Fuel Pump End Cap Reduces Contact Stress
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Solution Overview
Problem
High contact stresses between the piston and cam follower assembly in fuel pumps under increased pumping loads, and the need to reduce the mass of moving components to handle higher engine speeds and pressures effectively.
Innovation Solution
The introduction of an end cap with a contact surface that provides a larger contact area and is capable of withstanding higher loads, featuring a convex or part-spherical contact surface and a deformable circumferential flange to reduce stress concentrations, while the end cap is mounted via a press fit projection in a longitudinal bore of the piston, allowing for reduced mass and improved sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the contact area between piston and cam follower assembly is increased, then contact stresses are reduced, but the mass of moving components increases
Solution Approach 1:
The piston is divided into two separate components: the piston body and the end cap. The end cap is attached to the piston body and provides the extended contact surface with the cam follower assembly. This segmentation allows the contact area to be increased without increasing the mass of the piston body itself, as the end cap can be optimized separately for contact stress distribution.
Solution Approach 2:
The contact surface is extended in a radial direction by adding the end cap with a circumferential flange. This dimensional extension provides a larger contact area (annular surface) without significantly increasing the axial length or overall volume of the moving components, thereby reducing contact stress while minimizing mass increase.
2Speed
If the spring load is reduced to handle higher engine speeds, then separation between cam and cam follower assembly is inhibited, but the pumping load capacity decreases
Solution Approach 1:
The circumferential flange of the end cap is designed with a convex curved contact surface that matches the cam profile. This curvature allows for optimal contact geometry during reciprocation, distributing the dynamic loads generated at higher engine speeds more effectively across the contact area, reducing the need for excessive spring load to maintain contact.
Solution Approach 2:
The contact geometry parameters (radius of curvature, contact area distribution) are optimized to match the cam profile and operating conditions. By adjusting these geometric parameters, the contact stress distribution is improved, allowing the system to handle higher speeds with reduced spring load requirements while maintaining reliable cam-follower contact.
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 effectively reduces contact stresses and allows the fuel pump to handle higher pumping loads by distributing pressure more evenly, enhancing the durability and efficiency of the fuel pump's operation.
Implementation Method 1
A spring is compressed between the pump head member and the follower assembly in order to permanently bias the follower assembly against the cam
Implementation Method 2
The end cap is mounted via a press fit projection in a longitudinal bore of the piston
Data Source
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AI summary
The present disclosure relates to a fuel pump (10) having a head member (12) provided with a blind bore (14) in which a piston (26) is adapted to perform a pumping cycle by reciprocating along the main axis (X1) of the bore (14) between a top dead center (TDC) position and a bottom dead center (BDC) position. Fuel is pressurized during the cycle in a compression chamber (30) defined between the top extremity (28) of the piston and the blind end of the bore (14). The piston (26) reciprocates under the influence of a rotating cam (36) cooperating with a follower assembly (34) combined to the piston (26). The pump (10) also includes a spring (46) compressed between the head member (12) and the follower assembly (34) in order to bias the follower assembly (34) toward the cam (36). An end cap (48) is mounted to the piston (26) for engaging the follower assembly (34). The end cap (48) may locate a spring seat member (44) or may form a spring seat member (44).