Offset Coupling for Mud Motor Drive Shaft Eccentric Motion
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Solution Overview
Problem
Downhole tools, such as motors and pumps, face mechanical complexity and potential failure due to eccentric motion, which is often accommodated using articulating joints, constant velocity joints, or flexible shafts, increasing complexity and stress.
Innovation Solution
A rotary transfer mechanism that allows the rotor to rotate about its axis while orbiting around another axis, eliminating the need for articulating joints, CV joints, or flex shafts by coupling the rotor to the drive shaft at a radial offset, enabling torque transfer through orbiting motion rather than rotational motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If articulating joints or CV joints are used to accommodate eccentric motion, then the rotor can rotate about its axis while orbiting around another axis, but the device complexity increases and more components are required
Solution Approach 1:
The patent extracts and eliminates the articulating joints and CV joints from the system by using an offset pin coupling mechanism. The offset pin is radially offset from the drive shaft axis by an amount equal to the orbital radius of the rotor, which allows the rotor to orbit while transferring torque directly to the drive shaft without requiring complex joints.
Solution Approach 2:
Instead of using joints to accommodate the eccentric motion, the patent inverts the approach by making the coupling point itself offset. The offset pin is positioned at a radial distance equal to the orbital radius, so that the orbiting motion of the rotor naturally drives the rotation of the drive shaft through the offset coupling mechanism.
2Device complexity
If flexible shafts are used to reduce reliance on articulating joints, then fewer joints are required, but high bending moments are induced to surrounding components
Solution Approach 1:
The patent extracts the flexible shaft from the system entirely and replaces it with a rigid drive shaft coupled through an offset pin. This eliminates the bending moments that would be induced in a flexible shaft while maintaining the ability to accommodate eccentric motion through the offset coupling geometry.
3Adaptability or versatility
If special joints are used to accommodate eccentric motion, then multiple degrees of movement can be handled, but the reliability decreases due to increased possible failure modes
Solution Approach 1:
The patent removes the complex joint systems (articulating joints, CV joints) that create multiple failure modes and replaces them with a simple offset pin coupling mechanism. This reduces the number of potential failure points while maintaining the ability to handle eccentric motion and multiple degrees of movement through the geometric relationship between the offset pin and orbiting rotor.
Data Source
AI summary
A rotary transfer mechanism is disclosed for a motor, pump, or other downhole tool that accommodates the eccentric motion of a rotor without the need for a flex shaft, articulating joint or CV joint. In one configuration, the rotor is coupled to the drive shaft at a radial offset from the drive shaft axis. The orbiting motion of the rotor, rather than rotation of the rotor about its own axis, generates a torque on the drive shaft, by applying a tangential force to the drive shaft at the location of the radial offset. The radial offset may be set equal to the orbital radius so that no radial movement or flex is required at the drive shaft to accommodate the eccentric rotor movement.