Fuel Injection Valve Coupling Body With Two-Stage Press-Fit Control
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Solution Overview
Problem
In fuel injection valves, the coupling of small-diameter components by press-fitting faces challenges with dimensional tolerances and processing accuracy, leading to variations in coupling strength and the risk of galling, which affects the reliability of the coupling body.
Innovation Solution
A method involving a two-stage deformation process where a high-hardness component with a first-stage and second-stage cylindrical surface is press-fitted into a low-hardness component, allowing the fastening allowance to be determined by the step between these surfaces rather than the diameter difference, reducing the impact of processing accuracy and minimizing galling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the fastening allowance between two small-diameter components is set to be small to achieve precise coupling, then the coupling strength may be improved, but it becomes extremely difficult to set dimensional tolerances according to the narrow fastening allowance range due to machine tool processing accuracy and manufacturing cost
Solution Approach 1:
The peripheral surface of the high-hardness component is divided into two stages: a first-stage cylindrical surface and a second-stage cylindrical surface positioned closer to the rear side in the press-fitting direction. This segmentation allows the fastening allowance to be determined by the step between these surfaces rather than by the overall diameter difference, enabling precise control of the effective fastening allowance while maintaining reasonable dimensional tolerances for the components.
2Ease of manufacture
If the fastening allowance between the two components is set to be large from the viewpoint of processing accuracy and manufacturing cost, then the ease of manufacture is improved, but galling is likely to occur in the press-fitting portion which deteriorates the coupling strength
Solution Approach 1:
The invention applies different surface properties to different regions of the press-fitting interface. The first-stage cylindrical surface creates a controlled deformation zone that prevents galling, while the second-stage cylindrical surface provides the actual fastening allowance. This local differentiation allows for a larger overall fastening allowance that is easier to manufacture while preventing galling through the controlled deformation at the first stage.
3Device complexity
If a single-stage press-fitting is used to couple small-diameter components, then the device complexity is reduced, but the coupling strength varies due to dimensional tolerance accumulation
Solution Approach 1:
The peripheral surface is segmented into two distinct stages with a step between them. The first-stage cylindrical surface has a diameter that causes plastic deformation, while the second-stage cylindrical surface is positioned closer to the rear side and protrudes in the radial direction to form the step. This segmentation allows the fastening allowance to be determined by the step dimension rather than by the accumulation of dimensional tolerances of the entire component, significantly improving coupling strength consistency.
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 stabilizes the coupling strength by varying the fastening allowance within the processing accuracy range of the high-hardness component, reducing variations and preventing galling, thus enhancing the reliability of the coupling body without increasing processing accuracy.
Implementation Method 1
a first stage at which the peripheral surface of the low-hardness component is deformed in a plastic region by the first-stage cylindrical surface of the high-hardness component
Implementation Method 2
a second stage at which the peripheral surface of the low-hardness component subjected to the deformation in the plastic region is deformed by the second-stage cylindrical surface of the high-hardness component in an amount smaller than the deformation amount at the first stage
Data Source
AI summary
A method for manufacturing a coupling body includes a press-fitting step of press-fitting a coupling shaft-shaped portion of a valve member into a pit portion of a cap. A peripheral surface of a high-hardness component having a relatively high hardness of an outer peripheral surface of the coupling shaft-shaped portion of the valve member and an inner peripheral surface of the pit portion of the cap includes: a first-stage cylindrical surface having a diameter difference with respect to a peripheral surface of a low-hardness component; and a second-stage cylindrical surface positioned closer to a rear side in a press-fitting direction than the first-stage cylindrical outer peripheral surface and protruding in a radial direction to form a step with respect to the first-stage cylindrical surface. The press-fitting step includes: a first stage at which the peripheral surface of the low-hardness component is deformed in a plastic region by the first-stage cylindrical surface; and a second stage at which the peripheral surface subjected to the deformation in the plastic region is deformed by the second-stage cylindrical surface in an amount smaller than the deformation amount at the first stage.