Threaded Connection Radial Prestress High Pressure Injection
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Solution Overview
Problem
High-pressure medium-carrying components in internal combustion engine injection devices face challenges in fatigue strength due to large sealing diameters, requiring high preload forces and increased dynamic thread load, which existing solutions only partially address.
Innovation Solution
A press-fitted outer ring is applied to the tubular end section to introduce radial elastic prestress, targeting stress reduction in the internal thread by distributing screw force and reducing thread load, particularly in the first thread turn adjacent to the contact surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large sealing diameters are used for hydraulic reasons in common rail systems, then the sealing capacity is improved, but the thread load increases and fatigue strength decreases
Solution Approach 1:
The patent applies preliminary anti-action by pre-stressing the tubular end section through press-fitting an outer ring before the threaded connection is subjected to operational loads. This pre-compression counteracts the tensile stresses that will develop during operation, directly addressing the fatigue strength problem caused by large sealing diameters requiring high preload forces
2Reliability
If high preload forces are used to ensure sealing, then the sealing reliability is improved, but the dynamic load on the thread increases
Solution Approach 1:
The patent changes the stress state parameters of the threaded connection by introducing a pre-compressed state through the press-fitted outer ring. This parameter change allows the connection to withstand dynamic loads better by maintaining a more favorable stress distribution throughout the thread engagement, reducing the peak loads on individual thread turns
3Force
If the first thread turn is highly stressed to achieve clamping, then the clamping force is sufficient, but the fatigue strength of the first thread turn decreases
Solution Approach 1:
The patent applies local quality by creating a non-uniform stress distribution along the thread engagement length. The press-fitted outer ring generates highest compressive stresses at the free end of the tubular end section, which progressively decrease toward the clamping surface. This local variation in stress quality protects the first thread turn while maintaining sufficient overall clamping force through the cumulative effect across all thread turns
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 approach effectively reduces thread load by up to 50% and enhances load capacity, ensuring the threaded connection can withstand pressures of at least 150 N/mm2 without overloading the last thread, while improving fatigue strength and stress distribution.
Implementation Method 1
an outer ring is pressed onto the tubular end section, which applies an elastic prestress acting in the radial direction
Implementation Method 2
an outer ring which is fastened externally to the tubular end section by means of a press fit
Data Source
Figure 1
Figure 2
AI summary
The method involves forming an internal thread (21) at a tubular end section (20) of a component i.e. high pressure storage unit (6), into which another component i.e. support body (5) having an external thread (22) is threaded. The latter component is clamped against a conical support surface (24) of the former component. An outer ring (26) is pressed on a free end of the tubular end section to apply a resilient pretension that acts in a radial direction such that the components are bolted with each other after application of the resilient pretension. Independent claims are also included for the following: (1) a thread connection (2) a high pressure fluid-carrying component.