Conical Threaded Piston Unit for Clearance-Free Sealing
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Solution Overview
Problem
Existing connections between piston and piston rod in working cylinders suffer from notch effects, require additional sealing, and are complex to manufacture, while also failing to provide a reliable seal between working chambers.
Innovation Solution
A conical thread connection is used where the piston rod and piston have matching outer and inner threads with a taper angle of 0.3 to 5 degrees, forming a positive locking connection and ensuring a reliable seal without additional securing elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a welded connection or positive locking coupling is used between piston and piston rod, then a secure mechanical connection is achieved, but notch effects occur at the moulded sections and additional sealing is required
Solution Approach 1:
The patent merges the mechanical connection function and sealing function into a single integrated conical thread connection. The tapered outer thread of the piston rod engages with the tapered inner thread of the piston, creating both a secure mechanical coupling and a sealing interface simultaneously, eliminating the need for separate sealing components and reducing notch effects at moulded sections.
Solution Approach 2:
The conical thread connection serves multiple functions: it provides axial and radial positioning, transmits mechanical loads, prevents leakage between working chambers, and eliminates the need for additional sealing elements. This multi-functional design simplifies the overall structure while maintaining connection strength.
2Reliability
If a force-fit and positive locking connection with piston ring is used, then high quality and high reliability are achieved, but the coupling becomes comparatively demanding in terms of manufacture
Solution Approach 1:
The patent extracts the complex multi-component coupling mechanism (piston rings, clearance end positions, force-fit structures) and replaces it with a simplified conical thread connection. The tapered threads naturally provide both the mechanical coupling and sealing functions that previously required multiple separate components, significantly reducing manufacturing complexity while maintaining reliability.
Solution Approach 2:
The patent changes the geometric parameters of the thread connection by introducing a specific taper angle (alpha) between 0.3 to 5 degrees. This parameter change enables the thread flanks to abut without clearance in the coupled state, creating a self-locking mechanism that provides high reliability through elastic deformation within material limits, while simplifying the manufacturing process compared to traditional force-fit connections.
3Ease of manufacture
If traditional thread connections are used without taper, then manufacturing is simpler, but clearance exists between thread partners preventing reliable sealing
Solution Approach 1:
The patent introduces asymmetry into the thread geometry by applying a taper to both the outer and inner threads. This asymmetric design causes the thread flanks to abut against each other without clearance in the coupled state, creating a sealing plane that prevents leakage. The tapered geometry transforms the traditional clearance-based thread connection into a clearance-free sealing interface while maintaining manufacturability.
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
The conical thread connection provides a simple, compact, and reliable mechanical coupling with a seamless seal, reducing notch effects and manufacturing complexity, while maintaining structural integrity and sealing effectiveness under various load conditions.
Implementation Method 1
The outer thread and the inner thread are elastically deformed in the thread section in the coupling end position. According to the invention, the elastic deformation is within the elastic limits of the piston rod and piston.
Implementation Method 2
an oversize of the diameter of the piston rod relative to the piston is formed in the common thread section by the taper according to the invention by means of a wedge effect. This oversize causes the press fit and the elastic deformation of the thread partners.
Implementation Method 3
the thread partners are designed in such a manner that they abut against each other without any clearance in a coupling end position in the common thread section and form a sealing plane
Data Source
AI summary
A piston unit of a working cylinder includes a piston rod that has an outer thread on a piston-side coupling portion. A piston has an axial bore which has an inner thread and in which the piston rod is received. The outer thread and the inner thread define a common thread portion. The outer thread and the inner thread have a complementary conicity and a complementary thread geometry. The conicity has a conicity angle alpha of 0.3 to 5 degrees. The outer thread and the inner thread abut one another in a coupling end position in the thread portion in a gap and define a sealing plane. The outer thread and the inner thread have, in the thread portion in the coupling end position, an elastic deformation within the elastic limit of the piston rod and the piston. The elastic deformation is brought about by a surface pressure via a tightening torque. The piston rod and the piston are radially and axially fixed to one another without play in the coupling end position by the elastic deformation, and the elastic deformation is within the elastic limit both with and without an application of pressure by a pressure medium in the working cylinder.