Ball-CV PDM Transmission for Stable Torque Under Misalignment
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Solution Overview
Problem
Existing rotary power transmission assemblies in bottom hole assemblies face challenges with torque transfer due to misalignment, leading to instability and high stress concentrations, which result in wear and potential disengagement of torque transfer elements during eccentric rotation.
Innovation Solution
A ball/CV design is implemented with a shaft head having radial wings and a housing with receptacles, allowing the torque transfer elements to float and maintain contact during misalignment, optimizing the torque transfer angle and reducing stress concentrations through a more efficient interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Woodruff key designs are used to transfer torque, then large TTEs with longer aspect ratio 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 balls are received in spherical receptacles that allow them to maintain stable contact during misaligned rotation. The spherical geometry enables the balls to self-align and remain stable throughout the rotation cycle, eliminating the instability problems associated with elongated TTEs while maintaining torque transfer capability.
Solution Approach 2:
The patent creates a dynamic torque transfer system where balls are free to move within their receptacles during misaligned rotation. This dynamic arrangement allows the balls to adjust their position to maintain optimal contact with both the shaft wing and TTE, ensuring continuous stable engagement throughout the rotation cycle rather than being constrained in a fixed position.
2Stability of the object's composition
If bridge designs are used to provide stability to TTEs, then the aspect ratio is shorter in the circumferential direction, but torque transfer efficiency is reduced
Solution Approach 1:
The spherical ball design eliminates the need for compromised aspect ratios. The spherical geometry inherently provides stability in all directions during misaligned rotation, allowing optimal torque transfer angles to be achieved without the limitations of shortened circumferential dimensions imposed by bridge designs.
3Adaptability or versatility
If ball/CV designs with sliding TTE constrained by radial groove are used, then additional freedom for shaft head tilting is provided, but torque transfer capability is limited and balls physically disengage during misaligned rotation
Solution Approach 1:
The patent uses spherical receptacles instead of radial grooves to receive the balls. The spherical receptacle geometry allows the balls to maintain continuous contact with both the shaft wing and TTE throughout the entire misaligned rotation cycle, preventing physical disengagement while still providing the necessary freedom for shaft head tilting and articulation.
Solution Approach 2:
The patent creates a fully dynamic ball/CV joint where balls are free to move within spherical receptacles without being constrained by radial grooves. This dynamic design maintains continuous torque transfer through all positions of misaligned rotation, allowing the shaft head to tilt and articulate freely while preventing ball disengagement and maximizing torque transfer capability.
4Power
If conventional transmission designs are used, then torque is transferred through misaligned shafts, but high stress concentrations occur at contact surfaces leading to wear
Solution Approach 1:
The patent employs spherical contact surfaces between the balls, shaft wings, and TTEs. These spherical interfaces distribute contact stresses more evenly compared to conventional flat or point contacts, significantly reducing stress concentrations at contact surfaces and minimizing wear during torque transfer through misaligned shafts.
Data Source
AI summary
A ball-CV style transmission suitable for use in a Positive Displacement Motor (PDM). A shaft provides shaft wings received into housing receptacles on a housing. A ball and a Torque Transfer Element (TTE) is interposed between each shaft wing and housing within each housing receptacle, with the ball received into opposing recesses preferably on the shaft wing and the TTE. The TTEs float within their corresponding housing receptacles so as to maintain torque transfer contact between all thrust surfaces during articulated rotation of the shaft with respect to the housing. The TTEs preferably float generally radially towards the shaft centerline as angular deflection increases during articulated rotation.