torque transfer with reduced wear and optimized mechanical advantage, maintaining engagement of all components during misaligned rotation, thus enhancing the durability and performance of the transmission.
Implementation Method 1
The ball, at least in theory, provides additional freedom to allow the shaft head to 'tilt' with respect to shaft head during misaligned rotation
Data Source
AI summary
A knuckle-style ball-CV style transmission suitable for use in a Positive Displacement Motor (PDM). A knuckle head provides knuckle wings received into shaft cavity receptacles on a shaft. Each shaft cavity receptacle provides a shaft cavity recess. A Torque Transfer Element (TTE) and a ball is received into each shaft cavity receptacle, such that the TTE and ball are interposed between each knuckle wing and a corresponding shaft cavity recess within the shaft cavity recess. The TTEs float within their corresponding shaft cavity receptacles so as to maintain torque transfer contact between all thrust surfaces during articulated rotation of the shaft with respect to the knuckle head. The TTEs preferably float generally radially towards the shaft centerline as angular deflection increases during articulated rotation.