Hydraulic Accumulator Round Thread for Fatigue Fracture Resistance
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Solution Overview
Problem
Hydraulic accumulators suffer from fatigue fractures due to increased stress at thread undercuts, leading to failure under high pressure loads, especially when using metric standard threads with a trapezoidal gradient, which are sensitive to notch effects and manufacturing tool variations.
Innovation Solution
Implementing a round thread with a 60° flank angle and larger radii in the crest-side region and smaller radii in the root-side region for both internal and external threads, reducing notch effects and enhancing fatigue strength by allowing radial spacing between thread flanks, thus preventing undesirable fractures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metric standard threads with trapezoidal gradient are used to fix the cover part, then the connection strength is sufficient for high pressure loads, but fatigue fractures occur due to notch effects at thread undercuts
Solution Approach 1:
The patent replaces the traditional trapezoidal thread profile with a rounded thread profile where the thread flanks are curved instead of straight. This curvature eliminates the sharp corners and undercuts that cause stress concentration, thereby preventing fatigue fractures while maintaining connection strength under high pressure loads.
Solution Approach 2:
The patent modifies the geometric parameters of the thread profile by changing from a trapezoidal shape with sharp angles to a rounded shape with continuous curves. This parameter change alters the stress distribution pattern, eliminating stress concentration points and improving fatigue resistance while preserving the load-bearing capacity.
2Ease of operation
If the cover part is designed to be screwable for maintenance purposes, then ease of operation is improved, but fatigue fractures occur during operation under high pressure
Solution Approach 1:
By implementing a rounded thread profile, the patent enables the cover part to remain screwable for easy maintenance while eliminating the fatigue fracture issue that would otherwise occur during operational cycling under high pressure conditions.
3Ease of manufacture
If thread undercuts are present in the threaded section, then manufacturing is simplified, but stress concentration occurs leading to fracture at the first thread turn
Solution Approach 1:
The rounded thread profile eliminates the need for traditional thread undercuts while maintaining manufacturability. The continuous curved flanks prevent stress concentration at the first thread turn, thereby improving fracture strength without significantly complicating the manufacturing process.
Data Source
AI summary
The invention relates to a hydraulic accumulator having an accumulator housing (10) which is closed at least on a free end side by a cover part which is able to be fixed in the accumulator housing (10) via a threaded section, characterized in that, as part of the threaded section on the accumulator housing (10), an internal thread in the form of a round thread (26) is present, the individual thread flanks (28) of which enclose, in a notional extension, a flank angle (a) of 60° with one another, and in that the radius (R1) of the rounded portion is larger in the head-side region (30) than the radius (R1) in the root-side region (32) of the round thread (26).