Universal Joint Torque Transfer with Toroidal Elements
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Solution Overview
Problem
The existing universal joint assemblies for down hole drilling motors face capacity limitations due to zero contact surface area between drive balls and their mating components, leading to excessive wear and binding under high torque loads, resulting in bending stresses and potential failures.
Innovation Solution
The introduction of a universal joint assembly with first and second opposed cavities and torque transfer elements that engage these cavities, providing a multi-point contact area to increase the surface interaction without inhibiting pivotal movement, utilizing a drive key with internal and external shapes that complement the mating parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If drive balls with spherical shape are used in cylindrical recesses, then the universal joint can accommodate rotary input torque and thrust, but the contact surface area between mating surfaces becomes zero, leading to excessive wear and binding under high torque loads
Solution Approach 1:
The invention replaces the spherical drive ball with a toroidal (doughnut-shaped) torque transfer element. This curved geometry allows the element to engage with both the spherical cavity in the inner race and the cylindrical track in the outer race, creating line contact rather than point contact. The toroidal shape maintains the ability to accommodate rotary motion and thrust while significantly increasing the contact surface area between mating surfaces, thereby reducing wear and binding under high torque loads.
Solution Approach 2:
The invention transitions from a zero-dimensional point contact (spherical ball in cylindrical recess) to a one-dimensional line contact by introducing the toroidal geometry. The torque transfer element engages the inner race at one location and the outer race at another location along the axial direction, creating distributed contact areas. This dimensional change from point to line contact increases the effective contact surface area while maintaining the universal joint's ability to handle torque and thrust loads.
2Ease of operation
If drive balls are allowed to move axially in cylindrical recesses, then the shaft can pivot angularly, but the contact stresses exceed material limits under high torque loads, causing wear and bending stresses
Solution Approach 1:
The toroidal torque transfer element's curved geometry distributes the contact stresses across larger surface areas compared to the spherical drive ball. The element engages the inner race's spherical cavity and the outer race's cylindrical track with line contact, reducing peak contact stresses. This allows the shaft to pivot angularly with the same ease while preventing contact stresses from exceeding material limits, thereby eliminating wear and bending stresses.
Solution Approach 2:
The invention changes the geometric parameters of the torque transfer element from spherical to toroidal, which fundamentally alters the contact mechanics. The toroidal shape increases the contact area and distributes the load more evenly, reducing the contact stress parameter. This parameter change allows angular pivoting to continue smoothly while keeping contact stresses within acceptable material limits, preventing wear and structural failures.
3Device complexity
If spherical drive balls are used, then the universal joint structure is simple, but the surface area of contact between mating surfaces is zero, leading to rapid wear under high torque
Solution Approach 1:
The toroidal torque transfer element maintains the simplicity of the universal joint structure while improving reliability. The element can be manufactured as a single piece and installed in the same basic configuration as spherical drive balls. The toroidal geometry inherently provides line contact with both the inner and outer races, creating substantial contact surface area without adding complex mechanisms or multiple components. This simple geometric change eliminates rapid wear under high torque while keeping the device structure straightforward.
Data Source
AI summary
A universal joint carried by an elongate body having an axis. The universal joint has an inner race that pivots omni-directionally within an outer race and a series of first and second opposed cavities formed in the inner race and the outer race. There are a plurality of torque transfer elements, each torque transfer element having a first portion that engages a first cavity and a second portion that engages a corresponding second cavity. The first cavity is a socket that permits rotation of the first portion within the first cavity as the inner race pivots omni-directionally within the outer race and the second cavity is a track oriented in the direction of the axis of the elongate body. The second portion moves along the track as the inner race pivots omni-directionally within the outer race of the second portion along the track. The second portion has at least one drive surface that engages an inner surface of the track at more than one point along the direction of the track.