Common Rail Bush Orifice Design for Pressure Pulsation Control
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Solution Overview
Problem
Conventional common rail fuel injection systems face challenges in maintaining consistent fuel pressure and injection characteristics due to pressure pulsations, leading to variations in injection timing and amount among cylinders, and are costly to manufacture with complex orifice designs.
Innovation Solution
A common rail design featuring a bush with multiple stages of orifices and a press-fitted portion that deviates the smallest diameter orifice from the press-fitted area to prevent deformation, combined with an orifice forming member that attenuates pressure pulsations, reducing the need for additional springs and simplifying the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the orifice is formed directly in the rail main body by hole making process, then the manufacturing process is simple, but the crossing hole is small causing stress concentration and insufficient fatigue strength
Solution Approach 1:
The common rail is divided into a rail main body and a separate bush component. The orifice is formed in the bush rather than directly in the rail main body, separating the orifice formation process from the rail structure. This allows the rail main body to have a larger crossing hole for reduced stress concentration while the bush provides the precise orifice geometry needed for fuel injection.
Solution Approach 2:
The bush acts as an intermediary component between the rail main body and the fuel injection system. It is press-fitted into the inside-outside communication hole of the rail main body, providing the orifice function while protecting the rail main body from stress concentration. The bush transfers and distributes the stress from the high-pressure fuel, preventing direct concentration at the orifice opening in the rail main body.
2Strength
If the bush with orifice is press-fitted into the inside-outside communication hole, then the crossing hole is enlarged improving fatigue strength, but the distortion changes the inner diameter of the orifice
Solution Approach 1:
The design changes the geometric parameters of the bush, specifically making the orifice position asymmetric relative to the press-fitted portion. The orifice is positioned such that it does not overlap with the press-fitted area in the radial direction, allowing the bush to be press-fitted for strength improvement without the distortion affecting the orifice inner diameter.
Solution Approach 2:
Different portions of the bush have different functional requirements. The press-fitted portion is designed for mechanical strength and interference fit with the rail main body, while the orifice portion is designed for precise fuel flow control. By spatially separating these functions (making the orifice deviate from the press-fitted area), each portion can be optimized for its specific purpose without compromising the other.
3Ease of manufacture
If the orifice is positioned at the bottom of the inside-outside communication hole, then the hole making process is simplified, but the crossing hole is small causing stress concentration
Solution Approach 1:
The system is segmented into the rail main body with the inside-outside communication hole and the separate bush component. The hole making process is applied to create the communication hole in the rail main body, while the orifice is formed in the bush. This segmentation allows the communication hole to be larger for reduced stress concentration while the orifice in the bush provides the necessary flow restriction.
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 design stabilizes fuel pressure, reduces injection pressure and amount differences among cylinders, and lowers production costs by shortening the orifice forming process and minimizing parts.
Implementation Method 1
an orifice forming member that attenuates pressure pulsations
Data Source
AI summary
A bush incorporated in a common rail is formed with a smallest diameter orifice having a small inner diameter and an adjacent orifice having an inner diameter larger than that of the smallest diameter orifice on an inner peripheral face of the bush. A press-fitted portion, which is press-fitted into an inside-outside communication hole, and a non-press-fitted portion, which has a smaller outer diameter than the press-fitted portion, are formed on an outer peripheral face of the bush. The smallest diameter orifice and the press-fitted portion are deviated from each other in an axial direction of the bush to prevent an overlap in a radial direction of the bush. Thus, even if the bush is tightly press-fitted into the inside-outside communication hole, decrease of the inner diameter of the smallest diameter orifice can be averted.