Harmonic Drive Transmission for Downhole Drilling Torque Conversion
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Solution Overview
Problem
In downhole drilling, high-speed, low-torque outputs from turbine motors often result in suboptimal drilling operations, especially in soft formations, as existing planetary gear systems struggle to provide the necessary low-speed, high-torque rotation required for effective drilling.
Innovation Solution
The use of harmonic drive transmissions, which convert high-speed, low-torque rotation into low-speed, high-torque rotation through a gear ratio mechanism involving a wave generator, flexspline, and circular spline, allowing for adjustable gear ratios and the ability to stack multiple stages for optimal rotational speed and torque delivery to the drill bit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If planetary gear systems are used to convert high-speed, low-torque output into low-speed, high-torque rotation, then torque conversion is achieved, but the load-carrying shaft diameters become too small for the required torque load
Solution Approach 1:
The patent replaces the planetary gear system with a harmonic drive transmission system that uses a wave generator, flexspline, and circular spline. This substitution allows for larger load-carrying shaft diameters while achieving the required torque conversion, as the harmonic drive mechanism distributes loads across multiple contact points and utilizes the flexibility of the flexspline to accommodate the gear engagement geometry.
2Productivity
If high-speed, low-torque rotation is applied directly to the drill bit, then the turbine motor operates efficiently, but drilling operations become suboptimal, especially in soft formations
Solution Approach 1:
The patent applies parameter changes by using a harmonic drive transmission to convert the rotational speed and torque parameters from the turbine motor output. The wave generator creates a varying elliptical motion that engages and disengages the flexspline teeth with the circular spline, transforming high-speed, low-torque rotation into low-speed, high-torque rotation suitable for effective drilling operations in various formation conditions.
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 enables effective drilling operations by providing the appropriate rotational characteristics to the drill bit, enhancing drilling efficiency and adaptability to various drilling conditions by achieving desired rotational speeds and torque levels, even in challenging formations.
Implementation Method 1
harmonic drive transmissions, which convert high-speed, low-torque rotation into low-speed, high-torque rotation through a gear ratio mechanism involving a wave generator, flexspline, and circular spline
Data Source
AI summary
A drilling assembly positionable in a well bore includes a turbine motor couplable to a drill string and a harmonic drive transmission coupled to the turbine motor. The harmonic drive transmission includes a circular spline, a wave generator, a flexspline, and a sealing subsystem. The sealing subsystem defines a substantially sealed volume containing the circular spline, wave generator, and flexspline, and isolates the circular spline, wave generator, and flexspline from drilling fluid exiting the turbine motor and flowing through the harmonic drive transmission.