Common Rail Inner Recess for Deep Bore Chamfer Protection
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Solution Overview
Problem
The conventional manufacturing process of common rails with lengths greater than 400 mm is prone to axial deviation during deep hole drilling, which can damage the inlet chamfer and affect the sealing quality of high-pressure nozzles, leading to irreversible damage during autofrettage.
Innovation Solution
The method involves machining an inner recess with a larger diameter than the longitudinal bore, allowing the drill to open into the recess, preserving the geometry of the inlet chamfer and preventing damage during deep drilling and autofrettage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If deep hole drilling is performed from one end cavity through the rail blank to create a longitudinal through bore, then the inner volume for high pressure fuel is formed, but the longitudinal through bore may deviate from the main axis, especially in rails longer than 400 mm, risking destruction of the end bore chamfer of the second cavity
Solution Approach 1:
The patent applies preliminary action by first forming an inner recess with larger diameter at the bottom of the first cavity before performing deep hole drilling. This recess serves as a pre-prepared receiving space that guides the drill bit and prevents deviation from the main axis during drilling of the longitudinal through bore, thereby maintaining manufacturing precision while creating the required inner volume.
Solution Approach 2:
The inner recess acts as an intermediary element between the drilling operation and the end bore chamfer of the second cavity. By providing this intermediate structure with larger diameter, the drill bit is guided and constrained, preventing direct contact with and potential damage to the precise end bore chamfer, thus resolving the conflict between creating the through bore and maintaining alignment precision.
2Volume of moving object
If the longitudinal through bore is drilled with significant length (above 400 mm), then the required inner volume is achieved, but the axial deviation of the gun drill increases significantly, creating uncertainties about the exit area and risking damage to the end bore chamfer
Solution Approach 1:
The inner recess is formed in advance before the deep hole drilling operation. This preliminary structure provides a guided entry point for the drill bit, ensuring that even over long drilling distances (above 400 mm), the drill maintains proper alignment and the exit area is accurately positioned, thereby preserving the reliability of the sealing surfaces.
Solution Approach 2:
The inner recess with larger diameter serves as a cushioning zone that absorbs and compensates for potential drill bit deviation during long-distance drilling. This beforehand cushioning structure prevents the drill bit from directly impacting the precise end bore chamfer, protecting the sealing quality even when drilling lengths exceed 400 mm.
3Volume of moving object
If the inlet chamfer is destroyed or modified during deep drilling, then the positioning and sealing of nozzles is affected, but the inner volume for fuel can still be created
Solution Approach 1:
The inner recess serves as an intermediary protective structure between the drilling operation and the inlet chamfer. By providing this intermediate zone with larger diameter, the drill bit is guided and constrained, preventing direct contact with and potential damage to the precise inlet chamfer, thus maintaining ease of manufacture for nozzle sealing while still creating the required inner volume.
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 ensures accurate alignment and preservation of the inlet chamfer geometry, preventing damage to the sealing features and enhancing the sealing quality of the common rail, even in longer designs.
Implementation Method 1
the common rail is subjected to very high pressure, over material yield stress, causing internal portions of the rail to yield plastically, resulting in internal compressive residual stresses once the pressure is released
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention concerns a method of manufacturing a common rail (10) for a fuel injection system. A steel piece is forged into a rail blank having an elongate shape extending along a main axis (X), and the extremities thereof are machined to form a first (16) and second (18) cavities. The first extremity is further machined to form an inner recess (29) at a depth of between 3 to 5 mm under the bottom face, the inner recess (29) in fluid communication with the first cavity (16) through an intermediate passage (28) opening in the bottom face. An inlet chamfer is machined around the intermediate passage (28) adjacent the bottom face (23). The rail blank is drilled from the second cavity (18) along the main axis (X) to create a longitudinal through bore (20) having a length greater than 400 mm and a diameter of about 8 to 10 mm in order to form an inner volume receiving, in use, high pressure fuel, the longitudinal through bore (20) opening into the inner recess (29). The diameter ratio of the inner recess (29) with respect to the longitudinal bore (20) is at least 1.4.