Harmonic Drive Assembly for High-Temperature Downhole Torque
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Solution Overview
Problem
Existing downhole drilling systems face limitations such as high maintenance requirements, limited temperature range, and lateral vibration issues due to the use of elastomers and sliding contact in ball transfer mechanisms, which hinder efficient torque transmission and directional drilling performance.
Innovation Solution
The implementation of a harmonic drive assembly with a recirculating ball transfer system that converts harmonic, cycloidal, or polynomial motion into rotary motion, reducing friction and abrasive wear by using rolling motion instead of sliding contact, and integrating this with rotary piston motors to enhance torque and operational efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If ball transfer mechanisms with sliding contact are used, then torque transmission is achieved, but friction and abrasive wear increase
Solution Approach 1:
The patent replaces the traditional sliding contact ball transfer mechanism with a harmonic drive mechanism that uses rolling contact. The harmonic drive consists of a wave generator, flexible spline, and circular spline, where balls roll between the splines to transmit torque. This substitution eliminates the sliding friction and abrasive wear inherent in traditional ball transfer mechanisms while maintaining effective torque transmission capability.
2Reliability
If elastomers are used in downhole drilling systems, then sealing and cushioning are improved, but temperature range is limited
Solution Approach 1:
The patent changes the material parameters by replacing elastomeric materials with metal components and advanced coatings. The harmonic drive uses hardened steel splines and precision-machined surfaces that can withstand high temperatures. The wave generator and flexible spline are constructed from temperature-resistant alloys, eliminating the thermal limitations of elastomers while maintaining sealing and cushioning functions through precision engineering and surface treatments.
3Speed
If multi-lobed helical rotor with nutation is used, then rotor rotation is generated, but lateral vibration increases
Solution Approach 1:
The patent replaces the multi-lobed helical rotor nutation mechanism with a harmonic drive system. The harmonic drive generates rotor rotation through the wave generator that creates an elliptical motion pattern, causing the flexible spline to engage and disengage sequentially with the circular spline. This rolling engagement mechanism eliminates the lateral vibration and nutation inherent in multi-lobed rotor systems, providing smooth rotation without harmful vibrations.
4Use of energy by moving object
If rigid drill pipe rotation from surface is used, then rotational energy is transferred, but drill string curvature and thrust loads generate additional torque
Solution Approach 1:
The patent introduces a downhole harmonic drive motor as an intermediary device that converts reciprocating axial motion of a piston into continuous rotary motion directly at the drill bit. This eliminates the need to rotate the entire drill string from the surface, as the rotation is generated locally downhole. The harmonic drive mechanism efficiently converts linear piston motion into rotational output, overcoming the torque penalties associated with drilling through curved drill strings and thrust-loaded sections.
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
This solution improves torque characteristics, eliminates lateral vibration, allows drilling fluid to flow through the power section, and operates effectively at high temperatures, reducing maintenance needs and enhancing the overall performance and efficiency of downhole drilling systems.
Implementation Method 1
converting reciprocating axial motion to continuous rotary motion... using rolling motion instead of sliding contact
Data Source
AI summary
A harmonic drive assembly and fluid-powered linear motors with both axial pistons are rotary piston arrangements incorporating the harmonic drive assembly are disclosed. The motors may be used in downhole drilling applications, but the drive assembly and/or motors may be used in other applications. The assembly, motors and methods use advanced harmonic drives, advanced helical drives, and combinations thereof with 1) motors with axial pistons and reciprocating linear rings to convert reciprocative axial motion to continuous rotary motion, and 2) motors with rotary pistons and reciprocating linear rings to rectify reciprocative rotary motion to continual rotary motion to improve performance over prior configurations. Axial pistons provide a robust simple solution for generating rotation; Rotational pistons provide increased torque generation as the torque generated is proportional to motor length. Since downhole drills are long, a high-torque motor can be produced using this method.