Variable Diameter Return Spring for Diesel Fuel Pump Stress Reduction
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Solution Overview
Problem
Existing fuel pump return springs face high stress levels due to increased force requirements and dynamic conditions, leading to reduced fatigue strength and resonance-induced failure, which is exacerbated by the need for larger spring sizes to accommodate longer free lengths, compromising pump size and efficiency in tight spaces.
Innovation Solution
A return spring with varying diameters, featuring a frustoconical section and cylindrical sections, allows for a longer free length without increasing the pump size, reducing stress and eliminating resonance by varying the spring rate along its length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the spring is compressed to provide sufficient force to maintain contact between cam and roller, then the contact force is improved, but the stress in the spring material increases
Solution Approach 1:
The spring has different diameters at different locations along its length, creating local variations in mechanical properties. The larger diameter at the first end and smaller diameter at the second end create zones with different stress characteristics, allowing the spring to distribute and reduce peak stresses while maintaining the required contact force
2Stress or pressure
If the free length of the spring is increased to reduce stress, then the stress is reduced, but the pump envelope size increases
Solution Approach 1:
The spring with varying diameter is nested within the existing spring chamber of the pump. The tapered configuration allows the spring to achieve a longer effective free length for reduced stress while fitting within the constrained volume of the original pump envelope, effectively nesting a longer spring in the same space
3Reliability
If a progressively wound spring is used to eliminate resonance, then the resonance is reduced, but the pump envelope size increases
Solution Approach 1:
The spring incorporates a progressively wound section with varying pitch along its length, creating local variations in spring rate. This progressive winding eliminates resonance by varying the natural frequency during compression while the compact tapered design maintains the overall spring size within the existing pump envelope
4Stress or pressure
If the spring diameter is increased to reduce stress, then the stress is reduced, but the pump envelope size increases
Solution Approach 1:
The spring breaks the symmetry of uniform diameter by implementing an asymmetric diameter profile along its length. The first end has a larger diameter while the second end has a smaller diameter, creating an asymmetric structure that reduces stress through geometric variation without requiring an overall increase in the spring chamber area
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
The solution enables the use of springs with increased free length, maintaining contact force while reducing stress and preventing resonance, thereby enhancing the reliability and efficiency of the fuel pump, particularly in space-constrained applications.
Implementation Method 1
The return spring (also shown separately in Figure 2) comprises a cylindrical helical compression spring having a constant external diameter along its length, and is provided around the plunger, in a spring chamber provided in the cam box. The spring applies a force to the roller, via the roller/shoe guide, thereby ensuring that roller is in constant contact with the cam throughout the pump cycle.
Implementation Method 2
As the spring operates under dynamic conditions, it can be caused to resonate at a natural frequency, or a harmonic, of the spring. Resonating of the spring also leads to an increase in stress levels within the spring, and ultimately to failure of the spring due to fatigue.
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A return spring for a diesel fuel pump pumping mechanism, the spring having a variable external diameter, and having a greater diameter at an end abutting an inlet valve body, than at an opposite end abutting a seat proximate a roller/shoe guide, the spring is formed entirely of a frustoconical section or sections, or with an additional cylindrical section or sections; the spring exhibits decreased resonance during pumping, and has an increased free length, leading to a reduction in stresses in the spring.