Well Tractor Drive Arm Layout for Compact High-Force Borehole Traction
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Solution Overview
Problem
Existing well tractor drive sections face limitations in mechanical advantage due to centrally arranged arm bearings and actuator rods, leading to increased tool length, reduced space efficiency, and instability when encountering borehole restrictions, which restricts the number of tools that can be inserted and causes bending moments.
Innovation Solution
The well tractor drive section features wheel arm bearings and actuator rods positioned oppositely relative to the main axis, providing increased mechanical advantage and a compact design, with an angular gear housing and transmission gear train that allows transverse output shafts to be coaxial with arm bearings, enabling a shorter, more stable tool configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If wheel arm bearings are centrally arranged in the drive section body, then the structure is compact, but the mechanical advantage of the drive arms is reduced and the separation between actuator rods is limited
Solution Approach 1:
The patent applies asymmetry by displacing the wheel arm bearings from the central axis to opposite positions relative to it. This asymmetric arrangement increases the perpendicular distance from the actuator rod force application point to the bearing pivot point, thereby increasing the mechanical advantage of the drive arms while maintaining a compact overall structure.
2Force
If the tool length is increased to accommodate separated actuator rods, then the mechanical advantage increases, but the overall tractor length increases limiting the number of tools that can enter the well
Solution Approach 1:
The patent resolves the length conflict by changing the spatial arrangement from a longitudinal separation to a transverse arrangement. The bearings are positioned at opposite sides of the central axis in the same longitudinal section, allowing actuator rods to be separated laterally rather than axially. This maintains compact tool length while achieving sufficient mechanical advantage through increased lateral separation distance.
3Force
If single point forces are applied by drive wheels against the borehole wall, then the drive force is concentrated, but bending moments are incurred to the drive section and tractor body
Solution Approach 1:
The patent applies the counterweight principle by positioning drive wheels on opposite sides of the central axis. When both wheels apply force against the borehole wall, the forces create opposing bending moments that balance each other, reducing the net bending moment on the drive section and tractor body while maintaining concentrated drive force application.
4Device complexity
If wheel arms are actuated via a cogged wheel arranged axially at the pivot axis, then the drive mechanism is simplified, but the transverse axial length of the wheel arm increases reducing available space
Solution Approach 1:
The patent resolves the space conflict by changing the actuation mechanism arrangement from an axial configuration to a transverse configuration. The cogged wheels and actuator rods are arranged in the transverse direction rather than axially, reducing the transverse axial length of wheel arms and freeing up axial space within the cylindrical pressure housing while maintaining the same actuation functionality.
Data Source
AI summary
A well tractor drive section comprising—a drive section body (0) with main central axis (0x), with—first and second drive wheels (10A, 10B) on the outer ends of first and second wheel arms (12A, 12B); inner ends of said wheel arms (12A, 12B) arranged pivotally about first and second transverse axes (8Ax, 8Bx) in first and second transverse-axial wheel arm bearings (14A, 4B) for said wheel arms (12A, 12B) to rotate in a direction away from said main axis (0x) to engage said drive wheels (10A, 10B) with an inner wall of a well; —said first and second transverse-axes (8Ax, 8Bx) being mutually oppositely laterally displaced with a first separation (d1) from said main central axis (0x) in a common perpendicular plane (8P) relative to said main central axis (0x).