Threaded Fuel Rails for High-Pressure Direct Injection
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Solution Overview
Problem
Conventional high-pressure fuel rail assemblies face challenges in maintaining integrity and reliability due to suboptimal brazed joint connections, which can lead to fuel leakage and safety concerns, especially at pressures above 30 MPa, and existing materials like aluminum are inadequate for high-pressure direct injection engines.
Innovation Solution
The use of screw threads on components for reliable connections, eliminating the need for brazing, allows for higher pressure tolerance and structural reliability while reducing production costs, with threaded orifices and orientation notches ensuring secure engagement of injector sockets with the tube.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If brazed joint connections are used to assemble fuel rail components, then the assembly can be manufactured with conventional processes, but the connection reliability and integrity deteriorate at high pressures above 30 MPa
Solution Approach 1:
The patent replaces the thermal brazing process with a mechanical threaded connection system. Screw threads are provided on the fuel injector holder and engage with corresponding threads in the fuel rail tube, creating a mechanically secure connection that can be assembled without thermal processes. This mechanical fastening method provides reliable connections that maintain integrity at high pressures up to 35 MPa and beyond, eliminating the reliability issues associated with brazed joints while remaining manufacturable.
2Ease of manufacture
If brazing is used to connect injectors to the tube, then assembly is achieved, but dimensional accuracy and predictability deteriorate adjacent to the fuel injector holder
Solution Approach 1:
The mechanical threaded connection system eliminates the thermal distortion and dimensional variability inherent in brazing processes. The screw threads provide precise, repeatable positioning of fuel injectors relative to the tube, ensuring consistent dimensional accuracy and predictability. The threaded engagement allows for controlled assembly that maintains tight tolerances without the unpredictable effects of thermal expansion and contraction that occur during brazing.
3Ease of manufacture
If aluminum material is used for the fuel rail, then production costs are reduced, but the strength and pressure tolerance deteriorate at injection pressures of 150-250 MPa
Solution Approach 1:
The patent changes the material parameter from aluminum to stainless steel for the fuel rail tube and components. This material substitution provides the necessary strength and pressure tolerance to withstand high injection pressures of 150-250 MPa and beyond, while the threaded connection design optimizes the structural efficiency of the stainless steel construction. The material change enables the rail to safely operate at these extreme pressures while maintaining cost-effectiveness through the simplified assembly process that eliminates brazing.
Data Source
Figure 1~2
Figure 3~5
AI summary
A fuel rail assembly for gasoline direct injection fuel delivery to an engine. The assembly has a common rail tube (10). In the tube (10) there are threaded orifices (21) extending laterally. Injector sockets (12) are adapted to mate with the threaded orifices (21). Each injector socket (12) has a proximal nipple end region (22) connected to the tube (10) and a distal end region (24) through which fuel is delivered to the engine. Screw threads (26) are disposed around the proximal nipple end region (22). The screw threads (26) include a lead thread that is received by the threaded orifices (21), thereby forming mechanical connections between the injector sockets (12) and the tube (10) that are adapted to withstand maximum pressures of fuel up to 20 Mpa (2900 psi).