Downhole Piston-Cylinder Assembly with Solid Sealing and Separate Retention
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Solution Overview
Problem
Downhole tools, particularly rotary steerable tools, face challenges in maintaining reliable piston and cylinder assemblies due to harsh drilling environments, high stress concentrations, and the need for increased junk slot area to improve drilling efficiency and prevent tool failure.
Innovation Solution
The piston and cylinder assembly features a piston with a substantially circular periphery in direct sliding contact with the cylinder wall, utilizing a solid sealing technology without separate sealing elements, and includes a retainer with multiple retaining parts to securely hold the piston in place, maximizing the sealing interface and reducing material removal for stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate sealing elements are used in the piston and cylinder assembly, then the sealing function is provided, but the reliability decreases due to additional failure points and material removal for stress concentration
Solution Approach 1:
The patent removes separate sealing elements from the system entirely. Instead of using traditional seals, seal rings, or gaskets, the invention creates a direct metal-to-metal sealing interface between the piston outer wall and the cylinder bore. This extraction of the sealing function from a separate component to the structural components themselves eliminates additional failure points and reduces material removal requirements.
Solution Approach 2:
The sealing function is merged with the structural function of the piston and cylinder components. The piston outer wall and cylinder bore are designed with precision surfaces that simultaneously provide structural support and sealing. This merging eliminates the need for separate sealing elements and reduces the number of parts, thereby improving reliability.
2Force
If the piston diameter is increased to apply greater force, then the force application capability increases, but the junk slot area decreases
Solution Approach 1:
The piston is segmented into functional zones: the outer wall provides sealing contact with the cylinder bore, while the retained part (separate from the outer wall) provides structural retention. This segmentation allows the piston diameter to be optimized for force application while maintaining adequate junk slot area through efficient spatial arrangement of retained parts.
Solution Approach 2:
The patent separates the retaining function from the sealing surface by positioning retained parts at locations separate from the outer wall. This dimensional separation allows the piston to have sufficient diameter for force application while maintaining junk slot area in critical regions, as the retained parts do not necessarily coincide with the sealing interface.
3Device complexity
If retaining parts are integrated with the piston outer wall, then the structure is simplified, but the sealing interface is compromised
Solution Approach 1:
The retaining function is extracted from the sealing surface. The patent explicitly positions retained parts separate from the piston outer wall, allowing the outer wall to provide an uninterrupted sealing interface while retained parts provide structural retention functionality elsewhere on the piston body.
Solution Approach 2:
The piston is divided into distinct functional elements: the outer wall dedicated to sealing contact with the cylinder bore, and retained parts positioned separately for structural retention. This segmentation ensures that the sealing interface remains intact and uninterrupted while still providing adequate retention capability.
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 design enhances the mechanical seal, increases the piston diameter for greater force application, minimizes wear, and maximizes the junk slot area, thereby improving the reliability and service life of downhole tools while maintaining tool integrity and reducing the risk of fatigue and material failure.
Implementation Method 1
The piston and cylinder assembly features a piston with a substantially circular periphery in direct sliding contact with the cylinder wall, utilizing a solid sealing technology without separate sealing elements
Data Source
AI summary
A piston and cylinder assembly of a downhole tool including a rotary steerable tool. The piston has an outer wall in direct sliding contact with a wall of the cylinder. The cylinder has a retainer for the piston, the retainer has a retaining part and the piston has a retained part, such that the retaining part and the retained part cooperate to retain the piston in the cylinder. The invention separates the function of retaining the piston from sealing the piston to cylinder interface. The invention also relates to a method of assembling the piston and cylinder including rotating the piston relative to the cylinder so that at least a portion of the retained part becomes aligned with at least a portion of the retaining part, and locking the piston against subsequent rotation relative to the cylinder.